Tang, Dalin; Yang, Chun; Kobayashi, Shunichi; Zheng, Jie; Woodard, Pamela K; Teng, Zhongzhao; Billiar, Kristen; Bach, Richard; Ku, David N
2009-06-01
Heart attack and stroke are often caused by atherosclerotic plaque rupture, which happens without warning most of the time. Magnetic resonance imaging (MRI)-based atherosclerotic plaque models with fluid-structure interactions (FSIs) have been introduced to perform flow and stress/strain analysis and identify possible mechanical and morphological indices for accurate plaque vulnerability assessment. For coronary arteries, cyclic bending associated with heart motion and anisotropy of the vessel walls may have significant influence on flow and stress/strain distributions in the plaque. FSI models with cyclic bending and anisotropic vessel properties for coronary plaques are lacking in the current literature. In this paper, cyclic bending and anisotropic vessel properties were added to 3D FSI coronary plaque models so that the models would be more realistic for more accurate computational flow and stress/strain predictions. Six computational models using one ex vivo MRI human coronary plaque specimen data were constructed to assess the effects of cyclic bending, anisotropic vessel properties, pulsating pressure, plaque structure, and axial stretch on plaque stress/strain distributions. Our results indicate that cyclic bending and anisotropic properties may cause 50-800% increase in maximum principal stress (Stress-P1) values at selected locations. The stress increase varies with location and is higher when bending is coupled with axial stretch, nonsmooth plaque structure, and resonant pressure conditions (zero phase angle shift). Effects of cyclic bending on flow behaviors are more modest (9.8% decrease in maximum velocity, 2.5% decrease in flow rate, 15% increase in maximum flow shear stress). Inclusion of cyclic bending, anisotropic vessel material properties, accurate plaque structure, and axial stretch in computational FSI models should lead to a considerable improvement of accuracy of computational stress/strain predictions for coronary plaque vulnerability
Water hammer (with FSI): exact solution : parallelization and application
Loh, K.; Tijsseling, A.S.
2014-01-01
The 1D fully coupled Fluid-Structure Interaction (FSI) model can adequately describe the water hammer effect on the fluid, and the structural behaviour of the pipe. This paper attempts to increase the capability of using an exact solution of the 1D FSI problem applied to a straight pipe with a
Development of strongly coupled FSI technology involving thin walled structures
CSIR Research Space (South Africa)
Suliman, Ridhwaan
2011-01-01
Full Text Available A strongly coupled finite volume-finite element fluid-structure interaction (FSI) scheme is developed. Both an edge-based finite volume and Galerkin finite element scheme are implemented and evaluated for modelling the mechanics of solids...
Motion simulation of hydraulic driven safety rod using FSI method
International Nuclear Information System (INIS)
Jung, Jaeho; Kim, Sanghaun; Yoo, Yeonsik; Cho, Yeonggarp; Kim, Jong In
2013-01-01
Hydraulic driven safety rod which is one of them is being developed by Division for Reactor Mechanical Engineering, KAERI. In this paper the motion of this rod is simulated by fluid structure interaction (FSI) method before manufacturing for design verification and pump sizing. A newly designed hydraulic driven safety rod which is one of reactivity control mechanism is simulated using FSI method for design verification and pump sizing. The simulation is done in CFD domain with UDF. The pressure drop is changed slightly by flow rates. It means that the pressure drop is mainly determined by weight of moving part. The simulated velocity of piston is linearly proportional to flow rates so the pump can be sized easily according to the rising and drop time requirement of the safety rod using the simulation results
DTK C/Fortran Interface Development for NEAMS FSI Simulations
Energy Technology Data Exchange (ETDEWEB)
Slattery, Stuart R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lebrun-Grandie, Damien T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2016-09-19
This report documents the development of DataTransferKit (DTK) C and Fortran interfaces for fluid-structure-interaction (FSI) simulations in NEAMS. In these simulations, the codes Nek5000 and Diablo are being coupled within the SHARP framework to study flow-induced vibration (FIV) in reactor steam generators. We will review the current Nek5000/Diablo coupling algorithm in SHARP and the current state of the solution transfer scheme used in this implementation. We will then present existing DTK algorithms which may be used instead to provide an improvement in both flexibility and scalability of the current SHARP implementation. We will show how these can be used within the current FSI scheme using a new set of interfaces to the algorithms developed by this work. These new interfaces currently expose the mesh-free solution transfer algorithms in DTK, a C++ library, and are written in C and Fortran to enable coupling of both Nek5000 and Diablo in their native Fortran language. They have been compiled and tested on Cooley, the test-bed machine for Mira at ALCF.
O'Dor, Sarah L; Grasso, Damion J; Forbes, Danielle; Bates, John E; McCarthy, Kimberly J; Wakschlag, Lauren S; Briggs-Gowan, Margaret J
2017-04-01
Elucidating the complex mechanisms by which harsh parenting increases risk of child psychopathology is key to targeted prevention. This requires nuanced methods that capture the varied perceptions and experiences of diverse families. The Family Socialization Interview-Revised (FSI-R), adapted from an interview developed by Dodge et al. (Child Development, 65, 649-665, 1994), is a comprehensive, semi-structured interview for characterizing methods of parental discipline used with young children. The FSI-R coding system systematically rates parenting style, usual discipline techniques, and most intense physical and psychological discipline based on rater judgment across two eras: (1) birth to the previous year, and (2) the previous year to present. The current study examined the psychometric properties of the FSI-R in a diverse, high-risk community sample of 386 mothers and their children, ages 3 to 6 years. Interrater reliability was good to excellent for codes capturing physically and psychologically harsh parenting, and restrictive/punitive parenting styles. Findings supported the FSI-R's convergent and incremental validity. Importantly, the FSI-R demonstrated incremental utility, explaining unique variance in children's externalizing and internalizing symptoms beyond that explained by traditional surveys and observed parenting. The FSI-R appeared particularly promising for capturing risk associated with young children's depressive symptoms, as these were generally not significantly associated with other measures of harsh parenting. Overall, findings support the added value of the FSI-R within a multi-method assessment of disciplinary practices across early child development. Future implications for prevention are discussed.
O’Dor, Sarah L.; Grasso, Damion J.; Forbes, Danielle; Bates, John E.; McCarthy, Kimberly J.; Wakschlag, Lauren S.
2017-01-01
Elucidating the complex mechanisms by which harsh parenting increases risk of child psychopathology is key to targeted prevention. This requires nuanced methods that capture the varied perceptions and experiences of diverse families. The Family Socialization Interview—Revised (FSI-R), adapted from an interview developed by Dodge et al. (Child Development, 65,649–665,1994), is a comprehensive, semi-structured interview for characterizing methods of parental discipline used with young children. The FSI-R coding system systematically rates parenting style, usual discipline techniques, and most intense physical and psychological discipline based on rater judgment across two eras: (1) birth to the previous year, and (2) the previous year to present. The current study examined the psychometric properties of the FSI-R in a diverse, high-risk community sample of 386 mothers and their children, ages 3 to 6 years. Interrater reliability was good to excellent for codes capturing physically and psychologically harsh parenting, and restrictive/punitive parenting styles. Findings supported the FSI-R’s convergent and incremental validity. Importantly, the FSI-R demonstrated incremental utility, explaining unique variance in children’s externalizing and internalizing symptoms beyond that explained by traditional surveys and observed parenting. The FSI-R appeared particularly promising for capturing risk associated with young children’s depressive symptoms, as these were generally not significantly associated with other measures of harsh parenting. Overall, findings support the added value of the FSI-R within a multi-method assessment of disciplinary practices across early child development. Future implications for prevention are discussed. PMID:27718104
Quasi-Newton methods for implicit black-box FSI coupling
CSIR Research Space (South Africa)
Bogaers, Alfred EJ
2014-09-01
Full Text Available In this paper we introduce a new multi-vector update quasi-Newton (MVQN) method for implicit coupling of partitioned, transient FSI solvers. The new quasi-Newton method facilitates the use of 'black-box' field solvers and under certain circumstances...
FSI-based Overflow Assessment of the Seismically-Isolated SFP with Fuel Racks
Energy Technology Data Exchange (ETDEWEB)
Chung, Gil Y.; Park, Hyun T.; Chang, Soo-Hyuk [Korea Maintenance Co., Seoul (Korea, Republic of); Lee, Sang-Hoon [KEPCO E-C, Yongin (Korea, Republic of)
2014-10-15
To date, effectiveness of the seismic isolation systems for reducing seismic force effectively has been well demonstrated. In this context, practical application of the technology in nuclear engineering fields has become an important issue more and more. This is because fluid motion can be rather amplified due to the increased relative displacement between the base and superstructures by a long-period shift. Therefore, overflow assessment and prediction of the seismically-isolated SFP have to be conducted in design phase. For performing sloshing-induced overflow of the seismically-isolated SFP, a fluid-structure interaction(FSI) approach making a two-way coupling process between structural and fluid solvers is herein employed. In this study, fuel racks inside the SFP are included in FSI modeling to investigate effect of fuel-cell assemblies on SFP overflow. Accordingly, three different assembly sets of fuel cells are assumed to be inserted in fuel racks. In addition, floor acceleration time-histories produced from three different amplitudes of peak ground acceleration (PGA) are applied to the SFP base to investigate load effect on liquid overflow. An approach for the liquid overflow assessment of the seismically-isolated nuclear SFP with fuel storage racks based on FSI analysis was addressed. From the results of the identified cases, the following conclusions are drawn: (i) FSI technique can be effectively used to assess the seismically-isolated SFP overflow, (ii) In a conservative way, the isolated SFP without fuel racks can be used to assess its sloshing-induced overflow under earthquake since effect of fuel-cell assemblies on the SFP overflow is not significant, (iii) for given same conditions (e.g., constant design free surface, same fuel-cell assembly) except seismic loading, the higher PGA is, the more liquid overflow increases.
O’Dor, Sarah L.; Grasso, Damion J.; Forbes, Danielle; Bates, John E.; McCarthy, Kimberly J.; Wakschlag, Lauren S.; Briggs-Gowan, Margaret J.
2017-01-01
Elucidating the complex mechanisms by which harsh parenting increases risk of child psychopathology is key to targeted prevention. This requires nuanced methods that capture the varied perceptions and experiences of diverse families. The Family Socialization Interview—Revised (FSI-R), adapted from an interview developed by Dodge et al. (Child Development, 65,649–665,1994), is a comprehensive, semi-structured interview for characterizing methods of parental discipline used with young children....
A geometry-adaptive IB-LBM for FSI problems at moderate and high Reynolds numbers
Tian, Fangbao; Xu, Lincheng; Young, John; Lai, Joseph C. S.
2017-11-01
An FSI framework combining the LBM and an improved IBM is introduced for FSI problems at moderate and high Reynolds numbers. In this framework, the fluid dynamics is obtained by the LBM. The FSI boundary conditions are handled by an improved IBM based on the feedback scheme where the feedback coefficient is mathematically derived and explicitly approximated. The Lagrangian force is divided into two parts: one is caused by the mismatching of the flow velocity and the boundary velocity at previous time step, and the other is caused by the boundary acceleration. Such treatment significantly enhances the numerical stability. A geometry-adaptive refinement is applied to provide fine resolution around the immersed geometries. The overlapping grids between two adjacent refinements consist of two layers. The movement of fluid-structure interfaces only causes adding or removing grids at the boundaries of refinements. Finally, the classic Smagorinsky large eddy simulation model is incorporated into the framework to model turbulent flows at relatively high Reynolds numbers. Several validation cases are conducted to verify the accuracy and fidelity of the present solver over a range of Reynolds numbers. Mr L. Xu acknowledges the support of the University International Postgraduate Award by University of New South Wales. Dr. F.-B. Tian is the recipient of an Australian Research Council Discovery Early Career Researcher Award (Project Number DE160101098).
Cardiac re-entry dynamics and self-termination in DT-MRI based model of Human Foetal Heart
Biktasheva, Irina V.; Anderson, Richard A.; Holden, Arun V.; Pervolaraki, Eleftheria; Wen, Fen Cai
2018-02-01
The effect of human foetal heart geometry and anisotropy on anatomy induced drift and self-termination of cardiac re-entry is studied here in MRI based 2D slice and 3D whole heart computer simulations. Isotropic and anisotropic models of 20 weeks of gestational age human foetal heart obtained from 100μm voxel diffusion tensor MRI data sets were used in the computer simulations. The fiber orientation angles of the heart were obtained from the orientation of the DT-MRI primary eigenvectors. In a spatially homogeneous electrophysiological monodomain model with the DT-MRI based heart geometries, cardiac re-entry was initiated at a prescribed location in a 2D slice, and in the 3D whole heart anatomy models. Excitation was described by simplified FitzHugh-Nagumo kinetics. In a slice of the heart, with propagation velocity twice as fast along the fibres than across the fibers, DT-MRI based fiber anisotropy changes the re-entry dynamics from pinned to an anatomical re-entry. In the 3D whole heart models, the fiber anisotropy changes cardiac re-entry dynamics from a persistent re-entry to the re-entry self-termination. The self-termination time depends on the re-entry’s initial position. In all the simulations with the DT-MRI based cardiac geometry, the anisotropy of the myocardial tissue shortens the time to re-entry self-termination several folds. The numerical simulations depend on the validity of the DT-MRI data set used. The ventricular wall showed the characteristic transmural rotation of the helix angle of the developed mammalian heart, while the fiber orientation in the atria was irregular.
Performance of a reduced-order FSI model for flow-induced vocal fold vibration
Luo, Haoxiang; Chang, Siyuan; Chen, Ye; Rousseau, Bernard; PhonoSim Team
2017-11-01
Vocal fold vibration during speech production involves a three-dimensional unsteady glottal jet flow and three-dimensional nonlinear tissue mechanics. A full 3D fluid-structure interaction (FSI) model is computationally expensive even though it provides most accurate information about the system. On the other hand, an efficient reduced-order FSI model is useful for fast simulation and analysis of the vocal fold dynamics, which can be applied in procedures such as optimization and parameter estimation. In this work, we study performance of a reduced-order model as compared with the corresponding full 3D model in terms of its accuracy in predicting the vibration frequency and deformation mode. In the reduced-order model, we use a 1D flow model coupled with a 3D tissue model that is the same as in the full 3D model. Two different hyperelastic tissue behaviors are assumed. In addition, the vocal fold thickness and subglottal pressure are varied for systematic comparison. The result shows that the reduced-order model provides consistent predictions as the full 3D model across different tissue material assumptions and subglottal pressures. However, the vocal fold thickness has most effect on the model accuracy, especially when the vocal fold is thin.
Study on stress characteristics of Francis hydraulic turbine runner based on two-way FSI
International Nuclear Information System (INIS)
Zhu, W R; Xiao, R F; Yang, W; Wang, F J; Liu, J
2012-01-01
In recent years, cracking phenomenon occurs in many large-sized turbines both nationally and internationally, which has threatened the stable operation of hydraulic turbines. Consequently, Stress characteristics calculation and analysis of a Francis hydraulic turbine runner by application of fluid-structure interaction (FSI) technology become significantly important. In order to introduce two-way coupling technology to hydraulic machinery, two-way FSI technology is applied in this article to calculate and analyze stress characteristics. Through coordinate system transformation, the continuity equations and Navier-Stokes equations in the Cartesian coordinates system are firstly transformed to ALE coordinates system. The fluid field control equations are then constructed and discrete equations can be obtained by using flow-condition-based interpolation (FBIC-C). The structure static mechanics equations used are established in rotation coordinate system, and modeled with the finite method. Two-way coupling is computed by using iteration method. The fluid equations and structure equations are iterated until coupling coefficients converge. According to structure result, the maximum stress, displacement as well as its location can be found. As a result, the most easily wear position can be discovered which provides valuable basis for optimized design and stable operation of Francis hydraulic turbines. After comparing the results with that of one-way coupling, it is discovered that displacements is the key factors which affects the results of one-way and two-way coupling.
Hanoca, P.; Ramakrishna, H. V.
2018-03-01
This work is related to develop a methodology to model and simulate the TEHD using the sequential application of CFD and CSD. The FSI analyses are carried out using ANSYS Workbench. In this analysis steady state, 3D Navier-Stoke equations along with energy equation are solved. Liquid properties are introduced where the viscosity and density are the function of pressure and temperature. The cavitation phenomenon is adopted in the analysis. Numerical analysis has been carried at different speeds and surfaces temperatures. During the analysis, it was found that as speed increases, hydrodynamic pressures will also increases. The pressure profile obtained from the Roelands equation is more sensitive to the temperature as compared to the Barus equation. The stress distributions specify the significant positions in the bearing structure. The developed method is capable of giving latest approaching into the physics of elasto hydrodynamic lubrication.
Validation of a numerical FSI simulation of an aortic BMHV by in vitro PIV experiments.
Annerel, S; Claessens, T; Degroote, J; Segers, P; Vierendeels, J
2014-08-01
In this paper, a validation of a recently developed fluid-structure interaction (FSI) coupling algorithm to simulate numerically the dynamics of an aortic bileaflet mechanical heart valve (BMHV) is performed. This validation is done by comparing the numerical simulation results with in vitro experiments. For the in vitro experiments, the leaflet kinematics and flow fields are obtained via the particle image velocimetry (PIV) technique. Subsequently, the same case is numerically simulated by the coupling algorithm and the resulting leaflet kinematics and flow fields are obtained. Finally, the results are compared, revealing great similarity in leaflet motion and flow fields between the numerical simulation and the experimental test. Therefore, it is concluded that the developed algorithm is able to capture very accurately all the major leaflet kinematics and dynamics and can be used to study and optimize the design of BMHVs. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.
ZrFsy1, a high-affinity fructose/H+ symporter from fructophilic yeast Zygosaccharomyces rouxii.
Directory of Open Access Journals (Sweden)
Maria José Leandro
Full Text Available Zygosaccharomyces rouxii is a fructophilic yeast than can grow at very high sugar concentrations. We have identified an ORF encoding a putative fructose/H(+ symporter in the Z. rouxii CBS 732 genome database. Heterologous expression of this ORF in a S. cerevisiae strain lacking its own hexose transporters (hxt-null and subsequent kinetic characterization of its sugar transport activity showed it is a high-affinity low-capacity fructose/H(+ symporter, with Km 0.45 ± 0.07 mM and Vmax 0.57 ± 0.02 mmol h(-1 (gdw(-1. We named it ZrFsy1. This protein also weakly transports xylitol and sorbose, but not glucose or other hexoses. The expression of ZrFSY1 in Z. rouxii is higher when the cells are cultivated at extremely low fructose concentrations (<0.2% and on non-fermentable carbon sources such as mannitol and xylitol, where the cells have a prolonged lag phase, longer duplication times and change their microscopic morphology. A clear phenotype was determined for the first time for the deletion of a fructose/H(+ symporter in the genome where it occurs naturally. The effect of the deletion of ZrFSY1 in Z. rouxii cells is only evident when the cells are cultivated at very low fructose concentrations, when the ZrFsy1 fructose symporter is the main active fructose transporter system.
Fluid-Induced Vibration Analysis for Reactor Internals Using Computational FSI Method
Energy Technology Data Exchange (ETDEWEB)
Moon, Jong Sung; Yi, Kun Woo; Sung, Ki Kwang; Im, In Young; Choi, Taek Sang [KEPCO E and C, Daejeon (Korea, Republic of)
2013-10-15
This paper introduces a fluid-induced vibration analysis method which calculates the response of the RVI to both deterministic and random loads at once and utilizes more realistic pressure distribution using the computational Fluid Structure Interaction (FSI) method. As addressed above, the FIV analysis for the RVI was carried out using the computational FSI method. This method calculates the response to deterministic and random turbulence loads at once. This method is also a simple and integrative method to get structural dynamic responses of reactor internals to various flow-induced loads. Because the analysis of this paper omitted the bypass flow region and Inner Barrel Assembly (IBA) due to the limitation of computer resources, it is necessary to find an effective way to consider all regions in the RV for the FIV analysis in the future. Reactor coolant flow makes Reactor Vessel Internals (RVI) vibrate and may affect the structural integrity of them. U. S. NRC Regulatory Guide 1.20 requires the Comprehensive Vibration Assessment Program (CVAP) to verify the structural integrity of the RVI for Fluid-Induced Vibration (FIV). The hydraulic forces on the RVI of OPR1000 and APR1400 were computed from the hydraulic formulas and the CVAP measurements in Palo Verde Unit 1 and Yonggwang Unit 4 for the structural vibration analyses. In this method, the hydraulic forces were divided into deterministic and random turbulence loads and were used for the excitation forces of the separate structural analyses. These forces are applied to the finite element model and the responses to them were combined into the resultant stresses.
MRI-based preplanning in low-dose-rate prostate brachytherapy
International Nuclear Information System (INIS)
Tanaka, Osamu; Hayashi, Shinya; Matsuo, Masayuki; Nakano, Masahiro; Kubota, Yasuaki; Maeda, Sunaho; Ohtakara, Kazuhiro; Deguchi, Takashi; Hoshi, Hiroaki
2008-01-01
Purpose: To compare the dosimetric results between MRI-based and TRUS-based preplanning in permanent prostate brachytherapy, and to estimate the accuracy of MRI-based preplanning by comparing with CT/MRI fusion-based postimplant dosimetry. Methods and materials: Twenty-one patients were entered in this prospective study with written informed consent. MRI-based and TRUS-based preplanning were performed. The seed and needle locations were identical according to MRI-based and TRUS-based preplanning. MRI-based and TRUS-based preplanning were compared using DVH-related parameters. Following brachytherapy, the accuracy of the MRI-based preplanning was evaluated by comparing it with CT/MRI fusion-based postimplant dosimetry. Results: Mean MRI-based prostate volume was slightly underestimated (0.73 cc in mean volume) in comparison to TRUS-based volume. There were no significant differences in the mean DVH-related parameters except with rectal V 100 (cc) between TRUS-based and MRI-based preplanning. Mean rectal V 100 (cc) was 0.74 cc in TRUS-based and 0.29 cc in MRI-based preplanning, respectively, and the values demonstrated a statistical difference. There was no statistical difference in mean rectal V 150 (cc), and rectal V 100 (cc) between MRI-based preplanning and CT/MRI fusion-based postimplant dosimetry. Conclusion: Prostate volume estimation and DVH-related parameters in MRI-based preplanning were almost identical to TRUS-based preplanning. From the results of CT/MRI fusion-based postimplant dosimetry, MRI-based preplanning was therefore found to be a reliable and useful modality, as well as being helpful for TRUS-based preplanning. MRI-based preplanning can more accurately predict postimplant rectal dose than TRUS-based preplanning
MRI-based diagnostic imaging of the intratemporal facial nerve
International Nuclear Information System (INIS)
Kress, B.; Baehren, W.
2001-01-01
Detailed imaging of the five sections of the full intratemporal course of the facial nerve can be achieved by MRI and using thin tomographic section techniques and surface coils. Contrast media are required for tomographic imaging of pathological processes. Established methods are available for diagnostic evaluation of cerebellopontine angle tumors and chronic Bell's palsy, as well as hemifacial spasms. A method still under discussion is MRI for diagnostic evaluation of Bell's palsy in the presence of fractures of the petrous bone, when blood volumes in the petrous bone make evaluation even more difficult. MRI-based diagnostic evaluation of the idiopatic facial paralysis currently is subject to change. Its usual application cannot be recommended for routine evaluation at present. However, a quantitative analysis of contrast medium uptake of the nerve may be an approach to improve the prognostic value of MRI in acute phases of Bell's palsy. (orig./CB) [de
Precise MRI-based stereotaxic surgery in large animal models
DEFF Research Database (Denmark)
Glud, Andreas Nørgaard; Bech, Johannes; Tvilling, Laura
BACKGROUND: Stereotaxic neurosurgery in large animals is used widely in different sophisticated models, where precision is becoming more crucial as desired anatomical target regions are becoming smaller. Individually calculated coordinates are necessary in large animal models with cortical...... and subcortical anatomical differences. NEW METHOD: We present a convenient method to make an MRI-visible skull fiducial for 3D MRI-based stereotaxic procedures in larger experimental animals. Plastic screws were filled with either copper-sulphate solution or MRI-visible paste from a commercially available...... cranial head marker. The screw fiducials were inserted in the animal skulls and T1 weighted MRI was performed allowing identification of the inserted skull marker. RESULTS: Both types of fiducial markers were clearly visible on the MRÍs. This allows high precision in the stereotaxic space. COMPARISON...
Energy Technology Data Exchange (ETDEWEB)
Hideyuki, Morika; Tomomichi, Nakamura [Mitsubishi Heavy Industries Ltd., Takasago R and D Center, Hyogo (Japan); Toshio, Ichikawa; Kazuo, Hirota; Hiroyuki, Murakiso [Mitsubishi Heavy Industries Ltd., Kobe Shipyard and Machinery Works, Hyogo, Kobe (Japan); Minoru, Murota [Japan Atomic Power Co., Tokyo (Japan)
2004-07-01
A Neutron Reflector (NR) is a new structure designed for improving the structure reliability of Advanced Pressurized Water Reactors (APWR,). The NR is placed in a narrow gap between the NR and a Core Barrel (CB). In the case of a structure surrounded by liquid in a narrow gap, the added fluid mass and the damping increases compared with in the air. This effect is famous for Fluid-Structure Interaction effect (FSI effect) in the narrow gap and it depends on the vibration displacement of the structure. A new method to estimate the added fluid damping for this case has been introduced by some of the authors in 2001, which is based on a narrow passage flow theory (Morita et al., 2001). Following this theory, a vibration test was performed to assess the appropriateness of the analysis method employed to measure the response of the NR during an earthquake (Nakamura et al., 2002). In this paper, results of a model test are shown comparing the data with the calculated ones based on the new analysis method that is combined the above method with the ANSYS computer code. As a result, a new seismic analysis method using the above theory was developed. The analytical results are in good agreement with the test results. (authors)
LES with acoustics and FSI for deforming plates in gas flow
Energy Technology Data Exchange (ETDEWEB)
Nilsson, Per, E-mail: pnilsson@tuv-nord.com [European Spallation Source, Lund (Sweden); Lillberg, Eric [Westinghouse, Vaesteras (Sweden); Wikstroem, Niklas [FS Dynamics, Stockholm (Sweden)
2012-12-15
This concerns Flow Induced Vibrations (FIV) in nuclear reactors and numerical analysis of such. Special attention is paid to structural excitation by sound generated remotely and turbulent flow around the structure. One hypothesis was that these phenomena can interact, so that the structure accumulates more energy from the flow if it also excited by sound from another source. In the studies, Fluid-Structure Interaction (FSI) is simulated with Large Eddy Simulations (LESs). It is shown possible to simulate excitation due to both acoustic and turbulence loads using the reported methods, at least qualitatively. The excitation levels are even of the right order of magnitude in some parts. However, there are some shortcomings in the modeling. The most important is perhaps the lack of non-reflecting boundary conditions. Another problem is the strong numerical damping in combination with demanding numerics for the selected solid solution methodology. Three cases are simulated, two for validation and one applied about steam dryers. For the applied case, it is concluded unlikely that excitation by the acoustic and turbulence loads can interact. The main reason is that the flow is controlled more by static geometrical factors, such as solid rotation sharp edges, than small deformations due to vibrations.
Modeling of digestive processes in the stomach as a Fluid-Structure Interaction (FSI) phenomenon
Acharya, Shashank; Kou, Wenjun; Kahrilas, Peter J.; Pandolfino, John E.; Patankar, Neelesh A.
2017-11-01
The process of digestion in the gastro-intestinal (GI) tract is a complex mechanical and chemical process. Digestion in the stomach involves substantial mixing and breakup of food into smaller particles by muscular activity. In this work, we have developed a fully resolved model of the stomach (along with the esophagus) and its various muscle groups that deform the wall to agitate the contents inside. We use the Immersed Boundary finite-element method to model this FSI problem. From the resulting simulations, the mixing intensity is analyzed as a function of muscle deformation. As muscle deformation is controlled by changing the intensity of the neural signal, the material properties of the stomach wall will have a significant effect on the resultant kinematics. Thus, the model is then used to identify the source of common GI tract motility pathologies by replicating irregular motions as a consequence of varying the mechanical properties of the wall and the related activation signal patterns. This approach gives us an in-silico framework that can be used to study the effect of tissue properties & muscle activity on the mechanical response of the stomach wall. This work is supported by NIH Grant 5R01DK079902-09.
De Wilde, David; Trachet, Bram; Debusschere, Nic; Iannaccone, Francesco; Swillens, Abigail; Degroote, Joris; Vierendeels, Jan; De Meyer, Guido R Y; Segers, Patrick
2016-07-26
The ApoE(-)(/)(-) mouse is a common small animal model to study atherosclerosis, an inflammatory disease of the large and medium sized arteries such as the carotid artery. It is generally accepted that the wall shear stress, induced by the blood flow, plays a key role in the onset of this disease. Wall shear stress, however, is difficult to derive from direct in vivo measurements, particularly in mice. In this study, we integrated in vivo imaging (micro-Computed Tomography-µCT and ultrasound) and fluid-structure interaction (FSI) modeling for the mouse-specific assessment of carotid hemodynamics and wall shear stress. Results were provided for 8 carotid bifurcations of 4 ApoE(-)(/)(-) mice. We demonstrated that accounting for the carotid elasticity leads to more realistic flow waveforms over the complete domain of the model due to volume buffering capacity in systole. The 8 simulated cases showed fairly consistent spatial distribution maps of time-averaged wall shear stress (TAWSS) and relative residence time (RRT). Zones with reduced TAWSS and elevated RRT, potential indicators of atherosclerosis-prone regions, were located mainly at the outer sinus of the external carotid artery. In contrast to human carotid hemodynamics, no flow recirculation could be observed in the carotid bifurcation region. Copyright © 2015 Elsevier Ltd. All rights reserved.
Molecular MRI based on hyper-polarized xenon
International Nuclear Information System (INIS)
Tassali, Nawal
2012-01-01
Magnetic Resonance Imaging (MRI) has a high importance in medicine as it enables the observation of the organs inside the body without the use of radiative or invasive techniques. However it is known to suffer from poor sensitivity. To circumvent this limitation, a key solution resides in the use of hyper-polarized species. Among the entities with which we can drastically increase nuclear polarization, xenon has very specific properties through its interactions with its close environment that lead to a wide chemical shift bandwidth. The goal is thus to use it as a tracer. This PhD thesis focuses on the concept of 129 Xe MRI-based sensors for the detection of biological events. In this approach, hyper-polarized xenon is vectorized to biological targets via functionalized host systems, and then localized thanks to fast dedicated MRI sequences. The conception and set-up of a spin-exchange optical pumping device is first described. Then studies about the interaction of the hyper-polarized noble gas with new cryptophanes susceptible to constitute powerful host molecules are detailed. Also the implementation of recent MRI sequences optimized for the transient character of the hyper-polarization and taking profit of the xenon in-out exchange is described. Applications of this approach for the detection of metallic ions and cellular receptors are studied. Finally, our first in vivo results on a small animal model are presented. (author) [fr
MRI-based N-staging in esophageal cancer
International Nuclear Information System (INIS)
Krupski, G.; Lorenzen, J.; Nicolas, V.; Adam, G.; Gawad, K.; Izbicki, J.R.
2002-01-01
Purpose: For planning the therapeutic strategies and estimating the prognosis in esophageal cancer, N-staging is very important. To date, MRI still is of minor importance as imaging modality of the mediastinum despite promising developments in the past, like ECG-gating or 'averaging' sequences, e.g. LOTA (Long-term averaging), which facilitate mediastinal and thoracic MR-imaging. In a prospective approach, the value of MRI based N-staging was examined with respect to LOTA-sequences. Material and Methods: Within from weeks prior to esophagectomy, standardized MRI of the esophagus was performed in 15 patients (10 squamous-cell-carcinomas and 5 adenocarcinomas) using a 1.5 T whole body scanner. Imaging quality was classified based on depiction of aortic wall or tracheal wall layers. Criteria for malignant infiltration were a diameter of more than 15 mm or a round appearance of a lymph node together with GD-DTPA enhancement. All data were blinded and separately read by two radiologists. The data of the study were compared with those from the pathological workup of the resected specimen. Results: MRI had a sensitivity of 100% and a specificity of 78% for lymph node metastases. Due to incomplete depiction of the celiac trunk (M1), nodal metastasis in a non-enlarged node was missed. Conclusion: With modern MRI, N-staging is almost as accurate as the gold standard endoscopic ultrasound and should particularly be used in patients not suited for an endoscopic ultrasound examination. (orig.) [de
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
Lam, Wai Sze Tiffany
Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3x3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for
A stable partitioned FSI algorithm for incompressible flow and deforming beams
Energy Technology Data Exchange (ETDEWEB)
Li, L., E-mail: lil19@rpi.edu [Department of Mathematical Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Henshaw, W.D., E-mail: henshw@rpi.edu [Department of Mathematical Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Banks, J.W., E-mail: banksj3@rpi.edu [Department of Mathematical Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Schwendeman, D.W., E-mail: schwed@rpi.edu [Department of Mathematical Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Main, A., E-mail: amain8511@gmail.com [Department of Civil and Environmental Engineering, Duke University, Durham, NC 27708 (United States)
2016-05-01
An added-mass partitioned (AMP) algorithm is described for solving fluid–structure interaction (FSI) problems coupling incompressible flows with thin elastic structures undergoing finite deformations. The new AMP scheme is fully second-order accurate and stable, without sub-time-step iterations, even for very light structures when added-mass effects are strong. The fluid, governed by the incompressible Navier–Stokes equations, is solved in velocity-pressure form using a fractional-step method; large deformations are treated with a mixed Eulerian-Lagrangian approach on deforming composite grids. The motion of the thin structure is governed by a generalized Euler–Bernoulli beam model, and these equations are solved in a Lagrangian frame using two approaches, one based on finite differences and the other on finite elements. The key AMP interface condition is a generalized Robin (mixed) condition on the fluid pressure. This condition, which is derived at a continuous level, has no adjustable parameters and is applied at the discrete level to couple the partitioned domain solvers. Special treatment of the AMP condition is required to couple the finite-element beam solver with the finite-difference-based fluid solver, and two coupling approaches are described. A normal-mode stability analysis is performed for a linearized model problem involving a beam separating two fluid domains, and it is shown that the AMP scheme is stable independent of the ratio of the mass of the fluid to that of the structure. A traditional partitioned (TP) scheme using a Dirichlet–Neumann coupling for the same model problem is shown to be unconditionally unstable if the added mass of the fluid is too large. A series of benchmark problems of increasing complexity are considered to illustrate the behavior of the AMP algorithm, and to compare the behavior with that of the TP scheme. The results of all these benchmark problems verify the stability and accuracy of the AMP scheme. Results for
A stable partitioned FSI algorithm for incompressible flow and deforming beams
International Nuclear Information System (INIS)
Li, L.; Henshaw, W.D.; Banks, J.W.; Schwendeman, D.W.; Main, A.
2016-01-01
An added-mass partitioned (AMP) algorithm is described for solving fluid–structure interaction (FSI) problems coupling incompressible flows with thin elastic structures undergoing finite deformations. The new AMP scheme is fully second-order accurate and stable, without sub-time-step iterations, even for very light structures when added-mass effects are strong. The fluid, governed by the incompressible Navier–Stokes equations, is solved in velocity-pressure form using a fractional-step method; large deformations are treated with a mixed Eulerian-Lagrangian approach on deforming composite grids. The motion of the thin structure is governed by a generalized Euler–Bernoulli beam model, and these equations are solved in a Lagrangian frame using two approaches, one based on finite differences and the other on finite elements. The key AMP interface condition is a generalized Robin (mixed) condition on the fluid pressure. This condition, which is derived at a continuous level, has no adjustable parameters and is applied at the discrete level to couple the partitioned domain solvers. Special treatment of the AMP condition is required to couple the finite-element beam solver with the finite-difference-based fluid solver, and two coupling approaches are described. A normal-mode stability analysis is performed for a linearized model problem involving a beam separating two fluid domains, and it is shown that the AMP scheme is stable independent of the ratio of the mass of the fluid to that of the structure. A traditional partitioned (TP) scheme using a Dirichlet–Neumann coupling for the same model problem is shown to be unconditionally unstable if the added mass of the fluid is too large. A series of benchmark problems of increasing complexity are considered to illustrate the behavior of the AMP algorithm, and to compare the behavior with that of the TP scheme. The results of all these benchmark problems verify the stability and accuracy of the AMP scheme. Results for
Hwu, Chyanbin
2010-01-01
As structural elements, anisotropic elastic plates find wide applications in modern technology. The plates here are considered to be subjected to not only in plane load but also transverse load. In other words, both plane and plate bending problems as well as the stretching-bending coupling problems are all explained in this book. In addition to the introduction of the theory of anisotropic elasticity, several important subjects have are discussed in this book such as interfaces, cracks, holes, inclusions, contact problems, piezoelectric materials, thermoelastic problems and boundary element a
Energy Technology Data Exchange (ETDEWEB)
Perez-Nadal, Guillem [Universidad de Buenos Aires, Buenos Aires (Argentina)
2017-07-15
We consider a non-relativistic free scalar field theory with a type of anisotropic scale invariance in which the number of coordinates ''scaling like time'' is generically greater than one. We propose the Cartesian product of two curved spaces, the metric of each space being parameterized by the other space, as a notion of curved background to which the theory can be extended. We study this type of geometries, and find a family of extensions of the theory to curved backgrounds in which the anisotropic scale invariance is promoted to a local, Weyl-type symmetry. (orig.)
Anisotropic contrast optical microscope.
Peev, D; Hofmann, T; Kananizadeh, N; Beeram, S; Rodriguez, E; Wimer, S; Rodenhausen, K B; Herzinger, C M; Kasputis, T; Pfaunmiller, E; Nguyen, A; Korlacki, R; Pannier, A; Li, Y; Schubert, E; Hage, D; Schubert, M
2016-11-01
An optical microscope is described that reveals contrast in the Mueller matrix images of a thin, transparent, or semi-transparent specimen located within an anisotropic object plane (anisotropic filter). The specimen changes the anisotropy of the filter and thereby produces contrast within the Mueller matrix images. Here we use an anisotropic filter composed of a semi-transparent, nanostructured thin film with sub-wavelength thickness placed within the object plane. The sample is illuminated as in common optical microscopy but the light is modulated in its polarization using combinations of linear polarizers and phase plate (compensator) to control and analyze the state of polarization. Direct generalized ellipsometry data analysis approaches permit extraction of fundamental Mueller matrix object plane images dispensing with the need of Fourier expansion methods. Generalized ellipsometry model approaches are used for quantitative image analyses. These images are obtained from sets of multiple images obtained under various polarizer, analyzer, and compensator settings. Up to 16 independent Mueller matrix images can be obtained, while our current setup is limited to 11 images normalized by the unpolarized intensity. We demonstrate the anisotropic contrast optical microscope by measuring lithographically defined micro-patterned anisotropic filters, and we quantify the adsorption of an organic self-assembled monolayer film onto the anisotropic filter. Comparison with an isotropic glass slide demonstrates the image enhancement obtained by our method over microscopy without the use of an anisotropic filter. In our current instrument, we estimate the limit of detection for organic volumetric mass within the object plane of ≈49 fg within ≈7 × 7 μm 2 object surface area. Compared to a quartz crystal microbalance with dissipation instrumentation, where contemporary limits require a total load of ≈500 pg for detection, the instrumentation demonstrated here improves
Directory of Open Access Journals (Sweden)
Daogang Lu
2015-01-01
Full Text Available Huge water storage tank on the top of many buildings may affect the safety of the structure caused by fluid-structure interaction (FSI under the earthquake. AP1000 passive containment cooling system water storage tank (PCCWST placed at the top of shield building is a key component to ensure the safety of nuclear facilities. Under seismic loading, water will impact the wall of PCCWST, which may pose a threat to the integrity of the shield building. In the present study, an FE model of AP1000 shield building is built for the modal and transient seismic analysis considering the FSI. Six different water levels in PCCWST were discussed by comparing the modal frequency, seismic acceleration response, and von Mises stress distribution. The results show the maximum von Mises stress emerges at the joint of shield building roof and water around the air inlet. However, the maximum von Mises stress is below the yield strength of reinforced concrete. The results may provide a reference for design of the AP1000 and CAP1400 in the future.
Anisotropic constant-roll inflation
Energy Technology Data Exchange (ETDEWEB)
Ito, Asuka; Soda, Jiro [Kobe University, Department of Physics, Kobe (Japan)
2018-01-15
We study constant-roll inflation in the presence of a gauge field coupled to an inflaton. By imposing the constant anisotropy condition, we find new exact anisotropic constant-roll inflationary solutions which include anisotropic power-law inflation as a special case. We also numerically show that the new anisotropic solutions are attractors in the phase space. (orig.)
Anisotropic Concrete Compressive Strength
DEFF Research Database (Denmark)
Gustenhoff Hansen, Søren; Jørgensen, Henrik Brøner; Hoang, Linh Cao
2017-01-01
When the load carrying capacity of existing concrete structures is (re-)assessed it is often based on compressive strength of cores drilled out from the structure. Existing studies show that the core compressive strength is anisotropic; i.e. it depends on whether the cores are drilled parallel...
International Nuclear Information System (INIS)
Saleh, H Al; Erickson, B; Paulson, E
2015-01-01
Purpose: MRI-based adaptive brachytherapy (ABT) is an emerging treatment modality for patients with gynecological tumors. However, MR image intensity non-uniformities (IINU) can vary from fraction to fraction, complicating image interpretation and auto-contouring accuracy. We demonstrate here an automated MR image standardization and auto-contouring strategy for MRI-based ABT of cervix cancer. Methods: MR image standardization consisted of: 1) IINU correction using the MNI N3 algorithm, 2) noise filtering using anisotropic diffusion, and 3) signal intensity normalization using the volumetric median. This post-processing chain was implemented as a series of custom Matlab and Java extensions in MIM (v6.4.5, MIM Software) and was applied to 3D T2 SPACE images of six patients undergoing MRI-based ABT at 3T. Coefficients of variation (CV=σ/µ) were calculated for both original and standardized images and compared using Mann-Whitney tests. Patient-specific cumulative MR atlases of bladder, rectum, and sigmoid contours were constructed throughout ABT, using original and standardized MR images from all previous ABT fractions. Auto-contouring was performed in MIM two ways: 1) best-match of one atlas image to the daily MR image, 2) multi-match of all previous fraction atlas images to the daily MR image. Dice’s Similarity Coefficients (DSCs) were calculated for auto-generated contours relative to reference contours for both original and standardized MR images and compared using Mann-Whitney tests. Results: Significant improvements in CV were detected following MR image standardization (p=0.0043), demonstrating an improvement in MR image uniformity. DSCs consistently increased for auto-contoured bladder, rectum, and sigmoid following MR image standardization, with the highest DSCs detected when the combination of MR image standardization and multi-match cumulative atlas-based auto-contouring was utilized. Conclusion: MR image standardization significantly improves MR image
Energy Technology Data Exchange (ETDEWEB)
Saleh, H Al; Erickson, B; Paulson, E [Medical College of Wisconsin, Milwaukee, WI (United States)
2015-06-15
Purpose: MRI-based adaptive brachytherapy (ABT) is an emerging treatment modality for patients with gynecological tumors. However, MR image intensity non-uniformities (IINU) can vary from fraction to fraction, complicating image interpretation and auto-contouring accuracy. We demonstrate here an automated MR image standardization and auto-contouring strategy for MRI-based ABT of cervix cancer. Methods: MR image standardization consisted of: 1) IINU correction using the MNI N3 algorithm, 2) noise filtering using anisotropic diffusion, and 3) signal intensity normalization using the volumetric median. This post-processing chain was implemented as a series of custom Matlab and Java extensions in MIM (v6.4.5, MIM Software) and was applied to 3D T2 SPACE images of six patients undergoing MRI-based ABT at 3T. Coefficients of variation (CV=σ/µ) were calculated for both original and standardized images and compared using Mann-Whitney tests. Patient-specific cumulative MR atlases of bladder, rectum, and sigmoid contours were constructed throughout ABT, using original and standardized MR images from all previous ABT fractions. Auto-contouring was performed in MIM two ways: 1) best-match of one atlas image to the daily MR image, 2) multi-match of all previous fraction atlas images to the daily MR image. Dice’s Similarity Coefficients (DSCs) were calculated for auto-generated contours relative to reference contours for both original and standardized MR images and compared using Mann-Whitney tests. Results: Significant improvements in CV were detected following MR image standardization (p=0.0043), demonstrating an improvement in MR image uniformity. DSCs consistently increased for auto-contoured bladder, rectum, and sigmoid following MR image standardization, with the highest DSCs detected when the combination of MR image standardization and multi-match cumulative atlas-based auto-contouring was utilized. Conclusion: MR image standardization significantly improves MR image
Directory of Open Access Journals (Sweden)
Manfred Kerner
2018-02-01
Full Text Available Promising electrochemical and dynamical properties, as well as high thermal stability, have been the driving forces behind application of ionic liquids (ILs and polymerized ionic liquids (PILs as electrolytes for high-temperature lithium-ion batteries (HT-LIBs. Here, several ternary lithium-salt/IL/PIL electrolytes (PILel have been investigated for synergies of having both FSI and TFSI anions present, primarily in terms of physico-chemical properties, for unique application in HT-LIBs operating at 80 °C. All of the electrolytes tested have low Tg and are thermally stable ≥100 °C, and with TFSI as the exclusive anion the electrolytes (set A have higher thermal stabilities ≥125 °C. Ionic conductivities are in the range of 1 mS/cm at 100 °C and slightly higher for set A PILel, which, however, have lower oxidation stabilities than set B PILel with both FSI and TFSI anions present: 3.4–3.7 V vs. 4.2 V. The evolution of the interfacial resistance increases for all PILel during the first 40 h, but are much lower for set B PILel and generally decrease with increasing Li-salt content. The higher interfacial resistances only influence the cycling performance at high C-rates (1 C, where set B PILel with high Li-salt content performs better, while the discharge capacities at the 0.1 C rate are comparable. Long-term cycling at 0.5 C, however, shows stable discharge capacities for 100 cycles, with the exception of the set B PILel with high Li-salt content. Altogether, the presence of both FSI and TFSI anions in the PILel results in lower ionic conductivities and decreased thermal stabilities, but also higher oxidation stabilities and reduced interfacial resistances and, in total, result in an improved rate capability, but compromised long-term capacity retention. Overall, these electrolytes open for novel designs of HT-LIBs.
Xie, Qiong-Tao; Cui, Shuai; Cao, Jun-Peng; Amico, Luigi; Fan, Heng
2014-01-01
We define the anisotropic Rabi model as the generalization of the spin-boson Rabi model: The Hamiltonian system breaks the parity symmetry; the rotating and counterrotating interactions are governed by two different coupling constants; a further parameter introduces a phase factor in the counterrotating terms. The exact energy spectrum and eigenstates of the generalized model are worked out. The solution is obtained as an elaboration of a recently proposed method for the isotropic limit of th...
fs-i "2004" : linnamängud värvidega ja ilma / Maija Burima ; inglise keelest tlk. Silver Rattasepp
Burima, Maija
2007-01-01
Artiklis analüüsitakse fs-i luulekogu "2004" venekeelse tõlke põhjal. Artikli aluseks on ingliskeelne ettekanne Underi ja Tuglase Kirjanduskeskuse seminaril "Turn of the Century, Turns in Literature II : Estonian and Latvian Literature in the European Context at the Turn of the 20th/21st Centuries" Viinistus 22.-23. mail 2007
International Nuclear Information System (INIS)
Eshetu, Gebrekidan Gebresilassie; Grugeon, Sylvie; Gachot, Grégory; Mathiron, David; Armand, Michel; Laruelle, Stephane
2013-01-01
Lithium bis(fluorosulfonyl) imide (LiFSI) is regarded as an alternative to the classical LiPF 6 salt in today's LiFePO 4 /graphite-based Li-ion batteries electrolyte owing to its slightly higher conductivity and lower fluorine content. In an attempt to better evaluate the safety issues, here we report the comparative study of the LiFSI and LiPF 6 based electrolyte/lithiated graphite interface thermal behavior. DSC measurements with LiFSI-based electrolyte reveal a sharp exotherm with large heat release though at higher onset and peak temperatures compared to LiPF 6 -based electrolyte. With the help of GC/MS, 19 F NMR and ESI-HRMS analyses, we assume that this highly energetic peak around 200 °C, which is dependant upon the lithium content, is mainly related to electrochemical reduction of FSI − anion. In a strategy to limit the probability and damage of thermal runaway event, electrolyte additives such as vinylene carbonate (VC), fluoro ethylene carbonate (FEC), di-isocyanato hexane (DIH) and toluene di-isocyanate (TDI) have been investigated and shown to significantly lower the energy associated with the exothermic phenomenon
Anisotropic elliptic optical fibers
Kang, Soon Ahm
1991-05-01
The exact characteristic equation for an anisotropic elliptic optical fiber is obtained for odd and even hybrid modes in terms of infinite determinants utilizing Mathieu and modified Mathieu functions. A simplified characteristic equation is obtained by applying the weakly guiding approximation such that the difference in the refractive indices of the core and the cladding is small. The simplified characteristic equation is used to compute the normalized guide wavelength for an elliptical fiber. When the anisotropic parameter is equal to unity, the results are compared with the previous research and they are in close agreement. For a fixed value normalized cross-section area or major axis, the normalized guide wavelength lambda/lambda(sub 0) for an anisotropic elliptic fiber is small for the larger value of anisotropy. This condition indicates that more energy is carried inside of the fiber. However, the geometry and anisotropy of the fiber have a smaller effect when the normalized cross-section area is very small or very large.
Inhomogeneous anisotropic cosmology
International Nuclear Information System (INIS)
Kleban, Matthew; Senatore, Leonardo
2016-01-01
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with “flat” (including toroidal) and “open” (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are “flat” or “open”. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with “flat” or “open” topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
Transient anisotropic magnetic field calculation
International Nuclear Information System (INIS)
Jesenik, Marko; Gorican, Viktor; Trlep, Mladen; Hamler, Anton; Stumberger, Bojan
2006-01-01
For anisotropic magnetic material, nonlinear magnetic characteristics of the material are described with magnetization curves for different magnetization directions. The paper presents transient finite element calculation of the magnetic field in the anisotropic magnetic material based on the measured magnetization curves for different magnetization directions. For the verification of the calculation method some results of the calculation are compared with the measurement
Simple types of anisotropic inflation
International Nuclear Information System (INIS)
Barrow, John D.; Hervik, Sigbjoern
2010-01-01
We display some simple cosmological solutions of gravity theories with quadratic Ricci curvature terms added to the Einstein-Hilbert Lagrangian which exhibit anisotropic inflation. The Hubble expansion rates are constant and unequal in three orthogonal directions. We describe the evolution of the simplest of these homogeneous and anisotropic cosmological models from its natural initial state and evaluate the deviations they will create from statistical isotropy in the fluctuations produced during a period of anisotropic inflation. The anisotropic inflation is not a late-time attractor in these models but the rate of approach to a final isotropic de Sitter state is slow and is conducive to the creation of observable anisotropic statistical effects in the microwave background. The statistical anisotropy would not be scale invariant and the level of statistical anisotropy will grow with scale.
Energy Technology Data Exchange (ETDEWEB)
Korhonen, Juha, E-mail: juha.p.korhonen@hus.fi [Clinical Research Institute Helsinki University Central Hospital Ltd., POB-700, 00029 HUS, Finland and Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS (Finland); Kapanen, Mika [Clinical Research Institute Helsinki University Central Hospital Ltd., POB-700, 00029 HUS (Finland); Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS (Finland); Department of Medical Physics, Tampere University Hospital, POB-2000, 33521 Tampere (Finland); Keyriläinen, Jani; Seppälä, Tiina; Tenhunen, Mikko [Department of Oncology, Helsinki University Central Hospital, POB-180, 00029 HUS (Finland)
2014-01-15
Purpose: The lack of electron density information in magnetic resonance images (MRI) poses a major challenge for MRI-based radiotherapy treatment planning (RTP). In this study the authors convert MRI intensity values into Hounsfield units (HUs) in the male pelvis and thus enable accurate MRI-based RTP for prostate cancer patients with varying tissue anatomy and body fat contents. Methods: T{sub 1}/T{sub 2}*-weighted MRI intensity values and standard computed tomography (CT) image HUs in the male pelvis were analyzed using image data of 10 prostate cancer patients. The collected data were utilized to generate a dual model HU conversion technique from MRI intensity values of the single image set separately within and outside of contoured pelvic bones. Within the bone segment local MRI intensity values were converted to HUs by applying a second-order polynomial model. This model was tuned for each patient by two patient-specific adjustments: MR signal normalization to correct shifts in absolute intensity level and application of a cutoff value to accurately represent low density bony tissue HUs. For soft tissues, such as fat and muscle, located outside of the bone contours, a threshold-based segmentation method without requirements for any patient-specific adjustments was introduced to convert MRI intensity values into HUs. The dual model HU conversion technique was implemented by constructing pseudo-CT images for 10 other prostate cancer patients. The feasibility of these images for RTP was evaluated by comparing HUs in the generated pseudo-CT images with those in standard CT images, and by determining deviations in MRI-based dose distributions compared to those in CT images with 7-field intensity modulated radiation therapy (IMRT) with the anisotropic analytical algorithm and 360° volumetric-modulated arc therapy (VMAT) with the Voxel Monte Carlo algorithm. Results: The average HU differences between the constructed pseudo-CT images and standard CT images of each
Xie, Qiong-Tao; Cui, Shuai; Cao, Jun-Peng; Amico, Luigi; Fan, Heng
2014-04-01
We define the anisotropic Rabi model as the generalization of the spin-boson Rabi model: The Hamiltonian system breaks the parity symmetry; the rotating and counterrotating interactions are governed by two different coupling constants; a further parameter introduces a phase factor in the counterrotating terms. The exact energy spectrum and eigenstates of the generalized model are worked out. The solution is obtained as an elaboration of a recently proposed method for the isotropic limit of the model. In this way, we provide a long-sought solution of a cascade of models with immediate relevance in different physical fields, including (i) quantum optics, a two-level atom in single-mode cross-electric and magnetic fields; (ii) solid-state physics, electrons in semiconductors with Rashba and Dresselhaus spin-orbit coupling; and (iii) mesoscopic physics, Josephson-junction flux-qubit quantum circuits.
Directory of Open Access Journals (Sweden)
Qiong-Tao Xie
2014-06-01
Full Text Available We define the anisotropic Rabi model as the generalization of the spin-boson Rabi model: The Hamiltonian system breaks the parity symmetry; the rotating and counterrotating interactions are governed by two different coupling constants; a further parameter introduces a phase factor in the counterrotating terms. The exact energy spectrum and eigenstates of the generalized model are worked out. The solution is obtained as an elaboration of a recently proposed method for the isotropic limit of the model. In this way, we provide a long-sought solution of a cascade of models with immediate relevance in different physical fields, including (i quantum optics, a two-level atom in single-mode cross-electric and magnetic fields; (ii solid-state physics, electrons in semiconductors with Rashba and Dresselhaus spin-orbit coupling; and (iii mesoscopic physics, Josephson-junction flux-qubit quantum circuits.
Gohari, S. M. Iman; Sarkar, Sutanu; Korobenko, Artem; Bazilevs, Yuri
2017-11-01
Numerical simulations of wind turbines operating under different regimes of stability are performed using LES. A reduced model, based on the generalized actuator disk model (ADM), is implemented to represent the wind turbines within the ABL. Data from the fluid-solid interaction (FSI) simulations of wind turbines have been used to calibrate and validate the reduced model. The computational cost of this method to include wind turbines is affordable and incurs an overhead as low as 1.45%. Using this reduced model, we study the coupling of unsteady turbulent flow with the wind turbine under different ABL conditions: (i) A neutral ABL with zero heat-flux and inversion layer at 350m, in which the incoming wind has the maximum mean shear between the heights of upper-tip and lower-tip; (2) A shallow ABL with surface cooling rate of -1 K/hr wherein the low level jet occurs at the wind turbine hub height. We will discuss how the differences in the unsteady flow between the two ABL regimes impact the wind turbine performance.
Directory of Open Access Journals (Sweden)
Matthew M. Harkenrider
2017-03-01
Full Text Available Purpose : Adaptive magnetic resonance imaging (MRI-based brachytherapy results in improved local control and decreased high-grade toxicities compared to historical controls. Incorporating MRI into the workflow of a department can be a major challenge when initiating an MRI-based brachytherapy program. This project aims to describe the goals, challenges, and solutions when initiating an MRI-based cervical cancer brachytherapy program at our institution. Material and methods : We describe the 6-month multi-disciplinary planning phase to initiate an MRI-based brachytherapy program. We describe the specific challenges that were encountered prior to treating our first patient. Results : We describe the solutions that were realized and executed to solve the challenges that we faced to establish our MRI-based brachytherapy program. We emphasize detailed coordination of care, planning, and communication to make the workflow feasible. We detail the imaging and radiation physics solutions to safely deliver MRI-based brachytherapy. The focus of these efforts is always on the delivery of optimal, state of the art patient care and treatment delivery within the context of our available institutional resources. Conclusions : Previous publications have supported a transition to MRI-based brachytherapy, and this can be safely and efficiently accomplished as described in this manuscript.
MRI-based decision tree model for diagnosis of biliary atresia.
Kim, Yong Hee; Kim, Myung-Joon; Shin, Hyun Joo; Yoon, Haesung; Han, Seok Joo; Koh, Hong; Roh, Yun Ho; Lee, Mi-Jung
2018-02-23
To evaluate MRI findings and to generate a decision tree model for diagnosis of biliary atresia (BA) in infants with jaundice. We retrospectively reviewed features of MRI and ultrasonography (US) performed in infants with jaundice between January 2009 and June 2016 under approval of the institutional review board, including the maximum diameter of periportal signal change on MRI (MR triangular cord thickness, MR-TCT) or US (US-TCT), visibility of common bile duct (CBD) and abnormality of gallbladder (GB). Hepatic subcapsular flow was reviewed on Doppler US. We performed conditional inference tree analysis using MRI findings to generate a decision tree model. A total of 208 infants were included, 112 in the BA group and 96 in the non-BA group. Mean age at the time of MRI was 58.7 ± 36.6 days. Visibility of CBD, abnormality of GB and MR-TCT were good discriminators for the diagnosis of BA and the MRI-based decision tree using these findings with MR-TCT cut-off 5.1 mm showed 97.3 % sensitivity, 94.8 % specificity and 96.2 % accuracy. MRI-based decision tree model reliably differentiates BA in infants with jaundice. MRI can be an objective imaging modality for the diagnosis of BA. • MRI-based decision tree model reliably differentiates biliary atresia in neonatal cholestasis. • Common bile duct, gallbladder and periportal signal changes are the discriminators. • MRI has comparable performance to ultrasonography for diagnosis of biliary atresia.
Disadvantage factor for anisotropic scattering
International Nuclear Information System (INIS)
Saad, E.A.; Abdel Krim, M.S.; EL-Dimerdash, A.A.
1990-01-01
The invariant embedding method is used to solve the problem for a two region reactor with anisotropic scattering and to compute the disadvantage factor necessary for calculating some reactor parameters
Cracking on anisotropic neutron stars
Setiawan, A. M.; Sulaksono, A.
2017-07-01
We study the effect of cracking of a local anisotropic neutron star (NS) due to small density fluctuations. It is assumed that the neutron star core consists of leptons, nucleons and hyperons. The relativistic mean field model is used to describe the core of equation of state (EOS). For the crust, we use the EOS introduced by Miyatsu et al. [1]. Furthermore, two models are used to describe pressure anisotropic in neutron star matter. One is proposed by Doneva-Yazadjiev (DY) [2] and the other is proposed by Herrera-Barreto (HB) [3]. The anisotropic parameter of DY and HB models are adjusted in order the predicted maximum mass compatible to the mass of PSR J1614-2230 [4] and PSR J0348+0432 [5]. We have found that cracking can potentially present in the region close to the neutron star surface. The instability due cracking is quite sensitive to the NS mass and anisotropic parameter used.
Magnetostatics of anisotropic superconducting ellipsoid
International Nuclear Information System (INIS)
Saif, A.G.
1987-09-01
The magnetization and the magnetic field distribution inside (outside) an anisotropic type II superconducting ellipsoid, with filamentary structure, is formulated. We have shown that the magnetic field in this case is different from that of the general anisotropic one. The nucleations of the flux lines for specimens with large demagnetization factors are theoretically studied. We have shown that the nucleations of the flux lines, for specimens with large demagnetization factor, appears at a field larger than that of ellipsoidal shape. (author). 15 refs
Anisotropic nonequilibrium hydrodynamic attractor
Strickland, Michael; Noronha, Jorge; Denicol, Gabriel S.
2018-02-01
We determine the dynamical attractors associated with anisotropic hydrodynamics (aHydro) and the DNMR equations for a 0 +1 d conformal system using kinetic theory in the relaxation time approximation. We compare our results to the nonequilibrium attractor obtained from the exact solution of the 0 +1 d conformal Boltzmann equation, the Navier-Stokes theory, and the second-order Mueller-Israel-Stewart theory. We demonstrate that the aHydro attractor equation resums an infinite number of terms in the inverse Reynolds number. The resulting resummed aHydro attractor possesses a positive longitudinal-to-transverse pressure ratio and is virtually indistinguishable from the exact attractor. This suggests that an optimized hydrodynamic treatment of kinetic theory involves a resummation not only in gradients (Knudsen number) but also in the inverse Reynolds number. We also demonstrate that the DNMR result provides a better approximation of the exact kinetic theory attractor than the Mueller-Israel-Stewart theory. Finally, we introduce a new method for obtaining approximate aHydro equations which relies solely on an expansion in the inverse Reynolds number. We then carry this expansion out to the third order, and compare these third-order results to the exact kinetic theory solution.
