Quantum theory of many-particle systems
Fetter, Alexander L
2003-01-01
""Singlemindedly devoted to its job of educating potential many-particle theorists…deserves to become the standard text in the field."" - Physics Today""The most comprehensive textbook yet published in its field and every postgraduate student or teacher in this field should own or have access to a copy."" - EndeavorA self-contained, unified treatment of nonrelativistic many-particle systems, this text offers a solid introduction to procedures in a manner that enables students to adopt techniques for their own use. Its discussions of formalism and applications move easily between general theo
Dynamics and Thermodynamics of Many Particle Cold Atom Systems
2016-05-05
AFRL-AFOSR-VA-TR-2016-0219 Dynamics and Thermodynamics of Many Particle Cold Atom Systems Anatoli Polkovnikov TRUSTEES OF BOSTON UNIVERSITY Final...TITLE AND SUBTITLE Dynamics and Thermodynamics of Many Particle Cold Atom Systems 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-13-1-0039 5c. PROGRAM...FA9550-13-1-0039 “Dynamics and Thermodynamics of Many Particle Cold Atom Systems” by Anatoli Polkovnikov, Professor of Physics Department of Physics
Calculation of Theoretical Isotropic Compton Profile for Many Particle Systems
Alzubadi, Ali A.; Albayati, Khalil H.
Theoretical isotropic (spherically symmetric) Compton profiles (ICP) have been calculated for many particle systems' He, Li, Be and B atoms in their ground states. Our calculations were performed using Roothan-Hartree-Fock (RHF) wave function, HF wave function of Thakkar and re-optimized HF wave function of Clementi-Roetti, taking into account the impulse approximation. The theoretical analysis included a decomposition of the various intra and inter shells and their contributions in the total ICP. A high momentum region of up to 4 a.u. was investigated and a non-negligible tail was observed in all ICP curves. The existence of a high momentum tail was mainly due to the electron-electron interaction. The ICP for the He atom has been compared with the available experimental data and it is found that the ICP values agree very well with them. A few low order radial momentum expectation values and the total energy for these atomic systems have also been calculated and compared with their counterparts' wave functions.
Low-velocity collisions of a many-particle-system
Weidling, René; Blum, Jurgen; Güttler, Carsten
To understand the formation of planetesimals, it is important to study collisions between dust aggregates. As shown in the collision model by Güttler et al. (2010, Astronomy & Astrophysics, in press), the results of dust-aggregate collisions vary according to size, velocity and porosity of the particles. While many experiments were performed for velocities above ˜0.1 m/s, it is very difficult to achieve lower velocities. In our drop tower-experiment, an ensemble of dust-particles undergoes inelastic collisions and by this dynamically 'cools' down so that velocities below 1 cm/s can be reached. In order to achieve even lower velocities than in the drop tower, the experiment will be part of MEDEA-payload onboard a suborbital flight of Blue Origin, providing about 180 seconds of reduced gravity. During this time we will not only be able to observe many more collisions, but allow the many-particle system to show collective effects like clustering, which have so far never been studied in dust aggregation experiments.
Clogging transition of many-particle systems flowing through bottlenecks
Zuriguel, Iker; Parisi, Daniel Ricardo; Hidalgo, Raúl Cruz; Lozano, Celia; Janda, Alvaro; Gago, Paula Alejandra; Peralta, Juan Pablo; Ferrer, Luis Miguel; Pugnaloni, Luis Ariel; Clément, Eric; Maza, Diego; Pagonabarraga, Ignacio; Garcimartín, Angel
2014-12-01
When a large set of discrete bodies passes through a bottleneck, the flow may become intermittent due to the development of clogs that obstruct the constriction. Clogging is observed, for instance, in colloidal suspensions, granular materials and crowd swarming, where consequences may be dramatic. Despite its ubiquity, a general framework embracing research in such a wide variety of scenarios is still lacking. We show that in systems of very different nature and scale -including sheep herds, pedestrian crowds, assemblies of grains, and colloids- the probability distribution of time lapses between the passages of consecutive bodies exhibits a power-law tail with an exponent that depends on the system condition. Consequently, we identify the transition to clogging in terms of the divergence of the average time lapse. Such a unified description allows us to put forward a qualitative clogging state diagram whose most conspicuous feature is the presence of a length scale qualitatively related to the presence of a finite size orifice. This approach helps to understand paradoxical phenomena, such as the faster-is-slower effect predicted for pedestrians evacuating a room and might become a starting point for researchers working in a wide variety of situations where clogging represents a hindrance.
Clogging transition of many-particle systems flowing through bottlenecks.
Zuriguel, Iker; Parisi, Daniel Ricardo; Hidalgo, Raúl Cruz; Lozano, Celia; Janda, Alvaro; Gago, Paula Alejandra; Peralta, Juan Pablo; Ferrer, Luis Miguel; Pugnaloni, Luis Ariel; Clément, Eric; Maza, Diego; Pagonabarraga, Ignacio; Garcimartín, Angel
2014-12-04
When a large set of discrete bodies passes through a bottleneck, the flow may become intermittent due to the development of clogs that obstruct the constriction. Clogging is observed, for instance, in colloidal suspensions, granular materials and crowd swarming, where consequences may be dramatic. Despite its ubiquity, a general framework embracing research in such a wide variety of scenarios is still lacking. We show that in systems of very different nature and scale -including sheep herds, pedestrian crowds, assemblies of grains, and colloids- the probability distribution of time lapses between the passages of consecutive bodies exhibits a power-law tail with an exponent that depends on the system condition. Consequently, we identify the transition to clogging in terms of the divergence of the average time lapse. Such a unified description allows us to put forward a qualitative clogging state diagram whose most conspicuous feature is the presence of a length scale qualitatively related to the presence of a finite size orifice. This approach helps to understand paradoxical phenomena, such as the faster-is-slower effect predicted for pedestrians evacuating a room and might become a starting point for researchers working in a wide variety of situations where clogging represents a hindrance.
Random many-particle systems: applications from biology, and propagation of chaos in abstract models
Wennberg, Bernt
2011-01-01
The paper discusses a family of Markov processes that represent many particle systems, and their limiting behaviour when the number of particles go to infinity. The first part concerns model of biological systems: a model for sympatric speciation, i.e. the process in which a genetically homogeneous population is split in two or more different species sharing the same habitat, and models for swarming animals. The second part of the paper deals with abstract many particle systems, and methods for rigorously deriving mean field models.
A Nonlinear Schrödinger Model for Many-Particle Quantum Systems
Directory of Open Access Journals (Sweden)
Qiang Zhang
2012-01-01
Full Text Available Considering both effects of the s-wave scattering and the atom-atom interaction rather than only the effect of the s-wave scattering, we establish a nonlinear Schrödinger model for many-particle quantum systems and we prove the global existence of a solution to the model and obtain the expression of the solution. Furthermore, we show that the Hamilton energy and the total particle number both are conservative quantities.
Tornow, S.; Tong, N.-H.; Bulla, R.
2006-03-01
We investigate electron transfer processes in donor-acceptor systems with a coupling of the electronic degrees of freedom to a common bosonic bath. The model allows to study many-particle effects and the influence of the local Coulomb interaction U between electrons on donor and acceptor sites. Using the non-perturbative numerical renormalization group approach we find distinct differences between the electron transfer characteristics in the single- and two-particle subspaces. We calculate the critical electron-boson coupling αc as a function of U and show results for density-density correlation functions in the whole parameter space. The possibility of many-particle (bipolaronic) and Coulomb-assisted transfer is discussed.
Many-particle Systems in One Dimension in the Harmonic Approximation
DEFF Research Database (Denmark)
R. Armstrong, J.; Zinner, Nikolaj Thomas; V. Fedorov, D.;
2012-01-01
We consider energetics and structural properties of a many particle system in one dimension with pairwise contact interactions confined in a parabolic external potential. To render the problem analytically solvable, we use the harmonic approximation scheme at the level of the Hamiltonian. We...... investigate the scaling with particle number of the ground state energies for systems consisting of identical bosons or fermions. We then proceed to focus on bosonic systems and make a detailed comparison to known exact results in the absence of the parabolic external trap for three-body systems. We also...
INTERACTING MANY-PARTICLE SYSTEMS OF DIFFERENT PARTICLE TYPES CONVERGE TO A SORTED STATE
DEFF Research Database (Denmark)
Kokkendorff, Simon Lyngby; Starke, Jens; Hummel, N.
2010-01-01
system converges by self-organized pattern formation to a sorted state where particles of the same type share a common position and those of different types are separated from each other. This is proved in the sense that we show that the property of being sorted is asymptotically stable and all other......We consider a model class of interacting many-particle systems consisting of different types of particles defined by a gradient flow. The corresponding potential expresses attractive and repulsive interactions between particles of the same type and different types, respectively. The introduced...
The FermiFab Toolbox for Fermionic Many-Particle Quantum Systems
Mendl, Christian B
2011-01-01
This paper introduces the FermiFab toolbox for many-particle quantum systems. It is mainly concerned with the representation of (symbolic) fermionic wavefunctions and the calculation of corresponding reduced density matrices (RDMs). The toolbox transparently handles the inherent antisymmetrization of wavefunctions and incorporates the creation/annihilation formalism. Thus, it aims at providing a solid base for a broad audience to use fermionic wavefunctions with the same ease as matrices in Matlab, say. Leveraging symbolic computation, the toolbox can greatly simply tedious pen-and-paper calculations for concrete quantum mechanical systems, and serves as "sandbox" for theoretical hypothesis testing. FermiFab (including full source code) is freely available as a plugin for both Matlab and Mathematica.
Bi-partite and global entanglement in a many-particle system with collective spin coupling
Unanyan, R G; Fleischhauer, M
2004-01-01
Bipartite and global entanglement are analyzed for the ground state of a system of $N$ spin 1/2 particles interacting via a collective spin-spin coupling described by the Lipkin-Meshkov-Glick (LMG) Hamiltonian. Under certain conditions which includes the special case of a super-symmetry, the ground state can be constructed analytically. In the case of an anti-ferromagnetic coupling and for an even number of particles this state undergoes a smooth crossover as a function of the continuous anisotropy parameter $\\gamma $ from a separable ($\\gamma =\\infty $) to a maximally entangled many-particle state ($\\gamma =0$). From the analytic expression for the ground state, bipartite and global entanglement are calculated. In the thermodynamic limit a discontinuous change of the scaling behavior of the bipartite entanglement is found at the isotropy point $\\gamma =0$. For $% \\gamma =0$ the entanglement grows logarithmically with the system size with no upper bound, for $\\gamma \
Ten reasons why a thermalized system cannot be described by a many-particle wave function
Drossel, Barbara
2017-05-01
It is widely believed that the underlying reality behind statistical mechanics is a deterministic and unitary time evolution of a many-particle wave function, even though this is in conflict with the irreversible, stochastic nature of statistical mechanics. The usual attempts to resolve this conflict for instance by appealing to decoherence or eigenstate thermalization are riddled with problems. This paper considers theoretical physics of thermalized systems as it is done in practice and shows that all approaches to thermalized systems presuppose in some form limits to linear superposition and deterministic time evolution. These considerations include, among others, the classical limit, extensivity, the concepts of entropy and equilibrium, and symmetry breaking in phase transitions and quantum measurement. As a conclusion, the paper suggests that the irreversibility and stochasticity of statistical mechanics should be taken as a real property of nature. It follows that a gas of a macroscopic number N of atoms in thermal equilibrium is best represented by a collection of N wave packets of a size of the order of the thermal de Broglie wave length, which behave quantum mechanically below this scale but classically sufficiently far beyond this scale. In particular, these wave packets must localize again after scattering events, which requires stochasticity and indicates a connection to the measurement process.
The FermiFab toolbox for fermionic many-particle quantum systems
Mendl, Christian B.
2011-06-01
This paper introduces the FermiFab toolbox for many-particle quantum systems. It is mainly concerned with the representation of (symbolic) fermionic wavefunctions and the calculation of corresponding reduced density matrices (RDMs). The toolbox transparently handles the inherent antisymmetrization of wavefunctions and incorporates the creation/annihilation formalism. Thus, it aims at providing a solid base for a broad audience to use fermionic wavefunctions with the same ease as matrices in Matlab, say. Leveraging symbolic computation, the toolbox can greatly simply tedious pen-and-paper calculations for concrete quantum mechanical systems, and serves as "sandbox" for theoretical hypothesis testing. FermiFab (including full source code) is freely available as a plugin for both Matlab and Mathematica. Program summaryProgram title:FermiFab Catalogue identifier: AEIN_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIN_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Special license provided by the author No. of lines in distributed program, including test data, etc.: 1 165 461 No. of bytes in distributed program, including test data, etc.: 15 557 308 Distribution format: tar.gz Programming language: MATLAB 7.9, Mathematica 7.0, C Computer: PCs, Sun Solaris workstation Operating system: Any platform supporting MATLAB or Mathematica; tested with Windows (32 and 64 bit) and Sun Solaris. RAM: Case dependent Classification: 4.15 Nature of problem: Representation of fermionic wavefunctions, computation of RDMs (reduced density matrices) and handing of the creation/annihilation operator formalism. Solution method: Mapping of Slater determinants to bitfields, implementation of the creation/annihilation and RDM formalism by bit operations. Running time: Depends on the problem size; several seconds for the provided demonstration files.
Two-dimensional topological photonic systems
Sun, Xiao-Chen; He, Cheng; Liu, Xiao-Ping; Lu, Ming-Hui; Zhu, Shi-Ning; Chen, Yan-Feng
2017-09-01
The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.
Evolution of a quantum system of many particles interacting via the generalized Yukawa potential
Bogoliubov, N. N.; Rasulova, M. Yu.; Avazov, U. A.
2016-12-01
We study the evolution of a system of N particles that have identical masses and charges and interact via the generalized Yukawa potential. The system is placed in a bounded region. The evolution of such a system is described by the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) chain of quantum kinetic equations. Using semigroup theory, we prove the existence of a unique solution of the BBGKY chain of quantum kinetic equations with the generalized Yukawa potential.
Foerster, A.; Leymann, H. A. M.; Wiersig, J.
2017-03-01
We introduce an equation of motion approach that allows for an approximate evaluation of the time evolution of a quantum system, where the algebraic work to derive the equations of motion is done by the computer. The introduced procedures offer a variety of different types of approximations applicable for finite systems with strong coupling as well as for arbitrary large systems where augmented mean-field theories like the cluster expansion can be applied.
Entanglement entropy in quantum many-particle systems and their simulation via ansatz states
Energy Technology Data Exchange (ETDEWEB)
Barthel, Thomas
2009-12-10
A main topic of this thesis is the development of efficient numerical methods for the simulation of strongly correlated quantum lattice models. For one-dimensional systems, the density-matrix renormalization-group (DMRG) is such a very successful method. The physical states of interest are approximated within a certain class of ansatz states. These ansatz states are designed in a way that the number of degrees of freedom are prevented from growing exponentially. They are the so-called matrix product states. The first part of the thesis, therefore, provides analytical and numerical analysis of the scaling of quantum nonlocality with the system size or time in different, physically relevant scenarios. For example, the scaling of Renyi entropies and their dependence on boundary conditions is derived within the 1+1-dimensional conformal field theory. Conjectures and analytical indications concerning the properties of entanglement entropy in critical fermionic and bosonic systems are confirmed numerically with high precision. For integrable models in the thermodynamic limit, general preconditions are derived under which subsystems converge to steady states. These steady states are non-thermal and retain information about the initial state. It is shown that the entanglement entropy in such steady states is extensive. For short times, the entanglement entropy grows typically linearly with time, causing an exponential increase in computation costs for the DMRG method. The second part of the thesis focuses on the development and improvement of the abovementioned numerical techniques. The time-dependent DMRG is complemented with an extrapolation technique for the evaluated observables. In this way, the problem of the entropy increase can be circumvented, allowing for a precise determination of spectral functions. The method is demonstrated using the example of the Heisenberg antiferromagnet and results are compared to Bethe-Ansatz data for T=0 and quantum Monte Carlo data
Clogging and unclogging of many-particle systems passing through a bottleneck
Directory of Open Access Journals (Sweden)
Zuriguel Iker
2017-01-01
Full Text Available When a group of discrete particles pass through a narrowing, the flow may become arrested due to the development of structures that span over the size of the aperture. Then, it is said that the system is clogged. Here, we will discuss about the existence of a phase diagram for the clogged state that has been recently proposed, arguing on its usefulness to describe different systems of discrete bodies ranging from granular materials, to colloidal suspensions and live beings. This diagram is built based on the value of a flowing parameter which characterizes the intermittent flow observed in all these discrete systems provided that there is an external or internal energy supply. Such requirement, which is necessary to destabilize the clogging arches, is absent in a standard static silo, which is therefore examined as a particular case. This view will help to understand some a priori inconsistencies concerning the role of driving force in the clogging process that have been found in the last years.
Clogging and unclogging of many-particle systems passing through a bottleneck
Zuriguel, Iker; Janda, Álvaro; Arévalo, Roberto; Maza, Diego; Garcimartín, Ángel
2017-06-01
When a group of discrete particles pass through a narrowing, the flow may become arrested due to the development of structures that span over the size of the aperture. Then, it is said that the system is clogged. Here, we will discuss about the existence of a phase diagram for the clogged state that has been recently proposed, arguing on its usefulness to describe different systems of discrete bodies ranging from granular materials, to colloidal suspensions and live beings. This diagram is built based on the value of a flowing parameter which characterizes the intermittent flow observed in all these discrete systems provided that there is an external or internal energy supply. Such requirement, which is necessary to destabilize the clogging arches, is absent in a standard static silo, which is therefore examined as a particular case. This view will help to understand some a priori inconsistencies concerning the role of driving force in the clogging process that have been found in the last years.
Dynamics of local symmetry correlators for interacting many-particle systems
Schmelcher, P.; Krönke, S.; Diakonos, F. K.
2017-01-01
Recently [P. A. Kalozoumis et al. Phys. Rev. Lett. 113, 050403 (2014)] the concept of local symmetries in one-dimensional stationary wave propagation has been shown to lead to a class of invariant two-point currents that allow to generalize the parity and Bloch theorem. In the present work, we establish the theoretical framework of local symmetries for higher-dimensional interacting many-body systems. Based on the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, we derive the equations of motion of local symmetry correlators which are off-diagonal elements of the reduced one-body density matrix at symmetry related positions. The natural orbital representation yields equations of motion for the convex sum of the local symmetry correlators of the natural orbitals as well as for the local symmetry correlators of the individual orbitals themselves. An alternative integral representation with a unique interpretation is provided. We discuss special cases, such as the bosonic and fermionic mean field theory, and show in particular that the invariance of two-point currents is recovered in the case of the non-interacting one-dimensional stationary wave propagation. Finally we derive the equations of motion for anomalous local symmetry correlators which indicate the breaking of a global into a local symmetry in the stationary non-interacting case.
A variational formula for the free energy of an interacting many-particle system
Adams, Stefan; Konig, Wolfgang
2010-01-01
We consider $N$ bosons in a box in $\\R^d$ with volume $N/\\rho$ under the influence of a mutually repellent pair potential. The particle density $\\rho\\in(0,\\infty)$ is kept fixed. Our main result is the identification of the limiting free energy, $f(\\beta,\\rho)$, at positive temperature $1/\\beta$, in terms of an explicit variational formula, for any fixed $\\rho$ if $\\beta$ is sufficiently small, and for any fixed $\\beta$ if $\\rho$ is sufficiently small. The thermodynamic equilibrium is described by the symmetrised trace of ${\\rm e}^{-\\beta \\Hcal_N}$, where $\\Hcal_N$ denotes the corresponding Hamilton operator. The well-known Feynman-Kac formula reformulates this trace in terms of $N$ interacting Brownian bridges. Due to the symmetrisation, the bridges are organised in an ensemble of cycles of various lengths. The novelty of our approach is a description in terms of a marked Poisson point process whose marks are the cycles. This allows for an asymptotic analysis of the system via a large-deviations analysis of ...
Institute of Scientific and Technical Information of China (English)
许莹; 李晋斌
2012-01-01
采用随机级数展开的量子蒙特卡罗方法研究二维硬核的玻色-赫伯德模型的热力学性质.首先通过算符变换将模型映射成为二维反铁磁准海森伯模型.变换后的模型比通常的海森伯模型多一项,该项正比于系统的格点总数N,对于大粒子数的系统,该项使模拟耗时指数增加,所以难以计算大粒子数系统.采用非局域操作循环更新后,这个困难可以得到很好的解决,可使粒子数总数增大到几千个.研究结果表明,粒子数密度在0—0.5范围内增大时,能量呈递减趋势,并趋于某一定值,随着正方晶格系统尺度增大,能量也随之增大;正方晶格系统尺度一定时,能量和磁化强度随着温度的升高而增大,化学势的变化对能量和磁化强度没有影响,能量随着正方晶格系统尺度增大而增大,磁化强度却随之减小;正方晶格系统尺度一定时,化学势的增大对比热没有影响,随着温度的升高比热出现先增大后减小的趋势,最后趋于某个值,达到平衡,而正方晶格系统尺度越大,比热曲线增大部分的趋势越大,减小部分的趋势也更明显,参照朗道超流理论,本文模拟的能量和比热曲线趋势与朗道二流体模型下HeⅡ的理论研究一致;不同正方晶格系统尺度的影响不大,均匀磁化率倒数在0—0.5（J/k_B）的低温范围内有很小的波动,J为耦合能,k_B为玻尔兹曼常数,温度在0.5—2（J/k_B）的范围内,均匀磁化率的倒数随着温度的升高而增大,且曲线的趋势显示了一种类似近藤行为.%In this paper,the stochastic series expansion quantum Monte Carlo method is employed to investigate the thermodynamic properties of hardcore Bose-Hubbard model in two-dimensional space.The two-dimensional hardcore Bose-Hubbard model can be mapped into the two-dimensional antiferromagnetic quasi-Heisenberg model under transform of bosonic operators.There is an additional term which is proportional
Second invariant for two-dimensional classical super systems
Indian Academy of Sciences (India)
S C Mishra; Roshan Lal; Veena Mishra
2003-10-01
Construction of superpotentials for two-dimensional classical super systems (for ≥ 2) is carried out. Some interesting potentials have been studied in their super form and also their integrability.
Magnetoconductivity of two-dimensional electron systems
Kuehnel, Frank Oliver
The conductivity sigmaxx(o) of a low-density nondegenerate 2D electron gas is investigated under conditions where hoc ≫ kBT ≫ hgamma (oc is the cyclotron frequency and hgamma is the disorder-induced width of the Landau level). Such conditions have been met for electrons on helium surface, and can also be achieved in ultra high quality heterostructures. Because of the random potential of defects, single-electron states of the lowest Landau level form a band of a width hgamma ≪ hoc. Almost all of these states are localized. Therefore, for ho c ≫ kBT ≫ hgamma, the static single-electron conductivity sigma xx(0) may be expected to be equal to zero. Since for o ≫ gamma the conductivity should decay, on the whole sigma xx(o) has a peak at a finite frequency. From scaling arguments, we show that in the single-electron approximation sigma xx(o) ∝ omu for o → 0, with the exponent mu in the range from 0.21 to 0.22, whereas the frequency dependence of the cyclotron resonance absorption peak is non-critical. The far tails of the conductivity peaks are obtained using the method of optimal fluctuation and are shown to be Gaussian. In order to investigate the shape of the low frequency peak and cyclotron resonance absorption peak, we use the method of moments (MOM). In MOM, the low-frequency conductivity is restored from its 14 spectral moments, whereas the cyclotron resonance absorption is restored from the calculated 10 spectral moments using the continuous fraction expansion. In combination with the analytical asymptotics, both expansions converge rapidly with increasing number of included moments, and give numerically accurate results throughout the region of interest. The effect of electron-electron interaction (EEI) on the low frequency conductivity is also investigated. EEI makes the static conductivity finite. For a low-density system, the effect can be described using the notion of a fluctuational field Efl which drives an electron because of electron
Kurokawa, Yusaku I; Nakashima, Hiroyuki; Nakatsuji, Hiroshi
2014-06-07
We derived the necessary conditions that must be satisfied by the non-relativistic time-independent exact wave functions for many-particle systems at a two-particle coalescence (or cusp) point. Some simple conditions are known to be Kato's cusp condition (CC) and Rassolov and Chipman's CC. In a previous study, we derived an infinite number of necessary conditions that two-particle wave functions must satisfy at a coalescence point. In the present study, we extend these conditions to many-particle systems. They are called general coalescence conditions (GCCs), and Kato's CC and Rassolov and Chipman's CC are included as special conditions. GCCs can be applied not only to Coulombic systems but also to any system in which the interaction between two particles is represented in a power series of inter-particle distances. We confirmed the correctness of our derivation of the GCCs by applying the exact wave function of a harmonium in electron-electron and electron-nucleus coalescence situations. In addition, we applied the free complement (FC) wave functions of a helium atom to the GCCs to examine the accuracy of the FC wave function in the context of a coalescence situation.
Energy Technology Data Exchange (ETDEWEB)
Kurokawa, Yusaku I., E-mail: y-kurokawa@qcri.or.jp, E-mail: h.nakatsuji@qcri.or.jp; Nakashima, Hiroyuki; Nakatsuji, Hiroshi, E-mail: y-kurokawa@qcri.or.jp, E-mail: h.nakatsuji@qcri.or.jp [Quantum Chemistry Research Institute, Kyodai Katsura Venture Plaza 107, Goryo Oohara 1-36, Nishikyo-ku, Kyoto 615-8245 (Japan)
2014-06-07
We derived the necessary conditions that must be satisfied by the non-relativistic time-independent exact wave functions for many-particle systems at a two-particle coalescence (or cusp) point. Some simple conditions are known to be Kato's cusp condition (CC) and Rassolov and Chipman's CC. In a previous study, we derived an infinite number of necessary conditions that two-particle wave functions must satisfy at a coalescence point. In the present study, we extend these conditions to many-particle systems. They are called general coalescence conditions (GCCs), and Kato's CC and Rassolov and Chipman's CC are included as special conditions. GCCs can be applied not only to Coulombic systems but also to any system in which the interaction between two particles is represented in a power series of inter-particle distances. We confirmed the correctness of our derivation of the GCCs by applying the exact wave function of a harmonium in electron-electron and electron-nucleus coalescence situations. In addition, we applied the free complement (FC) wave functions of a helium atom to the GCCs to examine the accuracy of the FC wave function in the context of a coalescence situation.
Singular analysis of two-dimensional bifurcation system
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Bifurcation properties of two-dimensional bifurcation system are studied in this paper.Universal unfolding and transition sets of the bifurcation equations are obtained.The whole parametric plane is divided into several different persistent regions according to the type of motion,and the different qualitative bifurcation diagrams in different persistent regions are given.The bifurcation properties of the two-dimensional bifurcation system are compared with its reduced one-dimensional system.It is found that the system which is reduced to one dimension has lost many bifurcation properties.
Directory of Open Access Journals (Sweden)
N. A. Veretenov
2014-09-01
Full Text Available The paper deals with generalization of investigation materials performed by the authors in recent years and analysis of obtained results. The subject of the paper is accounting of many-particle interactions in molecular J-aggregates at their resonance excitation by laser radiation. In this case, not only twin interactions are taken into considerations, but also the interactions of a given particle with three and more particles simultaneously. Three basic directions can be denoted among carried out investigations. The first direction is connected with derivation (from the first principles of motion equations for molecular of J-aggregates in view of many-particle interactions, and also twin correlations between particles. The derivation of equations from the first principles leads in general to the system of coupled equations for the means of products of n operators relating to n different molecules. Since n increases in every following equation, the problems arise, connected with uncoupling of this system and also factorization of the means with the highest n. The most difficult and complicated problem in this process is correct calculation of relaxed terms, arising due to exciton-exciton annihilation. The first direction is connected concretely with solution of all above mentioned problems. Within the second direction the study of bistability has been carried out on the basis of obtained equations, in view of three-particle interactions. Meanwhile primary attention has been concentrated on analysis of homogeneous regimes in J-aggregates. It has been shown, in particular, that accounting of many-particle contributions leads to the shift of bistability boundary into region of smaller constants of exciton-exciton annihilation. And, at last, the third direction of investigations is connected with analysis of modulation instability for stationary states of J-aggregates considered earlier at bistability study. The study of stability region boundaries
Boundary-value problems for two-dimensional canonical systems
Hassi, Seppo; De Snoo, H; Winkler, Henrik
2000-01-01
The two-dimensional canonical system Jy' = -lHy where the nonnegative Hamiltonian matrix function H(x) is trace-normed on (0,∞) has been studied in a function-theoretic way by L. de Branges. We show that the Hamiltonian system induces a closed symmetric relation which can be reduced to a, not necess
A Many Particle Adiabatic Invariant
DEFF Research Database (Denmark)
Hjorth, Poul G.
1999-01-01
For a system of N charged particles moving in a homogeneous, sufficiently strong magnetic field, a many-particle adiabatic invariant constrains the collisional exchange of energy between the degrees of freedom perpendicular to and parallel to the magnetic field. A description of the phenomenon...
Coll Positioning systems: a two-dimensional approach
Ferrando, J J
2006-01-01
The basic elements of Coll positioning systems (n clocks broadcasting electromagnetic signals in a n-dimensional space-time) are presented in the two-dimensional case. This simplified approach allows us to explain and to analyze the properties and interest of these relativistic positioning systems. The positioning system defined in flat metric by two geodesic clocks is analyzed. The interest of the Coll systems in gravimetry is pointed out.
Thermodynamics of two-dimensional Yukawa systems across coupling regimes
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.
A two-dimensional approach to relativistic positioning systems
Coll, B; Morales, J A; Coll, Bartolom\\'{e}; Ferrando, Joan Josep; Morales, Juan Antonio
2006-01-01
A relativistic positioning system is a physical realization of a coordinate system consisting in four clocks in arbitrary motion broadcasting their proper times. The basic elements of the relativistic positioning systems are presented in the two-dimensional case. This simplified approach allow to explain and to analyze the properties and interest of these new systems. The positioning system defined by geodesic emitters in flat metric is developed in detail. The information that the data generated by a relativistic positioning system give on the space-time metric interval is analyzed, and the interest of these results in gravimetry is pointed out.
Two-dimensional localized structures in harmonically forced oscillatory systems
Ma, Y.-P.; Knobloch, E.
2016-12-01
Two-dimensional spatially localized structures in the complex Ginzburg-Landau equation with 1:1 resonance are studied near the simultaneous presence of a steady front between two spatially homogeneous equilibria and a supercritical Turing bifurcation on one of them. The bifurcation structures of steady circular fronts and localized target patterns are computed in the Turing-stable and Turing-unstable regimes. In particular, localized target patterns grow along the solution branch via ring insertion at the core in a process reminiscent of defect-mediated snaking in one spatial dimension. Stability of axisymmetric solutions on these branches with respect to axisymmetric and nonaxisymmetric perturbations is determined, and parameter regimes with stable axisymmetric oscillons are identified. Direct numerical simulations reveal novel depinning dynamics of localized target patterns in the radial direction, and of circular and planar localized hexagonal patterns in the fully two-dimensional system.
Directory of Open Access Journals (Sweden)
D. A. Fetisov
2015-01-01
Full Text Available The controllability conditions are well known if we speak about linear stationary systems: a linear stationary system is controllable if and only if the dimension of the state vector is equal to the rank of the controllability matrix. The concept of the controllability matrix is extended to affine systems, but relations between affine systems controllability and properties of this matrix are more complicated. Various controllability conditions are set for affine systems, but they deal as usual either with systems of some special form or with controllability in some small neighborhood of the concerned point. An affine system is known to be controllable if the system is equivalent to a system of a canonical form, which is defined and regular in the whole space of states. In this case, the system is said to be feedback linearizable in the space of states. However there are examples, which illustrate that a system can be controllable even if it is not feedback linearizable in any open subset in the space of states. In this article we deal with such systems.Affine systems with two-dimensional control are considered. The system in question is assumed to be equivalent to a system of a quasicanonical form with two-dimensional zero dynamics which is defined and regular in the whole space of states. Therefore the controllability of the original system is equivalent to the controllability of the received system of a quasicanonical form. In this article the sufficient condition for an available solution of the terminal problem is proven for systems of a quasicanonical form with two-dimensional control and two-dimensional zero dynamics. The condition is valid in the case of an arbitrary time interval and arbitrary initial and finite states of the system. Therefore the controllability condition is set for systems of a quasicanonical form with two-dimensional control and two-dimensional zero dynamics. An example is given which illustrates how the proved
Superfluid phase transition in two-dimensional excitonic systems
Energy Technology Data Exchange (ETDEWEB)
Apinyan, V.; Kopeć, T.K., E-mail: kopec@int.pan.wroc.pl
2014-03-01
We study the superfluid phase transition in the two-dimensional (2D) excitonic system. Employing the extended Falicov–Kimball model (EFKM) and considering the local quantum correlations in the system composed of conduction band electrons and valence band holes we demonstrate the existence of the excitonic insulator (EI) state in the system. We show that at very low temperatures, the particle phase stiffness in the pure-2D excitonic system, governed by the non-local cross correlations, is responsible for the vortex–antivortex binding phase-field state, known as the Berezinskii–Kosterlitz–Thouless (BKT) superfluid state. We demonstrate that the existence of excitonic insulator phase is a necessary prerequisite, leading to quasi-long-range order in the 2D excitonic system.
Crossed Andreev effects in two-dimensional quantum Hall systems
Hou, Zhe; Xing, Yanxia; Guo, Ai-Min; Sun, Qing-Feng
2016-08-01
We study the crossed Andreev effects in two-dimensional conductor/superconductor hybrid systems under a perpendicular magnetic field. Both a graphene/superconductor hybrid system and an electron gas/superconductor one are considered. It is shown that an exclusive crossed Andreev reflection, with other Andreev reflections being completely suppressed, is obtained in a high magnetic field because of the chiral edge states in the quantum Hall regime. Importantly, the exclusive crossed Andreev reflection not only holds for a wide range of system parameters, e.g., the size of system, the width of central superconductor, and the quality of coupling between the graphene and the superconductor, but also is very robust against disorder. When the applied bias is within the superconductor gap, a robust Cooper-pair splitting process with high-efficiency can be realized in this system.
Patched Green's function techniques for two-dimensional systems
DEFF Research Database (Denmark)
Settnes, Mikkel; Power, Stephen; Lin, Jun
2015-01-01
We present a numerically efficient technique to evaluate the Green's function for extended two-dimensional systems without relying on periodic boundary conditions. Different regions of interest, or “patches,” are connected using self-energy terms which encode the information of the extended parts...... of the system. The calculation scheme uses a combination of analytic expressions for the Green's function of infinite pristine systems and an adaptive recursive Green's function technique for the patches. The method allows for an efficient calculation of both local electronic and transport properties, as well...... as the inclusion of multiple probes in arbitrary geometries embedded in extended samples. We apply the patched Green's function method to evaluate the local densities of states and transmission properties of graphene systems with two kinds of deviations from the pristine structure: bubbles and perforations...
Two-dimensional nuclear magnetic resonance of quadrupolar systems
Energy Technology Data Exchange (ETDEWEB)
Wang, Shuanhu
1997-09-17
This dissertation describes two-dimensional nuclear magnetic resonance theory and experiments which have been developed to study quadruples in the solid state. The technique of multiple-quantum magic-angle spinning (MQMAS) is extensively reviewed and expanded upon in this thesis. Specifically, MQMAS is first compared with another technique, dynamic-angle spinning (DAS). The similarity between the two techniques allows us to extend much of the DAS work to the MQMAS case. Application of MQMAS to a series of aluminum containing materials is then presented. The superior resolution enhancement through MQMAS is exploited to detect the five- and six-coordinated aluminum in many aluminosilicate glasses. Combining the MQMAS method with other experiments, such as HETCOR, greatly expands the possibility of the use of MQMAS to study a large range of problems and is demonstrated in Chapter 5. Finally, the technique switching-angle spinning (SAS) is applied to quadrupolar nuclei to fully characterize a quadrupolar spin system in which all of the 8 NMR parameters are accurately determined. This dissertation is meant to demonstrate that with the combination of two-dimensional NMR concepts and new advanced spinning technologies, a series of multiple-dimensional NMR techniques can be designed to allow a detailed study of quadrupolar nuclei in the solid state.
Oscillation of Two-Dimensional Neutral Delay Dynamic Systems
Directory of Open Access Journals (Sweden)
Xinli Zhang
2013-01-01
Full Text Available We consider a class of nonlinear two-dimensional dynamic systems of the neutral type (x(t-a(tx(τ1(tΔ=p(tf1(y(t, yΔ(t=-q(tf2(x(τ2(t. We obtain sufficient conditions for all solutions of the system to be oscillatory. Our oscillation results when a(t=0 improve the oscillation results for dynamic systems on time scales that have been established by Fu and Lin (2010, since our results do not restrict to the case where f(u=u. Also, as a special case when =ℝ, our results do not require an to be a positive real sequence. Some examples are given to illustrate the main results.
Anomaly matching condition in two-dimensional systems
Dubinkin, O; Gubankova, E
2016-01-01
Based on Son-Yamamoto relation obtained for transverse part of triangle axial anomaly in ${\\rm QCD}_4$, we derive its analog in two-dimensional system. It connects the transverse part of mixed vector-axial current two-point function with diagonal vector and axial current two-point functions. Being fully non-perturbative, this relation may be regarded as anomaly matching for conductivities or certain transport coefficients depending on the system. We consider the holographic RG flows in holographic Yang-Mills-Chern-Simons theory via the Hamilton-Jacobi equation with respect to the radial coordinate. Within this holographic model it is found that the RG flows for the following relations are diagonal: Son-Yamamoto relation and the left-right polarization operator. Thus the Son-Yamamoto relation holds at wide range of energy scales.
Collective Modes in Two Dimensional Binary Yukawa Systems
Kalman, Gabor J; Donko, Zoltan; Golden, Kenneth I; Kyrkos, Stamatios
2013-01-01
We analyze via theoretical approaches and molecular dynamics simulations the collective mode structure of strongly coupled two-dimensional binary Yukawa systems, for selected density, mass and charge ratios, both in the liquid and crystalline solid phases. Theoretically, the liquid phase is described through the Quasi-Localized Charge Approximation (QLCA) approach, while in the crystalline phase we study the centered honeycomb and the staggered rectangular crystal structures through the standard harmonic phonon approximation. We identify "longitudinal" and "transverse" acoustic and optic modes and find that the longitudinal acoustic mode evolves from its weakly coupled counterpart in a discontinuous non-perturbative fashion. The low frequency acoustic excitations are governed by the oscillation frequency of the average atom, while the high frequency optic excitation frequencies are related to the Einstein frequencies of the systems.
Two-dimensional spatial patterning in developmental systems.
Torii, Keiko U
2012-08-01
Multicellular organisms produce complex tissues with specialized cell types. During animal development, numerous cell-cell interactions shape tissue patterning through mechanisms involving contact-dependent cell migration and ligand-receptor-mediated lateral inhibition. Owing to the presence of cell walls, plant cells neither migrate nor undergo apoptosis as a means to correct for mis-specified cells. How can plants generate functional tissue patterns? This review aims to deduce fundamental principles of pattern formation through examining two-dimensional (2-D) spatial tissue patterning in plants and animals. Turing's mathematical framework will be introduced and applied to classic examples of de novo 2-D patterning in both animal and plant systems. By comparing their regulatory circuits, new insights into the similarities and differences of the basic principles governing tissue patterning will be discussed. Copyright © 2012 Elsevier Ltd. All rights reserved.
Filtering and control for classes of two-dimensional systems
Wu, Ligang
2015-01-01
This book focuses on filtering, control and model-reduction problems for two-dimensional (2-D) systems with imperfect information. The time-delayed 2-D systems covered have system parameters subject to uncertain, stochastic and parameter-varying changes. After an initial introduction of 2-D systems and the ideas of linear repetitive processes, the text is divided into two parts detailing: · general theory and methods of analysis and optimal synthesis for 2-D systems; and · application of the general theory to the particular case of differential/discrete linear repetitive processes. The methods developed provide a framework for stability and performance analysis, optimal and robust controller and filter design and model approximation for the systems considered. Solutions to the design problems are couched in terms of linear matrix inequalities. For readers interested in the state of the art in linear filtering, control and model reduction, Filtering and Control for Classes of ...
Performance Estimation for Two-Dimensional Brownian Rotary Ratchet Systems
Tutu, Hiroki; Horita, Takehiko; Ouchi, Katsuya
2015-04-01
Within the context of the Brownian ratchet model, a molecular rotary system that can perform unidirectional rotations induced by linearly polarized ac fields and produce positive work under loads was studied. The model is based on the Langevin equation for a particle in a two-dimensional (2D) three-tooth ratchet potential of threefold symmetry. The performance of the system is characterized by the coercive torque, i.e., the strength of the load competing with the torque induced by the ac driving field, and the energy efficiency in force conversion from the driving field to the torque. We propose a master equation for coarse-grained states, which takes into account the boundary motion between states, and develop a kinetic description to estimate the mean angular momentum (MAM) and powers relevant to the energy balance equation. The framework of analysis incorporates several 2D characteristics and is applicable to a wide class of models of smooth 2D ratchet potential. We confirm that the obtained expressions for MAM, power, and efficiency of the model can enable us to predict qualitative behaviors. We also discuss the usefulness of the torque/power relationship for experimental analyses, and propose a characteristic for 2D ratchet systems.
Curved Two-Dimensional Electron Systems in Semiconductor Nanoscrolls
Peters, Karen; Mendach, Stefan; Hansen, Wolfgang
The perfect control of strain and layer thickness in epitaxial semiconductor bilayers is employed to fabricate semiconductor nanoscrolls with precisely adjusted scroll diameter ranging between a few nanometers and several tens of microns. Furthermore, semiconductor heteroepitaxy allows us to incorporate quantum objects such as quantum wells, quantum dots, or modulation doped low-dimensional carrier systems into the nanoscrolls. In this review, we summarize techniques that we have developed to fabricate semiconductor nanoscrolls with well-defined location, orientation, geometry, and winding number. We focus on magneto-transport studies of curved two-dimensional electron systems in such nanoscrolls. An externally applied magnetic field results in a strongly modulated normal-to-surface component leading to magnetic barriers, reflection of edge channels, and local spin currents. The observations are compared to finite-element calculations and discussed on the basis of simple models taking into account the influence of a locally modulated state density on the conductivity. In particular, it is shown that the observations in high magnetic fields can be well described considering the transport in edge channels according to the Landauer-Büttiker model if additional magnetic field induced channels aligned along magnetic barriers are accounted for.
Note: Unshielded bilateral magnetoencephalography system using two-dimensional gradiometers
Seki, Yusuke; Kandori, Akihiko; Ogata, Kuniomi; Miyashita, Tsuyoshi; Kumagai, Yukio; Ohnuma, Mitsuru; Konaka, Kuni; Naritomi, Hiroaki
2010-09-01
Magnetoencephalography (MEG) noninvasively measures neuronal activity with high temporal resolution. The aim of this study was to develop a new type of MEG system that can measure bilateral MEG waveforms without a magnetically shielded room, which is an obstacle to reducing both the cost and size of an MEG system. An unshielded bilateral MEG system was developed using four two-dimensional (2D) gradiometers and two symmetric cryostats. The 2D gradiometer, which is based on a low-Tc superconducting quantum interference device and wire-wound pickup coil detects a magnetic-field gradient in two orthogonal directions, or ∂/∂x(∂2Bz/∂z2), and reduces environmental magnetic-field noise by more than 50 dB. The cryostats can be symmetrically positioned in three directions: vertical, horizontal, and rotational. This makes it possible to detect bilateral neuronal activity in the cerebral cortex simultaneously. Bilateral auditory-evoked fields (AEF) of 18 elderly subjects were measured in an unshielded hospital environment using the MEG system. As a result, both the ipsilateral and the contralateral AEF component N100m, which is the magnetic counterpart of electric N100 in electroencephalography and appears about 100 ms after the onset of an auditory stimulus, were successfully detected for all the subjects. Moreover, the ipsilateral P50m and the contralateral P50m were also detected for 12 (67%) and 16 (89%) subjects, respectively. Experimental results demonstrate that the unshielded bilateral MEG system can detect MEG waveforms, which are associated with brain dysfunction such as epilepsy, Alzheimer's disease, and Down syndrome.
Criticality in Two-Dimensional Quantum Systems: Tensor Network Approach
Ran, Shi-Ju; Li, Wei; Lewenstein, Maciej; Su, Gang
2016-01-01
Determination and characterization of criticality in two-dimensional (2D) quantum many-body systems belong to the most important challenges and problems of quantum physics. In this paper we propose an efficient scheme to solve this problem by utilizing the infinite projected entangled pair state (iPEPS), and tensor network (TN) representations. We show that the criticality of a 2D state is faithfully reproduced by the ground state (dubbed as boundary state) of a one-dimensional effective Hamiltonian constructed from its iPEPS representation. We demonstrate that for a critical state the correlation length and the entanglement spectrum of the boundary state are essentially different from those of a gapped iPEPS. This provides a solid indicator that allows to identify the criticality of the 2D state. Our scheme is verified on the resonating valence bond (RVB) states on kagom\\'e and square lattices, where the boundary state of the honeycomb RVB is found to be described by a $c=1$ conformal field theory. We apply ...
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.
Torque magnetometry studies of two-dimensional electron systems
Schaapman, Maaike Ruth
2004-01-01
This thesis describes a study of the magnetization two-dimensional electron gases (2DEGs). To detect the typically small magnetization, a sensitive magnetometer with optical angular detection was developed. The magnetometer uses a quadrant detector to measure the rotation of the sample. By mounting
Torque magnetometry studies of two-dimensional electron systems
Schaapman, Maaike Ruth
2004-01-01
This thesis describes a study of the magnetization two-dimensional electron gases (2DEGs). To detect the typically small magnetization, a sensitive magnetometer with optical angular detection was developed. The magnetometer uses a quadrant detector to measure the rotation of the sample. By mounting
Energy Technology Data Exchange (ETDEWEB)
Czachor, Andrzej, E-mail: a.czachor@ncbj.gov.pl
2016-02-15
In this paper we consider the assembly of weakly interacting identical particles, where the occupation of single-particle energy-levels at thermal equilibrium is governed by statistics. The analytic form of the inter-energy-level jump matrix is derived and analytic solution of the related eigen-problem is given. It allows one to demonstrate the nature of decline in time of the energy emission (fluorescence, recombination) of such many-level system after excitation in a relatively simple and unifying way – as a multi-exponential de-excitation. For the system of L energy levels the number of the de-excitation lifetimes is L−1. The lifetimes depend on the energy level spectrum as a whole. Two- and three-level systems are considered in detail. The impact of the energy level degeneracy on the lifetimes is discussed.
Fault-tolerance in Two-dimensional Topological Systems
Anderson, Jonas T.
This thesis is a collection of ideas with the general goal of building, at least in the abstract, a local fault-tolerant quantum computer. The connection between quantum information and topology has proven to be an active area of research in several fields. The introduction of the toric code by Alexei Kitaev demonstrated the usefulness of topology for quantum memory and quantum computation. Many quantum codes used for quantum memory are modeled by spin systems on a lattice, with operators that extract syndrome information placed on vertices or faces of the lattice. It is natural to wonder whether the useful codes in such systems can be classified. This thesis presents work that leverages ideas from topology and graph theory to explore the space of such codes. Homological stabilizer codes are introduced and it is shown that, under a set of reasonable assumptions, any qubit homological stabilizer code is equivalent to either a toric code or a color code. Additionally, the toric code and the color code correspond to distinct classes of graphs. Many systems have been proposed as candidate quantum computers. It is very desirable to design quantum computing architectures with two-dimensional layouts and low complexity in parity-checking circuitry. Kitaev's surface codes provided the first example of codes satisfying this property. They provided a new route to fault tolerance with more modest overheads and thresholds approaching 1%. The recently discovered color codes share many properties with the surface codes, such as the ability to perform syndrome extraction locally in two dimensions. Some families of color codes admit a transversal implementation of the entire Clifford group. This work investigates color codes on the 4.8.8 lattice known as triangular codes. I develop a fault-tolerant error-correction strategy for these codes in which repeated syndrome measurements on this lattice generate a three-dimensional space-time combinatorial structure. I then develop an
Küppersbusch, C.S.
