WorldWideScience

Sample records for brittle cornea syndrome

  1. Brittle Cornea Syndrome Associated with a Missense Mutation in the Zinc-Finger 469 Gene

    DEFF Research Database (Denmark)

    Christensen, Anne Elisabeth; Knappskog, Per Morten; Midtbø, Marit;

    2010-01-01

    Purpose: To investigate the diverse clinical manifestations, identify the causative mutation and explain the association with red hair in a family with brittle cornea syndrome (BCS). Methods: Eight family members in three generations underwent ophthalmic, dental, and general medical examination...... mapping with SNP markers, DNA sequencing, and MC1R genotyping. Results: At 42 and 48 years of age, respectively, both affected individuals were blind due to retinal detachment and secondary glaucoma. They had extremely thin and bulging corneas, velvety skin, chestnut colored hair, scoliosis, reduced BMD......, dental anomalies, hearing loss and minor cardiac defects. The morphologies of the skin biopsies were normal except that in some areas slightly thinner collagen fibrils were seen in one of the affected individuals. Molecular genetic analysis revealed a novel missense mutation of ZNF469, c.10016G...

  2. A new lethal syndrome with cloudy corneae, diaphragmatic defects and distal limb deformities.

    Science.gov (United States)

    Fryns, J P; Moerman, F; Goddeeris, P; Bossuyt, C; Van den Berghe, H

    1979-01-01

    Two female sibs are reported with a possibly new lethal malformation pattern, the major anomalies of which are: coarse face with small eyes and cloudy corneae, cleft soft palate, hypoplasia and absence of lobulation of both lungs, diaphragmatic defects, digitalisation of thumbs and distal limb deformities. PMID:381161

  3. A role for repressive complexes and H3K9 di-methylation in PRDM5-associated brittle cornea syndrome

    DEFF Research Database (Denmark)

    Porter, Louise F; Galli, Giorgio G; Williamson, Sally;

    2015-01-01

    skin fibroblast expression microarrays from patients with PRDM5 mutations p.Arg590* and Δ exons 9-14, as well as from a PRDM5 ChIP-sequencing experiment. Gene ontology analysis of dysregulated PRDM5 target genes reveals enrichment for extracellular matrix (ECM) genes supporting vascular integrity...

  4. Regenerative approaches for the cornea.

    Science.gov (United States)

    Griffith, M; Alarcon, E I; Brunette, I

    2016-09-01

    The cornea is the transparent front part of the eye that transmits light to the back of the eye to generate vision. Loss of corneal transparency, if irreversible, leads to severe vision loss or blindness. For decades, corneal transplantation using human donor corneas has been the only option for treating corneal blindness. Despite recent improvement in surgical techniques, donor cornea transplantation remains plagued by risks of suboptimal optical results and visual acuity, immune rejection and eventually graft failure. Furthermore, the demand for suitable donor corneas is increasing faster than the number of donors, leaving thousands of curable patients untreated worldwide. Here, we critically review the state of the art of biomaterials for corneal regeneration. However, the lessons learned from the use of the cornea as a disease model will allow for extension of the biomaterials and techniques for regeneration of more complex organs such as the heart. PMID:27098482

  5. Fracture of brittle solids

    CERN Document Server

    Lawn, Brian

    1993-01-01

    This is an advanced text for higher degree materials science students and researchers concerned with the strength of highly brittle covalent-ionic solids, principally ceramics. It is a reconstructed and greatly expanded edition of a book first published in 1975. The book presents a unified continuum, microstructural and atomistic treatment of modern day fracture mechanics from a materials perspective. Particular attention is directed to the basic elements of bonding and microstructure that govern the intrinsic toughness of ceramics. These elements hold the key to the future of ceramics as high-technology materials--to make brittle solids strong, we must first understand what makes them weak. The underlying theme of the book is the fundamental Griffith energy-balance concept of crack propagation. The early chapters develop fracture mechanics from the traditional continuum perspective, with attention to linear and nonlinear crack-tip fields, equilibrium and non-equilibrium crack states. It then describes the at...

  6. Synthetic cornea: biocompatibility and optics

    Science.gov (United States)

    Parel, Jean-Marie A.; Kaminski, Stefan; Fernandez, Viviana; Alfonso, E.; Lamar, Peggy; Lacombe, Emmanuel; Duchesne, Bernard; Dubovy, Sander; Manns, Fabrice; Rol, Pascal O.

    2002-06-01

    Purpose. Experimentally find a method to provide a safe surgical technique and an inexpensive and long lasting mesoplant for the restoration of vision in patients with bilateral corneal blindness due to ocular surface and stromal diseases. Methods. Identify the least invasive and the safest surgical technique for synthetic cornea implantation. Identify the most compatible biomaterials and the optimal shape a synthetic cornea must have to last a long time when implanted in vivo. Results. Penetrating procedures were deemed too invasive, time consuming, difficult and prone to long term complications. Therefore a non-penetrating delamination technique with central trephination was developed to preserve the integrity of Descemet's membrane and the anterior segment. Even though this approach limits the number of indications, it is acceptable since the majority of patients only have opacities in the stroma. The prosthesis was designed to fit in the removed tissue plane with its skirt fitted under the delaminated stroma. To improve retention, the trephination wall was made conical with the smallest opening on the anterior surface and a hat-shaped mesoplant was made to fit. The skirt was perforated in its perimeter to allow passage of nutrients and tissues ingrowths. To simplify the fabrication procedure, the haptic and optic were made of the same polymer. The intrastromal biocompatibility of several hydrogels was found superior to current clinically used PMMA and PTFE materials. Monobloc mesoplants made of 4 different materials were implanted in rabbits and followed weekly until extrusion occurred. Some remained optically clear allowing for fundus photography. Conclusions. Hydrogel synthetic corneas can be made to survive for periods longer than 1 year. ArF excimer laser photoablation studies are needed to determine the refractive correction potential of these mesoplants. A pilot FDA clinical trial is needed to assess the mesoplant efficacy and very long-term stability.

  7. Lymphangiogenesis Occurring in Transplanted Corneas

    Institute of Scientific and Technical Information of China (English)

    LING Shiqi; XIAO Qing; HU Yanhua

    2006-01-01

    To study corneal lymphangiogenesis after corneal transplantation, corneal allogenic transplantation models were established in rats. 8 female Wister rats were used as donors, and 16 Sprague Dawley (SD) rats were used as recipients and 2 SD served as controls. Corneal lymphangiogenesis and hemangiogenesis was examined by electron microscopy 1 and 2 weeks after corneal penetrating transplantation, and the expression of lymphatic vessel endothelial receptor (LYVE-1) was examined 1, 3, 7, 14 days after the transplantation respectively. In addition, 19 allograft failed human corneas were examined by 5'-nase-alkaline phosphatase (5'-NA-ALP) doubleenzyme-histochemistry staining to detect corneal lymphangiogenesis and hemangiogenesis. By immunohistochemistry for LYVE-1, it was found that blown lymphatics were localized in the stroma 3days after the corneal transplantation. With electron microscopy, new lymphatic vessels and blood vessels were found 1 and 2 weeks after the corneal transplantation. By 5'-NA-ALP enzyme-histochemistry, corneal hemangiogenesis was found in all allograft failed huma n corneas and 5 of 19(26.3%) cases had developed corneal lymphangiogenesis. It is concluded that corneal lymphangiogenesis is present after corneal transplantation, which may play an important role in allograft rejection.

  8. Cornea procurement, preservation and transplantation

    International Nuclear Information System (INIS)

    Our experience on this subject is 40 years and we have seen the developments everywhere during this total period. Cornea procurement has been an unsurmountable problem in a large number of countries, mostly due to social and cultural reasons. The requirements for a simple eye bank to manage the supply for a local hospital are minimal. What is the most important is the donor base. In Sri Lanka nurtured in the traditions of Theravada Buddhism the donor base was easy to prepare. We had no difficulties with Christians and Hindus. For Muslims there are Fatwas in favour of donating eyes. But we always found them to be a reluctant group. But in predominantly Muslim countries, it is imperative that social workers should take up this issue, so those thousands may be helped. In all areas where attempts are made to procure comeas, it is important to have a day-and-night service available at short notice to collect any eyes offered. A trained technician with sterilised instruments to obtain eyes and blood sample must be available at a convenient location preferably in a large hospital. Even in places where the supply is infrequent, it is essential to have the readily-sterilised instruments to proceed to a donor site at short notice. To get eyes, general publicity in mass media alone is not sufficient. Such publicity makes people aware of the need for donor eyes and where a technician/doctor is available. What is more important is to canvass personally after a person has died For this purpose trained social workers may be employed, or the technician can do the motivation, as we do in Sri Lanka. Once eyes are removed, it is essential to pay careful attention to the appearance of the cadaver. It should not (and need not) cause any deformity as such event has a profound negative effect on the campaign. Many different preservation methods have been used over the years. Mc Carey-Kaufmann (MK) medium has been the standard for many years, and gives a life span of 4-5 days. The formula

  9. Construction of Tissue Engineering Artificial Cornea with Skin Stem Cells

    Institute of Scientific and Technical Information of China (English)

    Yuan LIU; Yan JIN

    2005-01-01

    @@ 1 Introduction The clinical need for an alternative to donor corneal tissue has encouraged much interests in recent years. An artificial cornea must fulfill the functions of the cornea it replaces. More recently, the idea of a bio-engineered cornea has risen. Corneal equivalents have been reconstructed by tissue engineering method. Aim of this study is to construct an artificial rabbit cornea by employing tissue engineering method and to determine if skin stem cells have a role in tissue engineered cornea construction.

  10. Soft matter: Brittle for breakfast

    Science.gov (United States)

    Vandewalle, Nicolas

    2015-10-01

    Crushing a brittle porous medium such as a box of cereal causes the grains to break up and rearrange themselves. A lattice spring model based on simple physical assumptions gives rise to behaviours that are complex enough to reproduce diverse compaction patterns.

  11. [Mathematical model of the rotation of cornea].

    Science.gov (United States)

    Karpouzas, I; Pouliquen, Y

    1990-01-01

    The aim of our study is to informatise the procedure, ie, design the computer system and software necessary to automatically define the parameters of our problem. To achieve this, we have used an image analyser which permits us to acquire and digitalise a photograph of the lesioned cornea. Digitalisation of the image allows us to determine the co-ordinates (x, y) of the points which lie on the lesion periphery as well as the co-ordinates of the corneal centre, ie, geometric centre of the cornea. One calculates the centre of trephination and the optimal diameter of trephination as a function of a point situated on the lesion edge. PMID:2290009

  12. Construction of Tissue Engineering Artificial Cornea with Skin Stem Cells

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    1 IntroductionThe clinical need for an alternative to donor corneal tissue has encouraged much interests in recent years. An artificial cornea must fulfill the functions of the cornea it replaces. More recently, the idea of a bio-engineered cornea has risen. Corneal equivalents have been reconstructed by tissue engineering method. Aim of this study is to construct an artificial rabbit cornea by employing tissue engineering method and to determine if skin stem cells have a role in tissue engineered cornea co...

  13. Protection of brittle film against cracking

    Science.gov (United States)

    Musil, J.; Sklenka, J.; Čerstvý, R.

    2016-05-01

    This article reports on the protection of the brittle Zrsbnd Sisbnd O film against cracking in bending by the highly elastic top film (over-layer). In experiments the Zrsbnd Sisbnd O films with different elemental composition and structure were used. Both the brittle and highly elastic films were prepared by magnetron sputtering using a dual magnetron. The brittle film easily cracks in bending. On the other hand, the highly elastic film exhibits enhanced resistance to cracking in bending. Main characteristic parameters of both the brittle and highly elastic films are given. Special attention is devoted to the effect of the structure (crystalline, amorphous) of both the brittle and highly elastic top film on the resistance of cracking of the brittle film. It was found that (1) both the X-ray amorphous and crystalline brittle films easily crack in bending, (2) the highly elastic film can have either X-ray amorphous or crystalline structure and (3) both the X-ray amorphous and crystalline, highly elastic top films perfectly protect the brittle films against cracking in bending. The structure, mechanical properties and optical transparency of the brittle and highly elastic sputtered Zrsbnd Sisbnd O films are described in detail. At the end of this article, the principle of the low-temperature formation of the highly elastic films is also explained.

  14. Alternative approach to fit irregular corneas

    OpenAIRE

    Espinosa Tomás, Julián; Pérez Rodríguez, Jorge; Mas Candela, David; Vázquez Ferri, Carmen; Illueca Contri, Carlos

    2010-01-01

    Comunicación presentada en 5th European Meeting on Visual and Physiological Optics (EMVPO), Stockholm, 22-24 August 2010. We propose a zonal Zernike fitting (combination of zonal and modal approaches) of corneal height data. It permits accurate analysis of the surface, diminishing the influence of smooth areas over irregular zones and vice versa. This fact will be of special interest in irregular corneas wavefront evaluation. This work has been supported by the Generalitat Valenciana pr...

  15. Fractal statistics of brittle fragmentation

    Directory of Open Access Journals (Sweden)

    M. Davydova

    2013-04-01

    Full Text Available The study of fragmentation statistics of brittle materials that includes four types of experiments is presented. Data processing of the fragmentation of glass plates under quasi-static loading and the fragmentation of quartz cylindrical rods under dynamic loading shows that the size distribution of fragments (spatial quantity is fractal and can be described by a power law. The original experimental technique allows us to measure, apart from the spatial quantity, the temporal quantity - the size of time interval between the impulses of the light reflected from the newly created surfaces. The analysis of distributions of spatial (fragment size and temporal (time interval quantities provides evidence of obeying scaling laws, which suggests the possibility of self-organized criticality in fragmentation.

  16. The morphology and thickness of cornea in patients with Marfan syndrome%马方综合征患者角膜形态及厚度的特点

    Institute of Scientific and Technical Information of China (English)

    刘秋平; 张广斌; 邵毅; 易敬林; 刘祖国; 谭叶辉; 陈伟; 毛祖红; 王乐

    2011-01-01

    Objective To search for the characteristics of MFS in corneal morphology and thickness. Methods Twenty-four patients (48 eyes) with MFS and 24 healthy age- and gender-matched volunteers (48 eyes) were recruited in this clinical prospective, and comparative series study. Firstly,biomicroscopic examination and Type-A ultrasonometry was conducted to search for ectopia lentis and axis length. Secondly, the corneal morphologic parameter[including the height of anterior and posterior surface,the centre corneal curvature, the mean astigmatism in the 3.0-mm central zone (Mean A), the mean simulated astigmatism (Sim A) , the mean keratometry in the 3.0-mm central zone (Mean K), the mean simulated keratometry (Sim K), the 3.0-mm zone irregularity (3.0ZI), the 5.0-mm zone irregularity (5.0ZI) ,corneal thickness index (CTI)] and thickness (at the central location and at eight midperipheral locations) were obtained by the the autorefractometer and the Orbscan Ⅱ Z corneal topography. Last, the statistics method including Crosstabs, One-way ANOVA, student-t test and discriminant analysis were applied and the correlations were established. Results There is no statistically significance between MFS group and control group in ages (38 ±7) and (37 ±8) years, gender (8/16) and (9/15), and axis length (23. 12 ±1.06) mm and (24. 26 ±2. 96) mm (age x2=0.091 ,P=0.763 ;gender t=0.324, axis length t=1.976,P >0.05). Flat cornea ratio (66. 7% and 12. 5%) and topography of the oval (25.0% and 16. 7%),irregular bow-shaped (41.7% and 37.5%) and irregular-shaped (12. 5% and 8. 3%) were increased significantly in patients with MFS. The corneal topography(MFS/control) showed that there are statistically significance in the thinnest thickness of cornea (489. 8 ± 42. 9) μm and (544. 8 ± 25.7) μm, Mean K (40.60±1.30) Dand (42.80± 1.40) D, Sim K (40.50±1.30) D and (42.80±1.20) D, Sim A(1.08 ± 0.86)D and (0.91 ±0.46) D, CTI 1.57±0.24 and 1.21 ±0.14, 3.0ZI (1.76±0.96) D and (1.54 ±0

  17. Awareness of Cornea Donation of Registered Tissue Donors in Nanjing

    Institute of Scientific and Technical Information of China (English)

    Ting Chu; Lin-nong Wang; Hao Yu; Ru-yang Zhang

    2013-01-01

    Objective To evaluate the current cornea donation awareness of tissue donors in the city of Nanjing,China. Methods Altogether 2000 registered tissue donors in the Red Cross Eye Bank of Nanjing by the end of 2010 and 2000 control residents of Nanjing in February to June 2011 were randomly selected to par-ticipate in our field questionnaire survey. The questionnaire consisted of questions regarding the understand-ing of cornea donation,the attitude toward cornea donation,and attitude toward legislation and free dona-tion. The awareness of cornea donation between the registered tissue donors and residents was compared. Related factors of the willingness to donate corneas and to become a tissue donor were evaluated with uni-variate and multiple logistic regression analysis. Results A total of 1867 (response rate: 93.4%) tissue donors and 1796 (response rate: 89.8%; ef-fective questionnaires: 1697) residents participated in this survey. For the questions about the knowledge of cornea donation,90.3% tissue donors (residents: 78.9%) knew that donated corneas could be used for transplantations; 71.2% tissue donors (residents: 47.6%) knew that the appearance would not be destroyed after cornea donation; 70.7% tissue donors (residents: 20.0%) knew the formalities to become a cornea do-nor. For attitude toward cornea donation,82.2% tissue donors (residents: 45.1%) were willing to donate corneas or eyeballs after death; 84.0% tissue donors (residents: 30.2%) had discussed with their families about donation; 85.1% tissue donors (residents: 24.8%) supported their families' or friends' cornea donation. For attitude toward legislation and free donation,88.3% tissue donors (residents: 61.3%) approved of legis-lation to regular cornea donation; 72.2% tissue donors (residents: 38.8%) thought that cornea or organ do-nation should be gratis. The difference between two groups was significant (P<0.001). However,some tissue donors did not know cornea donation well,some even opposed the

  18. Investigation of Friction-induced Damage to the Pig Cornea

    NARCIS (Netherlands)

    da Cruz Barros, Raquel; Van Kooten, Theo G.; Veeregowda, Deepak Halenahally

    2015-01-01

    Mechanical friction causes damage to the cornea. A friction measurement device with minimal intervention with the pig cornea tear film revealed a low friction coefficient of 0.011 in glycerine solution. Glycerine molecules presumably bind to water, mucins, and epithelial cells and therewith improve

  19. Refractive analysis of the human cornea through propagated fields

    OpenAIRE

    Illueca Contri, Carlos; Mas Candela, David; Pérez Rodríguez, Jorge; Pons Moreno, Álvaro Máximo; Artigas Verde, José María

    2000-01-01

    A new technique for analysing the optical quality of the human cornea is presented. Corneal maps are obtained through keratographies and then converted into phase maps. The propagated fields generated from this surface are plotted and studied. It is shown that any irregularity in the cornea affects the propagated field and the energy distribution at the focal plane. Simple applications are also indicated.

  20. Fracturing and brittleness index analyses of shales

    Science.gov (United States)

    Barnhoorn, Auke; Primarini, Mutia; Houben, Maartje

    2016-04-01

    The formation of a fracture network in rocks has a crucial control on the flow behaviour of fluids. In addition, an existing network of fractures , influences the propagation of new fractures during e.g. hydraulic fracturing or during a seismic event. Understanding of the type and characteristics of the fracture network that will be formed during e.g. hydraulic fracturing is thus crucial to better predict the outcome of a hydraulic fracturing job. For this, knowledge of the rock properties is crucial. The brittleness index is often used as a rock property that can be used to predict the fracturing behaviour of a rock for e.g. hydraulic fracturing of shales. Various terminologies of the brittleness index (BI1, BI2 and BI3) exist based on mineralogy, elastic constants and stress-strain behaviour (Jin et al., 2014, Jarvie et al., 2007 and Holt et al., 2011). A maximum brittleness index of 1 predicts very good and efficient fracturing behaviour while a minimum brittleness index of 0 predicts a much more ductile shale behaviour. Here, we have performed systematic petrophysical, acoustic and geomechanical analyses on a set of shale samples from Whitby (UK) and we have determined the three different brittleness indices on each sample by performing all the analyses on each of the samples. We show that each of the three brittleness indices are very different for the same sample and as such it can be concluded that the brittleness index is not a good predictor of the fracturing behaviour of shales. The brittleness index based on the acoustic data (BI1) all lie around values of 0.5, while the brittleness index based on the stress strain data (BI2) give an average brittleness index around 0.75, whereas the mineralogy brittleness index (BI3) predict values below 0.2. This shows that by using different estimates of the brittleness index different decisions can be made for hydraulic fracturing. If we would rely on the mineralogy (BI3), the Whitby mudstone is not a suitable

  1. The anisotropic material constitutive models for the human cornea.

    Science.gov (United States)

    Li, Long-yuan; Tighe, Brian

    2006-03-01

    This paper presents an anisotropic analysis model for the human cornea. The model is based on the assumption that the fibrils in the cornea are organised into lamellae, which may have preferential orientation along the superior-inferior and nasal-temporal directions, while the alignment of lamellae with different orientations is assumed to be random. Hence, the cornea can be regarded as a laminated composite shell. The constitutive equation describing the relationships between membrane forces, bending moments, and membrane strains, bending curvatures are derived. The influences of lamella orientations and the random alignment of lamellae on the stiffness coefficients of the constitutive equation are discussed. PMID:16426861

  2. Changing pattern of utilization of human donor cornea in India

    Directory of Open Access Journals (Sweden)

    Varun Gogia

    2015-01-01

    Full Text Available Purpose: To review the changing pattern of donor, corneal utilization in an eye bank at a Tertiary Care Center in Northern India by analyzing the trend in the years 2003, 2008, and 2011. Methods: A retrospective review of eye bank records for 3 years (2003, 2008, and 2011 was performed at the National Eye Bank. Details including a clinical grade of donor cornea, indication of corneal transplantation (therapeutic or optical, type of procedure (penetrating or lamellar keratoplasty [LK], and clinical diagnosis of the graft recipients were recorded. Primary outcome measure was to observe any preference toward LK, judicious usage of donor corneal tissue, and impact of lamellar corneal transplant in the usage of donor corneas. Secondary outcomes included overall utilization rate and change in trend of indication for keratoplasty. Results: A total of 673, 745, and 864 corneas were retrieved in the years 2003, 2008, and 2011, respectively. The percentage of donor corneal utilization increased significantly over time with the rate being 65.08%, 70.06%, and 68.29%, respectively, in the years 2003, 2008, and 2011 (P = 0.014; however, this change was reflected only in the usage of nonoptical grade corneas and not for the optical grade corneas. There was an overall increase in lamellar corneal procedures for any clinical grade of cornea (P = 0.0019; number of Descemet's stripping automated endothelial keratoplasty (DSAEK procedures increased significantly (P < 0.001, particularly for pseudophakic corneal edema (PCE (P = 0.0085 and failed graft (P = 0.002. Significant increase in the utilization of nonoptical grade corneas was observed over the years (P = 0.005, though the utilization did not increase significantly for optical purposes viz., LK (P = 0.08. Conclusions: Utilization rate of donor corneas increased over the years, primarily due to increase in usage of nonoptical grade corneas for therapeutic purposes. There was a procedural shift toward DSAEK for

  3. Ultrastructural changes in the retinopathy, globe enlarged (rge) chick cornea

    OpenAIRE

    Boote, Craig; Hayes, Sally; Robert D. Young; Kamma-Lorger, Christina S.; Hocking, Paul M.; Elsheikh, Ahmed; Inglehearn, Chris F.; Ali, Manir; Meek, Keith M.

    2009-01-01

    In the cornea, the precise organisation of fibrillar collagen and associated proteoglycans comprising the stromal extracellular matrix plays a major role in governing tissue form and function. Recently, abnormal collagen alignment was noted in the misshapen corneas of mature chickens affected by the retinopathy, globe enlarged (rge) mutation. Here we further characterize corneal ultrastructural changes as the rge eye develops post-hatch. Wide-angle X-ray scattering disclosed alteration to dom...

  4. CORRECTION OF MYOPIA USING CORNEA SPARING LASIK (ABLATION ON FLAP

    Directory of Open Access Journals (Sweden)

    Nikhilesh

    2015-02-01

    Full Text Available Cornea sparing lasik is useful tool allowing surgeons to preserve the posterior stroma. The study comprised of prospective evaluation of 17 eyes treated with CSL – Cornea Sparing Lasik at Mahatme Eye Bank Eye Hospital , N agpur India. Our results show that the laser ablation on the corneal flap is safe and effective procedure. The refractive , efficacy and safety outcomes were similar to those in routine Lasik ablation on posterior stroma.

  5. Ultraviolet laser effects on the cornea

    Science.gov (United States)

    Zuclich, Joseph A.

    1990-07-01

    Ultraviolet radiation in the ambient environment or from artificial sources may pose both acute and chronic hazards to the skin and the ocular tissues. In general terrestrial conditions have evolved such that there are only narrow safety margins between ambient UV levels and exposure levels harmful to the human. Obvious examples of acute consequences ofUV overexposure are sunburn and snowblindness as well as analogous conditions induced by artificial sources such as the welder''s arc mercury vapor lamps and UV-emitting lasers. Further chronic UV exposure is strongly implicated as a causative agent in certain types of cataract and skin cancer. This presentation will summarize a number of specific cases where UV radiation affected the primate cornea. Data presented will include the action spectra for far- and near-UV induced ocular damage the pulsewidth and total energy dependencies of ocular thresholds studies of cumulative effects of repeated UV exposures and quantitative determinations of tissue repair or recovery rates. Depending on the exposure parameters utilized photochemical thermal or photoablative damage mechanisms may prevail. 1.

  6. Collagen cross-linking in thin corneas

    Directory of Open Access Journals (Sweden)

    Prema Padmanabhan

    2013-01-01

    Full Text Available Collagen cross-linking (CXL has become the standard of care for progressive keratoconus, after numerous clinical studies have established its efficacy and safety in suitably selected eyes. The standard protocol is applicable in eyes which have a minimum corneal thickness of 400 μm after epithelial debridement. This prerequisite was stipulated to protect the corneal endothelium and intraocular tissues from the deleterious effect of ultraviolet-A (UVA radiation. However, patients with keratoconus often present with corneal thickness of less than 400 μm and could have otherwise benefited from this procedure. A few modifications of the standard procedure have been suggested to benefit these patients without a compromise in safety. Transepithelial cross-linking, pachymetry-guided epithelial debridement before cross-linking, and the use of hypoosmolar riboflavin are some of the techniques that have been attempted. Although clinical data is limited at the present time, these techniques are worth considering in patients with thin corneas. Further studies are needed to scientifically establish their efficacy and safety.

  7. Femtosecond lasers for microsurgery of cornea

    Energy Technology Data Exchange (ETDEWEB)

    Vartapetov, Sergei K; Khudyakov, D V; Lapshin, Konstantin E; Obidin, Aleksei Z; Shcherbakov, Ivan A

    2012-03-31

    The review of femtosecond laser installations for medical applications is given and a new femtosecond ophthalmologic system for creation of a flap of corneal tissue during the LASIK operation is described. An all-fibre femtosecond laser emitting {approx}400-fs pulses at 1067 nm is used. The pulse repetition rate can vary from 200 kHz up to 1 MHz. The output energy of the femtosecond system does not exceed 1 {mu}J. A specially developed objective with small spherical and chromatic aberrations is applied to focus laser radiation to an area of an eye cornea. The size of the focusing spot does not exceed 3 {mu}m. To process the required area, scanning by a laser beam is applied with a speed no less than 5 m s{sup -1}. At a stage of preliminary tests of the system, the {Kappa}8 glass, organic PMMA glass and specially prepared agarose gels are used as a phantom of an eye. The femtosecond system is successfully clinically tested on a plenty of eyes of a pig and on several human eyes. The duration of the procedure of creation of a corneal flap does not exceed 20 s.

  8. Measurement of the anisotropic thermal conductivity of the porcine cornea.

    Science.gov (United States)

    Barton, Michael D; Trembly, B Stuart

    2013-10-01

    Accurate thermal models for the cornea of the eye support the development of thermal techniques for reshaping the cornea and other scientific purposes. Heat transfer in the cornea must be quantified accurately so that a thermal treatment does not destroy the endothelial layer, which cannot regenerate, and yet is responsible for maintaining corneal transparency. We developed a custom apparatus to measure the thermal conductivity of ex vivo porcine corneas perpendicular to the surface and applied a commercial apparatus to measure thermal conductivity parallel to the surface. We found that corneal thermal conductivity is 14% anisotropic at the normal state of corneal hydration. Small numbers of ex vivo feline and human corneas had a thermal conductivity perpendicular to the surface that was indistinguishable from the porcine corneas. Aqueous humor from ex vivo porcine, feline, and human eyes had a thermal conductivity nearly equal to that of water. Including the anisotropy of corneal thermal conductivity will improve the predictive power of thermal models of the eye.

  9. Numerical experiments in revisited brittle fracture

    DEFF Research Database (Denmark)

    Bourdin, Blaise; Francfort, Gilles A; Marigo, Jean-Jacques

    2000-01-01

    The numerical implementation of the model of brittle fracture developed in~ Francfort and Marigo (1998) is presented. Various computational methods based on variational approximations of the original functional are proposed. They are tested on several antiplanar and planar examples that are beyond...

  10. Portable light transmission measuring system for preserved corneas

    Science.gov (United States)

    Ventura, Liliane; de Jesus, Gabriel Torres; de Oliveira, Gunter Camilo Dablas; Sousa, Sidney JF

    2005-01-01

    Background The authors have developed a small portable device for the objective measurement of the transparency of corneas stored in preservative medium, for use by eye banks in evaluation prior to transplantation. Methods The optical system consists of a white light, lenses, and pinholes that collimate the white light beams and illuminate the cornea in its preservative medium, and an optical filter (400–700 nm) that selects the range of the wavelength of interest. A sensor detects the light that passes through the cornea, and the average corneal transparency is displayed. In order to obtain only the tissue transparency, an electronic circuit was built to detect a baseline input of the preservative medium prior to the measurement of corneal transparency. The operation of the system involves three steps: adjusting the "0 %" transmittance of the instrument, determining the "100 %" transmittance of the system, and finally measuring the transparency of the preserved cornea inside the storage medium. Results Fifty selected corneas were evaluated. Each cornea was submitted to three evaluation methods: subjective classification of transparency through a slit lamp, quantification of the transmittance of light using a corneal spectrophotometer previously developed, and measurement of transparency with the portable device. Conclusion By comparing the three methods and using the expertise of eye bank trained personnel, a table for quantifying corneal transparency with the new device has been developed. The correlation factor between the corneal spectrophotometer and the new device is 0,99813, leading to a system that is able to standardize transparency measurements of preserved corneas, which is currently done subjectively. PMID:16372912

  11. An educational program on structural design with brittle /ceramic/ materials

    Science.gov (United States)

    Mueller, J. I.

    1978-01-01

    The organization of a proposed ceramic structural materials program is described, and a suggested course sequence for college-level and graduate-level courses is presented. The course work on ceramics and brittle fracture are intended to lead to a brittle material design project and a brittle material design problem. Criteria for the selection of appropriate projects/problems are considered.

  12. Critical evaluation of the ultrasonic pachymetry for "in vitro" corneas

    Science.gov (United States)

    Lincoln, Victor A. C.; Ventura, Liliane; Faria e Sousa, Sidney J.

    2011-03-01

    The measurement of central corneal thickness (CCT) is vastly useful for diagnostic and therapeutic evaluation. The ultrasound pachymetry is currently the most common CCT technique. This study was undertaken to determine the precision and correlation of measurements obtained by mechanical and ultrasound pachymetry. The ultrasound pachymetry was determined using an A-scan ultrasonic pachymeter. The probe tip was held perpendicular on the central cornea by a support that goes down smooth to avoid excessive pressure and instability. The mechanical pachymetry was determined using a micrometer with a tip of 2mm of diameter. The tip of the micrometer was held perpendicular on the central cornea by a support that keeps stabilized. A 10x optics increase and a digital video camera shows real time image of approach and full contact of the tip with the cornea. Eight human corneas were obtained from cadaveric eyes. Measurements in both systens were taken for three different users, each one performed five readings. The results for both systems has an average SD of 33 microns refers to the systematic error between users (for positioning, center, pinching). But the difference between systems was 120 microns, possibly refers to the imprecision of ultrasound pachymetry in measuring in vitro corneas.

  13. Aspects of brittle failure assessment for RPV

    Energy Technology Data Exchange (ETDEWEB)

    Zecha, H.; Hermann, T.; Hienstorfer, W. [TUeV SUeD Energietechnik GmbH Baden-Wuerttemberg, Filderstadt (Germany); Schuler, X. [Materialpruefungsanstalt, Univ. Stuttgart (Germany)

    2009-07-01

    This paper describes the process of pressurized thermal shock analysis (PTS) and brittle failure assessment for the reactor pressure vessel (RPV) of the nuclear power plants NECKAR I/II. The thermo-hydraulic part of the assessment provides the boundary conditions for the fracture mechanics analysis. In addition to the one dimensional thermo-hydraulic simulations CFD, analyses were carried out for selected transients. An extensive evaluation of material properties is necessary to provide the input data for a reliable fracture mechanics assessment. For the core weld and the flange weld it has shown that brittle crack initiation can be precluded for all considered load cases. For the cold and hot leg nozzle detailed linear-elastic and elasticplastic Finite Element Analyses (FEA) are performed to verify the integrity of the RPV. (orig.)

  14. Psychiatric and social aspects of brittle asthma.

    OpenAIRE

    Garden, G M; Ayres, J.G.

    1993-01-01

    BACKGROUND--Many studies have shown that emotional factors play a part in asthma, but few have compared patients with differing severities of asthma. It was our impression that patients with "brittle" asthma (BA; more than 40% diurnal variation in peak flow on 15 or more days a month over a period of at least six months, and persistent symptoms despite multiple drug treatment) had greater psychosocial morbidity than asthmatic patients with less variable asthma. METHODS--Twenty patients with B...

  15. Fabrication of brittle materials -- current status

    Energy Technology Data Exchange (ETDEWEB)

    Scattergood, R.O.

    1988-12-01

    The research initiatives in the area of precision fabrication will be continued in the upcoming year. Three students, T. Bifano (PhD), P. Blake (PhD) and E. Smith (MS), finished their research programs in the last year. Sections 13 and 14 will summarize the essential results from the work of the Materials Engineering students Blake and Smith. Further details will be presented in forthcoming publications that are now in preparation. The results from Bifano`s thesis have been published in adequate detail and need not be summarized further. Three new students, S. Blackley (MS), H. Paul (PhD), and S. Smith (PhD) have joined the program and will continue the research efforts in precision fabrication. The programs for these students will be outlined in Sections 15 and 16. Because of the success of the earlier work in establishing new process models and experimental techniques for the study of diamond turning and diamond grinding, the new programs will, in part, build upon the earlier work. This is especially true for investigations concerned with brittle materials. The basic understanding of material response of nominally brittle materials during machining or grinding operations remains as a challenge. The precision fabrication of brittle materials will continue as an area of emphasis for the Precision Engineering Center.

  16. Towards an Approach to Overcome Software Brittleness

    Energy Technology Data Exchange (ETDEWEB)

    OSBOURN,GORDON C.

    1999-11-01

    Development of bug-free, high-surety, complex software is quite difficult using current tools. The brittle nature of the programming constructs in popular languages such as C/C++ is one root cause. Brittle commands force the designer to rigidly specify the minutiae of tasks, e.g. using ''for(index=0;index>total;index++)'', rather than specifying the goals or intent of the tasks, e.g. ''ensure that all relevant data elements have been examined''. Specification of task minutiae makes code hard to comprehend, which in turn encourages design errors/limitations and makes future modifications quite difficult. This report describes an LDRD project to seed the development of a surety computer language, for stand-alone computing environments, to be implemented using the swarm intelligence of autonomous agents. The long term vision of this project was to develop a language with the following surety capabilities: (1) Reliability -- Autonomous agents can appropriate y decide when to act and when a task is complete, provide a natural means for avoiding brittle task specifications, and can overcome many hardware glitches. (2) Safety, security -- Watchdog safety and security agents can monitor other agents to prevent unauthorized or dangerous actions. (3) An immune system -- The small chunks of agent code can have an encryption scheme to enable detection and elimination of unauthorized and corrupted agents. This report describes the progress achieved during this small 9 month project and describes lessons learned.

  17. Expression of Interleukin 1 Receptor Antagonist in Human Cornea

    OpenAIRE

    Heur, Martin; Shyam S. Chaurasia; Wilson, Steven E.

    2008-01-01

    The purpose of this study was to confirm the expression of interleukin-1 receptor antagonist (IL-1 Ra) in the human cornea. Four samples of human ex vivo corneal epithelium were obtained from patients undergoing photorefractive keratectomy. RT-PCR was performed using mRNA isolated from the corneal epithelium and oligo-dT primers. PCR was performed on the cDNA products using primers specific for human IL-1Ra. The PCR products were subcloned and sequenced. Human cornea sections were prepared fr...

  18. Cornea regeneration in the Pacific giant octopus, Octopus dofleini, and the common octopus, O. vulgaris.

    Science.gov (United States)

    Dingerkus, G; Santoro, E D

    1981-04-15

    Cornea regeneration in a Pacific giant octopus, Octopus dofleini, occurred within 10 days after the injury was observed. Surgical removal of the cornea in a common octopi, O. vulgaris experimentally duplicated this cornea regeneration within a 10-day period. It is, therefore, concluded that besides sucking discs, arms, and nerve fibres, octopi can also regenerate corneal tissue. PMID:7238810

  19. Effect of Seawater Soaking on Explosive Cornea Injury

    Institute of Scientific and Technical Information of China (English)

    Suihua Chen; Zhenping Huang; Lili Wang; Yuwen Lu; Yi Wang

    2002-01-01

    Objective: To observe the changes in corneal tissue after explosive corneal injury and the effect of seawater soaking on the healing of cornea after explosive injury with the help ofoptical microscope. Methods: Make 10 similar explosive injury models of rabbit′s eyeball using 10 adult greyrabbits. For each rabbit, both eyes are artificially injured through explosion; its right eye is the comparison eye and after the injury the left eye is soaked in seawater for 30 minutes.Conduct slit lamp examinations, fluorescein dyeing, and ultrasonic cornea thickness metering on the corneas at intervals, that is, before the injury, 1 , 2, 3, 4, 5, 7, 9, 12, 15days after the injury respectively. Examine the corneas under the optical microscope andmake comparisons.Results: The corneal thickness of the experiment eye becomes apparently thicker than thatof the comparison eye after the injury. The corneal clouding of the former apparentlyaggravates compared with the latter. The healing of corneal epithelium in the injured eye isslower compared with that in the comparison eye. Comparative examination under the opticalmicroscope shows: after the injury, the corneal tissue of the experiment eye changesdistinctly, its healing is delayed and the vascularization degree becomes high in cornealstroma.Conclusion: Scars and vascularization of various degrees will appear in corneal stroma afterexplosive injuries. Seawater soaking will have bad effects on the healing of the corneainjured in explosions.

  20. Biomechanical Measurement of Rabbit Cornea by a Modified Scheimpflug Device

    Science.gov (United States)

    Zhang, Bo; Gu, Jianjun; Zhang, Xiaoxiao; Yang, Bin

    2016-01-01

    Purpose. To explore the probability and variation in biomechanical measurements of rabbit cornea by a modified Scheimpflug device. Methods. A modified Scheimpflug device was developed by imaging anterior segment of the model imitating the intact eye at various posterior pressures. The eight isolated rabbit corneas were mounted on the Barron artificial chamber and images of the anterior segment were taken at posterior pressures of 15, 30, 45, 60, and 75 mmHg by the device. The repeatability and reliability of the parameters including CCT, ACD, ACV, and CV were evaluated at each posterior pressure. All the variations of the parameters at the different posterior pressures were calculated. Results. All parameters showed good intraobserver reliability (Cronbach's alpha; intraclass correlation coefficient, α, ICC > 0.96) and repeatability in the modified Scheimpflug device. With the increase of posterior pressures, the ratio of CCT decreased linearly and the bulk modulus gradually reduced to a platform. The increase of ACD was almost linear with the posterior pressures elevated. Conclusions. The modified Scheimpflug device was a valuable tool to investigate the biomechanics of the cornea. The posterior pressure 15–75 mmHg range produced small viscoelastic deformations and nearly linear pressure-deformation response in the rabbit cornea. PMID:27446608

  1. Brittle and semi-brittle behaviours of a carbonate rock: influence of water and temperature

    Science.gov (United States)

    Nicolas, A.; Fortin, J.; Regnet, J. B.; Dimanov, A.; Guéguen, Y.

    2016-07-01

    Inelastic deformation can either occur with dilatancy or compaction, implying differences in porosity changes, failure and petrophysical properties. In this study, the roles of water as a pore fluid, and of temperature, on the deformation and failure of a micritic limestone (white Tavel limestone, porosity 14.7 per cent) were investigated under triaxial stresses. For each sample, a hydrostatic load was applied up to the desired confining pressure (from 0 up to 85 MPa) at either room temperature or at 70 °C. Two pore fluid conditions were investigated at room temperature: dry and water saturated. The samples were deformed up to failure at a constant strain rate of ˜10-5 s-1. The experiments were coupled with ultrasonic wave velocity surveys to monitor crack densities. The linear trend between the axial crack density and the relative volumetric strain beyond the onset of dilatancy suggests that cracks propagate at constant aspect ratio. The decrease of ultrasonic wave velocities beyond the onset of inelastic compaction in the semi-brittle regime indicates the ongoing interplay of shear-enhanced compaction and crack development. Water has a weakening effect on the onset of dilatancy in the brittle regime, but no measurable influence on the peak strength. Temperature lowers the confining pressure at which the brittle-semi-brittle transition is observed but does not change the stress states at the onset of inelastic compaction and at the post-yield onset of dilatancy.

  2. Permeability Evolution and Rock Brittle Failure

    Directory of Open Access Journals (Sweden)

    Sun Qiang

    2015-08-01

    Full Text Available This paper reports an experimental study of the evolution of permeability during rock brittle failure and a theoretical analysis of rock critical stress level. It is assumed that the rock is a strain-softening medium whose strength can be described by Weibull’s distribution. Based on the two-dimensional renormalization group theory, it is found that the stress level λ c (the ratio of the stress at the critical point to the peak stress depends mainly on the homogeneity index or shape parameter m in the Weibull’s distribution for the rock. Experimental results show that the evolution of permeability is closely related to rock deformation stages: the permeability has a rapid increase with the growth of cracks and their surface areas (i.e., onset of fracture coalescence point, and reaches the maximum at rock failure. Both the experimental and analytical results show that this point of rapid increase in permeability on the permeabilitypressure curve corresponds to the critical point on the stress-strain curve; for rock compression, the stress at this point is approximately 80% of the peak strength. Thus, monitoring the evolution of permeability may provide a new means of identifying the critical point of rock brittle fracture

  3. Research on basic characteristics of complex system brittleness

    Institute of Scientific and Technical Information of China (English)

    JIN Hong-zhang; GUO Jian; WEI Qi; LIN De-ming; LI Qi

    2004-01-01

    Tbe goal of this paper is to research one new characteristic of complex system. Brittleness, which is one new characteritic of complex system, is presented in this paper. The linguistic and qualitative descriptions of complex system are also given in this paper.Otherwise, the qualitative description of complex system is presented at first. On the basis of analyzing the existing brittleness problems, linguistic description and mathematic description of brittleness are given as well. Three kinds of phenomena to judge brittleness of complex system are also given, based on catastrophe theory. Basic characteristics of brittleness are given on the basis of its mathematic description. Two critical point sets are defined by using catastrophe theory. The definition of brittleness and its related theory can serve the control of complex system, and provide theoretical basis for the design and control of complex system.

  4. The role of brittleness in fracture of concrete

    International Nuclear Information System (INIS)

    Based on the analysis of load-deflection curves of concrete, mortar and hcp during fracture tests, we introduce a brittleness parameter to describe the failure pattern, and try to explore how the fracture energy, strength and the brittleness are mutually interdependent. It is proposed in this contribution that for practical use or design of materials, all three properties strength, fracture energy and brittleness have to be taken into consideration. (orig.)

  5. Live imaging of newly formed lymphatic vessels in the cornea

    Institute of Scientific and Technical Information of China (English)

    Don Yuen; Xiufeng Wu; Alex C Kwan; Jeffrey LeDue; Hui Zhang; Tatiana Ecoiffier; Bronislaw Pytowski; Lu Chen

    2011-01-01

    Dear Editor,Lymphatic research denotes a field of new discovery and has experienced exponential growth in recent years [1-3].Though lymphatic dysfunction has been found in a broad spectrum of disorders from transplant rejection to cancer metastasis,to date,there is still little effective treatment for lymphatic diseases,so it is a field with urgent demand for new experimental approaches and therapeutic protocols.The cornea provides an ideal site for lymphatic research due to its accessible location,transparent nature,and alymphatic status under normal condition [2,4].Indeed,the use of this tissue for tumor angiogenesis research dates back to 1970s [5].Most recently,we have demonstrated that the cornea possesses a full range of plasticity in lymphatic formation and regression [6].An advanced technology for live imaging of lymphatic vessels in this tissue would therefore have widespread applications in biomedical research.

  6. Management of chemical burns of the canine cornea

    OpenAIRE

    Christmas, Richard

    1991-01-01

    Significant clinical signs and general principles of treatment for chemical burns of the canine cornea are presented using three typical case studies for illustration. Alkali burns are more common in dogs than acid burns. The sources of alkali in this study were soap, cement, and mortar dust. Common signs of chemical burns are ocular pain, corneal ulceration, tear film inadequacy, corneal edema, and marked corneal neovascularity. Successful treatment requires thorough ocular lavage, treatment...

  7. Ultrastructural changes in the developing chicken cornea following caffeine administration.

    OpenAIRE

    Bartel Hieronim; Tosik Dariusz; Kujawa-Hadryś Monika

    2010-01-01

    Caffeine is one of the most frequently consumed psychoactive substances. It has been known for many years that caffeine at high concentrations exerts harmful effects on both women's and laboratory animals' fertility, moreover it may impair normal development of many organs in the prenatal period. So far there have been few studies performed that demonstrate teratogenic effects of caffeine on structures of the developing eye, particularly the cornea. The aim of the study was to show ultrastruc...

  8. National conference on brittle fracture of materials and structures

    International Nuclear Information System (INIS)

    The proceedings contain full texts of 28 contributions, out of which 10 fall within the INIS subject scope. These deal particularly with the effect of neutron radiation on the brittle fracture properties of structural steels used in nuclear facilities and with theoretical problems of brittle fracture of such steels in cyclic stress conditions. (Z.M.)

  9. Effect of substrate roughness on the contact damage of thin brittle films on brittle substrates

    Energy Technology Data Exchange (ETDEWEB)

    Weidner, Mirko [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Institute for Materials Science, Technische Universitaet Darmstadt, Petersenstrasse 23, 64287 Darmstadt (Germany); Borrero-Lopez, Oscar [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Departamento de Ingenieria Mecanica, Energetica y de los Materiales, Universidad de Extremadura, 06071, Badajoz (Spain); Hoffman, Mark, E-mail: mark.hoffman@unsw.edu.a [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Bendavid, Avi; Martin, Phil J. [CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield NSW 2070 (Australia)

    2010-07-01

    The effect of substrate and surface roughness on the contact fracture of diamond-like carbon coatings on brittle soda-lime glass substrates has been investigated. The average surface roughness (R{sub a}) of the examined samples ranged from 15 nm to 571 nm. Contact damage was simulated by means of spherical nanoindentation, and fracture was subsequently assessed by focused ion beam microscopy. It was found that, in the absence of sub-surface damage in the substrate, fracture occurs in the coating in the form of radial, and ring/cone cracks during loading, and lateral cracks during unloading. Increasing the surface roughness results in a decrease in the critical load for crack initiation during loading, and in the suppression of fracture modes during unloading from high loads. When sub-surface damage (lateral cracks) is present in the substrate, severe spalling takes place during loading, causing a large discontinuity in the load-displacement curve. The results have implications concerning the design of damage-tolerant coated systems consisting of a brittle film on a brittle substrate.

  10. pH of organ-culture-stored corneas.

    Science.gov (United States)

    Lass, J H; Greiner, J V; Meneses, P; Morgan, D C; Medcalf, S K; Collie, D M; Skelnik, D L; Glonek, T

    1988-10-01

    Changes in intracorneal and storage-medium pH values of organ-culture-stored cat corneas were monitored over a 4-week period. The intracorneal pH was determined using the phosphorus-31 magnetic resonance spectroscopy (31P MRS) chemical shift of inorganic orthophosphate in conjunction with a standard pH titration curve. We incubated 32 adult cat corneas using two similar standard organ-culture methods, one with chondroitin sulfate (method 1) and the other without (method 2). Time-course data at 0, 1, 3 and 4 weeks of storage were used to calculate the rate of pH change. The intracorneal pH was not changed significantly for either organ-culture method; however, the storage-medium pH rate of change declined significantly for both methods (method 1, 0.15 pH units/week; method 2, 0.12 pH units/week). The difference between intracorneal and storage-medium pH values over time increased at a rate of 0.12 and 0.11 pH units/week for method 1 and method 2, respectively. The declining storage-medium pH in conjunction with the maintenance of intracorneal pH contributes to an increased metabolic demand on the cornea. PMID:3218477

  11. Ultrastructural changes in the developing chicken cornea following caffeine administration.

    Directory of Open Access Journals (Sweden)

    Bartel Hieronim

    2010-11-01

    Full Text Available Caffeine is one of the most frequently consumed psychoactive substances. It has been known for many years that caffeine at high concentrations exerts harmful effects on both women's and laboratory animals' fertility, moreover it may impair normal development of many organs in the prenatal period. So far there have been few studies performed that demonstrate teratogenic effects of caffeine on structures of the developing eye, particularly the cornea. The aim of the study was to show ultrastructural changes in the developing cornea, as the effect of caffeine administration to chicken embryos. The experimental materials were 26 chicken embryos from incubated breeding eggs. Eggs were divided into two groups: control (n=30 in which Ringer liquid was administrated, and experimental (n=30 in which teratogenic dose of caffeine 3.5mg/egg was given. In 36th hour of incubation solutions were given with cannula through hole in an egg shell directly onto amniotic membrane. After closing the hole with a glass plate and paraffine, eggs were put back to incubator. In 10th and 19th day of incubation corneas were taken for morphological analysis with a use of electron microscopy. Administration of caffeine during chicken development causes changes of collagen fibers of Bowman's membrane patterns and of the corneal stroma but it also changes proportion of amount of collagen fibers and of the stromal cells.

  12. The brittleness model of complex system based on cellular automata

    Institute of Scientific and Technical Information of China (English)

    LIN De-ming; JIN Hong-zhang; LI Qi; WU Hong-mei

    2004-01-01

    Now the research on the complex system is a hot spot. Brittleness is one of the basic characteristics of a complex system. In a complex system, after one of subsystems is struck to be collapsed, the whole system will collapse. Meanwhile, cellular automata is a discrete dynamic system. When the rule is given, the cellular automata could be defined. Then it can imitate the complex action. Cellular automata is used to simulate the brittleness action in this study. Entropy was used to analyze the action and get the rule. Then,three normal brittleness models were given. The result shows that the brittleness of complex system is existent and in addition some important behavior mode of complex system brittleness has been achieved.

  13. Brittle and compaction creep in porous sandstone

    Science.gov (United States)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate

  14. Modeling failure in brittle porous ceramics

    Science.gov (United States)

    Keles, Ozgur

    Brittle porous materials (BPMs) are used for battery, fuel cell, catalyst, membrane, filter, bone graft, and pharmacy applications due to the multi-functionality of their underlying porosity. However, in spite of its technological benefits the effects of porosity on BPM fracture strength and Weibull statistics are not fully understood--limiting a wider use. In this context, classical fracture mechanics was combined with two-dimensional finite element simulations not only to account for pore-pore stress interactions, but also to numerically quantify the relationship between the local pore volume fraction and fracture statistics. Simulations show that even the microstructures with the same porosity level and size of pores differ substantially in fracture strength. The maximum reliability of BPMs was shown to be limited by the underlying pore--pore interactions. Fracture strength of BMPs decreases at a faster rate under biaxial loading than under uniaxial loading. Three different types of deviation from classic Weibull behavior are identified: P-type corresponding to a positive lower tail deviation, N-type corresponding to a negative lower tail deviation, and S-type corresponding to both positive upper and lower tail deviations. Pore-pore interactions result in either P-type or N-type deviation in the limit of low porosity, whereas S-type behavior occurs when clusters of low and high fracture strengths coexist in a fracture data.

  15. CONSERVATION LAWS IN FINITE MICROCRACKING BRITTLE SOLIDS

    Institute of Scientific and Technical Information of China (English)

    Wang Defa; Chen Yiheng; Fukui Takuo

    2005-01-01

    This paper addresses the conservation laws in finite brittle solids with microcracks.The discussion is limited to the 2-D cases. First, after considering the combination of the PseudoTraction Method and the indirect Boundary Element Method, a versatile method for solving multicrack interacting problems in finite plane solids is proposed, by which the fracture parameters (SIF and path-independent integrals) can be calculated with a desirable accuracy. Second, with the aid of the method proposed, the roles the conservation laws play in the fracture analysis for finite microcracking solids are studied. It is concluded that the conservation laws do play important roles in not only the fracture analysis but also the analysis of damage and stability for the finite microcracking system. Finally, the physical interpretation of the M-integral is discussed further.An explicit relation between the M-integral and the crack face area, I.e., M = GS, has been discovered using the analytical method, which can shed some light on the Damage Mechanics issues from a different perspective.

  16. The Ets transcription factor EHF as a regulator of cornea epithelial cell identity.

    Science.gov (United States)

    Stephens, Denise N; Klein, Rachel Herndon; Salmans, Michael L; Gordon, William; Ho, Hsiang; Andersen, Bogi

    2013-11-29

    The cornea is the clear, outermost portion of the eye composed of three layers: an epithelium that provides a protective barrier while allowing transmission of light into the eye, a collagen-rich stroma, and an endothelium monolayer. How cornea development and aging is controlled is poorly understood. Here we characterize the mouse cornea transcriptome from early embryogenesis through aging and compare it with transcriptomes of other epithelial tissues, identifying cornea-enriched genes, pathways, and transcriptional regulators. Additionally, we profiled cornea epithelium and stroma, defining genes enriched in these layers. Over 10,000 genes are differentially regulated in the mouse cornea across the time course, showing dynamic expression during development and modest expression changes in fewer genes during aging. A striking transition time point for gene expression between postnatal days 14 and 28 corresponds with completion of cornea development at the transcriptional level. Clustering classifies co-expressed, and potentially co-regulated, genes into biologically informative categories, including groups that exhibit epithelial or stromal enriched expression. Based on these findings, and through loss of function studies and ChIP-seq, we show that the Ets transcription factor EHF promotes cornea epithelial fate through complementary gene activating and repressing activities. Furthermore, we identify potential interactions between EHF, KLF4, and KLF5 in promoting cornea epithelial differentiation. These data provide insights into the mechanisms underlying epithelial development and aging, identifying EHF as a regulator of cornea epithelial identity and pointing to interactions between Ets and KLF factors in promoting epithelial fate. Furthermore, this comprehensive gene expression data set for the cornea is a powerful tool for discovery of novel cornea regulators and pathways.

  17. Delivery of antisense oligonucleotide to the cornea by iontophoresis.

    Science.gov (United States)

    Berdugo, M; Valamanesh, F; Andrieu, C; Klein, C; Benezra, D; Courtois, Y; Behar-Cohen, F

    2003-04-01

    We wished to evaluate the potential of iontophoresis to promote the delivery of antisense oligonucleotides (ODN) directed at the vascular endothelial growth factor (VEGF)-R2 receptor (KDR/Flk) to the cornea of the rat eye. Fluorescence (CY5)-labeled ODNs in phosphate-buffered saline (PBS) (20 microM) were locally administered to rat eyes, and their fate within the anterior segment was studied. Thirty-four male, 5-week-old Wistar rats were used for all experiments. The rats were divided in four groups. In group I (12 rats, 12 eyes), the ODNs (20 microM) were delivered by iontophoresis (300 microA for 5 minutes) using a specially designed corneal applicator. In group II (12 rats, 12 eyes), the ODNs (20 microM) were delivered using the same applicator, but no electrical current was applied. In group III (6 rats, 6 eyes), a corneal neovascular reaction was induced prior to the application of ODNs (20 microM), and iontophoresis electrical current was delivered as for group I rats. Group IV (4 rats, 4 eyes) received ODN (60 microM) iontophoresis application (300 microA for 5 minutes) and were used for ODN integrity studies. The animals were killed 5 minutes, 90 minutes, and 24 hours after a single ODN application and studied. Topically applied ODNs using the same iontophoresis applicator but without current do not penetrate the cornea and remain confined to the superficial epithelial layer. ODNs delivered with transcorneoscleral iontophoresis penetrate into all corneal layers and are also detected in the iris. In corneas with neovascularization, ODNs were particularly localized within the vascular endothelial cells of the stroma. ODNs extracted from eye tissues 24 hours after iontophoresis remained unaltered. The iontophoresis current did not cause any detectable ocular damage under these conditions. Iontophoresis promotes the delivery of ODNs to the anterior segment of the eye, including all corneal layers. Iontophoresis of ODNs directed at VEGF-R2 may be used for the

  18. Reversible temper brittleness on tensile tests at room temperature

    International Nuclear Information System (INIS)

    Tensile tests were carried out on unnotched test pieces at room temperature and three strain rates: 2,5x10-4, 2,5x10-3 and 1,0x10-2 s-1 in a low alloy No-Cr-Mo steel to observe the variation in its mechanical properties with the occurrence of reversible temper brittleness. The brittle samples showed a sensitivity of 500C in a 48 hour heat treatment at 5000C. The tests showed that at the strain rate of 2,5x10-4 s-1 there are statistically significant differences between the elongations of the material in the brittle and the nonbrittle and regenerated states. A short review of reversible temper brittleness is given and a theory suggested for the mechanism

  19. Scattering mechanical performances for brittle bulk metallic glasses

    Directory of Open Access Journals (Sweden)

    J. W. Qiao

    2014-11-01

    Full Text Available Scattering mechanical performances of brittle La- and Mg-based BMGs are found in the present study. Upon dynamic loading, there exist largely scattered fracture strengths even if the strain rates are under the same order, and the BMG systems are the same. The negative strain rate dependence for La- and Mg-based BMGs is obtained, i.e., a decreased fracture strength is dominating from quasi-static to dynamic compression. At cryogenic temperatures, distinguishingly low fracture strengths are available for these two brittle BMGs, and decreased tolerance to accommodate strains makes BMGs more and more brittle. It is concluded that the scattering mechanical performances of brittle BMGs should be carefully evaluated before actual applications.

  20. Universal behaviour in compressive failure of brittle materials.

    Science.gov (United States)

    Renshaw, C E; Schulson, E M

    2001-08-30

    Brittle failure limits the compressive strength of rock and ice when rapidly loaded under low to moderate confinement. Higher confinement or slower loading results in ductile failure once the brittle-ductile transition is crossed. Brittle failure begins when primary cracks initiate and slide, creating wing cracks at their tips. Under little to no confinement, wing cracks extend and link together, splitting the material into slender columns which then fail. Under low to moderate confinement, wing crack growth is restricted and terminal failure is controlled by the localization of damage along a narrow band. Early investigations proposed that localization results from either the linkage of wing cracks or the buckling of microcolumns created between adjacent wing cracks. Observations of compressive failure in ice suggest a mechanism whereby localization initiates owing to the bending-induced failure of slender microcolumns created between sets of secondary cracks emanating from one side of a primary crack. Here we analyse this mechanism, and show that it leads to a closed-form, quantitative model that depends only on independently measurable mechanical parameters. Our model predictions for both the brittle compressive strength and the brittle-ductile transition are consistent with data from a variety of crystalline materials, offering quantitative evidence for universal processes in brittle failure and for the broad applicability of the model. PMID:11528475

  1. An adaptive algorithm for the cornea modeling from keratometric data

    CERN Document Server

    Martinez-Finkelshtein, Andrei; Castro-Luna, Gracia M; Alio, Jorge L

    2010-01-01

    In this paper we describe an adaptive and multi-scale algorithm for the parsimonious fit of the corneal surface data that allows to adapt the number of functions used in the reconstruction to the conditions of each cornea. The method implements also a dynamical selection of the parameters and the management of noise. It can be used for the real-time reconstruction of both altimetric data and corneal power maps from the data collected by keratoscopes, such as the Placido rings based topographers, decisive for an early detection of corneal diseases such as keratoconus. Numerical experiments show that the algorithm exhibits a steady exponential error decay, independently of the level of aberration of the cornea. The complexity of each anisotropic gaussian basis functions in the functional representation is the same, but their parameters vary to fit the current scale. This scale is determined only by the residual errors and not by the number of the iteration. Finally, the position and clustering of their centers,...

  2. Morphology, topography, and optics of the orthokeratology cornea

    Science.gov (United States)

    Faria-Ribeiro, Miguel; Belsue, Rafael Navarro; López-Gil, Norberto; González-Méijome, José Manuel

    2016-07-01

    The goal of this work was to objectively characterize the external morphology, topography, and optics of the cornea after orthokeratology (ortho-k). A number of 24 patients between the ages of 17 and 30 years (median=24 years) were fitted with Corneal Refractive Therapy® contact lenses to correct myopia between -2.00 and -5.00 diopters (D) (median=-3.41 D). A classification algorithm was applied to conduct an automatic segmentation based on the mean local curvature. As a result, three zones (optical zone, transition zone, and peripheral zone) were delimited. Topographical analysis was provided through global and zonal fit to a general ellipsoid. Ray trace on partially customized eye models provided wave aberrations and retinal image quality. Monozone topographic description of the ortho-k cornea loses accuracy when compared with zonal description. Primary (C40) and secondary (C60) spherical aberration (SA) coefficients for a 5-mm pupil increased 3.68 and 19 times, respectively, after the treatments. The OZ area showed a strong correlation with C40 (r=-0.49, peye's positive SA after ortho-k is the major factor responsible for the decreased retinal optical quality of the unaccommodated eye.

  3. Comparison of confocal microscopy and two-photon microscopy in mouse cornea in vivo.

    Science.gov (United States)

    Lee, Jun Ho; Lee, Seunghun; Gho, Yong Song; Song, In Seok; Tchah, Hungwon; Kim, Myoung Joon; Kim, Ki Hean

    2015-03-01

    High-resolution imaging of the cornea is important for studying corneal diseases at cellular levels. Confocal microscopy (CM) has been widely used in the clinic, and two-photon microscopy (TPM) has recently been introduced in various pre-clinical studies. We compared the performance of CM and TPM in normal mouse corneas and neovascularized mouse corneas induced by suturing. Balb/C mice and C57BL/6 mice expressing green fluorescent protein (GFP) were used to compare modalities based on intrinsic contrast and extrinsic fluorescence contrast. CM based on reflection (CMR), CM based on fluorescence (CMF), and TPM based on intrinsic/extrinsic fluorescence and second harmonic generation (SHG) were compared by imaging the same sections of mouse corneas sequentially in vivo. In normal mouse corneas, CMR visualized corneal cell morphologies with some background noise, and CMF visualized GFP expressing corneal cells clearly. TPM visualized corneal cells and collagen in the stroma based on fluorescence and SHG, respectively. However, in neovascularized mouse corneas, CMR could not resolve cells deep inside the cornea due to high background noise from the effects of increased structural irregularity induced by suturing. CMF and TPM visualized cells and induced vasculature better than CMR because both collect signals from fluorescent cells only. Both CMF and TPM had signal decays with depth due to the structural irregularity, with CMF having faster signal decay than TPM. CMR, CMF, and TPM showed different degrees of image degradation in neovascularized mouse corneas.

  4. Validation of tissue quality parameters for donor corneas, designated for emergency cases: corneal graft survival

    NARCIS (Netherlands)

    W.J. Rijneveld; R. Wolff; H.J.M. Volker-Dieben; E. Pels

    2011-01-01

    Purpose: To validate tissue quality parameters for donor corneas designated for emergency grafting for corneal graft survival. Methods: In a longitudinal cohort follow-up study, 131 emergency penetrating grafts were studied. Grafts were performed with a pool of organ-cultured donor corneas designate

  5. Prevalence and clinical consequences of herpes simplex virus type 1 DNA in human cornea tissues

    NARCIS (Netherlands)

    L. Remeijer (Lies); R. Duan (Rui); J.M. van Dun (Jessica); M.A.W. Bettink; A.D.M.E. Osterhaus (Ab); G.M.G.M. Verjans (George)

    2009-01-01

    textabstractBackground. We determined the prevalence and clinical consequences of herpes simplex virus (HSV) type 1 (HSV-1), HSV type 2 (HSV-2), and varicella-zoster virus (VZV) in cornea tissues obtained after penetrating keratoplasty (PKP) was performed. Methods. The excised corneas of 83 patients

  6. Use of Fourier-Domain Optical Coherence Tomography to Evaluate Anterior Stromal Opacities in Donor Corneas

    Directory of Open Access Journals (Sweden)

    Matthew R. Bald

    2013-01-01

    Full Text Available Purpose. To evaluate Fourier-domain optical coherence tomography (FD-OCT as an adjunct to traditional slit lamp examination of donor corneas with suspected Anterior Stromal Opacities. Methods. Seven corneas suspected of having anterior stromal opacities by slit lamp examination were evaluated with FD-OCT. Each cornea was evaluated to confirm the presence of opacity and, if present, the depth of opacity was measured. Results. The opacity depth ranged from 82 μm to 624 μm. The initial slit lamp impressions of five of the seven corneas were confirmed by OCT. In two corneas, the OCT findings were different from the initial slit lamp impressions. Slit lamp examination of the first cornea gave the impression of anterior stromal scarring, but OCT showed that the opacity was limited to the epithelium. Slit lamp examination of the second cornea suggested opacity limited to the epithelium, but OCT identified significant sub-Bowman's scarring. In all cases, the Eye Bank Technicians reported that the location and depth of corneal opacity were more sharply defined by OCT than by slit lamp. Conclusion. The high resolution of OCT makes it easier to determine the location of corneal opacities compared to slit lamp examinations. This enhanced visualization can improve decisions regarding transplant suitability of donor corneas.

  7. [Alport's syndrome (author's transl)].

    Science.gov (United States)

    Huismans, H

    1978-05-01

    A case report is given of a 22-years old student (whose brother had Alport's syndrome) with recurrent central corneal swelling and paracentral erosions of the cornea of both eyes. Further signs of beginning Alport's syndrome in this case are disturbance of re-adaptation after dazzling (Mesoptometer) and paracentral scotomata in the visual fields. Remarkable was the small diameter of the disc in both eyes (1.37 mm). Local therapy was Scopolamin-eye-drops, Actihaemyl- and especially Cystein-Gel (2.4%). PMID:672101

  8. Optical transferences and their application to ray tracing through the human cornea*

    Directory of Open Access Journals (Sweden)

    S. D. Mathebula

    2011-12-01

    Full Text Available The purpose of this paper is two fold, firstly to describe aspects of the quantitative analysis of the linear optical character of the corneas of ten young and healthy subjects using the exp-mean-log-transference and secondly to illustrate how mean transference and ray vector fields or diagrams can be used to explain and understand the optical properties of corneas as thick optical systems.An Oculus Pentacam was used to obtain 43 successive measurements of the radii of curvature of the anterior and posterior corneal surfaces and the central corneal thicknesses of the right eyes of ten subjects. From these measurements 4×4 ray transferences were calculated. Mean transferences were obtained via multi-dimensional Hamiltonian space and these mean transferences were used to produce stereo-pairs of ray vector fields. The mean transferences are also important in understanding the behaviour of light through each of the corneas concerned. This paper provides the first order optical characters of corneas from the positions and inclinations of rays entering and leaving such systems. As anticipated, light rays through the cornea are deflected inwards when the refractive index of the cornea is greater than the index of the surrounding medium. The exp-mean-log transference for a specific cornea exists and is the optical transference of the averaged cornea of the sample of measurements for that cornea. Within the limitations of linear or paraxial optics, the corneas of the different eyes in this sample and their averages were found to be close to that of thin optical systems; but they were not truly thin and instead should be considered as being thick optical systems. (S Afr Optom 2011 70(4 156-167

  9. Evaluation of the efficacy of excimer laser ablation of cross-linked porcine cornea.

    Directory of Open Access Journals (Sweden)

    Shihao Chen

    Full Text Available BACKGROUND: Combination of riboflavin/UVA cross-linking (CXL and excimer laser ablation is a promising therapy for treating corneal ectasia. The cornea is strengthened by cross-linking, while the irregular astigmatism is reduced by laser ablation. This study aims to compare the efficacy of excimer laser ablation on porcine corneas with and without cross-linking. METHODS AND FINDINGS: The porcine cornea was de-epithelialized and treated with 0.1% riboflavin solution for 30 minutes. A half of the cornea was exposed to UVA-radiation for another 30 minutes while the controlled half of the cornea was protected from the UVA using a metal shield. Photo therapeutic keratectomy (PTK was then performed on the central cornea. Corneal thickness of 5 paired locations on the horizontal line, ± 0.5, ± 1.0, ± 1.5, ± 2.0, and ± 2.5 mm from the central spot, were measured using optical coherence tomography prior to and after PTK. The ablation depth was then determined by the corneal thickness. There was a 9% difference (P<0.001 in the overall ablation depth between the CXL-half corneas (158 ± 22 µm and the control-half corneas (174 ± 26 µm. The ablation depths of all 5 correspondent locations on the CXL-half were significantly smaller (P<0.001. CONCLUSION: The efficacy of the laser ablation seems to be lower in cross-linked cornea. Current ablation algorithms may need to be modified for cross-linked corneas.

