Imaging of patellofemoral instability

International Nuclear Information System (INIS)

Waldt, S.; Rummeny, E.J.

2012-01-01

Patellofemoral instability remains a diagnostic and therapeutic challenge due to its multifactorial genesis. The purpose of imaging is to systematically analyze predisposing factors, such as trochlear dysplasia, patella alta, tibial tuberosity-trochlear groove (TT-TG) distance, rotational deformities of the lower limb and patellar tilt. In order to evaluate anatomical abnormalities with a sufficient diagnostic accuracy, standardized measurement methods and implementation of various imaging modalities are necessary. Diagnosis of acute and often overlooked lateral patellar dislocation can be established with magnetic resonance imaging (MRI) because of its characteristic patterns of injury. Damage to the medial patellofemoral ligament (MPFL) has a significance just as high as the predisposing risk factors in relation to the cause of chronic instability. (orig.) [de

Optical instabilities and chaos due to the virtual formation of biexcitons

International Nuclear Information System (INIS)

Nguyen Trung Dan.

1994-07-01

Optical instabilities and chaos due to virtual formation of biexcitons in optically excited semiconductors are investigated. A complete linear stability analysis of steady-state bistable solutions of nonlinear coupled differential equations describing the nonlinear dynamics of semiconductors is carried out. The dynamical solutions are studied numerically using an iterative procedure. (author). 20 refs, 3 figs

Guidelines for Safety Evaluation of a Potential for PWR Steam Generator Tube Failure due to Fluid elastic Instability

Energy Technology Data Exchange (ETDEWEB)

Jo, Jong Chull; Do, Kyu Sik; Sheen, Cheol [Nuclear System Evaluation Dept., Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

2013-05-15

It was found that both SG tube rupture events occurred at North Anna Unit 1 in 1987 and at Mihama Unit 2 in 1991 were caused by a high cycle fatigue due to fluid elastic instability. Therefore, with regard to nuclear safety it is important to design the SG properly in a conservative manner so that the potential for SG U-tube failures due to fluid elastic instability can be minimized. This article provides guidelines for assessing the potential for SG U-tube damage due to fluid elastic instability. This article described guidelines for safety evaluation of a potential for PWR steam generator tube failure due to fluid elastic instability. The guidelines address the requirements for realistically performing the SG thermal-hydraulic analysis and the modal analysis of tubes as well as the criteria for conservatively determining the added mass, the damping ratio and the fluid elastic instability coefficient. The guidelines can be used to predict the potential SG tubes which are susceptible to failure due to fluid elastic instability at operating nuclear power plants and also to evaluate the safety and structural integrity of new SG designs at the licensing review stage. Failure of a pressurized water reactor (PWR) steam generator (SG) tube leads to a leakage of contaminated primary coolant to the secondary system, which has serious safety implications such as the potential for direct release of radioactive fission products to the environment and the loss of coolant. Excessive tube vibration excited by dynamic forces of internal or external fluid flow is called flow-induced vibration (FIV). Among the FIV mechanisms, the so-called fluid elastic instability of SG tubes in cross flow is the most important safety issue in the design of SGs because it may cause severe tube failure in a very short time.

Subjeans Condensations due to a Thermal Instability

Science.gov (United States)

Opher, R.; Valio, A.

1990-11-01

RESUMEN. Las observaciones recientes muestran que las nubes moleculares no son homogeneas, sino que tienen condensaciones. Se observa que estas condensaciones estan libres gravitacionalmente. C6mo se forman estas condensaciones? Sugerimos explicar estas conden sac jones como debidas a que la inestabilidad termica ayuda a la gravedad. Se estudi6 una funci5n de enfriamiento por gramo de la forma general A p T , en donde p y T son la densidad y la temperatura. Estamos interesados en el valor maximo de para la cual el colapso ocurre. Se estudiaron varios mode- los. Nuestros resultados indican que los valores de comparables con aquellos sugeridos por la literatura (1 son suficientes para provocar el colapso de masas inferiores a la masa de Jeans por medio de inestabilidad termica, ayudada por gravedad y asi se forman las condensaciones libres gravitacionalmente. ABSTRACT: Recent observations show that molecular clouds are not homogeneous, but clumpy. Some clumps are observed to be gravitationally unbound. How did these clumps then form? We suggest explaining these condensation as due to thermal instability aiding gravit y The cooling function per gram studied is of the general form A p T,where pand T are the density and temperature, respectively. We are interested in the maximum value of for which collapse still occurs. Various models are studied. Our results indicate that values comparable to those suggested in the literature (1 < %< 2) are sufficient to trigger the collapse of subjeans masses by thermal instability, when aided by gravity, and form the observed gravitationally unbound clumps. Keq o : HYDRODYNAMICS - INTERSTELLAR CLOUDS

Anomalous plasma transport due to electron temperature gradient instability

International Nuclear Information System (INIS)

Tokuda, Sinji; Ito, Hiroshi; Kamimura, Tetsuo.

1979-01-01

The collisionless drift wave instability driven by an electron temperature inhomogeneity (electron temperature gradient instability) and the enhanced transport processes associated with it are studied using a two-and-a-half dimensional particle simulation code. The simulation results show that quasilinear diffusion in phase space is an important mechanism for the saturation of the electron temperature gradient instability. Also, the instability yields particle fluxes toward the hot plasma regions. The heat conductivity of the electron temperature perpendicular to the magnetic field, T sub(e'), is not reduced by magnetic shear but remains high, whereas the heat conductivity of the parallel temperature, T sub(e''), is effectively reduced, and the instability stabilized. (author)

Short- to Medium-term Outcomes After a Modified Broström Repair for Lateral Ankle Instability With Immediate Postoperative Weightbearing.

Science.gov (United States)

Petrera, Massimo; Dwyer, Tim; Theodoropoulos, John S; Ogilvie-Harris, Darrell J

2014-07-01

Anatomic techniques of ankle ligament repair have the advantage of restoring the anatomy and kinematics of the joint. This study presents a technique for anatomic reconstruction of the lateral ligament complex by way of lateral ligament advancement using suture anchors associated with immediate protected full weightbearing; 2- to 5-year clinical outcomes are reported. This technique of providing an anatomic reconstruction with a secure fixation will enable early rehabilitation with immediate, protected weightbearing, with favorable outcomes. Case series; Level of evidence, 4. Fifty-five patients with chronic lateral ankle instability who failed nonoperative management underwent modified Broström repair (lateral ligament fibular advancement) between 2005 and 2008. The anterior talofibular ligament and calcaneofibular ligament were released from the fibula and advanced using 2 double-loaded metallic suture anchors (3.5 mm). Full weightbearing in a walking boot was allowed from the first postoperative day. Patients were assessed preoperatively and at a minimum 2-year follow-up using the Foot and Ankle Outcome Score. Complication, failure (recurrent instability), and return-to-sport rates were also recorded. Six patients (11%) were lost to follow-up, leaving a study group of 49 patients (23 men, 26 women). The mean age at the time of surgery was 25 years (range, 18-37 years), with a mean duration of symptoms of 1.8 years (range, 6 months to 5 years). The mean follow-up time was 42 months (range, 24-60 months). Significant improvement was seen in the Foot and Ankle Outcome Score from preoperatively to postoperatively (from 36 to 75.4, P ankle-related quality of life subscale from 35 to 78 (P anchor fixation is an effective procedure for the treatment of chronic lateral ankle instability and allows immediate weightbearing. © 2014 The Author(s).

Suppression of the Rayleigh-Taylor instability due to self-radiation in a multiablation target

International Nuclear Information System (INIS)

Fujioka, Shinsuke; Sunahara, Atsushi; Nishihara, Katsunobu; Johzaki, Tomoyuki; Shiraga, Hiroyuki; Shigemori, Keisuke; Nakai, Mitsuo; Ikegawa, Tadashi; Murakami, Masakatsu; Nagai, Keiji; Norimatsu, Takayoshi; Azechi, Hiroshi; Yamanaka, Tatsuhiko; Ohnishi, Naofumi

2004-01-01

A scheme to suppress the Rayleigh-Taylor instability has been investigated for a direct-drive inertial fusion target. In a high-Z doped-plastic target, two ablation surfaces are formed separately--one driven by thermal radiation and the other driven by electron conduction. The growth of the Rayleigh-Taylor instability is significantly suppressed on the radiation-driven ablation surface inside the target due to the large ablation velocity and long density scale length. A significant reduction of the growth rate was observed in simulations and experiments using a brominated plastic target. A new direct-drive pellet was designed using this scheme

Evaluation of the Talar Cartilage in Chronic Lateral Ankle Instability with Lateral Ligament Injury Using Biochemical T2* Mapping: Correlation with Clinical Symptoms.

Science.gov (United States)

Hu, Yiwen; Tao, Hongyue; Qiao, Yang; Ma, Kui; Hua, Yinghui; Yan, Xu; Chen, Shuang

2018-06-19

This study aims to quantitatively compare T2* measurements of the talar cartilage between chronic lateral ankle instability (LAI) patients with lateral ligament injury and healthy volunteers, and to assess the association of T2* value with American Orthopedic Foot and Ankle Society (AOFAS) score. Nineteen consecutive patients with chronic LAI (LAI group) and 19 healthy individuals (control group) were enrolled. Biochemical magnetic resonance examination of the ankle was performed in all participants using three-dimensional gradient-echo T2* mapping. Total talar cartilage was divided into six subcompartments, including medial anterior (MA), central medial, medial posterior, lateral anterior, central lateral (LC), and lateral posterior regions. T2* values of respective cartilage areas were measured and compared between the two groups using Student t test. AOFAS scoring was performed for clinical evaluation. Then, the association of T2* value with AOFAS score was evaluated by Pearson correlation. The T2* values of total talar cartilage, as well as MA and LC cartilage compartments, in the chronic LAI group were significantly higher than control values (P T2* value of MA in the chronic LAI group was negatively correlated with AOFAS score (r =-0.8089, P T2* measurements. The clinical score correlates highly with T2* value of the MA cartilage compartment, indicating that MA may be the principal cartilage area conferring clinical symptoms. Copyright © 2018 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.

Combined medial and lateral anatomic ligament reconstruction for chronic rotational instability of the ankle.

Science.gov (United States)

Buchhorn, Tomas; Sabeti-Aschraf, Manuel; Dlaska, Constantin E; Wenzel, Florian; Graf, Alexandra; Ziai, Pejman

2011-12-01

This study aimed to extend knowledge on the arthroscopic evaluation of the unstable ankle joint and the outcome of ligament reconstruction on rotational instability. In contrast to previous studies, we investigated the combined repair of lateral and medial ligaments. Ninety-six patients underwent medial and lateral ligament reconstruction between 2006 and 2008, 81 of whom, with a mean age of 31.9 (range, 14 to 44) years, completed the 12-month followup and were therefore included in this study (Table 1). Clinical, radiographic, and concomitant arthroscopic examination was performed prior to the ligament stabilization. Postoperative followup included clinical and radiographic evaluation after 3, 6, and 12 months. Arthroscopy showed a lesion of the anterior fibulotalar ligament (AFTL), calcaneofibular ligament (CFL), and tibiocalcanear ligament (TCL) (Deep part of deltoid ligament complex) in 67 patients. An avulsion of the proximal insertion point of the ATTL was additionally found in 14 cases. Clinical results 3 months after surgery showed a significant increase in the AOFAS-Hindfoot Score as well as a significant decrease of the Visual Analogue-Scale for pain (VAS) (p ankle joint in most cases has an injury of the lateral ligaments and a component of the deltoid, the TCL, but rarely with a combined lesion of the TCL and the anterior tibiotalar ligament (ATTL) (Superficial part of deltoid ligament complex). The combined lateral and medial ligament reconstruction with an anchor technique had a good clinical outcome with high patient satisfaction with few complications.

All-inside, anatomical lateral ankle stabilization for revision and complex primary lateral ankle stabilization: a technique guide.

Science.gov (United States)

Prissel, Mark A; Roukis, Thomas S

2014-12-01

Lateral ankle instability is a common mechanical problem that often requires surgical management when conservative efforts fail. Historically, myriad open surgical approaches have been proposed. Recently, consideration for arthroscopic management of lateral ankle instability has become popular, with promising results. Unfortunately, recurrent inversion ankle injury following lateral ankle stabilization can occur and require revision surgery. To date, arthroscopic management for revision lateral ankle stabilization has not been described. We present a novel arthroscopic technique combining an arthroscopic lateral ankle stabilization kit with a suture anchor ligament augmentation system for revision as well as complex primary lateral ankle stabilization. © 2014 The Author(s).

Plasma blob generation due to cooperative elliptic instability.

Science.gov (United States)

Manz, P; Xu, M; Müller, S H; Fedorczak, N; Thakur, S C; Yu, J H; Tynan, G R

2011-11-04

Using fast-camera measurements the generation mechanism of plasma blobs is investigated in the linear device CSDX. During the ejection of plasma blobs the plasma is dominated by an m=1 mode, which is a counterrotating vortex pair. These flows are known to be subject to the cooperative elliptic instability, which is characterized by a cooperative disturbance of the vortex cores and results in a three-dimensional breakdown of two-dimensional flows. The first experimental evidence of a cooperative elliptic instability preceding the blob-ejection is provided in terms of the qualitative evolution of the vortex geometries and internal wave patterns.

Kinetic Compensations due to Chronic Ankle Instability during Landing and Jumping.

Science.gov (United States)

Kim, Hyunsoo; Son, S Jun; Seeley, Matthew K; Hopkins, J Ty

2018-02-01

Skeletal muscles absorb and transfer kinetic energy during landing and jumping, which are common requirements of various forms of physical activity. Chronic ankle instability (CAI) is associated with impaired neuromuscular control and dynamic stability of the lower extremity. Little is known regarding an intralimb, lower-extremity joint coordination of kinetics during landing and jumping for CAI patients. We investigated the effect of CAI on lower-extremity joint stiffness and kinetic and energetic patterns across the ground contact phase of landing and jumping. One hundred CAI patients and 100 matched able-bodied controls performed five trials of a landing and jumping task (a maximal vertical forward jump, landing on a force plate with the test leg only, and immediate lateral jump toward the contralateral side). Functional analyses of variance and independent t-tests were used to evaluate between-group differences for lower-extremity net internal joint moment, power, and stiffness throughout the entire ground contact phase of landing and jumping. Relative to the control group, the CAI group revealed (i) reduced plantarflexion and knee extension and increased hip extension moments; (ii) reduced ankle and knee eccentric and concentric power, and increased hip eccentric and concentric power, and (iii) reduced ankle and knee joint stiffness and increased hip joint stiffness during the task. CAI patients seemed to use a hip-dominant strategy by increasing the hip extension moment, stiffness, and eccentric and concentric power during landing and jumping. This apparent compensation may be due to decreased capabilities to produce sufficient joint moment, stiffness, and power at the ankle and knee. These differences might have injury risk and performance implications.

Surface and bulk MHD instabilities due to insulator coating imperfections

International Nuclear Information System (INIS)

Xu Zengyu; Reed, C.B.; Pan Chuanjie

2002-01-01

Experiments were performed using copper electrodes inserted into the wall of a perfectly insulated duct to simulate insulator coating flaking or cracking. The results show that surface electric potential U and MHD pressure drop ΔP exhibit a non-monotonic behavior with increasing V 0 , while the magnetic field B 0 is held constant. Additional experiments were also performed keeping all external experimental conditions fixed while measuring the change of U, V 0 , B 0 , and ΔP with increasing time. It was found that while all external experimental conditions were kept constant, the system changed by itself and U, V 0 and ΔP exhibited a non-monotonic behavior with increasing time. The results seem contrary to the law of ΔP∝V 0 B 0 n , but are consistent with conservation of energy, which implies that the change is due to some inherent feature of the system, or possibly instabilities, which may occur due to insulator coating imperfections

Carpal instability

International Nuclear Information System (INIS)

Schmitt, R.; Froehner, S.; Coblenz, G.; Christopoulos, G.

2006-01-01

This review addresses the pathoanatomical basics as well as the clinical and radiological presentation of instability patterns of the wrist. Carpal instability mostly follows an injury; however, other diseases, like CPPD arthropathy, can be associated. Instability occurs either if the carpus is unable to sustain physiologic loads (''dyskinetics'') or suffers from abnormal motion of its bones during movement (''dyskinematics''). In the classification of carpal instability, dissociative subcategories (located within proximal carpal row) are differentiated from non-dissociative subcategories (present between the carpal rows) and combined patterns. It is essential to note that the unstable wrist initially does not cause relevant signs in standard radiograms, therefore being ''occult'' for the radiologic assessment. This paper emphasizes the high utility of kinematographic studies, contrast-enhanced magnetic resonance imaging (MRI) and MR arthrography for detecting these predynamic and dynamic instability stages. Later in the natural history of carpal instability, static malalignment of the wrist and osteoarthritis will develop, both being associated with significant morbidity and disability. To prevent individual and socio-economic implications, the handsurgeon or orthopedist, as well as the radiologist, is challenged for early and precise diagnosis. (orig.)

Evidence of Reliability for Persian Version of the “Cumberland Ankle Instability Tool (CAIT” in Iranian Athletes with lateral Ankle Sprain

Directory of Open Access Journals (Sweden)

Mitra Haji-Maghsoudi

2016-01-01

Full Text Available Objectives: The purpose of the present study was to evaluate the reliability of persian version of the “Cumberland Ankle Instability Tool (CAIT” in Iranian athletes with lateral ankle sprain. Matterials & Methods: The present study is a methodological and non-experimental study. After forward and backward translation of CAIT, 46 athletes were selected with convenient nonprobably sampling from Physical Education Faculty of Tehran university and Taekwondo Club. Questionnaire was given to participants who experienced at least one lateral ankle sprain based on doctor’s diagnosis. In the second phase (one week later the questionnaire was distributed among the participants again to test the reliability of the measured between the two tests. After collecting the data, the test-retest reliability of  Persian version of the questionnaire was evaluated by calculating the intraclass correlation coefficient, standard error of measurement, smallest detectable change and Cronbach’s alpha coefficients were calculated to assess the internal consistency of the questionnaire’s items. Results Cronbach’s alpha was 0.64, which is close to acceptable level of internal consistency (0.7-0.95. Factor analysis showed that questionnaires’ items can be classified  in 4 categories with maximum of 72% variance cover. The test-retest correlation coefficient ICC for the total score of CAIT was 0.95 (P>100.0, indicating excellent reproducibility of the Persian version of the questionnaire. The standard error of measurement (SEM was 1 and the smallest acceptable change (SDC was 2.76 with 95% confidence. Conclusion: The results show that the Persian version of the CAIT can be used in athletes with functional ankle instability as a reliable tool to detect instability and assess changes caused by therapeutic interventions.

Direct observation of mass oscillations due to ablative Richtmyer-Meshkov instability and feedout in planar plastic targets

International Nuclear Information System (INIS)

Aglitskiy, Y.; Velikovich, A.L.; Karasik, M.; Serlin, V.; Pawley, C.J.; Schmitt, A.J.; Obenschain, S.P.; Mostovych, A.N.; Gardner, J.H.; Metzler, N.

2002-01-01

Perturbations that seed Rayleigh-Taylor (RT) instability in laser-driven targets form during the early-time period. This time includes a shock wave transit from the front to the rear surface of the target, and a rarefaction wave transit in the opposite direction. During this time interval, areal mass perturbations caused by all sources of nonuniformity (laser imprint, surface ripple) are expected to oscillate. The first direct experimental observations of the areal mass oscillations due to ablative Richtmyer-Meshkov (RM) instability and feedout followed by the RT growth of areal mass modulation are discussed. The experiments were made with 40-99 μm thick planar plastic targets rippled either on the front or on the rear with a sine wave ripple with either 30 or 45 μm wavelength and with 0.5, 1, or 1.5 μm amplitude. Targets were irradiated with 4 ns long Nike KrF laser pulses at ∼50 TW/cm2. The oscillations were observed with our novel diagnostic technique, a monochromatic x-ray imager coupled to a streak camera. For the ablative RM instability (front side ripple), the mass modulation amplitude was typically observed to grow, reach a peak, and then decrease, after which the exponential RT growth started. In some cases, one phase reversal due to the ablative RM instability was observed. For the feedout geometry (rear side ripple), in all cases two phase reversals were observed: a distinct half-oscillation was followed by the onset of the RT growth, resulting in a second phase reversal

Instability behavior of stiffened dome liners under construction condition

International Nuclear Information System (INIS)

Jefts, A.R.; Guha-Majumdar, S.; Wanchoo, M.K.

1977-01-01

The purpose of this paper is to present techniques related to stability analysis, design concepts and behavior of dome liners. Various stiffening systems are examined from economy, schedule and constructablity point of view. The various failure modes can be classified as either buckling due to local instability or to an overall instability of the shell. Local instability may occur due to buckling of liner panel between a pair of rings and stringers or torsional and lateral buckling of the stiffeners. Methods are developed for proportioning stiffening system to preclude local buckling. Overall stability is a function of concrete pour height and thickness, loading distribution, time elapse between successive placements, rate of concrete placement, arrangement of stiffeners and other external supports. A computer program based on system energy minimization is used to study the overall instability of stiffened domes. Modelling techniques, effect of temperature and lack of bond, and their influence on results are discussed. Results for a self-standing stiffened hemispherical dome are presented in the form of mode shapes and buckling loads. Based on the results, a pouring scheme is recommended for an economical stiffening system. Recommendations are made to select the stiffening system and predict the buckling loads for preliminary analysis and design of the dome liner. Existing methods and code provisions related to tolerance, design criteria etc. are examined and recommendations made from practical considerations

Extensor Tendon Instability Due to Sagittal Band Injury in a Martial Arts Athlete: A Case Report.

Science.gov (United States)

Kochevar, Andrew; Rayan, Ghazi

2017-03-01

A Taekwondo participant sustained a hand injury from punching an opponent that resulted in painful instability of the ring finger extensor digitorum communis tendon due to sagittal band damage. His symptoms resolved after reconstructive surgery on the sagittal band (SB) with stabilization of the extensor tendon over the metacarpophalangeal joint.

Anisotropic gravitational instability

International Nuclear Information System (INIS)

Polyachenko, V.L.; Fridman, A.M.

1988-01-01

Exact solutions of stability problems are obtained for two anisotropic gravitational systems of different geometries - a layer of finite thickness at rest and a rotating cylinder of finite radius. It is shown that the anisotropic gravitational instability which develops in both cases is of Jeans type. However, in contrast to the classical aperiodic Jeans instability, this instability is oscillatory. The physics of the anisotropic gravitational instability is investigated. It is shown that in a gravitating layer this instability is due, in particular, to excitation of previously unknown interchange-Jeans modes. In the cylinder, the oscillatory Jeans instability is associated with excitation of a rotational branch, this also being responsible for the beam gravitational instability. This is the reason why this instability and the anisotropic gravitational instability have so much in common

Experimental evidence of lateral flow in unsaturated homogeneous isotropic sloping soil due to rainfall

Science.gov (United States)

Sinai, G.; Dirksen, C.

2006-12-01

This paper describes laboratory experimental evidence for lateral flow in the top layer of unsaturated sloping soil due to rainfall. Water was applied uniformly on horizontal and V-shaped surfaces of fine sand, at rates about 100 times smaller than the saturated hydraulic conductivity. Flow regimes near the surface and in the soil bulk were studied by using dyes. Streamlines and streak lines and wetting fronts were visually studied and photographed through a vertical glass wall. Near wetting fronts the flow direction was always perpendicular to the fronts owing to dominant matrix potential gradients. Thus, during early wetting of dry sloping sand, the flow direction is directed upslope. Far above a wetting front the flow was vertical due to the dominance of gravity. Downslope flow was observed during decreasing rainfall and dry periods. The lateral movement was largest near the soil surface and decayed with soil depth. Unstable downslope lateral flow close to the soil surface was attributed to non-Darcian flow due to variable temporal and spatial raindrop distributions. The experiments verify the theory that predicts unsaturated downslope lateral flow in sloping soil due to rainfall dynamics only, without apparent soil texture difference or anisotropy. This phenomenon could have significant implications for hillside hydrology, desert agriculture, irrigation management, etc., as well as for the basic mechanisms of surface runoff and erosion.

Two or more impingement and/or instability deformities are often present in patients with hip pain.

Science.gov (United States)

Tibor, Lisa M; Liebert, Gunnar; Sutter, Reto; Impellizzeri, Franco M; Leunig, Michael

2013-12-01

Damage to the hip can occur due to impingement or instability caused by anatomic factors such as femoral and acetabular version, neck-shaft angle, alpha angle, and lateral center-edge angle (CEA). The associations between these anatomic factors and how often they occur in a painful hip are unclear but if unaddressed might explain failed hip preservation surgery. We determined (1) the influence of sex on the expression of impingement-related or instability-related factors, (2) the associations among these factors, and (3) how often both impingement and/or instability factors occur in the same hip. We retrospectively reviewed a cohort of 170 hips (145 patients) undergoing MR arthrography of the hip for any reason. We excluded 58 hips with high-grade dysplasia, Perthes' sequelae, previous surgery, or incomplete radiographic information, leaving 112 hips (96 patients). We measured femoral version and alpha angles on MR arthrograms. Acetabular anteversion, lateral CEA, and neck-shaft angle were measured on pelvic radiographs. We observed a correlation between sex and alpha angle. Weak or no correlations were observed between the other five parameters. In 66% of hips, two or more (of five) impingement parameters, and in 51% of hips, two or more (of five) instability parameters were found. Patients with hip pain frequently have several anatomic factors potentially contributing to chondrolabral damage. To address pathologic hip loading due to impingement and/or instability, all of the anatomic influences should be known. As we found no associations between anatomic factors, we recommend an individualized assessment of each painful hip.

Cinerama sickness and postural instability.

Science.gov (United States)

Bos, Jelte E; Ledegang, Wietse D; Lubeck, Astrid J A; Stins, John F

2013-01-01

Motion sickness symptoms and increased postural instability induced by motion pictures have been reported in a laboratory, but not in a real cinema. We, therefore, carried out an observational study recording sickness severity and postural instability in 19 subjects before, immediately and 45 min after watching a 1 h 3D aviation documentary in a cinema. Sickness was significantly larger right after the movie than before, and in a lesser extent still so after 45 min. The average standard deviation of the lateral centre of pressure excursions was significantly larger only right afterwards. When low-pass filtered at 0.1 Hz, lateral and for-aft excursions were both significantly larger right after the movie, while for-aft excursions then remained larger even after 45 min. Speculating on previous findings, we predict more sickness and postural instability in 3D than in 2D movies, also suggesting a possible, but yet unknown risk for work-related activities and vehicle operation. Watching motion pictures may be sickening and posturally destabilising, but effects in a cinema are unknown. We, therefore, carried out an observational study showing that sickness then is mainly an issue during the exposure while postural instability is an issue afterwards.

Arthrography of the ankle joint in chronic instability

Energy Technology Data Exchange (ETDEWEB)

Dory, M.A.

1986-05-01

Papers on arthrography of injuries of the lateral ligaments of the ankle relate mainly to recent distortion of the joint. Arthrography performed at a later stage after injury generally is considered useless. In fact, changes in chronic instability are observed; they are subtle and consist either of small recesses adjacent to the lateral malleolus or communication of the joint with the peroneal tendon sheaths. Arthrography was assessed in 61 cases of recurrent lateral sprains of the ankle more than 2 weeks after acute injury; 38 were considered as positive. Twenty-five patients had operative evaluation, with four false negative and one false positive results. Small recesses adjacent to the lateral malleolus or opacification of the peroneal tendon sheaths are sequelae of an acute sprain with tear of the anterior talofibular and/or the calcaneofibular ligaments. Although false negative results occur, arthrography is useful in the preoperative assessment of chronic ankle instability.

Summary of longitudinal instabilities workshop

Energy Technology Data Exchange (ETDEWEB)

Chasman, R.

1976-01-01

A five-day ISABELLE workshop on longitudinal instabilities was held at Brookhaven, August 9-13, 1976. About a dozen outside accelerator experts, both from Europe and the U.S.A., joined the local staff for discussions of longitudinal instabilities in ISABELLE. An agenda of talks was scheduled for the first day of the workshop. Later during the week, a presentation was given on the subject ''A more rigorous treatment of Landau damping in longitudinal beam instabilities''. A few progress meetings were held in which disagreements regarding calculations of coupling impedances were clarified. A summary session was held on the last day. Heavy emphasis was put on single bunched beam instabilities in the microwave region extending above the cut-off frequency of the ISABELLE vacuum chamber.

Comparison of bone tunnel and suture anchor techniques in the modified Broström procedure for chronic lateral ankle instability.

Science.gov (United States)

Hu, Chang-Yong; Lee, Keun-Bae; Song, Eun-Kyoo; Kim, Myung-Sun; Park, Kyung-Soon

2013-08-01

The modified Broström procedure is frequently used to treat chronic lateral ankle instability. There are 2 common methods of the modified Broström procedure, which are the bone tunnel and suture anchor techniques. To compare the clinical outcomes of the modified Broström procedure using the bone tunnel and suture anchor techniques. Cohort study; Level of evidence, 2. Eighty-one patients (81 ankles) treated with the modified Broström procedure for chronic lateral ankle instability constituted the study cohort. The 81 ankles were divided into 2 groups, namely, a bone tunnel technique (BT group; 40 ankles) and a suture anchor technique (SA group; 41 ankles). The Karlsson score, American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score, anterior talar translation, and talar tilt angle were used to evaluate clinical and radiographic outcomes. The BT group consisted of 32 men and 8 women with a mean age of 34.8 years at surgery and a mean follow-up duration of 34.2 months. The SA group consisted of 33 men and 8 women with a mean age of 33.3 years at surgery and a mean follow-up duration of 32.8 months. Mean Karlsson scores improved significantly from 57.0 points preoperatively to 94.9 points at final follow-up in the BT group and from 59.9 points preoperatively to 96.4 points at final follow-up in the SA group. Mean AOFAS scores also improved from 64.2 points preoperatively to 97.8 points at final follow-up in the BT group and from 70.3 points preoperatively to 97.4 points at final follow-up in the SA group. Mean anterior talar translations in the BT group and SA group improved from 9.0 mm and 9.2 mm preoperatively to 6.5 mm and 6.8 mm at final follow-up, respectively. Mean talar tilt angles were 12.0° in the BT group and 12.5° in the SA group preoperatively and 8.8° at final follow-up for both groups. No significant differences were found between the 2 groups in terms of the Karlsson score, AOFAS score, anterior talar translation, and talar tilt

Instabilities due to anisotropic velocity distributions. Progress report, June 1, 1974--June 1, 1975

International Nuclear Information System (INIS)

Harris, E.G.

1975-01-01

A continuing theoretical study of plasma instabilities and related phenomena including nonlinear effects, particle and energy transport and heating schemes is presented. In the past year, a study of linear resistive instabilities with applications to Tokamaks was almost completed and is being prepared for publication. A sigma stability analysis is being worked on at the present time. Some thought was given to a nonlinear resistive instability analysis but not much progress has been made. A study of equilibrium and stability of elliptical cross section Tokamaks was completed. Considerable work was completed on plasma heating by rf waves at the lower hybrid frequency and by Alfven waves. This work is continuing. A study of instabilities excited by runaway beams of electrons in Tokamaks was largly completed. Some work was done on trapped particle instabilities in Tokamaks and their relation to other instabilities driven by gradients of density or temperature. Work is underway on diffusion and thermal conduction in the bumpy torus. (U.S.)

Arthrography of the ankle joint in chronic instability

International Nuclear Information System (INIS)

Dory, M.A.

1986-01-01

Papers on arthrography of injuries of the lateral ligaments of the ankle relate mainly to recent distortion of the joint. Arthrography performed at a later stage after injury generally is considered useless. In fact, changes in chronic instability are observed; they are subtle and consist either of small recesses adjacent to the lateral malleolus or communication of the joint with the peroneal tendon sheaths. Arthrography was assessed in 61 cases of recurrent lateral sprains of the ankle more than 2 weeks after acute injury; 38 were considered as positive. Twenty-five patients had operative evaluation, with four false negative and one false positive results. Small recesses adjacent to the lateral malleolus or opacification of the peroneal tendon sheaths are sequelae of an acute sprain with tear of the anterior talofibular and/or the calcaneofibular ligaments. Although false negative results occur, arthrography is useful in the preoperative assessment of chronic ankle instability. (orig.)

Methylene Blue Is Effective to Reverse Refractory Hemodynamic Instability due to Dimethoate Poisoning

Directory of Open Access Journals (Sweden)

Nick Youssefi

2015-09-01

Conclusion:MB treatment was effective to reverse hypotension and restore hemodynamic instability caused by dimethoate poisoning. This index case may pave way to further investigation of MB therapy for OP-induced hemodynamic instabilities.

[Patellar instability : diagnosis and treatment].

Science.gov (United States)

Ngo, Trieu Hoai Nam; Martin, Robin

2017-12-13

The aim of this paper is to present recent advances in surgical management of patellar instability. Several anatomical factors were reported to promote instability. We propose to classify them in two groups. Extra articular factors are valgus and torsion deformity. Articular factors include trochlea and patella dysplasia, tibial tubercle lateralization and medial patellofemoral ligament (MPFL) insufficiency. Acute patellar dislocations are treated conservatively, with exception for osteochondral and MPFL avulsion fractures that require acute reinsertion. Surgery is considered for recurrent instability. As we aim for a correction of all contributing elements, we prefer a two stages approach. Extra articular factors are treated first by osteotomy, followed by articular factors after 4-6 months. This allows separate rehabilitation protocols.

How to measure responses of the knee to lateral perturbations during gait? A proof-of-principle for quantification of knee instability.

Science.gov (United States)

van den Noort, Josien C; Sloot, Lizeth H; Bruijn, Sjoerd M; Harlaar, Jaap

2017-08-16

Knee instability is a major problem in patients with anterior cruciate ligament injury or knee osteoarthritis. A valid and clinically meaningful measure for functional knee instability is lacking. The concept of the gait sensitivity norm, the normalized perturbation response of a walking system to external perturbations, could be a sensible way to quantify knee instability. The aim of this study is to explore the feasibility of this concept for measurement of knee responses, using controlled external perturbations during walking in healthy subjects. Nine young healthy participants walked on a treadmill, while three dimensional kinematics were measured. Sudden lateral translations of the treadmill were applied at five different intensities during stance. Right knee kinematic responses and spatio-temporal parameters were tracked for the perturbed stride and following four cycles, to calculate perturbation response and gait sensitivity norm values (i.e. response/perturbation) in various ways. The perturbation response values in terms of knee flexion and abduction increased with perturbation intensity and decreased with an increased number of steps after perturbation. For flexion and ab/adduction during midswing, the gait sensitivity norm values were shown to be constant over perturbation intensities, demonstrating the potential of the gait sensitivity norm as a robust measure of knee responses to perturbations. These results show the feasibility of using the gait sensitivity norm concept for certain gait indicators based on kinematics of the knee, as a measure of responses during perturbed gait. The current findings in healthy subjects could serve as reference-data to quantify pathological knee instability. Copyright © 2017 Elsevier Ltd. All rights reserved.

Long-term sequel of posterolateral rotatory instability of the elbow: a case report

Directory of Open Access Journals (Sweden)

Cheng Chun-Ying

2010-01-01

Full Text Available Abstract The natural course of untreated posterior lateral rotatory instability of the elbow is unclear. A case of elbow arthrosis with progressing deformity and flexion contracture after an episode of elbow dislocation about 20 years ago presented the possibility the long term outcome of untreated posterior lateral rotatory instability of the elbow.

Slope Instability Risk Analysys of the Municipality of Comala, Colima , Mexico

Science.gov (United States)

Ramirez-Ruiz, J. J.

2017-12-01

Every year during the rainy season occur the problem of mass landslide in some areas of the community of Comala, Colima Mexico. Slope instability is studied in this volcanic region which is located in the southern part of the Volcan de Fuego de Colima. It occurs due to the combination of different factors existing in this area as: Precipitation, topography contrast, type and mechanical properties of deposits that constitute the rocks and soils of the region and the erosion due to the elimination of vegetation deck to develop and grow urban areas. To these geological factors we can extend the tectonic activity of the Western part of Mexico that originate high seismicity by the interaction of Cocos plate and North America plate forming the region of Graben de Colima, were is located this area. Here we will present a Zonification and determination of Slope Instability Risk Maps due to the rain and seismicity accelerators factors. This Study is parto of a proyect to reduce the risk of this phenomenon, it was carried out as part of the National Risk Map of Mexico analized using the CENAPRED methodology to zonificate the risk areas. The instability of slopes is determined both in its origin and in its development, by different mechanisms. In such a way that this process of instability can be grouped into four main categories: Falls or landslides, Flows, Slips and expansions or lateral landslides. Here it is presented the Risk analisis to this volcanic area that cover the municipality of Comala in the State of Colima, Mexico using the Susceptibility map, Risk Map and Risk analisis of the Municipality.

Tearing mode instability due to anomalous resistivity

International Nuclear Information System (INIS)

Furuya, Atsushi; Itoh, Sanae I.; Yagi, Masatoshi

2000-01-01

Tearing mode instability in the presence of microscopic truculence is investigates. The effects of microscopic turbulence on tearing mode are taken as drags which are calculated by one-point renormalization method and mean-field approximation. These effects are reduced to effective diffusivities in reduced MHD equations. Using these equations, the stability analyses of the tearing mode are performed. It is shown that a finite amplitude of fluctuation enhances the growth rate of tearing mode. For very high values of turbulent diffusivities, marginally stable state exists. The effects of each turbulent diffusivity on mode stability are examined near marginal stability boundary. Parameter dependence of the resistive ballooning mode turbulence on tearing mode is analyzed as an example. (author)

Prediction and discovery of extremely strong hydrodynamic instabilities due to a velocity jump: theory and experiments

International Nuclear Information System (INIS)

Fridman, A M

2008-01-01

The theory and the experimental discovery of extremely strong hydrodynamic instabilities are described, viz. the Kelvin-Helmholtz, centrifugal, and superreflection instabilities. The discovery of the last two instabilities was predicted and the Kelvin-Helmholtz instability in real systems was revised by us. (reviews of topical problems)

Numerical studies of the Kelvin-Hemholtz instability in a coronal jet

Science.gov (United States)

Zhao, Tian-Le; Ni, Lei; Lin, Jun; Ziegler, Udo

2018-04-01

Kelvin-Hemholtz (K-H) instability in a coronal EUV jet is studied via 2.5D MHD numerical simulations. The jet results from magnetic reconnection due to the interaction of the newly emerging magnetic field and the pre-existing magnetic field in the corona. Our results show that the Alfvén Mach number along the jet is about 5–14 just before the instability occurs, and it is even higher than 14 at some local areas. During the K-H instability process, several vortex-like plasma blobs with high temperature and high density appear along the jet, and magnetic fields have also been rolled up and the magnetic configuration including anti-parallel magnetic fields forms, which leads to magnetic reconnection at many X-points and current sheet fragments inside the vortex-like blob. After magnetic islands appear inside the main current sheet, the total kinetic energy of the reconnection outflows decreases, and cannot support the formation of the vortex-like blob along the jet any longer, then the K-H instability eventually disappears. We also present the results about how the guide field and flux emerging speed affect the K-H instability. We find that a strong guide field inhibits shock formation in the reconnecting upward outflow regions but helps secondary magnetic islands appear earlier in the main current sheet, and then apparently suppresses the K-H instability. As the speed of the emerging magnetic field decreases, the K-H instability appears later, the highest temperature inside the vortex blob gets lower and the vortex structure gets smaller.

Minor or occult ankle instability as a cause of anterolateral pain after ankle sprain.

Science.gov (United States)

Vega, Jordi; Peña, Fernando; Golanó, Pau

2016-04-01

The aim of this study was to determine which intra-articular injuries are associated with chronic anterolateral pain and functional instability after an ankle sprain. From 2008 to 2010, records of all patients who underwent ankle joint arthroscopy with anterolateral pain and functional instability after an ankle sprain were reviewed. A systematic arthroscopic examination of the intra-articular structures of the ankle joint was performed. Location and characteristics of the injuries were identified and recorded. A total of 36 ankle arthroscopic procedures were reviewed. A soft-tissue occupying mass over the lateral recess was present in 18 patients (50%). A partial injury of the anterior talofibular ligament (ATFL) was observed in 24 patients (66.6%). Cartilage abrasion due to the distal fascicle of the anteroinferior tibiofibular ligament coming into contact with the talus was seen in 21 patients (58.3%), but no thickening of the ligament was observed. Injury to the intra-articular posterior structures, including the transverse ligament in 19 patients (52.7%) and the posterior surface of the distal tibia in 21 patients (58.3%), was observed. Intra-articular pathological findings have been observed in patients affected by anterolateral pain after an ankle sprain. Despite no demonstrable abnormal lateral laxity, morphologic ATFL abnormality has been observed on arthroscopic evaluation. An injury of the ATFL is present in patients with chronic anterolateral pain and functional instability after an ankle sprain. A degree of microinstability due to a deficiency of the ATFL could explain the intra-articular pathological findings and the patients' complaints. IV.

Ionospheric modification and parametric instabilities

International Nuclear Information System (INIS)

Fejer, J.A.

1979-01-01

Thresholds and linear growth rates for stimulated Brillouin and Raman scattering and for the parametric decay instability are derived by using arguments of energy transfer. For this purpose an expression for the ponderomotive force is derived. Conditions under which the partial pressure force due to differential dissipation exceeds the ponderomotive force are also discussed. Stimulated Brillouin and Raman scattering are weakly excited by existing incoherent backscatter radars. The parametric decay instability is strongly excited in ionospheric heating experiments. Saturation theories of the parametric decay instability are therefore described. After a brief discussion of the purely growing instability the effect of using several pumps is discussed as well as the effects of inhomogenicity. Turning to detailed theories of ionospheric heating, artificial spread F is discussed in terms of a purely growing instability where the nonlinearity is due to dissipation. Field-aligned short-scale striations are explained in terms of dissipation of the parametrically excited Langmuir waves (plasma oscillations): they might be further amplified by an explosive instability (except the magnetic equator). Broadband absorption is probably responsible for the 'overshoot' effect: the initially observed level of parametrically excited Langmuir waves is much higher than the steady state level

Tearing instabilities in turbulence

International Nuclear Information System (INIS)

Ishizawa, A.; Nakajima, N.

2009-01-01

Full text: Effects of micro-turbulence on tearing instabilities are investigated by numerically solving a reduced set of two-fluid equations. Micro-turbulence excites both large-scale and small-scale Fourier modes through energy transfer due to nonlinear mode coupling. The energy transfer to large scale mode does not directly excite tearing instability but it gives an initiation of tearing instability. When tearing instability starts to grow, the excited small scale mode plays an important role. The mixing of magnetic flux by micro-turbulence is the dominant factor of non-ideal MHD effect at the resonant surface and it gives rise to magnetic reconnection which causes tearing instability. Tearing instabilities were investigated against static equilibrium or flowing equilibrium so far. On the other hand, the recent progress of computer power allows us to investigate interactions between turbulence and coherent modes such as tearing instabilities in magnetically confined plasmas by means of direct numerical simulations. In order to investigate effects of turbulence on tearing instabilities we consider a situation that tearing mode is destabilized in a quasi-equilibrium including micro-turbulence. We choose an initial equilibrium that is unstable against kinetic ballooning modes and tearing instabilities. Tearing instabilities are current driven modes and thus they are unstable for large scale Fourier modes. On the other hand kinetic ballooning modes are unstable for poloidal Fourier modes that are characterized by ion Larmor radius. The energy of kinetic ballooning modes spreads over wave number space through nonlinear Fourier mode coupling. We present that micro-turbulence affects tearing instabilities in two different ways by three-dimensional numerical simulation of a reduced set of two-fluid equations. One is caused by energy transfer to large scale modes, the other is caused by energy transfer to small scale modes. The former is the excitation of initial

Defocusing of an ion beam propagating in background plasma due to two-stream instability

Energy Technology Data Exchange (ETDEWEB)

Tokluoglu, Erinc; Kaganovich, Igor D. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2015-04-15

The current and charge neutralization of charged particle beams by background plasma enable ballistic beam propagation and have a wide range of applications in inertial fusion and high energy density physics. However, the beam-plasma interaction can result in the development of collective instabilities that may have deleterious effects on ballistic propagation of an ion beam. In the case of fast, light-ion beams, non-linear fields created by instabilities can lead to significant defocusing of the beam. We study an ion beam pulse propagating in a background plasma, which is subjected to two-stream instability between the beam ions and plasma electrons, using PIC code LSP. The defocusing effects of the instability on the beam can be much more pronounced in small radius beams. We show through simulations that a beamlet produced from an ion beam passed through an aperture can be used as a diagnostic tool to identify the presence of the two-stream instability and quantify its defocusing effects. The effect can be observed on the Neutralized Drift Compression Experiment-II facility by measuring the spot size of the extracted beamlet propagating through several meters of plasma.

Relativistic gravitational instabilities

International Nuclear Information System (INIS)

Schutz, B.F.

1987-01-01

The purpose of these lectures is to review and explain what is known about the stability of relativistic stars and black holes, with particular emphases on two instabilities which are due entirely to relativistic effects. The first of these is the post-Newtonian pulsational instability discovered independently by Chandrasekhar (1964) and Fowler (1964). This effectively ruled out the then-popular supermassive star model for quasars, and it sets a limit to the central density of white dwarfs. The second instability was also discovered by Chandrasekhar (1970): the gravitational wave induced instability. This sets an upper bound on the rotation rate of neutron stars, which is near that of the millisecond pulsar PSR 1937+214, and which is beginning to constrain the equation of state of neutron matter. 111 references, 5 figures

Posterolateral elbow joint instability

DEFF Research Database (Denmark)

Olsen, Bo Sanderhoff; Søjbjerg, Jens Ole; Nielsen, K K

1998-01-01

Thirty-five osteoligamentous elbows were included in a study on the kinematics of posterolateral elbow joint instability during the pivot shift test (PST) before and after separate ligament cuttings in the lateral collateral ligament complex (LCLC). Division of the annular ligament or the lateral...... ulnar collateral ligament caused no laxity during the PST. Division of the lateral collateral ligament caused maximal laxity of 4 degrees and 23 degrees during forced PST in valgus and external rotation (supination), respectively. Cutting of the LCLC at the ulnar or the humeral insertion was necessary...... for any PST stressed elbow joint laxity to occur. Total division of the LCLC induced a maximal laxity of 7.9 degrees and 37 degrees during forced PST in valgus and external rotation (supination), respectively. This study suggests the lateral collateral ligament to be the primary soft tissue constraint...

Treatment options for patellofemoral instability in sports traumatology

Directory of Open Access Journals (Sweden)

Philippe M. Tscholl

2013-09-01

Full Text Available Patellofemoral instability not only involves lateral patellar dislocation, patellar mal-tracking or subluxation but can also cause a limiting disability for sports activities. Its underlying causes are known as morphological anomalies of the patellofemoral joint or the mechanical axis, femorotibial malrotation, variants of the knee extensor apparatus, and ligamentous insufficiencies often accompanied by poor proprioception. Athletes with such predisposing factors are either suffering from unspecific anterior knee pain or from slightly traumatic or recurrent lateral patellar dislocation Treatment options of patellar instability are vast, and need to be tailored individually depending on the athlete’s history, age, complaints and physical demands. Different conservative and surgical treatment options are reviewed and discussed, especially limited expectations after surgery.

Medial Patellofemoral Ligament Reconstruction Using the Hamstring Tendon for Patellofemoral Joint Instability in an 81-Year-Old Female.

Science.gov (United States)

Takahashi, Tsuneari; Takeshita, Katsushi

2017-01-01

Chronic patellofemoral instability occurs mainly in adolescent females and can also be induced by medial patellofemoral ligament (MPFL) injury. There are no case reports of MPFL reconstruction for chronic patellofemoral instability due to MPFL injury in aged populations. 81-year-old female presented with left knee pain, giving way, and patellar instability while climbing stairs, which continued for 18 months. Patellar apprehension test was positive, and roentgenogram showed lateral patellar subluxation. Conservative therapy was not successful; hence, we performed a lateral release and MPFL reconstruction surgery. After arthroscopic lateral release, the hamstring tendon was harvested, and a graft composite made of doubled hamstring tendon and polyester tape with a suspensory fixation device was prepared. Then, a femoral bone tunnel was constructed in a socket shape at the anatomical footprint of the MPFL. The graft was passed through the femoral tunnel, and free ends of the graft composite were sutured to the periosteum of the patella, using two suture anchors at 60° of knee flexion with patellar reduction. Physiotherapy was gradually started using a patella-stabilizing orthosis on the first postoperative day. Her Kujala score improved from 66 to 97 points, and Barthel index score improved from 70 to 100 points at 1 year after surgery. She neither developed patellofemoral joint OA nor had any recurrence of symptoms at the 5-year postoperative follow up. MPFL reconstruction using the hamstring tendon is an effective procedure for patients with chronic patellofemoral instability even after the age of 80 years.

Gravitational Instabilities in Circumstellar Disks

Science.gov (United States)

Kratter, Kaitlin; Lodato, Giuseppe

2016-09-01

Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular

Kelvin-Helmholtz Instability: Lessons Learned and Ways Forward

Science.gov (United States)

Masson, A.; Nykyri, K.

2018-06-01

The Kelvin-Helmholtz instability (KHI) is a ubiquitous phenomenon across the Universe, observed from 500 m deep in the oceans on Earth to the Orion molecular cloud. Over the past two decades, several space missions have enabled a leap forward in our understanding of this phenomenon at the Earth's magnetopause. Key results obtained by these missions are first presented, with a special emphasis on Cluster and THEMIS. In particular, as an ideal instability, the KHI was not expected to produce mass transport. Simulations, later confirmed by spacecraft observations, indicate that plasma transport in Kelvin-Helmholtz (KH) vortices can arise during non-linear stage of its development via secondary process. In addition to plasma transport, spacecraft observations have revealed that KHI can also lead to significant ion heating due to enhanced ion-scale wave activity driven by the KHI. Finally, we describe what are the upcoming observational opportunities in 2018-2020, thanks to a unique constellation of multi-spacecraft missions including: MMS, Cluster, THEMIS, Van Allen Probes and Swarm.

Potential Flow Model for Compressible Stratified Rayleigh-Taylor Instability

Science.gov (United States)

Rydquist, Grant; Reckinger, Scott; Owkes, Mark; Wieland, Scott

2017-11-01

The Rayleigh-Taylor Instability (RTI) is an instability that occurs when a heavy fluid lies on top of a lighter fluid in a gravitational field, or a gravity-like acceleration. It occurs in many fluid flows of a highly compressive nature. In this study potential flow analysis (PFA) is used to model the early stages of RTI growth for compressible fluids. In the localized region near the bubble tip, the effects of vorticity are negligible, so PFA is applicable, as opposed to later stages where the induced velocity due to vortices generated from the growth of the instability dominate the flow. The incompressible PFA is extended for compressibility effects by applying the growth rate and the associated perturbation spatial decay from compressible linear stability theory. The PFA model predicts theoretical values for a bubble terminal velocity for single-mode compressible RTI, dependent upon the Atwood (A) and Mach (M) numbers, which is a parameter that measures both the strength of the stratification and intrinsic compressibility. The theoretical bubble terminal velocities are compared against numerical simulations. The PFA model correctly predicts the M dependence at high A, but the model must be further extended to include additional physics to capture the behavior at low A. Undergraduate Scholars Program - Montana State University.

[Left lateral gaze paresis due to subcortical hematoma in the right precentral gyrus].

Science.gov (United States)

Sato, K; Takamori, M

1998-03-01

We report a case of transient left lateral gaze paresis due to a hemorrhagic lesion restricted in the right precentral gyrus. A 74-year-old female experienced a sudden clumsiness of the left upper extremity. A neurological examination revealed a left central facial paresis, distal dominant muscle weakness in the left upper limb and left lateral gaze paresis. There were no other focal neurological signs. Laboratory data were all normal. Brain CTs and MRIs demonstrated a subcortical hematoma in the right precentral gyrus. The neurological symptoms and signs disappeared over seven days. A recent physiological study suggested that the human frontal eye field (FEF) is located in the posterior part of the middle frontal gyrus (Brodmann's area 8) and the precentral gyrus around the precentral sulcus. More recent studies stressed the role of the precentral sulcus and the precentral gyrus. Our case supports those physiological findings. The hematoma affected both the FEF and its underlying white matter in our case. We assume the lateral gaze paresis is attributable to the disruption of the fibers from the FEF. It is likely that fibers for motor control of the face, upper extremity, and lateral gaze lie adjacently in the subcortical area.

Analysis of beam transverse instability in electron linac

International Nuclear Information System (INIS)

Mondrus, I.N.; Shenderovich, A.M.

1990-01-01

Dispersion equations describing transverse beam instability in a single resonator section and in an accelerator comprising a sequence of resonator sections are derived. It is shown that close to parametric resonance of any multiplicity a reduction of cumulative instability incoherent takes place between nonsymmetric defocusing wave frequency and the frequency of accelerator cluster transport. Under exact resonance the increment equals to zero and under misalignment due to resonance depending on its sign and disturbance frequency an instability of either fast or slow wave takes place. It is shown that this effect leads to beam instability suppression of sections with the opposite sign of misalignment due to resonance are located in turn. The results obtained show that application of a parametric resonance through reducing slight the single section absolute instability threshold current, allows one to effectively suppress cumulative instability. The requirement to the accuracy of tuning to a resonance of identical sections is substantially reduced under the alternation of sections with different sign misalignment due to resonance and can be easily realized in practice

The Kelvin-Helmholtz instability in National Ignition Facility hohlraums as a source of gold-gas mixing

Energy Technology Data Exchange (ETDEWEB)

Vandenboomgaerde, M.; Bonnefille, M.; Gauthier, P. [CEA, DAM, DIF, F-91297 Arpajon (France)

2016-05-15

Highly resolved radiation-hydrodynamics FCI2 simulations have been performed to model laser experiments on the National Ignition Facility. In these experiments, cylindrical gas-filled hohlraums with gold walls are driven by a 20 ns laser pulse. For the first time, simulations show the appearance of Kelvin-Helmholtz (KH) vortices at the interface between the expanding wall material and the gas fill. In this paper, we determine the mechanisms which generate this instability: the increase of the gas pressure around the expanding gold plasma leads to the aggregation of an over-dense gold layer simultaneously with shear flows. At the surface of this layer, all the conditions are met for a KH instability to grow. Later on, as the interface decelerates, the Rayleigh-Taylor instability also comes into play. A potential scenario for the generation of a mixing zone at the gold-gas interface due to the KH instability is presented. Our estimates of the Reynolds number and the plasma diffusion width at the interface support the possibility of such a mix. The key role of the first nanosecond of the laser pulse in the instability occurrence is also underlined.

Revision allograft reconstruction of the lateral collateral ligament complex in elbows with previous failed reconstruction and persistent posterolateral rotatory instability.

Science.gov (United States)

Baghdadi, Yaser M K; Morrey, Bernard F; O'Driscoll, Shawn W; Steinmann, Scott P; Sanchez-Sotelo, Joaquin

2014-07-01

Primary reconstruction of the lateral collateral ligament complex (LCLC) using graft tissue restores elbow stability in many, but not all, elbows with acute or chronic posterolateral rotatory instability (PLRI). Revision reconstruction using a tendon allograft is occasionally considered for persistent PLRI, but the outcome of revision ligament reconstruction in this setting is largely unknown. We determined whether revision allograft ligament reconstruction can (1) restore the stability and (2) result in improved elbow scores for patients with persistent PLRI of the elbow after a previous failed primary reconstructive attempt and in the context of the diverse pathology being addressed. Between 2001 and 2011, 160 surgical elbow procedures were performed at our institution for the LCLC reconstruction using allograft tissue. Only patients undergoing revision allograft reconstruction of the LCLC for persistent PLRI with a previous failed primary reconstructive attempt using graft tissue and at least I year of followup were included in the study. Eleven patients (11 elbows) fulfilled our inclusion criteria and formed our study cohort. The cohort consisted of six female patients and five male patients. The mean age at the time of revision surgery was 36 years (range, 14-59 years). The revision allograft reconstruction was carried out after a mean of 3 years (range, 2.5 months to 9 years) from a failed attempted reconstruction of the LCLC. Osseous deficiency to some extent was identified in the preoperative radiographs of eight elbows. Mean followup was 5 years (range, 1-12 years). Revision allograft reconstruction of the LCLC restored elbow stability in eight of the 11 elbows; two of the three elbows with persistent instability were operated on a third time (at 6 and 7 months after allograft revision reconstruction). For elbows with no persistent instability, the mean Mayo Elbow Performance Score at most recent followup was 83 points (range, 60-100 points), and

Fluid Instabilities of Magnetar-Powered Supernovae

Science.gov (United States)

Chen, Ke-Jung

2017-05-01

Magnetar-powered supernova explosions are competitive models for explaining very luminous optical transits. Until recently, these explosion models were mainly calculated in 1D. Radiation emitted from the magnetar snowplows into the previous supernovae ejecta and causes a nonphysical dense shell (spike) found in previous 1D studies. This suggests that strong fluid instabilities may have developed within the magnetar-powered supernovae. Such fluid instabilities emerge at the region where luminous transits later occur, so they can affect the consequent observational signatures. We examine the magnetar-powered supernovae with 2D hydrodynamics simulations and find that the 1D dense shell transforms into the development of Rayleigh-Taylor and thin shell instabilities in 2D. The resulting mixing is able to fragment the entire shell and break the spherical symmetry of supernovae ejecta.

Morphological Instability in InAs/GaSb Superlattices due to Interfacial Bonds

International Nuclear Information System (INIS)

Li, J.H.; Moss, S.C.; Stokes, D.W.; Caha, O.; Bassler, K.E.; Ammu, S.L.; Bai, J.

2005-01-01

Synchrotron x-ray diffraction is used to compare the misfit strain and composition in a self-organized nanowire array in an InAs/GaSb superlattice with InSb interfacial bonds to a planar InAs/GaSb superlattice with GaAs interfacial bonds. It is found that the morphological instability that occurs in the nanowire array results from the large misfit strain that the InSb interfacial bonds have in the nanowire array. Based on this result, we propose that tailoring the type of interfacial bonds during the epitaxial growth of III-V semiconductor films provides a novel approach for producing the technologically important morphological instability in anomalously thin layers

Medio-lateral postural instability in subjects with tinnitus

Directory of Open Access Journals (Sweden)

Zoi eKapoula

2011-05-01

Full Text Available Background: Many patients show modulation of tinnitus by gaze, jaw or neck movements, reflecting abnormal sensorimotor integration and interaction between various inputs. Postural control is based on multi-sensory integration (visual, vestibular, somatosensory, and oculomotor and indeed there is now evidence that posture can also be influenced by sound. Perhaps tinnitus influences posture similarly to external sound. This study examines the quality of postural performance in quiet stance in patients with modulated tinnitus.Methods: Twenty-three patients with highly modulated tinnitus were selected in the ENT service. Twelve reported exclusively or predominately left tinnitus, eight right and three bilateral. Eighteen control subjects were also tested. Subjects were asked to fixate a target at 40cm for 51s; posturography was performed with the platform (Technoconcept, 40Hz for both the eyes open and eyes closed conditions.Results: For both conditions, tinnitus subjects showed abnormally high lateral body sway (SDx. This was corroborated by fast Fourrier Transformation (FFTx and wavelet analysis. For patients with left tinnitus only, medio-lateral sway increased significantly when looking away from the center. Conclusions: Similarly to external sound stimulation, tinnitus could influence lateral sway by activating attention shift, and perhaps vestibular responses. Poor integration of sensorimotor signals is another possibility. Such abnormalities would be accentuated in left tinnitus because of the importance of the right cerebral cortex in processing both auditory-tinnitus and attention.

