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Sample records for two-dimensional coupled model

  1. The XY model coupled to two-dimensional quantum gravity

    Science.gov (United States)

    Baillie, C. F.; Johnston, D. A.

    1992-09-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical expectation that the phase transition remains of KT type when the XY model is coupled to gravity. We also examine whether the universality we discovered in our earlier work on various Potts models with the same value of the central charge, c, carries over to the XY model, which has c=1.

  2. The XY Model Coupled to Two-Dimensional Quantum Gravity

    CERN Document Server

    Baillie, C F; 10.1016/0370-2693(92)91037-A

    2009-01-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical expectation that the phase transition remains of KT type when the XY model is coupled to gravity. We also examine whether the universality we discovered in our earlier work on various Potts models with the same value of the central charge, $c$, carries over to the XY model, which has $c=1$.

  3. Two-dimensional model of elastically coupled molecular motors

    Institute of Scientific and Technical Information of China (English)

    Zhang Hong-Wei; Wen Shu-Tang; Chen Gai-Rong; Li Yu-Xiao; Cao Zhong-Xing; Li Wei

    2012-01-01

    A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins.Extensive Langevin simulations of the model are performed.We discuss the dependences of motion and efficiency on the model parameters,including the external force and the temperature.A good qualitative agreement with the expected behavior is observed.

  4. Multiple Potts Models Coupled to Two-Dimensional Quantum Gravity

    CERN Document Server

    Baillie, C F

    1992-01-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of {\\it multiple} $q=2,3,4$ state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the $c>1$ region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for $c>1$. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for $c>1$.

  5. Multiple Potts models coupled to two-dimensional quantum gravity

    Science.gov (United States)

    Baillie, C. F.; Johnston, D. A.

    1992-07-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.

  6. Two-Dimensional Coupling Model on Social Deprivation and Its Application

    Science.gov (United States)

    Fu, Yun

    This paper qualitatively describes the deprivation under different coupling situations of two-dimensional indicators and then establishes the two-dimensional coupling model on social deprivation, using the social welfare function approach and Foster-Greer-Thorbecke P α method. Finally, this paper applies the model to evaluate the social deprivation of 31 provinces in China under the coupling state of capita disposable income and housing price.

  7. Potts models coupled to two-dimensional quantum gravity

    Science.gov (United States)

    Baillie, Clive F.

    We perform Monte Carlo simulations using the Wolff cluster algorithm of the q=2 (Ising), 3 and 4 Potts models on dynamical phi-cubed graphs of spherical topology with up to 5000 nodes. We find that the measured critical exponents are in reasonable agreement with those from the exact solution of the Ising model and with those calculated from KPZ scaling for q=3,4 where no exact solution is available.

  8. A Solvable Model in Two-Dimensional Gravity Coupled to a Nonlinear Matter Field

    Institute of Scientific and Technical Information of China (English)

    YAN Jun; WANG Shun-Jin; TAO Bi-You

    2001-01-01

    The two-dimensional gravity model with a coupling constant k = 4 and a vanishing cosmological constant coupled to a nonlinear matter field is investigated. We found that the classical equations of motion are exactly solvable and the static solutions of the induced metric and scalar curvature can be obtained analytically. These solutions may be used to describe the naked singularity at the origin.``

  9. Modelling floor heating systems using a validated two-dimensional ground coupled numerical model

    DEFF Research Database (Denmark)

    Weitzmann, Peter; Kragh, Jesper; Roots, Peter

    2005-01-01

    the floor. This model can be used to design energy efficient houses with floor heating focusing on the heat loss through the floor construction and foundation. It is found that it is impor-tant to model the dynamics of the floor heating system to find the correct heat loss to the ground, and further......This paper presents a two-dimensional simulation model of the heat losses and tempera-tures in a slab on grade floor with floor heating which is able to dynamically model the floor heating system. The aim of this work is to be able to model, in detail, the influence from the floor construction...... and foundation on the performance of the floor heating sys-tem. The ground coupled floor heating model is validated against measurements from a single-family house. The simulation model is coupled to a whole-building energy simu-lation model with inclusion of heat losses and heat supply to the room above...

  10. Coupled two-dimensional edge plasma and neutral gas modeling of tokamak scrape-off-layers

    Energy Technology Data Exchange (ETDEWEB)

    Maingi, R. [North Carolina State Univ., Raleigh, NC (United States)

    1992-08-01

    The objective of this study is to devise a detailed description of the tokamak scrape-off-layer (SOL), which includes the best available models of both the plasma and neutral species and the strong coupling between the two in many SOL regimes. A good estimate of both particle flux and heat flux profiles at the limiter/divertor target plates is desired. Peak heat flux is one of the limiting factors in determining the survival probability of plasma-facing-components at high power levels. Plate particle flux affects the neutral flux to the pump, which determines the particle exhaust rate. A technique which couples a two-dimensional (2-D) plasma and a 2-D neutral transport code has been developed (coupled code technique), but this procedure requires large amounts of computer time. Relevant physics has been added to an existing two-neutral-species model which takes the SOL plasma/neutral coupling into account in a simple manner (molecular physics model), and this model is compared with the coupled code technique mentioned above. The molecular physics model is benchmarked against experimental data from a divertor tokamak (DIII-D), and a similar model (single-species model) is benchmarked against data from a pump-limiter tokamak (Tore Supra). The models are then used to examine two key issues: free-streaming-limits (ion energy conduction and momentum flux) and the effects of the non-orthogonal geometry of magnetic flux surfaces and target plates on edge plasma parameter profiles.

  11. Two Dimensional Mathematical Model of Tumor Angiogenesis: Coupling of Avascular Growth and Vascularization

    Directory of Open Access Journals (Sweden)

    Farideh Hosseini

    2015-09-01

    Full Text Available Introduction As a tumor grows, the demand for oxygen and nutrients increases and it grows further if acquires the ability to induce angiogenesis. In this study, we aimed to present a two-dimensional continuous mathematical model for avascular tumor growth, coupled with a discrete model of angiogenesis. Materials and Methods In the avascular growth model, tumor is considered as a single mass, which uptakes oxygen through diffusion and invades the extracellular matrix (ECM. After the tumor reaches its maximum size in the avascular growth phase, tumor cells may be in three different states (proliferative, quiescent and apoptotic, depending on oxygen availability. Quiescent cells are assumed to secrete tumor angiogenic factors, which diffuse into the surrounding tissue until reaching endothelial cells. The mathematical model for tumor angiogenesis is consisted of a five-point finite difference scheme to simulate the progression of endothelial cells in ECM and their penetration into the tumor. Results The morphology of produced networks was investigated, based on various ECM degradation patterns. The generated capillary networks involved the rules of microvascular branching and anastomosis. Model predictions were in qualitative agreement with experimental observations and might have implications as a supplementary model to facilitate mathematical analyses for anti-cancer therapies. Conclusion Our numerical simulations could facilitate the qualitative comparison between three layers of tumor cells, their TAF-producing abilities and subsequent penetration of micro-vessels in order to determine the dynamics of microvascular branching and anastomosis in ECM and three different parts of the tumor.

  12. Properties of the two-dimensional spin-1/2 Heisenberg model on a honeycomb lattice with interlayer coupling

    Directory of Open Access Journals (Sweden)

    U. Löw

    2009-01-01

    Full Text Available The magnetic properties of the two-dimensional S=1/2 (quantum antiferromagnetic Heisenberg model on a honeycomb lattice with and without interlayer coupling are studied by means of a continuous Euclidean time Quantum Monte-Carlo algorithm. The internal energy, the magnetic susceptibility and the staggered magnetization are determined in the full temperature range. For the two-dimensional system the ground-state energy/bond is found to be E0hc=-0.36303(13, and the zero temperature staggered magnetization mst=0.2681(8. For coupled planes of honeycomb systems a phase transition from an ordered phase to a disordered phase is found at T/J=0.695(10.

  13. Evolution of desertification in a two-dimensional energy balance model coupled with thermodynamics and dynamics

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The relationship between desert evolution and change in albedo has been investigated quasi-analytically using a zonal mean two-dimensional energy balance model which considers the radiation transmission process due to thermodynamics and bound- ary layer movement caused by kinetics. A climate state including temperature, zonal wind, meridional wind and vertical wind can be simulated according to the current zonal distribution of albedo. Given desert distribution, characterized by the value and distribution of albedo, the response of climate on albedo has been studied to analyze the evolution of desert climate. One significant result is that the simple model can reproduce mean meridional circulation. Another result indicates that climate corresponds to two equilibria. This happens when the junction temperature between vegetation and desert is higher than a certain critical value. As for the first equilibrium, the desert belt is predicted to move southward in the northern hemisphere with the increasing values of albedo, which corresponds to the current trend of climate change. For the second equilibrium, vegetation will expand northward with increasing values of albedo, which would indicate a narrowing of the desert belt. In order to determine if the two equilibria exist, new physical models are needed.

  14. ONE- AND TWO-DIMENSIONAL COUPLED HYDRODYNAMICS MODEL FOR DAM BREAK FLOW

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    1-D and 2-D mathematical models for dam break flow were established and verified with the measured data in laboratory. The 1-D and 2-D models were then coupled, and used to simulate the dam break flow from the reservoir tail to the dam site, the propagation of dam break waves in the downstream channel, and the submergence of dam break flow in the downstream town with the hydrodynamics method. As a numerical example, the presented model was employed to simulate dam break flow of a hydropower station under construction. In simulation, different dam-break durations, upstream flows and water levels in front of dam were considered, and these influencing factors of dam break flow were analyzed, which could be referenced in planning and designing hydropower stations.

  15. Multi-scale coupling strategy for fully two-dimensional and depth-averaged models for granular flows

    Science.gov (United States)

    Pudasaini, Shiva P.; Domnik, Birte; Miller, Stephen A.

    2013-04-01

    We developed a full two-dimensional Coulomb-viscoplastic model and applied it for inclined channel flows of granular materials from initiation to their deposition. The model includes the basic features and observed phenomena in dense granular flows like the exhibition of a yield strength and a non-zero slip velocity. A pressure-dependent yield strength is proposed to account for the frictional nature of granular materials. The yield strength can be related to the internal friction angle of the material and plays an important role, for example, in deposition processes. The interaction of the flow with the solid boundary is modelled by a pressure and rate-dependent Coulomb-viscoplastic sliding law. We developed an innovative multi-scale strategy to couple the full two-dimensional, non depth-averaged model (N-DAM) with a one-dimensional, depth-averaged model (DAM). The coupled model reduces computational complexity dramatically by using DAM only in regions with smooth changes of flow variables. The numerics uses N-DAM in regions where depth-averaging becomes inaccurate, for instance, in the initiation and deposition regions, and (particularly) when the flow hits an obstacle or a defense structure. In these regions, momentum transfer must be, and is, considered in all directions. We observe very high coupling performance, and show that the numerical results deviate only slightly from results of the much more cumbersome full two-dimensional model. This shows that the coupled model, which retains all the basic physics of the flow, is an attractive alternative to an expensive, full two-dimensional simulations. We compare simulation results with different experimental data for shock waves appearing in rapid granular flows down inclined channels and impacting a wall. The model predicts the evolution of the strong shock wave and the impact force on a rigid wall for different inclination angles and sliding surfaces. It is demonstrated that the internal friction angle plays an

  16. a Numerical Test of Kpz Scaling:. Potts Models Coupled to Two-Dimensional Quantum Gravity

    Science.gov (United States)

    Baillie, C. F.; Johnston, D. A.

    We perform Monte-Carlo simulations using the Wolff cluster algorithm of the q=2 (Ising), 3, 4 and q=10 Potts models on dynamical phi-cubed graphs of spherical topology with up to 5000 nodes. We find that the measured critical exponents are in reasonable agreement with those from the exact solution of the Ising model and with those calculated from KPZ scaling for q=3, 4 where no exact solution is available. Using Binder’s cumulant we find that the q=10 Potts model displays a first order phase transition on a dynamical graph, as it does on a fixed lattice. We also examine the internal geometry of the graphs generated in the simulation, finding a linear relationship between ring length probabilities and the central charge of the Potts model.

  17. A Numerical Test of KPZ Scaling Potts Models Coupled to Two-Dimensional Quantum Gravity

    CERN Document Server

    Baillie, C F

    1992-01-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of the q=2 (Ising), 3, 4 and q=10 Potts models on dynamical phi-cubed graphs of spherical topology with up to 5000 nodes. We find that the measured critical exponents are in reasonable agreement with those from the exact solution of the Ising model and with those calculated from KPZ scaling for q=3,4 where no exact solution is available. Using Binder's cumulant we find that the q=10 Potts model displays a first order phase transition on a dynamical graph, as it does on a fixed lattice. We also examine the internal geometry of the graphs generated in the simulation, finding a linear relationship between ring length probabilities and the central charge of the Potts model

  18. A naive matrix-model approach to two-dimensional quantum gravity coupled to matter of arbitrary central charge

    CERN Document Server

    Brézin, E

    1992-01-01

    In the usual matrix-model approach to random discretized two-dimensional manifolds, one introduces n Ising spins on each cell, i.e. a discrete version of 2D quantum gravity coupled to matter with a central charge n/2. The matrix-model consists then of an integral over $2^{n}$ matrices, which we are unable to solve for $n>1$. However for a fixed genus we can expand in the cosmological constant g for arbitrary values of n, and a simple minded analysis of the series yields for n=0,1 and 2 the expected results for the exponent $\\gamma_{string}$ with an amazing precision given the small number of terms that we considered. We then proceed to larger values of n. Simple tests of universality are successfully applied; for instance we obtain the same exponents for n=3 or for one Ising model coupled to a one dimensional target space. The calculations are easily extended to states Potts models, through an integration over $q^{n}$ matrices. We see no sign of the tachyonic instability of the theory, but we have only consid...

  19. Continuum limit of susceptibility from strong coupling expansion: Two dimensional non-linear O(N) sigma model at N>= 3

    CERN Document Server

    Yamada, Hirofumi

    2012-01-01

    Based on the strong coupling expansion, we reinvestigate the scaling behavior of the susceptibility chi of two-dimensional O(N) sigma model on the square lattice by the use of Pade-Borel approximants. To exploit the Borel transform, we express the bare coupling g in series expansion in chi. At large N, Pade-Borel approximants exhibit the scaling behavior at the four-loop level. Then, the estimation of the non-perturbative constant associated with the susceptibility is performed for N>=3 and the results are compared with the available theoretical results and Monte Carlo data.

  20. Coupled One and Two Dimensional Model for River Network Flow and Sediment Transport%一二维耦合河网水沙模型研究

    Institute of Scientific and Technical Information of China (English)

    吕文丽; 张旭

    2011-01-01

    Based on previous research, a new one and two-dimensional coupled model of river water and sediment was proposed.With reference to the three-level solution for one-dimensional river network water mode, the two-dimensional river section will be generalized to river section within the river network.One and two dimensional coupled river network sediment model will be established with the balance of flow amount and sediment transport.The model sets up the chasing relationship between variables of water level and sediment content at the end and first section to further establish matrix equations of the whole one and two-dimensional river network node water level and sediment content.Though the verification and calculation for generalized river network from Datong to Zhenjiang in the lower reaches of the Yangtze River, it is found that the model is of great practical value.%借鉴河网水流的三级解法,将二维河段概化为河网内部河段,通过河网节点流量和输沙量的平衡,建立一二维耦合河网水沙模型.模型采用全隐式方法建立二维河段以首末断面的水位和含沙量为中间变量的矩阵追赶关系,进而建立整个一二维河网的节点水位及含沙量的矩阵方程组.对方程组的求解,可实现一二维水沙模型的耦合求解.通过对长江下游大通至镇江概化河网的验证计算,表明模型具有很好的实用价值.

  1. Two dimensional Coupled Eulerian Lagrangian (CEL) model for banded structure prediction in friction stir welding with trigonal tool

    Science.gov (United States)

    Tongne, A.; Robe, H.; Desrayaud, C.; Jahazi, M.; Feulvarch, E.

    2016-10-01

    A finite element model has been developed by means of a coupled Eulerian-Lagrangian approach. The banded structure which is related to the periodical material deposition is predicted in two dimensions as the experimental investigation shows that, during FSW with trigonal tool, the material flow operates mainly in the welded plates plan.

  2. Two-dimensional coupled mathematical modeling of fluvial processes with intense sediment transport and rapid bed evolution

    Institute of Scientific and Technical Information of China (English)

    YUE ZhiYuan; CAO ZhiXian; LI Xin; CHE Tao

    2008-01-01

    Alluvial rivers may experience intense sediment transport and rapid bed evolution under a high flow regime, for which traditional decoupled mathematical river mod-els based on simplified conservation equations are not applicable. A two-dimen-sional coupled mathematical model is presented, which is generally applicable to the fluvial processes with either intense or weak sediment transport. The governing equations of the model comprise the complete shallow water hydrodynamic equa-tions closed with Manning roughness for boundary resistance and empirical rela-tionships for sediment exchange with the erodible bed. The second-order Total-Variation-Diminishing version of the Weighted-Average-Flux method, along with the HLLC approximate Riemann Solver, is adapted to solve the governing equations, which can properly resolve shock waves and contact discontinuities. The model is applied to the pilot study of the flooding due to a sudden outburst of a real glacial-lake.

  3. Two-dimensional coupled mathematical modeling of fluvial processes with intense sediment transport and rapid bed evolution

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Alluvial rivers may experience intense sediment transport and rapid bed evolution under a high flow regime,for which traditional decoupled mathematical river mod-els based on simplified conservation equations are not applicable. A two-dimen-sional coupled mathematical model is presented,which is generally applicable to the fluvial processes with either intense or weak sediment transport. The governing equations of the model comprise the complete shallow water hydrodynamic equa-tions closed with Manning roughness for boundary resistance and empirical rela-tionships for sediment exchange with the erodible bed. The second-order Total-Variation-Diminishing version of the Weighted-Average-Flux method,along with the HLLC approximate Riemann Solver,is adapted to solve the governing equations,which can properly resolve shock waves and contact discontinuities. The model is applied to the pilot study of the flooding due to a sudden outburst of a real glacial-lake.

  4. Random-lattice models and simulation algorithms for the phase equilibria in two-dimensional condensed systems of particles with coupled internal and translational degrees of freedom

    DEFF Research Database (Denmark)

    Nielsen, Morten; Miao, Ling; Ipsen, John Hjorth;

    1996-01-01

    In this work we concentrate on phase equilibria in two-dimensional condensed systems of particles where both translational and internal degrees of freedom are present and coupled through microscopic interactions, with a focus on the manner of the macroscopic coupling between the two types...

  5. A three-dimensional coupled-mode model for the acoustic field in a two-dimensional waveguide with perfectly reflecting boundaries

    Science.gov (United States)

    Luo, Wen-Yu; Yu, Xiao-Lin; Yang, Xue-Feng; Zhang, Ze-Zhong; Zhang, Ren-He

    2016-12-01

    This paper presents a three-dimensional (3D) coupled-mode model using the direct-global-matrix technique as well as Fourier synthesis. This model is a full wave, two-way three-dimensional model, and is therefore capable of providing accurate acoustic field solutions. Because the problem of sound propagation excited by a point source in an ideal wedge with perfectly reflecting boundaries is one of a few three-dimensional problems with analytical solutions, the ideal wedge problem is chosen in this work to validate the presented three-dimensional model. Numerical results show that the field results by analytical solutions and those by the presented model are in excellent agreement, indicating that the presented model can serve as a benchmark model for three-dimensional sound propagation problems involving a planar two-dimensional geometry as well as a point source. Project supported by the National Natural Science Foundation of China (Grant Nos. 11125420, 11434012, and 41561144006) and the Knowledge Innovation Program of the Chinese Academy of Sciences.

  6. Thermodynamics of two-dimensional Yukawa systems across coupling regimes

    Science.gov (United States)

    Kryuchkov, Nikita P.; Khrapak, Sergey A.; Yurchenko, Stanislav O.

    2017-04-01

    Thermodynamics of two-dimensional Yukawa (screened Coulomb or Debye-Hückel) systems is studied systematically using molecular dynamics (MD) simulations. Simulations cover very broad parameter range spanning from weakly coupled gaseous states to strongly coupled fluid and crystalline states. Important thermodynamic quantities, such as internal energy and pressure, are obtained and accurate physically motivated fits are proposed. This allows us to put forward simple practical expressions to describe thermodynamic properties of two-dimensional Yukawa systems. For crystals, in addition to numerical simulations, the recently developed shortest-graph interpolation method is applied to describe pair correlations and hence thermodynamic properties. It is shown that the finite-temperature effects can be accounted for by using simple correction of peaks in the pair correlation function. The corresponding correction coefficients are evaluated using MD simulation. The relevance of the obtained results in the context of colloidal systems, complex (dusty) plasmas, and ions absorbed to interfaces in electrolytes is pointed out.

  7. Numerical Modeling and Investigation of Fluid-Driven Fracture Propagation in Reservoirs Based on a Modified Fluid-Mechanically Coupled Model in Two-Dimensional Particle Flow Code

    Directory of Open Access Journals (Sweden)

    Jian Zhou

    2016-09-01

    Full Text Available Hydraulic fracturing is a useful tool for enhancing rock mass permeability for shale gas development, enhanced geothermal systems, and geological carbon sequestration by the high-pressure injection of a fracturing fluid into tight reservoir rocks. Although significant advances have been made in hydraulic fracturing theory, experiments, and numerical modeling, when it comes to the complexity of geological conditions knowledge is still limited. Mechanisms of fluid injection-induced fracture initiation and propagation should be better understood to take full advantage of hydraulic fracturing. This paper presents the development and application of discrete particle modeling based on two-dimensional particle flow code (PFC2D. Firstly, it is shown that the modeled value of the breakdown pressure for the hydraulic fracturing process is approximately equal to analytically calculated values under varied in situ stress conditions. Furthermore, a series of simulations for hydraulic fracturing in competent rock was performed to examine the influence of the in situ stress ratio, fluid injection rate, and fluid viscosity on the borehole pressure history, the geometry of hydraulic fractures, and the pore-pressure field, respectively. It was found that the hydraulic fractures in an isotropic medium always propagate parallel to the orientation of the maximum principal stress. When a high fluid injection rate is used, higher breakdown pressure is needed for fracture propagation and complex geometries of fractures can develop. When a low viscosity fluid is used, fluid can more easily penetrate from the borehole into the surrounding rock, which causes a reduction of the effective stress and leads to a lower breakdown pressure. Moreover, the geometry of the fractures is not particularly sensitive to the fluid viscosity in the approximate isotropic model.

  8. Diffusion induced by bounded noise in a two-dimensional coupled memory system

    Directory of Open Access Journals (Sweden)

    Pengfei Xu

    2014-01-01

    Full Text Available The diffusion behavior driven by bounded noise under the influence of a coupled harmonic potential is investigated in a two-dimensional coupled-damped model. With the help of the Laplace analysis we obtain exact descriptions for a particle's two-time dynamics which is subjected to a coupled harmonic potential and a coupled damping. The time lag is used to describe the velocity autocorrelation function and mean square displacement of the diffusing particle. The diffusion behavior for the time lag is also discussed with respect to the coupled items and the amplitude of bounded noise.

  9. Computational Validation of a Two-Dimensional Semi-Empirical Model for Inductive Coupling in a Conical Pulsed Inductive Plasma Thruster

    Science.gov (United States)

    Hallock, Ashley K.; Polzin, Kurt A.

    2011-01-01

    A two-dimensional semi-empirical model of pulsed inductive thrust efficiency is developed to predict the effect of such a geometry on thrust efficiency. The model includes electromagnetic and gas-dynamic forces but excludes energy conversion from radial motion to axial motion, with the intention of characterizing thrust efficiency loss mechanisms that result from a conical versus a at inductive coil geometry. The range of conical pulsed inductive thruster geometries to which this model can be applied is explored with the use of finite element analysis. A semi-empirical relation for inductance as a function of current sheet radial and axial position is the limiting feature of the model, restricting the applicability as a function of half cone angle to a range from ten degrees to about 60 degrees. The model is nondimensionalized, yielding a set of dimensionless performance scaling parameters. Results of the model indicate that radial current sheet motion changes the axial dynamic impedance parameter at which thrust efficiency is maximized. This shift indicates that when radial current sheet motion is permitted in the model longer characteristic circuit timescales are more efficient, which can be attributed to a lower current sheet axial velocity as the plasma more rapidly decouples from the coil through radial motion. Thrust efficiency is shown to increase monotonically for decreasing values of the radial dynamic impedance parameter. This trend indicates that to maximize the radial decoupling timescale should be long compared to the characteristic circuit timescale.

  10. Extending models for two-dimensional constraints

    DEFF Research Database (Denmark)

    Forchhammer, Søren

    2009-01-01

    Random fields in two dimensions may be specified on 2 times 2 elements such that the probabilities of finite configurations and the entropy may be calculated explicitly. The Pickard random field is one example where probability of a new (non-boundary) element is conditioned on three previous...... elements. To extend the concept we consider extending such a field such that a vector or block of elements is conditioned on a larger set of previous elements. Given a stationary model defined on 2 times 2 elements, iterative scaling is used to define the extended model. The extended model may be used...

  11. Creative computing with Landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of Earth-surface dynamics

    Science.gov (United States)

    Hobley, Daniel E. J.; Adams, Jordan M.; Nudurupati, Sai Siddhartha; Hutton, Eric W. H.; Gasparini, Nicole M.; Istanbulluoglu, Erkan; Tucker, Gregory E.

    2017-01-01

    The ability to model surface processes and to couple them to both subsurface and atmospheric regimes has proven invaluable to research in the Earth and planetary sciences. However, creating a new model typically demands a very large investment of time, and modifying an existing model to address a new problem typically means the new work is constrained to its detriment by model adaptations for a different problem. Landlab is an open-source software framework explicitly designed to accelerate the development of new process models by providing (1) a set of tools and existing grid structures - including both regular and irregular grids - to make it faster and easier to develop new process components, or numerical implementations of physical processes; (2) a suite of stable, modular, and interoperable process components that can be combined to create an integrated model; and (3) a set of tools for data input, output, manipulation, and visualization. A set of example models built with these components is also provided. Landlab's structure makes it ideal not only for fully developed modelling applications but also for model prototyping and classroom use. Because of its modular nature, it can also act as a platform for model intercomparison and epistemic uncertainty and sensitivity analyses. Landlab exposes a standardized model interoperability interface, and is able to couple to third-party models and software. Landlab also offers tools to allow the creation of cellular automata, and allows native coupling of such models to more traditional continuous differential equation-based modules. We illustrate the principles of component coupling in Landlab using a model of landform evolution, a cellular ecohydrologic model, and a flood-wave routing model.

  12. Model analysis of magnetic susceptibility of Sr2IrO4 : A two-dimensional Jeff=1/2 Heisenberg system with competing interlayer couplings

    Science.gov (United States)

    Takayama, Tomohiro; Matsumoto, Akiyo; Jackeli, George; Takagi, Hidenori

    2016-12-01

    We report the analysis of magnetic susceptibility χ (T ) of Sr2IrO4 single crystal in the paramagnetic phase. We formulate the theoretical susceptibility based on isotropic Heisenberg antiferromagnetism incorporating the Dzyaloshinsky-Moriya interaction exactly, and include the interlayer couplings in a mean-field approximation. χ (T ) above TN was found to be well described by the model, indicating the predominant Heisenberg exchange consistent with the microscopic theory. The analysis points to a competition of nearest and next-nearest-neighbor interlayer couplings, which results in the up-up-down-down configuration of the in-plane canting moments identified by the diffraction experiments.

  13. Two-dimensional lattice Boltzmann model for magnetohydrodynamics.

    Science.gov (United States)

    Schaffenberger, Werner; Hanslmeier, Arnold

    2002-10-01

    We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results.

  14. Optimised polychromatic field-mediated suppression of H-atom tunnelling in a coupled symmetric double well: two-dimensional malonaldehyde model

    Science.gov (United States)

    Ghosh, Subhasree; Talukder, Srijeeta; Sen, Shrabani; Chaudhury, Pinaki

    2015-12-01

    The cis-cis isomerisation motion of malonaldehyde can be modelled as a symmetric double well coupled with an asymmetric double well, which includes the effect of the cis-trans out-of-plane motion on the cis-cis motion. We have presented an effective method for having control over the tunnelling dynamics of the symmetric double well which is coupled with the asymmetric double well by monitoring tunnelling splitting. When a suitable external field is allowed to interact with the system, the tunnelling splitting gets modified. As the external time perturbation is periodic in nature, the Floquet theory can be applied to calculate the quasi-energies of the perturbed system and hence the tunnelling splitting. The Floquet analysis is coupled with a stochastic optimiser in order to minimise the tunnelling splitting, which is related to slowering of the tunnelling process. The minimisation has been done by one of the stochastic optimisers, simulated annealing. Optimisation has been performed on the parameters which define the external polychromatic field, such as intensities and frequencies of the components of the polychromatic field. With the optimised sets of parameters, we have followed the dynamics of the system and have found suppression of tunnelling which is manifested by a much higher tunnelling time.

  15. Two-dimensional simulation of inductively coupled plasma based on COMSOL and comparison with experimental data

    Institute of Scientific and Technical Information of China (English)

    Cheng Jia; Ji Linhong; Wang Kesheng; Han Chuankun; Shi Yixiang

    2013-01-01

    A two-dimensional axisymmetric inductively coupled plasma (ICP) model,and its implementation in the COMSOL multiphysical software,is described.The simulations are compared with the experimental results of argon discharge from the gaseous electronics conference RF reference cell in the inductively coupled plasma mode.The general trends of the number density and temperature of electrons with radial scanning are approximately correct.Finally,we discuss the reasons why the comparisons are not in agreement,and then propose an improvement in the assumptions of the Maxwellian electron energy distribution function and reaction rate.

  16. Electromechanical coupling in suspended nanomechanical resonators with a two-dimensional electron gas

    Science.gov (United States)

    Shevyrin, A. A.; Pogosov, A. G.; Bakarov, A. K.; Shklyaev, A. A.

    2017-06-01

    A physical model describing the piezoelectric-effect-mediated influence of bending of a thin suspended cantilever with a two-dimensional electron gas on the conductivity is proposed. The model shows that the conductivity change is almost entirely caused by the rapid change in mechanical stress near the boundary of suspended and non-suspended areas, rather than by the stress itself. An experiment confirming that the electromechanical coupling is associated with the piezoelectric effect is performed. The experimentally measured conductance sensitivity to the cantilever’s vibrations agree with the developed physical model.

  17. Interlayer coupling in two-dimensional titanium carbide MXenes.

    Science.gov (United States)

    Hu, Tao; Hu, Minmin; Li, Zhaojin; Zhang, Hui; Zhang, Chao; Wang, Jingyang; Wang, Xiaohui

    2016-07-27

    Success in the exfoliation of the stacked T-functionalized titanium carbide MXenes Tin+1CnT2 (T = OH, O, and F) would potentially extend their application scope, which requires an understanding of the nature of interlayer coupling. Here, we report for the first time the intrinsic interlayer coupling in pristine MXenes on the basis of first-principles calculations by taking long-range interaction into account. It is demonstrated that the functional terminations (OH, O, and F) weaken the interlayer coupling as compared with the bare counterparts, whereas the coupling is significantly stronger than van der Waals bonding as specified by the fact that the binding energies of stacked Tin+1CnT2 are 2-6 times those of well-known graphite and MoS2 with weak interlayer coupling. With binding energies in the range of 1-3.3 J m(-2), the successful exfoliation of stacked Tin+1CnT2 into monolayers invariably requires further weakening of the interlayer coupling.

  18. Dynamical phase transitions in the two-dimensional ANNNI model

    Energy Technology Data Exchange (ETDEWEB)

    Barber, M.N.; Derrida, B.

    1988-06-01

    We study the phase diagram of the two-dimensional anisotropic next-nearest neighbor Ising (ANNNI) model by comparing the time evolution of two distinct spin configurations submitted to the same thermal noise. We clearly se several dynamical transitions between ferromagnetic, paramagnetic, antiphase, and floating phases. These dynamical transitions seem to occur rather close to the transition lines determined previously in the literature.

  19. Two-dimensional effects in nonlinear Kronig-Penney models

    DEFF Research Database (Denmark)

    Gaididei, Yuri Borisovich; Christiansen, Peter Leth; Rasmussen, Kim

    1997-01-01

    An analysis of two-dimensional (2D) effects in the nonlinear Kronig-Penney model is presented. We establish an effective one-dimensional description of the 2D effects, resulting in a set of pseudodifferential equations. The stationary states of the 2D system and their stability is studied...

  20. Piezoelectric Electromechanical Coupling in Nanomechanical Resonators with a Two-Dimensional Electron Gas

    Science.gov (United States)

    Shevyrin, A. A.; Pogosov, A. G.; Bakarov, A. K.; Shklyaev, A. A.

    2016-07-01

    The electrical response of a two-dimensional electron gas to vibrations of a nanomechanical cantilever containing it is studied. Vibrations of perpendicularly oriented cantilevers are experimentally shown to oppositely change the conductivity near their bases. This indicates the piezoelectric nature of electromechanical coupling. A physical model is developed, which quantitatively explains the experiment. It shows that the main origin of the conductivity change is a rapid change in the mechanical stress on the boundary between suspended and nonsuspended areas, rather than the stress itself.

  1. Towards a two dimensional model of surface piezoelectricity

    OpenAIRE

    Monge Víllora, Oscar

    2016-01-01

    We want to understand the behaviour of flexoelectricity and surface piezoelectricity and distinguish them in order to go deep into the controversies of the filed. This motivate the construction of a model of continuum flexoelectric theory. The model proposed is a two-dimensional model that integrates the electromechanical equations that include the elastic, dielectric, piezoelectric and flexoelectric effect on a rectangular sample. As the flexoelectric and the surface piezoelectric effects ap...

  2. Minor magnetization loops in two-dimensional dipolar Ising model

    Energy Technology Data Exchange (ETDEWEB)

    Sarjala, M. [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland); Seppaelae, E.T., E-mail: eira.seppala@nokia.co [Nokia Research Center, Itaemerenkatu 11-13, FI-00180 Helsinki (Finland); Alava, M.J., E-mail: mikko.alava@tkk.f [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland)

    2011-05-15

    The two-dimensional dipolar Ising model is investigated for the relaxation and dynamics of minor magnetization loops. Monte Carlo simulations show that in a stripe phase an exponential decrease can be found for the magnetization maxima of the loops, M{approx}exp(-{alpha}N{sub l}) where N{sub l} is the number of loops. We discuss the limits of this behavior and its relation to the equilibrium phase diagram of the model.

  3. A two-dimensional analytical model of petroleum vapor intrusion

    Science.gov (United States)

    Yao, Yijun; Verginelli, Iason; Suuberg, Eric M.

    2016-02-01

    In this study we present an analytical solution of a two-dimensional petroleum vapor intrusion model, which incorporates a steady-state diffusion-dominated vapor transport in a homogeneous soil and piecewise first-order aerobic biodegradation limited by oxygen availability. This new model can help practitioners to easily generate two-dimensional soil gas concentration profiles for both hydrocarbons and oxygen and estimate hydrocarbon indoor air concentrations as a function of site-specific conditions such as source strength and depth, reaction rate constant, soil characteristics and building features. The soil gas concentration profiles generated by this new model are shown in good agreement with three-dimensional numerical simulations and two-dimensional measured soil gas data from a field study. This implies that for cases involving diffusion dominated soil gas transport, steady state conditions and homogenous source and soil, this analytical model can be used as a fast and easy-to-use risk screening tool by replicating the results of 3-D numerical simulations but with much less computational effort.

  4. Phase Transitions in Two-Dimensional Traffic Flow Models

    CERN Document Server

    Cuesta, J A; Molera, J M; Cuesta, José A; Martinez, Froilán C; Molera, Juan M

    1993-01-01

    Abstract: We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.

  5. Phase Transitions in Two-Dimensional Traffic Flow Models

    CERN Document Server

    Cuesta, José A; Molera, Juan M; Escuela, Angel Sánchez; 10.1103/PhysRevE.48.R4175

    2009-01-01

    We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.

  6. Corner wetting transition in the two-dimensional Ising model

    Science.gov (United States)

    Lipowski, Adam

    1998-07-01

    We study the interfacial behavior of the two-dimensional Ising model at the corner of weakened bonds. Monte Carlo simulations results show that the interface is pinned to the corner at a lower temperature than a certain temperature Tcw at which it undergoes a corner wetting transition. The temperature Tcw is substantially lower than the temperature of the ordinary wetting transition with a line of weakened bonds. A solid-on-solid-like model is proposed, which provides a supplementary description of the corner wetting transition.

  7. AN APPROACH IN MODELING TWO-DIMENSIONAL PARTIALLY CAVITATING FLOW

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    An approach of modeling viscosity, unsteady partially cavitating flows around lifting bodies is presented. By employing an one-fluid Navier-Stokers solver, the algorithm is proved to be able to handle two-dimensional laminar cavitating flows at moderate Reynolds number. Based on the state equation of water-vapor mixture, the constructive relations of densities and pressures are established. To numerically simulate the cavity wall, different pseudo transition of density models are presumed. The finite-volume method is adopted and the algorithm can be extended to three-dimensional cavitating flows.

  8. Elastic models of defects in two-dimensional crystals

    Science.gov (United States)

    Kolesnikova, A. L.; Orlova, T. S.; Hussainova, I.; Romanov, A. E.

    2014-12-01

    Elastic models of defects in two-dimensional (2D) crystals are presented in terms of continuum mechanics. The models are based on the classification of defects, which is founded on the dimensionality of the specification region of their self-distortions, i.e., lattice distortions associated with the formation of defects. The elastic field of an infinitesimal dislocation loop in a film is calculated for the first time. The fields of the center of dilatation, dislocation, disclination, and circular inclusion in planar 2D elastic media, namely, nanofilms and graphenes, are considered. Elastic fields of defects in 2D and 3D crystals are compared.

  9. Approaches to verification of two-dimensional water quality models

    Energy Technology Data Exchange (ETDEWEB)

    Butkus, S.R. (Tennessee Valley Authority, Chattanooga, TN (USA). Water Quality Dept.)

    1990-11-01

    The verification of a water quality model is the one procedure most needed by decision making evaluating a model predictions, but is often not adequate or done at all. The results of a properly conducted verification provide the decision makers with an estimate of the uncertainty associated with model predictions. Several statistical tests are available for quantifying of the performance of a model. Six methods of verification were evaluated using an application of the BETTER two-dimensional water quality model for Chickamauga reservoir. Model predictions for ten state variables were compared to observed conditions from 1989. Spatial distributions of the verification measures showed the model predictions were generally adequate, except at a few specific locations in the reservoir. The most useful statistics were the mean standard error of the residuals. Quantifiable measures of model performance should be calculated during calibration and verification of future applications of the BETTER model. 25 refs., 5 figs., 7 tabs.

  10. Theoretical and experimental study of the normal modes in a coupled two-dimensional system

    CERN Document Server

    Giménez, Marcos H; Gómez-Tejedor, José Antonio; Velazquez, Luisberis; Monsoriu, Juan A

    2016-01-01

    In this work, the normal modes of a two-dimensional oscillating system have been studied from a theoretical and experimental point of view. The normal frequencies predicted by the Hessian matrix for a coupled two-dimensional particle system are compared to those obtained for a real system consisting of two oscillating smartphones coupled one to the other by springs. Experiments are performed on an air table in order to remove the friction forces. The oscillation data are captured by the acceleration sensor of the smartphones and exported to file for further analysis. The experimental frequencies compare reasonably well with the theoretical predictions, namely, within 1.7 % of discrepancy.

  11. On some classes of two-dimensional local models in discrete two-dimensional monatomic FPU lattice with cubic and quartic potential

    Institute of Scientific and Technical Information of China (English)

    Xu Quan; Tian Qiang

    2009-01-01

    This paper discusses the two-dimensional discrete monatomic Fermi-Pasta-Ulam lattice, by using the method of multiple-scale and the quasi-discreteness approach. By taking into account the interaction between the atoms in the lattice and their nearest neighbours, it obtains some classes of two-dimensional local models as follows: two-dimensional bright and dark discrete soliton trains, two-dimensional bright and dark line discrete breathers, and two-dimensional bright and dark discrete breather.

  12. Two dimensional hydrodynamic modeling of a high latitude braided river

    Science.gov (United States)

    Humphries, E.; Pavelsky, T.; Bates, P. D.

    2014-12-01

    Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.

  13. Inducing an Incipient Terahertz Finite Plasmonic Crystal in Coupled Two Dimensional Plasmonic Cavities

    CERN Document Server

    Dyer, Gregory C; Preu, Sascha; Vinh, N Q; Allen, S James; Reno, John L; Shaner, Eric A

    2016-01-01

    We measured a change in the current transport of an antenna-coupled, multi-gate, GaAs/AlGaAs field-effect transistor when terahertz electromagnetic waves irradiated the transistor and attribute the change to bolometric heating of the electrons in the two-dimensional electron channel. The observed terahertz absorption spectrum indicates coherence between plasmons excited under adjacent biased device gates. The experimental results agree quantitatively with a theoretical model we developed that is based on a generalized plasmonic transmission line formalism and describes an evolution of the plasmonic spectrum with increasing electron density modulation from homogeneous to the crystal limit. These results demonstrate an electronically induced and dynamically tunable plasmonic band structure.

  14. Two-dimensional Josephson junction arrays coupled through a high-Q cavity

    DEFF Research Database (Denmark)

    Filatrella, G.; Pedersen, Niels Falsig; Wiesenfeld, K.

    2001-01-01

    the cavity. The highly resonant cavity induces synchronized behavior, which is qualitatively different than what is familiar from other studies on nonlinear oscillator arrays, for example the Kuramoto model. We also address the effects of disorder, as well as the role of detuning between the spontaneous...... emission frequency of the junctions and the cavity resonant frequency. We show with a simple argument that we can predict the scaling behavior of disorder with the size of the array. The consequences for the design of microwave oscillators in the Gigahertz region are discussed......The problem of disordered two-dimensional arrays of underdamped Josephson junctions is addressed. Our simulations show that when coupled to a high-Q cavity, the array exhibits synchronized behavior, and the power emitted can be considerably increased once enough junctions are activated to pump...

  15. Ordering in Two-Dimensional Ising Models with Competing Interactions

    OpenAIRE

    2004-01-01

    We study the 2D Ising model on a square lattice with additional non-equal diagonal next-nearest neighbor interactions. The cases of classical and quantum (transverse) models are considered. Possible phases and their locations in the space of three Ising couplings are analyzed. In particular, incommensurate phases occurring only at non-equal diagonal couplings, are predicted. We also analyze a spin-pseudospin model comprised of the quantum Ising model coupled to XY spin chains in a particular ...

  16. Surface Ship Shock Modeling and Simulation: Two-Dimensional Analysis

    Directory of Open Access Journals (Sweden)

    Young S. Shin

    1998-01-01

    Full Text Available The modeling and simulation of the response of a surface ship system to underwater explosion requires an understanding of many different subject areas. These include the process of underwater explosion events, shock wave propagation, explosion gas bubble behavior and bubble-pulse loading, bulk and local cavitation, free surface effect, fluid-structure interaction, and structural dynamics. This paper investigates the effects of fluid-structure interaction and cavitation on the response of a surface ship using USA-NASTRAN-CFA code. First, the one-dimensional Bleich-Sandler model is used to validate the approach, and second, the underwater shock response of a two-dimensional mid-section model of a surface ship is predicted with a surrounding fluid model using a constitutive equation of a bilinear fluid which does not allow transmission of negative pressures.

  17. Two-dimensional Numerical Modeling Research on Continent Subduction Dynamics

    Institute of Scientific and Technical Information of China (English)

    WANG Zhimin; XU Bei; ZHOU Yaoqi; XU Hehua; HUANG Shaoying

    2004-01-01

    Continent subduction is one of the hot research problems in geoscience. New models presented here have been set up and two-dimensional numerical modeling research on the possibility of continental subduction has been made with the finite element software, ANSYS, based on documentary evidence and reasonable assumptions that the subduction of oceanic crust has occurred, the subduction of continental crust can take place and the process can be simplified to a discontinuous plane strain theory model. The modeling results show that it is completely possible for continental crust to be subducted to a depth of 120 km under certain circumstances and conditions. At the same time, the simulations of continental subduction under a single dynamical factor have also been made, including the pull force of the subducted oceanic lithosphere, the drag force connected with mantle convection and the push force of the mid-ocean ridge. These experiments show that the drag force connected with mantle convection is critical for continent subduction.

  18. Instability of a two-dimensional Bose–Einstein condensate with Rashba spin–orbit coupling at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    He, Pei-Song, E-mail: hepeisong@th.btbu.edu.cn; Zhao, Jia; Geng, Ai-Cong; Xu, Deng-Hui; Hu, Rong

    2013-11-01

    We prove that in a two-dimensional homogeneous boson system with Rashba spin–orbit coupling, Bose–Einstein condensate with plane-wave order is unstable at finite temperature. The calculations are based on a nonlinear sigma model scheme. The density wave contributions to the thermal deletions are divergent in the infrared limit. The behavior of the divergence is different from that without spin–orbit coupling.

  19. Equation of State of the Two-Dimensional Hubbard Model

    Science.gov (United States)

    Cocchi, Eugenio; Miller, Luke A.; Drewes, Jan H.; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-04-01

    The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0 ≲U /t ≲20 and temperatures, down to kBT /t =0.63 (2 ) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches.

  20. Two dimensional black-hole as a topological coset model of c=1 string theory

    CERN Document Server

    Mukhi, S

    1993-01-01

    We show that a special superconformal coset (with $\\hat c =3$) is equivalent to $c=1$ matter coupled to two dimensional gravity. This identification allows a direct computation of the correlation functions of the $c=1$ non-critical string to all genus, and at nonzero cosmological constant, directly from the continuum approach. The results agree with those of the matrix model. Moreover we connect our coset with a twisted version of a Euclidean two dimensional black hole, in which the ghost and matter systems are mixed.

  1. A two-dimensional mathematical model of percutaneous drug absorption

    Directory of Open Access Journals (Sweden)

    Kubota K

    2004-06-01

    Full Text Available Abstract Background When a drug is applied on the skin surface, the concentration of the drug accumulated in the skin and the amount of the drug eliminated into the blood vessel depend on the value of a parameter, r. The values of r depend on the amount of diffusion and the normalized skin-capillary clearence. It is defined as the ratio of the steady-state drug concentration at the skin-capillary boundary to that at the skin-surface in one-dimensional models. The present paper studies the effect of the parameter values, when the region of contact of the skin with the drug, is a line segment on the skin surface. Methods Though a simple one-dimensional model is often useful to describe percutaneous drug absorption, it may be better represented by multi-dimensional models. A two-dimensional mathematical model is developed for percutaneous absorption of a drug, which may be used when the diffusion of the drug in the direction parallel to the skin surface must be examined, as well as in the direction into the skin, examined in one-dimensional models. This model consists of a linear second-order parabolic equation with appropriate initial conditions and boundary conditions. These boundary conditions are of Dirichlet type, Neumann type or Robin type. A finite-difference method which maintains second-order accuracy in space along the boundary, is developed to solve the parabolic equation. Extrapolation in time is applied to improve the accuracy in time. Solution of the parabolic equation gives the concentration of the drug in the skin at a given time. Results Simulation of the numerical methods described is carried out with various values of the parameter r. The illustrations are given in the form of figures. Conclusion Based on the values of r, conclusions are drawn about (1 the flow rate of the drug, (2 the flux and the cumulative amount of drug eliminated into the receptor cell, (3 the steady-state value of the flux, (4 the time to reach the steady

  2. Use of real Dirac matrices in two-dimensional coupled linear optics

    Science.gov (United States)

    Baumgarten, C.

    2011-11-01

    The Courant-Snyder theory for two-dimensional coupled linear optics is presented, based on the systematic use of the real representation of the Dirac matrices. Since any real 4×4 matrix can be expressed as a linear combination of these matrices, the presented ansatz allows for a comprehensive and complete treatment of two-dimensional linear coupling. A survey of symplectic transformations in two dimensions is presented. A subset of these transformations is shown to be identical to rotations and Lorentz boosts in Minkowski space-time. The transformation properties of the classical state vector are formulated and found to be analog to those of a Dirac spinor. The equations of motion for a relativistic charged particle—the Lorentz force equations—are shown to be isomorph to envelope equations of two-dimensional linear coupled optics. A universal and straightforward method to decouple two-dimensional harmonic oscillators with constant coefficients by symplectic transformations is presented, which is based on this isomorphism. The method yields the eigenvalues (i.e., tunes) and eigenvectors and can be applied to a one-turn transfer matrix or directly to the coefficient matrix of the linear differential equation.

  3. Coherent two-dimensional spectroscopy of a Fano model

    CERN Document Server

    Poulsen, Felipe; Pullerits, Tõnu; Hansen, Thorsten

    2016-01-01

    The Fano lineshape arises from the interference of two excitation pathways to reach a continuum. Its generality has resulted in a tremendous success in explaining the lineshapes of many one-dimensional spectroscopies - absorption, emission, scattering, conductance, photofragmentation - applied to very varied systems - atoms, molecules, semiconductors and metals. Unravelling a spectroscopy into a second dimension reveals the relationship between states in addition to decongesting the spectra. Femtosecond-resolved two-dimensional electronic spectroscopy (2DES) is a four-wave mixing technique that measures the time-evolution of the populations, and coherences of excited states. It has been applied extensively to the dynamics of photosynthetic units, and more recently to materials with extended band-structures. In this letter, we solve the full time-dependent third-order response, measured in 2DES, of a Fano model and give the new system parameters that become accessible.

  4. Current fluctuations in a two dimensional model of heat conduction

    Science.gov (United States)

    Pérez-Espigares, Carlos; Garrido, Pedro L.; Hurtado, Pablo I.

    2011-03-01

    In this work we study numerically and analytically current fluctuations in the two-dimensional Kipnis-Marchioro-Presutti (KMP) model of heat conduction. For that purpose, we use a recently introduced algorithm which allows the direct evaluation of large deviations functions. We compare our results with predictions based on the Hydrodynamic Fluctuation Theory (HFT) of Bertini and coworkers, finding very good agreement in a wide interval of current fluctuations. We also verify the existence of a well-defined temperature profile associated to a given current fluctuation which depends exclusively on the magnitude of the current vector, not on its orientation. This confirms the recently introduced Isometric Fluctuation Relation (IFR), which results from the time-reversibility of the dynamics, and includes as a particular instance the Gallavotti-Cohen fluctuation theorem in this context but adds a completely new perspective on the high level of symmetry imposed by timereversibility on the statistics of nonequilibrium fluctuations.

  5. Mathematical modeling of the neuron morphology using two dimensional images.

    Science.gov (United States)

    Rajković, Katarina; Marić, Dušica L; Milošević, Nebojša T; Jeremic, Sanja; Arsenijević, Valentina Arsić; Rajković, Nemanja

    2016-02-01

    In this study mathematical analyses such as the analysis of area and length, fractal analysis and modified Sholl analysis were applied on two dimensional (2D) images of neurons from adult human dentate nucleus (DN). Using mathematical analyses main morphological properties were obtained including the size of neuron and soma, the length of all dendrites, the density of dendritic arborization, the position of the maximum density and the irregularity of dendrites. Response surface methodology (RSM) was used for modeling the size of neurons and the length of all dendrites. However, the RSM model based on the second-order polynomial equation was only possible to apply to correlate changes in the size of the neuron with other properties of its morphology. Modeling data provided evidence that the size of DN neurons statistically depended on the size of the soma, the density of dendritic arborization and the irregularity of dendrites. The low value of mean relative percent deviation (MRPD) between the experimental data and the predicted neuron size obtained by RSM model showed that model was suitable for modeling the size of DN neurons. Therefore, RSM can be generally used for modeling neuron size from 2D images.

  6. A two-dimensional global simulation study of inductive-dynamic magnetosphere-ionosphere coupling

    Science.gov (United States)

    Tu, Jiannan; Song, Paul

    2016-12-01

    We present the numerical methods and results of a global two-dimensional multifluid-collisional-Hall magnetohydrodynamic (MHD) simulation model of the ionosphere-thermosphere system, an extension of our one-dimensional three-fluid MHD model. The model solves, self-consistently, Maxwell's equations, continuity, momentum, and energy equations for multiple ion and neutral species incorporating photochemistry, collisions among the electron, ion and neutral species, and various heating sources in the energy equations. The inductive-dynamic approach (solving self-consistently Faraday's law and retaining inertia terms in the plasma momentum equations) used in the model retains all possible MHD waves, thus providing faithful physical explanation (not merely description) of the magnetosphere-ionosphere/thermosphere (M-IT) coupling. In the present study, we simulate the dawn-dusk cross-polar cap dynamic responses of the ionosphere to imposed magnetospheric convection. It is shown that the convection velocity at the top boundary launches velocity, magnetic, and electric perturbations propagating with the Alfvén speed toward the bottom of the ionosphere. Within the system, the waves experience reflection, penetration, and rereflection because of the inhomogeneity of the plasma conditions. The reflection of the Alfvén waves may cause overshoot (stronger than the imposed magnetospheric convection) of the plasma velocity in some regions. The simulation demonstrates dynamic propagation of the field-aligned currents and ionospheric electric field carried by the Alfvén waves, as well as formation of closure horizontal currents (Pedersen currents in the E region), indicating that in the dynamic stage the M-I coupling is via the Alfvén waves instead of field-aligned currents or electric field mapping as described in convectional M-I coupling models.

  7. Monte Carlo renormalization-group investigation of the two-dimensional O(4) sigma model

    Science.gov (United States)

    Heller, Urs M.

    1988-01-01

    An improved Monte Carlo renormalization-group method is used to determine the beta function of the two-dimensional O(4) sigma model. While for (inverse) couplings beta = greater than about 2.2 agreement is obtained with asymptotic scaling according to asymptotic freedom, deviations from it are obtained at smaller couplings. They are, however, consistent with the behavior of the correlation length, indicating 'scaling' according to the full beta function. These results contradict recent claims that the model has a critical point at finite coupling.

  8. Monte Carlo renormalization-group investigation of the two-dimensional O(4) sigma model

    Science.gov (United States)

    Heller, Urs M.

    1988-01-01

    An improved Monte Carlo renormalization-group method is used to determine the beta function of the two-dimensional O(4) sigma model. While for (inverse) couplings beta = greater than about 2.2 agreement is obtained with asymptotic scaling according to asymptotic freedom, deviations from it are obtained at smaller couplings. They are, however, consistent with the behavior of the correlation length, indicating 'scaling' according to the full beta function. These results contradict recent claims that the model has a critical point at finite coupling.

  9. The gauging of two-dimensional bosonic sigma models on world-sheets with defects

    CERN Document Server

    Gawedzki, Krzysztof; Waldorf, Konrad

    2013-01-01

    We extend our analysis of the gauging of rigid symmetries in bosonic two-dimensional sigma models with Wess-Zumino terms in the action to the case of world-sheets with defects. A structure that permits a non-anomalous coupling of such sigma models to world-sheet gauge fields of arbitrary topology is analysed, together with obstructions to its existence, and the classification of its inequivalent choices.

  10. Two-dimensional model for circulating fluidized-bed reactors

    Energy Technology Data Exchange (ETDEWEB)

    Schoenfelder, H.; Kruse, M.; Werther, J. [Technical Univ. Hamburg-Harburg, Hamburg (Germany). Dept. of Chemical Engineering

    1996-07-01

    Circulating fluidized bed reactors are widely used for the combustion of coal in power stations as well as for the cracking of heavy oil in the petroleum industry. A two-dimensional reactor model for circulating fluidized beds (CFB) was studied based on the assumption that at every location within the riser, a descending dense phase and a rising lean phase coexist. Fluid mechanical variables may be calculated from one measured radial solids flux profile (upward and downward). The internal mass-transfer behavior is described on the basis of tracer gas experiments. The CFB reactor model was tested against data from ozone decomposition experiments in a CFB cold flow model (15.6-m height, 0.4-m ID) operated in the ranges 2.5--4.5 m/s and 9--45 kg/(m{sup 2}{center_dot}s) of superficial gas velocity and solids mass flux, respectively. Based on effective reaction rate constants determined from the ozone exit concentration, the model was used to predict the spatial reactant distribution within the reactor. Model predictions agreed well with measurements.

  11. Modulation on the collective response behavior by the system size in two-dimensional coupled cell systems

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Jiqian; SHEN; Chuansheng; CUI; Zhifeng

    2006-01-01

    By the intracellular calcium ionic minimal model proposed by Berridge, we investigated the collective response of two-dimensional (N×N) coupled cell systems to the external stimulation using numerical simulation methods. With a coupled intensity fixed and an appropriate coupled cell number chosen, the kinetic system size resonance was discovered. At the same time, it was found that the system size responding to the external stimulation for different coupled intensities transferred too, especially when the coupled intensity increased, the range of the corresponding system size extended. These phenomena illustrate that the coupled cell number and the coupled intensity can play constructive roles in noisy coupled systems, by which the biology system would probably improve its capability to respond to the external stimulation.

  12. Two-dimensional coupled fluid and electrodynamic calculations for a MHD DCW channel with slag layers

    Science.gov (United States)

    Liu, B. L.