  10. Brittle and semibrittle creep in a low porosity carbonate rock

    Science.gov (United States)

    Nicolas, Aurélien; Fortin, Jérôme; Regnet, Jean-Baptiste; Dimanov, Alexandre; Guéguen, Yves

    2016-04-01

    The mechanical behavior of limestones at room temperature is brittle at low confining pressure and becomes semi-brittle with the increase of the confining pressure. The brittle behavior is characterized by a macroscopic dilatancy due to crack propagation, leading to a stress drop when cracks coalesce at failure. The semi-brittle behavior is characterized by diffuse deformation due to intra-crystalline plasticity (dislocation movements and twinning) and microcracking. The aim of this work is to examine the influence of pore fluid and time on the mechanical behavior. Constant strain rate triaxial deformation experiments and stress-stepping creep experiments were performed on white Tavel limestone (porosity 14.7%). Elastic wave velocity evolutions were recorded during each experiment and inverted to crack densities. Constant strain rate triaxial experiments were performed for confining pressure in the range of 5-90 MPa. For Pc≤55 MPa our results show that the behavior is brittle. In this regime, water-saturation decreases the differential stress at the onset of crack propagation and enhances macroscopic dilatancy. For Pc≥70 MPa, the behavior is semi-brittle. Inelastic compaction is due to intra-crystalline plasticity and micro-cracking. However, in this regime, our results show that water-saturation has no clear effect at the onset of inelastic compaction. Stress stepping creep experiments were performed in a range of confining pressures crossing the brittle-ductile transition. In the brittle regime, the time-dependent axial deformation is coupled with dilatancy and a decrease of elastic wave velocities, which is characteristic of crack propagation and/or nucleation. In the semi-brittle regime, the first steps are inelastic compactant because of plastic pore collapse. But, following stress steps are dilatant because of crack nucleation and/or propagation. However, our results show that the axial strain rate is always controlled by plastic phenomena, until the last

  11. Brittleness Generation Mechanism and Failure Model of High Strength Lightweight Aggregate Concrete

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The brittleness generation mechanism of high strength lightweight aggregate concrete(HSLWAC) was presented, and it was indicated that lightweight aggregate was the vulnerable spot,initiating brittleness. Based on the analysis of the brittleness failure by the load-deflection curve, the brittleness presented by HSLWAC was more prominent compared with ordinary lightweight aggregate concrete of the same strength grade. The model of brittleness failure was also established.

  12. Tissue Engineering the Cornea: The Evolution of RAFT

    Directory of Open Access Journals (Sweden)

    Hannah J. Levis

    2015-01-01

    Full Text Available Corneal blindness affects over 10 million people worldwide and current treatment strategies often involve replacement of the defective layer with healthy tissue. Due to a worldwide donor cornea shortage and the absence of suitable biological scaffolds, recent research has focused on the development of tissue engineering techniques to create alternative therapies. This review will detail how we have refined the simple engineering technique of plastic compression of collagen to a process we now call Real Architecture for 3D Tissues (RAFT. The RAFT production process has been standardised, and steps have been taken to consider Good Manufacturing Practice compliance. The evolution of this process has allowed us to create biomimetic epithelial and endothelial tissue equivalents suitable for transplantation and ideal for studying cell-cell interactions in vitro.

  13. Polymicrobial Infection of the Cornea Due to Contact Lens Wear

    Science.gov (United States)

    Sızmaz, Selçuk; Bingöllü, Sibel; Erdem, Elif; Kibar, Filiz; Koltaş, Soner; Yağmur, Meltem; Ersöz, Reha

    2016-01-01

    A 38-year-old male presented with pain and redness in his left eye. He had a history of wearing contact lenses. His ophthalmic examination revealed a large corneal ulcer with surrounding infiltrate. Cultures were isolated from the contact lenses, lens solutions, storage cases, and conjunctivae of both eyes and also corneal scrapings of the left eye. Fortified vancomycin and amikacin drops were started hourly. Culture results of conjunctivae of each eye and left cornea were positive for Pseudomonas aeruginosa; cultures from the contact lenses, lens solution and storage case of both eyes revealed Pseudomonas aeruginosa and Alcaligenes xylosoxidans. Polymerase chain reaction of the corneal scraping was positive for Acanthameoba. The topical antibiotics were changed with ones that both bacteria were sensitive to and anti-amoebic therapy was added. The patient had two recurrences following initial presentation despite intensive therapy. Keratitis occurred due to multiple pathogens; the relapsing course despite adequate therapy is potentially associated with this polymicrobial etiology. PMID:27800266

  14. Brittle and ductile friction and the physics of tectonic tremor

    Science.gov (United States)

    Daub, E.G.; Shelly, D.R.; Guyer, R.A.; Johnson, P.A.

    2011-01-01

    Observations of nonvolcanic tremor provide a unique window into the mechanisms of deformation and failure in the lower crust. At increasing depths, rock deformation gradually transitions from brittle, where earthquakes occur, to ductile, with tremor occurring in the transitional region. The physics of deformation in the transition region remain poorly constrained, limiting our basic understanding of tremor and its relation to earthquakes. We combine field and laboratory observations with a physical friction model comprised of brittle and ductile components, and use the model to provide constraints on the friction and stress state in the lower crust. A phase diagram is constructed that characterizes under what conditions all faulting behaviors occur, including earthquakes, tremor, silent transient slip, and steady sliding. Our results show that tremor occurs over a range of ductile and brittle frictional strengths, and advances our understanding of the physical conditions at which tremor and earthquakes take place. Copyright ?? 2011 by the American Geophysical Union.

  15. Effects of the holmium laser on the human cornea: a preliminary study

    Science.gov (United States)

    Mueller, Linda J.; Tassignon, Marie J.; Trau, Rene; Pels, Liesbeth; Vrensen, Gijs F.

    1996-12-01

    Treatment of peripheral post-mortem human corneas with the Holmium laser in a ring pattern resulted in opaque spots. One pair of treated eyes was immediately processed for light and electron microscopy and three other treated eyes were preserved for 4 days in medium in order to compare direct and short-term effects of the Holmium laser. Cross as well as frontal light microscopical sections of all eyes revealed interconnecting bands between the spots. At the ultrastructural level the anterior corneal tissue within these spots was characterized by coagulation of cells and collagen and shoed either a dramatic distorting effect on the epithelium in the eyes processed immediately or a single layer of flattened multi-nucleolated epithelial cells having more than one nucleolus per nucleus in the eyes stored in medium. Furthermore, the spots showed disturbed Bowman's layer, destroyed keratocytes and collagen fibrils which were either coagulated or organized chaotically. The interconnecting bands contained alternating normal and coagulated collagen fibers. The rest of the cornea outside the spots had a normal appearance. In corneas stored in medium, both keratocytes and epithelial cells over the entire cornea exhibited accumulations of cytoplasmic fibrils and glycogen particles. These phenomena were not observed in non-preserved corneas, suggesting that the differences are due to preservation and not due to the laser treatment. It is concluded that morphological changes occur mainly in the treated peripheral cornea whereas the central untreated cornea remains unaffected,indicating that the Holmium laser is a reliable instrument to treat hypermetropic patients.

  16. In the Initiation of Brittle Compressive Failure: Lessons From Ice

    Science.gov (United States)

    Renshaw, C. E.; Schulson, E. M.

    2001-12-01

    Brittle failure limits the compressive strength of rock and ice when rapidly loaded under low to moderate confinement. Higher confinement or slower loading results in ductile failure once the brittle-ductile transition is crossed. It is well established that the macroscopic brittle failure of rock, concrete and other brittle materials under compression is preceded by the initiation and sliding of microscopic primary cracks, creating wing cracks at their tips. In laboratory samples, microcracks begin to nucleate more or less uniformly throughout the sample at compressions equal to about 1/5 to 1/3 the terminal failure stress. Under little to no confinement, wing cracks extend and link together, splitting the material into slender columns which then fail. Under low to moderate confinement, wing crack growth is restricted and terminal failure is controlled by the localization of damage along discrete bands of intense damage inclined by approximately 30 degrees to the direction of the most compressive stress. Earlier investigators proposed that localization results from either the linkage of wing cracks or the buckling of microcolumns created between adjacent wing cracks. Observations of compressive failure in ice suggest a new mechanism whereby localization initiates due to the bending-induced failure of slender microcolumns created between sets of secondary cracks emanating from one side of a primary crack. Analysis of this mechanism leads to a closed-form, quantitative model that only depends on independently measureable mechanical parameters. We show that model predictions for both the brittle compressive strength and the brittle-ductile transition are consistent with data from a variety of crystalline materials.

  17. Cuttability Assessment of Selected Rocks Through Different Brittleness Values

    Science.gov (United States)

    Dursun, Arif Emre; Gokay, M. Kemal

    2016-04-01

    Prediction of cuttability is a critical issue for successful execution of tunnel or mining excavation projects. Rock cuttability is also used to determine specific energy, which is defined as the work done by the cutting force to excavate a unit volume of yield. Specific energy is a meaningful inverse measure of cutting efficiency, since it simply states how much energy must be expended to excavate a unit volume of rock. Brittleness is a fundamental rock property and applied in drilling and rock excavation. Brittleness is one of the most crucial rock features for rock excavation. For this reason, determination of relations between cuttability and brittleness will help rock engineers. This study aims to estimate the specific energy from different brittleness values of rocks by means of simple and multiple regression analyses. In this study, rock cutting, rock property, and brittleness index tests were carried out on 24 different rock samples with different strength values, including marble, travertine, and tuff, collected from sites around Konya Province, Turkey. Four previously used brittleness concepts were evaluated in this study, denoted as B 1 (ratio of compressive to tensile strength), B 2 (ratio of the difference between compressive and tensile strength to the sum of compressive and tensile strength), B 3 (area under the stress-strain line in relation to compressive and tensile strength), and B 9 = S 20, the percentage of fines (rocks using multiple regression analysis). The results suggest that the proposed simple regression-based prediction models including B 3, B 9, and B 9p outperform the other models including B 1 and B 2 and can be used for more accurate and reliable estimation of specific energy.

  18. A comparison of three methods of decellularization of pig corneas to reduce immunogenicity

    Institute of Scientific and Technical Information of China (English)

    Whayoung; Lee; Yuko; Miyagawa; Cassandra; Long; David; K.; C.; Cooper; Hidetaka; Hara

    2014-01-01

    ·AIM: To investigate whether decellularization using different techniques can reduce immunogenicity of the cornea, and to explore the decellularized cornea as a scaffold for cultured corneal endothelial cells(CECs).Transplantation of decellularized porcine corneas increases graft transparency and survival for longer periods compared with fresh grafts.·METHODS: Six-month-old wild-type pig corneas were cut into 100-200 μm thickness, and then decellularized by three different methods: 1) 0.1% sodium dodecyl sulfate(SDS); 2) hypoxic nitrogen(N2); and 3) hypertonic NaCl. Thickness and transparency were assessed visually. Fresh and decellularized corneas were stained with hematoxylin/eosin(H&E), and for the presence of galactose-α1,3-galactose(Gal) and N-glycolylneuraminic acid(NeuGc, a nonGal antigen). Also, a human IgM/IgG binding assay was performed. Cultured porcine CECs were seeded on the surface of the decellularized cornea and examined after H&E staining.· RESULTS: All three methods of decellularization reduced the number of keratocytes in the stromal tissue by >80% while the collagen structure remained preserved. No remaining nuclei stained positive for Gal or NeuGc, and expression of these oligosaccharides on collagen was also greatly decreased compared to expression on fresh corneas. Human IgM/IgG binding to decellularized corneal tissue was considerably reduced compared to fresh corneal tissue. The cultured CECs formed a confluent monolayer on the surface of decellularized tissue.· CONCLUSION: Though incomplete, the significant reduction in the cellular component of the decellularized cornea should be associated with a significantly reduced in vivo immune response compared to fresh corneas.

  19. Imaging of Keratoconic and normal human cornea with a Brillouin imaging system (Conference Presentation)

    Science.gov (United States)

    Besner, Sebastien; Shao, Peng; Scarcelli, Giuliano; Pineda, Roberto; Yun, Seok-Hyun (Andy)

    2016-03-01

    Keratoconus is a degenerative disorder of the eye characterized by human cornea thinning and morphological change to a more conical shape. Current diagnosis of this disease relies on topographic imaging of the cornea. Early and differential diagnosis is difficult. In keratoconus, mechanical properties are found to be compromised. A clinically available invasive technique capable of measuring the mechanical properties of the cornea is of significant importance for understanding the mechanism of keratoconus development and improve detection and intervention in keratoconus. The capability of Brillouin imaging to detect local longitudinal modulus in human cornea has been demonstrated previously. We report our non-contact, non-invasive, clinically viable Brillouin imaging system engineered to evaluate mechanical properties human cornea in vivo. The system takes advantage of a highly dispersive 2-stage virtually imaged phased array (VIPA) to detect weak Brillouin scattering signal from biological samples. With a 1.5-mW light beam from a 780-nm single-wavelength laser source, the system is able to detect Brillouin frequency shift of a single point in human cornea less than 0.3 second, at a 5μm/30μm lateral/axial resolution. Sensitivity of the system was quantified to be ~ 10 MHz. A-scans at different sample locations on a human cornea with a motorized human interface. We imaged both normal and keratoconic human corneas with this system. Whereas no significantly difference were observed outside keratocnic cones compared with normal cornea, a highly statistically significantly decrease was found in the cone regions.

  20. BRITTLE-DUCTILE TRANSITION OF POLYMERS AND ITS PERCOLATION MODEL

    Institute of Scientific and Technical Information of China (English)

    Wei Jiang; Li-jia An; Bing-zheng Jiang

    2003-01-01

    The brittle-ductile transition (BDT) of particle toughened polymers was extensively studied in terms of morphology, strain rate, and temperature. The calculation results showed that both the critical interparticle distance (IDc) and the brittle-ductile transition temperature (TBD) of polymers were a function of strain rate. The IDc reduced nonlinearly with increasing strain rate, whereas TBD increased considerably with increasing strain rate. The effects of temperature and plasticizer concentration on BDT were discussed using a percolation model. The results were in agreement with the experiments.

  1. A time-delay calibrated method for cornea hysteresis and intraocular pressure measurement

    Science.gov (United States)

    Wang, Kuo-Jen; Tsai, Che-Liang; Wang, Wai; Hsu, Long; Hsu, Ken-Yuh

    2016-04-01

    The presence of cornea hysteresis (CH) in characterizing the intraocular pressure (IOP) of a human eye deteriorates the accuracy of IOP. To suppress CH, the pressure gauge of a tonometer must be located as close as possible to the cornea. However, this arrangement is unpractical because appropriate working distance to the cornea is required. In this paper, a time-delay calibrated (TDC) method is proposed to counteract the undesired effect of CH in characterizing the IOP. Employing this TDC method, the CH approaches to zero for most eyes measured.

  2. Fracture mechanics applied to the machining of brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  3. Finite element modelling of fibre-reinforced brittle materials

    NARCIS (Netherlands)

    Kullaa, J.

    1997-01-01

    The tensile constitutive behaviour of fibre-reinforced brittle materials can be extended to two or three dimensions by using the finite element method with crack models. The three approaches in this study include the smeared and discrete crack concepts and a multi-surface plasticity model. The tensi

  4. Microscopic characteristics of different fracture modes of brittle rock

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Three types of rock specimens, three-point bending specimen, anti-symmetric four-point bending specimen and direct shearing specimen, were used to achieve Mode Ⅰ , Mode Ⅱ and mixed mode Ⅰ - Ⅱ fracture, respectively . Microscopic characteristics of the three fracture modes of brittle rock were studied by SEM technique in order to analyze fracture behaviors and better understand fracture mechanisms of different fracture modes of brittle rock. Test results show that the microscopic characteristics of different fracture modes correspond to different fracture mechanisms. The surface of Mode Ⅰ fracture has a great number of sparse and steep slip-steps with few tearing ridges and shows strong brittleness. In the surface of Mode Ⅱ fracture there exist many tearing ridges and densely distributed parallel slip-steps and it is attributed to the action of shear stress.The co-action of tensile and shear stresses results in brittle cleavage planes mixed with streamline patterns and tearing ridges in the surface of mixed mode Ⅰ - Ⅱ fracture. The measured Mode Ⅱ fracture toughness K Ⅱ c and mixed mode Ⅰ -Ⅱ fracture toughness Kmc are larger than Mode Ⅰ fracture toughness KⅠc. KⅡc is about 3.5times KI c, and KmC is about 1.2 times K Ⅰ c.

  5. A role for smoothened during murine lens and cornea development.

    Directory of Open Access Journals (Sweden)

    Janet J Y Choi

    Full Text Available Various studies suggest that Hedgehog (Hh signalling plays roles in human and zebrafish ocular development. Recent studies (Kerr et al., Invest Ophthalmol Vis Sci. 2012; 53, 3316-30 showed that conditionally activating Hh signals promotes murine lens epithelial cell proliferation and disrupts fibre differentiation. In this study we examined the expression of the Hh pathway and the requirement for the Smoothened gene in murine lens development. Expression of Hh pathway components in developing lens was examined by RT-PCR, immunofluorescence and in situ hybridisation. The requirement of Smo in lens development was determined by conditional loss-of-function mutations, using LeCre and MLR10 Cre transgenic mice. The phenotype of mutant mice was examined by immunofluorescence for various markers of cell cycle, lens and cornea differentiation. Hh pathway components (Ptch1, Smo, Gli2, Gli3 were detected in lens epithelium from E12.5. Gli2 was particularly localised to mitotic nuclei and, at E13.5, Gli3 exhibited a shift from cytosol to nucleus, suggesting distinct roles for these transcription factors. Conditional deletion of Smo, from ∼E12.5 (MLR10 Cre did not affect ocular development, whereas deletion from ∼E9.5 (LeCre resulted in lens and corneal defects from E14.5. Mutant lenses were smaller and showed normal expression of p57Kip2, c-Maf, E-cadherin and Pax6, reduced expression of FoxE3 and Ptch1 and decreased nuclear Hes1. There was normal G1-S phase but decreased G2-M phase transition at E16.5 and epithelial cell death from E14.5-E16.5. Mutant corneas were thicker due to aberrant migration of Nrp2+ cells from the extraocular mesenchyme, resulting in delayed corneal endothelial but normal epithelial differentiation. These results indicate the Hh pathway is required during a discrete period (E9.5-E12.5 in lens development to regulate lens epithelial cell proliferation, survival and FoxE3 expression. Defective corneal development occurs

  6. Accelerating repaired basement membrane after bevacizumab treatment on alkali-burned mouse cornea

    Directory of Open Access Journals (Sweden)

    Koon-Ja Lee

    2013-04-01

    Full Text Available To understand the corneal regeneration induced by bevacizumab,we investigated the structure changes of stroma andbasement membrane regeneration. A Stick soaked in 0.5 NNaOH onto the mouse cornea and 2.5 mg/ml of bevacizumabwas delivered into an alkali-burned cornea (2 μl by subconjunctivalinjections at 1 hour and 4 days after injury. At 7 daysafter injury, basement membrane regeneration was observedby transmission electron microscope. Uneven and thin epithelialbasement membrane, light density of hemidesmosomes,and edematous collagen fibril bundles are shown in thealkali-burned cornea. Injured epithelial basement membraneand hemidesmosomes and edematous collagen fibril bundlesresulting from alkali-burned mouse cornea was repaired bybevacizumab treatment. This study demonstrates that bevacizumabcan play an important role in wound healing in thecornea by accelerating the reestablishment of basementmembrane integrity that leads to barriers for scar formation.[BMB Reports 2013; 46(4: 195-200

  7. Screening human donor corneas during organ culture for the presence of guttae

    OpenAIRE

    Borderie, V; Sabolic, V.; Touzeau, O.; Scheer, S; Carvajal-Gonzalez, S.; Laroche, L.

    2001-01-01

    AIMS—To detect the presence of guttae by means of light microscopy during organ culture and to evaluate the influence of the presence of guttae in the donor tissue on transplantation outcome.
METHODS—Donor corneas were investigated for the presence of guttae by means of light microscopy at the end of organ culture. Recipient corneal buttons from patients with severe Fuchs' dystrophy and donor corneas with advanced guttae were first studied by light microscopy and subsequently by transmission ...

  8. Diabetic cornea wounds produce significantly weaker electric signals that may contribute to impaired healing

    OpenAIRE

    Yunyun Shen; Trisha Pfluger; Fernando Ferreira; Jiebing Liang; Navedo, Manuel F.; Qunli Zeng; Brian Reid; Min Zhao

    2016-01-01

    Wounds naturally produce electric signals which serve as powerful cues that stimulate and guide cell migration during wound healing. In diabetic patients, impaired wound healing is one of the most challenging complications in diabetes management. A fundamental gap in knowledge is whether diabetic wounds have abnormal electric signaling. Here we used a vibrating probe to demonstrate that diabetic corneas produced significantly weaker wound electric signals than the normal cornea. This was conf...

  9. Hyperglycemia-induced abnormalities in rat and human corneas: the potential of second harmonic generation microscopy.

    Directory of Open Access Journals (Sweden)

    Gaël Latour

    Full Text Available BACKGROUND: Second Harmonic Generation (SHG microscopy recently appeared as an efficient optical imaging technique to probe unstained collagen-rich tissues like cornea. Moreover, corneal remodeling occurs in many diseases and precise characterization requires overcoming the limitations of conventional techniques. In this work, we focus on diabetes, which affects hundreds of million people worldwide and most often leads to diabetic retinopathy, with no early diagnostic tool. This study then aims to establish the potential of SHG microscopy for in situ detection and characterization of hyperglycemia-induced abnormalities in the Descemet's membrane, in the posterior cornea. METHODOLOGY/PRINCIPAL FINDINGS: We studied corneas from age-matched control and Goto-Kakizaki rats, a spontaneous model of type 2 diabetes, and corneas from human donors with type 2 diabetes and without any diabetes. SHG imaging was compared to confocal microscopy, to histology characterization using conventional staining and transmitted light microscopy and to transmission electron microscopy. SHG imaging revealed collagen deposits in the Descemet's membrane of unstained corneas in a unique way compared to these gold standard techniques in ophthalmology. It provided background-free images of the three-dimensional interwoven distribution of the collagen deposits, with improved contrast compared to confocal microscopy. It also provided structural capability in intact corneas because of its high specificity to fibrillar collagen, with substantially larger field of view than transmission electron microscopy. Moreover, in vivo SHG imaging was demonstrated in Goto-Kakizaki rats. CONCLUSIONS/SIGNIFICANCE: Our study shows unambiguously the high potential of SHG microscopy for three-dimensional characterization of structural abnormalities in unstained corneas. Furthermore, our demonstration of in vivo SHG imaging opens the way to long-term dynamical studies. This method should be easily

  10. Polymicrobial Infection of the Cornea Due to Contact Lens Wear

    Directory of Open Access Journals (Sweden)

    Selçuk Sızmaz

    2016-04-01

    Full Text Available A 38-year-old male presented with pain and redness in his left eye. He had a history of wearing contact lenses. His ophthalmic examination revealed a large corneal ulcer with surrounding infiltrate. Cultures were isolated from the contact lenses, lens solutions, storage cases, and conjunctivae of both eyes and also corneal scrapings of the left eye. Fortified vancomycin and amikacin drops were started hourly. Culture results of conjunctivae of each eye and left cornea were positive for Pseudomonas aeruginosa; cultures from the contact lenses, lens solution and storage case of both eyes revealed Pseudomonas aeruginosa and Alcaligenes xylosoxidans. Polymerase chain reaction of the corneal scraping was positive for Acanthameoba. The topical antibiotics were changed with ones that both bacteria were sensitive to and anti-amoebic therapy was added. The patient had two recurrences following initial presentation despite intensive therapy. Keratitis occurred due to multiple pathogens; the relapsing course despite adequate therapy is potentially associated with this polymicrobial etiology.

  11. Cloudy corneas as an initial presentation of multiple myeloma

    Directory of Open Access Journals (Sweden)

    Sharma P

    2014-04-01

    Full Text Available Priyanka Sharma,1 Haifa A Madi,1 Richard Bonshek,2 Stephen J Morgan11Sunderland Eye Infirmary, Sunderland, UK; 2National Specialist Ophthalmic Pathology Service, Department of Histopathology, Manchester Royal Infirmary, Manchester, UKSummary: We report a case of previously unsuspected myeloma, presenting with cornea verticillata due to intracorneal paraprotein deposition.History: An 85-year-old female presented via her optician with a 4-month history of cloudy vision. She had undergone an uneventful bilateral phacoemulsification surgery 7 years earlier. Extensive spiraling corneal epithelial opacification was noted on slit-lamp examination. On further investigation, she was found to have a previously unsuspected low-grade multiple myeloma. We established the nature of the corneal deposits with corneal epithelial biopsy histopathology and electron microscopy. It is very rare for multiple myeloma to present in this fashion. Ophthalmologists should be aware that such a presentation may rarely be due to systemic multiple myeloma.Keywords: corneal crystals, multiple myeloma, crystalline keratopathy, vortex keratopathy

  12. Temperature control during diode laser welding in a human cornea

    Science.gov (United States)

    Rossi, Francesca; Matteini, Paolo; Pini, Roberto; Menabuoni, Luca

    2007-07-01

    Diode laser welding is a technique proposed in ophthalmic surgery to induce immediate sealing of clear corneal wounds. The welding effect is achieved irradiating the area, previously treated with a chromophore, by the use of a low power diode laser: the resulting thermal effect induces structural modifications in the stromal collagen, that welds upon cooling. We present a study on the temperature dynamics developing during welding in a human eye. An infrared thermocamera was used to measure the temperature variations on the surface of the cornea during clinical penetrating keratoplasty (corneal transplant). The experimental data were used as a starting point for a theoretical investigation of the temperature rising inside the ocular structures: we developed a mathematical model based on the bio-heat equation and solved by the use of the Finite Element Method (FEM). The predictive accuracy was verified by comparing the temperature post-processing description with the results obtained from the thermographic data. The model was then used to study the temperature rise and heat propagation inside the eye. Experimental results and model analysis indicated the occurrence of heat confinement during the treatment procedure and a modest enhancement of the temperature (reaching about 55°C inside the laser treated wound), thus evidencing the safety of the procedure in clinical applications.

  13. Intrastromal Injection of China Painting Ink in Corneas of Male Rabbits: Clinical and Histological Study

    Directory of Open Access Journals (Sweden)

    Alahmady Hamad Alsmman Hassan

    2016-01-01

    Full Text Available Background. Many patients with corneal opacity or complicated cataract in blind eye ask for cosmoses. In this study we tried to investigate the staining of corneas of male rabbits by Rotring China painting ink and to study the histological changes. Method. 10 eyes of 10 male Baladi Egyptian rabbits were injected (0.1 mL intrastromally in the cornea by the use of China painting ink (Rotring Tinta China through insulin syringe (27-gauge needle by single injection; clinical follow-up is for 6 months and lastly the rabbits were scarified and the stained eyes were enucleated for histological analysis. Results. Clinically the stain was stable in color and distribution in corneas with no major complications. Histological results of the stained rabbit corneas showed blackish pigmentation in the corneal stroma without any inflammatory cellular infiltration. Some fibroblast cells had pigment granules in their cytoplasm in the adjacent layers. Conclusion. Corneal staining by China painting ink is effective and safe in staining of male rabbits cornea; however further study in human corneas with longer follow-up period is advisable.

  14. Human cornea wound healing in organ culture after Er:YAG laser ablation

    Science.gov (United States)

    Shen, Jin-Hui; Joos, Karen M.; Robinson, Richard D.; Shetlar, Debra J.; O'Day, Denis M.

    1998-06-01

    Purpose: To study the healing process in cultured human corneas after Er:YAG laser ablation. Methods: Human cadaver corneas within 24 hours post mortem were ablated with a Q- switched Er:YAG laser at 2.94 micrometer wavelength. The radiant exposure was 500 mJ/cm2. The cornea was cultured on a tissue supporting frame immediately after the ablation. Culture media consisted of 92% minimum essential media, 8% fetal bovine serum, 0.125% HEPES buffer solution, 0.125% gentamicin, and 0.05% fungizone. The entire tissue frame and media container were kept in an incubator at 37 degrees Celsius and 5% CO2. Serial macroscopic photographs of the cultured corneas were taken during the healing process. Histology was performed after 30 days of culture. Results: A clear ablated crater into the stroma was observed immediately after the ablation. The thickness of thermal damage ranges between 1 and 25 micrometer. Haze development within the crater varies from the third day to the fourteenth day according to the depth and the roughness of the crater. Histologic sections of the cultured cornea showed complete re- epithelization of the lased area. Loose fibrous tissue is observed filling the ablated space beneath the epithelium. The endothelium appeared unaffected. Conclusions: The intensity and time of haze development appears dependent upon the depth of the ablation. Cultured human corneas may provide useful information regarding the healing process following laser ablation.

  15. Brittleness index and seismic rock physics model for anisotropic tight-oil sandstone reservoirs

    Institute of Scientific and Technical Information of China (English)

    Huang Xin-Rui; Huang Jian-Ping; Li Zhen-Chun; Yang Qin-Yong; Sun Qi-Xing; Cui Wei

    2015-01-01

    Brittleness analysis becomes important when looking for sweet spots in tight-oil sandstone reservoirs. Hence, appropriate indices are required as accurate brittleness evaluation criteria. We construct a seismic rock physics model for tight-oil sandstone reservoirs with vertical fractures. Because of the complexities in lithology and pore structure and the anisotropic characteristics of tight-oil sandstone reservoirs, the proposed model is based on the solid components, pore connectivity, pore type, and fractures to better describe the sandstone reservoir microstructure. Using the model, we analyze the brittleness sensitivity of the elastic parameters in an anisotropic medium and establish a new brittleness index. We show the applicability of the proposed brittleness index for tight-oil sandstone reservoirs by considering the brittleness sensitivity, the rock physics response characteristics, and cross-plots. Compared with conventional brittleness indexes, the new brittleness index has high brittleness sensitivity and it is the highest in oil-bearing brittle zones with relatively high porosity. The results also suggest that the new brittleness index is much more sensitive to elastic properties variations, and thus can presumably better predict the brittleness characteristics of sweet spots in tight-oil sandstone reservoirs.

  16. Trasplante de córnea Cornea transplant

    Directory of Open Access Journals (Sweden)

    A. Garralda

    2006-08-01

    Full Text Available La queratoplastia o trasplante de córnea es una de las técnicas quirúrgicas más antiguas de la oftalmología cuyas indicaciones son: 1 tectónicas, para preservar la anatomía e integridad corneal, 2 clínicas, para eliminar el tejido corneal inflamado en casos refractarios al tratamiento médico, 3 ópticas, para mejorar la agudeza visual y 4 cosméticas para mejorar el aspecto del ojo. El perfeccionamiento en la técnica y en el instrumental, así como en el tratamiento postoperatorio y en los medios de conservación del tejido donante han mejorado la supervivencia de los injertos realizados. El Modelo Pamplona de coordinación de trasplantes del Hospital Virgen del Camino (HVC está considerado como original y único en España, y en la logística de este programa se incluye el protocolo de detección y extracción de córneas así como el de queratoplastias.The keratoplasty, or corena transplant, is one of the oldest surgical techniques in opthalmology, whose indication are: 1 tectonic, in order to preserve corneal anatomy and integrity; 2 clinical, in order to eliminate the inflamed corneal tissue in cases refractory to medical treatment; 3 optical, in order to improve visual acuity; and 4 cosmetic, in order to improve the appearance of the eye. Improvements in technique and instruments, as well as in post-operative treatment and the means of preserving donated tissue, have improved survival of the grafts. The Pamplona Model of transplant coordination of the Virgen del Camino Hospital is considered to be original and unique in Spain. The logistics of this program include the protocol for detection and extraction of corneas as well as for keratoplasties.

  17. Effect of epithelial debridement on human cornea proteoglycans

    Directory of Open Access Journals (Sweden)

    E.S. Soriano

    2001-03-01

    Full Text Available Corneal transparency is attributed to the regular spacing and diameter of collagen fibrils, and proteoglycans may play a role in fibrillogenesis and matrix assembly. Corneal scar tissue is opaque and this opacity is explained by decreased ultrastructural order that may be related to proteoglycan composition. Thus, the objectives of the present study were to characterize the proteoglycans synthesized by human corneal explants and to investigate the effect of mechanical epithelial debridement. Human corneas unsuitable for transplants were immersed in F-12 culture medium and maintained under tissue culture conditions. The proteoglycans synthesized in 24 h were labeled metabolically by the addition of 35S-sulfate to the medium. These compounds were extracted by 4 M GuHCl and identified by a combination of agarose gel electrophoresis, enzymatic degradation with protease and mucopolysaccharidases, and immunoblotting. Decorin was identified as the main dermatan sulfate proteoglycan and keratan sulfate proteoglycans were also prominent components. When the glycosaminoglycan side chains were analyzed, only keratan sulfate and dermatan sulfate were detected (~50% each. Nevertheless, when these compounds were 35S-labeled metabolically, the label in dermatan sulfate was greater than in keratan sulfate, suggesting a lower synthesis rate for keratan sulfate. 35S-Heparan sulfate also appeared. The removal of the epithelial layer caused a decrease in heparan sulfate labeling and induced the synthesis of dermatan sulfate by the stroma. The increased deposit of dermatan sulfate proteoglycans in the stroma suggests a functional relationship between epithelium and stroma that could be related to the corneal opacity that may appear after epithelial cell debridement.

  18. Brittle fracture in associative polymers: the case of ionomer melts

    DEFF Research Database (Denmark)

    Shabbir, Aamir; Huang, Qian; Chen, Quan;

    2016-01-01

    with uniaxial extensional rheometry to delineate the mechanics leading to the brittle fracture of ionomer melts. When these ionomers are elongated at a rate higher than the inverse relaxation time of physical crosslinks, an edge fracture occurs at a critical stress. Parabolic fracture profiles provide evidence...... that the phenomenon is purely elastic and bulk dissipation has little impact on the crack profile. Experimental results are interpreted within the Griffiths theory for linear elastic materials and the de Gennes theory for viscoelastic materials....

  19. Guidelines for safe design of shipping packages against brittle fracture

    International Nuclear Information System (INIS)

    In 1992, the ninth meeting of the Standing Advisory Group on the Safe Transport of Radioactive Materials recommended the publication of this TECDOC in an effort to promote the widest debate on the criteria for the brittle fracture safe design of transport packages. The published IAEA advice on the influence of brittle fracture on material integrity is contained in Appendix IX of the Advisory Material for the IAEA Regulations for the Safety Transport of Radioactive Material (1985 Edition, as amended 1990), Safety Series No. 37. This guidance is limited in scope, dealing only with ferritic steels in general terms. It is becoming more common for designers to specify materials other than austenitic stainless steel for packaging components. The data on ferritic steels cannot be assumed to apply to other metals, hence the need for further guidance on the development of relationships describing material properties at low temperatures. The methods described in this TECDOC will be considered by the Revision Panel for inclusion in the 1996 Edition of the IAEA Regulations for the Safe Transport of Radioactive Material and the supporting documents. If accepted by the Revision Panel, this advice will be a candidate for upgrading to a Safety Practice. In the interim period, this TECDOC offers provisional advice on brittle fracture evaluation. It is acknowledged that, at this stage, the views expressed do not necessarily reflect those of the governments of Member States or organizations under whose auspices this manuscript was produced. Refs and figs

  20. On failure in polycrystalline and amorphous brittle materials

    Science.gov (United States)

    Bourne, Neil

    2009-06-01

    The response of brittle materials to uniaxial compressive shock loading is still not well understood. Describing the physical mechanisms resulting from the more complex triaxial states that result from impact and penetration is thus empirical. The physical interpretation of the yield point of brittle materials in one-dimensional strain (the Hugoniot elastic limit (HEL)), the rate dependence of this threshold, the form of stress histories and the effect of polycrystalline microstructure still remain to be comprehensively explained. However, evidence of failure occurring in glasses and ceramics behind a travelling front that follows a shock front has been accumulated and verified in several laboratories. Such a boundary has been called a failure front. The variations in properties across this front include complete loss of tensile strength, partial loss of shear strength, reduction in acoustic impedance, lowered sound speed and opacity to light. It is the object of this work to collect observations of these phenomena and their relation to failure and the HEL in brittle materials. Further, to relate these uniaxial strain measurements of their failed states to the depth of penetration (DoP) in the widely conducted test. British Crown Copyright MoD/2009.

  1. THEORETICAL STATISTICAL SOLUTION AND NUMERICAL SIMULATION OF HETEROGENEOUS BRITTLE MATERIALS

    Institute of Scientific and Technical Information of China (English)

    陈永强; 姚振汉; 郑小平

    2003-01-01

    The analytical stress-strain relation with heterogeneous parameters is derived for the heterogeneous brittle materials under a uniaxial extensional load,in which the distributions of the elastic modulus and the failure strength are assumed to be statistically independent.This theoretical solution gives an approximate estimate of the equivalent stress-strain relations for 3-D heterogeneous materials.In one-dimensional cases it may provide comparatively accurate results.The theoretical solution can help us to explain how the heterogeneity influences the mechanical behaviors.Further,a numerical approach is developed to model the non-linear behavior of three-dimensional heterogeneous brittle materials.The lattice approach and statistical techniques are applied to simulate the initial heterogeneity of heterogeneous materials.The load increment in each loading stage is adaptively determined so that the better approximation of the failure process can be realized.When the maximum tensile principal strain exceeds the failure strain,the elements are considered to be broken,which can be carried out by replacing its Young's modulus with a very small value.A 3-D heterogeneous brittle material specimen is simulated during a full failure process.The numerical results are in good agreement with the analytical solutions and experimental data.

  2. Diabetic cornea wounds produce significantly weaker electric signals that may contribute to impaired healing.

    Science.gov (United States)

    Shen, Yunyun; Pfluger, Trisha; Ferreira, Fernando; Liang, Jiebing; Navedo, Manuel F; Zeng, Qunli; Reid, Brian; Zhao, Min

    2016-01-01

    Wounds naturally produce electric signals which serve as powerful cues that stimulate and guide cell migration during wound healing. In diabetic patients, impaired wound healing is one of the most challenging complications in diabetes management. A fundamental gap in knowledge is whether diabetic wounds have abnormal electric signaling. Here we used a vibrating probe to demonstrate that diabetic corneas produced significantly weaker wound electric signals than the normal cornea. This was confirmed in three independent animal models of diabetes: db/db, streptozotocin-induced and mice fed a high-fat diet. Spatial measurements illustrated that diabetic cornea wound currents at the wound edge but not wound center were significantly weaker than normal. Time lapse measurements revealed that the electric currents at diabetic corneas lost the normal rising and plateau phases. The abnormal electric signals correlated significantly with impaired wound healing. Immunostaining suggested lower expression of chloride channel 2 and cystic fibrosis transmembrane regulator in diabetic corneal epithelium. Acute high glucose exposure significantly (albeit moderately) reduced electrotaxis of human corneal epithelial cells in vitro, but did not affect the electric currents at cornea wounds. These data suggest that weaker wound electric signals and impaired electrotaxis may contribute to the impaired wound healing in diabetes. PMID:27283241

  3. Cornea nerve fiber quantification and construction of phenotypes in patients with fibromyalgia

    Science.gov (United States)

    Oudejans, Linda; He, Xuan; Niesters, Marieke; Dahan, Albert; Brines, Michael; van Velzen, Monique

    2016-01-01

    Cornea confocal microscopy (CCM) is a novel non-invasive method to detect small nerve fiber pathology. CCM generally correlates with outcomes of skin biopsies in patients with small fiber pathology. The aim of this study was to quantify the morphology of small nerve fibers of the cornea of patients with fibromyalgia in terms of density, length and branching and further phenotype these patients using standardized quantitative sensory testing (QST). Small fiber pathology was detected in the cornea of 51% of patients: nerve fiber length was significantly decreased in 44% of patients compared to age- and sex-matched reference values; nerve fiber density and branching were significantly decreased in 10% and 28% of patients. The combination of the CCM parameters and sensory tests for central sensitization, (cold pain threshold, mechanical pain threshold, mechanical pain sensitivity, allodynia and/or windup), yielded four phenotypes of fibromyalgia patients in a subgroup analysis: one group with normal cornea morphology without and with signs of central sensitization, and a group with abnormal cornea morphology parameters without and with signs of central sensitization. In conclusion, half of the tested fibromyalgia population demonstrates signs of small fiber pathology as measured by CCM. The four distinct phenotypes suggest possible differences in disease mechanisms and may require different treatment approaches. PMID:27006259

  4. Systematic assessment of microneedle injection into the mouse cornea

    Directory of Open Access Journals (Sweden)

    Matthaei Mario

    2012-06-01

    Full Text Available Abstract Background Corneal intrastromal injection is an important mode of gene-vector application to subepithelial layers. In a mouse model, this procedure is substantially complicated by the reduced corneal dimensions. Furthermore, it may be difficult to estimate the corneal area reached by the volume of a single injection. This study aimed to investigate intrastromal injections into the mouse cornea using different microneedles and to quantify the effect of injecting varying volumes. A reproducible injection technique is described. Methods Forty eyes of 20 129 Sv/J mice were tested. India ink was intrastromally injected using 30° beveled 33 G needles, tri-surface 25° beveled 35 G needles, or hand-pulled and 25° beveled glass needles. Each eye received a single injection of a volume of 1 or 2 μL. Corneoscleral buttons were fixed and flat mounted for computer-assisted quantification of the affected corneal area. Histological assessment was performed to investigate the intrastromal location of the injected dye. Results A mean corneal area of 5.0 ±1.4 mm2 (mean ± SD and 7.7 ±1.4 mm2 was covered by intrastromal injections of 1 and 2 μL, respectively. The mean percentage of total corneal area reached ranged from 39% to 53% for 1 μL injections, and from 65% to 81% for 2 μL injections. Injections using the 33 G needles tended to provide the highest distribution area. Perforation rates were 8% for 30° beveled 33 G needles and 44% for tri-surface beveled 35 G needles. No perforation was observed with glass needle; however, intrastromal breakage of needle tips was noted in 25% of these cases. Conclusions Intracorneal injection using a 30° beveled 33 G needle was safe and effective. The use of tri-surface beveled 35 G needles substantially increased the number of corneal perforations. Glass needles may break inside the corneal stroma. Injections of 1 μL and 2 μL resulted in an overall mean of 49% and 73% respectively

  5. Bilateral cloudy cornea: is the usual suspect congenital hereditary endothelial dystrophy or stromal dystrophy?

    Science.gov (United States)

    Acar, Banu Torun; Bozkurt, Kansu Tahir; Duman, Erkan; Acar, Suphi

    2016-01-01

    We provide the diagnosis, treatment and follow-up period of a patient with cloudy cornea in both eyes from birth. A 4-year-old girl presented with blurring in both eyes. Penetrating keratoplasty (PK) was performed with the preliminary diagnosis of congenital hereditary endothelial dystrophy in June 2012. According to the pathology report for extracted host tissue, the Descemet's membrane (DM) and endothelium were healthy and diagnosis was reported to be congenital hereditary stromal dystrophy. Deep anterior lamellar keratoplasty was performed on the left eye. The DM was transparent at follow-up. Cornea transplantation is the only choice to provide visual rehabilitation in children with congenital cloudy cornea. However, it is known that the prognosis of traditional PK in the paediatric age group is not good. Therefore, when using alternative keratoplasty (deep anterior lamellar keratoplasty, Descemet's stripping automated endothelial keratoplasty) options, pathological examination of the host tissue should be made. PMID:27107055

  6. Ductile-to-brittle transition in a low alloy steel

    International Nuclear Information System (INIS)

    The mechanical properties of pressure vessel steel (and above all its resistance to brittle fracture) are a decisive factor in the complex safety assessment of nuclear power plants. The monitoring of neutron induced embrittlement is provided using Charpy impact tests on standard V-notch specimens due to their small size. Material's ductile-to-brittle transition temperature (DBTT) can be easily characterised using this test. However, Charpy impact energy cannot be immediately used for safety assessment, since fracture toughness is required. Some empirical formulas have been developed, but no direct relationship was still found. When the specimens are tested in the ductile-to-brittle transition region, cleavage crack initiation is preceded by ductile crack growth giving a large scatter to the values of fracture toughness and/or Charpy impact energy. Even if the cleavage initiation and propagation in steels containing isolated spheroidic carbides are qualitatively well understood, no one from existing models can explain the sharp upturn in ductile-to-brittle transition region. In the present work, French tempered bainitic steel 16MND5 (considered as equivalent to the American standard A508 Cl.3) is studied: The large fractographic analysis of CT and Charpy specimens broken in the DBTT range is undertaken to account for the evolution of cleavage fracture mechanisms. In addition to classical scanning electron microscopy, transmission electron microscopy and EBSD technique are used in order to study the propagation of cleavage crack. The classical fracture mechanics using KIc or Jc concepts can hardly describe the unstable brittle fracture in the DBTT range. Hence, the local approach, which aims to predict the fracture of any structural component using local criteria, providing that the mechanical fields in the structure are known, is used. The probability of cleavage fracture in the DBTT range is predicted using the Beremin model based on weakest link theory, e.g. 2

  7. Differentially expressed wound healing-related microRNAs in the human diabetic cornea.

    Directory of Open Access Journals (Sweden)

    Vincent A Funari

    Full Text Available MicroRNAs are powerful gene expression regulators, but their corneal repertoire and potential changes in corneal diseases remain unknown. Our purpose was to identify miRNAs altered in the human diabetic cornea by microarray analysis, and to examine their effects on wound healing in cultured telomerase-immortalized human corneal epithelial cells (HCEC in vitro. Total RNA was extracted from age-matched human autopsy normal (n=6 and diabetic (n=6 central corneas, Flash Tag end-labeled, and hybridized to Affymetrix® GeneChip® miRNA Arrays. Select miRNAs associated with diabetic cornea were validated by quantitative RT-PCR (Q-PCR and by in situ hybridization (ISH in independent samples. HCEC were transfected with human pre-miR™miRNA precursors (h-miR or their inhibitors (antagomirs using Lipofectamine 2000. Confluent transfected cultures were scratch-wounded with P200 pipette tip. Wound closure was monitored by digital photography. Expression of signaling proteins was detected by immunostaining and Western blot. Using microarrays, 29 miRNAs were identified as differentially expressed in diabetic samples. Two miRNA candidates showing the highest fold increased in expression in the diabetic cornea were confirmed by Q-PCR and further characterized. HCEC transfection with h-miR-146a or h-miR-424 significantly retarded wound closure, but their respective antagomirs significantly enhanced wound healing vs. controls. Cells treated with h-miR-146a or h-miR-424 had decreased p-p38 and p-EGFR staining, but these increased over control levels close to the wound edge upon antagomir treatment. In conclusion, several miRNAs with increased expression in human diabetic central corneas were found. Two such miRNAs inhibited cultured corneal epithelial cell wound healing. Dysregulation of miRNA expression in human diabetic cornea may be an important mediator of abnormal wound healing.

  8. [Cornea bank of Lyon: from quality diagnosis to ISO 9001 certification].

    Science.gov (United States)

    Pascal, P; Chalochet, A; Damour, O

    2001-12-01

    The tissue and cell bank of the HCL (Hospices Civils de Lyon) has, since 10 June 1999, consisted of two sections with related activities: cell culture for the Skin Substitutes Laboratory (Laboratoire des Substituts Cutanés, LSC) and preservation of corneas at 31 degrees C for the Cornea Bank. As the LSC had been ISO 9001 certified since March 1997 our aim, since merger, was to raise the Cornea Bank to the same level of quality as the LSC, so as to coincide with the renewal of the LSC certificate in February 2000. The methods we used (project, quality control, analysis and process optimization) led us to receive official certification only nine months after the merger. The procedure started with a program of quality control at the Cornea Bank from February 1999 onwards, in order to list the work and equipment required, evaluate its documentation system and what was needed to incorporate this new activity into the existing system of quality assurance at the LSC. On the 7th March 2000, the Tissue and Cell Bank of the HCL obtained an ISO 9001 certificate for its combined functions. As well as achieving our objectives and the strong points highlighted by the auditor during the renewal process, this quality assessment revealed many advantages: improvements in the conservation of corneas, economies in staff replacement and reductions in both the cost of maintaining quality, the cost of the corneas themselves, etc. The decree 'Banque' no. 99-741 of 30th August 1999, which put in place the system of authorization of tissue banks in France, demands quality control. Our application for certification which started in early 1999 had anticipated this regulation. This helped us enormously when compiling the dossier accompanying the official request and was an essential element in obtaining the favourable response of the ASSAPS on 21 June 2000.

  9. Interpreting finite element results for brittle materials in endodontic restorations

    Directory of Open Access Journals (Sweden)

    González-Lluch Carmen

    2011-06-01

    Full Text Available Abstract Background Finite element simulation has been used in last years for analysing the biomechanical performance of post-core restorations in endodontics, but results of these simulations have been interpreted in most of the works using von Mises stress criterion. However, the validity of this failure criterion for brittle materials, which are present in these restorations, is questionable. The objective of the paper is to analyse how finite element results for brittle materials of endodontic restorations should be interpreted to obtain correct conclusions about the possible failure in the restoration. Methods Different failure criteria (Von Mises, Rankine, Coulomb-Mohr, Modified Mohr and Christensen and material strength data (diametral tensile strength and flexural strength were considered in the study. Three finite element models (FEM were developed to simulate an endodontic restoration and two typical material tests: diametral tensile test and flexural test. Results Results showed that the Christensen criterion predicts similar results as the Von Mises criterion for ductile components, while it predicts similar results to all other criteria for brittle components. The different criteria predict different failure points for the diametral tensile test, all of them under multi-axial stress states. All criteria except Von Mises predict failure for flexural test at the same point of the specimen, with this point under uniaxial tensile stress. Conclusions From the results it is concluded that the Christensen criterion is recommended for FEM result interpretation in endodontic restorations and that the flexural test is recommended to estimate tensile strength instead of the diametral tensile test.

  10. Second harmonic generation imaging of collagen fibrils in cornea and sclera

    Science.gov (United States)

    Han, Meng; Giese, Günter; Bille, Josef F.

    2005-07-01

    Collagen, as the most abundant protein in the human body, determines the unique physiological and optical properties of the connective tissues including cornea and sclera. The ultrastructure of collagen, which conventionally can only be resolved by electron microscopy, now can be probed by optical second harmonic generation (SHG) imaging. SHG imaging revealed that corneal collagen fibrils are regularly packed as a polycrystalline lattice, accounting for the transparency of cornea. In contrast, scleral fibrils possess inhomogeneous, tubelike structures with thin hard shells, maintaining the high stiffness and elasticity of the sclera.

  11. Refractive power of a multilayer rotationally symmetric model of the human cornea and tear film

    Science.gov (United States)

    Barbero, Sergio

    2006-07-01

    Optical models of the human cornea and tear film typically employ a single homogeneous cornea with an average refractive index. I propose to use a more realistic multilayer model based on morphological data from the literature. The mathematical methodology to derive the refractive power equation of this model is presented. Special attention is given to the axial gradient index of the refraction structure of the stroma layer because of its optical implications. The importance of considering this multilayer model is quantified in a specific example (orthokeratology) with the help of the derived power equation.

  12. What controls the strength and brittleness of shale rocks?

    Science.gov (United States)

    Rybacki, Erik; Reinicke, Andreas; Meier, Tobias; Makasi, Masline; Dresen, Georg

    2014-05-01

    With respect to the productivity of gas shales, in petroleum science the mechanical behavior of shales is often classified into rock types of high and low 'brittleness', sometimes also referred to as 'fraccability'. The term brittleness is not well defined and different definitions exist, associated with elastic properties (Poisson's ratio, Young's modulus), with strength parameters (compressive and tensile strength), frictional properties (cohesion, friction coefficient), hardness (indentation), or with the strain or energy budget (ratio of reversible to the total strain or energy, respectively). Shales containing a high amount of clay and organic matter are usually considered as less brittle. Similarly, the strength of shales is usually assumed to be low if they contain a high fraction of weak phases. We performed mechanical tests on a series of shales with different mineralogical compositions, varying porosity, and low to high maturity. Using cylindrical samples, we determined the uniaxial and triaxial compressive strength, static Young's modulus, the tensile strength, and Mode I fracture toughness. The results show that in general the uniaxial compressive strength (UCS) linearly increases with increasing Young's modulus (E) and both parameters increase with decreasing porosity. However, the strength and elastic modulus is not uniquely correlated with the mineral content. For shales with a relatively low quartz and high carbonate content, UCS and E increase with increasing quartz content, whereas for shales with a relatively low amount for carbonates, but high quartz content, both parameters increase with decreasing fraction of the weak phases (clays, kerogen). In contrast, the average tensile strength of all shale-types appears to increase with increasing quartz fraction. The internal friction coefficient of all investigated shales decreases with increasing pressure and may approach rather high values (up to ≡ 1). Therefore, the mechanical strength and

  13. Cavitation-Induced Fracture Causes Nanocorrugations in Brittle Metallic Glasses.

    Science.gov (United States)

    Singh, I; Narasimhan, R; Ramamurty, Upadrasta

    2016-07-22

    Brittle metallic glasses exhibit a unique and intriguing fracture morphology of periodic nanocorrugations whose spacing and amplitude are of the order of tens of nanometers. We show through continuum simulations that they fail by spontaneous and simultaneous cavitation within multiple weak zones arising due to intrinsic atomic density fluctuations ahead of a notch tip. Dynamic crack growth would then occur along curved but narrowly confined shear bands that link the growing cavities. This mechanism involves little dissipation and also explains the formation of nanocorrugations. PMID:27494475

  14. Nanoscale Morphology in Tensile Fracture of a Brittle Amorphous Ribbon

    Institute of Scientific and Technical Information of China (English)

    Xifeng LI; Kaifeng ZHANG; Guofeng WANG

    2008-01-01

    The paper reports on the observation of nanoscale morphology on the tensile fracture surface of a brittle amorphous Fe-based ribbon. The formation of nanoscale damage cavity structure is a main characteristic morphology on the fracture surfaces. Approaching the ribbon boundary, these damage cavities assemble and form the nanoscale periodic corrugations, which are neither Wallner lines nor crack front waves. The periodic corrugations result from the interactions between the reflected elastic waves by the boundaries of amorphous ribbon and the stress fields of the crack tip.

  15. Acoustic emission during the compaction of brittle UO2 particles

    International Nuclear Information System (INIS)

    One of the options considered for recycling minor actinides is to incorporate about 10% to UO2 matrix. The presence of open pores interconnected within this fuel should allow the evacuation of helium and fission gases to prevent swelling of the pellet and ultimately its interaction with the fuel clad surrounding it. Implementation of minor actinides requires working in shielded cell, reducing their retention and outlawing additions of organic products. The use of fragmentable particles of several hundred micrometers seems a good solution to control the microstructure of the green compacts and thus control the open porosity after sintering. The goal of this study is to monitor the compaction of brittle UO2 particles by acoustic emission and to link the particle characteristics to the open porosity obtained after the compact sintering. The signals acquired during tensile strength tests on individual granules and compacts show that the acoustic emission allows the detection of the mechanism of fragmentation and enables identification of a characteristic waveform of this fragmentation. The influences of compaction stress, of the initial particle size distribution and of the internal cohesion of the granules, on the mechanical strength of the compact and on the microstructure and open porosity of the sintered pellets, are analyzed. By its ability to identify the range of fragmentation of the granules during compaction, acoustic emission appears as a promising technique for monitoring the compaction of brittle particles in the manufacture of a controlled porosity fuel. (author)

  16. Large strain bulk deformation and brittle tough transitions in polyethylenes

    CERN Document Server

    Hillmansen, S

    2001-01-01

    Some tough, crystalline polymers can fail by fast brittle fracture. This thesis explores the role of ductile 'shear lips', which form at the fracture surface verges, in brittle-tough transitions. A new laboratory method was used to isolate this region, and to test its ability to draw rapidly, in polyethylenes. The test uses a conventional Charpy type specimen that is deeply notched and impact loaded in three-point bending by a single striker. The ligament, rapidly loaded in almost pure tension, first yields, and then necks down until failure. Initial results are encouraging and correlate well with the in-service performance. A fundamental study of large strain deformation, that avoids the complexity associated with impact tests, was then conducted with the aim of isolating the dominating influences that furnish a polymer with the ability to sustain rapid large strain deformation. True stress vs. true strain curves have been interpreted using the one dimensional spring dashpot model of Haward and Thackray (H-T...

  17. Dynamic Initiation and Propagation of Multiple Cracks in Brittle Materials

    Directory of Open Access Journals (Sweden)

    Xiaodan Ren

    2013-07-01

    Full Text Available Brittle materials such as rock and ceramic usually exhibit apparent increases of strength and toughness when subjected to dynamic loading. The reasons for this phenomenon are not yet well understood, although a number of hypotheses have been proposed. Based on dynamic fracture mechanics, the present work offers an alternate insight into the dynamic behaviors of brittle materials. Firstly, a single crack subjected to stress wave excitations is investigated to obtain the dynamic crack-tip stress field and the dynamic stress intensity factor. Second, based on the analysis of dynamic stress intensity factor, the fracture initiation sizes and crack size distribution under different loading rates are obtained, and the power law with the exponent of −2/3 is derived to describe the fracture initiation size. Third, with the help of the energy balance concept, the dynamic increase of material strength is directly derived based on the proposed multiple crack evolving criterion. Finally, the model prediction is compared with the dynamic impact experiments, and the model results agree well with the experimentally measured dynamic increasing factor (DIF.

  18. Wavelength-dependent ultraviolet induction of cyclobutane pyrimidine dimers in the human cornea.

    Science.gov (United States)

    Mallet, Justin D; Rochette, Patrick J

    2013-08-01

    Exposition to ultraviolet (UV) light is involved in the initiation and the progression of skin cancer. The genotoxicity of UV light is mainly attributed to the induction of cyclobutane pyrimidine dimers (CPDs), the most abundant DNA damage generated by all UV types (UVA, B and C). The human cornea is also exposed to the harmful UV radiations, but no UV-related neoplasm has been reported in this ocular structure. The probability that a specific DNA damage leads to a mutation and eventually to cellular transformation is influenced by its formation frequency. To shed light on the genotoxic effect of sunlight in the human eye, we have analyzed CPD induction in the cornea and the iris following irradiation of ex vivo human eyes with UVA, B or C. The extent of CPD induction was used to establish the penetrance of the different UV types in the human cornea. We show that UVB- and UVC-induced CPDs are concentrated in the corneal epithelium and do not penetrate deeply beyond this corneal layer. On the other hand, UVA wavelengths penetrate deeper and induce CPDs in the entire cornea and in the first layers of the iris. Taken together, our results are undoubtedly an important step towards better understanding the consequences of UV exposure to the human eye.

  19. Successful treatment of Fusarium keratitis with cornea transplantation and topical and systemic voriconazole.

    NARCIS (Netherlands)

    Klont, R.R.; Eggink, C.A.; Rijs, A.J.M.M.; Wesseling, P.; Verweij, P.E.

    2005-01-01

    A case of invasive Fusarium keratitis in a previously healthy male patient was treated successfully with cornea transplantation and systemic and topical voriconazole after treatment failure with topical amphotericin B and systemic itraconazole. Topical voriconazole was well tolerated, and, in conjun

  20. Crosslinked collagen-gelatin-hyaluronic acid biomimetic film for cornea tissue engineering applications

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yang; Ren, Li, E-mail: psliren@scut.edu.cn; Wang, Yingjun, E-mail: imwangyj@163.com

    2013-01-01

    Cornea disease may lead to blindness and keratoplasty is considered as an effective treatment method. However, there is a severe shortage of donor corneas worldwide. This paper presents the crosslinked collagen (Col)-gelatin (Gel)-hyaluronic acid (HA) films developed by making use of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as the crosslinker. The test results on the physical and biological properties indicate that the CGH631 film (the mass ratio of Col:Gel:HA = 6:3:1) has appropriate optical performance, hydrophilicity and mechanical properties. The diffusion properties of the CGH631 film to NaCl and tryptophan are also satisfactory and the measured data are 2.43 Multiplication-Sign 10{sup -6} cm{sup 2}/s and 7.97 Multiplication-Sign 10{sup -7} cm{sup 2}/s, respectively. In addition, cell viability studies demonstrate that the CGH631 film has good biocompatibility, on which human corneal epithelial cells attached and proliferated well. This biocompatible film may have potential use in cornea tissue engineering. - Highlights: Black-Right-Pointing-Pointer Crosslinked collagen-gelatin-hyaluronic acid films were fabricated in this study. Black-Right-Pointing-Pointer The film had appropriate physical properties. Black-Right-Pointing-Pointer Diffusion coefficient of the film was comparable with the human cornea. Black-Right-Pointing-Pointer HCEC viability studies confirmed the biocompatibility of the film.

  1. Pathways and Mechanisms Underlying the Photophysics and Photochemistry of Riboflavin induced cornea crosslinking

    DEFF Research Database (Denmark)

    Breitenbach, Thomas; Ogilby, Peter Remsen

    In this talk, we will describe general pathways involved in the photophysics of a photosensitized process, which can lead to crosslinking due to light excitation of Riboflavin in the cornea. Furthermore, we will elucidate different aspects of reactions that can produce crosslinks, with respect to...

  2. Pretreatment methods to improve nerve immunostaining in corneas from long-term fixed embryonic quail eyes

    Science.gov (United States)

    Barrett, J. E.; Wells, D. C.; Conrad, G. W.

    1999-01-01

    Pretreatment methods were used to improve neurofilament immunostaining in corneas from embryonic day 16 Japanese quail corneas that had been stored in fixative solution for several months. A sequential combination of the following three pretreatments: brief microwave heating in saline, followed by extraction with sodium dodecyl sulfate (SDS) at 37 degrees C, followed by digestion with hyaluronidase at 37 degrees C, produced significantly increased antibody staining of corneal neurofilament proteins, compared with embryonic corneas subjected to no prior pretreatments or to single or two-step protocols. After applying the sequence of all three pretreatments, darkest nerve staining and increased numbers of fine branches were observed, together with lower background staining. Thus, the result of applying the three-step pretreatment sequence is better than that of applying any of its component single pretreatments or even combinations of any two of them. These findings therefore suggest that each of these three pretreatments causes a unique effect, beneficial to immunostaining of neurofilament proteins, and that their individual effects are independent and additive. In addition to embryonic corneas, the three-step procedure also may be useful for immunostaining of nerves in other very delicate, highly-hydrated tissues containing an abundance of extracellular matrix.

  3. Expression of VEGF-C in Rat Cornea after Alkali Injury

    Institute of Scientific and Technical Information of China (English)

    姜冬玲; 胡燕华; 凌士奇

    2004-01-01

    The expression of VEGF-C and molecular mechanisms of lymphangiogenesis in rat cornea after alkali injury was studied. The rat alkali injured corneal models were made. Under electron microscopy, the lymphatic vessels in the rat injured corneas were examined. The expression of VEGF-C proteins was detected by using immunohistochemical assay at day 1, 3, 5, 7, 9 after injury. The expression levels of VEGF-C mRNA were quantified with reverse transcription polymerase chain reaction (RT-PCR). The results showed that the lymphatic vessels were found in the injured rat corneas 14 days after the injury. The VEGF-C protein was detectable 3 days after injury,reached the peak 5 days after injury, and gradually decreased. In the control group, no VEGF-C proteins were detected. The VEGF-C mRNA was minimally detected in the normal rat corneas, but it was highly expressed 5 days after the injury. The difference was statistically significant. It was concluded that VEGF-C might be one of the most important relevant factors in corneal lymphangiogenesis after alkali injury.

  4. Delayed graft rejection in pre-vascularised corneas after subconjunctival injection of clodronate liposomes

    NARCIS (Netherlands)

    Slegers, TPAM; van Rooijen, N; van Rij, G; van der Gaag, R

    2000-01-01

    Purpose. To test the effects of clodronate liposomes on graft survival and neovascularisation after transplantation in pre-vascularised recipient corneas. Methods. Corneal neovascularisation was induced in F344 rats by injecting heat inactivated rabbit serum intrastromally. After 4 weeks F344 rats w

  5. Shape of the anterior cornea : Comparison of height data from 4 corneal topographers

    NARCIS (Netherlands)

    de Jong, Tim; Sheehan, Matthew T.; Dubbelman, Michiel; Koopmans, Steven A.; Jansonius, Nomdo M.

    2013-01-01

    PURPOSE: To compare the ability of clinical corneal topographers to describe the shape of the anterior cornea for optical modeling. SETTING: University Medical Center Groningen, Groningen, Netherlands. DESIGN: Cross-sectional study. METHODS: The anterior corneal shape of healthy subjects was assesse

  6. [Simple keratectomy in band-shaped degeneration of the cornea (author's transl)].

    Science.gov (United States)

    Kenyeres, P

    1980-01-01

    In a case of band-shaped keratopathy chemical solution of the opacity failed but it proved easy to remove Bowman's membrane by grasping it with a forceps and pulling it off. As a result the cornea became clear and vision improved up to 6/7ths.

  7. Spectroscopic measurements and terahertz imaging of the cornea using a rapid scanning terahertz time domain spectrometer

    Science.gov (United States)

    Wen-Quan, Liu; Yuan-Fu, Lu; Guo-Hua, Jiao; Xian-Feng, Chen; Zhi-Sheng, Zhou; Rong-Bin, She; Jin-Ying, Li; Si-Hai, Chen; Yu-Ming, Dong; Jian-Cheng, Lv

    2016-06-01

    Spectroscopic measurements and terahertz imaging of the cornea are carried out by using a rapid scanning terahertz time domain spectroscopy (THz-TDS) system. A voice coil motor stage based optical delay line (VCM-ODL) is developed to provide a rather simple and robust structure with both the high scanning speed and the large delay length. The developed system is used for THz spectroscopic measurements and imaging of the corneal tissue with different amounts of water content, and the measurement results show the consistence with the reported results, in which the measurement time using VCM-ODL is a factor of 360 shorter than the traditional motorized optical delay line (MDL). With reducing the water content a monotonic decrease of the complex permittivity of the cornea is observed. The two-term Debye relaxation model is employed to explain our experimental results, revealing that the fast relaxation time of a dehydrated cornea is much larger than that of a hydrated cornea and its dielectric behavior can be affected by the presence of the biological macromolecules. These results demonstrate that our THz spectrometer may be a promising candidate for tissue hydration sensing and practical application of THz technology. Project supported by the National Natural Science Foundation of China (Grant No. 61205101), the Shenzhen Municipal Research Foundation, China (Grant Nos. GJHZ201404171134305 and JCYJ20140417113130693), and the Marie Curie Actions-International Research Staff Exchange Scheme (IRSES) (Grant No. FP7 PIRSES-2013-612267).

  8. Determination of the Influence of c-BN+h-BN Coating Structure on Brittleness

    Institute of Scientific and Technical Information of China (English)

    MaciejKupczyk; AdamLejwoda; PrzemyslawCieszkowski; PrzemyslawLibuda

    2004-01-01

    In the article is presented the brittleness study of boron nitride coatings deposited on cutting edges made of cemented carbides by the pulse-plasma method (PPD). Influences of the structure (density, pores, microcracks) of coating material on the brittleness and on selected technological parameters of boron nitride formation by PPD method particularly taking into account discharge voltage on brittleness are shown. Differences between values of both a1(300) and a1(500)coefficients characterized susceptibility to coatings cracking of investigated coating manufactured using different values of discharge voltage were defined. Results of an investigations have been confirmed usefulness of Palmqyist's method for measurement of coating susceptibility to brittle cracking.

  9. Determination of the Influence of c-BN+h-BN Coating Structure on Brittleness

    Institute of Scientific and Technical Information of China (English)

    Maciej Kupczyk; Adam Lejwoda; Przemyslaw Cieszkowski; Przemyslaw Libuda

    2004-01-01

    In the article is presented the brittleness study of boron nitride coatings deposited on cutting edges made of cemented carbides by the pulse-plasma method (PPD). Influences of the structure (density, pores, microcracks) of coating material on the brittleness and on selected technological parameters of boron nitride formation by PPD method particularly taking into account discharge voltage on brittleness are shown. Differences between values of both a1(300) and a1(500)coefficients characterized susceptibility to coatings cracking of investigated coating manufactured using different values of discharge voltage were defined. Results of an investigations have been confirmed usefulness of Palmqvist's method for measurement of coating susceptibility to brittle cracking.

