NASA Astrophysics Data System (ADS)
Mishev, Alexander; Velinov, Peter
2016-07-01
The galactic cosmic rays (GCR) and solar energetic particles (SEP) could cause an excess of ionization in the atmosphere, specifically in polar and sub-polar regions. This effect is observed mainly in the middle atmosphere. The ionization effect could be strong at short time scales during major ground level enhancements (GLE)s of GCR. However, for the aims of recent atmospheric physics and atmospheric chemistry studies, namely the influence on the minor constituents and aerosols, it is important to derive the medium time scale ionization effect at various altitudes above the sea level. GLE 70 on December of 13, 2006 is the third strongest event of the previous solar cycle 23. The ionization effect in the Earth atmosphere is obtained for various latitudes on the basis of a full Monte Carlo simulation of CR induced atmospheric cascade at several altitudes, namely 35 km, 25 km, 15 km and 8 km above the sea level. Here we adopt previously reported ion production rate profiles obtained with Monte Carlo simulation of atmospheric cascade performed with the CORSIKA 6.990 code using FLUKA 2011 and QGSJET II hadron generators. A realistic winter atmospheric model is assumed. The 24-h ionization effect is computed for the sub-polar and polar regions, where it is expected to be the maximal effect of the planetary distribution on the Earth. Thus studied precipitation of energetic particles (GCR and SEP) is important and should be included in chemistry-climate models. Similar computations are performed for GLE 59 the so-called Bstille day event on 14 July 2000.
Neutron multiplicity recordings during GLE
NASA Astrophysics Data System (ADS)
Eduard, Vashenyuk; Leonid, Schur; Balabin, Yuri; Gvozdevsky, Boris
A neutron multiplicity can give the information on a spectrum of primary solar protons and its variations during ground level enhancements (GLE). Such rare events are detected by ground based neutron monitors. With the help of the multiplicity recorder designed in PGI the variations of multiplicities during the GLE of December 13, 2006 on the neutron monitor in Barentsburg (Spitsbergen) have been studied. The neutron monitor in Barentsburg (18-NM-64) was put into operation on April, 2003. The recently developed data acquisition system is based on a PC equipped with two extension cards. One of them is ADLINK PCI-7233H, which is a high-speed 32-channel digital input card. The other is ADLINK PCI-8554, 12-channel counter/timer card. The specially written collecting program runs continuously. It captures the data registered by the two cards and stores the data to the hard disk. The PCI-7233H card registers pulses from all 18 channels of the neutron monitor and intervals between them. PCI-8554 card counts pulses from atmospheric pressure and temperature sensors. On the basis of this device the multiplicity recorder is realized to register the count rates on multiplicities (2-10). During the GLE on 13 December, 2006 significant increase of the count rates of multiplicities from 2 up to 5 was detected. The multiplicity spectrum changes are compared with the solar proton spectrum dynamics during event. The spectra of relativistic solar protons were derived by modeling technique from the worldwide neutron monitor network.
Anisotropic eddy viscosity models
NASA Technical Reports Server (NTRS)
Carati, D.; Cabot, W.
1996-01-01
A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.
On the prediction of GLE events
NASA Astrophysics Data System (ADS)
Nunez, Marlon; Reyes, Pedro
2016-04-01
A model for predicting the occurrence of GLE events is presented. This model uses the UMASEP scheme based on the lag-correlation between the time derivatives of soft X-ray flux (SXR) and near-earth proton fluxes (Núñez, 2011, 2015). We extended this approach with the correlation between SXR and ground-level neutron measurements. This model was calibrated with X-ray, proton and neutron data obtained during the period 1989-2015 from the GOES/HEPAD instrument, and neutron data from the Neutron Monitor Data Base (NMDB). During this period, 32 GLE events were detected by neutron monitor stations. We consider that a GLE prediction is successful when it is triggered before the first GLE alert is issued by any neutron station of the NMDB network. For the most recent 16 years (2015-2000), the model was able to issue successful predictions for the 53.8% (7 of 13 GLE events), obtaining a false alarm ratio (FAR) of 36.4% (4/11), and an average warning time of 10 min. For the first years of the evaluation period (1989-1999), the model was able to issue successful predictions for the 31.6% (6 of 19 GLE events), obtaining a FAR of 33.3% (3/9), and an AWT of 17 min. A preliminary conclusion is that the model is not able to predict the promptest events but the more gradual ones. The final goal of this project, which is now halfway through its planned two-year duration, is the prediction of >500 MeV events. This project has received funding from the European Union's Horizon 2020 research and innovation programme under agreement No 637324.
A GLE multi-block model for the evaluation of seismic displacements of slopes
Bandini, V.; Cascone, E.; Biondi, G.
2008-07-08
The paper describes a multi-block displacement model for the evaluation of seismic permanent displacements of natural slopes with slip surface of general shape. A rigorous limit equilibrium method of stability analysis is considered and an application to an ideal clay slope is presented including the effect of excess pore pressure build-up on the displacement response.
Anisotropic models for compact stars
NASA Astrophysics Data System (ADS)
Maurya, S. K.; Gupta, Y. K.; Ray, Saibal; Dayanandan, Baiju
2015-05-01
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 with the help of both metric potentials and . Here we consider the same as Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) did, whereas 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.
New charged anisotropic compact models
NASA Astrophysics Data System (ADS)
Kileba Matondo, D.; Maharaj, S. D.
2016-07-01
We find new exact solutions to the Einstein-Maxwell field equations which are relevant in the description of highly compact stellar objects. The relativistic star is charged and anisotropic with a quark equation of state. Exact solutions of the field equations are found in terms of elementary functions. It is interesting to note that we regain earlier quark models with uncharged and charged matter distributions. A physical analysis indicates that the matter distributions are well behaved and regular throughout the stellar structure. A range of stellar masses are generated for particular parameter values in the electric field. In particular the observed mass for a binary pulsar is regained.
Anisotropic invariance in minisuperspace models
NASA Astrophysics Data System (ADS)
Chagoya, Javier; Sabido, Miguel
2016-06-01
In this paper we introduce invariance under anisotropic transformations to cosmology. This invariance is one of the key ingredients of the theory of quantum gravity at a Lifshitz point put forward by Hořava. We find that this new symmetry in the minisuperspace introduces characteristics to the model that can be relevant in the ultraviolet regime. For example, by canonical quantization we find a Schrödinger-type equation which avoids the problem of frozen time in quantum cosmology. For simple cases we obtain solutions to this quantum equation in a Kantowski–Sachs (KS) minisuperspace. At the classical level, we study KS and Friedmann–Robertson–Walker cosmologies, obtaining modifications to the solutions of general relativity that can be relevant in the early Universe.
Modeling of anisotropic wound healing
NASA Astrophysics Data System (ADS)
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.
Evolution of multidimensional flat anisotropic cosmological models
Beloborodov, A. ); Demianski, M. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw International Center for Relativistic Astrophysics , Universita di Roma I, La Sapienza, Rome ); Ivanov, P.; Polnarev, A.G. )
1993-07-15
We study the dynamics of a flat multidimensional anisotropic cosmological model filled with an anisotropic fluidlike medium. By an appropriate choice of variables, the dynamical equations reduce to a two-dimensional dynamical system. We present a detailed analysis of the time evolution of this system and the conditions of the existence of spacetime singularities. We investigate the conditions under which violent, exponential, and power-law inflation is possible. We show that dimensional reduction cannot proceed by anti-inflation (rapid contraction of internal space). Our model indicates that it is very difficult to achieve dimensional reduction by classical means.
Modeling of anisotropic hardening of sheet metals
NASA Astrophysics Data System (ADS)
Yoshida, Fusahito; Hamasaki, Hiroshi; Uemori, Takeshi
2013-12-01
To describe the evolution of anisotropy of sheet metals, in terms of both r-values and stresses, the present paper proposes anisotropic hardening models, where the shape of yield surface changes with increasing plastic strain. In this framework of modeling, any types of yield functions are able to be used. The evolution of anisotropy is expressed by updating the yield function as an interpolation between two yield functions defined at two different effective plastic strains. In this paper, two types of interpolation models, i.e., nonlinear interpolation model and piecewise interpolation model are presented. These models are validated by comparing the experimental data on 3003-O aluminum sheet (after Hu, Int J Plasticity 23, 620-639, 2007). To describe the Bauschinger effect, the combined anisotropic-kinematic hardening model is formulated based on Yoshida-Uemori kinematic hardening model.
Modelling Fracture Propagation in Anisotropic Rock Mass
NASA Astrophysics Data System (ADS)
Shen, Baotang; Siren, Topias; Rinne, Mikael
2015-05-01
Anisotropic rock mass is often encountered in rock engineering, and cannot be simplified as an isotropic problem in numerical models. A good understanding of rock fracturing processes and the ability to predict fracture initiation and propagation in anisotropic rock masses are required for many rock engineering problems. This paper describes the development of the anisotropic function in FRACOD—a specialized fracture propagation modelling software—and its recent applications to rock engineering issues. Rock anisotropy includes strength anisotropy and modulus anisotropy. The level of complexity in developing the anisotropic function for strength anisotropy and modulus anisotropy in FRACOD is significantly different. The strength anisotropy function alone does not require any alteration in the way that FRACOD calculates rock stress and displacement, and therefore is relatively straightforward. The modulus anisotropy function, on the other hand, requires modification of the fundamental equations of stress and displacement in FRACOD, a boundary element code, and hence is more complex and difficult. In actual rock engineering, the strength anisotropy is often considered to be more pronounced and important than the modulus anisotropy, and dominates the stability and failure pattern of the rock mass. The modulus anisotropy will not be considered in this study. This paper discusses work related to the development of the strength anisotropy in FRACOD. The anisotropy function has been tested using numerical examples. The predicted failure surfaces are mostly along the weakest planes. Predictive modelling of the Posiva's Olkiluoto Spalling Experiment was made. The model suggests that spalling is very sensitive to the direction of anisotropy. Recent observations from the in situ experiment showed that shear fractures rather than tensile fractures occur in the holes. According to the simulation, the maximum tensile stress is well below the tensile strength, but the maximum
Chromo-natural model in anisotropic background
Maleknejad, Azadeh; Erfani, Encieh E-mail: eerfani@ipm.ir
2014-03-01
In this work we study the chromo-natural inflation model in the anisotropic setup. Initiating inflation from Bianchi type-I cosmology, we analyze the system thoroughly during the slow-roll inflation, from both analytical and numerical points of view. We show that the isotropic FRW inflation is an attractor of the system. In other words, anisotropies are damped within few e-folds and the chromo-natural model respects the cosmic no-hair conjecture. Furthermore, we demonstrate that in the slow-roll limit, the anisotropies in both chromo-natural and gauge-flation models share the same dynamics.
Some analytical models of anisotropic strange stars
NASA Astrophysics Data System (ADS)
Murad, Mohammad Hassan
2016-01-01
Over the years of the concept of local isotropy has become a too stringent condition in modeling relativistic self-gravitating objects. Taking local anisotropy into consideration, in this work, some analytical models of relativistic anisotropic charged strange stars have been developed. The Einstein-Maxwell gravitational field equations have been solved with a particular form of one of the metric potentials. The radial pressure and the energy density have been assumed to follow the usual linear equation of state of strange quark matter, the MIT bag model.
Anisotropic Cloth Modeling for Material Fabric
NASA Astrophysics Data System (ADS)
Zhang, Mingmin; Pan, Zhigengx; Mi, Qingfeng
Physically based cloth simulation has been challenging the graphics community for more than three decades. With the developing of virtual reality and clothing CAD, it has become the key technique of virtual garment and try-on system. Although it has received considerable attention in computer graphics, due to its flexible property and realistic feeling that the textile engineers pay much attention to, there is not a successful methodology to simulate cloth both in visual realism and physical accuracy. We present a new anisotropic textile modeling method based on physical mass-spring system, which models the warps and wefts separately according to the different material fabrics. The simulation process includes two main steps: firstly the rigid object simulation and secondly the flexible mass simulation near to be equilibrium. A multiresolution modeling is applied to enhance the tradeoff fruit of the realistic presentation and computation cost. Finally, some examples and the analysis results show the efficiency of the proposed method.
Simple Models for Polymeric and Anisotropic Liquids
NASA Astrophysics Data System (ADS)
Kröger, Martin
We hope that the complexity of the world is neither in contrast with the simplicity of the basic laws of physics [1] nor with the simple physical models to be reviewed or proposed in the following. However, physical phenomena occurring in complex materials cannot be encapsulated within a single numerical paradigm. In fact, they should be described within hierarchical, multi-level numerical models in which each sub-model is responsible for different spatio-temporal behavior and passes out the averaged parameters to the model, which is next in the hierarchy (Fig. 1.1). Polymeric liquids far from equilibrium belong to the class of anisotropic liquids.1 This monograph is devoted to the understanding of the anisotropic properties of polymeric and complex fluids such as viscoelastic and orientational behavior of polymeric liquids, the rheological properties of ferrofluids and liquid crystals subjected to external fields, based on the architecture of their molecular constituents. The topic is of considerable concern in basic research for which models should be as simple as possible, but not simpler. Certainly, it is also of technological relevance. Statistical physics and nonequilibrium thermodynamics are challenged by the desired structure-property relationships. Experiments such as static and dynamic light and neutron scattering, particle tracking, flow birefringence etc. together with rheological measurements have been essential to adjust or test basic theoretical concepts, such as a ‘linear stressoptic rule’ which connects orientation and stress, or the effect of molecular weight, solvent conditions, and external field parameters on shape, diffusion, degradation, and alignment of molecules.
Relativistic Modelling of Stable Anisotropic Super-Dense Star
NASA Astrophysics Data System (ADS)
Maurya, S. K.; Gupta, Y. K.; Jasim, M. K.
2015-08-01
In the present article we have obtained new set of exact solutions of Einstein field equations for anisotropic fluid spheres by using the Herrera et al. [1] algorithm. The anisotropic fluid solutions so obtained join continuously to the Schwarzschild exterior solution across the pressure-free boundary. It is observed that most of the new anisotropic solutions are well-behaved and are used to construct the super-dense star models such as neutron stars and pulsars.
Constitutive modeling of inelastic anisotropic material response
NASA Technical Reports Server (NTRS)
Stouffer, D. C.
1984-01-01
A constitutive equation was developed to predict the inelastic thermomechanical response of single crystal turbine blades. These equations are essential for developing accurate finite element models of hot section components and contribute significantly to the understanding and prediction of crack initiation and propagation. The method used was limited to unified state variable constitutive equations. Two approaches to developing an anisotropic constitutive equation were reviewed. One approach was to apply the Stouffer-Bodner representation for deformation induced anisotropy to materials with an initial anisotropy such as single crystals. The second approach was to determine the global inelastic strain rate from the contribution of the slip in each of the possible crystallographic slip systems. A three dimensional finite element is being developed with a variable constitutive equation link that can be used for constitutive equation development and to predict the response of an experiment using the actual specimen geometry and loading conditions.
A realizable EDQNM model for anisotropic scalars
NASA Astrophysics Data System (ADS)
Collins, Lance; Ulitsky, Mark
1999-11-01
As noted in the previous talk and abstract, the direct application of the edqnm formalism to two scalars with different diffusivities leads to a scalar covariance spectrum that violates the Cauchy-Schwartz inequality. This can be remedied by eliminating the explicit dependence of the eddy damping time scales on the molecular diffusivities, which can be shown to be unphysical at short times. Here we present an extension of this idea to anisotropic scalars. Anisotropy in this case results from uniform mean gradients of the scalar concentration in one direction. The approach we take is similar to the one described in Herr, Wang and Collins (Phys. Fluids 8:1588, 1996), except we substitute the modified eddy damping coefficients derived earlier for the isotropic scalar. The resulting edqnm model yields a realizable covariance spectrum for all times and for all combinations of the scalar diffusivities we considered. Several example calculations will be presented.
MOSSFRAC: An anisotropic 3D fracture model
Moss, W C; Levatin, J L
2006-08-14
Despite the intense effort for nearly half a century to construct detailed numerical models of plastic flow and plastic damage accumulation, models for describing fracture, an equally important damage mechanism still cannot describe basic fracture phenomena. Typical fracture models set the stress tensor to zero for tensile fracture and set the deviatoric stress tensor to zero for compressive fracture. One consequence is that the simple case of the tensile fracture of a cylinder under combined compressive radial and tensile axial loads is not modeled correctly. The experimental result is a cylinder that can support compressive radial loads, but no axial load, whereas, the typical numerical result is a cylinder with all stresses equal to zero. This incorrect modeling of fracture locally also has a global effect, because material that is fracturing produces stress release waves, which propagate from the fracture and influence the surrounding material. Consequently, it would be useful to have a model that can describe the stress relief and the resulting anisotropy due to fracture. MOSSFRAC is a material model that simulates three-dimensional tensile and shear fracture in initially isotropic elastic-plastic materials, although its framework is also amenable to initially anisotropic materials. It differs from other models by accounting for the effects of cracks on the constitutive response of the material, so that the previously described experiment, as well as complicated fracture scenarios are simulated more accurately. The model is implemented currently in the LLNL hydrocodes DYNA3D, PARADYN, and ALE3D. The purpose of this technical note is to present a complete qualitative description of the model and quantitative descriptions of salient features.
Anisotropic multicluster model in light nuclei
NASA Astrophysics Data System (ADS)
Gijón, A.; Gálvez, F. J.; Arias de Saavedra, F.; Buendía, E.
2016-06-01
Multicluster models consider that the nucleons can be moving around different centers in the nuclei. These models have been widely used to describe light nuclei but always considering that the mean field is composed of isotropic harmonic oscillators with different centers. In this work, we propose an extension of these models by using anisotropic harmonic oscillators. The strengths of these oscillators, the distance among the different centers and the disposition of the nucleons inside every cluster are free parameters which have been fixed using the variational criterion. All the one-body and two-body matrix elements have been analytically calculated. Only a numerical integration on the Euler angles is needed to carry out the projection on the values of the total spin of the state and its third component. We have studied the ground state and the first excited states of 8Be, 12C and 10Be getting good results for the energies. The disposition of the nucleons in the different clusters have also been analyzed by using projection on the different Cartesian planes getting much more information than when the radial one-body density is used.
Anisotropic model-based SAR processing
NASA Astrophysics Data System (ADS)
Knight, Chad; Gunther, Jake; Moon, Todd
2013-05-01
Synthetic aperture radar (SAR) collections that integrate over a wide range of aspect angles hold the potentional for improved resolution and fosters improved scene interpretability and target detection. However, in practice it is difficult to realize the potential due to the anisotropic scattering of objects in the scene. The radar cross section (RCS) of most objects changes as a function of aspect angle. The isotropic assumption is tacitly made for most common image formation algorithms (IFA). For wide aspect scenarios one way to account for anistropy would be to employ a piecewise linear model. This paper focuses on such a model but it incorporates aspect and spatial magnitude filters in the image formation process. This is advantageous when prior knowledge is available regarding the desired targets' RCS signature spatially and in aspect. The appropriate filters can be incorporated into the image formation processing so that specific targets are emphasized while other targets are suppressed. This is demonstrated on the Air Force Research Laboratory (AFRL) GOTCHA1 data set to demonstrate the utility of the proposed approach.
Modelling Coulomb Collisions in Anisotropic Plasmas
NASA Astrophysics Data System (ADS)
Hellinger, P.; Travnicek, P. M.
2009-12-01
Collisional transport in anisotropic plasmas is investigated comparing the theoretical transport coefficients (Hellinger and Travnicek, 2009) for anisotropic particles with the results of the corresponding Langevin equation, obtained as a generalization of Manheimer et al. (1997). References: Hellinger, P., and P. M. Travnicek (2009), On Coulomb collisions in bi-Maxwellian plasmas, Phys. Plasmas, 16, 054501. Manheimer, W. M., M. Lampe and G. Joyce (1997), Langevin representation of Coulomb collisions in PIC simulations, J. Comput. Phys., 138, 563-584.
Anisotropic stress and stability in modified gravity models
Saltas, Ippocratis D.; Kunz, Martin
2011-03-15
The existence of anisotropic stress of a purely geometrical origin seems to be a characteristic of higher order gravity models, and has been suggested as a probe to test these models observationally, for example, in weak lensing experiments. In this paper, we seek to find a class of higher order gravity models of f(R,G) type that would give us a zero anisotropic stress and study the consequences for the viability of the actual model. For the special case of a de Sitter background, we identify a subclass of models with the desired property. We also find a direct link between anisotropic stress and the stability of the model as well as the presence of extra degrees of freedom, which seems to be a general feature of higher order gravity models. Particularly, setting the anisotropic stress equal to zero for a de Sitter background leads to a singularity that makes it impossible to reach the de Sitter evolution.
Anisotropic distributions in a multiphase transport model
NASA Astrophysics Data System (ADS)
Zhou, You; Xiao, Kai; Feng, Zhao; Liu, Feng; Snellings, Raimond
2016-03-01
With a multiphase transport (AMPT) model we investigate the relation between the magnitude, fluctuations, and correlations of the initial state spatial anisotropy ɛn and the final state anisotropic flow coefficients vn in Au+Au collisions at √{s NN}=200 GeV. It is found that the relative eccentricity fluctuations in AMPT account for the observed elliptic flow fluctuations, both are in agreement with the elliptic flow fluctuation measurements from the STAR collaboration. In addition, the studies based on two- and multiparticle correlations and event-by-event distributions of the anisotropies suggest that the elliptic-power function is a promising candidate of the underlying probability density function of the event-by-event distributions of ɛn as well as vn. Furthermore, the correlations between different order symmetry planes and harmonics in the initial coordinate space and final state momentum space are presented. Nonzero values of these correlations have been observed. The comparison between our calculations and data will, in the future, shed new insight into the nature of the fluctuations of the quark-gluon plasma produced in heavy ion collisions.
Deformation modeling and constitutive modeling for anisotropic superalloys
NASA Technical Reports Server (NTRS)
Milligan, Walter W.; Antolovich, Stephen D.
1989-01-01
A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed.
Folkmann, Andrew W.; Noble, Kristen N.; Cole, Charles N.
2011-01-01
Gene expression is a stepwise process involving distinct cellular processes including transcription, mRNA (mRNA) processing, mRNA export, and translation. As mRNAs are being synthesized, proteins associate with the RNA to form messenger ribonucleoprotein particles (mRNPs). Previous studies have demonstrated that the RNA-binding protein composition of these mRNPs is dynamic, changing as the mRNP moves through the different steps of gene expression, and playing a critical role in these events. An important step during this maturation process occurs at the cytoplasmic face of the nuclear pore complex (NPC) where the export protein Gle1 bound to inositol hexakisphosphate (IP6) spatially activates the ATP-hydrolysis and mRNP-remodeling activity of the DEAD-box protein Dbp5. Recent work from our laboratory and others has provided important insights into the function and regulation of Dbp5. These include a more detailed explanation of the mechanism of Dbp5 RNP remodeling, the role of Gle1-IP6 in stimulating Dbp5 ATPase activity, and the identification of a novel paradigm for regulation of Dbp5 by Nup159. Based on in vitro biochemical assays, X-ray crystallography, and corresponding in vivo phenotypes, we propose here an updated model of the Dbp5 cycle during mRNP export through the NPC. This takes into account all available data and provides a platform for future studies. PMID:22064466
Anisotropic subvoxel-smooth conduction model for bioelectromagnetism analysis
NASA Astrophysics Data System (ADS)
He, Zhi Zhu; Liu, Jing
2016-01-01
The bioelectric conduction model plays a key role in bioelectromagnetism analysis, such as solving electromagnetic forward and inverse problems. This paper is aimed to develop an anisotropic subvoxel-smooth conduction model (ASCM) to characterize the electrical conductivity tensor jump across the tissue interface, which is derived based on the interfacial continuity condition with asymptotic analysis method. This conduction model is furthermore combined with finite volume method to improve the numerical accuracy for solving electromagnetic forward problem. The performance of ASCM for electrical potential analysis is verified by comparison with analytic solution. The method is also applied to investigate the effect of anisotropic conduction on EEG analysis in a realistic human head model.
NASA Astrophysics Data System (ADS)
Placidi, Luca; Greve, Ralf; Seddik, Hakime; Faria, Sérgio H.
2010-03-01
A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is described by a generalization of Glen’s flow law, based on a scalar anisotropic enhancement factor. The enhancement factor depends on the orientation mass density, which is closely related to the orientation distribution function and describes the distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization) and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model is truly anisotropic despite the collinearity between the stress deviator and stretching tensors.
The anisotropic λ-deformed SU (2) model is integrable
NASA Astrophysics Data System (ADS)
Sfetsos, Konstantinos; Siampos, Konstantinos
2015-04-01
The all-loop anisotropic Thirring model interpolates between the WZW model and the non-Abelian T-dual of the anisotropic principal chiral model. We focus on the SU (2) case and we prove that it is classically integrable by providing its Lax pair formulation. We derive its underlying symmetry current algebra and use it to show that the Poisson brackets of the spatial part of the Lax pair, assume the Maillet form. In this way we procure the corresponding r and s matrices which provide non-trivial solutions to the modified Yang-Baxter equation.
Hysteresis modeling of anisotropic and isotropic nanocrystalline hard magnetic films
NASA Astrophysics Data System (ADS)
Cornejo, D. R.; Azevedo, A.; Rezende, S. M.
2003-05-01
In the Hauser model, the magnetic state of a system is obtained by minimizing the so-called total energy function for a statistical set of magnetic domains. In this article, this energetic model of ferromagnetic materials is used in order to calculate hysteresis loops of isotropic and anisotropic nanocrystalline SmCo films at room temperature. A qualitative very good agreement between the calculated and experimental curves is obtained, mainly in the anisotropic case. Also, it has been verified that, under suitable approximations, the free parameters of the model can tie with intrinsic characteristics of the reversal magnetization process.
What are the causes for the spread of GLE parameters deduced from NM data?
NASA Astrophysics Data System (ADS)
Bütikofer, R.; Flückiger, E.
2015-08-01
Investigations have shown that the analysis results of ground level enhancements (GLEs) based on neutron monitor (NM) data for a selected event can differ considerably depending the procedure used. This may have significant consequences e.g. for the assessment of radiation doses at flight altitudes. The reasons for the spread of the GLE parameters deduced from NM data can be manifold and are at present unclear. They include differences in specific properties of the various analysis procedures (e.g. NM response functions, different ways in taking into account the dynamics of the Earth's magnetospheric field), different characterisations of the solar particle flux near Earth as well as the specific selection of NM stations used for the analysis. In the present paper we quantitatively investigate this problem for a time interval during the maximum phase of the GLE on 13 December 2006. We present and discuss the changes in the resulting GLE parameters when using different NM response functions, different model representations of the Earth's magnetospheric field as well as different assumptions for the solar particle spectrum and pitch angle distribution near Earth. The results of the study are expected to yield a basis for the reduction in the spread of the GLE parameters deduced from NM data.
Shear-free anisotropic cosmological models in {f (R)} gravity
NASA Astrophysics Data System (ADS)
Abebe, Amare; Momeni, Davood; Myrzakulov, Ratbay
2016-04-01
We study a class of shear-free, homogeneous but anisotropic cosmological models with imperfect matter sources in the context of f( R) gravity. We show that the anisotropic stresses are related to the electric part of the Weyl tensor in such a way that they balance each other. We also show that within the class of orthogonal f( R) models, small perturbations of shear are damped, and that the electric part of the Weyl tensor and the anisotropic stress tensor decay with the expansion as well as the heat flux of the curvature fluid. Specializing in locally rotationally symmetric spacetimes in orthonormal frames, we examine the late-time behaviour of the de Sitter universe in f( R) gravity. For the Starobinsky model of f( R), we study the evolutionary behavior of the Universe by numerically integrating the Friedmann equation, where the initial conditions for the expansion, acceleration and jerk parameters are taken from observational data.
An anisotropic extension of Bodner's model of viscoplasticity: Model development
NASA Technical Reports Server (NTRS)
Robinson, David N.
1994-01-01
An anisotropic viscoplasticity model is developed as an extension of the well known Bodner model. The extension is made by replacing the effective stress of the isotropic Bodner model by one involving invariants for transverse isotropy. The resulting model retains the simplicity of Bodner's in the ease with which the material constants are determined experimentally. It allows a representation of strong initial anisotropy yet is based on the scalar state variable under the assertion that induced anisotropy is negligible relative to the strong initial anisotropy. Temperature dependence is taken as in the original Bodner theory. Account is made of fiber volume fraction through nonlinear rules of mixture applied to the stress history and anisotropy parameters. Focus is on the theoretical development of the model, however, application to a W/Cu composite is in progress and will be reported as a sequel to this report.
Time-independent Anisotropic Plastic Behavior by Mechanical Subelement Models
NASA Technical Reports Server (NTRS)
Pian, T. H. H.
1983-01-01
The paper describes a procedure for modelling the anisotropic elastic-plastic behavior of metals in plane stress state by the mechanical sub-layer model. In this model the stress-strain curves along the longitudinal and transverse directions are represented by short smooth segments which are considered as piecewise linear for simplicity. The model is incorporated in a finite element analysis program which is based on the assumed stress hybrid element and the iscoplasticity-theory.
Anisotropic bouncing scenario in F(X)-V(φ) model
NASA Astrophysics Data System (ADS)
Panda, Sukanta; Sharma, Manabendra
2016-02-01
We investigate the cosmology of a class of model with noncanonical scalar field and matter in an anisotropic time dependent background. Writing the Einstein Equations in terms of dimensionless dynamical variables appropriately defined for bouncing solutions, we find all the fixed points. While evolving the dynamical variables to their stable fixed points numerically, solutions satisfying non singular bounce are found.