2015-01-01
In the first part of the thesis I derive a full quantitative formula which describes the amplitude and frequency of magnetic oscillations in two-dimensional Dirac systems. The investigations are on the basis of graphene, but they generally also hold for other two-dimensional Dirac systems. Starting
Pattern Coarsening in a Two Dimensional Hexagonal System
Chaikin, Paul
2008-03-01
We have been studying the ordering, annealing, coarsening and alignment of two dimensional periodically ordered structures in thin films of diblock copolymers*. Coarsening by dislocation and disclination annihilation is clearly observed in AFM studies of monolayer films of cylindrical patterns with a time dependence given by t^α, with α about 1/4. However in hexagonal structures the mechanism is less well defined and appears to involve the collapse of small grains entrained in the grain boundaries of larger domains. Remarkably the exponent of α about 1/4 remains. We also report on shear aligned samples and samples quenched in a gradient after alignment. * Harrison C, Angelescu DE, Trawick M, Cheng ZD, Huse DA, Chaikin PM, Vega DA, Sebastian JM, Register RA, Adamson DH, EUROPHYSICS LETTERS 67 800-806 (2004)
Results from laboratory tests of the two-dimensional Time-Encoded Imaging System.
Energy Technology Data Exchange (ETDEWEB)
Marleau, Peter; Brennan, James S.; Brubaker, Erik; Gerling, Mark D; Le Galloudec, Nathalie Joelle
2014-09-01
A series of laboratory experiments were undertaken to demonstrate the feasibility of two dimensional time-encoded imaging. A prototype two-dimensional time encoded imaging system was designed and constructed. Results from imaging measurements of single and multiple point sources as well as extended source distributions are presented. Time encoded imaging has proven to be a simple method for achieving high resolution two-dimensional imaging with potential to be used in future arms control and treaty verification applications.
Deformed oscillator algebras for two dimensional quantum superintegrable systems
Bonatsos, Dennis; Kokkotas, K D; Bonatsos, Dennis
1994-01-01
Quantum superintegrable systems in two dimensions are obtained from their classical counterparts, the quantum integrals of motion being obtained from the corresponding classical integrals by a symmetrization procedure. For each quantum superintegrable systema deformed oscillator algebra, characterized by a structure function specific for each system, is constructed, the generators of the algebra being functions of the quantum integrals of motion. The energy eigenvalues corresponding to a state with finite dimensional degeneracy can then be obtained in an economical way from solving a system of two equations satisfied by the structure function, the results being in agreement to the ones obtained from the solution of the relevant Schrodinger equation. The method shows how quantum algebraic techniques can simplify the study of quantum superintegrable systems, especially in two dimensions.
Sadabadi, Mahdiye Sadat; Shafiee, Masoud; Karrari, Mehdi
2008-07-01
In this paper, parameter identification of two-dimensional continuous-time systems via two-dimensional modulating functions is proposed. In the proposed method, trigonometric functions and sine-cosine wavelets are used as modulating functions. By this, a partial differential equation on the finite-time intervals is converted into an algebraic equation linear in parameters. The parameters of the system can then be estimated using the least square algorithms. The underlying computations utilize a two-dimensional fast Fourier transform algorithm, without the need for estimating the unknown initial or boundary conditions, at the beginning of each finite-time interval. Numerical simulations are presented to show the effectiveness of the proposed algorithm.
Sequentially generated states for the study of two dimensional systems
Energy Technology Data Exchange (ETDEWEB)
Banuls, Mari-Carmen; Cirac, J. Ignacio [Max-Planck-Institut fuer Quantenoptik, Garching (Germany); Perez-Garcia, David [Depto. Analisis Matematico, Universidad Complutense de Madrid (Spain); Wolf, Michael M. [Niels Bohr Institut, Copenhagen (Denmark); Verstraete, Frank [Fakultaet fuer Physik, Universitaet Wien (Austria)
2009-07-01
The family of Matrix Product States represents a powerful tool for the study of physical one-dimensional quantum many-body systems, such as spin chains. Besides, Matrix Product States can be defined as the family of quantum states that can be sequentially generated in a one-dimensional system. We have introduced a new family of states which extends this sequential definition to two dimensions. Like in Matrix Product States, expectation values of few body observables can be efficiently evaluated and, for the case of translationally invariant systems, the correlation functions decay exponentially with the distance. We show that such states are a subclass of Projected Entangled Pair States and investigate their suitability for approximating the ground states of local Hamiltonians.
Zhao, Xujun; Hernandez-Ortiz, Juan; Karpeyev, Dmitry; de Pablo, Juan; Smith, Barry
In this work, we present an efficient parallel particle-in-mesh method for Brownian Dynamics simulations of many-particle systems confined in micro- and nano-fluidic devices. A general geometry Ewald-like method (GGEM) combined with finite element method is used to account for the hydrodynamic interaction. A fast parallel Krylov-type iterative solver with hybrid preconditioning techniques is developed for solving the large sparse systems of equations arising from finite element discretization of the Stokes equations. In addition, the current computer code is developed based on PETSc, a scalable library of numerical algorithms developed at Argonne, SLEPc - Scalable Library for Eigenvalue Problem Computations, and libMesh, a finite element library for numerical solution of PDEs built on top of PETSc, which allows for direct simulation of large scale systems with arbitrary confined geometries. This scheme is applied to Brownian dynamics simulations of flowing confined polymer solutions and colloidal dispersions in micro-fluid channels. The effects of hydrodynamics interactions and geometric confinement on the migration phenomena are illustrated.
Two-Dimensional Lattice Gravity as a Spin System
Beirl, W; Riedler, J
1994-01-01
Quantum gravity is studied in the path integral formulation applying the Regge calculus. Restricting the quadratic link lengths of the originally triangular lattice the path integral can be transformed to the partition function of a spin system with higher couplings on a Kagome lattice. Various measures acting as external field are considered. Extensions to matter fields and higher dimensions are discussed.
Two-dimensional diffusion limited system for cell growth
Energy Technology Data Exchange (ETDEWEB)
Hlatky, L.
1985-11-01
A new cell system, the ''sandwich'' system, was developed to supplement multicellular spheroids as tumor analogues. Sandwiches allow new experimental approaches to questions of diffusion, cell cycle effects and radiation resistance in tumors. In this thesis the method for setting up sandwiches is described both theoretically and experimentally followed by its use in x-ray irradiation studies. In the sandwich system, cells are grown in a narrow gap between two glass slides. Where nutrients and waste products can move into or out of the local environment of the cells only by diffusing through the narrow gap between the slides. Due to the competition between cells, self-created gradients of nutrients and metabolic products are set up resulting in a layer of cells which resembles a living spheroid cross section. Unlike the cells of the spheroid, however, cells in all regions of the sandwich are visible. Therefore, the relative sizes of the regions and their time-dependent growth can be monitored visually without fixation or sectioning. The oxygen and nutrient gradients can be ''turned off'' at any time without disrupting the spatial arrangement of the cells by removing the top slide of the assembly and subsequently turned back on if desired. Removal of the top slide also provides access to all the cells, including those near the necrotic center, of the sandwich. The cells can then be removed for analysis outside the sandwich system. 61 refs., 17 figs.
Occurrence conditions for two-dimensional Borromean systems
DEFF Research Database (Denmark)
G. Volosniev, A.; V. Fedorov, D.; S. Jensen, A.
2013-01-01
Borromean systems. We show that Borromean states can only appear for potentials with substantial attractive and repulsive parts. Borromean states are most easily found when a barrier is present outside an attractive pocket. Extensive numerical search did not reveal Borromean states for potentials without...
Undamped relativistic magnetoplasmons in lossy two-dimensional electron systems
Volkov, V. A.; Zabolotnykh, A. A.
2016-10-01
We address electrodynamic effects in plasma oscillations of a lossy 2D electron system whose dc 2D conductivity σ0 is comparable to the speed of light c . We argue that the perpendicular constant magnetic field B causes astonishing features of magnetoplasma dynamics. We show that plasmon-polariton spectra can be classified using a "relativistic" phase diagram σ0/c versus B . An extraordinarily low damping branch in magnetoplasmon-polariton spectra emerges at two phases of this diagram. Some magnetoplasmons at these phases are predicted to be undamped waves.
Undamped relativistic magnetoplasmons in lossy two-dimensional electron systems
Volkov, V A
2016-01-01
We address electrodynamic effects in plasma oscillations of a lossy 2D electron system whose dc 2D conductivity is comparable to the speed of light. We argue that the perpendicular dc magnetic field B causes astonishing features of magnetoplasma dynamics. We show that plasmon-polariton spectra can be classified using a "relativistic" phase diagram 2D conductivity divided by the speed of light versus B. A novel, extraordinarily low damping branch in magnetoplasmon-polariton spectra emerges at two phases of this diagram. Some magnetoplasmons at these phases are predicted to be undamped waves.
Aging in the two-dimensional random-field systems
Cheng, Xiang; Ma, Tianyu; Urazhdin, Sergei; Boettcher, Stefan
Random fields introduced into the classical Ising and Heisenberg spin models can roughen the energy landscape, leading to complex nonequilibrium dynamics. The effects of random fields on magnetism have been previously studied in the context of dilute antiferromagnets (AF), impure substrates, and magnetic alloys [ 1 ] . We utilized random-field spin models to simulate the observed magnetic aging in thin-film ferromagnet/antiferromagnet (F/AF) bilayers. Our experiments show extremely slow cooperative relaxation over a wide range of temperatures and magnetic fields [ 2 ] . In our simulations, the experimental system is coarse-grained into a random field Ising model on a 2D square lattice. Monte Carlo simulations indicate that aging processes may be associated with the glassy evolution of the magnetic domain walls, due to the pinning by the random fields. The scaling of the simulated aging agrees well with experiments. Both are consistent with either a small power-law or logarithmic dependence on time. We further discuss the topological effects on aging due to the dimensional crossover from the Ising to the Heisenberg regime. Supported through NSF grant DMR-1207431.
General criteria for determining rotation or oscillation in a two-dimensional axisymmetric system
Koyano, Yuki; Yoshinaga, Natsuhiko; Kitahata, Hiroyuki
2015-07-01
A self-propelled particle in a two-dimensional axisymmetric system, such as a particle in a central force field or confined in a circular region, may show rotational or oscillatory motion. These motions do not require asymmetry of the particle or the boundary, but arise through spontaneous symmetry breaking. We propose a generic model for a self-propelled particle in a two-dimensional axisymmetric system. A weakly nonlinear analysis establishes criteria for determining rotational or oscillatory motion.
Photodetectors based on graphene, other two-dimensional materials and hybrid systems.
Koppens, F H L; Mueller, T; Avouris, Ph; Ferrari, A C; Vitiello, M S; Polini, M
2014-10-01
Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms. The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges. These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies. Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides.
Performance of Thomas-Fermi and linear response approaches in periodic two-dimensional systems
Energy Technology Data Exchange (ETDEWEB)
Calderin, L; Stott, M J [Department of Physics, Queen' s University, Kingston, Ontario, K7 L 3N6 (Canada)], E-mail: calderin@physics.queensu.ca, E-mail: stott@mjs.phy.queensu.ca
2010-04-16
A study of the performance of Thomas-Fermi and linear response theories in the case of a two-dimensional periodic model system is presented. The calculated density distribution and total energy per unit cell compare very well with exact results except when there is a small number of particles per cell, even though the potential has narrow tight-binding bands. The results supplement earlier findings of Koivisto and Stott for a localized impurity in a two-dimensional uniform gas.
Thorneywork, Alice L; Roth, Roland; Aarts, Dirk G A L; Dullens, Roel P A
2014-04-28
Two-dimensional hard disks are a fundamentally important many-body model system in classical statistical mechanics. Despite their significance, a comprehensive experimental data set for two-dimensional single component and binary hard disks is lacking. Here, we present a direct comparison between the full set of radial distribution functions and the contact values of a two-dimensional binary colloidal hard sphere model system and those calculated using fundamental measure theory. We find excellent quantitative agreement between our experimental data and theoretical predictions for both single component and binary hard disk systems. Our results provide a unique and fully quantitative mapping between experiments and theory, which is crucial in establishing the fundamental link between structure and dynamics in simple liquids and glass forming systems.
Anisotropic dielectric properties of two-dimensional matrix in pseudo-spin ferroelectric system
Kim, Se-Hun
2016-10-01
The anisotropic dielectric properties of a two-dimensional (2D) ferroelectric system were studied using the statistical calculation of the pseudo-spin Ising Hamiltonian model. It is necessary to delay the time for measurements of the observable and the independence of the new spin configuration under Monte Carlo sampling, in which the thermal equilibrium state depends on the temperature and size of the system. The autocorrelation time constants of the normalized relaxation function were determined by taking temperature and 2D lattice size into account. We discuss the dielectric constants of a two-dimensional ferroelectric system by using the Metropolis method in view of the Slater-Takagi defect energies.
Theoretical and experimental study of the normal modes in a coupled two-dimensional system
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.
The two dimensional electron system as a nanoantenna in the microwave and terahertz bands
Iñarrea, Jesús
2011-12-01
We study the magnetoresistance of two-dimensional electron systems under several radiation sources of different frequencies for moderate power. We use the model of radiation-driven electron orbits extended to this regime. First, we consider the case of two different radiations and we find a regime of superposition or interference of harmonic motions, i.e., a modulated magnetoresistance response with pulses and beats. Finally, we consider a multiple photoexcitation case where we propose the two-dimensional electron system as a potential nanoantenna device or ultrasensitive detector for the microwave and terahertz bands. Thus, these results could be of special interest in nanophotonics and nanoelectronics.
On the equivalence between stochastic baker's maps and two-dimensional spin systems
Lindgren, K.
2010-05-01
We show that there is a class of stochastic bakers transformations that is equivalent to the class of equilibrium solutions of two-dimensional spin systems with finite interaction. The construction is such that the equilibrium distribution of the spin lattice is identical to the invariant measure in the corresponding bakers transformation. We illustrate the equivalence by deriving two stochastic bakers maps representing the Ising model at a temperature above and below the critical temperature, respectively. A calculation of the invariant measure and the free energy in the baker system is then shown to be in agreement with analytic results of the two-dimensional Ising model.
Construction of exact complex dynamical invariant of a two-dimensional classical system
Indian Academy of Sciences (India)
Fakir Chand; S C Mishra
2006-12-01
We present the construction of exact complex dynamical invariant of a two-dimensional classical dynamical system on an extended complex space utilizing Lie algebraic approach. These invariants are expected to play a vital role in understanding the complex trajectories of both classical and quantum systems.
Magnetic-field-induced suppression of tunnelling into a two-dimensional electron system
Energy Technology Data Exchange (ETDEWEB)
Reker, T.; Chung, Y.C.; Im, H.; Klipstein, P.C.; Nicholas, R.J. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford (United Kingdom); Shtrikman, Hadas [Braun Center for Submicron Research, Weizmann Institute of Science, Rehovot (Israel)
2002-06-10
Tunnelling between a three-dimensional emitter contact and a two-dimensional electron system (2DES) is studied in magnetic fields aligned perpendicular to the barriers of a double-barrier heterostructure. The differential conductance around the Fermi energy exhibits a magnetic-field-dependent pseudogap. This pseudogap is shown to be thermally activated and to depend on the two-dimensional electron density. We attribute this pseudogap to an extra energy that an electron tunnelling from the emitter into the 2DES has to overcome as a result of the correlated state of the 2DES. (author)
Non-monotonic magnetoresistance of two-dimensional electron systems in the ballistic regime
Kuntsevich, A. Yu.; Minkov, G. M.; Sherstobitov, A. A.; Pudalov, V. M.
2009-01-01
We report experimental observations of a novel magnetoresistance (MR) behavior of two-dimensional electron systems in perpendicular magnetic field in the ballistic regime, for k_BT\\tau/\\hbar>1. The MR grows with field and exhibits a maximum at fields B>1/\\mu, where \\mu is the electron mobility. As temperature increases the magnitude of the maximum grows and its position moves to higher fields. This effect is universal: it is observed in various Si- and GaAs- based two-dimensional electron sys...
Density of states of Frenkel excitons in strongly disordered two-dimensional systems
Siemann, Robert; Boukahil, Abdelkrim
2014-03-01
We present the calculation of the density of states of Frenkel excitons in strongly disordered two-dimensional systems. A random distribution of transition frequencies with variance σ2 characterizes the disorder. The Coherent Potential Approximation (CPA) calculations show a strong dependence of the density of states (DOS) on the disorder parameter σ.
Two-dimensional metric and tetrad gravities as constrained second order systems
Kiriushcheva, N; Ghalati, R N
2006-01-01
Using the Gitman-Lyakhovich-Tyutin generalization of the Ostrogradsky method for analyzing singular systems, we consider the Hamiltonian formulation of metric and tetrad gravities in two-dimensional Riemannian spacetime treating them as constrained higher-derivative theories. The algebraic structure of the Poisson brackets of the constraints and the corresponding gauge transformations are investigated in both cases.
Numerical Studies of Collective Phenomena in Two-Dimensional Electron and Cold Atom Systems
Energy Technology Data Exchange (ETDEWEB)
Rezayi, Edward
2013-07-25
Numerical calculations were carried out to investigate a number of outstanding questions in both two-dimensional electron and cold atom systems. These projects aimed to increase our understanding of the properties of and prospects for non-Abelian states in quantum Hall matter.
Absolute negative conductivity in two-dimensional electron systems under microwave radiation
Ryzhii, Victor
2004-01-01
We overview mechanisms of absolute negative conductivity in two-dimensional electron systems in a magnetic field irradiated with microwaves and provide plausible explanations of the features observed in recent experiments related to the so-called zero-resistance (zero-conductance) states.
Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems
Ferrari, A.C.; Dekker, C.; Vandersypen, L.M.K.; Van Der Zant, H.S.J.; et. al.
2014-01-01
We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphen
de Snoo, H; Winkler, Henrik
2005-01-01
The class of two-dimensional trace-normed canonical systems of differential equations on R is considered with selfadjoint interface conditions at 0. If one or both of the intervals around 0 are H-indivisible the interface conditions which give rise to selfadjoint relations (multi-valued operators) a
Feedback stabilisation of a two-dimensional pool-boiling system by modal control
van Gils, R.W.; Speetjens, M.F.M; Zwart, Heiko J.; Nijmeijer, H.
The present study concerns the feedback stabilisation of the unstable equilibria of a two-dimensional nonlinear pool-boiling system with essentially heterogeneous temperature distributions in the fluid-heater interface. Regulation of such equilibria has great potential for application in, for
Negative Dispersion of Lattice Waves in a Two-Dimensional Yukawa System
Institute of Scientific and Technical Information of China (English)
刘艳红; 刘斌; 杨思泽; 王龙
2002-01-01
Collective motion modes existing in a two-dimensional Yukawa system are investigated by molecular dynamics simulation. The dispersion relations of transverse and longitudinal lattice waves obtained for hexagonal lattice are in agreement with the theoretical results. The negative dispersion of the parallel longitudinal wave is demonstrated by the simulation, and is explained by a physical model.
Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems
Ferrari, Andrea C.; Bonaccorso, Francesco; Fal'ko, Vladimir; Novoselov, Konstantin S.; Roche, Stephan; Boggild, Peter; Borini, Stefano; Koppens, Frank H. L.; Palermo, Vincenzo; Pugno, Nicola; Garrido, Jose A.; Sordan, Roman; Bianco, Alberto; Ballerini, Laura; Prato, Maurizio; Lidorikis, Elefterios; Kivioja, Jani; Marinelli, Claudio; Ryhaenen, Tapani; Morpurgo, Alberto; Coleman, Jonathan N.; Nicolosi, Valeria; Colombo, Luigi; Fert, Albert; Garcia-Hernandez, Mar; Bachtold, Adrian; Schneider, Gregory F.; Guinea, Francisco; Dekker, Cees; Barbone, Matteo; Sun, Zhipei; Galiotis, Costas; Grigorenko, Alexander N.; Konstantatos, Gerasimos; Kis, Andras; Katsnelson, Mikhail; Vandersypen, Lieven; Loiseau, Annick; Morandi, Vittorio; Neumaier, Daniel; Treossi, Emanuele; Pellegrini, Vittorio; Polini, Marco; Tredicucci, Alessandro; Williams, Gareth M.; Hong, Byung Hee; Ahn, Jong-Hyun; Kim, Jong Min; Zirath, Herbert; van Wees, Bart J.; van der Zant, Herre; Occhipinti, Luigi; Di Matteo, Andrea; Kinloch, Ian A.; Seyller, Thomas; Quesnel, Etienne; Feng, Xinliang; Teo, Ken; Rupesinghe, Nalin; Hakonen, Pertti; Neil, Simon R. T.; Tannock, Quentin; Loefwander, Tomas; Kinaret, Jari
2015-01-01
We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European
Exact solutions and conservation laws of the system of two-dimensional viscous Burgers equations
Abdulwahhab, Muhammad Alim
2016-10-01
Fluid turbulence is one of the phenomena that has been studied extensively for many decades. Due to its huge practical importance in fluid dynamics, various models have been developed to capture both the indispensable physical quality and the mathematical structure of turbulent fluid flow. Among the prominent equations used for gaining in-depth insight of fluid turbulence is the two-dimensional Burgers equations. Its solutions have been studied by researchers through various methods, most of which are numerical. Being a simplified form of the two-dimensional Navier-Stokes equations and its wide range of applicability in various fields of science and engineering, development of computationally efficient methods for the solution of the two-dimensional Burgers equations is still an active field of research. In this study, Lie symmetry method is used to perform detailed analysis on the system of two-dimensional Burgers equations. Optimal system of one-dimensional subalgebras up to conjugacy is derived and used to obtain distinct exact solutions. These solutions not only help in understanding the physical effects of the model problem but also, can serve as benchmarks for constructing algorithms and validation of numerical solutions of the system of Burgers equations under consideration at finite Reynolds numbers. Independent and nontrivial conserved vectors are also constructed.
Growth and electronic properties of two-dimensional systems on (110) oriented GaAs
Energy Technology Data Exchange (ETDEWEB)
Fischer, F.
2005-07-01
As the only non-polar plane the (110) surface has a unique role in GaAs. Together with Silicon as a dopant it is an important substrate orientation for the growth of n-type or p-type heterostructures. As a consequence, this thesis will concentrate on growth and research on that surface. In the course of this work we were able to realize two-dimensional electron systems with the highest mobilities reported so far on this orientation. Therefore, we review the necessary growth conditions and the accompanying molecular process. The two-dimensional electron systems allowed the study of a new, intriguing transport anisotropy not explained by current theory. Moreover, we were the first growing a two-dimensional hole gas on (110) GaAs with Si as dopant. For this purpose we invented a new growth modulation technique necessary to retrieve high mobility systems. In addition, we discovered and studied the metal-insulator transition in thin bulk p-type layers on (110) GaAs. Besides we investigated the activation process related to the conduction in the valence band and a parallelly conducting hopping band. The new two-dimensional hole gases revealed interesting physics. We studied the zero B-field spin splitting in these systems and compared it with the known theory. Furthermore, we investigated the anisotropy of the mobility. As opposed to the expectations we observed a strong persistent photoconductivity in our samples. Landau levels for two dimensional hole systems are non-linear and can show anticrossings. For the first time we were able to resolve anticrossings in a transport experiment and study the corresponding activation process. Finally, we compared these striking results with theoretical calculations. (orig.)
Influence of disorder and magnetic field on conductance of “sandwich” type two dimensional system
Directory of Open Access Journals (Sweden)
Long LIU
2017-04-01
Full Text Available In order to discuss the transport phenomena and the physical properties of the doping of the disorder system under magnetic field, the electron transport in a two-dimensional system is studied by using Green function and scattering matrix theory. Base on the two-dimensional lattice model, the phenomenon of quantized conductance of the "sandwich" type electronic system is analyzed. The contact between the lead and the scatterer reduce the system's conductance, and whittle down the quantum conductance stair-stepping phenomenon; when an external magnetic field acts on to the system, the conductance presents a periodicity oscillation with the magnetic field. The intensity of this oscillation is related to the energy of the electron;with the increase of the impurity concentration, the conductance decreases.In some special doping concentration, the conductance of the system can reach the ideal step value corresponding to some special electron energy. The result could provide reference for further study of the conductance of the "sandwich" type two dimensional system.
Directory of Open Access Journals (Sweden)
Musa Danjuma SHEHU
2008-06-01
Full Text Available This paper lays emphasis on formulation of two dimensional differential games via optimal control theory and consideration of control systems whose dynamics is described by a system of Ordinary Differential equation in the form of linear equation under the influence of two controls U(. and V(.. Base on this, strategies were constructed. Hence we determine the optimal strategy for a control say U(. under a perturbation generated by the second control V(. within a given manifold M.
Two-dimensional atom localization via probe absorption in a four-level atomic system
Institute of Scientific and Technical Information of China (English)
Wang Zhi-Ping; Ge Qiang; Ruan Yu-Hua; Yu Ben-Li
2013-01-01
We have investigated the two-dimensional (2D) atom localization via probe absorption in a coherently driven fourlevel atomic system by means of a radio-frequency field driving a hyperfine transition.It is found that the detecting probability and precision of 2D atom localization can be significantly improved via adjusting the system parameters.As a result,our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.
Nonequilibrium Phase Transition in a Two-Dimensional Driven Open Quantum System
Directory of Open Access Journals (Sweden)
G. Dagvadorj
2015-11-01
Full Text Available The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is mediated by the proliferation of topological defects, governs the critical behavior of a wide range of equilibrium two-dimensional systems with a continuous symmetry, ranging from spin systems to superconducting thin films and two-dimensional Bose fluids, such as liquid helium and ultracold atoms. We show here that this phenomenon is not restricted to thermal equilibrium, rather it survives more generally in a dissipative highly nonequilibrium system driven into a steady state. By considering a quantum fluid of polaritons of an experimentally relevant size, in the so-called optical parametric oscillator regime, we demonstrate that it indeed undergoes a phase transition associated with a vortex binding-unbinding mechanism. Yet, the exponent of the power-law decay of the first-order correlation function in the (algebraically ordered phase can exceed the equilibrium upper limit: this shows that the ordered phase of driven-dissipative systems can sustain a higher level of collective excitations before the order is destroyed by topological defects. Our work suggests that the macroscopic coherence phenomena, observed recently in interacting two-dimensional light-matter systems, result from a nonequilibrium phase transition of the Berezinskii-Kosterlitz-Thouless rather than the Bose-Einstein condensation type.
EMC/FDTD/MD simulation of carrier transport and electrodynamics in two-dimensional electron systems
Sule, N.; Willis, K. J.; Hagness, S. C.; Knezevic, I.
2014-01-01
We present the implementation and application of a multiphysics simulation technique to carrier dynamics under electromagnetic excitation in supported two-dimensional electronic systems. The technique combines ensemble Monte Carlo (EMC) for carrier transport with finite-difference time-domain (FDTD) for electrodynamics and molecular dynamics (MD) for short-range Coulomb interactions among particles. We demonstrate the use of this EMC/FDTD/MD technique by calculating the room-temperature dc an...
The investigation on two-dimensional pilot-symbol-aided channel estimation method for OFDM system
Institute of Scientific and Technical Information of China (English)
Sun Juying; Zhang Yanhua
2008-01-01
Channel estimation for orthogonal frequency division multiplexing (OFDM) system has attracted widespread attention. In this paper, a novel efficient two-dimensional (2-D) channel estimation algorithm based on fast Fourier transform (FFT) is proposed for a time-variant, frequency-selective wideband wireless channel. Both theoretical analysis and simulation results are addressed in the paper. The simulation results prove that the proposed algorithm has simpler implementation, better performance and wider application than other traditional decision-directed algorithms.
STABILITY OF SYSTEM OF TWO-DIMENSIONAL NON-HYDROSTATIC REVOLVING FLUIDS
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Applying the theory of stratification, it is proved that the system of the two-dimensional non-hydrostatic revolving fluids is unstable in the two-order continuous function class. The construction of solution space is given and the solution approach is offered. The sufficient and necessary conditions of the existence of formal solutions are expressed for some typical initial and boundary value problems and the calculating formulae to formal solutions are presented in detail.
Modeling of the optical properties of a two-dimensional system of small conductive particles.
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.
Third order finite volume evolution Galerkin (FVEG) methods for two-dimensional wave equation system
Lukácová-Medvid'ová, Maria; Warnecke, Gerald; Zahaykah, Yousef
2003-01-01
The subject of the paper is the derivation and analysis of third order finite volume evolution Galerkin schemes for the two-dimensional wave equation system. To achieve this the first order approximate evolution operator is considered. A recovery stage is carried out at each level to generate a piecewise polynomial approximation from the piecewise constants, to feed into the calculation of the fluxes. We estimate the truncation error and give numerical examples to demonstrate the higher order...
2012-01-01
remark- able electronic properties observed in graphene. Chapter 2 reviews the basic physical con- cepts of 2DES including a brief introduction to...magnetotransport in high quality GaAs/ AlGaAs heterostructure two dimensional electron systems. The effect of microwave (MW) radiation on electron...This thesis consists of two parts. The rst part considers the e ect of microwave radiation on magnetotransport in high quality GaAs/ AlGaAs
On Relations between One-Dimensional Quantum and Two-Dimensional Classical Spin Systems
Directory of Open Access Journals (Sweden)
J. Hutchinson
2015-01-01
Full Text Available We exploit mappings between quantum and classical systems in order to obtain a class of two-dimensional classical systems characterised by long-range interactions and with critical properties equivalent to those of the class of one-dimensional quantum systems treated by the authors in a previous publication. In particular, we use three approaches: the Trotter-Suzuki mapping, the method of coherent states, and a calculation based on commuting the quantum Hamiltonian with the transfer matrix of a classical system. This enables us to establish universality of certain critical phenomena by extension from the results in the companion paper for the classical systems identified.
Critical wetting transitions in two-dimensional systems subject to long-ranged boundary fields
Drzewiński, A.; Maciołek, A.; Barasiński, A.; Dietrich, S.
2009-04-01
Using the quasiexact density-matrix renormalization-group method and ground-state analysis we study interface delocalization transitions in wide two-dimensional Ising strips subject to long-ranged boundary fields with opposite signs at the two surfaces. Based on this approach, our explicit calculations demonstrate that critical wetting transitions do exist for semi-infinite two-dimensional systems even if the corresponding effective interface potentials decay asymptotically for large ℓ as slow as ℓ-δ with δinterface position from the one-dimensional surface. This supersedes opposite claims by Kroll and Lipowsky [Phys. Rev. B 28, 5273 (1983)] and by Privman and Švrakić [Phys. Rev. B 37, 5974 (1988)] obtained within effective interface models. The corresponding wetting phase diagram is determined, including the cases δ=2 and δ=49 with the latter mimicking short-ranged surface fields. Our analysis highlights the limits of reliability of effective interface models.
Two-dimensional analysis of gold nanoparticle effects on dye molecule system
Energy Technology Data Exchange (ETDEWEB)
Qaradaghi, Vahid [School of Electrical and Computer Engineering, Tarbiat Modares University (TMU), P.O. Box 14115-194, Tehran (Iran, Islamic Republic of); Fathi, Davood, E-mail: davfathi@modares.ac.ir [School of Electrical and Computer Engineering, Tarbiat Modares University (TMU), P.O. Box 14115-194, Tehran (Iran, Islamic Republic of)
2013-01-15
This paper presents a two-dimensional analysis of a dye molecule system in the presence of a gold nanoparticle (AuNP). This configuration has been used widely for the practical applications such as optoelectronics and also the biomedical applications such as cancer. The effects of coupling between the nanoparticle (AuNP) and dye molecules around it are simulated and studied in a two-dimensional plane. The three relative momentum polarizations of dye molecule near the AuNP (perpendicular, parallel and random) are considered. With the change of nanoparticle radius and its distances from the dye molecules, the output fluorescence signal will be changed. The obtained results show that, the perpendicular polarized dye w.r.t. the AuNP surface leads to the increase of output fluorescence signal nearly 1.5 times the input intensity.
Critical wetting transitions in two-dimensional systems subject to long-ranged boundary fields.
Drzewiński, A; Maciołek, A; Barasiński, A; Dietrich, S
2009-04-01
Using the quasiexact density-matrix renormalization-group method and ground-state analysis we study interface delocalization transitions in wide two-dimensional Ising strips subject to long-ranged boundary fields with opposite signs at the two surfaces. Based on this approach, our explicit calculations demonstrate that critical wetting transitions do exist for semi-infinite two-dimensional systems even if the corresponding effective interface potentials decay asymptotically for large l as slow as l(-delta) with deltainterface position from the one-dimensional surface. This supersedes opposite claims by Kroll and Lipowsky [Phys. Rev. B 28, 5273 (1983)] and by Privman and Svrakić [Phys. Rev. B 37, 5974 (1988)] obtained within effective interface models. The corresponding wetting phase diagram is determined, including the cases delta=2 and delta=49 with the latter mimicking short-ranged surface fields. Our analysis highlights the limits of reliability of effective interface models.
Prediction of two-dimensional diluted magnetic semiconductors: Doped monolayer MoS2 systems
Cheng, Yingchun
2013-03-05
Using first-principles calculations, we propose a two-dimensional diluted magnetic semiconductor: monolayer MoS2 doped by transition metals. Doping of transition metal atoms from the IIIB to VIB groups results in nonmagnetic states, since the number of valence electrons is smaller or equal to that of Mo. Doping of atoms from the VIIB to IIB groups becomes energetically less and less favorable. Magnetism is observed for Mn, Fe, Co, Zn, Cd, and Hg doping, while for the other dopants from these groups it is suppressed by Jahn-Teller distortions. Analysis of the binding energies and magnetic properties indicates that (Mo,X)S2 (X=Mn, Fe, Co, and Zn) are promising systems to explore two-dimensional diluted magnetic semiconductors.
Quantum Hall effect in black phosphorus two-dimensional electron system.
Li, Likai; Yang, Fangyuan; Ye, Guo Jun; Zhang, Zuocheng; Zhu, Zengwei; Lou, Wenkai; Zhou, Xiaoying; Li, Liang; Watanabe, Kenji; Taniguchi, Takashi; Chang, Kai; Wang, Yayu; Chen, Xian Hui; Zhang, Yuanbo
2016-07-01
The development of new, high-quality functional materials has been at the forefront of condensed-matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the materials base of two-dimensional electron systems (2DESs). Here, we report the observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES. The high quality is achieved by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES and brings the carrier Hall mobility up to 6,000 cm(2) V(-1) s(-1). The exceptional mobility enabled us to observe the quantum Hall effect and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.
Many-particle entanglement criterion for superradiant-like states
Tasgin, Mehmet Emre
2016-01-01
We derive a many-particle inseparability criterion for mixed states using the relation between single-mode and many-particle nonclassicalities. It works very well not only in the vicinity of the Dicke states, but also for the superposition of them: superradiant ground state of finite/infinite number of particles and time evolution of single-photon superradiance. We also obtain a criterion for ensemble-field entanglement which works fine for such kind of states. Even though the collective excitations of the many-particle system is sub-Poissonian --which results in entanglement-- the wave function displays bunching.
Tupikov, Y.; Kuntsevich, A. Yu.; Pudalov, V. M.; Burmistrov, I. S.
2015-01-01
We report first thermodynamic measurements of the temperature derivative of chemical potential (d{\\mu}/dT) in two-dimensional (2D) electron systems. In order to test the technique we have chosen Schottky gated GaAs/AlGaAs heterojunctions and detected experimentally in this 2D system quantum magnetooscillations of d{\\mu}/dT. We also present a Lifshits-Kosevitch type theory for the d{\\mu}/dT magnetooscillations in 2D systems and compare the theory with experimental data. The magnetic field depe...
Doi, Hideo; Yasuoka, Kenji
2017-05-01
Confined systems exhibit interesting properties that are applied to the fields of lubrication, adhesion and nanotechnology. The replica exchange molecular simulation method was applied to calculate the phase equilibrium points of Lennard-Jones particles in a two-dimensional confined system. The liquid-solid phase equilibrium points and the solid structure with a dependency of the slit width were determined and the order parameter of the solid structure was analyzed. Such confined systems are shown to be favorable for manipulation of the phase equilibrium points.
The two-dimensional alternative binary L-J system: liquid-gas phase diagram
Institute of Scientific and Technical Information of China (English)
张陟; 陈立溁
2003-01-01
A two-dimensional (2D) binary system without considering the Lennard-Jones (L-J) potential has been studied by using the Collins model. In this paper, we introduce the L-J potential into the 2D binary system and consider the existence of the holes that are called the "molecular fraction". The liquid-gas phase diagram of the 2D alternative binary L-J system is obtained. The results are quite analogous to the behaviour of 3D substances.
Rabilloud, T; Vincon, M; Garin, J
1995-08-01
To improve the efficiency of one- and two-dimensional electrophoresis for micropreparative purposes, the use of gels polymerized with other initiators than the standard N,N,N',N'-tetramethylethylenediamine (TEMED)/persulfate systems for sodium dodecyl sulfate electrophoresis has been investigated. We show here that the recently described photoinitiator system, composed of methylene blue, toluene sulfinate and diphenyliodonium chloride, leads to a decreased resolution. Resolution can be restored if methylene blue is replaced by riboflavin. Two-dimensional electrophoresis with mg loadings of proteins has also been evaluated with these systems. Independently of the polymerization system, resolution for the first dimension is low with rod gels, increases with gel strips and is further improved when immobilized pH gradients are used. Here too, only the riboflavin/sulfinate/iodonium system results in a resolution that matches the one obtained with the standard TEMED/persulfate system. Gels polymerized with the riboflavin/sulfinate/iodonium system yield better results upon N-terminal microsequencing after blotting than gels polymerized with the standard TEMED/persulfate system.
Tunneling in two-dimensional systems using a higher-order Herman-Kluk approximation.
Hochman, Gili; Kay, Kenneth G
2009-02-14
A principal weakness of the Herman-Kluk (HK) semiclassical approximation is its failure to provide a reliably accurate description of tunneling between different classically allowed regions. It was previously shown that semiclassical corrections significantly improve the HK treatment of tunneling for the particular case of the one-dimensional Eckart system. Calculations presented here demonstrate that the lowest-order correction also substantially improves the HK description of tunneling across barriers in two-dimensional systems. Numerical convergence issues either do not arise or are easily overcome, so that the calculations require only a moderate number of ordinary, real, classical trajectories.
Spin current and polarization in impure two-dimensional electron systems with spin-orbit coupling.
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.
On the Classical Solutions of Two Dimensional Inviscid Rotating Shallow Water System
Cheng, Bin
2009-01-01
We prove global existence and asymptotic behavior of classical solutions for two dimensional inviscid Rotating Shallow Water system with small initial data subject to the zero-relative-vorticity constraint. One of the key steps is a reformulation of the problem into a symmetric quasilinear Klein-Gordon system, for which the global existence of classical solutions is then proved with combination of the vector field approach and the normal forms. We also probe the case of general initial data and reveal a lower bound for the lifespan that is almost inversely proportional to the size of the initial relative vorticity.
Simulation of Dynamics in Two-Dimensional Vortex Systems in Random Media
Institute of Scientific and Technical Information of China (English)
ZHANG Wei; SUN Li-Zhen; LUO Meng-Bo
2009-01-01
Dynamics in two-dimensional vortex systems with random pinning centres is investigated using molecular dy-namical simulations. The driving force and temperature dependences of vortex velocity are investigated. Below the critical depinning force Fc, a creep motion of vortex is found at low temperature. At forces slightly above Fc, a part of vortices flow in winding channels at zero temperature. In the vortex channel flow region, we ob-serve the abnormal behaviour of vortex dynamics: the velocity is roughly independent of temperature or even decreases with temperature at low temperatures. A phase diagram that describes different dynamics of vortices is presented.
Zero-differential resistance state of two-dimensional electron systems in strong magnetic fields.
Bykov, A A; Zhang, Jing-qiao; Vitkalov, Sergey; Kalagin, A K; Bakarov, A K
2007-09-14
We report the observation of a zero-differential resistance state (ZDRS) in response to a direct current above a threshold value I>I th applied to a two-dimensional system of electrons at low temperatures in a strong magnetic field. Entry into the ZDRS, which is not observable above several Kelvins, is accompanied by a sharp dip in the differential resistance. Additional analysis reveals an instability of the electrons for I>I th and an inhomogeneous, nonstationary pattern of the electric current. We suggest that the dominant mechanism leading to the new electron state is a redistribution of electrons in energy space induced by the direct current.
Energy Technology Data Exchange (ETDEWEB)
Barbaro, M. [ENEA, Centro Ricerche `Ezio Clementel`, Bologna (Italy). Dipt. Innovazione
1997-11-01
A numerical method is described which generates an orthogonal curvilinear mesh, subject to the constraint that mesh lines are matched to all boundaries of a closed, simply connected two-dimensional region of arbitrary shape. The method is based on the solution, by an iterative finite-difference technique, of an elliptic differential system of equations for the Cartesian coordinates of the orthogonal grid nodes. The interior grid distribution is controlled by a technique which ensures that coordinate lines can be concentrated as desired. Examples of orthogonal meshes inscribed in various geometrical figures are included.
Cyclotron resonance in two-dimensional electron system with self-organized antidots
Suchalkin, S D; Zundel, M; Nachtwei, G; Klitzing, K V; Eberl, K
2001-01-01
The data on the experimental study on the cyclotron resonance in the two-dimensional electron system with the random scattering potential, conditioned by the massif of the AlInAs self-organized quantum islands, formed in the AlGaAs/GaAs heterotransition plane, are presented. The sharp narrowing of the cyclotron resonance with increase in the magnetic field, explained by the charge scattering peculiarities in the given potential is established. The obtained results suggest the strongly correlated electron state in the strong magnetic fields by the carriers concentrations lesser than the antidots concentrations
Institute of Scientific and Technical Information of China (English)
Guangwei Yuan; Longjun Shen
2003-01-01
In this paper we are going to discuss the difference schemes with intrinsic parallelismfor the boundary value problem of the two dimensional semilinear parabolic systems. Theunconditional stability of the general finite difference schemes with intrinsic parallelismis justified in the sense of the continuous dependence of the discrete vector solution ofthe difference schemes on the discrete data of the original problems in the discrete W2(2,1)norms. Then the uniqueness of the discrete vector solution of this difference scheme followsas the consequence of the stability.
Resolution enhancement of scanning four-point-probe measurements on two-dimensional systems.
Hansen, Torben Mikael; Stokbro, Kurt; Hansen, Ole; Hassenkam, T.; Shiraki, I.; Hasegawa, S.; Bøggild, Peter
2003-01-01
A method to improve the resolution of four-point-probe measurements of two-dimensional (2D) and quasi-2D systems is presented. By mapping the conductance on a dense grid around a target area and postprocessing the data, the resolution can be improved by a factor of approximately 50 to better than 1/15 of the four-point-probe electrode spacing. The real conductance sheet is simulated by a grid of discrete resistances, which is optimized by means of a standard optimization algorithm, until the ...
Hall Conductivity in a Quasi-Two-Dimensional Disordered Electron System
Institute of Scientific and Technical Information of China (English)
YANG Yong-Hong; WANG Yong-Gang; LIU Mei
2002-01-01
By making use of the diagrammatic techniques in perturbation theory,we have investigated the Hall effect in a quasi-two-dimensional disordered electron system.In the weakly localized regime,the analytical expression for quantum correction to Hall conductivity has been obtained using the Kubo formalism and quasiclassical approximation.The relevant dimensional crossover behavior from three dimensions to two dimensions with decreasing the interlayer hopping energy is discussed.The quantum interference effect is shown to have a vanishing correction t,o the Hall coefficient.
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.
Shabani, Javad
2016-10-01
Theory suggests that the interface between a one-dimensional semiconductor (Sm) with strong spin-orbit coupling and a superconductor (S) hosts Majorana modes with nontrivial topological properties. A key challenge in fabrication of such hybrid devices is forming highly transparent contacts between the active electrons in the semiconductor and the superconducting metal. Recently, it has been shown that a near perfect interface and a highly transparent contact can be achieved using epitaxial growth of aluminum on InAs nanowires. In this work, we present the first two-dimensional epitaxial superconductor-semiconductor material system that can serve as a platform for topological superconductivity. We show that our material system, Al-InAs, satisfies all the requirements necessary to reach into the topological superconducting regime by individual characterization of the semiconductor two dimensional electron system, superconductivity of Al and performance of S-Sm-S junctions. This exciting development might lead to a number of useful applications ranging from spintronics to quantum computing.
Hybrid two-dimensional electronic systems and other applications of sp-2 bonded light elements
Kessler, Brian Maxwell
The field-effect is a cornerstone of modern technology lying at the heart of transistors in consumer electronics. Experimentally, it allows one to continuously vary the carrier concentration in a material while studying its properties. The recent isolation of graphene, the first truly two-dimensional crystal, allows application of the field effect to a much wider range of physical situations. In the first part of the thesis, we investigate hybrid materials formed by coupling metals to the two-dimensional electron gas (2DEG) in graphene. We couple superconducting materials to the graphene sheet by cluster deposition. This material displays a superconducting phase whose properties are tuned by the carrier density via the field effect. The transition temperature is well-described by Berezinskii-Kosterlitz-Thouless vortex unbinding. The ground state properties show interesting effects due to the distribution of cluster spacings. Observations related to other hybrid electronic systems including ferromagnets and normal metals are presented. The second part of this thesis involves energy applications of light element materials. The mechanisms affecting coating of carbon nanotubes using atomic layer deposition is developed and applied to photovoltaic systems. The gas adsorption properties of activated boron nitride are investigated and the relative influence of surface area and hydrogen binding affinity is elaborated. The third part of this thesis explores electromechanical properties of suspended graphene membranes. We investigate buckling and strain in exfoliated graphene membranes as well as their deformation under an applied gate potential.
Transport properties of magnetic-codoped two-dimensional hole system
Energy Technology Data Exchange (ETDEWEB)
Knott, Stefan; Wurstbauer, Ursula; Hansen, Wolfgang [Institut fuer Angewandte Physik, Universitaet Hamburg (Germany)
2009-07-01
The interaction of localized magnetic moments with a two dimensional hole system (2DHS) is studied with low-temperature magneto-transport measurements on molecular beam epitaxially grown InAs or InAlGaAs quantum-well structures that are C-modulation and Mn co-doped. Measurements in magnetic fields applied perpendicular to the 2DHS reveal the typical transport behaviour of a two-dimensional charge carrier system indicated by Shubnikov-de Haas oscillations and quantum-Hall plateaus. Investigations at milli-Kelvin temperatures show a metal-insulator transition in the low field region. The fully spin-polarized quantum Hall state at filling factor {nu}=1 is very pronounced, i.e. over a field range of more than 4 T the longitudinal resistance vanishes and the Hall resistance is constant. Surprisingly, the {nu}=2 state seems to be fully suppressed whereas the {nu}=3 state is clearly resolved by an indistinct structure in the Hall resistance and a minimum in the longitudinal resistance. Transport measurements in tilted magnetic fields are carried out to resolve the nature of the observed quantum-Hall states.
Iñarrea, Jesús
2011-04-01
We analyze theoretically magnetoresistance of high-mobility two-dimensional electron systems being illuminated by multiple radiation sources. In particular, we study the influence on the striking effect of microwave-induced resistance oscillations. We consider moderate radiation intensities without reaching the zero-resistance states regime. We use the model of radiation-driven Larmor orbits extended to several light sources. First, we study the case of two different radiations polarized in the same direction with different or equal frequencies. For both cases, we find a regime of superposition or interference of harmonic motions. When the frequencies are different, we obtain a modulated magnetoresistance response with pulses and beats. On the other hand, when the frequencies are the same, we find that the final result will depend on the phase difference between both radiation fields going from an enhanced response to a total collapse of oscillations, reaching an outcome similar to darkness. Finally, we consider a multiple photoexcitation case (three different frequencies) in which we propose the two-dimensional electron system as a potential nanoantenna device for microwaves.