  10. Reparative regeneration of cornea at nanostructured biopolymer of hyaluronic acid application

    Directory of Open Access Journals (Sweden)

    V.N. Kanyukov

    2014-04-01

    Full Text Available ABSTRACT Purpose. Estimation of corneal reparative regeneration processes course at application of bioplastic material – nanostructured biopolymer of hyaluronic acid on the model of chemical (alkaline and acid cornea burn. Material and methods. Experimental modeling of cornea chemical burn was carried out on 36 rabbits (72 eyes. The study had two series of cornea burn: alkaline (18 rabbits – 36 eyes and acid (18 rabbits – 36 eyes corneal burns. In each of the series there was identified: an experimental group, which used the applique of bioplastic material «hyamatrix» according to the method of prof. V.N. Kanyukov and control one with Solcoseryl instillations. The clinical study included an examination of the eye anterior segment using the focus and side lighting and photographic recording. At the of period of 3, 7, 14, 30 and 90 days the animals were removed from the experiment for the light-optical, immunocytochemistry and electron microscopy studies. Results. At conducting «hyamatrix» application conjunctiva edema and injection, corneal edema were reversed faster that reduced neovascularization risk in the outcome of corneal alkaline burn. Morphological studies at different periods of the experiment made it possible to determine the sequence of processes from the moment of cornea chemical burns application until the completion of its restoration, which were different in the experimental and control groups. Symptoms of toxic effect of the damaged cells decay products were determined morphologically. Endothelial cells remained intact. The use of «hyamatrix» application allowed reducing the recovery time with the improvement of cornea reparative processes. Conclusion. 1. Application of bioplastic material to the cornea in the early stages of cornea injuries treatment (alkaline and acid burn reduces the severity of edema and hyperemia, and as a result reduces the exudative phase of inflammation. 2. As a result of clinical and

  11. Oxygen transport through soft contact lens and cornea: Lens characterization and metabolic modeling

    Science.gov (United States)

    Chhabra, Mahendra

    The human cornea requires oxygen to sustain metabolic processes critical for its normal functioning. Any restriction to corneal oxygen supply from the external environment (e.g., by wearing a low oxygen-permeability contact lens) can lead to hypoxia, which may cause corneal edema (swelling), limbal hyperemia, neovascularization, and corneal acidosis. The need for adequate oxygen to the cornea is a major driving force for research and development of hypertransmissible soft contact lenses (SCLs). Currently, there is no standard technique for measuring oxygen permeability (Dk) of hypertransmissible silicone-hydrogel SCLs. In this work, an electrochemistry-based polarographic apparatus was designed, built, and operated to measure oxygen permeability in hypertransmissible SCLs. Unlike conventional methods where a range of lens thickness is needed for determining oxygen permeabilities of SCLs, this apparatus requires only a single lens thickness. The single-lens permeameter provides a reliable, efficient, and economic tool for measuring oxygen permeabilities of commercial hypertransmissible SCLs. The single-lens permeameter measures not only the product Dk, but, following modification, it measures separately diffusivity, D, and solubility, k, of oxygen in hypertransmissible SCLs. These properties are critical for designing better lens materials that ensure sufficient oxygen supply to the cornea. Metabolism of oxygen in the cornea is influenced by contact-lens-induced hypoxia, diseases such as diabetes, surgery, and drug treatment, Thus, estimation of the in-vivo corneal oxygen consumption rate is essential for gauging adequate oxygen supply to the cornea. Therefore, we have developed an unsteady-state reactive-diffusion model for the cornea-contact-lens system to determine in-vivo human corneal oxygen-consumption rate. Finally, a metabolic model was developed to determine the relation between contact-lens oxygen transmissibility (Dk/L) and corneal oxygen deficiency. A

  12. Lens regeneration from the cornea requires suppression of Wnt/β-catenin signaling.

    Science.gov (United States)

    Hamilton, Paul W; Sun, Yu; Henry, Jonathan J

    2016-04-01

    The frog, Xenopus laevis, possesses a high capacity to regenerate various larval tissues, including the lens, which is capable of complete regeneration from the cornea epithelium. However, the molecular signaling mechanisms of cornea-lens regeneration are not fully understood. Previous work has implicated the involvement of the Wnt signaling pathway, but molecular studies have been very limited. Iris-derived lens regeneration in the newt (Wolffian lens regeneration) has shown a necessity for active Wnt signaling in order to regenerate a new lens. Here we provide evidence that the Wnt signaling pathway plays a different role in the context of cornea-lens regeneration in Xenopus. We examined the expression of frizzled receptors and wnt ligands in the frog cornea epithelium. Numerous frizzled receptors (fzd1, fzd2, fzd3, fzd4, fzd6, fzd7, fzd8, and fzd10) and wnt ligands (wnt2b.a, wnt3a, wnt4, wnt5a, wnt5b, wnt6, wnt7b, wnt10a, wnt11, and wnt11b) are expressed in the cornea epithelium, demonstrating that this tissue is transcribing many of the ligands and receptors of the Wnt signaling pathway. When compared to flank epithelium, which is lens regeneration incompetent, only wnt11 and wnt11b are different (present only in the cornea epithelium), identifying them as potential regulators of cornea-lens regeneration. To detect changes in canonical Wnt/β-catenin signaling occurring within the cornea epithelium, axin2 expression was measured over the course of regeneration. axin2 is a well-established reporter of active Wnt/β-catenin signaling, and its expression shows a significant decrease at 24 h post-lentectomy. This decrease recovers to normal endogenous levels by 48 h. To test whether this signaling decrease was necessary for lens regeneration to occur, regenerating eyes were treated with either 6-bromoindirubin-3'-oxime (BIO) or 1-azakenpaullone - both activators of Wnt signaling - resulting in a significant reduction in the percentage of cases with successful

  13. Impression cytology and in vivo confocal microscopy in corneas with total limbal stem cell deficiency

    Directory of Open Access Journals (Sweden)

    Aline Lütz de Araújo

    2013-10-01

    Full Text Available PURPOSES: To describe corneal changes seen on in vivo confocal microscopy in patients with total limbal stem cell deficiency and to correlate them with cytological findings. METHODS: A prospective case series including 13 eyes (8 patients with total limbal deficiency was carried out. Stem cell deficiency was diagnosed clinically and by corneal impression cytology. Confocal images of the central cornea were taken with the Heidelberg Retina Tomograph II, Rostock Corneal Module (Heidelberg Engineering, Heidelberg, Germany. RESULTS: Impression cytology of the cornea revealed conjunctival epithelial cells and goblet cells in all cases. In vivo confocal microscopy showed disruption of normal layers of the corneal epithelium in all eyes. Confocal images showed cells with characteristics of conjunctival epithelium at the cornea in 76.9% of the total. These findings on confocal microscopy were compatible to limbal stem cell deficiency. Additionally, goblet cells, squamous metaplasia, inflammatory cells and dendritic cells were observed. The sub-basal nerve plexus was not identified in any of the corneas. Corneal neovessels were observed at the epithelium and stroma. All cases showed diffuse hyper-reflective images of the stroma corresponding to opacity of the tissue. CONCLUSIONS: Limbal stem cell deficiency had been confirmed by impression cytology in all cases, and 76.9% of the cases could also be diagnosed by in vivo confocal microscopy through the conjunctival epithelial cell visualization on the corneal surface. Frequent confocal microscopy findings were abnormal cells at the cornea (conjunctival epithelial, goblet and inflammatory cells, corneal neovessels and diffuse hyper-reflection of the stroma.

  14. Temporary brittle bone disease: relationship between clinical findings and judicial outcome

    Directory of Open Access Journals (Sweden)

    Colin R. Paterson

    2011-10-01

    Full Text Available There is a wide differential diagnosis for the child with unexplained fractures including non-accidental injury, osteogenesis imperfecta and vitamin D deficiency rickets. Over the last 20 years we and others have described a self-limiting syndrome characterised by fractures in the first year of life. This has been given the provisional name temporary brittle bone disease. This work had proved controversial mostly because the fractures, including rib fractures and metaphyseal fractures, were those previously regarded as typical or even diagnostic of non-accidental injury. Some have asserted that the condition does not exist. Over the years 1985 to 2000 we investigated 87 such cases with fractures with a view to determining the future care of the children. In 85 of these the judiciary was involved. We examined the clinical and radiological findings in the 33 cases in which there was a judicial finding of abuse, the 24 cases in which the parents were exonerated and the 28 cases in which no formal judicial finding was made. The three groups of patients were similar in terms of demographics, age at fracturing and details of the fractures. The clinical similarities between the three groups of patients contrasts with the very different results of the judicial process.

  15. Fracture statistics of brittle materials with intergranular cracks

    International Nuclear Information System (INIS)

    When brittle materials are used for structural purposes, the initial design must take their relatively large dispersion in fracture stress properly into account. This is difficult when failure probabilities must be extremely low, because empirically based statistical theories of fracture, such as that of Weibull, cannot reliably predict the stresses corresponding to failure probabilities much lower than n-1, where n is the number of specimens tested. Recently McClintock proposed a rational method of predicting the size distribution of intergranular cracks. The method assumed that large cracks are random aggregations of cracked grain boundaries. The present paper employs this method to find the size distribution of penny-shaped cracks, and also P(f), the probability of failure of a specimen of volume V subjected to a tensile stress sigma. The present paper is a pioneering effort, which should be applicable to ceramics and related materials

  16. Modeling Strain Rate Effect for Heterogeneous Brittle Materials

    Institute of Scientific and Technical Information of China (English)

    MA Guowei; DONG Aiai; LI Jianchun

    2006-01-01

    Rocks are heterogeneous from the point of microstructure which is of significance to their dynamic failure behavior.Both the compressive and tensile strength of rock-like materials is regarded different from the static strength.The present study adopts smoothed particle hydrodynamics (SPH) which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials.The SPH method is capable of simulating rock fracture,free of the mesh constraint of the traditional FEM and FDM models.A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling.The results show the compressive strength increases with the increase of strain rate as well as the tensile strength,which is important to the engineering design.

  17. Simulations of ductile flow in brittle material processing

    Energy Technology Data Exchange (ETDEWEB)

    Luh, M.H.; Strenkowski, J.S.

    1988-12-01

    Research is continuing on the effects of thermal properties of the cutting tool and workpiece on the overall temperature distribution. Using an Eulerian finite element model, diamond and steel tools cutting aluminum have been simulated at various, speeds, and depths of cut. The relative magnitude of the thermal conductivity of the tool and the workpiece is believed to be a primary factor in the resulting temperature distribution in the workpiece. This effect is demonstrated in the change of maximum surface temperatures for diamond on aluminum vs. steel on aluminum. As a preliminary step toward the study of ductile flow in brittle materials, the relative thermal conductivities of diamond on polycarbonate is simulated. In this case, the maximum temperature shifts from the rake face of the tool to the surface of the machined workpiece, thus promoting ductile flow in the workpiece surface.

  18. New criterion of material resistance for brittle fracture

    Directory of Open Access Journals (Sweden)

    M. Maj

    2010-01-01

    Full Text Available Wide variety of cast material applications and efforts to find optimum fields for casting operation are the reasons why it is so important to collect as many data on the properties of materials as possible. The problem of primary importance is to know how these materials will behave under the normally and rapidly changing loads, in other words – to know their fatigue strength. This study gives a short characteristic of fatigue tests and compares various data collected during measurements of the low-cycle fatigue strength coefficient K with the values of constant KIc, representing fracture toughness. The results of the investigations described here have revealed some important correlations that exist between the total elongation A5 and the proposed brittleness criterion B, conventional stress K, and fracture toughness KIc. The development of measurements seems to be of great importance and opens the field for further studies on practical implementation of this method.

  19. Design with brittle materials - An interdisciplinary educational program

    Science.gov (United States)

    Mueller, J. I.; Bollard, R. J. H.; Hartz, B. J.; Kobayashi, A. S.; Love, W. J.; Scott, W. D.; Taggart, R.; Whittemore, O. J.

    1980-01-01

    A series of interdisciplinary design courses being offered to senior and graduate engineering students at the University of Washington is described. Attention is given to the concepts and some of the details on group design projects that have been undertaken during the past two years. It is noted that ceramic materials normally demonstrate a large scatter in strength properties. As a consequence, when designing with these materials, the conventional 'mil standards' design stresses with acceptable margins of safety cannot by employed and the designer is forced to accept a probable number of failures in structures of a given brittle material. It is this prediction of the probability of failure for structures of given, well-characterized materials that forms the basis for this series of courses.

  20. Brittle fracture in associative polymers: the case of ionomer melts.

    Science.gov (United States)

    Shabbir, Aamir; Huang, Qian; Chen, Quan; Colby, Ralph H; Alvarez, Nicolas J; Hassager, Ole

    2016-09-28

    Ionomers are interesting due to their applications in coatings, adhesives, films and packaging materials. A study of the underlying mechanisms for fracture in ionomers is consequently of both practical as well as theoretical interest. In this study, we employ high speed imaging coupled with uniaxial extensional rheometry to delineate the mechanics leading to the brittle fracture of ionomer melts. When these ionomers are elongated at a rate higher than the inverse relaxation time of physical crosslinks, an edge fracture occurs at a critical stress. Parabolic fracture profiles provide evidence that the phenomenon is purely elastic and bulk dissipation has little impact on the crack profile. Experimental results are interpreted within the Griffiths theory for linear elastic materials and the de Gennes theory for viscoelastic materials. PMID:27539982

  1. Quantitative comparisons of numerical models of brittle wedge dynamics

    Science.gov (United States)

    Buiter, Susanne

    2010-05-01

    Numerical and laboratory models are often used to investigate the evolution of deformation processes at various scales in crust and lithosphere. In both approaches, the freedom in choice of simulation method, materials and their properties, and deformation laws could affect model outcomes. To assess the role of modelling method and to quantify the variability among models, we have performed a comparison of laboratory and numerical experiments. Here, we present results of 11 numerical codes, which use finite element, finite difference and distinct element techniques. We present three experiments that describe shortening of a sand-like, brittle wedge. The material properties of the numerical ‘sand', the model set-up and the boundary conditions are strictly prescribed and follow the analogue setup as closely as possible. Our first experiment translates a non-accreting wedge with a stable surface slope of 20 degrees. In agreement with critical wedge theory, all models maintain the same surface slope and do not deform. This experiment serves as a reference that allows for testing against analytical solutions for taper angle, root-mean-square velocity and gravitational rate of work. The next two experiments investigate an unstable wedge in a sandbox-like setup, which deforms by inward translation of a mobile wall. The models accommodate shortening by formation of forward and backward shear zones. We compare surface slope, rate of dissipation of energy, root-mean-square velocity, and the location, dip angle and spacing of shear zones. We show that we successfully simulate sandbox-style brittle behaviour using different numerical modelling techniques and that we obtain the same styles of deformation behaviour in numerical and laboratory experiments at similar levels of variability. The GeoMod2008 Numerical Team: Markus Albertz, Michelle Cooke, Tony Crook, David Egholm, Susan Ellis, Taras Gerya, Luke Hodkinson, Boris Kaus, Walter Landry, Bertrand Maillot, Yury Mishin

  2. Transfer of mesenchymal stem cells and cyclosporine A on alkali-injured rabbit cornea using nanofiber scaffolds strongly reduces corneal neovascularization and scar formation.

    Science.gov (United States)

    Cejka, Cestmir; Cejkova, Jitka; Trosan, Peter; Zajicova, Alena; Sykova, Eva; Holan, Vladimir

    2016-09-01

    The aim of this study was to examine whether nanofiber scaffolds seeded with rabbit bone marrow mesenchymal stem cells (MSCs nanofibers) transferred onto the damaged corneal surface and covered with cyclosporine A (CsA)-loaded nanofiber scaffolds (CsA nanofibers) enable healing of the rabbit cornea injured with 1N NaOH. The healing of damaged corneas was examined morphologically, immunohistochemically and biochemically on day 24 after the injury. Compared to untreated injured corneas, where corneal ulceration or large corneal thinning or even perforation were developed, injured corneas treated with drug free nanofibers healed without profound disturbances in a majority of cases, although with fibrosis and scar formation. In injured corneas treated with CsA nanofibers or MSCs nanofibers, the development of scar formation was reduced. Best healing results were obtained with a combination of MSCs and CsA nanofibers (MSCs-CsA nanofibers). Corneas healed with highly restored transparency. Neovascularization highly expressed in untreated injured corneas and reduced in corneas treated with CsA nanofibers or MSCs nanofibers, was suppressed in corneas treated with MSCs-CsA nanofibers. The levels of matrix metalloproteinase 9, inducible nitric oxide synthase, interleukin 6, α-smooth muscle actin, tumor growth factor β and vascular endothelial growth factor were significantly decreased in these corneas as compared to untreated corneas, where the levels of the above mentioned markers were high. In conclusion, MSCs-CsA nanofibers were effective in the treatment of severe alkali-induced corneal injury. PMID:26797822

  3. A proposal for an international brittle fracture acceptance criterion for nuclear material transport cask applications

    Energy Technology Data Exchange (ETDEWEB)

    Sorenson, K.B.; Salzbrenner, R.J.; Nickell, R.E.

    1989-01-01

    This paper presents a fundamental basis for a brittle fracture acceptance criterion, examine several existing criteria and propose examples for consideration as international brittle fracture acceptance criteria. The proposed criteria are intended to stimulate discussion in order to advance the development of a consensus approach. 8 refs., 1 fig., 1 tab.

  4. Microstructural features of intergranular brittle fracture and cold cracking in high strength aluminum alloys

    NARCIS (Netherlands)

    Lalpoor, M.; Eskin, D. G.; ten Brink, Gert; Katgerman, L.

    2010-01-01

    Intergranular brittle fracture has been mainly observed and reported in steel alloys and precipitation hardened At-alloys where intergranular precipitates cover a major fraction of the grain boundary area. 7xxx series aluminum alloys suffer from this problem in the as-cast condition when brittle int

  5. A combined analytical-experimental tensile test technique for brittle materials

    Science.gov (United States)

    Chu, M. L.; Scavuzzo, R. J.; Srivatsan, T. S.

    1992-01-01

    A semiconventional tensile test technique is developed for impact ices and other brittle materials. Accurate results have been obtained on ultimate strength and modulus of elasticity in a refrigerated ice test. It is noted that the technique can be used to determine the physical properties of impact ices accreted inside icing wind tunnels or other brittle materials.

  6. Efficacious and safe tissue-selective controlled gene therapy approaches for the cornea.

    Science.gov (United States)

    Mohan, Rajiv R; Sinha, Sunilima; Tandon, Ashish; Gupta, Rangan; Tovey, Jonathan C K; Sharma, Ajay

    2011-04-12

    Untargeted and uncontrolled gene delivery is a major cause of gene therapy failure. This study aimed to define efficient and safe tissue-selective targeted gene therapy approaches for delivering genes into keratocytes of the cornea in vivo using a normal or diseased rabbit model. New Zealand White rabbits, adeno-associated virus serotype 5 (AAV5), and a minimally invasive hair-dryer based vector-delivery technique were used. Fifty microliters of AAV5 titer (6.5×10(12) vg/ml) expressing green fluorescent protein gene (GFP) was topically applied onto normal or diseased (fibrotic or neovascularized) rabbit corneas for 2-minutes with a custom vector-delivery technique. Corneal fibrosis and neovascularization in rabbit eyes were induced with photorefractive keratectomy using excimer laser and VEGF (630 ng) using micropocket assay, respectively. Slit-lamp biomicroscopy and immunocytochemistry were used to confirm fibrosis and neovascularization in rabbit corneas. The levels, location and duration of delivered-GFP gene expression in the rabbit stroma were measured with immunocytochemistry and/or western blotting. Slot-blot measured delivered-GFP gene copy number. Confocal microscopy performed in whole-mounts of cornea and thick corneal sections determined geometric and spatial localization of delivered-GFP in three-dimensional arrangement. AAV5 toxicity and safety were evaluated with clinical eye exam, stereomicroscopy, slit-lamp biomicroscopy, and H&E staining. A single 2-minute AAV5 topical application via custom delivery-technique efficiently and selectively transduced keratocytes in the anterior stroma of normal and diseased rabbit corneas as evident from immunocytochemistry and confocal microscopy. Transgene expression was first detected at day 3, peaked at day 7, and was maintained up to 16 weeks (longest tested time point). Clinical and slit-lamp eye examination in live rabbits and H&E staining did not reveal any significant changes between AAV5-treated and

  7. Efficacious and safe tissue-selective controlled gene therapy approaches for the cornea.

    Directory of Open Access Journals (Sweden)

    Rajiv R Mohan

    Full Text Available Untargeted and uncontrolled gene delivery is a major cause of gene therapy failure. This study aimed to define efficient and safe tissue-selective targeted gene therapy approaches for delivering genes into keratocytes of the cornea in vivo using a normal or diseased rabbit model. New Zealand White rabbits, adeno-associated virus serotype 5 (AAV5, and a minimally invasive hair-dryer based vector-delivery technique were used. Fifty microliters of AAV5 titer (6.5×10(12 vg/ml expressing green fluorescent protein gene (GFP was topically applied onto normal or diseased (fibrotic or neovascularized rabbit corneas for 2-minutes with a custom vector-delivery technique. Corneal fibrosis and neovascularization in rabbit eyes were induced with photorefractive keratectomy using excimer laser and VEGF (630 ng using micropocket assay, respectively. Slit-lamp biomicroscopy and immunocytochemistry were used to confirm fibrosis and neovascularization in rabbit corneas. The levels, location and duration of delivered-GFP gene expression in the rabbit stroma were measured with immunocytochemistry and/or western blotting. Slot-blot measured delivered-GFP gene copy number. Confocal microscopy performed in whole-mounts of cornea and thick corneal sections determined geometric and spatial localization of delivered-GFP in three-dimensional arrangement. AAV5 toxicity and safety were evaluated with clinical eye exam, stereomicroscopy, slit-lamp biomicroscopy, and H&E staining. A single 2-minute AAV5 topical application via custom delivery-technique efficiently and selectively transduced keratocytes in the anterior stroma of normal and diseased rabbit corneas as evident from immunocytochemistry and confocal microscopy. Transgene expression was first detected at day 3, peaked at day 7, and was maintained up to 16 weeks (longest tested time point. Clinical and slit-lamp eye examination in live rabbits and H&E staining did not reveal any significant changes between AAV5

  8. Characterizing the effects of VPA, VC and RCCS on rabbit keratocytes onto decellularized bovine cornea.

    Directory of Open Access Journals (Sweden)

    Ying Dai

    Full Text Available To investigate the morphological and growth characteristics of rabbit keratocytes when cultured on decellularized cornea under simulate microgravity (SMG rotary cell culture system (RCCS and static culture or in plastic culture supplemented with small molecules of valproic acid (VPA and vitamin C (VC. Bovine corneas were firstly decellularized with Triton X-100 and NH(4OH and through short-term freezing process. Then cell count kit-8 (CCK-8 and flow cytometry were used to test the effects of VPA and VC on the proliferation, cell cycle and apoptosis of rabbit keratocytes. Hematoxylin-eosin (H&E staining and scanning electron microscopy (SEM imaging showed that cells were eliminated in the decellularized bovine corneas. The proliferation of cultured keratocytes was promoted by VPA and VC in the cell proliferation assay. VPA and VC moderately decreased the number of apoptotic cells and obviously promoted cell-cycle entrance of keratocytes. Rabbit keratocytes in plastic displayed spindle shape and rare interconnected with or without VPA and VC. Cells revealed dendritic morphology and reticular cellular connections when cultured on the carriers of decellularized corneas supplemented with VPA and VC even in the presence of 10% fetal bovine serum (FBS. When cultured in RCCS supplemented with VPA, VC and 10% FBS, keratocytes displayed round shape with many prominences and were more prone to grow into the pores of carriers with aggregation. Reverse transcription-polymerase chain reaction (RT-PCR analysis proved that the keratocytes cultured on decellularized bovine cornea under SMG with VPA and VC expressed keratocan and lumican. Keratocytes cultured on plastic expressed lumican but not keratocan. Immunofluorescence identification revealed that cells in all groups were positively immunostained for vimentin. Keratocytes on decellularized bovine cornea under SMG or in static culture were positively immunostained for keratocan and lumican. Thus, we

  9. Physicochemical properties of biodegradable polyvinyl alcohol-agar films from the red algae Hydropuntia cornea.

    Science.gov (United States)

    Madera-Santana, Tomás J; Robledo, Daniel; Freile-Pelegrín, Yolanda

    2011-08-01

    Agar obtained from the red alga Hydropuntia cornea was blended with polyvinyl alcohol (PVOH) in order to produce biodegradable films. In this study, we compare the properties of biopolymeric films formulated with agars extracted from H. cornea collected at different seasons (rainy and dry) in the Gulf of Mexico coast and PVOH as synthetic matrix. The films were prepared at different agar contents (0%, 25%, 50%, 75%, and 100%) and their optical, mechanical, thermal, and morphological properties analyzed. The tensile strength of PVOH-agar films increased when agar content was augmented. The formulation with 50% agar from rainy season (RS) had a significant higher tensile strength when compared to those from dry season (DS; p biodegradable packaging industry.

  10. Secondary Glaucoma Associated with Encircling Scleral Buckle Migration into the Cornea

    Directory of Open Access Journals (Sweden)

    Şengül Özdek

    2016-01-01

    Full Text Available Transmuscular migration of the encircling band through rectus muscles and straddling of the cornea has only been reported in a few cases previously in the literature. This rare condition has never been associated with glaucoma. In this report, we aimed to describe a unique case with transmuscular migration of encircling buckle as a probable cause of glaucoma. A 17-year-old female presented with transmuscular migration of buckle and high intraocular pressure (IOP. Limbal/corneal migration of the silicone band was thought to be the main reason for the IOP rise; therefore, scleral band removal was performed. One month after removal, the patient was free of glaucoma medications and IOP was within normal limits. The retina remained attached during all postoperative visits. Transmuscular migration of the encircling band through rectus muscles and straddling of the cornea may act as a trigger for glaucoma.

  11. Analysis of cornea curvature using radial basis functions - Part II: Fitting to data-set.

    Science.gov (United States)

    Griffiths, G W; Płociniczak, Ł; Schiesser, W E

    2016-10-01

    In part I we discussed the solution of corneal curvature using a 2D meshless method based on radial basis functions (RBFs). In Part II we use these methods to fit a full nonlinear thin membrane model to a measured data-set in order to generate a topological mathematical description of the cornea. In addition, we show how these results can lead to estimations for corneal radius of curvature and certain physical properties of the cornea; namely, tension and elasticity coefficient. Again all calculations and graphics generation were performed using the R language programming environment. The model describes corneal topology extremely well, and the estimated properties fall well within the expected range of values. The method is straight forward to implement and offers scope for further analysis using more detailed 3D models that include corneal thickness. PMID:27570056

  12. SAFOD Brittle Microstructure and Mechanics Knowledge Base (BM2KB)

    Science.gov (United States)

    Babaie, Hassan A.; Broda Cindi, M.; Hadizadeh, Jafar; Kumar, Anuj

    2013-07-01

    Scientific drilling near Parkfield, California has established the San Andreas Fault Observatory at Depth (SAFOD), which provides the solid earth community with short range geophysical and fault zone material data. The BM2KB ontology was developed in order to formalize the knowledge about brittle microstructures in the fault rocks sampled from the SAFOD cores. A knowledge base, instantiated from this domain ontology, stores and presents the observed microstructural and analytical data with respect to implications for brittle deformation and mechanics of faulting. These data can be searched on the knowledge base‧s Web interface by selecting a set of terms (classes, properties) from different drop-down lists that are dynamically populated from the ontology. In addition to this general search, a query can also be conducted to view data contributed by a specific investigator. A search by sample is done using the EarthScope SAFOD Core Viewer that allows a user to locate samples on high resolution images of core sections belonging to different runs and holes. The class hierarchy of the BM2KB ontology was initially designed using the Unified Modeling Language (UML), which was used as a visual guide to develop the ontology in OWL applying the Protégé ontology editor. Various Semantic Web technologies such as the RDF, RDFS, and OWL ontology languages, SPARQL query language, and Pellet reasoning engine, were used to develop the ontology. An interactive Web application interface was developed through Jena, a java based framework, with AJAX technology, jsp pages, and java servlets, and deployed via an Apache tomcat server. The interface allows the registered user to submit data related to their research on a sample of the SAFOD core. The submitted data, after initial review by the knowledge base administrator, are added to the extensible knowledge base and become available in subsequent queries to all types of users. The interface facilitates inference capabilities in the

  13. Brittle-tough transitions during crack growth in toughened adhesives

    Science.gov (United States)

    Thoules, Michael

    2008-03-01

    The use of structural adhesives in automotive applications relies on an effective understanding of their performance under crash conditions. In particular, there is considerable potential for mechanics-based modeling of the interaction between an adhesive layer and the adherends, to replace current empirical approaches to design. Since energy dissipation during a crash, mediated by plastic deformation of the structure, is a primary consideration for automotive applications, traditional approaches of fracture mechanics are not appropriate. Cohesive-zone models that use two fracture parameters - cohesive strength and toughness - have been shown to provide a method for quantitative mechanics analysis. Combined numerical and experimental techniques have been developed to deduce the toughness and strength parameters of adhesive layers, allowing qualitative modeling of the performance of adhesive joints. These techniques have been used to study the failure of joints, formed from a toughened adhesive and sheet metal, over a wide range of loading rates. Two fracture modes are observed: quasi-static crack growth and dynamic crack growth. The quasi-static crack growth is associated with a toughened mode of failure; the dynamic crack growth is associated with a more brittle mode of failure. The results of the experiments and analyses indicate that the fracture parameters for quasi-static crack growth in this toughened system are essentially rate independent, and that quasi-static crack growth can occur even at the highest crack velocities. Effects of rate appear to be limited to the ease with which a transition to dynamic fracture could be triggered. This transition appears to be stochastic in nature, and it does not appear to be associated with the attainment of any critical value for crack velocity or loading rate. Fracture-mechanics models exist in the literature for brittle-ductile transitions in rate-dependent polymers, which rely on rate dependent values of toughness

  14. Treatment of alkali-injured cornea by cyclosporine A-loaded electrospun nanofibers - An alternative mode of therapy.

    Science.gov (United States)

    Cejkova, Jitka; Cejka, Cestmir; Trosan, Peter; Zajicova, Alena; Sykova, Eva; Holan, Vladimir

    2016-06-01

    In this study we tried to develop a new approach to suppress inflammation and neovascularization in the alkali-injured rabbit cornea. For this reason Cyclosporine A (CsA)-loaded electrospun nanofibers were transferred onto the ocular surface injured with alkali (0.25 N NaOH). Damaged corneas were divided into the following groups: untreated, treated with CsA eye drops, treated with nanofibers drug-free and treated with CsA-loaded nanofibers. Healthy rabbit corneas served as controls. Drug-free nanofibers and CsA-loaded nanofibers were transferred onto the damaged corneal surface immediately after the injury and sutured to conjunctiva. On day five after the injury the nanofibers were removed. The animals from all groups were sacrificed on day twelve after the injury. The extent of the inflammatory reaction and corneal healing were examined macroscopically, immunohistochemically and biochemically. The central corneal thickness was measured using an ultrasonic pachymeter. When compared with untreated injured corneas, injured corneas treated with drug-free nanofibers or injured corneas treated with CsA eye drops, the number of CD3-positive cells (T lymphocytes) and the production of pro-inflammatory cytokines were strongly reduced in corneas treated with CsA-loaded nanofibers, which was associated with the significantly decreased expression of matrix metalloproteinase 9, inducible nitric oxide synthase, vascular endothelial growth factor and active caspase-3. CsA-loaded nanofibers effectively suppressed corneal inflammation and corneal neovascularization. Central corneal thickness restored to levels before injury only in corneas treated with CsA-loaded nanofibers. Corneal transparency was highly restored in these corneas. It is suggested that the beneficial effect of CsA-loaded nanofibers was associated with the continuous release of CsA from nanofibers and continuous affection of damaged cornea by CsA. The suture of nanofibers to conjunctiva and the closed eyes

  15. Premalignant melanosis of the conjunctiva and the cornea in xeroderma pigmentosum.

    OpenAIRE

    Paridaens, A D; McCartney, A C; Hungerford, J. L.

    1992-01-01

    Xeroderma pigmentosum is a rare autosomal recessive dermatosis. The neoplastic changes in sunlight-exposed areas of the skin and eyes may be related to the impaired replication of ultraviolet radiation-damaged DNA. A 38-year-old Greek woman is reported with a mild form of xeroderma pigmentosum and primary acquired melanosis with atypia of her right limbal conjunctiva and cornea. The development of this precursor of conjunctival malignant melanoma in a xeroderma pigmentosum patient may support...

  16. Pathogenic strains of Acanthamoeba are recognized by TLR4 and initiated inflammatory responses in the cornea.

    Directory of Open Access Journals (Sweden)

    Hassan Alizadeh

    Full Text Available Free-living amoebae of the Acanthamoeba species are the causative agent of Acanthamoeba keratitis (AK, a sight-threatening corneal infection that causes severe pain and a characteristic ring-shaped corneal infiltrate. Innate immune responses play an important role in resistance against AK. The aim of this study is to determine if Toll-like receptors (TLRs on corneal epithelial cells are activated by Acanthamoeba, leading to initiation of inflammatory responses in the cornea. Human corneal epithelial (HCE cells constitutively expressed TLR1, TLR2, TLR3, TLR4, and TLR9 mRNA, and A. castellanii upregulated TLR4 transcription. Expression of TLR1, TLR2, TLR3, and TLR9 was unchanged when HCE cells were exposed to A. castellanii. IL-8 mRNA expression was upregulated in HCE cells exposed to A. castellanii. A. castellanii and lipopolysaccharide (LPS induced significant IL-8 production by HCE cells as measured by ELISA. The percentage of total cells positive for TLR4 was higher in A. castellanii stimulated HCE cells compared to unstimulated HCE cells. A. castellanii induced upregulation of IL-8 in TLR4 expressing human embryonic kidney (HEK-293 cells, but not TLR3 expressing HEK-293 cells. TLR4 neutralizing antibody inhibited A. castellanii-induced IL-8 by HCE and HEK-293 cells. Clinical strains but not soil strains of Acanthamoeba activated TLR4 expression in Chinese hamster corneas in vivo and in vitro. Clinical isolates but not soil isolates of Acanthamoeba induced significant (P< 0.05 CXCL2 production in Chinese hamster corneas 3 and 7 days after infection, which coincided with increased inflammatory cells in the corneas. Results suggest that pathogenic species of Acanthamoeba activate TLR4 and induce production of CXCL2 in the Chinese hamster model of AK. TLR4 may be a potential target in the development of novel treatment strategies in Acanthamoeba and other microbial infections that activate TLR4 in corneal cells.

  17. A Cornea Substitute Derived from Fish Scale: 6-Month Followup on Rabbit Model

    OpenAIRE

    Fei Yuan; Liyan Wang; Chien-Chen Lin; Cheng-Hung Chou; Lei Li

    2014-01-01

    A fish scale-derived cornea substitute (Biocornea) is proposed as an alternative for human donor corneal tissue. We adopt a regenerative medicine approach to design a primary alternative to the use of fish scale for restoring sight by corneal replacement. Biocornea with corneal multilayer arrangement collagen was implanted to rabbits by pocket implantation. Our study demonstrated the safety and detailed morphologic and physiologic results from the 6 months of followup of rabbit model. In the ...

  18. Effects of Intracameral Injection of Lidocaine on The Cornea in A Rabbit Model. Scanning Electronmicroscopic Study

    OpenAIRE

    Ramadan, Wafaa S.

    2005-01-01

    Combined topical and intracameral anesthesia proved to be an alternative to peribulbar and retrobulbar anesthesia in cataract surgery especially in phacoemulsification approach.. So, in the present work the effect of intracameral injection of different concentrations of lidocaine on the structure of rabbit's cornea was studied using the freez-fracture technique and the scanning electron microscope . Fourteen baladi rabbits of both sexes weighing 2-3 kg.were used and divided into two groups ac...

  19. Synthesis of type III collagen by fibroblasts from the embryonic chick cornea

    OpenAIRE

    1980-01-01

    Synthesis of collagen types I, II, III, and IV in cells from the embryonic chick cornea was studied using specific antibodies and immunofluorescence. Synthesis of radioactively labeled collagen types I and III was followed by fluorographic detection of cyanogen bromide peptides on polyacrylamide slab gels and by carboxymethylcellulose chromatography followed by disc gel electrophoresis. Type III collagen had been detected previously by indirect immunofluorescence in the corneal epithelial cel...

  20. Atmospheric-Pressure Cold Plasma Induces Transcriptional Changes in Ex Vivo Human Corneas.

    Directory of Open Access Journals (Sweden)

    Umberto Rosani

    Full Text Available Atmospheric pressure cold plasma (APCP might be considered a novel tool for tissue disinfection in medicine since the active chemical species produced by low plasma doses, generated by ionizing helium gas in air, induces reactive oxygen species (ROS that kill microorganisms without substantially affecting human cells.In this study, we evaluated morphological and functional changes in human corneas exposed for 2 minutes (min to APCP and tested if the antioxidant n-acetyl l-cysteine (NAC was able to inhibit or prevent damage and cell death.Immunohistochemistry and western blotting analyses of corneal tissues collected at 6 hours (h post-APCP treatment demonstrated no morphological tissue changes, but a transient increased expression of OGG1 glycosylase that returned to control levels in 24 h. Transcriptome sequencing and quantitative real time PCR performed on different corneas revealed in the treated corneas many differentially expressed genes: namely, 256 and 304 genes showing expression changes greater than ± 2 folds in the absence and presence of NAC, respectively. At 6 h post-treatment, the most over-expressed gene categories suggested an active or enhanced cell functioning, with only a minority of genes specifically concerning oxidative DNA damage and repair showing slight over-expression values (<2 folds. Moreover, time-related expression analysis of eight genes up-regulated in the APCP-treated corneas overall demonstrated the return to control expression levels after 24 h.These findings of transient oxidative stress accompanied by wide-range transcriptome adjustments support the further development of APCP as an ocular disinfectant.

  1. Hyperglycemia-induced abnormalities in rat and human corneas: the potential of second harmonic generation microscopy.

    OpenAIRE

    Latour, Gaël; Kowalczuk, Laura; Savoldelli, Michèle; Bourges, Jean-Louis; Plamann, Karsten; Behar-Cohen, Francine; Schanne-Klein, Marie-Claire

    2012-01-01

    BACKGROUND: Second Harmonic Generation (SHG) microscopy recently appeared as an efficient optical imaging technique to probe unstained collagen-rich tissues like cornea. Moreover, corneal remodeling occurs in many diseases and precise characterization requires overcoming the limitations of conventional techniques. In this work, we focus on diabetes, which affects hundreds of million people worldwide and most often leads to diabetic retinopathy, with no early diagnostic tool. This study then a...

  2. Transient postoperative vascular endothelial growth factor (VEGF)-neutralisation improves graft survival in corneas with partly regressed inflammatory neovascularisation

    OpenAIRE

    Bachmann, B. O.; Lütjen-Drecoll, Elke; F. Bock; Wiegand, S. J.; Hos, D.; Dana, R; Kruse, F. E.; Cursiefen, C.

    2009-01-01

    Background: High-risk keratoplasties are usually performed after an uninflamed and quiescent interval in corneas with partly regressed blood and lymphatic vessels. We analysed whether the inhibition of post-keratoplasty revascularisation in mice with partly regressed corneal vessels (“intermediate-risk”) improves graft survival. Methods: Three interrupted stromal sutures (11-0) in corneas of Balb/c mice (6–8 weeks old) were placed for 6 weeks. Six months after suture removal, penetrating k...

  3. In vivo 3D measurement of moxifloxacin and gatifloxacin distributions in the mouse cornea using multiphoton microscopy

    OpenAIRE

    Seunghun Lee; Jun Ho Lee; Jin Hyoung Park; Yeoreum Yoon; Wan Kyun Chung; Hungwon Tchah; Myoung Joon Kim; Ki Hean Kim

    2016-01-01

    Moxifloxacin and gatifloxacin are fourth-generation fluoroquinolone antibiotics used in the clinic to prevent or treat ocular infections. Their pharmacokinetics in the cornea is usually measured from extracted ocular fluids or tissues, and in vivo direct measurement is difficult. In this study multiphoton microscopy (MPM), which is a 3D optical microscopic technique based on multiphoton fluorescence, was applied to the measurement of moxifloxacin and gatifloxacin distribution in the cornea. I...

  4. A Method to Prepare a Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) Graft Using Donor Corneas With Narrow Scleral Rims

    OpenAIRE

    Lin, Tzu-Yu; Hwang, Yih-Shiou; Ma, David Hui-Kang

    2015-01-01

    Abstract Donor corneas with narrow scleral rims are often disqualified for Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK), mainly because of fluid leak and low pressure when they are mounted onto an artificial anterior chamber (AAC). This report describes a novel method to tight-lock a donor cornea with a narrow scleral rim so that microkeratome cutting is possible, allowing a DSAEK procedure to be completed. A 50-year-old male suffering from Epstein–Barr virus (EBV) endothel...

  5. Safety of cornea and iris in ocular surgery with 355-nm lasers

    Science.gov (United States)

    Wang, Jenny; Chung, Jae Lim; Schuele, Georg; Vankov, Alexander; Dalal, Roopa; Wiltberger, Michael; Palanker, Daniel

    2015-09-01

    A recent study showed that 355-nm nanosecond lasers cut cornea with similar precision to infrared femtosecond lasers. However, use of ultraviolet wavelength requires precise assessment of ocular safety to determine the range of possible ophthalmic applications. In this study, the 355-nm nanosecond laser was evaluated for corneal and iris damage in rabbit, porcine, and human donor eyes as determined by minimum visible lesion (MVL) observation, live/dead staining of the endothelium, and apoptosis assay. Single-pulse damage to the iris was evaluated on porcine eyes using live/dead staining. In live rabbits, the cumulative median effective dose (ED50) for corneal damage was 231 J/cm2, as seen by lesion observation. Appearance of endothelial damage in live/dead staining or apoptosis occurred at higher radiant exposure of 287 J/cm2. On enucleated rabbit and porcine corneas, ED50 was 87 and 52 J/cm2, respectively, by MVL, and 241 and 160 J/cm2 for endothelial damage. In human eyes, ED50 for MVL was 110 J/cm2 and endothelial damage at 453 J/cm2. Single-pulse iris damage occurred at ED50 of 208 mJ/cm2. These values determine the energy permitted for surgical patterns and can guide development of ophthalmic laser systems. Lower damage threshold in corneas of enucleated eyes versus live rabbits is noted for future safety evaluation.

  6. Pigmentation of the Cornea Secondary to Tinted Soft Contact Lens Wear

    Directory of Open Access Journals (Sweden)

    Natasha Spiteri

    2012-01-01

    Full Text Available Purpose. To report a case of pigmented corneal iron lines following use of tinted soft contact lenses (CL. Methods. A retrospective case report. Results. A 16-year-old girl was referred with suspected CL-related keratopathy OU, having recently switched to tinted soft monthly disposable CLs (8.4/14.0 −3.00 OD, −3.25 OS Aquamarine SofLens Natural Colours, Bausch and Lomb, New York, USA. Both corneas exhibited symmetric superficial corneal pigmented iron lines, which gradually disappeared following discontinuation of CL wear. Conclusions. Pigmented corneal rings have been reported in normal ageing corneas, in certain pathological conditions, and in association with altered corneal topography following LASIK and orthokeratology. We suspect a poorly fitting CL resulted in localised tear pooling between the CL and cornea, and subsequent iron pigment deposition, similar to that seen with orthokeratology. Cosmetic CLs bought via the Internet can be used in an unsupervised manner, with possible impacts on visual function and potential complications.

  7. Dose-dependent ultrastructural changes in rat cornea after oral methylphenidate administration

    International Nuclear Information System (INIS)

    Objective was to investigate dose-dependent ultrastructural changes in rat cornea after oral methylphenidate (Ritalin) administration. This study was conducted in the Dept. of Anatomy, Gazi University, Faculty of Medicine, Ankara between March and May 2005, with a total of 27 female prepubertal Wistar albino rats, divided into 3 different dose groups (5mg/kg, 10 mg/kg, 20 mg/kg) and their control groups. They were treated orally with methylphenidate and eye tissue was removed to process for electron microscopic studies. We observed that all cells and prominently basal cells of the corneal epithelium show dose-dependent degenerative changes such as apoptotic bodies, chromatin condensation and ondulation in their nuclei and crystolysis of the mitochondrion. In the stroma, the most evident finding was the increase of the collagen fiber. In addition to dose-dependent changes related to apoptotic process, which is chromatin condensation in their nuclei, electron dense material accumulation and percicellular edema in the cytoplasm were also seen. In the endothelial cell lines, disruption of the junctional complexes, vacuolization in the cell cytoplasms and crystolysis of the mitochondrion's with rough endoplasmic reticulum cisternae activity were observed. Ritalin is inducing an evident degeneration, especially in epithelium cells with increasing doses. Ultrastructural cell organelle composition degeneration with stromal fibrosis has negative effect on cornea dehydration. In light of these findings, we believe that the Ritalin treatment dose needed to be kept to a minimum to maintain healthy cornea ultrastructure and related physiology. (author)

  8. Fractal analysis of AFM images of the surface of Bowman's membrane of the human cornea.

    Science.gov (United States)

    Ţălu, Ştefan; Stach, Sebastian; Sueiras, Vivian; Ziebarth, Noël Marysa

    2015-04-01

    The objective of this study is to further investigate the ultrastructural details of the surface of Bowman's membrane of the human cornea, using atomic force microscopy (AFM) images. One representative image acquired of Bowman's membrane of a human cornea was investigated. The three-dimensional (3-D) surface of the sample was imaged using AFM in contact mode, while the sample was completely submerged in optisol solution. Height and deflection images were acquired at multiple scan lengths using the MFP-3D AFM system software (Asylum Research, Santa Barbara, CA), based in IGOR Pro (WaveMetrics, Lake Oswego, OR). A novel approach, based on computational algorithms for fractal analysis of surfaces applied for AFM data, was utilized to analyze the surface structure. The surfaces revealed a fractal structure at the nanometer scale. The fractal dimension, D, provided quantitative values that characterize the scale properties of surface geometry. Detailed characterization of the surface topography was obtained using statistical parameters, in accordance with ISO 25178-2: 2012. Results obtained by fractal analysis confirm the relationship between the value of the fractal dimension and the statistical surface roughness parameters. The surface structure of Bowman's membrane of the human cornea is complex. The analyzed AFM images confirm a fractal nature of the surface, which is not taken into account by classical surface statistical parameters. Surface fractal dimension could be useful in ophthalmology to quantify corneal architectural changes associated with different disease states to further our understanding of disease evolution.

  9. A cornea substitute derived from fish scale: 6-month followup on rabbit model.

    Science.gov (United States)

    Yuan, Fei; Wang, Liyan; Lin, Chien-Chen; Chou, Cheng-Hung; Li, Lei

    2014-01-01

    A fish scale-derived cornea substitute (Biocornea) is proposed as an alternative for human donor corneal tissue. We adopt a regenerative medicine approach to design a primary alternative to the use of fish scale for restoring sight by corneal replacement. Biocornea with corneal multilayer arrangement collagen was implanted to rabbits by pocket implantation. Our study demonstrated the safety and detailed morphologic and physiologic results from the 6 months of followup of rabbit model. In the peripheral Biocornea, the collagen fibrils were arranged in reticular fashion. Slit lamp examination showed that haze and an ulcer were not observed in all groups at 3 months postoperatively while all corneas with Biocornea were clear at both 3 months and 6 months postoperatively. The interface of Biocornea and stromal tissue were filled successfully and without observable immune cells at postoperative day 180. Moreover, the Biocornea was not dissolved and degenerated but remained transparent and showed no apparent fragmentation. Our study demonstrated that the Biocornea derived from fish scale as a good substitute had high biocompatibility and support function after a long-term evaluation. This revealed that the new approach of using Biocornea may yield an ideal artificial cornea substitute for long-term inlay placement. PMID:25089206

  10. Reconstruction of auto-tissue-engineered lamellar cornea by dynamic culture for transplantation: a rabbit model.

    Directory of Open Access Journals (Sweden)

    Zheng Wu

    Full Text Available To construct an auto-tissue-engineered lamellar cornea (ATELC for transplantation, based on acellular porcine corneal stroma and autologous corneal limbal explants, a dynamic culture process, which composed of a submersion culture, a perfusion culture and a dynamic air-liquid interface culture, was performed using appropriate parameters. The results showed that the ATELC-Dynamic possessed histological structure and DNA content that were similar to native lamellar cornea (NLC, p>0.05. Compared to NLC, the protein contents of zonula occludens-1, desmocollin-2 and integrin β4 in ATELC-Dynamic reached 93%, 89% and 73%, respectively. The basal cells of ATELC-Dynamic showed a better differentiation phenotype (K3-, P63+, ABCG2+ compared with that of ATELC in static air-lift culture (ATELC-Static, K3+, P63-, ABCG2-. Accordingly, the cell-cloning efficiency of ATELC-Dynamic (9.72±3.5% was significantly higher than that of ATELC-Static (2.13±1.46%, p0.05. Rabbit lamellar keratoplasty showed that the barrier function of ATELC-Dynamic was intact, and there were no signs of epithelial shedding or neovascularization. Furthermore, the ATELC-Dynamic group had similar optical properties and wound healing processes compared with the NLC group. Thus, the sequential dynamic culture process that was designed according to corneal physiological characteristics could successfully reconstruct an auto-lamellar cornea with favorable morphological characteristics and satisfactory physiological function.

  11. Changes in thickness of each layer of developing chicken cornea after administration of caffeine.

    Directory of Open Access Journals (Sweden)

    Hieronim Bartel

    2010-08-01

    Full Text Available The aim of the study was the presentation of changes in thickness of each layer of a developing cornea, that came into being under an influence of caffeine which was administered to chicken embryos. Research materials were 26 chicken embryos from breeding eggs that had been incubated. Breeding eggs were divided into two groups: control (n=30 in which Ringer liquid was given, and experimental (n=30 in which teratogenic dose of caffeine was administrated - 3.5 mg/egg. In 36th hour of incubation solutions were given with cannula through a hole in an egg shell directly onto amniotic membrane. After closing the hole with paraffin, eggs were put back into incubator. On 10th and 19th day of incubation corneas were taken for morphometric and morphological analysis. In experimental groups reduction of corneal thickness, thickening of corneal epithelium and corneal endothelium as well as Bowman's and Descemet's membranes, decrease of thickness of corneal stroma in comparison with the control group have been observed. Caffeine causes thickness changes of all layers and decreases the total thickness of a developing cornea.

  12. A Cornea Substitute Derived from Fish Scale: 6-Month Followup on Rabbit Model

    Directory of Open Access Journals (Sweden)

    Fei Yuan

    2014-01-01

    Full Text Available A fish scale-derived cornea substitute (Biocornea is proposed as an alternative for human donor corneal tissue. We adopt a regenerative medicine approach to design a primary alternative to the use of fish scale for restoring sight by corneal replacement. Biocornea with corneal multilayer arrangement collagen was implanted to rabbits by pocket implantation. Our study demonstrated the safety and detailed morphologic and physiologic results from the 6 months of followup of rabbit model. In the peripheral Biocornea, the collagen fibrils were arranged in reticular fashion. Slit lamp examination showed that haze and an ulcer were not observed in all groups at 3 months postoperatively while all corneas with Biocornea were clear at both 3 months and 6 months postoperatively. The interface of Biocornea and stromal tissue were filled successfully and without observable immune cells at postoperative day 180. Moreover, the Biocornea was not dissolved and degenerated but remained transparent and showed no apparent fragmentation. Our study demonstrated that the Biocornea derived from fish scale as a good substitute had high biocompatibility and support function after a long-term evaluation. This revealed that the new approach of using Biocornea may yield an ideal artificial cornea substitute for long-term inlay placement.

  13. Analysis of cornea curvature using radial basis functions - Part I: Methodology.

    Science.gov (United States)

    Griffiths, G W; Płociniczak, Ł; Schiesser, W E

    2016-10-01

    We discuss the solution of cornea curvature using a meshless method based on radial basis functions (RBFs). A full two-dimensional nonlinear thin membrane partial differential equation (PDE) model is introduced and solved using the multiquadratic (MQ) and inverse multiquadratic (IMQ) RBFs. This new approach does not rely on radial symmetry or other simplifying assumptions in respect of the cornea shape. It also provides an alternative to corneal topography modeling methods requiring accurate material parameter values, such as Young's modulus and Poisson ratio, that may not be available. The results show good agreement with published corneal data and allow back calculations for estimating certain physical properties of the cornea, such as tension and elasticity coefficient. All calculations and generation of graphics were performed using the R language programming environment [34] and RStudio, the integrated development environment (IDE) for R [36], both of which are open source and free to download. Part II [48] of this paper demonstrates how the method has been used to provide a very accurate fit to a corneal measured data set. PMID:27614697

  14. Quantifying the effect of milli-molar glucose concentration on thickness of rabbit cornea with optical coherence tomography

    Science.gov (United States)

    Ghosn, Mohamad G.; Leba, Michael; Vijayananda, Astha; Ansari, Rafat R.; Larin, Kirill V.

    2009-02-01

    The cornea contributes about 65% of the eye's ability to refract light. Thus, any fluctuation in corneal thickness can cause noticeable changes in vision. The presence of glucose molecules induces a driving force for water to leave the collagen fibrils in the cornea due to the concentration gradient created, thus changing its thickness. In this study, the effect of various milli-molar glucose concentrations on corneal thickness was explored using Optical Coherence Tomography. Whole rabbit eyes were placed in a specially designed dish while immersed in saline to ensure proper hydration of the eye. The cornea was imaged for 10 minutes. In 30 minute increments, a higher concentration of glucose was added, bringing the overall glucose concentration to 10, 15, 20, 25, and 30 mM. The thickness of the cornea was measured every 2 minutes. Ultimately, an inverse relationship was observed, indicating that the increase in glucose concentration yielded a decrease in the corneal thickness. From three separate experiments, the cornea experienced 8 +/- 1, 27 +/- 1, 44 +/- 3, 58 +/- 3, and 64 +/- 3 μm decrease in thickness from its starting value while exposed to 10, 15, 20, 25, and 30 mM solutions of glucose, respectively. This relationship provides insight on the physiological changes of the cornea as a result of different glucose concentrations. This could potentially be useful in monitoring blood-glucose levels through the eye.

  15. A Maxwell elasto-brittle rheology for sea ice modelling

    Science.gov (United States)

    Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe

    2016-07-01

    A new rheological model is developed that builds on an elasto-brittle (EB) framework used for sea ice and rock mechanics, with the intent of representing both the small elastic deformations associated with fracturing processes and the larger deformations occurring along the faults/leads once the material is highly damaged and fragmented. A viscous-like relaxation term is added to the linear-elastic constitutive law together with an effective viscosity that evolves according to the local level of damage of the material, like its elastic modulus. The coupling between the level of damage and both mechanical parameters is such that within an undamaged ice cover the viscosity is infinitely large and deformations are strictly elastic, while along highly damaged zones the elastic modulus vanishes and most of the stress is dissipated through permanent deformations. A healing mechanism is also introduced, counterbalancing the effects of damaging over large timescales. In this new model, named Maxwell-EB after the Maxwell rheology, the irreversible and reversible deformations are solved for simultaneously; hence drift velocities are defined naturally. First idealized simulations without advection show that the model reproduces the main characteristics of sea ice mechanics and deformation: strain localization, anisotropy, intermittency and associated scaling laws.

  16. Comparison of ductile-to-brittle transition curve fitting approaches

    Energy Technology Data Exchange (ETDEWEB)

    Cao, L.W. [School of Materials Science and Engineering, Beihang University (BUAA), Beijing 100191 (China)] [Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR (United Kingdom); Wu, S.J., E-mail: wusj@buaa.edu.cn [School of Materials Science and Engineering, Beihang University (BUAA), Beijing 100191 (China); Flewitt, P.E.J. [Interface Analysis Centre, University of Bristol, Bristol BS2 8BS (United Kingdom)] [School of Physics, HH Wills Laboratory, University of Bristol, BS8 1TL (United Kingdom)

    2012-05-15

    Ductile-to-brittle transition (DBT) curve fitting approaches are compared over the transition temperature range for reactor pressure vessel steels with different kinds of data, including Charpy-V notch impact energy data and fracture toughness data. Three DBT curve fitting methods have been frequently used in the past, including the Burr S-Weibull and tanh distributions. In general there is greater scatter associated with test data obtained within the transition region. Therefore these methods give results with different accuracies, especially when fitting to small quantities of data. The comparison shows that the Burr distribution and tanh distribution can almost equally fit well distributed and large data sets extending across the test temperature range to include the upper and lower shelves. The S-Weibull distribution fit is poor for the lower shelf of the DBT curve. Overall for both large and small quantities of measured data the Burr distribution provides the best description. - Highlights: Black-Right-Pointing-Pointer Burr distribution offers a better fit than that of a S-Weibull and tanh fit. Black-Right-Pointing-Pointer Burr and tanh methods show similar fitting ability for a large data set. Black-Right-Pointing-Pointer Burr method can fit sparse data well distributed across the test temperature. Black-Right-Pointing-Pointer S-Weibull method cannot fit the lower shelf well and show poor fitting quality.

  17. THEORETICAL STATISTICAL SOLUTION AND NUMERICALSIMULATION OF HETEROGENEOUS BRITTLE MATERIALS

    Institute of Scientific and Technical Information of China (English)

    陈永强; 姚振汉; 郑小平

    2003-01-01

    The analytical stress-strain relation with heterogeneous parameters is derived for theheterogeneous brittle materials under a uniaxial extensional load, in which the distributions of theelastic modulus and the failure strength are assumed to be statistically independent. This theoreticalsolution gives an approximate estimate of the equivalent stress-strain relations for 3-D heterogeneousmaterials. In one-dimensional cases it may provide comparatively accurate results. The theoreticalsolution can help us to explain how the heterogeneity influences the mechanical behaviors, Further, anumerical approach is developed to model the non-linear behavior of three-dimensional heterogeneousbrittle materials. The lattice approach and statistical techniques are applied to simulate the initialheterogeneity of heterogeneous materials. The load increment in each loading stage is adaptivelydetermined so that the better approximation of the failure process can be realized. When the maximumtensile principal strain exceeds the failure strain, the elements are considered to be broken, which canbe carried out by replacing its Young's modulus with a very small value. A 3-D heterogeneous brittlematerial specimen is simulated during a full failure process. The numerical results are in good agreementwith the analytical solutions and experimental data.

  18. Ductile streaks in precision grinding of hard and brittle materials

    Indian Academy of Sciences (India)

    V C Venkatesh; S Izman; S Sharif; T T Mon; M Konneh

    2003-10-01

    Ductile streaks produced during diamond grinding of hard and brittle materials have aided the subsequent process of polishing. Two novel techniques were used to study the formation of ductile mode streaks during diamond grinding (primary process) of germanium, silicon, and glass. In the first technique, aspheric surfaces were generated on Ge and Si at conventional speeds (5000 rpm). In the second technique, diamond grinding of plano surfaces on glass and Si surfaces using high speed (100,000 rpm) was carried out. Form accuracy, surface finish and ductile mode grinding streaks are discussed in this paper. It was found that resinoid diamond wheels gave more ductile streaks than metal-bonded wheels but better form accuracy was obtained with the latter. Ductile streaks were obtained more easily with pyrex rather than with BK 7 glass thus necessitating very little time for polishing. Ductile streaks appeared in abundance on germanium rather than silicon. Both the novel grinding techniques were used on CNC machining centres.

  19. Reduced corneal swelling and deswelling response in the iridocorneal endothelial syndrome

    NARCIS (Netherlands)

    M.T.P. Odenthal; C.P. Nieuwendaal; H.W. Venema; J. Oosting; H.J. Volker-Dieben; A. Kijlstra

    2006-01-01

    Purpose. Despite severe abnormalities of the corneal endothelium in the iridocorneal endothelial (ICE) syndrome, the cornea can remain clear and maintain its normal thickness for years before corneal decompensation occurs. The aim of this study is to analyze this discrepancy by studying corneal hydr

  20. Correlation of Biomicroscopic Findings with Confocal Microscopy in Eyes with Amiodarone-Induced Cornea Verticillata

    Directory of Open Access Journals (Sweden)

    Emine Kaya

    2014-01-01

    Full Text Available Objectives: To investigate the correlation between biomicroscopic and confocal microscopic findings in eyes with amiodarone-induced cornea verticillata. Materials and Methods: Sixteen eyes of 8 patients with amiodarone-induced cornea verticillata were evaluated. Eyes with keratopathy were staged according to Orlando slit-lamp microscopy classification. Confocal laser-scanning microscopy was performed by Rostock cornea modulated to HRT II (Heidelberg Engineering GmbH, Heidelberg, Germany, and staging was done according to Falke’s classification that is based on the degree of epithelial basal cell deposit accumulation. The relation between biomicroscopic staging and corneal involvement detected on confocal microscopy was assessed by Spearman correlation analysis. Results: The mean age of the 8 patients (5 male, 3 female was 63.1±7.2 (50 to 69 years. The mean duration of drug treatment was 12.1±11.8 (3 to 36 months, and the mean drug treatment dose was 312.5±223.2 (100 to 800 mg/day. At the time of examination, 50% of the patients had already given up the treatment at a mean of 29.5±15.8 (6 to 40 months ago, whereas the other 50% were still on amiodarone therapy. Hyper-reflecting deposits were observed in the basal epithelium, anterior-, mid-and deep-stroma, and in the endothelium on confocal microscopic examination. Correlation was detected between biomicroscopic and confocal microscopic stages (r=0.770, p<0.001. Frequency of detecting deposits in the stroma and endothelium was found to be increasing as the biomicroscopic stage increased (r=0.844; p<0.001 and r=0.551; p<0.01, respectively. Conclusion: In amiodarone-induced cornea verticillata, correlated results were detected between biomicroscopic and confocal microscopic staging. Therefore, in clinics where confocal microscopy is not available, biomicroscopic staging can be used as a guiding parameter in eyes with amiodarone-induced cornea verticillata. (Turk J Ophthalmol 2014; 44: 63-67

  1. Chronic Lunar Dust Exposure on Rat Cornea: Evaluation by Gene Expression Profiling

    Science.gov (United States)

    Theriot, C. A.; Glass, A.; Lam, C-W.; James, J.; Zanello, S. B.

    2014-01-01

    Lunar dust is capable of entering habitats and vehicle compartments by sticking to spacesuits or other objects that are transferred into the spacecraft from the lunar surface and has been reported to cause irritation upon exposure. During the Apollo missions, crewmembers reported irritation specifically to the skin and eyes after contamination of the lunar and service modules. It has since been hypothesized that ocular irritation and abrasion might occur as a result of such exposure, impairing crew vision. Recent work has shown that both ultrafine and unground lunar dust exhibited minimal irritancy of the ocular surface (i.e., cornea); however, the assessment of the severity of ocular damage resulting from contact of lunar dust particles to the cornea has focused only on macroscopic signs of mechanical irritancy and cytotoxicity. Given the chemical reactive properties of lunar dust, exposure of the cornea may contribute to detrimental effects at the molecular level including but not limited to oxidative damage. Additionally, low level chronic exposures may confound any results obtained in previous acute studies. We report here preliminary results from a tissue sharing effort using 10-week-old Fischer 344 male rats chronically exposed to filtered air or jet milled lunar dust collected during Apollo 14 using a Jaeger-NYU nose-only chamber for a total of 120 hours (6 hours daily, 5 days a week) over a 4-week period. RNA was isolated from corneas collected from rats at 1 day and 7 days after being exposed to concentrations of 0, 20, and 60 mg/m3 of lunar dust. Microarray analysis was performed using the Affymetrix GeneChip Rat Genome 230 2.0 Array with Affymetrix Expression Console and Transcriptome Analysis Console used for normalization and secondary analysis. An Ingenuity iReport"TM" was then generated for canonical pathway identification. The number of differentially expressed genes identified increases with dose compared to controls suggesting a more severe

  2. In vitro permeation characteristics of moxifloxacin from oil drops through excised goat, sheep, buffalo and rabbit corneas.

    Science.gov (United States)

    Pawar, P K; Majumdar, D K

    2007-11-01

    The objective of present investigation was to study the in vitro permeation characteristics of moxifloxacin from oil drops through freshly excised goat, sheep, buffalo and rabbit corneas. Moxifloxacin, 0.043 to 0.048% (w/v) ophthalmic solutions with or without (0.5% v/v) benzyl alcohol were made in arachis, castor, cottonseed, olive, soybean, sunflower and sesame oils. Permeation studies were conducted by putting 1 ml oil formulation on cornea (0.50 cm2) fixed between donor and receptor compartments of an all glass modified Franz diffusion cell and measuring the drug permeated in receptor (containing 10 ml bicarbonate ringer, pH 7.4 at 37 degrees C under stirring) by spectrophotometry at 291 nm, after 120 min. Post permeation corneal hydration was measured to assess corneal damage. The study was designed with paired corneas i.e. one cornea of an animal received formulation without benzyl alcohol while the contralateral cornea received formulation with benzyl alcohol. Moxifloxacin ophthalmic solution in castor oil showed maximum permeation with all the corneas. Addition of benzyl alcohol, a preservative, to oil drops reduced permeation of moxifloxacin from each oil drop, with corneas of all the species. Partition experiments with moxifloxacin oil drops and phosphate buffer (pH 7.4) indicated higher partitioning of drug in the oil phase, in presence of benzyl alcohol. Thus results of permeation are consistent with the partition characteristics of drug between oil and aqueous phase. Corneal hydration obtained with all the formulations was between 75 to 80% indicating no corneal damage.

  3. Validation of an endothelial roll preparation for Descemet Membrane Endothelial Keratoplasty by a cornea bank using "no touch" dissection technique.

    Science.gov (United States)

    Marty, Anne-Sophie; Burillon, Carole; Desanlis, Adeline; Damour, Odile; Kocaba, Viridiana; Auxenfans, Céline

    2016-06-01

    Descemet Membrane Endothelial Keratoplasty (DMEK) selectively replaces the damaged posterior part of the cornea. However, the DMEK technique relies on a manually-performed dissection that is time-consuming, requires training and presents a potential risk of endothelial graft damages leading to surgery postponement when performed by surgeons in the operative room. To validate precut corneal tissue preparation for DMEK provided by a cornea bank in order to supply a quality and security precut endothelial tissue. The protocol was a technology transfer from the Netherlands Institute for Innovative Ocular Surgery (NIIOS) to Lyon Cornea Bank, after formation in NIIOS to the DMEK "no touch" dissection technique. The technique has been validated in selected conditions (materials, microscope) and after a learning curve, cornea bank technicians prepared endothelial tissue for DMEK. Endothelial cells densities (ECD) were evaluated before and after preparation, after storage and transport to the surgery room. Microbiological and histological controls have been done. Twenty corneas were manually dissected; 18 without tears. Nineteen endothelial grafts formed a double roll. The ECD loss after cutting was 3.3 % (n = 19). After transportation 7 days later, we found an ECD loss of 25 % (n = 12). Three days after cutting and transportation, we found 2.1 % of ECD loss (n = 7). Histology found an endothelial cells monolayer lying on Descemet membrane. The mean thickness was 12 ± 2.2 µm (n = 4). No microbial contamination was found (n = 19). Endothelial roll stability has been validated at 3 days in our cornea bank. Cornea bank technicians trained can deliver to surgeons an ECD controlled, safety and ready to use endothelial tissue, for DMEK by "no touch" technique, allowing time saving, quality and security for surgeons.

  4. Polymer Reinforced, Non-Brittle, Light-Weight Cryogenic Insulation for Reduced Life Cycle Costs Project

    Data.gov (United States)

    National Aeronautics and Space Administration — InnoSense LLC (ISL) proposes to fabricate a composite aerogel foam. This material is designed to be impact resistant, non-brittle, non-water-retaining and...

  5. Prediction of rock brittleness using nondestructive methods for hard rock tunneling

    Directory of Open Access Journals (Sweden)

    Rennie B. Kaunda

    2016-08-01

    Full Text Available The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brittleness using artificial neural networks (ANN. Herein hard rock brittleness is defined using Yagiz' method. A predictive model is developed using a comprehensive database compiled from 30 years' worth of rock tests at the Earth Mechanics Institute (EMI, Colorado School of Mines. The model is sensitive to density, elastic properties, and P- and S-wave velocities. The results show that the model is a better predictor of rock brittleness than conventional destructive strength-test based models and multiple regression techniques. While the findings have direct implications on intact rock, the methodology can be extrapolated to rock mass problems in both tunneling and underground mining where rock brittleness is an important control.

  6. Prediction of rock brittleness using nondestructive methods for hard rock tunneling

    Institute of Scientific and Technical Information of China (English)

    Rennie B. Kaunda; Brian Asbury

    2016-01-01

    The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brit-tleness using artificial neural networks (ANN). Herein hard rock brittleness is defined using Yagiz’ method. A predictive model is developed using a comprehensive database compiled from 30 years’ worth of rock tests at the Earth Mechanics Institute (EMI), Colorado School of Mines. The model is sensitive to density, elastic properties, and P-and S-wave velocities. The results show that the model is a better predictor of rock brittleness than conventional destructive strength-test based models and mul-tiple regression techniques. While the findings have direct implications on intact rock, the methodology can be extrapolated to rock mass problems in both tunneling and underground mining where rock brittleness is an important control.

  7. Development of a brittle fracture acceptance criterion for the International Atomic Energy Agency (IAEA)

    Energy Technology Data Exchange (ETDEWEB)

    Sorenson, K.B.; Salzbrenner, R. (Sandia National Labs., Albuquerque NM (United States)); Nickell, R.E.

    1993-01-01

    An effort has been undertaken to develop a brittle fracture acceptance criterion for structural components of nuclear material transportation casks. The need for such a criterion was twofold. First, new generation cask designs have proposed the use of ferritic steels and other materials to replace the austenitic stainless steel commonly used for structural components in transport casks. Unlike austenitic stainless steel which fails in a high-energy absorbing, ductile tearing mode, it is possible for these candidate materials to fail via brittle fracture when subjected to certain combinations of elevated loading rates and low temperatures. Second, there is no established brittle fracture criterion accepted by the regulatory community that covers a broad range of structural materials. Although the existing IAEA Safety Series no.37 addressed brittle fracture, its the guidance was dated and pertained only to ferritic steels. Consultant's Services Meetings held under the auspices of the IAEA have resulted in a recommended brittle fracture criterion. The brittle fracture criterion is based on linear elastic fracture mechanics, and is the result of a consensus of experts from six participating IAEA-member countries. The brittle fracture criterion allows three approaches to determine the fracture toughness of the structural material. The three approaches present the opportunity to balance material testing requirements and the conservatism of the material's fracture toughness which must be used to demonstrate resistance to brittle fracture. This work has resulted in a revised Appendix IX to Safety Series no.37 which will be released as an IAEA Technical Document within the coming year. (author).

  8. Development of a brittle fracture acceptance criterion for the International Atomic Energy Agency (IAEA)

    Energy Technology Data Exchange (ETDEWEB)

    Sorenson, Ken B.; Salzbrenner, Richard [Sandia National Labs., Albuquerque, NM (United States); Nickell, Robert E. [Applied Science and Technology, Inc., Poway, CA (United States)

    1992-01-01

    An effort has been undertaken to develop a brittle fracture acceptance criterion for structural components of nuclear material transportation casks. The need for such a criterion was twofold. First, new generation cask designs have proposed the use of ferritic steels and other materials to replace the austenitic stainless steel commonly used for structural components in transport casks. Unlike austenitic stainless steel which fails in a high-energy absorbing, ductile tearing mode, it is possible for these candidate materials to fail via brittle fracture when subjected to certain combinations of elevated loading rates and low temperatures. Second, there is no established brittle fracture criterion accepted by the regulatory community that covers a broad range of structural materials. Although the existing IAEA Safety Series {number sign}37 addressed brittle fracture, its the guidance was dated and pertained only to ferritic steels. Consultant's Services Meetings held under the auspices of the IAEA have resulted in a recommended brittle fracture criterion. The brittle fracture criterion is based on linear elastic fracture mechanics, and is the result of a consensus of experts from six participating IAEA-member countries. The brittle fracture criterion allows three approaches to determine the fracture toughness of the structural material. The three approaches present the opportunity to balance material testing requirements and the conservatism of the material's fracture toughness which must be used to demonstrate resistance to brittle fracture. This work has resulted in a revised Appendix IX to Safety Series {number sign}37 which will be released as an IAEA Technical Document within the coming year.