Analytical properties of the anisotropic cubic Ising model
Hansel, D.; Maillard, J.M.; Oitmaa, J.; Velgakis, M.J.
1987-07-01
The authors combine an exact functional relation, the inversion relation, with conventional high-temperature expansions to explore the analytic properties of the anisotropic Ising model on both the square and simple cubic lattice. In particular, they investigate the nature of the singularities that occur in partially resummed expansions of the partition function and of the susceptibility.
Massman, Bill
2016-01-01
This is the AmeriFlux version of the carbon flux data for the site US-GLE GLEES. Site Description - The Glacier Lakes Ecosystem Experiments Site (GLEES) site is located on land owned by the U.S. government and managed by US Forest Service as part of the Medicine Bow National Forest. Many of the trees in the immediate vicinity of the site are older than 400 years, inter-dispersed among trees much younger in age. This widespread age distribution is most likely a derivation of one of two scenarios: 1) A widespread stand replacement about 400 years ago followed by a slow replacement; 2) Intermittent random disturbances over the past 400 years (Bradford et al. 2008). A decade long spruce beetle outbreak that peaked in 2008 resulted in the mortality of 85% of the forested basal area. There are a few private land holdings in the area, with scattered uncorked mining claims. Following the establishment of the National Forest, mining was banned and grazing was closed in the early 1990's in the upper portion of the GLEES site. Recreation in the winter, when snow can remain in patches into the summer months, snow mobiling and cross country skiing are popular. During the limited summer, hiking, camping and fishing are common activities. The site is accessible by vehicle only during the summer on Forest Road FDR 317, and in the winter, the tower is only reachable via snowmobile.
A new model for spherically symmetric anisotropic compact star
NASA Astrophysics Data System (ADS)
Maurya, S. K.; Gupta, Y. K.; Dayanandan, Baiju; Ray, Saibal
2016-05-01
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.
Anisotropic Turbulence Modeling for Accurate Rod Bundle Simulations
Baglietto, Emilio
2006-07-01
An improved anisotropic eddy viscosity model has been developed for accurate predictions of the thermal hydraulic performances of nuclear reactor fuel assemblies. The proposed model adopts a non-linear formulation of the stress-strain relationship in order to include the reproduction of the anisotropic phenomena, and in combination with an optimized low-Reynolds-number formulation based on Direct Numerical Simulation (DNS) to produce correct damping of the turbulent viscosity in the near wall region. This work underlines the importance of accurate anisotropic modeling to faithfully reproduce the scale of the turbulence driven secondary flows inside the bundle subchannels, by comparison with various isothermal and heated experimental cases. The very low scale secondary motion is responsible for the increased turbulence transport which produces a noticeable homogenization of the velocity distribution and consequently of the circumferential cladding temperature distribution, which is of main interest in bundle design. Various fully developed bare bundles test cases are shown for different geometrical and flow conditions, where the proposed model shows clearly improved predictions, in close agreement with experimental findings, for regular as well as distorted geometries. Finally the applicability of the model for practical bundle calculations is evaluated through its application in the high-Reynolds form on coarse grids, with excellent results. (author)
Anisotropic Elastic Resonance Scattering model for the Neutron Transport equation
Mohamed Ouisloumen; Abderrafi M. Ougouag; Shadi Z. Ghrayeb
2014-11-24
The resonance scattering transfer cross-section has been reformulated to account for anisotropic scattering in the center-of-mass of the neutron-nucleus system. The main innovation over previous implementations is the relaxation of the ubiquitous assumption of isotropic scattering in the center-of-mass and the actual effective use of scattering angle distributions from evaluated nuclear data files in the computation of the angular moments of the resonant scattering kernels. The formulas for the high order anisotropic moments in the laboratory system are also derived. A multi-group numerical formulation is derived and implemented into a module incorporated within the NJOY nuclear data processing code. An ultra-fine energy mesh cross section library was generated using these new theoretical models and then was used for fuel assembly calculations with the PARAGON lattice physics code. The results obtained indicate a strong effect of this new model on reactivity, multi-group fluxes and isotopic inventory during depletion.
Modeling of ductile deformation in anisotropic rocks with slip surfaces
NASA Astrophysics Data System (ADS)
Dabrowski, Marcin
2013-04-01
Flanking structures and sheath folds can develop in layered rocks due to flow perturbation around slip surfaces in shear zones (Exner and Dabrowski, 2010; Reber et al., submitted). Mechanical anisotropy of the host rock has been shown to play a major role in determining the slip rate and the flow pattern around it (Kocher and Mancktelow, 2006; Fletcher, 2011). In addition, anisotropic fluids such as ductile foliated rocks have a 'memory' of deformation due to evolving microstructure. For example, the rotation of a rigid circular inclusion embedded in a layered host in layer-parallel shear results in the structural reorganization around it, which leads to the modification of the flow pattern in the host and in consequence to a massive reduction of the inclusion rotation rate (Dabrowski and Schmid, 2011). Willis (1964) derived an analytical elastic solution for an elliptical inclusion in a homogeneous anisotropic matrix subject to a uniform load in the far field. The solution can be reduced to the case of an incompressible viscous medium. The case of an arbitrarily oriented inviscid slit under shear parallel to the principal axis of anisotropy can be obtained by reducing it even further. Although derived for the initial state of homogeneous planar anisotropy, the solution provides useful insights into the large deformation behavior of the system. In this study, I will use different models and numerical modeling techniques to assess the impact of mechanical anisotropy and structural development on the perturbing flow around an inviscid slit (slip surface) embedded in a host comprising discrete isotropic layers in layer-parallel simple shear. In the limit of thin layers (the number of layers intercepting the slit tends to infinity), the host is modeled as an anisotropic fluid. The anisotropic viscosity is determined by the bulk anisotropic viscosity of the layered system. The layering is initially planar or equivalently the anisotropy is initially homogeneous. Both non
Anisotropic 2-dimensional Robin Hood model
NASA Astrophysics Data System (ADS)
Buldyrev, Sergey; Cwilich, Gabriel; Zypman, Fredy
2009-03-01
We have considered the Robin Hood model introduced by Zaitsev[1] to discuss flux creep and depinning of interfaces in a two dimensional system. Although the model has been studied extensively analytically in 1-d [2], its scaling laws have been verified numerically only in that case. Recent work suggest that its properties might be important to understand surface friction[3], where its 2-dimensional properties are important. We show that in the 2-dimensional case scaling laws can be found provided one considers carefully the anisotropy of the model, and different ways of introducing that anisotropy lead to different exponents and scaling laws, in analogy with directed percolation, with which this model is closely related[4]. We show that breaking the rotational symmetry between the x and y axes does not change the scaling properties of the model, but the introduction of a preferential direction of accretion (``robbing'' in the language of the model) leads to new scaling exponents. [1] S.I.Zaitsev, Physica A189, 411 (1992) [2] M. Pacuzki, S. Maslov and P.Bak, Phys Rev. E53, 414 (1996) [3] S. Buldyrev, J. Ferrante and F. Zypman Phys. Rev E64, 066110 (2006) [4] G. Odor, Rev. Mod. Phys. 76, 663 (2004) .
A new model for charged anisotropic compact star
NASA Astrophysics Data System (ADS)
Maurya, S. K.; Jasim, M. K.; Gupta, Y. K.; Smitha, T. T.
2016-05-01
In this paper, we have obtained a new singularity free charged anisotropic fluid solution of Einstein's field equations. The physical parameters as radial pressure, tangential pressure, energy density, charge density, electric field intensity, velocity of sound and red-shift are well behaved everywhere inside the star. The obtained compact star models can represent the observational compact objects as PSR 1937{+}21 and PSR J1614-2230.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2016-04-01
In this study, the modified anisotropic turbulence refractive-index fluctuations spectral model is derived based on the extended Rytov approximation theory for the theoretical investigations of optical plane and spherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. The anisotropic factor which parameterizes the asymmetry of turbulence cells or eddies in the horizontal and vertical directions is introduced. The general spectral power law in the range of 3-4 is also considered compared with the conventional classic value of 11/3 for Kolmogorov turbulence. Based on the modified anisotropic turbulence refractive-index fluctuations spectrum, the analytic expressions of the irradiance scintillation index are also derived for optical plane and spherical waves propagating through moderate-to-strong anisotropic non-Kolmogorov turbulence. They are applicable in a wide range of turbulence strengths and can reduce correctly to the previously published results in the special cases of weak anisotropic turbulence and moderate-to-strong isotropic turbulence. Calculations are performed to analyze the derived models. PMID:27140754
Anisotropic Mesoscale Eddy Transport in Ocean General Circulation Models
NASA Astrophysics Data System (ADS)
Reckinger, S. J.; Fox-Kemper, B.; Bachman, S.; Bryan, F.; Dennis, J.; Danabasoglu, G.
2014-12-01
Modern climate models are limited to coarse-resolution representations of large-scale ocean circulation that rely on parameterizations for mesoscale eddies. The effects of eddies are typically introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically in general circulation models. Thus, only a single parameter, namely the eddy diffusivity, is used at each spatial and temporal location to impart the influence of mesoscale eddies on the resolved flow. However, the diffusive processes that the parameterization approximates, such as shear dispersion, potential vorticity barriers, oceanic turbulence, and instabilities, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters to three: a major diffusivity, a minor diffusivity, and the principal axis of alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the newly introduced parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces global temperature and salinity biases. These effects can be improved even further by parameterizing the anisotropic transport mechanisms in the ocean.
Anisotropic models of the upper mantle
NASA Technical Reports Server (NTRS)
Regan, J.; Anderson, D. L.
1983-01-01
Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, were not simultaneously satisfied by an isotropic structure. Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, an elastic dispersion, sphericity, and gravity. The resulting models, for the average Earth, average ocean and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggested.
Life prediction and constitutive models for anisotropic materials
NASA Technical Reports Server (NTRS)
Bill, R. C.
1982-01-01
The intent of this program is to develop a basic understanding of cyclic creep-fatigue deformation mechanisms and damage accumulation, a capability for reliable life prediction, and the ability to model the constitutive behavior of anisotropic single crystal (SC) and directionally solidified or recrystallized (DSR) comprise the program, and the work breakdown for each option reflects a distinct concern for two classes of anisotropic materials, SC and DSR materials, at temperatures encountered in the primary gas path (airfoil temperatures), and at temperatures typical of the blade root attachment and shank area. Work directed toward the higher temperature area of concern in the primary gas path includes effects of coatings on the behavior and properties of the materials of interest. The blade root attachment work areas will address the effects of stress concentrations associated with attachment features.
Anisotropic mesoscale eddy transport in ocean general circulation models
NASA Astrophysics Data System (ADS)
Reckinger, Scott; Fox-Kemper, Baylor; Bachman, Scott; Bryan, Frank; Dennis, John; Danabasoglu, Gokhan
2014-11-01
In modern climate models, the effects of oceanic mesoscale eddies are introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically. However, the diffusive processes that the parameterization approximates, such as shear dispersion and potential vorticity barriers, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters from one to three: major diffusivity, minor diffusivity, and alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces temperature and salinity biases. These effects can be improved by parameterizing the oceanic anisotropic transport mechanisms.
The anisotropic material constitutive models for the human cornea.
Li, Long-yuan; Tighe, Brian
2006-03-01
This paper presents an anisotropic analysis model for the human cornea. The model is based on the assumption that the fibrils in the cornea are organised into lamellae, which may have preferential orientation along the superior-inferior and nasal-temporal directions, while the alignment of lamellae with different orientations is assumed to be random. Hence, the cornea can be regarded as a laminated composite shell. The constitutive equation describing the relationships between membrane forces, bending moments, and membrane strains, bending curvatures are derived. The influences of lamella orientations and the random alignment of lamellae on the stiffness coefficients of the constitutive equation are discussed. PMID:16426861
Anisotropic cosmological models in f(G) gravity
NASA Astrophysics Data System (ADS)
Farasat Shamir, M.
2016-04-01
The main objective of this manuscript is to study the anisotropic universe in f(G) Gravity. For this purpose, locally rotationally symmetric Bianchi type I spacetime is considered. A viable f(G) model is used to explore the exact solutions of modified field equations. In particular, two families involving power law and exponential type solutions have been discussed. Some important cosmological parameters are calculated for the obtained solutions. Moreover, energy density and pressure of the universe is analyzed for the model under consideration.
Hyperelastic anisotropic microplane constitutive model for annulus fibrosus.
Caner, Ferhun C; Guo, Zaoyang; Moran, Brian; Bazant, Zdenek P; Carol, Ignacio
2007-10-01
In a recent paper, Peng et al. (2006, "An Anisotropic Hyperelastic Constitutive Model With Fiber-Matrix Interaction for the Human Annulus Fibrosis," ASME J. Appl. Mech., 73(5), pp. 815-824) developed an anisotropic hyperelastic constitutive model for the human annulus fibrosus in which fiber-matrix interaction plays a crucial role in simulating experimental observations reported in the literature. Later, Guo et al. (2006, "A Composites-Based Hyperelastic Constitutive Model for Soft Tissue With Application to the Human Fibrosis," J. Mech. Phys. Solids, 54(9), pp. 1952-1971) used fiber reinforced continuum mechanics theory to formulate a model in which the fiber-matrix interaction was simulated using only composite effect. It was shown in these studies that the classical anisotropic hyperelastic constitutive models for soft tissue, which do not account for this shear interaction, cannot accurately simulate the test data on human annulus fibrosus. In this study, we show that the microplane model for soft tissue developed by Caner and Carol (2006, "Microplane Constitutive Model and Computational Framework for Blood Vessel Tissue," ASME J. Biomech. Eng., 128(3), pp. 419-427) can be adjusted for human annulus fibrosus and the resulting model can accurately simulate the experimental observations without explicit fiber-matrix interaction because, in microplane model, the shear interaction between the individual fibers distributed in the tissue provides the required additional rigidity to explain these experimental facts. The intensity of the shear interaction between the fibers can be adjusted by adjusting the spread in the distribution while keeping the total amount of the fiber constant. A comparison of results obtained from (i) a fiber-matrix parallel coupling model, which does not account for the fiber-matrix interaction, (ii) the same model but enriched with fiber-matrix interaction, and (iii) microplane model for soft tissue adapted to annulus fibrosus with two
Critical dynamics of anisotropic Bak-Sneppen model
NASA Astrophysics Data System (ADS)
Tirnakli, Ugur; Lyra, Marcelo L.
2004-10-01
A new damage spreading algorithm, which was introduced very recently in (Int. J. Mod. Phys. C 14 (2003) 85) has been applied to anisotropic Bak-Sneppen model of biological evolution. Since this new algorithm is able to capture both the short-time and long-time dynamics of extended systems which exhibits self-organized criticality, this analysis is expected to shed further light to the recent claim that the dynamics of such systems is similar to the one observed at the usual critical point of continuous phase-transitions and at the chaos threshold of low-dimensional dissipative maps.
Truncated Connectivities in a Highly Supercritical Anisotropic Percolation Model
NASA Astrophysics Data System (ADS)
Couto, Rodrigo G.; de Lima, Bernardo N. B.; Sanchis, Rémy
2013-12-01
We consider an anisotropic bond percolation model on , with p=( p h , p v )∈[0,1]2, p v > p h , and declare each horizontal (respectively vertical) edge of to be open with probability p h (respectively p v ), and otherwise closed, independently of all other edges. Let with 0< x 1< x 2, and . It is natural to ask how the two point connectivity function behaves, and whether anisotropy in percolation probabilities implies the strict inequality . In this note we give an affirmative answer in the highly supercritical regime.
A hydrostatic stress-dependent anisotropic model of viscoplasticity
NASA Technical Reports Server (NTRS)
Robinson, D. N.; Tao, Q.; Verrilli, M. J.
1994-01-01
A hydrostatic stress-dependent, anisotropic model of viscoplasticity is formulated as an extension of Bodner's model. This represents a further extension of the isotropic Bodner model over that made to anisotropy by Robinson and MitiKavuma. Account is made of the inelastic deformation that can occur in metallic composites under hydrostatic stress. A procedure for determining the material parameters is identified that is virtually identical to the established characterization procedure for the original Bodner model. Characterization can be achieved using longitudinal/transverse tensile and shear tests and hydrostatic stress tests; alternatively, four off-axis tensile tests can be used. Conditions for a yield stress minimum under off-axis tension are discussed. The model is applied to a W/Cu composite; characterization is made using off-axis tensile data generated at NASA Lewis Research Center (LeRC).
Inflationary weak anisotropic model with general dissipation coefficient
NASA Astrophysics Data System (ADS)
Sharif, M.; Saleem, Rabia
2016-03-01
This paper explores the dynamics of warm intermediate and logamediate inflationary models during weak dissipative regime with a general form of dissipative coefficient. We analyze these models within the framework of locally rotationally symmetric Bianchi type I universe. In both cases, we evaluate solution of inflaton, effective scalar potential, dissipative coefficient, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio under slow-roll approximation. We constrain the model parameters using recent data and conclude that anisotropic inflationary universe model with generalized dissipation coefficient remains compatible with WMAP9, Planck and BICEP2 data. Finally, we have checked the effects of bulk viscous pressure on this considered model and found that it remains compatible with recent data only for intermediate case.
The comparison of isotropic and anisotropic semivariogram for Gauss model
NASA Astrophysics Data System (ADS)
Sari, Rr. Kurnia Novita; Pasaribu, Udjianna S.
2014-03-01
Semivariogram is one of the models used to study the relationship between the sequence of random variables {Z(s),sɛR2} based on the location s. That model is a diagram of variance from the difference between the random variable that distance h, or γ(h) = Var[Z(s)-Z(s+h)]. Experimental variogram can be calculated through observations at several locations. One model that is chosen to be fitted to ̂γ(h) is the Gaussian. In application, ̂γ(h) often considered to depend on the direction (anisotropic semivariogram). This paper develop a nested Gaussian model by considering some angle intervals which is called geometric anisotropy semivariogram. For a case study, the distribution of Bradysia ocellaris insects at a Oyster Mushrooms cultivication is analyzed that the insects fly to follow the direction of light.
Nonlinear inversion for arbitrarily-oriented anisotropic models: Synthetic testing
NASA Astrophysics Data System (ADS)
Bremner, P. M.; Panning, M. P.
2010-12-01
We present an implementation of new 3-D finite-frequency kernels, based on the Born approximation, for inversion of a synthetic surface wave dataset. The kernels are formulated based on a hexagonal symmetry with an arbitrary orientation. Numerical tests are performed to achieve a robust inversion scheme. Nonlinear inversion schemes are examined for adequate recovery of three input models to include: isotropic, anisotropic, and both anisotropic and isotropic input models. Output models from inversions of calculated synthetic data are compared against these input models to test for accurate reproduction of input model features, and the resolution of those features. The focus of this study is on inverting for structure beneath western North America. The synthetic dataset consists of collected seismic waveforms of 128 earthquake mechanisms, of magnitude 6-7 from Dec 2006 to Feb 2009, from the IRIS database. Events were selected to correlate with USArray deployments, and to have as complete an azimuthal coverage as possible. The events occurred within a circular region of radius 150° centered about 44° lat, -110° lon (an arbitrary location within USArray coverage). The seismograms have been calculated within a simplified version of PREM in which the crust and 220 km discontinuity have been removed, dubbed PREM LIGHT, utilizing a spectral element code (SEM) coupled to a normal mode solution. The mesh consists of a 3-D heterogeneous outer shell, representing the upper mantle above 400 km depth, coupled to a spherically symmetric inner sphere. The SEM solves the weak formulation of the seismic wave equation in the outer shell, and uses normal mode summation methods for the inner sphere. To validate the results of the SEM, seismograms are benchmarked against seismograms calculated with a 1-D normal mode summation. From the synthetic dataset, multi-taper fundamental mode surface wave phase delay measurements are taken. The orthogonal 2.5π spheroidal wave function
Anisotropic rock physics models for interpreting pore structures in carbonate reservoirs
NASA Astrophysics Data System (ADS)
Li, Sheng-Jie; Shao, Yu; Chen, Xu-Qiang
2016-03-01
We developed an anisotropic effective theoretical model for modeling the elastic behavior of anisotropic carbonate reservoirs by combining the anisotropic self-consistent approximation and differential effective medium models. By analyzing the measured data from carbonate samples in the TL area, a carbonate pore-structure model for estimating the elastic parameters of carbonate rocks is proposed, which is a prerequisite in the analysis of carbonate reservoirs. A workflow for determining elastic properties of carbonate reservoirs is established in terms of the anisotropic effective theoretical model and the pore-structure model. We performed numerical experiments and compared the theoretical prediction and measured data. The result of the comparison suggests that the proposed anisotropic effective theoretical model can account for the relation between velocity and porosity in carbonate reservoirs. The model forms the basis for developing new tools for predicting and evaluating the properties of carbonate reservoirs.
Anisotropic electromagnetic wave propagation modeling using parabolic approximations
NASA Astrophysics Data System (ADS)
Brent, R. I.; Siegmann, W. L.; Jacobson, M. J.; Jacyna, G. M.
1990-12-01
A new method for the investigation of anisotropic electromagnetic wave propagation in the atmosphere is developed using parabolic approximations. Model equations for the electric field components are formulated which include the effects of both the inhomogeneous atmosphere and the static magnetic field of the earth. Application of parabolic-type approximations produces different systems of coupled parabolic equations. Each is valid for different relative magnitudes of components of the electric field. All admissible cases are then synthesized into one system which can be numerically examined, yielding solutions without a priori knowledge of electric field ratios. A specific example is presented and examined to understand static magnetic field effects on electromagnetic wave propagation. The influences of the earth's magnetic field are discussed and displayed in terms of electric components and the Poynting vector. Results demonstrate that the geomagnetic field can significantly influence HF atmospheric propagation.
Reentrance of disorder in the anisotropic shuriken Ising model
NASA Astrophysics Data System (ADS)
Pohle, Rico; Benton, Owen; Jaubert, L. D. C.
2016-07-01
Frustration is often a key ingredient for reentrance mechanisms. Here we study the frustrated anisotropic shuriken Ising model, where it is possible to extend the notion of reentrance between disordered phases, i.e., in absence of phase transitions. By tuning the anisotropy of the lattice, we open a window in the phase diagram where magnetic disorder prevails down to zero temperature, in a classical analogy with a quantum critical point. In this region, the competition between multiple disordered ground states gives rise to a double crossover where both the low- and high-temperature regimes are less correlated than the intervening classical spin liquid. This reentrance of disorder is characterized by an entropy plateau and a multistep Curie law crossover. Our theory is developed based on Monte Carlo simulations, analytical Husimi-tree calculations and an exact decoration-iteration transformation. Its relevance to experiments, in particular, artificial lattices, is discussed.
Lattice models of directed and semiflexible polymers in anisotropic environment
NASA Astrophysics Data System (ADS)
Haydukivska, K.; Blavatska, V.
2015-10-01
We study the conformational properties of polymers in presence of extended columnar defects of parallel orientation. Two classes of macromolecules are considered: the so-called partially directed polymers with preferred orientation along direction of the external stretching field and semiflexible polymers. We are working within the frames of lattice models: partially directed self-avoiding walks (PDSAWs) and biased self-avoiding walks (BSAWs). Our numerical analysis of PDSAWs reveals, that competition between the stretching field and anisotropy caused by presence of extended defects leads to existing of three characteristic length scales in the system. At each fixed concentration of disorder we found a transition point, where the influence of extended defects is exactly counterbalanced by the stretching field. Numerical simulations of BSAWs in anisotropic environment reveal an increase of polymer stiffness. In particular, the persistence length of semiflexible polymers increases in presence of disorder.
Anisotropic effects on constitutive model parameters of aluminum alloys
NASA Astrophysics Data System (ADS)
Brar, Nachhatter S.; Joshi, Vasant S.
2012-03-01
Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material models. Model constants are determined from tension, compression or torsion stress-strain at low and high strain rates at different temperatures. These model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloy. Johnson- Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1' thick Al-7075-T651plates. When simulation go well beyond minor parameter tweaking and experimental results show drastically different behavior it becomes important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic effects on the yield/flow stress of this alloy quasi-static and high strain rate tensile tests were performed on specimens fabricated in the longitudinal "L", transverse "T", and thickness "TH" directions of 1' thick Al7075 Plate. While flow stress at a strain rate of ~1/s as well as ~1100/s in the thickness and transverse directions are lower than the longitudinal direction. The flow stress in the bar was comparable to flow stress in the longitudinal direction of the plate. Fracture strain data from notched tensile specimens fabricated in the L, T, and Thickness directions of 1' thick plate are used to derive fracture constants.
Chiral Spin Liquid in a Frustrated Anisotropic Kagome Heisenberg Model
NASA Astrophysics Data System (ADS)
He, Yin-Chen; Sheng, D. N.; Chen, Yan
2014-04-01
Kalmeyer-Laughlin (KL) chiral spin liquid (CSL) is a type of quantum spin liquid without time-reversal symmetry, and it is considered as the parent state of an exotic type of superconductor—anyon superconductor. Such an exotic state has been sought for more than twenty years; however, it remains unclear whether it can exist in a realistic system where time-reversal symmetry is breaking (T breaking) spontaneously. By using the density matrix renormalization group, we show that KL CSL exists in a frustrated anisotropic kagome Heisenberg model, which has spontaneous T breaking. We find that our model has two topological degenerate ground states, which exhibit nonvanishing scalar chirality order and are protected by finite excitation gap. Furthermore, we identify this state as KL CSL by the characteristic edge conformal field theory from the entanglement spectrum and the quasiparticles braiding statistics extracted from the modular matrix. We also study how this CSL phase evolves as the system approaches the nearest-neighbor kagome Heisenberg model.
Anisotropic magnetoresistivity in structured elastomer composites: modelling and experiments.
Mietta, José Luis; Tamborenea, Pablo I; Martin Negri, R
2016-08-14
A constitutive model for the anisotropic magnetoresistivity in structured elastomer composites (SECs) is proposed. The SECs considered here are oriented pseudo-chains of conductive-magnetic inorganic materials inside an elastomer organic matrix. The pseudo-chains are formed by fillers which are simultaneously conductive and magnetic dispersed in the polymer before curing or solvent evaporation. The SEC is then prepared in the presence of a uniform magnetic field, referred to as Hcuring. This procedure generates the pseudo-chains, which are preferentially aligned in the direction of Hcuring. Electrical conduction is present in that direction only. The constitutive model for the magnetoresistance considers the magnetic pressure, Pmag, induced on the pseudo-chains by an external magnetic field, H, applied in the direction of the pseudo-chains. The relative changes in conductivity as a function of H are calculated by evaluating the relative increase of the electron tunnelling probability with Pmag, a magneto-elastic coupling which produces an increase of conductivity with magnetization. The model is used to adjust experimental results of magnetoresistance in a specific SEC where the polymer is polydimethylsiloxane, PDMS, and fillers are microparticles of magnetite-silver (referred to as Fe3O4[Ag]). Simulations of the expected response for other materials in both superparamagnetic and blocked magnetic states are presented, showing the influence of the Young's modulus of the matrix and filler's saturation magnetization. PMID:27418417
Anisotropic Effects on Constitutive Model Parameters of Aluminum Alloys
NASA Astrophysics Data System (ADS)
Brar, Nachhatter; Joshi, Vasant
2011-06-01
Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material models. The model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloys. Johnson-Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1' thick Al-7075-T651plates. When simulations go well beyond minor parameter tweaking and experimental results are drastically different it is important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic effects on the yield/flow stress of this alloy we performed quasi-static and high strain rate tensile tests on specimens fabricated in the longitudinal, transverse, and thickness directions of 1' thick Al7075-T651 plate. Flow stresses at a strain rate of ~1100/s in the longitudinal and transverse direction are similar around 670MPa and decreases to 620 MPa in the thickness direction. These data are lower than the flow stress of 760 MPa measured in Al7075-T651 bar stock.
Anisotropic cosmology and inflation from a tilted Bianchi IX model
NASA Astrophysics Data System (ADS)
Sundell, P.; Koivisto, T.
2015-12-01
The dynamics of the tilted axisymmetric Bianchi IX cosmological models are explored allowing energy flux in the source fluid. The Einstein equations and the continuity equation are presented treating the equation of state w and the tilt angle of the fluid λ as time-dependent functions, but when analyzing the phase space w and λ are considered free parameters and the shear, the vorticity and the curvature of the spacetime span a three-dimensional phase space that contains seven fixed points. One of them is an attractor that inflates the universe anisotropically, thus providing a counterexample to the cosmic no-hair conjecture. Also, examples of realistic though fine-tuned cosmologies are presented wherein the rotation can become significant towards the present epoch but the shear stays within the observational bounds. The examples suggest that the model used here can explain the parity-violating anomalies of the cosmic microwave background. The result significantly differs from an earlier study, where a nonaxisymmetric Bianchi IX type model with a tilted perfect dust source was found to induce too much shear for observationally significant vorticity.
NASA Astrophysics Data System (ADS)
Pekşen, Ertan; Yas, Türker; Kıyak, Alper
2014-09-01
We examine the one-dimensional direct current method in anisotropic earth formation. We derive an analytic expression of a simple, two-layered anisotropic earth model. Further, we also consider a horizontally layered anisotropic earth response with respect to the digital filter method, which yields a quasi-analytic solution over anisotropic media. These analytic and quasi-analytic solutions are useful tests for numerical codes. A two-dimensional finite difference earth model in anisotropic media is presented in order to generate a synthetic data set for a simple one-dimensional earth. Further, we propose a particle swarm optimization method for estimating the model parameters of a layered anisotropic earth model such as horizontal and vertical resistivities, and thickness. The particle swarm optimization is a naturally inspired meta-heuristic algorithm. The proposed method finds model parameters quite successfully based on synthetic and field data. However, adding 5 % Gaussian noise to the synthetic data increases the ambiguity of the value of the model parameters. For this reason, the results should be controlled by a number of statistical tests. In this study, we use probability density function within 95 % confidence interval, parameter variation of each iteration and frequency distribution of the model parameters to reduce the ambiguity. The result is promising and the proposed method can be used for evaluating one-dimensional direct current data in anisotropic media.