Experimental evidence of lateral flow in unsaturated homogeneous isotropic sloping soil due to rainfall

NARCIS (Netherlands)

Sinai, G.; Dirksen, C.

2006-01-01

This paper describes laboratory experimental evidence for lateral flow in the top layer of unsaturated sloping soil due to rainfall. Water was applied uniformly on horizontal and V-shaped surfaces of fine sand, at rates about 100 times smaller than the saturated hydraulic conductivity. Flow regimes

Pearling Instabilities of a Viscoelastic Thread

Science.gov (United States)

Deblais, A.; Velikov, K. P.; Bonn, D.

2018-05-01

Pearling instabilities of slender viscoelastic threads have received much attention, but remain incompletely understood. We study the instabilities in polymer solutions subject to uniaxial elongational flow. Two distinctly different instabilites are observed: beads on a string and blistering. The beads-on-a-string structure arises from a capillary instability whereas the blistering instability has a different origin: it is due to a coupling between stress and polymer concentration. By varying the temperature to change the solution properties we elucidate the interplay between flow and phase separation.

Hydromagnetic instability in a stellarator

Energy Technology Data Exchange (ETDEWEB)

Kruskal, M D; Gottlieb, M B; Johnson, J L; Goldman, L M [Project Matterhorn, Princeton University, Princeton, NJ (United States)

1958-07-01

It was noted that when there is a uniform externally imposed longitudinal field much larger than the field of the discharge current, one should expect instabilities in the form of a lateral displacement of the plasma column into a helix of large pitch. At the wavelength of fastest growth the e-folding time approximates the time it takes a sound wave in the plasma to traverse the radius of the plasma column. This problem has been re-examines under the conditions which might be expected to occur in the stellarator during ohmic heating, including the presence of external conductors. The theory is applied to the stellarator; and it is shown that the external conductors are in fact unimportant. The important effects due to the finite length of the Machine are discussed and the effects of more general current distributions are considered. The results from the experiments are given.

Lateral epicondylitis and beyond: imaging of lateral elbow pain with clinical-radiologic correlation

International Nuclear Information System (INIS)

Kotnis, Nikhil A.; Chiavaras, Mary M.; Harish, Srinivasan

2012-01-01

The diagnosis of lateral epicondylitis is often straightforward and can be made on the basis of clinical findings. However, radiological assessment is valuable where the clinical picture is less clear or where symptoms are refractory to treatment. Demographics, aspects of clinical history, or certain physical signs may suggest an alternate diagnosis. Knowledge of the typical clinical presentation and imaging findings of lateral epicondylitis, in addition to other potential causes of lateral elbow pain, is necessary. These include entrapment of the posterior interosseous and lateral antebrachial cutaneous nerves, posterolateral rotatory instability, posterolateral plica syndrome, Panner's disease, osteochondritis dissecans of the capitellum, radiocapitellar overload syndrome, occult fractures and chondral-osseous impaction injuries, and radiocapitellar arthritis. Knowledge of these potential masquerades of lateral epicondylitis and their characteristic clinical and imaging features is essential for accurate diagnosis. The goal of this review is to provide an approach to the imaging of lateral elbow pain, discussing the relevant anatomy, various causes, and discriminating factors, which will allow for an accurate diagnosis. (orig.)

Casimir effect and thermodynamics of horizon instabilities

International Nuclear Information System (INIS)

Hartnoll, Sean A.

2004-01-01

We propose a dual thermodynamic description of a classical instability of generalized black hole spacetimes. From a thermodynamic perspective, the instability is due to negative compressibility in regions where the Casimir pressure is large. The argument indicates how the correspondence between thermodynamic and classical instability for horizons may be extended to cases without translational invariance

Outcomes of the modified Brostrom procedure using suture anchors for chronic lateral ankle instability--a prospective, randomized comparison between single and double suture anchors.

Science.gov (United States)

Cho, Byung-Ki; Kim, Yong-Min; Kim, Dong-Soo; Choi, Eui-Sung; Shon, Hyun-Chul; Park, Kyoung-Jin

2013-01-01

The present prospective, randomized study was conducted to compare the clinical outcomes of the modified Brostrom procedure using single and double suture anchors for chronic lateral ankle instability. A total of 50 patients were followed up for more than 2 years after undergoing the modified Brostrom procedure. Of the 50 procedures, 25 each were performed using single and double suture anchors by 1 surgeon. The Karlsson scale had improved significantly to 89.8 points and 90.6 points in the single and double anchor groups, respectively. Using the Sefton grading system, 23 cases (92%) in the single anchor group and 22 (88%) in the double anchor group achieved satisfactory results. The talar tilt angle and anterior talar translation on stress radiographs using the Telos device had improved significantly to an average of 5.7° and 4.6 mm in the single anchor group and 4.5° and 4.3 mm in the double anchor group, respectively. The double anchor technique was superior with respect to the postoperative talar tilt. The single and double suture anchor techniques produced similar clinical and functional outcomes, with the exception of talar tilt as a reference of mechanical stability. The modified Brostrom procedure using both single and double suture anchors appears to be an effective treatment method for chronic lateral ankle instability. Copyright © 2013 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Projectile Aerodynamic Jump Due to Lateral Impulsives

National Research Council Canada - National Science Library

Cooper, Gene

2003-01-01

.... The formulation shows for sufficiently long-range target interception; lateral impulse trajectory response for a guided projectile is independent of when the impulse is activated during the yaw cycle...

RINGED ACCRETION DISKS: INSTABILITIES

Energy Technology Data Exchange (ETDEWEB)

Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

2016-04-01

We analyze the possibility that several instability points may be formed, due to the Paczyński mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.

Anticipatory and Compensatory Postural Adjustments in Response to External Lateral Shoulder Perturbations in Subjects with Parkinson's Disease.

Directory of Open Access Journals (Sweden)

Alexandre Kretzer E Castro de Azevedo

Full Text Available The purpose of this study was to investigate the anticipatory (APA and compensatory (CPA postural adjustments in individuals with Parkinson's disease (PD during lateral instability of posture. Twenty-six subjects (13 individuals with PD and 13 healthy matched controls were exposed to predictable lateral postural perturbations. The electromyographic (EMG activity of the lateral muscles and the displacement of the center of pressure (COP were recorded during four time intervals that are typical for postural adjustments, i.e., immediately before (APA1, APA2 and after (CPA1 and CPA2 the postural disturbances. The magnitude of the activity of the lateral muscles in the group with PD was lower only during the CPA time intervals and not during the anticipatory adjustments (APAs. Despite this finding, subjects with PD exhibit smaller COP excursions before and after the disturbance, probably due to lack of flexibility and proprioceptive impairments. The results of this study suggest that postural instability in subjects with PD can be partially explained by decreased postural sway, before and after perturbations, and reduced muscular activity after body disturbances. Our findings can motivate new studies to investigate therapeutic interventions that optimize the use of postural adjustment strategies in subjects with PD.

Arthroscopic Broström repair with Gould augmentation via an accessory anterolateral port for lateral instability of the ankle.

Science.gov (United States)

Matsui, Kentaro; Takao, Masato; Miyamoto, Wataru; Innami, Ken; Matsushita, Takashi

2014-10-01

Although several arthroscopic surgical techniques for the treatment of lateral instability of the ankle have been introduced recently, some concern remains over their procedural complexity, complications, and unclear clinical outcomes. We have simplified the arthroscopic technique of Broström repair with Gould augmentation. This technique requires only two small skin incisions for two ports (medial midline and accessory anterolateral ports), without needing a percutaneous procedure or extension of the skin incisions. The anterior talofibular ligament is reattached to its anatomical footprint on the fibula with suture anchor, under arthroscopic view. The inferior extensor retinaculum is directly visualized through the accessory anterolateral port and is attached to the fibula with another suture anchor under arthroscopic view via the anterolateral port. The use of two small ports offers a procedure that is simple to perform and less morbid for patients.

Radiation-induced instability of human genome

International Nuclear Information System (INIS)

Ryabchenko, N.N.; Demina, Eh.A.

2014-01-01

A brief review is dedicated to the phenomenon of radiation-induced genomic instability where the increased level of genomic changes in the offspring of irradiated cells is characteristic. Particular attention is paid to the problems of genomic instability induced by the low-dose radiation, role of the bystander effect in formation of radiation-induced instability, and its relationship with individual radiosensitivity. We believe that in accordance with the paradigm of modern radiobiology the increased human individual radiosensitivity can be formed due to the genome instability onset and is a significant risk factor for radiation-induced cancer

Ion-cyclotron instability in magnetic mirrors

International Nuclear Information System (INIS)

Pearlstein, L.D.

1987-01-01

This report reviews the role of ion-cyclotron frequency instability in magnetic mirrors. The modes discussed here are loss-cone or anisotropy driven. The discussion includes quasilinear theory, explosive instabilities of 3-wave interaction and non-linear Landau damping, and saturation due to non-linear orbits

Numerical analysis of anisotropic diffusion effect on ICF hydrodynamic instabilities

Directory of Open Access Journals (Sweden)

Olazabal-Loumé M.

2013-11-01

Full Text Available The effect of anisotropic diffusion on hydrodynamic instabilities in the context of Inertial Confinement Fusion (ICF flows is numerically assessed. This anisotropy occurs in indirect-drive when laminated ablators are used to modify the lateral transport [1,2]. In direct-drive, non-local transport mechanisms and magnetic fields may modify the lateral conduction [3]. In this work, numerical simulations obtained with the code PERLE [4], dedicated to linear stability analysis, are compared with previous theoretical results [5]. In these approaches, the diffusion anisotropy can be controlled by a characteristic coefficient which enables a comprehensive study. This work provides new results on the ablative Rayleigh-Taylor (RT, ablative Richtmyer-Meshkov (RM and Darrieus-Landau (DL instabilities.

Functional Results in Arthroscopic Treatment in Patients with Chronic Lateral Elbow Pain.

Science.gov (United States)

Phorkhar, Termphong; Chanlalit, Cholawish

2015-11-01

Modern surgery as elbow arthroscopic surgery is an accepted operation due to benefit in precise intra-articular lesion detection and minimally invasive surgery. To report the functional results when using arthroscopic surgery to treat chronic lateral elbow pain. The data was collected from 25 patients with chronic lateral elbow pain that failed in non-operative treatment and treated with elbow arthroscopic surgery. Five patients were excluded from this study due to diagnosed as instability that needed the ligament reconstruction. The etiology of pain were grouped in to tennis elbow (4 pts), plica (9 pts), tennis elbow combined with plica (4 pts) and cartilage lesion (3 pts). Thai quick DASH questionnaire was used to evaluate the functional results by comparing pre and post operation score and calculated statistic results with paired t-test by level of significance p tennis elbow mean score was 74 and 33, in plica lesion mean score was 65 and 11, combined lesions mean score was 60 and 18 and cartilage lesion mean score was 60 and 20. Approaching chronic lateral elbow pain with arthroscopy can maintain the signficant improvement of functional result in midterm follow-up.

Spondylolisthesis and Posterior Instability

International Nuclear Information System (INIS)

Niggemann, P.; Beyer, H.K.; Frey, H.; Grosskurth, D.; Simons, P.; Kuchta, J.

2009-01-01

We present the case of a patient with a spondylolisthesis of L5 on S1 due to spondylolysis at the level L5/S1. The vertebral slip was fixed and no anterior instability was found. Using functional magnetic resonance imaging (MRI) in an upright MRI scanner, posterior instability at the level of the spondylolytic defect of L5 was demonstrated. A structure, probably the hypertrophic ligament flava, arising from the spondylolytic defect was displaced toward the L5 nerve root, and a bilateral contact of the displaced structure with the L5 nerve root was shown in extension of the spine. To our knowledge, this is the first case described of posterior instability in patients with spondylolisthesis. The clinical implications of posterior instability are unknown; however, it is thought that this disorder is common and that it can only be diagnosed using upright MRI

Spondylolisthesis and Posterior Instability

Energy Technology Data Exchange (ETDEWEB)

Niggemann, P.; Beyer, H.K.; Frey, H.; Grosskurth, D. (Privatpraxis fuer Upright MRT, Koeln (Germany)); Simons, P.; Kuchta, J. (Media Park Klinik, Koeln (Germany))

2009-04-15

We present the case of a patient with a spondylolisthesis of L5 on S1 due to spondylolysis at the level L5/S1. The vertebral slip was fixed and no anterior instability was found. Using functional magnetic resonance imaging (MRI) in an upright MRI scanner, posterior instability at the level of the spondylolytic defect of L5 was demonstrated. A structure, probably the hypertrophic ligament flava, arising from the spondylolytic defect was displaced toward the L5 nerve root, and a bilateral contact of the displaced structure with the L5 nerve root was shown in extension of the spine. To our knowledge, this is the first case described of posterior instability in patients with spondylolisthesis. The clinical implications of posterior instability are unknown; however, it is thought that this disorder is common and that it can only be diagnosed using upright MRI.

Lateral epicondylitis and beyond: imaging of lateral elbow pain with clinical-radiologic correlation

Energy Technology Data Exchange (ETDEWEB)

Kotnis, Nikhil A. [McMaster University, Departments of Radiology, Hamilton, ON (Canada); Sheffield Teaching Hospitals, Department of Medical Physics and Medical Imaging, Sheffield (United Kingdom); Chiavaras, Mary M. [McMaster University, Departments of Radiology, Hamilton, ON (Canada); Harish, Srinivasan [McMaster University, Departments of Radiology, Hamilton, ON (Canada); St. Joseph' s Healthcare, Department of Diagnostic Imaging, Hamilton, ON (Canada)

2012-04-15

The diagnosis of lateral epicondylitis is often straightforward and can be made on the basis of clinical findings. However, radiological assessment is valuable where the clinical picture is less clear or where symptoms are refractory to treatment. Demographics, aspects of clinical history, or certain physical signs may suggest an alternate diagnosis. Knowledge of the typical clinical presentation and imaging findings of lateral epicondylitis, in addition to other potential causes of lateral elbow pain, is necessary. These include entrapment of the posterior interosseous and lateral antebrachial cutaneous nerves, posterolateral rotatory instability, posterolateral plica syndrome, Panner's disease, osteochondritis dissecans of the capitellum, radiocapitellar overload syndrome, occult fractures and chondral-osseous impaction injuries, and radiocapitellar arthritis. Knowledge of these potential masquerades of lateral epicondylitis and their characteristic clinical and imaging features is essential for accurate diagnosis. The goal of this review is to provide an approach to the imaging of lateral elbow pain, discussing the relevant anatomy, various causes, and discriminating factors, which will allow for an accurate diagnosis. (orig.)

Rayleigh-Taylor instability of cylindrical jets with radial motion

International Nuclear Information System (INIS)

Chen, X.M.; Schrock, V.E.; Peterson, P.F.

1997-01-01

Rayleigh-Taylor instability of an interface between fluids with different densities subjected to acceleration normal to itself has interested researchers for almost a century. The classic analyses of a flat interface by Rayleigh and Taylor have shown that this type of instability depends on the direction of acceleration and the density differences of the two fluids. Plesset later analyzed the stability of a spherically symmetric flows (and a spherical interface) and concluded that the instability also depends on the velocity of the interface as well as the direction and magnitude of radial acceleration. The instability induced by radial motion in cylindrical systems seems to have been neglected by previous researchers. This paper analyzes the Rayleigh-Taylor type of instability for a cylindrical surface with radial motions. The results of the analysis show that, like the spherical case, the radial velocity also plays an important role. As an application, the example of a liquid jet surface in an Inertial Confinement Fusion (ICF) reactor design is analyzed. (orig.)

Ion temperature gradient instability

International Nuclear Information System (INIS)

1989-01-01

Anomalous ion thermal conductivity remains an open physics issue for the present generation of high temperature Tokamaks. It is generally believed to be due to Ion Temperature Gradient Instability (η i mode). However, it has been difficult, if not impossible to identify this instability and study the anomalous transport due to it, directly. Therefore the production and identification of the mode is pursued in the simpler and experimentally convenient configuration of the Columbia Linear Machine (CLM). CLM is a steady state machine which already has all the appropriate parameters, except η i . This parameter is being increased to the appropriate value of the order of 1 by 'feathering' a tungsten screen located between the plasma source and the experimental cell to flatten the density profile and appropriate redesign of heating antennas to steepen the ion temperature profile. Once the instability is produced and identified, a thorough study of the characteristics of the mode can be done via a wide range of variation of all the critical parameters: η i , parallel wavelength, etc

Instability of flat space at finite temperature

International Nuclear Information System (INIS)

Gross, D.J.; Perry, M.J.; Yaffe, L.G.

1982-01-01

The instabilities of quantum gravity are investigated using the path-integral formulation of Einstein's theory. A brief review is given of the classical gravitational instabilities, as well as the stability of flat space. The Euclidean path-integral representation of the partition function is employed to discuss the instability of flat space at finite temperature. Semiclassical, or saddle-point, approximations are utilized. We show how the Jeans instability arises as a tachyon in the graviton propagator when small perturbations about hot flat space are considered. The effect due to the Schwarzschild instanton is studied. The small fluctuations about this instanton are analyzed and a negative mode is discovered. This produces, in the semiclassical approximation, an imaginary part of the free energy. This is interpreted as being due to the metastability of hot flat space to nucleate black holes. These then evolve by evaporation or by accretion of thermal gravitons, leading to the instability of hot flat space. The nucleation rate of black holes is calculated as a function of temperature

Jeans instability of self-gravitating magnetized strongly coupled plasma

International Nuclear Information System (INIS)

Prajapati, R P; Sharma, P K; Sanghvi, R K; Chhajlani, R K

2012-01-01

We investigate the Jeans instability of self-gravitating magnetized strongly coupled plasma. The equations of the problem are formulated using the generalized hydrodynamic model and a general dispersion relation is obtained using the normal mode analysis. This dispersion relation is discussed for transverse and longitudinal mode of propagations. The modified condition of Jeans instability is obtained for magnetized strongly coupled plasma. We find that strong coupling of plasma particles modify the fundamental criterion of Jeans gravitational instability. In transverse mode it is found that Jeans instability criterion gets modified due to the presence of magnetic field, shear viscosity and fluid viscosity but in longitudinal mode it is unaffected due to the presence of magnetic field. From the curves we found that all these parameters have stabilizing influence on the growth rate of Jeans instability.

Role of pathophysiology of patellofemoral instability in the treatment of spontaneous medial patellofemoral subluxation: a case report

Directory of Open Access Journals (Sweden)

Doğruyol Dağhan

2010-05-01

Full Text Available Abstract Introduction Medial patellar subluxation is usually seen after lateral retinacular release. Spontaneous medial subluxation of the patella is a very rare condition. There are few reports in the literature on the pathophysiology of iatrogenic medial patellar subluxation. To our knowledge, there are no reports of the pathophysiology of non-iatrogenic medial patellar subluxation in the English literature. In this study we present a case of spontaneous medial patellar instability that is more prominent in extension during weight bearing. We also try to define the treatment protocol based on pathophsiology. Case presentation We report the case of a 21-year-old Turkish man with spontaneous medial patellar instability. He had suffered right knee pain, clicking and popping sensation in the affected knee for three months prior to presentation. Clinical examination demonstrated medial patellar subluxation that is more prominent in extension during the weight bearing phase of gait and while standing. Increased medial tilt was observed when the patella was stressed medially. Conventional anterior to posterior, lateral and Merchant radiographs did not reveal any abnormalities. After three months of physical therapy, our patient was still suffering from right knee pain which disturbed his gait pattern. Throughout the surgery, medial patellar translation was tested following the imbrication of lateral structures. He still had a medial patellar translation that was more than 50% of his patellar width. Patellotibial ligament augmentation using an iliotibial band flap was added. When examined after surgery, the alignment of the patella was effectively corrected. Conclusions Chronic imbalance between the strengths of vastus lateralis and vastus medialis results in secondary changes in passive ligamentous structures and causes additional instability. Physical therapy modalities that aim to strengthen the vastus lateralis might be sufficient for the

3D Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. 1; Instability of a Static Column

Science.gov (United States)

Mizuno, Yosuke; Lyubarsky, Yuri; ishikawa, Ken-Ichi; Hardee, Philip E.

2010-01-01

We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the non-linear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the non-linear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the non-linear regime nearly ceases for increasing magnetic pitch.

THREE-DIMENSIONAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF CURRENT-DRIVEN INSTABILITY. I. INSTABILITY OF A STATIC COLUMN

International Nuclear Information System (INIS)

Mizuno, Yosuke; Nishikawa, Ken-Ichi; Lyubarsky, Yuri; Hardee, Philip E.

2009-01-01

We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic magnetohydrodynamic simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the nonlinear regime, the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depend moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and reaches the nonlinear regime at a later time than the case with constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the nonlinear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.

Stability of an expanding cylindrical plasma envelope: Rayleigh--Taylor instability

International Nuclear Information System (INIS)

Han, S.J.

1982-01-01

The stability of a cylindrically symmetric plasma envelope driven outward by blast waves is considered. The plasma fluid is assumed to be a compressible, isentropic gas describable as an ideal gas ( p = arho/sup γ/, γ>1). The stability problem of such an envelope undergoing self-similar motion is solved by considering the initial-value problem. It is shown that in the early phase of an expansion, the envelope is unstable to Rayleigh--Taylor modes which develop at the inner surface. In the later phase of the expansion, the Rayleigh--Taylor modes are weakened due to the geometrical divergence effect. The implications of the time-dependent behavior of the Rayleigh--Taylor instability for plasma switches are discussed

Collective instabilities of self-gravitating systems, 2

International Nuclear Information System (INIS)

Nakamura, Takashi; Takahara, Fumio; Ikeuchi, Satoru

1975-01-01

The instability modes of rotating self-gravitating systems are investigated on the assumption of infinitely long cylinder. The systems under consideration are a collisionless stellar system with anisotropic velocity dispersion and a gaseous system with anisotropic pressure. In the collisionless stellar system, the Jeans instability mode and the Harris instability mode exist. The dispersion relation is solved numerically and the following results are obtained: the Harris instability occurs even in the region where Wu did not treat, and although its growth rate amounts to the order of angular velocity of the system for sufficient anisotropy, the Harris instability always accompanies the Jeans instability and the latter is always greater than the former in growth rate. In the gaseous system exist the Jeans instability mode and a certain overstable mode, which are different from the Harris instability mode. It is shown that the overstable mode occurs due to coupling of modes. In relation to these results, some problems in galactic structure are discussed. (auth.)

[Capsular retensioning in anterior unidirectional glenohumeral instability].

Science.gov (United States)

Benítez Pozos, Leonel; Martínez Molina, Oscar; Castañeda Landa, Ezequiel

2007-01-01

To present the experience of the Orthopedics Service PEMEX South Central Hospital in the management of anterior unidirectional shoulder instability with an arthroscopic technique consisting of capsular retensioning either combined with other anatomical repair procedures or alone. Thirty-one patients with anterior unidirectional shoulder instability operated-on between January 1999 and December 2005 were included. Fourteen patients underwent capsular retensioning and radiofrequency, and in 17 patients, capsular retensioning was combined with suture anchors. Patients with a history of relapsing glenohumeral dislocations and subluxations, with anterior instability with or without associated Bankart lesions were selected; all of them were young. The results were assessed considering basically the occurrence of instability during the postoperative follow-up. No cases of recurring instability occurred. Two cases had neuroma and one experienced irritation of the suture site. Six patients had residual limitation of combined lateral rotation and abduction movements, of a mean of 10 degrees compared with the healthy contralateral side. The most frequent incident was the leak of solutions to the soft tissues. Capsular retensioning, whether combined or not with other anatomical repair techniques, has proven to result in a highly satisfactory rate of glenohumeral stabilization in cases of anterior unidirectional instabilities. The arthroscopic approach offers the well-known advantages of causing less damage to the soft tissues, and a shorter time to starting rehabilitation therapy and exercises.

Instability and star evolution

International Nuclear Information System (INIS)

Mirzoyan, L.V.

1981-01-01

The observational data are discussed which testify that the phenomena of dynamical instability of stars and stellar systems are definite manifestations of their evolution. The study of these phenomena has shown that the instability is a regular phase of stellar evolution. It has resulted in the recognition of the most important regularities of the process of star formation concerning its nature. This became possible due to the discovery in 1947 of stellar associations in our Galaxy. The results of the study of the dynamical instability of stellar associations contradict the predictions of classical hypothesis of stellar condensation. These data supplied a basis for a new hypothesis on the formation of stars and nebulae by the decay of superdense protostars [ru

Lateral dynamic flight stability of a model hoverfly in normal and inclined stroke-plane hovering

International Nuclear Information System (INIS)

Xu, Na; Sun, Mao

2014-01-01

Many insects hover with their wings beating in a horizontal plane (‘normal hovering’), while some insects, e.g., hoverflies and dragonflies, hover with inclined stroke-planes. Here, we investigate the lateral dynamic flight stability of a hovering model hoverfly. The aerodynamic derivatives are computed using the method of computational fluid dynamics, and the equations of motion are solved by the techniques of eigenvalue and eigenvector analysis. The following is shown: The flight of the insect is unstable at normal hovering (stroke-plane angle equals 0) and the instability becomes weaker as the stroke-plane angle increases; the flight becomes stable at a relatively large stroke-plane angle (larger than about 24°). As previously shown, the instability at normal hovering is due to a positive roll-moment/side-velocity derivative produced by the ‘changing-LEV-axial-velocity’ effect. When the stroke-plane angle increases, the wings bend toward the back of the body, and the ‘changing-LEV-axial-velocity’ effect decreases; in addition, another effect, called the ‘changing-relative-velocity’ effect (the ‘lateral wind’, which is due to the side motion of the insect, changes the relative velocity of its wings), becomes increasingly stronger. This causes the roll-moment/side-velocity derivative to first decrease and then become negative, resulting in the above change in stability as a function of the stroke-plane angle. (paper)

Kinetic simulations of Rayleigh-Taylor instabilities

International Nuclear Information System (INIS)

Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance

2014-01-01

We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role in the explosion mechanism of core-collapse supernovae. As a first test we study the evolution of a single-mode Rayleigh-Taylor instability at the interface of a light and a heavy fluid in the presence of a gravitational acceleration. To suppress small-wavelength instabilities caused by the irregularity in the separation layer we use a large particle mean free path. The latter leads to the development of a diffusion layer as particles propagate from one fluid into the other. For small amplitudes, when the instability is in the linear regime, we compare its position and shape to the analytic prediction. Despite the broadening of the fluid interface we see a good agreement with the analytic solution. At later times we observe the development of a mushroom like shape caused by secondary Kelvin-Helmholtz instabilities as seen in hydrodynamic simulations and consistent with experimental observations.

Analysis of Two Different Arthroscopic Broström Repair Constructs for Treatment of Chronic Lateral Ankle Instability in 110 Patients: A Retrospective Cohort Study.

Science.gov (United States)

Cottom, James M; Baker, Joseph; Plemmons, Britton S

Chronic lateral ankle instability is a common condition treated by most foot and ankle surgeons. Once conservative treatment has failed, patients often undergo surgical reconstruction, either anatomic or nonanatomic. The present retrospective cohort study compared the clinical outcomes of 2 different arthroscopic Broström procedures. A total of 110 patients (83 females [75.5%] and 27 males [24.5%]) were treated with 1 of the 2 lateral ankle stabilization techniques from October 1, 2014 to December 31, 2015. Of the 110 patients, 75 were included in the arthroscopic lateral ankle stabilization group with an additional suture anchor used proximally and 35 were included in the arthroscopic lateral ankle stabilization group using the knotless design. The age of the cohort was 46.05 ± 17.89 (range 12 to 83) years. The body mass index was 30.03 ± 7.42 (range 18.3 to 52.5) kg/m 2 . Of the 110 patients, 25 (22.7%) had undergone concomitant procedures during lateral ankle stabilization. Overall, postoperative complications occurred in 14 patients (12.7%). No statistically significant differences were found between the 2 groups regarding the complication rates, use of concomitant procedures, and the presence of diabetes and workers compensation claims. No statistically significant differences were found in the mean age, body mass index, or gender distribution between the 2 groups. The preoperative American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot scores were 50.85 ± 13.56 (range 18 to 76) and 51.26 ± 13.32 (range 18 to 69) in groups 1 and 2, respectively. The postoperative AOFAS Ankle-Hindfoot scores were 88.19 ± 10.72 (range 54 to 100) and 84 ± 15.41 (range 16 to 100) in groups 1 and 2, respectively. No statistically significant difference was found between these 2 groups. The preoperative visual analog scale score was 7.45 ± 1.39 (range 3 to 10) and 6.97 ± 1.25 (range 5 to 10), which had improved to 1.12 ± 1.38 (range 0 to 5) and

Clinical and radiological instability following standard fenestration discectomy

Directory of Open Access Journals (Sweden)

Mascarenhas Amrithlal

2009-01-01

Full Text Available Background: Post-surgical lumbar instability is an established complication but there is limited evidence in the literature regarding the incidence of lumbar instability following fenestration and discectomy. We analyzed our results following fenestration discectomy with a special focus on instability. Materials and Methods: Eighty-three patients between the age of 17 and 52 years who had undergone fenestration discectomy for a single-level lumbar intervertebral disc prolapse were followed-up for a period of 1-5 years. The criteria for instability included "instability catch,", "painful catch," and "apprehension." The working capacity of the patient and the outcome score of the surgery were assessed by means of the Oswestry disability score and the Prolo economic and functional outcome score. Flexion-extension lateral radiographs were taken and analyzed for abnormal tilt and translation. Results: Of the 83 patients included, 70 were men and 13 were women, with an average age of 37.35 years (17-52 years at 5 years follow-up. Clinical instability was seen in 10 (12.04% patients. Radiological instability was noted in 29 (34.9% patients. Only six (60% of the 10 patients who demonstrated clinical instability had radiological evidence of instability. Twenty (68.96% patients with radiological instability were asymptomatic. Three (10.34% patients with only radiological instability had unsatisfactory outcome. The Oswestry scoring showed an average score of 19.8%. Mild disability was noted in 59 (71.08% patients and moderate disability was seen in 24 (28.91% patients. None of the patients had severe disability. These outcomes were compared with the outcomes in other studies in the literature for microdiscectomy and the results were found to be comparable. Conclusion: The favorable outcome of this study is in good agreement with other studies on microdiscectomy. Clinical instability in 12.04% of the patients is in agreement with other studies. Radiological

Clinical forms of shoulder instability in pediatric patients

Directory of Open Access Journals (Sweden)

Yaroslav N. Proshchenko

2016-12-01

Full Text Available Background. The recurrence rate of adolescent chronic shoulder instability is approximately 56%–68%. However, this pathology is often missed in childhood and adolescence. Aim. To identify the clinical forms of shoulder joint instability in pediatric patients. Materials and methods. The authors present the data from 57 pediatric patients aged 3−17 years with a total of 61 unstable shoulder joints. All patients were divided into groups according to the form of instability. Traumatic chronic shoulder instability was identified in 40 patients (Bankart and Hill–Sachs injuries. Of these, non-traumatic shoulder instability was diagnose in 17, including five with recurrent dislocation, and spontaneous shoulder dislocation due to dysplasia of glenoid and labrum was diagnosed in 12. Of the 57 patients in the study cohort, 53 underwent surgery. Postoperatively, two patients developed recurrent shoulder dislocation (Andreev–Boichev technique due type III shoulder dysplasia in the first patient and multidirectional injury in the second. Conclusions. Shoulder joint instability should be considered as the traumatic or non-traumatic form. Treatment decisions should be based on anatomical characteristics that predispose to recurrent dislocation.

Identification of active release planes using ground-based differential InSAR at the Randa rock slope instability, Switzerland

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V. Gischig

2009-12-01

Full Text Available Five ground-based differential interferometric synthetic aperture radar (GB-DInSAR surveys were conducted between 2005 and 2007 at the rock slope instability at Randa, Switzerland. Resultant displacement maps revealed, for the first time, the presence of an active basal rupture zone and a lateral release surface daylighting on the exposed 1991 failure scarp. Structures correlated with the boundaries of interferometric displacement domains were confirmed using a helicopter-based LiDAR DTM and oblique aerial photography. Former investigations at the site failed to conclusively detect these active release surfaces essential for kinematic and hazard analysis of the instability, although their existence had been hypothesized. The determination of the basal and lateral release planes also allowed a more accurate estimate of the currently unstable volume of 5.7±1.5 million m³. The displacement patterns reveal that two different kinematic behaviors dominate the instability, i.e. toppling above 2200 m and translational failure below. In the toppling part of the instability the areas with the highest GB-DInSAR displacements correspond to areas of enhanced micro-seismic activity. The observation of only few strongly active discontinuities daylighting on the 1991 failure surface points to a rather uniform movement in the lower portion of the instability, while most of the slip occurs along the basal rupture plane. Comparison of GB-DInSAR displacements with mapped discontinuities revealed correlations between displacement patterns and active structures, although spatial offsets occur as a result of the effective resolution of GB-DInSAR. Similarly, comparisons with measurements from total station surveys generally showed good agreement. Discrepancies arose in several cases due to local movement of blocks, the size of which could not be resolved using GB-DInSAR.

Stabilization of Rayleigh-Taylor instability due to the spontaneous magnetic field in laser produced plasma

International Nuclear Information System (INIS)

Ogasawara, Masatada; Takita, Masami.

1981-08-01

Spontaneous magnetic fields due to the temperature gradient nabla T 0 produced by a focussed laser beam on one point of a pellet are taken into account in deriving the dispersion relation of Rayleigh-Taylor instability. Growth rate γ decreases with time. Density fluctuation with wavelength shorter than 1.5(R/L sub(T)) x (n sub(s)/n 0 )sup(1/2) μm is remarkably stabilized, where R, L sub(T), n sub(s) and n 0 are the radius of a pellet, L sub(T)sup(-1) = + nabla T 0 /T 0 + , number densities of solid and the pellet. Validity condition of the theory is γt 0 >> 1 or in another form R >> L, where t 0 is the time of thermal expansion of a pellet and L -1 = + nabla n 0 /n 0 + . (author)

Parallel numerical simulation of oscillating airfoil NACA0015 in the channel due to flutter instability

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Řidký Václav

2014-03-01

Full Text Available The work is devoted to 3D and 2D parallel numerical computation of pressure and velocity fields around an elastically supported airfoil self-oscillating due to interaction with the airflow. Numerical solution is computed in the OpenFOAM package, an open-source software package based on finite volume method. Movement of airfoil is described by translation and rotation, identified from experimental data. A new boundary condition for the 2DOF motion of the airfoil was implemented. The results of numerical simulations (velocity are compared with data measured in a wind tunnel, where a physical model of NACA0015 airfoil was mounted and tuned to exhibit the flutter instability. The experimental results were obtained previously in the Institute of Thermomechanics by interferographic measurements in a subsonic wind tunnel in Nový Knín.

Rayleigh-Taylor instability of cylindrical jets with radial motion

Energy Technology Data Exchange (ETDEWEB)

Chen, Xiang M. [GE Nuclear, Wilmington, NC (United States); Schrock, V.E.; Peterson, P.F. [Univ. of California, Berkeley, CA (United States)

1995-09-01

Rayleigh-Taylor instability of an interface between fluids with different densities subjected to accelleration normal to itself has interested researchers for almost a century. The classic analyses of a flat interface by Rayleigh and Taylor have shown that this type of instability depends on the direction of acceleration and the density differences of the two fluids. Plesset later analyzed the stability of a spherically symmetric flows (and a spherical interface) and concluded that the instability also depends on the velocity of the interface as well as the direction and magnitude of radial acceleration. The instability induced by radial motion in cylindrical systems seems to have been neglected by previous researchers. This paper analyzes the Rayleigh-Taylor type of the spherical case, the radial velocity also plays an important role. As an application, the example of a liquid jet surface in an Inertial Confinement Fusion (ICF) reactor design is analyzed.

Talar anchor placement for modified Brostrom lateral ankle stabilization procedure.

Science.gov (United States)

Angirasa, Arush K; Barrett, Michael J

2008-01-01

The modified Brostrom procedure has been a proven procedure with excellent utility in the treatment of lateral ankle instability within limitation. Multiple variations of the original technique have been described in the literature to date. Included in these variations are differences in anchor placement, suture technique, or both. In this research study, we propose placing a bone screw anchor into the lateral shoulder of the talus rather than the typical placement at the lateral malleolus for anatomic reconstruction of the lateral ankle ligaments.

Thermal shrinkage for shoulder instability.

Science.gov (United States)

Toth, Alison P; Warren, Russell F; Petrigliano, Frank A; Doward, David A; Cordasco, Frank A; Altchek, David W; O'Brien, Stephen J

2011-07-01

Thermal capsular shrinkage was popular for the treatment of shoulder instability, despite a paucity of outcomes data in the literature defining the indications for this procedure or supporting its long-term efficacy. The purpose of this study was to perform a clinical evaluation of radiofrequency thermal capsular shrinkage for the treatment of shoulder instability, with a minimum 2-year follow-up. From 1999 to 2001, 101 consecutive patients with mild to moderate shoulder instability underwent shoulder stabilization surgery with thermal capsular shrinkage using a monopolar radiofrequency device. Follow-up included a subjective outcome questionnaire, discussion of pain, instability, and activity level. Mean follow-up was 3.3 years (range 2.0-4.7 years). The thermal capsular shrinkage procedure failed due to instability and/or pain in 31% of shoulders at a mean time of 39 months. In patients with unidirectional anterior instability and those with concomitant labral repair, the procedure proved effective. Patients with multidirectional instability had moderate success. In contrast, four of five patients with isolated posterior instability failed. Thermal capsular shrinkage has been advocated for the treatment of shoulder instability, particularly mild to moderate capsular laxity. The ease of the procedure makes it attractive. However, our retrospective review revealed an overall failure rate of 31% in 80 patients with 2-year minimum follow-up. This mid- to long-term cohort study adds to the literature lacking support for thermal capsulorrhaphy in general, particularly posterior instability. The online version of this article (doi:10.1007/s11420-010-9187-7) contains supplementary material, which is available to authorized users.

Hydrodynamic instabilities in inertial confinement fusion

International Nuclear Information System (INIS)

Freeman, J.R.

1977-01-01

Inertial confinement fusion targets generally consist of hollow high-density spheres filled with low density thermonuclear fuel. Targets driven ablatively by electrons, ions, or lasers are potentially unstable during the initial acceleration phase. Later in time, the relatively low density fuel decelerates the dense inner portion of the sphere (termed the pusher), permitting unstable growth at the fuel-pusher interface. The instabilities are of the Rayleigh-Taylor variety, modified by thermal and viscous diffusion and convection. These problems have been analyzed by many in recent years using both linearized perturbation methods and direct numerical simulation. Examples of two-dimensional simulations of the fuel-pusher instability in electron beam fusion targets will be presented, along with a review of possible stabilization mechanisms

Developmental instability and fitness in Periploca laevigata experiencing grazing disturbance

Science.gov (United States)

Alados, C.L.; Giner, M.L.; Dehesa, L.; Escos, J.; Barroso, F.; Emlen, J.M.; Freeman, D.C.

2002-01-01

We investigated the sensitivity of developmental instability measurements (leaf fluctuating asymmetry, floral radial asymmetry, and shoot translational asymmetry) to a long‐standing natural stress (grazing) in a palatable tannin‐producing shrub (Periploca laevigata Aiton). We also assessed the relationship between these measures of developmental instability and fitness components (growth and floral production). Developmental instability, measured by translational asymmetry, was the most accurate estimator of a plant’s condition and, consequently, environmental stress. Plants with less translational asymmetry grew more and produced more flowers. Plants from the medium‐grazed population were developmentally more stable, as estimated by translational and floral asymmetry, than either more heavily or more lightly grazed populations. Leaf fluctuating asymmetry was positively correlated with tannin concentration. The pattern of internode growth also responded to grazing impact. Plants under medium to heavy grazing pressure accelerated early growth and consequently escaped herbivory later in the season, i.e., at the beginning of the spring, when grazing activity was concentrated in herbaceous plants. Periploca laevigata accelerated growth and finished growing sooner than in the other grazing treatment. Thus, its annual growth was more mature and less palatable later in the season when grazers typically concentrate on shrubs. The reduction of developmental instability under medium grazing is interpreted as a direct effect of grazing and not as the release from competition.

Single-leg drop landing movement strategies in participants with chronic ankle instability compared with lateral ankle sprain 'copers'.

Science.gov (United States)

Doherty, Cailbhe; Bleakley, Chris; Hertel, Jay; Caulfield, Brian; Ryan, John; Delahunt, Eamonn

2016-04-01

To compare the movement patterns and underlying energetics of individuals with chronic ankle instability (CAI) to ankle sprain 'copers' during a landing task. Twenty-eight (age 23.2 ± 4.9 years; body mass 75.5 ± 13.9 kg; height 1.7 ± 0.1 m) participants with CAI and 42 (age 22.7 ± 1.7 years; body mass 73.4 ± 11.3 kg; height 1.7 ± 0.1 m) ankle sprain 'copers' were evaluated 1 year after incurring a first-time lateral ankle sprain injury. Kinematics and kinetics of the hip, knee and ankle joints from 200 ms pre-initial contact (IC) to 200 ms post-IC, in addition to the vertical component of the landing ground reaction force, were acquired during performance of a drop land task. The CAI group adopted a position of increased hip flexion during the landing descent on their involved limb. This coincided with a reduced post-IC flexor pattern at the hip and increased overall hip joint stiffness compared to copers (-0.01 ± 0.05 vs. 0.02 ± 0.05°/Nm kg(-1), p = 0.03). Individuals with CAI display alterations in hip joint kinematics and energetics during a unipodal landing task compared to LAS 'copers'. These alterations may be responsible for the increased risk of injury experienced by individuals with CAI during landing manoeuvres. Thus, clinicians must recognise the potential for joints proximal to the affected ankle to contribute to impaired function following an acute lateral ankle sprain injury and to develop rehabilitation protocols accordingly. Level III.

Generalized laser filamentation instability coupled to cooling instability

International Nuclear Information System (INIS)

Liang, E.P.; Wong, J.; Garrison, J.

1984-01-01

We consider the propagation of laser light in an initially slightly nonuniform plasma. The classical dispersion relation for the laser filamentation growth rate (see e.g., B. Langdon, in the 1980 Lawrence Livermore National Laboratory Laser Program Annual Report, pp. 3-56, UCRL-50021-80, 1981) can be generalized to include other acoustical effects. For example, we find that the inclusion of potential imbalances in the heating and cooling rates of the ambient medium due to density and temperature perturbations can cause the laser filamentation mode to bifurcate into a cooling instability mode at long acoustic wavelengths. We also attempt to study semi-analytically the nonlinear evolution of this and related instabilities. These results have wide applications to a variety of chemical gas lasers and phenomena related to laser-target interactions (e.g., jet-like behavior)

The influence on the interferometry due to the instability of ground-based synthetic aperture radar work platform

Science.gov (United States)

Tao, Gang; Wei, Guohua; Wang, Xu; Kong, Ming

2018-03-01

There has been increased interest over several decades for applying ground-based synthetic aperture radar (GB-SAR) for monitoring terrain displacement. GB-SAR can achieve multitemporal surface deformation maps of the entire terrain with high spatial resolution and submilimetric accuracy due to the ability of continuous monitoring a certain area day and night regardless of the weather condition. The accuracy of the interferometric measurement result is very important. In this paper, the basic principle of InSAR is expounded, the influence of the platform's instability on the interferometric measurement results are analyzed. The error sources of deformation detection estimation are analyzed using precise geometry of imaging model. Finally, simulation results demonstrates the validity of our analysis.

The treatment of recurrent posterolateral instability of the elbow

DEFF Research Database (Denmark)

Olsen, Bo Sanderhoff; Søjbjerg, Jens Ole

2003-01-01

This study describes the surgical technique used for reconstruction and reinforcement of the lateral collateral ligament complex in patients with posterolateral instability of the elbow and the results. A triceps tendon graft from the ipsilateral elbow which was inserted through bone tunnels...

Instability of drift Alfven wave accompanying polar magnetic storm

International Nuclear Information System (INIS)

Higuchi, Yoshihiro

1974-01-01

As the micro plasma instability due to the plasma non-uniformity in magnetosphere, there is the instability of drift Alfven wave. With the data obtained with the network of multiple observation points for geomagnetism, attempt was made to prove the hypothesis that the instability of drift Alfven wave due to the electron temperature gradient at the inner boundary of plasma sheet may be one of the causes for the geomagnetic pulsation (Pi 1) accompanying polar magnetic storm. Up to date, final conclusion is yet impossible as to the problems in it due to the discussion based on the data from widely separated observation points. The installation of economically efficient multi-point observation network is necessary for the solution. (Mori, K.)

Causation of cancer by ionizing radiation and genomic instability

International Nuclear Information System (INIS)

Streffer, Christian

2013-01-01

The causation of cancer by ionizing radiation has been shown in many epidemiological (with exposed humans) as well as experimental studies with mammals especially mice but also rats, dogs and monkeys. Risk values have been determined in medium radiation dose ranges (∼100 to 2,000 mSv). However, in the low dose range (<100 mSv) the situation is unclear and unsolved up to now. A better knowledge of the mechanisms for the development of cancer in humans over decades after low to medium radiation exposures is necessary for the understanding of the open questions. An increase of chromosomal aberrations and other genetic changes have been frequently observed directly after radiation exposures in many cell systems including human cells. However, in 1989 it was found that an increase of genomic instability occurred after irradiation of mouse zygotes in the fibroblasts of the neonates developing from the irradiated zygotes. That means genomic instability developed many cell generations later in cells which never had been exposed to various qualities of ionizing radiations in vivo and any treatment and secondary cancers developed in photon irradiated M.Hodgkin patients preferentially in those patients who showed a comparatively high genomic instability in their lymphocytes. Since several decades it has been experienced that certain cancer patients show an extremely high radio-sensitivity. This clinical observation has been confirmed by experimental investigations with cells of such patients. It has been proven that this increased radio-sensitivity is due to genetic mutations. A number of syndromes could be defined on such a genetic basis like ataxia telangiectasia, bloom's syndrome, fanconi anemia, retinoblasoma and others. In all these syndromes mutations occur in genes which are to regulation of the cell cycle or DNA repair (preferentially repair of DSBs). These patients with an increased radio-sensitivity frequently develop cancer - very often lymphoma - and they also

Calcaneocuboid joint instability: a novel operative technique for anatomic reconstruction.

Science.gov (United States)

Lohrer, Heinz; Arentz, Sabine

2004-05-01

A case history of a 13-year-old female national top-level gymnast, suffering from calcaneocuboid joint instability, is presented. The procedure was done as an anatomic repair by capsular reefing, which was augmented using a local periosteal flap. Initially, the athlete twisted her ankle. Clinical investigation revealed no sign of a lateral ankle ligament injury, but following this initial examination, recurrent giving-way of the foot occurred. She additionally felt significant but diffuse pain on the lateral side of the foot during loading in training and competition. For 2 months she was unable to run and conservative treatment failed. Diagnosis of a calcaneocuboid instability was established 4 months after the initial lesion by clinical and x-ray stress examination of the calcaneocuboid joint. Open surgery was successfully performed. Early functional posttreatment was done and the patient returned to full high-level gymnastics ability 16 weeks after surgery. Two years later, a similar injury occurred to the opposite calcaneocuboid joint and the same operative procedure again led to full sports ability.

Centrifugally Driven Rayleigh-Taylor Instability

Science.gov (United States)

Scase, Matthew; Hill, Richard

2017-11-01

The instability that develops at the interface between two fluids of differing density due to the rapid rotation of the system may be considered as a limit of high-rotation rate Rayleigh-Taylor instability. Previously the authors have considered the effect of rotation on a gravitationally dominated Rayleigh-Taylor instability and have shown that some growth modes of instability may be suppressed completely by the stabilizing effect of rotation (Phys. Rev. Fluids 2:024801, Sci. Rep. 5:11706). Here we consider the case of very high rotation rates and a negligible gravitational field. The initial condition is of a dense inner cylinder of fluid surrounded by a lighter layer of fluid. As the system is rotated about the generating axis of the cylinder, the dense inner fluid moves away from the axis and the familiar bubbles and spikes of Rayleigh-Taylor instability develop at the interface. The system may be thought of as a ``fluid-fluid centrifuge''. By developing a model based on an Orr-Sommerfeld equation, we consider the effects of viscosity, surface tension and interface diffusion on the growth rate and modes of instability. We show that under particular circumstances some modes may be stabilized. School of Mathematical Sciences.

Emittance growth due to space charge compensation and beam intensity instabilities in negative ion beams

Directory of Open Access Journals (Sweden)

C. A. Valerio-Lizarraga

2018-03-01

Full Text Available The need to extract the maximum beam intensity with low transversal emittance often comes with the drawback of operating the ion source to limits where beam current instabilities arise, such fluctuations can change the beam properties producing a mismatch in the following sections of the machine. The space charge compensation (SCC generated by the beam particles colliding with the residual gas reaches a steady state after a build-up time. This paper shows how once in the steady state, the beam ends with a transversal emittance value bigger than the case without compensation. In addition, we study how the beam intensity variation can disturb the SCC dynamics and its impact on the beam properties. The results presented in this work come from 3-D simulations using tracking codes taking into account the secondary ions to estimate the degree of the emittance growth due to space charge and SCC.

Longitudinal beam instability due to the ring impedance at KEK's accelerator test facility damping ring

International Nuclear Information System (INIS)

Kim, Eun-San

2003-01-01

This paper shows the results of a numerical study of the impedance in the Accelerator Test Facility damping ring. The longitudinal impedance in the damping ring is shown to be inductive. It is shown that the total impedance |Z || /n| is 0.23 Ω and the inductance is L = 14 nH. In the extremely low emittance beam of the damping ring, bunch lengthening is caused by both the effects of potential-well distortion and intra-beam scattering. In this paper, the bunch-lengthening due to the ring impedance is numerically investigated, and the result shows qualitative agreement with the result of an analysis performed using the bunch-length measurement. With the calculated longitudinal impedance, the instability threshold in the damping ring is estimated to be a bunch population of 3.3 x 10 10 by using both a Vlasov equation approach and a multi-particle tracking method.

Electrothermal instability growth in magnetically driven pulsed power liners

International Nuclear Information System (INIS)

Peterson, Kyle J.; Sinars, Daniel B.; Yu, Edmund P.; Herrmann, Mark C.; Cuneo, Michael E.; Slutz, Stephen A.; Smith, Ian C.; Atherton, Briggs W.; Knudson, Marcus D.; Nakhleh, Charles

2012-01-01

This paper explores the role of electro-thermal instabilities on the dynamics of magnetically accelerated implosion systems. Electro-thermal instabilities result from non-uniform heating due to temperature dependence in the conductivity of a material. Comparatively little is known about these types of instabilities compared to the well known Magneto-Rayleigh-Taylor (MRT) instability. We present simulations that show electrothermal instabilities form immediately after the surface material of a conductor melts and can act as a significant seed to subsequent MRT instability growth. We also present the results of several experiments performed on Sandia National Laboratories Z accelerator to investigate signatures of electrothermal instability growth on well characterized initially solid aluminum and copper rods driven with a 20 MA, 100 ns risetime current pulse. These experiments show excellent agreement with electrothermal instability simulations and exhibit larger instability growth than can be explained by MRT theory alone.

Buneman instability in hot electron plasma (Te>>Ti)

International Nuclear Information System (INIS)

Khalil, S.M.; Sayed, Y.A.; Sayed, R.A.

1986-07-01

We shall investigate the linear excitation of electrostatic current Buneman instability in both unmagnetized and magnetized homogeneous plasma. The frequency, growth rate and conditions of excitation of such instability are obtained analytically. We consider that the current velocity u (due to relative streaming of ions and electrons) slightly exceeds the instability threshold velocity u cr and that the electron temperature is much higher than the ion temperature (T e >>T i ). (author)

Instabilities of higher dimensional compactifications

International Nuclear Information System (INIS)

Accetta, F.S.

1987-02-01

Various schemes for cosmological compactification of higher dimensional theories are considered. Possible instabilities which drive the ground state with static internal space to de Sitter-like expansion of all dimensions are discussed. These instabilities are due to semiclassical barrier penetration and classical thermal fluctuations. For the case of the ten dimensional Chapline-Manton action, it is possible to avoid such difficulties by balancing one-loop Casimir corrections against monopole contributions from the field strength H/sub MNP/ and fermionic condensates. 10 refs

Prevalence of knee instability in relation to sports activity

DEFF Research Database (Denmark)

Hahn, Thomas; Foldspang, Anders; Hansen, Thorsten Ingemann

2001-01-01

to be positively associated with female gender and different features of occupational work. In conclusion, knee instability is a commonly reported phenomenon among active athletes. It was found to be independent of the type and the amount of sports activity but highly dependent on female gender, type and amount......The objective was to estimate the prevalence of knee instability among active athletes and to investigate potential associations to type, amount and duration of sports participation. Based on a questionnaire, 339 athletes provided information about different features of occupation, sports activity...... and knee instability. The 12-month period prevalence of knee instability and constant or recurrent knee instability, and absence from sport and absence from work due to knee instability, was 22%, 14%, 5% and 1%, respectively. Knee instability as such, and constant or recurrent knee instability were found...

[Lateral epicondylitis: conservative - operative].

Science.gov (United States)

Altintas, Burak; Greiner, Stefan

2016-10-01

Lateral epicondylitis is a common disease of the common extensor origin at the lateral humerus. Despite its common self-limitation it can lead to chronic therapy-resistant pain with remarkable functional disability of the affected arm. Different conservative and operative treatment options of lateral epicondylitis are described and compared regarding benefits and risks. Additionally, recent surgical techniques and their complications are mentioned. Based on the current literature, it is shown which treatment option can be recommended. This review was based on the literature analysis in PubMed regarding "conservative and operative therapy of lateral epicondylitis" as well as the clinical experience of the authors. Conservative treatment is the primary choice for the treatment of lateral epicondylitis if concomitant pathologies such as instability among others can be excluded. It should include strengthening against resistance with eccentric stretching of the extensor group. In persistent cases, operative treatment is warranted. Resection of the pathologic tissue at the extensor origin with debridement and refixation of the healthy tendinous tissue yields good results. Most patients with lateral epicondylitis can be treated conservatively with success. Radiological evaluation should be performed in therapy-resistant cases. In the case of partial or complete rupture of the extensor origin, operative therapy is indicated.

Predictors of chronic ankle instability: Analysis of peroneal reaction time, dynamic balance and isokinetic strength.

Science.gov (United States)

Sierra-Guzmán, Rafael; Jiménez, Fernando; Abián-Vicén, Javier

2018-05-01

Previous studies have reported the factors contributing to chronic ankle instability, which could lead to more effective treatments. However, factors such as the reflex response and ankle muscle strength have not been taken into account in previous investigations. Fifty recreational athletes with chronic ankle instability and 55 healthy controls were recruited. Peroneal reaction time in response to sudden inversion, isokinetic evertor muscle strength and dynamic balance with the Star Excursion Balance Test and the Biodex Stability System were measured. The relationship between the Cumberland Ankle Instability Tool score and performance on each test was assessed and a backward multiple linear regression analysis was conducted. Participants with chronic ankle instability showed prolonged peroneal reaction time, poor performance in the Biodex Stability System and decreased reach distance in the Star Excursion Balance Test. No significant differences were found in eversion and inversion peak torque. Moderate correlations were found between the Cumberland Ankle Instability Tool score and the peroneal reaction time and performance on the Star Excursion Balance Test. Peroneus brevis reaction time and the posteromedial and lateral directions of the Star Excursion Balance Test accounted for 36% of the variance in the Cumberland Ankle Instability Tool. Dynamic balance deficits and delayed peroneal reaction time are present in participants with chronic ankle instability. Peroneus brevis reaction time and the posteromedial and lateral directions of the Star Excursion Balance Test were the main contributing factors to the Cumberland Ankle Instability Tool score. No clear strength impairments were reported in unstable ankles. Copyright © 2018 Elsevier Ltd. All rights reserved.

Influence of Passive Joint Stiffness on Proprioceptive Acuity in Individuals With Functional Instability of the Ankle.

Science.gov (United States)

Marinho, Hellen Veloso Rocha; Amaral, Giovanna Mendes; de Souza Moreira, Bruno; Araújo, Vanessa Lara; Souza, Thales Rezende; Ocarino, Juliana Melo; da Fonseca, Sérgio Teixeira

2017-12-01

Study Design Controlled laboratory study, cross-sectional. Background Deficits in ankle proprioceptive acuity have been reported in persons with functional instability of the ankle. Passive stiffness has been proposed as a possible mechanism underlying proprioceptive acuity. Objective To compare proprioceptive acuity and passive ankle stiffness in persons with and without functional ankle instability, and to assess the influence of passive joint stiffness on proprioceptive acuity in persons with functional ankle instability. Methods A sample of 18 subjects with and 18 without complaints of functional ankle instability following lateral ankle sprain participated. An isokinetic dynamometer was used to compare motion perception threshold, passive position sense, and passive ankle stiffness between groups. To evaluate the influence of passive stiffness on proprioceptive acuity, individuals in the lateral functional ankle instability group were divided into 2 subgroups: "high" and "low" passive ankle stiffness. Results The functional ankle instability group exhibited increased motion perception threshold when compared with the corresponding limb of the control group. Between-group differences were not found for passive position sense and passive ankle stiffness. Those in the functional ankle instability group with higher passive ankle stiffness had smaller motion perception thresholds than those with lower passive ankle stiffness. Conclusion Unlike motion perception threshold, passive position sense is not affected by the presence of functional ankle instability. Passive ankle stiffness appears to influence proprioceptive acuity in persons with functional ankle instability. J Orthop Sports Phys Ther 2017;47(12):899-905. Epub 7 Oct 2017. doi:10.2519/jospt.2017.7030.

Effective collision frequency due to ion-acoustic instability: Theory and simulations

Czech Academy of Sciences Publication Activity Database

Hellinger, Petr; Trávníček, Pavel; Menietti, J. D.