  9. Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Secitional Indention

    Institute of Scientific and Technical Information of China (English)

    SU Jian-yu; ZHANG Kun; CHEN Guang-nan

    2004-01-01

    The cross-sectional indentation method is extended to evaluate the interfacial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interfacial separation occurs due to the edge chipping of brittle coating. The corresponding models are established to elucidate interfacial separation processes. This work further highlights the advantages and potential of this novel indentation method.

  10. Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Sectional Indention

    Institute of Scientific and Technical Information of China (English)

    SUJian-yu; ZHANGKun; CHENGuang-nan

    2004-01-01

    The cross-sectional indentation method is extended to evaluate the interracial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interracial separation occurs due to the edge chipping of brittle coating. The comesponding models are established to elucidate interracial separation processes. This work further highlights the advantages and potential of this novel indentation method.

  11. Experimental study on the physical and chemical properties of the deep hard brittle shale

    OpenAIRE

    Jian Xiong; Xiangjun Liu; Lixi Liang; Yi Ding; Meng Lei

    2016-01-01

    In the hard brittle shale formation, rock composition, physical and chemical properties, mechanics property before and after interacting with fluid have direct relation with borehole problems, such as borehole wall collapse, mud loss, hole shrinkage. To achieve hard brittle shale micro-structure, physical–chemical properties and mechanics property, energy-dispersive X-ray diffraction (XRD), cation exchange capacity experiment and hardness test are conducted. The result of laboratory experimen...

  12. A new approach to rock brittleness and its usability at prediction of drillability

    Science.gov (United States)

    Özfırat, M. Kemal; Yenice, Hayati; Şimşir, Ferhan; Yaralı, Olgay

    2016-07-01

    Rock brittleness is one of the most important issues in rock drilling and cutting. The relations between drillability and brittleness will assist engineers in excavation works. The demand for representative rock parameters related to planning of underground excavations is increasing, as these parameters constitute fundamental input for obtaining the most reliable cost and time estimates. In rock cutting mechanics, the effects of the rock and brittleness on the efficiency of drilling and excavation are examined by many researchers. In this study, 41 different rock types were tested in laboratory to investigate the relations between the drilling rate index and different brittleness values. Firstly, the relations defined in literature are tested. Strength tests are made according to International Society for Rock Mechanics standards. In addition Norwegian University of Science and Technology standards are used to determine drilling rate index. Then, a new brittleness index is proposed which is the arithmetic average of uniaxial compressive strength and tensile strength. Considering the regression analysis carried out, it was seen that the proposed formula showed good correlation for these samples handled in this study. As a result of this study, a high correlation is obtained between the proposed index and drilling rate index values (R:0.84). The results are found to be at least reliable as well as other brittleness equations given in literature.

  13. Brittleness and Packing Density Effects on Blast-hole Cuttings Yield of Selected Rocks

    Directory of Open Access Journals (Sweden)

    B. Adebayo

    2016-06-01

    Full Text Available This paper evaluates brittleness and packing density to analysis their effects on blast-hole cutting yield for three selected rocks in Nigeria. Brittleness test (S20 was carried out in accordance with Norwegian Soil and Rock Engineering and the Brittleness Index (BI for the selected rocks were estimated. The packing density determined from the photomicrograph of the rock samples. The grain size of 45 blast-holes drill cuttings collected from three selected while drilling of these rocks were determined using standard method of America Society for Testing and Materials (ASTM D 2487. The brittleness values are 50%, 44% and 42% for micro granite, porphyritic granite and medium biotite granite respectively. The result of BI varied from 10.32 – 11.59 and they are rated as moderately brittle rocks. The values of packing density varied from 92.20 – 94.55%, 91.00 -92.96% and 92.92 – 94.96% for all the rocks. The maximum weights of blast-hole particle size retained at 75 µm are 106.00g, 103.28 g and 99.76 g for medium biotite granite, micro granite and porhyritic granite respectively. Packing density values have correlation to some extent with (S20 values hence, this influence the yield of blast-hole cuttings as drilling progresses. The minimum weight of blast-hole cuttings particle size retained at 150 µm agrees with brittleness index classification for micro granite.

  14. Corneal Collagen Cross-Linking with Hypoosmolar Riboflavin Solution in Keratoconic Corneas

    Directory of Open Access Journals (Sweden)

    Shaofeng Gu

    2014-01-01

    Full Text Available Purpose. To report the 12-month outcomes of corneal collagen cross-linking (CXL with a hypoosmolar riboflavin and ultraviolet-A (UVA irradiation in thin corneas. Methods. Eight eyes underwent CXL using a hypoosmolar riboflavin solution after epithelial removal. The corrected distance visual acuity (CDVA, manifest refraction, the mean thinnest corneal thickness (MTCT, and the endothelial cell density (ECD were evaluated before and 6 and 12 months after CXL. Results. The MTCT was 413.9 ± 12.4 μm before treatment and reduced to 381.1 ± 7.3 μm after the removal of the epithelium. After CXL, the thickness decreased to 410.3 ± 14.5 μm at the last follow-up. Before treatment, the mean K-value of the apex of the keratoconus corneas was 58.7 ± 3.5 diopters and slightly decreased (57.7 ± 4.9 diopters at 12 months. The mean CDVA was 0.54 ± 0.23 logarithm of the minimal angle of resolution before treatment and increased to 0.51 ± 0.21 logarithm at the last follow-up. The ECD was 2731.4 ± 191.8 cells/mm2 before treatment and was 2733.4 ± 222.6 cells/mm2 at 12 months after treatment. Conclusions. CXL with a hypoosmolar riboflavin in thin corneas seems to be a promising method for keratoconic eyes with the mean thinnest corneal thickness less than 400 μm without epithelium.

  15. Excitation by irritant chemical substances of sensory afferent units in the cat's cornea.

    Science.gov (United States)

    Belmonte, C; Gallar, J; Pozo, M A; Rebollo, I

    1991-01-01

    1. Single-unit electrical activity was recorded from thin myelinated sensory nerve fibres innervating the cornea of deeply anaesthetized cats. 2. Based on their responses to mechanical (calibrated von Frey hairs), chemical (10 mM-acetic acid and/or 616 mM-NaCl) and thermal (ice-cold or heat up to 51 degrees C) stimuli, corneal A delta fibres were classified as polymodal nociceptors (63%), high-threshold mechanoceptors (22%) and mechano-heat nociceptors (15%). Thin myelinated fibres responding only to cold were found in the limbus of the eye. 3. Application of 10 mM-acetic acid on the corneal surface for 30 s evoked in polymodal fibres a brisk discharge of impulses often followed by a low-frequency impulse activity. NaCl (616 mM) produced a more gradual and sustained firing response. 4. The responses of polymodal fibres to acid were proportional to extracellular pH values (pH range: 4.5-6.0). After sensitization to repeated heating, most mechano-heat units developed a sensitivity to acidic stimulation. 5. Topical 0.33 mM-capsaicin excited polymodal nociceptors of the cornea; 5 min after capsaicin about 15% of these fibres were inactivated to all subsequent stimuli. In the rest of the fibres, chemical and thermal sensitivity disappeared after 0.33-3.3 mM-capsaicin, but mechanosensitivity was preserved. 6. Corneal mechanoceptors and limbal cold receptors were not affected by capsaicin (up to 33 mM). 7. These experiments demonstrate that the cornea of the cat is innervated by polymodal as well as mechanoceptive A delta nociceptors. In polymodal nociceptive fibres, mechanical and chemical sensitivities appear to be subserved by separate transduction mechanisms. PMID:1890657

  16. Analysis of the progressive failure of brittle matrix composites

    Science.gov (United States)

    Thomas, David J.

    1995-01-01

    This report investigates two of the most common modes of localized failures, namely, periodic fiber-bridged matrix cracks and transverse matrix cracks. A modification of Daniels' bundle theory is combined with Weibull's weakest link theory to model the statistical distribution of the periodic matrix cracking strength for an individual layer. Results of the model predictions are compared with experimental data from the open literature. Extensions to the model are made to account for possible imperfections within the layer (i.e., nonuniform fiber lengths, irregular crack spacing, and degraded in-situ fiber properties), and the results of these studies are presented. A generalized shear-lag analysis is derived which is capable of modeling the development of transverse matrix cracks in material systems having a general multilayer configuration and under states of full in-plane load. A method for computing the effective elastic properties for the damaged layer at the global level is detailed based upon the solution for the effects of the damage at the local level. This methodology is general in nature and is therefore also applicable to (0(sub m)/90(sub n))(sub s) systems. The characteristic stress-strain response for more general cases is shown to be qualitatively correct (experimental data is not available for a quantitative evaluation), and the damage evolution is recorded in terms of the matrix crack density as a function of the applied strain. Probabilistic effects are introduced to account for the statistical nature of the material strengths, thus allowing cumulative distribution curves for the probability of failure to be generated for each of the example laminates. Additionally, Oh and Finney's classic work on fracture location in brittle materials is extended and combined with the shear-lag analysis. The result is an analytical form for predicting the probability density function for the location of the next transverse crack occurrence within a crack bounded

  17. Forecasting volcanic eruptions: the control of elastic-brittle deformation

    Science.gov (United States)

    Kilburn, Christopher; Robertson, Robert; Wall, Richard; Steele, Alexander

    2016-04-01

    At volcanoes reawakening after long repose, patterns of unrest normally reflect the elastic-brittle deformation of crust above a magma reservoir. Local fault movements, detected as volcano-tectonic (VT) earthquakes, increase in number with surface deformation, at first approximately exponentially and then linearly. The trends describe how crustal behaviour evolves from quasi-elastic deformation under an increasing stress to inelastic deformation under a constant stress. They have been quantified and verified against experiments for deformation in compression [1]. We have extended the analysis to extensional deformation. The results agree well with field data for crust being stretched by a pressurizing magmatic system [2]. They also provide new criteria for enhancing the definitions of alert levels and preferred times to eruption. The VT-deformation sequence is a field proxy for changes in deformation with applied stress. The transition from quasi-elastic to inelastic behaviour is characterised in extension by the ratio of differential failure stress SF to tensile strength σT. Unrest data from at least basaltic to andesitic stratovolcanoes, as well as large calderas, yield preferred values for SF/σT ≤ 4, coinciding with the range for tensile failure expected from established theoretical constraints (from Mohr-Coulomb-Griffiths failure). We thus associate the transition with the approach to tensile rupture at the wall of a pressurized magma reservoir. In particular, values of about 2 are consistent with the rupture of a cylindrical reservoir, such as a closed conduit within a volcanic edifice, whereas values of about 3 suggest an approximately spherical reservoir, such as may exist at deeper levels. The onset of inelastic behaviour reflects the emergence of self-accelerating crack growth under a constant stress. Applied to forecasting eruptions, it provides a new and objective criterion for raising alert levels during an emergency; it yields the classic linear

  18. Case report: a novel KERA mutation associated with cornea plana and its predicted effect on protein function

    DEFF Research Database (Denmark)

    Roos, Laura; Bertelsen, Birgitte; Harris, Pernille;

    2015-01-01

    Background: Cornea plana (CNA) is a hereditary congenital abnormality of the cornea characterized by reduced corneal curvature, extreme hypermetropia, corneal clouding and hazy corneal limbus. The recessive form, CNA2, is associated with homozygous or compound heterozygous mutations of the kerato......Background: Cornea plana (CNA) is a hereditary congenital abnormality of the cornea characterized by reduced corneal curvature, extreme hypermetropia, corneal clouding and hazy corneal limbus. The recessive form, CNA2, is associated with homozygous or compound heterozygous mutations...... of the keratocan gene (KERA) on chromosome 12q22. To date, only nine different disease-associated KERA mutations, including four missense mutations, have been described. Case presentation: In this report, we present clinical data from a Turkish family with autosomal recessive cornea plana. In some of the affected...... individuals, hypotrichosis was found. KERA was screened for mutations using Sanger sequencing. We detected a novel KERA variant, p.(Ile225Thr), that segregates with the disease in the homozygous form. The three-dimensional structure of keratocan protein was modelled, and we showed that this missense variation...

  19. In vivo 3D measurement of moxifloxacin and gatifloxacin distributions in the mouse cornea using multiphoton microscopy

    Science.gov (United States)

    Lee, Seunghun; Lee, Jun Ho; Park, Jin Hyoung; Yoon, Yeoreum; Chung, Wan Kyun; Tchah, Hungwon; Kim, Myoung Joon; Kim, Ki Hean

    2016-05-01

    Moxifloxacin and gatifloxacin are fourth-generation fluoroquinolone antibiotics used in the clinic to prevent or treat ocular infections. Their pharmacokinetics in the cornea is usually measured from extracted ocular fluids or tissues, and in vivo direct measurement is difficult. In this study multiphoton microscopy (MPM), which is a 3D optical microscopic technique based on multiphoton fluorescence, was applied to the measurement of moxifloxacin and gatifloxacin distribution in the cornea. Intrinsic multiphoton fluorescence properties of moxifloxacin and gatifloxacin were characterized, and their distributions in mouse cornea in vivo were measured by 3D MPM imaging. Both moxifloxacin and gatifloxacin had similar multiphoton spectra, while moxifloxacin had stronger fluorescence than gatifloxacin. MPM imaging of mouse cornea in vivo showed (1) moxifloxacin had good penetration through the superficial corneal epithelium, while gatifloxacin had relatively poor penetration, (2) both ophthalmic solutions had high intracellular distribution. In vivo MPM results were consistent with previous studies. This study demonstrates the feasibility of MPM as a method for in vivo direct measurement of moxifloxacin and gatifloxacin in the cornea.

  20. Comparison of Scheimpflug imaging parameters between steep and keratoconic corneas of Caucasian eyes

    Directory of Open Access Journals (Sweden)

    Huseynova T

    2016-04-01

    Full Text Available Tukezban Huseynova,1 Farah Abdulaliyeva,2 Michele Lanza3 1Briz-L Eye Clinic, 2National Ophthalmology Center, Baku, Azerbaijan; 3Second University of Naples, Caserta, Campania, Italy Purpose: To compare the keratometric and pachymetric parameters of healthy eyes with those affected by steep cornea and keratoconus (KC using Scheimpflug camera.Setting: Briz-L Eye Clinic, Baku, Azerbaijan.Design: A cross-sectional study.Methods: In this study, 49 KC (Amsler–Krumeich stage 1 eyes and 36 healthy eyes were enrolled. A complete ophthalmic evaluation and a Scheimpflug camera scan were performed in every eye included in the study. Tomographic parameters such as parameters from the front and back cornea, maximum keratometry reading (Kmax, corneal volume (CV, anterior chamber volume (ChV, anterior chamber depth (ACD, anterior chamber angle (AC angle, keratometric power deviation (KPD, maximum front elevation (Max FE, and maximum back elevation (Max BE, as well as pachymetric progression indices (PPI, Ambrosio relational thickness (ART, index of surface variance (ISV, index of vertical asymmetry (IVA, center keratoconus index (CKI, index of height asymmetry (IHA, index of height decentration (IHD, and radius minimum (RM were collected and statistically compared between the two groups.Results: PPI, ART, ISV, IVA, CKI, IHA, IHD, and RM parameter values were significantly different (P<0.05 between the KC and healthy eyes. There were no significant differences in K mean and Q values of the frontal corneal parameters, as well as in Kmax, AC angle, RM, back, and front astigmatism, between stage 1 keratoconic and normal Caucasian eyes with steep cornea. All other parameters such as K mean and Q values of the back corneal parameters, Max FE, Max BE, ACD, ChV, and CV showed significant differences between the groups (P<0.05 for all. Conclusion: Scheimpflug imaging is able to detect corneal morphological differences between stage 1 KC eyes and healthy eyes with

  1. Angular distribution of light emission from compound-eye cornea with conformal fluorescent coating

    Science.gov (United States)

    Martín-Palma, Raúl J.; Miller, Amy E.; Pulsifer, Drew P.; Lakhtakia, Akhlesh

    2014-09-01

    The complex morphology of the apposition compound eyes of insects of many species provides them a wide angular field of view. This characteristic makes these eyes attractive for bioreplication as artificial sources of light. The cornea of a blowfly eye was conformally coated with a fluorescent thin film with the aim of achieving wide field-of-view emission. On illumination by shortwave-ultraviolet light, the conformally coated eye emitted visible light whose intensity showed a weaker angular dependence than a fluorescent thin film deposited on a flat surface.

  2. Changes in thickness of each layer of developing chicken cornea after administration of caffeine.

    OpenAIRE

    Hieronim Bartel; Dariusz Tosik; Monika Kujawa-Hadryś

    2010-01-01

    The aim of the study was the presentation of changes in thickness of each layer of a developing cornea, that came into being under an influence of caffeine which was administered to chicken embryos. Research materials were 26 chicken embryos from breeding eggs that had been incubated. Breeding eggs were divided into two groups: control (n=30) in which Ringer liquid was given, and experimental (n=30) in which teratogenic dose of caffeine was administrated - 3.5 mg/egg. In 36th hour of incubati...

  3. X-ray scattering used to map the preferred collagen orientation in the human cornea and limbus.

    Science.gov (United States)

    Aghamohammadzadeh, Hossein; Newton, Richard H; Meek, Keith M

    2004-02-01

    Many properties of connective tissues are governed by the organization of the constituent collagen. For example, the organization of collagen in the cornea and the limbus, where the cornea and sclera meet, is an important determinant of corneal curvature and hence of the eye's focusing power. We have used synchrotron X-ray scattering to map the orientation of the collagen fibrils throughout the human cornea, limbus, and adjacent sclera. We demonstrate a preferred orientation of collagen in the vertical and horizontal directions that is maintained to within about 1 mm from the limbus, where a circular or tangential disposition of fibrils occurs. The data are also used to map the relative distribution of both the total and the preferentially aligned collagen in different parts of the tissue, revealing considerable anisotropy. The detailed structural information provided is an important step toward understanding the shape and the mechanical properties of the tissue. PMID:14962385

  4. Preparation and in vitro characterization of BC/PVA hydrogel composite for its potential use as artificial cornea biomaterial

    International Nuclear Information System (INIS)

    In order to investigate the potential use for bacterial cellulose (BC) as a novel artificial cornea replacement, BC/poly(vinyl alcohol) (BC/PVA) hydrogel composites were synthesized by freezing-thaw method. The BC/PVA composites were characterized by UV-Vis spectrophotometer (UV-Vis), X-ray diffraction (XRD), thermogravimetric (TG) analysis, mechanical property tests and scanning electron microscope (SEM) analyses. Our results showed that the resultant BC/PVA composites exhibited desirable properties as artificial cornea replacement biomaterial including high water content, high visible light transmittance and suitable UV absorbance, increased mechanical strength and appropriate thermal properties. Results of this work revealed that the BC/PVA composites exhibited some promising characteristics as artificial cornea composite material and may be improved further for its realistic applications.

  5. Mass fabrication technique for polymeric replicas of arrays of insect corneas

    International Nuclear Information System (INIS)

    Motivated to develop a technique for producing many high-fidelity replicas for the sacrifice of a single biotemplate, we combined a modified version of the conformal-evaporated-film-by-rotation technique and electroforming to produce a master negative made of nickel from a composite biotemplate comprising several corneas of common blowflies. This master negative can function as either a mold for casting multiple replicas or a die for stamping multiple replicas. An approximately 250 nm thick nickel film was thermally deposited on an array of blowfly corneas to capture the surface features with high fidelity and then a roughly 60 μm thick structural layer of nickel was electroformed onto the thin layer to give it the structural integrity needed for casting or stamping. The master negative concurrently captured the spatial features of the biotemplate at length scales ranging from 200 nm to a few millimeters. Polymer replicas produced thereafter by casting did faithfully reproduce features of a few micrometers and larger in dimension.

  6. Control of Scar Tissue Formation in the Cornea: Strategies in Clinical and Corneal Tissue Engineering

    Directory of Open Access Journals (Sweden)

    Samantha L. Wilson

    2012-09-01

    Full Text Available Corneal structure is highly organized and unified in architecture with structural and functional integration which mediates transparency and vision. Disease and injury are the second most common cause of blindness affecting over 10 million people worldwide. Ninety percent of blindness is permanent due to scarring and vascularization. Scarring caused via fibrotic cellular responses, heals the tissue, but fails to restore transparency. Controlling keratocyte activation and differentiation are key for the inhibition and prevention of fibrosis. Ophthalmic surgery techniques are continually developing to preserve and restore vision but corneal regression and scarring are often detrimental side effects and long term continuous follow up studies are lacking or discouraging. Appropriate corneal models may lead to a reduced need for corneal transplantation as presently there are insufficient numbers or suitable tissue to meet demand. Synthetic optical materials are under development for keratoprothesis although clinical use is limited due to implantation complications and high rejection rates. Tissue engineered corneas offer an alternative which more closely mimic the morphological, physiological and biomechanical properties of native corneas. However, replication of the native collagen fiber organization and retaining the phenotype of stromal cells which prevent scar-like tissue formation remains a challenge. Careful manipulation of culture environments are under investigation to determine a suitable environment that simulates native ECM organization and stimulates keratocyte migration and generation.

  7. Chromosome mutations and tissue regeneration in the cornea after the UV laser irradiation

    Science.gov (United States)

    Razhev, Alexander M.; Bagayev, Sergei N.; Lebedeva, Lidya I.; Akhmametyeva, Elena M.; Zhupikov, Andrey A.

    2003-06-01

    In present paper the findings on chromosome mutations, the nature of damage and the repair of the cornea tissue after UV irradiation by excimer lasers at 193, 223 and 248 nm were made. Structural mutations induced by short-pulses UV irradiation were shown to be similar to spontaneous ones by the type, time of formation in the mitotic cycle and location of acentrics. Ten hours after irradiation of the cornea with doses of 0,09 to 1,5 J/cm2 the incidence of cells with chromosome aberrations increased linearly with dose and amounted to 11,7% at 248 nm, 5,5% at 223 nm and 2,6% at 193 nm per 1 J/cm2. No induced chromosome aberrations occurred 72 hour following irradiation. Within the dose range from 3,0 to 18 J/cm2 the cytogenesis effect of radiation was less manifest than that with the doses mentioned above, the frequency of chromosome aberrations being independent of either radiation wavelength or radiation dose and amounted of 2,5 to 3,0%. Thus, large doses of powerful short-pulse UV radiation are safe according to the structural mutation criterion.

  8. Characterization of Ocular Iontophoretic Drug Transport of Ionic and Non-ionic Compounds in Isolated Rabbit Cornea and Conjunctiva.

    Science.gov (United States)

    Sekijima, Hidehisa; Ehara, Junya; Hanabata, Yusuke; Suzuki, Takumi; Kimura, Soichiro; Lee, Vincent H L; Morimoto, Yasunori; Ueda, Hideo

    2016-06-01

    Ocular iontophoresis (IP) in isolated rabbit cornea and conjunctiva was examined in terms of transport enhancement, tissue viability and integrity using electrophysiological parameters by the Ussing-type chamber technique. Lidocaine hydrochloride (LC, a cationic compound), sodium benzoate (BA, anionic compound), and fluorescein isothiocyanate labeled dextran (molecular weight 4400 Da, FD-4, hydrophilic large compound) were used as model permeants. Direct electric current was applied at 0.5-5.0 mA/cm(2) for the cornea and 0.5-20 mA/cm(2) for the conjunctiva for 30 min. LC and BA fluxes across the cornea and conjunctiva were significantly increased by the application of electric current up to 2.3- and 2.5-fold and 4.0- and 3.4-fold, respectively, and returned to their baseline level on stopping the current. Furthermore, a much higher increase by IP application was obtained for the FD-4 transport. The increased FD-4 flux in the conjunctiva returned to baseline on stopping the current, whereas the flux in the cornea was sustained at a higher level after stopping the current. The transepithelial electric resistance of the cornea and conjunctiva was lowered by electric current application but fully recovered after stopping the current up to 2.0 mA/cm(2) for the cornea and 10 mA/cm(2) for the conjunctiva, suggesting that the corneal and conjunctival viability and integrity are maintained even after application of these current densities. These results indicate that ocular IP may be a useful non-invasive technique to achieve drug delivery of hydrophilic large molecules into the eyes. PMID:27040754

  9. Assessing the viscoelasticity of green light induced CXL in the rabbit cornea by noncontact OCE and FEM

    Science.gov (United States)

    Han, Zhaolong; Li, Jiasong; Singh, Manmohan; Vantipalli, Srilatha; Aglyamov, Salavat R.; Wu, Chen; Liu, Chih-hao; Twa, Michael D.; Larin, Kirill V.

    2016-03-01

    The biomechanical properties of the cornea have a profound influence on its health and function. Rose bengal/green light corneal collagen cross-linking (RGX) has been proposed as an alternative to UV-A Riboflavin collagen cross-linking (UV-CXL) for treatment of keratoconus. However, the effects of RGX on the biomechanical properties of the cornea are not as well understood as UV-CXL. In this work, we demonstrate the feasibility of quantifying the viscoelasticity of the rabbit cornea before and after RGX using a noncontact method of phase-stabilized swept source optical coherence elastography (PhS-SSOCE) and finite element modeling (FEM). Viscoelastic FE models of the corneas were constructed to simulate the elastic wave propagation based on the OCE measurements. In addition, the effect of the fluid-structure interface (FSI) between the corneal posterior surface and aqueous humor on the elastic wave group velocity was also investigated. The effect of the FSI was first validated by OCE measurements and FEM simulations on contact lenses, and the OCE and FEM results were in good agreement. The Young's modulus of the rabbit cornea before RGX was assessed as E=80 kPa, and the shear viscosity was η=0.40 Pa•s at an intraocular pressure (IOP) of 15 mmHg. After RGX, the Young's modulus increased to E=112 kPa and shear viscosity decreased to η=0.37 Pa•s. Both the corneal OCE experiments and the FE simulations also demonstrated that the FSI significantly reduced the group velocity of the elastic wave, and thus, the FSI should be considered when determining the biomechanical properties of the cornea.

  10. Quantitative comparisons of analogue models of brittle wedge dynamics

    Science.gov (United States)

    Schreurs, Guido

    2010-05-01

    Analogue model experiments are widely used to gain insights into the evolution of geological structures. In this study, we present a direct comparison of experimental results of 14 analogue modelling laboratories using prescribed set-ups. A quantitative analysis of the results will document the variability among models and will allow an appraisal of reproducibility and limits of interpretation. This has direct implications for comparisons between structures in analogue models and natural field examples. All laboratories used the same frictional analogue materials (quartz and corundum sand) and prescribed model-building techniques (sieving and levelling). Although each laboratory used its own experimental apparatus, the same type of self-adhesive foil was used to cover the base and all the walls of the experimental apparatus in order to guarantee identical boundary conditions (i.e. identical shear stresses at the base and walls). Three experimental set-ups using only brittle frictional materials were examined. In each of the three set-ups the model was shortened by a vertical wall, which moved with respect to the fixed base and the three remaining sidewalls. The minimum width of the model (dimension parallel to mobile wall) was also prescribed. In the first experimental set-up, a quartz sand wedge with a surface slope of ˜20° was pushed by a mobile wall. All models conformed to the critical taper theory, maintained a stable surface slope and did not show internal deformation. In the next two experimental set-ups, a horizontal sand pack consisting of alternating quartz sand and corundum sand layers was shortened from one side by the mobile wall. In one of the set-ups a thin rigid sheet covered part of the model base and was attached to the mobile wall (i.e. a basal velocity discontinuity distant from the mobile wall). In the other set-up a basal rigid sheet was absent and the basal velocity discontinuity was located at the mobile wall. In both types of experiments

  11. Ultraprecision machining of micro-structured functional surfaces on brittle materials

    International Nuclear Information System (INIS)

    Ultraprecision micro-structured functional surfaces on hard and brittle materials, e.g. ceramic and glass, are gaining increasing application in a range of areas such as engineering optics and semiconductor and biomedical products. However, due to their tendency of being damaged in brittle fracture in machining, it is challenging to achieve both a high surface finish and complex surface shapes. In this paper, ultraprecision machining of micro-structured functional surfaces on brittle materials by fast tool servo diamond turning is studied. A machining model has been developed to ensure ductile regime machining of the brittle material, in which the material is removed by both plastic deformation and brittle fracture, but the cracks produced are prevented from being extended into the finished surface. Based on the model, an iterative numerical method has been proposed to predict the maximum feed rate for producing crack-free micro-structured surfaces. Machining experiments on typical micro-structured functional surfaces have been carried out to validate the effectiveness of the proposed method for producing ultraprecision micro-structured functional surfaces

  12. Brittle Rock Modeling Approach and its Validation Using Excavation-Induced Micro-Seismicity

    Science.gov (United States)

    Ma, Chun-Chi; Li, Tian-Bin; Xing, Hui-Lin; Zhang, Hang; Wang, Min-Jie; Liu, Tian-Yi; Chen, Guo-Qing; Chen, Zi-Quan

    2016-08-01

    With improvements to the bonded-particle model, a custom indicator of crack intensity is introduced to grade rock fractures accurately. Brittle fracturing of rock mass is studied using the bonded-particle model; here, "brittle" refers to the process where more energy is released towards making particles collide and disperse, and hence results in the quick emergence of "chain cracks". Certain principles concerning how to construct brittle rock are then proposed. Furthermore, a modeling approach for brittle rocks based on the adaptive continuum/discontinuum (AC/DC) method is proposed to aid the construction of large-scale models of tunnel excavations. To connect with actual tunneling conditions, fundamental mechanical properties, the mechanism for brittle fracturing, the joint distribution, and the initial stress field are considered in the modeling approach. Results from micro-seismic monitoring of a tunnel excavation confirmed the suitability of this modeling approach to simulate crack behavior, and results show that simulated cracking exhibit similar trends (evolution, location, and intensity) with micro-seismic cracking.

  13. Brittle fracture of T91 steel in liquid lead–bismuth eutectic alloy

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Changqing, E-mail: Changqing.ye@ed.univ-lille1.fr; Vogt, Jean-Bernard, E-mail: jean-bernard.vogt@univ-lille1.fr; Proriol-Serre, Ingrid, E-mail: ingrid.proriol-serre@univ-lille1.fr

    2014-12-15

    Highlights: • Tempering temperature is important for LBE embrittlement occurrence. • Brittle behaviour in LBE evidenced by small punch test and fatigue test. • Brittle behaviour in low oxygen LBE observed for low loading rate. - Abstract: The mechanical behaviour of the T91 martensitic steel has been studied in liquid lead–bismuth eutectic (LBE) and in inert atmosphere. Several conditions were considered to point out the most sensitive embrittling factors. Smooth and notched specimens were employed for respectively monotonic and cyclic loadings. The present investigation showed that T91 appeared in general as a ductile material, and became brittle in the considered conditions only if at least tests were performed in LBE. It turns out that the loading rate appeared as a critical parameter for the occurrence of liquid metal embrittlement of T91 in LBE. For the standard heat treatment condition, loading monotonically the T91 very slowly instead of rapidly in LBE resulted in brittle fracture. Also, under cyclic loading, the crack propagated in a brittle manner in LBE.

  14. Isolation and characterization of soluble sulfated polysaccharide from the red seaweed Glucaric cornea; Isolamento e caracterizacao do polissacarideo sulfatado soluvel extraido da alga vermelha Gracilaria cornea

    Energy Technology Data Exchange (ETDEWEB)

    Melo, Marcia R.S.; Freitas, Ana L.P. [Ceara Univ., Fortaleza, CE (Brazil). Dept. de Bioquimica e Biologia Molecular]. E-mail: rubiamelo@yahoo.com; Feitosa, Judith P.A.; Paula, Regina C.M. de [Ceara Univ., Fortaleza, CE (Brazil). Dept. de Quimica Organica e Inorganica]. E-mail: judith@dqoi.ufc.br

    2001-07-01

    The composition, structure and rheological properties of soluble sulphated polysaccharide Glucaric cornea from Brazilian red seaweeds were investigated. The main components of polysaccharide were 3,6-anhydrogalactose (24.7%) and galactose (64.6%). In addition, minor components as 6-O-methyl-galactose (8.5%), glucose (1.5%), xylose (0.7%) and sulfated groups (4.8%) were detected. Comparison between sulphates content determined by Ft-IR spectroscopy and micro elemental analysis was made. Data from {sup 13}C NMR and FT-IR provided evidence of sulphation in C-4 and C-6 of galactose. No gelation with 1.5, 2.0 and 3.0 % (w/v) aqueous solution was observed, even cooled up to 4 deg C. GPC indicated two majors polysaccharide fractions of M{sub pk} 7.4 x 10{sup 4} and 1.8 x 10{sup 4} g/mol and a minor fraction of M{sub pk} 2.1 x 10{sup 6} g/mol. (author)

  15. Beals Syndrome

    Science.gov (United States)

    ... Boards & Staff Annual Report & Financials Contact Us Donate Marfan & Related Disorders What is Marfan Syndrome? What are ... the syndrome. How does Beals syndrome compare with Marfan syndrome? People with Beals syndrome have many of ...

  16. BRITTLE-DUCTILE TRANSITION OF PP/EPDM/ELASTOMERIC NANO-PARTICLE TERNARY BLENDS

    Institute of Scientific and Technical Information of China (English)

    Yan Xiao; Wen Cao; Ke Wang; Hong Tan; Qin Zhang; Rong-ni Du; Qiang Fu

    2006-01-01

    The brittle-ductile transition is a very important phenomenon for polymer toughening. Polypropylene (PP) is often toughened by using rubbers, e.g., ethylene-propylene diene monomer (EPDM) has often been used as a modifier. In this article, the toughening of PP by using a new kind of rubber, known as elastomeric nano-particle (ENP), and the brittleductile transition of PP/EPDM/ENP was studied. Compared to PP/EPDM binary blends, the brittle-ductile transition of PP/EPDM/ENP ternary blends occurred at lower EPDM contents. SEM experiment was carried out to investigate the etched and impact-fractured surfaces. ENP alone had no effect on the impact strength of PP, however, with the same EPDM content,PP/EPDM/ENP ternary blends had smaller particle size, better dispersion and smaller interparticle distance in contrary to PP/EPDM binary blends, which promoted the brittle-ductile transition to occur earlier.

  17. Clinical performance of KeraSoft® IC in irregular corneas

    Directory of Open Access Journals (Sweden)

    Su S

    2015-10-01

    Full Text Available Stephanie Su,1 Lynette Johns,2 Marjorie J Rah,3 Robert Ryan,1 Joseph Barr3 1Visionary Eye Associates of Rochester, Rochester, NY, USA; 2Custom Lab Channel Business, Bausch & Lomb Incorporated, Wilmington, MA, USA; 3Medical Affairs – Vision Care, Bausch & Lomb Incorporated, Rochester, NY, USA Purpose: This study evaluated the clinical performance of KeraSoft® IC (KIC soft contact lenses in subjects with irregular corneas.Patients and methods: This was a 12-month, prospective, open-label, observational study, which enrolled 43 subjects who were 18 years of age or older with irregular corneas. Subjects were fit according to the KIC Fitting Manual (kerasoftic.com. After achieving best fit according to the fitting manual, lenses were assessed for comfort, vision, centration, rotation, and movement. Subjects were instructed to wear their lenses between 8 and 16 hours each day. Assessments at the exit visit included logMAR visual acuity with high and low contrast, spherocylindrical overrefraction, slit-lamp findings, adverse events, and subjective outcomes.Results: The average base curve was 8.17±0.32 mm (n=70 eyes, and the average diameter dispensed was 14.53±0.12 mm (n=70 eyes. From the baseline to 12 months, there was statistically significant improvement in logMAR visual acuity with high contrast (P=0.038, but no significant difference in low-contrast visual acuity was observed (P>0.05. Slit-lamp findings were ≤ grade 1 for the majority of subjects (89%. Two nonserious adverse events were reported for two of the 84 enrolled eyes (two subjects. At 12 months, subjects reported improvements from habitual baseline for comfort and vision, both upon insertion and just before removal of lenses.Conclusion: Clinical outcomes at 12 months showed good visual, safety, and subjective outcomes for subjects with corneal irregularities who wore KeraSoft® IC soft contact lenses. Keywords: irregular corneas, keratoconus, soft contact lenses, KeraSoft® IC

  18. Global and local contributions to surface curva- ture of healthy corneas

    Directory of Open Access Journals (Sweden)

    Alan Rubin

    2012-12-01

    Full Text Available This paper demonstrates for several healthy eyes the application of a simple model to understanding local and global contributions to short-term variation in anterior and posterior corneal curvature. Multiple axial anterior and posterior corneal radii and central corneal thicknesses for the right eyes of 10 young subjects were determined over time using a rotating Scheimpflug camera (Oculus Pentacam. The axial radii were transformed to corneal powers, and also to curvatures that were referred to a mid-corneal surface such that local and global contributions to short-term variation could be analyzed quantitatively.When variation of the anterior and posterior corneal surfaces of several healthy eyes are studied in terms of curvatures (rather than powers it is the posterior surfaces that are more variable withthe global or macroscopic rather than local effects dominating. (Harris and Gillan found the same for an eye with mild keratoconus. This finding is opposite to that when variation is considered in terms of dioptric power where the anterior corneal surface usually appears more variable. Possible reasons for this finding includes firstly that the posterior corneal surface has to be measured through the air-tear interface and anterior corneal surface,and thus some uncertainty in measurements of the posterior surface may relate to this limitation. Secondly, no attempt was made here to mathematically align the multiple surfaces as determined per eye and thus we cannot be certain that precisely the same central corneal region was measured each time.Investigators need to carefully consider whether they are more interested in the optical or physical nature of variation in surfaces such as the cornea since studies of the optical effects require theanalysis to be performed in terms of dioptric powers and  symmetric dioptric power space whereas studies of physical variation in the topography of the cornea and the possible reasons for such variability

  19. Changes in biomechanical properties of the cornea after modified transepithelial crosslinking

    Directory of Open Access Journals (Sweden)

    I. B. Medvedev

    2016-01-01

    Full Text Available The aim of the study was to evaluate changes in biomechanical properties of the cornea after conducting transepithelial crosslinking with the prior application of a 40 % glucose solution.Materials and methods. Just studied the biomechanical properties of the corneas of six rabbits breed Chinchilla (12 eyes. 4 rabbit entered in the experimental group, in which in one eye glucose solution was applied on the cornea and allowed to stay for 10 minutes, followed by the instillation of 0.1 % Riboflavin solution for 30 minutes. On a couple of the rabbit eye was applied a solution of Riboflavin without prior instillation of glucose. Then carried out the procedure of irradiation according to the conventional technology with UV with a wavelength of 370 μm and a beam energy of 3.0 mW / cm2. Two rabbits (4 eyes were included in the control group, in which crosslinking was not performed. After 1 month the euthanasia of the animals was performed with subsequent enucleation for corneal research on a tensile testing machine. In the control and experimental group compared, the relaxation curves and the following parameters were analyzed: initial stress (MPa, equilibrium stress (MPa modulus of elasticity.Results and their discussion. After the crosslinking the rise of the initial stress (in the control group and 0.7+0.1 MPa, in the experimental and 1.5+0.2 1.3+0.3 MPa, respectively. The stress relaxation is fast (equilibrium stress value is reached after 250 sec. and after the administration of glucose for approximately 75 seconds, which means a greater rigidity of experimental group of samples. In the experimental groups significantly changed and the modulus of elasticity: its value has increased approximately in 2 times in comparison with control samples. The equilibrium stress values in the experimental groups were different from the zero value that also indicates a change in the chemical structure of the samples.Conclusions. Holding transepithelial of

  20. Prediction of Brittle Failure for TBM Tunnels in Anisotropic Rock: A Case Study from Northern Norway

    Science.gov (United States)

    Dammyr, Øyvind

    2016-06-01

    Prediction of spalling and rock burst is especially important for hard rock TBM tunneling, because failure can have larger impact than in a drill and blast tunnel and ultimately threaten excavation feasibility. The majority of research on brittle failure has focused on rock types with isotropic behavior. This paper gives a review of existing theory and its application before a 3.5-m-diameter TBM tunnel in foliated granitic gneiss is used as a case to study brittle failure characteristics of anisotropic rock. Important aspects that should be considered in order to predict brittle failure in anisotropic rock are highlighted. Foliation is responsible for considerable strength anisotropy and is believed to influence the preferred side of v-shaped notch development in the investigated tunnel. Prediction methods such as the semi- empirical criterion, the Hoek- Brown brittle parameters, and the non-linear damage initiation and spalling limit method give reliable results; but only as long as the angle between compression axis and foliation in uniaxial compressive tests is relevant, dependent on the relation between tunnel trend/plunge, strike/dip of foliation, and tunnel boundary stresses. It is further demonstrated that local in situ stress variations, for example, due to the presence of discontinuities, can have profound impact on failure predictions. Other carefully documented case studies into the brittle failure nature of rock, in particular anisotropic rock, are encouraged in order to expand the existing and relatively small database. This will be valuable for future TBM planning and construction stages in highly stressed brittle anisotropic rock.

  1. Micromechanics-Based Permeability Evolution in Brittle Materials at High Strain Rates

    Science.gov (United States)

    Perol, Thibaut; Bhat, Harsha S.

    2016-08-01

    We develop a micromechanics-based permeability evolution model for brittle materials at high strain rates (≥ 100 s^{-1}). Extending for undrained deformation the mechanical constitutive description of brittle solids, whose constitutive response is governed by micro-cracks, we now relate the damage-induced strains to micro-crack aperture. We then use an existing permeability model to evaluate the permeability evolution. This model predicts both the percolative and connected regime of permeability evolution of Westerly Granite during triaxial loading at high strain rate. This model can simulate pore pressure history during earthquake coseismic dynamic ruptures under undrained conditions.

  2. Collection, processing and testing of bone, corneas, umbilical cord blood and haematopoietic stem cells by European Blood Alliance members

    DEFF Research Database (Denmark)

    Närhi, M; Natri, O; Desbois, I;

    2013-01-01

    A questionnaire study was carried out in collaboration with the European Blood Alliance (EBA) Tissues and Cells (T&C) working group. The aim was to assess the level of involvement and commonality of processes on the procurement, testing and storage of bone, corneas, umbilical cord blood (UCB...

  3. Corneal Sulfated Glycosaminoglycans and Their Effects on Trigeminal Nerve Growth Cone Behavior In Vitro: Roles for ECM in Cornea Innervation

    OpenAIRE

    Schwend, Tyler; Deaton, Ryan J.; Zhang, Yuntao; Caterson, Bruce; Conrad, Gary W.

    2012-01-01

    In this investigation, we describe differential spatiotemporal expression patterns of glycosaminoglycans KS, DS, and CSA/C during developmental stages of cornea innervation. We show that purified GAGs have divergent effects on trigeminal neuron behavior using in vitro neuronal explant cultures.

  4. Collagen Cross-linking in Keratoconus Patients with Thin Corneas: Short-Term Results

    Directory of Open Access Journals (Sweden)

    Nurullah Çağıl

    2012-10-01

    Full Text Available Pur po se: To study the effectiveness and safety of corneal collagen cross-linking with hypoosmolar riboflavin solution applied to keratoconus patients with thin corneas. Ma te ri al and Met hod: In this retrospective study, medical records of keratoconus patients planned for cross-linking surgery and having thinnest corneal thickness (TCT less than 400 μm after corneal epithelial removal were reviewed. There were 12 patients and 16 eyes in the study cohort. After the epithelium was removed, hypoosmolar solution was applied for 30 minutes and pachymetric measurements were taken. If corneal thickness became more than 400 μm, the cross-linking procedure was started; if not, hypoosmolar solution was continued until corneal thickness reached 400 μm. Maximum keratometry values (K Max, pachymetric measurements, uncorrected distance visual acuities (UDVA, and corrected distance visual acuities (CDVA were recorded. Comparison between preoperative measurements and measurements taken in sixth postoperative month were performed. Re sults: The mean TCT was 422.75±26.98 μm preoperatively (max: 450, min: 360. The mean TCT was reduced to 373.63±22.41 μm after epithelium was removed (max: 398, min: 325. There was a statistically significant difference between preoperative K max (62.62±5.09 and postoperative K max (61.55±5.80, (p=0.03. On the other hand, the difference between preoperative-postoperative UDVA (p=0.29 and preoperative-postoperative CDVA was not significant (p=058. There were no cases with significant corneal opacity or with any other complication. Dis cus si on: Corneal collagen cross-linking with hypoosmolar riboflavin solution in keratoconus patients with thin corneas is an effective procedure and can be considered as safe regarding preservation of visual acuities and absence of significant corneal opacity. (Turk J Ophthalmol 2012; 42: 316-20

  5. In vivo laser confocal microscopy findings of a cornea with osteogenesis imperfecta

    Directory of Open Access Journals (Sweden)

    Kobayashi A

    2014-02-01

    Full Text Available Akira Kobayashi, Tomomi Higashide, Hideaki Yokogawa, Natsuko Yamazaki, Toshinori Masaki, Kazuhisa Sugiyama Department of Ophthalmology, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan Objective: To report the in vivo laser confocal microscopy findings of a cornea with osteogenesis imperfecta (OI with special attention to the abnormality of Bowman's layer and sub-Bowman's fibrous structures (K-structures. Patients and methods: Two patients (67-year-old male and his 26-year-old son with OI type I were included in this study. Slit lamp biomicroscopic and in vivo laser confocal microscopic examinations were performed for both patients. Central corneal thickness and central endothelial cell density were also measured. Results: Although the corneas looked clear with normal endothelial density for both eyes in both patients, they were quite thin (386 µm oculus dexter (OD (the right eye and 384 µm oculus sinister (OS (the left eye in the father and 430 µm OD and 425 µm OS in the son. In both patients, slit lamp biomicroscopic and in vivo laser confocal microscopic examination showed similar results. Anterior corneal mosaics produced by rubbing the eyelid under fluorescein were completely absent in both eyes. In vivo laser confocal microscopy revealed an absent or atrophic Bowman's layer; a trace of a presumed Bowman's layer and/or basement membrane was barely visible with high intensity. Additionally, K-structures were completely absent in both eyes. Conclusion: The absence of K-structures and fluorescein anterior corneal mosaics strongly suggested an abnormality of Bowman's layer in these OI patients. Keywords: osteogenesis imperfecta, K-structure, confocal microscopy, Bowman's layer

  6. Targeting Imbalance between IL-1β and IL-1 Receptor Antagonist Ameliorates Delayed Epithelium Wound Healing in Diabetic Mouse Corneas.

    Science.gov (United States)

    Yan, Chenxi; Gao, Nan; Sun, Haijing; Yin, Jia; Lee, Patrick; Zhou, Li; Fan, Xianqun; Yu, Fu-Shin

    2016-06-01

    Patients with diabetes mellitus often develop corneal complications and delayed wound healing. How diabetes might alter acute inflammatory responses to tissue injury, leading to delayed wound healing, remains mostly elusive. Using a streptozotocin-induced type I diabetes mellitus mice and corneal epithelium-debridement wound model, we discovered that although wounding induced marked expression of IL-1β and the secreted form of IL-1 receptor antagonist (sIL-1Ra), diabetes suppressed the expressions of sIL-1Ra but not IL-1β in healing epithelia and both in whole cornea. In normoglycemic mice, IL-1β or sIL-1Ra blockade delayed wound healing and influenced each other's expression. In diabetic mice, in addition to delayed reepithelization, diabetes weakened phosphatidylinositol 3-kinase-Akt signaling, caused cell apoptosis, diminished cell proliferation, suppressed neutrophil and natural killer cell infiltrations, and impaired sensory nerve reinnervation in healing mouse corneas. Local administration of recombinant IL-1Ra partially, but significantly, reversed these pathological changes in the diabetic corneas. CXCL10 was a downstream chemokine of IL-1β-IL-1Ra, and exogenous CXCL10 alleviated delayed wound healing in the diabetic, but attenuated it in the normal corneas. In conclusion, the suppressed early innate/inflammatory responses instigated by the imbalance between IL-1β and IL-1Ra is an underlying cause for delayed wound healing in the diabetic corneas. Local application of IL-1Ra accelerates reepithelialization and may be used to treat chronic corneal and potential skin wounds of diabetic patients. PMID:27109611

  7. Amniotic membrane covering promotes healing of cornea epithelium and improves visual acuity after debridement for fungal keratitis

    Institute of Scientific and Technical Information of China (English)

    Bo; Zeng; Ping; Wang; Ling-Juan; Xu; Xin-Yu; Li; Hong; Zhang; Gui-Gang; Li

    2014-01-01

    AIM:To investigate the effect of amniotic membrane covering(AMC) on the healing of cornea epithelium and visual acuity for fungal keratitis after debridement.METHODS:Twenty fungal keratitis patients were divided into two groups randomly, the AMC group and the control group, ten patients each group. Both debridement of the infected cornea tissue and standard anti-fungus drugs treatments were given to every patients, monolayer amniotic membrane were sutured to the surface of the entire cornea and bulbar conjunctiva with 10-0 nylon suture for patients in the AMC group.The diameter of the ulcer was determined with slit lamp microscope and the depth of the infiltration was determined with anterior segment optical coherence tomography. Uncorrected visual acuity(UCVA) was tested before surgery and three month after healing of the epithelial layer. The healing time of the cornea epithelium, visual acuity(VA) was compared between the two groups using t- test.RESULTS:There was no statistical difference of the diameter of the ulcer, depth of the infiltration, height of the hypopyon and VA between the two groups beforesurgery(P >0.05). The average healing time of the AMC group was 6.89 ±2.98 d, which was statistically shorter than that of the control group(10.23±2.78d)(P <0.05).The average UCVA of the AMC group was 0.138 ±0.083,which was statistically better than that of the control group(0.053±0.068)(P <0.05).CONCLUSION:AMC surgery could promote healing of cornea epithelium after debridement for fungal keratitis and lead to better VA outcome.

  8. Brown–McLean syndrome: the role of iridodonesis

    Directory of Open Access Journals (Sweden)

    Suwan Y

    2016-04-01

    Full Text Available Yanin Suwan, Chaiwat Teekhasaenee, Kaevalin Lekhanont, Wasu Supakontanasan Department of Ophthalmology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand Purpose: The aim of this study was to report a case series of Brown–McLean syndrome (BMS.Methods: The charts of 28 patients with BMS at Ramathibodi and Rutnin Hospital from 1981 to 2015 were reviewed.Results: BMS is a rare condition with corneal edema involving the peripheral cornea with orange-brown pigment deposition underlying the edematous area. The edema typically starts inferiorly and advances circumferentially to superior cornea. Central cornea remains clear in most patients. We report 28 patients with BMS that occurred either spontaneously or after various intraocular procedures. Ultrasound biomicroscopy was performed to demonstrate the iridocorneal relationship.Conclusion: Iridocorneal relationship from the ultrasound biomicroscopy study in four patients did not support previous hypothesis about the role of iridodonesis impact on corneal endothelium. Patients with BMS can rarely progress to corneal decompensation; however, they should be periodically monitored and made aware of early clinical signs of their complications. Keywords: Brown–McLean syndrome, peripheral corneal edema, marginal corneal edema, corneal decompensation

  9. The Influence of Brittle Daniels System Characteristics on the Value of Load Monitoring Information

    DEFF Research Database (Denmark)

    Thöns, Sebastian; Schneider, Ronald

    This paper addresses the influence of deteriorating brittle Daniels system characteristics on the value of structural health monitoring (SHM). The value of SHM is quantified as the difference between the life cycle benefits with and without SHM. A value of SHM analysis is performed within...

  10. Friction effect in supports on resistance to brittle fracture under three-point bending

    International Nuclear Information System (INIS)

    Quasistatic bending of the beam of elastic material with fixed supports with an account of possible slip in the points of support and then with an account of friciton in the supports is investigated analytically. The method presented permits to improve precision of the determination of mechanical properties of the materials in brittle state (ceramics, cast iron, cast aluminium alloys) at the bending test

  11. Interaction between cracking, delamination and buckling in brittle elastic thin films

    NARCIS (Netherlands)

    Vellinga, W. P.; Van den Bosch, M.; Geers, M. G. D.

    2008-01-01

    A discrete lattice based model for the interaction of cracking, delamination and buckling of brittle elastic coatings is presented. The model is unique in its simultaneous incorporation of the coating and of disorder in the interface and material properties, leading to realistic 3D bending (and buck

  12. A map of competing buckling-driven failure modes of substrate-supported thin brittle films

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Zheng [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States); Peng, Cheng [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Lou, Jun, E-mail: jlou@rice.edu [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Li, Teng, E-mail: lit@umd.edu [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States)

    2012-08-31

    Our in situ experiments of polyimide-supported thin indium tin oxide (ITO) films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Although studies of individual buckling-driven failure mode exist, it still remains unclear what governs the competition between these two different failure modes in a given film/substrate structure. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Such a map can offer insight on the mechanical durability of functional thin films. For example, interestingly, we show that strongly bonded thin brittle films are more prone to buckling-driven cracking, a more detrimental failure mode for thin brittle ITO transparent conductors widely used in displays and flexible electronics. - Highlights: Black-Right-Pointing-Pointer Map of buckling-driven failure modes of thin brittle films on substrates. Black-Right-Pointing-Pointer We study key parameters that govern buckling-driven failure modes. Black-Right-Pointing-Pointer The map offers insights on optimal design of functional thin films.

  13. Morphological, Biochemical and Genetic Analysis of a Brittle Stalk Mutant of Maize Inserted by Mutator

    Institute of Scientific and Technical Information of China (English)

    FU Xue-qian; FENG Jing; YU Bin; GAO You-jun; ZHENG Yong-lian; YUE Bing

    2013-01-01

    Mutants on stalk strength are essential materials for the studies on the formation of plant cell wall. In this study, a brittle stalk mutant of maize, designated as Bk-x, was screened from a Mutator inserted mutant library. At the germination and early seedling stage, the mutant plants were indistinguishable from the normal ones. However, all of the plant organs were brittle after the 5th-leaf stage and remained brittle throughout the rest of the growing period. Microstructure observation showed that the cell wall in vascular bundle sheath of Bk-x was thinner than that in normal plants. The leaf mechanical strength in Bk-x was 77.9%of that in normal plants growing at Xishuangbanna (BN), Yunnan province and that was 61.7%in Wuhan (WH), Hubei Province, China. The proportion of cellulose was 12.3%in Bk-x, which was significantly lower than that in normal plants (26.7%), while the soluble sugar content was 36.1%in Bk-x, which is significantly higher than that in normal plants (12.4%). Genetic analysis using two F2 populations and one F2:3 families demonstrated that the trait of brittle stalk is controlled by a single recessive gene.

  14. Development of material model for assessment of brittle cracking behavior of plexiglas

    Science.gov (United States)

    Khan, A. J.; Iqbal, N.; Saeed, H. A.; Tarar, W. A.

    2016-08-01

    The objective of this study is to investigate the brittle cracking behavior of Plexiglas material when subjected to indentation loading. Indentation tests were conducted on Modified Vickers testing machine to acquire the experimental data in the form of load-displacement curve. Several mechanical properties such as hardness, yielding stress and fracture toughness have been ascertained from the analysis of the experimental data. The experimental data then used to create a mathematical model of Plexiglas for its brittle cracking behavior with indentation loading. Furthermore, a numerical simulation based study was carried out to simulate the brittle cracking in Plexiglas plate when subjected to indentation loading. The simulations were performed in the FE solver Abaqus. The brittle cracking model in Abaqus/Explicit is used which determines the required force and displacement to produce crack in Plexiglas. Finally a comparison of simulation results was made to the experimental data to validate the FEA procedures and accuracy of predictions. The numerical predictions of load-displacement curve found remarkably consistent with experimental results.

  15. Residual Stress and Deformation Energy Under Ground Surfaces of Brittle Solids

    NARCIS (Netherlands)

    Podzimek, O.; Heuvelman, C.J.

    1986-01-01

    This work deals with the determination and description of the deformation energy, which is accumulated under the surface of brittle solids, especially those of optical glass, during the free abrasive grinding process. The distribution of deformation energy density in depth under the ground surface w

  16. Brittle fracture phase-field modeling of a short-rod specimen

    Energy Technology Data Exchange (ETDEWEB)

    Escobar, Ivana [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Tupek, Michael R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bishop, Joseph E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    Predictive simulation capabilities for modeling fracture evolution provide further insight into quantities of interest in comparison to experimental testing. Based on the variational approach to fracture, the advent of phase-field modeling achieves the goal to robustly model fracture for brittle materials and captures complex crack topologies in three dimensions.

  17. A comparison study of Riboflavin/UV-A and Rose-Bengal/Green light cross-linking of the rabbit corneas using optical coherence elastography

    Science.gov (United States)

    Li, Jiasong; Singh, Manmohan; Han, Zhaolong; Vantipalli, Srilatha; Liu, Chih-Hao; Wu, Chen; Raghunathan, Raksha; Kazemi, Tina; Twa, Michael D.; Larin, Kirill V.

    2016-03-01

    The biomechanical properties of the cornea are critical factors which determine its health and subsequent visual acuity. Keratoconus is a structural degeneration of the cornea which can diminish vision quality. Riboflavin/UV-A corneal collagen cross-linking (UV-CXL) is an emerging treatment that increases the stiffness of the cornea and improves its ability to resist further degeneration. While UV-CXL has shown great promise for effective therapy of the keratoconus, there are concerns associated with the UV irradiation, such as keratocyte cytotoxicity. Rose-bengal/green light corneal collagen cross-linking (RGX) has been proposed as an alternative to UV-CXL. Because of the high absorbance of the rose-bengal dye at green wavelengths, the treatment time is significantly shorter than with UV-CXL. Moreover, because green light is used in lieu of UV irradiation, there are no cytotoxic side-effects. In this study, noncontact optical coherence elastography (OCE) was used to compare the outcomes of UV-CXL and RGX treatment in rabbit cornea. Low-amplitude (micrometer scale) elastic waves were induced by a focused air-pulse loading system. The elastic wave propagation was then imaged by a phase-stabilized swept source OCE (PhS-SSOCE) system. The changes in the viscoelasticity of the corneas were quantified by a previously developed modified Rayleigh Lamb frequency model. The depth-resolved micro-scale phase-velocity distribution in the cornea was used to reveal the depth-wise heterogeneity before and after both cross-linking techniques. Our results show that UV-CXL and RGX increased the stiffness of the corneas by ~54% and ~5% while reducing the viscosity by ~42% and ~17%, respectively. The depth-wise phase velocities showed that UV-CXL affected the anterior ~1/3 of the corneas, while RGX only affected the anterior ~1/7 of the corneas.

  18. Use of Cross-linked Donor Corneas as Carriers for the Boston Keratoprosthesis

    Science.gov (United States)

    2016-10-03

    Chemical Injuries; Unspecified Complication of Corneal Transplant; Autoimmune Diseases; Ocular Cicatricial Pemphigoid; Stevens Johnson Syndrome; Lupus Erythematosus, Systemic; Rheumatoid Arthritis; Other Autoimmune Diseases

  19. Auriculotemporal Syndrome (Frey Syndrome).

    Science.gov (United States)

    Motz, Kevin M; Kim, Young J

    2016-04-01

    Frey syndrome is a common sequela of parotidectomy, and although it is not frequently manifested clinically, it can cause significant morbidity for those affected. Frey syndrome results from synkinetic autonomic reinnervation by transected postganglionic parasympathetic nerve fiber within the parotid gland to the overlying sweat glands of the skin. Many surgical techniques have been proposed to prevent the development of Frey syndrome. For those who develop clinical symptoms of Frey syndrome, objective testing can be performed with a Minor starch-iodine test. Some of the current methods to prevent and treat symptomatic Frey syndrome are reviewed. PMID:26902982

  20. In-Vivo Slit Scanning Confocal Microscopy of Normal Corneas in Indian Eyes

    Directory of Open Access Journals (Sweden)

    Vanathi Murugesan

    2003-01-01

    Full Text Available Objective: To study the cellular populations of healthy corneas of Indian eyes using confocal microscopy and to evaluate the correlation with age, gender and laterality. Methods: The central corneas of 100 eyes of 50 healthy subjects were examined using an i n-vivo slit scanning confocal microscope (Confoscan 2. Images were analysed for cell densities of the epithelium, stroma and endothelium. Results: Good quality images enabling analysis of all cell layer populations were obtained in 74 eyes of 43 healthy subjects (22 males and 21 females with a mean age of 31.89 ± 13.47 (range 19-71 years. The basal epithelial cell density was 3601.38 ± 408.19 cells/mm2 (range 3017.3 -4231.1cells/mm2. The mean keratocyte nuclei density in the anterior stroma was 1005.02 ± 396.86 cells/mm2 (range 571.6 - 1249.6 cells/mm2 and in the posterior stroma was 654.32 ± 147.09 cells/mm2 (range 402.6 - 1049.1 cells/mm2. Posterior keratocyte nuclei density was 30.76% less than the anterior stromal keratocyte nuclei density. The difference in keratocyte nuclei density was statistically significant (P=0.001. The mean endothelial cell density was 2818.1 ± 361.03 cells/mm2 (range 2118.9 - 4434 cells/mm2 and the mean endothelial cell area was found to be 385.44 ± 42.66 mm2 (range 268.9 - 489.2 mm2. Hexagonal cells formed 22.5 - 69.4% of the endothelial cell populations (mean 42.04 ± 11.81%. Mean coefficient of cell size variation was 32.29 ± 3.06 (range 27.2 - 39.2. No statistically significant differences were found in cell densities of any corneal layer either between female and male patients or between right and left eyes. Basal epithelial cell density, anterior stromal keratocyte nuclei and posterior stromal keratocyte nuclei density were unaffected by age (r= 0.12, 0.07, - 0.12 respectively (P= 0.001. There was a statistically significant negative correlation between mean endothelial cell density and increase in age (r= - 0.42, P=0.001. Coefficient of cell size

  1. Social influence of a religious hero: the late Cardinal Stephen Kim Sou-hwan's effect on cornea donation and volunteerism.

    Science.gov (United States)

    Bae, Hyuhn-Suhck; Brown, William J; Kang, Seok

    2011-01-01

    This study examined the mediated influence of a celebrated religious hero in South Korea, Cardinal Stephen Kim, through two forms of involvement--parasocial interaction and identification--on intention toward cornea donation and volunteerism, and it investigated how the news media diffused of his death. A structural equation modeling analysis with a Web-based voluntary survey of more than 1,200 people in South Korea revealed a multistep social influence process, beginning with parasocial interaction with Cardinal Kim, leading to identification with him, which predicted intention toward cornea donation and volunteerism. Additional investigations found that news of Cardinal Kim's death diffused rapidly through media and interpersonal communication. Results of this study demonstrate that religious leaders who achieve a celebrity hero status can prompt public discussion of important issues rather quickly through extensive media coverage, enabling them to promote prosocial behavior and positively affect public health. PMID:21086210

  2. Oxidative stress to the cornea, changes in corneal optical properties, and advances in treatment of corneal oxidative injuries.

    Science.gov (United States)

    Cejka, Cestmir; Cejkova, Jitka

    2015-01-01

    Oxidative stress is involved in many ocular diseases and injuries. The imbalance between oxidants and antioxidants in favour of oxidants (oxidative stress) leads to the damage and may be highly involved in ocular aging processes. The anterior eye segment and mainly the cornea are directly exposed to noxae of external environment, such as air pollution, radiation, cigarette smoke, vapors or gases from household cleaning products, chemical burns from splashes of industrial chemicals, and danger from potential oxidative damage evoked by them. Oxidative stress may initiate or develop ocular injury resulting in decreased visual acuity or even vision loss. The role of oxidative stress in the pathogenesis of ocular diseases with particular attention to oxidative stress in the cornea and changes in corneal optical properties are discussed. Advances in the treatment of corneal oxidative injuries or diseases are shown. PMID:25861412

  3. Oxidative Stress to the Cornea, Changes in Corneal Optical Properties, and Advances in Treatment of Corneal Oxidative Injuries

    Directory of Open Access Journals (Sweden)

    Cestmir Cejka

    2015-01-01

    Full Text Available Oxidative stress is involved in many ocular diseases and injuries. The imbalance between oxidants and antioxidants in favour of oxidants (oxidative stress leads to the damage and may be highly involved in ocular aging processes. The anterior eye segment and mainly the cornea are directly exposed to noxae of external environment, such as air pollution, radiation, cigarette smoke, vapors or gases from household cleaning products, chemical burns from splashes of industrial chemicals, and danger from potential oxidative damage evoked by them. Oxidative stress may initiate or develop ocular injury resulting in decreased visual acuity or even vision loss. The role of oxidative stress in the pathogenesis of ocular diseases with particular attention to oxidative stress in the cornea and changes in corneal optical properties are discussed. Advances in the treatment of corneal oxidative injuries or diseases are shown.

  4. The role of connective tissue growth factor, transforming growth factor β1 and Smad signaling pathway in cornea wound healing

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ The cornea is a highly specialized and unique organ in the human body. Its main function is to project light from the external environment onto the retina, and it has a specific transparency to perform its function properly. The transparency and integrity of the cornea is of vital importance. The corneal wound, especially laceration deep to Bowman's membrane and stroma, which will inevitably cause scar formation, may cause the degeneration or even loss of sight. Injury can activate many biological factors in cornea as a strong stimulating signal. Transforming growth factors (TGF) and connective tissue growth factors (CTGF) are thought to be related to scar formation after injury. TGF can stimulate stroma cells of cornea and promote synthesis of matrix. Over expression of TGF causes scar formation.1,2 CTGF is a 38 kD cysteine-rich protein molecule and belongs to CCN family (CTGF/Fisp12, Cyr 61/CEF-10, Nov). In 1991, CTGF was firstly found in endothelial cells of human umbilical vein cultured in vitro.3,4 CTGF acts as an important molecule that intermediates the processes of fibrosis, scarring, wound repairing, angiogenesis and embryonic development in many cell types. CTGF plays a unique role in proliferation, differentiation and adhesion of fibroblast cells, which in turn produces large amounts of collagen and other extracellular matrix (ECM) proteins.5-8 CTGF is upregulated in fibrotic diseases, including lung-, skin-, pancreas-, liver-and kidney fibrosis.9,10 This study reports the expressions and interactions of TGF-β1 and CTGF in corneal wound in vivo. This study aimed at determining the expressions and interactions of CTGF and TGF-β1 in Smad signaling pathway during the period when corneal wound was healing.

  5. Richner-Hanhart syndrome (tyrosinemia type II). Case report and literature review.

    Science.gov (United States)

    al-Hemidan, A I; al-Hazzaa, S A

    1995-03-01

    Richner-Hanhart syndrome (Tyrosinemia Type II) is an autosomal recessive disorder of amino acid metabolism characterized by ocular changes, painful palmoplantar hyperkeratosis, and mental retardation. Serum tyrosine increases due to tyrosine aminotransferase deficiency resulting in the deposition of tyrosine crystals in the cornea and in corneal inflammation. Patients are often misdiagnosed as having herpes simplex keratitis. We report on a child who presented with bilateral keratitis secondary to Tyrosinemia Type II diagnosed as herpes simplex keratitis.

  6. Effect of In Vitro Transcorneal Approach of Aceclofenac Eye Drops through Excised Goat, Sheep, and Buffalo Corneas

    Directory of Open Access Journals (Sweden)

    Vivek Dave

    2015-01-01

    Full Text Available The current study involves the evaluation of factors that influence the transcorneal permeation of aqueous drops of aceclofenac ophthalmic formulation through freshly excised goat, sheep, and buffalo corneas. Aceclofenac formulation with different concentrations 0.1–0.5% (w/v and with different pH and different preservatives, was taken into account. The amount of drug permeated from different formulations was estimated using an Franz diffusion cell. A linear increase in drug permeation was observed with increase in pH (5.5 to 7.4. The apparent permeability coefficient was found to be maximum 15.01±0.45 on goat cornea and maximum transport of aceclofenac was observed at physiological pH of tears (i.e., 7. The results advocate that aceclofenac 0.5% (w/v ophthalmic solution (pH 7.0 containing BAK (0.01% provides maximum in vitro ocular permeability through goat, sheep, and buffalo corneas.

  7. Isolation and characterization of soluble sulfated polysaccharide from the red seaweed Glucaric cornea

    International Nuclear Information System (INIS)

    The composition, structure and rheological properties of soluble sulphated polysaccharide Glucaric cornea from Brazilian red seaweeds were investigated. The main components of polysaccharide were 3,6-anhydrogalactose (24.7%) and galactose (64.6%). In addition, minor components as 6-O-methyl-galactose (8.5%), glucose (1.5%), xylose (0.7%) and sulfated groups (4.8%) were detected. Comparison between sulphates content determined by Ft-IR spectroscopy and micro elemental analysis was made. Data from 13C NMR and FT-IR provided evidence of sulphation in C-4 and C-6 of galactose. No gelation with 1.5, 2.0 and 3.0 % (w/v) aqueous solution was observed, even cooled up to 4 deg C. GPC indicated two majors polysaccharide fractions of Mpk 7.4 x 104 and 1.8 x 104 g/mol and a minor fraction of Mpk 2.1 x 106 g/mol. (author)

  8. Advancement in polarimetric glucose sensing: simulation and measurement of birefringence properties of cornea

    Science.gov (United States)

    Malik, Bilal H.; Coté, Gerard L.

    2011-03-01

    Clinical guidelines dictate that frequent blood glucose monitoring in diabetic patients is critical towards proper management of the disease. Although, several different types of glucose monitors are now commercially available, most of these devices are invasive, thereby adversely affecting patient compliance. To this end, optical polarimetric glucose sensing through the eye has been proposed as a potential noninvasive means to aid in the control of diabetes. Arguably, the most critical and limiting factor towards successful application of such a technique is the time varying corneal birefringence due to eye motion artifact. We present a spatially variant uniaxial eye model to serve as a tool towards better understanding of the cornea's birefringence properties. The simulations show that index-unmatched coupling of light is spatially limited to a smaller range when compared to the index-matched situation. Polarimetric measurements on rabbits' eyes indicate relative agreement between the modeled and experimental values of corneal birefringence. In addition, the observed rotation in the plane of polarized light for multiple wavelengths demonstrates the potential for using a dual-wavelength polarimetric approach to overcome the noise due to timevarying corneal birefringence. These results will ultimately aid us in the development of an appropriate eye coupling mechanism for in vivo polarimetric glucose measurements.