International Nuclear Information System (INIS)
Tanaka, Osamu; Hayashi, Shinya; Matsuo, Masayuki; Sakurai, Kota; Nakano, Masahiro; Maeda, Sunaho; Kajita, Kimihiro R.T.; Deguchi, Takashi; Hoshi, Hiroaki
2006-01-01
Purpose: The aim of this study was to compare the outcomes between magnetic resonance imaging (MRI)-based and computed tomography (CT)/MRI fusion-based postimplant dosimetry methods in permanent prostate brachytherapy. Methods and Materials: Between October 2004 and March 2006, a total of 52 consecutive patients with prostate cancer were treated by brachytherapy, and postimplant dosimetry was performed using CT/MRI fusion. The accuracy and reproducibility were prospectively compared between MRI-based dosimetry and CT/MRI fusion-based dosimetry based on the dose-volume histogram (DVH) related parameters as recommended by the American Brachytherapy Society. Results: The prostate volume was 15.97 ± 6.17 cc (mean ± SD) in MRI-based dosimetry, and 15.97 ± 6.02 cc in CT/MRI fusion-based dosimetry without statistical difference. The prostate V100 was 94.5% and 93.0% in MRI-based and CT/MRI fusion-based dosimetry, respectively, and the difference was statistically significant (p = 0.002). The prostate D90 was 119.4% and 114.4% in MRI-based and CT/MRI fusion-based dosimetry, respectively, and the difference was statistically significant (p = 0.004). Conclusion: Our current results suggested that, as with fusion images, MR images allowed accurate contouring of the organs, but they tended to overestimate the analysis of postimplant dosimetry in comparison to CT/MRI fusion images. Although this MRI-based dosimetric discrepancy was negligible, MRI-based dosimetry was acceptable and reproducible in comparison to CT-based dosimetry, because the difference between MRI-based and CT/MRI fusion-based results was smaller than that between CT-based and CT/MRI fusion-based results as previously reported
Dynamics of anisotropic tissue growth
Energy Technology Data Exchange (ETDEWEB)
Bittig, Thomas; Juelicher, Frank [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany); Wartlick, Ortrud; Kicheva, Anna; Gonzalez-Gaitan, Marcos [Department of Biochemistry and Department of Molecular Biology, Geneva University, Sciences II, Quai Ernest-Ansermet 30, 1211 Geneva 4 (Switzerland)], E-mail: Marcos.Gonzalez@biochem.unige.ch, E-mail: julicher@pks.mpg.de
2008-06-15
We study the mechanics of tissue growth via cell division and cell death (apoptosis). The rearrangements of cells can on large scales and times be captured by a continuum theory which describes the tissue as an effective viscous material with active stresses generated by cell division. We study the effects of anisotropies of cell division on cell rearrangements and show that average cellular trajectories exhibit anisotropic scaling behaviors. If cell division and apoptosis balance, there is no net growth, but for anisotropic cell division the tissue undergoes spontaneous shear deformations. Our description is relevant for the study of developing tissues such as the imaginal disks of the fruit fly Drosophila melanogaster, which grow anisotropically.
Continuum mechanics of anisotropic materials
Cowin, Stephen C
2013-01-01
Continuum Mechanics of Anisotropic Materials(CMAM) presents an entirely new and unique development of material anisotropy in the context of an appropriate selection and organization of continuum mechanics topics. These features will distinguish this continuum mechanics book from other books on this subject. Textbooks on continuum mechanics are widely employed in engineering education, however, none of them deal specifically with anisotropy in materials. For the audience of Biomedical, Chemical and Civil Engineering students, these materials will be dealt with more frequently and greater accuracy in their analysis will be desired. Continuum Mechanics of Anisotropic Materials' author has been a leader in the field of developing new approaches for the understanding of anisotropic materials.
Anisotropic hydrodynamics: Motivation and methodology
Energy Technology Data Exchange (ETDEWEB)
Strickland, Michael
2014-06-15
In this proceedings contribution I review recent progress in our understanding of the bulk dynamics of relativistic systems that possess potentially large local rest frame momentum-space anisotropies. In order to deal with these momentum-space anisotropies, a reorganization of relativistic viscous hydrodynamics can be made around an anisotropic background, and the resulting dynamical framework has been dubbed “anisotropic hydrodynamics”. I also discuss expectations for the degree of momentum-space anisotropy of the quark–gluon plasma generated in relativistic heavy ion collisions at RHIC and LHC from second-order viscous hydrodynamics, strong-coupling approaches, and weak-coupling approaches.
Anisotropic solutions by gravitational decoupling
Ovalle, J.; Casadio, R.; da Rocha, R.; Sotomayor, A.
2018-02-01
We investigate the extension of isotropic interior solutions for static self-gravitating systems to include the effects of anisotropic spherically symmetric gravitational sources by means of the gravitational decoupling realised via the minimal geometric deformation approach. In particular, the matching conditions at the surface of the star with the outer Schwarzschild space-time are studied in great detail, and we describe how to generate, from a single physically acceptable isotropic solution, new families of anisotropic solutions whose physical acceptability is also inherited from their isotropic parent.
Anisotropic solutions by gravitational decoupling
Energy Technology Data Exchange (ETDEWEB)
Ovalle, J. [Silesian University in Opava, Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Opava (Czech Republic); Universidad Simon Bolivar, Departamento de Fisica, Caracas (Venezuela, Bolivarian Republic of); Casadio, R. [Alma Mater Universita di Bologna, Dipartimento di Fisica e Astronomia, Bologna (Italy); Istituto Nazionale di Fisica Nucleare, Bologna (Italy); Rocha, R. da [Universidade Federal do ABC (UFABC), Centro de Matematica, Computacao e Cognicao, Santo Andre, SP (Brazil); Sotomayor, A. [Universidad de Antofagasta, Departamento de Matematicas, Antofagasta (Chile)
2018-02-15
We investigate the extension of isotropic interior solutions for static self-gravitating systems to include the effects of anisotropic spherically symmetric gravitational sources by means of the gravitational decoupling realised via the minimal geometric deformation approach. In particular, the matching conditions at the surface of the star with the outer Schwarzschild space-time are studied in great detail, and we describe how to generate, from a single physically acceptable isotropic solution, new families of anisotropic solutions whose physical acceptability is also inherited from their isotropic parent. (orig.)
Clinically viable magnetic poly(lactide-co-glycolide) (PLGA) particles for MRI-based cell tracking
Granot, Dorit; Nkansah, Michael K.; Bennewitz, Margaret F.; Tang, Kevin S.; Markakis, Eleni A.; Shapiro, Erik M.
2013-01-01
Purpose To design, fabricate, characterize and in vivo assay clinically viable magnetic particles for MRI-based cell tracking. Methods PLGA encapsulated magnetic nano- and microparticles were fabricated. Multiple biologically relevant experiments were performed to assess cell viability, cellular performance and stem cell differentiation. In vivo MRI experiments were performed to separately test cell transplantation and cell migration paradigms, as well as in vivo biodegradation. Results Highly magnetic nano- (~100 nm) and microparticles (~1–2 μm) were fabricated. Magnetic cell labeling in culture occurred rapidly achieving 3–50 pg Fe/cell at 3 hrs for different particles types, and >100 pg Fe/cell after 10 hours, without the requirement of a transfection agent, and with no effect on cell viability. The capability of magnetically labeled mesenchymal or neural stem cells to differentiate down multiple lineages, or for magnetically labeled immune cells to release cytokines following stimulation, was uncompromised. An in vivo biodegradation study revealed that NPs degraded ~80% over the course of 12 weeks. MRI detected as few as 10 magnetically labeled cells, transplanted into the brains of rats. Also, these particles enabled the in vivo monitoring of endogenous neural progenitor cell migration in rat brains over 2 weeks. Conclusion The robust MRI properties and benign safety profile of these particles make them promising candidates for clinical translation for MRI-based cell tracking. PMID:23568825
Multi-atlas and label fusion approach for patient-specific MRI based skull estimation.
Torrado-Carvajal, Angel; Herraiz, Joaquin L; Hernandez-Tamames, Juan A; San Jose-Estepar, Raul; Eryaman, Yigitcan; Rozenholc, Yves; Adalsteinsson, Elfar; Wald, Lawrence L; Malpica, Norberto
2016-04-01
MRI-based skull segmentation is a useful procedure for many imaging applications. This study describes a methodology for automatic segmentation of the complete skull from a single T1-weighted volume. The skull is estimated using a multi-atlas segmentation approach. Using a whole head computed tomography (CT) scan database, the skull in a new MRI volume is detected by nonrigid image registration of the volume to every CT, and combination of the individual segmentations by label-fusion. We have compared Majority Voting, Simultaneous Truth and Performance Level Estimation (STAPLE), Shape Based Averaging (SBA), and the Selective and Iterative Method for Performance Level Estimation (SIMPLE) algorithms. The pipeline has been evaluated quantitatively using images from the Retrospective Image Registration Evaluation database (reaching an overlap of 72.46 ± 6.99%), a clinical CT-MR dataset (maximum overlap of 78.31 ± 6.97%), and a whole head CT-MRI pair (maximum overlap 78.68%). A qualitative evaluation has also been performed on MRI acquisition of volunteers. It is possible to automatically segment the complete skull from MRI data using a multi-atlas and label fusion approach. This will allow the creation of complete MRI-based tissue models that can be used in electromagnetic dosimetry applications and attenuation correction in PET/MR. © 2015 Wiley Periodicals, Inc.
Failure in imperfect anisotropic materials
DEFF Research Database (Denmark)
Legarth, Brian Nyvang
2005-01-01
The fundamental cause of crack growth, namely nucleation and growth of voids, is investigated numerically for a two phase imperfect anisotropic material. A unit cell approach is adopted from which the overall stress strain is evaluated. Failure is observed as a sudden stress drop and depending...
Magnetic relaxation in anisotropic magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1971-01-01
The line shape and the kinematic and thermodynamic slowing down of the critical and paramagnetic relaxation in axially anisotropic materials are discussed. Kinematic slowing down occurs only in the longitudinal relaxation function. The thermodynamic slowing down occurs in either the transverse...... or longitudinal relaxation function depending on the sign of the axial anisotropy....
Comparison of MRI-based estimates of articular cartilage contact area in the tibiofemoral joint.
Henderson, Christopher E; Higginson, Jill S; Barrance, Peter J
2011-01-01
Knee osteoarthritis (OA) detrimentally impacts the lives of millions of older Americans through pain and decreased functional ability. Unfortunately, the pathomechanics and associated deviations from joint homeostasis that OA patients experience are not well understood. Alterations in mechanical stress in the knee joint may play an essential role in OA; however, existing literature in this area is limited. The purpose of this study was to evaluate the ability of an existing magnetic resonance imaging (MRI)-based modeling method to estimate articular cartilage contact area in vivo. Imaging data of both knees were collected on a single subject with no history of knee pathology at three knee flexion angles. Intra-observer reliability and sensitivity studies were also performed to determine the role of operator-influenced elements of the data processing on the results. The method's articular cartilage contact area estimates were compared with existing contact area estimates in the literature. The method demonstrated an intra-observer reliability of 0.95 when assessed using Pearson's correlation coefficient and was found to be most sensitive to changes in the cartilage tracings on the peripheries of the compartment. The articular cartilage contact area estimates at full extension were similar to those reported in the literature. The relationships between tibiofemoral articular cartilage contact area and knee flexion were also qualitatively and quantitatively similar to those previously reported. The MRI-based knee modeling method was found to have high intra-observer reliability, sensitivity to peripheral articular cartilage tracings, and agreeability with previous investigations when using data from a single healthy adult. Future studies will implement this modeling method to investigate the role that mechanical stress may play in progression of knee OA through estimation of articular cartilage contact area.
TU-F-BRB-00: MRI-Based Motion Management for RT
International Nuclear Information System (INIS)
2015-01-01
The current clinical standard of organ respiratory imaging, 4D-CT, is fundamentally limited by poor soft-tissue contrast and imaging dose. These limitations are potential barriers to beneficial “4D” radiotherapy methods which optimize the target and OAR dose-volume considering breathing motion but rely on a robust motion characterization. Conversely, MRI imparts no known radiation risk and has excellent soft-tissue contrast. MRI-based motion management is therefore highly desirable and holds great promise to improve radiotherapy of moving cancers, particularly in the abdomen. Over the past decade, MRI techniques have improved significantly, making MR-based motion management clinically feasible. For example, cine MRI has high temporal resolution up to 10 f/s and has been used to track and/or characterize tumor motion, study correlation between external and internal motions. New MR technologies, such as 4D-MRI and MRI hybrid treatment machines (i.e. MR-linac or MR-Co60), have been recently developed. These technologies can lead to more accurate target volume determination and more precise radiation dose delivery via direct tumor gating or tracking. Despite all these promises, great challenges exist and the achievable clinical benefit of MRI-based tumor motion management has yet to be fully explored, much less realized. In this proposal, we will review novel MR-based motion management methods and technologies, the state-of-the-art concerning MRI development and clinical application and the barriers to more widespread adoption. Learning Objectives: Discuss the need of MR-based motion management for improving patient care in radiotherapy. Understand MR techniques for motion imaging and tumor motion characterization. Understand the current state of the art and future steps for clinical integration. Henry Ford Health System holds research agreements with Philips Healthcare. Research sponsored in part by a Henry Ford Health System Internal Mentored Grant
TU-F-BRB-00: MRI-Based Motion Management for RT
Energy Technology Data Exchange (ETDEWEB)
NONE
2015-06-15
The current clinical standard of organ respiratory imaging, 4D-CT, is fundamentally limited by poor soft-tissue contrast and imaging dose. These limitations are potential barriers to beneficial “4D” radiotherapy methods which optimize the target and OAR dose-volume considering breathing motion but rely on a robust motion characterization. Conversely, MRI imparts no known radiation risk and has excellent soft-tissue contrast. MRI-based motion management is therefore highly desirable and holds great promise to improve radiotherapy of moving cancers, particularly in the abdomen. Over the past decade, MRI techniques have improved significantly, making MR-based motion management clinically feasible. For example, cine MRI has high temporal resolution up to 10 f/s and has been used to track and/or characterize tumor motion, study correlation between external and internal motions. New MR technologies, such as 4D-MRI and MRI hybrid treatment machines (i.e. MR-linac or MR-Co60), have been recently developed. These technologies can lead to more accurate target volume determination and more precise radiation dose delivery via direct tumor gating or tracking. Despite all these promises, great challenges exist and the achievable clinical benefit of MRI-based tumor motion management has yet to be fully explored, much less realized. In this proposal, we will review novel MR-based motion management methods and technologies, the state-of-the-art concerning MRI development and clinical application and the barriers to more widespread adoption. Learning Objectives: Discuss the need of MR-based motion management for improving patient care in radiotherapy. Understand MR techniques for motion imaging and tumor motion characterization. Understand the current state of the art and future steps for clinical integration. Henry Ford Health System holds research agreements with Philips Healthcare. Research sponsored in part by a Henry Ford Health System Internal Mentored Grant.
International Nuclear Information System (INIS)
Park, Peter C.; Schreibmann, Eduard; Roper, Justin; Elder, Eric; Crocker, Ian; Fox, Tim; Zhu, X. Ronald; Dong, Lei; Dhabaan, Anees
2015-01-01
Purpose: Computed tomography (CT) artifacts can severely degrade dose calculation accuracy in proton therapy. Prompted by the recently increased popularity of magnetic resonance imaging (MRI) in the radiation therapy clinic, we developed an MRI-based CT artifact correction method for improving the accuracy of proton range calculations. Methods and Materials: The proposed method replaces corrupted CT data by mapping CT Hounsfield units (HU number) from a nearby artifact-free slice, using a coregistered MRI. MRI and CT volumetric images were registered with use of 3-dimensional (3D) deformable image registration (DIR). The registration was fine-tuned on a slice-by-slice basis by using 2D DIR. Based on the intensity of paired MRI pixel values and HU from an artifact-free slice, we performed a comprehensive analysis to predict the correct HU for the corrupted region. For a proof-of-concept validation, metal artifacts were simulated on a reference data set. Proton range was calculated using reference, artifactual, and corrected images to quantify the reduction in proton range error. The correction method was applied to 4 unique clinical cases. Results: The correction method resulted in substantial artifact reduction, both quantitatively and qualitatively. On respective simulated brain and head and neck CT images, the mean error was reduced from 495 and 370 HU to 108 and 92 HU after correction. Correspondingly, the absolute mean proton range errors of 2.4 cm and 1.7 cm were reduced to less than 2 mm in both cases. Conclusions: Our MRI-based CT artifact correction method can improve CT image quality and proton range calculation accuracy for patients with severe CT artifacts
Development of a brain MRI-based hidden Markov model for dementia recognition.
Chen, Ying; Pham, Tuan D
2013-01-01
Dementia is an age-related cognitive decline which is indicated by an early degeneration of cortical and sub-cortical structures. Characterizing those morphological changes can help to understand the disease development and contribute to disease early prediction and prevention. But modeling that can best capture brain structural variability and can be valid in both disease classification and interpretation is extremely challenging. The current study aimed to establish a computational approach for modeling the magnetic resonance imaging (MRI)-based structural complexity of the brain using the framework of hidden Markov models (HMMs) for dementia recognition. Regularity dimension and semi-variogram were used to extract structural features of the brains, and vector quantization method was applied to convert extracted feature vectors to prototype vectors. The output VQ indices were then utilized to estimate parameters for HMMs. To validate its accuracy and robustness, experiments were carried out on individuals who were characterized as non-demented and mild Alzheimer's diseased. Four HMMs were constructed based on the cohort of non-demented young, middle-aged, elder and demented elder subjects separately. Classification was carried out using a data set including both non-demented and demented individuals with a wide age range. The proposed HMMs have succeeded in recognition of individual who has mild Alzheimer's disease and achieved a better classification accuracy compared to other related works using different classifiers. Results have shown the ability of the proposed modeling for recognition of early dementia. The findings from this research will allow individual classification to support the early diagnosis and prediction of dementia. By using the brain MRI-based HMMs developed in our proposed research, it will be more efficient, robust and can be easily used by clinicians as a computer-aid tool for validating imaging bio-markers for early prediction of dementia.
Holographic models with anisotropic scaling
Brynjolfsson, E. J.; Danielsson, U. H.; Thorlacius, L.; Zingg, T.
2013-12-01
We consider gravity duals to d+1 dimensional quantum critical points with anisotropic scaling. The primary motivation comes from strongly correlated electron systems in condensed matter theory but the main focus of the present paper is on the gravity models in their own right. Physics at finite temperature and fixed charge density is described in terms of charged black branes. Some exact solutions are known and can be used to obtain a maximally extended spacetime geometry, which has a null curvature singularity inside a single non-degenerate horizon, but generic black brane solutions in the model can only be obtained numerically. Charged matter gives rise to black branes with hair that are dual to the superconducting phase of a holographic superconductor. Our numerical results indicate that holographic superconductors with anisotropic scaling have vanishing zero temperature entropy when the back reaction of the hair on the brane geometry is taken into account.
Anisotropic inflation with derivative couplings
Holland, Jonathan; Kanno, Sugumi; Zavala, Ivonne
2018-05-01
We study anisotropic power-law inflationary solutions when the inflaton and its derivative couple to a vector field. This type of coupling is motivated by D-brane inflationary models, in which the inflaton, and a vector field living on the D-brane, couple disformally (derivatively). We start by studying a phenomenological model where we show the existence of anisotropic solutions and demonstrate their stability via a dynamical system analysis. Compared to the case without a derivative coupling, the anisotropy is reduced and thus can be made consistent with current limits, while the value of the slow-roll parameter remains almost unchanged. We also discuss solutions for more general cases, including D-brane-like couplings.
Anisotropic models for compact stars
Energy Technology Data Exchange (ETDEWEB)
Maurya, S.K.; Dayanandan, Baiju [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Jaypee Institute of Information Technology University, Department of Mathematics, Noida, Uttar Pradesh (India); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India)
2015-05-15
In the present paper we obtain an anisotropic analog of the Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) perfect fluid solution. The methodology consists of contraction of the anisotropic factor Δ with the help of both metric potentials e{sup ν} and e{sup λ}. Here we consider e{sup λ} the same as Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) did, whereas e{sup ν} is as given by Lake (Phys Rev D 67:104015, 2003). The field equations are solved by the change of dependent variable method. The solutions set mathematically thus obtained are compared with the physical properties of some of the compact stars, strange star as well as white dwarf. It is observed that all the expected physical features are available related to the stellar fluid distribution, which clearly indicates the validity of the model. (orig.)
Anisotropic Ripple Deformation in Phosphorene.
Kou, Liangzhi; Ma, Yandong; Smith, Sean C; Chen, Changfeng
2015-05-07
Two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.
Anisotropic charged generalized polytropic models
Nasim, A.; Azam, M.
2018-06-01
In this paper, we found some new anisotropic charged models admitting generalized polytropic equation of state with spherically symmetry. An analytic solution of the Einstein-Maxwell field equations is obtained through the transformation introduced by Durgapal and Banerji (Phys. Rev. D 27:328, 1983). The physical viability of solutions corresponding to polytropic index η =1/2, 2/3, 1, 2 is analyzed graphically. For this, we plot physical quantities such as radial and tangential pressure, anisotropy, speed of sound which demonstrated that these models achieve all the considerable physical conditions required for a relativistic star. Further, it is mentioned here that previous results for anisotropic charged matter with linear, quadratic and polytropic equation of state can be retrieved.
Anisotropic superfluidity of hadronic matter
International Nuclear Information System (INIS)
Chela Flores, J.
1977-10-01
From a model of strong interactions with important general features (f-g model) and from recent experiments of Rudnick and co-workers on thin films of helium II, hadronic matter is considered as a new manifestation of anisotropic superfluidity. In order to test the validity of the suggestion, some qualitative features of multiparticle production of hadrons are considered, and found to have a natural explanation. A prediction is made following a recent experiment on π + p collisions
Anisotropic characterization of magnetorheological materials
Energy Technology Data Exchange (ETDEWEB)
Dohmen, E., E-mail: eike.dohmen@tu-dresden.de; Modler, N.; Gude, M.
2017-06-01
For the development of energy efficient lightweight parts novel function integrating materials are needed. Concerning this field of application magnetorheological (MR) fluids, MR elastomers and MR composites are promising materials allowing the adjustment of mechanical properties by an external magnetic field. A key issue for operating such structures in praxis is the magneto-mechanical description. Most rheological properties are gathered at laboratory conditions for high magnetic flux densities and a single field direction, which does not correspond to real praxis conditions. Although anisotropic formation of superstructures can be observed in MR suspensions (Fig. 1) or experimenters intentionally polymerize MR elastomers with anisotropic superstructures these MR materials are usually described in an external magnetic field as uniform, isotropic materials. This is due to missing possibilities for experimentally measuring field angle dependent properties and ways of distinguishing between material properties and frictional effects. Just a few scientific works experimentally investigated the influence of different field angles (Ambacher et al., 1992; Grants et al., 1990; Kuzhir et al., 2003) or the influence of surface roughness on the shear behaviour of magnetic fluids (Tang and Conrad, 1996) . The aim of this work is the introduction of a novel field angle cell allowing the determination of anisotropic mechanical properties for various MR materials depending on the applied magnetic field angle. - Highlights: • Novel magnetic field angle testing device (MFATD) presented. • Determination of magnetic field dependent anisotropic mechanical properties. • Experimental data for different field directions shown for a commercial MR fluid. • Material description of MR fluids as transversal-isotropic solids. • Magnetic field angle dependent variations in shear stresses experimentally measured. • Determination of frictional coefficients between the MR fluid and
Cracking of anisotropic cylindrical polytropes
Energy Technology Data Exchange (ETDEWEB)
Mardan, S.A. [University of the Management and Technology, Department of Mathematics, Lahore (Pakistan); Azam, M. [University of Education, Division of Science and Technology, Lahore (Pakistan)
2017-06-15
We study the appearance of cracking in charged anisotropic cylindrical polytropes with generalized polytropic equation. We investigate the existence of cracking in two different kinds of polytropes existing in the literature through two different assumptions: (a) local density perturbation with conformally flat condition, and (b) perturbing polytropic index, charge and anisotropy parameters. We conclude that cracking appears in both kinds of polytropes for a specific range of density and model parameters. (orig.)
MRI-based treatment planning for radiotherapy: Dosimetric verification for prostate IMRT
International Nuclear Information System (INIS)
Chen, Lili; Price, Robert A.; Wang Lu; Li Jinsheng; Qin Lihong; McNeeley, Shawn; Ma, C.-M. Charlie; Freedman, Gary M.; Pollack, Alan
2004-01-01
Purpose: Magnetic resonance (MR) and computed tomography (CT) image fusion with CT-based dose calculation is the gold standard for prostate treatment planning. MR and CT fusion with CT-based dose calculation has become a routine procedure for intensity-modulated radiation therapy (IMRT) treatment planning at Fox Chase Cancer Center. The use of MRI alone for treatment planning (or MRI simulation) will remove any errors associated with image fusion. Furthermore, it will reduce treatment cost by avoiding redundant CT scans and save patient, staff, and machine time. The purpose of this study is to investigate the dosimetric accuracy of MRI-based treatment planning for prostate IMRT. Methods and materials: A total of 30 IMRT plans for 15 patients were generated using both MRI and CT data. The MRI distortion was corrected using gradient distortion correction (GDC) software provided by the vendor (Philips Medical System, Cleveland, OH). The same internal contours were used for the paired plans. The external contours were drawn separately between CT-based and MR imaging-based plans to evaluate the effect of any residual distortions on dosimetric accuracy. The same energy, beam angles, dose constrains, and optimization parameters were used for dose calculations for each paired plans using a treatment optimization system. The resulting plans were compared in terms of isodose distributions and dose-volume histograms (DVHs). Hybrid phantom plans were generated for both the CT-based plans and the MR-based plans using the same leaf sequences and associated monitor units (MU). The physical phantom was then irradiated using the same leaf sequences to verify the dosimetry accuracy of the treatment plans. Results: Our results show that dose distributions between CT-based and MRI-based plans were equally acceptable based on our clinical criteria. The absolute dose agreement for the planning target volume was within 2% between CT-based and MR-based plans and 3% between measured dose
Neutron transfer with anisotropic scattering
International Nuclear Information System (INIS)
El Wakil, S.A.; Haggag, M.H.; Saad, E.A.
1979-01-01
The finite slab problem is reduced to a semi-infinite one by adding an infinitesimally thick layer such that both the added layer and the total layer are semi-infinite. The relation between the reflection and transmission functions for a finite slab and those for an infinite one are obtained in terms of an operator which satisfies a semigroup equation. The method is applied to anisotropic scattering with azimuthal dependence. Numerical calculations are made and the results compared with those of other workers. (author)
Anisotropic densification of reference steel
International Nuclear Information System (INIS)
Garner, F.A.; Bates, J.F.; Gilbert, E.R.
1975-09-01
A correlation is presented for the densification expected during neutron irradiation of 20 percent CW 316 stainless steel cladding of FTR specification. The densification is known to be a function of time, prior heat treatment, cold work level, irradiation temperature and minor element composition. For FTR fuel pin use, the temperature and carbon composition were chosen as the only relevant variables on which to base the correlation. The densification of FTR cladding is expected to be slightly anisotropic, leading to a diameter change somewhat less than that predicted by the isotropic relationship ΔD = -D 0 /3
Anisotropic and nonlinear optical waveguides
Someda, CG
1992-01-01
Dielectric optical waveguides have been investigated for more than two decades. In the last ten years they have had the unique position of being simultaneously the backbone of a very practical and fully developed technology, as well as an extremely exciting area of basic, forefront research. Existing waveguides can be divided into two sets: one consisting of waveguides which are already in practical use, and the second of those which are still at the laboratory stage of their evolution. This book is divided into two separate parts: the first dealing with anisotropic waveguides, an
A survey of MRI-based medical image analysis for brain tumor studies
Bauer, Stefan; Wiest, Roland; Nolte, Lutz-P.; Reyes, Mauricio
2013-07-01
MRI-based medical image analysis for brain tumor studies is gaining attention in recent times due to an increased need for efficient and objective evaluation of large amounts of data. While the pioneering approaches applying automated methods for the analysis of brain tumor images date back almost two decades, the current methods are becoming more mature and coming closer to routine clinical application. This review aims to provide a comprehensive overview by giving a brief introduction to brain tumors and imaging of brain tumors first. Then, we review the state of the art in segmentation, registration and modeling related to tumor-bearing brain images with a focus on gliomas. The objective in the segmentation is outlining the tumor including its sub-compartments and surrounding tissues, while the main challenge in registration and modeling is the handling of morphological changes caused by the tumor. The qualities of different approaches are discussed with a focus on methods that can be applied on standard clinical imaging protocols. Finally, a critical assessment of the current state is performed and future developments and trends are addressed, giving special attention to recent developments in radiological tumor assessment guidelines.
Directory of Open Access Journals (Sweden)
Sara eCalderoni
2016-03-01
Full Text Available Clinical and research evidence supports the efficacy of rehabilitative intervention for improving targeted skills or global outcomes in individuals with autism spectrum disorder (ASD. However, putative mechanisms of structural and functional brain changes are poorly understood. This review aims to investigate the research literature on the neural circuit modifications after non-pharmacological intervention. For this purpose, longitudinal studies that used magnetic resonance imaging (MRI-based techniques at the start and at the end of the trial to evaluate the neural effects of rehabilitative treatment in subjects with ASD were identified. The six included studies involved a limited number of patients in the active group (from 2 to 16, and differed by acquisition method (task-related and resting-state functional MRI as well as by functional MRI tasks. Overall, the results produced by the selected investigations demonstrated brain plasticity during the treatment interval that results in an activation/functional connectivity more similar to those of subjects with typical development. Repeated MRI evaluation may represent a promising tool for the detection of neural changes in response to treatment in patients with ASD. However, large-scale randomized controlled trials after standardized rehabilitative intervention are required before translating these preliminary results into clinical use.
MRI-based anatomical landmarks for the identification of thoracic vertebral levels
International Nuclear Information System (INIS)
Connor, S.E.J.; Shah, A.; Latifoltojar, H.; Lung, P.
2013-01-01
Aim: To identify soft-tissue and bony anatomical landmarks on dedicated thoracic spine magnetic resonance imaging (MRI), and to assess their detectability, reproducibility, and accuracy in predicting specific thoracic vertebral levels. Materials and methods: One hundred dedicated thoracic MRI studies were retrospectively analysed by two radiologists independently. Ten bone and soft-tissue landmarks were localized to the adjacent vertebral level. The true numerical thoracic vertebral level was subsequently determined and recorded by cross referencing with a sagittal cervico-thoracic “counting scan”. Results: Six landmarks were defined in ≥98% cases; however, there was a low interobserver percentage agreement for the defined vertebral levels (>70% for only one landmark). The most useful landmark for defining a specific vertebral level was the most superior rib (98% detection, 95% interobserver agreement, 98% at a single vertebral level, 0.07 SD). Eight landmarks localized to a specific thoracic segment in only 16–44% of cases, with a standard deviation of >0.5 vertebral levels and with a range which was greater than four vertebral levels. Conclusion: The C2 vertebra must be identified and cross referenced to the dedicated thoracic spine MRI, as other MRI-based anatomical landmarks are unreliable in determining the correct thoracic vertebral level
A fiducial skull marker for precise MRI-based stereotaxic surgery in large animal models.
Glud, Andreas Nørgaard; Bech, Johannes; Tvilling, Laura; Zaer, Hamed; Orlowski, Dariusz; Fitting, Lise Moberg; Ziedler, Dora; Geneser, Michael; Sangill, Ryan; Alstrup, Aage Kristian Olsen; Bjarkam, Carsten Reidies; Sørensen, Jens Christian Hedemann
2017-06-15
Stereotaxic neurosurgery in large animals is used widely in different sophisticated models, where precision is becoming more crucial as desired anatomical target regions are becoming smaller. Individually calculated coordinates are necessary in large animal models with cortical and subcortical anatomical differences. We present a convenient method to make an MRI-visible skull fiducial for 3D MRI-based stereotaxic procedures in larger experimental animals. Plastic screws were filled with either copper-sulfate solution or MRI-visible paste from a commercially available cranial head marker. The screw fiducials were inserted in the animal skulls and T1 weighted MRI was performed allowing identification of the inserted skull marker. Both types of fiducial markers were clearly visible on the MRÍs. This allows high precision in the stereotaxic space. The use of skull bone based fiducial markers gives high precision for both targeting and evaluation of stereotaxic systems. There are no metal artifacts and the fiducial is easily removed after surgery. The fiducial marker can be used as a very precise reference point, either for direct targeting or in evaluation of other stereotaxic systems. Copyright © 2017 Elsevier B.V. All rights reserved.
A survey of MRI-based medical image analysis for brain tumor studies
International Nuclear Information System (INIS)
Bauer, Stefan; Nolte, Lutz-P; Reyes, Mauricio; Wiest, Roland
2013-01-01
MRI-based medical image analysis for brain tumor studies is gaining attention in recent times due to an increased need for efficient and objective evaluation of large amounts of data. While the pioneering approaches applying automated methods for the analysis of brain tumor images date back almost two decades, the current methods are becoming more mature and coming closer to routine clinical application. This review aims to provide a comprehensive overview by giving a brief introduction to brain tumors and imaging of brain tumors first. Then, we review the state of the art in segmentation, registration and modeling related to tumor-bearing brain images with a focus on gliomas. The objective in the segmentation is outlining the tumor including its sub-compartments and surrounding tissues, while the main challenge in registration and modeling is the handling of morphological changes caused by the tumor. The qualities of different approaches are discussed with a focus on methods that can be applied on standard clinical imaging protocols. Finally, a critical assessment of the current state is performed and future developments and trends are addressed, giving special attention to recent developments in radiological tumor assessment guidelines. (topical review)
Theoretical and numerical study of highly anisotropic turbulent flows
Biferale, L.; Daumont, I.; Lanotte, A.; Toschi, F.
2004-01-01
We present a detailed numerical study of anisotropic statistical fluctuations in stationary, homogeneous turbulent flows. We address both problems of intermittency in anisotropic sectors, and the relative importance of isotropic and anisotropic fluctuations at different scales on a direct numerical
Electromagnetism on anisotropic fractal media
Ostoja-Starzewski, Martin
2013-04-01
Basic equations of electromagnetic fields in anisotropic fractal media are obtained using a dimensional regularization approach. First, a formulation based on product measures is shown to satisfy the four basic identities of the vector calculus. This allows a generalization of the Green-Gauss and Stokes theorems as well as the charge conservation equation on anisotropic fractals. Then, pursuing the conceptual approach, we derive the Faraday and Ampère laws for such fractal media, which, along with two auxiliary null-divergence conditions, effectively give the modified Maxwell equations. Proceeding on a separate track, we employ a variational principle for electromagnetic fields, appropriately adapted to fractal media, so as to independently derive the same forms of these two laws. It is next found that the parabolic (for a conducting medium) and the hyperbolic (for a dielectric medium) equations involve modified gradient operators, while the Poynting vector has the same form as in the non-fractal case. Finally, Maxwell's electromagnetic stress tensor is reformulated for fractal systems. In all the cases, the derived equations for fractal media depend explicitly on fractal dimensions in three different directions and reduce to conventional forms for continuous media with Euclidean geometries upon setting these each of dimensions equal to unity.
Sur, Shouvik; Lee, Sung-Sik
2016-11-01
We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.
Efficient Wavefield Extrapolation In Anisotropic Media
Alkhalifah, Tariq; Ma, Xuxin; Waheed, Umair bin; Zuberi, Mohammad Akbar Hosain
2014-01-01
Various examples are provided for wavefield extrapolation in anisotropic media. In one example, among others, a method includes determining an effective isotropic velocity model and extrapolating an equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield. The effective isotropic velocity model can be based upon a kinematic geometrical representation of an anisotropic, poroelastic or viscoelastic wavefield. Extrapolating the equivalent propagation can use isotopic, acoustic or elastic operators based upon the determined effective isotropic velocity model. In another example, non-transitory computer readable medium stores an application that, when executed by processing circuitry, causes the processing circuitry to determine the effective isotropic velocity model and extrapolate the equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield. In another example, a system includes processing circuitry and an application configured to cause the system to determine the effective isotropic velocity model and extrapolate the equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield.
Nonlinear constitutive relations for anisotropic elastic materials
Sokolova, Marina; Khristich, Dmitrii
2018-03-01
A general approach to constructing of nonlinear variants of connection between stresses and strains in anisotropic materials with different types of symmetry of properties is considered. This approach is based on the concept of elastic proper subspaces of anisotropic materials introduced in the mechanics of solids by J. Rychlewski and on the particular postulate of isotropy proposed by A. A. Il’yushin. The generalization of the particular postulate on the case of nonlinear anisotropic materials is formulated. Systems of invariants of deformations as lengths of projections of the strain vector into proper subspaces are developed. Some variants of nonlinear constitutive relations for anisotropic materials are offered. The analysis of these relations from the point of view of their satisfaction to general and limit forms of generalization of partial isotropy postulate on anisotropic materials is performed. The relations for particular cases of anisotropy are written.
Efficient Wavefield Extrapolation In Anisotropic Media
Alkhalifah, Tariq
2014-07-03
Various examples are provided for wavefield extrapolation in anisotropic media. In one example, among others, a method includes determining an effective isotropic velocity model and extrapolating an equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield. The effective isotropic velocity model can be based upon a kinematic geometrical representation of an anisotropic, poroelastic or viscoelastic wavefield. Extrapolating the equivalent propagation can use isotopic, acoustic or elastic operators based upon the determined effective isotropic velocity model. In another example, non-transitory computer readable medium stores an application that, when executed by processing circuitry, causes the processing circuitry to determine the effective isotropic velocity model and extrapolate the equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield. In another example, a system includes processing circuitry and an application configured to cause the system to determine the effective isotropic velocity model and extrapolate the equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield.
An MRI-based diagnostic framework for early diagnosis of dyslexia
International Nuclear Information System (INIS)
El-Baz, A.; Casanova, M.; Mott, M.; Switala, A.; Gimel'farb, G.
2008-01-01
A computer-aided diagnosis (CAD) system for early diagnosis of dyslexia was developed and tested. Dyslexia can severely impair the learning abilities of children so improved diagnostic methods are needed. Neuropathological studies show abnormal anatomy of the cerebral white matter (CWM) in dyslexic brains. We sought to develop an MRI-based macroscopic neuropathological correlate to the minicolumnopathy of dyslexia that relates to cortical connectivity: the gyral window. The brains of dyslexic patients often exhibit decreased gyrifications, so the thickness of gyral CWM for dyslexic subjects is greater than for normal subjects. We developed an MRI-based method for assessment of gyral CWM thickness with automated recognition of abnormal (e.g., dyslexic) brains. In vivo data was collected from 16 right-handed dyslexic men aged 18-40 years, and a group of 14 controls matched for gender, age, educational level, socioeconomic background, handedness and general intelligence. All the subjects were physically healthy and free of history of neurological diseases and head injury. Images were acquired with the same 1.5T MRI scanner (GE, Milwaukee, WI, USA) with voxel resolution 0.9375 x 0.9375 x 1.5 mm using a T1-weighted imaging sequence protocol. The ''ground truth'' diagnosis to evaluate the classification accuracy for each patient was given by the clinicians. The accuracy of diagnosis/classification of both the training and test subjects was evaluated using the Chi-square test at the three confidence levels - 85, 90 and 95% - in order to examine significant differences in the Levy distances. As expected, the 85% confidence level yielded the best results, the system correctly classified 16 out of 16 dyslexic subjects (a 100% accuracy) and 14 out of 14 control subjects (a 100% accuracy). At the 90% confidence level, 16 out of 16 dyslexic subjects were still classified correctly; however, only 13 out of 14 control subjects were correct, bringing the accuracy rate for the
An MRI-based diagnostic framework for early diagnosis of dyslexia
Energy Technology Data Exchange (ETDEWEB)
El-Baz, A. [University of Louisville, Bioengineering Department, Louisville, KY (United States); Casanova, M.; Mott, M.; Switala, A. [University of Louisville, Department of Psychiatry and Behavioral Science, Louisville, KY (United States); Gimel' farb, G. [University of Auckland, Computer Science Department, Auckland (New Zealand)
2008-09-15
A computer-aided diagnosis (CAD) system for early diagnosis of dyslexia was developed and tested. Dyslexia can severely impair the learning abilities of children so improved diagnostic methods are needed. Neuropathological studies show abnormal anatomy of the cerebral white matter (CWM) in dyslexic brains. We sought to develop an MRI-based macroscopic neuropathological correlate to the minicolumnopathy of dyslexia that relates to cortical connectivity: the gyral window. The brains of dyslexic patients often exhibit decreased gyrifications, so the thickness of gyral CWM for dyslexic subjects is greater than for normal subjects. We developed an MRI-based method for assessment of gyral CWM thickness with automated recognition of abnormal (e.g., dyslexic) brains. In vivo data was collected from 16 right-handed dyslexic men aged 18-40 years, and a group of 14 controls matched for gender, age, educational level, socioeconomic background, handedness and general intelligence. All the subjects were physically healthy and free of history of neurological diseases and head injury. Images were acquired with the same 1.5T MRI scanner (GE, Milwaukee, WI, USA) with voxel resolution 0.9375 x 0.9375 x 1.5 mm using a T1-weighted imaging sequence protocol. The ''ground truth'' diagnosis to evaluate the classification accuracy for each patient was given by the clinicians. The accuracy of diagnosis/classification of both the training and test subjects was evaluated using the Chi-square test at the three confidence levels - 85, 90 and 95% - in order to examine significant differences in the Levy distances. As expected, the 85% confidence level yielded the best results, the system correctly classified 16 out of 16 dyslexic subjects (a 100% accuracy) and 14 out of 14 control subjects (a 100% accuracy). At the 90% confidence level, 16 out of 16 dyslexic subjects were still classified correctly; however, only 13 out of 14 control subjects were correct, bringing the
MRI-based treatment planning with pseudo CT generated through atlas registration
Energy Technology Data Exchange (ETDEWEB)
Uh, Jinsoo, E-mail: jinsoo.uh@stjude.org; Merchant, Thomas E.; Hua, Chiaho [Department of Radiological Sciences, St. Jude Children' s Research Hospital, Memphis, Tennessee 38105 (United States); Li, Yimei; Li, Xingyu [Department of Biostatistics, St. Jude Children' s Research Hospital, Memphis, Tennessee 38105 (United States)
2014-05-15
Purpose: To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. Methods: A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration of conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. Results: The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787–0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%–98.7%) satisfied the criteria of chi-evaluation (<2% maximum dose and 2 mm range). The dose to 95% of the volume and the
MRI-based treatment planning with pseudo CT generated through atlas registration
International Nuclear Information System (INIS)
Uh, Jinsoo; Merchant, Thomas E.; Hua, Chiaho; Li, Yimei; Li, Xingyu
2014-01-01
Purpose: To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. Methods: A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration of conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. Results: The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787–0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%–98.7%) satisfied the criteria of chi-evaluation (<2% maximum dose and 2 mm range). The dose to 95% of the volume and the
Simulation of spatiotemporal CT data sets using a 4D MRI-based lung motion model.
Marx, Mirko; Ehrhardt, Jan; Werner, René; Schlemmer, Heinz-Peter; Handels, Heinz
2014-05-01
Four-dimensional CT imaging is widely used to account for motion-related effects during radiotherapy planning of lung cancer patients. However, 4D CT often contains motion artifacts, cannot be used to measure motion variability, and leads to higher dose exposure. In this article, we propose using 4D MRI to acquire motion information for the radiotherapy planning process. From the 4D MRI images, we derive a time-continuous model of the average patient-specific respiratory motion, which is then applied to simulate 4D CT data based on a static 3D CT. The idea of the motion model is to represent the average lung motion over a respiratory cycle by cyclic B-spline curves. The model generation consists of motion field estimation in the 4D MRI data by nonlinear registration, assigning respiratory phases to the motion fields, and applying a B-spline approximation on a voxel-by-voxel basis to describe the average voxel motion over a breathing cycle. To simulate a patient-specific 4D CT based on a static CT of the patient, a multi-modal registration strategy is introduced to transfer the motion model from MRI to the static CT coordinates. Differences between model-based estimated and measured motion vectors are on average 1.39 mm for amplitude-based binning of the 4D MRI data of three patients. In addition, the MRI-to-CT registration strategy is shown to be suitable for the model transformation. The application of our 4D MRI-based motion model for simulating 4D CT images provides advantages over standard 4D CT (less motion artifacts, radiation-free). This makes it interesting for radiotherapy planning.
MRI-Based Regional Muscle Use during Hamstring Strengthening Exercises in Elite Soccer Players.
Mendez-Villanueva, Alberto; Suarez-Arrones, Luis; Rodas, Gil; Fernandez-Gonzalo, Rodrigo; Tesch, Per; Linnehan, Richard; Kreider, Richard; Di Salvo, Valter
2016-01-01
The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel leg-curl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T2) shift from pre- to post-MRI were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T2 values increased substantially after flywheel leg-curl in all regions of the BFl (from 9±8 to 16±8%), BFs (41±6-71±11%), and ST (60±1-69±7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13±8-16±5%) and ST (15±7-17±5%). T2 values after the Russian belt deadlift substantially increased in all regions of the BFl (6±4-7±5%), ST (8±3-11±2%), SM (6±4-10±4%), and proximal and distal regions of BFs (6±6-8±5%). T2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFl (11±5-7±5%) and ST (7±3-12±4%). The relevance of such MRI-based inter- and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies.
Proton therapy of uveal melanomas. Intercomparison of MRI-based and conventional treatment planning
Energy Technology Data Exchange (ETDEWEB)
Marnitz, S.; Hinkelbein, W. [Dept. of Radiooncology, Charite Univ. Medicine, Berlin (Germany); Cordini, D.; Heufelder, J.; Simiantonakis, I.; Kluge, H. [Eye Tumor Therapy, Hahn-Meitner Inst., Berlin (Germany); Bendl, R. [Dept. of Medical Physics, German Cancer Research Center (DKFZ), Heidelberg (Germany); Lemke, A.J. [Dept. of Diagnostic Radiology, Charite Univ. Medicine, Berlin (Germany); Bechrakis, N.E.; Foerster, M.H. [Dept. of Ophthalmology, Charite Univ. Medicine, Berlin (Germany)
2006-07-15
Background and purpose: proton therapy for uveal melanoma provides high-conformal dose application to the target volume and, thus, an optimal saving of the organs at risk nearby. Treatment planning is done with the model-based treatment-planning system eyeplan. Tumor reconstruction is based only on a fundus composite, which often leads to an overestimation of the clinical target volume (CTV). The purpose was to exploit MRI on trial in a proton therapy-planning system by using the novel image-based treatment-planning system octopus. Patients and methods: ten patients with uveal melanomas received both a high-resolution planning CT and MRI of the eye. MR examinations were made with an eye coil. Eyeplan requires eye geometry data for modeling, and tantalum marker clips for submillimeter positioning and additional information from ultrasound and 3-D imaging. By contrast, octopus provides the full integration of 3-D imaging (e.g., CT, MRI). CTVs were delineated in each slice. For all patients, CTVs (eyeplan vs. octopus) were compared intraindividually. Results: octopus planning led to a mean reduction of the target volume by a factor of 1.7 (T1-weighted [T1w]) and 2.2 (T2w) without compromising safety. The corresponding field size could be scaled down on average by a factor of 1.2 (T1w) and 1.4 (T2w), respectively. Conclusion: compared with the conventional eyeplan, MRI-based treatment planning of ocular tumors with octopus could be a powerful tool for reducing the CTV and, consequently, the treatment volume and the field size. This might be translated into a better patient compliance during treatment and a decreased late toxicity. (orig.)
Proton therapy of uveal melanomas. Intercomparison of MRI-based and conventional treatment planning
International Nuclear Information System (INIS)
Marnitz, S.; Hinkelbein, W.; Cordini, D.; Heufelder, J.; Simiantonakis, I.; Kluge, H.; Bendl, R.; Lemke, A.J.; Bechrakis, N.E.; Foerster, M.H.
2006-01-01
Background and purpose: proton therapy for uveal melanoma provides high-conformal dose application to the target volume and, thus, an optimal saving of the organs at risk nearby. Treatment planning is done with the model-based treatment-planning system eyeplan. Tumor reconstruction is based only on a fundus composite, which often leads to an overestimation of the clinical target volume (CTV). The purpose was to exploit MRI on trial in a proton therapy-planning system by using the novel image-based treatment-planning system octopus. Patients and methods: ten patients with uveal melanomas received both a high-resolution planning CT and MRI of the eye. MR examinations were made with an eye coil. Eyeplan requires eye geometry data for modeling, and tantalum marker clips for submillimeter positioning and additional information from ultrasound and 3-D imaging. By contrast, octopus provides the full integration of 3-D imaging (e.g., CT, MRI). CTVs were delineated in each slice. For all patients, CTVs (eyeplan vs. octopus) were compared intraindividually. Results: octopus planning led to a mean reduction of the target volume by a factor of 1.7 (T1-weighted [T1w]) and 2.2 (T2w) without compromising safety. The corresponding field size could be scaled down on average by a factor of 1.2 (T1w) and 1.4 (T2w), respectively. Conclusion: compared with the conventional eyeplan, MRI-based treatment planning of ocular tumors with octopus could be a powerful tool for reducing the CTV and, consequently, the treatment volume and the field size. This might be translated into a better patient compliance during treatment and a decreased late toxicity. (orig.)
MRI-Based Regional Muscle Use during Hamstring Strengthening Exercises in Elite Soccer Players
Mendez-Villanueva, Alberto; Suarez-Arrones, Luis; Rodas, Gil; Fernandez-Gonzalo, Rodrigo; Tesch, Per; Linnehan, Richard; Kreider, Richard; Di Salvo, Valter
2016-01-01
The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel leg-curl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T2) shift from pre- to post-MRI were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T2 values increased substantially after flywheel leg-curl in all regions of the BFl (from 9±8 to 16±8%), BFs (41±6–71±11%), and ST (60±1–69±7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13±8–16±5%) and ST (15±7–17±5%). T2 values after the Russian belt deadlift substantially increased in all regions of the BFl (6±4–7±5%), ST (8±3–11±2%), SM (6±4–10±4%), and proximal and distal regions of BFs (6±6–8±5%). T2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFl (11±5–7±5%) and ST (7±3–12±4%). The relevance of such MRI-based inter- and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies. PMID:27583444
Stability of anisotropic stellar filaments
Bhatti, M. Zaeem-ul-Haq; Yousaf, Z.
2017-12-01
The study of perturbation of self-gravitating celestial cylindrical object have been carried out in this paper. We have designed a framework to construct the collapse equation by formulating the modified field equations with the background of f(R , T) theory as well as dynamical equations from the contracted form of Bianchi identities with anisotropic matter configuration. We have encapsulated the radial perturbations on metric and material variables of the geometry with some known static profile at Newtonian and post-Newtonian regimes. We examined a strong dependence of unstable regions on stiffness parameter which measures the rigidity of the fluid. Also, the static profile and matter variables with f(R , T) dark source terms control the instability of compact cylindrical system.
Warm anisotropic inflationary universe model
International Nuclear Information System (INIS)
Sharif, M.; Saleem, Rabia
2014-01-01
This paper is devoted to the study of warm inflation using vector fields in the background of a locally rotationally symmetric Bianchi type I model of the universe. We formulate the field equations, and slow-roll and perturbation parameters (scalar and tensor power spectra as well as their spectral indices) in the slow-roll approximation. We evaluate all these parameters in terms of the directional Hubble parameter during the intermediate and logamediate inflationary regimes by taking the dissipation factor as a function of the scalar field as well as a constant. In each case, we calculate the observational parameter of interest, i.e., the tensor-scalar ratio in terms of the inflaton. The graphical behavior of these parameters shows that the anisotropic model is also compatible with WMAP7 and the Planck observational data. (orig.)
Warm anisotropic inflationary universe model
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Saleem, Rabia [University of the Punjab, Department of Mathematics, Lahore (Pakistan)
2014-02-15
This paper is devoted to the study of warm inflation using vector fields in the background of a locally rotationally symmetric Bianchi type I model of the universe. We formulate the field equations, and slow-roll and perturbation parameters (scalar and tensor power spectra as well as their spectral indices) in the slow-roll approximation. We evaluate all these parameters in terms of the directional Hubble parameter during the intermediate and logamediate inflationary regimes by taking the dissipation factor as a function of the scalar field as well as a constant. In each case, we calculate the observational parameter of interest, i.e., the tensor-scalar ratio in terms of the inflaton. The graphical behavior of these parameters shows that the anisotropic model is also compatible with WMAP7 and the Planck observational data. (orig.)
Finite-volume scheme for anisotropic diffusion
Energy Technology Data Exchange (ETDEWEB)
Es, Bram van, E-mail: bramiozo@gmail.com [Centrum Wiskunde & Informatica, P.O. Box 94079, 1090GB Amsterdam (Netherlands); FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, The Netherlands" 1 (Netherlands); Koren, Barry [Eindhoven University of Technology (Netherlands); Blank, Hugo J. de [FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, The Netherlands" 1 (Netherlands)
2016-02-01
In this paper, we apply a special finite-volume scheme, limited to smooth temperature distributions and Cartesian grids, to test the importance of connectivity of the finite volumes. The area of application is nuclear fusion plasma with field line aligned temperature gradients and extreme anisotropy. We apply the scheme to the anisotropic heat-conduction equation, and compare its results with those of existing finite-volume schemes for anisotropic diffusion. Also, we introduce a general model adaptation of the steady diffusion equation for extremely anisotropic diffusion problems with closed field lines.
Fonder, G. P.; Hack, P. J.; Hughes, M. R.
This paper covers two topics related to Space Fence System development: Sensor Site One / Operations Center construction and integration status including risk reduction integration and test efforts at the Moorestown, NJ Integrated Test Bed (ITB); and the planned capability of Sensor Site Two. The AN/FSY-3 Space Fence System is a ground-based system of S-band radars integrated with an Operations Center designed to greatly enhance the Air Force Space Surveillance network. The radar architecture is based on Digital Beam-forming. This capability permits tremendous user-defined flexibility to customize volume surveillance and track sectors instantaneously without impacting routine surveillance functions. Space Fence provides unprecedented sensitivity, coverage and tracking accuracy, and contributes to key mission threads with the ability to detect, track and catalog small objects in LEO, MEO and GEO. The system is net-centric and will seamlessly integrate into the existing Space Surveillance Network, providing services to external users—such as JSpOC—and coordinating handoffs to other SSN sites. Sensor Site One construction on the Kwajalein Atoll is in progress and nearing completion. The Operations Center in Huntsville, Alabama has been configured and will be integrated with Sensor Site One in the coming months. System hardware, firmware, and software is undergoing integration testing at the Mooretown, NJ ITB and will be deployed at Sensor Site One and the Operations Center. The preliminary design for Sensor Site Two is complete and will provide critical coverage, timeliness, and operational flexibility to the overall system.
SU-E-J-153: MRI Based, Daily Adaptive Radiotherapy for Rectal Cancer: Contour Adaptation
International Nuclear Information System (INIS)
Kleijnen, J; Burbach, M; Verbraeken, T; Weggers, R; Zoetelief, A; Reerink, O; Lagendijk, J; Raaymakers, B; Asselen, B
2014-01-01
Purpose: A major hurdle in adaptive radiotherapy is the adaptation of the planning MRI's delineations to the daily anatomy. We therefore investigate the accuracy and time needed for online clinical target volume (CTV) adaptation by radiation therapists (RTT), to be used in MRI-guided adaptive treatments on a MRI-Linac (MRL). Methods: Sixteen patients, diagnosed with early stage rectal cancer, underwent a T2-weighted MRI prior to each fraction of short-course radiotherapy, resulting in 4–5 scans per patient. On these scans, the CTV was delineated according to guidelines by an experienced radiation oncologist (RO) and considered to be the gold standard. For each patient, the first MRI was considered as the planning MRI and matched on bony anatomy to the 3–4 daily MRIs. The planning MRI's CTV delineation was rigidly propagated to the daily MRI scans as a proposal for adaptation. Three RTTs in training started the adaptation of the CTV conform guidelines, after a two hour training lecture and a two patient (n=7) training set. To assess the inter-therapist variation, all three RTTs altered delineations of 3 patients (n=12). One RTT altered the CTV delineations (n=53) of the remaining 11 patients. Time needed for adaptation of the CTV to guidelines was registered.As a measure of agreement, the conformity index (CI) was determined between the RTTs' delineations as a group. Dice similarity coefficients were determined between delineations of the RTT and the RO. Results: We found good agreement between RTTs' and RO's delineations (average Dice=0.91, SD=0.03). Furthermore, the inter-observer agreement between the RTTs was high (average CI=0.94, SD=0.02). Adaptation time reduced from 10:33 min (SD= 3:46) to 2:56 min (SD=1:06) between the first and last ten delineations, respectively. Conclusion: Daily CTV adaptation by RTTs, seems a feasible and safe way to introduce daily, online MRI-based plan adaptation for a MRL
Comparison between MRI-based attenuation correction methods for brain PET in dementia patients
International Nuclear Information System (INIS)
Cabello, Jorge; Lukas, Mathias; Pyka, Thomas; Nekolla, Stephan G.; Ziegler, Sibylle I.; Rota Kops, Elena; Shah, N. Jon; Ribeiro, Andre; Yakushev, Igor
2016-01-01
The combination of Positron Emission Tomography (PET) with magnetic resonance imaging (MRI) in hybrid PET/MRI scanners offers a number of advantages in investigating brain structure and function. A critical step of PET data reconstruction is attenuation correction (AC). Accounting for bone in attenuation maps (μ-map) was shown to be important in brain PET studies. While there are a number of MRI-based AC methods, no systematic comparison between them has been performed so far. The aim of this work was to study the different performance obtained by some of the recent methods presented in the literature. To perform such a comparison, we focused on [ 18 F]-Fluorodeoxyglucose-PET/MRI neurodegenerative dementing disorders, which are known to exhibit reduced levels of glucose metabolism in certain brain regions. Four novel methods were used to calculate μ-maps from MRI data of 15 patients with Alzheimer's dementia (AD). The methods cover two atlas-based methods, a segmentation method, and a hybrid template/segmentation method. Additionally, the Dixon-based and a UTE-based method, offered by a vendor, were included in the comparison. Performance was assessed at three levels: tissue identification accuracy in the μ-map, quantitative accuracy of reconstructed PET data in specific brain regions, and precision in diagnostic images at identifying hypometabolic areas. Quantitative regional errors of -20-10 % were obtained using the vendor's AC methods, whereas the novel methods produced errors in a margin of ±5 %. The obtained precision at identifying areas with abnormally low levels of glucose uptake, potentially regions affected by AD, were 62.9 and 79.5 % for the two vendor AC methods, the former ignoring bone and the latter including bone information. The precision increased to 87.5-93.3 % in average for the four new methods, exhibiting similar performances. We confirm that the AC methods based on the Dixon and UTE sequences provided by the vendor are inferior
MRI-Based Nonrigid Motion Correction in Simultaneous PET/MRI
Chun, Se Young; Reese, Timothy G.; Ouyang, Jinsong; Guerin, Bastien; Catana, Ciprian; Zhu, Xuping; Alpert, Nathaniel M.; El Fakhri, Georges
2014-01-01
Respiratory and cardiac motion is the most serious limitation to whole-body PET, resulting in spatial resolution close to 1 cm. Furthermore, motion-induced inconsistencies in the attenuation measurements often lead to significant artifacts in the reconstructed images. Gating can remove motion artifacts at the cost of increased noise. This paper presents an approach to respiratory motion correction using simultaneous PET/MRI to demonstrate initial results in phantoms, rabbits, and nonhuman primates and discusses the prospects for clinical application. Methods Studies with a deformable phantom, a free-breathing primate, and rabbits implanted with radioactive beads were performed with simultaneous PET/MRI. Motion fields were estimated from concurrently acquired tagged MR images using 2 B-spline nonrigid image registration methods and incorporated into a PET list-mode ordered-subsets expectation maximization algorithm. Using the measured motion fields to transform both the emission data and the attenuation data, we could use all the coincidence data to reconstruct any phase of the respiratory cycle. We compared the resulting SNR and the channelized Hotelling observer (CHO) detection signal-to-noise ratio (SNR) in the motion-corrected reconstruction with the results obtained from standard gating and uncorrected studies. Results Motion correction virtually eliminated motion blur without reducing SNR, yielding images with SNR comparable to those obtained by gating with 5–8 times longer acquisitions in all studies. The CHO study in dynamic phantoms demonstrated a significant improvement (166%–276%) in lesion detection SNR with MRI-based motion correction as compared with gating (P < 0.001). This improvement was 43%–92% for large motion compared with lesion detection without motion correction (P < 0.001). CHO SNR in the rabbit studies confirmed these results. Conclusion Tagged MRI motion correction in simultaneous PET/MRI significantly improves lesion detection
Precision of MRI-based body composition measurements of postmenopausal women
Romu, Thobias; Thorell, Sofia; Lindblom, Hanna; Berin, Emilia; Holm, Anna-Clara Spetz; Åstrand, Lotta Lindh; Karlsson, Anette; Borga, Magnus; Hammar, Mats; Leinhard, Olof Dahlqvist
2018-01-01
Objectives To determine precision of magnetic resonance imaging (MRI) based fat and muscle quantification in a group of postmenopausal women. Furthermore, to extend the method to individual muscles relevant to upper-body exercise. Materials and methods This was a sub-study to a randomized control trial investigating effects of resistance training to decrease hot flushes in postmenopausal women. Thirty-six women were included, mean age 56 ± 6 years. Each subject was scanned twice with a 3.0T MR-scanner using a whole-body Dixon protocol. Water and fat images were calculated using a 6-peak lipid model including R2*-correction. Body composition analyses were performed to measure visceral and subcutaneous fat volumes, lean volumes and muscle fat infiltration (MFI) of the muscle groups’ thigh muscles, lower leg muscles, and abdominal muscles, as well as the three individual muscles pectoralis, latissimus, and rhomboideus. Analysis was performed using a multi-atlas, calibrated water-fat separated quantification method. Liver-fat was measured as average proton density fat-fraction (PDFF) of three regions-of-interest. Precision was determined with Bland-Altman analysis, repeatability, and coefficient of variation. Results All of the 36 included women were successfully scanned and analysed. The coefficient of variation was 1.1% to 1.5% for abdominal fat compartments (visceral and subcutaneous), 0.8% to 1.9% for volumes of muscle groups (thigh, lower leg, and abdomen), and 2.3% to 7.0% for individual muscle volumes (pectoralis, latissimus, and rhomboideus). Limits of agreement for MFI was within ± 2.06% for muscle groups and within ± 5.13% for individual muscles. The limits of agreement for liver PDFF was within ± 1.9%. Conclusion Whole-body Dixon MRI could characterize a range of different fat and muscle compartments with high precision, including individual muscles, in the study-group of postmenopausal women. The inclusion of individual muscles, calculated from the
Comparison between MRI-based attenuation correction methods for brain PET in dementia patients
Energy Technology Data Exchange (ETDEWEB)
Cabello, Jorge; Lukas, Mathias; Pyka, Thomas; Nekolla, Stephan G.; Ziegler, Sibylle I. [Technische Universitaet Muenchen, Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Munich (Germany); Rota Kops, Elena; Shah, N. Jon [Forschungszentrum Juelich GmbH, Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Juelich (Germany); Ribeiro, Andre [Forschungszentrum Juelich GmbH, Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Juelich (Germany); Institute of Biophysics and Biomedical Engineering, Lisbon (Portugal); Yakushev, Igor [Technische Universitaet Muenchen, Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Munich (Germany); Institute TUM Neuroimaging Center (TUM-NIC), Munich (Germany)
2016-11-15
The combination of Positron Emission Tomography (PET) with magnetic resonance imaging (MRI) in hybrid PET/MRI scanners offers a number of advantages in investigating brain structure and function. A critical step of PET data reconstruction is attenuation correction (AC). Accounting for bone in attenuation maps (μ-map) was shown to be important in brain PET studies. While there are a number of MRI-based AC methods, no systematic comparison between them has been performed so far. The aim of this work was to study the different performance obtained by some of the recent methods presented in the literature. To perform such a comparison, we focused on [{sup 18}F]-Fluorodeoxyglucose-PET/MRI neurodegenerative dementing disorders, which are known to exhibit reduced levels of glucose metabolism in certain brain regions. Four novel methods were used to calculate μ-maps from MRI data of 15 patients with Alzheimer's dementia (AD). The methods cover two atlas-based methods, a segmentation method, and a hybrid template/segmentation method. Additionally, the Dixon-based and a UTE-based method, offered by a vendor, were included in the comparison. Performance was assessed at three levels: tissue identification accuracy in the μ-map, quantitative accuracy of reconstructed PET data in specific brain regions, and precision in diagnostic images at identifying hypometabolic areas. Quantitative regional errors of -20-10 % were obtained using the vendor's AC methods, whereas the novel methods produced errors in a margin of ±5 %. The obtained precision at identifying areas with abnormally low levels of glucose uptake, potentially regions affected by AD, were 62.9 and 79.5 % for the two vendor AC methods, the former ignoring bone and the latter including bone information. The precision increased to 87.5-93.3 % in average for the four new methods, exhibiting similar performances. We confirm that the AC methods based on the Dixon and UTE sequences provided by the vendor are
MRI-based treatment planning with pseudo CT generated through atlas registration.