2004-01-01

Roč. 31, č. 10 (2004), L10806 ISSN 0094-8276 R&D Projects: GA MŠk ME 500; GA AV ČR IAA3042403 Grant - others:ESA PRODEX(XE) 14529/00/NL/SFe; NASA (US) NAG5-11942 Institutional research plan: CEZ:AV0Z3042911 Keywords : Magnetospheric Physics: Plasma waves and instabilities * Space Plasma Physics: Kinetic and MHD theory * Space Plasma Physics: Magnetic reconnection Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.378, year: 2004

Method to reduce levitation force decay of the bulk HTSC above the NdFeB guideway due to lateral movement

Energy Technology Data Exchange (ETDEWEB)

Ma, G T; Lin, Q X; Wang, J S; Wang, S Y; Deng, Z G; Lu, Y Y; Liu, M X; Zheng, J [Applied Superconductivity Lab, Mail Stop 152 Southwestern Jiaotong University, Chengdu, Sichuan 610031 (China)], E-mail: asclab@asclab.cn

2008-06-15

A magnetic levitation vehicle using bulk high-T{sub c} superconductors (HTSC) is considered as a promising transportation type thanks to its lateral inherent stability, but previous studies have found that the levitation force (LF) decays due to lateral movement. In this paper, a pre-load method is presented to reduce the LF decay, and the experimental results indicate that this method is very applicable in supressing this decay in spite of the applied field and material property of the bulk HTSC, and this effect can be ascribed to the reduction of the hysteresis loss in the bulk HTSC, i.e. more trapped magnetic flux after the pre-load case. In the end, experimental results indicate that the Halbach PMG has an advantage to reduce the cost of the PMG, but its rate of LF decay is also larger due to lateral movement.

Do instability markers predict satisfactory reduction and requirement for later surgery in emergency department patients with wrist fracture?

Science.gov (United States)

Winayak, Amar; Gossat, Alyza; Cooper, Jenny; Ritchie, Peter; Lim, Wei; Klim, Sharon; Kelly, Anne-Maree

2018-02-01

Research suggests that the presence of instability markers in patients with displaced distal radial fractures is associated with poorer outcome. Our aims were to determine whether the presence of previously defined instability markers could predict the likelihood of successful ED reduction and requirement for a secondary procedure after ED reduction. Retrospective cohort study performed by medical record review. Adult ED patients coded as having an isolated wrist fracture and having fracture reduction in ED were eligible for inclusion. Data collected included demographics, history of osteoporosis, mechanism of injury, radiological features on X-rays and performance of a secondary procedure. Outcomes of interest were the rate of successful fracture reduction in ED (against defined radiological criteria), the rate of secondary procedures and the association between the number of defined instability risk factors and successful reduction and performance of a secondary surgical procedure. Analysis was by χ 2 test, receiver operating characteristic curve, logistic regression analyses. Three hundred and nineteen patients were studied; median age 62 years, 77% female. Sixty-five per cent of patients had satisfactory fracture reduction in ED (95% CI 59%-70%). Eighty-six patients underwent a secondary procedure to reduce/stabilise their fracture (28%, 95% CI 23%-33%). Younger age, lack of satisfactory ED reduction and increased number of instability factors were independently predictive of the performance of a secondary procedure. Instability risk factors are common in patients with wrist fractures requiring reduction in ED. The number of instability factors is not a strong predictor of the performance of secondary procedures. © 2017 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine.

Early functional outcome of a modified Brostrom-Gould surgery using bioabsorbable suture anchor for chronic lateral ankle instability.

Science.gov (United States)

Shahrulazua, A; Ariff Sukimin, M S; Tengku Muzaffar, T M; Yusof, M I

2010-03-01

The purpose of this study was to evaluate the early functional outcome following the use of a bioabsorbable suture anchor to simplify the repair of injured lateral ankle structures as a variation of an established technique known as the Brostrom-Gould procedure. This was a prospective study of 30 ankles with chronic lateral instability that underwent a modified Brostrom-Gould surgery using a bioabsorbable suture anchor, performed by a single surgeon. A total of 29 patients, aged 15 to 52 (mean is 33) years, were enrolled in the study. The follow-up period ranged from three to six (mean is four) months. The function of the patients' ankles was scored using the Kaikkonen Functional Scale, both preoperatively and postoperatively. Preoperatively, all ankles had poor scores (less than 50). Postoperatively, 28 ankles showed excellent scores and two ankles showed good scores, while none obtained a fair or poor score. The difference in the overall means between the postoperative and preoperative scores was statistically significant (p-value is 0.001). Post surgery, 24 ankles had no symptoms, while six had only mild ankle tightness with extreme inversion movement at the last review. All patients were able to walk normally, and 29 ankles regained their normal running capability. There was marked improvement in the ability to descend stairs, to rise on heels and toes, to perform a single-limb stance, and in range of motions of the ankle dorsiflexion as well as in ankle laxity. The modified Brostrom-Gould procedure using a bioabsorbable suture anchor allowed for early ankle rehabilitation and offered a reproducible and excellent early functional outcome with minimal complications.

A fast beam-ion instability

Energy Technology Data Exchange (ETDEWEB)

Stupakov, G V [Stanford Linear Accelerator Center, Menlo Park, CA (United States)

1996-08-01

The ionization of residual gas by an electron beam in an accelerator generates ions that can resonantly couple to the beam through a wave propagating in the beam-ion system. Results of the study of a beam-ion instability are presented for a multi-bunch train taking into account the decoherence of ion oscillations due to the ion frequency spread and spatial variation of the ion frequency. It is shown that the combination of both effects can substantially reduce the growth rate of the instability. (author)

Imaging of patellofemoral instability; Bildgebung der patellofemoralen Instabilitaet

Energy Technology Data Exchange (ETDEWEB)

Waldt, S.; Rummeny, E.J. [Klinikum rechts der Isar, Technische Universitaet Muenchen, Institut fuer diagnostische und interventionelle Radiologie, Muenchen (Germany)

2012-11-15

Patellofemoral instability remains a diagnostic and therapeutic challenge due to its multifactorial genesis. The purpose of imaging is to systematically analyze predisposing factors, such as trochlear dysplasia, patella alta, tibial tuberosity-trochlear groove (TT-TG) distance, rotational deformities of the lower limb and patellar tilt. In order to evaluate anatomical abnormalities with a sufficient diagnostic accuracy, standardized measurement methods and implementation of various imaging modalities are necessary. Diagnosis of acute and often overlooked lateral patellar dislocation can be established with magnetic resonance imaging (MRI) because of its characteristic patterns of injury. Damage to the medial patellofemoral ligament (MPFL) has a significance just as high as the predisposing risk factors in relation to the cause of chronic instability. (orig.) [German] Die patellofemorale Instabilitaet stellt aufgrund ihrer multifaktoriellen Genese eine diagnostische und therapeutische Herausforderung dar. Aufgabe der Bildgebung ist es, anlagebedingte Risikofaktoren wie Trochleadysplasie, Patellahochstand, Torsionsfehlstellungen der unteren Extremitaet, TTTG-Abstand und Patellatilt systematisch zu analysieren. Um die aetiologischen Faktoren mit einer ausreichenden diagnostischen Genauigkeit zu bewerten, sind standardisierte und umfangreich evaluierte Messverfahren sowie der gezielte Einsatz verschiedener bildgebender Modalitaeten erforderlich. Die Diagnose einer traumatischen, oftmals klinisch inapparenten Patellaluxation kann anhand der charakteristischen Befundkonstellation in der MRT gestellt werden. Der Schaedigung des medialen patellofemoralen Ligaments (Elogantion/Ruptur) im Rahmen einer akuten Luxation wird, aehnlich wie den anlagebedingten Risikofaktoren, eine grosse Bedeutung im Hinblick auf die Entstehung einer chronischen Instabilitaet beigemessen. (orig.)

Lessons from non-Abelian plasma instabilities in two spatial dimensions

International Nuclear Information System (INIS)

Arnold, Peter; Leang, P.-S.

2007-01-01

Plasma instabilities can play a fundamental role in quark-gluon plasma equilibration in the high energy (weak coupling) limit. Early simulations of the evolution of plasma instabilities in non-Abelian gauge theory, performed in one spatial dimension, found behavior qualitatively similar to traditional QED plasmas. Later simulations of the fully three-dimensional theory found different behavior, unlike traditional QED plasmas. To shed light on the origin of this difference, we study the intermediate case of two spatial dimensions. Depending on how the 'two-dimensional' theory is formulated, we can obtain either behavior

Coherent betatron instability in the Tevatron

International Nuclear Information System (INIS)

Bogacz, S.A.; Harrison, M.; Ng, K.Y.

1988-01-01

The coherent betatron instability was first observed during the recent 1987-88 Tevatron fixed target run. In this operating mode 1000 consecutive bunches are loaded into the machine at 150 GeV with a bunch spacing of 18.8 /times/ 10 -9 sec (53 MHz). The normalized transverse emittance is typically 15 π /times/ 10 -6 m rad in each plane with a longitudinal emittance of about 1.5 eV-sec. The beam is accelerated to 800 GeV in 13 sec. and then it is resonantly extracted during a 23 sec flat top. As the run progressed the bunch intensities were increased until at about 1.4 /times/ 10 10 ppb (protons per bunch) we experienced the onset of a coherent horizontal oscillation taking place in the later stages of the acceleration cycle (>600 GeV). This rapidly developing coherent instability results in a significant emittance growth, which limits machine performance and in a catastrophic scenario it even prevents extraction of the beam. In this paper we will present a simple analytic description of the observed instability. We will show that a combination of a resistive wall coupled bunch effect and a single bunch slow head-tail instability is consistent with the above observations. Finally, a systematic numerical analysis of our model (growth-time vs chromaticity plots) points to the existence of the ≥1 slow head-tail modes as a plausible mechanism for the observed coherent instability. This last claim, as mentioned before, does not have conclusive experimental evidence, although it is based on a very good agreement between the measured values of the instability growth-time and the ones calculated on the basis of our model. 4 refs., 3 figs

Patellofemoral instability in children: T2 relaxation times of the patellar cartilage in patients with and without patellofemoral instability and correlation with morphological grading of cartilage damage.

Science.gov (United States)

Kang, Chang Ho; Kim, Hee Kyung; Shiraj, Sahar; Anton, Christopher; Kim, Dong Hoon; Horn, Paul S

2016-07-01

Patellofemoral instability is one of the most common causes of cartilage damage in teenagers. To quantitatively evaluate the patellar cartilage in patients with patellofemoral instability using T2 relaxation time maps (T2 maps), compare the values to those in patients without patellofemoral instability and correlate them with morphological grades in patients with patellofemoral instability. Fifty-three patients with patellofemoral instability (mean age: 15.9 ± 2.4 years) and 53 age- and gender-matched patients without patellofemoral instability were included. Knee MR with axial T2 map was performed. Mean T2 relaxation times were obtained at the medial, central and lateral zones of the patellar cartilage and compared between the two groups. In the patellofemoral instability group, morphological grading of the patellar cartilage (0-4) was performed and correlated with T2 relaxation times. Mean T2 relaxation times were significantly longer in the group with patellofemoral instability as compared to those of the control group across the patellar cartilage (Student's t-test, Ppatellofemoral instability, patellar cartilage damage occurs across the entire cartilage with the highest T2 values at the apex. T2 relaxation times directly reflect the severity in low-grade cartilage damage, which implies an important role for T2 maps in differentiating between normal and low-grade cartilage damage.

Relationship of physical examination test of shoulder instability to arthroscopic findings in dogs.

Science.gov (United States)

Devitt, Chad M; Neely, Marlon R; Vanvechten, Brian J

2007-10-01

To determine the diagnostic validity of commonly used physical examination maneuvers for shoulder instability. Retrospective study. Dogs (n=24) referred for shoulder arthroscopy. Results of physical maneuvers and arthroscopic findings were recorded and sensitivity, specificity, positive likelihood ratios (LR+), and negative likelihood ratios (LR-) were calculated for each of 4 physical examination test findings for arthroscopic changes in the medial, lateral, cranial, or caudal compartments of the shoulder joint viewed in dorsal recumbency by lateral and craniomedial portals. Distribution of compartment changes was: medial (17 dogs), caudal (15), cranial (12), and lateral (5). The biceps test had a moderate effect (LR+=9) on post-test probability of cranial compartment changes and a small effect on post-test probability of lateral and caudal compartment changes (LR+=3 and 2.4, respectively). Hyperabduction had a minimal effect and mediolateral instability test had a small effect (LR+=1.64 and 2.68, respectively) on post-test probability of medial compartment changes. Craniocaudal instability test had little to no effect on post-test probability of changes in any compartment. Physical examination tests evaluated were limited in their ability to predict the type of arthroscopic pathology in this study population. Clinicians should understand that a diagnostic test performs inconsistently based on prevalence of a condition in a given patient population. The use of likelihood ratios can assist clinicians in determining the probability of intraarticular changes from a group with a differing prevalence than the patient population presented.

Instability of the proximal tibiofibular joint associated with total knee arthroplasty

Directory of Open Access Journals (Sweden)

Martin Bédard, MD, FRCSC

2016-09-01

Full Text Available To our knowledge, proximal tibiofibular joint instability has never been reported in a patient with a total knee arthroplasty (TKA. We present the case of a patient with anterolateral proximal tibiofibular joint instability associated with a complex primary TKA. In 2010, a male patient of 47 years was referred for TKA after posttraumatic osteoarthritis. The patient's history includes a fracture of the left lateral tibial plateau in 2008 and removal of osteosynthesis material in 2009. TKA with a lateral metal augment and intramedullary stem was performed in 2010. After TKA, instability of the left proximal tibiofibular joint (PTFJ was diagnosed. The patient underwent PTFJ arthrodesis and, at 5 years' follow-up, had no residual pain, with full range of motion. In this case, arthrodesis was the only possible surgical option because reconstruction surgeries require the establishment of bone tunnels in the tibia and fibula for the passage of a graft. Low bone quality and the use of an intramedullary stem with a metal augment in the tibia made any reconstruction technique unfeasible because the proximal tibia was obliterated. Although several PTFJ reconstruction techniques are available, they are difficult to apply to patients with a complex TKA.

Faraday instability in deformable domains

International Nuclear Information System (INIS)

Pucci, G.

2013-01-01

Hydrodynamical instabilities are usually studied either in bounded regions or free to grow in space. In this article we review the experimental results of an intermediate situation, in which an instability develops in deformable domains. The Faraday instability, which consists in the formation of surface waves on a liquid experiencing a vertical forcing, is triggered in floating liquid lenses playing the role of deformable domains. Faraday waves deform the lenses from the initial circular shape and the mutual adaptation of instability patterns with the lens boundary is observed. Two archetypes of behaviour have been found. In the first archetype a stable elongated shape is reached, the wave vector being parallel to the direction of elongation. In the second archetype the waves exceed the response of the lens border and no equilibrium shape is reached. The lens stretches and eventually breaks into fragments that have a complex dynamics. The difference between the two archetypes is explained by the competition between the radiation pressure the waves exert on the lens border and its response due to surface tension.

Multiple sclerosis and employment: Associations of psychological factors and work instability.

Science.gov (United States)

Wicks, Charlotte Rose; Ward, Karl; Stroud, Amanda; Tennant, Alan; Ford, Helen L

2016-10-12

People with multiple sclerosis often stop working earlier than expected. Psychological factors may have an impact on job retention. Investigation may inform interventions to help people stay in work. To investigate the associations between psychological factors and work instability in people with multiple sclerosis. A multi-method, 2-phased study. Focus groups were held to identify key themes. Questionnaire packs using validated scales of the key themes were completed at baseline and at 8-month follow-up. Four key psychological themes emerged. Out of 208 study subjects 57.2% reported medium/high risk of job loss, with marginal changes at 8 months. Some psychological variables fluctuated significantly, e.g. depression fell from 24.6% to 14.5%. Work instability and anxiety and depression were strongly correlated (χ2 p work instability, and baseline depression levels also predicted later work instability (Hosmer-Lemeshow test 0.899; Nagelkerke R Square 0.579). Psychological factors fluctuated over the 8-month follow-up period. Some psychological variables, including anxiety and depression, were significantly associated with, and predictive of, work instability. Longitudinal analysis should further identify how these psychological attributes impact on work instability and potential job loss in the longer term.

C1-C2 instability with severe occipital headache in the setting of vertebral artery facet complex erosion.

Science.gov (United States)

Taher, Fadi; Bokums, Kristaps; Aichmair, Alexander; Hughes, Alexander P

2014-05-01

An exact understanding of patient vertebral artery anatomy is essential to safely place screws at the atlanto-axial level in posterior arthrodesis. We aim to report a case of erosion of the left vertebral artery into the C1-C2 facet complex with resultant rotatory and lateral listhesis presenting with severe occipital headache. This represents a novel etiology for this diagnosis and our report illustrates technical considerations when instrumenting the C1-C2 segment. We report a case of severe occipital headache due to C1-C2 instability with resultant left C2 nerve compression in the setting of erosion of the vertebral artery into the C1-C2 facet complex. A 68-year-old woman presented with a 12-month history of progressively debilitating headache and neck pain with atlanto-axial instability. Computed tomography (CT) angiography demonstrated erosion of the left vertebral artery into the left C1-C2 facet complex. In addition, the tortuous vertebral arteries had eroded into the C2 pedicles, eliminating the possibility for posterior pedicle screw placement. The patient underwent posterior arthrodesis of C1-C2 utilizing bilateral lateral mass fixation into C1 and bilateral trans-laminar fixation into C2 with resolution of all preoperative complaints. This study constitutes the first report of a tortuous vertebral artery causing the partial destruction of a C1-C2 facet complex, as well as instability, with the clinical presentation of severe occipital headache. It hereby presents a novel etiology for both the development of C1-C2 segment instability as well as the development of occipital headache. Careful evaluation of such lesions utilizing CT angiography is important when formulating a surgical plan.

Parametric instabilities excited by localized pumps near the lower-hybrid frequency

International Nuclear Information System (INIS)

Kuo, Y.Y.; Chen, L.

1976-04-01

Parametric instabilities excited in non-uniform plasmas by spatially localized pump fields oscillating near the local lower-hybrid frequency are analytically investigated. Corresponding threshold conditions, temporal growth rates, and spatial amplification factors are obtained for the oscillating-two-stream instability and the decay instabilities due to nonlinear electron and ion Landau dampings

A statistical model for instable thermodynamical systems

International Nuclear Information System (INIS)

Sommer, Jens-Uwe

2003-01-01

A generic model is presented for statistical systems which display thermodynamic features in contrast to our everyday experience, such as infinite and negative heat capacities. Such system are instable in terms of classical equilibrium thermodynamics. Using our statistical model, we are able to investigate states of instable systems which are undefined in the framework of equilibrium thermodynamics. We show that a region of negative heat capacity in the adiabatic environment, leads to a first order like phase transition when the system is coupled to a heat reservoir. This phase transition takes place without a phase coexistence. Nevertheless, all intermediate states are stable due to fluctuations. When two instable system are brought in thermal contact, the temperature of the composed system is lower than the minimum temperature of the individual systems. Generally, the equilibrium states of instable system cannot be simply decomposed into equilibrium states of the individual systems. The properties of instable system depend on the environment, ensemble equivalence is broken

The Rayleigh-Taylor instability in inertial fusion, astrophysical plasma and flames

International Nuclear Information System (INIS)

Bychkov, V; Modestov, M; Akkerman, V; Eriksson, L-E

2007-01-01

Previous results are reviewed and new results are presented on the Rayleigh-Taylor instability in inertial confined fusion, flames and supernovae including gravitational and thermonuclear explosion mechanisms. The instability couples micro-scale plasma effects to large-scale hydrodynamic phenomena. In inertial fusion the instability reduces target compression. In supernovae the instability produces large-scale convection, which determines the fate of the star. The instability is often accompanied by mass flux through the unstable interface, which may have either a stabilizing or a destabilizing influence. Destabilization happens due to the Darrieus-Landau instability of a deflagration front. Still, it is unclear whether the instabilities lead to well-organized large-scale structures (bubbles) or to relatively isotropic turbulence (mixing layer)

Topographic-driven instabilities in terrestrial bodies

Science.gov (United States)

Vantieghem, S.; Cebron, D.; Herreman, W.; Lacaze, L.

2013-12-01

Models of internal planetary fluid layers (core flows, subsurface oceans) commonly assume that these fluid envelopes have a spherical shape. This approximation however entails a serious restriction from the fluid dynamics point of view. Indeed, in the presence of mechanical forcings (precession, libration, nutation or tides) due to gravitational interaction with orbiting partners, boundary topography (e.g. of the core-mantle boundary) may excite flow instabilities and space-filling turbulence. These phenomena may affect heat transport and dissipation at the main order. Here, we focus on instabilities driven by longitudinal libration. Using a suite of theoretical tools and numerical simulations, we are able to discern a parameter range for which instability may be excited. We thereby consider deformations of different azimuthal order. This study gives the first numerical evidence of the tripolar instability. Furthermore, we explore the non-linear regime and investigate the amplitude as well as the dissipation of the saturated instability. Indeed, these two quantities control the torques on the solid layers and the thermal transport. Furthermore, based on this results, we address the issue of magnetic field generation associated with these flows (by induction or by dynamo process). This instability mechanism applies to both synchronized as non-synchronized bodies. As such, our results show that a tripolar instability might be present in various terrestrial bodies (Early Moon, Gallilean moons, asteroids, etc.), where it could participate in dynamo action. Simulation of a libration-driven tripolar instability in a deformed spherical fluid layer: snapshot of the velocity magnitude, where a complex 3D flow pattern is established.

On the instability of a quasivacuum regime in a plasma diode

International Nuclear Information System (INIS)

Zharinov, A.V.; Chikhachev, A.S.

1978-01-01

Instability of the plasma diode stationary state developing in the quasivacuum overcompensated regime is investigated by the method of plasma simulation with the charged sheet system. It is shown that instability developes during the time of the order of the electron transit time through the interelectrode space and is due to electron motion. Specific scale of growings disturbances decreases with current increase of electron emission and diminution of compensating parameter. Instability develops at current value exceeding critical one. The results obtained show, that instability under investigation is analogous to the Pierse instability

Lateral patellar retinacular release: changes over the last ten years

Directory of Open Access Journals (Sweden)

Leonardo Pini Rosalem Marciano da Fonseca

Full Text Available ABSTRACT Lateral retinacular release is a useful resource in knee surgery that can be used for disorders of the extensor mechanism. For many years, it was indiscriminately used in the treatment of the various patellofemoral joint alterations, with conflicting functional results. This study aimed to analyze the changes that have occurred in the indications and clinical effectiveness of lateral retinacular release by reviewing the relevant literature of the past ten years, comparing it to the classic literature on the subject. It was found that less extensive releases decompress the lateral patellar facet, helping with pain control, while decreasing the risks of medial subluxation. Nowadays, there is clear evidence for its indication in the lateral patellar hypercompression syndrome associated with anterior knee pain, as long as there is no related instability; furthermore, it will normally play an adjuvant role in extensor mechanism alignment surgeries for cases of recurrent patellar instability. The initial results for symptomatic patellofemoral osteoarthritis are promising when lateral release is combined with cartilage debridement; in total knee replacement, it is more commonly used for the correction of valgus deformity in order to improve the components’ congruency. Finally, distinguishing the different patellofemoral joint pathologies is seen as crucial in order to indicate this procedure. Further randomized control trials that compare surgical techniques with long-term results are still needed.

Effect of viscosity and surface tension on the growth of Rayleigh-Taylor instability and Richtmyer-Meshkov instability under nonlinear domain

International Nuclear Information System (INIS)

Rahul Banerjee; Khan, M.; Mandal, L.K.; Roy, S.; Gupta, M.R.

2010-01-01

Complete text of publication follows. The Rayleigh-Taylor (R-T) instability and Richtmyer-Meshkov (R-M) instability are well known problems in the formation of some astrophysical structures such as the supernova remnants in the Eagle and Crab nebula. A core collapse supernova is driven by an externally powerful shock, and strong shocks are the breeding ground of hydrodynamic instability such as Rayleigh-Taylor instability or Richtmyer-Meshkov instability. These instabilities are also important issues in the design of targets for inertial confinement fusion (ICF). In an ICF target, a high density fluid is frequently accelerated by the pressure of a low density fluid and after ablation the density quickly decays. So, small ripples at such an interface will grow. Under potential flow model, the perturbed interface between heavier fluid and lighter fluid form bubble and spike like structures. The bubbles are in the form of columns of lighter fluid interleaved by falling spike of heavy fluid. In this paper, we like to presented the effect of viscosity and surface tension on Rayleigh-Taylor instability and Richtmyer-Meshkov instability under the non-linear Layzer's approach and described the displacement curvature, growth and velocity of the tip of the bubble as well as spike. It is seen that, in absence of surface tension the lowering of the asymptotic velocity of the tip of the bubble which is formed when the lighter fluid penetrates into the denser fluid and thus encounters the viscous drag due to the denser fluid, which depends only on the denser fluid's viscosity coefficient. On the other hand the asymptotic velocity of the tip of the spike formed as the denser fluid penetrates into the lighter fluid is reduced by an amount which depends only on the viscosity coefficient of the lighter fluid and the spike is resisted by the viscous drag due to the lighter fluid. However, in presence of surface tension the asymptotic velocity of the tip of the bubble (spike) and

Resonant Drag Instabilities in protoplanetary disks: the streaming instability and new, faster-growing instabilities

Science.gov (United States)

Squire, Jonathan; Hopkins, Philip F.

2018-04-01

We identify and study a number of new, rapidly growing instabilities of dust grains in protoplanetary disks, which may be important for planetesimal formation. The study is based on the recognition that dust-gas mixtures are generically unstable to a Resonant Drag Instability (RDI), whenever the gas, absent dust, supports undamped linear modes. We show that the "streaming instability" is an RDI associated with epicyclic oscillations; this provides simple interpretations for its mechanisms and accurate analytic expressions for its growth rates and fastest-growing wavelengths. We extend this analysis to more general dust streaming motions and other waves, including buoyancy and magnetohydrodynamic oscillations, finding various new instabilities. Most importantly, we identify the disk "settling instability," which occurs as dust settles vertically into the midplane of a rotating disk. For small grains, this instability grows many orders of magnitude faster than the standard streaming instability, with a growth rate that is independent of grain size. Growth timescales for realistic dust-to-gas ratios are comparable to the disk orbital period, and the characteristic wavelengths are more than an order of magnitude larger than the streaming instability (allowing the instability to concentrate larger masses). This suggests that in the process of settling, dust will band into rings then filaments or clumps, potentially seeding dust traps, high-metallicity regions that in turn seed the streaming instability, or even overdensities that coagulate or directly collapse to planetesimals.

Instability in Thoracolumbar Trauma: Is a New Definition Warranted?

Science.gov (United States)

Abbasi Fard, Salman; Skoch, Jesse; Avila, Mauricio J; Patel, Apar S; Sattarov, Kamran V; Walter, Christina M; Baaj, Ali A

2017-10-01

Review of the articles. The objective of this study was to review all articles related to spinal instability to determine a consensus statement for a contemporary, practical definition applicable to thoracolumbar injuries. Traumatic fractures of the thoracolumbar spine are common. These injuries can result in neurological deficits, disability, deformity, pain, and represent a great economic burden to society. The determination of spinal instability is an important task for spine surgeons, as treatment strategies rely heavily on this assessment. However, a clinically applicable definition of spinal stability remains elusive. A review of the Medline database between 1930 and 2014 was performed limited to papers in English. Spinal instability, thoracolumbar, and spinal stability were used as search terms. Case reports were excluded. We reviewed listed references from pertinent search results and located relevant manuscripts from these lists as well. The search produced a total of 694 published articles. Twenty-five articles were eligible after abstract screening and underwent full review. A definition for spinal instability was described in only 4 of them. Definitions were primarily based on biomechanical and classification studies. No definitive parameters were outlined to define stability. Thirty-six years after White and Panjabi's original definition of instability, and many classification schemes later, there remains no practical and meaningful definition for spinal instability in thoracolumbar trauma. Surgeon expertise and experience remains an important factor in stability determination. We propose that, at an initial assessment, a distinction should be made between immediate and delayed instability. This designation should better guide surgeons in decision making and patient counseling.

Interplay between parametric instabilities in fusion - relevant laser plasmas

International Nuclear Information System (INIS)

Huller, St.

2003-01-01

The control of parametric instabilities plays an important role in laser fusion. They are driven by the incident laser beams in the underdense plasma surrounding a fusion capsule and hinder the absorption process of incident laser light which is necessary to heat the fusion target. Due to its high intensity and power, the laser light modifies the plasma density dynamically, such that two or more parametric instabilities compete, in particular stimulated Brillouin scattering and the filamentation instability. The complicated interplay between these parametric instabilities is studied in detail by developing an adequate model accompanied by numerical simulations with multidimensional codes. The model is applied to generic and to smoothed laser beams, which are necessary to limit parametric instabilities, with parameters close to experimental conditions. (author)

Linear waves and instabilities

International Nuclear Information System (INIS)

Bers, A.

1975-01-01

The electrodynamic equations for small-amplitude waves and their dispersion relation in a homogeneous plasma are outlined. For such waves, energy and momentum, and their flow and transformation, are described. Perturbation theory of waves is treated and applied to linear coupling of waves, and the resulting instabilities from such interactions between active and passive waves. Linear stability analysis in time and space is described where the time-asymptotic, time-space Green's function for an arbitrary dispersion relation is developed. The perturbation theory of waves is applied to nonlinear coupling, with particular emphasis on pump-driven interactions of waves. Details of the time--space evolution of instabilities due to coupling are given. (U.S.)

Genetic instability in urinary bladder cancer: An evolving hallmark.

Science.gov (United States)

Wadhwa, N; Mathew, B B; Jatawa, S K; Tiwari, A

2013-01-01

Bladder cancer is a major health-care concern. A successful treatment of bladder cancer depends on its early diagnosis at the initial stage. Genetic instability is an essential early step toward the development of bladder cancer. This instability is found more often at the chromosomal level than at the nucleotide level. Microsatellite and chromosomal instability markers can be used as a prognostic marker for screening bladder cancer. Bladder cancer can be distinguished in two different categories according to genetic instability: Cancers with chromosomal level instability and cancers with nucleotide level instability. Deoxyribonucleic acid (DNA) mismatch repair (MMR) system and its correlation with other biologic pathway, both are essential to understand the basic mechanisms of cancer development. Microsatellite instability occurs due to defects in DNA MMR genes, including human mutL homolog 1 and human mutL homolog 2. Chromosomal alterations including deletions on chromosome 3, 8, 9, 11, 13, 17 have been detected in bladder cancer. In the current review, the most recent literature of genetic instability in urinary bladder cancer has been summarized.

Genetic instability in urinary bladder cancer: An evolving hallmark

Directory of Open Access Journals (Sweden)

N Wadhwa

2013-01-01

Full Text Available Bladder cancer is a major health-care concern. A successful treatment of bladder cancer depends on its early diagnosis at the initial stage. Genetic instability is an essential early step toward the development of bladder cancer. This instability is found more often at the chromosomal level than at the nucleotide level. Microsatellite and chromosomal instability markers can be used as a prognostic marker for screening bladder cancer. Bladder cancer can be distinguished in two different categories according to genetic instability: Cancers with chromosomal level instability and cancers with nucleotide level instability. Deoxyribonucleic acid (DNA mismatch repair (MMR system and its correlation with other biologic pathway, both are essential to understand the basic mechanisms of cancer development. Microsatellite instability occurs due to defects in DNA MMR genes, including human mutL homolog 1 and human mutL homolog 2. Chromosomal alterations including deletions on chromosome 3, 8, 9, 11, 13, 17 have been detected in bladder cancer. In the current review, the most recent literature of genetic instability in urinary bladder cancer has been summarized.

Kinetic theory of instabilities responsible for magnetic turbulence in laboratory rotating plasma

International Nuclear Information System (INIS)

Mikhailovskii, A.B.; Lominadze, J.G.; Churikov, A.P.; Pustovitov, V.D.; Erokhin, N.N.; Konovalov, S.V.

2008-01-01

The problem of instabilities responsible for magnetic turbulence in collisionless laboratory rotating plasma is investigated. It is shown that the standard mechanism of driving the magnetorotational instability (MRI), due to negative rotation frequency gradient, disappears in such a plasma. Instead of it, a new driving mechanism due to plasma pressure gradient is predicted

Sociopolitical Instability and Economic Growth Empirical Evidence from Sri Lanka

OpenAIRE

Changsheng Xu; Santhirasegaram Selvarathinam; Wen X. Li

2007-01-01

Sociopolitical instability severely affects economic growth in short and long run. This study analyzes that sociopolitical instability measured by proxy measure; annual growth rate of tourist arrivals in Sri Lanka during 1960-2005 adversely affects economic growth. Our empirical findings based on ordinary lease square econometric estimation, show that sociopolitical instability negatively and significantly affect economic growth. Reduction of economic growth rate (-0.032) due to the sociopoli...

Radiation loss driven instabilities in laser heated plasmas

International Nuclear Information System (INIS)

Evans, R.G.

1985-01-01

Any plasma in which a significant part of the power balance is due to optically thin radiative losses may be subject to a radiation cooling instability. A simple analytical model gives the dispersion relation for the instability and inclusion of a realistic radiation loss term in a two dimensional hydrodynamic simulation shows that ''jet'' like features form in moderate to high Z plasmas

Canonical momenta and numerical instabilities in particle codes

International Nuclear Information System (INIS)

Godfrey, B.B.

1975-01-01

A set of warm plasma dispersion relations appropriate to a large class of electromagnetic plasma simulation codes is derived. The numerical Cherenkov instability is shown by analytic and numerical analysis of these dispersion relations to be the most significant nonphysical effect involving transverse electromagnetic waves. The instability arises due to a spurious phase shift between resonant particles and light waves, caused by a basic incompatibility between the Lagrangian treatment of particle positions and the Eulerian treatment of particle velocities characteristic of most PIC--CIC algorithms. It is demonstrated that, through the use of canonical momentum, this mismatch is alleviated sufficiently to completely eliminate the Cherenkov instability. Collateral effects on simulation accuracy and on other numerical instabilities appear to be minor

A trickle instability

Science.gov (United States)

Bossa, Benjamin

2005-11-01

We address the problem of the free fall of a long, horizontal and narrow liquid layer squeezed in a vertical open Hele-Shaw cell. The layer destabilizes as it falls down, evolving into a series of liquid blobs linked together by thin bridges, which ultimately break, leaving the initially connex fluid layer as a set a disjointed drops. The mechanism of this instability is the onset of a vertical pressure gradient due to the curvature difference of the moving contact line between the advancing interface and the rear interface. This instability, whose growth rate scales with a non-trivial power of the capillary number, amplifies indifferently a broad band of wavenumbers because of the flat shape of its dispersion relation in the thin layer limit. We will finally comment on the nature of the final fragmentation process and drop size distributions.

Mechanisms of cadmium induced genomic instability

Energy Technology Data Exchange (ETDEWEB)

Filipic, Metka, E-mail: metka.filipic@nib.si [National Institute of Biology, Department for Genetic Toxicology and Cancer Biology, Ljubljana (Slovenia)

2012-05-01

Cadmium is an ubiquitous environmental contaminant that represents hazard to humans and wildlife. It is found in the air, soil and water and, due to its extremely long half-life, accumulates in plants and animals. The main source of cadmium exposure for non-smoking human population is food. Cadmium is primarily toxic to the kidney, but has been also classified as carcinogenic to humans by several regulatory agencies. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Cadmium dose not induce direct DNA damage, however it induces increase in reactive oxygen species (ROS) formation, which in turn induce DNA damage and can also interfere with cell signalling. More important seems to be cadmium interaction with DNA repair mechanisms, cell cycle checkpoints and apoptosis as well as with epigenetic mechanisms of gene expression control. Cadmium mediated inhibition of DNA repair mechanisms and apoptosis leads to accumulation of cells with unrepaired DNA damage, which in turn increases the mutation rate and thus genomic instability. This increases the probability of developing not only cancer but also other diseases associated with genomic instability. In the in vitro experiments cadmium induced effects leading to genomic instability have been observed at low concentrations that were comparable to those observed in target organs and tissues of humans that were non-occupationally exposed to cadmium. Therefore, further studies aiming to clarify the relevance of these observations for human health risks due to cadmium exposure are needed.

Mechanisms of cadmium induced genomic instability

International Nuclear Information System (INIS)

Filipič, Metka

2012-01-01

Cadmium is an ubiquitous environmental contaminant that represents hazard to humans and wildlife. It is found in the air, soil and water and, due to its extremely long half-life, accumulates in plants and animals. The main source of cadmium exposure for non-smoking human population is food. Cadmium is primarily toxic to the kidney, but has been also classified as carcinogenic to humans by several regulatory agencies. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Cadmium dose not induce direct DNA damage, however it induces increase in reactive oxygen species (ROS) formation, which in turn induce DNA damage and can also interfere with cell signalling. More important seems to be cadmium interaction with DNA repair mechanisms, cell cycle checkpoints and apoptosis as well as with epigenetic mechanisms of gene expression control. Cadmium mediated inhibition of DNA repair mechanisms and apoptosis leads to accumulation of cells with unrepaired DNA damage, which in turn increases the mutation rate and thus genomic instability. This increases the probability of developing not only cancer but also other diseases associated with genomic instability. In the in vitro experiments cadmium induced effects leading to genomic instability have been observed at low concentrations that were comparable to those observed in target organs and tissues of humans that were non-occupationally exposed to cadmium. Therefore, further studies aiming to clarify the relevance of these observations for human health risks due to cadmium exposure are needed.

Recovery From a First-Time Lateral Ankle Sprain and the Predictors of Chronic Ankle Instability: A Prospective Cohort Analysis.

Science.gov (United States)

Doherty, Cailbhe; Bleakley, Chris; Hertel, Jay; Caulfield, Brian; Ryan, John; Delahunt, Eamonn

2016-04-01

Impairments in motor control may predicate the paradigm of chronic ankle instability (CAI) that can develop in the year after an acute lateral ankle sprain (LAS) injury. No prospective analysis is currently available identifying the mechanisms by which these impairments develop and contribute to long-term outcome after LAS. To identify the motor control deficits predicating CAI outcome after a first-time LAS injury. Cohort study (diagnosis); Level of evidence, 2. Eighty-two individuals were recruited after sustaining a first-time LAS injury. Several biomechanical analyses were performed for these individuals, who completed 5 movement tasks at 3 time points: (1) 2 weeks, (2) 6 months, and (3) 12 months after LAS occurrence. A logistic regression analysis of several "salient" biomechanical parameters identified from the movement tasks, in addition to scores from the Cumberland Ankle Instability Tool and the Foot and Ankle Ability Measure (FAAM) recorded at the 2-week and 6-month time points, were used as predictors of 12-month outcome. At the 2-week time point, an inability to complete 2 of the movement tasks (a single-leg drop landing and a drop vertical jump) was predictive of CAI outcome and correctly classified 67.6% of cases (sensitivity, 83%; specificity, 55%; P = .004). At the 6-month time point, several deficits exhibited by the CAI group during 1 of the movement tasks (reach distances and sagittal plane joint positions at the hip, knee and ankle during the posterior reach directions of the Star Excursion Balance Test) and their scores on the activities of daily living subscale of the FAAM were predictive of outcome and correctly classified 84.8% of cases (sensitivity, 75%; specificity, 91%; P < .001). An inability to complete jumping and landing tasks within 2 weeks of a first-time LAS and poorer dynamic postural control and lower self-reported function 6 months after a first-time LAS were predictive of eventual CAI outcome. © 2016 The Author(s).

Impact of the Wiggler Coherent Synchrotron Radiation Impedance on the Beam Instability

International Nuclear Information System (INIS)

Wu, Juhao

2003-01-01

Coherent Synchrotron Radiation (CSR) can play an important role by not only increasing the energy spread and emittance of a beam, but also leading to a potential instability. Previous studies of the CSR induced longitudinal instability were carried out for the CSR impedance due to dipole magnets. However, many storage rings include long wigglers where a large fraction of the synchrotron radiation is emitted. This includes high-luminosity factories such as DAPHNE, PEP-II, KEK-B, and CESR-C as well as the damping rings of future linear colliders. In this paper, the instability due to the CSR impedance from a wiggler is studied assuming a large wiggler parameter K. The primary consideration is a low frequency microwave-like instability, which arises near the pipe cut-off frequency. Detailed results are presented on the growth rate and threshold for the damping rings of several linear collider designs. Finally, the optimization of the relative fraction of damping due to the wiggler systems is discussed for the damping rings

Faraday instability of crystallization waves in 4He

International Nuclear Information System (INIS)

Abe, H; Ueda, T; Morikawa, M; Saitoh, Y; Nomura, R; Okuda, Y

2007-01-01

Periodic modulation of the gravity acceleration makes a flat surface of a fluid unstable and standing waves are parametrically excited on the surface. This phenomenon is called Faraday instability. Since a crystal-superfluid interface of 4 He at low temperatures is very mobile and behaves like a fluid surface, Saarloos and Weeks predicted that Faraday instability of the crystallization waves exists in 4 He and that the threshold excitation for the instability depends on the crystal growth coefficient. We successfully observed the Faraday instability of the crystal-liquid interface at 160 mK. Faraday waves were parametrically generated at one half of the driving frequency 90 Hz. Amplitude of the Faraday wave becomes smaller at higher temperature due to decrease of the crystal growth coefficient and disappears above 200 mK

Unified formulation for inhomogeneity-driven instabilities in the lower-hybrid range

International Nuclear Information System (INIS)

Silveira, O.J.G.; Ziebell, L.F.; Gaelzer, R.; Yoon, Peter H.

2002-01-01

A local dispersion relation that describes inhomogeneity-driven instabilities in the lower-hybrid range is derived following a procedure that correctly describes energy exchange between waves and particles in inhomogeneous media, correcting some inherent ambiguities associated with the standard formalism found in the literature. Numerical solutions of this improved dispersion relation show that it constitutes a unified formulation for the instabilities in the lower-hybrid range, describing the so-called modified two-stream instability, excited by the ion cross-field drift, including the ion Weibel instability, and also describing the lower-hybrid drift instability, which is due to inhomogeneity effects on the electron population

Charge density wave instabilities and incommensurate structural phase transformations

International Nuclear Information System (INIS)

Axe, J.D.

1977-10-01

Incommensurate structural phase transformations involve the appearance of modulated atomic displacements with spatial periodicity unrelated to the fundamental periodicity of the basic lattice. In the case of some quasi one- or two-dimensional metals such transformations are the result of Fermi-surface instabilities that also produce electronic charge density waves (CDW's) and soft phonon modes due to metallic electron screening singularities. Incommensurate soft mode instabilities have been found in insulators as well. Recent neutron scattering studies of both the statics and dynamics of incommensurate structural instabilities will be reviewed

Luminosity Loss due to Beam Distortion and the Beam-Beam Instability

CERN Document Server

Wu, Juhao; Raubenheimer, Tor O; Seryi, Andrei; Sramek, Christopher K

2005-01-01

In a linear collider, sources of emittance dilution such as transverse wakefields or dispersive errors will couple the vertical phase space to the longitudinal position within the beam (the so-called ‘banana effect'). When the Intersection Point (IP) disruption parameter is large, these beam distortions will be amplified by a single bunch kink instability which will lead to luminosity loss. We study this phenomena both analytically using linear theory and via numerical simulation. In particular, we examine the dependence of the luminosity loss on the wavelength of the beam distortions and the disruption parameter. This analysis may prove useful when optimizing the vertical disruption parameter for luminosity operation with given beam distortions.

Weibel instability due to inverse bremsstrahlung absorption

International Nuclear Information System (INIS)

Bendib, A.; Bendib, K.; Bendib, A.; Bendib, K.; Sid, A.; Bendib, K.

1997-01-01

A new Weibel source due to the inverse bremsstrahlung absorption is presented. It has been shown that in homogeneous plasmas, this mechanism may drive strong collisionless Weibel modes with growth rates of order of γ∼10 11 s -1 and negligible group velocities. In the laser-produced plasmas, for short laser wavelengths (λ L 10 14 W/cm 2 ), this Weibel source is most efficient as the ones due to the heat flux and the plasma expansion. The useful scaling law of the convective e-foldings, with respect to the laser and the plasma parameters, is also derived. copyright 1997 The American Physical Society

Control of Coherent Instabilities by Linear Coupling

CERN Document Server

Cappi, R; Möhl, D

2001-01-01

One of the main challenges in the design of high-energy colliders is the very high luminosity necessary to provide significant event rates. This imposes strong constraints to achieve and preserve beams of high brightness, i.e. intensity to emittance ratio, all along the injector chain. Amongst the phenomena that can blow up and even destroy the beam are transverse coherent instabilities. Two methods are widely used to damp these instabilities. The first one is Landau damping by non-linearities. The second consists in using an electronic feedback system. However, non-linearities are harmful to single-particle motion due to resonance phenomena, and powerful wideband feedback systems are expensive. It is shown in this paper that linear coupling is a further method that can be used to damp transverse coherent instabilities. The theory of collective motion is outlined, including the coupling of instability rise and damping rates, chromaticity and Landau damping. Experimental results obtained at the CERN PS are rep...

Patellofemoral instability in children: T2 relaxation times of the patellar cartilage in patients with and without patellofemoral instability and correlation with morphological grading of cartilage damage

International Nuclear Information System (INIS)

Kang, Chang Ho; Kim, Hee Kyung; Shiraj, Sahar; Anton, Christopher; Kim, Dong Hoon; Horn, Paul S.

2016-01-01

Patellofemoral instability is one of the most common causes of cartilage damage in teenagers. To quantitatively evaluate the patellar cartilage in patients with patellofemoral instability using T2 relaxation time maps (T2 maps), compare the values to those in patients without patellofemoral instability and correlate them with morphological grades in patients with patellofemoral instability. Fifty-three patients with patellofemoral instability (mean age: 15.9 ± 2.4 years) and 53 age- and gender-matched patients without patellofemoral instability were included. Knee MR with axial T2 map was performed. Mean T2 relaxation times were obtained at the medial, central and lateral zones of the patellar cartilage and compared between the two groups. In the patellofemoral instability group, morphological grading of the patellar cartilage (0-4) was performed and correlated with T2 relaxation times. Mean T2 relaxation times were significantly longer in the group with patellofemoral instability as compared to those of the control group across the patellar cartilage (Student's t-test, P<0.05) with the longest time at the central area. Positive correlation was seen between mean T2 relaxation time and morphological grading (Pearson correlation coefficiency, P<0.001). T2 increased with severity of morphological grading from 0 to 3 (mixed model, P<0.001), but no statistical difference was seen between grades 3 and 4. In patellofemoral instability, patellar cartilage damage occurs across the entire cartilage with the highest T2 values at the apex. T2 relaxation times directly reflect the severity in low-grade cartilage damage, which implies an important role for T2 maps in differentiating between normal and low-grade cartilage damage. (orig.)

Deltoid ligament and tibiofibular syndesmosis injury in chronic lateral ankle instability: Magnetic resonance imaging evaluation at 3T and comparison with arthroscopy

International Nuclear Information System (INIS)

Chun, Ka Young; Choi, Yun Sun; Lee, Seok Hoon; Kim, Jin Su; Young, Ki Won; Jeong, Min Sun; Kim, Dae Jung

2015-01-01

To evaluate the prevalence of deltoid ligament and distal tibiofibular syndesmosis injury on 3T magnetic resonance imaging (MRI) in patients with chronic lateral ankle instability (CLAI). Fifty patients (mean age, 35 years) who had undergone preoperative 3T MRI and surgical treatment for CLAI were enrolled. The prevalence of deltoid ligament and syndesmosis injury were assessed. The complexity of lateral collateral ligament complex (LCLC) injury was correlated with prevalence of deltoid or syndesmosis injuries. The diagnostic accuracy of ankle ligament imaging at 3T MRI was analyzed using arthroscopy as a reference standard. On MRI, deltoid ligament injury was identified in 18 (36%) patients as follows: superficial ligament alone, 9 (50%); deep ligament alone 2 (11%); and both ligaments 7 (39%). Syndesmosis abnormality was found in 21 (42%) patients as follows: anterior inferior tibiofibular ligament (AITFL) alone, 19 (90%); and AITFL and interosseous ligament, 2 (10%). There was no correlation between LCLC injury complexity and the prevalence of an accompanying deltoid or syndesmosis injury on both MRI and arthroscopic findings. MRI sensitivity and specificity for detection of deltoid ligament injury were 84% and 93.5%, and those for detection of syndesmosis injury were 91% and 100%, respectively. Deltoid ligament or syndesmosis injuries were common in patients undergoing surgery for CLAI, regardless of the LCLC injury complexity. 3T MRI is helpful for the detection of all types of ankle ligament injury. Therefore, careful interpretation of pre-operative MRI is essential

Deltoid ligament and tibiofibular syndesmosis injury in chronic lateral ankle instability: Magnetic resonance imaging evaluation at 3T and comparison with arthroscopy

Energy Technology Data Exchange (ETDEWEB)

Chun, Ka Young; Choi, Yun Sun; Lee, Seok Hoon; Kim, Jin Su; Young, Ki Won; Jeong, Min Sun; Kim, Dae Jung [Eulji Hospital, Eulji University, Seoul (Korea, Republic of)

2015-10-15

To evaluate the prevalence of deltoid ligament and distal tibiofibular syndesmosis injury on 3T magnetic resonance imaging (MRI) in patients with chronic lateral ankle instability (CLAI). Fifty patients (mean age, 35 years) who had undergone preoperative 3T MRI and surgical treatment for CLAI were enrolled. The prevalence of deltoid ligament and syndesmosis injury were assessed. The complexity of lateral collateral ligament complex (LCLC) injury was correlated with prevalence of deltoid or syndesmosis injuries. The diagnostic accuracy of ankle ligament imaging at 3T MRI was analyzed using arthroscopy as a reference standard. On MRI, deltoid ligament injury was identified in 18 (36%) patients as follows: superficial ligament alone, 9 (50%); deep ligament alone 2 (11%); and both ligaments 7 (39%). Syndesmosis abnormality was found in 21 (42%) patients as follows: anterior inferior tibiofibular ligament (AITFL) alone, 19 (90%); and AITFL and interosseous ligament, 2 (10%). There was no correlation between LCLC injury complexity and the prevalence of an accompanying deltoid or syndesmosis injury on both MRI and arthroscopic findings. MRI sensitivity and specificity for detection of deltoid ligament injury were 84% and 93.5%, and those for detection of syndesmosis injury were 91% and 100%, respectively. Deltoid ligament or syndesmosis injuries were common in patients undergoing surgery for CLAI, regardless of the LCLC injury complexity. 3T MRI is helpful for the detection of all types of ankle ligament injury. Therefore, careful interpretation of pre-operative MRI is essential.

The longitudinal wall impedance instability in a heavy-ion fusion driver

International Nuclear Information System (INIS)

Callahan, D.A.; Langdon, A.B.; Friedman, A.; Haber, I.

1997-01-01

For more than ten years [J. Bisognano, I. Haber, L. Smith, IEEE Trans. Nucl. Sci. NS-30, 2501 (1983)], the longitudinal wall impedance instability was thought to be a serious threat to the success of heavy-ion driven inertial confinement fusion. This instability is a open-quotes resistive wallclose quotes instability, driven by the impedance of the induction modules used to accelerate the beam. Early estimates of the instability growth rate predicted tens of e-folds due to the instability which would modulate the current and increase the longitudinal momentum spread and prevent focusing the ion beam on the small spot needed at the target. We have simulated this instability using an r-z particle-in-cell code which includes a model for the module impedance. These simulations, using driver parameters, show that growth due to the instability is smaller than in previous calculations. We have seen that growth is mainly limited to one head to tail transit by a space-charge wave. In addition, the capacitive component of the module impedance, which was neglected in the early work of Lee [E. P. Lee, Proc. Linear Accelerator Conference, (UCRL-86452), Santa Fe, NM, 1981] significantly reduces the growth rate. We have also included in the simulation intermittently applied axial confining fields which are thought to be the major source of perturbations to seed the longitudinal instability. Simulations show the beam can adjust to a systematic error in the longitudinal confining fields while a random error excites the most unstable wavelength of the instability. These simulations show that the longitudinal instability must be taken into account in a driver design, but it is not the major factor it was once thought to be. copyright 1997 American Institute of Physics

Kelvin-Helmholtz instability and kinetic internal kink modes in tokamaks

International Nuclear Information System (INIS)

Naitou, H.; Kobayashi, T.; Yagi, M.; Matsumoto, T.; Tokuda, S.; Kishimoto, Y.

2003-01-01

The m=1 (poloidal mode number) and n=1 (toroidal mode number) kinetic internal kink (KIK) mode in the presence of a density gradient is studied with the cylindrical version of the gyro-reduced MHD code, which is one of the extended MHD codes being able to treat the physics beyond resistive MHD. Electron inertia and electron finite temperature effects are included. The unstable KIK mode is observed in the parameter range in which the linear theory predicts complete stabilization due to the electron diamagnetic effect. The electrostatic potential profile in the linear stage of the KIK instability has the sheared poloidal flow with the m=1 mode structure. The vortexes are generated due to the Kelvin-Helmholtz (K-H) instability. The KIK is stabilized when the vortexes are formed, but it is destabilized again as the vortexes diminish due to the charge neutralizing electron motion along the magnetic field. These phenomena are observed in the early nonlinear stage of the KIK instability in which the width of the m=1 magnetic island is sufficiently small compared with the radial extent of the vortexes. The strong coupling between the vortexes and the KIK instability can be one of the candidates explaining the sudden onset of the sawtooth crash. (author)

Beam instability studies at the APS

International Nuclear Information System (INIS)

Teng, L.C.

1994-01-01

The Argonne Advanced Photon Source, APS (Fig. 1), is a 7-GeV positron storage ring with a circumference of 1104 m. It has a ''third generation, DBA or Chasman-Green'' lattice composed of 40 sectors each having a ∼6 m long zero-dispersion straight-section for accommodating insertion devices. Neighboring straight-sections are connected by a 360 degrees/40 = 9 degrees double-bend-achromatic bending section designed to produce the smallest emittance attainable with reasonable component parameter values and dynamic apertures. Thus, it is a very strongly focusing lattice with v x = 35.22 and v y = 14.30. The beam chamber of the storage ring including all rf, vacuum and photon beam components is designed to ensure that a beam current > 100 mA can be stably stored. We expect that the maximum stable beam current could be as high as 300 mA. This paper will give some details of the studies and computations to ensure the stability of such a beam. The discussions will be organized in the following three parts: Coupled-bunch instability caused by the higher-order modes (HOMs) of the rf cavities; Single-bunch instability due to the resistive wall impedance; and Single-bunch instability due to broadband impedances arising from beam chamber irregularities

Midflexion instability in primary total knee replacement: a review

Directory of Open Access Journals (Sweden)

Ramappa Manjunath

2015-01-01

Full Text Available Introduction: Midflexion instability in primary total knee replacement (TKR is an evolving concept. Successful treatment of instability requires an understanding of the different types of instability. Methods: A literature review was performed to identify information pertinent to midflexion instability in primary total knee replacement, utilising PRISMA guidelines. Databases searched included Embase, Medline, All of the Cochrane Library, PubMed and cross references. Results: Three factors, i.e., elevated joint line, multiradii femoral component and medial collateral ligament (MCL laxity, were identified to influence midflexion instability. Literature suggested mediolateral instability at 30–60° of flexion as diagnostic of midflexion instability. Literature search also revealed paucity in clinical studies analysing midflexion instability. Most of the evidence was obtained from cadaveric studies for elevated joint line and MCL laxity. Clinical studies on multiradii femoral component were limited by their small study size and early followup period. Conclusion: Elevated joint line, multiradii femoral component and MCL laxity have been suggested to cause midflexion laxity in primary TKR. Due to limitations in available evidence, this review was unable to raise the strength of overall evidence. Future well-designed clinical studies are essential to make definitive conclusions. This review serves as a baseline for future researchers and creates awareness for routine assessment of midflexion instability in primary total knee replacement.

A review of investigations on flow instabilities in natural circulation boiling loops

International Nuclear Information System (INIS)

Gonella V Durga Prasad; Manmohan Pandey; Manjeet S Kalra

2005-01-01

Full text of publication follows: Steam generation systems are subjected to flow instabilities due to parametric fluctuations, inlet conditions etc., which may result in mechanical vibrations of components (called flow induced vibrations) and system control problems. Analysis of these instabilities in natural circulation boiling loops is very important for the safety of nuclear reactors and other boiling systems. This paper presents the state of the art in this area by reviewing over 100 contributions made in the past 30 years. A large number of experimental and numerical investigations have been conducted to study and understand the conditions for inception of flow instabilities, parametric effects of instabilities, and the system behavior under such conditions. Work done on instabilities due to channel thermal-hydraulics as well as neutronics-thermohydraulics coupling has been reviewed. Different methods of analysis used by researchers and results obtained by them have been discussed. Various numerical techniques adopted and computer codes developed have also been discussed. The knowledge obtained from the investigations made in the past three decades has been summarized to present the state of the art of the understanding of flow instabilities. (authors)

Telomere dysfunction and chromosome instability

Energy Technology Data Exchange (ETDEWEB)

Murnane, John P., E-mail: jmurnane@radonc.ucsf.edu [Department of Radiation Oncology, University of California San Francisco, 2340 Sutter Street, San Francisco, CA 94143-1331 (United States)

2012-02-01

The ends of chromosomes are composed of a short repeat sequence and associated proteins that together form a cap, called a telomere, that keeps the ends from appearing as double-strand breaks (DSBs) and prevents chromosome fusion. The loss of telomeric repeat sequences or deficiencies in telomeric proteins can result in chromosome fusion and lead to chromosome instability. The similarity between chromosome rearrangements resulting from telomere loss and those found in cancer cells implicates telomere loss as an important mechanism for the chromosome instability contributing to human cancer. Telomere loss in cancer cells can occur through gradual shortening due to insufficient telomerase, the protein that maintains telomeres. However, cancer cells often have a high rate of spontaneous telomere loss despite the expression of telomerase, which has been proposed to result from a combination of oncogene-mediated replication stress and a deficiency in DSB repair in telomeric regions. Chromosome fusion in mammalian cells primarily involves nonhomologous end joining (NHEJ), which is the major form of DSB repair. Chromosome fusion initiates chromosome instability involving breakage-fusion-bridge (B/F/B) cycles, in which dicentric chromosomes form bridges and break as the cell attempts to divide, repeating the process in subsequent cell cycles. Fusion between sister chromatids results in large inverted repeats on the end of the chromosome, which amplify further following additional B/F/B cycles. B/F/B cycles continue until the chromosome acquires a new telomere, most often by translocation of the end of another chromosome. The instability is not confined to a chromosome that loses its telomere, because the instability is transferred to the chromosome donating a translocation. Moreover, the amplified regions are unstable and form extrachromosomal DNA that can reintegrate at new locations. Knowledge concerning the factors promoting telomere loss and its consequences is

Effects of balance training by knee joint motions on muscle activity in adult men with functional ankle instability.

Science.gov (United States)

Nam, Seung-Min; Kim, Won-Bok; Yun, Chang-Kyo

2016-05-01

[Purpose] This study examined the effects of balance training by applying knee joint movements on muscle activity in male adults with functional ankle instability. [Subjects and Methods] 28 adults with functional ankle instability, divided randomly into an experimental group, which performed balance training by applying knee joint movements for 20 minutes and ankle joint exercises for 10 minutes, and a control group, which performed ankle joint exercise for 30 minutes. Exercises were completed three times a week for 8 weeks. Electromyographic values of the tibialis anterior, peroneus longus, peroneus brevis, and the lateral gastrocnemius muscles were obtained to compare and analyze muscle activity before and after the experiments in each group. [Results] The experimental group had significant increases in muscle activity in the tibialis anterior, peroneus longus, and lateral gastrocnemius muscles, while muscle activity in the peroneus brevis increased without significance. The control group had significant increases in muscle activity in the tibialis anterior and peroneus longus, while muscle activity in the peroneus brevis and lateral gastrocnemius muscles increased without significance. [Conclusion] In conclusion, balance training by applying knee joint movements can be recommended as a treatment method for patients with functional ankle instability.