Fiber-optic interferometric two-dimensional scattering-measurement system.
Zhu, Yizheng; Giacomelli, Michael G; Wax, Adam
2010-05-15
We present a fiber-optic interferometric system for measuring depth-resolved scattering in two angular dimensions using Fourier-domain low-coherence interferometry. The system is a unique hybrid of the Michelson and Sagnac interferometer topologies. The collection arm of the interferometer is scanned in two dimensions to detect angular scattering from the sample, which can then be analyzed to determine the structure of the scatterers. A key feature of the system is the full control of polarization of both the illumination and the collection fields, allowing for polarization-sensitive detection, which is essential for two-dimensional angular measurements. System performance is demonstrated using a double-layer microsphere phantom. Experimental data from samples with different sizes and acquired with different polarizations show excellent agreement with Mie theory, producing structural measurements with subwavelength accuracy.
Non-Achievability of Metal-Insulator Transition in Two-Dimensional Systems
Institute of Scientific and Technical Information of China (English)
A. John Peter
2006-01-01
@@ We present a simple demonstration of the non feasibility of metal-insulator transition in an exactly two-dimensional (2D) system. The Hartree-Fock potential in the 3D system is suitably modified and presented for the 2D case.The many body effects are included in the screening function, and binding energies of a donor are obtained as a function of impurity concentration so as to find out the possible way leading metal-insulator transition in the 2D system. While solving for the binding energy for a shallow donor in an isolated well of a GaAs/Ga1-x Als As superlattice system within the effective mass approximation, it leads to unphysical results for higher concentrations.
Reddy, T. S. R.; Srivastava, R.; Mehmed, Oral
2002-01-01
An aeroelastic analysis system for flutter and forced response analysis of turbomachines based on a two-dimensional linearized unsteady Euler solver has been developed. The ASTROP2 code, an aeroelastic stability analysis program for turbomachinery, was used as a basis for this development. The ASTROP2 code uses strip theory to couple a two dimensional aerodynamic model with a three dimensional structural model. The code was modified to include forced response capability. The formulation was also modified to include aeroelastic analysis with mistuning. A linearized unsteady Euler solver, LINFLX2D is added to model the unsteady aerodynamics in ASTROP2. By calculating the unsteady aerodynamic loads using LINFLX2D, it is possible to include the effects of transonic flow on flutter and forced response in the analysis. The stability is inferred from an eigenvalue analysis. The revised code, ASTROP2-LE for ASTROP2 code using Linearized Euler aerodynamics, is validated by comparing the predictions with those obtained using linear unsteady aerodynamic solutions.
Hilbert-Schmidt Geometry of n-Level Jakobczyk-Siennicki Two-Dimensional Quantum Systems
Slater, P B
2005-01-01
Jakobczyk and Siennicki studied two-dimensional sections of a set of Bloch vectors corresponding to n x n density matrices of two-qubit systems (that is, the case n=4). They found essentially five different types of (nontrivial) separability regimes. We compute the Euclidean/Hilbert-Schmidt (HS) separability probabilities assigned to these regimes, and conduct parallel two-dimensional section analyses for the cases n=6,8,9 and 10. We obtain a very wide variety of exact HS-probabilities. For n>6, the probabilities are those of having a partial positive transpose (PPT). For the n=6 case, we also obtain biseparability probabilities; in the n=8,9 instances, bi-PPT probabilities; and for n=8, tri-PPT probabilities. By far, the most frequently recorded probability for n>4 is Pi/4 = 0.785398$. We also conduct a number of related analyses, pertaining to the (one-dimensional) boundaries (both exterior and interior) of the separability and PPT domains, and discuss some exact calculations pertaining to the 9-dimensional...
Two-dimensional habitat modeling in the Yellowstone/Upper Missouri River system
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.
Two-dimensional electron-hole capture in a disordered hopping system
Greenham, N. C.; Bobbert, P. A.
2003-12-01
We model the two-dimensional recombination of electrons and holes in a system where the mean free path is short compared with the thermal capture radius. This recombination mechanism is relevant to the operation of bilayer organic light-emitting diodes (LED’s), where electrons and holes accumulate on either side of the internal heterojunction. The electron-hole recombination rate can be limited by the time taken for these charge carriers to drift and diffuse to positions where electrons and holes are directly opposite to each other on either side of the interface, at which point rapid formation of an emissive neutral state can occur. In this paper, we use analytical and numerical techniques to find the rate of this two-dimensional electron-hole capture process. Where one species of carrier is significantly less mobile than the other, we find that the recombination rate depends superlinearly on the density of the less mobile carrier. Numerical simulations allow the effects of disorder to be taken into account in a microscopic hopping model. Direct solution of the master equation for hopping provides more efficient solutions than Monte Carlo simulations. The rate constants extracted from our model are consistent with efficient emission from bilayer LED’s without requiring independent hopping of electrons and holes over the internal barrier at the heterojunction.
Bill2d -- a software package for classical two-dimensional Hamiltonian systems
Solanpää, Janne; Räsänen, Esa
2016-01-01
We present Bill2d, a modern and efficient C++ package for classical simulations of two-dimensional Hamiltonian systems. Bill2d can be used for various billiard and diffusion problems with one or more charged particles with interactions, different external potentials, an external magnetic field, periodic and open boundaries, etc. The software package can also calculate many key quantities in complex systems such as Poincar\\'e sections, survival probabilities, and diffusion coefficients. While aiming at a large class of applicable systems, the code also strives for ease-of-use, efficiency, and modularity for the implementation of additional features. The package comes along with a user guide, a developer's manual, and a documentation of the application program interface (API).
BILL2D - A software package for classical two-dimensional Hamiltonian systems
Solanpää, J.; Luukko, P. J. J.; Räsänen, E.
2016-02-01
We present BILL2D, a modern and efficient C++ package for classical simulations of two-dimensional Hamiltonian systems. BILL2D can be used for various billiard and diffusion problems with one or more charged particles with interactions, different external potentials, an external magnetic field, periodic and open boundaries, etc. The software package can also calculate many key quantities in complex systems such as Poincaré sections, survival probabilities, and diffusion coefficients. While aiming at a large class of applicable systems, the code also strives for ease-of-use, efficiency, and modularity for the implementation of additional features. The package comes along with a user guide, a developer's manual, and a documentation of the application program interface (API).
Sunahara, Y.; Kojima, F.
1988-01-01
The purpose of this paper is to establish a method for identifying unknown parameters involved in the boundary state of a class of diffusion systems under noisy observations. A mathematical model of the system dynamics is given by a two-dimensional diffusion equation. Noisy observations are made by sensors allocated on the system boundary. Starting with the mathematical model mentioned above, an online parameter estimation algorithm is proposed within the framework of the maximum likelihood estimation. Existence of the optimal solution and related necessary conditions are discussed. By solving a local variation of the cost functional with respect to the perturbation of parameters, the estimation mechanism is proposed in a form of recursive computations. Finally, the feasibility of the estimator proposed here is demonstrated through results of digital simulation experiments.
Two-Dimensional River Flow Patterns Observed with a Pair of UHF Radar System
Directory of Open Access Journals (Sweden)
Yidong Hou
2017-01-01
Full Text Available A pair of ultrahigh-frequency (UHF radars system for measuring the two-dimensional river flow patterns is presented. The system consists of two all-digital UHF radars with exactly the same hardware structure, operating separately at 329–339 MHz and 341–351 MHz. The adoption of direct radio frequency (RF sampling technique and digital pulse compression simplifies the structure of radar system and eliminates the distortion introduced by the analog mixer, which improves the SNR and dynamic range of the radar. The field experiment was conducted at Hanjiang River, Hubei province, China. Over a period of several weeks, the radar-derived surface velocity has been very highly correlated with the measurements of EKZ-I, with a correlation coefficient of 0.958 and a mean square error of 0.084 m/s.
Structures and Dynamics of a Two-Dimensional Confined Dusty Plasma System
Institute of Scientific and Technical Information of China (English)
HUANG Feng; LIU Yan-Hong; WANG Long
2005-01-01
The influence of the confining potential strength and temperature on the structures and dynamics of a two-dimensional (2D) dusty plasma system is investigated through molecular dynamic (MD) simulation. The circular symmetric confining potential leads to the nonuniform packing of particles, that is, an inner core with a hexagon lattice surrounded by a few outer circular shells. Under the appropriate confining potential and temperature, the particle trajectories on middle shells form a series of concentric and nested hexagons due to tangential movements of particles.Mean square displacement, self-diffusion constant, pair correlation function, and the nearest bond are used to characterize the structural and dynamical properties of the system. With the increase of the confining potential, the radial and tangential movements of particles have different behaviors. With the increase of temperature, the radial and tangential motions strengthen, particle trajectories gradually become disordered, and the system gradually changes from a crystal or liquid state to a gas state.
Effect of pulse propagation on the two-dimensional photon echo spectrum of multilevel systems
Keusters, Dorine; Warren, Warren S.
2003-08-01
The effect of pulse propagation on the two-dimensional photon echo (2DPE) spectrum of multilevel systems is investigated using a perturbative method. At high optical densities (OD) peak profiles are broadened asymmetrically, in most cases more strongly along the ω2 direction than along the ω1 direction. The amount of broadening is determined both by the OD and by the dynamics of the system. In addition, especially if the different transitions in the system are of unequal strength, the relative intensity of the peaks changes with OD. But even if the transition strengths are the same, the behavior of the cross peaks is different from the diagonal peaks. Since peak shape and relative intensity are important parameters in the interpretation of 2DPE spectra, such OD effects should be taken into account.
Energy Technology Data Exchange (ETDEWEB)
Heinze, Stefan
2008-04-18
In the present dissertation different classes of quantum mechanical many body systems are investigated numerically and analytically considering symmetries in the formalism of second quantization. All algebraic ideas which are neccessary to develop a numerical computer code which is able to calculate the eigenvalues and eigenstates of a very general quantum many body hamiltonian are explained. The two most crucial problems are branching rules and the calculation of isoscalar factors. Methods are presented to solve these problems numerically for the general case. The most important point is the calculation of isoscalar factors with a nonrecursive method and without any numerical error. All presented ideas were implemented in the program '' ArbModel''. With this very flexible computer code at hand, systems of identical particles were investigated in general. General formulas were derived for the presence of dynamical symmetry. Weaker conditions are neccessary for the conservation of the so called seniority quantum number. This situation is called partial dynamical symmetry. These conditions were investigated in detail. Althouth other authors have previously investigated this problem, some new cases were discovered and new conditions could be derived. Most surprisingly, cases were found in which the seniority quantum number is generally broken except for some specific states. These states are solvable and formulae for their energies are presented. All analytically derived results were checked with ''ArbModel''. As further applications for the code, two selected models with distinguishable particles are investigated. The predictions of a very new theory, which connects quantum phase transitions and exceptional points, are verified with the sd-Interacting-Boson-Model 1 (sd-IBM1) and a very high particle number. For the Interacting-Boson-Fermion-Model a selected dynamical symmetry was investigated. The branching rules for this Bose
Density of states of two-dimensional systems with long-range logarithmic interactions
Energy Technology Data Exchange (ETDEWEB)
Somoza, Andrés M.; Ortuño, Miguel; Baturina, Tatyana I.; Vinokur, Valerii M.
2015-08-03
We investigate a single-particle density of states (DOS) in strongly disordered two- dimensional high dielectric permittivity systems with logarithmic Coulomb interaction between particles. We derive self-consistent DOS at zero temperature and show that it is appreciably suppressed as compared to the DOS expected from the Efros-Shklovskii approach.We carry out zero- and finite-temperature Monte Carlo numerical studies of the DOS and find the perfect agreement between the numerical and analytical results at zero temperature, observing, in particular, a hardening of the Coulomb gap with the increasing electrostatic screening length. At finite temperatures, we reveal a striking scaling of the DOS as a function of energy normalized to the temperature of the system.
Batrouni, George
2011-03-01
I will discuss pairing in fermionic systems in one- and two-dimensional optical lattices with population imbalance. This will be done in the context of the attractive fermionic Hubbard model using the Stochastic Green Function algorithm in d=1 while for d=2 we use Determinant Quantum Monte Carlo. This is the first exact QMC study examining the effects of finite temperature which is very important in experiments on ultra-cold atoms. Our results show that, in the ground state, the dominant pairing mechanism is at nonzero center of mass momentum, i.e. FFLO. I will then discuss the effect of finite temperature in the uniform and confined systems and present finite temperature phase diagrams. The numerical results will be compared with experiments. With M. J. Wolak (CQT, National University of Singapore) and V. G. Rousseau (Department of Physics and Astronomy, Louisiana State University).
Two-dimensional PSD based automatic docking of self-reconfiguration modular exploration robot system
Institute of Scientific and Technical Information of China (English)
Zhang Liping; Ma Shugen; Li Bin; Zhang Zheng; Cao Binggang
2007-01-01
Based on the design of a docking mechanism, this paper thoroughly investigates the space automatic docking of self-reconfiguration modular exploration robot system (RMERS). The method that leads robot to achieve space docking by using two-dimensional PSD is put forward innovatively for the median size robot system. At the same time, in order to enlarge the detecting extension and the precision of PSD and reduce its dependence on lighting signal, the PSD was remade by increasing the optical device over its light-sensitive surface. The emission board and LED light scheduling were designed according to docking arithmetic, and the operating principle of docking process was analyzed based on these. The simulation experiments were carried out and their results are presented.
Resonant state expansion applied to two-dimensional open optical systems
Doost, M B; Muljarov, E A
2013-01-01
The resonant state expansion (RSE), a rigorous perturbative method in electrodynamics, is applied to two-dimensional open optical systems. The analytically solvable homogeneous dielectric cylinder is used as unperturbed system, and its Green's function is shown to contain a cut in the complex frequency plane, which is included in the RSE basis. The complex eigenfrequencies of modes are calculated using the RSE for a selection of perturbations which mix unperturbed modes of different orbital momentum, such as half-cylinder, thin-film and thin-wire perturbation, demonstrating the accuracy and convergency of the method. The resonant states for the thin-wire perturbation are shown to reproduce an approximative analytical solution.
Wetting controlled phase transitions in two-dimensional systems of colloids
DEFF Research Database (Denmark)
Gil, Tamir; Ipsen, John Hjorth; Tejero, T.F.
1998-01-01
The phase behavior of disk colloids, embedded in a two-dimensional fluid matrix that undergoes a first-order phase transition, is studied in the complete wetting regime where the thermodynamically metastable fluid phase is stabilized at the surface of the disks. In dilute collections of disks......, the tendency to minimize the extent of the fluid-fluid interface and the extent of the unfavorable wetting phase in the system gives rise to aggregation phenomena and to separation of large domains of disks that have the characteristics of bulk colloidal phases. The conditions for phase transitions among...... cluster gas, liquid, and solid phases of the disk colloids are determined from the corresponding values of the disk chemical potential within an analytic representation of the grand partition function for the excess energy associated with a gas of disk clusters in the low-disk-density limit. The wetting...
Spontaneous chiral resolution in two-dimensional systems of patchy particles
Energy Technology Data Exchange (ETDEWEB)
Martínez-González, J. A.; Chapela, G. A. [Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186, Col. Vicentina, 09340 México D.F. (Mexico); Quintana-H, J., E-mail: jaq@unam.mx [Instituto de Química, Universidad Nacional Autónoma de México - Apdo. Postal 70213, 04510 Coyoacán, México D.F. (Mexico)
2014-05-21
Short ranged potentials and their anisotropy produce spontaneous chiral resolution in a two dimensional model of patchy particles introduced in this paper. This model could represent an equimolar binary mixture (racemic mixture) of two kinds of chiral molecules (enantiomers) adsorbed to a bi-dimensional domain where only lateral short ranged interactions are present. Most racemic mixtures undergo chiral resolution due to their spatial anisotropy, the combined effect of long range forces and the thermodynamic conditions. The patchy particles are modeled as a hard disk and four different bonding sites located to produce chirality. Phase behavior and structural properties are analysed using Discontinuous Molecular Dynamics in the canonical ensemble. When the four patchy particles are separated by the angles (60°, 120°, 60°, 120°), spontaneous chiral resolution is produced, given by the formation of homochiral clusters, if started from the corresponding racemic mixture. Gel behavior is also obtained in all the systems for low temperatures and low densities.
Two-dimensional NMR exchange spectroscopy. Quantitative treatment of multisite exchanging systems
Abel, Edward W.; Coston, Timothy P. J.; Orrell, Keith G.; Šik, Vladimir; Stephenson, David
A general method for evaluating rate constants in complex exchange networks with N-sites from two-dimensional EXSY (NOESY) NMR spectra is proposed. A computer program D2DNMR capable of performing signal intensity to exchange rate calculations (and vice versa), based on a matrix formalism, is outlined. The method is illustrated by 195Pt 2D NMR studies of the A ⇌ B ⇌ C spin system arising from pyramidal sulfur inversion in platinum(IV) complexes of type [Pt XMe 3(MeSCH 2CH 2SMe)] ( X = Cl, I). Comparison with 1H NMR bandshape analyses of the same compounds shows high agreement between the rate constants and activation parameters determined by both techniques. Mechanisms of 195Pt spin-lattice relaxation are briefly discussed.
Resolution enhancement of scanning four-point-probe measurements on two-dimensional systems
DEFF Research Database (Denmark)
Hansen, Torben Mikael; Stokbro, Kurt; Hansen, Ole;
2003-01-01
A method to improve the resolution of four-point-probe measurements of two-dimensional (2D) and quasi-2D systems is presented. By mapping the conductance on a dense grid around a target area and postprocessing the data, the resolution can be improved by a factor of approximately 50 to better than 1....../15 of the four-point-probe electrode spacing. The real conductance sheet is simulated by a grid of discrete resistances, which is optimized by means of a standard optimization algorithm, until the simulated voltage-to-current ratios converges with the measurement. The method has been tested against simulated...... data as well as real measurements and is found to successfully deconvolute the four-point-probe measurements. In conjunction with a newly developed scanning four-point probe with electrode spacing of 1.1 µm, the method can resolve the conductivity with submicron resolution. ©2003 American Institute...
Entanglement distribution in a two-dimensional 5-site frustrated J1-J2 spin system
Jafarpour, Mojtaba; Ghanavati, Soghra; Afshar, Davood
2015-11-01
We have studied several ground states and their entanglement structure for a two-dimensional 5-site frustrated J1-J2 system in the presence and absence of an external magnetic field. We have used concurrence as a measure of bipartite entanglement and the Meyer-Wallach measure and its generalizations as the measures of multipartite entanglement. They provide a total of eight measures which lead to 30 entanglement quantities for each possible ground state. Computing these 30 quantities for several ground states, we have provided a detailed exposition of the entanglement distribution in each state. We have also categorized them into separable states, not showing entanglement for any bipartition; globally-entangled states, showing entanglement for all the bipartitions, and the states in between. It turns out that by adjusting the external magnetic field, conditioned on the values of the interaction parameters, one may generate specific ground states belonging to a specific class, appropriate for specific tasks in quantum information theory.
The longitudinal optical conductivity in bilayer graphene and other two-dimensional systems
Energy Technology Data Exchange (ETDEWEB)
Yang, C.H., E-mail: chyang@nuist.edu.cn [School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044 (China); Ao, Z.M., E-mail: zhimin.ao@uts.edu.au [Centre for Clean Energy Technology, School of Chemistry and Forensic Science, University of Technology, Sydney ,PO Box 123, Broadway, Sydney, NSW 2007 (Australia); Wei, X.F. [West Anhui University, Luan 237012 (China); Jiang, J.J. [Department of Physics, Sanjing College, Nanjing 210012 (China)
2015-01-15
The longitudinal optical conductivity in bilayer graphene is calculated using the dielectric function by defining the density operator theoretically, while the effect of the broadening width determined by the scattering sources on the optical conductivity is also investigated. Some features, such as chirality, energy dispersion and density of state (DOS) in bilayer graphene, are similar to those in monolayer graphene and a traditional two-dimensional electron gas (2DEG). Therefore, in this paper, the bilayer graphene optical conductivity is compared with the results in these two systems. The analytical and numerical results show that the optical conductivity per graphene layer is almost a constant and close to e{sup 2}/(4ℏ), which agrees with the experimental results.
Phase coherence and spectral functions in the two-dimensional excitonic systems
Energy Technology Data Exchange (ETDEWEB)
Apinyan, V., E-mail: V.Apinyan@int.pan.wroc.pl; Kopeć, T.K.
2015-09-15
The nonlocal correlation mechanism between excitonic pairs is considered for a two dimensional exciton system. On the base of the unitary decomposition of the usual electron operator, we include the electron phase degrees of freedom into the problem of interacting excitons. Applying the path integral formalism, we treat the excitonic insulator state (EI) and the Bose–Einstein condensation (BEC) of preformed excitonic pairs as two independent problems. For the BEC of excitons the phase field variables play a crucial role. We derive the expression of the local EI order parameter by integrating out the phase variables. Then, considering the zero temperature limit, we obtain the excitonic BEC transition probability function, by integrating out the fermions. We calculate the normal excitonic Green functions for the conduction and valence band electrons and we derive the excitonic spectral functions, both analytically and numerically. Different values of the Coulomb interaction parameter are considered.
Reduced density-matrix functionals from many-particle theory
Schade, Robert; Kamil, Ebad; Blöchl, Peter
2017-07-01
In materials with strong electron correlation the proper treatment of local atomic physics described by orbital occupations is crucial. Reduced density-matrix functional theory is a natural extension of density functional theory for systems that are dominated by orbital physics. We review the current state of reduced density-matrix functional theory (RDMFT). For atomic structure relaxations or ab-initio molecular dynamics the combination of density functional theory (DFT) and dynamical mean-field theory (DMFT) possesses a number of disadvantages, like the cumbersome evaluation of forces. We therefore describe a method, DFT+RDMFT, that combines many-particle effects based on reduced density-matrix functional theory with a density functional-like framework. A recent development is the construction of density-matrix functionals directly from many-particle theory such as methods from quantum chemistry or many-particle Green's functions. We present the underlying exact theorems and describe current progress towards quantitative functionals.
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.
Two-dimensional hole systems in indium-based quantum well heterostructures
Energy Technology Data Exchange (ETDEWEB)
Loher, Josef
2016-08-01
The complex spin-orbit interaction (SOI) of two-dimensional hole gas (2DHG) systems - the relativistic coupling of the hole spin degree of freedom to their movement in an electric field - is of fundamental interest in spin physics due to its key role for spin manipulation in spintronic devices. In this work, we were able to evaluate the tunability of Rashba-SOI-related parameters in the 2DHG system of InAlAs/InGaAs/InAs:Mn quantum well heterostructures experimentally by analyzing the hole density evolution of quantum interference effects at low magnetic fields. We achieved to cover a significant range of hole densities by the joint action of the variation of the manganese modulation doping concentration during molecular beam epitaxy and external field-effect-mediated manipulation of the 2D carrier density in Hall bar devices by a metallic topgate. Within these magnetotransport experiments, a reproducible phenomenon of remarkable robustness emerged in the transverse Hall magnetoresistivity of the indium 2DHG systems which are grown on a special InAlAs step-graded metamorphic buffer layer structure to compensate crystal lattice mismatch. As a consequence of the strain relaxation process, these material systems are characterized by anisotropic properties along different crystallographic directions. We identify a puzzling offset phenomenon in the zero-field Hall magnetoresistance and demonstrate it to be a universal effect in systems with spatially anisotropic transport properties.
Structural analysis of a dipole system in two-dimensional channels.
Haghgooie, Ramin; Doyle, Patrick S
2004-12-01
A system of magnetic dipoles in two-dimensional (2D) channels was studied using Brownian dynamics simulations. The dipoles interact with a purely repulsive r(-3) potential and are confined by two hard walls in one of the dimensions. Solid crystals were annealed in the 2D channels and the structural properties of the crystals were investigated. The long-ranged nature of the purely repulsive dipoles combined with the presence of hard walls led to structural deviations from the unbounded (infinite) 2D dipolar crystal. The structures in the channels were characterized by a high density of particles along the walls. The particles along the wall became increasingly localized as the channel width was increased. The spacing of the walls was important in determining the properties of the structures formed in the channel. Small changes in the width of the channel induced significant structural changes in the crystal. These structural changes were manifested in the density profiles, defect concentrations, and local bond-orientation order of the system. Oscillations in the structural properties were observed as the channel width was increased, indicating the existence of magic-number channel widths for this system. As the channel width was increased the properties of the confined system approached those of the unbounded system surprisingly slowly.
Method and system for determining a volume of an object from two-dimensional images
Abercrombie, Robert K [Knoxville, TN; Schlicher, Bob G [Portsmouth, NH
2010-08-10
The invention provides a method and a computer program stored in a tangible medium for automatically determining a volume of three-dimensional objects represented in two-dimensional images, by acquiring at two least two-dimensional digitized images, by analyzing the two-dimensional images to identify reference points and geometric patterns, by determining distances between the reference points and the component objects utilizing reference data provided for the three-dimensional object, and by calculating a volume for the three-dimensional object.
Bifurcations of a two-dimensional discrete time plant-herbivore system
Khan, Abdul Qadeer; Ma, Jiying; Xiao, Dongmei
2016-10-01
In this paper, bifurcations of a two dimensional discrete time plant-herbivore system formulated by Allen et al. (1993) have been studied. It is proved that the system undergoes a transcritical bifurcation in a small neighborhood of a boundary equilibrium and a Neimark-Sacker bifurcation in a small neighborhood of the unique positive equilibrium. An invariant closed curve bifurcates from the unique positive equilibrium by Neimark-Sacker bifurcation, which corresponds to the periodic or quasi-periodic oscillations between plant and herbivore populations. For a special form of the system, which appears in Kulenović and Ladas (2002), it is shown that the system can undergo a supercritical Neimark-Sacker bifurcation in a small neighborhood of the unique positive equilibrium and a stable invariant closed curve appears. This bifurcation analysis provides a theoretical support on the earlier numerical observations in Allen et al. (1993) and gives a supportive evidence of the conjecture in Kulenović and Ladas (2002). Some numerical simulations are also presented to illustrate our theocratical results.
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...
Yang, Lei; Zhao, Xiao-Fang
2017-07-01
Chinese Spallation Neutron Source (CSNS) project will use numerous two-dimensional (2D) neutron detectors whose ZnS (Ag) scintillator is doped with 6Li. To ensure the consistency of all neutron detectors, a calibration system for the performance of 2D neutron detectors is designed. For radiation protection, the state control of the radiation source gets more and more strict. It is impossible to directly carry out experiments with massive radioactive particles. Thus, the following scheme has been designed. The controlled pulsed laser light source on a 2D mobile platform is used to replace the neutron bombardment to generate the photon. The pulse signal drives the laser diode to generate pulse light. The pulse light source located on the 2D platform is controlled by the core controller, and goes to the wavelength shift fiber through the optical fiber. The host computer (PC) receives the signal from the electronics system, processes data, and automatically calibrates the performance parameters. As shown by the experimental results, the pulse light source can perfectly meet all requirements of 2D neutron detector calibration system.
Classification of the sign of the critical Casimir force in two dimensional systems
Rajabpour, M A
2016-01-01
We classify the sign of the critical Casimir force between two finite objects separated by a large distance in the two dimensional systems that can be described by conformal field theory (CFT). In particular, we show that as far as the smallest scaling dimension present in the spectrum of the system is smaller than one, the sign of the force is independent of the shape of the objects and can be determined by the elements of the modular $S$-matrix of the CFT. The provided formula for the sign of the force indicates that the force is always attractive for equal boundary conditions independent of the shape of the objects. However, different boundary conditions can lead to attractive or repulsive forces. Using the derived formula, we prove the known results regarding the Ising model and the free bosons. As new examples, we give detailed results regarding the Q=3-states Potts model and the compactified bosons. In particular, for the latter model we show that Dirichlet boundary condition does not always lead to an ...
Energy Technology Data Exchange (ETDEWEB)
Pelliccione, M. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Bartel, J.; Goldhaber-Gordon, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305 (United States); Sciambi, A. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)
2014-11-03
Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250 nm resolution.
Nonlinear chemoconvection in the methylene-blue-glucose system: Two-dimensional shallow layers
Pons, A. J.; Batiste, O.; Bees, M. A.
2008-07-01
Interfacial hydrodynamic instabilities arise in a range of chemical systems. One mechanism for instability is the occurrence of unstable density gradients due to the accumulation of reaction products. In this paper we conduct two-dimensional nonlinear numerical simulations for a member of this class of system: the methylene-blue-glucose reaction. The result of these reactions is the oxidation of glucose to a relatively, but marginally, dense product, gluconic acid, that accumulates at oxygen permeable interfaces, such as the surface open to the atmosphere. The reaction is catalyzed by methylene-blue. We show that simulations help to disassemble the mechanisms responsible for the onset of instability and evolution of patterns, and we demonstrate that some of the results are remarkably consistent with experiments. We probe the impact of the upper oxygen boundary condition, for fixed flux, fixed concentration, or mixed boundary conditions, and find significant qualitative differences in solution behavior; structures either attract or repel one another depending on the boundary condition imposed. We suggest that measurement of the form of the boundary condition is possible via observation of oxygen penetration, and improved product yields may be obtained via proper control of boundary conditions in an engineering setting. We also investigate the dependence on parameters such as the Rayleigh number and depth. Finally, we find that pseudo-steady linear and weakly nonlinear techniques described elsewhere are useful tools for predicting the behavior of instabilities beyond their formal range of validity, as good agreement is obtained with the simulations.
Emergent topology and dynamical quantum phase transitions in two-dimensional closed quantum systems
Bhattacharya, Utso; Dutta, Amit
2017-07-01
Dynamical quantum phase transitions (DQPTs) manifested in the nonanalyticities in the temporal evolution of a closed quantum system generated by the time-independent final Hamiltonian, following a quench (or ramping) of a parameter of the Hamiltonian, is an emerging frontier of nonequilibrium quantum dynamics. We, here, introduce the notion of a dynamical topological order parameter (DTOP) that characterizes these DQPTs occurring in quenched (or ramped) two-dimensional closed quantum systems; this is quite a nontrivial generalization of the notion of DTOP introduced in Budich and Heyl [Phys. Rev. B 93, 085416 (2016), 10.1103/PhysRevB.93.085416] for one-dimensional situations. This DTOP is obtained from the "gauge-invariant" Pancharatnam phase extracted from the Loschmidt overlap, i.e., the modulus of the overlap between the initially prepared state and its time-evolved counterpart reached following a temporal evolution generated by the time-independent final Hamiltonian. This generic proposal is illustrated considering DQPTs occurring in the subsequent temporal evolution following a sudden quench of the staggered mass of the topological Haldane model on a hexagonal lattice where it stays fixed to zero or unity and makes a discontinuous jump between these two values at critical times at which DQPTs occur. What is remarkable is that while the topology of the equilibrium model is characterized by the Chern number, the emergent topology associated with the DQPTs is characterized by a generalized winding number.
Detection of topological states in two-dimensional Dirac systems by the dynamic spin susceptibility
Nakamura, Masaaki; Tokuno, Akiyuki
2016-08-01
We discuss dynamic spin susceptibility (DSS) in two-dimensional (2D) Dirac electrons with spin-orbit interactions to characterize topological insulators. The imaginary part of the DSS appears as an absorption rate in response to a transverse ac magnetic field, just as in an electron spin resonance experiment for localized spin systems. We found that when the system is in a static magnetic field, the topological state can be identified by an anomalous resonant peak of the imaginary part of the DSS as a function of the frequency of the transverse magnetic field ω . In the absence of a static magnetic field, the imaginary part of the DSS becomes a continuous function of ω with a threshold frequency ωc. In this case, the topological and the trivial phases can also be distinguished by the values of ωc and by the line shapes. Thus the DSS is an experimentally observable physical quantity to characterize a topological insulator directly from bulk properties, without observing a topological transition.
Unbinding transition in semi-infinite two-dimensional localized systems
Somoza, A. M.; Le Doussal, P.; Ortuño, M.
2015-04-01
We consider a two-dimensional strongly localized system defined in a half-plane and whose transfer integral in the edge can be different than in the bulk. We predict an unbinding transition, as the edge transfer integral is varied, from a phase where conduction paths are distributed across the bulk to a bound phase where propagation is mainly along the edge. At criticality the logarithm of the conductance follows the F1 Tracy-Widom distribution. We verify numerically these predictions for both the Anderson and the Nguyen, Spivak, and Shklovskii models. We also check that for a half-plane, i.e., when the edge transfer integral is equal to the bulk transfer integral, the distribution of the conductance is the F4 Tracy-Widom distribution. These findings are strong indications that random sign directed polymer models and their quantum extensions belong to the Kardar-Parisi-Zhang universality class. We have analyzed finite-size corrections at criticality and for a half-plane.
Quadratic band touching points and flat bands in two-dimensional topological Floquet systems
Du, Liang; Zhou, Xiaoting; Fiete, Gregory A.
2017-01-01
In this paper we theoretically study, using Floquet-Bloch theory, the influence of circularly and linearly polarized light on two-dimensional band structures with Dirac and quadratic band touching points, and flat bands, taking the nearest neighbor hopping model on the kagome lattice as an example. We find circularly polarized light can invert the ordering of this three-band model, while leaving the flat band dispersionless. We find a small gap is also opened at the quadratic band touching point by two-photon and higher order processes. By contrast, linearly polarized light splits the quadratic band touching point (into two Dirac points) by an amount that depends only on the amplitude and polarization direction of the light, independent of the frequency, and generally renders dispersion to the flat band. The splitting is perpendicular to the direction of the polarization of the light. We derive an effective low-energy theory that captures these key results. Finally, we compute the frequency dependence of the optical conductivity for this three-band model and analyze the various interband contributions of the Floquet modes. Our results suggest strategies for optically controlling band structure and interaction strength in real systems.
Spin-orbit edge states in semiconductor two-dimensional systems
Xu, L. L.; Ren, Shaola; Heremans, J. J.; Minic, Djordje; Gaspe, C. K.; Vijeyaragunathan, S.; Mishima, T. D.; Santos, M. B.
2013-03-01
The electromagnetic duality between the Aharonov-Casher and the Aharonov-Bohm topological phases can lead to magnetoelectronic edge effects in two-dimensional systems. Based on this duality, we propose and experimentally explore a quantized Hall effect in which magnetization transport may be quantized analogously to charge transport. When the magnetic moment is fully projected, the edge effect is a magnetization dual to the integer quantum Hall effect. An analogy also exists between this dual and the bosonic quantum Hall effect currently under investigation. In experiments we search for edge states induced by the equivalent vector potential from Rashba-type spin-orbit interaction. We use mesoscopic side-gated channel structures on InGaAs/InAlAs heterostructures where backscattering between edge states can experimentally form evidence for edge states. The side-gate voltage varies the effective gauge field and resistance as function of side-gate voltage is measured across the mesoscopic structures at either low applied magnetic field or at fixed magnetic filling factors to obtain states of defined spin (DOE DE-FG02-08ER46532, NSF DMR-0520550).
Su, Guoxiong; De, Debtanu; Hadjiev, Viktor G.; Peng, Haibing
2014-06-01
Layered two-dimensional (2D) semiconductors beyond graphene have been emerging as potential building blocks for the next-generation electronic/photonic applications. Representative metal chalcogenides, including the widely studied MoS2, possess similar layered crystal structures with weak interaction between adjacent layers, thus allowing the formation of stable thin-layer crystals with thickness down to a few or even single atomic layer. Other important chalcogenides, involving earth-abundant and environment-friendly materials desirable for sustainable applications, include SnS2 (band gap: 2.1 eV) and SnS (band gap: 1.1 eV). So far, commonly adopted for research purpose are mechanical and liquid exfoliation methods for creating thin layers of such 2D semiconductors. Most recently, chemical vapor deposition (CVD) was attracting significant attention as a practical method for producing thin films or crystal grains of MoS2. However, critical yet still absent is an effective experimental approach for controlling the positions of thin crystal grains of layered 2D semiconductors during the CVD process. Here we report the controlled CVD synthesis of thin crystal arrays of representative layered semiconductors (including SnS2 and SnS) at designed locations on chip, promising large-scale optoelectronic applications. Our work opens a window for future practical applications of layered 2D semiconductors in integrated nano-electronic/photonic systems.
New Frontiers in Optical Science: Terahertz Spectroscopy ot Two Dimensional Systems
Lee, Yun-Shik
2011-10-01
Terahertz (THz) radiation is electromagnetic radiation whose frequency lies between the microwave and infrared regions of the spectrum. Naturally occurring THz radiation fills up the space of everyday life providing warmth, yet this part of the spectrum remains the least explored region mainly due to the technical difficulties. The technological gap, however, has been rapidly diminishing for the last two decades. The new and exciting frontier of the THz science and technology has encroached on many different disciplines producing a broad range of applications such as medical imaging, sensing of biochemical agents, and ultra-high speed communication. Furthermore, the unique and advanced techniques of the THz spectroscopy have been proved to be a powerful tool to investigate the material properties inaccessible until recently. For example, THz waves strongly interact with electrons and holes in two dimensional systems, in which their dynamics are governed mainly by many-body Coulomb interactions. I will present our experimental studies demonstrating remarkable quantum effects in semiconductor nanostructures and exotic charge carrier dynamics in graphene.
Wu, Jingbo; Wood, Christopher D; Mistry, Divyang; Li, Lianhe; Muchenje, Wilson; Rosamond, Mark C; Chen, Li; Linfield, Edmund H; Davies, A Giles; Cunningham, John E
2015-01-01
Terahertz time domain spectroscopy employing free-space radiation has frequently been used to probe the elementary excitations of low-dimensional systems. The diffraction limit blocks its use for the in-plane study of individual laterally defined nanostructures, however. Here, we demonstrate a planar terahertz-frequency plasmonic circuit in which photoconductive material is monolithically integrated with a two-dimensional electron system. Plasmons with a broad spectral range (up to ~400 GHz) are excited by injecting picosecond-duration pulses, generated and detected by a photoconductive semiconductor, into a high mobility two-dimensional electron system. Using voltage modulation of a Schottky gate overlying the two-dimensional electron system, we form a tuneable plasmonic cavity, and observe electrostatic manipulation of the plasmon resonances. Our technique offers a direct route to access the picosecond dynamics of confined transport in a broad range of lateral nanostructures.
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.
Kaneko, Yuta
2014-01-01
Introducing a Clebsch-like parameterization, we have formulated a canonical Hamiltonian system on a symplectic leaf of reduced magnetohydrodynamics. An interesting structure of the equations is in that the Lorentz-force, which is a quadratic nonlinear term in the conventional formulation, appears as a linear term -{\\Delta}Q, just representing the current density (Q is a Clebsch variable, and {\\Delta} is the two-dimensional Laplacian); omitting this term reduces the system into the two-dimensional Euler vorticity equation of a neutral fluid. A heuristic estimate shows that current sheets grow exponentially (even in a fully nonlinear regime) together with the action variable P that is conjugate to Q. By numerical simulation, the predicted behavior of the canonical variables, yielding exponential growth of current sheets, has been demonstrated.
Digital communication of two-dimensional messages in a chaotic optical system
Institute of Scientific and Technical Information of China (English)
Zhou Yun; Wu Liang; Zhu Shi-Qun
2005-01-01
The digital communication of two-dimensional messages is investigated when two solid state multi-mode chaotic lasers are employed in a master-slave configuration. By introducing the time derivative of intensity difference between the receiver (carrier) and the transmittal (carrier plus signal), several signals can be encoded into a single pulse. If one signal contains several binary bits, two-dimensional messages in the form of a matrix can be encoded and transmitted on a single pulse. With these improvements in secure communications using chaotic multi-mode lasers, not only the transmission rate can be increased but also the privacy can be enhanced greatly.
Mi, Jian; Wang, Jianli; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Zhang, Chi
2016-09-01
In our high mobility p -type AlGaAs/GaAs two-dimensional hole samples, we originally observe the B -periodic oscillation induced by microwave (MW) in photovoltage (PV) measurements. In the frequency range of our measurements (5-40 GHz), the period (Δ B ) is inversely proportional to the microwave frequency (f ). The distinct oscillations come from the edge magnetoplasmon (EMP) in the high quality heavy hole system. Simultaneously, we observe the giant plasmon resonance signals in our measurements on the shallow two-dimensional hole system (2DHS).
Dorozhkin, S. I.
2015-07-01
Self-oscillations of a microwave photovoltage with irregular interruptions have been discovered in the states with vanishing dc dissipation emerging in two-dimensional electron systems under microwave irradiation. The observed picture can be caused by transitions between a stable pole and a limiting cycle in the phase space of the systems (Andronov-Hopf bifurcation) that occur owing to fluctuations.
Coherent electron dynamics in a two-dimensional random system with mobility edges
de Moura, F. A. B. F.; Lyra, M. L.; Dominguez-Adame, F.; Malyshev, V.A.
2007-01-01
We study numerically the dynamics of a one-electron wavepacket in a two-dimensional random lattice with long-range correlated diagonal disorder in the presence of a uniform electric field. The time-dependent Schrodinger equation is used for this purpose. We find that the wavepacket displays Bloch-li
Two-dimensional spectroscopy of molecular excitons in a model dimer system
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.
Tone, Florentina
2011-01-01
Pursuing our work in [18], [17], [20], [5], we consider in this article the two-dimensional thermohydraulics equations. We discretize these equations in time using the implicit Euler scheme and we prove that the global attractors generated by the numerical scheme converge to the global attractor of the continuous system as the time-step approaches zero.
Two-dimensional heteroclinic attractor in the generalized Lotka-Volterra system
Afraimovich, Valentin S.; Moses, Gregory; Young, Todd
2016-05-01
We study a simple dynamical model exhibiting sequential dynamics. We show that in this model there exist sets of parameter values for which a cyclic chain of saddle equilibria, O k , k=1,\\ldots,p , have two-dimensional unstable manifolds that contain orbits connecting each O k to the next two equilibrium points O k+1 and O k+2 in the chain ({{O}p+1}={{O}1} ). We show that the union of these equilibria and their unstable manifolds form a two-dimensional surface with a boundary that is homeomorphic to a cylinder if p is even and a Möbius strip if p is odd. If, further, each equilibrium in the chain satisfies a condition called ‘dissipativity’, then this surface is asymptotically stable.
Electronic transport in two-dimensional systems in the quantum hall regime
Tarquini, Vinicio
The integer and the fractional quantum Hall effects are essential to the exploration of quantum matters characterized by topological phases. A quantum Hall system hosts one-dimensional (1D) chiral edge channels that manifest zero magnetoresistance, dissipationless due to the broken time reversal symmetry, and quantized Hall resistance vhe2 with v being the topological invariant (or Chern number). The 1-1 correspondence between the conducting gapless edge channels to the gapped incompressible bulk states is a defining character of a topological insulator (TI). Understanding this correspondence in real systems, especially the origin of its robustness (in terms of the limit of breakdown), is important both fundamentally and practically (i.e. in relation to spintronics). However, the breakdown mechanism, especially in light of the edge-bulk correlation, is still an open question. We adopt GaAs two-dimensional (2D) high-mobility hole systems confined in a 20 nm wide (100)-GaAs quantum wells and have perform transport measurement for a range of charge densities between 4 and 5 x 1010 cm -2 with a carrier mobility of 2 - 4 x 106 cm 2/V·s down to millikelvin temperatures. Systematic characterization of the 2D systems through Shubnikov-de Haas (SdH) oscillations yields an effective mass between 0.30 and 0.50me, in good agreement with the cyclotron resonance results. We then modify a regular Hall bar system into a unique anti-Hall bar geometry that provides an extra set of independent chiral edge channels without altering the topological invariant. We perform systematic measurement of quantum oscillations via chiral edges while simultaneously probing the bulk dynamics, through measuring across independent edges, in respond to the edge excitations. The edge-bulk correspondence reveals a non-equilibrium dynamical development of the incompressible bulk states that leads to a novel asymmetrical 1-0 Hall potential distribution. Moreover, probing the breakdown via inner and outer
Control and measuring system of a two-dimensional scanning nanopositioning stage based on LabVIEW
Zhang, Rui-Jun; Gao, Si-Tian; Li, Wei; Chen, Ben-Yong; Shi, Yu-Shu; Li, Qi
2015-11-01
A control and measuring system of two-dimensional nanopositioning stage is designed for the multiple selection and combinations control based on LabVIEW. The signal generator of the system can not only generate the commonly used control signals such as sine, square, triangle and sawtooth waves, but also generate special signals such as trapezoidal wave and step wave with DAQ data acquisition card. The step wave can be triggered by the other signals for the strict timing corresponding relation between X-Y control signals. Finally, the performance of the control system of two-dimensional nanopositioning stage is conducted by the heterodyne interferometer. The results show that the operation of the system is stable and reliable and the noise peak - valley value is superior to 2nm while the stage moving with 6nm step. The system can apply to the field requiring the precise control to the positioning stage in nano-measurement and metrology.
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.
Parker, E. N.
1985-01-01
The dynamics of magnetic fibrils in the convective zone of a star is investigated analytically, deriving mean-field equations for the two-dimensional transverse motion of an incompressible fluid containing numerous small widely spaced circular cylinders. The equations of Parker (1982) are extended to account for the inertial effects of local flow around the cylinders. The linear field equation for the stream function at the onset of convection is then rewritten, neglecting large-scale heat transport, and used to construct a model of convective counterflow. The Kelvin impulse and fluid momentum, convective motion initiated by a horizontal impulse, and the effects of a viscous boundary layer are considered in appendices.
Existence and Uniqueness Theorems for the Two-Dimensional Ericksen-Leslie System
Chechkin, Gregory A.; Ratiu, Tudor S.; Romanov, Maxim S.; Samokhin, Vyacheslav N.
2016-09-01
In this paper we study the two dimensional Ericksen-Leslie equations for the nematodynamics of liquid crystals if the moment of inertia of the molecules does not vanish. We prove short time existence and uniqueness of strong solutions for the initial value problem in two situations: the space-periodic problem and the case of a bounded domain with spatial Dirichlet boundary conditions on the Eulerian velocity and the cross product of the director field with its time derivative. We also show that the speed of propagation of the director field is finite and give an upper bound for it.
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.
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.
Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems
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.
Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems.
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.
Lognormality of gradients of diffusive scalars in homogeneous, two-dimensional mixing systems
Kerstein, A. R.; Ashurst, W. T.
1984-12-01
Kolmogorov's third hypothesis, as extended by Gurvich and Yaglom, is found to be obeyed by a diffusive scalar for a class of homogeneous, two-dimensional mixing models. The mixing models all involve the advection of fluid by discrete vortices distributed in a square region with periodic boundary conditions. By computer simulation, it is found that the squared gradient of a diffusive scalar so advected is lognormally distributed, obeys the predicted scaling when a spatial smoothing is applied, and exhibits a power-law range in the spatial autocorrelation. In addition, it is found that the scaling property cuts off at the Batchelor length, as predicted by Gibson. Since the mixing models employed do not incorporate the dynamical features of high-Reynolds-number turbulence, these results suggest that scalar lognormality and associated scaling behavior may be more robust or persistent than the scaling laws of the flow field.
Mankov, Yu. I.; Tsikalov, D. S.
2010-03-01
This paper reports on the results of the investigation of the high-frequency susceptibility of a layered ferromagnetic structure in which, apart from a periodic change in the magnetic anisotropy parameter from layer to layer, this parameter varies along layers according to a random law (the superlattice with two-dimensional phase inhomogeneities). The evolution of the frequency dependence of the imaginary part of the averaged Green’s function in the range of the energy gap (band gap) in the spectrum of waves propagating along the superlattice axis due to the change in the relative root-mean-square fluctuations of the phase γ2 has been studied at the boundaries of the odd Brillouin zones. It has been found that, for all odd Brillouin zones, the imaginary part of the Green’s function exhibits a universal behavior: the peak corresponding to the edge of the band gap with a lower frequency remains unchanged, and the peak corresponding to the edge of the band gap with a higher frequency is smoothed with an increase in the quantity γ2. These effects, which were initially revealed at the boundary of the first Brillouin zone of the sinusoidal superlattice, have been explained, as before, by the specific features of the energy conservation laws for the incident and scattered waves in the lattice with two-dimensional inhomogeneities. It has been demonstrated that an increase in the Brillouin zone number leads to a decrease in the value of γ2 at which the peak at the edge of the band gap with a higher frequency disappears.