A kinematically driven anisotropic viscoelastic constitutive model applied to tires
NASA Astrophysics Data System (ADS)
Johnson, Arthur R.; Tanner, John A.; Mason, Angela J.
1995-08-01
Aircraft tires are composite structures manufactured with viscoelastic materials such as carbon black filled rubber and nylon cords. When loaded they experience large deflections and moderately large strains. Detailed structural models of tires require the use of either nonlinear shell or nonlinear three dimensional solid finite elements. Computational predictions of the dynamic response of tires must consider the composite viscoelastic material behavior in a realistic fashion. We describe a modification to a nonlinear anisotropic shell finite element so it can be used to model viscoelastic stresses during general deformations. The model is developed by introducing internal variables of the type used to model elastic strain energy. The internal variables are strains, curvatures, and transverse shear angles which are in a one-to-one correspondence with the generalized coordinates used to model the elastic strain energy for nonlinear response. A difference-relaxation equation is used to relate changes in the observable strain field to changes in the internal strain field. The internal stress state is introduced into the equilibrium equations by converting it to nodal loads associated with the element's displacement degrees of freedom. In this form the tangent matrix in the Newton-Raphson solution algorithm is not modified from its form for the nonlinear statics problem. Only the gradient vector is modified and the modification is not computationally costly. The existing finite element model for the Space Shuttle nose gear tire is used to provide examples of the algorithm. In the first example, the tire's rim is displaced at a constant rate up to a fixed value. In the second example, the tire's rim is enforced to follow a saw tooth load and unload curve to generate hysteresis loops.
A kinematically driven anisotropic viscoelastic constitutive model applied to tires
NASA Technical Reports Server (NTRS)
Johnson, Arthur R.; Tanner, John A.; Mason, Angela J.
1995-01-01
Aircraft tires are composite structures manufactured with viscoelastic materials such as carbon black filled rubber and nylon cords. When loaded they experience large deflections and moderately large strains. Detailed structural models of tires require the use of either nonlinear shell or nonlinear three dimensional solid finite elements. Computational predictions of the dynamic response of tires must consider the composite viscoelastic material behavior in a realistic fashion. We describe a modification to a nonlinear anisotropic shell finite element so it can be used to model viscoelastic stresses during general deformations. The model is developed by introducing internal variables of the type used to model elastic strain energy. The internal variables are strains, curvatures, and transverse shear angles which are in a one-to-one correspondence with the generalized coordinates used to model the elastic strain energy for nonlinear response. A difference-relaxation equation is used to relate changes in the observable strain field to changes in the internal strain field. The internal stress state is introduced into the equilibrium equations by converting it to nodal loads associated with the element's displacement degrees of freedom. In this form the tangent matrix in the Newton-Raphson solution algorithm is not modified from its form for the nonlinear statics problem. Only the gradient vector is modified and the modification is not computationally costly. The existing finite element model for the Space Shuttle nose gear tire is used to provide examples of the algorithm. In the first example, the tire's rim is displaced at a constant rate up to a fixed value. In the second example, the tire's rim is enforced to follow a saw tooth load and unload curve to generate hysteresis loops.
Relativistic model of anisotropic charged fluid sphere in general relativity
NASA Astrophysics Data System (ADS)
Pant, Neeraj; Pradhan, N.; Bansal, Rajeev K.
2016-01-01
In this present paper, we present a class of static, spherically symmetric charged anisotropic fluid models of super dense stars in isotropic coordinates by considering a particular type of metric potential, a specific choice of electric field intensity E and pressure anisotropy factor Δ which involve parameters K (charge) and α (anisotropy) respectively. The solutions so obtained are utilized to construct the models for super-dense stars like neutron stars and strange quark stars. Our solutions are well behaved within the following ranges of different constant parameters. In the absence of pressure anisotropy and charge present model reduces to the isotropic model Pant et al. (Astrophys. Space Sci. 330:353-359, 2010). Our solution is well behaved in all respects for all values of X lying in the range 0< X ≤ 0.18, α lying in the range 0 ≤ α ≤6.6, K lying in the range 0< K ≤ 6.6 and Schwarzschild compactness parameter "u" lying in the range 0< u ≤ 0.38. Since our solution is well behaved for a wide ranges of the parameters, we can model many different types of ultra-cold compact stars like quark stars and neutron stars. We have shown that corresponding to X=0.088, α=0.6 and K=4.3 for which u=0.2054 and by assuming surface density ρb = 4.6888 × 10^{14} g/cm3 the mass and radius are found to be 1.51 M_{\\varTheta} and 10.90 km respectively. Assuming surface density ρb = 2 × 10^{14} g/cm3 the mass and radius for a neutron star candidate are found to be 2.313 M_{\\varTheta} and 16.690 km respectively. Hence we obtain masses and radii that fall in the range of what is generally expected for quark stars and neutron stars.
NASA Astrophysics Data System (ADS)
Sari, Rr. Kurnia Novita; Neswan, Oki
2015-12-01
Anisotropic semivariogram modeling can be aplied in petroleum industry where the angle between a pair of wells has important function in defining the spatial correlation between wells. In geometry anisotropic, function of range is formulated in trigonometric functions of the angle between pairs of wells that have periodicity property. The fluctuations of range will affect on shifting geometry anisotropic models with different properties for each quadrant of angle. In three semivariogram models (exponential, spherical and gaussian), the increasing of angle give difference influence for range function and the shifting of semivariogram value.
An Anisotropic Fluid-Solid Model of the Mouse Heart
Carson, James P.; Kuprat, Andrew P.; Jiao, Xiangmin; del Pin, Facundo; Einstein, Daniel R.
2010-01-01
A critical challenge in biomechanical simulations is the spatial discretization of complex fluid-solid geometries created from imaging. This is especially important when dealing with Lagrangian interfaces, as there must be at a minimum both geometric and topological compatibility between fluid and solid phases, with exact matching of the interfacial nodes being highly desirable. We have developed a solution to this problem and applied the approach to the creation of a 3D fluidsolid mesh of the mouse heart. First, a 50 micron isotropic MRI dataset of a perfusion-fixed mouse heart was segmented into blood, tissue, and background using a customized multimaterial connected fuzzy thresholding algorithm. Then, a multimaterial marching cubes algorithm was applied to produce two compatible isosurfaces, one for the blood-tissue boundary and one for the tissue-background boundary. A multimaterial smoothing algorithm that rigorously conserves volume for each phase simultaneously smoothed the isosurfaces. Next we applied novel automated meshing algorithms to generate anisotropic hybrid meshes with the number of layers and the desired element anisotropy for each material as the only input parameters. As the meshes are scale-invariant within a material and include boundary layer prisms, fluid-structure interaction computations would have a relative error equilibrated over the entire mesh. The resulting model is highly detailed mesh representation of the mouse heart, including features such as chordae and coronary vasculature, that is also maximally efficient to produce the best simulation results for the computational resources available
A robust absorbing layer method for anisotropic seismic wave modeling
Métivier, L.; Brossier, R.; Labbé, S.; Operto, S.; Virieux, J.
2014-12-15
When applied to wave propagation modeling in anisotropic media, Perfectly Matched Layers (PML) exhibit instabilities. Incoming waves are amplified instead of being absorbed. Overcoming this difficulty is crucial as in many seismic imaging applications, accounting accurately for the subsurface anisotropy is mandatory. In this study, we present the SMART layer method as an alternative to PML approach. This method is based on the decomposition of the wavefield into components propagating inward and outward the domain of interest. Only outgoing components are damped. We show that for elastic and acoustic wave propagation in Transverse Isotropic media, the SMART layer is unconditionally dissipative: no amplification of the wavefield is possible. The SMART layers are not perfectly matched, therefore less accurate than conventional PML. However, a reasonable increase of the layer size yields an accuracy similar to PML. Finally, we illustrate that the selective damping strategy on which is based the SMART method can prevent the generation of spurious S-waves by embedding the source in a small zone where only S-waves are damped.
Modeling the anisotropic shock response of single-crystal RDX
NASA Astrophysics Data System (ADS)
Luscher, Darby
Explosives initiate under impacts whose energy, if distributed homogeneously throughout the material, translates to temperature increases that are insufficient to drive the rapid chemistry observed. Heterogeneous thermomechanical interactions at the meso-scale (i.e. between single-crystal and macroscale) leads to the formation of localized hot spots. Direct numerical simulations of mesoscale response can contribute to our understanding of hot spots if they include the relevant deformation mechanisms that are essential to the nonlinear thermomechanical response of explosive molecular crystals. We have developed a single-crystal model for the finite deformation thermomechanical response of cyclotrimethylene trinitramine (RDX). Because of the low symmetry of RDX, a complete description of nonlinear thermoelasticity requires a careful decomposition of free energy into components that represent the pressure-volume-temperature (PVT) response and the coupling between isochoric deformation and both deviatoric and hydrostatic stresses. An equation-of-state (EOS) based on Debye theory that defines the PVT response was constructed using experimental data and density functional theory calculations. This EOS replicates the equilibrium states of phase transformation from alpha to gamma polymorphs observed in static high-pressure experiments. Lattice thermoelastic parameters defining the coupled isochoric free energy were obtained from molecular dynamics calculations and previous experimental data. Anisotropic crystal plasticity is modeled using Orowan's expression relating slip rate to dislocation density and velocity. Details of the theory will be presented followed by discussion of simulations of flyer plate impact experiments, including recent experiments diagnosed with in situ X-ray diffraction at the Advanced Photon Source. Impact conditions explored within the experimental effort have spanned shock pressures ranging from 1-10 GPa for several crystallographic orientations
3D time-domain airborne EM modeling for an arbitrarily anisotropic earth
NASA Astrophysics Data System (ADS)
Yin, Changchun; Qi, Yanfu; Liu, Yunhe
2016-08-01
Time-domain airborne EM data is currently interpreted based on an isotropic model. Sometimes, it can be problematic when working in the region with distinct dipping stratifications. In this paper, we simulate the 3D time-domain airborne EM responses over an arbitrarily anisotropic earth with topography by edge-based finite-element method. Tetrahedral meshes are used to describe the abnormal bodies with complicated shapes. We further adopt the Backward Euler scheme to discretize the time-domain diffusion equation for electric field, obtaining an unconditionally stable linear equations system. We verify the accuracy of our 3D algorithm by comparing with 1D solutions for an anisotropic half-space. Then, we switch attentions to effects of anisotropic media on the strengths and the diffusion patterns of time-domain airborne EM responses. For numerical experiments, we adopt three typical anisotropic models: 1) an anisotropic anomalous body embedded in an isotropic half-space; 2) an isotropic anomalous body embedded in an anisotropic half-space; 3) an anisotropic half-space with topography. The modeling results show that the electric anisotropy of the subsurface media has big effects on both the strengths and the distribution patterns of time-domain airborne EM responses; this effect needs to be taken into account when interpreting ATEM data in areas with distinct anisotropy.
Modelling the shock response of a damageable anisotropic composite material
NASA Astrophysics Data System (ADS)
Lukyanov, Alexander A.
2012-09-01
The purpose of this paper is the investigation of the effect of fibre orientation on the shock response of a damageable carbon fibre-epoxy composite (CFEC). A carbon fibre-epoxy composite (CFEC) shock response in the through-thickness orientation and in one of the fibre directions is significantly different. Modelling the effect of fibre orientation on the shock response of a CFEC has been performed using a generalised decomposition of the stress tensor [A.A. Lukyanov, Int. J. Plasticity 24, 140 (2008)] and an accurate extrapolation of high-pressure shock Hugoniot states to other thermodynamics states for shocked CFEC materials. The analysis of the experimental data subject to the linear relation between shock velocities and particle velocities has shown that damage softening process produces discontinuities both in value and slope in the generalized bulk shock velocity and particle velocity relation [A.A. Lukyanov, Eur Phys J B 74, 35 (2010)]. Therefore, in order to remove these discontinuities, the three-wave structure (non-linear anisotropic, fracture and isotropic elastic waves) that accompanies damage softening process is proposed in this work for describing CFEC behavior under shock loading. A numerical calculation shows that Hugoniot Stress Levels (HELs) agree with the experimental data for selected CFEC material in different directions at low and at high intensities. In the through-thickness orientation, the material behaves similar to a simple polymer. In the fibre direction, the proposed model explains a pronounced ramp, before at sufficiently high stresses, and a much faster rising shock above it. The results are presented and discussed, and future studies are outlined.
Notes on shear viscosity bound violation in anisotropic models
NASA Astrophysics Data System (ADS)
Ge, XianHui
2016-03-01
The shear viscosity bound violation in Einstein gravity for anisotropic black branes is discussed, with the aim of constraining the deviation of the shear viscosity-entropy density ratio from the shear viscosity bound using causality and thermodynamics analysis. The results show that no stringent constraints can be imposed. The diffusion bound in anisotropic phases is also studied. Ultimately, it is concluded that shear viscosity violation always occurs in cases where the equation of motion of the metric fluctuations cannot be written in a form identical to that of the minimally coupled massless scalar fields.
An analytical model of anisotropic low-field electron mobility in wurtzite indium nitride
NASA Astrophysics Data System (ADS)
Wang, Shulong; Liu, Hongxia; Song, Xin; Guo, Yulong; Yang, Zhaonian
2014-03-01
This paper presents a theoretical analysis of anisotropic transport properties and develops an anisotropic low-field electron analytical mobility model for wurtzite indium nitride (InN). For the different effective masses in the Γ-A and Γ-M directions of the lowest valley, both the transient and steady state transport behaviors of wurtzite InN show different transport characteristics in the two directions. From the relationship between velocity and electric field, the difference is more obvious when the electric field is low in the two directions. To make an accurate description of the anisotropic transport properties under low field, for the first time, we present an analytical model of anisotropic low-field electron mobility in wurtzite InN. The effects of different ionized impurity scattering models on the low-field mobility calculated by Monte Carlo method (Conwell-Weisskopf and Brooks-Herring method) are also considered.
NASA Astrophysics Data System (ADS)
Burkett, Michael W.; Clancy, Sean P.; Maudlin, Paul J.; Holian, Kathleen S.
2002-07-01
Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength have been implemented in the three-dimensional Conejo hydrodynamics code. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to obtain rigid body rotation. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Simple rectangular shear problems, R-Value problems, and Taylor cylinder impact data were used to verify and validate the implementation of the anisotropic model. A stretching rod problem (involving large strain and high strain-rate deformation) was selected to investigate the effects of material anisotropy. Conejo simulations of rod topology were compared for two anisotropic cases.
3D, 9-C anisotropic seismic modeling and inversion
NASA Astrophysics Data System (ADS)
Rusmanugroho, Herurisa
The most complete representation of an elastic medium consists of an elastic tensor with 21 independent moduli. All 21 can be estimated from compressional and shear wave polarization and slowness vectors corresponding to wide apertures of polar and azimuth angles. In isotropic media, when seismic source and receiver components have the same orientation (such as XX and YY), the reflection amplitude contours align approximately perpendicular to the particle motions. The mixed components (such as XY and YX) have amplitude patterns that are in symmetrical pairs of either the same, or of opposite, polarity on either side of the diagonal of the 9-C response matrix. In anisotropic media, amplitude variations with azimuth show the same basic patterns and symmetries as for isotropic, but with a superimposed tendency for alignment parallel to the strike of the vertical cracks. Solutions for elastic tensor elements from synthetic slowness and polarization data calculated directly from the Christoffel equation are more sensitive to the polar angle aperture than to the azimuth aperture. Nine-component synthetic elastic vertical seismic profile data for a model with triclinic symmetry calculated by finite-differencing allows estimation of the elastic 21 tensor elements in the vicinity of a three-component borehole receiver. Wide polar angle and azimuth apertures are needed for accurately estimating the elastic tensor elements. The tensor elements become less independent as the data apertures decrease. Results obtained by extracting slowness and polarization data from the corresponding synthetic seismograms show similar results. The inversion algorithm has produced good results from field vertical seismic profile data set from the Weyburn Field in Southern Saskatchewan in Canada. Synthetic nine-component seismograms calculated from the extracted tensor are able to explain most of the significant features in the field data. The inverted stiffness elastic tensor shows orthorhombic
Asymptotic modelling of a thermopiezoelastic anisotropic smart plate
NASA Astrophysics Data System (ADS)
Long, Yufei
Motivated by the requirement of modelling for space flexible reflectors as well as other applications of plate structures in engineering, a general anisotropic laminated thin plate model and a monoclinic Reissner-Mindlin plate model with thermal deformation, two-way coupled piezoelectric effect and pyroelectric effect is constructed using the variational asymptotic method, without any ad hoc assumptions. Total potential energy contains strain energy, electric potential energy and energy caused by temperature change. Three-dimensional strain field is built based on the concept of warping function and decomposition of the rotation tensor. The feature of small thickness and large in-plane dimension of plate structure helped to asymptotically simplify the three-dimensional analysis to a two-dimensional analysis on the reference surface and a one-dimensional analysis through the thickness. For the zeroth-order approximation, the asymptotically correct expression of energy is derived into the form of energetic equation in classical laminated plate theory, which will be enough to predict the behavior of plate structures as thin as a space flexible reflector. A through-the-thickness strain field can be expressed in terms of material constants and two-dimensional membrane and bending strains, while the transverse normal and shear stresses are not predictable yet. In the first-order approximation, the warping functions are further disturbed into a high order and an asymptotically correct energy expression with derivatives of the two-dimensional strains is acquired. For the convenience of practical use, the expression is transformed into a Reissner-Mindlin form with optimization implemented to minimize the error. Transverse stresses and strains are recovered using the in-plane strain variables. Several numerical examples of different laminations and shapes are studied with the help of analytical solutions or shell elements in finite element codes. The constitutive relation is
Ilegbusi, Olusegun; Li, Ziang; Min, Yugang; Meeks, Sanford; Kupelian, Patrick; Santhanam, Anand P
2012-01-01
The aim of this paper is to model the airflow inside lungs during breathing and its fluid-structure interaction with the lung tissues and the lung tumor using subject-specific elastic properties. The fluid-structure interaction technique simultaneously simulates flow within the airway and anisotropic deformation of the lung lobes. The three-dimensional (3D) lung geometry is reconstructed from the end-expiration 3D CT scan datasets of humans with lung cancer. The lung is modeled as a poro-elastic medium with anisotropic elastic property (non-linear Young's modulus) obtained from inverse lung elastography of 4D CT scans for the same patients. The predicted results include the 3D anisotropic lung deformation along with the airflow pattern inside the lungs. The effect is also presented of anisotropic elasticity on both the spatio-temporal volumetric lung displacement and the regional lung hysteresis. PMID:22356987
NASA Astrophysics Data System (ADS)
Kim, Kihong; Fried, Laurence; Yoh, Jack
2013-06-01
Initiation of detonation in some high explosives has shown strong anisotropic sensitivity under mechanical impact. Preferred directions of crystal orientation on shock initiation have been experimentally observed in pentaerythritol tetranitrate (PETN), which resulted in dramatic difference in the detonation sensitivity upon shock compression in different directions. The ignition and growth model based on empirical observation on the pressure-dependent initiation of detonation has been widely used to date. Since the model is independent of direction of compression, it is impossible to address sensitivity associated with preferred crystal orientation for establishing the go/no-go criteria. In this paper, we have proposed a new reaction flow model that is consistent with avaialble PETN experiments and atomistic calculations. A general tensor notation is utilized to fully address three-dimensional effect of the strain rate dependence to anisotropic detonation of PETN. K. Kim was supported by post-doctoral research fellowship from the National Research Foundation of Korea.
Extension of the model of the magnetic characteristics of anisotropic metallic glasses
NASA Astrophysics Data System (ADS)
Szewczyk, Roman
2007-07-01
This paper presents an extension of the Jiles-Atherton model, applied for modelling the magnetic characteristics of anisotropic amorphous material. The presented extension of the model takes into account changes in the parameter k during the magnetization process. Such an extension is physically judged. Moreover, the extended model shows the possibility of a novel achievement of good agreement between experimental data and modelled hysteresis loops. As a result, the extended Jiles-Atherton model may be applied for both technical applications and fundamental research focused on understanding the physical aspects of the magnetization process of anisotropic soft magnetic materials.
Diffusively anisotropic model for the deflagration-to-detonation transition
NASA Astrophysics Data System (ADS)
Kagan, Leonid; Sivashinsky, Gregory
2014-03-01
To elucidate the key mechanisms responsible for the transition from deflagrative to detonative combustion in smooth-walled channels, a reactive flow with anisotropic thermal and molecular diffusivities is considered. Setting the transverse diffusivities large compared to longitudinal diffusivities, the initially formed deflagration (despite no-slip boundary conditions) appears to be nearly planar and not accelerating. This, however, does not prevent its eventual abrupt transition to Chapman-Jouguet detonation.
Deficiencies in numerical models of anisotropic nonlinearly elastic materials.
Ní Annaidh, A; Destrade, M; Gilchrist, M D; Murphy, J G
2013-08-01
Incompressible nonlinearly hyperelastic materials are rarely simulated in finite element numerical experiments as being perfectly incompressible because of the numerical difficulties associated with globally satisfying this constraint. Most commercial finite element packages therefore assume that the material is slightly compressible. It is then further assumed that the corresponding strain-energy function can be decomposed additively into volumetric and deviatoric parts. We show that this decomposition is not physically realistic, especially for anisotropic materials, which are of particular interest for simulating the mechanical response of biological soft tissue. The most striking illustration of the shortcoming is that with this decomposition, an anisotropic cube under hydrostatic tension deforms into another cube instead of a hexahedron with non-parallel faces. Furthermore, commercial numerical codes require the specification of a 'compressibility parameter' (or 'penalty factor'), which arises naturally from the flawed additive decomposition of the strain-energy function. This parameter is often linked to a 'bulk modulus', although this notion makes no sense for anisotropic solids; we show that it is essentially an arbitrary parameter and that infinitesimal changes to it result in significant changes in the predicted stress response. This is illustrated with numerical simulations for biaxial tension experiments of arteries, where the magnitude of the stress response is found to change by several orders of magnitude when infinitesimal changes in 'Poisson's ratio' close to the perfect incompressibility limit of 1/2 are made. PMID:23011411
Modeling of anisotropic ablation of the concrete during Molten Core Concrete Interaction
NASA Astrophysics Data System (ADS)
Kang, Kyoung Min
This work proposes a model to explain concrete anisotropic ablation by corium during a Molten Corium Concrete Interaction (MCCI). As a result of recent MCCI prototypic material experiments, CCI and VULCANO tests, one observes that concrete ablation behavior consistently depends on the concrete materials used in the experiments. Specifically, tests with Limestone-Common-Sand (LCS) concrete yielded isotropic concrete ablation; i.e., equal axial and radial concrete erosion. This is in comparison to anisotropic ablation in tests with Siliceous (SIL) concrete, where radial ablation was much larger than axial ablation. This was an unexpected result, because prior results of many MCCI simulant experiments indicated that nearly isotropic ablation was expected in prototypic material experiments regardless of concrete type. A new phenomenological model is proposed in this work based on a hypothesis that unifies the result of both previous simulant and prototypic material experiments; i.e., heat transfer area enhancement and delayed gas release caused by the presence of un-melted solid aggregate material that enters the molten pool. This model offers a logical and phenomenological explanation concerning anisotropic ablation as well as the capability to simulate anisotropic ablation. This model is implemented into the CORQUENCH code as part of this work. Comparisons of simulation results obtained with this new model to the CCI experiments for cases with siliceous concrete and anisotropic ablation show better agreement with the test data than the existing model.
Implementation of an anisotropic turbulence model in the COMMIX-1C/ATM computer code
NASA Astrophysics Data System (ADS)
Bottoni, M.; Chang, F. C.
The computer code COMMIX-1C/ATM, which describes single-phase, three-dimensional transient thermofluid dynamic problems, provided the framework for the extension of the standard kappa-epsilon turbulence model to a six-equation model with additional transport equations for the turbulence heat fluxes and the variance of temperature fluctuations. The new model which allows simulation of anisotropic turbulence in stratified shear flows is referred to as the Anisotropic Turbulence Model (ATM). The ATM has been verified with numerical computations of stable and unstable stratified shear flow between parallel plates.
Effects of the January 2005 GLE/SEP events on minor atmospheric components
NASA Astrophysics Data System (ADS)
Storini, M.; Damiani, A.
It is known from long ago that solar energetic charged particles, driven by the geomagnetic field, are able to produce ionization at different altitudes of the terrestrial atmosphere. Moreover, they can initiate catalytic cycles for the ozone depletion, involving NOx (N+NO+NO2) and HOx (H, OH, HO2) components. Nevertheless, only in recent years it was possible to compare chemical models involving atmospheric minor components with satellite data. In this work we looked for effects of the GLE/SEP events occurred during January 2005 on the OH and HNO3 species of the atmosphere. Results show that there is a response on the minor atmospheric components, which is different in the winter and summer terrestrial hemispheres. *: This topic is faced for COST 724 Action and supported by the Italian Antarctic Research Program in the frame of Solar-Terrestrial Relations and partly performed for a PhD thesis under development at Siena University/Dept. of Earth Science.
Modelling surface waves in anisotropic structures I. Theory
NASA Astrophysics Data System (ADS)
Thomson, C. J.
1997-02-01
Surface-wave theory in generally-anisotropic laterally-homogeneous media is partially reformulated in order to obtain intuitively-expected extensions of classic body-wave ideas such as Maslov plane-wave summation, the geometrical-ray/WKBJ limit and source-receiver reciprocity. This is done using the 'reversal' symmetry of Chapman [Chapman, C.H., 1994. Reflection/transmission coefficient reciprocities in anisotropic media. Geophys. J. Int. 116, 498-501] to generalize the point-source treatment of Kennett [Kennett, B.L N., 1983. Seismic Wave Propagation in Stratified Media. Cambridge Univ. Press, Cambridge, UK] to a stack of anisotropic layers with complex elastic parameters, lateral slowness and frequency. The 2D-integral representation over horizontal slownesses is reduced by residues to a 1D integral over each mode's slowness or dispersion curve at fixed frequency and this may be considered a 1D Maslov summation over local plane waves tangential to the phase front. The residue calculation involves a modified form of the usual variational principle, in which the Lagrangian now contains reversed modes. The 1D slowness integral may be reduced by stationary-phase arguments to the geometrical-ray or WKBJ limit, provided the dispersion-surface curvature does not vanish. This limit satisfies reciprocity, as the reversal symmetry shows. Dimples on the dispersion surface will correspond to folds on the phase front and multiple arrivals. An appendix contains a discussion of orthogonality of the surface-wave modes in relation to the various wave-equation symmetries.
Magnetically nonlinear and anisotropic iron core model of synchronous reluctance motor
NASA Astrophysics Data System (ADS)
Štumberger, G.; Štumberger, B.; Dolinar, D.
2003-01-01
The magnetically nonlinear and anisotropic iron core model of a synchronous reluctance motor (SRM) is presented. The iron core model is given by the current-dependent flux linkages and their partial derivatives. It is included in a dynamic SRM model and confirmed through the comparison of measured and calculated results in the case of current-controlled linear synchronous reluctance servomotor.
Anisotropic models with two fluids in linear and quadratic forms of f( T) gravitational theories
NASA Astrophysics Data System (ADS)
Nashed, Gamal G. L.
2015-06-01
Recent astronomical observations show that the universe may be anisotropic on large scales. The Union2 SnIa data hint that the universe has a preferred direction. If such a cosmological privileged axis indeed exists, one has to consider an anisotropic expanding universe, instead of the isotropic cosmological model. In this study, we apply the field equations of quadratic form of the modified teleparallel gravitational theories, f( T)= T+ ɛT 2, to anisotropic model. We assume two fluid components, the matter components have two equation of states (EoS). We study different equation of states for the linear case and show that there is no recombination era between the two fluids. For the quadratic one, we assume two equations of state corresponding to dark matter. In this model we obtain an inflation model and show that the values of the parameter, in the early universe, ɛ are depend on the sign of the cosmological constant.
A 3-D elasticity theory based model for acoustic radiation from multilayered anisotropic plates.
Shen, C; Xin, F X; Lu, T J
2014-05-01
A theoretical model built upon three-dimensional elasticity theory is developed to investigate the acoustic radiation from multilayered anisotropic plates subjected to a harmonic point force excitation. Fourier transform technique and stationary phase method are combined to predict the far-field radiated sound pressure of one-side water immersed plate. Compared to equivalent single-layer plate models, the present model based on elasticity theory can differentiate radiated sound pressure between dry-side and wet-side excited cases, as well as discrepancies induced by different layer sequences for multilayered anisotropic plates. These results highlight the superiority of the present theoretical model especially for handling multilayered anisotropic structures. PMID:24815294
Semi-analytical modeling of acoustic beam divergence in homogeneous anisotropic half-spaces.