Systematics of shoulder instability; Systematik der Schulterinstabilitaet

Energy Technology Data Exchange (ETDEWEB)

Kreitner, K.F.; Maehringer-Kunz, A. [Johannes-Gutenberg-Universitaet Mainz, Klinik und Poliklinik fuer Diagnostische und Interventionelle Radiologie, Mainz (Germany)

2015-03-01

Shoulder instability is defined as a symptomatic abnormal motion of the humeral head relative to the glenoid during active shoulder motion. Glenohumeral instabilities are classified according to the causative factors as the pathogenesis of instability plays an important role with respect to treatment options. Instabilities are classified into traumatic and atraumatic instabilities as part of a multidirectional instability syndrome and into microtraumatic instabilities. For diagnostics plain radiographs (''trauma series'') are performed to document shoulder dislocation and its successful repositioning. Direct magnetic resonance (MR) arthrography is the most important imaging modality for delineation of the different injury patterns of the labral-ligamentous complex and bony structures. Monocontrast computed tomography (CT) arthrography with the use of multidetector CT scanners represents an alternative imaging modality; however, MR imaging should be preferred in the work-up of shoulder instabilities due to the mostly younger age of patients. (orig.) [German] Unter einer Schulterinstabilitaet versteht man jede zu Beschwerden fuehrende Translation des Humeruskopfs in Relation zur Gelenkpfanne waehrend einer aktiven Bewegung der Schulter. Glenohumerale Instabilitaeten werden heute nach ihrer Aetiologie eingeteilt, da bei der Wahl der Therapie der Entstehungsmechanismus der Instabilitaet eine wichtige Rolle spielt. Danach unterscheidet man primaer traumatisch von atraumatisch entstandenen Instabilitaeten sowie Mikroinstabilitaeten. Bei der Diagnostik dienen konventionelle Roentgenuebersichtsaufnahmen nur noch zur Dokumentation einer Luxation und zur Beurteilung der Reposition. Die durch eine Instabilitaet hervorgerufenen Verletzungsfolgen am labroligamentaeren Komplex und den knoechernen Strukturen werden heute bevorzugt mit der direkten MR-Arthrographie dargestellt. Hierbei koennen unterschiedliche Verletzungsmuster dargestellt werden. Nach

Numerical modeling of flow boiling instabilities using TRACE

International Nuclear Information System (INIS)

Kommer, Eric M.

2015-01-01

Highlights: • TRACE was used to realistically model boiling instabilities in single and parallel channel configurations. • Model parameters were chosen to exactly mimic other author’s work in order to provide for direct comparison of results. • Flow stability maps generated by the model show unstable flow at operating points similar to other authors. • The method of adjudicating when a flow is “unstable” is critical in this type of numerical study. - Abstract: Dynamic flow instabilities in two-phase systems are a vitally important area of study due to their effects on a great number of industrial applications, including heat exchangers in nuclear power plants. Several next generation nuclear reactor designs incorporate once through steam generators which will exhibit boiling flow instabilities if not properly designed or when operated outside design limits. A number of numerical thermal hydraulic codes attempt to model instabilities for initial design and for use in accident analysis. TRACE, the Nuclear Regulatory Commission’s newest thermal hydraulic code is used in this study to investigate flow instabilities in both single and dual parallel channel configurations. The model parameters are selected as to replicate other investigators’ experimental and numerical work in order to provide easy comparison. Particular attention is paid to the similarities between analysis using TRACE Version 5.0 and RELAP5/MOD3.3. Comparison of results is accomplished via flow stability maps non-dimensionalized via the phase change and subcooling numbers. Results of this study show that TRACE does indeed model two phase flow instabilities, with the transient response closely mimicking that seen in experimental studies. When compared to flow stability maps generated using RELAP, TRACE shows similar results with differences likely due to the somewhat qualitative criteria used by various authors to determine when the flow is truly unstable

Coherent Instabilities of ILC Damping Ring

Energy Technology Data Exchange (ETDEWEB)

Heifets, S.; Stupakov, G.; Bane, K.; /SLAC

2006-09-27

The paper presents the first attempt to estimates the ILC damping ring impedance and compare thresholds of the classical instabilities for several designs initially proposed for the DR. The work was carried out in the spring of 2006. Since then the choice of the DR is narrowed. Nevertheless, the analysis described may be useful for the next iterations of the beam stability. Overall, the conventional instabilities will have little impact on the ring performance provided the careful design of the ring minimizes the impedance below acceptable level indicated above. The only exception is the transverse CB instability. The longitudinal CB is less demanding. However, even the transverse CB instability would have threshold current above nominal provided the aperture in the wigglers is increased from 8 mm to 16 mm. The microwave instability needs more studies. Nevertheless, we should remember that the ILC DR is different from existing high-current machines at least in two respects: absence of the beam-beam tune spread stabilizing beams in colliders, and unusual strict requirements for low emittance. That may cause new problems such as bunch emittance dilution due to high-frequency wakes (BPMs, grooves), etc. Even if such a possibility exists, it probably universal for all machines and ought be addressed in the design of vacuum components rather than have effect on the choice of the machine design.

Ion cyclotron emission due to collective instability of fusion products and beam ions in TFTR and JET

International Nuclear Information System (INIS)

Dendy, R.O.; Clements, K.G.; Lashmore-Davies, C.N.; Cottrell, G.A.; Majeski, R.; Cauffman, S.

1995-06-01

Ion cyclotron emission (ICE) has been observed from neutral beam-heated TFTR and JET tritium experiments at sequential cyclotron harmonics of both fusion products and beam ions. The emission originates from the outer mid-plane plasma, where fusion products and beam ions are likely to have a drifting ring-type velocity-space distribution which is anisotropic and sharply peaked. Fusion product-driven ICE in both TFTR and JET can be attributed to the magnetoacoustic cyclotron instability, which involves the excitation of obliquely propagating waves on the fast Alfven/ion Bernstein branch at cyclotron harmonics of the fusion products. Differences between ICE observations in JET and TFTR appear to reflect the sensitivity of the instability growth rate to the ratio υ birth /c A , where υ birth is the fusion product birth speed and c A is the local Alfven speed:for fusion products in the outer midplane edge of TFTR, υ birth A ; for alpha-particles in the outer midplane edge of JET, the opposite inequality applies. If sub-Alfvenic fusion products are isotropic or have undergone even a moderate degree of thermalization, the magnetoacoustic instability cannot occur. In contrast, the super-Alfvenic alpha-particles which are present in the outer mid-plane of JET can drive the magnetoacoustic cyclotron instability even if they are isotropic or have a relatively broad distribution of speeds. These conclusions may account for the observation that fusion product-driven ICE in JET persists for longer than fusion product-driven ICE in TFTR. (Author)

Assessment of Flow Instability in Passive Auxiliary Feedwater System (PAFS) Using RELAP5

Energy Technology Data Exchange (ETDEWEB)

Jeon, Seong-Su; Hong, Soon-Joon [FNC Tech., Yongin (Korea, Republic of); Cheon, Jong; Kim, Han-Gon [KHNP, Daejeon (Korea, Republic of)

2015-10-15

In this study, the occurrence possibility of both instabilities in PAFS is assessed with the best-estimate thermal hydraulic code, RELAP5. From the RELAP5 code analysis, the Ledinegg instability might not occur in PAFS. The DWO might occur in PAFS but the effect of the oscillation on the heat removal capacity of PAFS was not large. Therefore, it is concluded that PAFS is safe in terms of flow instabilities. Since PAFS is two-phase flow system, flow instabilities may occur. Flow instabilities may cause the severe deterioration of heat removal capability of PAFS due to the reduction of the condensate flow. For the reliable operation of PAFS, it is required to assess the flow instabilities in PAFS. The Ledinegg-type instability and the Density Wave Oscillation (DWO) are the representative static flow instability and the dynamic flow instability, respectively.

Neuromuscular control and ankle instability.

Science.gov (United States)

Gutierrez, Gregory M; Kaminski, Thomas W; Douex, Al T

2009-04-01

Lateral ankle sprains (LAS) are common injuries in athletics and daily activity. Although most are resolved with conservative treatment, others develop chronic ankle instability (AI)-a condition associated with persistent pain, weakness, and instability-both mechanical (such as ligamentous laxity) and functional (neuromuscular impairment with or without mechanical laxity). The predominant theory in AI is one of articular deafferentation from the injury, affecting closed-loop (feedback/reflexive) neuromuscular control, but recent research has called that theory into question. A considerable amount of attention has been directed toward understanding the underlying causes of this pathology; however, little is known concerning the neuromuscular mechanisms behind the development of AI. The purpose of this review is to summarize the available literature on neuromuscular control in uninjured individuals and individuals with AI. Based on available research and reasonable speculation, it seems that open-loop (feedforward/anticipatory) neuromuscular control may be more important for the maintenance of dynamic joint stability than closed-loop control systems that rely primarily on proprioception. Therefore, incorporating perturbation activities into patient rehabilitation schemes may be of some benefit in enhancing these open-loop control mechanisms. Despite the amount of research conducted in this area, analysis of individuals with AI during dynamic conditions is limited. Future work should aim to evaluate dynamic perturbations in individuals with AI, as well as subjects who have a history of at least one LAS and never experienced recurrent symptoms. These potential findings may help elucidate some compensatory mechanisms, or more appropriate neuromuscular control strategies after an LAS event, thus laying the groundwork for future intervention studies that can attempt to reduce the incidence and severity of acute and chronic lateral ankle injury.

Onset of Darrieus-Landau Instability in Expanding Flames

Science.gov (United States)

Mohan, Shikhar; Matalon, Moshe

2017-11-01

The effect of small amplitude perturbations on the propagation of circular flames in unconfined domains is investigated, computationally and analytically, within the context of the hydrodynamic theory. The flame, treated as a surface of density discontinuity separating fresh combustible mixture from the burnt gas, propagates at a speed dependent upon local curvature and hydrodynamic strain. For mixtures with Lewis numbers above criticality, thermodiffusive effects have stabilizing influences which largely affect the flame at small radii. The amplitude of these disturbances initially decay and only begin to grow once a critical radius is reached. This instability is hydrodynamic in nature and is a consequence of thermal expansion. Through linear stability analysis, predictions of critical flame radius at the onset of instability are obtained as functions of Markstein length and thermal expansion coefficients. The flame evolution is also examined numerically where the motion of the interface is tracked via a level-set method. Consistent with linear stability results, simulations show the flame initially remaining stable and the existence of a particular mode that will be first to grow and later determine the cellular structure observed experimentally at the onset of instability.

Adiabatic instability in coupled dark energy/dark matter models

International Nuclear Information System (INIS)

Bean, Rachel; Flanagan, Eanna E.; Trodden, Mark

2008-01-01

We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the Universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, which can also be thought of as a type of Jeans instability, is characterized by a negative sound speed squared of an effective coupled dark matter/dark energy fluid, and results in the exponential growth of small scale modes. We discuss the role of the instability in specific coupled cold dark matter and mass varying neutrino models of dark energy and clarify for these theories the regimes in which the instability can be evaded due to nonadiabaticity or weak coupling.

Experimental study on low pressure flow instability

International Nuclear Information System (INIS)

Jiang Shengyao; Wu Xinxin; Wu Shaorong; Bo Jinhai; Zhang Youjie

1997-05-01

The experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of the 5 MW reactor. The flow behavior for a wide range of inlet subcooling, in which the flow undergoes from single phase to two phase, is described in a natural circulation system at low pressure (p = 0.1, 0.24 MPa). Several kinds of flow instability, e.g. subcooled boiling instability, subcooled boiling induced flashing instability, pure flashing instability as well as flashing coupled density wave instability and high frequency flow oscillation, are investigated. The mechanism of flashing and flashing concerned flow instability, which has never been studied well in this field, is especially interpreted. The experimental results show that, firstly, for a low pressure natural circulation system the two phase flow is unstable in most of inlet subcooling conditions, the two phase stable flow can only be reached at very low inlet subcooling; secondly, at high inlet subcooling the flow instability is dominated by subcooled boiling in the heated section, and at middle inlet subcooling is dominated by void flashing in the adiabatic long riser; thirdly, in two phase stable flow region the condition for boiling out of the core, namely, single phase flow in the heated section, two phase flow in the riser due to vapor flashing, can be realized. The experimental results are very important for the design and accident analysis of the vessel and swimming pool type natural circulation nuclear heating reactor. (7 refs., 10 figs., 1 tab.)

Ion cyclotron instability saturation and turbulent plasma heating in the presence of ions moving across the magnetic field

International Nuclear Information System (INIS)

Mikhajlenko, V.S.; Stepanov, K.N.

1981-01-01

Ion cyclotron instability saturation is considered in terms of the turbulence theory when there is a beam of heavy ions with large thermal longitudinal velocity spread. The instability excitation is due to a cyclotron interaction with ions of the beam under the anomalous Doppler effect. The instability is shown to be saturated due to an induced plasma ion scattering of ion cyclotron waves when the beam ion charge number Zsub(b) is approximately 1. Decay processes, wave scattering by virtual wave polarization clouds and resonance broadening due to random walk of plasma ions in turbulent instability fields appear to be unimportant. For Zsub(b)>>1 the induced wave scattering by the beam ions is the main process determining the nonlinear stage of the instability. Estimates are given for the oscillation energy density in the instability saturation state and for the turbulent heating rate of plasma and beam ions [ru

TRANSMISSION LINE-WIRE DANCING (GALLOPING – LYAPUNOV INSTABILITY

Directory of Open Access Journals (Sweden)

V. I. Vanko

2014-01-01

Full Text Available This article describes aerodynamic losses of damping, or aerodynamic instability, which we observe in experiments and in engineering practice. As applied to industrial high-voltage lines this phenomenon is usually called galloping (dancing of phase line wires. This phenolmenon can be explained by Lyapunov’s instability of equilibrium state of wires profile (cross-section. In addition to known condition of Grauert-den-Hartog’s instability there was obtained practical condition of instability, which depends only on stationary aerodynamic profile’s factor – dimensionless coefficient of head resistance and lift coefficient, and also on their derivative with respect to the angle of attack.There was suggested an effective numerical-analytical method of investigation of stability for equilibrium of profile’s state in flow, which was developed at the department “Applied mathematics” of Bauman MSTU. This method allows to determine the stationary aerodynamics characteristics of profile by numerical simulation of profile flow under different angles of attack by vortex element method and later on the application of analytical conditions of stability and Lyapunov’s instability of equilibrium positions. The obtained results during the investigation of rhombic and square profiles stability, as well as general profile of iced wire, and their comparisons with the known experiments’ results in aerodynamic tubes indicate the precision of developed methods and algorithms. The usage of mesh-free Lagrange method of vortex elements and software for their realization allows to solve also dual problems of aerohydroelasticity and to carry out direct numerical simulation of profile movement in flow. In this article the investigations’ results of different authors in this field were taken into account.

Buneman instability and Pierce instability in a collisionless bounded plasma

International Nuclear Information System (INIS)

Iizuka, Satoru; Saeki, Koichi; Sato, Noriyoshi; Hatta, Yoshisuke

1983-01-01

A systematic experiment is performed on the Buneman instability and the Pierce instability in a bounded plasma consisting of beam electrons and stationary ions. Current fluctuations are confirmed to be induced by the Buneman instability. On the other hand, the Pierce instability gives rise to a current limitation. The phenomena are well explained by Mikhailovskii's theory taking account of ion motion in a bounded plasma. (author)

Stripes instability of an oscillating non-Brownian iso-dense suspension of spheres

Science.gov (United States)

Roht, Y. L.; Ippolito, I.; Hulin, J. P.; Salin, D.; Gauthier, G.

2018-03-01

We analyze experimentally the behavior of a non-Brownian, iso-dense suspension of spheres submitted to periodic square wave oscillations of the flow in a Hele-Shaw cell of gap H. We do observe an instability of the initially homogeneous concentration in the form of concentration variation stripes transverse to the flow. The wavelength of these regular spatial structures scales roughly as the gap of the cell and is independent of the particle concentration and of the period of oscillation. This instability requires large enough particle volume fractions φ≥ 0.25 and a gap large enough compared to the sphere diameter (H/d ≥ 8) . Mapping the domain of the existence of this instability in the space of the control parameters shows that it occurs only in a limited range of amplitudes of the fluid displacement. The analysis of the concentration distribution across the gap supports a scenario of particle migration towards the wall followed by an instability due to a particle concentration gradient with a larger concentration at the walls. In order to account for the main features of this stripes instability, we use the theory of longitudinal instability due to normal stresses difference and recent observations of a dependence of the first normal stresses difference on the particle concentration.

Reducing loss in lateral charged-particle equilibrium due to air cavities present in x-ray irradiated media by using longitudinal magnetic fields

International Nuclear Information System (INIS)

Naqvi, Shahid A.; Li, X. Allen; Ramahi, Shada W.; Chu, James C.; Ye, Sung-Joon

2001-01-01

The underdosing of lesions distal to air cavities, such as those found in upper respiratory passages, occurs due to the loss in lateral charged-particle equilibrium (CPE). The degree of underdosing worsens for smaller field sizes, resulting in more frequent recurrence of the cancer treated. Higher photon energies further aggravate the outcome by producing longer second build-up regions beyond the cavity. Besides underdosing, the larger lateral spread of secondary electron fluence in the air cavity produces diffuse dose distributions at the tissue-air interface for shaped or intensity modulated fields. These disequilibrium effects create undesirable deviations from the intended treatment. The clinical concern is further intensified by the failure of traditional treatment planning systems to even account for such defects. In this work, the use of longitudinal magnetic fields on the order of 0.5 T is proposed for alleviating lateral electronic disequilibrium due to the presence of air cavities in the irradiated volume. The magnetic field enforces lateral CPE by restricting the lateral range of electrons in the air cavity. The problem is studied in a simple water-air-water slab geometry using EGS4 Monte Carlo simulations for 6 MV photons. Electronic disequilibrium is evaluated for beams of various sizes, shapes and intensity distributions constructed by linear superposition of the dose distributions for 0.5x0.5 cm 2 beamlets. Comparison is also made with 60 Co irradiation. The results indicate that the lateral confinement of secondary electrons in the air cavity by sub-MRI strength longitudinal fields is effective in reducing deterioration of dose distributions near tissue-air interfaces. This can potentially reduce recurrence rates of cancers such as the larynx carcinoma

Blob Formation and Ejection in Coronal Jets due to the Plasmoid and Kelvin–Helmholtz Instabilities

Energy Technology Data Exchange (ETDEWEB)

Ni, Lei; Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming, 650216 (China); Zhang, Qing-Min [Key Laboratory for Dark Matter and Space Science, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Murphy, Nicholas A., E-mail: leini@ynao.ac.cn [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2017-05-20

We perform 2D resistive magnetohydrodynamic simulations of coronal jets driven by flux emergence along the lower boundary. The reconnection layers are susceptible to the formation of blobs that are ejected in the jet. Our simulation with low plasma β (Case I) shows that magnetic islands form easily and propagate upward in the jet. These islands are multithermal and thus are predicted to show up in hot channels (335 Å and 211 Å) and the cool channel (304 Å) in observations by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory . The islands have maximum temperatures of 8 MK, lifetimes of 120 s, diameters of 6 Mm, and velocities of 200 km s{sup −1}. These parameters are similar to the properties of blobs observed in extreme-ultraviolet (EUV) jets by AIA. The Kelvin–Helmholtz instability develops in our simulation with moderately high plasma β (Case II) and leads to the formation of bright vortex-like blobs above the multiple high magnetosonic Mach number regions that appear along the jet. These vortex-like blobs can also be identified in the AIA channels. However, they eventually move downward and disappear after the high magnetosonic Mach number regions disappear. In the lower plasma β case, the lifetime for the jet is shorter, the jet and magnetic islands are formed with higher velocities and temperatures, the current-sheet fragments are more chaotic, and more magnetic islands are generated. Our results show that the plasmoid instability and Kelvin–Helmholtz instability along the jet are both possible causes of the formation of blobs observed at EUV wavelengths.

Parametric instabilities in advanced gravitational wave detectors

International Nuclear Information System (INIS)

Gras, S; Zhao, C; Blair, D G; Ju, L

2010-01-01

As the LIGO interferometric gravitational wave detectors have finished gathering a large observational data set, an intense effort is underway to upgrade these observatories to improve their sensitivity by a factor of ∼10. High circulating power in the arm cavities is required, which leads to the possibility of parametric instability due to three-mode opto-acoustic resonant interactions between the carrier, transverse optical modes and acoustic modes. Here, we present detailed numerical analysis of parametric instability in a configuration that is similar to Advanced LIGO. After examining parametric instability for a single three-mode interaction in detail, we examine instability for the best and worst cases, as determined by the resonance condition of transverse modes in the power and signal recycling cavities. We find that, in the best case, the dual recycling detector is substantially less susceptible to instability than a single cavity, but its susceptibility is dependent on the signal recycling cavity design, and on tuning for narrow band operation. In all cases considered, the interferometer will experience parametric instability at full power operation, but the gain varies from 3 to 1000, and the number of unstable modes varies between 7 and 30 per test mass. The analysis focuses on understanding the detector complexity in relation to opto-acoustic interactions, on providing insights that can enable predictions of the detector response to transient disturbances, and of variations in thermal compensation conditions.

An instability due to the nonlinear coupling of p-modes to g-modes: Implications for coalescing neutron star binaries

International Nuclear Information System (INIS)

Weinberg, Nevin N.; Arras, Phil; Burkart, Joshua

2013-01-01

A weakly nonlinear fluid wave propagating within a star can be unstable to three-wave interactions. The resonant parametric instability is a well-known form of three-wave interaction in which a primary wave of frequency ω a excites a pair of secondary waves of frequency ω b + ω c ≅ ω a . Here we consider a nonresonant form of three-wave interaction in which a low-frequency primary wave excites a high-frequency p-mode and a low-frequency g-mode such that ω b + ω c >> ω a . We show that a p-mode can couple so strongly to a g-mode of similar radial wavelength that this type of nonresonant interaction is unstable even if the primary wave amplitude is small. As an application, we analyze the stability of the tide in coalescing neutron star binaries to p-g mode coupling. We find that the equilibrium tide and dynamical tide are both p-g unstable at gravitational wave frequencies f gw ≳ 20 Hz and drive short wavelength p-g mode pairs to significant energies on very short timescales (much less than the orbital decay time due to gravitational radiation). Resonant parametric coupling to the tide is, by contrast, either stable or drives modes at a much smaller rate. We do not solve for the saturation of the p-g instability and therefore we cannot say precisely how it influences the evolution of neutron star binaries. However, we show that if even a single daughter mode saturates near its wave breaking amplitude, the p-g instability of the equilibrium tide will (1) induce significant orbital phase errors (Δφ ≳ 1 radian) that accumulate primarily at low frequencies (f gw ≲ 50 Hz) and (2) heat the neutron star core to a temperature of T ∼ 10 10 K. Since there are at least ∼100 unstable p-g daughter pairs, Δφ and T are potentially much larger than these values. Tides might therefore significantly influence the gravitational wave signal and electromagnetic emission from coalescing neutron star binaries at much larger orbital separations than previously

It's time to change perspective! New diagnostic tools for lateral elbow pain.

Science.gov (United States)

Arrigoni, P; Cucchi, D; Menon, A; Randelli, P

2017-12-01

The presence of intra-articular findings that may complement the extra-articular pathology in lateral epicondilytis has been suggested, and a role for minor instability of the elbow as part of the causative process of this disease has been postulated. This study was designed to describe two new clinical tests, aimed at detecting intra-articular pathology in patients affected by recalcitrant lateral epicondylitis and investigate their diagnostic performance. Ten patients suffering of atraumatic lateral elbow pain unresponsive to conservative treatment were considered in this study. Two clinical tests were developed and administrated prior to arthroscopy: Supination and Antero-Lateral pain Test (SALT); Posterior Elbow Pain by Palpation-Extension of the Radiocapitellar joint (PEPPER). Sensitivity, specificity, predictive values and accuracy of SALT and PEPPER as diagnostic tests for seven intra-articular findings were calculated. In 90% of the patients, at least one test was positive. All patients with signs of lateral ligamentous patholaxity or intra-articular abnormal findings had a positive response to at least one of the two tests. SALT proved to have a high sensitivity but a low specificity and is accurate in detecting the presence of intra-articular abnormal findings, especially synovitis. PEPPER test was sensible, specific and accurate in the detection of radial head chondropathy. Two new diagnostic tests (SALT and PEPPER) were specifically designed to evoke pain from intra-articular structures. These tests could be a valid support in the diagnostic algorithm of recalcitrant lateral elbow pain. Positive findings may be indicative of a minor instability of the lateral elbow condition. Diagnostic study, development of diagnostic criteria on basis of consecutive patients, level II.

Preliminary results of an anteverting triple periacetabular osteotomy for the treatment of hip instability in Down syndrome.

Science.gov (United States)

Maranho, D A; Kim, Y-J; Williams, K A; Novais, E N

2018-02-01

To investigate the outcomes of an anteverting triple periacetabular osteotomy for the treatment of hip instability in skeletally immature patients with Down syndrome. We evaluated 16 patients (21 hips) with Down syndrome and hip instability who underwent an anteverting triple periacetabular osteotomy between 2007 and 2016. There were nine females and seven males with an average age of 7.4 years SD 2.0. We assessed the level of hip pain, gait ability and clinical stability at a minimum of one year after surgery. Radiographic evaluation included pre- and postoperative lateral centre-edge angle (LCEA), Tönnis acetabular angle and extrusion index. After an average follow-up of 4.1 years SD 2.6, 20 of 21 hips (95%) remained clinically stable. In all, 12 of 16 (75%) patients had a full gait without a major limp, but three patients (19%) had a persistent limp. Of the 21 procedures, one hip (5%) was considered a failure due to persistent instability. There was a mean increase of 18.3º SD 15.3º of the LCEA (p treatment of an infection; which was considered a major complication. The anteverting triple periacetabular osteotomy provided global deformity correction and achieved hip stability in 95% of the hips after a mean follow-up of 4.1 years. Therapeutic level IV.

Instabilities in inhomogeneous plasma

International Nuclear Information System (INIS)

Mikhailovsky, A.B.

1983-01-01

The plasma inhomogeneity across the magnetic field causes a wide class of instabilities which are called instabilities of an inhomogeneous plasma or gradient instabilities. The instabilities that can be studied in the approximation of a magnetic field with parallel straight field lines are treated first, followed by a discussion of the influence of shear on these instabilities. The instabilities of a weakly inhomogeneous plasma with the Maxwellian velocity distribution of particles caused by the density and temperature gradients are often called drift instabilities, and the corresponding types of perturbations are the drift waves. An elementary theory of drift instabilities is presented, based on the simplest equations of motion of particles in the field of low-frequency and long-wavelength perturbations. Following that is a more complete theory of inhomogeneous collisionless plasma instabilities which uses the permittivity tensor and, in the case of electrostatic perturbations, the scalar of permittivity. The results are used to study the instabilities of a strongly inhomogeneous plasma. The instabilities of a plasma in crossed fields are discussed and the electromagnetic instabilities of plasma with finite and high pressure are described. (Auth.)

Arthroscopic management of the contact athlete with instability.

Science.gov (United States)

Harris, Joshua D; Romeo, Anthony A

2013-10-01

The shoulder is the most commonly dislocated joint in the body, with a greater incidence of instability in contact and collision athletes. In contact and collision athletes that have failed nonoperative treatment, the most important factors to consider when planning surgery are amount of bone loss (glenoid, humeral head); patient age; and shoulder hyperlaxity. Clinical outcomes, instability recurrence rate, and return to sport rate are not significantly different between arthroscopic suture anchor and open techniques. Lateral decubitus positioning with distraction and four portal (including seven-degree and 5-o’clock positions) techniques allow for 360-degree access to the glenoid rim, with placement of at least three sutures anchors below 3 o’clock for optimal results. In patients with significant glenoid bone loss (>20%-25%, inverted pear glenoid), open bone augmentation techniques are indicated and arthroscopic techniques are contraindicated. Copyright © 2013 Elsevier Inc. All rights reserved.

Ion cyclotron emission due to collective instability of fusion products and beam ions in TFTR and JET

International Nuclear Information System (INIS)

Dendy, R.O.; McClements, K.G.; Lashmore Davies, C.N.; Cottrell, G.A.; Majeski, R.; Cauffman, S.

1995-01-01

Ion cyclotron emission (ICE) has been observed from neutral beam heated TFTR and JET tritium experiments at sequential cyclotron harmonics of both fusion products and beam ions. The emission originates from the outer midplane plasma, where fusion products and beam ions are likely to have a drifting ring-type velocity-space distribution that is anisotropic and sharply peaked. Fusion product driven ICE can be attributed to the magnetoacoustic cyclotron instability, which involves the excitation of obliquely propagating waves on the fast Alfven/ion Bernstein branch at cyclotron harmonics of the fusion products. Differences between ICE observations in JET and TFTR appear to reflect the sensitivity of the instability growth rate to the ratio υ birth /c A , where υ birth is the fusion product birth speed and c A is the local Alfven speed: for fusion products in the outer midplane edge of TFTR supershots, υ birth A ; for alpha particles in the outer midplane edge of JET, the opposite inequality applies. If sub-Alfvenic fusion products are isotropic or have undergone even a moderate degree of thermalization, the magnetoacoustic instability cannot occur. In contrast, the super-Alfvenic alpha particles that are present in the outer midplane of JET can drive the magnetoacoustic cyclotron instability even if they are isotropic or have a relatively broad distribution of speeds. These conclusions may account for the observation that fusion product driven ICE in JET persists for longer than fusion product driven ICE in TFTR. A separate mechanism is proposed for the excitation of beam driven ICE in TFTR: electrostatic ion cyclotron harmonic waves, supported by strongly sub-Alfvenic beam ions, can be destabilized by a low concentration of such ions with a very anrrow spread of velocities in the parallel direction. 25 refs, 14 figs

Instabilities of collisionless current sheets revisited: The role of anisotropic heating

International Nuclear Information System (INIS)

Muñoz, P. A.; Kilian, P.; Büchner, J.

2014-01-01

In this work, we investigate the influence of the anisotropic heating on the spontaneous instability and evolution of thin Harris-type collisionless current sheets, embedded in antiparallel magnetic fields. In particular, we explore the influence of the macroparticle shape-function using a 2D version of the PIC code ACRONYM. We also investigate the role of the numerical collisionality due to the finite number of macroparticles in PIC codes. It is shown that it is appropriate to choose higher order shape functions of the macroparticles compared to a larger number of macroparticles per cell. This allows to estimate better the anisotropic electron heating due to the collisions of macroparticles in a PIC code. Temperature anisotropies can stabilize the tearing mode instability and trigger additional current sheet instabilities. We found a good agreement between the analytically derived threshold for the stabilization of the anisotropic tearing mode and other instabilities, either spontaneously developing or initially triggered ones. Numerical effects causing anisotropic heating at electron time scales become especially important for higher mass ratios (above m i /m e =180). If numerical effects are carefully taken into account, one can recover the theoretical estimated linear growth rates of the tearing instability of thin isotropic collisionless current sheets, also for higher mass ratios

Kinetic instabilities in relativistic plasmas: the Harris instability revisited

International Nuclear Information System (INIS)

Tautz, R.C.

2008-01-01

Plasma instabilities that generate aperiodic fluctuations are of outstanding importance in the astrophysical context. Two prominent examples are the electromagnetic Weibel instability and the electrostatic Harris instability, which operate in initially non-magnetized and magnetized plasmas, respectively. In this talk, the original formulation of the Harris instability will be reviewed and generalizations will be presented such as the inclusion of (1) relativistic effects, (2) ion effects, and (3) mode coupling. It will be shown that, with these modifications, a powerful method has been developed for the determination of both the existence and the growth rate of low-frequency instabilities. Applications can be found in astrophysical jets, where the rest frame can be used and so no parallel motion is present. At the end of the talk, how the particle composition of gamma-ray burst jets can be predicted using the Harris technique. (author)

Simple model with damping of the mode-coupling instability

Energy Technology Data Exchange (ETDEWEB)

Pestrikov, D V [AN SSSR, Novosibirsk (Russian Federation). Inst. Yadernoj Fiziki

1996-08-01

In this paper we use a simple model to study the suppression of the transverse mode-coupling instability. Two possibilities are considered. One is due to the damping of particular synchrobetatron modes, and another - due to Landau damping, caused by the nonlinearity of betatron oscillations. (author)

Computer simulations of electromagnetic cool ion beam instabilities. [in near earth space

Science.gov (United States)

Gary, S. P.; Madland, C. D.; Schriver, D.; Winske, D.

1986-01-01

Electromagnetic ion beam instabilities driven by cool ion beams at propagation parallel or antiparallel to a uniform magnetic field are studied using computer simulations. The elements of linear theory applicable to electromagnetic ion beam instabilities and the simulations derived from a one-dimensional hybrid computer code are described. The quasi-linear regime of the right-hand resonant ion beam instability, and the gyrophase bunching of the nonlinear regime of the right-hand resonant and nonresonant instabilities are examined. It is detected that in the quasi-linear regime the instability saturation is due to a reduction in the beam core relative drift speed and an increase in the perpendicular-to-parallel beam temperature; in the nonlinear regime the instabilities saturate when half the initial beam drift kinetic energy density is converted to fluctuating magnetic field energy density.

Instability timescale for the inclination instability in the solar system

Science.gov (United States)

Zderic, Alexander; Madigan, Ann-Marie; Fleisig, Jacob

2018-04-01

The gravitational influence of small bodies is often neglected in the study of solar system dynamics. However, this is not always an appropriate assumption. For example, mutual secular torques between low mass particles on eccentric orbits can result in a self-gravity instability (`inclination instability'; Madigan & McCourt 2016). During the instability, inclinations increase exponentially, eccentricities decrease (detachment), and orbits cluster in argument of perihelion. In the solar system, the orbits of the most distant objects show all three of these characteristics (high inclination: Volk & Malhotra (2017), detachment: Delsanti & Jewitt (2006), and argument of perihelion clustering: Trujillo & Sheppard (2014)). The inclination instability is a natural explanation for these phenomena.Unfortunately, full N-body simulations of the solar system are unfeasible (N ≈ O(1012)), and the behavior of the instability depends on N, prohibiting the direct application of lower N simulations. Here we present the instability timescale's functional dependence on N, allowing us to extrapolate our simulation results to that appropriate for the solar system. We show that ~5 MEarth of small icy bodies in the Sedna region is sufficient for the inclination instability to occur in the outer solar system.

Nonlinear evolution of tearing and coalescence instability with free boundary conditions

International Nuclear Information System (INIS)

Malara, F.; Veltri, P.; Carbone, V.

1990-01-01

The nonlinear evolution of a reconnection instability in a plane current sheet is described. In particular, the appearance of coalescence instability was studied, which follows the formation of a chain of magnetic islands due to the tearing instability. In order to describe realistically this phonemenon, the time evolution of all the unstable modes which are present in the spectrum at the same time is considered. Moreover, this study allows to investigate the turbulent energy cascade which forms owing to the nonlinear coupling between such modes. (R.P.) 9 refs.; 6 figs

Arthroscopic resection of humeroradial synovial plica for persistent lateral elbow pain.

Science.gov (United States)

Rajeev, Aysha; Pooley, Joesph

2015-04-01

To review the outcome of 121 patients who underwent arthroscopic resection of a humeroradial synovial plica for persistent lateral elbow pain. 92 men and 29 women aged 24 to 56 (mean, 38) years with chronic lateral elbow pain underwent arthroscopic resection of a humeroradial synovial plica using a motorised soft tissue shaver, followed by intensive physiotherapy. The modified elbow score and range of motion were assessed, as were wound healing, infection, soft tissue swelling or effusion, tenderness, ligamentous instability, and motor strength. No patient had any ligamentous instability. 80 patients were pain-free at 3 months; only 3 patients were taking pain medication at 6 months. All patients had full pronation and supination; the mean range of motion was 3º to 135º of flexion. The mean modified elbow score at 12 months was 93.2 (range, 72-100). The percentages of patients with excellent, good, fair, and poor score were 70%, 17%, 8%, and 5% at 3 months, 74%, 20%, 3%, and 3% at 6 months, and 76%, 18%, 3%, and 3% at 12 months, respectively. A humeroradial synovial plica is one of the causes of chronic lateral elbow pain. Arthroscopic resection of the synovial plica followed by intensive physiotherapy achieved good outcome.

Current-driven plasmonic boom instability in three-dimensional gated periodic ballistic nanostructures

Science.gov (United States)

Aizin, G. R.; Mikalopas, J.; Shur, M.

2016-05-01

An alternative approach of using a distributed transmission line analogy for solving transport equations for ballistic nanostructures is applied for solving the three-dimensional problem of electron transport in gated ballistic nanostructures with periodically changing width. The structures with varying width allow for modulation of the electron drift velocity while keeping the plasma velocity constant. We predict that in such structures biased by a constant current, a periodic modulation of the electron drift velocity due to the varying width results in the instability of the plasma waves if the electron drift velocity to plasma wave velocity ratio changes from below to above unity. The physics of such instability is similar to that of the sonic boom, but, in the periodically modulated structures, this analog of the sonic boom is repeated many times leading to a larger increment of the instability. The constant plasma velocity in the sections of different width leads to resonant excitation of the unstable plasma modes with varying bias current. This effect (that we refer to as the superplasmonic boom condition) results in a strong enhancement of the instability. The predicted instability involves the oscillating dipole charge carried by the plasma waves. The plasmons can be efficiently coupled to the terahertz electromagnetic radiation due to the periodic geometry of the gated structure. Our estimates show that the analyzed instability should enable powerful tunable terahertz electronic sources.

An analytical study on excitation of nuclear-coupled thermal-hydraulic instability due to seismically induced resonance in BWR

Energy Technology Data Exchange (ETDEWEB)

Hirano, Masashi [Japan Atomic Energy Research Institute, Ibaraki-ken (Japan)

1997-07-01

This paper describes the results of a scoping study on seismically induced resonance of nuclear-coupled thermal-hydraulic instability in BWRs, which was conducted by using TRAC-BF1 within a framework of a point kinetics model. As a result of the analysis, it is shown that a reactivity insertion could occur accompanied by in-surge of coolant into the core resulted from the excitation of the nuclear-coupled instability by the external acceleration. In order to analyze this phenomenon more in detail, it is necessary to couple a thermal-hydraulic code with a three-dimensional nuclear kinetics code.

Translation, cross-cultural adaption and validation of the German version of the Foot and Ankle Ability Measure for patients with chronic ankle instability.

Science.gov (United States)

Nauck, T; Lohrer, H

2011-08-01

The evaluation of health-related quality of life and physical function is important for determining therapeutic strategies following ankle injuries. The Anglo-American Foot and Ankle Ability Measure (FAAM) is a valid and reliable self-reported measure to detect functional deficits in chronic lateral ankle instability. The purpose of this study was to translate, cross-culturally adapt and validate the FAAM questionnaire for use with German-speaking patients with chronic lateral ankle instability. Preoperative and conservatively treated patients with chronic lateral ankle instability. Sport students and volleyball athletes served as control groups. The FAAM was forward and back translated, cross-culturally adapted and validated. The study population completed the FAAM-G questionnaire twice within 3-5 days. Additionally, the patients were scored with the Good ankle laxity classification system. Test-Retest reliability, construct validity and internal consistency were calculated. Reliability and validity of the FAAM-G were examined in presurgical chronic ankle instability patients (n=24), conservatively treated chronic ankle instability patients (n=17), university sport students (n=31) and volleyballers (n=37). Test-retest reliability revealed fair, good, or excellent reliability (inter-class correlation coefficient (ICC)=0.590-0.998; ρ=0.528-1.000). Construct validity, tested between the FAAM-G subscores and the Good et al ankle laxity classification system demonstrated strong correlations (ρ = -0.819 to -0.861). The original FAAM questionnaire was successfully translated and cross-culturally adapted from English to German. Corresponding to the Anglo-American version, the FAAM-G is a reliable and valid questionnaire for self-reported assessment of pain and disability in German-speaking patients suffering from chronic ankle instability.

Pump instability phenomena generated by fluid forces

Science.gov (United States)

Gopalakrishnan, S.

1985-01-01

Rotor dynamic behavior of high energy centrifugal pumps is significantly affected by two types of fluid forces; one due to the hydraulic interaction of the impeller with the surrounding volute or diffuser and the other due to the effect of the wear rings. The available data on these forces is first reviewed. A simple one degree-of-freedom system containing these forces is analytically solved to exhibit the rotor dynamic effects. To illustrate the relative magnitude of these phenomena, an example of a multistage boiler feed pump is worked out. It is shown that the wear ring effects tend to suppress critical speed and postpone instability onset. But the volute-impeller forces tend to lower the critical speed and the instability onset speed. However, for typical boiler feed pumps under normal running clearances, the wear ring effects are much more significant than the destabilizing hydraulic interaction effects.

Classical and Ablative Richtmyer-Meshkov Instability and Other ICF-Relevant Plasma Flows Diagnosed With Monochromatic X-Ray Imaging

National Research Council Canada - National Science Library

Aglitskiy, Y; Karasik, M; Velikovich, A. L; Metzler, N; Zalesak, S; Schmitt, A. J; Gardner, J. H; Serlin, V; Weaver, J; Obenschain, S. P

2007-01-01

In inertial confinement fusion (ICF) and high-energy density physics (HEDP), the most important manifestations of the hydrodynamic instabilities and other mixing processes involve lateral motion of the accelerated plasmas...

Effect of polarization force on the Jeans instability of self-gravitating dusty plasma

International Nuclear Information System (INIS)

Prajapati, R.P.

2011-01-01

The effect of polarization force acting on massive charged dust grains is investigated analytically on the Jeans instability of self-gravitating dusty plasma. The gravitational force acting on the massive negatively charged interstellar dust grains are considered in presence of both electrical and polarization forces. The basic equations of the problem are formulated and a general dispersion relation is obtained using plane wave approximation in low frequency wave mode. The effect of polarization force in the dispersion relation of the problem, condition of the Jeans instability and expression of the critical Jeans wave number is examined. The unstable growing modes due to self-gravitational force are studied in the situation when polarization force on the dust grain exceeds over the electrical force in magnitude. It is observed that the polarization force increases the growth rate of the system. -- Highlights: → Jeans instability of gravitating dusty plasma with polarization force is investigated. → The fundamental Jeans instability criterion is modified due to polarization effect. → The critical Jeans length decreases due to increase in polarization force. → Polarization force destabilizes the unstable Jeans mode. → The collapsing of interstellar dusty cloud is discussed.

Convective instability of RCP modes for a magnetized chiral plasma

International Nuclear Information System (INIS)

Torres-Silva, Hector; Sakanaka, P.H.; Reggiani, N.

1998-01-01

Using the Maxwell's equations and the proposed constitutive relations for a chiral plasma medium, the dispersion relations for right circularly polarized waves, (RCP), depending on the characteristics of the distribution, a new mode conversion and instabilities are found due to the chiral effect. From the dispersion relations and considering that the chirowave magnetic field may be important when the condition of velocity isotropy is dropped, we find that growing modes (instabilities) can occur at resonance and for frequencies below the electron gyrofrequency. We study, in this paper, the convective instability of RCP waves in a two-component bi-Lorentzian chiroplasma which can model the solar wind particle distributions. (author)

Electromagnetic radiation from beam-plasma instabilities

International Nuclear Information System (INIS)

Stenzel, R.L.; Whelan, D.A.

1982-01-01

This chapter investigates the mechanism by which unstable electrostatic waves of an electron-beam plasma system are converted into observed electromagnetic waves. Electromagnetic radiation arises from both natural beam-plasma systems (e.g., type III solar bursts and kilometric radiation), and from man-made electron beams injected from rockets and spacecraft. A pulsed magnetized discharge plasma is produced with a 1 m diam. oxide-coated cathode and the discussed experiment is performed in the quiescent afterglow. The primary beam-plasma instability involves the excitation of electrostatic plasma waves. Electromagnetic radiation from the beam-plasma system is observed with microwave antennas outside the plasma (all probes removed) or with coax-fed dipoles which can be inserted radially and axially into the plasma. The physical process of mode coupling by which electromagnetic radiation is generated in an electrostatic beam-plasma instability is identified. The results are relevant to beam injection experiments from rockets or satellites into space plasmas. The limited penetration of the beam current into the plasma due to instabilities is demonstrated

Electromiography comparison of distal and proximal lower limb muscle activity patterns during external perturbation in subjects with and without functional ankle instability.

Science.gov (United States)

Kazemi, Khadijeh; Arab, Amir Massoud; Abdollahi, Iraj; López-López, Daniel; Calvo-Lobo, César

2017-10-01

Ankle sprain is one of the most common injuries among athletes and the general population. Most ankle injuries commonly affect the lateral ligament complex. Changes in postural sway and hip abductor muscle strength may be generated after inversion ankle sprain. Therefore, the consequences of ankle injury may affect proximal structures of the lower limb. The aim is to describe and compare the activity patterns of distal and proximal lower limb muscles following external perturbation in individuals with and without functional ankle instability. The sample consisted of 16 women with functional ankle instability and 18 healthy women were recruited to participate in this research. The external perturbation via body jacket using surface electromyography, amplitude and onset of muscle activity of gluteus maximums, gluteus medius, tibialis anterior, and peroneus longus was recorded and analyzed during external perturbation. There were differences between the onset of muscles activity due to perturbation direction in the two groups (healthy and functional ankle instability). In the healthy group, there were statistically significant differences in amplitude of proximal muscle activity with distal muscle activity during front perturbation with eyes open and closed. In the functional ankle instability group; there were statistically significant differences in amplitude of proximal muscle activity with distal muscle activity during perturbation of the front and back with eyes open. There were statistically significant differences in the onset of muscle activity and amplitude of muscle activity, with-in and between groups (Pankle instability, activation patterns of the lower limb proximal muscles may be altered. Copyright © 2017 Elsevier B.V. All rights reserved.

Nonlinear interaction of Rayleigh--Taylor and shear instabilities

International Nuclear Information System (INIS)

Finn, J.M.

1993-01-01

Results on the nonlinear behavior of the Rayleigh--Taylor instability and consequent development of shear flow by the shear instability [Phys. Fluids B 4, 488 (1992)] are presented. It is found that the shear flow is generated at sufficient amplitude to reduce greatly the convective transport. For high viscosity, the time-asymptotic state consists of an equilibrium with shear flow and vortex flow (with islands, or ''cat's eyes''), or a relaxation oscillation involving an interplay between the shear instability and the Rayleigh--Taylor instability in the presence of shear. For low viscosity, the dominant feature is a high-frequency nonlinear standing wave consisting of convective vortices localized near the top and bottom boundaries. The localization of these vortices is due to the smaller shear near the boundary regions. The convective transport is largest around these convective vortices near the boundary and there is a region of good confinement near the center. The possible relevance of this behavior to the H mode and edge-localized modes (ELM's) in the tokamak edge region is discussed

Theory of the corrugation instability of a piston-driven shock wave.

Science.gov (United States)

Bates, J W

2015-01-01

We analyze the two-dimensional stability of a shock wave driven by a steadily moving corrugated piston in an inviscid fluid with an arbitrary equation of state. For h≤-1 or h>h(c), where h is the D'yakov parameter and h(c) is the Kontorovich limit, we find that small perturbations on the shock front are unstable and grow--at first quadratically and later linearly--with time. Such instabilities are associated with nonequilibrium fluid states and imply a nonunique solution to the hydrodynamic equations. The above criteria are consistent with instability limits observed in shock-tube experiments involving ionizing and dissociating gases and may have important implications for driven shocks in laser-fusion, astrophysical, and/or detonation studies.

Sausage instability threshold in a low energy plasma focus

International Nuclear Information System (INIS)

Zakaullah, M.; Nasir, M.; Khattak, F.Y.; Murtaza, G.

1993-01-01

Development of sausage instability (m = 0 mode) is studied in a small low energy Mather-type plasma focus. A shadow graphic study of the current sheath has shown that the focused plasma necks off during the radial phase before the maximum compression. This may indicate the lowering of the instability threshold. Three hook-type structures are observed which may not be due to the multifoci formation. The bubble shape structure is observed to be developed in the expansion phase. (author)

An experimental investigation of flow instability between two heated parallel channels with supercritical water

Energy Technology Data Exchange (ETDEWEB)

Xi, Xi; Xiao, Zejun, E-mail: fabulous_2012@sina.com; Yan, Xiao; Li, Yongliang; Huang, Yanping

2014-10-15

Highlights: • Flow instability experiment between two heated channels with supercritical water is carried out. • Two kinds of out of phase flow instability are found and instability boundaries under different working conditions are obtained. • Dynamics characteristics of flow instability are analyzed. - Abstract: Super critical water reactor (SCWR) is the generation IV nuclear reactor in the world. Under normal operation, water enters SCWR from cold leg with a temperature of 280 °C and then leaves the core with a temperature of 500 °C. Due to the sharp change of temperature, there is a huge density change in the core, which could result in potential flow instability and the safety of reactor would be threatened consequently. So it is necessary to carry out relevant investigation in this field. An experimental investigation which concerns with out of phase flow instability between two heated parallel channels with supercritical water has been carried out in this paper. Due to two INCONEL 625 pipes with a thickness of 6.5 mm are adopted, more experimental results are attained. To find out the influence of axial power shape on the onset of flow instability, each heated channel is divided into two sections and the heating power of each section can be controlled separately. Finally the instability boundaries are obtained under different inlet temperatures, axial power shapes, total inlet mass flow rates and system pressures. The dynamics characteristics of out of phase oscillation are also analyzed.

Tail anisotropy instability during plasma current rise by lower-hybrid waves in a tokamak

International Nuclear Information System (INIS)

Yamagiwa, Mitsuru.

1986-01-01

Tail anisotropy instability during lower-hybrid current rise is investigated. Tail formation by lower-hybrid waves is studied by using a Fokker-Planck equation combined with the return field and the rf associated terms. Quasi-linear relaxation of the electron tail distribution under the influence of the plasma waves excited due to the instability is examined. It is found that the instability condition is related to the strength of the parallel diffusion by lower-hybrid waves and the ratio of the electron cyclotron frequency to the electron plasma frequency. The time scale between the instability spikes and the suppression of the instability by electron cyclotron heating are also discussed. (author)

Evidence of Rayleigh-Taylor instabilities in tri-layer targets

International Nuclear Information System (INIS)

Galmiche, D.; Holstein, P.A.; Meyer, B.; Rostaing, M.; Wilke, N.

1988-01-01

The results of the experiments carried out on a laser system are reported. The work is performed in order to investigate the problem of target instability under ablative acceleration and to get direct evidence of Rayleigh-Taylor instabilities. Tri-layer experiments assert the validity of X-ray spectroscopy measurements as experimental method to investigate the problem. A mixing zone is evidenced and general trends of mixing development versus target acceleration are coherent with numerical simulations. Results obtained with optical smoothing demonstrate that the apparent mixing is not due to large scale illumination non uniformities. Numerical simulations confirm that Rayleigh-Taylor instability seems to be the dominant process responsible for the mixing. Benefit of time resolved spectroscopy appears attractive and gives a real knowledge of the mixing layer

A Mechanistic Model of Onset of Flow Instability Due to Mergence of Bubble Layers in a Vertical Narrow Rectangular Channel

Energy Technology Data Exchange (ETDEWEB)

Lee, Juh Yung; Chang, Soon Heung; Jeong, Yong [KAIST, Daejeon (Korea, Republic of)

2016-05-15

The onset of flow instability (OFI) is the one of important boiling phenomena since it may induce the premature critical heat flux (CHF) at the lowest heat flux level due to sudden flow excursion in a single channel of multichannel configuration. Especially prediction of OFI for narrow rectangular channel is very crucial in relevant to thermal-hydraulic design and safety analysis of open pool-type research reactors (RRs) using plate-type fuels. Based on high speed video (HSV) technique, the authors observed and determined that OFI and the minimum premature CHF in a narrow rectangular channel are induced by abrupt pressure drop fluctuation due to the mergence of facing bubble boundary layers (BLs) on opposite boiling surfaces. In this study, new mechanistic OFI model for narrow rectangular channel heated on both sides has been derived, which satisfies with the real triggering phenomena. Force balance approach was used for modeling of the maximum BLT since the quantity is comparable to the bubble departure diameter. From the validation with OFI database, it was shown that the new model fairly well predicts OFI heat flux for wide range of conditions.

Investor’s Perceptions and Financial Instability in the Emerging Countries

OpenAIRE

Ionescu Cristian

2013-01-01

Due to the importance of the financial instability and of its negative consequences within the economies, especially in the emerging ones, it is important to sstudy the link between financial instability and investments, as a factor of economic stability. Therefore, the paper aims to analyze the relationship between the risk premium comprises by the financial instruments, the country-specific factors that influence spreads, the factors that influence the general perception of emerging market ...

Metamorphosis of helical magnetorotational instability in the presence of axial electric current.

Science.gov (United States)

Priede, Jānis

2015-03-01

This paper presents numerical linear stability analysis of a cylindrical Taylor-Couette flow of liquid metal carrying axial electric current in a generally helical external magnetic field. Axially symmetric disturbances are considered in the inductionless approximation corresponding to zero magnetic Prandtl number. Axial symmetry allows us to reveal an entirely new electromagnetic instability. First, we show that the electric current passing through the liquid can extend the range of helical magnetorotational instability (HMRI) indefinitely by transforming it into a purely electromagnetic instability. Two different electromagnetic instability mechanisms are identified. The first is an internal pinch-type instability, which is due to the interaction of the electric current with its own magnetic field. Axisymmetric mode of this instability requires a free-space component of the azimuthal magnetic field. When the azimuthal component of the magnetic field is purely rotational and the axial component is nonzero, a new kind of electromagnetic instability emerges. The latter, driven by the interaction of electric current with a weak collinear magnetic field in a quiescent fluid, gives rise to a steady meridional circulation coupled with azimuthal rotation.

Did Failure Occur Because of Medial Column Instability That Was Not Recognized, or Did It Develop After Surgery?

Science.gov (United States)

Kadakia, Anish R; Kelikian, Armen S; Barbosa, Mauricio; Patel, Milap S

2017-09-01

Medial column instability is a primary deforming force in the setting of pes planovalgus deformity. Consideration for medial column stabilization only after correction of the hindfoot deformity may result in creating a rigid hindfoot, compromising clinical outcomes. Careful analysis of the lateral radiograph to determine whether the deformity is secondary to the medial column or true peritalar subluxation may allow superior outcomes. Iatrogenic creation of an excessively rigid medial column may lead to significant instability of the remaining joints in the short term and arthrosis in the long term. Medial column arthrodesis should be used selectively to correct gross instability. Copyright © 2017 Elsevier Inc. All rights reserved.

FOKKER-PLANCK ANALYSIS OF TRANSVERSE COLLECTIVE INSTABILITIES IN ELECTRON STORAGE RINGS

Energy Technology Data Exchange (ETDEWEB)

Lindberg, R. R.

2017-06-25

We analyze single bunch transverse instabilities due to wakefields using a Fokker-Planck model. We expand on the work of Suzuki [1], writing out the linear matrix equation including chromaticity, both dipolar and quadrupolar transverse wakefields, and the effects of damping and diffusion due to the synchrotron radiation. The eigenvalues and eigenvectors determine the collective stability of the beam, and we show that the predicted threshold current for transverse instability and the profile of the unstable agree well with tracking simulations. In particular, we find that predicting collective stability for high energy electron beams at moderate to large values of chromaticity requires the full Fokker-Planck analysis to properly account for the effects of damping and diffusion due to synchrotron radiation.

Inertioelastic Flow Instability at a Stagnation Point

Science.gov (United States)

Burshtein, Noa; Zografos, Konstantinos; Shen, Amy Q.; Poole, Robert J.; Haward, Simon J.

2017-10-01

A number of important industrial applications exploit the ability of small quantities of high molecular weight polymer to suppress instabilities that arise in the equivalent flow of Newtonian fluids, a particular example being turbulent drag reduction. However, it can be extremely difficult to probe exactly how the polymer acts to, e.g., modify the streamwise near-wall eddies in a fully turbulent flow. Using a novel cross-slot flow configuration, we exploit a flow instability in order to create and study a single steady-state streamwise vortex. By quantitative experiment, we show how the addition of small quantities (parts per million) of a flexible polymer to a Newtonian solvent dramatically affects both the onset conditions for this instability and the subsequent growth of the axial vorticity. Complementary numerical simulations with a finitely extensible nonlinear elastic dumbbell model show that these modifications are due to the growth of polymeric stress within specific regions of the flow domain. Our data fill a significant gap in the literature between the previously reported purely inertial and purely elastic flow regimes and provide a link between the two by showing how the instability mode is transformed as the fluid elasticity is varied. Our results and novel methods are relevant to understanding the mechanisms underlying industrial uses of weakly elastic fluids and also to understanding inertioelastic instabilities in more confined flows through channels with intersections and stagnation points.

High lateral plantar pressure is related to an increased tibialis anterior/fibularis longus activity ratio in patients with recurrent lateral ankle sprain

Directory of Open Access Journals (Sweden)

Mineta S

2017-06-01

Full Text Available Shinshiro Mineta,1 Takayuki Inami,2 Raldy Mariano,3 Norikazu Hirose4 1Graduate School of Sport Sciences, 2Institute of Physical Education, Keio University, Hiyoshi, Yokohama, 3Graduate School of Asia-Pacific Studies, Waseda University, Shinjuku, Tokyo, 4Faculty of Sport Sciences, Waseda University, Higashifushimi, Nishitokyo, Japan Introduction: Center of pressure (COP is a sudden displacement at the time of a lateral ankle sprain (LAS. It has been suggested that the distribution of plantar pressure and the quantity of COP displacement are important for assessing the risk of LAS. Therefore, we evaluated the plantar pressure during a single-leg balance test with eyes closed (SLB-C to identify the factors and characteristics of plantar pressure in people with repeated cases of LAS.Methods: We recruited 22 collegiate athletes and divided them into an instability group (IG; n=11 and a control group (CG; n=11. We measured the distribution of plantar pressure and lower extremity muscle activity during a SLB-C along with static alignment and isometric ankle strength.Results: The fibularis longus (FL activity was significantly lower in the IG than in the CG. The lateral plantar pressure (LPP/medial plantar pressure (MPP ratio was also higher in the IG than in the CG. In addition, the LPP/MPP ratio was correlated with the tibialis anterior (TA/FL ratio.Conclusion: These results suggest that increased lateral plantar pressure is related to decreased FL activity and increased TA/FL ratio. Keywords: chronic ankle instability, ankle sprain, postural stability, soccer, prevention

Clinical and radiological evaluation of the integrity of the medial and lateral collateral ligaments of the elbow in dogs

International Nuclear Information System (INIS)

Montavon, P.M.; Savoldelli, D.