  9. Development of a microfabricated artificial limbus with micropockets for cell delivery to the cornea

    International Nuclear Information System (INIS)

    The aim of this study was to develop a synthetic alternative to the human corneal limbus for use initially as an ex vivo model in which to study corneal stem cell function within a niche environment and ultimately to develop an implantable limbus for future clinical use. Microstereolithography was used for the fabrication of polyethylene glycol diacrylate (PEGDA) based rings on a macroscopic (1.2 cm) scale containing unique microfeatures (pockets) which were then modified with fibronectin to promote cell adhesion. These rings were designed to mimic the limbal area of the eye containing structures of the approximate size and shape of the stem cell microenvironments found in the palisades of Vogt. The attachment of rabbit limbal fibroblasts and rabbit limbal epithelial cells to the PEGDA rings was increased by pretreating the microfabricated structures with biotinylated fibronectin. Cell outgrowth from fibronectin coated microfabricated structures was 50% greater than from rings without structures or fibronectin coating. The cell loaded rings were then placed on an ex vivo wounded cornea model and the outgrowth of cells to form a multilayered epithelium was observed. We suggest this is a new approach to investigating limbal stem cells niches and the first steps towards a new approach for corneal regeneration. (paper)

  10. Matrix metalloproteinase 14 modulates signal transduction and angiogenesis in the cornea.

    Science.gov (United States)

    Chang, Jin-Hong; Huang, Yu-Hui; Cunningham, Christy M; Han, Kyu-Yeon; Chang, Michael; Seiki, Motoharu; Zhou, Zhongjun; Azar, Dimitri T

    2016-01-01

    The cornea is transparent and avascular, and retention of these characteristics is critical to maintaining vision clarity. Under normal conditions, wound healing in response to corneal injury occurs without the formation of new blood vessels; however, neovascularization may be induced during corneal wound healing when the balance between proangiogenic and antiangiogenic mediators is disrupted to favor angiogenesis. Matrix metalloproteinases (MMPs), which are key factors in extracellular matrix remodeling and angiogenesis, contribute to the maintenance of this balance, and in pathologic instances, can contribute to its disruption. Here, we elaborate on the facilitative role of MMPs, specifically MMP-14, in corneal neovascularization. MMP-14 is a transmembrane MMP that is critically involved in extracellular matrix proteolysis, exosome transport, and cellular migration and invasion, processes that are critical for angiogenesis. To aid in developing efficacious therapies that promote healing without neovascularization, it is important to understand and further investigate the complex pathways related to MMP-14 signaling, which can also involve vascular endothelial growth factor, basic fibroblast growth factor, Wnt/β-catenin, transforming growth factor, platelet-derived growth factor, hepatocyte growth factor or chemokines, epidermal growth factor, prostaglandin E2, thrombin, integrins, Notch, Toll-like receptors, PI3k/Akt, Src, RhoA/RhoA kinase, and extracellular signal-related kinase. The involvement and potential contribution of these signaling molecules or proteins in neovascularization are the focus of the present review. PMID:26647161

  11. The use of glycerol-preserved corneas in the developing world

    Directory of Open Access Journals (Sweden)

    Feilmeier Michael

    2010-01-01

    Full Text Available Corneal opacity is the third leading cause of blindness in the developing world and encompasses a wide variety of infectious, inflammatory and degenerative eye diseases. Most caes of corneal blindness are treatable with partial or full-thickness keratoplasty, provided adequate corneal tissue and surgical skill is available. However, access to sight-restoring keratoplasty in developing countries is limited by the lack of developed eye banking networks and a critical shortage of tissue suitable for transplantation. Beyond the developed world, corneal transplantation using fresh corneal tissue (FCT is further hindered by unreliable storage and transportation facilities, unorganized distribution networks, the cost-prohibitive nature of imported tissue, unreliable compliance with medications and follow-up instructions and inadequate health and education services. Glycerol-preserved corneas overcome many of these limitations inherent to the use of FCT. As surgical innovation in lamellar corneal surgery expands the potential use of acellular corneal tissue, long-term preservation techniques are being revisited as a way to increase availability of corneal tissue to corneal surgeons throughout the developing world. Herein, we discuss the advantages of using and the applications for glycerol-preserved corneal tissue throughout the developing world.

  12. Overcoming the brittleness of glass through bio-inspiration and micro-architecture

    Science.gov (United States)

    Mirkhalaf, M.; Dastjerdi, A. Khayer; Barthelat, F.

    2014-01-01

    Highly mineralized natural materials such as teeth or mollusk shells boast unusual combinations of stiffness, strength and toughness currently unmatched by engineering materials. While high mineral contents provide stiffness and hardness, these materials also contain weaker interfaces with intricate architectures, which can channel propagating cracks into toughening configurations. Here we report the implementation of these features into glass, using a laser engraving technique. Three-dimensional arrays of laser-generated microcracks can deflect and guide larger incoming cracks, following the concept of ‘stamp holes’. Jigsaw-like interfaces, infiltrated with polyurethane, furthermore channel cracks into interlocking configurations and pullout mechanisms, significantly enhancing energy dissipation and toughness. Compared with standard glass, which has no microstructure and is brittle, our bio-inspired glass displays built-in mechanisms that make it more deformable and 200 times tougher. This bio-inspired approach, based on carefully architectured interfaces, provides a new pathway to toughening glasses, ceramics or other hard and brittle materials.

  13. Neutron irradiation effects on the ductile-brittle transition of ferritic/martensitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Klueh, R.L.; Alexander, D.J. [Oak Ridge National Lab., TN (United States)

    1997-08-01

    Ferritic/martensitic steels such as the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels have been considered potential structural materials for future fusion power plants. The major obstacle to their use is embrittlement caused by neutron irradiation. Observations on this irradiation embrittlement is reviewed. Below 425-450{degrees}C, neutron irradiation hardens the steels. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy, as measured by a Charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture.

  14. Steadiness and stop of brittle fracture driven by the forces in different distances

    Institute of Scientific and Technical Information of China (English)

    和雪松; 李世愚; 滕春凯

    2005-01-01

    Based on the principle of fracture mechanics, the stop criterion of brittle fracture is proposed and the equation of minimal crack stop is given. By using the zero frequency Green function, the steadiness and stop of brittle fracture driven by the concentrated force and simple distributed forces in different locales are analyzed. The critical loading, unsteady boundary line and location of stop points under some typical conditions are calculated. The steady growth caused by the near forces is significant in interpreting the creep and the forming of some tectonics. Whereas the unsteady propagation caused by the forces in different distances from the crack is significant in interpreting the occurring and stop of earthquakes. It is suggested that the strong earthquakes may be the result of compound of the near-field and far-field forces. The results of this paper are also valuable for investigation of the mechanism of induced earthquake.

  15. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Haoran; Chew, Huck Beng, E-mail: hbchew@illinois.edu [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Wang, Xueju; Xia, Shuman [Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

    2015-09-14

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of Li{sub x}Si electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ∼ 0.5 with the formation of a craze-like network of nanopores separated by Si–Si bonds, while subsequent failure is still brittle-like with the breaking of Si–Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li–Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the Li{sub x}Si alloys leads to significant strain recovery.

  16. Interim report of brittle-fracture impact studies: development of methodology

    International Nuclear Information System (INIS)

    A comprehensive methodology for characterizing the results of impact fracture of brittle waste forms is presented, and its use illustrated by application to available particle-size data obtained in impact tests of various materials. The respirable-size fraction and the total surface area of the fracture particulates are the major criteria for characterization. Particle-size distributions were all found to be characterized approximately by the two parameters of the lognormal probability function (the geometric mean diameter D/sub g/ and the geometric standard deviation sigma/sub g/). These results are explained in terms of the brittle-fracture process as it is described in the technical literature. The methodology appears promising both for standardized evaluation of the impact strength of various solid-waste compositions, either vitreous or crystalline, and for studying the deformation of canistered waste forms in scale-model tests

  17. Numerical Simulation on Failure Process in Brittle and Heterogeneous Matrix Filled with Randomly Distributed Particles

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yafang; TANG Chun'an; LIU Hao

    2006-01-01

    Based on an essential assumption of meso-heterogeneity of material, the macro characteristic of composite reinforced with particles, the crack initiation, propagation and the failure process in composite were studied by using a numerical code. The composite is subjected to a uniaxial tension, and stiff or soft particles are distributed at random manner but without overlapping or contacting. The effect of reinforcement particle properties on the fracture process and mechanism of composite with brittle matrix, furthermore, the influence of the particle volumetric fraction is also investigated. Numerical results present the different failure mode and re-produce the crack initiation, propagation and coalescence in brittle and heterogeneous matrix. The mechanism of such failure was also elucidated.

  18. Fracture propagation in brittle materials as a standard dissipative process: General theorems and crack tracking algorithms

    Science.gov (United States)

    Salvadori, A.; Fantoni, F.

    2016-10-01

    The present work frames the problem of three-dimensional quasi-static crack propagation in brittle materials into the theory of standard dissipative processes. Variational formulations are stated. They characterize the three dimensional crack front "quasi-static velocity" as minimizer of constrained quadratic functionals. An implicit in time crack tracking algorithm that computationally handles the constraint via the penalty method algorithm is introduced and proof of concept is provided.

  19. From boron carbide to glass: Absorption of an elongated high-speed projectile in brittle materials

    Science.gov (United States)

    Rumyantsev, B. V.

    2016-09-01

    Penetration into boron carbide of an elongated high-speed projectile in the form of a copper jet produced by an explosion of a cumulative charge is studied. The efficiency of absorption of a copper jet in different brittle materials for evaluating their protective ability is compared. Conditions for the absence of the influence of the lateral unloading wave on the penetration zone, which provide the minimum penetration depth, are determined.

  20. Failure Probabilities and Tough-Brittle Crossover of Heterogeneous Materials with Continuous Disorder

    OpenAIRE

    Wu, B. Q.; Leath, P. L.

    1998-01-01

    The failure probabilities or the strength distributions of heterogeneous 1D systems with continuous local strength distribution and local load sharing have been studied using a simple, exact, recursive method. The fracture behavior depends on the local bond-strength distribution, the system size, and the applied stress, and crossovers occur as system size or stress changes. In the brittle region, systems with continuous disorders have a failure probability of the modified-Gumbel form, similar...

  1. A continuous-discontinuous approach to simulate fracture processes in quasi-brittle materials

    OpenAIRE

    Moonen, Peter; Carmeliet, Jan; Sluys, Bert

    2009-01-01

    Abstract A macroscopic framework for the simulation of failure processes in quasi-brittle materials is proposed. The framework employs the partition of unity (PU) concept and introduces a new cohesive zone model, capturing the transition between the initial continuum state and the final localized damage state. The model is generic in a sense that it allows extending most continuum models to a discontinuous framework in an efficient and robust way, hereby adding the effect of macro-...

  2. Pinch and swell structures: evidence for brittle-viscous behaviour in the middle crust

    Science.gov (United States)

    Gardner, R.; Piazolo, S.; Daczko, N.

    2015-04-01

    The flow properties of middle to lower crustal rocks are commonly represented by viscous flow. However, examples of pinch and swell structures found in a mid-crustal high strain zone at St. Anne Point (Fiordland, New Zealand) suggest pinch and swell structures are initiated by brittle failure of the more competent layer in conjunction with material softening. On this basis we develop a flexible numerical model using brittle-viscous flow where Mohr-Coulomb failure is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow provided the competent layer has enough viscosity contrast and initially fails brittlely. The degree of material softening after initial failure is shown to impact pinch and swell characteristics with high rates of material softening causing the formation of thick necks between swells by limiting the successful localisation of strain. The flow regime and yielding characteristics of the matrix do not impact pinch and swell structure formation itself, so long as the matrix is less competent. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr-Coulomb behaviour combined with viscous flow is an appropriate way to represent the heterogeneous rocks of the middle to lower crust. This type of mid-crustal rheological behaviour has significant influence on the localization of strain at all scales. For example, inclusion of Mohr-Coulomb brittle failure with viscous flow in just some mid-crustal layers within a crustal scale model will result in strain localisation throughout the whole crustal section allowing the development of through-going high strain structures from the upper crust into the middle and lower crust. This localization then has a significant

  3. Mechanical behavior of quasi-brittle materials under cyclic loadings : from virtual testing to structural simulations

    OpenAIRE

    Vassaux, Maxime

    2015-01-01

    Macroscopic mechanical behavior models are developed for their light computational costs, allowing the simulation of large structural elements, and the precise description of mechanical phenomena observed by the material at lower scales. Such constitutive models are here developed in the seismic solicitation framework, therefore implying cyclic alternate loadings at the material scale, and applied to civil engineering buildings, often made of concrete, or more generally of quasi-brittle mater...

  4. Mechanical Properties of Brittle Materials and Their Single Fracture under Dynamic Loading

    OpenAIRE

    YASHIMA, Saburo; Kanda, Yoshiteru; Saito, Fumio; Sasaki, Toru; Iijima, Masayoshi; HASHIMOTO, Hitoshi

    1983-01-01

    The meaning of study on single particle crushing is recognized at which it is regarded the accumulation of single particle crushing as the comminution performed in practical operations stochastic phenomena. Especially, experimental data concerning the mechanical properties of brittle solids measured under dynamic loading are so far very few. Further, the experimental data concerning compressive strength, sphere compressive strength, fracture energy, new surface produced and fracture surface e...

  5. Micromechanics of brittle faulting and cataclastic flow in Alban Hills tuff

    OpenAIRE

    Zhu, W.; Baud, P.; Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Wong, T

    2011-01-01

    An understanding of how tuff deforms and fails is of importance in the mechanics of volcanic eruption as well as geotechnical and seismic applications related to the integrity of tuff structures and repositories. Previous rock mechanics studies have focused on the brittle strength. We conducted mechanical tests on nominally dry and water-saturated tuff samples retrieved from the Colli Albani drilling project, in conjunction with systematic microstructural observations on the deformed samples ...

  6. Numerical Study on Crack Propagation in Brittle Jointed Rock Mass Influenced by Fracture Water Pressure

    OpenAIRE

    Yong Li; Hao Zhou; Weishen Zhu; Shucai Li; Jian Liu

    2015-01-01

    The initiation, propagation, coalescence and failure mode of brittle jointed rock mass influenced by fissure water pressure have always been studied as a hot issue in the society of rock mechanics and engineering. In order to analyze the damage evolution process of jointed rock mass under fracture water pressure, a novel numerical model on the basis of secondary development in fast Lagrangian analysis of continua (FLAC3D) is proposed to simulate the fracture development of jointed rock mass u...

  7. Oblique Powder Blasting for Three-dimensional Micromachining of Brittle Materials

    OpenAIRE

    Belloy, E.; Sayah, A.; Gijs, M. A. M.

    2001-01-01

    We present oblique powder blasting as a three-dimensional micromachining technology for brittle materials. Powder blasting is a microfabrication process, based on the use of a pressurised air beam containing eroding Al2O3 particles. By varying the angle of incidence of the incoming particles to a substrate, covered by a mask, one can exploit the oblique slopes of micropatterned holes and mask underetching phenomena to generate new options for three-dimensional microstructuring. We have identi...

  8. Final report of experimental laboratory-scale brittle fracture studies of glasses and ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Jardine, L.J.; Mecham, W.J.; Reedy, G.T.; Steindler, M.J.

    1982-10-01

    An experimental program was conducted to characterize the fragments generated when brittle glasses and ceramics are impacted. The direct application of the results is to radioactive waste forms for which the effects of accidental impacts must be known or predictable. Two major measurable experimental responses used for characterization of these effects are (1) the size distribution of the fragments, including the sizes that are respirable, and (2) the increase in surface area of the brittle test specimen. This report describes the glass and ceramic materials characterized, the procedures and techniques used for the characterization of size distributions and surface areas, and the results of the two key responses of the impact tests. Five alternative methods of determining size distributions were compared. Also examined were the effects of diametral and axial specimen impact configurations and the use of mechanical stops to eliminate secondary crushing during testing. Microscopic characterizations of Pyrex and SRL 131 simulated waste glass and SYNROC fragments were also performed. Preliminary correlations of impact energy with key size-distribution parameters, fragment surface areas, and respirable fines were proposed as useful for future verification and for use with modeling and scale-up studies of brittle fracture of larger realistic waste forms. The impact fragments of all specimens could be described by lognormal size distributions.

  9. Formulation and computational aspects of plasticity and damage models with application to quasi-brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z.; Schreyer, H.L. [New Mexico Engineering Research Institute, Albuquerque, NM (United States)

    1995-09-01

    The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.

  10. Strain Rate Dependent Ductile-to-Brittle Transition of Graphite Platelet Reinforced Vinyl Ester Nanocomposites

    Directory of Open Access Journals (Sweden)

    Brahmananda Pramanik

    2014-01-01

    Full Text Available In previous research, the fractal dimensions of fractured surfaces of vinyl ester based nanocomposites were estimated applying classical method on 3D digital microscopic images. The fracture energy and fracture toughness were obtained from fractal dimensions. A noteworthy observation, the strain rate dependent ductile-to-brittle transition of vinyl ester based nanocomposites, is reinvestigated in the current study. The candidate materials of xGnP (exfoliated graphite nanoplatelets reinforced and with additional CTBN (Carboxyl Terminated Butadiene Nitrile toughened vinyl ester based nanocomposites that are subjected to both quasi-static and high strain rate indirect tensile load using the traditional Brazilian test method. High-strain rate indirect tensile testing is performed with a modified Split-Hopkinson Pressure Bar (SHPB. Pristine vinyl ester shows ductile deformation under quasi-static loading and brittle failure when subjected to high-strain rate loading. This observation reconfirms the previous research findings on strain rate dependent ductile-to-brittle transition of this material system. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Contribution of nanoreinforcement to the tensile properties is reported in this paper.

  11. TENSILE STRENGTH FOR SPLITTING FAILURE OF BRITTLE PARTICLES WITH CONSIDERATION OF POISSON'S RATIO

    Institute of Scientific and Technical Information of China (English)

    Guoming Hu; Yanmin Wang; Pingbo Xie; Zhidong Pan

    2004-01-01

    The core mechanism of comminution could be reduced to the breakage of individual particles that occurs through contact with other particles or with the grinding media, or with the solid walls of the mill. When brittle particles are loaded in compression or by impact, substantial tensile stresses are induced within the particles. These tensile stresses are responsible for splitting failure of brittle particles. Since many engineering materials have Poisson's ratios very close to 0.3, the influence of Poisson's ratio on the tensile strength is neglected in many studies. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the tensile stress at the centre of the particle is obtained. It is found reasonable to propose this tensile stress at the instant of failure as the tensile strength of the particle. Moreover, this tensile strength is a function of the Poisson's ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well.Therefore, it could be used as the tensile strength for brittle particles in general. The effect of Poisson's ratio on the tensile strength is discussed.

  12. Slip energy barriers in aluminum and implications for ductile versus brittle behavior

    CERN Document Server

    Sun, Y; Sun, Yuemin; Kaxiras, Efthimios

    1996-01-01

    We conisder the brittle versus ductile behavior of aluminum in the framework of the Peierls-model analysis of dislocation emission from a crack tip. To this end, we perform first-principles quantum mechanical calculations for the unstable stacking energy $\\gamma_{us}$ of aluminum along the Shockley partial slip route. Our calculations are based on density functional theory and the local density approximation and include full atomic and volume relaxation. We find that in aluminum $\\gamma_{us} = 0.224$ J/m$^2$. Within the Peierls-model analysis, this value would predict a brittle solid which poses an interesting problem since aluminum is typically considered ductile. The resolution may be given by one of three possibilites: (a) Aluminum is indeed brittle at zero temperature, and becomes ductile at a finite temperature due to motion of pre-existing dislocations which relax the stress concentration at the crack tip. (b) Dislocation emission at the crack tip is itself a thermally activated process. (c) Aluminum is...

  13. Fracture-mode map of brittle coatings: Theoretical development and experimental verification

    Science.gov (United States)

    He, Chong; Xie, Zhaoqian; Guo, Zhenbin; Yao, Haimin

    2015-10-01

    Brittle coatings, upon sufficiently high indentation load, tend to fracture through either ring cracking or radial cracking. In this paper, we systematically study the factors determining the fracture modes of bilayer material under indentation. By analyzing the stress field developed in a coating/substrate bilayer under indentation in combination with the application of the maximum-tensile-stress fracture criterion, we show that the fracture mode of brittle coatings due to indentation is determined synergistically by two dimensionless parameters being functions of the mechanical properties of coating and substrate, coating thickness and indenter tip radius. Such dependence can be graphically depicted by a diagram called 'fracture-mode map', whereby the fracture modes can be directly predicated based on these two dimensionless parameters. Experimental verification of the fracture-mode map is carried out by examining the fracture modes of fused quartz/cement bilayer materials under indentation. The experimental observation exhibits good agreement with the prediction by the fracture-mode map. Our finding in this paper may not only shed light on the mechanics accounting for the fracture modes of brittle coatings in bilayer structures but also pave a new avenue to combating catastrophic damage through fracture mode control.

  14. Final report of experimental laboratory-scale brittle fracture studies of glasses and ceramics

    International Nuclear Information System (INIS)

    An experimental program was conducted to characterize the fragments generated when brittle glasses and ceramics are impacted. The direct application of the results is to radioactive waste forms for which the effects of accidental impacts must be known or predictable. Two major measurable experimental responses used for characterization of these effects are (1) the size distribution of the fragments, including the sizes that are respirable, and (2) the increase in surface area of the brittle test specimen. This report describes the glass and ceramic materials characterized, the procedures and techniques used for the characterization of size distributions and surface areas, and the results of the two key responses of the impact tests. Five alternative methods of determining size distributions were compared. Also examined were the effects of diametral and axial specimen impact configurations and the use of mechanical stops to eliminate secondary crushing during testing. Microscopic characterizations of Pyrex and SRL 131 simulated waste glass and SYNROC fragments were also performed. Preliminary correlations of impact energy with key size-distribution parameters, fragment surface areas, and respirable fines were proposed as useful for future verification and for use with modeling and scale-up studies of brittle fracture of larger realistic waste forms. The impact fragments of all specimens could be described by lognormal size distributions

  15. Experimental study on the physical and chemical properties of the deep hard brittle shale

    Directory of Open Access Journals (Sweden)

    Jian Xiong

    2016-03-01

    Full Text Available In the hard brittle shale formation, rock composition, physical and chemical properties, mechanics property before and after interacting with fluid have direct relation with borehole problems, such as borehole wall collapse, mud loss, hole shrinkage. To achieve hard brittle shale micro-structure, physical–chemical properties and mechanics property, energy-dispersive X-ray diffraction (XRD, cation exchange capacity experiment and hardness test are conducted. The result of laboratory experiments indicates that, clay mineral and quartz is dominated in mineral composition. In clay mineral, illite and illite/semectite mixed layers are abundant and there is no sign of montmorillonite. Value of cation exchange capacity (CEC ranges from 102.5–330 mmol/kg and average value is 199.56 mmol/kg. High value of CEC and content of clay mineral means hard brittle shale has strong ability of hydration. The image of XRD shows well developed micro-cracks and pores, which make rock failure easily, especially when fluid invades rock inside. Shale sample soaked with anti-high temperature KCL drilling fluid on shorter immersing time has stronger strength, whereas shale sample soaked with plugging and film forming KCL drilling fluid on longer immersing time has stronger strength.

  16. Rock Drilling Performance Evaluation by an Energy Dissipation Based Rock Brittleness Index

    Science.gov (United States)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-08-01

    To reliably estimate drilling performance both tool-rock interaction laws along with a proper rock brittleness index are required to be implemented. In this study, the performance of a single polycrystalline diamond compact (PDC) cutter cutting and different drilling methods including PDC rotary drilling, roller-cone rotary drilling and percussive drilling were investigated. To investigate drilling performance by rock strength properties, laboratory PDC cutting tests were performed on different rocks to obtain cutting parameters. In addition, results of laboratory and field drilling on different rocks found elsewhere in literature were used. Laboratory and field cutting and drilling test results were coupled with values of a new rock brittleness index proposed herein and developed based on energy dissipation withdrawn from the complete stress-strain curve in uniaxial compression. To quantify cutting and drilling performance, the intrinsic specific energy in rotary-cutting action, i.e. the energy consumed in pure cutting action, and drilling penetration rate values in percussive action were used. The results show that the new energy-based brittleness index successfully describes the performance of different cutting and drilling methods and therefore is relevant to assess drilling performance for engineering applications.

  17. Stress localization in BCC polycrystals and its implications on the probability of brittle fracture

    International Nuclear Information System (INIS)

    Highlights: → Intergranular stress distributions in a bainitic steel. → Comparison of local mean stress field with neutron diffraction results. → Application of the local stress distribution in a brittle fracture model. - Abstract: The evaluation of the reliability of pressure vessels in nuclear plants relies on the evaluation of failure probability models. Micromechanical approaches are of great interest to refine their description, to better understand the underlying mechanisms leading to failure, and finally to improve the prediction of these models. The main purpose of this paper is to introduce the stress heterogeneities arising within the polycrystal in a probabilistic modeling of brittle fracture. Stress heterogeneities are evaluated from Finite-Element simulations performed on a large number of Statistical Volume Elements. Results are validated both on the measured averaged behavior and on the averaged stresses measured by neutron diffraction in five specific orientations. A probabilistic model for brittle fracture is then presented accounting for the carbide distribution and the stress distribution evaluated previously inside an elementary volume V0. Results are compared to a 'Beremin type' approach, assuming a homogeneous stress state inside V0.

  18. A short-term study of corneal collagen cross-linking with hypo-osmolar riboflavin solution in keratoconic corneas

    Institute of Scientific and Technical Information of China (English)

    Shao-Feng; Gu; Zhao-Shan; Fan; Li-Hua; Wang; Xiang-Chen; Tao; Yong; Zhang; Chun-Qin; Wang; Ya; Wang; Guo-Ying; Mu

    2015-01-01

    AIM: To report the 3mo outcomes of collagen crosslinking(CXL) with a hypo-osmolar riboflavin in thin corneas with the thinnest thickness less than 400 μm without epithelium.METHODS: Eight eyes in 6 patients with age 26.2±4.8y were included in the study. All patients underwent CXL using a hypo-osmolar riboflavin solution after its de-epithelization. Best corrected visual acuity, manifest refraction, the thinnest corneal thickness, and endothelial cell density were evaluated before and 3mo after the procedure.RESULTS: The mean thinnest thickness of the cornea was 408.5 ±29.0 μm before treatment and reduced to369.8 ±24.8 μm after the removal of epithelium. With the application of the hypo-osmolar riboflavin solution, the thickness increased to 445.0 ±26.5 μm before CXL and recover to 412.5 ±22.7 μm at 3mo after treatment, P =0.659). Before surgery, the mean K-value of the apex of the keratoconus corneas was 57.6 ±4.0 diopters, and slightly decreased(54.7±4.9 diopters) after surgery(P =0.085). Mean best-corrected visual acuity was 0.55 ±0.23 logarithm of the minimal angle of resolution, and increased to 0.53±0.26 logarithm after surgery(P =0.879).The endothelial cell density was 2706.4 ±201.6 cells/mm2 before treatment, and slightly decreased( 2641. 2 ±218.2 cells/mm2) at last fellow up(P =0.002).CONCLUSION: Corneal collagen cross-linking with a hypo-osmolar riboflavin in thin corneas seems to be a promising treatment. Further study should be done to evaluate the safety and efficiency of CXL in thin corneas for the long-term.

  19. Bi Syndrome (Arthralgia Syndrome)

    Institute of Scientific and Technical Information of China (English)

    ZHANG En-qin

    2010-01-01

    @@ The word 'Bi' (痹) in Chinese means an obstruction.Bi Syndrome refers the syndrome characterized by the obstruction of qi and blood in the meridians due to the invasion of external pathogenic wind, cold and dampness, manifested as soreness, pain, numbness,heavy sensation, swelling of joints and limbs, limitation of movements and so on.

  20. Deciphering the brittle evolution of SW Norway through a combined structural, mineralogical and geochronological approach

    Science.gov (United States)

    Scheiber, Thomas; Viola, Giulio; Fredin, Ola; Zwingmann, Horst; Wilkinson, Camilla Maya; Ganerød, Morgan

    2016-04-01

    SW Norway has experienced a complex brittle history after cessation of the Caledonian orogeny, and the recent discoveries of major hydrocarbon reserves in heavily fractured and weathered basement offshore SW Norway has triggered a renewed interest in understanding this complex tectonic evolution. In this contribution we present results from a multidisciplinary study combining lineament analysis, field work, paleo-stress inversion, mineralogical characterization and radiometric dating in the Bømlo area of SW Norway in order to develop a tectonic model for the brittle evolution of this important region. The study area mainly consists of the Rolvsnes granodiorite (U-Pb zircon age of ca. 466 Ma), which is devoid of penetrative ductile deformation features. The first identified brittle faults are muscovite-bearing top-to-the-NNW thrusts and E-W striking dextral strike-slip faults decorated with stretched biotite. These are mechanically compatible and are assigned to the same NNW-SSE transpressional regime. Ar-Ar muscovite and biotite dates of ca. 450 Ma (Late Ordovician) indicate fault activity in the course of a Taconian-equivalent orogenic event. During the subsequent Silurian Laurentia-Baltica collision variably oriented, lower-grade chlorite and epidote-coated faults formed in response to a ENE-WSW compressional stress regime. A large number of mainly N-S striking normal faults consist of variably thick fault gouge cores with illite, quartz, kaolinite, calcite and epidote mineralizations, accommodating mainly E-W extension. K-Ar dating of illites separated from representative fault gouges and zones of altered granodiorite constrain deformation ranging from the Permian to the Late Jurassic, indicating a long history of crustal extension where faults were repeatedly activated. In addition, a set of ca. SW-NE striking faults associated with alteration zones give Cretaceous dates, either representing a young phase of NW-SE extension or reactivation of previously formed

  1. The role of fluids on the brittle-ductile transition in the crust

    Science.gov (United States)

    Hirth, Greg; Beeler, Nick

    2015-04-01

    To characterize stress and deformation style at the base of the seismogenic zone we investigate how the mechanical properties of fluid-rock systems respond to variations in temperature and strain rate. The role of fluids on the processes responsible for the brittle-ductile transition in quartz-rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the Earth. Our initial analysis of this competition suggests that the effective pressure law for sliding friction should not work as effectively near the brittle-ductile transition (BDT) as it does at shallow conditions. Our motivation comes from three observations. First, extrapolation of quartzite flow laws indicates the brittle-ductile transition (BDT) occurs at ~300 °C at geologic strain rates for conditions where fault strength is controlled by a coefficient of friction of ~0.6 with a hydrostatic pore-fluid pressure gradient. Second, we suggest that the preservation of relatively high stress microstructures indicates that the effective stress law must sometimes evolve rapidly near the BDT. There is abundant evidence for the presence of fluids during viscous deformation of mylonites (e.g., recrystallization and redistribution of micas, dissolution and reprecipitation of quartz). The relatively high viscous stresses inferred from these microstructures are incompatible with the standard effective stress relationship. A similar "paradox" is evident at experimental conditions where viscous creep is studied in the laboratory. In this case, the presence of fluid (which should produce low effective stress) does not promote localized brittle failure, even though these experiments are conducted under undrained conditions. Third, experiments on partially molten rocks illustrate viscous creep behavior during both drained compaction and undrained triaxial deformation tests, even though the melt pressure approaches or equals

  2. Sequencing and analysis of the gastrula transcriptome of the brittle star Ophiocoma wendtii

    Directory of Open Access Journals (Sweden)

    Vaughn Roy

    2012-09-01

    Full Text Available Abstract Background The gastrula stage represents the point in development at which the three primary germ layers diverge. At this point the gene regulatory networks that specify the germ layers are established and the genes that define the differentiated states of the tissues have begun to be activated. These networks have been well-characterized in sea urchins, but not in other echinoderms. Embryos of the brittle star Ophiocoma wendtii share a number of developmental features with sea urchin embryos, including the ingression of mesenchyme cells that give rise to an embryonic skeleton. Notable differences are that no micromeres are formed during cleavage divisions and no pigment cells are formed during development to the pluteus larval stage. More subtle changes in timing of developmental events also occur. To explore the molecular basis for the similarities and differences between these two echinoderms, we have sequenced and characterized the gastrula transcriptome of O. wendtii. Methods Development of Ophiocoma wendtii embryos was characterized and RNA was isolated from the gastrula stage. A transcriptome data base was generated from this RNA and was analyzed using a variety of methods to identify transcripts expressed and to compare those transcripts to those expressed at the gastrula stage in other organisms. Results Using existing databases, we identified brittle star transcripts that correspond to 3,385 genes, including 1,863 genes shared with the sea urchin Strongylocentrotus purpuratus gastrula transcriptome. We characterized the functional classes of genes present in the transcriptome and compared them to those found in this sea urchin. We then examined those members of the germ-layer specific gene regulatory networks (GRNs of S. purpuratus that are expressed in the O. wendtii gastrula. Our results indicate that there is a shared ‘genetic toolkit’ central to the echinoderm gastrula, a key stage in embryonic development, though

  3. Brittle fracture at beam-to-column connection during earthquake; Kosei kyokyaku ramen gukakubu no jishinji zeiseika hakai

    Energy Technology Data Exchange (ETDEWEB)

    Miki, C.; Aizawa, T.; Anami, K. [Tokyo Institute of Technology, Tokyo (Japan)

    1998-04-21

    During the Great Hanshin-Awaji Earthquake, brittle fracture was caused at beam-to-column connection of P75 steel pier. In this study, concerning the brittle fracture at P75 pier, simulations of brittle fracture at beam-to-column connection are carried out by using large scale specimens simulating the P75 beam-to-column joint. Some improved specimens which include ribs at corners of connection are also used. As a result, there is a high possibility that brittle fracture is caused at corner of connection where there is a high strain concentration. Shapes of the damages characteristic in the experiment using the reinforcing model studied in this study were buckling on the web near the rib end and cracks generated from near the rib. 11 refs., 23 figs., 4 tabs.

  4. Static and fatigue failure of quasi brittle materials at a V-notch using a Dugdale model

    OpenAIRE

    Murer, S.; Leguillon, D.

    2009-01-01

    Abstract The prediction of crack nucleation at stress concentration points in brittle and quasi-brittle materials may generally rely on either an Irwin-like criterion, involving a critical value of the generalized stress intensity factor of the singularity associated to the stress concentration, or on cohesive zone models. Leguillon's criterion enters the first category and combines an energy condition and a stress one. Thanks to matched asymptotics procedures, the associated numer...

  5. Description of new dry granular materials of variable cohesion and friction coefficient: Implications for laboratory modeling of the brittle crust

    Science.gov (United States)

    Abdelmalak, M. M.; Bulois, C.; Mourgues, R.; Galland, O.; Legland, J.-B.; Gruber, C.

    2016-08-01

    Cohesion and friction coefficient are fundamental parameters for scaling brittle deformation in laboratory models of geological processes. However, they are commonly not experimental variable, whereas (1) rocks range from cohesion-less to strongly cohesive and from low friction to high friction and (2) strata exhibit substantial cohesion and friction contrasts. This brittle paradox implies that the effects of brittle properties on processes involving brittle deformation cannot be tested in laboratory models. Solving this paradox requires the use of dry granular materials of tunable and controllable brittle properties. In this paper, we describe dry mixtures of fine-grained cohesive, high friction silica powder (SP) and low-cohesion, low friction glass microspheres (GM) that fulfill this requirement. We systematically estimated the cohesions and friction coefficients of mixtures of variable proportions using two independent methods: (1) a classic Hubbert-type shear box to determine the extrapolated cohesion (C) and friction coefficient (μ), and (2) direct measurements of the tensile strength (T0) and the height (H) of open fractures to calculate the true cohesion (C0). The measured values of cohesion increase from 100 Pa for pure GM to 600 Pa for pure SP, with a sub-linear trend of the cohesion with the mixture GM content. The two independent cohesion measurement methods, from shear tests and tension/extensional tests, yield very similar results of extrapolated cohesion (C) and show that both are robust and can be used independently. The measured values of friction coefficients increase from 0.5 for pure GM to 1.05 for pure SP. The use of these granular material mixtures now allows testing (1) the effects of cohesion and friction coefficient in homogeneous laboratory models and (2) testing the effect of brittle layering on brittle deformation, as demonstrated by preliminary experiments. Therefore, the brittle properties become, at last, experimental variables.

  6. Antinociceptive and anti-inflammatory activities of sulphated polysaccharides from the red seaweed Gracilaria cornea.

    Science.gov (United States)

    Coura, Chistiane O; de Araújo, Ianna W F; Vanderlei, Edfranck S O; Rodrigues, José A G; Quinderé, Ana L G; Fontes, Bruno P; de Queiroz, Ismael N L; de Menezes, Dalgimar B; Bezerra, Mirna M; e Silva, Antonio A R; Chaves, Hellíada V; Jorge, Roberta J B; Evangelista, Janaina S A M; Benevides, Norma M B

    2012-04-01

    Seaweeds have attracted special interest as good sources of sulphated polysaccharides (SP) for use in pharmaceutical industries and biotechnology. In this study, we evaluated the effects of SP from the red seaweed Gracilaria cornea (Gc-TSP) in nociceptive and inflammatory models. In mice, Gc-TSP (3, 9 or 27 mg/kg) significantly reduced nociceptive responses, as measured by the number of writhes, at all tested doses. In a formalin test, Gc-TSP significantly reduced licking time in both phases of the test at a dose of 27 mg/kg. In a hot-plate test, the antinociceptive effect was observed only in animals treated with 27 mg/kg of Gc-TSP, suggesting that the analgesic effect occurs through a central action mechanism at the highest dose. Gc-TSP (3, 9 or 27 mg/kg) caused only a slight reduction in neutrophil migration in the rat peritoneal cavity. However, lower doses of Gc-TSP (3 and 9 mg/kg) significantly inhibited paw oedema induced by carrageenan, especially at 3 hr after treatment. Reduction in oedema was confirmed by myeloperoxidase activity in the affected paw tissue. In addition, treatment (s.c.) of animals with different doses of Gc-TSP inhibited paw oedema induced by dextran within the first hour in all doses tested. After 14 consecutive days of intraperitoneal administration of Gc-TSP (9 mg/kg), we measured the wet weight of the liver, kidney, heart, spleen and thymus and performed biochemical, haematological and histopathological evaluations. No systemic damage was found. These results indicate that Gc-TSP possesses analgesic and anti-inflammatory effects and is a potentially important tool worthy of further study.

  7. Visual pigments, oil droplets, lens, and cornea characterization in the whooping crane (Grus americana)

    Science.gov (United States)

    Porter, Megan L.; Kingston, Alexandra C. N.; McCready, Robert; Cameron, Evan G.; Hofmann, Christopher M.; Suarez, Lauren; Olsen, Glenn H.; Cronin, Thomas W.; Robinson, Phyllis R.

    2014-01-01

    Vision has been investigated in many species of birds, but few studies have considered the visual systems of large birds and the particular implications of large eyes and long-life spans on visual system capabilities. To address these issues we investigated the visual system of the whooping crane, Grus americana (Gruiformes: Gruidae). G. americana (an endangered species) is one of only two North American crane species and represents a large, long-lived bird where ultraviolet sensitivity may be degraded by chromatic aberrations and entrance of ultraviolet light into the eye could be detrimental to retinal tissues. To investigate the whooping crane visual system we used microspectrophotometry to determine the absorbance spectra of retinal oil droplets and to investigate if the ocular media (i.e., the lens and cornea) absorbs UV light. In vitro expression and reconstitution was used to determine the absorbance spectra of rod and cone visual pigments. The rod visual pigments had wavelengths of peak absorbance (λmax) at 500 nm, while the cone visual pigments λmax values were determined to be 404 nm (SWS1), 450 nm (SWS2), 499 nm (RH2), and 561 nm (LWS), similar to other characterized bird visual pigment absorbance values. The oil droplet cutoff wavelength (λcut) values similarly fell within ranges recorded from other avian species: 576 nm (R-type), 522 nm (Y-type), 506 nm (P-type), and 448 nm (C-type). We confirm that G. americana has a violet-sensitive visual system, although based on the λmax of the SWS1 visual pigment (404 nm) may also have some ability for UV sensitivity.

  8. Influence of the static strain ageing on the ductile-to-brittle transition in C-Mn steel

    International Nuclear Information System (INIS)

    Ferritic steels for industrial structures have a brittle-ductile transition toughness and impact energy with temperature. Their resistance to the brittle fracture plays an essential role in the safety certification of industrial structures. Nowadays, the performance and the durability are key issues for major players such as EDF. In these approaches ductile-to-brittle transition toughness and impact energy, toughness is predicted from resilience. Several previous studies have shown that the probability of cleavage fracture can be adequately described in brittle plateau by a local approach to fracture. However, these studies assume that the material does not undergo strain aging, which is rarely relevant for low carbon steels and low calmed down. The work consisted firstly to characterize the behavior and secondly to propose a robust and explicit modeling of the observed phenomena. Characterization consisted of performing tensile tests between -150 C and 20 C for several strain rates. A model able to simulate the static aging is identified by implementing an appropriate and systematic strategy. Impact resistance test allows us to build the curve of ductile-to-brittle transition of the material for different conditions to understand and observe the influence of static strain aging on the failure. Finally, the modeling of the brittle fracture has been described for all experimental conditions tested using the model developed and identified in the previous section to predict the transition for different material conditions. (author)

  9. Marfan Syndrome

    Science.gov (United States)

    Marfan syndrome is a disorder that affects connective tissue. Connective tissues are proteins that support skin, bones, ... fibrillin. A problem with the fibrillin gene causes Marfan syndrome. Marfan syndrome can be mild to severe, ...

  10. T-style keratoprosthesis based on surface-modified poly (2-hydroxyethyl methacrylate) hydrogel for cornea repairs

    Energy Technology Data Exchange (ETDEWEB)

    Xiang, Jun [Department of Ophthalmology, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China); Sun, Jianguo [Research Center, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China); State Key Laboratory of Molecular Engineering of Polymers, Fudan University (China); Hong, Jiaxu [Department of Ophthalmology, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China); Wang, Wentao [Research Center, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China); Wei, Anji [Department of Ophthalmology, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China); Le, Qihua [Research Center, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China); Xu, Jianjiang, E-mail: jianjiang-xu@163.com [Department of Ophthalmology, Eye & ENT Hospital, Shanghai Medical College, Fudan University (China); Key Laboratory of Myopia, Ministry of Health, Fudan University (China); Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University (China)

    2015-05-01

    Corneal disease is a common cause of blindness, and keratoplasty is considered as an effective treatment method. However, there is a severe shortage of donor corneas worldwide. This paper presents a novel T-style design of a keratoprosthesis and its preparation methods, in which a mechanically and structurally effective artificial cornea is made based on a poly(2-hydroxyethyl methacrylate) hydrogel. The porous skirt was modified with hyaluronic acid and cationized gelatin, and the bottom of the optical column was coated with poly(ethylene glycol). The physical properties of the T-style Kpro were analyzed using ultraviolet and visible spectrophotometry and electron scanning microscopy. The surface chemical properties were characterized using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface modification in the spongy skirt promoted cell adhesion and produced a firm bond between the corneal tissue and the implant device, while the surface modification in the optic column resisted cell adhesion and prevented retroprosthetic membrane formation. Through improved surgical techniques, the novel T-style keratoprosthesis provides enough mechanical stability to facilitate long-term biointegration with the host environment. In vivo implantation experiments showed that the T-style keratoprosthesis is a promising cornea alternative for patients with severe limbal stem cell deficiency and corneal opacity. - Highlights: • T-style keratoprosthesis was designed and prepared based on a PHEMA hydrogel. • Selective surface modifications effectively regulated cells' selective adhesion. • T-style keratoprosthesis provides enough mechanical stability to facilitate long-term biointegration with host tissues.

  11. THE VISCOUS TO BRITTLE TRANSITION IN CRYSTAL- AND BUBBLE-BEARING MAGMAS

    Directory of Open Access Journals (Sweden)

    Mattia ePistone

    2015-11-01

    Full Text Available The transition from viscous to brittle behaviour in magmas plays a decisive role in determining the style of volcanic eruptions. While this transition has been determined for one- or two-phase systems, it remains poorly constrained for natural magmas containing silicic melt, crystals, and gas bubbles. Here we present new experimental results on shear-induced fracturing of three-phase magmas obtained at high-temperature (673-1023 K and high-pressure (200 MPa conditions over a wide range of strain-rates (5·10-6 s-1 to 4·10-3 s-1. During the experiments bubbles are deformed (i.e. capillary number are in excess of 1 enough to coalesce and generate a porous network that potentially leads to outgassing. A physical relationship is proposed that quantifies the critical stress required for magmas to fail as a function of both crystal (0.24 to 0.65 and bubble volume fractions (0.09 to 0.12. The presented results demonstrate efficient outgassing for low crystal fraction ( 0.44 promote gas bubble entrapment and inhibit outgassing. The failure of bubble-free, crystal-bearing systems is enhanced by the presence of bubbles that lower the critical failure stress in a regime of efficient outgassing, while the failure stress is increased if bubbles remain trapped within the crystal framework. These contrasting behaviours have direct impact on the style of volcanic eruptions. During magma ascent, efficient outgassing reduces the potential for an explosive eruption and favours brittle behaviour, contributing to maintain low overpressures in an active volcanic system resulting in effusion or rheological flow blockage of magma at depth. Conversely, magmas with high crystallinity experience limited loss of exsolved gas, permitting the achievement of larger overpressures prior to a potential sudden transition to brittle behaviour, which could result in an explosive volcanic eruption.

  12. An experimental study on semi-brittle and plastic rheology of Panzhihua gabbro

    Institute of Scientific and Technical Information of China (English)

    何昌荣; 周永胜; 桑祖南

    2003-01-01

    We have carried out a systematic experimental study on semi-brittle and plastic deformation of fine-grained Panzhihua gabbro under dry condition with temperature range of 700-1100℃, confining pressure of 450-500 MPa, and strain rate of 1×10-4-3.1×10-6 s-1, using a triaxial testing system with a Griggs type solid medium pressure vessel. In terms of the parameters in the flow law and microstructure after deformation, the rate-dependent deformation can be categorized into three modes: (i) In temperature range of 700-800℃, the deformation is accommodated by semi-brittle flow, with activation energy Q = 612 ± 12 kJ/mol, and stress exponent n = 14.6. The deformation in microscopic scale corresponds to the dislocation glide accompanied with microfracturing. (ii) In temperature range of 900-950℃, the predominant deformation mechanisms in this phase are mechanical twinning and dislocation glide, with activation energy Q =720 ± 61 kJ/mol, and stress exponent n = 6.4. (iii) In temperature range of 1000-1150℃, the major deformation mechanisms are dislocation glide and dislocation climb with minor processes of partial melting, with activation energy Q = 699 ± 55 kJ/mol and stress exponent n = 4.1. The microstructure and deformation mechanism of our experiments are comparable to the results of clinopyroxene and diabase as observed in previous studies. The flow stress of a mafic lower crust is calculated based on the rheological parameters of dry fine-grained gabbro, which implies that a lower curst with mafic granulite may be brittle, and it is possible to fracture and produce frictional slips. This may be an important implication for earthquake nucleation in the lower crust.

  13. Hemolytic and cytotoxic effects of saponin like compounds isolated from Persian Gulf brittle star (Ophiocoma erinaceus)

    Institute of Scientific and Technical Information of China (English)

    Elaheh Amini; Mohammad Nabiuni; Javad Baharara; Kazem Parivar; Javad Asili

    2014-01-01

    Objective: To isolate and characterize the saponin from Persian Gulf brittle star (Ophiocomaerinaceus Methods: In an attempt to prepare saponin from brittle star, collected samples were minced and extracted with ethanol, dichloromethane, n-buthanol. Then, concentrated n-butanol extract were loaded on HP-20 resin and washed with dionized water, 80% ethanol and 100%ethanol respectively. Subsequently, detection of saponin was performed by foaming property, fourier transform infrared spectroscopy and hemolytic analysis on thin layer chromatography. The cytotoxic activity on HeLa cells was evaluated through 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide (MTT) assay and under invert microscopy.Results:) and to evaluate its hemolytic and cytotoxic potential. method. The presence of C-H bond, C-O-C and OH in fourier transform infrared spectrum of fraction 80% ethanol is characteristic feature in the many of saponin compounds. Hemolytic assay revealed HD50 value was 500 µg/mL. MTT assay exhibited that saponin extracted in IC50 value of 25 µg/mL inducsd potent cytotoxic activity against HeLa cells in 24 h and 12.5 µg/mL in 48 h, meanwhile in lower concentration did not have considerable effect against HeLa cells.Conclusions:The existence of saponin in Ophiocoma erinaceus were approved by phytochemical These findings showed that only 80% ethanol fraction Persian Gulf brittle star contained saponin like compounds with hemolytic activity which can be detected simply by phytochemical that can be appreciable for future anticancer research.

  14. Improved small punch testing and parameter identification of ductile to brittle materials

    International Nuclear Information System (INIS)

    Minimal invasive material testing is of special interest, when only small amounts of material are available or the material degradation of structural components in service has to be evaluated. The disc-shaped specimens used in the small punch test are small enough for local material sampling but representative for characterizing the macroscopic material behaviour. A small punch test device was developed which enables the testing of materials in the whole range from ductile to brittle failure and from ambient temperature down to −190 °C in a unique experimental set-up. The specimens are not clamped as usually in the small punch test. This is crucial for brittle fracture behaviour with little or without plastic deformation. The measured load displacement curve of the punch represents the non-linear response of the material due to elastic–plastic deformation. It contains relevant information about true material parameters, which can be made accessible by solving the inverse problem. Thus, plastic yield curves and Weibull parameters were identified by combining finite element simulations with non-linear optimization techniques. Examples for measured load displacement curves and related results of parameter identification are shown for a pressure vessel steel and a laser welded joint. The results obtained from the small punch test are verified by data from standard specimen tests. - Highlights: • Improved small punch test suited for the whole range of ductile to brittle materials. • Minimal invasive determination of true material parameters by means of numerical simulations. • Temperature dependent yield curve parameters were identified using a response surface approach. • Estimation of Weibull parameters of cleavage fracture for steels at low temperatures

  15. New perspectives on the transition between discrete fracture, fragmentation, and pulverization during brittle failure of rocks

    Science.gov (United States)

    Griffith, W. A.; Ghaffari, H.; Barber, T. J.; Borjas, C.

    2015-12-01

    The motions of Earth's tectonic plates are typically measured in millimeters to tens of centimeters per year, seemingly confirming the generally-held view that tectonic processes are slow, and have been throughout Earth's history. In line with this perspective, the vast majority of laboratory rock mechanics research focused on failure in the brittle regime has been limited to experiments utilizing slow loading rates. On the other hand, many natural processes that pose significant risk for humans (e.g., earthquakes and extraterrestrial impacts), as well as risks associated with human activities (blow-outs, explosions, mining and mine failures, projectile penetration), occur at rates that are hundreds to thousands of times faster than those typically simulated in the laboratory. Little experimental data exists to confirm or calibrate theoretical models explaining the connection between these dramatic events and the pulverized rocks found in fault zones, impacts, or explosions; however the experimental data that does exist is thought-provoking: At the earth's surface, the process of brittle fracture passes through a critical transition in rocks at high strain rates (101-103s-1) between regimes of discrete fracture and distributed fragmentation, accompanied by a dramatic increase in strength. Previous experimental works on this topic have focused on key thresholds (e.g., peak stress, peak strain, average strain rate) that define this transition, but more recent work suggests that this transition is more fundamentally dependent on characteristics (e.g., shape) of the loading pulse and related microcrack dynamics, perhaps explaining why for different lithologies different thresholds more effectively define the pulverization transition. In this presentation we summarize some of our work focused on this transition, including the evolution of individual defects at the microscopic, microsecond scale and the energy budget associated with the brittle fragmentation process as a

  16. Ultrastructure Features and Three-Dimensional Transmission Electron Tomography of Dhub Lizard (Uromastyx Aegyptia) Cornea and Its Adaptation to a Desert Environment.

    Science.gov (United States)

    Akhtar, Saeed; Alkhalaf, Mousa; Khan, Adnan A; Almubrad, Turki M

    2016-08-01

    We report ultrastructural features and transmission electron tomography of the dhub lizard (Uromastyx aegyptia) cornea and its adaptation to hot and dry environments. Six corneas of dhub lizards were fixed in 2.5% glutaraldehyde and processed for electron microscopy and tomography. The ultrathin sections were observed with a JEOL 1400 transmission electron microscope. The cornea of the dhub lizard is very thin (~28-30 µm). The epithelium constitutes ~14% of the cornea, whereas the stroma constitutes 80% of the cornea. The middle stromal lamellae are significantly thicker than anterior and posterior stromal lamellae. Collagen fibril (CF) diameters in the anterior stroma are variable in size (25-75 nm). Proteoglycans (PGs) are very large in the middle and posterior stroma, whereas they are small in the anterior stroma. Three-dimensional electron tomography was carried out to understand the structure and arrangement of the PG and CFs. The presence of large PGs in the posterior and middle stroma might help the animal retain a large amount of water to protect it from dryness. The dhub corneal structure is equipped to adapt to the dry and hot desert environment. PMID:27619263

  17. Continuous amperometric monitoring of glucose in a brittle diabetic chimpanzee with a miniature subcutaneous electrode

    OpenAIRE

    Wagner, J. G.; Schmidtke, D. W.; Quinn, C P; Fleming, T F; Bernacky, B.; Heller, A.

    1998-01-01

    The performance of an amperometric biosensor, consisting of a subcutaneously implanted miniature (0.29 mm diameter, 5 × 10−4 cm2 mass transporting area), 90 s 10–90% rise/decay time glucose electrode, and an on-the-skin electrocardiogram Ag/AgCl electrode was tested in an unconstrained, naturally diabetic, brittle, type I, insulin-dependent chimpanzee. The chimpanzee was trained to wear on her wrist a small electronic package and to present her heel for capillary blood samples. In five sets o...

  18. Relationships between brittle deformation, weathering and landscape development during the Mesozoic in Scandinavia

    Science.gov (United States)

    Viola, Giulio; Fredin, Ola; Scheiber, Thomas; Brönner, Marco; Zwingmann, Horst; Knies, Jochen

    2015-04-01

    Pre-Quaternary weathering is generally considered responsible for the formation of rather common, yet poorly constrained, saprolite remnants onshore Scandinavia. Understanding the genesis of these weathering products and placing them into an adequate tectonic and climatic framework is currently of great interest for two reasons. First, the origin of the landscape in Scandinavia, where deep weathering is thought to have played a fundamental role, is the subject of a lively debate hinged around the number and age of episodes of regional uplift and denudation. Second, there have been recent discoveries of major hydrocarbon reserves within weathered basement highs in the North Sea immediately offshore Norway. Invariably, these basement highs are also severely fractured and faulted and a genetic relationship between brittle deformation, weathering and landscape development is suggested by a number of observations. Within the recently launched BASE project, we aim to establish a temporal and conceptual framework for brittle tectonics, weathering patterns and landscape evolution by constraining the age and rate of weathering and by isotopically dating selected faults intimately linked to weathered basement blocks. Initial efforts have focused on fractured and weathered granitoid rocks of Caledonian age exposed in western Norway. There, saprolites are found as small pockets within a joint valley landscape, which was likely stripped by Quaternary glaciations. Saprolite distribution is mostly structurally controlled as deep weathering and alteration occur predominantly in association with fractures and along faulted corridors. Structural analysis has allowed the geometric and kinematic interpretation of the exposed fracture and fault patterns and we could assign them to a number of distinct brittle deformation episodes characterised by robust paleostress tensors. The K-Ar dating of illites separated from structurally constrained faults indicates a long strain localization

  19. Understanding brittle deformation at the Olkiluoto site. Literature compilation for site characterization and geological modelling

    International Nuclear Information System (INIS)

    The present report arose from the belief that geological modelling at Olkiluoto, Finland, where an underground repository for spent nuclear fuel is at present under construction, could be significantly improved by an increased understanding of the phenomena being modelled, in conjunction with the more sophisticated data acquisition and processing methods which are now being introduced. Since the geological model is the necessary basis for the rock engineering and hydrological models, which in turn provide the foundation for identifying suitable rock volumes underground and for demonstrating longterm safety, its scientific basis is of critical importance. As a contribution to improving this scientific basis, the literature on brittle deformation in the Earth's crust has been reviewed, and key references chosen and arranged, with the particular geology of the Olkiluoto site in mind. The result is a compilation of scientific articles, reports and books on some of the key topics, which are of significance for an improved understanding of brittle deformation of hard, crystalline rocks, such as those typical for Olkiluoto. The report is subdivided into six Chapters, covering (1) background information, (2) important aspects of the fabric of intact rock, (3) fracture mechanics and brittle microtectonics, (4) fracture data acquisition and processing, for the statistical characterisation and modelling of fracture systems, (5) the characterisation of brittle deformation zones for deterministic modelling, and (6) the regional geological framework of the Olkiluoto site. The Chapters are subdivided into a number of Sections, and each Section into a number of Topics. The citations are mainly collected under each Topic, embedded in a short explanatory text or listed chronologically without comment. The systematic arrangement of Chapters, Sections and Topics is such that the Table of Contents can be used to focus quickly on the theme of interest without the necessity of looking

  20. Brittle versus ductile deformation as the main control of the deep fluid circulation in continental crust

    Science.gov (United States)

    Violay, Marie; Madonna, Claudio; Burg, Jean-Pierre

    2016-04-01

    The Japan Beyond-Brittle Project (JBBP) and the Taupo Volcanic Zone-Deep geothermal drilling project in New Zealand (TVZ-DGDP) proposed a new concept of engineered geothermal development where reservoirs are created in ductile rocks. This system has several advantages including (1) a simpler design and control of the reservoir due to homogeneous rock properties and stress states in the ductile domain ,(2) possible extraction of supercritical fluids (3) less probability for induced earthquakes. However, it is at present unknwon what and how porosity and permeability can be engineered in such environments. It has been proposed that the magmatic chamber is surrounded by a hot and ductile carapace through which heat transfer is conductive because the plastic behaviour of the rock will close possible fluid pathways. Further outward, as temperature declines, the rock will encounter the brittle-ductile transition with a concomitant increase in porosity and permeability. The thickness of the conduction-dominated, ductile boundary zone between the magmatic chamber and the convecting geothermal fluid directly determines the rate of heat transfer. To examine the brittle to ductile transition in the context of the Japanese crust, we conducted deformation experiments on very-fine-grain granite in conventional servocontrolled, gas-medium triaxial apparatus (from Paterson instrument). Temperature ranged from 600° C to 1100° C and effective confining pressure from 100 to 150 MPa. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Permeability was measured under static conditions by transient pressure pulse method. Mechanical and micro-structural observations at experimental constant strain rate of 10-5 s-1 indicated that the granite was brittle and dilatant up to 900 ° C. At higher temperatures the deformation mode becomes macroscopically ductile, i

  1. Brittle versus ductile deformation as the main control of the deep fluid circulation in continental crust

    Science.gov (United States)

    Violay, Marie; Madonna, Claudio; Burg, Jean-Pierre

    2016-04-01

    The Japan Beyond-Brittle Project (JBBP) and the Taupo Volcanic Zone-Deep geothermal drilling project in New Zealand (TVZ-DGDP) proposed a new concept of engineered geothermal development where reservoirs are created in ductile rocks. This system has several advantages including (1) a simpler design and control of the reservoir due to homogeneous rock properties and stress states in the ductile domain ,(2) possible extraction of supercritical fluids (3) less probability for induced earthquakes. However, it is at present unknwon what and how porosity and permeability can be engineered in such environments. It has been proposed that the magmatic chamber is surrounded by a hot and ductile carapace through which heat transfer is conductive because the plastic behaviour of the rock will close possible fluid pathways. Further outward, as temperature declines, the rock will encounter the brittle-ductile transition with a concomitant increase in porosity and permeability. The thickness of the conduction-dominated, ductile boundary zone between the magmatic chamber and the convecting geothermal fluid directly determines the rate of heat transfer. To examine the brittle to ductile transition in the context of the Japanese crust, we conducted deformation experiments on very-fine-grain granite in conventional servocontrolled, gas-medium triaxial apparatus (from Paterson instrument). Temperature ranged from 600° C to 1100° C and effective confining pressure from 100 to 150 MPa. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Permeability was measured under static conditions by transient pressure pulse method. Mechanical and micro-structural observations at experimental constant strain rate of 10‑5 s‑1 indicated that the granite was brittle and dilatant up to 900 ° C. At higher temperatures the deformation mode becomes macroscopically ductile, i

  2. Micro mechanical analysis of the coupling between damage and permeability of brittle rocks

    International Nuclear Information System (INIS)

    This paper presents a coupled model for anisotropic damage and permeability variation in brittle rocks by micro-macro approach. The material damage is represented by space distribution of microcracks (crack orientation, crack length and crack aperture). The evolution of damage is determined from a crack propagation criterion. Effective properties of damaged material are studied using micro mechanical considerations. By using Darcy law for macroscopic fluid flow and assuming laminar flow inside microcracks, the total permeability of the cracked material is obtained by a volume averaging procedure taking into account crack aperture distribution in each orientation in the space. (authors)

  3. Modeling and mesoscopic damage constitutive relation of brittle short-fiber-reinforced composites

    Institute of Scientific and Technical Information of China (English)

    刘洪秋; 梁乃刚; 夏蒙棼

    1999-01-01

    Aimed at brittle composites reinforced by randomly distributed short-fibers with a relatively large aspect ratio, stiffness modulus and strength, a mesoscopic material model was proposed. Based on the statistical description,damage mechanisms, damage-induced anisotropy, damage rate effect and stress redistribution, the constitutive relation were derived. By taking glass fiber reinforced polypropylene polymers as an example, the effect of initial orientation distribution of fibers, damage-induced anisotropy, and damage-rate effect on macro-behaviors of composites were quantitatively analyzed. The theoretical predictions compared favorably with the experimental results.

  4. Lymphatic vessels growing apart from blood vessels in transplanted corneas after the blockade of vascular endothelial growth factor C

    Institute of Scientific and Technical Information of China (English)

    Ye Hui; Yan Hao; Zhong Lei; Wang Tao; Deng Juan; Ling Shi-qi

    2016-01-01

    BACKGROUND:Corneal lymphangiogenesis is beneficial to the transport of corneal antigenic materials, and accelerates the process of antigen presentation, thereby playing an important role in corneal immunity. However, due to the paral el outgrowth of corneal blood and lymphatic vessels in transplanted corneas, it is often difficult to accurately evaluate the role of corneal lymphatic vessels in allograft rejection. OBJECTIVE:To explore the development of corneal lymphangiogenesis and angiogenesis in transplanted rat corneas after the blockade of vascular endothelial growth factor C (VEGF-C). METHODS:130 rats used to establish corneal al ogenic transplantation models were equally randomized into two groups:the anti-VEGF-C group and the control group. VEGF-C was blocked in the anti-VEGF-C group by intraperitoneal injection of neutralizing monoclonal anti-VEGF-C antibody every other day for 2 consecutive weeks. Meanwhile, rats in control groups received intraperitoneal injections of saline. Corneal angiogenesis and lymphangiogenesis were characterized using whole mount immunofluorescence, and the immune rejection of the grafts was evaluated by scoring the rejection index (RI). In addition, the expression of VEGF-C was examined by real-time PCR. The relationship of corneal lymphangiogenesis and angiogenesis to RI in transplanted corneas was also characterized. RESULTS AND CONCLUSION:VEGF-C expression was markedly downregulated after VEGF-C blockade. Corneal lymphangiogenesis developed in parallel with corneal angiogenesis in the control group. While there was a mild reduction in blood vessel area (BVA) and a significant decrease in lymphatic vessel area (LVA) in the anti-VEGF-C group (P0.05). the graft survival time in the anti-VEGF-C group was significantly increased compared with that in the control group (P<0.05). Our results show that the outgrowth of lymphatic vessels is separated from that of blood vessels in transplanted corneas by blocking VEGF-C. The blockade

  5. Role of mesenchymal stem cells on cornea wound healing induced by acute alkali burn.

    Directory of Open Access Journals (Sweden)

    Lin Yao

    Full Text Available The aim of this study was to investigate the effects of subconjunctivally administered mesenchymal stem cells (MSCs on corneal wound healing in the acute stage of an alkali burn. A corneal alkali burn model was generated by placing a piece of 3-mm diameter filter paper soaked in NaOH on the right eye of 48 Sprague-Dawley female rats. 24 rats were administered a subconjunctival injection of a suspension of 2×10(6 MSCs in 0.1 ml phosphate-buffered saline (PBS on day 0 and day 3 after the corneal alkali burn. The other 24 rats were administered a subconjunctival injection of an equal amount of PBS as a control. Deficiencies of the corneal epithelium and the area of corneal neovascularization (CNV were evaluated on days 3 and 7 after the corneal alkali burn. Infiltrated CD68(+ cells were detected by immunofluorescence staining. The mRNA expression levels of macrophage inflammatory protein-1 alpha (MIP-1α, tumor necrosis factor-alpha (TNF-α, monocyte chemotactic protein-1 (MCP-1 and vascular endothelial growth factor (VEGF were analyzed using real-time polymerase chain reaction (real-time PCR. In addition, VEGF protein levels were analyzed using an enzyme-linked immunosorbent assay (ELISA. MSCs significantly enhanced the recovery of the corneal epithelium and decreased the CNV area compared with the control group. On day 7, the quantity of infiltrated CD68(+ cells was significantly lower in the MSC group and the mRNA levels of MIP-1α, TNF-α, and VEGF and the protein levels of VEGF were also down-regulated. However, the expression of MCP-1 was not different between the two groups. Our results suggest that subconjunctival injection of MSCs significantly accelerates corneal wound healing, attenuates inflammation and reduces CNV in alkaline-burned corneas; these effects were found to be related to a reduction of infiltrated CD68(+ cells and the down-regulation of MIP-1α, TNF-α and VEGF.

  6. Brittle metallic glass deforms plastically at room temperature in glassy multilayers

    Science.gov (United States)

    Sharma, Parmanand; Yubuta, Kunio; Kimura, Hisamichi; Inoue, Akihisa

    2009-07-01

    Bulk metallic glasses are emerging as a new class of materials that can have applications ranging from structural materials to materials for future nanotechnology. However, catastrophic mechanical failure is a serious issue hindering the use of these materials in engineering applications. Here we introduce an approach to understanding and solving the problem of brittleness of metallic glasses. We have shown that even a very brittle metallic glass (La based) can be forced to deform plastically at room temperature if it is made in the form of multilayers involving other metallic glasses, i.e., a two-phase glass. The mechanically soft glassy layer (La based) having a lower critical shear stress acts as a nucleation or an initiation site for shear bands and the mechanically hard glassy layer (Zr based) acts as an obstacle to the propagation of shear bands. This process results in the multiplication of shear bands. Since the shear bands are associated with a local rise in temperature, a large number of shear bands can raise the overall temperature of the soft layer and eventually can drive it to the supercooled liquid state, where deformation of metallic glass is very large and homogeneous. The results reported here not only clarify the mechanism of large plastic deformation in two-phase glassy alloys but also suggest the possibility of a different kind of two-phase bulk glassy alloys exhibiting large plastic deformation at room temperature.

  7. Brittle and Ductile Behavior in Deep-Seated Landslides: Learning from the Vajont Experience

    Science.gov (United States)

    Paronuzzi, Paolo; Bolla, Alberto; Rigo, Elia

    2016-06-01

    This paper analyzes the mechanical behavior of the unstable Mt. Toc slope before the 1963 catastrophic collapse, considering both the measured data (surface displacements and microseismicity) and the updated geological model of the prehistoric rockslide. From February 1960 up to 9 October 1963, the unstable mass behaved as a brittle-ductile `mechanical system,' characterized by remarkable microseismicity as well as by considerable surface displacements (up to 4-5 m). Recorded microshocks were the result of progressive rock fracturing of distinct resisting stiff parts made up of intact rock (indentations, undulations, and rock bridges). The main resisting stiff part was a large rock indentation located at the NE extremity of the unstable mass that acted as a mechanical constraint during the whole 1960-1963 period, inducing a progressive rototranslation toward the NE. This large constraint failed in autumn 1960, when an overall slope failure took place, as emphasized by the occurrence of the large perimetrical crack in the upper slope. In this circumstance, the collapse was inhibited by a reblocking phenomenon of the unstable mass that had been previously destabilized by the first reservoir filling. Progressive failure of localized intact rock parts progressively propagated westwards as a consequence of the two further filling-drawdown cycles of the reservoir (1962 and 1963). The characteristic brittle-ductile behavior of the Vajont landslide was made possible by the presence of a very thick (40-50 m) and highly deformable shear zone underlying the upper rigid rock mass (100-120 m thick).

  8. PREDICTION OF CHARACTERISTIC LENGTH AND FRACTURE TOUGHNESS IN DUCTILE-BRITTLE TRANSITION

    Energy Technology Data Exchange (ETDEWEB)

    Lam, P

    2008-04-15

    Finite element method was used to analyze the three-point bend experimental data of A533B-1 pressure vessel steel obtained by Sherry, Lidbury, and Beardsmore [1] from -160 to -45 C within the ductile-brittle transition regime. As many researchers have shown, the failure stress ({sigma}{sub f}) of the material could be approximated as a constant. The characteristic length, or the critical distance (r{sub c}) from the crack tip, at which {sigma}{sub f} is reached, is shown to be temperature dependent based on the crack tip stress field calculated by the finite element method. With the J-A{sub 2} two-parameter constraint theory in fracture mechanics, the fracture toughness (J{sub C} or K{sub JC}) can be expressed as a function of the constraint level (A{sub 2}) and the critical distance r{sub c}. This relationship is used to predict the fracture toughness of A533B-1 in the ductile-brittle transition regime with a constant {sigma}{sub f} and a set of temperature-dependent r{sub c}. It can be shown that the prediction agrees well with the test data for wide range of constraint levels from shallow cracks (a/W= 0.075) to deep cracks (a/W= 0.5), where a is the crack length and W is the specimen width.