    1982-01-01

    A fully coupled, two dimensional numerical method of modeling linear, coal-fired MHD generators is developed for the case of a plasma flow bounded by a slag layer on the channel walls. The governing partial differential equations for the plasma flow, slag layer and electrodynamics are presented and their coupling discussed. An iterative, numerical procedure employing non-uniform computational meshes and appropriate tridiagonal matrix solution schemes for the equations is presented. The method permits the investigation of the mutual plasma flow-slag layer development for prescribed wall temperatures, electrode geometry, slag properties and channel loading. In particular, the slag layer-plasma interface properties which require prior specification in an uncoupled analysis comprise part of the solution in the present approach. Results are presented for a short diagonally connected generator channel and include contour plots of the electric potential and current stream function as well as transverse and axial profiles of pertinent plasma properties. The results indicate that a thin electrode slag layer can be maintained in the presence of reasonable current density levels.

  13. A two-dimensional hydrodynamic model of a tidal estuary

    Science.gov (United States)

    Walters, Roy A.; Cheng, Ralph T.

    1979-01-01

    A finite element model is described which is used in the computation of tidal currents in an estuary. This numerical model is patterned after an existing algorithm and has been carefully tested in rectangular and curve-sided channels with constant and variable depth. One of the common uncertainties in this class of two-dimensional hydrodynamic models is the treatment of the lateral boundary conditions. Special attention is paid specifically to addressing this problem. To maintain continuity within the domain of interest, ‘smooth’ curve-sided elements must be used at all shoreline boundaries. The present model uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and a linear basis function for water surface elevation. An implicit time integration is used and the model is unconditionally stable. The resultant governing equations are nonlinear owing to the advective and the bottom friction terms and are solved iteratively at each time step by the Newton-Raphson method. Model test runs have been made in the southern portion of San Francisco Bay, California (South Bay) as well as in the Bay west of Carquinez Strait. Owing to the complex bathymetry, the hydrodynamic characteristics of the Bay system are dictated by the generally shallow basins which contain deep, relict river channels. Great care must be exercised to ensure that the conservation equations remain locally as well as globally accurate. Simulations have been made over several representative tidal cycles using this finite element model, and the results compare favourably with existing data. In particular, the standing wave in South Bay and the progressive wave in the northern reach are well represented.

  14. DISCRETE MODELLING OF TWO-DIMENSIONAL LIQUID FOAMS

    Institute of Scientific and Technical Information of China (English)

    Qicheng Sun

    2003-01-01

    Liquid foam is a dense random packing of gas or liquid bubbles in a small amount of immiscible liquid containing surfactants. The liquid within the Plateau borders, although small in volume, causes considerable difficulties to the investigation of the spatial structure and physical properties of foams, and the situation becomes even more complicated as the fluid flows. To solve these problems, a discrete model of two-dimensional liquid foams on the bubble scale is proposed in this work. The bubble surface is represented with finite number of nodes, and the liquid within Plateau borders is discretized into lattice particles. The gas in bubbles is treated as ideal gas at constant temperatures. This model is tested by choosing an arbitrary shape bubble as the initial condition. This then automatically evolves into a circular shape, which indicates that the surface energy minimum routine is obeyed without calling external controlling conditions. Without inserting liquid particle among the bubble channels, periodic ordered and disordered dry foams are both simulated, and the fine foam structures are developed. Wet foams are also simulated by inserting fluid among bubble channels. The calculated coordination number, as a function of liquid fractions, agrees well with the standard values.

  15. Development of two-dimensional hot pool model

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Yong Bum; Hahn, H. D

    2000-05-01

    During a normal reactor scram, the heat generation is reduced almost instantaneously while the coolant flow rate follows the pump coast-down. This mismatch between power and flow results in a situation where the core flow entering the hot pool is at a lower temperature than the temperature of the bulk pool sodium. This temperature difference leads to thermal stratification. Thermal stratification can occur in the hot pool region if the entering coolant is colder than the existing hot pool coolant and the flow momentum is not large enough to overcome the negative buoyancy force. Since the fluid of hot pool enters IHX{sub s}, the temperature distribution of hot pool can alter the overall system response. Hence, it is necessary to predict the pool coolant temperature distribution with sufficient accuracy to determine the inlet temperature conditions for the IHX{sub s} and its contribution to the net buoyancy head. Therefore, in this study two-dimensional hot pool model is developed instead of existing one-dimensional model to predict the hot pool coolant temperature and velocity distribution more accurately and is applied to the SSC-K code.

  16. Repulsively interacting fermions in a two-dimensional deformed trap with spin-orbit coupling

    DEFF Research Database (Denmark)

    Marchukov, O. V.; Fedorov, D. V.; Jensen, A. S.

    2015-01-01

    We investigate a two-dimensional system of fermions with two internal (spin) degrees of freedom. It is confined by a deformed harmonic trap and subject to a Zeeman field, Rashba or Dresselhaus one-body spin-orbit couplings and two-body short range repulsion. We obtain self-consistent mean-field $...... that cold atoms may be used to study quantum chaos both in the presence and absence of interactions....

  17. A Multifunctional Interface Method for Coupling Finite Element and Finite Difference Methods: Two-Dimensional Scalar-Field Problems

    Science.gov (United States)

    Ransom, Jonathan B.

    2002-01-01

    A multifunctional interface method with capabilities for variable-fidelity modeling and multiple method analysis is presented. The methodology provides an effective capability by which domains with diverse idealizations can be modeled independently to exploit the advantages of one approach over another. The multifunctional method is used to couple independently discretized subdomains, and it is used to couple the finite element and the finite difference methods. The method is based on a weighted residual variational method and is presented for two-dimensional scalar-field problems. A verification test problem and a benchmark application are presented, and the computational implications are discussed.

  18. Two Dimensional Symmetric Correlation Functions of the S Operator and Two Dimensional Fourier Transforms: Considering the Line Coupling for P and R Lines of Linear Molecules

    Science.gov (United States)

    Ma, Q.; Boulet, C.; Tipping, R. H.

    2014-01-01

    The refinement of the Robert-Bonamy (RB) formalism by considering the line coupling for isotropic Raman Q lines of linear molecules developed in our previous study [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013)] has been extended to infrared P and R lines. In these calculations, the main task is to derive diagonal and off-diagonal matrix elements of the Liouville operator iS1 - S2 introduced in the formalism. When one considers the line coupling for isotropic Raman Q lines where their initial and final rotational quantum numbers are identical, the derivations of off-diagonal elements do not require extra correlation functions of the ^S operator and their Fourier transforms except for those used in deriving diagonal elements. In contrast, the derivations for infrared P and R lines become more difficult because they require a lot of new correlation functions and their Fourier transforms. By introducing two dimensional correlation functions labeled by two tensor ranks and making variable changes to become even functions, the derivations only require the latters' two dimensional Fourier transforms evaluated at two modulation frequencies characterizing the averaged energy gap and the frequency detuning between the two coupled transitions. With the coordinate representation, it is easy to accurately derive these two dimensional correlation functions. Meanwhile, by using the sampling theory one is able to effectively evaluate their two dimensional Fourier transforms. Thus, the obstacles in considering the line coupling for P and R lines have been overcome. Numerical calculations have been carried out for the half-widths of both the isotropic Raman Q lines and the infrared P and R lines of C2H2 broadened by N2. In comparison with values derived from the RB formalism, new calculated values are significantly reduced and become closer to measurements.

  19. Improved actions for the two-dimensional sigma-model

    OpenAIRE

    Caracciolo, Sergio; Montanari, Andrea; Pelissetto, Andrea

    1997-01-01

    For the O(N) sigma-model we studied the improvement program for actions with two- and four-spin interactions. An interesting example is an action which is reflection-positive, on-shell improved, and has all the coupling defined on an elementary plaquette. We show the large N solution and preliminary Monte Carlo results for N=3.

  20. Two-Dimensional Electronic Spectroscopy of a Model Dimer System

    Directory of Open Access Journals (Sweden)

    Prokhorenko V.I.

    2013-03-01

    Full Text Available Two-dimensional spectra of a dimer were measured to determine the timescale for electronic decoherence at room temperature. Anti-correlated beats in the crosspeaks were observed only during the period corresponding to the measured homogeneous lifetime.

  1. Strong light-matter coupling in two-dimensional atomic crystals

    CERN Document Server

    Liu, Xiaoze; Sun, Zheng; Xia, Fengnian; Lin, Erh-chen; Lee, Yi-Hsien; Kéna-Cohen, Stéphane; Menon, Vinod M

    2014-01-01

    Two dimensional (2D) atomic crystals of graphene, and transition metal dichalcogenides have emerged as a class of materials that show strong light-matter interaction. This interaction can be further controlled by embedding such materials into optical microcavities. When the interaction is engineered to be stronger than the dissipation of light and matter entities, one approaches the strong coupling regime resulting in the formation of half-light half-matter bosonic quasiparticles called microcavity polaritons. Here we report the evidence of strong light-matter coupling and formation of microcavity polaritons in a two dimensional atomic crystal of molybdenum disulphide (MoS2) embedded inside a dielectric microcavity at room temperature. A Rabi splitting of 46 meV and highly directional emission is observed from the MoS2 microcavity owing to the coupling between the 2D excitons and the cavity photons. Realizing strong coupling effects at room temperature in a disorder free potential landscape is central to the ...

  2. An implicit logarithmic finite-difference technique for two dimensional coupled viscous Burgers’ equation

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Vineet K., E-mail: vineetsriiitm@gmail.com [ISRO Telemetry, Tracking and Command Network (ISTRAC), Bangalore-560058 (India); Awasthi, Mukesh K. [Department of Mathematics, University of Petroleum and Energy Studies, Dehradun-248007 (India); Singh, Sarita [Department of Mathematics, WIT- Uttarakhand Technical University, Dehradun-248007 (India)

    2013-12-15

    This article describes a new implicit finite-difference method: an implicit logarithmic finite-difference method (I-LFDM), for the numerical solution of two dimensional time-dependent coupled viscous Burgers’ equation on the uniform grid points. As the Burgers’ equation is nonlinear, the proposed technique leads to a system of nonlinear systems, which is solved by Newton's iterative method at each time step. Computed solutions are compared with the analytical solutions and those already available in the literature and it is clearly shown that the results obtained using the method is precise and reliable for solving Burgers’ equation.

  3. An implicit logarithmic finite-difference technique for two dimensional coupled viscous Burgers’ equation

    Directory of Open Access Journals (Sweden)

    Vineet K. Srivastava

    2013-12-01

    Full Text Available This article describes a new implicit finite-difference method: an implicit logarithmic finite-difference method (I-LFDM, for the numerical solution of two dimensional time-dependent coupled viscous Burgers’ equation on the uniform grid points. As the Burgers’ equation is nonlinear, the proposed technique leads to a system of nonlinear systems, which is solved by Newton's iterative method at each time step. Computed solutions are compared with the analytical solutions and those already available in the literature and it is clearly shown that the results obtained using the method is precise and reliable for solving Burgers’ equation.

  4. Spin current and polarization in impure two-dimensional electron systems with spin-orbit coupling.

    Science.gov (United States)

    Mishchenko, E G; Shytov, A V; Halperin, B I

    2004-11-26

    We derive the transport equations for two-dimensional electron systems with Rashba spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations, we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation and spin current in a finite-size sample for an arbitrary ratio between spin-orbit energy splitting Delta and elastic scattering rate tau(-1). We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.

  5. Phase diagram of a two-dimensional large- Q Potts model in an external field

    Science.gov (United States)

    Tsai, Shan-Ho; Landau, D. P.

    2009-04-01

    We use a two-dimensional Wang-Landau sampling algorithm to map out the phase diagram of a Q-state Potts model with Q⩽10 in an external field H that couples to one state. Finite-size scaling analyses show that for large Q the first-order phase transition point at H=0 is in fact a triple point at which three first-order phase transition lines meet. One such line is restricted to H=0; another line has H⩽0. The third line, which starts at the H=0 triple point, ends at a critical point (T,H) which needs to be located in a two-dimensional parameter space. The critical field H(Q) is positive and decreases with decreasing Q, which is in qualitative agreement with previous predictions.

  6. Two-dimensional lattice solitons in polariton condensates with spin-orbit coupling

    CERN Document Server

    Kartashov, Yaroslav V

    2016-01-01

    We study two-dimensional fundamental and vortex solitons in polariton condensates with spin-orbit coupling and Zeeman splitting evolving in square arrays of microcavity pillars. Due to repulsive excitonic nonlinearity such states are encountered in finite gaps in the spectrum of the periodic array. Spin-orbit coupling between two polarization components stemming from TE-TM energy splitting of the cavity photons acting together with Zeeman splitting lifts the degeneracy between vortex solitons with opposite topological charges and makes their density profiles different for a fixed energy. This results in formation of four distinct families of vortex solitons with topological charges m=+-1, all of which can be stable. At the same time, only two stable families of fundamental gap solitons characterized by domination of different polarization components are encountered.

  7. Strong coupling between Tamm plasmon polariton and two dimensional semiconductor excitons

    CERN Document Server

    Hu, Tao; Wu, Lin; Zhang, Long; Shan, Yuwei; Lu, Jian; Wang, Jun; Luo, Song; Zhang, Zhe; Liao, Liming; Wu, Shiwei; Shen, S C; Chen, Zhanghai

    2016-01-01

    Two dimensional (2D) semiconductor materials of transition-metal dichalcogenides (TMDCs) manifest many peculiar physical phenomena in the light-matter interaction. Due to their ultrathin property, strong interaction with light and the robust excitons at room temperature, they provide a perfect platform for studying the physics of strong coupling in low dimension and at room temperature. Here we report the strong coupling between 2D semiconductor excitons and Tamm plasmon polaritons (TPPs). We observe a Rabi splitting of about 54 meV at room temperature by measuring the angle resolved differential reflectivity spectra and simulate the theoretical results by using the transfer matrix method. Our results will promote the realization of the TPP based ultrathin polariton devices at room temperature.

  8. Hidden long-range order in a two-dimensional spin-orbit coupled Bose gas

    CERN Document Server

    Su, Shih-Wei; Gou, Shih-Chuan; Liao, Renyuan; Fialko, Oleksandr; Brand, Joachim

    2016-01-01

    A two-dimensional spin-orbit coupled Bose gas is shown to simultaneously possess quasi and true long-range orders in the total and relative phases, respectively. The total phase undergoes a conventional Berenzinskii- Kosterlitz-Thouless transition, where an quasi long-range order is expected. Additionally, the relative phase undergoes an Ising-type transition building up true long-range order, which is induced by the anisotropic spin- orbit coupling. Based on the Bogoliubov approach, expressions for the total- and relative-phase fluctuations are derived analytically for the low temperature regime. Numerical simulations of the stochastic projected Gross- Pitaevskii equation give a good agreement with the analytical predictions.

  9. Communication: Vibrational and vibronic coherences in the two dimensional spectroscopy of coupled electron-nuclear motion

    Energy Technology Data Exchange (ETDEWEB)

    Albert, Julian; Falge, Mirjam; Hildenbrand, Heiko; Engel, Volker [Universität Würzburg, Institut für Physikalische und Theoretische Chemie, Emil-Fischer-Str. 42, Campus Nord, Am Hubland, 97074 Würzburg (Germany); Gomez, Sandra; Sola, Ignacio R. [Departamento de Quimica Fisica, Universidad Complutense, 28040 Madrid (Spain)

    2015-07-28

    We theoretically investigate the photon-echo spectroscopy of coupled electron-nuclear quantum dynamics. Two situations are treated. In the first case, the Born-Oppenheimer (adiabatic) approximation holds. It is then possible to interpret the two-dimensional (2D) spectra in terms of vibrational motion taking place in different electronic states. In particular, pure vibrational coherences which are related to oscillations in the time-dependent third-order polarization can be identified. This concept fails in the second case, where strong non-adiabatic coupling leads to the breakdown of the Born-Oppenheimer-approximation. Then, the 2D-spectra reveal a complicated vibronic structure and vibrational coherences cannot be disentangled from the electronic motion.

  10. Ground-State Transition in a Two-Dimensional Frenkel-Kontorova Model

    Institute of Scientific and Technical Information of China (English)

    YUAN Xiao-Ping; ZHENG Zhi-Gang

    2011-01-01

    The ground state of a generalized Frenkel-Kontorova model with a transversaJ degree of freedom is studied. When the coupling strength, K, and the frequency of & single-Atom vibration in the transversaJ direction, ωou are increased, the ground state of the model undergoes a transition from a two-dimensional configuration to a one-dimensional one. This transition can manifest in different ways. Furthermore, we find that the prerequisite of a two-dimensionai ground state is θ≠1//q.%The ground state of a generalized Frenkel-Kontorova model with a transversal degree of freedom is studied.When the coupling strength,K,and the frequency of a single-atom vibration in the transversal direction,ωoy,are increased,the ground state of the model undergoes a transition from a two-dimensional configuration to a one-dimensional one.This transition can manifest in different ways.Furthermore,we find that the prerequisite of a two-dimensional ground state is θ ≠ 1/q.In recent years,the Frenkel-Kontorova (FK) model has been applied to a variety of physical systems,such as adsorbed monolayers,[1,2] Josephsonjunction arrays,[3-5] tribology[6-8] and charge-density waves.[9,10] Experimental and large-scale simulation data at the nanoscale have become available,and more complicated FK-type models have been investigated using simulations of molecular dynamics.[11

  11. p-wave superconductivity in a two-dimensional generalized Hubbard model

    Energy Technology Data Exchange (ETDEWEB)

    Millan, J. Samuel [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (UNAM), Apartado Postal 70-360, 04510, Mexico D.F. (Mexico); Facultad de Ingenieria, UNACAR, 24180, Cd. de Carmen, Campeche (Mexico); Perez, Luis A. [Instituto de Fisica, UNAM, Apartado Postal 20-364, 01000, Mexico D.F. (Mexico); Wang Chumin [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (UNAM), Apartado Postal 70-360, 04510, Mexico D.F. (Mexico)]. E-mail: chumin@servidor.unam.mx

    2005-02-21

    In this Letter, we consider a two-dimensional Hubbard model that includes a second-neighbor correlated hopping interaction, and we find a triplet p-wave superconducting ground state within the BCS formalism. A small distortion of the square-lattice right angles is introduced in order to break the degeneracy of kx+/-ky oriented p-wave pairing states. For the strong coupling limit, analytical results are obtained. An analysis of the superconducting critical temperature reveals the existence of an optimal electron density and the gap ratio exhibits a non-BCS behavior. Finally, the particular case of strontium ruthenate is examined.

  12. The Mott metal-insulator transition in half-filled two-dimensional Hubbard models

    Directory of Open Access Journals (Sweden)

    Peyman Sahebsara

    2008-06-01

    Full Text Available We study the Mott transition in the two dimensional Hubbard model by using the variational cluster approximation. The transition potential obtained is roughly Uc ≈ 2 and 6 for square and triangular lattices, respectively. A comparison between results of this approximation and other quantum cluster methods is presented. Our zero-temperature calculation at strong coupling show that the transition on the triangular and square lattices occur at lower values of compared with other numerical techniques such as DMFT, CDMFT, and DCA. We also study the thermodynamic limit by an extrapolation to infinite size.

  13. New generation of two-dimensional spintronic systems realized by coupling of Rashba and Dirac fermions.

    Science.gov (United States)

    Eremeev, Sergey V; Tsirkin, Stepan S; Nechaev, Ilya A; Echenique, Pedro M; Chulkov, Evgueni V

    2015-08-04

    Intriguing phenomena and novel physics predicted for two-dimensional (2D) systems formed by electrons in Dirac or Rashba states motivate an active search for new materials or combinations of the already revealed ones. Being very promising ingredients in themselves, interplaying Dirac and Rashba systems can provide a base for next generation of spintronics devices, to a considerable extent, by mixing their striking properties or by improving technically significant characteristics of each other. Here, we demonstrate that in BiTeI@PbSb2Te4 composed of a BiTeI trilayer on top of the topological insulator (TI) PbSb2Te4 weakly- and strongly-coupled Dirac-Rashba hybrid systems are realized. The coupling strength depends on both interface hexagonal stacking and trilayer-stacking order. The weakly-coupled system can serve as a prototype to examine, e.g., plasmonic excitations, frictional drag, spin-polarized transport, and charge-spin separation effect in multilayer helical metals. In the strongly-coupled regime, within ~100 meV energy interval of the bulk TI projected bandgap a helical state substituting for the TI surface state appears. This new state is characterized by a larger momentum, similar velocity, and strong localization within BiTeI. We anticipate that our findings pave the way for designing a new type of spintronics devices based on Rashba-Dirac coupled systems.

  14. Precision of meshfree methods and application to forward modeling of two-dimensional electromagnetic sources

    Science.gov (United States)

    Li, Jun-Jie; Yan, Jia-Bin; Huang, Xiang-Yu

    2015-12-01

    Meshfree method offers high accuracy and computational capability and constructs the shape function without relying on predefined elements. We comparatively analyze the global weak form meshfree methods, such as element-free Galerkin method (EFGM), the point interpolation method (PIM), and the radial point interpolation method (RPIM). Taking two dimensional Poisson equation as an example, we discuss the support-domain dimensionless size, the field nodes, and background element settings with respect to their effect on calculation accuracy of the meshfree method. RPIM and EFGM are applied to controlled-source two-dimensional electromagnetic modeling with fixed shape parameters. The accuracy of boundary conditions imposed directly and by a penalty function are discussed in the case of forward modeling of two-dimensional magnetotellurics in a homogeneous medium model. The coupling algorithm of EFG-PIM and EFG-RPIM are generated by integrating the PIM or RPIM and EFGM. The results of the numerical modeling suggest the following. First, the proposed meshfree method and corresponding coupled methods are well-suited for electromagnetic numerical modeling. The accuracy of the algorithm is the highest when the support-domain dimensionless size is 1.0 and the distribution of field nodes is consistent with the nodes of background elements. Second, the accuracy of PIM and RPIM are lower than that of EFGM for the Poisson equation but higher than EFGM for the homogeneous medium MT response. Third, RPIM overcomes the matrix inversion problem of PIM and has a wider selection of support-domain dimensionless sizes as compared to RPIM.

  15. A Two-Dimensional PEM Fuel Cell Model

    Science.gov (United States)

    Shi, Zhongying; Wang, Xia; Zhang, Zhuqian

    2006-11-01

    Proton Exchange Membrane (PEM) fuel cell is a typical low temperature cell, where hydrogen and air are fed into the porous anodic electrode and cathodic electrode though the gas distributors on the bipolar plates, respectively. Activated by the catalyst on anode side, hydrogen will spilt into protons and electrons. Since only protons will be allowed to pass through the membrane, electrons must go through an external circuit. Electrons and protons meet air on cathode side to produce water and heat catalyzed by the catalyst on the cathode side. Numerical simulations are useful tools to describe the basic transport and electrochemical phenomena of PEM fuel cells. The goal of the present work is to develop 2-D computational models of PEM fuel cells, which take into account fluid flow, multi- species transport, current distribution and electrical potential. The velocity field in free channel described by Navier-Stokes equation and the velocity field in porous media described by Darcy’s Law are coupled along the channel-MEA interface. The governing differential equations are solved over a single computational domain, which consists of two gas channel layers, two gas diffusion layers, two catalyst layers as well as a membrane. The model is solved with commercial software COMSOL Multiphysics 3.2b. Parametric study will be conducted to analyze the effects of various parameters on the performance of PEM fuel cells. The results, including the mass concentration, the polarization curve and the velocity distribution, will be presented.

  16. Analysis of optomechanical coupling in two-dimensional square lattice phoxonic crystal slab cavities

    Science.gov (United States)

    El-Jallal, Said; Oudich, Mourad; Pennec, Yan; Djafari-Rouhani, Bahram; Laude, Vincent; Beugnot, Jean-Charles; Martínez, Alejandro; Escalante, José María; Makhoute, Abdelkader

    2013-11-01

    We theoretically investigate phonon-photon interaction in cavities created in a phoxonic crystal slab constituted by a two-dimensional (2D) square array of holes in a silicon membrane. The structure without defects provides 2D band gaps for both electromagnetic and elastic waves. We consider two types of cavities, namely, an L3 cavity (a row of three holes is removed) and a cross-shape cavity, which both possess highly confined phononic and photonic localized modes suitable for enhancing their interaction. In our theoretical study, we take into account two mechanisms that contribute to optomechanical interaction, namely, the photoelastic and the interface motion effects. We show that, depending on the considered pair of photonic and phononic modes, the two mechanisms can have similar or very different magnitudes, and their contributions can be either in or out of phase. We find out that only acoustic modes with a specific symmetry are allowed to couple with photonic cavity modes. The coupling strength is quantified by two different methods. In the first method, we compute a direct estimation of coupling rates by overlap integrals, while in the second one, we analyze the temporal modulation of the resonant photonic frequency by the phonon-induced acoustic vibrational motion during one acoustic period. Interestingly, we obtain high optomechanical interaction, with the coupling rate reaching more than 2.4 MHz for some specific phonon-photon pairs.

  17. Two-dimensional, isothermal, multi-component model for a polymer electrolyte membrane fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Mahinpey, N.; Jagannathan, A.; Idem, R. [Regina Univ., SK (Canada). Faculty of Engineering

    2007-07-01

    A fuel cell is an electrochemical energy conversion device which is more efficient than an internal combustion engine in converting fuel to power. Numerous fuel cell models have been developed by a number of authors accounting for the various physical processes. Earlier models were restricted to being one dimensional, steady-state, and isothermal while more recent two-dimensional models had several limitations. This paper presented the results of a study that developed a two-dimensional computational fluid dynamics model of a polymer electrolyte membrane fuel cell using a finite element method to solve a multi-component transport model coupled with flow in porous media, charge balance, electrochemical kinetics, and rigorous water balance in the membrane. The mass transport, momentum transport, and electrochemical processes occurring in the membrane electrolyte and catalyst layers were modeled. The local equilibrium was assumed at the interfaces and the model was combined with the kinetics and was analytically solved for the anodic and cathodic current using an agglomerate spherical catalyst pellet. The paper compared the modeling results with previously published experimental data. The study investigated the effects of channel and bipolar plate shoulder size, porosity of the electrodes, temperature, relative humidity and current densities on the cell performance. It was concluded that smaller sized channels and bipolar plate shoulders were required to obtain higher current densities, although larger channels were satisfactory at moderate current densities. 13 refs., 5 figs.

  18. Electron spin resonance in a two-dimensional Fermi liquid with spin-orbit coupling

    Science.gov (United States)

    Maiti, Saurabh; Imran, Muhammad; Maslov, Dmitrii L.

    2016-01-01

    Electron spin resonance (ESR) is usually viewed as a single-particle phenomenon protected from the effect of many-body correlations. We show that this is not the case in a two-dimensional Fermi liquid (FL) with spin-orbit coupling (SOC). Depending on whether the in-plane magnetic field is below or above some critical value, ESR in such a system probes up to three chiral-spin collective modes, augmented by the spin mode in the presence of the field, or the Silin-Leggett mode. All the modes are affected by both SOC and FL renormalizations. We argue that ESR can be used as a probe not only for SOC but also for many-body physics.

  19. The two-dimensional Godunov scheme and what it means for macroscopic pedestrian flow models

    NARCIS (Netherlands)

    Van Wageningen-Kessels, F.L.M.; Daamen, W.; Hoogendoorn, S.P.

    2015-01-01

    An efficient simulation method for two-dimensional continuum pedestrian flow models is introduced. It is a two-dimensional and multi-class extension of the Go-dunov scheme for one-dimensional road traffic flow models introduced in the mid 1990’s. The method can be applied to continuum pedestrian flo

  20. Evidence for an unconventional universality class from a two-dimensional dimerized quantum heisenberg model.

    Science.gov (United States)

    Wenzel, Sandro; Bogacz, Leszek; Janke, Wolfhard

    2008-09-19

    The two-dimensional J-J' dimerized quantum Heisenberg model is studied on the square lattice by means of (stochastic series expansion) quantum Monte Carlo simulations as a function of the coupling ratio alpha=J'/J. The critical point of the order-disorder quantum phase transition in the J-J' model is determined as alpha_c=2.5196(2) by finite-size scaling for up to approximately 10 000 quantum spins. By comparing six dimerized models we show, contrary to the current belief, that the critical exponents of the J-J' model are not in agreement with the three-dimensional classical Heisenberg universality class. This lends support to the notion of nontrivial critical excitations at the quantum critical point.

  1. Scaling behavior of the dipole-coupling energy in two-dimensional disordered magnetic nanostructures

    Science.gov (United States)

    Jensen, P. J.; Pastor, G. M.

    2003-11-01

    Numerical calculations of the average dipole-coupling energy Edip in two-dimensional disordered magnetic nanostructures are performed as a function of the particle coverage C. We observe that Edip scales as Edip∝Cα* with an unusually small exponent α*≃0.8 1.0 for coverages C≲20%. This behavior is shown to be primarily given by the contributions of particle pairs at short distances, which is intrinsically related to the presence of an appreciable degree of disorder. The value of α* is found to be sensitive to the magnetic arrangement within the nanostructure and to the degree of disorder. For large coverages C≳20% we obtain Edip∝Cα with α=3/2, in agreement with the straightforward scaling of the dipole coupling as in a periodic particle setup. Taking into account the effect of single-particle anisotropies, we show that the scaling exponent can be used as a criterion to distinguish between weakly interacting (α*≃1.0) and strongly interacting (α*≃0.8) particle ensembles as a function of coverage.

  2. Coupled KdV Equations and Their Explicit Solutions Through Two-Dimensional Hamiltonian System with a Quartic Potential

    Institute of Scientific and Technical Information of China (English)

    GONG Lun-Xun; CAO Jian-Li; PAN Jun-Ting; ZHANG Hua; JIAO Wan-Tang

    2008-01-01

    Based on the second integrable case of known two-dimensional Hamiltonian system with a quartic potential, we propose a 4×4 matrix spectral problem and derive a hierarchy of coupled KdV equations and their Hamiltonian structures. It is shown that solutions of the coupled KdV equations in the hierarchy are reduced to solving two compatible systems of ordinary differential equations. As an application, quite a few explicit solutions of the coupled KdV equations are obtained via using separability for the second integrable case of the two-dimensional Hamiltonian system.

  3. Analytical two-dimensional model of solar cell current-voltage characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Caldararu, F.; Caldararu, M.; Nan, S.; Nicolaescu, D.; Vasile, S. (ICCE, Bucharest (RO). R and D Center for Electron Devices)

    1991-06-01

    This paper describes an analytical two-dimensional model for pn junction solar cell I-V characteristic. In order to solve the two-dimensional equations for the minority carrier concentration the Laplace transformation method is used. The model eliminates Hovel's assumptions concerning a one-dimensional model and provides an I-V characteristic that is simpler than those derived from the one-dimensional model. The method can be extended to any other device with two-dimensional symmetry. (author).

  4. Improved modeling and numerics to solve two-dimensional elliptic fluid flow and heat transfer problems

    Science.gov (United States)

    Chan, B. C.

    1986-05-01

    A basic, limited scope, fast-running computer model is presented for the solution of two-dimensional, transient, thermally-coupled fluid flow problems. This model is to be the module in the SSC (an LMFBR thermal-hydraulic systems code) for predicting complex flow behavior, as occurs in the upper plenum of the loop-type design or in the sodium pool of the pool-type design. The nonlinear Navier-Stokes equations and the two-equation (two-variable) transport model of turbulence are reduced to a set of linear algebraic equations in an implicit finite difference scheme, based on the control volume approach. These equations are solved iteratively in a line-by-line procedure using the tri-diagonal matrix algorithm. The results of calculational examplers are shown in the computer-generated plots.

  5. E and S hysteresis model for two-dimensional magnetic properties

    CERN Document Server

    Soda, N

    2000-01-01

    We define an effective hysteresis model of two-dimensional magnetic properties for the magnetic field analysis. Our hysteresis model is applicable to both alternating and rotating flux conditions. Moreover, we compare the calculated results with the measured ones, and verify the accuracy of this model. We can calculate iron losses in the magnetic materials exactly. As a result, it is shown that the hysteresis model is generally applicable to two-dimensional magnetic properties of some kinds of magnetic materials.

  6. Two-dimensional MHD model of the Jovian magnetodisk

    Science.gov (United States)

    Kislov, R. A.; Malova, H. V.; Vasko, I. Y.

    2015-09-01

    A self-consistent stationary axially symmetric MHD model of the Jovian magnetodisk is constructed. This model is a generalization of the models of plane current sheets that have been proposed earlier in order to describe the structure of the current sheet in the magnetotail of the Earth [1, 2]. The model takes centrifugal force, which is induced by the corotation electric field, and the azimuthal magnetic field into account. The configurations of the magnetic field lines for the isothermic (plasma temperature assumed to be constant) and the isentropic (plasma entropy assumed to be constant) models of the magnetodisk are determined. The dependence of the thickness of the magnetodisk on the distance to Jupiter is obtained. The thickness of the magnetodisk and the magnetic field distribution in the isothermic and isentropic models are similar. The inclusion of a low background plasma pressure results in a considerable reduction in the thickness of the magnetodisk. This effect may be attributed to the fact that centrifugal force prevails over the pressure gradient at large distances from the planet. The mechanism of unipolar induction and the related large-scale current system are analyzed. The direct and return Birkeland currents are determined in the approximation of a weak azimuthal magnetic field. The modeling results agree with theoretical estimates from other studies and experimental data.

  7. two - dimensional mathematical model of water flow in open ...

    African Journals Online (AJOL)

    ES Obe

    1996-09-01

    Sep 1, 1996 ... simplification of the system of the governing shallow water equations ... For optional design of the ... models. One of the facilities for preliminary appraisal of the ... distribution. ..... indicated for the individual methods, located ...

  8. Electron-phonon vertex in the two-dimensional one-band Hubbard model

    Science.gov (United States)

    Huang, Z. B.; Hanke, W.; Arrigoni, E.; Scalapino, D. J.

    2003-12-01

    Using quantum Monte Carlo techniques, we study the effects of electronic correlations on the effective electron-phonon (el-ph) coupling in a two-dimensional one-band Hubbard model. We consider a momentum-independent bare ionic el-ph coupling. In the weak- and intermediate-correlation regimes, we find that the on-site Coulomb interaction U acts to effectively suppress the ionic el-ph coupling at all electron and phonon momenta. In this regime, our numerical simulations are in good agreement with the results of perturbation theory to order U2. However, entering the strong-correlation regime, we find that the forward-scattering process stops decreasing and begins to substantially increase as a function of U, leading to an effective el-ph coupling which is peaked in the forward direction. Whereas at weak and intermediate Coulomb interactions, screening is the dominant correlation effect suppressing the el-ph coupling, at larger U values irreducible vertex corrections become more important and give rise to this increase. These vertex corrections depend crucially on the renormalized electronic structure of the strongly correlated system.

  9. Engineering the light propagating features through the two-dimensional coupled-cavity photonic crystal waveguides

    Institute of Scientific and Technical Information of China (English)

    Feng shuai; Wang Yi-Quan

    2011-01-01

    This paper studies the propagating characteristics of the electromagnetic waves through the coupled-resonator optical waveguides based on the two-dimensional square-lattice photonic crystals by the finite-difference time-domain method. When the traditional circular rods adjacent to the centre of the cavities are replaced by the oval rods, the simulated results show that the waveguide mode region can be adjusted only by the alteration of the oval rods' obliquity.When the obliquity of the oval rods around one cavity is different from the obliquity of that around the adjacent cavities,the group velocities of the waveguide modes can be greatly reduced and the information of different frequencies can be shared and chosen at the same time by the waveguide branches with different structures. If the obliquities of the oval rods around two adjacent cavities are equal and they alternate between two values, the group velocities can be further reduced and a maximum value of 0.0008c (c is the light velocity in vacuum) can be acquired.

  10. Plasmonic terahertz modulator based on a grating-coupled two-dimensional electron system

    Science.gov (United States)

    Huang, Y. D.; Yu, Y.; Qin, H.; Sun, J. D.; Zhang, Z. P.; Li, X. X.; Huang, J. J.; Cai, Y.

    2016-11-01

    Electrically driven broadband modulator with large modulation depth and high speed is in high demand to meet the technical advancing and applications in terahertz fields recently. So far, the single-particle non-resonant absorption mechanism described by the Drude conductivity has been utilized in most of the related researches but is still not efficient enough. Here we proposed and demonstrated a terahertz modulator based on the collective electron plasma excitations (plasmons) in a grating-coupled two-dimensional electron gas in GaN/AlGaN heterostructure. By switching between the resonant and non-resonant conditions of the 2D plasmon excitation enabled by applying proper gate biases, the transmission of terahertz electromagnetic waves can be efficiently manipulated. Taking advantage of its resonant characteristic combined with the strong electric field enhancement in the active region, we experimentally achieved a maximum intensity modulation depth of 93%, a 3 dB operation bandwidth of ˜400 kHz, and a small required driving voltage amplitude of 2 V at a cryogenic temperature of 8.7 K. Owing to its excellent performances, this active plasmon-based terahertz modulator may offer some promising solutions in several fields of terahertz technology in the future.

  11. Controlling Rashba spin orbit coupling in polar two-dimensional transition metal dichalcogenide

    CERN Document Server

    Yao, Qun-Fang; Tong, Wen-Yi; Gong, Shi-Jing; Wang, Ji-Qing; Wan, Xian-gang; Duan, Chun-Gang; Chu, J H

    2016-01-01

    Monolayer transition metal dichalcogenide (TMD) group of materials MXY (M=Mo, W, X(not equal to)Y=S, Se, Te) are two-dimensional polar semiconductors with Rashba spin orbit coupling (SOC). Setting WSeTe as an example and using density functional theory calculations, we investigate the influence of biaxial strain and electric field on Rashba SOC in MXY monolayer. The orbital analysis reveals that Rashba spin splitting around Gamma point occurs mainly through the SOC matrix elements between the W-dz2 and -dxz/yz orbitals, and those between the Se-pz and -px/y orbitals. We find the change of local electric field between Se and W atoms arising from the mirror symmetry breaking plays the critical role in forming the large Rashba SOC, and through a relatively small compressive/tensile strain (from -2% to 2%), a large tunability of Rashba SOC can be obtained due to the modified W-Se bonding interaction. In addition, we also explore the influence of electric field on Rashba SOC in WSeTe, which can impact the charge d...

  12. Two-dimensional biomass combustion modeling of CFB

    Energy Technology Data Exchange (ETDEWEB)

    Afsin Gungor [Nigde University, Nigde (Turkey). Department of Mechanical Engineering, Faculty of Engineering and Architecture

    2008-07-15

    In this study, a 2D model for a CFB biomass combustor has been developed which integrates and simultaneously predicts the hydrodynamics, heat transfer and combustion aspects. Combustor hydrodynamic is modeled taking into account previous work. Simulation model calculates the axial and radial distribution of voidage, velocity, particle size distribution, pressure drop, gas emissions and temperature at each time interval for gas and solid phase both for bottom and upper zones. The model results are compared with and validated against experimental data both for small-size and industrial-size biomass combustors which uses different types of biomass fuels given in the literature. As a result of sensitivity analysis, it is observed that: major portion of the combustion will take place in the upper zone, the air staging could improve combustion, for industrial-size CFB biomass combustors and the decrease of NOx adversely results in high CO emissions as air ratio decreases. Unexpected results concerning the emissions is caused by using data of different sized CFBs and is clearly an indicator of the necessity to compare the model results with various sized CFBs as far as possible. 71 refs., 10 figs., 5 tabs.

  13. Two-dimensional hydrologic modeling to evaluate aquatic habitat conditions

    Science.gov (United States)

    Pamela Edwards; Frederica Wood; Michael Little; Peter Vila; Peter Vila

    2006-01-01

    We describe the modeling and mapping procedures used to examine aquatic habitat conditions and habitat suitability of a small river in north- central West Virginia where fish survival and reproduction in specific reaches are poor. The study includes: (1) surveying cross sections of streambed reaches and measuring discharges and corresponding water-surface elevations,...

  14. Horizontal mixing coefficients for two-dimensional chemical models calculated from National Meteorological Center Data

    Science.gov (United States)

    Newman, P. A.; Schoeberl, M. R.; Plumb, R. A.

    1986-01-01

    Calculations of the two-dimensional, species-independent mixing coefficients for two-dimensional chemical models for the troposphere and stratosphere are performed using quasi-geostrophic potential vorticity fluxes and gradients from 4 years of National Meteorological Center data for the four seasons in both hemispheres. Results show that the horizontal mixing coefficient values for the winter lower stratosphere are broadly consistent with those currently employed in two-dimensional models, but the horizontal mixing coefficient values in the northern winter upper stratosphere are much larger than those usually used.

  15. Development and validation of a two-dimensional fast-response flood estimation model

    Energy Technology Data Exchange (ETDEWEB)

    Judi, David R [Los Alamos National Laboratory; Mcpherson, Timothy N [Los Alamos National Laboratory; Burian, Steven J [UNIV OF UTAK

    2009-01-01

    A finite difference formulation of the shallow water equations using an upwind differencing method was developed maintaining computational efficiency and accuracy such that it can be used as a fast-response flood estimation tool. The model was validated using both laboratory controlled experiments and an actual dam breach. Through the laboratory experiments, the model was shown to give good estimations of depth and velocity when compared to the measured data, as well as when compared to a more complex two-dimensional model. Additionally, the model was compared to high water mark data obtained from the failure of the Taum Sauk dam. The simulated inundation extent agreed well with the observed extent, with the most notable differences resulting from the inability to model sediment transport. The results of these validation studies complex two-dimensional model. Additionally, the model was compared to high water mark data obtained from the failure of the Taum Sauk dam. The simulated inundation extent agreed well with the observed extent, with the most notable differences resulting from the inability to model sediment transport. The results of these validation studies show that a relatively numerical scheme used to solve the complete shallow water equations can be used to accurately estimate flood inundation. Future work will focus on further reducing the computation time needed to provide flood inundation estimates for fast-response analyses. This will be accomplished through the efficient use of multi-core, multi-processor computers coupled with an efficient domain-tracking algorithm, as well as an understanding of the impacts of grid resolution on model results.

  16. Flow Modelling for partially Cavitating Two-dimensional Hydrofoils

    DEFF Research Database (Denmark)

    Krishnaswamy, Paddy

    2001-01-01

    The present work addresses te computational analysis of partial sheet hydrofoil cavitation in two dimensions. Particular attention is given to the method of simulating the flow at the end of the cavity. A fixed-length partially cavitating panel method is used to predict the height of the re...... of the model and comparing the present calculations with numerical results. The flow around the partially cavitating hydrofoil with a re-entrant jet has also been treated with a viscous/inviscid interactive method. The viscous flow model is based on boundary layer theory applied on the compound foil......, consisting of the union of the cavity and the hydrofoil surface. The change in the flow direction in the cavity closure region is seen to have a slightly adverse effect on the viscous pressure distribution. Otherwise, it is seen that the viscous re-entrant jet solution compares favourably with experimental...

  17. Numerical modeling of transient two-dimensional viscoelastic waves

    CERN Document Server

    Lombard, Bruno

    2010-01-01

    This paper deals with the numerical modeling of transient mechanical waves in linear viscoelastic solids. Dissipation mechanisms are described using the Zener model. No time convolutions are required thanks to the introduction of memory variables that satisfy local-in-time differential equations. By appropriately choosing the Zener parameters, it is possible to accurately describe a large range of materials, such as solids with constant quality factors. The evolution equations satisfied by the velocity, the stress, and the memory variables are written in the form of a first-order system of PDEs with a source term. This system is solved by splitting it into two parts: the propagative part is discretized explicitly, using a fourth-order ADER scheme on a Cartesian grid, and the diffusive part is then solved exactly. Jump conditions along the interfaces are discretized by applying an immersed interface method. Numerical experiments of wave propagation in viscoelastic and fluid media show the efficiency of this nu...

  18. Relations between two-dimensional models from dimensional reduction

    Energy Technology Data Exchange (ETDEWEB)

    Amaral, R.L.P.G.; Natividade, C.P. [Universidade Federal Fluminense, Niteroi, RJ (Brazil). Inst. de Fisica

    1998-12-31

    In this work we explore the consequences of dimensional reduction of the 3D Maxwell-Chern-Simons and some related models. A connection between topological mass generation in 3D and mass generation according to the Schwinger mechanism in 2D is obtained. Besides, a series of relationships are established by resorting to dimensional reduction and duality interpolating transformations. Nonabelian generalizations are also pointed out. (author) 10 refs.

  19. Model and observed seismicity represented in a two dimensional space

    Directory of Open Access Journals (Sweden)

    M. Caputo

    1976-06-01

    Full Text Available In recent years theoretical seismology lias introduced
    some formulae relating the magnitude and the seismic moment of earthquakes
    to the size of the fault and the stress drop which generated the
    earthquake.
    In the present paper we introduce a model for the statistics of the
    earthquakes based on these formulae. The model gives formulae which
    show internal consistency and are also confirmed by observations.
    For intermediate magnitudes the formulae reproduce also the trend
    of linearity of the statistics of magnitude and moment observed in all the
    seismic regions of the world. This linear trend changes into a curve with
    increasing slope for large magnitudes and moment.
    When a catalogue of the magnitudes and/or the seismic moment of
    the earthquakes of a seismic region is available, the model allows to estimate
    the maximum magnitude possible in the region.

  20. On Regularity Criteria for the Two-Dimensional Generalized Liquid Crystal Model

    Directory of Open Access Journals (Sweden)

    Yanan Wang

    2014-01-01

    Full Text Available We establish the regularity criteria for the two-dimensional generalized liquid crystal model. It turns out that the global existence results satisfy our regularity criteria naturally.

  1. Mesh-free Hamiltonian implementation of two dimensional Darwin model

    Science.gov (United States)

    Siddi, Lorenzo; Lapenta, Giovanni; Gibbon, Paul

    2017-08-01

    A new approach to Darwin or magnetoinductive plasma simulation is presented, which combines a mesh-free field solver with a robust time-integration scheme avoiding numerical divergence errors in the solenoidal field components. The mesh-free formulation employs an efficient parallel Barnes-Hut tree algorithm to speed up the computation of fields summed directly from the particles, avoiding the necessity of divergence cleaning procedures typically required by particle-in-cell methods. The time-integration scheme employs a Hamiltonian formulation of the Lorentz force, circumventing the development of violent numerical instabilities associated with time differentiation of the vector potential. It is shown that a semi-implicit scheme converges rapidly and is robust to further numerical instabilities which can develop from a dominant contribution of the vector potential to the canonical momenta. The model is validated by various static and dynamic benchmark tests, including a simulation of the Weibel-like filamentation instability in beam-plasma interactions.

  2. Two dimensional cellular automaton for evacuation modeling: hybrid shuffle update

    CERN Document Server

    Arita, Chikashi; Appert-Rolland, Cécile

    2015-01-01

    We consider a cellular automaton model with a static floor field for pedestrians evacuating a room. After identifying some properties of real pedestrian flows, we discuss various update schemes, and we introduce a new one, the hybrid shuffle update. The properties specific to pedestrians are incorporated in variables associated to particles called phases, that represent their step cycles. The dynamics of the phases gives naturally raise to some friction, and allows to reproduce several features observed in experiments. We study in particular the crossover between a low- and a high-density regime that occurs when the density of pedestrian increases, the dependency of the outflow in the strength of the floor field, and the shape of the queue in front of the exit.

  3. TWO-DIMENSIONAL MODELLING OF ACCIDENTAL FLOOD WAVES PROPAGATION

    Directory of Open Access Journals (Sweden)

    Lorand Catalin STOENESCU

    2011-05-01

    Full Text Available The study presented in this article describes a modern modeling methodology of the propagation of accidental flood waves in case a dam break; this methodology is applied in Romania for the first time for the pilot project „Breaking scenarios of Poiana Uzului dam”. The calculation programs used help us obtain a bidimensional calculation (2D of the propagation of flood waves, taking into consideration the diminishing of the flood wave on a normal direction to the main direction; this diminishing of the flood wave is important in the case of sinuous courses of water or with urban settlements very close to the minor river bed. In the case of Poiana Uzului dam, 2 scenarios were simulated with the help of Ph.D. Eng. Dan Stematiu, plausible scenarios but with very little chances of actually producing. The results were presented as animations with flooded surfaces at certain time steps successively.

  4. Staggered Flux State in Two-Dimensional Hubbard Models

    Science.gov (United States)

    Yokoyama, Hisatoshi; Tamura, Shun; Ogata, Masao

    2016-12-01

    The stability and other properties of a staggered flux (SF) state or a correlated d-density wave state are studied for the Hubbard (t-t'-U) model on extended square lattices, as a low-lying state that competes with the dx2 - y2-wave superconductivity (d-SC) and possibly causes the pseudogap phenomena in underdoped high-Tc cuprates and organic κ-BEDT-TTF salts. In calculations, a variational Monte Carlo method is used. In the trial wave function, a configuration-dependent phase factor, which is vital to treat a current-carrying state for a large U/t, is introduced in addition to ordinary correlation factors. Varying U/t, t'/t, and the doping rate (δ) systematically, we show that the SF state becomes more stable than the normal state (projected Fermi sea) for a strongly correlated (U/t ≳ 5) and underdoped (δ ≲ 0.16) area. The decrease in energy is sizable, particularly in the area where Mott physics prevails and the circular current (order parameter) is strongly suppressed. These features are consistent with those for the t-J model. The effect of the frustration t'/t plays a crucial role in preserving charge homogeneity and appropriately describing the behavior of hole- and electron-doped cuprates and κ-BEDT-TTF salts. We argue that the SF state does not coexist with d-SC and is not a "normal state" from which d-SC arises. We also show that a spin current (flux or nematic) state is never stabilized in the same regime.

  5. Critical phenomena in the majority voter model on two-dimensional regular lattices.

    Science.gov (United States)

    Acuña-Lara, Ana L; Sastre, Francisco; Vargas-Arriola, José Raúl

    2014-05-01

    In this work we studied the critical behavior of the critical point as a function of the number of nearest neighbors on two-dimensional regular lattices. We performed numerical simulations on triangular, hexagonal, and bilayer square lattices. Using standard finite-size scaling theory we found that all cases fall in the two-dimensional Ising model universality class, but that the critical point value for the bilayer lattice does not follow the regular tendency that the Ising model shows.

  6. The influence of the Rashba spin-orbit coupling on the two-dimensional magnetoexcitons

    Energy Technology Data Exchange (ETDEWEB)

    Hakioglu, T [Department of Physics, Bilkent University, 06800 Ankara (Turkey); Liberman, M A [Department of Physics, Uppsala University, Box 530, SE-751 21, Uppsala (Sweden); Moskalenko, S A; Podlesny, I V [Institute of Applied Physics, Academy of Sciences of Moldova, 5, Academiei street, MD-2028, Chisinau (Moldova, Republic of)

    2011-08-31

    The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field. (paper)

  7. Reentrant resistance and giant Andreev back scattering in a two-dimensional electron gas coupled to superconductors

    NARCIS (Netherlands)

    den Hartog, Sander; Wees, B.J. van; Nazarov, Yu.V.; Klapwijk, T.M.; Borghs, G.

    1998-01-01

    We first present the bias-voltage dependence of the superconducting phase-dependent reduction in the differential resistance of a disordered T-shaped two-dimensional electron gas (2DEG) coupled to two superconductors. This reduction exhibits a reentrant behavior, since it first increases upon loweri

  8. Comparison between one-dimensional and two-dimensional models for Josephson junctions of overlap type

    DEFF Research Database (Denmark)

    Eilbeck, J. C; Lomdahl, P.S.; Olsen, O.H.

    1985-01-01

    A two-dimensional model of Josephson junction of overlap type is presented. The energy input is provided through induced magnetic fields modeled by a set of boundary conditions. In the limit of a very narrow junction, this model reduces to the one-dimensional model. Further, an equation derived f...

  9. Two-dimensional coupled electron-hole layers in high magnetic fields

    NARCIS (Netherlands)

    Parlangeli, Andrea

    2000-01-01

    In solids, it is nowadays possible to create structures in which electrons are confined into a two-dimensional (2D) plane. The physics of a 2D electron gas (2DEG) has proved to be very rich, in particular in the presence of a transverse magnetic field. The Quantum Hall Effect, i.e. the quantization

  10. Two-dimensional analytical models for asymmetric fully depleted double-gate strained silicon MOSFETs

    Institute of Scientific and Technical Information of China (English)

    Liu Hong-Xia; Li Jin; Li Bin; Cao Lei; Yuan Bo

    2011-01-01

    This paper develops the simple and accurate two-dimensional analytical models for new asymmetric double-gate fully depleted strained-Si MOSFET. The models mainly include the analytical equations of the surface potential, surface electric field and threshold voltage, which are derived by solving two dimensional Poisson equation in strained-Si layer.The models are verified by numerical simulation. Besides offering the physical insight into device physics in the model,the new structure also provides the basic designing guidance for further immunity of short channel effect and drain-induced barrier-lowering of CMOS-based devices in nanometre scale.

  11. A Large Deformation Model for the Elastic Moduli of Two-dimensional Cellular Materials

    Institute of Scientific and Technical Information of China (English)

    HU Guoming; WAN Hui; ZHANG Youlin; BAO Wujun

    2006-01-01

    We developed a large deformation model for predicting the elastic moduli of two-dimensional cellular materials. This large deformation model was based on the large deflection of the inclined members of the cells of cellular materials. The deflection of the inclined member, the strain of the representative structure and the elastic moduli of two-dimensional cellular materials were expressed using incomplete elliptic integrals. The experimental results show that these elastic moduli are no longer constant at large deformation, but vary significantly with the strain. A comparison was made between this large deformation model and the small deformation model proposed by Gibson and Ashby.

  12. Numerical solution of two dimensional coupled viscous Burger equation using modified cubic B-spline differential quadrature method

    Directory of Open Access Journals (Sweden)

    H. S. Shukla

    2014-11-01

    Full Text Available In this paper, a numerical solution of two dimensional nonlinear coupled viscous Burger equation is discussed with appropriate initial and boundary conditions using the modified cubic B-spline differential quadrature method. In this method, the weighting coefficients are computed using the modified cubic B-spline as a basis function in the differential quadrature method. Thus, the coupled Burger equation is reduced into a system of ordinary differential equations. An optimal five stage and fourth-order strong stability preserving Runge–Kutta scheme is applied for solving the resulting system of ordinary differential equations. The accuracy of the scheme is illustrated by taking two numerical examples. Computed results are compared with the exact solutions and other results available in literature. Obtained numerical result shows that the described method is efficient and reliable scheme for solving two dimensional coupled viscous Burger equation.

  13. Coupling Green-Ampt infiltration method and two-dimensional kinematic wave theory for flood forecast in semi-arid catchment

    Directory of Open Access Journals (Sweden)

    L.-L. Wang

    2011-08-01

    Full Text Available Due to the specific characteristics of semi-arid catchments, this paper aims to establish a grid-and-Green-Ampt-and-two-dimensional-kinematic-wave-based distributed hydrological physical model (Grid-GA-2D model coupling Green-Ampt infiltration method and two dimensional overland flow routing model based on kinematic wave theory for flood simulation and forecasting with using GIS technology and digital elevation model (DEM. Taking into consideration the soil moisture redistribution at hillslope, Green-Ampt infiltration physical method is applied for grid-based runoff generation and two-dimensional implicit finite difference kinematic wave model is introduced to solve depressions water storing for grid-based overland flow concentration routing in the Grid-GA-2D model. The Grid-GA-2D model, the Grid-GA model with coupling Green-Ampt infiltration method and one-dimension kinematic wave theory, and Shanbei model were employed to the upper Kongjiapo catchment in Qin River, a tributary of the Yellow River, with an area of 1454 km2 for flood simulation. Results show that two grid-based distributed hydrological models perform better in flood simulation and can be used for flood forecasting in semi-arid catchments. Comparing with the Grid-GA model, the flood peak simulation accuracy of the newly developed model is higher.

  14. Coupling Green-Ampt infiltration method and two-dimensional kinematic wave theory for flood forecast in semi-arid catchment

    Science.gov (United States)

    Wang, L.-L.; Chen, D.-H.; Li, Z.-J.; Zhao, L.-N.

    2011-08-01

    Due to the specific characteristics of semi-arid catchments, this paper aims to establish a grid-and-Green-Ampt-and-two-dimensional-kinematic-wave-based distributed hydrological physical model (Grid-GA-2D model) coupling Green-Ampt infiltration method and two dimensional overland flow routing model based on kinematic wave theory for flood simulation and forecasting with using GIS technology and digital elevation model (DEM). Taking into consideration the soil moisture redistribution at hillslope, Green-Ampt infiltration physical method is applied for grid-based runoff generation and two-dimensional implicit finite difference kinematic wave model is introduced to solve depressions water storing for grid-based overland flow concentration routing in the Grid-GA-2D model. The Grid-GA-2D model, the Grid-GA model with coupling Green-Ampt infiltration method and one-dimension kinematic wave theory, and Shanbei model were employed to the upper Kongjiapo catchment in Qin River, a tributary of the Yellow River, with an area of 1454 km2 for flood simulation. Results show that two grid-based distributed hydrological models perform better in flood simulation and can be used for flood forecasting in semi-arid catchments. Comparing with the Grid-GA model, the flood peak simulation accuracy of the newly developed model is higher.