1995-01-01

In most cases of luxation of the elbow closed reduction constitutes the therapy of choice. Clinical retrospective studies showed signs of arthrosis in 50 % of the cases treated with this therapy, and persisting medial instability after the reduction in more than 50 % of the cases. In the present study the biomechanics of both the medial and the lateral collateral ligaments were analysed after selective severing. Severing of the medial collateral ligament led to an average increase of 30 deg of the pronation with the presence of crepitus on the lateral aspect of the elbow during passive motion. The medial instability of the elbow could be evidenced both clinically and radiographically. Severing of the lateral collateral ligament resulted in an average increase of 15 deg of the supination. Neither palpation nor radiological examination showed any evidence of subluxation

Longitudinal acoustic instabilities in slender solid propellant rockets : linear analysis

OpenAIRE

García Schafer, Juan Esteban; Liñán Martínez, Amable

2001-01-01

To describe the acoustic instabilities in the combustion chambers of laterally burning solid propellant rockets the interaction of the mean flow with the acoustic waves is analysed, using multiple scale techniques, for realistic cases in which the combustion chamber is slender and the nozzle area is small compared with the cross-sectional area of the chamber. Associated with the longitudinal acoustic oscillations we find vorticity and entropy waves, with a wavelength typically small compared ...

Instabilities responsible for magnetic turbulence in laboratory rotating plasma

International Nuclear Information System (INIS)

Mikhailovskii, A.B.; Lominadze, J.G.; Churikov, A.P.; Erokhin, N.N.; Pustovitov, V.D.; Konovalov, S.V.

2008-01-01

Instabilities responsible for magnetic turbulence in laboratory rotating plasma are investigated. It is shown that the plasma compressibility gives a new driving mechanism in addition to the known Velikhov effect due to the negative rotation frequency gradient. This new mechanism is related to the perpendicular plasma pressure gradient, while the density gradient gives an additional drive depending also on the pressure gradient. It is shown that these new effects can manifest themselves even in the absence of the equilibrium magnetic field, which corresponds to nonmagnetic instabilities

The Hall instability of unsteady inhomogeneous axially symmetric magnetized plasmas

International Nuclear Information System (INIS)

Shtemler, Yuri M.; Mond, Michael; Liverts, Edward

2004-01-01

The Hall instability in cylindrically symmetric resistive magnetized plasmas in vacuum is investigated. The unperturbed self-similar equilibrium solutions for imploding Z-pinches with time-dependent total current I t ∼t S ,S>1/3, are subjected by short-wave sausage perturbations. The instability criterion is derived in slow-time, frozen-radius approximation. In cylindrically symmetric configurations the instability is driven by the magnetic field curvature. The near-axis and near-edge branches of the neutral curve in the plane of the inverse Hall parameter and phase velocity with the frozen radial coordinate as a parameter are separated by the critical point, where the modified gradient from the unperturbed number density changes sign. The critical radius may be treated as a new characteristic size of the Z-pinch that emerges due to the instability: the pinch is envisaged restructured by the short-scale high-frequency Hall instability, in which a central stable core is surrounded by an outer shell. Such a modified equilibrium may explain the observed enhanced stability against magnetohydrodynamic modes

Hydrodynamic instabilities in inertial fusion

International Nuclear Information System (INIS)

Hoffman, N.M.

1994-01-01

This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interactions in intermediate-stage Rayleigh-Taylor instability

On the conventive instability evolution in a rotating gas disk

International Nuclear Information System (INIS)

Nikonov, S.V.; Solov'ev, L.S.

1986-01-01

The mechanism of formation of spiral configuration in a rotating gravitating gas disk, caused by the nonlinear development of the convective instability, is considered. The mechanism suggested may be considered as the model of formation of the galaxy spiral configuration in a rotating pregalactic gas disk due to the development of the convective instability. Unlike the popular at present conception of ''density waves'', formation of the spiral configuration, from this point of view, is the single process of the development of instability in the pregalactic gas cloud. The further advantageous star formation in the vicinity of the central region, in a strip and sleeves is caused by higher concentration of gas density and temperature in these regions

Location of Instability During a Bench Press Alters Movement Patterns and Electromyographical Activity.

Science.gov (United States)

Nairn, Brian C; Sutherland, Chad A; Drake, Janessa D M

2015-11-01

Instability training devices with the bench press exercise are becoming increasingly popular. Typically, the instability device is placed at the trunk/upper body (e.g., lying on a Swiss ball); however, a recent product called the Attitube has been developed, which places the location of instability at the hands by users lifting a water-filled tube. Therefore, the purpose of this study was to analyze the effects of different instability devices (location of instability) on kinematic and electromyographical patterns during the bench press exercise. Ten healthy males were recruited and performed 1 set of 3 repetitions for 3 different bench press conditions: Olympic bar on a stable bench (BENCH), Olympic bar on a stability ball (BALL), and Attitube on a stable bench (TUBE). The eccentric and concentric phases were analyzed in 10% intervals while electromyography was recorded from 24 electrode sites, and motion capture was used to track elbow flexion angle and 3-dimensional movement trajectories and vertical velocity of the Bar/Attitube. The prime movers tended to show a reduction in muscle activity during the TUBE trials; however, pectoralis major initially showed increased activation during the eccentric phase of the TUBE condition. The trunk muscle activations were greatest during the TUBE and smallest during the BAR. In addition, the TUBE showed decreased range of elbow flexion and increased medial-lateral movement of the Attitube itself. The results further support the notion that instability devices may be more beneficial for trunk muscles rather than prime movers.

Fluctuations and Instability in Sedimentation

KAUST Repository

Guazzelli, Élisabeth

2011-01-21

This review concentrates on the fluctuations of the velocities of sedimenting spheres, and on the structural instability of a suspension of settling fibers. For many years, theoretical estimates and numerical simulations predicted the fluctuations of the velocities of spheres to increase with the size of the container, whereas experiments found no such variation. Two ideas have increased our understanding. First, the correlation length of the velocity fluctuations was found experimentally to be 20 interparticle separations. Second, in dilute suspensions, a vertical variation in the concentration due to the spreading of the front with the clear fluid can inhibit the velocity fluctuations. In a very dilute regime, a homogeneous suspension of fibers suffers a spontaneous instability in which fast descending fiber-rich columns are separated by rising fiber-sparse columns. In a semidilute regime, the settling is hindered, more so than for spheres. © 2011 by Annual Reviews. All rights reserved.

Sedimentation and gravitational instability of Escherichia coli Suspension

Science.gov (United States)

Salin, Dominique; Douarche, Carine

2017-11-01

The successive runs and tumbles of Escherichia coli bacteria provide an active matter suspension of rod-like particles with a large swimming, Brownian like, diffusion. As opposed to inactive elongated particles, this diffusion prevents clustering of the particles and hence instability in the gravity field. We measure the time dependent E . coli concentration profile during their sedimentation. After some hours, due to the dioxygen consumption, a motile / non-motile front forms leading to a Rayleigh-Taylor type gravitational instability. Analysing both sedimentation and instability in the framework of active particle suspensions, we can measure the relevant bacteria hydrodynamic characteristics such as its single particle sedimentation velocity and its hindrance volume. Comparing these quantities to the ones of equivalent passive particles (ellipsoid, rod) we tentatively infer the effective shape and size of the bacteria involved in its buoyancy induced advection and diffusion. Laboratoire FAST University Paris Saclay France.

Measurement of angles of abduction for diagnosis of shoulder instability in dogs using goniometry and digital image analysis.

Science.gov (United States)

Cook, James L; Renfro, Daniel C; Tomlinson, James L; Sorensen, Jill E

2005-01-01

To compare abduction angles of shoulders with medial instability and unaffected shoulders in the same dogs and in age- and breed-matched dogs. Case-control study. Dogs with medial instability of the shoulder (n=33) and 26 control dogs. Dogs were sedated and positioned in lateral recumbency with both scapulas parallel to the table. With the elbow and shoulder in extension, the non-recumbent limb was maximally abducted and the angle between the scapular spine and lateral aspect of the brachium measured with a goniometer; a digital image was taken from the cranial aspect. Both techniques were performed in triplicate by 2 examiners. Mean abduction angles for each shoulder were determined from goniometric measurements and image analysis. Data were analyzed for significant differences between affected and unaffected shoulders, measurement techniques, and examiners. Strength of correlation between measurement techniques was determined. Mean abduction angles for shoulders with instability (53.7+/-4.7 degrees goniometric, 51.2+/-4.9 degrees image) were significantly (P<.001) larger than for all unaffected shoulders (32.6+/-2.0 degrees goniometric, 30.9+/-2.3 degrees image). In dogs diagnosed with instability, affected shoulders had significantly (P<.001) larger abduction angles than the contralateral (unaffected) shoulders. No significant differences were identified between right and left shoulders for control dogs, measurement techniques, or examiners. A strong (r=0.90) significant (P<.001) positive correlation between measurement techniques was noted. Shoulder abduction angles measured under sedation provide objective data for diagnosis of shoulder instability in dogs. Shoulders with clinical and arthroscopic evidence of medial instability have significantly higher abduction angles than shoulders that are considered normal. Determination of shoulder abduction angles should be included in the diagnostic protocol for forelimb lameness assessment in dogs.

Arthroscopic suture anchor repair of the lateral ligament ankle complex: a cadaveric study.

Science.gov (United States)

Giza, Eric; Shin, Edward C; Wong, Stephanie E; Acevedo, Jorge I; Mangone, Peter G; Olson, Kirstina; Anderson, Matthew J

2013-11-01

Operative treatment of mechanical ankle instability is indicated for patients with multiple sprains and continued episodes of instability. Open repair of the lateral ankle ligaments involves exposure of the attenuated ligaments and advancement back to their anatomic insertions on the fibula using bone tunnels or suture implants. Open and arthroscopic fixation are equal in strength to failure for anatomic Broström repair. Controlled laboratory study. Seven matched pairs of human cadaveric ankle specimens were randomized into 2 groups of anatomic Broström repair: open or arthroscopic. The calcaneofibular ligament and anterior talofibular ligament were excised from their origin on the fibula. In the open repair group, 2 suture anchors were used to reattach the ligaments to their anatomic origins. In the arthroscopic repair group, identical suture anchors were used for repair via an arthroscopic technique. The ligaments were cyclically loaded 20 times and then tested to failure. Torque to failure, degrees to failure, initial stiffness, and working stiffness were measured. A matched-pair analysis was performed. Power analysis of 0.8 demonstrated that 7 pairs needed to show a difference of 30%, with a 15% standard error at a significance level of α = .05. There was no difference in the degrees to failure, torque to failure, or stiffness for the repaired ligament complex. Nine of 14 specimens failed at the suture anchor. There is no statistical difference in strength or stiffness of a traditional open repair as compared with an arthroscopic anatomic repair of the lateral ligaments of the ankle. An arthroscopic technique can be considered for lateral ligament stabilization in patients with mild to moderate mechanical instability.

Chromosomal Instability in Gastric Cancer Biology

Directory of Open Access Journals (Sweden)

Saffiyeh Saboor Maleki

2017-05-01

Full Text Available Gastric cancer (GC is the fifth most common cancer in the world and accounts for 7% of the total cancer incidence. The prognosis of GC is dismal in Western countries due to late diagnosis: approximately 70% of the patients die within 5 years following initial diagnosis. Recently, integrative genomic analyses led to the proposal of a molecular classification of GC into four subtypes, i.e.,microsatellite-instable, Epstein-Barr virus–positive, chromosomal-instable (CIN, and genomically stable GCs. Molecular classification of GC advances our knowledge of the biology of GC and may have implications for diagnostics and patient treatment. Diagnosis of microsatellite-instable GC and Epstein-Barr virus–positive GC is more or less straightforward. Microsatellite instability can be tested by immunohistochemistry (MLH1, PMS2, MSH2, and MSH6 and/or molecular-biological analysis. Epstein-Barr virus–positive GC can be tested by in situ hybridization (Epstein-Barr virus encoded small RNA. However, with regard to CIN, testing may be more complicated and may require a more in-depth knowledge of the underlying mechanism leading to CIN. In addition, CIN GC may not constitute a distinct subgroup but may rather be a compilation of a more heterogeneous group of tumors. In this review, we aim to clarify the definition of CIN and to point out the molecular mechanisms leading to this molecular phenotype and the challenges faced in characterizing this type of cancer.

Genomic instability following irradiation

International Nuclear Information System (INIS)

Hacker-Klom, U.B.; Goehde, W.

2001-01-01

Ionising irradiation may induce genomic instability. The broad spectrum of stress reactions in eukaryontic cells to irradiation complicates the discovery of cellular targets and pathways inducing genomic instability. Irradiation may initiate genomic instability by deletion of genes controlling stability, by induction of genes stimulating instability and/or by activating endogeneous cellular viruses. Alternatively or additionally it is discussed that the initiation of genomic instability may be a consequence of radiation or other agents independently of DNA damage implying non nuclear targets, e.g. signal cascades. As a further mechanism possibly involved our own results may suggest radiation-induced changes in chromatin structure. Once initiated the process of genomic instability probably is perpetuated by endogeneous processes necessary for proliferation. Genomic instability may be a cause or a consequence of the neoplastic phenotype. As a conclusion from the data available up to now a new interpretation of low level radiation effects for radiation protection and in radiotherapy appears useful. The detection of the molecular mechanisms of genomic instability will be important in this context and may contribute to a better understanding of phenomenons occurring at low doses <10 cSv which are not well understood up to now. (orig.)

Experimental study on dynamic stabilization of the MHD instability in pinch plasmas surrounded by a conducting shell

International Nuclear Information System (INIS)

Yamamoto, Shunji; Ishii, Shozo; Kawamoto, Shigeshi; Hayashi, Izumi

1981-01-01

Experimental study on the dynamic stabilization of MHD instability with a pinch plasma generator was done, and the results were compared with the theoretical works. The previous results of theoretical analysis showed that a conducting shell worked effectively for the dynamic stabilization of MHD instability. The present experiment was carried out with a linear plasma generator which consisted of a discharge tube, a coil and a conducting shell. The macroscopic behavior of plasma was observed with an image converter camera, and the phenomena due to the instability was measured by a magnetic probe. A sine-cosine coil was employed for the observation of the growth of instability. The following results were obtained. When the frequency of RF current for dynamic stabilization was larger than the growth rate of instability, the experimental results were in agreement with the theoretical ones. The effect of a conducting shell was clearly seen. For the helical instability of short wave length, the dynamic stabilization was easily obtained even without a conducting shell. The self-reversal phenomena due to the helical instability of short wave length was suppressed by the RF current along the axis of a discharge tube. (Kato, T.)

Amplification due to two-stream instability of self-electric and magnetic fields of an ion beam propagating in background plasma

Science.gov (United States)

Tokluoglu, Erinc K.; Kaganovich, Igor D.; Carlsson, Johan A.; Hara, Kentaro; Startsev, Edward A.

2018-05-01

Propagation of charged particle beams in background plasma as a method of space charge neutralization has been shown to achieve a high degree of charge and current neutralization and therefore enables nearly ballistic propagation and focusing of charged particle beams. Correspondingly, the use of plasmas for propagation of charged particle beams has important applications for transport and focusing of intense particle beams in inertial fusion and high energy density laboratory plasma physics. However, the streaming of beam ions through a background plasma can lead to the development of two-stream instability between the beam ions and the plasma electrons. The beam electric and magnetic fields enhanced by the two-stream instability can lead to defocusing of the ion beam. Using particle-in-cell simulations, we study the scaling of the instability-driven self-electromagnetic fields and consequent defocusing forces with the background plasma density and beam ion mass. We identify plasma parameters where the defocusing forces can be reduced.

Remagnetization effects due to lateral displacement above a PMG on bulk HTS magnet

Science.gov (United States)

Liu, W.; Wang, J. S.; Ma, G. T.; Zheng, J.; Ren, J. F.; Li, L. L.; Yang, X. F.; Ye, C. Q.; Wang, S. Y.

2012-12-01

For a high-Tc superconducting (HTS) maglev system with large force requirements, the use of magnetized bulk high-Tc superconductor magnets (MBSCMs) is a good candidate because of its strong flux pinning ability and corresponding high trapped flux. Different from the rare-earth permanent magnet (PM), the trapped flux of a MBSCM is sustained by the supercurrent produced by a magnetizing process, so the trapped flux is sensitive to variations of the supercurrent. The lateral displacement of a MBSCM above a PM guideway (PMG) will provide disturbance of the applied field and then alter the supercurrent as a process of remagnetization. Different magnetization histories will bring different remagnetization characteristics and consequently diverse levitation performances for a MBSCM during the lateral displacements. When the MBSCMs are applied into the HTS maglev system, the influence of lateral displacements on levitation performance should be taken into consideration. This article investigates the remagnetization characteristics of a MBSCM when it is subject to the lateral displacements above a PMG with different trapped magnetic flux and opposite magnetization polarities. Relevant analyses about the internal supercurrent configuration based on the critical state model are also included to better understand the remagnetization characteristic of a MBSCM.

Patellofemoral Instability in Children: Correlation Between Risk Factors, Injury Patterns, and Severity of Cartilage Damage.

Science.gov (United States)

Kim, Hee Kyung; Shiraj, Sahar; Kang, Chang Ho; Anton, Christopher; Kim, Dong Hoon; Horn, Paul S

2016-06-01

The purpose of this study was to compare MRI findings between groups with and without patellofemoral instability and to correlate the MRI findings with the severity of patellar cartilage damage. Fifty-three children with patellofemoral instability and 53 age- and sex-matched children without patellofemoral instability (15.9 ± 2.4 years) were included. Knee MRI with T2-weighted mapping was performed. On MR images, femoral trochlear dysplasia, patellofemoral malalignment, medial retinaculum injury, and bone marrow edema were documented. The degree of patellar cartilage damage was evaluated on MR images by use of a morphologic grading scale (0-4) and on T2 maps with mean T2 values at the medial, central, and lateral facets. MRI findings were compared between the two groups. In cases of patellofemoral instability, MRI findings were correlated with the severity of cartilage damage at each region. Trochlear structure and alignment were significantly different between the two groups (Wilcoxon p patellofemoral instability, a high-riding patella was associated with central patellar cartilage damage with a higher morphologic grade and T2 value (Spearman p patellofemoral instability have significantly different trochlear structure and alignment than those who do not, and these differences are known risk factors for patellofemoral instability. However, the only risk factors or injury patterns that directly correlated with the severity of patellar cartilage damage were patella alta, medial stabilizer injury, and bone marrow edema.

Problems due to icing of overhead lines - Part II

International Nuclear Information System (INIS)

Havard, D.G.; Pon, C.J.; Krishnasamy, S.G.

1985-01-01

A companion paper describes uncertainties in overhead line design due to the variability of ice and wind loads. This paper reviews two other effects due to icing; conductor galloping and torsional instability, which require further study. (author)

Triclade: influence of a sinuous secondary instability on the Richtmyer-Meshkov instabilities

International Nuclear Information System (INIS)

Boulet, M.; Griffond, J.

2004-01-01

Occurrence of a secondary instability developing after the Richtmyer-Meshkov (primary) instability is emphasized thanks to numerical simulations with the TRICLADE code. We are mainly considering 2D perturbations describes by trigonometric function cosine or [cosine]. However, the 3D case is also tackled. The sinuous secondary instability is characterized by the loss of the symmetries in the direction normal to the interface at its crests. It reduces the late time growing rate of the 'mushrooms' formed by the Richtmyer-Meshkov instability. Related simplified problems, like symmetrical Riemann problems or the Mallier-Maslowe array of counter-rotating vortices, allow us to perform 2D linear stability analysis. Thus, we show that the sinuous secondary instability is not a numerical artifact and that is comes from the continuous incompressible velocity field in the interface region. This instability implies temporal limitations for the validity of single mode simulations; therefore multimode simulations are necessary to study the ]ate-time behaviour of interfaces bitted by shocks. (authors)

Instability of confined water films between elastic surfaces.

Science.gov (United States)

de Beer, Sissi; 't Mannetje, Dieter; Zantema, Sietske; Mugele, Frieder

2010-03-02

We investigated the dynamics of nanometer thin water films at controlled ambient humidity adsorbed onto two atomically smooth mica sheets upon rapidly bringing the surfaces into contact. Using a surface forces apparatus (SFA) in imaging mode, we found that the water films break up into a distribution of drops with a typical thickness of a few nanometers and a characteristic lateral size and spacing of several micrometers. Whereas the characteristic length is found to be independent of the ambient humidity, the characteristic time of the breakup decreases from approximately 1 to 0.01 s with increasing humidity. The existence of characteristic length and time scales shows that this breakup is controlled by an instability rather than a conventional nucleation and growth mechanism for SFA experiments. These findings cannot be explained by a dispersion-driven instability mechanism. In contrast, a model involving the elastic energies for the deformation of both the mica sheets and the underlying glue layer correctly reproduces the scaling of the characteristic length and time with humidity.

Effect of secondary electron emission on the Jeans instability in a dusty plasma

International Nuclear Information System (INIS)

Sarkar, Susmita; Roy, Banamali; Maity, Saumyen; Khan, Manoranjan; Gupta, M. R.

2007-01-01

In this paper the effect of secondary electron emission on Jeans instability in a dusty plasma has been investigated. Due to secondary electron emission, dust grains may have two stable equilibrium states out of which one is negative and the other is positive. Here both cases have been considered separately. It has been shown that secondary electron emission enhances Jeans instability when equilibrium dust charge is negative. It has also been shown that growth rate of Jeans instability reduces with increasing secondary electron emission when equilibrium dust charge is positive

Cavitation instabilities between fibres in a metal matrix composite

DEFF Research Database (Denmark)

Tvergaard, Viggo

2016-01-01

induced by bonding to the ceramics that only show elastic deformation. In an MMC the stress state in the metal matrix is highly non-uniform, varying between regions where shear stresses are dominant and regions where hydrostatic tension is strong. An Al–SiC whisker composite with a periodic pattern......Short fibre reinforced metal matrix composites (MMC) are studied here to investigate the possibility that a cavitation instability can develop in the metal matrix. The high stress levels needed for a cavitation instability may occur in metal–ceramic systems due to the constraint on plastic flow...... of transversely staggered fibres is here modelled by using an axisymmetric cell model analysis. First the critical stress level is determined for a cavitation instability in an infinite solid made of the Al matrix material. By studying composites with different distributions and aspect ratios of the fibres...

Observations and control of beam instabilities due to higher order modes in Indus-2

International Nuclear Information System (INIS)

Arora, Rajiv K.; Prasad, M.; Lad, M.; Hannurkar, P.R.

2013-01-01

In a synchrotron radiation source (SRS), the interaction between electron beam spectra and Higher Order Modes (HOMs) of RF cavities may give rise to coupled bunch instabilities. These instabilities may limit beam current and beam lifetime. Indus-2 SRS has four RF cavities equipped with precision temperature controller of cooling system and Higher Order Mode Frequency Shifter (HOMFS) to avoid harmful HOMs. Offline (i.e. without beam) and Online (i.e. with beam) measurements, observations and analysis of HOMs have been performed. Some of the Longitudinal modes such as L1 (∼ 950 MHz), L3 (∼ 1432 MHz), L4 (∼ 1521 MHz), L5 (∼1628 MHz) were observed to be quite prominent at specific operating conditions. Based on these studies, harmful HOMs were identified and suitable methods were evolved to avoid these HOMs. Experiments were performed to achieve high beam current in Indus-2. The precision chiller temperatures and HOMFS positions were set as per theoretical estimates and were further optimized in fine steps during experiments. With the optimized settings, beam current around 200 mA at Injection energy (550 MeV) and 157 mA at 2.5 GeV has been successfully achieved. At these settings of RF cavity water temperature and HOMFS, harmful HOMs were within safe limits during regular operation of Indus-2 at 2.5 GeV/100 mA in user mode for more than one year. In this paper, important observations, analysis and experiments to avoid harmful HOMs of RF cavities are presented. (author)

Instabilities of collisionless current sheets: Theory and simulations

International Nuclear Information System (INIS)

Silin, I.; Buechner, J.; Zelenyi, L.

2002-01-01

The problem of Harris current sheet stability is investigated. A linear dispersion relation in the long-wavelength limit is derived for instabilities, propagating in the neutral plane at an arbitrary angle to the magnetic field but symmetric across the sheet. The role of electrostatic perturbations is especially investigated. It appears, that for the tearing-mode instability electrostatic effects are negligible. However, for obliquely propagating modes the modulation of the electrostatic potential φ is essential. In order to verify the theoretical results, the limiting cases of tearing and sausage instabilities are compared to the two-dimensional (2D) Vlasov code simulations. For tearing the agreement between theory and simulations is good for all mass ratios. For sausage-modes, the theory predicts fast stabilization for mass ratios m i /m e ≥10. This is not observed in simulations due to the diminishing of the wavelength for higher mass ratios, which leads beyond the limit of applicability of the theory developed here

X-band microwave generation caused by plasma-sheath instability

International Nuclear Information System (INIS)

Bliokh, Y.; Felsteiner, J.; Slutsker, Ya. Z.

2012-01-01

It is well known that oscillations at the electron plasma frequency may appear due to instability of the plasma sheath near a positively biased electrode immersed in plasma. This instability is caused by transit-time effects when electrons, collected by this electrode, pass through the sheath. Such oscillations appear as low-power short spikes due to additional ionization of a neutral gas in the electrode vicinity. Herein we present first results obtained when the additional ionization was eliminated. We succeeded in prolonging the oscillations during the whole time a positive bias was applied to the electrode. These oscillations could be obtained at much higher frequency than previously reported (tens of GHz compared to few hundreds of MHz) and power of tens of mW. These results in combination with presented theoretical estimations may be useful, e.g., for plasma diagnostics.

Sedimentation from flocculated suspensions in the presence of settling-driven gravitational interface instabilities

Science.gov (United States)

Rouhnia, Mohamad; Strom, Kyle

2015-09-01

We experimentally examine sedimentation from a freshwater suspension of clay flocs overlying saltwater in the presence of gravitational instabilities. The study seeks to determine: (1) if flocculation hampers or alters interface instability formation; (2) how the removal rates of sediment from the buoyant layer compare to those predicted by individual floc settling; and (3) whether or not it is possible to develop a model for effective settling velocity. The experiments were conducted in a tank at isothermal conditions. All experiments were initially stably stratified but later developed instabilities near the interface that grew into downward convecting plumes of fluid and sediment. Throughout, we measured sediment concentration in the upper and lower layers, floc size, and plume descent rates. The data showed that flocculation modifies the mixture settling velocity, and therefore shifts the mode of interface instability from double-diffusive (what one would expect from unflocculated clay) to settling-driven leaking and Rayleigh-Taylor instability formation. Removal rates of sediment from the upper layer in the presence of these instabilities were on the same order of magnitude as those predicted by individual floc settling. However, removal rates were found to better correlate with the speed of the interface plumes. A simple force-balance model was found to be capable of reasonably describing plume velocity based on concentration in the buoyant layer. This relation, coupled with a critical Grashof number and geometry relations, allowed us to develop a model for the effective settling velocity of the mixture based solely on integral values of the upper layer.

The temporal interplay of self-esteem instability and affective instability in borderline personality disorder patients' everyday lives.

Science.gov (United States)

Santangelo, Philip S; Reinhard, Iris; Koudela-Hamila, Susanne; Bohus, Martin; Holtmann, Jana; Eid, Michael; Ebner-Priemer, Ulrich W

2017-11-01

Borderline personality disorder (BPD) is defined by a pervasive pattern of instability. Although there is ample empirical evidence that unstable self-esteem is associated with a myriad of BPD-like symptoms, self-esteem instability and its temporal dynamics have received little empirical attention in patients with BPD. Even worse, the temporal interplay of affective instability and self-esteem instability has been neglected completely, although it has been hypothesized recently that the lack of specificity of affective instability in association with BPD might be explained by the highly intertwined temporal relationship between affective and self-esteem instability. To investigate self-esteem instability, its temporal interplay with affective instability, and its association with psychopathology, 60 patients with BPD and 60 healthy controls (HCs) completed electronic diaries for 4 consecutive days during their everyday lives. Participants reported their current self-esteem, valence, and tense arousal levels 12 times a day in approximately one-hr intervals. We used multiple state-of-the-art statistical techniques and graphical approaches to reveal patterns of instability, clarify group differences, and examine the temporal interplay of self-esteem instability and affective instability. As hypothesized, instability in both self-esteem and affect was clearly elevated in the patients with BPD. In addition, self-esteem instability and affective instability were highly correlated. Both types of instability were related to general psychopathology. Because self-esteem instability could not fully explain affective instability and vice versa and neither affective instability nor self-esteem instability was able to explain psychopathology completely, our findings suggest that these types of instability represent unique facets of BPD. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

CHF Enhancement by Surface Patterning based on Hydrodynamic Instability Model

Energy Technology Data Exchange (ETDEWEB)

Seo, Han; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)

2015-05-15

If the power density of a device exceeds the CHF point, bubbles and vapor films will be covered on the whole heater surface. Because vapor films have much lower heat transfer capabilities compared to the liquid layer, the temperature of the heater surface will increase rapidly, and the device could be damaged due to the heater burnout. Therefore, the prediction and the enhancement of the CHF are essential to maximizing the efficient heat removal region. Numerous studies have been conducted to describe the CHF phenomenon, such as hydrodynamic instability theory, macrolayer dryout theory, hot/dry spot theory, and bubble interaction theory. The hydrodynamic instability model, proposed by Zuber, is the predominant CHF model that Helmholtz instability attributed to the CHF. Zuber assumed that the Rayleigh-Taylor (RT) instability wavelength is related to the Helmholtz wavelength. Lienhard and Dhir proposed a CHF model that Helmholtz instability wavelength is equal to the most dangerous RT wavelength. In addition, they showed the heater size effect using various heater surfaces. Lu et al. proposed a modified hydrodynamic theory that the Helmholtz instability was assumed to be the heater size and the area of the vapor column was used as a fitting factor. The modified hydrodynamic theories were based on the change of Helmholtz wavelength related to the RT instability wavelength. In the present study, the change of the RT instability wavelength, based on the heater surface modification, was conducted to show the CHF enhancement based on the heater surface patterning in a plate pool boiling. Sapphire glass was used as a base heater substrate, and the Pt film was used as a heating source. The patterning surface was based on the change of RT instability wavelength. In the present work the study of the CHF was conducted using bare Pt and patterned heating surfaces.

Circumferential buckling instability of a growing cylindrical tube

KAUST Repository

Moulton, D.E.

2011-03-01

A cylindrical elastic tube under uniform radial external pressure will buckle circumferentially to a non-circular cross-section at a critical pressure. The buckling represents an instability of the inner or outer edge of the tube. This is a common phenomenon in biological tissues, where it is referred to as mucosal folding. Here, we investigate this buckling instability in a growing elastic tube. A change in thickness due to growth can have a dramatic impact on circumferential buckling, both in the critical pressure and the buckling pattern. We consider both single- and bi-layer tubes and multiple boundary conditions. We highlight the competition between geometric effects, i.e. the change in tube dimensions, and mechanical effects, i.e. the effect of residual stress, due to differential growth. This competition can lead to non-intuitive results, such as a tube growing to be thinner and yet buckle at a higher pressure. © 2011 Elsevier Ltd. All rights reserved.

On the heterogeneous character of the heartbeat instability in complex (dusty) plasmas

Energy Technology Data Exchange (ETDEWEB)

Pustylnik, M. Y.; Ivlev, A. V.; Heidemann, R.; Mitic, S.; Thomas, H. M.; Morfill, G. E. [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, 85741 Garching (Germany); Sadeghi, N. [LIPhy, Universite de Grenoble 1/CNRS, UMR 5588, Grenoble 38401 (France)

2012-10-15

A hypothesis on the physical mechanism generating the heartbeat instability in complex (dusty) plasmas is presented. It is suggested that the instability occurs due to the periodically repeated critical transformation on the boundary between the microparticle-free area (void) and the complex plasma. The critical transformation is supposed to be analogous to the formation of the sheath in the vicinity of an electrode. The origin of the transformation is the loss of the electrons and ions on microparticles surrounding the void. We have shown that this hypothesis is consistent with the experimentally measured stability parameter range, with the evolution of the plasma glow intensity and microparticle dynamics during the instability, as well as with the observed excitation of the heartbeat instability by an intensity-modulated laser beam (inducing the modulation of plasma density).

Jeans instability of rotating magnetized quantum plasma: Influence of radiation

Energy Technology Data Exchange (ETDEWEB)

Joshi, H., E-mail: hjoshi8525@yahoo.com [Department of Physics, Mewar University, Chittorgarh (Raj.) India (India); Pensia, R. K. [Department of Physics, Govt. Girls College, Neemuch (M.P.) India (India)

2015-07-31

The effect of radiative heat-loss function and rotation on the Jeans instability of quantum plasma is investigated. The basic set of equations for this problem is constructed by considering quantum magnetohydrodynamic (QMHD) model. Using normal mode analysis, the general dispersion relation is obtained. This dispersion relation is studied in both, longitudinal and transverse direction of propagations. In both case of longitudinal and transverse direction of propagation, the Jeans instability criterion is modified due to presence of radiative heat-loss function and quantum correction.

Instability of shallow open channel flow with lateral velocity gradients

Energy Technology Data Exchange (ETDEWEB)

Lima, A C; Izumi, N, E-mail: adriano@eng.hokudai.ac.jp, E-mail: nizumi@eng.hokudai.ac.jp [River and Watershed Engineering Laboratory, Hokkaido University, Sapporo, 060-8628 (Japan)

2011-12-22

The turbulent flow in a wide rectangular open channel partially covered with vegetation is studied using linear stability analysis. In the base state normal flow condition, the water depth is constant and the transverse velocity vanishes, while there is a lateral gradient in the streamwise velocity with an inflexion point at the boundary between the vegetated zone and the main channel. The Reynolds stress is expressed by introducing the eddy viscosity, which is obtained from assuming a logarithmic distribution of the velocity near the bed. Perturbation expansions are introduced to the streamwise and transverse velocities, as well as to the water depth. The system of governing equations was solved in order to determine the maximum growth rate of the perturbations as a function of parameters which describe physical characteristics of the channel and the flow.

T2 -Mapping evaluation of early cartilage alteration of talus for chronic lateral ankle instability with isolated anterior talofibular ligament tear or combined with calcaneofibular ligament tear.

Science.gov (United States)

Tao, Hongyue; Hu, Yiwen; Qiao, Yang; Ma, Kui; Yan, Xu; Hua, Yinghui; Chen, Shuang

2018-01-01

To quantitatively evaluate the cartilage alteration of talus for chronic lateral ankle instability (LAI) with isolated anterior talofibular ligament (ATFL) tear and combined ATFL and calcaneofibular ligament (CFL) tear using T 2 -mapping at 3.0T. In all, 27 patients including 17 with isolated ATFL tear and 10 with ATFL+CFL tear, and 21 healthy subjects were recruited. All participants underwent T 2 -mapping scan at 3T and patients completed American Orthopaedic Foot and Ankle Society (AOFAS) scoring. The total talar cartilage (TTC) was segmented into six compartments: medial anterior (MA), medial center (MC), medial posterior (MP), lateral anterior (LA), lateral center (LC), and lateral posterior (LP). The T 2 value of each compartment was measured from T 2 -mapping images. Data were analyzed with one-way analysis of variance (ANOVA), Student's t-test, and Pearson's correlation coefficient. The T 2 values of MA, MC, MP, TTC in the ATFL group and MA, MC, MP, LC, LP, TTC in the ATFL+CFL group were higher than those in the control group (P < 0.05). Moreover, the T 2 values of MC, MP, LC, and TTC in the ATFL+CFL group were higher than those in the ATFL group (P < 0.05). The T 2 values of MA in both patient groups were negatively correlated with AOFAS scores (r = -0.596, r = -0.690, P < 0.05). Chronic LAI with ATFL tear had a trend of increasing cartilage T 2 values in talar trochlea, mainly involving medial cartilage compartments. Chronic LAI with ATFL+CFL tear might result in higher T 2 values in a much larger cartilage region than with ATFL tear. MA could be the main cartilage compartment that may affect the patient's clinical symptoms. 1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:69-77. © 2017 International Society for Magnetic Resonance in Medicine.

Review of two-phase instabilities

Energy Technology Data Exchange (ETDEWEB)

Kang, Han Ok; Seo, Han Ok; Kang, Hyung Suk; Cho, Bong Hyun; Lee, Doo Jeong

1997-06-01

KAERI is carrying out a development of the design for a new type of integral reactors. The once-through helical steam generator is important design features. The study on designs and operating conditions which prevent flow instability should precede the introduction of one-through steam generator. Experiments are currently scheduled to understand two-phase instability, evaluate the effect of each design parameter on the critical point, and determine proper inlet throttling for the prevention of instability. This report covers general two-phase instability with review of existing studies on this topics. The general classification of two phase flow instability and the characteristics of each type of instability are first described. Special attention is paid to BWR core flow instability and once-through steam generator instability. The reactivity feedback and the effect of system parameters are treated mainly for BWR. With relation to once-through steam generators, the characteristics of convective heating and dryout point oscillation are first investigated and then the existing experimental studies are summarized. Finally chapter summarized the proposed correlations for instability boundary conditions. (author). 231 refs., 5 tabs., 47 figs

Joint instability and osteoarthritis.

Science.gov (United States)

Blalock, Darryl; Miller, Andrew; Tilley, Michael; Wang, Jinxi

2015-01-01

Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA). Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA.

Three-dimensional Langmuir wave instabilities in type III solar radio bursts

International Nuclear Information System (INIS)

Bardwell, S.; Goldman, M.V.

1976-01-01

Assuming that type III solar radio bursts are associated with electron streams moving at about c/3, Langmuir waves should be strongly excited. We have studied all of the Langmuir-wave linear parametric instabilities excited in cylindrical symmetry by an electron-stream--driven Langmuir wave-pump propagating along the stream axis. Included in this unified homogeneous treatment are induced backscattering off ions, the oscillating two-stream instability, and a new ''stimulated modulational instability,'' previously unconsidered in this context. Near a few solar radii, the latter two deposit Langmuir wave energy into a forward-scattering cone about the stream axis. It is concluded that the linear stage of the forward-scattering instabilities involves transfer of energy to Langmuir waves which remain in resonance with the stream, and therefore probably do not prevent rapid depletion of the electron stream due to quasilinear plateau formation at these distances from the Sun

Development of beam instability in a plasma in the presence of ion-acoustic turbulence

International Nuclear Information System (INIS)

Popel', S.I.

1993-01-01

Effect of radiation-resonance interactions (RRI) of ion-acoustic waves and electrons is accounted for in consideration of the beam instability in a plasma in the presence of ion-acoustic turbulences. It is shown that variation of the superthermal part of the electron distribution function due to fast particle generation, conditioned by RRI of ion-acoustic waves and plasma electrons, leads to decreasing the increment of Langmuir wave swinging and may lead to beam instability stabilization. Conditions are obtained for excess of electron energy increase rate due to RRI over their energy increase rate due to nonlinear and quasi-linear interactions of resonant and nonresonant interactions with wave beam

The instability of internal gravity waves to localised disturbances

Directory of Open Access Journals (Sweden)

J. Vanneste

1995-02-01

Full Text Available The instability of an internal gravity wave due to nonlinear wave-wave interaction is studied theoretically and numerically. Three different aspects of this phenomenon are examined. 1. The influence of dissipation on both the resonant and the nonresonant interactions is analysed using a normal mode expansion of the basic equations. In particular, the modifications induced in the interaction domain are calculated and as a result some modes are shown to be destabilised by dissipation. 2. The evolution of an initial unstable disturbance of finite vertical extent is described as the growth of two secondary wave packets travelling at the same group velocity. A quasi-linear correction to the basic primary wave is calculated, corresponding to a localised amplitude decrease due to the disturbance growth. 3. Numerical experiments are carried out to study the effect of a basic shear on wave instability. It appears that the growing secondary waves can have a frequency larger than that of the primary wave, provided that the shear is sufficient. The instability of waves with large amplitude and long period, such as tides or planetary waves, could therefore be invoked as a possible mechanism for the generation of gravity waves with shorter period in the middle atmosphere.

MHD instabilities in astrophysical plasmas: very different from MHD instabilities in tokamaks!

Science.gov (United States)

Goedbloed, J. P.

2018-01-01

The extensive studies of MHD instabilities in thermonuclear magnetic confinement experiments, in particular of the tokamak as the most promising candidate for a future energy producing machine, have led to an ‘intuitive’ description based on the energy principle that is very misleading for most astrophysical plasmas. The ‘intuitive’ picture almost directly singles out the dominant stabilizing field line bending energy of the Alfvén waves and, consequently, concentrates on expansion schemes that minimize that contribution. This happens when the wave vector {{k}}0 of the perturbations, on average, is perpendicular to the magnetic field {B}. Hence, all macroscopic instabilities of tokamaks (kinks, interchanges, ballooning modes, ELMs, neoclassical tearing modes, etc) are characterized by satisfying the condition {{k}}0 \\perp {B}, or nearly so. In contrast, some of the major macroscopic instabilities of astrophysical plasmas (the Parker instability and the magneto-rotational instability) occur when precisely the opposite condition is satisfied: {{k}}0 \\parallel {B}. How do those instabilities escape from the dominance of the stabilizing Alfvén wave? The answer to that question involves, foremost, the recognition that MHD spectral theory of waves and instabilities of laboratory plasmas could be developed to such great depth since those plasmas are assumed to be in static equilibrium. This assumption is invalid for astrophysical plasmas where rotational and gravitational accelerations produce equilibria that are at best stationary, and the associated spectral theory is widely, and incorrectly, believed to be non-self adjoint. These complications are addressed, and cured, in the theory of the Spectral Web, recently developed by the author. Using this method, an extensive survey of instabilities of astrophysical plasmas demonstrates how the Alfvén wave is pushed into insignificance under these conditions to give rise to a host of instabilities that do not

Atypical Chronic Ankle Instability in a Pediatric Population Secondary to Distal Fibula Avulsion Fracture Nonunion.

Science.gov (United States)

El Ashry, Saad R; El Gamal, Tarek A; Platt, Simon R

Chronic ankle instability is a disabling condition, often occurring as a result of traumatic ankle injury. A paucity of published data is available documenting chronic ankle instability in the pediatric population. Much of the data has been confined to the adult population. We present 2 cases of chronic ankle instability, 1 in a 12-year-old and 1 in a 9-year-old patient. Unlike the typical adult etiology, the cause of instability was a dysfunctional lateral ligamentous complex as a consequence of bony avulsion of the tip of the fibula. Both patients had sustained a twisting injury to the ankle. The fractures failed to unite. The nonunion resulted in dysfunction of the anterior talofibular ligament with consequent chronic ankle instability. At the initial clinical assessment, magnetic resonance imaging was requested for both patients. In patient 1 (12 years old), the fracture was fixed with 2 headless screws and was immobilized in a plaster cast for 6 weeks. In patient 2 (9 years old), because of the small size of the avulsed fragment, fixation was not possible. A modified Gould-Broström procedure was undertaken, facilitating repair of the avulsed fragment using anchor sutures. Copyright © 2016 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Current Driven Instabilities and Anomalous Mobility in Hall-effect Thrusters

Science.gov (United States)

Tran, Jonathan; Eckhardt, Daniel; Martin, Robert

2017-10-01

Due to the extreme cost of fully resolving the Debye length and plasma frequency, hybrid plasma simulations utilizing kinetic ions and quasi-steady state fluid electrons have long been the principle workhorse methodology for Hall-effect thruster (HET) modeling. Plasma turbulence and the resulting anomalous electron transport in HETs is a promising candidate for developing predictive models for the observed anomalous transport. In this work, we investigate the implementation of an anomalous electron cross field transport model for hybrid HET simulations such a HPHall. A theory for anomalous transport in HETs and current driven instabilities has been recently studied by Lafleur et al. This work has shown collective electron-wave scattering due to large amplitude azimuthal fluctuations of the electric field. We will further adapt the previous results for related current driven instabilities to electric propulsion relevant mass ratios and conduct a preliminary study of resolving this instability with a modified hybrid (fluid electron and kinetic ion) simulation with the hope of integration with established hybrid HET simulations. This work is supported by the Air Force Office of Scientific Research award FA9950-17RQCOR465.

Modeling, measuring, and mitigating instability growth in liner implosions on Z

Science.gov (United States)

Peterson, Kyle

2015-11-01

Electro-thermal instabilities result from non-uniform heating due to temperature dependence in the conductivity of a material. In this talk, we will discuss the role of electro-thermal instabilities on the dynamics of magnetically accelerated implosion systems. We present simulations that show electro-thermal instabilities form immediately after the surface material of a conductor melts and can act as a significant seed to subsequent magneto-Rayleigh-Taylor (MRT) instability growth. We discuss measurement results from experiments performed on Sandia National Laboratories Z accelerator to investigate signatures of electro-thermal instability growth on well-characterized initially solid aluminum or beryllium rods driven with a 20 MA, 100 ns risetime current pulse. These measurements show good agreement with electro-thermal instability simulations and exhibit larger instability growth than can be explained by MRT theory alone. Recent experiments have confirmed simulation predictions of dramatically reduced instability growth in solid metallic rods when thick dielectric coatings are used to mitigate density perturbations arising from the electro-thermal instability. These results provide further evidence that the inherent surface roughness of the target is not the dominant seed for the MRT instability, in contrast with most inertial confinement fusion approaches. These results suggest a new technique for substantially reducing the integral MRT growth in magnetically driven implosions. Indeed, recent results on the Z facility with 100 km/s Al and Be liner implosions show substantially reduced growth. These new results include axially magnetized, CH-coated beryllium liner radiographs in which the inner liner surface is observed to be remarkably straight and uniform at a radius of about 120 microns (convergence ratio ~20). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under

Joint Instability and Osteoarthritis

Directory of Open Access Journals (Sweden)

Darryl Blalock

2015-01-01

Full Text Available Joint instability creates a clinical and economic burden in the health care system. Injuries and disorders that directly damage the joint structure or lead to joint instability are highly associated with osteoarthritis (OA. Thus, understanding the physiology of joint stability and the mechanisms of joint instability-induced OA is of clinical significance. The first section of this review discusses the structure and function of major joint tissues, including periarticular muscles, which play a significant role in joint stability. Because the knee, ankle, and shoulder joints demonstrate a high incidence of ligament injury and joint instability, the second section summarizes the mechanisms of ligament injury-associated joint instability of these joints. The final section highlights the recent advances in the understanding of the mechanical and biological mechanisms of joint instability-induced OA. These advances may lead to new opportunities for clinical intervention in the prevention and early treatment of OA.

Analysis of failed surgery for patellar instability in children with open growth plates.

Science.gov (United States)

Nelitz, Manfred; Theile, Michael; Dornacher, Daniel; Wölfle, Julia; Reichel, Heiko; Lippacher, Sabine

2012-05-01

Many surgical procedures have been proposed to treat recurrent patellar dislocation in children. In recent years, a more tailored approach considering the underlying pathology has been advocated. The aim of the study was to analyze a group of patients with recurrent patellofemoral instability after unsuccessful operative stabilization (Roux-Goldthwait procedure, lateral release, medial reefing or in combination) in childhood and adolescence. A total of 37 children and adolescents with recurrent patellofemoral instability despite previous surgery were analyzed retrospectively. Radiographic examination included AP and lateral views to assess patella alta and limb alignment. MRI was performed to evaluate trochlear dysplasia and tibial tubercle-trochlear groove (TTTG) distance. As a control group, 23 age- and sex-matched adolescents that were treated with a favorable outcome after medial reefing alone or combined with a Roux-Goldthwait procedure were analyzed. Severe trochlear dysplasia (type B-D according to Dejour) as detected on MRI scans was found significantly more often in the study group (89%) than in the control group (21%). No statistical difference of patellar height ratio (Insall-Salvati index) and TTTG distance between the two groups could be found. Of the measured parameters, only the incidence of trochlear dysplasia was increased. Trochlear dysplasia therefore seems to be a major risk factor for failure of operative stabilization of recurrent patellofemoral instability in children and adolescents. The results in children are in consensus with the literature in adults that a more tailored operative therapy including reconstruction of the MPFL and trochleaplasty has to be considered. Retrospective study, Level III.

Rayleigh-Taylor instability and mixing in SN 1987A

International Nuclear Information System (INIS)

Ebisuzaki, T.; Shigeyama, T.; Nomoto, K.

1989-01-01

The stability of the supernova ejecta is compared with the Rayleigh-Taylor instability for a realistic model of SN 1987A. A linear analysis indicates that the layers around the composition interface between the hydrogen-rich and helium zones, and become Rayleigh-Taylor unstable between the helium and metal zones. In these layers, the pressure increases outward because of deceleration due to the reverse shock which forms when the blast shock hits the massive hydrogen-rich envelope. On the contrary, the density steeply decreases outward because of the preexisting nuclear burning shell. Then, these layers undergo the Raleigh-Taylor instability because of the opposite signs of the pressure and density gradients. The estimated growth rate is larger than the expansion rate of the supernova. The Rayleigh-Taylor instability near the composition interface is likely to induce mixing, which has been strongly suggested from observations of SN 1987A. 25 refs

Estudo anatômico do ligamento patelofemoral lateral em joelho de cadáveres Anatomical study of the lateral patellofemoral ligament in cadaver knees

Directory of Open Access Journals (Sweden)

Marcelo Schmidt Navarro

2008-07-01

Full Text Available OBJETIVOS: Descrever o ligamento patelofemoral lateral (LPFL por meio de dissecação anatômica de joelhos de cadáveres frescos. Na literatura existe particular interesse pelo LPFL. Essa especial atenção é dada pela sua importância anatômica, biomecânica e pela necessidade da sua reconstrução nos casos de instabilidade medial da patela. MÉTODOS: O LPFL foi estudado em 20 joelhos de 20 cadáveres frescos por meio de dissecações anatômicas. As dissecações foram padronizadas e os dados anotados enviados para análise estatística. RESULTADOS: O LPFL apresentou em média 16,05mm de largura (desvio-padrão: 2,48, 42,10mm de comprimento (desvio-padrão: 8,84. Sua inserção femoral mostrou-se no epicôndilo femoral lateral e com expansão em forma de leque das suas fibras, predominantemente na região posterior e proximal ao epicôndilo lateral. Na patela a inserção encontrada foi na região súpero-lateral (na metade do terço superior no plano coronal, também com expansão das fibras, mas com menor intensidade. No plano sagital, o ligamento situava-se na metade posterior da borda da patela. O LPFL foi isolado na segunda camada retinacular lateral, o retináculo transverso profundo. CONCLUSÃO: O LPFL situa-se na camada retinacular transversa profunda, com a presença de uma expansão das suas fibras em forma de leque, tanto na inserção femoral quanto na patelar. No epicôndilo femoral a inserção encontra-se mais posterior e proximalmente e na patela está na metade posterior da borda patelar (plano sagital e no aspecto súpero-lateral.OBJECTIVES: To describe the lateral patellofemoral ligament (LPFL after anatomical dissection of fresh cadaver knees. The literature shows a particular interest for the LPFL. Such special attention is due to its anatomical and biomechanical importance, and also due to the need to reconstruct the ligament in the cases of medial patellar instability. METHODS: The LPFL was studied in 20 knees of 20

Effects of 2 ankle destabilization devices on electromyography measures during functional exercises in individuals with chronic ankle instability.

Science.gov (United States)

Donovan, Luke; Hart, Joseph M; Hertel, Jay

2015-03-01

Randomized crossover laboratory study. To determine the effects of ankle destabilization devices on surface electromyography (sEMG) measures of selected lower extremity muscles during functional exercises in participants with chronic ankle instability. Ankle destabilization devices are rehabilitation tools that can be worn as a boot or sandal to increase lower extremity muscle activation during walking in healthy individuals. However, they have not been tested in a population with pathology. Fifteen adults with chronic ankle instability participated. Surface electromyography electrodes were located over the anterior tibialis, fibularis longus, lateral gastrocnemius, rectus femoris, biceps femoris, and gluteus medius. The activity level of these muscles was recorded in a single testing session during unipedal stance with eyes closed, the Star Excursion Balance Test, lateral hops, and treadmill walking. Each task was performed under 3 conditions: shod, ankle destabilization boot, and ankle destabilization sandal. Surface electromyography signal amplitudes were measured for each muscle during each exercise for all 3 conditions. Participants demonstrated a significant increase, with moderate to large effect sizes, in sEMG signal amplitude of the fibularis longus in the ankle destabilization boot and ankle destabilization sandal conditions during the unipedal eyes-closed balance test, the Star Excursion Balance Test in the anterior and posteromedial directions, lateral hops, and walking, when compared to the shod condition. Both devices also resulted in an increase in sEMG signal amplitudes, with large effect sizes of the lateral gastrocnemius, rectus femoris, biceps femoris, and gluteus medius during the unipedal-stance-with-eyes-closed test, compared to the shod condition. Wearing ankle destabilization devices caused greater muscle activation during functional exercises in individuals with chronic ankle instability. Based on the magnitude of the effect, there were

Peierls instability and optical properties of bilayer polyacene

Energy Technology Data Exchange (ETDEWEB)

Zhang, Longlong, E-mail: zhanglonglong@tyut.edu.cn [The College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); Xie, Shijie [School of Physics, Shandong University, Jinan 250100 (China)

2017-05-03

Highlights: • The Peierls instability of bilayer polyacene is discussed. • The external electric field effect on bilayer polyacene is discussed. • The pressure effect on bilayer polyacene is discussed. • The optical properties of bilayer polyacene are discussed. - Abstract: We reveal that bilayer polyacene can be the gapped state due to the intralayer Peierls instability. There are six topologically inequivalent Peierls-distorted structures and they are degenerate in energy. The external electric field can tune the Peierls gap and induce the semiconductor-to-metallic phase transitions. The optical conductivity spectra are calculated in an attempt to categorize the Peierls-distorted structures. The strength of the interlayer coupling essentially affects the electronic properties and the optical selection rules.

Finite temperature instability for compactification

International Nuclear Information System (INIS)

Accetta, F.S.; Kolb, E.W.

1986-03-01

We consider finite temperature effects upon theories with extra dimensions compactified via vacuum stress energy (Casimir) effects. For sufficiently high temperature, a static configuration for the internal space is impossible. At somewhat lower temperatures, there is an instability due to thermal fluctuations of radius of the compact dimensions. For both cases, the Universe can evolve to a de Sitter-like expansion of all dimensions. Stability to late times constrains the initial entropy of the universe. 28 refs., 1 fig., 2 tabs

Richtmyer–Meshkov instability of a thermal interface in a two-fluid plasma

KAUST Repository

Bond, D.

2017-11-03

We computationally investigate the Richtmyer–Meshkov instability of a density interface with a single-mode perturbation in a two-fluid, ion–electron plasma with no initial magnetic field. Self-generated magnetic fields arise subsequently. We study the case where the density jump across the initial interface is due to a thermal discontinuity, and select plasma parameters for which two-fluid plasma effects are expected to be significant in order to elucidate how they alter the instability. The instability is driven via a Riemann problem generated precursor electron shock that impacts the density interface ahead of the ion shock. The resultant charge separation and motion generates electromagnetic fields that cause the electron shock to degenerate and periodically accelerate the electron and ion interfaces, driving Rayleigh–Taylor instability. This generates small-scale structures and substantially increases interfacial growth over the hydrodynamic case.

Finding the first cosmic explosions. III. Pulsational pair-instability supernovae

International Nuclear Information System (INIS)

Whalen, Daniel J.; Smidt, Joseph; Even, Wesley; Fryer, Chris L.; Woosley, S. E.; Heger, Alexander; Stiavelli, Massimo

2014-01-01

Population III supernovae have been the focus of growing attention because of their potential to directly probe the properties of the first stars, particularly the most energetic events that can be seen at the edge of the observable universe. But until now pulsational pair-instability supernovae, in which explosive thermonuclear burning in massive stars fails to unbind them but can eject their outer layers into space, have been overlooked as cosmic beacons at the earliest redshifts. These shells can later collide and, like Type IIn supernovae, produce superluminous events in the UV at high redshifts that could be detected in the near infrared today. We present numerical simulations of a 110 M ☉ pulsational pair-instability explosion done with the Los Alamos radiation hydrodynamics code Radiation Adaptive Grid Eulerian. We find that collisions between consecutive pulsations are visible in the near infrared out to z ∼ 15-20 and can probe the earliest stellar populations at cosmic dawn.

Age at migration, family instability, and timing of sexual onset.

Science.gov (United States)

Goldberg, Rachel E; Tienda, Marta; Adserà, Alícia

2017-03-01

This study builds on and extends previous research on nativity variations in adolescent health and risk behavior by addressing three questions: (1) whether and how generational status and age at migration are associated with timing of sexual onset among U.S. adolescents; (2) whether and how family instability mediates associations between nativity and sexual debut; and (3) whether and how these associations vary by gender. We find that first- and second-generation immigrant youth initiate sexual activity later than native youth. Foreign-born youth who migrate after the start of adolescence exhibit the latest sexual onset; boys' sexual behavior is particularly sensitive to age at migration. Parental union stability is protective for first- and second-generation youth, especially boys; however, instability in co-residence with parents accelerates sexual debut for foreign-born girls, and dilutes protections from parental marital stability. Use of a non-English language at home delays sexual onset for immigrant girls, but not boys. Copyright © 2016 Elsevier Inc. All rights reserved.

Prominence Bubble Shear Flows and the Coupled Kelvin-Helmholtz — Rayleigh-Taylor Instability

Science.gov (United States)

Berger, Thomas; Hillier, Andrew

2017-08-01

Prominence bubbles are large arched structures that rise from below into quiescent prominences, often growing to heights on the order of 10 Mm before going unstable and generating plume upflows. While there is general agreement that emerging flux below pre-existing prominences causes the structures, there is lack of agreement on the nature of the bubbles and the cause of the instability flows. One hypothesis is that the bubbles contain coronal temperature plasma and rise into the prominence above due to both magnetic and thermal buoyancy, eventually breaking down via a magnetic Rayleigh-Taylor (RT) instability to release hot plasma and magnetic flux and helicity into the overlying coronal flux rope. Another posits that the bubbles are actually just “arcades” in the prominence indicating a magnetic separator line between the bipole and the prominence fields with the observed upflows and downflows caused by reconnection along the separator. We analyze Hinode/SOT, SDO/AIA, and IRIS observations of prominence bubbles, focusing on characteristics of the bubble boundary layers that may discriminate between the two hypotheses. We find speeds on the order of 10 km/s in prominence plasma downflows and lateral shear flows along the bubble boundary. Inflows to the boundary gradually increase the thickness and brightness of the layer until plasma drains from there, apparently around the dome-like bubble domain. In one case, shear flow across the bubble boundary develops Kelvin-Helmholtz (KH) vortices that we use to infer flow speeds in the low-density bubble on the order of 100 km/sec. IRIS spectra indicate that plasma flows on the bubble boundary at transition region temperatures achieve Doppler speeds on the order of 50 km/s, consistent with this inference. Combined magnetic KH-RT instability analysis leads to flux density estimates of 10 G with a field angle of 30° to the prominence, consistent with vector magnetic field measurements. In contrast, we find no evidence

Experimental study of the Richtmyer-Meshkov instability induced by a Mach 3 shock wave

International Nuclear Information System (INIS)

BP Puranik; JG Oakley; MH Anderson; R Bonaazza

2003-01-01

OAK-B135 An experimental investigation of a shock-induced interfacial instability (Richtmyer-Meshkov instability) is undertaken in an effort to study temporal evolution of interfacial perturbations in the late stages of development. The experiments are performed in a vertical shock tube with a square cross-section. A membraneless interface is prepared by retracting a sinusoidally shaped metal plate initially separating carbon dioxide from air, with both gases initially at atmospheric pressure. With carbon dioxide above the plate, the Rayleigh-Taylor instability commences as the plate is retracted and the amplitude of the initial sinusoidal perturbation imposed on the interface begins to grow. The interface is accelerated by a strong shock wave (M=3.08) while its shape is still sinusoidal and before the Kelvin-Helmhotz instability distorts it into the well known mushroom-like structures; its initial amplitude to wavelength ratio is large enough that the interface evolution enters its nonlinear stage very shortly after shock acceleration. The pre-shock evolution of the interface due to the Rayleigh-Taylor instability and the post-shock evolution of the interface due to the Richtmyer-Meshkov instability are visualized using planar Mie scattering. The pre-shock evolution of the interface is carried out in an independent set of experiments. The initial conditions for the Richtmyer-Meshkov experiment are determined from the pre-shock Rayleigh-Taylor growth. One image of the post-shock interface is obtained per experiment and image sequences, showing the post-shock evolution of the interface, are constructed from several experiments. The growth rate of the perturbation amplitude is measured and compared with two recent analytical models of the Richtmyer-Meshkov instability

Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf.