Kono, Naoyuki; Hirose, Sohichi
2016-02-01
Beam divergences of acoustical fields in semi-infinite homogeneous anisotropic media are calculated based on a semi-analytical model. The model for a plane source in a semi-infinite homogeneous anisotropic medium is proposed as an extended model for a point source in an infinite medium. Beam divergences propagating along crystallographic axes 〈100〉, 〈110〉, and 〈111〉 in a cubic crystal, a single crystalline Ni-based alloy, are measured and compared to calculation results for verifying the model. The contribution of beam divergence attenuation to the total attenuation for propagating in anisotropic polycrystalline materials is quantitatively evaluated in isolation from scattering attenuation effects. PMID:26508085
NASA Astrophysics Data System (ADS)
Plainaki, Christina; Mavromichalaki, Helen; Laurenza, Monica; Gerontidou, Maria; Kanellakopoulos, Anastasios; Storini, Marisa
2014-04-01
In this work, we apply an updated version of the Neutron Monitor (NM) Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model, in order to derive the characteristics of the ground-level enhancement (GLE) on 2012 May 17 (GLE71), the spectral properties of the related solar energetic particle (SEP) event, the spatial distributions of the high-energy solar cosmic ray fluxes at the top of the atmosphere, and the time evolution of the location of the GLE source. Our modeling, based uniquely on the use of ground-level NM data, leads to the following main results. The SEP spectrum related to GLE71 was rather soft during the whole duration of the event, manifesting some weak acceleration episodes only during the initial phase (at ~01:55-02:00 UT) and at ~02:30-02:35 UT and ~02:55-03:00 UT. The spectral index of the modeled SEP spectrum supports the coronal mass ejection-shock driven particle acceleration scenario, in agreement with past results based on the analysis of satellite measurements. During the initial phase of GLE71, the solar proton source at the top of the atmosphere was located above the northern hemisphere, implying that the asymptotic directions of viewing of the northern hemisphere NMs were more favorably located for registering the event than the southern ones. The spatial distribution of the solar proton fluxes at the top of the atmosphere during the main phase manifested a large variation along longitude and latitude. At the rigidity of 1 GV, the maximum primary solar proton flux resulted on the order of ~3 × 104 part. m-2 s-1 sr-1 GV-1.
Plainaki, Christina; Laurenza, Monica; Storini, Marisa; Mavromichalaki, Helen; Gerontidou, Maria; Kanellakopoulos, Anastasios
2014-04-20
In this work, we apply an updated version of the Neutron Monitor (NM) Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model, in order to derive the characteristics of the ground-level enhancement (GLE) on 2012 May 17 (GLE71), the spectral properties of the related solar energetic particle (SEP) event, the spatial distributions of the high-energy solar cosmic ray fluxes at the top of the atmosphere, and the time evolution of the location of the GLE source. Our modeling, based uniquely on the use of ground-level NM data, leads to the following main results. The SEP spectrum related to GLE71 was rather soft during the whole duration of the event, manifesting some weak acceleration episodes only during the initial phase (at ∼01:55-02:00 UT) and at ∼02:30-02:35 UT and ∼02:55-03:00 UT. The spectral index of the modeled SEP spectrum supports the coronal mass ejection-shock driven particle acceleration scenario, in agreement with past results based on the analysis of satellite measurements. During the initial phase of GLE71, the solar proton source at the top of the atmosphere was located above the northern hemisphere, implying that the asymptotic directions of viewing of the northern hemisphere NMs were more favorably located for registering the event than the southern ones. The spatial distribution of the solar proton fluxes at the top of the atmosphere during the main phase manifested a large variation along longitude and latitude. At the rigidity of 1 GV, the maximum primary solar proton flux resulted on the order of ∼3 × 10{sup 4} part. m{sup –2} s{sup –1} sr{sup –1} GV{sup –1}.
Modeling anisotropic flow and heat transport by using mimetic finite differences
NASA Astrophysics Data System (ADS)
Chen, Tao; Clauser, Christoph; Marquart, Gabriele; Willbrand, Karen; Büsing, Henrik
2016-08-01
Modeling anisotropic flow in porous or fractured rock often assumes that the permeability tensor is diagonal, which means that its principle directions are always aligned with the coordinate axes. However, the permeability of a heterogeneous anisotropic medium usually is a full tensor. For overcoming this shortcoming, we use the mimetic finite difference method (mFD) for discretizing the flow equation in a hydrothermal reservoir simulation code, SHEMAT-Suite, which couples this equation with the heat transport equation. We verify SHEMAT-Suite-mFD against analytical solutions of pumping tests, using both diagonal and full permeability tensors. We compare results from three benchmarks for testing the capability of SHEMAT-Suite-mFD to handle anisotropic flow in porous and fractured media. The benchmarks include coupled flow and heat transport problems, three-dimensional problems and flow through a fractured porous medium with full equivalent permeability tensor. It shows firstly that the mimetic finite difference method can model anisotropic flow both in porous and in fractured media accurately and its results are better than those obtained by the multi-point flux approximation method in highly anisotropic models, secondly that the asymmetric permeability tensor can be included and leads to improved results compared the symmetric permeability tensor in the equivalent fracture models, and thirdly that the method can be easily implemented in existing finite volume or finite difference codes, which has been demonstrated successfully for SHEMAT-Suite.
Damage spreading in 2-dimensional isotropic and anisotropic Bak-Sneppen models
NASA Astrophysics Data System (ADS)
Bakar, B.; Tirnakli, U.
2008-03-01
We implement the damage spreading technique on 2-dimensional isotropic and anisotropic Bak-Sneppen models. Our extensive numerical simulations show that there exists a power-law sensitivity to the initial conditions at the statistically stationary state (self-organized critical state). Corresponding growth exponent α for the Hamming distance and the dynamical exponent z are calculated. These values allow us to observe a clear data collapse of the finite size scaling for both versions of the Bak-Sneppen model. Moreover, it is shown that the growth exponent of the distance in the isotropic and anisotropic Bak-Sneppen models is strongly affected by the choice of the transient time.
Accurate modelling of anisotropic effects in austenitic stainless steel welds
NASA Astrophysics Data System (ADS)
Nowers, O. D.; Duxbury, D. J.; Drinkwater, B. W.
2014-02-01
The ultrasonic inspection of austenitic steel welds is challenging due to the formation of highly anisotropic and heterogeneous structures post-welding. This is due to the intrinsic crystallographic structure of austenitic steel, driving the formation of dendritic grain structures on cooling. The anisotropy is manifested as both a `steering' of the ultrasonic beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the quantitative effects and relative impacts of these phenomena are not well-understood. A semi-analytical simulation framework has been developed to allow the study of anisotropic effects in austenitic stainless steel welds. Frequency-dependent scatterers are allocated to a weld-region to approximate the coarse grain-structures observed within austenitic welds and imaged using a simulated array. The simulated A-scans are compared against an equivalent experimental setup demonstrating excellent agreement of the Signal to Noise (S/N) ratio. Comparison of images of the simulated and experimental data generated using the Total Focusing Method (TFM) indicate a prominent layered effect in the simulated data. A superior grain allocation routine is required to improve upon this.
Accurate modelling of anisotropic effects in austenitic stainless steel welds
Nowers, O. D.; Duxbury, D. J.; Drinkwater, B. W.
2014-02-18
The ultrasonic inspection of austenitic steel welds is challenging due to the formation of highly anisotropic and heterogeneous structures post-welding. This is due to the intrinsic crystallographic structure of austenitic steel, driving the formation of dendritic grain structures on cooling. The anisotropy is manifested as both a ‘steering’ of the ultrasonic beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the quantitative effects and relative impacts of these phenomena are not well-understood. A semi-analytical simulation framework has been developed to allow the study of anisotropic effects in austenitic stainless steel welds. Frequency-dependent scatterers are allocated to a weld-region to approximate the coarse grain-structures observed within austenitic welds and imaged using a simulated array. The simulated A-scans are compared against an equivalent experimental setup demonstrating excellent agreement of the Signal to Noise (S/N) ratio. Comparison of images of the simulated and experimental data generated using the Total Focusing Method (TFM) indicate a prominent layered effect in the simulated data. A superior grain allocation routine is required to improve upon this.
NASA Technical Reports Server (NTRS)
Luchini, Chris B.
1997-01-01
Development of camera and instrument simulations for space exploration requires the development of scientifically accurate models of the objects to be studied. Several planned cometary missions have prompted the development of a three dimensional, multi-spectral, anisotropic multiple scattering model of cometary coma.
NASA Astrophysics Data System (ADS)
Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.
2010-06-01
Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.
Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.
2010-06-15
Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.
Model-size reduction for the buckling and vibration analyses of anisotropic panels
NASA Technical Reports Server (NTRS)
Noor, A. K.; Whitworth, S. L.
1986-01-01
A computational procedure is presented for reducing the size of the model used in the buckling and vibration analyses of symmetric anisotropic panels to that of the corresponding orthotropic model. The key elements of the procedure are the application of an operator splitting technique through the decomposition of the material stiffness matrix of the panel into the sum of orthotropic and nonorthotropic (anisotropic) parts and the use of a reduction method through successive application of the finite element method and the classical Rayleigh-Ritz technique. The effectiveness of the procedure is demonstrated by numerical examples.
Thermoelectric conductivities, shear viscosity, and stability in an anisotropic linear axion model
NASA Astrophysics Data System (ADS)
Ge, Xian-Hui; Ling, Yi; Niu, Chao; Sin, Sang-Jin
2015-11-01
We study thermoelectric conductivities and shear viscosities in a holographically anisotropic model, which is dual to a spatially anisotropic N =4 super-Yang-Mills theory at finite chemical potential. Momentum relaxation is realized through perturbing the linear axion field. Ac conductivity exhibits a coherent/incoherent metal transition. Deviations from the Wiedemann-Franz law are also observed in our model. The longitudinal shear viscosity for prolate anisotropy violates the bound conjectured by Kovtun-Son-Starinets. We also find that thermodynamic and dynamical instabilities are not always equivalent by examining the Gubser-Mitra conjecture.
Clancy, S.P.; Burkett, M.W.; Maudlin, P.J.
1998-02-01
Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength are implemented in the two dimensional MESA hydrodynamics code. Quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure are utilized. An associative flow strength formulation incorporating these yield functions is solved using a geometric normal return method. A stretching rod problem is selected to investigate the effects of material anisotropy on a tensile plastic instability (necking). The rod necking rate and topology are compared for MESA simulations performed for both isotropic and anisotropic cases utilizing the elastic-perfectly-plastic and the Mechanical Threshold Stress flow stress models.
Clancy, S.P.; Burkett, M.W.; Maudlin, P.J.
1997-05-01
Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength are implemented in the two-dimensional MESA hydrodynamics code. Quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure are utilized. An associative flow strength formulation incorporating these yield functions is solved using a geometric normal return method. A stretching rod problem is selected to investigate the effects of material anisotropy on a tensile plastic instability (necking). The rod necking rate and topology are compared for MESA simulations performed for both isotropic and anisotropic cases utilizing the Mechanical Threshold Stress flow stress model.
Thick brane isotropization in a generalized 5D anisotropic standing wave braneworld model
NASA Astrophysics Data System (ADS)
Gogberashvili, Merab; Herrera–Aguilar, Alfredo; Malagón–Morejón, Dagoberto; Mora–Luna, Refugio Rigel; Nucamendi, Ulises
2013-04-01
We study a smooth cosmological solution within a generalized 5D standing wave braneworld modeled by gravity and a phantom scalar field. In this model the 3-brane is anisotropically warped along its spatial dimensions and contains a novel time-dependent scale factor that multiplies the anisotropic spatial interval of the 5D metric, a fact that allows us to study cosmological effects. By explicitly solving the bulk field equations we found a natural mechanism which isotropizes the braneworld for a wide class of natural initial conditions. We are able to give a physical interpretation of the anisotropic dissipation: as the anisotropic energy of the 3-brane rapidly leaks into the bulk through the nontrivial components of the nonlocal Weyl tensor projected to the brane, the bulk becomes less isotropic. At the same time, under the action of the 4D cosmological constant, the anisotropic braneworld super-exponentially isotropizes by itself, rendering a 3-brane with de Sitter symmetry embedded in a 5D de Sitter space-time, while the phantom scalar field exponentially vanishes.
Analytic models of anisotropic strange stars in f(T) gravity with off-diagonal tetrad
NASA Astrophysics Data System (ADS)
Zubair, M.; Abbas, G.
2016-01-01
This paper is devoted to study the analytic models of anisotropic compact stars in f(T) gravity (where T is torsion scalar), with non-diagonal tetrad. By taking the anisotropic source inside the spherically symmetric star, the equations of motions have been derived in the context of f(T) gravity. Krori and Barua metric which satisfies the physical requirement of a realistic star, has been applied to describe the compact objects like strange stars. We use the power law form of f(T) model to determine explicit relations of matter variables. Further, we have found the anisotropic behavior, energy conditions, stability and surface redshift of stars. Using the masses and radii of 4U1820-30, Her X-1, SAX J 1808-3658, we have determined the constants involved in metric components. Finally we discuss the graphical behavior of the analytic description of strange star candidates.
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model
NASA Astrophysics Data System (ADS)
Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin
2016-02-01
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as a control parameter driving the second-order critical end point Tc of the metal-insulator transition down to zero at t⊥c/t ≃0.2 . Below t⊥c, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far.
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model.
Lenz, Benjamin; Manmana, Salvatore R; Pruschke, Thomas; Assaad, Fakher F; Raczkowski, Marcin
2016-02-26
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t_{⊥} acts as a control parameter driving the second-order critical end point T_{c} of the metal-insulator transition down to zero at t_{⊥}^{c}/t≃0.2. Below t_{⊥}^{c}, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t_{⊥}^{c}, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far. PMID:26967431
Stress distribution in a premolar 3D model with anisotropic and isotropic enamel.
Munari, Laís S; Cornacchia, Tulimar P M; Moreira, Allyson N; Gonçalves, Jason B; De Las Casas, Estevam B; Magalhães, Cláudia S
2015-08-01
The aim of this study was to compare the areas of stress concentration in a three-dimensional (3D) premolar tooth model with anisotropic or isotropic enamel using the finite element method. A computed tomography was imported to an image processing program to create the tooth model which was exported to a 3D modeling program. The mechanical properties and loading conditions were prescribed in Abaqus. In order to evaluate stresses, axial and oblique loads were applied simulating realistic conditions. Compression stress was observed on the side of load application, and tensile stress was observed on the opposite side. Tensile stress was concentrated mainly in the cervical region and in the alveolar insertion bone. Although stress concentration analyses of the isotropic 3D models produced similar stress distribution results when compared to the anisotropic models, tensile stress values shown by anisotropic models were smaller than the isotropic models. Oblique loads resulted in higher values of tensile stresses, which concentrate mainly in the cervical area of the tooth and in the alveolar bone insertion. Anisotropic properties must be utilized in enamel stress evaluation in non-carious cervical lesions. PMID:25850984
Forward modeling of marine DC resistivity method for a layered anisotropic earth
NASA Astrophysics Data System (ADS)
Yin, Chang-Chun; Zhang, Ping; Cai, Jing
2016-06-01
Since the ocean bottom is a sedimentary environment wherein stratification is well developed, the use of an anisotropic model is best for studying its geology. Beginning with Maxwell's equations for an anisotropic model, we introduce scalar potentials based on the divergence-free characteristic of the electric and magnetic (EM) fields. We then continue the EM fields down into the deep earth and upward into the seawater and couple them at the ocean bottom to the transmitting source. By studying both the DC apparent resistivity curves and their polar plots, we can resolve the anisotropy of the ocean bottom. Forward modeling of a high-resistivity thin layer in an anisotropic half-space demonstrates that the marine DC resistivity method in shallow water is very sensitive to the resistive reservoir but is not influenced by airwaves. As such, it is very suitable for oil and gas exploration in shallowwater areas but, to date, most modeling algorithms for studying marine DC resistivity are based on isotropic models. In this paper, we investigate one-dimensional anisotropic forward modeling for marine DC resistivity method, prove the algorithm to have high accuracy, and thus provide a theoretical basis for 2D and 3D forward modeling.
NASA Astrophysics Data System (ADS)
Tricerri, Paolo; Dedè, Luca; Deparis, Simone; Quarteroni, Alfio; Robertson, Anne M.; Sequeira, Adélia
2015-03-01
This paper considers numerical simulations of fluid-structure interaction (FSI) problems in hemodynamics for idealized geometries of healthy cerebral arteries modeled by both nonlinear isotropic and anisotropic material constitutive laws. In particular, it focuses on an anisotropic model initially proposed for cerebral arteries to characterize the activation of collagen fibers at finite strains. In the current work, this constitutive model is implemented for the first time in the context of an FSI formulation. In this framework, we investigate the influence of the material model on the numerical results and, in the case of the anisotropic laws, the importance of the collagen fibers on the overall mechanical behavior of the tissue. With this aim, we compare our numerical results by analyzing fluid dynamic indicators, vessel wall displacement, Von Mises stress, and deformations of the collagen fibers. Specifically, for an anisotropic model with collagen fiber recruitment at finite strains, we highlight the progressive activation and deactivation processes of the fibrous component of the tissue throughout the wall thickness during the cardiac cycle. The inclusion of collagen recruitment is found to have a substantial impact on the intramural stress, which will in turn impact the biological response of the intramural cells. Hence, the methodology presented here will be particularly useful for studies of mechanobiological processes in the healthy and diseased vascular wall.
Gle1 functions during mRNA export in an oligomeric complex that is altered in human disease
Folkmann, Andrew W.; Collier, Scott E.; Zhan, Xiaoyan; Aditi; Ohi, Melanie D.; Wente, Susan R.
2013-01-01
The conserved multifunctional protein Gle1 regulates gene expression at multiple steps: nuclear messenger (m)RNA export, translation initiation, and translation termination. A GLE1 mutation (FinMajor) is causally linked to human lethal congenital contracture syndrome-1 (LCCS1); however, the resulting perturbations on Gle1 molecular function were unknown. FinMajor results in a Proline-Phenylalanine-Glutamine peptide insertion within the uncharacterized Gle1 coiled-coil domain. Here we find that Gle1 self-associates both in vitro and in living cells via the coiled-coil domain. Electron microscopy reveals high molecular mass Gle1 oligomers form ∼26 nm in diameter disk-shaped particles. With the Gle1-FinMajor protein, these particles are malformed. Moreover, functional assays document a specific requirement for proper Gle1 oligomerization during mRNA export but not for Gle1’s roles in translation. These results identify a novel mechanistic step in Gle1’s mRNA export function at nuclear pore complexes, and directly implicate altered export in LCCS1 disease pathology. PMID:24243016
NASA Astrophysics Data System (ADS)
Burkett, Michael; Clancy, Sean; Maudlin, Paul; Holian, Kathleen
2001-06-01
: Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength has been implemented in the three-dimensional CONEJO hydrodynamics code. CONEJO is an explicit, Eulerian continuum mechanics code that is utilized to predict formation processes associated with material deformation at elevated strain-rates and is a code development project under the Accelerated Strategic Computing Initiative (ASCI) program. Some special features of CONEJO include a high-order advection algorithm, a material interface tracking scheme, and van Leer monotonic advection-limiting. The anisotropic constitutive modeling is posed in an unrotated material frame using the theorem of polar decomposition to describe rigid body rotation. An Euler-Rodrigues description is used to quantify the rigid body rotations. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Associative flow formulations incorporating these yield functions were solved using a geometric normal return method. Simple rectangular shear problems, "R-value" problems, and Taylor cylinder impact test data were utilized to verify and validate the implementation of the anisotropic model. A "stretching rod" problem (involving large strain and strain-rate deformation) was selected to investigate the effects of material anisotropy for this deformation process. The rod necking rate and topology was compared for CONEJO simulations using several isotropic and anisotropic descriptions that utilized the Mechanical Threshold Stress (MTS) model.
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model
NASA Astrophysics Data System (ADS)
Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as control parameter driving the second-order critical endpoint Tc of the metal-insulator transition down to zero at t⊥c / t ~= 0 . 2 . Below t⊥c the volume of hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors whose location remains elusive so far. We acknowledge support by DFG research units FOR1807 and FOR1346, ERC Starting Grant No. 306897 and NSF Grant No. PHY11-25915, and computer support by the GWDG and Jülich Supercomputing Centre.
Modeling anisotropic plasmon excitations in self-assembled fullerenes
NASA Astrophysics Data System (ADS)
Iurov, Andrii; Gumbs, Godfrey; Gao, Bo; Huang, Danhong
2014-05-01
The plasmon excitations in Coulomb-coupled spherical two-dimensional electron gases (S2DEGs) reveal an interesting dependence on the displacement vector between the centers of the spheres with respect to the axis of quantization for the angular momentum quantum number L. Specifically, plasmon modes for a bundle of three S2DEGs have been obtained within the random-phase approximation. The inter-sphere Coulomb interaction matrix elements and their symmetry properties were also investigated in detail. The case of a bundle gives an adequate picture of the way in which the Coulomb interaction depends on the orbital angular momentum quantum number L and its projection M. We concluded that the interaction between the S2DEGs aligned at an angle of 45° with the axis of quantization is negligible compared to the interaction along and perpendicular to the quantization axis, which are themselves unequal to each other. Consequently, the plasmon excitation frequencies reveal an interesting orientational anisotropic coupling to an external electromagnetic field probing the charge density oscillations. Our result on the spatial correlation may be experimentally observable. In this connection, there have already been some experimental reports pointing to a similar effect in nanoparticles.
A Model with Ellipsoidal Scatterers for Polarimetric Remote Sensing of Anisotropic Layered Media
NASA Technical Reports Server (NTRS)
Nghiem, S. V.; Kwok, R.; Kong, J. A.; Shin, R. T.
1993-01-01
This paper presents a model with ellipsoidal scatterers for applications to polarimetric remote sensing of anisotropic layered media at microwave frequencies. The physical configuration includes an isotropic layer covering an anisotropic layer above a homogeneous half space. The isotropic layer consists of randomly oriented spheroids. The anisotropic layer contains ellipsoidal scatterers with a preferential vertical alignment and random azimuthal orientations. Effective permittivities of the scattering media are calculated with the strong fluctuation theory extended to account for the nonspherical shapes and the scatterer orientation distributions. On the basis of the analytic wave theory, dyadic Green's functions for layered media are used to derive polarimetric backscattering coefficients under the distorted Born approximation. The ellipsoidal shape of the scatterers gives rise to nonzero cross-polarized returns from the untilted anisotropic medium in the first-order approximation. Effects of rough interfaces are estimated by an incoherent addition method. Theoretical results and experimental data are matched at 9 GHz for thick first-year sea ice with a bare surface and with a snow cover at Point Barrow, Alaska. The model is then used to study the sensitivity of polarimetric backscattering coefficients with respect to correlation lengths representing the geometry of brine inclusions. Polarimetric signatures of bare and snow-covered sea ice are also simulated based on the model to investigate effects of different scattering mechanisms.
Bianchi type-II models in the presence of perfect fluid and anisotropic dark energy
NASA Astrophysics Data System (ADS)
Kumar, Suresh; Akarsu, Özgür
2012-06-01
The spatially homogeneous but totally anisotropic and non-flat Bianchi type-II cosmological model has been studied in general relativity in the presence of two minimally interacting fluids; a perfect fluid as the matter fluid and a hypothetical anisotropic fluid as the dark energy fluid. The Einstein field equations have been solved by applying two kinematical Ansätze: we have assumed the variation law for the mean Hubble parameter that yields a constant value of the deceleration parameter, and one of the components of the shear tensor has been considered proportional to the mean Hubble parameter. We have particularly dwelled on the accelerating models with non-divergent expansion anisotropy as the Universe evolves. Yielding the anisotropic pressure, the fluid we consider in the context of dark energy can produce results that can be produced in the presence of isotropic fluid in accordance with the ΛCDM cosmology. However, the derived model gives additional opportunities by being able to allow kinematics that cannot be produced in the presence of fluids that yield only isotropic pressure. We have obtained well-behaving cases where the anisotropy of the expansion and the anisotropy of the fluid converge to finite values (include zero) in the late Universe. We have also showed that, although the metric we consider is totally anisotropic, the anisotropy of the dark energy is constrained to be axially symmetric, as long as the overall energy momentum tensor possesses zero shear stress.
Calculations of diffuser flows with an anisotropic K-epsilon model
NASA Astrophysics Data System (ADS)
Zhu, J.; Shih, T.-H.
1995-10-01
A newly developed anisotropic K-epsilon model is applied to calculate three axisymmetric diffuser flows with or without separation. The new model uses a quadratic stress-strain relation and satisfies the realizability conditions, i.e., it ensures both the positivity of the turbulent normal stresses and the Schwarz' inequality between any fluctuating velocities. Calculations are carried out with a finite-element method. A second-order accurate, bounded convection scheme and sufficiently fine grids are used to ensure numerical credibility of the solutions. The standard K-epsilon model is also used in order to highlight the performance of the new model. Comparison with the experimental data shows that the anisotropic K-epsilon model performs consistently better than does the standard K-epsilon model in all of the three test cases.
Calculations of Diffuser Flows with an Anisotropic K-Epsilon Model
NASA Technical Reports Server (NTRS)
Zhu, J.; Shih, T.-H.
1995-01-01
A newly developed anisotropic K-epsilon model is applied to calculate three axisymmetric diffuser flows with or without separation. The new model uses a quadratic stress-strain relation and satisfies the realizability conditions, i.e., it ensures both the positivity of the turbulent normal stresses and the Schwarz' inequality between any fluctuating velocities. Calculations are carried out with a finite-element method. A second-order accurate, bounded convection scheme and sufficiently fine grids are used to ensure numerical credibility of the solutions. The standard K-epsilon model is also used in order to highlight the performance of the new model. Comparison with the experimental data shows that the anisotropic K-epsilon model performs consistently better than does the standard K-epsilon model in all of the three test cases.
Aldrin, John C.; Sabbagh, Harold A.; Murphy, R. Kim; Sabbagh, Elias H.
2011-06-23
Recent advances are presented to model discontinuities in random anisotropies that arise in certain materials, such as titanium alloys. A numerical model is developed to provide a full anisotropic representation of each crystalline in a gridded region of the material. Several simulated and experimental demonstrations are presented highlighting the effect of grain noise on eddy current measurements. Agreement between VIC-3D(c) model calculations and experimental data in titanium alloy specimens with known flaws is demonstrated.
Evaluation of Springback for DP980 S Rail Using Anisotropic Hardening Models
NASA Astrophysics Data System (ADS)
Choi, Jisik; Lee, Jinwoo; Bae, Gihyun; Barlat, Frederic; Lee, Myoung-Gyu
2016-07-01
The effect of anisotropic hardening models on springback of an S-rail part was investigated. Two advanced constitutive models based on distortional and kinematic hardening, which captured the Bauschinger effect, transient hardening, and permanent softening during strain path change, were implemented in a finite element (FE) code. In-plane compression-tension tests were performed to identify the model parameters. The springback of the S-rail after forming a 980 MPa dual-phase steel sheet sample was measured and analyzed using different hardening models. The comparison between experimental and FE results demonstrated that the advanced anisotropic hardening models, which are particularly suitable for non-proportional loading, significantly improved the springback prediction capability of an advanced high strength steel.
Microscopic model of the Knight shift in anisotropic and correlated metals
NASA Astrophysics Data System (ADS)
Hall, Bianca E.; Klemm, Richard A.
2016-01-01
We present a microscopic model of nuclear magnetic resonance in metals. The spin-1/2 local nucleus and its surrounding orbital electrons interact with the arbitrary constant \\boldsymbol{B}{0} and perpendicular time-oscillatory magnetic inductions \\boldsymbol{B}{1}(t) and with each other via an anisotropic hyperfine interaction. An Anderson-like Hamiltonian describes the excitations of the relevant occupied local orbital electrons into the conduction bands, each band described by an anisotropic effective mass with corresponding Landau orbits and an anisotropic spin \\boldsymbol{g} tensor. Local orbital electron correlation effects are included using the mean-field decoupling procedure of Lacroix. The Knight resonance frequency and corresponding linewidth shifts are evaluated to leading orders in the hyperfine and Anderson excitation interactions. While respectively proportional to {{≤ft({{B}1}/{{B}0}\\right)}2} and a constant for weak {{B}0}\\gg {{B}1} , both highly anisotropic shifts depend strongly upon \\boldsymbol{B}{0} when a Landau level is near the Fermi energy. Electron correlations affect the anisotropy of the linewidth shift. The model is easily generalizable to arbitrary nuclear spin I.
Anisotropic Coarse-Grained Model for Proteins Based On Gay–Berne and Electric Multipole Potentials
2015-01-01
Gay–Berne anisotropic potential has been widely used to evaluate the nonbonded interactions between coarse-grained particles being described as elliptical rigid bodies. In this paper, we are presenting a coarse-grained model for twenty kinds of amino acids and proteins, based on the anisotropic Gay–Berne and point electric multipole (EMP) potentials. We demonstrate that the anisotropic coarse-grained model, namely GBEMP model, is able to reproduce many key features observed from experimental protein structures (Dunbrack Library), as well as from atomistic force field simulations (using AMOEBA, AMBER, and CHARMM force fields), while saving the computational cost by a factor of about 10–200 depending on specific cases and atomistic models. More importantly, unlike other coarse-grained approaches, our framework is based on the fundamental intermolecular forces with explicit treatment of electrostatic and repulsion-dispersion forces. As a result, the coarse-grained protein model presented an accurate description of nonbonded interactions (particularly electrostatic component) between hetero/homodimers (such as peptide–peptide, peptide–water). In addition, the encouraging performance of the model was reflected by the excellent correlation between GBEMP and AMOEBA models in the calculations of the dipole moment of peptides. In brief, the GBEMP model given here is general and transferable, suitable for simulating complex biomolecular systems. PMID:24659927
Estimation of the cosmic ray ionization in the Earth's atmosphere during GLE71
NASA Astrophysics Data System (ADS)
Lev, Dorman
2016-07-01
DYASTIMA is an application, based on Geant4, which simulates the cascades of particles that are generated due to the interactions of cosmic ray particles with the atmospheres of the planets. The first version of DYASTIMA has been successfully applied to the Earth's atmosphere, providing results that are in accordance with the publications of other models. Since then, important improvements and extensions have been made to this application, including a graphical user interface environment that allows the more effective management of the configuration parameters. Also, the actual modeling of the atmosphere has been changed allowing the definition of more complex cases and at the same time providing, in a more efficient way (with respect to the program's previous version) enhanced outputs. In this work, we combine the new version of DYASTIMA with the NMBANGLE PPOLA model, that estimates the spectrum of SEPs during relativistic proton events using ground level neutron monitor data from the worldwide network. Such a joint model has as a primary scope the simulation of a SEP event and of its secondary products at different altitudes in the Earth's atmosphere, providing at the same time an estimation of the respective ionization rates and of their spatial and temporal dependence. We apply this joint model to GLE 71, on 17 May 2012, and we discuss the results.
