Conductivity of a two-dimensional guiding center plasma.
Montgomery, D.; Tappert, F.
1972-01-01
The Kubo method is used to calculate the electrical conductivity of a two-dimensional, strongly magnetized plasma. The particles interact through (logarithmic) electrostatic potentials and move with their guiding center drift velocities (Taylor-McNamara model). The thermal equilibrium dc conductivity can be evaluated analytically, but the ac conductivity involves numerical solution of a differential equation. Both conductivities fall off as the inverse first power of the magnetic field strength.
Logarithmic divergent thermal conductivity in two-dimensional nonlinear lattices.
Wang, Lei; Hu, Bambi; Li, Baowen
2012-10-01
Heat conduction in three two-dimensional (2D) momentum-conserving nonlinear lattices are numerically calculated via both nonequilibrium heat-bath and equilibrium Green-Kubo algorithms. It is expected by mainstream theories that heat conduction in such 2D lattices is divergent and the thermal conductivity κ increases with lattice length N logarithmically. Our simulations for the purely quartic lattice firmly confirm it. However, very robust finite-size effects are observed in the calculations for the other two lattices, which well explain some existing studies and imply the extreme difficulties in observing their true asymptotic behaviors with affordable computation resources.
Anisotropic electronic conduction in stacked two-dimensional titanium carbide
Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui
2015-11-01
Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.
Thermal conductivity of disordered two-dimensional binary alloys.
Zhou, Yang; Guo, Zhi-Xin; Cao, Hai-Yuan; Chen, Shi-You; Xiang, Hong-Jun; Gong, Xin-Gao
2016-10-20
Using non-equilibrium molecular dynamics simulations, we have studied the effect of disorder on the thermal conductivity of two-dimensional (2D) C1-xNx alloys. We find that the thermal conductivity not only depends on the substitution concentration of nitrogen, but also strongly depends on the disorder distribution. A general linear relationship is revealed between the thermal conductivity and the participation ratio of phonons in 2D alloys. Localization mode analysis further indicates that the thermal conductivity variation in the ordered alloys can be attributed to the number of inequivalent atoms. As for the disordered alloys, we find that the thermal conductivity variation can be described by a simple linear formula with the disorder degree and the substitution concentration. The present study suggests some general guidance for phonon manipulation and thermal engineering in low dimensional alloys.
Current fluctuations in a two dimensional model of heat conduction
Pérez-Espigares, Carlos; Garrido, Pedro L.; Hurtado, Pablo I.
2011-03-01
In this work we study numerically and analytically current fluctuations in the two-dimensional Kipnis-Marchioro-Presutti (KMP) model of heat conduction. For that purpose, we use a recently introduced algorithm which allows the direct evaluation of large deviations functions. We compare our results with predictions based on the Hydrodynamic Fluctuation Theory (HFT) of Bertini and coworkers, finding very good agreement in a wide interval of current fluctuations. We also verify the existence of a well-defined temperature profile associated to a given current fluctuation which depends exclusively on the magnitude of the current vector, not on its orientation. This confirms the recently introduced Isometric Fluctuation Relation (IFR), which results from the time-reversibility of the dynamics, and includes as a particular instance the Gallavotti-Cohen fluctuation theorem in this context but adds a completely new perspective on the high level of symmetry imposed by timereversibility on the statistics of nonequilibrium fluctuations.
Transient Topology Optimization of Two-Dimensional Elastic Wave Propagation
DEFF Research Database (Denmark)
Matzen, René; Jensen, Jakob Søndergaard; Sigmund, Ole
2008-01-01
A tapering device coupling two monomodal waveguides is designed with the topology optimization method based on transient wave propagation. The gradient-based optimization technique is applied to predict the material distribution in the tapering area such that the squared output displacement (a...
Estimating the hydraulic conductivity of two-dimensional fracture networks
Leung, C. T.; Zimmerman, R. W.
2010-12-01
Most oil and gas reservoirs, as well as most potential sites for nuclear waste disposal, are naturally fractured. In these sites, the network of fractures will provide the main path for fluid to flow through the rock mass. In many cases, the fracture density is so high as to make it impractical to model it with a discrete fracture network (DFN) approach. For such rock masses, it would be useful to have recourse to analytical, or semi-analytical, methods to estimate the macroscopic hydraulic conductivity of the fracture network. We have investigated single-phase fluid flow through stochastically generated two-dimensional fracture networks. The centres and orientations of the fractures are uniformly distributed, whereas their lengths follow either a lognormal distribution or a power law distribution. We have considered the case where the fractures in the network each have the same aperture, as well as the case where the aperture of each fracture is directly proportional to the fracture length. The discrete fracture network flow and transport simulator NAPSAC, developed by Serco (Didcot, UK), is used to establish the “true” macroscopic hydraulic conductivity of the network. We then attempt to match this conductivity using a simple estimation method that does not require extensive computation. For our calculations, fracture networks are represented as networks composed of conducting segments (bonds) between nodes. Each bond represents the region of a single fracture between two adjacent intersections with other fractures. We assume that the bonds are arranged on a kagome lattice, with some fraction of the bonds randomly missing. The conductance of each bond is then replaced with some effective conductance, Ceff, which we take to be the arithmetic mean of the individual conductances, averaged over each bond, rather than over each fracture. This is in contrast to the usual approximation used in effective medium theories, wherein the geometric mean is used. Our
Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films.
Halim, Joseph; Lukatskaya, Maria R; Cook, Kevin M; Lu, Jun; Smith, Cole R; Näslund, Lars-Åke; May, Steven J; Hultman, Lars; Gogotsi, Yury; Eklund, Per; Barsoum, Michel W
2014-04-08
Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm(2) Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films' resistivity increases with decreasing temperature and they exhibit negative magnetoresistance-both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.
Numerical modeling of transient two-dimensional viscoelastic waves
Lombard, Bruno
2010-01-01
This paper deals with the numerical modeling of transient mechanical waves in linear viscoelastic solids. Dissipation mechanisms are described using the Zener model. No time convolutions are required thanks to the introduction of memory variables that satisfy local-in-time differential equations. By appropriately choosing the Zener parameters, it is possible to accurately describe a large range of materials, such as solids with constant quality factors. The evolution equations satisfied by the velocity, the stress, and the memory variables are written in the form of a first-order system of PDEs with a source term. This system is solved by splitting it into two parts: the propagative part is discretized explicitly, using a fourth-order ADER scheme on a Cartesian grid, and the diffusive part is then solved exactly. Jump conditions along the interfaces are discretized by applying an immersed interface method. Numerical experiments of wave propagation in viscoelastic and fluid media show the efficiency of this nu...
Two-Dimensional Mesoscale-Ordered Conducting Polymers
Liu, Shaohua; Zhang, Jian; Dong, Renhao; Gordiichuk, Pavlo; Zhang, Tao; Zhuang, Xiaodong; Mai, Yiyong; Liu, Feng; Herrmann, Andreas; Feng, Xinliang
2016-01-01
Despite the availability of numerous two-dimensional (2D) materials with structural ordering at the atomic or molecular level, direct construction of mesoscale-ordered superstructures within a 2D monolayer remains an enormous challenge. Here, we report the synergic manipulation of two types of assem
Two-Dimensional Mesoscale-Ordered Conducting Polymers
Liu, Shaohua; Zhang, Jian; Dong, Renhao; Gordiichuk, Pavlo; Zhang, Tao; Zhuang, Xiaodong; Mai, Yiyong; Liu, Feng; Herrmann, Andreas; Feng, Xinliang
2016-01-01
Despite the availability of numerous two-dimensional (2D) materials with structural ordering at the atomic or molecular level, direct construction of mesoscale-ordered superstructures within a 2D monolayer remains an enormous challenge. Here, we report the synergic manipulation of two types of
DEFF Research Database (Denmark)
Rode, Carsten
1998-01-01
Analytical theory of transient heat conduction.Fourier's law. General heat conducation equation. Thermal diffusivity. Biot and Fourier numbers. Lumped analysis and time constant. Semi-infinite body: fixed surface temperature, convective heat transfer at the surface, or constant surface heat flux...
Two Dimensional Steady State Eddy Current Analysis of a Spinning Conducting Cylinder
2017-03-09
UNCLASSIFIED UNCLASSIFIED AD-E403 855 Technical Report ARMET-TR-16045 TWO-DIMENSIONAL STEADY-STATE EDDY CURRENT ANALYSIS OF A ...any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN...August 2014 4. TITLE AND SUBTITLE TWO-DIMENSIONAL STEADY-STATE EDDY CURRENT ANALYSIS OF A SPINNING CONDUCTING CYLINDER 5a. CONTRACT NUMBER 5b
Full two-dimensional transient solutions of electrothermal aircraft blade deicing
Masiulaniec, K. C.; Keith, T. G., Jr.; Dewitt, K. J.; Leffel, K. L.
1985-01-01
Two finite difference methods are presented for the analysis of transient, two-dimensional responses of an electrothermal de-icer pad of an aircraft wing or blade with attached variable ice layer thickness. Both models employ a Crank-Nicholson iterative scheme, and use an enthalpy formulation to handle the phase change in the ice layer. The first technique makes use of a 'staircase' approach, fitting the irregular ice boundary with square computational cells. The second technique uses a body fitted coordinate transform, and maps the exact shape of the irregular boundary into a rectangular body, with uniformally square computational cells. The numerical solution takes place in the transformed plane. Initial results accounting for variable ice layer thickness are presented. Details of planned de-icing tests at NASA-Lewis, which will provide empirical verification for the above two methods, are also presented.
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.
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.
Transient two-dimensional IR spectrometer for probing nanosecond temperature-jump kinetics.
Chung, Hoi Sung; Khalil, Munira; Smith, Adam W; Tokmakoff, Andrei
2007-06-01
We have developed a Fourier transform two-dimensional infrared (2D IR) spectrometer to probe chemical reactions and biophysical processes triggered by a nanosecond temperature jump (T jump). The technical challenges for such a spectrometer involve (1) synchronization of a nanosecond T-jump laser and femtosecond laser system, (2) overcoming the decreased signal-to-noise ratio from low repetition rate data acquisition, and (3) performing an interferometric measurement through a sample with a density and index of refraction that varies with time delay after the T jump. The first challenge was overcome by synchronizing the two lasers to a clock derived from the Ti:sapphire oscillator, leading to timing accuracy of 2 ns for delays up to 50 ms. The data collection time is reduced by using undersampling with the improved signal-to-noise ratio obtained from a balanced detection scheme with a dual stripe array detector. Transient dispersed vibrational echo and 2D IR spectroscopy are applied to N-methylacetamide and ubiquitin, as examples, and the spectral responses by a temperature elevation and by structural changes of the protein are compared. The synchronization of 2D IR spectroscopy with a nanosecond temperature jump without losing its sensitivity at a low repetition rate opens a new applicability of the nonlinear spectroscopy to probe a variety of molecular structure changes induced by a nanosecond perturbation.
PRONTO 2D: A two-dimensional transient solid dynamics program
Energy Technology Data Exchange (ETDEWEB)
Taylor, L.M.; Flanagan, D.P.
1987-03-01
PRONTO 2D is a two-dimensional transient solid dynamics code for analyzing large deformations of highly nonlinear materials subjected to extremely high strain rates. This Lagrangian finite element program uses an explicit time integration operator to integrate the equations of motion. Four node uniform strain quadrilateral elements are used in the finite element formulation. A number of new numerical algorithms which have been developed for the code are described in this report. An adaptive time step control algorithm is described which greatly improves stability as well as performance in plasticity problems. A robust hourglass control scheme which eliminates hourglass distortions without disturbing the finite element solution is included. All constitutive models in PRONTO are cast in an unrotated configuration defined using the rotation determined from the polar decomposition of the deformation gradient. An accurate incremental algorithm was developed to determine this rotation and is described in detail. A robust contact algorithm was developed which allows for the impact and interaction of deforming contact surfaces of quite general geometry. A number of numerical examples are presented to demonstrate the utility of these algorithms. 41 refs., 51 figs., 5 tabs.
Crowdy, Darren
2015-06-01
A one parameter family of analytical solutions for the equilibrium shapes of two-dimensional charged conducting droplets on a substrate with 90° contact angle is presented. The solutions exhibit the tendency to dewet at the droplet centre as the electrostatic stress increases. Such electrostatic deformations are believed to underlie the recently observed stick-slip dynamics of nanodroplets on substrates. Our theoretical results complement a number of other recent analytical and numerical studies of this phenomenon.
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.
Institute of Scientific and Technical Information of China (English)
WANG Ru-Zhi; YAN Xiao-Hong
2000-01-01
By developing a transfer-matrix method, the resonant peaks splitting of ballistic conductance are investigated into the two-dimensional electron gas system with both electric and magnetic modulations of nanoscale periods. It is found that there exists the n-fold resonant peak splitting for ballistic conductance through n perpendicular magnetic barriers to n electric barriers. With a combination of m magnetic barriers and n electric barriers by increasing the amplitude of electric field, the folds of the splitting would shift from m － 1 to n － 1.
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.
Parameter estimation in heat conduction using a two-dimensional inverse analysis
Mohebbi, Farzad; Sellier, Mathieu
2016-07-01
This article is concerned with a two-dimensional inverse steady-state heat conduction problem. The aim of this study is to estimate the thermal conductivity, the heat transfer coefficient, and the heat flux in irregular bodies (both separately and simultaneously) using a two-dimensional inverse analysis. The numerical procedure consists of an elliptic grid generation technique to generate a mesh over the irregular body and solve for the heat conduction equation. This article describes a novel sensitivity analysis scheme to compute the sensitivity of the temperatures to variation of the thermal conductivity, the heat transfer coefficient, and the heat flux. This sensitivity analysis scheme allows for the solution of inverse problem without requiring solution of adjoint equation even for a large number of unknown variables. The conjugate gradient method (CGM) is used to minimize the difference between the computed temperature on part of the boundary and the simulated measured temperature distribution. The obtained results reveal that the proposed algorithm is very accurate and efficient.
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.
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.
Fan, Zhi-Qiang; Chen, Ke-Qiu
2014-08-07
Incorporating the characteristics of the single-layer graphene nanoribbon and the polyaniline molecule, we theoretically design a two-dimensional molecular device and investigate its transport properties by applying nonequilibrium Green's functions in combination with density-functional theory. The calculated results reveal that the arrangements of frontier molecular orbitals and the energy gap between the HOMO and the LUMO of an isolated polyaniline molecule are different between its two isolable states: full reduced leucoemeraldine base and full oxidized pernigraniline base. When a polyaniline molecule connects to two graphene nanoribbons as a two-dimensional molecular device, the conductance of its full oxidized pernigraniline base is much higher than the conductance of its full reduced leucoemeraldine base. The switch ratios of two bases' currents almost maintain a constant value before 0.8 V. In other word, the conductance switch behavior in our device is stable in a big bias region which makes it have a broader application in future logic and memory devices.
Zero-differential conductance of two-dimensional electrons in crossed electric and magnetic fields
Bykov, A. A.; Byrnes, Sean; Dietrich, Scott; Vitkalov, Sergey; Marchishin, I. V.; Dmitriev, D. V.
2013-02-01
An electronic state with zero-differential conductance is found in nonlinear response to an electric field E applied to two dimensional Corbino discs of highly mobile carriers placed in quantizing magnetic fields. The state occurs above a critical electric field E>Eth at low temperatures and is accompanied by an abrupt dip in the differential conductance. The proposed model considers a local instability of the electric field E as the origin of the observed phenomenon. Comparison between the observed electronic state and the state with zero differential resistance, occurring in Hall bar geometry, indicates that the nonlinear response of edge states and/or skipping orbits is not essential in the studied samples. The result confirms that quantal heating is the dominant nonlinear mechanism leading to electronic states with both zero differential resistance and conductance.
Drude Weight,Optical Conductivity of Two-Dimensional Hubbard Model at Half Filling
Institute of Scientific and Technical Information of China (English)
XU Lei; ZHANG Jun
2008-01-01
We study the Drude weight D and optical conductivity of the two-dimensional (2D) Hubbard model at half filling with staggered magnetic flux (SMF).When SMF being introduced,the hopping integrals are modulated by the magnetic flux.The optical sum rule,which is related to the mean kinetic energy of band electrons,is evaluated for this 2D Hubbard Hamiltonian.Our present result gives the dependence of the kinetic energy,D and the optical conductivity on SMF and U.At half filling D vanishes exponentially with system size.We also find in the frequency dependence of the optical conductivity,there is &function peak at ω≈2|m|U and the incoherent excitations begin to present themselves extended to a higher energy region.
Alzahrani, Faris S.; Abbas, Ibrahim A.
2016-08-01
The present paper is devoted to the study of a two-dimensional thermal shock problem with weak, normal and strong conductivity using the eigenvalue approach. The governing equations are taken in the context of the new consideration of heat conduction with fractional order generalized thermoelasticity with the Lord-Shulman model (LS model). The bounding surface of the half-space is taken to be traction free and subjected to a time-dependent thermal shock. The Laplace and the exponential Fourier transform techniques are used to obtain the analytical solutions in the transformed domain by the eigenvalue approach. Numerical computations have been done for copper-like material for weak, normal and strong conductivity and the results are presented graphically to estimate the effects of the fractional order parameter.
Yogeshwar, P.; Tezkan, B.
2017-01-01
Thick sedimentary sequences are deposited in the central area of the Azraq basin in Jordan consisting mostly of hyper-saline clay and various evaporates. These sediment successions form the 10 km × 10 km large Azraq mudflat and are promising archives for a palaeoclimatical reconstruction. Besides palaeoclimatical research, the Azraq area is of tremendous importance to Jordan due to groundwater and mineral resources. The heavy exploitation of groundwater has lead to a drastic decline of the water table and drying out of the former Azraq Oasis. Two 7 and 5 km long transects were investigated from the periphery of the mudflat across its center using a total of 150 central loop transient electromagnetic (TEM) soundings. The scope of the survey was to detect the thickness of sedimentary deposits along both transects and to provide a basis for future drilling activities. We derive a two-dimensional model which can explain the TEM data for all soundings along each profile simultaneously. Previously uncertain depths of geological boundaries were determined along both transects. Particularly the thickness of the deposited mudflat sediments was identified and ranges from 40 m towards the periphery down to approximately 130 m at the deepest location. Besides that, the depth and lateral extent of a buried basalt layer was identified. In the basin center the groundwater is hyper-saline. The lateral extent of the saline water body was determined precisely along both transects. In order to investigate the detectability of the basement below the high conductive mudflat sediments an elaborate two-dimensional modeling study was performed. Both, the resistivity and depth of the basement were varied systematically. The basement resistivity cannot be determined precisely in most zones and may range roughly between 1 and 100 Ωm without deteriorating the misfit. In contrast to that, the depth down to the basement is detected accurately in most zones and along both transects. Varying
DEFF Research Database (Denmark)
Kjærgaard, Morten; Nichele, F; Suominen, Henri Juhani;
2016-01-01
Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards...... topological matter is by coupling a 2D electron gas with strong spin-orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al......, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e(2)/h...
Numerical experiment of thermal conductivity in two-dimensional Yukawa liquids
Energy Technology Data Exchange (ETDEWEB)
Shahzad, Aamir, E-mail: aamirshahzad-8@hotmail.com [Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education (MOE), Xi' an Jiaotong University, Xi' an 710049 (China); Department of Physics, Government College University Faisalabad (GCUF), Allama Iqbal Road, Faisalabad 38000 (Pakistan); He, Mao-Gang, E-mail: mghe@mail.xjtu.edu.cn [Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education (MOE), Xi' an Jiaotong University, Xi' an 710049 (China)
2015-12-15
A newly improved homogenous nonequilibrium molecular dynamics simulation (HNEMDS) method, proposed by the Evans, has been used to compute the thermal conductivity of two-dimensional (2D) strongly coupled complex (dusty) plasma liquids (SCCDPLs), for the first time. The effects of equilibrium external field strength along with different system sizes and plasma states (Γ, κ) on the thermal conductivity of SCCDPLs have been calculated using an enhanced HNEMDS method. A simple analytical temperature representation of Yukawa 2D thermal conductivity with appropriate normalized frequencies (plasma and Einstein) has also been calculated. The new HNEMDS algorithm shows that the present method provides more accurate results with fast convergence and small size effects over a wide range of plasma states. The presented thermal conductivity obtained from HNEMDS method is found to be in very good agreement with that obtained through the previously known numerical simulations and experimental results for 2D Yukawa liquids (SCCDPLs) and with the three-dimensional nonequilibrium molecular dynamics simulation (MDS) and equilibrium MDS calculations. It is shown that the HNEMDS algorithm is a powerful tool, making the calculations very efficient and can be used to predict the thermal conductivity in 2D Yukawa liquid systems.
CHAOS-REGULARIZATION HYBRID ALGORITHM FOR NONLINEAR TWO-DIMENSIONAL INVERSE HEAT CONDUCTION PROBLEM
Institute of Scientific and Technical Information of China (English)
王登刚; 刘迎曦; 李守巨
2002-01-01
A numerical model of nonlinear two-dimensional steady inverse heat conduction problem was established considering the thermal conductivity changing with temperature.Combining the chaos optimization algorithm with the gradient regularization method, a chaos-regularization hybrid algorithm was proposed to solve the established numerical model.The hybrid algorithm can give attention to both the advantages of chaotic optimization algorithm and those of gradient regularization method. The chaos optimization algorithm was used to help the gradient regalarization method to escape from local optima in the hybrid algorithm. Under the assumption of temperature-dependent thermal conductivity changing with temperature in linear rule, the thermal conductivity and the linear rule were estimated by using the present method with the aid of boundary temperature measurements. Numerical simulation results show that good estimation on the thermal conductivity and the linear function can be obtained with arbitrary initial guess values, and that the present hybrid algorithm is much more efficient than conventional genetic algorithm and chaos optimization algorithm.
Two-dimensional nonlinear nonequilibrium kinetic theory under steady heat conduction.
Hyeon-Deuk, Kim
2005-04-01
The two-dimensional steady-state Boltzmann equation for hard-disk molecules in the presence of a temperature gradient has been solved explicitly to second order in density and the temperature gradient. The two-dimensional equation of state and some physical quantities are calculated from it and compared with those for the two-dimensional steady-state Bhatnagar-Gross-Krook equation and information theory. We have found that the same kind of qualitative differences as the three-dimensional case among these theories still appear in the two-dimensional case.
Valence and conduction band structure of the quasi-two-dimensional semiconductor Sn S2
Racke, David A.; Neupane, Mahesh R.; Monti, Oliver L. A.
2016-02-01
We present the momentum-resolved photoemission spectroscopy of both the valence and the conduction band region in the quasi-two-dimensional van der Waals-layered indirect band gap semiconductor Sn S2 . Using a combination of angle-resolved ultraviolet photoemission and angle-resolved two-photon photoemission (AR-2PPE) spectroscopy, we characterize the band structure of bulk Sn S2 . Comparison with density functional theory calculations shows excellent quantitative agreement in the valence band region and reveals several localized bands that likely originate from defects such as sulfur vacancies. Evidence for a moderate density of defects is also observed by AR-2PPE in the conduction band region, leading to localized bands not present in the computational results. The energetic structure and dispersion of the conduction bands is captured well by the computational treatment, with some quantitative discrepancies remaining. Our results provide a broader understanding of the electronic structure of Sn S2 in particular and van der Waals-layered semiconductors in general.
Lee, Myoung-Jae; Ahn, Ji-Hoon; Sung, Ji Ho; Heo, Hoseok; Jeon, Seong Gi; Lee, Woo; Song, Jae Yong; Hong, Ki-Ha; Choi, Byeongdae; Lee, Sung-Hoon; Jo, Moon-Ho
2016-06-21
In general, in thermoelectric materials the electrical conductivity σ and thermal conductivity κ are related and thus cannot be controlled independently. Previously, to maximize the thermoelectric figure of merit in state-of-the-art materials, differences in relative scaling between σ and κ as dimensions are reduced to approach the nanoscale were utilized. Here we present an approach to thermoelectric materials using tin disulfide, SnS2, nanosheets that demonstrated a negative correlation between σ and κ. In other words, as the thickness of SnS2 decreased, σ increased whereas κ decreased. This approach leads to a thermoelectric figure of merit increase to 0.13 at 300 K, a factor ∼1,000 times greater than previously reported bulk single-crystal SnS2. The Seebeck coefficient obtained for our two-dimensional SnS2 nanosheets was 34.7 mV K(-1) for 16-nm-thick samples at 300 K.
Lu, Zhicheng; Liu, Chen; Han, Heyou
2015-01-01
Two-dimensional (2D) colloidal crystals of polystyrene (PS) particles were used as a structure-controlling template to fabricate conductive Au films with an ordered array of nanoholes. The fabrication mainly involved the functionalization of the supporting substrate with polyelectrolyte (PE) functional layers, self-assembly of Au nanoparticles, and electroless deposition of gold. The self-assembly of Au nanoparticles and electroless deposition of gold were macroscopically monitored using ultraviolet-visible (UV-vis) spectroscopy based on the changes in both the extinction spectra of Au nanoparticles and the optical responses of ordered arrays of PS particles. By scanning electron microscopy (SEM) characterization, it was found that Au nanoparticles were assembled into a film structure with orderly dispersed nanoholes and the deposition of gold was confined to the preformed Au nanoparticle films. During the formation of Au films, PE layer structure, Au nanoparticle size and heating treatment applied to the PS template could influence the structures of conductive porous Au films such as the hole diameter, film thickness, and hole diameter/wall thickness ratio (D/W). In addition, this paper also described electrochemical cyclic voltammetry (CV) employed to demonstrate the porosity of the ultimate Au films.
Disparate Strain Dependent Thermal Conductivity of Two-dimensional Penta-Structures.
Liu, Huake; Qin, Guangzhao; Lin, Yuan; Hu, Ming
2016-06-08
Two-dimensional (2D) carbon allotrope called penta-graphene was recently proposed from first-principles calculations and various similar penta-structures emerged. Despite significant effort having been dedicated to electronic structures and mechanical properties, little research has been focused on thermal transport in penta-structures. Motivated by this, we performed a comparative study of thermal transport properties of three representative pentagonal structures, namely penta-graphene, penta-SiC2, and penta-SiN2, by solving the phonon Boltzmann transport equation with interatomic force constants extracted from first-principles calculations. Unexpectedly, the thermal conductivity of the three penta-structures exhibits diverse strain dependence, despite their very similar geometry structures. While the thermal conductivity of penta-graphene exhibits standard monotonic reduction by stretching, penta-SiC2 possesses an unusual nonmonotonic up-and-down behavior. More interestingly, the thermal conductivity of penta-SiN2 has 1 order of magnitude enhancement due to the strain induced buckled to planar structure transition. The mechanism governing the diverse strain dependence is identified as the competition between the change of phonon group velocity and phonon lifetime of acoustic phonon modes with combined effect from the unique structure transition for penta-SiN2. The disparate thermal transport behavior is further correlated to the fundamentally different bonding nature in the atomic structures with solid evidence from the distribution of deformation charge density and more in-depth molecular orbital analysis. The reported giant and robust tunability of thermal conductivity may inspire intensive research on other derivatives of penta-structures as potential materials for emerging nanoelectronic devices. The fundamental physics understood from this study also solidifies the strategy to engineer thermal transport properties of broad 2D materials by simple mechanical
Spin Hall conductivity in the impure two-dimensional Rashba s-wave superconductor
Biderang, M.; Yavari, H.
2016-06-01
Based on the Kubo formula approach, the spin Hall conductivity (SHC) of a two-dimensional (2D) Rashba s-wave superconductor in the presence of nonmagnetic impurities is calculated. We will show that by increasing the superconducting gap, the SHC decreases monotonically to zero, while by decreasing the concentration of impurities at zero gap, the SHC closes to the clean limit universal value - e/8 π. As a function of the impurity relaxation rate τ at Tc = 0.1 and γ = 0.01 (γ is the spin-orbit coupling in unit of eV · m), we will show that in the dirty limit (τ → 0) the SHC vanishes, and by increasing the relaxation time (τ → ∞) the SHC depends on the value of superconducting gap (Δ = 1.76Tc√{ 1 -T/Tc }), is changed from zero for full gap to -e/8 π in zero gap. At low temperatures, the SHC goes to zero exponentially and near the critical temperature depending on the concentration of the scattering centers, the SHC will tend to the value of normal state. We will also show that the SHC is independent of spin-orbit coupling (γ) in the clean limit.
Kjaergaard, M.; Nichele, F.; Suominen, H. J.; Nowak, M. P.; Wimmer, M.; Akhmerov, A. R.; Folk, J. A.; Flensberg, K.; Shabani, J.; Palmstrøm, C. J.; Marcus, C. M.
2016-01-01
Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards topological matter is by coupling a 2D electron gas with strong spin–orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e2/h, consistent with theory. The hard-gap semiconductor–superconductor system demonstrated here is amenable to top-down processing and provides a new avenue towards low-dissipation electronics and topological quantum systems. PMID:27682268
Conductive two-dimensional titanium carbide `clay' with high volumetric capacitance
Ghidiu, Michael; Lukatskaya, Maria R.; Zhao, Meng-Qiang; Gogotsi, Yury; Barsoum, Michel W.
2014-12-01
Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors--in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the `MXene' family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a `MAX' phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide `clay' have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.
Conductive two-dimensional titanium carbide 'clay' with high volumetric capacitance.
Ghidiu, Michael; Lukatskaya, Maria R; Zhao, Meng-Qiang; Gogotsi, Yury; Barsoum, Michel W
2014-12-04
Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors--in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the 'MXene' family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a 'MAX' phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide 'clay' have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.
Directory of Open Access Journals (Sweden)
Jun Takeda
2010-04-01
Full Text Available In this review, we demonstrate a real-time time-frequency two-dimensional (2D pump-probe imaging spectroscopy implemented on a single shot basis applicable to excited-state dynamics in solid-state organic and biological materials. Using this technique, we could successfully map ultrafast time-frequency 2D transient absorption signals of β-carotene in solid films with wide temporal and spectral ranges having very short accumulation time of 20 ms per unit frame. The results obtained indicate the high potential of this technique as a powerful and unique spectroscopic tool to observe ultrafast excited-state dynamics of organic and biological materials in solid-state, which undergo rapid photodegradation.
Tournier, Jean-Michel; El-Genk, Mohamed S.
1995-01-01
This report describes the user's manual for 'HPTAM,' a two-dimensional Heat Pipe Transient Analysis Model. HPTAM is described in detail in the UNM-ISNPS-3-1995 report which accompanies the present manual. The model offers a menu that lists a number of working fluids and wall and wick materials from which the user can choose. HPTAM is capable of simulating the startup of heat pipes from either a fully-thawed or frozen condition of the working fluid in the wick structure. The manual includes instructions for installing and running HPTAM on either a UNIX, MS-DOS or VMS operating system. Samples for input and output files are also provided to help the user with the code.
Patterning two-dimensional free-standing surfaces with mesoporous conducting polymers
Liu, Shaohua; Gordiichuk, Pavlo; Wu, Zhong-Shuai; Liu, Zhaoyang; Wei, Wei; Wagner, Manfred; Mohamed-Noriega, Nasser; Wu, Dongqing; Mai, Yiyong; Herrmann, Andreas; Müllen, Klaus; Feng, Xinliang
2015-01-01
The ability to pattern functional moieties with well-defined architectures is highly important in material science, nanotechnology and bioengineering. Although two-dimensional surfaces can serve as attractive platforms, direct patterning them in solution with regular arrays remains a major challenge
Tournier, Jean-Michel; El-Genk, Mohamed S.
1995-01-01
A two-dimensional Heat Pipe Transient Analysis Model, 'HPTAM,' was developed to simulate the transient operation of fully-thawed heat pipes and the startup of heat pipes from a frozen state. The model incorporates: (a) sublimation and resolidification of working fluid; (b) melting and freezing of the working fluid in the porous wick; (c) evaporation of thawed working fluid and condensation as a thin liquid film on a frozen substrate; (d) free-molecule, transition, and continuum vapor flow regimes, using the Dusty Gas Model; (e) liquid flow and heat transfer in the porous wick; and (f) thermal and hydrodynamic couplings of phases at their respective interfaces. HPTAM predicts the radius of curvature of the liquid meniscus at the liquid-vapor interface and the radial location of the working fluid level (liquid or solid) in the wick. It also includes the transverse momentum jump condition (capillary relationship of Pascal) at the liquid-vapor interface and geometrically relates the radius of curvature of the liquid meniscus to the volume fraction of vapor in the wick. The present model predicts the capillary limit and partial liquid recess (dryout) in the evaporator wick, and incorporates a liquid pooling submodel, which simulates accumulation of the excess liquid in the vapor core at the condenser end.
Two-dimensional superconductivity of SmFeAsO0.85 single crystals: A fluctuation-conductivity study
Lee, Hyun-Sook; Park, Jae-Hyun; Lee, Jae-Yeap; Kim, Ju-Young; Sung, Nak-Heon; Cho, B. K.; Lee, Hu-Jong
2010-12-01
Temperature dependence of the in-plane conductance of a SmFeAsO0.85 single crystal is measured in c-axis and planar magnetic fields up to 7 T. The conductivity near the superconducting transition is well described by two-dimensional (2D) thermal-fluctuation theory. The 2D superconductivity arises as the c-axis coherence length is much shorter than the spacing between neighboring FeAs layers.
Energy Technology Data Exchange (ETDEWEB)
Eaton, R.R.; Hopkins, P.L.
1992-08-01
LLUVIA-II is a program designed for the efficient solution of two- dimensional transient flow of liquid water through partially saturated, porous media. The code solves Richards equation using the method-of-lines procedure. This document describes the solution procedure employed, input data structure, output, and code verification.
Proskuryakov, Y. Y.; Savchenko, A. K.; Safonov, S. S.; Pepper, M; Simmons, M.Y.; Ritchie, D. A.
2001-01-01
On a high mobility two-dimensional hole gas (2DHG) in a GaAs/GaAlAs heterostructure we study the interaction correction to the Drude conductivity in the ballistic regime, $k_BT\\tau /\\hbar $ $>1$. It is shown that the 'metallic' behaviour of the resistivity ($d\\rho /dT>0$) of the low-density 2DHG is caused by hole-hole interaction effect in this regime. We find that the temperature dependence of the conductivity and the parallel-field magnetoresistance are in agreement with this description, a...