Science.gov (United States)

Garabato, Alberto C Naveira; Forryan, Alexander; Dutrieux, Pierre; Brannigan, Liam; Biddle, Louise C; Heywood, Karen J; Jenkins, Adrian; Firing, Yvonne L; Kimura, Satoshi

2017-02-09

The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth's albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

Fiber amplifiers under thermal loads leading to transverse mode instability

DEFF Research Database (Denmark)

Johansen, Mette Marie; Hansen, Kristian Rymann; Alkeskjold, Thomas Tanggaard

2014-01-01

Transverse mode instability (TMI) in rare-earth doped fiber amplifiers operating above an average power threshold is caused by intermodal stimulated thermal Rayleigh scattering due to quantum defect heating. We investigate thermally induced longitudinal waveguide perturbations causing power...

Extreme lateral approach in a case of acute-onset quadriplegia due to high cervical neurenteric cyst.

Science.gov (United States)

Abhishek, Agrawal; Anushree, Agrawal; Patir, Rana; Sehgal, A D

2007-01-01

Spinal neurenteric cysts are very rare intradural developmental lesions, predominantly localized anterior to the cervical cord and arising from misplaced endodermal cells in the 3rd week of embryonic life. An acute onset of symptoms can occur due to hemorrhage, but has not as yet been reported in relation to infection in the cyst. We report an 18-year-old male who presented with a rapid onset of respiratory distress and quadriplegia over a period of 6 h requiring intubation and ventilatory support. There was no respiratory effort with a dense sensory level from the neck. MRI of the cervical spine revealed an intradural extramedullary ventrally located cystic lesion at the C(2-3) level. There was no evidence of systemic infection elsewhere in the body. The lesion was radically excised using an extreme lateral approach as it provided excellent visualization of the cyst, thus permitting safe dissection without retraction of the cord. The cyst was tense and the contents turbid, thick, creamy and mucinous without any evidence of fresh or altered blood. Histopathological examination confirmed the cyst to be a neurenteric cyst. The cystic fluid, which was sent for culture, grew coagulase-negative Staphylococcus aureus. This is the first documented case of rapid neurological deterioration due to infection in a neurenteric cyst. In spite of an early effective surgical management, outcome was poor due to the rapid and profound neurological deficit. Copyright (c) 2007 S. Karger AG, Basel.

Active control of magneto-hydrodynamic instabilities in hot plasmas

CERN Document Server

2015-01-01

During the past century, world-wide energy consumption has risen dramatically, which leads to a quest for new energy sources. Fusion of hydrogen atoms in hot plasmas is an attractive approach to solve the energy problem, with abundant fuel, inherent safety and no long-lived radioactivity.  However, one of the limits on plasma performance is due to the various classes of magneto-hydrodynamic instabilities that may occur. The physics and control of these instabilities in modern magnetic confinement fusion devices is the subject of this book. Written by foremost experts, the contributions will provide valuable reference and up-to-date research reviews for "old hands" and newcomers alike.

Prevalence of chronic ankle instability and associated symptoms in university dance majors: an exploratory study.

Science.gov (United States)

Simon, Janet; Hall, Emily; Docherty, Carrie

2014-01-01

Previous investigations have established that dancers suffer a large number of injuries to the lower leg, foot, and ankle, with a portion of these being significant time loss injuries or in some cases career ending. Lateral ankle sprain is a common injury in dancers and can often lead to recurrent instability and repetitive injuries. Research in other active populations has linked ankle sprains to the development of chronic ankle instability (CAI). Therefore, the purpose of this study was to identify the prevalence of CAI and related symptoms of ankle sprain in a student dance population. Individuals were included if they were currently a modern or ballet dance major at the investigators' university (exclusion criterion: a history of fracture or surgery in the lower extremities). A self-reported demographic questionnaire and the Identification of Functional Ankle Instability survey were used to identify the presence and characteristics of CAI. A total of 83 questionnaires were collected, and after exclusions, 77 participants remained: 43 modern dancers and 34 ballet dancers (10 males and 67 females, mean age 19.61 ± 2.53 years, mean dance experience 13.61 ± 3.16 years). Of all dancers surveyed, 41 (53.2%) had CAI, and of those 24 (58.5%) were modern dancers, and 17 (41.5%) were ballet dancers. When looking only at those dancers who had a previous lateral ankle sprain, 75.9% were identified as having CAI. Chronic Ankle Instability can create long-term problems for anyone but especially female dancers, who place extreme stress on their feet and ankles from being en pointe or demi-pointe. It is important to educate dancers, instructors, and medical staff of the importance of recognizing CAI and seeking medical care for ankle sprains and their residual symptoms.

Extra-Articular Lateral Tenodesis for Anterior Cruciate Ligament Deficient Knee: A Case Report

Directory of Open Access Journals (Sweden)

Diego García-Germán

2013-01-01

Full Text Available We present the case of an extra-articular lateral tenodesis for an anterior cruciate ligament (ACL deficient knee. A 46-year-old male patient sustained an ACL graft rupture after a motorcycle accident. He complained of rotational instability and giving-way episodes. His previous graft was fixed by an intra-articular femoral staple that was not possible to remove at the time of the ACL revision. A modified Lemaire procedure was then performed. He gained rotational stability and was able to resume his sporting activities. We believe that isolated extra-articular reconstructions may still have a role in selected indications including moderate-demand patients complaining of rotational instability after ACL graft failure.

Extra-Articular Lateral Tenodesis for Anterior Cruciate Ligament Deficient Knee: A Case Report

Science.gov (United States)

García-Germán, Diego; Menéndez, Pablo; de la Cuadra, Pablo; Rodríguez-Arozena, Ricardo

2013-01-01

We present the case of an extra-articular lateral tenodesis for an anterior cruciate ligament (ACL) deficient knee. A 46-year-old male patient sustained an ACL graft rupture after a motorcycle accident. He complained of rotational instability and giving-way episodes. His previous graft was fixed by an intra-articular femoral staple that was not possible to remove at the time of the ACL revision. A modified Lemaire procedure was then performed. He gained rotational stability and was able to resume his sporting activities. We believe that isolated extra-articular reconstructions may still have a role in selected indications including moderate-demand patients complaining of rotational instability after ACL graft failure. PMID:24369517

Beyond the veil: Inner horizon instability and holography

International Nuclear Information System (INIS)

Balasubramanian, Vijay; Levi, Thomas S.

2004-01-01

We show that scalar perturbations of the eternal, rotating Banados-Teitelboim-Zanelli (BTZ) black hole should lead to an instability of the inner (Cauchy) horizon, preserving strong cosmic censorship. Because of backscattering from the geometry, plane-wave modes have a divergent stress tensor at the event horizon, but suitable wave packets avoid this difficulty, and are dominated at late times by quasinormal behavior. The wave packets have cuts in the complexified coordinate plane that are controlled by requirements of continuity, single-valuedness, and positive energy. Due to a focusing effect, regular wave packets nevertheless have a divergent stress energy at the inner horizon, signaling an instability. We propose that this instability, which is localized behind the event horizon, is detected holographically as a breakdown in the semiclassical computation of dual conformal field theory (CFT) expectation values in which the analytic behavior of wave packets in the complexified coordinate plane plays an integral role. In the dual field theory, this is interpreted as an encoding of physics behind the horizon in the entanglement between otherwise independent CFTs

Electron/electron acoustic instability

International Nuclear Information System (INIS)

Gary, S.P.

1987-01-01

The electron acoustic wave becomes a normal mode of an unmagnetized collisionless plasma in the presence of two electron components with similar densities, but strongly disparate temperatures. The characteristic frequency of this mode is the plasma frequency of the cooler electron component. If these two electron components have a relative drift speed several times the thermal speed of the cooler component, the electron/electron acoustic instability may arise. This paper describes the parametric dependences of the threshold drift speed and maximum growth rate of this instability, and compares these with the same properties of the electron/ion acoustic instability. Under the condition of zero current, the electron/ion acoustic instability typically has the lower threshold drift speed, so that observation of the electron/electron acoustic instability is a strong indication of the presence of an electrical current in the plasma

New aspects of the Jeans instability in dusty plasmas

International Nuclear Information System (INIS)

Verheest, Frank; Hellberg, Manfred A; Mace, Richard L

1998-01-01

In contrast to a gas, a dusty plasma can support a variety of wave modes each in principle able to impart to the dust grains the randomizing energy necessary to avoid Jeans collapse on some length scale. Consequently, the stability to Jeans collapse is more complex in a dusty plasma than it is for a charge-neutral gas. After recalling some of the fundamental ideas related to the ordinary Jeans instability in neutral gases, we will extend the discussion to plasmas containing charged dust grains. Besides the usual Jeans criterion based upon thermal agitation, various other ways of countering the gravitational collapse can be considered. One is via excitation of electrostatic dust-acoustic modes, the other via novel Alfven-Jeans instabilities for perpendicularly propagating electromagnetic waves on the extraordinary mode branch. The wavelengths that are unstable are modified due to the presence of a magnetic field and of charged particles. These mechanisms yield different minimum threshold length scales for the onset of instability/condensation

Kinetic instabilities in the solar wind: A short review

Energy Technology Data Exchange (ETDEWEB)

Matteini, Lorenzo, E-mail: l.matteini@imperial.ac.uk [Imperial College London, London SW7 2AZ (United Kingdom)

2016-03-25

We know from in situ measurements that solar wind plasma is far from thermal equilibrium. Distribution functions of its main constituents -electrons, protons, and alpha particles-show several departures from Maxwellian, including temperature anisotropy, relative drifts and secondary populations streaming along the local magnetic field. We present a short review of recent solar wind observations of these non-thermal features and associated signatures of wave-particle interactions. Several kinetic instabilities are expected to be at work in the solar wind during its expansion, playing a role in the continuous shaping of particle distributions with distance, and regulating the macroscopic behavior of the plasma. Over the past years, modeling of these processes by means of numerical simulations has been successful in reproducing and explaining the observations; these include the evolution of the plasma due to radial expansion and the response of individual species to different kinetic instabilities. Finally, the impact of local inhomogeneities, like current sheets and turbulence, on the development of kinetic instabilities is also discussed.

The Velikhov and anti-Velikhov effects in the theory of magnetorotational instability

International Nuclear Information System (INIS)

Mikhailovskii, A. B.; Lominadze, J. G.; Churikov, A. P.; Pustovitov, V. D.; Kharshiladze, O. A.

2008-01-01

A theory of magnetorotational instability (MRI) allowing an equilibrium plasma pressure gradient and nonaxisymmetry of perturbations is developed. This approach reveals that in addition to the Velikhov effect driving the MRI due to negative rotation frequency profile, dΘ 2 /dr < 0, there is an opposite effect (the anti-Velikhov effect) weakening this driving (here, Θ is the rotation frequency and r is the radial coordinate). It is shown that in addition to the Velikhov mechanism, two new mechanisms of MRI driving are possible, one of which is due to the pressure gradient squared and the other is due to the product of the pressure and density gradients. The analysis includes both the one-fluid magnetohydrodynamic plasma model and the kinetics allowing collisionless effects. In addition to the pure plasma containing ions and electrons, the dusty plasma is considered. The charged dust effect on stability is analyzed using the approximation of immobile dust. In the presence of dust, a term with the electric field appears in the one-fluid equation of plasma motion. This electric field affects the equilibrium plasma rotation and also gives rise to a family of instabilities of the rotating plasma, called the dust-induced rotational instabilities

Intravenous flurbiprofen axetil can stabilize the hemodynamic instability due to mesenteric traction syndrome--evaluation with continuous measurement of the systemic vascular resistance index using a FloTrac® sensor.

Science.gov (United States)

Takada, Motoshi; Taruishi, Chieko; Sudani, Tomoko; Suzuki, Akira; Iida, Hiroki

2013-08-01

Evaluation of the stabilizing effect of intravenous flurbiprofen axetil against hemodynamic instability due to mesenteric traction syndrome (MTS) by continuous measurement of systemic vascular resistance index (SVRI) using a FloTrac(®) sensor was evaluated. Prospective randomized trial. A single-center study performed in an educational hospital. Two prospective studies were carried out, each with 40 patients scheduled for elective open abdominal surgery. Twenty patients received 50 mg of flurbiprofen axetil after the recognition of MTS by the anesthesiologist (group FT). The remaining patients served as controls (groups CP and CT). SVRI data was collected every 20 seconds for 1 hour after starting the laparotomy. The average SVRI prior to skin incision was taken as the baseline. Following 3 values were devised to evaluate MTS: the S-value (sum total of changes in SVRI from baseline), the T-value (period during which SVRI remained 20% or more below baseline), and the M-value (maximum change in SVRI from baseline). In group FP, decrease in SVRI was smaller than in group CP, and statistical differences in the 3 values were found. In group FT, SVRI recovered earlier than in group CT, and statistical differences were found in S-value and T-value. However, the M-value had no statistical differences. Intravenous flurbiprofen axetil can stabilize the hemodynamic instability due to MTS. Copyright © 2013 Elsevier Inc. All rights reserved.

Two-phase flow instabilities in a silicon microchannels heat sink

International Nuclear Information System (INIS)

Bogojevic, D.; Sefiane, K.; Walton, A.J.; Lin, H.; Cummins, G.

2009-01-01

Two-phase flow instabilities are highly undesirable in microchannels-based heat sinks as they can lead to temperature oscillations with high amplitudes, premature critical heat flux and mechanical vibrations. This work is an experimental study of boiling instabilities in a microchannel silicon heat sink with 40 parallel rectangular microchannels, having a length of 15 mm and a hydraulic diameter of 194 μm. A series of experiments have been carried out to investigate pressure and temperature oscillations during the flow boiling instabilities under uniform heating, using water as a cooling liquid. Thin nickel film thermometers, integrated on the back side of a heat sink with microchannels, were used in order to obtain a better insight related to temperature fluctuations caused by two-phase flow instabilities. Flow regime maps are presented for two inlet water temperatures, showing stable and unstable flow regimes. It was observed that boiling leads to asymmetrical flow distribution within microchannels that result in high temperature non-uniformity and the simultaneously existence of different flow regimes along the transverse direction. Two types of two-phase flow instabilities with appreciable pressure and temperature fluctuations were observed, that depended on the heat to mass flux ratio and inlet water temperature. These were high amplitude/low frequency and low amplitude/high frequency instabilities. High speed camera imaging, performed simultaneously with pressure and temperature measurements, showed that inlet/outlet pressure and the temperature fluctuations existed due to alternation between liquid/two-phase/vapour flows. It was also determined that the inlet water subcooling condition affects the magnitudes of the temperature oscillations in two-phase flow instabilities and flow distribution within the microchannels.

Subatmospheric boiling study of the operation of a horizontal thermosyphon reboiler loop: Instability

International Nuclear Information System (INIS)

Agunlejika, Ezekiel O.; Langston, Paul A.; Azzopardi, Barry J.; Hewakandamby, Buddhika N.

2016-01-01

Graphical abstract: The highlight of the characteristics of the geysering instability from analysed WMS data. Pictorial view of geysering instability, heat flux 9 kW/m"2 (P_S = 1.14 bar(a)), Static head = 1.265 m, valve setting = 1.0, process side pressure = 0.5 bar(a). - Highlights: • Characteristics of geysering instability in a horizontal thermosyphon reboiler loop is highlighted using Wire Mesh Sensor. • Interconnection between geysering instability and accompanying churn flow is identified. • Effects of stability parameters and pressure drop feedbacks on the loop at low heat fluxes are described. - Abstract: Distillation and chemical processing under vacuum is of immense interest to petroleum and chemical industries due to lower energy costs and improved safety. To tap into these benefits, energy efficient reboilers with lower maintenance costs are required. Here, a horizontal thermosyphon reboiler is investigated at subatmospheric pressures and low heat fluxes. This paper presents detailed experimental data obtained using Wire Mesh Sensor in a gas-liquid flow with heat transfer as well as temperatures, pressures and recirculation rates around the loop. Flow regimes which have been previously identified in other systems were detected. The nature of the instability which underpins the mechanisms involved and conditions aiding instability are reported. Churn flow pattern is persistently detected during instability. The nature of the instability and existence of oscillatory churn flow are interconnected.

Option price and market instability

Science.gov (United States)

Baaquie, Belal E.; Yu, Miao

2017-04-01

An option pricing formula, for which the price of an option depends on both the value of the underlying security as well as the velocity of the security, has been proposed in Baaquie and Yang (2014). The FX (foreign exchange) options price was empirically studied in Baaquie et al., (2014), and it was found that the model in general provides an excellent fit for all strike prices with a fixed model parameters-unlike the Black-Scholes option price Hull and White (1987) that requires the empirically determined implied volatility surface to fit the option data. The option price proposed in Baaquie and Cao Yang (2014) did not fit the data during the crisis of 2007-2008. We make a hypothesis that the failure of the option price to fit data is an indication of the market's large deviation from its near equilibrium behavior due to the market's instability. Furthermore, our indicator of market's instability is shown to be more accurate than the option's observed volatility. The market prices of the FX option for various currencies are studied in the light of our hypothesis.

ANALYSIS OF THE INSTABILITY DUE TO GAS–DUST FRICTION IN PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

Shadmehri, Mohsen, E-mail: m.shadmehri@gu.ac.ir [Department of Physics, Faculty of Science, Golestan University, Gorgan 49138-15739 (Iran, Islamic Republic of)

2016-02-01

We study the stability of a dust layer in a gaseous disk subject to linear axisymmetric perturbations. Instead of considering single-size particles, however, the population of dust particles is assumed to consist of two grain species. Dust grains exchange momentum with the gas via the drag force and their self-gravity is also considered. We show that the presence of two grain sizes can increase the efficiency of the linear growth of drag-driven instability in the protoplanetary disks (PPDs). A second dust phase with a small mass, compared to the first dust phase, would reduce the growth timescale by a factor of two or more, especially when its coupling to the gas is weak. This means that once a certain amount of large dust particles form, even though it is much smaller than that of small dust particles, the dust layer becomes more unstable and dust clumping is accelerated. Thus, the presence of dust particles of various sizes must be considered in studies of dust clumping in PPDs where both large and small dust grains are present.

Instabilities in strongly coupled plasmas

CERN Document Server

Kalman, G J

2003-01-01

The conventional Vlasov treatment of beam-plasma instabilities is inappropriate when the plasma is strongly coupled. In the strongly coupled liquid state, the strong correlations between the dust grains fundamentally affect the conditions for instability. In the crystalline state, the inherent anisotropy couples the longitudinal and transverse polarizations, and results in unstable excitations in both polarizations. We summarize analyses of resonant and non-resonant, as well as resistive instabilities. We consider both ion-dust streaming and dust beam-plasma instabilities. Strong coupling, in general, leads to an enhancement of the growth rates. In the crystalline phase, a resonant transverse instability can be excited.

Patellar Instability Management: A Survey of the International Patellofemoral Study Group.

Science.gov (United States)

Liu, Joseph N; Steinhaus, Michael E; Kalbian, Irene L; Post, William R; Green, Daniel W; Strickland, Sabrina M; Shubin Stein, Beth E

2017-10-01

Although patellofemoral instability is among the most prevalent knee disorders, the management of patients with this condition is complex and remains variable, given the lack of long-term, high-level clinical outcome studies to compare various operative and nonoperative modalities. To discover a consensus within treatment controversies in patellofemoral instability among experienced knee surgeons with a specific interest in the patellofemoral joint. Expert opinion; Level of evidence, 5. A 3-step modified Delphi technique was used to establish a consensus. A 34-question, case-based online survey regarding patellofemoral instability was distributed to all active members of the International Patellofemoral Study Group. Consensus statements were generated if at least 66% of the respondents agreed and then redistributed to the same panel. Modifications to the consensus statements were made based on the iterative feedback process until no discordance was encountered in the third stage. Eight consensus statements were achieved. Nonoperative management is the current standard of care for a first-time dislocation in the absence of an osteochondral fragment or loose body requiring excision (100% agreement). In patients with a first-time dislocation with an operative osteochondral fracture requiring excision or repair, patellar instability should be addressed concurrently (89% agreement). Recurrent instability should be treated surgically, with most surgeons favoring medial reconstruction (77%-86% agreement). While there is general agreement that bony procedures should be performed to correct underlying bony deformities, there is no consensus regarding the most appropriate type of procedure performed. Lateral release should not be performed in isolation for the treatment of patellar instability (89% agreement). Despite the consensus generated in this study, our current understanding remains limited by a lack of high-level evidence as well as the numerous complex variables

The effect of a laser beam displacement on parametric oscillatory instabilities for Advanced LIGO

International Nuclear Information System (INIS)

Heinert, D.; Strigin, S.E.

2011-01-01

The arm cavities of real gravitational wave detectors can show small deviations like a tilt or a spatial shift between the cavity mirrors. These deviations lead to a separation of the optical mode centres with respect to the mirror's centre. In this Letter we perform the computation of parametric instable modes considering the described displacement. We further analyse the possibility of parametric oscillatory instability in the Advanced LIGO interferometer for the case of a displaced arm cavity. Our results reveal an additional number of optical and elastic mode combinations due to a displacement that can give rise to the undesirable effect of parametric oscillatory instability. -- Highlights: → We analyse the possibility of parametric oscillatory instability in the Advanced LIGO interferometer. → We perform the computation of parametric instable modes considering the mirror displacement. → Our results reveal an additional number of optical and elastic mode unstable combinations.

Effect of magnetic field on ablatively driven Richtmyer-Meshkov instability induced by interfacial nonlinear structure

International Nuclear Information System (INIS)

Labakanta Mandal; Banerjee, R.; Roy, S.; Khan, M.; Gupta, M.R.

2010-01-01

Complete text of publication follows. In an Inertial Confinement Fusion (ICF) situation, laser driven ablation front of an imploding capsule is subjected to the fluid instabilities like Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM) and Kelvin-Helmholtz (KH) instability. In this case dense core is compressed and accelerated by low density ablating plasma. During this process laser driven shocks interact the interface and hence it becomes unstable due to the formation of nonlinear structure like bubble and spike. The nonlinear structure is called bubble if the lighter fluid pushes inside the heavier fluid and spike, if opposite takes place. R-M instability causes non-uniform compression of ICF fuel pellets and needs to be mitigated. Scientists and researchers are much more interested on RM instability both from theoretical and experimental points of view. In this article, we have presented the analytical expression for the growth rate and velocity for the nonlinear structures due to the effect of magnetic field of fluid using potential flow model. The magnetic field is assumed to be parallel to the plane of two fluid interfaces. If the magnetic field is restricted only to either side of interface the R-M instability can be stabilized or destabilized depending on whether the magnetic pressure on the interface opposes the instability driving shock pressure or acts in the same direction. An interesting result is that if both the fluids are magnetized, interface as well as velocity of bubble and spike will show oscillating stabilization and R-M instability is mitigated. All analytical results are also supported by numerical results. Numerically it is seen that magnetic field above certain minimum value reduces the instability for compression the target in ICF.

Genomic instability and radiation

Energy Technology Data Exchange (ETDEWEB)

Little, John B [Harvard School of Public Health, Boston, MA 02115 (United States)

2003-06-01

Genomic instability is a hallmark of cancer cells, and is thought to be involved in the process of carcinogenesis. Indeed, a number of rare genetic disorders associated with a predisposition to cancer are characterised by genomic instability occurring in somatic cells. Of particular interest is the observation that transmissible instability can be induced in somatic cells from normal individuals by exposure to ionising radiation, leading to a persistent enhancement in the rate at which mutations and chromosomal aberrations arise in the progeny of the irradiated cells after many generations of replication. If such induced instability is involved in radiation carcinogenesis, it would imply that the initial carcinogenic event may not be a rare mutation occurring in a specific gene or set of genes. Rather, radiation may induce a process of instability in many cells in a population, enhancing the rate at which the multiple gene mutations necessary for the development of cancer may arise in a given cell lineage. Furthermore, radiation could act at any stage in the development of cancer by facilitating the accumulation of the remaining genetic events required to produce a fully malignant tumour. The experimental evidence for such induced instability is reviewed. (review)

Genomic instability and radiation

International Nuclear Information System (INIS)

Little, John B

2003-01-01

Genomic instability is a hallmark of cancer cells, and is thought to be involved in the process of carcinogenesis. Indeed, a number of rare genetic disorders associated with a predisposition to cancer are characterised by genomic instability occurring in somatic cells. Of particular interest is the observation that transmissible instability can be induced in somatic cells from normal individuals by exposure to ionising radiation, leading to a persistent enhancement in the rate at which mutations and chromosomal aberrations arise in the progeny of the irradiated cells after many generations of replication. If such induced instability is involved in radiation carcinogenesis, it would imply that the initial carcinogenic event may not be a rare mutation occurring in a specific gene or set of genes. Rather, radiation may induce a process of instability in many cells in a population, enhancing the rate at which the multiple gene mutations necessary for the development of cancer may arise in a given cell lineage. Furthermore, radiation could act at any stage in the development of cancer by facilitating the accumulation of the remaining genetic events required to produce a fully malignant tumour. The experimental evidence for such induced instability is reviewed. (review)

A Minimal Model to Explore the Influence of Distant Modes on Mode-Coupling Instabilities

Science.gov (United States)

Kruse, Sebastian; Hoffmann, Norbert

2010-09-01

The phenomenon of mode-coupling instability is one of the most frequently explored mechanisms to explain self-excited oscillation in sliding systems with friction. A mode coupling instability is usually due to the coupling of two modes. However, further modes can have an important influence on the coupling of two modes. This work extends a well-known minimal model to describe mode-coupling instabilities in order to explore the influence of a distant mode on the classical mode-coupling pattern. This work suggests a new minimal model. The model is explored and it is shown that a third mode can have significant influence on the classical mode-coupling instabilities where two modes are coupling. Different phenomena are analysed and it is pointed out that distant modes can only be ignored in very special cases and that the onset friction-induced oscillations can even be very sensitive to minimal variation of a distant mode. Due to the chosen academic minimal-model and the abandonment of a complex Finite-Element model the insight stays rather phenomenological but a better understanding of the mode-coupling mechnanism can be gained.

Ionization instabilities of an electromagnetic wave propagating in a tenuous gas

International Nuclear Information System (INIS)

Bian Zhigang; Antonsen, Thomas M. Jr.

2001-01-01

A theory is developed to study the scattering instability that occurs when a laser pulse propagates through and ionizes a gas. The instability is due to the intensity dependence of the ionization rate, which leads to a transversely structured free electron density. The instability is convective in the frame of the laser pulse, but can have a relatively short growth length scaling as L g ∼k 0 /k p 2 , where k 0 is the laser wave number, k p 2 =ω p 2 /c 2 and ω p is the plasma frequency. The most unstable perturbations correspond to a scattering angle for which the transverse wave number is around the plasma wave number, k p . The scattered light is frequency upshifted. The comparison between simple analytic theory and numerical simulation shows good agreement

Investigation of natural circulation instability and transients in passively safe novel modular reactor

Science.gov (United States)

Shi, Shanbin

The Purdue Novel Modular Reactor (NMR) is a new type small modular reactor (SMR) that belongs to the design of boiling water reactor (BWR). Specifically, the NMR is one third the height and area of a conventional BWR reactor pressure vessel (RPV) with an electric output of 50 MWe. The fuel cycle length of the NMR-50 is extended up to 10 years due to optimized neutronics design. The NMR-50 is designed with double passive engineering safety system. However, natural circulation BWRs (NCBWR) could experience certain operational difficulties due to flow instabilities that occur at low pressure and low power conditions. Static instabilities (i.e. flow excursion (Ledinegg) instability and flow pattern transition instability) and dynamic instabilities (i.e. density wave instability and flashing/condensation instability) pose a significant challenge in two-phase natural circulation systems. In order to experimentally study the natural circulation flow instability, a proper scaling methodology is needed to build a reduced-size test facility. The scaling analysis of the NMR uses a three-level scaling method, which was developed and applied for the design of the Purdue Multi-dimensional Integral Test Assembly (PUMA). Scaling criteria is derived from dimensionless field equations and constitutive equations. The scaling process is validated by the RELAP5 analysis for both steady state and startup transients. A new well-scaled natural circulation test facility is designed and constructed based on the scaling analysis of the NMR-50. The experimental facility is installed with different equipment to measure various thermal-hydraulic parameters such as pressure, temperature, mass flow rate and void fraction. Characterization tests are performed before the startup transient tests and quasi-steady tests to determine the loop flow resistance. The controlling system and data acquisition system are programmed with LabVIEW to realize the real-time control and data storage. The thermal

Instability during bunch shortening of an electron-cooled beam

Directory of Open Access Journals (Sweden)

M. Takanaka

2003-10-01

Full Text Available Bunch shortening causes an electron-cooled beam to be space charge dominated at low energies. Instability during the bunch shortening has been studied using a particle-tracking program where the 3D space-charge field due to the beam is calculated with a simplifying model.

Sudden onset odontoid fracture caused by cervical instability in hypotonic cerebral palsy.

Science.gov (United States)

Shiohama, Tadashi; Fujii, Katsunori; Kitazawa, Katsuhiko; Takahashi, Akiko; Maemoto, Tatsuo; Honda, Akihito

2013-11-01

Fractures of the upper cervical spine rarely occur but carry a high rate of mortality and neurological disabilities in children. Although odontoid fractures are commonly caused by high-impact injuries, cerebral palsy children with cervical instability have a risk of developing spinal fractures even from mild trauma. We herein present the first case of an odontoid fracture in a 4-year-old boy with cerebral palsy. He exhibited prominent cervical instability due to hypotonic cerebral palsy from infancy. He suddenly developed acute respiratory failure, which subsequently required mechanical ventilation. Neuroimaging clearly revealed a type-III odontoid fracture accompanied by anterior displacement with compression of the cervical spinal cord. Bone mineral density was prominently decreased probably due to his long-term bedridden status and poor nutritional condition. We subsequently performed posterior internal fixation surgically using an onlay bone graft, resulting in a dramatic improvement in his respiratory failure. To our knowledge, this is the first report of an odontoid fracture caused by cervical instability in hypotonic cerebral palsy. Since cervical instability and decreased bone mineral density are frequently associated with cerebral palsy, odontoid fractures should be cautiously examined in cases of sudden onset respiratory failure and aggravated weakness, especially in hypotonic cerebral palsy patients. Copyright © 2012 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.

Modes of storage ring coherent instabilities

Energy Technology Data Exchange (ETDEWEB)

Wang, J.M.

1986-12-01

Longitudinal impedance in a beam and various modes of longitudinal coherent instabilities are discussed. The coasting beam coherent instability, microwave instability, and single-bunch longitudinal coherent instabilities are considered. The Vlasov equation is formulated, and a method of solving it is developed. The synchrotron modes are treated, which take the possible bunch shape distortion fully into consideration. A method of treating the synchrotron mode coupling in the case of a small bunch is discussed which takes advantage of the fact that only a few of the synchrotron modes can contribute in such a case. The effect of many bunches on the coherent motion of the beam and the longitudinal symmetric coupled bunch modes are discussed. The transverse impedance is then introduced, and the transverse coasting beam instability is discussed. Various bunched beam instabilities are discussed, including both single bunch instabilities and coupled bunch instabilities. The Vlasov equation for transverse as well as longitudinal motion of particles is introduced as well as a method of solving it within a linear approximation. Head-tail modes and short bunch instabilities and strong coupling instabilities in the long bunch case are covered. (LEW)

Modes of storage ring coherent instabilities

International Nuclear Information System (INIS)

Wang, J.M.

1986-12-01

Longitudinal impedance in a beam and various modes of longitudinal coherent instabilities are discussed. The coasting beam coherent instability, microwave instability, and single-bunch longitudinal coherent instabilities are considered. The Vlasov equation is formulated, and a method of solving it is developed. The synchrotron modes are treated, which take the possible bunch shape distortion fully into consideration. A method of treating the synchrotron mode coupling in the case of a small bunch is discussed which takes advantage of the fact that only a few of the synchrotron modes can contribute in such a case. The effect of many bunches on the coherent motion of the beam and the longitudinal symmetric coupled bunch modes are discussed. The transverse impedance is then introduced, and the transverse coasting beam instability is discussed. Various bunched beam instabilities are discussed, including both single bunch instabilities and coupled bunch instabilities. The Vlasov equation for transverse as well as longitudinal motion of particles is introduced as well as a method of solving it within a linear approximation. Head-tail modes and short bunch instabilities and strong coupling instabilities in the long bunch case are covered

Rayleigh-Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. I

Science.gov (United States)

Zhou, Ye

2017-12-01

Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities play an important role in a wide range of engineering, geophysical, and astrophysical flows. They represent a triggering event that, in many cases, leads to large-scale turbulent mixing. Much effort has been expended over the past 140 years, beginning with the seminal work of Lord Rayleigh, to predict the evolution of the instabilities and of the instability-induced mixing layers. The objective of Part I of this review is to provide the basic properties of the flow, turbulence, and mixing induced by RT, RM, and Kelvin-Helmholtz (KH) instabilities. Historical efforts to study these instabilities are briefly reviewed, and the significance of these instabilities is discussed for a variety of flows, particularly for astrophysical flows and for the case of inertial confinement fusion. Early experimental efforts are described, and analytical attempts to model the linear, and nonlinear regimes of these mixing layers are examined. These analytical efforts include models for both single-mode and multi-mode initial conditions, as well as multi-scale models to describe the evolution. Comparisons of these models and theories to experimental and simulation studies are then presented. Next, attention is paid to the issue of the influence of stabilizing mechanisms (e.g., viscosity, surface tension, and diffuse interface) on the evolution of these instabilities, as well as the limitations and successes of numerical methods. Efforts to study these instabilities and mixing layers using group-theoretic ideas, as well as more formal notions of turbulence cascade processes during the later stages of the induced mixing layers, are inspected. A key element of the review is the discussion of the late-time self-similar scaling for the RT and RM growth factors, α and θ. These parameters are influenced by the initial conditions and much of the observed variation can be explained by this. In some cases, these instabilities

Shoulder instability in professional football players.

Science.gov (United States)

Leclere, Lance E; Asnis, Peter D; Griffith, Matthew H; Granito, David; Berkson, Eric M; Gill, Thomas J

2013-09-01

Shoulder instability is a common problem in American football players entering the National Football League (NFL). Treatment options include nonoperative and surgical stabilization. This study evaluated how the method of treatment of pre-NFL shoulder instability affects the rate of recurrence and the time elapsed until recurrence in players on 1 NFL team. Retrospective cohort. Medical records from 1980 to 2008 for 1 NFL team were reviewed. There were 328 players included in the study who started their career on the team and remained on the team for at least 2 years (mean, 3.9 years; range, 2-14 years). The history of instability prior to entering the NFL and the method of treatment were collected. Data on the occurrence of instability while in the NFL were recorded to determine the rate and timing of recurrence. Thirty-one players (9.5%) had a history of instability prior to entering the NFL. Of the 297 players with no history of instability, 39 (13.1%) had a primary event at a mean of 18.4 ± 22.2 months (range, 0-102 months) after joining the team. In the group of players with prior instability treated with surgical stabilization, there was no statistical difference in the rate of recurrence (10.5%) or the timing to the instability episode (mean, 26 months) compared with players with no history of instability. Twelve players had shoulder instability treated nonoperatively prior to the NFL. Five of these players (41.7%) had recurrent instability at a mean of 4.4 ± 7.0 months (range, 0-16 months). The patients treated nonoperatively had a significantly higher rate of recurrence (P = 0.02) and an earlier time of recurrence (P = 0.04). The rate of contralateral instability was 25.8%, occurring at a mean of 8.6 months. Recurrent shoulder instability is more common in NFL players with a history of nonoperative treatment. Surgical stabilization appears to restore the rate and timing of instability to that of players with no prior history of instability.

Fluid aspects of electron streaming instability in electron-ion plasmas

International Nuclear Information System (INIS)

Jao, C.-S.; Hau, L.-N.

2014-01-01

Electrons streaming in a background electron and ion plasma may lead to the formation of electrostatic solitary wave (ESW) and hole structure which have been observed in various space plasma environments. Past studies on the formation of ESW are mostly based on the particle simulations due to the necessity of incorporating particle's trapping effects. In this study, the fluid aspects and thermodynamics of streaming instabilities in electron-ion plasmas including bi-streaming and bump-on-tail instabilities are addressed based on the comparison between fluid theory and the results from particle-in-cell simulations. The energy closure adopted in the fluid model is the polytropic law of d(pρ −γ )/dt=0 with γ being a free parameter. Two unstable modes are identified for the bump-on-tail instability and the growth rates as well as the dispersion relation of the streaming instabilities derived from the linear theory are found to be in good agreement with the particle simulations for both bi-streaming and bump-on-tail instabilities. At the nonlinear saturation, 70% of the electrons are trapped inside the potential well for the drift velocity being 20 times of the thermal velocity and the pρ −γ value is significantly increased. Effects of ion to electron mass ratio on the linear fluid theory and nonlinear simulations are also examined

Analysis of intense beam instability in a general quadrupole focusing channel with image charge effect

Energy Technology Data Exchange (ETDEWEB)

Goswami, A., E-mail: animesh@vecc.gov.in; Sing Babu, P., E-mail: psb@vecc.gov.in; Pandit, V.S., E-mail: pandit@vecc.gov.in

2016-02-01

The stability properties of transverse envelopes of mismatched intense continuous charge particle beam propagating in a general quadrupole focusing channel have been investigated in the presence of image charge effect due to a cylindrical conducting pipe. Phase shifts and growth factors of the envelope oscillations in the case of instability are calculated by numerical evaluation of the eigenvalues of linearly perturbed envelope equations for small deviations from the matched beam conditions. A detailed study on the region of instability and its dependence on the system parameters like occupancy of the quadrupole focusing field, syncopation factor, zero current phase advance, beam intensity etc. have been carried out. It has been found that the strength and regions of envelope instability due to the lattice and confluent resonances in the parametric space are affected by the presence of image charge.

Plasma physics and instabilities

International Nuclear Information System (INIS)

Lashmore-Davies, C.N.

1981-01-01

These lectures procide an introduction to the theory of plasmas and their instabilities. Starting from the Bogoliubov, Born, Green, Kirkwood, and Yvon (BBGKY) hierarchy of kinetic equations, the additional concept of self-consistent fields leads to the fundamental Vlasov equation and hence to the warm two-fluid model and the one-fluid MHD, or cold, model. The properties of small-amplitude waves in magnetized (and unmagnetized) plasmas, and the instabilities to which they give rise, are described in some detail, and a complete chapter is devoted to Landau damping. The linear theory of plasma instabilities is illustrated by the current-driven electrostatic kind, with descriptions of the Penrose criterion and the energy principle of ideal MHD. There is a brief account of the application of feedback control. The non-linear theory is represented by three examples: quasi-linear velocity-space instabilities, three-wave instabilities, and the stability of an arbitrarily largeamplitude wave in a plasma. (orig.)

Stabilization of ablative Rayleigh-Taylor instability due to change of the Atwood number

International Nuclear Information System (INIS)

Ye Wenhua; He, X.T.; Zhang Weiyan

2002-01-01

Recent experiment [S.G. Glendinning et al., Phys. Rev. Lett. 78, 3318 (1997)] showed that the measured growth rate of laser ablative Rayleigh-Taylor (RT) instability with preheating is about 50% of the classic value and is reduced by about 18% compared with the simulated value obtained with the computer code LASNEX. By changing the temperature variation of the electron thermal conductivity at low temperatures, the density profile from the Bhatnagar-Gross-Krook approximation is recovered in the simulation, and the simulated RT growth rate is in good agreement with the experimental value from Glendinning et al. The preheated density profile on ablative RT stablization is studied numerically. A change of the Atwood number in the preheating case also leads to RT stabilization. The RT growth formula γ=√(Akg/(1+AkL))-2kV a agrees well with experiment and simulation, and is appropriate for the preheating case

New features of current-driven low-frequency instabilities in a Q-machine plasma

International Nuclear Information System (INIS)

Dimitriu, Dan-Gheorghe; Ignatescu, Valerian; Lozneanu, Erzilia; Sanduloviciu, Mircea; Ionita, Codrina; Schrittwieser, Roman Wolfgang

2001-01-01

Among the instabilities in a low-density magnetized plasma column, the electrostatic ion-cyclotron instability (EICI) and the potential relaxation instability (PRI) are the best known and most thoroughly investigated. Both instabilities are excited by drawing an electron current parallel to the magnetic field towards a circular collector (CO), which is inserted into the plasma column perpendicular to the axis. For the PRI, the radius of CO must be considerably larger than the ion gyroradius so that the ion trajectories can be approximated as one-dimensional. For the EICI, the radius of CO must be considerably smaller than that of the plasma column, but also larger than one ion gyroradius. A transition from the PRI into the EICI was reported earlier. A certain range of CO radii was found where both instabilities could be excited simultaneously. We report on a strong modulation of the EICI by the PRI, obtained for gradually increasing the CO bias, with the EICI appearing at first, and later the PRI. The EICI frequency was about four times larger than that of the PRI. The modulation not only affects the amplitude but also the frequency of the EICI. This leads to the formation of sidebands in the spectrum around f EICI with a frequency difference equal to ± f PRI . In addition, we find that the EICI frequency depends not only on the magnetic field strength but also on the CO current. Our data also show a strong non-linear dependence of the PRI frequency on the magnetic field strength. To explain these features, we propose a new phenomenological model, which is able to clarify the role of complex space charge configurations for low frequency instabilities in a low-density magnetized plasma column. (authors)

Parametric decay instabilities in ECR heated plasmas

International Nuclear Information System (INIS)

Porkolab, M.

1982-01-01

The possibility of parametric excitation of electron Bernstein waves and low frequency ion oscillations during ECR heating at omega/sub o/ approx. = l omega/sub ce/, l = 1,2 is examined. In particular, the thresholds for such instabilities are calculated. It is found that Bernstein waves and lower hybrid quasi-modes have relatively low homogeneous where T/sub e/ approx. = T/sub i/. Thus, these processes may lead to nonlinear absorption and/or scattering of the incident pump wave. The resulting Bernstein waves may lead to either more effective heating (especially during the start-up phase) or to loss of microwave energy if the decay waves propagate out of the system before their energy is absorbed by particles. While at omega/sub o/ = omega/sub UH/ the threshold is reduced due to the WKB enhancement of the pump wave, (and this instability may be important in tokamaks) in EBT's and tandem mirrors the instability at omega /sub o/ greater than or equal to 2 omega/sub ce/ may be important. The instability may persist even if omega > 2 omega/sub ce/ and this may be the case during finite beta depression of the magnetic field in which case the decay waves may be trapped in the local magnetic well so that convective losses are minimized. The excited fluctuations may lead to additional scattering of the ring electrons and the incident microwave fields. Application of these calculations to ECR heating of tokamaks, tandem mirrors, and EBT's will be examined

DIFFERENTIAL EQUATION SIMULATION IN CALCULATION OF LATERAL AND TRANSVERSE-LONGITUDINAL BENDING OF FRAME STRUCTURES WITHOUT AND WITH DUE ACCOUNT OF VISCOELASTIC MATERIAL PROPERTIES

Directory of Open Access Journals (Sweden)

V. M. Ovsianko

2012-01-01

Full Text Available The paper reveals a brand-new direction in simulation of frame and continual structures while calculating static and dynamic loads and stability.  An electronic model has been synthesized  for an investigated object and then it has been analyzed not with the help of  specialized analog computing techniques but by means of high-performance software package for electronic circuit calculation using a personal computer.The given paper contains exact algebraic equations corresponding to differential equations for lateral bending calculation of frame structures without and with due account of viscoelastic material properties in compliance with the Kelvin model.The exact algebraic equation for a beam on elastic supports (or elastic Winkler foundation has been derived for quartic differential equation.The paper presents a number of exact algebraic equations which are equivalent to differential equations for transverse-longitudinal bending calculation of frame structures without and with due account of viscoelastic material properties when lateral and longitudinal loads are applied in the form of  impulses with any periods of their duration and any interchangeability. 

Linear theory of the Rayleigh-Taylor instability in the equatorial ionsophere

International Nuclear Information System (INIS)

Russel, D.A.; Ott, E.

1979-01-01

We present a liner theory of the Rayleigh-Taylor instability in the equatorial ionosphere. For a purely exponential density profile, we find that no unstable eigenmode solutions exist. For a particular model ionosphere with an F peak, unstable eigenmode solutions exist only for sufficiently small horizontal wave numbers. In the later case, purely exponential growth at a rate identical to that for the sharp boundary instability is found. To clarify the situation in the case that eigenmodes do not exist, we solve the initial value problem for the linearized ion equation of motion in the long time asymptotic limit. Ion inertia and ion-neutral collisions are included. Assuming straight magnetic field lines, we find that when eigenmodes do not exist the growth of the response to an impulse is slower than exponential viz, t=/sup -1/2/ exp (γ/sup t/) below the F peak and t/sup -3/2/ exp(γ/sup t/) above the peak; and we determine γ

Electrostatic instabilities and turbulence in a toroidal magnetized plasma

International Nuclear Information System (INIS)

Poli, F. M.

2007-06-01

dominant instabilities to other spectral components and that this mechanism is independent of the nature of the instabilities. Nonlinear interactions between the mode and its nonlinearly generated harmonics are responsible for the filling of the spectral regions between harmonics. Later in the development along the convection path, the unstable mode transfers energy to spectral components with significantly larger frequencies. This transfer of energy can be interpreted in the investigated plasma scenarios as a forward cascade in wavenumbers, with transfer of energy from large to small scales. (author)

Stream instability countermeasures applied at Kansas Department of Transportation highway structures.

Science.gov (United States)

2008-11-01

This project considered stream instability countermeasures used by the Kansas Department of Transportation (KDOT) to protect the highway infrastructure at stream crossings from changes due to the dynamic nature of streams. Site visits were made to 13...

The effect of giant lateral collapses on magma pathways and the location of volcanism.

Science.gov (United States)

Maccaferri, Francesco; Richter, Nicole; Walter, Thomas R

2017-10-23

Flank instability and lateral collapse are recurrent processes during the structural evolution of volcanic edifices, and they affect and are affected by magmatic activity. It is known that dyke intrusions have the potential to destabilise the flanks of a volcano, and that lateral collapses may change the style of volcanism and the arrangement of shallow dykes. However, the effect of a large lateral collapse on the location of a new eruptive centre remains unclear. Here, we use a numerical approach to simulate the pathways of magmatic intrusions underneath the volcanic edifice, after the stress redistribution resulting from a large lateral collapse. Our simulations are quantitatively validated against the observations at Fogo volcano, Cabo Verde. The results reveal that a lateral collapse can trigger a significant deflection of deep magma pathways in the crust, favouring the formation of a new eruptive centre within the collapse embayment. Our results have implications for the long-term evolution of intraplate volcanic ocean islands.

Instability characteristics of fluidelastic instability of tube rows in crossflow

International Nuclear Information System (INIS)

Chen, S.S.; Jendrzejczyk, J.A.

1986-04-01

An experimental study is reported to investigate the jump phenomenon in critical flow velocities for tube rows with different pitch-to-diameter ratios and the excited and intrinsic instabilities for a tube row with a pitch-to-diameter ratio of 1.75. The experimental data provide additional insights into the instability phenomena of tube arrays in crossflow. 9 refs., 10 figs

The Halloween Lateral Canthotomy Model

Directory of Open Access Journals (Sweden)

Nur-Ain Nadir

2017-04-01

Full Text Available Audience: The Halloween Lateral Canthotomy Model” is designed to instruct Emergency Medicine residents PGY 1-4, as well as Emergency Medicine-bound students. Introduction: Although uncommon, retrobulbar hemorrhage associated with facial trauma is a potential cause of permanent vision loss due to orbital compartment syndrome. To prevent vision loss, treatment with lateral canthotomy is time-sensitive and to perform this procedure in an emergent setting requires properly trained practitioners. Objectives: The purpose of the model is to teach residents and students how to perform lateral canthotomy and to achieve competency in their skills. Method: Lateral canthotomy is an important skill to be proficient in for any Emergency Medicine Physician, as it is an uncommon, sight-saving procedure. It is indicated in scenarios of facial trauma that cause a retrobulbar hemorrhage. Patients are at risk for permanent vision loss due to acute orbital compartment syndrome if the procedure is not done expeditiously.1 A less likely cause of retrobulbar hemorrhage is spontaneous hemorrhage due to a bleeding disorder or anticoagulant use.2 The features of retrobulbar hemorrhage include acute loss of visual acuity, relative afferent pupillary defect, proptosis with resistance to retropulsion, increased intraocular pressure, and limited extra ocular movement.3 While the diagnosis is clinical, it can be confirmed by computed tomography (CT and measurement of intraocular pressure.2 When the diagnosis is established, lateral canthotomy and cantholysis should be performed emergently. Cantholysis is contraindicated when a globe rupture is suspected or with an orbital blowout fracture. Potential complications of this procedure include iatrogenic injury to the globe or lateral rectus muscle, damage to the elevator aponeurosis resulting in ptosis, injury to the lacrimal gland and lacrimal artery, bleeding and infection.3 This task trainer uses affordable materials to let

Effects of mass transfer on a resonance instability in the laminar ...

Indian Academy of Sciences (India)

pressible boundary layer flow due to a rotating-disk is investigated in this paper based on the linear stability theory. The possible .... Reynolds number limit to the inviscid modes strongly suggests that the resonance instability identified here ...

A coupled bunch instability due to beam-photoelectron interactions in KEKB-LER

Energy Technology Data Exchange (ETDEWEB)

Ohmi, Kazuhito [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan)

1996-08-01

LER of KEKB is designed to storage the positron beam of 2.6 A with multibunch operation. Nb = 3.3 x 10{sup 10} positrons are filled in a bunch and the bunch passes every 2ns through a beam chamber. The photoelectron instability may be serious for KEKB-LER. We consider a motion of photoelectrons produced by a bunch with a computer simulation technic. A cylindrical chamber with a diameter of 10 cm was used as a model chamber. About 15 times of the photoelectrons were produced by a bunch. The wake force was calculated for the loading bunches with displacements of 0.5 mm and 1 mm. The wake characteristics seems to be caused by the trapped electrons kicked by the loading bunch. The wake was saturated with the loading displacement of 0.5 mm. We obtained a growth rate by the wake force. It is very high rate, 2500s{sup -1} which exceeds damping rates of various mechanism, radiation, head-tail and feedback. Perhaps it is essential to remove the photoelectrons around the positron beam explicitly. If we apply magnetic field fo about 20 G, the growth rate will be reduced. (S.Y.)

Helical instability in film blowing process: Analogy to buckling instability

Science.gov (United States)

Lee, Joo Sung; Kwon, Ilyoung; Jung, Hyun Wook; Hyun, Jae Chun

2017-12-01

The film blowing process is one of the most important polymer processing operations, widely used for producing bi-axially oriented film products in a single-step process. Among the instabilities observed in this film blowing process, i.e., draw resonance and helical motion occurring on the inflated film bubble, the helical instability is a unique phenomenon portraying the snake-like undulation motion of the bubble, having the period on the order of few seconds. This helical instability in the film blowing process is commonly found at the process conditions of a high blow-up ratio with too low a freezeline position and/or too high extrusion temperature. In this study, employing an analogy to the buckling instability for falling viscous threads, the compressive force caused by the pressure difference between inside and outside of the film bubble is introduced into the simulation model along with the scaling law derived from the force balance between viscous force and centripetal force of the film bubble. The simulation using this model reveals a close agreement with the experimental results of the film blowing process of polyethylene polymers such as low density polyethylene and linear low density polyethylene.

Functional Instability of the Ankle Joint: Etiopathogenesis

Directory of Open Access Journals (Sweden)

Aydan ÖRSÇELİK

2016-09-01

Full Text Available Ankle sprain is one of the most common sports injuries. Chronic ankle instability is a common complication of ankle sprains. Two causes of chronic ankle instability are mechanical instability and functional instability. It is important to understand functional instability etiopathogenesis of the ankle joint in order to guide diagnosis and treatment. This article aims to understand the etiopathogenesis of functional ankle instability.

The role of arthroscopy in the treatment of functional instability of the ankle.

Science.gov (United States)

Kerr, Hui-Ling; Bayley, Edward; Jackson, Rosalyn; Kothari, Paresh

2013-12-01

Ankle sprains are common, the majority resolving with functional rehabilitation. Some patients are left with symptoms of functional instability (FI). Ankle arthroscopy in those with symptoms of FI is not well covered in the literature. Our aim was to assess its role in FI of the ankle. Retrospective case note analysis of patients with FI following an ankle sprain from 2005 to 2007. All underwent arthroscopy, provided mechanical instability was excluded (EUA and stress X-rays), and there were no signs of soft tissue impingement. These patients had exhausted all options of conservative therapy. Seventy-seven patients with a mean age of 38.1: five had true mechanical instability and were excluded. 72 underwent arthroscopy: 67 (93.1%) had significant amounts of scar tissue needing debridement, most commonly in the antero-lateral corner (58.3%). 52 patients improved (72.2%) at a minimum of 6 months follow-up. Our study supports the role of ankle arthroscopy in the treatment of FI following trauma. It should be considered when conservative measures have failed. Copyright © 2013 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.

POWER STABILITY MONITORING BASED ON VOLTAGE INSTABILITY PREDICTION APPROACH THROUGH WIDE AREA SYSTEM

OpenAIRE

H. H. Goh; Q. S. Chua; S. W. Lee; B. C. Kok; K. C. Goh; K. T.K. Teo

2014-01-01

Nowadays, power systems are being forced to operate closer to its security limit due to current economic growth and the difficulties to upgrade the existing grid infrastructure. With the sudden increment of power demand, voltage instability problem has become a main concern to the power system operator because voltage instability has led or crucially contributed to some major blackouts throughout the world. Hence, methods for early warning and early prevention are required to prevent the powe...

Ectopic Expression of Testis Germ Cell Proteins in Cancer and Its Potential Role in Genomic Instability

Directory of Open Access Journals (Sweden)

Aaraby Yoheswaran Nielsen

2016-06-01

Full Text Available Genomic instability is a hallmark of human cancer and an enabling factor for the genetic alterations that drive cancer development. The processes involved in genomic instability resemble those of meiosis, where genetic material is interchanged between homologous chromosomes. In most types of human cancer, epigenetic changes, including hypomethylation of gene promoters, lead to the ectopic expression of a large number of proteins normally restricted to the germ cells of the testis. Due to the similarities between meiosis and genomic instability, it has been proposed that activation of meiotic programs may drive genomic instability in cancer cells. Some germ cell proteins with ectopic expression in cancer cells indeed seem to promote genomic instability, while others reduce polyploidy and maintain mitotic fidelity. Furthermore, oncogenic germ cell proteins may indirectly contribute to genomic instability through induction of replication stress, similar to classic oncogenes. Thus, current evidence suggests that testis germ cell proteins are implicated in cancer development by regulating genomic instability during tumorigenesis, and these proteins therefore represent promising targets for novel therapeutic strategies.

Direct Numerical Simulation of Transition Due to Traveling Crossflow Vortices

Science.gov (United States)

Li, Fei; Choudhari, Meelan M.; Duan, Lian

2016-01-01

Previous simulations of laminar breakdown mechanisms associated with stationary crossflow instability over a realistic swept-wing configuration are extended to investigate the alternate scenario of transition due to secondary instability of traveling crossflow modes. Earlier analyses based on secondary instability theory and parabolized stability equations have shown that this alternate scenario is viable when the initial amplitude of the most amplified mode of the traveling crossflow instability is greater than approximately 0.03 times the initial amplitude of the most amplified stationary mode. The linear growth predictions based on the secondary instability theory and parabolized stability equations agree well with the direct numerical simulation. Nonlinear effects are initially stabilizing but subsequently lead to a rapid growth followed by the onset of transition when the amplitude of the secondary disturbance exceeds a threshold value. Similar to the breakdown of stationary vortices, the transition zone is rather short and the boundary layer becomes completely turbulent across a distance of less than 15 times the boundary layer thickness at the completion of transition.

Chromosomal instability induced by ionizing radiation

International Nuclear Information System (INIS)

Morgan, W.F.; Marder, B.A.; Day, J.P.

1995-01-01

There is accumulating evidence indicating genomic instability can manifest multiple generations after cellular exposure to DNA damaging agents. For instance, some cells surviving exposure to ionizing radiations show delayed reproductive cell death, delayed mutation and / or delayed chromosomal instability. Such instability, especially chromosome destabilization has been implicated in mutation, gene amplification, cellular transformation, and cell killing. To investigate chromosomal instability following DNA damage, we have used fluorescence in situ hybridization to detect chromosomal rearrangements in a human/hamster somatic hybrid cell line following exposure to ionizing radiation. Delayed chromosomal instability was detected when multiple populations of uniquely arranged metaphases were observed in clonal isolates raised from single cells. The relationship between delayed chromosomal destabilization and other endpoints of genomic instability, namely; delayed mutation and gene amplification will be discussed, as will the potential cytogenetic and molecular mechanisms contributing to delayed chromosomal instability

Fermi-Pasta-Ulam recurrence and modulation instability

Science.gov (United States)

Kuznetsov, E. A.

2017-01-01

We give a qualitative conceptual explanation of the Fermi-Pasta-Ulam (FPU) like recurrence in the onedimensional focusing nonlinear Schrodinger equation (NLSE). The recurrence can be considered as a result of the nonlinear development of the modulation instability. All known exact localized solitary wave solutions describing propagation on the background of the modulationally unstable condensate show the recurrence to the condensate state after its interaction with solitons. The condensate state locally recovers its original form with the same amplitude but a different phase after soliton leave its initial region. Based on the integrability of the NLSE, we demonstrate that the FPU recurrence takes place not only for condensate, but also for a more general solution in the form of the cnoidal wave. This solution is periodic in space and can be represented as a solitonic lattice. That lattice reduces to isolated soliton solution in the limit of large distance between solitons. The lattice transforms into the condensate in the opposite limit of dense soliton packing. The cnoidal wave is also modulationally unstable due to soliton overlapping. The recurrence happens at the nonlinear stage of the modulation instability. Due to generic nature of the underlying mathematical model, the proposed concept can be applied across disciplines and nonlinear systems, ranging from optical communications to hydrodynamics.