Uh, Jinsoo; Merchant, Thomas E; Li, Yimei; Li, Xingyu; Hua, Chiaho
2014-05-01
To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration of conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787-0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%-98.7%) satisfied the criteria of chi-evaluation (pediatric brain tumor patients. The doses calculated from pseudo CTs agreed well with those from real CTs
Anisotropic dynamic mass density for fluidsolid composites
Wu, Ying; Mei, Jun; Sheng, Ping
2012-01-01
By taking the low frequency limit of multiple-scattering theory, we obtain the dynamic effective mass density of fluidsolid composites with a two-dimensional rectangular lattice structure. The anisotropic mass density can be described by an angle
Anisotropic magnetoresistance in a Fermi glass
International Nuclear Information System (INIS)
Ovadyahu, Z.; Physics Department, Ben-Gurion University of the Negev, Beer-Sheva, Israel 84120)
1986-01-01
Insulating thin films of indium oxide exhibit negative, anisotropic magnetoresistance. The systematics of these results imply that the magnetoresistance mechanism may give different weight to the distribution of the localization lengths than that given by the hopping conductivity
Anisotropic stars obeying Chaplygin equation of state
Indian Academy of Sciences (India)
P Bhar
2017-12-14
Dec 14, 2017 ... Anisotropic effects may also originate from slow rotation of the core ... to include the effects of pressure anisotropy, electric charge, scalar field, dark energy and the cosmological constant in .... Generating solutions. In order to ...
Huang, Xueying; Teng, Zhongzhao; Canton, Gador; Ferguson, Marina; Yuan, Chun; Tang, Dalin
2010-01-01
Abstract Background Studies using medical images have shown that intraplaque hemorrhage may accelerate plaque progression and may produce a stimulus for atherosclerosis development by increasing lipid core and plaque volume and creating new destabilizing factors. Image-based 3D computational models with fluid-structure interactions (FSI) will be used to perform plaque mechanical analysis and investigate possible associations between intraplaque hemorrhage and both plaque wall stress (PWS) and...
Anisotropic rectangular metric for polygonal surface remeshing
Pellenard, Bertrand
2013-06-18
We propose a new method for anisotropic polygonal surface remeshing. Our algorithm takes as input a surface triangle mesh. An anisotropic rectangular metric, defined at each triangle facet of the input mesh, is derived from both a user-specified normal-based tolerance error and the requirement to favor rectangle-shaped polygons. Our algorithm uses a greedy optimization procedure that adds, deletes and relocates generators so as to match two criteria related to partitioning and conformity.
Anisotropic rectangular metric for polygonal surface remeshing
Pellenard, Bertrand; Morvan, Jean-Marie; Alliez, Pierre
2013-01-01
We propose a new method for anisotropic polygonal surface remeshing. Our algorithm takes as input a surface triangle mesh. An anisotropic rectangular metric, defined at each triangle facet of the input mesh, is derived from both a user-specified normal-based tolerance error and the requirement to favor rectangle-shaped polygons. Our algorithm uses a greedy optimization procedure that adds, deletes and relocates generators so as to match two criteria related to partitioning and conformity.
An anisotropic elastoplasticity model implemented in FLAG
Energy Technology Data Exchange (ETDEWEB)
Buechler, Miles Allen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Canfield, Thomas R. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-10-12
Many metals, including Tantalum and Zirconium, exhibit anisotropic elastoplastic behavior at the single crystal level, and if components are manufactured from these metals through forming processes the polycrystal (component) may also exhibit anisotropic elastoplastic behavior. This is because the forming can induce a preferential orientation of the crystals in the polycrystal. One example is a rolled plate of Uranium where the sti /strong orientation of the crystal (c-axis) tends to align itself perpendicular to the rolling direction. If loads are applied to this plate in di erent orientations the sti ness as well as the ow strength of the material will be greater in the through thickness direction than in other directions. To better accommodate simulations of such materials, an anisotropic elastoplasticity model has been implemented in FLAG. The model includes an anisotropic elastic stress model as well as an anisotropic plasticity model. The model could represent single crystals of any symmetry, though it should not be confused with a high- delity crystal plasticity model with multiple slip planes and evolutions. The model is most appropriate for homogenized polycrystalline materials. Elastic rotation of the material due to deformation is captured, so the anisotropic models are appropriate for arbitrary large rotations, but currently they do not account for signi cant change in material texture beyond the elastic rotation of the entire polycrystal.
Modeling of anisotropic wound healing
Valero, C.; Javierre, E.; García-Aznar, J. M.; Gómez-Benito, M. J.; Menzel, A.
2015-06-01
Biological soft tissues exhibit non-linear complex properties, the quantification of which presents a challenge. Nevertheless, these properties, such as skin anisotropy, highly influence different processes that occur in soft tissues, for instance wound healing, and thus its correct identification and quantification is crucial to understand them. Experimental and computational works are required in order to find the most precise model to replicate the tissues' properties. In this work, we present a wound healing model focused on the proliferative stage that includes angiogenesis and wound contraction in three dimensions and which relies on the accurate representation of the mechanical behavior of the skin. Thus, an anisotropic hyperelastic model has been considered to analyze the effect of collagen fibers on the healing evolution of an ellipsoidal wound. The implemented model accounts for the contribution of the ground matrix and two mechanically equivalent families of fibers. Simulation results show the evolution of the cellular and chemical species in the wound and the wound volume evolution. Moreover, the local strain directions depend on the relative wound orientation with respect to the fibers.
Rotational discontinuities in anisotropic plasmas
International Nuclear Information System (INIS)
Omidi, N.
1992-01-01
The kinetic structure of rotational discontinuities (RDs) in anisotropic plasmas with T perpendicular /T parallel > 1 is investigated by using a one-dimensional electromagnetic hybrid code. To form the RD, a new approach is used where the plasma is injected from one boundary and reflected from the other, resulting in the generation of a traveling fast shock and an RD. Unlike the previously used methods, no a priori assumptions are made regarding the initial structure (i.e. width or sense of rotation) of the rotational discontinuity. The results show that across the RD both the magnetic field strength and direction, as well as the plasma density change. Given that such a change can also be associated with an intermediate shock, the Rankine-Hugoniot relations are used to confirm that the observed structures are indeed RDs. It is found that the thickness of RDs is a few ion inertial lengths and is independent of the rotation angle. Also, the preferred sense of rotation is in the electron sense; however, RDs with a rotation angle larger than 180 degree are found to be unstable, changing their rotation to a stable ion sense
Mechanics of anisotropic spring networks.
Zhang, T; Schwarz, J M; Das, Moumita
2014-12-01
We construct and analyze a model for a disordered linear spring network with anisotropy. The modeling is motivated by, for example, granular systems, nematic elastomers, and ultimately cytoskeletal networks exhibiting some underlying anisotropy. The model consists of a triangular lattice with two different bond occupation probabilities, p(x) and p(y), for the linear springs. We develop an effective medium theory (EMT) to describe the network elasticity as a function of p(x) and p(y). We find that the onset of rigidity in the EMT agrees with Maxwell constraint counting. We also find beyond linear behavior in the shear and bulk modulus as a function of occupation probability in the rigid phase for small strains, which differs from the isotropic case. We compare our EMT with numerical simulations to find rather good agreement. Finally, we discuss the implications of extending the reach of effective medium theory as well as draw connections with prior work on both anisotropic and isotropic spring networks.
CT and MRI-based door-needle-times for acute stroke patients a quasi-randomized clinical trial
DEFF Research Database (Denmark)
Hansen, Christine Krarup; Christensen, Anders; Rodgers, Helen
2017-01-01
OBJECTIVES: Door-Needle-times (DNT) of 20min are feasible when Computer Tomography (CT) is used for first-line brain-imaging to assess stroke-patients' eligibility for intravenous-tissue-Plasminogen-Activator (iv-tPA), but the more time-consuming Magnetic Resonance Imaging (MRI)-based-evaluation ......OBJECTIVES: Door-Needle-times (DNT) of 20min are feasible when Computer Tomography (CT) is used for first-line brain-imaging to assess stroke-patients' eligibility for intravenous-tissue-Plasminogen-Activator (iv-tPA), but the more time-consuming Magnetic Resonance Imaging (MRI...
Anisotropic evaluation of synthetic surgical meshes.
Saberski, E R; Orenstein, S B; Novitsky, Y W
2011-02-01
The material properties of meshes used in hernia repair contribute to the overall mechanical behavior of the repair. The anisotropic potential of synthetic meshes, representing a difference in material properties (e.g., elasticity) in different material axes, is not well defined to date. Haphazard orientation of anisotropic mesh material can contribute to inconsistent surgical outcomes. We aimed to characterize and compare anisotropic properties of commonly used synthetic meshes. Six different polypropylene (Trelex(®), ProLite™, Ultrapro™), polyester (Parietex™), and PTFE-based (Dualmesh(®), Infinit) synthetic meshes were selected. Longitudinal and transverse axes were defined for each mesh, and samples were cut in each axis orientation. Samples underwent uniaxial tensile testing, from which the elastic modulus (E) in each axis was determined. The degree of anisotropy (λ) was calculated as a logarithmic expression of the ratio between the elastic modulus in each axis. Five of six meshes displayed significant anisotropic behavior. Ultrapro™ and Infinit exhibited approximately 12- and 20-fold differences between perpendicular axes, respectively. Trelex(®), ProLite™, and Parietex™ were 2.3-2.4 times. Dualmesh(®) was the least anisotropic mesh, without marked difference between the axes. Anisotropy of synthetic meshes has been underappreciated. In this study, we found striking differences between elastic properties of perpendicular axes for most commonly used synthetic meshes. Indiscriminate orientation of anisotropic mesh may adversely affect hernia repairs. Proper labeling of all implants by manufacturers should be mandatory. Understanding the specific anisotropic behavior of synthetic meshes should allow surgeons to employ rational implant orientation to maximize outcomes of hernia repair.
Yamada, Takashi; Hashimoto, Ryu-Ichiro; Yahata, Noriaki; Ichikawa, Naho; Yoshihara, Yujiro; Okamoto, Yasumasa; Kato, Nobumasa; Takahashi, Hidehiko; Kawato, Mitsuo
2017-10-01
Psychiatric research has been hampered by an explanatory gap between psychiatric symptoms and their neural underpinnings, which has resulted in poor treatment outcomes. This situation has prompted us to shift from symptom-based diagnosis to data-driven diagnosis, aiming to redefine psychiatric disorders as disorders of neural circuitry. Promising candidates for data-driven diagnosis include resting-state functional connectivity MRI (rs-fcMRI)-based biomarkers. Although biomarkers have been developed with the aim of diagnosing patients and predicting the efficacy of therapy, the focus has shifted to the identification of biomarkers that represent therapeutic targets, which would allow for more personalized treatment approaches. This type of biomarker (i.e., "theranostic biomarker") is expected to elucidate the disease mechanism of psychiatric conditions and to offer an individualized neural circuit-based therapeutic target based on the neural cause of a condition. To this end, researchers have developed rs-fcMRI-based biomarkers and investigated a causal relationship between potential biomarkers and disease-specific behavior using functional MRI (fMRI)-based neurofeedback on functional connectivity. In this review, we introduce a recent approach for creating a theranostic biomarker, which consists mainly of 2 parts: (1) developing an rs-fcMRI-based biomarker that can predict diagnosis and/or symptoms with high accuracy, and (2) the introduction of a proof-of-concept study investigating the relationship between normalizing the biomarker and symptom changes using fMRI-based neurofeedback. In parallel with the introduction of recent studies, we review rs-fcMRI-based biomarker and fMRI-based neurofeedback, focusing on the technological improvements and limitations associated with clinical use. © The Author 2017. Published by Oxford University Press on behalf of CINP.
Numerical simulation of anisotropic polymeric foams
Directory of Open Access Journals (Sweden)
Volnei Tita
Full Text Available This paper shows in detail the modelling of anisotropic polymeric foam under compression and tension loadings, including discussions on isotropic material models and the entire procedure to calibrate the parameters involved. First, specimens of poly(vinyl chloride (PVC foam were investigated through experimental analyses in order to understand the mechanical behavior of this anisotropic material. Then, isotropic material models available in the commercial software AbaqusTM were investigated in order to verify their ability to model anisotropic foams and how the parameters involved can influence the results. Due to anisotropy, it is possible to obtain different values for the same parameter in the calibration process. The obtained set of parameters are used to calibrate the model according to the application of the structure. The models investigated showed minor and major limitations to simulate the mechanical behavior of anisotropic PVC foams under compression, tension and multi-axial loadings. Results show that the calibration process and the choice of the material model applied to the polymeric foam can provide good quantitative results and save project time. Results also indicate what kind and order of error one will get if certain choices are made throughout the modelling process. Finally, even though the developed calibration procedure is applied to specific PVC foam, it still outlines a very broad drill to analyze other anisotropic cellular materials.
Effective medium theory for anisotropic metamaterials
Zhang, Xiujuan
2015-01-20
Materials with anisotropic material parameters can be utilized to fabricate many fascinating devices, such as hyperlenses, metasolids, and one-way waveguides. In this study, we analyze the effects of geometric anisotropy on a two-dimensional metamaterial composed of a rectangular array of elliptic cylinders and derive an effective medium theory for such a metamaterial. We find that it is possible to obtain a closed-form analytical solution for the anisotropic effective medium parameters, provided the aspect ratio of the lattice and the eccentricity of the elliptic cylinder satisfy certain conditions. The derived effective medium theory not only recovers the well-known Maxwell-Garnett results in the quasi-static regime, but is also valid beyond the long-wavelength limit, where the wavelength in the host medium is comparable to the size of the lattice so that previous anisotropic effective medium theories fail. Such an advance greatly broadens the applicable realm of the effective medium theory and introduces many possibilities in the design of structures with desired anisotropic material characteristics. A real sample of a recently theoretically proposed anisotropic medium, with a near-zero index to control the flux, is achieved using the derived effective medium theory, and control of the electromagnetic waves in the sample is clearly demonstrated.
Strassburg, Joachim; Junginger, Theo; Trinh, Trong; Püttcher, Olaf; Oberholzer, Katja; Heald, Richard J; Hermanek, Paul
2008-11-01
Is it possible to reduce the frequency of neoadjuvant therapy for rectal carcinoma and nevertheless achieve a rate of more than 90% circumferential resection margin (CRM)-negative resection specimens by a novel concept of magnetic resonance imaging (MRI)-based therapy planning? One hundred eighty-one patients from Berlin and Mainz, Germany, with primary rectal carcinoma, without distant metastasis, underwent radical surgery with curative intention. Surgical procedures applied were anterior resection with total mesorectal excision (TME) or partial mesorectal excision (PME; PME for tumours of the upper rectum) or abdominoperineal excision with TME. With MRI selection of the highest-risk cases, neoadjuvant therapy was given to only 62 of 181 (34.3%). The rate of CRM-negative resection specimens on histology was 170 of 181 (93.9%) for all patients, and in Berlin, only 1 of 93 (1%) specimens was CRM-positive. Patients selected for primary surgery had CRM-negative specimens on histology in 114 of 119 (95.8%). Those selected for neoadjuvant therapy had a lower rate of clear margin: 56 of 62 (90%). By applying a MRI-based indication, the frequency of neoadjuvant treatment with its acute and late adverse effects can be reduced to 30-35% without reduction of pathologically CRM-negative resection specimens and, thus, without the danger of worsening the oncological long-term results. This concept should be confirmed in prospective multicentre observation studies with quality assurance of MRI, surgery and pathology.
Obtuse triangle suppression in anisotropic meshes
Sun, Feng; Choi, Yi King; Wang, Wen Ping; Yan, Dongming; Liu, Yang; Lé vy, Bruno L.
2011-01-01
Anisotropic triangle meshes are used for efficient approximation of surfaces and flow data in finite element analysis, and in these applications it is desirable to have as few obtuse triangles as possible to reduce the discretization error. We present a variational approach to suppressing obtuse triangles in anisotropic meshes. Specifically, we introduce a hexagonal Minkowski metric, which is sensitive to triangle orientation, to give a new formulation of the centroidal Voronoi tessellation (CVT) method. Furthermore, we prove several relevant properties of the CVT method with the newly introduced metric. Experiments show that our algorithm produces anisotropic meshes with much fewer obtuse triangles than using existing methods while maintaining mesh anisotropy. © 2011 Elsevier B.V. All rights reserved.
Elastic properties of spherically anisotropic piezoelectric composites
International Nuclear Information System (INIS)
En-Bo, Wei; Guo-Qing, Gu; Ying-Ming, Poon
2010-01-01
Effective elastic properties of spherically anisotropic piezoelectric composites, whose spherically anisotropic piezoelectric inclusions are embedded in an infinite non-piezoelectric matrix, are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials under a uniform external strain are derived exactly. Taking into account of the coupling effects of elasticity, permittivity and piezoelectricity, the formula is derived for estimating the effective elastic properties based on the average field theory in the dilute limit. An elastic response mechanism is revealed, in which the effective elastic properties increase as inclusion piezoelectric properties increase and inclusion dielectric properties decrease. Moreover, a piezoelectric response mechanism, of which the effective piezoelectric response vanishes due to the symmetry of spherically anisotropic composite, is also disclosed. (condensed matter: structure, thermal and mechanical properties)
Obtuse triangle suppression in anisotropic meshes
Sun, Feng
2011-12-01
Anisotropic triangle meshes are used for efficient approximation of surfaces and flow data in finite element analysis, and in these applications it is desirable to have as few obtuse triangles as possible to reduce the discretization error. We present a variational approach to suppressing obtuse triangles in anisotropic meshes. Specifically, we introduce a hexagonal Minkowski metric, which is sensitive to triangle orientation, to give a new formulation of the centroidal Voronoi tessellation (CVT) method. Furthermore, we prove several relevant properties of the CVT method with the newly introduced metric. Experiments show that our algorithm produces anisotropic meshes with much fewer obtuse triangles than using existing methods while maintaining mesh anisotropy. © 2011 Elsevier B.V. All rights reserved.
Generalized Fractional Derivative Anisotropic Viscoelastic Characterization
Directory of Open Access Journals (Sweden)
Harry H. Hilton
2012-01-01
Full Text Available Isotropic linear and nonlinear fractional derivative constitutive relations are formulated and examined in terms of many parameter generalized Kelvin models and are analytically extended to cover general anisotropic homogeneous or non-homogeneous as well as functionally graded viscoelastic material behavior. Equivalent integral constitutive relations, which are computationally more powerful, are derived from fractional differential ones and the associated anisotropic temperature-moisture-degree-of-cure shift functions and reduced times are established. Approximate Fourier transform inversions for fractional derivative relations are formulated and their accuracy is evaluated. The efficacy of integer and fractional derivative constitutive relations is compared and the preferential use of either characterization in analyzing isotropic and anisotropic real materials must be examined on a case-by-case basis. Approximate protocols for curve fitting analytical fractional derivative results to experimental data are formulated and evaluated.
Anisotropic nanomaterials preparation, properties, and applications
Li, Quan
2015-01-01
In this book anisotropic one-dimensional and two-dimensional nanoscale building blocks and their assembly into fascinating and qualitatively new functional structures embracing both hard and soft components are explained. Contributions from leading experts regarding important aspects like synthesis, assembly, properties and applications of the above materials are compiled into a reference book. The anisotropy, i.e. the direction-dependent physical properties, of materials is fascinating and elegant and has sparked the quest for anisotropic materials with useful properties. With such a curiosi
Anisotropic Intervalley Plasmon Excitations in Graphene
International Nuclear Information System (INIS)
Chen Jian; Xu Huai-Zhe
2015-01-01
We investigate theoretically the intervalley plasmon excitations (IPEs) in graphene monolayer within the random-phase approximation. We derive an analytical expression of the real part of the dielectric function. We find a low-energy plasmon mode with a linear anisotropic dispersion which depends on the Fermi energy and the dielectric constant of substrate. The IPEs show strongly anisotropic behavior, which becomes significant around the zigzag crystallographic direction. More interestingly, the group velocity of IPE varies from negative to positive, and vanishes at special energy. (paper)
On cracking of charged anisotropic polytropes
Energy Technology Data Exchange (ETDEWEB)
Azam, M. [Division of Science and Technology, University of Education, Township Campus, Lahore-54590 (Pakistan); Mardan, S.A., E-mail: azam.math@ue.edu.pk, E-mail: syedalimardanazmi@yahoo.com [Department of Mathematics, University of the Management and Technology, C-II, Johar Town, Lahore-54590 (Pakistan)
2017-01-01
Recently in [1], the role of electromagnetic field on the cracking of spherical polytropes has been investigated without perturbing charge parameter explicitly. In this study, we have examined the occurrence of cracking of anisotropic spherical polytropes through perturbing parameters like anisotropic pressure, energy density and charge. We consider two different types of polytropes in this study. We discuss the occurrence of cracking in two different ways ( i ) by perturbing polytropic constant, anisotropy and charge parameter ( ii ) by perturbing polytropic index, anisotropy and charge parameter for each case. We conclude that cracking appears for a wide range of parameters in both cases. Also, our results are reduced to [2] in the absence of charge.
Modelling of CMUTs with Anisotropic Plates
DEFF Research Database (Denmark)
la Cour, Mette Funding; Christiansen, Thomas Lehrmann; Jensen, Jørgen Arendt
2012-01-01
Traditionally, CMUTs are modelled using the isotropic plate equation and this leads to deviations between analytical calculations and FEM simulations. In this paper, the deflection profile and material parameters are calculated using the anisotropic plate equation. It is shown that the anisotropic...... calculations match perfectly with FEM while an isotropic approach causes up to 10% deviations in deflection profile. Furthermore, we show how commonly used analytic modelling methods such as static calculations of the pull-in voltage and dynamic modelling through an equivalent circuit representation can...
Sign rules for anisotropic quantum spin systems
International Nuclear Information System (INIS)
Bishop, R. F.; Farnell, D. J. J.; Parkinson, J. B.
2000-01-01
We present exact ''sign rules'' for various spin-s anisotropic spin-lattice models. It is shown that, after a simple transformation which utilizes these sign rules, the ground-state wave function of the transformed Hamiltonian is positive definite. Using these results exact statements for various expectation values of off-diagonal operators are presented, and transitions in the behavior of these expectation values are observed at particular values of the anisotropy. Furthermore, the importance of such sign rules in variational calculations and quantum Monte Carlo calculations is emphasized. This is illustrated by a simple variational treatment of a one-dimensional anisotropic spin model
Anisotropic wave-equation traveltime and waveform inversion
Feng, Shihang; Schuster, Gerard T.
2016-01-01
The wave-equation traveltime and waveform inversion (WTW) methodology is developed to invert for anisotropic parameters in a vertical transverse isotropic (VTI) meidum. The simultaneous inversion of anisotropic parameters v0, ε and δ is initially
International Nuclear Information System (INIS)
Wolf, T.; Anjorin, A.; Abolmaali, N.; Posselt, H.; Smaczny, C.; Vogl, T.J.
2009-01-01
Development of pulmonary arterial hypertension (PH) is a common problem in the course of patients suffering from cystic fibrosis (CF). This study was performed to evaluate MRI based flow measurements (MR venc ; Velocity ENCoding) to detect signs of an evolving PH in patients suffering from CF. 48 patients (median age: 16 years, range: 10 - 40 years, 25 female) suffering from CF of different severity (mean FEV1: 74 % ± 23, mean Shwachman-score: 63 ± 10) were examined using MRI based flow measurements of the main pulmonary artery (MPA). Phase-contrast flash sequences (TR: 9.6 ms, TE: 2.5 ms, bandwidth: 1395 Hertz/Pixel) were utilized. Results were compared to an age- and sex-matched group of 48 healthy subjects. Analyzed flow data where: heart frequency (HF), cardiac output (HZV), acceleration time (AT), proportional acceleration time related to heart rate (ATr), mean systolic blood velocity (MFG), peak velocity (Peak), maximum flow (Fluss max ), mean flow (Fluss mitt ) and distensibility (Dist). The comparison of means revealed significant differences only for MFG, Fluss max and Dist, but overlap was marked. However, using a scatter-plot of AT versus MFG, it was possible to identify five CF-patients demonstrating definite signs of PH: AT = 81 ms ± 14, MFG = 46 ± 11 cm/s, Dist = 41 % ± 7. These CF-patients where the most severely affected in the investigated group, two of them were listed for complete heart and lung transplantation. The comparison of this subgroup and the remaining CF-patients revealed a highly significant difference for the AT (p = 0.000001) without overlap. Screening of CF-patients for the development of PH using MR venc of the MPA is not possible. In later stages of disease, the quantification of AT, MFG and Dist in the MPA may be useful for the detection, follow-up and control of therapy of PH. MR venc of the MPA completes the MRI-based follow-up of lung parenchyma damage in patients suffering from CF. (orig.)
A Variational Approach to Perturbed Discrete Anisotropic Equations
Directory of Open Access Journals (Sweden)
Amjad Salari
2016-01-01
Full Text Available We continue the study of discrete anisotropic equations and we will provide new multiplicity results of the solutions for a discrete anisotropic equation. We investigate the existence of infinitely many solutions for a perturbed discrete anisotropic boundary value problem. The approach is based on variational methods and critical point theory.
Anisotropic diffusion in a toroidal geometry
International Nuclear Information System (INIS)
Fischer, Paul F
2005-01-01
As part of the Department of Energy's applications oriented SciDAC project, three model problems have been proposed by the Center for Extended Magnetohydrodynamics Modeling to test the potential of numerical algorithms for challenging magnetohydrodynamics (MHD) problems that are required for future fusion development. The first of these, anisotropic diffusion in a toroidal geometry, is considered in this note
Anisotropic Interactions between Cold Rydberg Atoms
2015-09-28
AFRL-AFOSR-CL-TR-2015-0002 Anisotropic interactions between cold Rydberg atoms Luis Marcassa INSTITUTO DE FISICA DE SAO CARLOS Final Report 09/28...problem with the report +551633739806 Organization / Institution name Instituto de Fisica de Sao Carlos Grant/Contract Title The full title of the
Adaptive slices for acquisition of anisotropic BRDF
Czech Academy of Sciences Publication Activity Database
Vávra, Radomír; Filip, Jiří
(2018) ISSN 2096-0433 R&D Projects: GA ČR GA17-18407S Institutional support: RVO:67985556 Keywords : anisotropic BRDF * slice * sampling Subject RIV: BD - Theory of Information http://library.utia.cas.cz/separaty/2018/RO/vavra-0486116.pdf
Anisotropic Hanle line shape via magnetothermoelectric phenomena
Das, Kumar; Dejene, Fasil; van Wees, Bart; Vera Marun, Ivan
2016-01-01
We observe anisotropic Hanle line shape with unequal in-plane and out-of-plane nonlocal signals for spin precession measurements carried out on lateral metallic spin valves with transparent interfaces. The conventional interpretation for this anisotropy corresponds to unequal spin relaxation times
Jets in a strongly coupled anisotropic plasma
Energy Technology Data Exchange (ETDEWEB)
Fadafan, Kazem Bitaghsir [Shahrood University of Technology, Faculty of Physics, Shahrood (Iran, Islamic Republic of); University of Southampton, STAG Research Centre Physics and Astronomy, Southampton (United Kingdom); Morad, Razieh [University of Cape Town, Department of Physics, Rondebosch (South Africa)
2018-01-15
In this paper, we study the dynamics of the light quark jet moving through the static, strongly coupled N = 4, anisotropic plasma with and without charge. The light quark is presented by a 2-parameters point-like initial condition falling string in the context of the AdS/CFT. We calculate the stopping distance of the light quark in the anisotropic medium and compare it with its isotropic value. We study the dependency of the stopping distance to the both string initial conditions and background parameters such as anisotropy parameter or chemical potential. Although the typical behavior of the string in the anisotropic medium is similar to the one in the isotropic AdS-Sch background, the string falls faster to the horizon depending on the direction of moving. Particularly, the enhancement of quenching is larger in the beam direction. We find that the suppression of stopping distance is more prominent when the anisotropic plasma have the same temperature as the isotropic plasma. (orig.)
Effective medium theory for anisotropic metamaterials
Zhang, Xiujuan; Wu, Ying
2015-01-01
-dimensional metamaterial composed of a rectangular array of elliptic cylinders and derive an effective medium theory for such a metamaterial. We find that it is possible to obtain a closed-form analytical solution for the anisotropic effective medium parameters, provided
Algebraic solution of an anisotropic nonquadratic potential
International Nuclear Information System (INIS)
Boschi Filho, H.; Vaidya, A.N.
1990-06-01
We show that an anisotropic nonquadratic potential, for which a path integral treatment had been recently discussed in the literature, possesses the (SO(2,1)xSO(2,1))ΛSO(2,1) dynamical symmetry and constructs its Green function algebraically. A particular case which generates new eigenvalues and eigenfunctions is also discussed. (author). 11 refs
Nonlinear anisotropic parabolic equations in Lm
Directory of Open Access Journals (Sweden)
Fares Mokhtari
2014-01-01
Full Text Available In this paper, we give a result of regularity of weak solutions for a class of nonlinear anisotropic parabolic equations with lower-order term when the right-hand side is an Lm function, with m being ”small”. This work generalizes some results given in [2] and [3].
Casimir interactions for anisotropic magnetodielectric metamaterials
Energy Technology Data Exchange (ETDEWEB)
Da Rosa, Felipe S [Los Alamos National Laboratory; Dalvit, Diego A [Los Alamos National Laboratory; Milonni, Peter W [Los Alamos National Laboratory
2008-01-01
We extend our previous work on the generalization of the Casimir-Lifshitz theory to treat anisotropic magnetodielectric media, focusing on the forces between metals and magnetodielectric metamaterials and on the possibility of inferring magnetic effects by measurements of these forces.
Hydraulic fracturing in anisotropic and heterogeneous rocks
Valliappan, V.; Remmers, J.J.C.; Barnhoorn, A.; Smeulders, D.M.J.
2017-01-01
In this paper, we present a two dimensional model for modelling the hydraulic fracture process in anisotropic and heterogeneous rocks. The model is formulated using extended finite elements (XFEM) in combination with Newton-Raphson method for spatial and Euler's implicit scheme for time. The
Spin Wave Theory of Strongly Anisotropic Magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1977-01-01
A strong anisotropy gives rise to a non-spherical precession of the spins with different amplitudes in the x and y directions. The highly anharmonic exchange interaction thereby becomes effectively anisotropic. The possibility of detecting a genuine two-ion anisotropy is discussed, and comments...
On characterization of anisotropic plant protein structures
Krintiras, G.A.; Göbel, J.; Bouwman, W.G.; Goot, van der A.J.; Stefanidis, G.D.
2014-01-01
In this paper, a set of complementary techniques was used to characterize surface and bulk structures of an anisotropic Soy Protein Isolate (SPI)–vital wheat gluten blend after it was subjected to heat and simple shear flow in a Couette Cell. The structured biopolymer blend can form a basis for a
Data-driven imaging in anisotropic media
Energy Technology Data Exchange (ETDEWEB)
Volker, Arno; Hunter, Alan [TNO Stieltjes weg 1, 2600 AD, Delft (Netherlands)
2012-05-17
Anisotropic materials are being used increasingly in high performance industrial applications, particularly in the aeronautical and nuclear industries. Some important examples of these materials are composites, single-crystal and heavy-grained metals. Ultrasonic array imaging in these materials requires exact knowledge of the anisotropic material properties. Without this information, the images can be adversely affected, causing a reduction in defect detection and characterization performance. The imaging operation can be formulated in two consecutive and reciprocal focusing steps, i.e., focusing the sources and then focusing the receivers. Applying just one of these focusing steps yields an interesting intermediate domain. The resulting common focus point gather (CFP-gather) can be interpreted to determine the propagation operator. After focusing the sources, the observed travel-time in the CFP-gather describes the propagation from the focus point to the receivers. If the correct propagation operator is used, the measured travel-times should be the same as the time-reversed focusing operator due to reciprocity. This makes it possible to iteratively update the focusing operator using the data only and allows the material to be imaged without explicit knowledge of the anisotropic material parameters. Furthermore, the determined propagation operator can also be used to invert for the anisotropic medium parameters. This paper details the proposed technique and demonstrates its use on simulated array data from a specimen of Inconel single-crystal alloy commonly used in the aeronautical and nuclear industries.
Acoustic anisotropic wavefields through perturbation theory
Alkhalifah, Tariq Ali
2013-01-01
these restrictions are the inability to handle media with η<0 and the presence of shear-wave artifacts in the solution. Both limitations do not exist in the solution of the elliptical anisotropic acoustic wave equation. Using perturbation theory in developing
Modelling anisotropic water transport in polymer composite
Indian Academy of Sciences (India)
This work reports anisotropic water transport in a polymer composite consisting of an epoxy matrix reinforced with aligned triangular bars made of vinyl ester. By gravimetric experiments, water diffusion in resin and polymer composites were characterized. Parameters for Fickian diffusion and polymer relaxation models were ...
Directory of Open Access Journals (Sweden)
Krystyna Anna Mathiak
2015-06-01
Full Text Available Neurofeedback (NF based on real-time functional magnetic resonance imaging (rt-fMRI allows voluntary regulation of the activity in a selected brain region. For the training of this regulation, a well-designed feedback system is required. Social reward may serve as an effective incentive in NF paradigms, but its efficiency has not yet been tested. Therefore, we developed a social reward NF paradigm and assessed it in comparison with a typical visual NF paradigm (moving bar.We trained 24 healthy participants, on three consecutive days, to control activation in dorsal anterior cingulate cortex (ACC with fMRI-based NF. In the social feedback group, an avatar gradually smiled when ACC activity increased, whereas in the standard feedback group, a moving bar indicated the activation level. To assess a transfer of the NF training both groups were asked to up-regulate their brain activity without receiving feedback immediately before and after the NF training (pre- and post-test. Finally, the effect of the acquired NF training on ACC function was evaluated in a cognitive interference task (Simon task during the pre- and post-test.Social reward led to stronger activity in the ACC and reward-related areas during the NF training when compared to standard feedback. After the training, both groups were able to regulate ACC without receiving feedback, with a trend for stronger responses in the social feedback group. Moreover, despite a lack of behavioral differences, significant higher ACC activations emerged in the cognitive interference task, reflecting a stronger generalization of the NF training on cognitive interference processing after social feedback.Social reward can increase self-regulation in fMRI-based NF and strengthen its effects on neural processing in related tasks, such as cognitive interference. An advantage of social feedback is that a direct external reward is provided as in natural social interactions, opening perspectives for implicit
Directory of Open Access Journals (Sweden)
Anna Zilverstand
Full Text Available The goal of neurofeedback training is to provide participants with relevant information on their ongoing brain processes in order to enable them to change these processes in a meaningful way. Under the assumption of an intrinsic brain-behavior link, neurofeedback can be a tool to guide a participant towards a desired behavioral state, such as a healthier state in the case of patients. Current research in clinical neuroscience regarding the most robust indicators of pathological brain processes in psychiatric and neurological disorders indicates that fMRI-based functional connectivity measures may be among the most important biomarkers of disease. The present study therefore investigated the general potential of providing fMRI neurofeedback based on functional correlations, computed from short-window time course data at the level of single task periods. The ability to detect subtle changes in task performance with block-wise functional connectivity measures was evaluated based on imaging data from healthy participants performing a simple motor task, which was systematically varied along two task dimensions representing two different aspects of task difficulty. The results demonstrate that fMRI-based functional connectivity measures may provide a better indicator for an increase in overall (motor task difficulty than activation level-based measures. Windowed functional correlations thus seem to provide relevant and unique information regarding ongoing brain processes, which is not captured equally well by standard activation level-based neurofeedback measures. Functional connectivity markers, therefore, may indeed provide a valuable tool to enhance and monitor learning within an fMRI neurofeedback setup.
Hellmeier, Florian; Nordmeyer, Sarah; Yevtushenko, Pavlo; Bruening, Jan; Berger, Felix; Kuehne, Titus; Goubergrits, Leonid; Kelm, Marcus
2018-01-01
Modeling different treatment options before a procedure is performed is a promising approach for surgical decision making and patient care in heart valve disease. This study investigated the hemodynamic impact of different prostheses through patient-specific MRI-based CFD simulations. Ten time-resolved MRI data sets with and without velocity encoding were obtained to reconstruct the aorta and set hemodynamic boundary conditions for simulations. Aortic hemodynamics after virtual valve replacement with a biological and mechanical valve prosthesis were investigated. Wall shear stress (WSS), secondary flow degree (SFD), transvalvular pressure drop (TPD), turbulent kinetic energy (TKE), and normalized flow displacement (NFD) were evaluated to characterize valve-induced hemodynamics. The biological prostheses induced significantly higher WSS (medians: 9.3 vs. 8.6 Pa, P = 0.027) and SFD (means: 0.78 vs. 0.49, P = 0.002) in the ascending aorta, TPD (medians: 11.4 vs. 2.7 mm Hg, P = 0.002), TKE (means: 400 vs. 283 cm 2 /s 2 , P = 0.037), and NFD (means: 0.0994 vs. 0.0607, P = 0.020) than the mechanical prostheses. The differences between the prosthesis types showed great inter-patient variability, however. Given this variability, a patient-specific evaluation is warranted. In conclusion, MRI-based CFD offers an opportunity to assess the interactions between prosthesis and patient-specific boundary conditions, which may help in optimizing surgical decision making and providing additional guidance to clinicians. © 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.
International Nuclear Information System (INIS)
Rank, Christopher M; Tremmel, Christoph; Hünemohr, Nora; Nagel, Armin M; Jäkel, Oliver; Greilich, Steffen
2013-01-01
In order to benefit from the highly conformal irradiation of tumors in ion radiotherapy, sophisticated treatment planning and simulation are required. The purpose of this study was to investigate the potential of MRI for ion radiotherapy treatment plan simulation and adaptation using a classification-based approach. Firstly, a voxelwise tissue classification was applied to derive pseudo CT numbers from MR images using up to 8 contrasts. Appropriate MR sequences and parameters were evaluated in cross-validation studies of three phantoms. Secondly, ion radiotherapy treatment plans were optimized using both MRI-based pseudo CT and reference CT and recalculated on reference CT. Finally, a target shift was simulated and a treatment plan adapted to the shift was optimized on a pseudo CT and compared to reference CT optimizations without plan adaptation. The derivation of pseudo CT values led to mean absolute errors in the range of 81 - 95 HU. Most significant deviations appeared at borders between air and different tissue classes and originated from partial volume effects. Simulations of ion radiotherapy treatment plans using pseudo CT for optimization revealed only small underdosages in distal regions of a target volume with deviations of the mean dose of PTV between 1.4 - 3.1% compared to reference CT optimizations. A plan adapted to the target volume shift and optimized on the pseudo CT exhibited a comparable target dose coverage as a non-adapted plan optimized on a reference CT. We were able to show that a MRI-based derivation of pseudo CT values using a purely statistical classification approach is feasible although no physical relationship exists. Large errors appeared at compact bone classes and came from an imperfect distinction of bones and other tissue types in MRI. In simulations of treatment plans, it was demonstrated that these deviations are comparable to uncertainties of a target volume shift of 2 mm in two directions indicating that especially
Views on the Anisotropic Nature of Ilva Valley Region
Directory of Open Access Journals (Sweden)
GABRIELA-ALINA MUREŞAN
2012-01-01
Full Text Available There are two concepts important for the authors of this article: anisotropic region and anisotropic space. Anisotropic region is defined by A. Dauphiné, the geographer (-mathematician, as a territorial unit whose structure results from the organisation of space along one or more axes. From the point of view of a territorial system, this type of region has some characteristics which differentiate it both from the homogeneous region and from the polarised one. These specificities have been analysed for Ilva Valley. The region of Ilva Valley is formed along the morphological axis represented by the Ilva River. The aim is to identify these specificities or their absence within this region. In this way we can determine whether this region is an anisotropic one or just an anisotropic space, namely whether it can be considered as evolving towards an anisotropic region, not yet complying with all characteristics of anisotropic regions.
Wireless energy transfer between anisotropic metamaterials shells
Energy Technology Data Exchange (ETDEWEB)
Díaz-Rubio, Ana; Carbonell, Jorge; Sánchez-Dehesa, José, E-mail: jsdehesa@upv.es
2014-06-15
The behavior of strongly coupled Radial Photonic Crystals shells is investigated as a potential alternative to transfer electromagnetic energy wirelessly. These sub-wavelength resonant microstructures, which are based on anisotropic metamaterials, can produce efficient coupling phenomena due to their high quality factor. A configuration of selected constitutive parameters (permittivity and permeability) is analyzed in terms of its resonant characteristics. The coupling to loss ratio between two coupled resonators is calculated as a function of distance, the maximum (in excess of 300) is obtained when the shells are separated by three times their radius. Under practical conditions an 83% of maximum power transfer has been also estimated. -- Highlights: •Anisotropic metamaterial shells exhibit high quality factors and sub-wavelength size. •Exchange of electromagnetic energy between shells with high efficiency is analyzed. •Strong coupling is supported with high wireless transfer efficiency. •End-to-end energy transfer efficiencies higher than 83% can be predicted.
Wireless energy transfer between anisotropic metamaterials shells
International Nuclear Information System (INIS)
Díaz-Rubio, Ana; Carbonell, Jorge; Sánchez-Dehesa, José
2014-01-01
The behavior of strongly coupled Radial Photonic Crystals shells is investigated as a potential alternative to transfer electromagnetic energy wirelessly. These sub-wavelength resonant microstructures, which are based on anisotropic metamaterials, can produce efficient coupling phenomena due to their high quality factor. A configuration of selected constitutive parameters (permittivity and permeability) is analyzed in terms of its resonant characteristics. The coupling to loss ratio between two coupled resonators is calculated as a function of distance, the maximum (in excess of 300) is obtained when the shells are separated by three times their radius. Under practical conditions an 83% of maximum power transfer has been also estimated. -- Highlights: •Anisotropic metamaterial shells exhibit high quality factors and sub-wavelength size. •Exchange of electromagnetic energy between shells with high efficiency is analyzed. •Strong coupling is supported with high wireless transfer efficiency. •End-to-end energy transfer efficiencies higher than 83% can be predicted
Selective optical transmission in anisotropic multilayers structure
International Nuclear Information System (INIS)
Ouchani, N.; Bria, D.; Nougaoui, A.; Merad, A.E.
2007-08-01
We developed a Green's function method to study theoretically a single-defect photonic crystal composed of anisotropic dielectric materials. This structure can trap light of a given frequency range and filter only a certain frequency light with a very high quality. It is shown that the defect modes appear as peaks in the transmission spectrum. Their intensities and frequency positions depend on the incidence angle and the orientation of the principal axes of layers consisting of the superlattice and the layer defect. Our structure offers a great variety of possibilities for creating and controlling the number and transmitted intensities of defect modes. It can be a good candidate for realizing a selective electromagnetic filter. In addition to this filtration process, the defective anisotropic photonic crystal can be used to switch the modes when appropriate geometry is selected. (author)
Cosmological signatures of anisotropic spatial curvature
International Nuclear Information System (INIS)
Pereira, Thiago S.; Marugán, Guillermo A. Mena; Carneiro, Saulo
2015-01-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature
Cosmological signatures of anisotropic spatial curvature
Energy Technology Data Exchange (ETDEWEB)
Pereira, Thiago S. [Departamento de Física, Universidade Estadual de Londrina, 86057-970, Londrina – PR (Brazil); Marugán, Guillermo A. Mena [Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006, Madrid (Spain); Carneiro, Saulo, E-mail: tspereira@uel.br, E-mail: mena@iem.cfmac.csic.es, E-mail: saulo.carneiro@pq.cnpq.br [Instituto de Física, Universidade Federal da Bahia, 40210-340, Salvador – BA (Brazil)
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Anisotropic conducting films for electromagnetic radiation applications
Cavallo, Francesca; Lagally, Max G.; Rojas-Delgado, Richard
2015-06-16
Electronic devices for the generation of electromagnetic radiation are provided. Also provided are methods for using the devices to generate electromagnetic radiation. The radiation sources include an anisotropic electrically conducting thin film that is characterized by a periodically varying charge carrier mobility in the plane of the film. The periodic variation in carrier mobility gives rise to a spatially varying electric field, which produces electromagnetic radiation as charged particles pass through the film.
Anisotropic cosmological solutions in massive vector theories
Energy Technology Data Exchange (ETDEWEB)
Heisenberg, Lavinia [Institute for Theoretical Studies, ETH Zurich, Clausiusstrasse 47, 8092 Zurich (Switzerland); Kase, Ryotaro; Tsujikawa, Shinji, E-mail: Lavinia.heisenberg@googlemail.com, E-mail: r.kase@rs.tus.ac.jp, E-mail: shinji@rs.kagu.tus.ac.jp [Department of Physics, Faculty of Science, Tokyo University of Science, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan)
2016-11-01
In beyond-generalized Proca theories including the extension to theories higher than second order, we study the role of a spatial component v of a massive vector field on the anisotropic cosmological background. We show that, as in the case of the isotropic cosmological background, there is no additional ghostly degrees of freedom associated with the Ostrogradski instability. In second-order generalized Proca theories we find the existence of anisotropic solutions on which the ratio between the anisotropic expansion rate Σ and the isotropic expansion rate H remains nearly constant in the radiation-dominated epoch. In the regime where Σ/ H is constant, the spatial vector component v works as a dark radiation with the equation of state close to 1/3. During the matter era, the ratio Σ/ H decreases with the decrease of v . As long as the conditions |Σ| || H and v {sup 2} || φ{sup 2} are satisfied around the onset of late-time cosmic acceleration, where φ is the temporal vector component, we find that the solutions approach the isotropic de Sitter fixed point (Σ = 0 = v ) in accordance with the cosmic no-hair conjecture. In the presence of v and Σ the early evolution of the dark energy equation of state w {sub DE} in the radiation era is different from that in the isotropic case, but the approach to the isotropic value w {sub DE}{sup (iso)} typically occurs at redshifts z much larger than 1. Thus, apart from the existence of dark radiation, the anisotropic cosmological dynamics at low redshifts is similar to that in isotropic generalized Proca theories. In beyond-generalized Proca theories the only consistent solution to avoid the divergence of a determinant of the dynamical system corresponds to v = 0, so Σ always decreases in time.
Acoustic anisotropic wavefields through perturbation theory
Alkhalifah, Tariq Ali
2013-09-01
Solving the anisotropic acoustic wave equation numerically using finite-difference methods introduces many problems and media restriction requirements, and it rarely contributes to the ability to resolve the anisotropy parameters. Among these restrictions are the inability to handle media with η<0 and the presence of shear-wave artifacts in the solution. Both limitations do not exist in the solution of the elliptical anisotropic acoustic wave equation. Using perturbation theory in developing the solution of the anisotropic acoustic wave equation allows direct access to the desired limitation-free solutions, that is, solutions perturbed from the elliptical anisotropic background medium. It also provides a platform for parameter estimation because of the ability to isolate the wavefield dependency on the perturbed anisotropy parameters. As a result, I derive partial differential equations that relate changes in the wavefield to perturbations in the anisotropy parameters. The solutions of the perturbation equations represented the coefficients of a Taylor-series-type expansion of the wavefield as a function of the perturbed parameter, which is in this case η or the tilt of the symmetry axis. The expansion with respect to the symmetry axis allows use of an acoustic transversely isotropic media with a vertical symmetry axis (VTI) kernel to estimate the background wavefield and the corresponding perturbation coefficients. The VTI extrapolation kernel is about one-fourth the cost of the transversely isotropic model with a tilt in the symmetry axis kernel. Thus, for a small symmetry axis tilt, the cost of migration using a first-order expansion can be reduced. The effectiveness of the approach was demonstrated on the Marmousi model.
Entanglement of periodic anisotropic XY chains
International Nuclear Information System (INIS)
Zhang Lifa; Tong Peiqing
2005-01-01
By using the concept of concurrence, the entanglement of periodic anisotropic XY chains in a transverse field is studied numerically. It is found that the derivatives ∂ λ C(1) of nearest-neighbour concurrence diverge at quantum critical points. By proper scaling, we found that all the derivatives ∂ λ C(1) for periodic XY chains in the vicinity of quantum critical points have the same behaviours as that of a uniform chain
Surface instabilities during straining of anisotropic materials
DEFF Research Database (Denmark)
Legarth, Brian Nyvang; Richelsen, Ann Bettina
2006-01-01
The development of instabilities in traction-free surfaces is investigated numerically using a unit cell model. Full finite strain analyses are conducted using isotropic as well as anisotropic yield criteria and both plane strain tension and compression are considered. In the load range of tensio...... of principal overall strain. For other orientations surface instabilities are seen when non-associated plastic flow is taken into account. Compared to tension, smaller compressive deformations are needed in order to initiate a surface instability....
Symmetry analysis for anisotropic field theories
International Nuclear Information System (INIS)
Parra, Lorena; Vergara, J. David
2012-01-01
The purpose of this paper is to study with the help of Noether's theorem the symmetries of anisotropic actions for arbitrary fields which generally depend on higher order spatial derivatives, and to find the corresponding current densities and the Noether charges. We study in particular scale invariance and consider the cases of higher derivative extensions of the scalar field, electrodynamics and Chern-Simons theory.
Electromagnetic effects on cracking of anisotropic polytropes
Energy Technology Data Exchange (ETDEWEB)
Sharif, Muhammad; Sadiq, Sobia [University of the Punjab, Department of Mathematics, Lahore (Pakistan)
2016-10-15
In this paper, we study the electromagnetic effects on the stability of a spherically symmetric anisotropic fluid distribution satisfying two polytropic equations of state and construct the corresponding generalized Tolman-Oppenheimer-Volkoff equations. We apply perturbations on matter variables via the polytropic constant as well as the polytropic index and formulate the force distribution function. It is found that the compact object is stable for a feasible choice of perturbed polytropic index in the presence of charge. (orig.)
Anisotropic diffusion tensor applied to temporal mammograms
DEFF Research Database (Denmark)
Karemore, Gopal; Brandt, Sami; Sporring, Jon
2010-01-01
changes related to specific effects like Hormonal Replacement Therapy (HRT) and aging. Given effect-grouped patient data, we demonstrated how anisotropic diffusion tensor and its coherence features computed in an anatomically oriented breast coordinate system followed by statistical learning...
Anisotropic cosmological solutions in massive vector theories
International Nuclear Information System (INIS)
Heisenberg, Lavinia; Kase, Ryotaro; Tsujikawa, Shinji
2016-01-01
In beyond-generalized Proca theories including the extension to theories higher than second order, we study the role of a spatial component v of a massive vector field on the anisotropic cosmological background. We show that, as in the case of the isotropic cosmological background, there is no additional ghostly degrees of freedom associated with the Ostrogradski instability. In second-order generalized Proca theories we find the existence of anisotropic solutions on which the ratio between the anisotropic expansion rate Σ and the isotropic expansion rate H remains nearly constant in the radiation-dominated epoch. In the regime where Σ/ H is constant, the spatial vector component v works as a dark radiation with the equation of state close to 1/3. During the matter era, the ratio Σ/ H decreases with the decrease of v . As long as the conditions |Σ| || H and v 2 || φ 2 are satisfied around the onset of late-time cosmic acceleration, where φ is the temporal vector component, we find that the solutions approach the isotropic de Sitter fixed point (Σ = 0 = v ) in accordance with the cosmic no-hair conjecture. In the presence of v and Σ the early evolution of the dark energy equation of state w DE in the radiation era is different from that in the isotropic case, but the approach to the isotropic value w DE (iso) typically occurs at redshifts z much larger than 1. Thus, apart from the existence of dark radiation, the anisotropic cosmological dynamics at low redshifts is similar to that in isotropic generalized Proca theories. In beyond-generalized Proca theories the only consistent solution to avoid the divergence of a determinant of the dynamical system corresponds to v = 0, so Σ always decreases in time.
Longitudinal fluctuations and decorrelation of anisotropic flow
Energy Technology Data Exchange (ETDEWEB)
Pang, Long-Gang [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, 60438 Frankfurt am Main (Germany); Petersen, Hannah [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, 60438 Frankfurt am Main (Germany); Institute for Theoretical Physics, Goethe University, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main (Germany); GSI Helmholtzzentrum für Schwerionenforschung, Planckstr. 1, 64291 Darmstadt (Germany); Qin, Guang-You [Key Laboratory of Quark & Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, Wuhan 430079 (China); Roy, Victor [Institute for Theoretical Physics, Goethe University, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main (Germany); Wang, Xin-Nian [Key Laboratory of Quark & Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, Wuhan 430079 (China); Nuclear Science Division MS70R0319, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
2016-12-15
We investigate the decorrelation of 2nd and 3rd order anisotropic flow for charged particles in two different pseudo rapidity (η) windows by varying the pseudo rapidity gap, in an event-by-event (3+1)D ideal hydrodynamic model, with fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. We visualize the parton distribution at initial state for Pb+Pb collisions at LHC and Au+Au collisions at RHIC, and demonstrate the longitudinal fluctuations originating from the asymmetry between forward and backward going participants, the fluctuations of the string length and the fluctuations due to finite number of partons at different beam energies. The decorrelation of anisotropic flow of final hadrons with large η gaps is found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flow in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation than at LHC, indicating larger longitudinal fluctuations at lower beam energies.
Anisotropic hydrodynamics for conformal Gubser flow
Energy Technology Data Exchange (ETDEWEB)
Strickland, Michael; Nopoush, Mohammad [Kent State University, Kent OH 44242 (United States); Ryblewski, Radoslaw [The H. Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland)
2016-12-15
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3){sub q} symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
Bryan's effect and anisotropic nonlinear damping
Joubert, Stephan V.; Shatalov, Michael Y.; Fay, Temple H.; Manzhirov, Alexander V.
2018-03-01
In 1890, G. H. Bryan discovered the following: "The vibration pattern of a revolving cylinder or bell revolves at a rate proportional to the inertial rotation rate of the cylinder or bell." We call this phenomenon Bryan's law or Bryan's effect. It is well known that any imperfections in a vibratory gyroscope (VG) affect Bryan's law and this affects the accuracy of the VG. Consequently, in this paper, we assume that all such imperfections are either minimised or eliminated by some known control method and that only damping is present within the VG. If the damping is isotropic (linear or nonlinear), then it has been recently demonstrated in this journal, using symbolic analysis, that Bryan's law remains invariant. However, it is known that linear anisotropic damping does affect Bryan's law. In this paper, we generalise Rayleigh's dissipation function so that anisotropic nonlinear damping may be introduced into the equations of motion. Using a mixture of numeric and symbolic analysis on the ODEs of motion of the VG, for anisotropic light nonlinear damping, we demonstrate (up to an approximate average), that Bryan's law is affected by any form of such damping, causing pattern drift, compromising the accuracy of the VG.
Veselago focusing of anisotropic massless Dirac fermions
Zhang, Shu-Hui; Yang, Wen; Peeters, F. M.
2018-05-01
Massless Dirac fermions (MDFs) emerge as quasiparticles in various novel materials such as graphene and topological insulators, and they exhibit several intriguing properties, of which Veselago focusing is an outstanding example with a lot of possible applications. However, up to now Veselago focusing merely occurred in p-n junction devices based on the isotropic MDF, which lacks the tunability needed for realistic applications. Here, motivated by the emergence of novel Dirac materials, we investigate the propagation behaviors of anisotropic MDFs in such a p-n junction structure. By projecting the Hamiltonian of the anisotropic MDF to that of the isotropic MDF and deriving an exact analytical expression for the propagator, precise Veselago focusing is demonstrated without the need for mirror symmetry of the electron source and its focusing image. We show a tunable focusing position that can be used in a device to probe masked atom-scale defects. This study provides an innovative concept to realize Veselago focusing relevant for potential applications, and it paves the way for the design of novel electron optics devices by exploiting the anisotropic MDF.
ANALYSIS OF DEFORMABILITY OF ANISOTROPIC AGRILLITE CLAYSTONES
Directory of Open Access Journals (Sweden)
Ponomaryov Andrey Budimirovicn
2017-08-01
Full Text Available In the paper, the results of deformability study of agrillite claystones are used for determination of the Jointed rock model parameters. The number of stamp, pressuremeter and compressive tests allowed to research anisotropic deformability of argillite claystone in vertical and horizontal direction. The following problems were solved during the study: 1 the in-place and laboratory experiments to calculate the anisotropy coefficient were done for anisotropic agrillite claystones with both natural moisture and total water saturation; 2 the deformation parameters were determined and the numerical simulation of the stress-strain state of claystone in field tests was carried out with the use of Plaxis 2D software application; 3 the comparative analysis was done for calculated claystone deformation and the values obtained during the in-place tests. The authors proved that agrillite claystones shows two times less deformation under loading in the horizontal direction than vertically. The ratio is obtained to determine the parameters for numerical simulation of the Jointed Rock model used as a practical tool for analysis of stress-strain behavior of anisotropic soils. The authors provided a recommended practice for consideration of specific properties of argillite claystones when carrying out foundation works.