Energy Technology Data Exchange (ETDEWEB)
Wohlthat, Soeren; Reimers, Jeffrey R [School of Chemistry, The University of Sydney, Sydney, NSW 2006 (Australia); Pauly, Fabian [Institut fuer Theoretische Festkoerperphysik and DFG-Center for Functional Nanostructures, Universitaet Karlsruhe, 76128 Karlsruhe (Germany)], E-mail: reimers@chem.usyd.edu.au
2008-07-23
The conduction properties of phenanthroline-terminated, polycyclic extended {pi}-conjugated molecular wires are investigated using density functional theory (DFT) in combination with Green's function techniques and group theory. While these molecules could possibly be thought of as accessible graphene-like fragments, they are calculated to conduct poorly. The decay constant for their exponential decrease of conductance with length is in excess of 0.6 A{sup -1} for the addition of internal fused quinoxaline groups and in excess of 0.9 A{sup -1} for the addition of internal pyrazine-fused pyrene groups. Furthermore, while the bidentate phenanthroline connectors adhere strongly to gold, they are sometimes predicted to be less conductive than related monodentate connectors. Careful design is thus required for any graphene-like extended {pi}-system intended for single-molecule conduction applications.
Negative differential conductance in two-dimensional C-functionalized boronitrene
Obodo, J T
2015-09-10
It recently has been demonstrated that the large band gap of boronitrene can be significantly reduced by C functionalization. We show that specific defect configurations even can result in metallicity, raising interest in the material for electronic applications. We thus study the transport properties of C-functionalized boronitrene using the non-equilibrium Green\\'s function formalism. We investigate various zigzag and armchair defect configurations, spanning wide band gap semiconducting to metallic states. Unusual I–V characteristics are found and explained in terms of the energy and bias-dependent transmission coefficient and wavefunction. In particular, we demonstrate negative differential conductance with high peak-to-valley ratios, depending on the details of the substitutional doping, and identify the finite bias effects that are responsible for this behavior.
Two-dimensional nonstationary flow of a conducting fluid, induced by a rotating magnetic field
Energy Technology Data Exchange (ETDEWEB)
Kapusta, A.B.
1977-07-01
An examination is made of a full induction problem on the planar movement of a conducting fluid in a rotating magnetic field. The solution to this problem is sought by the method of degradation into Fourier series by harmonics of the rotating field. The initial system of partial differential equations is reduced to the system 2+1 of normal differential equations that bind the amplitudes of function harmonics and electrical vector potential. A solution to the problem for small anti ..omega.. was found with an accuracy up to the second approximation. The unsteadiness of flow was found to be manifested in a form of induced cross-sectional waves, traveling along the stream tubes of this flow at a speed that is equal to the phase velocity of the magnetic field. The appearance of wave effects is explained by considerations of symmetry. 5 references, 1 figure.
Proskuryakov, Y Y; Savchenko, A K; Safonov, S S; Pepper, M; Simmons, M Y; Ritchie, D A
2002-08-12
On a high-mobility two-dimensional hole gas (2DHG) in a GaAs/GaAlAs heterostructure we study the interaction correction to the Drude conductivity in the ballistic regime, k(B)Ttau/ variant Planck's over 2pi >1. It is shown that the "metallic" behavior of the resistivity (drho/dT>0) of the low-density 2DHG is caused by the hole-hole interaction effect in this regime. We find that the temperature dependence of the conductivity and the parallel-field magnetoresistance are in agreement with this description, and determine the Fermi-liquid interaction constant Fsigma0 which controls the sign of drho/dT.
Bachher, M.; Sarkar, N.
2016-11-01
An electromagneto-thermoelastic coupled problem for a homogeneous, isotropic, thermally and electrically conducting half-space solid whose surface is subjected to a thermal shock is considered in two-dimensional space. The equations of the theory of generalized electromagneto-thermoelasticity with fractional derivative heat transfer allowing the second sound effects are considered. An initial magnetic field acts parallel to the plane boundary of the half-space. The normal mode analysis and the eigenvalue approach techniques are used to solve the resulting nondimensional coupled field equations for the three theories. Numerical results for the temperature, displacements and thermal stresses distributions are presented graphically and discussed. A comparison is made with the results obtained in the presence and absence of the magnetic field.
Benmansour, Samia; Abhervé, Alexandre; Gómez-Claramunt, Patricia; Vallés-García, Cristina; Gómez-García, Carlos J
2017-08-09
We report the synthesis, magnetic properties, electrical conductivity, and delamination into thin nanosheets of two anilato-based Fe(II)/Fe(III) mixed-valence two-dimensional metal-organic frameworks (MOFs). Compounds [(H3O)(H2O)(phenazine)3][Fe(II)Fe(III)(C6O4X2)3]·12H2O [X = Cl (1) and Br (2)] present a honeycomb layered structure with an eclipsed packing that generates hexagonal channels containing the water molecules. Both compounds show ferrimagnetic ordering at ca. 2 K coexisting with electrical conductivity (with room temperature conductivities of 0.03 and 0.003 S/cm). Changing the X group from Cl to Br leads to a decrease in the ordering temperature and room temperature conductivity that is correlated with the decrease of the electronegativity of X. Despite the ionic charge of the anilato-based layers, these MOFs can be easily delaminated in thin nanosheets with the thickness of a few monolayers.
Ostroumov, Evgeny E; Mulvaney, Rachel M; Anna, Jessica M; Cogdell, Richard J; Scholes, Gregory D
2013-09-26
Excited state dynamics in LH2 complexes of two purple bacterial species were studied by broad-band two-dimensional electronic spectroscopy. The optical response was measured in the 500-600 nm spectral region on the 0-400 fs time scale. Global target analysis of two-dimensional (2D) transient spectra revealed the main energy transfer pathways between carotenoid S2, 1Bu(-) and S1 states and bacteriochlorophyll Qx state. Global analysis ascertained the evolutionary and vibration-associated spectra, which also indicated the presence of a higher-lying vibrational level in the carotenoid S1 state. The estimation of the spectral overlap between the 1Bu(-) state and the Qx state indicated a significant contribution of the 1Bu(-) state to the overall S2-to-Qx excitation energy transfer.
Kiefer, Thomas; Villanueva, Guillermo; Brugger, Jürgen
2009-08-01
In this study we investigate electrical conduction in finite rectangular random resistor networks in quasione and two dimensions far away from the percolation threshold p(c) by the use of a bond percolation model. Various topologies such as parallel linear chains in one dimension, as well as square and triangular lattices in two dimensions, are compared as a function of the geometrical aspect ratio. In particular we propose a linear approximation for conduction in two-dimensional systems far from p(c), which is useful for engineering purposes. We find that the same scaling function, which can be used for finite-size scaling of percolation thresholds, also applies to describe conduction away from p(c). This is in contrast to the quasi-one-dimensional case, which is highly nonlinear. The qualitative analysis of the range within which the linear approximation is legitimate is given. A brief link to real applications is made by taking into account a statistical distribution of the resistors in the network. Our results are of potential interest in fields such as nanostructured or composite materials and sensing applications.
Directory of Open Access Journals (Sweden)
Taeseong Woo
2017-05-01
Full Text Available A quantitative diagnosis using magnetic resonance imaging (MRI can be disturbed by radiofrequency (RF field inhomogeneity induced by the conductive implants. This inhomogeneity causes a local decrease of the signal intensity around the conductor, resulting in a deterioration of the accurate quantification. In a previous study, we developed an MRI imaging method using a two-dimensional selective excitation pulse (2D pulse to mitigate signal inhomogeneity induced by metallic implants. In this paper, the effect of 2D pulse was evaluated quantitatively by numerical simulation and MRI experiments. We introduced two factors for evaluation, spatial resolution and maximum compensation factor. Numerical simulations were performed with two groups. One group was composed of four models with different signal loss width, to evaluate the spatial resolution of the 2D pulse. The other group is also composed of four models with different amounts of signal loss for evaluating maximum compensation factor. In MRI experiments, we prepared phantoms containing conductors, which have different electrical conductivities related with the amounts of signal intensity decrease. The recovery of signal intensity was observed by 2D pulses, in both numerical simulations and experiments.
Conductivity of the two-dimensional electron gas at LaAlO3/SrTiO3 interface
Kirichenko, E. V.; Stephanovich, V. A.; Dugaev, V. K.
2017-02-01
We propose an analytical theory of metallic conductivity in the two-dimensional (2D) LaAlO3/SrTiO3 (LAO/STO) interface. For that we consider the electron-phonon interaction at the interface. The electronic part is taken from our previous work [Phys. Chem. Chem. Phys. 18, 2104 (2016), 10.1039/C5CP06627A], considering the conditions for the interfacial charge carrier (electron or hole) to become itinerant. The second ingredient deals with the atomic oscillations localized near the interface and decaying rapidly at its both sides, which can be regarded as 2D acoustic phonons. The dispersion of such phonons depends on the characteristics of phonon spectra of LAO and STO. Calculating the corresponding scattering rate by Fermi's golden rule, we show that the resulting resistivity (i.e., inverse conductivity) has typical metallic character, growing linearly with temperature and tending to zero (without defects forming so-called residual resistivity) at T →0 . The results of our calculations are in agreement with available experimental data.
National Research Council Canada - National Science Library
S Pamuk; N Pamuk
2014-01-01
In this paper, we obtain the particular exact solutions of the two-dimensional heat and mass transfer equation with power-law temperature-dependent thermal con- ductivity using the Adomian's decomposition method...
Directory of Open Access Journals (Sweden)
H. J. Harsan Ma
2015-08-01
Full Text Available The two-dimensional electron gas (2DEG formed at the perovskite oxides heterostructures is of great interest because of its potential applications in oxides electronics and nanoscale multifunctional devices. A canonical example is the 2DEG at the interface between a polar oxide LaAlO3 (LAO and non-polar SrTiO3 (STO. Here, the LAO polar oxide can be regarded as the modulating or doping layer and is expected to define the electronic properties of 2DEG at the LAO/STO interface. However, to practically implement the 2DEG in electronics and device design, desired properties such as tunable 2D carrier density are necessary. Here, we report the tuning of conductivity threshold, carrier density and electronic properties of 2DEG in LAO/STO heterostructures by insertion of a La0.5Sr0.5TiO3 (LSTO layer of varying thicknesses, and thus modulating the amount of polarization of the oxide over layers. Our experimental result shows an enhancement of carrier density up to a value of about five times higher than that observed at the LAO/STO interface. A complete thickness dependent metal-insulator phase diagram is obtained by varying the thickness of LAO and LSTO providing an estimate for the critical thickness needed for the metallic phase. The observations are discussed in terms of electronic reconstruction induced by polar oxides.
Mustapha Maliki; Nadia Laredj; Karim Bendani; Hanifi Missoum
2017-01-01
This paper reports on a transient heat, air and moisture transfer (HAM) model. The governing partial-differential equations are simultaneously solved for temperature and capillary pressure through multi-layered porous media, including the non-linear transfer and storage properties of materials. Using partial differential equations functions, some thermo-physical properties of porous media are converted into coefficients depending on temperature and capillary pressure. Major features of the mo...
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.
Directory of Open Access Journals (Sweden)
Mustapha Maliki
2017-01-01
Full Text Available This paper reports on a transient heat, air and moisture transfer (HAM model. The governing partial-differential equations are simultaneously solved for temperature and capillary pressure through multi-layered porous media, including the non-linear transfer and storage properties of materials. Using partial differential equations functions, some thermo-physical properties of porous media are converted into coefficients depending on temperature and capillary pressure. Major features of the model are multi-dimensional and transient coupling of heat, air and moisture transport. The coupled equations are solved using the COMSOL Multiphysics time-dependent solver. This solver enables HAM (Heat, Air, Moisture modeling in porous media. Besides, the good agreements obtained with a 2D benchmark suggest that the model can be used to assess the hygrothermal performance of building envelope components. This paper concludes that the total heat flux in the insulated wall represents only the quarter of that crossing the uninsulated concrete roof. On the other hand, the concrete having the lowest water vapour permeability of all used materials allows maintaining the vapour pressure levels close to the initial value (103 Pa. This induces a situation of interstitial condensation within the concrete of the roof. Being able to evaluate the hygrothermal behaviour, the proposed model may turn out to be a valuable tool to solve other building problems.
Energy Technology Data Exchange (ETDEWEB)
Weber, Christopher Phillip [Univ. of California, Berkeley, CA (United States)
2005-01-01
Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field.
Energy Technology Data Exchange (ETDEWEB)
Weber, Christopher P.
2005-12-15
Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field.
Energy Technology Data Exchange (ETDEWEB)
Kaindl, Robert A.; Hagele, D.; Carnahan, M. A.; Chemla, D. S.
2008-09-11
We report a comprehensive experimental study and detailed model analysis of the terahertz (THz) dielectric response and density kinetics of excitons and unbound electron-hole pairs in GaAs quantum wells. A compact expression is given, in absolute units, for the complex-valued THz dielectric function of intra-excitonic transitions between the 1s and higher-energy exciton and continuum levels. It closely describes the THz spectra of resonantly generated excitons. Exciton ionization and formation are further explored, where the THz response exhibits both intra-excitonic and Drude features. Utilizing a two-component dielectric function, we derive the underlying exciton and unbound pair densities. In the ionized state, excellent agreement is found with the Saha thermodynamic equilibrium, which provides experimental verification of the two-component analysis and density scaling. During exciton formation, in turn, the pair kinetics is quantitatively described by a Saha equilibrium that follows the carrier cooling dynamics. The THz-derived kinetics is, moreover, consistent with time-resolved luminescence measured for comparison. Our study establishes a basis for tracking pair densities via transient THz spectroscopy of photoexcited quasi-2D electron-hole gases.
Energy Technology Data Exchange (ETDEWEB)
Lee, Hyun-Sook; Park, Jae-Hyun; Lee, Jae-Yeap [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Kim, Ju-Young; Sung, Nak-Heon; Cho, B.K. [Department of Materials Science and Engineering, GIST, Gwangju 500-712 (Korea, Republic of); Lee, Hu-Jong, E-mail: hjlee@postech.ac.k [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)
2010-12-15
Temperature dependence of the in-plane conductance of a SmFeAsO{sub 0.85} single crystal is measured in c-axis and planar magnetic fields up to 7 T. The conductivity near the superconducting transition is well described by two-dimensional (2D) thermal-fluctuation theory. The 2D superconductivity arises as the c-axis coherence length is much shorter than the spacing between neighboring FeAs layers.
Li, Zhaoguo; Chen, Taishi; Pan, Haiyang; Song, Fengqi; Wang, Baigeng; Han, Junhao; Qin, Yuyuan; Wang, Xuefeng; Zhang, Rong; Wan, Jianguo; Xing, Dingyu; Wang, Guanghou
2012-01-01
The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se microflakes. The solely-B⊥-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such survived UCFs of the surface states result from the limited dephasing length of the bulk carriers in ternary crystals. The electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior.
DEFF Research Database (Denmark)
Petersen, Christian Leth; Hansen, Ole Per
1996-01-01
We have investigated the AC conductivity elements in the quantum Hall regime of two-dimensional electron gases coupled capacitively to electrodes with Corbino geometry. The samples are GaAlAs/GaAs single heterostructures, and the measurements are made at low frequencies, up to 20 kHz. The diagonal...... conductivity is derived from magnetocapacitance measurements. It increases with increasing frequency according to a power law at integer filling factors. The exponent of the power law depends on both temperature and filling factor. Ratios between Hall conductivities at different filling factors are obtained...
Ghattassi, Mohamed; Roche, Jean Rodolphe; Schmitt, Didier; Boutayeb, Mohamed
2016-01-01
This paper deals with local existence and uniqueness results for a transient two-dimensional combined nonlinear radiative-conductive system. This system describes the heat transfer for a grey, semi-transparent and non-scattering medium with homogeneous Dirichlet boundary conditions. We reformulate the full transient state system as a fixed-point problem. The existence and uniqueness proof rests upon the Banach fixed-point Theorem assuming the initial data T 0 is non-negative and sufficiently ...
Sun, Xiaobo; Ramesh, Palanisamy; Itkis, Mikhail E.; Bekyarova, Elena; Haddon, Robert C.
2010-08-01
We report the thermal conductivities of graphite nanoplatelet-epoxy composites prepared by exfoliation of natural graphite flakes of varying lateral sizes. We found that utilization of natural graphite flakes of the optimum lateral dimensions (~200-400 µm) as a starting material for exfoliation significantly enhanced the thermal conductivity of the composite. In order to understand this enhancement we developed a procedure for evaluation of the particle size distribution of graphite nanoplatelets and correlated the measured distributions with the resulting thermal conductivities. In order to expand the scope of our study we applied our statistical and thermal analysis to commercially available graphite nanoplatelet materials.
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)
Grigoriev, P.D., E-mail: grigorev@itp.ac.ru [L. D. Landau Institute for Theoretical Physics, Chernogolovka (Russian Federation)
2012-06-01
It is shown that in rather strong magnetic field the interlayer electron conductivity is exponentially damped by the Coulomb barrier arising from the formation of polaron around each localized electron state. The theoretical model is developed to describe this effect, and the calculation of the temperature and field dependence of interlayer magnetoresistance is performed. The results obtained agree well with the experimental data in GaAs/AlGaAs heterostructures and in strongly anisotropic organic metals. The proposed theory allows to use the experiments on interlayer magnetoresistance to investigate the electron states, localized by magnetic field and disorder.
Ozgit, Dilek; Hiralal, Pritesh; Amaratunga, Gehan A J
2014-12-10
In this article, the use of reduced graphene oxide (rGO) as a high-surface-area conductive additive for enhancing zinc-silver oxide (Zn-Ag2O) batteries is reported for the first time. Specific capacity, rate capability and cyclability are all improved with the addition of 5% thermally reduced graphene oxide to the electrode. It is shown that the rGO morphology becomes more beneficial as the active materials tend toward the nanoscale. The combination results in a better utilization of the active material, which in turn improves the specific capacity of the zinc-silver oxide batteries by ca. 50%, as a result of the more intimate contact with the nano (∼50 nm) electrode particles. The resulting rGO network also creates a high-surface-area conducting template for ZnO electrodeposition upon discharge, significantly reducing the overall particle size of the ZnO deposit, thus inhibiting the formation of dendrites, and increasing the number of achievable cycles from 4 to >160 with a basic cellulose separator. The morphology of the electrodes and its electrochemical parameters are studied as a function of cycling.
Yudin, Dmitry; Shelykh, Ivan A.
2016-10-01
A nonperturbative interaction of an electronic system with a laser field can substantially modify its physical properties. In particular, in two-dimensional (2D) materials with a lack of inversion symmetry, the achievement of a regime of strong light-matter coupling allows direct optical tuning of the strength of the Rashba spin-orbit interaction (SOI). Capitalizing on these results, we build a theory of the dynamical conductivity of a 2D electron gas with both Rashba and Dresselhaus SOIs coupled to an off-resonant high-frequency electromagnetic wave. We argue that strong light-matter coupling modifies qualitatively the dispersion of the electrons and can be used as a powerful tool to probe and manipulate the coupling strengths and adjust the frequency range where optical conductivity is essentially nonzero.
A new complex variable meshless method for transient heat conduction problems
Institute of Scientific and Technical Information of China (English)
Wang Jian-Fei; Cheng Yu-Min
2012-01-01
In this paper,based on the improved complex variable moving least-square (ICVMLS) approximation,a new complex variable meshless method (CVMM) for two-dimensional (2D) transient heat conduction problems is presented.The variational method is employed to obtain the discrete equations,and the essential boundary conditions are imposed by the penalty method.As the transient heat conduction problems are related to time,the Crank-Nicolson difference scheme for two-point boundary value problems is selected for the time discretization.Then the corresponding formulae of the CVMM for 2D heat conduction problems are obtained.In order to demonstrate the applicability of the proposed method,numerical examples are given to show the high convergence rate,good accuracy,and high efficiency of the CVMM presented in this paper.
Staton, Daniel Joseph
We describe the first, high-resolution magnetic images of applied currents and propagating action currents in slices of canine cardiac tissue. This tissue was maintained in vitro at 37^circC. Our main conclusions are summarized as follows: the action currents produce magnetic fields which are measurable; during the initial stages of the propagating action potential, small, expanding, quatrefoil loops of current develop; the magnetic fields produced by repolarization currents are larger than previously anticipated. Most of the current associated with the propagating action potential is confined within the wavefront and should be magnetically silent; however, differences in the intracellular and extracellular electrical conductivities, in both the longitudinal and transverse fiber directions, are great enough that expanding quatrefoil current densities are associated with the wavefront and produce measurable magnetic fields. Since action currents are affected by the electrical conductivities, it is of interest to determine their values, which depend not only upon the tissue characteristics, but also on the mathematical model used to interpret the measured data. In our analysis of current injection, we use the anisotropic bidomain model which incorporates a passive, linear membrane. We introduce theoretical techniques to calculate the anisotropic conductivities of a two-dimensional bidomain. To apply these techniques to magnetic fields resulting from current injection into cardiac tissue slices, we need to improve the higher spatial frequency content of our present measurements. This may be done by measuring the magnetic field closer to the cardiac slice (presently 2.5 mm), decreasing the sampling interval of the measurement, and increasing the sampling area of the field. Magnetic fields are produced by propagating action currents, which are in turn the result of the propagating action potential. From the magnetic field, we directly image isochronal transmembrane
Fujita, Toshiyuki; Sasaki, Takahiko; Yoneyama, Naoki; Kobayashi, Norio
2004-06-01
Current-voltage characteristics are measured in the quasi-two dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4 at temperatures down to 0.5 K and in the magnetic field up to 25 T. The non-linear conduction with a threshold electric field is found in the density wave state. The features of threshold electric field obtained in the low magnetic field region are explained by the unconventional charge density wave model. In the high magnetic field region, where the Shubnikov-de Haas oscillations appear, the current-voltage characteristics reveal that the density wave state synchronizes with the filling of the electron on the Landau level and continues even above a kink field 23 T.
Shegelski, Mark R. A.; Salayka-Ladouceur, Logan; Malmgren, Kevin
2017-01-01
We consider a one-dimensional molecule with a permanent electric dipole moment incident along the line of symmetry of a circular hole in an infinite two-dimensional conducting sheet. We calculate the probabilities of reflection p R and transmission p T of a centre of mass wave packet initially of the form of a Gaussian wave packet and moving toward the hole. We show the dependence of p T and p R on the charge Q of the atoms, the radius a of the hole as compared to the length scale 1/α of the bound molecular relative motion state, the mass and energy of the molecule. We compare a fully quantum mechanical treatment to a semiclassical approximation in which the distance between the atoms is constant. Some unexpected and surprising results emerge from this study.
Kang, Joon Sang; Ke, Ming; Hu, Yongjie
2017-03-08
Two-dimensional van der Waals materials have shown novel fundamental properties and promise for wide applications. Here, we report for the first time an experimental demonstration of the in situ characterization and highly reversible control of the anisotropic thermal conductivity of black phosphorus. We develop a novel platform based on lithium ion batteries that integrates ultrafast optical spectroscopy and electrochemical control to investigate the interactions between lithium ions and the lattices of the black phosphorus electrode. We discover a strong dependence of the thermal conductivity on battery charge states (lithium concentrations) during the discharge/charge process. The thermal conductivity of black phosphorus is reversibly tunable over a wide range of 2.45-3.86, 62.67-85.80, and 21.66-27.58 W·m(-1)·K(-1) in the cross-plan, zigzag, and armchair directions, respectively. The modulation in thermal conductivity is attributed to phonon scattering introduced by the ionic intercalation in between the interspacing layers and shows anisotropic phonon scattering mechanism based on semiclassical model. At the fully discharged state (x ∼ 3 in LixP), a dramatic reduction of thermal conductivity by up to 6 times from that of the pristine crystal has been observed. This study provides a unique approach to explore the fundamental energy transport involving lattices and ions in the layered structures and may open up new opportunities in controlling energy transport based on novel operation mechanisms and the rational design of nanostructures.
Energy Technology Data Exchange (ETDEWEB)
Kopeliovich, A.I. [B. Verkin Institute for Low Temperature Physics & Engineering, NAS of Ukraine (Ukraine); Pyshkin, P.V., E-mail: pavel.pyshkin@gmail.com [Ikerbasque, Basque Foundation for Science 48011, Bilbao (Spain); Department of Theoretical Physics and History of Science, The Basque Country University (EHU/UPV), PO Box 644, 48080 Bilbao (Spain); Kalinenko, A.N.; Yanovsky, A.V. [B. Verkin Institute for Low Temperature Physics & Engineering, NAS of Ukraine (Ukraine)
2016-02-15
It is shown that the normal electron–electron scattering is a source of electrical resistance on non-contact current excitation in two-dimensional spin–split electron systems. In contrast to the contact current injection, non-contact current excitation causes spatially inhomogeneous polarization in a two-dimensional conductor leading to new resistivity mechanisms.
Zimmerman, R. W.; Leung, C. T.
2009-12-01
Most oil and gas reservoirs, as well as most potential sites for nuclear waste disposal, are naturally fractured. In these sites, the network of fractures will provide the main path for fluid to flow through the rock mass. In many cases, the fracture density is so high as to make it impractical to model it with a discrete fracture network (DFN) approach. For such rock masses, it would be useful to have recourse to analytical, or semi-analytical, methods to estimate the macroscopic hydraulic conductivity of the fracture network. We have investigated single-phase fluid flow through generated stochastically two-dimensional fracture networks. The centers and orientations of the fractures are uniformly distributed, whereas their lengths follow a lognormal distribution. The aperture of each fracture is correlated with its length, either through direct proportionality, or through a nonlinear relationship. The discrete fracture network flow and transport simulator NAPSAC, developed by Serco (Didcot, UK), is used to establish the “true” macroscopic hydraulic conductivity of the network. We then attempt to match this value by starting with the individual fracture conductances, and using various upscaling methods. Kirkpatrick’s effective medium approximation, which works well for pore networks on a core scale, generally underestimates the conductivity of the fracture networks. We attribute this to the fact that the conductances of individual fracture segments (between adjacent intersections with other fractures) are correlated with each other, whereas Kirkpatrick’s approximation assumes no correlation. The power-law averaging approach proposed by Desbarats for porous media is able to match the numerical value, using power-law exponents that generally lie between 0 (geometric mean) and 1 (harmonic mean). The appropriate exponent can be correlated with statistical parameters that characterize the fracture density.
Inverse transient heat conduction problems and identification of thermal parameters
Atchonouglo, K.; Banna, M.; Vallée, C.; Dupré, J.-C.
2008-04-01
This work deals with the estimation of polymers properties. An inverse analysis based on finite element method is applied to identify simultaneously the constants thermal conductivity and heat capacity per unit volume. The inverse method algorithm constructed is validated from simulated transient temperature recording taken at several locations on the surface of the solid. Transient temperature measures taped with infrared camera on polymers were used for identifying the thermal properties. The results show an excellent agreement between manufacturer and identified values.
Theoretical analysis of transient heat conduction in sand
Institute of Scientific and Technical Information of China (English)
梁新刚; 过增元; 徐云生
1996-01-01
A simplified two-phase system model, with the heat transfer between phases considered, is presented and applied to the transient heat conduction in sand. The analytical results show that the one-dimensional Fourier’s law is not applicable to the transient heat conduction at very short time and there is no thermal wave described by C-V equation in sand. The two-phase system model correlates with experimental data well. Each ?phase responds to heating at different speeds in composite material, and consequently results in a temperature difference between phases. This difference will cause heat transfer between phases, which can be regarded as a heat source or sink to other phase. It is certain that Fourier’s law cannot describe the transient heat conduction in sand if a one-dimensional problem with equivalent thermal diffusivity is assumed.
Jia, Wen-Zhu; Wang, Xi-Feng; Song, Yuan-Hong; Wang, You-Nian
2017-04-01
Improving plasma uniformity during plasma processing in the microelectronics industry is of critical importance to the quality of etching or deposition. Compared to continuous wave (CW) plasmas, pulsed plasmas have drawn much attention with the introduction of additional pulse parameters, which would be helpful to improve the plasma properties. In this paper, a two-dimensional fluid model is developed to investigate a pulsed radio-frequency capacitively coupled plasma (CCP) sustained in SiH4/N2/O2 mixture at fixed operating conditions of 70V rf power, 300 mTorr (40 Pa) gas pressure and an SiH4/N2/O2 gas ratio of 2.5/92.5/5. First, we study the temporal dynamics of densities of the electron, positive ion and negative ion, at different positions in the pulsed CCP. Under the operation conditions, charged particles, instead of neutral particles, may basically respond to the applied modulated power. The electron density in the bulk could approach a quasi-steady value by the end of the activeglow. However, the achievement of a quasi-steady state of plasma like that in the CW condition not only depends on enough activeglow time of the pulse discharge but also relies on the observed position in the discharge. In addition, we investigate the impact of pulse parameters on plasma characteristics, showing that the radial inhomogeneity of plasma caused by the edge effect can be effectively suppressed by controlling the duty cycle (DC) rather than the pulse repetition frequency (PRF). Improvement of the plasma uniformity in pulsed discharge is due to the competition between the edge effects during the activeglow and diffusion of charged species during the afterglow. Moreover, the electron density undergoes a local minimum value in the temporal profile before it rises sharply beyond that of CW discharge, since production of electrons is less than loss by the spatial movement at the very beginning of one pulse. Also, there appears to be a peak value of ion bombardment energy at
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.
SOLUTION OF TRANSIENT HEAT CONDUCTION PROBLEM BY THE FINITE ELEMENT METHOD
Directory of Open Access Journals (Sweden)
Süleyman TAŞGETİREN
1995-01-01
Full Text Available Determination of temperature distribution is generally the first step in the design of machine elements subjected to ubnormal temperatures in their service life and for selection of materials. During this heat transfer analysis, the boundary and enviromental conditions must be modeled realistically and the geometry must be well represented. A variety of materials deviating from simple constant property isotropic material to composit materials having different properties according to direction of reinforcements are to be analysed. Then, the finite element method finds a large application area due to its use of same notation in heat transfer analysis and mechanical analysis of elements. In this study, the general formulation of two dimensional transient heat conduction is developed and a sample solution is given for arectangular bar subjected to convection baundary condition.
A complex variable meshless local Petrov-Galerkin method for transient heat conduction problems
Institute of Scientific and Technical Information of China (English)
Wang Qi-Fang; Dai Bao-Dong; Li Zhen-Feng
2013-01-01
On the basis of the complex variable moving least-square (CVMLS) approximation,a complex variable meshless local Petrov-Galerkin (CVMLPG) method is presented for transient heat conduction problems.The method is developed based on the CVMLS approximation for constructing shape functions at scattered points,and the Heaviside step function is used as a test function in each sub-domain to avoid the need for a domain integral in symmetric weak form.In the construction of the well-performed shape function,the trial function of a two-dimensional (2D) problem is formed with a one-dimensional (1 D) basis function,thus improving computational efficiency.The numerical results are compared with the exact solutions of the problems and the finite element method (FEM).This comparison illustrates the accuracy as well as the capability of the CVMLPG method.
Arc Conductance and Flow Velocity Affected by Transient Recovery Voltage
Fukuoka, Reo; Ishikawa, Yuya; Ono, Seisui; Sato, Ken; Yamamoto, Shinji; Iwao, Toru
2016-09-01
Recently, the stable supply of electric power is indispensable. The GCB (Gas Circuit Breaker) can prevent the spread of the fault current. However, it should have the reliability more. Therefore the GCB has been researched for performance improvement of the arc interruption of abnormal fault current without the fail. Therefore, it is important to prevent the breakdown such as the re-ignition and thermal re-ignition of arc after the arc interruption. It is necessary to reduce the arc conductance in order to prevent the re-ignition of arc. The arc conductance is derived from the temperature distribution and the volume of the arc. The temperature distribution of the arc is formed by convection. In this research, the arc conductance and flow velocity affected by transient recovery voltage are elucidated. The flow rate and temperature distribution of the arc is calculated with changing transient recovery voltage. In addition, the arc conductance is calculated in order to know the extinguish arc ability. As a result, when the transient recovery voltage increases, the probability of re-ignition increases. Therefore, the arc temperature and the arc conductance were increased.
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.
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.
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.
Gui, Daxiang; Zheng, Tao; Xie, Jian; Cai, Yawen; Wang, Yaxing; Chen, Lanhua; Diwu, Juan; Chai, Zhifang; Wang, Shuao
2016-12-19
A highly stable layered zirconium phosphate, (NH4)2[ZrF2(HPO4)2] (ZrP-1), was synthesized by an ionothermal method and contains an extremely dense two-dimensional hydrogen-bond network that is thermally stable up to 573 K, leading to combined ultrahigh water-assisted proton conductivities of 1.45 × 10(-2) S cm(-1) at 363 K/95% relative humidity and sustainable anhydrous proton conductivity of 1.1 × 10(-5) S cm(-1) at 503 K.
A new hybrid algorithm for solving transient combined conduction radiation heat transfer problems
Directory of Open Access Journals (Sweden)
Chaabane Raoudha
2011-01-01
Full Text Available A new algorithm based on the lattice Boltzmann method (LBM and the Control Volume Finite Element Method (CVFEM is proposed as an hybrid solver for two dimensional transient conduction and radiation heat transfer problems in an optically emitting, absorbing and scattering medium. The LBM was used to solve the energy equation and the CVFEM was used to compute the radiative information. The advantages of the proposed methodology is to avoid problems that confronted when previous techniques are used to predict radiative heat transfer, essentially, in complex geometries and when there is scattering and/or non-black boundaries surfaces. This method combination, which is applied for the first time to solve this unsteady combined mode of heat transfer, has been found to accurately predict the effects of various thermo-physical parameters such as the scattering albedo, the conduction-radiation parameter and the extinction coefficient on temperature distribution. The results of the LBM-CVFEM combination were found to be in excellent agreement with the LBM-CDM (Collapsed Dimension Methodthis proposed numerical approach include, among others, simple implementation on a computer, accurate CPU time, and capability of stable simulation.
Directory of Open Access Journals (Sweden)
Szymkiewicz Adam
2015-09-01
Full Text Available Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions, water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting. It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.