  9. Electromagnetic and neutron emissions from brittle rocks failure: Experimental evidence and geological implications

    Indian Academy of Sciences (India)

    A Carpinteri; G Lacidogna; O Borla; A Manuello; G Niccolini

    2012-02-01

    It has been observed energy emission in the form of electromagnetic radiation, clearly indicating charge redistribution, and neutron bursts, necessarily involving nuclear reactions, during the failure process of quasi-brittle materials such as rocks, when subjected to compression tests. The material used is Luserna stone, which presents a very brittle behaviour during compression failure. The observed phenomenon of high-energy particle emission, i.e., electrons and neutrons, can be explained in the framework of the superradiance applied to the solid state, where individual atoms lose their identity and become part of different plasmas, electronic and nuclear. Since the analysed material contains iron, it can be conjectured that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. These complex phenomenologies are confirmed by Energy Dispersive X-ray Spectroscopy (EDS) tests conducted on Luserna stone specimens, and found additional evidences at the Earth’s Crust scale, where electromagnetic and neutron emissions are observed just in correspondence with major earthquakes. In this context, the effects of piezonuclear reactions can be also considered from a geophysical and geological point of view.

  10. KrF excimer laser precision machining of hard and brittle ceramic biomaterials.

    Science.gov (United States)

    Huang, Yao-Xiong; Lu, Jian-Yi; Huang, Jin-Xia

    2014-06-01

    KrF excimer laser precision machining of porous hard-brittle ceramic biomaterials was studied to find a suitable way of machining the materials into various desired shapes and sizes without distorting their intrinsic structure and porosity. Calcium phosphate glass ceramics (CPGs) and hydroxyapatite (HA) were chosen for the study. It was found that KrF excimer laser can cut both CPGs and HA with high efficiency and precision. The ablation rates of CPGs and HA are respectively 0.081 µm/(pulse J cm(-2)) and 0.048 µm/(pulse  J cm(-2)), while their threshold fluences are individually 0.72 and 1.5 J cm(-2). The cutting quality (smoothness of the cut surface) is a function of laser repetition rate and cutting speed. The higher the repetition rate and lower the cutting speed, the better the cutting quality. A comparison between the cross sections of CPGs and HA cut using the excimer laser and using a conventional diamond cutting blade indicates that those cut by the excimer laser could retain their intrinsic porosity and geometry without distortion. In contrast, those cut by conventional machining had distorted geometry and most of their surface porosities were lost. Therefore, when cutting hard-brittle ceramic biomaterials to prepare scaffold and implant or when sectioning them for porosity evaluation, it is better to choose KrF excimer laser machining.

  11. An approach to scaling size effect on strength of quasi-brittle biomedical materials.

    Science.gov (United States)

    Lei, Wei-Sheng; Su, Peng

    2016-09-01

    Two-parameter Weibull statistics is commonly used for characterizing and modeling strength distribution of biomedical materials and its size dependence. The calibrated scale parameter and shape factor are usually sensitive to specimen size. Since Weibull statistics is subject to the weakest link postulate, this work proposed to directly resort to the weakest-link formulation for the cumulative failure probability to characterize size effect on strength distribution of quasi-brittle biomedical materials. As a preliminary examination, the approach was assessed by two sets of published strength data. It shows that the resultant expression for the cumulative probability follows either Weibull distribution or other type of distributions. The calibrated model parameters are independent of specimen size, so they can be used to transfer strength distribution from one set of specimens to another set of specimens with geometrical similarity under same loading mode. These initial results motivate a more comprehensive validation of the proposed approach to proceed via a larger set of case studies covering different quasi-brittle biomedical materials over a wider range of size variation. PMID:27266476

  12. Superior room-temperature ductility of typically brittle quasicrystals at small sizes.

    Science.gov (United States)

    Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

    2016-01-01

    The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ∼4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals-dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices. PMID:27515779

  13. Brittle Creep Failure, Critical Behavior, and Time-to-Failure Prediction of Concrete under Uniaxial Compression

    Directory of Open Access Journals (Sweden)

    Yingchong Wang

    2015-01-01

    Full Text Available Understanding the time-dependent brittle deformation behavior of concrete as a main building material is fundamental for the lifetime prediction and engineering design. Herein, we present the experimental measures of brittle creep failure, critical behavior, and the dependence of time-to-failure, on the secondary creep rate of concrete under sustained uniaxial compression. A complete evolution process of creep failure is achieved. Three typical creep stages are observed, including the primary (decelerating, secondary (steady state creep regime, and tertiary creep (accelerating creep stages. The time-to-failure shows sample-specificity although all samples exhibit a similar creep process. All specimens exhibit a critical power-law behavior with an exponent of −0.51 ± 0.06, approximately equal to the theoretical value of −1/2. All samples have a long-term secondary stage characterized by a constant strain rate that dominates the lifetime of a sample. The average creep rate expressed by the total creep strain over the lifetime (tf-t0 for each specimen shows a power-law dependence on the secondary creep rate with an exponent of −1. This could provide a clue to the prediction of the time-to-failure of concrete, based on the monitoring of the creep behavior at the steady stage.

  14. Nano finish grinding of brittle materials using electrolytic in-process dressing (ELID) technique

    Indian Academy of Sciences (India)

    M Rahman; A Senthil Kumar; H S Lim; K Fatima

    2003-10-01

    Recent developments in grinding have opened up new avenues for finishing of hard and brittle materials with nano-surface finish, high tolerance and accuracy. Grinding with superabrasive wheels is an excellent way to produce ultraprecision surface finish. However, superabrasive diamond grits need higher bonding strength while grinding, which metal-bonded grinding wheels can offer. Truing and dressing of the wheels are major problems and they tend to glaze because of wheel loading. When grinding with superabrasive wheels, wheel loading can be avoided by dressing periodically to obtain continuous grinding. Electrolytic inprocess dressing (ELID) is the most suitable process for dressing metal-bonded grinding wheels during the grinding process. Nano-surface finish can be achieved only when chip removal is done at the atomic level. Recent developments of ductile mode machining of hard and brittle materials show that plastically deformed chip removal minimizes the subsurface damage of the workpiece. When chip deformation takes place in the ductile regime, a defect-free nano-surface is possible and it completely eliminates the polishing process. ELID is one of the processes used for atomic level metal removal and nano-surface finish. However, no proper and detailed studies have been carried out to clarify the fundamental characteristics for making this process a robust one. Consequently, an attempt has been made in this study to understand the fundamental characteristics of ELID grinding and their influence on surface finish.

  15. Research on Ultrasonic Vibration Grinding of the Hard and Brittle Materials

    Institute of Scientific and Technical Information of China (English)

    YANG Xin-hong; HAN Jie-cai; ZHANG Yu-min; ZUO Hong-bo; ZHANG Xue-jun

    2006-01-01

    It is well known that grinding techniques are main methods to machine hard and brittle materials such as engineering ceramics. But the conventional grinding has many shortcomings such as poorer surface finish, quicker wear and tear of grinding tools, lower efficiency and so on. Ultrasonic vibration grinding (UVG) which combines ultrasonic machining and grinding emerged as a developing and promising technique in recent years. In this paper, experimental studies on UVG were conducted on several kinds of hard and brittle material by altering processing parameters such as vibration frequency and its amplitude, diamond abrasive grit size, cutting depth, feeding speed and rotary speed of tools. The experimental results show that alteration in any of above mentioned parameters will bring effects on the processed surface finish of these materials. Of them, the diamond abrasive grit size has the greatest. Moreover, conventional grinding experiments were also carried out on these materials. By comparison, it was found that the UVG is superior to the conventional method in terms of the ground surface quality, the working efficiency and the wear rate of tools.

  16. Visco-poroelastic damage model for brittle-ductile failure of porous rocks

    Science.gov (United States)

    Lyakhovsky, Vladimir; Zhu, Wenlu; Shalev, Eyal

    2015-04-01

    The coupling between damage accumulation, dilation, and compaction during loading of sandstones is responsible for different structural features such as localized deformation bands and homogeneous inelastic deformation. We distinguish and quantify the role of each deformation mechanism using new mathematical model and its numerical implementation. Formulation includes three different deformation regimes: (I) quasi-elastic deformation characterized by material strengthening and compaction; (II) cataclastic flow characterized by damage increase and compaction; and (III) brittle failure characterized by damage increase, dilation, and shear localization. Using a three-dimensional numerical model, we simulate the deformation behavior of cylindrical porous Berea sandstone samples under different confining pressures. The obtained stress, strain, porosity changes and macroscopic deformation features well reproduce the laboratory results. The model predicts different rock behavior as a function of confining pressures. The quasi-elastic and brittle regimes associated with formation of shear and/or dilatant bands occur at low effective pressures. The model also successfully reproduces cataclastic flow and homogeneous compaction under high pressures. Complex behavior with overlap of common features of all regimes is simulated under intermediate pressures, resulting with localized compaction or shear enhanced compaction bands. Numerical results elucidate three steps in the formation of compaction bands: (1) dilation and subsequent shear localization, (2) formation of shear enhanced compaction band, and (3) formation of pure compaction band.

  17. Analysis of two precipitation methods on the yield, structural features and activity of sulfated polysaccharides from Gracilaria cornea (Rhodophyta

    Directory of Open Access Journals (Sweden)

    Ricardo Basto Souza

    2015-03-01

    Full Text Available The global demand for natural products from seaweeds has increased worldwide; however, no description of the use of isoamly alcohol (IAA for obtaining of sulfated polysaccharides (SPs has been reported. We investigated the efficiency of two precipitation methods (M in obtaining SPs from the red seaweed Gracilaria cornea. SPs enzymatically isolated were concentrated with cetylpyridinium chloride (M I or IAA (M II and extracts were examined with regard to their yield, structural features and in vitro effects on the activated partial thromboplastin time (APTT using normal human plasma and standard heparin (193 IU mg-1. Yield difference reached 12.99%. Quantitative determination of sulfate was similar between the two methods (̴ 26%, but extracts revealed different pattern on charge density by agarose gel electrophoresis. Whereas both extracts revealed as agarocolloids, alternative M II was also efficient for lipids, proteins and nucleic acids according to the infrared analysis. Extracts had virtually no effect on APPT (1.95 and 2 IU mg-1 for M I and M II, respectively. The results revealed IAA as an alternative solvent for obtaining SPs from the red seaweed G. cornea, depending on the industry’ usage criterion.

  18. Nature-Derived Aloe Vera Gel Blended Silk Fibroin Film Scaffolds for Cornea Endothelial Cell Regeneration and Transplantation.

    Science.gov (United States)

    Kim, Do Kyung; Sim, Bo Ra; Khang, Gilson

    2016-06-22

    The goal of this study was to fabricate an appropriate replacement for cadaveric corneas to overcome a shortage of cadaveric corneas for transplantation. In this study, we fabricated transparent ultrathin film scaffolds with nature-derived aloe vera (AV) gel and silk fibroin (SF) for corneal endothelial cells (CECs). The scaffolds were subjected to analysis of transparency and contact angle using field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy to determine their physical and chemical properties. FESEM images revealed that the critical morphology of CECs was formed on the AV gel in the blend with SF rather than in the scaffold with SF alone. The cell proliferation, phenotype, and specific gene marker expressions for CECs were determined by MTT assays, immunofluorescence, and reverse transcription polymerase chain reactions. Incorporation of a small amount of AV gel increased the cell viability and maintained its functions well. The scaffolds were easily handled for transplantation into rabbit eyes with small incisions and examined by their transparency after transplantation and histological staining. The scaffolds attached to the surface of the corneal stroma and integrated with surrounding corneal tissue without a significant inflammatory reaction. These results indicate that AV blended SF film scaffolds might be a suitable substitute for alternative corneal grafts for transplantation. PMID:27243449

  19. In vitro evaluation of the permeation enhancing effect of polycarbophil-cysteine conjugates on the cornea of rabbits.

    Science.gov (United States)

    Hornof, Margit D; Bernkop-Schnürch, Andreas

    2002-12-01

    It was the aim of this study to investigate the permeation enhancing effect of thiolated polycarbophil on the cornea of rabbits in vitro. The proposed reaction mechanism involves the opening of the tight junctions in the corneal epithelium. The modification of polycarbophil was achieved via covalent attachment of L-cysteine mediated by a carbodiimide. Transcorneal permeation studies were performed in Ussing-type diffusion chambers. As model compounds, sodium fluorescein, as a marker for paracellular transport, and dexamethasone phosphate were used. To evaluate potential corneal damage the corneal hydration level of each cornea was determined. Polycarbophil-cysteine was found to increase the permeation of sodium fluorescein 2.2-fold and that of dexamethasone phosphate 2.4-fold in comparison to the unmodified polymer. The concentration of dexamethasone in the acceptor medium was 1.5-fold increased. As evidenced by the corneal hydration level, polycarbophil-cysteine did not damage the corneal tissues. Therefore, polycarbophil-cysteine conjugates seem to be promising excipients for ocular drug delivery systems where they might be used as safe permeation enhancers.

  20. Quantitative & qualitative analysis of endothelial cells of donor cornea before & after penetrating keratoplasty in different pathological conditions

    Directory of Open Access Journals (Sweden)

    Aruna K.R. Gupta

    2016-01-01

    Full Text Available Background & objectives: Endothelial cells of the donor cornea are known to be affected quantitatively and qualitatively in different pathological conditions after penetrating keratoplasty (PK and this has direct effect on the clarity of vision obtained after PK. This study was undertaken to analyze the qualitative and quantitative changes in donor endothelial cells before and after PK in different pathological conditions. Methods: A prospective investigational analysis of 100 consecutive donor corneas used for penetrating keratoplasty between June 2006 and June 2008, was conducted. The patients were evaluated on the first day, at the end of first week, first month, third and six months and one year. Results: A decrease was observed in endothelial cell count in all pathological conditions. After one year of follow up the loss was 33.1 per cent in corneal opacity, 45.9 per cent in acute infective keratitis (AIK, 58.5 per cent in regrafts, 28.5 per cent in pseudophakic bullous keratopathy (PBK, 37 per cent in descemetocele, 27 per cent in keratoconus and 35.5 per cent in aphakic bullous keratopathy (ABK cases. Interpretation & conclusions: The endothelial cell loss was highest in regraft cases which was significant (P<0.05, while the least endothelial cell loss was seen in keratoconus cases. The cell loss was associated with increase in coefficient of variation (CV, i.e. polymegathism and pleomorphism. Inspite of this polymegathism and pleomorphism, the clarity of the graft was maintained.

  1. Gaussian process prediction of the stress-free configuration of pre-deformed soft tissues: Application to the human cornea.

    Science.gov (United States)

    Businaro, Elena; Studer, Harald; Pajic, Bojan; Büchler, Philippe

    2016-04-01

    Image-based modeling is a popular approach to perform patient-specific biomechanical simulations. One constraint of this technique is that the shape of soft tissues acquired in-vivo is deformed by the physiological loads. Accurate simulations require determining the existing stress in the tissues or their stress-free configurations. This process is time consuming, which is a limitation to the dissemination of numerical planning solutions to clinical practice. In this study, we propose a method to determine the stress-free configuration of soft tissues using a Gaussian process (GP) regression. The prediction relies on a database of pre-calculated results to enable real time predictions. The application of this technique to the human cornea showed a level of accuracy five to ten times higher than the accuracy of the topographic device used to obtain the patients' anatomy; results showed that for almost all optical indices, the predicted curvature error did not exceed 0.025 D, while the wavefront aberration percentage error did not overcome 5%. In this context, we believe that GP models are suitable for predicting the stress free configuration of the cornea and can be used in planning tools based on patient-specific finite element simulations. Due to the high level of accuracy required in ophthalmology, this approach is likely to be appropriate for other applications requiring the definition of the relaxed shape of soft tissues. PMID:26920075

  2. Two-photon spectral fluorescence lifetime and second-harmonic generation imaging of the porcine cornea with a 12-femtosecond laser microscope

    Science.gov (United States)

    Batista, Ana; Breunig, Hans Georg; Uchugonova, Aisada; Morgado, António Miguel; König, Karsten

    2016-03-01

    Five dimensional microscopy with a 12-fs laser scanning microscope based on spectrally resolved two-photon autofluorescence lifetime and second-harmonic generation (SHG) imaging was used to characterize all layers of the porcine cornea. This setup allowed the simultaneous excitation of both metabolic cofactors, NAD(P)H and flavins, and their discrimination based on their spectral emission properties and fluorescence decay characteristics. Furthermore, the architecture of the stromal collagen fibrils was assessed by SHG imaging in both forward and backward directions. Information on the metabolic state and the tissue architecture of the porcine cornea were obtained with subcellular resolution, and high temporal and spectral resolutions.

  3. Transient creep, aseismic damage and slow failure in Carrara marble deformed across the brittle-ductile transition

    Science.gov (United States)

    Schubnel, A.; Walker, E.; Thompson, B. D.; Fortin, J.; Guéguen, Y.; Young, R. P.

    2006-09-01

    Two triaxial compression experiments were performed on Carrara marble at high confining pressure, in creep conditions across the brittle-ductile transition. During cataclastic deformation, elastic wave velocity decrease demonstrated damage accumulation (microcracks). Keeping differential stress constant and reducing normal stress induced transient creep events (i.e., fast accelerations in strain) due to the sudden increase of microcrack growth. Tertiary creep and brittle failure followed as damage came close to criticality. Coalescence and rupture propagation were slow (60-200 seconds with ~150 MPa stress drops and millimetric slips) and radiated little energy in the experimental frequency range (0.1-1 MHz). Microstructural analysis pointed out strong interactions between intra-crystalline plastic deformation (twinning and dislocation glide) and brittle deformation (microcracking) at the macroscopic level. Our observations highlight the dependence of acoustic efficiency on the material's rheology, at least in the ultrasonic frequency range, and the role played by pore fluid diffusion as an incubation process for delayed failure triggering.

  4. Estimation of brittle fracture behavior of SA508 carbon steel by considering temperature dependence of damage model

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Shin Beom; Jeong, Jae Uk; Choi, Jae Boong [Sungkyunkwan Univ., Seoul (Korea, Republic of); Chang, Yoon Suk [Kyunghee Univ., Seoul (Korea, Republic of); Kim, Min Chul [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of); Lee, Bong Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    The aim of this study was to determine the brittle fracture behavior of reactor pressure vessel steel by considering the temperature dependence of a damage model. A multi island genetic algorithm was linked to a Weibull stress model, which is the model typically used for brittle fracture evaluation, to improve the calibration procedure. The improved calibration procedure and fracture toughness test data for SA508 carbon steel at the temperatures -60 .deg. C, -80 .deg. C, and -100 .deg. C were used to decide the damage parameters required for the brittle fracture evaluation. The model was found to show temperature dependence, similar to the case of NUREG/CR 6930. Finally, on the basis of the quantification of the difference between 2- and 3-parameter Weibull stress models, an engineering equation that can help obtain more realistic fracture behavior by using the simpler 2-parameter Weibull stress model was proposed.

  5. 人工角膜及其相关材料%Artificial cornea and related materials

    Institute of Scientific and Technical Information of China (English)

    严拓; 敖宁建; 覃百花; 邓华

    2008-01-01

    学术背景:对于同种异体角膜移植失败的患者,人工角膜移植便成了复明的惟一希望.人工角膜的研究虽然已经跨越2个世纪,但由于各种因素限制,角膜植入术仍然只能在少数中心开展.近年来,由于相关学科的飞速发展,人工角膜也进入了快速发展时期.目的:从材料选择、片型设计、材料改性以及临床试验等角度进行叙述,比较不同结构人工角膜各自特点,并指出目前人工角膜所存在的主要问题,对理想的人工角膜提出了新的见解.检索策略:作者应用计算机检索中国全文期刊数据库(CNKI),Springer,EI,Blackwell数据库1993-01/2007-12与人工角膜相关文献.所用中文检索词有"人工角膜、角膜穿透术";英文榆索词包括"artificial cornea,penetrating keratoplasty".纳入标准:文章内容与人工角膜材料、片型设计、临床研究有关.排除标准:较为陈旧,重复性研究.文献评价:共检索到86篇相关文献,68篇文献符合上述要求,其中12篇为综述性文献,37篇为基础性研究文献,19篇为临床研究文献,从中选择30篇进行综述.资料综合:人工角膜材料包括光学镜柱材料(水凝胶、聚甲基丙烯酸甲酯、硅凝胶、玻璃)和支架材料(氟碳聚合物、羟基磷灰石、生物材料).材料改性包括材料化学改性、材料表面处理、材料表面修饰、材料表面等离子处理.不同的角膜片型设计中,较为成功的是AlphaCor和Osteo-Odonto,并获得了美国食品药品管理局批准,进入临床阶段.结论:提高人工角膜与组织黏附度,减少并发症是长期研究的重点领域,而材料选择、材料改性、片型设计等是解决的关键.

  6. Friction experiments of halite in brittle-ductile transition with high pore pressure

    Science.gov (United States)

    Noda, H.; Takahashi, M.; Katayama, I.

    2015-12-01

    Flow stress of rock (τ) approximately linearly depends on normal stress on a shear zone (σn) minus pore pressure (p) in a brittle regime, and insensitive to σn in a fully plastic regime where pores are isolated and filled with fluid of high pressure comparable to the mean stress, like oil drops in water. How p affects τ in the transitional regime is not fully understood, although it is a key to understanding many important geological problems such as role of fluids in deformation mechanism, stress and strength profile of the crust, seismogenic depth range, and so on. The effective normal stress σe is often given by σe = σn - α p (α: a constant around 1 in the brittle regime), and frictional resistance, by τ = f σe (f: friction coefficient). Recently, Hirth and Beeler [2015] proposed a model of the effective stress law in the transitional regime. Because of increasing ratio of real area of contact to nominal area of frictional interface, α may decrease to zero towards fully plastic regime, causing a sharper peak in the strength profile than a conventional Brace-Goetze strength profile which is sometimes referred to as "Christmas tree". We investigated this idea by means of friction experiments at high temperature and pore pressure. We used halite as an analogue material which undergoes a transition from brittle to fully plastic regime under convenient conditions [Shimamoto, 1986]. We conducted friction experiments of a pre-cut sliding interface filled with halite gouge with gas-medium triaxial apparatus in Hiroshima University, at 150 MPa confining pressure, from room temperature to 210 °C, and from atmospheric pressure to more than 100 MPa fluid (argon gas) pressure in a reservoir. Our preliminary result shows that the sharp peak in the flow stress is probably absent. A phenomenological smooth connection proposed by Shimamoto and Noda [2014] based on friction experiments without a jacket (i.e. atmospheric pore pressure) may work in explaining the

  7. Ultraprecision, high stiffness CNC grinding machines for ductile mode grinding of brittle materials

    Science.gov (United States)

    McKeown, Patrick A.; Carlisle, Keith; Shore, Paul; Read, R. F.

    1990-10-01

    Under certain controlled conditions it is now possible to machine brittle materials such as glasses and ceramics using single or multi-point diamond tools (grinding), so that material is removed by plastic flow, leaving crack-free surfaces. This process is called 'shear' or 'ductile' mode grinding. It represents a major breakthrough in modern manufacturing engineering since it promises to enable: - complex optical components, both transmission and reflecting to be generated by advanced CNC machines with very little (or even zero) subsequent polishing. - complex shaped components such as turbine blades, nozzle guide vanes, etc. to be finish machined after near net shape forming, to high precision in advanced ceramics such as silicon nitride, without inducing micro-cracking and thus lowering ultimate rupture strength and fatigue life. Ductile mode "damage free" grinding occurs when the volume of materials stressed by each grit of the grinding wheel is small enough to yield rather than exhibit brittle fracture, i.e. cracking. In practice, this means maintaining the undeformed chip thickness to below the ductile-brittle transition value; this varies from material to material but is generally in the order of 0.1 pm or 100 nm, (hence the term "nanogrinding" is sometimes used) . Thus the critical factors for operating successfully in the ductile regime are machine system accuracy and dynamic stiffness between each grit and the workpiece. In detail this means: (i) High precision 'truing' of the diamond grits, together with dressing of the wheel bond to ensure adequate ' openness'; (ii) Design and build of the grinding wheel spindle with very high dynamic stiffness; error motions, radial and axial, must be considerably less than 100 nfl. (iii) Design and build of the workpiece carriage motion system with very high dynamic stiffness; error motions, linear or rotary, must be well within 100 nm. (iv) Smooth, rumble-free, high-stiffness servo-drives controlling the motions

  8. De Novo Adult Transcriptomes of Two European Brittle Stars: Spotlight on Opsin-Based Photoreception.

    Directory of Open Access Journals (Sweden)

    Jérôme Delroisse

    Full Text Available Next generation sequencing (NGS technology allows to obtain a deeper and more complete view of transcriptomes. For non-model or emerging model marine organisms, NGS technologies offer a great opportunity for rapid access to genetic information. In this study, paired-end Illumina HiSeqTM technology has been employed to analyse transcriptomes from the arm tissues of two European brittle star species, Amphiura filiformis and Ophiopsila aranea. About 48 million Illumina reads were generated and 136,387 total unigenes were predicted from A. filiformis arm tissues. For O. aranea arm tissues, about 47 million reads were generated and 123,324 total unigenes were obtained. Twenty-four percent of the total unigenes from A. filiformis show significant matches with sequences present in reference online databases, whereas, for O. aranea, this percentage amounts to 23%. In both species, around 50% of the predicted annotated unigenes were significantly similar to transcripts from the purple sea urchin, the closest species to date that has undergone complete genome sequencing and annotation. GO, COG and KEGG analyses were performed on predicted brittle star unigenes. We focused our analyses on the phototransduction actors involved in light perception. Firstly, two new echinoderm opsins were identified in O. aranea: one rhabdomeric opsin (homologous to vertebrate melanopsin and one RGR opsin. The RGR-opsin is supposed to be involved in retinal regeneration while the r-opsin is suspected to play a role in visual-like behaviour. Secondly, potential phototransduction actors were identified in both transcriptomes using the fly (rhabdomeric and mammal (ciliary classical phototransduction pathways as references. Finally, the sensitivity of O.aranea to monochromatic light was investigated to complement data available for A. filiformis. The presence of microlens-like structures at the surface of dorsal arm plate of O. aranea could potentially explain phototactic

  9. Are magma chamber boundaries brittle or ductile? Rheological insights from thermal stressing experiments

    Science.gov (United States)

    Browning, John; Meredith, Philip G.; Gudmundsson, Agust; Lavallée, Yan; Drymoni, Kyriaki

    2015-04-01

    Rheological conditions at magma chamber boundaries remain poorly understood. Many field observations of deeply-eroded and well-exposed plutons, for example Slaufrudalur and Geitafell in SE Iceland, exhibit a sharp transition between what may have been a partially or fully molten magma chamber and its surrounding brittle host rock. Some studies have suggested a more gradual change in the rheological properties of chamber boundaries, marked by a ductile halo, which is likely to exert a significant impact on their rheological response. Understanding the state and rheological conditions of magma-rock interface and interaction is essential for constraining chamber-boundary failure conditions leading to dyke propagation, onset of volcanic eruption as well as caldera fault formation. We present results from a series of thermal stressing experiments in which we attempt to recreate the likely conditions at magma-chamber boundaries. Cores of volcanic material (25 mm diameter x 65 mm long) were heated to magmatic temperatures under controlled conditions in a horizontal tube furnace (at atmospheric pressure) and then held at those temperatures over variable dwell times. At the maximum temperatures reached, the inner part of the samples undergoes partial melting whilst the outer part remains solid. After cooling the brittle shells commonly exhibit axial, fissure-like fractures with protruded blobs of solidified melt. This phenomenon is interpreted as being the result of volume expansion during partial melting. The internal melt overpressure generates fluid-driven fractures analogous to filter-pressing textures or on a large scale, dykes. We complement our observations with acoustic emission and seismic velocity data obtained from measurements throughout the experiments. These complementary data are used to infer the style and timescale of fracture formation. Our results pinpoint the temperature ranges over which brittle fractures form as a result of internal melt overpressure

  10. Slip transfer across fault discontinuities within granitic rock at the brittle-ductile transition

    Science.gov (United States)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.

    2011-12-01

    Fault mechanics are strongly influenced by discontinuities in fault geometry and constitutive differences between the brittle and ductile regions of the lithosphere. This project uses field observations, laboratory analysis and numerical modeling to investigate deformational processes within a contractional step at the brittle-ductile transition, and in particular, how slip is transferred between faults via ductile deformation across the step. The Bear Creek field area (central Sierra Nevada, CA) is comprised of late Cretaceous biotite-hornblende granodiorite and experienced a period of faulting at the brittle-ductile transition. Abundant echelon faults in Bear Creek, some of which were seismically active, provide many textbook examples of contractional steps, which are characterized by well-developed ductile fabrics. The occurrence of hydrothermal alteration halos and hydrothermal minerals in fracture fill documents the presence of water, which we suggest played a weakening role in the constitutive behavior of the granodiorite. Furthermore, the mechanism that accomplishes slip transfer in contractional steps appears to be related to water-enhanced ductile deformation. We focus our investigation on Outcrop SG10, which features a 10cm thick aplite dike that is offset 0.45m through a contractional step between two sub-parallel left-lateral faults. Within the step, the aplite undergoes dramatic thinning (stretch ~1/10) and the granodiorite is characterized by a well-developed mylonitic foliation, in which quartz and biotite plastically flow around larger grains of feldspars, hornblende and opaque minerals. Electron backscatter diffraction (EBSD) analysis gives a more quantitative depiction of the active micromechanics and reveals how slip is accommodated at the crystal scale throughout the step. We use Abaqus, a commercial finite element software, to test several constitutive laws that may account for the deformation observed both macro- and microscopically throughout

  11. Capsules with evolving brittleness to resist the preparation of self-healing concrete

    Directory of Open Access Journals (Sweden)

    Gruyaert, E.

    2016-09-01

    Full Text Available Capsules for self-healing concrete have to possess multifunctional properties and it would be an enormous advantage in the valorization process when they could also be mixed in. Therefore, we aimed to develop capsules with evolving brittleness. Capsules with high initial flexibility were prepared by adding a plasticizer to an ethyl cellulose matrix. During hardening of the concrete, the plasticizing agent should leach out to the moist environment yielding more brittle capsules which break upon crack appearance. The tested capsules could easily be mixed in during concrete production. However, incompatibility issues between the capsule wall and the inner polymeric healing agent appeared. Moreover, the capsules became insufficiently brittle and the bond strength to the cementitious matrix was too weak. Consequently, multilayer capsules were tested. These capsules had a high impact resistance to endure concrete mixing and were able to break upon crack formation.Las cápsulas para la auto-reparación del hormigón tienen que poseer propiedades multifuncionales. Una enorme ventaja en el proceso para su valorización se obtendría si aquellas pudieran resistir con éxito el mezclado. Por lo tanto, nos propusimos desarrollar cápsulas cuya fragilidad evoluciona. Cápsulas con una alta flexibilidad inicial se prepararon mediante la adición de un plastificante a una matriz de etil celulosa. Durante el endurecimiento del hormigón, el agente plastificante debe filtrarse hacia el medio ambiente húmedo produciendo cápsulas más frágiles que se rompen con el surgimiento de fisuras. Las cápsulas pudieron ser fácilmente mezcladas durante la producción de hormigón. Sin embargo, aparecieron problemas de incompatibilidad entre la pared de la cápsula y el agente de curación polimérico interior. Por otra parte, las cápsulas se comportaron insuficientemente frágiles y con una baja adherencia hacia la matriz cementicia. En consecuencia, se probaron las c

  12. Numerical simulation of dynamic brittle fracture of pipeline steel subjected to DWTT using XFEM-based cohesive segment technique

    Directory of Open Access Journals (Sweden)

    Reza H. Talemi

    2016-03-01

    Full Text Available In the past several numerical studies have addressed the ductile mode of fracture propagation. However, the brittle mode of pipeline failure has not received as much attention yet. The main objective of this study is to predict brittle fracture behaviour of API X70 pipeline steel by means of a numerical approach. To this end, the eXtended Finite Element Method (XFEM-based cohesive segment technique is used to model Drop Weight Tear Test (DWTT of X70 pipeline steel at -100°C. In this model the dynamic stress intensity factor and crack velocity are calculated at the crack tip at each step of crack propagation.

  13. Resilience and Brittleness in a Nuclear Emergency Response Simulation: Focusing on Team Coordination Activity

    International Nuclear Information System (INIS)

    The current work presents results from a cognitive task analysis (CTA) of a nuclear disaster simulation. Audio-visual records were collected from an emergency room team composed of individuals from 26 different agencies as they responded to multiple scenarios in a simulated nuclear disaster. This simulation was part of a national emergency response training activity for a nuclear power plant located in a developing country. The objectives of this paper are to describe sources of resilience and brittleness in these activities, identify cues of potential improvements for future emergency simulations, and leveraging the resilience of the emergency response System in case of a real disaster. Multiple CTA techniques were used to gain a better understanding of the cognitive dimensions of the activity and to identify team coordination and crisis management patterns that emerged from the simulation training. (authors)

  14. Nucleating and propagating of nanocrack in dislocation-free zone in brittle materials

    Institute of Scientific and Technical Information of China (English)

    褚武扬; 高克玮; 陈奇志; 王燕斌; 肖纪美

    1995-01-01

    Nudeating and propagating of nanocrack forming in dislocation-free zone (DFZ) for a brittle material, TiAl alloy, was studied through in situ tensile test in TEM and analyzed using micro-fracture mechanics. The results show that many of dislocations can be emitted from a crack tip when the applied stress intensity KIa is larger than the stress intensity for dislocation emission KIe = 1.4MPa·m1/2 and a DFZ is formed after reaching equilibrium. The stress in a certain site in the DFZ, which is an elastic zone and is thinned gradually through dislocation multiplication and motion in the plastic zone, may be equal to the cohesive strength, resulting in initiating of a nanocrack in the DFZ or sometimes at the notch tip. The nanocrack forming in the DFZ is stable and can propagate into a cleavage microcrack through multiplication and movement of dislocations in the plastic zone under constant displacement condition.

  15. Generalized Continuum: from Voigt to the Modeling of Quasi-Brittle Materials

    Directory of Open Access Journals (Sweden)

    Jamile Salim Fuina

    2010-12-01

    Full Text Available This article discusses the use of the generalized continuum theories to incorporate the effects of the microstructure in the nonlinear finite element analysis of quasi-brittle materials and, thus, to solve mesh dependency problems. A description of the problem called numerically induced strain localization, often found in Finite Element Method material non-linear analysis, is presented. A brief historic about the Generalized Continuum Mechanics based models is presented, since the initial work of Voigt (1887 until the more recent studies. By analyzing these models, it is observed that the Cosserat and microstretch approaches are particular cases of a general formulation that describes the micromorphic continuum. After reporting attempts to incorporate the material microstructure in Classical Continuum Mechanics based models, the article shows the recent tendency of doing it according to assumptions of the Generalized Continuum Mechanics. Finally, it presents numerical results which enable to characterize this tendency as a promising way to solve the problem.

  16. Nominally brittle cracks in inhomogeneous solids: From microstructural disorder to continuum-level scale

    Science.gov (United States)

    Barés, Jonathan; Barlet, Marina; Rountree, Cindy; Barbier, Luc; Bonamy, Daniel

    2014-11-01

    We analyze the intermittent dynamics of cracks in heterogeneous brittle materials and the roughness of the resulting fracture surfaces by investigating theoretically and numerically crack propagation in an elastic solid of spatially-distributed toughness. The crack motion split up into discrete jumps, avalanches, displaying scale-free statistical features characterized by universal exponents. Conversely, the ranges of scales are non-universal and the mean avalanche size and duration depend on the loading microstructure and specimen parameters according to scaling laws which are uncovered. The crack surfaces are found to be logarithmically rough. Their selection by the fracture parameters is formulated in term of scaling laws on the structure functions measured on one-dimensional roughness profiles taken parallel and perpendicular to the direction of crack growth.

  17. Morphological study of elastic-plastic-brittle transitions in disordered media.

    Science.gov (United States)

    Kale, Sohan; Ostoja-Starzewski, Martin

    2014-10-01

    We use a spring lattice model with springs following a bilinear elastoplastic-brittle constitutive behavior with spatial disorder in the yield and failure thresholds to study patterns of plasticity and damage evolution. The elastic-perfectly plastic transition is observed to follow percolation scaling with the correlation length critical exponent ν≈1.59, implying the universality class corresponding to the long-range correlated percolation. A quantitative analysis of the plastic strain accumulation reveals a dipolar anisotropy (for antiplane loading) which vanishes with increasing hardening modulus. A parametric study with hardening modulus and ductility controlled through the spring level constitutive response demonstrates a wide spectrum of behaviors with varying degree of coupling between plasticity and damage evolution. PMID:25375508

  18. The Pore Collapse “Hot-Spots” Model Coupled with Brittle Damage for Solid Explosives

    Directory of Open Access Journals (Sweden)

    L. R. Cheng

    2014-01-01

    Full Text Available This paper is devoted to the building of a numerical pore collapse model with “hot-spots” formation for the impacted damage explosives. According to damage mechanical evolution of brittle material, the one-dimensional elastic-viscoplastic collapse model was improved to incorporate the impact damage during the dynamic collapse of pores. The damage of explosives was studied using the statistical crack mechanics (SCRAM. The effects of the heat conduction and the chemical reaction were taken into account in the formation of “hot-spots.” To verify the improved model, numerical simulations were carried out for different pressure states and used to model a multiple-impact experiment. The results show that repeated weak impacts can lead to the collapse of pores and the “hot-spots” may occur due to the accumulation of internal defects accompanied by the softening of explosives.

  19. A dimensional analysis approach to fatigue in quasi-brittle materials

    Directory of Open Access Journals (Sweden)

    Marco Paggi

    2009-10-01

    Full Text Available In this study, a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack growth is proposed in order to highlight and explain the deviations from the classical power-law equations used to characterize the fatigue behaviour of quasi-brittle materials. According to this theoretical approach, the microstructural-size (related to the volumetric content of fibres in fibre-reinforced concrete, the crack-size, and the size-scale effects on the Paris’ law and the Wöhler equation are presented within a unified mathematical framework. Relevant experimental results taken from the literature are used to confirm the theoretical trends and to determine the values of the incomplete self-similarity exponents. All these information are expected to be useful for the design of experiments, since the role of the different dimensionless numbers governing the phenomenon of fatigue is herein elucidated.

  20. A MIXED MODE FRACTURE CRITERION BASED ON THE MAXIMUM TANGENTIAL STRESS IN BRITTLE INCLUSION

    Institute of Scientific and Technical Information of China (English)

    Ji Changjiang; Li Zhonghua; Sun Jun

    2005-01-01

    A closed-form solution for predicting the tangential stress of an inclusion located in mixed mode Ⅰ and Ⅱ crack tip field was developed based on the Eshelby equivalent inclusion theory. Then a mixed mode fracture criterion, including the fracture direction and the critical load, was established based on the maximum tangential stress in the inclusion for brittle inclusioninduced fracture materials. The proposed fracture criterion is a function of the inclusion fracture stress, its size and volume fraction, as well as the elastic constants of the inclusion and the matrix material. The present criterion will reduce to the conventional one as the inclusion having the same elastic behavior as the matrix material. The proposed solutions are in good agreement with detailed finite element analysis and measurement.

  1. Characterization of Strength of Intact Brittle Rock Considering Confinement-Dependent Failure Processes

    Science.gov (United States)

    Kaiser, Peter K.; Kim, Bo-Hyun

    2015-01-01

    As technologies for deep underground development such as tunneling underneath mountains or mass mining at great depths (>1,000 m) are implemented, more difficult ground conditions in highly stressed environments are encountered. Moreover, the anticipated stress level at these depths easily exceeds the loading capacity of laboratory testing, so it is difficult to properly characterize what the rock behavior would be under high confinement stress conditions. If rock is expected to fail in a brittle manner, behavior changes associated with the relatively low tensile strength, such as transition from splitting to the shear failure, have to be considered and reflected in the adopted failure criteria. Rock failure in tension takes place at low confinement around excavations due to tensile or extensional failure in heterogeneous rocks. The prospect of tensile-dominant brittle failure diminishes as the confinement increases away from the excavation boundary. Therefore, it must be expected that the transition in the failure mechanism, from tensile to shear, occurs as the confinement level increases and conditions for extensional failure are prevented or strongly diminished. However, conventional failure criteria implicitly consider only the shear failure mechanism (i.e., failure envelopes touching Mohr stress circles), and thus, do not explicitly capture the transition of failure modes from tensile to shear associated with confinement change. This paper examines the methodologies for intact rock strength determination as the basic input data for engineering design of deep excavations. It is demonstrated that published laboratory test data can be reinterpreted and better characterized using an s-shaped failure criterion highlighting the transition of failure modes in brittle failing rock. As a consequence of the bi-modal nature of the failure envelope, intact rock strength data are often misinterpreted. If the intact rock strength is estimated by standard procedures from

  2. Fracture Testing at Small-Length Scales: From Plasticity in Si to Brittleness in Pt

    Science.gov (United States)

    Jaya, B. Nagamani; Jayaram, Vikram

    2016-01-01

    The field of micro-/nano-mechanics of materials has been driven, on the one hand by the development of ever smaller structures in devices, and, on the other, by the need to map property variations in large systems that are microstructurally graded. Observations of `smaller is stronger' have also brought in questions of accompanying fracture property changes in the materials. In the wake of scattered articles on micro-scale fracture testing of various material classes, this review attempts to provide a holistic picture of the current state of the art. In the process, various reliable micro-scale geometries are shown, challenges with respect to instrumentation to probe ever smaller length scales are discussed and examples from recent literature are put together to exhibit the expanse of unusual fracture response of materials, from ductility in Si to brittleness in Pt. Outstanding issues related to fracture mechanics of small structures are critically examined for plausible solutions.

  3. A graphene meta-interface for enhancing the stretchability of brittle oxide layers

    Science.gov (United States)

    Won, Sejeong; Jang, Jae-Won; Choi, Hyung-Jin; Kim, Chang-Hyun; Lee, Sang Bong; Hwangbo, Yun; Kim, Kwang-Seop; Yoon, Soon-Gil; Lee, Hak-Joo; Kim, Jae-Hyun; Lee, Soon-Bok

    2016-02-01

    Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers.Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05412e

  4. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility

    Science.gov (United States)

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J.

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

  5. Time-resolved study of femtosecond laser induced micro-modifications inside transparent brittle materials

    Science.gov (United States)

    Hendricks, F.; Matylitsky, V. V.; Domke, M.; Huber, Heinz P.

    2016-03-01

    Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultra-short laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultra-short pulse lasers allow cutting of the chemically strengthened glasses such as Corning Gorilla glass without cracking. Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for development of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials, namely soda-lime glass samples, on a time scale between one nanosecond to several tens of microseconds. The observed effects include acoustic wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have enabled us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the ClearShapeTM process.

  6. A damage mechanics approach for quantifying stress changes due to brittle failure of porous rocks

    Science.gov (United States)

    Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena

    2016-04-01

    Natural fault zones or man-made injection or production of fluid impact the regional stress distribution in Earth's crust and can be responsible for localized stress discontinuities. Understanding the processes controlling fracturing of the porous rocks and mechanical behaviour of fault zones is therefore of interest for several applications including geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes controlling the deformation of porous rocks during and after brittle failure. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To illustrate the model, simulation of a compaction experiment of a sandstone leading to shear failure will be presented which allows to quantify the stress drop accompanying the failure. Finally, we will demonstrate that this approach can also be used at the field scale to simulate hydraulic fracturing and assess the resulting changes in the stress field.

  7. Developing an Experimental Simulation Method for Rock Avalanches: Fragmentation Behavior of Brittle Analogue Material

    Science.gov (United States)

    Thordén Haug, Øystein; Rosenau, Matthias; Leever, Karen; Oncken, Onno

    2013-04-01

    Gravitational mass movement on earth and other planets show a scale dependent behavior, of which the physics is not fully understood. In particular, the runout distance for small to medium sized landslides (volume limited. To develop a new modeling technique to study the scale dependent runout behavior of rock avalanches, we designed, tested and verified several brittle materials allowing fragmentation to occur under normal gravity conditions. According to the model similarity theory, the analogue material must behave dynamically similar to the rocks in natural rock avalanches. Ideally, the material should therefore deform in a brittle manner with limited elastic and ductile strains up to a certain critical stress, beyond which the material breaks and deforms irreversibly. According to scaling relations derived from dimensional analysis and for a model-to-prototype length ratio of 1/1000, the appropriate yield strength for an analogue material is in the order of 10 kPa, friction coefficient around 0.8 and stiffness in the order of MPa. We used different sand (garnet, quartz) in combination with different matrix materials (sugar, salt, starch, plaster) to cement it. The deformation behavior and strength of the samples was tested using triaxial compression tests at atmospheric confining pressures. Proper material properties were obtained using well-sorted, well-rounded, medium grained quartz sand with gypsum plaster as matrix. The favored analogue material is produced by thoroughly mixing the quartz sand with gypsum and water. Afterwards, sufficient time is given to allow cementation by the gypsum. The material typically exhibits elastic deformation up to 0.3% strain and additionally

  8. The tricho-rhino-phalangeal syndrome revisited

    International Nuclear Information System (INIS)

    The tricho-rhino-phalangeal syndrome (TRPS) is a rare congenital disorder, characterized by (1) a peculiar and somewhat pear-shaped nose, (2) sparse and brittle scalp hair, and (3) radiographic evidence of coneshaped epiphyses of the hands. On the basis of clinical, radiographic and genetic criteria, two subtypes (type I and II) are discerned. We describe an intermediate 'hybrid' variant of the TRPS in a patient with clinical and radiographic features of TRPS type I, but with a clearly abnormal karyotype, consistent with TRPS type II. The radiographic findings of the syndrome are reviewed, with particular emphasis on the cone-shaped epiphyses in the hands, the changes in the coxo-femoral joints and the atypical appearance of the pubic symphysis. (orig.)

  9. Ultra-Precision Machining of Brittle Materials--A Review of Diamond-Cutting Brittle Materials%脆性材料的超精加工--脆性材料的钻石切削综述

    Institute of Scientific and Technical Information of China (English)

    房丰洲; 刘向东; LEE L C

    2003-01-01

    In ultra-precision machining of brittle materials, a very important phenomenon is the material transition from brittle to ductile mode. To successfully diamond-turn brittle materials to a mirror surface finish, it is critical to determine the transition point from between the two modes. This paper presents the experimental techniques to study this transition and discusses the mechanism of the surface generation. It has been recognized that the tool wear is a serious issue in diamond turning of brittle materials. Thus, it is suggested that the research in future should be concentrated on this field to enable the technology to be applied practically in production.%在脆性材料的超精加工中,一个十分重要的现象是材料由脆性状态向可延展性状态的转变.为了成功地对脆性材料进行钻石切削加工以获得镜面表面,两种状态转变点的确定十分关键.本文阐述研究这一转变的实验技术,并讨论表面生成的机理.发现在脆性材料的钻石切削中,刀具磨损是一个严重后果.建议今后的研究应集中在这一领域.

  10. Enhanced Wound Healing, Kinase and Stem Cell Marker Expression in Diabetic Organ-Cultured Human Corneas Upon MMP-10 and Cathepsin F Gene Silencing

    OpenAIRE

    Saghizadeh, Mehrnoosh; Epifantseva, Irina; Hemmati, David M.; Ghiam, Chantelle A.; Brunken, William J; Ljubimov, Alexander V

    2013-01-01

    Adenovirus-driven shRNA silencing of select proteinases upregulated in diabetic corneas restored normal wound healing time, the expression of diabetes-altered markers including limbal stem cell markers, and patterns of activated EGFR and Akt in human diabetic corneal organ cultures. The maximum effect was obtained combining proteinase shRNA with c-met overexpression.

  11. Turner Syndrome

    Science.gov (United States)

    Turner syndrome is a genetic disorder that affects a girl's development. The cause is a missing or incomplete ... t work properly. Other physical features typical of Turner syndrome are Short, "webbed" neck with folds of skin ...

  12. Cushing's Syndrome

    Science.gov (United States)

    Cushing's syndrome is a hormonal disorder. The cause is long-term exposure to too much cortisol, a hormone ... cause your body to make too much cortisol. Cushing's syndrome is rare. Some symptoms are Upper body obesity ...

  13. Cushing's Syndrome

    Science.gov (United States)

    ... Cushing's syndrome, also called hypercortisolism , is a rare endocrine disorder caused by chronic exposure of the body's tissues ... removing the tumor while minimizing the chance of endocrine deficiency or long-term ... for Cushing's Syndrome Clinical Trials ...

  14. Turner Syndrome

    Science.gov (United States)

    Turner syndrome is a genetic disorder that affects a girl's development. The cause is a missing or ... t work properly. Other physical features typical of Turner syndrome are Short, "webbed" neck with folds of ...

  15. National Down Syndrome Society

    Science.gov (United States)

    ... info@ndss.org Down Syndrome What Is Down Syndrome? Down Syndrome Facts Myths & Truths Preferred Language Guide Q& ... More » Follow us Down Syndrome What Is Down Syndrome? Down Syndrome Facts Myths & Truths Preferred Language Guide Q& ...

  16. Learning about Marfan Syndrome

    Science.gov (United States)

    ... genetic terms used on this page Learning About Marfan Syndrome What is Marfan syndrome? What are the ... Syndrome Additional Resources for Marfan Syndrome What is Marfan syndrome? Marfan syndrome is one of the most ...

  17. Three dimensional visualization and fractal analysis of mosaic patches in rat chimeras: cell assortment in liver, adrenal cortex and cornea.

    Directory of Open Access Journals (Sweden)

    Stephen Iannaccone

    Full Text Available The production of organ parenchyma in a rapid and reproducible manner is critical to normal development. In chimeras produced by the combination of genetically distinguishable tissues, mosaic patterns of cells derived from the combined genotypes can be visualized. These patterns comprise patches of contiguously similar genotypes and are different in different organs but similar in a given organ from individual to individual. Thus, the processes that produce the patterns are regulated and conserved. We have previously established that mosaic patches in multiple tissues are fractal, consistent with an iterative, recursive growth model with simple stereotypical division rules. Fractal dimensions of various tissues are consistent with algorithmic models in which changing a single variable (e.g. daughter cell placement after division switches the mosaic pattern from islands to stripes of cells. Here we show that the spiral pattern previously observed in mouse cornea can also be visualized in rat chimeras. While it is generally held that the pattern is induced by stem cell division dynamics, there is an unexplained discrepancy in the speed of cellular migration and the emergence of the pattern. We demonstrate in chimeric rat corneas both island and striped patterns exist depending on the age of the animal. The patches that comprise the pattern are fractal, and the fractal dimension changes with the age of the animal and indicates the constraint in patch complexity as the spiral pattern emerges. The spiral patterns are consistent with a loxodrome. Such data are likely to be relevant to growth and cell division in organ systems and will help in understanding how organ parenchyma are generated and maintained from multipotent stem cell populations located in specific topographical locations within the organ. Ultimately, understanding algorithmic growth is likely to be essential in achieving organ regeneration in vivo or in vitro from stem cell populations.

  18. LL-37 via EGFR transactivation to promote high glucose-attenuated epithelial wound healing in organ-cultured corneas.

    Science.gov (United States)

    Yin, Jia; Yu, Fu-Shin X

    2010-04-01

    Purpose. Patients with diabetes are at higher risk for delayed corneal reepithelialization and infection. Previous studies indicated that high glucose (HG) impairs epidermal growth factor receptor (EGFR) signaling and attenuates ex vivo corneal epithelial wound healing. The authors investigated the effects of antimicrobial peptide LL-37 on HG-attenuated corneal epithelial EGFR signaling and wound closure. Methods. Human corneal epithelial cells (HCECs) were stimulated with LL-37. Heparin-binding EGF-like growth factor (HB-EGF) shedding was assessed by measuring the release of alkaline phosphatase (AP) in a stable HCEC line expressing HB-EGF-AP. Activation of EGFR, phosphoinositide 3-kinase (PI3K), and extracellular signal-regulated kinases 1/2 (ERK1/2) was determined by Western blot analysis. Corneal epithelial wound closure was assessed in cultured HCECs and porcine corneas. LL-37 expression was determined by immune dot blot. Results. LL-37 induced HB-EGF-AP release and EGFR activation in a dose-dependent manner. LL-37 prolonged EGFR signaling in response to wounding. LL-37 enhanced the closure of a scratch wound in cultured HCECs and partially rescued HG-attenuated wound healing in an EGFR- and a PI3K-dependent manner and restored HG-impaired EGFR signaling in cultured porcine corneas. HG attenuated wounding-induced LL-37 expression in cultured HCECs. Conclusions. LL-37 is a tonic factor promoting EGFR signaling and enhancing epithelial wound healing in normal and high glucose conditions. With both antimicrobial and regenerative capabilities, LL-37 may be a potential therapeutic for diabetic keratopathy.

  19. Three dimensional visualization and fractal analysis of mosaic patches in rat chimeras: cell assortment in liver, adrenal cortex and cornea.

    Science.gov (United States)

    Iannaccone, Stephen; Zhou, Yue; Walterhouse, David; Taborn, Greg; Landini, Gabriel; Iannaccone, Philip

    2012-01-01

    The production of organ parenchyma in a rapid and reproducible manner is critical to normal development. In chimeras produced by the combination of genetically distinguishable tissues, mosaic patterns of cells derived from the combined genotypes can be visualized. These patterns comprise patches of contiguously similar genotypes and are different in different organs but similar in a given organ from individual to individual. Thus, the processes that produce the patterns are regulated and conserved. We have previously established that mosaic patches in multiple tissues are fractal, consistent with an iterative, recursive growth model with simple stereotypical division rules. Fractal dimensions of various tissues are consistent with algorithmic models in which changing a single variable (e.g. daughter cell placement after division) switches the mosaic pattern from islands to stripes of cells. Here we show that the spiral pattern previously observed in mouse cornea can also be visualized in rat chimeras. While it is generally held that the pattern is induced by stem cell division dynamics, there is an unexplained discrepancy in the speed of cellular migration and the emergence of the pattern. We demonstrate in chimeric rat corneas both island and striped patterns exist depending on the age of the animal. The patches that comprise the pattern are fractal, and the fractal dimension changes with the age of the animal and indicates the constraint in patch complexity as the spiral pattern emerges. The spiral patterns are consistent with a loxodrome. Such data are likely to be relevant to growth and cell division in organ systems and will help in understanding how organ parenchyma are generated and maintained from multipotent stem cell populations located in specific topographical locations within the organ. Ultimately, understanding algorithmic growth is likely to be essential in achieving organ regeneration in vivo or in vitro from stem cell populations.

  20. Confocal microscopy of epithelial and langerhans cells of the cornea in patients using travoprost drops containing two different preservatives.

    Science.gov (United States)

    Marsovszky, László; Resch, Miklós D; Visontai, Zsuzsanna; Németh, János

    2014-07-01

    The recently developed confocal cornea microscopy offers the opportunity to examine pathologies of the cornea and to gain insight into the activity of innate immunity. We aimed to investigate the corneal epithelial and Langerhans cell (LC) densities along with dry eye parameters in primary open-angle glaucoma (POAG) subjects, treated with either of two commercially available travoprost 0.004 % topical medications containing different preservatives. (1: benzalkonium chloride 0.015 % (TravBAK) and 2: polyquaternium-1 (PQ) 0.001 % (TravPQ). Consecutive case series of nineteen POAG patients on TravBAK (mean age: 64.8 ± 13.6 years), nineteen POAG patients on TravPQ (mean age: 66.8 ± 11.3 years) and nineteen age-matched healthy control subjects (63.8 ± 8.2 years). Ocular surface disease index (OSDI), lid parallel conjunctival folds (LIPCOF), Schirmer test (ST) and tear break up time (TBUT) were assessed, and then corneal epithelial and LC densities were investigated with confocal microscopy. Tear production was significantly reduced in both glaucoma patient groups compared to healthy individuals (p < 0.05). TBUT was significantly reduced and epithelial cell densities were significantly greater in patients treated with TravBAK compared to healthy individuals (p < 0.05 for all). LC densities were greater in both glaucoma groups compared to control subjects (p < 0.05 for all). Travoprost therapy may compromise ocular surface. The limited alertness of the corneal immune system found in patients with TravPQ can be considered as indicators of a less disturbed ocular surface and better controlled corneal homeostasis.

  1. Dumping Syndrome

    Science.gov (United States)

    ... Disease Organizations​​ (PDF, 341 KB)​​​​​ Alternate Language URL Dumping Syndrome Page Content On this page: What is ... Nutrition Points to Remember Clinical Trials What is dumping syndrome? Dumping syndrome occurs when food, especially sugar, ...

  2. Micromechanics of failure in brittle geomaterials. Final technical report (for 7/1/1994 - 8/31/2000)

    International Nuclear Information System (INIS)

    The overall objective was to provide a fundamental understanding of brittle failure processes in porous and compact geomaterials. This information is central to energy-related programs such as oil and gas exploration/production, reservoir engineering, drilling technology, geothermal energy recovery, nuclear waste isolation, and environmental remediation. The effects of key parameters such as grain boundary structure and cementation, damage state, and load path on the deformation and failure model of brittle geomaterials are still largely unknown. The research methodology emphasized the integration of experimental rock mechanical testing, quantitative microscopy, and detailed analysis using fracture mechanics, continuum plasticity theory, and numerical methods. Significant progress was made in elucidating the micromechanics of brittle failure in compact crystalline rocks, as well as high-porosity siliciclastic and carbonate rocks. Substantial effort was expended toward applying a new quantitative three-dimensional imaging technique to geomaterials and for developing enhanced image analysis capabilities. The research is presented under the following topics: technique for imaging the 3-D pore structure of geomaterials; mechanics of compressive failure in sandstone; effect of water on compressive failure of sandstone; micromechanics of compressive failure: observation and model; and the brittle-ductile transition in porous carbonate rocks

  3. Analysis of intergranular crack propagation in brittle polycrystals with a generalized finite element method and network algorithm

    NARCIS (Netherlands)

    Shabir, Z.; Van der Giessen, E.; Duarte, C.A.; Simone, A.

    2009-01-01

    Two different approaches to intergranular crack propagation in brittle polycrystals are contrasted. Crack paths resulting from a method that allows a detailed description of the stress field within a polycrystal are compared to cracks dictated by topological considerations. In the first approach, a

  4. A composite material model for investigation of micro-fracture mechanism of brittle rock subjected to uniaxial compression

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A two-phase model of rock was proposed in order to investigate the mechanism of brittle fracture due to uniaxial compression, in which rock was considered to be a composite material consisting of hard grains and colloids. The stress state in colloid region near grains was calculated using Finite Element Metnod ( FEM). The influence of the tensile stresses on the crack initiation and failure process of brittle rock subjected to uniaxial compression was investigated by numerical experiments. The FE results show that tensile stresses are induced easily in the neighboring area of hard grains with the maximum value near grain boundaries. The distribution of tensile stresses depends on the relative position of hard grains. The cracks initiated just near the boundary area of hare grains, which was governed by tensile stress. These results dearly reveal the micro-fracture mechanism of brittle rock loaded by uniaxial compression. It can be concluded that the failure mode of brittle rock under uniaxial compression is still tensile fracture from the point view of microstructure. However,since the wide colloid region is still under compressive stress state, further propagation of boundary, cracks through this region obviously needs more external load, thus causing the uniaxial compressive strength of rock much higher than its tensile strength obtained via Brazilian (splitting) experiment.

  5. OAS/PKR Pathways and α/β TCR+ T Cells are Required for Ad: IFN-γ Inhibition of HSV-1 in Cornea1

    Science.gov (United States)

    Austin, Bobbie Ann; Halford, William P.; Williams, Bryan R. G.; Carr, Daniel J. J.

    2007-01-01

    An adenoviral vector containing the muIFN-γ transgene (Ad:IFN-γ) was evaluated for its capacity to inhibit HSV-1. To measure effectiveness, viral titers were analyzed in cornea and trigeminal ganglia (TG) during acute ocular HSV-1 infection. Ad: IFN-γ potently suppressed HSV-1 replication in a dose-dependent fashion, requiring IFN-γ R. Moreover, Ad:IFN-γ was effective when delivered -72 and -24 h prior to infection as well as 24 h post infection. Associated with anti-viral opposition, TG from Ad: IFN-γ transduced mice harbored fewer T cells. Also related to T cell involvement, Ad:IFN-γ was effective but attenuated in TG from α/β TCR deficient mice. In corneas, α/β TCR+ T cells were obligatory for protection against viral multiplication. Type I IFN involvement amid anti-viral efficacy of Ad: IFN-γ was further investigated because type I and II IFN pathways have synergistic anti-HSV-1 activity. Ad:IFN-γ inhibited viral reproduction in corneas and TG from IFN-α/β R deficient (CD118 −/−) mice, although viral titers were 2–3 fold higher in cornea and TG, compared to wild type. The absence of IFN-stimulated anti-viral proteins, 2’-5’ oligoadenylate synthetase/RNase L and ds RNA dependent protein kinase R, completely eliminated the anti-viral effectiveness of Ad:IFN-γ. Collectively, the results demonstrate: (1) nonexistence of type I IFN R does not abolish defense of Ad:IFN-γ against HSV-1; (2) anti-viral pathways, OAS/RNase L and PKR are mandatory; and (3) α/β TCR+ T cells are compulsory for Ad: IFN-γ effectiveness against HSV-1 in cornea but not in TG. PMID:17404299

  6. [Dry eye syndrome in rheumatoid arthritis patients].

    Science.gov (United States)

    Polanská, V; Hlinomazová, Z; Fojtík, Z; Nemec, P

    2007-11-01

    The aim of this cross-sectional study was to review the incidence of the dry eye syndrome in rheumatoid arthritis (RA) patients, evaluate the association among the incidence of the dry eye syndrome, presence of positive rheumatoid factor (RF), the RA stage, and the duration of the disease. The group consisted of altogether 100 patients, 16 men and 84 women; the average age was 58.9 years (SD 14.6). The average duration of RA was 12.3 years, SD 11.0. In each patient, the Schirmer test I was performed, the presence of the LIPCOF (Lid Parallel Conjunctival Folds) on the slit lamp was assessed, the BUT (Tear Break-Up Time) was measured and vital fluorescein staining was performed. In each patient the data of the presence or absence of the RF in the serum, RA severity according to the X-ray examination, and the disease duration were recorded. The Pearson's association test for nominal variables was used for statistical evaluation of the association between the rheumatoid arthritis presence and the dry eye syndrome. In our group of 100 patients, the Schirmer test I was positive in 67% of patients. Positive BUT was marked in 84 % of patients. The conjunctival folds were present in 45 % of patients only. The pathological findings after cornea fluorescein staining appeared in 18 % of patients. The dry eye syndrome incidence was marked in 74% of patients with RA. Subjective difficulties were declared by 38.3% of patients only. The local treatment was already established in 23.0% of patients only. We did not find statistically significant correlation between the RF positive rheumatoid arthritis appearance and dry eye syndrome, nor between the stage of the rheumatoid arthritis and presence of the dry eye syndrome. We proved statistical connection between the presence of dry eye syndrome and the duration of rheumatoid arthritis longer than 10 years. Keratoconjunctivitis sicca is the most common ocular complication in rheumatoid arthritis patients. We proved the connection

  7. Effect of torsional mode phacoemulsification on cornea in eyes with/without pseudoexfoliation

    Institute of Scientific and Technical Information of China (English)

    Süleyman; Demircan; Mustafa; Atas; Yusufcan; Yurtsever

    2015-01-01

    AIM: To evaluate the effect of torsional mode phacoemulsification on central corneal thickness, corneal endothelial cell density, and morphology in eyes with/without pseudoexfoliation(PEX) syndrome.METHODS: Fourty-two consecutive patients with and42 patients without PEX as a control group scheduled for cataract surgery was studied. Phacoemulsification, using OZi L IP system, was performed with quick chop technique. Using noncontact specular microscopy, the central endothelial cell density(ECD), coefficient of variation, percentage of hexagonal cells, and the central corneal thickness(CCT) were evaluated preoperatively and postoperatively at 1, 7 and 30 d.RESULTS: The ECD in PEX syndrome was statistically significantly lower than that in the control group preoperatively and postoperatively(P ≤0.001).Percentage change in ECD was statistically significantly higher in PEX than that in control group after surgery follow up(P ≤0.04).There was no statistically significant difference between both groups comparing percentage of hexagonal cells and coefficient of variation in the cell size before and after the surgery. At 1 and 7d after surgery, percentage change in CCT was statistically significantly higher in PEX group than that in the control group(P ≤0.041).CONCLUSION: Although torsional mode phacoemulsification and intraocular lens(IOL) implantation provided a safe and favorable surgical outcome in patients with/without PEX, torsional phacoemulsification led to significantly higher ECD loss in the PEX group than that in the control group during the whole follow up period.In addition, more corneal swelling in the PEX group than that in the control group during the early postoperative period has indicated that the corneal endothelium, in presence of PEX endotheliopathy, seems to be more susceptible to the effects of phacoemulsification surgeryin eyes with PEX. The increased risk of anterior chamber manipulations in patients with PEX should be taken into account for

  8. Understanding brittle deformation at the Olkiluoto site. Literature Supplement 2010: an Update of Posiva Working Report 2006-25

    International Nuclear Information System (INIS)

    Posiva Working Report 2006-25 arose from the belief that geological modelling at Olkiluoto, Finland, where an underground repository for spent nuclear fuel is at present under construction, could be significantly improved by an increased understanding of the phenomena being modelled, in conjunction with the more sophisticated data acquisition and processing methods which are now being introduced. Since the geological model is the necessary basis for the rock engineering and hydrological models, which in turn provide the foundation for identifying suitable rock volumes underground and for demonstrating long-term safety, its scientific basis is of critical importance. As a contribution to improving this scientific basis, the literature on brittle deformation in the Earth's crust was reviewed up to and including year 2005. The result was a compilation of scientific articles, reports and books on some of the key topics of significance for an improved understanding of brittle deformation of hard, crystalline rocks, particularly heterogeneous migmatitic and metamorphic rocks like those that make up the Olkiluoto bedrock. The present report is a supplement to WR 2006-25, covering the 5-year period 2006-2010, with some key earlier references and an Annotated Bibliography. The present report is subdivided into five chapters, listing recent literature on (1) background subjects and basic principles, (2) the fabric of Olkiluoto-type intact rock (gneisses, migmatites, fault rocks), (3) formation and characteristics of brittle deformation features (fracture mechanics, brittle microtectonics), (4) fracture data acquisition and processing (statistical characterisation and modelling of fracture systems), and (5) the characterisation of brittle deformation zones (for deterministic and dynamic modelling), corresponding to the first five chapters of the earlier report

  9. Refeeding syndrome.

    Science.gov (United States)

    Fernández López, M T; López Otero, M J; Alvarez Vázquez, P; Arias Delgado, J; Varela Correa, J J

    2009-01-01

    Refeeding syndrome is a complex syndrome that occurs as a result of reintroducing nutrition (oral, enteral or parenteral) to patients who are starved or malnourished. Patients can develop fluid-balance abnormalities, electrolyte disorders (hypophosphataemia, hypokalaemia and hypomagnesaemia), abnormal glucose metabolism and certain vitamin deficiencies. Refeeding syndrome encompasses abnormalities affecting multiple organ systems, including neurological, pulmonary, cardiac, neuromuscular and haematological functions. Pathogenic mechanisms involved in the refeeding syndrome and clinical manifestations have been reviewed. We provide suggestions for the prevention and treatment of refeeding syndrome. The most important steps are to identify patients at risk, reintroduce nutrition cautiously and correct electrolyte and vitamin deficiencies properly.

  10. Brittle-to-viscous behaviour of quartz gouge in shear experiments

    Science.gov (United States)

    Richter, Bettina; Stunitz, Holger; Heilbronner, Renée

    2016-04-01

    In order to study the microstructure development across the brittle-viscous transition and to derive the corresponding flow laws, we performed shear experiments on quartz gouge in a Griggs-type deformation apparatus. The starting material is a crushed quartz single crystal (sieved grain size temperatures between 500 ° C and 1000 ° C at confining pressures of 0.5 GPa, 1.0 GPa or 1.5 GPa. Four strain-rate-stepping experiments were conducted at strain rates between ˜2.5 x 10‑6 s‑1 and ˜2.5 x 10‑4 s‑1. Other experiments were conducted at constant strain rates of ˜2.5 x 10‑6 s‑1, ˜2.5 x 10‑5 s‑1, ˜2.5 x 10‑4 s‑1 and ˜2.5 x 10‑3 s‑1. At high confining pressure, the strength of the samples decreases with increasing temperature for all strain rates. The largest decrease occurred between 650 ° C and 700 ° C at shear strain rates of ˜2.5 x 10‑5 s‑1. At the same time, the pressure dependence of strength is positive for T ≤ 650 ° C while an inverse pressure dependence is observed at T > 650 ° C. For T temperature, from 700-1000 ° C it shows a strong temperature dependence. Between 650 ° C and 700 ° C at shear strain rates of ˜2.5 x 10‑5 s‑1 a change in the deformation process occurs from one dominated by cataclastic flow to one dominated by crystal plasticity. The microstructure reveals a less abrupt transition in terms of operating processes, because brittle and viscous processes are equally active around 650 ° C. With increasing temperature the volume fraction of recrystallised grains increases, and at 900 ° C - 1000 ° C recrystallisation is nearly complete at strains of γ ˜ 3. The crystallographic preferred orientation of the c-axis evolves from a random distribution at low temperatures towards two peripheral maxima at intermediate temperatures. At high temperatures the c-axis show a single Y-maximum. At high temperature, the stress exponent is n = 2.1 ± 0.2. The activation energy Q is 193 ± 12 kJ/mol at strain rates

  11. Failure processes in soft and quasi-brittle materials with nonhomogeneous microstructures

    Science.gov (United States)

    Spring, Daniel W.