Energy Technology Data Exchange (ETDEWEB)
Ren, Qing-Bao [Department of Physics, Lishui University, Lishui 323000 (China); Luo, Meng-Bo, E-mail: Luomengbo@zju.edu.cn [Department of Physics, Zhejiang University, Hangzhou 310027 (China)
2013-10-30
We study the dynamics of a two-dimensional vortex system in a strong square pinning array at the second matching field. Two kinds of depinning behaviors, a continuous depinning transition at weak pinning and a discontinuous one at strong pinning, are found. We show that the two different kinds of vortex depinning transitions can be identified in transport as a function of the pinning strength and temperature. Moreover, interstitial vortex state can be probed from the transport properties of vortices.
Energy Technology Data Exchange (ETDEWEB)
Khanin, Yu. N.; Vdovin, E. E., E-mail: vdov62@yandex.ru [Russian Academy of Sciences, Institute of Microelectronics Technology and High Purity Materials (Russian Federation); Makarovsky, O. [University of Nottingham, School of Physics and Astronomy (United Kingdom); Henini, M. [University of Nottingham, School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Center (United Kingdom)
2013-09-15
Magnetotunneling between two-dimensional GaAs/InAs electron systems in vertical resonant tunneling GaAs/InAs/AlAs heterostructures is studied. A new-type of singularity in the tunneling density of states, specifically a dip at the Fermi level, is found; this feature is drastically different from that observed previously for the case of tunneling between two-dimensional GaAs tunnel systems in terms of both the kind of functional dependence and the energy and temperature parameters. As before, this effect manifests itself in the suppression of resonant tunneling in a narrow range near zero bias voltage in a high magnetic field parallel to the current direction. Magnetic-field and temperature dependences of the effect's parameters are obtained; these dependences are compared with available theoretical and experimental data. The observed effect can be caused by a high degree of disorder in two-dimensional correlated electron systems as a result of the introduction of structurally imperfect strained InAs layers.
Wimmer, K; Harant, H; Reiter, M; Blüml, G; Gaida, T; Katinger, H
1994-01-01
A recombinant Chinese hamster ovary cell line, producing human erythropoietin, was cultivated in a continuous mode in a stirred tank reactor applying different dilution rates. In order to monitor the stability of this expression system, product and non-product proteins of the cell culture supernatant were analyzed by two-dimensional electrophoresis. The consistency of the isoforms of the recombinant product was determined by western blot combined with specific staining. The same cell line was propagated in a high cell density cultivation system based on macro-cell-aggregates. The patterns of secreted proteins of the cell line cultivated in the different systems were compared in order to detect modifications in protein expression of the product and of non product proteins relevant for cell culture supernatant. Hardly any alterations in two-dimensional pattern were detectable. The isoforms of erythropoietin, as well as the overall pattern of secreted proteins, detectable with the two-dimensional electrophoresis method were remarkably stable under different cultivation conditions.
Casimir interaction of rodlike particles in a two-dimensional critical system
Eisenriegler, E.; Burkhardt, T. W.
2016-09-01
We consider the fluctuation-induced interaction of two thin, rodlike particles, or "needles," immersed in a two-dimensional critical fluid of Ising symmetry right at the critical point. Conformally mapping the plane containing the needles onto a simpler geometry in which the stress tensor is known, we analyze the force and torque between needles of arbitrary length, separation, and orientation. For infinite and semi-infinite needles we utilize the mapping of the plane bounded by the needles onto the half plane, and for two needles of finite length we use the mapping onto an annulus. For semi-infinite and infinite needles the force is expressed in terms of elementary functions, and we also obtain analytical results for the force and torque between needles of finite length with separation much greater than their length. Evaluating formulas in our approach numerically for several needle geometries and surface universality classes, we study the full crossover from small to large values of the separation to length ratio. In these two limits the numerical results agree with results for infinitely long needles and with predictions of the small-particle operator expansion, respectively.
Plasmonic terahertz modulator based on a grating-coupled two-dimensional electron system
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.
Kevrekidis, P G; Saxena, A; Frantzeskakis, D J; Bishop, A R
2014-01-01
We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anti-continuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual "extended" unstaggered bright solitons, in which all sites are excited in the AC limit, with the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being what was considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (analytically, whenever possible). Typical scenarios ...
Spin-orbit or Aharonov-Casher edge states in semiconductor two-dimensional systems
Xu, L. L.; Heremans, J. J.; Gaspe, C. K.; Vijeyaragunathan, S.; Mishima, T. D.; Santos, M. B.
2012-02-01
In semiconductors with spin-orbit interaction we experimentally search for edge states induced by the Aharonov-Casher vector potential or Rashba-type spin-orbit interaction. The Aharonov-Casher effect is electromagnetically dual to the Aharonov-Bohm effect and is predicted to lead to a possibly helical edge state structure at two-dimensional sample edges. We use InGaAs/InAlAs heterostructures patterned into mesoscopic side-gated channel structures, where the edge states can be induced, and where backscattering between edge states can be experimentally measured in the resistance. Sweeping side-gate voltage, low temperature resistances are measured across such mesoscopic closed-path structures at either low applied magnetic field, in-plane or normal to the plane, or at fixed magnetic filling factors of 5, 6, 7, and 8 to obtain states of defined spin. Resistance oscillations are observed at low magnetic fields and around filling factor 6 as function of side-gate voltage, and we analyze the oscillations in the light of the search for the edge states (DOE DE-FG02-08ER46532, NSF DMR-0520550).
Two-dimensional electromagnetically induced cross-grating in a four-level N-type atomic system
Wu, Jianchun; Ai, Baoquan
2015-06-01
We propose a scheme for a two-dimensional (2D) electromagnetically induced cross-grating (EICG) in a four-level N-type atomic system. By employing standing-wave fields interacting with the atomic system, the absorption and dispersion of the probe field will change with the spatial periodical modulation. The first-order diffraction intensity sensitively depends on the parameters (the probe detuning, and the amplitude and detuning of the standing-wave fields), and can reach its maximum on varying the system parameters. The present studies may be instructive to design new devices in all-optical switching and optical imaging.
Low-Lying States of the A+B-A+B- Coulomb Systems in Two-Dimensional Quantum Dots
Institute of Scientific and Technical Information of China (English)
XIE Wen-Fang
2001-01-01
The features of the low-lying spectra of four-body A+B-A+B- systems have been deduced based on symmetry. Using the method of few-body physics, we calculate the energy spectra of A + B- A + B- systems in a harmonic quantum dot. We find that the biexciton in a two-dimensional quantum dot may have other bound excited states and the quantum mechanical symmetry plays a crucialrole in determining the energy levels and structures of the low-lying states.
Institute of Scientific and Technical Information of China (English)
LIN Ming-Xi; QI Sheng-Wen; LIU Yu-Liang
2006-01-01
@@ Based on a two-dimensional electron system with pure gauge field, we demonstrate that the long range order of the electron pairing order parameter can be destroyed by the gauge fluctuation for both s-wave and d-wave symmetric Cooper pair parameters, even if the pure gauge field mediates attractive interaction between the spinup and spin-down electrons, while the signal of the Meissner effect is observable. This model can be used to explain the recent experimental data of the high Tc cuprate superconductors observed.
Sakuma, Ryusuke; Gunji, Atsuko; Goto, Takaaki; Kita, Yosuke; Koike, Toshihide; Kaga, Makiko; Inagaki, Masumi
2012-07-01
The current study sought to develop a new behavioral analysis methods to evaluate the effects of social skills training (SST). SST is known to be an effective method to improve the social skills of children with behavioral problems. However, current evaluation methods involve behavioral rating scales that are heavily dependent on evaluators' particular experiences they have had. To quantitatively examine the behavioral effects of SST, we examined subjects' head-movements related to social behavior, using a two-dimensional motion capture system (Kissei Comtec, Japan). Four children (three male, one female, 7-8 years of age) with pervasive developmental disorder (PDD) or attention deficit/hyperactivity disorder (AD/HD) participated in 16 sessions of SST. Before and after SST, head-coordinates on a two-dimensional plane were calculated using their behavior during a pair task, measured by four digital cameras. After SST, the number of communication behaviors was increased compared to before SST. In addition, children looked longer at another child within 30 degrees of the central visual field. Time-series analysis of the visual field during the detection of another child revealed significant auto-correlation from about -1.12 second. before to the beginning of communication behavior (p<0.05). The results suggested that our method can provide a quantitative index of characteristics related to skilled social behaviors. We conclude that a two-dimensional motion capture system would be useful for visualization of the interventional effects of SST, which would supplement assessments by the conventional observational strategies.
Convection and segregation in fluidised granular systems exposed to two-dimensional vibration
Windows-Yule, C. R. K.
2016-03-01
Convection and segregation in granular systems not only provide a rich phenomenology of scientifically interesting behaviours but are also crucial to numerous ‘real-world’ processes ranging from important and widely used industrial procedures to potentially cataclysmic geophysical phenomena. Simple, small-scale experimental or simulated test systems are often employed by researchers in order to gain an understanding of the fundamental physics underlying the behaviours of granular media. Such systems have been the subject of extensive research over several decades, with numerous system geometries and manners of producing excitation explored. Energy is commonly provided to granular assemblies through the application of vibration—the simplicity of the dynamical systems produced and the high degree of control afforded over their behaviour make vibrated granular beds a valuable canonical system by which to explore a diverse range of phenomena. Although a wide variety of vibrated systems have been explored in the existing literature, the vast majority are exposed to vibration along only a single spatial direction. In this paper, we study highly fluidised systems subjected to strong, multi-directional driving, providing a first insight into the dynamics and behaviours of these systems which may potentially hold valuable new information relevant to important industrial and natural processes. With a particular focus on the processes of convection and segregation, we analyse the various states and phase transitions exhibited by our system, detailing a number of previously unobserved dynamical phenomena and system states.
DEFF Research Database (Denmark)
Rudner, Mark Spencer; Lindner, Netanel; Berg, Erez;
2013-01-01
the crucial distinctions between static and driven 2D systems, and construct a new topological invariant that yields the correct edge-state structure in the driven case. We provide formulations in both the time and frequency domains, which afford additional insight into the origins of the “anomalous” spectra...... that arise in driven systems. Possibilities for realizing these phenomena in solid-state and cold-atomic systems are discussed....
Two-dimensional systems from introduction to state of the art
Benzaouia, Abdellah; Tadeo, Fernando
2016-01-01
A solution permitting the stabilization of 2-dimensional (2-D) continuous-time saturated system under state feedback control is presented in this book. The problems of delay and saturation are treated at the same time. The authors obtain novel results on continuous 2-D systems using the unidirectional Lyapunov function. The control synthesis and the saturation and delay conditions are presented as linear matrix inequalities. Illustrative examples are worked through to show the effectiveness of the approach and many comparisons are made with existing results. The second half of the book moves on to consider robust stabilization and filtering of 2-D systems with particular consideration being given to 2-D fuzzy systems. Solutions for the filter-design problems are demonstrated by computer simulation. The text builds up to the development of state feedback control for 2-D Takagi–Sugeno systems with stochastic perturbation. Conservatism is reduced by using slack matrices and the coupling between the Lyapunov ma...
Two-Dimensional Regular Shock Reflection for the Pressure Gradient System of Conservation Laws
Institute of Scientific and Technical Information of China (English)
Yuxi Zheng
2006-01-01
We establish the existence of a global solution to a regular reflection of a shock hitting a ramp for the pressure gradient system of equations. The set-up of the reflection is the same as that of Mach's experiment for the compressible Euler system, i.e., a straight shock hitting a ramp. We assume that the angle of the ramp is close to 90 degrees. The solution has a reflected bow shock wave, called the diffraction of the planar shock at the compressive corner, which is mathematically regarded as a free boundary in the self-similar variable plane.The pressure gradient system of three equations is a subsystem, and an approximation, of the full Euler system,and we offer a couple of derivations.
Numerical Bifurcation Diagram for the Two-Dimensional Boundary-fed CDIMA System
Setayeshgar, S
1999-01-01
We present numerical solution of the chlorine dioxide-iodine-malonic acid reaction-diffusion system in two dimensions in a boundary-fed system using a realistic model. The bifurcation diagram for the transition from non-symmetry breaking structures along boundary feed gradients to transverse symmetry breaking patterns in a single layer is numerically determined. We find this transition to be discontinuous. We make connection with earlier results and discuss prospects for future work.
Deep Learning the Quantum Phase Transitions in Random Two-Dimensional Electron Systems
Ohtsuki, Tomoki; Ohtsuki, Tomi
2016-12-01
Random electron systems show rich phases such as Anderson insulator, diffusive metal, quantum Hall and quantum anomalous Hall insulators, Weyl semimetal, as well as strong/weak topological insulators. Eigenfunctions of each matter phase have specific features, but owing to the random nature of systems, determining the matter phase from eigenfunctions is difficult. Here, we propose the deep learning algorithm to capture the features of eigenfunctions. Localization-delocalization transition, as well as disordered Chern insulator-Anderson insulator transition, is discussed.
Vides, Jeaniffer; Nkonga, Boniface; Audit, Edouard
2015-01-01
We derive a simple method to numerically approximate the solution of the two-dimensional Riemann problem for gas dynamics, using the literal extension of the well-known HLL formalism as its basis. Essentially, any strategy attempting to extend the three-state HLL Riemann solver to multiple space dimensions will by some means involve a piecewise constant approximation of the complex two-dimensional interaction of waves, and our numerical scheme is not the exception. In order to determine closed form expressions for the involved fluxes, we rely on the equivalence between the consistency condition and the use of Rankine-Hugoniot conditions that hold across the outermost waves. The proposed scheme is carefully designed to simplify its eventual numerical implementation and its advantages are analytically attested. In addition, we show that the proposed solver can be applied to obtain the edge-centered electric fields needed in the constrained transport technique for the ideal magnetohydrodynamic (MHD) equations. We present several numerical results for hydrodynamics and magnetohydrodynamics that display the scheme's accuracy and its ability to be applied to various systems of conservation laws.
Xu, Cenke
Several examples of quantum spin systems and pseudo spin systems have been studied, and unconventional states of matters and phase transitions have been realized in all these systems under consideration. In the p +/- ip superconductor Josephson lattice and the p--band cold atomic system trapped in optical lattices, novel phases which behave similarly to 1+1 dimensional systems are realized, despite the fact that the real physical systems are in two or three dimensional spaces. For instance, by employing a spin-wave analysis together with a new duality transformation, we establish the existence and stability of a novel gapless "critical phase", which we refer to as a "bond algebraic liquid". This novel critical phase is analogous to the 1+1 dimensional algebraic boson liquid phase. The reason for the novel physics is that there is a quasilocal gauge symmetry in the effective low energy Hamiltonian. In a spin-1 system on the kagome lattice, and a hard-core boson system on the honeycomb lattice, the low energy physics is controlled by two components of compact U(1) gauge symmetries that emerge at low energy. Making use of the confinement nature of the 2+1 dimensional compact gauge theories and the powerful duality between gauge theories and height field theories, the crystalline phase diagrams are studied for both systems, and the transitions to other phases are also considered. These phase diagrams might be accessible in strongly correlated materials, or atomic systems in optical lattices. A novel quantum ground state of matter is realized in a bosonic model on three dimensional fcc lattice with emergent low energy excitations. The novel phase obtained is a stable gapless boson liquid phase, with algebraic boson density correlations. The stability of this phase is protected against the instanton effect and superfluidity by self-duality and large gauge symmetries on both sides of the duality. The gapless collective excitations of this phase closely resemble the
Sunahara, Y.; Kojima, F.
1987-01-01
The purpose of this paper is to establish a method for identifying unknown parameters involved in the boundary state of a class of diffusion systems under noisy observations. A mathematical model of the system dynamics is given by a two-dimensional diffusion equation. Noisy observations are made by sensors allocated on the system boundary. Starting with the mathematical model mentioned above, an online parameter estimation algorithm is proposed within the framework of the maximum likelihood estimation. Existence of the optimal solution and related necessary conditions are discussed. By solving a local variation of the cost functional with respect to the perturbation of parameters, the estimation mechanism is proposed in a form of recursive computations. Finally, the feasibility of the estimator proposed here is demonstrated through results of digital simulation experiments.
Institute of Scientific and Technical Information of China (English)
Wang Jia; Hui Guo-Tao; Xie Xiang-Peng
2013-01-01
We study the stability analysis and control synthesis of uncertain discrete-time two-dimensional (2D) systems.The mathematical model of the discrete-time 2D system is established upon the well-known Roesser model,and the uncertainty phenomenon,which appears typically in practical environments,is modeled by a convex bounded (polytope type) uncertain domain.The stability analysis and control synthesis of uncertain discrete-time 2D systems are then developed by applying the Lyapunov stability theory.In the processes of stability analysis and control synthesis,the obtained stability/stabilzaition conditions become less conservative by applying some novel relaxed techniques.Moreover,the obtained results are formulated in the form of linear matrix inequalities,which can be easily solved via standard numerical software.Finally,numerical examples are given to demonstrate the effectiveness of the obtained results.
Development of an ultra-fast data-acquisition system for a two-dimensional microstrip gas chamber.
Ochi, A; Tanimori, T; Nishi, Y; Aoki, S; Nishi, Y
1998-05-01
A high-performance data-acquisition system has been developed in order to obtain time-resolved sequential images from a two-dimensional microstrip gas chamber (MSGC). This was achieved using fully digital processing with a synchronized pipeline method. Complex logical circuits for processing large numbers of signals are mounted on a small number of complex programmable logic devices. The system is operated with a 10 MHz synchronous clock, and has the capability of handling more than 3 x 10(6) counts s(-1) for asynchronous events. The system was examined using a 5 x 5 cm MSGC and the recently developed 10 x 10 cm MSGC (1024 outputs); the anticipated performances were achieved.
Energy Technology Data Exchange (ETDEWEB)
Li, Jian; Xu, Li [Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan 430030 (China); Shi, Zhi-guo, E-mail: shizg@whu.edu.cn [Department of Chemistry, Wuhan University, Wuhan 430072 (China); Hu, Min [Hubei Instrument for Food and Drug Control, Wuhan (China)
2015-08-15
Highlights: • A novel two-dimensional liquid chromatographic system was developed. • The 1st dimension was ODS to separate components in the sample. • The 2nd dimension was biopartitioning micellar chromatography to predict toxicity. • The system was used to screen toxicity of pharmaceuticals and related substances. • It was promising for fast online toxicity screening of complex sample in one step. - Abstract: In this study, a novel two-dimensional liquid chromatographic (2D-LC) system was developed for simultaneous separation and toxicity prediction of pharmaceutical and its related substances. A conventional ODS column was used on the 1st-D to separate the sample; while, bio-partitioning micellar chromatography served as the 2nd-D to predict toxicity of the components. The established system was tested for the toxicity of ibuprofen and its impurities with known toxicity. With only one injection, ibuprofen and its impurities were separated on the 1st-D; and LC50 values of individual impurity were obtained based on the quantitative retention–activity relationships, which agreed well with the reported data. Furthermore, LC50 values of photolysis transformation products (TPs) of carprofen, ketoprofen and diclofenac acid (as unknown compounds) were screened in this 2D-LC system, which could be an indicator of the toxicity of these TPs and was meaningful for the environmental monitoring and drinking water treatment. The established 2D-LC system was cost-effective, time-saving and reliable, and was promising for fast online screening of toxicity of known and unknown analytes in the complex sample in a single step. It may find applications in environment, pharmaceutical and food, etc.
Dephasing in the quasi-two-dimensional exciton-biexciton system
DEFF Research Database (Denmark)
Langbein, Wolfgang Werner; Hvam, Jørn Märcher
2000-01-01
The polarization decay in the exciton-biexciton system of a homogeneously broadened single quantum well is studied by transient four-wave mixing. All three decay rates in the exciton-biexciton three-level system are deduced. The relation between the rates unravels correlations between scattering...... processes of excitons and biexcitons. Density and temperature dependences show that the involved processes are mainly radiative decay and phonon scattering. The radiative decay rate of the biexcitons is found to be comparable to the one of the excitons, and the involved spontaneous photon emissions from...
Yatsuyanagi, Yuichi
2016-01-01
The drift term appearing in an anaylitically obtained kinetic equation for a point vortex system is evidenced numerically. It is revealed that the local temperature in a region where the vortices are frequently transported by the diffusion and the drift terms characterizes system temperature and its sign is definitely negative. Simulation results clearly show a ransport process of the vortices by the diffusion term (outside the clumps) and the drift term (inside the clumps), which gives a key mechanism of the self-organization, i.e., condensation of the same-sign vortices.
Walk-Rally Support System Using Two-Dimensional Codes and Mobile Phones
Miyagawa, Tetsuya; Yamagishi, Yoshio; Mizuno, Shun
2013-01-01
"Walk Rally" (WR), an orienteering-like recreation game, is common, especially in Japan. Numerous trials to combine WR with educational activities are being carried out by some educators. However, participants are always at the risk of straying and subjected to various accidents during the WR. We developed a WR support system based on…
2011-04-05
... HUMAN SERVICES National Institutes of Health Prospective Grant of Exclusive License: Device and System... continuing applications and foreign counterparts to 2-D Bio, LLC, having a place of business in Gaithersburg... exclusive license to the University of Maryland's rights in the invention. The prospective exclusive license...
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.
Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems
DEFF Research Database (Denmark)
Ferrari, Andrea C.; Bonaccorso, Francesco; Falko, Vladimir;
2015-01-01
We present the science and technology roadmap (STR) for graphene, related twodimensional (2d) crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. The roadmap was developed within the framework of the Euro...
Walk-Rally Support System Using Two-Dimensional Codes and Mobile Phones
Miyagawa, Tetsuya; Yamagishi, Yoshio; Mizuno, Shun
2013-01-01
"Walk Rally" (WR), an orienteering-like recreation game, is common, especially in Japan. Numerous trials to combine WR with educational activities are being carried out by some educators. However, participants are always at the risk of straying and subjected to various accidents during the WR. We developed a WR support system based on…
Two-dimensional electronic readout system for multi-step-avalanche chambers
Carlén, L.; Garpmann, S.; Gustafsson, H.-A.; Löhner, H.; Nystrand, J.; Oskarsson, A.; Otterlund, I.; Svensson, T.; Stenlund, E.; Söderström, K.; Whitlow, H.J.
1997-01-01
We present prototype studies of a new technical solution of detector readout for measurements of charged particles at very high particle densities. In particular, this paper describes a readout system for Multi-Step Avalanche Chambers designed for the WA98 experiment at the CERN SPS. Results from th
Numerical investigation into the existence of limit cycles in two-dimensional predator�prey systems
Directory of Open Access Journals (Sweden)
Quay van der Hoff
2013-05-01
Full Text Available There has been a surge of interest in developing and analysing models of interacting species in ecosystems, with specific interest in investigating the existence of limit cycles in systems describing the dynamics of these species. The original Lotka–Volterra model does not possess any limit cycles. In recent years this model has been modified to take disturbances into consideration and allow populations to return to their original numbers. By introducing logistic growth and a Holling Type II functional response to the traditional Lotka–Volterra-type models, it has been proven analytically that a unique, stable limit cycle exists. These proofs make use of Dulac functions, Liénard equations and invariant regions, relying on theory developed by Poincaré, Poincaré-Bendixson, Dulac and Liénard, and are generally perceived as difficult. Computer algebra systems are ideally suited to apply numerical methods to confirm or refute the analytical findings with respect to the existence of limit cycles in non-linear systems. In this paper a class of predator–prey models of a Gause type is used as the vehicle to illustrate the use of a simple, yet novel numerical algorithm. This algorithm confirms graphically the existence of at least one limit cycle that has analytically been proven to exist. Furthermore, adapted versions of the proposed algorithm may be applied to dynamic systems where it is difficult, if not impossible, to prove analytically the existence of limit cycles.
Construction of exact dynamical invariants of two-dimensional classical system
Indian Academy of Sciences (India)
S C Mishra; Fakir Chand
2006-03-01
A general method is used for the construction of second constant of motion of fourth order in momenta using the complex coordinates $(z, \\bar{z})$. A fourth-order potential equation is obtained whose solutions directly provide a large class of integrable systems. The potential equation is tested with an interesting example which admits second constants of motion.
Simulation study of localization of electromagnetic waves in two-dimensional random dipolar systems.
Wang, Ken Kang-Hsin; Ye, Zhen
2003-12-01
We study the propagation and scattering of electromagnetic waves by random arrays of dipolar cylinders in a uniform medium. A set of self-consistent equations, incorporating all orders of multiple scattering of the electromagnetic waves, is derived from first principles and then solved numerically for electromagnetic fields. For certain ranges of frequencies, spatially localized electromagnetic waves appear in such a simple but realistic disordered system. Dependence of localization on the frequency, radiation damping, and filling factor is shown. The spatial behavior of the total, coherent, and diffusive waves is explored in detail, and found to comply with a physical intuitive picture. A phase diagram characterizing localization is presented, in agreement with previous investigations on other systems.
Corner-Space Renormalization Method for Driven-Dissipative Two-Dimensional Correlated Systems.
Finazzi, S; Le Boité, A; Storme, F; Baksic, A; Ciuti, C
2015-08-21
We present a theoretical method to study driven-dissipative correlated quantum systems on lattices with two spatial dimensions (2D). The steady-state density matrix of the lattice is obtained by solving the master equation in a corner of the Hilbert space. The states spanning the corner space are determined through an iterative procedure, using eigenvectors of the density matrix of smaller lattice systems, merging in real space two lattices at each iteration and selecting M pairs of states by maximizing their joint probability. The accuracy of the results is then improved by increasing the dimension M of the corner space until convergence is reached. We demonstrate the efficiency of such an approach by applying it to the driven-dissipative 2D Bose-Hubbard model, describing lattices of coupled cavities with quantum optical nonlinearities.
Du, Di; Toffoletto, Frank; Biswal, Sibani Lisa
2014-04-01
Typically the force between paramagnetic particles in a uniform magnetic field is described using the dipolar model, which is inaccurate when particles are in close proximity to each other. Instead, the exact force between paramagnetic particles can be determined by solving a three-dimensional Laplace's equation for magnetostatics under specified boundary conditions and calculating the Maxwell stress tensor. The analytical solution to this multi-boundary-condition Laplace's equation can be obtained by using a solid harmonics expansion in conjunction with the Hobson formula. However, for a multibody system, finite truncation of the Hobson formula does not lead to convergence of the expansion at all points, which makes the approximation physically unrealistic. Here we present a numerical method for solving this Laplace's equation for magnetostatics. This method uses a smoothed representation to replace all the boundary conditions. A two-step propagation is used to dramatically accelerate the calculation without losing accuracy. Using this method, we calculate the force between two paramagnetic particles in a uniform and a rotational external field and compare our results with other models. Furthermore, the many-body effects for three-particle, ten-particle, and 24-particle systems are examined using the same method. We also calculate the interaction between particles with different magnetic susceptibilities and particle diameters. The Laplace's equation solver method described in this article that is used to determine the force between paramagnetic particles is shown to be very useful for dynamic simulations for both two-particle systems and a large cluster of particles.
Mardiansyah, Y.; Yulia; Khotimah, S. N.; Suprijadi; Viridi, S.
2016-08-01
Dynamics of pseudo-two dimensional granular material consisted of two layers cylinder piles positioned on top of a horizontally vibrated plate is reported in this work. It is aimed to observe structural change of the cylinder pile vibrated in certain frequency and amplitude. Dimensionless acceleration Γ= 4π2f2A/g (with g is gravitational acceleration), which is generally used in granular materials to observe transition between states, e.g. stable, rotating without slipping, rolling and slipping in Γ-f plane, does not work well for this system. For this system additional states for the piles can also be observed, e.g. stable and flowing states. Observations parameters are frequency f (measured in Hz) and amplitude A (measured in cm). These parameters are used to construct the A-f plane instead of Γ-f one.
Institute of Scientific and Technical Information of China (English)
YANG YongHong; WANG YongGang; LIU Mei; WANG Jin
2002-01-01
Two kinds of spin-depcndcnt scattering effects (magnetic-iinpurity and spin-orbit scatterings) axe investi-gated theoretically in a quasi-two-dimensional (quasi-2D) disordered electron system. By making use of the diagrammatictechniques in perturbation theory, we have calculated the dc conductivity and magnetoresistance due to weak-localizationeffects, the analytical expressions of them are obtained as functions of the interlayer hopping energy and the charac-teristic times: elastic, inelastic, magnetic and spin-orbit scattering times. The relevant dimensional crossover behaviorfrom 3D to 2D with decreasing the interlayer coupling is discussed, and the condition for the crossover is shown to bedependent on the aforementioned scattering times. At low temperature there exists a spin-dcpendent-scattering-induccddimensional crossover in this system.
Liu, Jun; Han, Jiuqiang; Lv, Hongqiang; Li, Bing
2015-04-16
With the continuing growth of highway construction and vehicle use expansion all over the world, highway vehicle traffic rule violation (TRV) detection has become more and more important so as to avoid traffic accidents and injuries in intelligent transportation systems (ITS) and vehicular ad hoc networks (VANETs). Since very few works have contributed to solve the TRV detection problem by moving vehicle measurements and surveillance devices, this paper develops a novel parallel ultrasonic sensor system that can be used to identify the TRV behavior of a host vehicle in real-time. Then a two-dimensional state method is proposed, utilizing the spacial state and time sequential states from the data of two parallel ultrasonic sensors to detect and count the highway vehicle violations. Finally, the theoretical TRV identification probability is analyzed, and actual experiments are conducted on different highway segments with various driving speeds, which indicates that the identification accuracy of the proposed method can reach about 90.97%.
Olariu, S.; Schwing, J.; Zhang, J.
1991-01-01
A bus system that can change dynamically to suit computational needs is referred to as reconfigurable. We present a fast adaptive convex hull algorithm on a two-dimensional processor array with a reconfigurable bus system (2-D PARBS, for short). Specifically, we show that computing the convex hull of a planar set of n points taken O(log n/log m) time on a 2-D PARBS of size mn x n with 3 less than or equal to m less than or equal to n. Our result implies that the convex hull of n points in the plane can be computed in O(1) time in a 2-D PARBS of size n(exp 1.5) x n.
DEFF Research Database (Denmark)
Powell, Daryl; Olesen, Peter Bjerg
2013-01-01
Companies use value stream mapping to identify waste, often in the early stages of a lean implementation. Though the tool helps users to visualize material and information flows and to identify improvement opportunities, a limitation of this approach is the lack of an integrated method for analys......Companies use value stream mapping to identify waste, often in the early stages of a lean implementation. Though the tool helps users to visualize material and information flows and to identify improvement opportunities, a limitation of this approach is the lack of an integrated method...... for analysing and re-designing the MPC system in order to support lean improvement. We reflect on the current literature regarding value stream mapping, and use practical insights in order to develop and propose a two-dimensional value stream mapping tool that integrates the design of the MPC system within...
Bose-Einstein Condensation in a Two-Dimensional System with Sixty Bosons
Institute of Scientific and Technical Information of China (English)
Bao Cheng-Guang
2000-01-01
A 60-boson system confined on a sphere has been qualitatively studied based on symmetry considerations. The low-lying spectrum is dominated by the ground rotation band based on the fullerene structure. In this band all the L＝1 to L＝5 states are found to be prohibited by symmetry. Therefore, there is a large gap lying between the ground state and the first excited state. The magnitude of this gap, which is associated with the critical temperature of Bose-Einstein condensation, has been evaluated. It is found that, the smaller the radius of the sphere of confinement, the higher the critical temperature.
Nature of transitions in uniformly frustrated two-dimensional planar spin systems
Berge, B.; Diep, H. T.; Ghazali, A.; Lallemand, P.
1987-04-01
We have investigated a generalized Villain's model by varying the strength η of the negative bond. We show that there exists a critical value ηc= (1)/(3) below which the twofold degeneracy disappears; the ground state becomes ferromagnetic. A detailed numerical study shows that, for a given η>ηc, the system exhibits in general, two distinct transitions: The low temperature one corresponds to Ising-type transition; the high temperature one corresponds to KT type. These two transitions seem to coincide in the Villain's model (η=1). Comparison with recent related models is presented.
Energy Technology Data Exchange (ETDEWEB)
Quinn, John
2009-11-30
Work related to this project introduced the idea of an effective monopole strength Q* that acted as the effective angular momentum of the lowest shell of composite Fermions (CF). This allowed us to predict the angular momentum of the lowest band of energy states for any value of the applied magnetic field simply by determining N{sub QP} the number of quasielectrons (QE) or quasiholes (QH) in a partially filled CF shell and adding angular momenta of the N{sub QP} Fermions excitations. The approach reported treated the filled CF level as a vacuum state which could support QE and QH excitations. Numerical diagonalization of small systems allowed us to determine the angular momenta, the energy, and the pair interaction energies of these elementary excitations. The spectra of low energy states could then be evaluated in a Fermi liquid-like picture, treating the much smaller number of quasiparticles and their interactions instead of the larger system of N electrons with Coulomb interactions.
Dynamics of a two-dimensional system of rational difference equations of Leslie--Gower type
Directory of Open Access Journals (Sweden)
Kulenović MRS
2011-01-01
Full Text Available Abstract We investigate global dynamics of the following systems of difference equations x n + 1 = α 1 + β 1 x n A 1 + y n y n + 1 = γ 2 y n A 2 + B 2 x n + y n , n = 0 , 1 , 2 , … where the parameters α 1, β 1, A 1, γ 2, A 2, B 2 are positive numbers, and the initial conditions x 0 and y 0 are arbitrary nonnegative numbers. We show that this system has rich dynamics which depends on the region of parametric space. We show that the basins of attractions of different locally asymptotically stable equilibrium points or non-hyperbolic equilibrium points are separated by the global stable manifolds of either saddle points or non-hyperbolic equilibrium points. We give examples of a globally attractive non-hyperbolic equilibrium point and a semi-stable non-hyperbolic equilibrium point. We also give an example of two local attractors with precisely determined basins of attraction. Finally, in some regions of parameters, we give an explicit formula for the global stable manifold. Mathematics Subject Classification (2000 Primary: 39A10, 39A11 Secondary: 37E99, 37D10
Harting, Benjamin; Slenzka, Klaus
2012-07-01
To investigate the influence of microgravity environments on photosynthetic organisms we designed a 2 dimensional clinostatexperiment for a suspended cell culture of Chlamydomonas reinhardtii. A novel approach of online measurments concerning relevant parameters important for the clasification of photosynthesis was obtained. To adress the photosynthesis rate we installed and validated an optical mesurement system to monitor the evolution and consumption of dissolved oxygen. Simultaneously a PAM sensor to analyse the flourescence quantum yield of the photochemical reaction was integarted. Thus it was possible to directly classify important parameters of the phototrophic metabolism during clinorotation. The experiment design including well suited light conditions and further biochemical analysis were directly performed for microalgal cell cultures. Changes in the photosynthetic efficiancy of phototrophic cyanobacteria has been observed during parabolic flight campaign but the cause is already not understood. Explenations could be the dependency of gravitaxis by intracellular ionconcentartion or the existance of mechanosensitive ionchannels for example associated in chloroplasts of Chlamydomonas reinhardtii. The purpuse of the microalgal clinostat are studies in a qasi microgravity environment for the process design of future bioregenerative life suport systems in spaceflight missions. First results has indicated the need for special nourishment of the cell culture during microgravity experiments. Further data will be presented during the assembly.
Random-fractal Ansatz for the configurations of two-dimensional critical systems
Lee, Ching Hua; Ozaki, Dai; Matsueda, Hiroaki
2016-12-01
Critical systems have always intrigued physicists and precipitated the development of new techniques. Recently, there has been renewed interest in the information contained in the configurations of classical critical systems, whose computation do not require full knowledge of the wave function. Inspired by holographic duality, we investigated the entanglement properties of the classical configurations (snapshots) of the Potts model by introducing an Ansatz ensemble of random fractal images. By virtue of the central limit theorem, our Ansatz accurately reproduces the entanglement spectra of actual Potts snapshots without any fine tuning of parameters or artificial restrictions on ensemble choice. It provides a microscopic interpretation of the results of previous studies, which established a relation between the scaling behavior of snapshot entropy and the critical exponent. More importantly, it elucidates the role of ensemble disorder in restoring conformal invariance, an aspect previously ignored. Away from criticality, the breakdown of scale invariance leads to a renormalization of the parameter Σ in the random fractal Ansatz, whose variation can be used as an alternative determination of the critical exponent. We conclude by providing a recipe for the explicit construction of fractal unit cells consistent with a given scaling exponent.
Some mathematical aspects of the scaling limit of critical two-dimensional systems
Indian Academy of Sciences (India)
Wendelin Werner
2005-05-01
It has been observed long ago that many systems from statistical physics behave randomly on macroscopic level at their critical temperature. In two dimensions, these phenomena have been classified by theoretical physicists thanks to conformal field theory, that led to the derivation of the exact value of various critical exponents that describe their behavior near the critical temperature. In the last couple of years, combining ideas of complex analysis and probability theory, mathematicians have constructed and studied a family of random fractals (called `Schramm–Loewner evolutions' or SLE) that describe the only possible conformally invariant limits of the interfaces for these models. This gives a concrete construction of these random systems, puts various predictions on a rigorous footing, and leads to further understanding of their behavior. The goal of this paper is to survey some of these recent mathematical developments, and to describe a couple of basic underlying ideas. We will also briefly describe some very recent and ongoing developments relating SLE, Brownian loop soups and conformal field theory.
Control of Limit Cycle Oscillations of a Two-Dimensional Aeroelastic System
Directory of Open Access Journals (Sweden)
M. Ghommem
2010-01-01
Full Text Available Linear and nonlinear static feedback controls are implemented on a nonlinear aeroelastic system that consists of a rigid airfoil supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. The normal form is used to investigate the Hopf bifurcation that occurs as the freestream velocity is increased and to analytically predict the amplitude and frequency of the ensuing limit cycle oscillations (LCO. It is shown that linear control can be used to delay the flutter onset and reduce the LCO amplitude. Yet, its required gains remain a function of the speed. On the other hand, nonlinear control can be effciently implemented to convert any subcritical Hopf bifurcation into a supercritical one and to significantly reduce the LCO amplitude.
Energy Technology Data Exchange (ETDEWEB)
Zhou Chenggang [Department of Electrical Engineering, Princeton University, Princeton, NJ 08544 (United States)], E-mail: zcf@ornl.gov; Bhatt, Ravin N. [Department of Electrical Engineering, Princeton Center for Theoretical Physics, and Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ 08544 (United States)
2008-04-01
We study the effect of mass anisotropy on the magnetic ordering of the Wigner crystal phase of low density electron systems in two dimensions at T=0. We apply the instanton approximation to various ring exchange processes, which includes the lowest order Gaussian fluctuations beyond the WKB approximation. The multi-particle exchange frequencies are calculated with effective mass anisotropy, both with and without ensuing lattice distortions. We find that when sufficient mass anisotropy is present, the two-spin exchange process between the nearest neighbors becomes more frequent than the three particle processes. Therefore, its corresponding antiferromagnetic exchange exceeds the ferromagnetic exchange from the three-spin process and becomes dominant. Numerical diagonalization of small clusters with two, three, and four-spin exchange terms shows a transition from a ferromagnetic to an antiferromagnetic ground state with increasing mass anisotropy.
2015-01-01
The optimized mean-trajectory (OMT) approximation is a semiclassical method for computing vibrational response functions from action-quantized classical trajectories connected by discrete transitions representing radiation–matter interactions. Here we apply this method to an anharmonic chromophore coupled to a harmonic bath. A forward–backward trajectory implementation of the OMT method is described that addresses the numerical challenges of applying the OMT to large systems with disparate frequency scales. The OMT is shown to well reproduce line shapes and waiting time dynamics in the pure dephasing limit of weak coupling to an off-resonant bath. The OMT is also shown to describe a case where energy transfer is the predominant source of line broadening. PMID:25275943
The quantum spectral analysis of the two-dimensional annular billiard system
Institute of Scientific and Technical Information of China (English)
Zhang Yan-Hui; Zhang Ji-Ouan; Xu Xue-You; Lin Sheng-Lu
2009-01-01
Based on the extended closed-orbit theory together with spectral analysis, this paper studies the correspondence between quantum mechanics and the classical counterpart in a two-dimeusional annular billiard. The results demonstrate that the Fourier-transformed quantum spectra are in very good accordance with the lengths of the classical ballistic trajectories, whereas spectral strength is intimately associated with the shapes of possible open orbits connecting arbitrary two points in the annular cavity. This approach facilitates an intuitive understanding of basic quantum features such as quantum interference, locations of the wavefunctions, and allows quantitative calculations in the range of high energies, where full quantum calculations may become impractical in general. This treatment provides a thread to explore the properties of microjunction transport and even quantum chaos under the much more general system.
Observations of the sedimentation of individual particles in a quasi-two dimensional system
Ramos, Eduardo; Lee, Andrew; Goldman, Daniel; Swinney, Harry
2002-11-01
We report observations of single sedimenting acrylic spheres (diameter = 3.175 mm, relative density = 1.19) in a vertical Hele-Shaw cell formed by two parallel glass plates and filled with water. The distance between walls of the cell varies from 1.1 to 1.3 sphere diameters; the corresponding sedimenting Reynolds number varies from 220 to 300. In the narrower cell, a wake was formed by an attached vortical region behind the sphere with two asymetrical branches. These branches oscillated and shed vortices alternately; this structure is similar to the Von Karman vortex street generated by a fixed cylinder exposed to a constant flow at approximately the same Reynolds number. In contrast, the wake of a sphere falling in a cell with a gap of 1.3 diameters was similar to that for a sphere in an infinite system at Reynolds numbers slightly larger than the threshhold for the onset of periodic wake oscillations (Re 300): the sphere sheds vortex loops, which are separated by counterotating pairs of vortex filaments.
Dostál, Jakub; Benešová, Barbora; Brixner, Tobias
2016-09-01
Excitation energy transfer in complex systems often proceeds through series of intermediate states. One of the goals of time-resolved spectroscopy is to identify the spectral signatures of all of them in the acquired experimental data and to characterize the energy transfer scheme between them. It is well known that in the case of transient absorption spectra such decomposition is ambiguous even if many simplifying considerations are taken. In contrast to transient absorption, absorptive 2D spectra intuitively resemble population transfer matrices. Therefore, it seems possible to decompose the 2D spectra unambiguously. Here we show that all necessary information is encoded in the combination of absorptive 2D and linear absorption spectra. We set up a simple model describing a broad class of absorptive 2D spectra and prove analytically that they can be inverted uniquely towards physical parameters fully determining the species-associated spectra of individual constituents together with all connecting intrinsic rate constants. Due to the matrix formulation of the model, it is suitable for fast computer calculation necessary to efficiently perform the inversion numerically by fitting the combination of experimental 2D and absorption spectra. Moreover, the model allows for decomposition of the 2D spectrum into its stimulated emission, ground-state bleach, and excited-state absorption components almost unambiguously. The numerical procedure is illustrated exemplarily.
Nonlinear photocurrents in two-dimensional systems based on graphene and boron nitride
Hipolito, F.; Pedersen, Thomas G.; Pereira, Vitor M.
2016-07-01
The dc photoelectrical currents can be generated purely as a nonlinear effect in uniform media lacking inversion symmetry without the need for a material junction or bias voltages to drive it, in what is termed photogalvanic effect. These currents are strongly dependent on the polarization state of the radiation, as well as on topological properties of the underlying Fermi surface such as its Berry curvature. In order to study the intrinsic photogalvanic response of gapped graphene, biased bilayer graphene (BBG), and hexagonal boron nitride (hBN), we compute the nonlinear current using a perturbative expansion of the density matrix. This allows a microscopic description of the quadratic response to an electromagnetic field in these materials, which we analyze as a function of temperature and electron density. We find that the intrinsic response is robust across these systems and allows for currents in the range of pA cm/W to nA cm/W. At the independent-particle level, the response of hBN-based structures is significant only in the ultraviolet due to their sizable band gap. However, when Coulomb interactions are accounted for by explicit solution of the Bethe-Salpeter equation, we find that the photoconductivity is strongly modified by transitions involving exciton levels in the gap region, whose spectral weight dominates in the overall frequency range. Biased bilayers and gapped monolayers of graphene have a strong photoconductivity in the visible and infrared window, allowing for photocurrent densities of several nA cm/W. We further show that the richer electronic dispersion of BBG at low energies and the ability to change its band gap on demand allows a higher tunability of the photocurrent, including not only its magnitude but also, and significantly, its polarity.
Dedeoglu, Reyhan; Şahin, Sezgin; Koka, Aida; Öztunç, Funda; Adroviç, Amra; Barut, Kenan; Cengiz, Dicle; Kasapçopur, Özgür
2016-08-01
The aim of this study was to investigate subclinical systolic and diastolic dysfunction in juvenile-onset systemic lupus erythematosus (j-SLE) patients with speckle tracking echocardiography (STE) and the effects of disease activity on left ventricular (LV) regional functions. Thirty-five patients with j-SLE and 30 healthy children (control group) were evaluated between January and August 2015. STE was performed on all patients and controls. Medical records, including diagnosis criteria, age at diagnosis, and duration of disease, were evaluated. SLE disease activity was assessed using the SLE Disease Activity Index (SLEDAI). j-SLE patients had lower ejection fraction than did control subjects but still within normal range. LV end-diastolic and end-systolic dimensions were significantly larger in j-SLE patients (32.43 ± 3.2 vs 28.3 ± 3.1 and 21.1 ± 1.9 vs 18.9.0 ± 2.2, respectively; p = 0.001). There was a significant reduction in longitudinal strain of LV segments in the j-SLE patients compared with controls. J-SLE patients were further divided into subgroups. Group 1 comprised patients having SLEDAI scores >8 at the onset of disease but who improved with therapy during follow-up. Group 2 included j-SLE patients with SLEDAI scores >8 at diagnosis and persistently >4 at the end of follow-up. In the LV mid-inferior and mid-inferolateral segments, STE strain measurements of group 2 were significantly lower than those of group 1 (15.9 ± 6.4 vs 20.0 ± 4.4, 17.9 ± 7.2 vs 23.2 ± 3.8; p = 0.075, p = 0.055, respectively). Simple and non-invasive STE would be helpful in predicting cardiovascular prognosis with new therapeutic medications/interventions or in objectively comparing the effects of immunosuppressive drugs in comparison with preceding STE evaluation.
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.
Chen, Y. F.; Tung, J. C.; Tuan, P. H.; Yu, Y. T.; Liang, H. C.; Huang, K. F.
2017-01-01
A general method is developed to characterize the family of classical periodic orbits from the quantum Green's function for the two-dimensional (2D) integrable systems. A decomposing formula related to the beta function is derived to link the quantum Green's function with the individual classical periodic orbits. The practicality of the developed formula is demonstrated by numerically analyzing the 2D commensurate harmonic oscillators and integrable quantum billiards. Numerical analyses reveal that the emergence of the classical features in quantum Green's functions principally comes from the superposition of the degenerate states for 2D harmonic oscillators. On the other hand, the damping factor in quantum Green's functions plays a critical role to display the classical features in mesoscopic regime for integrable quantum billiards, where the physical function of the damping factor is to lead to the coherent superposition of the nearly degenerate eigenstates.
Spin-Hall effect in two-dimensional electron systems with Rashba spin-orbit coupling and disorder.
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.