Szymkiewicz, Adam; Tisler, Witold; Burzyński, Kazimierz
2015-09-01
Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions), water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting). It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.
Lavoué, F.; Brossier, R.; Métivier, L.; Garambois, S.; Virieux, J.
2014-04-01
Full waveform inversion of ground-penetrating radar data is an emerging technique for the quantitative, high-resolution imaging of the near subsurface. Here, we present a 2-D frequency-domain full waveform inversion for the simultaneous reconstruction of the dielectric permittivity and of the electrical conductivity. The inverse problem is solved with a quasi-Newton optimization scheme, where the influence of the Hessian is approximated by the L-BFGS-B algorithm. This formulation can be considered to be fully multiparameter since it enables to update permittivity and conductivity values within the same descent step, provided we define scales of measurement through a reference permittivity, a reference conductivity, and an additional scaling factor. Numerical experiments on a benchmark from the literature demonstrate that the inversion is very sensitive to the parameter scaling, despite the consideration of the approximated Hessian that should correct for parameter dimensionalities. A proper scaling should respect the natural sensitivity of the misfit function and give priority to the parameter that has the most impact on the data (the permittivity, in our case). We also investigate the behaviour of the inversion with respect to frequency sampling, considering the selected frequencies either simultaneously or sequentially. As the relative imprint of permittivity and conductivity in the data varies with frequency, the simultaneous reconstruction of both parameters takes a significant benefit from broad frequency bandwidth data, so that simultaneous or cumulative strategies should be favoured. We illustrate our scaling approach with a realistic synthetic example for the imaging of a complex subsurface from on-ground multioffset data. Considering data acquired only from the ground surface increases the ill-posedness of the inverse problem and leads to a strong indetermination of the less-constrained conductivity parameters. A Tikhonov regularization can prevent the
Sengupta, Ananya; Datta, Subhadeep; Su, Chenliang; Herng, Tun Seng; Ding, Jun; Vittal, Jagadese J; Loh, Kian Ping
2016-06-29
The coordination chemistry between copper acetate [Cu2(OAc)4] and 5,10,15,20-tetra-4-pyridyl-21H,23H-porphine (porphyrin, H2TPyP) is found to give rise to either a 2D metal-organic framework (MOF) [Cu(TPyP)Cu2(O2CCH3)4] or a 3D MOF [Cu(TPyP)CuCl2]·2.5TCE·7H2O], depending on the choice of solvent. The 2D MOF can be made into a film, which was doped with 7,7,8,8-tetracyanoquinodimethane (TCNQ), and the electrical conductivity of the thin film was increased by 3 orders of magnitude with respect to that of the undoped Cu-MOF. The formation of a charge-transfer complex between TCNQ and the 2D Cu-MOF also imparts stronger paramagnetic properties than for the undoped MOF.
Burd, A. I.; Booker, J. R.; Mackie, R. L.; Pomposiello, C.; Favetto, A.; Larsen, J. C.
2010-12-01
Near 31.5°S, the subducted Nazca slab beneath Chile and western Argentina levels out near 100 km depth and does not roll over to plunge steeply into the mantle for several hundred km to the east. This flat slab prevents formation of an asthenospheric wedge under the Andes and consequently there are no active volcanoes. To the south this slab returns to a dip of ~30°, an asthenospheric wedge forms and there are active volcanoes south of 33.3°S in the Andean Southern Volcanic Zone (SVZ). The prevailing view is that the Nazca slab is warped continuously between its flat and dipping segments. Over the last decade, we have collected 83 magnetotelluric (MT) sites that form an array in Argentina from 60° - 70°W and 31.5° - 34°S. 18 sites extend this coverage along a profile near 31.5°S past where the flat slab plunges into the lower mantle. These data were initially collected as linear profiles. Eventually it became clear that the structure at mantle depth was 3D. The site geometry was thus expanded to its current 2D array. The final sites in this array were collected in late 2009. While each year’s data set was originally internally consistent, preparation of the complete data set required recalculation of the impedance tensor at each site so that all data are compatible and comparable. MT impedance tensor data (including vertical to horizontal magnetic field transfer functions) are being inverted for smoothest log conductivity using a 3D non-linear conjugate gradient (NLCG) algorithm. Initial results of this 3D study will be presented. Several conclusions have already emerged from 2D interpretations of subsets of the data. There is an asthenospheric wedge east of the flat slab. Its top at 100 km is probably at the base of the lithosphere through which it has not penetrated, presumably because of compressive stresses. This wedge is horizontally thin and is bounded to the east by the root of the Rio de la Plata Craton and to the west by the plunging slab. It
Taddei, Marco; Donnadio, Anna; Costantino, Ferdinando; Vivani, Riccardo; Casciola, Mario
2013-10-21
The reaction of two small phosphono-amino acids based on glycine (glyphosine and glyphosate) with zirconium under mild conditions led to the attainment of three related zirconium derivatives with 1D, 2D, and 3D structures of formulas ZrF[H3(O3PCH2NHCH2COO)2] (1), Zr3H8[(O3PCH2)2NCH2COO]4·2H2O (2), and Zr[(O3PCH2)(HO3PCH2)NHCH2COOH]2·2H2O (3), respectively, whose structures were solved by X-ray powder and single-crystal diffraction data. The glyphosate derivative has 1D ribbon-type structure whereas the dimensionality of the glyphosine-derived materials (2D and 3D) can be tuned by changing the synthesis conditions. The low-dimensional compounds (1 and 2) can be directly produced in the form of nanoparticles with different size and morphology whereas the 3D compound (3) has a higher crystallinity and can be obtained as single crystals with a prismatic shape. The different structural dimensionality reflects the shape and size of the crystals and also differently affects the proton conductivity properties, measured over a wide range of temperature at 95% relative humidity. Their high thermal and chemical stability together with the small size may promote their use as fillers for polymeric electrolyte membranes for fuel cells applications.
Schmidt, Aaron J; Chen, Xiaoyuan; Chen, Gang
2008-11-01
The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for measuring both cross-plane and in-plane thermal conductivities of thermally anisotropic thin films is described. As verification, the technique is used to extract the cross-plane and in-plane thermal conductivities of highly ordered pyrolytic graphite. Results are found to be in good agreement with literature values.
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...
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.
Transient heat conduction in a pebble fuel applying fractional model
Energy Technology Data Exchange (ETDEWEB)
Gomez A, R.; Espinosa P, G. [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Av. San Rafael Atlixco 186, Col. Vicentina, 09340 Mexico D. F. (Mexico)], e-mail: gepe@xanum.uam.mx
2009-10-15
In this paper we presents the equation of thermal diffusion of temporary-fractional order in the one-dimensional space in spherical coordinates, with the objective to analyze the heat transference between the fuel and coolant in a fuel element of a Pebble Bed Modular Reactor. The pebble fuel is the heterogeneous system made by microsphere constitutes by U O, pyrolytic carbon and silicon carbide mixed with graphite. To describe the heat transfer phenomena in the pebble fuel we applied a constitutive law fractional (Non-Fourier) in order to analyze the behaviour transient of the temperature distribution in the pebble fuel with anomalous thermal diffusion effects a numerical model is developed. (Author)
Model for predicting thermal conductivity using transient hot wire method
Kumar, Sublania Harish; Singh K., J.; Somani A., K.
2016-05-01
The use of the hot wire method for estimating the thermal conductivity measurement has recently known a significant increase. However, this method is theoretically not applicable to materials. Thermal conductivity values are necessary whenever a heat transfer problem is to be evaluated.
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...
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 ...
Nonequilibrium optical conductivity: General theory and application to transient phases
Kennes, D. M.; Wilner, E. Y.; Reichman, D. R.; Millis, A. J.
2017-08-01
A nonequilibrium theory of optical conductivity of dirty-limit superconductors and commensurate charge density wave is presented. We discuss the current response to different experimentally relevant light-field probe pulses and show that a single frequency definition of the optical conductivity σ (ω )≡j (ω )/E (ω ) is difficult to interpret out of the adiabatic limit. We identify characteristic time-domain signatures distinguishing between superconducting, normal-metal, and charge density wave states. We also suggest a route to directly address the instantaneous superfluid stiffness of a superconductor by shaping the probe light field.
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.
Mixed time integration schemes for transient conduction forced-convection analysis
Liu, W. K.; Lin, J. I.
1983-01-01
A partition procedure for forced-convection conduction transient problems is presented. Mixed time partitions are defined wherein coupled conduction force-matrix equations are discretized using an implicit integration method, followed by derivation of a mixed time integration technique. Explicit-implicit and explicit-explicit partitions are performed for a stability analysis for transient conditions, e.g., those found in an actively air-cooled engine and airframe structure.
A PC- Based Transient Method for Thermal Conductivity Measurement.
Directory of Open Access Journals (Sweden)
A.K. Singh
2000-10-01
Full Text Available In this paper, an indigenously developed thermal probe has been interfaced with a PC for automated measurement of thermal conductivity (K . The developed system has been calibrated and standardised by measuring K of glycerol. The maximum percentage error, for repeated sets of observations, was within 7.29 per cent of standard value reported for glycerol. This methodology has been successfully employed for measuring K of propellant oxidisers, additives, binders, etc.
Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System.
Roder, H M; Perkins, R A; Laesecke, A; Nieto de Castro, C A
2000-01-01
A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.
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.
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.
Transient radiation-conductive heat transfer problems: ``The quadrupole method''
Degiovanni, Alain; Remy, Benjamin; Andre, Stéphane
2002-11-01
This paper presents a statement of the works performed in L.E.M.T.A by the members of the thermal and mechanical heterogeneous media research group during the last six years concerning the solving of coupled conductive and radiative heat transfers within a multilayer and semi-transparent “wall”. Out of the authors, this paper allows to take inspiration from the works of D. Maillet, M. Lazard and V. Manias[19, 20, 21]. The aim of these works is to represent in a macroscopic way, with the minimum number of thermophysical parameters, the heat transfers in a plane system composed of semi-transparent media. The approach we propose is semi-analytic (Kernel substitution technique, Laplace transformation) and allow to obtain in the Laplace domain an analytical solution that can be easily used. This method can be applied in two main scopes of applications: the estimation of thermophysical properties (phononic conductivity, optical thickness, Planck number for instance) of semi-transparent materials (glasses, crystals, glass wool, semi-conductors, synthetic diamonds, vitroceramics and so on) and the modelling of processes with semitransparent walls (for instance bottles forming, flat glass production, drying of paper). The method will be first presented and validated and two examples of applications will be then given. This method can be applied to semitransparent walls that emit, absorb and scatter the radiant energy (participating medium). It appears from the principle of a Kernel substitution technique applied to the radiative flux expression and initially introduced by Lick[1] that allows to change the character of the governing heat equation from the integro-differential form to a purely differential one. In the case of limiting cases of purely scattering and purely absorbing media, the solution of the radiative transfer equation is exact. In the general case, we make a two-flux approximation. In all cases, we assume a linear transfer and use the Laplace transform
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.
DEFF Research Database (Denmark)
Zhu, Huayang; Ricote, Sandrine; Coors, W. Grover;
2014-01-01
A model-based approach is used to interpret equilibrium and transient conductivity measurements for 10% gadolinium-doped ceria: Ce0.9Gd0.1O1.95 − δ (GDC10). The measurements were carried out by AC impedance spectroscopy on slender extruded GDC10 rods. Although equilibrium conductivity measurements...
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.
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.
Institute of Scientific and Technical Information of China (English)
Bao-Lin Wang
2013-01-01
This paper studies the fracture behavior of a thermoelastic cylinder subjected to a sudden temperature change on its outer surface within the framework of non-classical heat conduction.The heat conduction equation is solved by separation of variable technique.Closed form solution for the temperature field and the associated thermal stress are established.The critical parameter governing the level of the transient thermal stress is identified.Exact expression for the transient stress intensity factor is obtained for a crack in the cylinder.The difference between the non-classical solutions and the classical solution are discussed.It is found that the traditional classical heat conduction considerably underestimates the transient thermal stress and thermal stress intensity factor.
The Interpolating Element-Free Galerkin Method for 2D Transient Heat Conduction Problems
Directory of Open Access Journals (Sweden)
Na Zhao
2014-01-01
Full Text Available An interpolating element-free Galerkin (IEFG method is presented for transient heat conduction problems. The shape function in the moving least-squares (MLS approximation does not satisfy the property of Kronecker delta function, so an interpolating moving least-squares (IMLS method is discussed; then combining the shape function constructed by the IMLS method and Galerkin weak form of the 2D transient heat conduction problems, the interpolating element-free Galerkin (IEFG method for transient heat conduction problems is presented, and the corresponding formulae are obtained. The main advantage of this approach over the conventional meshless method is that essential boundary conditions can be applied directly. Numerical results show that the IEFG method has high computational accuracy.
Two-dimensional investigation of forced bubble oscillation under microgravity
Institute of Scientific and Technical Information of China (English)
HONG Ruoyu; Masahiro KAWAJI
2003-01-01
Recent referential studies of fluid interfaces subjected to small vibration under microgravity conditions are reviewed. An experimental investigation was carried out aboard the American Space Shuttle Discovery. Two-dimensional (2-D) modeling and simulation were conducted to further understand the experimental results. The oscillation of a bubble in fluid under surface tension is governed by the incompressible Navier-Stokes equations. The SIMPLEC algorithm was used to solve the partial differential equations on an Eulerian mesh in a 2-D coordinate. Free surfaces were represented with the volume of fluid (VOF) obtained by solving a kinematic equation. Surface tension was modeled via a continuous surface force (CSF) algorithm that ensures robustness and accuracy. A new surface reconstruction scheme, alternative phase integration (API) scheme, was adopted to solve the kinematic equation, and was compared with referential schemes. Numerical computations were conducted to simulate the transient behavior of an oscillating gas bubble in mineral oil under different conditions. The bubble positions and shapes under different external vibrations were obtained numerically. The computed bubble oscillation amplitudes were compared with experimental data.
Stall flutter and nonlinear divergence of a two-dimensional flat plate wing
Dugundji, J.; Aravamudan, K.
1976-01-01
Tests were conducted in a small wind tunnel to study the torsional stall flutter behavior of a two-dimensional flat-plate wing pivoted about the midchord. The nonlinear static divergence equilibrium properties of the wing were well predicted from the measured static moment characteristics. Large amplitude limit cycles ranging from plus or minus 11 degrees to plus or minus 100 degrees were observed. Stall flutter occurred above a critical value of a reduced frequency of about 2. Self-excitation occurred for initial angles of attack between 0 and 8 degrees. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees.
Characterization of polyester films used in capacitors. 1: Transient and steady-state conductivity
Thielen, A.; Niezette, J.; Feyder, G.; Vanderschueren, J.
1994-10-01
Charging and discharging currents flowing through polyethylene terephthalate (PET) ultrathin films (1.5 - 12 micrometers) were measured by the use of a two-electrode configuration involving opposite lateral contacts. A study of the influence of electrification time, applied electric field, film thickness, nature of electrodes, and water content was carried out on both transient and steady-state conduction. The transient behavior can be interpreted in terms of dipolar orientation and relaxation processes while steady-state conductivity can be mainly accounted for in terms of Schottky emission. A comparison between PET and polyethylene naphthalate films is also reported.
Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System
Roder, Hans M.; Perkins, Richard A.; Laesecke, Arno; Nieto de Castro, Carlos A.
2000-01-01
A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relat...
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.
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.
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.
Transient Eddy Current Response Due to a Subsurface Crack in a Conductive Plate
Energy Technology Data Exchange (ETDEWEB)
Fu, Fangwei [Iowa State Univ., Ames, IA (United States)
2006-01-01
Eddy current nondestructive evaluation (NDE) is usually carried out by exciting a time harmonic field using an inductive probe. However, a viable alternative is to use transient eddy current NDE in which a current pulse in a driver coil produces a transient .eld in a conductor that decays at a rate dependent on the conductivity and the permeability of the material and the coil configuration. By using transient eddy current, it is possible to estimate the properties of the conductive medium and to locate and size potential .aws from the measured probe response. The fundamental study described in this dissertation seeks to establish a theoretical understanding of the transient eddy current NDE. Compared with the Fourier transform method, the derived analytical formulations are more convenient when the transient eddy current response within a narrow time range is evaluated. The theoretical analysis provides a valuable tool to study the effect of layer thickness, location of defect, crack opening as well as the optimization of probe design. Analytical expressions have been developed to evaluate the transient response due to eddy currents in a conductive plate based on two asymptotic series. One series converges rapidly for a short time regime and the other for a long time regime and both of them agree with the results calculated by fast Fourier transform over all the times considered. The idea of asymptotic expansion is further applied to determine the induced electromotive force (EMF) in a pick-up coil due to eddy currents in a cylindrical rod. Starting from frequency domain representation, a quasi-static time domain dyadic Green's function for an electric source in a conductive plate has been derived. The resulting expression has three parts; a free space term, multiple image terms and partial reflection terms. The dyadic Green's function serves as the kernel of an electric field integral equation which defines the interaction of an ideal crack with the
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....
Transient Coupled Radiative and Conductive Heat Transfer in a Composite of Semitransparent Media
Institute of Scientific and Technical Information of China (English)
Ping－YangWang; He－PingTan; 等
1999-01-01
The transient coupled radiative and conductive heat transfer in semitransparent composite under the complex boundary conditions is investigated by the ray tracing method in combination with Hottel's zonal method and the control-volume method.The composite is composed of two plane layers of nonscattering semitransparent media with the different thermophysical properties in each layer,Both boundary surfaces and the intermal interface are semitransparent.The reflections are assumed diffuse or specular.The transient temperature distributions in the composite are obtained for the combined thermal boundary conditions of incident radiation and convective heat transfer,Under diffuse reflection.the results in this paper are seqarately compared with the steady and transient results of previous work.The comparison shows the reliability and the high calculating accuracy of the formulas berived in this paper.the present analysis includes the effects of the optical thickness.the conduction-radiation parameter,the spectral property and the reflective mode on the transient temperature distributions.
MOT solution of the PMCHWT equation for analyzing transient scattering from conductive dielectrics
Uysal, Ismail Enes
2015-01-01
Transient electromagnetic interactions on conductive dielectric scatterers are analyzed by solving the Poggio-Miller-Chan-Harrington-Wu-Tsai (PMCHWT) surface integral equation with a marching on-in-time (MOT) scheme. The proposed scheme, unlike the previously developed ones, permits the analysis on scatterers with multiple volumes of different conductivity. This is achieved by maintaining an extra temporal convolution that only depends on permittivity and conductivity of these volumes. Its discretization and computation come at almost no additional cost and do not change the computational complexity of the resulting MOT solver. Accuracy and applicability of the MOT-PMCHWT solver are demonstrated by numerical examples.
Finite element methodology for transient conduction/forced-convection thermal analysis
Thornton, E. A.; Wieting, A. R.
1979-01-01
Finite element methodology for steady state thermal analysis of convectively cooled structures has been extended for transient analysis. The finite elements are based on representing the fluid passages by fluid bulk-temperature nodes and fluid-solid interface nodes. The formulation of the finite element equations for a typical flow passage is based on the weighted residual method with upwind weighting functions. Computer implementation of the convective finite element methodology using explicit and implicit time integration algorithms is described. Accuracy and efficiency of the methodology is evaluated by comparisons with analytical solutions and finite-difference lumped-parameter analyses. The comparative analyses demonstrate that finite element conduction/conduction methodology may be used to predict transient temperatures with an accuracy equal or superior to the lumped-parameter finite-difference method.
Institute of Scientific and Technical Information of China (English)
WANG Yi-bo; YANG Hai-tian; WU Rui-feng
2005-01-01
By modeling direct transient heat conduction problems via finite element method (FEM) and precise integral algorithm, a new approach is presented to solve transient inverse heat conduction problems with multi-variables. Firstly, the spatial space and temporal domain are discretized by FEM and precise integral algorithm respectively. Then, the high accuracy semi-analytical solution of direct problem can be got. Finally, based on the solution, the computing model of inverse problem and expression of sensitivity analysis are established. Single variable and variables combined identifications including thermal parameters, boundary conditions and source-related terms etc. are given to validate the approach proposed in 1-D and 2-D cases. The effects of noise data and initial guess on the results are investigated. The numerical examples show the effectiveness of this approach.
1986-01-01
1966). 3. Canale, R.P. and S.C. Chapra . Numerical Methods for Engineers with Personnel Computer Applications. New York: McGraw-Hill 509-533, ( 1985...This study looks at numerical % methods from an engineer’s view, a tool to be used in solving problems. This paper has given me much needed experience... numerical method in solving the transient heat conduction equation. The eigenvalue method was compared to five other numerical methods : Runge-Kutta
Directory of Open Access Journals (Sweden)
Mohammad Nili Ahmadabadi
2014-05-01
Full Text Available In this paper, the Method of Fundamental Solutions (MFS is extended to solve some special cases of the problem of transient heat conduction in functionally graded mate- rials. First, the problem is transformed to a heat equation with constant coecients using a suitable new transformation and then the MFS together with the Tikhonov regularization method is used to solve the resulting equation
Transient mid-IR study of electron dynamics in TiO2 conduction band.
Sá, Jacinto; Friedli, Peter; Geiger, Richard; Lerch, Philippe; Rittmann-Frank, Mercedes H; Milne, Christopher J; Szlachetko, Jakub; Santomauro, Fabio G; van Bokhoven, Jeroen A; Chergui, Majed; Rossi, Michel J; Sigg, Hans
2013-04-07
The dynamics of TiO2 conduction band electrons were followed with a novel broadband synchrotron-based transient mid-IR spectroscopy setup. The lifetime of conduction band electrons was found to be dependent on the injection method used. Direct band gap excitation results in a lifetime of 2.5 ns, whereas indirect excitation at 532 nm via Ru-N719 dye followed by injection from the dye into TiO2 results in a lifetime of 5.9 ns.
Yoo, Donghoon; Lee, Joohyun; Lee, Byeongchan; Kwon, Suyong; Koo, Junemo
2017-08-01
The Transient Hot-Wire Method (THWM) was developed to measure the absolute thermal conductivity of gases, liquids, melts, and solids with low uncertainty. The majority of nanofluid researchers used THWM to measure the thermal conductivity of test fluids. Several reasons have been suggested for the discrepancies in these types of measurements, including nanofluid generation, nanofluid stability, and measurement challenges. The details of the transient hot-wire method such as the test cell size, the temperature coefficient of resistance (TCR) and the sampling number are further investigated to improve the accuracy and consistency of the measurements of different researchers. It was observed that smaller test apparatuses were better because they can delay the onset of natural convection. TCR values of a coated platinum wire were measured and statistically analyzed to reduce the uncertainty in thermal conductivity measurements. For validation, ethylene glycol (EG) and water thermal conductivity were measured and analyzed in the temperature range between 280 and 310 K. Furthermore, a detailed statistical analysis was conducted for such measurements, and the results confirmed the minimum number of samples required to achieve the desired resolution and precision of the measurements. It is further proposed that researchers fully report the information related to their measurements to validate the measurements and to avoid future inconsistent nanofluid data.
A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids.
Perkins, R A; Roder, H M; Nieto de Castro, C A
1991-01-01
A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously used as electrical heat sources and as resistance thermometers. A microcomputer controls bridge nulling, applies the power pulse, monitors the bridge response, and stores the results. Performance of the instrument was verified with measurements on liquid toluene as well as argon and nitrogen gas. In particular, new data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented. These new data can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements. Thermal conductivity data for liquid toluene, which are corrected for radiation, are reported. The precision of the thermal conductivity data is ± 0.3% and the accuracy is about ±1%. The accuracy of the thermal diffusivity data is about ± 5%. From the measured thermal conductivity and thermal diffusivity, we can calculate the specific heat, Cp , of the fluid, provided that the density is measured, or available through an equation of state.
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.
Spectral Radiative Properties of Two-Dimensional Rough Surfaces
Xuan, Yimin; Han, Yuge; Zhou, Yue
2012-12-01
Spectral radiative properties of two-dimensional rough surfaces are important for both academic research and practical applications. Besides material properties, surface structures have impact on the spectral radiative properties of rough surfaces. Based on the finite difference time domain algorithm, this paper studies the spectral energy propagation process on a two-dimensional rough surface and analyzes the effect of different factors such as the surface structure, angle, and polarization state of the incident wave on the spectral radiative properties of the two-dimensional rough surface. To quantitatively investigate the spatial distribution of energy reflected from the rough surface, the concept of the bidirectional reflectance distribution function is introduced. Correlation analysis between the reflectance and different impact factors is conducted to evaluate the influence degree. Comparison between the theoretical and experimental data is given to elucidate the accuracy of the computational code. This study is beneficial to optimizing the surface structures of optoelectronic devices such as solar cells.
Two-Dimensional Phononic Crystals: Disorder Matters.
Wagner, Markus R; Graczykowski, Bartlomiej; Reparaz, Juan Sebastian; El Sachat, Alexandros; Sledzinska, Marianna; Alzina, Francesc; Sotomayor Torres, Clivia M
2016-09-14
The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder.
Transient heat conduction through a substrate of brine-spongy ice
Dehghani, S. R.; Naterer, G. F.; Muzychka, Y. S.
2017-03-01
An analytical model for heat conduction through brine-spongy ice is developed. This model fills a gap in knowledge related to transient heat conduction to a two-phase substrate which is crucial for modeling transient icing and deicing of cold surfaces in contact with salt water. The core of the model is based on the phase change of pure ice and brine pockets trapped in the structure of spongy ice. Freezing of brine pockets causes the release of the latent heat of fusion that is considered as the source of heat generation distributed throughout the brine-spongy ice. A nonlinear partial differential equation and a number of equations of state for ice, brine, and brine-spongy ice create governing equations of heat transfer through brine-spongy ice. A standard numerical scheme solves the set of equations in various initial conditions. The variation of temperature, volume fraction of brine and salinity of brine pockets are calculated numerically. Experimental samples of brine-spongy ice are examined under transient conditions and their surface temperatures are captured using an infrared thermal camera. The numerical results, which are for various overall salinities, are closely aligned with the measured surface temperatures.
Transient heat conduction through a substrate of brine-spongy ice
Dehghani, S. R.; Naterer, G. F.; Muzychka, Y. S.
2017-08-01
An analytical model for heat conduction through brine-spongy ice is developed. This model fills a gap in knowledge related to transient heat conduction to a two-phase substrate which is crucial for modeling transient icing and deicing of cold surfaces in contact with salt water. The core of the model is based on the phase change of pure ice and brine pockets trapped in the structure of spongy ice. Freezing of brine pockets causes the release of the latent heat of fusion that is considered as the source of heat generation distributed throughout the brine-spongy ice. A nonlinear partial differential equation and a number of equations of state for ice, brine, and brine-spongy ice create governing equations of heat transfer through brine-spongy ice. A standard numerical scheme solves the set of equations in various initial conditions. The variation of temperature, volume fraction of brine and salinity of brine pockets are calculated numerically. Experimental samples of brine-spongy ice are examined under transient conditions and their surface temperatures are captured using an infrared thermal camera. The numerical results, which are for various overall salinities, are closely aligned with the measured surface temperatures.
Unexpected behavior of transient current in thin PZT films caused by grain-boundary conduction
Delimova, L. A.; Guschina, E. V.; Seregin, D. S.; Vorotilov, K. A.; Sigov, A. S.
2017-06-01
The behavior of the transient current at different preliminary polarizations has been studied in Pb(ZrTi)O3 (PZT) films with various grain structures. To affect the grain structure, PZT films were prepared by chemical solution deposition with a two-step crystallization process using combination of seed layers with a low Pb excess and the main layers with a 30 wt. % Pb excess. Some films were prepared with a fixed Pb excess in all the deposited layers. We found that the lead excess and the seed layer crystalline structure can affect the grain-boundary conduction which, in turn, influences the polarization dependence of the transient current and the appearance of current peaks which look like the so-called negative differential resistance region in the current-voltage curves. We show that the emergence of the current peaks in the PZT films depends on (i) whether the current flows inside the ferroelectric phase (grains) or outside, along grain boundaries and (ii) whether the applied bias direction is parallel or opposite to the polarization vector. A correlation between the grain-boundary conduction and current-polarization dependences is confirmed by the local current distribution measured by conductive atomic force microscopy. Possible mechanisms responsible for specific features of the transient current and appearance of the current peaks are discussed. The effect of grain-boundary conduction on the behavior of the current may be significant and should be taken into account in ferroelectric random access memory whose readout operation assumes registration of the magnitude of the polarization switching current under positive bias.
DEFF Research Database (Denmark)
Bording, Thue Sylvester; Nielsen, Søren Bom; Balling, Niels
2016-01-01
Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Within the geosciences, this applies to all aspects regarding the determination of terrestrial heat flow...... and volumetric heat capacity, and thereby also thermal diffusivity, are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity may also be determined. Finite element formulation provides a flexible forward solution for heat transfer across the bar...... and subsurface temperature modelling. Several methods, including the classical divided-bar technique, are available for laboratory measurements of thermal conductivity, and much fewer for thermal diffusivity. We have generalized the divided-bar technique to the transient case, in which thermal conductivity...
DEFF Research Database (Denmark)
Bording, Thue Sylvester; Nielsen, Søren Bom; Balling, Niels
2016-01-01
Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Within the geosciences, this applies to all aspects regarding the determination of terrestrial heat flow...... and subsurface temperature modelling. Several methods, including the classical divided-bar technique, are available for laboratory measurements of thermal conductivity, and much fewer for thermal diffusivity. We have generalized the divided-bar technique to the transient case, in which thermal conductivity...... and volumetric heat capacity, and thereby also thermal diffusivity, are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity may also be determined. Finite element formulation provides a flexible forward solution for heat transfer across the bar...
Directory of Open Access Journals (Sweden)
Qihong Feng
2017-01-01
Full Text Available This work presents a discussion on the pressure transient response of multistage fractured horizontal well in tight oil reservoirs. Based on Green’s function, a semianalytical model is put forward to obtain the behavior. Our proposed model accounts for fluid flow in four contiguous regions of the tight formation by using pressure continuity and mass conservation. The time-dependent conductivity of hydraulic fractures, which is ignored in previous models but highlighted by recent experiments, is also taken into account in our proposed model. We also include the effect of pressure drop along a horizontal wellbore. We substantiate the validity of our model and analyze the different flow regimes, as well as the effects of initial conductivity, fracture distribution, and geometry on the pressure transient behavior. Our results suggest that the decrease of fracture conductivity has a tremendous effect on the well performance. Finally, we compare our model results with the field data from a multistage fractured horizontal well in Jimsar sag, Xinjiang oilfield, and a good agreement is obtained.
Analysis on conducted coupling of electrical fast transient burst in mines
Institute of Scientific and Technical Information of China (English)
FENG De-wang; LAN Jian-rong
2012-01-01
Under the inflammable or explosive environment,the direct measurement methods by opening up the explosion-proof shell of electrical installations were not adopted.So,it's impossible to have a quantitative analysis on the limit of conducted disturbance for electrical fast transient burst (EFT/B) in such dangerous environments.Transient conducted coupling model,which using EFT/B as its excitation source,can be built based on circuit and electromagnetic field theory.Furthermore,numerical analysis was performed.The results indicate that the capacitive coupling voltage is the same polarity as EFT/B,and is the main disturbance form of conducted coupling in mines.The inductive coupling voltage is reversed polarity with the capacitive coupling voltage,and both peaks appear only in the rising time of EFT/B,which increase with the rising of load resistance.Moreover,the cable coupling voltage on the side of disturbance source is higher than the one on the other side in tunnel.To reduce the common resistance can suppress the resistive coupling disturbance.
Thermal diode from two-dimensional asymmetrical Ising lattices.
Wang, Lei; Li, Baowen
2011-06-01
Two-dimensional asymmetrical Ising models consisting of two weakly coupled dissimilar segments, coupled to heat baths with different temperatures at the two ends, are studied by Monte Carlo simulations. The heat rectifying effect, namely asymmetric heat conduction, is clearly observed. The underlying mechanisms are the different temperature dependencies of thermal conductivity κ at two dissimilar segments and the match (mismatch) of flipping frequencies of the interface spins.
THERM3D -- A boundary element computer program for transient heat conduction problems
Energy Technology Data Exchange (ETDEWEB)
Ingber, M.S. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Mechanical Engineering
1994-02-01
The computer code THERM3D implements the direct boundary element method (BEM) to solve transient heat conduction problems in arbitrary three-dimensional domains. This particular implementation of the BEM avoids performing time-consuming domain integrations by approximating a ``generalized forcing function`` in the interior of the domain with the use of radial basis functions. An approximate particular solution is then constructed, and the original problem is transformed into a sequence of Laplace problems. The code is capable of handling a large variety of boundary conditions including isothermal, specified flux, convection, radiation, and combined convection and radiation conditions. The computer code is benchmarked by comparisons with analytic and finite element results.
NUMERICAL STUDY OF TRANSIENT THREE-DIMENSIONAL HEAT CONDUCTION PROBLEM WITH A MOVING HEAT SOURCE
Directory of Open Access Journals (Sweden)
Marko V Miloš
2011-01-01
Full Text Available A numerical study of transient three-dimensional heat conduction problem with a moving source is presented. For numerical solution Douglas-Gunn alternating direction implicit method is applied and for the moving heat source flux distribution Gaussian function is used. An influence on numerical solution of input parameters figuring in flux boundary conditions is examined. This include parameters appearing in Gaussian function and heat transfer coefficient from free convection boundaries. Sensitivity of cooling time from 800 to 500 °C with respect to input parameters is also tested.
A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids
Perkins, R. A.; Roder, H. M.; Nieto de Castro, C. A.
1991-01-01
A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously use...
Consideration of transient heat conduction in a semi-infinite medium using homotopy analysis method
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
In the current work, transient heat conduction in a semi-infinite medium is considered for its many applications in various heat fields. Hcre, the homotopy analysis method (HAM) is applied to solve this problem and analytical results are compared with those of the exact and integral methods results. The results show that the HAM can give much better approximations than the other approximate methods. Changes in heat fluxes and profiles of temperature are obtained at different times and positions for copper, iron and aluminum.
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.
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.
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...
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.
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.
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...