NASA Astrophysics Data System (ADS)
Souvatzoglou, G.; Papaioannou, A.; Mavromichalaki, H.; Dimitroulakos, J.; Sarlanis, C.
2014-11-01
Whenever a significant intensity increase is being recorded by at least three neutron monitor stations in real-time mode, a ground level enhancement (GLE) event is marked and an automated alert is issued. Although, the physical concept of the algorithm is solid and has efficiently worked in a number of cases, the availability of real-time data is still an open issue and makes timely GLE alerts quite challenging. In this work we present the optimization of the GLE alert that has been set into operation since 2006 at the Athens Neutron Monitor Station. This upgrade has led to GLE Alert Plus, which is currently based upon the Neutron Monitor Database (NMDB). We have determined the critical values per station allowing us to issue reliable GLE alerts close to the initiation of the event while at the same time we keep the false alert rate at low levels. Furthermore, we have managed to treat the problem of data availability, introducing the Go-Back-N algorithm. A total of 13 GLE events have been marked from January 2000 to December 2012. GLE Alert Plus issued an alert for 12 events. These alert times are compared to the alert times of GOES Space Weather Prediction Center and Solar Energetic Particle forecaster of the University of Málaga (UMASEP). In all cases GLE Alert Plus precedes the GOES alert by ≈8-52 min. The comparison with UMASEP demonstrated a remarkably good agreement. Real-time GLE alerts by GLE Alert Plus may be retrieved by http://cosray.phys.uoa.gr/gle_alert_plus.html, http://www.nmdb.eu, and http://swe.ssa.esa.int/web/guest/space-radiation. An automated GLE alert email notification system is also available to interested users.
An anisotropic thermomechanical damage model for concrete at transient elevated temperatures.
Baker, Graham; de Borst, René
2005-11-15
The behaviour of concrete at elevated temperatures is important for an assessment of integrity (strength and durability) of structures exposed to a high-temperature environment, in applications such as fire exposure, smelting plants and nuclear installations. In modelling terms, a coupled thermomechanical analysis represents a generalization of the computational mechanics of fracture and damage. Here, we develop a fully coupled anisotropic thermomechanical damage model for concrete under high stress and transient temperature, with emphasis on the adherence of the model to the laws of thermodynamics. Specific analytical results are given, deduced from thermodynamics, of a novel interpretation on specific heat, evolution of entropy and the identification of the complete anisotropic, thermomechanical damage surface. The model is also shown to be stable in a computational sense, and to satisfy the laws of thermodynamics. PMID:16243703
Microscopic model of the Knight shift in anisotropic and correlated metals
NASA Astrophysics Data System (ADS)
Klemm, Richard; Hall, Bianca
We present a microscopic model of nuclear magnetic resonance in metals. The spins of the spin-1/2 local nucleus and its surrounding orbital electrons interact with the arbitrary constant B0 and perpendicular time-oscillatory magnetic inductions B1 (t) and with each other via an anisotropic hyperfine interaction. An Anderson-like Hamiltonian describes the excitations of the relevant occupied local orbital electrons into the conduction bands, each band described by an anisotropic effective mass with corresponding Landau orbits and an anisotropic spin g tensor. Local orbital electron correlation effects are included using the mean-field decoupling procedure of Lacroix. The Knight resonance frequency and corresponding linewidth shifts are evaluated to leading orders in the hyperfine and Anderson excitation interactions. While respectively proportional to (B1 /B0) 2 and a constant for weak B0 > >B1 , both highly anisotropic shifts depend strongly upon B0 when a Landau level is near the Fermi energy. Electron correlations affect the anisotropy of the linewidth shift. The authors acknowledge support from an anonymous donor.
A rock physics model for analysis of anisotropic parameters in a shale reservoir in Southwest China
NASA Astrophysics Data System (ADS)
Qian, Keran; Zhang, Feng; Chen, Shuangquan; Li, Xiangyang; Zhang, Hui
2016-02-01
A rock physics model is a very effective tool to describe the anisotropy and mechanical properties of rock from a seismology perspective. Compared to a conventional reservoir, modelling a shale reservoir requires us to face two main challenges in modelling: the existence of organic matter and strong anisotropy. We construct an anisotropic rock physics workflow for a typical shale reservoir in Southwest China, in which the organic matter is treated separately from other minerals by using a combination of anisotropic self-consistent approximation and the differential effective medium method. The standard deviation of the distribution function is used to model the degree of lamination of clay and kerogen. A double scan workflow is introduced to invert the probability of pore aspect ratio and lamination simultaneously, which can give us a better understanding of the shale formation. The anisotropic properties of target formation have been analysed based on the proposed model. Inverted Thomsen parameters, especially the sign of delta, are analysed in terms of the physical properties of rock physics modelling.
NASA Astrophysics Data System (ADS)
Hallez, Hans; Staelens, Steven; Lemahieu, Ignace
2009-10-01
EEG source analysis is a valuable tool for brain functionality research and for diagnosing neurological disorders, such as epilepsy. It requires a geometrical representation of the human head or a head model, which is often modeled as an isotropic conductor. However, it is known that some brain tissues, such as the skull or white matter, have an anisotropic conductivity. Many studies reported that the anisotropic conductivities have an influence on the calculated electrode potentials. However, few studies have assessed the influence of anisotropic conductivities on the dipole estimations. In this study, we want to determine the dipole estimation errors due to not taking into account the anisotropic conductivities of the skull and/or brain tissues. Therefore, head models are constructed with the same geometry, but with an anisotropically conducting skull and/or brain tissue compartment. These head models are used in simulation studies where the dipole location and orientation error is calculated due to neglecting anisotropic conductivities of the skull and brain tissue. Results show that not taking into account the anisotropic conductivities of the skull yields a dipole location error between 2 and 25 mm, with an average of 10 mm. When the anisotropic conductivities of the brain tissues are neglected, the dipole location error ranges between 0 and 5 mm. In this case, the average dipole location error was 2.3 mm. In all simulations, the dipole orientation error was smaller than 10°. We can conclude that the anisotropic conductivities of the skull have to be incorporated to improve the accuracy of EEG source analysis. The results of the simulation, as presented here, also suggest that incorporation of the anisotropic conductivities of brain tissues is not necessary. However, more studies are needed to confirm these suggestions.
Automatic implementation of finite strain anisotropic hyperelastic models using hyper-dual numbers
NASA Astrophysics Data System (ADS)
Kiran, Ravi; Khandelwal, Kapil
2015-01-01
The main aim of this paper is to automate the implementation of finite strain anisotropic hyperelastic models into a general finite element framework. The automation presented in this paper enables the end-user to implement a hyperelastic model by programming its Helmholtz free energy function alone. The automation is achieved by employing hyper-dual number system to evaluate analytical quality derivatives. New perturbation techniques are introduced and are employed to extend the hyper-dual numbers system to evaluate tensor derivatives. The capability of the proposed automation scheme is demonstrated by implementing five finite strain anisotropic hyperelastic models. The merits and demerits of the proposed automation scheme are compared to an automation scheme based on the central difference method.
Short-time dynamics of isotropic and anisotropic Bak-Sneppen model: extensive simulation results
NASA Astrophysics Data System (ADS)
Tirnakli, Ugur; Lyra, Marcelo L.
2004-12-01
In this work, the short-time dynamics of the isotropic and anisotropic versions of the Bak-Sneppen (BS) model has been investigated using the standard damage spreading technique. Since the system sizes attained in our simulations are larger than the ones employed in previous studies, our results for the dynamic scaling exponents are expected to be more accurate than the results of the existing literature. The obtained scaling exponents of both versions of the BS model are found to be greater than the ones given in previous works. These findings are in agreement with the recent claim of Cafiero et al. (Eur. Phys. J. B7 (1999) 505). Moreover, it is found that the short-time dynamics of the anisotropic model is only slightly affected by finite-size effects and the reported estimate of α≃0.53 can be considered as a good estimate of the true exponent in the thermodynamic limit.
NASA Astrophysics Data System (ADS)
Yan, Dandan; Zhang, Jianwei; Wu, Weijuan; Ying, Xiaoyan; Wu, Xiangping
2009-10-01
This paper is focused on the sophisticated realistic head modeling based on inhomogeneous and anisotropic conductivity distribution of the head tissues. The finite element method (FEM) was used to model the five-layer head volume conductor models with hexahedral elements from segmentation and mapping of DT-MRI data. Then the inhomogeneous conductivities of the scalp, CSF and gray matter tissue were distributed according a normal distribution based on the mean value of respective tissues. The electric conductivity of the brain tissues dictates different inhomogeneous and anisotropic at some different microscopic levels. Including the inhomogeneous and anisotropy of the tissue would improve the accuracy of the MREIT, EEG and MEG problems in the simulation research.
NASA Astrophysics Data System (ADS)
Kondoh, Hiroshi; Matsushita, Mitsugu
1986-10-01
Diffusion-limited aggregation (DLA) model with anisotropic sticking probability Ps is computer-simulated on two dimensional square lattice. The cluster grows from a seed particle at the origin in the positive y area with the absorption-type boundary along x-axis. The cluster is found to grow anisotropically as R//˜Nν// and R\\bot˜Nν\\bot, where R\\bot and R// are the radii of gyration of the cluster along x- and y-axes, respectively, and N is the particle number constituting the cluster. The two exponents are shown to become assymptotically ν//{=}2/3, ν\\bot{=}1/3 whenever the sticking anisotropy exists. It is also found that the present model is fairly consistent with Hack’s law of river networks, suggesting that it is a good candidate of a prototype model for the evolution of the river network.
A heterogeneity model comparison of highly resolved statistically anisotropic aquifers
NASA Astrophysics Data System (ADS)
Siirila-Woodburn, Erica R.; Maxwell, Reed M.
2015-01-01
Aquifer heterogeneity is known to affect solute characteristics such as spatial spreading, mixing, and residence time, and is often modeled geostatistically to address aquifer uncertainties. While parameter uncertainty is often considered, the model uncertainty of the heterogeneity structure is frequently ignored. In this high-resolution heterogeneity model comparison, we perform a stochastic analysis utilizing spatial moment and breakthrough curve (BTC) metrics on Gaussian (G), truncated Gaussian (TG), and non-Gaussian, or "facies" (F) heterogeneous domains. Three-dimensional plume behavior is rigorously assessed with meter (horizontal) and cm (vertical) scale discretization over a ten-kilometer aquifer. Model differences are quantified as a function of statistical anisotropy, ε, by varying the x-direction integral scale of hydraulic conductivity, K, from 15 to 960 (m). We demonstrate that the model is important only for certain metrics within a range of ε. For example, spreading is insensitive to the model selection at low ε, but not at high ε. In contrast, center of mass is sensitive to the model selection at low ε, and not at high ε. A conceptual model to explain these trends is proposed and validated with BTC metrics. Simulations show that G model effective K, and 1st and 2nd spatial moments are much greater than that of TG and F models. A comparison of G and TG models (which only differ in K-distribution tails) reveal drastically different behavior, exemplifying how accurate characterization of the K-distribution may be important in modeling efforts, especially in aquifers where extreme K values are often not measured, or inadvertently overlooked.
Magnetization process modeling of anisotropic magnetoresistive permalloy films
NASA Astrophysics Data System (ADS)
Hauser, H.; Fulmek, P. L.
2003-01-01
The results of model calculations by the Jiles-Atherton approach and the energetic model (EM) of ferromagnetic hysteresis are discussed. In contrast to other phenomenological models, the EM parameters are calculated directly from the angle of the magnetization with respect to the easy axis. The transversal Kerr-effect is used to determine the magnetic properties of thin ferromagnetic permalloy films with uniaxial anisotropy.
Modeling anisotropic MHD turbulence in simulations of liquid metal flows
NASA Astrophysics Data System (ADS)
Widlund, O.
2001-06-01
The dynamical properties of the MHD turbulence model proposed by Widlund etal. are examined for the case of homogeneous decaying turbulence. The model is a Reynolds stress closure, extended with a transport equation for a dimensional anisotropy variable, α, which carries information about length scale anisotropy. The analysis suggests that the model term originally proposed for the nonlinear energy transfer in the α equation should be modified. A unique set of model coefficients could be determined, which makes the model consistent with theory and experiments for interaction parameters N ranging from zero to infinity. The model coincides with the standard K-eps model when there is no magnetic field. In the linear regime of large N, it produces the K˜ t^{-1/2} energy decay predicted by linear theory. When nonlinear effects are important, the model predicts K˜ t^{-1.7} and L_∥ ˜ t^{0.65}, in agreement with the classical experiments by Alemany etal. Figs 5, Refs 11.
Implementation of an anisotropic mechanical model for shale in Geodyn
Attaia, A.; Vorobiev, O.; Walsh, S.
2015-05-15
The purpose of this report is to present the implementation of a shale model in the Geodyn code, based on published rock material models and properties that can help a petroleum engineer in his design of various strategies for oil/gas recovery from shale rock formation.
NASA Astrophysics Data System (ADS)
Barrow, John D.; Ganguly, Chandrima
2016-06-01
We study the behaviour of Bianchi class A universes containing an ultra-stiff isotropic ghost field and a fluid with anisotropic pressures which is also ultra-stiff on the average. This allows us to investigate whether cyclic universe scenarios, like the ekpyrotic model, do indeed lead to isotropization on approach to a singularity (or bounce) in the presence of dominant ultra-stiff pressure anisotropies. We specialize to consider the closed Bianchi type IX universe, and show that when the anisotropic pressures are stiffer on average than any isotropic ultra-stiff fluid then, if they dominate on approach to the singularity, it will be anisotropic. We include an isotropic ultra-stiff ghost fluid with negative energy density in order to create a cosmological bounce at finite volume in the absence of the anisotropic fluid. When the dominant anisotropic fluid is present it leads to an anisotropic cosmological singularity rather than an isotropic bounce. The inclusion of anisotropic stresses generated by collisionless particles in an anisotropically expanding universe is therefore essential for a full analysis of the consequences of a cosmological bounce or singularity in cyclic universes.
An analysis of 3D anisotropic-viscoelastic forward modeling and dissipation
NASA Astrophysics Data System (ADS)
Yang, Chunying; Li, Xiang-Yang; Wang, Yun
2015-12-01
The anisotropic-viscoelastic wave equation is a generalized expression of a transversely isotropic-viscoelastic medium. The viscoelastic horizontal-tranverse isotropic (HTI) medium is a special case. Considering the horizontal symmetry axis of viscoelastic HTI media, we develop elasticities and wave equations for preserving its transverse isotropy. To model anisotropic-viscoelastic wave propagation, we apply the fourth-order Runge-Kutta and Fourier pseudospectral method to discretize the wave equation. The convolutional perfectly matched layer (CPML) absorbed boundary condition is applied to the 3D modeling algorithm and the result shows that it absorbs reflected energy efficiently. We present three models to investigate anisotropic-viscoelastic waves. Two half-space models demonstrate the azimuthal attenuation, which appears both on the PP and PSv wave. The quality factor is greater along the fracture direction for both the PP and PSv waves. Analysis shows that frequency-dependent amplitude attenuation behaves differently along the fracture azimuth. This demonstates that we can use this property for reservoir detection.
NASA Astrophysics Data System (ADS)
Jeong, Woo Chul; Wi, Hun; Sajib, Saurav Z. K.; Oh, Tong In; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je
2015-08-01
Electromagnetic fields provide fundamental data for the imaging of electrical tissue properties, such as conductivity and permittivity, in recent magnetic resonance (MR)-based tissue property mapping. The induced voltage, current density, and magnetic flux density caused by externally injected current are critical factors for determining the image quality of electrical tissue conductivity. As a useful tool to identify bio-electromagnetic phenomena, precise approaches are required to understand the exact responses inside the human body subject to an injected currents. In this study, we provide the numerical simulation results of electromagnetic field mapping of brain tissues using a MR-based conductivity imaging method. First, we implemented a realistic three-dimensional human anisotropic head model using high-resolution anatomical and diffusion tensor MR images. The voltage, current density, and magnetic flux density of brain tissues were imaged by injecting 1 mA of current through pairs of electrodes on the surface of our head model. The current density map of anisotropic brain tissues was calculated from the measured magnetic flux density based on the linear relationship between the water diffusion tensor and the electrical conductivity tensor. Comparing the current density to the previous isotropic model, the anisotropic model clearly showed the differences between the brain tissues. This originates from the enhanced signals by the inherent conductivity contrast as well as the actual tissue condition resulting from the injected currents.
Geodesic acoustic mode in anisotropic plasmas using double adiabatic model and gyro-kinetic equation
Ren, Haijun; Cao, Jintao
2014-12-15
Geodesic acoustic mode in anisotropic tokamak plasmas is theoretically analyzed by using double adiabatic model and gyro-kinetic equation. The bi-Maxwellian distribution function for guiding-center ions is assumed to obtain a self-consistent form, yielding pressures satisfying the magnetohydrodynamic (MHD) anisotropic equilibrium condition. The double adiabatic model gives the dispersion relation of geodesic acoustic mode (GAM), which agrees well with the one derived from gyro-kinetic equation. The GAM frequency increases with the ratio of pressures, p{sub ⊥}/p{sub ∥}, and the Landau damping rate is dramatically decreased by p{sub ⊥}/p{sub ∥}. MHD result shows a low-frequency zonal flow existing for all p{sub ⊥}/p{sub ∥}, while according to the kinetic dispersion relation, no low-frequency branch exists for p{sub ⊥}/p{sub ∥}≳ 2.
Analysis of a theoretical model for anisotropic enzyme membranes application to enzyme electrodes.
Pedersen, H; Chotani, G K
1981-12-01
A theoretical model of diffusion and reaction in an anisotropic enzyme membrane is presented with particular emphasis on the application of such membranes in enzyme electrodes. The dynamic response of systems in which the kinetics are linear, which comprises the practical operating regime for enzyme electrodes in analysis, is investigated via an analytic solution of the governing differential equations. The response is presented as a function of a single dimensionless group, Μ, that is the membrane modulus. PMID:24233978
NASA Astrophysics Data System (ADS)
Dani, I.; Tahiri, N.; Ez-Zahraouy, H.; Benyoussef, A.
2016-08-01
In this paper we study, using mean field theory (MFT), the effect of the anisotropic Dzyaloshinskii-Moriya (DM) interaction on the phase diagrams of the spin-half Ashkin-Teller model on hypercubic lattice. Different new phase diagrams are found by varying the anisotropy of DM interaction. The multicritical behavior is studied as a function of four-spin interaction coefficient J4 /J1 and for two fixed values of spin interaction coefficient J2 /J1.
Large scale behavior of a two-dimensional model of anisotropic branched polymers.
Knežević, Milan; Knežević, Dragica
2013-10-28
We study critical properties of anisotropic branched polymers modeled by semi-directed lattice animals on a triangular lattice. Using the exact transfer-matrix approach on strips of quite large widths and phenomenological renormalization group analysis, we obtained pretty good estimates of various critical exponents in the whole high-temperature region, including the point of collapse transition. Our numerical results suggest that this collapse transition belongs to the universality class of directed percolation. PMID:24182076
Large scale behavior of a two-dimensional model of anisotropic branched polymers
NASA Astrophysics Data System (ADS)
Knežević, Milan; Knežević, Dragica
2013-10-01
We study critical properties of anisotropic branched polymers modeled by semi-directed lattice animals on a triangular lattice. Using the exact transfer-matrix approach on strips of quite large widths and phenomenological renormalization group analysis, we obtained pretty good estimates of various critical exponents in the whole high-temperature region, including the point of collapse transition. Our numerical results suggest that this collapse transition belongs to the universality class of directed percolation.
Kao, Philip H; Lammers, Steven R; Hunter, Kendall; Stenmark, Kurt R; Shandas, Robin; Qi, H Jerry
2010-04-01
Many biological materials are composites composed of a soft matrix reinforced with stiffer fibers. These stiffer fibers may have a tortuous shape and wind through the soft matrix. At small material deformation, these fibers deform in a bending mode and contribute little to the material stiffness; at large material deformation, these fibers deform in a stretching mode and induce a stiffening effect in the material behavior. The transition from bending mode deformation to stretching mode deformation yields a characteristic J-shape stress-strain curve. In addition, the spatial distribution of these fibers may render the composite an anisotropic behavior. In this paper, we present an anisotropic finite-deformation hyperelastic constitutive model for such materials. Here, the matrix is modeled as an isotropic neo-Hookean material. "The behaviors of single tortuous fiber are represented by a crimped fiber model". The anisotropic behavior is introduced by a structure tensor representing the effective orientation distribution of crimped fibers. Parametric studies show the effect of fiber tortuosity and fiber orientation distribution on the overall stress-strain behaviors of the materials. PMID:21822502
Accelerating numerical modeling of wave propagation through 2-D anisotropic materials using OpenCL.
Molero, Miguel; Iturrarán-Viveros, Ursula
2013-03-01
We present an implementation of the numerical modeling of elastic waves propagation, in 2D anisotropic materials, using the new parallel computing devices (PCDs). Our study is aimed both to model laboratory experiments and explore the capabilities of the emerging PCDs by discussing performance issues. In the experiments a sample plate of an anisotropic material placed inside a water tank is rotated and, for every angle of rotation it is subjected to an ultrasonic wave (produced by a large source transducer) that propagates in the water and through the material producing some reflection and transmission signals that are recording by a "point-like" receiver. This experiment is numerically modeled by running a finite difference code covering a set of angles θ∈[-50°, 50°], and recorded the signals for the transmission and reflection results. Transversely anisotropic and weakly orthorhombic materials are considered. We accelerated the computation using an open-source toolkit called PyOpenCL, which lets one to easily access the OpenCL parallel computation API's from the high-level programming environment of Python. A speedup factor over 19 using the GPU is obtained when compared with the execution of the same program in parallel using a CPU multi-core (in this case we use the 4-cores that has the CPU). The performance for different graphic cards and operating systems is included together with the full 2-D finite difference code with PyOpenCL. PMID:23290584
Modeling of Anisotropic Rock Joints Under Cyclic Loading (Invited)
NASA Astrophysics Data System (ADS)
White, J. A.
2013-12-01
This work describes a constitutive framework for modeling the behavior of rough joints under cyclic loading. Particular attention is paid to the intrinsic links between dilatancy, surface degradation, and mobilized shear strength. The framework also accounts for the important effect of shear-induced anisotropy. Both the governing formulation and an algorithm for implicit numerical integration are presented. While the proposed methods are general, we also postulate a specific model that is compared with experimental data. It employs relatively few free parameters, but shows good agreement with laboratory tests.
Intersecting S-branes and an anisotropic models of dark energy
Orlov, Dmitry G.
2008-10-10
We consider an anisotropic S-brane (space-like hyperbrane) solutions in application to cosmological model. The gravity-dilaton-antisymmetric form field initial model is compactified of extra space and we get four dimensional space (space of three dimensional S-brane plus time coordinate). Dynamic of obtained model depends from the dynamic of compactified space. In all cases of extra space in such cosmological models the primordial inflationary phase was obtained. Focus attention to the question of an anisotropy of space and an improving a number of e-folding.
Anisotropic, nonsingular early universe model leading to a realistic cosmology
Dechant, Pierre-Philippe; Lasenby, Anthony N.; Hobson, Michael P.
2009-02-15
We present a novel cosmological model in which scalar field matter in a biaxial Bianchi IX geometry leads to a nonsingular 'pancaking' solution: the hypersurface volume goes to zero instantaneously at the 'big bang', but all physical quantities, such as curvature invariants and the matter energy density remain finite, and continue smoothly through the big bang. We demonstrate that there exist geodesics extending through the big bang, but that there are also incomplete geodesics that spiral infinitely around a topologically closed spatial dimension at the big bang, rendering it, at worst, a quasiregular singularity. The model is thus reminiscent of the Taub-NUT vacuum solution in that it has biaxial Bianchi IX geometry and its evolution exhibits a dimensionality reduction at a quasiregular singularity; the two models are, however, rather different, as we will show in a future work. Here we concentrate on the cosmological implications of our model and show how the scalar field drives both isotropization and inflation, thus raising the question of whether structure on the largest scales was laid down at a time when the universe was still oblate (as also suggested by [T. S. Pereira, C. Pitrou, and J.-P. Uzan, J. Cosmol. Astropart. Phys. 9 (2007) 6.][C. Pitrou, T. S. Pereira, and J.-P. Uzan, J. Cosmol. Astropart. Phys. 4 (2008) 4.][A. Guemruekcueoglu, C. Contaldi, and M. Peloso, J. Cosmol. Astropart. Phys. 11 (2007) 005.]). We also discuss the stability of our model to small perturbations around biaxiality and draw an analogy with cosmological perturbations. We conclude by presenting a separate, bouncing solution, which generalizes the known bouncing solution in closed FRW universes.
Anisotropic, nonsingular early universe model leading to a realistic cosmology
NASA Astrophysics Data System (ADS)
Dechant, Pierre-Philippe; Lasenby, Anthony N.; Hobson, Michael P.
2009-02-01
We present a novel cosmological model in which scalar field matter in a biaxial Bianchi IX geometry leads to a nonsingular “pancaking” solution: the hypersurface volume goes to zero instantaneously at the “big bang”, but all physical quantities, such as curvature invariants and the matter energy density remain finite, and continue smoothly through the big bang. We demonstrate that there exist geodesics extending through the big bang, but that there are also incomplete geodesics that spiral infinitely around a topologically closed spatial dimension at the big bang, rendering it, at worst, a quasiregular singularity. The model is thus reminiscent of the Taub-NUT vacuum solution in that it has biaxial Bianchi IX geometry and its evolution exhibits a dimensionality reduction at a quasiregular singularity; the two models are, however, rather different, as we will show in a future work. Here we concentrate on the cosmological implications of our model and show how the scalar field drives both isotropization and inflation, thus raising the question of whether structure on the largest scales was laid down at a time when the universe was still oblate (as also suggested by [T. S. Pereira, C. Pitrou, and J.-P. Uzan, J. Cosmol. Astropart. Phys.1475-7516 9 (2007) 6.10.1088/1475-7516/2007/09/006][C. Pitrou, T. S. Pereira, and J.-P. Uzan, J. Cosmol. Astropart. Phys.1475-7516 4 (2008) 4.10.1088/1475-7516/2008/04/004][A. Gümrükçüoǧlu, C. Contaldi, and M. Peloso, J. Cosmol. Astropart. Phys.1475-7516 11 (2007) 005.10.1088/1475-7516/2007/11/005]). We also discuss the stability of our model to small perturbations around biaxiality and draw an analogy with cosmological perturbations. We conclude by presenting a separate, bouncing solution, which generalizes the known bouncing solution in closed FRW universes.
Dynamical analysis of anisotropic cosmological model with quintessence
NASA Astrophysics Data System (ADS)
Chaubey, R.; Raushan, Rakesh
2016-07-01
The present work is a phase-plane analysis of LRS Bianchi type I cosmological model with a scalar field and exponential potential. The evolution equations are reduced to an autonomous system of ordinary equations by suitable transformation of variables. We also analyse the evolution of the effective equation of state parameter for different values of curvature. The nature of critical points is analysed and stable attractors are examined from the point of view of cosmology.
Sun, Weitao; He, Jing
2011-01-01
The criterion to determine residue contact is a fundamental problem in deriving knowledge-based mean-force potential energy calculations for protein structures. A frequently used criterion is to require the side chain center-to-center distance or the -to- atom distance to be within a pre-determined cutoff distance. However, the spatially anisotropic nature of the side chain determines that it is challenging to identify the contact pairs. This study compares three side chain contact models: the Atom Distance criteria (ADC) model, the Isotropic Sphere Side chain (ISS) model and the Anisotropic Ellipsoid Side chain (AES) model using 424 high resolution protein structures in the Protein Data Bank. The results indicate that the ADC model is the most accurate and ISS is the worst. The AES model eliminates about 95% of the incorrectly counted contact-pairs in the ISS model. Algorithm analysis shows that AES model is the most computational intensive while ADC model has moderate computational cost. We derived a dataset of the mis-estimated contact pairs by AES model. The most misjudged pairs are Arg-Glu, Arg-Asp and Arg-Tyr. Such a dataset can be useful for developing the improved AES model by incorporating the pair-specific information for the cutoff distance. PMID:21552527
NASA Astrophysics Data System (ADS)
Dayanandan, Baiju; Maurya, S. K.; Gupta, Y. K.; Smitha, T. T.