Institute of Scientific and Technical Information of China (English)
Chen Chen; Zhihua Xiong; Yisheng Zhong
2014-01-01
Based on the two-dimensional (2D) system theory, an integrated predictive iterative learning control (2D-IPILC) strategy for batch processes is presented. First, the output response and the error transition model predictions along the batch index can be calculated analytically due to the 2D Roesser model of the batch process. Then, an integrated framework of combining iterative learning control (ILC) and model predictive control (MPC) is formed reasonably. The output of feedforward ILC is estimated on the basis of the predefined process 2D model. By min-imizing a quadratic objective function, the feedback MPC is introduced to obtain better control performance for tracking problem of batch processes. Simulations on a typical batch reactor demonstrate that the satisfactory tracking performance as wel as faster convergence speed can be achieved than traditional proportion type (P-type) ILC despite the model error and disturbances.
Hu, Binhui; Kott, Tomasz M.; Kane, B. E.
2013-03-01
Two-dimensional electron systems (2DESs) on hydrogen-terminated Si(111) surfaces show very high quality. The peak electron mobility of 325,000 cm2/Vs can be reached at T =90 mK and 2D electron density n2 d = 4 . 15 ×1011 cm-2, and the device shows the fractional quantum hall effect[1]. 2DESs on H-Si(111) at lower densities may exhibit new physics, because both valley degeneracy and effective mass lead to a large Wigner-Seitz radius rs at accessible densities. In these devices, phosphorus ion implantation is used to defined the contacts to the 2DESs[2]. The contacts themselves work at low temperature. However, at lower 2D electron density (ion implantation annealing parameters are adjusted to mitigate the issue. Possible measurement technique is also explored to overcome the problem.
Classifying Two-dimensional Hyporeductive Triple Algebras
Issa, A Nourou
2010-01-01
Two-dimensional real hyporeductive triple algebras (h.t.a.) are investigated. A classification of such algebras is presented. As a consequence, a classification of two-dimensional real Lie triple algebras (i.e. generalized Lie triple systems) and two-dimensional real Bol algebras is given.
Energy Technology Data Exchange (ETDEWEB)
Qiu, Ying-Kun, E-mail: qyk@xmu.edu.cn; Chen, Fang-Fang; Zhang, Ling-Ling; Yan, Xia; Chen, Lin; Fang, Mei-Juan; Wu, Zhen, E-mail: wuzhen@xmu.edu.cn
2014-04-01
Highlights: • Preparative MDLC system was developed for separation of complicated natural products. • Medium-pressure LC and preparative HPLC were connected by interface of SPE. • Automated multi-step preparative separation of 25 compounds was achieved by using this system. - Abstract: An on-line comprehensive two-dimensional preparative liquid chromatography system was developed for preparative separation of minor amount components from complicated natural products. Medium-pressure liquid chromatograph (MPLC) was applied as the first dimension and preparative HPLC as the second one, in conjunction with trapping column and makeup pump. The performance of the trapping column was evaluated, in terms of column size, dilution ratio and diameter-height ratio, as well as system pressure from the view of medium pressure liquid chromatograph. Satisfactory trapping efficiency can be achieved using a commercially available 15 mm × 30 mm i.d. ODS pre-column. The instrument operation and the performance of this MPLC × preparative HPLC system were illustrated by gram-scale isolation of crude macro-porous resin enriched water extract of Rheum hotaoense. Automated multi-step preparative separation of 25 compounds, whose structures were identified by MS, {sup 1}H NMR and even by less-sensitive {sup 13}C NMR, could be achieved in a short period of time using this system, exhibiting great advantages in analytical efficiency and sample treatment capacity compared with conventional methods.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A two-dimensional model of unsteady turbulent flow induced by high-speed elevator system was established in the present study. The research was focused on the instantaneous variation of the aerodynamic force on the car structure during traversing motion of the counter weight in the hoistway. A dynamic meshing method was employed to treat the multi-body motion system to avoid poor distortion of meshes. A comprehensive understanding of this significant aspect was obtained by varying the horizontal gap (δ=0.1m, 0.2m, and 0.3m) between the elevator car and the counter weight, and the moving speed (U0=2m/s, 6m/s, and 10m/s) of the elevator system. A pulsed intensification of the aerodynamic force on the elevator car and subsequent appearance of large valley with negative aerodynamic force were clearly observed in the numerical results. In parameters studied (δ=0.1m, U0=2m/s, 6m/s, 10m/s), the peaked horizontal and vertical forces are respectively 7-11 and 4.3-5.65 times of that when the counter weight is far from the car. These results demonstrated the prominent influence of the traversing counter weight on aerodynamic force on the elevator car, which is of great significance to designers of high-speed elevator system.
Quantum supremacy of many-particle thermal machines
Jaramillo, J.; Beau, M.; del Campo, A.
2016-07-01
While the emergent field of quantum thermodynamics has the potential to impact energy science, the performance of thermal machines is often classical. We ask whether quantum effects can boost the performance of a thermal machine to reach quantum supremacy, i.e., surpassing both the efficiency and power achieved in classical thermodynamics. To this end, we introduce a nonadiabatic quantum heat engine operating an Otto cycle with a many-particle working medium, consisting of an interacting Bose gas confined in a time-dependent harmonic trap. It is shown that thanks to the interplay of nonadiabatic and many-particle quantum effects, this thermal machine can outperform an ensemble of single-particle heat engines with same resources, demonstrating the quantum supremacy of many-particle thermal machines.
Holland, Scott D.
1994-01-01
The present study examines the wind-tunnel blockage and actuation systems effectiveness in starting and forcibly unstarting a two-dimensional scramjet inlet in the NASA Langley 20-Inch Mach 6 Tunnel. The intent of the overall test program is to study (both experimentally and computationally) the dynamics of the inlet unstart; however, prior to the design and fabrication of an expensive, instrumented wind-tunnel model, it was deemed necessary first to examine potential wind-tunnel blockage issues related to model sizing and to examine the adequacy of the actuation systems in accomplishing the start and unstart. The model is equipped with both a moveable cowl and aft plug. Windows in the inlet sidewalls allow limited optical access to the internal shock structure; schlieren video was used to identify inlet start and unstart. A chronology of each actuation sequence is provided in tabular form along with still frames from the schlieren video. A pitot probe monitored the freestream conditions throughout the start/unstart process to determine if there was a blockage effect due to the model start or unstart. Because the purpose of this report is to make the phase I (blockage and actuation systems) data rapidly available to the community, the data is presented largely without analysis of the internal shock interactions or the unstart process. This series of tests indicated that the model was appropriately sized for this facility and identified operability limits required first to allow the inlet to start and second to force the unstart.
Critical behavior of two-dimensional spin systems under the random-bond six-state clock model
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.
Cheng, Guang-Ling; Cong, Lu; Chen, Ai-Xi
2016-04-01
A scheme for two-dimensional (2D) electromagnetically induced grating via spatial gain and phase modulation is presented in a two-level atomic system. Based on the interactions of two orthogonal standing-wave fields, the atom could diffract the weak probe beam into high-order directions and a 2D diffraction grating is generated. It is shown that the diffraction efficiency of the grating can be efficiently manipulated by controlling the Rabi frequencies of control fields, the detunings of the control and probe fields, and interaction length. Different from 2D cross-grating via electromagnetically induced transparency in a four-level atomic system, the present scheme results from the spatial modulation of gain and phase in a simple two-level system, which could lead to 2D gain-phase grating with larger diffraction intensities in the diffraction directions. The studies we present may have potential applications in developing photon devices for optical-switching, optical imaging and quantum information processing.
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.
Directory of Open Access Journals (Sweden)
Jun Liu
2015-04-01
Full Text Available With the continuing growth of highway construction and vehicle use expansion all over the world, highway vehicle traffic rule violation (TRV detection has become more and more important so as to avoid traffic accidents and injuries in intelligent transportation systems (ITS and vehicular ad hoc networks (VANETs. Since very few works have contributed to solve the TRV detection problem by moving vehicle measurements and surveillance devices, this paper develops a novel parallel ultrasonic sensor system that can be used to identify the TRV behavior of a host vehicle in real-time. Then a two-dimensional state method is proposed, utilizing the spacial state and time sequential states from the data of two parallel ultrasonic sensors to detect and count the highway vehicle violations. Finally, the theoretical TRV identification probability is analyzed, and actual experiments are conducted on different highway segments with various driving speeds, which indicates that the identification accuracy of the proposed method can reach about 90.97%.
Fluctuations in an ordered c (2×2) two-dimensional lattice-gas system with repulsive interactions
Argyrakis, P.; Chumak, A. A.; Maragakis, M.
2005-06-01
Fluctuations of the particle density in an ordered c(2×2) two-dimensional lattice-gas system are studied both analytically and by means of Monte Carlo simulations. The ordering is caused by a strong interparticle repulsive interaction resulting in the second order phase transition. The lattice of adsorption sites is divided into two sublattices (almost filled and almost empty sublattices) each of which contains a small number of structural “defects,” i.e., vacancies and excess particles. The relaxation of the correlation function of fluctuations turns out to be governed by two different functions. This peculiarity is to be contrasted with the traditional fluctuation theory which predicts the existence of a single damping constant, determined by the collective diffusion coefficient. A specific thesis of the proposed approach is that transport phenomena in ordered systems may be described in terms of both displacements and generation-recombination of structural defects. Accordingly, the correlation function of fluctuations depends on diffusion coefficients of two defect species as well as on the generation-recombination frequency. Our theory reduces to the usual one when fluctuations occur under local equilibrium conditions, i.e., for a sufficiently large size of probe areas and not too great values of interaction parameter. The analytical results agree well with those obtained in the Monte Carlo framework.
One- and two-dimensional solitons in PT-symmetric systems emulating the spin-orbit coupling
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.
Komura, Yukihiro
2012-01-01
We present the GPU calculation with the common unified device architecture (CUDA) for the Swendsen-Wang multi-cluster algorithm of two-dimensional classical spin systems. We adjust the two connected component labeling algorithms recently proposed with CUDA for the assignment of the cluster in the Swendsen-Wang algorithm. Starting with the q-state Potts model, we extend our implementation to the system of vector spins, the q-state clock model, with the idea of embedded cluster. We test the performance, and the calculation time on GTX580 is obtained as 2.51 nano sec per a spin flip for the q=2 Potts model (Ising model) and 2.42 nano sec per a spin flip for the q=6 clock model with the linear size L=4096 at the critical temperature, respectively. The computational speed for the q=2 Potts model on GTX580 is 12.4 times as fast as the calculation speed on a current CPU core. That for the q=6 clock model on GTX580 is 35.6 times as fast as the calculation speed on a current CPU core.
Rajabpour, M. A.
2016-11-01
We classify the sign of the critical Casimir force between two finite objects separated by a large distance in the two-dimensional systems that can be described by conformal field theory (CFT). Specifically, we show that, as long as the smallest scaling dimension present in the spectrum of the system is smaller than one, the sign of the force is independent of the shape of the objects and can be determined by the elements of the modular S matrix of the CFT. The provided formula for the sign of the force indicates that the force is always attractive for equal boundary conditions, independent of the shape of the objects. However, different boundary conditions can lead to attractive or repulsive forces. Using the derived formula, we prove the known results regarding the Ising model and the free bosons. As new examples, we give detailed results regarding the Q =3 state Potts model and the compactified bosons. For example, for the latter model we show that the Dirichlet boundary condition does not always lead to an attractive force.
Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures.
Liu, Hong-Chao; Li, Hui; He, Qing Lin; Sou, Iam Keong; Goh, Swee K; Wang, Jiannong
2016-05-17
The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years' air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena.
Differential Evolution for Many-Particle Adaptive Quantum Metrology
Lovett, N.B.; Crosnier, C.; Perarnau- Llobet, M.; Sanders, B.
2013-01-01
We devise powerful algorithms based on differential evolution for adaptive many-particle quantum metrology. Our new approach delivers adaptive quantum metrology policies for feedback control that are orders-of-magnitude more efficient and surpass the few-dozen-particle limitation arising in methods
Directory of Open Access Journals (Sweden)
D.F. Schwanzer
2011-09-01
Full Text Available We have investigated the effect of a disordered porous matrix on the cluster microphase formation of a two dimensional system where particles interact via competing interactions. To this end we have performed extensive Monte Carlo simulations and have systematically varied the densities of the fluid and of the matrix as well as the interaction between the matrix particles and between the matrix and fluid particles. Our results provide evidence that the matrix {it does} have a distinct effect on the microphase formation of the fluid particles: as long as the particles interact both among themselves as well as with the fluid particles via a simple hard sphere potential, they essentially reduce the available space, in which the fluid particles form a cluster microphase. On the other hand, if we turn on a long-range tail in the matrix-matrix and in the matrix-fluid interactions, the matrix particles become nucleation centers for the clusters formed by the fluid particles.
D'Andrea, Antonello; D'Alto, Michele; Di Maio, Marco; Vettori, Serena; Benjamin, Nicola; Cocchia, Rosangela; Argiento, Paola; Romeo, Emanuele; Di Marco, Giovanni; Russo, Maria Giovanna; Valentini, Gabriele; Calabrò, Raffaele; Bossone, Eduardo; Grünig, Ekkehard
2016-07-01
Enlargement and dysfunction of the right atrium might be an early sign for pulmonary hypertension in systemic sclerosis (SSc). This is the first study to analyse right atrial morphology and function in SSc patients compared to healthy controls by speckle-tracking two-dimensional strain echocardiography (2DSE) at rest and during exercise. Furthermore, right atrial function was correlated with further clinical findings. Adult patients with SSc for >3 years (n = 90) and 55 age- and gender-matched healthy controls underwent a panel of non-invasive assessments including transthoracic echocardiography, pulsed Doppler myocardial imaging and 2DSE at rest and during exercise. Furthermore, serological tests and high-resolution chest computed tomography were performed. SSc patients showed significant impairment of right atrial function and the right atrial enlargement, measured by 2DSE at rest and during exercise compared to controls (both p right atrial lateral strain was significantly associated with PAPs during effort, right atrial area, left ventricle stroke volume and inferior vena cava diameter using multivariable analysis. The findings of this study suggest that a high proportion of SSc patients reveal right atrial dysfunction even without manifest pulmonary hypertension. Impaired right atrial function occurred mostly in patients with pulmonary fibrosis and/or elevated PAPs during exercise, was independently associated with prognostic factors and may therefore be useful for risk stratification. Further studies are needed to analyse if right atrial dysfunction assessed by 2DSE may help to improve early diagnosis of pulmonary hypertension.
Yang, Kesong; Nazir, Safdar; Behtash, Maziar; Cheng, Jianli
2016-10-01
The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO3 and SrTiO3 (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO3-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests. Of these, Al-, Ga-, Sc-, and Ta-based compounds can form a 2DEG with STO, while In-based compounds exhibit a strain-induced strong polarization when deposited on STO substrate. In particular, the Ta-based compounds can form 2DEG with potentially high electron mobility at (TaO2)+/(SrO)0 interface. Our approach, by defining materials descriptors solely based on the bulk materials properties, and by relying on the perovskite-oriented quantum materials repository, opens new avenues for the discovery of perovskite-oxide-based functional interface materials in a HT fashion.
Gurarie, V
2004-01-01
We examine two-dimensional conformal field theories (CFTs) at central charge c=0. These arise typically in the description of critical systems with quenched disorder, but also in other contexts including dilute self-avoiding polymers and percolation. We show that such CFTs must in general possess, in addition to their stress energy tensor T(z), an extra field whose holomorphic part, t(z), has conformal weight two. The singular part of the Operator Product Expansion (OPE) between T(z) and t(z) is uniquely fixed up to a single number b, defining a new `anomaly' which is a characteristic of any c=0 CFT, and which may be used to distinguish between different such CFTs. The extra field t(z) is not primary (unless b=0), and is a so-called `logarithmic operator' except in special cases which include affine (Kac-Moody) Lie-super current algebras. The number b controls the question of whether Virasoro null-vectors arising at certain conformal weights contained in the c=0 Kac table may be set to zero or not, in these n...
Energy Technology Data Exchange (ETDEWEB)
Hanu, A.R., E-mail: hanua@mcmaster.ca [Department of Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4K1 (Canada); NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Prestwich, W.V.; Byun, S.H. [Department of Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4K1 (Canada)
2015-04-21
We present a data acquisition (DAQ) system for two-dimensional position sensitive micropattern gas detectors using the delay-line method for readout. The DAQ system consists of a field programmable gate array (FPGA) as the main data processor and our time-to-digital (TDC) mezzanine card for making time measurements. We developed the TDC mezzanine card around the Acam TDC-GPX ASIC and it features four independent stop channels referenced to a common start, a typical timing resolution of ~81 ps, and a 17-bit measurement range, and is compliant with the VITA 57.1 standard. For our DAQ system, we have chosen the Xilinx SP601 development kit which features a single Spartan 6 FPGA, 128 MB of DDR2 memory, and a serial USB interface for communication. Output images consist of 1024×1024 square pixels, where each pixel has a 32-bit depth and corresponds to a time difference of 162 ps relative to its neighbours. When configured for a 250 ns acquisition window, the DAQ can resolve periodic event rates up to 1.8×10{sup 6} Hz without any loses and will report a maximum event rate of 6.11×10{sup 5} Hz for events whose arrival times follow Poisson statistics. The integral and differential non-linearities have also been measured and are better than 0.1% and 1.5%, respectively. Unlike commercial units, our DAQ system implements the delay-line image reconstruction algorithm entirely in hardware and is particularly attractive for its modularity, low cost, ease of integration, excellent linearity, and high throughput rate.
Event-chain Monte Carlo algorithms for three- and many-particle interactions
Harland, J.; Michel, M.; Kampmann, T. A.; Kierfeld, J.
2017-02-01
We generalize the rejection-free event-chain Monte Carlo algorithm from many-particle systems with pairwise interactions to systems with arbitrary three- or many-particle interactions. We introduce generalized lifting probabilities between particles and obtain a general set of equations for lifting probabilities, the solution of which guarantees maximal global balance. We validate the resulting three-particle event-chain Monte Carlo algorithms on three different systems by comparison with conventional local Monte Carlo simulations: i) a test system of three particles with a three-particle interaction that depends on the enclosed triangle area; ii) a hard-needle system in two dimensions, where needle interactions constitute three-particle interactions of the needle end points; iii) a semiflexible polymer chain with a bending energy, which constitutes a three-particle interaction of neighboring chain beads. The examples demonstrate that the generalization to many-particle interactions broadens the applicability of event-chain algorithms considerably.
Lee, Ching-Ping; Komiyama, Susumu; Chen, Jeng-Chung
2015-03-01
High mobility two-dimensional electron gas (2DEG) formed in the interface of a GaAs/AlGaAs hetero-structure in high magnetic field (B) exhibits interring nonlinear response either under microwave radiation or to a dc electric field (E). It is general believed that this kind nonlinear behavior is closely related to the occurrence of negative-differential conductance (NDC) in the presence of strong B and E. We observe a new type NDC state driven by a direct current above a threshold value (Ith) applied to a 2DEG as a function of B at relatively high temperatures (T). A current instability is observed in 2DEG system at high B ~6-8 T and at high T ~ 20- 30 K while the applied current is over Ith. The longitudinal voltage Vxx shows sub-linear behavior with the increase of I. As the current exceed Ith, Vxx suddenly drops a ΔVxx and becomes irregular associated with the appearance of hysteresis with sweeping I. We find that Ith increases with the increase of B and of T; meanwhile, ΔVxx is larger at higher B but lower T. Data analysis suggest that the onset of voltage fluctuation can be described by a NDC model proposed by Kurosawa et al. in 1976. The general behaviors of T and B dependence of current instability are analog to those recently reported at lower both T and B. This consistence suggests the same genuine mechanism of NDC phenomena observed in 2DEG system.
Yang, Kesong
As a rapidly growing area of materials science, high-throughput (HT) computational materials design is playing a crucial role in accelerating the discovery and development of novel functional materials. In this presentation, I will first introduce the strategy of HT computational materials design, and take the HT discovery of topological insulators (TIs) as a practical example to show the usage of such an approach. Topological insulators are one of the most studied classes of novel materials because of their great potential for applications ranging from spintronics to quantum computers. Here I will show that, by defining a reliable and accessible descriptor, which represents the topological robustness or feasibility of the candidate, and by searching the quantum materials repository aflowlib.org, we have automatically discovered 28 TIs (some of them already known) in five different symmetry families. Next, I will talk about our recent research work on the HT computational design of the perovskite-based two-dimensional electron gas (2DEG) systems. The 2DEG formed on the perovskite oxide heterostructure (HS) has potential applications in next-generation nanoelectronic devices. In order to achieve practical implementation of the 2DEG in the device design, desired physical properties such as high charge carrier density and mobility are necessary. Here I show that, using the same strategy with the HT discovery of TIs, by introducing a series of combinatorial descriptors, we have successfully identified a series of candidate 2DEG systems based on the perovskite oxides. This work provides another exemplar of applying HT computational design approach for the discovery of advanced functional materials.
Ross, Matthew R.
The primary focus of this work is the development of a mid-infrared pulse shaping system. The primary motivation for this system is for two-dimensional infrared (2DIR) spectroscopy, however, the mid-infrared pulse shaper also allows for more sophisticated spectroscopic experiments not previously attempted in the mid-infrared. Moreover, many can be implemented without changes or realignment of the optical setup. Example spectra are presented along with a discussion of capabilities and diagnostics. A second major project presented is 2DIR spectroscopy of iron pentacarbonyl, Fe(CO)5, a small metal carbonyl. This molecule undergoes Berry pseudorotation, a form of fluxtionality. This fast exchange of ligands mixes axial and equatorial modes and occurs on a timescale of picoseconds, too fast for NMR and other methods of measuring chemical structure and isomerization. Ultrafast chemical exchange spectroscopy, a measurement within 2DIR spectroscopy, is capable of resolving the time scales of this motion. We found that this process is affected by the solvent environment, specifically the solvent viscosity in alkanes and hydrogen bonding environments in alcohols. Lastly, a study is presented in which a series of synthetic metalloenzymes with a metal active site are studied by 2DIR spectroscopy. In this case a carbonyl is ligated to a copper-I atom in the active site, which then serves as our spectroscopic probe. We find, unexpectedly, that the shape of the carbonyl vibrational potential, as measured by the anharmonicity, is time-dependent. We attribute this to a geometrical rearrangement and are able to suggest that this effect is dependent on local site structure and dynamics and not significantly affected by electric potential near the peptide.
On the Quantum Mechanical Scattering Statistics of Many Particles
Dürr, Detlef; Moser, Tilo; Römer, Sarah
2010-01-01
The probability of a quantum particle being detected in a given solid angle is determined by the $S$-matrix. The explanation of this fact in time dependent scattering theory is often linked to the quantum flux, since the quantum flux integrated against a (detector-) surface and over a time interval can be viewed as the probability that the particle crosses this surface within the given time interval. Regarding many particle scattering, however, this argument is no longer valid, as each particle arrives at the detector at its own random time. While various treatments of this problem can be envisaged, here we present a straightforward Bohmian analysis of many particle potential scattering from which the $S$-matrix probability emerges in the limit of large distances.
Liu, Da-Jiang; Evans, J. W.
2002-10-01
We present a comparison of the predictions of atomistic and continuum models for the sintering of pairs of near-square two-dimensional nanoclusters adsorbed on the (100) surface in fcc metal homoepitaxial systems. Mass transport underlying these processes is dominated by periphery diffusion (PD) of adatoms along the edge of the clusters. A Mullins-type continuum model for cluster evolution incorporates anisotropy in the step edge stiffness (reflecting the energetics and adsorption site lattice structure in the atomistic model), and can also account for anisotropy in the step edge mobility (reflecting details of the kinetics). In such continuum treatments, the characteristic time τeq for relaxation of clusters with linear size of order L satisfies τeq~L4. Deviations may generally be expected for small sizes L or low temperatures T. However, for the relaxation of dumbbell-shaped clusters (formed by corner-to-corner coalescence of square clusters), atomistic simulations for PD with no kink rounding barrier (δ=0) reveal that τeq~L4 always applies. In contrast, atomistic simulations with a large kink rounding barrier (δ>0) reveal distinct scaling with τeq~L3, for low T or small L, thus providing an effective way to test for δ>0. For the relaxation of faceted rectangular clusters (formed by side-to-side coalescence of square clusters), atomistic simulations for PD with δ=0 reveal that τeq~L2, for low T or small L. This is consistent with a recent proposal by Combe and Larralde. For large δ>0, τeq has an even weaker dependence on L. We elucidate scaling behavior and the effective activation barrier for relaxation in terms of the individual atomistic PD processes and their barriers.
Topological defects in two-dimensional crystals
Chen, Yong; Qi, Wei-Kai
2008-01-01
By using topological current theory, we study the inner topological structure of the topological defects in two-dimensional (2D) crystal. We find that there are two elementary point defects topological current in two-dimensional crystal, one for dislocations and the other for disclinations. The topological quantization and evolution of topological defects in two-dimensional crystals are discussed. Finally, We compare our theory with Brownian-dynamics simulations in 2D Yukawa systems.
Mesoscopic quantum interference experiments in InGaAs and GaAs two-dimensional systems
Ren, Shaola
The study of quantum interference in solid-state systems yields insight in fundamental properties of mesoscopic systems. Electron quantum interference constitutes an important method to explore mesoscopic physics and quantum decoherence. This dissertation focuses on two-dimensional (2D) electron systems in delta-Si doped n-type In0:64Ga0:36As/In 0:45Al0:55As, 2D hole systems in Si-doped p-type GaAs/Al 0:35Ga0:65As and C-doped p-type GaAs/Al0:24Ga 0:76As heterostructures. The low temperature experiments study the magnetotransport of nano- and micro-scale lithographically defined devices fabricated on the heterostructures. These devices include a single ring interferometer and a ring interferometer array in 2D electron system, Hall bar geometries and narrow wires in 2D hole systems. The single ring interferometer yields pronounced Aharonov-Bohm (AB) oscillations with magnetic flux periodicity of h/e over a wide range of magnetic field. The periodicity was confirmed by Fourier transformation of the oscillations. The AB oscillation amplitude shows a quasi-periodic modulation over applied magnetic field due to local magnetic flux threading through the interferometer arms. Further study of current and temperature dependence of the amplitude of the oscillations indicates that the Thouless energy forms the measure of excitation energies giving quantum decoherence. An in-plane magnetic field was applied to the single ring interferometer to study the Berry's phase and the Aharonov-Casher effect. The ring interferometer array yields both AB oscillations and Altshuler-Aronov-Spivak (AAS) oscillations, the latter with magnetic flux periodicity of h/2e. The AAS oscillations require time-reversal symmetry and hence can be used to qualify time-reversal symmetry breaking. More importantly, the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length, can be obtained by the analysis of the AAS
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...
Viazzi, S.; Bahr, C.; Hertem, van T.; Schlageter-Tello, A.; Romanini, C.E.B.; Halachmi, I.; Lokhorst, C.; Berckmans, D.
2014-01-01
In this study, two different computer vision techniques to automatically measure the back posture in dairy cows were tested and evaluated. A two-dimensional and a three-dimensional camera system were used to extract the back posture from walking cows, which is one measurement used by experts to
Liu, S Y; Lei, X. L.; Horing, Norman J. M.
2011-01-01
Considering screeening of electron scattering interactions in terms of the finite-temperature STLS theory and solving the linearized Boltzmann equation (with no appeal to a relaxation time approximation), we present a theoretical analysis of the low-temperature Seebeck effect in two-dimensional semiconductors with dilute electron densities. We find that the temperature ($T$) dependencies of the diffusion and phonon-drag thermoelectric powers ($S_d$ and $S_g$) can no longer be described by the...
Differential evolution for many-particle adaptive quantum metrology.
Lovett, Neil B; Crosnier, Cécile; Perarnau-Llobet, Martí; Sanders, Barry C
2013-05-31
We devise powerful algorithms based on differential evolution for adaptive many-particle quantum metrology. Our new approach delivers adaptive quantum metrology policies for feedback control that are orders-of-magnitude more efficient and surpass the few-dozen-particle limitation arising in methods based on particle-swarm optimization. We apply our method to the binary-decision-tree model for quantum-enhanced phase estimation as well as to a new problem: a decision tree for adaptive estimation of the unknown bias of a quantum coin in a quantum walk and show how this latter case can be realized experimentally.
Osserman, Robert
2011-01-01
The basic component of several-variable calculus, two-dimensional calculus is vital to mastery of the broader field. This extensive treatment of the subject offers the advantage of a thorough integration of linear algebra and materials, which aids readers in the development of geometric intuition. An introductory chapter presents background information on vectors in the plane, plane curves, and functions of two variables. Subsequent chapters address differentiation, transformations, and integration. Each chapter concludes with problem sets, and answers to selected exercises appear at the end o
Juday, Richard D. (Inventor)
1992-01-01
A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.
Brookes, Jennifer Faith
Iron-nitrosyl systems, particularly in the form of heme proteins, with their iron metal active sites play an important role in biological systems. Heme proteins act as storage, transporters, and receptors for nitric oxide (NO), a signaling molecule that is important in immune, nervous, and cardiovascular systems of mammals. By better understanding the local environment of the active site of NO binding heme proteins we can gain insight into disease in which the NO pathways have been implicated. This is an important step to being able to develop pharmaceuticals targeting NO pathways in humans. Sodium nitroprusside ((SNP, Na2[Fe(CN)5is NO]·2H 2O) investigated as a model system for the active site of nitric oxide binding heme proteins. Using two-dimensional infrared spectroscopy (2D IR) to obtain dephasing dynamics of the nitrosyl stretch (nuNO) in a series of solvents we are able to better understand the local environment of the more complicated metalloproteins. Rigorous line shape analysis is performed by using nonlinear response theory to simulate 2D IR spectra which are then fit to experimental data in an iterative process to extract frequency-frequency correlation functions (FFCFs). The time scales obtained are then correlated to empirical solvent polarity parameters. The analysis of the 2D IR lineshapes reveal that the spectral diffusion timescale of the nuNO in SNP varies from 0.8 -- 4 ps and is negatively correlated with the empirical solvent polarity scales. We continue to investigate NO binding of metalloproteins through 2D IR experiments on nitrophorin 4 (NP4). NP4 is a pH-sensitive NO transporter protein present in the salivary gland of the blood sucking insect Rhodius prolixus which undergoes a pH sensitive structural change between a closed and open conformation allowing for the storage and delivery of NO. The two structures are observed spectroscopically as two distinct pH-dependent nu NO frequencies at ~1904 and ~1917 cm-1. We obtain FFCFs by globally
Noether's Theorem and its complement in many-particle systems
Smilga, Walter
2016-01-01
Noether's Theorem has gained outstanding importance in theoretical particle physics, because it leads to strong conservation laws, such as the conservation of momentum and of angular momentum. Closely related to this theorem, but unnoticed so far, is a law that requires the exchange of momentum between two particles that are described by an irreducible two-particle representation of the Poincare group. The exchange of momentum determines an interaction. On closer inspection, this interaction is identified as the electromagnetic interaction. This sheds new light on the particle interactions described by the Standard Model and, in particular, on the perturbation algorithm of quantum electrodynamics.
Energy Technology Data Exchange (ETDEWEB)
Dasgupta, Shivaji
2009-02-15
In this work two-dimensional electron systems (2DESs) based on AlAs/AlGaAs heterostructures doped with Si are investigated. The electrons are confined in AlAs quantum wells (QWs) sandwiched between AlGaAs buffers. Analytical calculations and simulations for AlAs QWs are presented in the first chapter. The results show a cross-over width, above which the wide (001)-oriented QWs show double valley occupancy and wide (110)-oriented QWs show single valley occupancy. We solve the Schroedinger equation analytically for anisotropic masses. The solution shows the orientation dependence of the elliptical cyclotron orbit due to the anisotropic mass. We also present an introduction to the Landau level crossings based on g{sup *}m{sup *} product. In the next chapter, we present experimental results for the double-valley (001)-oriented AlAs QWs. We present the different structures of the deep AlAs QWs along with the low temperature magnetotransport data for these QWs. Thereafter, we present the results on shallow AlAs QWs. We achieved a mobility of 4.2 x 10{sup 5} cm{sup 2}/Vs at 330 mK for the deep backside doped AlAs QW. For the shallow QWs, we achieved a mobility of2.3 x 10{sup 5} cm{sup 2}/Vs at 330 mK, for a density of 2.9 x 10{sup 11} cm{sup -2}. From the magneto-transport data, we see evidence of the double-valley occupation for the (001)-oriented AlAs wide QWs. In the next chapter, we present experimental results for the single-valley (110)-oriented AlAs QWs. We deduced the donor binding energy and the doping efficiency for this facet from a doping series of double-sided doped QWs. Thereafter, we designed different structures for the (110)-oriented AlAs QWs, which we present along with their respective low temperature magneto-transport data. We measured one of the double-sided doped AlAs QWs at very high magnetic fields and low temperatures, down to 60 mK. At the end of the chapter, we present a spike feature observed in the magneto-transport data of these QWs. This
A semiclassical hybrid approach to many particle quantum dynamics
Grossmann, Frank
2006-07-01
We analytically derive a correlated approach for a mixed semiclassical many particle dynamics, treating a fraction of the degrees of freedom by the multitrajectory semiclassical initial value method of Herman and Kluk [Chem. Phys. 91, 27 (1984)] while approximately treating the dynamics of the remaining degrees of freedom with fixed initial phase space variables, analogously to the thawed Gaussian wave packet dynamics of Heller [J. Chem. Phys. 62, 1544 (1975)]. A first application of this hybrid approach to the well studied Secrest-Johnson [J. Chem. Phys. 45, 4556 (1966)] model of atom-diatomic collisions is promising. Results close to the quantum ones for correlation functions as well as scattering probabilities could be gained with considerably reduced numerical effort as compared to the full semiclassical Herman-Kluk approach. Furthermore, the harmonic nature of the different degrees of freedom can be determined a posteriori by comparing results with and without the additional approximation.
Two-dimensional optical spectroscopy
Cho, Minhaeng
2009-01-01
Discusses the principles and applications of two-dimensional vibrational and optical spectroscopy techniques. This book provides an account of basic theory required for an understanding of two-dimensional vibrational and electronic spectroscopy.
Two-Dimensional Planetary Surface Lander
Hemmati, H.; Sengupta, A.; Castillo, J.; McElrath, T.; Roberts, T.; Willis, P.
2014-06-01
A systems engineering study was conducted to leverage a new two-dimensional (2D) lander concept with a low per unit cost to enable scientific study at multiple locations with a single entry system as the delivery vehicle.
Gwarda, Radosław Łukasz; Dzido, Tadeusz Henryk
2013-10-18
Among many advantages of planar techniques, two-dimensional (2D) separation seems to be the most important for analysis of complex samples. Here we present quick, simple and efficient two-dimensional high-performance thin-layer chromatography (2D HPTLC) of bovine albumin digest using commercial HPTLC RP-18W plates (silica based stationary phase with chemically bonded octadecyl ligands of coverage density 0.5μmol/m(2) from Merck, Darmstadt). We show, that at low or high concentration of water in the mobile phase comprised methanol and some additives the chromatographic systems with the plates mentioned demonstrate normal- or reversed-phase liquid chromatography properties, respectively, for separation of peptides obtained. These two systems show quite different separation selectivity and their combination into 2D HPTLC process provides excellent separation of peptides of the bovine albumin digest. Copyright © 2013 Elsevier B.V. All rights reserved.
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.
Joe, Yong S; Lee, Sun H; Hedin, Eric R; Kim, Young D
2013-06-01
We utilize a two-dimensional four-channel DNA model, with a tight-binding (TB) Hamiltonian, and investigate the temperature and the magnetic field dependence of the transport behavior of a short DNA molecule. Random variation of the hopping integrals due to the thermal structural disorder, which partially destroy phase coherence of electrons and reduce quantum interference, leads to a reduction of the localization length and causes suppressed overall transmission. We also incorporate a variation of magnetic field flux density into the hopping integrals as a phase factor and observe Aharonov-Bohm (AB) oscillations in the transmission. It is shown that for non-zero magnetic flux, the transmission zero leaves the real-energy axis and moves up into the complex-energy plane. We also point out that the hydrogen bonds between the base pair with flux variations play a role to determine the periodicity of AB oscillations in the transmission.
Two-dimensional liquid chromatography
DEFF Research Database (Denmark)
Græsbøll, Rune
Two-dimensional liquid chromatography has received increasing interest due to the rise in demand for analysis of complex chemical mixtures. Separation of complex mixtures is hard to achieve as a simple consequence of the sheer number of analytes, as these samples might contain hundreds or even...... dimensions. As a consequence of the conclusions made within this thesis, the research group has, for the time being, decided against further development of online LC×LC systems, since it was not deemed ideal for the intended application, the analysis of the polar fraction of oil. Trap-and...
Shibata, Y; Manabe, T; Kajita, S; Ohno, N; Takagi, M; Tsuchiya, H; Morisaki, T
2014-09-01
A compact and high-particle-flux thermal-lithium-beam source for two-dimensional measurement of electron density profiles has been developed. The thermal-lithium-beam oven is heated by a carbon heater. In this system, the maximum particle flux of the thermal lithium beam was ~4 × 10(19) m(-2) s(-1) when the temperature of the thermal-lithium-beam oven was 900 K. The electron density profile was evaluated in the small tokamak device HYBTOK-II. The electron density profile was reconstructed using the thermal-lithium-beam probe data and this profile was consistent with the electron density profile measured with a Langmuir electrostatic probe. We confirm that the developed thermal-lithium-beam probe can be used to measure the two-dimensional electron density profile with high time and spatial resolutions.
Energy Technology Data Exchange (ETDEWEB)
Higashikawa, K., E-mail: kohei@super.ees.kyushu-u.ac.jp [Department of Electrical Engineering, Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Inoue, M.; Kawaguchi, T.; Shiohara, K.; Imamura, K.; Kiss, T. [Department of Electrical Engineering, Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Iijima, Y.; Kakimoto, K.; Saitoh, T. [Material Technology Laboratory, Fujikura, 1-5-1, Kiba, Koto-ku, Tokyo 135-8512 (Japan); Izumi, T. [Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062 (Japan)
2011-11-15
Nondestructive characterization method of in-plane distribution of critical current density for coated conductors. Current distribution in a coated conductor compared with that from theoretical analysis. Relationship between local critical current density and local magnetic field. We have developed a characterization method for two-dimensional imaging of critical current density in coated conductors (CCs) based on scanning Hall-probe microscopy (SHPM). The distributions of the magnetic field around a sample were measured for several different conditions of external magnetic fields, and then were converted to those of the sheet current density which flowed to shield the external magnetic field or to trap the penetrated magnetic field. As a result, it was found that the amplitude of the sheet current density corresponded to that of critical current density almost in all the area of the sample except for the region where current direction changed. This indicates that we could obtain an in-plane distribution of the critical current density with a spatial resolution of around 100 {mu}m in non-destructive manner by this method. We believe that this measurement will be a multifunctional and comprehensive characterization method for coated conductors.
Rathjen, K. A.
1977-01-01
A digital computer code CAVE (Conduction Analysis Via Eigenvalues), which finds application in the analysis of two dimensional transient heating of hypersonic vehicles is described. The CAVE is written in FORTRAN 4 and is operational on both IBM 360-67 and CDC 6600 computers. The method of solution is a hybrid analytical numerical technique that is inherently stable permitting large time steps even with the best of conductors having the finest of mesh size. The aerodynamic heating boundary conditions are calculated by the code based on the input flight trajectory or can optionally be calculated external to the code and then entered as input data. The code computes the network conduction and convection links, as well as capacitance values, given basic geometrical and mesh sizes, for four generations (leading edges, cooled panels, X-24C structure and slabs). Input and output formats are presented and explained. Sample problems are included. A brief summary of the hybrid analytical-numerical technique, which utilizes eigenvalues (thermal frequencies) and eigenvectors (thermal mode vectors) is given along with aerodynamic heating equations that have been incorporated in the code and flow charts.
Many particle approximation of the Aw-Rascle-Zhang second order model for vehicular traffic.
Francesco, Marco Di; Fagioli, Simone; Rosini, Massimiliano D
2017-02-01
We consider the follow-the-leader approximation of the Aw-Rascle-Zhang (ARZ) model for traffic flow in a multi population formulation. We prove rigorous convergence to weak solutions of the ARZ system in the many particle limit in presence of vacuum. The result is based on uniform BV estimates on the discrete particle velocity. We complement our result with numerical simulations of the particle method compared with some exact solutions to the Riemann problem of the ARZ system.
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.
Wu, Wei; Xu, Jing-Bo
2016-08-01
We investigate the quantum phase transitions of spin systems in one and two dimensions by employing trace distance and multipartite entanglement along with the real-space quantum renormalization group method. As illustration examples, a one-dimensional and a two-dimensional XY models are considered. It is shown that the quantum phase transitions of these spin-chain systems can be revealed by the singular behaviors of the first derivatives of renormalized trace distance and multipartite entanglement in the thermodynamics limit. Moreover, we find that the renormalized trace distance and multipartite entanglement obey certain universal exponential-type scaling laws in the vicinity of the quantum critical points.
Classical Solution of a Two-Dimensional Dynamics System for Pure Forest%一个二维纯林发展系统的古典解
Institute of Scientific and Technical Information of China (English)
徐龙封; 吴慧
2011-01-01
The research of two-dimensional forest dynamics system model is still open. First, for the peculiarity of two-dimensional forest dynamics systems with initial state depending only on total quantity of forest, and boundary condition depending only on initial state again, boundary of system not satisfying one of 3 kinds common conditions, by introducing a class of special family curves in presence region of " stand age-diameter", the problem of boundary conditions is avoided. Secondly, using the technique of selecting measure dimension of lumber diameter properly, a well-posed two-dimensional forest dynamics system model is propounded. At last, colligating the technique of pulling characteristic curve, a prior estimate, structuring integral equation of initial state, iteration, the existence and uniqueness of the global classical solution are proved for this system.%二维森林发展系统模型的研究还未见到任何结果.针对这类系统初始状态依赖于林木总量,而边界状态又依赖于初始状态,系统的边界不满足通常的三类条件之一的特点,采用在“树龄-直径”存在区域内引进一类特殊的曲线族,避开了提边界条件问题.再利用适当地选择林木直径尺度量纲的技巧,提出了一个适定的二维纯林发展系统模型,最后综合拉特征线、先验估计、构造初始状态积分方程、迭代等技巧证明了这个系统整体古典解的存在唯一性.
Spin Squeezing and Entanglement of Many-Particle Spin-Half States
Institute of Scientific and Technical Information of China (English)
YAN Dong; WANG Xiao-Guang; WU Ling-An
2005-01-01
@@ In many-particle spin-half systems with exchange symmetry, we find that the spin squeezing is related to two types of entanglement, the bipartite and the pairwise entanglement. A quantitative relationship is revealed for the spin squeezing parameter, the tangle, and the concurrence. We find that a class of states is spin squeezed if the pairwise entanglement is stronger than the bipartite entanglement.
Matoz-Fernandez, D. A.; Linares, D. H.; Ramirez-Pastor, A. J.
2007-01-01
Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior and universality for the isotropic-nematic phase transition in a system of long straight rigid rods of length $k$ ($k$-mers) on two-dimensional lattices. The nematic phase, characterized by a big domain of parallel $k$-mers, is separated from the isotropic state by a continuous transition occurring at a finite density. The determination of the critical exponents, along with the behavi...
Energy Technology Data Exchange (ETDEWEB)
Dorozhkin, S. I., E-mail: dorozh@issp.ac.ru; Sychev, D. V.; Kapustin, A. A. [Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow district (Russian Federation)
2014-11-28
We have implemented a new bolometric method to detect resonances in magneto-absorption of microwave radiation by two-dimensional electron systems (2DES) in selectively doped GaAs/AlGaAs heterostructures. Radiation is absorbed by the 2DES and the thermally activated conductivity of the doping layer supplying electrons to the 2DES serves as a thermometer. The resonant absorption brought about by excitation of the confined magnetoplasma modes appears as peaks in the magnetic field dependence of the low-frequency impedance measured between the Schottky gate and 2DES.
Energy Technology Data Exchange (ETDEWEB)
Wu, Jingbo; Mayorov, Alexander S.; Wood, Christopher D.; Mistry, Divyang; Li, Lianhe; Linfield, Edmund H.; Giles Davies, A.; Cunningham, John E., E-mail: j.e.cunningham@leeds.ac.uk [School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom); Sydoruk, Oleksiy [Optical and Semiconductor Devices Group, Department of Electrical and Electronic Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ (United Kingdom)
2016-02-29
We have investigated terahertz (THz) frequency magnetoplasmon resonances in a two-dimensional electron system through the direct injection of picosecond duration current pulses. The evolution of the time-domain signals was measured as a function of magnetic field, and the results were found to be in agreement with calculations using a mode-matching approach for four modes observed in the frequency range above 0.1 THz. This introduces a generic technique suitable for sampling ultrafast carrier dynamics in low-dimensional semiconductor nanostructures at THz frequencies.
Two-dimensional cubic convolution.
Reichenbach, Stephen E; Geng, Frank
2003-01-01
The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2] x [-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance.
Steffen, T; Tanimura, Y
2000-01-01
The quantum Fokker-Planck equation is derived for a system nonlinearly coupled to a harmonic oscillator bath. The system-bath interaction is assumed to be linear in the bath coordinates but quadratic in the system coordinate. The relaxation induced dynamics of a harmonic system are investigated by s
Institute of Scientific and Technical Information of China (English)
李志斌; 陈天华
2002-01-01
An algorithm for constructing exact solitary wave solutions and singular solutions for a class of nonlinear dissipative-dispersive system is presented. With the aid of symbolic manipulation system Maple, some explicit solutions are obtained for the system in physically interesting but non-integrable cases.
Tanimura, Y; Steffen, T
2000-01-01
The relaxation processes in a quantum system nonlinearly coupled to a harmonic Gaussian-Markovian heat bath are investigated by the quantum Fokker-Planck equation in the hierarchy form. This model describes frequency fluctuations in the quantum system with an arbitrary correlation time and thus
Kuhls-Gilcrist, Andrew T.; Gupta, Sandesh K.; Bednarek, Daniel R.; Rudin, Stephen
2010-01-01
The MTF, NNPS, and DQE are standard linear system metrics used to characterize intrinsic detector performance. To evaluate total system performance for actual clinical conditions, generalized linear system metrics (GMTF, GNNPS and GDQE) that include the effect of the focal spot distribution, scattered radiation, and geometric unsharpness are more meaningful and appropriate. In this study, a two-dimensional (2D) generalized linear system analysis was carried out for a standard flat panel detector (FPD) (194-micron pixel pitch and 600-micron thick CsI) and a newly-developed, high-resolution, micro-angiographic fluoroscope (MAF) (35-micron pixel pitch and 300-micron thick CsI). Realistic clinical parameters and x-ray spectra were used. The 2D detector MTFs were calculated using the new Noise Response method and slanted edge method and 2D focal spot distribution measurements were done using a pin-hole assembly. The scatter fraction, generated for a uniform head equivalent phantom, was measured and the scatter MTF was simulated with a theoretical model. Different magnifications and scatter fractions were used to estimate the 2D GMTF, GNNPS and GDQE for both detectors. Results show spatial non-isotropy for the 2D generalized metrics which provide a quantitative description of the performance of the complete imaging system for both detectors. This generalized analysis demonstrated that the MAF and FPD have similar capabilities at lower spatial frequencies, but that the MAF has superior performance over the FPD at higher frequencies even when considering focal spot blurring and scatter. This 2D generalized performance analysis is a valuable tool to evaluate total system capabilities and to enable optimized design for specific imaging tasks. PMID:21243038
Curry, Mark A (Inventor); Senibi, Simon D (Inventor); Banks, David L (Inventor)
2010-01-01
A system and method for detecting damage to a structure is provided. The system includes a voltage source and at least one capacitor formed as a layer within the structure and responsive to the voltage source. The system also includes at least one sensor responsive to the capacitor to sense a voltage of the capacitor. A controller responsive to the sensor determines if damage to the structure has occurred based on the variance of the voltage of the capacitor from a known reference value. A method for sensing damage to a structure involves providing a plurality of capacitors and a controller, and coupling the capacitors to at least one surface of the structure. A voltage of the capacitors is sensed using the controller, and the controller calculates a change in the voltage of the capacitors. The method can include signaling a display system if a change in the voltage occurs.