Paul, William; Oliver, David; Miyahara, Yoichi; Grütter, Peter
2013-11-29
We report on transient adhesion and conductance phenomena associated with tip wetting in mechanical contacts produced by the indentation of a clean W(111) tip into a Au(111) surface. A combination of atomic force microscopy and scanning tunneling microscopy was used to carry out indentation and to image residual impressions in ultra-high vacuum. The ∼7 nm radii tips used in these experiments were prepared and characterized by field ion microscopy in the same instrument. The very first indentations of the tungsten tips show larger conductance and pull-off adhesive forces than subsequent indentations. After ∼30 indentations to a depth of ∼1.7 nm, the maximum conductance and adhesion forces reach steady state values approximately 12 × and 6 × smaller than their initial value. Indentation of W(111) tips into Cu(100) was also performed to investigate the universality of tip wetting phenomena with a different substrate. We propose a model from contact mechanics considerations which quantitatively reproduces the observed decay rate of the conductance and adhesion drops with a 1/e decay constant of 9-14 indentation cycles. The results show that the surface composition of an indenting tip plays an important role in defining the mechanical and electrical properties of indentation contacts.
Garnier, J. P.; Gallier, J.; Mercx, B.; Dudoignon, P.; Milcent, D.
2010-06-01
The transient hot-wire (THW) technique is widely used for measurements of the thermal-conductivity of most fluids and some attempts have also been carried out for simultaneous measurements of the thermal-diffusivity with the same hot wire. This technique was also tried to determine thermal properties of soils by the mean of probes which can be considered as wire with some assumptions. The purpose of this paper is to validate the thermal conductivity measurement by the THW technique in geomaterials, composed of compacted sand + clay mineral that can be used for earth construction (Compacted Earth Brick). The thermal transfer behaviors are mainly governed by the texture and moisture of the geomaterials. Thus the investigations were performed (1) in media made of glass beads of different diameters in dry and saturated state in order to observe the role of grain sizes and saturation state on the wire temperature (Δt) measurements and (2) in the compacted clay-geomaterial at different moisture states. The Δt / ln(t) diagrams allow the calculation of two thermal conductivities. The first one, measured in the short time acquisition (thermal conductivity of the material.
Directory of Open Access Journals (Sweden)
Milcent D.
2010-06-01
Full Text Available The transient hot-wire (THW technique is widely used for measurements of the thermal-conductivity of most fluids and some attempts have also been carried out for simultaneous measurements of the thermal-diffusivity with the same hot wire. This technique was also tried to determine thermal properties of soils by the mean of probes which can be considered as wire with some assumptions. The purpose of this paper is to validate the thermal conductivity measurement by the THW technique in geomaterials, composed of compacted sand + clay mineral that can be used for earth construction (Compacted Earth Brick. The thermal transfer behaviors are mainly governed by the texture and moisture of the geomaterials. Thus the investigations were performed (1 in media made of glass beads of different diameters in dry and saturated state in order to observe the role of grain sizes and saturation state on the wire temperature (Δt measurements and (2 in the compacted clay-geomaterial at different moisture states. The Δt / ln(t diagrams allow the calculation of two thermal conductivities. The first one, measured in the short time acquisition (< 1s, characterizes the microtexture of the material and its hydrated state. The second one, measured for longer time acquisitions, characterizes the mean thermal conductivity of the material.
Dyal, P.; Parkin, C. W.; Daily, W. D.
1974-01-01
Magnetometers were deployed at four Apollo sites on the moon to measure remanent and induced lunar magnetic fields. Measurements from this network of instruments were used to calculate the electrical conductivity, temperature, magnetic permeability, and iron abundance of the lunar interior. Global lunar fields due to eddy currents, induced in the lunar interior by magnetic transients in the geomagnetic tail field, were analyzed to calculate an electrical conductivity profile for the moon: the conductivity increases rapidly with depth from 10 to the minus 9 power mhos/meter at the lunar surface to .0001 mhos/meter at 200 km depth, then less rapidly to .02 mhos/meter at 1000 km depth. A temperature profile is calculated from conductivity: temperature rises rapidly with depth to 1100 K at 200 km depth, then less rapidly to 1800 K at 1000 km depth. Velocities and thicknesses of the earth's magnetopause and bow shock are estimated from simultaneous magnetometer measurements. Average speeds are determined to be about 50 km/sec for the magnetopause and 70 km/sec for the bow shock, although there are large variations in the measurements for any particular boundary crossing.
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The experimental results of the thermal conductivities of xonotlite-type calcium silicate insulation materials were presented at different temperatures and pressures.Two appropriative surroundings,i.e.an elevated temperature surrounding from ambient temperature to 1450 K and a vacuum surrounding from atmosphere pressure to 10-3 Pa,were designed for the transient hot-strip (THS) method.The thermal conduetivities of xonotlite-type calcium silicate with four densities from ambient temperature to 1000 K and 0.045 Pa to atmospheric pressure were measured.The results show that the thermal conductivity of xunotlite-type calcium silicate decreases apparently with the fall of density,and decreases apparently with the drop of pressure,and reaches the least value at about 100 Pa.The thermal conductivity of xonotlite-type calcium silicate increases almost linearly with T3,and increases more abundantly with low density than with high density.The thermal conductivity measurement uncertainty is estimated to be approximately 3% at ambient temperature,and 6% at 800 K.
Room temperature screening of thermal conductivity by means of thermal transient measurements
García-Cañadas, Jorge; Cheng, Shudan; Márquez-García, Lourdes; Prest, Martin J.; Akbari-Rahimabadi, Ahmad; Min, Gao
2016-10-01
A proof of concept of the possibility to estimate thermal conductivity of bulk disc samples at room temperature by means of thermal decays is demonstrated. An experimental set-up was designed and fabricated, which is able to perform thermal transient measurements by using a specially designed multifunctional probe that has the ability to measure temperature at its tip. Initially, the probe is heated by a heater coil located in its interior until the tip temperature reaches a steady state. Then, the probe is contacted with a disc sample which produces a temperature decay until a new state is reached. The difference between the initial and final states temperatures shows a correlation with the thermal conductivity of the sample. Employing a calibration equation, obtained using reference materials, the thermal conductivity can be calculated. Reasonably good random and systematic errors (<13% and ~9% respectively) are obtained. Theoretical simulations performed using COMSOL show a good qualitative agreement with experimental results. This new method involves an inexpensive and simple set-up which can be especially useful for thermal conductivity screening and high-throughput measurements.
Hybrid graded element model for transient heat conduction in functionally graded materials
Institute of Scientific and Technical Information of China (English)
Lei-Lei Cao; Qing-Hua Qin; Ning Zhao
2012-01-01
This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials (FGMs).First,a Laplace transform approach is used to handle the time variable.Then,a fundamental solution in Laplace space for FGMs is constructed.Next,a hybrid graded element is formulated based on the obtained fundamental solution and a frame field.As a result,the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field.Further,Stefest's algorithm is employed to convert the results in Laplace space back into the time-space domain.Finally,the performance of the proposed method is assessed by several benchmark examples.The results demonstrate well the efficiency and accuracy of the proposed method.
Directory of Open Access Journals (Sweden)
Susanna B Park
Full Text Available BACKGROUND: Oxaliplatin, a platinum-based chemotherapy utilised in the treatment of colorectal cancer, produces two forms of neurotoxicity--acute sensorimotor neuropathic symptoms and a dose-limiting chronic sensory neuropathy. Given that a Na(+ channelopathy has been proposed as the mechanism underlying acute oxaliplatin-induced neuropathy, the present study aimed to determine specific mechanisms of Na(+ channel dysfunction. METHODOLOGY/PRINCIPAL FINDINGS: Specifically the function of transient and persistent Na(+ currents were followed during treatment and were investigated in relation to oxaliplatin dose level. Eighteen patients were assessed before and after a single oxaliplatin infusion with motor and sensory axonal excitability studies performed on the median nerve at the wrist. While refractoriness (associated with Na(+ channel inactivation was significantly altered post-oxaliplatin infusion in both motor (Pre: 31.7±6.4%; Post: 68.8±14.5%; P≤.001 and sensory axons (Pre: 31.4±5.4%; Post: 21.4±5.5%; P<.05, strength-duration time constant (marker of persistent Na(+ conductances was not significantly altered post-infusion (Motor Pre: 0.395±0.01 ms; Post: 0.394±0.02 ms; NS; Sensory Pre:0.544±0.03 ms; Post: 0.535±0.05 ms; NS. However, changes in strength-duration time constant were significantly correlated with changes in refractoriness in motor and sensory axons (Motor correlation coefficient = -.65; P<.05; Sensory correlation coefficient = .67; P<.05. CONCLUSIONS/SIGNIFICANCE: It is concluded that the predominant effect of acute oxaliplatin exposure in human motor and sensory axons is mediated through changes in transient rather than persistent Na(+ conductances. These findings are likely to have implications for the design and trial of neuroprotective strategies.
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 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.
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.
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.
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.
Erdal, Daniel; Cirpka, Olaf A.
2017-04-01
Regional groundwater flow strongly depends on groundwater recharge and hydraulic conductivity. While conductivity is a spatially variable field, recharge can vary in both space and time. None of the two fields can be reliably observed on larger scales, and their estimation from other sparse data sets is an open topic. Further, common hydraulic-head observations may not suffice to constrain both fields simultaneously. In the current work we use the Ensemble Kalman filter to estimate spatially variable conductivity, spatiotemporally variable recharge and porosity for a synthetic phreatic aquifer. We use transient hydraulic-head and one spatially distributed set of environmental tracer observations to constrain the estimation. As environmental tracers generally reside for a long time in an aquifer, they require long simulation times and carries a long memory that makes them highly unsuitable for use in a sequential framework. Therefore, in this work we use the environmental tracer information to precondition the initial ensemble of recharge and conductivities, before starting the sequential filter. Thereby, we aim at improving the performance of the sequential filter by limiting the range of the recharge to values similar to the long-term annual recharge means and by creating an initial ensemble of conductivities that show similar pattern and values to the true field. The sequential filter is then used to further improve the parameters and to estimate the short term temporal behavior as well as the temporally evolving head field needed for short term predictions within the aquifer. For a virtual reality covering a subsection of the river Neckar it is shown that the use of environmental tracers can improve the performance of the filter. Results using the EnKF with and without this preconditioned initial ensemble are evaluated and discussed.
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.
Design of Thermal Conductivity Apparatus Base on Transient-state Radial Cylinder Method
Directory of Open Access Journals (Sweden)
Bambang Dwi Argo
2013-01-01
Full Text Available Thermal properties i.e. thermal conductivity (k of agricultural products provide critical information and data for the design and manufacture of equipment and machines for their processing. Literature generally abounds in information on wide and common agricultural products but lack on some locally grown products. The aim of the present study was to design and construct the thermal conductivity apparatus embedded with controlled temperature system and equipped with record system supported with personal computer as data processor. The apparatus designed based on transient-state radial cylinder method, consist of three main parts i.e. measurement chamber, controls panel and data acquisition processor. Measurement chamber was cylinder equipped by radially sixteen node of thermocouple with controlled temperature heater on center cylinder axis. It was placed in temperature controlled box generated by air flow system to eliminate the effect of surrounding temperature outside chamber. Controls panel functioned as link bridge and control unit that connect the measurement chamber to data acquisition processor. It consists of some electronic circuit e.g. analog to digital converter (ADC to control and acquire data from some thermocouple and sensors. Personal computer as data acquisition processor embedded with software developed with Borland Delphi. Developed software featured with calibrating, recording, calculating mode and displaying all obtained data graphically. Testing procedure was conducted with empty and filled chamber condition to adjust and calibrate data captured by thermocouples and sensors and displayed on personal computer, compared with actual condition. After some adjustment and calibration, all system was well functioned. The outcomes were in good agreements with thermal conductivity (k of agricultural products reported in the literatures.Keywords—
Bording, Thue S.; Nielsen, Søren B.; Balling, Niels
2016-04-01
Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Within the geosciences, this applies to all aspects regarding the determination of terrestrial heat flow and subsurface temperature modelling. Several methods, including the classical divided-bar technique, are available for laboratory measurements of thermal conductivity, and much fewer for thermal diffusivity. We have generalized the divided-bar technique to the transient case, in which thermal conductivity and volumetric heat capacity, and thereby also thermal diffusivity, are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity may also be determined. Finite element formulation provides a flexible forward solution for heat transfer across the bar and thermal properties are estimated by inverse Monte Carlo modelling. This methodology enables a proper quantification of experimental uncertainties on measured thermal properties. The developed methodology was applied to laboratory measurements of various materials, including a standard ceramic material and different rock samples, and measuring results were compared with results applying traditional steady-state divided-bar and an independent line-source method. All measurements show highly consistent results and with excellent reproducibility and high accuracy. For conductivity, uncertainty is typically 1-3 %, and for diffusivity uncertainty may be reduced to about 3-5 %. The main uncertainty originates from the presence of thermal contact resistance associated with the internal interfaces of the bar. They are not resolved during inversion, and it is highly important that they are minimized by careful sample preparation.
Finite element method formulation in polar coordinates for transient heat conduction problems
Duda, Piotr
2016-04-01
The aim of this paper is the formulation of the finite element method in polar coordinates to solve transient heat conduction problems. It is hard to find in the literature a formulation of the finite element method (FEM) in polar or cylindrical coordinates for the solution of heat transfer problems. This document shows how to apply the most often used boundary conditions. The global equation system is solved by the Crank-Nicolson method. The proposed algorithm is verified in three numerical tests. In the first example, the obtained transient temperature distribution is compared with the temperature obtained from the presented analytical solution. In the second numerical example, the variable boundary condition is assumed. In the last numerical example the component with the shape different than cylindrical is used. All examples show that the introduction of the polar coordinate system gives better results than in the Cartesian coordinate system. The finite element method formulation in polar coordinates is valuable since it provides a higher accuracy of the calculations without compacting the mesh in cylindrical or similar to tubular components. The proposed method can be applied for circular elements such as boiler drums, outlet headers, flux tubes. This algorithm can be useful during the solution of inverse problems, which do not allow for high density grid. This method can calculate the temperature distribution in the bodies of different properties in the circumferential and the radial direction. The presented algorithm can be developed for other coordinate systems. The examples demonstrate a good accuracy and stability of the proposed method.
Chirdon, William M.; Patil, Abhijeet P.
2011-10-01
An oscillating boundary temperature (OBT) method is proposed to simultaneously determine transient thermal properties including thermal conductivity, thermal diffusivity, internal heat generation, and volumetric heat capacity for exothermic solids and semi-solids over a narrow, controlled temperature range by using internal temperature measurements of the thermal wave. A comparison of this method and a transient hot-wire (THW) method is conducted in the presence of heat generation using physical properties which change over time. The advantages and disadvantages of both methods are discussed. The OBT method is potentially useful for the analysis of exothermic solid or semi-solid materials such as hydrating (freshly mixed) cement and concrete, polymers and composites undergoing polymerization reactions, and biological tissues.
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.
Transient heat conduction in a solid slab using multiple-scale analysis
Energy Technology Data Exchange (ETDEWEB)
Bautista, O.; Campos, I. [ITESM, Division de Ingenieria y Arquitectura, Mexico, DF (Mexico); Mendez, F. [UNAM, Facultad de Ingenieria, Mexico, DF (Mexico)
2005-12-01
In this paper we study the unsteady heat conduction due to a sudden temperature step in the external surfaces of a solid slab. In order to estimate the temperature profile in the solid, we applied the multiple-scale perturbation technique by identifying the ''early'' and ''late'' transient regimes for small values of the Biot number, Bi. In this sense, we have re-visited the classical lumped method, incorporating this particular case as an asymptotic limit, which is fully described by the ''late'' regime for small values of Bi. Once the temperature distribution is analytically predicted, this solution is compared against the exact solution and with other analytical results obtained by using regular perturbation techniques, for different values of the Biot number Bi. Observing a good agreement between the corresponding comparisons, we obtain a very simple and useful formula to predict the nondimensional temperature of the solid slab. (orig.)
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.
Nonlinear transport in a two dimensional holographic superconductor
Zeng, Hua Bi; Tian, Yu; Fan, Zhe Yong; Chen, Chiang-Mei
2016-06-01
The problem of nonlinear transport in a two-dimensional superconductor with an applied oscillating electric field is solved by the holographic method. The complex conductivity can be computed from the dynamics of the current for both the near- and nonequilibrium regimes. The limit of weak electric field corresponds to the near-equilibrium superconducting regime, where the charge response is linear and the conductivity develops a gap determined by the condensate. A larger electric field drives the system into a superconducting nonequilibrium steady state, where the nonlinear conductivity is quadratic with respect to the electric field. Increasing the amplitude of the applied electric field results in a far-from-equilibrium nonsuperconducting steady state with a universal linear conductivity of one. In the lower temperature regime we also find chaotic behavior of the superconducting gap, which results in a nonmonotonic field-dependent nonlinear conductivity.
Nonlinear Transport in a Two Dimensional Holographic Superconductor
Zeng, Hua Bi; Fan, Zhe Yong; Chen, Chiang-Mei
2016-01-01
The problem of nonlinear transport in a two dimensional superconductor with an applied oscillating electric field is solved by the holographic method. The complex conductivity can be computed from the dynamics of the current for both near- and non-equilibrium regimes. The limit of weak electric field corresponds to the near equilibrium superconducting regime, where the charge response is linear and the conductivity develops a gap determined by the condensate. A larger electric field drives the system into a superconducting non-equilibrium steady state, where the nonlinear conductivity is quadratic with respect to the electric field. Keeping increasing the amplitude of applied electric field results in a far-from-equilibrium non-superconducting steady state with a universal linear conductivity of one. In lower temperature regime we also find chaotic behavior of superconducting gap, which results in a non-monotonic field dependent nonlinear conductivity.
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.
Alexiev, D; Mo, L; Rosenfeld, A H
1999-01-01
The use of conventional capacitance-based deep-level transient spectroscopy is not applicable when defect concentrations approach the background carrier concentration. Due to this limitation the technique cannot be used for examining heavily irradiated silicon, or semi-insulating semiconductor materials. Optical deep-level transient conductance spectroscopy can overcome the limitations of capacitance-based techniques through the measurement of a conductance transient measured with a marginal oscillator. This paper provides details of the application of this method to heavily damaged high-purity silicon. Silicon-based PIN detector structures irradiated with 1 MeV neutrons, to approximately 3x10 sup 1 sup 3 n/cm sup 2 and detectors irradiated with 24 GeV/c protons, to 3.8x10 sup 1 sup 3 p/cm sup 2 , were examined. (author)
The Rare Two-Dimensional Materials with Dirac Cones
Wang, Jinying; Deng, Shibin; Liu, Zhongfan; Liu, Zhirong
2014-01-01
Inspired by the great development of graphene, more and more works have been conducted to seek new two-dimensional (2D) materials with Dirac cones. Although 2D Dirac materials possess many novel properties and physics, they are rare compared with the numerous 2D materials. To provide explanation for the rarity of 2D Dirac materials as well as clues in searching for new Dirac systems, here we review the recent theoretical aspects of various 2D Dirac materials, including graphene, silicene, ger...
Theories on Frustrated Electrons in Two-Dimensional Organic Solids
Directory of Open Access Journals (Sweden)
Chisa Hotta
2012-08-01
Full Text Available Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to many interesting states of matter in the two insulators and in the metals adjacent to them. This review is concerned with the theoretical studies on such issue over the past ten years, and provides the systematic understanding on exotic metals, dielectrics, and spin liquids, which are the consequences of the competing correlation and fluctuation under frustration.
Graphene and Two-Dimensional Materials for Optoelectronic Applications
Directory of Open Access Journals (Sweden)
Andreas Bablich
2016-03-01
Full Text Available This article reviews optoelectronic devices based on graphene and related two-dimensional (2D materials. The review includes basic considerations of process technology, including demonstrations of 2D heterostructure growth, and comments on the scalability and manufacturability of the growth methods. We then assess the potential of graphene-based transparent conducting electrodes. A major part of the review describes photodetectors based on lateral graphene p-n junctions and Schottky diodes. Finally, the progress in vertical devices made from 2D/3D heterojunctions, as well as all-2D heterostructures is discussed.
Smoothed Particle Hydrodynamics Method for Two-dimensional Stefan Problem
Tarwidi, Dede
2016-01-01
Smoothed particle hydrodynamics (SPH) is developed for modelling of melting and solidification. Enthalpy method is used to solve heat conduction equations which involved moving interface between phases. At first, we study the melting of floating ice in the water for two-dimensional system. The ice objects are assumed as solid particles floating in fluid particles. The fluid and solid motion are governed by Navier-Stokes equation and basic rigid dynamics equation, respectively. We also propose a strategy to separate solid particles due to melting and solidification. Numerical results are obtained and plotted for several initial conditions.
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.
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.
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.
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.
Thermal conductivity and thermal diffusivity are two important physical properties essential for designing any food engineering processes. Recently a new transient plane-source method was developed to measure a variety of materials, but its application in foods has not been documented. Therefore, ...
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)
Miroslav M Živković; Aleksandar V Nikolić; Radovan B Slavković; Fatima T Živić
2010-01-01
This paper deals with transient nonlinear heat conduction through the insulation wall of the tank for transportation of liquid aluminum. Tanks designed for this purpose must satisfy certain requirements regarding temperature of loading and unloading, during transport. Basic theoretical equations are presented, which describe the problem of heat conduction finite element (FE) analysis, starting from the differential equation of energy balance, taking into account the initial and boundary condi...
Zmywaczyk, J.; Koniorczyk, P.
2009-08-01
The problem of simultaneous identification of the thermal conductivity Λ(T) and the asymmetry parameter g of the Henyey-Greenstein scattering phase function is under consideration. A one-dimensional configuration in a grey participating medium with respect to silica fibers for which the thermophysical and optical properties are known from the literature is accepted. To find the unknown parameters, it is assumed that the thermal conductivity Λ(T) may be represented in a base of functions {1, T, T 2, . . .,T K } so the inverse problem can be applied to determine a set of coefficients {Λ0, Λ1, . . ., Λ K ; g}. The solution of the inverse problem is based on minimization of the ordinary squared differences between the measured and model temperatures. The measured temperatures are considered known. Temperature responses measured or theoretically generated at several different distances from the heat source along an x axis of the specimen set are known as a result of the numerical solution of the transient coupled heat transfer in a grey participating medium. An implicit finite volume method (FVM) is used for handling the energy equation, while a finite difference method (FDM) is applied to find the sensitivity coefficients with respect to the unknown set of coefficients. There are free parameters in a model, so these parameters are changed during an iteration process used by the fitting procedure. The Levenberg- Marquardt fitting procedure is iteratively searching for best fit of these parameters. The source term in the governing conservation-of-energy equation taking into account absorption, emission, and scattering of radiation is calculated by means of a discrete ordinate method together with an FDM while the scattering phase function approximated by the Henyey-Greenstein function is expanded in a series of Legendre polynomials with coefficients {c l } = (2l + 1)g l . The numerical procedure proposed here also allows consideration of some cases of coupled heat
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....
Two-dimensional gas of massless Dirac fermions in graphene.
Novoselov, K S; Geim, A K; Morozov, S V; Jiang, D; Katsnelson, M I; Grigorieva, I V; Dubonos, S V; Firsov, A A
2005-11-10
Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.
Commensurability oscillations in a two-dimensional lateral superlattice
Davies, John; Long, Andrew; Grant, David; Chowdhury, Suja
2000-03-01
We have calculated and measured conduction in a two-dimensional electron gas subject to a weak two-dimensional periodic potential and a normal magnetic field. Simulations with a potential Vx \\cos(2π x/a) + Vy \\cos(2π y/a) show the usual commensurability oscillations in ρ_xx(B) with Vx alone. The introduction of Vy suppresses these oscillations, rather than introducing the additional oscillations in ρ_yy(B) expected from previous perturbation theories. We explain this in terms of drift of the guiding center of cyclotron motion along contours of an effective potential: open orbits of the guiding center contribute to conduction but closed orbits do not. All orbits are closed in a symmetric superlattice with |V_x| = |V_y| and commensurability oscillations are therefore quenched. Experiments on etched superlattices confirm this picture. Conventional lattice-matched samples give a symmetric potential and weak oscillations; the symmetry is broken by the piezoelectric effect in stressed samples, leading to strong oscillations. Periodic modulation of the magnetic field can be treated in the same way, which explains previous experimental results.
Directory of Open Access Journals (Sweden)
Miroslav M Živković
2010-01-01
Full Text Available This paper deals with transient nonlinear heat conduction through the insulation wall of the tank for transportation of liquid aluminum. Tanks designed for this purpose must satisfy certain requirements regarding temperature of loading and unloading, during transport. Basic theoretical equations are presented, which describe the problem of heat conduction finite element (FE analysis, starting from the differential equation of energy balance, taking into account the initial and boundary conditions of the problem. General 3D problem for heat conduction is considered, from which solutions for two- and one-dimensional heat conduction can be obtained, as special cases. Forming of the finite element matrices using Galerkin method is briefly described. The procedure for solving equations of energy balance is discussed, by methods of resolving iterative processes of nonlinear transient heat conduction. Solution of this problem illustrates possibilities of PAK-T software package, such as materials properties, given as tabular data, or analytical functions. Software also offers the possibility to solve nonlinear and transient problems with incremental methods. Obtained results for different thicknesses of the tank wall insulation materials enable its comparison in regards to given conditions
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.
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...
Comparative Two-Dimensional Fluorescence Gel Electrophoresis.
Ackermann, Doreen; König, Simone
2018-01-01
Two-dimensional comparative fluorescence gel electrophoresis (CoFGE) uses an internal standard to increase the reproducibility of coordinate assignment for protein spots visualized on 2D polyacrylamide gels. This is particularly important for samples, which need to be compared without the availability of replicates and thus cannot be studied using differential gel electrophoresis (DIGE). CoFGE corrects for gel-to-gel variability by co-running with the sample proteome a standardized marker grid of 80-100 nodes, which is formed by a set of purified proteins. Differentiation of reference and analyte is possible by the use of two fluorescent dyes. Variations in the y-dimension (molecular weight) are corrected by the marker grid. For the optional control of the x-dimension (pI), azo dyes can be used. Experiments are possible in both vertical and horizontal (h) electrophoresis devices, but hCoFGE is much easier to perform. For data analysis, commercial software capable of warping can be adapted.
Two-dimensional hexagonal semiconductors beyond graphene
Nguyen, Bich Ha; Hieu Nguyen, Van
2016-12-01
The rapid and successful development of the research on graphene and graphene-based nanostructures has been substantially enlarged to include many other two-dimensional hexagonal semiconductors (THS): phosphorene, silicene, germanene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs) such as MoS2, MoSe2, WS2, WSe2 as well as the van der Waals heterostructures of various THSs (including graphene). The present article is a review of recent works on THSs beyond graphene and van der Waals heterostructures composed of different pairs of all THSs. One among the priorities of new THSs compared to graphene is the presence of a non-vanishing energy bandgap which opened up the ability to fabricate a large number of electronic, optoelectronic and photonic devices on the basis of these new materials and their van der Waals heterostructures. Moreover, a significant progress in the research on TMDCs was the discovery of valley degree of freedom. The results of research on valley degree of freedom and the development of a new technology based on valley degree of freedom-valleytronics are also presented. Thus the scientific contents of the basic research and practical applications os THSs are very rich and extremely promising.
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.
Radiation effects on two-dimensional materials
Energy Technology Data Exchange (ETDEWEB)
Walker, R.C. II; Robinson, J.A. [Department of Materials Science, Penn State, University Park, PA (United States); Center for Two-Dimensional Layered Materials, Penn State, University Park, PA (United States); Shi, T. [Department of Mechanical and Nuclear Engineering, Penn State, University Park, PA (United States); Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI (United States); Silva, E.C. [GlobalFoundries, Malta, NY (United States); Jovanovic, I. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI (United States)
2016-12-15
The effects of electromagnetic and particle irradiation on two-dimensional materials (2DMs) are discussed in this review. Radiation creates defects that impact the structure and electronic performance of materials. Determining the impact of these defects is important for developing 2DM-based devices for use in high-radiation environments, such as space or nuclear reactors. As such, most experimental studies have been focused on determining total ionizing dose damage to 2DMs and devices. Total dose experiments using X-rays, gamma rays, electrons, protons, and heavy ions are summarized in this review. We briefly discuss the possibility of investigating single event effects in 2DMs based on initial ion beam irradiation experiments and the development of 2DM-based integrated circuits. Additionally, beneficial uses of irradiation such as ion implantation to dope materials or electron-beam and helium-beam etching to shape materials have begun to be used on 2DMs and are reviewed as well. For non-ionizing radiation, such as low-energy photons, we review the literature on 2DM-based photo-detection from terahertz to UV. The majority of photo-detecting devices operate in the visible and UV range, and for this reason they are the focus of this review. However, we review the progress in developing 2DMs for detecting infrared and terahertz radiation. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Photodetectors based on two dimensional materials
Zheng, Lou; Zhongzhu, Liang; Guozhen, Shen
2016-09-01
Two-dimensional (2D) materials with unique properties have received a great deal of attention in recent years. This family of materials has rapidly established themselves as intriguing building blocks for versatile nanoelectronic devices that offer promising potential for use in next generation optoelectronics, such as photodetectors. Furthermore, their optoelectronic performance can be adjusted by varying the number of layers. They have demonstrated excellent light absorption, enabling ultrafast and ultrasensitive detection of light in photodetectors, especially in their single-layer structure. Moreover, due to their atomic thickness, outstanding mechanical flexibility, and large breaking strength, these materials have been of great interest for use in flexible devices and strain engineering. Toward that end, several kinds of photodetectors based on 2D materials have been reported. Here, we present a review of the state-of-the-art in photodetectors based on graphene and other 2D materials, such as the graphene, transition metal dichalcogenides, and so on. Project supported by the National Natural Science Foundation of China (Nos. 61377033, 61574132, 61504136) and the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.
Asymptotics for Two-dimensional Atoms
DEFF Research Database (Denmark)
Nam, Phan Thanh; Portmann, Fabian; Solovej, Jan Philip
2012-01-01
We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E^{\\TF}(\\lambd......We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E......^{\\TF}(\\lambda)$ is given by a Thomas-Fermi type variational problem and $c^{\\rm H}\\approx -2.2339$ is an explicit constant. We also show that the radius of a two-dimensional neutral atom is unbounded when $Z\\to \\infty$, which is contrary to the expected behavior of three-dimensional atoms....
Predicting Two-Dimensional Silicon Carbide Monolayers.
Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I
2015-10-27
Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.
Institute of Scientific and Technical Information of China (English)
BAI Su-Yuan; TANG Zhen-An; HUANG Zheng-Xing; YU Jun; WANG Jia-Qi
2008-01-01
Thermal conductivity of submicron-thick aluminium oxide thin films prepared by middle frequency magnetron sputtering is measured using a transient thermo-reflectance technique.A three-layer model based on transmission line theory and the gentic algorithm optimization method are employed to obtain the thermal conductivity of thin films and the interfacial thermal resistance.The results show that the average thermal conductivity of 3301000nm aluminium oxide thin films is 3.3Wm-1 K-1 at room temperature.No significant thickness dependence is found.The uncertainty of the measurement is less than 10%.
DEFF Research Database (Denmark)
Titova, Lyubov V.; Harthy, Rahma Al; Cooke, David
We use time-resolved THz spectroscopy and transient optical absorption spectroscopy as two complementary techniques to study ultrafast carrier dynamics in silicon nanocrystal thin films. We find that the photoconductive dynamics in these materials is dominated by interface trapping, and we observe...... several different relaxation mechanisms for photoexcited carriers...
Experimental evidence for a two-dimensional quantized Hall insulator
Hilke, M.; Shahar, D.; Song, S. H.; Tsui, D. C.; Xie, Y. H.; Monroe, Don
1998-10-01
The general theoretical definition of an insulator is a material in which the conductivity vanishes at the absolute zero of temperature. In classical insulators, such as materials with a band gap, vanishing conductivities lead to diverging resistivities. But other insulators can show more complex behaviour, particularly in the presence of a high magnetic field, where different components of the resistivity tensor can display different behaviours: the magnetoresistance diverges as the temperature approaches absolute zero, but the transverse (Hall) resistance remains finite. Such a system is known as a Hall insulator. Here we report experimental evidence for a quantized Hall insulator in a two-dimensional electron system-confined in a semiconductor quantum well. The Hall resistance is quantized in the quantum unit of resistance h/e2, where h is Planck's constant and e the electronic charge. At low fields, the sample reverts to being a normal Hall insulator.
Interaction of two-dimensional magnetoexcitons
Dumanov, E. V.; Podlesny, I. V.; Moskalenko, S. A.; Liberman, M. A.
2017-04-01
We study interaction of the two-dimensional magnetoexcitons with in-plane wave vector k→∥ = 0 , taking into account the influence of the excited Landau levels (ELLs) and of the external electric field perpendicular to the surface of the quantum well and parallel to the external magnetic field. It is shown that the account of the ELLs gives rise to the repulsion between the spinless magnetoexcitons with k→∥ = 0 in the Fock approximation, with the interaction constant g decreasing inverse proportional to the magnetic field strength B (g (0) ∼ 1 / B) . In the presence of the perpendicular electric field the Rashba spin-orbit coupling (RSOC), Zeeman splitting (ZS) and nonparabolicity of the heavy-hole dispersion law affect the Landau quantization of the electrons and holes. They move along the new cyclotron orbits, change their Coulomb interactions and cause the interaction between 2D magnetoexcitons with k→∥ = 0 . The changes of the Coulomb interactions caused by the electrons and by the holes moving with new cyclotron orbits are characterized by some coefficients, which in the absence of the electric field turn to be unity. The differences between these coefficients of the electron-hole pairs forming the magnetoexcitons determine their affinities to the interactions. The interactions between the homogeneous, semihomogeneous and heterogeneous magnetoexcitons forming the symmetric states with the same signs of their affinities are attractive whereas in the case of different sign affinities are repulsive. In the heterogeneous asymmetric states the interactions have opposite signs in comparison with the symmetric states. In all these cases the interaction constant g have the dependence g (0) 1 /√{ B} .