Streaming instabilities in a collisional dusty plasma

International Nuclear Information System (INIS)

Mamun, A. A.; Shukla, P. K.

2000-01-01

A pair of low-frequency electrostatic modes, which are very similar to those experimentally observed by Praburam and Goree [Phys. Plasmas 3, 1212 (1996)], are found to exist in a dusty plasma with a significant background neutral pressure and background ion streaming. One of these two modes is the dust-acoustic mode and the other one is a new mode which is due to the combined effects of the ion streaming and ion--neutral collisions. It has been shown that in the absence of the ion streaming, the dust-acoustic mode is damped due to the combined effects of the ion--neutral and dust--neutral collisions and the electron--ion recombination onto the dust grain surface. This result disagrees with Kaw and Singh [Phys. Rev. Lett. 79, 423 (1997)], who reported collisional instability of the dust-acoustic mode in such a dusty plasma. It has also been found that a streaming instability with the growth rate of the order of the dust plasma frequency is triggered when the background ion streaming speed relative to the charged dust particles is comparable or higher than the ion--thermal speed. This point completely agrees with Rosenberg [J. Vac. Soc. Technol. A 14, 631 (1996)

Study on Influence of Tube Arrays on Fluid Elastic Instability

Science.gov (United States)

Ishihara, Kunihiko; Kitayama, Gen

The tube bank is used in boilers, heat exchangers in power plants and steam generators in nuclear plants. These tubes sometimes vibrate violently and come to the fatigue failure due to the flow induced vibration which is caused by the cross flow. This phenomenon is that the large vibrations arise at the critical flow velocity and it is called fluid elastic instability. However the relation between the onset velocity of fluid elastic instability and the tube array's geometry has not been clarified sufficiently. There is a few reference related to the relation between the pitch to diameter ratio and the onset velocity even in the lattice arrays. In this paper, the influence of tube arrays on fluid elastic instability is examined by experiments. As a result, it is clarified that the tube vibrations become large as T/D increases and L/D decreases, and the tube vibrations strongly depend on the dynamic characteristics of tubes such as the natural frequency and the damping ability.

Invited Review. Combustion instability in spray-guided stratified-charge engines. A review

Energy Technology Data Exchange (ETDEWEB)

Fansler, Todd D. [Univ. of Wisconsin, Madison, WI (United States); Reuss, D. L. [Univ. of Michigan, Ann Arbor, MI (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sick, V. [Univ. of Michigan, Ann Arbor, MI (United States); Dahms, R. N. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

2015-02-02

Our article reviews systematic research on combustion instabilities (principally rare, random misfires and partial burns) in spray-guided stratified-charge (SGSC) engines operated at part load with highly stratified fuel -air -residual mixtures. Results from high-speed optical imaging diagnostics and numerical simulation provide a conceptual framework and quantify the sensitivity of ignition and flame propagation to strong, cyclically varying temporal and spatial gradients in the flow field and in the fuel -air -residual distribution. For SGSC engines using multi-hole injectors, spark stretching and locally rich ignition are beneficial. Moreover, combustion instability is dominated by convective flow fluctuations that impede motion of the spark or flame kernel toward the bulk of the fuel, coupled with low flame speeds due to locally lean mixtures surrounding the kernel. In SGSC engines using outwardly opening piezo-electric injectors, ignition and early flame growth are strongly influenced by the spray's characteristic recirculation vortex. For both injection systems, the spray and the intake/compression-generated flow field influence each other. Factors underlying the benefits of multi-pulse injection are identified. Finally, some unresolved questions include (1) the extent to which piezo-SGSC misfires are caused by failure to form a flame kernel rather than by flame-kernel extinction (as in multi-hole SGSC engines); (2) the relative contributions of partially premixed flame propagation and mixing-controlled combustion under the exceptionally late-injection conditions that permit SGSC operation on E85-like fuels with very low NO_x and soot emissions; and (3) the effects of flow-field variability on later combustion, where fuel-air-residual mixing within the piston bowl becomes important.

Gait Biomechanics in Participants, Six Months after First-time Lateral Ankle Sprain.

Science.gov (United States)

Doherty, C; Bleakley, C; Hertel, J; Caulfield, B; Ryan, J; Delahunt, E

2016-06-01

No research currently exists predicating a link between the injury-affiliated sensorimotor deficits of acute ankle sprain and those of chronic ankle instability during gait. This analysis evaluates participants with a 6-month history of ankle sprain injury to affirm this link. 69 participants with a 6-month history of acute first-time lateral ankle sprain were divided into subgroups ('chronic ankle instability' and 'coper') based on their self-reported disability and compared to 20 non-injured participants during a gait task. Lower extremity kinematic and kinetic data were collected from 200 ms pre- to 200 ms post-heel strike (period 1) and from 200 ms pre- to 200 ms post-toe off (period 2). The 'chronic ankle instability' subgroup (who reported greater disability) displayed increased knee flexion during period 1. During period 2, this subgroup exhibited greater total displacement at their ankle joint and greater extensor dominance at their knee. That many of these features are present, both in individuals with acute ankle sprain and those with chronic ankle instability may advocate a link between acute deficits and long-term outcome. Clinicians must be aware that the sensorimotor deficits of ankle sprain may persevere beyond the acute stage of injury and be cognizant of the capacity for impairments to pervade proximally. © Georg Thieme Verlag KG Stuttgart · New York.

Surgical management of cervical spine instability in Rheumatoid Arthritis patients

Directory of Open Access Journals (Sweden)

Pedro Miguel Marques

2015-01-01

Full Text Available Aim: Cross-sectional study that aims to evaluate the results of cervical spine surgeries due to rheumatoid arthritis (RA instability, between January of 2000 and of 2012 in a main Portuguese centre Methods: Patients followed on Rheumatology submitted to cervical spine fusion due to atlantoaxial (AAI, sub-axial (SAI or cranio-cervical (CCI instabilities between 2000-2012 were included. Information about the surgical procedure and associated complications was gathered and imagiologic and clinical indexes before and after surgery (as anterior and posterior atlanto-axial interval and Ranawat index were evaluated and compared using adequate statistics. Results: Forty-five patients with RA were included: 25 with AAI, 13 with CCI and 7 with SAI. Ten AAI and 4 CCI patients were submitted to wiring stabilization techniques; 15 AAI and 9 CCI patients to rigid ones; and in all patients with SAI an anterior cervical arthrodesis was chosen. There is a significant increase in PADI and a decrease in AADI in the postoperative evaluation (p

Air pollution and genomic instability: The role of particulate matter in lung carcinogenesis

International Nuclear Information System (INIS)

Santibáñez-Andrade, Miguel; Quezada-Maldonado, Ericka Marel; Osornio-Vargas, Álvaro; Sánchez-Pérez, Yesennia; García-Cuellar, Claudia M.

2017-01-01

In this review, we summarize and discuss the evidence regarding the interaction between air pollution, especially particulate matter (PM), and genomic instability. PM has been widely studied in the context of several diseases, and its role in lung carcinogenesis gained relevance due to an increase in cancer cases for which smoking does not seem to represent the main risk factor. According to epidemiological and toxicological evidence, PM acts as a carcinogenic factor in humans, inducing high rates of genomic alterations. Here, we discuss not only how PM is capable of inducing genomic instability during the carcinogenic process but also how our genetic background influences the response to the sources of damage. - Highlights: • Air pollution represents a worldwide problem with impact on human health. • Particulate matter (PM) has a recognized carcinogenic potential in humans. • Lung cancer susceptibility depends on gene-environment interactions. • Epidemiological and experimental evidence links PM exposure to genomic instability. • PM and genomic instability are co-dependent factors during cancer continuum. - We summarize the association between particulate matter (a component of air pollution) and genomic instability as well as discuss how new strategies to study the impact of air pollution on genomic instability and lung-cancer development could improve our understanding of the lung-cancer genome.

Nonlinear evolution of MHD instabilities

International Nuclear Information System (INIS)

Bateman, G.; Hicks, H.R.; Wooten, J.W.; Dory, R.A.

1975-01-01

A 3-D nonlinear MHD computer code was used to study the time evolution of internal instabilities. Velocity vortex cells are observed to persist into the nonlinear evolution. Pressure and density profiles convect around these cells for a weak localized instability, or convect into the wall for a strong instability. (U.S.)

Possible parametric instabilities of beat waves in a transversely magnetized plasma

International Nuclear Information System (INIS)

Salimullah, M.

1988-05-01

The effect of an external magnetic field on the various possible parametric instabilities of the longitudinal beat wave at the difference frequency of two incident laser beams in a hot plasma has been thoeretically investigated. The kinetic equation is employed to obtain the nonlinear response of the magnetized electrons due to the nonlinear coupling of the beat wave with the low-frequency electrostatic plasma modes. It is noted that the growth rates of the three-wave and the four-wave parametric instabilities can be influenced by the external transverse magnetic field. (author). 20 refs, 3 figs

Dietary factors and microsatellite instability in sporadic colon carcinomas

NARCIS (Netherlands)

Diergaarde, B.; Braam, H.; Muijen, van G.N.P.; Ligtenberg, M.J.L.; Kok, F.J.; Kampman, E.

2003-01-01

Microsatellite instability (MSI) occurs in 10-20% of the sporadic colon carcinomas and appears to be primarily due to alterations in hMLH1 and hMSH2. Little is known about the role of diet in MSI-related colon carcinogenesis. We used data from a Dutch population-based case-control study on sporadic

Dietary factors and microsatellite instability in sporadic colon carcinomas.

NARCIS (Netherlands)

Diergaarde, B.; Braam, H.; Muijen, G.N.P. van; Ligtenberg, M.J.L.; Kok, F.J.; Kampman, E.

2003-01-01

Microsatellite instability (MSI) occurs in 10-20% of the sporadic colon carcinomas and appears to be primarily due to alterations in hMLH1 and hMSH2. Little is known about the role of diet in MSI-related colon carcinogenesis. We used data from a Dutch population-based case-control study on sporadic

Coherent structures in ablatively compressed ICF targets and Rayleigh-Taylor instability

International Nuclear Information System (INIS)

Pant, H.C.; Desai, T.

1996-01-01

One of the major issues in laser induced inertial confinement fusion (ICF) is a stable ablative compression of spherical fusion pellets. The main impediment in achievement of this objective is Rayleigh-Taylor instability at the pellet's ablation front. Under sufficiently high acceleration this instability can grow out of noise. However, it can also arise either due to non-uniform laser intensity distribution over the pellet surface or due to pellet wall areal mass irregularity. Coherent structures in the dense target behind the ablation front can be effectively utilised for stabilisation of the Rayleigh-Taylor phenomenon. Such coherent structures in the form of a super lattice can be created by doping the pellet pusher with high atomic number (Z) micro particles. A compressed-cool pusher under laser irradiation behaves like a strongly correlated non ideal plasma when compressed to sufficiently high density such that the non ideality parameter exceeds unity. Moreover, the nonideality parameter for high Z microinclusions may exceed a critical value of 180 and as a consequence they remain in the form of intact clusters, maintaining the superlattice intact during ablative acceleration. Micro-hetrogeneity and its superlattice plays an important role in stabilization of Rayleigh-Taylor instability, through a variety of mechanisms. (orig.)

Instabilities, turbulence and transport in a magnetized plasma

International Nuclear Information System (INIS)

Garbet, X.

2001-06-01

The purpose of this work is to introduce the main processes that occur in a magnetized plasma. During the last 2 decades, the understanding of turbulence has made great progress but analytical formulas and simulations are far to produce reliable predictions. The values of transport coefficients in a tokamak plasma exceed by far those predicted by the theory of collisional transport. This phenomenon is called abnormal transport and might be due to plasma fluctuations. An estimation of turbulent fluxes derived from the levels of fluctuations, is proposed. A flow description of plasma allows the understanding of most micro-instabilities. The ballooning representation deals with instabilities in a toric geometry. 3 factors play an important role to stabilize plasmas: density pinch, magnetic shear and speed shear. The flow model of plasma gives an erroneous value for the stability threshold, this is due to a bad description of the resonant interaction between wave and particle. As for dynamics, flow models can be improved by adding dissipative terms so that the linear response nears the kinetic response. The kinetic approach is more accurate but is complex because of the great number of dimensions involved. (A.C.)

Dynamical Instability and Soliton Concept

International Nuclear Information System (INIS)

Kartavenko, V.G.

1994-01-01

The problem of dynamical instability and clustering (stable fragments formation) in a breakup of excited nuclear systems are considered from the points of view of the soliton concept. It is noted that the volume (spinodal) instability can be associated with nonlinear terms, and the surface (Rayleigh-Taylor type) instability, with the dispersion terms in the evolution equations. The spinodal instability and the Rayleigh-Taylor instability may compensate each other and lead to stable quasi-soliton type objects. The simple analytical model is presented to illustrate this physical picture. The time evolution of an initially compressed cold nuclear system is analysed in the framework of the inverse mean-field method. It is demonstrated that the nonlinearity and dispersion terms of the evolution equations can lead to clusterization in the final channel. 8 p

The urgency of surgical decompression in acute central cord injuries with spondylosis and without instability.

Science.gov (United States)

Lenehan, Brian; Fisher, Charles G; Vaccaro, Alex; Fehlings, Michael; Aarabi, Bizhan; Dvorak, Marcel F

2010-10-01

spinal cord compression due to developmental cervical spinal canal stenosis without fracture or instability. Those with less severe deficit (ASIA = D) can be treated with initial observation with surgery potentially at a later date depending on the extent and temporal profile of the patients neurologic recovery.

Langmuir instability in partially spin polarized bounded degenerate plasma

Science.gov (United States)

Iqbal, Z.; Jamil, M.; Murtaza, G.

2018-04-01

Some new features of waves inside the cylindrical waveguide on employing the separated spin evolution quantum hydrodynamic model are evoked. Primarily, the instability of Langmuir wave due to the electron beam in a partially spin polarized degenerate plasma considering a nano-cylindrical geometry is discussed. Besides, the evolution of a new spin-dependent wave (spin electron acoustic wave) due to electron spin polarization effects in the real wave spectrum is elaborated. Analyzing the growth rate, it is found that in the absence of Bohm potential, the electron spin effects or exchange interaction reduce the growth rate as well as k-domain but the inclusion of Bohm potential increases both the growth rate and k-domain. Further, we investigate the geometry effects expressed by R and pon and find that they have opposite effects on the growth rate and k-domain of the instability. Additionally, how the other parameters like electron beam density or streaming speed of beam electrons influence the growth rate is also investigated. This study may find its applications for the signal analysis in solid state devices at nanoscales.

Nonlinear full two-fluid study of m=0 sausage instabilities in an axisymmetric Z pinch

International Nuclear Information System (INIS)

Loverich, J.; Shumlak, U.

2006-01-01

A nonlinear full five-moment two-fluid model is used to study axisymmetric instabilities in a Z pinch. When the electron velocity due to the current J is greater than the ion acoustic speed, high wave-number sausage instabilities develop that initiate shock waves in the ion fluid. This condition corresponds to a pinch radius on the order of a few ion Larmor radii

Assessment of postural instability in patients with Parkinson's disease.

Science.gov (United States)

Błaszczyk, J W; Orawiec, R; Duda-Kłodowska, D; Opala, G

2007-10-01

Postural instability is one of the most disabling features of idiopathic Parkinson's disease (PD). In this study, we focused on postural instability as the main factor predisposing parkinsonians to falls. For this purpose, changes in sway characteristics during quiet stance due to visual feedback exclusion were studied. We searched for postural sway measures that could be potential discriminators for an increased fall risk. A group of 110 subjects: 55 parkinsonians (Hoehn and Yahr: 1-3), and 55 age-matched healthy volunteers participated in the experiment. Their spontaneous sway characteristics while standing quiet with eyes open and eyes closed were analyzed. We found that an increased mediolateral sway and sway area while standing with eyes closed are characteristic of parkinsonian postural instability and may serve to quantify well a tendency to fall. These sway indices significantly correlated with disease severity rated both by the Hoehn and Yahr scale as well as by the Motor Section of the UPDRS. A forward shift of a mean COP position in parkinsonians which reflects their flexed posture was also significantly greater to compare with the elderly subjects and exhibited a high sensitivity to visual conditions. Both groups of postural sway abnormalities identified here may be used as accessible and reliable measures which allow for quantitative assessment of postural instability in Parkinson's disease.

Modal instability of rod fiber amplifiers: a semi-analytic approach

DEFF Research Database (Denmark)

Jørgensen, Mette Marie; Hansen, Kristian Rymann; Laurila, Marko

2013-01-01

The modal instability (MI) threshold is estimated for four rod fiber designs by combining a semi-analytic model with the finite element method. The thermal load due to the quantum defect is calculated and used to numerically determine the mode distributions on which the expression for the onset o...

Initiation of genome instability and preneoplastic processes through loss of Fhit expression.

Directory of Open Access Journals (Sweden)

Joshua C Saldivar

Full Text Available Genomic instability drives tumorigenesis, but how it is initiated in sporadic neoplasias is unknown. In early preneoplasias, alterations at chromosome fragile sites arise due to DNA replication stress. A frequent, perhaps earliest, genetic alteration in preneoplasias is deletion within the fragile FRA3B/FHIT locus, leading to loss of Fhit protein expression. Because common chromosome fragile sites are exquisitely sensitive to replication stress, it has been proposed that their clonal alterations in cancer cells are due to stress sensitivity rather than to a selective advantage imparted by loss of expression of fragile gene products. Here, we show in normal, transformed, and cancer-derived cell lines that Fhit-depletion causes replication stress-induced DNA double-strand breaks. Using DNA combing, we observed a defect in replication fork progression in Fhit-deficient cells that stemmed primarily from fork stalling and collapse. The likely mechanism for the role of Fhit in replication fork progression is through regulation of Thymidine kinase 1 expression and thymidine triphosphate pool levels; notably, restoration of nucleotide balance rescued DNA replication defects and suppressed DNA breakage in Fhit-deficient cells. Depletion of Fhit did not activate the DNA damage response nor cause cell cycle arrest, allowing continued cell proliferation and ongoing chromosomal instability. This finding was in accord with in vivo studies, as Fhit knockout mouse tissue showed no evidence of cell cycle arrest or senescence yet exhibited numerous somatic DNA copy number aberrations at replication stress-sensitive loci. Furthermore, cells established from Fhit knockout tissue showed rapid immortalization and selection of DNA deletions and amplifications, including amplification of the Mdm2 gene, suggesting that Fhit loss-induced genome instability facilitates transformation. We propose that loss of Fhit expression in precancerous lesions is the first step in the

Medial release and lateral imbrication for intractable anterior knee pain: diagnostic process, technique, and results

Directory of Open Access Journals (Sweden)

Meldrum AR

2015-01-01

Full Text Available Alexander R Meldrum,1 Jeremy R Reed,2 Megan D Dash3 1Department of Surgery, Section of Orthopedic Surgery, University of Calgary, Calgary, AB, Canada; 2Department of Surgery, University of Saskatchewan College of Medicine, Regina, SK, Canada; 3Department of Family Medicine, College of Medicine, University of Saskatchewan, Regina, SK, Canada Purpose: To present two cases of intractable patellofemoral pain syndrome treated with a novel procedure, arthroscopic medial release, and lateral imbrication of the patellar retinaculum. Patients and methods: This case series presents the treatment of three knees in two patients (one bilateral in whom an all-inside arthroscopic medial release and lateral imbrication of the patellar retinaculum was performed. Subjective measurement of pain was the primary outcome measurement, and subjective patellofemoral instability was the secondary outcome measurement. Results: Subjectively the two patients had full resolution of their pain, without any patellofemoral instability. Conclusion: Medial release and lateral imbrication of the patellar retinaculum is a new surgical procedure that has been used in the treatment of intractable patellofemoral pain syndrome. This is the first report of its kind in the literature. While outcome measurements were less than ideal, the patients had positive outcomes, both functionally and in terms of pain. Keywords: anterior knee pain syndrome, chondromalacia patellae, runners knee, patellar chondropathy, patellofemoral dysfunction, patellofemoral tracking disorder

Secondary Instability of Stationary Crossflow Vortices in Mach 6 Boundary Layer Over a Circular Cone

Science.gov (United States)

Li, Fei; Choudhari, Meelan M.; Paredes-Gonzalez, Pedro; Duan, Lian

2015-01-01

Hypersonic boundary layer flows over a circular cone at moderate incidence can support strong crossflow instability. Due to more efficient excitation of stationary crossflow vortices by surface roughness, such boundary layer flows may transition to turbulence via rapid amplification of the high-frequency secondary instabilities of finite amplitude stationary crossflow vortices. The amplification characteristics of these secondary instabilities are investigated for crossflow vortices generated by an azimuthally periodic array of roughness elements over a 7-degree half-angle circular cone in a Mach 6 free stream. Depending on the local amplitude of the stationary crossflow mode, the most unstable secondary disturbances either originate from the second (i.e., Mack) mode instabilities of the unperturbed boundary layer or correspond to genuine secondary instabilities that reduce to stable disturbances at sufficiently small amplitudes of the stationary crossflow vortex. The predicted frequencies of dominant secondary disturbances are similar to those measured during wind tunnel experiments at Purdue University and the Technical University of Braunschweig, Germany.

Language Lateralization Shifts with Learning by Adults

Science.gov (United States)

Plante, Elena; Almryde, Kyle; Patterson, Dianne K.; Vance, Christopher J.; Asbjørnsen, Arve E.

2014-01-01

For the majority of the population, language is a left hemisphere lateralized function. During childhood, a pattern of increasing left lateralization for language has been described in brain imaging studies, suggesting this trait develops. This development could reflect change due to brain maturation or change due to skill acquisition, given that children acquire and refine language skills as they mature. We test the possibility that skill acquisition, independent of age-associated maturation can result in shifts in language lateralization in classic language cortex. We imaged adults exposed to unfamiliar language during three successive fMRI scans. Participants were then asked to identify specific words embedded in Norwegian sentences. Exposure to these sentences, relative to complex tones, resulted in consistent activation in the left and right superior temporal gyrus. Activation in this region became increasingly left lateralized with repeated exposure to the unfamiliar language. These results demonstrate that shifts in lateralization can be produced in the short-term within a learning context, independent of maturation. PMID:25285756

Beam instability Workshop - plenary sessions

International Nuclear Information System (INIS)

2001-01-01

The purpose of this workshop was to provide a review of the mechanisms of limiting beam instabilities, their cures, including feedback, and beam measurement for synchrotron radiation light sources. 12 plenary sessions took place whose titles are: 1) challenging brilliance and lifetime issues with increasing currents; 2) limiting instabilities in multibunch; 3) experience from high currents in B factories; 4) longitudinal dynamics in high intensity/bunch; 5) Transverse instabilities for high intensity/bunch; 6) working group introduction from ESRF experience; 7) impedance modelling: simulations, minimization; 8) report on the broadband impedance measurements and modelling workshop; 9) feedback systems for synchrotron light sources; 10) beam instabilities diagnostics; 11) harmonic cavities: the pros and cons; and 12) experimental study of fast beam-ion instabilities at PLS. This document gathers the 12 articles that were presented during these sessions

Beam instability Workshop - plenary sessions

Energy Technology Data Exchange (ETDEWEB)

NONE

2001-07-01

The purpose of this workshop was to provide a review of the mechanisms of limiting beam instabilities, their cures, including feedback, and beam measurement for synchrotron radiation light sources. 12 plenary sessions took place whose titles are: 1) challenging brilliance and lifetime issues with increasing currents; 2) limiting instabilities in multibunch; 3) experience from high currents in B factories; 4) longitudinal dynamics in high intensity/bunch; 5) Transverse instabilities for high intensity/bunch; 6) working group introduction from ESRF experience; 7) impedance modelling: simulations, minimization; 8) report on the broadband impedance measurements and modelling workshop; 9) feedback systems for synchrotron light sources; 10) beam instabilities diagnostics; 11) harmonic cavities: the pros and cons; and 12) experimental study of fast beam-ion instabilities at PLS. This document gathers the 12 articles that were presented during these sessions.

Character of decay instability

International Nuclear Information System (INIS)

Polovin, R.V.; Demutskii, V.P.

1981-01-01

If the initial wave is unstable in the upper half plane Im ω>0 and there are no branch points of the quasiwave number, or if waves traveling in the same direction coalesce at a branch point, the instability is convective. On the other hand, if a branch point k(ω) does exist in the upper half-plane Im ω>0, and not all the waves that merge at this point travel in the same direction, the instability is absolute. A Green's function that describes the evolution of the perturbations of the initial wave in space and in time is constructed. The growth rates of the decay instability of the harmonics are determined. The produced waves are richer in harmonics than the initial waves. It is shown that the decay instability of an Alfven wave is absolute

A comparative study of plasma heating by ion acoustic and modified two-stream instabilities at subcritical quasi-perpendicular shocks

International Nuclear Information System (INIS)

Winske, D.; Giacalone, J.; Thomsen, M.F.; Mellott, M.M.

1987-01-01

Plasma heating due to the ion instability and the modified two-stream instability is examined for quasi-perpendicular subcritical shocks. Electron and ion heating is investigated as a function of upstream electron to ion temperature ratio and plasma beta using second-order heating rates. A simple shock model is employed in which the cross-field electron-ion drift speed is adjusted until the total (adiabatic plus anomalous) heating matches that required by the Rankine-Hugoniot relations. Quantities such as the width of the shock and the maximum electric field fluctuations are also calculated, and the results are compared with the ISEE data set of subcritical box shock crossings. The observed width of the shock, the amount of plasma heating, and the low-frequency electric field intensity are in reasonably good agreement with the calculations for the modified two-stream instability. On the other hand, the wave intensities at higher frequency are about 4 orders of magnitude smaller than those predicted for the ion acoustic instability at saturation, consistent with the fact that the measured shock widths imply cross-field drift speeds that are below threshold for this instability. It is therefore concluded that the dissipation at these shocks is most likely due to the lower frequency, modified two-stream instability

On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability

International Nuclear Information System (INIS)

Meyers, M.D.; Huang, C.-K.; Zeng, Y.; Yi, S.A.; Albright, B.J.

2015-01-01

The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models

On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability

Science.gov (United States)

Meyers, M. D.; Huang, C.-K.; Zeng, Y.; Yi, S. A.; Albright, B. J.

2015-09-01

The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models.

Sausage instabilities in electron current channels and the problem of fast ignition

International Nuclear Information System (INIS)

Das, A.

2002-01-01

In the fast ignition concept of laser fusion, an intense picosecond laser pulse incident on an overdense pellet is absorbed by nonlinear mechanisms and gets converted into inward propagating fast electron currents. PIC simulations show that the return shielding currents due to cold plasma interact with the incoming currents and intense Weibel, tearing and coalescence instabilities take place, which organize the current into a few current channels. The stability of these current channels is thus a topic of great interest. We have carried out linear and nonlinear studies of 2 - dimensional sausage instabilities of a slab model of the current channels in the framework of electron magnetohydrodynamic fluid approximation. The analytic calculations and numerical simulations for some simple velocity profiles show the presence of linear instability driven by velocity shear. Nonlinear studies on the saturation of instabilities and their reaction back on the relaxation of the velocity profile have also been made. A discussion of the consequences of such EMHD turbulence induced relaxation and stopping of fast electrons, for the fast ignition concept will be presented. (author)

Instability in Parent-Child Coresidence and Adolescent Development in Urban South Africa.

Science.gov (United States)

Marteleto, Letícia J; Cavanagh, Shannon; Prickett, Kate; Clark, Shelley

2016-03-01

There is widespread recognition of the importance of family stability for child development. South Africa presents an interesting context in which to study the consequences of family instability because of the traditionally fluid nature of household composition due to labor migration, child fostering, and non-marital fertility. More recently, the HIV pandemic has added another source of instability. Within South Africa, however, patterns of instability differ markedly across racial groups. We use the Cape Area Panel Study (CAPS) data to examine the implications of changes in parent-child coresidence for educational and sexual development of young South Africans. We show that changes in maternal and paternal coresidence have implications for the timing of sexual initiation for both black and coloured adolescents. Maternal and paternal transitions also lead to poorer educational outcomes for coloured adolescents, but parental disruptions are not significantly related to educational outcomes for blacks. These findings suggest that the implications of coresidential instability vary by race, reflecting racial differences with respect to cultural, social, and economic conditions. © 2016 The Population Council, Inc.

Observation of parametric instabilities in the quarter critical density region driven by the Nike KrF laser

Energy Technology Data Exchange (ETDEWEB)

Weaver, J. L.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J. [U.S. Naval Research Laboratory, Washington DC 20375 (United States); Oh, J.; Lehmberg, R. H.; Mclean, E.; Manka, C. [Research Support Instruments, Lanham, Maryland 20905 (United States); Phillips, L. [Alogus Research Corporation, McLean, Virginia 22101 (United States); Afeyan, B. [Polymath Research, Inc., Pleasanton, California 94566 (United States); Seely, J.; Feldman, U. [Berkeley Research Associates, Inc., Beltsville, Maryland 20705 (United States)

2013-02-15

The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength ({lambda}=248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers ({lambda}=351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns{<=}{tau}{<=}1.25 ns) and intensities (up to 2 Multiplication-Sign 10{sup 15} W/cm{sup 2}). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.

Observation of parametric instabilities in the quarter critical density region driven by the Nike KrF laser

International Nuclear Information System (INIS)

Weaver, J. L.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Oh, J.; Lehmberg, R. H.; Mclean, E.; Manka, C.; Phillips, L.; Afeyan, B.; Seely, J.; Feldman, U.

2013-01-01

The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (λ=248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (λ=351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns≤τ≤1.25 ns) and intensities (up to 2×10 15 W/cm 2 ). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.

Observation of parametric instabilities in the quarter critical density region driven by the Nike KrF laser

Science.gov (United States)

Weaver, J. L.; Oh, J.; Phillips, L.; Afeyan, B.; Seely, J.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Feldman, U.; Lehmberg, R. H.; Mclean, E.; Manka, C.

2013-02-01

The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (λ =248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (λ =351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns≤τ≤1.25 ns) and intensities (up to 2×1015 W/cm2). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.

A 2-DOF microstructure-dependent model for the coupled torsion/bending instability of rotational nanoscanner

Science.gov (United States)

Keivani, M.; Abadian, N.; Koochi, A.; Mokhtari, J.; Abadyan, M.

2016-10-01

It has been well established that the physical performance of nanodevices might be affected by the microstructure. Herein, a two-degree-of-freedom model base on the modified couple stress theory is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nanoscanner. Effect of microstructure dependency on the instability parameters is determined as a function of the microstructure parameter, bending/torsion coupling ratio, van der Waals force parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the scanners especially those with long rotational beam elements. Impact of microstructure on instability voltage of the nanoscanner depends on coupling ratio and the conquering bending mode over torsion mode. This effect is more highlighted for higher values of coupling ratio. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to microstructure) and softening behavior (due to torsion/bending coupling) of the nanoscanners.

Modeling multi-lateral wells

Energy Technology Data Exchange (ETDEWEB)

Su, H. J.; Fong, W. S. [Chevron Petroleum Technology Company (United States)

1998-12-31

A method for modeling multi-lateral wells by using a computational scheme embedded in a general-purpose, finite difference simulator was described. The calculation of wellbore pressure profile for each lateral included the frictional pressure drop along the wellbore and proper fluid mixing at lateral connection points. To obtain a good production profile the Beggs and Brill correlation, a homogenous flow model, and the model proposed by Ouyang et al, which includes an acceleration term and accounts for the lubrication effect due to radial influx, were implemented. Well performance prediction results were compared using the three models. The impact of different tubing sizes on the well performance and the prediction contribution from each lateral were also studied. Results of the study in the hypothetical example and under normal field operating conditions were reviewed. 7 refs., 10 tabs., 3 figs.

Partition instability in water-immersed granular systems.

Science.gov (United States)

Clement, C P; Pacheco-Martinez, H A; Swift, Michael R; King, P J

2009-07-01

It is well known that a system of grains, vibrated vertically in a cell divided into linked columns, may spontaneously move into just one of the columns due to the inelastic nature of their collisions. Here we study the behavior of a water-immersed system of spherical barium titanate particles in a rectangular cell which is divided into two columns, linked by two connecting holes, one at the top and one at the bottom of the cell. Under vibration the grains spontaneously move into just one of the columns via a gradual transfer of grains through the connecting hole at the base of the cell. We have developed numerical simulations that are able to reproduce this behavior and provide detailed information on the instability mechanism. We use this knowledge to propose a simple analytical model for this fluid-driven partition instability based on two coupled granular beds vibrated within an incompressible fluid.

Evaluation of instability after transtrochanteric anterior rotational osteotomy for nontraumatic osteonecrosis of the femoral head

International Nuclear Information System (INIS)

Hiranuma, Yasunari; Atsumi, Takashi; Kajiwara, Toshihisa; Tamaoki, Satoshi; Asakura, Yasuhiro

2009-01-01

Transtrochanteric anterior rotational osteotomy results in improvement of joint congruity and prevention of progressive collapse and osteoarthritic changes in patients with femoral head osteonecrosis. However, this procedure remains controversial for patients with extensive collapse due to potential osteoarthritis caused by postoperative instability. The purpose of this study was to evaluate hip instability after osteotomy and determine the relation between instability and radiological and clinical outcomes. In all, 27 hips of 24 patients that were followed up for a mean period of 3.8 years were included. Instability was defined as more than 1 mm translation of the femoral head in transverse computed tomography scans obtained at 0 deg and 45 deg flexion of the hip joint. Hips were divided into instability and stability groups. Eleven hips (40%) developed instability after surgery. Osteophytes on the femoral head in 10 hips of the instability group and 2 hips of the stability group had increased in size at follow-up. There was a significant relation between postoperative instability and osteophyte formation. Joint space narrowing was not seen in any of the cases. There was no significant difference between the groups in either the postoperative intact ratio of the femoral head or the Japanese Orthopaedic Association hip score. Neither instability nor osteophyte formation on the femoral head after transtrochanteric anterior rotational osteotomy correlated with progressive osteoarthritic changes or clinical outcome in the presence of an adequate femoral head intact ratio facing the weight-bearing area. (author)

Relação entre o ligamento patelofemoral lateral e a largura da faceta patelar lateral Relationship between the lateral patellofemoral ligament and the width of the lateral patellar facet

Directory of Open Access Journals (Sweden)

Marcelo Schmidt Navarro

2010-01-01

Full Text Available OBJETIVO: Avaliar a relação entre o comprimento e largura do ligamento patelofemoral lateral (LPFL e a largura da faceta articular patelar lateral (FAPL em cadáveres. A instabilidade patelofemoral está intimamente relacionada com a morfologia patelar e com a tensão das estruturas retinaculares laterais. Estudos evidenciam que quanto mais larga a faceta patelar lateral e quanto mais tenso o retináculo lateral, maior a propensão do desenvolvimento de uma enfermidade na articulação patelofemoral. MÉTODOS: Foram dissecados 20 joelhos em 20 cadáveres. Identificamos as peças quanto ao gênero, idade, lado dissecado, comprimento e largura do LPFL e a largura da FAPL. Foi utilizado o nível de significância estatística de 5% (0,050 e a aplicação da análise de correlação de Spearman. RESULTADOS: O LPFL apresentou em média 16,05 milímetros de largura (desvio-padrão 2,48 e 42,10 milímetros de comprimento (desvio-padrão 8,84. A largura da FAPL variou de 23 a 37 milímetros (média 28,1. A relação entre a largura da FAPL e a largura do LPFL é estatisticamente não-significante (p=0,271, enquanto que a relação entre a largura FAPL e o comprimento do LPFL é estatisticamente significante (p=0,009. CONCLUSÃO: O comprimento do LPFL e a largura FAPL apresentam valores inversamente proporcionais.OBJECTIVE: The aim of this study, with cadavers, is to evaluate the relationship between the width and length of the lateral patellofemoral ligament (LPFL and the size of the lateral patellar articulate facet (LPAF. Patellofemoral instability is closely related to patellar morphology and the lateral retinacular layers. Studies evidence that the wider the lateral patellar facet and the more strained the lateral retinacule, the greater the tendency for development of pathology in the patellofemoral joint. METHODS: 20 knees were dissected in 20 cadavers. The parts were identified according to gender, age, dissected side, length and width of LPFL

Star formation through thermal instability of radiative plasma with finite electron inertia and finite Larmor radius corrections

Energy Technology Data Exchange (ETDEWEB)

Kaothekar, Sachin, E-mail: sackaothekar@gmail.com [Department of Physics, Mahakal Institute of Technology, Ujjain-456664, Madhya Pradesh (India)

2016-08-15

I have studied the effects of finite electron inertia, finite ion Larmor radius (FLR) corrections, and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effect of thermal conductivity for star formation in interstellar medium (ISM). A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instability criterion is get modified into radiative instability criterion by inclusion of radiative heat-loss functions with thermal conductivity. The viscosity of medium removes the effect of FLR corrections from the condition of radiative instability. Numerical calculation shows stabilizing effect of heat-loss function, viscosity and FLR corrections, and destabilizing effect of finite electron inertia on the thermal instability. Results carried out in this paper shows that stars are formed in interstellar medium mainly due to thermal instability.

Star formation through thermal instability of radiative plasma with finite electron inertia and finite Larmor radius corrections

Directory of Open Access Journals (Sweden)

Sachin Kaothekar

2016-08-01

Full Text Available I have studied the effects of finite electron inertia, finite ion Larmor radius (FLR corrections, and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effect of thermal conductivity for star formation in interstellar medium (ISM. A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instability criterion is get modified into radiative instability criterion by inclusion of radiative heat-loss functions with thermal conductivity. The viscosity of medium removes the effect of FLR corrections from the condition of radiative instability. Numerical calculation shows stabilizing effect of heat-loss function, viscosity and FLR corrections, and destabilizing effect of finite electron inertia on the thermal instability. Results carried out in this paper shows that stars are formed in interstellar medium mainly due to thermal instability.

Eden-Hybinette and Pectoralis Major Transfer for Recurrent Shoulder Instability Due to Failed Latarjet and Chronic Subscapularis Rupture.

Science.gov (United States)

Li, Xinning; Cusano, Antonio; Eichinger, Josef

2017-01-01

Shoulder dislocations are a common injury, with anterior shoulder dislocation among male patients being the most common presentation. A patient with recurrent shoulder instability, anterior-superior escape, and chronic subscapularis tendon rupture following multiple shoulder stabilization surgeries presents the surgeon with a complex and challenging case. This report describes a 40-year-old man with an extensive left shoulder history that included a failed Latarjet procedure, an irreparable, chronic subscapularis tear with grade 4 Goutallier fatty infiltration, and associated anterior-superior escape. Given his marked dysfunction, weakness, pain, and recurrent instability in the absence of glenohumeral arthritis, he underwent an open Eden-Hybinette procedure (iliac crest autograft), a pectoralis major transfer, and an anterior capsule repair. The patient returned to his previous work activities without limitations. To the authors' knowledge, this is the first report describing a combination of anterior glenoid bone grafting with a full pectoralis major muscle transfer for a patient with chronic subscapularis rupture and anterior-superior escape after a failed Latarjet procedure with minimum glenoid bone loss. Furthermore, the authors provide a biomechanical rationale for the reconstruction used for this problem. [Orthopedics. 2017; 40(1):e182-e187.]. Copyright 2016, SLACK Incorporated.

History of shoulder instability surgery.

Science.gov (United States)

Randelli, Pietro; Cucchi, Davide; Butt, Usman

2016-02-01

The surgical management of shoulder instability is an expanding and increasingly complex area of study within orthopaedics. This article describes the history and evolution of shoulder instability surgery, examining the development of its key principles, the currently accepted concepts and available surgical interventions. A comprehensive review of the available literature was performed using PubMed. The reference lists of reviewed articles were also scrutinised to ensure relevant information was included. The various types of shoulder instability including anterior, posterior and multidirectional instability are discussed, focussing on the history of surgical management of these topics, the current concepts and the results of available surgical interventions. The last century has seen important advancements in the understanding and treatment of shoulder instability. The transition from open to arthroscopic surgery has allowed the discovery of previously unrecognised pathologic entities and facilitated techniques to treat these. Nevertheless, open surgery still produces comparable results in the treatment of many instability-related conditions and is often required in complex or revision cases, particularly in the presence of bone loss. More high-quality research is required to better understand and characterise this spectrum of conditions so that successful evidence-based management algorithms can be developed. IV.

Flow instability in laminar jet flames driven by alternating current electric fields

KAUST Repository

Kim, Gyeong Taek

2016-10-13

The effect of electric fields on the instability of laminar nonpremixed jet flames was investigated experimentally by applying the alternating current (AC) to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames in laminar jet flow configurations, which occurred when AC electric fields were applied. The results indicated that a twin-lifted jet flame originated from cold jet instability, caused by interactions between negative ions in the jet flow via electron attachment as O +e→O when AC electric fields were applied. This was confirmed by conducting systematic, parametric experiment, which included changing gaseous component in jets and applying different polarity of direct current (DC) to the nozzle. Using two deflection plates installed in parallel with the jet stream, we found that only negative DC on the nozzle could charge oxygen molecules negatively. Meanwhile, the cold jet instability occurred only for oxygen-containing jets. A shedding frequency of jet stream due to AC driven instability showed a good correlation with applied AC frequency exhibiting a frequency doubling. However, for the applied AC frequencies over 80Hz, the jet did not respond to the AC, indicating an existence of a minimum flow induction time in a dynamic response of negative ions to external AC fields. Detailed regime of the instability in terms of jet velocity, AC voltage and frequency was presented and discussed. Hypothesized mechanism to explain the instability was also proposed.

Structural instability and ground state of the U_2Mo compound

International Nuclear Information System (INIS)

Losada, E.L.; Garcés, J.E.

2015-01-01

This work reports on the structural instability at T = 0 °K of the U_2Mo compound in the C11_b structure under the distortion related to the C_6_6 elastic constant. The electronic properties of U_2Mo such as density of states (DOS), bands and Fermi surface (FS) are studied to understand the source of the instability. The C11_b structure can be interpreted as formed by parallel linear chains along the z-directions each one composed of successive U–Mo–U blocks. Hybridization due to electronic interactions inside the U–Mo–U blocks is slightly modified under the D_6 distortion. The change in distance between chains modifies the U–U interaction and produces a split of f-states. The distorted structure is stabilized by a decrease in energy of the hybridized states, mainly between d-Mo and f-U states, together with the f-band split. Consequently, an induced Peierls distortion is produced in U_2Mo due to the D_6 distortion. It is important to note that the results of this work indicate that the structure of the ground state of the U_2Mo compound is not the assumed C11_b structure. It is suggested for the ground state a structure with hexagonal symmetry (P6 #168), ∼0.1 mRy below the energy of the recently proposed Pmmn structure. - Highlights: • Structural instability of the C11b compound due to the D6 deformation. • Induced Peierls distortion due to the D6 deformation. • Distorted structure is stabilized by hybridization and split of f-Uranium state. • P6 (#168) suggested ground state for the U_2Mo compound.

Instabilities in mimetic matter perturbations

Energy Technology Data Exchange (ETDEWEB)

Firouzjahi, Hassan; Gorji, Mohammad Ali [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Mansoori, Seyed Ali Hosseini, E-mail: firouz@ipm.ir, E-mail: gorji@ipm.ir, E-mail: shosseini@shahroodut.ac.ir, E-mail: shossein@ipm.ir [Physics Department, Shahrood University of Technology, P.O. Box 3619995161 Shahrood (Iran, Islamic Republic of)

2017-07-01

We study cosmological perturbations in mimetic matter scenario with a general higher derivative function. We calculate the quadratic action and show that both the kinetic term and the gradient term have the wrong sings. We perform the analysis in both comoving and Newtonian gauges and confirm that the Hamiltonians and the associated instabilities are consistent with each other in both gauges. The existence of instabilities is independent of the specific form of higher derivative function which generates gradients for mimetic field perturbations. It is verified that the ghost instability in mimetic perturbations is not associated with the higher derivative instabilities such as the Ostrogradsky ghost.

Strong stabilization of the Rayleigh-Taylor instability by material strength at Mbar pressures

Energy Technology Data Exchange (ETDEWEB)

Park, H S; Lorenz, K T; Cavallo, R M; Pollaine, S M; Prisbrey, S T; Rudd, R E; Becker, R C; Bernier, J V; Remington, B A

2009-11-19

Experimental results showing significant reductions from classical in the Rayleigh-Taylor (RT) instability growth rate due to high pressure effective lattice viscosity are presented. Using a laser created ramped drive, vanadium samples are compressed and accelerated quasi-isentropically at {approx}1 Mbar pressures, while maintaining the sample in the solid-state. Comparisons with simulations and theory indicate that the high pressure, high strain rate conditions trigger a phonon drag mechanism, resulting in the observed high effective lattice viscosity and strong stabilization of the RT instability.

Feedback stabilization of plasma instabilities

International Nuclear Information System (INIS)

Cap, F.F.

1977-01-01

This paper reviews the theoretical and experimental aspects of feedback stabilization. After giving an outline of a general theoretical model for electrostatic instabilities the author provides a theoretical analysis of the suppression of various types of instability. Experiments which have been carried out on the feedback stabilization of various types of plasma instability are reported. An extensive list of references is given. (B.R.H.)

Theoretical aspects of some collective instabilities in high-energy particle storage rings

International Nuclear Information System (INIS)

Ruggiero, F.

1986-01-01

After an introduction to single-particle dynamics, based on a unified Hamiltonian treatment of betatron and synchrotron oscillations, we consider two examples of collective instabilities which can limit the performances of high-energy storage rings: the transverse mode coupling instability, due to wake fields, and the incoherent beam-beam instability. Special emphasis is placed on the localization of the interactions between particles and surrounding structures, such as the accelerating RF cavities. We derive an exact invariant for the linearized synchrotron motion and, starting from the Vlasov equation, we discuss the coherent synchro-betatron resonances caused by localized impedance. Under suitable assumptions, we show that the effect of the beam-beam kicks in electron-positron machines can be described by new diffusive terms in a ''renormalized'' Fokker-Planck equation and is therefore equivalent to an additional source of noise for the betatron oscillations. (orig.)

Application of autoregressive methods and Lyapunov coefficients for instability studies of nuclear reactors

International Nuclear Information System (INIS)

Aruquipa Coloma, Wilmer

2017-01-01

Nuclear reactors are susceptible to instability, causing oscillations in reactor power in specific working regions characterized by determined values of power and coolant mass flow. During reactor startup, there is a greater probability that these regions of instability will be present; another reason may be due to transient processes in some reactor parameters. The analysis of the temporal evolution of the power reveals a stable or unstable process after the disturbance in a light water reactor of type BWR (Boiling Water Reactor). In this work, the instability problem was approached in two ways. The first form is based on the ARMA (Autoregressive Moving Average models) model. This model was used to calculate the Decay Ratio (DR) and natural frequency (NF) of the oscillations, parameters that indicate if the one power signal is stable or not. In this sense, the DRARMA code was developed. In the second form, the problems of instability were analyzed using the classical concepts of non-linear systems, such as Lyapunov exponents, phase space and attractors. The Lyapunov exponents quantify the exponential divergence of the trajectories initially close to the phase space and estimate the amount of chaos in a system; the phase space and the attractors describe the dynamic behavior of the system. The main aim of the instability phenomena studies in nuclear reactors is to try to identify points or regions of operation that can lead to power oscillations conditions. The two approaches were applied to two sets of signals. The first set comes from signals of instability events of the commercial Forsmark reactors 1 and 2 and were used to validate the DRARMA code. The second set was obtained from the simulation of transient events of the Peach Bottom reactor; for the simulation, the PARCS and RELAP5 codes were used for the neutronic/thermal hydraulic coupling calculation. For all analyzes made in this work, the Matlab software was used due to its ease of programming and

Erosion waves: Transverse instabilities and fingering

Science.gov (United States)

Malloggi, F.; Lanuza, J.; Andreotti, B.; Clément, E.

2006-09-01

Two laboratory scale experiments of dry and underwater avalanches of non-cohesive granular materials are investigated. We trigger solitary waves and study the conditions under which the front is transversally stable. We show the existence of a linear instability followed by a coarsening dynamics and finally the onset of a fingering pattern. Due to the different operating conditions, both experiments strongly differ by the spatial and time scales involved. Nevertheless, the quantitative agreement between the stability diagram, the wavelengths selected and the avalanche morphology suggest a common scenario for an erosion/deposition process.

Multifragmentation: Surface instabilities or statistical decay

International Nuclear Information System (INIS)

Moretto, L.G.; Tso, K.; Delis, D.; Colonna, N.; Wozniak, G.J.

1992-11-01

Boltzmann-Nordheim-Vlasov calculations show multifragmentation that seems to originate from surface instabilities. These instabilities are traced to a sheet instability caused by the proximity interaction. Experimental data, on the other hand, suggest that multifragmentation may be dominated by phase space

An Objective Functional Characterisation of Head Movement Impairment in Individuals with Neck Muscle Weakness Due to Amyotrophic Lateral Sclerosis.

Directory of Open Access Journals (Sweden)

Silvia Pancani

Full Text Available Neck muscle weakness and head drop are well recognised in patients with Amyotrophic lateral sclerosis (ALS, but an objective characterisation of the consequent head movement impairment is lacking. The aim of this study was to quantitatively characterise head movements in ALS compared to aged matched controls.We evaluated two groups, one of thirteen patients with ALS and one of thirteen age-matched controls, during the execution of a series of controlled head movements, performed while wearing two inertial sensors attached on the forehead and sternum, respectively. We quantified the differences between the two groups from the sensor data using indices of velocity, smoothness and movement coupling (intended as a measure of undesired out of plane movements.Results confirmed a general limitation in the ability of the ALS patients to perform and control head movements. High inter-patient variability was observed due to a wide range of observed functional impairment levels. The ability to extend the head backward and flex it laterally were the most compromised, with significantly lower angular velocity (P 0.8, reduced smoothness and greater presence of coupled movements with respect to the controls. A significant reduction of angular velocity (P 0.8 in extension, axial rotation and lateral flexion was observed when patients were asked to perform the movements as fast as possible.This pilot study is the first study providing a functional objective quantification of head movements in ALS. Further work involving different body areas and correlation with existing methods of evaluating neuromuscular function, such as dynamometry and EMG, is needed to explore the use of this approach as a marker of disease progression in ALS.

Pannus regression after posterior decompression and occipito-cervical fixation in occipito-atlanto-axial instability due to rheumatoid arthritis: case report and literature review.

Science.gov (United States)

Landi, Alessandro; Marotta, Nicola; Morselli, Carlotta; Marongiu, Alessandra; Delfini, Roberto

2013-02-01

Several techniques have been proposed for treating cervical spine instability due to rheumatoid arthritis. The aim of this study was to screen the different treatment options used in this pathology to evaluate the best form of treatment when the progression of rheumatoid disease affected the cranio-vertebral junction (CVJ) stability. The most important purpose of this study was to achieve both the efficacy of occipito-cervical fusion (OCF) to stabilize the occipitocervical junction and stop pannus progression. The authors describe their case example and stress, in the light of a literature review, the hypothesis that a stable biomechanical system extended to all the spaces involved, has both direct and indirect effects on RA pannus progression and the condition responsible for its formation, such as inflammation and articular hypermobility. Hence, the aim of this study is to advance this thesis, which may be extended to a wider statistical sample, with the same characteristics. A systematic literature research of case report articles, review articles, original articles, and prospective cohort studies, published from 1978 to 2011, was performed using PUBMED to analyze the different surgical strategies of RA involving CVJ and the role of OCF in these conditions. The key words used for the search the were: "inflammatory cervical pannus regression", "rheumatoid arthritis of the cranio-cervical junction", "occipito-cervical fusion", "treatment option in rheumatoid cervical instability", "altanto-axial dislocation", "craniovertebral junction" and "surgical technique". In addition, the authors reported their experience in a patient affected by erosive rheumatoid arthritis (ERA) with an anterior and posterior pannus involving C0-C1-C2. They decided to report this exemplative case to emphasize their own assumptions concerning the association between a posterior bony fusion, the arrest of anterior pannus progression and the improvement of functional outcome, without, however

Nonlinear response of vessel walls due to short-time thermomechanical loading

International Nuclear Information System (INIS)

Pfeiffer, P.A.; Kulak, R.F.

1994-01-01

Maintaining structural integrity of the reactor pressure vessel (RPV) during a postulated core melt accident is an important safety consideration in the design of the vessel. This study addresses the failure predictions of the vessel due to thermal and pressure loadings fro the molten core debris depositing on the lower head of the vessel. Different loading combinations were considered based on the dead load, yield stress assumptions, material response and internal pressurization. The analyses considered only short term failure (quasi static) modes, long term failure modes were not considered. Short term failure modes include plastic instabilities of the structure and failure due to exceeding the failure strain. Long term failure odes would be caused by creep rupture that leads to plastic instability of the structure. Due to the sort time durations analyzed, creep was not considered in the analyses presented

Graphical analysis of electron inertia induced acoustic instability

International Nuclear Information System (INIS)

Karmakar, P.K.; Deka, U.; Dwivedi, C.B.

2005-01-01

Recently, the practical significance of the asymptotic limit of m e /m i →0 for electron density distribution has been judged in a two-component plasma system with drifting ions. It is reported that in the presence of drifting ions with drift speed exceeding the ion acoustic wave speed, the electron inertial delay effect facilitates the resonance coupling of the usual fluid ion acoustic mode with the ion-beam mode. In this contribution the same instability is analyzed by graphical and numerical methods. This is to note that the obtained dispersion relation differs from those of the other known normal modes of low frequency ion plasma oscillations and waves. This is due to consideration of electron inertial delay in derivation of the dispersion relation of the ion acoustic wave fluctuations. Numerical calculations of the dispersion relation and wave energy are carried out to depict the graphical appearance of poles and positive-negative energy modes. It is found that the electron inertia induced ion acoustic wave instability arises out of linear resonance coupling between the negative and positive energy modes. Characterization of the resonance nature of the instability in Mach number space for different wave numbers of the ion acoustic mode is presented

Coordination and Symmetry Patterns During the Drop Vertical Jump in People With Chronic Ankle Instability and Lateral Ankle Sprain Copers.

Science.gov (United States)

Doherty, Cailbhe; Bleakley, Chris; Hertel, Jay; Caulfield, Brian; Ryan, John; Sweeney, Kevin; Patterson, Matthew R; Delahunt, Eamonn

2016-08-01

The drop vertical jump (DVJ) task has previously been used to identify movement patterns associated with a number of injury types. However, no current research exists evaluating people with chronic ankle instability (CAI) compared with people coping with lateral ankle sprain (LAS) (referred to as "LAS copers") during this task. The aim of this study was to identify the coping movement and motor control patterns of LAS copers in comparison with individuals with CAI during the DVJ task. This was a case-control study. Seventy individuals were recruited at convenience within 2-weeks of sustaining a first-time acute LAS injury. One year following recruitment, these individuals were stratified into 2 groups: 28 with CAI and 42 LAS copers. They attended the testing laboratory to complete a DVJ task. Three-dimensional kinematic and sagittal-plane kinetic profiles were plotted for the lower extremity joints of both limbs for the drop jump phase (phase 1) and drop landing phase (phase 2) of the DVJ. The rate of impact modulation relative to body weight during both phases of the DVJ also was determined. Compared with LAS copers, participants with CAI displayed significant increases in hip flexion on their "involved" limb during phase 1 of the DVJ (23° vs 18°) and bilaterally during phase 2 (15° vs 10°). These movement patterns coincided with altered moment-of-force patterns at the hip on the "uninvolved" limb. It is unknown whether these movement and motor control patterns preceded or occurred as a result of the initial LAS injury. Participants with CAI displayed hip-centered changes in movement and motor control patterns during a DVJ task compared with LAS copers. The findings of this study may give an indication of the coping mechanism underlying outcome following initial LAS injury. © 2016 American Physical Therapy Association.

Neutron star pulsations and instabilities

International Nuclear Information System (INIS)

Lindblom, L.

2001-01-01

Gravitational radiation (GR) drives an instability in certain modes of rotating stars. This instability is strong enough in the case of the r-modes to cause their amplitudes to grow on a timescale of tens of seconds in rapidly rotating neutron stars. GR emitted by these modes removes angular momentum from the star at a rate which would spin it down to a relatively small angular velocity within about one year, if the dimensionless amplitude of the mode grows to order unity. A pedagogical level discussion is given here on the mechanism of GR instability in rotating stars, on the relevant properties of the r-modes, and on our present understanding of the dissipation mechanisms that tend to suppress this instability in neutron stars. The astrophysical implications of this GR driven instability are discussed for young neutron stars, and for older systems such as low mass x-ray binaries. Recent work on the non-linear evolution of the r-modes is also presented. (author)

Fluidelastic instability in a flexible Weir: A theoretical model

International Nuclear Information System (INIS)

Aita, S.; Gibert, R.J.

1986-01-01

A new type fluidelastic instability was discovered during the hot tests of Superphenix LMFBR. This instability is due to the fluid discharge, over a flexible weir shell which separates two of these fluid sheets (the feeding and restitution collectors). An analytical nonlinear model was realised. The flow and force sources at the top of the collectors are described and projected on the modal basis of the system formed by the collectors and the weir shell. Simplified formulas were extracted allowing a practical prediction of the stability. More generally, the complete model can be used to estimate the vibratory level when a steady state is reached by the effect of nonlinearities. Computer calculation for such a model are made with OSCAR code, part of CASTEM 2000 finite element computer system. (author)

Estimates of CSR Instability Thresholds for Various Storage Rings

CERN Document Server

Zimmermann, Frank

2010-01-01

We review the key predictions and conditions by several authors for the onset of longitudinal instabilities due to coherent synchrotron radiation (CSR), and evaluate them numerically for various storage rings, namely the KEKB High Energy Ring (HER) & Low Energy Ring (LER), SuperKEKB HER & LER, old and new designs of the SuperKEKB Damping Ring (DR), SuperB HER & LER, CLIC DR (2009 and 2010 design parameters), SLC DR, and ATF DR. We show that the theoretical uncertainty in the instability onset is at least at the level of 20-30% in bunch intensity. More importantly, we present some doubts about the general applicability for many of these storage rings of some commonly used formulae. To cast further light on these questions, an experiment at lower beam energy on the ATF Damping Ring is proposed.

Multifragmentation: surface instabilities or statistical decay?

International Nuclear Information System (INIS)

Moretto, L.G.; Tso, K.; Delis, D.; Colonna, N.; Wozniak, G.J.

1993-01-01

Boltzmann-Nordheim-Vlasov calculations show multifragmentation that seems to originate from surface instabilities. These instabilities are traced to a sheet instability caused by the proximity interaction. Experimental data, on the other hand, suggest that multifragmentation may be dominated by phase space. (author)

Dynamic ultrasound of peroneal tendon instability.