Boukahil, A.; Huber, D. L.
2014-12-01
We investigate the optical absorption and the density of states of a Frenkel exciton system on a square lattice with nearest-neighbor interactions and a Gaussian distribution of transition frequencies (i.e. Gaussian diagonal disorder). Results are presented for the absorption and the density of states of direct and indirect edge systems for a range of variances. There is reasonable agreement with the corresponding finite array calculations of Schreiber and Toyozawa. The existence of an Urbach tail is also investigated.
Institute of Scientific and Technical Information of China (English)
魏益焕
2011-01-01
由文献[4]中方程（2．25）-（2．31b）给出了对杂化弦EH型线性系统的分析。结果表明该线性系统等同于由文献[4]中方程（2．17）-（2．24b）给出的EH型线性系统。%An analysis is made of the EH - type linear system based on two - dimensional heterotic string theory, as is indicated in the equation of （2.25） - （2.31 b） in Bibliography [ 4 ]. The result shows that this system is equivalent to the EH -type linear system in the equations of （2.17） - （2.24b） in Bibliography [4].
Leitner, Daniel; Felderer, Bernd; Vontobel, Peter; Schnepf, Andrea
2014-01-01
Root system traits are important in view of current challenges such as sustainable crop production with reduced fertilizer input or in resource-limited environments. We present a novel approach for recovering root architectural parameters based on image-analysis techniques. It is based on a graph representation of the segmented and skeletonized image of the root system, where individual roots are tracked in a fully automated way. Using a dynamic root architecture model for deciding whether a specific path in the graph is likely to represent a root helps to distinguish root overlaps from branches and favors the analysis of root development over a sequence of images. After the root tracking step, global traits such as topological characteristics as well as root architectural parameters are computed. Analysis of neutron radiographic root system images of lupine (Lupinus albus) grown in mesocosms filled with sandy soil results in a set of root architectural parameters. They are used to simulate the dynamic development of the root system and to compute the corresponding root length densities in the mesocosm. The graph representation of the root system provides global information about connectivity inside the graph. The underlying root growth model helps to determine which path inside the graph is most likely for a given root. This facilitates the systematic investigation of root architectural traits, in particular with respect to the parameterization of dynamic root architecture models.
Groenland, J.P.J.; Fluitman, J.H.J.
1981-01-01
The system described is built around a very accurate positioner into which a sensitive transducer and the object of analysis is mounted. The properties of the applied magnetoresistive transducer are described. This transducer, a very narrow permalloy strip placed at the edge of a glass substratum,
Hou, X. N.; Liu, Y. H.; Huang, F.; Jiang, S. Z.; Chen, Z. Y.; Zhang, R. Y.
2016-09-01
Effects of radial electric field on the structures and dynamics of dust dipoles are studied by molecular dynamics simulations. The dipoles' configuration and mean distance to the system center are used to illustrate the structures of the whole system. It is shown that the dipole particles can arrange themselves into ring-like structures in the absence of external electric field, which can gradually transform to vortex, and then to radial arrangement with the increase of the strength of electric field. The trajectories, mean square displacement, and the mean speed in radial and tangential directions of dipoles are investigated to depict the effects of the radial electric filed on the collective motion of dust dipolar particles, which are closely associated with the growth of dust particle, especially for the formation of rod-like and some other complex fractal dust particles.
Song, Zhen; Moore, Kevin L.; Chen, YangQuan; Bahl, Vikas
2003-09-01
As an outgrowth of series of projects focused on mobility of unmanned ground vehicles (UGV), an omni-directional (ODV), multi-robot, autonomous mobile parking security system has been developed. The system has two types of robots: the low-profile Omni-Directional Inspection System (ODIS), which can be used for under-vehicle inspections, and the mid-sized T4 robot, which serves as a ``marsupial mothership'' for the ODIS vehicles and performs coarse resolution inspection. A key task for the T4 robot is license plate recognition (LPR). For a successful LPR task without compromising the recognition rate, the robot must be able to identify the bumper locations of vehicles in the parking area and then precisely position the LPR camera relative to the bumper. This paper describes a 2D-laser scanner based approach to bumper identification and laser servoing for the T4 robot. The system uses a gimbal-mounted scanning laser. As the T4 robot travels down a row of parking stalls, data is collected from the laser every 100ms. For each parking stall in the range of the laser during the scan, the data is matched to a ``bumper box'' corresponding to where a car bumper is expected, resulting in a point cloud of data corresponding to a vehicle bumper for each stall. Next, recursive line-fitting algorithms are used to determine a line for the data in each stall's ``bumper box.'' The fitting technique uses Hough based transforms, which are robust against segmentation problems and fast enough for real-time line fitting. Once a bumper line is fitted with an acceptable confidence, the bumper location is passed to the T4 motion controller, which moves to position the LPR camera properly relative to the bumper. The paper includes examples and results that show the effectiveness of the technique, including its ability to work in real-time.
Energy Technology Data Exchange (ETDEWEB)
Grunwald, Torben
2009-12-17
This thesis deals with the THz response of two-dimensional charge carrier systems in different semiconductor heterostructures under varying conditions. The utilized spectrometer is suitable for time-resolved optical pump - THz probe experiments, as well as for optical pump-probe experiments in the near infrared for identical conditions. It allows the investigation of the transverse dielectric function of both, a (GaIn)As/GaAs quantum well and a two-dimensional electron gas in a GaAs-based heterostructure. First, the THz response of an electron-hole plasma is examined for different carrier densities. The plasma is generated by interband transitions in a (GaIn)As/GaAs quantum well. The measured transverse dielectric function reveals that the plasma behaves in accordance with the classical Drude oscillator model. It also conforms to the microscopic theory of the THz response of corresponding many-body systems. Evidence of a plasma resonance in the negative imaginary part of the inverse dielectric function is found. The squared peak frequency of the resonance is proportional to the carrier density of the plasma. This behavior corresponds to the plasma frequency of a three-dimensional plasma. Overall, it can be shown that the transverse THz response of a two-dimensional electron-hole plasma behaves like the response of a three-dimensional plasma. Therefore, the transversal THz response of an electron-hole plasma seems to be independent of the dimension of the charge carrier system. Secondly, the behavior of the quantum well for a 1s-exciton dominated carrier system is investigated. A good agreement between experiment and microscopic theory is obtained for the dielectric function. The negative imaginary part of the inverse dielectric function shows a resonance at the intraexcitonic 1s-2p transition frequency, even in weakly excited excitonic systems. Increasing the carrier density leads to a plasma-like behavior of the system. However, in these densities a significant
Energy Technology Data Exchange (ETDEWEB)
Grunwald, Torben
2009-12-17
This thesis deals with the THz response of two-dimensional charge carrier systems in different semiconductor heterostructures under varying conditions. The utilized spectrometer is suitable for time-resolved optical pump - THz probe experiments, as well as for optical pump-probe experiments in the near infrared for identical conditions. It allows the investigation of the transverse dielectric function of both, a (GaIn)As/GaAs quantum well and a two-dimensional electron gas in a GaAs-based heterostructure. First, the THz response of an electron-hole plasma is examined for different carrier densities. The plasma is generated by interband transitions in a (GaIn)As/GaAs quantum well. The measured transverse dielectric function reveals that the plasma behaves in accordance with the classical Drude oscillator model. It also conforms to the microscopic theory of the THz response of corresponding many-body systems. Evidence of a plasma resonance in the negative imaginary part of the inverse dielectric function is found. The squared peak frequency of the resonance is proportional to the carrier density of the plasma. This behavior corresponds to the plasma frequency of a three-dimensional plasma. Overall, it can be shown that the transverse THz response of a two-dimensional electron-hole plasma behaves like the response of a three-dimensional plasma. Therefore, the transversal THz response of an electron-hole plasma seems to be independent of the dimension of the charge carrier system. Secondly, the behavior of the quantum well for a 1s-exciton dominated carrier system is investigated. A good agreement between experiment and microscopic theory is obtained for the dielectric function. The negative imaginary part of the inverse dielectric function shows a resonance at the intraexcitonic 1s-2p transition frequency, even in weakly excited excitonic systems. Increasing the carrier density leads to a plasma-like behavior of the system. However, in these densities a significant
Directory of Open Access Journals (Sweden)
Flor-Henry Michel
2004-11-01
Full Text Available Abstract Background All living organisms emit spontaneous low-level bioluminescence, which can be increased in response to stress. Methods for imaging this ultra-weak luminescence have previously been limited by the sensitivity of the detection systems used. Results We developed a novel configuration of a cooled charge-coupled device (CCD for 2-dimensional imaging of light emission from biological material. In this study, we imaged photon emission from plant leaves. The equipment allowed short integration times for image acquisition, providing high resolution spatial and temporal information on bioluminescence. We were able to carry out time course imaging of both delayed chlorophyll fluorescence from whole leaves, and of low level wound-induced luminescence that we showed to be localised to sites of tissue damage. We found that wound-induced luminescence was chlorophyll-dependent and was enhanced at higher temperatures. Conclusions The data gathered on plant bioluminescence illustrate that the equipment described here represents an improvement in 2-dimensional luminescence imaging technology. Using this system, we identify chlorophyll as the origin of wound-induced luminescence from leaves.
Fujie, Kentarou; Senba, Takasi
2016-08-01
This paper deals with positive radially symmetric solutions of the Neumann boundary value problem for the fully parabolic chemotaxis system, {ut=Δu-∇ṡ(u∇χ(v))in Ω×(0,∞),τvt=Δv-v+uin Ω×(0,∞), in a ball Ω \\subset {{{R}}2} with general sensitivity function χ (v) satisfying {χ\\prime}>0 and decaying property {χ\\prime}(s)\\to 0 (s\\to ∞ ), parameter τ \\in ≤ft(0,1\\right] and nonnegative radially symmetric initial data. It is shown that if τ \\in ≤ft(0,1\\right] is sufficiently small, then the problem has a unique classical radially symmetric solution, which exists globally and remains uniformly bounded in time. Especially, this result establishes global existence of solutions in the case χ (v)={χ0}log v for all {χ0}>0 , which has been left as an open problem.
Lim, Sung-Hwan; Jang, Hyung-Sik; Ha, Jae-Min; Kim, Tae-Hwan; Kwasniewski, Pawel; Narayanan, Theyencheri; Jin, Kyeong Sik; Choi, Sung-Min
2014-11-10
We report a highly ordered intercalated hexagonal binary superlattice of hydrophilically functionalized single-walled carbon nanotubes (p-SWNTs) and surfactant (C12 E5 ) cylindrical micelles. When p-SWNTs (with a diameter slightly larger than that of the C12 E5 cylinders) were added to the hexagonally packed C12 E5 cylindrical-micellar system, p-SWNTs positioned themselves in such a way that the free-volume entropies for both p-SWNTs and C12 E5 cylinders were maximized, thus resulting in the intercalated hexagonal binary superlattice. In this binary superlattice, a hexagonal array of p-SWNTs is embedded in a honeycomb lattice of C12 E5 cylinders. The intercalated hexagonal binary superlattice can be highly aligned in one direction by an oscillatory shear field and remains aligned after the shear is removed.
Motevalli, Benyamin; Taherifar, Neda; Liu, Zhe
We report a cooperative reformable channel system in a coordination porous polymer, named as ZIF-L. Three types of local flexible ligands coexist in the crystal structure of this polymer, resulting in ultra-flexibility. The reformable channel is able to regulate permeation of a nonspherical guest molecule, such as N2 or CO2, based on its longer molecular dimension, which is in a striking contrast to conventional molecular sieves that regulate the shorter cross-sectional dimension of the guest molecules. Our density functional theory (DFT) calculations reveal that the guest molecule induces dynamic motion of the flexible ligands, leading to the channel reformation, and then the guest molecule reorientates itself to fit in the reformed channel. Such a unique ``induced fit-in'' mechanism causes the gas molecule to pass through 6 membered-ring windows in the c- crystal direction of ZIF-L with its longer axis parallel to the window plane. Our experimental permeance of N2 through the ZIF-L membranes is about three times greater than that of CO2, supporting the DFT simulation predictions.
Mo, Yike; Karaman, Hakki; Greenhalgh, Stewart
2014-05-01
To tackle the challenges and imaging problems of complex structures, we have recently assembled within the Wave Propagation Lab at ETH Zürich a simple 2D ultrasonic model facility in which the simulated geological structures are constructed from thin (2 mm thickness) metal and plastic sheets, cut and bonded together. The models were used, in full recognition of the similitude relations, to investigate reflections from beneath a low velocity distorting overburden. Besides uniform and irregular near surface layers, flat and dipping interfaces as well as rectangular high and low velocity block inserts were investigated. The experiments entailed the use of a piezoelectric source driven by a pulse amplifier at ultrasonic frequencies (20-300 kHz) to generate Lamb waves in the plate, which are detected by piezoelectric receivers and recorded digitally on a National Instruments recording system, under SignalExpress software control. In the lab system, a single cycle sinusoidal pulse with a negative onset (5 μs pulse width and 600 V pulse voltage) was selected as the optimized source pulse. Transducers can be placed along the thin edges of the plate in reflection mode (same edge) or transmission mode (opposite edges, or perpendicular edges). Alternatively they can be mounted on the flat planar surface of the plate to simulate a crosshole survey. Data were originally collected in all different recording geometries over a homogenous aluminium model for calibration purposes and to examine wave modes and propagation characteristics. The two dominant Lamb waves recorded are the fundamental symmetric mode (non-dispersive) and the fundamental antisymmetric (flexural) dispersive mode, which is normally absent when the source transducer is located on a model edge but dominant when it is on the flat planar surface of the plate. Only the symmetric Lamb mode can be used as a proxy for 2D propagation in an extended medium (the field situation). Experimental group and phase velocity
Diagnostics of many-particle electronic states: non-stationary currents and residual charge dynamics
Maslova, N. S.; Mantsevich, V. N.; Arseyev, P. I.
2017-01-01
We propose the method for identifying many particle electronic states in the system of coupled quantum dots (impurities) with Coulomb correlations. We demonstrate that different electronic states can be distinguished by the complex analysis of localized charge dynamics and non-stationary characteristics. We show that localized charge time evolution strongly depends on the properties of initial state and analyze different time scales in charge kinetics for initially prepared singlet and triplet states. We reveal the conditions for existence of charge trapping effects governed by the selection rules for electron transitions between the states with different occupation numbers.
Lin Zhang, Jia; Hong Liang Zhang, Kelvin; Qiang Zhong, Jian; Chao Niu, Tian; Chen, Wei
2012-02-01
Atomic scale investigation of temperature-dependent two-dimensional (2 D) crystallization processes of fullerene-C60 on pentacene-covered Ag(111) surface has been carried out by in situ low-temperature scanning tunneling microscopy (LT-STM) experiments. To evaluate the effect of molecule-substrate interfacial interactions on the 2 D crystallization of C60: pentacene binary system, we also carried out the same self-assembly experiments of C60 on monolayer pentacene covered graphite substrate. It is revealed that temperature-dependent structural transition of various ordered C60 nanoassemblies is strongly influenced by the molecule-Ag(111) interfacial interactions, and further mediated by the weak C60-pentacene intermolecular interactions. In situ ultraviolet photoelectron spectroscopy (UPS) has been used to evaluate the nature of the intermolecular interactions between C60 and pentacene films.
Dorozhkin, S. I.; Umansky, V.; von Klitzing, K.; Smet, J. H.
2016-11-01
It has been found on a sample of the GaAs/AlGaAs heterostructure with the two-dimensional electron system that different configurations of domains of a spontaneous electric field are possible within one microwave- induced state with the resistance tending to zero. Transitions between such configurations are observed at the variation of the radiation power and magnetic field. In the general case, the configuration of domains is more complicated than existing models. The fragment of the distribution of the electric field in the sample for one of the observed configurations is in agreement with the rhombic domain structure considered by I. G. Finkler and B. I. Halperin, Phys. Rev. B 79, 085315 (2009).
Sibley, David N; Kalliadasis, Serafim
2012-01-01
We consider the spreading of a thin two-dimensional droplet on a planar substrate as a prototype system to compare the contemporary model for contact line motion based on interface formation of Shikhmurzaev [Int. J. Multiphas. Flow 19, 589 (1993)], to the more commonly used continuum fluid dynamical equations augmented with the Navier-slip condition. Considering quasistatic droplet evolution and using the method of matched asymptotics, we find that the evolution of the droplet radius using the interface formation model reduces to an equivalent expression for a slip model, where the prescribed microscopic dynamic contact angle has a velocity dependent correction to its static value. This result is found for both the original interface formation model formulation and for a more recent version, where mass transfer from bulk to surface layers is accounted for through the boundary conditions. Various features of the model, such as the pressure behaviour and rolling motion at the contact line, and their relevance, ...
Kronecker Product of Two-dimensional Arrays
Institute of Scientific and Technical Information of China (English)
Lei Hu
2006-01-01
Kronecker sequences constructed from short sequences are good sequences for spread spectrum communication systems. In this paper we study a similar problem for two-dimensional arrays, and we determine the linear complexity of the Kronecker product of two arrays. Our result shows that similar good property on linear complexity holds for Kronecker product of arrays.
Two-Dimensional Toda-Heisenberg Lattice
Directory of Open Access Journals (Sweden)
Vadim E. Vekslerchik
2013-06-01
Full Text Available We consider a nonlinear model that is a combination of the anisotropic two-dimensional classical Heisenberg and Toda-like lattices. In the framework of the Hirota direct approach, we present the field equations of this model as a bilinear system, which is closely related to the Ablowitz-Ladik hierarchy, and derive its N-soliton solutions.
Saeki, Tatsuya; Sugamura, Yuriko; Hosokawa, Masahito; Yoshino, Tomoko; Lim, Tae-Kyu; Harada, Manabu; Matsunaga, Tadashi; Tanaka, Tsuyoshi
2015-05-15
This study presents a novel method for CD4 testing based on one-shot large-field imaging. The large-field imaging system was fabricated by a microcavity array and a two-dimensional (2D) photosensor within the desk-top-sized instrument. The microcavity array was employed to separate leukocytes from whole blood based on differences in the size of leukocytes and other blood cells. The large-field imaging system with lower side irradiation enabled acquisition of cell signatures with high signal-to-noise ratio, because the metallic substrate of the microcavity array obstructed excessive excitation light. In this setting, dual-color imaging of CD4(+) and CD8(+) T cells was achieved within the entire image area (64 mm(2)) in 2s. The practical performance of the large-field imaging system was demonstrated by determining the CD4/CD8 ratio in a few microliter of control whole blood as small as those obtained by a finger prick. The CD4/CD8 ratios measured using the large-field imaging system correlated well with those measured by microscopic analysis. These results indicate that our proposed system provides a simple and rapid CD4 testing for the application of HIV/AIDS treatment. Copyright © 2014 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Muir, D.W.; Davidson, J.W.; Dudziak, D.J.; Davierwalla, D.M.; Higgs, C.E.; Stepanek, J.
1988-01-01
The lack of suitable benchmark problems makes it difficult to test sensitivity codes with a covariance library. A benchmark problem has therefore been defined for one- and two-dimensional sensitivity and uncertainity analysis codes and code systems. The problem, representative of a fusion reactor blanket, has a simple, three-zone )tau)-z geometry containing a D-T fusion neutron source distributed in a central void region surrounded by a thick /sup 6/LiH annulus. The response of interest is the /sup 6/Li tritium production per source neutron, T/sub 6/. The calculation has been performed with SENSIBL using other codes from the AARE code system as a test of both SENSIBL and the linked, modular system. The caluclation was performed using the code system in the standard manner with a covariance data library in the COVFILS-2 format but modified to contain specifically tailored covariance data for H and /sup 6/Li (Path A). The calculation was also performed by a second method which uses specially perturbed H and Li cross sections (Path B). This method bypasses SENSIBL and allows a hand calculation of the benchmark T/sub 6/ uncertainties. The results of Path A and Path B were total uncertainties in T/sub 6/ of 0.21% and 0.19%, respectively. The closeness of the results for this challenging test gives confidence that SENSIBL and the AARE system will perform well for realistic sensitivity and uncertainty analyses
Two-dimensional liquid chromatography
DEFF Research Database (Denmark)
Græsbøll, Rune
of this thesis is on online comprehensive two-dimensional liquid chromatography (online LC×LC) with reverse phase in both dimensions (online RP×RP). Since online RP×RP has not been attempted before within this research group, a significant part of this thesis consists of knowledge and experience gained...
Energy Technology Data Exchange (ETDEWEB)
Griesbeck, Michael
2012-11-22
Since many years there has been great effort to explore the spin dynamics in low-dimensional electron systems embedded in GaAs/AlGaAs based heterostructures for the purpose of quantum computation and spintronics applications. Advances in technology allow for the design of high quality and well-defined two-dimensional electron systems (2DES), which are perfectly suited for the study of the underlying physics that govern the dynamics of the electron spin system. In this work, spin dynamics in high-mobility 2DES is studied by means of the all-optical time-resolved Kerr/Faraday rotation technique. In (001)-grown 2DES, a strong in-plane spin dephasing anisotropy is studied, resulting from the interference of comparable Rashba and Dresselhaus contributions to the spin-orbit field (SOF). The dependence of this anisotropy on parameters like the confinement length of the 2DES, the sample temperature, as well as the electron density is demonstrated. Furthermore, coherent spin dynamics of an ensemble of ballistically moving electrons is studied without and within an applied weak magnetic field perpendicular to the sample plane, which forces the electrons to move on cyclotron orbits. Finally, strongly anisotropic spin dynamics is investigated in symmetric (110)-grown 2DES, using the resonant spin amplification method. Here, extremely long out-of-plane spin dephasing times can be achieved, in consequence of the special symmetry of the Dresselhaus SOF.
Structure, single-particle and many-particle coefficients of Lennard–Jones liquid Al
Indian Academy of Sciences (India)
G A Adebayo; O akinlade; O A Malomo; L A Hussain
2005-08-01
We investigate the effects of temperature and density on the single-particle and many-particle coefficients as well as on the structures of homogenous systems in which the particles are assumed to interact via a continuous soft sphere potential in the microcanonical ensemble. The pair distribution function and therefore the structures of the systems studied are affected by temperature close to and above the melting point through migrations of atoms from the first shell in the pair distribution function. The dynamics of atomic pairs in the short-time regime in liquid aluminium may be said to be governed by the potential of mean force, which depends on the static structure of liquid Al at all investigated temperatures. A polynomial dependence of on density and temperature was observed in contradiction to Arrhenius law. The shear viscosities of the systems studied are largely nonlinear. It was observed that the soft sphere potential used in our calculations overestimates the Stoke–Einstein relation.
Energy Technology Data Exchange (ETDEWEB)
Ramanayaka, A.N.; Ye, Tianyu; Liu, H.-C. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Wegscheider, W. [Laboratorium fuer Festkoerperphysik, ETH Zurich, 8093 Zurich (Switzerland); Mani, R.G., E-mail: rmani@gsu.edu [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States)
2014-11-15
The influence of microwave excitation on the magnetotransport properties of the high mobility two-dimensional electron system (2DES) in the GaAs/AlGaAs heterostructure system is investigated by exploring (a) the dependence of the amplitude of the microwave-induced magnetoresistance-oscillations on the polarization direction of the linearly polarized microwaves and (b) the microwave reflection from the 2DES. The polarization study indicates that the amplitude of the magnetoresistance oscillations is remarkably responsive to the relative orientation between the linearly polarized microwaves and the current-axis in the specimen. At low microwave power, P, experiments indicate a strong sinusoidal variation in the diagonal resistance R{sub xx} vs. θ at the oscillatory extrema of the microwave-induced magnetoresistance oscillations. The reflection study indicates strong correlations between the microwave induced magnetoresistance oscillations and oscillatory features in the microwave reflection in a concurrent measurement of the magnetoresistance and the microwave magnetoreflection from the 2DES. The correlations are followed as a function of the microwave frequency and the microwave power, and the results are reported.
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.
Optical investigation of the quasi-two-dimensional Mott system Ca_2-xSr_xRuO4 (0.0<= x<= 2.0)
Lee, J. S.; Noh, T. W.; Lee, Y. S.; Oh, S.-J.; Nakatsuji, S.; Maeno, Y.
2002-03-01
The doping and temperature dependent optical conductivity spectra σ (ω ) in the ab-plane of the quasi-two-dimensional system Ca_2-xSr_xRuO4 (0.0= 0.2, the σ (ω ) show features of the Mott-Hubbard system. However, the insulating spectra of x=0.00 and 0.06 show an unusual two-peak structure around 1.0 and 2.0 eV. From the systematic changes with doping, it was found that both excitations have the correlation-induced Ru 4 d characters. Interestingly, for the x=0.06 sample, softening of the streching phonon mode and strong spectral weight redistribution between these two peaks were observed with decreasing temperature. These could be understood by the orbital occupancy changes with the RuO6 octahedral flattening. Possible connections to the critical behaviors of the specific heat and susceptibility at x=0.5 will be also discussed.
WAF SYSTEM BASED ON TWO-DIMENSIONAL SECURITY PROTECTION ARCHITECTURE%基于二维安全防护体系的WAF系统
Institute of Scientific and Technical Information of China (English)
王坤; 关溪; 张阳; 蔡镇
2012-01-01
针对Web攻击,传统防火墙对应用层防护存在不足,而Web 应用防火墙可利用其架构的技术优势,应对繁多的攻击方式.给出二维安全防护系统及Web 服务器核心内嵌模型,进一步给出Web 应用防火墙设计实现方案.实验表明,该系统能够解决Web应用安全问题,具有较高的网络性能,支持策略的定制与扩展.%In light of the Web attacks, traditional firewall has its weakness in application layer protection, but Web application firewall can use its architecture technology advantage to deal with the various attack methods. The two-dimensional security protection system and the embedded model of Web server core are presented, and the Web application firewall design and implementation scheme are further provided. Experimental results show that, the system can solve the security problems of Web application, and has preferable network performance, and supports the customisation and extension of strategies as well.
Energy Technology Data Exchange (ETDEWEB)
Rizo, P J; Pugzlys, A; Slachter, A; Denega, S Z; Van Loosdrecht, P H M; Van der Wal, C H [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747AG Groningen (Netherlands); Reuter, D; Wieck, A D, E-mail: c.h.van.der.wal@rug.n [Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
2010-11-15
The electron spin dynamics in a GaAs/AlGaAs heterojunction system containing a high-mobility two-dimensional electron gas (2DEG) have been studied in this paper by using pump-probe time-resolved Kerr rotation experiments. Owing to the complex layer structure of this material, the transient Kerr response contains information about electron spins in the 2DEG, an epilayer and the substrate. We analyzed the physics that underlies this Kerr response, and established the conditions under which it is possible to unravel the signatures of the various photo-induced spin populations. This was used to explore how the electron spin dynamics of the various populations depend on the temperature, magnetic field and pump-photon density. The results show that the D'Yakonov-Perel' mechanism for spin dephasing (by spin-orbit fields) plays a prominent role in both the 2DEG and bulk populations over a wide range of temperatures and magnetic fields. Our results are of importance for future studies on the 2DEG in this type of heterojunction system, which offers interesting possibilities for spin manipulation and control of spin relaxation via tunable spin-orbit effects.
Quantum mechanics of many particles defined on twisted N-enlarged Newton-Hooke space-times
Daszkiewicz, Marcin
2013-01-01
We provide the quantum mechanics of many particles moving in twisted N-enlarged Newton-Hooke space-time. In particular, we consider the example of such noncommutative system - the set of M particles moving in Coulomb field of external point-like source and interacting each other also by Coulomb potential.
Shackman, Jonathan G; Kleintop, Brent L
2014-10-01
Pharmaceutical formulations containing multiple active components challenge the development of analytical methods, especially as the individual active ingredients diverge in their physicochemical properties. Establishing specificity, especially peak purity, is one of the major evaluation criteria when developing a related substances method for drug substances or products. Fixed-dose combination products may not be amenable to common strategies for assessing peak purity, such as performing orthogonal separations, due to the complexity of the separation and/or diversity of the active ingredients. An alternate approach to evaluating peak purity is demonstrated for a triple-active component fixed-dose combination product under development. A commercially available automated two-dimensional liquid chromatography system was used to perform a selective comprehensive multidimensional separation of an active ingredient peak. The first dimension performed the drug product impurity/degradant profiling method; the second dimension assayed these fractions using the drug substance profiling method, which was pseudo-orthogonal to the first dimension. A total of 14 targeted fractions were sampled across the first dimension main peak, with 11 containing detectable analytes and the remaining fractions bracketing the main peak. This degree of sampling allowed profiling of a coeluting degradant present at a 0.2% w/w level throughout the main peak.
Zhukovsky, V. Ch.; Krevchik, V. D.; Semenov, M. B.; Krevchik, P. V.; Zaytsev, R. V.; Egorov, I. A.
2016-11-01
The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current-voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.
Two dimensional unstable scar statistics.
Energy Technology Data Exchange (ETDEWEB)
Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)
2006-12-01
This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.
Juday, Richard D.
1992-01-01
Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.
MPPhys—A many-particle simulation package for computational physics education
Müller, Thomas
2014-03-01
In a first course to classical mechanics elementary physical processes like elastic two-body collisions, the mass-spring model, or the gravitational two-body problem are discussed in detail. The continuation to many-body systems, however, is deferred to graduate courses although the underlying equations of motion are essentially the same and although there is a strong motivation for high-school students in particular because of the use of particle systems in computer games. The missing link between the simple and the more complex problem is a basic introduction to solve the equations of motion numerically which could be illustrated, however, by means of the Euler method. The many-particle physics simulation package MPPhys offers a platform to experiment with simple particle simulations. The aim is to give a principle idea how to implement many-particle simulations and how simulation and visualization can be combined for interactive visual explorations. Catalogue identifier: AERR_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERR_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 111327 No. of bytes in distributed program, including test data, etc.: 608411 Distribution format: tar.gz Programming language: C++, OpenGL, GLSL, OpenCL. Computer: Linux and Windows platforms with OpenGL support. Operating system: Linux and Windows. RAM: Source Code 4.5 MB Complete package 242 MB Classification: 14, 16.9. External routines: OpenGL, OpenCL Nature of problem: Integrate N-body simulations, mass-spring models Solution method: Numerical integration of N-body-simulations, 3D-Rendering via OpenGL. Running time: Problem dependent
Kalyanapu, A. J.; Dullo, T. T.; Thornton, J. C.; Auld, L. A.
2015-12-01
Obion River, is located in the northwestern Tennessee region, and discharges into the Mississippi River. In the past, the river system was largely channelized for agricultural purposes that resulted in increased erosion, loss of wildlife habitat and downstream flood risks. These impacts are now being slowly reversed mainly due to wetland restoration. The river system is characterized by a large network of "loops" around the main channels that hold water either from excess flows or due to flow diversions. Without data on each individual channel, levee, canal, or pond it is not known where the water flows from or to. In some segments along the river, the natural channel has been altered and rerouted by the farmers for their irrigation purposes. Satellite imagery can aid in identifying these features, but its spatial coverage is temporally sparse. All the alterations that have been done to the watershed make it difficult to develop hydraulic models, which could predict flooding and droughts. This is especially true when building one-dimensional (1D) hydraulic models compared to two-dimensional (2D) models, as the former cannot adequately simulate lateral flows in the floodplain and in complex terrains. The objective of this study therefore is to study the performance of 1D and 2D flood models in this complex river system, evaluate the limitations of 1D models and highlight the advantages of 2D models. The study presents the application of HEC-RAS and HEC-2D models developed by the Hydrologic Engineering Center (HEC), a division of the US Army Corps of Engineers. The broader impacts of this study is the development of best practices for developing flood models in channelized river systems and in agricultural watersheds.
Cacciola, Francesco; Donato, Paola; Giuffrida, Daniele; Torre, Germana; Dugo, Paola; Mondello, Luigi
2012-09-14
A comprehensive normal-phase × reversed-phase (NP-LC × RP-LC) liquid chromatography system was developed, and applied for analysis of the intact carotenoid composition of red chili peppers, with photodiode array and mass spectrometry detection. A micro-bore cyano column (250 mm × 1.0 mm, 5 μm d.p.) was chosen for the first dimension ((1)D) separation, interfaced to a second dimension ((2)D) C18 column (30 mm × 4.6 mm, 2.7 μm d.p.) packed with fused-core particles. Subsequently, two columns of the same stationary phase were coupled serially for second dimension separation, and operated under ultra high pressure LC conditions (UHPLC), within a cycle time of 1.50 or 1.00 min, and equal modulation times. Performances of the three different set-ups were evaluated, in terms of peak capacity values (n(c)), and afterwards corrected by taking into account both the under-sampling, and the orthogonality effects. After these adjustments, the peak capacity values were estimated as follows: n(c) 526, for the NP-LC × RP-LC system, n(c) 373, for the NP-LC × RP-UHPLC system with a 1.50 min modulation time, n(c) 639, for the NP-LC × RP-UHPLC system, with a 1.00 min modulation time. A total of 33 compounds were separated into 10 different chemical classes in the two-dimensional space, and identified by accurate IT-TOF (ion trap-time of flight) MS detection. Copyright © 2012 Elsevier B.V. All rights reserved.
Two-dimensional supramolecular electron spin arrays.
Wäckerlin, Christian; Nowakowski, Jan; Liu, Shi-Xia; Jaggi, Michael; Siewert, Dorota; Girovsky, Jan; Shchyrba, Aneliia; Hählen, Tatjana; Kleibert, Armin; Oppeneer, Peter M; Nolting, Frithjof; Decurtins, Silvio; Jung, Thomas A; Ballav, Nirmalya
2013-05-07
A bottom-up approach is introduced to fabricate two-dimensional self-assembled layers of molecular spin-systems containing Mn and Fe ions arranged in a chessboard lattice. We demonstrate that the Mn and Fe spin states can be reversibly operated by their selective response to coordination/decoordination of volatile ligands like ammonia (NH3). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Shen, Shu-Huei; Guo, Wan-Yuo; Hung, Jeng-Hsiu
2007-09-01
To evaluate the value of two-dimensional fast imaging employing steady-state acquisition (2D FIESTA) cine MR with parallel imaging techniques in the diagnosis of fetal non-central nervous system (CNS) anomalies. A total of 28 pregnant women were referred for further MR evaluation on fetuses after abnormal sonographic results. A total of 33 fetal MR examinations were performed by a 1.5 T MR scanner with eight-channel phase-arrayed body coils. Single-shot fast spin-echo (SSFSE(R), GE) of three orthogonal planes and 2D FIESTA for cine fetal MR of three sagittal planes (midsagittal and 10 mm off midline on left and right) were routinely acquired. Additional planes on target organs with variable imaging frames were added if indicated. Nine of the 33 examinations (9/33; 27.3%) had motion artifacts obscuring the detail in SSFSE imaging; 2D FIESTA imaging provided motion-artifact-free imaging in all of them. Cine 2D FIESTA imaging provided additional information on the visceral peristalsis. The information helped in differentiating dilated gastrointestinal (GI) tract from other intraabdominal cystic lesions and in confirming the nature and level of GI tract obstruction. With sub-half-second temporal resolution of the 2D FIESTA sequences, fetal movement is no longer problematic. In addition to the anatomical information also provided by conventional SSFSE sequences, 2D FIESTA demonstrates information on motility and peristalsis of hollow organs and helps the diagnosis of fetal visceral anomalies. (c) 2007 Wiley-Liss, Inc.
Spegazzini, Nicolas; Siesler, Heinz W; Ozaki, Yukihiro
2012-10-02
A sequential identification approach by two-dimensional (2D) correlation analysis for the identification of a chemical reaction model, activation, and thermodynamic parameters is presented in this paper. The identification task is decomposed into a sequence of subproblems. The first step is the construction of a reaction model with the suggested information by model-free 2D correlation analysis using a novel technique called derivative double 2D correlation spectroscopy (DD2DCOS), which enables one to analyze intensities with nonlinear behavior and overlapped bands. The second step is a model-based 2D correlation analysis where the activation and thermodynamic parameters are estimated by an indirect implicit calibration or a calibration-free approach. In this way, a minimization process for the spectral information by sample-sample 2D correlation spectroscopy and kinetic hard modeling (using ordinary differential equations) of the chemical reaction model is carried out. The sequential identification by 2D correlation analysis is illustrated with reference to the isomeric structure of diphenylurethane synthesized from phenylisocyanate and phenol. The reaction was investigated by FT-IR spectroscopy. The activation and thermodynamic parameters of the isomeric structures of diphenylurethane linked through a hydrogen bonding equilibrium were studied by means of an integration of model-free and model-based 2D correlation analysis called a sequential identification approach. The study determined the enthalpy (ΔH = 15.25 kJ/mol) and entropy (TΔS = 13.20 kJ/mol) of C═O···H hydrogen bonding of diphenylurethane through direct calculation from the differences in the kinetic parameters (δΔ(‡)H, -TδΔ(‡)S) at equilibrium in the chemical reaction system.
Generalized Sturmian Solutions for Many-Particle Schrödinger Equations
DEFF Research Database (Denmark)
Avery, John; Avery, James Emil
2004-01-01
The generalized Sturmian method for obtaining solutions to the many-particle Schrodinger equation is reviewed. The method makes use of basis functions that are solutions of an approximate Schrodinger equation with a weighted zeroth-order potential. The weighting factors are especially chosen so......-the calculation of atomic spectra. Avery, J.: Generalized Sturmian Solutions for Many-Particle Schrödinger Equations. J. Phys. Chem. A 108, 8848. Available from: http://www.researchgate.net/publication/230557991_Avery_J._Generalized_Sturmian_Solutions_for_Many-Particle_Schrdinger_Equations._J._Phys._Chem._A_108...
Electronics based on two-dimensional materials.
Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K; Colombo, Luigi
2014-10-01
The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.
Two-Dimensional NMR Lineshape Analysis
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-04-01
NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions.
Two-dimensional capillary origami
Energy Technology Data Exchange (ETDEWEB)
Brubaker, N.D., E-mail: nbrubaker@math.arizona.edu; Lega, J., E-mail: lega@math.arizona.edu
2016-01-08
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid. - Highlights: • Full solution set of the two-dimensional capillary origami problem. • Fluid does not necessarily wet the entire plate. • Global energy approach provides exact differential equations satisfied by minimizers. • Bifurcation diagrams highlight three different regimes. • Conditions for spontaneous encapsulation are identified.
Topological aspect of disclinations in two-dimensional crystals
Institute of Scientific and Technical Information of China (English)
Qi Wei-Kai; Zhu Tao; Chen Yong; Ren Ji-Rong
2009-01-01
By using topological current theory, this paper studies the inner topological structure of disclinations during the melting of two-dimensional systems. From two-dimensional elasticity theory, it finds that there are topological currents for topological defects in homogeneous equation. The evolution of disclinations is studied, and the branch conditions for generating, annihilating, crossing, splitting and merging of disclinations are given.
Two-dimensional quantum repeaters
Wallnöfer, J.; Zwerger, M.; Muschik, C.; Sangouard, N.; Dür, W.
2016-11-01
The endeavor to develop quantum networks gave rise to a rapidly developing field with far-reaching applications such as secure communication and the realization of distributed computing tasks. This ultimately calls for the creation of flexible multiuser structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multiuser applications. To address this challenge, we propose a two-dimensional quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and imperfect local control operations. The scheme is based on the creation of self-similar multiqubit entanglement structures at growing scale, where variants of entanglement swapping and multiparty entanglement purification are combined to create high-fidelity entangled states. We show how such networks can be implemented using trapped ions in cavities.
Two-dimensional capillary origami
Brubaker, N. D.; Lega, J.
2016-01-01
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.
Shevchenko, O. S.; Kopeliovich, A. I.
2016-03-01
The energy spectrum of a quasi-two-dimensional electron gas in an in-plane magnetic field is studied using the perturbation theory and quasiclassical approach in the presence of the Rashba and Dresselhaus spin-orbit coupling. The existence of the intersection of energy sublevels in electron spectrum is demonstrated. The reciprocal mass tensor of electrons is analyzed. The heat capacity of the degenerate electron gas is examined, and its relations with the key features of the spectrum are shown.
Catastrophes in non-equilibrium many-particle wave functions: universality and critical scaling
Mumford, J.; Kirkby, W.; O’Dell, D. H. J.
2017-02-01
As part of the quest to uncover universal features of quantum dynamics, we study catastrophes that form in simple many-particle wave functions following a quench, focusing on two-mode systems that include the two-site Bose–Hubbard model, and under some circumstances optomechanical systems and the Dicke model. When the wave function is plotted in Fock space certain characteristic shapes, that we identify as cusp catastrophes, appear under generic conditions. In the vicinity of a cusp the wave function takes on a universal structure described by the Pearcey function and obeys scaling relations which depend on the total number of particles N. In the thermodynamic limit (N\\to ∞ ) the cusp becomes singular, but at finite N it is decorated by an interference pattern. This pattern contains an intricate network of vortex–antivortex pairs, initiating a theory of topological structures in Fock space. In the case where the quench is a δ-kick the problem can be solved analytically and we obtain scaling exponents for the size and position of the cusp, as well as those for the amplitude and characteristic length scales of its interference pattern. Finally, we use these scalings to describe the wave function in the critical regime of a {{{Z}}}2 symmetry-breaking dynamical phase transition.
Xiong, Guo-Ming
1991-02-01
By introducing a defect zone instead of a single defect line in the bulk, a modified form of the AB model of Forgacs, Svrakic, and Privman is investigated. It is found that when the defect zone is far away from the substrate the first-order unbinding transition still exists at a temperature T1 below the critical point of the two-dimensional Ising model, while when it is near the substrate no wetting transition can take place because the inhomogeneity constrains the formation of the wetting layer.
Institute of Scientific and Technical Information of China (English)
姚立; 刘幺和
2012-01-01
GPS positioning and two-dimensional bar code scanning system based on ARM is presented, using the linux operating system and the associated software is provided. System can tin ly locate the positon of the goods on the transporting way and timely read the infor-mation in the two-dimensional code of the goods. Thereby increasing the efficiency of the system.%文章提出了一种以嵌入式ARM为核心,以GPS定位和二维条码扫描为基础的系统,采用Linux操作系统,并给出了相关的软件程序设计.系统可以在物品运输的途中实时的定位,并且还可以实时的了解物品上二维码的信息,从而提高了系统的效率.
Two-dimensional function photonic crystals
Wu, Xiang-Yao; Liu, Xiao-Jing; Liang, Yu
2016-01-01
In this paper, we have firstly proposed two-dimensional function photonic crystals, which the dielectric constants of medium columns are the functions of space coordinates $\\vec{r}$, it is different from the two-dimensional conventional photonic crystals constituting by the medium columns of dielectric constants are constants. We find the band gaps of two-dimensional function photonic crystals are different from the two-dimensional conventional photonic crystals, and when the functions form of dielectric constants are different, the band gaps structure should be changed, which can be designed into the appropriate band gaps structures by the two-dimensional function photonic crystals.
Many-particle effects in the bond length alternation of alternant hydrocarbons
Böhm, Michael C.; Schütt, Johannes
The local approach (LA) method has been employed to investigate the correlated ground state wavefunction in alternant monocyclic and linear hydrocarbon π systems as a function of the bond length alternation δ. The LA has been supplemented by a simple model-Hamiltonian developed in the ZDO (zero differential overlap) approximation. The integrals have been calculated ab initio in a Slater-type basis. To quantify many-particle effects in the studied systems we have determined the interatomic π correlation energy Ecorr and a π electron localization parameter Δi as a function of δ. Δi measures the reduction of the charge fluctuations due to electronic correlations and is thus a convenient measure for the atomic electron density localization. It is demonstrated that monocyclic 4n + 2 (n = 1,2,3, …) Hückel rings allow for a coincidence of increasing |Ecorr| numbers and increasing atomic electron density delocalization with enlarged δ values. The δ variation of Δi reflects in a transparent form that hydrocarbon π networks are generally distortive. For smaller 4n annulenes and polyenes we find a mutual exclusion between increasing atomic electron density delocalization and enhanced |Ecorr| numbers. Bond alternation enhances here the π delocalization, but reduces the |Ecorr| values. It is suggested that a traditional picture in chemistry should be corrected. Bond length alternation in conjugated π systems is not equivalent with an enhancement of the atomic electron density localization; the opposite is true. In this description 'electronic delocalization' is understood as a dynamic property which is not related to the static charge density, but to the mean square deviation of the electron charge around the respective mean value.
Entanglement Entropy for time dependent two dimensional holographic superconductor
Mazhari, N S; Myrzakulov, Kairat; Myrzakulov, R
2016-01-01
We studied entanglement entropy for a time dependent two dimensional holographic superconductor. We showed that the conserved charge of the system plays the role of the critical parameter to have condensation.
Chrzanowska, Agnieszka
2017-06-01
A replica method for calculation of smectic liquid crystal properties within the Onsager theory has been presented and applied to an exemplary case of two-dimensional perfectly aligned needlelike boomerangs. The method allows one to consider the complete influence of the interaction terms in contrast to the Fourier expansion method which uses mostly first or second order terms of expansion. The program based on the replica algorithm is able to calculate a single representative layer as an equivalent set of layers, depending on the size of the considered width of the sample integration interval. It predicts successfully smectic density distributions, energies, and layer thicknesses for different types of layer arrangement—of the antiferroelectric or of the smectic A order type. Specific features of the algorithm performance and influence of the numerical accuracy on the physical properties are presented. Future applications of the replica method to freely rotating molecules are discussed.
Lee, Yueh-Ning
2016-01-01
Most stars are born in the gaseous proto-cluster environment. The knowledge of this intermediate stage gives more accurate constraints on star formation characteristics. We demonstrate that a virialized globally supported structure, in which star formation happens, is formed out of a collapsing molecular cloud, and derive a mapping from the parent cloud parameters to the proto-cluster to predict its properties, with a view to confront analytical calculations with observations and simulations. The virial theorem is decomposed into two dimensions to account for the rotation and the flattened geometry. Equilibrium is found by balancing rotation, turbulence and self-gravity, while turbulence is maintained by accretion driving and dissipates in one crossing time. The angular momentum and the accretion rate of the proto-cluster are estimated from the parent cloud properties. The two-dimensional virial model predicts the size and velocity dispersion given the mass of the proto-cluster and that of the parent cloud. T...
Influence of many-particle interactions on slow light phenomena in quantum dots
DEFF Research Database (Denmark)
Houmark-Nielsen, Jakob; Jauho, Antti-Pekka; Nielsen, Torben Roland;
2008-01-01
We investigate the impact of many-particle interactions on group-velocity slowdown achieved via Electromagnetically Induced Transparency (EIT) in quantum dots. Using a ladder scheme we find in the steady-state an increase in maximum slow-down as compared to the non-interacting case, which can...
A Remark on Different Norms and Analyticity for Many-Particle Interactions
van Enter, Aernout; Fernandez, R.
1989-01-01
We compare a recent result of Dobrushin and Martirosyan with previous results by Gallavotti and Miracle-Sole and by Israel and point out that the analytic behavior at high temperatures for many-particle interactions is different depending on whether the interactions are weighted with a lattice-gas o
A remark on different norms and analyticity for many-particle interactions
Energy Technology Data Exchange (ETDEWEB)
van Enter, A.C.D.; Fernandez, R. (Univ. of Texas, Austin (USA))
1989-09-01
The authors compare a recent result of Dobrushin and Martirosyan with previous results by Gallavotti and Miracle-Sole and by Israel and point out that the analytic behavior at high temperatures for many-particle interactions is different depending on whether the interactions are weighted with a lattice-gas or Ising norm or, on the other hand, with the supremum norm.