Anisotropic hydrodynamics for conformal Gubser flow
International Nuclear Information System (INIS)
Strickland, Michael; Nopoush, Mohammad; Ryblewski, Radoslaw
2016-01-01
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3)_q symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
Anisotropic and Hierarchical Porosity in Multifunctional Ceramics
Lichtner, Aaron Zev
The performance of multifunctional porous ceramics is often hindered by the seemingly contradictory effects of porosity on both mechanical and non-structural properties and yet a sufficient body of knowledge linking microstructure to these properties does not exist. Using a combination of tailored anisotropic and hierarchical materials, these disparate effects may be reconciled. In this project, a systematic investigation of the processing, characterization and properties of anisotropic and isotropic hierarchically porous ceramics was conducted. The system chosen was a composite ceramic intended as the cathode for a solid oxide fuel cell (SOFC). Comprehensive processing investigations led to the development of approaches to make hierarchical, anisotropic porous microstructures using directional freeze-casting of well dispersed slurries. The effect of all the important processing parameters was investigated. This resulted in an ability to tailor and control the important microstructural features including the scale of the microstructure, the macropore size and total porosity. Comparable isotropic porous ceramics were also processed using fugitive pore formers. A suite of characterization techniques including x-ray tomography and 3-D sectional scanning electron micrographs (FIB-SEM) was used to characterize and quantify the green and partially sintered microstructures. The effect of sintering temperature on the microstructure was quantified and discrete element simulations (DEM) were used to explain the experimental observations. Finally, the comprehensive mechanical properties, at room temperature, were investigated, experimentally and using DEM, for the different microstructures.
SU-G-BRA-03: PCA Based Imaging Angle Optimization for 2D Cine MRI Based Radiotherapy Guidance
Energy Technology Data Exchange (ETDEWEB)
Chen, T; Yue, N; Jabbour, S; Zhang, M [Rutgers University, New Brunswick, NJ (United States)
2016-06-15
Purpose: To develop an imaging angle optimization methodology for orthogonal 2D cine MRI based radiotherapy guidance using Principal Component Analysis (PCA) of target motion retrieved from 4DCT. Methods: We retrospectively analyzed 4DCT of 6 patients with lung tumor. A radiation oncologist manually contoured the target volume at the maximal inhalation phase of the respiratory cycle. An object constrained deformable image registration (DIR) method has been developed to track the target motion along the respiration at ten phases. The motion of the center of the target mass has been analyzed using the PCA to find out the principal motion components that were uncorrelated with each other. Two orthogonal image planes for cineMRI have been determined using this method to minimize the through plane motion during MRI based radiotherapy guidance. Results: 3D target respiratory motion for all 6 patients has been efficiently retrieved from 4DCT. In this process, the object constrained DIR demonstrated satisfactory accuracy and efficiency to enable the automatic motion tracking for clinical application. The average motion amplitude in the AP, lateral, and longitudinal directions were 3.6mm (min: 1.6mm, max: 5.6mm), 1.7mm (min: 0.6mm, max: 2.7mm), and 5.6mm (min: 1.8mm, max: 16.1mm), respectively. Based on PCA, the optimal orthogonal imaging planes were determined for cineMRI. The average angular difference between the PCA determined imaging planes and the traditional AP and lateral imaging planes were 47 and 31 degrees, respectively. After optimization, the average amplitude of through plane motion reduced from 3.6mm in AP images to 2.5mm (min:1.3mm, max:3.9mm); and from 1.7mm in lateral images to 0.6mm (min: 0.2mm, max:1.5mm), while the principal in plane motion amplitude increased from 5.6mm to 6.5mm (min: 2.8mm, max: 17mm). Conclusion: DIR and PCA can be used to optimize the orthogonal image planes of cineMRI to minimize the through plane motion during radiotherapy
SU-G-BRA-03: PCA Based Imaging Angle Optimization for 2D Cine MRI Based Radiotherapy Guidance
International Nuclear Information System (INIS)
Chen, T; Yue, N; Jabbour, S; Zhang, M
2016-01-01
Purpose: To develop an imaging angle optimization methodology for orthogonal 2D cine MRI based radiotherapy guidance using Principal Component Analysis (PCA) of target motion retrieved from 4DCT. Methods: We retrospectively analyzed 4DCT of 6 patients with lung tumor. A radiation oncologist manually contoured the target volume at the maximal inhalation phase of the respiratory cycle. An object constrained deformable image registration (DIR) method has been developed to track the target motion along the respiration at ten phases. The motion of the center of the target mass has been analyzed using the PCA to find out the principal motion components that were uncorrelated with each other. Two orthogonal image planes for cineMRI have been determined using this method to minimize the through plane motion during MRI based radiotherapy guidance. Results: 3D target respiratory motion for all 6 patients has been efficiently retrieved from 4DCT. In this process, the object constrained DIR demonstrated satisfactory accuracy and efficiency to enable the automatic motion tracking for clinical application. The average motion amplitude in the AP, lateral, and longitudinal directions were 3.6mm (min: 1.6mm, max: 5.6mm), 1.7mm (min: 0.6mm, max: 2.7mm), and 5.6mm (min: 1.8mm, max: 16.1mm), respectively. Based on PCA, the optimal orthogonal imaging planes were determined for cineMRI. The average angular difference between the PCA determined imaging planes and the traditional AP and lateral imaging planes were 47 and 31 degrees, respectively. After optimization, the average amplitude of through plane motion reduced from 3.6mm in AP images to 2.5mm (min:1.3mm, max:3.9mm); and from 1.7mm in lateral images to 0.6mm (min: 0.2mm, max:1.5mm), while the principal in plane motion amplitude increased from 5.6mm to 6.5mm (min: 2.8mm, max: 17mm). Conclusion: DIR and PCA can be used to optimize the orthogonal image planes of cineMRI to minimize the through plane motion during radiotherapy
Directory of Open Access Journals (Sweden)
Kiyotaka Nemoto
Full Text Available Neurological and psychiatric disorders are a burden on social and economic resources. Therefore, maintaining brain health and preventing these disorders are important. While the physiological functions of the brain are well studied, few studies have focused on keeping the brain healthy from a neuroscientific viewpoint. We propose a magnetic resonance imaging (MRI-based quotient for monitoring brain health, the Brain Healthcare Quotient (BHQ, which is based on the volume of gray matter (GM and the fractional anisotropy (FA of white matter (WM. We recruited 144 healthy adults to acquire structural neuroimaging data, including T1-weighted images and diffusion tensor images, and data associated with both physical (BMI, blood pressure, and daily time use and social (subjective socioeconomic status, subjective well-being, post-materialism and Epicureanism factors. We confirmed that the BHQ was sensitive to an age-related decline in GM volume and WM integrity. Further analysis revealed that the BHQ was critically affected by both physical and social factors. We believe that our BHQ is a simple yet highly sensitive, valid measure for brain health research that will bridge the needs of the scientific community and society and help us lead better lives in which we stay healthy, active, and sharp.
Friese, Uwe; Meindl, Thomas; Herpertz, Sabine C; Reiser, Maximilian F; Hampel, Harald; Teipel, Stefan J
2010-01-01
We report evidence that multivariate analyses of deformation-based morphometry and diffusion tensor imaging (DTI) data can be used to discriminate between healthy participants and patients with Alzheimer's disease (AD) with comparable diagnostic accuracy. In contrast to other studies on MRI-based biomarkers which usually only focus on a single modality, we derived deformation maps from high-dimensional normalization of T1-weighted images, as well as mean diffusivity maps and fractional anisotropy maps from DTI of the same group of 21 patients with AD and 20 healthy controls. Using an automated multivariate analysis of the entire brain volume, widespread decreased white matter integrity and atrophy effects were found in cortical and subcortical regions of AD patients. Mean diffusivity maps and deformation maps were equally effective in discriminating between AD patients and controls (AUC =0.88 vs. AUC=0.85) while fractional anisotropy maps performed slightly inferior. Combining the maps from different modalities in a logistic regression model resulted in a classification accuracy of AUC=0.86 after leave-one-out cross-validation. It remains to be shown if this automated multivariate analysis of DTI-measures can improve early diagnosis of AD in predementia stages.
Energy Technology Data Exchange (ETDEWEB)
Alizai, Hamza [Boston University School of Medicine, Quantitative Imaging Center, Department of Radiology, Boston, MA (United States); Aspetar Orthopaedic and Sports Medicine Hospital, Doha (Qatar); University of Texas Health Science Center at San Antonio, Department of Radiology, San Antonio, TX (United States); Roemer, Frank W. [Boston University School of Medicine, Quantitative Imaging Center, Department of Radiology, Boston, MA (United States); Aspetar Orthopaedic and Sports Medicine Hospital, Doha (Qatar); University of Erlangen-Nuremberg, Department of Radiology, Erlangen (Germany); Hayashi, Daichi [Boston University School of Medicine, Quantitative Imaging Center, Department of Radiology, Boston, MA (United States); Aspetar Orthopaedic and Sports Medicine Hospital, Doha (Qatar); Yale University School of Medicine, Department of Radiology, Bridgeport Hospital, Bridgeport, CT (United States); Crema, Michel D. [Boston University School of Medicine, Quantitative Imaging Center, Department of Radiology, Boston, MA (United States); Aspetar Orthopaedic and Sports Medicine Hospital, Doha (Qatar); Hospital do Coracao and Teleimagem, Department of Radiology, Sao Paulo (Brazil); Felson, David T. [Boston University School of Medicine, Clinical Epidemiology Research and Training Unit, Boston, MA (United States); Guermazi, Ali [Boston University School of Medicine, Quantitative Imaging Center, Department of Radiology, Boston, MA (United States); Aspetar Orthopaedic and Sports Medicine Hospital, Doha (Qatar); Boston Medical Center, Boston, MA (United States)
2014-11-07
Arthroscopy-based semiquantitative scoring systems such as Outerbridge and Noyes' scores were the first to be developed for the purpose of grading cartilage defects. As magnetic resonance imaging (MRI) became available faor evaluation of the osteoarthritic knee joint, these systems were adapted for use with MRI. Later on, grading methods such as the Whole Organ Magnetic Resonance Score, the Boston-Leeds Osteoarthritis Knee Score and the MRI Osteoarthritis Knee Score were designed specifically for performing whole-organ assessment of the knee joint structures, including cartilage. Cartilage grades on MRI obtained with these scoring systems represent optimal outcome measures for longitudinal studies, and are designed to enhance understanding of the knee osteoarthritis disease process. The purpose of this narrative review is to describe cartilage assessment in knee osteoarthritis using currently available MRI-based semiquantitative whole-organ scoring systems, and to provide an update on the risk factors for cartilage loss in knee osteoarthritis as assessed with these scoring systems. (orig.)
Tsunoda, A; Mitsuoka, H; Sato, K; Kanayama, S
2000-06-01
Our purpose was to quantify the intracranial cerebrospinal fluid (CSF) volume components using an original MRI-based segmentation technique and to investigate whether a CSF volume index is useful for diagnosis of normal pressure hydrocephalus (NPH). We studied 59 subjects: 16 patients with NPH, 14 young and 13 elderly normal volunteers, and 16 patients with cerebrovascular disease. Images were acquired on a 1.5-T system, using a 3D-fast asymmetrical spin-echo (FASE) method. A region-growing method (RGM) was used to extract the CSF spaces from the FASE images. Ventricular volume (VV) and intracranial CSF volume (ICV) were measured, and a VV/ICV ratio was calculated. Mean VV and VV/ICV ratio were higher in the NPH group than in the other groups, and the differences were statistically significant, whereas the mean ICV value in the NPH group was not significantly increased. Of the 16 patients in the NPH group, 13 had VV/ICV ratios above 30%. In contrast, no subject in the other groups had a VV/ICV ratios higher than 30%. We conclude that these CSF volume parameters, especially the VV/ICV ratio, are useful for the diagnosis of NPH.
International Nuclear Information System (INIS)
Tsunoda, A.; Mitsuoka, H.; Sato, K.; Kanayama, S.
2000-01-01
Our purpose was to quantify the intracranial cerebrospinal fluid (CSF) volume components using an original MRI-based segmentation technique and to investigate whether a CSF volume index is useful for diagnosis of normal pressure hydrocephalus (NPH). We studied 59 subjects: 16 patients with NPH, 14 young and 13 elderly normal volunteers, and 16 patients with cerebrovascular disease. Images were acquired on a 1.5-T system, using a 3D-fast asymmetrical spin- echo (FASE) method. A region-growing method (RGM) was used to extract the CSF spaces from the FASE images. Ventricular volume (VV) and intracranial CSF volume (ICV) were measured, and a VV/ICV ratio was calculated. Mean VV and VV/ICV ratio were higher in the NPH group than in the other groups, and the differences were statistically significant, whereas the mean ICV value in the NPH group was not significantly increased. Of the 16 patients in the NPH group, 13 had VV/ICV ratios above 30%. In contrast, no subject in the other groups had a VV/ICV ratios higher than 30%. We conclude that these CSF volume parameters, especially the VV/ICV ratio, are useful for the diagnosis of NPH. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Tsunoda, A. [Department of Neurosurgery, Koshigaya Municipal Hospital, 10-47-1 Higashikoshigaya, Koshigaya City, Saitama 343-0023 (Japan); Mitsuoka, H.; Sato, K. [Department of Neurosurgery, Juntendo University (Japan); Kanayama, S. [Research and Development Centre, Toshiba Corporation (Japan)
2000-06-01
Our purpose was to quantify the intracranial cerebrospinal fluid (CSF) volume components using an original MRI-based segmentation technique and to investigate whether a CSF volume index is useful for diagnosis of normal pressure hydrocephalus (NPH). We studied 59 subjects: 16 patients with NPH, 14 young and 13 elderly normal volunteers, and 16 patients with cerebrovascular disease. Images were acquired on a 1.5-T system, using a 3D-fast asymmetrical spin- echo (FASE) method. A region-growing method (RGM) was used to extract the CSF spaces from the FASE images. Ventricular volume (VV) and intracranial CSF volume (ICV) were measured, and a VV/ICV ratio was calculated. Mean VV and VV/ICV ratio were higher in the NPH group than in the other groups, and the differences were statistically significant, whereas the mean ICV value in the NPH group was not significantly increased. Of the 16 patients in the NPH group, 13 had VV/ICV ratios above 30%. In contrast, no subject in the other groups had a VV/ICV ratios higher than 30%. We conclude that these CSF volume parameters, especially the VV/ICV ratio, are useful for the diagnosis of NPH. (orig.)
Nemoto, Kiyotaka; Oka, Hiroki; Fukuda, Hiroki; Yamakawa, Yoshinori
2017-01-01
Neurological and psychiatric disorders are a burden on social and economic resources. Therefore, maintaining brain health and preventing these disorders are important. While the physiological functions of the brain are well studied, few studies have focused on keeping the brain healthy from a neuroscientific viewpoint. We propose a magnetic resonance imaging (MRI)-based quotient for monitoring brain health, the Brain Healthcare Quotient (BHQ), which is based on the volume of gray matter (GM) and the fractional anisotropy (FA) of white matter (WM). We recruited 144 healthy adults to acquire structural neuroimaging data, including T1-weighted images and diffusion tensor images, and data associated with both physical (BMI, blood pressure, and daily time use) and social (subjective socioeconomic status, subjective well-being, post-materialism and Epicureanism) factors. We confirmed that the BHQ was sensitive to an age-related decline in GM volume and WM integrity. Further analysis revealed that the BHQ was critically affected by both physical and social factors. We believe that our BHQ is a simple yet highly sensitive, valid measure for brain health research that will bridge the needs of the scientific community and society and help us lead better lives in which we stay healthy, active, and sharp.
International Nuclear Information System (INIS)
Alizai, Hamza; Roemer, Frank W.; Hayashi, Daichi; Crema, Michel D.; Felson, David T.; Guermazi, Ali
2015-01-01
Arthroscopy-based semiquantitative scoring systems such as Outerbridge and Noyes' scores were the first to be developed for the purpose of grading cartilage defects. As magnetic resonance imaging (MRI) became available faor evaluation of the osteoarthritic knee joint, these systems were adapted for use with MRI. Later on, grading methods such as the Whole Organ Magnetic Resonance Score, the Boston-Leeds Osteoarthritis Knee Score and the MRI Osteoarthritis Knee Score were designed specifically for performing whole-organ assessment of the knee joint structures, including cartilage. Cartilage grades on MRI obtained with these scoring systems represent optimal outcome measures for longitudinal studies, and are designed to enhance understanding of the knee osteoarthritis disease process. The purpose of this narrative review is to describe cartilage assessment in knee osteoarthritis using currently available MRI-based semiquantitative whole-organ scoring systems, and to provide an update on the risk factors for cartilage loss in knee osteoarthritis as assessed with these scoring systems. (orig.)
Analysis of electromagnetic scattering by uniaxial anisotropic bispheres.
Li, Zheng-Jun; Wu, Zhen-Sen; Li, Hai-Ying
2011-02-01
Based on the generalized multiparticle Mie theory and the Fourier transformation approach, electromagnetic (EM) scattering of two interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes is investigated. By introducing the Fourier transformation, the EM fields in the uniaxial anisotropic spheres are expanded in terms of the spherical vector wave functions. The interactive scattering coefficients and the expansion coefficients of the internal fields are derived through the continuous boundary conditions on which the interaction of the bispheres is considered. Some selected calculations on the effects of the size parameter, the uniaxial anisotropic absorbing dielectric, and the sphere separation distance are described. The backward radar cross section of two uniaxial anisotropic spheres with a complex permittivity tensor changing with the sphere separation distance is numerically studied. The authors are hopeful that the work in this paper will help provide an effective calibration for further research on the scattering characteristic of an aggregate of anisotropic spheres or other shaped anisotropic particles.
Orthonormal bases for anisotropic α-modulation spaces
DEFF Research Database (Denmark)
Rasmussen, Kenneth Niemann
2012-01-01
In this article we construct orthonormal bases for bi-variate anisotropic α-modulation spaces. The construction is based on generating a nice anisotropic α-covering and using carefully selected tensor products of univariate brushlet functions with regards to this covering. As an application, we...... show that n-term nonlinear approximation with the orthonormal bases in certain anisotropic α-modulation spaces can be completely characterized....
Orthonormal bases for anisotropic α-modulation spaces
DEFF Research Database (Denmark)
Rasmussen, Kenneth Niemann
In this article we construct orthonormal bases for bi-variate anisotropic α-modulation spaces. The construction is based on generating a nice anisotropic α-covering and using carefully selected tensor products of univariate brushlet functions with regards to this covering. As an application, we...... show that n-term nonlinear approximation with the orthonormal bases in certain anisotropic α-modulation spaces can be completely characterized....
Arlt, Sönke; Buchert, Ralph; Spies, Lothar; Eichenlaub, Martin; Lehmbeck, Jan T; Jahn, Holger
2013-06-01
Fully automated magnetic resonance imaging (MRI)-based volumetry may serve as biomarker for the diagnosis in patients with mild cognitive impairment (MCI) or dementia. We aimed at investigating the relation between fully automated MRI-based volumetric measures and neuropsychological test performance in amnestic MCI and patients with mild dementia due to Alzheimer's disease (AD) in a cross-sectional and longitudinal study. In order to assess a possible prognostic value of fully automated MRI-based volumetry for future cognitive performance, the rate of change of neuropsychological test performance over time was also tested for its correlation with fully automated MRI-based volumetry at baseline. In 50 subjects, 18 with amnestic MCI, 21 with mild AD, and 11 controls, neuropsychological testing and T1-weighted MRI were performed at baseline and at a mean follow-up interval of 2.1 ± 0.5 years (n = 19). Fully automated MRI volumetry of the grey matter volume (GMV) was performed using a combined stereotactic normalisation and segmentation approach as provided by SPM8 and a set of pre-defined binary lobe masks. Left and right hippocampus masks were derived from probabilistic cytoarchitectonic maps. Volumes of the inner and outer liquor space were also determined automatically from the MRI. Pearson's test was used for the correlation analyses. Left hippocampal GMV was significantly correlated with performance in memory tasks, and left temporal GMV was related to performance in language tasks. Bilateral frontal, parietal and occipital GMVs were correlated to performance in neuropsychological tests comprising multiple domains. Rate of GMV change in the left hippocampus was correlated with decline of performance in the Boston Naming Test (BNT), Mini-Mental Status Examination, and trail making test B (TMT-B). The decrease of BNT and TMT-A performance over time correlated with the loss of grey matter in multiple brain regions. We conclude that fully automated MRI-based
Stability conditions for the Bianchi type II anisotropically inflating universes
International Nuclear Information System (INIS)
Kao, W.F.; Lin, Ing-Chen
2009-01-01
Stability conditions for a class of anisotropically inflating solutions in the Bianchi type II background space are shown explicitly in this paper. These inflating solutions were known to break the cosmic no-hair theorem such that they do not approach the de Sitter universe at large times. It can be shown that unstable modes of the anisotropic perturbations always exist for this class of expanding solutions. As a result, we show that these set of anisotropically expanding solutions are unstable against anisotropic perturbations in the Bianchi type II space
Silicon as an anisotropic mechanical material
DEFF Research Database (Denmark)
Thomsen, Erik Vilain; Reck, Kasper; Skands, Gustav Erik
2014-01-01
While silicon is an anisotropic material it is often in literature treated as an isotropic material when it comes to plate calculations. This leads to considerable errors in the calculated deflection. To overcome this problem, we present an in-depth analysis of the bending behavior of thin crysta...... analytical models involving crystalline plates, such as those often found in the field of micro electro mechanical systems. The effect of elastic boundary conditions is taken into account by using an effective radius of the plate....
Anisotropic perturbations due to dark energy
International Nuclear Information System (INIS)
Battye, Richard A.; Moss, Adam
2006-01-01
A variety of observational tests seem to suggest that the Universe is anisotropic. This is incompatible with the standard dogma based on adiabatic, rotationally invariant perturbations. We point out that this is a consequence of the standard decomposition of the stress-energy tensor for the cosmological fluids, and that rotational invariance need not be assumed, if there is elastic rigidity in the dark energy. The dark energy required to achieve this might be provided by point symmetric domain wall network with P/ρ=-2/3, although the concept is more general. We illustrate this with reference to a model with cubic symmetry and discuss various aspects of the model
An approach to anisotropic cosmologies. 6
International Nuclear Information System (INIS)
Raychaudhuri, A.K.
1989-01-01
In this paper the motivation for the study of anisotropic cosmological models is set out. Then the mathematical basis for the study of such models as well as the description of some of the exact solutions of this genre are given. Killing vectors that spell out spacetime symmetries, are defined and the Bianchi classification of spacetimes based on the structure of the Killing vectors described. After a consideration of the kinematics of matter flow some of the known solutions are presented and their properties described. (author)
The quantum cosmology of an anisotropic universe
International Nuclear Information System (INIS)
Duncan, M.J.; Jensen, L.G.
1989-01-01
Surveys of the microwave background indicate that the universe is isotropic to more than one part in 10 5 . Due to the arbitrariness of the initial conditions of the universe at the big bang singularity one cannot predict this; it is usually put in by hand. We therefore construct the quantum cosmology of an anisotropic universe according to the 'no-boundary' prescription of Hartle and Hawking. Such a model has a well-defined behavior at the classical singularity. We then show it also implies that a large universe, such as ours, is isotropic. (orig.)
Quantum cosmology of an anisotropic universe
Energy Technology Data Exchange (ETDEWEB)
Duncan, M.J.; Jensen, L.G.
1989-01-23
Surveys of the microwave background indicate that the universe is isotropic to more than one part in 10/sup 5/. Due to the arbitrariness of the initial conditions of the universe at the big bang singularity one cannot predict this; it is usually put in by hand. We therefore construct the quantum cosmology of an anisotropic universe according to the 'no-boundary' prescription of Hartle and Hawking. Such a model has a well-defined behavior at the classical singularity. We then show it also implies that a large universe, such as ours, is isotropic.
Critical state of anisotropic hard superconductors
Energy Technology Data Exchange (ETDEWEB)
Romero-Salazar, C; Perez-RodrIguez, F [Instituto de FIsica, Universidad Autonoma de Puebla, Apdo Post J-48, Puebla, Pue 72570 (Mexico)
2003-11-01
The magnetic response of anisotropic irreversible type-II superconductors is investigated theoretically. Using an elliptic vertical law for the electric field E as a function of the current density J, we have reproduced available experimental magnetization curves of YBCO samples with the c axis lying in the sample plane. Specifically, we could reproduce quantitatively and interpret correctly the appearance of additional extrema and segments with relatively small slopes of the virgin magnetization curves when the direction of the applied magnetic field differs from the principal axes. The notable deformation of magnetization curves in a tilted magnetic field is connected to the strong coupling between the components of the magnetic induction.
Generalised model for anisotropic compact stars
Energy Technology Data Exchange (ETDEWEB)
Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Raj Kumar Goel Institute of Technology, Department of Mathematics, Ghaziabad, Uttar Pradesh (India); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India); Deb, Debabrata [Indian Institute of Engineering Science and Technology, Shibpur, Department of Physics, Howrah, West Bengal (India)
2016-12-15
In the present investigation an exact generalised model for anisotropic compact stars of embedding class 1 is sought with a general relativistic background. The generic solutions are verified by exploring different physical aspects, viz. energy conditions, mass-radius relation, stability of the models, in connection to their validity. It is observed that the model presented here for compact stars is compatible with all these physical tests and thus physically acceptable as far as the compact star candidates RXJ 1856-37, SAX J 1808.4-3658 (SS1) and SAX J 1808.4-3658 (SS2) are concerned. (orig.)
Many-dimensional anisotropic anharmonic oscillator
International Nuclear Information System (INIS)
Turbiner, A.V.
1987-01-01
Precision calculation of energies of several first states at d=2 and first 17 states at d=3 has been performed within the framework of a unique method based on ''nonlinearization'' method for d-dimension anisotropic an harmonic oscillator. Spectrum behaviour within the limit d → ∞ has been investigated and problems of the given approach accuracy have been studied. For the first time properties of nodal surfaces of the given task have been investigated. Routine perturbation theory in degrees of a perturbation parameter has been constructed for several first states
Theory of Random Anisotropic Magnetic Alloys
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1976-01-01
A mean-field-crystal-field theory is developed for random, multicomponent, anisotropic magnetic alloys. It is specially applicable to rare-earth alloys. A discussion is given of multicritical points and phase transitions between various states characterized by order parameters with different...... spatial directions or different ordering wave vectors. Theoretical predictions based on known parameters for the phase diagrams and magnetic moments for the binary rare-earth alloys of Tb, Dy, Ho, and Er, Tb-Tm, Nd-Pr, and pure double-hcp Nd agree qualitatively with the experimental observations...... fluctuation corrections in the mean-field results is also discussed....
Effective Medium Theory for Anisotropic Metamaterials
Zhang, Xiujuan
2017-11-12
This dissertation includes the study of effective medium theories (EMTs) and their applications in describing wave propagation in anisotropic metamaterials, which can guide the design of metamaterials. An EMT based on field averaging is proposed to describe a peculiar anisotropic dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. This dispersion relation is associated with the topological transition of the iso-frequency contours (IFCs), suggesting interesting wave propagation behaviors from beam shaping to beam splitting. In the framework of coherent potential approximation, an analytical EMT is further developed, with the ability to build a direct connection between the microscopic structure and the macroscopic material properties, which overcomes the requirement of prior knowledge of the field distributions. The derived EMT is valid beyond the long-wavelength limit. Using the EMT, an anisotropic zero-index metamaterial is designed. Moreover, the derived EMT imposes a condition that no scattered wave is generated in the ambient medium, which suggests the input signal cannot detect any object that might exist, making it invisible. Such correspondence between the EMT and the invisibilityinspires us to explore the wave cloaking in the same framework of coherent potential approximation. To further broaden the application realm of EMT, an EMT using the parameter retrieval method is studied in the regimes where the previously-developed EMTs are no longer accurate. Based on this study, in conjunction with the EMT mentioned above, a general scheme to realize coherent perfect absorption (CPA) in anisotropic metamaterials is proposed. As an exciting area in metamaterials, the field of metasurfaces has drawn great attention recently. As an easily attainable device, a grating may be the simplest version of metasurfaces. Here, an analytical EMT for gratings made of cylinders is developed by using the multiple scattering
Local thermodynamics of a magnetized, anisotropic plasma
International Nuclear Information System (INIS)
Hazeltine, R. D.; Mahajan, S. M.; Morrison, P. J.
2013-01-01
An expression for the internal energy of a fluid element in a weakly coupled, magnetized, anisotropic plasma is derived from first principles. The result is a function of entropy, particle density and magnetic field, and as such plays the role of a thermodynamic potential: it determines in principle all thermodynamic properties of the fluid element. In particular it provides equations of state for the magnetized plasma. The derivation uses familiar fluid equations, a few elements of kinetic theory, the MHD version of Faraday's law, and certain familiar stability and regularity conditions.
RELATIVISTIC CYCLOTRON INSTABILITY IN ANISOTROPIC PLASMAS
Energy Technology Data Exchange (ETDEWEB)
López, Rodrigo A.; Moya, Pablo S.; Muñoz, Víctor; Valdivia, J. Alejandro [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Navarro, Roberto E.; Araneda, Jaime A. [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Viñas, Adolfo F., E-mail: rlopez186@gmail.com [NASA Goddard Space Flight Center, Heliophysics Science Division, Geospace Physics Laboratory, Mail Code 673, Greenbelt, MD 20771 (United States)
2016-11-20
A sufficiently large temperature anisotropy can sometimes drive various types of electromagnetic plasma micro-instabilities, which can play an important role in the dynamics of relativistic pair plasmas in space, astrophysics, and laboratory environments. Here, we provide a detailed description of the cyclotron instability of parallel propagating electromagnetic waves in relativistic pair plasmas on the basis of a relativistic anisotropic distribution function. Using plasma kinetic theory and particle-in-cell simulations, we study the influence of the relativistic temperature and the temperature anisotropy on the collective and noncollective modes of these plasmas. Growth rates and dispersion curves from the linear theory show a good agreement with simulations results.
Creating an anisotropic plasma resistivity with waves
International Nuclear Information System (INIS)
Fisch, N.J.; Boozer, A.H.
1980-05-01
An anisotropic plasma resistivity may be created by preferential heating of electrons traveling in one direction. This can result in a steady-state toroidal current in a tokamak even in the absence of net wave momentum. In fact, at high wave phase velocities, the current associated with the change in resistivity is greater than that associated with net momentum input. An immediate implication is that other waves, such as electron cyclotron waves, may be competitive with lower-hybrid waves as a means for generating current. An analytical expression is derived for the current generated per power dissipated which agrees remarkably well with numerical calculations
Analysis of anisotropic shells containing flowing fluid
International Nuclear Information System (INIS)
Lakis, A.A.
1983-01-01
A general theory for the dynamic analysis of anisotropic thin cylindrical shells containing flowing fluid is presented. The shell may be uniform or non-uniform, provided it is geometrically axially symmetric. This is a finite- element theory, using cylindrical finite elements, but the displacement functions are determined by using classical shell theory. A new solution of the wave equation of the liquid finite element leads to an expression of the fluid pressure, p, as a function of the nodal displacements of the element and three operative forces (inertia, centrifugal and Coriolis) of the moving fluid. (Author) [pt
International Nuclear Information System (INIS)
Lorenzoni, José; David, Philippe; Levivier, Marc
2012-01-01
Purpose: To describe the anatomical characteristics and patterns of neurovascular compression in patients suffering classic trigeminal neuralgia (CTN), using high-resolution magnetic resonance imaging (MRI). Materials and methods: The analysis of the anatomy of the trigeminal nerve, brain stem and the vascular structures related to this nerve was made in 100 consecutive patients treated with a Gamma Knife radiosurgery for CTN between December 1999 and September 2004. MRI studies (T1, T1 enhanced and T2-SPIR) with axial, coronal and sagital simultaneous visualization were dynamically assessed using the software GammaPlan™. Three-dimensional reconstructions were also developed in some representative cases. Results: In 93 patients (93%), there were one or several vascular structures in contact, either, with the trigeminal nerve, or close to its origin in the pons. The superior cerebellar artery was involved in 71 cases (76%). Other vessels identified were the antero-inferior cerebellar artery, the basilar artery, the vertebral artery, and some venous structures. Vascular compression was found anywhere along the trigeminal nerve. The mean distance between the nerve compression and the origin of the nerve in the brainstem was 3.76 ± 2.9 mm (range 0–9.8 mm). In 39 patients (42%), the vascular compression was located proximally and in 42 (45%) the compression was located distally. Nerve dislocation or distortion by the vessel was observed in 30 cases (32%). Conclusions: The findings of this study are similar to those reported in surgical and autopsy series. This non-invasive MRI-based approach could be useful for diagnostic and therapeutic decisions in CTN, and it could help to understand its pathogenesis.
Energy Technology Data Exchange (ETDEWEB)
Kress, B.; Baehren, W. [Bundeswehrkrankenhaus Ulm (Germany). Abt. fuer Radiologie
2001-07-01
Detailed imaging of the five sections of the full intratemporal course of the facial nerve can be achieved by MRI and using thin tomographic section techniques and surface coils. Contrast media are required for tomographic imaging of pathological processes. Established methods are available for diagnostic evaluation of cerebellopontine angle tumors and chronic Bell's palsy, as well as hemifacial spasms. A method still under discussion is MRI for diagnostic evaluation of Bell's palsy in the presence of fractures of the petrous bone, when blood volumes in the petrous bone make evaluation even more difficult. MRI-based diagnostic evaluation of the idiopatic facial paralysis currently is subject to change. Its usual application cannot be recommended for routine evaluation at present. However, a quantitative analysis of contrast medium uptake of the nerve may be an approach to improve the prognostic value of MRI in acute phases of Bell's palsy. (orig./CB) [German] Die detaillierte kernspintomographische Darstellung des aus 5 Abschnitten bestehenden intratemporalen Verlaufes des N. facialis gelingt mit der MRI unter Einsatz von Duennschichttechniken und Oberflaechenspulen. Zur Darstellung von pathologischen Vorgaengen ist die Gabe von Kontrastmittel notwendig. Die Untersuchung in der Diagnostik von Kleinhirnbrueckenwinkeltumoren und der chronischen Facialisparese ist etabliert, ebenso wie die Diagnostik des Hemispasmus facialis. In der Diskussion ist die MRI zur Dokumentation der Facialisparese bei Felsenbeinfrakturen, wobei die Einblutungen im Felsenbein die Beurteilung erschweren. Die kernspintomographische Diagnostik der idiopathischen Facialisparese befindet sich im Wandel. In der herkoemmlichen Form wird sie nicht zur Routinediagnostik empfohlen. Die quantitative Analyse der Kontrastmittelaufnahme im Nerv koennte jedoch die prognostische Bedeutung der MRI in der Akutphase der Bell's palsy erhoehen. (orig.)
International Nuclear Information System (INIS)
Pagnozzi, Alex M.; Fiori, Simona; Boyd, Roslyn N.; Guzzetta, Andrea; Doecke, James; Rose, Stephen; Dowson, Nicholas; Gal, Yaniv
2016-01-01
Several scoring systems for measuring brain injury severity have been developed to standardize the classification of MRI results, which allows for the prediction of functional outcomes to help plan effective interventions for children with cerebral palsy. The aim of this study is to use statistical techniques to optimize the clinical utility of a recently proposed template-based scoring method by weighting individual anatomical scores of injury, while maintaining its simplicity by retaining only a subset of scored anatomical regions. Seventy-six children with unilateral cerebral palsy were evaluated in terms of upper limb motor function using the Assisting Hand Assessment measure and injuries visible on MRI using a semiquantitative approach. This cohort included 52 children with periventricular white matter injury and 24 with cortical and deep gray matter injuries. A subset of the template-derived cerebral regions was selected using a data-driven region selection algorithm. Linear regression was performed using this subset, with interaction effects excluded. Linear regression improved multiple correlations between MRI-based and Assisting Hand Assessment scores for both periventricular white matter (R squared increased to 0.45 from 0, P < 0.0001) and cortical and deep gray matter (0.84 from 0.44, P < 0.0001) cohorts. In both cohorts, the data-driven approach retained fewer than 8 of the 40 template-derived anatomical regions. The equal or better prediction of the clinically meaningful Assisting Hand Assessment measure using fewer anatomical regions highlights the potential of these developments to enable enhanced quantification of injury and prediction of patient motor outcome, while maintaining the clinical expediency of the scoring approach. (orig.)
Pagnozzi, Alex M; Fiori, Simona; Boyd, Roslyn N; Guzzetta, Andrea; Doecke, James; Gal, Yaniv; Rose, Stephen; Dowson, Nicholas
2016-02-01
Several scoring systems for measuring brain injury severity have been developed to standardize the classification of MRI results, which allows for the prediction of functional outcomes to help plan effective interventions for children with cerebral palsy. The aim of this study is to use statistical techniques to optimize the clinical utility of a recently proposed template-based scoring method by weighting individual anatomical scores of injury, while maintaining its simplicity by retaining only a subset of scored anatomical regions. Seventy-six children with unilateral cerebral palsy were evaluated in terms of upper limb motor function using the Assisting Hand Assessment measure and injuries visible on MRI using a semiquantitative approach. This cohort included 52 children with periventricular white matter injury and 24 with cortical and deep gray matter injuries. A subset of the template-derived cerebral regions was selected using a data-driven region selection algorithm. Linear regression was performed using this subset, with interaction effects excluded. Linear regression improved multiple correlations between MRI-based and Assisting Hand Assessment scores for both periventricular white matter (R squared increased to 0.45 from 0, P < 0.0001) and cortical and deep gray matter (0.84 from 0.44, P < 0.0001) cohorts. In both cohorts, the data-driven approach retained fewer than 8 of the 40 template-derived anatomical regions. The equal or better prediction of the clinically meaningful Assisting Hand Assessment measure using fewer anatomical regions highlights the potential of these developments to enable enhanced quantification of injury and prediction of patient motor outcome, while maintaining the clinical expediency of the scoring approach.
Energy Technology Data Exchange (ETDEWEB)
Pagnozzi, Alex M. [Royal Brisbane and Women' s Hospital, CSIRO Digital Productivity and Services Flagship, The Australian e-Health Research Centre, Herston, QLD (Australia); The University of Queensland, School of Medicine, Brisbane (Australia); Fiori, Simona [Stella Maris Scientific Institute, Pisa (Italy); Boyd, Roslyn N. [The University of Queensland, Queensland Cerebral Palsy and Rehabilitation Research Centre, School of Medicine, Brisbane (Australia); Guzzetta, Andrea [Stella Maris Scientific Institute, Pisa (Italy); University of Pisa, Department of Clinical and Experimental Medicine, Pisa (Italy); Doecke, James; Rose, Stephen; Dowson, Nicholas [Royal Brisbane and Women' s Hospital, CSIRO Digital Productivity and Services Flagship, The Australian e-Health Research Centre, Herston, QLD (Australia); Gal, Yaniv [The University of Queensland, Centre for Medical Diagnostic Technologies in Queensland, Brisbane (Australia)
2016-02-15
Several scoring systems for measuring brain injury severity have been developed to standardize the classification of MRI results, which allows for the prediction of functional outcomes to help plan effective interventions for children with cerebral palsy. The aim of this study is to use statistical techniques to optimize the clinical utility of a recently proposed template-based scoring method by weighting individual anatomical scores of injury, while maintaining its simplicity by retaining only a subset of scored anatomical regions. Seventy-six children with unilateral cerebral palsy were evaluated in terms of upper limb motor function using the Assisting Hand Assessment measure and injuries visible on MRI using a semiquantitative approach. This cohort included 52 children with periventricular white matter injury and 24 with cortical and deep gray matter injuries. A subset of the template-derived cerebral regions was selected using a data-driven region selection algorithm. Linear regression was performed using this subset, with interaction effects excluded. Linear regression improved multiple correlations between MRI-based and Assisting Hand Assessment scores for both periventricular white matter (R squared increased to 0.45 from 0, P < 0.0001) and cortical and deep gray matter (0.84 from 0.44, P < 0.0001) cohorts. In both cohorts, the data-driven approach retained fewer than 8 of the 40 template-derived anatomical regions. The equal or better prediction of the clinically meaningful Assisting Hand Assessment measure using fewer anatomical regions highlights the potential of these developments to enable enhanced quantification of injury and prediction of patient motor outcome, while maintaining the clinical expediency of the scoring approach. (orig.)
Byk, Katarzyna; Jasinski, Krzysztof; Bartel, Zaneta; Jasztal, Agnieszka; Sitek, Barbara; Tomanek, Boguslaw; Chlopicki, Stefan; Skorka, Tomasz
2016-12-01
To assess alterations in perfusion and liver function in the concanavalin A (ConA)-induced mouse model of acute liver failure (ALF) using two magnetic resonance imaging (MRI)-based methods: dynamic contrast-enhanced MRI (DCE-MRI) with Gd-EOB-DTPA contrast agent and arterial spin labelling (ASL). BALB/c mice were studied using a 9.4 T MRI system. The IntraGateFLASH TM and FAIR-EPI pulse sequences were used for optimum mouse abdomen imaging. The average perfusion values for the liver of the control and ConA group were equal to 245 ± 20 and 200 ± 32 ml/min/100 g (p = 0.008, respectively). DCE-MRI showed that the time to the peak of the image enhancement was 6.14 ± 1.07 min and 9.72 ± 1.69 min in the control and ConA group (p < 0.001, respectively), while the rate of the contrast wash-out in the control and ConA group was 0.037 ± 0.008 and 0.021 ± 0.008 min -1 (p = 0.004, respectively). These results were consistent with hepatocyte injury in the ConA-treated mice as confirmed by histopathological staining. Both the ASL and DCE-MRI techniques represent a reliable methodology to assess alterations in liver perfusion and hepatocyte integrity in murine hepatitis.
Huang, Xueying; Teng, Zhongzhao; Canton, Gador; Ferguson, Marina; Yuan, Chun; Tang, Dalin
2010-12-31
Studies using medical images have shown that intraplaque hemorrhage may accelerate plaque progression and may produce a stimulus for atherosclerosis development by increasing lipid core and plaque volume and creating new destabilizing factors. Image-based 3D computational models with fluid-structure interactions (FSI) will be used to perform plaque mechanical analysis and investigate possible associations between intraplaque hemorrhage and both plaque wall stress (PWS) and flow shear stress (FSS). In vivo MRI data of carotid plaques from 5 patients with intraplaque hemorrhage confirmed by histology were acquired. 3D multi-component FSI models were constructed for each plaque to obtain mechanical stresses. Plaque Wall Stress (PWS) and Flow Shear Stress (FSS) were extracted from all nodal points on the lumen surface of each plaque for analysis. The mean PWS value from all hemorrhage nodes of the 5 plaques combined was higher than that from non-hemorrhage nodes (75.6 versus 68.1 kPa, P = 0.0003). The mean PWS values from hemorrhage nodes for each of the 5 plaques were all significantly higher (5 out of 5) than those from non-hemorrhage nodes (P shear stress values from individual cases showed mixed results: only one out of five plaques showed mean FSS value from hemorrhage nodes was higher than that from non-hemorrhage nodes; three out of five plaques showed that their mean FSS values from hemorrhage nodes were lower than those from non-hemorrhage nodes; and one plaque showed that the difference had no statistical significance. The results of this study suggested that intraplaque hemorrhage nodes were associated with higher plaque wall stresses. Compared to flow shear stress, plaque wall stress has a better correlation with plaque component feature (hemorrhage) linked to plaque progression and vulnerability. With further validation, plaque stress analysis may provide additional stress indicators for image-based vulnerability assessment.
Directory of Open Access Journals (Sweden)
Canton Gador
2010-12-01
Full Text Available Abstract Background Studies using medical images have shown that intraplaque hemorrhage may accelerate plaque progression and may produce a stimulus for atherosclerosis development by increasing lipid core and plaque volume and creating new destabilizing factors. Image-based 3D computational models with fluid-structure interactions (FSI will be used to perform plaque mechanical analysis and investigate possible associations between intraplaque hemorrhage and both plaque wall stress (PWS and flow shear stress (FSS. Methods In vivo MRI data of carotid plaques from 5 patients with intraplaque hemorrhage confirmed by histology were acquired. 3D multi-component FSI models were constructed for each plaque to obtain mechanical stresses. Plaque Wall Stress (PWS and Flow Shear Stress (FSS were extracted from all nodal points on the lumen surface of each plaque for analysis. Results The mean PWS value from all hemorrhage nodes of the 5 plaques combined was higher than that from non-hemorrhage nodes (75.6 versus 68.1 kPa, P = 0.0003. The mean PWS values from hemorrhage nodes for each of the 5 plaques were all significantly higher (5 out of 5 than those from non-hemorrhage nodes (P 2, P = 0.0002. However, the mean flow shear stress values from individual cases showed mixed results: only one out of five plaques showed mean FSS value from hemorrhage nodes was higher than that from non-hemorrhage nodes; three out of five plaques showed that their mean FSS values from hemorrhage nodes were lower than those from non-hemorrhage nodes; and one plaque showed that the difference had no statistical significance. Conclusion The results of this study suggested that intraplaque hemorrhage nodes were associated with higher plaque wall stresses. Compared to flow shear stress, plaque wall stress has a better correlation with plaque component feature (hemorrhage linked to plaque progression and vulnerability. With further validation, plaque stress analysis may provide
Finite-difference schemes for anisotropic diffusion
Energy Technology Data Exchange (ETDEWEB)
Es, Bram van, E-mail: es@cwi.nl [Centrum Wiskunde and Informatica, P.O. Box 94079, 1090GB Amsterdam (Netherlands); FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM (Netherlands); Koren, Barry [Eindhoven University of Technology (Netherlands); Blank, Hugo J. de [FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM (Netherlands)
2014-09-01
In fusion plasmas diffusion tensors are extremely anisotropic due to the high temperature and large magnetic field strength. This causes diffusion, heat conduction, and viscous momentum loss, to effectively be aligned with the magnetic field lines. This alignment leads to different values for the respective diffusive coefficients in the magnetic field direction and in the perpendicular direction, to the extent that heat diffusion coefficients can be up to 10{sup 12} times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods used to approximate the MHD-equations since any misalignment of the grid may cause the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. Currently the common approach is to apply magnetic field-aligned coordinates, an approach that automatically takes care of the directionality of the diffusive coefficients. This approach runs into problems at x-points and at points where there is magnetic re-connection, since this causes local non-alignment. It is therefore useful to consider numerical schemes that are tolerant to the misalignment of the grid with the magnetic field lines, both to improve existing methods and to help open the possibility of applying regular non-aligned grids. To investigate this, in this paper several discretization schemes are developed and applied to the anisotropic heat diffusion equation on a non-aligned grid.
Anisotropic pressure and hyperons in neutron stars
International Nuclear Information System (INIS)
Sulaksono, A.
2015-01-01
We study the effects of anisotropic pressure (AI-P) on properties of the neutron stars (NSs) with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of AI-P on NS matter is to increase the stiffness of the equation of state EOS, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of AI-P model h ≤ 0.8 [L. Herrera and W. Barreto, Phys. Rev. D 88 (2013) 084022.] and Λ ≤ -1.15 [D. D. Doneva and S. S. Yazadjiev, Phys. Rev. D 85 (2012) 124023.]. The radius of the corresponding NS at M = 1.4 M ⊙ is more than 13 km, while the effect of AI-P on the minimum mass of NS is insignificant. Furthermore, due to the AI-P in the NS, the maximum mass limit of higher than 2.1 M ⊙ cannot rule out the presence of hyperons in the NS core. (author)
Gravitomagnetic Instabilities in Anisotropically Expanding Fluids
Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos, Demetrios B.; Vlahos, Loukas
Gravitational instabilities in a magnetized Friedman-Robertson-Walker (FRW) universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became evident that the external magnetic field disfavors the perturbations' growth, suppressing the corresponding rate by an amount proportional to its strength. However, the spatial isotropy of the FRW universe is not compatible with the presence of large-scale magnetic fields. Therefore, in this paper we use the general-relativistic version of the (linearized) perturbed magnetohydrodynamic equations with and without resistivity, to discuss a generalized Jeans criterion and the potential formation of density condensations within a class of homogeneous and anisotropically expanding, self-gravitating, magnetized fluids in curved space-time. We find that, for a wide variety of anisotropic cosmological models, gravitomagnetic instabilities can lead to subhorizontal, magnetized condensations. In the nonresistive case, the power spectrum of the unstable cosmological perturbations suggests that most of the power is concentrated on large scales (small k), very close to the horizon. On the other hand, in a resistive medium, the critical wave-numbers so obtained, exhibit a delicate dependence on resistivity, resulting in the reduction of the corresponding Jeans lengths to smaller scales (well bellow the horizon) than the nonresistive ones, while increasing the range of cosmological models which admit such an instability.
Electrically Anisotropic Layered Perovskite Single Crystal
Li, Ting-You
2016-04-01
Organic-inorganic hybrid perovskites (OIHPs), which are promising materials for electronic and optoelectronic applications (1-10), have made into layered organic-inorganic hybrid perovskites (LOIHPs). These LOIHPs have been applied to thin-film transistors, solar cells and tunable wavelength phosphors (11-18). It is known that devices fabricated with single crystal exhibit the superior performance, which makes the growth of large-sized single crystals critical for future device applications (19-23). However, the difficulty in growing large-sized LOIHPs single crystal with superior electrical properties limits their practical applications. Here, we report a method to grow the centimeter-scaled LOIHP single crystal of [(HOC2H4NH3)2PbI4], demonstrating the potentials in mass production. After that, we reveal anisotropic electrical and optoelectronic properties which proved the carrier propagating along inorganic framework. The carrier mobility of in-inorganic-plane (in-plane) devices shows the average value of 45 cm2 V–1 s–1 which is about 100 times greater than the record of LOIHP devices (15), showing the importance of single crystal in device application. Moreover, the LOIHP single crystals show its ultra-short carrier lifetime of 42.7 ps and photoluminescence quantum efficiency (PLQE) of 25.4 %. We expect this report to be a start of LOIHPs for advanced applications in which the anisotropic properties are needed (24-25), and meets the demand of high-speed applications and fast-response applications.
The Effective Coherence Length in Anisotropic Superconductors
International Nuclear Information System (INIS)
Polturak, E.; Koren, G.; Nesher, O
1999-01-01
If electrons are transmitted from a normal conductor(N) into a superconductor(S), common wisdom has it that the electrons are converted into Cooper pairs within a coherence length from the interface. This is true in conventional superconductors with an isotropic order parameter. We have established experimentally that the situation is rather different in high Tc superconductors having an anisotropic order parameter. We used epitaxial thin film S/N bilayers having different interface orientations in order to inject carriers from S into N along different directions. The distance to which these carriers penetrate were determined through their effect on the Tc of the bilayers. We found that the effective coherence length is 20A only along the a or b directions, while in other directions we find a length of 250dr20A out of plane, and an even larger value for in-plane, off high symmetry directions. These observations can be explained using the Blonder-Tinkham-Klapwijk model adapted to anisotropic superconductivity. Several implications of our results on outstanding problems with high Tc junctions will be discussed
Lyotropic Liquid Crystal Phases from Anisotropic Nanomaterials
Directory of Open Access Journals (Sweden)
Ingo Dierking
2017-10-01
Full Text Available Liquid crystals are an integral part of a mature display technology, also establishing themselves in other applications, such as spatial light modulators, telecommunication technology, photonics, or sensors, just to name a few of the non-display applications. In recent years, there has been an increasing trend to add various nanomaterials to liquid crystals, which is motivated by several aspects of materials development. (i addition of nanomaterials can change and thus tune the properties of the liquid crystal; (ii novel functionalities can be added to the liquid crystal; and (iii the self-organization of the liquid crystalline state can be exploited to template ordered structures or to transfer order onto dispersed nanomaterials. Much of the research effort has been concentrated on thermotropic systems, which change order as a function of temperature. Here we review the other side of the medal, the formation and properties of ordered, anisotropic fluid phases, liquid crystals, by addition of shape-anisotropic nanomaterials to isotropic liquids. Several classes of materials will be discussed, inorganic and mineral liquid crystals, viruses, nanotubes and nanorods, as well as graphene oxide.
Scaling Argument of Anisotropic Random Walk
International Nuclear Information System (INIS)
Xu Bingzhen; Jin Guojun; Wang Feifeng
2005-01-01
In this paper, we analytically discuss the scaling properties of the average square end-to-end distance (R 2 ) for anisotropic random walk in D-dimensional space (D≥2), and the returning probability P n (r 0 ) for the walker into a certain neighborhood of the origin. We will not only give the calculating formula for (R 2 ) and P n (r 0 ), but also point out that if there is a symmetric axis for the distribution of the probability density of a single step displacement, we always obtain (R p erpendicular n 2 )∼n, where perpendicular refers to the projections of the displacement perpendicular to each symmetric axes of the walk; in D-dimensional space with D symmetric axes perpendicular to each other, we always have (R n 2 )∼n and the random walk will be like a purely random motion; if the number of inter-perpendicular symmetric axis is smaller than the dimensions of the space, we must have (R n 2 )∼n 2 for very large n and the walk will be like a ballistic motion. It is worth while to point out that unlike the isotropic random walk in one and two dimensions, which is certain to return into the neighborhood of the origin, generally there is only a nonzero probability for the anisotropic random walker in two dimensions to return to the neighborhood.
Anisotropic hydrodynamics with a scalar collisional kernel
Almaalol, Dekrayat; Strickland, Michael
2018-04-01
Prior studies of nonequilibrium dynamics using anisotropic hydrodynamics have used the relativistic Anderson-Witting scattering kernel or some variant thereof. In this paper, we make the first study of the impact of using a more realistic scattering kernel. For this purpose, we consider a conformal system undergoing transversally homogenous and boost-invariant Bjorken expansion and take the collisional kernel to be given by the leading order 2 ↔2 scattering kernel in scalar λ ϕ4 . We consider both classical and quantum statistics to assess the impact of Bose enhancement on the dynamics. We also determine the anisotropic nonequilibrium attractor of a system subject to this collisional kernel. We find that, when the near-equilibrium relaxation-times in the Anderson-Witting and scalar collisional kernels are matched, the scalar kernel results in a higher degree of momentum-space anisotropy during the system's evolution, given the same initial conditions. Additionally, we find that taking into account Bose enhancement further increases the dynamically generated momentum-space anisotropy.
Transient electromagnetic scattering on anisotropic media
International Nuclear Information System (INIS)
Stewart, R.D.
1990-01-01
This dissertation treats the problem of transient scattering of obliquely incident electromagnetic plane waves on a stratified anisotropic dielectric slab. Scattering operators are derived for the reflective response of the medium. The internal fields are calculated. Wave splitting and invariant imbedding techniques are used. These techniques are first presented for fields normally incident on a stratified, isotropic dielectric medium. The techniques of wave splitting and invariant imbedding are applied to normally incident plane waves on an anisotropic medium. An integro-differential equation is derived for the reflective response and the direct and inverse scattering problems are discussed. These techniques are applied to the case of obliquely incident plane waves. The reflective response is derived and the direct and inverse problems discussed and compared to those for the normal incidence case. The internal fields are investigated for the oblique incidence via a Green's function approach. A numerical scheme is presented to calculate the Green's function. Finally, symmetry relations of the reflective response are discussed
Making of Magnet Barium Ferit Anisotropic
International Nuclear Information System (INIS)
Idayati, Novrita; Dedi
2003-01-01
Barium Hexa ferrite (BaFe 12 O 19 ) is ceramic and materials which usually used for making of permanent magnet. In this research Barium Hexa ferrite were made Anisotropic, and applied for loudspeaker, electro motors, dynamo, KWh metre, etc. this Magnet is commonly used due to its high Induction of Remanen (Br) and coercivity (high Hc). Besides it applies a more simple and easier process technology, cheaper raw material, and easy to find it, hence the magnetic component is much cheaper. Powder Metallurgy was used for the process technology, by reacting all materials in the powder (oxide), with a certain size distribution and a tight preparation step. The next step was mixing ferrite and Barium Carbonate (in the form of oxide), calcination, compaction, cantering and characterisation. The Anisotropic particle effects a high Induce Remanen (Br) and of koersifitas (high Hc). All the process steps will is determine physical and chemical characteristics of the magnet. The best Magnet characteristic of the magnet produced in this research is Induction of Remanen (Br) = 4,27 kg, Coercivity (Hc) = 1,745 kOe, Energy Product max (BHmaks) = 2,31 MGOe
Relativistic model for anisotropic strange stars
Deb, Debabrata; Chowdhury, Sourav Roy; Ray, Saibal; Rahaman, Farook; Guha, B. K.
2017-12-01
In this article, we attempt to find a singularity free solution of Einstein's field equations for compact stellar objects, precisely strange (quark) stars, considering Schwarzschild metric as the exterior spacetime. To this end, we consider that the stellar object is spherically symmetric, static and anisotropic in nature and follows the density profile given by Mak and Harko (2002) , which satisfies all the physical conditions. To investigate different properties of the ultra-dense strange stars we have employed the MIT bag model for the quark matter. Our investigation displays an interesting feature that the anisotropy of compact stars increases with the radial coordinate and attains its maximum value at the surface which seems an inherent property for the singularity free anisotropic compact stellar objects. In this connection we also perform several tests for physical features of the proposed model and show that these are reasonably acceptable within certain range. Further, we find that the model is consistent with the energy conditions and the compact stellar structure is stable with the validity of the TOV equation and Herrera cracking concept. For the masses below the maximum mass point in mass vs radius curve the typical behavior achieved within the framework of general relativity. We have calculated the maximum mass and radius of the strange stars for the three finite values of bag constant Bg.
Building an Anisotropic Meniscus with Zonal Variations
Higashioka, Michael M.; Chen, Justin A.; Hu, Jerry C.
2014-01-01
Toward addressing the difficult problems of knee meniscus regeneration, a self-assembling process has been used to re-create the native morphology and matrix properties. A significant problem in such attempts is the recapitulation of the distinct zones of the meniscus, the inner, more cartilaginous and the outer, more fibrocartilaginous zones. In this study, an anisotropic and zonally variant meniscus was produced by self-assembly of the inner meniscus (100% chondrocytes) followed by cell seeding the outer meniscus (coculture of chondrocytes and meniscus cells). After 4 weeks in culture, the engineered, inner meniscus exhibited a 42% increase in both instantaneous and relaxation moduli and a 62% increase in GAG/DW, as compared to the outer meniscus. In contrast, the circumferential tensile modulus and collagen/DW of the outer zone was 101% and 129% higher, respectively, than the values measured for the inner zone. Furthermore, there was no difference in the radial tensile modulus between the control and zonal engineered menisci, suggesting that the inner and outer zones of the engineered zonal menisci successfully integrated. These data demonstrate that not only can biomechanical and biochemical properties be engineered to differ by the zone, but they can also recapitulate the anisotropic behavior of the knee meniscus. PMID:23931258
Pulse splitting in nonlinear media with anisotropic dispersion properties
DEFF Research Database (Denmark)
Bergé, L.; Juul Rasmussen, J.; Schmidt, M.R.
1998-01-01
The nonlinear self-focusing of beams in media with anisotropic (mix-signed) dispersion is investigated. Theoretical predictions employing virial-type arguments and self-similar techniques suggest that a pulse propagating in a nonlinear medium with anisotropic dispersion will not collapse...
Anisotropic microporous supports impregnated with polymeric ion-exchange materials
Friesen, Dwayne; Babcock, Walter C.; Tuttle, Mark
1985-05-07
Novel ion-exchange media are disclosed, the media comprising polymeric anisotropic microporous supports containing polymeric ion-exchange or ion-complexing materials. The supports are anisotropic, having small exterior pores and larger interior pores, and are preferably in the form of beads, fibers and sheets.
Anisotropic Flow Measurements in ALICE at the Large Hadron Collider
Bilandzic, A.
2012-01-01
Anisotropic ﬂow is one of the observables which is sensitive to the properties of the created hot and dense system in heavy-ion collisions. In noncentral heavy-ion collisions the initial volume of the interacting system is anisotropic in coordinate space. Due to multiple interactions this anisotropy
Remarks on the relativistic magnetohydrodynamics of an anisotropic fluid
International Nuclear Information System (INIS)
Ignat, M.
1980-01-01
Considering a pressure tensor of a general form, a relativistic rarefied, anisotropic, infinite electrically conducting and nondissipative plasma is studied. For this purpose, the method of the orthonormal frame of reference is used. The choice of the frame of reference is made adequately to the problem. Some thermodynamical properties of such a relativistic, anisotropic plasma are also given. (author)
Anisotropic conductivity imaging with MREIT using equipotential projection algorithm
Energy Technology Data Exchange (ETDEWEB)
Degirmenci, Evren [Department of Electrical and Electronics Engineering, Mersin University, Mersin (Turkey); Eyueboglu, B Murat [Department of Electrical and Electronics Engineering, Middle East Technical University, 06531, Ankara (Turkey)
2007-12-21
Magnetic resonance electrical impedance tomography (MREIT) combines magnetic flux or current density measurements obtained by magnetic resonance imaging (MRI) and surface potential measurements to reconstruct images of true conductivity with high spatial resolution. Most of the biological tissues have anisotropic conductivity; therefore, anisotropy should be taken into account in conductivity image reconstruction. Almost all of the MREIT reconstruction algorithms proposed to date assume isotropic conductivity distribution. In this study, a novel MREIT image reconstruction algorithm is proposed to image anisotropic conductivity. Relative anisotropic conductivity values are reconstructed iteratively, using only current density measurements without any potential measurement. In order to obtain true conductivity values, only either one potential or conductivity measurement is sufficient to determine a scaling factor. The proposed technique is evaluated on simulated data for isotropic and anisotropic conductivity distributions, with and without measurement noise. Simulation results show that the images of both anisotropic and isotropic conductivity distributions can be reconstructed successfully.