Science.gov (United States)

Pesquer, Lionel; Guillo, Stéphane; Poussange, Nicolas; Pele, Eric; Meyer, Philippe; Dallaudière, Benjamin

2016-07-01

Ankle snapping may be caused by peroneal tendon instability. Anterior instability occurs after traumatic superior peroneal retinaculum injury, whereas peroneal tendon intrasheath subluxation is atraumatic. Whereas subluxation is mainly dynamic, ultrasound allows for the diagnosis and classification of peroneal instability because it allows for real-time exploration. The purpose of this review is to describe the anatomic and physiologic bases for peroneal instability and to heighten the role of dynamic ultrasound in the diagnosis of snapping.

Gravity Wave Dynamics in a Mesospheric Inversion Layer: 1. Reflection, Trapping, and Instability Dynamics

Science.gov (United States)

Laughman, Brian; Wang, Ling; Lund, Thomas S.; Collins, Richard L.

2018-01-01

Abstract An anelastic numerical model is employed to explore the dynamics of gravity waves (GWs) encountering a mesosphere inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. Instabilities occur within the MIL when the GW amplitude approaches that required for GW breaking due to compression of the vertical wavelength accompanying the increasing static stability. Thus, MILs can cause large‐amplitude GWs to yield instabilities and turbulence below the altitude where they would otherwise arise. Smaller‐amplitude GWs encountering a MIL do not lead to instability and turbulence but do exhibit partial reflection and transmission, and the transmission is a smaller fraction of the incident GW when instabilities and turbulence arise within the MIL. Additionally, greater GW transmission occurs for weaker MILs and for GWs having larger vertical wavelengths relative to the MIL depth and for lower GW intrinsic frequencies. These results imply similar dynamics for inversions due to other sources, including the tropopause inversion layer, the high stability capping the polar summer mesopause, and lower frequency GWs or tides having sufficient amplitudes to yield significant variations in stability at large and small vertical scales. MILs also imply much stronger reflections and less coherent GW propagation in environments having significant fine structure in the stability and velocity fields than in environments that are smoothly varying. PMID:29576994

Electron beam instabilities in gyrotron beam tunnels

International Nuclear Information System (INIS)

Pedrozzi, M.; Alberti, S.; Hogge, J.P.; Tran, M.Q.; Tran, T.M.

1997-10-01

Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability, the Bernstein instability and the Langmuir instability. The low magnetic field gradient in drift tubes of QOG makes that the electron cyclotron maser instability can develop in the drift tube at very low electron beam currents. Experimental measurements show that with a proper choice of absorbing structures in the beam tunnel, this instability can be suppressed. At high beam currents, the electrostatic Bernstein instability can induce a significant energy spread at the entrance of the interaction region. The induced energy spread scales approximately linearly with the electron beam density and for QOG one observes that the beam density is significantly higher than the beam density of an equivalent cylindrical cavity gyrotron. (author) figs., tabs., refs

Mode-locking via dissipative Faraday instability.

Science.gov (United States)

Tarasov, Nikita; Perego, Auro M; Churkin, Dmitry V; Staliunas, Kestutis; Turitsyn, Sergei K

2016-08-09

Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system-spectrally dependent losses-achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.

Clinical examination results in individuals with functional ankle instability and ankle-sprain copers.

Science.gov (United States)

Wright, Cynthia J; Arnold, Brent L; Ross, Scott E; Ketchum, Jessica; Ericksen, Jeffrey; Pidcoe, Peter

2013-01-01

Why some individuals with ankle sprains develop functional ankle instability and others do not (ie, copers) is unknown. Current understanding of the clinical profile of copers is limited. To contrast individuals with functional ankle instability (FAI), copers, and uninjured individuals on both self-reported variables and clinical examination findings. Cross-sectional study. Sports medicine research laboratory. Participants consisted of 23 individuals with a history of 1 or more ankle sprains and at least 2 episodes of giving way in the past year (FAI: Cumberland Ankle Instability Tool [CAIT] score = 20.52 ± 2.94, episodes of giving way = 5.8 ± 8.4 per month), 23 individuals with a history of a single ankle sprain and no subsequent episodes of instability (copers: CAIT score = 27.74 ± 1.69), and 23 individuals with no history of ankle sprain and no instability (uninjured: CAIT score = 28.78 ± 1.78). Self-reported disability was recorded using the CAIT and Foot and Ankle Ability Measure for Activities of Daily Living and for Sports. On clinical examination, ligamentous laxity and tenderness, range of motion (ROM), and pain at end ROM were recorded. Questionnaire scores for the CAIT, Foot and Ankle Ability Measure for Activities of Daily Living and for Sports, ankle inversion and anterior drawer laxity scores, pain with palpation of the lateral ligaments, ankle ROM, and pain at end ROM. Individuals with FAI had greater self-reported disability for all measures (P < .05). On clinical examination, individuals with FAI were more likely to have greater talar tilt laxity, pain with inversion, and limited sagittal-plane ROM than copers (P < .05). Differences in both self-reported disability and clinical examination variables distinguished individuals with FAI from copers at least 1 year after injury. Whether the deficits could be detected immediately postinjury to prospectively identify potential copers is unknown.

Hydrodynamic electronic fluid instability in GaAs MESFETs at terahertz frequencies

Science.gov (United States)

Li, Kang; Hao, Yue; Jin, Xiaoqi; Lu, Wu

2018-01-01

III-V compound semiconductor field effect transistors (FETs) are potential candidates as solid state THz emitters and detectors due to plasma wave instability in these devices. Using a 2D hydrodynamic model, here we present the numerical studies of electron fluid instability in a FET structure. The model is implemented in a GaAs MESFET structure with a gate length of 0.2 µm as a testbed by taking into account the non-equilibrium transport and multi-valley non-parabolicity energy bands. The results show that the electronic density instability in the channel can produce stable periodic oscillations at THz frequencies. Along with stable oscillations, negative differential resistance in output characteristics is observed. The THz emission energy density increases monotonically with the drain bias. The emission frequency of electron density oscillations can be tuned by both gate and drain biases. The results suggest that III-V FETs can be a kind of versatile THz devices with good tunability on both radiative power and emission frequency.

Self-Field Effects in Magneto-Thermal Instabilities for Nb-Sn Strands

CERN Document Server

Bordini, B; Fehér, S; Rossi, L; Zlobin, A V

2008-01-01

Recent advancements in the critical current density (Jc) of Nb$_{3}$Sn conductors, coupled with a large effective filament size, have drawn attention to the problem of magnetothermal instabilities. At low magnetic fields, the quench current of such high Jc Nb$_{3}$Sn strands is significantly lower than their critical current because of the above-mentioned instabilities. An adiabatic model to calculate the minimum current at which a strand can quench due to magneto-thermal instabilities is developed. The model is based on an 'integral' approach already used elsewhere [1]. The main difference with respect to the previous model is the addition of the self-field effect that allows to describe premature quenches of non-magnetized Nb$_{3}$Sn strands and to better calculate the quench current of strongly magnetized strands. The model is in good agreement with experimental results at 4.2 K obtained at Fermilab using virgin Modified Jelly Roll (MJR) strands with a low Residual Resistivity Ratio (RRR) of the stabilizin...

Genomic instability and radiation effects

International Nuclear Information System (INIS)

Christian Streffer

2007-01-01

Complete text of publication follows. Cancer, genetic mutations and developmental abnormalities are apparently associated with an increased genomic instability. Such phenomena have been frequently shown in human cancer cells in vitro and in situ. It is also well-known that individuals with a genetic predisposition for cancer proneness, such as ataxia telangiectesia, Fanconi anaemia etc. demonstrate a general high genomic instability e.g. in peripheral lymphocytes before a cancer has developed. Analogous data have been found in mice which develop a specific congenital malformation which has a genetic background. Under these aspects it is of high interest that ionising radiation can increase the genomic instability of mammalian cells after exposures in vitro an in vivo. This phenomenon is expressed 20 to 40 cell cycles after the exposure e.g. by de novo chromosomal aberrations. Such effects have been observed with high and low LET radiation, high LET radiation is more efficient. With low LET radiation a good dose response is observed in the dose range 0.2 to 2.0 Gy, Recently it has been reported that senescence and genomic instability was induced in human fibroblasts after 1 mGy carbon ions (1 in 18 cells are hit), apparently bystander effects also occurred under these conditions. The instability has been shown with DNA damage, chromosomal aberrations, gene mutation and cell death. It is also transferred to the next generation of mice with respect to gene mutations, chromosomal aberrations and congenital malformations. Several mechanisms have been discussed. The involvement of telomeres has gained interest. Genomic instability seems to be induced by a general lesion to the whole genome. The transmission of one chromosome from an irradiated cell to an non-irradiated cell leads to genomic instability in the untreated cells. Genomic instability increases mutation rates in the affected cells in general. As radiation late effects (cancer, gene mutations and congenital

[Lateral column lengthening osteotomy of calcaneus].

Science.gov (United States)

Hintermann, B

2015-08-01

Lengthening of the lateral column for adduction of forefoot and restoration of the medial arch. Stabilization of the ankle joint complex. Supple flatfoot deformity (posterior tibial tendon dysfunction stage II). Instability of the medial ankle joint complex (superficial deltoid and spring ligament). Posttraumatic valgus and pronation deformity of the foot. Rigid flatfoot deformity (posterior tibial tendon dysfunction stage III and IV). Talocalcaneal and naviculocalcaneal coalition. Osteoarthritis of calcaneocuboid joint. Exposition of calcaneus at sinus tarsi. Osteotomy through sinus tarsi and widening until desired correction of the foot is achieved. Insertion of bone graft. Screw fixation. Immobilization in a cast for 6 weeks. Weight-bearing as tolerated from the beginning. In the majority of cases, part of hindfoot reconstruction. Reliable and stable correction. Safe procedure with few complications.

Stabilization effect of Weibel modes due to inverse bremsstrahlung ...

Indian Academy of Sciences (India)

2016-11-04

Nov 4, 2016 ... In this work, the Weibel instability due to inverse bremsstrahlung absorption in laser fusion plasma ... pling of self-generated magnetic field with the laser wave field. This is ... To describe fully ionized plasma where the interac-.

Carpal instabilities and secondary degenerative changes due to lesions of the radiocarpal ligament complex

International Nuclear Information System (INIS)

Stabler, A.; Berger, H.; Lissner, J.

1990-01-01

This paper reports on trauma, rheumatoid arthritis, calcium pyrophosphate dihydrate crystal deposition (CPDD), neurologic disease, and beta 2 -microglobulin-related amyloid deposits in patients undergoing chronic hemodialysis that can lead to distinct lesions of the radiocarpal ligament complex, causing rotational subluxation of the scaphoid and ulnar translocation of the carpus. The clinical and radiologic findings were analyzed in 35 patients, examined from 1985 to 1989. Degenerative changes in rotational subluxation of the scaphoid develop in three steps. First there is osteoarthritis at the styloid process, then the degeneration progresses into the central midcarpal joint, and finally it progresses to the ulnar midcarpal joint. Despite different etiologies of ligament failure, the radiologic features are very similar, because the mechanism of degeneration is identical in posttraumatic, inflammatory, neurogenic, CPDD, or beta 2 -microglobulin-related instability. However, there are some distinct radiologic differences in relation to the primary cause of the ligament defect

Combustion instability control in the model of combustion chamber

International Nuclear Information System (INIS)

Akhmadullin, A N; Ahmethanov, E N; Iovleva, O V; Mitrofanov, G A

2013-01-01

An experimental study of the influence of external periodic perturbations on the instability of the combustion chamber in a pulsating combustion. As an external periodic disturbances were used sound waves emitted by the electrodynamics. The purpose of the study was to determine the possibility of using the method of external periodic perturbation to control the combustion instability. The study was conducted on a specially created model of the combustion chamber with a swirl burner in the frequency range from 100 to 1400 Hz. The study found that the method of external periodic perturbations may be used to control combustion instability. Depending on the frequency of the external periodic perturbation is observed as an increase and decrease in the amplitude of the oscillations in the combustion chamber. These effects are due to the mechanisms of synchronous and asynchronous action. External periodic disturbance generated in the path feeding the gaseous fuel, showing the high efficiency of the method of management in terms of energy costs. Power required to initiate periodic disturbances (50 W) is significantly smaller than the thermal capacity of the combustion chamber (100 kW)

Anesthetic management of a child with Down’s Syndrome having atlanto axial instability

Directory of Open Access Journals (Sweden)

Basant Bhattarai

2009-01-01

Full Text Available Down's syndrome is the most commonly encountered congenital anomaly in medical practice. These patients are of special concern to medical practice because of their associated problems with regard to respiratory, cardiovascular and other systemic problems. As these patients present for repeated surgeries like dental extraction, facial reconstruction and fixation of cervical spine, these patients pose challenges to the anesthesiologist because of their unique set of problems, namely atlantoaxial instability, small trachea, congenital heart disease and repeated chest infections due to lowered immunity. Their reactivity to inhalational anesthetics and atropine is variable. Here we present an interesting case report of a child with Down's syndrome who presented with atlantoaxial instability for MRI of cervical spine under general anesthesia. KeyWords:atlanto axial instability, down’s syndrome, trisomy 21

Difference in postural control between patients with functional and mechanical ankle instability.

Science.gov (United States)

Chen, Henry; Li, Hong-Yun; Zhang, Jian; Hua, Ying-Hui; Chen, Shi-Yi

2014-10-01

Lateral ankle sprain is one of the most common injuries. Since the structural and pathological differences in mechanical ankle instability (MAI) and functional ankle instability (FAI) may not be the same, it may be better to treat these as separate groups. The purpose of this study was to compare the difference in postural sway between MAI and FAI in patients with chronic ankle instability (CAI). Twenty-six patients with CAI and 14 healthy control participants were included in the study. The CAI patients were subdivided into MAI (15 patients) and FAI (11 patients) groups. Patients who were diagnosed with lateral ankle ligaments rupture by magnetic resonance imaging and ultrasonography were assigned to the MAI group. All participants performed single-limb postural sway tests 3 times on each leg with eyes closed and open. The average distances from the mean center of pressure position in the mediolateral and anteroposterior directions were recorded and compared among the 3 groups. The unstable ankles in the MAI group showed significantly greater postural sway in the anterior, posterior, and medial directions compared with those in the control group with eyes closed. With eyes open, significantly greater postural sway was found in the anterior direction. In the FAI group, no difference was found in postural sway compared with those in the control group. The MAI group showed significantly greater postural sway in the anterior direction compared with the FAI group with eyes closed and open. No significant difference in postural sway was found between the unstable and stable ankles in the MAI or FAI groups, with or without vision. Patients with MAI have deficits in postural control, especially in anterior-posterior directions. However, no difference was found in postural sway in patients with FAI compared with healthy people. As MAI patients suffer from deficits in postural control, balance training should be applied in those patients. In addition, special training

On broadened definitions of instability for stars in thermal imbalance

International Nuclear Information System (INIS)

Simon, N.R.

1977-01-01

The classical theory of stability of dynamical systems is employed to demonstrate that traditional definitions of pulsational instability cannot be directly applied to stars in thermal imbalance. In particular, it is shown that, for the case of thermal imbalance, pulsational displacements and pulsational velocities have separate and distinct e-folding times. This being true, a broadened set of definitions becomes necessary, and such a set is formulated again with reference to the classical theory. In accordance with the new definitions, it is argued that the development of observable pulsations requires as a necessary condition infinitesimal instability of both absolute displacement and velocity. If either one is unstable without the other, this constitutes a class of (probably) non-pulsational instability, not previously treated in the astrophysical literature. Finally, it is shown that the stability of stars in thermal imbalance may be evaluated according to the present definitions by employing either of two existing theories - the energy approach due to Demaret (1974; 1975; 1976) or the small perturbation technique of Cox et al. (1973). (Auth.)

Theoretical study on flow-induced vibration of a cylindrical weir due to fluid discharge

International Nuclear Information System (INIS)

Fujita, Katsuhisa; Ito, Tomohiro; Hirota, Kazuo; Kodama, Tetsuhiko

1994-01-01

In a FBR, the inside of the reactor vessel is cooled by liquid sodium. Liquid sodium is supplied to the upper plenum from its bottom and discharges over the top of the cylindrical weir down to the lower plenum. The weir is so thin in order to decrease the thermal stress on it that the fluid--structure interaction becomes predominant. A fluidelastic vibration of the weir due to fluid discharge was discovered in a French FBR. In this study, a theoretical model was developed on the ''fluid--elastic mode'' instability of a cylindrical weir due to fluid discharge from the upper plenum to the lower plenum. In the analysis, the fluctuation of both the discharge flow rate over a weir due to the vibration of the cylindrical shell and the pressure in the lower plenum due to fluid discharge were formulated. Instability criteria was derived from the added damping ratio due to fluid discharge using modal analysis. The natural modes and modal mass of the weir were obtained by the analysis using the FEM code taking the fluid - structure interaction into consideration. The theoretical instability range in terms of the fall height and the flow rate is compared with the experimental results. The theoretical values showed a good agreement with the experimental ones

Topography and instability of monolayers near domain boundaries

International Nuclear Information System (INIS)

Diamant, H.; Witten, T. A.; Ege, C.; Gopal, A.; Lee, K. Y. C.

2001-01-01

We theoretically study the topography of a biphasic surfactant monolayer in the vicinity of domain boundaries. The differing elastic properties of the two phases generally lead to a nonflat topography of 'mesas,' where domains of one phase are elevated with respect to the other phase. The mesas are steep but low, having heights of up to 10 nm. As the monolayer is laterally compressed, the mesas develop overhangs and eventually become unstable at a surface tension of about K(δc 0 ) 2 (δc 0 being the difference in spontaneous curvature and K a bending modulus). In addition, the boundary is found to undergo a topography-induced rippling instability upon compression, if its line tension is smaller than about Kδc 0 . The effect of diffuse boundaries on these features and the topographic behavior near a critical point are also examined. We discuss the relevance of our findings to several experimental observations related to surfactant monolayers: (i) small topographic features recently found near domain boundaries; (ii) folding behavior observed in mixed phospholipid monolayers and model lung surfactants; (iii) roughening of domain boundaries seen under lateral compression; (iv) the absence of biphasic structures in tensionless surfactant films

Outcomes and complications following graft reconstruction for anterior sternoclavicular joint instability.

Science.gov (United States)

Willinger, Lukas; Schanda, Jakob; Herbst, Elmar; Imhoff, Andreas B; Martetschläger, Frank

2016-12-01

Publications describing tendon graft reconstruction for anterior sternoclavicular joint (SCJ) instability are rare and usually refer to small patient numbers. The aim of this study was to systematically review the literature regarding outcomes and complications following tendon graft reconstruction techniques for anterior SCJ instability. An online database was systematically searched to identify studies on graft reconstruction for anterior SCJ instability. Reported outcome scores were graded as excellent, good, fair and poor to summarize the study results. All reported complications were recorded. Five articles with a total of 80 patients met the inclusion criteria. Reported outcomes were excellent in 10 %, good in 89 % and fair in 1 %. Recurrent instability was found in 10 % of the patients, and 5 % underwent revision surgery due to persistent impairment of shoulder function related to SCJ instability or osteoarthritis. Surgical stabilization techniques for the SCJ using autologous tendon grafts have shown to be safe and reliable and make better patients' pain situation and shoulder function. However, a certain amount of impairment might persist, which needs to be discussed with patients. Severe complications were rare and revision rates were as low as 5 %. Therefore, graft reconstruction techniques should be considered for patients with chronic anterior SCJ instability after a course of failed conservative treatment. This study is valuable for clinicians in daily clinical practice when dealing with this difficult-to-treat pathology and can help surgeons to better predict the clinical outcomes and complications following SCJ graft reconstruction. It should, however, not lead to underestimation of the potential risks of the procedure. Systematic review, Level IV.

Unusual Spinal Epidural Lipomatosis and Lumbosacral Instability

Directory of Open Access Journals (Sweden)

David Ruiz Picazo

2016-01-01

Full Text Available Introduction. Epidural lipomatosis is most frequently observed in patients on chronic steroid treatment. Only a few idiopathic epidural lipomatosis cases have been described. Material and Methods. 64-year-old male patient presented with low back pain and left leg pain. Later, the patient experienced neurogenic claudication and radicular pain in the left leg without urinary dysfunction. Plain radiography and magnetic resonance imaging demonstrated an abnormal fat tissue overgrowth in the epidural space with compression of the dural sac, degenerative disc disease at L4-L5 level, and instability at L5-S1. Endocrinopathic diseases and chronic steroid therapy were excluded. If conservative treatment failed, surgical treatment can be indicated. Results. After surgery, there was a gradual improvement in symptoms and signs, and six months later the patient returned to daily activities and was neurologically normal. Conclusion. In the absence of common causes of neurogenic claudication, epidural lipomatosis should be considered. The standard test for the diagnosis of epidural lipomatosis is magnetic resonance (MR. At first, conservative treatment must be considered; weight loss and the suspension of prior corticosteroid therapy are indicated. In the presence of neurological impairment, the operative treatment of wide surgical decompression must be performed soon after diagnosis.

Drain Current Stress-Induced Instability in Amorphous InGaZnO Thin-Film Transistors with Different Active Layer Thicknesses

Directory of Open Access Journals (Sweden)

Dapeng Wang

2018-04-01

Full Text Available In this study, the initial electrical properties, positive gate bias stress (PBS, and drain current stress (DCS-induced instabilities of amorphous indium gallium zinc oxide (a-IGZO thin-film transistors (TFTs with various active layer thicknesses (TIGZO are investigated. As the TIGZO increased, the turn-on voltage (Von decreased, while the subthreshold swing slightly increased. Furthermore, the mobility of over 13 cm2·V−1·s−1 and the negligible hysteresis of ~0.5 V are obtained in all of the a-IGZO TFTs, regardless of the TIGZO. The PBS results exhibit that the Von shift is aggravated as the TIGZO decreases. In addition, the DCS-induced instability in the a-IGZO TFTs with various TIGZO values is revealed using current–voltage and capacitance–voltage (C–V measurements. An anomalous hump phenomenon is only observed in the off state of the gate-to-source (Cgs curve for all of the a-IGZO TFTs. This is due to the impact ionization that occurs near the drain side of the channel and the generated holes that flow towards the source side along the back-channel interface under the lateral electric field, which cause a lowered potential barrier near the source side. As the TIGZO value increased, the hump in the off state of the Cgs curve was gradually weakened.

Thermal Shrinkage for Shoulder Instability

OpenAIRE

Toth, Alison P.; Warren, Russell F.; Petrigliano, Frank A.; Doward, David A.; Cordasco, Frank A.; Altchek, David W.; O’Brien, Stephen J.

2010-01-01

Thermal capsular shrinkage was popular for the treatment of shoulder instability, despite a paucity of outcomes data in the literature defining the indications for this procedure or supporting its long-term efficacy. The purpose of this study was to perform a clinical evaluation of radiofrequency thermal capsular shrinkage for the treatment of shoulder instability, with a minimum 2-year follow-up. From 1999 to 2001, 101 consecutive patients with mild to moderate shoulder instability underwent...

Two-stream cyclotron radiative instabilities due to the marginally mirror-trapped fraction for fustion alphas in tokamaks

Energy Technology Data Exchange (ETDEWEB)

Arunasalam, V.

1995-07-01

It is shown here that the marginally mirror-trapped fraction of the newly-born fusion alpha particles in the deuterium-tritium (DT) reaction dominated tokamak plasmas can induce a two-stream cyclotron radiative instability for the fast Alfven waves propagating near the harmonics of the alpha particle cyclotron frequency {omega}{sub c{alpha}}. This can explain both the experimentally observed time behavior and the spatially localized origin of the fusion product ion cyclotron emission (ICE) in TFTR at frequencies {omega} {approx} m{omega}{sub c{alpha}}.

Two-stream cyclotron radiative instabilities due to the marginally mirror-trapped fraction for fustion alphas in tokamaks

International Nuclear Information System (INIS)

Arunasalam, V.

1995-07-01

It is shown here that the marginally mirror-trapped fraction of the newly-born fusion alpha particles in the deuterium-tritium (DT) reaction dominated tokamak plasmas can induce a two-stream cyclotron radiative instability for the fast Alfven waves propagating near the harmonics of the alpha particle cyclotron frequency ω cα . This can explain both the experimentally observed time behavior and the spatially localized origin of the fusion product ion cyclotron emission (ICE) in TFTR at frequencies ω ∼ mω cα

Ballooning mode instability due to slowed-down ALPHA -particles and associated transport

International Nuclear Information System (INIS)

Itoh, Sanae; Itoh, Kimitaka; Tuda, Takashi; Tokuda, Shinji.

1982-01-01

The microscopic stability of tokamak plasma, which contains slowed-down alpha-particles and the anomalous fluxes enhanced by the fluctuation, was studied. The local maxwellian distribution with the density inhomogeneity as the equilibrium distribution of electrons, ions and alpha-particles was closen. In the zero-beta limit, two branches of eigenmodes, which are electrostatic, were obtained. The electrostatic ballooning mode became unstable by the grad B drift of particles in the toroidal plasma. It should be noted that there was no critical alpha-particle density and no critical beta-value for the onset of the instability in toroidal plasma even in the presence of the magnetic shear. When the beta-value exceeded the critical beta-value of the MHD ballooning mode, the growth rate approached to that of the MHD mode, and the mode sturcture became very close to that of the MHD mode. The unstable mode in toroidal plasma was the ballooning mode, and was unstable for all plasma parameters. The associated cross-field transport by the ballooning mode is considered. It was found that if the distribution function was assumed to be the birth distribution, the loss rate was very slow and slower than the slowing down time. The effect of alpha-particles on the large scale MHD activity of plasma is discussed. (Kato, T.)

Development of a Program for Predicting Flow Instability in a Once-through Sodium-Heated Steam Generator (III)

Energy Technology Data Exchange (ETDEWEB)

Kim, Eui Kwang; Yoon, Jung; Kim, Jong Bum; Jeong, Jiyoung [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

Two-phase flow systems can be subjected to several types of instability problems. Density-wave oscillation is the most common and important type of instability in boiling channels. Such instability gives difficulties in predictions of system performance and system control, and component failure due to thermal fatigue. A computer program developed for predicting two-phase flow instability in a steam generator heated by liquid sodium was presented in the previous works. Limit cycle was predicted even in a fixed node system. The amplitude of inlet flow rate is larger than that of outlet flow rate. The amplitude of phase change location oscillation within boiling-to-vapor boundary node is larger than that of liquid-to-boiling boundary node. Sodium and steam temperature are invariant at tube exit.

The risk of PCI damage to 8x8 fuel rods during limit cycle instability

Energy Technology Data Exchange (ETDEWEB)

Schrire, D.; Oguma, R.; Malen, K.

1994-12-31

A BWR reactor core may experience thermal-hydraulic instability under certain operating conditions. Generally, the instability results in neutron flux (i e generated neutronic power) and coolant flow and pressure oscillations, which reach a maximum `limit cycle` amplitude. The cladding response to power transients has been studied using noise analysis. These results have been compared to results from code calculations using the fuel code TOODEE 2. From these results the risk for fuel rod failure due to pellet-clad mechanical interaction and possible failure due to stress corrosion cracking (PCI) has been estimated. It turns out that for the oscillation frequencies of interest (0,3-0,5 Hz) the fuel response amplitude reduction makes PCI-failure improbable. 17 refs.

Experimental observation of microwave absorption and electron heating due to the two plasmon decay instability and resonance absorption

International Nuclear Information System (INIS)

Rasmussen, D.A.

1981-01-01

The interaction of intense microwaves with an inhomogeneous plasma is studied in two experimental devices. In the first device an investigation was made of microwave absorption and electron heating due to the parametric decay of microwaves into electron plasma waves (Two Plasmon Decay instability, TPDI), modeling a process which can occur near the quarter critical surface in laser driven pellets. P-polarized microwave (f = 1.2 GHz, P 0 less than or equal to 12 kW) are applied to an essentially collisionless, inhomogeneous plasma, in an oversized waveguide, in the U.C. Davis Prometheus III device. The initial density scale length near the quarter critical surface is quite long (L/lambda/sub De/ approx. = 3000 or k 0 L approx. = 15). The observed threshold power for the TPDI is quite low (P/sub T/approx. = 0.1 kW or v/sub os//v/sub e/ approx. = 0.1). Near the threshold the decay waves only occur near the quarter critical surface. As the incident power is increased above threshold, the decay waves spread to lower densities, and for P 0 greater than or equal to lkW, (v/sub os//v/sub e/ greater than or equal to 0.3) suprathermal electron heating is strong for high powers (T/sub H/ less than or equal to 12 T/sub e/ for P 0 less than or equal to 8 kW or v/sub os//v/sub e/ less than or equal to 0.9)

Knee motion variability in patients with knee osteoarthritis: the effect of self-reported instability

Science.gov (United States)

Gustafson, Jonathan A.; Robinson, Megan E.; Fitzgerald, G. Kelley; Tashman, Scott; Farrokhi, Shawn

2015-01-01

Background Knee osteoarthritis has been previously associated with a stereotypical knee-stiffening gait pattern and reduced knee joint motion variability due to increased antagonist muscle co-contractions and smaller utilized arc of motion during gait. However, episodic self-reported instability may be a sign of excessive motion variability for a large subgroup of patients with knee osteoarthritis. The objective of this work was to evaluate the differences in knee joint motion variability during gait in patients with knee osteoarthritis with and without self-reported instability compared to a control group of older adults with asymptomatic knees. Methods Forty-three subjects, 8 with knee osteoarthritis but no reports of instability (stable), 11 with knee osteoarthritis and self-reported instability (unstable), and 24 without knee osteoarthritis or instability (control) underwent Dynamic Stereo X-ray analysis during a decline gait task on a treadmill. Knee motion variability was assessed using parametric phase plots during the loading response phase of decline gait. Findings The stable group demonstrated decreased sagittal-plane motion variability compared to the control group (p=0.04), while the unstable group demonstrated increased sagittal-plane motion variability compared to the control (p=0.003) and stable groups (pknee motion variability in patients with knee osteoarthritis without self-reported instability supports previous research. However, presence of self-reported instability is associated with increased knee motion variability in patients with knee osteoarthritis and warrants further investigation. PMID:25796536

Kelvin-Helmholtz instability and kinetic internal kink modes in tokamaks

International Nuclear Information System (INIS)

Naitou, H.

2002-01-01

The m=1 and n=1 kinetic internal kink (KIK) mode with a nonuniform density profile is studied by the cylindrical version of the gyro-reduced-MHD code which is one of the extended MHD codes being able to treat the physics beyond resistive MHD. Electron inertia and electron finite temperature effects are crucial. The linear mode structure of KIK mode includes the sheared poloidal flow with m=1, which excites the vortexes due to the Kelvin-Helmholtz (K-H) instability. We have found that there is a strong coupling between the KIK mode and the K-H mode even in the early nonlinear stage of KIK instability in which the width of the m=1 magnetic island is sufficiently small. (author)

Roles of bulk viscosity on Rayleigh-Taylor instability: Non-equilibrium thermodynamics due to spatio-temporal pressure fronts

Energy Technology Data Exchange (ETDEWEB)

Sengupta, Tapan K., E-mail: tksen@iitk.ac.in; Bhole, Ashish; Shruti, K. S. [HPCL, Department of Aerospace Engineering, IIT Kanpur, Kanpur, UP (India); Sengupta, Aditi [Department of Engineering, University of Cambridge, Cambridge (United Kingdom); Sharma, Nidhi [Graduate Student, HPCL, Department of Aerospace Engineering, IIT Kanpur, Kanpur, UP (India); Sengupta, Soumyo [Department of Mechanical and Aerospace Engineering, Ohio State University, Columbus, Ohio 43210 (United States)

2016-09-15

Direct numerical simulations of Rayleigh-Taylor instability (RTI) between two air masses with a temperature difference of 70 K is presented using compressible Navier-Stokes formulation in a non-equilibrium thermodynamic framework. The two-dimensional flow is studied in an isolated box with non-periodic walls in both vertical and horizontal directions. The non-conducting interface separating the two air masses is impulsively removed at t = 0 (depicting a heaviside function). No external perturbation has been used at the interface to instigate the instability at the onset. Computations have been carried out for rectangular and square cross sections. The formulation is free of Boussinesq approximation commonly used in many Navier-Stokes formulations for RTI. Effect of Stokes’ hypothesis is quantified, by using models from acoustic attenuation measurement for the second coefficient of viscosity from two experiments. Effects of Stokes’ hypothesis on growth of mixing layer and evolution of total entropy for the Rayleigh-Taylor system are reported. The initial rate of growth is observed to be independent of Stokes’ hypothesis and the geometry of the box. Following this stage, growth rate is dependent on the geometry of the box and is sensitive to the model used. As a consequence of compressible formulation, we capture pressure wave-packets with associated reflection and rarefaction from the non-periodic walls. The pattern and frequency of reflections of pressure waves noted specifically at the initial stages are reflected in entropy variation of the system.

Political Instability and Economic Growth

OpenAIRE

Alberto Alesina; Sule Ozler; Nouriel Roubini; Phillip Swagel

1992-01-01

This paper investigates the relationship between political instability and per capita GDP growth in a sample of 113 countries for the period 1950-1982. We define ?political instability? as the propensity of a government collapse, and we estimate a model in which political instability and economic growth are jointly determined. The main result of this paper is that in countries and time periods with a high propensity of government collapse, growth is significantly lower than otherwise. This ef...

Kinetic theory of tearing instabilities

International Nuclear Information System (INIS)

Drake, J.F.; Lee, Y.C.

1977-01-01

The transition of the tearing instability from the collisional to the collisionless regime is investigated kinetically using a Fokker--Planck collision operator to represent electron-ion collisions. As a function of the collisionality of the plasma, the tearing instability falls into three regions, which are referred to as collisionless, semi-collisional, and collisional. The width Δ of the singular layer around kxB 0 =0 is limited by electron thermal motion along B 0 in the collisional and semi-collisional regimes and is typically smaller than rho/sub i/, the ion Larmor radius. Previously accepted theories, which are based on the assumption Δvery-much-greater-thanrho/sub i/, are found to be valid only in the collisional regime. The effects of density and temperature gradients on the instabilities are also studied. The tearing instability is only driven by the temperature gradient in the collisional and semi-collisional regimes. Numerical calculations indicate that the semi-collisional tearing instability is particularly relevant to present day high temperature tokamak discharges

Magnetic viscosity by localized shear flow instability in magnetized accretion disks

International Nuclear Information System (INIS)

Matsumoto, R.; Tajima, T.

1995-01-01

Differentially rotating disks are subject to the axisymmetric instability for perfectly conducting plasma in the presence of poloidal magnetic fields. For nonaxisymmetric perturbations, the authors find localized unstable eigenmodes whose eigenfunction is confined between two Alfven singularities at ω d = ± ω A , where ω d is the Doppler-shifted wave frequency, and ω A = k parallel v A is the Alfven frequency. The radial width of the unstable eigenfunction is Δx ∼ ω A /(Ak y ), where A is the Oort's constant, and k y is the azimuthal wave number. The growth rate of the fundamental mode is larger for smaller value of k y /k z . The maximum growth rate when k y /k z ∼ 0.1 is ∼ 0.2Ω for the Keplerian disk with local angular velocity Ω. It is found that the purely growing mode disappears when k y /k z > 0.12. In a perfectly conducting disk, the instability grows even when the seed magnetic field is infinitesimal. Inclusion of the resistivity, however, leads to the appearance of an instability threshold. When the resistivity η depends on the instability-induced turbulent magnetic fields δB as η([δB 2 ]), the marginal stability condition self-consistently determines the α parameter of the angular momentum transport due to the magnetic stress. For fully ionized disks, the magnetic viscosity parameter α B is between 0.001 and 1. The authors' three-dimensional MHD simulation confirms these unstable eigenmodes. It also shows that the α parameter observed in simulation is between 0.01 and 1, in agreement with theory. The observationally required smaller α in the quiescent phase of accretion disks in dwarf novae may be explained by the decreased ionization due to the temperature drop

The Rayleigh-Taylor instability in the spherical pinch

International Nuclear Information System (INIS)

Chen, H.B.; Hilko, B.; Panarella, E.

1994-01-01

The spherical pinch (SP) concept is an outgrowth of the inertial confinement model (ICF). Unlike the ICF where instabilities, especially the Rayleigh-Taylor instability, have been studied extensively, the instability study of the spherical pinch has just begun. The Raleigh-Taylor instability is investigated for the first time in the SP in the present work. By using the simple condition for the Rayleigh-Taylor instability ∇p · ∇p < O (density and pressure gradients have opposite direction), we have qualitatively identified the regions for development of instabilities in the SP. It is found that the explosion phase (central discharge) is stable and instabilities take place in the imploding phase. However, the growth rate for the instability is not in exponential form, and the appearance of the Rayleigh-Taylor instability does not prevent the main shock wave from converging to the center of the sphere

Modeling of Instabilities and Self-organization at the Frictional Interface

Science.gov (United States)

Mortazavi, Vahid

The field of friction-induced self-organization and its practical importance remains unknown territory to many tribologists. Friction is usually thought of as irreversible dissipation of energy and deterioration; however, under certain conditions, friction can lead to the formation of new structures at the interface, including in-situ tribofilms and various patterns at the interface. This thesis studies self-organization and instabilities at the frictional interface, including the instability due to the temperature-dependency of the coefficient of friction, the transient process of frictional running-in, frictional Turing systems, the stick-and-slip phenomenon, and, finally, contact angle (CA) hysteresis as an example of solid-liquid friction and dissipation. All these problems are chosen to bridge the gap between fundamental interest in understanding the conditions leading to self-organization and practical motivation. We study the relationship between friction-induced instabilities and friction-induced self-organization. Friction is usually thought of as a stabilizing factor; however, sometimes it leads to the instability of sliding, in particular when friction is coupled with another process. Instabilities constitute the main mechanism for pattern formation. At first, a stationary structure loses its stability; after that, vibrations with increasing amplitude occur, leading to a limit cycle corresponding to a periodic pattern. The self-organization is usually beneficial for friction and wear reduction because the tribological systems tend to enter a state with the lowest energy dissipation. The introductory chapter starts with basic definitions related to self-organization, instabilities and friction, literature review, and objectives. We discuss fundamental concepts that provide a methodological tool to investigate, understand and enhance beneficial processes in tribosystems which might lead to self-organization. These processes could result in the ability of a

Instability following total knee arthroplasty.

Science.gov (United States)

Rodriguez-Merchan, E Carlos

2011-10-01

Background Knee prosthesis instability (KPI) is a frequent cause of failure of total knee arthroplasty. Moreover, the degree of constraint required to achieve immediate and long-term stability in total knee arthroplasty (TKA) is frequently debated. Questions This review aims to define the problem, analyze risk factors, and review strategies for prevention and treatment of KPI. Methods A PubMed (MEDLINE) search of the years 2000 to 2010 was performed using two key words: TKA and instability. One hundred and sixty-five initial articles were identified. The most important (17) articles as judged by the author were selected for this review. The main criteria for selection were that the articles addressed and provided solutions to the diagnosis and treatment of KPI. Results Patient-related risk factors predisposing to post-operative instability include deformity requiring a large surgical correction and aggressive ligament release, general or regional neuromuscular pathology, and hip or foot deformities. KPI can be prevented in most cases with appropriate selection of implants and good surgical technique. When ligament instability is anticipated post-operatively, the need for implants with a greater degree of constraint should be anticipated. In patients without significant varus or valgus malalignment and without significant flexion contracture, the posterior cruciate ligament (PCL) can be retained. However, the PCL should be sacrificed when deformity exists particularly in patients with rheumatoid arthritis, previous patellectomy, previous high tibial osteotomy or distal femoral osteotomy, and posttraumatic osteoarthritis with disruption of the PCL. In most cases, KPI requires revision surgery. Successful outcomes can only be obtained if the cause of KPI is identified and addressed. Conclusions Instability following TKA is a common cause of the need for revision. Typically, knees with deformity, rheumatoid arthritis, previous patellectomy or high tibial osteotomy, and

Stabilizing effect of passive conductors with arbitrary shape for positional instabilities

International Nuclear Information System (INIS)

Seki, Shogo; Ninomiya, Hiromasa; Yoshida, Hidetoshi

1983-10-01

For positional instabilities in the tokamak, the stabilizing index nsub(s) is an adequate parameter to characterize the stabilizing effect produced by several kinds of passive conductors around a plasma column such as vacuum vessel and poloidal field coils. Since a system of passive conductors with arbitrary shape can be involved into multiple L-R circuits, this parameter nsub(s) of those passive conductors is expressed in a simple form by using a method of the eigen mode expansion of multiple L-R circuits. This parameter nsub(s) is very useful to estimate not only a growth rate of positional instability and its feedback stabilization but also an inward shift of plasma column due to a minor disruption. (author)

Structural instability and ground state of the U{sub 2}Mo compound

Energy Technology Data Exchange (ETDEWEB)

Losada, E.L., E-mail: losada@cab.cnea.gov.ar [SIM" 3, Centro Atómico Bariloche, Comisión Nacional de Energía Atómica (Argentina); Garcés, J.E. [Gerencia de Investigación y Aplicaciones Nucleares, Comisión Nacional de Energía Atómica (Argentina)

2015-11-15

This work reports on the structural instability at T = 0 °K of the U{sub 2}Mo compound in the C11{sub b} structure under the distortion related to the C{sub 66} elastic constant. The electronic properties of U{sub 2}Mo such as density of states (DOS), bands and Fermi surface (FS) are studied to understand the source of the instability. The C11{sub b} structure can be interpreted as formed by parallel linear chains along the z-directions each one composed of successive U–Mo–U blocks. Hybridization due to electronic interactions inside the U–Mo–U blocks is slightly modified under the D{sub 6} distortion. The change in distance between chains modifies the U–U interaction and produces a split of f-states. The distorted structure is stabilized by a decrease in energy of the hybridized states, mainly between d-Mo and f-U states, together with the f-band split. Consequently, an induced Peierls distortion is produced in U{sub 2}Mo due to the D{sub 6} distortion. It is important to note that the results of this work indicate that the structure of the ground state of the U{sub 2}Mo compound is not the assumed C11{sub b} structure. It is suggested for the ground state a structure with hexagonal symmetry (P6 #168), ∼0.1 mRy below the energy of the recently proposed Pmmn structure. - Highlights: • Structural instability of the C11b compound due to the D6 deformation. • Induced Peierls distortion due to the D6 deformation. • Distorted structure is stabilized by hybridization and split of f-Uranium state. • P6 (#168) suggested ground state for the U{sub 2}Mo compound.

Instabilities in thin tunnel junctions

International Nuclear Information System (INIS)

Konkin, M.K.; Adler, J.G.

1978-01-01

Tunnel junctions prepared for inelastic electron tunneling spectroscopy are often plagued by instabilities in the 0-500-meV range. This paper relates the bias at which the instability occurs to the barrier thickness

Heritability of asymmetry and lateral plate number in the threespine stickleback.

Directory of Open Access Journals (Sweden)

John Loehr

Full Text Available The estimation of individual fitness and quality are important elements of evolutionary ecological research. Over the past six decades, there has been great interest in using fluctuating asymmetry (FA to represent individual quality, yet, serious technical problems have hampered efforts to estimate the heritability of FA, which, in turn, has limited progress in the investigation of FA from an evolutionary perspective. Here we estimate the heritability of number of lateral plates, their FA and directional asymmetry (DA in threespine stickleback, Gasterosteus aculeatus. By (i using a meristic trait and (ii basing our calculations on a large half-sib design experiment involving 2,079 offspring from 84 families, we overcame many of the difficulties faced by earlier FA studies. Both lateral plate number and FA in lateral plates were heritable (h(2 = 0.46 and 0.21, respectively, even after controlling for marker genotypes linked to EDA (the major locus influencing plate number. Likewise, DA in lateral plates was heritable h(2 = 0.23. The additive genetic component of FA in lateral plates makes it a prime candidate for further investigation into the evolutionary implications of FA and the genetic underpinnings of developmental instability. This discovery in an evolutionary model species holds the possibility to invigorate the study of FA from an evolutionary perspective.

Instability of ties in compression

DEFF Research Database (Denmark)

Buch-Hansen, Thomas Cornelius

2013-01-01

Masonry cavity walls are loaded by wind pressure and vertical load from upper floors. These loads results in bending moments and compression forces in the ties connecting the outer and the inner wall in a cavity wall. Large cavity walls are furthermore loaded by differential movements from...... the temperature gradient between the outer and the inner wall, which results in critical increase of the bending moments in the ties. Since the ties are loaded by combined compression and moment forces, the loadbearing capacity is derived from instability equilibrium equations. Most of them are iterative, since...... exact instability solutions are complex to derive, not to mention the extra complexity introducing dimensional instability from the temperature gradients. Using an inverse variable substitution and comparing an exact theory with an analytical instability solution a method to design tie...

Experiment and simulation on the thermal instability of a heavily deformed Cu-Fe composite

International Nuclear Information System (INIS)

Qu Lei; Wang Engang; Zuo Xiaowei; Zhang Lin; He Jicheng

2011-01-01

Research highlights: → Fe fibers undergo thermal instability at temperature above 600 deg. C. → Longitudinal boundary splitting is the dominant instability process. → Instability of cylindrical fibers is controlled by breakup, growth and coarsening. → Breakup times can be predicted by Rayleigh perturbation model accurately. → The increase of fiber diameters is due to the coarsening and growth. - Abstract: The thermal instability of the Fe fibers in the heavily deformed Cu-12.8 wt.%Fe composites is investigated experimentally and numerically. The fiber evolution is characterized by a field emission scanning electron microscopy (FESEM). The results show that the dominant instability of the Fe fibers is the longitudinal boundary splitting which is determined by the greater cross sectional aspect ratio (width/thickness, w/t) and the larger ratio of boundary to interfacial energy (γ B /γ S ). The longitudinal boundary splitting makes the ribbon-like Fe fibers evolve into a series of cylindrical fibers. Then the cylindrical Fe fibers undergo the instability process in terms of the breakup, growth and coarsening concurrently. The breakup times are accurately predicted by the Rayleigh perturbation model. The growth process primarily contributes to the higher increasing rate of the fiber radius during isothermal annealing at 700 deg. C than that calculated by the coarsening theory developed for cylindrical fibers, since the Cu-matrix of composites is highly supersaturated after casting/cold-working process.

High-frequency instabilities of stationary crossflow vortices in a hypersonic boundary layer

Science.gov (United States)

Li, Fei; Choudhari, Meelan; Paredes, Pedro; Duan, Lian

2016-09-01

Hypersonic boundary layer flows over a circular cone at moderate incidence angle can support strong crossflow instability in between the windward and leeward rays on the plane of symmetry. Due to more efficient excitation of stationary crossflow vortices by surface roughness, such boundary layer flows may transition to turbulence via rapid amplification of the high-frequency secondary instabilities of finite-amplitude stationary crossflow vortices. The amplification characteristics of these secondary instabilities are investigated for crossflow vortices generated by an azimuthally periodic array of roughness elements over a 7° half-angle circular cone in a Mach 6 free stream. The analysis is based on both quasiparallel stability theory in the form of a partial-differential-equation-based eigenvalue analysis and plane marching parabolized stability equations that account for the effects of the nonparallel basic state on the growth of secondary disturbances. Depending on the local amplitude of the stationary crossflow mode, the most unstable high-frequency disturbances either originate from the second (i.e., Mack) mode instabilities of the unperturbed boundary layer or correspond to genuine secondary instabilities that reduce to stable disturbances at sufficiently small amplitudes of the stationary crossflow vortex. The predicted frequencies of the dominant secondary disturbances of either type are similar to those measured during wind tunnel experiments at Purdue University and the Technical University of Braunschweig, Germany. Including transverse surface curvature within the quasiparallel predictions does not alter the topology of the unstable modes; however, the resulting changes in both mode shape and disturbance growth rate are rather significant and curvature can be either stabilizing or destabilizing depending on the disturbance frequency and mode type. Nonparallel effects are shown to be strongly destabilizing for secondary instabilities originating from

-MoS2 Lateral Heterojunctions

KAUST Repository

Li, Ming-yang

2018-02-28

2D layered heterostructures have attracted intensive interests due to their unique optical, transport, and interfacial properties. The laterally stitched heterojunction based on dissimilar 2D transition metal dichalcogenides forms an intrinsic p–n junction without the necessity of applying an external voltage. However, no scalable processes are reported to construct the devices with such lateral heterostructures. Here, a scalable strategy, two-step and location-selective chemical vapor deposition, is reported to synthesize self-aligned WSe2–MoS2 monolayer lateral heterojunction arrays and demonstrates their light-emitting devices. The proposed fabrication process enables the growth of high-quality interfaces and the first successful observation of electroluminescence at the WSe2–MoS2 lateral heterojunction. The electroluminescence study has confirmed the type-I alignment at the interface rather than commonly believed type-II alignment. This self-aligned growth process paves the way for constructing various 2D lateral heterostructures in a scalable manner, practically important for integrated 2D circuit applications.

Active ankle motion may result in changes to the talofibular interval in individuals with chronic ankle instability and ankle sprain copers: a preliminary study.

Science.gov (United States)

Croy, Theodore; Cosby, Nicole L; Hertel, Jay

2013-08-01

Alterations in talocrural joint arthrokinematics related to repositioning of the talus or fibula following ankle sprain have been reported in radiological and clinical studies. It is unclear if these changes can result from normal active ankle motion. The study objective was to determine if active movement created changes in the sagittal plane talofibular interval in ankles with a history of lateral ankle sprain and instability. Three subject groups [control (n = 17), ankle sprain copers (n = 20), and chronic ankle instability (n = 20)] underwent ultrasound imaging of the anterolateral ankle gutter to identify the lateral malleolus and talus over three trials. Between trials, subjects actively plantar and dorsiflexed the ankle three times. The sagittal plane talofibular interval was assessed by measuring the anteroposterior distance (mm) between the lateral malleolus and talus from an ultrasound image. Between group and trial differences were analyzed with repeated measures analysis of variance and post-hoc t-tests. Fifty-seven subjects participated. A significant group-by-trial interaction was observed (F4,108 = 3.5; P = 0.009). The talofibular interval was increased in both copers [2.4±3.6 mm; 95% confidence interval (CI): 0.73-4.1; P = 0.007] and chronic ankle instability (4.1±4.6 mm; 95% CI: 1.9-6.2; P = 0.001) at trial 3 while no changes were observed in control ankle talar position (0.06±2.8mm; 95% CI: -1.5-1.4; P = 0.93). The talofibular interval increased only in subjects with a history of lateral ankle sprain with large clinical effect sizes observed. These findings suggest that an alteration in the position of the talus or fibula occurred with non-weight bearing sagittal plane motion. These findings may have diagnostic and therapeutic implications for manual therapists.

Comparison of the Modified Broström Procedure for Chronic Lateral Ankle Instability With and Without Subfibular Ossicle.

Science.gov (United States)

Ahn, Hyeon-Wook; Lee, Keun-Bae

2016-12-01

Subfibular ossicles are frequently found in patients with chronic lateral ankle instability (CLAI). However, there is a lack of consensus about the optimal surgical treatment for CLAI with subfibular ossicle. To evaluate the clinical and radiographic outcomes of the modified Broström procedure with subfibular ossicle excision compared with the same procedure for CLAI without subfibular ossicle. Cohort study; Level of evidence, 3. Ninety-six patients (96 ankles) treated with the modified Broström procedure using bone tunnel and suture anchor techniques for CLAI constituted the study cohort. The 96 ankles were divided into 2 groups with and without subfibular ossicles. The ossicle group (42 ankles) and nonossicle group (54 ankles) consisted of patients with a mean age of 26.6 and 30.3 years, respectively, at the time of surgery with a mean follow-up duration of 63.7 and 62.1 months, respectively. Subfibular ossicles were excised in the ossicle group. Mean Karlsson scores improved from 55.2 to 95.3 in the ossicle group and from 56.4 to 94.8 in the nonossicle group at final follow-up. Mean American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot scores also improved from 63.3 to 95.9 in the ossicle group and from 62.8 to 95.1 in the nonossicle group at final follow-up. Mean talar tilt angles were 14.0° in the ossicle group and 12.2° in the nonossicle group preoperatively and 7.6° and 6.8° at the final follow-up, respectively. Mean anterior talar translations in the ossicle group and nonossicle groups improved from 9.3 and 9.4 mm preoperatively to 5.8 and 5.7 mm at final follow-up, respectively. No significant differences were found between the 2 groups in terms of Karlsson score, AOFAS score, talar tilt angle, and anterior talar translation at final follow-up (P > .05). The modified Broström procedure with subfibular ossicle excision provided similarly good clinical and radiographic outcomes compared with the same procedure without subfibular ossicle

Parametric instabilities of parallel propagating incoherent Alfven waves in a finite ion beta plasma

International Nuclear Information System (INIS)

Nariyuki, Y.; Hada, T.; Tsubouchi, K.

2007-01-01

Large amplitude, low-frequency Alfven waves constitute one of the most essential elements of magnetohydrodynamic (MHD) turbulence in the fast solar wind. Due to small collisionless dissipation rates, the waves can propagate long distances and efficiently convey such macroscopic quantities as momentum, energy, and helicity. Since loading of such quantities is completed when the waves damp away, it is important to examine how the waves can dissipate in the solar wind. Among various possible dissipation processes of the Alfven waves, parametric instabilities have been believed to be important. In this paper, we numerically discuss the parametric instabilities of coherent/incoherent Alfven waves in a finite ion beta plasma using a one-dimensional hybrid (superparticle ions plus an electron massless fluid) simulation, in order to explain local production of sunward propagating Alfven waves, as suggested by Helios/Ulysses observation results. Parameter studies clarify the dependence of parametric instabilities of coherent/incoherent Alfven waves on the ion and electron beta ratio. Parametric instabilities of coherent Alfven waves in a finite ion beta plasma are vastly different from those in the cold ions (i.e., MHD and/or Hall-MHD systems), even if the collisionless damping of the Alfven waves are neglected. Further, ''nonlinearly driven'' modulational instability is important for the dissipation of incoherent Alfven waves in a finite ion beta plasma regardless of their polarization, since the ion kinetic effects let both the right-hand and left-hand polarized waves become unstable to the modulational instability. The present results suggest that, although the antisunward propagating dispersive Alfven waves are efficiently dissipated through the parametric instabilities in a finite ion beta plasma, these instabilities hardly produce the sunward propagating waves

Fringe instability in constrained soft elastic layers.

Science.gov (United States)

Lin, Shaoting; Cohen, Tal; Zhang, Teng; Yuk, Hyunwoo; Abeyaratne, Rohan; Zhao, Xuanhe

2016-11-04

Soft elastic layers with top and bottom surfaces adhered to rigid bodies are abundant in biological organisms and engineering applications. As the rigid bodies are pulled apart, the stressed layer can exhibit various modes of mechanical instabilities. In cases where the layer's thickness is much smaller than its length and width, the dominant modes that have been studied are the cavitation, interfacial and fingering instabilities. Here we report a new mode of instability which emerges if the thickness of the constrained elastic layer is comparable to or smaller than its width. In this case, the middle portion along the layer's thickness elongates nearly uniformly while the constrained fringe portions of the layer deform nonuniformly. When the applied stretch reaches a critical value, the exposed free surfaces of the fringe portions begin to undulate periodically without debonding from the rigid bodies, giving the fringe instability. We use experiments, theory and numerical simulations to quantitatively explain the fringe instability and derive scaling laws for its critical stress, critical strain and wavelength. We show that in a force controlled setting the elastic fingering instability is associated with a snap-through buckling that does not exist for the fringe instability. The discovery of the fringe instability will not only advance the understanding of mechanical instabilities in soft materials but also have implications for biological and engineered adhesives and joints.

Boundary modulation effects on MHD instabilities in Heliotrons

International Nuclear Information System (INIS)

Nakajima, N.; Hudson, S.R.; Hegna, C.C.; Nakamura, Y.

2005-01-01

In three-dimensional configurations, the confinement region is surrounded by the stochastic magnetic field lines related to magnetic islands or separatrix, leading to the fact that the plasma-vacuum boundary is not so definite compared with tokamaks that the various modulations of the plasma-vacuum boundary will be induced around the stochastic region by a large Shafranov shift of the whole plasma, in especially high-β operations. To examine such the modulation effects of the plasma boundary on MHD instabilities, high-β plasmas allowing a large Shafranov shift are considered in the inward-shifted LHD configurations with the vacuum magnetic axis R ax of 3.6m, for which previous theoretical analyses indicate that pressure-driven modes are significantly more unstable compared with experimental observations. It is shown that the boundary modulation due to a free motion of the equilibrium plasma has not only significant stabilizing effects on ideal MHD instabilities, but also characteristics consistent to experimental observations. (author)

Feedback scheme for kink instability in ERL based electron ion collider

International Nuclear Information System (INIS)

Hao, Y.; Litvinenko, V.N.; Ptitsyn, V.

2011-01-01

Kink instability presents one of the limiting factors from achieving higher luminosity in ERL based electron ion collider (EIC). However, we can take advantage of the flexibility of the linac and design a feedback system to cure the instability. This scheme raises the threshold of kink instability dramatically and provides opportunity for higher luminosity. We studied the effectiveness of this system and its dependence on the amplitude and phase of the feedback. In this paper we present results of theses studies of this scheme and describe its theoretical and practical limitations. The main advantage of an energy recovery linac (ERL) based electron ion collider (EIC) over a ring-ring type counterpart is the higher achievable luminosity. In ERL-based version, one electron beam collides with the opposing ion beam only once so that the beam-beam parameter can largely exceed the usual limitation in an electron collider ring, while the beam-beam parameter for the ion beam remains small values. The resulting luminosity may be enhanced by one order of magnitude. The beam dynamics related challenges also arise as the luminosity boost in ERL based EIC due to the significant beam-beam effect on the electron beam. The effects on the electron beam include the additional large beam-beam tune shift and nonlinear emittance growth, which are discussed. The ion beam may develop a head-tail type instability, referred as 'kink instability', through the interaction with the electron beam. In this paper, we discuss the feasibility of an active feedback system to mitigate the kink instability, by taking advantage of the flexibility of ERL. Throughout the paper, we will discuss the collision between proton and electron beam. Any other ion species can be scaled by its charge Z and ion mass A.

Relativistic centrifugal instability

Science.gov (United States)

Gourgouliatos, Konstantinos N.; Komissarov, Serguei S.

2018-03-01

Near the central engine, many astrophysical jets are expected to rotate about their axis. Further out they are expected to go through the processes of reconfinement and recollimation. In both these cases, the flow streams along a concave surface and hence, it is subject to the centrifugal force. It is well known that such flows may experience the centrifugal instability (CFI), to which there are many laboratory examples. The recent computer simulations of relativistic jets from active galactic nuclei undergoing the process of reconfinement show that in such jets CFI may dominate over the Kelvin-Helmholtz instability associated with velocity shear (Gourgouliatos & Komissarov). In this letter, we generalize the Rayleigh criterion for CFI in rotating fluids to relativistic flows using a heuristic analysis. We also present the results of computer simulations which support our analytic criterion for the case of an interface separating two uniformly rotating cylindrical flows. We discuss the difference between CFI and the Rayleigh-Taylor instability in flows with curved streamlines.

Dispersive properties and attraction instability of low-frequency collective modes in dusty plasmas

International Nuclear Information System (INIS)