    Material failure pervades the fields of materials science and engineering; it occurs at various scales and in various contexts. Understanding the mechanisms by which a material fails can lead to advancements in the way we design and build the world around us. For example, in structural engineering, understanding the fracture of concrete and steel can lead to improved structural systems and safer designs; in geological engineering, understanding the fracture of rock can lead to increased efficiency in oil and gas extraction; and in biological engineering, understanding the fracture of bone can lead to improvements in the design of bio-composites and medical implants. In this thesis, we numerically investigate a wide spectrum of failure behavior; in soft and quasi-brittle materials with nonhomogeneous microstructures considering a statistical distribution of material properties. The first topic we investigate considers the influence of interfacial interactions on the macroscopic constitutive response of particle reinforced elastomers. When a particle is embedded into an elastomer, the polymer chains in the elastomer tend to adsorb (or anchor) onto the surface of the particle; creating a region in the vicinity of each particle (often referred to as an interphase) with distinct properties from those in the bulk elastomer. This interphasial region has been known to exist for many decades, but is primarily omitted in computational investigations of such composites. In this thesis, we present an investigation into the influence of interphases on the macroscopic constitutive response of particle filled elastomers undergoing large deformations. In addition, at large deformations, a localized region of failure tends to accumulate around inclusions. To capture this localized region of failure (often referred to as interfacial debonding), we use cohesive zone elements which follow the Park-Paulino-Roesler traction-separation relation. To account for friction, we present a new

  12. Brittle-ductile shear zone formation in the McKim Limestone: eastern Monument Upwarp, Utah

    Science.gov (United States)

    Seyum, S.; Pollard, D. D.

    2011-12-01

    The McKim Limestone is part of a regressive, marine sedimentary sequence of strata that was deposited in the Pennsylvanian to Permian periods. It is well-exposed across large portions of Raplee anticline and Comb monocline; a pair of kilometer-scale folds that mark the Monument Upwarp of the Colorado Plateau in southeastern Utah. Two conjugate sets of echelon vein arrays, with complementary echelon pressure solution seam arrays, occur as bed-perpendicular, systematic deformation features in the 1-3 m thick McKim Limestone unit. Based on large vein to vein array angles, large vein aperture to length ratios, and the presence of vein-perpendicular pressure solution seams, these structures are interpreted to have developed within localized, brittle-ductile shear zones. Topics of debate among structural geologists regarding the formation mechanism of echelon veins include the initiation mode of vein segments (tensile or shear), the relative age between shear zone initiation and vein formation, the interpretation of strain within a shear zone, and the development of sigmoidal veins as being indicative of rotation. These concepts often are founded on geometric observations and kinematic models of deformation (e.g. simple shear) that are independent of the constitutive properties of the rock, are not constrained by the equations of motion, and do not honor the boundary conditions on the vein surfaces. Here we show a more realistic representation of brittle-ductile shear zone formation by introducing numerical models that consider the mechanical properties of limestone, are constrained by the equations of motion, and explicitly define the vein surfaces and their boundary conditions. The commercial finite element software, Abaqus FEA, is used to investigate the deformed geometry of model echelon vein arrays as a function of the remotely applied stress, the initial geometry of the vein arrays, and the constitutive properties of the solid. These geometric patterns are compared

  13. Mucous membrane grafting for the post-Steven-Johnson syndrome symblepharon: A case report

    Directory of Open Access Journals (Sweden)

    Jayanta Kumar Das

    2011-01-01

    Full Text Available An 18-year-old woman was referred with late sequelae of chloroquine-induced Steven-Johnson syndrome. At the time of presentation, the symblepharon was involving the upper lids to almost the whole of the cornea, and part of the lower bulbar conjunctiva with the lower lid bilaterally. Other ocular examinations were not possible due to the symblepharon. B-scan ultrasonography revealed acoustically clear vitreous, normal chorioretinal thickness, and normal optic nerve head, with an attached retina. Conjunctivo-corneal adhesion released by superficial lamellar dissection of the cornea. Ocular surface reconstruction was carried out with a buccal mucous membrane. A bandage contact lens was placed over the cornea followed by the symblepharon ring to prevent further adhesion. The mucosal graft was well taken up along with corneal re-epithelization. Best corrected visual acuity of 20/120 in both sides after 1 month and 20/80 after 3 months was achieved and maintained till the 2.5-year follow-up.

  14. Poly (ε-caprolactone nanofibrous ring surrounding a polyvinyl alcohol hydrogel for the development of a biocompatible two-part artificial cornea

    Directory of Open Access Journals (Sweden)

    Bakhshandeh H

    2011-07-01

    Full Text Available Haleh Bakhshandeh1, Masoud Soleimani2, Saied Shah Hosseini3, Hassan Hashemi3, Iman Shabani4, Abbas Shafiee5, Amir Houshang Behesht Nejad6, Mohammad Erfan1, Rassoul Dinarvand7, Fatemeh Atyabi71Department of Pharmaceutics, School of Pharmacy, Shaheed Beheshti Medical University, Tehran, Iran; 2Hematology Department, Faculty of Medical Science, Tarbiat Modares University, Tehran, Iran; 3Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran; 4Nanotechnology and Tissue Engineering Department, Stem Cell Technology Research Center, Tehran, Iran; 5Stem Cell Biology Department, Stem Cell Technology Research Center, Tehran, Iran; 6Ophthalmology Department, Tehran University of Medical Sciences, Tehran, Iran; 7Nanotechnology Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, IranAbstract: The study aimed to fabricate and characterize a 2-part artificial cornea as a substitute for penetrating keratoplasty in patients with corneal blindness. The peripheral part of the artificial cornea consisted of plasma-treated electrospun poly (ε-caprolactone (PCL nanofibers, which were attached to a hydrogel disc of polyvinyl alcohol (PVA as a central optical part. The physical properties of the prepared artificial cornea, including morphology, mechanical properties, light transmittance, and contact angle, were assessed. Cell attachment and proliferation studies were performed on rabbit limbal stem cells. The SEM image of the polymeric system showed that the peripheral part formed a highly porous scaffold that could facilitate tissue biointegration. Assessment of the mechanical properties of the peripheral nanofibrous part and the hydrogel optical part showed suitable elasticity. Young’s modulus values of the electrospun PCL skirt and PVA hydrogel core were 7.5 and 5.3 MPa, respectively, which is in line with the elasticity range of natural human cornea (0.3–7 MPa. The light transmittance of the central part was >85

  15. Large-scale 3D modeling of projectile impact damage in brittle plates

    Science.gov (United States)

    Seagraves, A.; Radovitzky, R.

    2015-10-01

    The damage and failure of brittle plates subjected to projectile impact is investigated through large-scale three-dimensional simulation using the DG/CZM approach introduced by Radovitzky et al. [Comput. Methods Appl. Mech. Eng. 2011; 200(1-4), 326-344]. Two standard experimental setups are considered: first, we simulate edge-on impact experiments on Al2O3 tiles by Strassburger and Senf [Technical Report ARL-CR-214, Army Research Laboratory, 1995]. Qualitative and quantitative validation of the simulation results is pursued by direct comparison of simulations with experiments at different loading rates and good agreement is obtained. In the second example considered, we investigate the fracture patterns in normal impact of spheres on thin, unconfined ceramic plates over a wide range of loading rates. For both the edge-on and normal impact configurations, the full field description provided by the simulations is used to interpret the mechanisms underlying the crack propagation patterns and their strong dependence on loading rate.

  16. Rice Brittleness Mutants: A Way to Open the 'Black Box' of Monocot Cell Wall Biosynthesis

    Institute of Scientific and Technical Information of China (English)

    Baocai Zhang; Yihua Zhou

    2011-01-01

    Rice is a model organism for studying the mechanism of cell wall biosynthesis and remolding in Gramineae.Mechanical strength is an important agronomy trait of rice(Oryza sativa L.)plants that affects crop lodging and grain yield.As a prominent physical property of cell walls,mechanical strength reflects upon the structure of different wall polymers and how they interact.Studies on the mechanisms that regulate the mechanical strength therefore consequently results in uncovering the genes functioning in cell wall biosynthesis and remodeling.Our group focuses on the study of isolation of brittle culm(bc)mutants and characterization of their corresponding genes.To date,several bc mutants have been reported.The identified genes have covered several pathways of cell wall biosynthesis,revealing many secrets of monocot cell wall biosynthesis.Here,we review the progress achieved in this research field and also highlight the perspectives in expectancy.All of those lend new insights into mechanisms of cell wall formation and are helpful for harnessing the waste rice straws for biofuel production.

  17. Standard test method for splitting tensile strength for brittle nuclear waste forms

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    1989-01-01

    1.1 This test method is used to measure the static splitting tensile strength of cylindrical specimens of brittle nuclear waste forms. It provides splitting tensile-strength data that can be used to compare the strength of waste forms when tests are done on one size of specimen. 1.2 The test method is applicable to glass, ceramic, and concrete waste forms that are sufficiently homogeneous (Note 1) but not to coated-particle, metal-matrix, bituminous, or plastic waste forms, or concretes with large-scale heterogeneities. Cementitious waste forms with heterogeneities >1 to 2 mm and 5 mm can be tested using this procedure provided the specimen size is increased from the reference size of 12.7 mm diameter by 6 mm length, to 51 mm diameter by 100 mm length, as recommended in Test Method C 496 and Practice C 192. Note 1—Generally, the specimen structural or microstructural heterogeneities must be less than about one-tenth the diameter of the specimen. 1.3 This test method can be used as a quality control chec...

  18. A fiber-bundle model for the continuum deformation of brittle material

    CERN Document Server

    Nanjo, K Z

    2016-01-01

    The deformation of brittle material is primarily accompanied by micro-cracking and faulting. However, it has often been found that continuum fluid models, usually based on a non-Newtonian viscosity, are applicable. To explain this rheology, we use a fiber-bundle model, which is a model of damage mechanics. In our analyses, yield stress was introduced. Above this stress, we hypothesize that the fibers begin to fail and a failed fiber is replaced by a new fiber. This replacement is analogous to a micro-crack or an earthquake and its iteration is analogous to stick-slip motion. Below the yield stress, we assume that no fiber failure occurs, and the material behaves elastically. We show that deformation above yield stress under a constant strain rate for a sufficient amount of time can be modeled as an equation similar to that used for non-Newtonian viscous flow. We expand our rheological model to treat viscoelasticity and consider a stress relaxation problem. The solution can be used to understand aftershock tem...

  19. Controlling the ductile to brittle transition in Fe–9%Cr ODS steels

    International Nuclear Information System (INIS)

    Probably the most important range of materials for consideration as the blanket material for the tokamak design for fusion reactors ITER and DEMO is the high alloy Fe–9Cr oxide dispersion strengthened ferritic steels. Ferritic steels possess exceptional thermal conductivity and low thermal expansion and are resistant to void swelling. Their main drawback is high ductile to brittle transition temperatures, particularly in the oxide dispersion strengthened versions. This paper describes attempts to reduce the DBTT in an un-irradiated ferritic steel by a novel heat treatment procedure. New batches of high alloy Fe–9Cr oxide dispersion strengthened (Eurofer) ferritic steel have been produced by a powder metallurgy route, and relatively homogeneous material has been produced by hot isostatic pressing (HIP). Mini-Charpy test specimens were made from materials which had been subjected to a matrix of heat treatments with varying solution treatment temperature (ST), cooling rate from the ST temperature, and tempering treatment. The initial DBTT was in the range of 150–200 °C (423–473 K). Downward shifts of up to approximately 200 °C (473 K) have been observed after solution treatment at 1300 °C (1573 K) followed by slow cooling. This paper describes the microstructure of this material, and discussion is made of the likely microstructural factors needed to produce these DBTT downward shifts

  20. Numerical Study on Crack Propagation in Brittle Jointed Rock Mass Influenced by Fracture Water Pressure

    Directory of Open Access Journals (Sweden)

    Yong Li

    2015-06-01

    Full Text Available The initiation, propagation, coalescence and failure mode of brittle jointed rock mass influenced by fissure water pressure have always been studied as a hot issue in the society of rock mechanics and engineering. In order to analyze the damage evolution process of jointed rock mass under fracture water pressure, a novel numerical model on the basis of secondary development in fast Lagrangian analysis of continua (FLAC3D is proposed to simulate the fracture development of jointed rock mass under fracture water pressure. To validate the feasibility of this numerical model, the failure process of a numerical specimen under uniaxial compression containing pre-existing fissures is simulated and compared with the results obtained from the lab experiments, and they are found to be in good agreement. Meanwhile, the propagation of cracks, variations of stress and strain, peak strength and crack initiation principles are further analyzed. It is concluded that the fissure water has a significant reducing effect on the strength and stability of the jointed rock mass.

  1. New Methods in Exploring Old Topics: Case Studying Brittle Diabetes in the Family Context

    Science.gov (United States)

    Günther, Moritz Philipp; Winker, Peter; Wudy, Stefan A.; Brosig, Burkhard

    2016-01-01

    Background. In questing for a more refined quantitative research approach, we revisited vector autoregressive (VAR) modeling for the analysis of time series data in the context of the so far poorly explored concept of family dynamics surrounding instable diabetes type 1 (or brittle diabetes). Method. We adopted a new approach to VAR analysis from econometrics referred to as the optimized multivariate lag selection process and applied it to a set of raw data previously analyzed through standard approaches. Results. We illustrated recurring psychosomatic circles of cause and effect relationships between emotional and somatic parameters surrounding glycemic control of the child's diabetes and the affective states of all family members. Conclusion. The optimized multivariate lag selection process allowed for more specific, dynamic, and statistically reliable results (increasing R2 tenfold in explaining glycemic variability), which were derived from a larger window of past explanatory variables (lags). Such highly quantitative versus historic more qualitative approaches to case study analysis of psychosomatics surrounding diabetes in adolescents were reflected critically. PMID:26634215

  2. Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

    Science.gov (United States)

    Moradian, Zabihallah; Einstein, Herbert H.; Ballivy, Gerard

    2016-03-01

    Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress-strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

  3. Evaluation of Crashworthiness for SAE Materials under Ductile to Brittle Transition Temperature (DBTT

    Directory of Open Access Journals (Sweden)

    Amol Bhanage

    2014-10-01

    Full Text Available The concept of crashworthy coaches came into existence after a crash. This demands, avoid vehicle deformation of other/central parts. For this, the behaviour of plastic deformation of the material is necessary to be known. So, these results are required to study the crashworthy behaviour of the structure. In this research, Comparative study has been taken on the automotive materials of SAE 1026, SAE 4140, SAE 5120 and SAE8620. This paper presents the results of fracture toughness, impact energy and stress required for crack propagation from Charpy v-notch impact test and tensile test. The mechanical behaviour of SAE 1026, SAE 4140, SAE 5120 and SAE 8620 are important to describe response during actual loading condition properties used in the crash analysis of the component. The Charpy impact test was conducted at temperature ranging from room temperature 24°C, 0°C, -20°C, - 40°C, -60°C. Specimens oriented in T-L direction are tested. The materials SAE 1026, SAE 4140, SAE 5120 and SAE8620 shown that the ductile to brittle transition temperature, based on 19.5 J, 10.5 J, 113 J, 59.5 J, absorbed energy is about 1.2°C, -3°C, -38°C, -10°C respectively.

  4. Optimization Of Laboratory Hot Rolling Of Brittle Fe-40at.%Al-Zr-B Aluminide

    Directory of Open Access Journals (Sweden)

    Schindler I.

    2015-09-01

    Full Text Available Use of the protective steel capsules enabled to manage the laboratory hot flat rolling of the extremely brittle as-cast aluminide Fe-40at.%Al-Zr-B with the total height reduction of almost 70 %. The hot rolling parameters were optimized to obtain the best combination of deformation temperature (from 1160°C up to 1240°C and rolling speed (from 0.14 m·s−1 to 0.53 m·s−1. The resistance against cracking and refinement of the highly heterogeneous cast microstructure were the main criteria. Both experiments and mathematical simulations based on FEM demonstrated that it is not possible to exploit enhanced plasticity of the investigated alloy at low strain rates in the hot rolling process. The heat flux from the sample to the working rolls is so intensive at low rolling speed that even the protective capsule does not prevent massive appearance of the surface transverse cracking. The homogeneity and size of product’s grain was influenced significantly by temperature of deformation, whereas the effect of rolling speed was relatively negligible. The optimal forming parameters were found as rolling temperature 1200°C and the rolling speed 0.35 m·s−1. The effective technology of the iron aluminide Fe-40at.% Al-Zr-B preparation by simple processes of melting, casting and hot rolling was thus established and optimized.

  5. Insensitivity to Flaws Leads to Damage Tolerance in Brittle Architected Meta-Materials

    Science.gov (United States)

    Montemayor, L. C.; Wong, W. H.; Zhang, Y.-W.; Greer, J. R.

    2016-02-01

    Cellular solids are instrumental in creating lightweight, strong, and damage-tolerant engineering materials. By extending feature size down to the nanoscale, we simultaneously exploit the architecture and material size effects to substantially enhance structural integrity of architected meta-materials. We discovered that hollow-tube alumina nanolattices with 3D kagome geometry that contained pre-fabricated flaws always failed at the same load as the pristine specimens when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. Samples with (a/w) > 0.3, and notch length-to-unit cell size ratios of (a/l) > 5.2, failed at a lower peak loads because of the higher sample compliance when fewer unit cells span the intact region. Finite element simulations show that the failure is governed by purely tensile loading for (a/w) structural meta-materials may give rise to their damage tolerance and insensitivity of failure to the presence of flaws even when made entirely of intrinsically brittle materials.

  6. Fracture toughness from atomistic simulations: Brittleness induced by emission of sessile dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, D. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Materials Science and Engineering

    1998-08-04

    Using atomistic simulations of crack response for intermetallic materials the author shows that when the emitted dislocations are sessile and stay in the immediate vicinity of the crack tip the emitted dislocations can actually lead to brittle failure. She present the results of an atomistic simulation study of the simultaneous dislocation emission and crack propagation process in this class of materials. She used a molecular statics technique with embedded atom (EAM) potentials developed for NiAl. The crystal structure of NiAl is the CsCl type (B2) with a lattice parameter of 0.287 nm, which is reproduced by the potential together with the cohesive energy and elastic constants. The compound stays ordered up to the melting point, indicating a strong tendency towards chemical ordering with a relatively high energy of the antiphase boundary (APB). As a result of this relatively large energy the dislocations of 1/2<111> type Burgers vectors imply a high energy and the deformation process occurs via the larger <100> type dislocations.

  7. Mechanical properties and material removal characteristics of soft-brittle HgCdTe single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Irwan, R. [School of Mechanical and Mining Engineering, the University of Queensland, Brisbane, QLD 4072 (Australia); Huang, H., E-mail: han.huang@uq.edu.au [School of Mechanical and Mining Engineering, the University of Queensland, Brisbane, QLD 4072 (Australia); Zheng, H.Y.; Wu, H. [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075 (Singapore)

    2013-01-01

    Mechanical properties and material removal characteristics of mercury cadmium telluride (Hg{sub 0.84}C{sub 0.16}Te) single crystals were investigated by the use of indentation and single point diamond turning. The nanoindentation tests showed that the average values of elastic modulus and hardness were 40 and 0.55 GPa, respectively. The fracture toughness estimated by Vickers indentation fracture toughness test was 0.200 MPa m{sup 1/2}, in the predicted range of 0.204-0.235 MPa m{sup 1/2} by the Bifano model. The diamond turning experiments revealed that there was a threshold value in depth of cut that was responsible for the transition from ductile to brittle removal modes during the cutting of the Hg{sub 0.84}C{sub 0.16}Te single crystals. The measured critical depth of cut was between 1.5 and 2 {mu}m, in agreement with that of 1.541 {mu}m calculated by the Bifano model.

  8. An ESPI experimental study on the phenomenon of fracture in glass. Is it brittle or plastic?

    Science.gov (United States)

    Ferretti, Daniele; Rossi, Marco; Royer-Carfagni, Gianni

    2011-07-01

    The crack opening displacement (COD) in annealed soda-lime (float) glass has been measured with an electronic speckle pattern interferometry (ESPI) apparatus using coherent laser light. Specimens, naturally pre-cracked with a particular technique, were loaded under strain-driven bending until crack propagated; at regular intervals loading was paused to let the crack reach subcritical equilibrium and the COD measured. By using a post-processing algorithm comparing four images lighted with phase-shifted laser beams, surface displacements could be measured at a resolution of 0.01 μm. Glass transparency has allowed to see through that the propagating crack front is not sharp but curved, jagged and merged in an opaque neighborhood. Numerical simulations show that the measured CODs cannot be reproduced if cohesive surface forces à la Barenblatt-Dugdale bridge the crack lips; instead a plastic-like region must form in a bulk neighborhood of the tip, where inelastic strains are associated with volume increase rather than deviatoric distortion. For this, a Gurson-Tvergaard model of porous plasticity, accounting for the formation of microvoids/microcracks, has been found more efficient than classical von Mises plasticity. This study confirms the formation at the crack tip of a process zone, whose occurrence in brittle materials like glass is still a subject of controversy.

  9. Insensitivity to Flaws Leads to Damage Tolerance in Brittle Architected Meta-Materials.

    Science.gov (United States)

    Montemayor, L C; Wong, W H; Zhang, Y-W; Greer, J R

    2016-01-01

    Cellular solids are instrumental in creating lightweight, strong, and damage-tolerant engineering materials. By extending feature size down to the nanoscale, we simultaneously exploit the architecture and material size effects to substantially enhance structural integrity of architected meta-materials. We discovered that hollow-tube alumina nanolattices with 3D kagome geometry that contained pre-fabricated flaws always failed at the same load as the pristine specimens when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. Samples with (a/w) > 0.3, and notch length-to-unit cell size ratios of (a/l) > 5.2, failed at a lower peak loads because of the higher sample compliance when fewer unit cells span the intact region. Finite element simulations show that the failure is governed by purely tensile loading for (a/w) discrete-continuum duality of architected structural meta-materials may give rise to their damage tolerance and insensitivity of failure to the presence of flaws even when made entirely of intrinsically brittle materials. PMID:26837581

  10. On the initiation of shear faults during brittle compressive failure: A new mechanism

    Science.gov (United States)

    Schulson, Erland M.; Iliescu, Daniel; Renshaw, Carl E.

    1999-01-01

    Brittle materials loaded under compression generally fail by shear faulting. This paper addresses the initiation of the fault. It presents direct observational evidence from ice, which is used as a model material for rock, and shows that wing cracking and "splay cracking" are important processes in the localization of deformation, both prior to and during fault initiation. Wing cracks develop at the tips of sliding intergranular cracks and tend to align with the maximum principal stress. Splay cracks emanate from one side of the sliding parent crack. The theme of the paper is that the splay cracks play the dominant role in triggering the fault. The central idea is that the slender columns between the splay cracks are more likely to buckle and fail than are the columns between adjacent wing cracks because they do not have two fixed ends; instead, the end stemming from the inclined parent crack is free. A moment is then applied by frictional sliding of the parent inclined crack, and this causes the fixed-free columns to break at a much lower stress than the fixed-fixed columns. Columns created near a free surface are more likely to fail than those created elsewhere, and this explains the observation that shear localization tends to initiate near free surfaces. A first-order calculation shows that the failure stress of the splay-created columns is of the same order of magnitude as the terminal failure stress.

  11. Controlling the ductile to brittle transition in Fe–9%Cr ODS steels

    Energy Technology Data Exchange (ETDEWEB)

    Di Martino, S.F., E-mail: s.f.di-martino@lboro.ac.uk; Riddle, N.B.; Faulkner, R.G.

    2013-11-15

    Probably the most important range of materials for consideration as the blanket material for the tokamak design for fusion reactors ITER and DEMO is the high alloy Fe–9Cr oxide dispersion strengthened ferritic steels. Ferritic steels possess exceptional thermal conductivity and low thermal expansion and are resistant to void swelling. Their main drawback is high ductile to brittle transition temperatures, particularly in the oxide dispersion strengthened versions. This paper describes attempts to reduce the DBTT in an un-irradiated ferritic steel by a novel heat treatment procedure. New batches of high alloy Fe–9Cr oxide dispersion strengthened (Eurofer) ferritic steel have been produced by a powder metallurgy route, and relatively homogeneous material has been produced by hot isostatic pressing (HIP). Mini-Charpy test specimens were made from materials which had been subjected to a matrix of heat treatments with varying solution treatment temperature (ST), cooling rate from the ST temperature, and tempering treatment. The initial DBTT was in the range of 150–200 °C (423–473 K). Downward shifts of up to approximately 200 °C (473 K) have been observed after solution treatment at 1300 °C (1573 K) followed by slow cooling. This paper describes the microstructure of this material, and discussion is made of the likely microstructural factors needed to produce these DBTT downward shifts.

  12. Thrust-wrench fault interference in a brittle medium: new insights from analogue modelling experiments

    Science.gov (United States)

    Rosas, Filipe; Duarte, Joao; Schellart, Wouter; Tomas, Ricardo; Grigorova, Vili; Terrinha, Pedro

    2015-04-01

    We present analogue modelling experimental results concerning thrust-wrench fault interference in a brittle medium, to try to evaluate the influence exerted by different prescribed interference angles in the formation of morpho-structural interference fault patterns. All the experiments were conceived to simulate simultaneous reactivation of confining strike-slip and thrust faults defining a (corner) zone of interference, contrasting with previously reported discrete (time and space) superposition of alternating thrust and strike-slip events. Different interference angles of 60°, 90° and 120° were experimentally investigated by comparing the specific structural configurations obtained in each case. Results show that a deltoid-shaped morpho-structural pattern is consistently formed in the fault interference (corner) zone, exhibiting a specific geometry that is fundamentally determined by the different prescribed fault interference angle. Such angle determines the orientation of the displacement vector shear component along the main frontal thrust direction, determining different fault confinement conditions in each case, and imposing a complying geometry and kinematics of the interference deltoid structure. Model comparison with natural examples worldwide shows good geometric and kinematic similarity, pointing to the existence of matching underlying dynamic process. Acknowledgments This work was sponsored by the Fundação para a Ciência e a Tecnologia (FCT) through project MODELINK EXPL/GEO-GEO/0714/2013.

  13. Fracture property of Y-shaped cracks of brittle materials under compression.

    Science.gov (United States)

    Zhang, Xiaoyan; Zhu, Zheming; Liu, Hongjie

    2014-01-01

    In order to investigate the properties of Y-shaped cracks of brittle materials under compression, compression tests by using square cement mortar specimens with Y-shaped crack were conducted. A true triaxial loading device was applied in the tests, and the major principle stresses or the critical stresses were measured. The results show that as the branch angle θ between the branch crack and the stem crack is 75°, the cracked specimen has the lowest strength. In order to explain the test results, numerical models of Y-shaped cracks by using ABAQUS code were established, and the J-integral method was applied in calculating crack tip stress intensity factor (SIF). The results show that when the branch angle θ increases, the SIF K I of the branch crack increases from negative to positive and the absolute value K II of the branch crack first increases, and as θ is 50°, it is the maximum, and then it decreases. Finally, in order to further investigate the stress distribution around Y-shaped cracks, photoelastic tests were conducted, and the test results generally agree with the compressive test results. PMID:25013846

  14. Residual stress evaluation in brittle coatings using indentation technique combined with in-situ bending

    International Nuclear Information System (INIS)

    The indentation crack length approach was adopted and further elaborated to evaluate residual stress and toughness of the brittle coatings: two kinds of glass coatings on steel. The influence of the residual stress on indentation cracking was examined in as-received coating condition and by in-situ superimposing a counteracting tensile stress. For purpose of providing reference toughness values stress-free pieces of separated coating material have also been examined. Thus results of the two complementary sets of experiments were assumed to prove self-consistently toughness and residual stress data of the coating. In particular, the in-situ bending of specimen in combination with the indentation test allowed us to vary deliberately the residual stress situation in glass coating. Thus experiments which utilized the combination of bending test and micro-indentation were introduced as a method to provide unambiguous information about residual compressive stress. Toughness and residual compressive stress of glass coatings used in this study were 0.46-0.50 MPa·m1/2 and 94-111 MPa, respectively. Furthermore, a thermoelastic calculation of the residual compressive stress was performed and it is found that the value of residual compressive stress at coating surface of specimen was 90-102 MPa. (author)

  15. A Criterion for Brittle Failure of Rocks Using the Theory of Critical Distances

    Science.gov (United States)

    Castro, Jorge; Cicero, Sergio; Sagaseta, César

    2016-01-01

    This paper presents a new analytical criterion for brittle failure of rocks and heavily over-consolidated soils. Griffith's model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith's criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as half of the critical distance. This fracture criterion is known as the point method, and is part of the theory of critical distances, which is utilised in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, σ 0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/ L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, σ c and σ t. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils ( σ c/ σ t = 3-50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low-confining stresses.

  16. Estudo comparativo entre duas plataformas para realização de Lasik personalizado para correção de miopia e astigmatismo: Alcon CustomCornea® versus Bausch & Lomb Zyoptix® Wavefront-Guided Lasik for low to moderate myopia: CustomCornea® versus Zyoptix®

    Directory of Open Access Journals (Sweden)

    Telma Pereira Barreiro

    2009-08-01

    Full Text Available OBJETIVO: Comparar os resultados obtidos após o Lasik personalizado utilizando duas plataformas diferentes. MÉTODOS: Estudo prospectivo, randomizado com 50 pacientes míopes submetidos a cirurgia refrativa em ambos os olhos. Foram selecionados para o estudo, pacientes com equivalente esférico semelhante entre os olhos. Todos foram submetidos a Lasik bilateral e simultâneo, sendo que um olho foi operado pela plataforma CustomCornea® e o outro pela Zyoptix®. Acuidade visual sem e com correção, refração dinâmica e estática, medida das aberrações oculares, teste de sensibilidade ao contraste foram realizados no período pré-operatório e pós-operatório de 1, 3 e 6 meses. RESULTADOS: No período pré-operatório a média do equivalente esférico era de -3,29 ± 1,56 D no grupo CustomCornea® e de -3,22 ± 1,50 D no Zyoptix® (p=0,267. No sexto mês de pós-operatório, a média do equivalente esférico no grupo CustomCornea® era de -0,077 ± 0,23 D e -0,282 ± 0,30 D no Zyoptix® (p 20/20 foi alcançada em 86% dos olhos no grupo CustomCornea® e 70% no grupo Zyoptix® (p=0,094. Nenhum paciente perdeu duas ou mais linhas da melhor acuidade visual corrigida. Cem por cento dos olhos CustomCornea® e 88% dos Zyoptix® ficaram entre ± 0,50 D da emetropia (p=0,014*. Melhora da sensibilidade ao contraste em todas as frequências espaciais testadas foi observada em ambos os grupos. A aberração esférica apresentou aumento em ambos os grupos, porém este foi estatisticamente maior na plataforma Zyoptix® (pPURPOSE: To compare the visual and clinical outcomes of Wavefront-guided laser in situ keratomileusis (Lasik with Alcon CustomCornea® and Zyoptix® systems. METHODS: A prospective, randomized, masked and bilateral study was conducted. Fifty patients with preoperative spherical equivalent ranging from -1.00 to -6.50 D were enrolled for customized ablation in both eyes. All of them were submitted to Lasik CustomCornea® treatment in one

  17. Waardenburg syndrome.

    OpenAIRE

    Read, A P; Newton, V E

    1997-01-01

    Auditory-pigmentary syndromes are caused by physical absence of melanocytes from the skin, hair, eyes, or the stria vascularis of the cochlea. Dominantly inherited examples with patchy depigmentation are usually labelled Waardenburg syndrome (WS). Type I WS, characterised by dystopia canthorum, is caused by loss of function mutations in the PAX3 gene. Type III WS (Klein-Waardenburg syndrome, with abnormalities of the arms) is an extreme presentation of type I; some but not all patients are ho...

  18. Metabolic syndrome

    Directory of Open Access Journals (Sweden)

    Gogia Atul

    2006-02-01

    Full Text Available The Metabolic syndrome is a widely prevalent and multi-factorial disorder. The syndrome has been given several names, including- the metabolic syndrome, the insulin resistance syndrome, the plurimetabolic syndrome, and the deadly quartet. With the formulation of NCEP/ATP III guidelines, some uniformity and standardization has occurred in the definition of metabolic syndrome and has been very useful for epidemiological purposes. The mechanisms underlying the metabolic syndrome are not fully known; however resistance to insulin stimulated glucose uptake seems to modify biochemical responses in a way that predisposes to metabolic risk factors. The clinical relevance of the metabolic syndrome is related to its role in the development of cardiovascular disease. Management of the metabolic syndrome involves patient-education and intervention at various levels. Weight reduction is one of the main stays of treatment. In this article we comprehensively discuss this syndrome- the epidemiology, pathogenesis, clinical relevance and management. The need to do a comprehensive review of this particular syndrome has arisen in view of the ever increasing incidence of this entitiy. Soon, metabolic syndrome will overtake cigarette smoking as the number one risk factor for heart disease among the US population. Hardly any issue of any primary care medical journal can be opened without encountering an article on type 2 diabetes, dyslipidemia or hypertension. It is rare to see type 2 diabetes, dyslipidemia, obesity or hypertension in isolation. Insulin resistance and resulting hyperinsulinemia have been implicated in the development of glucose intolerance (and progression to type 2 diabetes, hypertriglyceridemia, hypertension, polycystic ovary yndrome, hypercoagulability and vascular inflammation, as well as the eventual development of atherosclerotic cardiovascular disease manifested as myocardial infarction, stroke and myriad end organ diseases. Conversely

  19. Revesz syndrome

    Directory of Open Access Journals (Sweden)

    Dayane Cristine Issaho

    2015-04-01

    Full Text Available Revesz syndrome is a rare variant of dyskeratosis congenita and is characterized by bilateral exudative retinopathy, alterations in the anterior ocular segment, intrauterine growth retardation, fine sparse hair, reticulate skin pigmentation, bone marrow failure, cerebral calcification, cerebellar hypoplasia and psychomotor retardation. Few patients with this syndrome have been reported, and significant clinical variations exist among patients. This report describes the first Brazilian case of Revesz syndrome and its ocular and clinical features.

  20. Sweet Syndrome

    OpenAIRE

    Kasapçopur, Özgür; Sever, Lale; Çalışkan, Salim; Kodakoğlu, Ramazan; Mat, Cem; Kaner, Gültekin; Arısoy, Nil

    1996-01-01

    Sweet syndrome is a vasculitis characterized with fever leucocytosis neutrophilia and dermal neutrophilic infiltration In children Sweet syndrome usually occurs with secondary to infection and in adults to malignancy We report a Sweet syndrome in a five years old girl with respiratory infections otitis dactylitis long lasting fever and cutaneous rash A neutrophilic dermal infiltration is noted in cutaneous biopsy These signs have disappeared with corticosteroid treatment In conclusion Sweet s...

  1. Brugada syndrome

    Directory of Open Access Journals (Sweden)

    Bockeria O.L.

    2015-03-01

    Full Text Available Brugada syndrome is characterized by sudden death associated with one of several ECG patterns including incomplete right bundle-branch block and ST-segment elevation in the anterior precordial leads. According to the ECG patterns there are three types of Brugada syndrome. Brugada syndrome is genetically determined and has an autosomal dominant pattern of transmission in about 50% of familial cases. Nowadays implantation of cardioverter-defibrillator is the only proven method of sudden cardiac death prevention.

  2. Coloured cornea replacements with anti-infective properties: expanding the safe use of silver nanoparticles in regenerative medicine

    Science.gov (United States)

    Alarcon, E. I.; Vulesevic, B.; Argawal, A.; Ross, A.; Bejjani, P.; Podrebarac, J.; Ravichandran, R.; Phopase, J.; Suuronen, E. J.; Griffith, M.

    2016-03-01

    Despite the broad anti-microbial and anti-inflammatory properties of silver nanoparticles (AgNPs), their use in bioengineered corneal replacements or bandage contact lenses has been hindered due to their intense yellow coloration. In this communication, we report the development of a new strategy to pre-stabilize and incorporate AgNPs with different colours into collagen matrices for fabrication of corneal implants and lenses, and assessed their in vitro and in vivo activity.Despite the broad anti-microbial and anti-inflammatory properties of silver nanoparticles (AgNPs), their use in bioengineered corneal replacements or bandage contact lenses has been hindered due to their intense yellow coloration. In this communication, we report the development of a new strategy to pre-stabilize and incorporate AgNPs with different colours into collagen matrices for fabrication of corneal implants and lenses, and assessed their in vitro and in vivo activity. Electronic supplementary information (ESI) available: Collagen hydrogel, moulded as a cornea, prepared containing collagen protected AgNPs and representative images for collagen hydrogels, moulded as corneas, containing Blue AgNPs either unprotected or protected with LL37-SH; representative TEM images for Green-1 AgNPs prepared in this work; changes on surface plasmon band after synthesis for Green-2 AgNPs without LL37-SH; representative picture of the powder obtained for Green-1 AgNPs capped with LL37-SH after 72 h lyophilization, see main text; representative TEM images for Blue and Green-1 AgNPs prepared in this work; absorption spectra for the supernatants for collagen hydrogels containing Blue AgNPs; absorbance at 600 nm of PAO1 cultures prepared in 25% LB media incubated for 14 h at 37 °C in the presence of different concentrations of AgNPs, Green-1 or Blue, or silver nitrate; HECC cell density (cells per cm2) measured on gels with and without silver nitrate after 1 day of cell incubation; total silver concentration

  3. Marfan Syndrome (For Teens)

    Science.gov (United States)

    ... How Can I Help a Friend Who Cuts? Marfan Syndrome KidsHealth > For Teens > Marfan Syndrome Print A ... a genetic disorder called Marfan syndrome. What Is Marfan Syndrome? Marfan syndrome is named after Antoine Marfan, ...

  4. What Is Down Syndrome?

    Science.gov (United States)

    ... NDSS Home » Down Syndrome » What Is Down Syndrome? What Is Down Syndrome? In every cell in the ... chromosome 21 causes the characteristics of Down syndrome. What Causes Down Syndrome? Regardless of the type of ...

  5. Damage law identification of a quasi brittle ceramic from a b ending test using digital image correlation

    Directory of Open Access Journals (Sweden)

    Meille S.

    2010-06-01

    Full Text Available The quasi brittle ceramics show a non linear mechanical behaviour resulting most of the time in a dissymetry between their tensile and compressive stress-strain laws. The characterization of their fracture strengths might be biased if elastic linear formulae are used to analyze classical tests like bending tests. Based on Digital Image Correlation (DIC, a methodology is proposed to characterize materials with dissymmetric behaviours. Applying specific DIC decomposition functions for bending, compressive and tensile tests, a stress-strain model and its damage law are identified for aluminium titanate, a damageable micro cracked ceramic. This identification method using DIC can obviously be applied to other quasi brittle materials.

  6. Brittle fracture safety analysis of RPV based on progressive thermo hydraulic analysis; Sproedbruchsicherheitsnachweise von Reaktordruckbehaeltern auf Basis fortschrittlicher thermohydraulischer Analysen

    Energy Technology Data Exchange (ETDEWEB)

    Keim, E.; Hertlein, R. [AREVA NP GmbH (Germany); Ilg, U.; Koenig, G. [AREVA NP GmbH (Germany)]|[EnBW Kernkraft GmbH (Germany); Schlueter, N.; Widera, M. [RWE Power AG (Germany)

    2007-07-01

    The fundamentals of brittle fracture safety analysis of RPV in case of LCA are presented in the following steps: 1. Proof of flawlessness of the RPV and plating after production; 2. Crack postulate: Internal defect with defect depth x safety factor 2 according to non-destructive test and defect type a/2c = 1/6; 3. Exclusion of crack initiation with RT{sub NDT} concept and consideration of maximum load; 4.If necessary, crack arrest as a further barrier. This concept is applied to three types of nuclear power plant: a) KKE, KKPL2, GKN II; b) GKN I; c) Biblis A/B. The thermohydraulic and fracture-mechanical calculaitons and the subsequent safety assessment showed that brittle fracture of RPV in case of LCA can be excluded for all parts of the RPV and for all accident scenarios. (orig.)

  7. The influence of coarse aggregate size and volume on the fracture behavior and brittleness of self-compacting concrete

    International Nuclear Information System (INIS)

    This paper presents the results of an experimental investigation on fracture characteristics and brittleness of self-compacting concrete (SCC), involving the tests of 185 three point bending beams with different coarse aggregate size and content. Generally, the parameters were analyzed by the work of fracture method (WFM) and the size effect method (SEM). The results showed that with increase of size and content of coarse aggregate, (a) the fracture energy increases which is due to the change in fractal dimensions, (b) behavior of SCC beams approaches strength criterion, (c) characteristic length, which is deemed as an index of brittleness, increases linearly. It was found with decrease of w/c ratio that fracture energy increases which may be explained by the improvement in structure of aggregate-paste transition zone. Also, the results showed that there is a correlation between the fracture energy measured by WFM (GF) and the value measured through SEM (Gf) (GF = 3.11Gf)

  8. Auto-refrigeration/brittle fracture analysis of existing olefins plants--translation of lessons learned to other processes.

    Science.gov (United States)

    King, Ralph E

    2007-04-11

    This paper describes the use of process hazards analysis (PHA) techniques and "API 579 Recommended Practice for Fitness-for-Service, Assessment of Existing Equipment for Brittle Fracture" to evaluate existing olefins plants. It also examines some of the identified transient process excursions that can result in operations below vessel minimum allowable temperature (MAT), creating the potential for brittle fracture, and the methods of the evaluation are described. The importance of identifying transient process conditions and making materials-of-construction selections based on these conditions is emphasized. Translation of the typical findings and lessons learned to other processes handling light-liquid hydrocarbon materials in carbon steel equipment is discussed, as well as the importance of operator training and response. PMID:16982139

  9. Intergranular brittle fracture of a low alloy steel induced by grain boundary segregation of impurities: influence of the microstructure

    International Nuclear Information System (INIS)

    The study contributes to improve the comprehension of intergranular embrittlement induced by the phosphorus segregation along prior austenitic grain boundaries of low alloy steels used in pressurized power reactor vessel. A part of this study was performed using a A533 steel which contains chemical fluctuations (ghost lines) with two intensities. Axi-symmetrically notched specimens were tested and intergranular brittle de-cohesions were observed in the ghost lines. The fracture initiation sites observed on fracture surfaces were identified as MnS inclusions. A bimodal statistic obtained in a probabilistic model of the fracture is explained by the double population of ghost lines' intensities. A metallurgical study was performed on the same class of steel by studying the influence of the microstructure on the susceptibility to temper embrittlement. Brittle fracture properties of such microstructures obtained by dilatometric experiments were tested on sub-sized specimens to measure the V-notched fracture toughness. Fraction areas of brittle fracture modes were determined on surface fractures. A transition of the fracture mode with the microstructure is observed. It is shown that tempered microstructures of martensite and lower bainite are more susceptible to intergranular embrittlement than tempered upper bainitic microstructure. The intergranular fracture is the most brittle mode. The analysis of crystalline mis-orientations shows a grain boundary structure appreciably more coherent for tempered microstructures of martensite and lower bainite. The higher density of random grain boundaries is susceptible to drag the phosphorus in the upper bainitic matrix and to make the quantity of free phosphorus decreasing. Microstructure observations show a difference in the size and the spatial distribution of carbides, essentially cementite, between tempered martensite and upper bainite. It can explain the bigger susceptibility of this last microstructure to cleavage mode

  10. The Ductile to Brittle Transition Behavior of the Modified 9Cr-1Mo Steel and Its Laser Welds

    Institute of Scientific and Technical Information of China (English)

    H.C.Wu; R.K.Shiue; C.Chen

    2004-01-01

    The ductile to brittle transition temperature (DBTT) of the modified 9Cr-1Mo steel and its laser welds was studied. The increase in grain size of the weld structure ascended the DBTT of the steel significantly. The transformation of retained austenite at martensite interlath boundaries into untempered and/or twinned martensite could also contribute to increased DBTTs of the steel and its welds tempered at 540℃.

  11. Existence of a threshold for brittle grains crushing strength: two-versus three- parameter Weibull distribution fitting

    OpenAIRE

    Stefanou, Ioannis; Sulem, Jean

    2015-01-01

    International audience Grain crushing plays an important role in the mechanical behavior of granular media, in chemo-hydro-thermo-mechanical couplings, in instabilities related to strain localization such as shear bands and compaction bands, in geophysical and geotechnical processes, in reservoir and petroleum engineering and in many other domains. The strength of brittle particles seems to be quite well described by a two-parameter Weibull distribution. Nevertheless, such a distribution p...

  12. MUC19 expression in human ocular surface and lacrimal gland and its alteration in Sjögren syndrome patients.

    Science.gov (United States)

    Yu, D F; Chen, Y; Han, J M; Zhang, H; Chen, X P; Zou, W J; Liang, L Y; Xu, C C; Liu, Z G

    2008-02-01

    This study investigated the expression of MUC19, a newly discovered gel-forming mucin gene, in normal human lacrimal functional unit components and its alteration in Sjögren syndrome patients. Real-time PCR and immunohistochemistry were performed to determine the expression of MUC19 and MUC5AC in human cornea, conjunctiva, and lacrimal gland tissues. Conjunctival impression cytology specimens were collected from normal control subjects and Sjögren syndrome patients for Real-time PCR, PAS staining, and immunohistochemistry assays. In addition, conjunctiva biopsy specimens from both groups were examined for the expression differences of MUC19 and MUC5AC at both mRNA and protein level. The MUC19 mRNA was found to be present in cornea, conjunctiva and lacrimal gland tissues. The immunohistochemical staining of mucins showed that MUC19 was expressed in epithelial cells from corneal, conjunctival, and lacrimal gland tissues. In contrast, MUC5AC mRNA was only present in conjunctiva and lacrimal gland tissues, but not in cornea. Immunostaining demonstrates the co-staining of MUC19 and MUC5AC in conjunctival goblet cells. Consistent with the significant decrease of mucous secretion, both MUC19 and MUC5AC were decreased in conjunctiva of Sjögren syndrome patients compared to normal subjects. Considering the contribution of gel-forming mucins to the homeostasis of the ocular surface, the decreased expression of MUC19 and MUC5AC in Sjögren syndrome patients suggested that these mucins may be involved in the disruption of the ocular surface homeostasis in this disease.

  13. MUC19 expression in human ocular surface and lacrimal gland and its alteration in Sjögren syndrome patients.

    Science.gov (United States)

    Yu, D F; Chen, Y; Han, J M; Zhang, H; Chen, X P; Zou, W J; Liang, L Y; Xu, C C; Liu, Z G

    2008-02-01

    This study investigated the expression of MUC19, a newly discovered gel-forming mucin gene, in normal human lacrimal functional unit components and its alteration in Sjögren syndrome patients. Real-time PCR and immunohistochemistry were performed to determine the expression of MUC19 and MUC5AC in human cornea, conjunctiva, and lacrimal gland tissues. Conjunctival impression cytology specimens were collected from normal control subjects and Sjögren syndrome patients for Real-time PCR, PAS staining, and immunohistochemistry assays. In addition, conjunctiva biopsy specimens from both groups were examined for the expression differences of MUC19 and MUC5AC at both mRNA and protein level. The MUC19 mRNA was found to be present in cornea, conjunctiva and lacrimal gland tissues. The immunohistochemical staining of mucins showed that MUC19 was expressed in epithelial cells from corneal, conjunctival, and lacrimal gland tissues. In contrast, MUC5AC mRNA was only present in conjunctiva and lacrimal gland tissues, but not in cornea. Immunostaining demonstrates the co-staining of MUC19 and MUC5AC in conjunctival goblet cells. Consistent with the significant decrease of mucous secretion, both MUC19 and MUC5AC were decreased in conjunctiva of Sjögren syndrome patients compared to normal subjects. Considering the contribution of gel-forming mucins to the homeostasis of the ocular surface, the decreased expression of MUC19 and MUC5AC in Sjögren syndrome patients suggested that these mucins may be involved in the disruption of the ocular surface homeostasis in this disease. PMID:18184611

  14. Normalization of wound healing and stem cell marker patterns in organ-cultured human diabetic corneas by gene therapy of limbal cells.

    Science.gov (United States)

    Saghizadeh, Mehrnoosh; Dib, Christian M; Brunken, William J; Ljubimov, Alexander V

    2014-12-01

    Overexpression of c-met and suppression of matrix metalloproteinase-10 (MMP-10) and cathepsin F genes was previously shown to normalize wound healing, epithelial and stem cell marker patterns in organ-cultured human diabetic corneas. We now examined if gene therapy of limbal cells only would produce similar effects. Eight pairs of organ-cultured autopsy human diabetic corneas were used. One cornea of each pair was treated for 48 h with adenoviruses (Ad) harboring full-length c-met mRNA or a mixture (combo) of Ad with c-met and shRNA to MMP-10 and cathepsin F genes. Medium was kept at the limbal level to avoid transduction of central corneal epithelium. Fellow corneas received control Ad with EGFP gene. After additional 5 (c-met) or 10 days (combo) incubation, central corneal epithelial debridement with n-heptanol was performed, and wound healing times were determined microscopically. Corneal cryostat sections were immunostained for diabetic and putative limbal stem cell markers, α3β1 integrin, nidogen-1, fibronectin, laminin γ3 chain, ΔNp63α, keratins 14, 15, and 17, as well as for activated signaling intermediates, phosphorylated EGFR, Akt, and p38. Limbal c-met overexpression significantly accelerated healing of 8.5-mm epithelial wounds over EGFP controls (6.3 days vs. 9.5 days, p treatment produced a similar result (6.75 days vs. 13.5 days, p stem cell compartment has a beneficial effect on the diabetic corneal wound healing and on diabetic and stem cell marker expression, and shows potential for alleviating symptoms of diabetic keratopathy.

  15. Corneal thickness changes during corneal collagen cross-linking with UV-A irradiation and hypo-osmolar riboflavin in thin corneas

    Directory of Open Access Journals (Sweden)

    Belquiz Amaral Nassaralla

    2013-06-01

    Full Text Available PURPOSE: To evaluate the thinnest corneal thickness changes during and after corneal collagen cross-linking treatment with ultraviolet-A irradiation, using hypo-osmolar riboflavin solution in thin corneas. METHODS: Eighteen eyes of 18 patients were included in this study. After epithelium removal, iso-osmolar 0.1% riboflavin solution was instilled to the cornea every 3 minutes for 30 minutes. Hypo-osmolar 0.1% riboflavin solution was then applied every 20 seconds for 5 minutes or until the thinnest corneal thickness reached 400 µm. Ultraviolet-A irradiation was performed for 30 minutes. During irradiation, iso-osmolar 0.1% riboflavin drops were applied every 5 minutes. Ultrasound pachymetry was performed at approximately the thinnest point of the cornea preoperatively, after epithelial removal, after iso-osmolar riboflavin instillation, after hypo-osmolar riboflavin instillation, after ultraviolet-A irradiation, and at 1, 6 and 12 months after treatment. RESULTS: Mean preoperative thinnest corneal thickness was 380 ± 11 µm. After epithelial removal it decreased to 341 ± 11 µm, and after 30 minutes of iso-osmolar 0.1% riboflavin drops, to 330 ± 7.6 µm. After hypo-osmolar 0.1% riboflavin drops, mean thinnest corneal thickness increased to 418 ± 11 µm. After UVA irradiation, it was 384 ± 10 µm. At 1, 6 and 12 months after treatment, it was 372 ± 10 µm, 381 ± 12.7, and 379 ± 15 µm, respectively. No intraoperative, early postoperative, or late postoperative complications were noted. CONCLUSIONS: Hypo-osmolar 0.1% riboflavin solution seems to be effective for swelling thin corneas. The swelling effect is transient and short acting. Corneal thickness should be monitored throughout the procedure. Larger sample sizes and longer follow-up are required in order to make meaningful conclusions regarding safety.

  16. The Effect and Experience of Animal Cornea Application in Ophthalmology Trainee%眼角膜疾病见习中的教学效果和体会

    Institute of Scientific and Technical Information of China (English)

    杨硕; 李学东; 华文; 卢弘

    2016-01-01

    在眼科教学中,传统的角膜病见习内容往往不能达到良好的教学效果。在近年的教学中,进行了见习内容改革,将动物眼球作为教具引入眼科见习中,增加了实际解剖操作、基本显微操作等内容,并通过具体病例分析角膜移植的临床意义、介绍国内外角膜器官捐献现状并结合医学伦理学进行讨论。从中,提高了医学生的学习兴趣,培养了医学生的观察力和动手能力,同时还培养了学员的医学伦理思维,这种见习模式获得了理想的教学效果。%In the past, courses of cornea mainly focused on the theoretical knowledge and cognition of keratopathy. Students always feel so tasteless about the course. Therefore, traditional courses can’ t achieve good teaching effects. In the recent years, we try to change this teaching mode and adjust course contents: including application of animal cornea to replace the traditional teaching aids, the actual dissection, microscopic operation, analysis on significance of cornea transplantation, introduction of domestic and foreign cornea organ donation status and discussion of medical ethics issues. The new teaching method has obtained ideal effects.

  17. Localization of type V collagen and type IV collagen in human cornea, lung, and skin. Immunohistochemical evidence by anti-collagen antibodies characterized by immunoelectroblotting.

    OpenAIRE

    Konomi, H.; Hayashi, T.; NAKAYASU, K.; Arima, M.

    1984-01-01

    Tissue distribution of Type V collagen in comparison with Type IV collagen was investigated by indirect immunofluorescence microscopy. Affinity-purified rat antibodies to Type IV and Type V collagens obtained from human placenta reacted specifically only with the corresponding type of collagen in both native and denatured conformations. In indirect immunofluorescent stainings of human skin, lung, and cornea tissues, Type IV and Type V collagens showed distinct distributions. Type IV collagen ...

  18. Embryonic development of the cornea in the eye of the clearnose skate, Raja eglanteria: I. Stromal development in the absence of an endothelium

    Science.gov (United States)

    Conrad, G. W.; Paulsen, A. Q.; Luer, C. A.; Spooner, B. S. (Principal Investigator)

    1994-01-01

    Embryos of the clearnose skate, Raja eglanteria, develop in sea water at 20-22 degrees C, hatching after 82 +/- 4 days (Luer and Gilbert, Environ. Biol. Fishes, 13:161-171, 1985). Eyes develop as steadily enlarging spheres whose corneas have the same radius of curvature as the sclera. The cornea begins development as a 2-cell thick epithelium beneath which by Day 12 there is only a basal lamina and a wispy matrix separating it from the underlying lens. This matrix, modified by Day 16, is displaced on Day 22 by a few orthogonal plies of fibrillar primary stroma. Ply number increases to at least 13 by Day 30, reaching the final number of 20 +/- 2 by Day 42. Stromal fibroblasts (keratocytes) appear at the corneal periphery by Day 22, and in increased numbers by Day 30, a time at which no keratocytes are seen in the central stroma. However, by Day 40, many fibroblasts are present at the corneal periphery, invading the primary stroma between plies, occasionally reaching even the central cornea. By Day 53, keratocytes are present between all plies, from corneal periphery to center. Thickness of each ply in this secondary stroma increases, but the number of plies remains the same as in the primary stroma. Bowman's layer, non-invaded matrix beneath the epithelial basal lamina, is not evident until Day 53. Sutural fibers, first seen on Day 22, originate in the corneal epithelial basal lamina, traversing perpendicularly the plies of the primary stroma. Sutural fibers persist throughout development of the secondary stroma and into adulthood. In contrast to chicks, skate corneas remain transparent throughout development, and never form an endothelium.

  19. A two-scale model for frictional cracks in 3D fractured brittle media with the extended finite element method

    Science.gov (United States)

    Liu, F.; Borja, R. I.

    2009-12-01

    Stress concentration induced by the heterogeneity in brittle geomaterials is generally considered as the driving force in the evolution of the microstructure (such as the crack and pore microstructure). Specifically, modeling heterogeneity is key to properly predicting the nucleation, coalescence and propagation of micro-cracks in brittle solids. In this paper, we propose a two-scale model for frictional cracks in fractured brittle media. The major crack in the study domain is modeled at a macro level, while the micro-cracks are modeled at a finer scale. The macro-scale behavior is described by a standard boundary value problem. The finer-scale problem is modeled using the notion of representative elementary volume (REV) consisting of a solid volume with distributed micro-cracks. Periodic boundary condition and small strain formulation are assumed in the finer-scale analysis. The scale bridging mechanism is borrowed from the standard homogenization technique. The proposed model is implemented with the extended finite element method. The macro stress at each Gauss point in the finite element formulation is computed as the volume average of finer-scale stresses in each corresponding REV. The macro tangent operator is computed using a perturbation method. For 3D problems, six independent linear perturbation analyses are carried out for each numerical integration point. Our numerical examples capture the nucleation and coalescence of micro-cracks, which can be used to infer the potential propagation direction of the major crack.

  20. Numerical simulation of triaxial compression test for brittle rock sample using a modified constitutive law considering degradation and dilation behavior

    Institute of Scientific and Technical Information of China (English)

    谭鑫

    2015-01-01

    The understanding of the rock deformation and failure process and the development of appropriate constitutive models are the basis for solving problems in rock engineering. In order to investigate progressive failure behavior in brittle rocks, a modified constitutive model was developed which follows the principles of the continuum damage mechanics method. It incorporates non-linear Hoek-Brown failure criterion, confining pressure-dependent strength degradation and volume dilation laws, and is able to represent the nonlinear degradation and dilation behaviors of brittle rocks in the post-failure region. A series of triaxial compression tests were carried out on Eibenstock (Germany) granite samples. Based on a lab data fitting procedure, a consistent parameter set for the modified constitutive model was deduced and implemented into the numerical code FLAC3D. The good agreement between numerical and laboratory results indicates that the modified constitutive law is well suited to represent the nonlinear mechanical behavior of brittle rock especially in the post-failure region.

  1. A Study on the Low Temperature Brittleness by Cyclic Cooling-Heating of Low Carbon Hot Rolled Steel Plate

    International Nuclear Information System (INIS)

    The ductile-brittle transition phenomenon of low carbon steel has been investigated using the standard Charpy V-notch specimen. Dry ice and acetone were used as refrigerants. Notched specimens were cut from the hot rolled plate produced at POSCO for the Olsen impact test. The effect of cyclic cooling and heating of 0.14% carbon steel on the embrittlement was extensively examined. The ductile-brittle transition temperature was found to be approximately-30 .deg. C. The transition temperature was gradually increased as the number of cooling-heating cycles increased. On a typical V-notch fracture surface it was found that the ductile fracture surface showed a thick and fibrous structure, while the brittle fracture surface a small and light grain with irregular disposition. As expected, the transition temperature was also increased as the carbon content of steel increased. Compared with the case of 0.14% carbon steel, the transition temperature of 0.17% carbon steel was found to be increased about 12 .deg. C

  2. Simulation of seismic waves at the Earth crust (brittle-ductile transition based on the Burgers model

    Directory of Open Access Journals (Sweden)

    J. M. Carcione

    2014-06-01

    Full Text Available The Earth crust presents two dissimilar rheological behaviours depending on the in-situ stress-temperature conditions. The upper, cooler, part is brittle while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress–strain relation including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behaviour is based on the Burgers mechanical model to describe the effects of seismic attenuation and steady-state creep flow. The shear Lamé constant of the brittle and ductile media depends on the in-situ stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the P-S and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge–Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. A realistic example illustrates the computation of surface and reverse-VSP synthetic seismograms in the presence of an abrupt brittle-ductile transition.

  3. Benchmarking the Sandbox: Quantitative Comparisons of Numerical and Analogue Models of Brittle Wedge Dynamics (Invited)

    Science.gov (United States)

    Buiter, S.; Schreurs, G.; Geomod2008 Team

    2010-12-01

    When numerical and analogue models are used to investigate the evolution of deformation processes in crust and lithosphere, they face specific challenges related to, among others, large contrasts in material properties, the heterogeneous character of continental lithosphere, the presence of a free surface, the occurrence of large deformations including viscous flow and offset on shear zones, and the observation that several deformation mechanisms may be active simultaneously. These pose specific demands on numerical software and laboratory models. By combining the two techniques, we can utilize the strengths of each individual method and test the model-independence of our results. We can perhaps even consider our findings to be more robust if we find similar-to-same results irrespective of the modeling method that was used. To assess the role of modeling method and to quantify the variability among models with identical setups, we have performed a direct comparison of results of 11 numerical codes and 15 analogue experiments. We present three experiments that describe shortening of brittle wedges and that resemble setups frequently used by especially analogue modelers. Our first experiment translates a non-accreting wedge with a stable surface slope. In agreement with critical wedge theory, all models maintain their surface slope and do not show internal deformation. This experiment serves as a reference that allows for testing against analytical solutions for taper angle, root-mean-square velocity and gravitational rate of work. The next two experiments investigate an unstable wedge, which deforms by inward translation of a mobile wall. The models accommodate shortening by formation of forward and backward shear zones. We compare surface slope, rate of dissipation of energy, root-mean-square velocity, and the location, dip angle and spacing of shear zones. All models show similar cross-sectional evolutions that demonstrate reproducibility to first order. However

  4. From brittle to ductile: a structure dependent ductility of diamond nanothread

    Science.gov (United States)

    Zhan, Haifei; Zhang, Gang; Tan, Vincent B. C.; Cheng, Yuan; Bell, John M.; Zhang, Yong-Wei; Gu, Yuantong

    2016-05-01

    As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp3 bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different mechanical responses than other 1D carbon allotropes. Analogously, the SW defects behave like a grain boundary that interrupts the consistency of the poly-benzene sections. For a DNT with a fixed length, the yield strength fluctuates in the vicinity of a certain value and is independent of the ``grain size''. On the other hand, both yield strength and yield strain show a clear dependence on the total length of DNT, which is due to the fact that the failure of the DNT is dominated by the SW defects. Its highly tunable ductility together with its ultra-light density and high Young's modulus makes diamond nanothread ideal for the creation of extremely strong three-dimensional nano-architectures.As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp3 bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different

  5. Brittle fault analysis from the immediate southern side of the Insubric fault

    Science.gov (United States)

    Pleuger, Jan; Mancktelow, Neil

    2013-04-01

    The Insubric segment of the Periadriatic fault is characterised in its central part between Lago Maggiore and Valle d'Ossola by two greenschist-facies mylonitic belts which together are about 1 km thick. The northern, external belt has a north-side-up kinematics generally with a minor dextral component and the southern internal belt is dextral, locally with a considerable south-side-up component. Overprinting relations locally show that the internal belt is younger than the external one (e.g. Schmid et al., 1987). The absolute age of dextral shearing is probably given by K-Ar white mica ages ranging mostly between from c. 27 to 23 Ma (Zingg and Hunziker, 1990). We analysed fault-slip data from various locations in the Southern Alps immediately south of the Insubric Fault. From the results, two different patterns of orientations of contraction (P-axes) and extension (T-axes) axes can be distinguished. One group (group 1) of analyses is compatible with dextral transpression (i.e. both P- and T-axes are subhorizontal) and the other (group 2) with roughly orogen-perpendicular extension (i.e. subvertical P-axes and subhorizontal T-axes). The orientations of subhorizontal axes (P- and T-axes in group 1, T-axes in group 2) show a tendency to follow the curved shape of the Insubric fault, i.e. P-axes of group 1 and T-axes of group 2 change from NNW-SSE in the east where the Insubric fault trends east-west to WNW-ESE in the west where the Insubric fault trends northeast-southwest. We speculate that group 1 formed at the same time as dextral shearing on in the internal mylonite belt while none of our fault analyses reflects the north-side-up reverse faulting that is observed in the external mylonite belt. The northwest-southeast extension documented in the analyses of group 2 is not associated with a continuous mylonitic belt or brittle fault plane along the Insubric fault. Instead, an uplift of the Southern Alps with respect to the northern block was accommodated by

  6. Predicting the Relationship Between System Vibration with Rock Brittleness Indexes in Rock Sawing Process

    Science.gov (United States)

    Mikaeil, Reza; Ataei, Mohammad; Ghadernejad, Saleh; Sadegheslam, Golsa

    2014-03-01

    The system vibration is a very significant measure of the sawing performance, because it indicates the amount of energy required to saw the rock. The maintenance cost of system is also dependant on system vibration. A few increases in system vibration cause a huge increase in the maintenance cost of the system. In this paper, the vibration of system in terms of RMSa was investigated and models for estimation of vibration by means of rock brittleness indexes and operational specifications were designed via statistical models and multiple curvilinear regression analysis. In this study, the relationships between rock brittleness indexes and operational specifications were investigated by regression analysis in statistical package for social science (SPSS) and the results of determination coefficients have been presented. In the second part, the diagrams show that a point lying on the line indicates an exact estimation. In the plot for model, the points are scattered uniformly about the diagonal line, suggesting that the models are good. It is very useful to evaluate the vibration of system and select the suitable operational characteristics by only some mechanical properties of rock. Drgania układu uważane są za miernik wydajności procesu urabiania, ponieważ pokazują ilość energii niezbędnej do urabiania skały. Od poziomu drgań zależą także koszty eksploatacji systemu. Nieznaczny nawet wzrost poziomu drgań prowadzi do znacznego zwiększenia kosztów eksploatacyjnych urządzenia. W pracy tej przeprowadzono analizę drgań (ich wartości skutecznych) i opracowano model estymacji poziomu drgań w oparciu o współczynnik kruchości skał i parametry eksploatacyjne urządzenia. W pracy wykorzystano modele statystyczne i wielokrotną analizę metodą regresji krzywoliniowej. W pracy obecnej związek pomiędzy współczynnikiem kruchości skał a parametrami eksploatacyjnymi urządzenia badano z wykorzystaniem analizy metodą regresji dostępnej w

  7. Simultaneous imaging and measurement of tensile stress on cornea by using a common-path optical coherence tomography system with an external contact reference

    Institute of Scientific and Technical Information of China (English)

    Utkarsh Sharma; Jin U. Kang

    2008-01-01

    The objective of this study is to demonstrate that tensile stress resulting due to applied force on cornea can be accurately measured by using a time-domain common-path optical coherence tomography (OCT) system with an external contact reference. The unique design of the common-path OCT is utilized to set up an imaging system in which a chicken eye is placed adjacent to a glass plate serving as the external reference plane for the imaging system. As the force is applied to the chicken eye, it presses against the reference glass plate. The modified OCT image obtained is used to calculate the size of contact area, which is then used to derive the tensile stress on the cornea. The drop in signal levels upon contact of reference glass plate with the tissue are extremely sharp because of the sharp decline in reference power levels itself, thus providing us with an accurate measurement of contact area. The experimental results were in good agreement with the numerical predictions. The results of this study might be useful in providing new insights and ideas to improve the precision and safety of currently used ophthalmic surgical techniques. This research outlines a method which could be used to provide high resolution OCT images and a precise feedback of the forces applied to the cornea simultaneously.

  8. Effect of the Multiglycoside of Tripterygium Wilfordii Hookf.(Tii)on Cornea Allograft Rejection Model in Rabbit

    Institute of Scientific and Technical Information of China (English)

    ZhijieLi; ChenLi

    1995-01-01

    Purpose:Toexamine the effect of Tii treatment of cornea graft survival in a rab-bit model.Methods:Tii was administrated orally after eccentrical corneal transplantation.Survival times were determined by biomicroscopy.Cytotoxic T lymphocytes(CTL)and delayed-type hypersensitivity(DTH)responses to donor alloantigens were assessed at ady 16after heterotopic corneal grafts.Results:Administration of Tii reduced the incidence and prologed the graft sur-vival time.Both CTLand DTH responses to donor alloantigens were severely ed-pressed in hosts treated with Tii.However,combination of Tii and cyclosporine further enhanced the immunosuppressive effects described above.Conclusions:Tii is a potent immunosuppressant with the ability to prolong allo-graft survival in the rabbit penetrating keratoplasty model and may have coordi-native effects with CsA through different mechanisms.Further studies are neces-sary to define any potentially coordinative role in the prevention of allograft rejec-tion in human keratoplasty.Eye Science 1995;11:168-172.

  9. Late Stage of Corneal Decompensation Caused by Progressive Keratoconus: Can We Treat It and Save the Cornea?

    Directory of Open Access Journals (Sweden)

    Igor Knezović

    2015-01-01

    Full Text Available Aim. To report a case of 40-year-old male with progressive bilateral keratoconus who had undergone transepithelial phototherapeutic keratectomy (TE-PTK and corneal collagen cross-linking (CXL using hypoosmolar riboflavin solution in a same day procedure. Methods. Eye examination showed that UCDVA on both eyes was 0,01 according to Snellen charts, and slit lamp biomicroscopy showed paracentral diffuse intrastromal corneal haze. Anterior OCT marked stromal hyperreflective zones and localized paracentral thinning of the cornea. Scheimpflug tomography noted keratoconus stages III-IV on both eyes. After 40/35 microns TE-PTK, a CXL was performed for 30 minutes using hypoosmolar riboflavin solution. The left eye was treated first and the right eye 1 month after. Follow-up period was 10 months. Results. One month after the treatment both eyes showed improvement in corneal topography and the UCDVA was better. Eight months after the treatment BSCVA improved to 0,6 in both eyes using Rose K2 contact lenses and remained stable. Conclusion. TE-PTK and CXL using hypotonic riboflavin solution as a same day procedure have been shown to be a safe and promising method in this case of progressive keratoconus. It was necessary to consider certain parameters that could influence the safety and the final outcome of this combined protocol.

  10. Chronic Electromagnetic Exposure at Occupational Safety Level Does Not Affect the Metabolic Profile nor Cornea Healing after LASIK Surgery.