  15. Quantum search on the two-dimensional lattice using the staggered model with Hamiltonians

    Science.gov (United States)

    Portugal, R.; Fernandes, T. D.

    2017-04-01

    Quantum search on the two-dimensional lattice with one marked vertex and cyclic boundary conditions is an important problem in the context of quantum algorithms with an interesting unfolding. It avails to test the ability of quantum walk models to provide efficient algorithms from the theoretical side and means to implement quantum walks in laboratories from the practical side. In this paper, we rigorously prove that the recent-proposed staggered quantum walk model provides an efficient quantum search on the two-dimensional lattice, if the reflection operators associated with the graph tessellations are used as Hamiltonians, which is an important theoretical result for validating the staggered model with Hamiltonians. Numerical results show that on the two-dimensional lattice staggered models without Hamiltonians are not as efficient as the one described in this paper and are, in fact, as slow as classical random-walk-based algorithms.

  16. Modelling of Oscillations in Two-Dimensional Echo-Spectra of the Fenna-Matthews-Olson Complex

    CERN Document Server

    Hein, Birgit; Kramer, Tobias; Rodríguez, Mirta

    2011-01-01

    Recent experimental observations of time-dependent beatings in the two-dimensional echo-spectra of light-harvesting complexes at ambient temperatures have opened up the question whether coherence and wave-like behaviour plays a significant role in photosynthesis. We perform a numerical study of the absorption and echo-spectra of the Fenna-Matthews-Olson (FMO) complex in chlorobium tepidum and analyse the requirements in the theoretical model needed to reproduce beatings in the calculated spectra. The energy transfer in the FMO pigment-protein complex is theoretically described by an exciton Hamiltonian coupled to a phonon bath which account for the pigments electronic and vibrational excitations respectively. We use the hierarchical equations of motions method to treat the strong couplings in a non-perturbative way. We show that the oscillations in the two-dimensional echo-spectra persist in the presence of thermal noise and static disorder.

  17. One- and two-dimensional solitons in PT-symmetric systems emulating the spin-orbit coupling

    CERN Document Server

    Sakaguchi, Hidetsugu

    2016-01-01

    We introduce a two-dimensional (2D) system, which can be implemented in dual-core planar optical couplers with the Kerr nonlinearity in its cores, making it possible to blend effects of the PT symmetry, represented by the balanced linear gain and loss in the two cores, and spin-orbit coupling (SOC), emulated by a spatially biased coupling between the cores. Families of 1D and 2D solitons and their stability boundaries are identified. In the 1D setting, the addition of the SOC terms leads, at first, to shrinkage of the stability area for PT-symmetric solitons, which is followed by its rapid expansion. 2D solitons have their stability region too, in spite of the simultaneous action of two major destabilizing factors, viz., the collapse driven by the Kerr nonlinearity, and a trend towards spontaneous breakup of the gain-loss balance. In the limit of the SOC terms dominating over the intrinsic diffraction, the 1D system gives rise to a new model for gap solitons, which admits exact analytical solutions.

  18. USTIFICATION OF A TWO-DIMENSIONAL NONLINEAR SHELL MODEL OF KOITER'S TYPE

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A two-dimensional nonlinear shell model"of Koiter's type"has recently been proposed by the first author. It is shown here that, according to two mutually exclusive sets of assumptions bearing on the associated manifold of admissible inextensional displacements, the leading term of a formal asymptotic expansion of the solution of this two-dimensional model, with the thickness as the"small" parameter, satisfies either the two-dimensional equations of a nonlinearly elastic "membrane" shell or those of a nonlinearly elastic "flexural" shell. These conclusions being identical to those recently drawn by B. Miara, then by V. Lods and B. Miara, for the leading term of a formal asymptotic expansion of the solution of the equations of three-dimensional nonlinear elasticity, again with the thickness as the "small" parameter, the nonlinear shell model of Koiter's type considered here is thus justified, at least formally.

  19. The exact interface model for wetting in the two-dimensional Ising model

    OpenAIRE

    Upton, P. J.

    2002-01-01

    We use exact methods to derive an interface model from an underlying microscopic model, i.e., the Ising model on a square lattice. At the wetting transition in the two-dimensional Ising model, the long Peierls contour (or interface) gets depinned from the substrate. Using exact transfer-matrix methods, we find that on sufficiently large length scales (i.e., length scales sufficiently larger than the bulk correlation length) the distribution of the long contour is given by a unique probability...

  20. A Defect Effect to Light Transmission through Acute Bending Coupled Cavity Waveguide in a Two-Dimensional Photonic Crystal

    Institute of Scientific and Technical Information of China (English)

    HUANG Yin; LU Yan-Wu

    2009-01-01

    @@ Light propagation through a coupled-defect waveguide with a 63.5°bend in a two-dimensional (2D) photonic crystal is investigated. The waveguide modes are non-degenerate monopole state and dipole defect state of a square lattice for two different branches. To increase the transmission in the bending waveguide, we propose a method to rotate the localized state by introducing a new type defect with a sheared square rod into coupled cavity. The higher coupling efficiency and transmission in the bending waveguide are obtained with proper shear shift.

  1. Development and transition of spiral wave in the coupled Hindmarsh-Rose neurons in two-dimensional space

    Institute of Scientific and Technical Information of China (English)

    Ma Jun; Ying He-Ping; Liu Yong; Li Shi-Rong

    2009-01-01

    The dynamics and the transition of spiral waves in the couplcd Hindmarsh-Rose (H-R) neurons in two-dimensional space are investigated in the paper. It is found that the spiral wave can be induced and developed in the coupled HR neurons in two-dimensional space, with appropriate initial values and a parameter region given. However, the spiral wave could encounter instability when the intensity of the external current reaches a threshold value of 1.945. The transition of spiral wave is found to be affected by coupling intensity D and bifurcation parameter r. The spiral wave becomes sparse as the coupling intensity increases, while the spiral wave is eliminated and the whole neuronal system becomes homogeneous as the bifurcation parameter increases to a certain threshold value. Then the coupling action of the four sub-adjacent neurons, which is described by coupling coefficient DI, is also considered, and it is found that the spiral wave begins to breakup due to the introduced coupling action from the sub-adjacent neurons (or sites) and together with the coupling action of the nearest-neighbour neurons, which is described by the coupling intensity D.

  2. Stationary states of the two-dimensional nonlinear Schrödinger model with disorder

    DEFF Research Database (Denmark)

    Gaididei, Yuri Borisovich; Hendriksen, D.; Christiansen, Peter Leth

    1998-01-01

    Solitonlike excitations in the presence of disorder in the two-dimensional cubic nonlinear Schrodinger equation are analyzed. The continuum as well as the discrete problem are analyzed. In the continuum model, otherwise unstable excitations are stabilized in the presence of disorder. In the discr......Solitonlike excitations in the presence of disorder in the two-dimensional cubic nonlinear Schrodinger equation are analyzed. The continuum as well as the discrete problem are analyzed. In the continuum model, otherwise unstable excitations are stabilized in the presence of disorder...

  3. A Direct Calculation of Critical Exponents of Two-Dimensional Anisotropic Ising Model

    Institute of Scientific and Technical Information of China (English)

    XIONG Gang; WANG Xiang-Rong

    2006-01-01

    Using an exact solution of the one-dimensional quantum transverse-field Ising model, we calculate the critical exponents of the two-dimensional anisotropic classicalIsing model (IM). We verify that the exponents are the same as those of isotropic classical IM. Our approach provides an alternative means of obtaining and verifying these well-known results.

  4. Two-dimensional quantum compass model in a staggered field: some rigorous results

    Institute of Scientific and Technical Information of China (English)

    He Pei-Song; You Wen-Long; Tian Guang-Shan

    2011-01-01

    We study the properties of the two-dimensional quantum compass model in a staggered field. Using the PerronFr(o)enius theorem and the reflection positivity method, we rigorously determine the low energy spectrum of this model and its global ground state Ψ0. Furthermore, we show that Ψ0 has a directional long-range order.

  5. Modelling and experimental validation of two-dimensional transverse vibrations in a flexible robot link

    DEFF Research Database (Denmark)

    Sørensen, Paul Haase; Baungaard, Jens Rane

    1996-01-01

    A general model for a rotating homogenous flexible robot link is developed. The model describes two-dimensional transverse vibrations induced by the actuator due to misalignment of the actuator axis of rotation relative to the link symmetry axis and due to translational acceleration of the link...

  6. A two-dimensional global simulation study of inductive-dynamic magnetosphere-ionosphere/thermosphere coupling

    Science.gov (United States)

    Tu, J.; Song, P.

    2016-12-01

    We have developed a new numerical simulation model of the ionosphere/thermosphere by using an inductive-dynamic approach (including self-consistent solutions of Faraday's law and retaining inertia terms in ion momentum equations), that is, based on magnetic field B and plasma velocity v (B, v paradigm), which is distinctive from the conventional modeling based on electric field E and current j. The model solves self-consistently time-dependent continuity, momentum, and energy equations for multiple species of ions and neutrals including photochemistry, and Maxwell's equations. The governing equations solved in the model are a set of multifluid-collisional-Hall MHD equations which are one of unique features of our ionosphere/thermosphere model. With such an inductive-dynamic approach, not only sound wave mode but also all possible MHD wave modes are retained in the solutions of the governing equations so that the dynamic coupling between the magnetosphere and ionosphere and among different regions of the ionosphere can be self-consistently investigated. In the present study, we demonstrate dynamic propagation of field-aligned currents and ionospheric electric field carried by Alfven waves, as well as formation of closure horizontal currents (Pedersen currents in the E-region), indicating that the M-I coupling is via the Alfven waves instead of the field-aligned currents or electric field mapping. The simulation results also show that the Poynting flux and strongest energy dissipation in the ionosphere/thermosphere is in the regions of the largest ion velocities and not necessarily in the auroral oval where the field-aligned currents reside. The frictional heating increases plasma temperature and thus drives ion upflows. The frictional heating also increase neutral temperature and produces neutral upflows but in a much longer time scale. Furthermore, the coupling of high-to-low latitude ionosphere is investigated in terms of propagation of fast MHD waves.

  7. Modeling of the financial market using the two-dimensional anisotropic Ising model

    Science.gov (United States)

    Lima, L. S.

    2017-09-01

    We have used the two-dimensional classical anisotropic Ising model in an external field and with an ion single anisotropy term as a mathematical model for the price dynamics of the financial market. The model presented allows us to test within the same framework the comparative explanatory power of rational agents versus irrational agents with respect to the facts of financial markets. We have obtained the mean price in terms of the strong of the site anisotropy term Δ which reinforces the sensitivity of the agent's sentiment to external news.

  8. Existence and Stability of Two-Dimensional Compact-Like Discrete Breathers in Discrete Two-Dimensional Monatomic Square Lattices

    Institute of Scientific and Technical Information of China (English)

    XU Quan; TIAN Qiang

    2007-01-01

    Two-dimensional compact-like discrete breathers in discrete two-dimensional monatomic square lattices are investigated by discussing a generafized discrete two-dimensional monatomic model.It is proven that the twodimensional compact-like discrete breathers exist not only in two-dimensional soft Ф4 potentials but also in hard two-dimensional Ф4 potentials and pure two-dimensional K4 lattices.The measurements of the two-dimensional compact-like discrete breather cores in soft and hard two-dimensional Ф4 potential are determined by coupling parameter K4,while those in pure two-dimensional K4 lattices have no coupling with parameter K4.The stabilities of the two-dimensional compact-like discrete breathers correlate closely to the coupling parameter K4 and the boundary condition of lattices.

  9. Finite-time scaling via linear driving: application to the two-dimensional Potts model.

    Science.gov (United States)

    Huang, Xianzhi; Gong, Shurong; Zhong, Fan; Fan, Shuangli

    2010-04-01

    We apply finite-time scaling to the q-state Potts model with q=3 and 4 on two-dimensional lattices to determine its critical properties. This consists in applying to the model a linearly varying external field that couples to one of its q states to manipulate its dynamics in the vicinity of its criticality and that drives the system out of equilibrium and thus produces hysteresis and in defining an order parameter other than the usual one and a nonequilibrium susceptibility to extract coercive fields. From the finite-time scaling of the order parameter, the coercivity, and the hysteresis area and its derivative, we are able to determine systematically both static and dynamic critical exponents as well as the critical temperature. The static critical exponents obtained in general and the magnetic exponent delta in particular agree reasonably with the conjectured ones. The dynamic critical exponents obtained appear to confirm the proposed dynamic weak universality but unlikely to agree with recent short-time dynamic results for q=4. Our results also suggest an alternative way to characterize the weak universality.

  10. Simple Two-Dimensional Corrections for One-Dimensional Pulse Tube Models

    Science.gov (United States)

    Lee, J. M.; Kittel, P.; Timmerhaus, K. D.; Radebaugh, R.

    2004-01-01

    One-dimensional oscillating flow models are very useful for designing pulse tubes. They are simple to use, not computationally intensive, and the physical relationship between temperature, pressure and mass flow are easy to understand when used in conjunction with phasor diagrams. They do not possess, however, the ability to directly calculate thermal and momentum diffusion in the direction transverse to the oscillating flow. To account for transverse effects, lumped parameter corrections, which are obtained though experiment, must be used. Or two-dimensional solutions of the differential fluid equations must be obtained. A linear two-dimensional solution to the fluid equations has been obtained. The solution provides lumped parameter corrections for one-dimensional models. The model accounts for heat transfer and shear flow between the gas and the tube. The complex Nusselt number and complex shear wall are useful in describing these corrections, with phase relations and amplitudes scaled with the Prandtl and Valensi numbers. The calculated ratio, a, between a two-dimensional solution of the oscillating temperature and velocity and a one-dimensional solution for the same shows a scales linearly with Va for Va less than 30. In this region alpha less than 0.5, that is, the enthalpy flow calculated with a two-dimensional model is 50% of a calculation using a one-dimensional model. For Va greater than 250, alpha = 0.8, showing that diffusion is still important even when it is confined to a thing layer near the tube wall.

  11. On two-dimensionalization of three-dimensional turbulence in shell models

    DEFF Research Database (Denmark)

    Chakraborty, Sagar; Jensen, Mogens Høgh; Sarkar, A.

    2010-01-01

    Applying a modified version of the Gledzer-Ohkitani-Yamada (GOY) shell model, the signatures of so-called two-dimensionalization effect of three-dimensional incompressible, homogeneous, isotropic fully developed unforced turbulence have been studied and reproduced. Within the framework of shell...

  12. A Two-Dimensional Analytic Thermal Model for a High-Speed PMSM Magnet

    CSIR Research Space (South Africa)

    Grobler, AJ

    2015-11-01

    Full Text Available TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 62, NO. 11, NOVEMBER 2015 A Two-Dimensional Analytic Thermal Model for a High-Speed PMSM Magnet Andries J. Groblera, Stanley Robert Holmb, and George van Schoorc a School of Electrical, Electronic...

  13. Proton transport in a membrane protein channel: two-dimensional infrared spectrum modeling.

    NARCIS (Netherlands)

    Liang, C.; Knoester, J.; Jansen, T.L.Th.A.

    2012-01-01

    We model the two-dimensional infrared (2DIR) spectrum of a proton channel to investigate its applicability as a spectroscopy tool to study the proton transport process in biological systems. Proton transport processes in proton channels are involved in numerous fundamental biochemical reactions. How

  14. Solitary excitations in discrete two-dimensional nonlinear Schrodinger models with dispersive dipole-dipole interactions

    DEFF Research Database (Denmark)

    Christiansen, Peter Leth; Gaididei, Yuri Borisovich; Johansson, M.

    1998-01-01

    The dynamics of discrete two-dimensional nonlinear Schrodinger models with long-range dispersive interactions is investigated. In particular, we focus on the cases where the dispersion arises from a dipole-dipole interaction, assuming the dipole moments at each lattice site to be aligned either...

  15. Two-dimensional cellular automaton model of traffic flow with open boundaries

    CERN Document Server

    Tadaki, S I

    1996-01-01

    A two-dimensional cellular automaton model of traffic flow with open boundaries are investigated by computer simulations. The outflow of cars from the system and the average velocity are investigated. The time sequences of the outflow and average velocity have flicker noises in a jamming phase. The low density behavior are discussed with simple jam-free approximation.

  16. Lattice Methods for Pricing American Strangles with Two-Dimensional Stochastic Volatility Models

    Directory of Open Access Journals (Sweden)

    Xuemei Gao

    2014-01-01

    Full Text Available The aim of this paper is to extend the lattice method proposed by Ritchken and Trevor (1999 for pricing American options with one-dimensional stochastic volatility models to the two-dimensional cases with strangle payoff. This proposed method is compared with the least square Monte-Carlo method via numerical examples.

  17. Resonant scattering and mode coupling in two-dimensional textured planar waveguides.

    Science.gov (United States)

    Cowan, A R; Paddon, P; Pacradouni, V; Young, J F

    2001-05-01

    A heuristic formalism is developed for efficiently determining the specular reflectivity spectrum of two-dimensionally textured planar waveguides. The formalism is based on a Green's function approach wherein the electric fields are assumed to vary little over the thickness of the textured part of the waveguide. Its accuracy, when the thickness of the textured region is much smaller than the wavelength of relevant radiation, is verified by comparison with a much less efficient, exact finite difference solution of Maxwell's equations. In addition to its numerical efficiency, the formalism provides an intuitive explanation of Fano-like features evident in the specular reflectivity spectrum when the incident radiation is phase matched to excite leaky electromagnetic modes attached to the waveguide. By associating various Fourier components of the scattered field with bare slab modes, the dispersion, unique polarization properties, and lifetimes of these Fano-like features are explained in terms of photonic eigenmodes that reveal the renormalization of the slab modes due to interaction with the two-dimensional grating. An application of the formalism, in the analysis of polarization-insensitive notch filters, is also discussed.

  18. Berezinskii-Kosterlitz-Thouless phase transitions in two-dimensional non-Abelian spin models.

    Science.gov (United States)

    Borisenko, Oleg; Chelnokov, Volodymyr; Cuteri, Francesca; Papa, Alessandro

    2016-07-01

    It is argued that two-dimensional U(N) spin models for any N undergo a Berezinskii-Kosterlitz-Thouless (BKT)-like phase transition, similarly to the famous XY model. This conclusion follows from the Berezinskii-like calculation of the two-point correlation function in U(N) models, approximate renormalization group analysis, and numerical investigations of the U(2) model. It is shown, via Monte Carlo simulations, that the universality class of the U(2) model coincides with that of the XY model. Moreover, preliminary numerical results point out that two-dimensional SU(N) spin models with the fundamental and adjoint terms and N>4 exhibit two phase transitions of BKT type, similarly to Z(N) vector models.

  19. Variational tensor network renormalization in imaginary time: Two-dimensional quantum compass model at finite temperature

    Science.gov (United States)

    Czarnik, Piotr; Dziarmaga, Jacek; Oleś, Andrzej M.

    2016-05-01

    Progress in describing thermodynamic phase transitions in quantum systems is obtained by noticing that the Gibbs operator e-β H for a two-dimensional (2D) lattice system with a Hamiltonian H can be represented by a three-dimensional tensor network, the third dimension being the imaginary time (inverse temperature) β . Coarse graining the network along β results in a 2D projected entangled-pair operator (PEPO) with a finite bond dimension D . The coarse graining is performed by a tree tensor network of isometries. The isometries are optimized variationally, taking into account full tensor environment, to maximize the accuracy of the PEPO. The algorithm is applied to the isotropic quantum compass model on an infinite square lattice near a symmetry-breaking phase transition at finite temperature. From the linear susceptibility in the symmetric phase and the order parameter in the symmetry-broken phase, the critical temperature is estimated at Tc=0.0606 (4 ) J , where J is the isotropic coupling constant between S =1/2 pseudospins.

  20. Two-dimensional spectroscopy of molecular excitons in a model dimer system

    Science.gov (United States)

    Halpin, Alexei

    The physics of molecular excitons has been the subject of many recent studies using electronic two-dimensional photon-echo spectroscopy (2DPE), particularly in the context of light harvesting in photosynthesis. Since the spectra for multichromophoric aggregates are congested, particularly so at room temperature, we present a study of a model dimer comprised of identical chromophores with a well defined electronic coupling strength, to provide clear signatures for coherences between vibronic excitons in 2D spectra. We begin by describing the design of a broadband passively phase-stabilized interferometer for collection of 2D spectra, which also allows for the investigation of state preparation in 2D spectroscopy by using shaped excitation pulses. In experiments on the model dimer we observe strong oscillating off-diagonal features in the 2D spectra which are present only before the onset of dephasing, which occurs in less than 100 fs due to strong system-bath coupling. This is in contrast with the parent dye, where low amplitude oscillations associated with Raman active vibrations persist for several ps following excitation. The results of this comparative study indicate that the signals observed earlier in photosynthetic proteins likely reflect vibrational motion in isolated pigments, and not delocalized quantum coherence. While long-lived vibrational coherences are of questionable biological relevance at face value, we conclude with a discussion on initial findings using coherently controlled 2D spectroscopy, where we observe long-lived signatures associated to vibronic coherences at room temperature. These results point to new directions of study using multidimensional spectroscopy to unravel the role of coherence in excitation energy transfer in molecular aggregates in an experimentally direct fashion.

  1. Eighth-order phase-field-crystal model for two-dimensional crystallization

    OpenAIRE

    Jaatinen, A.; Ala-Nissila, T.

    2010-01-01

    We present a derivation of the recently proposed eighth order phase field crystal model [Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase field crystal models. We find that among the phase field crystal models...

  2. Logarithmic discretization and systematic derivation of shell models in two-dimensional turbulence.

    Science.gov (United States)

    Gürcan, Ö D; Morel, P; Kobayashi, S; Singh, Rameswar; Xu, S; Diamond, P H

    2016-09-01

    A detailed systematic derivation of a logarithmically discretized model for two-dimensional turbulence is given, starting from the basic fluid equations and proceeding with a particular form of discretization of the wave-number space. We show that it is possible to keep all or a subset of the interactions, either local or disparate scale, and recover various limiting forms of shell models used in plasma and geophysical turbulence studies. The method makes no use of the conservation laws even though it respects the underlying conservation properties of the fluid equations. It gives a family of models ranging from shell models with nonlocal interactions to anisotropic shell models depending on the way the shells are constructed. Numerical integration of the model shows that energy and enstrophy equipartition seem to dominate over the dual cascade, which is a common problem of two-dimensional shell models.

  3. GIS-based data model and tools for creating and managing two-dimensional cross sections

    Science.gov (United States)

    Whiteaker, Timothy L.; Jones, Norm; Strassberg, Gil; Lemon, Alan; Gallup, Doug

    2012-02-01

    While modern Geographic Information Systems (GIS) software is robust in handling maps and data in plan view, the software generally falls short when representing features in section view. Further complicating the issue is the fact that geologic cross sections are often drawn by connecting a series of wells together that do not fall along a single straight line. In this case, the x-axis of the cross section represents the distance along the set of individual lines connecting the series of wells, effectively "flattening out" the cross section along this path to create a view of the subsurface with which geologists often work in printed folios. Even 3D-enabled GIS cannot handle this type of cross section. A GIS data model and tools for creating and working with two-dimensional cross sections are presented. The data model and tools create a framework that can be applied using ESRI's ArcGIS software, enabling users to create, edit, manage, and print two-dimensional cross sections from within one of the most well-known GIS software packages. The data model is a component of the arc hydro groundwater data model, which means all two-dimensional cross sections are inherently linked to other features in the hydrogeologic domain, including those represented by xyz coordinates in real world space. Thus, the creation of two-dimensional cross sections can be guided by or completely driven from standard GIS data, and geologic interpretations established on two-dimensional cross sections can be translated back to real world coordinates to create three-dimensional features such as fence diagrams, giving GIS users the capacity to characterize the subsurface environment in a variety of integrated views that was not possible before. A case study for the Sacramento Regional Model in California demonstrates the application of the methodology in support of a regional groundwater management plan.

  4. Manipulation of surface plasmon polariton propagation on isotropic and anisotropic two-dimensional materials coupled to boron nitride heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Inampudi, Sandeep; Nazari, Mina; Forouzmand, Ali; Mosallaei, Hossein, E-mail: hosseinm@coe.neu.edu [Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Ave., Boston, Massachusetts 02115 (United States)

    2016-01-14

    We present a comprehensive analysis of surface plasmon polariton dispersion characteristics associated with isotropic and anisotropic two-dimensional atomically thin layered materials (2D sheets) coupled to h-BN heterostructures. A scattering matrix based approach is presented to compute the electromagnetic fields and related dispersion characteristics of stacked layered systems composed of anisotropic 2D sheets and uniaxial bulk materials. We analyze specifically the surface plasmon polariton (SPP) dispersion characteristics in case of isolated and coupled two-dimensional layers with isotropic and anisotropic conductivities. An analysis based on residue theorem is utilized to identify optimum optical parameters (surface conductivity) and geometrical parameters (separation between layers) to maximize the SPP field at a given position. The effect of type and degree of anisotropy on the shapes of iso-frequency curves and propagation characteristics is discussed in detail. The analysis presented in this paper gives an insight to identify optimum setup to enhance the SPP field at a given position and in a given direction on the surface of two-dimensional materials.

  5. Model of two-dimensional electron gas formation at ferroelectric interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Aguado-Puente, P.; Bristowe, N. C.; Yin, B.; Shirasawa, R.; Ghosez, Philippe; Littlewood, P. B.; Artacho, Emilio

    2015-07-01

    The formation of a two-dimensional electron gas at oxide interfaces as a consequence of polar discontinuities has generated an enormous amount of activity due to the variety of interesting effects it gives rise to. Here, we study under what circumstances similar processes can also take place underneath ferroelectric thin films. We use a simple Landau model to demonstrate that in the absence of extrinsic screening mechanisms, a monodomain phase can be stabilized in ferroelectric films by means of an electronic reconstruction. Unlike in the LaAlO3/SrTiO3 heterostructure, the emergence with thickness of the free charge at the interface is discontinuous. This prediction is confirmed by performing first-principles simulations of free-standing slabs of PbTiO3. The model is also used to predict the response of the system to an applied electric field, demonstrating that the two-dimensional electron gas can be switched on and off discontinuously and in a nonvolatile fashion. Furthermore, the reversal of the polarization can be used to switch between a two-dimensional electron gas and a two-dimensional hole gas, which should, in principle, have very different transport properties. We discuss the possible formation of polarization domains and how such configuration competes with the spontaneous accumulation of free charge at the interfaces.

  6. Symmetric two dimensional photonic crystal coupled waveguide with point defect for optical switch application

    CERN Document Server

    Hardhienata, Hendradi

    2012-01-01

    Two dimensional (2D) photonic crystals are well known for its ability to manipulate the propagation of electromagnetic wave inside the crystal. 1D and 2D photonic crystals are relatively easier to fabricate than 3D because the former work in the microwave and far infrared regions whereas the later work in the visible region and requires smaller lattice constants. In this paper, simulation for a modified 2D PC with two symmetric waveguide channels where a defect is located inside one of the channel is performed. The simulation results show that optical switching is possible by modifying the refractive index of the defect. If more than one structure is applied this feature can potentially be applied to produce a cascade optical switch.

  7. Universality class of the two-dimensional site-diluted Ising model.

    Science.gov (United States)

    Martins, P H L; Plascak, J A

    2007-07-01

    In this work, we evaluate the probability distribution function of the order parameter for the two-dimensional site-diluted Ising model. Extensive Monte Carlo simulations have been performed for different spin concentrations p (0.70universality class of the diluted Ising model seems to be independent of the amount of dilution. Logarithmic corrections of the finite-size critical temperature behavior of the model can also be inferred even for such small lattices.

  8. Measurement of the Equation of State of the Two-Dimensional Hubbard Model

    Science.gov (United States)

    Miller, Luke; Cocchi, Eugenio; Drewes, Jan; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Koehl, Michael

    2016-05-01

    The subtle interplay between kinetic energy, interactions and dimensionality challenges our comprehension of strongly-correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions, 0 constitute benchmarks for state-of-the-art theoretical approaches.

  9. Numerical Modeling of Two-Dimensional Temperature Dynamics Across Ice-Wedge Polygons

    Science.gov (United States)

    Garayshin, Viacheslav V.

    The ice wedges on the North Slope of Alaska have been forming for many millennia, when the ground cracked and the cracks were filled with snowmelt water. The infiltrated water then became frozen and turned into ice. When the annual and summer air temperatures become higher, the depth of the active layer increases. A deeper seasonal thawing may cause melting of ice wedges from their tops. Consequently, the ground starts to settle and a trough begins to form above the ice wedge. The forming trough creates a local temperature anomaly in the surrounding ground, and the permafrost located immediately under the trough starts degrading further. Once the trough is formed, the winter snow cover becomes deeper at the trough area further degrading the permafrost. In this thesis we present a computational approach to study the seasonal temperature dynamics of the ground surrounding an ice wedge and ground subsidence associated with ice wedge degradation. A thermo-mechanical model of the ice wedge based on principles of macroscopic thermodynamics and continuum mechanics was developed and will be presented. The model includes heat conduction and quasi-static mechanical equilibrium equations, a visco-elastic rheology for ground deformation, and an empirical formula which relates unfrozen water content to temperature. The complete system is reduced to a computationally convenient set of coupled equations for temperature, ground displacement and ground porosity in a two-dimensional domain. A finite element method and an implicit scheme in time were utilized to construct a non-linear system of equations, which was solved iteratively. The model employs temperature and moisture content data collected from a field experiment at the Next-Generation Ecosystem Experiments (NGEE) sites in Barrow, Alaska. The model describes seasonal dynamics of temperature and the long-term ground motion near the ice wedges and helps to explain destabilization of the ice wedges north of Alaska's Brooks

  10. Analysis of Two-Layered Random Interfaces for Two Dimensional Widom-Rowlinson's Model

    Directory of Open Access Journals (Sweden)

    Jun Wang

    2011-01-01

    Full Text Available The statistical behaviors of two-layered random-phase interfaces in two-dimensional Widom-Rowlinson's model are investigated. The phase interfaces separate two coexisting phases of the lattice Widom-Rowlinson model; when the chemical potential μ of the model is large enough, the convergence of the probability distributions which describe the fluctuations of the phase interfaces is studied. In this paper, the backbones of interfaces are introduced in the model, and the corresponding polymer chains and cluster expansions are developed and analyzed for the polymer weights. And the existence of the free energy for two-layered random-phase interfaces of the two-dimensional Widom-Rowlinson model is given.

  11. Two-dimensional NMR measurement and point dipole model prediction of paramagnetic shift tensors in solids

    Energy Technology Data Exchange (ETDEWEB)

    Walder, Brennan J.; Davis, Michael C.; Grandinetti, Philip J. [Department of Chemistry, Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210 (United States); Dey, Krishna K. [Department of Physics, Dr. H. S. Gour University, Sagar, Madhya Pradesh 470003 (India); Baltisberger, Jay H. [Division of Natural Science, Mathematics, and Nursing, Berea College, Berea, Kentucky 40403 (United States)

    2015-01-07

    A new two-dimensional Nuclear Magnetic Resonance (NMR) experiment to separate and correlate the first-order quadrupolar and chemical/paramagnetic shift interactions is described. This experiment, which we call the shifting-d echo experiment, allows a more precise determination of tensor principal components values and their relative orientation. It is designed using the recently introduced symmetry pathway concept. A comparison of the shifting-d experiment with earlier proposed methods is presented and experimentally illustrated in the case of {sup 2}H (I = 1) paramagnetic shift and quadrupolar tensors of CuCl{sub 2}⋅2D{sub 2}O. The benefits of the shifting-d echo experiment over other methods are a factor of two improvement in sensitivity and the suppression of major artifacts. From the 2D lineshape analysis of the shifting-d spectrum, the {sup 2}H quadrupolar coupling parameters are 〈C{sub q}〉 = 118.1 kHz and 〈η{sub q}〉 = 0.88, and the {sup 2}H paramagnetic shift tensor anisotropy parameters are 〈ζ{sub P}〉 = − 152.5 ppm and 〈η{sub P}〉 = 0.91. The orientation of the quadrupolar coupling principal axis system (PAS) relative to the paramagnetic shift anisotropy principal axis system is given by (α,β,γ)=((π)/2 ,(π)/2 ,0). Using a simple ligand hopping model, the tensor parameters in the absence of exchange are estimated. On the basis of this analysis, the instantaneous principal components and orientation of the quadrupolar coupling are found to be in excellent agreement with previous measurements. A new point dipole model for predicting the paramagnetic shift tensor is proposed yielding significantly better agreement than previously used models. In the new model, the dipoles are displaced from nuclei at positions associated with high electron density in the singly occupied molecular orbital predicted from ligand field theory.

  12. Hadamard States and Two-dimensional Gravity

    CERN Document Server

    Salehi, H

    2001-01-01

    We have used a two-dimensional analog of the Hadamard state-condition to study the local constraints on the two-point function of a linear quantum field conformally coupled to a two-dimensional gravitational background. We develop a dynamical model in which the determination of the state of the quantum field is essentially related to the determination of a conformal frame. A particular conformal frame is then introduced in which a two-dimensional gravitational equation is established.

  13. Two-dimensional model and experimental comparison of an inductively coupled plasma%感应耦合等离子体二维模型与实验对比

    Institute of Scientific and Technical Information of China (English)

    程嘉; 季林红; 朱煜

    2010-01-01

    为研究感应耦合等离子体(inductively coupled plasma,ICP)的建模方法,针对GECRC(gaseous electronics conference radio frequency reference cell)标准等离子体实验平台,利用商业软件CFD-ACE+中的等离子体、电磁场及流体等模块建立了二维流体ICP模型.仿真结果与平台在ICP模式下的放电实验进行了对比分析,在等离子体参数的量级与变化趋势上均取得了较好的一致性.同时对比发现,该模型与Bukowski等(J.Appl.Phys.,1996,80(5):2614)开发的模型的仿真精度处于相同水平,均可定性表征ICP等离子体的分布特性.

  14. Normally attracting manifolds and periodic behavior in one-dimensional and two-dimensional coupled map lattices

    Science.gov (United States)

    Giberti, Claudio; Vernia, Cecilia

    1994-12-01

    We consider diffusively coupled logistic maps in one- and two-dimensional lattices. We investigate periodic behaviors as the coupling parameter varies, i.e., existence and bifurcations of some periodic orbits with the largest domain of attraction. Similarity and differences between the two lattices are shown. For small coupling the periodic behavior appears to be characterized by a number of periodic orbits structured in such a way to give rise to distinct, reverse period-doubling sequences. For intermediate values of the coupling a prominent role in the dynamics is played by the presence of normally attracting manifolds that contain periodic orbits. The dynamics on these manifolds is very weakly hyperbolic, which implies long transients. A detailed investigation allows the understanding of the mechanism of their formation. A complex bifurcation is found which causes an attracting manifold to become unstable.

  15. A two-dimensional analytical model of laminar flame in lycopodium dust particles

    Energy Technology Data Exchange (ETDEWEB)

    Rahbari, Alireza [Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of); Shakibi, Ashkan [Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Bidabadi, Mehdi [Combustion Research Laboratory, Narmak, Tehran (Iran, Islamic Republic of)

    2015-09-15

    A two-dimensional analytical model is presented to determine the flame speed and temperature distribution of micro-sized lycopodium dust particles. This model is based on the assumptions that the particle burning rate in the flame front is controlled by the process of oxygen diffusion and the flame structure consists of preheat, reaction and post flame zones. In the first step, the energy conservation equations for fuel-lean condition are expressed in two dimensions, and then these differential equations are solved using the required boundary condition and matching the temperature and heat flux at the interfacial boundaries. Consequently, the obtained flame temperature and flame speed distributions in terms of different particle diameters and equivalence ratio for lean mixture are compared with the corresponding experimental data for lycopodium dust particles. Consequently, it is shown that this two-dimensional model demonstrates better agreement with the experimental results compared to the previous models.

  16. Canonical quantization of a two-dimensional model with anomalous breaking of gauge invariance

    OpenAIRE

    Girotti, Horacio Oscar; Rothe, Heinz J.; Rothe, Klaus D.

    1986-01-01

    We investigate in detail the operator quantum dynamics of a two-dimensional model exhibiting anomalous breaking of gauge invariance. The equal-time algebra is systematically obtained by using the Dirac-bracket formalism for constrained systems. For certain values of the regularization parameter the system is shown to undergo drastic changes. For the value of the parameter corresponding to the chiral Schwinger model no operator solutions are found to exist.

  17. Striped periodic minimizers of a two-dimensional model for martensitic phase transitions

    CERN Document Server

    Giuliani, Alessandro

    2010-01-01

    In this paper we consider a simplified two-dimensional scalar model for the formation of mesoscopic domain patterns in martensitic shape-memory alloys at the interface between a region occupied by the parent (austenite) phase and a region occupied by the product (martensite) phase, which can occur in two variants (twins). The model, first proposed by Kohn and Mueller, is defined by the following functional:

  18. Tensor renormalization group approach to two-dimensional classical lattice models.

    Science.gov (United States)

    Levin, Michael; Nave, Cody P

    2007-09-21

    We describe a simple real space renormalization group technique for two-dimensional classical lattice models. The approach is similar in spirit to block spin methods, but at the same time it is fundamentally based on the theory of quantum entanglement. In this sense, the technique can be thought of as a classical analogue of the density matrix renormalization group method. We demonstrate the method - which we call the tensor renormalization group method - by computing the magnetization of the triangular lattice Ising model.

  19. On the geometry of classically integrable two-dimensional non-linear sigma models

    Energy Technology Data Exchange (ETDEWEB)

    Mohammedi, N., E-mail: nouri@lmpt.univ-tours.f [Laboratoire de Mathematiques et Physique Theorique (CNRS - UMR 6083), Universite Francois Rabelais de Tours, Faculte des Sciences et Techniques, Parc de Grandmont, F-37200 Tours (France)

    2010-11-11

    A master equation expressing the zero curvature representation of the equations of motion of a two-dimensional non-linear sigma models is found. The geometrical properties of this equation are outlined. Special attention is paid to those representations possessing a spectral parameter. Furthermore, a closer connection between integrability and T-duality transformations is emphasised. Finally, new integrable non-linear sigma models are found and all their corresponding Lax pairs depend on a spectral parameter.

  20. Thermalization of mutual and tripartite information in strongly coupled two dimensional CFTs

    CERN Document Server

    Balasubramanian, V; Copland, N; Craps, B; Galli, F

    2011-01-01

    The mutual and tripartite information between pairs and triples of disjoint regions in a quantum field theory are sensitive probes of the spread of correlations in an equilibrating system. We compute these quantities in strongly coupled 2d CFTs with a gravity dual following the homogenous deposition of energy. The injected energy is modeled in AdS space as an infalling shell, and the information shared by disjoint intervals is computed in terms of geodesic lengths in this background. For given widths and separation of the intervals, the mutual information typically starts at its vacuum value, then increases in time to reach a maximum, and then declines to the value at thermal equilibrium. A simple causality argument qualitatively explains this behavior. The tripartite information is generically non-zero and time-dependent throughout the process. This contrasts with (but does not contradict) the time-independent tripartite information one finds after a 2d quantum quench in the limit of large time and distance ...

  1. Analysis of fatty alcohol derivatives with comprehensive two-dimensional liquid chromatography coupled with mass spectrometry.

    Science.gov (United States)

    Elsner, Victoria; Laun, Sabrina; Melchior, David; Köhler, Michael; Schmitz, Oliver J

    2012-12-14

    A simultaneous separation of anionic (fatty alcohol sulfates, fatty alcohol ether sulfates), non-ionic (alkyl polyglucosides, fatty alcohol ethoxylates) and amphoteric (cocamidopropyl betaines) surfactants was performed by comprehensive two-dimensional liquid chromatography (LCxLC) utilizing a ZIC(®)-HILIC column in the first dimension, a Reprosphere 100 C8-Aqua column in the second dimension and a 10-port two position valve as the interface. The volume of the two sample loops were 25 or 50 μL and allow a one or two minute modulation at a 25 μL/min flow rate. In the first dimension, a gradient of acetonitrile and an ammonium acetate buffer was used to separate polyethoxylated surfactants by their degree of ethoxylation (EO number) whereas in the second dimension, a separation by alkyl chain was performed using a methanol/ammonium acetate buffer gradient. A baseline separation of the above mentioned surfactants according to both EO number and alkyl chain was achieved. The best performance was used to compare two different LCxLC-QTOF MS systems, which demonstrate that a transfer of the method from one system to a totally different system is possible. However, because of the differences in delay volume and extra-column volume between these systems the separation power is changed.

  2. Spin-Hall effect in two-dimensional electron systems with Rashba spin-orbit coupling and disorder.

    Science.gov (United States)

    Sheng, L; Sheng, D N; Ting, C S

    2005-01-14

    Using the four-terminal Landauer-Bu ttiker formula and Green's function approach, we calculate numerically the spin-Hall conductance in a two-dimensional junction system with the Rashba spin-orbit (SO) coupling and disorder. We find that the spin-Hall conductance can be much greater or smaller than the universal value e/8pi, depending on the magnitude of the SO coupling, the electron Fermi energy, and the disorder strength. The spin-Hall conductance does not vanish with increasing sample size for a wide range of disorder strength. Our numerical calculation reveals that a nonzero SO coupling can induce electron delocalization for disorder strength smaller than a critical value, and the nonvanishing spin-Hall effect appears mainly in the metallic regime.

  3. A Novel Machine Learning Strategy Based on Two-Dimensional Numerical Models in Financial Engineering

    Directory of Open Access Journals (Sweden)

    Qingzhen Xu

    2013-01-01

    Full Text Available Machine learning is the most commonly used technique to address larger and more complex tasks by analyzing the most relevant information already present in databases. In order to better predict the future trend of the index, this paper proposes a two-dimensional numerical model for machine learning to simulate major U.S. stock market index and uses a nonlinear implicit finite-difference method to find numerical solutions of the two-dimensional simulation model. The proposed machine learning method uses partial differential equations to predict the stock market and can be extensively used to accelerate large-scale data processing on the history database. The experimental results show that the proposed algorithm reduces the prediction error and improves forecasting precision.

  4. Modeling of the optical properties of a two-dimensional system of small conductive particles.

    Science.gov (United States)

    Kondikov, A. A.; Tonkaev, P. A.; Chaldyshev, V. V.; Vartanyan, T. A.

    2016-08-01

    Software was developed for quick numerical calculations and graphic display of the absorption, reflection and transmittance spectra of two-dimensional systems of small conductive particles. It allowed us to make instant comparison of calculation results and experimental data. A lattice model was used to simulate nearly distributed particles, and the coherent-potential approximation was applied to obtain a solution to the problem of interacting particles. The Delphi programming environment was used.

  5. Spontaneous supersymmetry breaking in the two-dimensional N=1 Wess-Zumino model

    CERN Document Server

    Steinhauer, Kyle

    2014-01-01

    We study the phase diagram of the two-dimensional N=1 Wess-Zumino model on the lattice using Wilson fermions and the fermion loop formulation. We give a complete nonperturbative determination of the ground state structure in the continuum and infinite volume limit. We also present a determination of the particle spectrum in the supersymmetric phase, in the supersymmetry broken phase and across the supersymmetry breaking phase transition. In the supersymmetry broken phase we observe the emergence of the Goldstino particle.

  6. Inflation Cosmological Solutions in Two-Dimensional Brans-Dicke Gravity Model

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The purpose of this paper is to study cosmological properties of two-dimensional Brans-Dicke gravity model. For massless scalar field, the new cosmological solutions are found by integration of field equation, these solutions correspond to the inflation solutions with positive cosmological constant. The result of this paper show that the inflation process of universe is controlled by the classical and quantum effect of the scalar field.

  7. Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model.

    Science.gov (United States)

    Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter

    2016-03-04

    We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Néel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.

  8. Quantum Monte Carlo simulation of a two-dimensional Majorana lattice model

    Science.gov (United States)

    Hayata, Tomoya; Yamamoto, Arata

    2017-07-01

    We study interacting Majorana fermions in two dimensions as a low-energy effective model of a vortex lattice in two-dimensional time-reversal-invariant topological superconductors. For that purpose, we implement ab initio quantum Monte Carlo simulation to the Majorana fermion system in which the path-integral measure is given by a semipositive Pfaffian. We discuss spontaneous breaking of time-reversal symmetry at finite temperatures.

  9. Coupling Navier-stokes and Cahn-hilliard Equations in a Two-dimensional Annular flow Configuration

    KAUST Repository

    Vignal, Philippe

    2015-06-01

    In this work, we present a novel isogeometric analysis discretization for the Navier-Stokes- Cahn-Hilliard equation, which uses divergence-conforming spaces. Basis functions generated with this method can have higher-order continuity, and allow to directly discretize the higher- order operators present in the equation. The discretization is implemented in PetIGA-MF, a high-performance framework for discrete differential forms. We present solutions in a two- dimensional annulus, and model spinodal decomposition under shear flow.

  10. Nonequilibrium critical dynamics of the two-dimensional Ising model quenched from a correlated initial state.

    Science.gov (United States)

    Környei, László; Pleimling, Michel; Iglói, Ferenc

    2008-01-01

    The universality class, even the order of the transition, of the two-dimensional Ising model depends on the range and the symmetry of the interactions (Onsager model, Baxter-Wu model, Turban model, etc.), but the critical temperature is generally the same due to self-duality. Here we consider a sudden change in the form of the interaction and study the nonequilibrium critical dynamical properties of the nearest-neighbor model. The relaxation of the magnetization and the decay of the autocorrelation function are found to display a power law behavior with characteristic exponents that depend on the universality class of the initial state.

  11. Modeling two-dimensional water flow and bromide transport in a heterogeneous lignitic mine soil

    Energy Technology Data Exchange (ETDEWEB)

    Buczko, U.; Gerke, H.H. [Brandenburg University of Technology, Cottbus (Germany)

    2006-02-15

    Water and solute fluxes in lignitic mine soils and in many other soils are often highly heterogeneous. Here, heterogeneity reflects dumping-induced inclined structures and embedded heterogeneous distributions of sediment mixtures and of lignitic fragments. Such two-scale heterogeneity effects may be analyzed through the application of two-dimensional models for calculating water and solute fluxes. The objective of this study was to gain more insight to what extent spatial heterogeneity of soil hydraulic parameters contributes to preferential flow at a lignitic mine soil. The simulations pertained to the 'Barenbrucker Hohe' site in Germany where previously water fluxes and applied tracers had been monitored with a cell lysimeter, and from where a soil block had been excavated for detailed two-dimensional characterization of the hydraulic parameters using pedotransfer functions. Based on those previous studies, scenarios with different distributions of hydraulic parameters were simulated. The results show that spatial variability of hydraulic parameters alone can hardly explain the observed flow patterns. The observed preferential flow at the site was probably caused by additional factors such as hydrophobicity, the presence of root channels, anisotropy in the hydraulic conductivity, and heterogeneous root distributions. To study the relative importance of these other factors by applying two-dimensional flow models to such sites, the experimental database must be improved. Single-continuum model approaches may be insufficient for such sites.

  12. Construction of wave operator for two-dimensional Klein-Gordon-Schrodinger systems with Yukawa coupling

    Directory of Open Access Journals (Sweden)

    Kai Tsuruta

    2013-05-01

    Full Text Available We prove the existence of the wave operator for the Klein-Gordon-Schrodinger system with Yukawa coupling. This non-linearity type is below Strichartz scaling, and therefore classic perturbation methods will fail in any Strichartz space. Instead, we follow the "first iteration method" to handle these critical non-linearities.

  13. FUZZY MODEL FOR TWO-DIMENSIONAL RIVER WATER QUALITY SIMULATION UNDER SUDDEN POLLUTANTS DISCHARGED

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the fuzziness and impreciseness of water environmental system, the fuzzy arithmetic was used to simulate the fuzzy and imprecise relations in modeling river water quality. By defining the parameters of water quality model as symmetrical triangular fuzzy numbers, a two-dimensional fuzzy water quality model for sudden pollutant discharge is established. From the fuzzy model, the pollutant concentrations, corresponding to the specified confidence level of α, can be obtained by means of the α-cut technique and arithmetic operations of triangular fuzzy numbers. Study results reveal that it is feasible in theory and reliable on calculation applying triangular fuzzy numbers to the simulation of river water quality.

  14. Photon-Phonon-Enhanced Infrared Rectification in a Two-Dimensional Nanoantenna-Coupled Tunnel Diode

    Science.gov (United States)

    Kadlec, Emil A.; Jarecki, Robert L.; Starbuck, Andrew; Peters, David W.; Davids, Paul S.

    2016-12-01

    The interplay of strong infrared photon-phonon coupling with electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast photon-assisted tunneling in metal-oxide-semiconductor (MOS) structures. Infrared active optical phonon modes in polar oxides lead to strong dispersion and enhanced electric fields at material interfaces. We find that the infrared dispersion of SiO2 near a longitudinal optical phonon mode can effectively impedance match a photonic surface mode into a nanoscale tunnel gap that results in large transverse-field confinement. An integrated 2D nanoantenna structure on a distributed large-area MOS tunnel-diode rectifier is designed and built to resonantly excite infrared surface modes and is shown to efficiently channel infrared radiation into nanometer-scale gaps in these MOS devices. This enhanced-gap transverse-electric field is converted to a rectified tunneling displacement current resulting in a dc photocurrent. We examine the angular and polarization-dependent spectral photocurrent response of these 2D nanoantenna-coupled tunnel diodes in the photon-enhanced tunneling spectral region. Our 2D nanoantenna-coupled infrared tunnel-diode rectifier promises to impact large-area thermal energy harvesting and infrared direct detectors.

  15. Electronic equivalence of optical negative refraction and retroreflection in the two-dimensional systems with inhomogeneous spin-orbit couplings

    Science.gov (United States)

    Lv, Bo; Ma, Zhongshui

    2013-01-01

    The negative refracted transmission and retroreflection of electrons in low-electron-density semiconductors, in the presence of spin-orbit coupling, are theoretically predicted. It is shown that negative electronic transport may occur owing to the occurrence of additional states whose wave vectors are antiparallel to their group velocities. We conclude that the transport emerges as negative in nature in the scattering process if the sign of its ray equation is reversed with respect to that of the incidence's. We demonstrate this finding in the hybrid of two-dimensional electron gases with different Rashba spin-orbit couplings. We also show that the fundamental of negative electric transport is promising to focus a divergent electronic beam in a spintronic sandwich structure with flat surfaces.

  16. Wave mode coupling due to plasma wakes in two-dimensional plasma crystals: In-depth view

    CERN Document Server

    Couëdel, L; Ivlev, A V; Nosenko, V; Thomas, H M; Morfill, G E

    2011-01-01

    Experiments with two-dimensional (2D) plasma crystals are usually carried out in rf plasma sheaths, where the interparticle interactions are modified due to the presence of plasma wakes. The wake-mediated interactions result in the coupling between wave modes in 2D crystals, which can trigger the mode-coupling instability and cause melting. The theory predicts a number of distinct fingerprints to be observed upon the instability onset, such as the emergence of a new hybrid mode, a critical angular dependence, a mixed polarization, and distinct thresholds. In this paper we summarize these key features and provide their detailed discussion, analyze the critical dependence on experimental parameters, and highlight the outstanding issues.

  17. Temperature dependence of universal fluctuations in the two-dimensional harmonic XY model.

    Science.gov (United States)

    Palma, G

    2006-04-01

    We compute exact analytical expressions for the skewness and kurtosis in the two-dimensional harmonic XY model. These quantities correspond to the third and fourth normalized moments of the probability density function (PDF) of the magnetization of the model. From their behavior, we conclude that they depend explicitly on the system temperature even in the thermodynamic limit, and hence the PDF itself must depend on it. Our results correct the hypothesis called universal fluctuations, they confirm and extend previous results which showed a T dependence of the PDF, including perturbative expansions within the XY model up to first order in temperature.

  18. Eighth-order phase-field-crystal model for two-dimensional crystallization

    OpenAIRE

    Jaatinen, A.; Ala-Nissilä, Tapio

    2010-01-01

    We present a derivation of the recently proposed eighth-order phase-field crystal model [A. Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two-dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase-field crystal models. We find that among the phase-field crystal mod...

  19. Neimark-Sacker bifurcation of a two-dimensional discrete-time predator-prey model.

    Science.gov (United States)

    Khan, A Q

    2016-01-01

    In this paper, we study the dynamics and bifurcation of a two-dimensional discrete-time predator-prey model in the closed first quadrant [Formula: see text]. The existence and local stability of the unique positive equilibrium of the model are analyzed algebraically. It is shown that the model can undergo a Neimark-Sacker bifurcation in a small neighborhood of the unique positive equilibrium and an invariant circle will appear. Some numerical simulations are presented to illustrate our theocratical results and numerically it is shown that the unique positive equilibrium of the system is globally asymptotically stable.

  20. Two-dimensional modeling of apparent resistivity pseudosections in the Cerro Prieto region

    Energy Technology Data Exchange (ETDEWEB)

    Vega, R.; Martinez, M.

    1981-01-01

    Using a finite-difference program (Dey, 1976) for two-dimensional modeling of apparent resistivity pseudosections obtained by different measuring arrays, four apparent resistivity pseudosections obtained at Cerro Prieto with a Schlumberger array by CFE personnel were modeled (Razo, 1978). Using geologic (Puente and de la Pena, 1978) and lithologic (Diaz, et al., 1981) data from the geothermal region, models were obtained which show clearly that, for the actual resistivity present in the zone, the information contained in the measured pseudosections is primarily due to the near-surface structure and does not show either the presence of the geothermal reservoir or the granitic basement which underlies it.

  1. Functional scale-free networks in the two-dimensional Abelian sandpile model

    Science.gov (United States)

    Zarepour, M.; Niry, M. D.; Valizadeh, A.

    2015-07-01

    Recently, the similarity of the functional network of the brain and the Ising model was investigated by Chialvo [Nat. Phys. 6, 744 (2010), 10.1038/nphys1803]. This similarity supports the idea that the brain is a self-organized critical system. In this study we derive a functional network of the two-dimensional Bak-Tang-Wiesenfeld sandpile model as a self-organized critical model, and compare its characteristics with those of the functional network of the brain, obtained from functional magnetic resonance imaging.

  2. Boundary magnetization of a two-dimensional Ising model with inhomogeneous nearest-neighbor interactions

    Science.gov (United States)

    Pelizzola, Alessandro

    1994-11-01

    An explicit formula for the boundary magnetization of a two-dimensional Ising model with a strip of inhomogeneous interactions is obtained by means of a transfer matrix mean-field method introduced by Lipowski and Suzuki. There is clear numerical evidence that the formula is exact By taking the limit where the width of the strip approaches infinity and the interactions have well defined bulk limits, I arrive at the boundary magnetization for a model which includes the Hilhorst-van Leeuwen model. The rich critical behavior of the latter magnetization is thereby rederived with little effort.

  3. Two-dimensional Thermal Modeling of Lithium-ion Battery Cell Based on Electrothermal Impedance Spectroscopy

    DEFF Research Database (Denmark)

    Swierczynski, Maciej Jozef; Stroe, Daniel Loan; Knap, Vaclav

    2016-01-01

    Thermal modeling of lithium-ion batteries is gaining its importance together with increasing power density and compact design of the modern battery systems in order to assure battery safety and long lifetime. Thermal models of lithium-ion batteries are usually either expensive to develop...... and accurate or equivalent thermal circuit based with moderate accuracy and without spatial temperature distribution. This work presents initial results that can be used as a fundament for the cost-efficient development of the two-dimensional thermal model of lithium-ion battery based on multipoint...

  4. Two-dimensional analysis of coupled heat and moisture transport in masonry structures

    Science.gov (United States)

    Krejčí, Tomáš

    2016-06-01

    Reconstruction and maintenance of historical buildings and bridges require good knowledge of temperature and moisture distribution. Sharp changes in the temperature and moisture can lead to damage. This paper describes analysis of coupled heat and moisture transfer in masonry based on two-level approach. Macro-scale level describes the whole structure while meso-scale level takes into account detailed composition of the masonry. The two-level approach is very computationally demanding and it was implemented in parallel. The two-level approach was used in analysis of temperature and moisture distribution in Charles bridge in Prague, Czech Republic.

  5. A two-dimensional conjugated aromatic polymer via C-C coupling reaction

    Science.gov (United States)

    Liu, Wei; Luo, Xin; Bao, Yang; Liu, Yan Peng; Ning, Guo-Hong; Abdelwahab, Ibrahim; Li, Linjun; Nai, Chang Tai; Hu, Zhi Gang; Zhao, Dan; Liu, Bin; Quek, Su Ying; Loh, Kian Ping

    2017-06-01

    The fabrication of crystalline 2D conjugated polymers with well-defined repeating units and in-built porosity presents a significant challenge to synthetic chemists. Yet they present an appealing target because of their desirable physical and electronic properties. Here we report the preparation of a 2D conjugated aromatic polymer synthesized via C-C coupling reactions between tetrabromopolyaromatic monomers. Pre-arranged monomers in the bulk crystal undergo C-C coupling driven by endogenous solid-state polymerization to produce a crystalline polymer, which can be mechanically exfoliated into micrometre-sized lamellar sheets with a thickness of 1 nm. Isothermal gas-sorption measurements of the bulk material reveal a dominant pore size of ~0.6 nm, which indicates uniform open channels from the eclipsed stacking of the sheets. When employed as an organic anode in an ambient-temperature sodium cell, the material allows a fast charge/discharge of sodium ions, with impressive reversible capacity, rate capability and stability metrics.