2016-05-01
We present a detailed investigation of the stability of anisotropic compact star models by introducing Matese and Whitman (Phys. Rev. D 11:1270, 1980) solution in general relativity. We have particularly looked into the detailed investigation of the measurements of basic physical parameters such as radial pressure, tangential pressure, energy density, red shift, sound velocity, masses and radii are affected by unknown effects such as loss, accretion and diffusion of mass. Those give insight into the characteristics of the compact astrophysical object with anisotropic matter distribution as well as the physical reality. The results obtained for the physical feature of compact stars such as, Her. X-1, RXJ 1856-37, SAX J1808.4-3658(SS2) and SAX J1808.4-3658(SS1) are compared to the recently observed massive compact object.
Spreading and wandering of Gaussian–Schell model laser beams in an anisotropic turbulent ocean
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Zhu, Yun; Hu, Zhengda
2016-09-01
The effect of anisotropic turbulence on the spreading and wandering of Gaussian–Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens–Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.
Model-size reduction technique for the analysis of symmetric anisotropic structures
NASA Technical Reports Server (NTRS)
Noor, A. K.; Peters, J. M.
1985-01-01
A two-step computational procedure is presented for reducing the size of the analysis model for an anisotropic symmetric structure to that of the corresponding orthotropic structure. The key elements of the procedure are: (1) decomposition of the stiffness matrix into the sum of an orthotropic and nonorthotropic (anisotropic) parts; and (2) successive application of the finite element method and the classical Rayleigh-Ritz technique. The finite element method is first used to generate few global approximation vectors (or modes). Then the amplitudes of these modes are computed by using the Rayleigh-Ritz technique. The global approximation vectors are selected to be the solution corresponding to zero nonorthotropic matrix and its various-order derivatives with respect to an anisotropic tracing parameter (identifying the nonorthotropic material coefficients). The size of the analysis model used in generating the global approximation vectors is identical to that of the corresponding orthotropic structure. The effectiveness of the proposed technique is demonstrated by means of numerical examples and its potential for solving other quasi-symmetric problems is discussed.
Formation of Bragg band gaps in anisotropic phononic crystals analyzed with the empty lattice model
Wang, Yan -Feng; Maznev, Alexei; Laude, Vincent
2016-05-11
Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic andmore » anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg "planes" which give rise to phononic band gaps, are generally not flat planes but curved surfaces. Lastly, the same is found to be the case for avoided crossings between shear (transverse) and longitudinal bands in the isotropic case.« less
Towards an Anisotropic Whole Mantle 3D Elastic Velocity Model
NASA Astrophysics Data System (ADS)
Panning, M. P.; Romanowicz, B.; Gung, Y.
2001-12-01
Many studies have documented the existence of anisotropy in the earth's upper mantle, concentrated in the top 200 km. This evidence comes from the study of surface waves as well as shear wave splitting. There is also evidence for shear wave splitting in D", at least in well sampled regions. There are some hints of anisotropy at the base of the transition zone. Tomographic models of the upper mantle have been developed with simplifying assumptions about the nature of the anisotropy, in order to minimize the number of free parameters in the inversions. Some assume transverse isotropy (e.g Ekström and Dziewonski, 1997), others include additional degrees of freedom with some realistic constraints on mineralogy (e.g. Montagner and Tanimoto, 1991). Our goal is to investigate anisotropy in the whole mantle, using the framework of waveform inversion, and the nonlinear asymptotic mode coupling theory (NACT), previously developed and applied to the construction of whole-mantle SH velocity models (Li and Romanowicz, 1996; Mégnin and Romanowicz, 2000). For this we require a 3 component dataset, and we have extended our automatic transverse (T) component wavepicking procedures to the vertical (Z) and longitudinal (L) component - a non-trivial task given the large number of phases present in the coupled P-SV system. A useful initial assumption, for which the theory has been readily adapted, is that of transverse isotropy. As a first step towards this, we have been investigating inversions using T component and Z,L component data separately. In particular, this allows us to explore the sampling that can be achieved with Z,L component data alone in the deepest part of the mantle. Indeed, D" is in general much better sampled in SH than in SV, owing to the availability of SHdiff at large distances, while SVdiff decays more rapidly due to mantle-core coupling. We present the results of our resolution experiments and discuss the differences between the 3D SV model obtained in well
Stripe orientation in an anisotropic t-J model
Kampf, Arno P.; Scalapino, Douglas J.; White, Steven R.
2001-08-01
The tilt pattern of the CuO{sub 6} octahedra in the low-temperature tetragonal (LTT) phase of the cuprate superconductors leads to planar anisotropies for the exchange coupling and hopping integrals. Here, we show that these anisotropies provide a possible structural mechanism for the orientation of stripes. A t{sub x}-t{sub y}-J{sub x}-J{sub y} model thus serves as an effective Hamiltonian to describe stripe formation and orientation in LTT-phase cuprates.
GLE Observations in 23rd Solar Cycle at the Baksan Air Shower Arrays Andyrchy and Carpet
NASA Astrophysics Data System (ADS)
Karpov, S. N.; Alekseenko, V. V.; Djappuev, D. D.; Karpova, Z. M.; Khaerdinov, N. S.; Petkov, V. B.; Radchenkov, A. V.; Zaichenko, A. N.
2003-07-01
Total counting rates of two Baksan extensive air shower arrays Andyrchy and Carp et were examined during 10 Ground Level Enhancements (GLE) of Solar Cosmic Rays (SCR) observed in current 23rd cycle of solar activity. In this case the threshold primary energy is equal to geomagnetic cut-off, Emin = 5.8 GeV. Significant increases (>3 st.dev.) above the galactic cosmic ray background were found during 6 GLE events from 10. The amplitudes of all increases make the tenth shares of percent. Therefore, they can not be registered by neutron monitors with a close geomagnetic cut-off.
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Modeling anisotropic properties of media with oriented fractures
NASA Astrophysics Data System (ADS)
Chergoleishvili, T. T.; Balabuyev, A. A.; Mandzhgaladze, P. F.
1984-05-01
Fracture formation at the focus of an impending earthquake occurs along a definite orientation governed by tectonic shears. The effectiveness of the many methods used in the theoretical computation of the elastic properties of such media was assessed in laboratory experiments using models with controllable parameters. The propagation velocity of longitudinal and transverse waves were investigated. Experimental results are compared with computations made by different methods. The curves corresponding to different theories quantitatively differ greatly from one another but there is a satisfactory correspondence of the shape of both the theoretical and experimental curves, revealing a uniformity of the dependence of wave propagation velocity on angle of approach to the oriented system of fractures. An attempt is made to resolve various discrepancies.
Synthetic Seismograms for Realistic 3D Earth Model with Anisotropic Inner Core
NASA Astrophysics Data System (ADS)
Tsuboi, S.; Tono, Y.
2006-12-01
We have demonstrated that we can calculate global theoretical seismograms for realistic 3D Earth models based upon the combination of a precise numerical technique (the spectral-element method) and a sufficiently fast supercomputer (the Earth Simulator) [Tsuboi et al, 2003]. Here we have calculated synthetic seismograms by using model S20RTS of the mantle (Ritsema et al., 1999), model CRUST2.0 of the crust (Basin et al., 2000), topography and bathymetry model ETOPO5, and anisotropic inner core model (Ishii 2002). The calculations are performed on 4056 processors, which require 507 out of 640 nodes of the Earth Simulator. These synthetics are computed by using SPECFEM3D(Komatitsch and Tromp, 2002) and are accurate up to 3.5 seconds. We have calculated these synthetics with aisotropic inner core model for several earthquakes and compared with the synthetics which are calculated for isotropic inner core model. Preliminary comparison shows that the travel time differences between anisotropic inner core model and isotropic core model for PKPab phases are at most a few seconds. There seems to be no significant differences in waveforms of PKP phases. These differences in travel times may help us to improve inner core fine structure by comparing these synthetics with observation.
Inter-comparison of isotropic and anisotropic sea ice rheology in a fully coupled model
NASA Astrophysics Data System (ADS)
Roberts, A.; Cassano, J. J.; Maslowski, W.; Osinski, R.; Seefeldt, M. W.; Hughes, M.; Duvivier, A.; Nijssen, B.; Hamman, J.; Hutchings, J. K.; Hunke, E. C.
2015-12-01
We present the sea ice climate of the Regional Arctic System Model (RASM), using a suite of new physics available in the Los Alamos Sea Ice Model (CICE5). RASM is a high-resolution fully coupled pan-Arctic model that also includes the Parallel Ocean Program (POP), the Weather Research and Forecasting Model (WRF) and Variable Infiltration Capacity (VIC) land model. The model domain extends from ~45˚N to the North Pole and is configured to run at ~9km resolution for the ice and ocean components, coupled to 50km resolution atmosphere and land models. The baseline sea ice model configuration includes mushy-layer sea ice thermodynamics and level-ice melt ponds. Using this configuration, we compare the use of isotropic and anisotropic sea ice mechanics, and evaluate model performance using these two variants against observations including Arctic buoy drift and deformation, satellite-derived drift and deformation, and sea ice volume estimates from ICESat. We find that the isotropic rheology better approximates spatial patterns of thickness observed across the Arctic, but that both rheologies closely approximate scaling laws observed in the pack using buoys and RGPS data. A fundamental component of both ice mechanics variants, the so called Elastic-Viscous-Plastic (EVP) and Anisotropic-Elastic-Plastic (EAP), is that they are highly sensitive to the timestep used for elastic sub-cycling in an inertial-resolving coupled framework, and this has a significant affect on surface fluxes in the fully coupled framework.
Rullmann, M.; Anwander, A.; Dannhauer, M.; Warfield, S.K.; Duffy, F.H.; Wolters, C.H.
2009-01-01
The major goal of the evaluation in presurgical epilepsy diagnosis for medically intractable patients is the precise reconstruction of the epileptogenic foci, preferably with non-invasive methods. This paper evaluates whether surface electroencephalography (EEG) source analysis based on a 1mm anisotropic finite element (FE) head model can provide additional guidance for presurgical epilepsy diagnosis and whether it is practically feasible in daily routine. A 1mm hexahedra FE volume conductor model of the patient’s head with special focus on accurately modeling the compartments skull, cerebrospinal fluid (CSF) and the anisotropic conducting brain tissues was constructed using non-linearly co-registered T1-, T2- and diffusion-tensor- magnetic resonance imaging data. The electrodes of intra-cranial EEG (iEEG) measurements were extracted from a co-registered computed tomography image. Goal function scan (GFS), minimum norm least squares (MNLS), standardized low resolution electromagnetic tomography (sLORETA) and spatio-temporal current dipole modeling inverse methods were then applied to the peak of the averaged ictal discharges EEG data. MNLS and sLORETA pointed to a single center of activity. Moving and rotating single dipole fits resulted in an explained variance of more than 97%. The non-invasive EEG source analysis methods localized at the border of the lesion and at the border of the iEEG electrodes which mainly received ictal discharges. Source orientation was towards the epileptogenic tissue. For the reconstructed superficial source, brain conductivity anisotropy and the lesion conductivity had only a minor influence, whereas a correct modeling of the highly conducting CSF compartment and the anisotropic skull was found to be important. The proposed FE forward modeling approach strongly simplifies meshing and reduces run-time (37 Milliseconds for one forward computation in the model with 3.1 Million unknowns), corroborating the practical feasibility of the
Self-Similar Cosmologies in 5D: Spatially Flat Anisotropic Models
NASA Astrophysics Data System (ADS)
Ponce de Leon, J.
In the context of theories of the Kaluza-Klein type, with a large extra dimension, we study self-similar cosmological models in 5D that are homogeneous, anisotropic and spatially flat. The "ladder" to go between the physics in 5D and in 4D is provided by Campbell-Maagard's embedding theorems. We show that the 5D field equations RAB = 0 determine the form of the similarity variable. There are three different possibilities: homothetic, conformal and "wavelike" solutions in 5D. We derive the most general homothetic and conformal solutions to the 5D field equations. They require the extra dimension to be spacelike, and are given in terms of one arbitrary function of the similarity variable and three parameters. The Riemann tensor in 5D is not zero, except in the isotropic limit, which corresponds to the case where the parameters are equal to each other. The solutions can be used as 5D embeddings for a great variety of 4D homogeneous cosmological models, with and without matter, including the Kasner universe. Since the extra dimension is spacelike, the 5D solutions are invariant under the exchange of spatial coordinates. Therefore they also embed a family of spatially inhomogeneous models in 4D. We show that these models can be interpreted as vacuum solutions in braneworld theory. Our work (I) generalizes the 5D embeddings used for FLRW models; (II) shows that anisotropic cosmologies are, in general, curved in 5D, in contrast with FLRW models, which can always be embedded in a 5D Riemann-flat (Minkowski) manifold; and (III) reveals that anisotropic cosmologies can be curved and devoid of matter, both in 5D and in 4D, even when the metric in 5D explicitly depends on the extra coordinate, which is quite different from the isotropic case.
NASA Astrophysics Data System (ADS)
Qin, Linjiang; Yang, Changfu
2016-06-01
The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In this study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modelling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.
NASA Astrophysics Data System (ADS)
Linjiang, QIN; Changfu, YANG
2016-03-01
The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In the present study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modeling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.
Life prediction and constitutive models for engine hot section anisotropic materials program
NASA Technical Reports Server (NTRS)
Swanson, G. A.
1985-01-01
The purpose is to develop life prediction models for coated anisotropic materials used in gas temperature airfoils. Two single crystal alloys and two coatings are now being tested. These include PWA 1480; Alloy 185; overlay coating, PWA 286; and aluminide coating, PWA 273. Constitutive models are also being developed for these materials to predict the plastic and creep strain histories of the materials in the lab tests and for actual design conditions. This nonlinear material behavior is particularily important for high temperature gas turbine applications and is basic to any life prediction system.
NASA Astrophysics Data System (ADS)
Bolokhov, S. V.; Ivashchuk, V. D.
We analyse the global causal structure of a family of multidimensional spherically-symmetric solutions with a horizon which appear in the model with 1-component anisotropic fluid. This family can be considered as a generalized analogs of the well-known black hole solutions (including the Reissner--Nordström one) and some black brane solutions. The structure of regular horizons and singular boundaries is studied, and the corresponding Carter--Penrose diagrams are constructed for various values of the parameters of the model.
Adaptive Phase-Field Modeling of Anisotropic Wetting with Line Tension at the Triple Junction.
Yeh, S Y; Lan, C W
2015-09-01
Line tension could affect the contact angle at triple junction, especially in micro- to nanoscale wetting. We have developed an adaptive phase-field model to consider the line tension quantitatively. This model is coupled to the smoothed boundary method for treating the contact line with the solid phase, while the volume constraint is imposed. Our calculated contact angles are in good agreement with the modified Young's equation. Further examples are illustrated for the anisotropic wetting on hydrophilic/hydrophobic stripes and rectangular grooves. PMID:26274914
Dynamic analysis of rotor flex-structure based on nonlinear anisotropic shell models
NASA Astrophysics Data System (ADS)
Bauchau, Olivier A.; Chiang, Wuying
1991-05-01
In this paper an anisotropic shallow shell model is developed that accommodates transverse shearing deformations and arbitrarily large displacements and rotations, but strains are assumed to remain small. Two kinematic models are developed, the first using two DOF to locate the direction of the normal to the shell's midplane, the second using three. The latter model allows for an automatic compatibility of the shell model with beam models. The shell model is validated by comparing its predictions with several benchmark problems. In actual helicopter rotor blade problems, the shell model of the flex structure is shown to give very different results shown compared to beam models. The lead-lag and torsion modes in particular are strongly affected, whereas flapping modes seem to be less affected.
Debbaut, Charlotte; Vierendeels, Jan; Siggers, Jennifer H; Repetto, Rodolfo; Monbaliu, Diethard; Segers, Patrick
2014-01-01
The hepatic blood circulation is complex, particularly at the microcirculatory level. Previously, 2D liver lobule models using porous media and a 3D model using real sinusoidal geometries have been developed. We extended these models to investigate the role of vascular septa (VS) and anisotropic permeability. The lobule was modelled as a hexagonal prism (with or without VS) and the tissue was treated as a porous medium (isotropic or anisotropic permeability). Models were solved using computational fluid dynamics. VS inclusion resulted in more spatially homogeneous perfusion. Anisotropic permeability resulted in a larger axial velocity component than isotropic permeability. A parameter study revealed that results are most sensitive to the lobule size and radial pressure drop. Our model provides insight into hepatic microhaemodynamics, and suggests that inclusion of VS in the model leads to perfusion patterns that are likely to reflect physiological reality. The model has potential for applications to unphysiological and pathological conditions. PMID:23237543
Nonlinear inversion for arbitrarily-oriented anisotropic models II: Inversion techniques
NASA Astrophysics Data System (ADS)
Bremner, P. M.; Panning, M. P.
2011-12-01
We present output models from inversion of a synthetic surface wave dataset. We implement new 3-D finite-frequency kernels, based on the Born approximation, to invert for upper mantle structure beneath western North America. The kernels are formulated based on a hexagonal symmetry with an arbitrary orientation. Numerical tests were performed to achieve a robust inversion scheme. Four synthetic input models were created, to include: isotropic, constant strength anisotropic, variable strength anisotropic, and both anisotropic and isotropic together. The reference model was a simplified version of PREM (dubbed PREM LIGHT) in which the crust and 220 km discontinuity have been removed. Output models from inversions of calculated synthetic data are compared against these input models to test for accurate reproduction of input model features, and the resolution of those features. The object of this phase of the study was to determine appropriate nonlinear inversion schemes that adequately recover the input models. The synthetic dataset consists of collected seismic waveforms of 126 earthquake mechanisms, of magnitude 6-7 from Dec 2006 to Feb 2009, from the IRIS database. Events were selected to correlate with USArray deployments, and to have as complete an azimuthal coverage as possible. The events occurred within a circular region of radius 150o centered about 44o lat, -110o lon (an arbitrary location within USArray coverage). Synthetic data were calculated utilizing a spectral element code (SEM) coupled to a normal mode solution. The mesh consists of a 3-D heterogeneous outer shell, representing the upper mantle above 450 km depth, coupled to a spherically symmetric inner sphere. From the synthetic dataset, multi-taper fundamental mode surface wave phase delay measurements are taken. The orthogonal 2.5π -prolate spheroidal wave function eigentapers (Slepian tapers) reduce noise biasing, and can provide error estimates in phase delay measurements. This study is a
Identification and analysis of LNO1-Like and AtGLE1-Like Nucleoporins in plants
Braud, Christopher; Zheng, Wenguang; Xiao, Wenyan
2013-01-01
Nucleoporins (Nups) are building blocks of the nuclear pore complex (NPC) that mediate cargo trafficking between the nucleus and the cytoplasm. Although the physical structure of the NPC is well studied in yeast and vertebrates, little is known about the structure of NPCs or the function of most Nups in plants. Recently we demonstrated two Nups in Arabidopsis: LONO1 (LNO1), homolog of human NUP214 and yeast Nup159, and AtGLE1, homolog of yeast Gle1, are required for early embryogenesis and seed development. To identify LNO1 and AtGLE1 homologs in other plant species, we searched the protein databases and identified 30 LNO1-like and 35 AtGLE1-like proteins from lower plant species to higher plants. Furthermore, phylogenetic analyses indicate that the evolutionary trees of these proteins follow expected plant phylogenies. High sequence homology and conserved domain structure of these nucleoporins suggest important functions of these proteins in nucleocytoplasmic transport, growth and development in plants. PMID:24384931
A new anisotropic compact star model having Matese & Whitman mass function
NASA Astrophysics Data System (ADS)
Bhar, Piyali; Ratanpal, B. S.
2016-07-01
Present paper proposed a new singularity free model of anisotropic compact star. The Einstein field equations are solved in closed form by utilizing Matese & Whitman mass function. The model parameters ρ, pr and pt all are well behaved inside the stellar interior and our model satisfies all the required conditions to be physically acceptable. The model given in the present work is compatible with observational data of compact objects like SAX J 1808.4-3658 (SS1), SAX J 1808.4-3658 (SS2) and 4U 1820-30. A particular model of 4U 1820-30 is studied in detail and found that it satisfies all the condition needed for physically acceptable model. The present work is the generalization of Sharma and Ratanpal (Int. J. Mod. Phys. D 22:1350074, 2013) model for compact stars admitting quadratic equation of state.
NASA Astrophysics Data System (ADS)
Thesberg, Mischa; Sørensen, Erik S.
2014-10-01
Ground- and excited-state quantum fidelities in combination with generalized quantum fidelity susceptibilites, obtained from exact diagonalizations, are used to explore the phase diagram of the anisotropic next-nearest-neighbour triangular Heisenberg model. Specifically, the J‧ - J2 plane of this model, which connects the J1 - J2 chain and the anisotropic triangular lattice Heisenberg model, is explored using these quantities. Through the use of a quantum fidelity associated with the first excited-state, in addition to the conventional ground-state fidelity, the BKT-type transition and Majumdar-Ghosh point of the J1 - J2 chain (J‧ = 0) are found to extend into the J‧ - J2 plane and connect with points on the J2 = 0 axis thereby forming bounded regions in the phase diagram. These bounded regions are then explored through the generalized quantum fidelity susceptibilities χρ, χ120\\circ , χD and χCAF which are associated with the spin stiffness, 120° spiral order parameter, dimer order parameter and collinear antiferromagnetic order parameter respectively. These quantities are believed to be extremely sensitive to the underlying phase and are thus well suited for finite-size studies. Analysis of the fidelity susceptibilities suggests that the J‧, J2 ≪ J phase of the anisotropic triangular model is either a collinear antiferromagnet or possibly a gapless disordered phase that is directly connected to the Luttinger phase of the J1 - J2 chain. Furthermore, the outer region is dominated by incommensurate spiral physics as well as dimer order.
NASA Astrophysics Data System (ADS)
Seddik, Hakime; Greve, Ralf; Placidi, Luca; Hamann, Ilka; Gagliardini, Olivier
We present an application of the newly developed CAFFE model (Continuum-mechanical, Anisotropic Flow model based on an anisotropic Flow Enhancement factor) to the EPICA ice core at Kohnen Station, Dronning Maud Land, Antarctica (referred to as the EDML core). A one-dimensional flow model for the site is devised, which includes the anisotropic flow law and the fabric evolution equation of the CAFFE model. Three different solution methods are employed: (1) computing the ice flow based on the flow law of the CAFFE model and the measured fabrics; (2) solving the CAFFE fabric evolution equation under the simplifying assumption of transverse isotropy; and (3) solving the unrestricted CAFFE fabric evolution equation. Method (1) demonstrates clearly the importance of the anisotropic fabric in the ice column for the flow velocity. The anisotropic enhancement factor produced with method (2) agrees reasonably well with that of method (1), even though the measured fabric shows a girdle structure (which breaks the transverse isotropy) in large parts of the ice core. For method (3), we find that the measured fabric is reproduced well by the model down to ˜2100m depth. Systematic deviations at greater depths are attributed to the disregard of migration recrystallization in the model.
Multiscale Gaussian network model (mGNM) and multiscale anisotropic network model (mANM)
NASA Astrophysics Data System (ADS)
Xia, Kelin; Opron, Kristopher; Wei, Guo-Wei
2015-11-01
Gaussian network model (GNM) and anisotropic network model (ANM) are some of the most popular methods for the study of protein flexibility and related functions. In this work, we propose generalized GNM (gGNM) and ANM methods and show that the GNM Kirchhoff matrix can be built from the ideal low-pass filter, which is a special case of a wide class of correlation functions underpinning the linear scaling flexibility-rigidity index (FRI) method. Based on the mathematical structure of correlation functions, we propose a unified framework to construct generalized Kirchhoff matrices whose matrix inverse leads to gGNMs, whereas, the direct inverse of its diagonal elements gives rise to FRI method. With this connection, we further introduce two multiscale elastic network models, namely, multiscale GNM (mGNM) and multiscale ANM (mANM), which are able to incorporate different scales into the generalized Kirchhoff matrices or generalized Hessian matrices. We validate our new multiscale methods with extensive numerical experiments. We illustrate that gGNMs outperform the original GNM method in the B-factor prediction of a set of 364 proteins. We demonstrate that for a given correlation function, FRI and gGNM methods provide essentially identical B-factor predictions when the scale value in the correlation function is sufficiently large. More importantly, we reveal intrinsic multiscale behavior in protein structures. The proposed mGNM and mANM are able to capture this multiscale behavior and thus give rise to a significant improvement of more than 11% in B-factor predictions over the original GNM and ANM methods. We further demonstrate the benefits of our mGNM through the B-factor predictions of many proteins that fail the original GNM method. We show that the proposed mGNM can also be used to analyze protein domain separations. Finally, we showcase the ability of our mANM for the analysis of protein collective motions.
Multiscale Gaussian network model (mGNM) and multiscale anisotropic network model (mANM).
Xia, Kelin; Opron, Kristopher; Wei, Guo-Wei
2015-11-28
Gaussian network model (GNM) and anisotropic network model (ANM) are some of the most popular methods for the study of protein flexibility and related functions. In this work, we propose generalized GNM (gGNM) and ANM methods and show that the GNM Kirchhoff matrix can be built from the ideal low-pass filter, which is a special case of a wide class of correlation functions underpinning the linear scaling flexibility-rigidity index (FRI) method. Based on the mathematical structure of correlation functions, we propose a unified framework to construct generalized Kirchhoff matrices whose matrix inverse leads to gGNMs, whereas, the direct inverse of its diagonal elements gives rise to FRI method. With this connection, we further introduce two multiscale elastic network models, namely, multiscale GNM (mGNM) and multiscale ANM (mANM), which are able to incorporate different scales into the generalized Kirchhoff matrices or generalized Hessian matrices. We validate our new multiscale methods with extensive numerical experiments. We illustrate that gGNMs outperform the original GNM method in the B-factor prediction of a set of 364 proteins. We demonstrate that for a given correlation function, FRI and gGNM methods provide essentially identical B-factor predictions when the scale value in the correlation function is sufficiently large. More importantly, we reveal intrinsic multiscale behavior in protein structures. The proposed mGNM and mANM are able to capture this multiscale behavior and thus give rise to a significant improvement of more than 11% in B-factor predictions over the original GNM and ANM methods. We further demonstrate the benefits of our mGNM through the B-factor predictions of many proteins that fail the original GNM method. We show that the proposed mGNM can also be used to analyze protein domain separations. Finally, we showcase the ability of our mANM for the analysis of protein collective motions. PMID:26627949
NASA Astrophysics Data System (ADS)
Vitillo, F.; Vitale Di Maio, D.; Galati, C.; Caruso, G.
2015-11-01
A CFD analysis has been carried out to study the thermal-hydraulic behavior of liquid metal coolant in a fuel assembly of triangular lattice. In order to obtain fast and accurate results, the isotropic two-equation RANS approach is often used in nuclear engineering applications. A different approach is provided by Non-Linear Eddy Viscosity Models (NLEVM), which try to take into account anisotropic effects by a nonlinear formulation of the Reynolds stress tensor. This approach is very promising, as it results in a very good numerical behavior and in a potentially better fluid flow description than classical isotropic models. An Anisotropic Shear Stress Transport (ASST) model, implemented into a commercial software, has been applied in previous studies, showing very trustful results for a large variety of flows and applications. In the paper, the ASST model has been used to perform an analysis of the fluid flow inside the fuel assembly of the ALFRED lead cooled fast reactor. Then, a comparison between the results of wall-resolved conjugated heat transfer computations and the results of a decoupled analysis using a suitable thermal wall-function previously implemented into the solver has been performed and presented.
Mietta, José Luis; Tamborenea, Pablo I; Martin Negri, R
2016-01-14
Structured elastomeric composites (SECs) with electrically conductive fillers display anisotropic piezoresistivity. The fillers do not form string-of-particle structures but pseudo-chains formed by grouping micro-sized clusters containing nanomagnetic particles surrounded by noble metals (e.g. silver, Ag). The pseudo-chains are formed when curing or preparing the composite in the presence of a uniform magnetic field, thus pseudo-chains are aligned in the direction of the field. The electrical conduction through pseudo-chains is analyzed and a constitutive model for the anisotropic reversible piezoresistivity in SECs is proposed. Several effects and characteristics, such as electron tunnelling, conduction inside the pseudo-chains, and chain-contact resistivity, are included in the model. Experimental results of electrical resistance, R, as a function of the normal stress applied in the direction of the pseudo-chains, P, are very well fitted by the model in the case of Fe3O4[Ag] microparticles magnetically aligned while curing in polydimethylsiloxane, PDMS. The cross sensitivity of different parameters (like the potential barrier and the effective distance for electron tunnelling) is evaluated. The model predicts the presence of several gaps for electron tunnelling inside the pseudo-chains. Estimates of those parameters for the mentioned experimental system under strains up to 20% are presented. Simulations of the expected response for other systems are performed showing the influence of Young's modulus and other parameters on the predicted piezoresistivity. PMID:26477664
Modelling the deformation and force balance of anisotropic Arctic Sea Ice
NASA Astrophysics Data System (ADS)
Heorton, Harry; Feltham, Daniel; Tsamados, Michel; Schroeder, David
2016-04-01
The movement and spatial distribution of Arctic sea ice is due to its response to external forces. The deformation of Arctic sea ice is observed to have structural alignment on all length scales. By considering the alignment of diamond-shaped sea ice floes an anisotropic rheology has been developed for use in a climate sea ice model. Here we present investigations into the role of anisotropy in calculating the internal stress gradient of Arctic sea ice over climate length and time scales in a state-of-the-art climate sea ice model, the Los Alamos Sea Ice model. Our investigations are focused on the link between the external dynamical forcing and the emergent properties of sea ice such as its drift speed and thickness distribution. We analyse the model's response to external forcing over short time scales showing the characteristics of deformation events for different sea ice states and anisotropic alignment. We show how these events add up to produce the full seasonal stress balance and sea ice state over the Arctic ocean.
Dynamics of Anisotropic Bianchi Type-III Bulk Viscous String Model with Magnetic Field
NASA Astrophysics Data System (ADS)
Singh, M. K.; Ram, Shri
2014-07-01
In this paper, we discuss the dynamics of spatially homogeneous and anisotropic Bianchi type-III string cosmological model in presence of bulk viscous fluid and electromagnetic field. Exact solutions of Einstein's field equations are obtained by assuming (i) a special form of the deceleration parameter and (ii) the component of the shear scalar tensor is proportional to mean Hubble parameter. The source of magnetic field is due to an electric current produced along z-axis. The role of bulk viscosity and magnetic field in establishing string phase of universe is presented. The physical and kinematical features of solutions are also discussed in detail.
Anisotropic modified holographic Ricci dark energy cosmological model with hybrid expansion law
NASA Astrophysics Data System (ADS)
Das, Kanika; Sultana, Tazmin
2015-11-01
Here in this paper we present a locally rotationally symmetric Bianchi type-II metric filled with dark matter and anisotropic modified holographic Ricci dark energy. To solve the Einstein's field equations we have taken the hybrid expansion law (HEL) which exhibits a cosmic transition of the universe from decelerating to accelerating phase. We have investigated the physical and geometrical properties of the model. It is observed that the anisotropy of the universe and that of the modified holographic Ricci dark energy tends to zero at later times and the universe becomes homogeneous, isotropic and flat. We have also studied the cosmic jerk parameter.
Anisotropic induced Compton scattering - Constraints on models of active galactic nuclei
NASA Technical Reports Server (NTRS)
Coppi, P.; Blandford, R. D.; Rees, M. J.
1993-01-01
A model for nonlinear radiative transfer on a lattice is used to explore observational signatures of anisotropic induced Compton scattering. Ways in which an intense beam of radiation may be altered in passing through a slab of plasma that is optically thin to spontaneous Thomson scattering are explained. A numerical approach to induced Compton scattering which involves solving the equations of nonlinear transfer on a lattice is described. Results of calculations for some simple geometrical configurations (spheres, disks, cylindrical 'jets', etc.) are presented. Some possible applications of these results to the interpretation of actual data on compact radio sources are outlined, and the FIR spectra of AGN are considered.
Modeling the viscosity and aggregation of suspensions of highly anisotropic nanoparticles.
Puisto, A; Illa, X; Mohtaschemi, M; Alava, M J
2012-01-01
The rheology of nanofiber suspensions is studied solving numerically the Population Balance Equations (PBE). To account for the anisotropic nature of nanofibers, a relation is proposed for their hydrodynamic volume. The suspension viscosity is calculated using the computed aggregate size distributions together with the Krieger-Dougherty constitutive equation. The model is fitted to experimental flow curves for Carbon NanoFibers (CNF) and for NanoFibrillated Cellulose (NFC), giving a first estimation of the microscopic anisotropy parameter, and yielding information on the structural properties and rheology of each system. PMID:22282294
Modelling And Analysis Of Permeability Of Anisotropic Compressed Non-Woven Filters
NASA Astrophysics Data System (ADS)
Prieur du Plessis, J.; Woudberg, Sonia; Le Coq, Laurence
2010-05-01
An existing geometrical pore-scale model for flow through isotropic spongelike media is adapted to predict flow through anisotropic non-woven glass fibre filters. Model predictions are compared to experimental results for the permeability obtained for a filter under different stages of compression to demonstrate the capability of the model to adjust to changes in porosity. The experimental data used are for a glass fibre paper with a uniform fibre diameter. The input parameters of the pore-scale model are the porosity, fibre diameter and some measure of the anisotropy between the in-plane and normal directions to the paper. Correlation between the predictions and the experimental results is satisfactory and provides confidence in the modelling procedure. It is shown that the permeability is very sensitive to changes in the level of anisotropy, i.e. the level of compression of the nonwoven material.
NASA Astrophysics Data System (ADS)
Duan, K.; Kwok, C. Y.
2016-04-01
The aim of this study is to better understand the mechanisms controlling the initiation, propagation, and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings. A two-dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs. Both isotropic and anisotropic hollow square-shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale. The isotropic model is validated by comparing the stress distribution around borehole wall and along X axis direction with analytical solutions. Effects of different factors including the particle size distribution, borehole diameter, far-field stress anisotropy, and rock anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation. Simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks. Reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure. Rock anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress. Far-field stress anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings. Results from this study can provide fundamental insights on the underlying particle-scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic rock.
NASA Astrophysics Data System (ADS)
Del Pozo Garcia, Eduardo
Eduardo del Pozo Garcia Geophysics and Astronomy Institute Havana, Cuba pozo@iga.cu Following Perez- Peraza and collaborators works on GLE prediction on basis to Cosmic Ray periodicities and cycles, in particular with 1,2 year cycle, effect prognosis of GLE occurrence was determine, I present here a possible interpretation of their results. Here I present the time distribution of the observed GLE in respect to each GLE nearly Sun-Earth-Jupiter alignment time. At the histogram the X axis cero is the alignment time. These alignments take place cyclically every 1,1 year. The histogram shows a modulation-like GLE distribution. The occurrence increments are near the alignment time and, about 125 days before and after the alignment time. Besides, a work hypothesis is proposed: “The Jupiter and Earth magnetospheres must deflect cosmic rays and, at some Jupiter and Earth positions according the current interplanetary magnetic field, may be favorable to increase the energetic particle flux over current Sun active regions, giving place to a modulation-like GLE distribution. Also, by the cosmic rays action some particle flux increase over active regions may come from radiation belts” This effect means that, during solar activity this is a factor that contributes to: - An accumulative activity increase of sunspot groups and their magnetic configuration complexity - Eventually, over complex active region some increase of high energy particle flux help to trigger GLE, or intensify solar proton events in progress, and become a GLE. This effect is taken into account for GLE prediction.
Wang, Y. T.; Xu, L. X.; Gui, Y. X.
2010-10-15
In this paper, we investigate the integrated Sachs-Wolfe effect in the quintessence cold dark matter model with constant equation of state and constant speed of sound in dark energy rest frame, including dark energy perturbation and its anisotropic stress. Comparing with the {Lambda}CDM model, we find that the integrated Sachs-Wolfe (ISW)-power spectrums are affected by different background evolutions and dark energy perturbation. As we change the speed of sound from 1 to 0 in the quintessence cold dark matter model with given state parameters, it is found that the inclusion of dark energy anisotropic stress makes the variation of magnitude of the ISW source uncertain due to the anticorrelation between the speed of sound and the ratio of dark energy density perturbation contrast to dark matter density perturbation contrast in the ISW-source term. Thus, the magnitude of the ISW-source term is governed by the competition between the alterant multiple of (1+3/2xc-circumflex{sub s}{sup 2}) and that of {delta}{sub de}/{delta}{sub m} with the variation of c-circumflex{sub s}{sup 2}.
Three-dimensional DC anisotropic resistivity modelling using finite elements on unstructured grids
NASA Astrophysics Data System (ADS)
Wang, Wei; Wu, Xiaoping; Spitzer, Klaus
2013-05-01
We present a newly developed finite element program for direct current resistivity modelling, which can handle arbitrary 3-D electric anisotropy. For this purpose, it is of particular importance to construct appropriate grids because artificial anisotropy can be introduced through preferential directions associated with regular grid structures. Therefore, results from different kinds of grids (structured hexahedral, structured tetrahedral and unstructured tetrahedral) are checked for symmetry. After a series of comparisons, we conclude that unstructured tetrahedral grids generally perform best. In addition, this grid type allows for local refinement, which greatly reduces the number of nodes and, consequently, lowers the computational costs significantly. A singularity removal technique is applied, which improves the accuracy considerably. The resulting system of linear equations is solved by a conjugate gradient method with a symmetric successive overrelaxation pre-conditioner. Comparisons with analytical solutions prove the code to be highly accurate for both isotropic and anisotropic models. More complex models are investigated to analyse the response of anisotropic structures, for example, in form of the P2 tensor invariant. Finally, we apply the code to a hot dry rock scenario and show that anisotropy reveals significant information on the hydraulically induced fracture system.
NASA Astrophysics Data System (ADS)
Yan, Bo; Li, Yuguo; Liu, Ying
2016-07-01
In this paper, we present an adaptive finite element (FE) algorithm for direct current (DC) resistivity modeling in 2-D generally anisotropic conductivity structures. Our algorithm is implemented on an unstructured triangular mesh that readily accommodates complex structures such as topography and dipping layers and so on. We implement a self-adaptive, goal-oriented grid refinement algorithm in which the finite element analysis is performed on a sequence of refined grids. The grid refinement process is guided by an a posteriori error estimator. The problem is formulated in terms of total potentials where mixed boundary conditions are incorporated. This type of boundary condition is superior to the Dirichlet type of conditions and improves numerical accuracy considerably according to model calculations. We have verified the adaptive finite element algorithm using a two-layered earth with azimuthal anisotropy. The FE algorithm with incorporation of mixed boundary conditions achieves high accuracy. The relative error between the numerical and analytical solutions is less than 1% except in the vicinity of the current source location, where the relative error is up to 2.4%. A 2-D anisotropic model is used to demonstrate the effects of anisotropy upon the apparent resistivity in DC soundings.
Anisotropic Bianchi-III cosmological model in f (R, T) gravity
NASA Astrophysics Data System (ADS)
Sahoo, P. K.; Sahu, S. K.; Nath, A.
2016-01-01
An anisotropic Bianchi type-III universe is investigated in the presence of a perfect fluid within the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the source of matter. Here we have considered the first two cases of the f(R,T) model, i.e. f(R,T)=R+2f(T) and f(R,T)=f1(R)+f2(T). We have shown that the field equations of f(R,T) gravity are solvable for any arbitrary function of a scale factor. To get a physically realistic model of the universe, we have assumed a simple power-law form of a scale factor. The exact solutions of the field equations are obtained, which represent an expanding model of the universe which starts expanding with a big bang at t = 0 . The physical behaviours of the model are discussed.
Mekhiche, M.; Pera, T.; Marechal, Y.
1995-05-01
The anisotropic and nonlinear behavior of doubly oriented and non-oriented sheets are modeled using the coenergy density. These models have been implemented in a finite element computation. A large generator has been modeled and the advantages of doubly oriented sheets compared to the conventional non-oriented ones are shown.
NASA Astrophysics Data System (ADS)
Haider, Mohammad Faisal; Haider, Md. Mushfique; Yasmeen, Farzana
2016-07-01
Heterogeneous materials, such as composites consist of clearly distinguishable constituents (or phases) that show different electrical properties. Multifunctional composites have anisotropic electrical properties that can be tailored for a particular application. The effective anisotropic electrical conductivity of composites is strongly affected by many parameters including volume fractions, distributions, and orientations of constituents. Given the electrical properties of the constituents, one important goal of micromechanics of materials consists of predicting electrical response of the heterogeneous material on the basis of the geometries and properties of the individual phases, a task known as homogenization. The benefit of homogenization is that the behavior of a heterogeneous material can be determined without resorting or testing it. Furthermore, continuum micromechanics can predict the full multi-axial properties and responses of inhomogeneous materials, which are anisotropic in nature. Effective electrical conductivity estimation is performed by using classical micromechanics techniques (composite cylinder assemblage method) that investigates the effect of the fiber/matrix electrical properties and their volume fractions on the micro scale composite response. The composite cylinder assemblage method (CCM) is an analytical theory that is based on the assumption that composites are in a state of periodic structure. The CCM was developed to extend capabilities variable fiber shape/array availability with same volume fraction, interphase analysis, etc. The CCM is a continuum-based micromechanics model that provides closed form expressions for upper level length scales such as macro-scale composite responses in terms of the properties, shapes, orientations and constituent distributions at lower length levels such as the micro-scale.
Ma, Songyun; Scheider, Ingo; Bargmann, Swantje
2016-09-01
An anisotropic constitutive model is proposed in the framework of finite deformation to capture several damage mechanisms occurring in the microstructure of dental enamel, a hierarchical bio-composite. It provides the basis for a homogenization approach for an efficient multiscale (in this case: multiple hierarchy levels) investigation of the deformation and damage behavior. The influence of tension-compression asymmetry and fiber-matrix interaction on the nonlinear deformation behavior of dental enamel is studied by 3D micromechanical simulations under different loading conditions and fiber lengths. The complex deformation behavior and the characteristics and interaction of three damage mechanisms in the damage process of enamel are well captured. The proposed constitutive model incorporating anisotropic damage is applied to the first hierarchical level of dental enamel and validated by experimental results. The effect of the fiber orientation on the damage behavior and compressive strength is studied by comparing micro-pillar experiments of dental enamel at the first hierarchical level in multiple directions of fiber orientation. A very good agreement between computational and experimental results is found for the damage evolution process of dental enamel. PMID:27294283
Anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets
NASA Astrophysics Data System (ADS)
Li, Yao-Dong; Wang, Xiaoqun; Chen, Gang
2016-07-01
Motivated by the recent experimental progress on the strong spin-orbit-coupled rare-earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120∘ state and two distinct stripe-ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3 , RZn3P3 , RCd3As3 , RZn3As3 , and R2O2CO3 .
Modeling of DNA-Mediated Self-Assembly from Anisotropic Nanoparticles: A Molecular Dynamics Study
NASA Astrophysics Data System (ADS)
Millan, Jaime; Girard, Martin; Brodin, Jeffrey; O'Brien, Matt; Mirkin, Chad; Olvera de La Cruz, Monica
The programmable selectivity of DNA recognition constitutes an elegant scheme to self-assemble a rich variety of superlattices from versatile nanoscale building blocks, where the natural interactions between building blocks are traded by complementary DNA hybridization interactions. Recently, we introduced and validated a scale-accurate coarse-grained model for a molecular dynamics approach that captures the dynamic nature of DNA hybridization events and reproduces the experimentally-observed crystallization behavior of various mixtures of spherical DNA-modified nanoparticles. Here, we have extended this model to robustly reproduce the assembly of nanoparticles with the anisotropic shapes observed experimentally. In particular, we are interested in two different particle types: (i) regular shapes, namely the cubic and octahedral polyhedra shapes commonly observed in gold nanoparticles, and (ii) irregular shapes akin to those exhibited by enzymes. Anisotropy in shape can provide an analog to the atomic orbitals exhibited by conventional atomic crystals. We present results for the assembly of enzymes or anisotropic nanoparticles and the co-assembly of enzymes and nanoparticles.
NASA Astrophysics Data System (ADS)
Wang, Lei; Wang, Xiaodong
2014-06-01
Resulting from the nature of anisotropy of coal media, it is a meaningful work to evaluate pressure transient behavior and flow characteristics within coals. In this article, a complete analytical model called the elliptical flow model is established by combining the theory of elliptical flow in anisotropic media and Fick's laws about the diffusion of coalbed methane. To investigate pressure transient behavior, analytical solutions were first obtained through introducing a series of special functions (Mathieu functions), which are extremely complex and are hard to calculate. Thus, a computer program was developed to establish type curves, on which the effects of the parameters, including anisotropy coefficient, storage coefficient, transfer coefficient and rate constant, were analyzed in detail. Calculative results show that the existence of anisotropy would cause great pressure depletion. To validate new analytical solutions, previous results were used to compare with the new results. It is found that a better agreement between the solutions obtained in this work and the literature was achieved. Finally, a case study is used to explain the effects of the parameters, including rock total compressibility coefficient, coal medium porosity and anisotropic permeability, sorption time constant, Langmuir volume and fluid viscosity, on bottom-hole pressure behavior. It is necessary to coordinate these parameters so as to reduce the pressure depletion.
NASA Astrophysics Data System (ADS)
Filippov, Alexander E.; Gorb, Stanislav N.
2016-03-01
Previous experimental data clearly revealed anisotropic friction on the ventral scale surface of snakes. However, it is known that frictional properties of the ventral surface of the snake skin range in a very broad range and the degree of anisotropy ranges as well to a quite strong extent. This might be due to the variety of species studied, diversity of approaches used for the friction characterization, and/or due to the variety of substrates used as a counterpart in the experiments. In order to understand the interactions between the nanostructure arrays of the ventral surface of the snake skin, this study was undertaken, which is aimed at numerical modeling of frictional properties of the structurally anisotropic surfaces in contact with various size of asperities. The model shows that frictional anisotropy appears on the snake skin only on the substrates with a characteristic range of roughness, which is less or comparable with dimensions of the skin microstructure. In other words, scale of the skin relief should reflect an adaptation to the particular range of surfaces asperities of the substrate.
Filippov, Alexander E.; Gorb, Stanislav N.
2016-01-01
Previous experimental data clearly revealed anisotropic friction on the ventral scale surface of snakes. However, it is known that frictional properties of the ventral surface of the snake skin range in a very broad range and the degree of anisotropy ranges as well to a quite strong extent. This might be due to the variety of species studied, diversity of approaches used for the friction characterization, and/or due to the variety of substrates used as a counterpart in the experiments. In order to understand the interactions between the nanostructure arrays of the ventral surface of the snake skin, this study was undertaken, which is aimed at numerical modeling of frictional properties of the structurally anisotropic surfaces in contact with various size of asperities. The model shows that frictional anisotropy appears on the snake skin only on the substrates with a characteristic range of roughness, which is less or comparable with dimensions of the skin microstructure. In other words, scale of the skin relief should reflect an adaptation to the particular range of surfaces asperities of the substrate. PMID:27005001
The phase transition in the anisotropic Heisenberg model with long range dipolar interactions
NASA Astrophysics Data System (ADS)
Mól, L. A. S.; Costa, B. V.
2014-03-01
In this work we have used extensive Monte Carlo calculations to study the planar to paramagnetic phase transition in the two-dimensional anisotropic Heisenberg model with dipolar interactions (AHd) considering the true long-range character of the dipolar interactions by means of the Ewald summation. Our results are consistent with an order-disorder phase transition with unusual critical exponents in agreement with our previous results for the Planar Rotator model with dipolar interactions. Nevertheless, our results disagree with the Renormalization Group results of Maier and Schwabl [Phys. Rev. B, 70, 134430 (2004)] [13] and the results of Rapini et al. [Phys. Rev. B, 75, 014425 (2007)] [12], where the AHd was studied using a cut-off in the evaluation of the dipolar interactions. We argue that besides the long-range character of dipolar interactions their anisotropic character may have a deeper effect in the system than previously believed. Besides, our results show that the use of a cut-off radius in the evaluation of dipolar interactions must be avoided when analyzing the critical behavior of magnetic systems, since it may lead to erroneous results.
Composite model for the anisotropic elastic moduli of lean oil shale
Rundle, J.B.; Schuler, K.W.
1981-02-01
A model to predict the anisotropic elastic moduli of lean oil shale is formulated. Deformation of a homogeneous ellipsoidal inclusion in a host matrix is used as the basis for computing the deformation of the composite. Both inclusions and the host rock are presumed to be separately isotropic. Anisotropy of the composite arises from the nonspherical shape of the kerogen inclusions. Six parameters are needed to quantify the model fully: 2 elastic moduli for the host rock, 2 for the inclusions, the kerogen content, and the inclusion aspect ratio. The model is compared to a set of statically measured elastic moduli. Good agreement with lean oil shale data was found. However, some systematic differences appear in comparison with moduli measured ultrasonically. 20 references.
Mbengue, Serigne Saliou; Buiron, Nicolas; Lanfranchi, Vincent
2016-01-01
During the manufacturing process and use of ferromagnetic sheets, operations such as rolling, cutting, and tightening induce anisotropy that changes the material’s behavior. Consequently for more accuracy in magnetization and magnetostriction calculations in electric devices such as transformers, anisotropic effects should be considered. In the following sections, we give an overview of a macroscopic model which takes into account the magnetic and magnetoelastic anisotropy of the material for both magnetization and magnetostriction computing. Firstly, a comparison between the model results and measurements from a Single Sheet Tester (SST) and values will be shown. Secondly, the model is integrated in a finite elements code to predict magnetostrictive deformation of an in-house test bench which is a stack of 40 sheets glued together by the Vacuum-Pressure Impregnation (VPI) method. Measurements on the test bench and Finite Elements results are presented. PMID:27092513
Mbengue, Serigne Saliou; Buiron, Nicolas; Lanfranchi, Vincent
2016-01-01
During the manufacturing process and use of ferromagnetic sheets, operations such as rolling, cutting, and tightening induce anisotropy that changes the material's behavior. Consequently for more accuracy in magnetization and magnetostriction calculations in electric devices such as transformers, anisotropic effects should be considered. In the following sections, we give an overview of a macroscopic model which takes into account the magnetic and magnetoelastic anisotropy of the material for both magnetization and magnetostriction computing. Firstly, a comparison between the model results and measurements from a Single Sheet Tester (SST) and values will be shown. Secondly, the model is integrated in a finite elements code to predict magnetostrictive deformation of an in-house test bench which is a stack of 40 sheets glued together by the Vacuum-Pressure Impregnation (VPI) method. Measurements on the test bench and Finite Elements results are presented. PMID:27092513
NASA Astrophysics Data System (ADS)
Chen, Cheng; Chen, Zheng; Zhang, Jing; Yang, Tao; Du, Xiu-Juan
2012-11-01
We modify the anisotropic phase-field crystal model (APFC), and present a semi-implicit spectral method to numerically solve the dynamic equation of the APFC model. The process results in the acceleration of computations by orders of magnitude relative to the conventional explicit finite-difference scheme, thereby, allowing us to work on a large system and for a long time. The faceting transitions introduced by the increasing anisotropy in crystal growth are then discussed. In particular, we investigate the morphological evolution in heteroepitaxial growth of our model. A new formation mechanism of misfit dislocations caused by vacancy trapping is found. The regular array of misfit dislocations produces a small-angle grain boundary under the right conditions, and it could significantly change the growth orientation of epitaxial layers.
Hu, Xuan; Cueff, Sébastien; Romeo, Pedro Rojo; Orobtchouk, Régis
2015-01-26
We present a numerical method to accurately model the electro-optic interaction in anisotropic materials. Specifically, we combine a full-vectorial finite-difference optical mode solver with a radio-frequency solver to analyze the overlap between optical modes and applied electric field. This technique enables a comprehensive understanding on how electro-optic effects modify individual elements in the permittivity tensor of a material. We demonstrate the interest of this approach by designing a modulator that leverages the Pockels effect in a hybrid silicon-BaTiO_{3} slot waveguide. Optimized optical confinement in the active BaTiO_{3} layer as well as design of travelling-wave index-matched electrodes is presented. Most importantly, we show that the overall electro-optic modulation is largely governed by off-diagonal elements in the permittivity tensor. As most of active electro-optic materials are anisotropic, this method paves the way to better understand the physics of electro-optic effects and to improve optical modulators. PMID:25835926
The numerical simulation for a 3D two-phase anisotropic medium based on BISQ model
NASA Astrophysics Data System (ADS)
Wang, Zhejiang; He, Qiaodeng; Wang, Deli
2008-03-01
Biot-flow and squirt-flow are the two most important fluid flow mechanisms in porous media containing fluids. Based on the BISQ (Biot-Squirt) model where the two mechanisms are treated simultaneously, the elastic wave-field simulation in the porous medium is limited to two-dimensions and two-components (2D2C) or two-dimensions and three-components (2D3C). There is no previous report on wave simulation in three-dimensions and three-components. Only through three dimensional numerical simulations can we have an overall understanding of wave field coupling relations and the spatial distribution characteristics between the solid and fluid phases in the dual-phase anisotropic medium. In this paper, based on the BISQ equation, we present elastic wave propagation in a three dimensional dual-phase anisotropic medium simulated by the staggered-grid high-order finite-difference method. We analyze the resulting wave fields and show that the results are an improvement.
Analytical modeling of equilibrium of strongly anisotropic plasma in tokamaks and stellarators
Lepikhin, N. D.; Pustovitov, V. D.
2013-08-15
Theoretical analysis of equilibrium of anisotropic plasma in tokamaks and stellarators is presented. The anisotropy is assumed strong, which includes the cases with essentially nonuniform distributions of plasma pressure on magnetic surfaces. Such distributions can arise at neutral beam injection or at ion cyclotron resonance heating. Then the known generalizations of the standard theory of plasma equilibrium that treat p{sub ‖} and p{sub ⊥} (parallel and perpendicular plasma pressures) as almost constant on magnetic surfaces are not applicable anymore. Explicit analytical prescriptions of the profiles of p{sub ‖} and p{sub ⊥} are proposed that allow modeling of the anisotropic plasma equilibrium even with large ratios of p{sub ‖}/p{sub ⊥} or p{sub ⊥}/p{sub ‖}. A method for deriving the equation for the Shafranov shift is proposed that does not require introduction of the flux coordinates and calculation of the metric tensor. It is shown that for p{sub ⊥} with nonuniformity described by a single poloidal harmonic, the equation for the Shafranov shift coincides with a known one derived earlier for almost constant p{sub ⊥} on a magnetic surface. This does not happen in the other more complex case.
A Whole-Mantle Three Dimensional Radially Anisotropic S Velocity Model
NASA Astrophysics Data System (ADS)
Panning, M. P.; Romanowicz, B. A.
2004-12-01
We present a 3D radially anisotropic model of the whole mantle obtained using a large three component surface and body waveform dataset and an iterative inversion for structure and source parameters based on Nonlinear Asymptotic Coupling Theory (NACT) (Li and Romanowicz, 1995). The model is parameterized by isotropic VS up to spherical harmonic degree 24 and ξ (ξ = VSH2 / VSV2), a measurement of radial anisotropy in shear velocity, up to degree 16. While the isotropic portion of the model is consistent with previous shear velocity tomographic models, the anisotropic portion suggests relationships between flow and anisotropy in a vairety of depth ranges. In the uppermost mantle, we confirm observations of regions with VSH}>V{SV starting at ˜80 km under oceanic regions and ˜250 km under old continental lithosphere, suggesting horizontal flow beneath the lithosphere (Gung et al., 2003). We also observe a VSV}>V{SH signature at ˜200-300 km depth beneath major ridge systems with amplitude significantly correlated with spreading rate for fast-spreading segments. In the transition zone (400-700 km depth), regions of subducted slab material are associated with VSV}>V{SH. We also confirm the observation of strong radially symmetric VSH}>V{SV in the lowermost 300 km (Panning and Romanowicz, 2004). The 3D deviations from this degree 0 signature are associated with the transition to the large-scale low-velocity superplumes under the central Pacific and Africa, suggesting that VSH}>V{SV is generated in the predominant horizontal flow of a mechanical boundary layer, with a change in signature related to transition to upwelling at the superplumes. We also solve for source perturbations in an interative procedure. Source perturbations are generally small compared to published Harvard CMT solutions, but significantly improve the fit to the data. The sources in the circum-Pacific subduction zones show small but clearly systematic shifts in location due to an improved structural
Anisotropic shear-wave velocity structure of the Earth's mantle: A global model
NASA Astrophysics Data System (ADS)
Kustowski, B.; EkströM, G.; DziewońSki, A. M.
2008-06-01
We combine a new, large data set of surface wave phase anomalies, long-period waveforms, and body wave travel times to construct a three-dimensional model of the anisotropic shear wave velocity in the Earth's mantle. Our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model, simultaneous inversion for velocity and anisotropy, as well as discontinuity topographies, and implementation of nonlinear crustal corrections for waveforms. A comparison of our new three-dimensional model, S362ANI, with two other models derived from comparable data sets but using different techniques reveals persistent features: (1) strong, ˜200-km-thick, high-velocity anomalies beneath cratons, likely representing the continental lithosphere, underlain by weaker, fast anomalies extending below 250 km, which may represent continental roots, (2) weak velocity heterogeneity between 250 and 400 km depths, (3) fast anomalies extending horizontally up to 2000-3000 km in the mantle transition zone beneath subduction zones, (4) lack of strong long-wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle-lower mantle boundary, and (5) slow-velocity superplumes beneath the Pacific and Africa. The shear wave radial anisotropy is strongest at 120 km depth, in particular beneath the central Pacific. Lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths. Tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle.
NASA Astrophysics Data System (ADS)
Liu, Mao; Tieu, Kiet Anh; Zhou, Kun; Peng, Ching-Tun
2016-03-01
A crystal plasticity finite element method constitutive model was developed to investigate the anisotropic mechanical behaviors of (001), (011), and (111) initially orientated copper (Cu) single crystals during nanoindentation deformation. The numerical load-indentation depth curve and hardness-indentation depth curve were compared with experimental observations to validate the established three-dimensional (3D) CPFEM model. The difference of indentation loads between (111) crystal and (001) crystal is ~10.68 pct, and the difference of indentation modulus between (111) surface and (001) surface is ~10.80 pct. The numerical results show the noticeable indentation size effect for three crystals, and slightly different hardness values on different crystallographic planes. The equivalent plastic strain and lattice rotation angles were also analyzed on three through-thickness cross sections to study the plastic deformation-induced texture anisotropy.
Halim, Suhaila Abd; Razak, Rohayu Abd; Ibrahim, Arsmah; Manurung, Yupiter HP
2014-06-19
In image processing, it is important to remove noise without affecting the image structure as well as preserving all the edges. Perona Malik Anisotropic Diffusion (PMAD) is a PDE-based model which is suitable for image denoising and edge detection problems. In this paper, the Peaceman Rachford scheme is applied on PMAD to remove unwanted noise as the scheme is efficient and unconditionally stable. The capability of the scheme to remove noise is evaluated on several digital radiography weld defect images computed using MATLAB R2009a. Experimental results obtained show that the Peaceman Rachford scheme improves the image quality substantially well based on the Peak Signal to Noise Ratio (PSNR). The Peaceman Rachford scheme used in solving the PMAD model successfully removes unwanted noise in digital radiographic image.
NASA Astrophysics Data System (ADS)
Liu, Mao; Tieu, Kiet Anh; Zhou, Kun; Peng, Ching-Tun
2016-06-01
A crystal plasticity finite element method constitutive model was developed to investigate the anisotropic mechanical behaviors of (001), (011), and (111) initially orientated copper (Cu) single crystals during nanoindentation deformation. The numerical load-indentation depth curve and hardness-indentation depth curve were compared with experimental observations to validate the established three-dimensional (3D) CPFEM model. The difference of indentation loads between (111) crystal and (001) crystal is ~10.68 pct, and the difference of indentation modulus between (111) surface and (001) surface is ~10.80 pct. The numerical results show the noticeable indentation size effect for three crystals, and slightly different hardness values on different crystallographic planes. The equivalent plastic strain and lattice rotation angles were also analyzed on three through-thickness cross sections to study the plastic deformation-induced texture anisotropy.
NASA Astrophysics Data System (ADS)
Lima, L. S.
2016-07-01
We use the SU(3) Schwinger's boson theory to study the spin transport properties of the two-dimensional anisotropic frustrated Heisenberg model in a honeycomb lattice at T=0. We have investigated the behavior of the spin conductivity for this model which presents a single-ion anisotropy and J1 and J2 exchange interactions. We study the spin transport in the Bose-Einstein condensation regime where we have that the tz bosons are condensed and the following condition is valid:
Exact work statistics of quantum quenches in the anisotropic XY model.
Bayocboc, Francis A; Paraan, Francis N C
2015-09-01
We derive exact analytic expressions for the average work done and work fluctuations in instantaneous quenches of the ground and thermal states of a one-dimensional anisotropic XY model. The average work and a quantum fluctuation relation is used to determine the amount of irreversible entropy produced during the quench, eventually revealing how the closing of the excitation gap leads to increased dissipated work. The work fluctuation is calculated and shown to exhibit nonanalytic behavior as the prequench anisotropy parameter and transverse field are tuned across quantum critical points. Exact compact formulas for the average work and work fluctuation in ground state quenches of the transverse field Ising model allow us to calculate the first singular field derivative at the critical field values. PMID:26465461
Warm Forming of Aluminum Alloys using a Coupled Thermo-Mechanical Anisotropic Material Model
Abedrabbo, Nader; Pourboghrat, Farhang; Carsley, John E.
2005-08-05
Temperature-dependant anisotropic material models for two types of automotive aluminum alloys (5754-O and 5182-O) were developed and implemented in LS-Dyna as a user material subroutine (UMAT) for coupled thermo-mechanical finite element analysis (FEA) of warm forming of aluminum alloys. The anisotropy coefficients of the Barlat YLD2000 plane stress yield function for both materials were calculated for the range of temperatures 25 deg. C-260 deg. C. Curve fitting was used to calculate the anisotropy coefficients of YLD2000 and the flow stress as a function of temperature. This temperature-dependent material model was successfully applied to the coupled thermo-mechanical analysis of stretching of aluminum sheets and results were compared with experiments.
Warm Forming of Aluminum Alloys using a Coupled Thermo-Mechanical Anisotropic Material Model
NASA Astrophysics Data System (ADS)
Abedrabbo, Nader; Pourboghrat, Farhang; Carsley, John E.
2005-08-01
Temperature-dependant anisotropic material models for two types of automotive aluminum alloys (5754-O and 5182-O) were developed and implemented in LS-Dyna as a user material subroutine (UMAT) for coupled thermo-mechanical finite element analysis (FEA) of warm forming of aluminum alloys. The anisotropy coefficients of the Barlat YLD2000 plane stress yield function for both materials were calculated for the range of temperatures 25°C-260°C. Curve fitting was used to calculate the anisotropy coefficients of YLD2000 and the flow stress as a function of temperature. This temperature-dependent material model was successfully applied to the coupled thermo-mechanical analysis of stretching of aluminum sheets and results were compared with experiments.
Spin superfluidity in the anisotropic XY model in the triangular lattice
NASA Astrophysics Data System (ADS)
Lima, L. S.
2016-07-01
We use the SU(3) Schwinger's boson theory to study the spin transport properties in the two-dimensional anisotropic frustrated Heisenberg model in the triangular lattice at T=0. We have investigated the behavior of the spin conductivity for this model which presents an single-ion anisotropy. We study the spin transport in the Bose-Einstein condensation regime where we have that the tz bosons are condensed and the following condition is valid:
Monogamy of quantum correlations in the one-dimensional anisotropic XY model
NASA Astrophysics Data System (ADS)
Xu, Shuai; Song, Xue-Ke; Ye, Liu
2014-01-01
In this paper, the monogamy properties of some quantum correlations, including the geometric quantum discord, concurrence, entanglement of formation and entropy quantum discord, in the anisotropic spin-1/2 XY model with staggered Dzyaloshinskii—Moriya (DM) interaction have been investigated using the quantum renormalization group (QRG) method. We summarize the monogamy relation for different quantum correlation measures and make an explicit comparison. Through mathematical calculations and analysis, we obtain that no matter whether the QRG steps are carried out, the monogamy of the given states are always unaltered. Moreover, we conclude that the geometric quantum discord and concurrence obey the monogamy property while other quantum correlation measures, such as entanglement of formation and quantum discord, violate it for this given model.
Chen, F.H. |; Horng, W.C.; Hsu, H.T.; Tseng, T.Y.
1995-02-01
The field-cooled magnetization of high-{Tc} superconducting ceramics measured in low magnetic field exhibits the paramagnetic Meissner effect (PME), i.e., the diamagnetic signal initially increases with decrease in temperature but reaches a maximum at temperature T{sub d} and later decreases with decrease in temperature. Even in some samples the signal is ultimately able to transform inversely into a paramagnetic regime once the sample is cooled below a temperature T{sub p} as long as the applied field is sufficiently small. This PME has been observed in various high-{Tc} cuprates and is explained by disparate aspects. An anisotropic model, in which the granular superconductors are assumed to be ideally anisotropic, was first alternatively proposed in the present work so as to theoretically account for this effect. On the other hand, an isotropic model, suitable for granular superconductors with randomly oriented grains, was proposed to deal with the samples prepared by a conventional solid-state reaction method. The anomalous magnetization behavior in the present model was demonstrated to be the superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, over the paramagnetic one due to the induction of the intergranular component induced by these currents where the intergranular one behaved as the effective pinning centers. The PME was demonstrated by this model to exist parasitically in granular superconductors. This intergranular effect is therefore worthy of remark when evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field.
A Numerical Model of Anisotropic Mass Transport Through Grain Boundary Networks
NASA Astrophysics Data System (ADS)
Wang, Yibo
Tin (Sn) thin films are commonly used in electronic circuit applications as coatings on contacts and solders for joining components. It is widely observed, for some such system, that whiskers---long, thin crystalline structures---emerge and grow from the film. The Sn whisker phenomenon has become a highly active research area since Sn whiskers have caused a large amount of damage and loss in manufacturing, military, medical and power industries. Though lead (Pb) addition to Sn has been used to solve this problem for over five decades, the adverse environmental and health effects of Pb have motivated legislation to severely constrain Pb use in society. People are researching and seeking the reasons which cause whiskers and corresponding methods to solve the problem. The contributing factors to cause a Sn whisker are potentially many and much still remains unknown. Better understanding of fundamental driving forces should point toward strategies to improve (a) the accuracy with which we can predict whisker formation, and (b) our ability to mitigate the phenomenon. This thesis summarizes recent important research achievements in understanding Sn whisker formation and growth, both experimentally and theoretically. Focus is then placed on examining the role that anisotropy in grain boundary diffusivity plays in determining whisker characteristics (specifically, whether they form and, if so, where on a surface). To study this aspect of the problem and to enable future studies on stress driven grain boundary diffusion, this thesis presents a numerical anisotropic mass transport model. In addition to presenting details of the model and implementation, model predictions for a set of increasingly complex grain boundary networks are discussed. Preliminary results from the model provide evidence that anisotropic grain boundary diffusion may be a primary driving mechanism in whisker formation.
43 CFR Appendix III to Part 11 - Format for Data Inputs and Modifications to the NRDAM/GLE
Code of Federal Regulations, 2010 CFR
2010-10-01
... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false Format for Data Inputs and Modifications to the NRDAM/GLE III Appendix III to Part 11 Public Lands: Interior Office of the Secretary of the Interior NATURAL RESOURCE DAMAGE ASSESSMENTS Pt. 11, App. III Appendix III to Part 11—Format for Data Inputs and Modifications to the NRDAM/GLE...
The effect of cosmic rays on biological systems - an investigation during GLE events
NASA Astrophysics Data System (ADS)
Belisheva, N. K.; Lammer, H.; Biernat, H. K.; Vashenuyk, E. V.
2012-01-01
In this study, first direct and circumstantial evidences of the effects of cosmic rays (CR) on biological systems are presented. A direct evidence of biological effects of CR is demonstrated in experiments with three cellular lines growing in culture during three events of Ground Level Enhancement (GLEs) in the neutron count rate detected by ground-based neutron monitor in October 1989. Various phenomena associated with DNA lesion on the cellular level demonstrate coherent dynamics of radiation effects in all cellular lines coincident with the time of arrival of high-energy solar particles to the near-Earth space and with the main peak in GLE. These results were obtained in the course of six separate experiments, with partial overlapping of the time of previous and subsequent experiments, which started and finished in the quiet period of solar activity (SA). A significant difference between the values of multinuclear cells in all cellular lines in the quiet period and during GLE events indicates that the cause of radiation effects in the cell cultures is an exposure of cells to the secondary solar CR near the Earth's surface. The circumstantial evidence was obtained by statistical analysis of cases of congenital malformations (CM) at two sites in the Murmansk region. The number of cases of all classes of CM reveals a significant correlation with the number of GLE events. The number of cases of CM with pronounced chromosomal abnormalities clearly correlates with the GLE events that occurred a year before the birth of a child. We have found a significant correlation between modulations of the water properties and daily background variations of CR intensity. We believe that the effects of CR on biological systems can be also mediated by fluctuations in water properties, considered as one of possible mechanisms controlling the effects of CRs on biological systems.
Li, Guohui; Shen, Hujun; Zhang, Dinglin; Li, Yan; Wang, Honglei
2016-02-01
In this work, we attempt to apply a coarse-grained (CG) model, which is based on anisotropic Gay-Berne and electric multipole (EMP) potentials, to the modeling of nucleic acids. First, a comparison has been made between the CG and atomistic models (AMBER point-charge model) in the modeling of DNA and RNA hairpin structures. The CG results have demonstrated a good quality in maintaining the nucleic acid hairpin structures, in reproducing the dynamics of backbone atoms of nucleic acids, and in describing the hydrogen-bonding interactions between nucleic acid base pairs. Second, the CG and atomistic AMBER models yield comparable results in modeling double-stranded DNA and RNA molecules. It is encouraging that our CG model is capable of reproducing many elastic features of nucleic acid base pairs in terms of the distributions of the interbase pair step parameters (such as shift, slide, tilt, and twist) and the intrabase pair parameters (such as buckle, propeller, shear, and stretch). Finally, The GBEMP model has shown a promising ability to predict the melting temperatures of DNA duplexes with different lengths. PMID:26717419
Wang, Jing; Zhu, Shijun; Wang, Haiyan; Cai, Yangjian; Li, Zhenhua
2016-05-30
Recently, we introduced a new class of radially polarized cosine-Gaussian correlated Schell-model (CGCSM) beams of rectangular symmetry based on the partially coherent electromagnetic theory [Opt. Express23, 33099 (2015)]. In this paper, we extend the work to study the second-order statistics such as the average intensity, the spectral degree of coherence, the spectral degree of polarization and the state of polarization in anisotropic turbulence based on an extended von Karman power spectrum with a non-Kolmogorov power law α and an effective anisotropic parameter. Analytical formulas for the cross-spectral density matrix elements of a radially polarized CGCSM beam in anisotropic turbulence are derived. It is found that the second-order statistics are greatly affected by the source correlation function, and the change in the turbulent statistics induces relatively small effect. The significant effect of anisotropic turbulence on the beam parameters mainly appears nearα=3.1, and decreases with the increase of the anisotropic parameter. Furthermore, the polarization state exhibits self-splitting property and each beamlet evolves into a radially polarized structure in the far field. Our work enriches the classical coherence theory and may be important for free-space optical communications. PMID:27410089
Instability of Interacting Ghost Dark Energy Model in an Anisotropic Universe
NASA Astrophysics Data System (ADS)
Azimi, N.; Barati, F.
2016-07-01
A new dark energy model called "ghost dark energy" was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ Λ = α H, where α is a constant of order {Λ }3_{QCD} and Λ Q C D ˜ 100 M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed {vs2} the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe.
Anisotropic viscoelastic-viscoplastic continuum model for high-density cellulose-based materials
NASA Astrophysics Data System (ADS)
Tjahjanto, D. D.; Girlanda, O.; Östlund, S.
2015-11-01
A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic solid model expressed in terms of Boltzmann hereditary integral form, which is coupled to a rate-dependent viscoplastic formulation to describe the irreversible plastic part of the overall strain. An anisotropic hardening law with a kinematic effect is particularly adopted in order to capture the complex stress-strain hysteresis typically observed in polymeric materials. In addition, the present model accounts for the effects of material densification associated with through-thickness compression, which are captured using an exponential law typically applied in the continuum description of elasticity in porous media. Material parameters used in the present model are calibrated to the experimental data for high-density (press)boards. The experimental characterization procedures as well as the calibration of the parameters are highlighted. The results of the model simulations are systematically analyzed and validated against the corresponding experimental data. The comparisons show that the predictions of the present model are in very good agreement with the experimental observations for both stationary and transient load cases.
Life prediction and constitutive models for engine hot section anisotropic materials
NASA Technical Reports Server (NTRS)
Swanson, G. A.; Linask, I.; Nissley, D. M.; Norris, P. P.; Meyer, T. G.; Walker, K. P.
1987-01-01
The results are presented of a program designed to develop life prediction and constitutive models for two coated single crystal alloys used in gas turbine airfoils. The two alloys are PWA 1480 and Alloy 185. The two oxidation resistant coatings are PWA 273, an aluminide coating, and PWA 286, an overlay NiCoCrAlY coating. To obtain constitutive and fatigue data, tests were conducted on uncoated and coated specimens loaded in the CH76 100 CH110 , CH76 110 CH110 , CH76 111 CH110 and CH76 123 CH110 crystallographic directions. Two constitutive models are being developed and evaluated for the single crystal materials: a micromechanic model based on crystallographic slip systems, and a macroscopic model which employs anisotropic tensors to model inelastic deformation anisotropy. Based on tests conducted on the overlay coating material, constitutive models for coatings also appear feasible and two initial models were selected. A life prediction approach was proposed for coated single crystal materials, including crack initiation either in the coating or in the substrate. The coating initiated failures dominated in the tests at load levels typical of gas turbine operation. Coating life was related to coating stress/strain history which was determined from specimen data using the constitutive models.
Instability of Interacting Ghost Dark Energy Model in an Anisotropic Universe
NASA Astrophysics Data System (ADS)
Azimi, N.; Barati, F.
2016-02-01
A new dark energy model called "ghost dark energy" was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ Λ = α H, where α is a constant of order {Λ }3_{QCD} and Λ Q C D ˜ 100M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed {vs2} the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe.
Hills, M E; Olsen, A L; Nichols, L W
1968-08-01
Cary model 14 spectrophotometers like other prism and grating instruments have polarization characteristics that affect the transmittance values of anisotropic or dichroic materials. In the uv, the degree of polarization is fairly constant from 3000 A to 4000 A, whereas in the visible, it shows some variation with wavelength. In the near ir, the variation of the degree of polarization with wavelength is large, showing sharply defined maxima at approximately 0.77 micro, 0.97 micro, and 1.27 micro. The spectral transmittance of optical quality sapphire, a uniaxial crystal, cut at 45 degrees , 60 degrees , and 90 degrees to the c axis, showed undulations for certain orientations of the privileged directions. PMID:20068821
Anisotropic string cosmological models in Heckmann-Schucking space-time
NASA Astrophysics Data System (ADS)
Goswami, G. K.; Dewangan, R. N.; Yadav, A. K.; Pradhan, A.
2016-02-01
In the present work we have searched the existence of the late time acceleration of the universe with string fluid as source of matter in anisotropic Heckmann-Schucking space-time by using 287 high red shift (0.3 ≤ z≤1.4) SN Ia data of observed absolute magnitude along with their possible error from Union 2.1 compilation. It is found that the best fit values for (\\varOmegam)0, (\\varOmega_{\\varLambda})0, (\\varOmega_{σ })0 and (q)0 are 0.2820, 0.7177, 0.0002 & -0.5793 respectively. Several physical aspects and geometrical properties of the model are discussed in detail.
NASA Astrophysics Data System (ADS)
Mbengue, Serigne Saliou; Buiron, Nicolas; Lanfranchi, Vincent
2016-04-01
Magnetic and magnetoelastic properties of soft ferromagnetic materials, used as laminated sheets, are sensitive to manufacturing processes such as rolling, cutting and coating. One of the effects of these processes is to induce an anisotropic behavior of materials. Therefore, an anhysteretic magnetostriction and magnetization calculation taking into account the anisotropy effect at macroscopic scale is presented. This model is based on the expression and then the minimization of the total energy in order to determine magnetization and magnetostriction at equilibrium. The total energy to minimize depends on energy terms identified from measurements of the magnetization and magnetostriction at a scale large enough to neglect the heterogeneity due to grains. Therefore, this approach attempts to reproduce ferromagnetic polycrystal behavior at macroscopic without knowing texture (Orientation Density Function) nor grain properties.
NASA Astrophysics Data System (ADS)
Higdon, J. C.
1984-10-01
A model of anisotropic magnetogasdynamic turbulence is developed in order to investigate quantitatively a turbulent fluid origin for the small spatial scale density fluctuations observed in 1981 by Armstrong, Cordes, and Rickett in the interstellar medium. The anisotropy at these small spatial scales results from the presence of a large-scale approximately uniform magnetic field that is a sum of the steady-state galactic magnetic field and the large-scale turbulent magnetic field fluctuations. The observed density fluctuations are interpreted to be two-dimensional isobaric entropy variations with oppositely directed gradients in temperature and density projected transverse to the local approximately uniform magnetic field. Three possible sites - cloud shell H II regions, diffuse H II regions produced by O stars, and the tenuous intercloud medium - are investigated as possible locations for turbulent flows.
Convergence dynamics of 2-dimensional isotropic and anisotropic Bak Sneppen models
NASA Astrophysics Data System (ADS)
Bakar, Burhan; Tirnakli, Ugur
2008-09-01
The conventional Hamming distance measurement captures only short-time dynamics of the displacement between uncorrelated random configurations. The minimum difference technique introduced by Tirnakli and Lyra [U. Tirnakli, M.L. Lyra. Int. J. Mod. Phys. C 14 (2003) 805] is used to study short-time and long-time dynamics of the two distinct random configurations of isotropic and anisotropic Bak-Sneppen models on a square lattice. Similar to a 1-dimensional case, the time evolution of the displacement is intermittent. The scaling behavior of the jump activity rate and waiting time distribution reveal the absence of typical spatial-temporal scales in the mechanism of displacement jumps used to quantify convergence dynamics.
Sudden death of distillability in a two-qutrit anisotropic Heisenberg spin model
NASA Astrophysics Data System (ADS)
Guo, You-neng; Fang, Mao-fa; Zou, Hong-mei; Zhang, Shi-yang; Liu, Xiang
2015-06-01
Sudden death of distillability for a two-qutrit anisotropic Heisenberg XX chain with Dzyaloshinskii-Moriya (DM) interaction in an inhomogeneous magnetic field is studied in detail. By using the negativity and realignment criterion, we show that certain initial prepared free entangled states may become bound entangled or separable states in a finite time. Moreover, the influences of the isotropic bilinear interaction parameter, the external magnetic field strength, the DM interaction parameter, as well as the intrinsic decoherence parameter on the possibility of distillability sudden death (DSD) have been studied. The results show, controlling the isotropic bilinear interaction parameter, the external magnetic field strength, the DM interaction parameter, as well as the intrinsic decoherence parameter, can accelerate the possibility of DSD in the present model.
The luminosity law of ellipticals; a test of a family of anisotropic models on eight galaxies.
NASA Astrophysics Data System (ADS)
Bertin, G.; Saglia, R. P.; Stiavelli, M.
An important clue to the structure and dynamics of elliptical galaxies is provided by the empirical r1/4 luminosity law proposed by de Vaucouleurs (1948). The existence of such a law is indicative of a common underlying mass distribution in these galaxies. The fact that this law is universal suggests that essentially a single physical mechanism characterizes the formation of ellipticals. The authors report on a recent study where they have analyzed published photometric and kinematical data for a set of bright elliptical galaxies (NGC 3379, NGC 4374, NGC 4472, NGC 4486, NGC 4636, NGC 7562, NGC 7619, and NGC 7626) in terms of self-consistent anisotropic models under the assumption of constant mass-to-light ratio.
The monogamy relation and quantum phase transition in one-dimensional anisotropic XXZ model
NASA Astrophysics Data System (ADS)
Song, Xue-ke; Wu, Tao; Ye, Liu
2013-10-01
In the paper, we have researched the monogamy relation and the quantum phase transition (QPT) in the anisotropic spin XXZ model by exploiting the quantum renormalization group method. The results show that there exits QPT after several iterations of renormalization in the present system. And we can find out that the monogamy inequality of entanglement of formation (EOF) and entropy quantum discord develop two saturated values which associate with spin-liquid and Néel phases after several iterations of the renormalization. Furthermore, we can also find out that the renormalization of EOF and entropy quantum discord violate the monogamy property while the renormalized geometric quantum discord obeys it no matter whether the QPT iterations are carried out. As a byproduct, the nonanalytic phenomenon and scaling behavior of the spin system are analyzed in detail.
Xia, Fei; Tong, Dudu; Lu, Lanyuan
2013-08-13
A computational method called the progressive fluctuation matching (PFM) is developed for constructing robust heterogeneous anisotropic network models (HANMs) for biomolecular systems. An HANM derived through the PFM approach consists of harmonic springs with realistic positive force constants, and yields the calculated B-factors that are basically identical to the experimental ones. For the four tested protein systems including crambin, trypsin inhibitor, HIV-1 protease, and lysozyme, the root-mean-square deviations between the experimental and the computed B-factors are only 0.060, 0.095, 0.247, and 0.049 Å(2), respectively, and the correlation coefficients are 0.99 for all. By comparing the HANM/ANM normal modes to their counterparts derived from both an atomistic force field and an NMR structure ensemble, it is found that HANM may provide more accurate results on protein dynamics. PMID:26584122
Khayyeri, Hanifeh; Longo, Giacomo; Gustafsson, Anna; Isaksson, Hanna
2016-08-01
The incidence of tendon injury (tendinopathy) has increased over the past decades due to greater participation in sports and recreational activities. But little is known about the aetiology of tendon injuries because of our limited knowledge in the complex structure-function relationship in tendons. Computer models can capture the biomechanical behaviour of tendons and its structural components, which is essential for understanding the underlying mechanisms of tendon injuries. This study compares three structural constitutive material models for the Achilles tendon and discusses their application on different biomechanical simulations. The models have been previously used to describe cardiovascular tissue and articular cartilage, and one model is novel to this study. All three constitutive models captured the tensile behaviour of rat Achilles tendon (root mean square errors between models and experimental data are 0.50-0.64). They further showed that collagen fibres are the main load-bearing component and that the non-collagenous matrix plays a minor role in tension. By introducing anisotropic behaviour also in the non-fibrillar matrix, the new biphasic structural model was also able to capture fluid exudation during tension and high values of Poisson׳s ratio that is reported in tendon experiments. PMID:27108350
Anisotropic Multishell Analytical Modeling of an Intervertebral Disk Subjected to Axial Compression.
Demers, Sébastien; Nadeau, Sylvie; Bouzid, Abdel-Hakim
2016-04-01
Studies on intervertebral disk (IVD) response to various loads and postures are essential to understand disk's mechanical functions and to suggest preventive and corrective actions in the workplace. The experimental and finite-element (FE) approaches are well-suited for these studies, but validating their findings is difficult, partly due to the lack of alternative methods. Analytical modeling could allow methodological triangulation and help validation of FE models. This paper presents an analytical method based on thin-shell, beam-on-elastic-foundation and composite materials theories to evaluate the stresses in the anulus fibrosus (AF) of an axisymmetric disk composed of multiple thin lamellae. Large deformations of the soft tissues are accounted for using an iterative method and the anisotropic material properties are derived from a published biaxial experiment. The results are compared to those obtained by FE modeling. The results demonstrate the capability of the analytical model to evaluate the stresses at any location of the simplified AF. It also demonstrates that anisotropy reduces stresses in the lamellae. This novel model is a preliminary step in developing valuable analytical models of IVDs, and represents a distinctive groundwork that is able to sustain future refinements. This paper suggests important features that may be included to improve model realism. PMID:26833355
Relevance of near-Earth magnetic field modeling in deriving SEP properties using ground-based data
NASA Astrophysics Data System (ADS)
Kanellakopoulos, Anastasios; Plainaki, Christina; Mavromichalaki, Helen; Laurenza, Monica; Gerontidou, Maria; Storini, Marisa; Andriopoulou, Maria
2014-05-01
Ground Level Enhancements (GLEs) are short-term increases observed in cosmic ray intensity records of ground-based particle detectors such as neutron monitors (NMs) or muon detectors; they are related to the arrival of solar relativistic particles in the terrestrial environment. Hence, GLE events are related to the most energetic class of solar energetic particle (SEP) events. In this work we investigate how the use of different magnetospheric field models can influence the derivation of the relativistic SEP properties when modeling GLE events. As a case study, we examine the event of 2012 May 17 (also known as GLE71), registered by ground-based NMs. We apply the Tsyganenko 89 and the Tsyganenko 96 models in order to calculate the trajectories of the arriving SEPs in the near-Earth environment. We show that the intersection of the SEP trajectories with the atmospheric layer at ~20 km from the Earth's surface (i.e., where the flux of the generated secondary particles is maximum), forms for each ground-based neutron monitor a specified viewing region that is dependent on the magnetospheric field configuration. Then, we apply the Neutron Monitor Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model (Plainaki et al. 2010, Solar Phys, 264, 239), in order to derive the spectral properties of the related SEP event and the spatial distributions of the SEP fluxes impacting the Earth's atmosphere. We examine the dependence of the results on the used magnetic field models and evaluate their range of validity. Finally we discuss information derived by modeling the SEP spectrum in the frame of particle acceleration scenarios.
Jiao, Yang Chawla, Nikhilesh
2014-03-07
We present a framework to model and characterize the microstructure of heterogeneous materials with anisotropic inclusions of secondary phases based on the directional correlation functions of the inclusions. Specifically, we have devised an efficient method to incorporate both directional two-point correlation functions S{sub 2} and directional two-point cluster functions C{sub 2} that contain non-trivial topological connectedness information into the simulated annealing microstructure reconstruction procedure. Our framework is applied to model an anisotropic aluminum alloy and the accuracy of the reconstructed structural models is assessed by quantitative comparison with the actual microstructure obtained via x-ray tomography. We show that incorporation of directional clustering information via C{sub 2} significantly improves the accuracy of the reconstruction. In addition, a set of analytical “basis” correlation functions are introduced to approximate the actual S{sub 2} and C{sub 2} of the material. With the proper choice of basis functions, the anisotropic microstructure can be represented by a handful of parameters including the effective linear sizes of the iron-rich and silicon-rich inclusions along three orthogonal directions. This provides a general and efficient means for heterogeneous material modeling that enables one to significantly reduce the data set required to characterize the anisotropic microstructure.
NASA Technical Reports Server (NTRS)
Dame, L. T.; Stouffer, D. C.
1986-01-01
A tool for the mechanical analysis of nickel base single crystal superalloys, specifically Rene N4, used in gas turbine engine components is developed. This is achieved by a rate dependent anisotropic constitutive model implemented in a nonlinear three dimensional finite element code. The constitutive model is developed from metallurigical concepts utilizing a crystallographic approach. A non Schmid's law formulation is used to model the tension/compression asymmetry and orientation dependence in octahedral slip. Schmid's law is a good approximation to the inelastic response of the material in cube slip. The constitutive equations model the tensile behavior, creep response, and strain rate sensitivity of these alloys. Methods for deriving the material constants from standard tests are presented. The finite element implementation utilizes an initial strain method and twenty noded isoparametric solid elements. The ability to model piecewise linear load histories is included in the finite element code. The constitutive equations are accurately and economically integrated using a second order Adams-Moulton predictor-corrector method with a dynamic time incrementing procedure. Computed results from the finite element code are compared with experimental data for tensile, creep and cyclic tests at 760 deg C. The strain rate sensitivity and stress relaxation capabilities of the model are evaluated.
NASA Astrophysics Data System (ADS)
Parente, Walter E. F.; Pacobahyba, J. T. M.; Araújo, Ijanílio G.; Neto, Minos A.; Ricardo de Sousa, J.
2015-11-01
We will study phase diagram the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii-Moriya interaction (D) and a uniform longitudinal (H) magnetic field, where we have observed an anomaly at low temperatures. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagram in the H - D plane on a simple cubic lattice (z=6). We analyzed the cases: anisotropic Heisenberg - case I: (Δ = 1), anisotropic Heisenberg - case II: (Δ = 0.5) and anisotropic Heisenberg - case III: (Δ = 0), where only second order phase transitions are observed.