    Science.gov (United States)

    Crouzier, David; Dabouis, Vincent; Gentilhomme, Edgar; Vignal, Rodolphe; Bourbon, Fréderic; Fauvelle, Florence; Debouzy, Jean-Claude

    2014-01-01

    LASIK eye surgery has become a very common practice for myopic people, especially those in the military. Sometimes undertaken by people who need to keep a specific medical aptitude, this surgery could be performed in secret from the hierarchy and from the institute medical staff. However, even though the eyes have been previously described as one of the most sensitive organs to electromagnetic fields in the human body, no data exist on the potential deleterious effects of electromagnetic fields on the healing eye. The consequences of chronic long-lasting radar exposures at power density, in accordance with the occupational safety standards (9.71 GHz, 50 W/m(2)), were investigated on cornea healing. The metabolic and clinical statuses after experimental LASIK keratotomy were assessed on the different eye segments in a New Zealand rabbit model. The analysis methods were performed after 5 months of exposure (1 hour/day, 3 times/week). Neither clinical or histological examinations, nor experimental data, such as light scattering, (1)H-NMR HRMAS metabolomics, (13)C-NMR spectra of lipidic extracts, and antioxidant status, evidenced significant modifications. It was concluded that withdrawing the medical aptitude of people working in electromagnetic field environments (i.e., radar operators in the navy) after eye surgery was not justified. PMID:24757560

  11. Late Stage of Corneal Decompensation Caused by Progressive Keratoconus: Can We Treat It and Save the Cornea?

    Science.gov (United States)

    Knezović, Igor; Belovari Višnjić, Mirna; Raguž, Hrvoje

    2015-01-01

    Aim. To report a case of 40-year-old male with progressive bilateral keratoconus who had undergone transepithelial phototherapeutic keratectomy (TE-PTK) and corneal collagen cross-linking (CXL) using hypoosmolar riboflavin solution in a same day procedure. Methods. Eye examination showed that UCDVA on both eyes was 0,01 according to Snellen charts, and slit lamp biomicroscopy showed paracentral diffuse intrastromal corneal haze. Anterior OCT marked stromal hyperreflective zones and localized paracentral thinning of the cornea. Scheimpflug tomography noted keratoconus stages III-IV on both eyes. After 40/35 microns TE-PTK, a CXL was performed for 30 minutes using hypoosmolar riboflavin solution. The left eye was treated first and the right eye 1 month after. Follow-up period was 10 months. Results. One month after the treatment both eyes showed improvement in corneal topography and the UCDVA was better. Eight months after the treatment BSCVA improved to 0,6 in both eyes using Rose K2 contact lenses and remained stable. Conclusion. TE-PTK and CXL using hypotonic riboflavin solution as a same day procedure have been shown to be a safe and promising method in this case of progressive keratoconus. It was necessary to consider certain parameters that could influence the safety and the final outcome of this combined protocol. PMID:26064737

  12. Chronic Electromagnetic Exposure at Occupational Safety Level Does Not Affect the Metabolic Profile nor Cornea Healing after LASIK Surgery

    Directory of Open Access Journals (Sweden)

    David Crouzier

    2014-01-01

    Full Text Available LASIK eye surgery has become a very common practice for myopic people, especially those in the military. Sometimes undertaken by people who need to keep a specific medical aptitude, this surgery could be performed in secret from the hierarchy and from the institute medical staff. However, even though the eyes have been previously described as one of the most sensitive organs to electromagnetic fields in the human body, no data exist on the potential deleterious effects of electromagnetic fields on the healing eye. The consequences of chronic long-lasting radar exposures at power density, in accordance with the occupational safety standards (9.71 GHz, 50 W/m2, were investigated on cornea healing. The metabolic and clinical statuses after experimental LASIK keratotomy were assessed on the different eye segments in a New Zealand rabbit model. The analysis methods were performed after 5 months of exposure (1 hour/day, 3 times/week. Neither clinical or histological examinations, nor experimental data, such as light scattering, 1H-NMR HRMAS metabolomics, 13C-NMR spectra of lipidic extracts, and antioxidant status, evidenced significant modifications. It was concluded that withdrawing the medical aptitude of people working in electromagnetic field environments (i.e., radar operators in the navy after eye surgery was not justified.

  13. Cadmium Accumulation and Its Toxicity in Brittle Culm 1 (bc1), a Fragile Rice Mutant

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Cadmium (Cd) accumulation and toxicity in rice plants were characterized and identified by using brittle culm 1 (bc1), a fragile rice mutant and its wild type (Shuangkezao, an indica rice) as materials by hydroponics. The low Cd level didn't obviously affect the growth parameters in both rice genotypes, but under high Cd levels (1.0 and 5.0 μmol/L), the growth of both rice plants were substantially inhibited. Moreover, bc1 tended to suffer more seriously from Cd toxicity than Shuangkezao. Cd accumulation in both rice plants increased with the increase of Cd levels. There was a significant difference in Cd accumulation between the two rice genotypes with constantly higher Cd concentration in bc1, which also accumulated more Cd at 0, 0.1, and 1.0 μmol/L Cd levels. The same case was found in the two rice plants grown on Cd-contaminated soil. This suggested that cell wall might play an important role in Cd accumulation in rice plants by the physiological mechanisms. The malondialdehyde (MDA) content, superoxide dismutase (SOD) and peroxidase (POD)activities in rice plants were affected differently under Cd treatments, and which implied that POD might play the main role in detoxifying active oxygen free radical. A significant difference in antioxidative system between the two rice genotypes was found with constantly higher MDA content, SOD and POD activities in bc1. In summary, bc1 accumulated more Cd and appeared to be more sensitive to Cd stress compared with its wild type.

  14. The effect of welding residual stresses on brittle fracture in an internal surface cracked pipe

    International Nuclear Information System (INIS)

    The change in brittle fracture properties due to the presence of welding residual stresses (RS) is studied in a pipe. Welding RS are simulated by using a 3-D finite element (FE) model and experimentally verified. An internal circumferential thumbnail crack is introduced at the weld line. The modified Beremin model is used as local approach method to predict toughness distributions in the presence of welding RS. The model is calibrated using experimental fracture tests at −150 °C consisting of low and high constraint specimens. The results indicate that, in the welded pipe, the fracture toughness will decrease dramatically in comparison with the as-received pipe. For the same fracture probability of 90%, fracture toughness will decrease from 65 to 40 MPa √m. This is due to the influence of tensile welding RS on the crack tip stress state, which result in a decrease in the opening mode stresses at the near crack tip up to 40%. - Highlights: • A Two-pass pipe welding process is simulated and obtained residual stresses (RS) are experimentally verified. • An internal semi-elliptical circumferential cracked pipe is considered and Modified Beremin model is used. • Two sets of specimens with high and low crack-tip constraint are used for model calibration. • Welding RS will cause to change crack-tip stress field and fracture probability, dramatically. • RS cause 40% increase in maximum opening stress and 38% decrease in fracture toughness, for a fracture probability of 90%

  15. A visco-poroelastic damage model for modelling compaction and brittle failure of porous rocks

    Science.gov (United States)

    Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena

    2016-04-01

    Hydraulic stimulation of geothermal wells is often used to increase heat extraction from deep geothermal reservoirs. Initiation and propagation of fractures due to pore pressure build-up increase the effective permeability of the porous medium. Understanding the processes controlling the initiation of fractures, the evolution of their geometries and the hydro-mechanical impact on transport properties of the porous medium is therefore of great interest for geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes occurring during deformation of a porous rock. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To validate and illustrate the model, simulations of the deformation behaviour of cylindrical porous Bentheimer sandstone samples under different confining pressures are compared to experiments. The first experiment under low confining pressure leads to shear failure, the second for high confining pressure leads to cataclastic compaction and the third one with intermediate confining pressure correspond to a transitional regime between the two firsts. Finally, we will demonstrate that this approach can also be used at the field

  16. Linear Elastic and Cohesive Fracture Analysis to Model Hydraulic Fracture in Brittle and Ductile Rocks

    Science.gov (United States)

    Yao, Yao

    2012-05-01

    Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a Perkins-Kern-Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone

  17. Limit of the local approach application of the brittle fracture on hydrogen charged steels

    International Nuclear Information System (INIS)

    The local approach of the brittle fracture by cleavage developed by BEREMIN relies the macroscopic mechanical properties to local criteria. It allows to predict the probability of failure of the structure by performing detailed calculation of the stress and deformation fields in the different element volumes within this structure. It also takes into account the distribution of the defects initiating the fracture in a specific zone. The local approach allows then the determination of a statistical criterion to be applied on cleavage fracture. The cumulative distribution function PR, over a small volume V0 ahead of a crack tip or defect can be expressed as: PR 1 - exp[-σw/σu)m] where σw WEIBULL stress and σu mean cleavage stress defined as the stress / volume leading to PR = 0.63 and m is an empirically determined parameter presenting the degree of scatter in measured strength values. The paper deals with the application of this approach on three steels in absence and in presence of hydrogen: railway steel FM80, with pearlitic structure, 35CD4 steel employed in tool's joints in a tempered martensitic state and a bainitic A508.3 used in nuclear power plants. The goal of this work is to show that in the case hydrogenated steel, the local approach is improved if the defects promoted by high stress triaxiality and local critical hydrogen concentration do not exceed the element volume V0 in which the material is considered to be statistically homogeneous. The results show that in the two first steel the local approach is improved even in presence of hydrogen. In the hydrogenated bainitic steel (A508.3), the application of this method is not possible due to development in the material of fish eyes which the size is very large with respect to V0. (author). 7 refs., 4 figs., 1 tab

  18. Brittle Culm1, a COBRA-like protein, functions in cellulose assembly through binding cellulose microfibrils.

    Directory of Open Access Journals (Sweden)

    Lifeng Liu

    Full Text Available Cellulose represents the most abundant biopolymer in nature and has great economic importance. Cellulose chains pack laterally into crystalline forms, stacking into a complicated crystallographic structure. However, the mechanism of cellulose crystallization is poorly understood. Here, via functional characterization, we report that Brittle Culm1 (BC1, a COBRA-like protein in rice, modifies cellulose crystallinity. BC1 was demonstrated to be a glycosylphosphatidylinositol (GPI anchored protein and can be released into cell walls by removal of the GPI anchor. BC1 possesses a carbohydrate-binding module (CBM at its N-terminus. In vitro binding assays showed that this CBM interacts specifically with crystalline cellulose, and several aromatic residues in this domain are essential for binding. It was further demonstrated that cell wall-localized BC1 via the CBM and GPI anchor is one functional form of BC1. X-ray diffraction (XRD assays revealed that mutations in BC1 and knockdown of BC1 expression decrease the crystallite width of cellulose; overexpression of BC1 and the CBM-mutated BC1s caused varied crystallinity with results that were consistent with the in vitro binding assay. Moreover, interaction between the CBM and cellulose microfibrils was largely repressed when the cell wall residues were pre-stained with two cellulose dyes. Treating wild-type and bc1 seedlings with the dyes resulted in insensitive root growth responses in bc1 plants. Combined with the evidence that BC1 and three secondary wall cellulose synthases (CESAs function in different steps of cellulose production as revealed by genetic analysis, we conclude that BC1 modulates cellulose assembly by interacting with cellulose and affecting microfibril crystallinity.

  19. Role of Austenite in Brittle Fracture of Bond Region of Super Duplex Stainless Steel

    Science.gov (United States)

    Kitagawa, Yoshihiko; Ikeuchi, Kenji; Kuroda, Toshio

    Weld simulation of heat-affected zone (HAZ) was performed to investigate the mechanism by which austenite affects the toughness of super duplex stainless steel. Thermal cycles of various peak temperatures in the range from 1373 K to 1673 K corresponding to the HAZ were applied to SAF2507 super duplex stainless steel specimens. Charpy impact test was carried out using the specimens after the weld simulation, and the fracture surfaces were observed by SEM using three-dimensionally reconstruction technique. Austenite content decreased with increasing the peak temperature when the peak temperature exceeded 1473 K and the impact value decreased with increasing the peak temperature and decreasing the austenite content. The thermal cycle of the peak temperature of 1673 K corresponding to weld bond region caused decreasing of austenite content which was 22% lower than that of the base metal. The ductile-brittle transition temperature was measured. As a result the temperature increased rapidly in the weld bond region, the peak temperature of which exceeded 1623 K by the grain growth of ferrite matrix occurring subsequently to the completely dissolution of austenite. The morphology of the fracture surfaces after impact testing at 77 K showed cleavage fracture of ferrite. The {100} orientations of cleavage fracture facets were measured using three-dimensional images of the fracture surfaces and the results were visualized as the orientation color maps. The results showed that there were cleavage fractures consisting of a few facets parallel to each other. It was considered that a few facets existed in one ferrite grain. It was concluded that Widmanstätten austenite divided the large fracture into smaller cleavage facets in a ferrite grain and then suppressed the degradation of bond toughness of duplex stainless steel.

  20. Turner Syndrome

    Directory of Open Access Journals (Sweden)

    Ravinder K. Gupta, Ritu Gupta, Sunil Dutt Sharma

    2006-10-01

    Full Text Available Turner Syndrome is one of the important chromosomal disorders characterised by loss (total or part ofsex chromosome. The manifestations being peripheral edema, short stature, extra skin fold, webbing ofneck, renal and cardiovascular anomalies, sexual infantilism, learning disability etc. We present here aone month female baby who had classical features of Turner Syndrome. The karyotape analysis wasconsistent with the diagnosis.

  1. Antiphospholipid syndrome

    DEFF Research Database (Denmark)

    Cervera, Ricard; Piette, Jean-Charles; Font, Josep;

    2002-01-01

    To analyze the clinical and immunologic manifestations of antiphospholipid syndrome (APS) in a large cohort of patients and to define patterns of disease expression.......To analyze the clinical and immunologic manifestations of antiphospholipid syndrome (APS) in a large cohort of patients and to define patterns of disease expression....

  2. Myelodysplastic Syndromes

    Science.gov (United States)

    ... your body, the white blood cells that fight infections, and the platelets that help with blood clotting. If you have a myelodysplastic syndrome, the stem cells do not mature into healthy blood cells. ... anemia, or easy bleeding. Myelodysplastic syndromes often do ...

  3. Bloom's Syndrome

    Science.gov (United States)

    ... Niemann-Pick Disease, Type A Spinal Muscular Atrophy Tay-Sachs Disease Usher Syndrome, Type 1F and Type III ... Niemann-Pick Disease, Type A Spinal Muscular Atrophy Tay-Sachs Disease Usher Syndrome, Type 1F and Type III ...

  4. Poland syndrome

    Directory of Open Access Journals (Sweden)

    Chandra Madhur Sharma

    2014-01-01

    Full Text Available Poland′s syndrome is a rare congenital condition, characterized by the absence of the sternal or breastbone portion of the pectoralis major muscle, which may be associated with the absence of nearby musculoskeletal structures. We hereby report an 8-year-old boy with typical features of Poland syndrome, the first documented case from Uttar Pradesh, India.

  5. Franceschetti syndrome

    Directory of Open Access Journals (Sweden)

    Vikrant Kasat

    2011-01-01

    Full Text Available Franceschetti syndrome is an autosomal dominant disorder of craniofacial development with variable expressivity. It is commonly known as Treacher Collins syndrome (TCS. It is named after E. Treacher Collins who described the essential components of the condition. It affects both genders equally. This article reports a case of TCS in an 18-year-old female.

  6. Turner Syndrome

    Directory of Open Access Journals (Sweden)

    Akcan AB.

    2013-06-01

    Full Text Available Turner syndrome is an important cause of short stature in girls and primer amenorrhea in young women that is usually caused by loss of part or all of an X chromosome. This topic will review the clinical manifestations, diagnosis and management of Turner syndrome.

  7. Proteus syndrome

    Directory of Open Access Journals (Sweden)

    George Renu

    1993-01-01

    Full Text Available A case of proteus syndrome in a 20 year old male is repoted. Hemihypertrophy, asymmetric megalodactyly, linear epidermal naevus, naevus flammeus, angiokeratoma, lymphangioma circumscriptum, thickening of the palms and soles, scoliosis and varicose veins were present. There are only few reports of these cases in adults. The syndrome has not been reported from India.

  8. Burnout Syndrome

    OpenAIRE

    Panova, Gordana; Panov, Nenad; Stojanov, H; Sumanov, Gorgi; Panova, Blagica; Stojanovski, Angel; Nikolovska, Lence; Jovevska, Svetlana; Trajanovski, D; Asanova, D

    2013-01-01

    Introduction: Increasing work responsibilities, allocation of duties, loss of energy and motivation in everyday activities, emotional exhaustion, lack of time for themselves, insuffi cient time for rest and recreation, dissatisfaction in private life. All these symptoms can be cause of Burnout Syndrome. Aim: To see the importance of this syndrome, the consequences of job dissatisfaction, the environment, family and expression in drastic chan...

  9. Noonan Syndrome

    Directory of Open Access Journals (Sweden)

    Sanjeev K. Digra, Deep Aman Singh, Vikram Gupta, Ghanshyam Saini

    2004-10-01

    Full Text Available We report a 11 year old boy and his father both Noonan’s. Noonan syndrome occurs in 1 out of 2000live births. Short stature, webbing of neck, pectus carinatum or pectus excavatum, hypertelorismcubitus valgus, epicanthus, downward slanted palpebral fissures, ptosis, microganthia and earabnormalities are the common features of Noonan syndrome.

  10. Study of the competition between ductile tearing and brittle fracture : Application to the mechanical strength of C-Mn pipes and their welded joints.

    OpenAIRE

    Le Corre, Vincent

    2006-01-01

    This study deals with the fracture behaviour of welded thin structures in the ductile to brittle transition range. It aims to propose a criterion to define the conditions for which the risk of fracture per cleavage does not exist on a cracked structure.The literature review shows that the difficulties of prediction of the fracture behaviour of a structure are related to the dependence of the fracture probability to the mechanical fields at the crack tip. The ductile to brittle transition rang...

  11. Microbiota bacteriana aeróbia da conjuntiva de doadores de córnea Aerobic bacterial microbiota of the conjunctiva of cornea donors

    Directory of Open Access Journals (Sweden)

    Paula Fontana Lorenzini

    2007-03-01

    Full Text Available OBJETIVOS: Determinar a microbiota bacteriana aeróbia da conjuntiva de doadores de córnea e seu padrão de suscetibilidade a antibióticos; verificar o número de córneas utilizadas para transplante e a média de tempo de preservação em solução preservante com gentamicina e estreptomicina; traçar o perfil dos doadores e receptores de córnea. MÉTODOS: Espécimes clínicos foram colhidos de saco inferior da conjuntiva de ambos os olhos, de 40 doadores de córnea. As amostras foram inoculadas em ágar sangue azida, ágar chocolate e ágar MacConkey e o antibiograma foi realizado pelo método de Kirby-Bauer. RESULTADOS: A freqüência de cultura positiva da conjuntiva de doadores de córnea foi de 72,5%, sendo que Gram-positivos totalizaram 81,6% e apenas 18,4% das amostras foram identificadas como Gram-negativos. Vancomicina inibiu 100% dos Gram-positivos, ao passo que a sensibilidade dos Gram-negativos à gentamicina foi de 53,8% e à estreptomicina foi de 30%. O sexo masculino predominou entre os doadores e receptores, a média de tempo entre o óbito e a enucleação foi de 2h e a de preservação em solução preservante com gentamicina e estreptomicina foi de 7 dias. Neoplasia e mais de uma causa associada foram as causas de óbito mais freqüentes. O ceratocone foi a principal indicação para transplante (51,7%. CONCLUSÕES: Staphylococcus coagulase negativo foi o microrganismo com o maior número de isolamentos, apresentando sensibilidade variada aos antimicrobianos. A quantidade de córneas utilizadas para transplante foi bastante inferior em relação ao total de captações. O perfil dos doadores e receptores de córnea mostrou-se heterogêneo para grande parte das variáveis analisadas.PURPOSE: To determine aerobic bacterial microbiota of the conjunctiva of cornea donors and its patterns of susceptibility to antibiotics; verify the number of corneas used for transplant and the average time of preservation in solutions with

  12. Kounis syndrome.

    Science.gov (United States)

    Ntuli, P M; Makambwa, E

    2015-10-01

    Kounis syndrome is characterised by a group of symptoms that manifest as unstable vasospastic or non-vasospastic angina secondary to a hypersensitivity reaction. It was first described by Kounis and Zavras in 1991 as the concurrence of an allergic response with an anaphylactoid or anaphylactic reaction and coronary artery spasm or even myocardial infarction. Since then, this condition has evolved to include a number of mast cell activation disorders associated with acute coronary syndrome. There are many triggering factors, including reactions to multiple medications, exposure to radiological contrast media, poison ivy, bee stings, shellfish and coronary stents. In addition to coronary arterial involvement, Kounis syndrome comprises other arterial systems with similar physiologies, such as mesenteric and cerebral circulation resulting in ischaemia/infarction of the vital organs. The incidence of this condition is difficult to establish owing to the number of potential instigating factors and its relatively infrequent documentation in the literature.We report the case of an HIV-negative 39-year-old man with no coronary risk factors or family history of premature coronary artery disease, who developed Kounis syndrome after the administration of fluoroquinolone for dysuria. However, to the best of our knowledge,no data on the incidence and prevalence of Kounis syndrome in South Africa have ever been reported in the literature. The recent understanding of Kounis syndrome has led to the condition being classified into three syndrome variants. PMID:26636160

  13. HYDROLETHALUS SYNDROME

    Directory of Open Access Journals (Sweden)

    Aradhana

    2013-06-01

    Full Text Available INTRODUCTION: Hydrolethalus Syndrome (HLS is a rare lethal genetic syndrome, recognized as a consequence of a study on Meckle syndrome in Finland .1 HLS is characterized by multiple developmental defects of fetus which include fetal hydrocephalus, agenesis of corpus callosum, absent midline structures of brain, Cleft lip and cleft palate, defective lobulation of lungs, micrognathia and very characteristic abnormality of polydactyly. About 80% of patients have polydactyly, in hands it is postaxial and preaxial in feet with duplicated big toe. A highly characteristic hallux duplex is seen in almost no other situation .2 Club feet is also common.

  14. Neuroacanthocytosis Syndromes

    Directory of Open Access Journals (Sweden)

    Walker Ruth H

    2011-10-01

    Full Text Available Abstract Neuroacanthocytosis (NA syndromes are a group of genetically defined diseases characterized by the association of red blood cell acanthocytosis and progressive degeneration of the basal ganglia. NA syndromes are exceptionally rare with an estimated prevalence of less than 1 to 5 per 1'000'000 inhabitants for each disorder. The core NA syndromes include autosomal recessive chorea-acanthocytosis and X-linked McLeod syndrome which have a Huntington´s disease-like phenotype consisting of a choreatic movement disorder, psychiatric manifestations and cognitive decline, and additional multi-system features including myopathy and axonal neuropathy. In addition, cardiomyopathy may occur in McLeod syndrome. Acanthocytes are also found in a proportion of patients with autosomal dominant Huntington's disease-like 2, autosomal recessive pantothenate kinase-associated neurodegeneration and several inherited disorders of lipoprotein metabolism, namely abetalipoproteinemia (Bassen-Kornzweig syndrome and hypobetalipoproteinemia leading to vitamin E malabsorption. The latter disorders are characterized by a peripheral neuropathy and sensory ataxia due to dorsal column degeneration, but movement disorders and cognitive impairment are not present. NA syndromes are caused by disease-specific genetic mutations. The mechanism by which these mutations cause neurodegeneration is not known. The association of the acanthocytic membrane abnormality with selective degeneration of the basal ganglia, however, suggests a common pathogenetic pathway. Laboratory tests include blood smears to detect acanthocytosis and determination of serum creatine kinase. Cerebral magnetic resonance imaging may demonstrate striatal atrophy. Kell and Kx blood group antigens are reduced or absent in McLeod syndrome. Western blot for chorein demonstrates absence of this protein in red blood cells of chorea-acanthocytosis patients. Specific genetic testing is possible in all NA syndromes

  15. Hubris syndrome.

    Science.gov (United States)

    Owen, David

    2008-08-01

    Hubris syndrome is associated with power, more likely to manifest itself the longer the person exercises power and the greater the power they exercise. A syndrome not to be applied to anyone with existing mental illness or brain damage. Usually symptoms abate when the person no longer exercises power. It is less likely to develop in people who retain a personal modesty, remain open to criticism, have a degree of cynicism or well developed sense of humour. Four heads of government in the last 100 years are singled out as having developed hubris syndrome: David Lloyd George, Margaret Thatcher, George W Bush and Tony Blair.

  16. Impact cratering experiments in brittle targets with variable thickness: Implications for deep pit craters on Mars

    Science.gov (United States)

    Michikami, T.; Hagermann, A.; Miyamoto, H.; Miura, S.; Haruyama, J.; Lykawka, P. S.

    2014-06-01

    High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1-6 cm, and a bulk density of 1550 kg/m3 by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2±0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead. Craters are formed on the opposite impact side even when no penetration

  17. Identification of the fragmentation of brittle particles during compaction process by the acoustic emission technique.

    Science.gov (United States)

    Favretto-Cristini, Nathalie; Hégron, Lise; Sornay, Philippe

    2016-04-01

    Some nuclear fuels are currently manufactured by a powder metallurgy process that consists of three main steps, namely preparation of the powders, powder compaction, and sintering of the compact. An optimum between size, shape and cohesion of the particles of the nuclear fuels must be sought in order to obtain a compact with a sufficient mechanical strength, and to facilitate the release of helium and fission gases during irradiation through pores connected to the outside of the pellet after sintering. Being simple to adapt to nuclear-oriented purposes, the Acoustic Emission (AE) technique is used to control the microstructure of the compact by monitoring the compaction of brittle Uranium Dioxide (UO2) particles of a few hundred micrometers. The objective is to identify in situ the mechanisms that occur during the UO2 compaction, and more specifically the particle fragmentation that is linked to the open porosity of the nuclear matter. Three zones of acoustic activity, strongly related to the applied stress, can be clearly defined from analysis of the continuous signals recorded during the compaction process. They correspond to particle rearrangement and/or fragmentation. The end of the noteworthy fragmentation process is clearly defined as the end of the significant process that increases the compactness of the material. Despite the fact that the wave propagation strongly evolves during the compaction process, the acoustic signature of the fragmentation of a single UO2 particle and a bed of UO2 particles under compaction is well identified. The waveform, with a short rise time and an exponential-like decay of the signal envelope, is the most reliable descriptor. The impact of the particle size and cohesion on the AE activity, and then on the fragmentation domain, is analyzed through the discrete AE signals. The maximum amplitude of the burst signals, as well as the mean stress corresponding to the end of the recorded AE, increase with increasing mean diameter of

  18. Quasi-brittle material behavior under cyclic loading: from virtual testing to structural computation

    International Nuclear Information System (INIS)

    Macroscopic constitutive laws are developed not only because they allow for large-scale computations but also because refine dissipative mechanisms observed at lower scales. Within the framework of this study, the development of such models is carried out in the context of seismic loading, that is to say reverse cyclic loading, applied to the quasi-brittle materials and more precisely, concrete-like materials. Nowadays, robust and predictive macroscopic constitutive laws are still rare because of the complexity of cracking related phenomena. Among the challenges to face, the material parameters identification is far from being the easiest due to the lack of experimental data. Indeed, the difficulties to carry out cyclic tests on concrete-like materials are numerous. To overcome these difficulties, a virtual testing approach based on a refine model is proposed in this study in order to feed continuum models with the missing material parameters. Adopting a microscopic point of view, a representative volume element is seen as a structure. The microscopic model has been developed with the aim to require a minimal number of material parameters which only need basic mechanical tests to be identified. From an existing lattice model developed to deal with monotonic loading, several enhancements have been realized in order to extend its range of applicability, making it capable of dealing with complex multi-axial cyclic loadings. The microscopic model has been validated as a virtual testing machine that is able to help the identification procedure of continuous constitutive laws. This identification approach has been applied on a new constitutive law developed within the framework of isotropic continuum damage mechanics accounting for cyclic related effects. In particular, the concept of regularized unilateral effect has been introduced to describe the progressive crack closure. The macroscopic model has been calibrated with the help from the aforementioned virtual testing

  19. Drilling on Mars---Mathematical Model for Rotary-Ultrasonic Core Drilling of Brittle Materials

    Science.gov (United States)

    Horne, Mera Fayez

    The results from the Phoenix mission led scientists to believe it is possible that primitive life exists below the Martian surface. Therefore, drilling in Martian soil in search for organisms is the next logical step. Drilling on Mars is a major engineering challenge due to the drilling depth requirement. Mars lacks a thick atmosphere and a continuous magnetic field that shield the planet's surface from solar radiation and solar flares. As a result, the Martian surface is sterile and if life ever existed, it must be found below the surface. In 2001, NASA's Mars Exploration Payload Advisory Group proposed that drilling should be considered as a priority investigation on Mars in an effort of finding evidence of extinct or extant life. On August 6, 2012, the team of engineers landed the spacecraft Curiosity on the surface of Mars by using a revolutionary hovering platform. The results from the Curiosity mission suggested the next logical step, which is drilling six meters deep in the red planet in search of life. Excavation tools deployed to Mars so far have been able to drill to a maximum depth of 6.5 cm. Thus, the drilling capabilities need to be increased by a factor or approximately 100 to achieve the goal of drilling six meters deep. This requirement puts a demand on developing a new and more effective technologies to reach this goal. Previous research shows evidence of a promising drilling mechanism in rotary-ultrasonic for what it offers in terms of high surface quality, faster rate of penetration and higher material removal rate. This research addresses the need to understand the mechanics of the drill bit tip and rock interface in rotary-ultrasonic drilling of brittle materials. A mathematical model identifying all contributing independent parameters, such as drill bit design parameters, drilling process parameters, ultrasonic wave amplitude and rocks' material properties, that have effect on rate of penetration is developed. Analytical and experimental

  20. Mechanisms involved in the anti-inflammatory action of a polysulfated fraction from Gracilaria cornea in rats.

    Science.gov (United States)

    Coura, Chistiane Oliveira; Souza, Ricardo Basto; Rodrigues, José Ariévilo Gurgel; Vanderlei, Edfranck de Sousa Oliveira; de Araújo, Ianna Wivianne Fernandes; Ribeiro, Natássia Albuquerque; Frota, Annyta Fernandes; Ribeiro, Kátia Alves; Chaves, Hellíada Vasconcelos; Pereira, Karuza Maria Alves; da Cunha, Rodrigo Maranguape Silva; Bezerra, Mirna Marques; Benevides, Norma Maria Barros

    2015-01-01

    The anti-inflammatory mechanisms of the sulfated polysaccharidic fraction obtained from red marine alga Gracilaria cornea (Gc-FI) were investigated using a paw edema model induced in rats by different inflammatory agents (carrageenan, dextran, serotonin, bradykinin, compound 48/80 or L-arginine). Gc-FI at the doses of 3, 9 or 27 mg/kg, subcutaneously--s.c., significantly inhibited rat paw edema induced by carrageenan and dextran, as confirmed by myeloperoxidase and Evans' blue assessments, respectively. Gc-FI (9 mg/kg, s.c.) inhibited rat paw edema induced by histamine, compound 48/80 and L-arginine. Additionally, Gc-FI (9 mg/kg, s.c.) inhibited Cg-induced edema in animals with intact mast cells but did not inhibit that with degranulated mast cells by compound 48/80, revealing a protective role on mast cell membranes. Gc-FI down-regulated the IL-1β, TNF-α and COX-2 mRNA and protein levels compared with those of the carrageenan group, based on qRT-PCR and immunohistochemistry analyses. After inhibition with ZnPP IX, a specific heme oxygenase-1 (HO-1) inhibitor, the anti-inflammatory effect of Gc-FI was not observed in Cg-induced paw edema, suggesting that the anti-inflammatory effect of Gc-FI is, in part, dependent on the integrity of the HO-1 pathway. Gc-FI can target a combination of multiple points involved in inflammatory phenomena.

  1. Mechanisms involved in the anti-inflammatory action of a polysulfated fraction from Gracilaria cornea in rats.

    Directory of Open Access Journals (Sweden)

    Chistiane Oliveira Coura

    Full Text Available The anti-inflammatory mechanisms of the sulfated polysaccharidic fraction obtained from red marine alga Gracilaria cornea (Gc-FI were investigated using a paw edema model induced in rats by different inflammatory agents (carrageenan, dextran, serotonin, bradykinin, compound 48/80 or L-arginine. Gc-FI at the doses of 3, 9 or 27 mg/kg, subcutaneously--s.c., significantly inhibited rat paw edema induced by carrageenan and dextran, as confirmed by myeloperoxidase and Evans' blue assessments, respectively. Gc-FI (9 mg/kg, s.c. inhibited rat paw edema induced by histamine, compound 48/80 and L-arginine. Additionally, Gc-FI (9 mg/kg, s.c. inhibited Cg-induced edema in animals with intact mast cells but did not inhibit that with degranulated mast cells by compound 48/80, revealing a protective role on mast cell membranes. Gc-FI down-regulated the IL-1β, TNF-α and COX-2 mRNA and protein levels compared with those of the carrageenan group, based on qRT-PCR and immunohistochemistry analyses. After inhibition with ZnPP IX, a specific heme oxygenase-1 (HO-1 inhibitor, the anti-inflammatory effect of Gc-FI was not observed in Cg-induced paw edema, suggesting that the anti-inflammatory effect of Gc-FI is, in part, dependent on the integrity of the HO-1 pathway. Gc-FI can target a combination of multiple points involved in inflammatory phenomena.

  2. Effect of Biometric Characteristics on the Change of Biomechanical Properties of the Human Cornea due to Cataract Surgery

    Directory of Open Access Journals (Sweden)

    Xuefei Song

    2014-01-01

    Full Text Available Purpose. To determine the impact of biometric characteristics on changes of biomechanical properties of the human cornea due to standard cataract surgery using biomechanical analysis. Patients and Methods. This prospective consecutive cross-sectional study comprised 54 eyes with cataract in stages I or II that underwent phacoemulsification and IOL implantation. CH, CRF, IOPg, and IOPcc intraocular pressure were measured by biomechanical analysis preoperatively and at 1 month postoperatively. Changes (Δ were calculated as preoperative value versus postoperative value. Biometrical data were extracted from TMS-5 (CSI and SAI, IOLMaster (AL, and EM-3000 (CCT and ECC preoperatively. Results. The average values of the changes were ΔCH=-0.45±1.27 mmHg, ΔCRF=-0.88±1.1 mmHg, ΔIOPg=-1.58±3.15 mmHg, and ΔIOPcc=-1.45±3.93 mmHg. The higher the CSI the smaller the decrease in CH (r=0.302, P=0.028. The higher the CCT the larger the decrease in CRF (r=-0.371, P=0.013. The higher the AL the smaller the decrease in IOPg (r=0.417, P=0.005. The higher the AL, SAI, and EEC the smaller the decrease in IOPcc (r=0.351, P=0.001; r=-0.478, P<0.001; r=0.339, P=0.013. Conclusions. Corneal biomechanical properties were affected by comprehensive factors after cataract surgery, including corneal endothelium properties, biometry, and geometrical characteristics.

  3. 真菌毒素与角膜真菌感染%Mycotoxins and fungal infection of cornea

    Institute of Scientific and Technical Information of China (English)

    吴福进; 胡建章; 韩晓丽

    2013-01-01

    Mycotoxins are secondary metabolites produced by the toxigenic fungi in suitable environmental conditions,the main toxicity of which are carcinogenesis,genotoxicity,teratogenesis,hepatotoxicity and immunosuppression.After fungal infects the cornea,it may release mycotoxins to cause corneal damage.However what roles do the mycotoxins play in fungal keratitis is still unclear.The biosynthesis of mycotoxinis is regulated by a series of related function genes ; in addition,pH value,carbon nitrogen ratio and other environmental conditions are the influence factors as well.This article reviews the common harms,regulatory factors and their possible roles in the occurrence and development of keratomycosis.%真菌毒素(Mycotoxin)是由产毒真菌在适宜的环境条件下产生的具有毒性的次级代谢产物,主要毒性有致癌作用、遗传毒性、致畸作用、肝细胞毒性和免疫抑制等.真菌感染角膜后可能释放真菌毒素导致角膜损害,但至今对真菌毒素在真菌性角膜炎中究竟扮演什么角色,仍不明确.真菌毒素的生物合成受到一系列相关功能基因的调控;此外,pH值、碳氮比等环境条件也能影响其产量.本文就常见的真菌毒素的危害、调控因素及其可能在真菌性角膜炎发生发展中的作用进行综述.

  4. Microbiota bacteriana da conjuntiva de doadores de córnea Bacterial microbiota of the conjunctiva of donor corneas

    Directory of Open Access Journals (Sweden)

    Maria Emília Xavier dos Santos Araújo

    2004-12-01

    Full Text Available OBJETIVOS: Quantificar e qualificar a microbiota aeróbia da conjuntiva de doadores de córnea segundo a interferência do intervalo de tempo entre o óbito e a colheita do espécime conjuntival, a causa do óbito e a idade do doador e avaliar a atividade biocida de determinados antibióticos aos microrganismos isolados. MÉTODOS: Entre janeiro e março de 1994 foram colhidos espécimes da conjuntiva de 242 olhos de doadores de córnea. O material transportado em meio de Stuart foi semeado em ágares sangue, chocolate, sangue azida, MacConkey e caldo tioglicolato. Foi registrada a idade do doador, hora e causa do óbito. A atividade biocida dos antibióticos foi avaliada pela metodologia de Kirby e Bauer. A análise estatística utilizou os testes do qui-quadrado, exato de Fisher e Mann-Whitney. RESULTADOS: A freqüência de cultura positiva da conjuntiva de doadores de córnea foi de 91,7%. A mediana da idade dos doadores foi de 62 anos e do intervalo de tempo entre o óbito e a colheita do espécime foi de 4,2 horas. A causa mais freqüente de óbito foi doença cardiovascular (26,4%. Não houve diferença significante entre a cultura positiva e as variáveis estudadas. A vancomicina inibiu 100% das cepas de bactérias Gram-positivas e a sensibilidade dos bacilos Gram-negativos à gentamicina variou de 36,7% a 92,3%. CONCLUSÕES: O estudo revelou freqüência elevada de cultura positiva da conjuntiva de doadores de córneas. Staphylococcus coagulase negativo foi a espécie com maior número de isolamentos positivos. Não foi encontrada associação entre os fatores de risco avaliados e cultura positiva. Os antibióticos tiveram atividade biocida variável sobre os Gram-negativos e 100% dos Gram-positivos foram sensíveis à vancomicina.PURPOSE: To identify and qualify bacterial organisms in conjunctival tissue of donor corneas. To correlate the frequency of positive cultures with donor age, cause of death, and time from death to collection of

  5. [Mobius syndrome].

    Science.gov (United States)

    Vladuţiu, Cristina; Duma, Ionela

    2012-01-01

    Mobius syndrom, an anomaly in cranial nerve developement, presents with a remarkable clinical polymorphism. The rare occurence of this pathology and the questions raised by the diagnosis and treatment determined us to make this presentation.

  6. Gardner Syndrome

    Science.gov (United States)

    ... syndromes. For more information, talk with an assisted reproduction specialist at a fertility clinic. How common is ... detected X-ray or computed tomography (CT or CAT) scan of the small bowel if adenomas are ...

  7. [Heptopulmonary syndrome].

    Science.gov (United States)

    Cuadrado, Antonio; Díaz, Ainhoa; Iruzubieta, Paula; Salcines, José Ramón; Crespo, Javier

    2015-01-01

    Hepatopulmonary syndrome is characterized by the presence of liver disease, pulmonary vascular dilatations, and arterial hypoxemia. It is usually associated with cirrhosis of any origin, but has been described in other liver diseases, both acute and chronic, and not always associated with portal hypertension. The gold standard method to detect pulmonary vascular dilations is contrast enhancement echocardiography with saline and is essential for the diagnosis of hepatopulmonary syndrome. These dilatations reflect changes in the pulmonary microvasculature (vasodilatation, intravascular monocyte accumulation, and angiogenesis) and induce a ventilation/perfusion mismatch, or even true intrapulmonary shunts, which eventually trigger hypoxemia. This syndrome worsens patients' prognosis and impairs their quality of life and may lead to the need for liver transplantation, which is the only effective and definitive treatment. In this article, we review the etiological, pathophysiological, clinical and therapeutic features of this syndrome. PMID:25840463

  8. Piriformis syndrome

    Science.gov (United States)

    ... Wallet sciatica; Hip socket neuropathy; Pelvic outlet syndrome; Low back pain - piriformis ... medical help immediately if: You have sudden severe pain in your lower back or legs, along with muscle weakness or numbness ...

  9. Potter syndrome

    Science.gov (United States)

    Potter phenotype ... In Potter syndrome, the primary problem is kidney failure. The kidneys fail to develop properly as the baby is ... kidneys normally produce the amniotic fluid (as urine). Potter phenotype refers to a typical facial appearance that ...

  10. Pendred Syndrome

    Science.gov (United States)

    ... Health & Human Services National Institutes of Health Search Search form Search A–Z Index Español Menu Home ... children, the thyroid is important for normal growth and development. Children with Pendred syndrome, however, rarely have problems ...

  11. [Refeeding syndrome].

    Science.gov (United States)

    Ševela, Stanislav; Novák, František; Kazda, Antonín; Brodská, Helena

    2016-01-01

    Despite being known more than 60 years, refeeding syndrome (RS) still bears many uncertainties. For example, its definition is not clear and definite, and the attitude to it varies from the complete neglect to over-prevention.The term "refeeding syndrome" refers to electrolyte and metabolic changes occurring in malnourished patients after the readministration of nutrition. These changes concern especially to phosphates and ions. Potassium, magnesium, naturism and fluids balance are involved. The changes lead to cell energetic metabolism and electric potential disturbances, with related clinical symptoms.Fully developed refeeding syndrome is quite rare; nevertheless it can be fatal for the patient. However, even its development can lead to many complications increasing the patient's morbidity and the length of stay in the hospital. Yet the refeeding syndrome is more or less predictable and if kept in mind also preventable.The aim of this article is to get the reader to know more about this metabolic phenomenon and possible attitudes towards it.

  12. Marfan Syndrome in an Iranian Family: A Case Series

    Directory of Open Access Journals (Sweden)

    Mohammad Hossein Davari

    2015-07-01

    Full Text Available Marfan syndrome (MFS is a genetic disorder which is inherited by autosomal dominant traits. In MFS, lens displacement and cardiovascular involvement are important causes of morbidity and mortality in the clinical course of the disease. In this case study, the ocular involvement in a family with severe penetration of MFS is reported. Twelve members of a family (father, two daughters, three sons, and six grandchildren had MFS. Lens ectopia was the most common ophthalmic involvement among the family (100%. Other ocular involvements were as follows; Hypoplastic iris or ciliary’s muscle hypoplasia (50%, on gated eyeball (42%, flat cornea (30%, glaucoma and cataract (25%, retinal detachment (16%. Three members of the family underwent eye surgery including lens extraction, glaucoma surgery and retinal surgery.

  13. Summary on Clinical Experience of Acupuncture Treating Dry Eye Syndromes

    Institute of Scientific and Technical Information of China (English)

    马晓芃; 杨玲; 莫文权; 施征; 赵粹英

    2009-01-01

    @@ Dry eye syndromes(DES)refer to discomfort in the eye region,visual disturbance,poor stability of lacrimal film,inflammation of eve surface and its potential iniury due to many factors of abnonnal lacrimation[1].Patients with this condition can experience a dry sensation in the eyes,foreign body sensation,burning and itching sensation in the eyes,and blurred vision.The lingering pathological change can lead to decreased transparency of the cornea and hypopsia,affecting the work,study and life,and even resulting in blindness.With popularization of computers,and change in lifestyles,the incidence of DES rises gradually and tends to occur in young age.

  14. Turner Syndrome

    OpenAIRE

    Ramachandran Sudarshan; G Sree Vijayabala; KS Prem Kumar

    2012-01-01

    Turner syndrome is a genetic disorder that affects mostly females. Affected females have characteristic features such as short stature, premature ovarian failure, and several other features. Oral manifestations of this condition are not much discussed in the literature. But reported literature includes teeth, palate, periodontal and salivary changes. So the aim of this review is to illustrate the general manifestations, and especially the oral manifestations of Turner syndrome and evaluate th...

  15. Pendred's syndrome

    International Nuclear Information System (INIS)

    This report describes Pendred's syndrome in three siblings of a consanguineous marriage, belonging to Rahimyar Khan. The children presented with deafmutism and goiters. The investigations included scintigram, perchlorate discharge test and audiometery. The perchlorate discharge was positive in index case. Bilateral sensorineural hearing defect was detected on Pure Tone Average (PTA) audiometry. Meticulous clinical and laboratory evaluation is mandatory for the detection of rare disorders like Pendred's syndrome. (author)

  16. An Experimental and Numerical Study on Cracking Behavior of Brittle Sandstone Containing Two Non-coplanar Fissures Under Uniaxial Compression

    Science.gov (United States)

    Yang, Sheng-Qi; Tian, Wen-Ling; Huang, Yan-Hua; Ranjith, P. G.; Ju, Yang

    2016-04-01

    To understand the fracture mechanism in all kinds of rock engineering, it is important to investigate the fracture evolution behavior of pre-fissured rock. In this research, we conducted uniaxial compression experiments to evaluate the influence of ligament angle on the strength, deformability, and fracture coalescence behavior of rectangular prismatic specimens (80 × 160 × 30 mm) of brittle sandstone containing two non-coplanar fissures. The experimental results show that the peak strength of sandstone containing two non-coplanar fissures depends on the ligament angle, but the elastic modulus is not closely related to the ligament angle. With the increase of ligament angle, the peak strength decreased at a ligament angle of 60°, before increasing up to our maximum ligament angle of 120°. Crack initiation, propagation, and coalescence were all observed and characterized from the inner and outer tips of pre-existing non-coplanar fissures using photographic monitoring. Based on the results, the sequence of crack evolution in sandstone containing two non-coplanar fissures was analyzed in detail. In order to fully understand the crack evolution mechanism of brittle sandstone, numerical simulations using PFC2D were performed for specimens containing two non-coplanar fissures under uniaxial compression. The results are in good agreement with the experimental results. By analyzing the stress field, the crack evolution mechanism in brittle sandstone containing two non-coplanar fissures under uniaxial compression is revealed. These experimental and numerical results are expected to improve the understanding of the unstable fracture mechanism of fissured rock engineering structures.

  17. Burning Mouth Syndrome

    Science.gov (United States)

    ... OralHealth > Topics > Burning Mouth Syndrome > Burning Mouth Syndrome Burning Mouth Syndrome Main Content Key Points Symptoms Diagnosis Primary and Secondary BMS Treatment Helpful Tips Key Points Burning mouth syndrome is burning pain in the mouth that may ...

  18. Learning about Down Syndrome

    Science.gov (United States)

    ... for the genetic terms used on this page Learning About Down Syndrome What is Down syndrome? What ... Down syndrome? People who have Down syndrome have learning difficulties, mental retardation, a characteristic facial appearance, and ...

  19. Exogenous Cushing syndrome

    Science.gov (United States)

    Cushing syndrome - corticosteroid induced; Corticosteroid-induced Cushing syndrome; Iatrogenic Cushing syndrome ... Cushing syndrome is a disorder that occurs when your body has a higher than normal level of the ...

  20. Turner Syndrome: Other FAQs

    Science.gov (United States)

    ... NICHD Research Information Clinical Trials Resources and Publications Turner Syndrome: Other FAQs Skip sharing on social media links ... been diagnosed with Turner syndrome. Now what? Is Turner syndrome inherited? Turner syndrome is usually not inherited, but ...

  1. Laboratory tests and numerical simulations of brittle marble and squeezing schist at Jinping II hydropower station,China

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Four 16.7 km-long tunnels with diameters ranging from 12.4 to 14.6 m are now under construction at Jinping II hydropower station along the Yalong River.The tunnels pass through Triassic rocks below Jinping Mountain.The tunnels are characterized with high overburden,long alignment and complex geological conditions.Brittle failure in marble and squeezing in schist are the primary problems in tunnelling.This paper introduces the studies of laboratory tests on Jinping II marble as well as numerical prediction o...

  2. Effect of thermomechanical treatment on the resistance of low-carbon low-alloy steel to brittle fracture

    Science.gov (United States)

    Schastlivtsev, V. M.; Tabatchikova, T. I.; Yakovleva, I. L.; Del'gado Reina, S. Yu.; Golosienko, S. A.; Pazilova, U. A.; Khlusova, E. I.

    2015-02-01

    Structure and mechanical properties of rolled plates (20-35 mm thick) of low-carbon low-alloy steel subjected to thermomechanical treatment (TMT) according to various regimes under laboratory and industrial conditions have been studied. Structural factors that favor obtaining high mechanical properties have been established. The retarding action of TMT on softening upon tempering has been revealed. The reasons for the decrease in the resistance to brittle fracture of the steel subjected to TMT, repeated quenching from the temperature of the furnace heating, and tempering have been determined.

  3. THE EFFECT OF MATRIX TOUGHNESS ON THE BRITTLE-DUCTILE TRANSITION OF HDPE/CaCO3 BLENDS

    Institute of Scientific and Technical Information of China (English)

    FU Qiang; ZHANG Yulin; WANG Guiheng

    1994-01-01

    The effects of HDPE matrix toughness on the brittle-ductile transition of HDPE/CaCO3 blends are investigated. Not all HDPE can be toughened by CaCO3 particles. The ability of the matrix to yield plays a fundamental role in determing whether HDPE can be toughened or not.There exists a critical matrix toughness (Isc≈45J/m) below which HDPE can not be toughened observably by CaCO3 particle at given average size, and above which the critical matrix ligament thickness (τc) is proportional to matrix impact strength.

  4. Revealing stiffening and brittling of chronic myelogenous leukemia hematopoietic primary cells through their temporal response to shear stress

    Science.gov (United States)

    Laperrousaz, B.; Berguiga, L.; Nicolini, F. E.; Martinez-Torres, C.; Arneodo, A.; Maguer Satta, V.; Argoul, F.

    2016-06-01

    Cancer cell transformation is often accompanied by a modification of their viscoelastic properties. When capturing the stress-to-strain response of primary chronic myelogenous leukemia (CML) cells, from two data sets of CD34+ hematopoietic cells isolated from healthy and leukemic bone marrows, we show that the mean shear relaxation modulus increases upon cancer transformation. This stiffening of the cells comes along with local rupture events, detected as reinforced sharp local maxima of this modulus, suggesting that these cancer cells respond to a local mechanical stress by a cascade of local brittle failure events.

  5. Swedish Work on Brittle-Fracture Problems in Nuclear Reactor Pressure Vessels

    International Nuclear Information System (INIS)

    After a short review of the part of the Swedish nuclear energy program that is of interest in this context the Swedish reactor pressure vessels and the reasoning behind the choice of materials are surveyed. Problems and desirable aims for future reactors are discussed. Much work is now being done on new types of pressure vessel steels with high strength, low transition temperature and good corrosion resistance. These steels are of the martensitic austenitic type Bofors 2RMO (13 % Cr, 6 % Ni, 1. 5 % Mo) and of the ferritic martensitic austenitic type Avesta 248 SV (16 % Cr, 5 % Ni, 1 % Mo). An applied philosophy for estimating the brittle-fracture tendency of pressure vessels is described. As a criterion of this tendency we use the crack-propagation transition temperature, e. g. as measured by the Robertson isothermal crack-arrest test. An estimate of this transition temperature at the end of the reactor' s lifetime must take increases due to fabrication, welding, geometry, ageing and irradiation into account. The transition temperature vs. stress curve moves towards higher temperatures during the reactor' s lifetime. As long as this curve does not cross the reactor vessel stress vs. temperature curve the vessel is considered safe. The magnitude of the different factors influencing the final transition temperature are discussed and data for the Marviken reactor's pressure vessel are presented. At the end of the reactor's lifetime the estimated transition temperature is 115 deg C, which is below the maximum permissible value. A program for the study of strain ageing has been initiated owing to the uncertainty as to the extent of strain ageing at low strains. A study of a simple crack-arrest test, developed in Sweden, is in progress. An extensive irradiation-effects program on several steels is in progress. Results from tests on the Swedish carbon-manganese steels 2103/R3, SIS 142103 and SIS 142102, the low-alloy steels Degerfors DE-631A, Bofors NO 345 and Fortiweld

  6. Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia)

    Science.gov (United States)

    Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo

    2016-04-01

    The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the

  7. Analysis of the effect of the fluid-structure interface on elastic wave velocity in cornea-like structures by OCE and FEM

    Science.gov (United States)

    Han, Zhaolong; Li, Jiasong; Singh, Manmohan; Vantipalli, Srilatha; Aglyamov, Salavat R.; Wu, Chen; Liu, Chih-hao; Raghunathan, Raksha; Twa, Michael D.; Larin, Kirill V.

    2016-03-01

    Air-pulse optical coherence elastography (OCE) is a promising technique for quantifying biomechanical properties of the cornea. This technique typically involves imaging and analysis of the propagation of the air-pulse induced elastic waves to reconstruct corneal biomechanical properties using an analytical model. However, the effect of the fluid-structure interface (FSI) at the corneal posterior surface on the elastic wave velocity is not accounted for in many models. In this study, we examined the effect of the FSI with OCE experiments on contact lenses with and without fluid in the posterior gap. Finite element models (FEM), also with and without the FSI, were constructed to simulate the elastic wave propagation based on the OCE measurements. The FEM and OCE results were in good agreement demonstrating the feasibility of the method. To further investigate the effect of the FSI, OCE experiments and subsequent FEM simulations were conducted on in situ rabbit corneas before and after rose bengal/green light corneal collagen cross-linking (RGX). Both the OCE experiments and the FE simulations demonstrated that the FSI significantly reduced the group velocity of the elastic wave, and thus, should be considered when determining corneal biomechanical properties from an appropriate mechanical model. By matching the FEM-calculated velocity to the OCE-measured velocity, the corneal elasticity was quantified. The Young’s modulus of the rabbit cornea before RGX was E  =  65  ±  10 kPa at a controlled intraocular pressure (IOP) of 15 mmHg. After RGX, the Young’s modulus increased to E  =  102  ±  7 kPa at the same IOP.

  8. Conhecimento de estudantes de medicina sobre o processo de doação de córneas The knowledge of medical students about cornea donation

    Directory of Open Access Journals (Sweden)

    Rodrigo França de Espíndola

    2007-08-01

    Full Text Available OBJETIVO: Avaliar o conhecimento de estudantes de medicina sobre o processo de doação de córneas, comparando-o entre aqueles que já cursaram a disciplina de Oftalmologia com os demais. MÉTODOS: Foi aplicado um questionário a estudantes de medicina do interior de São Paulo, contendo dados como: idade, sexo, ano de graduação e 10 perguntas de múltipla escolha sobre o tema. As questões abordaram o limite de idade para doação, contra-indicações para o transplante, tempo para retirada das córneas, dentre outras. Foi comparado o conhecimento (% de acertos entre aqueles que haviam cursado a disciplina de Oftalmologia (Grupo A com os demais (Grupo B. RESULTADOS: Foram entrevistados 402 estudantes. Destes, 140 eram do grupo A e 262 do grupo B. Não houve diferença estatisticamente significante entre os dois grupos (p=0,8328. CONCLUSÃO: O conhecimento sobre o processo de doação de córneas mostrou-se insuficiente entre os alunos entrevistados, mesmo para aqueles que haviam cursado a disciplina de Oftalmologia, apontando a necessidade de aperfeiçoamento do conhecimento divulgado nas escolas médicas.PURPOSE: To compare knowledge of medical students about the cornea donation process among those who already studied Ophthalmology and the others. METHODOS: A questionnaire containing data as: age, sex, graduation year, and 10 multiple-choice questions about the subject was applied to medical students from the interior of São Paulo state, Brazil. The questions were: age for donation, contraindication for transplants, the time limit to remove the cornea, among others. The knowledge regarding cornea donation was compared between the two groups: students who already studied Ophthalmology (Group A and the others (Group B. RESULTS: The study group was composed of 402 students, of whom 140 were of group A and 262 of group B. Knowledge between the two groups was different, but not statistically significant (p=0.8328. CONCLUSION: Knowledge about

  9. Ocular lesions associated with attachment of the copepod Ommatokoita elongata (Lernaeopodidae: Siphonostomatoida) to corneas of Pacific sleeper sharks Somniosus pacificus captured off Alaska in Prince William Sound.

    Science.gov (United States)

    Benz, George W; Borucinska, Joanna D; Lowry, Lloyd F; Whiteley, Herbert E

    2002-06-01

    Twenty eyes from 10 Pacific sleeper sharks Somniosus pacificus, infected with the copepod Ommatokoita elongata, were collected in Prince William Sound, Alaska, and the eyes of an additional 18 S. pacificus captured in the same area were inspected for copepods. Prevalence of infection by adult female O. elongata was 97% (n = 28); mean intensity of infection was 1.89 (+/-1SD = 0.32) adult female copepods per infected shark and 1.0 (+/- 1SD = 0.0) adult female copepods per infected eye. Five of the 20 collected eyes were infected by O. elongata chalimi, and 9 of 20 eyes had 1 to several remnants of bullae embedded in the cornea. Bullae were each associated with a corneal opacity, and anchoring plugs of chalimi were associated with pinpoint lesions in the cornea or conjunctiva. All eyes exhibited marked edema and erosion of the bulbar conjunctiva, and this torus-shaped lesion corresponded to each O. elongata adult female's presumed feeding and abrasion radius. Histological examinations revealed lesions in the anterior segment of eyes to be generally similar, but graded, in severity, and in all eyes they involved the conjunctiva, cornea, filtration angle, and iris. Epithelial lesions were characterized by corneal ulceration, dysplasia, hyperplasia, and heterophilic keratitis, and by ulcerative conjunctivitis accompanied by epithelial hyperplasia with rete peg formation. Disorganization of fibers, necrosis, mineralization, minimal heterophilic influx, and perilimbic neovascularization were associated with bullae in the corneal stroma. Within the limbus there was diffuse histiocytic and lymphocytic inflammation and marked lymphofollicular hyperplasia. Heterophilic and mononuclear anterior uveitis affecting the filtration angle and anterior surface of the iris was also observed in most eyes. One eye had a partial transcorneal prolapse of a ruptured lens, with degenerative changes in the ruptured lens and severe keratitis associated with the anchoring devices of an adult

  10. Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

    OpenAIRE

    Kaluzhny, Yulia; Kandárová, Helena; d’Argembeau-Thornton, Laurence; Kearney, Paul; Klausner, Mitchell

    2015-01-01

    To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and accurate assessment of ocular toxicity in man are needed. To address this need, we have developed an eye irritation test (EIT) which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model that is based on normal human cells. The EIT is able to separate ocular irritants and corrosives (GHS Categories 1 and 2 ...

  11. Pfeiffer syndrome

    Directory of Open Access Journals (Sweden)

    Fryns Jean-Pierre

    2006-06-01

    Full Text Available Abstract Pfeiffer syndrome is a rare autosomal dominantly inherited disorder that associates craniosynostosis, broad and deviated thumbs and big toes, and partial syndactyly on hands and feet. Hydrocephaly may be found occasionally, along with severe ocular proptosis, ankylosed elbows, abnormal viscera, and slow development. Based on the severity of the phenotype, Pfeiffer syndrome is divided into three clinical subtypes. Type 1 "classic" Pfeiffer syndrome involves individuals with mild manifestations including brachycephaly, midface hypoplasia and finger and toe abnormalities; it is associated with normal intelligence and generally good outcome. Type 2 consists of cloverleaf skull, extreme proptosis, finger and toe abnormalities, elbow ankylosis or synostosis, developmental delay and neurological complications. Type 3 is similar to type 2 but without a cloverleaf skull. Clinical overlap between the three types may occur. Pfeiffer syndrome affects about 1 in 100,000 individuals. The disorder can be caused by mutations in the fibroblast growth factor receptor genes FGFR-1 or FGFR-2. Pfeiffer syndrome can be diagnosed prenatally by sonography showing craniosynostosis, hypertelorism with proptosis, and broad thumb, or molecularly if it concerns a recurrence and the causative mutation was found. Molecular genetic testing is important to confirm the diagnosis. Management includes multiple-staged surgery of craniosynostosis. Midfacial surgery is performed to reduce the exophthalmos and the midfacial hypoplasia.

  12. Antiphospholipid syndrome.

    Science.gov (United States)

    Ruiz-Irastorza, Guillermo; Crowther, Mark; Branch, Ware; Khamashta, Munther A

    2010-10-30

    The antiphospholipid syndrome causes venous, arterial, and small-vessel thrombosis; pregnancy loss; and preterm delivery for patients with severe pre-eclampsia or placental insufficiency. Other clinical manifestations are cardiac valvular disease, renal thrombotic microangiopathy, thrombocytopenia, haemolytic anaemia, and cognitive impairment. Antiphospholipid antibodies promote activation of endothelial cells, monocytes, and platelets; and overproduction of tissue factor and thromboxane A2. Complement activation might have a central pathogenetic role. Of the different antiphospholipid antibodies, lupus anticoagulant is the strongest predictor of features related to antiphospholipid syndrome. Therapy of thrombosis is based on long-term oral anticoagulation and patients with arterial events should be treated aggressively. Primary thromboprophylaxis is recommended in patients with systemic lupus erythematosus and probably in purely obstetric antiphospholipid syndrome. Obstetric care is based on combined medical-obstetric high-risk management and treatment with aspirin and heparin. Hydroxychloroquine is a potential additional treatment for this syndrome. Possible future therapies for non-pregnant patients with antiphospholipid syndrome are statins, rituximab, and new anticoagulant drugs. PMID:20822807

  13. Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility

    Science.gov (United States)

    An, Qi; Goddard, William A.

    2015-09-01

    Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B4C ), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (˜200 000 atoms /cell ) reactive-molecular-dynamics simulations of shear deformations of B4C , using the quantum-mechanics-derived reactive force field simulation. We examined the (0001 )/⟨10 1 ¯ 0 ⟩ slip system related to deformation twinning and the (01 1 ¯ 1 ¯ )/⟨1 ¯ 101 ⟩ slip system related to amorphous band formation. We find that brittle failure in B4C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B4C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

  14. The influence of synchrotron radiation-induced strain on the growth and dissolution of brittle and ductile materials

    Science.gov (United States)

    Ristic, R. I.; Shekunov, B. Yu.; Sherwood, J. N.

    1997-08-01

    Sodium chlorate (brittle) and sodium nitrate (ductile) crystals were irradiated by synchrotron radiation to produce samples in which one-half of a particular crystal was strained by radiation damage and the other not. The growth and dissolution kinetics of these samples were investigated using in situ laser interferometry and X-ray topography. An appreciable difference was observed in the growth and dissolution kinetics of the irradiated and nonirradiated halves. In the region of very low supersaturation, σ < σ c = 0.32% for sodium chlorate and σ < σ c = 0.065% for sodium nitrate, the irradiated portions of both types of crystals dissolved; simultaneously, the nonirradiated portions grew. Above the critical supersaturation, σ c, both halves grew. This defines a difference in solubility between the irradiated and nonirradiated material. The significant difference between the two critical supersaturations in the two materials confirms our earlier findings that a larger amount of elastic strain per unit volume can be introduced into brittle materials than into ductile ones. This, in turn, has a much stronger effect on both growth and dissolution kinetics. Irradiation is shown to yield pure point defect strain and not to introduce dislocations in the system. A possible mechanism by which strain influences the growth and dissolution kinetics is discussed.

  15. Detecting Acoustic Emissions With/Without Dehydration of Serpentine Outside P-T Field of Conventional Brittle Failure

    Science.gov (United States)

    Jung, H.; Fei, Y.; Silver, P. G.; Green, H. W.

    2005-12-01

    It is currently thought that earthquakes cannot be triggered at depths greater than ~60 km by unassisted brittle failure or frictional sliding, but could be triggered by dehydration embrittlement of hydrous minerals (Raleigh and Paterson, 1965; Green and Houston, 1995; Kirby, 1995; Jung et al., 2004). Using a new multianvil-based system for detecting acoustic emissions with four channels at high pressure and high temperature that was recently developed (Jung et al., 2005), we tested this hypothesis by deforming samples of serpentine. We found that acoustic emissions were detected not only during/after the dehydration of serpentine, but even in the absence of dehydration. These emissions occurred at high pressure and high temperature, and thus outside pressure-temperature field of conventional brittle failure. Backscattered-electron images of microstructures of the post-run specimen revealed fault slip at elevated pressure, with offsets of up to ~500 μm, even without dehydration. Analysis of P-wave travel times from the four sensors confirmed that the acoustic emissions originated from within the specimen during fault slip. These observations suggest that earthquakes can be triggered by slip along a fault containing serpentine at significantly higher pressure and temperature conditions than that previously thought, even without dehydration. They are thus consistent with faulting mechanisms that appeal to dehydration embrittlement, as well as those that rely solely on the rheology of non-dehydrated serpentine.

  16. Combined effects of phosphorus segregation and partial intergranular fracture on the ductile-brittle transition temperature in structural alloy steels

    International Nuclear Information System (INIS)

    Research highlights: → Effective P segregation was proposed by segregated P and intergranular fracture. → The DBTT of aged and irradiated steel was analyzed by effective P segregation. → The DBTT of two classes of steels are controlled by differing mechanisms. → Hardening strongly influenced the embrittling potency of segregated P. - Abstract: This article introduced effective P segregation in terms of the product of the amount of segregated P and partial intergranular fracture to account for the combined effects on the ductile-brittle transition temperature (DBTT) measured by dynamic and static notched bar tests on several alloy steels. Effective P segregation characterized a DBTT shift caused by thermal ageing and/or neutron irradiation in various A533B and 2.25Cr-1Mo steels, while P segregation controlled the DBTT independent of the fraction of intergranular fracture in thermally aged 3.5Ni-1.7Cr steels with and without Mo and V. These DBTT behaviors of the two classes of steels are related to differing brittle fracture mechanisms. The present analysis enables one to investigate how the embrittling potency of segregated P in association with partial intergranular fracture is influenced by the differing plasticity and the addition of several alloying elements under dynamic and static loading conditions.

  17. Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility.

    Science.gov (United States)

    An, Qi; Goddard, William A

    2015-09-01

    Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B(4)C), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (∼200,000  atoms/cell) reactive-molecular-dynamics simulations of shear deformations of B(4)C, using the quantum-mechanics-derived reactive force field simulation. We examined the (0001)/⟨101̅0⟩ slip system related to deformation twinning and the (011̅1̅)/⟨1̅101⟩ slip system related to amorphous band formation. We find that brittle failure in B(4)C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B(4)C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

  18. On strain-rate sensitivity and size effect of brittle solids: transition from cooperative phenomena to microcrack nucleation

    Science.gov (United States)

    Mastilovic, Sreten

    2013-03-01

    An idealized brittle microscale system is subjected to dynamic uniaxial tension in the medium-to-high strain-rate range (dot \\varepsilon in [100s^{-1},1 × 107 s^{-1}]) to investigate its mechanical response under constrained spatial and temporal scales. The setup of dynamic simulations is designed to ensure practically identical in-plane stress conditions on a system of continuum particles forming a two-dimensional, geometrically and structurally disordered, lattice. The rate sensitivity of size effects is observed as well as the ordering effect of kinetic energy. A simple phenomenological expression is developed to account for the tensile strength sensitivity of the small-sized brittle systems to the strain-rate and extrinsic size effects, which may serve as a guideline for formulation of constitutive relations in the MEMS design. The representative sample is defined as a square lattice size for which the tensile strength becomes rate-insensitive and an expression is proposed to model its evolution between two asymptotes corresponding to the limiting loading rates. The dynamics of damage accumulation is analyzed as a function of sample size and loading rate.

  19. Towards fully automatic modelling of the fracture process in quasi-brittle and ductile materials: a unified crack growth criterion

    Institute of Scientific and Technical Information of China (English)

    Zhen-jun YANG; Guo-hua LIU

    2008-01-01

    Fully automatic finite element (FE) modelling of the fracture process in quasi-brittle materials such as concrete and rocks and ductile materials such as metals and alloys, is of great significance in assessing structural integrity and presents tremendous challenges to the engineering community. One challenge lies in the adoption of an objective and effective crack propagation criterion. This paper proposes a crack propagation criterion based on the principle of energy conservation and the cohesive zone model (CZM). The virtual crack extension technique is used to calculate the differential terms in the criterion. A fully-automatic discrete crack modelling methodology, integrating the developed criterion, the CZM to model the crack, a simple remeshing procedure to accommodate crack propagation, the J2 flow theory implemented within the incremental plasticity framework to model the ductile materials, and a local arc-length solver to the nonlinear equation system, is developed and implemented in an in-house program. Three examples, i.e., a plain concrete beam with a single shear crack, a reinforced concrete (RC) beam with multiple cracks and a compact-tension steel specimen, are simulated. Good agreement between numerical predictions and experimental data is found, which demonstrates the applicability of the criterion to both quasi-brittle and ductile materials.

  20. Hallermann–Streiff syndrome with severe bilateral enophthalmos and radiological evidence of silent brain syndrome: a new congenital silent brain syndrome?

    Directory of Open Access Journals (Sweden)

    Nucci P

    2011-07-01

    Full Text Available Paolo Nucci¹, Carlo de Conciliis², Matteo Sacchi¹, Massimiliano Serafino¹¹Eye Clinic, San Giuseppe Hospital, University of Milan, ²Eye Clinic, Istituto Auxologico Italiano, Milan, ItalyBackground: We present the first case of a congenital form of silent brain syndrome (SBS in a young patient affected by Hallermann–Streiff syndrome (HSS and the surgical management of the associated eyelid anomalies.Methods: HSS signs were evaluated according to the Francois criteria. Orbital computed tomography (CT and genetic analysis were performed. An upper eyelid retractor-free recession was performed. Follow-up visits were performed at day 1, weeks 1 and 3, and months 3, 6, 9 (for both eyes, and 12 (for left eye after surgery.Results: The patient exhibited six of the seven signs of HSS. Orbital CT showed bilateral enophthalmos and upward bowing of the orbital roof with air entrapment under the upper eyelid as previously described for SBS. Genetic analysis showed a 2q polymorphism. During follow-up, the cornea showed absence of epithelial damage and the upper eyelids were lowered symmetrically, with a regular contour.Conclusion: Our HSS patient shares features with SBS. We postulate that SBS could include more than one pattern, ie, an acquired form following ventriculoperitoneal shunting and this newly reported congenital form in our HSS patient in whom typical syndromic skull anomalies led to this condition. The surgical treatment has been effective in restoring an appropriate lid level, with good globe apposition and a good cosmetic result.Keywords: Hallermann–Streiff syndrome, silent brain syndrome, upper eyelid entropion