  6. Thermal metal in network models of a disordered two-dimensional superconductor

    Science.gov (United States)

    Chalker, J. T.; Read, N.; Kagalovsky, V.; Horovitz, B.; Avishai, Y.; Ludwig, A. W.

    2002-01-01

    We study the symmetry class for localization which arises from models of noninteracting quasiparticles in disordered superconductors that have neither time-reversal nor spin-rotation invariance. Two-dimensional systems in this category, which is known as class D, can display phases with three different types of quasiparticle dynamics: metallic, localized, or with a quantized (thermal) Hall conductance. Correspondingly, they can show a variety of delocalization transitions. We illustrate this behavior by investigating numerically the phase diagrams of network models with the appropriate symmetry and show the appearance of the metallic phase.

  7. Digital hardware implementation of a stochastic two-dimensional neuron model.

    Science.gov (United States)

    Grassia, F; Kohno, T; Levi, T

    2017-02-22

    This study explores the feasibility of stochastic neuron simulation in digital systems (FPGA), which realizes an implementation of a two-dimensional neuron model. The stochasticity is added by a source of current noise in the silicon neuron using an Ornstein-Uhlenbeck process. This approach uses digital computation to emulate individual neuron behavior using fixed point arithmetic operation. The neuron model's computations are performed in arithmetic pipelines. It was designed in VHDL language and simulated prior to mapping in the FPGA. The experimental results confirmed the validity of the developed stochastic FPGA implementation, which makes the implementation of the silicon neuron more biologically plausible for future hybrid experiments.

  8. Two-dimensional model of intrinsic magnetic flux losses in helical flux compression generators

    CERN Document Server

    Haurylavets, V V

    2012-01-01

    Helical Flux Compression Generators (HFCG) are used for generation of mega-amper current and high magnetic fields. We propose the two dimensional HFCG filament model based on the new description of the stator and armature contact point. The model developed enables one to quantitatively describe the intrinsic magnetic flux losses and predict the results of experiments with various types of HFCGs. We present the effective resistance calculations based on the non-linear magnetic diffusion effect describing HFCG performance under the strong conductor heating by currents.

  9. Two-Dimensional Wang-Landau Sampling of AN Asymmetric Ising Model

    Science.gov (United States)

    Tsai, Shan-Ho; Wang, Fugao; Landau, D. P.

    We study the critical endpoint behavior of an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. We use a two-dimensional Wang-Landau sampling method to determine the density of states for this model. An accurate density of states allowed us to map out the phase diagram accurately and observe a clear divergence of the curvature of the spectator phase boundary and of the derivative of the magnetization coexistence diameter near the critical endpoint, in agreement with previous theoretical predictions.

  10. Nanolithographic Fabrication and Heterogeneous Reaction Studies ofTwo-Dimensional Platinum Model Catalyst Systems

    Energy Technology Data Exchange (ETDEWEB)

    Contreras, Anthony Marshall [Univ. of California, Berkeley, CA (United States)

    2006-05-20

    In order to better understand the fundamental components that govern catalytic activity, two-dimensional model platinum nanocatalyst arrays have been designed and fabricated. These catalysts arrays are meant to model the interplay of the metal and support important to industrial heterogeneous catalytic reactions. Photolithography and sub-lithographic techniques such as electron beam lithography, size reduction lithography and nanoimprint lithography have been employed to create these platinum nanoarrays. Both in-situ and ex-situ surface science techniques and catalytic reaction measurements were used to correlate the structural parameters of the system to catalytic activity.

  11. An Integrative Biosensor Based on Contra-Directional Coupling Two-dimensional Photonic Crystal Waveguides

    Institute of Scientific and Technical Information of China (English)

    MAO Xiao-Yu; YAO Di-Bi; ZHAO Ling-Yun; HUANG Yi-Dong; ZHANG Wei; PENG Jiang-De

    2008-01-01

    We propose an integrative biochemical sensor utilizing the dip in the transmission spectrum of a normal singleline defect photonic crystal(PC)waveguide,which has a contra-directional coupling with another PC waveguide.When the air holes in the PC slab are filled with a liquid analyte with different refractive indices,the dip has a wavelength shift.By detecting the output power variation at a certain fixed wavelength,a sensitivity of 1.2×10-4is feasible.This structure is easy for integration due to its plane waveguide structure and omissible pump source.In addition,high signal to noise ratio can be expected because signal transmits via a normal single-line defect PC waveguide instead of the PC hole area or analyte.

  12. Comprehensive two-dimensional river ice model based on boundary-fitted coordinate transformation method

    Directory of Open Access Journals (Sweden)

    Ze-yu MAO

    2014-01-01

    Full Text Available River ice is a natural phenomenon in cold regions, influenced by meteorology, geomorphology, and hydraulic conditions. River ice processes involve complex interactions between hydrodynamic, mechanical, and thermal processes, and they are also influenced by weather and hydrologic conditions. Because natural rivers are serpentine, with bends, narrows, and straight reaches, the commonly-used one-dimensional river ice models and two-dimensional models based on the rectangular Cartesian coordinates are incapable of simulating the physical phenomena accurately. In order to accurately simulate the complicated river geometry and overcome the difficulties of numerical simulation resulting from both complex boundaries and differences between length and width scales, a two-dimensional river ice numerical model based on a boundary-fitted coordinate transformation method was developed. The presented model considers the influence of the frazil ice accumulation under ice cover and the shape of the leading edge of ice cover during the freezing process. The model is capable of determining the velocity field, the distribution of water temperature, the concentration distribution of frazil ice, the transport of floating ice, the progression, stability, and thawing of ice cover, and the transport, accumulation, and erosion of ice under ice cover. A MacCormack scheme was used to solve the equations numerically. The model was validated with field observations from the Hequ Reach of the Yellow River. Comparison of simulation results with field data indicates that the model is capable of simulating the river ice process with high accuracy.

  13. Retention modelling of polychlorinated biphenyls in comprehensive two-dimensional gas chromatography.

    Science.gov (United States)

    D'Archivio, Angelo Antonio; Incani, Angela; Ruggieri, Fabrizio

    2011-01-01

    In this paper, we use a quantitative structure-retention relationship (QSRR) method to predict the retention times of polychlorinated biphenyls (PCBs) in comprehensive two-dimensional gas chromatography (GC×GC). We analyse the GC×GC retention data taken from the literature by comparing predictive capability of different regression methods. The various models are generated using 70 out of 209 PCB congeners in the calibration stage, while their predictive performance is evaluated on the remaining 139 compounds. The two-dimensional chromatogram is initially estimated by separately modelling retention times of PCBs in the first and in the second column ((1) t (R) and (2) t (R), respectively). In particular, multilinear regression (MLR) combined with genetic algorithm (GA) variable selection is performed to extract two small subsets of predictors for (1) t (R) and (2) t (R) from a large set of theoretical molecular descriptors provided by the popular software Dragon, which after removal of highly correlated or almost constant variables consists of 237 structure-related quantities. Based on GA-MLR analysis, a four-dimensional and a five-dimensional relationship modelling (1) t (R) and (2) t (R), respectively, are identified. Single-response partial least square (PLS-1) regression is alternatively applied to independently model (1) t (R) and (2) t (R) without the need for preliminary GA variable selection. Further, we explore the possibility of predicting the two-dimensional chromatogram of PCBs in a single calibration procedure by using a two-response PLS (PLS-2) model or a feed-forward artificial neural network (ANN) with two output neurons. In the first case, regression is carried out on the full set of 237 descriptors, while the variables previously selected by GA-MLR are initially considered as ANN inputs and subjected to a sensitivity analysis to remove the redundant ones. Results show PLS-1 regression exhibits a noticeably better descriptive and predictive

  14. Ultrathin two-dimensional superconductivity with strong spin–orbit coupling

    Science.gov (United States)

    Nam, Hyoungdo; Chen, Hua; Liu, Tijiang; Kim, Jisun; Zhang, Chendong; Yong, Jie; Lemberger, Thomas R.; Kratz, Philip A.; Kirtley, John R.; Moler, Kathryn; Adams, Philip W.; MacDonald, Allan H.; Shih, Chih-Kang

    2016-01-01

    We report on a study of epitaxially grown ultrathin Pb films that are only a few atoms thick and have parallel critical magnetic fields much higher than the expected limit set by the interaction of electron spins with a magnetic field, that is, the Clogston–Chandrasekhar limit. The epitaxial thin films are classified as dirty-limit superconductors because their mean-free paths, which are limited by surface scattering, are smaller than their superconducting coherence lengths. The uniformity of superconductivity in these thin films is established by comparing scanning tunneling spectroscopy, scanning superconducting quantum interference device (SQUID) magnetometry, double-coil mutual inductance, and magneto-transport, data that provide average superfluid rigidity on length scales covering the range from microscopic to macroscopic. We argue that the survival of superconductivity at Zeeman energies much larger than the superconducting gap can be understood only as the consequence of strong spin–orbit coupling that, together with substrate-induced inversion-symmetry breaking, produces spin splitting in the normal-state energy bands that is much larger than the superconductor’s energy gap. PMID:27601678

  15. Ultrathin two-dimensional superconductivity with strong spin-orbit coupling.

    Science.gov (United States)

    Nam, Hyoungdo; Chen, Hua; Liu, Tijiang; Kim, Jisun; Zhang, Chendong; Yong, Jie; Lemberger, Thomas R; Kratz, Philip A; Kirtley, John R; Moler, Kathryn; Adams, Philip W; MacDonald, Allan H; Shih, Chih-Kang

    2016-09-20

    We report on a study of epitaxially grown ultrathin Pb films that are only a few atoms thick and have parallel critical magnetic fields much higher than the expected limit set by the interaction of electron spins with a magnetic field, that is, the Clogston-Chandrasekhar limit. The epitaxial thin films are classified as dirty-limit superconductors because their mean-free paths, which are limited by surface scattering, are smaller than their superconducting coherence lengths. The uniformity of superconductivity in these thin films is established by comparing scanning tunneling spectroscopy, scanning superconducting quantum interference device (SQUID) magnetometry, double-coil mutual inductance, and magneto-transport, data that provide average superfluid rigidity on length scales covering the range from microscopic to macroscopic. We argue that the survival of superconductivity at Zeeman energies much larger than the superconducting gap can be understood only as the consequence of strong spin-orbit coupling that, together with substrate-induced inversion-symmetry breaking, produces spin splitting in the normal-state energy bands that is much larger than the superconductor's energy gap.

  16. A two-dimensional CA model for traffic flow with car origin and destination

    Science.gov (United States)

    In-nami, Junji; Toyoki, Hiroyasu

    2007-05-01

    Dynamic phase transitions in a two-dimensional traffic flow model defined on a decorated square-lattice are studied numerically. The square-lattice point and the decorated site denote intersections and roads, respectively. In the present model, a car has a finite deterministic path between the origin and the destination, which is assigned to the car from the beginning. In this new model, we found a new phase between the free-flow phase and the frozen-jam phase that is absent from previous models. The new model is characterized by the persistence of a macroscopic cluster. Furthermore, the behavior in this macroscopic cluster phase is classified into three regions characterized by the shape of the cluster. The boundary of the three regions is phenomenologically estimated. When the trip length is short and the car density is high, both ends of the belt-like cluster connect to each other through the periodic boundary with some probability. This type of cluster is classified topologically as a string on a two-dimensional torus.

  17. Two-dimensional habitat modeling in the Yellowstone/Upper Missouri River system

    Science.gov (United States)

    Waddle, T. J.; Bovee, K.D.; Bowen, Z.H.

    1997-01-01

    This study is being conducted to provide the aquatic biology component of a decision support system being developed by the U.S. Bureau of Reclamation. In an attempt to capture the habitat needs of Great Plains fish communities we are looking beyond previous habitat modeling methods. Traditional habitat modeling approaches have relied on one-dimensional hydraulic models and lumped compositional habitat metrics to describe aquatic habitat. A broader range of habitat descriptors is available when both composition and configuration of habitats is considered. Habitat metrics that consider both composition and configuration can be adapted from terrestrial biology. These metrics are most conveniently accessed with spatially explicit descriptors of the physical variables driving habitat composition. Two-dimensional hydrodynamic models have advanced to the point that they may provide the spatially explicit description of physical parameters needed to address this problem. This paper reports progress to date on applying two-dimensional hydraulic and habitat models on the Yellowstone and Missouri Rivers and uses examples from the Yellowstone River to illustrate the configurational metrics as a new tool for assessing riverine habitats.

  18. Numerical model for the shear rheology of two-dimensional wet foams with deformable bubbles.

    Science.gov (United States)

    Kähärä, T; Tallinen, T; Timonen, J

    2014-09-01

    Shearing of two-dimensional wet foam is simulated using an introduced numerical model, and results are compared to those of experiments. This model features realistically deformable bubbles, which distinguishes it from previously used models for wet foam. The internal bubble dynamics and their contact interactions are also separated in the model, making it possible to investigate the effects of the related microscale properties of the model on the macroscale phenomena. Validity of model assumptions was proved here by agreement between the simulated and measured Herschel-Bulkley rheology, and shear-induced relaxation times. This model also suggests a relationship between the shear stress and normal stress as well as between the average degree of bubble deformation and applied shear stress. It can also be used to analyze suspensions of bubbles and solid particles, an extension not considered in this work.

  19. Fermionic Symmetry-Protected Topological Phase in a Two-Dimensional Hubbard Model

    Science.gov (United States)

    Chen, Cheng-Chien; Muechler, Lukas; Car, Roberto; Neupert, Titus; Maciejko, Joseph

    2016-08-01

    We study the two-dimensional (2D) Hubbard model using exact diagonalization for spin-1 /2 fermions on the triangular and honeycomb lattices decorated with a single hexagon per site. In certain parameter ranges, the Hubbard model maps to a quantum compass model on those lattices. On the triangular lattice, the compass model exhibits collinear stripe antiferromagnetism, implying d -density wave charge order in the original Hubbard model. On the honeycomb lattice, the compass model has a unique, quantum disordered ground state that transforms nontrivially under lattice reflection. The ground state of the Hubbard model on the decorated honeycomb lattice is thus a 2D fermionic symmetry-protected topological phase. This state—protected by time-reversal and reflection symmetries—cannot be connected adiabatically to a free-fermion topological phase.

  20. Dynamics of a multimode system coupled to multiple heat baths probed by two-dimensional infrared spectroscopy.

    Science.gov (United States)

    Ishizaki, Akihito; Tanimura, Yoshitaka

    2007-09-27

    Reduced equation of motion for a multimode system coupled to multiple heat baths is constructed by extending the quantum Fokker-Planck equation with low-temperature correction terms (J. Phys. Soc. Jpn. 2005, 74, 3131). Unlike such common approaches used to describe intramolecular multimode vibration as a Bloch-Redfield theory and a stochastic theory, the present formalism is defined by the molecular coordinates. To explore the correlation among different modes through baths, we consider two cases of system-bath couplings. One is a correlated case in which two modes are coupled to a single bath, and the other is an uncorrelated case in which each mode is coupled to a different bath. We further classify the correlated case into two cases, the plus- and minus-correlated cases, according to distinct correlation manners. For these, one-dimensional and two-dimensional infrared (2D-IR) spectra are calculated numerically by solving the equation of motion. It is demonstrated that 2D-IR spectroscopy has the ability to analyze the correlation of fluctuation-dissipation processes among different modes.

  1. Resonance and Rectification in a Two-Dimensional Frenkel-Kontorova Model with Triangular Symmetry

    Institute of Scientific and Technical Information of China (English)

    YANG Yang; WANG Cang-Long; DUAN Wen-Shan; CHEN Jian-Min

    2011-01-01

    The mode-locking phenomena in the dc- and ac-driven overdamped two-dimensional Frenkel-Kontorova model with triangular symmetric structures are studied. The obtained results show that the transverse velocitylongitudinal velocity(vy) can occur when n is an odd number. It is also found in our simulations that the critical depinning force oscillates with the amplitude of ac-driven force, i.e., the system is dominated by the ac-driven force. The oscillatory behavior is strongly determined by the initial phase of ac force.

  2. Topological Invariants of Edge States for Periodic Two-Dimensional Models

    Energy Technology Data Exchange (ETDEWEB)

    Avila, Julio Cesar; Schulz-Baldes, Hermann, E-mail: schuba@mi.uni-erlangen.de; Villegas-Blas, Carlos [Instituto de Matematicas, UNAM (Mexico)

    2013-06-15

    Transfer matrix methods and intersection theory are used to calculate the bands of edge states for a wide class of periodic two-dimensional tight-binding models including a sublattice and spin degree of freedom. This allows to define topological invariants by considering the associated Bott-Maslov indices which can be easily calculated numerically. For time-reversal symmetric systems in the symplectic universality class this leads to a Z{sub 2} -invariant for the edge states. It is shown that the edge state invariants are related to Chern numbers of the bulk systems and also to (spin) edge currents, in the spirit of the theory of topological insulators.

  3. Existence of a line of critical points in a two-dimensional Lebwohl Lasher model

    Energy Technology Data Exchange (ETDEWEB)

    Shabnam, Sabana [Department of Physics, Lady Brabourne College, Kolkata 700017 (India); DasGupta, Sudeshna, E-mail: sudeshna.dasgupta10@gmail.com [Department of Physics, Lady Brabourne College, Kolkata 700017 (India); Roy, Soumen Kumar [Department of Physics, Jadavpur University, Kolkata 700032 (India)

    2016-02-15

    Controversy regarding transitions in systems with global symmetry group O(3) has attracted the attention of researchers and the detailed nature of this transition is still not well understood. As an example of such a system in this paper we have studied a two-dimensional Lebwohl Lasher model, using the Wolff cluster algorithm. Though we have not been able to reach any definitive conclusions regarding the order present in the system, from finite size scaling analysis, hyperscaling relations and the behavior of the correlation function we have obtained strong indications regarding the presence of quasi-long range order and the existence of a line of critical points in our system.

  4. Existence of a line of critical points in a two-dimensional Lebwohl Lasher model

    Science.gov (United States)

    Shabnam, Sabana; DasGupta, Sudeshna; Roy, Soumen Kumar

    2016-02-01

    Controversy regarding transitions in systems with global symmetry group O(3) has attracted the attention of researchers and the detailed nature of this transition is still not well understood. As an example of such a system in this paper we have studied a two-dimensional Lebwohl Lasher model, using the Wolff cluster algorithm. Though we have not been able to reach any definitive conclusions regarding the order present in the system, from finite size scaling analysis, hyperscaling relations and the behavior of the correlation function we have obtained strong indications regarding the presence of quasi-long range order and the existence of a line of critical points in our system.

  5. Topological invariants of edge states for periodic two-dimensional models

    CERN Document Server

    Avila, Julio Cesar; Villegas-Blas, Carlos

    2012-01-01

    Transfer matrix methods and intersection theory are used to calculate the bands of edge states for a wide class of periodic two-dimensional tight-binding models including a sublattice and spin degree of freedom. This allows to define topological invariants by considering the associated Bott-Maslov indices which can be easily calculated numerically. For time-reversal symmetric systems in the symplectic universality class this leads to a Z_2-invariant for the edge states. It is shown that the edge state invariants are related to Chern numbers of the bulk systems and also to (spin) edge currents, in the spirit of the theory of topological insulators.

  6. The Model for Two-dimensional Layout Optimization Problem with Performance Constraints and Its Optimality Function

    Institute of Scientific and Technical Information of China (English)

    Xu Zhang; En-min Feng

    2004-01-01

    This paper studies the two-dimensional layout optimization problem.An optimization model with performance constraints is presented.The layout problem is partitioned intofinite subproblems in terms of graph theory,in such a way of that each subproblem overcomes its on-o inature optimal variable.A minimax problem is constructed that is locally equivalent to each subproblem.By using this minimax problem,we present the optimality function for every subproblem and prove that the first order necessary optimality condition is satisfied at a point if and only if this point is a zero of optimality function.

  7. Heteroepitaxial growth modes with dislocations in a two-dimensional elastic lattice model

    Science.gov (United States)

    Katsuno, Hiroyasu; Uwaha, Makio; Saito, Yukio

    2008-11-01

    We study equilibrium shapes of adsorbate crystals by allowing a possibility of dislocations on an elastic substrate in a two-dimensional lattice model. The ground state energy is calculated numerically with the use of an elastic lattice Green's function. From the equilibrium shapes determined for various coverages, we infer the growth mode. As the misfit parameter increases, the growth mode changes from the Frank-van der Merwe (FM) to the Stranski-Krastanov (SK), further to the FM with dislocations for a parameter range of ordinary semiconductor materials. Conceivable growth modes such as the SK with dislocations appear in a parameter range between the SK and the FM with dislocations.

  8. Scaling and universality in the two-dimensional Ising model with a magnetic field.

    Science.gov (United States)

    Mangazeev, Vladimir V; Dudalev, Michael Yu; Bazhanov, Vladimir V; Batchelor, Murray T

    2010-06-01

    The scaling function of the two-dimensional Ising model on the square and triangular lattices is obtained numerically via Baxter's variational corner transfer-matrix approach. The use of Aharony-Fisher nonlinear scaling variables allowed us to perform calculations sufficiently away from the critical point and to confirm all predictions of the scaling and universality hypotheses. Our results are in excellent agreement with quantum field theory calculations of Fonseca and Zamolodchikov as well as with many previously known exact and numerical calculations, including susceptibility results by Barouch, McCoy, Tracy, and Wu.

  9. Two-dimensional airflow modeling underpredicts the wind velocity over dunes.

    Science.gov (United States)

    Michelsen, Britt; Strobl, Severin; Parteli, Eric J R; Pöschel, Thorsten

    2015-11-17

    We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune's symmetry axis - that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected.

  10. Two-dimensional airflow modeling underpredicts the wind velocity over dunes

    OpenAIRE

    Britt Michelsen; Severin Strobl; Parteli, Eric J. R.; Thorsten Pöschel

    2015-01-01

    We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune’s symmetry axis — that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barc...

  11. Hamiltonian dynamics of the two-dimensional lattice {phi}{sup 4} model

    Energy Technology Data Exchange (ETDEWEB)

    Caiani, Lando [Scuola Internazionale Superiore di Studi Avanzati (SISSA/ISAS), Trieste (Italy); Casetti, Lapo [Istituto Nazionale di Fisica della Materia (INFM), Unita di Ricerca del Politecnico di Torino, Dipartimento di Fisica, Politecnico di Torino, Turin (Italy); Pettini, Marco [Osservatorio Astrofisico di Arcetri, Florence (Italy)

    1998-04-17

    The Hamiltonian dynamics of the classical {phi}{sup 4} model on a two-dimensional square lattice is investigated by means of numerical simulations. The macroscopic observables are computed as time averages. The results clearly reveal the presence of the continuous phase transition at a finite energy density and are consistent both qualitatively and quantitatively with the predictions of equilibrium statistical mechanics. The Hamiltonian microscopic dynamics also exhibits critical slowing down close to the transition. Moreover, the relationship between chaos and the phase transition is considered, and interpreted in the light of a geometrization of dynamics. (author)

  12. Scaling of cluster heterogeneity in the two-dimensional Potts model.

    Science.gov (United States)

    Lv, Jian-Ping; Yang, Xianqing; Deng, Youjin

    2012-08-01

    Cluster heterogeneity, the number of clusters of mutually distinct sizes, has been recently studied for explosive percolation and standard percolation [H. K. Lee et al., Phys. Rev. E 84, 020101(R) (2011); J. D. Noh et al., Phys. Rev. E 84, 010101(R) (2011)]. In this work we study the scaling of various quantities related with cluster heterogeneity in a broader context of two-dimensional q-state Potts model. We predict, via an analytic approach, the critical exponents for most of the measured quantities, and confirm these predications for various q values using extensive Monte Carlo simulations.

  13. Phase Diagram of the Two-Dimensional Ising Model with Dipolar Interaction

    Institute of Scientific and Technical Information of China (English)

    SUN Gang; CHU Qian-Jin

    2001-01-01

    We treat the two-dimensional Ising model with the dipolar interaction by the numerical calculation under the restriction that the spin configurations are distributed with a 4 × 4 period. The phase diagram with respect to temperature and dipolar interaction strength is constructed. Most characters of the phase diagram are consistent with those obtained in the references by the Monte Carlo simulation, except that we find a new rectangle phase, which is ordered in the spin structure with the 1 × 2 rectangle.

  14. Nonlinear kinetic modeling and simulations of Raman scattering in a two-dimensional geometry

    Directory of Open Access Journals (Sweden)

    Bénisti Didier

    2013-11-01

    Full Text Available In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering (SRS by the means of envelope equations, whose coefficients have been derived using a mixture of perturbative and adiabatic calculations. First examples of the numerical resolution of these envelope equations in a two-dimensional homogeneous plasma are given, and the results are compared against those of particle-in-cell (PIC simulations. These preliminary comparisons are encouraging since our envelope code provides threshold intensities consistent with those of PIC simulations while requiring computational resources reduced by 4 to 5 orders of magnitude compared to full-kinetic codes.

  15. An Investigation of Two-Dimensional CAD Generated Models with Body Decoupled Cartesian Grids for DSMC

    Energy Technology Data Exchange (ETDEWEB)

    OTAHAL,THOMAS J.; GALLIS,MICHAIL A.; BARTEL,TIMOTHY J.

    2000-06-27

    This paper presents an investigation of a technique for using two-dimensional bodies composed of simple polygons with a body decoupled uniform Cmtesian grid in the Direct Simulation Monte Carlo method (DSMC). The method employs an automated grid pre-processing scheme beginning form a CAD geometry definition file, and is based on polygon triangulation using a trapezoid algorithm. A particle-body intersection time comparison is presented between the Icarus DSMC code using a body-fitted structured grid and using a structured body-decoupled Cartesian grid with both linear and logarithmic search techniques. A comparison of neutral flow over a cylinder is presented using the structured body fitted grid and the Cartesian body de-coupled grid.

  16. An incompressible two-dimensional multiphase particle-in-cell model for dense particle flows

    Energy Technology Data Exchange (ETDEWEB)

    Snider, D.M. [SAIC, Albuquerque, NM (United States); O`Rourke, P.J. [Los Alamos National Lab., NM (United States); Andrews, M.J. [Texas A and M Univ., College Station, TX (United States). Dept. of Mechanical Engineering

    1997-06-01

    A two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to a Eulerian grid and then mapping back computed stress tensors to particle positions. This approach utilizes the best of Eulerian/Eulerian continuum models and Eulerian/Lagrangian discrete models. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The computational method is implicit with respect to pressure, velocity, and volume fraction in the continuum solution thus avoiding courant limits on computational time advancement. MP-PIC simulations are compared with one-dimensional problems that have analytical solutions and with two-dimensional problems for which there are experimental data.

  17. Nebular Spectra of SN 1998bw Revisited: Detailed Study by One and Two Dimensional Models

    CERN Document Server

    Maeda, K; Mazzali, P A; Deng, J

    2006-01-01

    Refined one- and two-dimensional models for the nebular spectra of the hyper-energetic Type Ic supernova (SN) 1998bw, associated with the gamma-ray burst GRB980425, from 125 to 376 days after B-band maximum are presented. One dimensional, spherically symmetric spectrum synthesis calculations show that reproducing features in the observed spectra, i.e., the sharply peaked [OI] 6300\\AA doublet and MgI] 4570\\AA emission, and the broad [FeII] blend around 5200\\AA, requires the existence of a high-density O-rich core expanding at low velocities ($\\lsim 8,000$ km s$^{-1}$) and of Fe-rich material moving faster than the O-rich material. Synthetic spectra at late phases from aspherical (bipolar) explosion models are also computed with a two-dimensional spectrum synthesis code. The above features are naturally explained by the aspherical model if the explosion is viewed from a direction close to the axis of symmetry ($\\sim 30^{\\rm o}$), since the aspherical model yields a high-density O-rich region confined along the ...

  18. Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate.

    Science.gov (United States)

    Liu, Yu; Begin-Colin, Sylvie; Pichon, Benoît P; Leuvrey, Cedric; Ihiawakrim, Dris; Rastei, Mircea; Schmerber, Guy; Vomir, Mircea; Bigot, Jean Yves

    2014-10-21

    The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices.

  19. Large-Scale and Deep Quantitative Proteome Profiling Using Isobaric Labeling Coupled with Two-Dimensional LC-MS/MS.

    Science.gov (United States)

    Gritsenko, Marina A; Xu, Zhe; Liu, Tao; Smith, Richard D

    2016-01-01

    Comprehensive, quantitative information on abundances of proteins and their posttranslational modifications (PTMs) can potentially provide novel biological insights into diseases pathogenesis and therapeutic intervention. Herein, we introduce a quantitative strategy utilizing isobaric stable isotope-labeling techniques combined with two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) for large-scale, deep quantitative proteome profiling of biological samples or clinical specimens such as tumor tissues. The workflow includes isobaric labeling of tryptic peptides for multiplexed and accurate quantitative analysis, basic reversed-phase LC fractionation and concatenation for reduced sample complexity, and nano-LC coupled to high resolution and high mass accuracy MS analysis for high confidence identification and quantification of proteins. This proteomic analysis strategy has been successfully applied for in-depth quantitative proteomic analysis of tumor samples and can also be used for integrated proteome and PTM characterization, as well as comprehensive quantitative proteomic analysis across samples from large clinical cohorts.

  20. Measuring and modeling two-dimensional irrigation infiltration under film-mulched furrows

    Institute of Scientific and Technical Information of China (English)

    YongYong Zhang; PuTe Wu; XiNing Zhao; WenZhi Zhao

    2016-01-01

    Furrow irrigation with film-mulched agricultural beds is being promoted in the arid region of northwest China because it improves water utilization. Two-dimensional infiltration patterns under film-mulched furrows can provide guidelines and criteria for irrigation design and operation. Our objective was to investigate soil water dynamics during ponding irrigation infiltration of mulched furrows in a cross-sectional ridge-furrow configuration, using laboratory experiments and math-ematical simulations. Six experimental treatments, with two soil types (silt loam and sandy loam), were investigated to monitor the wetting patterns and soil water distribution in a cuboid soil chamber. Irrigation of mulched furrows clearly increased water lateral infiltration on ridge shoulders and ridges, due to enhancement of capillary driving force. Increases to both initial soil water content (SWC) and irrigation water level resulted in increased wetted soil volume. Empirical regression equations accurately estimated the wetted lateral distance (Rl) and downward distance (Rd) with elapsed time in a variably wetted soil medium. Optimization of model parameters followed by the Inverse approach resulted in satisfactory agreement between observed and predicted cumulative infiltration and SWC. On the basis of model calibration, HYDRUS-2D model can accurately simulate two-dimensional soil water dynamics under irrigation of mulched furrows. There were significant differences in wetting patterns between unmulched and mulched furrow irrigation using HYDRUS-2D simulation. The Rd under the mulched furrows was 32.14%less than the unmulched furrows. Therefore, film-mulched furrows are recommended in a furrow irrigation system.

  1. Computer model of two-dimensional solute transport and dispersion in ground water

    Science.gov (United States)

    Konikow, Leonard F.; Bredehoeft, J.D.

    1978-01-01

    This report presents a model that simulates solute transport in flowing ground water. The model is both general and flexible in that it can be applied to a wide range of problem types. It is applicable to one- or two-dimensional problems involving steady-state or transient flow. The model computes changes in concentration over time caused by the processes of convective transport, hydrodynamic dispersion, and mixing (or dilution) from fluid sources. The model assumes that the solute is non-reactive and that gradients of fluid density, viscosity, and temperature do not affect the velocity distribution. However, the aquifer may be heterogeneous and (or) anisotropic. The model couples the ground-water flow equation with the solute-transport equation. The digital computer program uses an alternating-direction implicit procedure to solve a finite-difference approximation to the ground-water flow equation, and it uses the method of characteristics to solve the solute-transport equation. The latter uses a particle- tracking procedure to represent convective transport and a two-step explicit procedure to solve a finite-difference equation that describes the effects of hydrodynamic dispersion, fluid sources and sinks, and divergence of velocity. This explicit procedure has several stability criteria, but the consequent time-step limitations are automatically determined by the program. The report includes a listing of the computer program, which is written in FORTRAN IV and contains about 2,000 lines. The model is based on a rectangular, block-centered, finite difference grid. It allows the specification of any number of injection or withdrawal wells and of spatially varying diffuse recharge or discharge, saturated thickness, transmissivity, boundary conditions, and initial heads and concentrations. The program also permits the designation of up to five nodes as observation points, for which a summary table of head and concentration versus time is printed at the end of the

  2. A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows

    CERN Document Server

    Mininni, P D; Pouquet, A G

    2004-01-01

    We explore some consequences of the ``alpha model,'' also called the ``Lagrangian-averaged'' model, for two-dimensional incompressible magnetohydrodynamic (MHD) turbulence. This model is an extension of the smoothing procedure in fluid dynamics which filters velocity fields locally while leaving their associated vorticities unsmoothed, and has proved useful for high Reynolds number turbulence computations. We consider several known effects (selective decay, dynamic alignment, inverse cascades, and the probability distribution functions of fluctuating turbulent quantities) in magnetofluid turbulence and compare the results of numerical solutions of the primitive MHD equations with their alpha-model counterparts' performance for the same flows, in regimes where available resolution is adequate to explore both. The hope is to justify the use of the alpha model in regimes that lie outside currently available resolution, as will be the case in particular in three-dimensional geometry or for magnetic Prandtl number...

  3. An evaluation of the role of eddy diffusion in stratospheric interactive two-dimensional models

    Science.gov (United States)

    Schneider, Hans R.; Ko, Malcolm K. W.; Sze, Nien Dak; Shi, Guang-Yu; Wang, Wei-Chyung

    1989-01-01

    An interactive two-dimensional model of the stratosphere, consisting of a primitive equation dynamics module, a simplified HO(x) ozone model, and a full radiative transfer scheme, is used to study the effect of eddy diffusion in the model. Consideration is given to the effects of nonlocal forcing from dissipation in the model troposphere and frictional drag at mesospheric levels, mechanical damping in the stratosphere itself, and potential vorticity flux due to large scale waves. It is found that the ozone distributions generated with the model are very sensitive to the choice of values for the friction and the eddy diffusion coefficients. It is shown that reasonable latitudinal gradients of ozone may be obtained by using small values for the mechanical damping for the mid- and high-latitude stratopsphere.

  4. Two dimensional, two fluid model for sodium boiling in LMFBR fuel assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Granziera, M.R.; Kazimi, M.S.

    1980-05-01

    A two dimensional numerical model for the simulation of sodium boiling transient was developed using the two fluid set of conservation equations. A semiimplicit numerical differencing scheme capable of handling the problems associated with the ill-posedness implied by the complex characteristic roots of the two fluid problems was used, which took advantage of the dumping effect of the exchange terms. Of particular interest in the development of the model was the identification of the numerical problems caused by the strong disparity between the axial and radial dimensions of fuel assemblies. A solution to this problem was found which uses the particular geometry of fuel assemblies to accelerate the convergence of the iterative technique used in the model. Three sodium boiling experiments were simulated with the model, with good agreement between the experimental results and the model predictions.

  5. Many-body basis-set reduction applied to the two-dimensional t-Jz model

    Science.gov (United States)

    Riera, J.; Dagotto, E.

    1993-06-01

    A simple variation of the Lanczos method is discussed. The technique is based on a systematic reduction of the size of the Hilbert space of the model under consideration, and it has many similarities with the basis-set-reduction approach recently introduced by Wenzel and Wilson in the context of quantum chemistry. As an example, the two-dimensional t-Jz model of strongly correlated electrons is studied. Accurate results for the ground-state energy can be obtained on clusters of up to 50 sites, which are unreachable by conventional Lanczos approaches. In particular, the energy of one and two holes is analyzed as a function of Jz/t. In the bulk limit, the numerical results suggest that a finite coupling Jz/t]c~0.18 is necessary to induce ``binding'' of holes in the model.

  6. One- and two-dimensional Stirling machine simulation using experimentally generated reversing flow turbuulence models

    Energy Technology Data Exchange (ETDEWEB)

    Goldberg, L.F. [Univ. of Minnesota, Minneapolis, MN (United States)

    1990-08-01

    The activities described in this report do not constitute a continuum but rather a series of linked smaller investigations in the general area of one- and two-dimensional Stirling machine simulation. The initial impetus for these investigations was the development and construction of the Mechanical Engineering Test Rig (METR) under a grant awarded by NASA to Dr. Terry Simon at the Department of Mechanical Engineering, University of Minnesota. The purpose of the METR is to provide experimental data on oscillating turbulent flows in Stirling machine working fluid flow path components (heater, cooler, regenerator, etc.) with particular emphasis on laminar/turbulent flow transitions. Hence, the initial goals for the grant awarded by NASA were, broadly, to provide computer simulation backup for the design of the METR and to analyze the results produced. This was envisaged in two phases: First, to apply an existing one-dimensional Stirling machine simulation code to the METR and second, to adapt a two-dimensional fluid mechanics code which had been developed for simulating high Rayleigh number buoyant cavity flows to the METR. The key aspect of this latter component was the development of an appropriate turbulence model suitable for generalized application to Stirling simulation. A final-step was then to apply the two-dimensional code to an existing Stirling machine for which adequate experimental data exist. The work described herein was carried out over a period of three years on a part-time basis. Forty percent of the first year`s funding was provided as a match to the NASA funds by the Underground Space Center, University of Minnesota, which also made its computing facilities available to the project at no charge.

  7. Remarks on Two-Dimensional Power Correction in Soft Wall Model

    Institute of Scientific and Technical Information of China (English)

    HUANG Tao; ZUO Fen

    2008-01-01

    We present a direct derivation of the two-point correlation function of the vector current in the soft wall model by using the AdS/CFT dictionary. The resulting correlator is exactly the same as the one previously obtained from dispersion relation with the same spectral function as in this model. The coeffcient C2 of the two-dimensional power correction is found to be C2 = -c/2 with c the slope of the Regge trajectory, rather than C2 = -c/3 derived from the strategy of the first quantized string theory. Taking the slope of the p trajectory c ≈ 0.9 CeV2 as input, we then obtain C2 ≈ -0.45 GeV2. The gluon condensate is found to be (αsG2) ≈ 0.064 GeV4, which is almost identical to the QCD sum rule estimation. By comparing these two equivalent derivation of the correlator of scalar glueball operator, we demonstrate that the two-dimensionai correction cannot be eliminated by including the non-leading solution in the bulk-to-boundary propagator, as carried out by Colangelo et al.[arXiv:0711.4747].In other words, the two-dimensional correction does exist in the scalar glueball case. Also it is manifest by using the dispersion relation that the minus sign of gluon condensate and violation of the low energy theorem are related to the subtraction scheme.

  8. A two dimensional thermal network model for a photovoltaic solar wall

    Energy Technology Data Exchange (ETDEWEB)

    Dehra, Himanshu [1-140 Avenue Windsor, Lachine, Quebec (Canada)

    2009-11-15

    A two dimensional thermal network model is proposed to predict the temperature distribution for a section of photovoltaic solar wall installed in an outdoor room laboratory in Concordia University, Montreal, Canada. The photovoltaic solar wall is constructed with a pair of glass coated photovoltaic modules and a polystyrene filled plywood board as back panel. The active solar ventilation through a photovoltaic solar wall is achieved with an exhaust fan fixed in the outdoor room laboratory. The steady state thermal network nodal equations are developed for conjugate heat exchange and heat transport for a section of a photovoltaic solar wall. The matrix solution procedure is adopted for formulation of conductance and heat source matrices for obtaining numerical solution of one dimensional heat conduction and heat transport equations by performing two dimensional thermal network analyses. The temperature distribution is predicted by the model with measurement data obtained from the section of a photovoltaic solar wall. The effect of conduction heat flow and multi-node radiation heat exchange between composite surfaces is useful for predicting a ventilation rate through a solar ventilation system. (author)

  9. Dual geometric worm algorithm for two-dimensional discrete classical lattice models

    Science.gov (United States)

    Hitchcock, Peter; Sørensen, Erik S.; Alet, Fabien

    2004-07-01

    We present a dual geometrical worm algorithm for two-dimensional Ising models. The existence of such dual algorithms was first pointed out by Prokof’ev and Svistunov [N. Prokof’ev and B. Svistunov, Phys. Rev. Lett. 87, 160601 (2001)]. The algorithm is defined on the dual lattice and is formulated in terms of bond variables and can therefore be generalized to other two-dimensional models that can be formulated in terms of bond variables. We also discuss two related algorithms formulated on the direct lattice, applicable in any dimension. These latter algorithms turn out to be less efficient but of considerable intrinsic interest. We show how such algorithms quite generally can be “directed” by minimizing the probability for the worms to erase themselves. Explicit proofs of detailed balance are given for all the algorithms. In terms of computational efficiency the dual geometrical worm algorithm is comparable to well known cluster algorithms such as the Swendsen-Wang and Wolff algorithms, however, it is quite different in structure and allows for a very simple and efficient implementation. The dual algorithm also allows for a very elegant way of calculating the domain wall free energy.

  10. Hybrid-space density matrix renormalization group study of the doped two-dimensional Hubbard model

    Science.gov (United States)

    Ehlers, G.; White, S. R.; Noack, R. M.

    2017-03-01

    The performance of the density matrix renormalization group (DMRG) is strongly influenced by the choice of the local basis of the underlying physical lattice. We demonstrate that, for the two-dimensional Hubbard model, the hybrid-real-momentum-space formulation of the DMRG is computationally more efficient than the standard real-space formulation. In particular, we show that the computational cost for fixed bond dimension of the hybrid-space DMRG is approximately independent of the width of the lattice, in contrast to the real-space DMRG, for which it is proportional to the width squared. We apply the hybrid-space algorithm to calculate the ground state of the doped two-dimensional Hubbard model on cylinders of width four and six sites; at n =0.875 filling, the ground state exhibits a striped charge-density distribution with a wavelength of eight sites for both U /t =4.0 and 8.0 . We find that the strength of the charge ordering depends on U /t and on the boundary conditions. Furthermore, we investigate the magnetic ordering as well as the decay of the static spin, charge, and pair-field correlation functions.

  11. Research of MPPT for photovoltaic generation based on two-dimensional cloud model

    Science.gov (United States)

    Liu, Shuping; Fan, Wei

    2013-03-01

    The cloud model is a mathematical representation to fuzziness and randomness in linguistic concepts. It represents a qualitative concept with expected value Ex, entropy En and hyper entropy He, and integrates the fuzziness and randomness of a linguistic concept in a unified way. This model is a new method for transformation between qualitative and quantitative in the knowledge. This paper is introduced MPPT (maximum power point tracking, MPPT) controller based two- dimensional cloud model through analysis of auto-optimization MPPT control of photovoltaic power system and combining theory of cloud model. Simulation result shows that the cloud controller is simple and easy, directly perceived through the senses, and has strong robustness, better control performance.

  12. Eighth-order phase-field-crystal model for two-dimensional crystallization

    Science.gov (United States)

    Jaatinen, A.; Ala-Nissila, T.

    2010-12-01

    We present a derivation of the recently proposed eighth-order phase-field crystal model [A. Jaatinen , Phys. Rev. E 80, 031602 (2009)10.1103/PhysRevE.80.031602] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two-dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase-field crystal models. We find that among the phase-field crystal models studied, the eighth-order fitting scheme gives results in good agreement with the density functional theory for both static and dynamic properties, suggesting it is an accurate and computationally efficient approximation to the density functional theory.

  13. A two-dimensional analytical model for short channel junctionless double-gate MOSFETs

    Science.gov (United States)

    Jiang, Chunsheng; Liang, Renrong; Wang, Jing; Xu, Jun

    2015-05-01

    A physics-based analytical model of electrostatic potential for short-channel junctionless double-gate MOSFETs (JLDGMTs) operated in the subthreshold regime is proposed, in which the full two-dimensional (2-D) Poisson's equation is solved in channel region by a method of series expansion similar to Green's function. The expression of the proposed electrostatic potential is completely rigorous and explicit. Based on this expression, analytical models of threshold voltage, subthreshold swing, and subthreshold drain current for JLDGMTs were derived. Subthreshold behavior was studied in detail by changing different device parameters and bias conditions, including doping concentration, channel thickness, gate length, gate oxide thickness, drain voltage, and gate voltage. Results predicted by all the analytical models agree well with numerical solutions from the 2-D simulator. These analytical models can be used to investigate the operating mechanisms of nanoscale JLDGMTs and to optimize their device performance.

  14. Two-dimensional modeling of electrochemical and transport phenomena in the porous structures of a PEMFC

    Energy Technology Data Exchange (ETDEWEB)

    Sahraoui, Melik [Institut Preparatoire aux Etudes d' Ingenieurs de Tunis (IPEIT) (Tunisia); Kharrat, Chafik; Halouani, Kamel [UR: Micro-Electro-Thermal Systems (METS-ENIS), Industrial Energy Systems Group, Institut Preparatoire aux Etudes d' Ingenieurs de Sfax (IPEIS), University of Sfax, B.P: 1172, 3018 Sfax (Tunisia)

    2009-04-15

    A two-dimensional CFD model of PEM fuel cell is developed by taking into account the electrochemical, mass and heat transfer phenomena occurring in all of its regions simultaneously. The catalyst layers and membrane are each considered as distinct regions with finite thickness and calculated properties such as permeability, local protonic conductivity, and local dissolved water diffusion. This finite thickness model enables to model accurately the protonic current in these regions with higher accuracy than using an infinitesimal interface. In addition, this model takes into account the effect of osmotic drag in the membrane and catalyst layers. General boundary conditions are implemented in a way taking into consideration any given species concentration at the fuel cell inlet, such as water vapor which is a very important parameter in determining the efficiency of fuel cells. Other operating parameters such as temperature, pressure and porosity of the porous structure are also investigated to characterize their effect on the fuel cell efficiency. (author)

  15. Simple Screened Hydrogen Model of Excitons in Two-Dimensional Materials

    DEFF Research Database (Denmark)

    Olsen, Thomas; Latini, Simone; Rasmussen, Filip Anselm;

    2016-01-01

    We present a generalized hydrogen model for the binding energies (EB) and radii of excitons in two-dimensional (2D) materials that sheds light on the fundamental differences between excitons in two and three dimensions. In contrast to the well-known hydrogen model of three-dimensional (3D) excitons...... the recently observed linear scaling of exciton binding energies with band gap. It is also shown that the model accurately reproduces the nonhydrogenic Rydberg series in WS2 and can account for screening from the environment....... that only depends on the excitonic mass and the 2D polarizability α. The model is shown to produce accurate results for 51 transition metal dichalcogenides. Remarkably, over a wide range of polarizabilities the binding energy becomes independent of the mass and we obtain E2DB≈3/(4πα), which explains...

  16. Two-dimensional mathematical model of a reciprocating room-temperature Active Magnetic Regenerator

    DEFF Research Database (Denmark)

    Petersen, Thomas Frank; Pryds, Nini; Smith, Anders;

    2008-01-01

    heat exchanger. The model simulates the different steps of the AMR refrigeration cycle and evaluates the performance in terms of refrigeration capacity and temperature span between the two heat exchangers. The model was used to perform an analysis of an AMR with a regenerator made of gadolinium...... and water as the heat transfer fluid. The results show that the AMR is able to obtain a no-load temperature span of 10.9 K in a 1 T magnetic field with a corresponding work input of 93.0 kJ m−3 of gadolinium per cycle. The model shows significant temperature differences between the regenerator and the heat...... transfer fluid during the AMR cycle. This indicates that it is necessary to use two-dimensional models when a parallel-plate regenerator geometry is used....

  17. Finite Element Model for Failure Study of Two-Dimensional Triaxially Braided Composite

    Science.gov (United States)

    Li, Xuetao; Binienda, Wieslaw K.; Goldberg, Robert K.

    2010-01-01

    A new three-dimensional finite element model of two-dimensional triaxially braided composites is presented in this paper. This meso-scale modeling technique is used to examine and predict the deformation and damage observed in tests of straight sided specimens. A unit cell based approach is used to take into account the braiding architecture as well as the mechanical properties of the fiber tows, the matrix and the fiber tow-matrix interface. A 0 deg / plus or minus 60 deg. braiding configuration has been investigated by conducting static finite element analyses. Failure initiation and progressive degradation has been simulated in the fiber tows by use of the Hashin failure criteria and a damage evolution law. The fiber tow-matrix interface was modeled by using a cohesive zone approach to capture any fiber-matrix debonding. By comparing the analytical results to those obtained experimentally, the applicability of the developed model was assessed and the failure process was investigated.

  18. More on two-dimensional O (N ) models with N =(0 ,1 ) supersymmetry

    Science.gov (United States)

    Peterson, Adam J.; Kurianovych, Evgeniy; Shifman, Mikhail

    2016-03-01

    We study the behavior of two-dimensional supersymmetric connections of n copies of O (N ) models with an N =(0 ,1 ) heterotic deformation generated by a right-moving fermion. We develop the model in analogy with the connected N =(0 ,2 ) C P (N -1 ) models for the case of a single connecting fermionic superfield. We calculate the effective potential in the large-N limit and determine the vacuum field configurations. Similarly to other supersymmetry (SUSY) connected models we find that SUSY is unbroken under certain conditions despite the vanishing of the Witten index. Specifically, this preservation of SUSY occurs when we have an even number n of O (N ) families. As in previous cases we show that this result follows from a Zn symmetry under a particular exchange of the O (N ) families. This leads to a definition of a modified Witten index, which guarantees the preservation of SUSY in this case.

  19. Two-dimensional models as testing ground for principles and concepts of local quantum physics

    Science.gov (United States)

    Schroer, Bert

    2006-02-01

    In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g., chiral models, factorizing models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work, I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: (1) a modular interpretation of the chiral model Diff( S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime and (2) a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational chiral theories. The SL (2, Z) modular Verlinde relation is a special case of this thermal duality and (within the family of rational models) the matrix S appearing in the thermal duality relation becomes identified with the statistics character matrix S. The relevant angular "Euclideanization" is done in the setting of the Tomita-Takesaki modular formalism of operator algebras. I find it appropriate to dedicate this work to the memory of J.A. Swieca with whom I shared the interest in two-dimensional models as a testing ground for QFT for more than one decade. This is a significantly extended version of an "Encyclopedia of Mathematical Physics" contribution hep-th/0502125.

  20. Two-dimensional models as testing ground for principles and concepts of local quantum physics

    Energy Technology Data Exchange (ETDEWEB)

    Schroer, Bert [FU Berlin (Germany). Institut fuer Theoretische Physik

    2005-04-15

    In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g. chiral models, factoring models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: (1) a modular interpretation of the chiral model Diff(S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime and (2) a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational chiral theories. The SL(2,Z) modular Verlinde relation is a special case of this thermal duality and (within the family of rational models) the matrix S appearing in the thermal duality relation becomes identified with the statistics character matrix S. The relevant angular 'Euclideanization' is done in the setting of the Tomita-Takesaki modular formalism of operator algebras. I find it appropriate to dedicate this work to the memory of J. A. Swieca with whom I shared the interest in two-dimensional models as a testing ground for QFT for more than one decade. This is a significantly extended version of an 'Encyclopedia of Mathematical Physics' contribution hep-th/0502125. (author)

  1. Two-dimensional models of early-type fast rotating stars: the ESTER project

    CERN Document Server

    Rieutord, Michel

    2015-01-01

    In this talk I present the latest results of the ESTER project that has taken up the challenge of building two dimensional (axisymmetric) models of stars rotating at any rotation rate. In particular, I focus on main sequence massive and intermediate mass stars. I show what should be expected in such stars as far as the differential rotation and the associated meridional circulation are concerned, notably the emergence of a Stewartson layer along the tangent cylinder of the core. I also indicate what may be inferred about the evolution of an intermediate-mass star at constant angular momentum and how Be stars may form. I finally give some comparisons between models and observations of the gravity darkening on some nearby fast rotators as it has been derived from interferometric observations. In passing, I also discuss how 2D models can help to recover the fundamental parameters of a star.

  2. Hydrodynamics for a model of a confined quasi-two-dimensional granular gas.

    Science.gov (United States)

    Brey, J Javier; Buzón, V; Maynar, P; García de Soria, M I

    2015-05-01

    The hydrodynamic equations for a model of a confined quasi-two-dimensional gas of smooth inelastic hard spheres are derived from the Boltzmann equation for the model, using a generalization of the Chapman-Enskog method. The heat and momentum fluxes are calculated to Navier-Stokes order, and the associated transport coefficients are explicitly determined as functions of the coefficient of normal restitution and the velocity parameter involved in the definition of the model. Also an Euler transport term contributing to the energy transport equation is considered. This term arises from the gradient expansion of the rate of change of the temperature due to the inelasticity of collisions, and it vanishes for elastic systems. The hydrodynamic equations are particularized for the relevant case of a system in the homogeneous steady state. The relationship with previous works is analyzed.

  3. Present status of two-dimensional ESTER models: Application to Be stars

    CERN Document Server

    Rieutord, M

    2013-01-01

    ESTER two-dimensional models solve the steady state structure of fast rotating early-type stars including the large scale flows associated with the baroclinicity of the radiative zones. Models are compared successfully to the fundamental parameters of the two main components of the triple system $\\delta$ Velorum that have been derived from interferometric and orbit measurements. Testing the models on the Be star Achernar ($\\alpha$ Eri), we cannot reproduce the data and conclude that this star has left the main sequence and is likely crossing the Herzsprung gap. Computing main sequence evolution of fast rotating stars at constant angular momentum shows that their criticality increases with time suggesting that the Be phenomenon and the ensuing mass ejections is the result of evolution.

  4. An extended two-dimensional mathematical model of vertical ring furnaces

    Science.gov (United States)

    Peter, S.; Charette, A.; Bui, R. T.; Tomsett, A.; Potocnik, V.

    1996-04-01

    An extended two-dimensional (2-D+) mathematical model of vertical anode baking furnaces has been developed. The work was motivated by the fact that a previous 2-D model was unable to predict the nonuniform baking in the transverse direction, i.e., perpendicular to the longitudinal axis of the furnace. The modeling strategy based on dividing each section in four zones (underlid, pit, underpit, head wall and fire shaft zones) and introducing two symmetry planes in the exterior pits is explained. The basic heat-transfer relations used are also detailed. Selected results shown include draught and oxygen concentration profiles in the flue, gas and anode temperature distributions and fuel consumption in the back fire ramp. Simulation and experimental results are compared.

  5. A two-dimensional model for the study of interpersonal attraction.

    Science.gov (United States)

    Montoya, R Matthew; Horton, Robert S

    2014-02-01

    We describe a model for understanding interpersonal attraction in which attraction can be understood as a product of the initial evaluations we make about others. The model posits that targets are evaluated on two basic dimensions, capacity and willingness, such that affective and behavioral attraction result from evaluations of (a) a target's capacity to facilitate the perceiver's goals/needs and (b) a target's potential willingness to facilitate those goals/needs. The plausibility of the two-dimensional model of attraction is evaluated vis-à-vis the extant literature on various attraction phenomena including the reciprocity of liking effect, pratfall effect, matching hypothesis, arousal effects, and similarity effect. We conclude that considerable evidence across a wide range of phenomena supports the idea that interpersonal attraction is principally determined by inferences about the target's capacity and willingness.

  6. Statistical mechanics of two-dimensional foams: Physical foundations of the model.

    Science.gov (United States)

    Durand, Marc

    2015-12-01

    In a recent series of papers, a statistical model that accounts for correlations between topological and geometrical properties of a two-dimensional shuffled foam has been proposed and compared with experimental and numerical data. Here, the various assumptions on which the model is based are exposed and justified: the equiprobability hypothesis of the foam configurations is argued. The range of correlations between bubbles is discussed, and the mean-field approximation that is used in the model is detailed. The two self-consistency equations associated with this mean-field description can be interpreted as the conservation laws of number of sides and bubble curvature, respectively. Finally, the use of a "Grand-Canonical" description, in which the foam constitutes a reservoir of sides and curvature, is justified.

  7. Two-dimensional numerical modeling of the longitudinal and lateral channel deformations in alluvial rivers

    Institute of Scientific and Technical Information of China (English)

    XIA Junqiang; WANG Guangqian; WU Baosheng

    2004-01-01

    Two kinds of bank erosion mechanisms were analyzed, including fluvial and non-fluvial controlled mechanisms, and mechanical methods of simulating the erosion processes of cohesive, non-cohesive and composite riverbanks were improved. Then a two-dimensional numerical model of the channel deformation was developed, consisting of a 2D flow and sediment transport submodel and bank-erosion submodels of different soil riverbanks. In the model, a new technique for updating the bank geometry during the bed evolution was presented, which combines closely two kinds of submodels. The proposed model is capable of not only predicting the processes of flood routing and longitudinal channel deformation in natural rivers, but also simulating the processes of lateral channel deformation, especially the processes of lateral erosion and failure of cohesive, non-cohesive and composite riverbanks.