Institute of Scientific and Technical Information of China (English)
Chen Li; Ma He-Ping; Cheng Yu-Min
2013-01-01
In this paper,the complex variable reproducing kernel particle (CVRKP) method and the finite element (FE) method are combined as the CVRKP-FE method to solve transient heat conduction problems.The CVRKP-FE method not only conveniently imposes the essential boundary conditions,but also exploits the advantages of the individual methods while avoiding their disadvantages,then the computational efficiency is higher.A hybrid approximation function is applied to combine the CVRKP method with the FE method,and the traditional difference method for two-point boundary value problems is selected as the time discretization scheme.The corresponding formulations of the CVRKP-FE method are presented in detail.Several selected numerical examples of the transient heat conduction problems are presented to illustrate the performance of the CVRKP-FE method.
Two-dimensional materials and their prospects in transistor electronics.
Schwierz, F; Pezoldt, J; Granzner, R
2015-05-14
During the past decade, two-dimensional materials have attracted incredible interest from the electronic device community. The first two-dimensional material studied in detail was graphene and, since 2007, it has intensively been explored as a material for electronic devices, in particular, transistors. While graphene transistors are still on the agenda, researchers have extended their work to two-dimensional materials beyond graphene and the number of two-dimensional materials under examination has literally exploded recently. Meanwhile several hundreds of different two-dimensional materials are known, a substantial part of them is considered useful for transistors, and experimental transistors with channels of different two-dimensional materials have been demonstrated. In spite of the rapid progress in the field, the prospects of two-dimensional transistors still remain vague and optimistic opinions face rather reserved assessments. The intention of the present paper is to shed more light on the merits and drawbacks of two-dimensional materials for transistor electronics and to add a few more facets to the ongoing discussion on the prospects of two-dimensional transistors. To this end, we compose a wish list of properties for a good transistor channel material and examine to what extent the two-dimensional materials fulfill the criteria of the list. The state-of-the-art two-dimensional transistors are reviewed and a balanced view of both the pros and cons of these devices is provided.
The two dimensional fold test in paleomagnetism using ipython notebook
Setiabudidaya, Dedi; Piper, John D. A.
2016-01-01
One aspect of paleomagnetic analysis prone to controversy is the result of the fold test used to evaluate the age of a magnetisation component relative to the age of a structural event. Initially, the fold test was conducted by comparing the Fisherian precision parameter (k) to results from different limbs of a fold structure before and after tilt adjustment. To accommodate synfolding magnetisation, the tilt correction can be performed in stepwise fashion to both limbs simultaneously, here called one dimensional (1D) fold test. The two dimensional (2D) fold test described in this paper is carried out by applying stepwise tilt adjustment to each limb of the fold separately. The rationale for this is that tilts observed on contrasting limbs of deformed structure may not be synchronous or even belong to the same episode of deformation. A program for the procedure is presented here which generates two dimensional values of the k-parameter visually presented in contoured form. The use of ipython notebook enables this 2D fold test to be performed interactively and yield a more precise evaluation than the primitive 1D fold test.
Directory of Open Access Journals (Sweden)
Behzad Bahraminejad
2010-05-01
Full Text Available In this study, the ability of the Capillary-attached conductive gas sensor (CGS in real-time gas identification was investigated. The structure of the prototype fabricated CGS is presented. Portions were selected from the beginning of the CGS transient response including the first 11 samples to the first 100 samples. Different feature extraction and classification methods were applied on the selected portions. Validation of methods was evaluated to study the ability of an early portion of the CGS transient response in target gas (TG identification. Experimental results proved that applying extracted features from an early part of the CGS transient response along with a classifier can distinguish short-chain alcohols from each other perfectly. Decreasing time of exposition in the interaction between target gas and sensing element improved the reliability of the sensor. Classification rate was also improved and time of identification was decreased. Moreover, the results indicated the optimum interval of the early transient response of the CGS for selecting portions to achieve the best classification rates.
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
Aerodynamics of two-dimensional flapping wings in tandem configuration
Lua, K. B.; Lu, H.; Zhang, X. H.; Lim, T. T.; Yeo, K. S.
2016-12-01
This paper reports a fundamental investigation on the aerodynamics of two-dimensional flapping wings in tandem configuration in forward flight. Of particular interest are the effects of phase angle (φ) and center-to-center distance (L) between the front wing and the rear wing on the aerodynamic force generation at a Reynolds number of 5000. Both experimental and numerical methods were employed. A force sensor was used to measure the time-history aerodynamic forces experienced by the two wings and digital particle image velocimetry was utilized to obtain the corresponding flow structures. Both the front wing and the rear wing executed the same simple harmonic motions with φ ranging from -180° to 180° and four values of L, i.e., 1.5c, 2c, 3c, and 4c (c is the wing chord length). Results show that at fixed L = 2c, tandem wings perform better than the sum of two single wings that flap independently in terms of thrust for phase angle approximately from -90° to 90°. The maximum thrust on the rear wing occurs during in-phase flapping (φ = 0°). Correlation of transient thrust and flow structure indicates that there are generally two types of wing-wake interactions, depending on whether the rear wing crosses the shear layer shed from the front wing. Finally, increasing wing spacing has similar effect as reducing the phase angle, and an approximate mathematical model is derived to describe the relationship between these two parameters.
Short-pulsed laser transport in two-dimensional scattering media by natural element method.
Zhang, Yong; Yi, Hong-Liang; Xie, Ming; Tan, He-Ping
2014-04-01
The natural element method (NEM) is extended to solve transient radiative transfer (TRT) in two-dimensional semitransparent media subjected to a collimated short laser irradiation. The least-squares (LS) weighted residuals approach is employed to spatially discretize the transient radiative heat transfer equation. First, for the case of the refractive index matched boundary, LSNEM solutions to TRT are validated by comparison with results reported in the literature. Effects of the incident angle on time-resolved signals of transmittance and reflectance are investigated. Afterward, the accuracy of this algorithm for the case of the refractive index mismatched boundary is studied. Finally, the LSNEM is extended to study the TRT in a two-dimensional semitransparent medium with refractive index discontinuity irradiated by the short pulse laser. The effects of scattering albedo, optical thickness, scattering phase function, and refractive index on transmittance and reflectance signals are investigated. Several interesting trends on the time-resolved signals are observed and analyzed.
Yu, XiaoChun; Bai, YuGuang; Cui, Miao; Gao, XiaoWei
2013-05-01
This paper presents a new inverse analysis approach to sensitivity analysis and material property identification in transient non-homogeneous and non-linear heat conduction Boundary Element Method (BEM) analysis based on Complex Variable Differentiation Method (CVDM). In this approach, the material properties are taken as the optimization variables, and the sensitivity coefficients are computed by CVDM. The advantages of using CVDM are that the computation of partial derivatives of an implicit function is reduced to function calculation in a complex domain, and the parameter sensitivity coefficients can be determined in a more accurate way than the traditional Finite Difference Method (FDM). Based on BEM and CVDM in evaluation of the sensitivity matrix of heat flux, the parameter such as thermal conductivity can be accurately identified. Six numerical examples are given to demonstrate the potential of the proposed approach. The results indicate that the presented method is efficient for identifying the thermal conductivity with single or multiple parameters.
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.
Approaches to verification of two-dimensional water quality models
Energy Technology Data Exchange (ETDEWEB)
Butkus, S.R. (Tennessee Valley Authority, Chattanooga, TN (USA). Water Quality Dept.)
1990-11-01
The verification of a water quality model is the one procedure most needed by decision making evaluating a model predictions, but is often not adequate or done at all. The results of a properly conducted verification provide the decision makers with an estimate of the uncertainty associated with model predictions. Several statistical tests are available for quantifying of the performance of a model. Six methods of verification were evaluated using an application of the BETTER two-dimensional water quality model for Chickamauga reservoir. Model predictions for ten state variables were compared to observed conditions from 1989. Spatial distributions of the verification measures showed the model predictions were generally adequate, except at a few specific locations in the reservoir. The most useful statistics were the mean standard error of the residuals. Quantifiable measures of model performance should be calculated during calibration and verification of future applications of the BETTER model. 25 refs., 5 figs., 7 tabs.
Coherent two-dimensional spectroscopy of a Fano model
Poulsen, Felipe; Pullerits, Tõnu; Hansen, Thorsten
2016-01-01
The Fano lineshape arises from the interference of two excitation pathways to reach a continuum. Its generality has resulted in a tremendous success in explaining the lineshapes of many one-dimensional spectroscopies - absorption, emission, scattering, conductance, photofragmentation - applied to very varied systems - atoms, molecules, semiconductors and metals. Unravelling a spectroscopy into a second dimension reveals the relationship between states in addition to decongesting the spectra. Femtosecond-resolved two-dimensional electronic spectroscopy (2DES) is a four-wave mixing technique that measures the time-evolution of the populations, and coherences of excited states. It has been applied extensively to the dynamics of photosynthetic units, and more recently to materials with extended band-structures. In this letter, we solve the full time-dependent third-order response, measured in 2DES, of a Fano model and give the new system parameters that become accessible.
Thinnest two-dimensional nanomaterial-graphene for solar energy.
Hu, Yun Hang; Wang, Hui; Hu, Bo
2010-07-19
Graphene is a rapidly rising star in materials science. This two-dimensional material exhibits unique properties, such as low resistance, excellent optical transmittance, and high mechanical and chemical stabilities. These exceptional advantages possess great promise for its potential applications in photovoltaic devices. In this Review, we present the status of graphene research for solar energy with emphasis on solar cells. Firstly, the preparation and properties of graphene are described. Secondly, applications of graphene as transparent conductive electrodes and counter electrodes are presented. Thirdly, graphene-based electron- (or hole) accepting materials for solar energy conversion are evaluated. Fourthly, the promoting effect of graphene on photovoltaic devices and the photocatalytic property of graphene-semiconductor composites are discussed. Finally, the challenges to increase the power conversion efficiency of graphene-based solar cells are explored.
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.
Fabre, Antoine; Hristov, Jordan
2016-04-01
Closed form approximate solutions to nonlinear transient heat conduction with linearly temperature-dependent thermal diffusivity have been developed by the integral-balance integral method under transient conditions. The solutions uses improved direct approaches of the integral method and avoid the commonly used linearization by the Kirchhoff transformation. The main steps in the new solutions are improvements in the integration technique of the double-integration technique and the optimization of the exponent of the approximate parabolic profile with unspecified exponent. Solutions to Dirichlet and Neumann boundary condition problems have been developed as examples by the classical Heat-balance integral method (HBIM) and the Double-integration method (DIM). Additional examples with HBIM and DIM solutions to cases when the Kirchhoff transform is initially applied have been developed.
Double-Humped Transverse Density Profile in Two-Dimensional Chute Flow with Rough Sidewalls
Institute of Scientific and Technical Information of China (English)
HU Guo-Qi; ZHANG Xun-Sheng; BAO De-Song; TANG Xiao-Wei
2006-01-01
@@ We study a two-dimensional granular rapid flow with rough sidewalls stuck with the same size discs by molecular dynamics simulation. A transient state of the double-humped density profile in the flowing process has been found, which appears and moves as travelling wave and is the same as the phenomena in the recent experiments [Acta Phys. Sin. 53 (2004) 3389 (in Chinese)].
Two-dimensional thermal modeling of power monolithic microwave integrated circuits (MMIC's)
Fan, Mark S.; Christou, Aris; Pecht, Michael G.
1992-01-01
Numerical simulations of the two-dimensional temperature distributions for a typical GaAs MMIC circuit are conducted, aiming at understanding the heat conduction process of the circuit chip and providing temperature information for device reliability analysis. The method used is to solve the two-dimensional heat conduction equation with a control-volume-based finite difference scheme. In particular, the effects of the power dissipation and the ambient temperature are examined, and the criterion for the worst operating environment is discussed in terms of the allowed highest device junction temperature.
The convolution theorem for two-dimensional continuous wavelet transform
Institute of Scientific and Technical Information of China (English)
ZHANG CHI
2013-01-01
In this paper , application of two -dimensional continuous wavelet transform to image processes is studied. We first show that the convolution and correlation of two continuous wavelets satisfy the required admissibility and regularity conditions ,and then we derive the convolution and correlation theorem for two-dimensional continuous wavelet transform. Finally, we present numerical example showing the usefulness of applying the convolution theorem for two -dimensional continuous wavelet transform to perform image restoration in the presence of additive noise.
Two Dimensional Thermal-Hydraulic Analysis for a Packed Bed Regenerator Used in a Reheating Furnace
Directory of Open Access Journals (Sweden)
Chien-Nan Lin
2016-11-01
Full Text Available Packed bed is widely used for different industries and technologies, such as heat exchangers, heat recovery, thermal energy storage and chemical reactors. In modern steel industry, packed bed regenerator is widely utilized in the reheating furnace to increase the furnace efficiency. This study established a two dimensional numerical model to simulate a packed bed used in regenerative furnaces. The physical properties of fluids and packed stuffing (such as density, thermal conductivity, and specific heat are considered as functions of temperature to adapt the large temperature variation in operation. The transient temperature profiles of the flue gas, packed bed, and air during the heating and regeneration period are examined for various switching time (30, 60, 120, and 240 s. The results reveal that, during the heating period, the spanwise averaged heat transfer coefficient is decreased along the longitudinal downstream direction, while during the regeneration period, the opposite trend is true. Moreover, the regenerator thermal effectiveness is decreased by increasing the switching time.
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
Two-dimensional protonic percolation on lightly hydrated purple membrane.
Rupley, J A; Siemankowski, L; Careri, G; Bruni, F
1988-12-01
The capacitance and dielectric loss factor were measured for a sample of purple membrane of Halobacterium halobium as a function of hydration level (0.017 to >0.2 g of water/g of membrane) and frequency (10 kHz to 10 MHz). The capacitance and the derived conductivity show explosive growth above a threshold hydration level, h(c) approximately 0.0456. The conductivity shows a deuterium isotope effect, H/(2)H = 1.38, in close agreement with expectation for a protonic process. The level h(c) is frequency independent and shows no deuterium isotope effect. These properties are analogous to those found for lysozyme in a related study. Protonic conduction for the purple membrane can be considered, as for lysozyme, within the framework of a percolation model. The critical exponent, t, which describes the conductivity of a percolative system near the threshold, has the value 1.23. This number is in close agreement with expectation from theory for a two-dimensional percolative process. The dielectric properties of the purple membrane are more complex than those of lysozyme, seen in the value of h(c) and in the frequency and hydration dependence of the loss factor. There appear to be preferred regions of proton conduction. The percolation model is based upon stochastic behavior of a system partially populated with conducting elements. This model suggests that ion transport in membranes and its control can be based on pathways formed of randomly connected conducting elements and that a fixed geometry (a proton wire) is not the only possible basis for a mechanism of conduction.
T, M P Ramirez
2012-01-01
Using a conjecture that allows to approach separable-variables conductivity functions, the elements of the Modern Pseudoanalytic Function Theory are used, for the first time, to numerically solve the Dirichlet boundary value problem of the two-dimensional Electrical Impedance Equation, when the conductivity function arises from geometrical figures, located within bounded domains.
Directory of Open Access Journals (Sweden)
Sohel Rana
2014-01-01
Full Text Available Non-Fourier heat conduction model with dual phase lag wave-diffusion model was analyzed by using well-conditioned asymptotic wave evaluation (WCAWE and finite element method (FEM. The non-Fourier heat conduction has been investigated where the maximum likelihood (ML and Tikhonov regularization technique were used successfully to predict the accurate and stable temperature responses without the loss of initial nonlinear/high frequency response. To reduce the increased computational time by Tikhonov WCAWE using ML (TWCAWE-ML, another well-conditioned scheme, called mass effect (ME T-WCAWE, is introduced. TWCAWE with ME (TWCAWE-ME showed more stable and accurate temperature spectrum in comparison to asymptotic wave evaluation (AWE and also partial Pade AWE without sacrificing the computational time. However, the TWCAWE-ML remains as the most stable and hence accurate model to analyze the fast transient thermal analysis of non-Fourier heat conduction model.
Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals
Energy Technology Data Exchange (ETDEWEB)
Stavroula Foteinopoulou
2003-12-12
In this dissertation, they have undertaken the challenge to understand the unusual propagation properties of the photonic crystal (PC). The photonic crystal is a medium where the dielectric function is periodically modulated. These types of structures are characterized by bands and gaps. In other words, they are characterized by frequency regions where propagation is prohibited (gaps) and regions where propagation is allowed (bands). In this study they focus on two-dimensional photonic crystals, i.e., structures with periodic dielectric patterns on a plane and translational symmetry in the perpendicular direction. They start by studying a two-dimensional photonic crystal system for frequencies inside the band gap. The inclusion of a line defect introduces allowed states in the otherwise prohibited frequency spectrum. The dependence of the defect resonance state on different parameters such as size of the structure, profile of incoming source, etc., is investigated in detail. For this study, they used two popular computational methods in photonic crystal research, the Finite Difference Time Domain method (FDTD) and the Transfer Matrix Method (TMM). The results for the one-dimensional defect system are analyzed, and the two methods, FDTD and TMM, are compared. Then, they shift their attention only to periodic two-dimensional crystals, concentrate on their band properties, and study their unusual refractive behavior. Anomalous refractive phenomena in photonic crystals included cases where the beam refracts on the ''wrong'' side of the surface normal. The latter phenomenon, is known as negative refraction and was previously observed in materials where the wave vector, the electric field, and the magnetic field form a left-handed set of vectors. These materials are generally called left-handed materials (LHM) or negative index materials (NIM). They investigated the possibility that the photonic crystal behaves as a LHM, and how this behavior relates
The Chandrasekhar's Equation for Two-Dimensional Hypothetical White Dwarfs
De, Sanchari
2014-01-01
In this article we have extended the original work of Chandrasekhar on the structure of white dwarfs to the two-dimensional case. Although such two-dimensional stellar objects are hypothetical in nature, we strongly believe that the work presented in this article may be prescribed as Master of Science level class problem for the students in physics.
Beginning Introductory Physics with Two-Dimensional Motion
Huggins, Elisha
2009-01-01
During the session on "Introductory College Physics Textbooks" at the 2007 Summer Meeting of the AAPT, there was a brief discussion about whether introductory physics should begin with one-dimensional motion or two-dimensional motion. Here we present the case that by starting with two-dimensional motion, we are able to introduce a considerable…
Spatiotemporal surface solitons in two-dimensional photonic lattices.
Mihalache, Dumitru; Mazilu, Dumitru; Lederer, Falk; Kivshar, Yuri S
2007-11-01
We analyze spatiotemporal light localization in truncated two-dimensional photonic lattices and demonstrate the existence of two-dimensional surface light bullets localized in the lattice corners or the edges. We study the families of the spatiotemporal surface solitons and their properties such as bistability and compare them with the modes located deep inside the photonic lattice.
Explorative data analysis of two-dimensional electrophoresis gels
DEFF Research Database (Denmark)
Schultz, J.; Gottlieb, D.M.; Petersen, Marianne Kjerstine;
2004-01-01
Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening...
Mechanics of Apparent Horizon in Two Dimensional Dilaton Gravity
Cai, Rong-Gen
2016-01-01
In this article, we give a definition of apparent horizon in a two dimensional general dilaton gravity theory. With this definition, we construct the mechanics of the apparent horizon by introducing a quasi-local energy of the theory. Our discussion generalizes the apparent horizons mechanics in general spherically symmetric spactimes in four or higher dimensions to the two dimensional dilaton gravity case.
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.
Optical Spectroscopy of Two Dimensional Graphene and Boron Nitride
Ju, Long
a charge transfer process between graphene and BN when the exposure of visible light is introduced. We show this photo-induced doping in graphene resembles the modulation doping technique in traditional semiconductor heterojunctions, where a charge doping is introduced while the high mobility is maintained. This work reveals importance of interactions between stacked 2D materials on the overall properties and demonstrate a repeatable and convenient way of fabricating high quality graphene devices with active control of doping patterning. Along this direction, we did further STM experiment to visualize and manipulate charged defects in boron nitride with the help of graphene. The last theme is about the interesting properties of bilayer graphene, which is to some extent more interesting than monolayer graphene due to its electric-field dependent band structures. Firstly, we visualized the stacking boundary within exfoliated bilayer graphene by near field infrared microscopy. In dual-gated field-effect-transistor devices fabricated on the boundaries, we demonstrated the existence of topologically protected one dimensional conducting channels at the boundary through electric transport measurement. The 1D boundary states also demonstrated the first graphene-based valleytronic device. The topics we are going to talk about in this thesis are quite diversified. Just like the versatile nature of optical spectroscopy, we never limit ourself to a specific technique and do incremental things. Most of the experiments are driven by the important and interesting problems in the two dimensional materials field and we chose the right tool and conceive the right experiment to answer that question. Both pure optical methods and combinations with electric transport and STM measurements were used. I believe the flexibility of optical spectroscopy and its compatibility with other experimental techniques provide a powerful toolbox to explore many possibilities beyond the reach of a
Invariant Subspaces of the Two-Dimensional Nonlinear Evolution Equations
Directory of Open Access Journals (Sweden)
Chunrong Zhu
2016-11-01
Full Text Available In this paper, we develop the symmetry-related methods to study invariant subspaces of the two-dimensional nonlinear differential operators. The conditional Lie–Bäcklund symmetry and Lie point symmetry methods are used to construct invariant subspaces of two-dimensional differential operators. We first apply the multiple conditional Lie–Bäcklund symmetries to derive invariant subspaces of the two-dimensional operators. As an application, the invariant subspaces for a class of two-dimensional nonlinear quadratic operators are provided. Furthermore, the invariant subspace method in one-dimensional space combined with the Lie symmetry reduction method and the change of variables is used to obtain invariant subspaces of the two-dimensional nonlinear operators.
Directory of Open Access Journals (Sweden)
B. Merckx
2012-01-01
Full Text Available The thermal conductivity measurement by a simplified transient hot-wire technique is applied to geomaterials in order to show the relationships which can exist between effective thermal conductivity, texture, and moisture of the materials. After a validation of the used “one hot-wire” technique in water, toluene, and glass-bead assemblages, the investigations were performed (1 in glass-bead assemblages of different diameters in dried, water, and acetone-saturated states in order to observe the role of grain sizes and saturation on the effective thermal conductivity, (2 in a compacted earth brick at different moisture states, and (3 in a lime-hemp concrete during 110 days following its manufacture. The lime-hemp concrete allows the measurements during the setting, desiccation and carbonation steps. The recorded Δ/ln( diagrams allow the calculation of one effective thermal conductivity in the continuous and homogeneous fluids and two effective thermal conductivities in the heterogeneous solids. The first one measured in the short time acquisitions (<1 s mainly depends on the contact between the wire and grains and thus microtexture and hydrated state of the material. The second one, measured for longer time acquisitions, characterizes the mean effective thermal conductivity of the material.
Evaluation of finite element formulations for transient conduction forced-convection analysis
Thornton, E. A.; Wieting, A. R.
1979-01-01
Numerical studies clarifying the advantages and disavantages of conventional versus upwind convective finite elements are presented along with lumped versus consistent formulations for practical conduction forced-convection analysis. A finite-element procedure for treatment of negligible capacitance fluid nodes is presented. The procedure is based on procedures used in finite-element structural dynamics to treat nodes with negligible structural mass. Two finite-element programs and a finite-difference lumped-parameter program used in the studies are discussed. Evaluation studies utilizing three convection and two combined conduction-convection problems are then presented and discussed. Additionally, the computational time saving offered by the finite element procedure is considered for a practical combined conduction-convection problem.
Two-dimensional materials based transparent flexible electronics
Yu, Lili; Ha, Sungjae; El-Damak, Dina; McVay, Elaine; Ling, Xi; Chandrakasan, Anantha; Kong, Jing; Palacios, Tomas
2015-03-01
Two-dimensional (2D) materials have generated great interest recently as a set of tools for electronics, as these materials can push electronics beyond traditional boundaries. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. These thin, lightweight, bendable, highly rugged and low-power devices may bring dramatic changes in information processing, communications and human-electronic interaction. In this report, for the first time, we demonstrate two complex transparent flexible systems based on molybdenum disulfide (MoS2) grown by chemical vapor method: a transparent active-matrix organic light-emitting diode (AMOLED) display and a MoS2 wireless link for sensor nodes. The 1/2 x 1/2 square inch, 4 x 5 pixels AMOLED structures are built on transparent substrates, containing MoS2 back plane circuit and OLEDs integrated on top of it. The back plane circuit turns on and off the individual pixel with two MoS2 transistors and a capacitor. The device is designed and fabricated based on SPICE simulation to achieve desired DC and transient performance. We have also demonstrated a MoS2 wireless self-powered sensor node. The system consists of as energy harvester, rectifier, sensor node and logic units. AC signals from the environment, such as near-field wireless power transfer, piezoelectric film and RF signal, are harvested, then rectified into DC signal by a MoS2 diode. CIQM, CICS, SRC.
DEFF Research Database (Denmark)
Ricote, Sandrine; Zhu, Huayang; Coors, W. Grover
2014-01-01
between 700 and 900°C. From the obtained Brouwer diagrams, the activation energies of the oxide ions and cerium small polarons are estimated to be 0.77 and 2.45eV respectively. Conductivity relaxation measurements from strongly reducing conditions (4% H2, 3% H2O, 93% Ar) to strongly oxidizing conditions...... (97% O2, 3% H2O) and vice versa reveal great asymmetries in relaxation times. Virtually instantaneous relaxations are observed in the first case, while the oxidizing-to-reducing relaxations take as long as 0.5h. This paper reports conductivity relaxations with over 20 orders of magnitude in the gas...
Muschol, Martin; Kosterin, Paul; Ichikawa, Michinori; Salzberg, B M
2003-12-10
Using millisecond time-resolved optical recordings of transmembrane voltage and intraterminal calcium, we have determined how activity-dependent changes in the population action potential are related to a concurrent modulation of calcium transients in the neurohypophysis. We find that repetitive stimulation dramatically alters the amplitude of the population action potential and significantly increases its temporal dispersion. The population action potentials and the calcium transients exhibit well correlated frequency-dependent amplitude depression, with broadening of the action potential playing only a limited role. High-speed camera recordings indicate that the magnitude of the spike modulation is uniform throughout the neurohypophysis, thereby excluding propagation failure as the underlying mechanism. In contrast, temporal dispersion and latency of the population spike do increase with distance from the stimulation site. This increase is enhanced during repeated stimulation and by raising the stimulation frequency. Changes in Ca influx directly affect the decline in population spike amplitude, consistent with electrophysiological measurements of the local loss of excitability in nerve terminals and varicosities, mediated by a Ca-activated K conductance. Our observations suggest a model of "stuttering conduction": repeated action potential stimulation causes excitability failures limited to nerve terminals and varicosities, which account for the rapid decline in the population spike amplitude. These failures, however, do not block action potential propagation but generate the cumulative increases in spike latency.
Saikia, Bijaylakshmi; Ramachandran, Ashwin; Sinha, Krishnendu; Govindarajan, Rama
2017-02-01
Accurate prediction of laminar to turbulent transition in compressible flows is a challenging task, as it can be affected by a combination of factors. Compressibility causes large variations in thermodynamic as well as transport properties of a gas, which in turn are known to affect flow stability. We study the stratification of individual transport properties and their combined behavior. We also examine the effect of a change in the magnitude of viscosity and conductivity on flow stability. The Couette flow of a perfect gas is our model problem and both modal and non-modal analyses are carried out. We notice a large destabilizing role of the increase in the conductivity value and a dramatic stabilizing effect of mean viscosity stratification, over a range of free-stream Mach number, Reynolds number, Prandtl number, and disturbance wavenumber. In the combined case, viscosity stratification plays a dominant role. We find this to be the case for finite-time transient growth in the parameter regime below linear instability as well as asymptotically at large time. A budget of the transient growth energy amplification is also shown to identify the effects of transport properties on the constituents of perturbation energy. The extensive results presented in this paper, we believe should motivate those studying more realistic flows to examine how these contrasting effects of stratification come together.
Mendez, Sergio; AungYong, Lisa
2014-01-01
To help students make the connection between the concepts of heat conduction and convection to real-world phenomenon, we developed a combined experimental and computational module that can be incorporated into lecture or lab courses. The experimental system we present requires materials and apparatus that are readily accessible, and the procedure…
Mendez, Sergio; AungYong, Lisa
2014-01-01
To help students make the connection between the concepts of heat conduction and convection to real-world phenomenon, we developed a combined experimental and computational module that can be incorporated into lecture or lab courses. The experimental system we present requires materials and apparatus that are readily accessible, and the procedure…
Two-dimensional discrete gap breathers in a two-dimensional discrete diatomic Klein-Gordon lattice
Institute of Scientific and Technical Information of China (English)
XU Quan; QIANG Tian
2009-01-01
We study the existence and stability of two-dimensional discrete breathers in a two-dimensional discrete diatomic Klein-Gordon lattice consisting of alternating light and heavy atoms, with nearest-neighbor harmonic coupling.Localized solutions to the corresponding nonlinear differential equations with frequencies inside the gap of the linear wave spectrum, i.e. two-dimensional gap breathers, are investigated numerically. The numerical results of the corresponding algebraic equations demonstrate the possibility of the existence of two-dimensional gap breathers with three types of symmetries, i.e., symmetric, twin-antisymmetric and single-antisymmetric. Their stability depends on the nonlinear on-site potential (soft or hard), the interaction potential (attractive or repulsive)and the center of the two-dimensional gap breather (on a light or a heavy atom).
Directory of Open Access Journals (Sweden)
Raseelo J. Moitsheki
2008-01-01
Full Text Available Lie point symmetry analysis is performed for an unsteady nonlinear heat diffusion problem modeling thermal energy storage in a medium with a temperature-dependent power law thermal conductivity and subjected to a convective heat transfer to the surrounding environment at the boundary through a variable heat transfer coefficient. Large symmetry groups are admitted even for special choices of the constants appearing in the governing equation. We construct one-dimensional optimal systems for the admitted Lie algebras. Following symmetry reductions, we construct invariant solutions.
Two Dimensional Hydrodynamic Analysis of the Moose Creek Floodway
2012-09-01
ER D C/ CH L TR -1 2 -2 0 Two Dimensional Hydrodynamic Analysis of the Moose Creek Floodway C oa st al a n d H yd ra u lic s La b or at...distribution is unlimited. ERDC/CHL TR-12-20 September 2012 Two Dimensional Hydrodynamic Analysis of the Moose Creek Floodway Stephen H. Scott, Jeremy A...A two-dimensional Adaptive Hydraulics (AdH) hydrodynamic model was developed to simulate the Moose Creek Floodway. The Floodway is located
RESEARCH ON TWO-DIMENSIONAL LDA FOR FACE RECOGNITION
Institute of Scientific and Technical Information of China (English)
Han Ke; Zhu Xiuchang
2006-01-01
The letter presents an improved two-dimensional linear discriminant analysis method for feature extraction. Compared with the current two-dimensional methods for feature extraction, the improved two-dimensional linear discriminant analysis method makes full use of not only the row and the column direction information of face images but also the discriminant information among different classes. The method is evaluated using the Nanjing University of Science and Technology (NUST) 603 face database and the Aleix Martinez and Robert Benavente (AR) face database. Experimental results show that the method in the letter is feasible and effective.
ONE-DIMENSIONAL AND TWO-DIMENSIONAL LEADERSHIP STYLES
Directory of Open Access Journals (Sweden)
Nikola Stefanović
2007-06-01
Full Text Available In order to motivate their group members to perform certain tasks, leaders use different leadership styles. These styles are based on leaders' backgrounds, knowledge, values, experiences, and expectations. The one-dimensional styles, used by many world leaders, are autocratic and democratic styles. These styles lie on the two opposite sides of the leadership spectrum. In order to precisely define the leadership styles on the spectrum between the autocratic leadership style and the democratic leadership style, leadership theory researchers use two dimensional matrices. The two-dimensional matrices define leadership styles on the basis of different parameters. By using these parameters, one can identify two-dimensional styles.
Antoniadis, Konstantinos D.; Tertsinidou, Georgia J.; Assael, Marc J.; Wakeham, William A.
2016-08-01
The paper considers the conditions that are necessary to secure accurate measurement of the apparent thermal conductivity of two-phase systems comprising nanoscale particles of one material suspended in a fluid phase of a different material. It is shown that instruments operating according to the transient hot-wire technique can, indeed, produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the exact geometry of the hot wire. Furthermore, it is shown that an approximate analytic solution can be employed with equal success, over the time range of 0.1 s to 1 s, provided that (a) two wires are employed, so that end effects are canceled, (b) each wire is very thin, less than 30 \\upmu m diameter, so that the line source model and the corresponding corrections are valid, (c) low values of the temperature rise, less than 4 K, are employed in order to minimize the effect of convection on the heat transfer in the time of measurement of 1 s, and (d) insulated wires are employed for measurements in electrically conducting or polar liquids to avoid current leakage or other electrical distortions. According to these criteria, a transient hot-wire instrument has been designed, constructed, and employed for the measurement of the enhancement of the thermal conductivity of water when TiO2 or multi-wall carbon nanotubes (MWCNT) are added. These new results, together with a critical evaluation of other measurements, demonstrate the importance of proper implementation of the technique.
Directory of Open Access Journals (Sweden)
Emil Roduner
2012-06-01
Full Text Available Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring the incurred current, followed by Fourier transformation and plotting the impedance against the frequency in a conventional Bode diagram. To test the potential and limitations of this novel method, we present a feasibility study using an identical hydrogen atmosphere at a well-defined relative humidity on both sides of the membrane. It is demonstrated that good quality impedance spectra are obtained in a frequency range of 0.2–1,000 Hz. The extracted polarization curves exhibit a maximum current which cannot be explained by typical diffusion effects. Simulation based on equivalent circuits requires a Nernst element for restricted diffusion in the membrane which suggests that this effect is based on the potential dependence of the electrolyte resistance in the high overpotential region.
Hink, Steffen; Wagner, Norbert; Bessler, Wolfgang G.; Roduner, Emil
2012-01-01
Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring the incurred current, followed by Fourier transformation and plotting the impedance against the frequency in a conventional Bode diagram. To test the potential and limitations of this novel method, we present a feasibility study using an identical hydrogen atmosphere at a well-defined relative humidity on both sides of the membrane. It is demonstrated that good quality impedance spectra are obtained in a frequency range of 0.2–1000 Hz. The extracted polarization curves exhibit a maximum current which cannot be explained by typical diffusion effects. Simulation based on equivalent circuits requires a Nernst element for restricted diffusion in the membrane which suggests that this effect is based on the potential dependence of the electrolyte resistance in the high overpotential region. PMID:24958175
Assael, Marc J.; Antoniadis, Konstantinos D.; Metaxa, Ifigeneia N.; Mylona, Sofia K.; Assael, John-Alexander M.; Wu, Jiangtao; Hu, Miaomiao
2015-11-01
A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of solids over a range of 0.2 { W}{\\cdot }m^{-1}{\\cdot }{K}^{-1} to 4 { W}{\\cdot }m^{-1}{\\cdot }{K}^{-1} is presented. The new instrument is characterized by three novelties: (a) an innovative two-wires sensor which provides robustness and portability, while at the same time employs a soft silicone layer to eliminate the effect of the contact resistance between the wires and the sample, (b) a newly designed compact portable printed electronic board employing an FPGA architecture CPU to the control output voltage and data processing—the new board replaces the traditional, large in size Wheatstone-type bridge system required to perform the experimental measurements, and (c) a cutting-edge software suite, developed for the mesh describing the structure of the sensor, and utilizing the Finite Elements Method to model the heat flow. The estimation of thermal conductivity is modeled as a minimization problem and is solved using Bayesian Optimization. Our revolutionizing proposed methodology exhibits radical speedups of up to × 120, compared to previous approaches, and considerably reduces the number of simulations performed, achieving convergence only in a few minutes. The new instrument was successfully employed to measure, at room temperature, the thermal conductivity of two thermal conductivity reference materials, Pyroceram 9606 and Pyrex 7740, and two possible candidate glassy solids, PMMA and BK7, with an absolute low uncertainty of 2 %.
Further studies of stall flutter and nonlinear divergence of two-dimensional wings
Dugundji, J.; Chopra, I.
1975-01-01
An experimental investigation is made of the purely torsional stall flutter of a two-dimensional wing pivoted about the midchord, and also of the bending-torsion stall flutter of a two-dimensional wing pivoted about the quarterchord. For the purely torsional flutter case, large amplitude limit cycles ranging from + or - 11 to + or - 160 degrees were observed. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees. Reasonable nondimensional correlation was obtained for several wing configurations. For the bending-torsion flutter case, large amplitude coupled limit cycles were observed with torsional amplitudes as large as + or - 40 degrees. The torsion amplitudes first increased, then decreased with increasing velocity. Additionally, a small amplitude, predominantly torsional flutter was observed when the static equilibrium angle was near the stall angle.
Schapers, T; Nitta, J; Heersche, HB; Takayanagi, H
2002-01-01
The spin dependent conductance of a ferromagnet/two-dimensional electron gas ferromagnet structure is theoretically examined in the ballistic transport regime. It is shown that the spin signal can be improved considerably by making use of the spin filtering effect of a barrier at the ferromagnet two
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)
Grant, David E.; Long, Andrew R.; Davies, John H.
2000-05-01
We have simulated conduction in a two-dimensional electron gas subject to a weak two-dimensional periodic potential Vx cos(2πx/a)+Vy cos(2πy/a). The usual commensurability oscillations in ρxx(B) are seen with Vx alone. An increase of Vy suppresses these oscillations, rather than introducing the additional oscillations in ρyy(B) expected from previous perturbation theories. We show that this behavior arises from drift of the guiding center of cyclotron motion along contours of an effective potential. Periodic modulation in the magnetic field can be treated in the same way.
A study of two-dimensional magnetic polaron
Institute of Scientific and Technical Information of China (English)
LIU; Tao; ZHANG; Huaihong; FENG; Mang; WANG; Kelin
2006-01-01
By using the variational method and anneal simulation, we study in this paper the self-trapped magnetic polaron (STMP) in two-dimensional anti-ferromagnetic material and the bound magnetic polaron (BMP) in ferromagnetic material. Schwinger angular momentum theory is applied to changing the problem into a coupling problem of carriers and two types of Bosons. Our calculation shows that there are single-peak and multi-peak structures in the two-dimensional STMP. For the ferromagnetic material, the properties of the two-dimensional BMP are almost the same as that in one-dimensional case; but for the anti-ferromagnetic material, the two-dimensional STMP structure is much richer than the one-dimensional case.
UPWIND DISCONTINUOUS GALERKIN METHODS FOR TWO DIMENSIONAL NEUTRON TRANSPORT EQUATIONS
Institute of Scientific and Technical Information of China (English)
袁光伟; 沈智军; 闫伟
2003-01-01
In this paper the upwind discontinuous Galerkin methods with triangle meshes for two dimensional neutron transport equations will be studied.The stability for both of the semi-discrete and full-discrete method will be proved.
Two-Dimensionally-Modulated, Magnetic Structure of Neodymium Metal
DEFF Research Database (Denmark)
Lebech, Bente; Bak, P.
1979-01-01
The incipient magnetic order of dhcp Nd is described by a two-dimensional, incommensurably modulated structure ("triple-q" structure). The ordering is accompanied by a lattice distortion that forms a similar pattern....
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.
Decoherence in a Landau Quantized Two Dimensional Electron Gas
Directory of Open Access Journals (Sweden)
McGill Stephen A.
2013-03-01
Full Text Available We have studied the dynamics of a high mobility two-dimensional electron gas as a function of temperature. The presence of satellite reflections in the sample and magnet can be modeled in the time-domain.
Quantization of Two-Dimensional Gravity with Dynamical Torsion
Lavrov, P M
1999-01-01
We consider two-dimensional gravity with dynamical torsion in the Batalin - Vilkovisky and Batalin - Lavrov - Tyutin formalisms of gauge theories quantization as well as in the background field method.
Spatiotemporal dissipative solitons in two-dimensional photonic lattices.
Mihalache, Dumitru; Mazilu, Dumitru; Lederer, Falk; Kivshar, Yuri S
2008-11-01
We analyze spatiotemporal dissipative solitons in two-dimensional photonic lattices in the presence of gain and loss. In the framework of the continuous-discrete cubic-quintic Ginzburg-Landau model, we demonstrate the existence of novel classes of two-dimensional spatiotemporal dissipative lattice solitons, which also include surface solitons located in the corners or at the edges of the truncated two-dimensional photonic lattice. We find the domains of existence and stability of such spatiotemporal dissipative solitons in the relevant parameter space, for both on-site and intersite lattice solitons. We show that the on-site solitons are stable in the whole domain of their existence, whereas most of the intersite solitons are unstable. We describe the scenarios of the instability-induced dynamics of dissipative solitons in two-dimensional lattices.
Bound states of two-dimensional relativistic harmonic oscillators
Institute of Scientific and Technical Information of China (English)
Qiang Wen-Chao
2004-01-01
We give the exact normalized bound state wavefunctions and energy expressions of the Klein-Gordon and Dirac equations with equal scalar and vector harmonic oscillator potentials in the two-dimensional space.
A two-dimensional polymer prepared by organic synthesis.
Kissel, Patrick; Erni, Rolf; Schweizer, W Bernd; Rossell, Marta D; King, Benjamin T; Bauer, Thomas; Götzinger, Stephan; Schlüter, A Dieter; Sakamoto, Junji
2012-02-05
Synthetic polymers are widely used materials, as attested by a production of more than 200 millions of tons per year, and are typically composed of linear repeat units. They may also be branched or irregularly crosslinked. Here, we introduce a two-dimensional polymer with internal periodicity composed of areal repeat units. This is an extension of Staudinger's polymerization concept (to form macromolecules by covalently linking repeat units together), but in two dimensions. A well-known example of such a two-dimensional polymer is graphene, but its thermolytic synthesis precludes molecular design on demand. Here, we have rationally synthesized an ordered, non-equilibrium two-dimensional polymer far beyond molecular dimensions. The procedure includes the crystallization of a specifically designed photoreactive monomer into a layered structure, a photo-polymerization step within the crystal and a solvent-induced delamination step that isolates individual two-dimensional polymers as free-standing, monolayered molecular sheets.
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.
One- and two-dimensional fluids properties of smectic, lamellar and columnar liquid crystals
Jakli, Antal
2006-01-01
Smectic and lamellar liquid crystals are three-dimensional layered structures in which each layer behaves as a two-dimensional fluid. Because of their reduced dimensionality they have unique physical properties and challenging theoretical descriptions, and are the subject of much current research. One- and Two-Dimensional Fluids: Properties of Smectic, Lamellar and Columnar Liquid Crystals offers a comprehensive review of these phases and their applications. The book details the basic structures and properties of one- and two-dimensional fluids and the nature of phase transitions. The later chapters consider the optical, magnetic, and electrical properties of special structures, including uniformly and non-uniformly aligned anisotropic films, lyotropic lamellar systems, helical and chiral structures, and organic anisotropic materials. Topics also include typical and defective features, magnetic susceptibility, and electrical conductivity. The book concludes with a review of current and potential applications ...
Electrical Oscillations in Two-Dimensional Microtubular Structures
Cantero, María Del Rocío; Perez, Paula L.; Smoler, Mariano; Villa Etchegoyen, Cecilia; Cantiello, Horacio F.
2016-06-01
Microtubules (MTs) are unique components of the cytoskeleton formed by hollow cylindrical structures of αβ tubulin dimeric units. The structural wall of the MT is interspersed by nanopores formed by the lateral arrangement of its subunits. MTs are also highly charged polar polyelectrolytes, capable of amplifying electrical signals. The actual nature of these electrodynamic capabilities remains largely unknown. Herein we applied the patch clamp technique to two-dimensional MT sheets, to characterize their electrical properties. Voltage-clamped MT sheets generated cation-selective oscillatory electrical currents whose magnitude depended on both the holding potential, and ionic strength and composition. The oscillations progressed through various modes including single and double periodic regimes and more complex behaviours, being prominent a fundamental frequency at 29 Hz. In physiological K+ (140 mM), oscillations represented in average a 640% change in conductance that was also affected by the prevalent anion. Current injection induced voltage oscillations, thus showing excitability akin with action potentials. The electrical oscillations were entirely blocked by taxol, with pseudo Michaelis-Menten kinetics and a KD of ~1.29 μM. The findings suggest a functional role of the nanopores in the MT wall on the genesis of electrical oscillations that offer new insights into the nonlinear behaviour of the cytoskeleton.
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.
Two-Dimensional Heat Transfer in a Heterogeneous Fracture Network
Gisladottir, V. R.; Roubinet, D.; Tartakovsky, D. M.
2015-12-01
Geothermal energy harvesting requires extraction and injection of geothermal fluid. Doing so in an optimal way requires a quantitative understanding of site-specific heat transfer between geothermal fluid and the ambient rock. We develop a heat transfer particle-tracking approach to model that interaction. Fracture-network models of heat transfer in fractured rock explicitly account for the presence of individual fractures, ambient rock matrix, and fracture-matrix interfaces. Computational domains of such models span the meter scale, whereas fracture apertures are on the millimeter scale. The computations needed to model these multi-scale phenomenon can be prohibitively expensive, even for methods using nonuniform meshes. Our approach appreciably decreases the computational costs. Current particle-tracking methods usually assume both infinite matrix and one-dimensional (1D) heat transfer in the matrix blocks. They rely on 1D analytical solutions for heat transfer in a single fracture, which can lead to large predictive errors. Our two-dimensional (2D) heat transfer simulation algorithm is mesh-free and takes into account both longitudinal and transversal heat conduction in the matrix. It uses a probabilistic model to transfer particle to the appropriate neighboring fracture unless it returns to the fracture of origin or remains in the matrix. We use this approach to look at the impact of a fracture-network topology (e.g. the importance of smaller scale fractures), as well as the matrix block distribution on the heat transport in heterogeneous fractured rocks.
Diamagnetic phase transitions in two-dimensional conductors
Bakaleinikov, L. A.; Gordon, A.
2014-11-01
A theory describing the susceptibility amplitude and the magnetic induction bifurcation near the dHvA driven diamagnetic phase transitions in quasi two-dimensional (2D) organic conductors of the (ET)2X with X=Cu(NCS)2, KHg(SCN)4, I3, AuBr2, IBr2, etc. is presented. We show that there is a drastic increase in the temperature and magnetic field dependence of the susceptibility amplitude on approaching the diamagnetic phase transition point. Near the phase transition point the temperature and magnetic field dependences are fitted by the ones typical of the mean-field phase transition theory. These dependences confirm the long-range character of the magnetic interactions among the conduction electrons leading to diamagnetic phase transitions. We demonstrate that the magnetic induction splitting of nuclear magnetic resonance (NMR) and muon spin-rotation spectroscopy (μSR) lines due to two Condon domains decreases tending to zero on approaching the diamagnetic phase transition. This decrease is fitted by the temperature and magnetic field dependence of the susceptibility characteristic of the mean-field theory of phase transitions. Performing new susceptibility, NMR and μSR experiments will enable to detect diamagnetic phase transitions and Condon domains in quasi 2D metals.
Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures
Energy Technology Data Exchange (ETDEWEB)
Azad, Abul K [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Han, Jiaguang [OSU; Lu, Xinchao [OSU; Zhang, Weili [OSU
2009-01-01
The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.
Two dimensional discriminant neighborhood preserving embedding in face recognition
Pang, Meng; Jiang, Jifeng; Lin, Chuang; Wang, Binghui
2015-03-01
One of the key issues of face recognition is to extract the features of face images. In this paper, we propose a novel method, named two-dimensional discriminant neighborhood preserving embedding (2DDNPE), for image feature extraction and face recognition. 2DDNPE benefits from four techniques, i.e., neighborhood preserving embedding (NPE), locality preserving projection (LPP), image based projection and Fisher criterion. Firstly, NPE and LPP are two popular manifold learning techniques which can optimally preserve the local geometry structures of the original samples from different angles. Secondly, image based projection enables us to directly extract the optimal projection vectors from twodimensional image matrices rather than vectors, which avoids the small sample size problem as well as reserves useful structural information embedded in the original images. Finally, the Fisher criterion applied in 2DDNPE can boost face recognition rates by minimizing the within-class distance, while maximizing the between-class distance. To evaluate the performance of 2DDNPE, several experiments are conducted on the ORL and Yale face datasets. The results corroborate that 2DDNPE outperforms the existing 1D feature extraction methods, such as NPE, LPP, LDA and PCA across all experiments with respect to recognition rate and training time. 2DDNPE also delivers consistently promising results compared with other competing 2D methods such as 2DNPP, 2DLPP, 2DLDA and 2DPCA.
Transient Heat Conduction in a Wall Exposed to a Fire: an Analytic Approach
Casano, G.; Piva, S.
2017-01-01
Fire safety engineering requires a detailed understanding of fire behaviour and of its effects on structures and people. Currently, advanced numerical codes for the prediction of the fire behaviour are available. However, they often require heavy calculations and long times. In this context analytical solutions can be useful for a fast analysis of simplified schematizations. It allows a more effective final utilization of the advanced fire codes. In this contribution, for a separation wall exposed to a fire the temperature history is analysed of the unexposed wall surface. Due to the limitations of the model, the temperature in the fire room changes stepwise, with a final value typical of a post-flashover condition. Nevertheless, with an appropriate choice of the heat transfer coefficient, the thermal action on the surface exposed to fire becomes that due to a fire following the standard temperature-time curve. The solution is then obtained by applying the separation of variables to the heat conduction equation. The problem is made dimensionless and the results are analysed in order to validate their significance. This simplified model allows to obtain useful information on the magnitude of the temperature reached.
Extreme paths in oriented two-dimensional percolation
Andjel, E. D.; Gray, L. F.
2016-01-01
International audience; A useful result about leftmost and rightmost paths in two dimensional bond percolation is proved. This result was introduced without proof in \\cite{G} in the context of the contact process in continuous time. As discussed here, it also holds for several related models, including the discrete time contact process and two dimensional site percolation. Among the consequences are a natural monotonicity in the probability of percolation between different sites and a somewha...
Two Dimensional Nucleation Process by Monte Carlo Simulation
T., Irisawa; K., Matsumoto; Y., Arima; T., Kan; Computer Center, Gakushuin University; Department of Physics, Gakushuin University
1997-01-01
Two dimensional nucleation process on substrate is investigated by Monte Carlo simulation, and the critical nucleus size and its waiting time are measured with a high accuracy. In order to measure the critical nucleus with a high accuracy, we calculate the attachment and the detachment rate to the nucleus directly, and define the critical nucleus size when both rate are equal. Using the kinematical nucleation theory by Nishioka, it is found that, our obtained kinematical two dimensional criti...
Controlled Interactions between Two Dimensional Layered Inorganic Nanosheets and Polymers
2016-06-15
polymers . 2. Introduction . Research objectives: This research aims to study the physical (van der Waals forces: crystal epitaxy and π-π...AFRL-AFOSR-JP-TR-2016-0071 Controlled Interactions between Two Dimensional Layered Inorganic Nanosheets and Polymers Cheolmin Park YONSEI UNIVERSITY...Interactions between Two Dimensional Layered Inorganic Nanosheets and Polymers 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA2386-14-1-4054 5c. PROGRAM ELEMENT
Two-Dimensional Weak Pseudomanifolds on Eight Vertices
Indian Academy of Sciences (India)
Basudeb Datta; Nandini Nilakantan
2002-05-01
We explicitly determine all the two-dimensional weak pseudomanifolds on 8 vertices. We prove that there are (up to isomorphism) exactly 95 such weak pseudomanifolds, 44 of which are combinatorial 2-manifolds. These 95 weak pseudomanifolds triangulate 16 topological spaces. As a consequence, we prove that there are exactly three 8-vertex two-dimensional orientable pseudomanifolds which allow degree three maps to the 4-vertex 2-sphere.
Measured Two-Dimensional Ice-Wedge Polygon Thermal Dynamics
Cable, William; Romanovsky, Vladimir; Busey, Robert
2016-04-01
necessarily found in areas of higher MAGT. Active layer thickness does not appear to be correlated to mean annual air temperature but rather is a function of summer air temperature or thawing degree-days. While the refreezing of the active layer initiated at nearly the same time for all locations and polygons, we find differences in the proportion of top-down versus bottom-up freezing and the length of time required to complete the refreezing process. Examination of the daily temperature dynamics using interpolated two-dimensional temperature fields reveal that during the summer, the predominate temperature gradient is vertical while the isotherms tend to follow the topography. However, as the active layer begins to refreeze and snow accumulates, the thermal regime diverges. The fall shows an increased temperature gradient horizontally with landscape positions containing higher soil moisture and/or snow depth (low centers and troughs) cooling more slowly than the adjacent ground (rims and high centers). This two-dimensional effect is greatest as the active layer refreezes and persists until mid-winter, by which time the temperature gradients are again mostly vertical and the isotherms follow the topography. Our findings demonstrate the complexity and two-dimensionality of the temperature dynamics in these landscapes.
Energy Technology Data Exchange (ETDEWEB)
Daw, J.E.; Knudson, D.L. [Idaho National Laboratory, Idaho Falls, ID 83415, (United States); Villard, J.F.; Liothin, J.; Destouches, C. [CEA, DEN, DER, Instrumentation Sensors and Dosimetry Laboratory, Cadarache, F-13108 St Paul-Lez-Durance, (France); Rempe, J.L. [Rempe and Associates, LLC, Idaho Falls, ID, 83404 (United States); Matheron, P. [CEA, DEN, DEC, Uranium Fuels Laboratory, Cadarache, F-13108 St Paul-Lez-Durance, (France); Lambert, T. [CEA, DEN, DEC, Innovative Fuel Design and Irradiation Laboratory, Cadarache, F-13108 St Paul-Lez-Durance, (France)
2015-07-01
Thermal conductivity is a key property that must be known for proper design, testing, and deployment of new fuels and structural materials in nuclear reactors. Thermal conductivity is highly dependent on the physical structure, chemical composition, and the state of the material. Typically, thermal conductivity changes that occur during irradiation are currently measured out-of-pile using a 'cook and look' approach. But repeatedly removing samples from a test reactor to make measurements is expensive, has the potential to disturb phenomena of interest, and only provides understanding of the sample's end state when each measurement is made. There are also limited thermo-physical property data available for advanced fuels; and such data are needed for simulation codes, the development of next generation reactors, and advanced fuels for existing nuclear plants. Being able to quickly characterize fuel thermal conductivity during irradiation can improve the fidelity of data, reduce costs of post-irradiation examinations, increase understanding of how fuels behave under irradiation, and confirm or improve existing thermal conductivity measurement techniques. This paper discusses efforts to develop and evaluate an innovative in-pile thermal conductivity sensor based on the transient hot wire thermal conductivity method (THWM), using a single needle probe (NP) containing a line heat source and thermocouple embedded in the fuel. The sensor that has been designed and manufactured by the Idaho National Laboratory (INL) includes a unique combination of materials, geometry, and fabrication techniques that make the hot wire method suitable for in-pile applications. In particular, efforts were made to minimize the influence of the sensor and maximize fuel hot-wire heating. The probe has a thermocouple-like construction with high temperature resistant materials that remain ductile while resisting transmutation and materials interactions. THWM-NP prototypes were
Two-Dimensional Materials for Sensing: Graphene and Beyond
Directory of Open Access Journals (Sweden)
Seba Sara Varghese
2015-09-01
Full Text Available Two-dimensional materials have attracted great scientific attention due to their unusual and fascinating properties for use in electronics, spintronics, photovoltaics, medicine, composites, etc. Graphene, transition metal dichalcogenides such as MoS2, phosphorene, etc., which belong to the family of two-dimensional materials, have shown great promise for gas sensing applications due to their high surface-to-volume ratio, low noise and sensitivity of electronic properties to the changes in the surroundings. Two-dimensional nanostructured semiconducting metal oxide based gas sensors have also been recognized as successful gas detection devices. This review aims to provide the latest advancements in the field of gas sensors based on various two-dimensional materials with the main focus on sensor performance metrics such as sensitivity, specificity, detection limit, response time, and reversibility. Both experimental and theoretical studies on the gas sensing properties of graphene and other two-dimensional materials beyond graphene are also discussed. The article concludes with the current challenges and future prospects for two-dimensional materials in gas sensor applications.
Benoit, Merckx; Jean-Didier, Mertz; Patrick, Dudoignon; David, Giovannacci; Jean-Philippe, Garnier
2013-04-01
Alteration of inorganic materials in monuments is mainly related to relative humidity change in the porous network. Characterization of water content is a complex issue, specially in case of non-intrusive measurement. An innovative method is developed to quantify the water content using a direct calculation of the thermal conductivity. In order to validate the non-intrusive application to heritage stone, a control of the influence of the rock-sensor interface is required. The study was carried out on five sedimentary french rocks : three limestones (lithographic, oolithic and micritic), a sandstone of Fontainebleau and the so-called Tuffeau limestone. The textural properties are characterized by optical and electronical microscopy, X-ray diffraction, and mercury intrusion porosimetry. The transient hot-wire method is useful to obtain a quick value of effective conductivity of material. Initially used in liquids and gas, It's now more and more used for solid materials. The calculation of one effective thermal conductivity is formulated by the slope of recorded DT/ln(t) diagrams. In case of continuous and homogeneous media, only one slope can be measured. For heterogeneous solids a typical curve present two slopes : the first one measured in the short time acquisitions (arithmetic average roughness (Sa) is ranged between 44 µm and 1 µm, respectively for the coarse-grained limestone (Bretigny) and the finest one (Migné). According to the relative error of the apparatus (10%), the conductivity value is constant, independently of the surface polishing state. Thus, this evolution confirms that the method could be used on many stony materials as they are present in the built cultural heritage.
Cellular neural network analysis for two-dimensional bioheat transfer equation.
Niu, J H; Wang, H Z; Zhang, H X; Yan, J Y; Zhu, Y S
2001-09-01
The cellular neural network (CNN) method is applied to solve the Pennes bioheat transfer equation, and its feasibility is demonstrated. Numerical solutions were obtained for a cellular neural network for a two-dimensional steady-state temperature field obtained from focused and unfocused ultrasound heat sources. Transient-state temperature fields were also studied and compared with experimental results obtained elsewhere. The cellular neural networks' key features of asynchronous parallel processing, continuous-time dynamics and local interaction enable real-time temperature field estimation for clinical hyperthermia.
Cavity-enhanced ultrafast two-dimensional spectroscopy using higher order modes
Allison, Thomas K.
2017-02-01
We describe methods using frequency combs and optical resonators for recording two-dimensional (2D) ultrafast spectroscopy signals with high sensitivity. By coupling multiple frequency combs to higher-order modes of one or more optical cavities, background-free, cavity-enhanced 2D spectroscopy signals are naturally generated via phase cycling. As in cavity-enhanced ultrafast transient absorption spectroscopy, the signal to noise is enhanced by a factor proportional to the cavity finesse squared, so even using cavities of modest finesse, a very high sensitivity is expected, enabling ultrafast 2D spectroscopy experiments in dilute molecular beams.
Cavity-enhanced ultrafast two-dimensional spectroscopy using higher-order modes
Allison, Thomas K
2016-01-01
We describe methods using frequency combs and optical resonators for recording two-dimensional (2D) ultrafast spectroscopy signals with high sensitivity. By coupling multiple frequency combs to higher-order modes of one or more optical cavities, background-free, cavity-enhanced 2D spectroscopy signals are naturally generated via phase cycling. As in cavity-enhanced ultrafast transient absorption spectroscopy (CE-TAS), the signal to noise is enhanced by a factor proportional to the cavity finesse squared, so even using cavities of modest finesse, a very high sensitivity is expected, enabling ultrafast 2D spectroscopy experiments in dilute molecular beams.
A New Class of Resonances at the Edge of the Two Dimensional Electron Gas
Zhitenev, N. B.; Brodsky, M; Ashoori, R. C.; Melloch, M. R.
1996-01-01
We measure the frequency dependent capacitance of a gate covering the edge and part of a two-dimensional electron gas in the quantum Hall regime. In applying a positive gate bias, we create a metallic puddle under the gate surrounded by an insulating region. Charging of the puddle occurs via electron tunneling from a metallic edge channel. Analysis of the data allows direct extraction of this tunneling conductance. Novel conductance resonances appear as a function of gate bias. Samples with g...
Diamagnetic phase transitions in two-dimensional conductors
Energy Technology Data Exchange (ETDEWEB)
Bakaleinikov, L.A., E-mail: bakal.ammp@mail.ioffe.ru [A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); Department of Mathematics and Physics, Faculty of Natural Sciences, University of Haifa, Campus Oranim, Tivon 36006 (Israel); Gordon, A. [Department of Mathematics and Physics, Faculty of Natural Sciences, University of Haifa, Campus Oranim, Tivon 36006 (Israel)
2014-11-15
A theory describing the susceptibility amplitude and the magnetic induction bifurcation near the dHvA driven diamagnetic phase transitions in quasi two-dimensional (2D) organic conductors of the (ET){sub 2}X with X=Cu(NCS){sub 2},KHg(SCN){sub 4},I{sub 3},AuBr{sub 2},IBr{sub 2}, etc. is presented. We show that there is a drastic increase in the temperature and magnetic field dependence of the susceptibility amplitude on approaching the diamagnetic phase transition point. Near the phase transition point the temperature and magnetic field dependences are fitted by the ones typical of the mean-field phase transition theory. These dependences confirm the long-range character of the magnetic interactions among the conduction electrons leading to diamagnetic phase transitions. We demonstrate that the magnetic induction splitting of nuclear magnetic resonance (NMR) and muon spin-rotation spectroscopy (μSR) lines due to two Condon domains decreases tending to zero on approaching the diamagnetic phase transition. This decrease is fitted by the temperature and magnetic field dependence of the susceptibility characteristic of the mean-field theory of phase transitions. Performing new susceptibility, NMR and μSR experiments will enable to detect diamagnetic phase transitions and Condon domains in quasi 2D metals. - Highlights: • A theory of diamagnetic phase transitions (DPTs) is presented in 2D organic conductors. • The behaviour of the susceptibility amplitude and the induction splitting is shown near the DPT. • The calculated quantities are described by the mean-field theory of phase transitions.
Two-dimensional simulation of polymer electrolyte membrane fuel cells
Energy Technology Data Exchange (ETDEWEB)
Hum, B.; Li, X. [Waterloo Univ., ON (Canada). Dept. of Mechanical Engineering
2002-07-01
Polymer electrolyte membrane (PEM) fuel cells have fast startup, are highly energy efficient and have high power density, rendering them very suitable for use in zero-emission vehicles and on-site power cogeneration. Before the PEM fuel cell can reach widespread commercial use, the performance has to be improved regarding the minimization of all transport resistances. This can be done by considering the electrochemical reactions in the catalyst layers along with the physical transport of reactant gas flows, product and process water, heat and the charged particles in the individual cells and stacks. This paper presents the results of a two-dimensional numerical simulation of a steady, isothermal, fully humidified PEM fuel cell which was conducted to examine what happens in the catalyst layers. The finite volume method was used together with the alternating direction implicit algorithm. It was determined that the cathode catalyst layer has more pronounced changes in potential, reaction rate and current density generation compared to the anode catalyst layer. This is because of the large cathode activation overpotential and the low diffusion coefficient of oxygen. It was demonstrated that catalyst layers, by nature, are 2 dimensional, particularly in areas of low reactant concentrations. Maximum power density is limited by the depletion of one of the reactants in the catalyst layer. Both the fuel and oxidant supply must be managed simultaneously for optimal cell performance. It was concluded that cell performance is not greatly affected by flow direction. It was noted that this analysis can also be used for more complex cell design, such as cross flow between reactant streams and practical serpentine flow channel design. 11 refs., 2 tabs., 10 figs.
Tracking dynamics of two-dimensional continuous attractor neural networks
Fung, C. C. Alan; Wong, K. Y. Michael; Wu, Si
2009-12-01
We introduce an analytically solvable model of two-dimensional continuous attractor neural networks (CANNs). The synaptic input and the neuronal response form Gaussian bumps in the absence of external stimuli, and enable the network to track external stimuli by its translational displacement in the two-dimensional space. Basis functions of the two-dimensional quantum harmonic oscillator in polar coordinates are introduced to describe the distortion modes of the Gaussian bump. The perturbative method is applied to analyze its dynamics. Testing the method by considering the network behavior when the external stimulus abruptly changes its position, we obtain results of the reaction time and the amplitudes of various distortion modes, with excellent agreement with simulation results.
Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.
Wang, Qing Hua; Kalantar-Zadeh, Kourosh; Kis, Andras; Coleman, Jonathan N; Strano, Michael S
2012-11-01
The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.
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.
Control Operator for the Two-Dimensional Energized Wave Equation
Directory of Open Access Journals (Sweden)
Sunday Augustus REJU
2006-07-01
Full Text Available This paper studies the analytical model for the construction of the two-dimensional Energized wave equation. The control operator is given in term of space and time t independent variables. The integral quadratic objective cost functional is subject to the constraint of two-dimensional Energized diffusion, Heat and a source. The operator that shall be obtained extends the Conjugate Gradient method (ECGM as developed by Hestenes et al (1952, [1]. The new operator enables the computation of the penalty cost, optimal controls and state trajectories of the two-dimensional energized wave equation when apply to the Conjugate Gradient methods in (Waziri & Reju, LEJPT & LJS, Issues 9, 2006, [2-4] to appear in this series.
Two-Dimensional Electronic Spectroscopy Using Incoherent Light: Theoretical Analysis
Turner, Daniel B; Sutor, Erika J; Hendrickson, Rebecca A; Gealy, M W; Ulness, Darin J
2012-01-01
Electronic energy transfer in photosynthesis occurs over a range of time scales and under a variety of intermolecular coupling conditions. Recent work has shown that electronic coupling between chromophores can lead to coherent oscillations in two-dimensional electronic spectroscopy measurements of pigment-protein complexes measured with femtosecond laser pulses. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pulses with physiological illumination conditions. Noisy-light spectroscopy can begin to address this question. In this work we present the theoretical analysis of incoherent two-dimensional electronic spectroscopy, I(4) 2D ES. Simulations reveal diagonal peaks, cross peaks, and coherent oscillations similar to those observed in femtosecond two-dimensional electronic spectroscopy experiments. The results also expose fundamental differences between the femtosecond-pulse and noisy-light techniques; the differences lead to new challenges and opp...
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-06-22
Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials.
Two dimensional convolute integers for machine vision and image recognition
Edwards, Thomas R.
1988-01-01
Machine vision and image recognition require sophisticated image processing prior to the application of Artificial Intelligence. Two Dimensional Convolute Integer Technology is an innovative mathematical approach for addressing machine vision and image recognition. This new technology generates a family of digital operators for addressing optical images and related two dimensional data sets. The operators are regression generated, integer valued, zero phase shifting, convoluting, frequency sensitive, two dimensional low pass, high pass and band pass filters that are mathematically equivalent to surface fitted partial derivatives. These operators are applied non-recursively either as classical convolutions (replacement point values), interstitial point generators (bandwidth broadening or resolution enhancement), or as missing value calculators (compensation for dead array element values). These operators show frequency sensitive feature selection scale invariant properties. Such tasks as boundary/edge enhancement and noise or small size pixel disturbance removal can readily be accomplished. For feature selection tight band pass operators are essential. Results from test cases are given.
Optical modulators with two-dimensional layered materials
Sun, Zhipei; Wang, Feng
2016-01-01
Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that two-dimensional layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. In this review, we cover the state-of-the-art of optical modulators based on two-dimensional layered materials including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as two-dimensional heterostructures, plasmonic structures, and silicon/fibre integrated structures. We also take a look at future perspectives and discuss the potential of yet relatively unexplored mechanisms such as magneto-optic and acousto-optic modulation.
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.
TreePM Method for Two-Dimensional Cosmological Simulations
Indian Academy of Sciences (India)
Suryadeep Ray
2004-09-01
We describe the two-dimensional TreePM method in this paper. The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid code combines the 2d Barnes and Hut Tree method and the 2d Particle–Mesh method. We describe the splitting of force between the PM and the Tree parts. We also estimate error in force for a realistic configuration. Finally, we discuss some tests of the code.
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.
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....
Nonlinear excitations in two-dimensional molecular structures with impurities
DEFF Research Database (Denmark)
Gaididei, Yuri Borisovich; Rasmussen, Kim; Christiansen, Peter Leth
1995-01-01
We study the nonlinear dynamics of electronic excitations interacting with acoustic phonons in two-dimensional molecular structures with impurities. We show that the problem is reduced to the nonlinear Schrodinger equation with a varying coefficient. The latter represents the influence of the imp......We study the nonlinear dynamics of electronic excitations interacting with acoustic phonons in two-dimensional molecular structures with impurities. We show that the problem is reduced to the nonlinear Schrodinger equation with a varying coefficient. The latter represents the influence...... excitations. Analytical results are in good agreement with numerical simulations of the nonlinear Schrodinger equation....
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.
Two-dimensional hazard estimation for longevity analysis
DEFF Research Database (Denmark)
Fledelius, Peter; Guillen, M.; Nielsen, J.P.
2004-01-01
the two-dimensional mortality surface. Furthermore we look at aggregated synthetic population metrics as 'population life expectancy' and 'population survival probability'. For Danish women these metrics indicate decreasing mortality with respect to chronological time. The metrics can not directly be used......We investigate developments in Danish mortality based on data from 1974-1998 working in a two-dimensional model with chronological time and age as the two dimensions. The analyses are done with non-parametric kernel hazard estimation techniques. The only assumption is that the mortality surface...... for analysis of economic implications arising from mortality changes....
Field analysis of two-dimensional focusing grating couplers
Borsboom, P.-P.; Frankena, H. J.
1995-05-01
A different technique was developed by which several two-dimensional dielectric optical gratings, consisting 100 or more corrugations, were treated in a numerical reliable approach. The numerical examples that were presented were restricted to gratings made up of sequences of waveguide sections symmetric about the x = 0 plane. The newly developed method was effectively used to investigate the field produced by a two-dimensional focusing grating coupler. Focal-region fields were determined for three symmetrical gratings with 19, 50, and 124 corrugations. For focusing grating coupler with limited length, high-frequency intensity variations were noted in the focal region.
Self-assembly of two-dimensional DNA crystals
Institute of Scientific and Technical Information of China (English)
SONG Cheng; CHEN Yaqing; WEI Shuai; YOU Xiaozeng; XIAO Shoujun
2004-01-01
Self-assembly of synthetic oligonucleotides into two-dimensional lattices presents a 'bottom-up' approach to the fabrication of devices on nanometer scale. We report the design and observation of two-dimensional crystalline forms of DNAs that are composed of twenty-one plane oligonucleotides and one phosphate-modified oligonucleotide. These synthetic sequences are designed to self-assemble into four double-crossover (DX) DNA tiles. The 'sticky ends' of these tiles that associate according to Watson-Crick's base pairing are programmed to build up specific periodic patterns upto tens of microns. The patterned crystals are visualized by the transmission electron microscopy.
Dynamics of vortex interactions in two-dimensional flows
DEFF Research Database (Denmark)
Juul Rasmussen, J.; Nielsen, A.H.; Naulin, V.
2002-01-01
a critical value, a(c). Using the Weiss-field, a(c) is estimated for vortex patches. Introducing an effective radius for vortices with distributed vorticity, we find that 3.3 a(c) ...The dynamics and interaction of like-signed vortex structures in two dimensional flows are investigated by means of direct numerical solutions of the two-dimensional Navier-Stokes equations. Two vortices with distributed vorticity merge when their distance relative to their radius, d/R-0l. is below...
Two-dimensional assignment with merged measurements using Langrangrian relaxation
Briers, Mark; Maskell, Simon; Philpott, Mark
2004-01-01
Closely spaced targets can result in merged measurements, which complicate data association. Such merged measurements violate any assumption that each measurement relates to a single target. As a result, it is not possible to use the auction algorithm in its simplest form (or other two-dimensional assignment algorithms) to solve the two-dimensional target-to-measurement assignment problem. We propose an approach that uses the auction algorithm together with Lagrangian relaxation to incorporate the additional constraints resulting from the presence of merged measurements. We conclude with some simulated results displaying the concepts introduced, and discuss the application of this research within a particle filter context.
Two-dimensional lattice Boltzmann model for magnetohydrodynamics.
Schaffenberger, Werner; Hanslmeier, Arnold
2002-10-01
We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results.
Quasinormal frequencies of asymptotically flat two-dimensional black holes
Lopez-Ortega, A
2011-01-01
We discuss whether the minimally coupled massless Klein-Gordon and Dirac fields have well defined quasinormal modes in single horizon, asymptotically flat two-dimensional black holes. To get the result we solve the equations of motion in the massless limit and we also calculate the effective potentials of Schrodinger type equations. Furthermore we calculate exactly the quasinormal frequencies of the Dirac field propagating in the two-dimensional uncharged Witten black hole. We compare our results on its quasinormal frequencies with other already published.
Spin dynamics in a two-dimensional quantum gas
DEFF Research Database (Denmark)
Pedersen, Poul Lindholm; Gajdacz, Miroslav; Deuretzbacher, Frank
2014-01-01
We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimp......We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions...
Electronic, Vibrational and Thermoelectric Properties of Two-Dimensional Materials
Wickramaratne, Darshana
The discovery of graphene's unique electronic and thermal properties has motivated the search for new two-dimensional materials. Examples of these materials include the layered two-dimensional transition metal dichalcogenides (TMDC) and metal mono-chalcogenides. The properties of the TMDCs (eg. MoS 2, WS2, TaS2, TaSe2) and the metal mono-chalcogenides (eg. GaSe, InSe, SnS) are diverse - ranging from semiconducting, semi-metallic and metallic. Many of these materials exhibit strongly correlated phenomena and exotic collective states such as exciton condensates, charge density waves, Lifshitz transitions and superconductivity. These properties change as the film thickness is reduced down to a few monolayers. We use first-principles simulations to discuss changes in the electronic and the vibrational properties of these materials as the film thickness evolves from a single atomic monolayer to the bulk limit. In the semiconducting TMDCs (MoS2, MoSe2, WS2 and WSe2) and monochalcogenides (GaS, GaSe, InS and InSe) we show confining these materials to their monolayer limit introduces large band degeneracies or non-parabolic features in the electronic structure. These changes in the electronic structure results in increases in the density of states and the number of conducting modes. Our first-principles simulations combined with a Landauer approach show these changes can lead to large enhancements up to an order of magnitude in the thermoelectric performance of these materials when compared to their bulk structure. Few monolayers of the TMDCs can be misoriented with respect to each other due to the weak van-der-Waals (vdW) force at the interface of two monolayers. Misorientation of the bilayer semiconducting TMDCs increases the interlayer van-der-Waals gap distance, reduces the interlayer coupling and leads to an increase in the magnitude of the indirect bandgap by up to 100 meV compared to the registered bilayer. In the semi-metallic and metallic TMDC compounds (TiSe2, Ta
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.)
Institute of Scientific and Technical Information of China (English)
Xu Quan; Tian Qiang
2009-01-01
This paper discusses the two-dimensional discrete monatomic Fermi-Pasta-Ulam lattice, by using the method of multiple-scale and the quasi-discreteness approach. By taking into account the interaction between the atoms in the lattice and their nearest neighbours, it obtains some classes of two-dimensional local models as follows: two-dimensional bright and dark discrete soliton trains, two-dimensional bright and dark line discrete breathers, and two-dimensional bright and dark discrete breather.
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.
Waiting Time Dynamics in Two-Dimensional Infrared Spectroscopy
Jansen, Thomas L. C.; Knoester, Jasper
We review recent work on the waiting time dynamics of coherent two-dimensional infrared (2DIR) spectroscopy. This dynamics can reveal chemical and physical processes that take place on the femto- and picosecond time scale, which is faster than the time scale that may be probed by, for example,
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 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
Low-frequency scattering from two-dimensional perfect conductors
DEFF Research Database (Denmark)
Hansen, Thorkild; Yaghjian, A.D
1991-01-01
Exact expressions have been obtained for the leading terms in the low-frequency expansions of the far fields scattered from three different types of two-dimensional perfect conductors: a cylinder with finite cross section, a cylindrical bump on an infinite ground plane, and a cylindrical dent...
Piezoelectricity and Piezomagnetism: Duality in two-dimensional checkerboards
Fel, Leonid G.
2002-05-01
The duality approach in two-dimensional two-component regular checkerboards is extended to piezoelectricity and piezomagnetism. The relation between the effective piezoelectric and piezomagnetic moduli is found for a checkerboard with the p6'mm'-plane symmetry group (dichromatic triangle).
Specification of a Two-Dimensional Test Case
DEFF Research Database (Denmark)
Nielsen, Peter Vilhelm
This paper describes the geometry and other boundary conditions for a test case which can be used to test different two-dimensional CFD codes in the lEA Annex 20 work. The given supply opening is large compared with practical openings. Therefore, this geometry will reduce the need for a high number...... of grid points in the wall jet region....
Operator splitting for two-dimensional incompressible fluid equations
Holden, Helge; Karper, Trygve K
2011-01-01
We analyze splitting algorithms for a class of two-dimensional fluid equations, which includes the incompressible Navier-Stokes equations and the surface quasi-geostrophic equation. Our main result is that the Godunov and Strang splitting methods converge with the expected rates provided the initial data are sufficiently regular.
Chaotic dynamics for two-dimensional tent maps
Pumariño, Antonio; Ángel Rodríguez, José; Carles Tatjer, Joan; Vigil, Enrique
2015-02-01
For a two-dimensional extension of the classical one-dimensional family of tent maps, we prove the existence of an open set of parameters for which the respective transformation presents a strange attractor with two positive Lyapounov exponents. Moreover, periodic orbits are dense on this attractor and the attractor supports a unique ergodic invariant probability measure.
Divorticity and dihelicity in two-dimensional hydrodynamics
DEFF Research Database (Denmark)
Shivamoggi, B.K.; van Heijst, G.J.F.; Juul Rasmussen, Jens
2010-01-01
A framework is developed based on the concepts of divorticity B (≡×ω, ω being the vorticity) and dihelicity g (≡vB) for discussing the theoretical structure underlying two-dimensional (2D) hydrodynamics. This formulation leads to the global and Lagrange invariants that could impose significant...
Spin-orbit torques in two-dimensional Rashba ferromagnets
Qaiumzadeh, A.; Duine, R. A.|info:eu-repo/dai/nl/304830127; Titov, M.
2015-01-01
Magnetization dynamics in single-domain ferromagnets can be triggered by a charge current if the spin-orbit coupling is sufficiently strong. We apply functional Keldysh theory to investigate spin-orbit torques in metallic two-dimensional Rashba ferromagnets in the presence of spin-dependent
Numerical blowup in two-dimensional Boussinesq equations
Yin, Zhaohua
2009-01-01
In this paper, we perform a three-stage numerical relay to investigate the finite time singularity in the two-dimensional Boussinesq approximation equations. The initial asymmetric condition is the middle-stage output of a $2048^2$ run, the highest resolution in our study is $40960^2$, and some signals of numerical blowup are observed.
Exact two-dimensional superconformal R symmetry and c extremization.
Benini, Francesco; Bobev, Nikolay
2013-02-08
We uncover a general principle dubbed c extremization, which determines the exact R symmetry of a two-dimensional unitary superconformal field theory with N=(0,2) supersymmetry. To illustrate its utility, we study superconformal theories obtained by twisted compactifications of four-dimensional N=4 super-Yang-Mills theory on Riemann surfaces and construct their gravity duals.
Zero sound in a two-dimensional dipolar Fermi gas
Lu, Z.K.; Matveenko, S.I.; Shlyapnikov, G.V.
2013-01-01
We study zero sound in a weakly interacting two-dimensional (2D) gas of single-component fermionic dipoles (polar molecules or atoms with a large magnetic moment) tilted with respect to the plane of their translational motion. It is shown that the propagation of zero sound is provided by both mean-f
Topology optimization of two-dimensional elastic wave barriers
DEFF Research Database (Denmark)
Van Hoorickx, C.; Sigmund, Ole; Schevenels, M.
2016-01-01
Topology optimization is a method that optimally distributes material in a given design domain. In this paper, topology optimization is used to design two-dimensional wave barriers embedded in an elastic halfspace. First, harmonic vibration sources are considered, and stiffened material is insert...
Non perturbative methods in two dimensional quantum field theory
Abdalla, Elcio; Rothe, Klaus D
1991-01-01
This book is a survey of methods used in the study of two-dimensional models in quantum field theory as well as applications of these theories in physics. It covers the subject since the first model, studied in the fifties, up to modern developments in string theories, and includes exact solutions, non-perturbative methods of study, and nonlinear sigma models.
Thermodynamics of Two-Dimensional Black-Holes
Nappi, Chiara R.; Pasquinucci, Andrea
1992-01-01
We explore the thermodynamics of a general class of two dimensional dilatonic black-holes. A simple prescription is given that allows us to compute the mass, entropy and thermodynamic potentials, with results in agreement with those obtained by other methods, when available.
Influence of index contrast in two dimensional photonic crystal lasers
DEFF Research Database (Denmark)
Jørgensen, Mette Marie; Petersen, Sidsel Rübner; Christiansen, Mads Brøkner;
2010-01-01
The influence of index contrast variations for obtaining single-mode operation and low threshold in dye doped polymer two dimensional photonic crystal (PhC) lasers is investigated. We consider lasers made from Pyrromethene 597 doped Ormocore imprinted with a rectangular lattice PhC having a cavit...
Magnetic order in two-dimensional nanoparticle assemblies
Georgescu, M
2008-01-01
This thesis involves a fundamental study of two-dimensional arrays of magnetic nanoparticles using non-contact Atomic Force Microscopy, Magnetic Force Microscopy, and Atomic Force Spectroscopy. The goal is to acquire a better understanding of the interactions between magnetic nanoparticles and the
Dynamical phase transitions in the two-dimensional ANNNI model
Energy Technology Data Exchange (ETDEWEB)
Barber, M.N.; Derrida, B.
1988-06-01
We study the phase diagram of the two-dimensional anisotropic next-nearest neighbor Ising (ANNNI) model by comparing the time evolution of two distinct spin configurations submitted to the same thermal noise. We clearly se several dynamical transitions between ferromagnetic, paramagnetic, antiphase, and floating phases. These dynamical transitions seem to occur rather close to the transition lines determined previously in the literature.
Two-dimensional static black holes with pointlike sources
Melis, M
2004-01-01
We study the static black hole solutions of generalized two-dimensional dilaton-gravity theories generated by pointlike mass sources, in the hypothesis that the matter is conformally coupled. We also discuss the motion of test particles. Due to conformal coupling, these follow the geodesics of a metric obtained by rescaling the canonical metric with the dilaton.
Magnetic order in two-dimensional nanoparticle assemblies
Georgescu, M
2008-01-01
This thesis involves a fundamental study of two-dimensional arrays of magnetic nanoparticles using non-contact Atomic Force Microscopy, Magnetic Force Microscopy, and Atomic Force Spectroscopy. The goal is to acquire a better understanding of the interactions between magnetic nanoparticles and the r
Two-Dimensional Chirality in Three-Dimensional Chemistry.
Wintner, Claude E.
1983-01-01
The concept of two-dimensional chirality is used to enhance students' understanding of three-dimensional stereochemistry. This chirality is used as a key to teaching/understanding such concepts as enaniotropism, diastereotopism, pseudoasymmetry, retention/inversion of configuration, and stereochemical results of addition to double bonds. (JN)
Field analysis of two-dimensional focusing grating
Borsboom, P.P.; Frankena, H.J.
1995-01-01
The method that we have developed [P-P. Borsboom, Ph.D. dissertation (Delft University of Technology, Delft, The Netherlands); P-P. Borsboom and H. J. Frankena, J. Opt. Soc. Am. A 12, 1134–1141 (1995)] is successfully applied to a two-dimensional focusing grating coupler. The field in the focal regi
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
Vibrations of Thin Piezoelectric Shallow Shells: Two-Dimensional Approximation
Indian Academy of Sciences (India)
N Sabu
2003-08-01
In this paper we consider the eigenvalue problem for piezoelectric shallow shells and we show that, as the thickness of the shell goes to zero, the eigensolutions of the three-dimensional piezoelectric shells converge to the eigensolutions of a two-dimensional eigenvalue problem.
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...
Forensic potential of comprehensive two-dimensional gas chromatography
Sampat, A.; Lopatka, M.; Sjerps, M.; Vivo-Truyols, G.; Schoenmakers, P.; van Asten, A.
2016-01-01
In this study, the application of comprehensive two-dimensional (2D) gas chromatography (GC × GC) in forensic science is reviewed. The peer-reviewed publications on the forensic use of GC × GC and 2D gas chromatography with mass spectrometric detection (GC × GC-MS) have been studied in detail, not o
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
Two Dimensional F(R) Horava-Lifshitz Gravity
Kluson, J
2016-01-01
We study two-dimensional F(R) Horava-Lifshitz gravity from the Hamiltonian point of view. We determine constraints structure with emphasis on the careful separation of the second class constraints and global first class constraints. We determine number of physical degrees of freedom and also discuss gauge fixing of the global first class constraints.
Localization of Tight Closure in Two-Dimensional Rings
Indian Academy of Sciences (India)
Kamran Divaani-Aazar; Massoud Tousi
2005-02-01
It is shown that tight closure commutes with localization in any two-dimensional ring of prime characteristic if either is a Nagata ring or possesses a weak test element. Moreover, it is proved that tight closure commutes with localization at height one prime ideals in any ring of prime characteristic.
Cryptanalysis of the Two-Dimensional Circulation Encryption Algorithm
Directory of Open Access Journals (Sweden)
Bart Preneel
2005-07-01
Full Text Available We analyze the security of the two-dimensional circulation encryption algorithm (TDCEA, recently published by Chen et al. in this journal. We show that there are several flaws in the algorithm and describe some attacks. We also address performance issues in current cryptographic designs.
New directions in science and technology: two-dimensional crystals
Energy Technology Data Exchange (ETDEWEB)
Neto, A H Castro [Graphene Research Centre, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Novoselov, K, E-mail: phycastr@nus.edu.sg, E-mail: konstantin.novoselov@manchester.ac.uk [School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)
2011-08-15
Graphene is possibly one of the largest and fastest growing fields in condensed matter research. However, graphene is only one example in a large class of two-dimensional crystals with unusual properties. In this paper we briefly review the properties of graphene and look at the exciting possibilities that lie ahead.
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
On the continua in two-dimensional nonadiabatic magnetohydrodynamic spectra
De Ploey, A.; Van der Linden, R. A. M.; Belien, A. J. C.
2000-01-01
The equations for the continuous subspectra of the linear magnetohydrodynamic (MHD) normal modes spectrum of two-dimensional (2D) plasmas are derived in general curvilinear coordinates, taking nonadiabatic effects in the energy equation into account. Previously published derivations of continuous sp
Dislocation climb in two-dimensional discrete dislocation dynamics
Davoudi, K.M.; Nicola, L.; Vlassak, J.J.
2012-01-01
In this paper, dislocation climb is incorporated in a two-dimensional discrete dislocation dynamics model. Calculations are carried out for polycrystalline thin films, passivated on one or both surfaces. Climb allows dislocations to escape from dislocation pile-ups and reduces the strain-hardening r
SAR Processing Based On Two-Dimensional Transfer Function
Chang, Chi-Yung; Jin, Michael Y.; Curlander, John C.
1994-01-01
Exact transfer function, ETF, is two-dimensional transfer function that constitutes basis of improved frequency-domain-convolution algorithm for processing synthetic-aperture-radar, SAR data. ETF incorporates terms that account for Doppler effect of motion of radar relative to scanned ground area and for antenna squint angle. Algorithm based on ETF outperforms others.
Sound waves in two-dimensional ducts with sinusoidal walls
Nayfeh, A. H.
1974-01-01
The method of multiple scales is used to analyze the wave propagation in two-dimensional hard-walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.
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.
Imperfect two-dimensional topological insulator field-effect transistors
Vandenberghe, William G.; Fischetti, Massimo V.
2017-01-01
To overcome the challenge of using two-dimensional materials for nanoelectronic devices, we propose two-dimensional topological insulator field-effect transistors that switch based on the modulation of scattering. We model transistors made of two-dimensional topological insulator ribbons accounting for scattering with phonons and imperfections. In the on-state, the Fermi level lies in the bulk bandgap and the electrons travel ballistically through the topologically protected edge states even in the presence of imperfections. In the off-state the Fermi level moves into the bandgap and electrons suffer from severe back-scattering. An off-current more than two-orders below the on-current is demonstrated and a high on-current is maintained even in the presence of imperfections. At low drain-source bias, the output characteristics are like those of conventional field-effect transistors, at large drain-source bias negative differential resistance is revealed. Complementary n- and p-type devices can be made enabling high-performance and low-power electronic circuits using imperfect two-dimensional topological insulators. PMID:28106059
Bounds on the capacity of constrained two-dimensional codes
DEFF Research Database (Denmark)
Forchhammer, Søren; Justesen, Jørn
2000-01-01
Bounds on the capacity of constrained two-dimensional (2-D) codes are presented. The bounds of Calkin and Wilf apply to first-order symmetric constraints. The bounds are generalized in a weaker form to higher order and nonsymmetric constraints. Results are given for constraints specified by run...
Miniature sensor for two-dimensional magnetic field distributions
Fluitman, J.H.J.; Krabbe, H.W.
1972-01-01
Describes a simple method of production of a sensor for two-dimensional magnetic field distributions. The sensor consists of a strip of Ni-Fe(81-19), of which the magnetoresistance is utilized. Typical dimensions of the strip, placed at the edge of a glass substrate, are: length 100 mu m, width 2 or
Forensic potential of comprehensive two-dimensional gas chromatography
Sampat, A.; Lopatka, M.; Sjerps, M.; Vivo-Truyols, G.; Schoenmakers, P.; van Asten, A.
2016-01-01
In this study, the application of comprehensive two-dimensional (2D) gas chromatography (GC × GC) in forensic science is reviewed. The peer-reviewed publications on the forensic use of GC × GC and 2D gas chromatography with mass spectrometric detection (GC × GC-MS) have been studied in detail, not o
Spontaneous emission in two-dimensional photonic crystal microcavities
DEFF Research Database (Denmark)
Søndergaard, Thomas
2000-01-01
The properties of the radiation field in a two-dimensional photonic crystal with and without a microcavity introduced are investigated through the concept of the position-dependent photon density of states. The position-dependent rate of spontaneous radiative decay for a two-level atom with random...
Linkage analysis by two-dimensional DNA typing
te Meerman, G J; Mullaart, E; van der Meulen, M A; den Daas, J H; Morolli, B; Uitterlinden, A G; Vijg, J
1993-01-01
In two-dimensional (2-D) DNA typing, genomic DNA fragments are separated, first according to size by electrophoresis in a neutral polyacrylamide gel and second according to sequence by denaturing gradient gel electrophoresis, followed by hybridization analysis using micro- and minisatellite core pro
Phase conjugated Andreev backscattering in two-dimensional ballistic cavities
Morpurgo, A.F.; Holl, S.; Wees, B.J.van; Klapwijk, T.M; Borghs, G.
1997-01-01
We have experimentally investigated transport in two-dimensional ballistic cavities connected to a point contact and to two superconducting electrodes with a tunable macroscopic phase difference. The point contact resistance oscillates as a function of the phase difference in a way which reflects
Two-dimensional manifold with point-like defects
Gani, Vakhid A; Rubin, Sergei G
2014-01-01
We study a class of two-dimensional extra spaces isomorphic to the $S^2$ sphere in the framework of the multidimensional gravitation. We show that there exists a family of stationary metrics that depend on the initial (boundary) conditions. All these geometries have a singular point. We also discuss the possibility for these deformed extra spaces to be considered as dark matter candidates.
Instability of two-dimensional heterotic stringy black holes
Azreg-Ainou, M
1999-01-01
We solve the eigenvalue problem of general relativity for the case of charged black holes in two-dimensional heterotic string theory, derived by McGuigan et al. For the case of $m^{2}>q^{2}$, we find a physically acceptable time-dependent growing mode; thus the black hole is unstable. The extremal case $m^{2}=q^{2}$ is stable.
Institute of Scientific and Technical Information of China (English)
XIONG Lei; LI haijiao; ZHANG Lewen
2008-01-01
The fourth-order B spline wavelet scaling functions are used to solve the two-dimensional unsteady diffusion equation. The calculations from a case history indicate that the method provides high accuracy and the computational efficiency is enhanced due to the small matrix derived from this method.The respective features of 3-spline wavelet scaling functions, 4-spline wavelet scaling functions and quasi-wavelet used to solve the two-dimensional unsteady diffusion equation are compared. The proposed method has potential applications in many fields including marine science.
Ludván, Brigitta; Bór, József; Steinbach, Péter; Novák, Attila; Sátori, Gabriella
2015-04-01
Schumann resonance transients (SRTs) are extremely low frequency (ELF, 3-3000 Hz) wave packets of high amplitude electromagnetic (EM) waves produced by intense lightning discharges worldwide. Near the lower end of the ELF band, frequencies are close to the lowest spherical eigenfrequencies of the closed EM waveguide formed by the surface of the Earth and the lower ionosphere. Therefore, these waves suffer little attenuation during their propagation and can be detected globally at any point on Earth. SRTs detected both in the vertical electric and in the horizontal magnetic components of the atmospheric EM field at the Széchenyi István Geophysical Observatory (NCK, 16.7 E, 47.6 N) on 1st and 2nd August, 2012 have been analyzed. Azimuths of their parent lightning discharges were calculated from the horizontal components of the corresponding Poynting vector. Parent lightning strokes of the considered SRTs (342 and 245 events on the first and on the second day, respectively) have been identified in the records of the World Wide Lightning Location Network (WWLLN) using the detection times of the events in the two datasets. It was found that the azimuths of the sources at NCK station deduced from ELF records systematically differ from source azimuths calculated using WWLLN provided lightning locations. The difference between the corresponding azimuth values from the two methods shows the same pattern on both examined days when it is plotted as function of the WWLLN data based source azimuth. The symmetry of this pattern agrees well with the symmetry of the conductivity variations of the Earth's crust determined by independent magnetotelluric methods at NCK station. The differences have similar diurnal variation, too, on the two days with the largest difference occurring near midnight, local time. Our results agree well with findings of Füllekrug and Sukhorukov (GRL, 1999) and support the idea that the azimuthal dependence of source azimuth differences can be related
Analytical Studies of Two-Dimensional Channel Turbulent Flow Subjected to Coriolis Force
鬼頭, 修己; 中林, 功一; キトウ, オサミ; Kito, Osami
1992-01-01
Coriolis effects on fully developed turbulent flow in a two-dimensional channel rotating about an axis perpendicular to its axis are considered. The Coriolis force has stabilizing/destabilizing effects on turbulence, and the mean velocity distribution changes accordingly. Experimental and numerical studies on the velocity characteristics have already been conducted by other researchers for various conditions. However, we cannot assemble the overall picture of the Coriolis effect on the veloci...
Interaction-induced huge magnetoresistance in a high mobility two-dimensional electron gas
Energy Technology Data Exchange (ETDEWEB)
Bockhorn, L.; Haug, R. J. [Institut für Festkörperphysik, Leibniz Universität Hannover, D-30167 Hannover (Germany); Gornyi, I. V. [Institut für Nanotechnologie, Karlsruher Institut of Technology, D-76021 Karlsruhe (Germany); Schuh, D. [Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93053 Regensburg (Germany); Wegscheider, W. [ETH Zürich (Switzerland)
2013-12-04
A strong negative magnetoresistance is observed in a high-mobility two-dimensional electron gas in a GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum well. We discuss that the negative magnetoresistance consists of a small peak induced by a combination of two types of disorder and a huge magnetoresistance explained by the interaction correction to the conductivity for mixed disorder.
Synthesis and Characterization of One-dimensional and Two-Dimensional Porphyrin Polymers* (Ⅰ)
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
@@Porphyrin polymers are of interest in relation to conductive materials[1, 2], catalysts for photosynthetic charge separation[3], or the fundamental features in biological systems[4]. There have been many versatile studies about them[5,6]. The one-dimensional “Shish Kebab” porphyrin polymers synthesized with a new method different from those reported and Schiff base porphyrin polymers with two-dimensional nano-structure have provided a new field of study. The present paper covers highly ordered porphyrin polymers.
Spatial statistics of magnetic field in two-dimensional chaotic flow in the resistive growth stage
Kolokolov, I. V.
2017-03-01
The correlation tensors of magnetic field in a two-dimensional chaotic flow of conducting fluid are studied. It is shown that there is a stage of resistive evolution where the field correlators grow exponentially with time. The two- and four-point field correlation tensors are computed explicitly in this stage in the framework of Batchelor-Kraichnan-Kazantsev model. They demonstrate strong temporal intermittency of the field fluctuations and high level of non-Gaussianity in spatial field distribution.
Synthesis of two-dimensional materials by selective extraction.
Naguib, Michael; Gogotsi, Yury
2015-01-20
CONSPECTUS: Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials. The most common synthesis approach in general is by reacting different elements or compounds to form a new compound. However, this approach does not necessarily work well for low-dimensional structures, since it favors formation of energetically preferred 3D (bulk) solids. Many 2D materials are produced by exfoliation of van der Waals solids, such as graphite or MoS2, breaking large particles into 2D layers. However, these approaches are not universal; for example, 2D transition metal carbides cannot be produced by any of them. An alternative but less studied way of material synthesis is the selective extraction process, which is based on the difference in reactivity and stability between the different components (elements or structural units) of the original material. It can be achieved using thermal, chemical, or electrochemical processes. Many 2D materials have been synthesized using selective extraction, such as graphene from SiC, transition metal oxides (TMO) from layered 3D salts, and transition metal carbides or carbonitrides (MXenes) from MAX phases. Selective extraction synthesis is critically important when the bonds between the building blocks of the material are too strong (e.g., in carbides) to be broken mechanically in order to form nanostructures. Unlike extractive metallurgy, where the extracted metal is the goal of the process, selective extraction of one or more elements from
Two-dimensional Confinement of Heavy Fermions in Artificial Superlattices
Shishido, Hiroaki
2011-03-01
Low dimensionality and strong electron-electron Coulomb interactions are both key parameters for novel quantum states of condensed matter. A metallic system with the strongest electron correlations is reported in rare-earth and actinide compounds with f electrons, known as heavy-fermion compounds, where the effective mass of the conduction electrons are strikingly enhanced by the electron correlations up to some hundreds times the free electron mass. To date the electronic structure of all heavy-fermion compounds is essentially three-dimensional. We realized experimentally a two-dimensional heavy fermion system, adjusting the dimensionality in a controllable fashion. We grew artificial superlattices of CeIn 3 (m)/ LaIn 3 (n), in which m -layers of heavy-fermion antiferromagnet CeIn 3 and n -layers of a non-magnetic isostructual compound LaIn 3 are stacked alternately, by a molecular beam epitaxy. By reducing the thickness of the CeIn 3 layers, the magnetic order was suppressed and the effective electron mass was further enhanced. The Néel temperature becomes zero at around m = 2 , concomitant with striking deviations from the standard Fermi liquid low-temperature electronic properties. Standard Fermi liquid behaviors are, however, recovered under high magnetic field. These behaviors imply new ``dimensional tuning'' towards a quantum critical point. We also succeeded to fabricate artificial superlattices of a heavy fermion superconductor CeCoIn 5 and non-magnetic divalent Yb-compound YbCoIn 5 . Superconductivity survives even in CeCoIn 5 (3)/ YbCoIn 5 (5) films, while the thickness of CeCoIn 5 layer, 2.3 nm, is comparable to the c -axis coherence length ξc ~ 2 nm. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T. Shibauchi, T. Terashima and Y. Matsuda.superconductivity is realized in the artificial superlattices. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T
Two dimensional soft material: new faces of graphene oxide.
Kim, Jaemyung; Cote, Laura J; Huang, Jiaxing
2012-08-21
Graphite oxide sheets, now called graphene oxide (GO), can be made from chemical exfoliation of graphite by reactions that have been known for 150 years. Because GO is a promising solution-processable precursor for the bulk production of graphene, interest in this old material has resurged. The reactions to produce GO add oxygenated functional groups to the graphene sheets on their basal plane and edges, and this derivatization breaks the π-conjugated network, resulting in electrically insulating but highly water-dispersible sheets. Apart from making graphene, GO itself has many intriguing properties. Like graphene, GO is a two-dimensional (2D) sheet with feature sizes at two abruptly different length scales. The apparent thickness of the functionalized carbon sheet is approximately 1 nm, but the lateral dimensions can range from a few nanometers to hundreds of micrometers. Therefore, researchers can think of GO as either a single molecule or a particle, depending on which length scale is of greater interest. At the same time, GO can be viewed as an unconventional soft material, such as a 2D polymer, highly anisotropic colloid, membrane, liquid crystal, or amphiphile. In this Account, we highlight the soft material characteristics of GO. GO consists of nanographitic patches surrounded by largely disordered, oxygenated domains. Such structural characteristics effectively make GO a 2D amphiphile with a hydrophilic periphery and largely hydrophobic center. This insight has led to better understanding of the solution properties of GO for making thin films and new applications of GO as a surfactant. Changes in pH and sheet size can tune the amphiphilicity of GO, leading to intriguing interfacial activities. In addition, new all-carbon composites made of only graphitic nanostructures using GO as a dispersing agent have potential applications in photovoltaics and energy storage. On the other hand, GO can function as a 2D random diblock copolymer, one block graphitic and
2015-01-01
A two-dimensional single-phase model is developed for the steady-state and transient analysis of polymer electrolyte membrane fuel cells (PEMFC). Based on diluted and concentrated solution theories, viscous flow is introduced into a phenomenological multi-component modeling framework in the membrane. Characteristic variables related to the water uptake are discussed. A ButlereVolmer formulation of the current-overpotential relationship is developed based on an elementary mechanism of elect...
Shevyrin, A. A.; Pogosov, A. G.; Bakarov, A. K.; Shklyaev, A. A.
2017-06-01
A physical model describing the piezoelectric-effect-mediated influence of bending of a thin suspended cantilever with a two-dimensional electron gas on the conductivity is proposed. The model shows that the conductivity change is almost entirely caused by the rapid change in mechanical stress near the boundary of suspended and non-suspended areas, rather than by the stress itself. An experiment confirming that the electromechanical coupling is associated with the piezoelectric effect is performed. The experimentally measured conductance sensitivity to the cantilever’s vibrations agree with the developed physical model.
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.
The separation of whale myoglobins with two-dimensional electrophoresis.
Spicer, G S
1988-10-01
Five myoglobins (sperm whale, Sei whale, Hubbs' beaked whale, pilot whale, and Amazon River dolphin) were examined using two-dimensional electrophoresis. Previous reports indicated that none of these proteins could be separated by using denaturing (in the presence of 8-9 M urea) isoelectric focusing. This result is confirmed in the present study. However, all the proteins could be separated by using denaturing nonequilibrium pH-gradient electrophoresis in the first dimension. Additionally, all the myoglobins have characteristic mobilities in the second dimension (sodium dodecyl sulfate), but these mobilities do not correspond to the molecular weights of the proteins. We conclude that two-dimensional electrophoresis can be more sensitive to differences in primary protein structure than previous studies indicate and that the assessment seems to be incorrect that this technique can separate only proteins that have a unit charge difference.
Entanglement Entropy in Two-Dimensional String Theory.
Hartnoll, Sean A; Mazenc, Edward A
2015-09-18
To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space.
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...
The Persistence Problem in Two-Dimensional Fluid Turbulence
Perlekar, Prasad; Mitra, Dhrubaditya; Pandit, Rahul
2010-01-01
We present a natural framework for studying the persistence problem in two-dimensional fluid turbulence by using the Okubo-Weiss parameter {\\Lambda} to distinguish between vortical and extensional regions. We then use a direct numerical simulation (DNS) of the two-dimensional, incompressible Navier-Stokes equation with Ekman friction to study probability distribution functions (PDFs) of the persistence times of vortical and extensional regions by employing both Eulerian and Lagrangian measurements. We find that, in the Eulerian case, the persistence-time PDFs have exponential tails; by contrast, this PDF for Lagrangian particles, in vortical regions, has a power-law tail with a universal exponent {\\theta} = 3.1 \\pm 0.2.
On Dirichlet eigenvectors for neutral two-dimensional Markov chains
Champagnat, Nicolas; Miclo, Laurent
2012-01-01
We consider a general class of discrete, two-dimensional Markov chains modeling the dynamics of a population with two types, without mutation or immigration, and neutral in the sense that type has no influence on each individual's birth or death parameters. We prove that all the eigenvectors of the corresponding transition matrix or infinitesimal generator \\Pi\\ can be expressed as the product of "universal" polynomials of two variables, depending on each type's size but not on the specific transitions of the dynamics, and functions depending only on the total population size. These eigenvectors appear to be Dirichlet eigenvectors for \\Pi\\ on the complement of triangular subdomains, and as a consequence the corresponding eigenvalues are ordered in a specific way. As an application, we study the quasistationary behavior of finite, nearly neutral, two-dimensional Markov chains, absorbed in the sense that 0 is an absorbing state for each component of the process.
Statistical mechanics of two-dimensional and geophysical flows
Bouchet, Freddy
2011-01-01
The theoretical study of the self-organization of two-dimensional and geophysical turbulent flows is addressed based on statistical mechanics methods. This review is a self-contained presentation of classical and recent works on this subject; from the statistical mechanics basis of the theory up to applications to Jupiter's troposphere and ocean vortices and jets. Emphasize has been placed on examples with available analytical treatment in order to favor better understanding of the physics and dynamics. The equilibrium microcanonical measure is built from the Liouville theorem. On this theoretical basis, we predict the output of the long time evolution of complex turbulent flows as statistical equilibria. This is applied to make quantitative models of two-dimensional turbulence, the Great Red Spot and other Jovian vortices, ocean jets like the Gulf-Stream, and ocean vortices. We also present recent results for non-equilibrium situations, for the studies of either the relaxation towards equilibrium or non-equi...
Two-dimensional hazard estimation for longevity analysis
DEFF Research Database (Denmark)
Fledelius, Peter; Guillen, M.; Nielsen, J.P.
2004-01-01
We investigate developments in Danish mortality based on data from 1974-1998 working in a two-dimensional model with chronological time and age as the two dimensions. The analyses are done with non-parametric kernel hazard estimation techniques. The only assumption is that the mortality surface...... the two-dimensional mortality surface. Furthermore we look at aggregated synthetic population metrics as 'population life expectancy' and 'population survival probability'. For Danish women these metrics indicate decreasing mortality with respect to chronological time. The metrics can not directly be used...... for prediction purposes. However, we suggest that life insurance companies use the estimation technique and the cross-validation for bandwidth selection when analyzing their portfolio mortality. The non-parametric approach may give valuable information prior to developing more sophisticated prediction models...
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.
Extension of modified power method to two-dimensional problems
Zhang, Peng; Lee, Hyunsuk; Lee, Deokjung
2016-09-01
In this study, the generalized modified power method was extended to two-dimensional problems. A direct application of the method to two-dimensional problems was shown to be unstable when the number of requested eigenmodes is larger than a certain problem dependent number. The root cause of this instability has been identified as the degeneracy of the transfer matrix. In order to resolve this instability, the number of sub-regions for the transfer matrix was increased to be larger than the number of requested eigenmodes; and a new transfer matrix was introduced accordingly which can be calculated by the least square method. The stability of the new method has been successfully demonstrated with a neutron diffusion eigenvalue problem and the 2D C5G7 benchmark problem.
Two Dimensional Lattice Boltzmann Method for Cavity Flow Simulation
Directory of Open Access Journals (Sweden)
Panjit MUSIK
2004-01-01
Full Text Available This paper presents a simulation of incompressible viscous flow within a two-dimensional square cavity. The objective is to develop a method originated from Lattice Gas (cellular Automata (LGA, which utilises discrete lattice as well as discrete time and can be parallelised easily. Lattice Boltzmann Method (LBM, known as discrete Lattice kinetics which provide an alternative for solving the Navier–Stokes equations and are generally used for fluid simulation, is chosen for the study. A specific two-dimensional nine-velocity square Lattice model (D2Q9 Model is used in the simulation with the velocity at the top of the cavity kept fixed. LBM is an efficient method for reproducing the dynamics of cavity flow and the results which are comparable to those of previous work.
Transport behavior of water molecules through two-dimensional nanopores
Energy Technology Data Exchange (ETDEWEB)
Zhu, Chongqin; Li, Hui; Meng, Sheng, E-mail: smeng@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)
2014-11-14
Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.
Transport behavior of water molecules through two-dimensional nanopores
Zhu, Chongqin; Li, Hui; Meng, Sheng
2014-11-01
Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.
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.
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.
CORPORATE VALUATION USING TWO-DIMENSIONAL MONTE CARLO SIMULATION
Directory of Open Access Journals (Sweden)
Toth Reka
2010-12-01
Full Text Available In this paper, we have presented a corporate valuation model. The model combine several valuation methods in order to get more accurate results. To determine the corporate asset value we have used the Gordon-like two-stage asset valuation model based on the calculation of the free cash flow to the firm. We have used the free cash flow to the firm to determine the corporate market value, which was calculated with use of the Black-Scholes option pricing model in frame of the two-dimensional Monte Carlo simulation method. The combined model and the use of the two-dimensional simulation model provides a better opportunity for the corporate value estimation.
Two-dimensional magnetostriction under vector magnetic characteristic
Wakabayashi, D.; Enokizono, M.
2015-05-01
This paper presents two-dimensional magnetostriction of electrical steel sheet under vector magnetic characteristic. In conventional measurement method using Single Sheet Tester, the magnetic flux density, the magnetic field strength, and the magnetostriction have been measured in one direction. However, an angle between the magnetic flux density vector and the magnetic field strength vector exists because the magnetic property is vector quantity. An angle between the magnetic flux density vector and the direction of maximum magnetostriction also exists. We developed a new measurement method, which enables measurement of these angles. The vector magnetic characteristic and the two-dimensional magnetostriction have been measured using the new measurement method. The BH and Bλ curves considering the angles are shown in this paper. The analyzed results considering the angles are also made clear.
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.
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.
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.
Folding two dimensional crystals by swift heavy ion irradiation
Energy Technology Data Exchange (ETDEWEB)
Ochedowski, Oliver; Bukowska, Hanna [Fakultät für Physik and CENIDE, Universität Duisburg-Essen, D-47048 Duisburg (Germany); Freire Soler, Victor M. [Fakultät für Physik and CENIDE, Universität Duisburg-Essen, D-47048 Duisburg (Germany); Departament de Fisica Aplicada i Optica, Universitat de Barcelona, E08028 Barcelona (Spain); Brökers, Lara [Fakultät für Physik and CENIDE, Universität Duisburg-Essen, D-47048 Duisburg (Germany); Ban-d' Etat, Brigitte; Lebius, Henning [CIMAP (CEA-CNRS-ENSICAEN-UCBN), 14070 Caen Cedex 5 (France); Schleberger, Marika, E-mail: marika.schleberger@uni-due.de [Fakultät für Physik and CENIDE, Universität Duisburg-Essen, D-47048 Duisburg (Germany)
2014-12-01
Ion irradiation of graphene, the showcase model of two dimensional crystals, has been successfully applied to induce various modifications in the graphene crystal. One of these modifications is the formation of origami like foldings in graphene which are created by swift heavy ion irradiation under glancing incidence angle. These foldings can be applied to locally alter the physical properties of graphene like mechanical strength or chemical reactivity. In this work we show that the formation of foldings in two dimensional crystals is not restricted to graphene but can be applied for other materials like MoS{sub 2} and hexagonal BN as well. Further we show that chemical vapour deposited graphene forms foldings after swift heavy ion irradiation while chemical vapour deposited MoS{sub 2} does not.
Explorative data analysis of two-dimensional electrophoresis gels
DEFF Research Database (Denmark)
Schultz, J.; Gottlieb, D.M.; Petersen, Marianne Kjerstine
2004-01-01
Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening...... of gels is presented. First, an approach is demonstrated in which no prior knowledge of the separated proteins is used. Alignment of the gels followed by a simple transformation of data makes it possible to analyze the gels in an automated explorative manner by principal component analysis, to determine...... if the gels should be further analyzed. A more detailed approach is done by analyzing spot volume lists by principal components analysis and partial least square regression. The use of spot volume data offers a mean to investigate the spot pattern and link the classified protein patterns to distinct spots...
Two-dimensional model of elastically coupled molecular motors
Institute of Scientific and Technical Information of China (English)
Zhang Hong-Wei; Wen Shu-Tang; Chen Gai-Rong; Li Yu-Xiao; Cao Zhong-Xing; Li Wei
2012-01-01
A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins.Extensive Langevin simulations of the model are performed.We discuss the dependences of motion and efficiency on the model parameters,including the external force and the temperature.A good qualitative agreement with the expected behavior is observed.
Minor magnetization loops in two-dimensional dipolar Ising model
Energy Technology Data Exchange (ETDEWEB)
Sarjala, M. [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland); Seppaelae, E.T., E-mail: eira.seppala@nokia.co [Nokia Research Center, Itaemerenkatu 11-13, FI-00180 Helsinki (Finland); Alava, M.J., E-mail: mikko.alava@tkk.f [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland)
2011-05-15
The two-dimensional dipolar Ising model is investigated for the relaxation and dynamics of minor magnetization loops. Monte Carlo simulations show that in a stripe phase an exponential decrease can be found for the magnetization maxima of the loops, M{approx}exp(-{alpha}N{sub l}) where N{sub l} is the number of loops. We discuss the limits of this behavior and its relation to the equilibrium phase diagram of the model.
Cryptography Using Multiple Two-Dimensional Chaotic Maps
Directory of Open Access Journals (Sweden)
Ibrahim S. I. Abuhaiba
2012-08-01
Full Text Available In this paper, a symmetric key block cipher cryptosystem is proposed, involving multiple two-dimensional chaotic maps and using 128-bits external secret key. Computer simulations indicate that the cipher has good diffusion and confusion properties with respect to the plaintext and the key. Moreover, it produces ciphertext with random distribution. The computation time is much less than previous related works. Theoretic analysis verifies its superiority to previous cryptosystems against different types of attacks.
A UNIVERSAL VARIATIONAL FORMULATION FOR TWO DIMENSIONAL FLUID MECHANICS
Institute of Scientific and Technical Information of China (English)
何吉欢
2001-01-01
A universal variational formulation for two dimensional fluid mechanics is obtained, which is subject to the so-called parameter-constrained equations (the relationship between parameters in two governing equations). By eliminating the constraints, the generalized variational principle (GVPs) can be readily derived from the formulation. The formulation can be applied to any conditions in case the governing equations can be converted into conservative forms. Some illustrative examples are given to testify the effectiveness and simplicity of the method.
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.
Extraction of plant proteins for two-dimensional electrophoresis
Granier, Fabienne
1988-01-01
Three different extraction procedures for two-dimensional electrophoresis of plant proteins are compared: (i) extraction of soluble proteins with a nondenaturing Tris-buffer, (ii) denaturing extraction in presence of sodium dodecyl sulfate at elevated temperature allowing the solubilization of membrane proteins in addition to a recovery of soluble proteins, and (iii) a trichloroacetic acid-acetone procedure allowing the direct precipitation of total proteins.
Lyapunov Computational Method for Two-Dimensional Boussinesq Equation
Mabrouk, Anouar Ben
2010-01-01
A numerical method is developed leading to Lyapunov operators to approximate the solution of two-dimensional Boussinesq equation. It consists of an order reduction method and a finite difference discretization. It is proved to be uniquely solvable and analyzed for local truncation error for consistency. The stability is checked by using Lyapunov criterion and the convergence is studied. Some numerical implementations are provided at the end of the paper to validate the theoretical results.
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.
Two-dimensional hydrogen negative ion in a magnetic field
Institute of Scientific and Technical Information of China (English)
Xie Wen-Fang
2004-01-01
Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of a two-dimensional hydrogen negative ion H- in a magnetic field. The results show that the ground and low-excited states of H- in low-dimensional space are more stable than those in three-dimensional space and there may exist more bound states.
А heuristic algorithm for two-dimensional strip packing problem
Dayong, Cao; Kotov, V.M.
2011-01-01
In this paper, we construct an improved best-fit heuristic algorithm for two-dimensional rectangular strip packing problem (2D-RSPP), and compare it with some heuristic and metaheuristic algorithms from literatures. The experimental results show that BFBCC could produce satisfied packing layouts than these methods, especially for the large problem of 50 items or more, BFBCC could get better results in shorter time.
Chronology Protection in Two-Dimensional Dilaton Gravity
Mishima, T; Mishima, Takashi; Nakamichi, Akika
1994-01-01
The global structure of 1 + 1 dimensional compact Universe is studied in two-dimensional model of dilaton gravity. First we give a classical solution corresponding to the spacetime in which a closed time-like curve appears, and show the instability of this spacetime due to the existence of matters. We also observe quantum version of such a spacetime having closed timelike curves never reappear unless the parameters are fine-tuned.
Phase Transitions in Two-Dimensional Traffic Flow Models
Cuesta, J A; Molera, J M; Cuesta, José A; Martinez, Froilán C; Molera, Juan M
1993-01-01
Abstract: We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.
Phase Transitions in Two-Dimensional Traffic Flow Models
Cuesta, José A; Molera, Juan M; Escuela, Angel Sánchez; 10.1103/PhysRevE.48.R4175
2009-01-01
We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.
SU(1,2) invariance in two-dimensional oscillator
Krivonos, Sergey
2016-01-01
Performing the Hamiltonian analysis we explicitly established the canonical equivalence of the deformed oscillator, constructed in arXiv:1607.03756[hep-th], with the ordinary one. As an immediate consequence, we proved that the SU(1,2) symmetry is the dynamical symmetry of the ordinary two-dimensional oscillator. The characteristic feature of this SU(1,2) symmetry is a non-polynomial structure of its generators written it terms of the oscillator variables.
Multiple Potts Models Coupled to Two-Dimensional Quantum Gravity
Baillie, C F
1992-01-01
We perform Monte Carlo simulations using the Wolff cluster algorithm of {\\it multiple} $q=2,3,4$ state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the $c>1$ region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for $c>1$. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for $c>1$.
Multiple Potts models coupled to two-dimensional quantum gravity
Baillie, C. F.; Johnston, D. A.
1992-07-01
We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.
Colloidal interactions in two-dimensional nematic emulsions
Indian Academy of Sciences (India)
N M Silvestre; P Patrício; M M Telo Da Gama
2005-06-01
We review theoretical and experimental work on colloidal interactions in two-dimensional (2D) nematic emulsions. We pay particular attention to the effects of (i) the nematic elastic constants, (ii) the size of the colloids, and (iii) the boundary conditions at the particles and the container. We consider the interactions between colloids and fluid (deformable) interfaces and the shape of fluid colloids in smectic-C films.
Numerical Study of Two-Dimensional Viscous Flow over Dams
Institute of Scientific and Technical Information of China (English)
王利兵; 刘宇陆; 涂敏杰
2003-01-01
In this paper, the characteristics of two-dimensional viscous flow over two dams were numerically investigated. The results show that the behavior of the vortices is closely related to the space between two dams, water depth, Fr number and Reynolds number. In addition, the flow properties behind each dam are different, and the changes over two dams are more complex than over one dam. Finally, the relevant turbulent characteristics were analyzed.
Spirals and Skyrmions in two dimensional oxide heterostructures.
Li, Xiaopeng; Liu, W Vincent; Balents, Leon
2014-02-14
We construct the general free energy governing long-wavelength magnetism in two dimensional oxide heterostructures, which applies irrespective of the microscopic mechanism for magnetism. This leads, in the relevant regime of weak but non-negligible spin-orbit coupling, to a rich phase diagram containing in-plane ferromagnetic, spiral, cone, and Skyrmion lattice phases, as well as a nematic state stabilized by thermal fluctuations.
Acoustic Bloch oscillations in a two-dimensional phononic crystal.
He, Zhaojian; Peng, Shasha; Cai, Feiyan; Ke, Manzhu; Liu, Zhengyou
2007-11-01
We report the observation of acoustic Bloch oscillations at megahertz frequency in a two-dimensional phononic crystal. By creating periodically arrayed cavities with a decreasing gradient in width along one direction in the phononic crystal, acoustic Wannier-Stark ladders are created in the frequency domain. The oscillatory motion of an incident Gaussian pulse inside the sample is demonstrated by both simulation and experiment.
Exact analytic flux distributions for two-dimensional solar concentrators.
Fraidenraich, Naum; Henrique de Oliveira Pedrosa Filho, Manoel; Vilela, Olga C; Gordon, Jeffrey M
2013-07-01
A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the method's versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers.
Tricritical behavior in a two-dimensional field theory
Hamber, Herbert
1980-05-01
The critical behavior of a two-dimensional scalar Euclidean field theory with a potential term that allows for three minima is analyzed using an approximate position-space renormalization-group transformation on the equivalent quantum spin Hamiltonian. The global phase diagram shows a tricritical point separating a critical line from a line of first-order transitions. Other critical properties are examined, and good agreement is found with results on classical spin models belonging to the same universality class.
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.
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.
Two-dimensional correlation spectroscopy in polymer study
Park, Yeonju; Noda, Isao; Jung, Young Mee
2015-01-01
This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted. PMID:25815286
Interior design of a two-dimensional semiclassic black hole
Levanony, Dana; 10.1103/PhysRevD.80.084008
2009-01-01
We look into the inner structure of a two-dimensional dilatonic evaporating black hole. We establish and employ the homogenous approximation for the black-hole interior. The field equations admit two types of singularities, and their local asymptotic structure is investigated. One of these singularities is found to develop, as a spacelike singularity, inside the black hole. We then study the internal structure of the evaporating black hole from the horizon to the singularity.
Towards a two dimensional model of surface piezoelectricity
Monge Víllora, Oscar
2016-01-01
We want to understand the behaviour of flexoelectricity and surface piezoelectricity and distinguish them in order to go deep into the controversies of the filed. This motivate the construction of a model of continuum flexoelectric theory. The model proposed is a two-dimensional model that integrates the electromechanical equations that include the elastic, dielectric, piezoelectric and flexoelectric effect on a rectangular sample. As the flexoelectric and the surface piezoelectric effects ap...
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...
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.
Static Structure of Two-Dimensional Granular Chain
Institute of Scientific and Technical Information of China (English)
WEN Ping-Ping; LI Liang-Sheng; ZHENG Ning; SHI Qing-Fan
2010-01-01
@@ Static packing structures of two-dimensional granular chains are investigated experimentally.It is shown that the packing density approximates the saturation with the exponential law as the length of chain increases.The packing structures are globally disordered,while the local square crystallization is found by using the radial distribution function.This characteristic phase of chain packing is similar to a liquid crystal state,and has properties between a conventional liquid and solid crystal.
THE DEGENERACY PROBLEM OF TWO-DIMENSIONAL LINEAR RECURRING ARRAYS
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The degeneracy degree and degeneracy position sets of a wo-dimensional linear recurrence relation set are characterized. The fact that a linear recurring array is essentially a doubly periodic array is shown. By using the Grbner base theory, a calculation formula for degeneracy degree is given and the existence of a special degeneracy position set is proved. In the present paper, the degeneracy problem of the two-dimensional linear recurring arrays is completely solved.
Two-Dimensional Identification of Fetal Tooth Germs.
Seabra, Mariana; Vaz, Paula; Valente, Francisco; Braga, Ana; Felino, António
2017-03-01
To demonstrate the efficiency and applicability of two-dimensional ultrasonography in the identification of tooth germs and in the assessment of potential pathology. Observational, descriptive, cross-sectional study. Prenatal Diagnosis Unit of Centro Hospitalar de Vila Nova de Gaia / Espinho-Empresa Pública in Portugal. A total of 157 white pregnant women (median age, 32 years; range, 14 to 47 years) undergoing routine ultrasound exams. Description of the fetal tooth germs, as visualized by two-dimensional ultrasonography, including results from prior fetal biometry and detailed screening for malformations. In the first trimester group, ultrasonography identified 10 tooth germs in the maxilla and 10 tooth germs in the mandible in all fetuses except for one who presented eight maxillary tooth germs. This case was associated with a chromosomal abnormality (trisomy 13) with a bilateral cleft palate. In the second and third trimesters group, ultrasonography identified a larger range of tooth germs: 81.2% of fetuses showed 10 tooth germs in the maxilla and 85.0% of fetuses had 10 tooth germs in the mandible. Hypodontia was more prevalent in the maxilla than in the mandible, which led us to use qualitative two-dimensional ultrasonography to analyze the possible association between hypodontia and other variables such as fetal pathology, markers, head, nuchal, face, and spine. We recommend using this method as the first exam to evaluate fetal morphology and also to help establish accurate diagnosis of abnormalities in pregnancy.
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.
a First Cryptosystem for Security of Two-Dimensional Data
Mishra, D. C.; Sharma, Himani; Sharma, R. K.; Kumar, Naveen
In this paper, we present a novel technique for security of two-dimensional data with the help of cryptography and steganography. The presented approach provides multilayered security of two-dimensional data. First layer security was developed by cryptography and second layer by steganography. The advantage of steganography is that the intended secret message does not attract attention to itself as an object of scrutiny. This paper proposes a novel approach for encryption and decryption of information in the form of Word Data (.doc file), PDF document (.pdf file), Text document, Gray-scale images, and RGB images, etc. by using Vigenere Cipher (VC) associated with Discrete Fourier Transform (DFT) and then hiding the data behind the RGB image (i.e. steganography). Earlier developed techniques provide security of either PDF data, doc data, text data or image data, but not for all types of two-dimensional data and existing techniques used either cryptography or steganography for security. But proposed approach is suitable for all types of data and designed for security of information by cryptography and steganography. The experimental results for Word Data, PDF document, Text document, Gray-scale images and RGB images support the robustness and appropriateness for secure transmission of these data. The security analysis shows that the presented technique is immune from cryptanalytic. This technique further provides security while decryption as a check on behind which RGB color the information is hidden.
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.
A Two-dimensional Magnetohydrodynamics Scheme for General Unstructured Grids
Livne, Eli; Dessart, Luc; Burrows, Adam; Meakin, Casey A.
2007-05-01
We report a new finite-difference scheme for two-dimensional magnetohydrodynamics (MHD) simulations, with and without rotation, in unstructured grids with quadrilateral cells. The new scheme is implemented within the code VULCAN/2D, which already includes radiation hydrodynamics in various approximations and can be used with arbitrarily moving meshes (ALEs). The MHD scheme, which consists of cell-centered magnetic field variables, preserves the nodal finite difference representation of divB by construction, and therefore any initially divergence-free field remains divergence-free through the simulation. In this paper, we describe the new scheme in detail and present comparisons of VULCAN/2D results with those of the code ZEUS/2D for several one-dimensional and two-dimensional test problems. The code now enables two-dimensional simulations of the collapse and explosion of the rotating, magnetic cores of massive stars. Moreover, it can be used to simulate the very wide variety of astrophysical problems for which multidimensional radiation magnetohydrodynamics (RMHD) is relevant.
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.
A two-dimensional analytical model of petroleum vapor intrusion
Yao, Yijun; Verginelli, Iason; Suuberg, Eric M.
2016-02-01
In this study we present an analytical solution of a two-dimensional petroleum vapor intrusion model, which incorporates a steady-state diffusion-dominated vapor transport in a homogeneous soil and piecewise first-order aerobic biodegradation limited by oxygen availability. This new model can help practitioners to easily generate two-dimensional soil gas concentration profiles for both hydrocarbons and oxygen and estimate hydrocarbon indoor air concentrations as a function of site-specific conditions such as source strength and depth, reaction rate constant, soil characteristics and building features. The soil gas concentration profiles generated by this new model are shown in good agreement with three-dimensional numerical simulations and two-dimensional measured soil gas data from a field study. This implies that for cases involving diffusion dominated soil gas transport, steady state conditions and homogenous source and soil, this analytical model can be used as a fast and easy-to-use risk screening tool by replicating the results of 3-D numerical simulations but with much less computational effort.
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.
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.
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.
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.
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
Two-dimensional Green`s function Poisson solution appropriate for cylindrical-symmetry simulations
Energy Technology Data Exchange (ETDEWEB)
Riley, M.E.
1998-04-01
This report describes the numerical procedure used to implement the Green`s function method for solving the Poisson equation in two-dimensional (r,z) cylindrical coordinates. The procedure can determine the solution to a problem with any or all of the applied voltage boundary conditions, dielectric media, floating (insulated) conducting media, dielectric surface charging, and volumetric space charge. The numerical solution is reasonably fast, and the dimension of the linear problem to be solved is that of the number of elements needed to represent the surfaces, not the whole computational volume. The method of solution is useful in the simulation of plasma particle motion in the vicinity of complex surface structures as found in microelectronics plasma processing applications. This report is a stand-alone supplement to the previous Sandia Technical Report SAND98-0537 presenting the two-dimensional Cartesian Poisson solver.
Clausius-Mossotti Lorentz-Lorenz relations and retardation effects for two-dimensional crystals
Dell'Anna, Luca
2016-01-01
The macroscopic surface electric susceptibility determines the linear optical properties of an insulating single-layer two-dimensional atomic crystal, and can be expressed in terms of the microscopic polarizability of the atoms. We compute the local electric field acting on a single atom, both for the static and the dynamic case, as the superposition of the external applied electric field and the fields generated by the induced dipoles in the crystal. We find that, in the dynamic case, retardation effects dephase the local electric field with respect to the incident one. This explains why the Fresnel coefficients of a single-layer two-dimensional atomic crystal are intrinsically complex quantities, even when a null macroscopic surface conductivity is assumed.
Electrical transport across metal/two-dimensional carbon junctions: Edge versus side contacts
Directory of Open Access Journals (Sweden)
Yihong Wu
2012-03-01
Full Text Available Metal/two-dimensional carbon junctions are characterized by using a nanoprobe in an ultrahigh vacuum environment. Significant differences were found in bias voltage (V dependence of differential conductance (dI/dV between edge- and side-contact; the former exhibits a clear linear relationship (i.e., dI/dV ∝ V, whereas the latter is characterized by a nonlinear dependence, dI/dV ∝ V3/2. Theoretical calculations confirm the experimental results, which are due to the robust two-dimensional nature of the carbon materials under study. Our work demonstrates the importance of contact geometry in graphene-based electronic devices.
Freely configurable quantum simulator based on a two-dimensional array of individually trapped ions
Mielenz, Manuel; Wittemer, Matthias; Hakelberg, Frederick; Schmied, Roman; Blain, Matthew; Maunz, Peter; Leibfried, Dietrich; Warring, Ulrich; Schaetz, Tobias
2015-01-01
A custom-built and precisely controlled quantum system may offer access to a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analog quantum simulator that makes the relevant observables, interactions, and states of a quantum model accessible could permit experimental insight into complex quantum dynamics that are intractable on conventional computers. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here we characterise two-dimensional arrays of three ions trapped by radio-frequency fields in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 micrometer. In our approach, which is scalable to arbitrary two dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as tuning of crucial couplings be...
Institute of Scientific and Technical Information of China (English)
XU Quan; TIAN Qiang
2009-01-01
We restrict our attention to the discrete two-dimensional monatomic β-FPU lattice. We look for twodimensional breather lattice solutions and two-dimensional compact-like discrete breathers by using trying method and analyze their stability by using Aubry's linearly stable theory. We obtain the conditions of existence and stability of two-dimensional breather lattice solutions and two-dimensional compact-like discrete breathers in the discrete twodimensional monatomic β-FPU lattice.
Shevyrin, A. A.; Pogosov, A. G.; Bakarov, A. K.; Shklyaev, A. A.
2016-07-01
The electrical response of a two-dimensional electron gas to vibrations of a nanomechanical cantilever containing it is studied. Vibrations of perpendicularly oriented cantilevers are experimentally shown to oppositely change the conductivity near their bases. This indicates the piezoelectric nature of electromechanical coupling. A physical model is developed, which quantitatively explains the experiment. It shows that the main origin of the conductivity change is a rapid change in the mechanical stress on the boundary between suspended and nonsuspended areas, rather than the stress itself.
Numerical analysis of biological clogging in two-dimensional sand box experiments
DEFF Research Database (Denmark)
Kildsgaard, J.; Engesgaard, Peter Knudegaard
2001-01-01
Two-dimensional models for biological clogging and sorptive tracer transport were used to study the progress of clogging in a sand box experiment. The sand box had been inoculated with a strip of bacteria and exposed to a continuous injection of nitrate and acetate. Brilliant Blue was regularly...... with the assumed linear constant Kd behaviour. It is demonstrated that the dimensionality of sand box experiments in comparison to column experiments results in a much lower reduction in hydraulic conductivity Žfactor of 100. and that the bulk hydraulic conductivity of the sand box decreased only slightly. However...
Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet
Lima, L. S.
2017-01-01
We use the Self Consistent Harmonic Approximation together with the Kubo formalism of the Linear Response Theory to study the spin transport in the two-dimensional frustrated Heisenberg antiferromagnet in a square lattice with easy-plane ion single anisotropy. The regular part of the spin conductivity σreg(ω) is determined for several values of the critical ion single parameter Dc, that separates the low D region from the large D quantum paramagnetic phase. We have obtained an abrupt change in the spin conductivity in the discontinuity points of the graphic Dc vs. η, where the system presents a quantum phase transition.
Return probability and recurrence for the random walk driven by two-dimensional Gaussian free field
Biskup, Marek; Ding, Jian; Goswami, Subhajit
2016-01-01
Given any $\\gamma>0$ and for $\\eta=\\{\\eta_v\\}_{v\\in \\mathbb Z^2}$ denoting a sample of the two-dimensional discrete Gaussian free field on $\\mathbb Z^2$ pinned at the origin, we consider the random walk on $\\mathbb Z^2$ among random conductances where the conductance of edge $(u, v)$ is given by $\\mathrm{e}^{\\gamma(\\eta_u + \\eta_v)}$. We show that, for almost every $\\eta$, this random walk is recurrent and that, with probability tending to 1 as $T\\to \\infty$, the return probability at time $2...
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 ...
Two-dimensional Tissue Image Reconstruction Based on Magnetic Field Data
Directory of Open Access Journals (Sweden)
J. Dedkova
2012-09-01
Full Text Available This paper introduces new possibilities within two-dimensional reconstruction of internal conductivity distribution. In addition to the electric field inside the given object, the injected current causes a magnetic field which can be measured either outside the object by means of a Hall probe or inside the object through magnetic resonance imaging. The Magnetic Resonance method, together with Electrical impedance tomography (MREIT, is well known as a bio-imaging modality providing cross-sectional conductivity images with a good spatial resolution from the measurements of internal magnetic flux density produced by externally injected currents. A new algorithm for the conductivity reconstruction, which utilizes the internal current information with respect to corresponding boundary conditions and the external magnetic field, was developed. A series of computer simulations has been conducted to assess the performance of the proposed algorithm within the process of estimating electrical conductivity changes in the lungs, heart, and brain tissues captured in two-dimensional piecewise homogeneous chest and head models. The reconstructed conductivity distribution using the proposed method is compared with that using a conventional method based on Electrical Impedance Tomography (EIT. The acquired experience is discussed and the direction of further research is proposed.
Identifying the Flow Physics and Modeling Transient Forces on Two-Dimensional Wings
2016-09-02
becomes smaller relative to the random component of the error (indicated by the size of the confidence ellipse). This means that the modifications to...understanding the dynamics of these unsteady flows, and uses state-of-the-art techniques, both for measuring these phenomena in experiments (using an...art techniques, both for measuring these phenomena in experiments (using an unsteady wind tunnel at IIT), and for analyzing the data and developing
The characters of nonlinear vibration in the two-dimensional discrete monoatomic lattice
Institute of Scientific and Technical Information of China (English)
XU Quan; TIAN Qiang
2005-01-01
The two-dimensional discrete monoatomic lattice is analyzed. Taking nearest-neighbor interaction into account, the characters of the nonlinear vibration in two-dimensional discrete monoatomic lattice are described by the two-dimensional cubic nonlinear Schrodinger equation. Considering the quartic nonlinear potential, the two-dimensional discrete-soliton trains and the solutions perturbed by the neck mode are presented.