Characterization of Anisotropic Behavior for High Grade Pipes
Yang, Kun; Huo, Chunyong; Ji, Lingkang; Li, Yang; Zhang, Jiming; Ma, Qiurong
With the developing requirement of nature gas, the property needs of steel for pipe line are higher and higher, especially in strength and toughness. It is necessary to improve the steel grade in order to ensure economic demand and safety. However, with the rise of steel grade, the differences on properties in different orientations (anisotropic behaviors) become more and more obvious after the process of hot rolling, which may affect the prediction of fracture for the pipes seriously (Thinking of isotropic mechanical properties for material in traditional predict way). In order to get the reason for anisotropic mechanics, a series of tests are carried out for high grade steel pipes, including not only mechanical properties but also microstructures. Result indicates that there are obviously anisotropic behaviors for high grade steel pipes in two orientations (rolling orientation and transverse orientation). Strength is better in T orientation because Rm is higher and Rt 0.5 rises more in T orientation, and toughness is better in L orientation because of the higher Akv and SA in L orientation under a same temperature. Banded structures are formed in T orientation, and the spatial distribution of inclusion and precipitated phases are different in T, L and S orientation. The anisotropic arrangement for the matrix in space (banded structures), which is formed after the process of hot rolling, may affect the mechanical properties in different orientation. Moreover, the elasticity modulus of particles is different from the elasticity modulus of matrix, deformation between particles and matrix may cause stress concentration, and damage forms in this place. Because of the different distribution of particles in space, the level of damage is anisotropic in different orientations, and the anisotropic mechanical properties occur finally. Therefore, the anisotropic mechanical properties are determined by the anisotropic microstructures, both the anisotropic of matrix and the
Anisotropic phenomena in gauge/gravity duality
International Nuclear Information System (INIS)
Zeller, Hansjoerg
2014-01-01
In this thesis we use gauge/gravity duality to model anisotropic effects realised in nature. Firstly we analyse transport properties in holographic systems with a broken rotational invariance. Secondly we discuss geometries dual to IR fixed points with anisotropic scaling behaviour, which are related to quantum critical points in condensed matter systems. Gauge/gravity duality relates a gravity theory in Anti-de Sitter space to a lower dimensional strongly coupled quantum field theory in Minkowski space. Over the past decade this duality provided many insights into systems at strong coupling, e.g. quark-gluon plasma and condensed matter close to quantum critical points. One very important result computed in this framework is the value of the shear viscosity divided by the entropy density in strongly coupled theories. The quantitative result agrees very well with measurements of the ratio in quark-gluon plasma. However, for isotropic two derivative Einstein gravity it is temperature independent. We show that by breaking the rotational symmetry of a system we obtain a temperature dependent shear viscosity over entropy density. This is important to make contact with real world systems, since substances in nature display such dependence. In addition, we derive various transport properties in strongly coupled anisotropic systems using the gauge/gravity dictionary. The most notable results include an electrical conductivity with Drude behaviour in the low frequency region. This resembles conductors with broken translational invariance. However, we did not implement the breaking explicitly. Furthermore, our analysis shows that this setup models effects, resembling the piezoelectric and exoelectric effects, known from liquid crystals. In a second project we discuss a geometry with non-trivial scaling behaviour in order to model an IR fixed point of condensed matter theories. We construct the UV completion of this geometry and analyse its properties by computing the
Anisotropic phenomena in gauge/gravity duality
Energy Technology Data Exchange (ETDEWEB)
Zeller, Hansjoerg
2014-05-26
In this thesis we use gauge/gravity duality to model anisotropic effects realised in nature. Firstly we analyse transport properties in holographic systems with a broken rotational invariance. Secondly we discuss geometries dual to IR fixed points with anisotropic scaling behaviour, which are related to quantum critical points in condensed matter systems. Gauge/gravity duality relates a gravity theory in Anti-de Sitter space to a lower dimensional strongly coupled quantum field theory in Minkowski space. Over the past decade this duality provided many insights into systems at strong coupling, e.g. quark-gluon plasma and condensed matter close to quantum critical points. One very important result computed in this framework is the value of the shear viscosity divided by the entropy density in strongly coupled theories. The quantitative result agrees very well with measurements of the ratio in quark-gluon plasma. However, for isotropic two derivative Einstein gravity it is temperature independent. We show that by breaking the rotational symmetry of a system we obtain a temperature dependent shear viscosity over entropy density. This is important to make contact with real world systems, since substances in nature display such dependence. In addition, we derive various transport properties in strongly coupled anisotropic systems using the gauge/gravity dictionary. The most notable results include an electrical conductivity with Drude behaviour in the low frequency region. This resembles conductors with broken translational invariance. However, we did not implement the breaking explicitly. Furthermore, our analysis shows that this setup models effects, resembling the piezoelectric and exoelectric effects, known from liquid crystals. In a second project we discuss a geometry with non-trivial scaling behaviour in order to model an IR fixed point of condensed matter theories. We construct the UV completion of this geometry and analyse its properties by computing the
SU-E-J-232: Feasibility of MRI-Based Preplan On Low Dose Rate Prostate Brachytherapy
Energy Technology Data Exchange (ETDEWEB)
Huang, Y; Tward, J; Rassiah-Szegedi, P; Zhao, H; Sarkar, V; Huang, L; Szegedi, M; Kokeny, K; Salter, B [University of Utah Huntsman Cancer Institute, Salt Lake City, UT (United States)
2015-06-15
Purpose: To investigate the feasibility of using MRI-based preplan for low dose rate prostate brachytherapy. Methods: 12 patients who received transrectal ultrasound (TRUS) guided prostate brachytherapy with Pd-103 were retrospectively studied. Our care-standard of the TRUS-based preplan served as the control. One or more prostate T2-weighted wide and/or narrow-field of view MRIs obtained within the 3 months prior to the implant were imported into the MIM Symphony software v6.3 (MIM Software Inc., Cleveland, OH) for each patient. In total, 37 MRI preplans (10 different image sequences with average thickness of 4.8mm) were generated. The contoured prostate volume and the seed counts required to achieve adequate dosimetric coverage from TRUS and MRI preplans were compared for each patient. The effects of different MRI sequences and image thicknesses were also investigated statistically using Student’s t-test. Lastly, the nomogram from the MRI preplan and TRUS preplan from our historical treatment data were compared. Results: The average prostate volume contoured on the TRUS and MRI were 26.6cc (range: 12.6∼41.3cc), and 27.4 cc (range: 14.3∼50.0cc), respectively. Axial MRI thicknesses (range: 3.5∼8.1mm) did not significantly affect the contoured volume or the number of seeds required on the preplan (R2 = 0.0002 and 0.0012, respectively). Four of the MRI sequences (AX-T2, AX-T2-Whole-Pelvis, AX-T2-FSE, and AXIALT2- Hi-Res) showed statistically significant better prostate volume agreement with TRUS than the other seven sequences (P <0.01). Nomogram overlay between the MRI and TRUS preplans showed good agreement; indicating volumes contoured on MRI preplan scan reliably predict how many seeds are needed for implant. Conclusion: Although MRI does not allow for determination of the actual implant geometry, it can give reliable volumes for seed ordering purposes. Our future work will investigate if MRI is sufficient to reliably replace TRUS preplanning in patients
Energy Technology Data Exchange (ETDEWEB)
Chen, X; Dalah, E; Prior, P; Lawton, C; Li, X [Medical College of Wisconsin, Milwaukee, WI (United States)
2015-06-15
Purpose: Apparent diffusion coefficient (ADC) map may help to delineate the gross tumor volume (GTV) in prostate gland. Dose painting with external beam radiotherapy for GTV might increase the local tumor control. The purpose of this study is to explore the maximum boosting dose on GTV using VMAT without sacrificing sparing of organs at risk (OARs) in MRI based planning. Methods: VMAT plans for 5 prostate patients were generated following the commonly used dose volume (DV) criteria based on structures contoured on T2 weighted MRI with bulk electron density assignment using electron densities derived from ICRU46. GTV for each patient was manually delineated based on ADC maps and fused to T2-weighted image set for planning study. A research planning system with Monte Carlo dose engine (Monaco, Elekta) was used to generate the VMAT plans with boosting dose on GTV gradually increased from 85Gy to 100Gy. DV parameters, including V(boosting-dose) (volume covered by boosting dose) for GTV, V75.6Gy for PTV, V45Gy, V70Gy, V72Gy and D1cc (Maximum dose to 1cc volume) for rectum and bladder, were used to measure plan quality. Results: All cases achieve at least 99.0% coverage of V(boosting-dose) on GTV and 95% coverage of V75.6Gy to the PTV. All the DV criteria, V45Gy≤50% and V70Gy≤15% for bladder and rectum, D1cc ≤77Gy (Rectum) and ≤80Gy (Bladder), V72Gy≤5% (rectum and bladder) were maintained when boosting GTV to 95Gy for all cases studied. Except for two patients, all the criteria were also met when the boosting dose goes to 100Gy. Conclusion: It is dosimetrically feasible safe to boost the dose to at least 95Gy to ADC defined GTV in prostate cancer using MRI guided VMAT delivery. Conclusion: It is dosimetrically feasible safe to boost the dose to at least 95Gy to ADC defined GTV in prostate cancer using MRI guided VMAT delivery. This research is partially supported by Elekta Inc.
Liao, Zhaoliang; Koster, Gertjan; Huijben, Mark; Rijnders, A.J.H.M.
2017-01-01
An anisotropic double exchange interaction driven giant transport anisotropy is demonstrated in a canonic double exchange system of La2/3Sr1/3MnO3 ultrathin films epitaxially grown on NdGaO3 (110) substrates. The oxygen octahedral coupling at the La2/3Sr1/3MnO3/NdGaO3 interface induces a planar
Anisotropic gradients in the upper mantle
International Nuclear Information System (INIS)
Garmany, J.
1981-01-01
Pn amplitudes in some widely spaced sets of orthogonal marine refraction lines on young oceanic crust are greater in the fast direction than in the slow direction. This is inconsistent with the predicted amplitude behavior for simple head waves, but can be explained by an increase in anisotropy with depth. It appears that these gradients are due to increasing olivine crystal orientation, although changes in the relative abundance of two anisotropic minerals without variable tectonization could also account for the observations. Depth variation of tectonization most probably indicates very high temperature gradients at the Moho. This would imply a substantial amount of convective heat transport in the whole oceanic crust near mid-ocean rises
Turbulent Output-Based Anisotropic Adaptation
Park, Michael A.; Carlson, Jan-Renee
2010-01-01
Controlling discretization error is a remaining challenge for computational fluid dynamics simulation. Grid adaptation is applied to reduce estimated discretization error in drag or pressure integral output functions. To enable application to high O(10(exp 7)) Reynolds number turbulent flows, a hybrid approach is utilized that freezes the near-wall boundary layer grids and adapts the grid away from the no slip boundaries. The hybrid approach is not applicable to problems with under resolved initial boundary layer grids, but is a powerful technique for problems with important off-body anisotropic features. Supersonic nozzle plume, turbulent flat plate, and shock-boundary layer interaction examples are presented with comparisons to experimental measurements of pressure and velocity. Adapted grids are produced that resolve off-body features in locations that are not known a priori.
Extended phase graphs with anisotropic diffusion
Weigel, M.; Schwenk, S.; Kiselev, V. G.; Scheffler, K.; Hennig, J.
2010-08-01
The extended phase graph (EPG) calculus gives an elegant pictorial description of magnetization response in multi-pulse MR sequences. The use of the EPG calculus enables a high computational efficiency for the quantitation of echo intensities even for complex sequences with multiple refocusing pulses with arbitrary flip angles. In this work, the EPG concept dealing with RF pulses with arbitrary flip angles and phases is extended to account for anisotropic diffusion in the presence of arbitrary varying gradients. The diffusion effect can be expressed by specific diffusion weightings of individual magnetization pathways. This can be represented as an action of a linear operator on the magnetization state. The algorithm allows easy integration of diffusion anisotropy effects. The formalism is validated on known examples from literature and used to calculate the effective diffusion weighting in multi-echo sequences with arbitrary refocusing flip angles.
Long-range interaction of anisotropic systems
Zhang, Junyi
2015-02-01
The first-order electrostatic interaction energy between two far-apart anisotropic atoms depends not only on the distance between them but also on their relative orientation, according to Rayleigh-Schrödinger perturbation theory. Using the first-order interaction energy and the continuum model, we study the long-range interaction between a pair of parallel pristine graphene sheets at zero temperature. The asymptotic form of the obtained potential density, &epsi:(D) &prop: ?D ?3 ?O(D?4), is consistent with the random phase approximation and Lifshitz theory. Accordingly, neglectance of the anisotropy, especially the nonzero first-order interaction energy, is the reason why the widely used Lennard-Jones potential approach and dispersion corrections in density functional theory give a wrong asymptotic form ε(D) &prop: ?D?4. © EPLA, 2015.
Spectral functions from anisotropic lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Aarts, G.; Allton, C. [Department of Physics, Swansea University, Swansea SA2 8PP, Wales (United Kingdom); Amato, A. [Helsinki Institute of Physics and University of Helsinki, Helsinki (Finland); Evans, W. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics Universitat Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland); Giudice, P. [Institut für Theoretische Physik, Universität Münster, D–48149 Münster (Germany); Harris, T. [School of Mathematics, Trinity College, Dublin 2 (Ireland); Kelly, A. [Department of Mathematical Physics, Maynooth University, Maynooth, Co Kildare (Ireland); Kim, S.Y. [Department of Physics, Sejong University, Seoul 143-747 (Korea, Republic of); Lombardo, M.P. [INFN–Laboratori Nazionali di Frascati, I–00044 Frascati (RM) (Italy); Praki, K. [Department of Physics, Swansea University, Swansea SA2 8PP, Wales (United Kingdom); Ryan, S.M. [School of Mathematics, Trinity College, Dublin 2 (Ireland); Skullerud, J.-I. [Department of Mathematical Physics, Maynooth University, Maynooth, Co Kildare (Ireland)
2016-12-15
The FASTSUM collaboration has been carrying out lattice simulations of QCD for temperatures ranging from one third to twice the crossover temperature, investigating the transition region, as well as the properties of the Quark Gluon Plasma. In this contribution we concentrate on quarkonium correlators and spectral functions. We work in a fixed scale scheme and use anisotropic lattices which help achieving the desirable fine resolution in the temporal direction, thus facilitating the (ill posed) integral transform from imaginary time to frequency space. We contrast and compare results for the correlators obtained with different methods, and different temporal spacings. We observe robust features of the results, confirming the sequential dissociation scenario, but also quantitative differences indicating that the methods' systematic errors are not yet under full control. We briefly outline future steps towards accurate results for the spectral functions and their associated statistical and systematic errors.
Long-range interaction of anisotropic systems
Zhang, Junyi; Schwingenschlö gl, Udo
2015-01-01
The first-order electrostatic interaction energy between two far-apart anisotropic atoms depends not only on the distance between them but also on their relative orientation, according to Rayleigh-Schrödinger perturbation theory. Using the first-order interaction energy and the continuum model, we study the long-range interaction between a pair of parallel pristine graphene sheets at zero temperature. The asymptotic form of the obtained potential density, &epsi:(D) &prop: ?D ?3 ?O(D?4), is consistent with the random phase approximation and Lifshitz theory. Accordingly, neglectance of the anisotropy, especially the nonzero first-order interaction energy, is the reason why the widely used Lennard-Jones potential approach and dispersion corrections in density functional theory give a wrong asymptotic form ε(D) &prop: ?D?4. © EPLA, 2015.
Inverse anisotropic conductivity from internal current densities
International Nuclear Information System (INIS)
Bal, Guillaume; Guo, Chenxi; Monard, François
2014-01-01
This paper concerns the reconstruction of a fully anisotropic conductivity tensor γ from internal current densities of the form J = γ∇u, where u solves a second-order elliptic equation ∇ · (γ∇u) = 0 on a bounded domain X with prescribed boundary conditions. A minimum number of n + 2 such functionals known on Y⊂X, where n is the spatial dimension, is sufficient to guarantee a unique and explicit reconstruction of γ locally on Y. Moreover, we show that γ is reconstructed with a loss of one derivative compared to errors in the measurement of J in the general case and no loss of derivatives in the special case where γ is scalar. We also describe linear combinations of mixed partial derivatives of γ that exhibit better stability properties and hence can be reconstructed with better resolution in practice. (paper)
Stability of anisotropic beams with space charge
International Nuclear Information System (INIS)
Hofmann, I.
1997-07-01
We calculate coherent frequencies and stability properties of anisotropic or ''non-equipartitioned'' beams with different focusing constants and emittances in the two transverse directions. Based on the self-consistent Vlasov-Poisson equations the dispersion relations of transverse multipole oscillations with quadrupolar, sextupolar and octupolar symmetry are solved numerically. The eigenfrequencies give the coherent space charge tune shift for linear or nonlinear resonances in circular accelerators. We find that for sufficiently large energy anisotropy some of the eigenmodes become unstable in the space-charge-dominated regime. The properties of these anisotropy instabilities are used to show that ''non-equipartitioned'' beams can be tolerated in high-current linear accelerators. It is only in beams with strongly space-charge-depressed betatron tunes where harmful instabilities leading to emittance exchange should be expected. (orig.)
Anisotropic thermal expansion in flexible materials
Romao, Carl P.
2017-10-01
A definition of the Grüneisen parameters for anisotropic materials is derived based on the response of phonon frequencies to uniaxial stress perturbations. This Grüneisen model relates the thermal expansion in a given direction (αi i) to one element of the elastic compliance tensor, which corresponds to the Young's modulus in that direction (Yi i). The model is tested through ab initio prediction of thermal expansion in zinc, graphite, and calcite using density functional perturbation theory, indicating that it could lead to increased accuracy for structurally complex systems. The direct dependence of αi i on Yi i suggests that materials which are flexible along their principal axes but rigid in other directions will generally display both positive and negative thermal expansion.
Effective stress law for anisotropic elastic deformation
International Nuclear Information System (INIS)
Carroll, M.M.
1979-01-01
An effective stress law is derived analytically to describe the effect of pore fluid pressure on the linearly elastic response of saturated porous rocks which exhibit anisotropy. For general anisotropy the difference between the effective stress and the applied stress is not hydrostatic. The effective stress law involves two constants for transversely isotropic response and three constants for orthotropic response; these constants can be expressed in terms of the moduli of the porous material and of the solid material. These expressions simplify considerably when the anisotropy is structural rather than intrinsic, i.e., in the case of an isotropic solid material with an anisotropic pore structure. In this case the effective stress law involves the solid or grain bulk modulus and two or three moduli of the porous material, for transverse isotropy and orthotropy, respectively. The law reduces, in the case of isotropic response, to that suggested by Geertsma (1957) and by Skempton (1961) and derived analytically by Nur and Byerlee
Analytical study of anisotropic compact star models
Energy Technology Data Exchange (ETDEWEB)
Ivanov, B.V. [Bulgarian Academy of Science, Institute for Nuclear Research and Nuclear Energy, Sofia (Bulgaria)
2017-11-15
A simple classification is given of the anisotropic relativistic star models, resembling the one of charged isotropic solutions. On the ground of this database, and taking into account the conditions for physically realistic star models, a method is proposed for generating all such solutions. It is based on the energy density and the radial pressure as seeding functions. Numerous relations between the realistic conditions are found and the need for a graphic proof is reduced just to one pair of inequalities. This general formalism is illustrated with an example of a class of solutions with linear equation of state and simple energy density. It is found that the solutions depend on three free constants and concrete examples are given. Some other popular models are studied with the same method. (orig.)
Derivation of the optical constants of anisotropic
Aronson, J. R.; Emslie, A. G.; Smith, E. M.; Strong, P. F.
1985-07-01
This report concerns the development of methods for obtaining the optical constants of anisotropic crystals of the triclinic and monoclinic systems. The principal method used, classical dispersion theory, is adapted to these crystal systems by extending the Lorentz line parameters to include the angles characterizing the individual resonances, and by replacing the dielectric constant by a dielectric tensor. The sample crystals are gypsium, orthoclase and chalcanthite. The derived optical constants are shown to be suitable for modeling the optical properties of particulate media in the infrared spectral region. For those materials where suitable size single crystals are not available, an extension of a previously used method is applied to alabaster, a polycrystalline material of the monoclinic crystal system.
Anisotropic dynamic mass density for fluidsolid composites
Wu, Ying
2012-10-01
By taking the low frequency limit of multiple-scattering theory, we obtain the dynamic effective mass density of fluidsolid composites with a two-dimensional rectangular lattice structure. The anisotropic mass density can be described by an angle-dependent dipole solution, to the leading-order of solid concentration. The angular dependence vanishes for the square lattice, but at high solid concentrations there is a structure-dependent factor that contributes to the leading-order solution. In all cases, Woods formula is found to be accurately valid for the effective bulk modulus, independent of the structures. Numerical evaluations from the solutions are shown to be in excellent agreement with finite-element simulations. © 2012 Elsevier B.V.
An Anisotropic Hardening Model for Springback Prediction
Zeng, Danielle; Xia, Z. Cedric
2005-08-01
As more Advanced High-Strength Steels (AHSS) are heavily used for automotive body structures and closures panels, accurate springback prediction for these components becomes more challenging because of their rapid hardening characteristics and ability to sustain even higher stresses. In this paper, a modified Mroz hardening model is proposed to capture realistic Bauschinger effect at reverse loading, such as when material passes through die radii or drawbead during sheet metal forming process. This model accounts for material anisotropic yield surface and nonlinear isotropic/kinematic hardening behavior. Material tension/compression test data are used to accurately represent Bauschinger effect. The effectiveness of the model is demonstrated by comparison of numerical and experimental springback results for a DP600 straight U-channel test.
An Anisotropic Hardening Model for Springback Prediction
International Nuclear Information System (INIS)
Zeng, Danielle; Xia, Z. Cedric
2005-01-01
As more Advanced High-Strength Steels (AHSS) are heavily used for automotive body structures and closures panels, accurate springback prediction for these components becomes more challenging because of their rapid hardening characteristics and ability to sustain even higher stresses. In this paper, a modified Mroz hardening model is proposed to capture realistic Bauschinger effect at reverse loading, such as when material passes through die radii or drawbead during sheet metal forming process. This model accounts for material anisotropic yield surface and nonlinear isotropic/kinematic hardening behavior. Material tension/compression test data are used to accurately represent Bauschinger effect. The effectiveness of the model is demonstrated by comparison of numerical and experimental springback results for a DP600 straight U-channel test
Anisotropic magnetism in field-structured composites
International Nuclear Information System (INIS)
Martin, James E.; Venturini, Eugene; Odinek, Judy; Anderson, Robert A.
2000-01-01
Magnetic field-structured composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g., rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chainlike particle structures, and a biaxial field produces sheetlike particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCs of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material. (c) 2000 The American Physical Society
Isotropic and anisotropic surface wave cloaking techniques
International Nuclear Information System (INIS)
McManus, T M; Spada, L La; Hao, Y
2016-01-01
In this paper we compare two different approaches for surface waves cloaking. The first technique is a unique application of Fermat’s principle and requires isotropic material properties, but owing to its derivation is limited in its applicability. The second technique utilises a geometrical optics approximation for dealing with rays bound to a two dimensional surface and requires anisotropic material properties, though it can be used to cloak any smooth surface. We analytically derive the surface wave scattering behaviour for both cloak techniques when applied to a rotationally symmetric surface deformation. Furthermore, we simulate both using a commercially available full-wave electromagnetic solver and demonstrate a good level of agreement with their analytically derived solutions. Our analytical solutions and simulations provide a complete and concise overview of two different surface wave cloaking techniques. (paper)
Isotropic and anisotropic surface wave cloaking techniques
McManus, T. M.; La Spada, L.; Hao, Y.
2016-04-01
In this paper we compare two different approaches for surface waves cloaking. The first technique is a unique application of Fermat’s principle and requires isotropic material properties, but owing to its derivation is limited in its applicability. The second technique utilises a geometrical optics approximation for dealing with rays bound to a two dimensional surface and requires anisotropic material properties, though it can be used to cloak any smooth surface. We analytically derive the surface wave scattering behaviour for both cloak techniques when applied to a rotationally symmetric surface deformation. Furthermore, we simulate both using a commercially available full-wave electromagnetic solver and demonstrate a good level of agreement with their analytically derived solutions. Our analytical solutions and simulations provide a complete and concise overview of two different surface wave cloaking techniques.
Recent developments in anisotropic heterogeneous shell theory
Grigorenko, Alexander Ya; Grigorenko, Yaroslav M; Vlaikov, Georgii G
2016-01-01
This volume focuses on the relevant general theory and presents some first applications, namely those based on classical shell theory. After a brief introduction, during which the history and state-of-the-art are discussed, the first chapter presents the mechanics of anisotropic heterogeneous shells, covering all relevant assumptions and the basic relations of 3D elasticity, classical and refined shell models. The second chapter examines the numerical techniques that are used, namely discrete orthogonalization, spline-collocation and Fourier series, while the third highlights applications based on classical theory, in particular, the stress-strain state of shallow shells, non-circular shells, shells of revolution, and free vibrations of conical shells. The book concludes with a summary and an outlook bridging the gap to the second volume.
Effective orthorhombic anisotropic models for wavefield extrapolation
Ibanez-Jacome, W.
2014-07-18
Wavefield extrapolation in orthorhombic anisotropic media incorporates complicated but realistic models to reproduce wave propagation phenomena in the Earth\\'s subsurface. Compared with the representations used for simpler symmetries, such as transversely isotropic or isotropic, orthorhombic models require an extended and more elaborated formulation that also involves more expensive computational processes. The acoustic assumption yields more efficient description of the orthorhombic wave equation that also provides a simplified representation for the orthorhombic dispersion relation. However, such representation is hampered by the sixth-order nature of the acoustic wave equation, as it also encompasses the contribution of shear waves. To reduce the computational cost of wavefield extrapolation in such media, we generate effective isotropic inhomogeneous models that are capable of reproducing the firstarrival kinematic aspects of the orthorhombic wavefield. First, in order to compute traveltimes in vertical orthorhombic media, we develop a stable, efficient and accurate algorithm based on the fast marching method. The derived orthorhombic acoustic dispersion relation, unlike the isotropic or transversely isotropic ones, is represented by a sixth order polynomial equation with the fastest solution corresponding to outgoing P waves in acoustic media. The effective velocity models are then computed by evaluating the traveltime gradients of the orthorhombic traveltime solution, and using them to explicitly evaluate the corresponding inhomogeneous isotropic velocity field. The inverted effective velocity fields are source dependent and produce equivalent first-arrival kinematic descriptions of wave propagation in orthorhombic media. We extrapolate wavefields in these isotropic effective velocity models using the more efficient isotropic operator, and the results compare well, especially kinematically, with those obtained from the more expensive anisotropic extrapolator.
Measuring anisotropic muscle stiffness properties using elastography.
Green, M A; Geng, G; Qin, E; Sinkus, R; Gandevia, S C; Bilston, L E
2013-11-01
Physiological and pathological changes to the anisotropic mechanical properties of skeletal muscle are still largely unknown, with only a few studies quantifying changes in vivo. This study used the noninvasive MR elastography (MRE) technique, in combination with diffusion tensor imaging (DTI), to measure shear modulus anisotropy in the human skeletal muscle in the lower leg. Shear modulus measurements parallel and perpendicular to the fibre direction were made in 10 healthy subjects in the medial gastrocnemius, soleus and tibialis anterior muscles. The results showed significant differences in the medial gastrocnemius (μ‖ = 0.86 ± 0.15 kPa; μ⊥ = 0.66 ± 0.19 kPa, P < 0.001), soleus (μ‖ = 0.83 ± 0.22 kPa; μ⊥ = 0.65 ± 0.13 kPa, P < 0.001) and the tibialis anterior (μ‖ = 0.78 ± 0.24 kPa; μ⊥ = 0.66 ± 0.16 kPa, P = 0.03) muscles, where the shear modulus measured in the direction parallel is greater than that measured in the direction perpendicular to the muscle fibres. No significant differences were measured across muscle groups. This study provides the first direct estimates of the anisotropic shear modulus in the triceps surae muscle group, and shows that the technique may be useful for the probing of mechanical anisotropy changes caused by disease, aging and injury. Copyright © 2013 John Wiley & Sons, Ltd.
Radial stability of anisotropic strange quark stars
Energy Technology Data Exchange (ETDEWEB)
Arbañil, José D.V.; Malheiro, M., E-mail: jose.arbanil@upn.pe, E-mail: malheiro@ita.br [ITA—Instituto Tecnológico de Aeronáutica—Departamento de Física, 12228-900, São José dos Campos, São Paulo (Brazil)
2016-11-01
The influence of the anisotropy in the equilibrium and stability of strange stars is investigated through the numerical solution of the hydrostatic equilibrium equation and the radial oscillation equation, both modified from their original version to include this effect. The strange matter inside the quark stars is described by the MIT bag model equation of state. For the anisotropy two different kinds of local anisotropic σ = p {sub t} − p {sub r} are considered, where p {sub t} and p {sub r} are respectively the tangential and the radial pressure: one that is null at the star's surface defined by p {sub r} ( R ) = 0, and one that is nonnull at the surface, namely, σ {sub s} = 0 and σ {sub s} {sub ≠} {sub 0}. In the case σ {sub s} = 0, the maximum mass value and the zero frequency of oscillation are found at the same central energy density, indicating that the maximum mass marks the onset of the instability. For the case σ {sub s} {sub ≠} {sub 0}, we show that the maximum mass point and the zero frequency of oscillation coincide in the same central energy density value only in a sequence of equilibrium configurations with the same value of σ {sub s} . Thus, the stability star regions are determined always by the condition dM / d ρ {sub c} {sub >} {sub 0} only when the tangential pressure is maintained fixed at the star surface's p {sub t} ( R ). These results are also quite important to analyze the stability of other anisotropic compact objects such as neutron stars, boson stars and gravastars.
Effective orthorhombic anisotropic models for wavefield extrapolation
Ibanez-Jacome, W.; Alkhalifah, Tariq Ali; Waheed, Umair bin
2014-01-01
Wavefield extrapolation in orthorhombic anisotropic media incorporates complicated but realistic models to reproduce wave propagation phenomena in the Earth's subsurface. Compared with the representations used for simpler symmetries, such as transversely isotropic or isotropic, orthorhombic models require an extended and more elaborated formulation that also involves more expensive computational processes. The acoustic assumption yields more efficient description of the orthorhombic wave equation that also provides a simplified representation for the orthorhombic dispersion relation. However, such representation is hampered by the sixth-order nature of the acoustic wave equation, as it also encompasses the contribution of shear waves. To reduce the computational cost of wavefield extrapolation in such media, we generate effective isotropic inhomogeneous models that are capable of reproducing the firstarrival kinematic aspects of the orthorhombic wavefield. First, in order to compute traveltimes in vertical orthorhombic media, we develop a stable, efficient and accurate algorithm based on the fast marching method. The derived orthorhombic acoustic dispersion relation, unlike the isotropic or transversely isotropic ones, is represented by a sixth order polynomial equation with the fastest solution corresponding to outgoing P waves in acoustic media. The effective velocity models are then computed by evaluating the traveltime gradients of the orthorhombic traveltime solution, and using them to explicitly evaluate the corresponding inhomogeneous isotropic velocity field. The inverted effective velocity fields are source dependent and produce equivalent first-arrival kinematic descriptions of wave propagation in orthorhombic media. We extrapolate wavefields in these isotropic effective velocity models using the more efficient isotropic operator, and the results compare well, especially kinematically, with those obtained from the more expensive anisotropic extrapolator.
Tunneling anisotropic magnetoresistance driven by magnetic phase transition.
Chen, X Z; Feng, J F; Wang, Z C; Zhang, J; Zhong, X Y; Song, C; Jin, L; Zhang, B; Li, F; Jiang, M; Tan, Y Z; Zhou, X J; Shi, G Y; Zhou, X F; Han, X D; Mao, S C; Chen, Y H; Han, X F; Pan, F
2017-09-06
The independent control of two magnetic electrodes and spin-coherent transport in magnetic tunnel junctions are strictly required for tunneling magnetoresistance, while junctions with only one ferromagnetic electrode exhibit tunneling anisotropic magnetoresistance dependent on the anisotropic density of states with no room temperature performance so far. Here, we report an alternative approach to obtaining tunneling anisotropic magnetoresistance in α'-FeRh-based junctions driven by the magnetic phase transition of α'-FeRh and resultantly large variation of the density of states in the vicinity of MgO tunneling barrier, referred to as phase transition tunneling anisotropic magnetoresistance. The junctions with only one α'-FeRh magnetic electrode show a magnetoresistance ratio up to 20% at room temperature. Both the polarity and magnitude of the phase transition tunneling anisotropic magnetoresistance can be modulated by interfacial engineering at the α'-FeRh/MgO interface. Besides the fundamental significance, our finding might add a different dimension to magnetic random access memory and antiferromagnet spintronics.Tunneling anisotropic magnetoresistance is promising for next generation memory devices but limited by the low efficiency and functioning temperature. Here the authors achieved 20% tunneling anisotropic magnetoresistance at room temperature in magnetic tunnel junctions with one α'-FeRh magnetic electrode.
Development of laser ablation plasma by anisotropic self-radiation
Directory of Open Access Journals (Sweden)
Ohnishi Naofumi
2013-11-01
Full Text Available We have proposed a method for reproducing an accurate solution of low-density ablation plasma by properly treating anisotropic radiation. Monte-Carlo method is employed for estimating Eddington tensor with limited number of photon samples in each fluid time step. Radiation field from ablation plasma is significantly affected by the anisotropic Eddington tensor. Electron temperature around the ablation surface changes with the radiation field and is responsible for the observed emission. An accurate prediction of the light emission from the laser ablation plasma requires a careful estimation of the anisotropic radiation field.
On Pokrovskii's anisotropic gap equations in superconductivity theory
Yang, Yisong
2003-11-01
An existence and uniqueness theorem for Pokrovskii's zero-temperature anisotropic gap equation is proved. Furthermore, it is shown that Pokrovskii's finite-temperature equation is inconsistent with the Bardeen-Cooper-Schrieffer (BCS) theory. A reformulation of the anisotropic gap equation is presented along the line of Pokrovskii and it is shown that the new equation is consistent with the BCS theory for the whole temperature range. As an application, the Markowitz-Kadanoff model for anisotropic superconductivity is considered and a rigorous proof of the half-integer-exponent isotope effect is obtained. Furthermore, a sharp estimate of the gap solution near the transition temperature is established.
International Nuclear Information System (INIS)
Satter, M.A.
1990-08-01
In this paper, a formalism for studying the anisotropic interaction between two substitutional magnetic impurities and the magnetic anisotropic effect in a dilute noble metal- transition metal magnetic alloy has been developed from relativistic scattering theory. The theoretical development and the computational techniques of this formalism are based on relativistic spin-polarized scattering theory and relativistic band structure frameworks. For studying the magnetic anisotropic effect a convenient ''working'' frame of reference with its axes oriented along the fcc crystal axes is set up. This formalism is applied to study the situation for two Fe impurities in paramagnetic Au hosts. For AuFe dilute alloy, the two impurity site interaction as a function of separation is not oscillatory and the anisotropic effect is found to be less than the two site interaction itself only by an order of magnitude. Apart from the anisotropic coupling of the two impurity spins to the separation vector, for the first time, another weak anisotropic coupling to the crystal axes is also contained in the two site interaction. These anisotropic effects are the results of the relativistic spin-orbit interaction which are incorporated into the formalism. (author). 22 refs, 5 figs
Anisotropic nature of radially strained metal tubes
Strickland, Julie N.
Metal pipes are sometimes swaged by a metal cone to enlarge them, which increases the strain in the material. The amount of strain is important because it affects the burst and collapse strength. Burst strength is the amount of internal pressure that a pipe can withstand before failure, while collapse strength is the amount of external pressure that a pipe can withstand before failure. If the burst or collapse strengths are exceeded, the pipe may fracture, causing critical failure. Such an event could cost the owners and their customers millions of dollars in clean up, repair, and lost time, in addition to the potential environmental damage. Therefore, a reliable way of estimating the burst and collapse strength of strained pipe is desired and valuable. The sponsor currently rates strained pipes using the properties of raw steel, because those properties are easily measured (for example, yield strength). In the past, the engineers assumed that the metal would be work-hardened when swaged, so that yield strength would increase. However, swaging introduces anisotropic strain, which may decrease the yield strength. This study measured the yield strength of strained material in the transverse and axial direction and compared them to raw material, to determine the amount of anisotropy. This information will be used to more accurately determine burst and collapse ratings for strained pipes. More accurate ratings mean safer products, which will minimize risk for the sponsor's customers. Since the strained metal has a higher yield strength than the raw material, using the raw yield strength to calculate burst and collapse ratings is a conservative method. The metal has even higher yield strength after strain aging, which indicates that the stresses are relieved. Even with the 12% anisotropy in the strained and 9% anisotropy in the strain aged specimens, the raw yield strengths are lower and therefore more conservative. I recommend that the sponsor continue using the raw
Timescales of isotropic and anisotropic cluster collapse
Bartelmann, M.; Ehlers, J.; Schneider, P.
1993-12-01
From a simple estimate for the formation time of galaxy clusters, Richstone et al. have recently concluded that the evidence for non-virialized structures in a large fraction of observed clusters points towards a high value for the cosmological density parameter Omega0. This conclusion was based on a study of the spherical collapse of density perturbations, assumed to follow a Gaussian probability distribution. In this paper, we extend their treatment in several respects: first, we argue that the collapse does not start from a comoving motion of the perturbation, but that the continuity equation requires an initial velocity perturbation directly related to the density perturbation. This requirement modifies the initial condition for the evolution equation and has the effect that the collapse proceeds faster than in the case where the initial velocity perturbation is set to zero; the timescale is reduced by a factor of up to approximately equal 0.5. Our results thus strengthens the conclusion of Richstone et al. for a high Omega0. In addition, we study the collapse of density fluctuations in the frame of the Zel'dovich approximation, using as starting condition the analytically known probability distribution of the eigenvalues of the deformation tensor, which depends only on the (Gaussian) width of the perturbation spectrum. Finally, we consider the anisotropic collapse of density perturbations dynamically, again with initial conditions drawn from the probability distribution of the deformation tensor. We find that in both cases of anisotropic collapse, in the Zel'dovich approximation and in the dynamical calculations, the resulting distribution of collapse times agrees remarkably well with the results from spherical collapse. We discuss this agreement and conclude that it is mainly due to the properties of the probability distribution for the eigenvalues of the Zel'dovich deformation tensor. Hence, the conclusions of Richstone et al. on the value of Omega0 can be
Chiral magnetic effect in the anisotropic quark-gluon plasma
International Nuclear Information System (INIS)
Ali-Akbari, Mohammad; Taghavi, Seyed Farid
2015-01-01
An anisotropic thermal plasma phase of a strongly coupled gauge theory can be holographically modelled by an anisotropic AdS black hole. The temperature and anisotropy parameter of the AdS black hole background of interest http://dx.doi.org/10.1007/JHEP07(2011)054 is specified by the location of the horizon and the value of the Dilaton field at the horizon. Interestingly, for the first time, we obtain two functions for the values of the horizon and Dilaton field in terms of the temperature and anisotropy parameter. Then by introducing a number of spinning probe D7-branes in the anisotropic background, we compute the value of the chiral magnetic effect (CME). We observe that in the isotropic and anisotropic plasma the value of the CME is equal for the massless quarks. However, at fixed temperature, raising the anisotropy in the system will increase the value of the CME for the massive quarks.
Waves and discontinuities in relativistic and anisotropic magnetohydrodynamics
International Nuclear Information System (INIS)
Cissoko, Mahdy
1975-01-01
This work is devoted to the relativistic study of a non-dissipative anisotropic fluid diagram of infinite conductivity. Such a fluid diagram is constructed in part one. Starting from a macroscopic viewpoint a hydrothermodynamic study of the fluid diagram considered is carried out and the fundamental differential system of anisotropic magnetohydrodynamics is deduced. Part two concerns the study of characteristic varieties and propagation of waves for a polytropic anisotropic fluid diagram. Three types of characteristic varieties are revealed: entropy waves (or material waves), magnetosonic waves and Alfven waves. The propagation rates of Alfven and magnetosonic waves are situated with respect to each other. The study of wave cones showed up on the one hand certain special features of wave propagation in anisotropic magnetohydrodynamics and on the other hand the hyperbolic nature of differential operators associated with the various waves [fr
Angle-domain common-image gathers from anisotropic Gaussian ...
Indian Academy of Sciences (India)
3State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology,. Chengdu ... studied the extraction scheme of ADCIGs by using. Kirchhoff ..... The effect of shale properties on anisotropic brittleness.
Propagation of waves in a gravitating and rotating anisotropic heat ...
African Journals Online (AJOL)
Bheema
astrophysical plasmas. These plasmas are usually self-gravitating, rotating and embedded in a .... gravitational potential, and P denotes the anisotropic pressure tensor defined as. ൌ ୄ ሺ צǦ ..... Nonlinear Processes Geophysics, 11 :731.
Hydrodynamic cavitation in Stokes flow of anisotropic fluids
Stieger, Tillmann; Agha, Hakam; Schoen, Martin; Mazza, Marco G.; Sengupta, Anupam
2017-05-01
Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domain nucleates due to sudden pressure drop upon flow past a cylindrical obstacle within a microchannel. For an anisotropic fluid, the inception and growth of the cavitation domain ensued in the Stokes regime, while no cavitation was observed in isotropic liquids flowing under similar hydrodynamic parameters. Using simulations we identify a critical value of the Reynolds number for cavitation inception that scales inversely with the order parameter of the fluid. Strikingly, the critical Reynolds number for anisotropic fluids can be 50% lower than that of isotropic fluids.
Acoustic frequency filter based on anisotropic topological phononic crystals
Chen, Zeguo
2017-11-02
We present a design of acoustic frequency filter based on a two-dimensional anisotropic phononic crystal. The anisotropic band structure exhibits either a directional or a combined (global + directional) bandgap at certain frequency regions, depending on the geometry. When the time-reversal symmetry is broken, it may introduce a topologically nontrivial bandgap. The induced nontrivial bandgap and the original directional bandgap result in various interesting wave propagation behaviors, such as frequency filter. We develop a tight-binding model to characterize the effective Hamiltonian of the system, from which the contribution of anisotropy is explicitly shown. Different from the isotropic cases, the Zeeman-type splitting is not linear and the anisotropic bandgap makes it possible to achieve anisotropic propagation characteristics along different directions and at different frequencies.
Anisotropic Third-Order Regularization for Sparse Digital Elevation Models
Lellmann, Jan; Morel, Jean-Michel; Schö nlieb, Carola-Bibiane
2013-01-01
features of the contours while ensuring smoothness across level lines. We propose an anisotropic third-order model and an efficient method to adaptively estimate both the surface and the anisotropy. Our experiments show that the approach outperforms AMLE
Efficient anisotropic wavefield extrapolation using effective isotropic models
Alkhalifah, Tariq Ali; Ma, X.; Waheed, Umair bin; Zuberi, Mohammad
2013-01-01
Isotropic wavefield extrapolation is more efficient than anisotropic extrapolation, and this is especially true when the anisotropy of the medium is tilted (from the vertical). We use the kinematics of the wavefield, appropriately represented
On plasma stability under anisotropic random electric field influence
International Nuclear Information System (INIS)
Rabich, L.N.; Sosenko, P.P.
1987-01-01
The influence of anisotropic random field on plasma stability is studied. The thresholds and instability increments are obtained. The stabilizing influence of frequency missmatch and external magnetic field is pointed out
3-D waveform tomography sensitivity kernels for anisotropic media
Djebbi, Ramzi; Alkhalifah, Tariq Ali
2014-01-01
The complications in anisotropic multi-parameter inversion lie in the trade-off between the different anisotropy parameters. We compute the tomographic waveform sensitivity kernels for a VTI acoustic medium perturbation as a tool to investigate
Modelling of anisotropic compact stars of embedding class one
Energy Technology Data Exchange (ETDEWEB)
Bhar, Piyali [Government General Degree College, Department of Mathematics, Singur, Hooghly, West Bengal (India); Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Raj Kumar Goel Institute of Technology, Department of Mathematics, Ghaziabad, U.P. (India); Manna, Tuhina [St. Xavier' s College, Department of Commerce (Evening), Kolkata, West Bengal (India)
2016-10-15
In the present article, we have constructed static anisotropic compact star models of Einstein field equations for the spherical symmetric metric of embedding class one. By assuming the particular form of the metric function ν, we have solved the Einstein field equations for anisotropic matter distribution. The anisotropic models represent the realistic compact objects such as SAX J 1808.4-3658 (SS1), Her X-1, Vela X-12, PSR J1614-2230 and Cen X-3. We have reported our results in details for the compact star Her X-1 on the ground of physical properties such as pressure, density, velocity of sound, energy conditions, TOV equation and red-shift etc. Along with these, we have also discussed about the stability of the compact star models. Finally we made a comparison between our anisotropic stars with the realistic objects on the key aspects as central density, central pressure, compactness and surface red-shift. (orig.)
Jet quenching in a strongly coupled anisotropic plasma
Chernicoff, Mariano; Fernández, Daniel; Mateos, David; Trancanelli, Diego
2012-08-01
The jet quenching parameter of an anisotropic plasma depends on the relative orientation between the anisotropic direction, the direction of motion of the parton, and the direction along which the momentum broadening is measured. We calculate the jet quenching parameter of an anisotropic, strongly coupled {N} = 4 plasma by means of its gravity dual. We present the results for arbitrary orientations and arbitrary values of the anisotropy. The anisotropic value can be larger or smaller than the isotropic one, and this depends on whether the comparison is made at equal temperatures or at equal entropy densities. We compare our results to analogous calculations for the real-world quark-gluon plasma and find agreement in some cases and disagreement in others.
Acoustic frequency filter based on anisotropic topological phononic crystals
Chen, Zeguo; Zhao, Jiajun; Mei, Jun; Wu, Ying
2017-01-01
We present a design of acoustic frequency filter based on a two-dimensional anisotropic phononic crystal. The anisotropic band structure exhibits either a directional or a combined (global + directional) bandgap at certain frequency regions, depending on the geometry. When the time-reversal symmetry is broken, it may introduce a topologically nontrivial bandgap. The induced nontrivial bandgap and the original directional bandgap result in various interesting wave propagation behaviors, such as frequency filter. We develop a tight-binding model to characterize the effective Hamiltonian of the system, from which the contribution of anisotropy is explicitly shown. Different from the isotropic cases, the Zeeman-type splitting is not linear and the anisotropic bandgap makes it possible to achieve anisotropic propagation characteristics along different directions and at different frequencies.
Anisotropic plasma with flows in tokamak: Steady state and stability
International Nuclear Information System (INIS)
Ilgisonis, V.I.
1996-01-01
An adequate description of equilibrium and stability of anisotropic plasma with macroscopic flows in tokamaks is presented. The Chew-Goldberger-Low (CGL) approximation is consistently used to analyze anisotropic plasma dynamics. The admissible structure of a stationary flow is found to be the same as in the ideal magnetohydrodynamics with isotropic pressure (MHD), which means an allowance for the same relabeling symmetry as in ideal MHD systems with toroidally nested magnetic surfaces. A generalization of the Grad-Shafranov equation for the case of anisotropic plasma with flows confined in the axisymmetric magnetic field is derived. A variational principle was obtained, which allows for a stability analysis of anisotropic pressure plasma with flows, and takes into account the conservation laws resulting from the relabeling symmetry. This principle covers the previous stability criteria for static CGL plasma and for ideal MHD flows in isotropic plasma as well. copyright 1996 American Institute of Physics
Finite-difference modelling of anisotropic wave scattering in discrete ...
Indian Academy of Sciences (India)
A M Ekanem
2018-04-05
Apr 5, 2018 ... scattering characteristics in fractured media and thus, validate the practical utility of using anisotropic .... to fluid flow. ... account the porosity of the host rock and assumes .... The free surface boundary conditions generally.
Anisotropic wave-equation traveltime and waveform inversion
Feng, Shihang
2016-09-06
The wave-equation traveltime and waveform inversion (WTW) methodology is developed to invert for anisotropic parameters in a vertical transverse isotropic (VTI) meidum. The simultaneous inversion of anisotropic parameters v0, ε and δ is initially performed using the wave-equation traveltime inversion (WT) method. The WT tomograms are then used as starting background models for VTI full waveform inversion. Preliminary numerical tests on synthetic data demonstrate the feasibility of this method for multi-parameter inversion.
Hydrodynamic cavitation in Stokes flow of anisotropic fluids
Stieger, Tillmann; Agha, Hakam; Schoen, Martin; Mazza, Marco G.; Sengupta, Anupam
2017-01-01
Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domai...
Hybrid anisotropic materials for wind power turbine blades
Golfman, Yosif
2012-01-01
Based on rapid technological developments in wind power, governments and energy corporations are aggressively investing in this natural resource. Illustrating some of the crucial new breakthroughs in structural design and application of wind energy generation machinery, Hybrid Anisotropic Materials for Wind Power Turbine Blades explores new automated, repeatable production techniques that expand the use of robotics and process controls. These practices are intended to ensure cheaper fabrication of less-defective anisotropic material composites used to manufacture power turbine blades. This boo
Anisotropic modelling of the electrical conductivity of fractured bedrock
International Nuclear Information System (INIS)
Flykt, M.J.; Sihvola, A.H.; Eloranta, E.H.
1995-01-01
The electromagnetic characterization of fractured bedrock is of importance when studying the final disposal of nuclear waste. The different types of discontinuities at all scales in rocks can be viewed as an inhomogeneity. In some cases there are reasons to assume the influence of the discontinuities on electrical conductivity is anisotropic in character. The effort has been made to use electromagnetic mixing rules in the definition of an equivalent homogeneous anisotropic conductivity tensor for such fractured rock mass. (author) (16 refs., 6 figs.)
Algebraic collapsing acceleration of the characteristics method with anisotropic scattering
International Nuclear Information System (INIS)
Le Tellier, R.; Hebert, A.; Roy, R.
2004-01-01
In this paper, the characteristics solvers implemented in the lattice code Dragon are extended to allow a complete anisotropic treatment of the collision operator. An efficient synthetic acceleration method, called Algebraic Collapsing Acceleration (ACA), is presented. Tests show that this method can substantially speed up the convergence of scattering source iterations. The effect of boundary conditions, either specular or white reflections, on anisotropic scattering lattice-cell problems is also considered. (author)
Hybrid localized waves supported by resonant anisotropic metasurfaces
DEFF Research Database (Denmark)
Bogdanov, A. A.; Yermakov, O. Y.; Ovcharenko, A. I.
2016-01-01
We study both theoretically and experimentally a new class of surface electromagnetic waves supported by resonant anisotropic metasurface. At certain frequency this type of metasurface demonstrates the topological transition from elliptical to hyperbolic regime.......We study both theoretically and experimentally a new class of surface electromagnetic waves supported by resonant anisotropic metasurface. At certain frequency this type of metasurface demonstrates the topological transition from elliptical to hyperbolic regime....
Thermal fluctuations and critical behavior in a magnetized, anisotropic plasma
International Nuclear Information System (INIS)
Hazeltine, R. D.; Mahajan, S. M.
2013-01-01
Thermal fluctuations in a magnetized, anisotropic plasma are studied by applying standard methods, based on the Einstein rule, to the known thermodynamic potential of the system. It is found in particular that magnetic fluctuations become critical when the anisotropy p ∥ −p ⊥ changes sign. By examining the critical region, additional insight on the equations of state for near-critical anisotropic plasma is obtained
A unified theoretical and experimental study of anisotropic hardening
International Nuclear Information System (INIS)
Boehler, J.P.; Raclin, J.
1981-01-01
The purpose of this work is to develop a consistent formulation of the constitutive relations regarding anisotropic hardening materials. Attention is focused on the appearance and the evolution of mechanical anisotropies during irreversible processes, such as plastic forming and inelastic deformation of structures. The representation theorems for anisotropic tensor functions constitute a theoretical basis, allowing to reduce arbitrariness and to obtain a unified formulation of anisotropic hardening. In this approach, a general three-dimensional constitutive law is developed for prestrained initially orthotropic materials. Introduction of the plastic behavior results in the general forms of both the flow-law and the yield criterion. The developed theory is then specialized for the case of plane stress and different modes of anisotropic hardening are analyzed. A new generalization of the Von Mises criterion is proposed, in considering a homogeneous form of order two in stress and employing the simplest combinations of the basic invariants entering the general form of the yield condition. The proposed criterion involves specific terms accounting for the initial anisotropy, the deformation induced anisotropy and correlative terms between initial and induced anisotropy. The effects of prestrainings result in both isotropic and anisotropic hardening. An adequate experimental program, consisting of uniaxial tensile tests on oriented specimens of prestrained sheet-metal, was performed, in order to determine the specific form and the evolution of the anisotropic failure criterion for soft-steel subjected to different irreversible prestrainings. (orig.)
Schroedinger covariance states in anisotropic waveguides
International Nuclear Information System (INIS)
Angelow, A.; Trifonov, D.
1995-03-01
In this paper Squeezed and Covariance States based on Schroedinger inequality and their connection with other nonclassical states are considered for particular case of anisotropic waveguide in LiNiO 3 . Here, the problem of photon creation and generation of squeezed and Schroedinger covariance states in optical waveguides is solved in two steps: 1. Quantization of electromagnetic field is provided in the presence of dielectric waveguide using normal-mode expansion. The photon creation and annihilation operators are introduced, expanding the solution A-vector(r-vector,t) in a series in terms of the Sturm - Liouville mode-functions. 2. In terms of these operators the Hamiltonian of the field in a nonlinear waveguide is derived. For such Hamiltonian we construct the covariance states as stable (with nonzero covariance), which minimize the Schroedinger uncertainty relation. The evolutions of the three second momenta of q-circumflex j and p-circumflex j are calculated. For this Hamiltonian all three momenta are expressed in terms of one real parameters s only. It is found out how covariance, via this parameter s, depends on the waveguide profile n(x,y), on the mode-distributions u-vector j (x,y), and on the waveguide phase mismatching Δβ. (author). 37 refs
Polarization dynamics in nonlinear anisotropic fibers
International Nuclear Information System (INIS)
Komarov, Andrey; Komarov, Konstantin; Meshcheriakov, Dmitry; Amrani, Foued; Sanchez, Francois
2010-01-01
We give an extensive study of polarization dynamics in anisotropic fibers exhibiting a third-order index nonlinearity. The study is performed in the framework of the Stokes parameters with the help of the Poincare sphere. Stationary states are determined, and their stability is investigated. The number of fixed points and their stability depend on the respective magnitude of the linear and nonlinear birefringence. A conservation relation analogous to the energy conservation in mechanics allows evidencing a close analogy between the movement of the polarization in the Poincare sphere and the motion of a particle in a potential well. Two distinct potentials are found, leading to the existence of two families of solutions, according to the sign of the total energy of the equivalent mechanical system. The mechanical analogy allows us to fully characterize the solutions and also to determine analytically the associated beat lengths. General analytical solutions are given for the two families in terms of Jacobi's functions. The intensity-dependent transmission of a fiber placed between two crossed polarizers is calculated. Optimal conditions for efficient nonlinear switching compatible with mode-locking applications are determined. The general case of a nonlinear fiber ring with an intracavity polarizer placed between two polarization controllers is also considered.
Zonal flows in tokamaks with anisotropic pressure
International Nuclear Information System (INIS)
Ren, Haijun
2014-01-01
Zonal flows (ZFs) in a tokamak plasma with anisotropic pressure are investigated. The dynamics of perpendicular and parallel pressures are determined by the Chew-Goldberger-Low double equations and low-β condition is adopted, where β is the ratio of plasma pressure to the magnetic field pressure. The dispersion relation is analytically derived and illustrates two branches of ZFs. The low frequency zonal flow (LFZF) branch becomes unstable when χ, the ratio of the perpendicular pressure to the parallel one, is greater than a threshold value χ c , which is about 3.8. In the stable region, its frequency increases first and then decreases with increasing χ. For χ = 1, the frequency of LFZF agrees well with the experimental observation. For the instability, the growth rate of LFZF increases with χ. The geodesic acoustic mode branch is shown to be always stable with a frequency increasing with χ. The safety factor is shown to diminish the frequencies of both branches or the growth rate of LFZF
Cartesian anisotropic mesh adaptation for compressible flow
International Nuclear Information System (INIS)
Keats, W.A.; Lien, F.-S.
2004-01-01
Simulating transient compressible flows involving shock waves presents challenges to the CFD practitioner in terms of the mesh quality required to resolve discontinuities and prevent smearing. This paper discusses a novel two-dimensional Cartesian anisotropic mesh adaptation technique implemented for compressible flow. This technique, developed for laminar flow by Ham, Lien and Strong, is efficient because it refines and coarsens cells using criteria that consider the solution in each of the cardinal directions separately. In this paper the method will be applied to compressible flow. The procedure shows promise in its ability to deliver good quality solutions while achieving computational savings. The convection scheme used is the Advective Upstream Splitting Method (Plus), and the refinement/ coarsening criteria are based on work done by Ham et al. Transient shock wave diffraction over a backward step and shock reflection over a forward step are considered as test cases because they demonstrate that the quality of the solution can be maintained as the mesh is refined and coarsened in time. The data structure is explained in relation to the computational mesh, and the object-oriented design and implementation of the code is presented. Refinement and coarsening algorithms are outlined. Computational savings over uniform and isotropic mesh approaches are shown to be significant. (author)
Gauge unification in highly anisotropic string compactifications
International Nuclear Information System (INIS)
Hebecker, A.; Trapletti, M.
2005-01-01
It is well known that heterotic string compactifications have, in spite of their conceptual simplicity and aesthetic appeal, a serious problem with precision gauge coupling unification in the perturbative regime of string theory. Using both a duality-based and a field-theoretic definition of the boundary of the perturbative regime, we reevaluate the situation in a quantitative manner. We conclude that the simplest and most promising situations are those where some of the compactification radii are exceptionally large, corresponding to highly anisotropic orbifold models. Thus, one is led to consider constructions which are known to the effective field-theorist as higher-dimensional or orbifold grand unified theories (orbifold GUTs). In particular, if the discrete symmetry used to break the GUT group acts freely, a non-local breaking in the larger compact dimensions can be realized, leading to a precise gauge coupling unification as expected on the basis of the MSSM particle spectrum. Furthermore, a somewhat more model dependent but nevertheless very promising scenario arises if the GUT breaking is restricted to certain singular points within the manifold spanned by the larger compactification radii
Birkeland currents in an anisotropic, magnetostatic plasma
International Nuclear Information System (INIS)
Birmingham, T.J.
1992-01-01
An expression for the parallel current density is derived for a plasma characterized by negligible bulk flow (magnetostatic) velocity and a two-component (anisotropic) pressure tensor by expanding the equilibrium Vlasov equation for each species in the adiabatic parameter until such point as a nonvanishing moment j parallel = ∫ d 3 vv parallel is identified. The result is a nonlocal one: it relates j parallel at one point s along a field line to j parallel at another (reference) point s 0 plus an integral function of the pressure and magnetic field between them. It is a generalization and elaboration of results obtained by Bostrom (1975), Heinemann (1990), and Heinemann and Pontius (1991). The expression could have been obtained by integrating the current continuity equation with -∇ x j perpendicular as a source term and j perpendicular given by perpendicular momentum balance. The authors explicitly show the equivalency. The widely used Vasyliunas (1970) equation follows when P perpendicular is set equal to P parallel and s and s 0 are taken to be at the ionosphere and the equator. An extended discussion of the relationship of results derived here to others in the literature is carried out in an effort to bring unity and perspective to this problem area
International Nuclear Information System (INIS)
Udomsamuthirun, P.; Peamsuwan, R.; Kumvongsa, C.
2009-01-01
The effect of anisotropic order parameter on the specific heat of anisotropic two-band superconductors in BCS weak-coupling limit is investigated. An analytical specific heat jump and the numerical specific heat are shown by using anisotropic order parameters, and the electron-phonon interaction and non-electron-phonon interaction. The two models of anisotropic order parameters are used for numerical calculation that we find little effect on the numerical results. The specific heat jump of MgB 2 , Lu 2 Fe 3 Si 5 and Nb 3 Sn superconductors can fit well with both of them. By comparing the experimental data with overall range of temperature, the best fit is Nb 3 Sn, MgB 2 , and Lu 2 Fe 3 Si 5 superconductors.
Directory of Open Access Journals (Sweden)
Dwayne R Roach
Full Text Available Pig hepatocytes are an important investigational tool for optimizing hepatocyte transplantation schemes in both allogeneic and xenogeneic transplant scenarios. MRI can be used to serially monitor the transplanted cells, but only if the hepatocytes can be labeled with a magnetic particle. In this work, we describe culture conditions for magnetic cell labeling of cells from two different pig hepatocyte cell sources; primary pig hepatocytes (ppHEP and stem cell-derived hepatocytes (PICM-19FF. The magnetic particle is a micron-sized iron oxide particle (MPIO that has been extensively studied for magnetic cell labeling for MRI-based cell tracking. ppHEP could endocytose MPIO with labeling percentages as high as 70%, achieving iron content as high as ~55 pg/cell, with >75% viability. PICM-19FF had labeling >97%, achieving iron content ~38 pg/cell, with viability >99%. Extensive morphological and functional assays indicated that magnetic cell labeling was benign to the cells. The results encourage the use of MRI-based cell tracking for the development and clinical use of hepatocyte transplantation methodologies. Further, these results generally highlight the importance of functional cell assays in the evaluation of contrast agent biocompatibility.
Energy Technology Data Exchange (ETDEWEB)
Lisson, Catharina S.; Lisson, Christoph G.; Flosdorf, Kerstin; Meier, Reinhard; Beer, Meinrad; Schmidt, Stefan A. [University Hospital of Ulm, Department of Diagnostic and Interventional Radiology, Ulm (Germany); Mayer-Steinacker, Regine [University Hospital of Ulm, Department of Internal Medicine III, Ulm (Germany); Schultheiss, Markus; Baer, Alexandra von [University Hospital of Ulm, Department of Trauma Surgery, Ulm (Germany); Barth, Thomas F.E. [University of Ulm, Institute of Pathology, Ulm (Germany); Beer, Ambros J. [University Hospital of Ulm, Department of Nuclear Medicine, Ulm (Germany); Baumhauer, Matthias [Mint Medical, Dossenheim (Germany)
2018-02-15
To explore the diagnostic value of MRI-based 3D texture analysis to identify texture features that can be used for discrimination of low-grade chondrosarcoma from enchondroma. Eleven patients with low-grade chondrosarcoma and 11 patients with enchondroma were retrospectively evaluated. Texture analysis was performed using mint Lesion: Kurtosis, entropy, skewness, mean of positive pixels (MPP) and uniformity of positive pixel distribution (UPP) were obtained in four MRI sequences and correlated with histopathology. The Mann-Whitney U-test and receiver operating characteristic (ROC) analysis were performed to identify most discriminative texture features. Sensitivity, specificity, accuracy and optimal cut-off values were calculated. Significant differences were found in four of 20 texture parameters with regard to the different MRI sequences (p<0.01). The area under the ROC curve values to discriminate chondrosarcoma from enchondroma were 0.876 and 0.826 for kurtosis and skewness in contrast-enhanced T1 (ceT1w), respectively; in non-contrast T1, values were 0.851 and 0.822 for entropy and UPP, respectively. The highest discriminatory power had kurtosis in ceT1w with a cut-off ≥3.15 to identify low-grade chondrosarcoma (82 % sensitivity, 91 % specificity, accuracy 86 %). MRI-based 3D texture analysis might be able to discriminate low-grade chondrosarcoma from enchondroma by a variety of texture parameters. (orig.)
International Nuclear Information System (INIS)
Karlo, C.; Reiner, C.S.; Stolzmann, P.; Breitenstein, S.; Marincek, B.; Weishaupt, D.; Frauenfelder, T.
2010-01-01
Objective: To compare virtual volume to intraoperative volume and weight measurements of resected liver specimen and calculate appropriate conversion factors to reach better correlation. Methods: Preoperative (CT-group, n = 30; MRI-group, n = 30) and postoperative MRI (n = 60) imaging was performed in 60 patients undergoing partial liver resection. Intraoperative volume and weight of the resected liver specimen was measured. Virtual volume measurements were performed by two readers (R1,R2) using dedicated software. Conversion factors were calculated. Results: Mean intraoperative resection weight/volume: CT: 855 g/852 mL; MRI: 872 g/860 mL. Virtual resection volume: CT: 960 mL(R1), 982 mL(R2); MRI: 1112 mL(R1), 1115 mL(R2). Strong positive correlation for both readers between intraoperative and virtual measurements, mean of both readers: CT: R = 0.88(volume), R = 0.89(weight); MRI: R = 0.95(volume), R = 0.92(weight). Conversion factors: 0.85(CT), 0.78(MRI). Conclusion: CT- or MRI-based volumetry of resected liver specimen is accurate and recommended for preoperative planning. A conversion of the result is necessary to improve intraoperative and virtual measurement correlation. We found 0.85 for CT- and 0.78 for MRI-based volumetry the most appropriate conversion factors.
Scalar particle creation in an anisotropic universe
International Nuclear Information System (INIS)
Berger, B.K.
1975-01-01
The problem of quantized scalar field creation in an anisotropic spatially homogeneous background universe is reexamined from a Schroedinger-picture point of view. For each mode a complete set of orthonormal wave functions, psi/subN/, is obtained using the method of Salusti and Zirilli. These wave functions are valid at all times even if there is an initial cosmological singularity and depend only on the solution of the classical equation of motion. The wave functions are fixed completely by requiring the classical solution to have positive-frequency WKB form when the universe reaches the stage of adiabatic expansion. These wave functions are eigenfunctions of a conserved number operator which has the usual particle interpretation in the adiabatic regime. An intitial state near the singularity is chosen as a superposition of the wave functions, psi/subN/, and the particle number in the adiabatic regime is calculated. For plane-wave initial states, which follow the classical behavior near the singularity, the final particle number depends only on the parameters of the initial wave packet. For an initial state which instantaneously diagonalizes the Hamiltonian, an (arbitrary) initial time must be chosen. If the mode in question is in the adiabatic regime at that time almost no particle creation occurs. If it is not adiabatic, creation occurs and becomes infinite if the initial time is taken to be that of the singularity. This creation is a consequence of the failure of particle number to be well defined in this regime. Comparisons with other particle-creation studies are made
Theory of Langmuir probes in anisotropic plasmas
International Nuclear Information System (INIS)
Sudit, I.D.; Woods, R.C.
1994-01-01
A theory has been developed for electron retardation by Langmuir probes of several geometries in a general anisotropic plasma with arbitrary probe orientation and valid for any sheath thickness. Electron densities and electron velocity distribution functions (EVDFs) are obtained from the second derivative of probe I-V curves, as in Druyvesteyn's original method, which was developed for isotropic plasmas. Fedorov had extended the latter method in the context of a thin sheath approximation, to axisymmetric plasmas, in which the EVDF is expanded in a series of Legendary polynomials. In the present work an expansion in a series of spherical harmonics is employed, and the coordinate transformations are handled using the irreducible representation of the three dimensional rotation group. It is shown that the Volterra integral equations that must be solved to obtain the expansion coefficients of the EVDF from the second derivative data are no more complicated in the general case that hose for the axisymmetric plasma. Furthermore in the latter case the results can be shown to be equivalent to Fedrov's thin sheath expression. For the case of planar probes a formulation based on first derivatives of the I-V curves has been obtained. If data is obtained at enough different probe orientation of a one sided planar disc probe, any number of spherical harmonic coefficient functions may be obtained by inverting a set of linear equations and the complete EVDF deduced. For a cylindrical probe or a two-sided planar disc probe the integration of the second derivative of the probe current gives the exact electron density with any arbitrary probe orientation and any degree of plasma anisotropy
Catana, Ciprian; van der Kouwe, Andre; Benner, Thomas; Michel, Christian J; Hamm, Michael; Fenchel, Matthias; Fischl, Bruce; Rosen, Bruce; Schmand, Matthias; Sorensen, A Gregory
2010-09-01
Several factors have to be considered for implementing an accurate attenuation-correction (AC) method in a combined MR-PET scanner. In this work, some of these challenges were investigated, and an AC method based entirely on the MRI data obtained with a single dedicated sequence was developed and used for neurologic studies performed with the MR-PET human brain scanner prototype. The focus was on the problem of bone-air segmentation, selection of the linear attenuation coefficient for bone, and positioning of the radiofrequency coil. The impact of these factors on PET data quantification was studied in simulations and experimental measurements performed on the combined MR-PET scanner. A novel dual-echo ultrashort echo time (DUTE) MRI sequence was proposed for head imaging. Simultaneous MR-PET data were acquired, and the PET images reconstructed using the proposed DUTE MRI-based AC method were compared with the PET images that had been reconstructed using a CT-based AC method. Our data suggest that incorrectly accounting for the bone tissue attenuation can lead to large underestimations (>20%) of the radiotracer concentration in the cortex. Assigning a linear attenuation coefficient of 0.143 or 0.151 cm(-1) to bone tissue appears to give the best trade-off between bias and variability in the resulting images. Not identifying the internal air cavities introduces large overestimations (>20%) in adjacent structures. On the basis of these results, the segmented CT AC method was established as the silver standard for the segmented MRI-based AC method. For an integrated MR-PET scanner, in particular, ignoring the radiofrequency coil attenuation can cause large underestimations (i.e.,
Band gaps in periodically magnetized homogeneous anisotropic media
Merzlikin, A. M.; Levy, M.; Vinogradov, A. P.; Wu, Z.; Jalali, A. A.
2010-11-01
In [A. M. Merzlikin, A. P. Vinogradov, A. V. Dorofeenko, M. Inoue, M. Levy, A. B. Granovsky, Physica B 394 (2007) 277] it is shown that in anisotropic magnetophotonic crystal made of anisotropic dielectric layers and isotropic magneto-optical layers the magnetization leads to formation of additional band gaps (BG) inside the Brillouin zones. Due to the weakness of the magneto-optical effects the width of these BG is much smaller than that of usual BG forming on the boundaries of Brillouin zones. In the present communication we show that though the anisotropy suppresses magneto-optical effects. An anisotropic magnetophotonic crystal made of anisotropic dielectric layers and anisotropic magneto-optical; the width of additional BG may be much greater than the width of the usual Brillouin BG. Anisotropy tends to suppress Brillouin zone boundary band gap formation because the anisotropy suppresses magneto-optical properties, while degenerate band gap formation occurs around points of effective isotropy and is not suppressed.
3-D waveform tomography sensitivity kernels for anisotropic media
Djebbi, Ramzi
2014-01-01
The complications in anisotropic multi-parameter inversion lie in the trade-off between the different anisotropy parameters. We compute the tomographic waveform sensitivity kernels for a VTI acoustic medium perturbation as a tool to investigate this ambiguity between the different parameters. We use dynamic ray tracing to efficiently handle the expensive computational cost for 3-D anisotropic models. Ray tracing provides also the ray direction information necessary for conditioning the sensitivity kernels to handle anisotropy. The NMO velocity and η parameter kernels showed a maximum sensitivity for diving waves which results in a relevant choice of those parameters in wave equation tomography. The δ parameter kernel showed zero sensitivity; therefore it can serve as a secondary parameter to fit the amplitude in the acoustic anisotropic inversion. Considering the limited penetration depth of diving waves, migration velocity analysis based kernels are introduced to fix the depth ambiguity with reflections and compute sensitivity maps in the deeper parts of the model.
Debonding analyses in anisotropic materials with strain- gradient effects
DEFF Research Database (Denmark)
Legarth, Brian Nyvang
2012-01-01
A unit cell approach is adopted to numerically analyze the effect of plastic anisotropy on damage evolution in a micro-reinforced composite. The matrix material exhibit size effects and a visco-plastic anisotropic strain gradient plasticity model accounting for such size effects is adopted....... A conventional cohesive law is extended such that both the average as well as the jump in plastic strain across the fiber-matrix interface are accounted for. Results are shown for both conventional isotropic and anisotropic materials as well as for higher order isotropic and anisotropic materials...... with and without debonding. Generally, the strain gradient enhanced material exhibits higher load carry capacity compared to the corresponding conventional material. A sudden stress drop occurs in the macroscopic stress-strain response curve due to fiber-matrix debonding and the results show that a change in yield...
Modeling of charged anisotropic compact stars in general relativity
Energy Technology Data Exchange (ETDEWEB)
Dayanandan, Baiju; Maurya, S.K.; T, Smitha T. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman)
2017-06-15
A charged compact star model has been determined for anisotropic fluid distribution. We have solved the Einstein-Maxwell field equations to construct the charged compact star model by using the radial pressure, the metric function e{sup λ} and the electric charge function. The generic charged anisotropic solution is verified by exploring different physical conditions like causality condition, mass-radius relation and stability of the solution (via the adiabatic index, TOV equations and the Herrera cracking concept). It is observed that the present charged anisotropic compact star model is compatible with the star PSR 1937+21. Moreover, we also presented the EOS ρ = f(p) for the present charged compact star model. (orig.)
Anisotropic light scattering of individual sickle red blood cells.
Kim, Youngchan; Higgins, John M; Dasari, Ramachandra R; Suresh, Subra; Park, YongKeun
2012-04-01
We present the anisotropic light scattering of individual red blood cells (RBCs) from a patient with sickle cell disease (SCD). To measure light scattering spectra along two independent axes of elongated-shaped sickle RBCs with arbitrary orientation, we introduce the anisotropic Fourier transform light scattering (aFTLS) technique and measured both the static and dynamic anisotropic light scattering. We observed strong anisotropy in light scattering patterns of elongated-shaped sickle RBCs along its major axes using static aFTLS. Dynamic aFTLS analysis reveals the significantly altered biophysical properties in individual sickle RBCs. These results provide evidence that effective viscosity and elasticity of sickle RBCs are significantly different from those of the healthy RBCs.
Anisotropic temperature relaxation of plasmas in an external magnetic field
International Nuclear Information System (INIS)
Hassan, M.H.A.
1977-01-01
The magnetized kinetic equation derived in an earlier paper (Hassan and Watson, 1977) is used to study the problem of relaxation of anisotropic electron and ion temperatures in a magnetized plasma. In the case of anisotropic electron temperature relaxation, it is shown that for small anisotropies the exchange of energy within the electrons between the components parallel and perpendicular to the magnetic field direction determine the relaxation rate. For anisotropic ion temperature relaxation it is shown that the essential mechanism for relaxation is provided by energy transfer between ions and electrons, and that the expression for the relaxation rate perpendicular to the magnetic field contains a significant term proportional to ln eta 0 ln (msub(e)/msub(i)) (where eta 0 = Ωsub(e)/ksub(D)Vsub(e perpendicular to)), in addition to the term proportional to the Coulomb logarithm. (author)
Adaptive weighted anisotropic diffusion for computed tomography denoising
Energy Technology Data Exchange (ETDEWEB)
Yang, Zhi; Silver, Michael D. [Toshiba Medical Research Institute USA, Inc., Vernon Hills, IL (United States); Noshi, Yasuhiro [Toshiba Medical System Corporation, Tokyo (Japan)
2011-07-01
With increasing awareness of radiation safety, dose reduction has become an important task of modern CT system development. This paper proposes an adaptive weighted anisotropic diffusion method and an adaptive weighted sharp source anisotropic diffusion method as image domain filters to potentially help dose reduction. Different from existing anisotropic diffusion methods, the proposed methods incorporate an edge-sensitive adaptive source term as part of the diffusion iteration. It provides better edge and detail preservation. Visual evaluation showed that the new methods can reduce noise substantially without apparent edge and detail loss. The quantitative evaluations also showed over 50% of noise reduction in terms of noise standard deviations, which is equivalent to over 75% of dose reduction for a normal dose image quality. (orig.)
Adaptive anisotropic diffusion filtering of Monte Carlo dose distributions
International Nuclear Information System (INIS)
Miao Binhe; Jeraj, Robert; Bao Shanglian; Mackie, Thomas R
2003-01-01
The Monte Carlo method is the most accurate method for radiotherapy dose calculations, if used correctly. However, any Monte Carlo dose calculation is burdened with statistical noise. In this paper, denoising of Monte Carlo dose distributions with a three-dimensional adaptive anisotropic diffusion method was investigated. The standard anisotropic diffusion method was extended by changing the filtering parameters adaptively according to the local statistical noise. Smoothing of dose distributions with different noise levels in an inhomogeneous phantom, a conventional and an IMRT treatment case is shown. The resultant dose distributions were analysed using several evaluating criteria. It is shown that the adaptive anisotropic diffusion method can reduce statistical noise significantly (two to five times, corresponding to the reduction of simulation time by a factor of up to 20), while preserving important gradients of the dose distribution well. The choice of free parameters of the method was found to be fairly robust
Nonlinear, anisotropic, and giant photoconductivity in intrinsic and doped graphene
Singh, Ashutosh; Ghosh, Saikat; Agarwal, Amit
2018-01-01
We present a framework to calculate the anisotropic and nonlinear photoconductivity for two band systems with application to graphene. In contrast to the usual perturbative (second order in the optical field strength) techniques, we calculate photoconductivity to all orders in the optical field strength. In particular, for graphene, we find the photoresponse to be giant (at large optical field strengths) and anisotropic. The anisotropic photoresponse in graphene is correlated with polarization of the incident field, with the response being similar to that of a half-wave plate. We predict that the anisotropy in the simultaneous measurement of longitudinal (σx x) and transverse (σy x) photoconductivity, with four probes, offers a unique experimental signature of the photovoltaic response, distinguishing it from the thermal-Seebeck and bolometric effects in photoresponse.
Anomalously large anisotropic magnetoresistance in a perovskite manganite
Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X. Z.; Matsui, Y.; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E. Ward; Zhang, Jiandi
2009-01-01
The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La0.69Ca0.31MnO3, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a “colossal” AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings. PMID:19706504
Self-force on dislocation segments in anisotropic crystals
International Nuclear Information System (INIS)
Fitzgerald, S P; Aubry, S
2010-01-01
A dislocation segment in a crystal experiences a 'self-force', by virtue of the orientation dependence of its elastic energy. If the crystal is elastically isotropic, this force is manifested as a couple acting to rotate the segment toward the lower energy of the pure screw orientation (i.e. acting to align the dislocation line with its Burgers vector). If the crystal is anisotropic, there are additional contributions to the couple, arising from the more complex energy landscape of the lattice itself. These effects can strongly influence the dynamic evolution of dislocation networks, and via their governing role in dislocation multiplication phenomena, control plastic flow in metals. In this paper we develop a model for dislocation self-forces in a general anisotropic crystal, and briefly consider the technologically important example of α-iron, which becomes increasingly anisotropic as the temperature approaches that of the α-γ phase transition at 912 0 C.
Energy Technology Data Exchange (ETDEWEB)
Saint-Aubert, L.; Nemmi, F.; Peran, P. [Inserm, Imagerie Cerebrale et Handicaps neurologiques UMR 825, Centre Hospitalier Universitaire de Toulouse, Toulouse (France); Centre Hospitalier Universitaire de Toulouse, Universite de Toulouse, UPS, Imagerie Cerebrale et Handicaps Neurologiques UMR 825, Toulouse (France); Barbeau, E.J. [Universite de Toulouse, UPS, Centre de Recherche Cerveau et Cognition, France, CNRS, CerCo, Toulouse (France); Service de Neurologie, Pole Neurosciences, Centre Hospitalier Universitaire de Toulouse, Toulouse (France); Payoux, P. [Inserm, Imagerie Cerebrale et Handicaps neurologiques UMR 825, Centre Hospitalier Universitaire de Toulouse, Toulouse (France); Centre Hospitalier Universitaire de Toulouse, Universite de Toulouse, UPS, Imagerie Cerebrale et Handicaps Neurologiques UMR 825, Toulouse (France); Service de Medecine Nucleaire, Pole Imagerie, Centre Hospitalier Universitaire de Toulouse, Toulouse (France); Chollet, F.; Pariente, J. [Inserm, Imagerie Cerebrale et Handicaps neurologiques UMR 825, Centre Hospitalier Universitaire de Toulouse, Toulouse (France); Centre Hospitalier Universitaire de Toulouse, Universite de Toulouse, UPS, Imagerie Cerebrale et Handicaps Neurologiques UMR 825, Toulouse (France); Service de Neurologie, Pole Neurosciences, Centre Hospitalier Universitaire de Toulouse, Toulouse (France)
2014-05-15
Florbetapir (AV-45) has been shown to be a reliable tool for assessing in vivo amyloid load in patients with Alzheimer's disease from the early stages. However, nonspecific white matter binding has been reported in healthy subjects as well as in patients with Alzheimer's disease. To avoid this issue, cortical quantification might increase the reliability of AV-45 PET analyses. In this study, we compared two quantification methods for AV-45 binding, a classical method relying on PET template registration (route 1), and a MRI-based method (route 2) for cortical quantification. We recruited 22 patients at the prodromal stage of Alzheimer's disease and 17 matched controls. AV-45 binding was assessed using both methods, and target-to-cerebellum mean global standard uptake values (SUVr) were obtained for each of them, together with SUVr in specific regions of interest. Quantification using the two routes was compared between the clinical groups (intragroup comparison), and between groups for each route (intergroup comparison). Discriminant analysis was performed. In the intragroup comparison, differences in uptake values were observed between route 1 and route 2 in both groups. In the intergroup comparison, AV-45 uptake was higher in patients than controls in all regions of interest using both methods, but the effect size of this difference was larger using route 2. In the discriminant analysis, route 2 showed a higher specificity (94.1 % versus 70.6 %), despite a lower sensitivity (77.3 % versus 86.4 %), and D-prime values were higher for route 2. These findings suggest that, although both quantification methods enabled patients at early stages of Alzheimer's disease to be well discriminated from controls, PET template-based quantification seems adequate for clinical use, while the MRI-based cortical quantification method led to greater intergroup differences and may be more suitable for use in current clinical research. (orig.)
An anisotropic diffusion approximation to thermal radiative transfer
International Nuclear Information System (INIS)
Johnson, Seth R.; Larsen, Edward W.
2011-01-01
This paper describes an anisotropic diffusion (AD) method that uses transport-calculated AD coefficients to efficiently and accurately solve the thermal radiative transfer (TRT) equations. By assuming weak gradients and angular moments in the radiation intensity, we derive an expression for the radiation energy density that depends on a non-local function of the opacity. This nonlocal function is the solution of a transport equation that can be solved with a single steady-state transport sweep once per time step, and the function's second angular moment is the anisotropic diffusion tensor. To demonstrate the AD method's efficacy, we model radiation flow down a channel in 'flatland' geometry. (author)
Longitudinal disordering of vortex lattices in anisotropic superconductors
International Nuclear Information System (INIS)
Harshman, D.R.; Brandt, E.H.; Fiory, A.T.; Inui, M.; Mitzi, D.B.; Schneemeyer, L.F.; Waszczak, J.V.
1993-01-01
Vortex disordering in superconducting crystals is shown to be markedly sensitive to penetration-depth anisotropy. At low temperature and high magnetic field, the muon-spin-rotation spectra for the highly anisotropic Bi 2 Sr 2 CaCu 2 O 8+δ material are found to be anomalously narrow and symmetric about the applied field, in a manner consistent with a layered vortex sublattice structure with pinning-induced misalignment between layers. In contrast, spectra for the less-anisotropic YBa 2 Cu 3 O 7-δ compounds taken at comparable fields are broader and asymmetric, showing that the vortex lattices are aligned parallel to the applied-field direction
Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs
Energy Technology Data Exchange (ETDEWEB)
Mannix, A. J.; Zhou, X. -F.; Kiraly, B.; Wood, J. D.; Alducin, D.; Myers, B. D.; Liu, X.; Fisher, B. L.; Santiago, U.; Guest, J. R.; Yacaman, M. J.; Ponce, A.; Oganov, A. R.; Hersam, M. C.; Guisinger, N. P.
2015-12-17
At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal.
The traces of anisotropic dark energy in light of Planck
Energy Technology Data Exchange (ETDEWEB)
Cardona, Wilmar; Kunz, Martin [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, 24 Quai Ernest Ansermet, 1211 Genève 4 (Switzerland); Hollenstein, Lukas, E-mail: wilmar.cardona@unige.ch, E-mail: lukas.hollenstein@zhaw.ch, E-mail: martin.kunz@unige.ch [IAS Institute of Applied Simulation, ZHAW Zurich University of Applied Sciences, Grüental, PO Box, 8820 Wädenswil (Switzerland)
2014-07-01
We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.
Study of anisotropic mechanical properties for aeronautical PMMA
Directory of Open Access Journals (Sweden)
Wei Shang
Full Text Available For the properties of polymer are relative to its structure, the main purpose of the present work is to investigate the mechanical properties of the aeronautical PMMA which has been treated by the directional tensile technology. Isodyne images reveal the stress state in directional PMMA. And then, an anisotropic mechanical model is established. Furthermore, all mechanical parameters are measured by the digital image correlation method. Finally, based on the anisotropic mechanical model and mechanical parameters, the FEM numerical simulation and experimental methods are applied to analyze the fracture mechanical properties along different directions.
All spherically symmetric charged anisotropic solutions for compact stars
Energy Technology Data Exchange (ETDEWEB)
Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Raj Kumar Goel Institute of Technology, Department of Mathematics, Ghaziabad, UP (India); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India)
2017-06-15
In the present paper we develop an algorithm for all spherically symmetric anisotropic charged fluid distributions. Considering a new source function ν(r) we find a set of solutions which is physically well behaved and represents compact stellar models. A detailed study specifically shows that the models actually correspond to strange stars in terms of their mass and radius. In this connection we investigate several physical properties like energy conditions, stability, mass-radius ratio, electric charge content, anisotropic nature and surface redshift through graphical plots and mathematical calculations. All the features from these studies are in excellent agreement with the already available evidence in theory as well as observations. (orig.)
Lower critical field of an anisotropic type-II superconductor
International Nuclear Information System (INIS)
Klemm, R.A.; Clem, J.R.
1980-01-01
We consider the Ginzburg-Landau free energy of the anisotropic mass form in the presence of a magnetic field of arbitrary fixed direction. It is shown that the free energy may be transformed into the isotropic Ginsburg-Landau form with a kappa that depends upon the direction of the magnetic induction B relative to the crystal lattice. The lower critical field H/sub c/1 is then found for arbitrary direction of B. For highly anisotropic crystals the angular dependence of H/sub c/1 can exhibit a discontinuity or a cusp. The special case of a crystal with uniaxial symmetry is considered in detail
Tunable waveguide bends with graphene-based anisotropic metamaterials
Chen, Zhao-xian; Chen, Ze-guo; Ming, Yang; Wu, Ying; Lu, Yan-qing
2016-01-01
We design tunable waveguide bends filled with graphene-based anisotropic metamaterials to achieve a nearly perfect bending effect. The anisotropic properties of the metamaterials can be described by the effective medium theory. The nearly perfect bending effect is demonstrated by finite element simulations of various structures with different bending curvatures and shapes. This effect is attributed to zero effective permittivity along the direction of propagation and matched effective impedance at the interfaces between the bending part and the dielectric waveguides. We envisage that the design will be applicable in the far-infrared and terahertz frequency ranges owing to the tunable dielectric responses of graphene.
Understanding nanoparticle-mediated nucleation pathways of anisotropic nanoparticles
Laramy, Christine R.; Fong, Lam-Kiu; Jones, Matthew R.; O'Brien, Matthew N.; Schatz, George C.; Mirkin, Chad A.
2017-09-01
Several seed-mediated syntheses of low symmetry anisotropic nanoparticles yield broad product distributions with multiple defect structures. This observation challenges the role of the nanoparticle precursor as a seed for certain syntheses and suggests the possibility of alternate nucleation pathways. Herein, we report a method to probe the role of the nanoparticle precursor in anisotropic nanoparticle nucleation with compositional and structural 'labels' to track their fate. We use the synthesis of gold triangular nanoprisms (Au TPs) as a model system. We propose a mechanism in which, rather than acting as a template, the nanoparticle precursor catalyzes homogenous nucleation of Au TPs.
MHz gravitational waves from short-term anisotropic inflation
International Nuclear Information System (INIS)
Ito, Asuka; Soda, Jiro
2016-01-01
We reveal the universality of short-term anisotropic inflation. As a demonstration, we study inflation with an exponential type gauge kinetic function which is ubiquitous in models obtained by dimensional reduction from higher dimensional fundamental theory. It turns out that an anisotropic inflation universally takes place in the later stage of conventional inflation. Remarkably, we find that primordial gravitational waves with a peak amplitude around 10 −26 ∼10 −27 are copiously produced in high-frequency bands 10 MHz∼100 MHz. If we could detect such gravitational waves in future, we would be able to probe higher dimensional fundamental theory.
Tunable waveguide bends with graphene-based anisotropic metamaterials
Chen, Zhao-xian
2016-01-15
We design tunable waveguide bends filled with graphene-based anisotropic metamaterials to achieve a nearly perfect bending effect. The anisotropic properties of the metamaterials can be described by the effective medium theory. The nearly perfect bending effect is demonstrated by finite element simulations of various structures with different bending curvatures and shapes. This effect is attributed to zero effective permittivity along the direction of propagation and matched effective impedance at the interfaces between the bending part and the dielectric waveguides. We envisage that the design will be applicable in the far-infrared and terahertz frequency ranges owing to the tunable dielectric responses of graphene.
Fourier Multipliers on Anisotropic Mixed-Norm Spaces of Distributions
DEFF Research Database (Denmark)
Cleanthous, Galatia; Georgiadis, Athanasios; Nielsen, Morten
2018-01-01
A new general Hormander type condition involving anisotropies and mixed norms is introduced, and boundedness results for Fourier multi- pliers on anisotropic Besov and Triebel-Lizorkin spaces of distributions with mixed Lebesgue norms are obtained. As an application, the continuity of such operat......A new general Hormander type condition involving anisotropies and mixed norms is introduced, and boundedness results for Fourier multi- pliers on anisotropic Besov and Triebel-Lizorkin spaces of distributions with mixed Lebesgue norms are obtained. As an application, the continuity...
Anisotropic behavior of quantum transport in graphene superlattices
DEFF Research Database (Denmark)
Pedersen, Jesper Goor; Cummings, Aron W.; Roche, Stephan
2014-01-01
We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength of multi......We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength...
Czech Academy of Sciences Publication Activity Database
Červený, V.; Pšenčík, Ivan
2015-01-01
Roč. 25, - (2015), s. 109-155 ISSN 2336-3827 Institutional support: RVO:67985530 Keywords : integral superposition of paraxial Gaussian beams * inhomogeneous anisotropic media * S waves in weakly anisotropic media Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Tunable plasmon resonances in anisotropic metal nanostructures
Penninkhof, J. J.
2006-09-01
Coherent oscillations of free electrons in a metal, localized in a small volume or at an interface between a metal and a dielectric medium, have attracted a lot of attention in the past decades. These so-called surface plasmons have special optical properties that can be used in many applications ranging from optoelectronics to sensing of small quantities of molecules. One of the key issues is that electromagnetic energy can be confined to a relatively small volume close to the metal surface. This field enhancement and the resonance frequency strongly depend on the shape and size of the metal structures. In this thesis, several fabrication methods to create these metal structures on the nanometer to micrometer scale are presented. The optical properties are studied with a special emphasis on the effect of shape anisotropy. Self-assembled 2D colloidal crystals are used as mask to fabricate arrays of metal triangles on a substrate. One of the limitations of this nanosphere lithography technique is that the size of the holes in the colloidal mask (through which the metal is evaporated) is determined by the size of the colloids in the mask. The masks, however, can be modified by use of MeV ion beams and/or wet-chemical growth of a thin layer of silica, resulting in a reduced hole size. Arbitrary symmetry and spacing can be obtained by use of optical tweezers and angle-resolved metal deposition. In contrast to pure metals, amorphous materials like silica are known to show anisotropic plastic deformation at constant volume when subject to MeV ion irradiation. Gold cores embedded in a silica matrix, however, show an elongation along the direction of the ion beam, whereas silver cores rather disintegrate. Silver nanocrystals in an ion-exchanged soda-lime glass redistribute themselves in arrays along the ion beam direction. The optical extinction becomes polarization-dependent, with red- and blue-shifts of the plasmon resonances for polarizations longitudinal and transverse
A Morphing framework to couple non-local and local anisotropic continua
Azdoud, Yan
2013-05-01
In this article, we develop a method to couple anisotropic local continua with anisotropic non-local continua with central long-range forces. First, we describe anisotropic non-local models based on spherical harmonic descriptions. We then derive compatible classic continuum models. Finally, we apply the morphing method to these anisotropic non-local models and present three-dimensional numerical examples to validate the efficiency of the technique. © 2013 Elsevier Ltd. All rights reserved.
Anisotropic mechanical properties and Stone-Wales defects in graphene monolayer: A theoretical study
International Nuclear Information System (INIS)
Fan, B.B.; Yang, X.B.; Zhang, R.
2010-01-01
We investigate the mechanical properties of graphene monolayer via the density functional theoretical (DFT) method. We find that the strain energies are anisotropic for the graphene under large strain. We attribute the anisotropic feature to the anisotropic sp 2 hybridization in the hexagonal lattice. We further identify that the formation energies of Stone-Wales (SW) defects in the graphene monolayer are determined by the defect concentration and also the direction of applied tensile strain, correlating with the anisotropic feature.
Viscoelastic materials with anisotropic rigid particles: stress-deformation behavior
Sagis, L.M.C.; Linden, van der E.
2001-01-01
In this paper we have derived constitutive equations for the stress tensor of a viscoelastic material with anisotropic rigid particles. We have assumed that the material has fading memory. The expressions are valid for slow and small deformations from equilibrium, and for systems that are nearly
Field theoretic approach to structure formation in an anisotropic medium
International Nuclear Information System (INIS)
Joy, Minu; Kuriakose, V.C.
2003-01-01
Considering a real scalar field distribution which is assumed to be locally anisotropic and coupled to a Bianchi type-I background spacetime, the energy density and pressure associated with the anisotropic matter field distribution are evaluated. The vanishing of the expectation values of the nondiagonal components of T μν allows us to treat the scalar field in complete analogy with the distribution of fluid. The primeval density perturbations produced by the vacuum fluctuations of the scalar field are considered and the Jeans criterion for structure formation is obtained. The metric and matter field perturbations are considered and it is found that for the present anisotropic case the perturbations of the pressure in the radial and tangential directions are different. The Jeans instability is discussed and the Jeans wave number for the present case is evaluated. It is found that for the anisotropic case the Jeans length depends on the velocity of the fluctuations in the radial and transverse directions and thus on the direction of propagation of the perturbations
On the origins of the anisotropic mechanical behaviour of extruded ...
Indian Academy of Sciences (India)
This paper presents some experimental investigations about the origins of the anisotropic behaviour in cyclic loadings of AA2017 aluminium alloy. In the first step, fatigue damage evolutions were quantified for controlled proportional cyclic loadings in axial and shear directions. In this stage, the aim was to confirm the ...
Anisotropic cosmological models and generalized scalar tensor theory
Indian Academy of Sciences (India)
Abstract. In this paper generalized scalar tensor theory has been considered in the background of anisotropic cosmological models, namely, axially symmetric Bianchi-I, Bianchi-III and Kortowski–. Sachs space-time. For bulk viscous fluid, both exponential and power-law solutions have been stud- ied and some assumptions ...
Anisotropic cosmological models and generalized scalar tensor theory
Indian Academy of Sciences (India)
In this paper generalized scalar tensor theory has been considered in the background of anisotropic cosmological models, namely, axially symmetric Bianchi-I, Bianchi-III and Kortowski–Sachs space-time. For bulk viscous ﬂuid, both exponential and power-law solutions have been studied and some assumptions among the ...
Three anisotropic benchmark problems for adaptive finite element methods
Czech Academy of Sciences Publication Activity Database
Šolín, Pavel; Čertík, O.; Korous, L.
2013-01-01
Roč. 219, č. 13 (2013), s. 7286-7295 ISSN 0096-3003 R&D Projects: GA AV ČR IAA100760702 Institutional support: RVO:61388998 Keywords : benchmark problem * anisotropic solution * boundary layer Subject RIV: BA - General Mathematics Impact factor: 1.600, year: 2013
Fluid-like elasticity induced by anisotropic effective mass density
DEFF Research Database (Denmark)
Ma, Guancong; Fu, Caixing; Wang, Guanghao
We present a three-dimensional anisotropic elastic metamaterial, which can generate dipolar resonances. Repeating these subwavelength units can lead to one-dimensional arrays, which are essentially elastic rods that can withstand both longitudinal, and flexural vibrations. Band structure analysis...
Anisotropic Bianchi-I universe with phantom field and cosmological ...
Indian Academy of Sciences (India)
India. *Corresponding author. E-mail: bcpaul@iucaa.ernet.in. MS received 23 May ... We study an anisotropic Bianchi-I universe in the presence of a phantom ... The phantom cosmology has been analysed adopting phase space analysis ... the second part we study the critical points corresponding to the set of autonomous.
Neutron transport in two dissimilar media anisotropic scattering
International Nuclear Information System (INIS)
Burkart, A.R.; Ishiguro, Y.; Siewert, C.E.
1976-01-01
The elementary solution of the one-speed neutron-transport equation with linearly anisotropic scattering are used in conjunction with Chandrasekhar's invariance principles to solve in a concise manner the Milne problem for two adjoining half-spaces and the critical reactor problem for a reflected slab
Anisotropic plastic deformation by viscous flow in ion tracks
van Dillen, T; Polman, A; Onck, PR; van der Giessen, E
2005-01-01
A model describing the origin of ion beam-induced anisotropic plastic deformation is derived and discussed. It is based on a viscoelastic thermal spike model for viscous flow in single ion tracks derived by Trinkaus and Ryazanov. Deviatoric (shear) stresses, brought about by the rapid thermal
Investigation of Tooling for Anisotropic Optical Functional Surfaces
DEFF Research Database (Denmark)
Li, Dongya; Regi, Francesco; Zhang, Yang
This paper studied steel inserts with anisotropic surfaces for injection moulding. The inserts surfaces were machined by a five-axis micro-milling machine and the surface structures will be replicated by injection moulding. The aim of the surface structuring is to maximize visible contrast betwee...
Wave propagation in a general anisotropic poroelastic medium ...
Indian Academy of Sciences (India)
equations (Auriault et al 1985) in terms of solid displacement and fluid pressure, whereas Biot's equations were in terms of displacements of both the solid and fluid phases. Homogenisation has proven that .... (8) to (10) imply that, in homogenisation approach, the anisotropic inertial coupling is hiding in the tensor {ˆρij}.
Plasma resonance in anisotropic layered high-Tc superconductors
DEFF Research Database (Denmark)
Sakai, Shigeki; Pedersen, Niels Falsig
1999-01-01
The plasma resonance is described theoretically by the inductive coupling model for a large stacked Josephson-junction system such as the intrinsic Josephson-junction array in anisotropic high- T-c superconductors. Eigenmodes of the plasma oscillation are analytically described and a numerical...
Anisotropic properties of aligned SWNT modified poly (methyl ...
Indian Academy of Sciences (India)
The electrical and mechanical properties of PMMA/SWNT composite were studied as a function of SWNT orientation and concentration. The aligned SWNT modified PMMA/SWNT composite presented highly anisotropic properties. The experimental results showed that the electrical conductivity and mechanical properties of ...
Crystal structure of vanadite: Refinement of anisotropic displacement parameters
Czech Academy of Sciences Publication Activity Database
Laufek, F.; Skála, Roman; Haloda, J.; Císařová, I.
2006-01-01
Roč. 51, 3-4 (2006), s. 271-275 ISSN 1210-8197 Institutional research plan: CEZ:AV0Z30130516 Keywords : anisotropic displacement parameter * crystal structure * single-crystal X-ray refinement * vanadinite Subject RIV: DB - Geology ; Mineralogy
Comparison of two anisotropic layer models applied to induction motors
Sprangers, R.L.J.; Paulides, J.J.H.; Boynov, K.O.; Waarma, J.; Lomonova, E.
2013-01-01
A general description of the Anisotropic Layer Theory, derived in the polar coordinate system, and applied to the analysis of squirrel-cage induction motors (IMs), is presented. The theory considers non-conductive layers, layer with predefined current density and layers with induced current density.
Fourth-order discrete anisotropic boundary-value problems
Directory of Open Access Journals (Sweden)
Maciej Leszczynski
2015-09-01
Full Text Available In this article we consider the fourth-order discrete anisotropic boundary value problem with both advance and retardation. We apply the direct method of the calculus of variations and the mountain pass technique to prove the existence of at least one and at least two solutions. Non-existence of non-trivial solutions is also undertaken.
A new noise erosion operator for anisotropic diffusion
Institute of Scientific and Technical Information of China (English)
蔡超; 丁名跃; 周成平; 张天序
2004-01-01
A noise erosion operator based on partial differential equation (PDE) is introduced, which has an excellent ability of noise removal and edge preservation for two-dimensional (2D) gradient data. The operator is applied to estimate a new diffusion coefficient. Experimental results demonstrate that anisotropic diffusion based on this new erosion operator can efficiently reduce noise and sharpen object boundaries.
Remarks on the percolation problem in anisotropic systems
International Nuclear Information System (INIS)
Chaves, C.M.G.F.; Oliveira, P.M.C. de; Queiroz, S.L.A. de; Riera, R.
1979-07-01
The bond percolation problem is discused in an anisotropic square lattice using the position space renormalization group. It is shown that, due to symmetry, this treatment reproduces known exact results for this problem. The phase diagram and the flow lines in parameter space are also shown. Results are in agreement with universality.(Author) [pt
Anisotropic colloids: bulk phase behavior and equilibrium sedimentation
Marechal, M.A.T.
2009-01-01
This thesis focuses on the phase behavior of anisotropically shaped (i.e. non-spherical) colloids using computer simulations. Only hard-core interactions between the colloids are taken into account to investigate the effects of shape alone. The bulk phase behavior of three different shapes of
Theory of Spin Waves in Strongly Anisotropic Magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker; Cooke, J. F.
1976-01-01
A new infinite-order perturbation approach to the theory of spin waves in strongly anisotropic magnets is introduced. The system is transformed into one with effective two-ion anisotropy and considerably reduced ground-state corrections. A general expression for the spin-wave energy, valid to any...
Anisotropic Born-Mayer potential in lattice dynamics of Vanadium
International Nuclear Information System (INIS)
Onwuagba, B.N.
1988-01-01
A microscopic theory of the lattice dynamics of the transition metal vanadium is developed based on the Animalu's transition metal model potential (TMMP). The Born-Mayer potential associated with the distribution of the transition metal d-electrons is treated as anisotropic. Good agreement with experimental phonon dispersion curves longitudinal branches in the [111] direction
Anisotropic ordering in a two-temperature lattice gas
DEFF Research Database (Denmark)
Szolnoki, Attila; Szabó, György; Mouritsen, Ole G.
1997-01-01
We consider a two-dimensional lattice gas model with repulsive nearest- and next-nearest-neighbor interactions that evolves in time according to anisotropic Kawasaki dynamics. The hopping of particles along the principal directions is governed by two heat baths at different temperatures T-x and T...
Characterization of highly anisotropic three-dimensionally nanostructured surfaces
International Nuclear Information System (INIS)
Schmidt, Daniel
2014-01-01
Generalized ellipsometry, a non-destructive optical characterization technique, is employed to determine geometrical structure parameters and anisotropic dielectric properties of highly spatially coherent three-dimensionally nanostructured thin films grown by glancing angle deposition. The (piecewise) homogeneous biaxial layer model approach is discussed, which can be universally applied to model the optical response of sculptured thin films with different geometries and from diverse materials, and structural parameters as well as effective optical properties of the nanostructured thin films are obtained. Alternative model approaches for slanted columnar thin films, anisotropic effective medium approximations based on the Bruggeman formalism, are presented, which deliver results comparable to the homogeneous biaxial layer approach and in addition provide film constituent volume fraction parameters as well as depolarization or shape factors. Advantages of these ellipsometry models are discussed on the example of metal slanted columnar thin films, which have been conformally coated with a thin passivating oxide layer by atomic layer deposition. Furthermore, the application of an effective medium approximation approach to in-situ growth monitoring of this anisotropic thin film functionalization process is presented. It was found that structural parameters determined with the presented optical model equivalents for slanted columnar thin films agree very well with scanning electron microscope image estimates. - Highlights: • Summary of optical model strategies for sculptured thin films with arbitrary geometries • Application of the rigorous anisotropic Bruggeman effective medium applications • In-situ growth monitoring of atomic layer deposition on biaxial metal slanted columnar thin film
Wave velocities in a pre-stressed anisotropic elastic medium
Indian Academy of Sciences (India)
Modiﬁed Christoffel equations are derived for three-dimensional wave propagation in a general anisotropic medium under initial stress.The three roots of a cubic equation deﬁne the phase velocities of three quasi-waves in the medium.Analytical expressions are used to calculate the directional derivatives of phase ...
A new model for spherically symmetric anisotropic compact star
Energy Technology Data Exchange (ETDEWEB)
Maurya, S.K.; Dayanandan, Baiju [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Raj Kumar Goel Institute of Technology, Department of Mathematics, Ghaziabad, UP (India); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India)
2016-05-15
In this article we obtain a new anisotropic solution for Einstein's field equations of embedding class one metric. The solution represents realistic objects such as Her X-1 and RXJ 1856-37. We perform a detailed investigation of both objects by solving numerically the Einstein field equations with anisotropic pressure. The physical features of the parameters depend on the anisotropic factor i.e. if the anisotropy is zero everywhere inside the star then the density and pressures will become zero and the metric turns out to be flat. We report our results and compare with the above mentioned two compact objects as regards a number of key aspects: the central density, the surface density onset and the critical scaling behaviour, the effective mass and radius ratio, the anisotropization with isotropic initial conditions, adiabatic index and red shift. Along with this we have also made a comparison between the classical limit and theoretical model treatment of the compact objects. Finally we discuss the implications of our findings for the stability condition in a relativistic compact star. (orig.)
Existence of longitudinal waves in pre-stressed anisotropic elastic ...
Indian Academy of Sciences (India)
waves is truly longitudinal. Longitudinal wave in an anisotropic elastic medium is defined as the wave motion in which the particle motion (i.e., the. Keywords. General anisotropy; elastic stiffness; pre-stress; group velocity; ray direction; longitudinal waves; polarization. J. Earth Syst. Sci. 118, No. 6, December 2009, pp. 677– ...
Microwave holography in a uniaxial anial anisotropic plasma
International Nuclear Information System (INIS)
Nagai, Keinosuke; Suzuki, Michio
1974-01-01
Properties of a hologram constructed in a uniaxial anisotropic medium, namely in a gyro-plasma were investigated theoretically. We considered the interference patterns of ordinary waves and extraordinary waves from a source such as a hologram. An element of permitivity tensor can be measured by the reconstruction process from this hologram. (auth.)
Propagation of waves in a gravitating and rotating anisotropic heat ...
African Journals Online (AJOL)
An inviscid, unbounded, collisionless, gravitating, rotating and heat conducting anisotropic plasma medium which is drifting is considered. The medium is assumed to be embedded in a strong magnetic field. A general dispersion relation is derived using normal mode analysis and its various limiting cases are discussed, ...
Nonlinear anisotropic elliptic equations with variable exponents and degenerate coercivity
Directory of Open Access Journals (Sweden)
Hocine Ayadi
2018-02-01
Full Text Available In this article, we prove the existence and the regularity of distributional solutions for a class of nonlinear anisotropic elliptic equations with $p_i(x$ growth conditions, degenerate coercivity and $L^{m(\\cdot}$ data, with $m(\\cdot$ being small, in appropriate Lebesgue-Sobolev spaces with variable exponents. The obtained results extend some existing ones [8,10].
Ray-optics analysis of inhomogeneous biaxially anisotropic media
Sluijter, M.; De Boer, D.K.G.; Urbach, H.P.
2009-01-01
Firm evidence of the biaxial nematic phase in liquid crystals, not induced by a magnetic or electric field, has been established only recently. The discovery of these biaxially anisotropic liquid crystals has opened up new areas of both fundamental and applied research. The advances in biaxial
Prestack exploding reflector modelling and migration for anisotropic media
Alkhalifah, Tariq Ali
2014-10-09
The double-square-root equation is commonly used to image data by downward continuation using one-way depth extrapolation methods. A two-way time extrapolation of the double-square-root-derived phase operator allows for up and downgoing wavefields but suffers from an essential singularity for horizontally travelling waves. This singularity is also associated with an anisotropic version of the double-square-root extrapolator. Perturbation theory allows us to separate the isotropic contribution, as well as the singularity, from the anisotropic contribution to the operator. As a result, the anisotropic residual operator is free from such singularities and can be applied as a stand alone operator to correct for anisotropy. We can apply the residual anisotropy operator even if the original prestack wavefield was obtained using, for example, reverse-time migration. The residual correction is also useful for anisotropic parameter estimation. Applications to synthetic data demonstrate the accuracy of the new prestack modelling and migration approach. It also proves useful in approximately imaging the Vertical Transverse Isotropic Marmousi model.
Pseudorapidity Dependence of Anisotropic Azimuthal Flow with the ALICE Detector
DEFF Research Database (Denmark)
Hansen, Alexander Colliander
In ultra-relativistic heavy-ion collisions a new state of matter known as the strongly interacting quark-gluon plasma (sQGP) is produced. A key observable in the study of the sQGP is anisotropic azimuthal ow. The anisotropies are described by ow harmonics, vn. In this thesis, bias arising from non...
Quark–gluon plasma phenomenology from anisotropic lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Skullerud, Jon-Ivar; Kelly, Aoife [Department of Mathematical Physics, Maynooth University, Maynooth, Co Kildare (Ireland); Aarts, Gert; Allton, Chris; Amato, Alessandro; Evans, P. Wynne M.; Hands, Simon [Department of Physics, Swansea University, Swansea SA2 8PP, Wales (United Kingdom); Burnier, Yannis [Institut de Théorie des Phénomènes Physiques, Ecole Polytechnique Fédérale de Lausanne, CH–1015 Lausanne (Switzerland); Giudice, Pietro [Institut für Theoretische Physik, Universität Münster, D–48149 Münster (Germany); Harris, Tim; Ryan, Sinéad M. [School of Mathematics, Trinity College, Dublin 2 (Ireland); Kim, Seyong [Department of Physics, Sejong University, Seoul 143-747 (Korea, Republic of); Lombardo, Maria Paola [INFN–Laboratori Nazionali di Frascati, I–00044 Frascati (RM) (Italy); Oktay, Mehmet B. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States); Rothkopf, Alexander [Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, D–69120 Heidelberg (Germany)
2016-01-22
The FASTSUM collaboration has been carrying out simulations of N{sub f} = 2 + 1 QCD at nonzero temperature in the fixed-scale approach using anisotropic lattices. Here we present the status of these studies, including recent results for electrical conductivity and charge diffusion, and heavy quarkonium (charm and beauty) physics.
Anisotropic Bianchi-I universe with phantom field and cosmological ...
Indian Academy of Sciences (India)
We study an anisotropic Bianchi-I universe in the presence of a phantom field and a cosmological constant. Cosmological solutions are obtained when the kinetic energy of the phantom field is of the order of anisotropy and dominates over the potential energy of the field. The anisotropy of the universe decreases and the ...
Effect of anisotropic plasticity on mixed mode interface crack growth
DEFF Research Database (Denmark)
Tvergaard, Viggo; Legarth, Brian Nyvang
2007-01-01
different anisotropic yield criteria to account for the plastic anisotropy. Conditions of small-scale yielding are assumed, and due to the mismatch of elastic properties across the interface the corresponding oscillating stress singularity field is applied as boundary conditions on the outer edge...
Double anisotropic electrically conductive flexible Janus-typed membranes.
Li, Xiaobing; Ma, Qianli; Tian, Jiao; Xi, Xue; Li, Dan; Dong, Xiangting; Yu, Wensheng; Wang, Xinlu; Wang, Jinxian; Liu, Guixia
2017-12-07
Novel type III anisotropic conductive films (ACFs), namely flexible Janus-typed membranes, were proposed, designed and fabricated for the first time. Flexible Janus-typed membranes composed of ordered Janus nanobelts were constructed by electrospinning, which simultaneously possess fluorescence and double electrically conductive anisotropy. For the fabrication of the Janus-typed membrane, Janus nanobelts comprising a conductive side and an insulative-fluorescent side were primarily fabricated, and then the Janus nanobelts are arranged into parallel arrays using an aluminum rotary drum as the collector to obtain a single anisotropically conductive film. Subsequently, a secondary electrospinning process was applied to the as-prepared single anisotropically conductive films to acquire the final Janus-typed membrane. For this Janus-typed membrane, namely its left-to-right structure, anisotropic electrical conduction synchronously exists on both sides, and furthermore, the two electrically conductive directions are perpendicular. By modulating the amount of Eu(BA) 3 phen complex and conducting polyaniline (PANI), the characteristics and intensity of the fluorescence-electricity dual-function in the membrane can be tuned. The high integration of this peculiar Janus-typed membrane with simultaneous double electrically conductive anisotropy-fluorescent dual-functionality is successfully realized in this study. This design philosophy and preparative technique will provide support for the design and construction of new types of special nanostructures with multi-functionality.
Ray-optics analysis of inhomogeneous optically anisotropic media
Sluijter, M.
2010-01-01
When the optical behavior of light in a medium depends on the direction in which light is traveling, the medium is called optically anisotropic. Light is an electromagnetic wave and in this thesis, we discuss the electromagnetic theory on optical anisotropy. We do this with the assumption that the
Fracture of anisotropic materials with plastic strain-gradient effects
DEFF Research Database (Denmark)
Legarth, Brian Nyvang
2013-01-01
A unit cell is adopted to numerically analyze the effect of plastic anisotropy on frac-ture evolution in a micro-reinforced fiber-composite. The matrix material exhibit size-effects and an anisotropic strain-gradient plasticity model accounting for such size-effects through a mate-rial length scale...
Anisotropic interpolation theorems of Musielak-Orlicz type
Directory of Open Access Journals (Sweden)
Jinxia Li
2016-10-01
Full Text Available Abstract Anisotropy is a common attribute of Nature, which shows different characterizations in different directions of all or part of the physical or chemical properties of an object. The anisotropic property, in mathematics, can be expressed by a fairly general discrete group of dilations { A k : k ∈ Z } $\\{A^{k}: k\\in\\mathbb{Z}\\}$ , where A is a real n × n $n\\times n$ matrix with all its eigenvalues λ satisfy | λ | > 1 $|\\lambda|>1$ . Let φ : R n × [ 0 , ∞ → [ 0 , ∞ $\\varphi: \\mathbb{R}^{n}\\times[0, \\infty\\to[0,\\infty$ be an anisotropic Musielak-Orlicz function such that φ ( x , ⋅ $\\varphi(x,\\cdot$ is an Orlicz function and φ ( ⋅ , t $\\varphi(\\cdot,t$ is a Muckenhoupt A ∞ ( A $\\mathbb {A}_{\\infty}(A$ weight. The aim of this article is to obtain two anisotropic interpolation theorems of Musielak-Orlicz type, which are weighted anisotropic extension of Marcinkiewicz interpolation theorems. The above results are new even for the isotropic weighted settings.
Comparison of two anisotropic layer models applied to induction motors
Sprangers, R.L.J.; Paulides, J.J.H.; Boynov, K.O.; Lomonova, E.A.; Waarma, J.
2014-01-01
A general description of the Anisotropic Layer Theory, derived in the polar coordinate system, and applied to the analysis of squirrel-cage induction motors (IMs), is presented. The theory considers non-conductive layers, layer with predefined current density and layers with induced current density.
Dynamical anisotropic response of black phosphorus under magnetic field
Liu, Xuefeng; Lu, Wei; Zhou, Xiaoying; Zhou, Yang; Zhang, Chenglong; Lai, Jiawei; Ge, Shaofeng; Sekhar, M. Chandra; Jia, Shuang; Chang, Kai; Sun, Dong
2018-04-01
Black phosphorus (BP) has emerged as a promising material candidate for next generation electronic and optoelectronic devices due to its high mobility, tunable band gap and highly anisotropic properties. In this work, polarization resolved ultrafast mid-infrared transient reflection spectroscopy measurements are performed to study the dynamical anisotropic optical properties of BP under magnetic fields up to 9 T. The relaxation dynamics of photoexcited carrier is found to be insensitive to the applied magnetic field due to the broadening of the Landau levels and large effective mass of carriers. While the anisotropic optical response of BP decreases with increasing magnetic field, its enhancement due to the excitation of hot carriers is similar to that without magnetic field. These experimental results can be well interpreted by the magneto-optical conductivity of the Landau levels of BP thin film, based on an effective k · p Hamiltonian and linear response theory. These findings suggest attractive possibilities of multi-dimensional control of anisotropic response (AR) of BP with light, electric and magnetic field, which further introduces BP to the fantastic magnetic field sensitive applications.
Anisotropic swim stress in active matter with nematic order
Yan, Wen; Brady, John F.
2018-05-01
Active Brownian particles (ABPs) transmit a swim pressure {{{\\Pi }}}{{swim}}=n\\zeta {D}{{swim}} to the container boundaries, where ζ is the drag coefficient, D swim is the swim diffusivity and n is the uniform bulk number density far from the container walls. In this work we extend the notion of the isotropic swim pressure to the anisotropic tensorial swim stress {{\\boldsymbol{σ }}}{{swim}}=-n\\zeta {{\\boldsymbol{D}}}{{swim}}, which is related to the anisotropic swim diffusivity {{\\boldsymbol{D}}}{{swim}}. We demonstrate this relationship with ABPs that achieve nematic orientational order via a bulk external field. The anisotropic swim stress is obtained analytically for dilute ABPs in both 2D and 3D systems. The anisotropy, defined as the ratio of the maximum to the minimum of the three principal stresses, is shown to grow exponentially with the strength of the external field. We verify that the normal component of the anisotropic swim stress applies a pressure {{{\\Pi }}}{{swim}}=-({{\\boldsymbol{σ }}}{{swim}}\\cdot {\\boldsymbol{n}})\\cdot {\\boldsymbol{n}} on a wall with normal vector {\\boldsymbol{n}}, and, through Brownian dynamics simulations, this pressure is shown to be the force per unit area transmitted by the active particles. Since ABPs have no friction with a wall, the difference between the normal and tangential stress components—the normal stress difference—generates a net flow of ABPs along the wall, which is a generic property of active matter systems.
Finite-difference modelling of anisotropic wave scattering in discrete ...
Indian Academy of Sciences (India)
2
cells containing equivalent anisotropic medium by the use of the linear slip equivalent model. Our. 16 results show ...... frequency regression predicted by equation (21) can be distorted by the effects of multiple scattering. 337 ..... other seismic attributes, at least for the relatively simple geometries of subsurface structure. 449.
Minimal Sampling for Effective Acquisition of Anisotropic BRDFs
Czech Academy of Sciences Publication Activity Database
Vávra, Radomír; Filip, Jiří
2016-01-01
Roč. 35, č. 7 (2016), s. 299-309 ISSN 0167-7055 R&D Projects: GA ČR(CZ) GA14-02652S Institutional support: RVO:67985556 Keywords : BRDF * anisotropic * measurement Subject RIV: BD - Theory of Information Impact factor: 1.611, year: 2016 http://library.utia.cas.cz/separaty/2016/RO/vavra-0463872.pdf
Finite-size effects for anisotropic bootstrap percolation : Logarithmic corrections
van Enter, Aernout C. D.; Hulshof, Tim
In this note we analyse an anisotropic, two-dimensional bootstrap percolation model introduced by Gravner and Griffeath. We present upper and lower bounds on the finite-size effects. We discuss the similarities with the semi-oriented model introduced by Duarte.
Metastability Thresholds for Anisotropic Bootstrap Percolation in Three Dimensions
Enter, Aernout C.D. van; Fey, Anne
In this paper we analyze several anisotropic bootstrap percolation models in three dimensions. We present the order of magnitude for the metastability thresholds for a fairly general class of models. In our proofs, we use an adaptation of the technique of dimensional reduction. We find that the
Finite-size effects for anisotropic bootstrap percolation: logerithmic corrections
Enter, van A.C.D.; Hulshof, T.
2007-01-01
In this note we analyse an anisotropic, two-dimensional bootstrap percolation model introduced by Gravner and Griffeath. We present upper and lower bounds on the finite-size effects. We discuss the similarities with the semi-oriented model introduced by Duarte.
An optimization-based framework for anisotropic simplex mesh adaptation
Yano, Masayuki; Darmofal, David L.
2012-09-01
We present a general framework for anisotropic h-adaptation of simplex meshes. Given a discretization and any element-wise, localizable error estimate, our adaptive method iterates toward a mesh that minimizes error for a given degrees of freedom. Utilizing mesh-metric duality, we consider a continuous optimization problem of the Riemannian metric tensor field that provides an anisotropic description of element sizes. First, our method performs a series of local solves to survey the behavior of the local error function. This information is then synthesized using an affine-invariant tensor manipulation framework to reconstruct an approximate gradient of the error function with respect to the metric tensor field. Finally, we perform gradient descent in the metric space to drive the mesh toward optimality. The method is first demonstrated to produce optimal anisotropic meshes minimizing the L2 projection error for a pair of canonical problems containing a singularity and a singular perturbation. The effectiveness of the framework is then demonstrated in the context of output-based adaptation for the advection-diffusion equation using a high-order discontinuous Galerkin discretization and the dual-weighted residual (DWR) error estimate. The method presented provides a unified framework for optimizing both the element size and anisotropy distribution using an a posteriori error estimate and enables efficient adaptation of anisotropic simplex meshes for high-order discretizations.
Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights
Directory of Open Access Journals (Sweden)
Tianshou Ma
2018-01-01
Full Text Available Strength anisotropy is one of the most distinct features of anisotropic rocks, and it also normally reveals strong anisotropy in Brazilian test Strength (“BtS”. Theoretical research on the “BtS” of anisotropic rocks is seldom performed, and in particular some significant factors, such as the anisotropic tensile strength of anisotropic rocks, the initial Brazilian disc fracture points, and the stress distribution on the Brazilian disc, are often ignored. The aim of the present paper is to review the state of the art in the experimental studies on the “BtS” of anisotropic rocks since the pioneering work was introduced in 1964, and to propose a novel theoretical method to underpin the failure mechanisms and predict the “BtS” of anisotropic rocks under Brazilian test conditions. The experimental data of Longmaxi Shale-I and Jixi Coal were utilized to verify the proposed method. The results show the predicted “BtS” results show strong agreement with experimental data, the maximum error is only ~6.55% for Longmaxi Shale-I and ~7.50% for Jixi Coal, and the simulated failure patterns of the Longmaxi Shale-I are also consistent with the test results. For the Longmaxi Shale-I, the Brazilian disc experiences tensile failure of the intact rock when 0° ≤ βw ≤ 24°, shear failure along the weakness planes when 24° ≤ βw ≤ 76°, and tensile failure along the weakness planes when 76° ≤ βw ≤ 90°. For the Jixi Coal, the Brazilian disc experiences tensile failure when 0° ≤ βw ≤ 23° or 76° ≤ βw ≤ 90°, shear failure along the butt cleats when 23° ≤ βw ≤ 32°, and shear failure along the face cleats when 32° ≤ βw ≤ 76°. The proposed method can not only be used to predict the “BtS” and underpin the failure mechanisms of anisotropic rocks containing a single group of weakness planes, but can also be generalized for fractured rocks containing multi-groups of weakness planes.
Directory of Open Access Journals (Sweden)
Silvia Rodríguez Villalba
2016-10-01
Full Text Available Purpose : To study outcome and toxicity in 59 patients with locally advanced cervix carcinoma treated with computed tomography (CT-based Martinez universal perineal interstitial template (MUPIT and the new magnetic resonance imaging (MRI-compatible template Benidorm (TB. Material and methods: From December 2005 to October 2015, we retrospectively analyzed 34 patients treated with MUPIT and 25 treated with the TB. Six 4 Gy fractions were prescribed to the clinical target volume (CTV combined with external beam radiotherapy (EBRT. The organs at risk (OARs and the CTV were delineated by CT scan in the MUPIT implants and by MRI in the TB implants. Dosimetry was CT-based for MUPIT and exclusively MRI-based for TB. Dose values were biologically normalized to equivalent doses in 2 Gy fractions (EQD2. Results : Median CTV volumes were 163.5 cm3 for CT-based MUPIT (range 81.8-329.4 cm3 and 91.9 cm3 for MRI-based TB (range 26.2-161 cm3. Median D90 CTV (EBRT + BT was 75.8 Gy for CT-based MUPIT (range 69-82 Gy and 78.6 Gy for MRI-based TB (range 62.5-84.2. Median D2cm3 for the rectum was 75.3 Gy for CT-based MUPIT (range 69.8-132.1 Gy and 69.9 Gy for MRI-based TB (range 58.3-83.7 Gy. Median D2cm3 for the bladder was 79.8 Gy for CT-based MUPIT (range 71.2-121.1 Gy and 77.1 Gy for MRI-based TB (range 60.5-90.8 Gy. Local control (LC was 88%. Overall survival (OS, disease free survival (DFS, and LC were not statistically significant in either group. Patients treated with CT-based MUPIT had a significantly higher percentage of rectal bleeding G3 (p = 0.040 than those treated with MRI-based TB, 13% vs. 2%. Conclusions : Template Benidorm treatment using MRI-based dosimetry provides advantages of MRI volume definition, and allows definition of smaller volumes that result in statistically significant decreased rectal toxicity compared to that seen with CT-based MUPIT treatment.
Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy
Alkhalifah, Tariq Ali
2014-01-01
Spectral methods provide artefact-free and generally dispersion-free wavefield extrapolation in anisotropic media. Their apparent weakness is in accessing the medium-inhomogeneity information in an efficient manner. This is usually handled through a velocity-weighted summation (interpolation) of representative constant-velocity extrapolated wavefields, with the number of these extrapolations controlled by the effective rank of the original mixed-domain operator or, more specifically, by the complexity of the velocity model. Conversely, with pseudo-spectral methods, because only the space derivatives are handled in the wavenumber domain, we obtain relatively efficient access to the inhomogeneity in isotropic media, but we often resort to weak approximations to handle the anisotropy efficiently. Utilizing perturbation theory, I isolate the contribution of anisotropy to the wavefield extrapolation process. This allows us to factorize as much of the inhomogeneity in the anisotropic parameters as possible out of the spectral implementation, yielding effectively a pseudo-spectral formulation. This is particularly true if the inhomogeneity of the dimensionless anisotropic parameters are mild compared with the velocity (i.e., factorized anisotropic media). I improve on the accuracy by using the Shanks transformation to incorporate a denominator in the expansion that predicts the higher-order omitted terms; thus, we deal with fewer terms for a high level of accuracy. In fact, when we use this new separation-based implementation, the anisotropy correction to the extrapolation can be applied separately as a residual operation, which provides a tool for anisotropic parameter sensitivity analysis. The accuracy of the approximation is high, as demonstrated in a complex tilted transversely isotropic model. © 2014 European Association of Geoscientists & Engineers.
Influence of copper foil polycrystalline structure on graphene anisotropic etching
Energy Technology Data Exchange (ETDEWEB)
Sharma, Kamal P. [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Mahyavanshi, Rakesh D. [Department of Physical Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Department of Physical Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Tanemura, Masaki [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Department of Physical Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)
2017-01-30
Graphical abstract: Hexagonal hole formation with anisotropic etching independent of the stripes and wrinkles in the synthesized graphene. We also observed variation in etched pattern of the graphene depending on the base Cu grain orientations, attributing to difference in nucleation and growth process. - Highlights: • Reveal the influence of copper polycrystalline structure on anisotropic etching of graphene. • Hexagonal hole formation with etching is observed to be independent of stripes and wrinkles in graphene. • Variation in etched pattern of graphene depending on the base Cu grain is confirmed. • This finding will help to understand the nature of microscopic etched pattern in graphene. - Abstract: Anisotropic etching of graphene and other two dimensional materials is an important tool to understand the growth process as well as enabling fabrication of various well-defined structures. Here, we reveal the influence of copper foil polycrystalline structure on anisotropic etching process of as-synthesized graphene. Graphene crystals were synthesized on the polycrystalline Cu foil by a low-pressure chemical vapor deposition (LPCVD) system. Microscopic analysis shows difference in shape, size and stripes alignment of graphene crystals with dissimilar nucleation within closure vicinity of neighboring Cu grains. Post-growth etching of such graphene crystals also significantly affected by the crystallographic nature of Cu grains as observed by the field emission scanning electron microscope (FE-SEM) and electron back scattered diffraction (EBSD) analysis. Hexagonal hole formation with anisotropic etching is observed to be independent of the stripes and wrinkles in the synthesized graphene. We also observed variation in etched pattern of the graphene depending on the base Cu grain orientations, attributing to difference in nucleation and growth process. The findings can facilitate to understand the nature of microscopic etched pattern depending on metal
Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy
Alkhalifah, Tariq Ali
2014-04-30
Spectral methods provide artefact-free and generally dispersion-free wavefield extrapolation in anisotropic media. Their apparent weakness is in accessing the medium-inhomogeneity information in an efficient manner. This is usually handled through a velocity-weighted summation (interpolation) of representative constant-velocity extrapolated wavefields, with the number of these extrapolations controlled by the effective rank of the original mixed-domain operator or, more specifically, by the complexity of the velocity model. Conversely, with pseudo-spectral methods, because only the space derivatives are handled in the wavenumber domain, we obtain relatively efficient access to the inhomogeneity in isotropic media, but we often resort to weak approximations to handle the anisotropy efficiently. Utilizing perturbation theory, I isolate the contribution of anisotropy to the wavefield extrapolation process. This allows us to factorize as much of the inhomogeneity in the anisotropic parameters as possible out of the spectral implementation, yielding effectively a pseudo-spectral formulation. This is particularly true if the inhomogeneity of the dimensionless anisotropic parameters are mild compared with the velocity (i.e., factorized anisotropic media). I improve on the accuracy by using the Shanks transformation to incorporate a denominator in the expansion that predicts the higher-order omitted terms; thus, we deal with fewer terms for a high level of accuracy. In fact, when we use this new separation-based implementation, the anisotropy correction to the extrapolation can be applied separately as a residual operation, which provides a tool for anisotropic parameter sensitivity analysis. The accuracy of the approximation is high, as demonstrated in a complex tilted transversely isotropic model. © 2014 European Association of Geoscientists & Engineers.
Influence of copper foil polycrystalline structure on graphene anisotropic etching
International Nuclear Information System (INIS)
Sharma, Kamal P.; Mahyavanshi, Rakesh D.; Kalita, Golap; Tanemura, Masaki
2017-01-01
Graphical abstract: Hexagonal hole formation with anisotropic etching independent of the stripes and wrinkles in the synthesized graphene. We also observed variation in etched pattern of the graphene depending on the base Cu grain orientations, attributing to difference in nucleation and growth process. - Highlights: • Reveal the influence of copper polycrystalline structure on anisotropic etching of graphene. • Hexagonal hole formation with etching is observed to be independent of stripes and wrinkles in graphene. • Variation in etched pattern of graphene depending on the base Cu grain is confirmed. • This finding will help to understand the nature of microscopic etched pattern in graphene. - Abstract: Anisotropic etching of graphene and other two dimensional materials is an important tool to understand the growth process as well as enabling fabrication of various well-defined structures. Here, we reveal the influence of copper foil polycrystalline structure on anisotropic etching process of as-synthesized graphene. Graphene crystals were synthesized on the polycrystalline Cu foil by a low-pressure chemical vapor deposition (LPCVD) system. Microscopic analysis shows difference in shape, size and stripes alignment of graphene crystals with dissimilar nucleation within closure vicinity of neighboring Cu grains. Post-growth etching of such graphene crystals also significantly affected by the crystallographic nature of Cu grains as observed by the field emission scanning electron microscope (FE-SEM) and electron back scattered diffraction (EBSD) analysis. Hexagonal hole formation with anisotropic etching is observed to be independent of the stripes and wrinkles in the synthesized graphene. We also observed variation in etched pattern of the graphene depending on the base Cu grain orientations, attributing to difference in nucleation and growth process. The findings can facilitate to understand the nature of microscopic etched pattern depending on metal
International Nuclear Information System (INIS)
Verhaart, René F.; Paulides, Margarethus M.; Fortunati, Valerio; Walsum, Theo van; Veenland, Jifke F.; Verduijn, Gerda M.; Lugt, Aad van der
2014-01-01
Purpose: In current clinical practice, head and neck (H and N) hyperthermia treatment planning (HTP) is solely based on computed tomography (CT) images. Magnetic resonance imaging (MRI) provides superior soft-tissue contrast over CT. The purpose of the authors’ study is to investigate the relevance of using MRI in addition to CT for patient modeling in H and N HTP. Methods: CT and MRI scans were acquired for 11 patients in an immobilization mask. Three observers manually segmented on CT, MRI T1 weighted (MRI-T1w), and MRI T2 weighted (MRI-T2w) images the following thermo-sensitive tissues: cerebrum, cerebellum, brainstem, myelum, sclera, lens, vitreous humor, and the optical nerve. For these tissues that are used for patient modeling in H and N HTP, the interobserver variation of manual tissue segmentation in CT and MRI was quantified with the mean surface distance (MSD). Next, the authors compared the impact of CT and CT and MRI based patient models on the predicted temperatures. For each tissue, the modality was selected that led to the lowest observer variation and inserted this in the combined CT and MRI based patient model (CT and MRI), after a deformable image registration. In addition, a patient model with a detailed segmentation of brain tissues (including white matter, gray matter, and cerebrospinal fluid) was created (CT and MRI db ). To quantify the relevance of MRI based segmentation for H and N HTP, the authors compared the predicted maximum temperatures in the segmented tissues (T max ) and the corresponding specific absorption rate (SAR) of the patient models based on (1) CT, (2) CT and MRI, and (3) CT and MRI db . Results: In MRI, a similar or reduced interobserver variation was found compared to CT (maximum of median MSD in CT: 0.93 mm, MRI-T1w: 0.72 mm, MRI-T2w: 0.66 mm). Only for the optical nerve the interobserver variation is significantly lower in CT compared to MRI (median MSD in CT: 0.58 mm, MRI-T1w: 1.27 mm, MRI-T2w: 1.40 mm). Patient
Energy Technology Data Exchange (ETDEWEB)
Verhaart, René F., E-mail: r.f.verhaart@erasmusmc.nl; Paulides, Margarethus M. [Hyperthermia Unit, Department of Radiation Oncology, Erasmus MC - Cancer Institute, Groene Hilledijk 301, Rotterdam 3008 AE (Netherlands); Fortunati, Valerio; Walsum, Theo van; Veenland, Jifke F. [Biomedical Imaging Group of Rotterdam, Department of Medical Informatics and Radiology, Erasmus MC, Dr. Molewaterplein 50/60, Rotterdam 3015 GE (Netherlands); Verduijn, Gerda M. [Department of Radiation Oncology, Erasmus MC - Cancer Institute, Groene Hilledijk 301, Rotterdam 3008 AE (Netherlands); Lugt, Aad van der [Department of Radiology, Erasmus MC, Dr. Molewaterplein 50/60, Rotterdam 3015 GE (Netherlands)
2014-12-15
Purpose: In current clinical practice, head and neck (H and N) hyperthermia treatment planning (HTP) is solely based on computed tomography (CT) images. Magnetic resonance imaging (MRI) provides superior soft-tissue contrast over CT. The purpose of the authors’ study is to investigate the relevance of using MRI in addition to CT for patient modeling in H and N HTP. Methods: CT and MRI scans were acquired for 11 patients in an immobilization mask. Three observers manually segmented on CT, MRI T1 weighted (MRI-T1w), and MRI T2 weighted (MRI-T2w) images the following thermo-sensitive tissues: cerebrum, cerebellum, brainstem, myelum, sclera, lens, vitreous humor, and the optical nerve. For these tissues that are used for patient modeling in H and N HTP, the interobserver variation of manual tissue segmentation in CT and MRI was quantified with the mean surface distance (MSD). Next, the authors compared the impact of CT and CT and MRI based patient models on the predicted temperatures. For each tissue, the modality was selected that led to the lowest observer variation and inserted this in the combined CT and MRI based patient model (CT and MRI), after a deformable image registration. In addition, a patient model with a detailed segmentation of brain tissues (including white matter, gray matter, and cerebrospinal fluid) was created (CT and MRI{sub db}). To quantify the relevance of MRI based segmentation for H and N HTP, the authors compared the predicted maximum temperatures in the segmented tissues (T{sub max}) and the corresponding specific absorption rate (SAR) of the patient models based on (1) CT, (2) CT and MRI, and (3) CT and MRI{sub db}. Results: In MRI, a similar or reduced interobserver variation was found compared to CT (maximum of median MSD in CT: 0.93 mm, MRI-T1w: 0.72 mm, MRI-T2w: 0.66 mm). Only for the optical nerve the interobserver variation is significantly lower in CT compared to MRI (median MSD in CT: 0.58 mm, MRI-T1w: 1.27 mm, MRI-T2w: 1.40 mm
Verhaart, René F; Fortunati, Valerio; Verduijn, Gerda M; van der Lugt, Aad; van Walsum, Theo; Veenland, Jifke F; Paulides, Margarethus M
2014-12-01
In current clinical practice, head and neck (H&N) hyperthermia treatment planning (HTP) is solely based on computed tomography (CT) images. Magnetic resonance imaging (MRI) provides superior soft-tissue contrast over CT. The purpose of the authors' study is to investigate the relevance of using MRI in addition to CT for patient modeling in H&N HTP. CT and MRI scans were acquired for 11 patients in an immobilization mask. Three observers manually segmented on CT, MRI T1 weighted (MRI-T1w), and MRI T2 weighted (MRI-T2w) images the following thermo-sensitive tissues: cerebrum, cerebellum, brainstem, myelum, sclera, lens, vitreous humor, and the optical nerve. For these tissues that are used for patient modeling in H&N HTP, the interobserver variation of manual tissue segmentation in CT and MRI was quantified with the mean surface distance (MSD). Next, the authors compared the impact of CT and CT and MRI based patient models on the predicted temperatures. For each tissue, the modality was selected that led to the lowest observer variation and inserted this in the combined CT and MRI based patient model (CT and MRI), after a deformable image registration. In addition, a patient model with a detailed segmentation of brain tissues (including white matter, gray matter, and cerebrospinal fluid) was created (CT and MRIdb). To quantify the relevance of MRI based segmentation for H&N HTP, the authors compared the predicted maximum temperatures in the segmented tissues (Tmax) and the corresponding specific absorption rate (SAR) of the patient models based on (1) CT, (2) CT and MRI, and (3) CT and MRIdb. In MRI, a similar or reduced interobserver variation was found compared to CT (maximum of median MSD in CT: 0.93 mm, MRI-T1w: 0.72 mm, MRI-T2w: 0.66 mm). Only for the optical nerve the interobserver variation is significantly lower in CT compared to MRI (median MSD in CT: 0.58 mm, MRI-T1w: 1.27 mm, MRI-T2w: 1.40 mm). Patient models based on CT (Tmax: 38.0 °C) and CT and MRI
International Nuclear Information System (INIS)
Hoogcarspel, Stan J; Van der Velden, Joanne M; Lagendijk, Jan J W; Van Vulpen, Marco; Raaymakers, Bas W
2014-01-01
The purpose of this study was to investigate what pseudo-CT (pCT) strategy is sufficient for online MRI based treatment plan adaptation of a stereotactic treatment for spinal bone metastases. For this purpose, the dosimetric accuracy of five increasingly complex pCT strategies was evaluated using the planning CT data of 20 patients suffering from spinal metastases. For each pCT, a treatment plan was developed and simulated on both the pCT and the original CT data of the patient. The two resulting dose distributions were compared using gamma analysis of 2%/2 mm. In this paper, a Gamma Pass Rate (GPR) of ⩾95% within the Target Volume (TV) was considered clinically acceptable. We additionally demonstrated in this paper the automatic generation of each investigated pCT strategy with the use of dedicated MRI data complemented with pre-treatment CT data of a patient in treatment position. The dosimetric accuracy of a pCT increases when additional bulk densities are utilized for a pCT. However, the dosimetric accuracy of even the most complex ‘bulk density’ pCT strategy used in this study had an average GPR of only 78% within the TV. However, if information on the heterogeneous electron density distribution within the affected vertebral body was available, a clinically acceptable 99% mean GPR was observed. All pCTs could successfully be generated using the MRI data in combination with the CT data of a patient in treatment position. The results presented in this study show that a simple ‘bulk density’ pseudo-CT strategy is not feasible for online MRI based treatment plan adaptation for spinal bone metastases. However, a clinically acceptable result is generated if the information on the heterogeneous electron density (ED) distribution within the affected vertebral bone is available. Therefore, any pCT strategy for this tumor site should include a method which can estimate the heterogeneous ED of the affected vertebral bone. (paper)
Complex Anisotropic Structure of the Mantle Wedge Beneath Kamchatka Volcanoes
Levin, V.; Park, J.; Gordeev, E.; Droznin, D.
2002-12-01
A wedge of mantle material above the subducting lithospheric plate at a convergent margin is among the most dynamic environments of the Earth's interior. Deformation and transport of solid and volatile phases within this region control the fundamental process of elemental exchange between the surficial layers and the interior of the planet. A helpful property in the study of material deformation and transport within the upper mantle is seismic anisotropy, which may reflect both microscopic effects of preferentialy aligned crystals of olivine and orthopyroxene and macroscopic effects of systematic cracks, melt lenses, layering etc. Through the mapping of anisotropic properties within the mantle wedge we can establish patterns of deformation. Volatile content affects olivine alignment, so regions of anomalous volatile content may be evident. Indicators of seismic anisotropy commonly employed in upper mantle studies include shear wave birefringence and mode-conversion between compressional and shear body waves. When combined together, these techniques offer complementary constraints on the location and intensity of anisotropic properties. The eastern coast of southern Kamchatka overlies a vigorous convergent margin where the Pacific plate descends at a rate of almost 80 mm/yr towards the northwest. We extracted seismic anisotropy indicators from two data sets sensitive to the anisotropic properties of the uppermost mantle. Firstly, we evaluated teleseismic receiver functions for a number of sites, and found ample evidence for anisotropicaly-influenced P-to-S mode conversion. Secondly, we measured splitting in S waves of earthquakes with sources within the downgoing slab. The first set of observations provides constraints on the depth ranges where strong changes in anisotropic properties take place. The local splitting data provides constraints on the cumulative strength of anisotropic properties along specific pathways through the mantle wedge and possibly parts of
Modelling of ultrasonic nondestructive testing in anisotropic materials - Rectangular crack
International Nuclear Information System (INIS)
Bostroem, A.
2001-12-01
Nondestructive testing with ultrasound is a standard procedure in the nuclear power industry when searching for defects, in particular cracks. To develop and qualify testing procedures extensive experimental work on test blocks is usually required. This can take a lot of time and therefore be quite costly. A good mathematical model of the testing situation is therefore of great value as it can reduce the experimental work to a great extent. A good model can be very useful for parametric studies and as a pedagogical tool. A further use of a model is as a tool in the qualification of personnel. In anisotropic materials, e.g. austenitic welds, the propagation of ultrasound becomes much more complicated as compared to isotropic materials. Therefore, modelling is even more useful for anisotropic materials, and it in particular has a greater pedagogical value. The present project has been concerned with a further development of the anisotropic capabilities of the computer program UTDefect, which has so far only contained a strip-like crack as the single defect type for anisotropic materials. To be more specific, the scattering by a rectangular crack in an anisotropic component has been studied and the result is adapted to include transmitting and receiving ultrasonic probes. The component under study is assumed to be anisotropic with arbitrary anisotropy. On the other hand, it is assumed to be homogeneous, and this in particular excludes most welds, where it is seldom an adequate approximation to assume homogeneity. The anisotropy may be arbitrarily oriented and the same is true of the rectangular crack. The crack may also be located near a backside of the component. To solve the scattering problem for the crack an integral equation method is used. The probe model has been developed in an earlier project and to compute the signal response in the receiving probe an electromechanical reciprocity argument is employed. As a rectangle is a truly 3D scatterer the sizes of the
Directory of Open Access Journals (Sweden)
Meng-jie PAN
2018-04-01
Full Text Available Objective To observe characteristics of resting-state functional magnetic resonance imaging (rs-fMRI in patients with major depression and explore the possible pathogenesis. Methods A total of 24 major depression patients and 26 sex-, age- and education-matched healthy controls were scanned with rs-fMRI based on amplitude of low-frequency fluctuation (ALFF. The correlation between mALFF values of brain regions and Hamilton Depression Rating Scale-17 (HAMD-17 score was analyzed by Spearman rank correlation analysis. Results Compared with control group, mALFF values in bilateral dorsolateral prefrontal cortex (DLPFC, right orbital superior frontal gyrus, right inferior temporal gyrus, left operculum inferior frontal gyrus, left medial superior frontal gyrus and left gyrus rectus in major depression group were significantly increased (P 0.05, for all. Conclusions Abnormal brain spontaneous activity within default mode network (DMN and limbic system could emerge in major depression patients during resting-state, which may be neurobiological substrate of major depression. DOI: 10.3969/j.issn.1672-6731.2018.03.005
Choi, Young Joon; Constantino, Jason; Vedula, Vijay; Trayanova, Natalia; Mittal, Rajat
2015-01-01
A methodology for the simulation of heart function that combines an MRI-based model of cardiac electromechanics (CE) with a Navier–Stokes-based hemodynamics model is presented. The CE model consists of two coupled components that simulate the electrical and the mechanical functions of the heart. Accurate representations of ventricular geometry and fiber orientations are constructed from the structural magnetic resonance and the diffusion tensor MR images, respectively. The deformation of the ventricle obtained from the electromechanical model serves as input to the hemodynamics model in this one-way coupled approach via imposed kinematic wall velocity boundary conditions and at the same time, governs the blood flow into and out of the ventricular volume. The time-dependent endocardial surfaces are registered using a diffeomorphic mapping algorithm, while the intraventricular blood flow patterns are simulated using a sharp-interface immersed boundary method-based flow solver. The utility of the combined heart-function model is demonstrated by comparing the hemodynamic characteristics of a normal canine heart beating in sinus rhythm against that of the dyssynchronously beating failing heart. We also discuss the potential of coupled CE and hemodynamics models for various clinical applications. PMID:26442254
Energy Technology Data Exchange (ETDEWEB)
Borgne, H.
2004-12-01
Seismic imaging is an important tool for ail exploration. From the filtered seismic traces and a subsurface velocity model, migration allows to localize the reflectors and to estimate physical properties of these interfaces. The subsurface is split up into a reference medium, corresponding to the low spatial frequencies (a smooth medium), and a perturbation medium, corresponding to the high spatial frequencies. The propagation of elastic waves in the medium of reference is modelled by the ray theory. The association of this theory with a principle of diffraction or reflection allows to take into account the high spatial frequencies: the Kirchhoff approach represents so the medium of perturbations with continuous surfaces, characterized by reflection coefficients. The target of the quantitative migration is to reconstruct this reflection coefficient, notably its behaviour according to the incidence angle. These information will open the way to seismic characterization of the reservoir domain, with. a stratigraphic inversion for instance. In order to improve the qualitative and quantitative migration results, one of the current challenges is to take into account the anisotropy of the subsurface. Taking into account rocks anisotropy in the imaging process of seismic data requires two improvements from the isotropic case. The first one roughly concerns the modelling aspect: an anisotropic propagator should be used to avoid a mis-positioning or bad focusing of the imaged reflectors. The second correction concerns the migration aspect: as anisotropy affects the reflectivity of subsurface, a specific anisotropic imaging formula should be applied in the migration kernel, in order to recover the correct A V A behavior of the subsurface reflectors, If the first correction is DOW made in most so-called anisotropic imaging algorithms, the second one is currently ignored. The first part of my work concerns theoretical aspects. 1 study first the preservation of amplitudes in the
Interactions, strings and isotopies in higher order anisotropic superspaces
Vacaru, Sergiu Ion
2001-01-01
The monograph summarizes the author's results on the geometry of anholonomic and locally anisotropic interactions, published in J. Math. Phys., Nucl. Phys. B, Ann. Phys. (NY), JHEP, Rep. Math. Phys., Int. J. Theor. Phys. and in some former Soviet Union and Romanian scientific journals. The main subjects are in the theory of field interactions, strings and diffusion processes on spaces, superspaces and isospaces with higher order anisotropy and inhomogeneity. The approach proceeds by developing the concept of higher order anisotropic (super)space which unifies the logical and manthematical aspects of modern Kaluza--Klein theories and generalized Lagrange and Finsler geometry and leads to modeling of physical processes on higher order fiber (super)bundles provided with nonlinear and distinguished connections and metric structures. This book can be also considered as a pedagogical survey on the mentioned subjects.
Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts.
Schöneberg, J; Otte, F; Néel, N; Weismann, A; Mokrousov, Y; Kröger, J; Berndt, R; Heinze, S
2016-02-10
Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin-orbit coupling. This work shows that engineering the AMR at the single atom level is feasible.
Anisotropic deformations of spatially open cosmology in massive gravity theory
Energy Technology Data Exchange (ETDEWEB)
Mazuet, Charles; Volkov, Mikhail S. [Laboratoire de Mathématiques et Physique Théorique CNRS-UMR 7350, Université de Tours, Parc de Grandmont, 37200 Tours (France); Mukohyama, Shinji, E-mail: charles.mazuet@lmpt.univ-tours.fr, E-mail: shinji.mukohyama@yukawa.kyoto-u.ac.jp, E-mail: volkov@lmpt.univ-tours.fr [Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, 606-8502, Kyoto (Japan)
2017-04-01
We combine analytical and numerical methods to study anisotropic deformations of the spatially open homogeneous and isotropic cosmology in the ghost free massive gravity theory with flat reference metric. We find that if the initial perturbations are not too strong then the physical metric relaxes back to the isotropic de Sitter state. However, the dumping of the anisotropies is achieved at the expense of exciting the Stueckelberg fields in such a way that the reference metric changes and does not share anymore with the physical metric the same rotational and translational symmetries. As a result, the universe evolves towards a fixed point which does not coincide with the original solution, but for which the physical metric is still de Sitter. If the initial perturbation is strong, then its evolution generically leads to a singular anisotropic state or, for some parameter values, to a decay into flat spacetime. We also present an infinite dimensional family of new homogeneous and isotropic cosmologies in the theory.
Three-dimensional magnetotelluric axial anisotropic forward modeling and inversion
Cao, Hui; Wang, Kunpeng; Wang, Tao; Hua, Boguang
2018-06-01
Magnetotelluric (MT) data has been widely used to image underground electrical structural. However, when the significant axial resistivity anisotropy presents, how this influences three-dimensional MT data has not been resolved clearly yet. We here propose a scheme for three-dimensional modeling of MT data in presence of axial anisotropic resistivity, where the electromagnetic fields are decomposed into primary and secondary components. A 3D staggered-grid finite difference method is then used to resolve the resulting 3D governing equations. Numerical tests have completed to validate the correctness and accuracy of the present algorithm. A limited-memory Broyden-Fletcher-Goldfarb-Shanno method is then utilized to realize the 3D MT axial anisotropic inversion. The testing results show that, compared to the results of isotropic resistivity inversion, taking account the axial anisotropy can much improve the inverted results.
Anisotropic cosmological constant and the CMB quadrupole anomaly
International Nuclear Information System (INIS)
Rodrigues, Davi C.
2008-01-01
There are evidences that the cosmic microwave background (CMB) large-angle anomalies imply a departure from statistical isotropy and hence from the standard cosmological model. We propose a ΛCDM model extension whose dark energy component preserves its nondynamical character but wields anisotropic vacuum pressure. Exact solutions for the cosmological scale factors are presented, upper bounds for the deformation parameter are evaluated and its value is estimated considering the elliptical universe proposal to solve the quadrupole anomaly. This model can be constructed from a Bianchi I cosmology with a cosmological constant from two different ways: (i) a straightforward anisotropic modification of the vacuum pressure consistently with energy-momentum conservation; (ii) a Poisson structure deformation between canonical momenta such that the dynamics remain invariant under scale factors rescalings
Statistical ensembles and molecular dynamics studies of anisotropic solids. II
International Nuclear Information System (INIS)
Ray, J.R.; Rahman, A.
1985-01-01
We have recently discussed how the Parrinello--Rahman theory can be brought into accord with the theory of the elastic and thermodynamic behavior of anisotropic media. This involves the isoenthalpic--isotension ensemble of statistical mechanics. Nose has developed a canonical ensemble form of molecular dynamics. We combine Nose's ideas with the Parrinello--Rahman theory to obtain a canonical form of molecular dynamics appropriate to the study of anisotropic media subjected to arbitrary external stress. We employ this isothermal--isotension ensemble in a study of a fcc→ close-packed structural phase transformation in a Lennard-Jones solid subjected to uniaxial compression. Our interpretation of the Nose theory does not involve a scaling of the time variable. This latter fact leads to simplifications when studying the time dependence of quantities
Anisotropic Josephson-vortex dynamics in layered organic superconductors
International Nuclear Information System (INIS)
Yasuzuka, S.; Uji, S.; Satsukawa, H.; Kimata, M.; Terashima, T.; Koga, H.; Yamamura, Y.; Saito, K.; Akutsu, H.; Yamada, J.
2010-01-01
To study the anisotropic Josephson-vortex dynamics in the d-wave superconductors, the interplane resistance has been measured on layered organic superconductors κ-(ET) 2 Cu(NCS) 2 and β-(BDA-TTP) 2 SbF 6 under magnetic fields precisely parallel to the conducting planes. For κ-(ET) 2 Cu(NCS) 2 , in-plane angular dependence of the Josephson-vortex flow resistance is mainly described by the fourfold symmetry and dip structures appear when the magnetic field is applied parallel to the b- and c-axes. The obtained results have a relation to the d-wave superconducting gap symmetry. However, the absence of in-plane fourfold anisotropy was found for β-(BDA-TTP) 2 SbF 6 . The different anisotropic behavior is discussed in terms of the interlayer coupling strength.
Anisotropic Josephson-vortex dynamics in layered organic superconductors
Energy Technology Data Exchange (ETDEWEB)
Yasuzuka, S., E-mail: yasuzuka@chem.tsukuba.ac.j [Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan); Uji, S.; Satsukawa, H.; Kimata, M.; Terashima, T. [National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0003 (Japan); Koga, H.; Yamamura, Y.; Saito, K. [Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan); Akutsu, H.; Yamada, J. [Department of Material Science, Graduate School of Material Science, University of Hyogo, Ako-gun, Hyogo 678-1297 (Japan)
2010-06-01
To study the anisotropic Josephson-vortex dynamics in the d-wave superconductors, the interplane resistance has been measured on layered organic superconductors {kappa}-(ET){sub 2}Cu(NCS){sub 2} and {beta}-(BDA-TTP){sub 2}SbF{sub 6} under magnetic fields precisely parallel to the conducting planes. For {kappa}-(ET){sub 2}Cu(NCS){sub 2}, in-plane angular dependence of the Josephson-vortex flow resistance is mainly described by the fourfold symmetry and dip structures appear when the magnetic field is applied parallel to the b- and c-axes. The obtained results have a relation to the d-wave superconducting gap symmetry. However, the absence of in-plane fourfold anisotropy was found for {beta}-(BDA-TTP){sub 2}SbF{sub 6}. The different anisotropic behavior is discussed in terms of the interlayer coupling strength.
Dynamics of anisotropic power-law f(R) cosmology
International Nuclear Information System (INIS)
Shamir, M. F.
2016-01-01
Modified theories of gravity have attracted much attention of the researchers in the recent years. In particular, the f(R) theory has been investigated extensively due to important f(R) gravity models in cosmological contexts. This paper is devoted to exploring an anisotropic universe in metric f(R) gravity. A locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. Exact solutions of modified field equations are obtained for a well-known f(R) gravity model. The energy conditions are also discussed for the model under consideration. The viability of the model is investigated via graphical analysis using the present-day values of cosmological parameters. The model satisfies null energy, weak energy, and dominant energy conditions for a particular range of the anisotropy parameter while the strong energy condition is violated, which shows that the anisotropic universe in f(R) gravity supports the crucial issue of accelerated expansion of the universe.
Dynamics of anisotropic power-law f(R) cosmology
Energy Technology Data Exchange (ETDEWEB)
Shamir, M. F., E-mail: farasat.shamir@nu.edu.pk [National University of Computer and Emerging Sciences, Lahore Campus, Department of Sciences and Humanities (Pakistan)
2016-12-15
Modified theories of gravity have attracted much attention of the researchers in the recent years. In particular, the f(R) theory has been investigated extensively due to important f(R) gravity models in cosmological contexts. This paper is devoted to exploring an anisotropic universe in metric f(R) gravity. A locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. Exact solutions of modified field equations are obtained for a well-known f(R) gravity model. The energy conditions are also discussed for the model under consideration. The viability of the model is investigated via graphical analysis using the present-day values of cosmological parameters. The model satisfies null energy, weak energy, and dominant energy conditions for a particular range of the anisotropy parameter while the strong energy condition is violated, which shows that the anisotropic universe in f(R) gravity supports the crucial issue of accelerated expansion of the universe.
A crossover in anisotropic nanomechanochemistry of van der Waals crystals
International Nuclear Information System (INIS)
Shimamura, Kohei; Misawa, Masaaki; Li, Ying; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya; Shimojo, Fuyuki
2015-01-01
In nanoscale mechanochemistry, mechanical forces selectively break covalent bonds to essentially control chemical reactions. An archetype is anisotropic detonation of layered energetic molecular crystals bonded by van der Waals (vdW) interactions. Here, quantum molecular dynamics simulations reveal a crossover of anisotropic nanomechanochemistry of vdW crystal. Within 10 −13 s from the passage of shock front, lateral collision produces NO 2 via twisting and bending of nitro-groups and the resulting inverse Jahn-Teller effect, which is mediated by strong intra-layer hydrogen bonds. Subsequently, as we transition from heterogeneous to homogeneous mechanochemical regimes around 10 −12 s, shock normal to multilayers becomes more reactive, producing H 2 O assisted by inter-layer N-N bond formation. These time-resolved results provide much needed atomistic understanding of nanomechanochemistry that underlies a wider range of technologies
Coupled polaritonic band gaps in the anisotropic piezoelectric superlattices
Tang, Zheng-Hua; Jiang, Zheng-Sheng; Chen, Tao; Jiang, Chun-Zhi; Lei, Da-Jun; Huang, Jian-Quan; Qiu, Feng; Yao, Min; Huang, Xiao-Yi
2018-01-01
Anisotropic piezoelectric superlattices (APSs) with the periodic arrangement of polarized anisotropic piezoelectric domains in a certain direction are presented, in which the coupled polaritonic band gaps (CPBGs) can be obtained in the whole Brillouin Zone and the maximum relative bandwidth (band-gap sizes divided by their midgap frequencies) of 5.1% can be achieved. The general characteristics of the APSs are similar to those of the phononic crystals composed of two types of materials, with the main difference being the formation mechanism of the CPBGs, which originate from the couplings between lattice vibrations along two different directions and electromagnetic waves rather than from the periodical modulation of density and elastic constants. In addition, there are no lattice mismatches because the APSs are made of the same material. Thus, the APSs can also be extended to the construction of novel acousto-optic devices.
Anisotropic mechanical properties of graphene sheets from molecular dynamics
International Nuclear Information System (INIS)
Ni Zhonghua; Bu Hao; Zou Min; Yi Hong; Bi Kedong; Chen Yunfei
2010-01-01
Anisotropic mechanical properties are observed for a sheet of graphene along different load directions. The anisotropic mechanical properties are attributed to the hexagonal structure of the unit cells of the graphene. Under the same tensile loads, the edge bonds bear larger load in the longitudinal mode (LM) than in the transverse mode (TM), which causes fracture sooner in LM than in TM. The Young's modulus and the third order elastic modulus for the LM are slightly larger than that for the TM. Simulation also demonstrates that, for both LM and TM, the loading and unloading stress-strain response curves overlap as long as the graphene is unloaded before the fracture point. This confirms that graphene sustains complete elastic and reversible deformation in the elongation process.
Local deposition of anisotropic nanoparticles using scanning electrochemical microscopy (SECM).
Fedorov, Roman G; Mandler, Daniel
2013-02-28
We demonstrate localized electrodeposition of anisotropic metal nanoobjects, namely Au nanorods (GNR), on indium tin oxide (ITO) using scanning electrochemical microscopy (SECM). A gold microelectrode was the source of the gold ions whereby double pulse chronoamperometry was employed to generate initially Au seeds which were further grown under controlled conditions. The distance between the microelectrode and the ITO surface as well as the different experimental parameters (electrodeposition regime, solution composition and temperature) were optimized to produce faceted gold seeds with the required characteristics (size and distribution). Colloidal chemical synthesis was successfully exploited for better understanding the role of the surfactant and different additives in breaking the crystallographic symmetry and anisotropic growth of GNR. Experiments performed in a conventional three-electrode cell revealed the most appropriate electrochemical conditions allowing high yield synthesis of nanorods with well-defined shape as well as nanocubes and bipyramids.
Meson life time in the anisotropic quark-gluon plasma
International Nuclear Information System (INIS)
Ali-Akbari, Mohammad; Allahbakhshi, Davood
2014-01-01
In the hot (an)isotropic plasma the meson life time τ is defined as a time scale after which the meson dissociates. According to the gauge/gravity duality, this time can be identified with the inverse of the imaginary part of the frequency of the quasinormal modes, ω_I, in the (an)isotropic black hole background. In the high temperature limit, we numerically show that at fixed temperature(entropy density) the life time of the mesons decreases(increases) as the anisotropy parameter raises. For general case, at fixed temperature we introduce a polynomial function for ω_I and observe that the meson life time decreases. Moreover, we realize that (s/T"3)"6, where s and T are entropy density and temperature of the plasma respectively, can be expressed as a function of anisotropy parameter over temperature. Interestingly, this function is a Padé approximant.
Coherent manipulation of dipolar coupled spins in an anisotropic environment
Baibekov, E. I.; Gafurov, M. R.; Zverev, D. G.; Kurkin, I. N.; Malkin, B. Z.; Barbara, B.
2014-11-01
We study coherent dynamics in a system of dipolar coupled spin qubits diluted in a solid and subjected to a driving microwave field. In the case of rare earth ions, an anisotropic crystal background results in anisotropic g tensor and thus modifies the dipolar coupling. We develop a microscopic theory of spin relaxation in a transient regime for the frequently encountered case of axially symmetric crystal field. The calculated decoherence rate is nonlinear in the Rabi frequency. We show that the direction of a static magnetic field that corresponds to the highest spin g factor is preferable in order to obtain a higher number of coherent qubit operations. The results of calculations are in excellent agreement with our experimental data on Rabi oscillations recorded for a series of CaW O4 crystals with different concentrations of N d3 + ions.
Anisotropic Friction of Wrinkled Graphene Grown by Chemical Vapor Deposition.
Long, Fei; Yasaei, Poya; Yao, Wentao; Salehi-Khojin, Amin; Shahbazian-Yassar, Reza
2017-06-21
Wrinkle structures are commonly seen on graphene grown by the chemical vapor deposition (CVD) method due to the different thermal expansion coefficient between graphene and its substrate. Despite the intensive investigations focusing on the electrical properties, the nanotribological properties of wrinkles and the influence of wrinkle structures on the wrinkle-free graphene remain less understood. Here, we report the observation of anisotropic nanoscale frictional characteristics depending on the orientation of wrinkles in CVD-grown graphene. Using friction force microscopy, we found that the coefficient of friction perpendicular to the wrinkle direction was ∼194% compare to that of the parallel direction. Our systematic investigation shows that the ripples and "puckering" mechanism, which dominates the friction of exfoliated graphene, plays even a more significant role in the friction of wrinkled graphene grown by CVD. The anisotropic friction of wrinkled graphene suggests a new way to tune the graphene friction property by nano/microstructure engineering such as introducing wrinkles.
Newton–Hooke-type symmetry of anisotropic oscillators
International Nuclear Information System (INIS)
Zhang, P.M.; Horvathy, P.A.; Andrzejewski, K.; Gonera, J.; Kosiński, P.
2013-01-01
Rotation-less Newton–Hooke-type symmetry, found recently in the Hill problem, and instrumental for explaining the center-of-mass decomposition, is generalized to an arbitrary anisotropic oscillator in the plane. Conversely, the latter system is shown, by the orbit method, to be the most general one with such a symmetry. Full Newton–Hooke symmetry is recovered in the isotropic case. Star escape from a galaxy is studied as an application. -- Highlights: ► Rotation-less Newton–Hooke (NH) symmetry is generalized to an arbitrary anisotropic oscillator. ► The orbit method is used to find the most general case for rotation-less NH symmetry. ► The NH symmetry is decomposed into Heisenberg algebras based on chiral decomposition
Anisotropic properties of single crystals of high Tc superconductors
International Nuclear Information System (INIS)
Tholence, J.L.; Saint-Paul, M.; Laborde, O.; Monceau, P.; Guillot, M.; Niel, H.; Levet, J.C.; Potel, M.; Padiou, J.; Gougeon, P.
1990-01-01
In this article the authors make a review of some of the anisotropic properties of high T c compounds, essentially RE Ba 2 Cu 3 O 7 , Bi-SR-Ca-Cu-O and Tl-Ca-Ba-Cu-O systems. In section 2 a short description of the crystal growth is reported. Section 3 deals with the anisotropic elastic properties measured by ultrasonic techniques. In section 4 the authors discuss the anisotropy in magnetization measurements and consequently on the critical currents. Section 5 concerns the magnetoresistance measurements, and the determination of the superconducting critical magnetic field H c2 . Finally in section 6, in conclusion of result described in sections 4 and 5, the authors discuss on the pinning force and on the controversial Lorentz force for explaining the broadening of the superconducting transition under magnetic field. The authors apologize for not having quoted all the works published on these different topics, which is in fact practically impossible
Effect of neutron anisotropic scattering in fast reactor analysis
International Nuclear Information System (INIS)
Chiba, Gou
2004-01-01
Numerical tests were performed about an effect of a neutron anisotropic scattering on criticality in the Sn transport calculation. The simplest approximation, the consistent P approximation and the extended transport approximation were compared with each other in one-dimensional slab fast reactor models. JAERI fast set which has been used for fast reactor analyses is inadequate to evaluate the effect because it doesn't include the scattering matrices and the self-shielding factors to calculate the group-averaged cross sections weighted by the higher-order moment of angular flux. In the present study, the sub-group method was used to evaluate the group-averaged cross sections. Results showed that the simplest approximation is inadequate and the transport approximation is effective for evaluating the anisotropic scattering. (author)
Ultraviolet laser-induced voltage in anisotropic shale
Miao, Xinyang; Zhu, Jing; Li, Yizhang; Zhao, Kun; Zhan, Honglei; Yue, Wenzheng
2018-01-01
The anisotropy of shales plays a significant role in oil and gas exploration and engineering. Owing to various problems and limitations, anisotropic properties were seldom investigated by direct current resistivity methods. Here in this work, a 248 nm ultraviolet laser was employed to assess the anisotropic electrical response of a dielectric shale. Angular dependence of laser-induced voltages (V p) were obtained, with a data symmetry at the location of 180° and a ~62.2% V p anisotropy of the sample. The double-exponential functions have provided an explanation for the electrical field controlled carrier transportation process in horizontal and vertical directions. The results demonstrate that the combination of optics and electrical logging analysis (Opti-electrical Logging) is a promising technology for the investigation of unconventional reservoirs.
Timoshenko beam element with anisotropic cross-sectional properties
DEFF Research Database (Denmark)
Stäblein, Alexander; Hansen, Morten Hartvig
2016-01-01
Beam models are used for the aeroelastic time and frequency domain analysis of wind turbines due to their computational efficiency. Many current aeroelastic tools for the analysis of wind turbines rely on Timoshenko beam elements with classical crosssectional properties (EA, EI, etc.). Those cross......-sectional properties do not reflect the various couplings arising from the anisotropic behaviour of the blade material. A twonoded, three-dimensional Timoshenko beam element was therefore extended to allow for anisotropic cross-sectional properties. For an uncoupled beam, the resulting shape functions are identical...... to the original formulation. The new element was implemented into a co-rotational formulation and validated against natural frequencies and several static load cases of previous works....
A resistor interpretation of general anisotropic cardiac tissue.
Shao, Hai; Sampson, Kevin J; Pormann, John B; Rose, Donald J; Henriquez, Craig S
2004-02-01
This paper describes a spatial discretization scheme for partial differential equation systems that contain anisotropic diffusion. The discretization method uses unstructured finite volumes, or the boxes, that are formed as a secondary geometric structure from an underlying triangular mesh. We show how the discretization can be interpreted as a resistive circuit network, where each resistor is assigned at each edge of the triangular element. The resistor is computed as an anisotropy dependent geometric quantity of the local mesh structure. Finally, we show that under certain conditions, the discretization gives rise to negative resistors that can produce non-physical hyperpolarizations near depolarizing stimuli. We discuss how the proper choice of triangulation (anisotropic Delaunay triangulation) can ensure monotonicity (i.e. all resistors are positive).
Dirac directional emission in anisotropic zero refractive index photonic crystals.
He, Xin-Tao; Zhong, Yao-Nan; Zhou, You; Zhong, Zhi-Chao; Dong, Jian-Wen
2015-08-14
A certain class of photonic crystals with conical dispersion is known to behave as isotropic zero-refractive-index medium. However, the discrete building blocks in such photonic crystals are limited to construct multidirectional devices, even for high-symmetric photonic crystals. Here, we show multidirectional emission from low-symmetric photonic crystals with semi-Dirac dispersion at the zone center. We demonstrate that such low-symmetric photonic crystal can be considered as an effective anisotropic zero-refractive-index medium, as long as there is only one propagation mode near Dirac frequency. Four kinds of Dirac multidirectional emitters are achieved with the channel numbers of five, seven, eleven, and thirteen, respectively. Spatial power combination for such kind of Dirac directional emitter is also verified even when multiple sources are randomly placed in the anisotropic zero-refractive-index photonic crystal.
Anisotropic hypersonic phonon propagation in films of aligned ellipsoids.
Beltramo, Peter J; Schneider, Dirk; Fytas, George; Furst, Eric M
2014-11-14
A material with anisotropic elastic mechanical properties and a direction-dependent hypersonic band gap is fabricated using ac electric field-directed convective self-assembly of colloidal ellipsoids. The frequency of the gap, which is detected in the direction perpendicular to particle alignment and entirely absent parallel to alignment, and the effective sound velocities can be tuned by the particle aspect ratio. We hypothesize that the band gap originates from the primary eigenmode peak, the m-splitted (s,1,2) mode, of the particle resonating with the effective medium. These results reveal the potential for powerful control of the hypersonic phononic band diagram by combining anisotropic particles and self-assembly.
SO-FDTD analysis of anisotropic magnetized plasma
International Nuclear Information System (INIS)
Yang Hongwei; Nanjing Univ. of Science and Technology, Nanjing; Yuan Hong; Chen Rushan; Yang Yang
2007-01-01
A novel finite-difference time-domain (FDTD) method, called shift operator FDTD (SO-FDTD) method is developed for anisotropic magnetized dispersive media. The recursive relation between operators is used. In this paper, some expressions containing the dielectric constants of magnetized dispersive media are written as rational polynomial function. The SO-FDTD formulation for anisotropic magnetized plasma is derived. The high efficiency and effectiveness of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer, with the direction of the propagation parallel to the direction of the biasing field. A comparison with frequency domain analytic results is included. The CPU time was several times shorter than that of the JEC method. (authors)
Nanoscale Rheology and Anisotropic Diffusion Using Single Gold Nanorod Probes
Molaei, Mehdi; Atefi, Ehsan; Crocker, John C.
2018-03-01
The complex rotational and translational Brownian motion of anisotropic particles depends on their shape and the viscoelasticity of their surroundings. Because of their strong optical scattering and chemical versatility, gold nanorods would seem to provide the ultimate probes of rheology at the nanoscale, but the suitably accurate orientational tracking required to compute rheology has not been demonstrated. Here we image single gold nanorods with a laser-illuminated dark-field microscope and use optical polarization to determine their three-dimensional orientation to better than one degree. We convert the rotational diffusion of single nanorods in viscoelastic polyethylene glycol solutions to rheology and obtain excellent agreement with bulk measurements. Extensions of earlier models of anisotropic translational diffusion to three dimensions and viscoelastic fluids give excellent agreement with the observed motion of single nanorods. We find that nanorod tracking provides a uniquely capable approach to microrheology and provides a powerful tool for probing nanoscale dynamics and structure in a range of soft materials.
A crossover in anisotropic nanomechanochemistry of van der Waals crystals
Energy Technology Data Exchange (ETDEWEB)
Shimamura, Kohei [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan); Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan); Misawa, Masaaki [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan); Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Li, Ying [Argonne Leadership Computing Facility, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Shimojo, Fuyuki [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)
2015-12-07
In nanoscale mechanochemistry, mechanical forces selectively break covalent bonds to essentially control chemical reactions. An archetype is anisotropic detonation of layered energetic molecular crystals bonded by van der Waals (vdW) interactions. Here, quantum molecular dynamics simulations reveal a crossover of anisotropic nanomechanochemistry of vdW crystal. Within 10{sup −13} s from the passage of shock front, lateral collision produces NO{sub 2} via twisting and bending of nitro-groups and the resulting inverse Jahn-Teller effect, which is mediated by strong intra-layer hydrogen bonds. Subsequently, as we transition from heterogeneous to homogeneous mechanochemical regimes around 10{sup −12} s, shock normal to multilayers becomes more reactive, producing H{sub 2}O assisted by inter-layer N-N bond formation. These time-resolved results provide much needed atomistic understanding of nanomechanochemistry that underlies a wider range of technologies.
Modeling of CMUTs with Multiple Anisotropic Layers and Residual Stress
DEFF Research Database (Denmark)
Engholm, Mathias; Thomsen, Erik Vilain
2014-01-01
Usually the analytical approach for modeling CMUTs uses the single layer plate equation to obtain the deflection and does not take anisotropy and residual stress into account. A highly accurate model is developed for analytical characterization of CMUTs taking an arbitrary number of layers...... and residual stress into account. Based on the stress-strain relation of each layer and balancing stress resultants and bending moments, a general multilayered anisotropic plate equation is developed for plates with an arbitrary number of layers. The exact deflection profile is calculated for a circular...... clamped plate of anisotropic materials with residual bi-axial stress. From the deflection shape the critical stress for buckling is calculated and by using the Rayleigh-Ritz method the natural frequency is estimated....
Modeling of plates with multiple anisotropic layers and residual stress
DEFF Research Database (Denmark)
Engholm, Mathias; Pedersen, Thomas; Thomsen, Erik Vilain
2016-01-01
Usually the analytical approach for modeling of plates uses the single layer plate equation to obtain the deflection and does not take anisotropy and residual stress into account. Based on the stress–strain relation of each layer and balancing stress resultants and bending moments, a general...... multilayered anisotropic plate equation is developed for plates with an arbitrary number of layers. The exact deflection profile is calculated for a circular clamped plate of anisotropic materials with residual bi-axial stress.From the deflection shape the critical stress for buckling is calculated......, and an excellent agreement between the two models is seen with a relative difference of less than 2% for all calculations. The model was also used to extract the cell capacitance, the parasitic capacitance and the residual stress of a pressure sensor composed of a multilayered plate of silicon and silicon oxide...
Anisotropic charged physical models with generalized polytropic equation of state
Energy Technology Data Exchange (ETDEWEB)
Nasim, A.; Azam, M. [University of Education, Division of Science and Technology, Lahore (Pakistan)
2018-01-15
In this paper, we found the exact solutions of Einstein-Maxwell equations with generalized polytropic equation of state (GPEoS). For this, we consider spherically symmetric object with charged anisotropic matter distribution. We rewrite the field equations into simple form through transformation introduced by Durgapal (Phys Rev D 27:328, 1983) and solve these equations analytically. For the physically acceptability of these solutions, we plot physical quantities like energy density, anisotropy, speed of sound, tangential and radial pressure. We found that all solutions fulfill the required physical conditions. It is concluded that all our results are reduced to the case of anisotropic charged matter distribution with linear, quadratic as well as polytropic equation of state. (orig.)
Holographic Fermions in Anisotropic Einstein-Maxwell-Dilaton-Axion Theory
International Nuclear Information System (INIS)
Kuang, Xiao-Mei; Fang, Li-Qing
2015-01-01
We investigate the properties of the holographic Fermionic system dual to an anisotropic charged black brane bulk in Einstein-Maxwell-Dilaton-Axion gravity theory. We consider the minimal coupling between the Dirac field and the gauge field in the bulk gravity theory and mainly explore the dispersion relation exponents of the Green functions of the dual Fermionic operators in the dual field theory. We find that along both the anisotropic and the isotropic directions the Fermi momentum will be effected by the anisotropy of the bulk theory. However, the anisotropy has influence on the dispersion relation which is almost linear for massless Fermions with charge q=2. The universal properties that the mass and the charge of the Fermi possibly correspond to nonlinear dispersion relation are also investigated
Inflationary perturbations in anisotropic, shear-free universes
International Nuclear Information System (INIS)
Pereira, Thiago S.; Carneiro, Saulo; Marugan, Guillermo A. Mena
2012-01-01
In this work, the linear and gauge-invariant theory of cosmological perturbations in a class of anisotropic and shear-free spacetimes is developed. After constructing an explicit set of complete eigenfunctions in terms of which perturbations can be expanded, we identify the effective degrees of freedom during a generic slow-roll inflationary phase. These correspond to the anisotropic equivalent of the standard Mukhanov-Sasaki variables. The associated equations of motion present a remarkable resemblance to those found in perturbed Friedmann-Robertson-Walker spacetimes with curvature, apart from the spectrum of the Laplacian, which exhibits the characteristic frequencies of the underlying geometry. In particular, it is found that the perturbations cannot develop arbitrarily large super-Hubble modes
Anisotropic to Isotropic Phase Transitions in the Early Universe
Directory of Open Access Journals (Sweden)
Ajaib M. A.
2012-04-01
Full Text Available We attempt to develop a minimal formalism to describe an anisotropic to isotropic tran- sition in the early Universe. Assuming an underlying theory that violates Lorentz in- variance, we start with a Dirac like equation, involving four massless fields, and which does not exhibit Lorentz invariance. We then perform transformations that restore it to its covariant form along with a mass term for the fermion field. It is proposed that these transformations can be visualized as waves traveling in an anisotropic media. The trans- formation it = ℏ ! is then utilized to transit to a statistical thermodynamics system and the partition function then gives a better insight into the character of this transition. The statistical system hence realized is a two level system with each state doubly degenerate. We propose that modeling the transition this way can help explain the matter antimatter asymmetry of the Universe.
Anisotropic shift of the irreversibility line by neutron irradiation
International Nuclear Information System (INIS)
Sauerzopf, F.M.; Wiesinger, H.P.; Weber, H.W.; Crabtree, G.W.; Frischherz, M.C.; Kirk, M.A.
1991-09-01
The irreversibility line of high-T c superconductors is shifted considerably by irradiating the material with fast neutrons. The anisotropic and non-monotonous shift is qualitatively explained by a simple model based on an interaction between three pinning mechanisms, the intrinsic pinning by the ab-planes, the weak pinning by the pre-irradiation defect structure, and strong pinning by neutron induced defect cascades. A correlation between the cascade density and the position of the irreversibility line is observed
Anisotropic 3D texture synthesis with application to volume rendering
DEFF Research Database (Denmark)
Laursen, Lasse Farnung; Ersbøll, Bjarne Kjær; Bærentzen, Jakob Andreas
2011-01-01
images using a 12.1 megapixel camera. Next, we extend the volume rendering pipeline by creating a transfer function which yields not only color and opacity from the input intensity, but also texture coordinates for our synthesized 3D texture. Thus, we add texture to the volume rendered images....... This method is applied to a high quality visualization of a pig carcass, where samples of meat, bone, and fat have been used to produce the anisotropic 3D textures....
Catastrophes in the interaction of light waves in anisotropic resonator
International Nuclear Information System (INIS)
Mkrtchyan, A.R.; Nersisyan, S.R.; Tabiryan, N.V.
1993-01-01
An origin of jump-like and hysteresical phenomena is predicted theoretically. Those are caused by the ruling of the state of non-linear anisotropic resonator with an orthogonal polarization of light waves. The resonator creates a turned connection as well as causes a complex tying between the waves. The later conditions a whole number of the interacting waves regimes because of a big number of ruling parameters. 5 refs
Model and calculation of in situ stresses in anisotropic formations
Energy Technology Data Exchange (ETDEWEB)
Yuezhi, W.; Zijun, L.; Lixin, H. [Jianghan Petroleum Institute, (China)
1997-08-01
In situ stresses in transversely isotropic material in relation to wellbore stability have been investigated. Equations for three horizontal in- situ stresses and a new formation fracture pressure model were described, and the methodology for determining the elastic parameters of anisotropic rocks in the laboratory was outlined. Results indicate significantly smaller differences between theoretically calculated pressures and actual formation pressures than results obtained by using the isotropic method. Implications for improvements in drilling efficiency were reviewed. 13 refs., 6 figs.
Anisotropic square lattice Potts ferromagnet: renormalization group treatment
International Nuclear Information System (INIS)
Oliveira, P.M.C. de; Tsallis, C.
1981-01-01
The choice of a convenient self-dual cell within a real space renormalization group framework enables a satisfactory treatment of the anisotropic square lattice q-state Potts ferromagnet criticality. The exact critical frontier and dimensionality crossover exponent PHI as well as the expected universality behaviour (renormalization flow sense) are recovered for any linear scaling factor b and all values of q(q - [pt
Anisotropic static solutions in modelling highly compact bodies
Indian Academy of Sciences (India)
x2µ(x)dx which is the mass function. The radial pressure pr = p + 2S/. √. 3 and the tangential pressure p⊥ = p − S/. √. 3 are not equal for anisotropic matter. The magnitude S provides a measure of anisotropy. The field equations (1)–(3) were integrated by Chaisi and Maharaj [12] for the energy density. µ = j r2. + k + lr2,. (4).
Charged anisotropic star on paraboloidal space-time
Indian Academy of Sciences (India)
dr2 − r2 ( dθ2 + sin2 θdφ2). ,. (1) with the energy–momentum tensor for anisotropic charged fluid,. Tij = diag. ( ρ + E2, pr − E2, pt + E2, pt + E2). ,. (2) where ρ is the energy density, pr is the radial pressure, pt is the tangential pressure and. E is the electric field intensity. These quantities are measured relative to the comoving.
An auxiliary differential equation FDTD method for anisotropic magnetized plasmas
International Nuclear Information System (INIS)
Liu Shaobin; Mo Jinjun; Yuan Naichang
2004-01-01
An auxiliary differential equation finite-difference time-domain (ADE-FDTD) methodology for anisotropic magnetized plasmas is derived. The method is based on a difference approximation of the auxiliary differential equation. A comparison with the JEC method is included. The CPU time saving by several times and accuracy of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer with the direction of propagation parallel to the direction of the biasing field
Giant spin torque in systems with anisotropic exchange interaction
Korenev, Vladimir L.
2012-01-01
Control of magnetic domain wall movement by the spin-polarized current looks promising for creation of a new generation of magnetic memory devices. A necessary condition for this is the domain wall shift by a low-density current. Here I show that a strongly anisotropic exchange interaction between mobile heavy holes and localized magnetic moments enormously increases the current-induced torque on the domain wall as compared to systems with isotropic exchange. This enables one to control the d...
Wave propagation in layered anisotropic media with application to composites
Nayfeh, AH
1995-01-01
Recent advances in the study of the dynamic behavior of layered materials in general, and laminated fibrous composites in particular, are presented in this book. The need to understand the microstructural behavior of such classes of materials has brought a new challenge to existing analytical tools. This book explores the fundamental question of how mechanical waves propagate and interact with layered anisotropic media. The chapters are organized in a logical sequence depending upon the complexity of the physical model and its mathematical treatment.
Circumferential gap propagation in an anisotropic elastic bacterial sacculus
Taneja, Swadhin; Levitan, Benjamin A.; Rutenberg, Andrew D.
2013-01-01
We have modelled stress concentration around small gaps in anisotropic elastic sheets, corresponding to the peptidoglycan sacculus of bacterial cells, under loading corresponding to the effects of turgor pressure in rod-shaped bacteria. We find that under normal conditions the stress concentration is insufficient to mechanically rupture bacteria, even for gaps up to a micron in length. We then explored the effects of stress-dependent smart-autolysins, as hypothesised by Arthur L Koch [Advance...
Complex eigenvalues for neutron transport equation with quadratically anisotropic scattering
International Nuclear Information System (INIS)
Sjoestrand, N.G.
1981-01-01
Complex eigenvalues for the monoenergetic neutron transport equation in the buckling approximation have been calculated for various combinations of linearly and quadratically anisotropic scattering. The results are discussed in terms of the time-dependent case. Tables are given of complex bucklings for real decay constants and of complex decay constants for real bucklings. The results fit nicely into the pattern of real and purely imaginary eigenvalues obtained earlier. (author)
Anisotropic magnetoresistance of GaMnAs ferromagnetic semiconductors
Czech Academy of Sciences Publication Activity Database
Vašek, Petr; Svoboda, Pavel; Novák, Vít; Cukr, Miroslav; Výborný, Karel; Jurka, Vlastimil; Stuchlík, Jiří; Orlita, Milan; Maude, D. K.
2010-01-01
Roč. 23, č. 6 (2010), 1161-1163 ISSN 1557-1939 R&D Projects: GA AV ČR KAN400100652; GA MŠk MEB020928 Grant - others:EU EuroMagNET II(XE) Egide 19535NF Institutional research plan: CEZ:AV0Z10100521 Keywords : GaMnAs * anisotropic magnetoresistance * hydrogenation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.014, year: 2010
Stoner–Wohlfarth model for the anisotropic case
Energy Technology Data Exchange (ETDEWEB)
Campos, Marcos F. de, E-mail: mcampos@metal.eeimvr.uff.br [Programa de Pós-graduação em Engenharia Metalúrgica-PUVR, Universidade Federal Fluminense, Av dos Trabalhadores 420,27255-125 Volta Redonda, Rio de Janeiro (Brazil); Sampaio da Silva, Fernanda A. [Programa de Pós-graduação em Engenharia Metalúrgica-PUVR, Universidade Federal Fluminense, Av dos Trabalhadores 420,27255-125 Volta Redonda, Rio de Janeiro (Brazil); Perigo, Elio A. [Laboratory for the Physics of Advanced Materials, University of Luxembourg, L1511 Luxembourg (Luxembourg); Castro, José A. de [Programa de Pós-graduação em Engenharia Metalúrgica-PUVR, Universidade Federal Fluminense, Av dos Trabalhadores 420,27255-125 Volta Redonda, Rio de Janeiro (Brazil)
2013-11-15
The Stoner–Wohlfarth (SW) model was calculated for the anisotropic case, by assuming crystallographical texture distributions as Gaussian, Lorentzian and Cos{sup n} (alpha). All these distributions were tested and both Gaussian and Cos{sup n} (alpha) give similar results for M{sub r}/M{sub s} above 0.8. However, the use of Cos{sup n} (alpha) makes it easier to find analytical expressions representing texture. The Lorentzian distribution is a suitable choice for not well aligned magnets, or magnets with a high fraction of misaligned grains. It is discussed how to obtain the alignment degree M{sub r}/M{sub s} directly from two measurements of magnetic remanence at the transverse and parallel directions to the alignment direction of the magnet. It is demonstrated that even the well aligned magnets with M{sub r}/M{sub s}=0.96 present coercive field of 60–70% of the anisotropy field, depending on the chosen distribution. The anisotropic SW model was used for discussing hysteresis squareness. Improving the crystalographical texture, the loop squareness also increases. - Highlights: • The Stoner–Wohlfarth model was calculated for the anisotropic case. • Different distribution functions for texture description were compared and discussed. • Lorentzian distribution is adequate for not well oriented magnets. • Determination of the alignment ratio M{sub r}/M{sub s} from 2 remanence measurements. • Prediction of the coercive field in Stoner–Wohlfarth aligned magnets.
On the creation of scalar particles in some anisotropic universe
International Nuclear Information System (INIS)
Nariai, Hidekazu.
1978-01-01
Because of an importance of the particle creation (especially, its possible fulfilment of the black-body law with a definite temperature) in an early universe to various other cosmological problems we study how the creation of scalar particles occurs in the Bianchi-type I anisotropic universe adopted in our previous works on the quantized scalar field. It is shown that, as in a special isotropic case dealt with in recent papers, the creation may occur at the sacrifice of the requirement that the quantization procedure should reproduce the usual theory for a free field in the limit when the anisotropic universe changes into the Minkowski space-time. It is further shown that the creation occurs in accordance with the black-body law only in a 2-dimensional hyper-surface relating to the anisotropic cosmic expansion, provided that we fix two arbitrary constants appearing in a general expression for the Feynman propagator in terms of a procedure similar to that in the isotropic case. A speculation on the isotropization of our model-universe is also made from the standpoint of seeking for how the thermal equilibrium in the whole universe is attained. (auth.)
Effective Elliptic Models for Efficient Wavefield Extrapolation in Anisotropic Media
Waheed, Umair bin
2014-05-01
Wavefield extrapolation operator for elliptically anisotropic media offers significant cost reduction compared to that of transversely isotropic media (TI), especially when the medium exhibits tilt in the symmetry axis (TTI). However, elliptical anisotropy does not provide accurate focusing for TI media. Therefore, we develop effective elliptically anisotropic models that correctly capture the kinematic behavior of the TTI wavefield. Specifically, we use an iterative elliptically anisotropic eikonal solver that provides the accurate traveltimes for a TI model. The resultant coefficients of the elliptical eikonal provide the effective models. These effective models allow us to use the cheaper wavefield extrapolation operator for elliptic media to obtain approximate wavefield solutions for TTI media. Despite the fact that the effective elliptic models are obtained by kinematic matching using high-frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including the frequency dependency and caustics, if present, with reasonable accuracy. The methodology developed here offers a much better cost versus accuracy tradeoff for wavefield computations in TTI media, considering the cost prohibitive nature of the problem. We demonstrate the applicability of the proposed approach on the BP TTI model.
The TT, TB, EB and BB correlations in anisotropic inflation
Energy Technology Data Exchange (ETDEWEB)
Chen, Xingang [Department of Physics, The University of Texas at Dallas, Richardson, TX 75083 (United States); Emami, Razieh [School of Physics, Institute for Research in Fundamental Sciences (IPM), P. O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Firouzjahi, Hassan [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P. O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Wang, Yi, E-mail: Xingang.Chen@utdallas.edu, E-mail: emami@ipm.ir, E-mail: firouz@ipm.ir, E-mail: yw366@cam.ac.uk [Centre for Theoretical Cosmology, DAMTP, University of Cambridge, Cambridge CB3 0WA (United Kingdom)
2014-08-01
The ongoing and future experiments will measure the B-mode from different sky coverage and frequency bands, with the potential to reveal non-trivial features in polarization map. In this work we study the TT, TB, EB and BB correlations associated with the B-mode polarization of CMB map in models of charged anisotropic inflation. The model contains a chaotic-type large field complex inflaton which is charged under the U(1) gauge field. We calculate the statistical anisotropies generated in the power spectra of the curvature perturbation, the tensor perturbation and their cross-correlation. It is shown that the asymmetry in tensor power spectrum is a very sensitive probe of the gauge coupling. While the level of statistical anisotropy in temperature power spectrum can be small and satisfy the observational bounds, the interactions from the gauge coupling can induce large directional dependence in tensor modes. This will leave interesting anisotropic fingerprints in various correlations involving the B-mode polarization such as the TB cross-correlation which may be detected in upcoming Planck polarization data. In addition, the TT correlation receives an anisotropic contribution from the tensor sector which naturally decays after l ∼> 100. We expect that the mechanism of using tensor sector to induce asymmetry at low l to be generic which can also be applied to address other low l CMB anomalies.
Speckle Suppression by Weighted Euclidean Distance Anisotropic Diffusion
Directory of Open Access Journals (Sweden)
Fengcheng Guo
2018-05-01
Full Text Available To better reduce image speckle noise while also maintaining edge information in synthetic aperture radar (SAR images, we propose a novel anisotropic diffusion algorithm using weighted Euclidean distance (WEDAD. Presented here is a modified speckle reducing anisotropic diffusion (SRAD method, which constructs a new edge detection operator using weighted Euclidean distances. The new edge detection operator can adaptively distinguish between homogenous and heterogeneous image regions, effectively generate anisotropic diffusion coefficients for each image pixel, and filter each pixel at different scales. Additionally, the effects of two different weighting methods (Gaussian weighting and non-linear weighting of de-noising were analyzed. The effect of different adjustment coefficient settings on speckle suppression was also explored. A series of experiments were conducted using an added noise image, GF-3 SAR image, and YG-29 SAR image. The experimental results demonstrate that the proposed method can not only significantly suppress speckle, thus improving the visual effects, but also better preserve the edge information of images.
On the creation of scalar particles in some anisotropic universe
International Nuclear Information System (INIS)
Nariai, Hidekazu
1978-01-01
Because of an importance of the particle creation (especially, its possible fulfilment of the black-body law with a definite temperature) in an early universe to various other cosmological problems, we study how the creation of scalar particles occurs in the Bianchi-type I anisotropic universe adopted in our previous works on the quantized scalar field. It is shown that, as in a special isotropic case dealt with in recent papers, the creation may occur at the sacrifice of the requirement that the quantization procedure should reproduce the usual theory for a free field in the limit when the anisotropic universe changes into the Minkowski space-time. It is further shown that the creation occurs in accordance with the black-body law only in a 2-dimensional hyper-surface relating to the anisotropic cosmic expansion, provided that we fix two arbitrary constants appearing in a general expression for the Feynman propagator in terms of a procedure similar to that in the isotropic case. A speculation on the isotropization of our model-universe is also made from the standpoint of seeking the attainment of the thermal equilibrium in the whole universe. (author)
Anisotropic silk fibroin/gelatin scaffolds from unidirectional freezing
Energy Technology Data Exchange (ETDEWEB)
Asuncion, Maria Christine Tankeh, E-mail: christine.asuncion@u.nus.edu [National University of Singapore, Department of Biomedical Engineering (Singapore); Goh, James Cho-Hong [National University of Singapore, Department of Biomedical Engineering (Singapore); National University of Singapore, Department of Orthopedic Surgery (Singapore); Toh, Siew-Lok [National University of Singapore, Department of Biomedical Engineering (Singapore); National University of Singapore, Department of Mechanical Engineering (Singapore)
2016-10-01
Recent studies have underlined the importance of matching scaffold properties to the biological milieu. Tissue, and thus scaffold, anisotropy is one such property that is important yet sometimes overlooked. Methods that have been used to achieve anisotropic scaffolds present challenges such as complicated fabrication steps, harsh processing conditions and toxic chemicals involved. In this study, unidirectional freezing was employed to fabricate anisotropic silk fibroin/gelatin scaffolds in a simple and mild manner. Morphological, mechanical, chemical and cellular compatibility properties were investigated, as well as the effect of the addition of gelatin to certain properties of the scaffold. It was shown that scaffold properties were suitable for cell proliferation and that mesenchymal stem cells were able to align themselves along the directed fibers. The fabricated scaffolds present a platform that can be used for anisotropic tissue engineering applications such as cardiac patches. - Highlights: • Silk/gelatin scaffolds with unidirectional alignment were fabricated using a simple and scalable process • Presence of gelatin in silk resulted to lesser shrinkage, better water retention and improved cell proliferation. • Mesenchymal stem cells were shown to align themselves according to the fiber alignment.
Measurement of Anisotropic Particle Interactions with Nonuniform ac Electric Fields.
Rupp, Bradley; Torres-Díaz, Isaac; Hua, Xiaoqing; Bevan, Michael A
2018-02-20
Optical microscopy measurements are reported for single anisotropic polymer particles interacting with nonuniform ac electric fields. The present study is limited to conditions where gravity confines particles with their long axis parallel to the substrate such that particles can be treated using quasi-2D analysis. Field parameters are investigated that result in particles residing at either electric field maxima or minima and with long axes oriented either parallel or perpendicular to the electric field direction. By nonintrusively observing thermally sampled positions and orientations at different field frequencies and amplitudes, a Boltzmann inversion of the time-averaged probability of states yields kT-scale energy landscapes (including dipole-field, particle-substrate, and gravitational potentials). The measured energy landscapes show agreement with theoretical potentials using particle conductivity as the sole adjustable material property. Understanding anisotropic particle-field energy landscapes vs field parameters enables quantitative control of local forces and torques on single anisotropic particles to manipulate their position and orientation within nonuniform fields.
Anisotropic diffusion of volatile pollutants at air-water interface
Directory of Open Access Journals (Sweden)
Li-ping Chen
2013-04-01
Full Text Available The volatile pollutants that spill into natural waters cause water pollution. Air pollution arises from the water pollution because of volatilization. Mass exchange caused by turbulent fluctuation is stronger in the direction normal to the air-water interface than in other directions due to the large density difference between water and air. In order to explore the characteristics of anisotropic diffusion of the volatile pollutants at the air-water interface, the relationship between velocity gradient and mass transfer rate was established to calculate the turbulent mass diffusivity. A second-order accurate smooth transition differencing scheme (STDS was proposed to guarantee the boundedness for the flow and mass transfer at the air-water interface. Simulations and experiments were performed to study the trichloroethylene (C2HCl3 release. By comparing the anisotropic coupling diffusion model, isotropic coupling diffusion model, and non-coupling diffusion model, the features of the transport of volatile pollutants at the air-water interface were determined. The results show that the anisotropic coupling diffusion model is more accurate than the isotropic coupling diffusion model and non-coupling diffusion model. Mass transfer significantly increases with the increase of the air-water relative velocity at a low relative velocity. However, at a higher relative velocity, an increase in the relative velocity has no effect on mass transfer.
Investigation of Anisotropic Bonded Magnets in Permanent Magnet Machine Applications
Khazdozian, H. A.; McCall, S. K.; Kramer, M. J.; Paranthaman, M. P.; Nlebedim, I. C.
Rare earth elements (REE) provide the high energy product necessary for permanent magnets, such as sintered Nd2Fe14B, in many applications like wind energy generators. However, REEs are considered critical materials due to risk in their supply. To reduce the use of critical materials in permanent magnet machines, the performance of anisotropic bonded NdFeB magnets, aligned under varying magnetic field strength, was simulated using 3D finite element analysis in a 3MW direct-drive permanent magnet generator (DDPMG), with sintered N42 magnets used as a baseline for comparison. For direct substitution of the anisotropic bonded magnets, approximately 85% of the efficiency of the baseline model was achieved, irrespective of the alignment field. The torque and power generation of the DDPMG was not found to vary significantly with increase in the alignment field. Finally, design changes were studied to allow for the achievement of rated torque and power with the use of anisotropic bonded magnets, demonstrating the potential for reduction of critical materials in permanent magnets for renewable energy applications. This work was supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.
Anisotropic fluid spheres of embedding class one using Karmarkar condition
Energy Technology Data Exchange (ETDEWEB)
Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Maharaj, S.D. [School of Mathematics, Statistics and Computer Science, University of KwaZulu-Natal, Astrophysics and Cosmology Research Unit, Private Bag X54001, Durban (South Africa)
2017-05-15
We obtain a new anisotropic solution for spherically symmetric spacetimes by analyzing the Karmarkar embedding condition. For this purpose we construct a suitable form of one of the gravitational potentials to obtain a closed form solution. This form of the remaining gravitational potential allows us to solve the embedding equation and integrate the field equations. The resulting new anisotropic solution is well behaved, which can be utilized to construct realistic static fluid spheres. Also we estimated the masses and radii of fluid spheres for LMC X-4, EXO 1785-248, PSR J1903+327 and 4U 1820-30 by using observational data set values. The masses and radii obtained show that our anisotropic solution can represent fluid spheres to a very good degree of accuracy. The physical validity of the solution depends on the parameter values of a, b and c. The solution is well behaved for the wide range of parameters values 0.00393 ≤ a ≤ 0.0055, 0.0002 ≤ b ≤ 0.0025 and 0.0107 ≤ c ≤ 0.0155. The range of corresponding physical parameters for the different compact stars are 0.3266 ≤ v{sub r0} ≤ 0.3708, 0.1583 ≤ v{sub t0} ≤ 0.2558, 0.3256 ≤ z{sub s} ≤ 0.4450 and 4.3587 ≤ Γ{sub 0} ≤ 5.6462. (orig.)
Pattern formation of a nonlocal, anisotropic interaction model
Burger, Martin
2017-11-24
We consider a class of interacting particle models with anisotropic, repulsive–attractive interaction forces whose orientations depend on an underlying tensor field. An example of this class of models is the so-called Kücken–Champod model describing the formation of fingerprint patterns. This class of models can be regarded as a generalization of a gradient flow of a nonlocal interaction potential which has a local repulsion and a long-range attraction structure. In contrast to isotropic interaction models the anisotropic forces in our class of models cannot be derived from a potential. The underlying tensor field introduces an anisotropy leading to complex patterns which do not occur in isotropic models. This anisotropy is characterized by one parameter in the model. We study the variation of this parameter, describing the transition between the isotropic and the anisotropic model, analytically and numerically. We analyze the equilibria of the corresponding mean-field partial differential equation and investigate pattern formation numerically in two dimensions by studying the dependence of the parameters in the model on the resulting patterns.
Pattern formation of a nonlocal, anisotropic interaction model
Burger, Martin; Dü ring, Bertram; Kreusser, Lisa Maria; Markowich, Peter A.; Schö nlieb, Carola-Bibiane
2017-01-01
We consider a class of interacting particle models with anisotropic, repulsive–attractive interaction forces whose orientations depend on an underlying tensor field. An example of this class of models is the so-called Kücken–Champod model describing the formation of fingerprint patterns. This class of models can be regarded as a generalization of a gradient flow of a nonlocal interaction potential which has a local repulsion and a long-range attraction structure. In contrast to isotropic interaction models the anisotropic forces in our class of models cannot be derived from a potential. The underlying tensor field introduces an anisotropy leading to complex patterns which do not occur in isotropic models. This anisotropy is characterized by one parameter in the model. We study the variation of this parameter, describing the transition between the isotropic and the anisotropic model, analytically and numerically. We analyze the equilibria of the corresponding mean-field partial differential equation and investigate pattern formation numerically in two dimensions by studying the dependence of the parameters in the model on the resulting patterns.
Overview of thermal conductivity models of anisotropic thermal insulation materials
Skurikhin, A. V.; Kostanovsky, A. V.
2017-11-01
Currently, the most of existing materials and substances under elaboration are anisotropic. It makes certain difficulties in the study of heat transfer process. Thermal conductivity of the materials can be characterized by tensor of the second order. Also, the parallelism between the temperature gradient vector and the density of heat flow vector is violated in anisotropic thermal insulation materials (TIM). One of the most famous TIM is a family of integrated thermal insulation refractory material («ITIRM»). The main component ensuring its properties is the «inflated» vermiculite. Natural mineral vermiculite is ground into powder state, fired by gas burner for dehydration, and its precipitate is then compressed. The key feature of thus treated batch of vermiculite is a package structure. The properties of the material lead to a slow heating of manufactured products due to low absorption and high radiation reflection. The maximum of reflection function is referred to infrared spectral region. A review of current models of heat propagation in anisotropic thermal insulation materials is carried out, as well as analysis of their thermal and optical properties. A theoretical model, which allows to determine the heat conductivity «ITIRM», can be useful in the study of thermal characteristics such as specific heat capacity, temperature conductivity, and others. Materials as «ITIRM» can be used in the metallurgy industry, thermal energy and nuclear power-engineering.
A methodology for developing anisotropic AAA phantoms via additive manufacturing.
Ruiz de Galarreta, Sergio; Antón, Raúl; Cazón, Aitor; Finol, Ender A
2017-05-24
An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of biomechanical factors for rupture risk assessment. AAA phantoms could be used for experimental validation of the numerical studies and for pre-intervention testing of endovascular grafts. We have applied multi-material 3D printing technology to manufacture idealized AAA phantoms with anisotropic mechanical behavior. Different composites were fabricated and the phantom specimens were characterized by biaxial tensile tests while using a constitutive model to fit the experimental data. One composite was chosen to manufacture the phantom based on having the same mechanical properties as those reported in the literature for human AAA tissue; the strain energy and anisotropic index were compared to make this choice. The materials for the matrix and fibers of the selected composite are, respectively, the digital materials FLX9940 and FLX9960 developed by Stratasys. The fiber proportion for the composite is equal to 0.15. The differences between the composite behavior and the AAA tissue are small, with a small difference in the strain energy (0.4%) and a maximum difference of 12.4% in the peak Green strain ratio. This work represents a step forward in the application of 3D printing technology for the manufacturing of AAA phantoms with anisotropic mechanical behavior. Copyright © 2017 Elsevier Ltd. All rights reserved.
DNA-nanoparticle superlattices formed from anisotropic building blocks
Jones, Matthew R.; Macfarlane, Robert J.; Lee, Byeongdu; Zhang, Jian; Young, Kaylie L.; Senesi, Andrew J.; Mirkin, Chad A.
2010-11-01
Directional bonding interactions in solid-state atomic lattices dictate the unique symmetries of atomic crystals, resulting in a diverse and complex assortment of three-dimensional structures that exhibit a wide variety of material properties. Methods to create analogous nanoparticle superlattices are beginning to be realized, but the concept of anisotropy is still largely underdeveloped in most particle assembly schemes. Some examples provide interesting methods to take advantage of anisotropic effects, but most are able to make only small clusters or lattices that are limited in crystallinity and especially in lattice parameter programmability. Anisotropic nanoparticles can be used to impart directional bonding interactions on the nanoscale, both through face-selective functionalization of the particle with recognition elements to introduce the concept of valency, and through anisotropic interactions resulting from particle shape. In this work, we examine the concept of inherent shape-directed crystallization in the context of DNA-mediated nanoparticle assembly. Importantly, we show how the anisotropy of these particles can be used to synthesize one-, two- and three-dimensional structures that cannot be made through the assembly of spherical particles.
Double-grooved nanofibre surfaces with enhanced anisotropic hydrophobicity.
Liang, Meimei; Chen, Xin; Xu, Yang; Zhu, Lei; Jin, Xiangyu; Huang, Chen
2017-11-02
This study reports a facile method for fabricating double-grooved fibrous surfaces. The primary grooves of the surface are formed by aligned fibres, while the secondary grooves are achieved by oriented nanogrooves on the fibre surface. Investigation into the formation mechanism reveals that the nanogrooves can be readily tailored through adjusting the solvent ratio and relative humidity. With this understanding, a variety of polymers have been successfully electrospun into fibres having the same nanogrooved feature. These fibres show high resemblance to natural hierarchical structures, and thereby endowing the corresponding double-grooved surface with enhanced anisotropic hydrophobicity. A water droplet at a parallel direction to the grooves exhibits a much higher contact angle and a lower roll-off angle than the droplet at a perpendicular direction. The application potential of such anisotropic hydrophobicity has been demonstrated via a fog collection experiment, in which the double-grooved surface can harvest the largest amount of water. Moreover, the fabrication method requires neither post-treatment nor sophisticated equipment, making us anticipate that the double-grooved surface would be competitive in areas where a highly ordered surface, a large surface area and an anisotropic hydrophobicity are preferred.
Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn.
Galceran, R; Fina, I; Cisneros-Fernández, J; Bozzo, B; Frontera, C; López-Mir, L; Deniz, H; Park, K-W; Park, B-G; Balcells, Ll; Martí, X; Jungwirth, T; Martínez, B
2016-10-20
Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature.
Anisotropic semivortices in dipolar spinor condensates controlled by Zeeman splitting
Liao, Bingjin; Li, Shoubo; Huang, Chunqing; Luo, Zhihuan; Pang, Wei; Tan, Haishu; Malomed, Boris A.; Li, Yongyao
2017-10-01
Spatially anisotropic solitary vortices, i.e., bright anisotropic vortex solitons (AVSs), supported by anisotropic dipole-dipole interactions, were recently predicted in spin-orbit-coupled binary Bose-Einstein condensates (BECs), in the form of two-dimensional semivortices (complexes built of zero-vorticity and vortical components). We demonstrate that the shape of the AVSs—horizontal or vertical, with respect to the in-plane polarization of the atomic dipole moments in the underlying BEC—may be effectively controlled by the strength Ω of the Zeeman splitting (ZS). A transition from the horizontal to vertical shape with the increase of Ω is found numerically and explained analytically. At the transition point, the AVS assumes the shape of an elliptical ring. The mobility of horizontal AVSs is studied, too, with the conclusion that, with the increase of Ω , their negative effective mass changes the sign to positive via a point at which the effective mass diverges. Lastly, we report a new species of inverted AVSs, with the zero-vorticity and vortex component placed in lower- and higher-energy components, as defined by the ZS. They are excited states, with respect to the ground states provided by the usual AVSs. Quite surprisingly, inverted AVSs are stable in a large parameter region.
Surface Waves Propagating on Grounded Anisotropic Dielectric Slab
Directory of Open Access Journals (Sweden)
Zhuozhu Chen
2018-01-01
Full Text Available This paper investigates the characteristics of surface waves propagating on a grounded anisotropic dielectric slab. Distinct from the existing analyses that generally assume that the fields of surface wave uniformly distribute along the transverse direction of the infinitely large grounded slab, our method takes into account the field variations along the transverse direction of a finite-width slab. By solving Maxwell’s equations in closed-form, it is revealed that no pure transverse magnetic (TM or transverse electric (TE mode exists if the fields are non-uniformly distributed along the transverse direction of the grounded slab. Instead, two hybrid modes, namely quasi-TM and quasi-TE modes, are supported. In addition, the propagation characteristics of two hybrid modes supported by the grounded anisotropic slab are analyzed in terms of the slab thickness, slab width, as well as the relative permittivity tensor of the anisotropic slab. Furthermore, different methods are employed to compare the analyses, as well as to validate our derivations. The proposed method is very suitable for practical engineering applications.
Directional radiative properties of anisotropic rough silicon and gold surfaces
Energy Technology Data Exchange (ETDEWEB)
Lee, H.J.; Chen, Y.B.; Zhang, Z.M. [George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States)
2006-11-15
Recent studies have shown that the topography of some chemically etched microrough silicon surfaces is non-Gaussian and may be strongly anisotropic. However, the bidirectional reflectance distribution function (BRDF) of anisotropic surfaces has not been fully understood. The present study uses the Monte Carlo method to investigate the out-of-plane BRDF, multiple scattering, and the change of the polarization state upon reflection. Two ray-tracing algorithms are developed that incorporate the surface topography or slope distribution of the samples obtained by the use of an atomic force microscope. The predicted BRDFs for silicon surfaces with or without a gold coating are in reasonable agreement with the results measured using a laser scatterometer at a wavelength of 635nm. The employment of surface topographic data is indispensable to the BRDF modeling of anisotropic surfaces. While first-order scattering makes the dominant contribution to reflections from the studied surfaces, it is critical to consider the polarization state change in order to correctly predict the out-of-plane BRDF. The versatile Monte Carlo modeling tools developed through the present study help gain a better understanding of the directional radiative properties of microrough surfaces and, furthermore, will have an impact on thermal metrology in the semiconductor industry. (author)
The Control of Anisotropic Transport in Manganites by Stripy Domains
Ju, Changcheng; Lu, Xiaomei; Chu, Yinghao
2014-03-01
Epitaxial thin film acts as a significant tool to investigate novel phenomena of complex oxide systems. Extrinsic constraint1 of uniform or certain designed buffer layer strain could be easily implanted to these materials. However, the strain distribution might be quite complicated by involving micro- or nano-lattice distortions which could partially relax the strain and determine the complex phase diagrams of thin film, meanwhile introducing structural and physical inhomogeneities. In this work , we report 71° striped ferroelectric domains created in BFO can also epitaxially lock the perovskite manganites leading to the emerge of ordered structural domain. LSMO/BFO hetero-epitaxial samples are deposited by PLD. The 71° periodic striped domains and coherent growth are demonstrated by PFM and X-ray analysis. Plan-view TEM and X-ray RSM have been used to confirm the epitaxial relationships of the functional layers and IP lattice constant. Both the simulation and structural analysis demonstrate we can create a periodic ordered stripe structural domain in LSMO. And this will leave an anisotropic distribution of structural domain walls which makes it possible to capture the anisotropic tunneling for strong electron-lattice coupling in manganites. Temperature-dependent resistivity measurements reveal a substantial anisotropic resistivities and a remarkable shift of the MI transition between the perpendicular and parallel to the stripe domain directions.
Effective Elliptic Models for Efficient Wavefield Extrapolation in Anisotropic Media
Waheed, Umair bin; Alkhalifah, Tariq Ali
2014-01-01
Wavefield extrapolation operator for elliptically anisotropic media offers significant cost reduction compared to that of transversely isotropic media (TI), especially when the medium exhibits tilt in the symmetry axis (TTI). However, elliptical anisotropy does not provide accurate focusing for TI media. Therefore, we develop effective elliptically anisotropic models that correctly capture the kinematic behavior of the TTI wavefield. Specifically, we use an iterative elliptically anisotropic eikonal solver that provides the accurate traveltimes for a TI model. The resultant coefficients of the elliptical eikonal provide the effective models. These effective models allow us to use the cheaper wavefield extrapolation operator for elliptic media to obtain approximate wavefield solutions for TTI media. Despite the fact that the effective elliptic models are obtained by kinematic matching using high-frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including the frequency dependency and caustics, if present, with reasonable accuracy. The methodology developed here offers a much better cost versus accuracy tradeoff for wavefield computations in TTI media, considering the cost prohibitive nature of the problem. We demonstrate the applicability of the proposed approach on the BP TTI model.
Directory of Open Access Journals (Sweden)
Hyeon Seo
Full Text Available Subdural cortical stimulation (SuCS is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5 that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information.
Skrypnyk, T.
2017-08-01
We study the problem of separation of variables for classical integrable Hamiltonian systems governed by non-skew-symmetric non-dynamical so(3)\\otimes so(3) -valued elliptic r-matrices with spectral parameters. We consider several examples of such models, and perform separation of variables for classical anisotropic one- and two-spin Gaudin-type models in an external magnetic field, and for Jaynes-Cummings-Dicke-type models without the rotating wave approximation.
TOPICAL REVIEW Textured silicon nitride: processing and anisotropic properties
Directory of Open Access Journals (Sweden)
Xinwen Zhu and Yoshio Sakka
2008-01-01
Full Text Available Textured silicon nitride (Si3N4 has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si3N4, with emphasis on the anisotropic and abnormal grain growth of β-Si3N4, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW and templated grain growth (TGG. The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for β-Si3N4 seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3 N4 and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si3N4 with a unique microstructure composed of oriented elongated β-Si3N4 and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured
International Nuclear Information System (INIS)
Popovtzer, Aron; Cao Yue; Feng, Felix Y.; Eisbruch, Avraham
2009-01-01
Purpose: Dysfunction of pharyngeal constrictors (PCs) after chemo-irradiation of head and neck (HN) cancer has been proposed as major cause of dysphagia. We conducted prospective MRI study to evaluate anatomical changes in the PCs after chemo-irradiation, to gain insight of the mechanism of their dysfunction and their dose-effect relationships. The PCs were compared to the sternocleidomastoid muscles (SCMs), which receive high doses but do not relate to swallowing. Patients and methods: Twelve patients with stage III-IV HN cancer underwent MRI before and 3 months after completing chemo-irradiation. T1- and T2-weighted signals and muscle thickness were evaluated for PCs (superior, middle, and inferior), and SCMs. Mean muscle doses were determined after registration with the planning CT. Results: T1-weighted signals decreased in both PCs and SCMs receiving >50 Gy (p 2 = 0.34, p = 0.01). The T2 signal changes in the PCs were significantly higher than the T2 changes in the SCMs (p 50 Gy gaining significantly more thickness than PCs receiving lesser doses (p = 0.02). In contrast, the SCM thickness decreased post-therapy (p = 0.002). Conclusions: These MRI-based findings, notably the differences between PCs and SCMs, suggest that underlying causes of PC dysfunction are inflammation and edema, likely consequential to acute mucositis affecting the submucosa-lying PCs. These results support reducing mean PC doses to ≤50 Gy, as well as reducing acute mucositis, to improve long-term dysphagia.
International Nuclear Information System (INIS)
Park, P; Schreibmann, E; Fox, T; Roper, J; Elder, E; Tejani, M; Crocker, I; Curran, W; Dhabaan, A
2014-01-01
Purpose: Severe CT artifacts can impair our ability to accurately calculate proton range thereby resulting in a clinically unacceptable treatment plan. In this work, we investigated a novel CT artifact correction method based on a coregistered MRI and investigated its ability to estimate CT HU and proton range in the presence of severe CT artifacts. Methods: The proposed method corrects corrupted CT data using a coregistered MRI to guide the mapping of CT values from a nearby artifact-free region. First patient MRI and CT images were registered using 3D deformable image registration software based on B-spline and mutual information. The CT slice with severe artifacts was selected as well as a nearby slice free of artifacts (e.g. 1cm away from the artifact). The two sets of paired MRI and CT images at different slice locations were further registered by applying 2D deformable image registration. Based on the artifact free paired MRI and CT images, a comprehensive geospatial analysis was performed to predict the correct CT HU of the CT image with severe artifact. For a proof of concept, a known artifact was introduced that changed the ground truth CT HU value up to 30% and up to 5cm error in proton range. The ability of the proposed method to recover the ground truth was quantified using a selected head and neck case. Results: A significant improvement in image quality was observed visually. Our proof of concept study showed that 90% of area that had 30% errors in CT HU was corrected to 3% of its ground truth value. Furthermore, the maximum proton range error up to 5cm was reduced to 4mm error. Conclusion: MRI based CT artifact correction method can improve CT image quality and proton range calculation for patients with severe CT artifacts
Schuster, Christina; Hardiman, Orla; Bede, Peter
2016-01-01
Despite significant advances in quantitative neuroimaging, the diagnosis of ALS remains clinical and MRI-based biomarkers are not currently used to aid the diagnosis. The objective of this study is to develop a robust, disease-specific, multimodal classification protocol and validate its diagnostic accuracy in independent, early-stage and follow-up data sets. 147 participants (81 ALS patients and 66 healthy controls) were divided into a training sample and a validation sample. Patients in the validation sample underwent follow-up imaging longitudinally. After removing age-related variability, indices of grey and white matter integrity in ALS-specific pathognomonic brain regions were included in a cross-validated binary logistic regression model to determine the probability of individual scans indicating ALS. The following anatomical regions were assessed for diagnostic classification: average grey matter density of the left and right precentral gyrus, the average fractional anisotropy and radial diffusivity of the left and right superior corona radiata, inferior corona radiata, internal capsule, mesencephalic crus of the cerebral peduncles, pontine segment of the corticospinal tract, and the average diffusivity values of the genu, corpus and splenium of the corpus callosum. Using a 50% probability cut-off value of suffering from ALS, the model was able to discriminate ALS patients and HC with good sensitivity (80.0%) and moderate accuracy (70.0%) in the training sample and superior sensitivity (85.7%) and accuracy (78.4%) in the independent validation sample. This diagnostic classification study endeavours to advance ALS biomarker research towards pragmatic clinical applications by providing an approach of automated individual-data interpretation based on group-level observations.
Telles, Shirley; Bhardwaj, Abhishek K.; Gupta, Ram K.; Sharma, Sachin K.; Monro, Robin; Balkrishna, Acharya
2016-01-01
Background The present study aimed at determining whether 12 weeks of yoga practice in patients with chronic LBP and MRI-based degenerative changes would result in differences in: (i) self-reported pain, anxiety, and spinal flexibility; and (ii) the structure of the discs or vertebrae. Material/Methods Sixty-two persons with MRI-proven degenerative intervertebral discs (group mean ±S.D., 36.2±6.4 years; 30 females) were randomly assigned to yoga and control groups. However, testing was conducted on only 40 subjects, so only their data are included in this study. The assessments were: self-reported pain, state anxiety, spinal flexibility, and MRI of the lumbosacral spine, performed using a 1.5 Tesla system with a spinal surface column. The yoga group was taught light exercises, physical postures, breathing techniques, and yoga relaxation techniques for 1 hour daily for 3 months. No intervention was given to the control group except for routine medical care. A repeated-measures analysis of variance (ANOVA) with post hoc analyses (which was Bonferroni-adjusted) was used. The Ethics Committee of Patanjali Research Foundation had approved the study which had been registered in the Clinical Trials Registry of India (CTRI/2012/11/003094). Results The yoga group showed a significant reduction in self-reported pain and state anxiety in a before/after comparison at 12 weeks. A few patients in both groups showed changes in the discs and vertebrae at post-intervention assessment. Conclusions Within 12 weeks, yoga practice reduced pain and state anxiety but did not alter MRI-proven changes in the intervertebral discs and in the vertebrae.
Energy Technology Data Exchange (ETDEWEB)
Goettler, Jens; Preibisch, Christine [TU Muenchen, Department of Neuroradiology, Klinikum rechts der Isar, Munich (Germany); TU Muenchen, TUM Neuroimaging Center (TUM-NIC), Klinikum rechts der Isar, Munich (Germany); Lukas, Mathias; Mustafa, Mona; Schwaiger, Markus; Pyka, Thomas [TU Muenchen, Department of Nuclear Medicine, Klinikum rechts der Isar, Munich (Germany); Kluge, Anne; Kaczmarz, Stephan; Zimmer, Claus [TU Muenchen, Department of Neuroradiology, Klinikum rechts der Isar, Munich (Germany); Gempt, Jens; Ringel, Florian; Meyer, Bernhard [TU Muenchen, Department of Neurosurgery, Klinikum rechts der Isar, Munich (Germany); Foerster, Stefan [TU Muenchen, TUM Neuroimaging Center (TUM-NIC), Klinikum rechts der Isar, Munich (Germany); TU Muenchen, Department of Nuclear Medicine, Klinikum rechts der Isar, Munich (Germany); Klinikum Bayreuth, Department of Nuclear Medicine, Bayreuth (Germany)
2017-03-15
{sup 18}F-fluorethyltyrosine-(FET)-PET and MRI-based relative cerebral blood volume (rCBV) have both been used to characterize gliomas. Recently, inter-individual correlations between peak static FET-uptake and rCBV have been reported. Herein, we assess the local intra-lesional relation between FET-PET parameters and rCBV. Thirty untreated glioma patients (27 high-grade) underwent simultaneous PET/MRI on a 3 T hybrid scanner obtaining structural and dynamic susceptibility contrast sequences. Static FET-uptake and dynamic FET-slope were correlated with rCBV within tumour hotspots across patients and intra-lesionally using a mixed-effects model to account for inter-individual variation. Furthermore, maximal congruency of tumour volumes defined by FET-uptake and rCBV was determined. While the inter-individual relationship between peak static FET-uptake and rCBV could be confirmed, our intra-lesional, voxel-wise analysis revealed significant positive correlations (median r = 0.374, p < 0.0001). Similarly, significant inter- and intra-individual correlations were observed between FET-slope and rCBV. However, rCBV explained only 12% of the static and 5% of the dynamic FET-PET variance and maximal overlap of respective tumour volumes was 37% on average. Our results show that the relation between peak values of MR-based rCBV and static FET-uptake can also be observed intra-individually on a voxel basis and also applies to a dynamic FET parameter, possibly determining hotspots of higher biological malignancy. However, just a small part of the FET-PET signal variance is explained by rCBV and tumour volumes determined by the two modalities showed only moderate overlap. These findings indicate that FET-PET and MR-based rCBV provide both congruent and complimentary information on glioma biology. (orig.)
Göttler, Jens; Lukas, Mathias; Kluge, Anne; Kaczmarz, Stephan; Gempt, Jens; Ringel, Florian; Mustafa, Mona; Meyer, Bernhard; Zimmer, Claus; Schwaiger, Markus; Förster, Stefan; Preibisch, Christine; Pyka, Thomas
2017-03-01
18 F-fluorethyltyrosine-(FET)-PET and MRI-based relative cerebral blood volume (rCBV) have both been used to characterize gliomas. Recently, inter-individual correlations between peak static FET-uptake and rCBV have been reported. Herein, we assess the local intra-lesional relation between FET-PET parameters and rCBV. Thirty untreated glioma patients (27 high-grade) underwent simultaneous PET/MRI on a 3 T hybrid scanner obtaining structural and dynamic susceptibility contrast sequences. Static FET-uptake and dynamic FET-slope were correlated with rCBV within tumour hotspots across patients and intra-lesionally using a mixed-effects model to account for inter-individual variation. Furthermore, maximal congruency of tumour volumes defined by FET-uptake and rCBV was determined. While the inter-individual relationship between peak static FET-uptake and rCBV could be confirmed, our intra-lesional, voxel-wise analysis revealed significant positive correlations (median r = 0.374, p dynamic FET-PET variance and maximal overlap of respective tumour volumes was 37% on average. Our results show that the relation between peak values of MR-based rCBV and static FET-uptake can also be observed intra-individually on a voxel basis and also applies to a dynamic FET parameter, possibly determining hotspots of higher biological malignancy. However, just a small part of the FET-PET signal variance is explained by rCBV and tumour volumes determined by the two modalities showed only moderate overlap. These findings indicate that FET-PET and MR-based rCBV provide both congruent and complimentary information on glioma biology.
Lerer, Assaf; Nykamp, Stephanie G; Harriss, Alexandra B; Gibson, Thomas W G; Koch, Thomas G; Brown, Stephen H M
2015-11-01
Human studies have revealed a link between muscle degeneration and low back pain, although the cause and effect of this relationship is not clear. Dogs provide a naturally developing model of intervertebral disc (IVD)-related low back pain that may provide insight into relationships between IVD and muscle degeneration. This study aimed to quantify, via magnetic resonance imaging (MRI), the magnitude and location of fatty infiltration in spine muscles of chondrodystrophic (CD) and non-chondrodystrophic (NCD) dogs suffering from both intervertebral disc herniation (IVDH) and non-disc-related spinal disorders, and relate this to intervertebral disc degeneration (IVDD). This study used retrospective MRI-based analysis of IVDD and muscle fatty infiltration in CD and NCD dogs. A portion of this study was funded ($1,000) by the Pet Trust Fund, Ontario Veterinary College. Magnetic resonance imaging from 180 dogs were separated into four groups: (1) CD with IVDH; (2) CD with non-IVDH spinal pathology; (3) NCD with IVDH; (4) NCD with non-IVDH spinal pathology. For each dog at intervertebral levels T12-T13 to L6-L7, IVDD was subjectively graded and muscle-fat indices (MFIndices) were quantified for multifidus, erector spinae, and psoas muscle groups. Intervertebral disc degeneration grade was higher (ppathology. Muscle-fat indices of multifidus and psoas were higher (ppathology compared with dogs with IVDH. Erector spinae demonstrated higher (ppathology. Dog groups with higher average IVDD grades demonstrated less fatty infiltration within their multifidus and psoas muscles, compared with groups with lower IVDD grades. This finding was consistent across both CD and NCD breeds as well as across dogs presenting with IVDH and those presenting with a non-IVDH spinal pathology. Thus, the presence or severity of IVDD is not uniquely related to fatty infiltration in these muscles, but rather the presence, or possibly severity or chronicity, of general spine pathology is likely a
On a hierarchical construction of the anisotropic LTSN solution from the isotropic LTSN solution
International Nuclear Information System (INIS)
Foletto, Taline; Segatto, Cynthia F.; Bodmann, Bardo E.; Vilhena, Marco T.
2015-01-01
In this work, we present a recursive scheme targeting the hierarchical construction of anisotropic LTS N solution from the isotropic LTS N solution. The main idea relies in the decomposition of the associated LTS N anisotropic matrix as a sum of two matrices in which one matrix contains the isotropic and the other anisotropic part of the problem. The matrix containing the anisotropic part is considered as the source of the isotropic problem. The solution of this problem is made by the decomposition of the angular flux as a truncated series of intermediate functions and replace in the isotropic equation. After the replacement of these into the split isotropic equation, we construct a set of isotropic recursive problems, that are readily solved by the classic LTS N isotropic method. We apply this methodology to solve problems considering homogeneous and heterogeneous anisotropic regions. Numerical results are presented and compared with the classical LTS N anisotropic solution. (author)
Lin, Guoxing
2018-05-01
Anomalous diffusion exists widely in polymer and biological systems. Pulsed-field gradient (PFG) anomalous diffusion is complicated, especially in the anisotropic case where limited research has been reported. A general PFG signal attenuation expression, including the finite gradient pulse (FGPW) effect for free general anisotropic fractional diffusion { 0 integral modified-Bloch equation, were extended to obtain general PFG signal attenuation expressions for anisotropic anomalous diffusion. Various cases of PFG anisotropic anomalous diffusion were investigated, including coupled and uncoupled anisotropic anomalous diffusion. The continuous-time random walk (CTRW) simulation was also carried out to support the theoretical results. The theory and the CTRW simulation agree with each other. The obtained signal attenuation expressions and the three-dimensional fractional modified-Bloch equations are important for analyzing PFG anisotropic anomalous diffusion in NMR and MRI.
Khateri, Parisa; Saligheh Rad, Hamidreza; Jafari, Amir Homayoun; Fathi Kazerooni, Anahita; Akbarzadeh, Afshin; Shojae Moghadam, Mohsen; Aryan, Arvin; Ghafarian, Pardis; Ay, Mohammad Reza
2015-12-01
The aim of this study is to generate a four-class magnetic resonance imaging (MRI)-based attenuation map (μ-map) for attenuation correction of positron emission tomography (PET) data of the head area using a novel combination of short echo time (STE)/Dixon-MRI and a dedicated image segmentation method. MR images of the head area were acquired using STE and two-point Dixon sequences. μ-maps were derived from MRI images based on a fuzzy C-means (FCM) clustering method along with morphologic operations. Quantitative assessment was performed to evaluate generated MRI-based μ-maps compared to X-ray computed tomography (CT)-based μ-maps. The voxel-by-voxel comparison of MR-based and CT-based segmentation results yielded an average of more than 95 % for accuracy and specificity in the cortical bone, soft tissue, and air region. MRI-based μ-maps show a high correlation with those derived from CT scans (R (2) > 0.95). Results indicate that STE/Dixon-MRI data in combination with FCM-based segmentation yields precise MR-based μ-maps for PET attenuation correction in hybrid PET/MRI systems.
Energy Technology Data Exchange (ETDEWEB)
Filippov, V. V., E-mail: wwfilippow@mail.ru [Lipetsk State Pedagogical University (Russian Federation); Bormontov, E. N. [Voronezh State University (Russian Federation)
2013-07-15
A macroscopic model of the Hall effects and magnetoresistance in anisotropic semiconductor wafers is developed. The results obtained by solving the electrodynamic boundary problem allow the potential and eddy currents in anisotropic semiconductors to be calculated at different current-contact locations, depending on the parameters of the sample material's anisotropy. The results of this study are of great practical importance for investigating the physical properties of anisotropic semiconductors and simulating the electron-transport phenomena in devices based on anisotropic semiconductors.
International Nuclear Information System (INIS)
Filippov, V. V.; Bormontov, E. N.
2013-01-01
A macroscopic model of the Hall effects and magnetoresistance in anisotropic semiconductor wafers is developed. The results obtained by solving the electrodynamic boundary problem allow the potential and eddy currents in anisotropic semiconductors to be calculated at different current-contact locations, depending on the parameters of the sample material’s anisotropy. The results of this study are of great practical importance for investigating the physical properties of anisotropic semiconductors and simulating the electron-transport phenomena in devices based on anisotropic semiconductors
National Research Council Canada - National Science Library
Lyon, L
2000-01-01
This volume contains a series of papers originally presented at Symposium C, "Anisotropic Nanoparticles Synthesis, Characterization and Applications," at the 2000 MRS Fall Meeting in Boston, Massachusetts...
Directory of Open Access Journals (Sweden)
Chao Wan
2012-01-01
Full Text Available The history of methods for the electromagnetic scattering by an anisotropic sphere has been reviewed. Two main methods, angular expansion method and T-matrix method, which are widely used for the anisotropic sphere, are expressed in Cartesian coordinate firstly. The comparison of those and the further exploration on the scattering field are illustrated afterwards. Based on the most general form concluded by variable separation method, the coupled electric field and magnetic field of radial anisotropic sphere can be derived. By simplifying the condition, simpler case of uniaxial anisotropic media is expressed with confirmed coefficients for the internal and external field. Details of significant phenomenon are presented.
Numerical investigation of nanoparticles transport in anisotropic porous media
Salama, Amgad
2015-07-13
In this work the problem related to the transport of nanoparticles in anisotropic porous media is investigated numerically using the multipoint flux approximation. Anisotropy of porous media properties are an essential feature that exist almost everywhere in subsurface formations. In anisotropic media, the flux and the pressure gradient vectors are no longer collinear and therefore interesting patterns emerge. The transport of nanoparticles in subsurface formations is affected by several complex processes including surface charges, heterogeneity of nanoparticles and soil grain collectors, interfacial dynamics of double-layer and many others. We use the framework of the theory of filtration in this investigation. Processes like particles deposition, entrapment, as well as detachment are accounted for. From the numerical methods point of view, traditional two-point flux finite difference approximation cannot handle anisotropy of media properties. Therefore, in this work we use the multipoint flux approximation (MPFA). In this technique, the flux components are affected by more neighboring points as opposed to the mere two points that are usually used in traditional finite volume methods. We also use the experimenting pressure field approach which automatically constructs the global system of equations by solving multitude of local problems. This approach facilitates to a large extent the construction of the global system. A set of numerical examples is considered involving two-dimensional rectangular domain. A source of nanoparticles is inserted in the middle of the anisotropic layer. We investigate the effects of both anisotropy angle and anisotropy ratio on the transport of nanoparticles in saturated porous media. It is found that the concentration plume and porosity contours follow closely the principal direction of anisotropy of permeability of the central domain.
Analysis and interpretation of diffraction data from complex, anisotropic materials
Tutuncu, Goknur
Most materials are elastically anisotropic and exhibit additional anisotropy beyond elastic deformation. For instance, in ferroelectric materials the main inelastic deformation mode is via domains, which are highly anisotropic crystallographic features. To quantify this anisotropy of ferroelectrics, advanced X-ray and neutron diffraction methods were employed. Extensive sets of data were collected from tetragonal BaTiO3, PZT and other ferroelectric ceramics. Data analysis was challenging due to the complex constitutive behavior of these materials. To quantify the elastic strain and texture evolution in ferroelectrics under loading, a number of data analysis techniques such as the single peak and Rietveld methods were used and their advantages and disadvantages compared. It was observed that the single peak analysis fails at low peak intensities especially after domain switching while the Rietveld method does not account for lattice strain anisotropy although it overcomes the low intensity problem via whole pattern analysis. To better account for strain anisotropy the constant stress (Reuss) approximation was employed within the Rietveld method and new formulations to estimate lattice strain were proposed. Along the way, new approaches for handling highly anisotropic lattice strain data were also developed and applied. All of the ceramics studied exhibited significant changes in their crystallographic texture after loading indicating non-180° domain switching. For a full interpretation of domain switching the spherical harmonics method was employed in Rietveld. A procedure for simultaneous refinement of multiple data sets was established for a complete texture analysis. To further interpret diffraction data, a solid mechanics model based on the self-consistent approach was used in calculating lattice strain and texture evolution during the loading of a polycrystalline ferroelectric. The model estimates both the macroscopic average response of a specimen and its hkl
Numerical investigation of nanoparticles transport in anisotropic porous media
Salama, Amgad; Negara, Ardiansyah; El Amin, Mohamed; Sun, Shuyu
2015-01-01
In this work the problem related to the transport of nanoparticles in anisotropic porous media is investigated numerically using the multipoint flux approximation. Anisotropy of porous media properties are an essential feature that exist almost everywhere in subsurface formations. In anisotropic media, the flux and the pressure gradient vectors are no longer collinear and therefore interesting patterns emerge. The transport of nanoparticles in subsurface formations is affected by several complex processes including surface charges, heterogeneity of nanoparticles and soil grain collectors, interfacial dynamics of double-layer and many others. We use the framework of the theory of filtration in this investigation. Processes like particles deposition, entrapment, as well as detachment are accounted for. From the numerical methods point of view, traditional two-point flux finite difference approximation cannot handle anisotropy of media properties. Therefore, in this work we use the multipoint flux approximation (MPFA). In this technique, the flux components are affected by more neighboring points as opposed to the mere two points that are usually used in traditional finite volume methods. We also use the experimenting pressure field approach which automatically constructs the global system of equations by solving multitude of local problems. This approach facilitates to a large extent the construction of the global system. A set of numerical examples is considered involving two-dimensional rectangular domain. A source of nanoparticles is inserted in the middle of the anisotropic layer. We investigate the effects of both anisotropy angle and anisotropy ratio on the transport of nanoparticles in saturated porous media. It is found that the concentration plume and porosity contours follow closely the principal direction of anisotropy of permeability of the central domain.
Quarkonium states in an anisotropic quark-gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Guo Yun
2009-09-10
In this work we study the properties of quarkonium states in a quark-gluon plasma which, due to expansion and non-zero viscosity, exhibits a local anisotropy in momentum space. We determine the hard-loop resummed gluon propagator in an anisotropic QCD plasma in general linear gauges and define a potential between heavy quarks from the Fourier transform of its static limit. This potential which arises due to one-gluon exchange describes the force between a quark and anti-quark at short distances. It is closer to the vacuum potential as compared to the isotropic Debye screened potential which indicates the reduced screening in an anisotropic QCD plasma. In addition, angular dependence appears in the potential; we find that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment. The potential at long distances, however, is non-perturbative and modeled as a QCD string which is screened at the same scale as the Coulomb field. At asymptotic separation the potential energy is non-zero and inversely proportional to the temperature. With a phenomenological potential model which incorporates the different behaviors at short and long distances, we solve the three-dimensional Schroedinger equation. Our numerical results show that quarkonium binding is stronger at non-vanishing viscosity and expansion rate, and that the anisotropy leads to polarization of the P-wave states. Furthermore, we determine viscosity corrections to the imaginary part of the heavy-quark potential in the weak-coupling hard-loop approximation. The imaginary part is found to be smaller (in magnitude) than at vanishing viscosity. This implies a smaller decay width of quarkonium bound states in an anisotropic plasma. (orig.)
Quarkonium states in an anisotropic quark-gluon plasma
International Nuclear Information System (INIS)
Guo Yun
2009-01-01
In this work we study the properties of quarkonium states in a quark-gluon plasma which, due to expansion and non-zero viscosity, exhibits a local anisotropy in momentum space. We determine the hard-loop resummed gluon propagator in an anisotropic QCD plasma in general linear gauges and define a potential between heavy quarks from the Fourier transform of its static limit. This potential which arises due to one-gluon exchange describes the force between a quark and anti-quark at short distances. It is closer to the vacuum potential as compared to the isotropic Debye screened potential which indicates the reduced screening in an anisotropic QCD plasma. In addition, angular dependence appears in the potential; we find that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment. The potential at long distances, however, is non-perturbative and modeled as a QCD string which is screened at the same scale as the Coulomb field. At asymptotic separation the potential energy is non-zero and inversely proportional to the temperature. With a phenomenological potential model which incorporates the different behaviors at short and long distances, we solve the three-dimensional Schroedinger equation. Our numerical results show that quarkonium binding is stronger at non-vanishing viscosity and expansion rate, and that the anisotropy leads to polarization of the P-wave states. Furthermore, we determine viscosity corrections to the imaginary part of the heavy-quark potential in the weak-coupling hard-loop approximation. The imaginary part is found to be smaller (in magnitude) than at vanishing viscosity. This implies a smaller decay width of quarkonium bound states in an anisotropic plasma. (orig.)
Out-of-Bounds Hydrodynamics in Anisotropic Dirac Fluids
Link, Julia M.; Narozhny, Boris N.; Kiselev, Egor I.; Schmalian, Jörg
2018-05-01
We study hydrodynamic transport in two-dimensional, interacting electronic systems with merging Dirac points at charge neutrality. The dispersion along one crystallographic direction is Dirac-like, while it is Newtonian-like in the orthogonal direction. As a result, the electrical conductivity is metallic in one and insulating in the other direction. The shear viscosity tensor contains six independent components, which can be probed by measuring an anisotropic thermal flow. One of the viscosity components vanishes at zero temperature leading to a generalization of the previously conjectured lower bound for the shear viscosity to entropy density ratio.
Comparing energy levels in isotropic and anisotropic potentials
Energy Technology Data Exchange (ETDEWEB)
Pikovski, Alexander, E-mail: alexander.pikovski@colorado.edu
2015-11-06
Qualitative information about the quantized energy levels of a system can be of great value. We study the relationship between the bound-state energies of an anisotropic potential and those of its spherical average. It is shown that the two ground-state energies satisfy an inequality, and there is a similar inequality for the first excited states. - Highlights: • Quantized energy levels in an arbitrary non-central potential are studied. • We derive inequalities between energies in a potential and its spherical average. • The results hold in three and two dimensions for any ground state and, with additional symmetry requirements for the first excited state.
Existence and uniqueness in anisotropic conductivity reconstruction with Faraday's law
Lee, Min-Gi
2015-03-18
We show that three sets of internal current densities are the right amount of data that give the existence and the uniqueness at the same time in reconstructing an anisotropic conductivity in two space dimensions. The curl free equation of Faraday’s law is taken instead of the usual divergence free equation of the electrical impedance to- mography. Boundary conditions related to given current densities are introduced which complete a well determined problem for conductivity reconstruction together with Fara- day’s law.
The spatially anisotropic triangular lattice antiferromagnet: Popov-Fedotov method
International Nuclear Information System (INIS)
Nga, Pham Thi Thanh; Trang, Phan Thu; Thang, Nguyen Toan
2017-01-01
We present an analysis of the antiferromagnetic Heisenberg model on an triangular lattice with spatially anisotropic J 1 - J 2 exchange interactions. We apply the Popov-Fedotov method based on introducing an imaginary valued chemical potential to enforce the auxiliary fermion constraint exactly. The staggered magnetization, magnon spectra, free energy are computed in one loop approximation and compared using two different constraints: exact and on average. In the limit of zero temperature the results are identical, whereas at higher temperature significant differences are found. The comparisons with the results obtained by other methods are discussed. (paper)
Scheme for achieving coherent perfect absorption by anisotropic metamaterials
Zhang, Xiujuan
2017-02-22
We propose a unified scheme to achieve coherent perfect absorption of electromagnetic waves by anisotropic metamaterials. The scheme describes the condition on perfect absorption and offers an inverse design route based on effective medium theory in conjunction with retrieval method to determine practical metamaterial absorbers. The scheme is scalable to frequencies and applicable to various incident angles. Numerical simulations show that perfect absorption is achieved in the designed absorbers over a wide range of incident angles, verifying the scheme. By integrating these absorbers, we further propose an absorber to absorb energy from two coherent point sources.
Elastoplastic simulation coupled to the induced anisotropic damage for argilites
International Nuclear Information System (INIS)
Chiarelli, A.S.; Shao, J.F.
2002-01-01
A constitutive model coupling plastic deformation and induced damage is proposed to describe the mechanical behaviour of a shale rock, the argilites of East. The plastic behaviour is produced by a typical cohesive-frictional model. The material damage is represented by a second rank symmetric tensor. The damage criterion and evolution rate is related to tensile strains. The damage effect on plastic flow is also considered by an anisotropic transformation. The model formulation and a simple procedure for the determination of model parameters from standards tests is proposed. The validity of the model is checked against experimental data in various loading conditions. (author)