Hasei, Tomohiro; Nakanishi, Haruka; Toda, Yumiko; Watanabe, Tetsushi
2012-08-31
3-Nitrobenzanthrone (3-NBA) is an extremely strong mutagen and carcinogen in rats inducing squamous cell carcinoma and adenocarcinoma. We developed a new sensitive analytical method, a two-dimensional HPLC system coupled with on-line reduction, to quantify non-fluorescent 3-NBA as fluorescent 3-aminobenzanthrone (3-ABA). The two-dimensional HPLC system consisted of reversed-phase HPLC and normal-phase HPLC, which were connected with a switch valve. 3-NBA was purified by reversed-phase HPLC and reduced to 3-ABA with a catalyst column, packed with alumina coated with platinum, in ethanol. An alcoholic solvent is necessary for reduction of 3-NBA, but 3-ABA is not fluorescent in the alcoholic solvent. Therefore, 3-ABA was separated from alcohol and impurities by normal-phase HPLC and detected with a fluorescence detector. Extracts from surface soil, airborne particles, classified airborne particles, and incinerator dust were applied to the two-dimensional HPLC system after clean-up with a silica gel column. 3-NBA, detected as 3-ABA, in the extracts was found as a single peak on the chromatograms without any interfering peaks. 3-NBA was detected in 4 incinerator dust samples (n=5). When classified airborne particles, that is, those 7.0 μm in size, were applied to the two-dimensional HPLC system after purified using a silica gel column, 3-NBA was detected in those particles with particle sizes NBA in airborne particles and the detection of 3-NBA in incinerator dust. Copyright © 2012 Elsevier B.V. All rights reserved.
GPU-accelerated algorithms for many-particle continuous-time quantum walks
Piccinini, Enrico; Benedetti, Claudia; Siloi, Ilaria; Paris, Matteo G. A.; Bordone, Paolo
2017-06-01
Many-particle continuous-time quantum walks (CTQWs) represent a resource for several tasks in quantum technology, including quantum search algorithms and universal quantum computation. In order to design and implement CTQWs in a realistic scenario, one needs effective simulation tools for Hamiltonians that take into account static noise and fluctuations in the lattice, i.e. Hamiltonians containing stochastic terms. To this aim, we suggest a parallel algorithm based on the Taylor series expansion of the evolution operator, and compare its performances with those of algorithms based on the exact diagonalization of the Hamiltonian or a 4th order Runge-Kutta integration. We prove that both Taylor-series expansion and Runge-Kutta algorithms are reliable and have a low computational cost, the Taylor-series expansion showing the additional advantage of a memory allocation not depending on the precision of calculation. Both algorithms are also highly parallelizable within the SIMT paradigm, and are thus suitable for GPGPU computing. In turn, we have benchmarked 4 NVIDIA GPUs and 3 quad-core Intel CPUs for a 2-particle system over lattices of increasing dimension, showing that the speedup provided by GPU computing, with respect to the OPENMP parallelization, lies in the range between 8x and (more than) 20x, depending on the frequency of post-processing. GPU-accelerated codes thus allow one to overcome concerns about the execution time, and make it possible simulations with many interacting particles on large lattices, with the only limit of the memory available on the device.
Hadamard States and Two-dimensional Gravity
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.
Ohta, Tadayuki; Kimura, Toshiei
1993-10-01
The second post-Coulombian Lagrangian of Wheeler-Feynman electrodynamics for a many-particle system is treated according to a canonical formalism of a singular Lagrangian with higher derivatives. The canonical equations are given in terms of a reduced Hamiltonian with Dirac brackets, but they are transformed to be expressed in terms of ordinary Poisson brackets by redefinition of canonical variables. The reduced Hamiltonian includes a characteristic form of three-particle and four-particle potentials. Finally a direct pathway to the reduced Hamiltonian is presented via first-order formalism of the Maxwell theory with charged particles.
Local doping of two-dimensional materials
Wong, Dillon; Velasco, Jr, Jairo; Ju, Long; Kahn, Salman; Lee, Juwon; Germany, Chad E.; Zettl, Alexander K.; Wang, Feng; Crommie, Michael F.
2016-09-20
This disclosure provides systems, methods, and apparatus related to locally doping two-dimensional (2D) materials. In one aspect, an assembly including a substrate, a first insulator disposed on the substrate, a second insulator disposed on the first insulator, and a 2D material disposed on the second insulator is formed. A first voltage is applied between the 2D material and the substrate. With the first voltage applied between the 2D material and the substrate, a second voltage is applied between the 2D material and a probe positioned proximate the 2D material. The second voltage between the 2D material and the probe is removed. The first voltage between the 2D material and the substrate is removed. A portion of the 2D material proximate the probe when the second voltage was applied has a different electron density compared to a remainder of the 2D material.
Two-dimensional fourier transform spectrometer
Energy Technology Data Exchange (ETDEWEB)
DeFlores, Lauren; Tokmakoff, Andrei
2016-10-25
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Two-dimensional fourier transform spectrometer
DeFlores, Lauren; Tokmakoff, Andrei
2013-09-03
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Strongly interacting two-dimensional Dirac fermions
Lim, L.K.; Lazarides, A.; Hemmerich, Andreas; de Morais Smith, C.
2009-01-01
We show how strongly interacting two-dimensional Dirac fermions can be realized with ultracold atoms in a two-dimensional optical square lattice with an experimentally realistic, inherent gauge field, which breaks time reversal and inversion symmetries. We find remarkable phenomena in a temperature
Topology optimization of two-dimensional waveguides
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard; Sigmund, Ole
2003-01-01
In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss.......In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss....
Lee, Yueh-Ning; Hennebelle, Patrick
2016-06-01
Context. Most stars are born in the gaseous protocluster environment where the gas is reprocessed after the global collapse from the diffuse molecular cloud. The knowledge of this intermediate step gives more accurate constraints on star formation characteristics. Aims: We demonstrate that a virialized globally supported structure, in which star formation happens, is formed out of a collapsing molecular cloud, and we derive a mapping from the parent cloud parameters to the protocluster to predict its properties with a view to confront analytical calculations with observations and simulations. Methods: We decomposed the virial theorem into two dimensions to account for the rotation and the flattened geometry. Equilibrium was found by balancing rotation, turbulence, and self-gravity, while turbulence was maintained through accretion driving and it dissipates in one crossing time. We estimated the angular momentum and the accretion rate of the protocluster from the parent cloud properties. Results: The two-dimensional virial model predicts the size and velocity dispersion given the mass of the protocluster and that of the parent cloud. The gaseous protoclusters lie on a sequence of equilibrium with the trend R ~ M0.5 with limited variations, depending on the evolutionary stage, parent cloud, and parameters that are not well known, such as turbulence driving efficiency by accretion and turbulence anisotropy. The model reproduces observations and simulation results successfully. Conclusions: The properties of protoclusters follow universal relations and they can be derived from that of the parent cloud. The gaseous protocluster is an important primary stage of stellar cluster formation, and should be taken into account when studying star formation. Using simple estimates to infer the peak position of the core mass function (CMF) we find a weak dependence on the cluster mass, suggesting that the physical conditions inside protoclusters may contribute to set a CMF, and by
Equivalency of two-dimensional algebras
Energy Technology Data Exchange (ETDEWEB)
Santos, Gildemar Carneiro dos; Pomponet Filho, Balbino Jose S. [Universidade Federal da Bahia (UFBA), BA (Brazil). Inst. de Fisica
2011-07-01
Full text: Let us consider a vector z = xi + yj over the field of real numbers, whose basis (i,j) satisfy a given algebra. Any property of this algebra will be reflected in any function of z, so we can state that the knowledge of the properties of an algebra leads to more general conclusions than the knowledge of the properties of a function. However structural properties of an algebra do not change when this algebra suffers a linear transformation, though the structural constants defining this algebra do change. We say that two algebras are equivalent to each other whenever they are related by a linear transformation. In this case, we have found that some relations between the structural constants are sufficient to recognize whether or not an algebra is equivalent to another. In spite that the basis transform linearly, the structural constants change like a third order tensor, but some combinations of these tensors result in a linear transformation, allowing to write the entries of the transformation matrix as function of the structural constants. Eventually, a systematic way to find the transformation matrix between these equivalent algebras is obtained. In this sense, we have performed the thorough classification of associative commutative two-dimensional algebras, and find that even non-division algebra may be helpful in solving non-linear dynamic systems. The Mandelbrot set was used to have a pictorial view of each algebra, since equivalent algebras result in the same pattern. Presently we have succeeded in classifying some non-associative two-dimensional algebras, a task more difficult than for associative one. (author)
Institute of Scientific and Technical Information of China (English)
李彬; 熊文靓
2015-01-01
近年来，日本“二次元”动漫产业已成为动漫界热议的焦点。基于耗散结构理论解析日本“二次元”动漫产业系统发现其具有远离平衡态、非线性、突变性和涨落等耗散结构特点。支撑日本“二次元”动漫产业系统的体系包括政府支持、人才输送、知识产权法律、投融资渠道等。日本经验启示中国发展动漫产业应采取建立激励保健机制、创建学科交叉平台、增加信息技术投入和变“走出去”为“融进去”等措施。%In recent years, Japanese two-dimensional animation industry has become the focus of the debate in animation industry. Based on the theory of dissipative structure, the deconstruction of Japanese two-dimensional animation industry system is found to be far from equilibrium, nonlinear, mutability and lfuctuation etc. The support system of Japanese two-dimensional animation industry system mainly includes the support from the government, intellectual property act, investment and ifnancing. system. Taking examples from Japan's experience, countermeasures are ought to be taken, that establishing incentive care mechanism, creating a platform of cross-disciplines, increasing information technology investment, and "going out" to "blend in", on the current situation of the development of animation industry in China.
Institute of Scientific and Technical Information of China (English)
李宗泽; 史成军
2016-01-01
The cloud model is a powerful tool to achieve qualitative and quantitative uncertainty transforming. It integrates the fuzziness and randomness of objective things and solves the problem of nonlinear and uncertainties. For the nonlinearity, time-variability and uncertainty of excitation system in ship power system, the cloud model is applied to synchronous generator excitation control and two dimensional cloud model of PID excitation is designed. The forward cloud model is utilized to represent the voltage difference of synchronous generator and rate of voltage difference change concepts. Then the backward cloud generator is employed to generate the three parameters of PID concepts. Thus the cloud reasoning rule of double condition multi-rules of two dimensional cloud model is formulated and PID parameters of excitation controller are self-tuned. Through the establishment of models of synchronous generator controllable phase compound brushless excitation system and the two dimensional cloud model PID excitation system, the result of simulation shows that the two dimensional cloud model PID excitation controllable system model has better robustness and better adaptive ability.%云模型可以实现定性概念与定量之间的转换，集成了概念的模糊性与随机性，可以解决非线性与不确定性问题。针对船舶电力系统中励磁系统非线性、时变性、不确定性的特点，将云模型应用到同步发电机励磁控制中，设计出二维云模型PID励磁控制器。其过程是将同步发电机端电压差及其变化率进行概念表示，形成前件二维云模型，然后根据PID三个参数信息构造成后件云模型，并制定出二维云模型双条件多规则的映射语言形式，实现对PID参数的模糊推理自整定。与可控相复励无刷励磁系统进行对比，仿真实验结果表明了二维云模型PID励磁控制系统模型具有更好的鲁棒性和自适应能力。
Many-particle interference beyond many-boson and many-fermion statistics
DEFF Research Database (Denmark)
Tichy, Malte C.; Tiersch, Markus; Mintert, Florian
2012-01-01
that the collective interference of three or more particles leads to much more diverse behavior than expected from the boson–fermion dichotomy known from quantum statistical mechanics. The emerging complexity of many-particle interference is tamed by a simple law for the strict suppression of events in the Bell...... multiport beam splitter. The law shows that counting events are governed by widely species-independent interference, such that bosons and fermions can even exhibit identical interference signatures, while their statistical character remains subordinate. Recent progress in the preparation of tailored many...
Institute of Scientific and Technical Information of China (English)
杨涌涛; 谢鹏; 陈康宁; 黄河清; 贺伟峰
2013-01-01
Objective To establish two-dimensional gel electrophoresis system for rat cortex mitochondria. Methods The adult male SD rats were sacrificed by cervical dislocation , the brain tissues quickly harvested and thecortex isolated on ice. The mitochondria were extracted and purified twice by density gradient centrifugation. Two-dimensional gel electrophoresis was performed. Immobilized pH gradient isoelectric focusing (IPG-IEF) was modified and carried out. The gels were focused at 3500 V for a total of 14000Vh and then subjected to SDS-PAGE and silver staining. Results Electrophoregram of rat cerebral cortex mitochondria was obtained with high resolu -tion by using the established two -dimensional gel electrophoresis system. Conclusion The two-dimensional gel electrophoresis system for rat cortex mitochondria was successfully established , which provides a theoretical basis and a technical support for research of cerebral cortex mitochondrion pro -teins in diseases.%目的 构建稳定的大鼠皮层线粒体双向凝胶电泳体系.方法 SD大鼠在规定的时间内快速断头取脑,冰上分离大脑皮层组织,两次密度梯度离心纯化线粒体.利用双向凝胶电泳技术改良等电聚焦的电压在3 500V聚焦,总伏小时固定为14 000 Vh.以12%的SDS-PAGE进行第二向电泳,银染显色.结果得到了分辨率较高的皮层线粒体蛋白双向凝胶电泳图谱.结论 利用改进的方法构建了高质量的双向电泳图谱,为各种疾病状态下皮层线粒体差异蛋白的研究提供了实验基础.
Two Dimensional Plasmonic Cavities on Moire Surfaces
Balci, Sinan; Kocabas, Askin; Karabiyik, Mustafa; Kocabas, Coskun; Aydinli, Atilla
2010-03-01
We investigate surface plasmon polariton (SPP) cavitiy modes on two dimensional Moire surfaces in the visible spectrum. Two dimensional hexagonal Moire surface can be recorded on a photoresist layer using Interference lithography (IL). Two sequential exposures at slightly different angles in IL generate one dimensional Moire surfaces. Further sequential exposure for the same sample at slightly different angles after turning the sample 60 degrees around its own axis generates two dimensional hexagonal Moire cavity. Spectroscopic reflection measurements have shown plasmonic band gaps and cavity states at all the azimuthal angles (omnidirectional cavity and band gap formation) investigated. The plasmonic band gap edge and the cavity states energies show six fold symmetry on the two dimensional Moire surface as measured in reflection measurements.
Two-dimensional function photonic crystals
Liu, Xiao-Jing; Liang, Yu; Ma, Ji; Zhang, Si-Qi; Li, Hong; Wu, Xiang-Yao; Wu, Yi-Heng
2017-01-01
In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.
Perspective: Two-dimensional resonance Raman spectroscopy
Molesky, Brian P.; Guo, Zhenkun; Cheshire, Thomas P.; Moran, Andrew M.
2016-11-01
Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in complex systems. The 2DRR method can leverage electronic resonance enhancement to selectively probe chromophores embedded in complex environments (e.g., a cofactor in a protein). In addition, correlations between the two dimensions of the 2DRR spectrum reveal information that is not available in traditional Raman techniques. For example, distributions of reactant and product geometries can be correlated in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this perspective article, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide and myoglobin. We also address key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopies. Most notably, it has been shown that these two techniques are subject to a tradeoff between sensitivity to anharmonicity and susceptibility to artifacts. Overall, recent experimental developments and applications of the 2DRR method suggest great potential for the future of the technique.
Institute of Scientific and Technical Information of China (English)
田美; 申欣; 程汉良; 孟学平
2009-01-01
Coelomactra antiquata is a high value economic shellfish which is famous treasure feast food and medical care of aquaculture consumption.The border cells of C.antiquata mantle can secrete calcium carbonate to form shells.By comparing the experimental analysis of different pH gradient strips,the optimal conditions of hydration,and different staining methods on the impact of the results of two-dimensional gel electrophoresis,we established the mantle proteome two-dimensional gel electrophoresis system of C.antiquata,which provide the basis to study the protein composition of formation of C.antiquata mantle from the protein level case.The results showed that:using pH 4～7 with the non-linear strip,the inclusion of hydration desalting step,staining method using silver nitrate staining,can obtain the two-dimensional gel electrophoresis map with a high-resolution and high reproducibility which laid the foundation for further research the protein composition of C.antiquata mantle.%建立了西施舌(Coelomactra antiquata)外套膜蛋白质组的双向凝胶电泳体系,比较分析了不同pH梯度胶条、水化条件的优化及不同染色方法对双向电泳结果的影响.结果表明:用pH 4～7的非线性胶条,水化时加上除盐步骤,采用硝酸银染色,即可获得高分辨率、高重现性的双向电泳图谱,为进一步研究西施舌外套膜蛋白质的组成奠定了基础.
Two-dimensional superconductors with atomic-scale thickness
Uchihashi, Takashi
2017-01-01
Recent progress in two-dimensional superconductors with atomic-scale thickness is reviewed mainly from the experimental point of view. The superconducting systems treated here involve a variety of materials and forms: elemental metal ultrathin films and atomic layers on semiconductor surfaces; interfaces and superlattices of heterostructures made of cuprates, perovskite oxides, and rare-earth metal heavy-fermion compounds; interfaces of electric-double-layer transistors; graphene and atomic sheets of transition metal dichalcogenide; iron selenide and organic conductors on oxide and metal surfaces, respectively. Unique phenomena arising from the ultimate two dimensionality of the system and the physics behind them are discussed.
Critical Behaviour of a Two-Dimensional Random Antiferromagnet
DEFF Research Database (Denmark)
Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.
1976-01-01
A neutron scattering study of the order parameter, correlation length and staggered susceptibility of the two-dimensional random antiferromagnet Rb2Mn0.5Ni0.5F4 is reported. The system is found to exhibit a well-defined phase transition with critical exponents identical to those of the isomorphou...... pure materials K2NiF4 and K2MnF4. Thus, in these systems, which have the asymptotic critical behaviour of the two-dimensional Ising model, randomness has no measurable effect on the phase-transition behaviour....
Vortices in the Two-Dimensional Simple Exclusion Process
Bodineau, T.; Derrida, B.; Lebowitz, Joel L.
2008-06-01
We show that the fluctuations of the partial current in two dimensional diffusive systems are dominated by vortices leading to a different scaling from the one predicted by the hydrodynamic large deviation theory. This is supported by exact computations of the variance of partial current fluctuations for the symmetric simple exclusion process on general graphs. On a two-dimensional torus, our exact expressions are compared to the results of numerical simulations. They confirm the logarithmic dependence on the system size of the fluctuations of the partial flux. The impact of the vortices on the validity of the fluctuation relation for partial currents is also discussed in an Appendix.
Mapping two-dimensional polar active fluids to two-dimensional soap and one-dimensional sandblasting
Chen, Leiming; Lee, Chiu Fan; Toner, John
2016-07-01
Active fluids and growing interfaces are two well-studied but very different non-equilibrium systems. Each exhibits non-equilibrium behaviour distinct from that of their equilibrium counterparts. Here we demonstrate a surprising connection between these two: the ordered phase of incompressible polar active fluids in two spatial dimensions without momentum conservation, and growing one-dimensional interfaces (that is, the 1+1-dimensional Kardar-Parisi-Zhang equation), in fact belong to the same universality class. This universality class also includes two equilibrium systems: two-dimensional smectic liquid crystals, and a peculiar kind of constrained two-dimensional ferromagnet. We use these connections to show that two-dimensional incompressible flocks are robust against fluctuations, and exhibit universal long-ranged, anisotropic spatio-temporal correlations of those fluctuations. We also thereby determine the exact values of the anisotropy exponent ζ and the roughness exponents χx,y that characterize these correlations.
Leitner, Daniel; Felderer, Bernd; Vontobel, Peter; Schnepf, Andrea
2014-01-01
Root system traits are important in view of current challenges such as sustainable crop production with reduced fertilizer input or in resource-limited environments. We present a novel approach for recovering root architectural parameters based on image-analysis techniques. It is based on a graph representation of the segmented and skeletonized image of the root system, where individual roots are tracked in a fully automated way. Using a dynamic root architecture model for deciding whether a specific path in the graph is likely to represent a root helps to distinguish root overlaps from branches and favors the analysis of root development over a sequence of images. After the root tracking step, global traits such as topological characteristics as well as root architectural parameters are computed. Analysis of neutron radiographic root system images of lupine (Lupinus albus) grown in mesocosms filled with sandy soil results in a set of root architectural parameters. They are used to simulate the dynamic development of the root system and to compute the corresponding root length densities in the mesocosm. The graph representation of the root system provides global information about connectivity inside the graph. The underlying root growth model helps to determine which path inside the graph is most likely for a given root. This facilitates the systematic investigation of root architectural traits, in particular with respect to the parameterization of dynamic root architecture models. PMID:24218493
Interpolation by two-dimensional cubic convolution
Shi, Jiazheng; Reichenbach, Stephen E.
2003-08-01
This paper presents results of image interpolation with an improved method for two-dimensional cubic convolution. Convolution with a piecewise cubic is one of the most popular methods for image reconstruction, but the traditional approach uses a separable two-dimensional convolution kernel that is based on a one-dimensional derivation. The traditional, separable method is sub-optimal for the usual case of non-separable images. The improved method in this paper implements the most general non-separable, two-dimensional, piecewise-cubic interpolator with constraints for symmetry, continuity, and smoothness. The improved method of two-dimensional cubic convolution has three parameters that can be tuned to yield maximal fidelity for specific scene ensembles characterized by autocorrelation or power-spectrum. This paper illustrates examples for several scene models (a circular disk of parametric size, a square pulse with parametric rotation, and a Markov random field with parametric spatial detail) and actual images -- presenting the optimal parameters and the resulting fidelity for each model. In these examples, improved two-dimensional cubic convolution is superior to several other popular small-kernel interpolation methods.
Hamiltonian formalism of two-dimensional Vlasov kinetic equation.
Pavlov, Maxim V
2014-12-08
In this paper, the two-dimensional Benney system describing long wave propagation of a finite depth fluid motion and the multi-dimensional Russo-Smereka kinetic equation describing a bubbly flow are considered. The Hamiltonian approach established by J. Gibbons for the one-dimensional Vlasov kinetic equation is extended to a multi-dimensional case. A local Hamiltonian structure associated with the hydrodynamic lattice of moments derived by D. J. Benney is constructed. A relationship between this hydrodynamic lattice of moments and the two-dimensional Vlasov kinetic equation is found. In the two-dimensional case, a Hamiltonian hydrodynamic lattice for the Russo-Smereka kinetic model is constructed. Simple hydrodynamic reductions are presented.
Institute of Scientific and Technical Information of China (English)
杨延强; 易维明; 李志合; 柏雪源; 李永军
2012-01-01
In the cold PIV (particle image velocimetry) system of the laminar entrained flow reactor, the relative position between the camera and the measuring tube was an important condition to ensure accurate test data. To make the PIV operation more convenient, accurate, and fast in the test, two-dimensional PIV automatic control system was designed. And the reliability of the system was tested in the cold simulation equipment of laminar flow furnace, compared with no using two-dimensional PIV automatic control system, the results showed that in different sections of the measuring tube, the particle speed of the axial center achieves a smooth transition, and eliminates the jump change; when collection distance is 350mm and main air flow rate is 1. 5 mVh, the relative error of particle residence time is 9. 218% ; and the operation saves time and effort in the test process. These suggested that the two-dimensional PIV automatic control system could satisfy the cold test of the laminar entrained flow reactor needs, achieve uniform and continuous test, reduce human error and improve the accuracy of test data.%在层流炉冷态粒子图像测速( PIV)系统中,相机与测量管的相对位置是保证试验数据精确的重要条件.为使试验过程中整个PIV系统操作起来更加方便、准确、快捷,设计了二维PIV自动控制系统,并在层流炉冷态模拟装置上对该系统的可靠性进行了试验验证.与没有使用二维PIV自动控制系统之前的试验结果相比:各测量段颗粒的轴向中心速度相互之间的衔接实现了平滑过渡,消除了跳跃性变化；收集距离为350 mm,主气流流量为1.5 m3/h时,层流炉内颗粒停留时间的相对误差为9.218％.说明该二维PIV自动控制系统能够满足层流炉冷态试验需要,实现了均匀、连续拍摄,减少了人为误差,提高了试验数据的准确性.
Liang, Qianqian; Xu, Wenhai; Ma, Qisheng; Yang, Deshan; Zhang, Wang; Fu, Ying
2016-10-01
The acceleration of large coal base construction needs the modern management technology of heap storage as a guarantee. And the inventory of coal and other bulk commodities is an important aspect in the modern management technology of heap storage. Therefore, a rapid, accurate and simple method to measure the volume and quality of coal heaps for scientific management, economic benefit evaluation and storage evaluation of heap storage is very important which has a significant application value. In this paper, we introduce the structural features, working principle and application status of a new type portable heap bulk inventory system. Actual measurements have been carried out in the coal base located in Huanghua port, Tianjin and Qinhuangdao. The measurement results indicate that the system can measure the volume of bulk commodities efficiently, quickly and accurately, and it has extensive application prospects.
Sverdlova, Nina S; Lambertz, Markus; Witzel, Ulrich; Perry, Steven F
2012-01-01
Various parts of the respiratory system play an important role in temperature control in birds. We create a simplified computational fluid dynamics (CFD) model of heat exchange in the trachea and air sacs of the domestic fowl (Gallus domesticus) in order to investigate the boundary conditions for the convective and evaporative cooling in these parts of the respiratory system. The model is based upon published values for respiratory times, pressures and volumes and upon anatomical data for this species, and the calculated heat exchange is compared with experimentally determined values for the domestic fowl and a closely related, wild species. In addition, we studied the trachea histologically to estimate the thickness of the heat transfer barrier and determine the structure and function of moisture-producing glands. In the transient CFD simulation, the airflow in the trachea of a 2-dimensional model is evoked by changing the volume of the simplified air sac. The heat exchange between the respiratory system and the environment is simulated for different ambient temperatures and humidities, and using two different models of evaporation: constant water vapour concentration model and the droplet injection model. According to the histological results, small mucous glands are numerous but discrete serous glands are lacking on the tracheal surface. The amount of water and heat loss in the simulation is comparable with measured respiratory values previously reported. Tracheal temperature control in the avian respiratory system may be used as a model for extinct or rare animals and could have high relevance for explaining how gigantic, long-necked dinosaurs such as sauropoda might have maintained a high metabolic rate.
Directory of Open Access Journals (Sweden)
Nina S Sverdlova
Full Text Available Various parts of the respiratory system play an important role in temperature control in birds. We create a simplified computational fluid dynamics (CFD model of heat exchange in the trachea and air sacs of the domestic fowl (Gallus domesticus in order to investigate the boundary conditions for the convective and evaporative cooling in these parts of the respiratory system. The model is based upon published values for respiratory times, pressures and volumes and upon anatomical data for this species, and the calculated heat exchange is compared with experimentally determined values for the domestic fowl and a closely related, wild species. In addition, we studied the trachea histologically to estimate the thickness of the heat transfer barrier and determine the structure and function of moisture-producing glands. In the transient CFD simulation, the airflow in the trachea of a 2-dimensional model is evoked by changing the volume of the simplified air sac. The heat exchange between the respiratory system and the environment is simulated for different ambient temperatures and humidities, and using two different models of evaporation: constant water vapour concentration model and the droplet injection model. According to the histological results, small mucous glands are numerous but discrete serous glands are lacking on the tracheal surface. The amount of water and heat loss in the simulation is comparable with measured respiratory values previously reported. Tracheal temperature control in the avian respiratory system may be used as a model for extinct or rare animals and could have high relevance for explaining how gigantic, long-necked dinosaurs such as sauropoda might have maintained a high metabolic rate.
Osenda, Omar; Tamarit, Francisco A; Cannas, Sergio A
2009-08-01
We present a lattice spin model that mimics a system of interacting particles through a short-range repulsive potential and a long-range attractive power-law decaying potential. We perform a detailed analysis of the general equilibrium phase diagram of the model at finite temperature, showing that the only possible equilibrium phases are the ferromagnetic and the antiferromagnetic ones. We then study the nonequilibrium behavior of the model after a quench to subcritical temperatures, in the antiferromagnetic region of the phase diagram region, where the pair interaction potential behaves in the same qualitative way as in a Lennard-Jones gas. We find that even in the absence of quenched disorder or geometric frustration, the competition between interactions gives rise to nonequilibrium disordered structures at low enough temperatures that strongly slow down the relaxation of the system. This nonequilibrium state presents several features characteristic of glassy systems such as subaging, nontrivial fuctuation dissipation relations, and possible logarithmic growth of free-energy barriers to coarsening.
TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION
Energy Technology Data Exchange (ETDEWEB)
Wang, Yougang; Xu, Yidong; Chen, Xuelei [Key Laboratory of Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 China (China); Park, Changbom [School of Physics, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of); Kim, Juhan, E-mail: wangyg@bao.ac.cn, E-mail: cbp@kias.re.kr [Center for Advanced Computation, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of)
2015-11-20
We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two-dimensional genus curve for the early, middle, and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometre Array.
Two dimensional topology of cosmological reionization
Wang, Yougang; Xu, Yidong; Chen, Xuelei; Kim, Juhan
2015-01-01
We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two dimensional genus curve for the early, middle and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometer Array.
Yoshimura, Kazuyoshi; Michioka, Chishiro; Matsui, Mami; Ohta, Hiroto; Yang, Jinhu; Fang, Minghu
2011-06-01
Intrinsic spin susceptibility of the novel layered superconducting and magnetic system Fe1+δTe1-xSex was investigated by means of the magnetization measurements in comparing with the 125Te NMR Knight shift 125K. The macroscopic uniform susceptibility in Fe1+δTe1-xSex consists of the itinerant magnetization originated in the Fe(1) site, localized one in the Fe(2) site and the ferromagnetic-like impurity which is frequently sandwiched by the thin film-like single crystals. Unlike the macroscopic magnetization, Knight shift 125K is mainly attributed to the itinerant magnetism of the Fe(1) site, which is important for the superconductivity and the magnetism in the Fe1+δTe1-xSex system. The magnetic susceptibility estimated in the high-field region agrees well with 125K. The uniform susceptibility of the superconducting Fe1+δTe1-xSex gradually decreases with decreasing temperature in the normal state accompanied by the growth of antiferromagnetic spin afluctuations.
Matsuda, Hiroyuki; Daimon, Hiroshi; Tóth, László; Matsui, Fumihiko
2007-04-01
This paper provides a way of focusing wide-angle charged-particle beams in multiple lens systems. In previous papers [H. Matsuda , Phys. Rev. E 71, 066503 (2005); 74, 036501 (2006)], it was shown that an ellipsoidal mesh, combined with electrostatic lenses, enables correction of spherical aberration over wide acceptance angles up to ±60° . In this paper, practical situations where ordinary electron lenses are arranged behind the wide-angle electrostatic lenses are taken into account using ray tracing calculation. For practical realization of the wide-angle lens systems, the acceptance angle is set to ±50° . We note that the output beams of the wide-angle electrostatic lenses have somewhat large divergence angles which cause unacceptable or non-negligible spherical aberration in additional lenses. A solution to this problem is presented showing that lens combinations to cancel spherical aberration are available, whereby wide-angle charged-particle beams can be finely focused with considerably reduced divergence angles less than ±5° .
Gaquerel, Emmanuel; Baldwin, Ian T
2013-01-01
Plant volatile organic compound (VOC) production requires a complex network of biochemical pathways, which, although well mapped from a biochemical point of view, remains only partly understood with regard to its physiological and genetic regulation. Additionally, although analytical procedures for plant VOC measurement have become increasingly faster and more sensitive in recent years, pinpointing relevant shifts in VOC production from the thousands of molecular fragments that are generated by modern mass spectrometer instruments remains challenging. Here we discuss novel opportunities for system-wide analysis provided by the implementation of non-targeted data processing and multivariate statistics in VOC analysis. We illustrate the value of implementing non-targeted data processing with examples of recent findings from our group on the interactive control exerted by salivary components of a lepidopteran herbivore, Manduca sexta, on herbivory-induced VOC emissions in the wild tobacco Nicotiana attenuata. Finally, we briefly discuss the use of multi-platform data integration for probing the nature of metabolic and regulatory systems underlying VOC emissions.
Two-dimensional x-ray diffraction
He, Bob B
2009-01-01
Written by one of the pioneers of 2D X-Ray Diffraction, this useful guide covers the fundamentals, experimental methods and applications of two-dimensional x-ray diffraction, including geometry convention, x-ray source and optics, two-dimensional detectors, diffraction data interpretation, and configurations for various applications, such as phase identification, texture, stress, microstructure analysis, crystallinity, thin film analysis and combinatorial screening. Experimental examples in materials research, pharmaceuticals, and forensics are also given. This presents a key resource to resea
Matching Two-dimensional Gel Electrophoresis' Spots
DEFF Research Database (Denmark)
Dos Anjos, António; AL-Tam, Faroq; Shahbazkia, Hamid Reza
2012-01-01
This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches. This ar......This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches...
Mobility anisotropy of two-dimensional semiconductors
Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong
2016-12-01
The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.
Towards two-dimensional search engines
Ermann, Leonardo; Chepelianskii, Alexei D.; Shepelyansky, Dima L.
2011-01-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way the ranking of nodes becomes two-dimensional that paves the way for development of two-dimensional search engines of new type. Statistical properties of inf...
The partition function of two-dimensional string theory
Dijkgraaf, Robbert; Moore, Gregory; Plesser, Ronen
1993-04-01
We derive a compact and explicit expression for the generating functional of all correlation functions of tachyon operators in two-dimensional string theory. This expression makes manifest relations of the c = 1 system to KP flow nd W 1 + ∞ constraints. Moreover we derive a Kontsevich-Penner integral representation of this generating functional.
The partition function of two-dimensional string theory
Energy Technology Data Exchange (ETDEWEB)
Dijkgraaf, R. (School of Natural Sciences, Inst. for Advanced Study, Princeton, NJ (United States) Dept. of Mathematics, Univ. Amsterdam (Netherlands)); Moore, G.; Plesser, R. (Dept. of Physics, Yale Univ., New Haven, CT (United States))
1993-04-12
We derive a compact and explicit expression for the generating functional of all correlation functions of tachyon operators in two-dimensional string theory. This expression makes manifest relations of the c=1 system to KP flow and W[sub 1+[infinity
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...
Easy interpretation of optical two-dimensional correlation spectra
Lazonder, K.; Pshenichnikov, M.S.; Wiersma, D.A.
2006-01-01
We demonstrate that the value of the underlying frequency-frequency correlation function can be retrieved from a two-dimensional optical correlation spectrum through a simple relationship. The proposed method yields both intuitive clues and a quantitative measure of the dynamics of the system. The t
Confined two-dimensional fermions at finite density
De Francia, M; Loewe, M; Santangelo, E M; De Francia, M; Falomir, H; Loewe, M; Santangelo, E M
1995-01-01
We introduce the chemical potential in a system of two-dimensional massless fermions, confined to a finite region, by imposing twisted boundary conditions in the Euclidean time direction. We explore in this simple model the application of functional techniques which could be used in more complicated situations.
Directory of Open Access Journals (Sweden)
Javier Achury Varila
2010-04-01
Full Text Available La inestabilidad en la combustión es una condición indeseada en algunos sistemas de combustión como en turbinas de gas por ejemplo. Se refiere a la presencia autogenerada de oscilaciones en la presión que pueden afectar a la cámara de combustión y de paso llegar a generar ruido. Una reciente tendencia generalizada en los procesos de combustión apunta al uso de mezclas pobres para la reducción de contaminantes, no obstante que este tipo de mezclas son más susceptibles a la inestabilidad en la combustión. Las complicadas relaciones que gobiernan el fenómeno se pueden resumir como el acoplamiento entre la llama y la acústica del sistema. En el presente trabajo se presenta un planteamiento numérico que permite aproximarse al fenómeno a través de la solución de un modelo de combustión básico implementado computacionalmente. En este modelo se simula una autoexcitación del sistema a través de oscilaciones en la entrada de flujos de reactantes. Finalmente, se comparan los resultados de la simulación numérica con otras simulaciones y datos experimentales.The Combustion instability is an undesirable condition reached in some combustion systems, as during the operation of gas turbines. It refers to self-excited oscillations of pressure that may affect the combustion chamber and generate noise. A recent generalized tendency in combustion processes aims to the use of lean combustion (low fuel/air ratios for pollutants reduction, nevertheless this sort of mixtures are more susceptible to combustion instabilities. The complex relationship that generates the phenomenon can be summarized as the coupling between flame and acoustics. In this paper it is outlined a numerical approach to this phenomenon by solving a basic computational combustion model (by Direct Numerical Simulation. In this model a self-excited system is simulated through imposed oscillations in reactants flows. Finally, results for this numerical simulation are compared
De Angelis, Elena; Ravanetti, Francesca; Martelli, Paolo; Cacchioli, Antonio; Ivanovska, Ana; Corradi, Attilio; Nasi, Sonia; Bianchera, Annalisa; Passeri, Benedetta; Canelli, Elena; Bettini, Ruggero; Borghetti, Paolo
2017-06-15
The present study investigated the biocompatibility of chitosan films and scaffolds modified with d-(+)raffinose and their capability to support the growth and maintenance of the differentiation of articular chondrocytes in vitro. Primary equine articular chondrocytes were cultured on films and scaffolds of modified d-(+) raffinose chitosan. Their behavior was compared to that of chondrocytes grown in conventional bi- and three-dimensional culture systems, such as micromasses and alginate beads. Chitosan films maintained the phenotype of differentiated chondrocytes (typical round morphology) and sustained the synthesis of cartilaginous extracellular matrix (ECM), even at 4weeks of culture. Indeed, starting from 2weeks of culture, chondrocytes seeded on chitosan scaffolds were able to penetrate the surface pores and to colonize the internal matrix. Moreover they produced ECM expressing the genes of typical chondrocytes differentiation markers such as collagen II and aggrecan. In conclusion, chitosan modified with d-raffinose represents an ideal support for chondrocyte adhesion, proliferation and for the maintenance of cellular phenotypic and genotypic differentiation. This novel biomaterial could potentially be a reliable support for the re-differentiation of dedifferentiated chondrocytes. Copyright © 2017 Elsevier Ltd. All rights reserved.
Jezierska, Aneta; Panek, Jarosław J
2008-03-01
Car-Parrinello Molecular Dynamics simulations were performed for selected anharmonic systems, i.e., Schiff and Mannich base-type compounds, to investigate the vibrational properties associated with O-H stretching. All calculations were performed in the gas phase to compare them with available experimental data. First the vibrational properties of the two compounds were analyzed on the basis of well-established approaches: Fourier transformation of the autocorrelation function of both the atomic velocities and dipole moments. Then path integral molecular dynamics simulations were performed to demonstrate the influence of quantum effects on the proton's position in the hydrogen bridge. In addition, quantum effects were incorporated a posteriori into calculations of O-H stretching envelopes for the Schiff and Mannich bases. Proton potential snapshots were extracted from the ab initio molecular dynamics trajectory. Vibrational Schrödinger equations (one- and two-dimensional) were solved numerically for the snapshots, and the O-H stretching envelopes were calculated as a superposition of the 0→1 transitions. Subsequently, one- and two-dimensional potentials of mean force (1D and 2D pmf) were calculated for the proton stretching mode from the proton vibrational eigenfunctions and eigenvalues incorporating statistical sampling and nuclear quantum effects. The results show that the applied methodologies are in good agreement with experimental infrared spectra. Additionally, it is demonstrated that the 2D pmf method could be applied in systems with strong anharmonicity to describe the properties of the O-H stretching mode more accurately. Future applications of the 2D pmf technique include, in principle, large biomolecular systems treated within the QM/MM framework.
Kramers and non-Kramers Phase Transitions in Many-Particle Systems with Dynamical Constraint
Herrmann, Michael; Velázquez, Juan J L
2011-01-01
We study a Fokker-Planck equation with double-well potential that is nonlocally driven by a dynamical constraint and involves two small parameters. Relying on formal asymptotics we identify several parameter regimes and derive reduced dynamical models for different types of phase transitions.
Liu, Chieh-Wen; Liu, Chieh-I.; Liang, C.-T.; Kim, Gil-Ho; Huang, C. F.; Hang, D. R.; Chang, Y. H.; Ritchie, D. A.
2017-08-01
Temperature-driven flow lines are studied in the conductivity plane in a GaAs-based two-dimensional electron system containing self-assembled InAs dots when Landau level filling factor ν = 2-4. In the insulator-quantum Hall (I-QH) transition resulting from the floating-up of the extended states, the flow diagram shows the critical behavior and we observed the expected semicircle in the strongest disorder case. By decreasing the effective disorder, we find that such flow lines can leave the I-QH regime and correspond to the plateau-plateau transition between ν = 4 and 2. The evolution of the conductivity curve at low magnetic fields demonstrates the importance of Landau-level mixing to the semicircle when the extended states float up.
Piezoelectricity in Two-Dimensional Materials
Wu, Tao
2015-02-25
Powering up 2D materials: Recent experimental studies confirmed the existence of piezoelectricity - the conversion of mechanical stress into electricity - in two-dimensional single-layer MoS2 nanosheets. The results represent a milestone towards embedding low-dimensional materials into future disruptive technologies. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
A novel two dimensional particle velocity sensor
Pjetri, Olti; Wiegerink, Remco J.; Lammerink, Theo S.; Krijnen, Gijs J.
2013-01-01
In this paper we present a two wire, two-dimensional particle velocity sensor. The miniature sensor of size 1.0x2.5x0.525 mm, consisting of only two crossed wires, shows excellent directional sensitivity in both directions, thus requiring no directivity calibration, and is relatively easy to fabrica
Two-dimensional microstrip detector for neutrons
Energy Technology Data Exchange (ETDEWEB)
Oed, A. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Because of their robust design, gas microstrip detectors, which were developed at ILL, can be assembled relatively quickly, provided the prefabricated components are available. At the beginning of 1996, orders were received for the construction of three two-dimensional neutron detectors. These detectors have been completed. The detectors are outlined below. (author). 2 refs.
Two-dimensional magma-repository interactions
Bokhove, O.
2001-01-01
Two-dimensional simulations of magma-repository interactions reveal that the three phases --a shock tube, shock reflection and amplification, and shock attenuation and decay phase-- in a one-dimensional flow tube model have a precursor. This newly identified phase ``zero'' consists of the impact of
Two-dimensional subwavelength plasmonic lattice solitons
Ye, F; Hu, B; Panoiu, N C
2010-01-01
We present a theoretical study of plasmonic lattice solitons (PLSs) formed in two-dimensional (2D) arrays of metallic nanowires embedded into a nonlinear medium with Kerr nonlinearity. We analyze two classes of 2D PLSs families, namely, fundamental and vortical PLSs in both focusing and defocusing media. Their existence, stability, and subwavelength spatial confinement are studied in detai
A two-dimensional Dirac fermion microscope
DEFF Research Database (Denmark)
Bøggild, Peter; Caridad, Jose; Stampfer, Christoph
2017-01-01
in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2...
Design of an Automatic Two-dimensional Liquid Chromatograph Control System%全自动二维液相色谱仪控制系统的设计
Institute of Scientific and Technical Information of China (English)
常剑; 罗飞
2011-01-01
Based on the theory of two-dimensional chromatogram the liquid chromatograph employs two chromatographic columns to gradually separate substances, and thus solves the challenge of separating natural substances in traditional Chinese medicine.Firstly the structure of the two-dimensional liquid chromatograph is introduced, then two methods for controlling stream paths and separating substances, on-line separating and off-line separating are discussed in details.And then the design for controlling the stream paths is illustrated which is aimed at the realization of time-sharing control of various valves and the realization of separating substances and steady operating of systems in different separating ways.And in the substance collecting step, an algorithm is adopted for the analysis of chromatogram wave.As is shown by the result, the system can collect substances efficiently.%二维液相色谱仪根据二维液相色谱的原理,采用两根色谱柱逐步分离,解决了中药中天然物质分离难度大的问题.本文首先介绍了二维液相色谱仪控制系统的架构,接着讨论了整体流路及分离的两种工作方法:在线工作方式和离线工作方式.然后设计控制流路实现对各种阀门的分时控制,以实现不同分离方法下的系统运行及物质分离.在最后收集阶段,采用一种算法对色谱波峰进行分析,实现有效收集.
Sutherland, Roderick I.
2016-11-01
A Lagrangian formulation is constructed for particle interpretations of quantum mechanics, a well-known example of such an interpretation being the Bohm model. The advantages of such a description are that the equations for particle motion, field evolution and conservation laws can all be deduced from a single Lagrangian density expression. The formalism presented is Lorentz invariant. This paper follows on from a previous one which was limited to the single-particle case. The present paper treats the more general case of many particles in an entangled state. It is found that describing more than one particle while maintaining a relativistic description requires the specification of final boundary conditions as well as the usual initial ones, with the experimenter's controllable choice of the final conditions thereby exerting a backwards-in-time influence. This retrocausality then allows an important theoretical step forward to be made, namely that it becomes possible to dispense with the usual, many-dimensional description in configuration space and instead revert to a description in space-time using separate, single-particle wavefunctions.
Scott, Tony C.
It has been shown that the Fokker-Wheeler-Feynman (FWF) model could be rewritten to yield a physically acceptable relativistic many-particle Lagrangian. Contrary to Wheeler and Feynman's postulates, the model satisfies causality and can be generalised to include arbitrary forces. The 1/c power series of the FWF Lagrangian to order (1/c) ^4 contains accelerations. A procedure of quantizing the theory for such a Lagrangian is presented and it is then found that the accelerations approximately introduce an independent harmonic mode which is in agreement with resonances recently observed in Positronium collisions processes. This result may be of fundamental physical importance and requires further investigation. However, the refinement of this calculation requires the creation of new computational tools. To this end, a new method is presented in which both the eigenfunctions and eigenenergies are determined algebraically as power series in the order parameter, where each coefficient of the series is obtained in closed form. This method avoids the complications of a basis set and makes extensive use of symbolic computation. It is then applied to two model problems, namely the one-body Dirac equation for testing purposes and a special case of the two-body Dirac equation for which one obtains previously unknown closed form solutions.
Kim, Yon-Lae; Chung, Jin-Beom; Kim, Jae-Sung; Lee, Jeong-Woo; Choi, Kyoung-Sik
2014-04-01
The aim of this study was to compare the dosimetric performance and to evaluate the pretreatment quality assurance (QA) of a portal dosimetry and a commercial two-dimensional (2-D) array system. In the characteristics comparison study, the measured values for the dose linearity, dose rate response, reproducibility, and field size dependence for 6-MV photon beams were analyzed for both detector systems. To perform the qualitative evaluations of the 10 IMRT and the 10 VMAT plans, we used the Gamma index for quantifying the agreement between calculations and measurements. The performance estimates for both systems show that overall, minimal differences in the dosimetric characteristics exist between the Electron portal imaging device (EPID) and 2-D array system. In the qualitative analysis for pretreatment quality assurance, the EPID and 2-D array system yield similar passing rate results for the majority of clinical Intensity-modulated radiation therapy (IMRT) and Volumetric-modulated arc therapy (VMAT) cases. These results were satisfactory for IMRT and VMAT fields and were within the acceptable criteria of γ%≤1, γ avg <0.5. The EPDI and the 2-D array systems showed comparable dosimetric results. In this study, the results revealed both systems to be suitable for patient-specific QA measurements for IMRT and VMAT. We conclude that, depending on the status of clinic, both systems can be used interchangeably for routine pretreatment QA.
Topology in two-dimensional systems
Beukman, A.J.A.
2016-01-01
This thesis includes two research directions both aim to discover a building block for topological quantum computing. First, in Chapter 3, a novel setup is designed, built, and tested, that can electrostatically gate a material without endangering the materials pristine quality. The setup was design
Topology in two-dimensional systems
Beukman, A.J.A.
2016-01-01
This thesis includes two research directions both aim to discover a building block for topological quantum computing. First, in Chapter 3, a novel setup is designed, built, and tested, that can electrostatically gate a material without endangering the materials pristine quality. The setup was design
Quantum entanglement in a two-dimensional ion trap
Institute of Scientific and Technical Information of China (English)
王成志; 方卯发
2003-01-01
In this paper, we investigate the quantum entanglement in a two-dimensional ion trap system. We discuss the quantum entanglement between the ion and phonons by using reduced entropy, and that between two degrees of freedom of the vibrational motion along x and y directions by using quantum relative entropy. We discuss also the influence of initial state of the system on the quantum entanglement and the relation between two entanglements in the trapped ion system.