  8. Two-dimensional modeling of volatile organic compounds adsorption onto beaded activated carbon.

    Science.gov (United States)

    Tefera, Dereje Tamiru; Jahandar Lashaki, Masoud; Fayaz, Mohammadreza; Hashisho, Zaher; Philips, John H; Anderson, James E; Nichols, Mark

    2013-10-15

    A two-dimensional heterogeneous computational fluid dynamics model was developed and validated to study the mass, heat, and momentum transport in a fixed-bed cylindrical adsorber during the adsorption of volatile organic compounds (VOCs) from a gas stream onto a fixed bed of beaded activated carbon (BAC). Experimental validation tests revealed that the model predicted the breakthrough curves for the studied VOCs (acetone, benzene, toluene, and 1,2,4-trimethylbenzene) as well as the pressure drop and temperature during benzene adsorption with a mean relative absolute error of 2.6, 11.8, and 0.8%, respectively. Effects of varying adsorption process variables such as carrier gas temperature, superficial velocity, VOC loading, particle size, and channelling were investigated. The results obtained from this study are encouraging because they show that the model was able to accurately simulate the transport processes in an adsorber and can potentially be used for enhancing absorber design and operation.

  9. Two-Dimensional ARMA Modeling for Breast Cancer Detection and Classification

    CERN Document Server

    Bouaynaya, Nidhal; Schonfeld, Dan

    2009-01-01

    We propose a new model-based computer-aided diagnosis (CAD) system for tumor detection and classification (cancerous v.s. benign) in breast images. Specifically, we show that (x-ray, ultrasound and MRI) images can be accurately modeled by two-dimensional autoregressive-moving average (ARMA) random fields. We derive a two-stage Yule-Walker Least-Squares estimates of the model parameters, which are subsequently used as the basis for statistical inference and biophysical interpretation of the breast image. We use a k-means classifier to segment the breast image into three regions: healthy tissue, benign tumor, and cancerous tumor. Our simulation results on ultrasound breast images illustrate the power of the proposed approach.

  10. Two-dimensional mathematical model of a packed bed dryer and experimentation

    Energy Technology Data Exchange (ETDEWEB)

    Basirat-Tabrizi, H.; Saffar-Avval, M.; Assarie, M.R. [Amirkabir University of Technology, Tehran (Iran). Dept. of Mechanical Engineering

    2002-04-01

    A comprehensive heat and mass transfer model, based on the Eulerian two fluid model (TFM), developed for a packed-bed-drying process. The temperature and moisture content in a particle was considered with the conjugate effects between the gas and particles in a packed bed. Numerical study of the model was carried out on two-dimensional, axi-symmetrical cylindrical coordinates in order to investigate the effects of the different parameters such as particle size, variation of inlet gas temperature on the moisture content, and temperature of solid and gas outlet. For experimental observations, an experimental apparatus was designed and utilized. The theoretical results were then compared to the experimental data, which indicated good agreement. (author)

  11. Synchronizability of Small-World Networks Generated from a Two-Dimensional Kleinberg Model

    Directory of Open Access Journals (Sweden)

    Yi Zhao

    2013-01-01

    Full Text Available This paper investigates the synchronizability of small-world networks generated from a two-dimensional Kleinberg model, which is more general than NW small-world network. The three parameters of the Kleinberg model, namely, the distance of neighbors, the number of edge-adding, and the edge-adding probability, are analyzed for their impacts on its synchronizability and average path length. It can be deduced that the synchronizability becomes stronger as the edge-adding probability increases, and the increasing edge-adding probability could make the average path length of the Kleinberg small-world network go smaller. Moreover, larger distance among neighbors and more edges to be added could play positive roles in enhancing the synchronizability of the Kleinberg model. The lorentz oscillators are employed to verify the conclusions numerically.

  12. Duality and Fisher zeros in the two-dimensional Potts model on a square lattice.

    Science.gov (United States)

    Astorino, Marco; Canfora, Fabrizio

    2010-05-01

    A phenomenological approach to the ferromagnetic two-dimensional (2D) Potts model on square lattice is proposed. Our goal is to present a simple functional form that obeys the known properties possessed by the free energy of the q-state Potts model. The duality symmetry of the 2D Potts model together with the known results on its critical exponent α allows us to fix consistently the details of the proposed expression for the free energy. The agreement of the analytic ansatz with numerical data in the q=3 case is very good at high and low temperatures as well as at the critical point. It is shown that the q>4 cases naturally fit into the same scheme and that one should also expect a good agreement with numerical data. The limiting q=4 case is shortly discussed.

  13. Test of quantum thermalization in the two-dimensional transverse-field Ising model

    Science.gov (United States)

    Blaß, Benjamin; Rieger, Heiko

    2016-12-01

    We study the quantum relaxation of the two-dimensional transverse-field Ising model after global quenches with a real-time variational Monte Carlo method and address the question whether this non-integrable, two-dimensional system thermalizes or not. We consider both interaction quenches in the paramagnetic phase and field quenches in the ferromagnetic phase and compare the time-averaged probability distributions of non-conserved quantities like magnetization and correlation functions to the thermal distributions according to the canonical Gibbs ensemble obtained with quantum Monte Carlo simulations at temperatures defined by the excess energy in the system. We find that the occurrence of thermalization crucially depends on the quench parameters: While after the interaction quenches in the paramagnetic phase thermalization can be observed, our results for the field quenches in the ferromagnetic phase show clear deviations from the thermal system. These deviations increase with the quench strength and become especially clear comparing the shape of the thermal and the time-averaged distributions, the latter ones indicating that the system does not completely lose the memory of its initial state even for strong quenches. We discuss our results with respect to a recently formulated theorem on generalized thermalization in quantum systems.

  14. Multi-kW high-brightness fiber coupled diode laser based on two dimensional stacked tailored diode bars

    Science.gov (United States)

    Bayer, Andreas; Unger, Andreas; Köhler, Bernd; Küster, Matthias; Dürsch, Sascha; Kissel, Heiko; Irwin, David A.; Bodem, Christian; Plappert, Nora; Kersten, Maik; Biesenbach, Jens

    2016-03-01

    The demand for high brightness fiber coupled diode laser devices in the multi kW power region is mainly driven by industrial applications for materials processing, like brazing, cladding and metal welding, which require a beam quality better than 30 mm x mrad and power levels above 3kW. Reliability, modularity, and cost effectiveness are key factors for success in the market. We have developed a scalable and modular diode laser architecture that fulfills these requirements through use of a simple beam shaping concept based on two dimensional stacking of tailored diode bars mounted on specially designed, tap water cooled heat sinks. The base element of the concept is a tailored diode laser bar with an epitaxial and lateral structure designed such that the desired beam quality in slow-axis direction can be realized without using sophisticated beam shaping optics. The optical design concept is based on fast-axis collimator (FAC) and slow-axis collimator (SAC) lenses followed by only one additional focusing optic for efficient coupling into a 400 μm fiber with a numerical aperture (NA) of 0.12. To fulfill the requirements of scalability and modularity, four tailored bars are populated on a reduced size, tap water cooled heat sink. The diodes on these building blocks are collimated simply via FAC and SAC. The building blocks can be stacked vertically resulting in a two-dimensional diode stack, which enables a compact design of the laser source with minimum beam path length. For a single wavelength, up to eight of these building blocks, implying a total of 32 tailored bars, can be stacked into a submodule, polarization multiplexed, and coupled into a 400 μm, 0.12NA fiber. Scalability into the multi kW region is realized by wavelength combining of replaceable submodules in the spectral range from 900 - 1100 nm. We present results of a laser source based on this architecture with an output power of more than 4 kW and a beam quality of 25 mm x mrad.

  15. Comprehensive two-dimensional gas chromatography coupled with fast sulphur-chemiluminescence detection: implications of detector electronics.

    Science.gov (United States)

    Blomberg, Jan; Riemersma, Toby; van Zuijlen, Manfred; Chaabani, Hassan

    2004-09-24

    Within the petrochemical industry, there has been a growing interest in methods capable of providing detailed information on the distribution of sulphur-containing compounds in various product streams, going down to the level of separating and quantifying individual sulphur species. Since no single capillary gas chromatographic column is able to perform this separation, a refuge to multi-dimensional separation techniques has to be taken. In this respect, comprehensive two-dimensional gas chromatography (GC x GC) coupled with sulphur chemiluminescence detection (SCD) has shown to be highly promising. It has been suggested, however, that the detector volume of an SCD restricts its potential to keep up with the fast second-dimension separations of contemporary GC x GC. In this paper, we will demonstrate that the lack of speed of the SCD does not originate from its physical dimensions, but is largely determined by the speed of the electronics used. Additionally, some typical examples will be presented to illustrate the potential of GC x GC coupled with fast SCD.

  16. Absence of localization in disordered two-dimensional electron gas at weak magnetic field and strong spin-orbit coupling

    Science.gov (United States)

    Su, Ying; Wang, C.; Avishai, Y.; Meir, Yigal; Wang, X. R.

    2016-09-01

    The one-parameter scaling theory of localization predicts that all states in a disordered two-dimensional system with broken time reversal symmetry are localized even in the presence of strong spin-orbit coupling. While at constant strong magnetic fields this paradigm fails (recall the quantum Hall effect), it is believed to hold at weak magnetic fields. Here we explore the nature of quantum states at weak magnetic field and strongly fluctuating spin-orbit coupling, employing highly accurate numerical procedure based on level spacing distribution and transfer matrix technique combined with one parameter finite-size scaling hypothesis. Remarkably, the metallic phase, (known to exist at zero magnetic field), persists also at finite (albeit weak) magnetic fields, and eventually crosses over into a critical phase, which has already been confirmed at high magnetic fields. A schematic phase diagram drawn in the energy-magnetic field plane elucidates the occurrence of localized, metallic and critical phases. In addition, it is shown that nearest-level statistics is determined solely by the symmetry parameter β and follows the Wigner surmise irrespective of whether states are metallic or critical.

  17. Interplay between Rashba spin-orbit coupling and adiabatic rotation in a two-dimensional Fermi gas

    Science.gov (United States)

    Doko, E.; Subaşı, A. L.; Iskin, M.

    2017-01-01

    We explore the trap profiles of a two-dimensional atomic Fermi gas in the presence of a Rashba spin-orbit coupling and under an adiabatic rotation. We first consider a noninteracting gas and show that the competition between the effects of Rashba coupling on the local density of single-particle states and the Coriolis effects caused by rotation gives rise to a characteristic ring-shaped density profile that survives at experimentally accessible temperatures. Furthermore, Rashba splitting of the Landau levels gives the density profiles a ziggurat shape in the rapid-rotation limit. We then consider an interacting gas under the BCS mean-field approximation for local pairing, and study the pair-breaking mechanism that is induced by the Coriolis effects on superfluidity, where we calculate the critical rotation frequencies both for the onset of pair breaking and for the complete destruction of superfluidity in the system. In particular, by comparing the results of a fully-quantum-mechanical Bogoliubov-de Gennes approach with those of a semiclassical local-density approximation, we construct extensive phase diagrams for a wide range of parameter regimes in the trap where the aforementioned competition may, e.g., favor an outer normal edge that is completely phase separated from the central superfluid core by vacuum.

  18. Two-dimensional modeling of the back amorphous-crystalline silicon heterojunction (BACH) photovoltaic device

    Science.gov (United States)

    Chowdhury, Zahidur R.; Chutinan, Alongkarn; Gougam, Adel B.; Kherani, Nazir P.; Zukotynski, Stefan

    2010-06-01

    Back Amorphous-Crystalline Silicon Heterojunction (BACH)1 solar cell can be fabricated using low temperature processes while integrating high efficiency features of heterojunction silicon solar cells and back-contact homojunction solar cells. This article presents a two-dimensional modeling study of the BACH cell concept. A parametric study of the BACH cell has been carried out using Sentaurus after benchmarking the software. A detailed model describing the optical generation is defined. Solar cell efficiency of 24.4% is obtained for AM 1.5 global spectrum with VOC of greater than 720 mV and JSC exceeding 40 mA/cm2, considering realistic surface passivation quality and other dominant recombination processes.

  19. Finite element model to study two dimensional unsteady state calcium distribution in cardiac myocytes

    Directory of Open Access Journals (Sweden)

    Kunal Pathak

    2016-09-01

    Full Text Available The calcium signaling plays a crucial role in expansion and contraction of cardiac myocytes. This calcium signaling is achieved by calcium diffusion, buffering mechanisms and influx in cardiac myocytes. The various calcium distribution patterns required for achieving calcium signaling in myocytes are still not well understood. In this paper an attempt has been made to develop a model of calcium distribution in myocytes incorporating diffusion of calcium, point source and excess buffer approximation. The model has been developed for a two dimensional unsteady state case. Appropriate boundary conditions and initial condition have been framed. The finite element method has been employed to obtain the solution. The numerical results have been used to study the effect of buffers and source amplitude on calcium distribution in myocytes.

  20. Thermodynamics of the two-dimensional XY model from functional renormalization

    CERN Document Server

    Jakubczyk, Pawel

    2016-01-01

    We solve the nonperturbative renormalization-group flow equations for the two-dimensional XY model at the truncation level of the (complete) second-order derivative expansion. We compute the thermodynamic properties in the high-temperature phase and compare the non-universal features specific to the XY model with results from Monte Carlo simulations. In particular, we study the position and magnitude of the specific heat peak as a function of temperature. The obtained results compare well with Monte Carlo simulations. We additionally gauge the accuracy of simplified nonperturbative renormalization-group treatments relying on $\\phi^4$-type truncations. Our computation indicates that such an approximation is insufficient in the high-$T$ phase and a correct analysis of the specific heat profile requires account of an infinite number of interaction vertices.

  1. Identification of the heat transfer coefficient in the two-dimensional model of binary alloy solidification

    Science.gov (United States)

    Hetmaniok, Edyta; Hristov, Jordan; Słota, Damian; Zielonka, Adam

    2017-05-01

    The paper presents the procedure for solving the inverse problem for the binary alloy solidification in a two-dimensional space. This is a continuation of some previous works of the authors investigating a similar problem but in the one-dimensional domain. Goal of the problem consists in identification of the heat transfer coefficient on boundary of the region and in reconstruction of the temperature distribution inside the considered region in case when the temperature measurements in selected points of the alloy are known. Mathematical model of the problem is based on the heat conduction equation with the substitute thermal capacity and with the liquidus and solidus temperatures varying in dependance on the concentration of the alloy component. For describing this concentration the Scheil model is used. Investigated procedure involves also the parallelized Ant Colony Optimization algorithm applied for minimizing a functional expressing the error of approximate solution.

  2. Two-dimensional water quality modeling of Town Creek embayment on Guntersville Reservoir

    Energy Technology Data Exchange (ETDEWEB)

    Bender, M.D.; Shiao, Ming C.; Hauser, G.E. (Tennessee Valley Authority, Norris, TN (USA). Engineering Lab.); Butkus, S.R. (Tennessee Valley Authority, Norris, TN (USA). Water Quality Dept.)

    1990-09-01

    TVA investigated water quality of Town Creek embayment using a branched two-dimensional model of Guntersville Reservoir. Simulation results were compared in terms of algal biomass, nutrient concentrations, and volume of embayment with depleted dissolved oxygen. Stratification and flushing play a significant role in the embayment water quality. Storms introduce large loadings of organics, nutrients, and suspended solids. Dissolved oxygen depletion is most severe after storms followed by low flow that fails to flush the embayment. Embayment water quality responses to potential animal waste and erosion controls were explored. Modeling indicated animal waste controls were much more cost-effective than erosion controls. Erosion controls will decrease embayment suspended solids and thereby increase algal biomass due to greater light penetration. 29 refs., 16 figs., 4 tabs.

  3. Mathematical analysis of a two-dimensional population model of metastatic growth including angiogenesis

    CERN Document Server

    Benzekry, Sebastien

    2010-01-01

    Angiogenesis is a key process in the tumoral growth which allows the cancerous tissue to impact on its vasculature in order to improve the nutrient's supply and the metastatic process. In this paper, we introduce a model for the density of metastasis which takes into account for this feature. It is a two dimensional structured equation with a vanishing velocity field and a source term on the boundary. We present here the mathematical analysis of the model, namely the well-posedness of the equation and the asymptotic behavior of the solutions, whose natural regularity led us to investigate some basic properties of the space $\\Wd(\\Om)=\\{V\\in L^1;\\;\\div(GV)\\in L^1\\}$, where $G$ is the velocity field of the equation.

  4. A Two-Dimensional Cloud Model for Condition Assessment of HVDC Converter Transformers

    Directory of Open Access Journals (Sweden)

    Linjie Zhao

    2012-01-01

    Full Text Available Converter transformers are the key and the most important components in high voltage direct current (HVDC power transmission systems. Statistics show that the failure rate of HVDC converter transformers is approximately twice of that of transformers in AC power systems. This paper presents an approach integrated with a two-dimensional cloud model and an entropy-based weight model to evaluate the condition of HVDC converter transformers. The integrated approach can describe the complexity of HVDC converter transformers and achieve an effective assessment of their condition. Data from electrical testing, DGA, oil testing, and visual inspection were chosen to form the double-level assessment index system. Analysis results show that the integrated approach is capable of providing a relevant and effective assessment which in turn, provides valuable information for the maintenance of HVDC converter transformers.

  5. A meron cluster solution for the sign problem of the two-dimensional O(3) model

    CERN Document Server

    Brechtefeld, F

    2002-01-01

    The two-dimensional O(3) model at a vacuum angle theta=pi is investigated. This model has a severe sign problem. By a Wolff cluster algorithm an integer or half-integer topological charge is assigned to each cluster. The meron clusters (clusters with half-integer topological charge) are used to construct an improved estimator for the correlation function of two spins at theta=pi. Only configurations with 0 and 2 merons contribute to this correlation function. An algorithm, that generates configurations with only 0 and 2 merons, is constructed and numerical simulations at theta=pi are performed. The numerical results indicate the presence of long range correlations at theta=pi.

  6. Quantum Phase Transition in the Two-Dimensional Random Transverse-Field Ising Model

    Science.gov (United States)

    Pich, C.; Young, A. P.

    1998-03-01

    We study the quantum phase transition in the random transverse-field Ising model by Monte Carlo simulations. In one-dimension it has been established that this system has the following striking behavior: (i) the dynamical exponent is infinite, and (ii) the exponents for the divergence of the average and typical correlation lengths are different. An important issue is whether this behavior is special to one-dimension or whether similar behavior persists in higher dimensions. Here we attempt to answer this question by studies of the two-dimensional model. Our simulations use the Wolff cluster algorithm and the results are analyzed by anisotropic finite size scaling, paying particular attention to the Binder ratio of moments of the order parameter distribution and the distribution of the spin-spin correlation functions for various distances.

  7. Two-dimensional modeling of stepped planing hulls with open and pressurized air cavities

    Directory of Open Access Journals (Sweden)

    Konstantin I. Matveev

    2012-06-01

    Full Text Available A method of hydrodynamic discrete sources is applied for two-dimensional modeling of stepped planing surfaces. The water surface deformations, wetted hull lengths, and pressure distribution are calculated at given hull attitude and Froude number. Pressurized air cavities that improve hydrodynamic performance can also be modeled with the current method. Presented results include validation examples, parametric calculations of a single-step hull, effect of trim tabs, and performance of an infinite series of periodic stepped surfaces. It is shown that transverse steps can lead to higher lift-drag ratio, although at reduced lift capability, in comparison with a stepless hull. Performance of a multi-step configuration is sensitive to the wave pattern between hulls, which depends on Froude number and relative hull spacing.

  8. Velocity selection at large undercooling in a two-dimensional nonlocal model of solidification

    Science.gov (United States)

    Barbieri, Angelo

    1987-01-01

    The formation of needle-crystal dendrites from an undercooled melt is investigated analytically, applying the method of Caroli et al. (1986) to Langer's (1980) symmetric two-dimensional nonlocal model of solidification with finite anisotropy in the limit of large undercooling. A solution based on the WKB approximation is obtained, and a saddle-point evaluation is performed. It is shown that needle-crystal solutions exist only if the capillary anisotropy is nonzero, in which case a particular value of the growth velocity can be selected. This finding and the expression for the dependence of the selected velocity on the singular perturbation parameter and the strength of the anisotropy are found to be in complete agreement with the results of a boundary-layer model (Langer and Hong, 1986).

  9. Thermodynamics of the two-dimensional XY model from functional renormalization.

    Science.gov (United States)

    Jakubczyk, P; Eberlein, A

    2016-06-01

    We solve the nonperturbative renormalization-group flow equations for the two-dimensional XY model at the truncation level of the (complete) second-order derivative expansion. We compute the thermodynamic properties in the high-temperature phase and compare the nonuniversal features specific to the XY model with results from Monte Carlo simulations. In particular, we study the position and magnitude of the specific-heat peak as a function of temperature. The obtained results compare well with Monte Carlo simulations. We additionally gauge the accuracy of simplified nonperturbative renormalization-group treatments relying on ϕ^{4}-type truncations. Our computation indicates that such an approximation is insufficient in the high-T phase and a correct analysis of the specific-heat profile requires account of an infinite number of interaction vertices.

  10. Averaged model for probabilistic coalescence avalanches in two-dimensional emulsions: Insights into uncertainty propagation

    Science.gov (United States)

    Danny Raj, M.; Rengaswamy, R.

    2017-03-01

    A two-dimensional concentrated emulsion exhibits spontaneous rapid destabilization through an avalanche of coalescence events which propagate through the assembly stochastically. We propose a deterministic model to explain the average dynamics of the avalanching process. The dynamics of the avalanche phenomenon is studied as a function of a composite parameter, the decay time ratio, which characterizes the ratio of the propensity of coalescence to cease propagation to that of propagation. When this ratio is small, the avalanche grows autocatalytically to destabilize the emulsion. Using a scaling analysis, we unravel the relation between a local characteristic of the system and a global system wide effect. The anisotropic nature of local coalescence results in a system size dependent transition from nonautocatalytic to autocatalytic behavior. By incorporating uncertainty into the parameters in the model, several possible realizations of the coalescence avalanche are generated. The results are compared with the Monte Carlo simulations to derive insights into how the uncertainty propagates in the system.

  11. Interfacial adsorption in two-dimensional pure and random-bond Potts models

    Science.gov (United States)

    Fytas, Nikolaos G.; Theodorakis, Panagiotis E.; Malakis, Anastasios

    2017-03-01

    We use Monte Carlo simulations to study the finite-size scaling behavior of the interfacial adsorption of the two-dimensional square-lattice q -states Potts model. We consider the pure and random-bond versions of the Potts model for q =3 ,4 ,5 ,8 , and 10, thus probing the interfacial properties at the originally continuous, weak, and strong first-order phase transitions. For the pure systems our results support the early scaling predictions for the size dependence of the interfacial adsorption at both first- and second-order phase transitions. For the disordered systems, the interfacial adsorption at the (disordered induced) continuous transitions is discussed, applying standard scaling arguments and invoking findings for bulk critical properties. The self-averaging properties of the interfacial adsorption are also analyzed by studying the infinite limit-size extrapolation of properly defined signal-to-noise ratios.

  12. Phase diagram of the two-dimensional O(3) model from dual lattice simulations

    CERN Document Server

    Bruckmann, Falk; Kloiber, Thomas; Sulejmanpasic, Tin

    2016-01-01

    We have simulated the asymptotically free two-dimensional O(3) model at nonzero chemical potential using the model's dual representation. We first demonstrate how the latter solves the sign (complex action) problem. The system displays a crossover at nonzero temperature, while at zero temperature it undergoes a quantum phase transition when mu reaches the particle mass (generated dynamically similar to QCD). The density follows a square root behavior universal for repulsive bosons in one spatial dimension. We have also measured the spin stiffness, known to be sensitive to the spatial correlation length, using different scaling trajectories to zero temperature and infinite size. It points to a dynamical critical exponent z=2. Comparisons to thermodynamic Bethe ansaetze are shown as well.

  13. Numerical simulations of blast wave characteristics with a two-dimensional axisymmetric room model

    Science.gov (United States)

    Sugiyama, Y.; Homae, T.; Wakabayashi, K.; Matsumura, T.; Nakayama, Y.

    2017-01-01

    This paper numerically visualizes explosion phenomena in order to discuss blast wave characteristics with a two-dimensional axisymmetric room model. After the shock wave exits via an opening, the blast wave propagates into open space. In the present study, a parametric study was conducted to determine the blast wave characteristics from the room exit by changing the room shape and the mass of the high explosive. Our results show that the blast wave characteristics can be correctly estimated using a scaling factor proposed in the present paper that includes the above parameters. We conducted normalization of the peak overpressure curve using the shock overpressure at the exit and the length scale of the room volume. In the case where the scaling factor has the same value, the normalized peak overpressure curve does not depend on the calculation conditions, and the scaling factor describes the blast wave characteristics emerging from the current room model.

  14. Grain coarsening in two-dimensional phase-field models with an orientation field

    Science.gov (United States)

    Korbuly, Bálint; Pusztai, Tamás; Henry, Hervé; Plapp, Mathis; Apel, Markus; Gránásy, László

    2017-05-01

    In the literature, contradictory results have been published regarding the form of the limiting (long-time) grain size distribution (LGSD) that characterizes the late stage grain coarsening in two-dimensional and quasi-two-dimensional polycrystalline systems. While experiments and the phase-field crystal (PFC) model (a simple dynamical density functional theory) indicate a log-normal distribution, other works including theoretical studies based on conventional phase-field simulations that rely on coarse grained fields, like the multi-phase-field (MPF) and orientation field (OF) models, yield significantly different distributions. In a recent work, we have shown that the coarse grained phase-field models (whether MPF or OF) yield very similar limiting size distributions that seem to differ from the theoretical predictions. Herein, we revisit this problem, and demonstrate in the case of OF models [R. Kobayashi, J. A. Warren, and W. C. Carter, Physica D 140, 141 (2000), 10.1016/S0167-2789(00)00023-3; H. Henry, J. Mellenthin, and M. Plapp, Phys. Rev. B 86, 054117 (2012), 10.1103/PhysRevB.86.054117] that an insufficient resolution of the small angle grain boundaries leads to a log-normal distribution close to those seen in the experiments and the molecular scale PFC simulations. Our paper indicates, furthermore, that the LGSD is critically sensitive to the details of the evaluation process, and raises the possibility that the differences among the LGSD results from different sources may originate from differences in the detection of small angle grain boundaries.

  15. Review of simplified Pseudo-two-Dimensional models of lithium-ion batteries

    Science.gov (United States)

    Jokar, Ali; Rajabloo, Barzin; Désilets, Martin; Lacroix, Marcel

    2016-09-01

    Over the last decade, many efforts have been deployed to develop models for the prediction, the control, the optimization and the parameter estimation of Lithium-ion (Li-ion) batteries. It appears that the most successful electrochemical-based model for Li-ion battery is the Pseudo-two-Dimensional model (P2D). Due to the fact that the governing equations are complex, this model cannot be used in real-time applications like Battery Management Systems (BMSs). To remedy the situation, several investigations have been carried out to simplify the P2D model. Mathematical and physical techniques are employed to reduce the order of magnitude of the P2D governing equations. The present paper is a review of the studies on the modeling of Li-ion batteries with simplified P2D models. The assumptions on which these models rest are stated, the calculation methods are examined, the advantages and the drawbacks of the models are discussed and their applications are presented. Suggestions for overcoming the shortcomings of the models are made. Challenges and future directions in the modeling of Li-ion batteries are also discussed.

  16. Application of Corner Transfer Matrix Renormalization Group Method to the Correlation Function of a Two-Dimensional Ising Model

    Institute of Scientific and Technical Information of China (English)

    何春山; 李志兵

    2003-01-01

    The correlation function of a two-dimensionalIsing model is calculated by the corner transfer matrix renormalization group method.We obtain the critical exponent η= 0.2496 with few computer resources.

  17. Two-dimensional electron gas in the regime of strong light-matter coupling: Dynamical conductivity and all-optical measurements of Rashba and Dresselhaus coupling

    Science.gov (United States)

    Yudin, Dmitry; Shelykh, Ivan A.

    2016-10-01

    A nonperturbative interaction of an electronic system with a laser field can substantially modify its physical properties. In particular, in two-dimensional (2D) materials with a lack of inversion symmetry, the achievement of a regime of strong light-matter coupling allows direct optical tuning of the strength of the Rashba spin-orbit interaction (SOI). Capitalizing on these results, we build a theory of the dynamical conductivity of a 2D electron gas with both Rashba and Dresselhaus SOIs coupled to an off-resonant high-frequency electromagnetic wave. We argue that strong light-matter coupling modifies qualitatively the dispersion of the electrons and can be used as a powerful tool to probe and manipulate the coupling strengths and adjust the frequency range where optical conductivity is essentially nonzero.

  18. Solutions of the Two-Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms

    Science.gov (United States)

    LeBlanc, J. P. F.; Antipov, Andrey E.; Becca, Federico; Bulik, Ireneusz W.; Chan, Garnet Kin-Lic; Chung, Chia-Min; Deng, Youjin; Ferrero, Michel; Henderson, Thomas M.; Jiménez-Hoyos, Carlos A.; Kozik, E.; Liu, Xuan-Wen; Millis, Andrew J.; Prokof'ev, N. V.; Qin, Mingpu; Scuseria, Gustavo E.; Shi, Hao; Svistunov, B. V.; Tocchio, Luca F.; Tupitsyn, I. S.; White, Steven R.; Zhang, Shiwei; Zheng, Bo-Xiao; Zhu, Zhenyue; Gull, Emanuel; Simons Collaboration on the Many-Electron Problem

    2015-10-01

    Numerical results for ground-state and excited-state properties (energies, double occupancies, and Matsubara-axis self-energies) of the single-orbital Hubbard model on a two-dimensional square lattice are presented, in order to provide an assessment of our ability to compute accurate results in the thermodynamic limit. Many methods are employed, including auxiliary-field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed-node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock methods. Comparison of results obtained by different methods allows for the identification of uncertainties and systematic errors. The importance of extrapolation to converged thermodynamic-limit values is emphasized. Cases where agreement between different methods is obtained establish benchmark results that may be useful in the validation of new approaches and the improvement of existing methods.

  19. Solutions of the Two Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms

    Science.gov (United States)

    Leblanc, James

    In this talk we present numerical results for ground state and excited state properties (energies, double occupancies, and Matsubara-axis self energies) of the single-orbital Hubbard model on a two-dimensional square lattice. In order to provide an assessment of our ability to compute accurate results in the thermodynamic limit we employ numerous methods including auxiliary field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock. We illustrate cases where agreement between different methods is obtained in order to establish benchmark results that should be useful in the validation of future results.

  20. Continuous and discrete modeling of the decay of two-dimensional nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Castez, Marcos F; Albano, Ezequiel V [Instituto de Investigaciones FisicoquImicas Teoricas y Aplicadas (INIFTA), CCT La Plata, Casilla de Correo 16, Sucursal 4, (1900) La Plata, UNLP, CONICET (Argentina)

    2009-07-01

    In this work we review some recent research on the surface diffusion-mediated decay of two-dimensional nanostructures. These results include both a continuous, vectorial model and a discrete kinetic Monte Carlo approach. Predictions from the standard linear continuous theory of surface-diffusion-driven interface decay are contrasted with simulational results both from kinetic and morphological points of view. In particular, we focused our attention on high-aspect-ratio nanostructures, where strong deviations from linear theory take place, including nonexponential amplitude decay and the emergence of several interesting nanostructures such as overhangs developing, nanoislands and nanovoids formation, loss of convexity, nanostructures-pinch off and nanostructures-break off, etc. (topical review)

  1. Drude Weight,Optical Conductivity of Two-Dimensional Hubbard Model at Half Filling

    Institute of Scientific and Technical Information of China (English)

    XU Lei; ZHANG Jun

    2008-01-01

    We study the Drude weight D and optical conductivity of the two-dimensional (2D) Hubbard model at half filling with staggered magnetic flux (SMF).When SMF being introduced,the hopping integrals are modulated by the magnetic flux.The optical sum rule,which is related to the mean kinetic energy of band electrons,is evaluated for this 2D Hubbard Hamiltonian.Our present result gives the dependence of the kinetic energy,D and the optical conductivity on SMF and U.At half filling D vanishes exponentially with system size.We also find in the frequency dependence of the optical conductivity,there is &function peak at ω≈2|m|U and the incoherent excitations begin to present themselves extended to a higher energy region.

  2. Superconducting phase and pairing fluctuations in the half-filled two-dimensional Hubbard model.

    Science.gov (United States)

    Sentef, Michael; Werner, Philipp; Gull, Emanuel; Kampf, Arno P

    2011-09-16

    The two-dimensional Hubbard model exhibits superconductivity with d-wave symmetry even at half-filling in the presence of a next-nearest neighbor hopping. Using plaquette cluster dynamical mean-field theory with a continuous-time quantum Monte Carlo impurity solver, we reveal the non-Fermi liquid character of the metallic phase in proximity to the superconducting state. Specifically, the low-frequency scattering rate for momenta near (π, 0) varies nonmonotonically at low temperatures, and the dc conductivity is T linear at elevated temperatures with an upturn upon cooling. Evidence is provided that pairing fluctuations dominate the normal-conducting state even considerably above the superconducting transition temperature.

  3. A two-dimensional volatility basis set – Part 3: Prognostic modeling and NOx dependence

    Directory of Open Access Journals (Sweden)

    W. K. Chuang

    2015-06-01

    Full Text Available When NOx is introduced to organic emissions, aerosol production is sometimes, but not always, reduced. Under certain conditions, these interactions will instead increase aerosol concentrations. We expanded the two-dimensional volatility basis set (2-D-VBS to include the effects of NOx on aerosol formation. This includes the formation of organonitrates, where the addition of a nitrate group contributes to a decrease of 2.5 orders of magnitude in volatility. With this refinement, we model outputs from experimental results, such as the atomic N : C ratio, organonitrate mass, and nitrate fragments in AMS measurements. We also discuss the mathematical methods underlying the implementation of the 2-D-VBS and provide the complete code in the Supplemental material. A developer version is available on Bitbucket, an online community repository.

  4. Isotropic model of fractional transport in two-dimensional bounded domains.

    Science.gov (United States)

    Kullberg, A; del-Castillo-Negrete, D; Morales, G J; Maggs, J E

    2013-05-01

    A two-dimensional fractional Laplacian operator is derived and used to model nonlocal, nondiffusive transport. This integro-differential operator appears in the long-wavelength, fluid description of quantities undergoing non-Brownian random walks without characteristic length scale. To study bounded domains, a mask function is introduced that modifies the kernel in the fractional Laplacian and removes singularities at the boundary. Green's function solutions to the fractional diffusion equation are presented for the unbounded domain and compared to the one-dimensional Cartesian approximations. A time-implicit numerical integration scheme is presented to study fractional diffusion in a circular disk with azimuthal symmetry. Numerical studies of steady-state reveal temperature profiles in which the heat flux and temperature gradient are in the same direction, i.e., uphill transport. The response to off-axis heating, scaling of confinement time with system size, and propagation of cold pulses are investigated.

  5. Two-dimensional physical habitat modeling of effects of habitat structures on urban stream restoration

    Directory of Open Access Journals (Sweden)

    Dongkyun IM

    2011-12-01

    Full Text Available River corridors, even if highly modified or degraded, still provide important habitats for numerous biological species, and carry high aesthetic and economic values. One of the keys to urban stream restoration is recovery and maintenance of ecological flows sufficient to sustain aquatic ecosystems. In this study, the Hongje Stream in the Seoul metropolitan area of Korea was selected for evaluating a physically-based habitat with and without habitat structures. The potential value of the aquatic habitat was evaluated by a weighted usable area (WUA using River2D, a two-dimensional hydraulic model. The habitat suitability for Zacco platypus in the Hongje Stream was simulated with and without habitat structures. The computed WUA values for the boulder, spur dike, and riffle increased by about 2%, 7%, and 131%, respectively, after their construction. Also, the three habitat structures, especially the riffle, can contribute to increasing hydraulic heterogeneity and enhancing habitat diversity.

  6. Subtlety in the Critical Behavior of the Two Dimensional XY Model

    Science.gov (United States)

    Kim, Jae-Kwon

    1996-03-01

    We study the two dimensional classical XY model using the single cluster Monte Carlo algorithm^1. We present extensive high -temperature -phase bulk data that are extracted based on a novel finite- size- scaling Monte Carlo technique^2. The largest value of the estimated bulk correlation length is 1390 in lattice units. Our data reveal that η=1/4 sets in near criticality. The standard finite-size-scaling analysis of the data close to criticality, however, seems to indicate that η=1/4 is compatible only for a critical temperature (T_c) over the range 0.900 Wolff, Phys. Rev. Lett. 62, 361 (1989) ^2 J.-K. Kim, Euro. Phys. Lett. 28, 211 (1994) Research supported in part by the NSF

  7. Breakdown of the Nagaoka phase in the two-dimensional t-J model

    Science.gov (United States)

    Eisenberg, E.; Berkovits, R.; Huse, David A.; Altshuler, B. L.

    2002-04-01

    In the limit of weak exchange J at low hole concentration δ the ground state of the two-dimensional t-J model is believed to be ferromagnetic. We study the leading instability of this Nagaoka state, which emerges with increasing J. Both exact diagonalization of small clusters, and a semiclassical analytical calculation of larger systems show that above a certain critical value of the exchange, Jcr~tδ2, Nagaoka's state is unstable to phase separation. In a finite-size system a bubble of antiferromagnetic Mott insulator appears in the ground state above this threshold. The size of this bubble depends on δ and scales as a power of the system size N.

  8. Nonlocal Coulomb interaction in the two-dimensional spin-1/2 Falicov–Kimball model

    Indian Academy of Sciences (India)

    S K Bhowmick; N K Ghosh

    2012-02-01

    The two-dimensional (2D) extended Falicov–Kimball model has been studied to observe the role of nonlocal Coulomb interaction (nc) using an exact diagonalization technique. The f-state occupation ($n^f$), the f–d intersite correlation function (fd), the specific heat (), entropy () and the specific heat coefficient () have been examined. Nonlocal Coulomb interaction-induced discontinuous insulator-to-metal transition occurs at a critical f-level energy. More ordered state is obtained with the increase of nc. In the specific heat curves, two-peak structure as well as a singlepeak structure appears. At low-temperature region, a sharp rise in the specific heat coefficient is observed. The peak value of shifts to the higher temperature region with nc.

  9. Pairing in the two-dimensional Hubbard model: An exact diagonalization study

    Science.gov (United States)

    Lin, H. Q.; Hirsch, J. E.; Scalapino, D. J.

    1988-05-01

    We have studied the pair susceptibilities for all possible pair wave functions that fit on a two-dimensional (2D) eight-site Hubbard cluster by exact diagonalization of the Hamiltonian. Band fillings corresponding to four and six electrons were studied (two or four holes in the half-filled band) for a wide range of Hubbard interaction strengths and temperatures. Our results show that all pairing susceptibilities are suppressed by the Hubbard repulsion. We have also carried out perturbation-theory calculations which show that the leading-order U2 contributions to the d-wave pair susceptibility suppresses d-wave pairing over a significant temperature range. These results are consistent with recent Monte Carlo results and provide further evidence suggesting that the 2D Hubbard model does not exhibit superconductivity.

  10. Critical Casimir force scaling functions of the two-dimensional Ising model for various boundary conditions

    CERN Document Server

    Hobrecht, Hendrik

    2016-01-01

    We present a systematic method to calculate the scaling functions for the critical Casimir force and the according potential of the two-dimensional Ising model with various boundary conditions. Therefore we start with the dimer representation of the corresponding partition function $Z$ on an $L\\times M$ square lattice, wrapped around a torus with aspect ratio $\\rho=L/M$. By assuming periodic boundary conditions and translational invariance in at least one direction, we systematically reduce the problem to a $2\\times2$ transfer matrix representation. For the torus we first reproduce the results by Kaufman and then give a detailed calculation of the scaling functions. Afterwards we present the calculation for the cylinder with open boundary conditions. All scaling functions are given in form of combinations of infinite products and integrals. Our results reproduce the known scaling functions in the limit of thin films $\\rho\\to 0$. Additionally, for the cylinder at criticality our result confirms the predictions...

  11. DISPLAY-2: a two-dimensional shallow layer model for dense gas dispersion including complex features.

    Science.gov (United States)

    Venetsanos, A G; Bartzis, J G; Würtz, J; Papailiou, D D

    2003-04-25

    A two-dimensional shallow layer model has been developed to predict dense gas dispersion, under realistic conditions, including complex features such as two-phase releases, obstacles and inclined ground. The model attempts to predict the time and space evolution of the cloud formed after a release of a two-phase pollutant into the atmosphere. The air-pollutant mixture is assumed ideal. The cloud evolution is described mathematically through the Cartesian, two-dimensional, shallow layer conservation equations for mixture mass, mixture momentum in two horizontal directions, total pollutant mass fraction (vapor and liquid) and mixture internal energy. Liquid mass fraction is obtained assuming phase equilibrium. Account is taken in the conservation equations for liquid slip and eventual liquid rainout through the ground. Entrainment of ambient air is modeled via an entrainment velocity model, which takes into account the effects of ground friction, ground heat transfer and relative motion between cloud and surrounding atmosphere. The model additionally accounts for thin obstacles effects in three ways. First a stepwise description of the obstacle is generated, following the grid cell faces, taking into account the corresponding area blockage. Then obstacle drag on the passing cloud is modeled by adding flow resistance terms in the momentum equations. Finally the effect of extra vorticity generation and entrainment enhancement behind obstacles is modeled by adding locally into the entrainment formula without obstacles, a characteristic velocity scale defined from the obstacle pressure drop and the local cloud height.The present model predictions have been compared against theoretical results for constant volume and constant flux gravity currents. It was found that deviations of the predicted cloud footprint area change with time from the theoretical were acceptably small, if one models the frictional forces between cloud and ambient air, neglecting the Richardson

  12. Assessment of the reliability of reproducing two-dimensional resistivity models using an image processing technique.

    Science.gov (United States)

    Ishola, Kehinde S; Nawawi, Mohd Nm; Abdullah, Khiruddin; Sabri, Ali Idriss Aboubakar; Adiat, Kola Abdulnafiu

    2014-01-01

    This study attempts to combine the results of geophysical images obtained from three commonly used electrode configurations using an image processing technique in order to assess their capabilities to reproduce two-dimensional (2-D) resistivity models. All the inverse resistivity models were processed using the PCI Geomatica software package commonly used for remote sensing data sets. Preprocessing of the 2-D inverse models was carried out to facilitate further processing and statistical analyses. Four Raster layers were created, three of these layers were used for the input images and the fourth layer was used as the output of the combined images. The data sets were merged using basic statistical approach. Interpreted results show that all images resolved and reconstructed the essential features of the models. An assessment of the accuracy of the images for the four geologic models was performed using four criteria: the mean absolute error and mean percentage absolute error, resistivity values of the reconstructed blocks and their displacements from the true models. Generally, the blocks of the images of maximum approach give the least estimated errors. Also, the displacement of the reconstructed blocks from the true blocks is the least and the reconstructed resistivities of the blocks are closer to the true blocks than any other combined used. Thus, it is corroborated that when inverse resistivity models are combined, most reliable and detailed information about the geologic models is obtained than using individual data sets.

  13. A Vertical Two-Dimensional Model to Simulate Tidal Hydrodynamics in A Branched Estuary

    Institute of Scientific and Technical Information of China (English)

    LIU Wen-Cheng; WU Chung-Hsing

    2005-01-01

    A vertical (laterally averaged) two-dimensional hydrodynamic model is developed for tides, tidal current, and salinity in a branched estuarine system. The governing equations are solved with the hydrostatic pressure distribution assumption and the Boussinesq approximation. An explicit scheme is employed to solve the continuity equations. The momentum and mass balance equations are solved implicitly in the Cartesian coordinate system. The tributaries are governed by the same dynamic equations. A control volume at the junctions is designed to conserve mass and volume transport in the finite difference schemes, based on the physical principle of continuum medium of fluid. Predictions by the developed model are compared with the analytic solutions of steady wind-driven circulatory flow and tidal flow. The model results for the velocities and water surface elevations coincide with analytic results. The model is then applied to the Tanshui River estuarine system. Detailed model calibration and verification have been conducted with measured water surface elevations,tidal current, and salinity distributions. The overall performance of the model is in qualitative agreement with the available field data. The calibrated and verified numerical model has been used to quantify the tidal prism and flushing rate in the Tanshui River-Tahan Stream, Hsintien Stream, and Keelung River.

  14. A Monte Carlo Uncertainty Analysis of Ozone Trend Predictions in a Two Dimensional Model. Revision

    Science.gov (United States)

    Considine, D. B.; Stolarski, R. S.; Hollandsworth, S. M.; Jackman, C. H.; Fleming, E. L.

    1998-01-01

    We use Monte Carlo analysis to estimate the uncertainty in predictions of total O3 trends between 1979 and 1995 made by the Goddard Space Flight Center (GSFC) two-dimensional (2D) model of stratospheric photochemistry and dynamics. The uncertainty is caused by gas-phase chemical reaction rates, photolysis coefficients, and heterogeneous reaction parameters which are model inputs. The uncertainty represents a lower bound to the total model uncertainty assuming the input parameter uncertainties are characterized correctly. Each of the Monte Carlo runs was initialized in 1970 and integrated for 26 model years through the end of 1995. This was repeated 419 times using input parameter sets generated by Latin Hypercube Sampling. The standard deviation (a) of the Monte Carlo ensemble of total 03 trend predictions is used to quantify the model uncertainty. The 34% difference between the model trend in globally and annually averaged total O3 using nominal inputs and atmospheric trends calculated from Nimbus 7 and Meteor 3 total ozone mapping spectrometer (TOMS) version 7 data is less than the 46% calculated 1 (sigma), model uncertainty, so there is no significant difference between the modeled and observed trends. In the northern hemisphere midlatitude spring the modeled and observed total 03 trends differ by more than 1(sigma) but less than 2(sigma), which we refer to as marginal significance. We perform a multiple linear regression analysis of the runs which suggests that only a few of the model reactions contribute significantly to the variance in the model predictions. The lack of significance in these comparisons suggests that they are of questionable use as guides for continuing model development. Large model/measurement differences which are many multiples of the input parameter uncertainty are seen in the meridional gradients of the trend and the peak-to-peak variations in the trends over an annual cycle. These discrepancies unambiguously indicate model formulation

  15. Secretomic analysis of large cell lung cancer cell lines using two-dimensional gel electrophoresis coupled to mass spectrometry

    Directory of Open Access Journals (Sweden)

    Zahra Yousefi

    2012-10-01

    Full Text Available

    The secretome of cancer cells is a valuable source of biomarkers that can ultimately reach the serum or other body fluids. Cancer biomarkers can facilitate early diagnosis and monitoring of the disease, contribute to our understanding of tumor biology, and support the development of more efficient therapies. Recently, high-throughput proteomic analysis of the conditioned media of cancer cell lines has shown potential to identify novel biomarkers in cancer. We used two-dimensional gel electrophoresis coupled to liquid chromatography tandem mass spectrometry to identify the secretome of the large cell lung cancer cell lines QU-DB and Mehr-80, which they were established from a Canadian and a Persian patient, respectively. A total of 130 distinct protein species were identified. Of these, 124 were previously found in serum or other body fluids, the membrane compartment or conditioned media of other cancer cell lines. Some of the proteins that we identified, e.g. IL-6, triosephosphate isomerase, PGP9.5, α-enolase, Dickkopf-1, and peroxiredoxin-1 are known putative serum markers for lung cancer, whereas others might be candidate markers for further validation in lung cancer body fluids such as IL-25, stathmin, vimentin, peptidyl-prolyl cis-trans isomerase A, transgelin-2, and chloride intracellular channel protein 4.

  16. Large-Scale and Deep Quantitative Proteome Profiling Using Isobaric Labeling Coupled with Two-Dimensional LC-MS/MS

    Energy Technology Data Exchange (ETDEWEB)

    Gritsenko, Marina A.; Xu, Zhe; Liu, Tao; Smith, Richard D.

    2016-02-12

    Comprehensive, quantitative information on abundances of proteins and their post-translational modifications (PTMs) can potentially provide novel biological insights into diseases pathogenesis and therapeutic intervention. Herein, we introduce a quantitative strategy utilizing isobaric stable isotope-labelling techniques combined with two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) for large-scale, deep quantitative proteome profiling of biological samples or clinical specimens such as tumor tissues. The workflow includes isobaric labeling of tryptic peptides for multiplexed and accurate quantitative analysis, basic reversed-phase LC fractionation and concatenation for reduced sample complexity, and nano-LC coupled to high resolution and high mass accuracy MS analysis for high confidence identification and quantification of proteins. This proteomic analysis strategy has been successfully applied for in-depth quantitative proteomic analysis of tumor samples, and can also be used for integrated proteome and PTM characterization, as well as comprehensive quantitative proteomic analysis across samples from large clinical cohorts.

  17. Analysis of special surfactants by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry.

    Science.gov (United States)

    Wulf, Volker; Wienand, Nils; Wirtz, Michaela; Kling, Hans-Willi; Gäb, Siegmar; Schmitz, Oliver J

    2010-01-29

    Multidimensional gas-chromatographic analyses of olesochemically based nonionic, anionic and several cationic surfactants in industrial cleaners are demonstrated. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry allows the simultaneous determination of fatty alcohols, fatty alcohol sulphates and alkyl polyglucosides. In addition, the determination of fatty alcohol ethoxylates up to C(10)EO(8) (highest degree of ethoxylation) and C(18)EO(5) (longest C-chain at an ethoxylation degree of five) and the analysis of fatty alcohol alkoxylates that contain ethoxy (EO) and propoxy (PO) groups could be realized. Because of decomposition in the injector and a weak EI-fragmentation, cationic surfactants such as alkyl benzyl dimethyl ammonium chloride could also be identified by their characteristic fragments. Thermogravimetric analyses confirmed that the temperature in a normal GC injector is not high enough to cause thermal decomposition of esterquats. However, we could demonstrate that a modified silylation procedure forms decomposition products of esterquats in the GC injector which are detectable by GCxGC-(TOF)MS and allows the identification of such GC-atypical analytes.

  18. Quasilongitudinal soliton in a two-dimensional strongly coupled complex dusty plasma in the presence of an external magnetic field

    Science.gov (United States)

    Ghosh, Samiran

    2014-09-01

    The propagation of a nonlinear low-frequency mode in two-dimensional (2D) monolayer hexagonal dusty plasma crystal in presence of external magnetic field and dust-neutral collision is investigated. The standard perturbative approach leads to a 2D Korteweg-de Vries (KdV) soliton for the well-known dust-lattice mode. However, the Coriolis force due to crystal rotation and Lorentz force due to magnetic field on dust particles introduce a linear forcing term, whereas dust-neutral drag introduce the usual damping term in the 2D KdV equation. This new nonlinear equation is solved both analytically and numerically to show the competition between the linear forcing and damping in the formation of quasilongitudinal soliton in a 2D strongly coupled complex (dusty) plasma. Numerical simulation on the basis of the typical experimental plasma parameters and the analytical solution reveal that the neutral drag force is responsible for the usual exponential decay of the soliton, whereas Coriolis and/or Lorentz force is responsible for the algebraic decay as well as the oscillating tail formation of the soliton. The results are discussed in the context of the plasma crystal experiment.

  19. Two-dimensional models as testing ground for principles and concepts of local quantum physics

    CERN Document Server

    Schrör, B

    2005-01-01

    In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g. chiral models, factorizing models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) and a modular interpretation of the chiral model Diff(S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime. As a special case of the thermal duality, the SL(2,Z) modular Verlinde relation is thus a consequence of the principles of thermal QFT togeth...

  20. Turbulence models and Reynolds analogy for two-dimensional supersonic compression ramp flow

    Science.gov (United States)

    Wang, Chi R.; Bidek, Maleina C.

    1994-01-01

    Results of the application of turbulence models and the Reynolds analogy to the Navier-Stokes computations of Mach 2.9 two-dimensional compression ramp flows are presented. The Baldwin-Lomax eddy viscosity model and the kappa-epsilon turbulence transport equations for the turbulent momentum flux modeling in the Navier-Stokes equations are studied. The Reynolds analogy for the turbulent heat flux modeling in the energy equation was also studied. The Navier-Stokes equations and the energy equation were numerically solved for the flow properties. The Reynolds shear stress, the skin friction factor, and the surface heat transfer rate were calculated and compared with their measurements. It was concluded that with a hybrid kappa-epsilon turbulence model for turbulence modeling, the present computations predicted the skin friction factors of the 8 deg and 16 deg compression ramp flows and with the turbulent Prandtl number Pr(sub t) = 0.93 and the ratio of the turbulent thermal and momentum transport coefficients mu(sub q)/mu(sub t) = 2/Prt, the present computations also predicted the surface heat transfer rates beneath the boundary layer flow of the 16 compression ramp.

  1. Milgrom Relation Models for Spiral Galaxies from Two-Dimensional Velocity Maps

    CERN Document Server

    Barnes, E I; Sellwood, J A; Barnes, Eric I.; Kosowsky, Arthur; Sellwood, Jerry A.

    2007-01-01

    Using two-dimensional velocity maps and I-band photometry, we have created mass models of 40 spiral galaxies using the Milgrom relation (the basis of modified Newtonian dynamics, or MOND) to complement previous work. A Bayesian technique is employed to compare several different dark matter halo models to Milgrom and Newtonian models. Pseudo-isothermal dark matter halos provide the best statistical fits to the data in a majority of cases, while the Milgrom relation generally provides good fits as well. We also find that Milgrom models give mass-to-light ratios that roughly correlate with galaxy color, as predicted by stellar population models. A subsample of galaxies in the Hydra cluster follow a tight relation between mass-to-light and color, but one that is significantly different from relations found in previous studies. Ruling out the Milgrom relation with rotational kinematics is difficult due to systematic uncertainties in the observations as well as underlying model assumptions. We discuss in detail two...

  2. A two-dimensional CFD model of a refrigerated display case

    Energy Technology Data Exchange (ETDEWEB)

    Stribling, D.; Tassou, S.A. [Brunel Univ., Uxbridge (United Kingdom). Dept. of Mechanical Engineering; Marriott, D. [Safeway Stores plc, Middlesex (United Kingdom)

    1997-12-31

    The discomfort caused by the cold air overspill from vertical refrigerated display cases in supermarkets is widely accepted as being a problem to customers. This, together with the adverse effect on case performance caused by heat and moisture transfer across the air curtain, suggests that there may be room for improvement in the design and fundamental operation of these display fixtures. This paper presents a two-dimensional computational fluid dynamics (CFD) model of a vertical dairy display case that could be used in the design and optimization of such equipment. Comparisons are also made with experimentally obtained values of velocity and temperature measured around the case in order to assess the accuracy and viability of such a model. Parameters of the computer model, such as the size of the calculation grid, the turbulence model, and the discretization scheme, were also varied to determine their effect on the converged solution, and these results are presented. The CFD model showed good qualitative agreement with measured values and requires only fine tuning to make it quantitatively accurate.

  3. Effect of a levee setback on aquatic resources using two-dimensional flow and bioenergetics models

    Science.gov (United States)

    Black, Robert W.; Czuba, Christiana R.; Magirl, Christopher S.; McCarthy, Sarah; Berge, Hans; Comanor, Kyle

    2016-04-05

    Watershed restoration is the focus of many resource managers and can include a multitude of restoration actions each with specific restoration objectives. For the White River flowing through the cities of Pacific and Sumner, Washington, a levee setback has been proposed to reconnect the river with its historical floodplain to help reduce flood risks, as well as provide increased habitat for federally listed species of salmonids. The study presented here documents the use of a modeling framework that integrates two-dimensional hydraulic modeling with process-based bioenergetics modeling for predicting how changes in flow from reconnecting the river with its floodplain affects invertebrate drift density and the net rate of energy intake of juvenile salmonids. Modeling results were calculated for flows of 25.9 and 49.3 cubic meters per second during the spring, summer, and fall. Predicted hypothetical future mean velocities and depths were significantly lower and more variable when compared to current conditions. The abundance of low energetic cost and positive growth locations for salmonids were predicted to increase significantly in the study reach following floodplain reconnection, particularly during the summer. This modeling framework presents a viable approach for evaluating the potential fisheries benefits of reconnecting a river to its historical floodplain that integrates our understanding of hydraulic, geomorphology, and organismal biology.

  4. A two-dimensional model of the methane cycle in a sedimentary accretionary wedge

    Directory of Open Access Journals (Sweden)

    D. E. Archer

    2012-08-01

    Full Text Available A two-dimensional model of sediment column geophysics and geochemistry has been adapted to the problem of an accretionary wedge formation, patterned after the margin of the Juan de Fuca plate as it subducts under the North American plate. Much of the model description is given in a companion paper about the application of the model to an idealized passive margin setting; here we build on that formulation to simulate the impact of the sediment deformation, as it approaches the subduction zone, on the methane cycle. The active margin configuration of the model shares sensitivities with the passive margin configuration, in that sensitivities to organic carbon deposition and respiration kinetics, and to vertical bubble transport and redissolution in the sediment, are stronger than the sensitivity to ocean temperature. The active margin simulation shows a complex sensitivity of hydrate inventory to plate subduction velocity, with results depending strongly on the geothermal heat flux. In low heat-flux conditions, the model produces a larger inventory of hydrate per meter of coastline in the passive margin than active margin configurations. However, the local hydrate concentrations, as pore volume saturation, are higher in the active setting than in the passive, as generally observed in the field.

  5. TWO-DIMENSIONAL CELLULAR AUTOMATON MODEL FOR THE EVOLUTION OF ACTIVE REGION CORONAL PLASMAS

    Energy Technology Data Exchange (ETDEWEB)

    López Fuentes, Marcelo [Instituto de Astronomía y Física del Espacio, CONICET-UBA, CC. 67, Suc. 28, 1428 Buenos Aires (Argentina); Klimchuk, James A., E-mail: lopezf@iafe.uba.ar [NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771 (United States)

    2015-02-01

    We study a two-dimensional cellular automaton (CA) model for the evolution of coronal loop plasmas. The model is based on the idea that coronal loops are made of elementary magnetic strands that are tangled and stressed by the displacement of their footpoints by photospheric motions. The magnetic stress accumulated between neighbor strands is released in sudden reconnection events or nanoflares that heat the plasma. We combine the CA model with the Enthalpy Based Thermal Evolution of Loops model to compute the response of the plasma to the heating events. Using the known response of the X-Ray Telescope on board Hinode, we also obtain synthetic data. The model obeys easy-to-understand scaling laws relating the output (nanoflare energy, temperature, density, intensity) to the input parameters (field strength, strand length, critical misalignment angle). The nanoflares have a power-law distribution with a universal slope of –2.5, independent of the input parameters. The repetition frequency of nanoflares, expressed in terms of the plasma cooling time, increases with strand length. We discuss the implications of our results for the problem of heating and evolution of active region coronal plasmas.

  6. Two-Dimensional Depth-Averaged Beach Evolution Modeling: Case Study of the Kizilirmak River Mouth, Turkey

    DEFF Research Database (Denmark)

    Baykal, Cüneyt; Ergin, Ayşen; Güler, Işikhan

    2014-01-01

    transformation model, a two-dimensional depth-averaged numerical waveinduced circulation model, a sediment transport model, and a bottom evolution model. To validate and verify the numerical model, it is applied to several cases of laboratory experiments. Later, the model is applied to a shoreline change problem...

  7. One- and two-dimensional modelling of overland flow in semiarid shrubland, Jornada basin, New Mexico

    Science.gov (United States)

    Howes, David A.; Abrahams, Athol D.; Pitman, E. Bruce

    2006-03-01

    Two distributed parameter models, a one-dimensional (1D) model and a two-dimensional (2D) model, are developed to simulate overland flow in two small semiarid shrubland watersheds in the Jornada basin, southern New Mexico. The models are event-based and represent each watershed by an array of 1-m2 cells, in which the cell size is approximately equal to the average area of the shrubs.Each model uses only six parameters, for which values are obtained from field surveys and rainfall simulation experiments. In the 1D model, flow volumes through a fixed network are computed by a simple finite-difference solution to the 1D kinematic wave equation. In the 2D model, flow directions and volumes are computed by a second-order predictor-corrector finite-difference solution to the 2D kinematic wave equation, in which flow routing is implicit and may vary in response to flow conditions.The models are compared in terms of the runoff hydrograph and the spatial distribution of runoff. The simulation results suggest that both the 1D and the 2D models have much to offer as tools for the large-scale study of overland flow. Because it is based on a fixed flow network, the 1D model is better suited to the study of runoff due to individual rainfall events, whereas the 2D model may, with further development, be used to study both runoff and erosion during multiple rainfall events in which the dynamic nature of the terrain becomes an important consideration.

  8. Two-dimensional finite elements model for boron management in agroforestry sites.

    Science.gov (United States)

    Tayfur, Gokmen; Tanji, Kenneth K; Baba, Alper

    2010-01-01

    Agroforesty systems, which are recommended as a management option to lower the shallow groundwater level and to reuse saline subsurface drainage waters from the tile-drained croplands in the drainage-impacted areas of Jan Joaquin Valley of California, have resulted in excessive boron buildup in the soil root zone. To assess the efficacy of the long-term impacts of soil boron buildup in agroforesty systems, a mathematical model was developed to simulate non-conservative boron transport. The developed dynamic two-dimensional finite element model simulates water flow and boron transport in saturated-unsaturated soil system, including boron sorption and boron uptake by root-water extraction processes. The simulation of two different observed field data sets by the developed model is satisfactory, with mean absolute error of 1.5 mg/L and relative error of 6.5%. Application of the model to three different soils shows that boron adsorption is higher in silt loam soil than that in sandy loam and clay loam soils. This result agrees with the laboratory experimental observations. The results of the sensitivity analysis indicate that boron uptake by root-water extraction process influences the boron concentration distribution along the root zone. Also, absorption coefficient and maximum adsorptive capacity of a soil for boron are found to be sensitive parameters.

  9. Spatiotemporal chaos and two-dimensional dissipative rogue waves in Lugiato-Lefever model

    Science.gov (United States)

    Panajotov, Krassimir; Clerc, Marcel G.; Tlidi, Mustapha

    2017-06-01

    Driven nonlinear optical cavities can exhibit complex spatiotemporal dynamics. We consider the paradigmatic Lugiato-Lefever model describing driven nonlinear optical resonator. This model is one of the most-studied nonlinear equations in optics. It describes a large spectrum of nonlinear phenomena from bistability, to periodic patterns, localized structures, self-pulsating localized structures and to a complex spatiotemporal behavior. The model is considered also as prototype model to describe several optical nonlinear devices such as Kerr media, liquid crystals, left handed materials, nonlinear fiber cavity, and frequency comb generation. We focus our analysis on a spatiotemporal chaotic dynamics in one-dimension. We identify a route to spatiotemporal chaos through an extended quasiperiodicity. We have estimated the Kaplan-Yorke dimension that provides a measure of the strange attractor complexity. Likewise, we show that the Lugiato-Leferver equation supports rogues waves in two-dimensional settings. We characterize rogue-wave formation by computing the probability distribution of the pulse height. Contribution to the Topical Issue "Theory and Applications of the Lugiato-Lefever Equation", edited by Yanne K. Chembo, Damia Gomila, Mustapha Tlidi, Curtis R. Menyuk.

  10. Two-Dimensional Core-Collapse Supernova Models with Multi-Dimensional Transport

    CERN Document Server

    Dolence, Joshua C; Zhang, Weiqun

    2014-01-01

    We present new two-dimensional (2D) axisymmetric neutrino radiation/hydrodynamic models of core-collapse supernova (CCSN) cores. We use the CASTRO code, which incorporates truly multi-dimensional, multi-group, flux-limited diffusion (MGFLD) neutrino transport, including all relevant $\\mathcal{O}(v/c)$ terms. Our main motivation for carrying out this study is to compare with recent 2D models produced by other groups who have obtained explosions for some progenitor stars and with recent 2D VULCAN results that did not incorporate $\\mathcal{O}(v/c)$ terms. We follow the evolution of 12, 15, 20, and 25 solar-mass progenitors to approximately 600 milliseconds after bounce and do not obtain an explosion in any of these models. Though the reason for the qualitative disagreement among the groups engaged in CCSN modeling remains unclear, we speculate that the simplifying ``ray-by-ray' approach employed by all other groups may be compromising their results. We show that ``ray-by-ray' calculations greatly exaggerate the ...

  11. Nonequilibrium critical dynamics of two dimensional interacting monomer-dimer model: non-Ising criticality

    Science.gov (United States)

    Nam, Keekwon; Kim, Bongsoo; Jong Lee, Sung

    2014-08-01

    We investigate the nonequilibrium relaxation dynamics of an interacting monomer-dimer model with nearest neighbor repulsion on a square lattice, which possesses two symmetric absorbing states. The model is known to exhibit two nearby continuous transitions: the Z2 symmetry-breaking order-disorder transition and the absorbing transition with directed percolation criticality. We performed a more detailed analysis of our extensive simulations on bigger lattice systems which reaffirms that the symmetry-breaking transition exhibits a non-Ising critical behavior with β ≃ 0.149(2) and η ≃ 0.30(1) that are distinct from those values of a pure two dimensional Ising model. Finite size scaling of dimer density near the symmetry breaking transition gives logarithmic scaling (α = 0.0) which is consistent with the hyperscaling relation but the corresponding exponent of νB ≃ 1.37(2) exhibits a conspicuous deviation from the pure Ising value of 1. The value of dynamic critical exponent z, however, is found to be close to that of the kinetic Ising model as 1/z ≃ 0.466(5) from the relaxation of staggered magnetization (and also similar but slightly smaller values from coarsening).

  12. Ca2+ movement in smooth muscle cells studied with one- and two-dimensional diffusion models.

    Science.gov (United States)

    Kargacin, G; Fay, F S

    1991-11-01

    Although many of the processes involved in the regulation of Ca2+ in smooth muscle have been studied separately, it is still not well known how they are integrated into an overall regulatory system. To examine this question and to study the time course and spatial distribution of Ca2+ in cells after activation, one- and two-dimensional diffusion models of the cell that included the major processes thought to be involved in Ca regulation were developed. The models included terms describing Ca influx, buffering, plasma membrane extrusion, and release and reuptake by the sarcoplasmic reticulum. When possible these processes were described with known parameters. Simulations with the models indicated that the sarcoplasmic reticulum Ca pump is probably primarily responsible for the removal of cytoplasmic Ca2+ after cell activation. The plasma membrane Ca-ATPase and Na/Ca exchange appeared more likely to be involved in the long term regulation of Ca2+. Pumping processes in general had little influence on the rate of rise of Ca transients. The models also showed that spatial inhomogeneities in Ca2+ probably occur in cells during the spread of the Ca signal following activation and during the subsequent return of Ca2+ to its resting level.

  13. Integrated remote sensing imagery and two-dimensional hydraulic modeling approach for impact evaluation of flood on crop yields

    Science.gov (United States)

    Chen, Huili; Liang, Zhongyao; Liu, Yong; Liang, Qiuhua; Xie, Shuguang

    2017-10-01

    The projected frequent occurrences of extreme flood events will cause significant losses to crops and will threaten food security. To reduce the potential risk and provide support for agricultural flood management, prevention, and mitigation, it is important to account for flood damage to crop production and to understand the relationship between flood characteristics and crop losses. A quantitative and effective evaluation tool is therefore essential to explore what and how flood characteristics will affect the associated crop loss, based on accurately understanding the spatiotemporal dynamics of flood evolution and crop growth. Current evaluation methods are generally integrally or qualitatively based on statistic data or ex-post survey with less diagnosis into the process and dynamics of historical flood events. Therefore, a quantitative and spatial evaluation framework is presented in this study that integrates remote sensing imagery and hydraulic model simulation to facilitate the identification of historical flood characteristics that influence crop losses. Remote sensing imagery can capture the spatial variation of crop yields and yield losses from floods on a grid scale over large areas; however, it is incapable of providing spatial information regarding flood progress. Two-dimensional hydraulic model can simulate the dynamics of surface runoff and accomplish spatial and temporal quantification of flood characteristics on a grid scale over watersheds, i.e., flow velocity and flood duration. The methodological framework developed herein includes the following: (a) Vegetation indices for the critical period of crop growth from mid-high temporal and spatial remote sensing imagery in association with agricultural statistics data were used to develop empirical models to monitor the crop yield and evaluate yield losses from flood; (b) The two-dimensional hydraulic model coupled with the SCS-CN hydrologic model was employed to simulate the flood evolution process

  14. Two Dimensional Analytical Modeling for SOI and SON MOSFET and Their Performance Comparison

    Directory of Open Access Journals (Sweden)

    Saptarsi Ghosh

    2011-01-01

    Full Text Available During last few decade continuous device performance improvements have been achieved through a combination of device scaling, new device structures and material property improvement to its fundamental limits. Conventional silicon (bulk CMOS technology can’t overcome the fundamental physical limitations belong to sub-micro or nanometer region which leads to alternative device technology like Silicon-on-Insulator (SOI technology and its recent innovative modification Silicon-On-Nothing (SON MOSFET. Analytical simulation is very important to understand the relative performance of those devices under different structural and operational parameter variations. For present analytical simulation asymmetric structure of Silicon-On-Insulator (SOI MOSFET and Silicon-On-Nothing (SON MOSFET are considered. The proposed structure of SON MOSFET is similar to that of the SOI MOSFET with the only exception being the oxide layer here is substituted with air which has much lower permittivity than Silicon-dioxide. Variation of threshold voltage against effective channel lengths is compared for both the structures. From our simulation it is observed that the proposed SON model has lower drain to source current (IDS than SOI model. In our modeling based on solution of two dimensional Poisson’s equation short channel effects such as DIBL and fringing field effects are also taken into account. SON is found to provide better suppression of SCE s than SOI. The results predicted by our analytical simulation hold good agreement with experimental results.

  15. A New Paradigm of Modeling Two-Dimensional Overland Watershed Water Quality

    Science.gov (United States)

    Zhang, F.; Yeh, G. G.

    2003-12-01

    This paper presents the development of sediment and reactive chemical transport under non-isotherm condition in two-dimensional overland watershed system. Through decomposition of reaction network via Gauss-Jordan column reduction, (a) redundant fast reactions and irrelevant kinetic reactions are removed from the system; (b) fast reactions and slow reactions can be decoupled; (c) species reaction equations are transformed into two sets: equilibrium species mass action equations and kinetic-variable reaction equations. This enable our model to include as many types of reactions as possible, choose kinetic-variables instead of chemical species as primary dependent variables, and simplify the reaction terms in transport equations. In our model two options are provided to solve the advection-dispersion transport equation: Lagrangian-Eulerian approach, and Finite Element Method in Conservative Form, and three options to deal with the reaction term: Fully-implicit, Predictor-corrector, and Operator-splitting methods. The production-consumption rate of chemical species is determined by reaction-based formulations. One example problem is employed to demonstrate the design capability of the model and the robustness of the numerical simulations.

  16. Phase diagram and correlation functions of the two-dimensional dissipative quantum XY model

    Science.gov (United States)

    Hou, Changtao; Varma, Chandra M.

    2016-11-01

    The two-dimensional quantum XY model, with a Caldeira-Leggett form of dissipation, is applicable to the quantum-critical properties of diverse experimental systems, ranging from superconductor to insulator transitions, ferromagnetic and antiferromagnetic transitions in metals, to the loop-current order transition in cuprates. We solve the reexpression of this model in terms of orthogonal topological excitations, vortices, and a variety of instantons, by renormalization group methods. The calculations explain the extraordinary properties of the model discovered in Monte Carlo calculations: the product form of the quantum-critical fluctuations in space and time, a spatial correlation length proportional to the logarithm of the temporal correlation length near the transition from a disordered to a fully ordered state, and the occurrence of a phase with spatial order without temporal order. They are intimately related to the flow of the metric of time in relation to the metric of space, i.e., of the dynamical critical exponent z . These properties appear to be essential in understanding the strange metallic phase found in a variety of quantum-critical transitions as well as the accompanying high-temperature superconductivity.

  17. Efficient two-dimensional magnetotellurics modelling using implicitly restarted Lanczos method

    Indian Academy of Sciences (India)

    Krishna Kumar; Pravin K Gupta; Sri Niwas

    2011-08-01

    This paper presents an efficient algorithm, FDA2DMT (Free Decay Analysis for 2D Magnetotellurics (MT)), based on eigenmode approach to solve the relevant partial differential equation, for forward computation of two-dimensional (2D) responses. The main advantage of this approach lies in the fact that only a small subset of eigenvalues and corresponding eigenvectors are required for satisfactory results. This small subset (pre-specified number) of eigenmodes are obtained using shift and invert implementation of Implicitly Restarted Lanczos Method (IRLM). It has been established by experimentation that only 15–20% smallest eigenvalue and corresponding eigenvectors are sufficient to secure the acceptable accuracy. Once the single frequency response is computed using eigenmode approach, the responses for subsequent frequencies can be obtained in negligible time. Experiment design results for validation of FDA2DMT are presented by considering two synthetic models from COMMEMI report, Brewitt-Taylor and Weaver (1976) model and a field data based model from Garhwal Himalaya.

  18. Design considerations for pulsed-flow comprehensive two-dimensional GC: dynamic flow model approach.

    Science.gov (United States)

    Harvey, Paul McA; Shellie, Robert A; Haddad, Paul R

    2010-04-01

    A dynamic flow model, which maps carrier gas pressures and carrier gas flow rates through the first dimension separation column, the modulator sample loop, and the second dimension separation column(s) in a pulsed-flow modulation comprehensive two-dimensional gas chromatography (PFM-GCxGC) system is described. The dynamic flow model assists design of a PFM-GCxGC modulator and leads to rapid determination of pneumatic conditions, timing parameters, and the dimensions of the separation columns and connecting tubing used to construct the PFM-GCxGC system. Three significant innovations are introduced in this manuscript, which were all uncovered by using the dynamic flow model. A symmetric flow path modulator improves baseline stability, appropriate selection of the flow restrictors in the first dimension column assembly provides a generally more stable and robust system, and these restrictors increase the modulation period flexibility of the PFM-GCxGC system. The flexibility of a PFM-GCxGC system resulting from these innovations is illustrated using the same modulation interface to analyze Special Antarctic Blend (SAB) diesel using 3 s and 9 s modulation periods.

  19. Probability-changing cluster algorithm for two-dimensional XY and clock models

    Science.gov (United States)

    Tomita, Yusuke; Okabe, Yutaka

    2002-05-01

    We extend the newly proposed probability-changing cluster (PCC) Monte Carlo algorithm to the study of systems with the vector order parameter. Wolff's idea of the embedded cluster formalism is used for assigning clusters. The Kosterlitz-Thouless (KT) transitions for the two-dimensional (2D) XY and q-state clock models are studied by using the PCC algorithm. Combined with the finite-size scaling analysis based on the KT form of the correlation length, ξ~exp(c/(T/TKT-1)), we determine the KT transition temperature and the decay exponent η as TKT=0.8933(6) and η=0.243(4) for the 2D XY model. We investigate two transitions of the KT type for the 2D q-state clock models with q=6,8,12 and confirm the prediction of η=4/q2 at T1, the low-temperature critical point between the ordered and XY-like phases, systematically.

  20. Stable topological modes in two-dimensional Ginzburg-Landau models with trapping potentials

    CERN Document Server

    Mihalache, D; Skarka, V; Malomed, B A; Leblond, H; Aleksić, N B; Lederer, F

    2010-01-01

    Complex Ginzburg-Landau (CGL) models of laser media (with the cubic-quintic nonlinearity) do not contain an effective diffusion term, which makes all vortex solitons unstable in these models. Recently, it has been demonstrated that the addition of a two-dimensional periodic potential, which may be induced by a transverse grating in the laser cavity, to the CGL equation stabilizes compound (four-peak) vortices, but the most fundamental "crater-shaped" vortices (CSVs), alias vortex rings, which are, essentially, squeezed into a single cell of the potential, have not been found before in a stable form. In this work we report families of stable compact CSVs with vorticity S=1 in the CGL model with the external potential of two different types: an axisymmetric parabolic trap, and the periodic potential. In both cases, we identify stability region for the CSVs and for the fundamental solitons (S=0). Those CSVs which are unstable in the axisymmetric potential break up into robust dipoles. All the vortices with S=2 a...

  1. Infiltration effects on a two-dimensional molecular dynamics model of landslides

    CERN Document Server

    Martelloni, Gianluca

    2012-01-01

    In this paper we propose a two-dimensional (2D) computational model, based on a molecular dynamics (MD) approach, for deep landslides triggered by rainfall. Our model is based on interacting particles or grains and describes the behavior of a fictitious granular material along a slope consisting of a vertical section, i.e. with a wide thickness. The triggering of the landslide is caused by the passing of two conditions: a threshold speed and a condition on the static friction of the particles, the latter based on the Mohr-Coulomb failure criterion (Coulomb 1776; Mohr 1914). The inter-particle interactions are through a potential that, in the absence of suitable experimental data and due to the arbitrariness of the grain dimension is modeled by means of a potential similar to the Lennard-Jones one (Lennard-Jones 1924), i.e., with an attractive and a repulsive part. For the updating of the particle positions we use a MD method which results to be very suitable to simulate this type of systems (Herrmann and Ludi...

  2. A two-dimensional modeling of solid oxide fuel cell button cells with detailed electrochemistry mechanism

    Science.gov (United States)

    Li, Jingde; Bai, Zhengyu; Croiset, Eric

    2016-11-01

    A two-dimensional model of nickel/yttria-stabilized zirconia (Ni/YSZ) solid oxide fuel cell (SOFC) was developed for a button cell system. The model integrates the detailed catalytic, electrochemical elementary reactions with ionic/electronic conduction and multiple gas transport processes in SOFC. The model is validated using published experimental data for H2-H2O fuel gas under different cell sizes and operating conditions. The distributions of gas/surface phase species concentration and current density were predicted and the effects of operating temperature, fuel gas composition and fuel channel tube design on the cell performance were studied. The results show that the electrochemical reaction processes occurs mainly within a 20 μm distance from the anode/electrolyte interface and that the Ni catalyst surface is covered mainly by H(s). For the chamber channel design, the calculations show that the tube chamber should have a diameter no smaller than the cathode electrode to obtain the best SOFC performance.

  3. Understanding Ground Motion in Las Vegas: Insights from Data Analysis and Two-Dimensional Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Rodgers, A; Tkalcic, H; McCallen, D

    2004-02-05

    Seismic ground motions are amplified in low velocity sedimentary basins relative to adjacent sites on high velocity hard rock. We used historical recordings of NTS nuclear explosions and earthquake recordings in Las Vegas Valley to quantify frequency-dependent basin amplification using Standard Spectral Ratios. We show that amplifications, referred to as site response, can reach a factor of 10 in the frequency band 0.4-2.0 Hz. Band-averaged site response between 0.4-2.0 Hz is strongly correlated with basin depth. However, it is also well known that site response is related to shallow shear-wave velocity structure. We simulated low frequency (f<1Hz) ground motion and site response with two-dimensional elastic finite difference simulations. We demonstrate that physically plausible models of the shallow subsurface, including low velocity sedimentary structure, can predict relative amplification as well as some of the complexity in the observed waveforms. This study demonstrates that site response can be modeled without invoking complex and computationally expensive three-dimensional structural models.

  4. Verification of the two-dimensional hydrodynamic model based on remote sensing

    Science.gov (United States)

    Sazonov, Alexey; Mikhailukova, Polina; Krylenko, Inna; Frolova, Natalya; Kireeva, Mariya

    2016-04-01

    Mathematical modeling methods are used more and more actively to evaluate possible damage, identify potential flood zone and the influence of individual factors affecting the river during the passage of the flood. Calculations were performed by means of domestic software complex «STREAM-2D» which is based on the numerical solution of two-dimensional St. Venant equations. One of the major challenges in mathematical modeling is the verification of the model. This is usually made using data on water levels from hydrological stations: the smaller the difference of the actual level and the simulated one, the better the quality of the model used. Data from hydrological stations are not always available, so alternative sources of verification, such as remote sensing, are increasingly used. The aim of this work is to develop a method of verification of hydrodynamic model based on a comparison of actual flood zone area, which in turn is determined on the basis of the automated satellite image interpretation methods for different imaging systems and flooded area obtained in the course of the model. The study areas are Lena River, The North Dvina River, Amur River near Blagoveshchensk. We used satellite images made by optical and radar sensors: SPOT-5/HRG, Resurs-F, Radarsat-2. Flooded area were calculated using unsupervised classification (ISODATA and K-mean) for optical images and segmentation for Radarsat-2. Knowing the flow rate and the water level at a given date for the upper and lower limits of the model, respectively, it is possible to calculate flooded area by means of program STREAM-2D and GIS technology. All the existing vector layers with the boundaries of flooding are included in a GIS project for flood area calculation. This study was supported by the Russian Science Foundation, project no. 14-17-00155.

  5. Coexistence in the two-dimensional May-Leonard model with random rates

    Science.gov (United States)

    He, Q.; Mobilia, M.; Täuber, U. C.

    2011-07-01

    We employ Monte Carlo simulations to numerically study the temporal evolution and transient oscillations of the population densities, the associated frequency power spectra, and the spatial correlation functions in the (quasi-) steady state in two-dimensional stochastic May-Leonard models of mobile individuals, allowing for particle exchanges with nearest-neighbors and hopping onto empty sites. We therefore consider a class of four-state three-species cyclic predator-prey models whose total particle number is not conserved. We demonstrate that quenched disorder in either the reaction or in the mobility rates hardly impacts the dynamical evolution, the emergence and structure of spiral patterns, or the mean extinction time in this system. We also show that direct particle pair exchange processes promote the formation of regular spiral structures. Moreover, upon increasing the rates of mobility, we observe a remarkable change in the extinction properties in the May-Leonard system (for small system sizes): (1) as the mobility rate exceeds a threshold that separates a species coexistence (quasi-) steady state from an absorbing state, the mean extinction time as function of system size N crosses over from a functional form ˜ e c N / N (where c is a constant) to a linear dependence; (2) the measured histogram of extinction times displays a corresponding crossover from an (approximately) exponential to a Gaussian distribution. The latter results are found to hold true also when the mobility rates are randomly distributed.

  6. Two-Dimensional Aerodynamic Models of Insect Flight for Robotic Flapping Wing Mechanisms of Maximum Efficiency

    Institute of Scientific and Technical Information of China (English)

    Thien-Tong Nguyen; Doyoung Byun

    2008-01-01

    In the "modified quasi-steady" approach, two-dimensional (2D) aerodynamic models of flapping wing motions are analyzed with focus on different types of wing rotation and different positions of rotation axis to explain the force peak at the end of each half stroke. In this model, an additional velocity of the mid chord position due to rotation is superimposed on the translational relative velocity of air with respect to the wing. This modification produces augmented forces around the end of eachstroke. For each case of the flapping wing motions with various combination of controlled translational and rotational velocities of the wing along inclined stroke planes with thin figure-of-eight trajectory, discussions focus on lift-drag evolution during one stroke cycle and efficiency of types of wing rotation. This "modified quasi-steady" approach provides a systematic analysis of various parameters and their effects on efficiency of flapping wing mechanism. Flapping mechanism with delayed rotation around quarter-chord axis is an efficient one and can be made simple by a passive rotation mechanism so that it can be useful for robotic application.

  7. Experiment and modeling of a two-dimensional piezoelectric energy harvester

    Science.gov (United States)

    Yang, Yaowen; Wu, Hao; Kiong Soh, Chee

    2015-12-01

    Vibration energy harvesting using piezoelectric materials has attracted much research interest in recent years. Numerous efforts have been devoted to improving the efficiency of vibration energy harvesters and broadening their bandwidths. In most reported literature, energy harvesters are designed to harvest energy from vibration source with a specific excitation direction. However, a practical environmental vibration source may include multiple components from different directions. Thus, it is an important concern to design a vibration energy harvester to be adaptive to multiple excitation directions. In this article, a piezoelectric energy harvester with frame configuration is proposed to achieve two-dimensional (2D) vibration energy harvesting. The harvester works in two fundamental modes, i.e., its vertical and horizontal vibration modes. By tuning the structural parameters, the harvester can capture vibration energy from arbitrary directions in a 2D plane. Experimental studies are carried out to prove its feasibility. A finite element model and an equivalent circuit model are built to simulate the system and validate the experiment outcomes. The study of this 2D energy harvester indicates its promising potential in practical vibration scenarios.

  8. Quantitative evaluation and modeling of two-dimensional neovascular network complexity: the surface fractal dimension

    Directory of Open Access Journals (Sweden)

    Franceschini Barbara

    2005-02-01

    Full Text Available Abstract Background Modeling the complex development and growth of tumor angiogenesis using mathematics and biological data is a burgeoning area of cancer research. Architectural complexity is the main feature of every anatomical system, including organs, tissues, cells and sub-cellular entities. The vascular system is a complex network whose geometrical characteristics cannot be properly defined using the principles of Euclidean geometry, which is only capable of interpreting regular and smooth objects that are almost impossible to find in Nature. However, fractal geometry is a more powerful means of quantifying the spatial complexity of real objects. Methods This paper introduces the surface fractal dimension (Ds as a numerical index of the two-dimensional (2-D geometrical complexity of tumor vascular networks, and their behavior during computer-simulated changes in vessel density and distribution. Results We show that Ds significantly depends on the number of vessels and their pattern of distribution. This demonstrates that the quantitative evaluation of the 2-D geometrical complexity of tumor vascular systems can be useful not only to measure its complex architecture, but also to model its development and growth. Conclusions Studying the fractal properties of neovascularity induces reflections upon the real significance of the complex form of branched anatomical structures, in an attempt to define more appropriate methods of describing them quantitatively. This knowledge can be used to predict the aggressiveness of malignant tumors and design compounds that can halt the process of angiogenesis and influence tumor growth.

  9. A two-dimensional (azimuthal-axial) particle-in-cell model of a Hall thruster

    Energy Technology Data Exchange (ETDEWEB)

    Coche, P.; Garrigues, L., E-mail: laurent.garrigues@laplace.univ-tlse.fr [LAPLACE (Laboratoire Plasma et Conversion d' Energie), Université de Toulouse, UPS, INPT Toulouse 118, route de Narbonne, F-31062 Toulouse cedex 9 (France); CNRS, LAPLACE, F-31062 Toulouse (France)

    2014-02-15

    We have developed a two-dimensional Particle-In-Cell model in the azimuthal and axial directions of the Hall thruster. A scaling method that consists to work at a lower plasma density to overcome constraints on time-step and grid-spacing is used. Calculations are able to reproduce the breathing mode due to a periodic depletion of neutral atoms without the introduction of a supplementary anomalous mechanism, as in fluid and hybrid models. Results show that during the increase of the discharge current, an electron-cyclotron drift instability (frequency in the range of MHz and wave number on the order of 3000 rad s{sup −1}) is formed in the region of the negative gradient of magnetic field. During the current decrease, an axial electric wave propagates from the channel toward the exhaust (whose frequency is on the order of 400 kHz) leading to a broadening of the ion energy distribution function. A discussion about the influence of the scaling method on the calculation results is also proposed.

  10. Numerical Simulations of an atmospheric pressure discharge using a two dimensional fluid model

    Science.gov (United States)

    Iqbal, Muhammad M.; Turner, Miles M.

    2008-10-01

    We present numerical simulations of a parallel-plate dielectric barrier discharge using a two-dimensional fluid model with symmetric boundary conditions in pure helium and He-N2 gases at atmospheric pressure. The periodic stationary pattern of electrons and molecular helium ions density is shown at different times during one breakdown pulse for the pure helium gas. The temporal behavior of the helium metastables and excimers species density is examined and their influences on the discharge characteristics are exhibited for an APD. The atmospheric pressure discharge modes (APGD and APTD) are affected with small N2 impurities and the discharge mode structures are described under different operating conditions. The uniform and filamentary behavior of the discharge is controlled with the variable relative permittivity of the dielectric barrier material. The influence of nitrogen impurities plays a major role for the production of the filaments in the after glow phase of He-N2 discharge and the filaments are clearly observed with the increased recombination coefficient of nitrogen ions. The creation and annihilation mechanism of filaments is described with the production and destruction of nitrogen ions at different applied voltages and driving frequencies for a complete cycle. The results of the fluid model are validated by comparison with the experimental atmospheric pressure discharge results in He-N2 plasma discharge.

  11. Detailed compositional characterization of plastic waste pyrolysis oil by comprehensive two-dimensional gas-chromatography coupled to multiple detectors.

    Science.gov (United States)

    Toraman, Hilal E; Dijkmans, Thomas; Djokic, Marko R; Van Geem, Kevin M; Marin, Guy B

    2014-09-12

    The detailed compositional characterization of plastic waste pyrolysis oil was performed with comprehensive two-dimensional GC (GC×GC) coupled to four different detectors: a flame ionization detector (FID), a sulfur chemiluminescence detector (SCD), a nitrogen chemiluminescence detector (NCD) and a time of flight mass spectrometer (TOF-MS). The performances of different column combinations were assessed in normal i.e. apolar/mid-polar and reversed configurations for the GC×GC-NCD and GC×GC-SCD analyses. The information obtained from the four detectors and the use of internal standards, i.e. 3-chlorothiophene for the FID and the SCD and 2-chloropyridine for the NCD analysis, enabled the identification and quantification of the pyrolysis oil in terms of both group type and carbon number: hydrocarbon groups (n-paraffins, iso-paraffins, olefins and naphthenes, monoaromatics, naphthenoaromatics, diaromatics, naphthenodiaromatics, triaromatics, naphthenotriaromatics and tetra-aromatics), nitrogen (nitriles, pyridines, quinolines, indole, caprolactam, etc.), sulfur (thiols/sulfides, thiophenes/disulfides, benzothiophenes, dibenzothiophenes, etc.) and oxygen containing compounds (ketones, phenols, aldehydes, ethers, etc.). Quantification of trace impurities is illustrated for indole and caprolactam. The analyzed pyrolysis oil included a significant amount of nitrogen containing compounds (6.4wt%) and to a lesser extent sulfur containing compounds (0.6wt%). These nitrogen and sulfur containing compounds described approximately 80% of the total peak volume for respectively the NCD and SCD analysis. TOF-MS indicated the presence of the oxygen containing compounds. However only a part of the oxygen containing compounds (2.5wt%) was identified because of their low concentrations and possible overlap with the complex hydrocarbon matrix as no selective detector or preparative separation for oxygen compounds was used.

  12. Sensitivity of two-dimensional model predictions of ozone response to stratospheric aircraft: An update

    Energy Technology Data Exchange (ETDEWEB)

    Considine, D.B.; Douglass, A.R.; Jackman, C.H. [Applied Research Corp., Landover, MD (United States)]|[NASA, Goddard Space Flight Center, Greenbelt, MD (United States)

    1995-02-01

    The Goddard Space Flight Center (GSFC) two-dimensional model of stratospheric photochemistry and dynamics has been used to calculate the O3 response to stratospheric aircraft (high-speed civil transport (HSCT)) emissions. The sensitivity of the model O3 response was examined for systematic variations of five parameters and two reaction rates over a wide range, expanding on calculations by various modeling groups for the NASA High Speed Research Program and the World Meteorological Organization. In all, 448 model runs were required to test the effects of variations in the latitude, altitude, and magnetitude of the aircraft emissions perturbation, the background chlorine levels, the background sulfate aerosol surface area densities, and the rates of two key reactions. No deviation from previous conclusions concerning the response of O3 to HSCTs was found in this more exhaustive exploration of parameter space. Maximum O3 depletions occur for high-altitude, low altitude HSCT perturbations. Small increases in global total O3 can occur for low-altitude, high-altitude injections. Decreasing aerosol surface area densities and background chlorine levels increases the sensitivity of model O3 to the HSCT perturbations. The location of the aircraft emissions is the most important determinant of the model response. Response to the location of the HSCT emissions is not changed qualitatively by changes in background chlorine and aerosol loading. The response is also not very sensitive to changes in the rates of the reactions NO + HO2 yields NO2 + OH and HO2 + O3 yields OH + 2O2 over the limits of their respective uncertainties. Finally, levels of lower stratospheric HO(sub x) generally decrease when the HSCT perturbation is included, even though there are large increases in H2O due to the perturbation.

  13. Two-dimensional modeling of a polymer electrolyte membrane fuel cell with long flow channel. Part I. Model development

    OpenAIRE

    2015-01-01

    A two-dimensional single-phase model is developed for the steady-state and transient analysis of polymer electrolyte membrane fuel cells (PEMFC). Based on diluted and concentrated solution theories, viscous flow is introduced into a phenomenological multi-component modeling framework in the membrane. Characteristic variables related to the water uptake are discussed. A ButlereVolmer formulation of the current-overpotential relationship is developed based on an elementary mechanism of elect...

  14. Two-dimensional numerical modelling of dissolved and particulate pollutant transport in the Three Gorges Reservoir

    Science.gov (United States)

    Hu, W.; Wang, L.-J.; Chen, H.; Holbach, A.; Zheng, B.-H.; Norra, S.; Westrich, B.

    2012-04-01

    After impoundment of the Three Gorges Reservoir (TGR) in 2003, hydrological regimes of the Yangtze River, upstream and downstream of the Three Gorges Dam, have been changed enormously, leading to significant environmental, ecological and social impacts. Nutrients and pollutants from agriculture, industry and municipalities are of concern due to their impact on the aquatic environment and hence, transport behavior of sediment associated pollutants must be modeled and analyzed to establish a sustainable water reservoir management. As part of the Chinese-German Yangtze-Project [1], two-dimensional numerical model TELEMAC is applied to study the dissolved and particulate pollutant transport at different locations of concern in the TGR. In-situ measurement campaigns for morphology and water quality data using mobile measuring device (MINIBAT) are carried out to provide detailed information for the different water bodies at different time. Additional morphological data are taken from cross-section profiles in the literature, the digital elevation model (DEM) of Shuttle Radar Topography Mission (SRTM) from CGIAR. Daily and hourly water level and discharge, suspended sediment concentration and pollutant loads are obtained from the authorities and extracted from literature. The model describes the spatial-temporal flow field, transport and dispersion of sediment associated pollutants with emphasis on the dynamic interaction and mutual influence of the river Yangtze, its major tributaries and adjacent lagoon-like dead water bodies due to the 30 meter annual reservoir water level fluctuation. Since algae bloom, especially in the tributaries and side arms of the mainstream, is one of the major issues occurred after 2003, the results of the numerical modeling together with the statistical analysis of the MINIBAT measurements are used for the eutrophication status analysis. Acknowledgments The Yangtze-Project is funded by the Federal Ministry of Education and Research (BMBF

  15. Nonequilibrium critical dynamics of the two-dimensional Ashkin-Teller model at the Baxter line

    Science.gov (United States)

    Fernandes, H. A.; da Silva, R.; Caparica, A. A.; de Felício, J. R. Drugowich

    2017-04-01

    We investigate the short-time universal behavior of the two-dimensional Ashkin-Teller model at the Baxter line by performing time-dependent Monte Carlo simulations. First, as preparatory results, we obtain the critical parameters by searching the optimal power-law decay of the magnetization. Thus, the dynamic critical exponents θm and θp, related to the magnetic and electric order parameters, as well as the persistence exponent θg, are estimated using heat-bath Monte Carlo simulations. In addition, we estimate the dynamic exponent z and the static critical exponents β and ν for both order parameters. We propose a refined method to estimate the static exponents that considers two different averages: one that combines an internal average using several seeds with another, which is taken over temporal variations in the power laws. Moreover, we also performed the bootstrapping method for a complementary analysis. Our results show that the ratio β /ν exhibits universal behavior along the critical line corroborating the conjecture for both magnetization and polarization.

  16. A Method for Geometry Optimization in a Simple Model of Two-Dimensional Heat Transfer

    CERN Document Server

    Peng, Xiaohui; Protas, Bartosz

    2013-01-01

    This investigation is motivated by the problem of optimal design of cooling elements in modern battery systems. We consider a simple model of two-dimensional steady-state heat conduction described by elliptic partial differential equations and involving a one-dimensional cooling element represented by a contour on which interface boundary conditions are specified. The problem consists in finding an optimal shape of the cooling element which will ensure that the solution in a given region is close (in the least squares sense) to some prescribed target distribution. We formulate this problem as PDE-constrained optimization and the locally optimal contour shapes are found using a gradient-based descent algorithm in which the Sobolev shape gradients are obtained using methods of the shape-differential calculus. The main novelty of this work is an accurate and efficient approach to the evaluation of the shape gradients based on a boundary-integral formulation which exploits certain analytical properties of the sol...

  17. Non-equilibrium relaxation in a two-dimensional stochastic lattice Lotka-Volterra model

    Science.gov (United States)

    Chen, Sheng; Täuber, Uwe C.

    We employ Monte Carlo simulations to study a stochastic Lotka-Volterra model on a two-dimensional square lattice with periodic boundary conditions. There are stable states when the predators and prey coexist. If the local prey carrying capacity is finite, there emerges an extinction threshold for the predator population at a critical value of the predation rate. We investigate the non-equilibrium relaxation of the predator density in the vicinity of this critical point. The expected power law dependence between the relaxation time and predation rate is observed (critical slowing down). The numerically determined associated critical exponents are in accord with the directed percolation universality class. Following a sudden predation rate change to its critical value, one observes critical aging for the predator density autocorrelation function with a universal scaling exponent. This aging scaling signature of the absorbing state phase transition emerges at significantly earlier times than stationary critical power laws, and could thus serve as an advanced indicator of the population's proximity to its extinction threshold. This research is supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award DE-FG02-09ER46613.

  18. Critical Casimir force scaling functions of the two-dimensional Ising model at finite aspect ratios

    Science.gov (United States)

    Hobrecht, Hendrik; Hucht, Alfred

    2017-02-01

    We present a systematic method to calculate the universal scaling functions for the critical Casimir force and the according potential of the two-dimensional Ising model with various boundary conditions. Therefore we start with the dimer representation of the corresponding partition function Z on an L× M square lattice, wrapped around a torus with aspect ratio ρ =L/M . By assuming periodic boundary conditions and translational invariance in at least one direction, we systematically reduce the problem to a 2× 2 transfer matrix representation. For the torus we first reproduce the results by Kaufman and then give a detailed calculation of the scaling functions. Afterwards we present the calculation for the cylinder with open boundary conditions. All scaling functions are given in form of combinations of infinite products and integrals. Our results reproduce the known scaling functions in the limit of thin films ρ \\to 0 . Additionally, for the cylinder at criticality our results confirm the predictions from conformal field theory.

  19. Nonlinear sigma model in the case of N x. cap alpha. N rectangular matrices in two-dimensional euclidean space

    Energy Technology Data Exchange (ETDEWEB)

    Chekhov, L.O.

    1985-12-01

    Matrix nonlinear sigma models are discussed and the matrix nonlinear sigma model in the case of N x ..cap alpha..N rectangular matrices is considered. The authors show that in two-dimensional Euclidean space, the model is renormalizable with respect to ..cap alpha.. and 1/N. The fulfillment of the chirality identity is demonstrated in the operator expansion for the renormalized theory.

  20. HPTAM, a two-dimensional Heat Pipe Transient Analysis Model, including the startup from a frozen state

    Science.gov (United States)

    Tournier, Jean-Michel; El-Genk, Mohamed S.

    1995-01-01

    A two-dimensional Heat Pipe Transient Analysis Model, 'HPTAM,' was developed to simulate the transient operation of fully-thawed heat pipes and the startup of heat pipes from a frozen state. The model incorporates: (a) sublimation and resolidification of working fluid; (b) melting and freezing of the working fluid in the porous wick; (c) evaporation of thawed working fluid and condensation as a thin liquid film on a frozen substrate; (d) free-molecule, transition, and continuum vapor flow regimes, using the Dusty Gas Model; (e) liquid flow and heat transfer in the porous wick; and (f) thermal and hydrodynamic couplings of phases at their respective interfaces. HPTAM predicts the radius of curvature of the liquid meniscus at the liquid-vapor interface and the radial location of the working fluid level (liquid or solid) in the wick. It also includes the transverse momentum jump condition (capillary relationship of Pascal) at the liquid-vapor interface and geometrically relates the radius of curvature of the liquid meniscus to the volume fraction of vapor in the wick. The present model predicts the capillary limit and partial liquid recess (dryout) in the evaporator wick, and incorporates a liquid pooling submodel, which simulates accumulation of the excess liquid in the vapor core at the condenser end.

  1. Phase transitions in the two-dimensional Anisotropic Biquadratic Heisenberg Model

    Energy Technology Data Exchange (ETDEWEB)

    Moura, A.R., E-mail: armoura@infis.ufu.br [Universidade Federal de Uberlândia (Brazil); Pires, A.S.T., E-mail: antpires@fisica.ufmg.br [Universidade Federal de Minas Gerais (Brazil); Pereira, A.R., E-mail: apereira@ufv.br [Universidade Federal de Viçosa (Brazil)

    2014-05-01

    In this paper we study the influence of the single-ion anisotropy in the two-dimensional biquadratic Heisenberg model (ABHM) on the square lattice at zero and finite low temperatures. It is common to represent the bilinear and biquadratic terms by J{sub 1}=Jcosθ and J{sub 2}=Jsinθ, respectively, and the many phases present in the model as a function of θ are well documented. However we have adopted a constant value for the bilinear constant (J{sub 1}=1) and small values of the biquadratic term (|J{sub 2}|D{sub c}, the excited states are gapped and there is no spin long-range order (LRO) even at zero temperature. Using Schwinger bosonic representation and Self-Consistent Harmonic Approximation (SCHA), we have studied the quantum and thermal phase transitions as a function of the bilinear and biquadratic constants. - Highlights: • We study the anisotropic biquadric bilinear Heisenberg model on a square lattice. • We show the quantum phase transition associated with the anisotropic constant. • We obtain a thermal phase transition similar to the BKT transition.

  2. Tunable two-dimensional arrays of single Rydberg atoms for realizing quantum Ising models.

    Science.gov (United States)

    Labuhn, Henning; Barredo, Daniel; Ravets, Sylvain; de Léséleuc, Sylvain; Macrì, Tommaso; Lahaye, Thierry; Browaeys, Antoine

    2016-06-30

    Spin models are the prime example of simplified many-body Hamiltonians used to model complex, strongly correlated real-world materials. However, despite the simplified character of such models, their dynamics often cannot be simulated exactly on classical computers when the number of particles exceeds a few tens. For this reason, quantum simulation of spin Hamiltonians using the tools of atomic and molecular physics has become a very active field over the past years, using ultracold atoms or molecules in optical lattices, or trapped ions. All of these approaches have their own strengths and limitations. Here we report an alternative platform for the study of spin systems, using individual atoms trapped in tunable two-dimensional arrays of optical microtraps with arbitrary geometries, where filling fractions range from 60 to 100 per cent. When excited to high-energy Rydberg D states, the atoms undergo strong interactions whose anisotropic character opens the way to simulating exotic matter. We illustrate the versatility of our system by studying the dynamics of a quantum Ising-like spin-1/2 system in a transverse field with up to 30 spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. For geometries where the anisotropy is expected to have small effects on the dynamics, we find excellent agreement with ab initio simulations of the spin-1/2 system, while for strongly anisotropic situations the multilevel structure of the D states has a measurable influence. Our findings establish arrays of single Rydberg atoms as a versatile platform for the study of quantum magnetism.

  3. Two-dimensional thermal modeling of power monolithic microwave integrated circuits (MMIC's)

    Science.gov (United States)

    Fan, Mark S.; Christou, Aris; Pecht, Michael G.

    1992-01-01

    Numerical simulations of the two-dimensional temperature distributions for a typical GaAs MMIC circuit are conducted, aiming at understanding the heat conduction process of the circuit chip and providing temperature information for device reliability analysis. The method used is to solve the two-dimensional heat conduction equation with a control-volume-based finite difference scheme. In particular, the effects of the power dissipation and the ambient temperature are examined, and the criterion for the worst operating environment is discussed in terms of the allowed highest device junction temperature.

  4. Spin transport in the two-dimensional quantum disordered anisotropic Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Lima, L.S. [Departamento de Física e Matemática, Centro Federal de Educação Tecnológica de Minas Gerais, 30510-000 Belo Horizonte, MG (Brazil); Pires, A.S.T.; Costa, B.V. [Departamento de Física ICEx, UFMG, CP 702, 31270-901 Belo Horizonte, MG (Brazil)

    2014-12-15

    We use the self consistent harmonic approximation together with the Linear Response Theory to study the effect of nonmagnetic disorder on spin transport in the quantum diluted two-dimensional anisotropic Heisenberg model with spin S=1 in a square lattice. The model has a BKT transition at zero dilution. We calculate the regular part of the spin conductivity σ{sup reg}(ω) and the Drude weight D{sub S}(T) as a function of the non-magnetic concentration, x. Our calculations show that the spin conductivity drops abruptly to zero at x{sub c}{sup SCHA}≈0.5 indicating that the system changes from an ideal spin conductor state to an insulator. This value is far above the site percolation threshold x{sub c}{sup site}≈0.41. Although the SCHA fails in determining precisely the percolation threshold, both the spin conductivity and the Drude weight show a quite regular behavior inside 0≤x≤x{sub c}{sup SCHA} indicating that the transition stays in the same universality class all along the interval. - Highlights: • The site dilution generates a large influence on regular part of the spin conductivity, σ{sup reg}(ω), and in the Drude weight, D(T). • In a concentration of impurities about x≈0.5, the regular part of the spin conductivity and the Drude weight fall to zero. • In this point we have a change in the state of the system from an ideal spin conductor to a spin insulator.

  5. On the two-dimensional dynamical Ising model in the phase coexistence region

    Science.gov (United States)

    Martinelli, F.

    1994-09-01

    We consider a Glauber dynamics reversible with respect to the two-dimensional Ising model in a finite square of side L, in the absence of an external field and at large inverse temperature β. We first consider the gap in the spectrum of the generator of the dynamics in two different cases: with plus and open boundary conditions. We prove that, when the symmetry under global spin flip is broken by the boundary conditions, the gap is much larger than the case in which the symmetry is present. For this latter we compute exactly the asymptotics of -(1/β L) log(gap) as L→∞ and show that it coincides with the surface tension along one of the coordinate axes. As a consequence we are able to study quite precisely the large deviations in time of the magnetization and to obtain an upper bound on the spin-spin time correlation in the infinite-volume plus phase. Our results establish a connection between the dynamical large deviations and those of the equilibrium Gibbs measure studied by Shlosman in the framework of the rigorous description of the Wulff shape for the Ising model. Finally we show that, in the case of open boundary conditions, it is possible to rescale the time with L in such a way that, as L→∞, the finite-dimensional distributions of the time-rescaled magnetization converge to those of a symmetric continuous-time Markov chain on the two-state space {- m *(β), m *(β)}, m *(β) being the spontaneous magnetization. Our methods rely upon a novel combination of techniques for bounding from below the gap of symmetric Markov chains on complicated graphs, developed by Jerrum and Sinclair in their Markov chain approach to hard computational problems, and the idea of introducing "block Glauber dynamics" instead of the standard single-site dynamics, in order to put in evidence more effectively the effect of the boundary conditions in the approach to equilibrium.

  6. Transfer matrix computation of critical polynomials for two-dimensional Potts models

    Science.gov (United States)

    Lykke Jacobsen, Jesper; Scullard, Christian R.

    2013-02-01

    In our previous work [1] we have shown that critical manifolds of the q-state Potts model can be studied by means of a graph polynomial PB(q, v), henceforth referred to as the critical polynomial. This polynomial may be defined on any periodic two-dimensional lattice. It depends on a finite subgraph B, called the basis, and the manner in which B is tiled to construct the lattice. The real roots v = eK - 1 of PB(q, v) either give the exact critical points for the lattice, or provide approximations that, in principle, can be made arbitrarily accurate by increasing the size of B in an appropriate way. In earlier work, PB(q, v) was defined by a contraction-deletion identity, similar to that satisfied by the Tutte polynomial. Here, we give a probabilistic definition of PB(q, v), which facilitates its computation, using the transfer matrix, on much larger B than was previously possible. We present results for the critical polynomial on the (4, 82), kagome, and (3, 122) lattices for bases of up to respectively 96, 162, and 243 edges, compared to the limit of 36 edges with contraction-deletion. We discuss in detail the role of the symmetries and the embedding of B. The critical temperatures vc obtained for ferromagnetic (v > 0) Potts models are at least as precise as the best available results from Monte Carlo simulations or series expansions. For instance, with q = 3 we obtain vc(4, 82) = 3.742 489 (4), vc(kagome) = 1.876 459 7 (2), and vc(3, 122) = 5.033 078 49 (4), the precision being comparable or superior to the best simulation results. More generally, we trace the critical manifolds in the real (q, v) plane and discuss the intricate structure of the phase diagram in the antiferromagnetic (v < 0) region.

  7. Two-dimensional time-dependent modelling of fume formation in a pulsed gas metal arc welding process

    Science.gov (United States)

    Boselli, M.; Colombo, V.; Ghedini, E.; Gherardi, M.; Sanibondi, P.

    2013-06-01

    Fume formation in a pulsed gas metal arc welding (GMAW) process is investigated by coupling a time-dependent axi-symmetric two-dimensional model, which takes into account both droplet detachment and production of metal vapour, with a model for fume formation and transport based on the method of moments for the solution of the aerosol general dynamic equation. We report simulative results of a pulsed process (peak current = 350 A, background current 30 A, period = 9 ms) for a 1 mm diameter iron wire, with Ar shielding gas. Results showed that metal vapour production occurs mainly at the wire tip, whereas fume formation is concentrated in the fringes of the arc in the spatial region close to the workpiece, where metal vapours are transported by convection. The proposed modelling approach allows time-dependent tracking of fumes also in plasma processes where temperature-time variations occur faster than nanoparticle transport from the nucleation region to the surrounding atmosphere, as is the case for most pulsed GMAW processes.

  8. Self Organized Criticality in a two dimensional Cellular Automaton model of a magnetic flux tube with background flow

    CERN Document Server

    Danila, Bogdan; Mocanu, Gabriela

    2015-01-01

    We investigate the transition to Self Organized Criticality in a two-dimensional model of a flux tube with a background flow. The magnetic induction equation, represented by a partial differential equation with a stochastic source term, is discretized and implemented on a two dimensional cellular automaton. The energy released by the automaton during one relaxation event is the magnetic energy. As a result of the simulations we obtain the time evolution of the energy release, of the system control parameter, of the event lifetime distribution and of the event size distribution, respectively, and we establish that a Self Organized Critical state is indeed reached by the system. Moreover, energetic initial impulses in the magnetohydrodynamic flow can lead to one dimensional signatures in the magnetic two dimensional system, once the Self Organized Critical regime is established. The applications of the model for the study of Gamma Ray Bursts is briefly considered, and it is shown that some astrophysical paramet...

  9. Nonlinear sigma-model in the case of rectangular Nx. alpha. N matrices in two-dimensional euclidean space

    Energy Technology Data Exchange (ETDEWEB)

    Chekhov, L.O.

    1985-06-01

    Matrix nonlinear sigma-model is considered in the case of rectangular matrices of the dimension Nx..alpha..N. Renormalizability of the model with respect to ..alpha.. and 1/N is demonstrated for the case of two-dimensional Euclidean space. Validity of the chiral identity is proved in the operator expansion for the renormalized theory.

  10. A Complex Automata approach for in-stent restenosis: two-dimensional multiscale modelling and simulations

    NARCIS (Netherlands)

    Caiazzo, A.; Evans, D.; Falcone, J.-L.; Hegewald, J.; Lorenz, E.; Stahl, B.; Wang, D.; Bernsdorf, J.; Chopard, B.; Gunn, J.; Hose, R.; Krafczyk, M.; Lawford, P.; Smallwood, R.; Walker, D.; Hoekstra, A.

    2011-01-01

    In-stent restenosis, the maladaptive response of a blood vessel to injury caused by the deployment of a stent, is a multiscale system involving a large number of biological and physical processes. We describe a Complex Automata model for in-stent restenosis, coupling bulk flow, drug diffusion, and s

  11. Model for ballistic spin-transport in ferromagnet/two-dimensional electron gas/ferromagnet structures

    NARCIS (Netherlands)

    Schapers, T; Nitta, J; Heersche, HB; Takayanagi, H

    2002-01-01

    The spin dependent conductance of a ferromagnet/two-dimensional electron gas ferromagnet structure is theoretically examined in the ballistic transport regime. It is shown that the spin signal can be improved considerably by making use of the spin filtering effect of a barrier at the ferromagnet two

  12. Collapse arresting in an inhomogeneous two-dimensional nonlinear Schrodinger model

    DEFF Research Database (Denmark)

    Schjødt-Eriksen, Jens; Gaididei, Yuri Borisovich; Christiansen, Peter Leth

    2001-01-01

    Collapse of (2 + 1)-dimensional beams in the inhomogeneous two-dimensional cubic nonlinear Schrodinger equation is analyzed numerically and analytically. It is shown that in the vicinity of a narrow attractive inhomogeneity, the collapse of beams that in a homogeneous medium would collapse may...

  13. Two-dimensional discrete mathematical model of tumor-induced angiogenesis

    Institute of Scientific and Technical Information of China (English)

    Gai-ping ZHAO; Er-yun CHEN; Jie WU; Shi-xiong XU; M.W. Collins; Quan LONG

    2009-01-01

    A 2D discrete mathematical model of a nine-point finite difference scheme is built to simulate tumor-induced angiogenesis. Nine motion directions of an individual endothelial cell and two parent vessels are extended in the present model. The process of tumor-induced angiogenesis is performed by coupling random motility, chemotaxis, and haptotaxis of endothelial cell in different mechanical environments inside and outside the tumor. The results show that nearly realistic tumor microvascular networks with neoplastic pathophysiological characteristics can be generated from the present model. Moreover, the theoretical capillary networks generated in numerical simulations of the discrete model may provide useful information for further clinical research.

  14. Critical behavior of two-dimensional spin systems under the random-bond six-state clock model

    Science.gov (United States)

    Wu, Raymond P. H.; Lo, Veng-cheong; Huang, Haitao

    2012-09-01

    The critical behavior of the clock model in two-dimensional square lattice is studied numerically using Monte Carlo method with Wolff algorithm. The Kosterlitz-Thouless (KT) transition is observed in the six-state clock model, where an intermediate phase exists between the low-temperature ordered phase and the high-temperature disordered phase. The bond randomness is introduced to the system by assuming a Gaussian distribution for the coupling coefficients with the mean μ =1 and different values of variance, from σ2=0.1 to σ2=3.0. An abrupt jump in the helicity modulus at the transition, which is the key characteristic of the KT transition, is verified with a stability argument. The critical temperature Tc for both pure and disordered systems is determined from the critical exponent η(Tc)=1/4. The results showed that a small amount of disorder (small σ) reduces the critical temperature of the system, without altering the nature of transition. However, a larger amount of disorder changes the transition from the KT-type into that of non-KT-type.

  15. A two-dimensional algebraic quantum liquid produced by an atomic simulator of the quantum Lifshitz model.

    Science.gov (United States)

    Po, Hoi Chun; Zhou, Qi

    2015-08-13

    Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.

  16. Metastability of the Two-Dimensional Blume-Capel Model with Zero Chemical Potential and Small Magnetic Field

    Science.gov (United States)

    Landim, C.; Lemire, P.

    2016-07-01

    We consider the two-dimensional Blume-Capel model with zero chemical potential and small magnetic field evolving on a large but finite torus. We obtain sharp estimates for the transition time, we characterize the set of critical configurations, and we prove the metastable behavior of the dynamics as the temperature vanishes.

  17. Improved energy extrapolation with infinite projected entangled-pair states applied to the two-dimensional Hubbard model

    NARCIS (Netherlands)

    Corboz, P.

    2016-01-01

    An infinite projected entangled-pair state (iPEPS) is a variational tensor network ansatz for two-dimensional wave functions in the thermodynamic limit where the accuracy can be systematically controlled by the bond dimension D. We show that for the doped Hubbard model in the strongly correlated reg

  18. Application of two-dimensional infrared spectroscopy to benchmark models for the amide I band of proteins

    NARCIS (Netherlands)

    Bondarenko, Anna S.; Jansen, Thomas L. C.

    2015-01-01

    In this paper, we present a novel benchmarking method for validating the modelling of vibrational spectra for the amide I region of proteins. We use the linear absorption spectra and two-dimensional infrared spectra of four experimentally well-studied proteins as a reference and test nine combinatio

  19. Two-dimensional vertical moisture-pressure dynamics above groundwater waves: Sand flume experiments and modelling

    Science.gov (United States)

    Shoushtari, Seyed Mohammad Hossein Jazayeri; Cartwright, Nick; Perrochet, Pierre; Nielsen, Peter

    2017-01-01

    This paper presents a new laboratory dataset on the moisture-pressure relationship above a dispersive groundwater wave in a two-dimensional vertical unconfined sand flume aquifer driven by simple harmonic forcing. A total of five experiments were conducted in which all experimental parameters were kept constant except for the oscillation period, which ranged from 268 s to 2449 s between tests. Moisture content and suction head sensor pairings were co-located at two locations in the unsaturated zone both approximately 0.2 m above the mean watertable elevation and respectively 0.3 m and 0.75 m from the driving head boundary. For all oscillation periods except for the shortest (T = 268s), the formation of a hysteretic moisture-pressure scanning loop was observed. Consistent with the decay of the saturated zone groundwater wave, the size of the observed moisture-pressure scanning loops decayed with increasing distance landward and the decay rate is larger for the shorter oscillation periods. At the shortest period (T = 268s), the observed moisture-pressure relationship was observed to be non-hysteretic but with a capillary capacity that differs from that of the static equilibrium wetting and drying curves. This finding is consistent with observations from existing one-dimensional vertical sand column experiments. The relative damping of the moisture content with distance landward is higher than that for the suction head consistent with the fact that transmission of pressure through a porous medium occurs more readily than mass transfer. This is further supported by the fact that observed phase lags for the unsaturated zone variables (i.e. suction head and moisture content) relative to the driving head are greater than the saturated zone variables (i.e. piezometric head). Harmonic analysis of the data reveals no observable generation of higher harmonics in either moisture or pressure despite the strongly non-linear relationship between the two. In addition, a phase lag

  20. Solutions of the Two-Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms

    Directory of Open Access Journals (Sweden)

    2015-12-01

    Full Text Available Numerical results for ground-state and excited-state properties (energies, double occupancies, and Matsubara-axis self-energies of the single-orbital Hubbard model on a two-dimensional square lattice are presented, in order to provide an assessment of our ability to compute accurate results in the thermodynamic limit. Many methods are employed, including auxiliary-field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed-node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock methods. Comparison of results obtained by different methods allows for the identification of uncertainties and systematic errors. The importance of extrapolation to converged thermodynamic-limit values is emphasized. Cases where agreement between different methods is obtained establish benchmark results that may be useful in the validation of new approaches and the improvement of existing methods.

  1. Two dimensional modelling of flood flows and suspended sedimenttransport: the case of the Brenta River, Veneto (Italy

    Directory of Open Access Journals (Sweden)

    P. Martini

    2004-01-01

    Full Text Available The paper presents a numerical model for the simulation of flood waves and suspended sediment transport in a lowland river basin of North Eastern Italy. The two dimensional depth integrated momentum and continuity equations are modified to take into account the bottom irregularities that strongly affect the hydrodynamics in partially dry areas, as for example, in the first stages of an inundation process or in tidal flow. The set of equations are solved with a standard Galerkin finite element method using a semi-implicit numerical scheme where the effects of both the small channel network and the regulation devices on the flood wave propagation are accounted for. Transport of suspended sediment and bed evolution are coupled with the hydrodynamics using an appropriate form of the advection-dispersion equation and Exner's equation. Applications to a case study are presented in which the effects of extreme flooding on the Brenta River (Italy are examined. Urban and rural flood risk areas are identified and the effects of a alleviating action based on a diversion channel flowing into Venice Lagoon are simulated. The results show that this solution strongly reduces the flood risk in the downstream areas and can provide an important source of sediment for the Venice Lagoon. Finally, preliminary results of the sediment dispersion due to currents and waves in the Venice Lagoon are presented.

  2. Construction of two-dimensional quantum field models through Longo-Witten endomorphisms

    CERN Document Server

    Tanimoto, Yoh

    2013-01-01

    We present a procedure to construct families of local, massive and interacting Haag-Kastler nets on the two-dimensional spacetime through an operator-algebraic method. An existence proof of local observable is given without relying on modular nuclearity. By a similar technique, another family of wedge-local nets is constructed using certain endomorphisms of conformal nets recently studied by Longo and Witten.

  3. Graphene as a Prototypical Model for Two-Dimensional Continuous Mechanics

    Directory of Open Access Journals (Sweden)

    Philippe Lambin

    2017-08-01

    Full Text Available This paper reviews a few problems where continuous-medium theory specialized to two-dimensional media provides a qualitatively correct picture of the mechanical behavior of graphene. A critical analysis of the parameters involved is given. Among other results, a simple mathematical description of a folded graphene sheet is proposed. It is also shown how the graphene–graphene adhesion interaction is related to the cleavage energy of graphite and its C 33 bulk elastic constant.

  4. An immersed interface method for two-dimensional modelling of stratified flow in pipes

    OpenAIRE

    Berthelsen, Petter Andreas

    2004-01-01

    This thesis deals with the construction of a numerical method for solving two-dimensional elliptic interface problems, such as fully developed stratified flow in pipes. Interface problems are characterized by its non-smooth and often discontinuous behaviour along a sharp boundary separating the fluids or other materials. Classical numerical schemes are not suitable for these problems due to the irregular geometry of the interface. Standard finite difference discretization across the interface...

  5. Dynamics of kinks in one- and two-dimensional hyperbolic models with quasidiscrete nonlinearities.

    Science.gov (United States)

    Rotstein, H G; Mitkov, I; Zhabotinsky, A M; Epstein, I R

    2001-06-01

    We study the evolution of fronts in the Klein-Gordon equation when the nonlinear term is inhomogeneous. Extending previous works on homogeneous nonlinear terms, we describe the derivation of an equation governing the front motion, which is strongly nonlinear, and, for the two-dimensional case, generalizes the damped Born-Infeld equation. We study the motion of one- and two-dimensional fronts finding a much richer dynamics than in the homogeneous system case, leading, in most cases, to the stabilization of one phase inside the other. For a one-dimensional front, the function describing the inhomogeneity of the nonlinear term acts as a "potential function" for the motion of the front, i.e., a front initially placed between two of its local maxima asymptotically approaches the intervening minimum. Two-dimensional fronts, with radial symmetry and without dissipation can either shrink to a point in finite time, grow unboundedly, or their radius can oscillate, depending on the initial conditions. When dissipation effects are present, the oscillations either decay spirally or not depending on the value of the damping dissipation parameter. For fronts with a more general shape, we present numerical simulations showing the same behavior.

  6. A two-dimensional model of the plasmasphere - Refilling time constants

    Science.gov (United States)

    Rasmussen, Craig E.; Guiter, Steven M.; Thomas, Steven G.

    1993-01-01

    A 2D model of the plasmasphere has been developed to study the temporal evolution of plasma density in the equatorial plane of the magnetosphere. This model includes the supply and loss of hydrogen ions due to ionosphere-magnetosphere coupling as well as the effects of E x B convection. A parametric model describing the required coupling fluxes has been developed which utilizes empirical models of the neutral atmosphere, the ionosphere and the saturated plasmasphere. The plasmaspheric model has been used to examine the time it takes for the plasmasphere to refill after it has been depleted by a magnetic storm. The time it takes for the plasmasphere to reach 90 percent of its equilibrium level ranges from 3 days at L = 3 during solar minimum to as high as 100 days at L = 5 during solar maximum. Refilling is also dependent on the month of the year, with refilling requiring a longer period of time at solar maximum during June than during December for L greater than 3.2.

  7. Controlling Feynman diagrammatic expansions: Physical nature of the pseudogap in the two-dimensional Hubbard model

    Science.gov (United States)

    Wu, Wei; Ferrero, Michel; Georges, Antoine; Kozik, Evgeny

    2017-07-01

    We introduce a method for summing Feynman's perturbation series based on diagrammatic Monte Carlo that significantly improves its convergence properties. This allows us to investigate in a controllable manner the pseudogap regime of the Hubbard model and to study the nodal/antinodal dichotomy at low doping and intermediate coupling. Marked differences from the weak-coupling scenario are manifest, such as a higher degree of incoherence at the antinodes than at the "hot spots". Our results show that the pseudogap and reduction of quasiparticle coherence at the antinode is due to antiferromagnetic spin correlations centered around the commensurate (π ,π ) wave vector. In contrast, the dominant source of scattering at the node is associated with incommensurate momentum transfer. Umklapp scattering is found to play a key role in the nodal/antinodal dichotomy.

  8. [Characterization of aromatic hydrocarbons in heavy gas oil using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry].

    Science.gov (United States)

    Guo, Kun; Zhou, Jian; Liu, Zelong

    2012-02-01

    An analytical method for separating and identifying the aromatic hydrocarbons in heavy gas oil using comprehensive two-dimensional gas chromatography (GC x GC) coupled to time-of-flight mass spectrometry (TOF MS) was established. The two-dimensional distribution by ring number of the aromatic hydrocarbons was obtained. Besides phenanthrene and methyl-phenanthrene, many other polycyclic aromatic hydrocarbons (PAHs) such as pyrene and benzo [a] anthracene were identified by using the retention times, standard mass spectra or literature reports. The method was successfully applied to the hydrotreating process of heavy gas oil and the hydrotreated products of phenanthrene, pyrene were identified. This method provided technical support for the characterization of aromatic hydrocarbons in heavy gas oil and the investigation of hydrogenation mechanism of polycyclic aromatic hydrocarbons. Compared with the conventional method, gas chromatography coupled to mass spectrometry (GC-MS), the GC x GC-TOF MS method illustrated the obvious advantages for heavy gas oil analysis.

  9. Vortex solitons in two-dimensional spin-orbit coupled Bose-Einstein condensates: effects of the Rashba-Dresselhaus coupling and the Zeeman splitting

    CERN Document Server

    Sakaguchi, Hidetsugu; Malomed, Boris A

    2016-01-01

    We present an analysis of two-dimensional (2D) matter-wave solitons, governed by the pseudo-spinor system of Gross-Pitaevskii equations with self- and cross-attraction, which includes the spin-orbit coupling (SOC) in the general Rashba-Dresselhaus form, and, separately, the Rashba coupling and the Zeeman splitting. Families of semi-vortex (SV) and mixed-mode (MM) solitons are constructed, which exist and are stable in free space, as the SOC terms prevent the onset of the critical collapse and create the otherwise missing ground states in the form of the solitons. The Dresselhaus SOC produces a destructive effect on the vortex solitons, while the Zeeman term tends to convert the MM states into the SV ones, which eventually suffer delocalization. Existence domains and stability boundaries are identified for the soliton families. For physically relevant parameters of the SOC system, the number of atoms in the 2D solitons is limited by $\\sim 1.5\\times 10^{4}$. The results are obtained by means of combined analyti...

  10. Vortex solitons in two-dimensional spin-orbit coupled Bose-Einstein condensates: Effects of the Rashba-Dresselhaus coupling and Zeeman splitting

    Science.gov (United States)

    Sakaguchi, Hidetsugu; Sherman, E. Ya.; Malomed, Boris A.

    2016-09-01

    We present an analysis of two-dimensional (2D) matter-wave solitons, governed by the pseudospinor system of Gross-Pitaevskii equations with self- and cross attraction, which includes the spin-orbit coupling (SOC) in the general Rashba-Dresselhaus form, and, separately, the Rashba coupling and the Zeeman splitting. Families of semivortex (SV) and mixed-mode (MM) solitons are constructed, which exist and are stable in free space, as the SOC terms prevent the onset of the critical collapse and create the otherwise missing ground states in the form of the solitons. The Dresselhaus SOC produces a destructive effect on the vortex solitons, while the Zeeman term tends to convert the MM states into the SV ones, which eventually suffer delocalization. Existence domains and stability boundaries are identified for the soliton families. For physically relevant parameters of the SOC system, the number of atoms in the 2D solitons is limited by ˜1.5 ×104 . The results are obtained by means of combined analytical and numerical methods.

  11. Two-dimensional time-dependent model of the transport of minor species in the Venus night side upper atmosphere

    Science.gov (United States)

    Collet, Arnaud; Cox, Cédric; Gérard, Jean-Claude

    2010-12-01

    We present a numerical tool developed to quantify the role of processes controlling the spatio-temporal distribution of the NO ultraviolet and O2(Δg1) infrared nightglows in the Venus night side upper atmosphere, observed with the VIRTIS and SPICAV instruments on board Venus Express. This numerical tool consists in a two-dimensional chemical-transport time-dependent model which computes in a hypothetical rectangular solving domain the spatio-temporal distributions of the number densities of the four minor species at play in these two nightglow emissions. The coupled nonlinear system of the four partial differential equations, describing the spatio-temporal variations of the minor species, has been solved using a finite volume method with a forward Euler method for the time integration scheme. As an application, we have first simulated a time-constant supply of atoms through the upper boundary of the solving domain. The fluxes are inhomogeneous relative to its horizontal direction, in order to simulate regions of enhanced downward flow of oxygen and nitrogen giving rise to NO and O 2 brightening. Given that these two emissions show large time variations, we have also simulated a time-dependent downward flux of O and N atoms. It results from these simulations that the lack of correlation between the NO and O2(Δg1) nightglows largely result from to the coupling between horizontal and vertical transport processes and the very different chemical lifetimes of the two species. In particular, we have quantified the role of each process generating spatio-temporal de-correlations between the NO and O2(Δg1) nightglows.

  12. Disordered loops in the two-dimensional antiferromagnetic spin-fermion model

    Energy Technology Data Exchange (ETDEWEB)

    Enss, T. [CNR-INFM-SMC Center and Dipartimento di Fisica, Universita di Roma ' La Sapienza' , P.le A. Moro 5, 00185 Roma (Italy)], E-mail: tilman.enss@gmail.com; Caprara, S.; Castellani, C.; Di Castro, C.; Grilli, M. [CNR-INFM-SMC Center and Dipartimento di Fisica, Universita di Roma ' La Sapienza' , P.le A. Moro 5, 00185 Roma (Italy)

    2008-06-01

    The spin-fermion model has long been used to describe the quantum-critical behavior of 2d electron systems near an antiferromagnetic (AFM) instability. Recently, the standard procedure to integrate out the fermions and obtain an effective action for spin waves has been questioned in the clean case. We show that, in the presence of disorder, the single fermion loops display two crossover scales: upon lowering the energy, the singularities of the clean fermionic loops are first cut off, but below a second scale new singularities arise that lead again to marginal scaling. In addition, impurity lines between different fermion loops generate new relevant couplings which dominate at low energies. We outline a non-linear {sigma} model formulation of the single-loop problem, which allows to control the higher singularities and provides an effective model in terms of low-energy diffusive as well as spin modes.

  13. Numerical model for two-dimensional hydrodynamics and energy transport. [VECTRA code

    Energy Technology Data Exchange (ETDEWEB)

    Trent, D.S.

    1973-06-01

    The theoretical basis and computational procedure of the VECTRA computer program are presented. VECTRA (Vorticity-Energy Code for TRansport Analysis) is designed for applying numerical simulation to a broad range of intake/discharge flows in conjunction with power plant hydrological evaluation. The code computational procedure is based on finite-difference approximation of the vorticity-stream function partial differential equations which govern steady flow momentum transport of two-dimensional, incompressible, viscous fluids in conjunction with the transport of heat and other constituents.

  14. Modeling A.C. Electronic Transport through a Two-Dimensional Quantum Point Contact

    Energy Technology Data Exchange (ETDEWEB)

    Aronov, I.E.; Beletskii, N.N.; Berman, G.P.; Campbell, D.K.; Doolen, G.D.; Dudiy, S.V.

    1998-12-07

    We present the results on the a.c. transport of electrons moving through a two-dimensional (2D) semiconductor quantum point contact (QPC). We concentrate our attention on the characteristic properties of the high frequency admittance ({omega}{approximately}0 - 50 GHz), and on the oscillations of the admittance in the vicinity of the separatrix (when a channel opens or closes), in presence of the relaxation effects. The experimental verification of such oscillations in the admittance would be a strong confirmation of the semi-classical approach to the a.c. transport in a QPC, in the separatrix region.

  15. Modelling and design of complete photonic band gaps in two-dimensional photonic crystals

    Indian Academy of Sciences (India)

    Yogita Kalra; R K Sinha

    2008-01-01

    In this paper, we investigate the existence and variation of complete photonic band gap size with the introduction of asymmetry in the constituent dielectric rods with honeycomb lattices in two-dimensional photonic crystals (PhC) using the plane-wave expansion (PWE) method. Two examples, one consisting of elliptical rods and the other comprising of rectangular rods in honeycomb lattices are considered with a view to estimate the design parameters for maximizing the complete photonic band gap. Further, it has been shown that complete photonic band gap size changes with the variation in the orientation angle of the constituent dielectric rods.

  16. A discontinuous Galerkin method for two-dimensional PDE models of Asian options

    Science.gov (United States)

    Hozman, J.; Tichý, T.; Cvejnová, D.

    2016-06-01

    In our previous research we have focused on the problem of plain vanilla option valuation using discontinuous Galerkin method for numerical PDE solution. Here we extend a simple one-dimensional problem into two-dimensional one and design a scheme for valuation of Asian options, i.e. options with payoff depending on the average of prices collected over prespecified horizon. The algorithm is based on the approach combining the advantages of the finite element methods together with the piecewise polynomial generally discontinuous approximations. Finally, an illustrative example using DAX option market data is provided.

  17. An efficient two-dimensional ALE modelling and experimental validation for pulsed laser-matter interaction

    Science.gov (United States)

    Zhao, Qiang; Dong, Zhiwei

    2016-11-01

    We have developed two-dimensional Arbitrary Lagrangian Eulerian (ALE) code which is used to study the physical processes, the plasma absorption, the crater profile, and the temperature distribution on metallic target and below the surface. The ALE method overcomes problems with Lagrangian moving mesh distortion by mesh smoothing and conservative quantities remapping from Lagrangian mesh to smoothed one. The results of numerical simulation of pulsed laser ablation are presented. The study presents particular interest for the analysis of experimental results obtained during pulsed laser ablation.

  18. Modeling strong motions produced by earthquakes with two-dimensional numerical codes

    OpenAIRE

    Helmberger, Donald V.; Vidale, John E.

    1988-01-01

    We present a scheme for generating synthetic point-source seismograms for shear dislocation sources using line source (two-dimensional) theory. It is based on expanding the complete three-dimensional solution of the wave equation expressed in cylindrical coordinates in an asymptotic form which provides for the separation of the motions into SH and P-SV systems. We evaluate the equations of motion with the aid of the Cagniard-de Hoop technique and derive close-formed expressions appropriate fo...

  19. Spin-Orbit Splitting in Semiconductor Quantum Dots with a Two-Dimensional Ring Model

    Institute of Scientific and Technical Information of China (English)

    FENG Jun-Sheng; LIU Zheng

    2009-01-01

    We present a theoretical study of the energy levels with two-dimensional ring confining potential in the presence of the Rashba spin-orbit interaction.The features of some low-lying states in various strengths of the Rashba spin-orbit interaction are investigated.The Rashba spin-orbit splitting can also be influenced by the width of the potential barrier.The computed results show that the spin-polarized electronic states can be more easily achieved in a weakly confined dot when the confinement strength for the Rashba spin-orbit interaction is larger than a critical value.

  20. Modeling of pressure sensors based on two-dimensional photonic crystals

    Institute of Scientific and Technical Information of China (English)

    Xuehui XIONG; Ping LU; Deming LIU

    2009-01-01

    A pressure sensor based on the two-dimensional photonic crystal (2D PC) has been proposed. Under the condition of different pressure, the photonic band gap of the sensor has been studied by means of the plane wave expansion method (PWM). The results show that there is a good linear relation between the cutoff wavelength and the pressure. Apart from being easily implemented, the presented 2D PC pressure sensor holds many characteristics such as high-pressure sensitivity and convenience in achieving demanded pressure range.

  1. Two-dimensional modelling of overwash at Santa Rosa Island during Hurricane Ivan

    Science.gov (United States)

    McCall, R. T.; van Thiel de Vries, J. S. M.; Roelvink, J. A.; van Dongeren, A. R.; Thompson, D. M.; Plant, N. G.

    2009-04-01

    Approximately 10% of the world's coastline consists of low-lying barrier coasts, which are susceptible to coastal flooding, dune overwash and breaching. Although several numerical cross shore models exist to calculate beach and dune profile change during storms, overwash and breaching are not necessarily incorporated. Additionally, these models assume longshore uniformity and therefore do not include longshore variation in for instance dune height, shoreline angle and wave conditions. In order to simulate overwash on a barrier island we use a new numerical model for the nearshore and coast called XBeach (Roelvink et al., ICCE 2008). This process-based and time dependent model solves coupled short and long wave propagation, sediment transport and morphology in 2DH. The model has a robust numerical scheme, allowing it to simulate flooding and drying, thereby removing the need for separate dry and wet domains and procedures. XBeach is used to model a section of Santa Rosa Island, Florida, during Hurricane Ivan in 2004. This island was heavily overwashed during the hurricane and breached in one location. The model is set-up using high resolution airborne LIDAR altimetry and bathymetry data and forced using surge and wave data from larger scale numerical models. The modelled final bed elevation is compared to airborne LIDAR data acquired three days after the storm. The results show that XBeach is capable of simulating the complex hydrodynamics that occur during extreme overwash events. It is shown that the model can recreate the morphological developments that occurred on the island during the storm and that the model has considerable quantitative skill in predicting the final bed elevation.

  2. Validation and application of a two-dimensional model to simulate soil salt transport under mulched drip irrigation

    Science.gov (United States)

    Jiao, Huiqing; Zhao, Chengyi; Sheng, Yu; Chen, Yan; Shi, Jianchu; Li, Baoguo

    2017-04-01

    Water shortage and soil salinization increasingly become the main constraints for sustainable development of agriculture in Southern Xinjiang, China. Mulched drip irrigation, as a high-efficient water-saving irrigation method, has been widely applied in Southern Xinjiang for cotton production. In order to analyze the reasonability of describing the three-dimensional soil water and salt transport processes under mulched drip irrigation with a relatively simple two-dimensional model, a field experiment was conducted from 2007 to 2015 at Aksu of Southern Xinjiang, and soil water and salt transport processes were simulated through the three-dimensional and two-dimensional models based on COMSOL. Obvious differences were found between three-dimensional and two-dimensional simulations for soil water flow within the early 12 h of irrigation event and for soil salt transport in the area within 15 cm away from drip tubes during the whole irrigation event. The soil water and salt contents simulated by the two-dimensional model, however, agreed well with the mean values between two adjacent emitters simulated by the three-dimensional model, and also coincided with the measurements as corresponding RMSE less than 0.037 cm3 cm-3 and 1.80 g kg-1, indicating that the two-dimensional model was reliable for field irrigation management. Subsequently, the two-dimensional model was applied to simulate the dynamics of soil salinity for five numerical situations and for a widely adopted irrigation pattern in Southern Xinjiang (about 350 mm through mulched drip irrigation during growing season of cotton and total 400 mm through flooding irrigations before sowing and after harvesting). The simulation results indicated that the contribution of transpiration to salt accumulation in root layer was about 75% under mulched drip irrigation. Moreover, flooding irrigations before sowing and after harvesting were of great importance for salt leaching of arable layer, especially in bare strip where

  3. ANALYSIS OF WATER QUALITY IN SHALLOW LAKES WITH A TWO-DIMENSIONAL FLOW-SEDIMENT MODEL

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The governing equation for sediment pollutions was derived based on the turbulent diffusion of pollutants in shallow lakes. Coupled with shallow water equations, a depth-averaged 2-D flow and water quality model was developed. By means of the conservation law, a proposed differential equation for the change of sediment pollutants was linked to the 2-D equations. Under the framework of the finite volume method, the Osher approximate Riemann solver was employed to solve the equations. An analytical resolution was used to examine the model capabilities. Simulated results matched the exact solutions especially well. As an example, the simulation of CODMn in the Wuli Lake, a part of the Taihu lake, was conducted, which led to reasonable results. This study provides a new approach and a practical tool for the simulation of flow and water quality in shallow lakes.

  4. Validating two-dimensional leadership models on three-dimensionally structured fish schools

    Science.gov (United States)

    Nagy, Máté; Holbrook, Robert I.; Biro, Dora; Burt de Perera, Theresa

    2017-01-01

    Identifying leader–follower interactions is crucial for understanding how a group decides where or when to move, and how this information is transferred between members. Although many animal groups have a three-dimensional structure, previous studies investigating leader–follower interactions have often ignored vertical information. This raises the question of whether commonly used two-dimensional leader–follower analyses can be used justifiably on groups that interact in three dimensions. To address this, we quantified the individual movements of banded tetra fish (Astyanax mexicanus) within shoals by computing the three-dimensional trajectories of all individuals using a stereo-camera technique. We used these data firstly to identify and compare leader–follower interactions in two and three dimensions, and secondly to analyse leadership with respect to an individual's spatial position in three dimensions. We show that for 95% of all pairwise interactions leadership identified through two-dimensional analysis matches that identified through three-dimensional analysis, and we reveal that fish attend to the same shoalmates for vertical information as they do for horizontal information. Our results therefore highlight that three-dimensional analyses are not always required to identify leader–follower relationships in species that move freely in three dimensions. We discuss our results in terms of the importance of taking species' sensory capacities into account when studying interaction networks within groups.

  5. Coupling between Fano and Bragg bands in photonic band structure of two-dimensional metallic photonic structures

    CERN Document Server

    Markos, Peter

    2016-01-01

    Frequency and transmission spectrum of two-dimensional array of metallic rods is investigated numerically. Based on the recent analysis of the band structure of two-dimensional photonic crystal with dielectric rods [P. Marko\\v{s}, Phys. Rev. A 92 043814 (2015)] we identify two types of bands in the frequency spectrum: Bragg (P) bands resulting from a periodicity and Fano (F) bands which arise from Fano resonances associated with each of the cylinders within the periodic structure. It is shown that the existence of Fano band in a certain frequency range is manifested by a Fano resonance in the transmittance. In particular, we re-examine the symmetry properties of the H- polarized band structure in the frequency range where the spectrum consists of the localized modes associated with the single scatterer resonances and we explore process of formation of Fano bands by identifying individual terms in the expansion of the LCAO states. We demonstrate how the interplay between the two scattering mechanisms affects p...

  6. Second-order phase transition in two-dimensional cellular automaton model of traffic flow containing road sections

    Science.gov (United States)

    Shi, Xiao-Qiu; Wu, Yi-Qi; Li, Hong; Zhong, Rui

    2007-11-01

    Two-dimensional cellular automaton model has been broadly researched for traffic flow, as it reveals the main characteristics of the traffic networks in cities. Based on the BML models, a first-order phase transition occurs between the low-density moving phase in which all cars move at maximal speed and the high-density jammed phase in which all cars are stopped. However, it is not a physical result of a realistic system. We propose a new traffic rule in a two-dimensional traffic flow model containing road sections, which reflects that a car cannot enter into a road crossing if the road section in front of the crossing is occupied by another car. The simulation results reveal a second-order phase transition that separates the free flow phase from the jammed phase. In this way the system will not be entirely jammed (“don’t block the box” as in New York City).

  7. Dynamic Critical Behavior of Multi-Grid Monte Carlo for Two-Dimensional Nonlinear $\\sigma$-Models

    OpenAIRE

    Mana, Gustavo; Mendes, Tereza; Pelissetto, Andrea; Sokal, Alan D.

    1995-01-01

    We introduce a new and very convenient approach to multi-grid Monte Carlo (MGMC) algorithms for general nonlinear $\\sigma$-models: it is based on embedding an $XY$ model into the given $\\sigma$-model, and then updating the induced $XY$ model using a standard $XY$-model MGMC code. We study the dynamic critical behavior of this algorithm for the two-dimensional $O(N)$ $\\sigma$-models with $N = 3,4,8$ and for the $SU(3)$ principal chiral model. We find that the dynamic critical exponent $z$ vari...

  8. Acoustic phonon-limited resistivity of spin-orbit coupled two-dimensional electron gas: the deformation potential and piezoelectric scattering.

    Science.gov (United States)

    Biswas, Tutul; Ghosh, Tarun Kanti

    2013-01-23

    We study the interaction between electron and acoustic phonons in a Rashba spin-orbit coupled two-dimensional electron gas using Boltzmann transport theory. Both the deformation potential and piezoelectric scattering mechanisms are considered in the Bloch-Grüneisen (BG) regime as well as in the equipartition (EP) regime. The effect of the Rashba spin-orbit interaction on the temperature dependence of the resistivity in the BG and EP regimes is discussed. We find that the effective exponent of the temperature dependence of the resistivity in the BG regime decreases due to spin-orbit coupling.

  9. Suppression of Direct Spin Hall Currents in Two-Dimensional Electronic Systems with both Rashba and Dresselhaus Spin-Orbit Couplings

    Institute of Scientific and Technical Information of China (English)

    XIONG Jian-Wen; HU Liang-Bin; ZHANG Zhen-Xi

    2006-01-01

    @@ Based on the Heisenberg equations of motion for the electron orbital and spin degrees of freedom in two-dimensional electronic systems with both Rashba and Dresselhaus spin-orbit couplings, we show that an ac electric field can cause an ac spin Hall current in such a system. In contrast to some previous theoretical prediction, the spin Hall current will be suppressed completely in the dc limit. We argue that the suppression of dc spin Hall currents in such a system is actually a much natural result of the dynamic spin evolution due to the combined action of a dc external electric field and the intrinsic spin-orbit coupling.

  10. Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior

    Science.gov (United States)

    Brambleby, J.; Goddard, P. A.; Singleton, J.; Jaime, M.; Lancaster, T.; Huang, L.; Wosnitza, J.; Topping, C. V.; Carreiro, K. E.; Tran, H. E.; Manson, Z. E.; Manson, J. L.

    2017-01-01

    We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.

  11. A two-dimensional threshold voltage analytical model for metal-gate/high-k/SiO2/Si stacked MOSFETs

    Institute of Scientific and Technical Information of China (English)

    Ma Fei; Liu Hong-Xia; Fan Ji-Bin; Wang Shu-Long

    2012-01-01

    In this paper the influences of the metal-gate and high-k/SiO2/Si stacked structure on the metal-oxidesemiconductor field-effect transistor (MOSFET) axe investigated.The flat-band voltage is revised by considering the influences of stacked structure and metal-semiconductor work function fluctuation. The two-dimensional Poisson's equation of potential distribution is presented.A threshold voltage analytical model for metal-gate/high-k/SiO2/Si stacked MOSFETs is developed by solving these Poisson's equations using the boundary conditions.The model is verified by a two-dimensional device simulator,which provides the basic design guidance for metal-gate/high-k/SiO2/Si stacked MOSFETs.

  12. Two-dimensional modelling of benzene transport and biodegradation in a laboratory-scale aquifer.

    Science.gov (United States)

    Choi, N C; Choi, J W; Kim, S B; Park, S J; Kim, D J

    2009-01-01

    In this study biodegradation of aqueous benzene during transport in a laboratory-scale aquifer model was investigated by conducting a 2-D plume test and numerical modelling. Benzene biodegradation and transport was simulated with the 2-D numerical model developed for solute transport coupled with a Haldane-Andrews type function for inclusion of an inhibition constant which is effective for high concentrations. Experimental data revealed that in the early stages the benzene plume showed a rather clear shape but lost its shape with increased travel time. The mass recoveries of benzene at 9, 16, and 22 h were 37, 13 and 8%, respectively, showing that a significant mass reduction of aqueous benzene occurred in the model aquifer. The major processes responsible for the mass reduction were biodegradation and irreversible sorption. The modelling results also indicated that the simulation based on the microbial parameters from the batch experiments slightly overestimated the mass reduction of benzene during transport. The sensitivity analysis demonstrated that the benzene plume was sensitive to the maximum specific growth rate and slightly sensitive to the half-saturation constant of benzene but almost insensitive to the Haldane inhibition constant. The insensitivity to the Haldane inhibition constant was due to the rapid decline of the benzene peak concentration by natural attenuation such as hydrodynamic dispersion and irreversible sorption. An analysis of the model simulation also indicated that the maximum specific growth rate was the key parameter controlling the plume behaviour, but its impact on the plume was affected by competing parameter such as the irreversible sorption rate coefficient.

  13. Two-grain nanoindentation using the quasicontinuum method: Two-dimensional model approach

    Energy Technology Data Exchange (ETDEWEB)

    Iglesias, Rodrigo A. [Instituto de Investigaciones en Fisicoquimica de Cordoba (INFIQC), Consejo Nacional de Investigaciones, Cientificas y Tecnicas (CONICET), Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Edificio Integrador, Ciudad Universitaria, Cordoba, CP 5000 (Argentina)]. E-mail: riglesias@mail.fcq.unc.edu.ar; Leiva, Ezequiel P.M. [Instituto de Investigaciones en Fisicoquimica de Cordoba (INFIQC), Consejo Nacional de Investigaciones, Cientificas y Tecnicas (CONICET), Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Edificio Integrador, Ciudad Universitaria, Cordoba, CP 5000 (Argentina)

    2006-06-15

    The quasicontinuum method (two-dimensional) developed by Tadmor et al. [Tadmor EB, Ortiz M, Phillips R. Philos Mag 1996;73:1529] is applied to an indentation process taking account of the atomic structure of the indenter and the substrate subject to indentation. Slip vectors, dislocation nucleation and nanostructure formation are analyzed for different indenter materials (Ag, Cu and Pd) and indenter crystal orientations. Slip vectors near to the contact region show that, depending on the material and orientation of the indenter, plastic deformations occur either inside the indenter or the substrate. Long-range material deformations appear during the indentation or retraction of the indenter. All of these aspects mainly dictate the formation of nanoclusters or nanoholes on the substrate surface.

  14. Two-dimensional-lattice spin models with long-range antiferromagnetic interactions

    Science.gov (United States)

    Romano, S.

    1991-10-01

    We consider a classical system, consisting of m-component unit vectors (m=2,3), associated with a two-dimensional lattice \\{uk||k∈openZ2\\} and interacting via translationally and rotationally invariant antiferromagnetic pair potentials of the long-range form W=Wjk=ɛ||xj-xk||-puj.uk, p>2, where ɛ is a positive quantity, setting energy and temperature scales (i.e., T*=kBT/ɛ), and xk are the coordinates of the lattice sites. A spin-wave approach predicts orientational disorder (in the thermodynamic limit) at all finite temperatures and for all p>2 this agrees with available rigorous results for p>=4, whereas no such theorems are known in the literature when 22.

  15. Hydrodynamic limit for an evolutional model of two-dimensional Young diagrams

    CERN Document Server

    Funaki, Tadahisa

    2009-01-01

    We construct dynamics of two-dimensional Young diagrams, which are naturally associated with their grandcanonical ensembles, by allowing the creation and annihilation of unit squares located at the boundary of the diagrams. The grandcanonical ensembles, which were introduced by Vershik, are uniform measures under conditioning on their size (or equivalently, area). We then show that, as the averaged size of the diagrams diverges, the corresponding height variable converges to a solution of a certain non-linear partial differential equation under a proper hydrodynamic scaling. Furthermore, the stationary solution of the limit equation is identified with the so-called Vershik curve. We discuss both uniform and restricted uniform statistics for the Young diagrams.

  16. Two-dimensional structure in a generic model of triangular proteins and protein trimers.

    Science.gov (United States)

    Camp, Philip J; Duncan, Peter D

    2006-04-01

    Motivated by the diversity and complexity of two-dimensional (2D) crystals formed by triangular proteins and protein trimers, we have investigated the structures and phase behavior of hard-disk trimers. In order to mimic specific binding interactions, each trimer possesses an "attractive" disk which can interact with similar disks on other trimers via an attractive square-well potential. At low density and low temperature, the fluid phase mainly consists of tetramers, pentamers, or hexamers. Hexamers provide the structural motif for a high-density, low-temperature periodic solid phase, but we also identify a metastable periodic structure based on a tetramer motif. At high density there is a transition between orientationally ordered and disordered solid phases. The connections between simulated structures and those of 2D protein crystals--as seen in electron microscopy--are briefly discussed.

  17. Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems

    Science.gov (United States)

    Zhong, Jian-Qiang; Wang, Mengen; Akter, Nusnin; Kestell, John D.; Boscoboinik, Alejandro M.; Kim, Taejin; Stacchiola, Dario J.; Lu, Deyu; Boscoboinik, J. Anibal

    2017-07-01

    The confinement of noble gases on nanostructured surfaces, in contrast to bulk materials, at non-cryogenic temperatures represents a formidable challenge. In this work, individual Ar atoms are trapped at 300 K in nano-cages consisting of (alumino)silicate hexagonal prisms forming a two-dimensional array on a planar surface. The trapping of Ar atoms is detected in situ using synchrotron-based ambient pressure X-ray photoelectron spectroscopy. The atoms remain in the cages upon heating to 400 K. The trapping and release of Ar is studied combining surface science methods and density functional theory calculations. While the frameworks stay intact with the inclusion of Ar atoms, the permeability of gasses (for example, CO) through them is significantly affected, making these structures also interesting candidates for tunable atomic and molecular sieves. These findings enable the study of individually confined noble gas atoms using surface science methods, opening up new opportunities for fundamental research.

  18. Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems.

    Science.gov (United States)

    Zhong, Jian-Qiang; Wang, Mengen; Akter, Nusnin; Kestell, John D; Boscoboinik, Alejandro M; Kim, Taejin; Stacchiola, Dario J; Lu, Deyu; Boscoboinik, J Anibal

    2017-07-17

    The confinement of noble gases on nanostructured surfaces, in contrast to bulk materials, at non-cryogenic temperatures represents a formidable challenge. In this work, individual Ar atoms are trapped at 300 K in nano-cages consisting of (alumino)silicate hexagonal prisms forming a two-dimensional array on a planar surface. The trapping of Ar atoms is detected in situ using synchrotron-based ambient pressure X-ray photoelectron spectroscopy. The atoms remain in the cages upon heating to 400 K. The trapping and release of Ar is studied combining surface science methods and density functional theory calculations. While the frameworks stay intact with the inclusion of Ar atoms, the permeability of gasses (for example, CO) through them is significantly affected, making these structures also interesting candidates for tunable atomic and molecular sieves. These findings enable the study of individually confined noble gas atoms using surface science methods, opening up new opportunities for fundamental research.

  19. Superfluid-insulator transition in a disordered two-dimensional quantum rotor model with random on-site interactions

    Science.gov (United States)

    An, Taeyang; Cha, Min-Chul

    2013-03-01

    We study the superfluid-insulator quantum phase transition in a disordered two-dimensional quantum rotor model with random on-site interactions in the presence of particle-hole symmetry. Via worm-algorithm Monte Carlo calculations of superfluid density and compressibility, we find the dynamical critical exponent z ~ 1 . 13 (2) and the correlation length critical exponent 1 / ν ~ 1 . 1 (1) . These exponents suggest that the insulating phase is a incompressible Mott glass rather than a Bose glass.

  20. A Hybrid Support Vector Machines and Two-dimensional Risk Matrix Model for Supply Chain Risk Assessment

    OpenAIRE

    Fan Jiang; Junfei Chen

    2014-01-01

    In recent years, the supply chain managements have been paid more and more attention. The supply chain risk management is an important content for enterprises implementing supply chain management. Therefore, how to measure the risk of supply chain is quite important. In this study, a supply chain risk evaluation model based on support vector machines and two-dimensional risk matrix is proposed. The index system of supply chain risk assessment which includes 14 indices is established. The case...

  1. Exact field-driven interface dynamics in the two-dimensional stochastic Ising model with helicoidal boundary conditions

    OpenAIRE

    de Mendonça, J. Ricardo G.

    2012-01-01

    We investigate the interface dynamics of the two-dimensional stochastic Ising model in an external field under helicoidal boundary conditions. At sufficiently low temperatures and fields, the dynamics of the interface is described by an exactly solvable high-spin asymmetric quantum Hamiltonian that is the infinitesimal generator of the zero range process. Generally, the critical dynamics of the interface fluctuations is in the Kardar-Parisi-Zhang universality class of critical behavior. We re...

  2. Two-dimensional magnetic modeling of ferromagnetic materials by using a neural networks based hybrid approach

    Energy Technology Data Exchange (ETDEWEB)

    Cardelli, E.; Faba, A. [Department of Engineering, University of Perugia, Via G. Duranti 93, 06125 Perugia (Italy); Laudani, A.; Lozito, G.M.; Riganti Fulginei, F.; Salvini, A. [Department of Engineering, Roma Tre University, Via V. Volterra 62, 00146 Rome (Italy)

    2016-04-01

    This paper presents a hybrid neural network approach to model magnetic hysteresis at macro-magnetic scale. That approach aims to be coupled together with numerical treatments of magnetic hysteresis such as FEM numerical solvers of the Maxwell's equations in time domain, as in case of the non-linear dynamic analysis of electrical machines, and other similar devices, allowing a complete computer simulation with acceptable run times. The proposed Hybrid Neural System consists of four inputs representing the magnetic induction and magnetic field components at each time step and it is trained by 2D and scalar measurements performed on the magnetic material to be modeled. The magnetic induction B is assumed as entry point and the output of the Hybrid Neural System returns the predicted value of the field H at the same time step. Within the Hybrid Neural System, a suitably trained neural network is used for predicting the hysteretic behavior of the material to be modeled. Validations with experimental tests and simulations for symmetric, non-symmetric and minor loops are presented.

  3. A neural approach for the numerical modeling of two-dimensional magnetic hysteresis

    Science.gov (United States)

    Cardelli, E.; Faba, A.; Laudani, A.; Riganti Fulginei, F.; Salvini, A.

    2015-05-01

    This paper deals with a neural network approach to model magnetic hysteresis at macro-magnetic scale. Such approach to the problem seems promising in order to couple the numerical treatment of magnetic hysteresis to FEM numerical solvers of the Maxwell's equations in time domain, as in case of the non-linear dynamic analysis of electrical machines, and other similar devices, making possible a full computer simulation in a reasonable time. The neural system proposed consists of four inputs representing the magnetic field and the magnetic inductions components at each time step and it is trained by 2-d measurements performed on the magnetic material to be modeled. The magnetic induction B is assumed as entry point and the output of the neural system returns the predicted value of the field H at the same time step. A suitable partitioning of the neural system, described in the paper, makes the computing process rather fast. Validations with experimental tests and simulations for non-symmetric and minor loops are presented.

  4. The Research of Mobile phone Entrance Guard System Model based on the Encryption Two-dimensional Code

    Directory of Open Access Journals (Sweden)

    Chu Jianli

    2013-09-01

    Full Text Available This article designs a new mobile-phone entrance guard system, uses the encryption two-dimensional code for identity authentication. Different from other similar products in the market, this system does not rely on specialized mobile phone card or NFC (near field communication module. It can be directly realized through mobile-phone software, and it can be operated simple and safer. This article designs the whole system model, includes structure, function and workflow. It also analyzes and researches the main algorithms used in the system, which include security policy algorithm, encryption two-dimensional code algorithm and image recognition algorithm. Finally, it provides the solution method for the problem in the experimental simulation. It also evaluated and summarized the experimental results.

  5. Analysis of bandgap characteristics of two-dimensional periodic structures by using the source-model technique.

    Science.gov (United States)

    Ludwig, Alon; Leviatan, Yehuda

    2003-08-01

    We introduce a solution based on the source-model technique for periodic structures for the problem of electromagnetic scattering by a two-dimensional photonic bandgap crystal slab illuminated by a transverse-magnetic plane wave. The proposed technique takes advantage of the periodicity of the slab by solving the problem within the unit cell of the periodic structure. The results imply the existence of a frequency bandgap and provide a valuable insight into the relationship between the dimensions of a finite periodic structure and its frequency bandgap characteristics. A comparison shows a discrepancy between the frequency bandgap obtained for a very thick slab and the bandgap obtained by solving the corresponding two-dimensionally infinite periodic structure. The final part of the paper is devoted to explaining in detail this apparent discrepancy.

  6. Enhancement of acousto-optical coupling in two-dimensional air-slot phoxonic crystal cavities by utilizing surface acoustic waves

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Tian-Xue [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Wang, Yue-Sheng, E-mail: yswang@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Zhang, Chuanzeng [Department of Civil Engineering, University of Siegen, D-57068 Siegen (Germany)

    2017-01-30

    A phoxonic crystal is a periodically patterned material that can simultaneously localize optical and acoustic modes. The acousto-optical coupling in two-dimensional air-slot phoxonic crystal cavities is investigated numerically. The photons can be well confined in the slot owing to the large electric field discontinuity at the air/dielectric interfaces. Besides, the surface acoustic modes lead to the localization of the phonons near the air-slot. The high overlap of the photonic and phononic cavity modes near the slot results in a significant enhancement of the moving interface effect, and thus strengthens the total acousto-optical interaction. The results of two cavities with different slot widths show that the coupling strength is dependent on the slot width. It is expected to achieve a strong acousto-optical/optomechanical coupling in air-slot phoxonic crystal structures by utilizing surface acoustic modes. - Highlights: • Two-dimensional air-slot phoxonic crystal cavities which can confine simultaneously optical and acoustic waves are proposed. • The acoustic and optical waves are highly confined near/in the air-slot. • The high overlap of the photonic and phononic cavity modes significantly enhances the moving interface effect. • Different factors which affect the acousto-optical coupling are discussed.

  7. Accurate two-dimensional model of an arrayed-waveguide grating demultiplexer and optimal design based on the reciprocity theory.

    Science.gov (United States)

    Dai, Daoxin; He, Sailing

    2004-12-01

    An accurate two-dimensional (2D) model is introduced for the simulation of an arrayed-waveguide grating (AWG) demultiplexer by integrating the field distribution along the vertical direction. The equivalent 2D model has almost the same accuracy as the original three-dimensional model and is more accurate for the AWG considered here than the conventional 2D model based on the effective-index method. To further improve the computational efficiency, the reciprocity theory is applied to the optimal design of a flat-top AWG demultiplexer with a special input structure.

  8. Finite size scaling study of dynamical phase transitions in two dimensional models: ferromagnet, symmetric and non symmetric spin glasses

    Energy Technology Data Exchange (ETDEWEB)

    Neumann, A.U.; Derrida, B.

    1988-10-01

    We study the time evolution of two configurations submitted to the same thermal noise for several two dimensional models (Ising ferromagnet, symmetric spin glass, non symmetric spin glass). For all these models, we find a non zero critical temperature above which the two configurations always meet. Using finite size scaling ideas, we determine for these three models this dynamical phase transition and some of the critical exponents. For the ferromagnet, the transition T/sub c/ approx. = 2.25 coincides with the Curie temperature whereas for the two spin glass models +- J distribution of bonds) we obtain T/sub c/ approx. = 1.5-1.7.

  9. Two-dimensional liquid chromatography coupled to tandem mass spectrometry for vitamin D metabolite profiling including the C3-epimer-25-monohydroxyvitamin D3.

    Science.gov (United States)

    Mena-Bravo, A; Priego-Capote, F; Luque de Castro, M D

    2016-06-17

    A method based on automated on-line solid phase extraction coupled to two-dimensional liquid chromatography with tandem mass spectrometry detection (SPE-2DLC-MS/MS) is here reported for vitamin D metabolite profiling in human serum with absolute quantitation. Two-dimensional LC was configured with two complementary analytical columns, pentafluorophenyl (PFP) and C18 phases, for determination of 25 hydroxyvitamin D3 epimers and the resting bioactive metabolites of vitamin D (D3 and D2)-25-hydroxyvitamin D2, 1,25-dihydroxyvitamin D3, 1,25-dihydroxyvitamin D2 and 24,25-dihydroxyvitamin D3. Quantitative determination was supported on the use of a stable isotopic labelled internal standard for each analyte and the resulting method was validated by analysis of a standard reference material certified by the National Institute of Standards & Technology (NIST-972a) and 5 samples provided by the vitamin D External Quality Assurance Scheme (DEQAS). The limits of detection were between 9 and 90pg/mL for the eight analytes, and precision, expressed as relative standard deviation, was lower than 11.6%. Two-dimensional LC has shown to be the key to discriminate between 25 hydroxyvitamin D3 epimers in a quantitative analysis also involving dihydroxyvitamin D metabolites.

  10. Offline coupling of high-speed counter-current chromatography and gas chromatography/mass spectrometry generates a two-dimensional plot of toxaphene components.

    Science.gov (United States)

    Kapp, Thomas; Vetter, Walter

    2009-11-20

    High-speed counter-current chromatography (HSCCC), a separation technique based solely on the partitioning of solutes between two immiscible liquid phases, was applied for the fractionation of technical toxaphene, an organochlorine pesticide which consists of a complex mixture of structurally closely related compounds. A solvent system (n-hexane/methanol/water 34:24:1, v/v/v) was developed which allowed to separate compounds of technical toxaphene (CTTs) with excellent retention of the stationary phase (S(f) = 88%). Subsequent analysis of all HSCCC fractions by gas chromatography coupled to electron-capture negative ion mass spectrometry (GC/ECNI-MS) provided a wealth of information regarding separation characteristics of HSCCC and the composition of technical toxaphene. The visualization of the large amount of data obtained from the offline two-dimensional HSCCC-GC/ECNI-MS experiment was facilitated by the creation of a two-dimensional (2D) contour plot. The contour plot not only provided an excellent overview of the HSCCC separation progress, it also illustrated the differences in selectivity between HSCCC and GC. The results of this proof-of-concept study showed that the 2D chromatographic approach involving HSCCC facilitated the separation of CTTs that coelute in unidimensional GC. Furthermore, the creation of 2D contour plots may provide a useful means of enhancing data visualization for other offline two-dimensional separations.

  11. DNA sequencing by two-dimensional materials: As theoretical modeling meets experiments.

    Science.gov (United States)

    Liang, Lijun; Shen, Jia-Wei; Zhang, Zhisen; Wang, Qi

    2017-03-15

    Owing to their extraordinary electrical, chemical, optical, mechanical and structural properties, two-dimensional (2D) materials (mainly including graphene, boron nitride, MoS2 etc.) have stimulated exploding interests in sensor applications. 2D-material based nanoscale DNA sequencing is a single-molecule technique with revolutionary potential. In this paper, we review the methodology of DNA sequencing based on the measurements of ionic current, force peak, and transverse electrical currents etc. by 2D materials. The advantages and disadvantages of DNA sequencing by 2D materials are discussed. Besides the recent development of experiments, we will focus on the theoretical calculations of DNA sequencing, which have been played a critical role in the development of this field. Special emphasis will focus on the disagreements between experiments and theoretical calculations, and the explanations for the discrepancy will be highlighted. Finally, some new plausible sequencing methods from computational studies will be discussed, which may be applied in the realistic DNA sequencing experiments in future.

  12. Two-dimensional modeling and analysis of a nanometer transistor as a THz emitter

    Science.gov (United States)

    Rahmatallahpur, Sh.; Rostami, Ali

    2016-10-01

    In this paper, we report on the influences of quantum effects, electron exchange-correlation, Fermi velocity, gate to channel distance and viscosity on the plasma frequency and instability of the plasma waves in a nanometer transistor. By extending the analysis to two-dimensional case, allowing oblique wave propagation, including viscosity and departing from gradual channel approximation, we obtain a general analytical expression for dispersion relation, plasma frequency, and "increment." We found that, while the plasma frequency decreases with the electron exchange-correlation effect, it increases with quantum effects and Fermi velocity. It is shown that the spectrums of plasma waves are discrete both in longitudinal and lateral (transverse) direction. We also express the total radiated power in terms of transistor parameters especially the lateral dimension. Viscosity which is inherently presented in the structure and cannot be neglected, dramatically decrease the emitted power and set a lower limit on the length of transistor. We show that a nanometer transistor with a long width (a long lateral dimension) has advantages for the realization of practical terahertz emitters.

  13. Influences of spin accumulation on the intrinsic spin Hall effect in two dimensional electron gases with Rashba spin-orbit coupling

    OpenAIRE

    Shen, SQ; Ma, X.; Hu, L.; R. Tao

    2004-01-01

    In a two-dimensional electron gas with Rashba spin-orbit coupling, the external electric field may cause a spin Hall current in the direction perpendicular to the electric field. This effect was called the intrinsic spin Hall effect. In this paper, we investigate the influences of spin accumulation on this intrinsic spin Hall effect. We show that due to the existence of boundaries in a real sample, the spin Hall current generated by the intrinsic spin Hall effect will cause spin accumulation ...

  14. Modelling spatial trends in sorghum breeding field trials using a two-dimensional P-spline mixed model.

    Science.gov (United States)

    Velazco, Julio G; Rodríguez-Álvarez, María Xosé; Boer, Martin P; Jordan, David R; Eilers, Paul H C; Malosetti, Marcos; van Eeuwijk, Fred A

    2017-07-01

    A flexible and user-friendly spatial method called SpATS performed comparably to more elaborate and trial-specific spatial models in a series of sorghum breeding trials. Adjustment for spatial trends in plant breeding field trials is essential for efficient evaluation and selection of genotypes. Current mixed model methods of spatial analysis are based on a multi-step modelling process where global and local trends are fitted after trying several candidate spatial models. This paper reports the application of a novel spatial method that accounts for all types of continuous field variation in a single modelling step by fitting a smooth surface. The method uses two-dimensional P-splines with anisotropic smoothing formulated in the mixed model framework, referred to as SpATS model. We applied this methodology to a series of large and partially replicated sorghum breeding trials. The new model was assessed in comparison with the more elaborate standard spatial models that use autoregressive correlation of residuals. The improvements in precision and the predictions of genotypic values produced by the SpATS model were equivalent to those obtained using the best fitting standard spatial models for each trial. One advantage of the approach with SpATS is that all patterns of spatial trend and genetic effects were modelled simultaneously by fitting a single model. Furthermore, we used a flexible model to adequately adjust for field trends. This strategy reduces potential parameter identification problems and simplifies the model selection process. Therefore, the new method should be considered as an efficient and easy-to-use alternative for routine analyses of plant breeding trials.

  15. A Semi-implicit Numerical Scheme for a Two-dimensional, Three-field Thermo-Hydraulic Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Moonkyu; Jeong, Jaejoon

    2007-07-15

    The behavior of two-phase flow is modeled, depending on the purpose, by either homogeneous model, drift flux model, or separated flow model, Among these model, in the separated flow model, the behavior of each flow phase is modeled by its own governing equation, together with the interphase models which describe the thermal and mechanical interactions between the phases involved. In this study, a semi-implicit numerical scheme for two-dimensional, transient, two-fluid, three-field is derived. The work is an extension to the previous study for the staggered, semi-implicit numerical scheme in one-dimensional geometry (KAERI/TR-3239/2006). The two-dimensional extension is performed by specifying a relevant governing equation set and applying the related finite differencing method. The procedure for employing the semi-implicit scheme is also described in detail. Verifications are performed for a 2-dimensional vertical plate for a single-phase and two-phase flows. The calculations verify the mass and energy conservations. The symmetric flow behavior, for the verification problem, also confirms the momentum conservation of the numerical scheme.

  16. A Hybrid Support Vector Machines and Two-dimensional Risk Matrix Model for Supply Chain Risk Assessment

    Directory of Open Access Journals (Sweden)

    Fan Jiang

    2014-03-01

    Full Text Available In recent years, the supply chain managements have been paid more and more attention. The supply chain risk management is an important content for enterprises implementing supply chain management. Therefore, how to measure the risk of supply chain is quite important. In this study, a supply chain risk evaluation model based on support vector machines and two-dimensional risk matrix is proposed. The index system of supply chain risk assessment which includes 14 indices is established. The case study shows that the proposed model is reasonable, effective and it can provide an important reference for supply chain risk management.

  17. Effects of engine emissions from high-speed civil transport aircraft: A two-dimensional modeling study, part 2

    Science.gov (United States)

    Ko, Malcolm K. W.; Weisenstein, Debra K.; Sze, Nein Dak; Shia, Run-Lie; Rodriguez, Jose M.; Heisey, Curtis

    1991-01-01

    The AER two-dimensional chemistry-transport model is used to study the effect of supersonic and subsonic aircraft operation in the 2010 atmosphere on stratospheric ozone (O3). The results show that: (1) the calculated O3 response is smaller in the 2010 atmosphere compared to previous calculations performed in the 1980 atmosphere; (2) with the emissions provided, the calculated decrease in O3 column is less than 1 percent; and (3) the effect of model grid resolution on O3 response is small provided that the physics is not modified.

  18. A two-dimensional model for gas mixing in the upper dilute zone of a circulating fluidized bed

    Energy Technology Data Exchange (ETDEWEB)

    Kruse, M.; Schoenfelder, H.; Werther, J. [Technical University of Hamburg-Harburg, Hamburg (Germany)

    1995-10-01

    A two-dimensional two-phase flow model for gas/solid flow and gas mixing in the upper zone of a circulating fluidized bed is described. Continuous functions are used to describe variations of local flow parameters horizontally and vertically. Numerical values of dispersion parameters and interfacial mass transfer coefficients are derived from the results of tracer gas mixing experiments. There is good agreement between calculated and measured tracer gas profiles in the upper dilute zone of the circulating fluidized bed. The model is applicable to calculation of chemical reactions in CFB risers. 37 refs., 26 figs., 3 tabs.

  19. Survivors of early childhood trauma: evaluating a two-dimensional diagnostic model of the impact of trauma and neglect

    Directory of Open Access Journals (Sweden)

    Marleen Wildschut

    2014-04-01

    Full Text Available Background: A two-dimensional diagnostic model for (complex trauma-related and personality disorders has been proposed to assess the severity and prognosis of the impact of early childhood trauma and emotional neglect. An important question that awaits empirical examination is whether a distinction between trauma-related disorders and personality disorders reflects reality when focusing on survivors of early childhood trauma. And, is a continuum of trauma diagnoses a correct assumption and, if yes, what does it look like? Objective: We describe the design of a cross-sectional cohort study evaluating this two-dimensional model of the impact of trauma and neglect. To provide the rationale of our study objectives, we review the existing literature on the impact of early childhood trauma and neglect on trauma-related disorders and personality disorders. Aims of the study are to: (1 quantify the two-dimensional model and test the relation with trauma and neglect; and (2 compare the two study groups. Method: A total of 200 consecutive patients referred to two specific treatment programs (100 from a personality disorder program and 100 from a trauma-related disorder program in the north of Holland will be included. Data are collected at the start of treatment. The assessments include all DSM-5 trauma-related and personality disorders, and general psychiatric symptoms, trauma history, and perceived emotional neglect. Discussion: The results will provide an evaluation of the model and an improvement of the understanding of the relationship between trauma-related disorders and personality disorders and early childhood trauma and emotional neglect. This may improve both diagnostic as well as indication procedures. We will discuss possible strengths and limitations of the design.

  20. Investigation of Efficient Turbulence Model for Two-Dimensional Nozzle Designed for Supersonic Cruise Using STAR-CCM+

    Directory of Open Access Journals (Sweden)

    Karthik Mummidisetti

    2013-08-01

    Full Text Available In the present work, investigation of various turbulence models has been carried out for predicting the efficient turbulence model for a two-dimensional nozzle designed for a supersonic cruise nozzle. Initially, a computational domain was created for a two-dimensional nozzle for a supersonic cruise, then, with an appropriate mesh size, various turbulence models has been used for simulations. The main objective of the present work is to determine the efficient turbulence model for nozzle designs. As till date, commercial software’s are implementing many advanced technique, the test of turbulence model is very much needed for today’s research. The results obtained from the computational approach were compared with experimental approach which was conducted in the Langley 16-Foot Transonic Tunnel at Mach numbers from 0.8 to 1.2 by NASA Langley Research Centre, Virginia. These supersonic cruise nozzles have a wide range of applications in designing Fighter jets and supersonic cruise aircraft's. The present work was conducted by using the commercial Computational Fluid Dynamics Software, STAR-CCM+. Initially, Nozzle at a free stream Mach number 0.9 was designed and all the initial and boundary conditions were calculated. From the results obtained in the present investigation, we can conclude that there was an excellent correlation between the experimental and computational data for K-Epsilon turbulence model.

  1. Simultaneous determination of bromate, chlorite and haloacetic acids by two-dimensional matrix elimination ion chromatography with coupled conventional and capillary columns.

    Science.gov (United States)

    Teh, Hui Boon; Li, Sam Fong Yau

    2015-02-27

    A new, highly sensitive and reliable two-dimensional matrix elimination ion chromatography (IC) method was developed for simultaneous detection of bromate, chlorite and five haloacetic acids. This method combined the conventional IC in first dimension with capillary IC in the second dimension coupled with suppressed conductivity detection. The first dimension utilizes a high capacity column to partially resolve matrix from target analytes. By optimizing the cut window, the target analytes were selectively cut and trapped in a trap column through the use of a six-port valve, while the separated matrix were diverted to waste. The trapped target analytes were delivered on to the capillary column for further separation and detection. Temperature programming was used to improve selectivity in second dimension column to obtain complete resolution of the target analytes. Compared to the performance of one-dimensional IC, the two-dimensional approach resulted in a significant increase in sensitivity for all target analytes with limit of detection ranging from 0.30 to 0.64μg/L and provided more reliable analysis due to second column confirmation. Good linearity was obtained for all the target analytes with correlation coefficients >0.998. The proposed method was successfully applied to the determination of oxyhalides and haloacetic acids in various matrices with recoveries ranging from 90 to 116% and RSD less than 6.1%. The method allows direct injection of samples and the use of columns with different selectivity, thus significantly reduces the level of false positive results. The method is fully automated and simple, making it practical for routine monitoring of water quality. The satisfactory results also demonstrated that the two-dimensional matrix elimination method coupled with capillary IC is a promising approach for detection of trace substances in complex matrices.

  2. Simple vibration modeling of structural fuzzy with continuous boundary by including two-dimensional spatial memory

    DEFF Research Database (Denmark)

    Friis, Lars; Ohlrich, Mogens

    2008-01-01

    -dimensional continuous boundary. Additionally, a simple method for determining the so-called equivalent coupling factor is presented. The validity of this method is demonstrated by numerical simulations of the vibration response of a master plate structure with fuzzy attachments. It is revealed that the method performs...

  3. One-dimensional lattices topologically equivalent to two-dimensional lattices within the context of the lattice gas model

    Science.gov (United States)

    Costanza, E. F.; Costanza, G.

    2016-10-01

    Continuum partial differential equations are obtained from a set of discrete stochastic evolution equations of both non-Markovian and Markovian processes and applied to the diffusion within the context of the lattice gas model. A procedure allowing to construct one-dimensional lattices that are topologically equivalent to two-dimensional lattices is described in detail in the case of a rectangular lattice. This example shows the general features that possess the procedure and extensions are also suggested in order to provide a wider insight in the present approach.

  4. A model of the two-dimensional quantum harmonic oscillator in an $AdS_3$ background

    CERN Document Server

    Frick, Rudolf

    2016-01-01

    In this paper we study a model of the two-dimensional quantum harmonic oscillator in a 3-dimensional anti-de Sitter background. We use a generalized Schr\\"odinger picture in which the analogs of the Schr\\"odinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the $AdS_3$ spacetime. In this picture, we have a metamorphosis of the Heisenberg's uncertainty relations.

  5. A model of the two-dimensional quantum harmonic oscillator in an AdS{sub 3} background

    Energy Technology Data Exchange (ETDEWEB)

    Frick, R. [Universitaet zu Koeln, Institut fuer Theoretische Physik, Cologne (Germany)

    2016-10-15

    In this paper we study a model of the two-dimensional quantum harmonic oscillator in a three-dimensional anti-de Sitter background. We use a generalized Schroedinger picture in which the analogs of the Schroedinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the AdS{sub 3} spacetime. In this picture, we have a metamorphosis of the Heisenberg uncertainty relations. (orig.)

  6. Critical behavior of the Higgs- and Goldstone-mass gaps for the two-dimensional S=1 XY model

    Directory of Open Access Journals (Sweden)

    Yoshihiro Nishiyama

    2015-08-01

    Full Text Available Spectral properties for the two-dimensional quantum S=1 XY model were investigated with the exact diagonalization method. In the symmetry-broken phase, there appear the massive Higgs and massless Goldstone excitations, which correspond to the longitudinal and transverse modes of the spontaneous magnetic moment, respectively. The former excitation branch is embedded in the continuum of the latter, and little attention has been paid to the details, particularly, in proximity to the critical point. The finite-size-scaling behavior is improved by extending the interaction parameters. An analysis of the critical amplitude ratio for these mass gaps is made.

  7. Dynamic Proportional Reinsurance and Approximations for Ruin Probabilities in the Two-Dimensional Compound Poisson Risk Model

    Directory of Open Access Journals (Sweden)

    Yan Li

    2012-01-01

    Full Text Available We consider the dynamic proportional reinsurance in a two-dimensional compound Poisson risk model. The optimization in the sense of minimizing the ruin probability which is defined by the sum of subportfolio is being ruined. Via the Hamilton-Jacobi-Bellman approach we find a candidate for the optimal value function and prove the verification theorem. In addition, we obtain the Lundberg bounds and the Cramér-Lundberg approximation for the ruin probability and show that as the capital tends to infinity, the optimal strategies converge to the asymptotically optimal constant strategies. The asymptotic value can be found by maximizing the adjustment coefficient.

  8. Quantitative characterization of solid epoxy resins using comprehensive two dimensional liquid chromatography coupled with electrospray ionization-time of flight mass spectrometry.

    Science.gov (United States)

    Julka, Samir; Cortes, Hernan; Harfmann, Robert; Bell, Bruce; Schweizer-Theobaldt, Andreas; Pursch, Matthias; Mondello, Luigi; Maynard, Shawn; West, David

    2009-06-01

    A comprehensive multidimensional liquid chromatography system coupled to Electrospray Ionization-Mass Spectrometry (LCxLC-ESI-MS) was developed for detailed characterization and quantitation of solid epoxy resin components. The two orthogonal modes of separation selected were size exclusion chromatography (SEC) in the first dimension and liquid chromatography at critical conditions (LCCC) in the second dimension. Different components present in the solid epoxy resins were separated and quantitated for the first time based on the functional groups and molecular weight heterogeneity. Coupling LCxLC separations with mass spectrometry enabled the identification of components resolved in the two-dimensional space. Several different functional group families of compounds were separated and identified, including epoxy-epoxy and epoxy-alpha-glycol functional oligomers, and their individual molecular weight ranges were determined. Repeatability obtained ranged from 0.5% for the main product to 21% for oligomers at the 0.4% concentration level.

  9. Two-dimensional numerical and eco-toxicological modeling of chemical spills

    Institute of Scientific and Technical Information of China (English)

    Suiliang HUANG; Yafei JIA; Sam S. Y. WANG

    2009-01-01

    The effects of chemical spills on aquatic nontarget organisms were evaluated in this study. Based on a review of three types of current eco-toxicological models of chemicals, i.e., ACQUATOX model of the US-EPA, Hudson River Model of PCBs, and critical body residual (CBR) model and dynamic energy budget (DEBtox)model, this paper presents an uncoupled numerical ecotoxicological model. The transport and transformation of spilled chemicals were simulated by a chemical transport model (including flow and sediment transport), and the mortalities of an organism caused by the chemicals were simulated by the extended threshold damage model,separately. Due to extreme scarcity of data, this model was applied to two hypothetical cases of chemical spills happening upstream of a lake. Theoretical analysis and simulated results indicated that this model is capable of reasonably predicting the acute effects of chemical spills on aquatic ecosystems or organism killings.

  10. A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tingwen; Zhang, Yongmin

    2013-10-11

    Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.

  11. Evaluation of excess carbon 14 and strontium 90 data for suitability to test two-dimensional stratospheric models

    Science.gov (United States)

    Johnston, Harold

    1989-12-01

    From reports by the Atomic Energy Commission concerning the atmospheric distribution of radionucleides following the nuclear bomb tests of 1958-1959 and 1961-1962, excess carbon 14 data from the period 1959-1970 and strontium 90 data from 1963-1967 are reviewed for possible use as inert tracers to test two-dimensional stratospheric-tropospheric models. Contrary to some views expressed in the literature, it is concluded that the carbon 14 data are suitable to test (1) the altitude (at 4 latitudes) of the transition region between troposphere and stratosphere with respect to transport of an inert tracer, (2) some aspects of transport between the northern and southern hemispheres, (3) horizontal and vertical transport as the vertical profile between 4.5 and 33 km and at 31°N evolves from a skewed Gaussian in 1963 to an almost stair-step profile in 1966, and (4) the long-term one-dimensional aspect of a two-dimensional model over the period 1966-1970. More tentatively, it is concluded that the strontium 90 data may be used as a model for the distribution and gross settling rate of the natural stratospheric aerosol layer between 15 and 25 km. Data from difficultly obtained laboratory reports and suggested initial conditions and boundary conditions are included as a microfiche supplement to this paper.

  12. Degenerate ground states and multiple bifurcations in a two-dimensional q-state quantum Potts model.

    Science.gov (United States)

    Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T; Zhou, Huan-Qiang

    2014-06-01

    We numerically investigate the two-dimensional q-state quantum Potts model on the infinite square lattice by using the infinite projected entangled-pair state (iPEPS) algorithm. We show that the quantum fidelity, defined as an overlap measurement between an arbitrary reference state and the iPEPS ground state of the system, can detect q-fold degenerate ground states for the Z_{q} broken-symmetry phase. Accordingly, a multiple bifurcation of the quantum ground-state fidelity is shown to occur as the transverse magnetic field varies from the symmetry phase to the broken-symmetry phase, which means that a multiple-bifurcation point corresponds to a critical point. A (dis)continuous behavior of quantum fidelity at phase transition points characterizes a (dis)continuous phase transition. Similar to the characteristic behavior of the quantum fidelity, the magnetizations, as order parameters, obtained from the degenerate ground states exhibit multiple bifurcation at critical points. Each order parameter is also explicitly demonstrated to transform under the Z_{q} subgroup of the symmetry group of the Hamiltonian. We find that the q-state quantum Potts model on the square lattice undergoes a discontinuous (first-order) phase transition for q=3 and q=4 and a continuous phase transition for q=2 (the two-dimensional quantum transverse Ising model).

  13. Simulations of low field helicon discharges using a two-dimensional hybrid plasma equipment model

    Energy Technology Data Exchange (ETDEWEB)

    Kinder, R.L.; Kushner, M.J.

    1999-07-01

    As the semiconductor industry moves towards larger wafers, a greater degree of process uniformity than is currently available with conventional inductively coupled plasma reactors will be necessary. Due to their high ionization efficiency, high flux density and their ability to deposit power within the volume of the plasma, helicon reactors are being developed for downstream etching and deposition. The power coupling of the antenna radiation to the plasma is of concern due to issues related to process uniformity. Furthermore, operation of helicon discharges at low magnetic fields (5--20 G) is not only economically attractive, but lower fields provide greater ion flux uniformity to the substrate. At low magnetic fields, it has been observed that there is a resonant peak in the power deposition and plasma density. This has been attributed to the occurrence of an electron cyclotron wave, or Trivelpiece-Gould (TG) mode, when {omega}/{omega}{sub c} is of order unity. To investigate these issues, the authors have improved the electromagnetics module of the HPEM to resolve the helicon wave structure of a m = 0 mode. The electrostatic component of the wave equation has been neglected, so this work focuses on the effects of the helicon mode. Plasma dynamics are coupled to the electromagnetic fields through a tensor form of Ohm's law and an effective collision frequency for Landau damping has been incorporated. Using a solenoidal magnetic field and an antenna operating at 13.65 MHz, studies show a shift in the power deposition towards the center of the reactor as the magnetic field is decreased below 30 G. Furthermore, peak values and wave structure is sensitive to the magnetic field configuration. Results for process relevant gas mixtures are examined and the dependence on magnetic field strength, field configuration and power are discussed.

  14. A Two-dimensional Heat Transfer Model for Atmosphere-land System in the Lake-dominated Alaskan Arctic

    Institute of Scientific and Technical Information of China (English)

    LING Feng; ZHANG Ting-jun

    2002-01-01

    Understanding lake ice growth and its sensitivity to climate change is vital to understand the thermal regime of thaw lake systems and predict their response to climate change. In this paper, a physically-based, two-dimensional, non-steady mathematical model is developed for studying the role of shallow tundra lakes in the Alaskan Arctic. Both the radiation absorption in lake water and the phasechange in permafrost are considerd in the model. The materials the model includes are snow, ice, water, unfrozen and frozen soil (peat, silt,sand and gravel). The basic inputs to the model observed mean daily air temperature and snow depth. The ability of this model to simulate lake ice growth and thickness variation, lake water temperature distribution, the thermal regime of permafrost and talik dynamics beneath lakes, and thawing rate of permafrost below and adjacent to shallow thaw lakes offers the potential to describe the effects of climate change in the Alaskan Arctic.

  15. A restricted dimer model on a two-dimensional random causal triangulation

    DEFF Research Database (Denmark)

    Ambjørn, Jan; Durhuus, Bergfinnur; Wheater, J. F.

    2014-01-01

    We introduce a restricted hard dimer model on a random causal triangulation that is exactly solvable and generalizes a model recently proposed by Atkin and Zohren (2012 Phys. Lett. B 712 445–50). We show that the latter model exhibits unusual behaviour at its multicritical point; in particular, its...

  16. [Apply fourier transform infrared spectra coupled with two-dimensional correlation analysis to study the evolution of humic acids during composting].

    Science.gov (United States)

    Bu, Gui-jun; Yu, Jing; Di, Hui-hui; Luo, Shi-jia; Zhou, Da-zhai; Xiao, Qiang

    2015-02-01

    The composition and structure of humic acids formed during composting play an important influence on the quality and mature of compost. In order to explore the composition and evolution mechanism, municipal solid wastes were collected to compost and humic and fulvic acids were obtained from these composted municipal solid wastes. Furthermore, fourier transform infrared spectra and two-dimensional correlation analysis were applied to study the composition and transformation of humic and fulvic acids during composting. The results from fourier transform infrared spectra showed that, the composition of humic acids was complex, and several absorbance peaks were observed at 2917-2924, 2844-2852, 2549, 1662, 1622, 1566, 1454, 1398, 1351, 990-1063, 839 and 711 cm(-1). Compared to humic acids, the composition of fulvci acids was simple, and only three peaks were detected at 1725, 1637 and 990 cm(-1). The appearance of these peaks showed that both humic and fulvic acids comprised the benzene originated from lignin and the polysaccharide. In addition, humic acids comprised a large number of aliphatic and protein which were hardly detected in fulvic acids. Aliphatic, polysaccharide, protein and lignin all were degraded during composting, however, the order of degradation was different between humic and fulvci acids. The result from two-dimensional correlation analysis showed that, organic compounds in humic acids were degraded in the following sequence: aliphatic> protein> polysaccharide and lignin, while that in fulvic acids was as following: protein> polysaccharide and aliphatic. A large number of carboxyl, alcohols and ethers were formed during the degradation process, and the carboxyl was transformed into carbonates. It can be concluded that, fourier transform infrared spectra coupled with two-dimensional correlation analysis not only can analyze the function group composition of humic substances, but also can characterize effectively the degradation sequence of these

  17. Dynamical scaling, domain-growth kinetics, and domain-wall shapes of quenched two-dimensional anisotropic XY models

    DEFF Research Database (Denmark)

    Mouritsen, Ole G.; Praestgaard, Eigil

    1988-01-01

    temperature, the domain-growth kinetics is found to be independent of the value of this parameter over several decades of its range. This suggests that a universal principle is operative. The domain-wall shape is analyzed and shown to be well represented by a hyperbolic tangent function. The growth process......The domain-growth kinetics in two different anisotropic two-dimensional XY-spin models is studied by computer simulation. The models have uniaxial and cubic anisotropy which leads to ground-state orderings which are twofold and fourfold degenerate, respectively. The models are quenched from...... infinite to zero temperature as well as to nonzero temperatures below the ordering transition. The continuous nature of the spin variables causes the domain walls to be ‘‘soft’’ and characterized by a finite thickness. The steady-state thickness of the walls can be varied by a model parameter, P. At zero...

  18. Numerical study of an ion-exchanged glass waveguide using both two-dimensional and three-dimensional models

    Science.gov (United States)

    Wang, Pengfei; Semenova, Yuliya; Zheng, Jie; Wu, Qiang; Muhamad Hatta, Agus; Farrell, Gerald

    2011-06-01

    A numerical study is carried out to compare the two-dimensional (2-D) case and three-dimensional (3-D) case for the modelling of an ion-exchanged glass waveguide. It is shown that different waveguide widths on the photomask correspond to different ion concentration distributions after an annealing process. A numerical example is presented of two waveguide sections with different widths indicates that due to the abrupt change of the waveguide width, a 3-D theoretical model is required for an accurate prediction of the parameters of ion-exchanged glass waveguides. The good agreement between the modelled and measured results proves that the developed 3-D numerical model can be beneficially utilized in the generalized design of optical devices based on ion-exchange waveguides.

  19. Two-dimensional Model of Ciliwung River Flood in DKI Jakarta for Development of the Regional Flood Index Map

    Directory of Open Access Journals (Sweden)

    Adam Formánek

    2013-12-01

    Full Text Available The objective of this study was to present a sophisticated method of developing supporting material for flood control implementation in DKI Jakarta. High flow rates in the Ciliwung River flowing through Jakarta regularly causes extensive flooding in the rainy season. The affected area comprises highly densely populated villages. For developing an efficient early warning system in view of decreasing the vulnerability of the locations a flood index map has to be available. This study analyses the development of a flood risk map of the inundation area based on a two-dimensional modeling using FESWMS. The reference event used for the model was the most recent significant flood in 2007. The resulting solution represents flood characteristics such as inundation area, inundation depth and flow velocity. Model verification was performed by confrontation of the results with survey data. The model solution was overlaid with a street map of Jakarta. Finally, alternatives for flood mitigation measures are discussed.

  20. More on Two-Dimensional $O(N)$ Models with $\\mathcal{N} = (0,1)$ Supersymmetry

    CERN Document Server

    Peterson, Adam J; Shifman, Mikhail

    2015-01-01

    We study the behavior of two dimensional supersymmetric connections of $n$ copies of $O(N)$ models with an $\\mathcal{N} = (0,1)$ heterotic deformation generated by a right moving fermion. We develop the model in analogy with the connected $\\mathcal{N}=(0,2)$ $CP(N-1)$ models for the case of a single connecting fermionic superfield. We calculate the effective potential in the large $N$ limit and determine the vacuum field configurations. Similarily to other SUSY connected models we find that SUSY is unbroken under certain conditions despite the vanishing of the Witten index. Specifically, this preservation of SUSY occurs when we have an even number $n$ of $O(N)$ families. As in previous cases we show that this result follows from a $Z_n$ symmetry under a particular exchange of the $O(N)$ families. This leads to a definition of a modified Witten index, which gaurantees the preservation of SUSY in this case.

  1. A two-dimensional mathematical model of a Zn-MnO2 alkaline cell(1)%A two-dimensional mathematical model of a Zn-MnO2 alkaline cell (1)

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yue-min; CHEH Huk-yuk

    2007-01-01

    A two-dimensional mathematical model based on the macrohomogeneous theory of porous electrodes was developed for a cylindrical Zn-MnO2 alkaline cell. The model was applied to understand the effect of the length of the anode current collector on the cell performance. Results are presented for the continuous discharge at a high rate of lA and a moderate rate of 0.2A for a AA - sized cell.With a typical length of an anode current collector at about 70% of the cell height, the analysis showed that an increase in the length of the anode current collector would benefit the lower rate of discharge more than the higher rate of discharge.

  2. DEVELOPMENT OF TWO-DIMENSIONAL HYDRODYNAMIC AND WATER QUALITY MODEL FOR HUANGPU RIVER

    Institute of Scientific and Technical Information of China (English)

    Xu Zu-xin; Yin Hai-long

    2003-01-01

    Based on numerical computation model RMA2 and RMA4 with open source code, finite element meshes representing the study domain are created, then the finite element hydrodynamic and water quality model for Huangpu River is developed and calibrated, and the simulation results are analyzed. This developed hydrodynamic and water quality model is used to analyze the influence of discharged wastewater from planning Wastwater Treatment Plant (WWTP) on Huangpu River's water quality.

  3. A substitute model of two-dimensional dry friction exposed to dither generated by rolling contact of wheel and rail

    Science.gov (United States)

    Piotrowski, Jerzy

    2012-10-01

    Dither generated by rolling contact of wheel and rail smoothes dry friction damping provided by the primary suspension dampers of freight wagons and it should be taken into account in numerical simulations. But numerically the problem is non-smooth and this leads to long execution time during simulation, especially when the vehicle with friction dampers is modelled in the environment of an multi-body system simulation program, whose solver has to cope with many strong non-linearities. The other difficulty is the necessity of handling within the code a number of big volume files of recorded dither sampled with high frequency. To avoid these difficulties, a substitute model of two-dimensional dry friction exposed to dither is proposed that does not need application of dither during simulation, but it behaves as if dither were applied. Due to this property of the model, the excitation of the vehicle model by track irregularities may be supplied as low-frequency input, which allows fast execution and, the necessity of handling high-volume files of recorded dither is avoided. The substitute model is numerically effective. To identify parameters of the substitute model, a pre-processing employing a sample of the realistic dither is carried-out on a simple two-degrees-of-freedom system. The substitute model is anisotropic, describing anisotropic properties of the two-dimensional friction arising in the presence of one-dimensional dither. The model may be applied in other branches of engineering, for example, in mechatronics and robotics, where application of dither may improve the accuracy of positioning devices.

  4. Wavelet-based spatial comparison technique for analysing and evaluating two-dimensional geophysical model fields

    Directory of Open Access Journals (Sweden)

    S. Saux Picart

    2011-11-01

    Full Text Available Complex numerical models of the Earth's environment, based around 3-D or 4-D time and space domains are routinely used for applications including climate predictions, weather forecasts, fishery management and environmental impact assessments. Quantitatively assessing the ability of these models to accurately reproduce geographical patterns at a range of spatial and temporal scales has always been a difficult problem to address. However, this is crucial if we are to rely on these models for decision making. Satellite data are potentially the only observational dataset able to cover the large spatial domains analysed by many types of geophysical models. Consequently optical wavelength satellite data is beginning to be used to evaluate model hindcast fields of terrestrial and marine environments. However, these satellite data invariably contain regions of occluded or missing data due to clouds, further complicating or impacting on any comparisons with the model. A methodology has recently been developed to evaluate precipitation forecasts using radar observations. It allows model skill to be evaluated at a range of spatial scales and rain intensities. Here we extend the original method to allow its generic application to a range of continuous and discontinuous geophysical data fields, and therefore allowing its use with optical satellite data. This is achieved through two major improvements to the original method: (i all thresholds are determined based on the statistical distribution of the input data, so no a priori knowledge about the model fields being analysed is required and (ii occluded data can be analysed without impacting on the metric results. The method can be used to assess a model's ability to simulate geographical patterns over a range of spatial scales. We illustrate how the method provides a compact and concise way of visualising the degree of agreement between spatial features in two datasets. The application of the new method, its

  5. Two-dimensional surrogate contact modeling for computationally efficient dynamic simulation of total knee replacements.

    Science.gov (United States)

    Lin, Yi-Chung; Haftka, Raphael T; Queipo, Nestor V; Fregly, Benjamin J

    2009-04-01

    Computational speed is a major limiting factor for performing design sensitivity and optimization studies of total knee replacements. Much of this limitation arises from extensive geometry calculations required by contact analyses. This study presents a novel surrogate contact modeling approach to address this limitation. The approach involves fitting contact forces from a computationally expensive contact model (e.g., a finite element model) as a function of the relative pose between the contacting bodies. Because contact forces are much more sensitive to displacements in some directions than others, standard surrogate sampling and modeling techniques do not work well, necessitating the development of special techniques for contact problems. We present a computational evaluation and practical application of the approach using dynamic wear simulation of a total knee replacement constrained to planar motion in a Stanmore machine. The sample points needed for surrogate model fitting were generated by an elastic foundation (EF) contact model. For the computational evaluation, we performed nine different dynamic wear simulations with both the surrogate contact model and the EF contact model. In all cases, the surrogate contact model accurately reproduced the contact force, motion, and wear volume results from the EF model, with computation time being reduced from 13 min to 13 s. For the practical application, we performed a series of Monte Carlo analyses to determine the sensitivity of predicted wear volume to Stanmore machine setup issues. Wear volume was highly sensitive to small variations in motion and load inputs, especially femoral flexion angle, but not to small variations in component placements. Computational speed was reduced from an estimated 230 h to 4 h per analysis. Surrogate contact modeling can significantly improve the computational speed of dynamic contact and wear simulations of total knee replacements and is appropriate for use in design sensitivity

  6. A two-dimensional simulation model of phosphorus uptake including crop growth and P-response

    NARCIS (Netherlands)

    Mollier, A.; Willigen, de P.; Heinen, M.; Morel, C.; Schneider, A.; Pellerin, S.

    2008-01-01

    Modelling nutrient uptake by crops implies considering and integrating the processes controlling the soil nutrient supply, the uptake by the root system and relationships between the crop growth response and the amount of nutrient absorbed. We developed a model that integrates both dynamics of maize

  7. Spin Dynamics of $La_{2}CuO_{4}$ and the Two-Dimensional Heisenberg Model

    CERN Document Server

    Sandvik, A W; Barbara, U C S; Barbara, UC Santa

    1994-01-01

    The spin-lattice relaxation rate $1/T_1$ and the spin echo decay rate $1/T_{2G}$ for the 2D Heisenberg model are calculated using quantum Monte Carlo and maximum entropy analytic continuation. The results are compared to recent experiments on La$_2$CuO$_4$, as well as predictions based on the non-linear $\\sigma$-model.

  8. A method for geometric modelling of magnetic anomalies: Two dimensional bodies

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, T.C.S.

    for bodies of different shapes. A procedure has been evolved to compute the anomalies for all types of step and dyke models from a single formula by suitably reorienting the 'step model and by redefining its edges and the slope or dip angle. This method also...

  9. Two-Dimensional Model Test Study of the New Caisson Breakwater at Playa Blanca, Lanzarote

    DEFF Research Database (Denmark)

    Andersen, Thomas Lykke; Garborg, Karsten; Stagsted, Esben Rubech

    This report present the results of 2-D physical model tests (length scale 1:42.5) carried out in a wave flume at Department of Civil Engineering, Aalborg University (AAU) on behalf of SENER Ingenera y Sistemas S.A. Associate Prof. Thomas Lykke Andersen was in charge of the model tests, assisted...

  10. The relationship between four-dimensional θ = π Yang-Mills theory and the two-dimensional Wess-Zumino-Novikov-Witten model

    Institute of Scientific and Technical Information of China (English)

    寇谡鹏

    2002-01-01

    Used the dimensional reduction in the sense of Parisi and Sourlas, the gauge fixing term of the four-dimensionalYang-Mills field without the theta term is reduced to a two-dimensional principal chiral model. By adding the θ term(θ = π), the two-dimensional principal chiral model changes into the two-dimensional level 1 Wess-Zumino-Novikov-Witten model. The non-trivial fixed point indicates that Yang-Mills theory at θ = π is a critical theory without massgap and confinement.

  11. Two-dimensional lattice Boltzmann model for compressible flows with high Mach number

    Science.gov (United States)

    Gan, Yanbiao; Xu, Aiguo; Zhang, Guangcai; Yu, Xijun; Li, Yingjun

    2008-03-01

    In this paper we present an improved lattice Boltzmann model for compressible Navier-Stokes system with high Mach number. The model is composed of three components: (i) the discrete-velocity-model by M. Watari and M. Tsutahara [Phys. Rev. E 67 (2003) 036306], (ii) a modified Lax-Wendroff finite difference scheme where reasonable dissipation and dispersion are naturally included, (iii) artificial viscosity. The improved model is convenient to compromise the high accuracy and stability. The included dispersion term can effectively reduce the numerical oscillation at discontinuity. The added artificial viscosity helps the scheme to satisfy the von Neumann stability condition. Shock tubes and shock reflections are used to validate the new scheme. In our numerical tests the Mach numbers are successfully increased up to 20 or higher. The flexibility of the new model makes it suitable for tracking shock waves with high accuracy and for investigating nonlinear nonequilibrium complex systems.

  12. Two-dimensional time-domain finite-difference modeling for viscoelastic seismic wave propagation

    Science.gov (United States)

    Fan, Na; Zhao, Lian-Feng; Xie, Xiao-Bi; Ge, Zengxi; Yao, Zhen-Xing

    2016-09-01

    Real Earth media are not perfectly elastic. Instead, they attenuate propagating mechanical waves. This anelastic phenomenon in wave propagation can be modeled by a viscoelastic mechanical model consisting of several standard linear solids. Using this viscoelastic model, we approximate a constant Q over a frequency band of interest. We use a four-element viscoelastic model with a trade-off between accuracy and computational costs to incorporate Q into 2-D time-domain first-order velocity-stress wave equations. To improve the computational efficiency, we limit the Q in the model to a list of discrete values between 2 and 1000. The related stress and strain relaxation times that characterize the viscoelastic model are pre-calculated and stored in a database for use by the finite-difference calculation. A viscoelastic finite-difference scheme that is second order in time and fourth order in space is developed based on the MacCormack algorithm. The new method is validated by comparing the numerical result with analytical solutions that are calculated using the generalized reflection/transmission coefficient method. The synthetic seismograms exhibit greater than 95 per cent consistency in a two-layer viscoelastic model. The dispersion generated from the simulation is consistent with the Kolsky-Futterman dispersion relationship.

  13. Backbone exponents of the two-dimensional q-state Potts model: a Monte Carlo investigation.

    Science.gov (United States)

    Deng, Youjin; Blöte, Henk W J; Nienhuis, Bernard

    2004-02-01

    We determine the backbone exponent X(b) of several critical and tricritical q-state Potts models in two dimensions. The critical systems include the bond percolation, the Ising, the q=2-sqrt[3], 3, and 4 state Potts, and the Baxter-Wu model, and the tricritical ones include the q=1 Potts model and the Blume-Capel model. For this purpose, we formulate several efficient Monte Carlo methods and sample the probability P2 of a pair of points connected via at least two independent paths. Finite-size-scaling analysis of P2 yields X(b) as 0.3566(2), 0.2696(3), 0.2105(3), and 0.127(4) for the critical q=2-sqrt[3], 1,2, 3, and 4 state Potts model, respectively. At tricriticality, we obtain X(b)=0.0520(3) and 0.0753(6) for the q=1 and 2 Potts model, respectively. For the critical q-->0 Potts model it is derived that X(b)=3/4. From a scaling argument, we find that, at tricriticality, X(b) reduces to the magnetic exponent, as confirmed by the numerical results.

  14. Two-Dimensional Numerical Modeling of Intracontinental Extension: A Case Study Of the Baikal Rift Formation

    DEFF Research Database (Denmark)

    Yang, H.; Chemia, Zurab; Artemieva, Irina

    and geophysical studies, the geodynamic origin and evolution of the BRZ is still debated. We applytwo-dimensional finite difference code to model the lithosphere-scale de-formation in several locations across the strike of the Baikal Rift zone. The model se-tup takes an advantage of regional geophysical models...... to determinethe set of parameters that may define regional li-thosphere evolution towards the present lithosphere structure, which we further con-trol by gravity data, regional volcanism, and the age of the BRZ formation. We dem-onstrate the roleof pre-existing faults on the BRZ evolution and on formation of "off...

  15. A Two-Dimensional Modeling Procedure to Estimate the Loss Equivalent Resistance Including the Saturation Effect

    Directory of Open Access Journals (Sweden)

    Rosa Ana Salas

    2013-11-01

    Full Text Available We propose a modeling procedure specifically designed for a ferrite inductor excited by a waveform in time domain. We estimate the loss resistance in the core (parameter of the electrical model of the inductor by means of a Finite Element Method in 2D which leads to significant computational advantages over the 3D model. The methodology is validated for an RM (rectangular modulus ferrite core working in the linear and the saturation regions. Excellent agreement is found between the experimental data and the computational results.

  16. Neel order in the two-dimensional S=1/2 Heisenberg Model

    OpenAIRE

    Löw, Ute

    2007-01-01

    The existence of Neel order in the S=1/2 Heisenberg model on the square lattice at T=0 is shown using inequalities set up by Kennedy, Lieb and Shastry in combination with high precision Quantum Monte Carlo data.

  17. Two-dimensional analytic modeling of acoustic diffraction for ultrasonic beam steering by phased array transducers.

    Science.gov (United States)

    Wang, Tiansi; Zhang, Chong; Aleksov, Aleksandar; Salama, Islam; Kar, Aravinda

    2017-04-01

    Phased array ultrasonic transducers enable modulating the focal position of the acoustic waves, and this capability is utilized in many applications, such as medical imaging and non-destructive testing. This type of transducers also provides a mechanism to generate tilted wavefronts in acousto-optic deflectors to deflect laser beams for high precision advanced laser material processing. In this paper, a theoretical model is presented for the diffraction of ultrasonic waves emitted by several phased array transducers into an acousto-optic medium such as TeO2 crystal. A simple analytic expression is obtained for the distribution of the ultrasonic displacement field in the crystal. The model prediction is found to be in good agreement with the results of a numerical model that is based on a non-paraxial multi-Gaussian beam (NMGB) model.

  18. A homogenization-based constitutive model for two-dimensional viscoplastic porous media

    Science.gov (United States)

    Danas, Kostas; Idiart, Martin I.; Ponte Castañeda, Pedro

    2008-01-01

    An approximate model based on the so-called 'second-order' nonlinear homogenization method is proposed to estimate the effective behavior of viscoplastic porous materials exhibiting transversely isotropic symmetry. The model is constructed in such a way that it reproduces exactly the behavior of a 'composite-cylinder assemblage' in the limit of in-plane hydrostatic loading, and therefore coincides with the hydrostatic limit of Gurson's criterion for plastic porous materials. As a consequence, the new model improves on earlier 'second-order' homogenization estimates, which have been found to be overly stiff at sufficiently high triaxialities and nonlinearities. The proposed model is compared with exact results obtained for a special class of porous materials with sequentially laminated microstructures. The agreement is found to be excellent for the entire range of stress triaxialities, and all values of the porosity and nonlinearity considered. To cite this article: K. Danas et al., C. R. Mecanique 336 (2008).

  19. Two-Dimensional Saddle Point Equation of Ginzburg-Landau Hamiltonian for the Diluted Ising Model

    Institute of Scientific and Technical Information of China (English)

    WU Xin-Tian

    2006-01-01

    @@ The saddle point equation of Ginzburg-Landau Hamiltonian for the diluted Ising model is developed. The ground state is solved numerically in two dimensions. The result is partly explained by the coarse-grained approximation.

  20. Large Deviations for Stochastic Models of Two-Dimensional Second Grade Fluids

    Energy Technology Data Exchange (ETDEWEB)

    Zhai, Jianliang, E-mail: zhaijl@ustc.edu.cn [University of Science and Technology of China, School of Mathematical Sciences (China); Zhang, Tusheng, E-mail: Tusheng.Zhang@manchester.ac.uk [University of Manchester, School of Mathematics (United Kingdom)

    2017-06-15

    In this paper, we establish a large deviation principle for stochastic models of incompressible second grade fluids. The weak convergence method introduced by Budhiraja and Dupuis (Probab Math Statist 20:39–61, 2000) plays an important role.

  1. A two-dimensional model for the dynamics of granular avalanches

    OpenAIRE

    2005-01-01

    Zoning of avalanche risk areas is one important task of land-use planning in alpine areas. The lack of records, due to the low frequency of these events, makes it dicult to implement a statistical analysis. Simulations made with physical and mathematical models can improve the knowledge of the dynamics of these events. In this thesis three didifferent mathematical and numerical models, based on the rheological theory of Savage and Hutter for granular flows, are introduced. A one dimensi...

  2. A nonlinear vertex-based model for animation of two-dimensional dry foam

    DEFF Research Database (Denmark)

    Kelager, Micky; Erleben, Kenny

    2010-01-01

    Foam is the natural phenomenon of bubbles that arise due to nucleation of gas in liquids. The current state of art in Computer Graphics rarely includes foam effects on large scales. In this paper we introduce a vertexbased, quasi-static equilibrium model from the field of Computational Physics as...... simulations with free dynamic boundary conditions. The presented model is interesting and well suited for 2D graphics applications like video games and procedural or animated textures....

  3. A Two Dimensional Infinite Element Model to Study Temperature Distribution in Human Dermal Regions due to Tumors

    Directory of Open Access Journals (Sweden)

    K. R. pardasani

    2005-01-01

    Full Text Available In this study, a two dimensional infinite element model has been developed to study thermal effect in human dermal regions due to tumors. This model incorporates the effect of blood mass flow rate, metabolic heat generation and thermal conductivity of the tissues.The dermal region is divided into three natural layers, namely, epidermis, dermis and subdermal tissues. A uniformly perfused tumor is assumed to be present in the dermis. The domain is assumed to be finite along the depth and infinite along the breadth. The whole dermis region involving tumor is modelled with the help of triangular finite elements to incorporate the geometry of the region. These elements are surrounded by infinite domain elements along the breadth. Appropriate boundary conditions has been incorporated. A computer program has been developed to obtain the numerical results.

  4. Two-dimensional physically based semi-analytical model of source/drain series resistance in MOSFETs

    Science.gov (United States)

    He, Pei; Ke, Daoming; Hu, Pengfei

    2016-01-01

    In this study, a two-dimensional physically based semi-analytical model of source/drain series resistance in MOSFETs is developed, in which only one parameter needs to be extracted by measurement and the extracted parameter can be repeatedly used when the structure size of the source or drain is changed. The model at the first time separates the resistance into two independent parameters that multiply each other. One is the extracted parameter that is only related to the resistivity. The other one is calculated by the expressions obtained by using the semi-analytical method and Eigen function expansion method, and is only related to the structure size of the source or drain area. The model provides a new approach to solve the resistance problem and matches well with simulation results. It can be used easily to estimate the resistance when the device structure changes in device design.

  5. Using the hydrophobic subtraction model to choose orthogonal columns for online comprehensive two-dimensional liquid chromatography

    DEFF Research Database (Denmark)

    Græsbøll, Rune; Nielsen, Nikoline Juul; Christensen, Jan H.

    2014-01-01

    A method for choosing orthogonal columns for a specific sample set in on-line comprehensive two-dimensional liquid chromatography (LC×LC) was developed on the basis of the hydrophobic subtraction model. The method takes into account the properties of the sample analytes by estimating new F...... by Gilroy et al. [1], (3) F-weights determined from the retention of sample analytes but using principal component analysis (PCA) for the estimation, and (4) the Gilroy F-weights modified by excluding the C-term in the hydrophobic subtraction model, as suggested by Dolan and Snyder [2]. The retention of 13...... neutral and 4 acidic oxygenated polycyclic aromatic compounds (PACs) and 3 nitrogen-containing PAC bases was measured isocratically on 12 columns. The isocratic runs were used to determine the hydrophobic subtraction model analyte parameters, and these were used to estimate new F-weights and predict...

  6. Two-dimensional time dependent hurricane overwash and erosion modeling at Santa Rosa Island

    Science.gov (United States)

    McCall, R.T.; Van Theil de Vries, J. S. M.; Plant, N.G.; Van Dongeren, A. R.; Roelvink, J.A.; Thompson, D.M.; Reniers, A.J.H.M.

    2010-01-01

    A 2DH numerical, model which is capable of computing nearshore circulation and morphodynamics, including dune erosion, breaching and overwash, is used to simulate overwash caused by Hurricane Ivan (2004) on a barrier island. The model is forced using parametric wave and surge time series based on field data and large-scale numerical model results. The model predicted beach face and dune erosion reasonably well as well as the development of washover fans. Furthermore, the model demonstrated considerable quantitative skill (upwards of 66% of variance explained, maximum bias - 0.21 m) in hindcasting the post-storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied. The prediction skill ranged between 0.66 and 0.77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied. The sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay. The model sensitivity to the sheet flow sediment transport limiter, which served as a proxy for unknown factors controlling the resistance to erosion, was significantly greater than the sensitivity to the hydraulic forcing parameters. If no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response.

  7. A two-dimensional simulation model for the molded underfill process in flip chip packaging

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Xue Ru; Young, Wen Bin [National Cheng Kung University, Tainan (China)

    2015-07-15

    The flip chip process involves the deposition of solder bumps on the chip surface and their subsequent direct attachment and connection to a substrate. Underfilling traditional flip chip packaging is typically performed following a two-step approach. The first step uses capillary force to fill the gap between the chip and the substrate, and the second step uses epoxy molding compound (EMC) to overmold the package. Unlike traditional flip chip packaging, the molded underfill (MUF) concept uses a single-step approach to simultaneously achieve both underfill and overmold. MUF is a simpler and faster process. In this study, a 2D numerical model is developed to simulate the front movement of EMC flow and the void formation for different geometric parameters. The 2D model simplifies the procedures of geometric modeling and reduces the modeling time for the MUF simulation. Experiments are conducted to verify the prediction results of the model. The effect on void formation for different geometric parameters is investigated using a 2D model.

  8. AQMAN; linear and quadratic programming matrix generator using two-dimensional ground-water flow simulation for aquifer management modeling

    Science.gov (United States)

    Lefkoff, L.J.; Gorelick, S.M.

    1987-01-01

    A FORTRAN-77 computer program code that helps solve a variety of aquifer management problems involving the control of groundwater hydraulics. It is intended for use with any standard mathematical programming package that uses Mathematical Programming System input format. The computer program creates the input files to be used by the optimization program. These files contain all the hydrologic information and management objectives needed to solve the management problem. Used in conjunction with a mathematical programming code, the computer program identifies the pumping or recharge strategy that achieves a user 's management objective while maintaining groundwater hydraulic conditions within desired limits. The objective may be linear or quadratic, and may involve the minimization of pumping and recharge rates or of variable pumping costs. The problem may contain constraints on groundwater heads, gradients, and velocities for a complex, transient hydrologic system. Linear superposition of solutions to the transient, two-dimensional groundwater flow equation is used by the computer program in conjunction with the response matrix optimization method. A unit stress is applied at each decision well and transient responses at all control locations are computed using a modified version of the U.S. Geological Survey two dimensional aquifer simulation model. The program also computes discounted cost coefficients for the objective function and accounts for transient aquifer conditions. (Author 's abstract)

  9. A two-dimensional model of the passive coastal margin deep sedimentary carbon and methane cycles

    Directory of Open Access Journals (Sweden)

    D. E. Archer

    2012-03-01

    Full Text Available We present a new geologic-time and basin-spatial scale model of the continental margin methane cycle. The model, SpongeBOB, is used to simulate evolution of the carbon cycle in a passive sedimentary continental margin in response to changing oceanographic and geologic forcing over a time scale of 140 million years. The model is somewhat less sensitive to temperature than our previous results with a one-dimensional model, but is more sensitive to reasonable changes in POC than it is to reasonable changes in temperature. This behavior could lead to higher inventories of hydrate during hothouse climate conditions, rather than lower as generally assumed, due to the enrichment of the sediments in organic carbon. The hydrate inventory in the model is extremely sensitive to the ability of methane bubbles to rise within the sediment column, and how far gas-phase methane can get through the sediment column before it redissolves when it reaches undersaturated conditions. Hydrate formation is also sensitive to deep respiration of migrating petroleum in the model. The geochemistry of the sediment column is altered by the addition of vertical high-permeability chimneys intended to mimic the effects of heterogeneity in the real sediment column due to faults and chimneys, and produces results consistent with measured pore-water tracers SO42− and 129I. Pore water DIC concentrations are consistent with chemical weathering at depth within the sediment column. The carbon isotopic composition of the DIC is consistent with a methane production efficiency from POC of 50%, which is somewhat lower than redox balance with the H/C of organic matter in the model. Other phenomena which we simulated had only small impact on the hydrate inventory, including thermogenic methane, dissolved organic carbon, and sediment transport characteristics.

  10. Improved non-local electron thermal transport model for two-dimensional radiation hydrodynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Duc; Moses, Gregory [University of Wisconsin—Madison, 1500 Engineering Drive, Madison, Wisconsin 53706 (United States); Delettrez, Jacques [Laboratory for Laser Energetics of the University of Rochester, 250 East River Road, Rochester, New York 14623 (United States)

    2015-08-15

    An implicit, non-local thermal conduction algorithm based on the algorithm developed by Schurtz, Nicolai, and Busquet (SNB) [Schurtz et al., Phys. Plasmas 7, 4238 (2000)] for non-local electron transport is presented and has been implemented in the radiation-hydrodynamics code DRACO. To study the model's effect on DRACO's predictive capability, simulations of shot 60 303 from OMEGA are completed using the iSNB model, and the computed shock speed vs. time is compared to experiment. Temperature outputs from the iSNB model are compared with the non-local transport model of Goncharov et al. [Phys. Plasmas 13, 012702 (2006)]. Effects on adiabat are also examined in a polar drive surrogate simulation. Results show that the iSNB model is not only capable of flux-limitation but also preheat prediction while remaining numerically robust and sacrificing little computational speed. Additionally, the results provide strong incentive to further modify key parameters within the SNB theory, namely, the newly introduced non-local mean free path. This research was supported by the Laboratory for Laser Energetics of the University of Rochester.

  11. Computational two-dimensional modeling of the stress intensity factor in a cracked metallic material

    Science.gov (United States)

    Rolón, J. E.; Cendales, E. D.; Cruz, I. M.

    2016-02-01

    Cracking of metallic engineering materials is of great importance due cost of replacing mechanical elements cracked and the danger of sudden structural failure of these elements. One of the most important parameters during consideration of the mechanical behavior of machine elements having cracking and that are subject to various stress conditions is the stress intensity factor near the crack tip called factor Kic. In this paper a computational model is developed for the direct assessment of stress concentration factor near to the crack tip and compared with the results obtained in the literature in which other models have been established, which consider continuity of the displacement of the crack tip (XBEM). Based on this numerical approximation can be establish that computational XBEM method has greater accuracy in Kic values obtained than the model implemented by the method of finite elements for the virtual nodal displacement through plateau function.

  12. Crop growth and two dimensional modeling of soil water transport in drip irrigated potatoes

    DEFF Research Database (Denmark)

    Plauborg, Finn; Iversen, Bo Vangsø; Mollerup, Mikkel

    2009-01-01

    Drip irrigation can be an effective way to improve water and nitrogen use efficiency in soil and hence to reduce the environmental pollution. In the EU project SAFIR ( http://www.safir4eu.org/ ) a potato experiment was carried out in lysimeters on three different soil types: coarse sand, loamy sand...... of abscisic acid (ABA). Model outputs from the mechanistic simulation model Daisy, in SAFIR developed to include 2D soil processes and gas exchange processes based on Ball et al. and Farquhar were compared with measured crop dynamics, final DM yield and volumetric water content in the soil measured by TDR...... probes. The probes were installed parallel to the tillage direction at different positions in the potato ridge. The new Daisy 2D model showed to be able to simulate crop growth, water use and soil water distribution fairly well...

  13. Evaporation-condensation transition of the two-dimensional Potts model in the microcanonical ensemble

    KAUST Repository

    Nogawa, Tomoaki

    2011-12-05

    The evaporation-condensation transition of the Potts model on a square lattice is numerically investigated by the Wang-Landau sampling method. An intrinsically system-size-dependent discrete transition between supersaturation state and phase-separation state is observed in the microcanonical ensemble by changing constrained internal energy. We calculate the microcanonical temperature, as a derivative of microcanonical entropy, and condensation ratio, and perform a finite-size scaling of them to indicate the clear tendency of numerical data to converge to the infinite-size limit predicted by phenomenological theory for the isotherm lattice gas model. © 2011 American Physical Society.

  14. A two-dimensional model for the transport of pollutants in an urban basin

    Science.gov (United States)

    Liu, C. Y.; Goodin, W. R.

    1977-01-01

    The distribution of carbon monoxide emitted mainly from an automobile exhaust is investigated. Carbon monoxide is assumed to be chemically inert. The transport model, in analogy with the shallow-water theory in fluid dynamics, considers variation of all physical quantities in the horizontal direction below the temperature inversion layer. Pollutants are found to be carried primarily by the wind; turbulent diffusion in a normal day plays only a minor role. The concentration of CO predicted by the present model for the entire Los Angeles basin is compared with observed data at nine stations. Accuracy of four different numerical schemes, the effect of turbulent diffusivity, and the source strengths are examined.

  15. A two-dimensional model of the passive coastal margin deep sedimentary carbon and methane cycles

    OpenAIRE

    2012-01-01

    We present a new geologic-time and basin-spatial scale model of the continental margin methane cycle. The model, SpongeBOB, is used to simulate evolution of the carbon cycle in a passive sedimentary continental margin in response to changing oceanographic and geologic forcing over a time scale of 200 million years. The geochemistry of the sediment column is altered by the addition of vertical high-permeability channels intended to mimic the effects of heterogeneity in the real sediment column...

  16. Experimental investigations and validation of two dimensional model for multistream plate fin heat exchangers

    Science.gov (United States)

    Goyal, Mukesh; Chakravarty, Anindya; Atrey, M. D.

    2017-03-01

    Experimental investigations are carried out using a specially developed three-layer plate fin heat exchanger (PFHE), with helium as the working fluid cooled to cryogenic temperatures using liquid nitrogen (LN2) as a coolant. These results are used for validation of an already proposed and reported numerical model based on finite volume analysis for multistream (MS) plate fin heat exchangers (PFHE) for cryogenic applications (Goyal et al., 2014). The results from the experiments are presented and a reasonable agreement is observed with the already reported numerical model.

  17. TWO-DIMENSIONAL AXISYMMETRIC MODELING OF COMBUSTION IN AN IRON ORE SINTERING BED

    DEFF Research Database (Denmark)

    Lafmejani, Saeed Sadeghi; Davazdah Emami, Mohsen; Panjehpour, Masoud;

    2013-01-01

    A twodimensional model, based on conservation of mass, momentum and energy equations, is represented in this paper in which the coke combustion process, for iron ore sintering in a packed bed, is simulated numerically. The aforementioned packed bed consists of iron ore, coke, limestone and moisture...... of species are solved numerically by using a computational fluid dynamics code in a discrete solving domain. Modeling of iron ore sintering has complex and various features like coke combustion, complicated physical changes of solid phase particles and different modes of heat transfer, for example convection...

  18. A two dimensional model for magnetic flux fractionalization in high Tc superconductors

    CERN Document Server

    Cristofano, G; Naddeo, A; Niccoli, G

    2004-01-01

    We show how the recently proposed effective theory for a Quantum Hall system at "paired states" filling nu=1 (Mod.Phys.Lett. A 15 (2000) 1679; Nucl. Phys. B 641(2002) 547), the twisted model (TM), well adapts to describe self-generated half-integer flux quanta observed near grain boundaries (GBs). We stress the key role of our theory in describing the phenomenology of linear Josephson Junction Arrays (JJAs) which have been proposed as a model of YBCO grain boundaries, in particular we focus on "closed" geometries which appear promising as "protected" qubits for the implementation of an ideal quantum computer.

  19. Spin correlations in the two-dimensional quantum s=1/2 XY model

    Science.gov (United States)

    Sznajd, J.

    1995-08-01

    A quantum version of the Niemeijer-van Leeuwen real-space renormalization-group method is used to study the temperature dependence of the two- and four-spin correlations in the quantum XY model on the triangular lattice. The first-order cumulant expansion results suggest, similarly to other methods, a low-temperature phase of an essentially different kind from that predicted for the classical model. The possible explanation of the origin of the spurious 2D Heisenberg-like nontrivial fixed point in some renormalization-group calculations is also proposed.

  20. BIFURCATION IN A TWO-DIMENSIONAL NEURAL NETWORK MODEL WITH DELAY

    Institute of Scientific and Technical Information of China (English)

    WEI Jun-jie; ZHANG Chun-rui; LI Xiu-ling

    2005-01-01

    A kind of 2-dimensional neural network model with delay is considered. By analyzing the distribution of the roots of the characteristic equation associated with the model, a bifurcation diagram was drawn in an appropriate parameter plane. It is found that a line is a pitchfork bifurcation curve. Further more, the stability of each fixed point and existence of Hopf bifurcation were obtained. Finally, the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions were determined by using the normal form method and centre manifold theory.