Institute of Scientific and Technical Information of China (English)
王殊轶; 钱省三; 张敏燕; 周颖
2009-01-01
Complicated characteristic of facial modality acquisition and measurement is commonly needed in clinical environment.Two different methods were compared, one method was acquisition two-dimensional character based on the principle of machine vision with a charge-coupled device (CCD) capturing image, and another method was acquisition three-dimensional character based on the technology of Reverse Engineering with laser scanning capturing image. The principle, composition of the system, calibration and characteristics of different method are analyzed. Two-dimensional and three-dimensional facial data of thirty undergraduates was used to compare different methods. The application and restriction of different methods are concluded. The conclusion of this paper provided a reference for face plastic surgery, facial paralysis, facial surgical evaluation and rehabilitation design.%临床医学中常需要对复杂的面部形态进行特征提取与测量.文章比较了利用CCD进行面部软组织图像采集获得二维特征参量和利用逆向工程技术的激光面部软组织三维数据提取三维特征的两种方法,分析各自的原理、系统组成、标定方法与各自特点,利用这两种方法对30人进行了面部二维和三维特征数据提取比较,得出了两种方法的适用条件与限制.试验结果可为整形设计、面瘫、脸部外科手术评估、康复研究等临床应用提供参考.
Analysis of one dimensional and two dimensional fuzzy controllers
Institute of Scientific and Technical Information of China (English)
Ban Xiaojun; Gao Xiaozhi; Huang Xianlin; Wu Tianbao
2006-01-01
The analytical structures and the corresponding mathematical properties of the one dimensional and two dimensional fuzzy controllers are first investigated in detail.The nature of these two kinds of fuzzy controllers is next probed from the perspective of control engineering. For the one dimensional fuzzy controller, it is concluded that this controller is a combination of a saturation element and a nonlinear proportional controller, and the system that employs the one dimensional fuzzy controller is the combination of an open-loop control system and a closedloop control system. For the latter case, it is concluded that it is a hybrid controller, which comprises the saturation part, zero-output part, nonlinear derivative part, nonlinear proportional part, as well as nonlinear proportional-derivative part, and the two dimensional fuzzy controller-based control system is a loop-varying system with varying number of control loops.
Phase-sensitive two-dimensional neutron shearing interferometer and Hartmann sensor
Energy Technology Data Exchange (ETDEWEB)
Baker, Kevin
2015-12-08
A neutron imaging system detects both the phase shift and absorption of neutrons passing through an object. The neutron imaging system is based on either of two different neutron wavefront sensor techniques: 2-D shearing interferometry and Hartmann wavefront sensing. Both approaches measure an entire two-dimensional neutron complex field, including its amplitude and phase. Each measures the full-field, two-dimensional phase gradients and, concomitantly, the two-dimensional amplitude mapping, requiring only a single measurement.
Diagrammatic approach to orbital quantum impurities interacting with a many-particle environment
Bighin, G.; Lemeshko, M.
2017-08-01
Recently it was shown that an impurity exchanging orbital angular momentum with a surrounding bath can be described in terms of the angulon quasiparticle [Phys. Rev. Lett. 118, 095301 (2017), 10.1103/PhysRevLett.118.095301]. The angulon consists of a quantum rotor dressed by a many-particle field of boson excitations and can be formed out of, for example, a molecule or a nonspherical atom in superfluid helium or out of an electron coupled to lattice phonons or a Bose condensate. Here we develop an approach to the angulon based on the path-integral formalism, which sets the ground for a systematic, perturbative treatment of the angulon problem. The resulting perturbation series can be interpreted in terms of Feynman diagrams, from which, in turn, one can derive a set of diagrammatic rules. These rules extend the machinery of the graphical theory of angular momentum—well known from theoretical atomic spectroscopy—to the case where an environment with an infinite number of degrees of freedom is present. In particular, we show that each diagram can be interpreted as a `skeleton', which enforces angular momentum conservation, dressed by an additional many-body contribution. This connection between the angulon theory and the graphical theory of angular momentum is particularly important as it allows us to systematically and substantially simplify the analytical representation of each diagram. In order to exemplify the technique, we calculate the one- and two-loop contributions to the angulon self-energy, the spectral function, and the quasiparticle weight. The diagrammatic theory we develop paves the way to investigate next-to-leading order quantities in a more compact way compared to the variational approaches.
Stress Wave Propagation in Two-dimensional Buckyball Lattice
Xu, Jun; Zheng, Bowen
2016-11-01
Orderly arrayed granular crystals exhibit extraordinary capability to tune stress wave propagation. Granular system of higher dimension renders many more stress wave patterns, showing its great potential for physical and engineering applications. At nanoscale, one-dimensionally arranged buckyball (C60) system has shown the ability to support solitary wave. In this paper, stress wave behaviors of two-dimensional buckyball (C60) lattice are investigated based on square close packing and hexagonal close packing. We show that the square close packed system supports highly directional Nesterenko solitary waves along initially excited chains and hexagonal close packed system tends to distribute the impulse and dissipates impact exponentially. Results of numerical calculations based on a two-dimensional nonlinear spring model are in a good agreement with the results of molecular dynamics simulations. This work enhances the understanding of wave properties and allows manipulations of nanoscale lattice and novel design of shock mitigation and nanoscale energy harvesting devices.
Two-dimensional ranking of Wikipedia articles
Zhirov, A. O.; Zhirov, O. V.; Shepelyansky, D. L.
2010-10-01
The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists ab aeterno. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. While PageRank highlights very well known nodes with many ingoing links, CheiRank highlights very communicative nodes with many outgoing links. In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.
Towards two-dimensional search engines
Ermann, Leonardo; Shepelyansky, Dima L
2011-01-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way the ranking of nodes becomes two-dimensional that paves the way for development of two-dimensional search engines of new type. Information flow properties on PageRank-CheiRank plane are analyzed for networks of British, French and Italian Universities, Wikipedia, Linux Kernel, gene regulation and other networks. Methods of spam links control are also analyzed.
Toward two-dimensional search engines
Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.
2012-07-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.
A two-dimensional Dirac fermion microscope
Bøggild, Peter; Caridad, José M.; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads
2017-06-01
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
A two-dimensional Dirac fermion microscope.
Bøggild, Peter; Caridad, José M; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads
2017-06-09
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
Two-Dimensional Scheduling: A Review
Directory of Open Access Journals (Sweden)
Zhuolei Xiao
2013-07-01
Full Text Available In this study, we present a literature review, classification schemes and analysis of methodology for scheduling problems on Batch Processing machine (BP with both processing time and job size constraints which is also regarded as Two-Dimensional (TD scheduling. Special attention is given to scheduling problems with non-identical job sizes and processing times, with details of the basic algorithms and other significant results.
Two dimensional fermions in four dimensional YM
Narayanan, R
2009-01-01
Dirac fermions in the fundamental representation of SU(N) live on a two dimensional torus flatly embedded in $R^4$. They interact with a four dimensional SU(N) Yang Mills vector potential preserving a global chiral symmetry at finite $N$. As the size of the torus in units of $\\frac{1}{\\Lambda_{SU(N)}}$ is varied from small to large, the chiral symmetry gets spontaneously broken in the infinite $N$ limit.
Two-dimensional Kagome photonic bandgap waveguide
DEFF Research Database (Denmark)
Nielsen, Jens Bo; Søndergaard, Thomas; Libori, Stig E. Barkou;
2000-01-01
The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes...... is investigated with respect to the width of the 2-D Kagome waveguide, and the number of modes existing for specific frequencies and waveguide widths is mapped out....
String breaking in two-dimensional QCD
Hornbostel, K J
1999-01-01
I present results of a numerical calculation of the effects of light quark-antiquark pairs on the linear heavy-quark potential in light-cone quantized two-dimensional QCD. I extract the potential from the Q-Qbar component of the ground-state wavefunction, and observe string breaking at the heavy-light meson pair threshold. I briefly comment on the states responsible for the breaking.
Velocity Statistics in the Two-Dimensional Granular Turbulence
Isobe, Masaharu
2003-01-01
We studied the macroscopic statistical properties on the freely evolving quasi-elastic hard disk (granular) system by performing a large-scale (up to a few million particles) event-driven molecular dynamics systematically and found that remarkably analogous to an enstrophy cascade process in the decaying two-dimensional fluid turbulence. There are four typical stages in the freely evolving inelastic hard disk system, which are homogeneous, shearing (vortex), clustering and final state. In the...
Two dimensional echocardiographic detection of intraatrial masses.
DePace, N L; Soulen, R L; Kotler, M N; Mintz, G S
1981-11-01
With two dimensional echocardiography, a left atrial mass was detected in 19 patients. Of these, 10 patients with rheumatic mitral stenosis had a left atrial thrombus. The distinctive two dimensional echocardiographic features of left atrial thrombus included a mass of irregular nonmobile laminated echos within an enlarged atrial cavity, usually with a broad base of attachment to the posterior left atrial wall. Seven patients had a left atrial myxoma. Usually, the myxoma appeared as a mottled ovoid, sharply demarcated mobile mass attached to the interatrial septum. One patient had a right atrial angiosarcoma that appeared as a nonmobile mass extending from the inferior vena caval-right atrial junction into the right atrial cavity. One patient had a left atrial leiomyosarcoma producing a highly mobile mass attached to the lateral wall of the left atrium. M mode echocardiography detected six of the seven myxomas, one thrombus and neither of the other tumors. Thus, two dimensional echocardiography appears to be the technique of choice in the detection, localization and differentiation of intraatrial masses.
Ultrafast two dimensional infrared chemical exchange spectroscopy
Fayer, Michael
2011-03-01
The method of ultrafast two dimensional infrared (2D IR) vibrational echo spectroscopy is described. Three ultrashort IR pulses tuned to the frequencies of the vibrational transitions of interest are directed into the sample. The interaction of these pulses with the molecular vibrational oscillators produces a polarization that gives rise to a fourth pulse, the vibrational echo. The vibrational echo pulse is combined with another pulse, the local oscillator, for heterodyne detection of the signal. For fixed time between the second and third pulses, the waiting time, the first pulse is scanned. Two Fourier transforms of the data yield a 2D IR spectrum. The waiting time is increased, and another spectrum is obtained. The change in the 2D IR spectra with increased waiting time provides information on the time evolution of the structure of the molecular system under observation. In a 2D IR chemical exchange experiment, two species A and B, are undergoing chemical exchange. A's are turning into B's, and B's are turning into A's, but the overall concentrations of the species are not changing. The kinetics of the chemical exchange on the ground electronic state under thermal equilibrium conditions can be obtained 2D IR spectroscopy. A vibration that has a different frequency for the two species is monitored. At very short time, there will be two peaks on the diagonal of the 2D IR spectrum, one for A and one for B. As the waiting time is increased, chemical exchange causes off-diagonal peaks to grow in. The time dependence of the growth of these off-diagonal peaks gives the chemical exchange rate. The method is applied to organic solute-solvent complex formation, orientational isomerization about a carbon-carbon single bond, migration of a hydrogen bond from one position on a molecule to another, protein structural substate interconversion, and water hydrogen bond switching between ions and water molecules. This work was supported by the Air Force Office of Scientific
Molecular assembly on two-dimensional materials
Kumar, Avijit; Banerjee, Kaustuv; Liljeroth, Peter
2017-02-01
Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule–substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging
Topological states in two-dimensional hexagon lattice bilayers
Zhang, Ming-Ming; Xu, Lei; Zhang, Jun
2016-10-01
We investigate the topological states of the two-dimensional hexagon lattice bilayer. The system exhibits a quantum valley Hall (QVH) state when the interlayer interaction t⊥ is smaller than the nearest neighbor hopping energy t, and then translates to a trivial band insulator state when t⊥ / t > 1. Interestingly, the system is found to be a single-edge QVH state with t⊥ / t = 1. The topological phase transition also can be presented via changing bias voltage and sublattice potential in the system. The QVH states have different edge modes carrying valley current but no net charge current. The bias voltage and external electric field can be tuned easily in experiments, so the present results will provide potential application in valleytronics based on the two-dimensional hexagon lattice.
Bhattacharjee, Suraka; Chaudhury, Ranjan
2016-11-01
The generalized spin stiffness constant for a doped quantum antiferromagnet has been investigated both analytically and numerically as a function of doping concentration at zero temperature, based on the strongly correlated t-J model on two-dimensional square lattice. The nature of the theoretical dependence of the stiffness constant on doping shows a striking similarity with that of the effective exchange constant, obtained from the combination of other theoretical and experimental techniques in the low doping region. This correspondence once again establishes that spin stiffness can very well play the role of an effective exchange constant even in the strongly correlated semi-itinerant systems. Our theoretical plot of the stiffness constant against doping concentration in the whole doping region exhibits the various characteristic features like a possible crossover in the higher doping regions and persistence of short range ordering even for very high doping with the complete vanishing of spin stiffness occurring only close to 100% doping. Our results receive very good support from various other theoretical approaches and also brings out a few limitations of some of them. Our detailed analysis highlights the crucial importance of the study of spin stiffness for the proper understanding of magnetic correlations in a semi-itinerant magnetic system described by the strongly correlated t-J model. Moreover, our basic formalism can also be utilized for determination of the effective exchange constant and magnetic correlations for itinerant magnetic systems, in general in a novel way.
Two-dimensional capillary electrophoresis using tangentially connected capillaries.
Sahlin, Eskil
2007-06-22
A novel type of fused silica capillary system is described where channels with circular cross-sections are tangentially in contact with each other and connected through a small opening at the contact area. Since the channels are not crossing each other in the same plane, the capillaries can easily be filled with different solutions, i.e. different solutions will be in contact with each other at the contact point. The system has been used to perform different types of two-dimensional separations and the complete system is fully automated where a high voltage switch is used to control the location of the high voltage in the system. Using two model compounds it is demonstrated that a type of two-dimensional separation can be performed using capillary zone electrophoresis at two different pH values. It is also shown that a compound with acid/base properties can be concentrated using a dynamic pH junction mechanism when transferred from the first separation to the second separation. In addition, the system has been used to perform a comprehensive two-dimensional capillary electrophoresis separation of tryptic digest of bovine serum albumin using capillary zone electrophoresis followed by micellar electrokinetic chromatography.
Strongly correlated two-dimensional plasma explored from entropy measurements.
Kuntsevich, A Y; Tupikov, Y V; Pudalov, V M; Burmistrov, I S
2015-06-23
Charged plasma and Fermi liquid are two distinct states of electronic matter intrinsic to dilute two-dimensional electron systems at elevated and low temperatures, respectively. Probing their thermodynamics represents challenge because of lack of an adequate technique. Here, we report a thermodynamic method to measure the entropy per electron in gated structures. Our technique appears to be three orders of magnitude superior in sensitivity to a.c. calorimetry, allowing entropy measurements with only 10(8) electrons. This enables us to investigate the correlated plasma regime, previously inaccessible experimentally in two-dimensional electron systems in semiconductors. In experiments with clean two-dimensional electron system in silicon-based structures, we traced entropy evolution from the plasma to Fermi liquid regime by varying electron density. We reveal that the correlated plasma regime can be mapped onto the ordinary non-degenerate Fermi gas with an interaction-enhanced temperature-dependent effective mass. Our method opens up new horizons in studies of low-dimensional electron systems.
Nonlocal bottleneck effect in two-dimensional turbulence
Biskamp, D; Schwarz, E
1998-01-01
The bottleneck pileup in the energy spectrum is investigated for several two-dimensional (2D) turbulence systems by numerical simulation using high-order diffusion terms to amplify the effect, which is weak for normal diffusion. For 2D magnetohydrodynamic (MHD) turbulence, 2D electron MHD (EMHD) turbulence and 2D thermal convection, which all exhibit direct energy cascades, a nonlocal behavior is found resulting in a logarithmic enhancement of the spectrum.
Level crossings in complex two-dimensional potentials
Indian Academy of Sciences (India)
Qing-Hai Wang
2009-08-01
Two-dimensional $\\mathcal{PT}$-symmetric quantum-mechanical systems with the complex cubic potential 12 = 2 + 2 + 2 and the complex Hénon–Heiles potential HH = 2 + 2 + (2 − 3/3) are investigated. Using numerical and perturbative methods, energy spectra are obtained to high levels. Although both potentials respect the $\\mathcal{PT}$ symmetry, the complex energy eigenvalues appear when level crossing happens between same parity eigenstates.
Complex dynamical invariants for two-dimensional complex potentials
Indian Academy of Sciences (India)
J S Virdi; F Chand; C N Kumar; S C Mishra
2012-08-01
Complex dynamical invariants are searched out for two-dimensional complex potentials using rationalization method within the framework of an extended complex phase space characterized by $x = x_{1} + ip_{3}. y = x_{2} + ip_{4}, p_{x} = p_{1} + ix_{3}, p_{y} = p_{2} + ix_{4}$. It is found that the cubic oscillator and shifted harmonic oscillator admit quadratic complex invariants. THe obtained invariants may be useful for studying non-Hermitian Hamiltonian systems.
Statistical study of approximations to two dimensional inviscid turbulence
Energy Technology Data Exchange (ETDEWEB)
Glaz, H.M.
1977-09-01
A numerical technique is developed for studying the ergodic and mixing hypotheses for the dynamical systems arising from the truncated Fourier transformed two-dimensional inviscid Navier-Stokes equations. This method has the advantage of exactly conserving energy and entropy (i.e., total vorticity) in the inviscid case except for numerical error in solving the ordinary differential equations. The development of the mathematical model as an approximation to a real physical (turbulent) flow and the numerical results obtained are discussed.
Weakly disordered two-dimensional Frenkel excitons
Boukahil, A.; Zettili, Nouredine
2004-03-01
We report the results of studies of the optical properties of weakly disordered two- dimensional Frenkel excitons in the Coherent Potential Approximation (CPA). An approximate complex Green's function for a square lattice with nearest neighbor interactions is used in the self-consistent equation to determine the coherent potential. It is shown that the Density of States is very much affected by the logarithmic singularities in the Green's function. Our CPA results are in excellent agreement with previous investigations by Schreiber and Toyozawa using the Monte Carlo simulation.
Two-dimensional photonic crystal surfactant detection.
Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A
2012-08-07
We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants.
Theory of two-dimensional transformations
Kanayama, Yutaka J.; Krahn, Gary W.
1998-01-01
The article of record may be found at http://dx.doi.org/10.1109/70.720359 Robotics and Automation, IEEE Transactions on This paper proposes a new "heterogeneous" two-dimensional (2D) transformation group ___ to solve motion analysis/planning problems in robotics. In this theory, we use a 3×1 matrix to represent a transformation as opposed to a 3×3 matrix in the homogeneous formulation. First, this theory is as capable as the homogeneous theory, Because of the minimal size, its implement...
Two-dimensional ranking of Wikipedia articles
Zhirov, A O; Shepelyansky, D L
2010-01-01
The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists {\\it ab aeterno}. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. We analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.
Mobility anisotropy of two-dimensional semiconductors
Lang, Haifeng; Liu, Zhirong
2016-01-01
The carrier mobility of anisotropic two-dimensional (2D) semiconductors under longitudinal acoustic (LA) phonon scattering was theoretically studied with the deformation potential theory. Based on Boltzmann equation with relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was deduced, which shows that the influence of effective mass to the mobility anisotropy is larger than that of deformation potential constant and elastic modulus. Parameters were collected for various anisotropic 2D materials (black phosphorus, Hittorf's phosphorus, BC$_2$N, MXene, TiS$_3$, GeCH$_3$) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio was overestimated in the past.
Sums of two-dimensional spectral triples
DEFF Research Database (Denmark)
Christensen, Erik; Ivan, Cristina
2007-01-01
construct a sum of two dimensional modules which reflects some aspects of the topological dimensions of the compact metric space, but this will only give the metric back approximately. At the end we make an explicit computation of the last module for the unit interval in. The metric is recovered exactly......, the Dixmier trace induces a multiple of the Lebesgue integral but the growth of the number of eigenvalues is different from the one found for the standard differential operator on the unit interval....
Binding energy of two-dimensional biexcitons
DEFF Research Database (Denmark)
Singh, Jai; Birkedal, Dan; Vadim, Lyssenko;
1996-01-01
Using a model structure for a two-dimensional (2D) biexciton confined in a quantum well, it is shown that the form of the Hamiltonian of the 2D biexciton reduces into that of an exciton. The binding energies and Bohr radii of a 2D biexciton in its various internal energy states are derived...... analytically using the fractional dimension approach. The ratio of the binding energy of a 2D biexciton to that of a 2D exciton is found to be 0.228, which agrees very well with the recent experimental value. The results of our approach are compared with those of earlier theories....
Dynamics of film. [two dimensional continua theory
Zak, M.
1979-01-01
The general theory of films as two-dimensional continua are elaborated upon. As physical realizations of such a model this paper examines: inextensible films, elastic films, and nets. The suggested dynamic equations have enabled us to find out the characteristic speeds of wave propagation of the invariants of external and internal geometry and formulate the criteria of instability of their shape. Also included herein is a detailed account of the equation describing the film motions beyond the limits of the shape stability accompanied by the formation of wrinkles. The theory is illustrated by examples.
Procedures for two-dimensional electrophoresis of proteins
Energy Technology Data Exchange (ETDEWEB)
Tollaksen, S.L.; Giometti, C.S.
1996-10-01
High-resolution two-dimensional gel electrophoresis (2DE) of proteins, using isoelectric focusing in the first dimension and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) in the second, was first described in 1975. In the 20 years since those publications, numerous modifications of the original method have evolved. The ISO-DALT system of 2DE is a high-throughput approach that has stood the test of time. The problem of casting many isoelectric focusing gels and SDS-PAGE slab gels (up to 20) in a reproducible manner has been solved by the use of the techniques and equipment described in this manual. The ISO-DALT system of two-dimensional gel electrophoresis originated in the late 1970s and has been modified many times to improve its high-resolution, high-throughput capabilities. This report provides the detailed procedures used with the current ISO-DALT system to prepare, run, stain, and photograph two-dimensional gels for protein analysis.
Energy Technology Data Exchange (ETDEWEB)
Xu, Lijun, E-mail: lijunxu@buaa.edu.cn; Liu, Chang; Jing, Wenyang; Cao, Zhang [School of Instrument Science and Opto-Electronic Engineering, Beihang University, Beijing 100191 (China); Ministry of Education’s Key Laboratory of Precision Opto-Mechatronics Technology, Beijing 100191 (China); Xue, Xin; Lin, Yuzhen [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China)
2016-01-15
To monitor two-dimensional (2D) distributions of temperature and H{sub 2}O mole fraction, an on-line tomography system based on tunable diode laser absorption spectroscopy (TDLAS) was developed. To the best of the authors’ knowledge, this is the first report on a multi-view TDLAS-based system for simultaneous tomographic visualization of temperature and H{sub 2}O mole fraction in real time. The system consists of two distributed feedback (DFB) laser diodes, a tomographic sensor, electronic circuits, and a computer. The central frequencies of the two DFB laser diodes are at 7444.36 cm{sup −1} (1343.3 nm) and 7185.6 cm{sup −1} (1391.67 nm), respectively. The tomographic sensor is used to generate fan-beam illumination from five views and to produce 60 ray measurements. The electronic circuits not only provide stable temperature and precise current controlling signals for the laser diodes but also can accurately sample the transmitted laser intensities and extract integrated absorbances in real time. Finally, the integrated absorbances are transferred to the computer, in which the 2D distributions of temperature and H{sub 2}O mole fraction are reconstructed by using a modified Landweber algorithm. In the experiments, the TDLAS-based tomography system was validated by using asymmetric premixed flames with fixed and time-varying equivalent ratios, respectively. The results demonstrate that the system is able to reconstruct the profiles of the 2D distributions of temperature and H{sub 2}O mole fraction of the flame and effectively capture the dynamics of the combustion process, which exhibits good potential for flame monitoring and on-line combustion diagnosis.
Jia, Dan; Chen, Xiaofei; Cao, Yan; Wu, Xunxun; Ding, Xuan; Zhang, Hai; Zhang, Chuan; Chai, Yifeng; Zhu, Zhenyu
2016-01-25
Cell membrane chromatography (CMC) is a bioaffinity chromatography technique for characterizing interactions between drugs and membrane receptors and has been widely used to screen active components from complex samples such as herbal medicines (HMs). However, it has never been applied in vivo due to its relatively high limit of detection (LOD) and the matrix interferences. In this study, a novel on-line comprehensive two-dimensional HepG2/CMC/enrich columns/high performance liquid chromatography/time-of-flight mass spectrometry system was developed to rapidly screen potential anti-hepatoma components from drug-containing serum of rats after oral administration of Radix scutellariae. A matrix interference deduction method with a home-written program in MATLAB was developed, which could successfully eliminate the interference of endogenous substances in serum. Baicalein, wogonin, chrysin, oroxylin A, neobaicalein and rivularin from Radix scutellariae extraction were significantly retained in the HepG2/CMC column. Three potential active components, wogonin, oroxylin A and neobaicalein were firstly screened from the drug-containing serum as well. The cell counting kit-8 assay demonstrated that wogonin, oroxylin A and chrysin showed high inhibitory activities in a dose-dependent manner on HepG2 cells at the concentration of 12.5-200 μM (pactive components from complex biological samples and could be applied to other biochromatography models.
Energy Technology Data Exchange (ETDEWEB)
Her, J L; Matsuda, Y H; Suga, K; Kindo, K; Takeyama, S [Institute for Solid State Physics, University of Tokyo (Japan); Berger, H [Institutes of Physics of Complex Matter, EPFL, Lausanne (Switzerland); Yang, H D [Department of Physics, Center for Nanoscience and Nanotechnology, National Sun Yat-sen University, Taiwan (China)
2009-10-28
The high-field magnetization, M(H), of Ni{sub 5}(TeO{sub 3}){sub 4}X{sub 2} (X = Br, Cl) was measured by using a pulse magnet. These compounds have a two-dimensional crystal structure and a distorted Kagome spin frustrated system which is built from the Ni{sup 2+} ions (S = 1). The Neel transition temperatures are T{sub N}approx28 and 23 K for X = Br and Cl, respectively. When T
Topological defect motifs in two-dimensional Coulomb clusters
Radzvilavičius, A; 10.1088/0953-8984/23/38/385301
2012-01-01
The most energetically favourable arrangement of low-density electrons in an infinite two-dimensional plane is the ordered triangular Wigner lattice. However, in most instances of contemporary interest one deals instead with finite clusters of strongly interacting particles localized in potential traps, for example, in complex plasmas. In the current contribution we study distribution of topological defects in two-dimensional Coulomb clusters with parabolic lateral confinement. The minima hopping algorithm based on molecular dynamics is used to efficiently locate the ground- and low-energy metastable states, and their structure is analyzed by means of the Delaunay triangulation. The size, structure and distribution of geometry-induced lattice imperfections strongly depends on the system size and the energetic state. Besides isolated disclinations and dislocations, classification of defect motifs includes defect compounds --- grain boundaries, rosette defects, vacancies and interstitial particles. Proliferatio...
Phase separation under two-dimensional Poiseuille flow.
Kiwata, H
2001-05-01
The spinodal decomposition of a two-dimensional binary fluid under Poiseuille flow is studied by numerical simulation. We investigated time dependence of domain sizes in directions parallel and perpendicular to the flow. In an effective region of the flow, the power-law growth of a characteristic length in the direction parallel to the flow changes from the diffusive regime with the growth exponent alpha=1/3 to a new regime. The scaling invariance of the growth in the perpendicular direction is destroyed after the diffusive regime. A recurrent prevalence of thick and thin domains which determines log-time periodic oscillations has not been observed in our model. The growth exponents in the infinite system under two-dimensional Poiseuille flow are obtained by the renormalization group.
Enstrophy inertial range dynamics in generalized two-dimensional turbulence
Iwayama, Takahiro; Watanabe, Takeshi
2016-07-01
We show that the transition to a k-1 spectrum in the enstrophy inertial range of generalized two-dimensional turbulence can be derived analytically using the eddy damped quasinormal Markovianized (EDQNM) closure. The governing equation for the generalized two-dimensional fluid system includes a nonlinear term with a real parameter α . This parameter controls the relationship between the stream function and generalized vorticity and the nonlocality of the dynamics. An asymptotic analysis accounting for the overwhelming dominance of nonlocal triads allows the k-1 spectrum to be derived based upon a scaling analysis. We thereby provide a detailed analytical explanation for the scaling transition that occurs in the enstrophy inertial range at α =2 in terms of the spectral dynamics of the EDQNM closure, which extends and enhances the usual phenomenological explanations.
Two-dimensional gauge theoretic supergravities
Cangemi, D.; Leblanc, M.
1994-05-01
We investigate two-dimensional supergravity theories, which can be built from a topological and gauge invariant action defined on an ordinary surface. One is the N = 1 supersymmetric extension of the Jackiw-Teitelboim model presented by Chamseddine in a superspace formalism. We complement the proof of Montano, Aoaki and Sonnenschein that this extension is topological and gauge invariant, based on the graded de Sitter algebra. Not only do the equations of motion correspond to the supergravity ones and do gauge transformations encompass local supersymmetries, but we also identify the ∫-theory with the superfield formalism action written by Chamseddine. Next, we show that the N = 1 supersymmetric extension of string-inspired two-dimensional dilaton gravity put forward by Park and Strominger cannot be written as a ∫-theory. As an alternative, we propose two topological and gauge theories that are based on a graded extension of the extended Poincaré algebra and satisfy a vanishing-curvature condition. Both models are supersymmetric extensions of the string-inspired dilaton gravity.
Two-Dimensional Theory of Scientific Representation
Directory of Open Access Journals (Sweden)
A Yaghmaie
2013-03-01
Full Text Available Scientific representation is an interesting topic for philosophers of science, many of whom have recently explored it from different points of view. There are currently two competing approaches to the issue: cognitive and non-cognitive, and each of them claims its own merits over the other. This article tries to provide a hybrid theory of scientific representation, called Two-Dimensional Theory of Scientific Representation, which has the merits of the two accounts and is free of their shortcomings. To do this, we will argue that although scientific representation needs to use the notion of intentionality, such a notion is defined and realized in a simply structural form contrary to what cognitive approach says about intentionality. After a short introduction, the second part of the paper is devoted to introducing theories of scientific representation briefly. In the third part, the structural accounts of representation will be criticized. The next step is to introduce the two-dimensional theory which involves two key components: fixing and structural fitness. It will be argued that fitness is an objective and non-intentional relation, while fixing is intentional.
Two-dimensional shape memory graphene oxide
Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G.; Yan, Wenyi; Liu, Jefferson Zhe
2016-06-01
Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices.
Electromagnetically induced two-dimensional grating assisted by incoherent pump
Energy Technology Data Exchange (ETDEWEB)
Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang, E-mail: wrg@snnu.edu.cn
2017-04-25
We propose a scheme for realizing electromagnetically induced two-dimensional grating in a double-Λ system driven simultaneously by a coherent field and an incoherent pump field. In such an atomic configuration, the absorption is suppressed owing to the incoherent pumping process and the probe can be even amplified, while the refractivity is mainly attributed to the dynamically induced coherence. With the help of a standing-wave pattern coherent field, we obtain periodically modulated refractive index without or with gain, and therefore phase grating or gain-phase grating which diffracts a probe light into high-order direction efficiently can be formed in the medium via appropriate manipulation of the system parameters. The diffraction efficiency attainable by the present gratings can be controlled by tuning the coherent field intensity or the interaction length. Hence, the two-dimensional grating can be utilized as all-optical splitter or router in optical networking and communication. - Highlights: • Two-dimensional grating is coherently induced in four-level atoms. • Phase and gain-phase gratings are obtained assisted by incoherent pump. • The diffraction power is improved due to the enhanced refraction modulation. • The gratings can be utilized as multi-channel all-optical splitter and router.
Augmented reality simulator for training in two-dimensional echocardiography.
Weidenbach, M; Wick, C; Pieper, S; Quast, K J; Fox, T; Grunst, G; Redel, D A
2000-02-01
In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to establish spatial and temporal congruence. The heart model, together with an animated ultrasound sector represents a reference scenario, which displays the currently selected two-dimensional echocardiographic cutting plane calculated from the volume data set. Modifications of the cutting plane within the echocardiographic data are transferred and visualized simultaneously and in real time within the reference scenario. The trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by an animated ultrasound probe, whose position is controlled by an electromagnetic tracking system. The tracking system is attached to a dummy transducer and placed on a plastic puppet to give a realistic impression of a two-dimensional echocardiographic examination.
Two-dimensional oxides: multifunctional materials for advanced technologies.
Pacchioni, Gianfranco
2012-08-13
The last decade has seen spectacular progress in the design, preparation, and characterization down to the atomic scale of oxide ultrathin films of few nanometers thickness grown on a different material. This has paved the way towards several sophisticated applications in advanced technologies. By playing around with the low-dimensionality of the oxide layer, which sometimes leads to truly two-dimensional systems, one can exploit new properties and functionalities that are not present in the corresponding bulk materials or thick films. In this review we provide some clues about the most recent advances in the design of these systems based on modern electronic structure theory and on their preparation and characterization with specifically developed growth techniques and analytical methods. We show how two-dimensional oxides can be used in mature technologies by providing added value to existing materials, or in new technologies based on completely new paradigms. The fields in which two-dimensional oxides are used are classified based on the properties that are exploited, chemical or physical. With respect to chemical properties we discuss use of oxide ultrathin films in catalysis, solid oxide fuel cells, gas sensors, corrosion protection, and biocompatible materials; regarding the physical properties we discuss metal-oxide field effect transistors and memristors, spintronic devices, ferroelectrics and thermoelectrics, and solar energy materials. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Energy Technology Data Exchange (ETDEWEB)
Palistrant, M. E., E-mail: mepalistrant@yandex.com; Ursu, V. A. [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of)
2013-04-15
A theory of thermodynamic properties of a spin density wave (SDW) in a quasi-two-dimensional system (with a preset impurity concentration x) is constructed. We choose an anisotropic dispersion relation for the electron energy and assume that external magnetic field H has an arbitrary direction relative to magnetic moment M{sub Q}. The system of equations defining order parameters M{sub Q}{sup z}, M{sub Q}{sup {sigma}}, M{sub z}, and M{sup {sigma}} is constructed and transformed with allowance for the Umklapp processes. Special cases when H Double-Vertical-Line M{sub Q} and H Up-Tack M{sub Q} (H{sub Z}H{sup {sigma}} = 0) are considered in detail as well as cases of weak fields H of arbitrary direction. The condition for the transition of the system to the commensurate and incommensurate states of the SDW is analyzed. The concentration dependence of magnetic transition temperature T{sub M} is calculated, and the components of the order parameter for the incommensurate phase are determined. The phase diagram (T,{approx}x) is constructed. The effect of the magnetic field on magnetic transition temperature T{sub M} is analyzed for H{sub Z}H{sup {sigma}} = 0, and longitudinal magnetic susceptibility {chi} Double-Vertical-Line is calculated; this quantity demonstrates the temperature dependence corresponding to a system with a gap for x < x{sub c} and to a gapless state for x > x{sub c}. In the immediate vicinity of the critical impurity concentration (x {approx} x{sub c}), the temperature dependence of the magnetic susceptibility acquires a local maximum. The effect of anisotropy of the electron energy spectrum on the investigated physical quantities is also analyzed.
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.
Two-dimensional photon counting imaging detector based on a Vernier position sensitive anode readout
Institute of Scientific and Technical Information of China (English)
鄢秋荣; 赵宝升; 刘永安; 杨颢; 盛立志; 韦永林
2011-01-01
A two-dimensional photon counting imaging detector based on a Vernier position sensitive anode is reported. The decode principle and design of a two-dimensional Vernier anode are introduced in detail. A photon counting imaging system was built based on a
Experimental realization of two-dimensional boron sheets.
Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui
2016-06-01
A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp(2) hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.
The problem of friction in two-dimensional relative motion
Grech, D K; Grech, Dariusz; Mazur, Zygmunt
2000-01-01
We analyse a mechanical system in two-dimensional relative motion with friction. Although the system is simple, the peculiar interplay between two kinetic friction forces and gravity leads to the wide range of admissible solutions exceeding most intuitive expectations. In particular, the strong qualitative dependence between behaviour of the system, boundary conditions and parameters involved in its description is emphasised. The problem is intended to be discussed in theoretical framework and might be of interest for physics and mechanics students as well as for physics teachers.
Topological Quantum Optics in Two-Dimensional Atomic Arrays
Perczel, J.; Borregaard, J.; Chang, D. E.; Pichler, H.; Yelin, S. F.; Zoller, P.; Lukin, M. D.
2017-07-01
We demonstrate that two-dimensional atomic emitter arrays with subwavelength spacing constitute topologically protected quantum optical systems where the photon propagation is robust against large imperfections while losses associated with free space emission are strongly suppressed. Breaking time-reversal symmetry with a magnetic field results in gapped photonic bands with nontrivial Chern numbers and topologically protected, long-lived edge states. Due to the inherent nonlinearity of constituent emitters, such systems provide a platform for exploring quantum optical analogs of interacting topological systems.
Optimal excitation of two dimensional Holmboe instabilities
Constantinou, Navid C
2010-01-01
Highly stratified shear layers are rendered unstable even at high stratifications by Holmboe instabilities when the density stratification is concentrated in a small region of the shear layer. These instabilities may cause mixing in highly stratified environments. However these instabilities occur in tongues for a limited range of parameters. We perform Generalized Stability analysis of the two dimensional perturbation dynamics of an inviscid Boussinesq stratified shear layer and show that Holmboe instabilities at high Richardson numbers can be excited by their adjoints at amplitudes that are orders of magnitude larger than by introducing initially the unstable mode itself. We also determine the optimal growth that obtains for parameters for which there is no instability. We find that there is potential for large transient growth regardless of whether the background flow is exponentially stable or not and that the characteristic structure of the Holmboe instability asymptotically emerges for parameter values ...
Phonon hydrodynamics in two-dimensional materials.
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-03-06
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.
Probabilistic Universality in two-dimensional Dynamics
Lyubich, Mikhail
2011-01-01
In this paper we continue to explore infinitely renormalizable H\\'enon maps with small Jacobian. It was shown in [CLM] that contrary to the one-dimensional intuition, the Cantor attractor of such a map is non-rigid and the conjugacy with the one-dimensional Cantor attractor is at most 1/2-H\\"older. Another formulation of this phenomenon is that the scaling structure of the H\\'enon Cantor attractor differs from its one-dimensional counterpart. However, in this paper we prove that the weight assigned by the canonical invariant measure to these bad spots tends to zero on microscopic scales. This phenomenon is called {\\it Probabilistic Universality}. It implies, in particular, that the Hausdorff dimension of the canonical measure is universal. In this way, universality and rigidity phenomena of one-dimensional dynamics assume a probabilistic nature in the two-dimensional world.
Two-dimensional position sensitive neutron detector
Indian Academy of Sciences (India)
A M Shaikh; S S Desai; A K Patra
2004-08-01
A two-dimensional position sensitive neutron detector has been developed. The detector is a 3He + Kr filled multiwire proportional counter with charge division position readout and has a sensitive area of 345 mm × 345 mm, pixel size 5 mm × 5 mm, active depth 25 mm and is designed for efficiency of 70% for 4 Å neutrons. The detector is tested with 0.5 bar 3He + 1.5 bar krypton gas mixture in active chamber and 2 bar 4He in compensating chamber. The pulse height spectrum recorded at an anode potential of 2000 V shows energy resolution of ∼ 25% for the 764 keV peak. A spatial resolution of 8 mm × 6 mm is achieved. The detector is suitable for SANS studies in the range of 0.02–0.25 Å-1.
Two-dimensional heterostructures for energy storage
Pomerantseva, Ekaterina; Gogotsi, Yury
2017-07-01
Two-dimensional (2D) materials provide slit-shaped ion diffusion channels that enable fast movement of lithium and other ions. However, electronic conductivity, the number of intercalation sites, and stability during extended cycling are also crucial for building high-performance energy storage devices. While individual 2D materials, such as graphene, show some of the required properties, none of them can offer all properties needed to maximize energy density, power density, and cycle life. Here we argue that stacking different 2D materials into heterostructured architectures opens an opportunity to construct electrodes that would combine the advantages of the individual building blocks while eliminating the associated shortcomings. We discuss characteristics of common 2D materials and provide examples of 2D heterostructured electrodes that showed new phenomena leading to superior electrochemical performance. We also consider electrode fabrication approaches and finally outline future steps to create 2D heterostructured electrodes that could greatly expand current energy storage technologies.
Rationally synthesized two-dimensional polymers.
Colson, John W; Dichtel, William R
2013-06-01
Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.
Janus Spectra in Two-Dimensional Flows
Liu, Chien-Chia; Cerbus, Rory T.; Chakraborty, Pinaki
2016-09-01
In large-scale atmospheric flows, soap-film flows, and other two-dimensional flows, the exponent of the turbulent energy spectra, α , may theoretically take either of two distinct values, 3 or 5 /3 , but measurements downstream of obstacles have invariably revealed α =3 . Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which α transitions from 3 to 5 /3 for the streamwise fluctuations but remains equal to 3 for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows.
FACE RECOGNITION USING TWO DIMENSIONAL LAPLACIAN EIGENMAP
Institute of Scientific and Technical Information of China (English)
Chen Jiangfeng; Yuan Baozong; Pei Bingnan
2008-01-01
Recently,some research efforts have shown that face images possibly reside on a nonlinear sub-manifold. Though Laplacianfaces method considered the manifold structures of the face images,it has limits to solve face recognition problem. This paper proposes a new feature extraction method,Two Dimensional Laplacian EigenMap (2DLEM),which especially considers the manifold structures of the face images,and extracts the proper features from face image matrix directly by using a linear transformation. As opposed to Laplacianfaces,2DLEM extracts features directly from 2D images without a vectorization preprocessing. To test 2DLEM and evaluate its performance,a series of ex-periments are performed on the ORL database and the Yale database. Moreover,several experiments are performed to compare the performance of three 2D methods. The experiments show that 2DLEM achieves the best performance.
Saldin, D. K.; Shneerson, V. L.; Spence, J. C. H.; Howells, M. R.; Marchesini, S.; Chapman, H. N.; Bogan, M.; Shapiro, D.; Kirian, Richard; Weierstall, U.; Schmidt, K. E.
2010-01-01
In this paper is demonstrated a complete algorithm for determining the electron density of an individual particle from diffraction patterns of many particles, randomly oriented about a single axis. The algorithm operates on angular correlations among the measured intensity distributions. We also demonstrate the ability to recover the angular correlation functions of a single particle from measured diffraction patterns.
Institute of Scientific and Technical Information of China (English)
宜晨虹; 慕青松; 苗天德
2009-01-01
The discrete element method is used to research the distribution of forces within the two-dimensional granular system under gravity. The force chains among the particles are generated according to the magnitudes of the forces. Then the simulation results are compared with the well-known q-model, a-model and experimental results obtained through the photoelastic test under the same conditions. According to the computational solution, we conclude that the simulation results are similar to the experimental results are some what different from the two probability models. In addition, we also obtained that the probability distribution of the force is very uneven. The probability of the large force decays exponentially and the distribution of the force chains takes on a fraetal character.%用离散元的方法模拟了仅有重力作用的二维颗粒系统内部力的分布情况,并根据力的大小得到颗粒之间的应力链.模拟结果与颗粒介质研究中的两个著名模型q模型和a模型作了对比,并与光弹实验的结果作了比较.对比结果表明,模拟结果与实验相似,而与两个概率模型有一定的差异.另外计算结果还表明,颗粒介质中力大小的概率分布极为不均匀,较大的力概率呈指数衰减,应力链的分布具有分形特征.
Al-Kassou, Baravan; Tzikas, Apostolos; Stock, Friederike; Neikes, Fabian; Völz, Alexander; Omran, Heyder
2017-04-20
Correct sizing of a left atrial appendage (LAA) closure system is important to avoid redeployment of the device and peri-device leaks. The aims of this study were to assess the significance of two-dimensional transoesophageal echocardiography (2D-TEE), real-time 3D transoesophageal echocardiography (RT 3D-TEE) and angiography for measuring the size of the LAA landing zone and to determine the impact on sizing an LAA closure device. Furthermore, we investigated the relevance of volume loading on LAA size. In a prospective study, 46 patients underwent 2D-TEE and RT 3D-TEE 24 hours prior to LAA closure, at the beginning of the procedure and just before the procedure after volume loading with an average of 1,035±246 ml. Angiography was performed immediately before the implantation. Maximal diameter (2.2±0.4 versus 2.3±0.4 cm; pcorrelation (R) between measurements and LAA device size was found for RT 3D-TEE-derived perimeter (R=0.97) and area (R=0.96), whereas the maximal diameter (R=0.78) measured by 2D-TEE and angiography (R=0.76) correlated less closely. Sizing based on an RT 3D-TEE-measured perimeter resulted only in 4% of undersizing the implanted device. Peri-device leaks occurred in seven cases (15%) and were associated with a lower compression of LAA devices (7±1.3% versus 14±3.2% for patients without leaks, pcorrelation to LAA closure device size than 2D-TEE or angiographic measurements.
浅谈设计型二维码在品牌识别系统中的应用%Application of Design Two-dimensional Code in Brand Recognition System
Institute of Scientific and Technical Information of China (English)
高立伟
2013-01-01
With the continuous development of image recognition technology and wireless communication technology, two-dimensional code technology has a wide range of application in the new media such as mobile phone. Creative two-dimensional code with high reorganization is significant to the improvement of enterprise's brand image the increase of consumer's attention and fancy to brand for brand design and communication. The current design of two-dimensional code in our country is made of the simple black and white squares, and it is more and more difficult to meet the increasing demand of consumer, and is difficult to make the brand stand out form the general two-dimensional code design. The paper puts forward that the new design philosophy that changing line and color, adding drawing and graphics elements for increasing the design sense of two-dimensional code and improving its reorganization and affinity, and states the necessity of the two-dimensional code with design sense and its development trend in order to promote the progress of two-dimensional code design.%随着无线通信技术、图像识别技术的不断发展，二维码技术在手机等新媒体上的应用也更为广泛，在品牌设计与传播中，充满创意、辨识度较高的二维码对提升企业品牌形象，增加消费者对于品牌的关注和喜爱具有重要意义。然而当前我国的二维码设计大多还停留在在简单的黑白格子上，越来越难以满足消费者日益增大的求新求异需求，难以让品牌在同一的二维码设计中脱颖而出，因此本文提出在传统二维码中改变线条、颜色，加入手绘、图形等元素，增加二维码的设计感，提升其辨别度和亲和度，并对发展这种有设计感的二维码的必要性及其未来发展趋势做了阐述，以期促进我国二维码设计的进步。
On numerical evaluation of two-dimensional phase integrals
DEFF Research Database (Denmark)
Lessow, H.; Rusch, W.; Schjær-Jacobsen, Hans
1975-01-01
The relative advantages of several common numerical integration algorithms used in computing two-dimensional phase integrals are evaluated.......The relative advantages of several common numerical integration algorithms used in computing two-dimensional phase integrals are evaluated....
Janus spectra in two-dimensional flows
Liu, Chien-Chia; Chakraborty, Pinaki
2016-01-01
In theory, large-scale atmospheric flows, soap-film flows and other two-dimensional flows may host two distinct types of turbulent energy spectra---in one, $\\alpha$, the spectral exponent of velocity fluctuations, equals $3$ and the fluctuations are dissipated at the small scales, and in the other, $\\alpha=5/3$ and the fluctuations are dissipated at the large scales---but measurements downstream of obstacles have invariably revealed $\\alpha = 3$. Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which $\\alpha$ has transitioned from $3$ to $5/3$ for the streamwise fluctuations but remains equal to $3$ for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows...