QUENCH2D. Two-Dimensional IHCP Code
Osman, A.; Beck, J.V.
1995-01-01
QUENCH2D* is developed for the solution of general, non-linear, two-dimensional inverse heat transfer problems. This program provides estimates for the surface heat flux distribution and/or heat transfer coefficient as a function of time and space by using transient temperature measurements at appropriate interior points inside the quenched body. Two-dimensional planar and axisymmetric geometries such as turnbine disks and blades, clutch packs, and many other problems can be analyzed using QUENCH2D*.
CBEAM. 2-D: a two-dimensional beam field code
Dreyer, K.A.
1985-05-01
CBEAM.2-D is a two-dimensional solution of Maxwell's equations for the case of an electron beam propagating through an air medium. Solutions are performed in the beam-retarded time frame. Conductivity is calculated self-consistently with field equations, allowing sophisticated dependence of plasma parameters to be handled. A unique feature of the code is that it is implemented on an IBM PC microcomputer in the BASIC language. Consequently, it should be available to a wide audience.
Dragging two-dimensional discrete solitons by moving linear defects
Brazhnyi, Valeriy A.; Malomed, Boris A.
2011-07-15
We study the mobility of small-amplitude solitons attached to moving defects which drag the solitons across a two-dimensional (2D) discrete nonlinear Schroedinger lattice. Findings are compared to the situation when a free small-amplitude 2D discrete soliton is kicked in a uniform lattice. In agreement with previously known results, after a period of transient motion the free soliton transforms into a localized mode pinned by the Peierls-Nabarro potential, irrespective of the initial velocity. However, the soliton attached to the moving defect can be dragged over an indefinitely long distance (including routes with abrupt turns and circular trajectories) virtually without losses, provided that the dragging velocity is smaller than a certain critical value. Collisions between solitons dragged by two defects in opposite directions are studied too. If the velocity is small enough, the collision leads to a spontaneous symmetry breaking, featuring fusion of two solitons into a single one, which remains attached to either of the two defects.
Magnus force in discrete and continuous two-dimensional superfluids
Gecse, Z.; Khlebnikov, S.
2005-08-01
Motion of vortices in two-dimensional superfluids in the classical limit is studied by solving the Gross-Pitaevskii equation numerically on a uniform lattice. We find that, in the presence of a superflow directed along one of the main lattice periods, vortices move with the superflow on fine lattices but perpendicular to it on coarse ones. We interpret this result as a transition from the full Magnus force in a Galilean-invariant limit to vanishing effective Magnus force in a discrete system, in agreement with the existing experiments on vortex motion in Josephson junction arrays.
Atoms dictating shape: The discrete geometry of conformal two-dimensional materials
NASA Astrophysics Data System (ADS)
Mehboudi, Mehrshad; Utt, Kainen; Terrones, Humberto; Pacheco, Alejandro; Harriss, Edmund; Barraza-Lopeez, Salvador
2015-03-01
The electronic, optical, thermal, mechanical and chemical behavior of two-dimensional (2D) materials depends on their shape (geometry). 2D materials are nets, with covalent bonds representing edges, and where atoms are vertices. Here we use a mathematical language to tell the shape of meshes and discuss the geometry of 2D materials of varied lattice structures, such as: hexagonal boron nitride, black phosphorus monolayers, low-buckled silicene, germanene, blue phosphorous, newly predicted III-V buckled 2D compounds such as AlP, conformal ``thicker'' layered materials such as 2D tin, ``single-layer'' transition metal dichalcogenides (MX2's), and a single-quintuple-layer of the topological insulator Bi2Se3. We characterize the geometry of each atom position without recourse to a continuum parametric model. The new framework generalizes the discrete geometry we introduced recently for graphene.
Method for coupling two-dimensional to three-dimensional discrete ordinates calculations
Thompson, J.L.; Emmett, M.B.; Rhoades, W.A.; Dodds, H.L. Jr.
1985-01-01
A three-dimensional (3-D) discrete ordinates transport code, TORT, has been developed at the Oak Ridge National Laboratory for radiation penetration studies. It is not feasible to solve some 3-D penetration problems with TORT, such as a building located a large distance from a point source, because (1) the discretized 3-D problem is simply too big to fit on the computer or (2) the computing time (and corresponding cost) is prohibitive. Fortunately, such problems can be solved with a hybrid approach by coupling a two-dimensional (2-D) description of the point source, which is assumed to be azimuthally symmetric, to a 3-D description of the building, the region of interest. The purpose of this paper is to describe this hybrid methodology along with its implementation and evaluation in the DOTTOR (Discrete Ordinates to Three-dimensional Oak Ridge Transport) code.
Two-dimensional discrete solitons in rotating lattices
Cuevas, Jesus; Kevrekidis, P. G.
2007-10-15
We introduce a two-dimensional discrete nonlinear Schroedinger (DNLS) equation with self-attractive cubic nonlinearity in a rotating reference frame. The model applies to a Bose-Einstein condensate stirred by a rotating strong optical lattice, or light propagation in a twisted bundle of nonlinear fibers. Two types of localized states are constructed: off-axis fundamental solitons (FSs), placed at distance R from the rotation pivot, and on-axis (R=0) vortex solitons (VSs), with vorticities S=1 and 2. At a fixed value of rotation frequency {omega}, a stability interval for the FSs is found in terms of the lattice coupling constant C, 0
Two-dimensional HID light source radiative transfer using discrete ordinates method
NASA Astrophysics Data System (ADS)
Ghrib, Basma; Bouaoun, Mohamed; Elloumi, Hatem
2016-08-01
This paper shows the implementation of the Discrete Ordinates Method for handling radiation problems in High Intensity Discharge (HID) lamps. Therefore, we start with presenting this rigorous method for treatment of radiation transfer in a two-dimensional, axisymmetric HID lamp. Furthermore, the finite volume method is used for the spatial discretization of the Radiative Transfer Equation. The atom and electron densities were calculated using temperature profiles established by a 2D semi-implicit finite-element scheme for the solution of conservation equations relative to energy, momentum, and mass. Spectral intensities as a function of position and direction are first calculated, and then axial and radial radiative fluxes are evaluated as well as the net emission coefficient. The results are given for a HID mercury lamp on a line-by-line basis. A particular attention is paid on the 253.7 nm resonance and 546.1 nm green lines.
F2D users manual: A two-dimensional compressible gas flow code
NASA Astrophysics Data System (ADS)
Suo-Anttila, A.
1993-08-01
The F2D computer code is a general purpose, two-dimensional, fully compressible thermal-fluids code that models most of the phenomena found in situations of coupled fluid flow and heat transfer. The code solves momentum, continuity, gas-energy, and structure-energy equations using a predictor-corrector solution algorithm. The corrector step includes a Poisson pressure equation. The finite difference form of the equation is presented along with a description of input and output. Several example problems are included that demonstrate the applicability of the code in problems ranging from free fluid flow, shock tubes, and flow in heated porous media.
F2D. A Two-Dimensional Compressible Gas Flow Code
Suo-Anttila, A.
1993-08-01
F2D is a general purpose, two dimensional, fully compressible thermal-fluids code that models most of the phenomena found in situations of coupled fluid flow and heat transfer. The code solves momentum, continuity, gas-energy, and structure-energy equations using a predictor-correction solution algorithm. The corrector step includes a Poisson pressure equation. The finite difference form of the equation is presented along with a description of input and output. Several example problems are included that demonstrate the applicability of the code in problems ranging from free fluid flow, shock tubes and flow in heated porous media.
F2D users manual: A two-dimensional compressible gas flow code
Suo-Anttila, A.
1993-08-01
The F2D computer code is a general purpose, two-dimensional, fully compressible thermal-fluids code that models most of the phenomena found in situations of coupled fluid flow and heat transfer. The code solves momentum, continuity, gas-energy, and structure-energy equations using a predictor-corrector solution algorithm. The corrector step includes a Poisson pressure equation. The finite difference form of the equation is presented along with a description of input and output. Several example problems are included that demonstrate the applicability of the code in problems ranging from free fluid flow, shock tubes and flow in heated porous media.
Two-dimensional (2D) correlation coefficient analyses of heavily overlapped near-infrared spectra.
Sasić, Slobodan; Sato, Harumi; Shimoyama, Masahiko; Ozaki, Yukihiro
2005-05-01
Two-dimensional (2D) correlation coefficient analysis is employed to classify and characterize spectral variations among heavily overlapped near-infrared spectra of pellets and films of three kinds of polyethylene (PE), high-density (HD), low density (LD), and linear low-density (LLD) polyethylene, and five kinds of ivory signature seals. The sample-sample (SS) 2D correlation maps are used for classification while the wavenumber-wavenumber (WW) 2D correlation maps are used for determining spectral variation among the above materials. Both correlation maps are obtained by multiplying the original data with themselves. It is found that the NIR spectra of pellets and films of HD PE are clearly different from those of LD PE and LLD PE, while the NIR spectra of five kinds of ivory seals yield easily discernable squares in the SS correlation maps. The background variation is thought to be behind the differentiation of the PE samples because the WW correlation maps do not indicate appearance of new bands. The correlation results are compared with those of principal component analysis (PCA). This study is a novel application of 2D correlation coefficient analysis which reveals that a comprehensive description of demanding spectral systems is achievable by utterly simple mathematical means because 2D correlation maps are obtained via a single mathematical operation.
Two-dimensional potential double layers and discrete auroras
NASA Technical Reports Server (NTRS)
Kan, J. R.; Lee, L. C.; Akasofu, S.-I.
1979-01-01
This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.
BILL2D - A software package for classical two-dimensional Hamiltonian systems
NASA Astrophysics Data System (ADS)
Solanpää, J.; Luukko, P. J. J.; Räsänen, E.
2016-02-01
We present BILL2D, a modern and efficient C++ package for classical simulations of two-dimensional Hamiltonian systems. BILL2D can be used for various billiard and diffusion problems with one or more charged particles with interactions, different external potentials, an external magnetic field, periodic and open boundaries, etc. The software package can also calculate many key quantities in complex systems such as Poincaré sections, survival probabilities, and diffusion coefficients. While aiming at a large class of applicable systems, the code also strives for ease-of-use, efficiency, and modularity for the implementation of additional features. The package comes along with a user guide, a developer's manual, and a documentation of the application program interface (API).
Hallquist, J.O.
1982-02-01
This revised report provides an updated user's manual for DYNA2D, an explicit two-dimensional axisymmetric and plane strain finite element code for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. A contact-impact algorithm permits gaps and sliding along material interfaces. By a specialization of this algorithm, such interfaces can be rigidly tied to admit variable zoning without the need of transition regions. Spatial discretization is achieved by the use of 4-node solid elements, and the equations-of motion are integrated by the central difference method. An interactive rezoner eliminates the need to terminate the calculation when the mesh becomes too distorted. Rather, the mesh can be rezoned and the calculation continued. The command structure for the rezoner is described and illustrated by an example.
MULTI2D - a computer code for two-dimensional radiation hydrodynamics
NASA Astrophysics Data System (ADS)
Ramis, R.; Meyer-ter-Vehn, J.; Ramírez, J.
2009-06-01
Simulation of radiation hydrodynamics in two spatial dimensions is developed, having in mind, in particular, target design for indirectly driven inertial confinement energy (IFE) and the interpretation of related experiments. Intense radiation pulses by laser or particle beams heat high-Z target configurations of different geometries and lead to a regime which is optically thick in some regions and optically thin in others. A diffusion description is inadequate in this situation. A new numerical code has been developed which describes hydrodynamics in two spatial dimensions (cylindrical R-Z geometry) and radiation transport along rays in three dimensions with the 4 π solid angle discretized in direction. Matter moves on a non-structured mesh composed of trilateral and quadrilateral elements. Radiation flux of a given direction enters on two (one) sides of a triangle and leaves on the opposite side(s) in proportion to the viewing angles depending on the geometry. This scheme allows to propagate sharply edged beams without ray tracing, though at the price of some lateral diffusion. The algorithm treats correctly both the optically thin and optically thick regimes. A symmetric semi-implicit (SSI) method is used to guarantee numerical stability. Program summaryProgram title: MULTI2D Catalogue identifier: AECV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 151 098 No. of bytes in distributed program, including test data, etc.: 889 622 Distribution format: tar.gz Programming language: C Computer: PC (32 bits architecture) Operating system: Linux/Unix RAM: 2 Mbytes Word size: 32 bits Classification: 19.7 External routines: X-window standard library (libX11.so) and corresponding heading files (X11/*.h) are
Two dimensional spectroscopy of Liquids in THz-domain: THz analogue of 2D Raman spectroscopy
NASA Astrophysics Data System (ADS)
Okumura, K.; Tanimura, Y.
1998-03-01
After the initial proposal(Y. Tanimura and S. Mukamel, J. Chem. Phys. 99, 9496 (1993)), the two dimensional Raman spectroscopy in the liquid phase has been received a considerable attention. Both experimental and theoretical activity of this field has been quite high. Since we have two controllable delay times, we can obtain more information than the lower-order experiments such as OKE. The new information includes that on heterogeneous distribution in liquids. Recently, it is found that the coupling between the modes in liquids can be investigated by the technique, both experimentally and theoretically(A. Tokmakoff, M.J. Lang, D.S. Larsen, G.R. Fleming, V. Chernyak, and S. Mukamel, Phys. Rev. Lett. (in press))^,(K. Okumura and Y. Tanimura, Chem. Phys. Lett. 278, 175 (1997)) In this talk, we will emphasize that we can perform the THz analogue of the 2D Raman spectroscopy if the THz short-pulse laser becomes available, which may not be in the far future. Theoretically, we can formulate this novel THz spectroscopy on the same footing as the 2D Raman spectroscopy. We will clarify new aspects of this technique comparing with the 2D Raman spectroscopy--- the reason it worth trying the tough experiment. See
Removal of interfering substances in samples prepared for two-dimensional (2-D) electrophoresis.
Berkelman, Tom
2008-01-01
Biological samples may contain contaminants that interfere with analysis by two-dimensional (2-D) electrophoresis. Lysates or biological fluids are complex mixtures that contain a wide variety of nonprotein substances in addition to the proteins to be analyzed. These substances often interfere with the resolution of the electrophoretic separation or the visualization of the result. Macromolecules (e.g., polysaccharides and DNA) can interfere with electrophoretic separation by clogging gel pores. Small ionic molecules can impair isoelectric focusing (IEF) separation by rendering the sample too conductive. Other substances (e.g., phenolics and lipids) can bind to proteins, influencing their electrophoretic properties or solubility. In many cases, measures to remove interfering substances can result in significantly clearer 2-D patterns with more visible spots and better resolution. It should be borne in mind, however, that analysis of samples by 2-D electrophoresis is usually most successful and informative when performed with minimally processed samples, so it is important that any steps taken to remove interfering substance be appropriate to the sample and only performed when necessary. Procedures for the removal of interfering substances therefore represent a compromise between removing nonprotein contaminants, and minimizing interference with the integrity and relative abundances of the sample proteins. This chapter presents a number of illustrative examples of optimized sample preparation methods in which specific interfering substances are removed by a variety of different strategies.
Computer program BL2D for solving two-dimensional and axisymmetric boundary layers
NASA Technical Reports Server (NTRS)
Iyer, Venkit
1995-01-01
This report presents the formulation, validation, and user's manual for the computer program BL2D. The program is a fourth-order-accurate solution scheme for solving two-dimensional or axisymmetric boundary layers in speed regimes that range from low subsonic to hypersonic Mach numbers. A basic implementation of the transition zone and turbulence modeling is also included. The code is a result of many improvements made to the program VGBLP, which is described in NASA TM-83207 (February 1982), and can effectively supersede it. The code BL2D is designed to be modular, user-friendly, and portable to any machine with a standard fortran77 compiler. The report contains the new formulation adopted and the details of its implementation. Five validation cases are presented. A detailed user's manual with the input format description and instructions for running the code is included. Adequate information is presented in the report to enable the user to modify or customize the code for specific applications.
Computer program BL2D for solving two-dimensional and axisymmetric boundary layers
NASA Astrophysics Data System (ADS)
Iyer, Venkit
1995-05-01
This report presents the formulation, validation, and user's manual for the computer program BL2D. The program is a fourth-order-accurate solution scheme for solving two-dimensional or axisymmetric boundary layers in speed regimes that range from low subsonic to hypersonic Mach numbers. A basic implementation of the transition zone and turbulence modeling is also included. The code is a result of many improvements made to the program VGBLP, which is described in NASA TM-83207 (February 1982), and can effectively supersede it. The code BL2D is designed to be modular, user-friendly, and portable to any machine with a standard fortran77 compiler. The report contains the new formulation adopted and the details of its implementation. Five validation cases are presented. A detailed user's manual with the input format description and instructions for running the code is included. Adequate information is presented in the report to enable the user to modify or customize the code for specific applications.
Dipolar matter-wave solitons in two-dimensional anisotropic discrete lattices
NASA Astrophysics Data System (ADS)
Chen, Huaiyu; Liu, Yan; Zhang, Qiang; Shi, Yuhan; Pang, Wei; Li, Yongyao
2016-05-01
We numerically demonstrate two-dimensional (2D) matter-wave solitons in the disk-shaped dipolar Bose-Einstein condensates (BECs) trapped in strongly anisotropic optical lattices (OLs) in a disk's plane. The considered OLs are square lattices which can be formed by interfering two pairs of plane waves with different intensities. The hopping rates of the condensates between two adjacent lattices in the orthogonal directions are different, which gives rise to a linearly anisotropic system. We find that when the polarized orientation of the dipoles is parallel to disk's plane with the same direction, the combined effects of the linearly anisotropy and the nonlocal nonlinear anisotropy strongly influence the formations, as well as the dynamics of the lattice solitons. Particularly, the isotropy-pattern solitons (IPSs) are found when these combined effects reach a balance. Motion, collision, and rotation of the IPSs are also studied in detail by means of systematic simulations. We further find that these IPSs can move freely in the 2D anisotropic discrete system, hence giving rise to an anisotropic effective mass. Four types of collisions between the IPSs are identified. By rotating an external magnetic field up to a critical angular velocity, the IPSs can still remain localized and play as a breather. Finally, the influences from the combined effects between the linear and the nonlocal nonlinear anisotropy with consideration of the contact and/or local nonlinearity are discussed too.
A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds
Li, Tingwen; Zhang, Yongmin
2013-10-11
Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.
A Study of Two Dimensional Electron Gas Using 2D Fourier Transform Spectroscopy
NASA Astrophysics Data System (ADS)
McIntyre, Carl; Paul, Jagannath; Karaiskaj, Denis
2015-03-01
The dephasing of FES was measured in a symmetrically modulation doped 12 nm single quantum well GaAs/AlGaAs two dimensional electron gas system using time integrated four wave mixing (TIFWM) and a two dimensional Fourier transform spectroscopy (2DFTS). At high in-well carrier densities of ~4 x 1011 cm-2, many body effects that are prevalent and measurable with non-linear optical spectroscopy. Effects of exciton-exciton and exciton-phonon scattering events, exciton populations, and biexciton formation are detectable at these carrier concentrations. Homogeneous linewidths obtained from 2DFT and TIFWM yield a zero Kelvin linewidth of 1.42 meV and an acoustic phonon scattering coefficient of 158 μ eV/K. These observations indicate a rapid increase in homogeneous linewidth with increased temperature. NSF REU Grant # DMR-1263066: REU Site in Applied Physics at USF.
GEO2D - Two-Dimensional Computer Model of a Ground Source Heat Pump System
James Menart
2013-06-07
This file contains a zipped file that contains many files required to run GEO2D. GEO2D is a computer code for simulating ground source heat pump (GSHP) systems in two-dimensions. GEO2D performs a detailed finite difference simulation of the heat transfer occurring within the working fluid, the tube wall, the grout, and the ground. Both horizontal and vertical wells can be simulated with this program, but it should be noted that the vertical wall is modeled as a single tube. This program also models the heat pump in conjunction with the heat transfer occurring. GEO2D simulates the heat pump and ground loop as a system. Many results are produced by GEO2D as a function of time and position, such as heat transfer rates, temperatures and heat pump performance. On top of this information from an economic comparison between the geothermal system simulated and a comparable air heat pump systems or a comparable gas, oil or propane heating systems with a vapor compression air conditioner. The version of GEO2D in the attached file has been coupled to the DOE heating and cooling load software called ENERGYPLUS. This is a great convenience for the user because heating and cooling loads are an input to GEO2D. GEO2D is a user friendly program that uses a graphical user interface for inputs and outputs. These make entering data simple and they produce many plotted results that are easy to understand. In order to run GEO2D access to MATLAB is required. If this program is not available on your computer you can download the program MCRInstaller.exe, the 64 bit version, from the MATLAB website or from this geothermal depository. This is a free download which will enable you to run GEO2D..
Development of models for the two-dimensional, two-fluid code for sodium boiling NATOF-2D. [LMFBR
Zielinski, R.G.; Kazimi, M.S.
1981-09-01
Several features were incorporated into NATOF-2D, a two-dimensional, two fluid code developed at MIT for the purpose of analysis of sodium boiling transients under LMFBR conditions. They include improved interfacial mass, momentum and energy exchange rate models, and a cell-to-cell radial heat conduction mechanism which was calibrated by simulation of Westinghouse Blanket Heat Transfer Test Program Runs 544 and 545. Finally, a direct method of pressure field solution was implemented into a direct method of pressure field solution was implemented into NATOF-2D, replacing the iterative technique previously available, and resulted in substantially reduced computational costs.
Discrete vortex analysis of unsteady flow about two-dimensional cambered plates
Sarpkaya, T.
1987-10-30
The evolution of a two-dimensional, incompressible, rapidly decelerating, time-dependent viscous flow about three cambered plates with included angles of 120, 180, and 240 degrees is simulated through the use of the discrete vortex model. Vorticity is represented by a distribution of discrete vortices. Each vortex is convected in the velocity field, calculated locally using the Biot-Savart law. The roll-up of the vortex sheets, the distribution of velocity and pressure on the cambers, and the drag force are calculated at suitable time intervals for a prescribed time-dependent flow. The results are compared with those obtained experimentally. 59 figs.
FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide
NASA Technical Reports Server (NTRS)
Wawrzynek, Paul; Ingraffea, Anthony
1994-01-01
FRANC 2D (FRacture ANalysis Code, 2 Dimensions) is a menu driven, interactive finite element computer code that performs fracture mechanics analyses of 2-D structures. The code has an automatic mesh generator for triangular and quadrilateral elements. FRANC2D calculates the stress intensity factor using linear elastic fracture mechanics and evaluates crack extension using several methods that may be selected by the user. The code features a mesh refinement and adaptive mesh generation capability that is automatically developed according to the predicted crack extension direction and length. The code also has unique features that permit the analysis of layered structure with load transfer through simulated mechanical fasteners or bonded joints. The code was written for UNIX workstations with X-windows graphics and may be executed on the following computers: DEC DecStation 3000 and 5000 series, IBM RS/6000 series, Hewlitt-Packard 9000/700 series, SUN Sparc stations, and most Silicon Graphics models.
Mitri, F G
2015-09-01
The optical theorem for plane waves is recognized as one of the fundamental theorems in optical, acoustical and quantum wave scattering theory as it relates the extinction cross-section to the forward scattering complex amplitude function. Here, the optical theorem is extended and generalized in a cylindrical coordinates system for the case of 2D beams of arbitrary character as opposed to plane waves of infinite extent. The case of scalar monochromatic acoustical wavefronts is considered, and generalized analytical expressions for the extinction, absorption and scattering cross-sections are derived and extended in the framework of the scalar resonance scattering theory. The analysis reveals the presence of an interference scattering cross-section term describing the interaction between the diffracted Franz waves with the resonance elastic waves. The extended optical theorem in cylindrical coordinates is applicable to any object of arbitrary geometry in 2D located arbitrarily in the beam's path. Related investigations in optics, acoustics and quantum mechanics will benefit from this analysis in the context of wave scattering theory and other phenomena closely connected to it, such as the multiple scattering by a cloud of particles, as well as the resulting radiation force and torque.
Mitri, F G
2015-09-01
The optical theorem for plane waves is recognized as one of the fundamental theorems in optical, acoustical and quantum wave scattering theory as it relates the extinction cross-section to the forward scattering complex amplitude function. Here, the optical theorem is extended and generalized in a cylindrical coordinates system for the case of 2D beams of arbitrary character as opposed to plane waves of infinite extent. The case of scalar monochromatic acoustical wavefronts is considered, and generalized analytical expressions for the extinction, absorption and scattering cross-sections are derived and extended in the framework of the scalar resonance scattering theory. The analysis reveals the presence of an interference scattering cross-section term describing the interaction between the diffracted Franz waves with the resonance elastic waves. The extended optical theorem in cylindrical coordinates is applicable to any object of arbitrary geometry in 2D located arbitrarily in the beam's path. Related investigations in optics, acoustics and quantum mechanics will benefit from this analysis in the context of wave scattering theory and other phenomena closely connected to it, such as the multiple scattering by a cloud of particles, as well as the resulting radiation force and torque. PMID:25773968
Karavitis, G.A.
1984-01-01
The SIMSYS2D two-dimensional water-quality simulation system is a large-scale digital modeling software system used to simulate flow and transport of solutes in freshwater and estuarine environments. Due to the size, processing requirements, and complexity of the system, there is a need to easily move the system and its associated files between computer sites when required. A series of job control language (JCL) procedures was written to allow transferability between IBM and IBM-compatible computers. (USGS)
Avalanche dynamics of magnetic flux in a two-dimensional discrete superconductor
Ginzburg, S. L.; Nakin, A. V.; Savitskaya, N. E.
2006-11-15
The critical state of a two-dimensional discrete superconductor in an external magnetic field is studied. This state is found to be self-organized in the generalized sense, i.e., is a set of metastable states that transform to each other by means of avalanches. An avalanche is characterized by the penetration of a magnetic flux to the system. The sizes of the occurring avalanches, i.e., changes in the magnetic flux, exhibit the power-law distribution. It is also shown that the size of the avalanche occurring in the critical state and the external magnetic field causing its change are statistically independent quantities.
Kevrekidis, P. G.; Malomed, Boris A.; Saxena, Avadh; Bishop, A. R.; Frantzeskakis, D. J.
2015-04-07
We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anticontinuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual “extended” unstaggered bright solitons, in which all sites are excited in the AC limit, with the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being those considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (also analytically, when possible). As a result, typical scenarios of instability development are exhibited through direct simulations.
Kevrekidis, P. G.; Malomed, Boris A.; Saxena, Avadh; Bishop, A. R.; Frantzeskakis, D. J.
2015-04-07
We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anticontinuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual “extended” unstaggered bright solitons, in which all sites are excited in the AC limit, withmore » the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being those considered as 1D bright solitons in the above-mentioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (also analytically, when possible). As a result, typical scenarios of instability development are exhibited through direct simulations.« less
Two-dimensional crystal melting and D4-D2-D0 on toric Calabi-Yau singularities
NASA Astrophysics Data System (ADS)
Nishinaka, Takahiro; Yamaguchi, Satoshi; Yoshida, Yutaka
2014-05-01
We construct a two-dimensional crystal melting model which reproduces the BPS index of D2-D0 states bound to a non-compact D4-brane on an arbitrary toric CalabiYau singularity. The crystalline structure depends on the toric divisor wrapped by the D4-brane. The molten crystals are in one-to-one correspondence with the torus fixed points of the moduli space of the quiver gauge theory on D-branes. The F- and D-term constraints of the gauge theory are regarded as a generalization of the ADHM constraints on instantons. We also show in several examples that our model is consistent with the wall-crossing formula for the BPS index.
Efficient architectures for two-dimensional discrete wavelet transform using lifting scheme.
Xiong, Chengyi; Tian, Jinwen; Liu, Jian
2007-03-01
Novel architectures for 1-D and 2-D discrete wavelet transform (DWT) by using lifting schemes are presented in this paper. An embedded decimation technique is exploited to optimize the architecture for 1-D DWT, which is designed to receive an input and generate an output with the low- and high-frequency components of original data being available alternately. Based on this 1-D DWT architecture, an efficient line-based architecture for 2-D DWT is further proposed by employing parallel and pipeline techniques, which is mainly composed of two horizontal filter modules and one vertical filter module, working in parallel and pipeline fashion with 100% hardware utilization. This 2-D architecture is called fast architecture (FA) that can perform J levels of decomposition for N * N image in approximately 2N2(1 - 4(-J))/3 internal clock cycles. Moreover, another efficient generic line-based 2-D architecture is proposed by exploiting the parallelism among four subband transforms in lifting-based 2-D DWT, which can perform J levels of decomposition for N * N image in approximately N2(1 - 4(-J))/3 internal clock cycles; hence, it is called high-speed architecture. The throughput rate of the latter is increased by two times when comparing with the former 2-D architecture, but only less additional hardware cost is added. Compared with the works reported in previous literature, the proposed architectures for 2-D DWT are efficient alternatives in tradeoff among hardware cost, throughput rate, output latency and control complexity, etc. PMID:17357722
Spiral waves are stable in discrete element models of two-dimensional homogeneous excitable media
NASA Technical Reports Server (NTRS)
Feldman, A. B.; Chernyak, Y. B.; Cohen, R. J.
1998-01-01
The spontaneous breakup of a single spiral wave of excitation into a turbulent wave pattern has been observed in both discrete element models and continuous reaction-diffusion models of spatially homogeneous 2D excitable media. These results have attracted considerable interest, since spiral breakup is thought to be an important mechanism of transition from the heart rhythm disturbance ventricular tachycardia to the fatal arrhythmia ventricular fibrillation. It is not known whether this process can occur in the absence of disease-induced spatial heterogeneity of the electrical properties of the ventricular tissue. Candidate mechanisms for spiral breakup in uniform 2D media have emerged, but the physical validity of the mechanisms and their applicability to myocardium require further scrutiny. In this letter, we examine the computer simulation results obtained in two discrete element models and show that the instability of each spiral is an artifact resulting from an unphysical dependence of wave speed on wave front curvature in the medium. We conclude that spiral breakup does not occur in these two models at the specified parameter values and that great care must be exercised in the representation of a continuous excitable medium via discrete elements.
FireStem2D--a two-dimensional heat transfer model for simulating tree stem injury in fires.
Chatziefstratiou, Efthalia K; Bohrer, Gil; Bova, Anthony S; Subramanian, Ravishankar; Frasson, Renato P M; Scherzer, Amy; Butler, Bret W; Dickinson, Matthew B
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes.
NASA Astrophysics Data System (ADS)
Shinzawa, Hideyuki; Hagihara, Hideaki; Suda, Hiroyuki; Mizukado, Jyunji
2016-11-01
Application of the two-dimensional (2D) correlation spectroscopy is extended to Chemiluminescence (CL) spectra of isotactic polypropylene (iPP) under thermally induced oxidation. Upon heating, the polymer chains of the iPP undergoes scissoring and fragmentation to develop several intermediates. While different chemical species provides the emission at different wavelength regions, entire feature of the time-dependent CL spectra of the iPP samples were complicated by the presence of overlapped contributions from singlet oxygen (1O2) and carbonyl species within sample. 2D correlation spectra showed notable enhancement of the spectral resolution to provide penetrating insight into the thermodynamics of the polymer system. For example, the, oxidation induce scissoring and fragmentation of the polymer chains to develop the carbonyl group. Further reaction results in the consumption of the carbonyl species and subsequent production of different 1O2 species each developed in different manner. Consequently, key information on the thermal oxidation can be extracted in a surprisingly simple manner without any analytical expression for the actual response curves of spectral intensity signals during the reaction.
FireStem2D – A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires
Chatziefstratiou, Efthalia K.; Bohrer, Gil; Bova, Anthony S.; Subramanian, Ravishankar; Frasson, Renato P. M.; Scherzer, Amy; Butler, Bret W.; Dickinson, Matthew B.
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes. PMID:23894599
Flocking with discrete symmetry: The two-dimensional active Ising model
NASA Astrophysics Data System (ADS)
Solon, A. P.; Tailleur, J.
2015-10-01
We study in detail the active Ising model, a stochastic lattice gas where collective motion emerges from the spontaneous breaking of a discrete symmetry. On a two-dimensional lattice, active particles undergo a diffusion biased in one of two possible directions (left and right) and align ferromagnetically their direction of motion, hence yielding a minimal flocking model with discrete rotational symmetry. We show that the transition to collective motion amounts in this model to a bona fide liquid-gas phase transition in the canonical ensemble. The phase diagram in the density-velocity parameter plane has a critical point at zero velocity which belongs to the Ising universality class. In the density-temperature "canonical" ensemble, the usual critical point of the equilibrium liquid-gas transition is sent to infinite density because the different symmetries between liquid and gas phases preclude a supercritical region. We build a continuum theory which reproduces qualitatively the behavior of the microscopic model. In particular, we predict analytically the shapes of the phase diagrams in the vicinity of the critical points, the binodal and spinodal densities at coexistence, and the speeds and shapes of the phase-separated profiles.
Fayer, Michael D; Moilanen, David E; Wong, Daryl; Rosenfeld, Daniel E; Fenn, Emily E; Park, Sungnam
2009-09-15
Water is ubiquitous in nature, but it exists as pure water infrequently. From the ocean to biology, water molecules interact with a wide variety of dissolved species. Many of these species are charged. In the ocean, water interacts with dissolved salts. In biological systems, water interacts with dissolved salts as well as charged amino acids, the zwitterionic head groups of membranes, and other biological groups that carry charges. Water plays a central role in a vast number of chemical processes because of its dynamic hydrogen-bond network. A water molecule can form up to four hydrogen bonds in an approximately tetrahedral arrangement. These hydrogen bonds are continually being broken, and new bonds are being formed on a picosecond time scale. The ability of the hydrogen-bond network of water to rapidly reconfigure enables water to accommodate and facilitate chemical processes. Therefore, the influence of charged species on water hydrogen-bond dynamics is important. Recent advances in ultrafast coherent infrared spectroscopy have greatly expanded our understanding of water dynamics. Two-dimensional infrared (2D IR) vibrational echo spectroscopy is providing new observables that yield direct information on the fast dynamics of molecules in their ground electronic state under thermal equilibrium conditions. The 2D IR vibrational echoes are akin to 2D nuclear magnetic resonance (NMR) but operate on time scales that are many orders of magnitude shorter. In a 2D IR vibrational echo experiment (see the Conspectus figure), three IR pulses are tuned to the vibrational frequency of interest, which in this case is the frequency of the hydroxyl stretching mode of water. The first two pulses "label" the initial molecular structures by their vibrational frequencies. The system evolves between pulses two and three, and the third pulse stimulates the emission of the vibrational echo pulse, which is the signal. The vibrational echo pulse is heterodyne, detected by combining it
Daskalov, G.M.; Baker, R.S.; Little, R.C.; Rogers, D.W.O.; Williamson, J.F.
2000-02-01
The DANTSYS discrete ordinates computer code system is applied to quantitative estimation of water kerma rate distributions in the vicinity of discrete photon sources with energies in the 20- to 800-keV range in two-dimensional cylindrical r-z geometry. Unencapsulated sources immersed in cylindrical water phantoms of 40-cm diameter and 40-cm height are modeled in either homogeneous phantoms or shielded by Ti, Fe, and Pb filters with thicknesses of 1 and 2 mean free paths. The obtained dose results are compared with corresponding photon Monte Carlo simulations. A 210-group photon cross-section library for applications in this energy range is developed and applied, together with a general-purpose 42-group library developed at Los Alamos National Laboratory, for DANTSYS calculations. The accuracy of DANTSYS with the 42-group library relative to Monte Carlo exhibits large pointwise fluctuations from {minus}42 to +84%. The major cause for the observed discrepancies is determined to be the inadequacy of the weighting function used for the 42-group library derivation. DANTSYS simulations with a finer 210-group library show excellent accuracy on and off the source transverse plane relative to Monte Carlo kerma calculations, varying from {minus}4.9 to 3.7%. The P{sub 3} Legendre polynomial expansion of the angular scattering function is shown to be sufficient for accurate calculations. The results demonstrate that DANTSYS is capable of calculating photon doses in very good agreement with Monte Carlo and that the multigroup cross-section library and efficient techniques for mitigation of ray effects are critical for accurate discrete ordinates implementation.
Decoding human motor activity from EEG single trials for a discrete two-dimensional cursor control.
Huang, Dandan; Lin, Peter; Fei, Ding-Yu; Chen, Xuedong; Bai, Ou
2009-08-01
This study aims to explore whether human intentions to move or cease to move right and left hands can be decoded from spatiotemporal features in non-invasive EEG in order to control a discrete two-dimensional cursor movement for a potential multidimensional brain-computer interface (BCI). Five naïve subjects performed either sustaining or stopping a motor task with time locking to a predefined time window by using motor execution with physical movement or motor imagery. Spatial filtering, temporal filtering, feature selection and classification methods were explored. The performance of the proposed BCI was evaluated by both offline classification and online two-dimensional cursor control. Event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were observed on the contralateral hemisphere to the hand moved for both motor execution and motor imagery. Feature analysis showed that EEG beta band activity in the contralateral hemisphere over the motor cortex provided the best detection of either sustained or ceased movement of the right or left hand. The offline classification of four motor tasks (sustain or cease to move right or left hand) provided 10-fold cross-validation accuracy as high as 88% for motor execution and 73% for motor imagery. The subjects participating in experiments with physical movement were able to complete the online game with motor execution at an average accuracy of 85.5 +/- 4.65%; the subjects participating in motor imagery study also completed the game successfully. The proposed BCI provides a new practical multidimensional method by noninvasive EEG signal associated with human natural behavior, which does not need long-term training.
Decoding human motor activity from EEG single trials for a discrete two-dimensional cursor control
NASA Astrophysics Data System (ADS)
Huang, Dandan; Lin, Peter; Fei, Ding-Yu; Chen, Xuedong; Bai, Ou
2009-08-01
This study aims to explore whether human intentions to move or cease to move right and left hands can be decoded from spatiotemporal features in non-invasive EEG in order to control a discrete two-dimensional cursor movement for a potential multidimensional brain-computer interface (BCI). Five naïve subjects performed either sustaining or stopping a motor task with time locking to a predefined time window by using motor execution with physical movement or motor imagery. Spatial filtering, temporal filtering, feature selection and classification methods were explored. The performance of the proposed BCI was evaluated by both offline classification and online two-dimensional cursor control. Event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were observed on the contralateral hemisphere to the hand moved for both motor execution and motor imagery. Feature analysis showed that EEG beta band activity in the contralateral hemisphere over the motor cortex provided the best detection of either sustained or ceased movement of the right or left hand. The offline classification of four motor tasks (sustain or cease to move right or left hand) provided 10-fold cross-validation accuracy as high as 88% for motor execution and 73% for motor imagery. The subjects participating in experiments with physical movement were able to complete the online game with motor execution at an average accuracy of 85.5 ± 4.65%; the subjects participating in motor imagery study also completed the game successfully. The proposed BCI provides a new practical multidimensional method by noninvasive EEG signal associated with human natural behavior, which does not need long-term training.
Tensor representation of color images and fast 2D quaternion discrete Fourier transform
NASA Astrophysics Data System (ADS)
Grigoryan, Artyom M.; Agaian, Sos S.
2015-03-01
In this paper, a general, efficient, split algorithm to compute the two-dimensional quaternion discrete Fourier transform (2-D QDFT), by using the special partitioning in the frequency domain, is introduced. The partition determines an effective transformation, or color image representation in the form of 1-D quaternion signals which allow for splitting the N × M-point 2-D QDFT into a set of 1-D QDFTs. Comparative estimates revealing the efficiency of the proposed algorithms with respect to the known ones are given. In particular, a proposed method of calculating the 2r × 2r -point 2-D QDFT uses 18N2 less multiplications than the well-known column-row method and method of calculation based on the symplectic decomposition. The proposed algorithm is simple to apply and design, which makes it very practical in color image processing in the frequency domain.
NASA Astrophysics Data System (ADS)
Banton, J.; Villard, P.; Jongmans, D.; Scavia, C.
2009-11-01
Application of the discrete element method (DEM) to model avalanches of granular materials requires determining the correct geometric and rheological parameters for and between the particles as well as for the basal surface. The use of spherical (circular in 2-D) particles enhances particle rolling, yielding excessive runout values. The solution usually adopted to correct this effect is to introduce a drag force which artificially slows down the particle velocities. The aim of this study is to test the capability of the DEM to simulate well-controlled unsteady channelized granular flows, considering the measured properties of the particles and of the basal surface which naturally contribute to dissipate energy. We first performed a parametrical analysis on a simple 2-D model in order to estimate the influence of particle shape, friction parameters, and restitution coefficients on the dynamics of the flow and on the deposit geometry. We then simulated three channelized laboratory experiments performed with two materials and two bed linings. Using the geometrical layout and the values of the mechanical parameters provided by the authors, we obtained a remarkable agreement between the observed and 2-D simulated deposit shapes for the three experiments. Also, the computed mass evolution with time was very consistent with the experimental snapshots in all cases. These results highlight the capability of the DEM technique for modeling avalanche of granular material when the particle shape as well as the friction and restitution coefficients are properly considered.
Hobson, D J; Rupa, P; Diaz, G J; Zhang, H; Yang, M; Mine, Y; Turner, P V; Kirby, G M
2007-12-01
There is a need to develop reliable methods to assess the safety of genetically modified and other novel foods. The aim of this study was to identify protein biomarkers of food allergy in mice exposed to ovomucoid (OVM), a major food allergen found in chicken egg white. BALB/c mice were repeatedly sensitized by gavage with OVM and cholera toxin (CT) and control mice were exposed to a mixture of amino acids with CT. At the endpoint, all mice were challenged intraperitoneally with OVM and alum. Type-1 hypersensitivity was confirmed in OVM-sensitized mice by observation of clinical signs of anaphylaxis and elevated levels of plasma histamine, OVM-specific IgE and OVM-specific IgG by ELISA. Differential protein expression was assessed in albumin-depleted plasma as well as in mesenteric lymph node, liver, spleen, and ileum by two-dimensional difference gel electrophoresis (2D-DIGE). Differentially expressed proteins were identified by liquid chromatography with tandem mass spectrometry. Plasma proteins overexpressed in OVM-sensitized mice included haptoglobin (41-fold), serum amyloid A (19-fold) and peroxiredoxin-2 (1.9-fold). Further validation of these plasma proteins in other animal models of food allergy with different food allergens is required to assess their potential as candidate biomarkers for use in evaluating the allergenicity of novel foods.
Bifurcations of a two-dimensional discrete time plant-herbivore system
NASA Astrophysics Data System (ADS)
Khan, Abdul Qadeer; Ma, Jiying; Xiao, Dongmei
2016-10-01
In this paper, bifurcations of a two dimensional discrete time plant-herbivore system formulated by Allen et al. (1993) have been studied. It is proved that the system undergoes a transcritical bifurcation in a small neighborhood of a boundary equilibrium and a Neimark-Sacker bifurcation in a small neighborhood of the unique positive equilibrium. An invariant closed curve bifurcates from the unique positive equilibrium by Neimark-Sacker bifurcation, which corresponds to the periodic or quasi-periodic oscillations between plant and herbivore populations. For a special form of the system, which appears in Kulenović and Ladas (2002), it is shown that the system can undergo a supercritical Neimark-Sacker bifurcation in a small neighborhood of the unique positive equilibrium and a stable invariant closed curve appears. This bifurcation analysis provides a theoretical support on the earlier numerical observations in Allen et al. (1993) and gives a supportive evidence of the conjecture in Kulenović and Ladas (2002). Some numerical simulations are also presented to illustrate our theocratical results.
NASA Technical Reports Server (NTRS)
Reddy, T. S. R.
1995-01-01
This guide describes the input data required for using ECAP2D (Euler Cascade Aeroelastic Program-Two Dimensional). ECAP2D can be used for steady or unsteady aerodynamic and aeroelastic analysis of two dimensional cascades. Euler equations are used to obtain aerodynamic forces. The structural dynamic equations are written for a rigid typical section undergoing pitching (torsion) and plunging (bending) motion. The solution methods include harmonic oscillation method, influence coefficient method, pulse response method, and time integration method. For harmonic oscillation method, example inputs and outputs are provided for pitching motion and plunging motion. For the rest of the methods, input and output for pitching motion only are given.
NASA Astrophysics Data System (ADS)
Lü, Bin-Bin; Tian, Qiang
2009-10-01
In this paper we study the existence and stability of two-dimensional discrete gap breathers in a two-dimensional diatomic face-centered square lattice consisting of alternating light and heavy atoms, with on-site potential and coupling potential. This study is focused on two-dimensional breathers with their frequency in the gap that separates the acoustic and optical bands of the phonon spectrum. We demonstrate the possibility of the existence of two-dimensional gap breathers by using a numerical method. Six types of two-dimensional gap breathers are obtained, i.e., symmetric, mirror-symmetric and asymmetric, whether the center of the breather is on a light or a heavy atom. The difference between one-dimensional discrete gap breathers and two-dimensional discrete gap breathers is also discussed. We use Aubry's theory to analyze the stability of discrete gap breathers in the two-dimensional diatomic face-centered square lattice.
Soliton Theory of Two-Dimensional Lattices: The Discrete Nonlinear Schroedinger Equation
Arevalo, Edward
2009-06-05
We theoretically investigate the motion of collective excitations in the two-dimensional nonlinear Schroedinger equation with cubic nonlinearity. The form of these excitations for a broad range of parameters is derived. Their evolution and interaction is numerically studied and the modulation instability is discussed. The case of saturable nonlinearity is revisited.
Bonaccorso, Francesco; Colombo, Luigi; Yu, Guihua; Stoller, Meryl; Tozzini, Valentina; Ferrari, Andrea C; Ruoff, Rodney S; Pellegrini, Vittorio
2015-01-01
Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.
NASA Technical Reports Server (NTRS)
Hua, Chongyu; Volakis, John L.
1990-01-01
AUTOMESH-2D is a computer program specifically designed as a preprocessor for the scattering analysis of two dimensional bodies by the finite element method. This program was developed due to a need for reproducing the effort required to define and check the geometry data, element topology, and material properties. There are six modules in the program: (1) Parameter Specification; (2) Data Input; (3) Node Generation; (4) Element Generation; (5) Mesh Smoothing; and (5) Data File Generation.
NASA Astrophysics Data System (ADS)
Fal'ko, Vladimir I.
2014-06-01
On behalf of the Editorial Board and IOP Publishing, I am pleased to announce the opening of 2D Materials. Research on two-dimensional materials, such as graphene, now involves thousands of researchers worldwide cutting across physics, chemistry, engineering and biology, and extending from fundamental science to novel applications. It is this situation which defines the scope and mission of 2D Materials, a new journal that will serve all sides of this multidisciplinary field by publishing urgent research of the highest quality and impact.
Two-dimensional discrete model for DNA dynamics: Longitudinal wave propagation and denaturation
NASA Astrophysics Data System (ADS)
Muto, V.; Lomdahl, P. S.; Christiansen, P. L.
1990-12-01
In this paper, a simple, two-dimensional model of the deoxyribonucleic acid (DNA) is presented. In the model the two polynucleotide strands are linked together through the hydrogen bonds. The phosphodiester bridges in the backbone are described by the anharmonic potential of Toda kind, while the hydrogen bonds are described by the Lennard-Jones potential. Longitudinal wave propagation on ring-shaped DNA molecules is investigated. The model predicts a significant increase in the lifetime of the open states of the hydrogen bonds at physiological temperatures. Thus anharmonicity may play a role in DNA denaturation.
Filho, J. F. P.
2013-07-01
In this work, an analytical discrete ordinates method is used to solve a nodal formulation of a neutron transport problem in x, y-geometry. The proposed approach leads to an important reduction in the order of the associated eigenvalue systems, when combined with the classical level symmetric quadrature scheme. Auxiliary equations are proposed, as usually required for nodal methods, to express the unknown fluxes at the boundary introduced as additional unknowns in the integrated equations. Numerical results, for the problem defined by a two-dimensional region with a spatially constant and isotropically emitting source, are presented and compared with those available in the literature. (authors)
Two-dimensional B-C-O alloys: a promising class of 2D materials for electronic devices.
Zhou, Si; Zhao, Jijun
2016-04-28
Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor forming alternate patterns into the chain- or ring-like structures embedded in the pristine graphene regions. These B-C-O hybrid sheets can be either metals or semiconductors depending on the B : O ratio. The semiconducting (B2O)nCm and (B6O3)nCm phases exist under the B- and O-rich conditions, and possess a tunable band gap of 1.0-3.8 eV and high carrier mobility, retaining ∼1000 cm2 V(-1) s(-1) even for half coverage of B and O atoms. These B-C-O alloys form a new class of 2D materials that are promising candidates for high-speed electronic devices.
Yang, L M; Shu, C; Wang, Y
2016-03-01
In this work, a discrete gas-kinetic scheme (DGKS) is presented for simulation of two-dimensional viscous incompressible and compressible flows. This scheme is developed from the circular function-based GKS, which was recently proposed by Shu and his co-workers [L. M. Yang, C. Shu, and J. Wu, J. Comput. Phys. 274, 611 (2014)]. For the circular function-based GKS, the integrals for conservation forms of moments in the infinity domain for the Maxwellian function-based GKS are simplified to those integrals along the circle. As a result, the explicit formulations of conservative variables and fluxes are derived. However, these explicit formulations of circular function-based GKS for viscous flows are still complicated, which may not be easy for the application by new users. By using certain discrete points to represent the circle in the phase velocity space, the complicated formulations can be replaced by a simple solution process. The basic requirement is that the conservation forms of moments for the circular function-based GKS can be accurately satisfied by weighted summation of distribution functions at discrete points. In this work, it is shown that integral quadrature by four discrete points on the circle, which forms the D2Q4 discrete velocity model, can exactly match the integrals. Numerical results showed that the present scheme can provide accurate numerical results for incompressible and compressible viscous flows with roughly the same computational cost as that needed by the Roe scheme. PMID:27078488
Two-dimensional B-C-O alloys: a promising class of 2D materials for electronic devices
NASA Astrophysics Data System (ADS)
Zhou, Si; Zhao, Jijun
2016-04-01
Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor forming alternate patterns into the chain- or ring-like structures embedded in the pristine graphene regions. These B-C-O hybrid sheets can be either metals or semiconductors depending on the B : O ratio. The semiconducting (B2O)nCm and (B6O3)nCm phases exist under the B- and O-rich conditions, and possess a tunable band gap of 1.0-3.8 eV and high carrier mobility, retaining ~1000 cm2 V-1 s-1 even for half coverage of B and O atoms. These B-C-O alloys form a new class of 2D materials that are promising candidates for high-speed electronic devices.Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor
Nieber, J.L.; Friedel, M.J.; Munir, H.M.
1994-01-01
This information circular describes a computer program called VARSAT2D, a comprehensive unsaturated fluid flow simulator developed by the U.S. Bureau of Mines. VARSAT2D solves for either a vertical or horizontal, transient or steady-state solution in variably saturated, heterogeneous, anisotropic porous media using the Galerkin finite-element approach. Simplex triangular elements are used. Moisture retention characteristics are described by specifying either the Brooks and Corey, Brutsaert, or Van Genuchten power functions, with hysteresis described using the Maulem independent domain model. Boundary conditions may include any combination of time-varying seepage, pressure along solution domain boundaries and/or at internal node points, unit hydraulic gradient at the lower boundary, and a uniform source and/or sink. The program should be a welcome addition for mining and environmental hydrologists, researchers, and engineers interested in modeling unsaturated fluid flow.
Drews, Oliver; Görg, Angelika
2005-01-01
DynaProt 2D presents an advanced online database for dynamic access to proteomes and two-dimensional (2D) gels. The database was designed to administer complete in silico proteomes and links them with experimental proteomic data in the manner of 2D electrophoresis gels (IPG-Dalt). The 2D gels serve as reference maps in 2D gel analysis as well as tools for navigation of the database to switch between experimental and predicted data. Therefore, all identified spots in the gels are clickable and linked with summarized protein information. The protein information tables contain calculated characteristics, which are often used in proteomics, such as the molecular weight, isoelectric point, codon adaptation index, grand average of hydropathicity, etc. The design of the database permits online extension of gel data and protein attributes without knowledge of any software language. Besides navigation via 2D gels, the clear graphical user interface permits quick and intuitive searching throughout complete proteomes and supports, e.g. the search for proteins with isoelectric points within pH ranges of interest or protein classes (e.g. ribosomal proteins or transporters). The first organism implemented in the database is Lactococcus lactis. The database is available at www.wzw.tum.de/proteomik/lactis. PMID:15608266
NASA Astrophysics Data System (ADS)
Tang, Shanzhi; Yu, Shengrui; Han, Qingfu; Li, Ming; Wang, Zhao
2016-09-01
Circular test is an important tactic to assess motion accuracy in many fields especially machine tool and coordinate measuring machine. There are setup errors due to using directly centring of the measuring instrument for both of contact double ball bar and existed non-contact methods. To solve this problem, an algorithm for circular test using function construction based on matrix operation is proposed, which is not only used for the solution of radial deviation (F) but also should be applied to obtain two other evaluation parameters especially circular hysteresis (H). Furthermore, an improved optical configuration with a single laser is presented based on a 2D laser heterodyne interferometer. Compared with the existed non-contact method, it has a more pure homogeneity of the laser sources of 2D displacement sensing for advanced metrology. The algorithm and modeling are both illustrated. And error budget is also achieved. At last, to validate them, test experiments for motion paths are implemented based on a gantry machining center. Contrast test results support the proposal.
Brûlé, Yoann; Demésy, Guillaume; Gralak, Boris; Popov, Evgeny
2015-04-01
An extensive numerical study of diffraction of a plane monochromatic wave by a single gold cone on a plane gold substrate and by a periodical array of such cones shows formation of curls in the map of the Poynting vector. They result from the interference between the incident wave, the wave reflected by the substrate, and the field scattered by the cone(s). In case of a single cone, when going away from its base along the surface, the main contribution in the scattered field is given by the plasmon surface wave (PSW) excited on the surface. As expected, it has a predominant direction of propagation, determined by the incident wave polarization. Two particular cones with height approximately 1/6 and 1/3 of the wavelength are studied in detail, as they present the strongest absorption and field enhancement when arranged in a periodic array. While the PSW excited by the smaller single cone shows an energy flux globally directed along the substrate surface, we show that curls of the Poynting vector generated with the larger cone touch the diopter surface. At this point, their direction is opposite to the energy flow of the PSW, which is then forced to jump over the vortex regions. Arranging the cones in a two-dimensional subwavelength periodic array (diffraction grating), supporting a specular reflected order only, resonantly strengthens the field intensity at the tip of cones and leads to a field intensity enhancement of the order of 10 000 with respect to the incident wave intensity. The enhanced field is strongly localized on the rounded top of the cones. It is accompanied by a total absorption of the incident light exhibiting large angular tolerances. This strongly localized giant field enhancement can be of much interest in many applications, including fluorescence spectroscopy, label-free biosensing, surface-enhanced Raman scattering (SERS), nonlinear optical effects and photovoltaics.
FTOM-2D: a two-dimensional approach to model the detailed thermal behavior of nonplanar surfaces
NASA Astrophysics Data System (ADS)
Bartos, B.; Stein, K.
2015-10-01
The Fraunhofer thermal object model (FTOM) predicts the temperature of an object as a function of the environmental conditions. The model has an outer layer exchanging radiation and heat with the environment and a stack of layers beyond modifying the thermal behavior. The innermost layer is at a constant or variable temperature called core temperature. The properties of the model (6 parameters) are fitted to minimize the difference between the prediction and a time series of measured temperatures. The model can be used for very different objects like backgrounds (e.g. meadow, forest, stone, or sand) or objects like vehicles. The two dimensional enhancement was developed to model more complex objects with non-planar surfaces and heat conduction between adjacent regions. In this model we call the small thermal homogenous interacting regions thermal pixels. For each thermal pixel the orientation and the identities of the adjacent pixels are stored in an array. In this version 7 parameters have to be fitted. The model is limited to a convex geometry to reduce the complexity of the heat exchange and allow for a higher number of thermal pixels. For the test of the model time series of thermal images of a test object (CUBI) were analyzed. The square sides of the cubes were modeled as 25 thermal pixels (5 × 5). In the time series of thermal images small areas in the size of the thermal pixels were analyzed to generate data files that can easily be read by the model. The program was developed with MATLAB and the final version in C++ using the OpenMP multiprocessor library. The differential equation for the heat transfer is the time consuming part in the computation and was programmed in C. The comparison show a good agreement of the fitted and not fitted thermal pixels with the measured temperatures. This indicates the ability of the model to predict the temperatures of the whole object.
Strain hardening in 2D discrete dislocation dynamics simulations: A new '2.5D' algorithm
NASA Astrophysics Data System (ADS)
Keralavarma, S. M.; Curtin, W. A.
2016-10-01
The two-dimensional discrete dislocation dynamics (2D DD) method, consisting of parallel straight edge dislocations gliding on independent slip systems in a plane strain model of a crystal, is often used to study complicated boundary value problems in crystal plasticity. However, the absence of truly three dimensional mechanisms such as junction formation means that forest hardening cannot be modeled, unless additional so-called '2.5D' constitutive rules are prescribed for short-range dislocation interactions. Here, results from three dimensional dislocation dynamics (3D DD) simulations in an FCC material are used to define new constitutive rules for short-range interactions and junction formation between dislocations on intersecting slip systems in 2D. The mutual strengthening effect of junctions on preexisting obstacles, such as precipitates or grain boundaries, is also accounted for in the model. The new '2.5D' DD model, with no arbitrary adjustable parameters beyond those obtained from lower scale simulation methods, is shown to predict athermal hardening rates, differences in flow behavior for single and multiple slip, and latent hardening ratios. All these phenomena are well-established in the plasticity of crystals and quantitative results predicted by the model are in good agreement with experimental observations.
NASA Astrophysics Data System (ADS)
Genkawa, Takuma; Kanematsu, Wataru; Shinzawa, Hideyuki
2014-07-01
Dynamic absorption behavior of oleic acid (OA) onto silica gel was probed by infrared (IR) spectroscopy. Once OA is injected into silica gel placed on a horizontal attenuated total reflectance prism, the silica gel starts to absorb the OA molecules due to the molecular-level interaction based on hydrogen bonding between the COOH of OA and the OH of silica gel. The substantial level of variation of spectral feature is readily observed during the absorption of OA onto silica gel. 2D correlation analysis of the time-dependent IR spectra reveals fine details of absorption dynamics of OA molecules depending on the molecular structure. The predominant absorption of the monomers occurs at the onset of the absorption, and it is then quickly followed by the decrease in the dimers. In other words, the dissociation of the liquid crystals occurs via the disuniting of the tightly packed OA dimers.
NASA Astrophysics Data System (ADS)
Shinzawa, Hideyuki; Mizukado, Junji
2016-11-01
Evolutionary change in supermolecular structure of Nylon 6 during its melt-quenched process was studied by Near-infrared (NIR) spectroscopy. Time-resolved NIR spectra was measured by taking the advantage of high-speed NIR monitoring based on an acousto-optic tunable filter (AOTF). Fine spectral features associated with the variation of crystalline and amorphous structure occurring in relatively short time scale were readily captured. For example, synchronous and asynchronous 2D correlation spectra reveal the initial decrease in the contribution of the NIR band at 1485 nm due to the amorphous structure, predominantly existing in the melt Nylon 6. This is then followed by the emerging contribution of the band intensity at 1535 nm associated with the crystalline structure. Consequently, the results clearly demonstrate a definite advantage of the high-speed NIR monitoring for analyzing fleeting phenomena.
NASA Astrophysics Data System (ADS)
Das, Saptarshi
2016-10-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS).
Das, Saptarshi
2016-01-01
This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS). PMID:27721489
NASA Astrophysics Data System (ADS)
Seo, Hyemi; Chae, Boknam; Im, Ji Hyuk; Jung, Young Mee; Lee, Seung Woo
2014-07-01
Two-dimensional (2D) gradient mapping method and 2D correlation analysis of in situ FTIR spectra were used to probe the thermal imidization-induced spectral changes in 6FDA-ODA poly(amic acid) (PAA) films prepared by a reaction of 4,4‧-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4,4‧-oxydianiline (ODA) in N,N‧-dimethylacetamide. Large spectral changes in the in situ FTIR spectra of 6FDA-ODA PAA film were observed in the range, 130-230 °C. The thermal imidization of 6FDA-ODA PAA films strongly affects the spectral changes in amic acid groups in the PAA unit. The spectral change in the amic acid groups occurred before those of the imide ring. The cyclic anhydrides, isoimdes and intermolecular links are present together with the imide ring in the thermally-cured 6FDA-ODA PAA films.
NASA Astrophysics Data System (ADS)
Chae, Boknam; Son, Seok Ho; Kwak, Young Jun; Jung, Young Mee; Lee, Seung Woo
2016-11-01
The pH-induced structural changes to surface immobilized poly (L-glutamic acid) (PLGA) films were examined by Fourier transform infrared (FTIR) spectroscopy and two-dimensional (2D) correlation analysis. Significant spectral changes were observed in the FTIR spectra of the surface immobilized PLGA film between pH 6 and 7. The 2D correlation spectra constructed from the pH-dependent FTIR spectra of the surface immobilized PLGA films revealed the spectral changes induced by the alternations of the protonation state of the carboxylic acid group in the PLGA side chain. When the pH was increased from 6 to 8, weak spectral changes in the secondary structure of the PLGA main chain were induced by deprotonation of the carboxylic acid side group.
NASA Astrophysics Data System (ADS)
Yang, L. M.; Shu, C.; Wang, Y.
2016-03-01
In this work, a discrete gas-kinetic scheme (DGKS) is presented for simulation of two-dimensional viscous incompressible and compressible flows. This scheme is developed from the circular function-based GKS, which was recently proposed by Shu and his co-workers [L. M. Yang, C. Shu, and J. Wu, J. Comput. Phys. 274, 611 (2014), 10.1016/j.jcp.2014.06.033]. For the circular function-based GKS, the integrals for conservation forms of moments in the infinity domain for the Maxwellian function-based GKS are simplified to those integrals along the circle. As a result, the explicit formulations of conservative variables and fluxes are derived. However, these explicit formulations of circular function-based GKS for viscous flows are still complicated, which may not be easy for the application by new users. By using certain discrete points to represent the circle in the phase velocity space, the complicated formulations can be replaced by a simple solution process. The basic requirement is that the conservation forms of moments for the circular function-based GKS can be accurately satisfied by weighted summation of distribution functions at discrete points. In this work, it is shown that integral quadrature by four discrete points on the circle, which forms the D2Q4 discrete velocity model, can exactly match the integrals. Numerical results showed that the present scheme can provide accurate numerical results for incompressible and compressible viscous flows with roughly the same computational cost as that needed by the Roe scheme.
Sakami, M.; Charette, A.
1999-07-01
Radiative transfer is the dominant mode of heat transfer in many applications. Examples of such applications include combustion chambers, space, greenhouses, rocket plume sensing, to name only a few. However, due to the difficulty in finding an exact analytical solution to the integro-differential radiative transfer equation (RTE) in general absorbing-emitting-scattering media, a diversity of numerical methods have been worked out over the last forty years. In this work, an extension of a modified discrete ordinates method recently proposed by other researchers is presented. It is intended to counter the ray effect inherent in this method. The media analyzed are absorbing, emitting and isotropically or anisotropically scattering and the enclosure geometry is arbitrary. Cases where obstructions are present are also treated. The radiative intensity is broken into two parts: the wall-related intensity and the medium-related intensity. The former is treated separately by rigorous integration over the entire solid boundary. The new differencing scheme recently developed by the authors and based on triangular grids is used for the treatment of the medium-related intensity. Results confirm that the proposed method is a good general remedy for anomalies caused by the ray effect due to the geometry.
Extreme Local Extrema of Two-Dimensional Discrete Gaussian Free Field
NASA Astrophysics Data System (ADS)
Biskup, Marek; Louidor, Oren
2016-07-01
We consider the discrete Gaussian Free Field in a square box in {mathbb{Z}^2} of side length N with zero boundary conditions and study the joint law of its properly-centered extreme values ( h) and their scaled spatial positions ( x) in the limit as {N to infty}. Restricting attention to extreme local maxima, i.e., the extreme points that are maximal in an r N -neighborhood thereof, we prove that the associated process tends, whenever {r_N to infty} and {r_N/N to 0}, to a Poisson point process with intensity measure {Z{(dx)}e^{-α h} dh}, where {α:= 2/√{g}} with g: = 2/π and where Z(dx) is a random Borel measure on [0, 1]2. In particular, this yields an integral representation of the law of the absolute maximum, similar to that found in the context of Branching Brownian Motion. We give evidence that the random measure Z is a version of the derivative martingale associated with the continuum Gaussian Free Field.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes
Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.
2016-04-08
Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less
Kuhls-Gilcrist, Andrew T.; Gupta, Sandesh K.; Bednarek, Daniel R.; Rudin, Stephen
2010-01-01
The MTF, NNPS, and DQE are standard linear system metrics used to characterize intrinsic detector performance. To evaluate total system performance for actual clinical conditions, generalized linear system metrics (GMTF, GNNPS and GDQE) that include the effect of the focal spot distribution, scattered radiation, and geometric unsharpness are more meaningful and appropriate. In this study, a two-dimensional (2D) generalized linear system analysis was carried out for a standard flat panel detector (FPD) (194-micron pixel pitch and 600-micron thick CsI) and a newly-developed, high-resolution, micro-angiographic fluoroscope (MAF) (35-micron pixel pitch and 300-micron thick CsI). Realistic clinical parameters and x-ray spectra were used. The 2D detector MTFs were calculated using the new Noise Response method and slanted edge method and 2D focal spot distribution measurements were done using a pin-hole assembly. The scatter fraction, generated for a uniform head equivalent phantom, was measured and the scatter MTF was simulated with a theoretical model. Different magnifications and scatter fractions were used to estimate the 2D GMTF, GNNPS and GDQE for both detectors. Results show spatial non-isotropy for the 2D generalized metrics which provide a quantitative description of the performance of the complete imaging system for both detectors. This generalized analysis demonstrated that the MAF and FPD have similar capabilities at lower spatial frequencies, but that the MAF has superior performance over the FPD at higher frequencies even when considering focal spot blurring and scatter. This 2D generalized performance analysis is a valuable tool to evaluate total system capabilities and to enable optimized design for specific imaging tasks. PMID:21243038
NASA Astrophysics Data System (ADS)
Tarantino, Nicolas; Fidkowski, Lukasz
2016-09-01
We construct exactly solved commuting projector Hamiltonian lattice models for all known (2+1)-dimensional (2+1D) fermionic symmetry protected topological phases (SPTs) with on-site unitary symmetry group Gf=G ×Z2f , where G is finite and Z2f is the fermion parity symmetry. In particular, our models transcend the class of group supercohomology models, which realize some, but not all, fermionic SPTs in 2+1D. A natural ingredient in our construction is a discrete form of the spin structure of the 2D spatial surface M on which our model is defined, namely a "Kasteleyn" orientation of a certain graph associated with the lattice. As a special case, our construction yields commuting projector models for all eight members of the Z8 classification of 2D fermionic SPTs with G =Z2 .
Bohlin, Alexis; Kliewer, Christopher J
2013-06-14
Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15,000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm(2). PMID:23781772
NASA Astrophysics Data System (ADS)
Bohlin, Alexis; Kliewer, Christopher J.
2013-06-01
Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15 000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm2.
Bohlin, Alexis; Kliewer, Christopher J.
2013-01-01
Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15, 000 spatially correlated rotational CARS spectra in N_{2} and air over a 2D field of 40 mm^{2}.
Rago, T; Bencivelli, W; Scutari, M; Di Cosmo, C; Rizzo, C; Berti, P; Miccoli, P; Pinchera, A; Vitti, P
2006-05-01
The newly developed three-dimensional (3D) and two-dimensional (2D) thyroid ultrasound (US) were compared in assessing thyroid volume (TV) in 104 patients: 53 had an isolated thyroid nodule, 32 toxic diffuse goiter, 17 non-toxic multinodular goiter, 1 toxic multinodular goiter and 1 a toxic adenoma. A real-time Technos apparatus (Esaote SpA, Italy) with a 7,5 MHz linear transducer was used. The volume of thyroid lobes by 2D was calculated according to the ellipsoid formula. In the same session, TV by 3D US was calculated using a probe tracking system (in vivo ScanNT Esaote 3.4 MedCom. Darmasdt) and software to reconstruct 3D images, directly giving the lobe volume. There was a very good agreement between 2D and 3D, but in 94/208 lobes with nodular lesions 2D showed a 10% systematic overestimation compared to 3D, the percentage error being higher in lobes with lower volumes. A possible explanation for this result is the inadequacy of the ellipsoid formula in forecasting the correct lobe profile in the presence of nodules. This intrinsic defect of 2D US should be taken into account when evaluating TV in patients with nodular goiter.
NASA Astrophysics Data System (ADS)
Shinzawa, Hideyuki; Murakami, Takurou N.; Nishida, Masakazu; Kanematsu, Wataru; Noda, Isao
2014-07-01
Multiple-perturbation two-dimensional (2D) correlation spectroscopy was applied to sets of near-infrared (NIR) imaging data of polylactic acid (PLA) nanocomposite samples undergoing UV degradation. Incorporation of clay nanoparticles substantially lowers the surface free energy barrier for the nucleation of PLA and eventually increases the frequency of the spontaneous nucleation of PLA crystals. Thus, when exposed to external stimuli such as UV light, PLA nanocomposite may show different structure alternation depending on the clay dispersion. Multiple-perturbation 2D correlation analysis of the PLA nanocomposite samples revealed different spatial variation between crystalline and amorphous structure of PLA, and the phenomenon especially becomes acute in the region where the clay particles are coagulated. The incorporation of the clay leads to the cleavage-induced crystallization of PLA when the sample is subjected to the UV light. The additional development of the ordered crystalline structure then works favorably to restrict the initial degradation of the polymer, providing the delay in the weight loss of the PLA.
Peng, Rui; Liang, Liangbo; Hood, Zachary D.; Boulesbaa, Abdelaziz; Puretzky, Alexander; Ievlev, Anton V.; Come, Jeremy; Ovchinnikova, Olga S.; Wang, Hui; Ma, Cheng; et al
2016-08-30
Two-dimensional (2D) single-layer MoS2 nanosheets are demonstrated as efficient photocatalysts for hydrogen evolution reaction (HER) from water reduction, thanks to specific in-plane heterojunctions constructed in the MoS2 monolayer. These functional heterojunctions are formed among the different phases of chemically exfoliated MoS2 monolayers: semiconducting 2H, metallic 1T, and quasi-metallic 1T' phases. The proportion of the three MoS2 phases can be systematically controlled via thermal annealing of the nanosheets. Interestingly, a volcano relationship is observed between the photocatalytic HER activity and the annealing temperature with an optimum activity obtained after annealing at 60 °C. First-principles calculations were integrated with experimental studies tomore » shed light on the role of the multiphases of MoS2 and reveal that optimum photocatalytic HER activity results from the formation of the in-plane heterojunctions between 1T' MoS2 and 2H MoS2. Importantly, this facilitates not only balanced light absorption and charge generation by the 2H phase, efficient charge separation at the 1T'/2H interface, but also favorable HER over the basal sites of 1T' MoS2. Furthermore, our work manifests how the confluence of the optical, electronic and chemical properties of 2D MoS2 monolayers can be fully captured for efficient photocatalytic water reduction.« less
Non-fragile robust optimal guaranteed cost control of uncertain 2-D discrete state-delayed systems
NASA Astrophysics Data System (ADS)
Tandon, Akshata; Dhawan, Amit
2016-10-01
This paper is concerned with the problem of non-fragile robust optimal guaranteed cost control for a class of uncertain two-dimensional (2-D) discrete state-delayed systems described by the general model with norm-bounded uncertainties. Our attention is focused on the design of non-fragile state feedback controllers such that the resulting closed-loop system is asymptotically stable and the closed-loop cost function value is not more than a specified upper bound for all admissible parameter uncertainties and controller gain variations. A sufficient condition for the existence of such controllers is established under the linear matrix inequality framework. Moreover, a convex optimisation problem is proposed to select a non-fragile robust optimal guaranteed cost controller stabilising the 2-D discrete state-delayed system as well as achieving the least guaranteed cost for the resulting closed-loop system. The proposed method is compared with the previously reported criterion. Finally, illustrative examples are given to show the potential of the proposed technique.
Sebastian Schunert; Yousry Y. Azmy; Damien Fournier
2011-05-01
We present a comprehensive error estimation of four spatial discretization schemes of the two-dimensional Discrete Ordinates (SN) equations on Cartesian grids utilizing a Method of Manufactured Solution (MMS) benchmark suite based on variants of Larsen’s benchmark featuring different orders of smoothness of the underlying exact solution. The considered spatial discretization schemes include the arbitrarily high order transport methods of the nodal (AHOTN) and characteristic (AHOTC) types, the discontinuous Galerkin Finite Element method (DGFEM) and the recently proposed higher order diamond difference method (HODD) of spatial expansion orders 0 through 3. While AHOTN and AHOTC rely on approximate analytical solutions of the transport equation within a mesh cell, DGFEM and HODD utilize a polynomial expansion to mimick the angular flux profile across each mesh cell. Intuitively, due to the higher degree of analyticity, we expect AHOTN and AHOTC to feature superior accuracy compared with DGFEM and HODD, but at the price of potentially longer grind times and numerical instabilities. The latter disadvantages can result from the presence of exponential terms evaluated at the cell optical thickness that arise from the semianalytical solution process. This work quantifies the order of accuracy and the magnitude of the error of all four discretization methods for different optical thicknesses, scattering ratios and degrees of smoothness of the underlying exact solutions in order to verify or contradict the aforementioned intuitive expectation.
Minor, B.M.
1993-09-01
The exponential characteristic spatial quadrature for discrete ordinates neutral particle transport with rectangular cells is developed. Numerical problems arising in the derivation required the development of exponential moment functions. These functions are used to remove indeterminant forms which can cause catastrophic cancellations. The EC method is positive and nonlinear. It conserves particles and satisfies first moment balance. Comparisons of the EC method's performance to other methods in optically thin and thick spatial cells were performed. For optically thin cells, the EC method was shown to converge to the correct answer, with third order truncation error in the thin cell limit. In deep penetration problems, the EC method attained its highest computational efficiencies compared to the other methods. For all the deep penetration problems examined, the number of spatial cells required by the EC method to attain a desired accuracy was less than the other methods.... Mathematics functions, Nuclear radiation, Nuclear engineering, Radiation attenuation, Radiation shielding, Transport theory, Radiation transport.
Robinson, Nicholas P
2013-01-01
Branched DNA molecules are generated by the essential processes of replication and recombination. Owing to their distinctive extended shapes, these intermediates migrate differently from linear double-stranded DNA under certain electrophoretic conditions. However, these branched species exist in the cell at much low abundance than the bulk linear DNA. Consequently, branched molecules cannot be visualized by conventional electrophoresis and ethidium bromide staining. Two-dimensional native-native agarose electrophoresis has therefore been developed as a method to facilitate the separation and visualization of branched replication and recombination intermediates. A wide variety of studies have employed this technique to examine branched molecules in eukaryotic, archaeal, and bacterial cells, providing valuable insights into how DNA is duplicated and repaired in all three domains of life.
Effective filtering and interpolation of 2D discrete velocity fields with Navier-Stokes equations
NASA Astrophysics Data System (ADS)
Saumier, Louis-Philippe; Khouider, Boualem; Agueh, Martial
2016-11-01
We introduce a new variational technique to interpolate and filter a two-dimensional velocity vector field which is discretely sampled in a region of {{{R}}}2 and sampled only once at a time, on a small time-interval [0,{{Δ }}t]. The main idea is to find a solution of the Navier-Stokes equations that is closest to a prescribed field in the sense that it minimizes the l 2 norm of the difference between this solution and the target field. The minimization is performed on the initial vorticity by expanding it into radial basis functions of Gaussian type, with a fixed size expressed by a parameter ɛ. In addition, a penalty term with parameter k e is added to the minimizing functional in order to select a solution with a small kinetic energy. This additional term makes the minimizing functional strongly convex, and therefore ensures that the minimization problem is well-posed. The interplay between the parameters k e and ɛ effectively contributes to smoothing the discrete velocity field, as demonstrated by the numerical experiments on synthetic and real data.
Biffle, J.H.; Blanford, M.L.
1994-05-01
JAC2D is a two-dimensional finite element program designed to solve quasi-static nonlinear mechanics problems. A set of continuum equations describes the nonlinear mechanics involving large rotation and strain. A nonlinear conjugate gradient method is used to solve the equations. The method is implemented in a two-dimensional setting with various methods for accelerating convergence. Sliding interface logic is also implemented. A four-node Lagrangian uniform strain element is used with hourglass stiffness to control the zero-energy modes. This report documents the elastic and isothermal elastic/plastic material model. Other material models, documented elsewhere, are also available. The program is vectorized for efficient performance on Cray computers. Sample problems described are the bending of a thin beam, the rotation of a unit cube, and the pressurization and thermal loading of a hollow sphere.
NASA Astrophysics Data System (ADS)
Lisjak, A.; Liu, Q.; Zhao, Q.; Mahabadi, O. K.; Grasselli, G.
2013-10-01
Stress waves, known as acoustic emissions (AEs), are released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical models have been developed to simulate the deformation and damage processes of rocks, such as non-linear stress-strain behaviour and localization of failure, only a limited number have been capable of providing quantitative information regarding the associated seismicity. Moreover, the majority of these studies have adopted a pseudo-static approach based on elastic strain energy dissipation that completely disregards elastodynamic effects. This paper describes a new AE modelling technique based on the combined finite-discrete element method (FEM/DEM), a numerical tool that simulates material failure by explicitly considering fracture nucleation and propagation in the modelling domain. Given the explicit time integration scheme of the solver, stress wave propagation and the effect of radiated seismic energy can be directly captured. Quasi-dynamic seismic information is extracted from a FEM/DEM model with a newly developed algorithm based on the monitoring of internal variables (e.g. relative displacements and kinetic energy) in proximity to propagating cracks. The AE of a wing crack propagation model based on this algorithm are cross-analysed by traveltime inversion and energy estimation from seismic recordings. Results indicate a good correlation of AE initiation times and locations, and scaling of energies, independently calculated with the two methods. Finally, the modelling technique is validated by simulating a laboratory compression test on a granite sample. The micromechanical parameters of the heterogeneous model are first calibrated to reproduce the macroscopic stress-strain response measured during standard laboratory tests. Subsequently, AE frequency-magnitude statistics, spatial clustering of source locations and the evolution of AE rate are investigated. The distribution of
A two-dimensional angular-resolved proton spectrometer
NASA Astrophysics Data System (ADS)
Yang, Su; Yuan, Xiaohui; Fang, Yuan; Ge, Xulei; Deng, Yanqing; Wei, Wenqing; Gao, Jian; Fu, Feichao; Jiang, Tao; Liao, Guoqian; Liu, Feng; Chen, Min; Li, Yutong; Zhao, Li; Ma, Yanyun; Sheng, Zhengming; Zhang, Jie
2016-10-01
We present a novel design of two-dimensional (2D) angular-resolved spectrometer for full beam characterization of ultrashort intense laser driven proton sources. A rotated 2D pinhole array was employed, as selective entrance before a pair of parallel permanent magnets, to sample the full proton beam into discrete beamlets. The proton beamlets are subsequently dispersed without overlapping onto a planar detector. Representative experimental result of protons generated from femtosecond intense laser interaction with thin foil target is presented.
Bailey, T S; Adams, M L; Chang, J H
2008-10-01
We present a new spatial discretization of the discrete-ordinates transport equation in two-dimensional cylindrical (RZ) geometry for arbitrary polygonal meshes. This discretization is a discontinuous finite element method that utilizes the piecewise linear basis functions developed by Stone and Adams. We describe an asymptotic analysis that shows this method to be accurate for many problems in the thick diffusion limit on arbitrary polygons, allowing this method to be applied to radiative transfer problems with these types of meshes. We also present numerical results for multiple problems on quadrilateral grids and compare these results to the well-known bi-linear discontinuous finite element method.
A 2D Electromechanical Model of Human Atrial Tissue Using the Discrete Element Method
Brocklehurst, Paul; Adeniran, Ismail; Yang, Dongmin; Sheng, Yong; Zhang, Henggui; Ye, Jianqiao
2015-01-01
Cardiac tissue is a syncytium of coupled cells with pronounced intrinsic discrete nature. Previous models of cardiac electromechanics often ignore such discrete properties and treat cardiac tissue as a continuous medium, which has fundamental limitations. In the present study, we introduce a 2D electromechanical model for human atrial tissue based on the discrete element method (DEM). In the model, single-cell dynamics are governed by strongly coupling the electrophysiological model of Courtemanche et al. to the myofilament model of Rice et al. with two-way feedbacks. Each cell is treated as a viscoelastic body, which is physically represented by a clump of nine particles. Cell aggregations are arranged so that the anisotropic nature of cardiac tissue due to fibre orientations can be modelled. Each cell is electrically coupled to neighbouring cells, allowing excitation waves to propagate through the tissue. Cell-to-cell mechanical interactions are modelled using a linear contact bond model in DEM. By coupling cardiac electrophysiology with mechanics via the intracellular Ca2+ concentration, the DEM model successfully simulates the conduction of cardiac electrical waves and the tissue's corresponding mechanical contractions. The developed DEM model is numerically stable and provides a powerful method for studying the electromechanical coupling problem in the heart. PMID:26583141
1997-11-18
QUENCH2D* is developed for the solution of general, non-linear, two-dimensional inverse heat transfer problems. This program provides estimates for the surface heat flux distribution and/or heat transfer coefficient as a function of time and space by using transient temperature measurements at appropriate interior points inside the quenched body. Two-dimensional planar and axisymmetric geometries such as turnbine disks and blades, clutch packs, and many other problems can be analyzed using QUENCH2D*.
2D resistivity inversion using conjugate gradients for a finite element discretization
NASA Astrophysics Data System (ADS)
Bortolozo, C. A.; Santos, F. M.; Porsani, J. L.
2014-12-01
In this work we present a DC 2D inversion algorithm using conjugate gradients relaxation to solve the maximum likelihood inverse equations. We apply, according to Zhang (1995), the maximum likelihood inverse theory developed by Tarantola and Valette (1982) to our 2D resistivity inversion. This algorithm was chosen to this research because it doesn't need to calculate the field's derivatives. Since conjugate gradient techniques only need the results of the sensitivity matrix Ã or its transpose ÃT multiplying a vector, the actual computation of the sensitivity matrix are not performed, according to the methodology described in Zhang (1995). In Zhang (1995), the terms Ãx and ÃTy, are dependent of the stiffness matrix K and its partial derivative ∂K⁄∂ρ. The inversion methodology described in Zhang (1995) is for the case of 3D electrical resistivity by finite differences discretization. So it was necessary to make a series of adjustments to obtain a satisfactory result for 2D electrical inversion using finite element method. The difference between the modeling of 3D resistivity with finite difference and the 2D finite element method are in the integration variable, used in the 2D case. In the 2D case the electrical potential are initially calculated in the transformed domain, including the stiffness matrix, and only in the end is transformed in Cartesian domain. In the case of 3D, described by Zhang (1995) this is done differently, the calculation is done directly in the Cartesian domain. In the literature was not found any work describing how to deal with this problem. Because the calculations of Ãx and ÃTy must be done without having the real stiffness matrix, the adaptation consist in calculate the stiffness matrix and its partial derivative using a set of integration variables. We transform those matrix in the same form has in the potential case, but with different sets of variables. The results will be presented and are very promising.
NASA Astrophysics Data System (ADS)
Rockwood, Matthew; Green, Melissa
2012-11-01
In experimental, three-dimensional vortex-dominated flows, common particle image velocimetry (PIV) data is often collected in only the plane of interest due to equipment constraints. For flows with significant out of plane velocities or velocity gradients, this can create large discrepancies in Lagrangian analyses that require accurate particle trajectories. A Finite Time Lyapunov Exponent (FTLE) analysis is one such example, and has been shown to be very powerful at examining vortex dynamics and interactions in a variety of aperiodic flows. In this work, FTLE analysis of a turbulent channel simulation was conducted using both full three-dimensional velocity data and modified planar data extracted from the same computational domain. When the out of plane velocity component is neglected the difference in FTLE fields is non-trivial. A quantitative comparison and computation of error is presented for several planes across the width of the channel to determine the efficacy of using 2D analyses on the inherently 3D flows.
A framework for grand scale parallelization of the combined finite discrete element method in 2d
NASA Astrophysics Data System (ADS)
Lei, Z.; Rougier, E.; Knight, E. E.; Munjiza, A.
2014-09-01
Within the context of rock mechanics, the Combined Finite-Discrete Element Method (FDEM) has been applied to many complex industrial problems such as block caving, deep mining techniques (tunneling, pillar strength, etc.), rock blasting, seismic wave propagation, packing problems, dam stability, rock slope stability, rock mass strength characterization problems, etc. The reality is that most of these were accomplished in a 2D and/or single processor realm. In this work a hardware independent FDEM parallelization framework has been developed using the Virtual Parallel Machine for FDEM, (V-FDEM). With V-FDEM, a parallel FDEM software can be adapted to different parallel architecture systems ranging from just a few to thousands of cores.
Application of the 2-D discrete-ordinates method to multiple scattering of laser radiation
Zardecki, A.; Gerstl, S.A.W.; Embury, J.F.
1983-05-01
The discrete-ordinates finite-element radiation transport code twotran is applied to describe the multiple scattering of a laser beam from a reflecting target. For a model scenario involving a 99% relative humidity rural aerosol we compute the average intensity of the scattered radiation and correction factors to the Beer-Lambert law arising from multiple scattering. As our results indicate, 2-D x-y and r-z geometry modeling can reliably describe a realistic 3-D scenario. Specific results are presented for the two visual ranges of 1.52 and 0.76 km which show that, for sufficiently high aerosol concentrations (e.g., equivalent to V = 0.76 km), the target signature in a distant detector becomes dominated by multiply scattered radiation from interactions of the laser light with the aerosol environment. The merits of the scaling group and the delta-M approximation for the transfer equation are also explored.
A new stationary gridline artifact suppression method based on the 2D discrete wavelet transform
Tang, Hui; Tong, Dan; Dong Bao, Xu; Dillenseger, Jean-Louis
2015-04-15
Purpose: In digital x-ray radiography, an antiscatter grid is inserted between the patient and the image receptor to reduce scattered radiation. If the antiscatter grid is used in a stationary way, gridline artifacts will appear in the final image. In most of the gridline removal image processing methods, the useful information with spatial frequencies close to that of the gridline is usually lost or degraded. In this study, a new stationary gridline suppression method is designed to preserve more of the useful information. Methods: The method is as follows. The input image is first recursively decomposed into several smaller subimages using a multiscale 2D discrete wavelet transform. The decomposition process stops when the gridline signal is found to be greater than a threshold in one or several of these subimages using a gridline detection module. An automatic Gaussian band-stop filter is then applied to the detected subimages to remove the gridline signal. Finally, the restored image is achieved using the corresponding 2D inverse discrete wavelet transform. Results: The processed images show that the proposed method can remove the gridline signal efficiently while maintaining the image details. The spectra of a 1D Fourier transform of the processed images demonstrate that, compared with some existing gridline removal methods, the proposed method has better information preservation after the removal of the gridline artifacts. Additionally, the performance speed is relatively high. Conclusions: The experimental results demonstrate the efficiency of the proposed method. Compared with some existing gridline removal methods, the proposed method can preserve more information within an acceptable execution time.
NASA Astrophysics Data System (ADS)
Mendoza-Torres, F.; Diaz-Viera, M. A.
2015-12-01
In many natural fractured porous media, such as aquifers, soils, oil and geothermal reservoirs, fractures play a crucial role in their flow and transport properties. An approach that has recently gained popularity for modeling fracture systems is the Discrete Fracture Network (DFN) model. This approach consists in applying a stochastic boolean simulation method, also known as object simulation method, where fractures are represented as simplified geometric objects (line segments in 2D and polygons in 3D). One of the shortcomings of this approach is that it usually does not consider the dependency relationships that may exist between the geometric properties of fractures (direction, length, aperture, etc), that is, each property is simulated independently. In this work a method for modeling such dependencies by copula theory is introduced. In particular, a nonparametric model using Bernstein copulas for direction-length fracture dependency in 2D is presented. The application of this method is illustrated in a case study for a fractured rock sample from a carbonate reservoir outcrop.
Slater, C.O.
1990-07-01
Results are reported for two-dimensional discrete ordinates, X-Y geometry calculations performed for seven Halden Heavy Boiling Water Reactor core configurations. The calculations were performed in support of an effort to reassess the neutron fluence received by the reactor vessel. Nickel foil measurement data indicated considerable underprediction of fluences by the previously used multigroup removal- diffusion method. Therefore, calculations by a more accurate method were deemed appropriate. For each core configuration, data are presented for (1) integral fluxes in the core and near the vessel wall, (2) neutron spectra at selected locations, (3) isoflux contours superimposed on the geometry models, (4) plots of the geometry models, and (5) input for the calculations. The initial calculations were performed with several mesh sizes. Comparisons of the results from these calculations indicated that the uncertainty in the calculated fluxes should be less than 10%. However, three-dimensional effects (such as axial asymmetry in the fuel loading) could contribute to much greater uncertainty in the calculated neutron fluxes. 7 refs., 22 figs., 11 tabs.
Simulation of growth normal fault sandbox tests using the 2D discrete element method
NASA Astrophysics Data System (ADS)
Chu, Sheng-Shin; Lin, Ming-Lang; Huang, Wen-Chao; Nien, Wei-Tung; Liu, Huan-Chi; Chan, Pei-Chen
2015-01-01
A fault slip can cause the deformation of shallow soil layers and destroy infrastructures. The Shanchiao Fault on the west side of the Taipei Basin is one such fault. The activities of the Shanchiao Fault have caused the quaternary sediment beneath the Taipei Basin to become deformed, damaging structures, traffic construction, and utility lines in the area. Data on geological drilling and dating have been used to determine that a growth fault exists in the Shanchiao Fault. In an experiment, a sandbox model was built using noncohesive sandy soil to simulate the existence of a growth fault in the Shanchiao Fault and forecast the effect of the growth fault on shear-band development and ground differential deformation. The experimental results indicated that when a normal fault contains a growth fault at the offset of the base rock, the shear band develops upward beside the weak side of the shear band of the original-topped soil layer, and surfaces considerably faster than that of the single-topped layer. The offset ratio required is approximately one-third that of the single-cover soil layer. In this study, a numerical simulation of the sandbox experiment was conducted using a discrete element method program, PFC2D, to simulate the upper-covering sand layer shear-band development pace and the scope of a growth normal fault slip. The simulation results indicated an outcome similar to that of the sandbox experiment, which can be applied to the design of construction projects near fault zones.
Theory of two-dimensional microcavity lasers
Harayama, Takahisa; Sunada, Satoshi; Ikeda, Kensuke S.
2005-07-15
We present theoretical models of two-dimensional (2D) microcavity lasers. The relation between stationary lasing modes and resonances or metastable states is elucidated for arbitrary shapes of 2D resonant microcavities.
NASA Astrophysics Data System (ADS)
Suriano, Mark Allen
2001-07-01
Accurate, reliable, and robust discrete neutral particle radiation transport codes are needed in order to perform realistic 3D engineering calculations. Current neutron transport codes use low order spatial quadratures that are inaccurate unless a highly refined spatial mesh is used. In this work various higher order characteristic spatial quadratures are derived, implemented, and tested. Regular meshes of rectangular (2D) and of rectangular parallelepiped (boxoid) cells are supported. Short characteristic (linear characteristic [LC] and exponential characteristic [EC]) methods are compared with the corresponding independent characteristic (ILC and IEC) methods. The latter readily provide for plane parallel implementation. All transport results were benchmarked against Monte Carlo calculations. The diamond difference (DD) method was also tested and compared to the characteristic spatial quadratures. IEC and EC were found to be robust, reliable, and accurate for thin, intermediate, and optically thick cells. LC was robust, reliable, and accurate for cells of thin to intermediate (approximately 2 mean free paths) optical thickness. ILC was not pursued in 3D due to its anticipated excessive computational cost. DD was unreliable (as expected) over the range of test problems. We conclude that IEC and EC are apt methods for a wide range of problems, and provide the ability to perform realistic engineering calculations on coarse cells given nonnegative group-to-group, ordinate-to-ordinate cross section data.
NASA Astrophysics Data System (ADS)
Ouyanga, Chaojun; Lia, Zhenhuan; Huanga, Minsheng; Hua, Lili; Houa, Chuantao
2009-11-01
2D discrete dislocation dynamic modeling of compressed micro-pillars attached on a huge base is executed to study the size-dependent microplastic behavior of micro-pillars and the corresponding size effect. In addition to the conventional dimensional parameters of the micro-pillar such as the micro-pillar size and the height-to-width ratio, the micro-pillar taper angle and the dislocation slip plane orientation angle in the micro-pillar are also considered to address the size effect and its rich underlying mechanism. Computational results show that there are at least two operating mechanisms responsible for the plastic behavior of micro-pillars. One is associated with the dislocation free slip-out from the micro-pillar sidewall; the other is related to the dislocation pile-up at the base and the top end of the pillar. The overall mechanism governing the size effect of the micro-pillar rests with multi-factors, including the micro-pillar size, the height-to-width ratio, the micro-pillar taper and the slip plane orientation angle; however, whether the "free slip band" exists or not is the most important denotation. The well-known Schmid law still validates in the slender micro-pillars due to existence of the free slip band, whereas it may fail in the podgier micro-pillars due to absence of the free slip band; as a result, a complicated even "reverse" size effect appears.
Basins of attraction for a discrete dynamical system derived from the 2-D Navier-Stokes equations
NASA Astrophysics Data System (ADS)
Bible, Stewart A.; McDonough, J. M.
2000-11-01
It has previously been shown that a system of coupled logistic maps can be derived via Fourier analysis of the 2-D incompressible Navier-Stokes equations. Numerical studies of this 2-D discrete dynamical system (DDS) have demonstrated that uniqueness of solutions found for the usual 1-D logistic map no longer holds in 2-D, in accord with analytical results. If such DDSs are to be used as components of LES subgrid-scale models (as proposed in Hylin & McDonough, Int. J. Fluid Mech. Res. 26, 539, 1999), it is necessary to obtain an accurate delineation of the basins of attraction for each of their regimes. This presentation reports results of a preliminary study aimed at providing such information. In the current work we will present results for a restricted set of bifurcation parameter values selected from ``interesting'' regions of the overall regime map constructed by McDonough & Huang (submitted to Phys. Fluids, 2000). A not unexpected result has been the identification of ``holes'' and ``islands'' (see Abraham et al., Chaos in Discrete Dynamical Systems, 1997) for this regime map associated with sets of initial data having (apparently) nonzero measure. Implications of this in the context of model construction will be discussed.
Two-Dimensional Planetary Surface Lander
NASA Astrophysics Data System (ADS)
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.
Effective Temperature of 2D Dusty Plasma Liquids at the Discrete Level
Io, C.-W.; Chan, C.-L.; I Lin
2007-07-13
Fluctuation-dissipation theory has been used to measure the effective temperature of non-equilibrium system. In this work, using a 2D dusty plasma liquid formed by the negatively charged fine particles suspending in weakly ionized discharges and sheared by two CW counter parallel laser beams, we measure the micro-transport at the kinetic level. The effective temperatures Teff at different time scales are obtained through the Stokes-Einstein relation which relates the diffusion coefficient (D) and the viscosity ({eta}). The external energy is cascaded from the slow hopping modes to the fast caging modes through mutual coupling, which leads to the higher effective temperature of the slow hopping modes.
Effect of excluded volume on 2D discrete stochastic chemical kinetics
Lampoudi, Sotiria; Gillespie, Dan T.; Petzold, Linda R.
2009-01-01
The Stochastic Simulation Algorithm (SSA) is widely used in the discrete stochastic simulation of chemical kinetics. The propensity functions which play a central role in this algorithm have been derived under the point-molecule assumption, i.e., that the total volume of the molecules is negligible compared to the volume of the container. It has been shown analytically that for a one dimensional system and the A+A reaction, when the point molecule assumption is relaxed, the propensity function need only be adjusted by replacing the total volume of the system with the free volume of the system. In this paper we investigate via numerical simulations the impact of relaxing the point-molecule assumption in two dimensions. We find that the distribution of times to the first collision is close to exponential in most cases, so that the formalism of the propensity function is still applicable. In addition, we find that the area excluded by the molecules in two dimensions is usually higher than their close-packed area, requiring a larger correction to the propensity function than just the replacement of the total volume by the free volume. PMID:19360139
Order Parameters for Two-Dimensional Networks
NASA Astrophysics Data System (ADS)
Kaatz, Forrest; Bultheel, Adhemar; Egami, Takeshi
2007-10-01
We derive methods that explain how to quantify the amount of order in ``ordered'' and ``highly ordered'' porous arrays. Ordered arrays from bee honeycomb and several from the general field of nanoscience are compared. Accurate measures of the order in porous arrays are made using the discrete pair distribution function (PDF) and the Debye-Waller Factor (DWF) from 2-D discrete Fourier transforms calculated from the real-space data using MATLAB routines. An order parameter, OP3, is defined from the PDF to evaluate the total order in a given array such that an ideal network has the value of 1. When we compare PDFs of man-made arrays with that of our honeycomb we find OP3=0.399 for the honeycomb and OP3=0.572 for man's best hexagonal array. The DWF also scales with this order parameter with the least disorder from a computer-generated hexagonal array and the most disorder from a random array. An ideal hexagonal array normalizes a two-dimensional Fourier transform from which a Debye-Waller parameter is derived which describes the disorder in the arrays. An order parameter S, defined by the DWF, takes values from [0, 1] and for the analyzed man-made array is 0.90, while for the honeycomb it is 0.65. This presentation describes methods to quantify the order found in these arrays.
2D hexagonal quaternion Fourier transform in color image processing
NASA Astrophysics Data System (ADS)
Grigoryan, Artyom M.; Agaian, Sos S.
2016-05-01
In this paper, we present a novel concept of the quaternion discrete Fourier transform on the two-dimensional hexagonal lattice, which we call the two-dimensional hexagonal quaternion discrete Fourier transform (2-D HQDFT). The concept of the right-side 2D HQDFT is described and the left-side 2-D HQDFT is similarly considered. To calculate the transform, the image on the hexagonal lattice is described in the tensor representation when the image is presented by a set of 1-D signals, or splitting-signals which can be separately processed in the frequency domain. The 2-D HQDFT can be calculated by a set of 1-D quaternion discrete Fourier transforms (QDFT) of the splitting-signals.
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 photonic crystal surfactant detection.
Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A
2012-08-01
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. PMID:22720790
2005-07-01
Aniso2d is a two-dimensional seismic forward modeling code. The earth is parameterized by an X-Z plane in which the seismic properties Can have monoclinic with x-z plane symmetry. The program uses a user define time-domain wavelet to produce synthetic seismograms anrwhere within the two-dimensional media.
NASA Technical Reports Server (NTRS)
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.
Slater, C.O.
1992-01-01
The DRC2 code, which couples MASH or MASHX adjoint leakages with DORT 2-D discrete ordinates forward directional fluences, is described. The forward fluences are allowed to vary both axially and radially over the coupling surface, as opposed to the strictly axial variation allowed by the predecessor DRC code. Input instructions are presented along with descriptions and results from several sample problems. Results from the sample problems are used to compare DRC2 with DRC, DRC2 with DORT, and DRC2 with itself for the case of x-y dependence versus no x-y dependence of the forward fluence. The test problems demonstrate that for small systems DRC and DRC2 give essentially the same results. Some significant differences are noted for larger systems. Additionally, DRC2 results with no x-y dependence of the forward directional fluences are practically the same as those calculated by DRC.
Modeling complexly magnetized two-dimensional bodies of arbitrary shape
Mariano, J.; Hinze, W.J. . Dept. of Earth and Atmospheric Sciences)
1993-05-01
A method has been devised for the forward computation of magnetic anomalies due to two-dimensional (2-D) polygonal bodies with heterogeneously directed magnetization. The calculations are based on the equivalent line source approach wherein the source is subdivided into discrete elements that vary spatially in their magnetic properties. This equivalent dipole line method provides a fast and convenient means of representing and computing magnetic anomalies for bodies possessing complexly varying magnitude and direction of magnetization. The algorithm has been tested and applied to several generalized cases to verify the accuracy of the computation. The technique has also been used to model observed aeromagnetic anomalies associated with the structurally deformed, remanently magnetized Keweenawan volcanic rocks in eastern Lake Superior. This method is also easily adapted to the calculation of anomalies due to two and one-half-dimensional (2.5-D) and three-dimensional (3-D) heterogeneously magnetized sources.
Intrinsic two-dimensional features as textons
NASA Technical Reports Server (NTRS)
Barth, E.; Zetzsche, C.; Rentschler, I.
1998-01-01
We suggest that intrinsic two-dimensional (i2D) features, computationally defined as the outputs of nonlinear operators that model the activity of end-stopped neurons, play a role in preattentive texture discrimination. We first show that for discriminable textures with identical power spectra the predictions of traditional models depend on the type of nonlinearity and fail for energy measures. We then argue that the concept of intrinsic dimensionality, and the existence of end-stopped neurons, can help us to understand the role of the nonlinearities. Furthermore, we show examples in which models without strong i2D selectivity fail to predict the correct ranking order of perceptual segregation. Our arguments regarding the importance of i2D features resemble the arguments of Julesz and co-workers regarding textons such as terminators and crossings. However, we provide a computational framework that identifies textons with the outputs of nonlinear operators that are selective to i2D features.
Nonlinear localized modes in dipolar Bose-Einstein condensates in two-dimensional optical lattices
NASA Astrophysics Data System (ADS)
Rojas-Rojas, Santiago; Naether, Uta; Delgado, Aldo; Vicencio, Rodrigo A.
2016-09-01
We analyze the existence and properties of discrete localized excitations in a Bose-Einstein condensate loaded into a periodic two-dimensional optical lattice, when a dipolar interaction between atoms is present. The dependence of the Number of Atoms (Norm) on the energy of solutions is studied, along with their stability. Two important features of the system are shown, namely, the absence of the Norm threshold required for localized solutions to exist in finite 2D systems, and the existence of regions in the parameter space where two fundamental solutions are simultaneously unstable. This feature enables mobility of localized solutions, which is an uncommon feature in 2D discrete nonlinear systems. With attractive dipolar interaction, a non-trivial behavior of the Norm dependence is obtained, which is well described by an analytical model.
Coherence resonance in the two-dimensional neural map driven by non-Gaussian colored noise
NASA Astrophysics Data System (ADS)
Li, Dongxi; Hu, Bing; Wang, Jia; Jing, Yingchuan; Hou, Fangmei
2016-01-01
Based on the two-dimensional (2D) neural map, we investigate the impacts of non-Gaussian colored noise on the firing activity of discrete system. Taking the coherence parameter R to measure the regularity of firing behavior, it is demonstrated that coherence parameter R has a pronounced minimum value with the noise intensity and the correlation time of non-Gaussian colored noise, which is the so-called phenomenon of coherence resonance (CR). Besides, the firing activity is not sensitive to the non-Gaussian parameter which determines the departure from the Gaussian distribution when the correlation time is large enough.
Two-dimensional nuclear magnetic resonance petrophysics.
Sun, Boqin; Dunn, Keh-Jim
2005-02-01
Two-dimensional nuclear magnetic resonance (2D NMR) opens a wide area for exploration in petrophysics and has significant impact to petroleum logging technology. When there are multiple fluids with different diffusion coefficients saturated in a porous medium, this information can be extracted and clearly delineated from CPMG measurements of such a system either using regular pulsing sequences or modified two window sequences. The 2D NMR plot with independent variables of T2 relaxation time and diffusion coefficient allows clear separation of oil and water signals in the rocks. This 2D concept can be extended to general studies of fluid-saturated porous media involving other combinations of two or more independent variables, such as chemical shift and T1/T2 relaxation time (reflecting pore size), proton population and diffusion contrast, etc. PMID:15833623
NASA Astrophysics Data System (ADS)
Wang, Shiyong; Wang, Weihua; Tan, Liang Z.; Li, Xing Guang; Shi, Zilang; Kuang, Guowen; Liu, Pei Nian; Louie, Steven G.; Lin, Nian
2013-12-01
We report on the modulation of two-dimensional (2D) bands of Cu(111) surface-state electrons by three isostructural supramolecular honeycomb architectures with different periodicity or constituent molecules. Using Fourier-transformed scanning tunneling spectroscopy and model calculations, we resolved the 2D band structures and found that the intrinsic surface-state band is split into discrete bands. The band characteristics including band gap, band bottom, and bandwidth are controlled by the network unit cell size and the nature of the molecule-surface interaction. In particular, Dirac cones emerge where the second and third bands meet at the K points of the Brillouin zone of the supramolecular lattice.
Two-dimensional probe absorption in coupled quantum dots
NASA Astrophysics Data System (ADS)
Liu, Ningwu; Zhang, Yan; Kang, Chengxian; Wang, Zhiping; Yu, Benli
2016-07-01
We investigate the two-dimensional (2D) probe absorption in coupled quantum dots. It is found that, due to the position-dependent quantum interference effect, the 2D optical absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state quantum communication.
An atlas of two-dimensional materials.
Miró, Pere; Audiffred, Martha; Heine, Thomas
2014-09-21
The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect band gaps ranging from ultraviolet to infrared throughout the visible range. Thus, they have the potential to play a fundamental role in the future of nanoelectronics, optoelectronics and the assembly of novel ultrathin and flexible devices. We categorize the 2D materials according to their structure, composition and electronic properties. In this review we distinguish atomically thin materials (graphene, silicene, germanene, and their saturated forms; hexagonal boron nitride; silicon carbide), rare earth, semimetals, transition metal chalcogenides and halides, and finally synthetic organic 2D materials, exemplified by 2D covalent organic frameworks. Our exhaustive data collection presented in this Atlas demonstrates the large diversity of electronic properties, including band gaps and electron mobilities. The key points of modern computational approaches applied to 2D materials are presented with special emphasis to cover their range of application, peculiarities and pitfalls. PMID:24825454
An atlas of two-dimensional materials.
Miró, Pere; Audiffred, Martha; Heine, Thomas
2014-09-21
The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect band gaps ranging from ultraviolet to infrared throughout the visible range. Thus, they have the potential to play a fundamental role in the future of nanoelectronics, optoelectronics and the assembly of novel ultrathin and flexible devices. We categorize the 2D materials according to their structure, composition and electronic properties. In this review we distinguish atomically thin materials (graphene, silicene, germanene, and their saturated forms; hexagonal boron nitride; silicon carbide), rare earth, semimetals, transition metal chalcogenides and halides, and finally synthetic organic 2D materials, exemplified by 2D covalent organic frameworks. Our exhaustive data collection presented in this Atlas demonstrates the large diversity of electronic properties, including band gaps and electron mobilities. The key points of modern computational approaches applied to 2D materials are presented with special emphasis to cover their range of application, peculiarities and pitfalls.
Can Two-Dimensional Boron Superconduct?
Penev, Evgeni S; Kutana, Alex; Yakobson, Boris I
2016-04-13
Two-dimensional boron is expected to exhibit various structural polymorphs, all being metallic. Additionally, its small atomic mass suggests strong electron-phonon coupling, which in turn can enable superconducting behavior. Here we perform first-principles analysis of electronic structure, phonon spectra, and electron-phonon coupling of selected 2D boron polymorphs and show that the most stable structures predicted to feasibly form on a metal substrate should also exhibit intrinsic phonon-mediated superconductivity, with estimated critical temperature in the range of Tc ≈ 10-20 K.
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. PMID:26394207
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.
Epitaxial Growth of Two-Dimensional Stanene
NASA Astrophysics Data System (ADS)
Jia, Jinfeng
Ultrathin semiconductors present various novel electronic properties. The first experimental realized two-dimensional (2D) material is graphene. Searching 2D materials with heavy elements bring the attention to Si, Ge and Sn. 2D buckled Si-based silicene was realized by molecular beam epitaxy (MBE) growth. Ge-based germanene was realized by mechanical exfoliation. Sn-based stanene has its unique properties. Stanene and its derivatives can be 2D topological insulators (TI) with a very large band gap as proposed by first-principles calculations, or can support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall (QAH) effect. For the first time, in this work, we report a successful fabrication of 2D stanene by MBE. The atomic and electronic structures were determined by scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) in combination with first-principles calculations. This work will stimulate the experimental study and exploring the future application of stanene. In cooperation with Fengfeng Zhu, Wei-jiong Chen, Yong Xu, Chun-lei Gao, Dan-dan Guan, Canhua Liu, Dong Qian, Shou-Cheng Zhang.
Epitaxial growth of two-dimensional stanene
NASA Astrophysics Data System (ADS)
Zhu, Feng-Feng; Chen, Wei-Jiong; Xu, Yong; Gao, Chun-Lei; Guan, Dan-Dan; Liu, Can-Hua; Qian, Dong; Zhang, Shou-Cheng; Jia, Jin-Feng
2015-10-01
Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect.
Two-dimensional dipolar nematic colloidal crystals.
Skarabot, M; Ravnik, M; Zumer, S; Tkalec, U; Poberaj, I; Babic, D; Osterman, N; Musevic, I
2007-11-01
We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal. PMID:18233658
Light evolution in arbitrary two-dimensional waveguide arrays
Szameit, Alexander; Pertsch, Thomas; Dreisow, Felix; Nolte, Stefan; Tuennermann, Andreas; Peschel, Ulf; Lederer, Falk
2007-05-15
We introduce an analytical formula for the dynamics of light propagation in a two-dimensional waveguide lattice including diagonal coupling. A superposition of infinite arrays created by imaginary sources is used to derive an expression for boundary reflections. It is shown analytically that for large propagation distances the propagating field reaches uniformity. Furthermore, periodic field recovery is studied and discrete anomalous refraction and diffraction are investigated in arbitrary two-dimensional lattices.
On 2D bisection method for double eigenvalue problems
Ji, X.
1996-06-01
The two-dimensional bisection method presented in (SIAM J. Matrix Anal. Appl. 13(4), 1085 (1992)) is efficient for solving a class of double eigenvalue problems. This paper further extends the 2D bisection method of full matrix cases and analyses its stability. As in a single parameter case, the 2D bisection method is very stable for the tridiagonal matrix triples satisfying the symmetric-definite condition. Since the double eigenvalue problems arise from two-parameter boundary value problems, an estimate of the discretization error in eigenpairs is also given. Some numerical examples are included. 42 refs., 1 tab.
Cloaking two-dimensional fermions
Lin, De-Hone
2011-09-15
A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.
Two-dimensional cyanates: stabilization through hydrogenation.
Tsetseris, Leonidas
2016-06-01
According to first-principles calculations, it should be possible to grow two-dimensional (2D) forms of copper thio-cyanate (CuSCN) and copper seleno-cyanate (CuSeCN) since their energies are only marginally higher than those of their most stable three-dimensional (3D) wurtzite structures. Here we show using the same theoretical approach that chemisorption reactions of hydrogen molecules with the above-mentioned 2D CuSCN and CuSeCN systems enhance their stability as they decrease the energy difference with respect to the corresponding hydrogenated forms of the wurtzite crystals. Hydrogenation causes a sizeable decrease in the energy band gap by 0.56 eV and 0.65 eV for hydrogenated 2D-CuSCN (CuSCNH2) and 2D-CuSeCN (CuSeCNH2), respectively. Finally, we describe the stability of hydrogen vacancies in CuSCNH2 and CuSeCNH2 and show that the presence of isolated single H vacancies or di-vacancies does not affect significantly the electronic properties of the host systems close to the valence and conduction band edges. PMID:27183226
Two-dimensional atomic crystals beyond graphene
NASA Astrophysics Data System (ADS)
Kaul, Anupama B.
2014-06-01
Carbon-based nanostructures have been the center of intense research and development for more than two decades now. Of these materials, graphene, a two-dimensional (2D) layered material system, has had a significant impact on science and technology over the past decade after monolayers of this material were experimentally isolated in 2004. The recent emergence of other classes of 2D graphene-like layered materials has added yet more exciting dimensions for research in exploring the diverse properties and applications arising from these 2D material systems. For example, hexagonal-BN, a layered material closest in structure to graphene, is an insulator, while NbSe2, a transition metal di-chalcogenide, is metallic and monolayers of other transition metal di-chalcogenides such as MoS2 are direct band-gap semiconductors. The rich spectrum of properties that 2D layered material systems offer can potentially be engineered ondemand, and creates exciting prospects for using such materials in applications ranging from electronics, sensing, photonics, energy harvesting and flexible electronics over the coming years.
Two-dimensional vibrational-electronic spectroscopy
NASA Astrophysics Data System (ADS)
Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.; Khalil, Munira
2015-10-01
Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (νCN) and either a ligand-to-metal charge transfer transition ([FeIII(CN)6]3- dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN)5FeIICNRuIII(NH3)5]- dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific νCN modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a wide range of complex molecular, material, and biological systems.
Two-dimensional vibrational-electronic spectroscopy
Courtney, Trevor L.; Fox, Zachary W.; Slenkamp, Karla M.; Khalil, Munira
2015-10-21
Two-dimensional vibrational-electronic (2D VE) spectroscopy is a femtosecond Fourier transform (FT) third-order nonlinear technique that creates a link between existing 2D FT spectroscopies in the vibrational and electronic regions of the spectrum. 2D VE spectroscopy enables a direct measurement of infrared (IR) and electronic dipole moment cross terms by utilizing mid-IR pump and optical probe fields that are resonant with vibrational and electronic transitions, respectively, in a sample of interest. We detail this newly developed 2D VE spectroscopy experiment and outline the information contained in a 2D VE spectrum. We then use this technique and its single-pump counterpart (1D VE) to probe the vibrational-electronic couplings between high frequency cyanide stretching vibrations (ν{sub CN}) and either a ligand-to-metal charge transfer transition ([Fe{sup III}(CN){sub 6}]{sup 3−} dissolved in formamide) or a metal-to-metal charge transfer (MMCT) transition ([(CN){sub 5}Fe{sup II}CNRu{sup III}(NH{sub 3}){sub 5}]{sup −} dissolved in formamide). The 2D VE spectra of both molecules reveal peaks resulting from coupled high- and low-frequency vibrational modes to the charge transfer transition. The time-evolving amplitudes and positions of the peaks in the 2D VE spectra report on coherent and incoherent vibrational energy transfer dynamics among the coupled vibrational modes and the charge transfer transition. The selectivity of 2D VE spectroscopy to vibronic processes is evidenced from the selective coupling of specific ν{sub CN} modes to the MMCT transition in the mixed valence complex. The lineshapes in 2D VE spectra report on the correlation of the frequency fluctuations between the coupled vibrational and electronic frequencies in the mixed valence complex which has a time scale of 1 ps. The details and results of this study confirm the versatility of 2D VE spectroscopy and its applicability to probe how vibrations modulate charge and energy transfer in a
Universal Conductance Fluctuation in Two-Dimensional Topological Insulators
Choe, Duk-Hyun; Chang, K. J.
2015-01-01
Despite considerable interest in two-dimensional (2D) topological insulators (TIs), a fundamental question still remains open how mesoscopic conductance fluctuations in 2D TIs are affected by spin-orbit interaction (SOI). Here, we investigate the effect of SOI on the universal conductance fluctuation (UCF) in disordered 2D TIs. Although 2D TI exhibits UCF like any metallic systems, the amplitude of these fluctuations is distinguished from that of conventional spin-orbit coupled 2D materials. Especially, in 2D systems with mirror symmetry, spin-flip scattering is forbidden even in the presence of strong intrinsic SOI, hence increasing the amplitude of the UCF by a factor of compared with extrinsic SOI that breaks mirror symmetry. We propose an easy way to experimentally observe the existence of such spin-flip scattering in 2D materials. Our findings provide a key to understanding the emergence of a new universal behavior in 2D TIs. PMID:26055574
Practical Algorithm For Computing The 2-D Arithmetic Fourier Transform
NASA Astrophysics Data System (ADS)
Reed, Irving S.; Choi, Y. Y.; Yu, Xiaoli
1989-05-01
Recently, Tufts and Sadasiv [10] exposed a method for computing the coefficients of a Fourier series of a periodic function using the Mobius inversion of series. They called this method of analysis the Arithmetic Fourier Transform(AFT). The advantage of the AFT over the FN 1' is that this method of Fourier analysis needs only addition operations except for multiplications by scale factors at one stage of the computation. The disadvantage of the AFT as they expressed it originally is that it could be used effectively only to compute finite Fourier coefficients of a real even function. To remedy this the AFT developed in [10] is extended in [11] to compute the Fourier coefficients of both the even and odd components of a periodic function. In this paper, the improved AFT [11] is extended to a two-dimensional(2-D) Arithmetic Fourier Transform for calculating the Fourier Transform of two-dimensional discrete signals. This new algorithm is based on both the number-theoretic method of Mobius inversion of double series and the complex conjugate property of Fourier coefficients. The advantage of this algorithm over the conventional 2-D FFT is that the corner-turning problem needed in a conventional 2-D Discrete Fourier Transform(DFT) can be avoided. Therefore, this new 2-D algorithm is readily suitable for VLSI implementation as a parallel architecture. Comparing the operations of 2-D AFT of a MxM 2-D data array with the conventional 2-D FFT, the number of multiplications is significantly reduced from (2log2M)M2 to (9/4)M2. Hence, this new algorithm is faster than the FFT algorithm. Finally, two simulation results of this new 2-D AFT algorithm for 2-D artificial and real images are given in this paper.
NASA Astrophysics Data System (ADS)
Vilardy, Juan M.; Giacometto, F.; Torres, C. O.; Mattos, L.
2011-01-01
The two-dimensional Fast Fourier Transform (FFT 2D) is an essential tool in the two-dimensional discrete signals analysis and processing, which allows developing a large number of applications. This article shows the description and synthesis in VHDL code of the FFT 2D with fixed point binary representation using the programming tool Simulink HDL Coder of Matlab; showing a quick and easy way to handle overflow, underflow and the creation registers, adders and multipliers of complex data in VHDL and as well as the generation of test bench for verification of the codes generated in the ModelSim tool. The main objective of development of the hardware architecture of the FFT 2D focuses on the subsequent completion of the following operations applied to images: frequency filtering, convolution and correlation. The description and synthesis of the hardware architecture uses the XC3S1200E family Spartan 3E FPGA from Xilinx Manufacturer.
Two-dimensional thermofield bosonization
Amaral, R.L.P.G.
2005-12-15
The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.
Two dimensional unstable scar statistics.
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.
Two-Dimensional Optical Storage
NASA Astrophysics Data System (ADS)
van der Lee, Alexander; Bruls, Dominique; Busch, Christopher; Immink, Andre; Coene, Wim; Hekstra, Andries
2004-07-01
Two-dimensional optical storage aims at increasing the data capacity and data rate for a given physical read-out system. It uses parallel read-out in combination with advanced signal-processing. Experimental results results on read only memory (ROM) discs are presented that proof the concept. Laser beam recorded discs proof the concept, and electron beam recorded disc show the feasibility at real physical parameters for a density at 35 GB with ample tilt margins.
Two-dimensional soft nanomaterials: a fascinating world of materials.
Zhuang, Xiaodong; Mai, Yiyong; Wu, Dongqing; Zhang, Fan; Feng, Xinliang
2015-01-21
The discovery of graphene has triggered great interest in two-dimensional (2D) nanomaterials for scientists in chemistry, physics, materials science, and related areas. In the family of newly developed 2D nanostructured materials, 2D soft nanomaterials, including graphene, Bx Cy Nz nanosheets, 2D polymers, covalent organic frameworks (COFs), and 2D supramolecular organic nanostructures, possess great advantages in light-weight, structural control and flexibility, diversity of fabrication approaches, and so on. These merits offer 2D soft nanomaterials a wide range of potential applications, such as in optoelectronics, membranes, energy storage and conversion, catalysis, sensing, biotechnology, etc. This review article provides an overview of the development of 2D soft nanomaterials, with special highlights on the basic concepts, molecular design principles, and primary synthesis approaches in the context.
Two-dimensional heterostructures: fabrication, characterization, and application
Wang, Hong; Liu, Fucai; Fu, Wei; Fang, Zheyu; Zhou, Wu; Liu, Zheng
2014-08-13
Two-dimensional (2D) materials such as graphene, hexagonal boron nitrides (hBN), and transition metal dichalcogenides (TMDs, e.g., MoS2) have attracted considerable attention in the past few years because of their novel properties and versatile potential applications. These 2D layers can be integrated into a monolayer (lateral 2D heterostructure) or a multilayer stack (vertical 2D heterostructure). The resulting artificial 2D structures provide access to new properties and applications beyond their component 2D atomic crystals and hence, they are emerging as a new exciting field of research. Lastly, in this article, we review recent progress on the fabrication, characterization, and applications of variousmore » 2D heterostructures.« less
Two-dimensional heterostructures: fabrication, characterization, and application
Wang, Hong; Liu, Fucai; Fu, Wei; Fang, Zheyu; Zhou, Wu; Liu, Zheng
2014-08-13
Two-dimensional (2D) materials such as graphene, hexagonal boron nitrides (hBN), and transition metal dichalcogenides (TMDs, e.g., MoS_{2}) have attracted considerable attention in the past few years because of their novel properties and versatile potential applications. These 2D layers can be integrated into a monolayer (lateral 2D heterostructure) or a multilayer stack (vertical 2D heterostructure). The resulting artificial 2D structures provide access to new properties and applications beyond their component 2D atomic crystals and hence, they are emerging as a new exciting field of research. Lastly, in this article, we review recent progress on the fabrication, characterization, and applications of various 2D heterostructures.
Seismic isolation of two dimensional periodic foundations
Yan, Y.; Mo, Y. L.; Laskar, A.; Cheng, Z.; Shi, Z.; Menq, F.; Tang, Y.
2014-07-28
Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.
Photodetectors based on two dimensional materials
NASA Astrophysics Data System (ADS)
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.
Viscoelastic effects in a two-dimensional classical electron liquid
NASA Astrophysics Data System (ADS)
Mehrotra, Ravi
1987-08-01
The shear viscosity of a classical two-dimensional (2D) electron liquid is estimated by adapting the theory of Kirkwood, Buff, and Green for three dimensions to two dimensions. It is found to be large enough so that shear modes, if not overdamped by other scattering mechanisms, should be able to propagate through the electron liquid above a minimum temperature-dependent frequency, which is a small fraction of the highest frequency in the corresponding 2D electron solid.
An integrated microfluidic device for two-dimensional combinatorial dilution†
Jang, Yun-Ho; Hancock, Matthew J.; Kim, Sang Bok; Selimović, Šeila; Sim, Woo Young; Bae, Hojae; Khademhosseini, Ali
2012-01-01
High-throughput preparation of multi-component solutions is an integral process in biology, chemistry and materials science for screening, diagnostics and analysis. Compact microfluidic systems enable such processing with low reagent volumes and rapid testing. Here we present a microfluidic device that incorporates two gradient generators, a tree-like generator and a new microfluidic active injection system, interfaced by intermediate solution reservoirs to generate diluted combinations of input solutions within an 8 × 8 or 10 × 10 array of isolated test chambers. Three input solutions were fed into the device, two to the tree-like gradient generator and one to pre-fill the test chamber array. The relative concentrations of these three input solutions in the test chambers completely characterized device behaviour and were controlled by the number of injection cycles and the flow rate. Device behaviour was modelled by computational fluid dynamics simulations and an approximate analytic formula. The device may be used for two-dimensional (2D) combinatorial dilution by adding two solutions in different relative concentrations to each of its three inputs. By appropriate choice of the two-component input solutions, test chamber concentrations that span any triangle in 2D concentration space may be obtained. In particular, explicit inputs are given for a coarse screening of a large region in concentration space followed by a more refined screening of a smaller region, including alternate inputs that span the same concentration region but with different distributions. The ability to probe arbitrary subspaces of concentration space and to control the distribution of discrete test points within those subspaces makes the device of potential benefit for high-throughput cell biology studies and drug screening. PMID:21837312
Two-dimensional signal processing with application to image restoration
NASA Technical Reports Server (NTRS)
Assefi, T.
1974-01-01
A recursive technique for modeling and estimating a two-dimensional signal contaminated by noise is presented. A two-dimensional signal is assumed to be an undistorted picture, where the noise introduces the distortion. Both the signal and the noise are assumed to be wide-sense stationary processes with known statistics. Thus, to estimate the two-dimensional signal is to enhance the picture. The picture representing the two-dimensional signal is converted to one dimension by scanning the image horizontally one line at a time. The scanner output becomes a nonstationary random process due to the periodic nature of the scanner operation. Procedures to obtain a dynamical model corresponding to the autocorrelation function of the scanner output are derived. Utilizing the model, a discrete Kalman estimator is designed to enhance the image.
NASA Astrophysics Data System (ADS)
Oppel, M.; Paramonov, G. K.
1998-06-01
Selective excitation of the vibrational bound and the continuum states, controlled by subpicosecond infrared (IR) laser pulses, is simulated within the Schrödinger wave function formalism for a two-dimensional model of the HONO 2 molecule in the ground electronic state. State-selective excitation of the OH bond is achieved by single optimal laser pulses, with the probability being 97% for the bound states and more than 91% for the resonances. Stable, long-living continuum states are prepared with more than 96% probability by two optimal laser pulses, with the expectation energy of the molecule being well above the dissociation threshold of the ON single bond, and its life-time being at least 100 ps. The length of the ON single bond can be controlled selectively: stretching and contraction by about 45% of its equilibrium length are demonstrated. Laser separation of spatial conformers of HONO 2 in inhomogeneous conditions occurring on an anisotropic surface or created by a direct current (DC) electric field is analysed. The relative yields of target conformers may be very high, ranging from 10 to 10 8, and the absolute yields of up to 40% and more are calculated.
Two-dimensional swimming behavior of bacteria
NASA Astrophysics Data System (ADS)
Li, Ye; Zhai, He; Sanchez, Sandra; Kearns, Daniel; Wu, Yilin
Many bacteria swim by flagella motility which is essential for bacterial dispersal, chemotaxis, and pathogenesis. Here we combined single-cell tracking, theoretical analysis, and computational modeling to investigate two-dimensional swimming behavior of a well-characterized flagellated bacterium Bacillus subtilis at the single-cell level. We quantified the 2D motion pattern of B. subtilis in confined space and studied how cells interact with each other. Our findings shed light on bacterial colonization in confined environments, and will serve as the ground for building more accurate models to understand bacterial collective motion. Mailing address: Room 306 Science Centre North Block, The Chinese University of Hong Kong, Shatin, N.T. Hong Kong SAR. Phone: +852-3943-6354. Fax: +852-2603-5204. E-mail: ylwu@phy.cuhk.edu.hk.
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.
Two-dimensional fourier transform spectrometer
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.
Equilibrium structural properties of two-dimensional nonideal systems
NASA Astrophysics Data System (ADS)
Vaulina, O. S.; Vasilieva, E. V.; Petrov, O. F.; Fortov, V. E.
2011-12-01
The pair correlation functions and the mean squared displacements of charged dust particles were studied experimentally for quasi-two-dimensional (2D) nonideal systems. The experiments were carried out in a plasma of a capacitive radio-frequency (RF-) discharge in argon for monolayers of monodispersed (melamine formaldehyde) spheres. A comparison with the existing theoretical and numerical data is presented.
Adapting Grids For Computing Two-Dimensional Flows
NASA Technical Reports Server (NTRS)
Davies, Carol B.; Venkatapathy, Ethiraj
1992-01-01
SAGE2D is two-dimensional implementation of Self Adaptive Grid Evolution computer program that intelligently redistributes initial grid points on basis of initial flow-field solution. Grids modified according to initial computed flows enabling recomputation at greater accuracy. Written in FORTRAN 77.
2011-12-31
Mesh2d is a Fortran90 program designed to generate two-dimensional structured grids of the form [x(i),y(i,j)] where [x,y] are grid coordinates identified by indices (i,j). The x(i) coordinates alone can be used to specify a one-dimensional grid. Because the x-coordinates vary only with the i index, a two-dimensional grid is composed in part of straight vertical lines. However, the nominally horizontal y(i,j0) coordinates along index i are permitted to undulate or otherwise vary. Mesh2d also assignsmore » an integer material type to each grid cell, mtyp(i,j), in a user-specified manner. The complete grid is specified through three separate input files defining the x(i), y(i,j), and mtyp(i,j) variations.« less
Two-dimensional material confined water.
Li, Qiang; Song, Jie; Besenbacher, Flemming; Dong, Mingdong
2015-01-20
CONSPECTUS: The interface between water and other materials under ambient conditions is of fundamental importance due to its relevance in daily life and a broad range of scientific research. The structural and dynamic properties of water at an interface have been proven to be significantly difference than those of bulk water. However, the exact nature of these interfacial water adlayers at ambient conditions is still under debate. Recent scanning probe microscopy (SPM) experiments, where two-dimensional (2D) materials as ultrathin coatings are utilized to assist the visualization of interfacial water adlayers, have made remarkable progress on interfacial water and started to clarify some of these fundamental scientific questions. In this Account, we review the recently conducted research exploring the properties of confined water between 2D materials and various surfaces under ambient conditions. Initially, we review the earlier studies of water adsorbed on hydrophilic substrates under ambient conditions in the absence of 2D coating materials, which shows the direct microscopic results. Subsequently, we focus on the studies of water adlayer growth at both hydrophilic and hydrophobic substrates in the presence of 2D coating materials. Ice-like water adlayers confined between hydrophobic graphene and hydrophilic substrates can be directly observed in detail by SPM. It was found that the packing structure of the water adlayer was determined by the hydrophilic substrates, while the orientation of intercalation water domains was directed by the graphene coating. In contrast to hydrophilic substrates, liquid-like nanodroplets confined between hydrophobic graphene and hydrophobic substrates appear close to step edges and atomic-scale surface defects, indicating that atomic-scale surface defects play significant roles in determining the adsorption of water on hydrophobic substrates. In addition, we also review the phenomena of confined water between 2D hydrophilic MoS2 and
Two-dimensional material confined water.
Li, Qiang; Song, Jie; Besenbacher, Flemming; Dong, Mingdong
2015-01-20
CONSPECTUS: The interface between water and other materials under ambient conditions is of fundamental importance due to its relevance in daily life and a broad range of scientific research. The structural and dynamic properties of water at an interface have been proven to be significantly difference than those of bulk water. However, the exact nature of these interfacial water adlayers at ambient conditions is still under debate. Recent scanning probe microscopy (SPM) experiments, where two-dimensional (2D) materials as ultrathin coatings are utilized to assist the visualization of interfacial water adlayers, have made remarkable progress on interfacial water and started to clarify some of these fundamental scientific questions. In this Account, we review the recently conducted research exploring the properties of confined water between 2D materials and various surfaces under ambient conditions. Initially, we review the earlier studies of water adsorbed on hydrophilic substrates under ambient conditions in the absence of 2D coating materials, which shows the direct microscopic results. Subsequently, we focus on the studies of water adlayer growth at both hydrophilic and hydrophobic substrates in the presence of 2D coating materials. Ice-like water adlayers confined between hydrophobic graphene and hydrophilic substrates can be directly observed in detail by SPM. It was found that the packing structure of the water adlayer was determined by the hydrophilic substrates, while the orientation of intercalation water domains was directed by the graphene coating. In contrast to hydrophilic substrates, liquid-like nanodroplets confined between hydrophobic graphene and hydrophobic substrates appear close to step edges and atomic-scale surface defects, indicating that atomic-scale surface defects play significant roles in determining the adsorption of water on hydrophobic substrates. In addition, we also review the phenomena of confined water between 2D hydrophilic MoS2 and
Two-dimensional colloidal alloys.
Law, Adam D; Buzza, D Martin A; Horozov, Tommy S
2011-03-25
We study the structure of mixed monolayers of large (3 μm diameter) and small (1 μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations. PMID:21517357
Two-Dimensional Colloidal Alloys
NASA Astrophysics Data System (ADS)
Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.
2011-03-01
We study the structure of mixed monolayers of large (3μm diameter) and small (1μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.
Two-dimensional crystals: managing light for optoelectronics.
Eda, Goki; Maier, Stefan A
2013-07-23
Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light-matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.
Two-Dimensional Layered Materials-Based Spintronics
NASA Astrophysics Data System (ADS)
Su, Guohui; Wu, Xing; Tong, Wenqi; Duan, Chungang
2015-12-01
The recent emergence of two-dimensional (2D) layered materials — graphene and transition metal dichalcogenides — opens a new avenue for exploring the internal quantum degrees of freedom of electrons and their potential for new electronics. Here, we provide a brief review of experimental achievements concerning electrical spin injection, spin transport, graphene nanoribbons spintronics and transition metal dichalcogenides spin and pseudospins. Future research in 2D layered materials spintronics will need to address the development of applications such as spin transistors and spin logic devices, as well as exotic physical properties including pseudospins-valley phenomena in graphene and other 2D materials.
Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs.
Mannix, Andrew J; Zhou, Xiang-Feng; Kiraly, Brian; Wood, Joshua D; Alducin, Diego; Myers, Benjamin D; Liu, Xiaolong; Fisher, Brandon L; Santiago, Ulises; Guest, Jeffrey R; Yacaman, Miguel Jose; Ponce, Arturo; Oganov, Artem R; Hersam, Mark C; Guisinger, Nathan P
2015-12-18
At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal.
Independent Pixel and Two Dimensional Estimates of LANDSAT-Derived Cloud Field Albedo
NASA Technical Reports Server (NTRS)
Chambers, L. H.; Wielicki, Bruce A.; Evans, K. F.
1996-01-01
A theoretical study has been conducted on the effects of cloud horizontal inhomogeneity on cloud albedo bias. A two-dimensional (2D) version of the Spherical Harmonic Discrete Ordinate Method (SHDOM) is used to estimate the albedo bias of the plane parallel (PP-IPA) and independent pixel (IPA-2D) approximations for a wide range of 2D cloud fields obtained from LANDSAT. They include single layer trade cumulus, open and closed cell broken stratocumulus, and solid stratocumulus boundary layer cloud fields over ocean. Findings are presented on a variety of averaging scales and are summarized as a function of cloud fraction, mean cloud optical depth, cloud aspect ratio, standard deviation of optical depth, and the gamma function parameter Y (a measure of the width of the optical depth distribution). Biases are found to be small for small cloud fraction or mean optical depth, where the cloud fields under study behave linearly. They are large (up to 0.20 for PP-IPA bias, -0.12 for IPA-2D bias) for large v. On a scene average basis PP-IPA bias can reach 0.30, while IPA-2D bias reaches its largest magnitude at -0.07. Biases due to horizontal transport (IPA-2D) are much smaller than PP-IPA biases but account for 20% RMS of the bias overall. Limitations of this work include the particular cloud field set used, assumptions of conservative scattering, constant cloud droplet size, no gas absorption or surface reflectance, and restriction to 2D radiative transport. The LANDSAT data used may also be affected by radiative smoothing.
Two-dimensional Gel Electrophoresis (2DE)
NASA Astrophysics Data System (ADS)
Kłodzińska, Ewa; Buszewski, Bogusław
The chemical compounds, which are present in the environment, increasingly cause bad effects on health. The most serious effects are tumors and various mutations at the cellular level. Such compounds, from the analytical point of view, can serve the function of biomarkers, constituting measurable changes in the organism's cells and biochemical processes occurring therein. The challenge of the twenty-first century is therefore searching for effective and reliable methods of identification of biomarkers as well as understanding bodily functions, which occur in living organisms at the molecular level. The irreplaceable tool for these examinations is proteomics, which includes both quality and quantity analysis of proteins composition, and also makes it possible to learn their functions and expressions. The success of proteomics examinations lies in the usage of innovative analytical techniques, such as electromigration technique, two-dimensional electrophoresis in polyacrylamide gel (2D PAGE), liquid chromatography, together with high resolution mass spectrometry and bio-informatical data analysis. Proteomics joins together a number of techniques used for analysis of hundreds or thousands of proteins. Its main task is not the examination of proteins inside the particular tissue but searching for the differences in the proteins' profile between bad and healthy tissues. These differences can tell us a lot regarding the cause of the sickness as well as its consequences. For instance, using the proteomics analysis it is possible to find relatively fast new biomarkers of tumor diseases, which in the future will be used for both screening and foreseeing the course of illness. In this chapter we focus on two-dimensional electrophoresis because as it seems, it may be of enormous importance when searching for biomarkers of cancer diseases.
Nanoscale integration of two-dimensional materials by lateral heteroepitaxy.
Sutter, Peter; Huang, Yuan; Sutter, Eli
2014-08-13
Materials integration in heterostructures with novel properties different from those of the constituents has become one of the most powerful concepts of modern materials science. Two-dimensional (2D) crystals represent a new class of materials from which such engineered structures can be envisioned. Calculations have predicted emergent properties in 2D heterostructures with nanoscale feature sizes, but methods for their controlled fabrication have been lacking. Here, we use sequential graphene and boron nitride growth on Ru(0001) to show that lateral heteroepitaxy, the joining of 2D materials by preferential incorporation of different atomic species into exposed 1D edges during chemical vapor deposition on a metal substrate, can be used for the bottom-up synthesis of 2D heterostructures with characteristic dimensions on the nanoscale. Our results suggest that on a proper substrate, this method lends itself to building nanoheterostructures from a wide range of 2D materials.
Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons
NASA Astrophysics Data System (ADS)
Alekseev, P. S.
2016-10-01
At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.
Fourier analysis of cell-wise Block-Jacobi splitting in two-dimensional geometry
Rosa, Massimiliano; Warsa, James S; Kelley, Timothy M
2009-01-01
A Fourier analysis is conducted in two-dimensional (2D) geometry for the discrete-ordinates (SN) approximation of the neutron transport problem solved with Richardson iteration (Source Iteration) using the cell-wise Block-Jacobi (B1) algorithm. The results of the Fourier analysis show that convergence of cell-wise BJ can degrade, leading to a spectral radius equal to 1, in problems containing optically thin cells. For problems containing cells that are optically thick, instead, the spectral radius tends to O. Hence, in the optically thick-cell regime, cell-wise BJ is rapidly convergent even for problems that are scattering dominated, with a scattering ratio c close to I.
Design of an effective energy storage cavity in two-dimensional photonic crystal slab
NASA Astrophysics Data System (ADS)
Liu, Yazhao; Salemink, H. W. M.
2012-06-01
A design of a point-defect cavity in two-dimensional photonic crystal slab with both high Q factor and high transmission intensity has been achieved by adjusting the radii and position of lattice points in both parallel and perpendicular directions. Analysis shows that discrete resonant modes have been found in the 1550 wavelength range with Q factors up to 40,000. Moreover, the cavity was verified to subject to minor intensity decrease of 1.2 dB due to the introducing of external waveguide access. All these features make the cavity a very promising candidate for light transmission and detection in practical application. We also demonstrate the potential application of such a cavity being used as a sensitive index sensor with a high sensitivity of 400nm/refractive index unit.
Two-dimensional electronic spectroscopy using incoherent light: theoretical analysis.
Turner, Daniel B; Howey, Dylan J; Sutor, Erika J; Hendrickson, Rebecca A; Gealy, M W; Ulness, Darin J
2013-07-25
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 new opportunities.
Two-Dimensional Recall: Immediate Identification of Clusters in Episodic and Semantic Memory
ERIC Educational Resources Information Center
Buschke, Herman
1977-01-01
To show the organization of recall, items that are remembered together can be written on the same line of a two-dimensional (2D) grid. Such 2D recall does not induce the clustering it reveals. Various aspects of 2D recall and the clustering it reveals are discussed. (Author/RM)
Creating tuneable microwave media from a two-dimensional lattice of re-entrant posts
Goryachev, Maxim; Tobar, Michael E.
2015-11-28
The potential capabilities of resonators based on two dimensional arrays of re-entrant posts is demonstrated. Such posts may be regarded as magnetically coupled lumped element microwave harmonic oscillators, arranged in a 2D lattices structure, which is enclosed in a 3D cavity. By arranging these elements in certain 2D patterns, we demonstrate how to achieve certain requirements with respect to field localisation and device spectra. Special attention is paid to symmetries of the lattices, mechanical tuning, design of areas of high localisation of magnetic energy; this in turn creates unique discrete mode spectra. We demonstrate analogies between systems designed on the proposed platform and well known physical phenomena such as polarisation, frustration, and Whispering Gallery Modes. The mechanical tunability of the cavity with multiple posts is analysed, and its consequences to optomechanical applications is calculated. One particular application to quantum memory is demonstrated with a cavity design consisting of separate resonators analogous to discrete Fabry–Pérot resonators. Finally, we propose a generalised approach to a microwave system design based on the concept of Programmable Cavity Arrays.
Phase-sensitive two-dimensional neutron shearing interferometer and Hartmann sensor
Baker, Kevin
2015-12-08
A neutron imaging system detects both the phase shift and absorption of neutrons passing through an object. The neutron imaging system is based on either of two different neutron wavefront sensor techniques: 2-D shearing interferometry and Hartmann wavefront sensing. Both approaches measure an entire two-dimensional neutron complex field, including its amplitude and phase. Each measures the full-field, two-dimensional phase gradients and, concomitantly, the two-dimensional amplitude mapping, requiring only a single measurement.
Two-dimensional dynamic fluid bowtie attenuators.
Hermus, James R; Szczykutowicz, Timothy P
2016-01-01
Fluence field modulated (FFM) CT allows for improvements in image quality and dose reduction. To date, only one-dimensional modulators have been proposed, as the extension to two-dimensional (2-D) modulation is difficult with solid-metal attenuation-based fluence field modulated designs. This work proposes to use liquid and gas to attenuate the x-ray beam, as unlike solids, these materials can be arranged allowing for 2-D fluence modulation. The thickness of liquid and the pressure for a given path length of gas were determined that provided the same attenuation as 30 cm of soft tissue at 80, 100, 120, and 140 kV. Liquid iodine, zinc chloride, cerium chloride, erbium oxide, iron oxide, and gadolinium chloride were studied. Gaseous xenon, uranium hexafluoride, tungsten hexafluoride, and nickel tetracarbonyl were also studied. Additionally, we performed a proof-of-concept experiment using a 96 cell array in which the liquid thickness in each cell was adjusted manually. Liquid thickness varied as a function of kV and chemical composition, with erbium oxide allowing for the smallest thickness. For the gases, tungsten hexaflouride required the smallest pressure to compensate for 30 cm of soft tissue. The 96 cell iodine attenuator allowed for a reduction in both dynamic range to the detector and scatter-to-primary ratio. For both liquids and gases, when k-edges were located within the diagnostic energy range used for imaging, the mean beam energy exhibited the smallest change with compensation amount. The thickness of liquids and the gas pressure seem logistically implementable within the space constraints of C-arm-based cone beam CT (CBCT) and diagnostic CT systems. The gas pressures also seem logistically implementable within the space and tube loading constraints of CBCT and diagnostic CT systems. PMID:26835499
Band engineering for novel two-dimensional atomic layers.
Zeng, Qingsheng; Wang, Hong; Fu, Wei; Gong, Yongji; Zhou, Wu; Ajayan, Pulickel M; Lou, Jun; Liu, Zheng
2015-04-24
The discovery of graphene has sparked much interest in science and lead to the development of an ample variety of novel two-dimensional (2D) materials. With increasing research interest in the field of 2D materials in recent years, the researchers have shifted their focus from the synthesis to the modification of 2D materials, emphasizing their electronic structures. In this review, the possibilities of altering the band structures are discussed via three different approches: (1) alloying 2D materials, so called ternary 2D materials, such as hexagonal carbonized boron nitrides (h-BCN) and transition metal dichalcogenides (TMDs) ternary materials; (2) stacking 2D materials vertically, which results in 2D heterostructures named van der Waals (vdW) solids (using hexagonal boron nitrides (h-BN)/graphene and TMDs stacking as examples), and growing lateral TMDs heterostructrues; (3) controlling the thickness of 2D materials, that is, the number of layers. The electronic properties of some 2D materials are very sensitive to the thickness, such as in TMDs and black phosphorus (BP). The variations of band structures and the resulting physical properties are systematically discussed.
Development of Novel Two-dimensional Layers, Alloys and Heterostructures
NASA Astrophysics Data System (ADS)
Liu, Zheng
2015-03-01
The one-atom-think graphene has fantastic properties and attracted tremendous interests in these years, which opens a window towards various two-dimensional (2D) atomic layers. However, making large-size and high-quality 2D layers is still a great challenge. Using chemical vapor deposition (CVD) method, we have successfully synthesized a wide varieties of highly crystalline and large scale 2D atomic layers, including h-BN, metal dichalcogenides e.g. MoS2, WS2, CdS, GaSe and MoSe2 which belong to the family of binary 2D materials. Ternary 2D alloys including BCN and MoS2xSe2 (1 - x) are also prepared and characterized. In addition, synthesis of 2D heterostructures such as vertical and lateral graphene/h-BN, vertical and lateral TMDs are also demonstrated. Complementary to CVD grown 2D layers, 2D single-crystal (bulk) such as Phosphorene (P), WTe2, SnSe2, PtS2, PtSe2, PdSe2, WSe2xTe2 (1 - x), Ta2NiS5andTa2NiSe5 are also prepared by solid reactions. There work provide a better understanding of the atomic layered materials in terms of the synthesis, atomic structure, alloying and their physical properties. Potential applications of these 2D layers e.g. optoelectronic devices, energy device and smart coating have been explored.
Transport behavior of water molecules through two-dimensional nanopores.
Zhu, Chongqin; Li, Hui; Meng, Sheng
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
2014-11-14
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.
Current status of one- and two-dimensional numerical models: Successes and limitations
NASA Technical Reports Server (NTRS)
Schwartz, R. J.; Gray, J. L.; Lundstrom, M. S.
1985-01-01
The capabilities of one and two-dimensional numerical solar cell modeling programs (SCAP1D and SCAP2D) are described. The occasions when a two-dimensional model is required are discussed. The application of the models to design, analysis, and prediction are presented along with a discussion of problem areas for solar cell modeling.
2d PDE Linear Symmetric Matrix Solver
1983-10-01
ICCG2 (Incomplete Cholesky factorized Conjugate Gradient algorithm for 2d symmetric problems) was developed to solve a linear symmetric matrix system arising from a 9-point discretization of two-dimensional elliptic and parabolic partial differential equations found in plasma physics applications, such as resistive MHD, spatial diffusive transport, and phase space transport (Fokker-Planck equation) problems. These problems share the common feature of being stiff and requiring implicit solution techniques. When these parabolic or elliptic PDE''s are discretized withmore » finite-difference or finite-element methods,the resulting matrix system is frequently of block-tridiagonal form. To use ICCG2, the discretization of the two-dimensional partial differential equation and its boundary conditions must result in a block-tridiagonal supermatrix composed of elementary tridiagonal matrices. The incomplete Cholesky conjugate gradient algorithm is used to solve the linear symmetric matrix equation. Loops are arranged to vectorize on the Cray1 with the CFT compiler, wherever possible. Recursive loops, which cannot be vectorized, are written for optimum scalar speed. For matrices lacking symmetry, ILUCG2 should be used. Similar methods in three dimensions are available in ICCG3 and ILUCG3. A general source containing extensions and macros, which must be processed by a pre-compiler to obtain the standard FORTRAN source, is provided along with the standard FORTRAN source because it is believed to be more readable. The pre-compiler is not included, but pre-compilation may be performed by a text editor as described in the UCRL-88746 Preprint.« less
2d PDE Linear Asymmetric Matrix Solver
1983-10-01
ILUCG2 (Incomplete LU factorized Conjugate Gradient algorithm for 2d problems) was developed to solve a linear asymmetric matrix system arising from a 9-point discretization of two-dimensional elliptic and parabolic partial differential equations found in plasma physics applications, such as plasma diffusion, equilibria, and phase space transport (Fokker-Planck equation) problems. These equations share the common feature of being stiff and requiring implicit solution techniques. When these parabolic or elliptic PDE''s are discretized with finite-difference or finite-elementmore » methods, the resulting matrix system is frequently of block-tridiagonal form. To use ILUCG2, the discretization of the two-dimensional partial differential equation and its boundary conditions must result in a block-tridiagonal supermatrix composed of elementary tridiagonal matrices. A generalization of the incomplete Cholesky conjugate gradient algorithm is used to solve the matrix equation. Loops are arranged to vectorize on the Cray1 with the CFT compiler, wherever possible. Recursive loops, which cannot be vectorized, are written for optimum scalar speed. For problems having a symmetric matrix ICCG2 should be used since it runs up to four times faster and uses approximately 30% less storage. Similar methods in three dimensions are available in ICCG3 and ILUCG3. A general source, containing extensions and macros, which must be processed by a pre-compiler to obtain the standard FORTRAN source, is provided along with the standard FORTRAN source because it is believed to be more readable. The pre-compiler is not included, but pre-compilation may be performed by a text editor as described in the UCRL-88746 Preprint.« less
NASA Astrophysics Data System (ADS)
Xi, Caiping; Zhang, Shunning; Xiong, Gang; Zhao, Huichang
2016-07-01
Multifractal detrended fluctuation analysis (MFDFA) and multifractal detrended moving average (MFDMA) algorithm have been established as two important methods to estimate the multifractal spectrum of the one-dimensional random fractal signal. They have been generalized to deal with two-dimensional and higher-dimensional fractal signals. This paper gives a brief introduction of the two-dimensional multifractal detrended fluctuation analysis (2D-MFDFA) and two-dimensional multifractal detrended moving average (2D-MFDMA) algorithm, and a detailed description of the application of the two-dimensional fractal signal processing by using the two methods. By applying the 2D-MFDFA and 2D-MFDMA to the series generated from the two-dimensional multiplicative cascading process, we systematically do the comparative analysis to get the advantages, disadvantages and the applicabilities of the two algorithms for the first time from six aspects such as the similarities and differences of the algorithm models, the statistical accuracy, the sensitivities of the sample size, the selection of scaling range, the choice of the q-orders and the calculation amount. The results provide a valuable reference on how to choose the algorithm from 2D-MFDFA and 2D-MFDMA, and how to make the schemes of the parameter settings of the two algorithms when dealing with specific signals in practical applications.
SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.
Hromadka, T.V.; Lai, Chintu
1985-01-01
A simplification of the two-dimensional (2-D) continuity and momentum equations is the diffusion equation. To investigate its capability, the numerical model using the diffusion approach is applied to a hypothetical failure problem of a regional water reservoir. The model is based on an explicit, integrated finite-difference scheme, and the floodplain is simulated by a popular home computer which supports 64K FORTRAN. Though simple, the 2-D model can simulate some interesting flooding effects that a 1-D full dynamic model cannot.
Nanocavity absorption enhancement for two-dimensional material monolayer systems.
Song, Haomin; Jiang, Suhua; Ji, Dengxin; Zeng, Xie; Zhang, Nan; Liu, Kai; Wang, Chu; Xu, Yun; Gan, Qiaoqiang
2015-03-23
Here we propose a strategy to enhance the light-matter interaction of two-dimensional (2D) material monolayers based on strong interference effect in planar nanocavities, and overcome the limitation between optical absorption and the atomically-thin thickness of 2D materials. By exploring the role of spacer layers with different thicknesses and refractive indices, we demonstrate that a nanocavity with an air spacer layer placed between a graphene monolayer and an aluminum reflector layer will enhance the exclusive absorption in the graphene monolayer effectively, which is particularly useful for the development of atomically-thin energy harvesting/conversion devices.
Ultra-subwavelength two-dimensional plasmonic circuits.
Andress, William F; Yoon, Hosang; Yeung, Kitty Y M; Qin, Ling; West, Ken; Pfeiffer, Loren; Ham, Donhee
2012-05-01
We report electronics regime (GHz) two-dimensional (2D) plasmonic circuits, which locally and nonresonantly interface with electronics, and thus offer to electronics the benefits of their ultrasubwavelength confinement, with up to 440,000-fold mode-area reduction. By shaping the geometry of 2D plasmonic media 80 nm beneath an unpatterned metallic gate, plasmons are routed freely into various types of reflections and interferences, leading to a range of plasmonic circuits, e.g., plasmonic crystals and plasmonic-electromagnetic interferometers, offering new avenues for electronics.
Two-dimensional molecular crystals of phosphonic acids on graphene.
Prado, Mariana C; Nascimento, Regiane; Moura, Luciano G; Matos, Matheus J S; Mazzoni, Mario S C; Cancado, Luiz G; Chacham, Helio; Neves, Bernardo R A
2011-01-25
The synthesis and characterization of two-dimensional (2D) molecular crystals composed of long and linear phosphonic acids atop graphene is reported. Using scanning probe microscopy in combination with first-principles calculations, we show that these true 2D crystals are oriented along the graphene armchair direction only, thereby enabling an easy determination of graphene flake orientation. We have also compared the doping level of graphene flakes via Raman spectroscopy. The presence of the molecular crystal atop graphene induces a well-defined shift in the Fermi level, corresponding to hole doping, which is in agreement with our ab initio calculations.
Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy
NASA Astrophysics Data System (ADS)
Bixner, O.; Christensson, N.; Hauer, J.; Milota, F.; Mančal, T.; Lukeš, V.; Kauffmann, H. F.
2013-03-01
Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.
Functionalization of Two-Dimensional Transition-Metal Dichalcogenides.
Chen, Xin; McDonald, Aidan R
2016-07-01
Two-dimensional (2D) layered transition-metal dichalcogenides (TMDs) are a fascinating class of nanomaterials that have the potential for application in catalysis, electronics, photonics, energy storage, and sensing. TMDs are rather inert, and thus pose problems for chemical derivatization. However, to further modify the properties of TMDs and fully harness their capabilities, routes towards their chemical functionalization must be identified. Herein, recent efforts toward the chemical (bond-forming) functionalization of 2D TMDs are critically reviewed. Recent successes are highlighted, along with areas where further detailed analyses and experimentation are required. This burgeoning field is very much in its infancy but has already provided several important breakthroughs. PMID:26848815
Application of two dimensional periodic molecular dynamics to interfaces.
NASA Astrophysics Data System (ADS)
Gay, David H.; Slater, Ben; Catlow, C. Richard A.
1997-08-01
We have applied two-dimensional molecular dynamics to the surface of a crystalline aspartame and the interface between the crystal face and a solvent (water). This has allowed us to look at the dynamic processes at the surface. Understanding the surface structure and properties are important to controlling the crystal morphology. The thermodynamic ensemble was constant Number, surface Area and Temperature (NAT). The calculations have been carried out using a 2D Ewald summation and 2D periodic boundary conditions for the short range potentials. The equations of motion integration has been carried out using the standard velocity Verlet algorithm.
Scalable Transfer of Suspended Two-Dimensional Single Crystals.
Li, Bo; He, Yongmin; Lei, Sidong; Najmaei, Sina; Gong, Yongji; Wang, Xin; Zhang, Jing; Ma, Lulu; Yang, Yingchao; Hong, Sanghyun; Hao, Ji; Shi, Gang; George, Antony; Keyshar, Kunttal; Zhang, Xiang; Dong, Pei; Ge, Liehui; Vajtai, Robert; Lou, Jun; Jung, Yung Joon; Ajayan, Pulickel M
2015-08-12
Large-scale suspended architectures of various two-dimensional (2D) materials (MoS2, MoSe2, WS2, and graphene) are demonstrated on nanoscale patterned substrates with different physical and chemical surface properties, such as flexible polymer substrates (polydimethylsiloxane), rigid Si substrates, and rigid metal substrates (Au/Ag). This transfer method represents a generic, fast, clean, and scalable technique to suspend 2D atomic layers. The underlying principle behind this approach, which employs a capillary-force-free wet-contact printing method, was studied by characterizing the nanoscale solid-liquid-vapor interface of 2D layers with respect to different substrates. As a proof-of-concept, a photodetector of suspended MoS2 has been demonstrated with significantly improved photosensitivity. This strategy could be extended to several other 2D material systems and open the pathway toward better optoelectronic and nanoelectromechnical systems.
Nonlinear plasmonics in a two-dimensional plasma layer
NASA Astrophysics Data System (ADS)
Eliasson, Bengt; Liu, Chuan Sheng
2016-05-01
The nonlinear electron dynamics in a two-dimensional (2D) plasma layer are investigated theoretically and numerically. In contrast to the Langmuir oscillations in a three-dimensional (3D) plasma, a well-known feature of the 2D system is the square root dependence of the frequency on the wavenumber, which leads to unique dispersive properties of 2D plasmons. It is found that for large amplitude plasmonic waves there is a nonlinear frequency upshift similar to that of periodic gravity waves (Stokes waves). The periodic wave train is subject to a modulational instability, leading to sidebands growing exponentially in time. Numerical simulations show the breakup of a 2D wave train into localized wave packets and later into wave turbulence with immersed large amplitude solitary spikes. The results are applied to systems involving massless Dirac fermions in graphene as well as to sheets of electrons on liquid helium.
MAGNUM-2D computer code: user's guide
England, R.L.; Kline, N.W.; Ekblad, K.J.; Baca, R.G.
1985-01-01
Information relevant to the general use of the MAGNUM-2D computer code is presented. This computer code was developed for the purpose of modeling (i.e., simulating) the thermal and hydraulic conditions in the vicinity of a waste package emplaced in a deep geologic repository. The MAGNUM-2D computer computes (1) the temperature field surrounding the waste package as a function of the heat generation rate of the nuclear waste and thermal properties of the basalt and (2) the hydraulic head distribution and associated groundwater flow fields as a function of the temperature gradients and hydraulic properties of the basalt. MAGNUM-2D is a two-dimensional numerical model for transient or steady-state analysis of coupled heat transfer and groundwater flow in a fractured porous medium. The governing equations consist of a set of coupled, quasi-linear partial differential equations that are solved using a Galerkin finite-element technique. A Newton-Raphson algorithm is embedded in the Galerkin functional to formulate the problem in terms of the incremental changes in the dependent variables. Both triangular and quadrilateral finite elements are used to represent the continuum portions of the spatial domain. Line elements may be used to represent discrete conduits. 18 refs., 4 figs., 1 tab.
NASA Astrophysics Data System (ADS)
Sui, Liansheng; Duan, Kuaikuai; Liang, Junli
2016-05-01
A secure double-image sharing scheme is proposed by using the Shamir's three-pass protocol in the discrete multiple-parameter fractional angular transform domain. First, an enlarged image is formed by assembling two plain images successively in the horizontal direction and scrambled in the chaotic permutation process, in which the sequences of chaotic pairs are generated by the two-dimensional Sine Logistic modulation map. Second, the scrambled image is divided into two components which are used to constitute a complex image. One component is normalized and regarded as the phase part of the complex image as well as other is considered as the amplitude part. Finally, the complex image is shared between the sender and the receiver by using the Shamir's three-pass protocol, in which the discrete multiple-parameter fractional angular transform is used as the encryption function due to its commutative property. The proposed double-image sharing scheme has an obvious advantage that the key management is convenient without distributing the random phase mask keys in advance. Moreover, the security of the image sharing scheme is enhanced with the help of extra parameters of the discrete multiple-parameter fractional angular transform. To the best of our knowledge, this is the first report on integrating the Shamir's three-pass protocol with double-image sharing scheme in the information security field. Simulation results and security analysis verify the feasibility and effectiveness of the proposed scheme.
Separation of colloidal two dimensional materials by density gradient ultracentrifugation
Kuang, Yun; Song, Sha; Huang, Jinyang; Sun, Xiaoming
2015-04-15
Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials. Isopycnic separation was applied on thickness-dependent separation of graphene nanosheets. And rate-zonal separation, as a more versatile separation method, demonstrated its capability in sorting nanosheets of chemically modified single layered graphene, layered double hydroxide, and even metallic Ag. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Graphical abstract: Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials according to their size of thickness difference. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Highlights: • Density gradient ultracentrifugation was applied on size separation of 2D material. • Isopycnic separation was applied on separation of low density materials. • Rate-zonal separation was applied on separation of large density materials. • Size
Jesus, Danilo A; Iskander, D Robert
2015-12-01
Ray tracing is a powerful technique to understand the light behavior through an intricate optical system such as that of a human eye. The prediction of visual acuity can be achieved through characteristics of an optical system such as the geometrical point spread function. In general, its precision depends on the number of discrete rays and the accurate surface representation of each eye's components. Recently, a method that simplifies calculation of the geometrical point spread function has been proposed for circularly symmetric systems [Appl. Opt.53, 4784 (2014)]. An extension of this method to 2D noncircularly symmetric systems is proposed. In this method, a two-dimensional ray tracing procedure for an arbitrary number of surfaces and arbitrary surface shapes has been developed where surfaces, rays, and refractive indices are all represented in functional forms being approximated by Chebyshev polynomials. The Liou and Brennan anatomically accurate eye model has been adapted and used for evaluating the method. Further, real measurements of the anterior corneal surface of normal, astigmatic, and keratoconic eyes were substituted for the first surface in the model. The results have shown that performing ray tracing, utilizing the two-dimensional Chebyshev function approximation, is possible for noncircularly symmetric models, and that such calculation can be performed with a newly created Chebfun toolbox.
Synthesis of Two-Dimensional Materials for Capacitive Energy Storage.
Mendoza-Sánchez, Beatriz; Gogotsi, Yury
2016-08-01
The unique properties and great variety of two-dimensional (2D) nanomaterials make them highly attractive for energy storage applications. Here, an insight into the progress made towards the application of 2D nanomaterials for capacitive energy storage is provided. Synthesis methods, and electrochemical performance of various classes of 2D nanomaterials, particularly based on graphene, transition metal oxides, dichalcogenides, and carbides, are presented. The factors that directly influence capacitive performance are discussed throughout the text and include nanosheet composition, morphology and texture, electrode architecture, and device configuration. Recent progress in the fabrication of 2D-nanomaterials-based microsupercapacitors and flexible and free-standing supercapacitors is presented. The main electrode manufacturing techniques with emphasis on scalability and cost-effectiveness are discussed, and include laser scribing, printing, and roll-to-roll manufacture. Various issues that prevent the use of the full energy-storage potential of 2D nanomaterials and how they have been tackled are discussed, and include nanosheet aggregation and the low electrical conductivity of some 2D nanomaterials. Particularly, the design of hybrid and hierarchical 2D and 3D structures based on 2D nanomaterials is presented. Other challenges and opportunities are discussed and include: control of nanosheets size and thickness, chemical and electrochemical instability, and scale-up of electrode films. PMID:27254831
Synthesis of Two-Dimensional Materials for Capacitive Energy Storage
Mendoza-Sánchez, Beatriz; Gogotsi, Yury
2016-06-02
The unique properties and great variety of two-dimensional (2D) nanomaterials make them highly attractive for energy storage applications. Here, an insight into the progress made towards the application of 2D nanomaterials for capacitive energy storage is provided. Moreover, synthesis methods, and electrochemical performance of various classes of 2D nanomaterials, particularly based on graphene, transition metal oxides, dichalcogenides, and carbides, are presented. Some factors that directly influence capacitive performance are discussed throughout the text and include nanosheet composition, morphology and texture, electrode architecture, and device configuration. Recent progress in the fabrication of 2D-nanomaterials-based microsupercapacitors and flexible and free-standing supercapacitors is presented.more » The main electrode manufacturing techniques with emphasis on scalability and cost-effectiveness are discussed, and include laser scribing, printing, and roll-to-roll manufacture. Some various issues that prevent the use of the full energy-storage potential of 2D nanomaterials and how they have been tackled are discussed, and include nanosheet aggregation and the low electrical conductivity of some 2D nanomaterials. In particular, the design of hybrid and hierarchical 2D and 3D structures based on 2D nanomaterials is presented. Other challenges and opportunities are discussed and include: control of nanosheets size and thickness, chemical and electrochemical instability, and scale-up of electrode films.« less
Tunable states of interlayer cations in two-dimensional materials
Sato, K.; Numata, K.; Dai, W.; Hunger, M.
2014-03-31
The local state of cations inside the Ångstrom-scale interlayer spaces is one of the controlling factors for designing sophisticated two-dimensional (2D) materials consisting of 2D nanosheets. In the present work, the molecular mechanism on how the interlayer cation states are induced by the local structures of the 2D nanosheets is highlighted. For this purpose, the local states of Na cations in inorganic 2D materials, in which the compositional fluctuations of a few percent are introduced in the tetrahedral and octahedral units of the 2D nanosheets, were systematically studied by means of {sup 23}Na magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and {sup 23}Na multiple-quantum MAS (MQMAS) NMR spectroscopy. In contrast with an uniform distribution of Na cations expected so far, various well-defined cation states sensitive to the local structures of the 2D nanosheets were identified. The tunability of the interlayer cation states along with the local structure of the 2D nanosheets, as the smallest structural unit of the 2D material, is discussed.
Recent Advances in Two-Dimensional Materials Beyond Graphene
Meunier, Vincent; Sumpter, Bobby G.; Terrones Maldonado, Mauricio; Terrones Maldonado, Humberto; Liang, Liangbo; Cooper, Valentino R.; Bhimanapati, Ganesh; Lin, Zhong; Jung, Yeongwoong; Cha, Judy; Das, Saptarshi; Xiao, Di; Son, Youngwoo; Strano, Michael; Louie, Steven G.; Ringe, Emilie; Xia, Fengnian; Wang, Yeliang; Akinwande, Deji; Zhu, Jun; Schuller, John; Schaak, Raymond; Robinson, Joshua A
2015-11-06
The isolation of graphene in 2004 by peeling apart the atomically-thin sheets that comprise graphite was a defining moment for the birth of a field: Two-dimensional (2D) materials. In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement. Here we review significant recent advances and important new developments in 2D materials beyond graphene . We provide insight into the theoretical modeling and understanding of the van der Waals forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies. Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (i.e., silicene, phosphorene, etc.) and transition metal carbide- and carbon nitride-based MXenes. We then discuss the doping and functionalization of 2D materials beyond graphene, which enable device applications, followed by advances in electronic, optoelectronic, and magnetic devices and theory. Finally, we provide perspectives on the future of 2D materials beyond graphene.
Recent Advances in Two-Dimensional Materials beyond Graphene.
Bhimanapati, Ganesh R; Lin, Zhong; Meunier, Vincent; Jung, Yeonwoong; Cha, Judy; Das, Saptarshi; Xiao, Di; Son, Youngwoo; Strano, Michael S; Cooper, Valentino R; Liang, Liangbo; Louie, Steven G; Ringe, Emilie; Zhou, Wu; Kim, Steve S; Naik, Rajesh R; Sumpter, Bobby G; Terrones, Humberto; Xia, Fengnian; Wang, Yeliang; Zhu, Jun; Akinwande, Deji; Alem, Nasim; Schuller, Jon A; Schaak, Raymond E; Terrones, Mauricio; Robinson, Joshua A
2015-12-22
The isolation of graphene in 2004 from graphite was a defining moment for the "birth" of a field: two-dimensional (2D) materials. In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement. Here, we review significant recent advances and important new developments in 2D materials "beyond graphene". We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies. Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (i.e., silicene, phosphorene, etc.) and transition metal carbide- and carbon nitride-based MXenes. We then discuss the doping and functionalization of 2D materials beyond graphene that enable device applications, followed by advances in electronic, optoelectronic, and magnetic devices and theory. Finally, we provide perspectives on the future of 2D materials beyond graphene. PMID:26544756
Recent Advances in Two-Dimensional Materials beyond Graphene.
Bhimanapati, Ganesh R; Lin, Zhong; Meunier, Vincent; Jung, Yeonwoong; Cha, Judy; Das, Saptarshi; Xiao, Di; Son, Youngwoo; Strano, Michael S; Cooper, Valentino R; Liang, Liangbo; Louie, Steven G; Ringe, Emilie; Zhou, Wu; Kim, Steve S; Naik, Rajesh R; Sumpter, Bobby G; Terrones, Humberto; Xia, Fengnian; Wang, Yeliang; Zhu, Jun; Akinwande, Deji; Alem, Nasim; Schuller, Jon A; Schaak, Raymond E; Terrones, Mauricio; Robinson, Joshua A
2015-12-22
The isolation of graphene in 2004 from graphite was a defining moment for the "birth" of a field: two-dimensional (2D) materials. In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement. Here, we review significant recent advances and important new developments in 2D materials "beyond graphene". We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies. Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (i.e., silicene, phosphorene, etc.) and transition metal carbide- and carbon nitride-based MXenes. We then discuss the doping and functionalization of 2D materials beyond graphene that enable device applications, followed by advances in electronic, optoelectronic, and magnetic devices and theory. Finally, we provide perspectives on the future of 2D materials beyond graphene.
Recent Advances in Two-Dimensional Materials Beyond Graphene
Meunier, Vincent; Sumpter, Bobby G.; Terrones Maldonado, Mauricio; Terrones Maldonado, Humberto; Liang, Liangbo; Cooper, Valentino R.; Bhimanapati, Ganesh; Lin, Zhong; Jung, Yeongwoong; Cha, Judy; et al
2015-11-06
The isolation of graphene in 2004 by peeling apart the atomically-thin sheets that comprise graphite was a defining moment for the birth of a field: Two-dimensional (2D) materials. In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement. Here we review significant recent advances and important new developments in 2D materials beyond graphene . We provide insight into the theoretical modeling and understanding of the van der Waals forces that hold together the 2D layers in bulkmore » solids, as well as their excitonic properties and growth morphologies. Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (i.e., silicene, phosphorene, etc.) and transition metal carbide- and carbon nitride-based MXenes. We then discuss the doping and functionalization of 2D materials beyond graphene, which enable device applications, followed by advances in electronic, optoelectronic, and magnetic devices and theory. Finally, we provide perspectives on the future of 2D materials beyond graphene.« less
NASA Astrophysics Data System (ADS)
Sanmiguel-Rojas, Enrique; Ortega-Casanova, Joaquin; del Pino, Carlos; Fernandez-Feria, Ramon
2004-11-01
A method for generating a non-uniform cartesian grid for irregular two-dimensional (2D) geometries such that all the boundary points are regular mesh points is given. The resulting non-uniform grid is used to discretize the Navier-Stokes equations for 2D incompressible viscous flows using finite difference approximations. To that end, finite-difference approximations of the derivatives on a non-uniform mesh are given. We test the method with two different examples: the shallow water flow on a lake with irregular contour, and the pressure driven flow through an irregular array of circular cylinders.
DOGS: a collection of graphics for support of discrete ordinates codes
Ingersoll, D.T.; Slater, C.O.
1980-03-01
A collection of computer codes called DOGS (Discrete Ordinates Graphics Support) has been developed to assist in the display and presentation of data generated by commonly used discrete ordinates transport codes. The DOGS codes include: EGAD for plotting two-dimensional geometries, ISOPLOT4 for plotting 2-D fluxes in a contour line fashion, FORM for plotting 2-D fluxes in a 3-D surface fashion, ACTUAL for calculating 2-D activities, TOOTH for calculating and plotting space-energy contributon fluxes, and ASPECT for plotting energy spectra. All of the codes use FIDO input formats and DISSPLA graphics software including the DISSPOP post processors.
A geometrical approach to two-dimensional Conformal Field Theory
NASA Astrophysics Data System (ADS)
Dijkgraaf, Robertus Henricus
1989-09-01
This thesis is organized in the following way. In Chapter 2 we will give a brief introduction to conformal field theory along the lines of standard quantum field theory, without any claims to originality. We introduce the important concepts of the stress-energy tensor, the Virasoro algebra, and primary fields. The general principles are demonstrated by fermionic and bosonic free field theories. This also allows us to discuss some general aspects of moduli spaces of CFT's. In particular, we describe in some detail the space of iiiequivalent toroidal comi)actificalions, giving examples of the quantum equivalences that we already mentioned. In Chapter 3 we will reconsider general quantum field theory from a more geometrical point of view, along the lines of the so-called operator formalism. Crucial to this approach will be the consideration of topology changing amplitudes. After a simple application to 2d topological theories, we proceed to give our second introduction to CFT, stressing the geometry behind it. In Chapter 4 the so-called rational conformal field theories are our object of study. These special CFT's have extended symmetries with only a finite number of representations. If an interpretation as non-linear sigma model exists, this extra symmetry can be seen as a kind of resonance effect due to the commensurability of the size of the string and the target space-time. The structure of rational CFT's is extremely rigid, and one of our results will be that the operator content of these models is—up to some discrete choices—completely determined by the symmetry algebra. The study of rational models is in its rigidity very analogous to finite group theory. In Chapter 5 this analogy is further pursued and substantiated. We will show how one can construct from general grounds rational conformal field theories from finite groups. These models are abstract versions of non-linear o-models describing string propagation on 'orbifoids.' An orbifold is a singular
A two dimensional artificial reality
NASA Technical Reports Server (NTRS)
Krueger, Myron W.
1991-01-01
The current presumption is that it is necessary to don goggles, gloves and a data suit to experience artificial reality. However, there is another technology that offers an alternative or complement to the encumbering techniques associated with NASA. In VIDEOPLACE, your image appears in a 2D graphic world created by a computer. The VIDEOPLACE computer can analyze a person's image in 1/30 second and can detect when an object is touched. Thus, it can generate a graphic or auditory response to an illusory contact. VIDEOPLACE technology exists in two formats: the VIDEODESK and the VIDEOPLACE. In the VIDEODESK environment, the image of your hands can be used to perform the normal mouse functions, such as menuing and drawing. In addition, you have the advantage of multipoint control. For instance, you can use the thumbs and forefingers of each hand as control points for a spline curve. Perhaps most important, the image of your hands can be compressed and transmitted to a colleague over an ISDN voice channel to appear on the remote screen superimposed over identical information. Likewise, the image of your colleague's hands can appear on both screens. The result is that the two of you can use your hands to point to features on your respective screens as you speak, exactly as you would if you were sitting together. In the VIDEOPLACE environment, you can interact with graphic creatures and the images of other people in other locations in a graphic world. Your whole body can be moved, scaled and rotated in real-time without regard to the laws of physics. Thus, VIDEOPLACE can be used to create a fantasy world in which the laws of cause and effect are composed by an artist.
van der Waals epitaxy and photoresponse of two-dimensional CdSe plates
NASA Astrophysics Data System (ADS)
Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min
2016-06-01
Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices.
Baiz, Carlos R.; Schach, Denise; Tokmakoff, Andrei
2014-01-01
We describe a microscope for measuring two-dimensional infrared (2D IR) spectra of heterogeneous samples with μm-scale spatial resolution, sub-picosecond time resolution, and the molecular structure information of 2D IR, enabling the measurement of vibrational dynamics through correlations in frequency, time, and space. The setup is based on a fully collinear “one beam” geometry in which all pulses propagate along the same optics. Polarization, chopping, and phase cycling are used to isolate the 2D IR signals of interest. In addition, we demonstrate the use of vibrational lifetime as a contrast agent for imaging microscopic variations in molecular environments. PMID:25089490
Electronic transport in two-dimensional high dielectric constant nanosystems
Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.
2015-04-10
There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screeningmore » length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.« less
Electronic transport in two-dimensional high dielectric constant nanosystems
NASA Astrophysics Data System (ADS)
Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.
2015-04-01
There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screening length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.
Electronic transport in two-dimensional high dielectric constant nanosystems
Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.
2015-04-10
There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screening length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.
Two-Dimensional Atomic Crystals: Paving New Ways for Nanoelectronics
NASA Astrophysics Data System (ADS)
Fan, Jincheng; Li, Tengfei; Djerdj, Igor
2015-11-01
Two-dimensional (2D) atomic crystals are attractive for use in next-generation nanoelectronics, due to their unique performances, which may lead to the resolution of the technological and fundamental challenges in semiconductor industry. Based on the introduction of 2D atomic crystal-based transistors and ambipolar behavior, the review presents a brief summary of 2D atomic crystal integration circuits, including memory, logic gate, amplifier, inverter, oscillator, mixer, switch and modulator. The devices show promising performances for the application in future nanoelectronics. In particular, the 2D atomic crystals, such as graphene, demonstrate good compatibility with the existing semiconductor process. The quaternary digital modulations have been achieved with flexible and transparent all-graphene circuits. Moreover, the heterojunction based on 2D atomic crystals may enable new devices beyond conventional field-effect transistors. The results make us be optimistic that practical 2D atomic crystal technologies with complex functionality will be achieved in the near future. Therefore, 2D atomic crystals are paving new ways for nanoelectronics.
Two-dimensional photonic crystal chemical and biomolecular sensors.
Cai, Zhongyu; Smith, Natasha L; Zhang, Jian-Tao; Asher, Sanford A
2015-01-01
We review recent progress in the development of two-dimensional (2-D) photonic crystal (PC) materials for chemical and biological sensing applications. Self-assembly methods were developed in our laboratory to fabricate 2-D particle array monolayers on mercury and water surfaces. These hexagonal arrays strongly forward Bragg diffract light to report on their array spacings. By embedding these 2-D arrays onto responsive hydrogel surfaces, 2-D PC sensing materials can be fabricated. The 2-D PC sensors utilize responsive polymer hydrogels that are chemically functionalized to show volume phase transitions in selective response to particular chemical species. Novel hydrogels were also developed in our laboratory by cross-linking proteins while preserving their native structures to maintain their selective binding affinities. The volume phase transitions swell or shrink the hydrogels, which alter their 2-D array spacings, and shift their diffraction wavelengths. These shifts can be visually detected or spectrally measured. These 2-D PC sensing materials have been used for the detection of many analytes, such as pH, surfactants, metal ions, proteins, anionic drugs, and ammonia. We are exploring the use of organogels that use low vapor pressure ionic liquids as their mobile phases for sensing atmospheric analytes. PMID:25867803
Measuring Monotony in Two-Dimensional Samples
ERIC Educational Resources Information Center
Kachapova, Farida; Kachapov, Ilias
2010-01-01
This note introduces a monotony coefficient as a new measure of the monotone dependence in a two-dimensional sample. Some properties of this measure are derived. In particular, it is shown that the absolute value of the monotony coefficient for a two-dimensional sample is between /"r"/ and 1, where "r" is the Pearson's correlation coefficient for…
2-D Animation's Not Just for Mickey Mouse.
ERIC Educational Resources Information Center
Weinman, Lynda
1995-01-01
Discusses characteristics of two-dimensional (2-D) animation; highlights include character animation, painting issues, and motion graphics. Sidebars present Silicon Graphics animations tools and 2-D animation programs for the desktop computer. (DGM)
Feng, Xiao; Ding, Xuesong; Chen, Long; Wu, Yang; Liu, Lili; Addicoat, Matthew; Irle, Stephan; Dong, Yuping; Jiang, Donglin
2016-01-01
Highly ordered discrete assemblies of chlorophylls that are found in natural light-harvesting antennae are key to photosynthesis, which converts light energy to chemical energy and is the principal producer of organic matter on Earth. Porphyrins and phthalocyanines, which are analogues of chlorophylls, exhibit a strong absorbance of visible and near-infrared light, respectively. A highly ordered porphyrin-co-phthalocyanine antennae would harvest photons over the entire solar spectrum for chemical transformation. However, such a robust antennae has not yet been synthesised. Herein, we report a strategy that merges covalent bonds and noncovalent forces to produce highly ordered two-dimensional porphyrin-co-phthalocyanine antennae. This methodology enables control over the stoichiometry and order of the porphyrin and phthalocyanine units; more importantly, this approach is compatible with various metalloporphyrin and metallophthalocyanine derivatives and thus may lead to the generation of a broad structural diversity of two-dimensional artificial antennae. These ordered porphyrin-co-phthalocyanine two-dimensional antennae exhibit unique optical properties and catalytic functions that are not available with single-component or non-structured materials. These 2D artificial antennae exhibit exceptional light-harvesting capacity over the entire solar spectrum as a result of a synergistic light-absorption effect. In addition, they exhibit outstanding photosensitising activities in using both visible and near-infrared photons for producing singlet oxygen.
Feng, Xiao; Ding, Xuesong; Chen, Long; Wu, Yang; Liu, Lili; Addicoat, Matthew; Irle, Stephan; Dong, Yuping; Jiang, Donglin
2016-01-01
Highly ordered discrete assemblies of chlorophylls that are found in natural light-harvesting antennae are key to photosynthesis, which converts light energy to chemical energy and is the principal producer of organic matter on Earth. Porphyrins and phthalocyanines, which are analogues of chlorophylls, exhibit a strong absorbance of visible and near-infrared light, respectively. A highly ordered porphyrin-co-phthalocyanine antennae would harvest photons over the entire solar spectrum for chemical transformation. However, such a robust antennae has not yet been synthesised. Herein, we report a strategy that merges covalent bonds and noncovalent forces to produce highly ordered two-dimensional porphyrin-co-phthalocyanine antennae. This methodology enables control over the stoichiometry and order of the porphyrin and phthalocyanine units; more importantly, this approach is compatible with various metalloporphyrin and metallophthalocyanine derivatives and thus may lead to the generation of a broad structural diversity of two-dimensional artificial antennae. These ordered porphyrin-co-phthalocyanine two-dimensional antennae exhibit unique optical properties and catalytic functions that are not available with single-component or non-structured materials. These 2D artificial antennae exhibit exceptional light-harvesting capacity over the entire solar spectrum as a result of a synergistic light-absorption effect. In addition, they exhibit outstanding photosensitising activities in using both visible and near-infrared photons for producing singlet oxygen. PMID:27622274
Feng, Xiao; Ding, Xuesong; Chen, Long; Wu, Yang; Liu, Lili; Addicoat, Matthew; Irle, Stephan; Dong, Yuping; Jiang, Donglin
2016-01-01
Highly ordered discrete assemblies of chlorophylls that are found in natural light-harvesting antennae are key to photosynthesis, which converts light energy to chemical energy and is the principal producer of organic matter on Earth. Porphyrins and phthalocyanines, which are analogues of chlorophylls, exhibit a strong absorbance of visible and near-infrared light, respectively. A highly ordered porphyrin-co-phthalocyanine antennae would harvest photons over the entire solar spectrum for chemical transformation. However, such a robust antennae has not yet been synthesised. Herein, we report a strategy that merges covalent bonds and noncovalent forces to produce highly ordered two-dimensional porphyrin-co-phthalocyanine antennae. This methodology enables control over the stoichiometry and order of the porphyrin and phthalocyanine units; more importantly, this approach is compatible with various metalloporphyrin and metallophthalocyanine derivatives and thus may lead to the generation of a broad structural diversity of two-dimensional artificial antennae. These ordered porphyrin-co-phthalocyanine two-dimensional antennae exhibit unique optical properties and catalytic functions that are not available with single-component or non-structured materials. These 2D artificial antennae exhibit exceptional light-harvesting capacity over the entire solar spectrum as a result of a synergistic light-absorption effect. In addition, they exhibit outstanding photosensitising activities in using both visible and near-infrared photons for producing singlet oxygen. PMID:27622274
NASA Astrophysics Data System (ADS)
Feng, Xiao; Ding, Xuesong; Chen, Long; Wu, Yang; Liu, Lili; Addicoat, Matthew; Irle, Stephan; Dong, Yuping; Jiang, Donglin
2016-09-01
Highly ordered discrete assemblies of chlorophylls that are found in natural light-harvesting antennae are key to photosynthesis, which converts light energy to chemical energy and is the principal producer of organic matter on Earth. Porphyrins and phthalocyanines, which are analogues of chlorophylls, exhibit a strong absorbance of visible and near-infrared light, respectively. A highly ordered porphyrin-co-phthalocyanine antennae would harvest photons over the entire solar spectrum for chemical transformation. However, such a robust antennae has not yet been synthesised. Herein, we report a strategy that merges covalent bonds and noncovalent forces to produce highly ordered two-dimensional porphyrin-co-phthalocyanine antennae. This methodology enables control over the stoichiometry and order of the porphyrin and phthalocyanine units; more importantly, this approach is compatible with various metalloporphyrin and metallophthalocyanine derivatives and thus may lead to the generation of a broad structural diversity of two-dimensional artificial antennae. These ordered porphyrin-co-phthalocyanine two-dimensional antennae exhibit unique optical properties and catalytic functions that are not available with single-component or non-structured materials. These 2D artificial antennae exhibit exceptional light-harvesting capacity over the entire solar spectrum as a result of a synergistic light-absorption effect. In addition, they exhibit outstanding photosensitising activities in using both visible and near-infrared photons for producing singlet oxygen.
Lateral and Vertical Two-Dimensional Layered Topological Insulator Heterostructures.
Li, Yanbin; Zhang, Jinsong; Zheng, Guangyuan; Sun, Yongming; Hong, Seung Sae; Xiong, Feng; Wang, Shuang; Lee, Hye Ryoung; Cui, Yi
2015-11-24
The heterostructured configuration between two-dimensional (2D) semiconductor materials has enabled the engineering of the band gap and the design of novel devices. So far, the synthesis of single-component topological insulator (TI) 2D materials such as Bi2Se3, Bi2Te3, and Sb2Te3 has been achieved through vapor phase growth and molecular beam epitaxy; however, the spatial controlled fabrication of 2D lateral heterostructures in these systems has not been demonstrated yet. Here, we report an in situ two-step synthesis process to form TI lateral heterostructures. Scanning transmission electron microscopy and energy-dispersive X-ray mapping results show the successful spatial control of chemical composition in these as-prepared heterostructures. The edge-induced growth mechanism is revealed by the ex situ atomic force microscope measurements. Electrical transport studies demonstrate the existence of p-n junctions in Bi2Te3/Sb2Te3 heterostructures.
Quasi-Two-Dimensional Magnetism in Co-Based Shandites
NASA Astrophysics Data System (ADS)
Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki
2016-06-01
We report quasi-two-dimensional (Q2D) itinerant electron magnetism in the layered Co-based shandites. Comprehensive magnetization measurements were performed using single crystals of Co3Sn2-xInxS2 (0 ≤ x ≤ 2) and Co3-yFeySn2S2 (0 ≤ y ≤ 0.5). The magnetic parameters of both systems; the Curie temperature TC, effective moment peff and spontaneous moment ps; exhibit almost identical variations against the In- and Fe-concentrations, indicating significance of the electron count on the magnetism in the Co-based shandite. The ferromagnetic-nonmagnetic quantum phase transition is found around xc ˜ 0.8. Analysis based on the extended Q2D spin fluctuation theory clearly reveals the highly Q2D itinerant electron character of the ferromagnetism in the Co-based shandites.
Two-dimensional electronic spectroscopy with birefringent wedges
Réhault, Julien; Maiuri, Margherita; Oriana, Aurelio; Cerullo, Giulio
2014-12-15
We present a simple experimental setup for performing two-dimensional (2D) electronic spectroscopy in the partially collinear pump-probe geometry. The setup uses a sequence of birefringent wedges to create and delay a pair of phase-locked, collinear pump pulses, with extremely high phase stability and reproducibility. Continuous delay scanning is possible without any active stabilization or position tracking, and allows to record rapidly and easily 2D spectra. The setup works over a broad spectral range from the ultraviolet to the near-IR, it is compatible with few-optical-cycle pulses and can be easily reconfigured to two-colour operation. A simple method for scattering suppression is also introduced. As a proof of principle, we present degenerate and two-color 2D spectra of the light-harvesting complex 1 of purple bacteria.
A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy
El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens E-mail: bredenbeck@biophysik.uni-frankfurt.de
2015-08-15
A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported.
Extended quantum jump description of vibronic two-dimensional spectroscopy
Albert, Julian; Falge, Mirjam; Keß, Martin; Wehner, Johannes G.; Engel, Volker; Zhang, Pan-Pan; Eisfeld, Alexander
2015-06-07
We calculate two-dimensional (2D) vibronic spectra for a model system involving two electronic molecular states. The influence of a bath is simulated using a quantum-jump approach. We use a method introduced by Makarov and Metiu [J. Chem. Phys. 111, 10126 (1999)] which includes an explicit treatment of dephasing. In this way it is possible to characterize the influence of dissipation and dephasing on the 2D-spectra, using a wave function based method. The latter scales with the number of stochastic runs and the number of system eigenstates included in the expansion of the wave-packets to be propagated with the stochastic method and provides an efficient method for the calculation of the 2D-spectra.
Extended quantum jump description of vibronic two-dimensional spectroscopy.
Albert, Julian; Falge, Mirjam; Keß, Martin; Wehner, Johannes G; Zhang, Pan-Pan; Eisfeld, Alexander; Engel, Volker
2015-06-01
We calculate two-dimensional (2D) vibronic spectra for a model system involving two electronic molecular states. The influence of a bath is simulated using a quantum-jump approach. We use a method introduced by Makarov and Metiu [J. Chem. Phys. 111, 10126 (1999)] which includes an explicit treatment of dephasing. In this way it is possible to characterize the influence of dissipation and dephasing on the 2D-spectra, using a wave function based method. The latter scales with the number of stochastic runs and the number of system eigenstates included in the expansion of the wave-packets to be propagated with the stochastic method and provides an efficient method for the calculation of the 2D-spectra. PMID:26049460
Nonlinear optical response of a two-dimensional atomic crystal.
Merano, Michele
2016-01-01
The theory of Bloembergen and Pershan for the light waves at the boundary of nonlinear media is extended to a nonlinear two-dimensional (2D) atomic crystal, i.e., a single planar atomic lattice, placed between linear bulk media. The crystal is treated as a zero-thickness interface, a real 2D system. Harmonic waves emanate from it. Generalization of the laws of reflection and refraction give the direction and the intensity of the harmonic waves. As a particular case that contains all the essential physical features, second-order harmonic generation is considered. The theory, due to its simplicity that stems from the special character of a single planar atomic lattice, is able to elucidate and explain the rich experimental details of harmonic generation from a 2D atomic crystal.
Two dimensional WS2 lateral heterojunctions by strain modulation
NASA Astrophysics Data System (ADS)
Meng, Lan; Zhang, Yuhan; Hu, Song; Wang, Xiangfu; Liu, Chunsheng; Guo, Yandong; Wang, Xinran; Yan, Xiaohong
2016-06-01
"Strain engineering" has been widely used to tailor the physical properties of layered materials, like graphene, black phosphorus, and transition-metal dichalcogenides. Here, we exploit thermal strain engineering to construct two dimensional (2D) WS2 in-plane heterojunctions. Kelvin probe force microscopy is used to investigate the surface potentials and work functions of few-layer WS2 flakes, which are grown on SiO2/Si substrates by chemical vapor deposition, followed by a fast cooling process. In the interior regions of strained WS2 flakes, work functions are found to be much larger than that of the unstrained regions. The difference in work functions, together with the variation of band gaps, endows the formation of heterojunctions in the boundaries between inner and outer domains of WS2 flakes. This result reveals that the existence of strain offers a unique opportunity to modulate the electronic properties of 2D materials and construct 2D lateral heterojunctions.
Coherent transfer by adiabatic passage in two-dimensional lattices
Longhi, Stefano
2014-09-15
Coherent tunneling by adiabatic passage (CTAP) is a well-established technique for robust spatial transport of quantum particles in linear chains. Here we introduce two exactly-solvable models where the CTAP protocol can be extended to two-dimensional lattice geometries. Such bi-dimensional lattice models are synthesized from time-dependent second-quantization Hamiltonians, in which the bosonic field operators evolve adiabatically like in an ordinary three-level CTAP scheme thus ensuring adiabatic passage in Fock space. - Highlights: • New ways of coherent transport by adiabatic passage (CTAP) in 2D lattices. • Synthesis of exactly-solvable 2D lattices from a simple three-well model. • CTAP in 2D lattices can be exploited for quantum state transfer.
Generates 2D Input for DYNA NIKE & TOPAZ
Hallquist, J. O.; Sanford, Larry
1996-07-15
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
MAZE96. Generates 2D Input for DYNA NIKE & TOPAZ
Sanford, L.; Hallquist, J.O.
1992-02-24
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
Two-dimensional Imaging Velocity Interferometry: Technique and Data Analysis
Erskine, D J; Smith, R F; Bolme, C; Celliers, P; Collins, G
2011-03-23
We describe the data analysis procedures for an emerging interferometric technique for measuring motion across a two-dimensional image at a moment in time, i.e. a snapshot 2d-VISAR. Velocity interferometers (VISAR) measuring target motion to high precision have been an important diagnostic in shockwave physics for many years Until recently, this diagnostic has been limited to measuring motion at points or lines across a target. We introduce an emerging interferometric technique for measuring motion across a two-dimensional image, which could be called a snapshot 2d-VISAR. If a sufficiently fast movie camera technology existed, it could be placed behind a traditional VISAR optical system and record a 2d image vs time. But since that technology is not yet available, we use a CCD detector to record a single 2d image, with the pulsed nature of the illumination providing the time resolution. Consequently, since we are using pulsed illumination having a coherence length shorter than the VISAR interferometer delay ({approx}0.1 ns), we must use the white light velocimetry configuration to produce fringes with significant visibility. In this scheme, two interferometers (illuminating, detecting) having nearly identical delays are used in series, with one before the target and one after. This produces fringes with at most 50% visibility, but otherwise has the same fringe shift per target motion of a traditional VISAR. The 2d-VISAR observes a new world of information about shock behavior not readily accessible by traditional point or 1d-VISARS, simultaneously providing both a velocity map and an 'ordinary' snapshot photograph of the target. The 2d-VISAR has been used to observe nonuniformities in NIF related targets (polycrystalline diamond, Be), and in Si and Al.
Extension of modified power method to two-dimensional problems
NASA Astrophysics Data System (ADS)
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.
Dipeptide Structural Analysis Using Two-Dimensional NMR for the Undergraduate Advanced Laboratory
ERIC Educational Resources Information Center
Gonzalez, Elizabeth; Dolino, Drew; Schwartzenburg, Danielle; Steiger, Michelle A.
2015-01-01
A laboratory experiment was developed to introduce students in either an organic chemistry or biochemistry lab course to two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy using simple biomolecules. The goal of this experiment is for students to understand and interpret the information provided by a 2D NMR spectrum. Students are…
Ryu, Soo Ryeon; Noda, Isao; Lee, Chang-Hee; Lee, Phil Ho; Hwang, Hyonseok; Jung, Young Mee
2011-04-01
In this study, we demonstrate the potentials and pitfalls of using various waterfall plots, such as conventional waterfall plots, two-dimensional (2D) gradient maps, moving window two-dimensional analysis (MW2D), perturbation-correlation moving window two-dimensional analysis (PCMW2D), and moving window principal component analysis two-dimensional correlation analysis (MWPCA2D), in the detection of the existence of band position shifts. Waterfall plots of the simulated spectral datasets are compared with conventional 2D correlation spectra. Different waterfall plots give different features in differentiating the behaviors of frequency shift versus two overlapped bands. Two-dimensional correlation spectra clearly show the very characteristic cluster pattern for both band position shifts and two overlapped bands. The vivid pattern differences are readily detectable in various waterfalls plots. Various types of waterfall plots of temperature-dependent infrared (IR) spectra of ethylene glycol, which does not have the actual band shift but only two overlapped bands, and of Fourier transform infrared (FT-IR) spectra of 2 wt% acetone in a mixed solvent of CHCl(3)/CCl(4) demonstrate that waterfall plots are not able to unambiguously detect the difference between real band shift and two overlapped bands. Thus, the presence or lack of the asynchronous 2D butterfly pattern seems like the most effective diagnostic tool for band shift detection. PMID:21396181
Ryu, Soo Ryeon; Noda, Isao; Lee, Chang-Hee; Lee, Phil Ho; Hwang, Hyonseok; Jung, Young Mee
2011-04-01
In this study, we demonstrate the potentials and pitfalls of using various waterfall plots, such as conventional waterfall plots, two-dimensional (2D) gradient maps, moving window two-dimensional analysis (MW2D), perturbation-correlation moving window two-dimensional analysis (PCMW2D), and moving window principal component analysis two-dimensional correlation analysis (MWPCA2D), in the detection of the existence of band position shifts. Waterfall plots of the simulated spectral datasets are compared with conventional 2D correlation spectra. Different waterfall plots give different features in differentiating the behaviors of frequency shift versus two overlapped bands. Two-dimensional correlation spectra clearly show the very characteristic cluster pattern for both band position shifts and two overlapped bands. The vivid pattern differences are readily detectable in various waterfalls plots. Various types of waterfall plots of temperature-dependent infrared (IR) spectra of ethylene glycol, which does not have the actual band shift but only two overlapped bands, and of Fourier transform infrared (FT-IR) spectra of 2 wt% acetone in a mixed solvent of CHCl(3)/CCl(4) demonstrate that waterfall plots are not able to unambiguously detect the difference between real band shift and two overlapped bands. Thus, the presence or lack of the asynchronous 2D butterfly pattern seems like the most effective diagnostic tool for band shift detection.
NASA Technical Reports Server (NTRS)
Evans, K. F.
1993-01-01
A new two-dimensional monochromatic method that computes the transfer of solar or thermal radiation through atmospheres with arbitrary optical properties is described. The model discretizes the radiative transfer equation by expanding the angular part of the radiance field in a spherical harmonic series and representing the spatial part with a discrete grid. The resulting sparse coupled system of equations is solved iteratively with the conjugate gradient method. A Monte Carlo model is used for extensive verification of outgoing flux and radiance values from both smooth and highly variable (multifractal) media. The spherical harmonic expansion naturally allows for different levels of approximation, but tests show that the 2D equivalent of the two-stream approximation is poor at approximating variations in the outgoing flux. The model developed here is shown to be highly efficient so that media with tens of thousands of grid points can be computed in minutes. The large improvement in efficiency will permit quick, accurate radiative transfer calculations of realistic cloud fields and improve our understanding of the effect of inhomogeneity on radiative transfer in cloudy atmospheres.
Efficient Algorithms for the Two-Dimensional Ising Model with a Surface Field
NASA Astrophysics Data System (ADS)
Wu, Xintian
2014-12-01
The bond propagation and site propagation algorithms are extended to the two-dimensional (2D) Ising model with a surface field. With these algorithms we can calculate the free energy, internal energy, specific heat, magnetization, correlation functions, surface magnetization, surface susceptibility and surface correlations. The method can handle continuous and discrete bond and surface-field disorder and is especially efficient in the case of bond or site dilution. To test these algorithms, we study the wetting transition of the 2D Ising model, which was solved exactly by Abraham. We can locate the transition point accurately with a relative error of . We carry out the calculation of the specific heat and surface susceptibility on lattices with sizes up to . The results show that a finite jump develops in the specific heat and surface susceptibility at the transition point as the lattice size increases. For lattice size the parallel correlation length exponent is , while Abraham's exact result is . The perpendicular correlation length exponent for lattice size is , whereas its exact value is.
Prum, R. O.; Torres, R.; Williamson, S.; Dyck, J.
1999-01-01
We conducted two-dimensional (2D) discrete Fourier analyses of the spatial variation in refractive index of the spongy medullary keratin from four different colours of structurally coloured feather barbs from three species of bird: the rose-faced lovebird, Agapornis roseicollis (Psittacidae), the budgerigar, Melopsittacus undulatus (Psittacidae), and the Gouldian finch, Poephila guttata (Estrildidae). These results indicate that the spongy medullary keratin is a nanostructured tissue that functions as an array of coherent scatterers. The nanostructure of the medullary keratin is nearly uniform in all directions. The largest Fourier components of spatial variation in refractive index in the tissue are of the appropriate size to produce the observed colours by constructive interference alone. The peaks of the predicted reflectance spectra calculated from the 2D Fourier power spectra are congruent with the reflectance spectra measured by using microspectrophotometry. The alternative physical models for the production of these colours, the Rayleigh and Mie theories, hypothesize that medullary keratin is an incoherent array and that scattered waves are independent in phase. This assumption is falsified by the ring-like Fourier power spectra of these feathers, and the spacing of the scattering air vacuoles in the medullary keratin. Structural colours of avian feather barbs are produced by constructive interference of coherently scattered light waves from the optically heterogeneous matrix of keratin and air in the spongy medullary layer.
Simulation study of seemingly Fickian but heterogeneous dynamics of two dimensional colloids.
Kim, Jeongmin; Kim, Chanjoong; Sung, Bong June
2013-01-25
A two-dimensional (2D) solid lacks long-range positional order and is diffusive by means of the cooperative motion of particles. We find from molecular dynamics simulations of hard discs that 2D colloids in solid and hexatic phases show seemingly Fickian but strongly heterogeneous dynamics. Beyond translational relaxation time, the mean-square displacement is linear with time, t, implying that discs would undergo Brownian diffusion and the self-part of the van Hove correlation function [G(s)(r,t)] might be Gaussian. But dynamics is still heterogeneous and G(s)(r,t) is exponential at large r and oscillatory with multiple peaks at intermediate length. We attribute the existence of several such peaks to the observation that there are several clusters of discs with discretized mobility. The cluster of marginally mobile discs grows with time and begins to percolate around translational relaxation time while clusters of fast discs emerge in the middle of the marginally mobile cluster.
Ab Initio Prediction of Piezoelectricity in Two-Dimensional Materials.
Blonsky, Michael N; Zhuang, Houlong L; Singh, Arunima K; Hennig, Richard G
2015-10-27
Two-dimensional (2D) materials present many unique materials concepts, including material properties that sometimes differ dramatically from those of their bulk counterparts. One of these properties, piezoelectricity, is important for micro- and nanoelectromechanical systems applications. Using symmetry analysis, we determine the independent piezoelectric coefficients for four groups of predicted and synthesized 2D materials. We calculate with density-functional perturbation theory the stiffness and piezoelectric tensors of these materials. We determine the in-plane piezoelectric coefficient d11 for 37 materials within the families of 2D metal dichalcogenides, metal oxides, and III-V semiconductor materials. A majority of the structures, including CrSe2, CrTe2, CaO, CdO, ZnO, and InN, have d11 coefficients greater than 5 pm/V, a typical value for bulk piezoelectric materials. Our symmetry analysis shows that buckled 2D materials exhibit an out-of-plane coefficient d31. We find that d31 for 8 III-V semiconductors ranges from 0.02 to 0.6 pm/V. From statistical analysis, we identify correlations between the piezoelectric coefficients and the electronic and structural properties of the 2D materials that elucidate the origin of the piezoelectricity. Among the 37 2D materials, CdO, ZnO, and CrTe2 stand out for their combination of large piezoelectric coefficient and low formation energy and are recommended for experimental exploration. PMID:26312745
Ab Initio Prediction of Piezoelectricity in Two-Dimensional Materials.
Blonsky, Michael N; Zhuang, Houlong L; Singh, Arunima K; Hennig, Richard G
2015-10-27
Two-dimensional (2D) materials present many unique materials concepts, including material properties that sometimes differ dramatically from those of their bulk counterparts. One of these properties, piezoelectricity, is important for micro- and nanoelectromechanical systems applications. Using symmetry analysis, we determine the independent piezoelectric coefficients for four groups of predicted and synthesized 2D materials. We calculate with density-functional perturbation theory the stiffness and piezoelectric tensors of these materials. We determine the in-plane piezoelectric coefficient d11 for 37 materials within the families of 2D metal dichalcogenides, metal oxides, and III-V semiconductor materials. A majority of the structures, including CrSe2, CrTe2, CaO, CdO, ZnO, and InN, have d11 coefficients greater than 5 pm/V, a typical value for bulk piezoelectric materials. Our symmetry analysis shows that buckled 2D materials exhibit an out-of-plane coefficient d31. We find that d31 for 8 III-V semiconductors ranges from 0.02 to 0.6 pm/V. From statistical analysis, we identify correlations between the piezoelectric coefficients and the electronic and structural properties of the 2D materials that elucidate the origin of the piezoelectricity. Among the 37 2D materials, CdO, ZnO, and CrTe2 stand out for their combination of large piezoelectric coefficient and low formation energy and are recommended for experimental exploration.
Two-Dimensional Ffowcs Williams/Hawkings Equation Solver
NASA Technical Reports Server (NTRS)
Lockard, David P.
2005-01-01
FWH2D is a Fortran 90 computer program that solves a two-dimensional (2D) version of the equation, derived by J. E. Ffowcs Williams and D. L. Hawkings, for sound generated by turbulent flow. FWH2D was developed especially for estimating noise generated by airflows around such approximately 2D airframe components as slats. The user provides input data on fluctuations of pressure, density, and velocity on some surface. These data are combined with information about the geometry of the surface to calculate histories of thickness and loading terms. These histories are fast-Fourier-transformed into the frequency domain. For each frequency of interest and each observer position specified by the user, kernel functions are integrated over the surface by use of the trapezoidal rule to calculate a pressure signal. The resulting frequency-domain signals are inverse-fast-Fourier-transformed back into the time domain. The output of the code consists of the time- and frequency-domain representations of the pressure signals at the observer positions. Because of its approximate nature, FWH2D overpredicts the noise from a finite-length (3D) component. The advantage of FWH2D is that it requires a fraction of the computation time of a 3D Ffowcs Williams/Hawkings solver.
Electrical contacts to two-dimensional semiconductors
NASA Astrophysics Data System (ADS)
Allain, Adrien; Kang, Jiahao; Banerjee, Kaustav; Kis, Andras
2015-12-01
The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.
Electrical contacts to two-dimensional semiconductors.
Allain, Adrien; Kang, Jiahao; Banerjee, Kaustav; Kis, Andras
2015-12-01
The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.
Two Dimensional Mechanism for Insect Hovering
Jane Wang, Z.
2000-09-04
Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient. (c) 2000 The American Physical Society.
Two-dimensional interpreter for field-reversed configurations
Steinhauer, Loren
2014-08-15
An interpretive method is developed for extracting details of the fully two-dimensional (2D) “internal” structure of field-reversed configurations (FRC) from common diagnostics. The challenge is that only external and “gross” diagnostics are routinely available in FRC experiments. Inferring such critical quantities as the poloidal flux and the particle inventory has commonly relied on a theoretical construct based on a quasi-one-dimensional approximation. Such inferences sometimes differ markedly from the more accurate, fully 2D reconstructions of equilibria. An interpreter based on a fully 2D reconstruction is needed to enable realistic within-the-shot tracking of evolving equilibrium properties. Presented here is a flexible equilibrium reconstruction with which an extensive data base of equilibria was constructed. An automated interpreter then uses this data base as a look-up table to extract evolving properties. This tool is applied to data from the FRC facility at Tri Alpha Energy. It yields surprising results at several points, such as the inferences that the local β (plasma pressure/external magnetic pressure) of the plasma climbs well above unity and the poloidal flux loss time is somewhat longer than previously thought, both of which arise from full two-dimensionality of FRCs.
Two-dimensional order and disorder thermofields
Belvedere, L. V.
2006-11-15
The main objective of this paper was to obtain the two-dimensional order and disorder thermal operators using the Thermofield Bosonization formalism. We show that the general property of the two-dimensional world according with the bosonized Fermi field at zero temperature can be constructed as a product of an order and a disorder variables which satisfy a dual field algebra holds at finite temperature. The general correlation functions of the order and disorder thermofields are obtained.
Efficient Two-Dimensional-FFT Program
NASA Technical Reports Server (NTRS)
Miko, J.
1992-01-01
Program computes 64 X 64-point fast Fourier transform in less than 17 microseconds. Optimized 64 X 64 Point Two-Dimensional Fast Fourier Transform combines performance of real- and complex-valued one-dimensional fast Fourier transforms (FFT's) to execute two-dimensional FFT and coefficients of power spectrum. Coefficients used in many applications, including analyzing spectra, convolution, digital filtering, processing images, and compressing data. Source code written in C, 8086 Assembly, and Texas Instruments TMS320C30 Assembly languages.
Thermopower in Two-Dimensional Electron Systems
NASA Astrophysics Data System (ADS)
Chickering, William Elbridge
The subject of this thesis is the measurement and interpretation of thermopower in high-mobility two-dimensional electron systems (2DESs). These 2DESs are realized within state-of-the-art GaAs/AlGaAs heterostructures that are cooled to temperatures as low as T = 20 mK. Much of this work takes place within strong magnetic fields where the single-particle density of states quantizes into discrete Landau levels (LLs), a regime best known for the quantum Hall effect (QHE). In addition, we review a novel hot-electron technique for measuring thermopower of 2DESs that dramatically reduces the influence of phonon drag. Early chapters concentrate on experimental materials and methods. A brief overview of GaAs/AlGaAs heterostructures and device fabrication is followed by details of our cryogenic setup. Next, we provide a primer on thermopower that focuses on 2DESs at low temperatures. We then review our experimental devices, temperature calibration methods, as well as measurement circuits and protocols. Latter chapters focus on the physics and thermopower results in the QHE regime. After reviewing the basic phenomena associated with the QHE, we discuss thermopower in this regime. Emphasis is given to the relationship between diffusion thermopower and entropy. Experimental results demonstrate this relationship persists well into the fractional quantum Hall (FQH) regime. Several experimental results are reviewed. Unprecedented observations of the diffusion thermopower of a high-mobility 2DES at temperatures as high as T = 2 K are achieved using our hot-electron technique. The composite fermion (CF) effective mass is extracted from measurements of thermopower at LL filling factor nu = 3/2. The thermopower versus magnetic field in the FQH regime is shown to be qualitatively consistent with a simple entropic model of CFs. The thermopower at nu = 5/2 is shown to be quantitatively consistent with the presence of non-Abelian anyons. An abrupt collapse of thermopower is observed at
A Two-Dimensional Compressible Gas Flow Code
1995-03-17
F2D is a general purpose, two dimensional, fully compressible thermal-fluids code that models most of the phenomena found in situations of coupled fluid flow and heat transfer. The code solves momentum, continuity, gas-energy, and structure-energy equations using a predictor-correction solution algorithm. The corrector step includes a Poisson pressure equation. The finite difference form of the equation is presented along with a description of input and output. Several example problems are included that demonstrate the applicabilitymore » of the code in problems ranging from free fluid flow, shock tubes and flow in heated porous media.« less
Two-dimensional aperture coding for magnetic sector mass spectrometry.
Russell, Zachary E; Chen, Evan X; Amsden, Jason J; Wolter, Scott D; Danell, Ryan M; Parker, Charles B; Stoner, Brian R; Gehm, Michael E; Brady, David J; Glass, Jeffrey T
2015-02-01
In mass spectrometer design, there has been a historic belief that there exists a fundamental trade-off between instrument size, throughput, and resolution. When miniaturizing a traditional system, performance loss in either resolution or throughput would be expected. However, in optical spectroscopy, both one-dimensional (1D) and two-dimensional (2D) aperture coding have been used for many years to break a similar trade-off. To provide a viable path to miniaturization for harsh environment field applications, we are investigating similar concepts in sector mass spectrometry. Recently, we demonstrated the viability of 1D aperture coding and here we provide a first investigation of 2D coding. In coded optical spectroscopy, 2D coding is preferred because of increased measurement diversity for improved conditioning and robustness of the result. To investigate its viability in mass spectrometry, analytes of argon, acetone, and ethanol were detected using a custom 90-degree magnetic sector mass spectrometer incorporating 2D coded apertures. We developed a mathematical forward model and reconstruction algorithm to successfully reconstruct the mass spectra from the 2D spatially coded ion positions. This 2D coding enabled a 3.5× throughput increase with minimal decrease in resolution. Several challenges were overcome in the mass spectrometer design to enable this coding, including the need for large uniform ion flux, a wide gap magnetic sector that maintains field uniformity, and a high resolution 2D detection system for ion imaging. Furthermore, micro-fabricated 2D coded apertures incorporating support structures were developed to provide a viable design that allowed ion transmission through the open elements of the code. PMID:25510933
NASA Astrophysics Data System (ADS)
Romero Kalmanovitz, Natalia
2009-12-01
The nonlinear behavior of low-dimensional electron systems has attracted a great deal of attention for its fundamental interest as well as for potentially important applications in nanoelectronics. This work focuses on experimental results related to the nonlinear behavior of two dimensional electron systems. We first observed the non-linear zero-differential resistance state (ZDRS) that occurs for highly mobile two dimensional electron systems in response to a dc bias in the presence of a strong magnetic field applied perpendicular to the electron plane is suppressed. We found that it disappears gradually as the magnetic field is tilted away from the perpendicular at fixed filling factor. Good agreement is found with a model that considers the effect of the Zeeman splitting of Landau levels enhanced by the in-plane component of the magnetic field. Furthermore, we observed that when an electric field is applied to conductors, it heats electric charge carriers. It is demonstrated that an electric field applied to a conductor with a discrete electron spectrum produces a non-equilibrium electron distribution, which cannot be described by temperature. Such electron distribution changes significantly the conductivity of the electrons in a magnetic field, and forces them into a state with a zero differential resistance. Most importantly, the results demonstrate that in general, the effective overheating in the systems with discrete spectrum is significantly stronger than the one in systems with continuous and homogeneous distribution of the energy levels at the same input power. In the last part we observed non-linear behavior in a silicon MOSFET. Measurements of the rectification of microwave radiation at the boundary between two-dimensional electron systems separated by a narrow gap on a silicon surface for different temperatures, electron densities and microwave power, were performed. A theory is proposed that attributes the rectification to the thermoelectric
Ultrafast Band Structure Control of a Two-Dimensional Heterostructure.
Ulstrup, Søren; Čabo, Antonija Grubišić; Miwa, Jill A; Riley, Jonathon M; Grønborg, Signe S; Johannsen, Jens C; Cacho, Cephise; Alexander, Oliver; Chapman, Richard T; Springate, Emma; Bianchi, Marco; Dendzik, Maciej; Lauritsen, Jeppe V; King, Phil D C; Hofmann, Philip
2016-06-28
The electronic structure of two-dimensional (2D) semiconductors can be significantly altered by screening effects, either from free charge carriers in the material or by environmental screening from the surrounding medium. The physical properties of 2D semiconductors placed in a heterostructure with other 2D materials are therefore governed by a complex interplay of both intra- and interlayer interactions. Here, using time- and angle-resolved photoemission, we are able to isolate both the layer-resolved band structure and, more importantly, the transient band structure evolution of a model 2D heterostructure formed of a single layer of MoS2 on graphene. Our results reveal a pronounced renormalization of the quasiparticle gap of the MoS2 layer. Following optical excitation, the band gap is reduced by up to ∼400 meV on femtosecond time scales due to a persistence of strong electronic interactions despite the environmental screening by the n-doped graphene. This points to a large degree of tunability of both the electronic structure and the electron dynamics for 2D semiconductors embedded in a van der Waals-bonded heterostructure. PMID:27267820
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
2016-09-26
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 assemblies in different dimensions to achieve 2D conducting polymer nanosheets with structural ordering at the mesoscale. The supramolecular assemblies of amphipathic perfluorinated carboxylic acids and block co-polymers serve as 2D interfaces and meso-inducing moieties, respectively, which guide the polymerization of aniline into 2D, free-standing mesoporous conducting polymer nanosheets. Grazing-incidence small-angle X-ray scattering combined with various microscopy demonstrates that the resulting mesoscale-ordered nanosheets have hexagonal lattice with d-spacing of about 30 nm, customizable pore sizes of 7-18 nm and thicknesses of 13-45 nm, and high surface area. Such template-directed assembly produces polyaniline nanosheets with enhanced π-π stacking interactions, thereby resulting in anisotropic and record-high electrical conductivity of approximately 41 S cm(-1) for the pristine polyaniline nanosheet based film and approximately 188 S cm(-1) for the hydrochloric acid-doped counterpart. Our moldable approach creates a new family of mesoscale-ordered structures as well as opens avenues to the programmed assembly of multifunctional materials. PMID:27603275
Two Dimensional Organometal Halide Perovskite Nanorods with Tunable Optical Properties.
Aharon, Sigalit; Etgar, Lioz
2016-05-11
Organo-metal halide perovskite is an efficient light harvester in photovoltaic solar cells. Organometal halide perovskite is used mainly in its "bulk" form in the solar cell. Confined perovskite nanostructures could be a promising candidate for efficient optoelectronic devices, taking advantage of the superior bulk properties of organo-metal halide perovskite, as well as the nanoscale properties. In this paper, we present facile low-temperature synthesis of two-dimensional (2D) lead halide perovskite nanorods (NRs). These NRs show a shift to higher energies in the absorbance and in the photoluminescence compared to the bulk material, which supports their 2D structure. X-ray diffraction (XRD) analysis of the NRs demonstrates their 2D nature combined with the tetragonal 3D perovskite structure. In addition, by alternating the halide composition, we were able to tune the optical properties of the NRs. Fast Fourier transform, and electron diffraction show the tetragonal structure of these NRs. By varying the ligands ratio (e.g., octylammonium to oleic acid) in the synthesis, we were able to provide the formation mechanism of these novel 2D perovskite NRs. The 2D perovskite NRs are promising candidates for a variety of optoelectronic applications, such as light-emitting diodes, lasing, solar cells, and sensors. PMID:27089497
Gate-induced superconductivity in two-dimensional atomic crystals
NASA Astrophysics Data System (ADS)
Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro
2016-09-01
Two-dimensional (2D) crystals are attracting growing interest in condensed matter physics, since these systems exhibit not only rich electronic and photonic properties but also exotic electronic phase transitions including superconductivity and charge density wave. Moreover, owing to the recent development of transfer methods after exfoliation and electric-double-layer transistors, superconducting 2D atomic crystals, the thicknesses of which are below 1–2 nm, have been successfully obtained. Here, we present a topical review on the recent discoveries of 2D crystalline superconductors by ionic-liquid gating and a series of their novel properties. In particular, we highlight two topics; quantum metallic states (or possible metallic ground states) and superconductivity robust against in-plane magnetic fields. These phenomena can be discussed with the effects of weakened disorder and/or broken spacial inversion symmetry leading to valley-dependent spin-momentum locking (spin-valley locking). These examples suggest the superconducting 2D crystals are new platforms for investigating the intrinsic quantum phases as well as exotic nature in 2D superconductors.
Gate-induced superconductivity in two-dimensional atomic crystals
NASA Astrophysics Data System (ADS)
Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro
2016-09-01
Two-dimensional (2D) crystals are attracting growing interest in condensed matter physics, since these systems exhibit not only rich electronic and photonic properties but also exotic electronic phase transitions including superconductivity and charge density wave. Moreover, owing to the recent development of transfer methods after exfoliation and electric-double-layer transistors, superconducting 2D atomic crystals, the thicknesses of which are below 1-2 nm, have been successfully obtained. Here, we present a topical review on the recent discoveries of 2D crystalline superconductors by ionic-liquid gating and a series of their novel properties. In particular, we highlight two topics; quantum metallic states (or possible metallic ground states) and superconductivity robust against in-plane magnetic fields. These phenomena can be discussed with the effects of weakened disorder and/or broken spacial inversion symmetry leading to valley-dependent spin-momentum locking (spin-valley locking). These examples suggest the superconducting 2D crystals are new platforms for investigating the intrinsic quantum phases as well as exotic nature in 2D superconductors.
3D reconstruction of two-dimensional crystals.
Stahlberg, Henning; Biyani, Nikhil; Engel, Andreas
2015-09-01
Electron crystallography of two-dimensional (2D) crystals determines the structure of membrane proteins in the lipid bilayer by imaging with cryo-electron microscopy and image processing. Membrane proteins can be packed in regular 2D arrays by their reconstitution in the presence of lipids at low lipid to protein weight-to-weight ratio. The crystal quality depends on the protein purity and homogeneity, its stability, and on the crystallization conditions. A 2D crystal presents the membrane protein in a functional and fully lipidated state. Electron crystallography determines the 3D structure even of small membrane proteins up to atomic resolution, but 3D density maps have a better resolution in the membrane plane than in the vertical direction. This problem can be partly eliminated by applying an iterative algorithm that exploits additional known constraints about the 2D crystal. 2D electron crystallography is particularly attractive for the structural analysis of membrane proteins that are too small for single particle analyses and too unstable to form 3D crystals. With the recent introduction of direct electron detector cameras, the routine determination of the atomic 3D structure of membrane-embedded membrane proteins is in reach. PMID:26093179
Photocurrent generation with two-dimensional van der Waals semiconductors.
Buscema, Michele; Island, Joshua O; Groenendijk, Dirk J; Blanter, Sofya I; Steele, Gary A; van der Zant, Herre S J; Castellanos-Gomez, Andres
2015-06-01
Two-dimensional (2D) materials have attracted a great deal of interest in recent years. This family of materials allows for the realization of versatile electronic devices and holds promise for next-generation (opto)electronics. Their electronic properties strongly depend on the number of layers, making them interesting from a fundamental standpoint. For electronic applications, semiconducting 2D materials benefit from sizable mobilities and large on/off ratios, due to the large modulation achievable via the gate field-effect. Moreover, being mechanically strong and flexible, these materials can withstand large strain (>10%) before rupture, making them interesting for strain engineering and flexible devices. Even in their single layer form, semiconducting 2D materials have demonstrated efficient light absorption, enabling large responsivity in photodetectors. Therefore, semiconducting layered 2D materials are strong candidates for optoelectronic applications, especially for photodetection. Here, we review the state-of-the-art in photodetectors based on semiconducting 2D materials, focusing on the transition metal dichalcogenides, novel van der Waals materials, black phosphorus, and heterostructures.
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
2016-09-26
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 assemblies in different dimensions to achieve 2D conducting polymer nanosheets with structural ordering at the mesoscale. The supramolecular assemblies of amphipathic perfluorinated carboxylic acids and block co-polymers serve as 2D interfaces and meso-inducing moieties, respectively, which guide the polymerization of aniline into 2D, free-standing mesoporous conducting polymer nanosheets. Grazing-incidence small-angle X-ray scattering combined with various microscopy demonstrates that the resulting mesoscale-ordered nanosheets have hexagonal lattice with d-spacing of about 30 nm, customizable pore sizes of 7-18 nm and thicknesses of 13-45 nm, and high surface area. Such template-directed assembly produces polyaniline nanosheets with enhanced π-π stacking interactions, thereby resulting in anisotropic and record-high electrical conductivity of approximately 41 S cm(-1) for the pristine polyaniline nanosheet based film and approximately 188 S cm(-1) for the hydrochloric acid-doped counterpart. Our moldable approach creates a new family of mesoscale-ordered structures as well as opens avenues to the programmed assembly of multifunctional materials.
CAS2D- NONROTATING BLADE-TO-BLADE, STEADY, POTENTIAL TRANSONIC CASCADE FLOW ANALYSIS CODE
NASA Technical Reports Server (NTRS)
Dulikravich, D. S.
1994-01-01
An exact, full-potential-equation model for the steady, irrotational, homoentropic, and homoenergetic flow of a compressible, inviscid fluid through a two-dimensional planar cascade together with its appropriate boundary conditions has been derived. The CAS2D computer program numerically solves an artificially time-dependent form of the actual full-potential-equation, providing a nonrotating blade-to-blade, steady, potential transonic cascade flow analysis code. Comparisons of results with test data and theoretical solutions indicate very good agreement. In CAS2D, the governing equation is discretized by using type-dependent, rotated finite differencing and the finite area technique. The flow field is discretized by providing a boundary-fitted, nonuniform computational mesh. This mesh is generated by using a sequence of conformal mapping, nonorthogonal coordinate stretching, and local, isoparametric, bilinear mapping functions. The discretized form of the full-potential equation is solved iteratively by using successive line over relaxation. Possible isentropic shocks are captured by the explicit addition of an artificial viscosity in a conservative form. In addition, a four-level, consecutive, mesh refinement feature makes CAS2D a reliable and fast algorithm for the analysis of transonic, two-dimensional cascade flows. The results from CAS2D are not directly applicable to three-dimensional, potential, rotating flows through a cascade of blades because CAS2D does not consider the effects of the Coriolis force that would be present in the three-dimensional case. This program is written in FORTRAN IV for batch execution and has been implemented on an IBM 370 series computer with a central memory requirement of approximately 200K of 8 bit bytes. The CAS2D program was developed in 1980.
2001-01-31
This software reduces the data from two-dimensional kSA MOS program, k-Space Associates, Ann Arbor, MI. Initial MOS data is recorded without headers in 38 columns, with one row of data per acquisition per lase beam tracked. The final MOSS 2d data file is reduced, graphed, and saved in a tab-delimited column format with headers that can be plotted in any graphing software.
Perspectives for spintronics in 2D materials
NASA Astrophysics Data System (ADS)
Han, Wei
2016-03-01
The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.
Two-dimensional SLIM with application to pulse Doppler MIMO radars
NASA Astrophysics Data System (ADS)
Jabbarian-Jahromi, Mohammad; Kahaei, Mohammad Hossein
2015-12-01
A two-dimensional (2D) sparse signal model is developed for pulse Doppler MIMO radars. Using this model, we develop the 2D sparse learning via iterative minimization (2D SLIM) algorithm. Simulation results show that the 2D SLIM compared to the 1D SLIM drastically reduces the computational burden while both of them have the same performance. Also, for estimation of range-angle-Doppler parameters, the 2D SLIM outperforms the matched filter (MF), smoothed L0-norm (SL0), iterative adaptive approach (IAA), and spectral projected gradient for l 1-norm minimization (SPGL1) algorithms.
Analytic Solution of a Two-Dimensional Hydrogen Atom
NASA Astrophysics Data System (ADS)
Yang, Xiao-Li.
1990-03-01
The two dimensional hydrogen atom problem is solved analytically in both the relativistic and non-relativistic cases. In the nonrelativistic case, exact formulae for energy eigenvalues and eigenfunctions for both the discrete and continuous parts of the spectrum, dipole matrix elements, DC Stark effect, single- and two-photon transition rate, fine and hyperfine structures are obtained. The binding energy of the ground state is found to be reduced by a factor of four from that of a three dimensional hydrogen atom. In the relativistic case, exact analytic expressions for discrete eigen energy and normalized eigen wave function are derived. It is shown that the solution to the Dirac equation is disjoint in the spin-coordinate space (four -component spinor) in contrast to the three dimensional counterpart. This surprising result is a consequence of the planar motion of the electron.
Two-Dimensional Electronic Spectroscopy in the Ultraviolet Wavelength Range.
West, Brantley A; Moran, Andrew M
2012-09-20
Coherent two-dimensional (2D) spectroscopies conducted at visible and infrared wavelengths are having a transformative impact on the understanding of numerous processes in condensed phases. The extension of 2D spectroscopy to the ultraviolet spectral range (2DUV) must contend with several challenges, including the attainment of adequate laser bandwidth, interferometric phase stability, and the suppression of undesired nonlinearities in the sample medium. Solutions to these problems are motivated by the study of a wide range of biological systems whose lowest-frequency electronic resonances are found in the UV. The development of 2DUV spectroscopy also makes possible the attainment of new insights into elementary chemical reaction dynamics (e.g., electrocyclic ring opening in cycloalkenes). Substantial progress has been made in both the implementation and application of 2DUV spectroscopy in the past several years. In this Perspective, we discuss 2DUV methodology, review recent applications, and speculate on what the future will hold.
Two-dimensional freezing criteria for crystallizing colloidal monolayers.
Wang, Ziren; Alsayed, Ahmed M; Yodh, Arjun G; Han, Yilong
2010-04-21
Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Lowen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At the freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing. PMID:20423183
Two-dimensional freezing criteria for crystallizing colloidal monolayers
Wang Ziren; Han Yilong; Alsayed, Ahmed M.
2010-04-21
Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Loewen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At the freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing.
Exchange interactions of magnetic surfaces below two-dimensional materials
NASA Astrophysics Data System (ADS)
Friedrich, Rico; Caciuc, Vasile; Atodiresei, Nicolae; Blügel, Stefan
2016-06-01
In this theoretical investigation we demonstrate that the adsorption of spatially extended two-dimensional (2D) π systems such as graphene and hexagonal boron nitride on the ferromagnetic fcc Co(111) surface leads to a specific behavior of the in-plane and interlayer Co-Co magnetic exchange interactions. More specifically, for both systems the magnetic exchange coupling within the first Co layer is enhanced, while the one between the first and the second Co layer is not modified, in contrast to the magnetic interlayer softening induced by organic molecules. Importantly, the in-plane magnetic hardening effect is mainly due to the hybridization between the pz states of the 2D π system and the d states of the Co surface.
Dispersion-free continuum two-dimensional electronic spectrometer.
Zheng, Haibin; Caram, Justin R; Dahlberg, Peter D; Rolczynski, Brian S; Viswanathan, Subha; Dolzhnikov, Dmitriy S; Khadivi, Amir; Talapin, Dmitri V; Engel, Gregory S
2014-03-20
Electronic dynamics span broad energy scales with ultrafast time constants in the condensed phase. Two-dimensional (2D) electronic spectroscopy permits the study of these dynamics with simultaneous resolution in both frequency and time. In practice, this technique is sensitive to changes in nonlinear dispersion in the laser pulses as time delays are varied during the experiment. We have developed a 2D spectrometer that uses broadband continuum generated in argon as the light source. Using this visible light in phase-sensitive optical experiments presents new challenges in implementation. We demonstrate all-reflective interferometric delays using angled stages. Upon selecting an ~180 nm window of the available bandwidth at ~10 fs compression, we probe the nonlinear response of broadly absorbing CdSe quantum dots and electronic transitions of Chlorophyll a.
Pressure Gradient Effects On Two-Dimensional Plasma Expansion
Moon, S; Smith, R F; Dunn, J; Keenan, R; Nilsen, J; Hunter, J R; Filevich, J; Rocca, J J; Marconi, M C; Shlyaptsev, V N
2004-10-05
Recent advances in interferometry has allowed for the characterization of the electron density expansion within a laser produced plasma to within 10 {micro}m of the target surface and over picosecond timescales. This technique employs the high brightness output of the transient gain Ni-like Pd collisional x-ray laser at 14.7 nm to construct an effective moving picture of the two-dimensional (2-D) expansion of the plasma. We present experimentally measured density profiles of an expanding Al plasma generated through laser irradiation in a 14mm line focus geometry. Significant lateral expansion was observed at all times as well as a pronounced on-axis electron density dip. Detailed modeling with a 2-D plasma physics code gives good agreement to experimental observations. Large pressure gradients associated with the tight focal spot conditions are calculated to dominate in shaping the plasma density profile.
Two-Dimensional Hexagonal Transition-Metal Oxide for Spintronics.
Kan, Erjun; Li, Ming; Hu, Shuanglin; Xiao, Chuanyun; Xiang, Hongjun; Deng, Kaiming
2013-04-01
Two-dimensional materials have been the hot subject of studies due to their great potential in applications. However, their applications in spintronics have been blocked by the difficulty in producing ordered spin structures in 2D structures. Here we demonstrated that the ultrathin films of recently experimentally realized wurtzite MnO can automatically transform into a stable graphitic structure with ordered spin arrangement via density functional calculation, and the stability of graphitic structure can be enhanced by external strain. Moreover, the antiferromagnetic ordering of graphitic MnO single layer can be switched into half-metallic ferromagnetism by small hole-doping, and the estimated Curie temperature is higher than 300 K. Thus, our results highlight a promising way toward 2D magnetic materials.
Nonlinear screening in large two-dimensional Coulomb clusters.
Kong, Minghui; Vagov, A; Partoens, B; Peeters, F M; Ferreira, W P; Farias, G A
2004-11-01
The distortion due to a fixed point impurity with variable charge placed in the center of a classical harmonically confined two-dimensional (2D) large Coulomb cluster is studied. We find that the net topological charge (N(-)-N+ ) of the system is always equal to six independent of the position and charge of the impurity. In comparison with a 2D cluster without impurity charge, only the breathing mode remains unchanged. The screening length is found to be a highly nonlinear function of the impurity charge. For values of the impurity charge smaller than the charge of the other particles, the system has almost the same screening strength. When the impurity charge is larger, the screening length is strongly enhanced. This result can be explained by the competition between the different forces active in the system.
Nonlinear screening in large two-dimensional Coulomb clusters
Kong, Minghui; Vagov, A.; Partoens, B.; Peeters, F.M.; Ferreira, W.P.; Farias, G.A.
2004-11-01
The distortion due to a fixed point impurity with variable charge placed in the center of a classical harmonically confined two-dimensional (2D) large Coulomb cluster is studied. We find that the net topological charge (N{sub -}-N{sub +}) of the system is always equal to six independent of the position and charge of the impurity. In comparison with a 2D cluster without impurity charge, only the breathing mode remains unchanged. The screening length is found to be a highly nonlinear function of the impurity charge. For values of the impurity charge smaller than the charge of the other particles, the system has almost the same screening strength. When the impurity charge is larger, the screening length is strongly enhanced. This result can be explained by the competition between the different forces active in the system.
Ultrabroadband two-quantum two-dimensional electronic spectroscopy
NASA Astrophysics Data System (ADS)
Gellen, Tobias A.; Bizimana, Laurie A.; Carbery, William P.; Breen, Ilana; Turner, Daniel B.
2016-08-01
A recent theoretical study proposed that two-quantum (2Q) two-dimensional (2D) electronic spectroscopy should be a background-free probe of post-Hartree-Fock electronic correlations. Testing this theoretical prediction requires an instrument capable of not only detecting multiple transitions among molecular excited states but also distinguishing molecular 2Q signals from nonresonant response. Herein we describe a 2Q 2D spectrometer with a spectral range of 300 nm that is passively phase stable and uses only beamsplitters and mirrors. We developed and implemented a dual-chopping balanced-detection method to resolve the weak molecular 2Q signals. Experiments performed on cresyl violet perchlorate and rhodamine 6G revealed distinct 2Q signals convolved with nonresonant response. Density functional theory computations helped reveal the molecular origin of these signals. The experimental and computational results demonstrate that 2Q electronic spectra can provide a singular probe of highly excited electronic states.
Nonlinear compressional waves in a two-dimensional Yukawa lattice.
Avinash, K; Zhu, P; Nosenko, V; Goree, J
2003-10-01
A modified Korteweg-de Vries (KdV) equation is obtained for studying the propagation of nonlinear compressional waves and pulses in a chain of particles including the effect of damping. Suitably altering the linear phase velocity makes this equation useful also for the problem of phonon propagation in a two-dimensional (2D) lattice. Assuming a Yukawa potential, we use this method to model compressional wave propagation in a 2D plasma crystal, as in a recent experiment. By integrating the modified KdV equation the pulse is allowed to evolve, and good agreement with the experiment is found. It is shown that the speed of a compressional pulse increases with its amplitude, while the speed of a rarefactive pulse decreases. It is further discussed how the drag due to the background gas has a crucial role in weakening nonlinear effects and preventing the emergence of a soliton. PMID:14683049
Two-dimensional atom localization induced by a squeezed vacuum
NASA Astrophysics Data System (ADS)
Wang, Fei; Xu, Jun
2016-10-01
A scheme of two-dimensional (2D) atom localization induced by a squeezed vacuum is proposed, in which the three-level V-type atoms interact with two classical standing-wave fields. It is found that when the environment is changed from an ordinary vacuum to a squeezed vacuum, the 2D atom localization is realized by detecting the position-dependent resonance fluorescence spectrum. For comparison, we demonstrate that the atom localization originating from the quantum interference effect is distinct from that induced by a squeezed vacuum. Furthermore, the combined effects of the squeezed vacuum and quantum interference are also discussed under appropriate conditions. The internal physical mechanism is analyzed in terms of dressed-state representation. Project supported by the National Natural Science Foundation of China (Grant Nos. 11574179 and 11204099) and the Natural Science Foundation of Hubei Province, China (Grant No. 2014CFC1148).
Superfluid response of two-dimensional parahydrogen clusters in confinement
Idowu, Saheed; Boninsegni, Massimo
2015-04-07
We study by computer simulations the effect of confinement on the superfluid properties of small two-dimensional (2D) parahydrogen clusters. For clusters of fewer than twenty molecules, the superfluid response in the low temperature limit is found to remain comparable in magnitude to that of free clusters, within a rather wide range of depth and size of the confining well. The resilience of the superfluid response is attributable to the “supersolid” character of these clusters. We investigate the possibility of establishing a bulk 2D superfluid “cluster crystal” phase of p-H{sub 2}, in which a global superfluid response would arise from tunnelling of molecules across adjacent unit cells. The computed energetics suggests that for clusters of about ten molecules, such a phase may be thermodynamically stable against the formation of the equilibrium insulating crystal, for values of the cluster crystal lattice constant possibly allowing tunnelling across adjacent unit cells.
Dynamic metastability in the two-dimensional Potts ferromagnet.
Ibáñez Berganza, Miguel; Petri, Alberto; Coletti, Pietro
2014-05-01
We investigate the nonequilibrium dynamics of the two-dimensional (2D) Potts model on the square lattice after a quench below the discontinuous transition point. By means of numerical simulations of systems with q=12, 24, and 48, we observe the onset of a stationary regime below the temperature-driven transition, in a temperature interval decreasing with the system size and increasing with q. These results obtained dynamically agree with those obtained from the analytical continuation of the free energy [J. L. Meunier and A. Morel, Eur. Phys. J. B 13, 341 (2000)], from which metastability in the 2D Potts model results to be a finite-size effect. PMID:25353747
Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides.
Jana, Manoj K; Rao, C N R
2016-09-13
The discovery of graphene marks a major event in the physics and chemistry of materials. The amazing properties of this two-dimensional (2D) material have prompted research on other 2D layered materials, of which layered transition metal dichalcogenides (TMDCs) are important members. Single-layer and few-layer TMDCs have been synthesized and characterized. They possess a wide range of properties many of which have not been known hitherto. A typical example of such materials is MoS2 In this article, we briefly present various aspects of layered analogues of graphene as exemplified by TMDCs. The discussion includes not only synthesis and characterization, but also various properties and phenomena exhibited by the TMDCs.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.
Two-dimensional Topology of Cosmological Reionization
NASA Astrophysics Data System (ADS)
Wang, Yougang; Park, Changbom; Xu, Yidong; Chen, Xuelei; Kim, Juhan
2015-11-01
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 Kilometre Array.
TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION
Wang, Yougang; Xu, Yidong; Chen, Xuelei; Park, Changbom; Kim, Juhan E-mail: cbp@kias.re.kr
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.
Pressure profiles of nonuniform two-dimensional atomic Fermi gases
NASA Astrophysics Data System (ADS)
Martiyanov, Kirill; Barmashova, Tatiana; Makhalov, Vasiliy; Turlapov, Andrey
2016-06-01
Spatial profiles of the pressure have been measured in atomic Fermi gases with primarily two-dimensional (2D) kinematics. The in-plane motion of the particles is confined by a Gaussian-shape potential. The two-component deeply degenerate Fermi gases are prepared at different values of the s -wave attraction. The pressure profile is found using the force-balance equation, from the measured density profile and the trapping potential. The pressure is compared to zero-temperature models within the local density approximation. In the weakly interacting regime, the pressure lies above a Landau Fermi-liquid theory and below the ideal-Fermi-gas model, whose prediction coincides with that of the Cooper-pair mean-field theory. The values closest to the data are provided by the approach where the mean field of Cooper pairs is supplemented with fluctuations. In the regime of strong interactions, in response to the increasing attraction, the pressure shifts below this model reaching lower values calculated within Monte Carlo methods. Comparison to models shows that interaction-induced departure from 2D kinematics is either small or absent. In particular, comparison with a lattice Monte Carlo suggests that kinematics is two dimensional in the strongly interacting regime.
Statistical mechanics of shell models for two-dimensional turbulence
NASA Astrophysics Data System (ADS)
Aurell, E.; Boffetta, G.; Crisanti, A.; Frick, P.; Paladin, G.; Vulpiani, A.
1994-12-01
We study shell models that conserve the analogs of energy and enstrophy and hence are designed to mimic fluid turbulence in two-dimensions (2D). The main result is that the observed state is well described as a formal statistical equilibrium, closely analogous to the approach to two-dimensional ideal hydrodynamics of Onsager [Nuovo Cimento Suppl. 6, 279 (1949)], Hopf [J. Rat. Mech. Anal. 1, 87 (1952)], and Lee [Q. Appl. Math. 10, 69 (1952)]. In the presence of forcing and dissipation we observe a forward flux of enstrophy and a backward flux of energy. These fluxes can be understood as mean diffusive drifts from a source to two sinks in a system which is close to local equilibrium with Lagrange multipliers (``shell temperatures'') changing slowly with scale. This is clear evidence that the simplest shell models are not adequate to reproduce the main features of two-dimensional turbulence. The dimensional predictions on the power spectra from a supposed forward cascade of enstrophy and from one branch of the formal statistical equilibrium coincide in these shell models in contrast to the corresponding predictions for the Navier-Stokes and Euler equations in 2D. This coincidence has previously led to the mistaken conclusion that shell models exhibit a forward cascade of enstrophy. We also study the dynamical properties of the models and the growth of perturbations.
Comprehensive two-dimensional liquid chromatographic analysis of poloxamers.
Malik, Muhammad Imran; Lee, Sanghoon; Chang, Taihyun
2016-04-15
Poloxamers are low molar mass triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), having number of applications as non-ionic surfactants. Comprehensive one and two-dimensional liquid chromatographic (LC) analysis of these materials is proposed in this study. The separation of oligomers of both types (PEO and PPO) is demonstrated for several commercial poloxamers. This is accomplished at the critical conditions for one of the block while interaction for the other block. Reversed phase LC at CAP of PEO allowed for oligomeric separation of triblock copolymers with regard to PPO block whereas normal phase LC at CAP of PPO renders oligomeric separation with respect to PEO block. The oligomeric separation with regard to PEO and PPO are coupled online (comprehensive 2D-LC) to reveal two-dimensional contour plots by unconventional 2D IC×IC (interaction chromatography) coupling. The study provides chemical composition mapping of both PEO and PPO, equivalent to combined molar mass and chemical composition mapping for several commercial poloxamers.
Two-dimensional Cu2Si monolayer with planar hexacoordinate copper and silicon bonding.
Yang, Li-Ming; Bačić, Vladimir; Popov, Ivan A; Boldyrev, Alexander I; Heine, Thomas; Frauenheim, Thomas; Ganz, Eric
2015-02-25
Two-dimensional (2D) materials with planar hypercoordinate motifs are extremely rare due to the difficulty in stabilizing the planar hypercoordinate configurations in extended systems. Furthermore, such exotic motifs are often unstable. We predict a novel Cu2Si 2D monolayer featuring planar hexacoordinate copper and planar hexacoordinate silicon. This is a global minimum in 2D space which displays reduced dimensionality and rule-breaking chemical bonding. This system has been studied with density functional theory, including molecular dynamics simulations and electronic structure calculations. Bond order analysis and partitioning reveals 4c-2e σ bonds that stabilize the two-dimensional structure. We find that the system is quite stable during short annealing simulations up to 900 K, and predict that it is a nonmagnetic metal. This work opens up a new branch of hypercoordinate two-dimensional materials for study.
NASA Astrophysics Data System (ADS)
Warisarn, C.; Losuwan, T.; Supnithi, P.; Kovintavewat, P.
2014-05-01
At high recording density, the readback signal of two-dimensional magnetic recording is inevitably corrupted by the two-dimensional (2D) interference consisting of inter-symbol interference and inter-track interference (ITI), which can significantly degrade the overall system performance. This paper proposes an iterative ITI mitigation method using three modified 2D soft-output Viterbi algorithm (2D-SOVA) detectors in conjunction with an iterative processing technique to combat the 2D interference. The codeword of the outer code is divided and then written on three separate tracks. For every iteration, all 2D-SOVA detectors exchange the soft information to improve the reliability of the a priori information and use it in the branch metric calculation, before feeding the refined soft information to the outer decoder. Simulation results show that the proposed method outperforms the conventional receiver and the existing partial ITI mitigation method.
Grain boundaries in hybrid two-dimensional materials
NASA Astrophysics Data System (ADS)
Zhang, Zhuhua; Yang, Yang; Yakobson, Boris I.
2014-10-01
In two-dimensional (2D) materials, bisector grain boundaries (GBs) are energetically favorable as they allow perfect match of neighbor grains. We demonstrate here a contrasting behavior for GBs in hybrid 2D materials, which tend to be non-bisector and obey a universal law to optimally match the heterogeneous grains: the ratio of cosines of the rotation angles of two neighbor grains equals the ratio of constituent's lattice parameters, reminiscent of Snell's law for light refraction. Details of the optimal GB structures are further formulated in terms of tilt angle, lattice mismatch strain and deviation angle from the bisector line, in good agreement with comprehensive numerical analyses. The ground state structures of the GBs manifest as a series of laterally misaligned bisector segments, which are verified by intensive first-principle calculations. Our findings not only provide a general guidance for exploring GBs in various hybrid 2D materials but also serve as an important stepping stone for understanding mechanical and electronic behaviors in these 2D nanoscale patchworks.
Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2010-01-01
Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence.The se features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo.Recently, the origin of broken ergodicity in 3-D MHD turbulence that is manifest in the lowest wavenumbers was explained. Here, a detailed description of the origins of broken ergodicity in 2-D MHD turbulence is presented. It will be seen that broken ergodicity in ideal 2-D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions.T he origins of broken ergodicity in ideal 2-D homogeneous MHD turbulence are found through an eigen analysis of the covariance matrices of the modal probability density functions.It will also be shown that when the lowest wavenumber magnetic field becomes quasi-stationary, the higher wavenumber modes can propagate as Alfven waves on these almost static large-scale magnetic structures
Correlating hydrodynamic radii with that of two-dimensional nanoparticles
Yue, Yuan; Kan, Yuwei; Clearfield, Abraham; Choi, Hyunho; Liang, Hong
2015-12-21
Dynamic light scattering (DLS) is one of the most adapted methods to measure the size of nanoparticles, as referred to the hydrodynamic radii (R{sub h}). However, the R{sub h} represents only that of three-dimensional spherical nanoparticles. In the present research, the size of two-dimensional (2D) nanoparticles of yttrium oxide (Y{sub 2}O{sub 3}) and zirconium phosphate (ZrP) was evaluated through comparing their hydrodynamic diameters via DLS with lateral sizes obtained using scanning and transmission electron microscopy. We demonstrate that the hydrodynamic radii are correlated with the lateral sizes of both square and circle shaped 2D nanoparticles. Two proportional coefficients, i.e., correcting factors, are proposed for the Brownian motion status of 2D nanoparticles. The correction is possible by simplifying the calculation of integrals in the case of small thickness approximation. The correcting factor has great significance for investigating the translational diffusion behavior of 2D nanoparticles in a liquid and in effective and low-cost measurement in terms of size and morphology of shape-specific nanoparticles.
Two-dimensional ultrasound image matching system for photodynamic therapy
NASA Astrophysics Data System (ADS)
Zaim, Amjad; Keck, Rick W.; Selman, Steven H.; Jankun, Jerzy
2001-05-01
Two-dimensional (2D) ultrasound imaging is commonly used for diagnosis in a variety of medical fields. However, there are several drawbacks of conventional 2D-ultrasound imaging. These include prostate or transducer movement that produces sets of different images that are difficult to interpret. Also during patient's reexamination correspondence between sets of images before reexamination and after is difficult to establish. This can be described as a problem of correlation between two sets of images: the first created before distortion or examination, the second one after. We propose a method to register 2D ultrasound volumes based on external markers introduced in the prostate. The metal balls are inserted in the prostate at three distinct locations in the prostate. These appear as bright dots in the ultrasound field, serve as reference points, are then outlined through a user-interactive program from two sets of images. Then, the computer program rotates and translates till they match respectively, and displays the mapped points with their corresponding location. Based on this idea we developed an image-guided system for PDT that require high-precision placement of implants. In the planning stage, the system performs an automatic acquisition of 2D transrectal ultrasound images that will ultimately be used to construct the treatment plan. At the time of the therapy, new sets of ultrasound images are acquired and a match is established between the virtual world and the patient's real world with the aid of manually introduced markers and image matching algorithms.
Two-dimensional state in driven magnetohydrodynamic turbulence
Bigot, Barbara; Galtier, Sebastien
2011-02-15
The dynamics of the two-dimensional (2D) state in driven three-dimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond, respectively, to spectral fluctuations in the plane k{sub ||}=0 and in the area k{sub ||}>0. It is shown that if initially the 2D state is set to zero it becomes nonnegligible in few turnover times, particularly when the external magnetic field is strong. The maintenance of a large-scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped, the previous break is removed and a decay phase emerges with Alfvenic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state, and in all situations a pinning effect is observed at small scales.
Effective viscosity of two-dimensional suspensions: Confinement effects
NASA Astrophysics Data System (ADS)
Doyeux, Vincent; Priem, Stephane; Jibuti, Levan; Farutin, Alexander; Ismail, Mourad; Peyla, Philippe
2016-08-01
We study the rheology of a sheared two-dimensional (2D) suspension of non-Brownian disks in the presence of walls. Although it is of course possible today with modern computers and powerful algorithms to perform direct numerical simulations that fully account for multiparticle 3D interactions in the presence of walls, the analysis of the simple case of a 2D suspension provides valuable insights and helps in the understanding of 3D results. Due to the direct visualization of the whole 2D flow (the shear plane), we are able to give a clear interpretation of the full hydrodynamics of semidilute confined suspensions. For instance, we examine the role of disk-wall and disk-disk interactions to determine the dissipation of confined sheared suspensions whose effective viscosity depends on the area fraction ϕ of the disks as ηeff=η0[1 +[η ] ϕ +β ϕ2+O (ϕ3) ] . We provide numerical estimates of [η ] and β for a wide range of confinements. As a benchmark for our simulations, we compare the numerical results obtained for [η ] and β for very weak confinements with analytical values [η] ∞ and β∞ obtained for an infinite fluid. If the value [η] ∞=2 is well known in the literature, much less is published on the value of β . Here we analytically calculate with very high precision β∞=3.6 . We also reexamine the 3D case in the light of our 2D results.
Two-dimensional state in driven magnetohydrodynamic turbulence.
Bigot, Barbara; Galtier, Sébastien
2011-02-01
The dynamics of the two-dimensional (2D) state in driven three-dimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond, respectively, to spectral fluctuations in the plane k(∥)=0 and in the area k(∥)>0. It is shown that if initially the 2D state is set to zero it becomes nonnegligible in few turnover times, particularly when the external magnetic field is strong. The maintenance of a large-scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped, the previous break is removed and a decay phase emerges with Alfvénic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state, and in all situations a pinning effect is observed at small scales.
Correlating hydrodynamic radii with that of two-dimensional nanoparticles
NASA Astrophysics Data System (ADS)
Yue, Yuan; Kan, Yuwei; Choi, Hyunho; Clearfield, Abraham; Liang, Hong
2015-12-01
Dynamic light scattering (DLS) is one of the most adapted methods to measure the size of nanoparticles, as referred to the hydrodynamic radii (Rh). However, the Rh represents only that of three-dimensional spherical nanoparticles. In the present research, the size of two-dimensional (2D) nanoparticles of yttrium oxide (Y2O3) and zirconium phosphate (ZrP) was evaluated through comparing their hydrodynamic diameters via DLS with lateral sizes obtained using scanning and transmission electron microscopy. We demonstrate that the hydrodynamic radii are correlated with the lateral sizes of both square and circle shaped 2D nanoparticles. Two proportional coefficients, i.e., correcting factors, are proposed for the Brownian motion status of 2D nanoparticles. The correction is possible by simplifying the calculation of integrals in the case of small thickness approximation. The correcting factor has great significance for investigating the translational diffusion behavior of 2D nanoparticles in a liquid and in effective and low-cost measurement in terms of size and morphology of shape-specific nanoparticles.
Performance Estimation for Two-Dimensional Brownian Rotary Ratchet Systems
NASA Astrophysics Data System (ADS)
Tutu, Hiroki; Horita, Takehiko; Ouchi, Katsuya
2015-04-01
Within the context of the Brownian ratchet model, a molecular rotary system that can perform unidirectional rotations induced by linearly polarized ac fields and produce positive work under loads was studied. The model is based on the Langevin equation for a particle in a two-dimensional (2D) three-tooth ratchet potential of threefold symmetry. The performance of the system is characterized by the coercive torque, i.e., the strength of the load competing with the torque induced by the ac driving field, and the energy efficiency in force conversion from the driving field to the torque. We propose a master equation for coarse-grained states, which takes into account the boundary motion between states, and develop a kinetic description to estimate the mean angular momentum (MAM) and powers relevant to the energy balance equation. The framework of analysis incorporates several 2D characteristics and is applicable to a wide class of models of smooth 2D ratchet potential. We confirm that the obtained expressions for MAM, power, and efficiency of the model can enable us to predict qualitative behaviors. We also discuss the usefulness of the torque/power relationship for experimental analyses, and propose a characteristic for 2D ratchet systems.
Low-cost two-dimensional gel densitometry.
Levenson, R M; Maytin, E V; Young, D A
1986-11-01
A major obstacle to full utilization of the powerful technique of two-dimensional (2-D) gel electrophoresis is the expense and complexity of quantifying the results. Using an analog-to-digital converter already present in the widely available Commodore 64 or Commodore 128 microcomputer, we have developed a 2-D gel densitometer (GELSCAN) which adds only $20.00 to the cost of the Commodore system (currently around $700.00). The system is designed to work with autoradiograms of 2-D gels. Spots of interest are identified visually and then positioned manually over a light source. A pinhole photoelectric sensor mounted in a hand-held, Plexiglas holder, or "mouse," is briefly rubbed over each spot. Maximum density of the spot is determined and its value is converted to counts per minute via an internal calibration curve which corrects for the nonlinear response of film to radiation. Local spot backgrounds can be subtracted and values can be normalized between gels to adjust for variation in amount of radioactivity applied or in exposure time. Reproducibility is excellent and the technique has some practical as well as theoretical advantages over other more complicated approaches to 2-D gel densitometry. In addition, the GELSCAN system can also be used for scanning individual bands in 1-D gels, quantitation of "dot-blot" autoradiograms and other tasks involving transmission densitometry.
Two-dimensional NMR spectroscopy. Applications for chemists and biochemists
Croasmun, W.R.; Carlson, R.M.K.
1987-01-01
Two-dimensional nuclear magnetic resonance spectroscopy (2-D NMR) has become a very powerful class of experiments (in the hands of an adept scientist) with broad adaptability to new situations. It is the product of a happy marriage between modern pulse FT-NMR technology, with its large memory and high-speed computers, and the physicists and chemists who love to manipulate spin systems. Basic 2-D experiments are now a standard capability of modern NMR spectrometers, and this timely book intends to make 2-D NMR users of those who are familiar with normal 1-D NMR. The 2-D NMR goal is correlation of the lines of the observed NMR spectrum with other properties of the system. This book deals with applications to high-resolution spectrum analysis, utilizing either coupling between the NMR-active nuclei or chemical exchange to perform the correlation. The coupling can be scalar (through bonds) or direct through space (within 5 A). The coupling may be homonuclear (between like nuclei) or heteronuclear.
Two-dimensional nanocrystals of molecular Janus particles.
Liu, Hao; Hsu, Chih-Hao; Lin, Zhiwei; Shan, Wenpeng; Wang, Jing; Jiang, Jing; Huang, Mingjun; Lotz, Bernard; Yu, Xinfei; Zhang, Wen-Bin; Yue, Kan; Cheng, Stephen Z D
2014-07-30
This paper describes a rational strategy to obtain self-assembled two-dimensional (2D) nanocrystals with definite and uniform thickness from a series of molecular Janus particles based on molecular nanoparticles (MNPs). MNPs are 3D framework with rigid shapes. Three different types of MNPs based on derivatives of polyhedral oligomeric silsesquioxane (POSS), [60]fullerene (C60), and Lindqvist-type polyoxometalate (POM) are used as building blocks to construct these amphiphilic molecular Janus particles by covalently connecting hydrophobic crystalline BPOSS with a charged hydrophilic MNP. The formation of 2D nanocrystals with an exact thickness of double layers of molecules is driven by directional crystallization of the BPOSS MNP and controlled by various factors such as solvent polarity, number of counterions, and sizes of the MNPs. Strong solvating interactions of the ionic MNPs in polar solvents (e.g., acetonitrile and dimethylformamide) are crucial to provide repulsive interactions between the charged outlying ionic MNPs and suppress further aggregation along the layer normal direction. The number of counterions per molecule plays a major role in determining the self-assembled morphologies. Size matching of the hydrophobic and ionic MNPs is another critical factor in the formation of 2D nanocrystals. Self-assembly of rationally designed molecular Janus particles provides a unique "bottom-up" strategy to engineer 2D nanostructures.
Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes).
Anasori, Babak; Xie, Yu; Beidaghi, Majid; Lu, Jun; Hosler, Brian C; Hultman, Lars; Kent, Paul R C; Gogotsi, Yury; Barsoum, Michel W
2015-10-27
The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), M'2M″C2 and M'2M″2C3, where M' and M″ are two different early transition metals. In these solids, M' layers sandwich M″ carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes' chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties.
Two-Dimensional Halide Perovskites: Tuning Electronic Activities of Defects.
Liu, Yuanyue; Xiao, Hai; Goddard, William A
2016-05-11
Two-dimensional (2D) halide perovskites are emerging as promising candidates for nanoelectronics and optoelectronics. To realize their full potential, it is important to understand the role of those defects that can strongly impact material properties. In contrast to other popular 2D semiconductors (e.g., transition metal dichalcogenides MX2) for which defects typically induce harmful traps, we show that the electronic activities of defects in 2D perovskites are significantly tunable. For example, even with a fixed lattice orientation one can change the synthesis conditions to convert a line defect (edge or grain boundary) from electron acceptor to inactive site without deep gap states. We show that this difference originates from the enhanced ionic bonding in these perovskites compared with MX2. The donors tend to have high formation energies and the harmful defects are difficult to form at a low halide chemical potential. Thus, we unveil unique properties of defects in 2D perovskites and suggest practical routes to improve them.
1990-04-25
Version 00 TPTRIA calculates reactivity, effective delayed neutron fractions and mean generation time for two-dimensional triangular geometry on the basis of neutron transport perturbation theory. DIAMANT2 (also designated as CCC-414), is a multigroup two-dimensional discrete ordinates transport code system for triangular and hexagonal geometry which calculates direct and adjoint angular fluxes.
NASA Astrophysics Data System (ADS)
Li, Xiao-Dong; Ho, John K. L.
2011-06-01
This article is concerned with some further results on iterative learning control (ILC) algorithms with convergence conditions for linear time-variant discrete systems. By converting two-Dimensional (2-D) ILC process of the linear time-variant discrete systems into 1-D linear time-invariant discrete systems, this article presents convergent ILC algorithms with necessary and sufficient conditions for two classes of linear time-variant discrete systems. Main results in (Li, X.-D., Ho, J.K.L., and Chow, T.W.S. (2005), 'Iterative Learning Control for Linear Time-variant Discrete Systems Based on 2-D System Theory', IEE Proceedings, Control Theory and Applications, 152, 13-18 and Huang, S.N., Tan, K.K., and Lee, T.H. (2002), 'Necessary and Sufficient Condition for Convergence of Iterative Learning Algorithm', Automatica 38, 1257-1260) are extended and generalised.
Two-Dimensional Turbulence in Magnetized Plasmas
ERIC Educational Resources Information Center
Kendl, A.
2008-01-01
In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…
Two-Dimensional Motions of Rockets
ERIC Educational Resources Information Center
Kang, Yoonhwan; Bae, Saebyok
2007-01-01
We analyse the two-dimensional motions of the rockets for various types of rocket thrusts, the air friction and the gravitation by using a suitable representation of the rocket equation and the numerical calculation. The slope shapes of the rocket trajectories are discussed for the three types of rocket engines. Unlike the projectile motions, the…
High-resolution two dimensional advective transport
Smith, P.E.; Larock, B.E.
1989-01-01
The paper describes a two-dimensional high-resolution scheme for advective transport that is based on a Eulerian-Lagrangian method with a flux limiter. The scheme is applied to the problem of pure-advection of a rotated Gaussian hill and shown to preserve the monotonicity property of the governing conservation law.
Valley excitons in two-dimensional semiconductors
Yu, Hongyi; Cui, Xiaodong; Xu, Xiaodong; Yao, Wang
2014-12-30
Monolayer group-VIB transition metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include: the visible range direct band gap ideal for exploring optoelectronic applications; the intriguing physics associated with spin and valley pseudospin of carriers which implies potentials for novel electronics based on these internal degrees of freedom; the exceptionally strong Coulomb interaction due to the two-dimensional geometry and the large effective masses. The physics of excitons, the bound states of electrons and holes, has been one of the most actively studied topics on these two-dimensional semiconductors, where the excitons exhibit remarkably new features due to the strong Coulomb binding, the valley degeneracy of the band edges, and the valley dependent optical selection rules for interband transitions. Here we give a brief overview of the experimental and theoretical findings on excitons in two-dimensional transition metal dichalcogenides, with focus on the novel properties associated with their valley degrees of freedom.
Valley excitons in two-dimensional semiconductors
Yu, Hongyi; Cui, Xiaodong; Xu, Xiaodong; Yao, Wang
2014-12-30
Monolayer group-VIB transition metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include: the visible range direct band gap ideal for exploring optoelectronic applications; the intriguing physics associated with spin and valley pseudospin of carriers which implies potentials for novel electronics based on these internal degrees of freedom; the exceptionally strong Coulomb interaction due to the two-dimensional geometry and the large effective masses. The physics of excitons, the bound states of electrons and holes, has been one of the most actively studied topics on these two-dimensional semiconductors, where the excitons exhibitmore » remarkably new features due to the strong Coulomb binding, the valley degeneracy of the band edges, and the valley dependent optical selection rules for interband transitions. Here we give a brief overview of the experimental and theoretical findings on excitons in two-dimensional transition metal dichalcogenides, with focus on the novel properties associated with their valley degrees of freedom.« less
Program Generates Two-Dimensional Computational Grids
NASA Technical Reports Server (NTRS)
Vu, Bruce T.
1994-01-01
TDIGG is fast and versatile computer program for generating two-dimensional computational grids for use in programs solving equations of flow by finite-difference methods. Both algebraic and elliptic grid-generation systems included. Enables user to view results of each iteration. Written in FORTRAN 77.
Anisotropic dielectric properties of two-dimensional matrix in pseudo-spin ferroelectric system
NASA Astrophysics Data System (ADS)
Kim, Se-Hun
2016-10-01
The anisotropic dielectric properties of a two-dimensional (2D) ferroelectric system were studied using the statistical calculation of the pseudo-spin Ising Hamiltonian model. It is necessary to delay the time for measurements of the observable and the independence of the new spin configuration under Monte Carlo sampling, in which the thermal equilibrium state depends on the temperature and size of the system. The autocorrelation time constants of the normalized relaxation function were determined by taking temperature and 2D lattice size into account. We discuss the dielectric constants of a two-dimensional ferroelectric system by using the Metropolis method in view of the Slater-Takagi defect energies.
Two-dimensional materials for novel liquid separation membranes.
Ying, Yulong; Yang, Yefeng; Ying, Wen; Peng, Xinsheng
2016-08-19
Demand for a perfect molecular-level separation membrane with ultrafast permeation and a robust mechanical property for any kind of species to be blocked in water purification and desalination is urgent. In recent years, due to their intrinsic characteristics, such as a unique mono-atom thick structure, outstanding mechanical strength and excellent flexibility, as well as facile and large-scale production, graphene and its large family of two-dimensional (2D) materials are regarded as ideal membrane materials for ultrafast molecular separation. A perfect separation membrane should be as thin as possible to maximize its flux, mechanically robust and without failure even if under high loading pressure, and have a narrow nanochannel size distribution to guarantee its selectivity. The latest breakthrough in 2D material-based membranes will be reviewed both in theories and experiments, including their current state-of-the-art fabrication, structure design, simulation and applications. Special attention will be focused on the designs and strategies employed to control microstructures to enhance permeation and selectivity for liquid separation. In addition, critical views on the separation mechanism within two-dimensional material-based membranes will be provided based on a discussion of the effects of intrinsic defects during growth, predefined nanopores and nanochannels during subsequent fabrication processes, the interlayer spacing of stacking 2D material flakes and the surface charge or functional groups. Furthermore, we will summarize the significant progress of these 2D material-based membranes for liquid separation in nanofiltration/ultrafiltration and pervaporation. Lastly, we will recall issues requiring attention, and discuss existing questionable conclusions in some articles and emerging challenges. This review will serve as a valuable platform to provide a compact source of relevant and timely information about the development of 2D material-based membranes as
Two-dimensional materials for novel liquid separation membranes.
Ying, Yulong; Yang, Yefeng; Ying, Wen; Peng, Xinsheng
2016-08-19
Demand for a perfect molecular-level separation membrane with ultrafast permeation and a robust mechanical property for any kind of species to be blocked in water purification and desalination is urgent. In recent years, due to their intrinsic characteristics, such as a unique mono-atom thick structure, outstanding mechanical strength and excellent flexibility, as well as facile and large-scale production, graphene and its large family of two-dimensional (2D) materials are regarded as ideal membrane materials for ultrafast molecular separation. A perfect separation membrane should be as thin as possible to maximize its flux, mechanically robust and without failure even if under high loading pressure, and have a narrow nanochannel size distribution to guarantee its selectivity. The latest breakthrough in 2D material-based membranes will be reviewed both in theories and experiments, including their current state-of-the-art fabrication, structure design, simulation and applications. Special attention will be focused on the designs and strategies employed to control microstructures to enhance permeation and selectivity for liquid separation. In addition, critical views on the separation mechanism within two-dimensional material-based membranes will be provided based on a discussion of the effects of intrinsic defects during growth, predefined nanopores and nanochannels during subsequent fabrication processes, the interlayer spacing of stacking 2D material flakes and the surface charge or functional groups. Furthermore, we will summarize the significant progress of these 2D material-based membranes for liquid separation in nanofiltration/ultrafiltration and pervaporation. Lastly, we will recall issues requiring attention, and discuss existing questionable conclusions in some articles and emerging challenges. This review will serve as a valuable platform to provide a compact source of relevant and timely information about the development of 2D material-based membranes as
Two-dimensional materials for novel liquid separation membranes
NASA Astrophysics Data System (ADS)
Ying, Yulong; Yang, Yefeng; Ying, Wen; Peng, Xinsheng
2016-08-01
Demand for a perfect molecular-level separation membrane with ultrafast permeation and a robust mechanical property for any kind of species to be blocked in water purification and desalination is urgent. In recent years, due to their intrinsic characteristics, such as a unique mono-atom thick structure, outstanding mechanical strength and excellent flexibility, as well as facile and large-scale production, graphene and its large family of two-dimensional (2D) materials are regarded as ideal membrane materials for ultrafast molecular separation. A perfect separation membrane should be as thin as possible to maximize its flux, mechanically robust and without failure even if under high loading pressure, and have a narrow nanochannel size distribution to guarantee its selectivity. The latest breakthrough in 2D material-based membranes will be reviewed both in theories and experiments, including their current state-of-the-art fabrication, structure design, simulation and applications. Special attention will be focused on the designs and strategies employed to control microstructures to enhance permeation and selectivity for liquid separation. In addition, critical views on the separation mechanism within two-dimensional material-based membranes will be provided based on a discussion of the effects of intrinsic defects during growth, predefined nanopores and nanochannels during subsequent fabrication processes, the interlayer spacing of stacking 2D material flakes and the surface charge or functional groups. Furthermore, we will summarize the significant progress of these 2D material-based membranes for liquid separation in nanofiltration/ultrafiltration and pervaporation. Lastly, we will recall issues requiring attention, and discuss existing questionable conclusions in some articles and emerging challenges. This review will serve as a valuable platform to provide a compact source of relevant and timely information about the development of 2D material-based membranes as
[CSNP discovery by two-dimensional gene scanning (TDGS)].
Suh, Y
2001-04-21
Challenges in the post-genomic era are to use genetic information in correlating individual gene variations (SNPs; single nucleotide polymorphisms, the most common form of genetic variation) with medically important parameters, such as disease susceptibility, individual responses to drugs and prognostic variables. What is missing is a high-throughput technology to identify all possible SNPs in essentially all human genes in population-based studies with high accuracy and speed in a cost-effective manner. Most tests advocated for their high throughput at low cost are actually SNP screening tests. That is, they screen samples for the presence of one or multiple previously identified SNPs. Such screening methods are only useful when all relevant SNPs in the genes of interest are known, which is presently not the case. Moreover, the usefulness of any one SNP varies enormously from population to population. Indeed, for the Korean population, where no information on possible sequence variation is available, a mutational scanning method, capable to detect all possible gene variations will be most useful. Two-Dimensional Gene Scanning (TDGS) is a high-throughput platform that enables to detect all possible SNPs in an entire gene in one gel under one set of conditions, with high sensitivity and specificity. TDGS is based on automated two-dimensional (2-D) DNA electrophoresis according to size and base pair sequence to detect DNA fragments containing all possible variations. Because the 2-D format permits the analysis of as many as 40 fragments of 250 bp on average in parallel, TDGS allows extensive multiplex PCR (megaplex PCR), i.e. up to 26 fragments in one single reaction, resulting in a significant cost reduction. TDGS tests are designed using a computer program to optimally position PCR primers around the relevant target sequences (exons). A simple automated 2-D instrument allows scanning all exons of a large gene in 8 different samples well within 3 hours. Using three
CAS2D: FORTRAN program for nonrotating blade-to-blade, steady, potential transonic cascade flows
NASA Technical Reports Server (NTRS)
Dulikravich, D. S.
1980-01-01
An exact, full-potential-equation (FPE) model for the steady, irrotational, homentropic and homoenergetic flow of a compressible, homocompositional, inviscid fluid through two dimensional planar cascades of airfoils was derived, together with its appropriate boundary conditions. A computer program, CAS2D, was developed that numerically solves an artificially time-dependent form of the actual FPE. The governing equation was discretized by using type-dependent, rotated finite differencing and the finite area technique. The flow field was discretized by providing a boundary-fitted, nonuniform computational mesh. The mesh was generated by using a sequence of conforming mapping, nonorthogonal coordinate stretching, and local, isoparametric, bilinear mapping functions. The discretized form of the FPE was solved iteratively by using successive line overrelaxation. The possible isentropic shocks were correctly captured by adding explicitly an artificial viscosity in a conservative form. In addition, a three-level consecutive, mesh refinement feature makes CAS2D a reliable and fast algorithm for the analysis of transonic, two dimensional cascade flows.
Observer-based H∞ controller for 2-D T-S fuzzy model
NASA Astrophysics Data System (ADS)
Li, Lizhen
2016-10-01
This paper develops a method of fuzzy observer-based H∞ controller design for two-dimensional (2-D) discrete Takagi-Sugeno (T-S) fuzzy systems. By reformulating the system, a linear matrix inequality (LMI)-based sufficient condition is derived. Then the fuzzy controller and the fuzzy observer can be independently designed, which guarantee an H∞ noise attenuation γ of the whole system. Owing to the introduction of free matrices, the presented design method has a wider range of application and can guarantee a better H∞ performance of the closed-loop fuzzy control system. Simulation results have demonstrated the effectiveness of the proposed method.
Synthesis of Two-Dimensional Materials by Selective Extraction
Naguib, Michael; Gogotsi, Yury
2014-12-09
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 tomore » 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 the
Synthesis of Two-Dimensional Materials by Selective Extraction
Naguib, Michael; Gogotsi, Yury
2014-12-09
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 the precursor
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
Numerical simulation of two-dimensional spatially-developing mixing layers
NASA Technical Reports Server (NTRS)
Wilson, R. V.; Demuren, A. O.
1994-01-01
Two-dimensional, incompressible, spatially developing mixing layer simulations are performed at Re = 10(exp 2) and 10(exp 4) with two classes of perturbations applied at the inlet boundary; combinations of discrete modes from linear stability theory, and a broad spectrum of modes derived from experimentally measured velocity spectra. The effect of the type and strength of inlet perturbations on vortex dynamics and time-averaged properties are explored. Two-point spatial velocity and autocorrelations are used to estimate the size and lifetime of the resulting coherent structures and to explore possible feedback effects. The computed time-averaged properties such as mean velocity profiles, turbulent statistics, and spread rates show good agreement with experimentally measured values. It is shown that by forcing with a broad spectrum of modes derived from an experimental energy spectrum many experimentally observed phenomena can be reproduced by a 2-D simulation. The strength of the forcing merely affected the length required for the dominant coherent structures to become fully-developed. Thus intensities comparable to those of the background turbulence in many wind tunnel experiments produced the same results, given sufficient simulation length.
Two-dimensional plasma grating by non-collinear femtosecond filament interaction in air
Liu Jia; Li Wenxue; Pan Haifeng; Zeng Heping
2011-10-10
We experimentally demonstrated that two-dimensional (2D) plasma gratings could be generated in air by nonlinear interaction of three femtosecond filaments. The intensity interference of non-collinearly overlapped filaments was self-projected along a relatively long distance and accompanied with a wavelength-scale periodic change of the refractive index in the encircling air due to periodic plasma density modulation. The 2D plasma gratings supported 2D diffraction of the generated third-harmonic pulses. By using in-line time-resolved holographic imaging and time-delayed diffraction, the 2D plasma gratings were evidenced to last a few tens picoseconds after the excitation pulses.
Two-Dimensional NMR Lineshape Analysis
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-01-01
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. PMID:27109776
Two-dimensional ranking of Wikipedia articles
NASA Astrophysics Data System (ADS)
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.
Plasmonics with two-dimensional conductors
Yoon, Hosang; Yeung, Kitty Y. M.; Kim, Philip; Ham, Donhee
2014-01-01
A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics. PMID:24567472
Plasmonics with two-dimensional conductors.
Yoon, Hosang; Yeung, Kitty Y M; Kim, Philip; Ham, Donhee
2014-03-28
A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics.
Two-dimensional optimal sensor placement
Zhang, H.
1995-05-01
A method for determining the optimal two-dimensional spatial placement of multiple sensors participating in a robot perception task is introduced in this paper. This work is motivated by the fact that sensor data fusion is an effective means of reducing uncertainties in sensor observations, and that the combined uncertainty varies with the relative placement of the sensors with respect to each other. The problem of optimal sensor placement is formulated and a solution is presented in the two dimensional space. The algebraic structure of the combined sensor uncertainty with respect to the placement of sensor is studied. A necessary condition for optimal placement is derived and this necessary condition is used to obtain an efficient closed-form solution for the global optimal placement. Numerical examples are provided to illustrate the effectiveness and efficiency of the solution. 11 refs.
Mobility and Diffusion-Ordered Two-Dimensional NMR Spectroscopy
NASA Astrophysics Data System (ADS)
Morris, Kevin Freeman
Mobility and diffusion-ordered two-dimensional nuclear magnetic resonance spectroscopy experiments have been developed for the analysis of mixtures. In the mobility -ordered experiments, the full range of positive and negative electrophoretic mobilities is displayed in one dimension and chemical shifts are displayed in the other. A concentric cylindrical tube electrophoresis chamber was designed to reduce the effective pathlength for current and to provide unidirectional flow for ions of interest. Techniques based upon the reverse precession method were also implemented to recover the signs of the mobilities and improved resolution in the mobility dimension was obtained by replacing Fourier transformation of truncated data sets with a linear prediction analysis. In the diffusion-ordered two-dimensional NMR experiments, the conventional chemical shift spectrum is resolved in one dimension and spectra of diffusion rates or molecular radii are resolved in the other. Diffusion dependent pulsed field gradient NMR data sets were inverted by means of the computer programs SPLMOD or DISCRETE, when discrete diffusion coefficients were present, and CONTIN when continuous distributions were present. Since the inversion is ill -conditioned, it was necessary to introduce additional information to limit the range of the solutions. In addition to prior knowledge of the decay kernels and non-negativity of amplitudes and damping constants, a set of rejection criteria was constructed for the discrete analysis case that took into account physical limits on diffusion coefficients, experimentally accessible values, and variations in effective decay kernels resulting from instrumental non-linearities. Examples of analyses of simulated data and experimental data for mixtures are presented as well as two-dimensional spectra generated by CONTIN for polydisperse polymer samples. Also, resolution in the diffusion dimension was increased by performing experiments on hydrophobic molecules in
Two dimensional wedge/translating shroud nozzle
NASA Technical Reports Server (NTRS)
Maiden, D. L. (Inventor)
1978-01-01
A jet propulsion exhaust nozzle is reported for multi-engine installations which produces high internal/external, thrust-minus-drag, performance for transonic cruise or transonic acceleration as well as improved performance at subsonic and supersonic speeds. A two dimensional wedge/translating shroud provides the variable nozzle exit geometry needed to achieve high engine performance over a wide range of throttle power settings.
Deeply subrecoil two-dimensional Raman cooling
Boyer, V.; Phillips, W.D.; Lising, L.J.; Rolston, S.L.
2004-10-01
We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of 30 nK (0.15T{sub rec}). This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.
ELRIS2D: A MATLAB Package for the 2D Inversion of DC Resistivity/IP Data
NASA Astrophysics Data System (ADS)
Akca, Irfan
2016-04-01
ELRIS2D is an open source code written in MATLAB for the two-dimensional inversion of direct current resistivity (DCR) and time domain induced polarization (IP) data. The user interface of the program is designed for functionality and ease of use. All available settings of the program can be reached from the main window. The subsurface is discretized using a hybrid mesh generated by the combination of structured and unstructured meshes, which reduces the computational cost of the whole inversion procedure. The inversion routine is based on the smoothness constrained least squares method. In order to verify the program, responses of two test models and field data sets were inverted. The models inverted from the synthetic data sets are consistent with the original test models in both DC resistivity and IP cases. A field data set acquired in an archaeological site is also used for the verification of outcomes of the program in comparison with the excavation results.
Ishiyama, Tatsuya; Morita, Akihiro; Tahara, Tahei
2015-06-07
Two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectra at vapor/water interface were studied by molecular dynamics (MD) simulation with a classical flexible and nonpolarizable model. The present model well describes the spectral diffusion of 2D infrared spectrum of bulk water as well as 2D HD-VSFG at the interface. The effect of isotopic dilution on the 2D HD-VSFG was elucidated by comparing the normal (H{sub 2}O) water and HOD water. We further performed decomposition analysis of 2D HD-VSFG into the hydrogen-bonding and the dangling (or free) OH vibrations, and thereby disentangled the different spectral responses and spectral diffusion in the 2D HD-VSFG. The present MD simulation demonstrated the role of anharmonic coupling between these modes on the cross peak in the 2D HD-VSFG spectrum.
Two-dimensional photonic crystal sensors for visual detection of lectin concanavalin A.
Zhang, Jian-Tao; Cai, Zhongyu; Kwak, Daniel H; Liu, Xinyu; Asher, Sanford A
2014-09-16
We fabricated a two-dimensional (2-D) photonic crystal lectin sensing material that utilizes light diffraction from a 2-D colloidal array attached to the surface of a hydrogel that contains mannose carbohydrate groups. Lectin-carbohydrate interactions create hydrogel cross-links that shrink the hydrogel volume and decrease the 2-D particle spacing. This mannose containing 2-D photonic crystal sensor detects Concanavalin A (Con A) through shifts in the 2-D diffraction wavelength. Con A concentrations can be determined by measuring the diffracted wavelength or visually determined from the change in the sensor diffraction color. The concentrations are easily monitored by measuring the 2-D array Debye ring diameter. Our observed detection limit for Con A is 0.02 mg/mL (0.7 μM). The 2-D photonic crystal sensors are completely reversible and can monitor Con A solution concentration changes. PMID:25162117
Criteria for two-dimensional kinematics in an interacting Fermi gas
NASA Astrophysics Data System (ADS)
Dyke, P.; Fenech, K.; Peppler, T.; Lingham, M. G.; Hoinka, S.; Zhang, W.; Peng, S.-G.; Mulkerin, B.; Hu, H.; Liu, X.-J.; Vale, C. J.
2016-01-01
Ultracold Fermi gases subject to tight transverse confinement offer a highly controllable setting to study the two-dimensional (2D) BCS to Berezinskii-Kosterlitz-Thouless superfluid crossover. Achieving the 2D regime requires confining particles to their transverse ground state which presents challenges in interacting systems. Here, we establish the conditions for an interacting Fermi gas to display 2D kinematics. Transverse excitations are detected by measuring the transverse expansion rate which displays a sudden increase when the atom number exceeds a critical value N2 D signifying a density driven departure from 2D kinematics. For weak interactions N2 D is set by the aspect ratio of the trap. Close to a Feshbach resonance, however, the stronger interactions reduce N2 D and excitations appear at lower density.
Two-dimensional boron nitride structures functionalization: first principles studies.
Ponce-Pérez, R; Cocoletzi, Gregorio H; Takeuchi, Noboru
2016-09-01
Density functional theory calculations have been performed to investigate two-dimensional hexagonal boron nitride (2D hBN) structures functionalization with organic molecules. 2x2, 4x4 and 6x6 periodic 2D hBN layers have been considered to interact with acetylene. To deal with the exchange-correlation energy the generalized gradient approximation (GGA) is invoked. The electron-ion interaction is treated with the pseudopotential method. The GGA with the Perdew-Burke-Ernzerhoff (PBE) functionals together with van der Waals interactions are considered to deal with the composed systems. To investigate the functionalization two main configurations have been explored; in one case the molecule interacts with the boron atom and in the other with the nitrogen atom. Results of the adsorption energies indicate chemisorption in both cases. The total density of states (DOS) displays an energy gap in both cases. The projected DOS indicate that the B-p and N-p orbitals are those that make the most important contribution in the valence band and the H-s and C-p orbitals provide an important contribution in the conduction band to the DOS. Provided that the interactions of the acetylene with the 2D layer modify the structural and electronic properties of the hBN the possibility of structural functionalization using organic molecules may be concluded.
Two-dimensional van der Waals C60 molecular crystal
Reddy, C. D.; Gen Yu, Zhi; Zhang, Yong-Wei
2015-01-01
Two-dimensional (2D) atomic crystals, such as graphene and transition metal dichalcogenides et al. have drawn extraordinary attention recently. For these 2D materials, atoms within their monolayer are covalently bonded. An interesting question arises: Can molecules form a 2D monolayer crystal via van der Waals interactions? Here, we first study the structural stability of a free-standing infinite C60 molecular monolayer using molecular dynamic simulations, and find that the monolayer is stable up to 600 K. We further study the mechanical properties of the monolayer, and find that the elastic modulus, ultimate tensile stress and failure strain are 55–100 GPa, 90–155 MPa, and 1.5–2.3%, respectively, depending on the stretching orientation. The monolayer fails due to shearing and cavitation under uniaxial tensile loading. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the monolayer are found to be delocalized and as a result, the band gap is reduced to only 60% of the isolated C60 molecule. Interestingly, this band gap can be tuned up to ±30% using strain engineering. Owing to its thermal stability, low density, strain-tunable semi-conducting characteristics and large bending flexibility, this van der Waals molecular monolayer crystal presents aplenty opportunities for developing novel applications in nanoelectronics. PMID:26183501
Temporal enhancement of two-dimensional color doppler echocardiography
NASA Astrophysics Data System (ADS)
Terentjev, Alexey B.; Settlemier, Scott H.; Perrin, Douglas P.; del Nido, Pedro J.; Shturts, Igor V.; Vasilyev, Nikolay V.
2016-03-01
Two-dimensional color Doppler echocardiography is widely used for assessing blood flow inside the heart and blood vessels. Currently, frame acquisition time for this method varies from tens to hundreds of milliseconds, depending on Doppler sector parameters. This leads to low frame rates of resulting video sequences equal to tens of Hz, which is insufficient for some diagnostic purposes, especially in pediatrics. In this paper, we present a new approach for reconstruction of 2D color Doppler cardiac images, which results in the frame rate being increased to hundreds of Hz. This approach relies on a modified method of frame reordering originally applied to real-time 3D echocardiography. There are no previous publications describing application of this method to 2D Color Doppler data. The approach has been tested on several in-vivo cardiac 2D color Doppler datasets with approximate duration of 30 sec and native frame rate of 15 Hz. The resulting image sequences had equivalent frame rates to 500Hz.
Elastic coupling between layers in two-dimensional materials
NASA Astrophysics Data System (ADS)
Gao, Yang; Kim, Suenne; Zhou, Si; Chiu, Hsiang-Chih; Nélias, Daniel; Berger, Claire; de Heer, Walt; Polloni, Laura; Sordan, Roman; Bongiorno, Angelo; Riedo, Elisa
2015-07-01
Two-dimensional materials, such as graphene and MoS2, are films of a few atomic layers in thickness with strong in-plane bonds and weak interactions between the layers. The in-plane elasticity has been widely studied in bending experiments where a suspended film is deformed substantially; however, little is known about the films’ elastic modulus perpendicular to the planes, as the measurement of the out-of-plane elasticity of supported 2D films requires indentation depths smaller than the films’ interlayer distance. Here, we report on sub-ångström-resolution indentation measurements of the perpendicular-to-the-plane elasticity of 2D materials. Our indentation data, combined with semi-analytical models and density functional theory, are then used to study the perpendicular elasticity of few-layer-thick graphene and graphene oxide films. We find that the perpendicular Young’s modulus of graphene oxide films reaches a maximum when one complete water layer is intercalated between the graphitic planes. This non-destructive methodology can map interlayer coupling and intercalation in 2D films.
Two-dimensional chirped-pulse Fourier transform microwave spectroscopy.
Wilcox, David S; Hotopp, Kelly M; Dian, Brian C
2011-08-18
Two-dimensional (2D) correlation techniques are developed for chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The broadband nature of the spectrometer coupled with fast digital electronics permits the generation of arbitrary pulse sequences and simultaneous detection of the 8-18 GHz region of the microwave spectrum. This significantly increases the number of rotation transitions that can be simultaneously probed, as well as the bandwidth in both frequency dimensions. We theoretically and experimentally evaluate coherence transfer of three- and four-level systems to relate the method with previous studies. We then extend the principles of single-quantum and autocorrelation to incorporate broadband excitation and detection. Global connectivity of the rotational energy level structure is demonstrated through the transfer of multiple coherences in a single 2D experiment. Additionally, open-system effects are observed from irradiating many-level systems. Quadrature detection in the indirectly measured frequency dimension and phase cycling are also adapted for 2D CP-FTMW spectroscopy.
Two-dimensional boron nitride structures functionalization: first principles studies.
Ponce-Pérez, R; Cocoletzi, Gregorio H; Takeuchi, Noboru
2016-09-01
Density functional theory calculations have been performed to investigate two-dimensional hexagonal boron nitride (2D hBN) structures functionalization with organic molecules. 2x2, 4x4 and 6x6 periodic 2D hBN layers have been considered to interact with acetylene. To deal with the exchange-correlation energy the generalized gradient approximation (GGA) is invoked. The electron-ion interaction is treated with the pseudopotential method. The GGA with the Perdew-Burke-Ernzerhoff (PBE) functionals together with van der Waals interactions are considered to deal with the composed systems. To investigate the functionalization two main configurations have been explored; in one case the molecule interacts with the boron atom and in the other with the nitrogen atom. Results of the adsorption energies indicate chemisorption in both cases. The total density of states (DOS) displays an energy gap in both cases. The projected DOS indicate that the B-p and N-p orbitals are those that make the most important contribution in the valence band and the H-s and C-p orbitals provide an important contribution in the conduction band to the DOS. Provided that the interactions of the acetylene with the 2D layer modify the structural and electronic properties of the hBN the possibility of structural functionalization using organic molecules may be concluded. PMID:27566317
Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
2014-01-01
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 cm2 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. PMID:24741204
Two-dimensional copper thio- and seleno-cyanates.
Tsetseris, Leonidas
2016-03-21
Based on density-functional theory calculations we identify two-dimensional (2D) forms of copper thio-cyanate (CuSCN) and copper seleno-cyanate (CuSeCN). CuSCN is known to crystallize in two three-dimensional polymorphs, the beta wurtzite and the alpha structure, both with tetrahedral bonding networks. Here we find that CuSCN and CuSeCN may be stabilized also in monolayer geometries with SCN or SeCN groups protruding out of Cu planes. The cohesive energies of stacks made out of these sheets are comparable to those of the alpha and beta structures, so, in principle, 2D CuSCN and CuSeCN may be formed under the appropriate experimental conditions. Other 2D CuSCN and CuSeCN phases with honeycomb-like structures also correspond to local energy minima, but are less stable with respect to the above-mentioned systems. PMID:26911411
Interactions between lasers and two-dimensional transition metal dichalcogenides.
Lu, Junpeng; Liu, Hongwei; Tok, Eng Soon; Sow, Chorng-Haur
2016-05-01
The recent increasing research interest in two-dimensional (2D) layered materials has led to an explosion of in the discovery of novel physical and chemical phenomena in these materials. Among the 2D family, group-VI transition metal dichalcogenides (TMDs), such as represented by MoS2 and WSe2, are remarkable semiconductors with sizable energy band gaps, which make the TMDs promising building blocks for new generation optoelectronics. On the other hand, the specificity and tunability of the band gaps can generate particularly strong light-matter interactions between TMD crystals and specific photons, which can trigger complex and interesting phenomena such as photo-scattering, photo-excitation, photo-destruction, photo-physical modification, photochemical reaction and photo-oxidation. Herein, we provide an overview of the phenomena explained by various interactions between lasers and the 2D TMDs. Characterizations of the optical fundamentals of the TMDs via laser spectroscopies are reviewed. Subsequently, photoelectric conversion devices enabled by laser excitation and the functionality extension and performance improvement of the TMDs materials via laser modification are comprehensively summarized. Finally, we conclude the review by discussing the prospects for further development in this research area.
Two-Dimensional Crystals of Icosahedral Viruses at Liquid interfaces
NASA Astrophysics Data System (ADS)
Fukuto, Masafumi; Yang, Lin; Checco, Antonio; Kuzmenko, Ivan; Nguyen, Quyen; Mank, Nick; Wang, Qian
2012-02-01
Two-dimensional (2D) assembly of turnip yellow mosaic virus (TYMV) on cationic lipid monolayers is investigated at the air-water interface. TYMV, an icosahedral virus with a diameter of 28 nm, exhibits well-defined roughness, charge distribution, and hydrophilic/hydrophobic patches on its surface. The electrostatic attraction to the lipid-coated aqueous interface provides means to impose a specific virus orientation and hence reduce the number of possible inter-particle interactions. The 2D geometry is particularly advantageous in dissecting the role of anisotropy in aqueous-media assembly, which involves various types of similarly weak interactions. We show that the assembly approach used not only facilitates crystallization but also provides insights on how complex anisotropic interactions can be exploited to generate long-range order. Specifically, we report an in situ x-ray scattering observation of novel 2D crystal forms of TYMV that reflect the virus' icosahedral symmetry. The symmetry, shape, and surface heterogeneities of TYMV suggest a mechanism by which these crystals are stabilized by a combination of hydrophobic, electrostatic, and steric interactions.
Two-Dimensional Phosphorus Porous Polymorphs with Tunable Band Gaps.
Zhuo, Zhiwen; Wu, Xiaojun; Yang, Jinlong
2016-06-01
Exploring stable two-dimensional (2D) crystalline structures of phosphorus with tunable properties is of considerable importance partly due to the novel anisotropic behavior in phosphorene and potential applications in high-performance devices. Here, 21 new 2D phosphorus allotropes with porous structure are reported based on topological modeling method and first-principles calculations. We establish that stable 2D phosphorus crystals can be obtained by topologically assembling selected phosphorus monomer, dimer, trimer, tetramer, and hexamer. Nine of reported structures are predicted to be more stable than white phosphorus. Their dynamic and thermal stabilities are confirmed by the calculated vibration spectra and Born-Oppenheimer molecular dynamic simulation at temperatures up to 1500 K. These phosphorus porous polymorphs have isotropic mechanic properties that are significantly softer than phosphorene. The electronic band structures calculated with the HSE06 method indicate that new structures are semiconductors with band gaps ranging widely from 0.15 to 3.42 eV, which are tuned by the basic units assembled in the network. Of particular importance is that the position of both conduction and valence band edges of some allotropes matches well with the chemical reaction potential of H2/H(+) and O2/H2O, which can be used as element photocatalysts for visible-light-driven water splitting. PMID:27171121
Exploring brain connectivity with two-dimensional neural maps.
Jianu, Radu; Demiralp, Çağatay; Laidlaw, David H
2012-06-01
We introduce two-dimensional neural maps for exploring connectivity in the brain. For this, we create standard streamtube models from diffusion-weighted brain imaging data sets along with neural paths hierarchically projected into the plane. These planar neural maps combine desirable properties of low-dimensional representations, such as visual clarity and ease of tract-of-interest selection, with the anatomical familiarity of 3D brain models and planar sectional views. We distribute this type of visualization both in a traditional stand-alone interactive application and as a novel, lightweight web-accessible system. The web interface integrates precomputed neural-path representations into a geographical digital-maps framework with associated labels, metrics, statistics, and linkouts. Anecdotal and quantitative comparisons of the present method with a recently proposed 2D point representation suggest that our representation is more intuitive and easier to use and learn. Similarly, users are faster and more accurate in selecting bundles using the 2D path representation than the 2D point representation. Finally, expert feedback on the web interface suggests that it can be useful for collaboration as well as quick exploration of data.
Volumetric display containing multiple two-dimensional color motion pictures
NASA Astrophysics Data System (ADS)
Hirayama, R.; Shiraki, A.; Nakayama, H.; Kakue, T.; Shimobaba, T.; Ito, T.
2014-06-01
We have developed an algorithm which can record multiple two-dimensional (2-D) gradated projection patterns in a single three-dimensional (3-D) object. Each recorded pattern has the individual projected direction and can only be seen from the direction. The proposed algorithm has two important features: the number of recorded patterns is theoretically infinite and no meaningful pattern can be seen outside of the projected directions. In this paper, we expanded the algorithm to record multiple 2-D projection patterns in color. There are two popular ways of color mixing: additive one and subtractive one. Additive color mixing used to mix light is based on RGB colors and subtractive color mixing used to mix inks is based on CMY colors. We made two coloring methods based on the additive mixing and subtractive mixing. We performed numerical simulations of the coloring methods, and confirmed their effectiveness. We also fabricated two types of volumetric display and applied the proposed algorithm to them. One is a cubic displays constructed by light-emitting diodes (LEDs) in 8×8×8 array. Lighting patterns of LEDs are controlled by a microcomputer board. The other one is made of 7×7 array of threads. Each thread is illuminated by a projector connected with PC. As a result of the implementation, we succeeded in recording multiple 2-D color motion pictures in the volumetric displays. Our algorithm can be applied to digital signage, media art and so forth.
Interactions between lasers and two-dimensional transition metal dichalcogenides.
Lu, Junpeng; Liu, Hongwei; Tok, Eng Soon; Sow, Chorng-Haur
2016-05-01
The recent increasing research interest in two-dimensional (2D) layered materials has led to an explosion of in the discovery of novel physical and chemical phenomena in these materials. Among the 2D family, group-VI transition metal dichalcogenides (TMDs), such as represented by MoS2 and WSe2, are remarkable semiconductors with sizable energy band gaps, which make the TMDs promising building blocks for new generation optoelectronics. On the other hand, the specificity and tunability of the band gaps can generate particularly strong light-matter interactions between TMD crystals and specific photons, which can trigger complex and interesting phenomena such as photo-scattering, photo-excitation, photo-destruction, photo-physical modification, photochemical reaction and photo-oxidation. Herein, we provide an overview of the phenomena explained by various interactions between lasers and the 2D TMDs. Characterizations of the optical fundamentals of the TMDs via laser spectroscopies are reviewed. Subsequently, photoelectric conversion devices enabled by laser excitation and the functionality extension and performance improvement of the TMDs materials via laser modification are comprehensively summarized. Finally, we conclude the review by discussing the prospects for further development in this research area. PMID:27141556
Imaging two-dimensional mechanical waves of skeletal muscle contraction.
Grönlund, Christer; Claesson, Kenji; Holtermann, Andreas
2013-02-01
Skeletal muscle contraction is related to rapid mechanical shortening and thickening. Recently, specialized ultrasound systems have been applied to demonstrate and quantify transient tissue velocities and one-dimensional (1-D) propagation of mechanical waves during muscle contraction. Such waves could potentially provide novel information on musculoskeletal characteristics, function and disorders. In this work, we demonstrate two-dimensional (2-D) mechanical wave imaging following the skeletal muscle contraction. B-mode image acquisition during multiple consecutive electrostimulations, speckle-tracking and a time-stamp sorting protocol were used to obtain 1.4 kHz frame rate 2-D tissue velocity imaging of the biceps brachii muscle contraction. The results present novel information on tissue velocity profiles and mechanical wave propagation. In particular, counter-propagating compressional and shear waves in the longitudinal direction were observed in the contracting tissue (speed 2.8-4.4 m/s) and a compressional wave in the transverse direction of the non-contracting muscle tissue (1.2-1.9 m/s). In conclusion, analysing transient 2-D tissue velocity allows simultaneous assessment of both active and passive muscle tissue properties.
Soap film flows: Statistics of two-dimensional turbulence
Vorobieff, P.; Rivera, M.; Ecke, R.E.
1999-08-01
Soap film flows provide a very convenient laboratory model for studies of two-dimensional (2-D) hydrodynamics including turbulence. For a gravity-driven soap film channel with a grid of equally spaced cylinders inserted in the flow, we have measured the simultaneous velocity and thickness fields in the irregular flow downstream from the cylinders. The velocity field is determined by a modified digital particle image velocimetry method and the thickness from the light scattered by the particles in the film. From these measurements, we compute the decay of mean energy, enstrophy, and thickness fluctuations with downstream distance, and the structure functions of velocity, vorticity, thickness fluctuation, and vorticity flux. From these quantities we determine the microscale Reynolds number of the flow R{sub {lambda}}{approx}100 and the integral and dissipation scales of 2D turbulence. We also obtain quantitative measures of the degree to which our flow can be considered incompressible and isotropic as a function of downstream distance. We find coarsening of characteristic spatial scales, qualitative correspondence of the decay of energy and enstrophy with the Batchelor model, scaling of energy in {ital k} space consistent with the k{sup {minus}3} spectrum of the Kraichnan{endash}Batchelor enstrophy-scaling picture, and power-law scalings of the structure functions of velocity, vorticity, vorticity flux, and thickness. These results are compared with models of 2-D turbulence and with numerical simulations. {copyright} {ital 1999 American Institute of Physics.}
Furukawa, Shuhei; Uji-i, Hiroshi; Tahara, Kazukuni; Ichikawa, Tomoyuki; Sonoda, Motohiro; De Schryver, Frans C; Tobe, Yoshito; De Feyter, Steven
2006-03-22
We present here the formation of a molecular Kagomé network within a two-dimensional (2D) crystal on a surface. This system provides a clear example of how, by design, molecular geometry can be expressed at the level of the 2D crystal lattice, leading to the formation of open networks. Key elements to control molecular network formation are core symmetry, location and orientation of interacting and connecting substituents, as well as symmetry matching between the networks and the surface.
2-d Finite Element Code Postprocessor
1996-07-15
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forcesmore » along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.« less
Biological and environmental interactions of emerging two-dimensional nanomaterials.
Wang, Zhongying; Zhu, Wenpeng; Qiu, Yang; Yi, Xin; von dem Bussche, Annette; Kane, Agnes; Gao, Huajian; Koski, Kristie; Hurt, Robert
2016-03-21
Two-dimensional materials have become a major focus in materials chemistry research worldwide with substantial efforts centered on synthesis, property characterization, and technological application. These high-aspect ratio sheet-like solids come in a wide array of chemical compositions, crystal phases, and physical forms, and are anticipated to enable a host of future technologies in areas that include electronics, sensors, coatings, barriers, energy storage and conversion, and biomedicine. A parallel effort has begun to understand the biological and environmental interactions of synthetic nanosheets, both to enable the biomedical developments and to ensure human health and safety for all application fields. This review covers the most recent literature on the biological responses to 2D materials and also draws from older literature on natural lamellar minerals to provide additional insight into the essential chemical behaviors. The article proposes a framework for more systematic investigation of biological behavior in the future, rooted in fundamental materials chemistry and physics. That framework considers three fundamental interaction modes: (i) chemical interactions and phase transformations, (ii) electronic and surface redox interactions, and (iii) physical and mechanical interactions that are unique to near-atomically-thin, high-aspect-ratio solids. Two-dimensional materials are shown to exhibit a wide range of behaviors, which reflect the diversity in their chemical compositions, and many are expected to undergo reactive dissolution processes that will be key to understanding their behaviors and interpreting biological response data. The review concludes with a series of recommendations for high-priority research subtopics at the "bio-nanosheet" interface that we hope will enable safe and successful development of technologies related to two-dimensional nanomaterials. PMID:26923057
Visualising the strain distribution in suspended two-dimensional materials under local deformation
NASA Astrophysics Data System (ADS)
Elibol, Kenan; Bayer, Bernhard C.; Hummel, Stefan; Kotakoski, Jani; Argentero, Giacomo; Meyer, Jannik C.
2016-06-01
We demonstrate the use of combined simultaneous atomic force microscopy (AFM) and laterally resolved Raman spectroscopy to study the strain distribution around highly localised deformations in suspended two-dimensional materials. Using the AFM tip as a nanoindentation probe, we induce localised strain in suspended few-layer graphene, which we adopt as a two-dimensional membrane model system. Concurrently, we visualise the strain distribution under and around the AFM tip in situ using hyperspectral Raman mapping via the strain-dependent frequency shifts of the few-layer graphene’s G and 2D Raman bands. Thereby we show how the contact of the nm-sized scanning probe tip results in a two-dimensional strain field with μm dimensions in the suspended membrane. Our combined AFM/Raman approach thus adds to the critically required instrumental toolbox towards nanoscale strain engineering of two-dimensional materials.
Visualising the strain distribution in suspended two-dimensional materials under local deformation
Elibol, Kenan; Bayer, Bernhard C.; Hummel, Stefan; Kotakoski, Jani; Argentero, Giacomo; Meyer, Jannik C.
2016-01-01
We demonstrate the use of combined simultaneous atomic force microscopy (AFM) and laterally resolved Raman spectroscopy to study the strain distribution around highly localised deformations in suspended two-dimensional materials. Using the AFM tip as a nanoindentation probe, we induce localised strain in suspended few-layer graphene, which we adopt as a two-dimensional membrane model system. Concurrently, we visualise the strain distribution under and around the AFM tip in situ using hyperspectral Raman mapping via the strain-dependent frequency shifts of the few-layer graphene’s G and 2D Raman bands. Thereby we show how the contact of the nm-sized scanning probe tip results in a two-dimensional strain field with μm dimensions in the suspended membrane. Our combined AFM/Raman approach thus adds to the critically required instrumental toolbox towards nanoscale strain engineering of two-dimensional materials. PMID:27346485
Quantum creep in a highly crystalline two-dimensional superconductor
NASA Astrophysics Data System (ADS)
Saito, Yu; Kasahara, Yuichi; Ye, Jianting; Iwasa, Yoshihiro; Nojima, Tsutomu
Conventional studies on quantum phase transitions, especially on superconductor-insulator or superconductor-metal-insulator transitions have been performed in deposited metallic thin films such as Bismuth or MoGe. Although the techniques of thin films deposition have been considerably improved, unintentional disorder such as impurities and deficiencies, generating the pinning centers, seems to still exist in such systems. The mechanical exfoliated highly crystalline two-dimensional material can be a good candidate to realize a less-disordered 2D superconductor with extremely weak pinning, combined with transfer method or ionic-liquid gating. We report on the quantum metal, namely, magnetic-field-induced metallic state observed in an ion-gated two-dimensional superconductor based on an ultra-highly crystalline layered band insulator, ZrNCl. We found that the superconducting state is extremely fragile against external magnetic fields; that is, zero resistance state immediately disappears, once an external magnetic field switches on. This is because the present system is relatively clean and the pinning potential is extremely weak, which cause quantum tunneling and flux flow of vortices, resulting in metallic ground state.
Flexoelectricity in two-dimensional crystalline and biological membranes.
Ahmadpoor, Fatemeh; Sharma, Pradeep
2015-10-28
The ability of a material to convert electrical stimuli into mechanical deformation, i.e. piezoelectricity, is a remarkable property of a rather small subset of insulating materials. The phenomenon of flexoelectricity, on the other hand, is universal. All dielectrics exhibit the flexoelectric effect whereby non-uniform strain (or strain gradients) can polarize the material and conversely non-uniform electric fields may cause mechanical deformation. The flexoelectric effect is strongly enhanced at the nanoscale and accordingly, all two-dimensional membranes of atomistic scale thickness exhibit a strong two-way coupling between the curvature and electric field. In this review, we highlight the recent advances made in our understanding of flexoelectricity in two-dimensional (2D) membranes-whether the crystalline ones such as dielectric graphene nanoribbons or the soft lipid bilayer membranes that are ubiquitous in biology. Aside from the fundamental mechanisms, phenomenology, and recent findings, we focus on rapidly emerging directions in this field and discuss applications such as energy harvesting, understanding of the mammalian hearing mechanism and ion transport among others. PMID:26399878
Two-dimensional gene scanning: exploring human genetic variability.
Vijg, J; van Orsouw, N J
1999-06-01
Current methods for mutation detection are not optimized for the generation of highly accurate data on multiple genes of hundreds of individuals in population-based studies. Two-dimensional gene scanning (TDGS) is a high-resolution system for detecting mutational variants in multiple genes in parallel. TDGS is based on a combination of extensive multiplex polymerase chain reaction (PCR) and two-dimensional (2-D) DNA electrophoresis. The latter involves a size separation step followed by denaturing gradient gel electrophoresis (DGGE). TDGS tests for a number of large human disease genes have been designed, using a computer program to optimally position PCR primers around the relevant target sequences (e.g., exons) and evaluated using panels of samples with previously detected mutations. The results indicate a high sensitivity and specificity, equal to nucleotide sequencing, which is generally considered as the gold standard. Here, we describe the different components of the TDGS process and its potential application as a high-throughput system for the systematic identification of human gene variants.
Two-dimensional radiant energy array computers and computing devices
NASA Technical Reports Server (NTRS)
Schaefer, D. H.; Strong, J. P., III (Inventor)
1976-01-01
Two dimensional digital computers and computer devices operate in parallel on rectangular arrays of digital radiant energy optical signal elements which are arranged in ordered rows and columns. Logic gate devices receive two input arrays and provide an output array having digital states dependent only on the digital states of the signal elements of the two input arrays at corresponding row and column positions. The logic devices include an array of photoconductors responsive to at least one of the input arrays for either selectively accelerating electrons to a phosphor output surface, applying potentials to an electroluminescent output layer, exciting an array of discrete radiant energy sources, or exciting a liquid crystal to influence crystal transparency or reflectivity.
Finite volume model for two-dimensional shallow environmental flow
Simoes, F.J.M.
2011-01-01
This paper presents the development of a two-dimensional, depth integrated, unsteady, free-surface model based on the shallow water equations. The development was motivated by the desire of balancing computational efficiency and accuracy by selective and conjunctive use of different numerical techniques. The base framework of the discrete model uses Godunov methods on unstructured triangular grids, but the solution technique emphasizes the use of a high-resolution Riemann solver where needed, switching to a simpler and computationally more efficient upwind finite volume technique in the smooth regions of the flow. Explicit time marching is accomplished with strong stability preserving Runge-Kutta methods, with additional acceleration techniques for steady-state computations. A simplified mass-preserving algorithm is used to deal with wet/dry fronts. Application of the model is made to several benchmark cases that show the interplay of the diverse solution techniques.
Acoustic resonances in two-dimensional radial sonic crystal shells
NASA Astrophysics Data System (ADS)
Torrent, Daniel; Sánchez-Dehesa, José
2010-07-01
Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sánchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts.
Real-time two-dimensional temperature imaging using ultrasound.
Liu, Dalong; Ebbini, Emad S
2009-01-01
We present a system for real-time 2D imaging of temperature change in tissue media using pulse-echo ultrasound. The frontend of the system is a SonixRP ultrasound scanner with a research interface giving us the capability of controlling the beam sequence and accessing radio frequency (RF) data in real-time. The beamformed RF data is streamlined to the backend of the system, where the data is processed using a two-dimensional temperature estimation algorithm running in the graphics processing unit (GPU). The estimated temperature is displayed in real-time providing feedback that can be used for real-time control of the heating source. Currently we have verified our system with elastography tissue mimicking phantom and in vitro porcine heart tissue, excellent repeatability and sensitivity were demonstrated.
Flat Chern Band in a Two-Dimensional Organometallic Framework
NASA Astrophysics Data System (ADS)
Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng
2013-03-01
By combining exotic band dispersion with nontrivial band topology, an interesting type of band, namely the flat chern band (FCB), has recently been proposed, in which carriers experience strong Coulomb interaction as well as topological frustration that in together spawn unprecedented topological strongly-correlated electronic states, such as high-temperature fractional quantum hall state. Despite the proposal of several theoretical lattice models, however, it remains a doubt whether such a ``romance of flatland'' could exist in a real material. Here, we present a first-principles design to realize a nearly FCB right around the Fermi level in a two-dimensional (2D) Indium-Phenylene Organometallic Framework (IPOF). Our design in addition provides a general strategy to synthesize topologically nontrivial materials in virtue of organic chemistry and nanotechnology. Supported by DOE-BES and ARL
Exploring the thermodynamics of a two-dimensional Bose gas.
Yefsah, Tarik; Desbuquois, Rémi; Chomaz, Lauriane; Günter, Kenneth J; Dalibard, Jean
2011-09-23
Using in situ measurements on a quasi-two-dimensional, harmonically trapped (87)Rb gas, we infer various equations of state for the equivalent homogeneous fluid. From the dependence of the total atom number and the central density of our clouds with chemical potential and temperature, we obtain the equations of state for the pressure and the phase-space density. Then, using the approximate scale invariance of this 2D system, we determine the entropy per particle and find very low values (below 0.1k(B)) in the strongly degenerate regime. This shows that this gas can constitute an efficient coolant for other quantum fluids. We also explain how to disentangle the various contributions (kinetic, potential, interaction) to the energy of the trapped gas using a time-of-flight method, from which we infer the reduction of density fluctuations in a nonfully coherent cloud.
Guest Editorial: Two-Dimensional Optical Signal Processing
NASA Astrophysics Data System (ADS)
Kooij, Theo; Ludman, Jacques E.; Stilwell, P. D., Jr.
1982-10-01
When some optical processing systems firms proposed to the Defense Advanced Research Project Agency (DARPA) and the U.S. Navy some years ago that they could beat the ILLIAC-IV-that venerable supercomputer, which until recently was the world's largest by at least a factor of 100, it sounded too good to be true. But they were right, and they did not even have to try hard. The problem was a two-dimensional (2-D) processing task of generating ambiguity surfaces to test whether two received signals came from a common origin, with unknown time and Doppler shifts. The ILLIAC, going all out as an in-line processor for the Acoustic Research Center near San Francisco, California, could just make a handful of such surfaces per second; the optical processors made hundreds, literally sucking their digital inputs dry.
Domain engineering of physical vapor deposited two-dimensional materials
Alam, Tarek; Wang, Baoming; Pulavarthy, Raghu; Haque, M. A.; Muratore, Christopher; Glavin, Nicholas; Roy, Ajit K.; Voevodin, Andrey A.
2014-11-24
Physical vapor deposited two-dimensional (2D) materials span larger areas compared to exfoliated flakes, but suffer from very small grain or domain sizes. In this letter, we fabricate freestanding molybdenum disulfide (MoS{sub 2}) and amorphous boron nitride (BN) specimens to expose both surfaces. We performed in situ heating in a transmission electron microscope to observe the domain restructuring in real time. The freestanding MoS{sub 2} specimens showed up to 100× increase in domain size, while the amorphous BN transformed in to polycrystalline hexagonal BN (h-BN) at temperatures around 600 °C much lower than the 850–1000 °C range cited in the literature.
Plasmon excitations in two-dimensional atomic cluster systems
NASA Astrophysics Data System (ADS)
Yu, Yan-Qin; Yu, Ya-Bin; Xue, Hong-Jie; Wang, Ya-Xin; Chen, Jie
2016-09-01
Properties of plasmon excitations in two-dimensional (2D) atomic cluster systems are theoretically studied within an extended Hubbard model. The collective oscillation equations of charge, plasmon eigen-equations and the energy-absorption spectrum formula are presented. The calculated results show that different symmetries of plasmons exist in the cluster systems, and the symmetry of charge distribution in the plasmon resonance originate from the intrinsic symmetry of the corresponding eigen-plasmon modes, but not from the symmetry of applied external fields; however, the plasmon excitation with a certain polarization direction should be excited by the field in this direction, the dipole mode of plasmons can be excited by both uniform and non-uniform fields, but multipole ones cannot be excited by an uniform field. In addition, we show that for a given electron density, plasmon spectra are red-shifted with increasing size of the systems.
Microwave near-field imaging of two-dimensional semiconductors.
Berweger, Samuel; Weber, Joel C; John, Jimmy; Velazquez, Jesus M; Pieterick, Adam; Sanford, Norman A; Davydov, Albert V; Brunschwig, Bruce; Lewis, Nathan S; Wallis, Thomas M; Kabos, Pavel
2015-02-11
Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS2 and n- and p-doped WSe2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects.
Domain engineering of physical vapor deposited two-dimensional materials
NASA Astrophysics Data System (ADS)
Alam, Tarek; Wang, Baoming; Pulavarthy, Raghu; Haque, M. A.; Muratore, Christopher; Glavin, Nicholas; Roy, Ajit K.; Voevodin, Andrey A.
2014-11-01
Physical vapor deposited two-dimensional (2D) materials span larger areas compared to exfoliated flakes, but suffer from very small grain or domain sizes. In this letter, we fabricate freestanding molybdenum disulfide (MoS2) and amorphous boron nitride (BN) specimens to expose both surfaces. We performed in situ heating in a transmission electron microscope to observe the domain restructuring in real time. The freestanding MoS2 specimens showed up to 100× increase in domain size, while the amorphous BN transformed in to polycrystalline hexagonal BN (h-BN) at temperatures around 600 °C much lower than the 850-1000 °C range cited in the literature.
USING TWO-DIMENSIONAL HYDRODYNAMIC MODELS AT SCALES OF ECOLOGICAL IMPORTANCE. (R825760)
Modeling of flow features that are important in assessing stream habitat conditions has been a long-standing interest of stream biologists. Recently, they have begun examining the usefulness of two-dimensional (2-D) hydrodynamic models in attaining this objective. Current modelin...
Analysis Of Phase Transitions In Quasi-Two-Dimensional Dusty Systems In RF-Discharge Plasma
Adamovich, X. G.; Vaulina, O. S.; Khrustalev, Yu. V.; Nekhaevsky, Yu. Yu.; Petrov, O. F.; Fortov, V. E.
2008-09-07
In this work, we investigate the phase transitions in quasi-two-dimensional systems of dusty plasma in RF discharge. The quasi-2D systems are considered, where the areas with different phase states (dusty liquid and dusty crystal) coexist. The parameters of these areas of dusty subsystem are estimated, the obtained results are analysed and compared with theoretical predictions.
Comparison of one- and two-dimensional sodium-boiling models. [LMFBR
Carbajo, J.J.
1983-01-01
Prediction of sodium boiling and dryout in the fuel subassemblies of a Liquid Metal Fast Breeder Reactor (LMFBR) under certain accident aconditions is of paramount importance in LMFBR safety. In the present paper, boiling and dryout calculations performed by two computer codes, one-dimensional (1-D), LOOP-1 and two-dimensional (2-D), THORAX are presented and compared with experimental data.
Technology Transfer Automated Retrieval System (TEKTRAN)
A proteomic approach based on two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) for protein separation and subsequent mass spectrometry (MS) for protein identification was applied to establish a proteomic reference map for the soybean embryonic axis. Proteins were extracted from dissecte...
Picture Perception in Infants: Generalization from Two-Dimensional to Three-Dimensional Displays
ERIC Educational Resources Information Center
Jowkar-Baniani, Gelareh; Schmuckler, Mark A.
2011-01-01
Two experiments investigated 9-month-old infants' abilities to recognize the correspondence between an actual three-dimensional (3D) object and its two-dimensional (2D) representation, looking specifically at representations that did not literally depict the actual object: schematic line drawings. In Experiment 1, infants habituated to a line…
Electronic nanobiosensors based on two-dimensional materials
NASA Astrophysics Data System (ADS)
Ping, Jinglei
Atomically-thick two-dimensional (2D) nanomaterials have tremendous potential to be applied as transduction elements in biosensors and bioelectronics. We developed scalable methods for synthesis and large-area transfer of two-dimensional nanomaterials, particularly graphene and metal dichalcogenides (so called ``MX2'' materials). We also developed versatile fabrication methods for large arrays of field-effect transistors (FETs) and micro-electrodes with these nanomaterials based on either conventional photolithography or innovative approaches that minimize contamination of the 2D layer. By functionalizing the FETs with a computationally redesigned water-soluble mu-opioid receptor, we created selective and sensitive biosensors suitable for detection of the drug target naltrexone and the neuropeptide enkephalin at pg/mL concentrations. We also constructed DNA-functionalized biosensors and nano-particle decorated biosensors by applying related bio-nano integration techniques. Our methodology paves the way for multiplexed nanosensor arrays with all-electronic readout suitable for inexpensive point-of-care diagnostics, drug-development and biomedical research. With graphene field-effect transistors, we investigated the graphene/solution interface and developed a quantitative model for the effect of ionic screening on the graphene carrier density based on theories of the electric double layer. Finally, we have developed a technique for measuring low-level Faradaic charge-transfer current (fA) across the graphene/solution interface via real-time charge monitoring of graphene microelectrodes in ionic solution. This technique enables the development of flexible and transparent pH sensors that are promising for in vivo applications. The author acknowledges the support from the Defense Advanced Research Projects Agency (DARPA) and the U. S. Army Research Office under Grant Number W911NF1010093.
Two-Dimensional Synthetic-Aperture Radiometer
NASA Technical Reports Server (NTRS)
LeVine, David M.
2010-01-01
A two-dimensional synthetic-aperture radiometer, now undergoing development, serves as a test bed for demonstrating the potential of aperture synthesis for remote sensing of the Earth, particularly for measuring spatial distributions of soil moisture and ocean-surface salinity. The goal is to use the technology for remote sensing aboard a spacecraft in orbit, but the basic principles of design and operation are applicable to remote sensing from aboard an aircraft, and the prototype of the system under development is designed for operation aboard an aircraft. In aperture synthesis, one utilizes several small antennas in combination with a signal processing in order to obtain resolution that otherwise would require the use of an antenna with a larger aperture (and, hence, potentially more difficult to deploy in space). The principle upon which this system is based is similar to that of Earth-rotation aperture synthesis employed in radio astronomy. In this technology the coherent products (correlations) of signals from pairs of antennas are obtained at different antenna-pair spacings (baselines). The correlation for each baseline yields a sample point in a Fourier transform of the brightness-temperature map of the scene. An image of the scene itself is then reconstructed by inverting the sampled transform. The predecessor of the present two-dimensional synthetic-aperture radiometer is a one-dimensional one, named the Electrically Scanned Thinned Array Radiometer (ESTAR). Operating in the L band, the ESTAR employs aperture synthesis in the cross-track dimension only, while using a conventional antenna for resolution in the along-track dimension. The two-dimensional instrument also operates in the L band to be precise, at a frequency of 1.413 GHz in the frequency band restricted for passive use (no transmission) only. The L band was chosen because (1) the L band represents the long-wavelength end of the remote- sensing spectrum, where the problem of achieving adequate
Gauge equivalence in two-dimensional gravity
Fujiwara, T. ); Igarashi, Y. ); Kubo, J. ); Tabei, T. )
1993-08-15
Two-dimensional quantum gravity is identified as a second-class system which we convert into a first-class system via the Batalin-Fradkin (BF) procedure. Using the extended phase space method, we then formulate the theory in the most general class of gauges. The conformal gauge action suggested by David, Distler, and Kawai is derived from first principles. We find a local, light-cone gauge action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature equation [partial derivative][sub [minus
Quasicondensation in Two-Dimensional Fermi Gases.
Wu, Chien-Te; Anderson, Brandon M; Boyack, Rufus; Levin, K
2015-12-11
In this paper we follow the analysis and protocols of recent experiments, combined with simple theory, to arrive at a physical understanding of quasi-condensation in two dimensional Fermi gases. A key signature of quasi-condensation, which contains aspects of Berezinskiĭ-Kosterlitz-Thouless behavior, is a strong zero momentum peak in the pair momentum distribution. Importantly, this peak emerges at a reasonably well defined onset temperature. The resulting phase diagram, pair momentum distribution, and algebraic power law decay are compatible with recent experiments throughout the continuum from BEC to BCS. PMID:26705613
Pressure of two-dimensional Yukawa liquids
NASA Astrophysics Data System (ADS)
Feng, Yan; Goree, J.; Liu, Bin; Wang, Lei; Tian, Wen-de
2016-06-01
A simple analytic expression for the pressure of a two-dimensional Yukawa liquid is found by fitting results from a molecular dynamics simulation. The results verify that the pressure can be written as the sum of a potential term which is a simple multiple of the Coulomb potential energy at a distance of the Wigner-Seitz radius, and a kinetic term which is a multiple of the one for an ideal gas. Dimensionless coefficients for each of these terms are found empirically, by fitting. The resulting analytic expression, with its empirically determined coefficients, is plotted as isochores, or curves of constant area. These results should be applicable to monolayer dusty plasmas.
Program For Two-Dimensional Thermoplastic Deformation
NASA Technical Reports Server (NTRS)
Orient, George E.
1993-01-01
SOLAS contains number of utility programs for use with finite-element simulations. Designed to handle two-dimensional problems of quasi-static thermoplastic deformation. Includes optional postprocessing software, independent of solution codes, generating unified element-by-element list of quantitative results of computation, plus file containing signed equivalent stresses, equivalent strains, and multiaxiality factor parameter. Signs of equivalent quantities expressed either with respect to maximum principal quantities or with respect to directions defined by user. Written in UNIX shell script and FORTRAN 77.
Numerical simulations of two-dimensional QED
Carson, S.R.; Kenway, R.D.
1986-02-01
We describe the computer simulation of two-dimensional QED on a 64 x 64 Euclidean space-time lattice using the Susskind lattice fermion action. Theorder parameter for chiral symmetry breaking and the low-lying meson masses are calculated for both the model with two continuum flavours, which arises naturally in this formulation, and the model with one continuum falvour obtained by including a nonsymmetric mass term and setting one fermion mass equal to the cut-off. Results are compared with those obtined using the quenched approximation, and with analytic predictions.
FRACFLO. Two-Dimensional Ground Water Transport
Gureghian, A.B.
1990-07-01
FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturated with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.
DYNA2D96. Explicit 2-D Hydrodynamic FEM Program
Whirley, R.G.
1992-04-01
DYNA2D is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
Two-dimensional shape memory graphene oxide
Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G.; Yan, Wenyi; Liu, Jefferson Zhe
2016-01-01
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. PMID:27325441
Two-dimensional shape memory graphene oxide
NASA Astrophysics Data System (ADS)
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.
Two-dimensional shape memory graphene oxide.
Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G; Yan, Wenyi; Liu, Jefferson Zhe
2016-01-01
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.
Electronic structures and optical properties of two-dimensional ScN and YN nanosheets
Liu, Jian; Li, Xi-Bo; Zhang, Hui; Yin, Wen-Jin; Liu, Li-Min E-mail: limin.liu@csrc.ac.cn; Zhang, Hai-Bin; Peng, Ping E-mail: limin.liu@csrc.ac.cn
2014-03-07
Two-dimensional (2D) materials exhibit different electronic properties than their bulk materials. Here, we present a systematic study of 2D tetragonal materials of ScN and YN using density functional theory calculations. Several thermodynamically stable 2D tetragonal structures were determined, and such novel tetragonal structures have good electronic and optical properties. Both bulk ScN and YN are indirect band gap semiconductors while the electronic structures of 2D ScN and YN are indirect gap semiconductors, with band gaps of 0.62–2.21 eV. The calculated optical spectra suggest that 2D tetragonal ScN and YN nanosheets have high visible light absorption efficiency. These electronic properties indicate that 2D ScN and YN have great potential for applications in photovoltaics and photocatalysis.
Recent advances in optoelectronic properties and applications of two-dimensional metal chalcogenides
NASA Astrophysics Data System (ADS)
Congxin, Xia; Jingbo, Li
2016-05-01
Since two-dimensional (2D) graphene was fabricated successfully, many kinds of graphene-like 2D materials have attracted extensive attention. Among them, the studies of 2D metal chalcogenides have become the focus of intense research due to their unique physical properties and promising applications. Here, we review significant recent advances in optoelectronic properties and applications of 2D metal chalcogenides. This review highlights the recent progress of synthesis, characterization and isolation of single and few layer metal chalcogenides nanosheets. Moreover, we also focus on the recent important progress of electronic, optical properties and optoelectronic devices of 2D metal chalcogenides. Additionally, the theoretical model and understanding on the band structures, optical properties and related physical mechanism are also reviewed. Finally, we give some personal perspectives on potential research problems in the optoelectronic characteristics of 2D metal chalcogenides and related device applications.
Comparing two-dimensional electrophoretic gel images across the Internet.
Lemkin, P F
1997-01-01
Scientists around the world often work on similar data so the need to share results and compare data arises periodically. We describe a method of comparing two two-dimensional (2-D) protein gels of similar samples created in different laboratories to help identify or suggest protein spot identification. Now that 2-D gels and associated databases frequently appear on the Internet, this opens up the possibility of visually comparing one's own experimental 2-D gel image data with data from another gel in a remote Internet database. In general, there are a few ways to compare images: (i) slide one gel (autoradiograph or stained gel) over the other while back-illuminated, or (ii) build a 2-D gel computer database from both gels after scanning and analyzing these gels. These are impractical since in the first case the gel from the Internet database is not locally available. In the second, the costs of building a multi-gel database solely to answer the question of whether a spot is the same spot may be excessive if only a single visual comparison is needed. We describe a distributed gel comparison program (URL: http://www-lmmb.ncifcrf.gov/flicker) which runs on any World Wide Web (WWW) connected computer and is invoked from a Java-capable web browser. One gel image is read from any Internet 2-D gel database (e.g. SWISS-2DPAGE) and the other may reside on the investigator's computer. Images may be more easily compared by first applying spatial warping or other transforms interactively on the user's computer. First, regions of interest are "landmarked" with several corresponding points in each gel image, then one gel image is warped to the geometry of the other. As the two gels are rapidly alternated, or flickered, in the same window, the user can slide one gel past the other to visually align corresponding spots by matching local morphology. This flicker-comparison technique may be applied to analyzing other types of one-dimensional and 2-D biomedical images.
Two-dimensional stimulated resonance Raman spectroscopy of molecules with broadband x-ray pulses
Biggs, Jason D.; Zhang, Yu; Healion, Daniel; Mukamel, Shaul
2012-01-01
Expressions for the two-dimensional stimulated x-ray Raman spectroscopy (2D-SXRS) signal obtained using attosecond x-ray pulses are derived. The 1D- and 2D-SXRS signals are calculated for trans-N-methyl acetamide (NMA) with broad bandwidth (181 as, 14.2 eV FWHM) pulses tuned to the oxygen and nitrogen K-edges. Crosspeaks in 2D signals reveal electronic Franck-Condon overlaps between valence orbitals and relaxed orbitals in the presence of the core-hole. PMID:22583220
Disentangling electronic and vibronic coherences in two-dimensional echo spectra.
Kreisbeck, Christoph; Kramer, Tobias; Aspuru-Guzik, Alán
2013-08-15
The prevalence of long-lasting oscillatory signals in two-dimensional (2D) echo spectroscopy of light-harvesting complexes has led to a search for possible mechanisms. We investigate how two causes of oscillatory signals are intertwined: (i) electronic coherences supporting delocalized wavelike motion and (ii) narrow bands in the vibronic spectral density. To disentangle the vibronic and electronic contributions, we introduce a time-windowed Fourier transform of the signal amplitude. We find that 2D spectra can be dominated by excitations of pathways which are absent in excitonic energy transport. This leads to an underestimation of the lifetime of electronic coherences by 2D spectra.
Melting in three-dimensional and two-dimensional Yukawa systems.
Vaulina, О S; Koss, X G
2015-10-01
Solid-liquid phase transitions in three-dimensional (3D) and two-dimensional (2D) Yukawa systems were studied numerically and analytically, including the melting of the fcc and bcc 3D lattices, and of a hexagonal primitive (hp) 2D lattice. An approach is proposed for the determination of the melting lines in these systems. The suggested approach takes into account the nonlinearity (anharmonicity) of pair interaction forces and allows one to correctly predict the conditions of melting for 3D and 2D crystal systems. The obtained results are compared with the existing theoretical and numerical data. PMID:26565216
Fabrication of two-dimensional metallic photonic crystals using laser interference ablation
NASA Astrophysics Data System (ADS)
Pang, Zhaoguang; Zhang, Xinping; Liu, Hongmei; Zhai, Tianrui
2012-11-01
We demonstrate the fabrication of two-dimensional (2D) metallic photonic crystals (MPCs) based on colloidal gold nanoparticles, where laser interference ablation combining subsequent high temperature annealing is employed for the construction of 2D gold nano-dot arrays in square lattices. The microscopic and spectroscopic properties of the 2-D MPCs are systematically characterized by the scanning electron microscope and the angle-resolved optical extinction spectroscopic measurements, the strong coupling between the waveguide resonance mode and the particle plasmon resonance of the MPCs imply the success of the fabrication method, which show potential applications in optoelectronic devices and sensors.
Two-dimensional quantitative measurements of methyl radicals in methane/air flame.
Wu, Yue; Zhang, Zhili
2015-01-10
Two-dimensional (2D) quantitative measurements of methyl (CH3) radicals in a methane/air Hencken flame at atmospheric pressure are performed using coherent microwave Rayleigh scattering (Radar) from Resonance Enhanced Multi-Photon Ionization (REMPI) technique. The 2D scanning and subsequent quantification are employed for Radar REMPI. The 2D quantitative results are used to verify the numerical calculations. The line-integral effect was involved in the calculation due to the real experimental configuration. A 25% difference existed between the experimental results and numerical calculation, while the overall concentration distributions between experiment and modeling of single flamelet have fairly good agreement with each other. PMID:25967612
Simulated annealing applied to two-dimensional low-beta reduced magnetohydrodynamics
Chikasue, Y.; Furukawa, M.
2015-02-15
The simulated annealing (SA) method is applied to two-dimensional (2D) low-beta reduced magnetohydrodynamics (R-MHD). We have successfully obtained stationary states of the system numerically by the SA method with Casimir invariants preserved. Since the 2D low-beta R-MHD has two fields, the relaxation process becomes complex compared to a single field system such as 2D Euler flow. The obtained stationary state can have fine structure. We have found that the fine structure appears because the relaxation processes are different between kinetic energy and magnetic energy.
Intelligent Automated Correction of Baseplane and Systematic Noise in Two-Dimensional NMR Spectra
NASA Astrophysics Data System (ADS)
Levy, G. C.; Jeong, G. W.; Yu, J. Q.; Wang, K.
A computer program useful for 2D NMR data is described that provides automatic two-dimensional baseplane correction and subsequent tl and t2 ridge suppression. The algorithm per forms combined correction of smooth baseplane distortions and sharp ridges in 2D NMR spectra through five steps: (1) identification of resonance peaks and ridges, (2) extraction of initial, putative global baseplane, (3) window filtering of the corresponding time domain, (4) construction of a 2D spectrum free of baseplane distortion, and (5) suppression of ridges, The optimal parameters for baseplane and ridge correction are automatically decided by the program, yielding a greatly improved spectrum, together with more accurate spectral information.
Two-dimensional fluorescence difference gel electrophoresis for comparative proteomics profiling
Tannu, Nilesh S; Hemby, Scott E
2007-01-01
Quantitative proteomics is the workhorse of the modern proteomics initiative. The gel-based and MuDPIT approaches have facilitated vital advances in the measurement of protein expression alterations in normal and disease phenotypic states. The methodological advance in two-dimensional gel electrophoresis (2DGE) has been the multiplexing fluorescent two-dimensional fluorescence difference gel electrophoresis (2D-DIGE). 2D-DIGE is based on direct labeling of lysine groups on proteins with cyanine CyDye DIGE Fluor minimal dyes before isoelectric focusing, enabling the labeling of 2–3 samples with different dyes and electrophoresis of all the samples on the same 2D gel. This capability minimizes spot pattern variability and the number of gels in an experiment while providing simple, accurate and reproducible spot matching. This protocol can be completed in 3–5 weeks depending on the sample size of the experiment and the level of expertise of the investigator. PMID:17487156
Strain engineering in semiconducting two-dimensional crystals.
Roldán, Rafael; Castellanos-Gomez, Andrés; Cappelluti, Emmanuele; Guinea, Francisco
2015-08-12
One of the fascinating properties of the new families of two-dimensional crystals is their high stretchability and the possibility to use external strain to manipulate, in a controlled manner, their optical and electronic properties. Strain engineering, understood as the field that study how the physical properties of materials can be tuned by controlling the elastic strain fields applied to it, has a perfect platform for its implementation in the atomically thin semiconducting materials. The object of this review is to give an overview of the recent progress to control the optical and electronics properties of 2D crystals, by means of strain engineering. We will concentrate on semiconducting layered materials, with especial emphasis in transition metal dichalcogenides (MoS2, WS2, MoSe2 and WSe2). The effect of strain in other atomically thin materials like black phosphorus, silicene, etc, is also considered. The benefits of strain engineering in 2D crystals for applications in nanoelectronics and optoelectronics will be revised, and the open problems in the field will be discussed. PMID:26199038
Beliaev damping in quasi-two-dimensional dipolar condensates
NASA Astrophysics Data System (ADS)
Wilson, Ryan M.; Natu, Stefan
2016-05-01
We study the effects of quasiparticle interactions in a quasi-two-dimensional (quasi-2D), zero-temperature Bose-Einstein condensate of dipolar atoms, which can exhibit a roton-maxon feature in its quasiparticle spectrum. Our focus is the Beliaev damping process, in which a quasiparticle collides with the condensate and resonantly decays into a pair of quasiparticles. Remarkably, the rate for this process exhibits a highly nontrivial dependence on the quasiparticle momentum and the dipolar interaction strength. For weak interactions, low-energy phonons experience no damping, and higher-energy quasiparticles undergo anomalously weak damping. In contrast, the Beliaev damping rates become anomalously large for stronger dipolar interactions, as rotons become energetically accessible as final states. When the dipoles are tilted off the axis of symmetry, the damping rates acquire an anisotropic character. Surprisingly, this anisotropy does not simply track the anisotropy of the dipolar interactions, rather, the mechanisms for damping are qualitatively modified in the anisotropic case. Our study reveals the unconventional nature of Beliaev damping in dipolar condensates, and has important implications for ongoing studies of equilibrium and nonequilibrium dynamics in these systems. Further, our results are relevant for other 2D superfluids with roton excitations, including spin-orbit-coupled Bose gases, magnon condensates, and 4He films.
Two-dimensional electronic spectroscopy signatures of the glass transition
Lewis, K. L. .. M.; Myers, J. A.; Fuller, F.; Tekavec, P. F.; Ogilvie, J. P.
2010-01-01
Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump–probe geometry with a pulse shaper [ Optics Express 15 (2007), 16681-16689; Optics Express 16 (2008), 17420-17428], we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longermore » waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency–frequency correlation function [ Optics Letters 31 (2006), 3354–3356]. Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreting temperature-dependent dynamics of biological systems.« less
Dissipation in quasi-two-dimensional flowing foams
NASA Astrophysics Data System (ADS)
Raufaste, Christophe; Foulon, Amandine; Dollet, Benjamin
2009-05-01
The dissipation between two-dimensional (2D) monolayers of bubbles, the so-called quasi-2D foams, and a wall is investigated in two setups: a "liquid pool" system, where the foam is confined between a soap solution and a glass coverslip, and a Hele-Shaw cell, where the foam occupies the narrow gap between two plates. This experimental study reports dissipation measurements for mobile gas/liquid interfaces (free shear boundary condition) over a large range of parameters: in the liquid pool system, velocity and bubble area; in the Hele-Shaw cell, velocity and liquid fraction. The effect of the latter quantity is measured for the first time over more than three orders of magnitude. A full comparison between our results and other experimental studies is proposed and enables to rescale all measurements on a single master curve. It shows that for mobile gas/liquid interfaces, the existing models systematically underestimate the dissipation in flowing foams. This is quantified by a discrepancy factor ξ, ratio of the experimental dissipation measurements to the theoretical predictions, which scales as ξ =1.4(RP/√A )-0.5 with RP the Plateau border radius and A the bubble area, showing that the discrepancy is higher for dry foams.
GW-BSE calculations on two-dimensional MXene phases
NASA Astrophysics Data System (ADS)
Li, Zhenglu; Hong, Liang; Jornada, Felipe; Cao, Ting; Ogut, Serdar; Louie, Steven G.
2015-03-01
MXene is a promising candidate for new useful two-dimensional (2D) crystals. Experimentally, few-layer samples have been made from the bulk, and they demonstrate many excellent properties for electric and thermal transport, as well as other novel physics. In this work, we have performed GW-BSE calculations based on first-principles calculations to study some of the MXene family. We find that monolayer Ti2CO2 possesses insulating properties. Furthermore, the 2D screening effect is very strong, resulting in a GW band gap correction of almost 1 eV. Based on these initial results, we expect that optical properties of these materials will also have strong excitonic effects. This research was supported by the DOE Theory Program at the Lawrence Berkeley National Lab under Contract No. DE-AC02-05CH11231 and by the National Science Foundation under Grant No. DMR10-1006184. This research used resources NERSC, supported by US DOE.
Two-dimensional magnetic liquid froth: Coarsening and topological correlations
NASA Astrophysics Data System (ADS)
Elias, Florence; Flament, Cyrille; Bacri, Jean-Claude; Cardoso, Olivier; Graner, François
1997-09-01
We present an experimental study of a cellular system which may be formed in a two-dimensional (2D) layer made of an immiscible mixture of a magnetic fluid and an oil. We obtain a wet or a dry 2D froth, the characteristics of which are determined by the strength of an externally applied magnetic field. The froth is formed in an equilibrium state; the topological and geometrical features of the froth are fixed by the value of the applied field. The cellular pattern of the froth is stable in time, and a coarseninglike behavior is observed on decreasing the amplitude of the field. This cellular system can be used as a model to study topological processes in the equilibrium state, contrary to soap froths which are nonequilibrium systems because gas diffusion occurs. We show that the topological characteristics are statistically reversible after a magnetic-field cycle, and we present a statistical study of the froth features as a function of the amplitude of the field. The topological correlations between neighboring cells are well described by the Aboav-Weaire law. Finally, we consider the area of an n-sided cell, and show that its growth rate (magnetic field dependent) is, in a surprising manner, proportional to n-6, similarly to the Von Neumann law.
Diamagnetic phase transitions in two-dimensional conductors
NASA Astrophysics Data System (ADS)
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.
pentahexoctite: A new two-dimensional allotrope of carbon
NASA Astrophysics Data System (ADS)
Sharma, Babu Ram; Manjanath, Aaditya; Singh, Abhishek K.
2014-11-01
The ability of carbon to exist in many forms across dimensions has spawned search in exploring newer allotropes consisting of either, different networks of polygons or rings. While research on various 3D phases of carbon has been extensive, 2D allotropes formed from stable rings are yet to be unearthed. Here, we report a new sp2 hybridized two-dimensional allotrope consisting of continuous 5-6-8 rings of carbon atoms, named as ``pentahexoctite''. The absence of unstable modes in the phonon spectra ensures the stability of the planar sheet. Furthermore, this sheet has mechanical strength comparable to graphene. Electronically, the sheet is metallic with direction-dependent flat and dispersive bands at the Fermi level ensuring highly anisotropic transport properties. This sheet serves as a precursor for stable 1D nanotubes with chirality-dependent electronic and mechanical properties. With these unique properties, this sheet becomes another exciting addition to the family of robust novel 2D allotropes of carbon.
Pentahexoctite: a new two-dimensional allotrope of carbon.
Sharma, Babu Ram; Manjanath, Aaditya; Singh, Abhishek K
2014-01-01
The ability of carbon to exist in many forms across dimensions has spawned search in exploring newer allotropes consisting of either, different networks of polygons or rings. While research on various 3D phases of carbon has been extensive, 2D allotropes formed from stable rings are yet to be unearthed. Here, we report a new sp(2) hybridized two-dimensional allotrope consisting of continuous 5-6-8 rings of carbon atoms, named as "pentahexoctite". The absence of unstable modes in the phonon spectra ensures the stability of the planar sheet. Furthermore, this sheet has mechanical strength comparable to graphene. Electronically, the sheet is metallic with direction-dependent flat and dispersive bands at the Fermi level ensuring highly anisotropic transport properties. This sheet serves as a precursor for stable 1D nanotubes with chirality-dependent electronic and mechanical properties. With these unique properties, this sheet becomes another exciting addition to the family of robust novel 2D allotropes of carbon.
A two dimensional silicon-based photonic crystal microcavity biosensor
NASA Astrophysics Data System (ADS)
Lee, Mindy; Fauchet, Philippe M.
2006-08-01
The optical properties of photonic bandgap (PBG) structures are highly sensitive to environmental variation. PBG structures thus are an attractive platform for biosensing applications. We experimentally demonstrate a label-free biosensor based on a two-dimensional (2-D) photonic crystal microcavity slab. The microcavity is fabricated on a silicon-on-insulator substrate and integrated with tapered ridge waveguides for light coupling. The Finite-Difference Time-Domain (FDTD) method is used to model the sensor. The resonance of the microcavity is designed to be around 1.58 μm. In order to capture the target biological materials, the internal surface of the photonic crystal is first functionalized. Binding of the targets is monitored by observing a red shift of the transmission resonance. The magnitude of the shift depends on the amount of material captured by the internal surface. Compared to 1-D PBG biosensors, 2-D devices require a smaller amount of target material and can accommodate larger targets. Experimental results are compared with the predictions obtained from the FDTD simulations.
Mathematical modeling of the neuron morphology using two dimensional images.
Rajković, Katarina; Marić, Dušica L; Milošević, Nebojša T; Jeremic, Sanja; Arsenijević, Valentina Arsić; Rajković, Nemanja
2016-02-01
In this study mathematical analyses such as the analysis of area and length, fractal analysis and modified Sholl analysis were applied on two dimensional (2D) images of neurons from adult human dentate nucleus (DN). Using mathematical analyses main morphological properties were obtained including the size of neuron and soma, the length of all dendrites, the density of dendritic arborization, the position of the maximum density and the irregularity of dendrites. Response surface methodology (RSM) was used for modeling the size of neurons and the length of all dendrites. However, the RSM model based on the second-order polynomial equation was only possible to apply to correlate changes in the size of the neuron with other properties of its morphology. Modeling data provided evidence that the size of DN neurons statistically depended on the size of the soma, the density of dendritic arborization and the irregularity of dendrites. The low value of mean relative percent deviation (MRPD) between the experimental data and the predicted neuron size obtained by RSM model showed that model was suitable for modeling the size of DN neurons. Therefore, RSM can be generally used for modeling neuron size from 2D images.
pentahexoctite: A new two-dimensional allotrope of carbon
Sharma, Babu Ram; Manjanath, Aaditya; Singh, Abhishek K.
2014-01-01
The ability of carbon to exist in many forms across dimensions has spawned search in exploring newer allotropes consisting of either, different networks of polygons or rings. While research on various 3D phases of carbon has been extensive, 2D allotropes formed from stable rings are yet to be unearthed. Here, we report a new sp2 hybridized two-dimensional allotrope consisting of continuous 5-6-8 rings of carbon atoms, named as “pentahexoctite”. The absence of unstable modes in the phonon spectra ensures the stability of the planar sheet. Furthermore, this sheet has mechanical strength comparable to graphene. Electronically, the sheet is metallic with direction-dependent flat and dispersive bands at the Fermi level ensuring highly anisotropic transport properties. This sheet serves as a precursor for stable 1D nanotubes with chirality-dependent electronic and mechanical properties. With these unique properties, this sheet becomes another exciting addition to the family of robust novel 2D allotropes of carbon. PMID:25418419
Two-Dimensional Low-Turbulence Tunnel
NASA Technical Reports Server (NTRS)
1937-01-01
Construction of the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a
Two-Dimensional Low-Turbulence Tunnel
NASA Technical Reports Server (NTRS)
1938-01-01
Construction of the wood frame for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the
Two-Dimensional Low-Turbulence Tunnel
NASA Technical Reports Server (NTRS)
1938-01-01
Manometer for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space
Multiscale modeling of two-dimensional contacts.
Luan, B Q; Hyun, S; Molinari, J F; Bernstein, N; Robbins, Mark O
2006-10-01
A hybrid simulation method is introduced and used to study two-dimensional single-asperity and multi-asperity contacts both quasistatically and dynamically. The method combines an atomistic treatment of the interfacial region with a finite-element method description of subsurface deformations. The dynamics in the two regions are coupled through displacement boundary conditions applied at the outer edges of an overlap region. The two solutions are followed concurrently but with different time resolution. The method is benchmarked against full atomistic simulations. Accurate results are obtained for contact areas, pressures, and static and dynamic friction forces. The time saving depends on the fraction of the system treated atomistically and is already more than a factor of 20 for the relatively small systems considered here.
Two-Dimensional Speckle Strain Imaging
Pignatelli, Ricardo; Law, Mark A.; Martinez, Hugo; Altman, Carolyn; Ayres, Nancy; Jefferies, John L.; Ganame, Javier
2012-01-01
Two-dimensional speckle-tracking strain imaging (speckle strain imaging) is useful for evaluating left ventricular myocardial function in patients with ischemic heart disease and cardiomyopathy, including hypertrophic and dilated phenotypes. The usefulness of speckle strain imaging in patients with pheochromocytoma who are undergoing adrenal surgery has been described, but we found no reports of the use of this method to evaluate ventricular dysfunction longitudinally in children. Herein, we describe the case of a 10-year-old girl with a paraganglioma, acute junctional tachycardia, and myocardial dysfunction. After control of the tachycardia and partial resection of the tumor, speckle strain imaging enabled clinical management that led to substantial improvement in the patient's initially diffuse myocardial dysfunction. Because conventional echocardiographic methods alone may be inadequate to guide the management of pediatric patients with partially resected neuroendocrine tumors, we recommend speckle strain imaging as an additional noninvasive option for treatment guidance and monitoring of cardiac tissue response. PMID:22412245
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. PMID:27661693
Two-dimensional ultrasound and cardiac operations.
Spotnitz, H M
1982-01-01
Two-dimensional ultrasound was employed for qualitative and quantitative studies during cardiac operations in 74 patients. A gas-sterilized phased-array transducer applied directly to the anterior surface of the heart produced high-quality images without a water path or other special manipulations. The techniques employed were successful in demonstrating alterations in cardiac anatomy associated with valve disease and cardiac tumors. Continuous clouds of microbubbles ejected from the left ventricle immediately following cardiopulmonary bypass were detected in 42% of 45 patients studied. Measurement of short-axis area change during systole proved useful for evaluation of intraoperative changes in left ventricular function. In the perioperative period, with the chest closed, the method detected increasing left ventricular mass during transplant rejection and was useful for monitoring changes in left ventricular performance when image quality was sufficient. The capabilities and limitations of this technique for special studies during cardiac operations should be familiar to surgeons with access to the method.
Two-dimensional Inductive Position Sensing System
NASA Technical Reports Server (NTRS)
Youngquist, Robert C. (Inventor); Starr, Stanley O. (Inventor)
2015-01-01
A two-dimensional inductive position sensing system uses four drive inductors arranged at the vertices of a parallelogram and a sensing inductor positioned within the parallelogram. The sensing inductor is movable within the parallelogram and relative to the drive inductors. A first oscillating current at a first frequency is supplied to a first pair of the drive inductors located at ends of a first diagonal of the parallelogram. A second oscillating current at a second frequency is supplied to a second pair of the drive inductors located at ends of a second diagonal of the parallelogram. As a result, the sensing inductor generates a first output voltage at the first frequency and a second output voltage at the second frequency. A processor determines a position of the sensing inductor relative to the drive inductors using the first output voltage and the second output voltage.
Janus Spectra in Two-Dimensional Flows
NASA Astrophysics Data System (ADS)
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.
Two-Dimensional Ground Water Transport
1992-03-05
FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturatedmore » with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.« less
NASA Astrophysics Data System (ADS)
Rasmussen, Filip A.; Schmidt, Per S.; Winther, Kirsten T.; Thygesen, Kristian S.
2016-10-01
Calculating the quasiparticle (QP) band structure of two-dimensional (2D) materials within the GW self-energy approximation has proven to be a rather demanding computational task. The main reason is the strong q dependence of the 2D dielectric function around q =0 that calls for a much denser sampling of the Brillouin zone (BZ) than is necessary for similar three-dimensional solids. Here, we use an analytical expression for the small q limit of the 2D response function to perform the BZ integral over the critical region around q =0 . This drastically reduces the requirements on the q -point mesh and implies a significant computational speedup. For example, in the case of monolayer MoS2, convergence of the G0W0 band gap to within ˜0.1 eV is achieved with 12 ×12 q points rather than the 36 ×36 mesh required with discrete BZ sampling techniques. We perform a critical assessment of the band gap of the three prototypical 2D semiconductors, MoS2, h -BN, and phosphorene, including the effect of self-consistency at the GW0 level. The method is implemented in the open source code gpaw.
Two-dimensionally-periodic diffractive optical elements: limitations of scalar analysis.
Glytsis, Elias N
2002-04-01
The range of validity of the scalar diffraction analysis is quantified for the case of two-dimensionally-periodic diffractive optical elements (crossed gratings). Three canonical classes of two-dimensionally-periodic grating structures are analyzed by using the rigorous coupled-wave analysis as well as the scalar diffraction analysis. In all cases the scalar-analysis diffraction efficiencies are compared with the exact diffraction efficiencies. The error in using the scalar analysis is then determined as a function of the grating-period(s)-to-wavelength ratio(s), the minimum feature size, the grating depth, the refractive index of the grating, the incident polarization, and the number of phase levels. The three classes of two-dimensional (2-D) unit cells are as follows: (1) a rectangular pillar, (2) an elliptical pillar, and (3) an arbitrarily pixellated multilevel 2-D unit cell that is representative of more complicated diffractive optical elements such as computer-generated holograms. In all cases a normally incident electromagnetic plane wave is considered. It is shown that the error of the scalar diffraction analysis in the case of two-dimensionally-periodic diffractive optical elements is greater than that for the corresponding one-dimensionally-periodic counterparts. In addition, the accuracy of the scalar diffraction analysis degrades with increasing refractive index, grating thickness, and asymmetry of the 2-D unit cell and with decreasing grating-period-to-wavelength ratio and feature size.
Two-dimensional virtual impactors. Final report
Forney, L.J.; Ravenhall, D.G.
1980-12-01
Theoretical predictions using both potential flow analyses and solutions to Navier-Stokes equations are made for the operating characteristics of a two-dimensional virtual impactor. Experiments were performed with 2.5 ..mu..m, uranine tagged, di-octylphthalate (DOP) oil droplets for a wide range of prototype geometries to measure the magnitude of internal losses and to fully characterize the instrument response. The influence of geometry including the throat angle (38/sup 0/ less than or equal to ..beta../sub 0/ less than or equal to 58.2/sup 0/) and normalized void width (0.7 less than or equal to h/w less than or equal to 1.5) on the particle cutoff diameter, efficiency curve steepness and properties of the internal particle loss factor are presented for fixed instrument Reynolds numbers Re = 1540 and bleed flow f = 0.1. The theory, supported by trends in the empirical data, predicts that internal particle losses reduce to zero as the normalized void width increases to h/w = 1.4 +- .1 while the data show a minimum at h/w = 1.6 +- .1. Increasing the void width, however, is shown to substantially reduce the steepness of the particle efficiency curves. Visual observations of the onset of fluid separation for two-dimensional jets impinging upon a void were conducted with a scaled-up water model and correlated with theory. It was found that the limiting void width h/sub lim//w marking the onset of fluid instabilities peaked for an intermediate value of the fluid deflecting plate angle ..beta.. approx. = 80/sup 0/ with larger values of h/sub lim//w corresponding to smaller throat angles ..beta../sub 0/. The limiting void width h/sub lim//w also increased with larger bleed flows into the void. These instabilities may make it difficult to correlate experimental virtual impactor data with theory.
Graphene and graphene-like two-dimensional materials in photodetection: mechanisms and methodology.
Sun, Zhenhua; Chang, Haixin
2014-05-27
Graphene and graphene-like two-dimensional (2D) materials have attracted much attention due to its extraordinary electronic and optical properties, which accommodate a large potential in optoelectronic applications such as photodetection. However, although much progress has been made, many challenges exist in fundamental and practical aspects hindering graphene and graphene-like 2D materials from photodetector and other photonic and optoelectronic applications. Here, we review the recent progress in photodetection based on graphene and graphene-like 2D materials and start with the summary of some most important physical mechanisms, including photoelectric, photo-thermoelectric, and photo-bolometric regimes. Then methodology-level discussions are given from viewpoints of state-of-the-art designs in device geometry and materials. It is worth emphasizing that emerging photodetection and photodetectors based on graphene-like 2D materials such as metal chalcogenide nanosheets are reviewed systematically. Finally, we conclude this review in a brief discussion with remaining challenges in photodetection of two-dimensional photonics and optoelectronics (2D POE) and note that complete understandings of 2D materials and 2D POE may inspire solar energy conversion and other new applications.
Imaging hemodynamic changes in preterm infant brains with two-dimensional diffuse optical tomography
NASA Astrophysics Data System (ADS)
Gao, Feng; Ma, Yiwen; Yang, Fang; Zhao, Huijuan; Jiang, Jingying; Kusaka, Takashi; Ueno, Masanori; Yamada, Yukio
2008-02-01
We present our preliminary results on two-dimensional (2-D) optical tomographic imaging of hemodynamic changes of two preterm infant brains in different ventilation settings conditions. The investigations use the established two-wavelength, 16-channel time-correlated single photon counting system for the detection, and the generalized pulse spectrum technique based algorithm for the image reconstruction. The experiments demonstrate that two-dimensional diffuse optical tomography may be a potent and relatively simple way of investigating the functions and neural development of infant brains in the perinatal period.
Kato, Takaumi; Sone, Shusaku; Funamoto, Kenichi; Hayase, Toshiyuki; Kadowaki, Hiroko; Taniguchi, Nobuyuki
2016-09-01
Two-dimensional ultrasonic-measurement-integrated (2D-UMI) simulation correctly reproduces hemodynamics even with an inexact inflow velocity distribution. This study aimed to investigate which is superior, a two-dimensional ordinary (2D-O) simulation with an accurate inflow velocity distribution or a 2D-UMI simulation with an inaccurate one. 2D-O and 2D-UMI simulations were performed for blood flow in a carotid artery with four upstream velocity boundary conditions: a velocity profile with backprojected measured Doppler velocities (condition A), and velocity profiles with a measured Doppler velocity distribution, a parabolic one, and a uniform one, magnitude being obtained by inflow velocity estimation (conditions B, C, and D, respectively). The error of Doppler velocity against the measurement data was sensitive to the inflow velocity distribution in the 2D-O simulation, but not in the 2D-UMI simulation with the inflow velocity estimation. Among the results in conditions B, C, and D, the error in the worst 2D-UMI simulation with condition D was 31 % of that in the best 2D-O simulation with condition B, implying the superiority of the 2D-UMI simulation with an inaccurate inflow velocity distribution over the 2D-O simulation with an exact one. Condition A resulted in a larger error than the other conditions in both the 2D-O and 2D-UMI simulations.
Internetwork magnetic field as revealed by two-dimensional inversions
NASA Astrophysics Data System (ADS)
Danilovic, S.; van Noort, M.; Rempel, M.
2016-09-01
Context. Properties of magnetic field in the internetwork regions are still fairly unknown because of rather weak spectropolarimetric signals. Aims: We address the matter by using the two-dimensional (2D) inversion code, which is able to retrieve the information on smallest spatial scales up to the diffraction limit, while being less susceptible to noise than most of the previous methods used. Methods: Performance of the code and the impact of various effects on the retrieved field distribution is tested first on the realistic magneto-hydrodynamic (MHD) simulations. The best inversion scenario is then applied to the real data obtained by Spectropolarimeter (SP) on board Hinode. Results: Tests on simulations show that: (1) the best choice of node position ensures a decent retrieval of all parameters; (2) the code performs well for different configurations of magnetic field; (3) slightly different noise levels or slightly different defocus included in the spatial point spread function (PSF) produces no significant effect on the results; and (4) temporal integration shifts the field distribution to a stronger, more horizontally inclined field. Conclusions: Although the contribution of the weak field is slightly overestimated owing to noise, 2D inversions are able to recover well the overall distribution of the magnetic field strength. Application of the 2D inversion code on the Hinode SP internetwork observations reveals a monotonic field strength distribution. The mean field strength at optical depth unity is ~ 130 G. At higher layers, field strength drops as the field becomes more horizontal. Regarding the distribution of the field inclination, tests show that we cannot directly retrieve it with the observations and tools at hand, however, the obtained distributions are consistent with those expected from simulations with a quasi-isotropic field inclination after accounting for observational effects.
NASA Astrophysics Data System (ADS)
Duan, Zhaoxia; Xiang, Zhengrong; Karimi, Hamid Reza
2014-07-01
This paper is concerned with the state feedback control problem for a class of two-dimensional (2D) discrete-time stochastic systems with time-delays, randomly occurring uncertainties and nonlinearities. Both the sector-like nonlinearities and the norm-bounded uncertainties enter into the system in random ways, and such randomly occurring uncertainties and nonlinearities obey certain mutually uncorrelated Bernoulli random binary distribution laws. Sufficient computationally tractable linear matrix inequality-based conditions are established for the 2D nonlinear stochastic time-delay systems to be asymptotically stable in the mean-square sense, and then the explicit expression of the desired controller gains is derived. An illustrative example is provided to show the usefulness and effectiveness of the proposed method.
2D materials for nanophotonic devices
NASA Astrophysics Data System (ADS)
Xu, Renjing; Yang, Jiong; Zhang, Shuang; Pei, Jiajie; Lu, Yuerui
2015-12-01
Two-dimensional (2D) materials have become very important building blocks for electronic, photonic, and phononic devices. The 2D material family has four key members, including the metallic graphene, transition metal dichalcogenide (TMD) layered semiconductors, semiconducting black phosphorous, and the insulating h-BN. Owing to the strong quantum confinements and defect-free surfaces, these atomically thin layers have offered us perfect platforms to investigate the interactions among photons, electrons and phonons. The unique interactions in these 2D materials are very important for both scientific research and application engineering. In this talk, I would like to briefly summarize and highlight the key findings, opportunities and challenges in this field. Next, I will introduce/highlight our recent achievements. We demonstrated atomically thin micro-lens and gratings using 2D MoS2, which is the thinnest optical component around the world. These devices are based on our discovery that the elastic light-matter interactions in highindex 2D materials is very strong. Also, I would like to introduce a new two-dimensional material phosphorene. Phosphorene has strongly anisotropic optical response, which creates 1D excitons in a 2D system. The strong confinement in phosphorene also enables the ultra-high trion (charged exciton) binding energies, which have been successfully measured in our experiments. Finally, I will briefly talk about the potential applications of 2D materials in energy harvesting.
Optical Spectroscopy of Two Dimensional Graphene and Boron Nitride
NASA Astrophysics Data System (ADS)
Ju, Long
This dissertation describes the use of optical spectroscopy in studying the physical properties of two dimensional nano materials like graphene and hexagonal boron nitride. Compared to bulk materials, atomically thin two dimensional materials have a unique character that is the strong dependence of physical properties on external control. Both electronic band structure and chemical potential can be tuned in situ by electric field-which is a powerful knob in experiment. Therefore the optical study at atomic thickness scale can greatly benefit from modern micro-fabrication technique and electric control of the material properties. As will be shown in this dissertation, such control of both gemometric and physical properties enables new possibilities of optical spectroscopic measurement as well as opto-electronic studies. Other experimental techniques like electric transport and scanning tunneling microscopy and spectroscopy are also combined with optical spectroscopy to reveal the physics that is beyond the reach of each individual technique. There are three major themes in the dissertation. The first one is focused on the study of plasmon excitation of Dirac electrons in monolayer graphene. Unlike plasmons in ordinary two dimensional electron gas, plasmons of 2D electrons as in graphene obey unusual scaling laws. We fabricate graphene micro-ribbon arrays with photolithography technique and use optical absorption spectroscopy to study its absorption spectrum. The experimental result demonstrates the extraordinarily strong light-plasmon coupling and its novel dependence on both charge doping and geometric dimensions. This work provides a first glance at the fundamental properties of graphene plasmons and forms the basis of an emerging subfield of graphene research and applications such as graphene terahertz metamaterials. The second part describes the opto-electronic response of heterostructures composed of graphene and hexagonal boron nitride. We found that there is
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
Two-Dimensional Numerical Modeling of Anthropogenic Beach Berm Erosion
NASA Astrophysics Data System (ADS)
Shakeri Majd, M.; Schubert, J.; Gallien, T.; Sanders, B. F.
2014-12-01
Anthropogenic beach berms (sometimes called artificial berms or artificial dunes) temporarily enhance the ability of beaches to withstand overtopping and thus guard against coastal flooding. However, the combination of a rising tide, storm surge, and/or waves may erode anthropogenic berms in a matter of hours or less and cause flooding [1]. Accurate forecasts of coastal flooding therefore demand the ability to predict where and when berms fail and the volume of water that overtops into defended coastal lowlands. Here, a two-dimensional numerical model of swash zone waves and erosion is examined as a tool for predicting the erosion of anthropogenic beach berms. The 2D model is known as a Debris Flow Model (DFM) because it tightly couples flow and sediment transport within an approximate Riemann solver and is able to resolve shocks in fluid/sediment interface [2]. The DFM also includes a two dimensional avalanching scheme to account for gravity-driven slumping of steep slopes. The performance of the DFM is examined with field-scale anthropogenic berm erosion data collected at Newport Beach, California. Results show that the DFM can be applied in the swash zone to resolve wave-by-wave flow and sediment transport. Results also show that it is possible to calibrate the model for a particular event, and then predict erosion for another event, but predictions are sensitive to model parameters, such as erosion and avalanching. References: [1] Jochen E. Schubert, Timu W. Gallien, Morteza Shakeri Majd, and Brett F. Sanders. Terrestrial laser scanning of anthropogenic beach berm erosion and overtopping. Journal of Coastal Research In-Press, 2014. [2] Morteza Shakeri Majd and Brett F. Sanders. The LHLLC scheme for Two-Layer and Two-Phase transcritical flows over a mobile bed with avalanching, wetting and drying. Advances in Water Resources, 64, 16-31, 2014.
The Instability of Terahertz Plasma Waves in Two Dimensional Gated and Ungated Quantum Electron Gas
NASA Astrophysics Data System (ADS)
Zhang, Liping
2016-04-01
The instability of terahertz (THz) plasma waves in two-dimensional (2D) quantum electron gas in a nanometer field effect transistor (FET) with asymmetrical boundary conditions has been investigated. We analyze THz plasma waves of two parts of the 2D quantum electron gas: gated and ungated regions. The results show that the radiation frequency and the increment (radiation power) in 2D ungated quantum electron gas are much higher than that in 2D gated quantum electron gas. The quantum effects always enhance the radiation power and enlarge the region of instability in both cases. This allows us to conclude that 2D quantum electron gas in the transistor channel is important for the emission and detection process and both gated and ungated parts take part in that process. supported by National Natural Science Foundation of China (No. 10975114)
Two-Dimensional Graphene as a Matrix for MALDI Imaging Mass Spectrometry
NASA Astrophysics Data System (ADS)
Friesen, William L.; Schultz, Brian J.; Destino, Joel F.; Alivio, Theodore E. G.; Steet, Joseph R.; Banerjee, Sarbajit; Wood, Troy D.
2015-11-01
Here, a matrix using two-dimensional (2D) graphene is demonstrated for the first time in the context of MALDI IMS using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Although graphene flakes have been used previously in MALDI, it is described here how a single 2D layer of graphene is applied directly on top of rat brain sections and soybean leaves. Several classes of molecules are desorbed and ionized off of the surface of the tissues examined using 2D graphene, with minimal background interference from the matrix. Moreover, no solvents are employed in application of 2D graphene, eliminating the potential for analyte diffusion in liquid droplets during matrix application. Because 2D graphene is an elemental form of carbon, an additional advantage is its high compatibility with the long duration needed for many IMS experiments.
Two-dimensional graphene as a matrix for MALDI imaging mass spectrometry.
Friesen, William L; Schultz, Brian J; Destino, Joel F; Alivio, Theodore E G; Steet, Joseph R; Banerjee, Sarbajit; Wood, Troy D
2015-11-01
Here, a matrix using two-dimensional (2D) graphene is demonstrated for the first time in the context of MALDI IMS using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Although graphene flakes have been used previously in MALDI, it is described here how a single 2D layer of graphene is applied directly on top of rat brain sections and soybean leaves. Several classes of molecules are desorbed and ionized off of the surface of the tissues examined using 2D graphene, with minimal background interference from the matrix. Moreover, no solvents are employed in application of 2D graphene, eliminating the potential for analyte diffusion in liquid droplets during matrix application. Because 2D graphene is an elemental form of carbon, an additional advantage is its high compatibility with the long duration needed for many IMS experiments. Graphical Abstract ᅟ.
Rodriguez, Justo J.; Mukamel, Shaul
2012-01-01
Two-dimensional (2D) electronic spectra of Mg-porphyrin dimers with circularly polarized laser pulses are simulated for two molecular geometries. The Zeeman shift of the non-chiral 2D spectra induced by a magnetic field highlights spectral regions that are dominated by exciton states with large total angular momentum, and are particularly sensitive to the geometry. These 2D shifts show much higher sensitivity to the molecular array than the absorption spectrum shifts. For different molecular geometries, only the intensity of the 2D spectrum peaks changes while the form of the Zeeman shifts in the 2D frequency space is modified. PMID:23206037
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. PMID:27580163
Two-dimensional Dirac signature of germanene
Zhang, L.; Bampoulis, P.; Houselt, A. van; Zandvliet, H. J. W.
2015-09-14
The structural and electronic properties of germanene coated Ge{sub 2}Pt clusters have been determined by scanning tunneling microscopy and spectroscopy at room temperature. The interior of the germanene sheet exhibits a buckled honeycomb structure with a lattice constant of 4.3 Å and a buckling of 0.2 Å. The zigzag edges of germanene are reconstructed and display a 4× periodicity. The differential conductivity of the interior of the germanene sheet has a V-shape, which is reminiscent of the density of states of a two-dimensional Dirac system. The minimum of the differential conductivity is located close to the Fermi level and has a non-zero value, which we ascribe to the metallic character of the underlying Ge{sub 2}Pt substrate. Near the reconstructed germanene zigzag edges the shape of the differential conductivity changes from a V-shape to a more parabolic-like shape, revealing that the reconstructed germanene zigzag edges do not exhibit a pronounced metallic edge state.
Braid Entropy of Two-Dimensional Turbulence.
Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael
2015-12-22
The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length NE of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy SBraid. The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of NE is positively skewed and shows strong exponential tails. Our results suggest that SBraid may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data.
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.
Dynamics of two-dimensional dipole systems
Golden, Kenneth I.; Kalman, Gabor J.; Hartmann, Peter; Donko, Zoltan
2010-09-15
Using a combined analytical/molecular dynamics approach, we study the current fluctuation spectra and longitudinal and transverse collective mode dispersions of the classical two-dimensional (point) dipole system (2DDS) characterized by the {phi}{sub D}(r)={mu}{sup 2}/r{sup 3} repulsive interaction potential; {mu} is the electric dipole strength. The interest in the 2DDS is twofold. First, the quasi-long-range 1/r{sup 3} interaction makes the system a unique classical many-body system, with a remarkable collective mode behavior. Second, the system may be a good model for a closely spaced semiconductor electron-hole bilayer, a system that is in the forefront of current experimental interest. The longitudinal collective excitations, which are of primary interest for the liquid phase, are acoustic at long wavelengths. At higher wave numbers and for sufficiently high coupling strength, we observe the formation of a deep minimum in the dispersion curve preceded by a sharp maximum; this is identical to what has been observed in the dispersion of the zero-temperature bosonic dipole system, which in turn emulates so-called roton-maxon excitation spectrum of the superfluid {sup 4}He. The analysis we present gives an insight into the emergence of this apparently universal structure, governed by strong correlations. We study both the liquid and the crystalline solid state. We also observe the excitation of combination frequencies, resembling the roton-roton, roton-maxon, etc. structures in {sup 4}He.
Braid Entropy of Two-Dimensional Turbulence
Francois, Nicolas; Xia, Hua; Punzmann, Horst; Faber, Benjamin; Shats, Michael
2015-01-01
The evolving shape of material fluid lines in a flow underlies the quantitative prediction of the dissipation and material transport in many industrial and natural processes. However, collecting quantitative data on this dynamics remains an experimental challenge in particular in turbulent flows. Indeed the deformation of a fluid line, induced by its successive stretching and folding, can be difficult to determine because such description ultimately relies on often inaccessible multi-particle information. Here we report laboratory measurements in two-dimensional turbulence that offer an alternative topological viewpoint on this issue. This approach characterizes the dynamics of a braid of Lagrangian trajectories through a global measure of their entanglement. The topological length of material fluid lines can be derived from these braids. This length is found to grow exponentially with time, giving access to the braid topological entropy . The entropy increases as the square root of the turbulent kinetic energy and is directly related to the single-particle dispersion coefficient. At long times, the probability distribution of is positively skewed and shows strong exponential tails. Our results suggest that may serve as a measure of the irreversibility of turbulence based on minimal principles and sparse Lagrangian data. PMID:26689261
Compact Two-Dimensional Spectrometer Optics
NASA Technical Reports Server (NTRS)
Hong, John
2008-01-01
The figure is a simplified depiction of a proposed spectrometer optical unit that would be suitable for incorporation into a remote-sensing instrumentation system. Relative to prior spectrometer optical assemblies, this unit would be compact and simple, largely by virtue of its predominantly two-dimensional character. The proposed unit would be a combination of two optical components. One component would be an arrayed-waveguide grating (AWG) an integrated-optics device, developed for use in wavelength multiplexing in telecommunications. The other component would be a diffraction grating superimposed on part of the AWG. The function of an AWG is conceptually simple. Input light propagates along a single-mode optical waveguide to a point where it is split to propagate along some number (N) of side-by-side waveguides. The lengths of the optical paths along these waveguides differ such that, considering the paths in a sequence proceeding across the array of waveguides, the path length increases linearly. These waveguides launch quasi-free-space waves into a planar waveguide-coupling region. The waves propagate through this region to interfere onto an array of output waveguides. Through proper choice of key design parameters (waveguide lengths, size and shape of the waveguide coupling region, and lateral distances between waveguides), one can cause the input light to be channeled into wavelength bins nominally corresponding to the output waveguides.
Two-dimensional laser interferometry analysis
NASA Astrophysics Data System (ADS)
Mehr, Leo; Concepcion, Ricky; Duggan, Robert; Moore, Hannah; Novick, Asher; Ransohoff, Lauren; Gourdain, Pierre-Alexandre; Hammer, David; Kusse, Bruce
2013-10-01
The objective of our research was to create a two-dimensional interferometer which we will use to measure plasma densities at the Cornell Research Beam Accelerator (COBRA). We built two shearing interferometers and mounted them on an optics table. They intercept the probe laser beam which travels directly through the plasma and is captured by a 16-bit CCD camera. In comparing the interferometer images before the shot and during the plasma shot, we observed both lateral and vertical shifts in the interference pattern caused by the change of the refractive index due to the plasma electrons. We developed a computer program using Matlab to map a vector field depicting the shift between the two images. This shift is proportional to the line integral of electron density through the plasma chamber. We show this method provides a reliable way to determine the plasma electron density profile. Additionally, we hope this method can improve upon the diagnostic capabilities and efficiency of data collection used with standard one-dimensional interferometry. Undergraduate.
Calculation of two-dimensional lambda modes
Belchior, A. Jr. ); Moreira, J.M.L. )
1991-01-01
A system for on-line monitoring of power distribution in small reactors (known as MAP) is under development at COPESP-IPEN. Signals of self-powered neutron detectors are input to a program that estimates the power distribution as an expansion of lambda modes. The modal coefficients are obtained from a least-mean-squares technique adequate for real-time analysis. Three-dimensional lambda modes are synthesized out of one- and two-dimensional lambda modes. As a part of this project, a modification of a computer code was carried out in order to obtain the lambda modes. The results of this effort are summarized. The lambda modes are the solutions of the time-independent multigroup neutron diffusion equation, an eigenvalue equation. Normally, the computer codes produce the fundamental mode corresponding to the largest eigenvalue; their respective interpretations are neutron flux distribution and effective multiplication factor. For calculating higher order lambda modes it is usually necessary to eliminate the contribution of the lower modes from the fission source.
Galfsky, Tal; Sun, Zheng; Considine, Christopher R; Chou, Cheng-Tse; Ko, Wei-Chun; Lee, Yi-Hsien; Narimanov, Evgenii E; Menon, Vinod M
2016-08-10
The low quantum yield observed in two-dimensional semiconductors of transition metal dichalcogenides (TMDs) has motivated the quest for approaches that can enhance the light emission from these systems. Here, we demonstrate broadband enhancement of spontaneous emission and increase in Raman signature from archetype two-dimensional semiconductors: molybdenum disulfide (MoS2) and tungsten disulfide (WS2) by placing the monolayers in the near field of a photonic hypercrystal having hyperbolic dispersion. Hypercrystals are characterized by a large broadband photonic density of states due to hyperbolic dispersion while having enhanced light in/out coupling by a subwavelength photonic crystal lattice. This dual advantage is exploited here to enhance the light emission from the 2D TMDs and can be utilized for developing light emitters and solar cells using two-dimensional semiconductors. PMID:27420735
Quasi two-dimensional astigmatic solitons in soft chiral metastructures.
Laudyn, Urszula A; Jung, Paweł S; Karpierz, Mirosław A; Assanto, Gaetano
2016-01-01
We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response. PMID:26975651
Noise from two-dimensional vortices
NASA Technical Reports Server (NTRS)
Sanders, N. D.; Stockman, N. O.
1972-01-01
The fluctuating flow in an idealized model of a turbulent shear layer composed of many discrete vortices is analyzed. Computer solutions reveal irregular motions which are similar in many respects to observed flows in turbulent three-dimensional layers. The model is further simplified to a pair of equal co-rotating vortices and the noise generation is analyzed in terms of equivalent quadrupole oscillations. Results of the analysis in a uniform medium are consistent with Lighthill's results. New results are obtained for the effects of mean velocity gradients, compressibility, temperature inhomogenities, and gradients of the mean Mach number.
NASA Astrophysics Data System (ADS)
Kiani, Keivan
2014-09-01
Useful nonlocal discrete and continuous models are developed to explain free vibration of two-dimensional (2D) ensembles of single-walled carbon nanotubes (SWCNTs) in bending. For this purpose, the models are constructed based on the nonlocal Rayleigh, Timoshenko, and higher-order beam theories. In contrast to an individual SWCNT exhibits identical bending behavior in different directions, for 2D ensemble networks of SWCNTs, it is shown that such a fact is completely dissimilar. Such an important issue leads to the definition of in-plane and out-of-plane flexural behaviors for such nanostructures. Subsequently, their corresponding fundamental frequencies are evaluated based on the proposed nonlocal models. The capabilities of the proposed nonlocal continuous models in predicting flexural frequencies of SWCNTs' ensembles with different numbers of SWCNTs as well as various levels of slenderness ratios are then explained. Such investigations confirm the high efficiency of the proposed continuous models. This matter would be of great importance in vibration analysis of highly populated ensembles of SWCNTs in which the discrete models may suffer from the size of the governing equations. The roles of the number of SWCNTs, slenderness ratio, intertube distance, small-scale parameter, and radius of the SWCNT on both in-plane and out-of-plane fundamental frequencies are addressed.
Sun, Jing; Zhang, Hui; Guo, Liang-Hong; Zhao, Lixia
2013-12-26
A graphene-based two-dimensional (2D) nanoplatform provides new opportunities for fabricating 2D heterojunction interfaces to fortify charge transfer in semiconductor assemblies. In this report, TiO2 nanosheet/graphene composite based 2D-2D heterojunctions were fabricated by a solvothermal process. Microscopic and spectroscopic characterization revealed a homogeneous sheetlike morphology with intimate interfacial contact between the TiO2 nanosheet and graphene due to chemical interactions. Compared with 0D-2D Degussa P25 (TiO2)/graphene and 1D-2D TiO2 nanotube/graphene composites, the 2D-2D TiO2 nanosheet/graphene hybrid demonstrated higher photocatalytic activity toward the degradation of rhodamine B and 2,4-dichlorophenol under UV irradiation. Radical trapping and ESR experiments revealed the enhanced generation of ·OH and O2(•-) in the 2D-2D heterojunction system. By analyzing TiO2 excited state deactivation lifetime, the interfacial electron transfer rates determined for 0D-2D, 1D-2D, and 2D-2D TiO2/graphene composites were 1.15 × 10(8) s(-1), 3.47 × 10(8) s(-1), and 1.06 × 10(9) s(-1), respectively. It was therefore proposed that the fast charge separation in the TiO2 nanosheet/graphene photocatalyst promoted the generation of reactive oxygen species and enhanced the photodegradation reactions. The results underscore the key role of nanomaterial dimensionality in interfacial charge transfer processes. PMID:24308534
Brewster Angle Microscope Investigations of Two Dimensional Phase Transitions
NASA Astrophysics Data System (ADS)
Schuman, Adam William
The liquid-liquid interface is investigated by microscopic and thermodynamic means to image and measure interfacial properties when the system undergoes a two-dimensional (2D) phase transition of a Gibbs monolayer by varying the sample temperature. An in-house Brewster angle microscope (BAM) is constructed to visualize the interface during this transition while a quasi-elastic light scattering technique is used to determine the interfacial tension. These results complement x-ray investigations of the same systems. Evidence of interfacial micro-separated structure, microphases, comes from observations across a hexane-water interface with the inclusion of a long-chain fluorinated alcohol surfactant into the bulk hexane. Microphases take the form of spatially modulated structure to the density of the surfactant as it spans laterally across the interface. The surfactant monolayer exhibits microphase morphology over a range of a couple degrees as the temperature of the system is scanned through the 2D gas-solid phase transition. Microphase structure was observed for heating and cooling the hexane-water system and structural comparisons are given when the temperature step and quench depth of the cooling process is varied. A complete sequence of morphological structure was observed from 2D gas to cluster to labyrinthine stripe to a 2D solid mosaic pattern. Two characteristic length scales emerge giving rise to speculation of an elastic contribution to the standard repulsive and attractive competitive forces stabilizing the microphase. The benefit of BAM to laterally image very thin films across the surface of an interface on the micrometer length scale nicely complements x-ray reflectivity methods that average structural data transverse to the liquid interface on a molecular scale. To properly analyze x-ray reflectivity data, the interface is required to be laterally homogeneous. BAM can sufficiently characterize the interface for this purpose as is done for a Langmuir
Assessment of OPC effectiveness using two-dimensional metrics
NASA Astrophysics Data System (ADS)
Wiaux, Vincent; Philipsen, Vicky; Jonckheere, Rik M.; Vandenberghe, Geert; Verhaegen, Staf; Hoffmann, Thomas; Ronse, Kurt G.; Howard, William B.; Maurer, Wilhelm; Preil, Moshe E.
2002-07-01
A complete evaluation of the optical proximity effects (OPE) and of their corrections (OPC) requires a quantitative description of two-dimensional (2D) parameters, both at resist- and at reticle-level. Because the 2D behaviour at line-ends and at line-corners can become a limiting factor for the yield, it should be taken into account when characterising a process, just as the CD- and pitch-linearity are already kept under control. This implies the measurement of 2D-metrics in a precise way. We used an SEM Image Analysis tool (ProDATA SIAM) to define and measure various OPC-relevant metrics for a C013 process. For the METAL (M1) process, we show that the overlap between line-ends of M1-trenches and underlying nominal contacts is a relevant metric to describe the effectiveness of hammerheads. Moreover, it is an interesting metric to combine with the CD process window. For the GATE process, we demonstrate that for a given set of metrics there is a degree of OPC aggressiveness beyond which it is not worth to go. We considered both line-end shortening (LES) and corner rounding affecting the poly linewidth close to a contact pad, and this on various logic circuits having received different degrees of fragmentation. Finally the knowledge of the actual line-end contour on the reticle allows one to simulate separately the printing effect of that area loss at reticle line-ends. The area loss measured by comparing the extracted contour to the target one is regarded as a combination of pull-back and area loss at corners. For our C013 gate process, and for the 130nm lines at a 1:1.25 duty cycle, those two parameters contribute together to approximetely 40% of the measured LES in the resist. This fact raises the question of specifications on 2D reticle parameters. We also find a linear correlation between the area loss at reticle line-end corners and the corresponding increase of LES on the wafer, which suggests a way towards putting specifications on the reticle line-ends.
ORMDIN. 2-D Nonlinear Inverse Heat Conduction
Bass, B.R.
1990-05-01
ORMDIN is a finite-element program developed for two-dimensional nonlinear inverse heat conduction analysis as part of the Oak Ridge National Laboratory Pressurized Water Reactor Blowdown Heat Transfer (BDHT) program. One of the primary objectives of the program was to determine the transient surface temperature and surface heat flux of fuel pin simulators from internal thermocouple signals obtained during a loss-of-coolant accident experiment in the Thermal-Hydraulic Test Facility (THTF). ORMDIN was designed primarily to perform a transient two-dimensional nonlinear inverse heat conduction analysis of the THTF bundle 3 heater rod; however, it can be applied to other cylindrical geometries for which the thermophysical properties are prescribed functions of temperature. The program assumes that discretized temperature histories are provided at three thermocouple locations in the interior of the cylinder. Concurrent with the two-dimensional analysis, ORMDIN also generates one-dimensional solutions for each of the three thermocouple radial planes.
Dynamics of two-dimensional bubbles.
Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón
2015-06-01
The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps. PMID:26172798
Dynamics of two-dimensional bubbles
NASA Astrophysics Data System (ADS)
Piedra, Saúl; Ramos, Eduardo; Herrera, J. Ramón
2015-06-01
The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.
Dynamics of two-dimensional bubbles.
Piedra, Saúl; Ramos, Eduardo; Herrera, J Ramón
2015-06-01
The dynamics of two-dimensional bubbles ascending under the influence of buoyant forces is numerically studied with a one-fluid model coupled with the front-tracking technique. The bubble dynamics are described by recording the position, shape, and orientation of the bubbles as functions of time. The qualitative properties of the bubbles and their terminal velocities are described in terms of the Eötvos (ratio of buoyancy to surface tension) and Archimedes numbers (ratio of buoyancy to viscous forces). The terminal Reynolds number result from the balance of buoyancy and drag forces and, consequently, is not an externally fixed parameter. In the cases that yield small Reynolds numbers, the bubbles follow straight paths and the wake is steady. A more interesting behavior is found at high Reynolds numbers where the bubbles follow an approximately periodic zigzag trajectory and an unstable wake with properties similar to the Von Karman vortex street is formed. The dynamical features of the motion of single bubbles are compared to experimental observations of air bubbles ascending in a water-filled Hele-Shaw cell. Although the comparison is not strictly valid in the sense that the effect of the lateral walls is not incorporated in the model, most of the dynamical properties observed are in good qualitative agreement with the numerical calculations. Hele-Shaw cells with different gaps have been used to determine the degree of approximation of the numerical calculation. It is found that for the relation between the terminal Reynolds number and the Archimedes number, the numerical calculations are closer to the observations of bubble dynamics in Hele-Shaw cells of larger gaps.
Note: Unshielded bilateral magnetoencephalography system using two-dimensional gradiometers
NASA Astrophysics Data System (ADS)
Seki, Yusuke; Kandori, Akihiko; Ogata, Kuniomi; Miyashita, Tsuyoshi; Kumagai, Yukio; Ohnuma, Mitsuru; Konaka, Kuni; Naritomi, Hiroaki
2010-09-01
Magnetoencephalography (MEG) noninvasively measures neuronal activity with high temporal resolution. The aim of this study was to develop a new type of MEG system that can measure bilateral MEG waveforms without a magnetically shielded room, which is an obstacle to reducing both the cost and size of an MEG system. An unshielded bilateral MEG system was developed using four two-dimensional (2D) gradiometers and two symmetric cryostats. The 2D gradiometer, which is based on a low-Tc superconducting quantum interference device and wire-wound pickup coil detects a magnetic-field gradient in two orthogonal directions, or ∂/∂x(∂2Bz/∂z2), and reduces environmental magnetic-field noise by more than 50 dB. The cryostats can be symmetrically positioned in three directions: vertical, horizontal, and rotational. This makes it possible to detect bilateral neuronal activity in the cerebral cortex simultaneously. Bilateral auditory-evoked fields (AEF) of 18 elderly subjects were measured in an unshielded hospital environment using the MEG system. As a result, both the ipsilateral and the contralateral AEF component N100m, which is the magnetic counterpart of electric N100 in electroencephalography and appears about 100 ms after the onset of an auditory stimulus, were successfully detected for all the subjects. Moreover, the ipsilateral P50m and the contralateral P50m were also detected for 12 (67%) and 16 (89%) subjects, respectively. Experimental results demonstrate that the unshielded bilateral MEG system can detect MEG waveforms, which are associated with brain dysfunction such as epilepsy, Alzheimer's disease, and Down syndrome.
Two dimensionality in quasi-one-dimensional cobalt oxides
NASA Astrophysics Data System (ADS)
Sugiyama, J.; Nozaki, H.; Brewer, J. H.; Ansaldo, E. J.; Morris, G. D.; Takami, T.; Ikuta, H.; Mizutani, U.
2006-03-01
Magnetism of quasi-one-dimensional (1D) cobalt oxides ACoO ( A=Ca, Sr and Ba, n=1-5 and ∞) was investigated by μ+SR using polycrystalline samples, at temperatures from 300 K down to 1.8 K. The wTF- μ+SR experiments showed the existence of a magnetic transition in all six samples investigated. The onset temperature of the transition (Tcon) was found to decrease with n; that is, 100±25, 90±10, 85±10, 65±10 50±10, and 15±1 K for n=1-5, and ∞, respectively. In particular, for the samples with n=2-5, Tcon was detected only by the present μ+SR measurements. A muon spin oscillation was clearly observed in both Ca 3Co 2O 6(n=1) and BaCoO 3(n=∞), whereas only a fast relaxation is apparent even at 1.8 K in the other four samples ( n=2-5). Taking together with the fact that the paramagnetic Curie temperature ranges from -150 to -200 K for the compound with n=2 and 3, the μ+SR result indicates that a two-dimensional (2D) short-range antiferromagnetic (AF) order, which has been thought to be unlikely to exist at high T due to a relatively strong 1D F interaction, appears below Tcon for all compounds with n=1-5; but quasi-static long-range AF order formed only in Ca 3Co 2O 6, below 25 K. For BaCoO 3(n=∞), as T decreased from 300 K, 1D F order appeared below 53 K, and a sharp 2D AF transition occurred at 15 K.
NASA Technical Reports Server (NTRS)
Hoffman, R. N.; Leidner, S. M.; Henderson, J. M.; Atlas, R.; Ardizzone, J. V.; Bloom, S. C.; Atlas, Robert (Technical Monitor)
2001-01-01
In this study, we apply a two-dimensional variational analysis method (2d-VAR) to select a wind solution from NASA Scatterometer (NSCAT) ambiguous winds. 2d-VAR determines a "best" gridded surface wind analysis by minimizing a cost function. The cost function measures the misfit to the observations, the background, and the filtering and dynamical constraints. The ambiguity closest in direction to the minimizing analysis is selected. 2d-VAR method, sensitivity and numerical behavior are described. 2d-VAR is compared to statistical interpolation (OI) by examining the response of both systems to a single ship observation and to a swath of unique scatterometer winds. 2d-VAR is used with both NSCAT ambiguities and NSCAT backscatter values. Results are roughly comparable. When the background field is poor, 2d-VAR ambiguity removal often selects low probability ambiguities. To avoid this behavior, an initial 2d-VAR analysis, using only the two most likely ambiguities, provides the first guess for an analysis using all the ambiguities or the backscatter data. 2d-VAR and median filter selected ambiguities usually agree. Both methods require horizontal consistency, so disagreements occur in clumps, or as linear features. In these cases, 2d-VAR ambiguities are often more meteorologically reasonable and more consistent with satellite imagery.
Two-dimensional finite element multigroup diffusion theory for neutral atom transport in plasmas
Hasan, M.Z.; Conn, R.W.
1986-02-01
Solution of the energy dependent diffusion equation in two dimensions is formulated by multigroup approximation of the energy variable and general triangular mesh, finite element discretization of the spatial domain. Finite element formulation is done by Galerkin's method. Based on this formulation, a two-dimensional multigroup finite element diffusion theory code, FENAT, has been developed for the transport of neutral atoms in fusion plasmas. FENAT solves the multigroup diffusion equation in X-Y cartesian and R-Z cylindrical/toroidal geometries. Use of the finite element method allows solution of problems in which the plasma cross-section has an arbitrary shape. The accuracy of FENAT has been verified by comparing results to those obtained using the two-dimensional discrete ordinate transport theory code, DOT-4.3. Results of application of FENAT to the transport of limiter-originated neutral atoms in a tokamak fusion machine are presented.
Li, Mingda Snider, Gregory; Jena, Debdeep; Grace Xing, Huili; Esseni, David
2014-02-21
The single particle tunneling in a vertical stack consisting of monolayers of two-dimensional semiconductors is studied theoretically, and its application to a novel Two-dimensional Heterojunction Interlayer Tunneling Field Effect Transistor (Thin-TFET) is proposed and described. The tunneling current is calculated by using a formalism based on the Bardeen's transfer Hamiltonian, and including a semi-classical treatment of scattering and energy broadening effects. The misalignment between the two 2D materials is also studied and found to influence the magnitude of the tunneling current but have a modest impact on its gate voltage dependence. Our simulation results suggest that the Thin-TFETs can achieve very steep subthreshold swing, whose lower limit is ultimately set by the band tails in the energy gaps of the 2D materials produced by energy broadening. The Thin-TFET is thus very promising as a low voltage, low energy solid state electronic switch.
Two-dimensional imaging with a single-sided NMR probe.
Casanova, F; Blümich, B
2003-07-01
A new low field unilateral NMR sensor equipped with a two-dimensional gradient coil system was built. A new NMR-MOUSE concept using a simple bar magnet instead of the classical U-shaped geometry was used to produce magnetic field profiles comparatively homogeneous in extended lateral planes defining a suitable field of view for 2D spatial localization. Slice selection along the depth direction is obtained by means of the highly constant static magnetic field gradient produced by this magnet geometry. Implementing a two-dimensional phase-encoding imaging method 2D cross sections of objects were obtained with high spatial resolution. By retuning the probe it was possible to change the depth of the selected slice obtaining a 3D imaging method. The details of the construction of the new device are presented together with imaging tests to show the quality of space encoding. PMID:12852905
Two-dimensional quantum walk under artificial magnetic field
NASA Astrophysics Data System (ADS)
Yalcinkaya, Iskender; Gedik, Zafer
We introduce the Peierls substitution to a two-dimensional discrete-time quantum walk on a square lattice to examine the spreading dynamics and the coin-position entanglement in the presence of an artificial gauge field. We use the ratio of the magnetic flux through the unit cell to the flux quantum as a control parameter. For a given flux ratio, we obtain faster spreading for a small number of steps and the walker tends to be highly localized around the origin. Moreover, the spreading of the walk can be suppressed and decreased within a limited time interval for specific rational values of flux ratio. When the flux ratio is an irrational number, even for a large number of steps, the spreading exhibit diffusive behavior rather than the well-known ballistic one as in the classical random walk and there is a significant probability of finding the walker at the origin. We also analyze the coin-position entanglement and show that the asymptotic behavior vanishes when the flux ratio is different from zero and the coin-position entanglement become nearly maximal in a periodic manner in a long time range.
Monolithic multigrid methods for two-dimensional resistive magnetohydrodynamics
Adler, James H.; Benson, Thomas R.; Cyr, Eric C.; MacLachlan, Scott P.; Tuminaro, Raymond S.
2016-01-06
Magnetohydrodynamic (MHD) representations are used to model a wide range of plasma physics applications and are characterized by a nonlinear system of partial differential equations that strongly couples a charged fluid with the evolution of electromagnetic fields. The resulting linear systems that arise from discretization and linearization of the nonlinear problem are generally difficult to solve. In this paper, we investigate multigrid preconditioners for this system. We consider two well-known multigrid relaxation methods for incompressible fluid dynamics: Braess--Sarazin relaxation and Vanka relaxation. We first extend these to the context of steady-state one-fluid viscoresistive MHD. Then we compare the two relaxationmore » procedures within a multigrid-preconditioned GMRES method employed within Newton's method. To isolate the effects of the different relaxation methods, we use structured grids, inf-sup stable finite elements, and geometric interpolation. Furthermore, we present convergence and timing results for a two-dimensional, steady-state test problem.« less
Interaction and Correlation Effects in Quasi Two-dimensional Materials
NASA Astrophysics Data System (ADS)
Louie, Steven G.
2015-03-01
Experimental and theoretical studies of atomically thin quasi two-dimensional materials (typically related to some parent van der Waals layered crystals) and their nanostructures have revealed that these systems can exhibit highly unusual behaviors. In this talk, we discuss some theoretical studies of the electronic, transport and optical properties of such systems. We present results on graphene and graphene nanostructures as well as other quasi-2D systems such as monolayer and few-layer transition metal dichalcogenides (e.g., MoS2, MoSe2, WS2, and WSe2) and metal monochalcogenides (such as GaSe and FeSe). Owing to their reduced dimensionality, these systems present opportunities for unusual manifestation of concepts and phenomena that may not be so prominent or have not been seen in bulk materials. Symmetry and many-body interaction effects often play a critical role in shaping qualitatively and quantitatively their properties. Several quantum phenomena are discussed, including novel and dominant exciton effects, tunable magnetism, electron supercollimation by disorder, unusual plasmon behaviors, and possible enhanced superconductivity in some of these systems. We investigate their physical origins and compare theoretical predictions with experimental data. This work was supported by DOE under Contract No. DE-AC02-05CH11231 and by NSF under Grant No. DMR10-1006184. I would like to acknowledge collaborations with members of the Louie group and the experimental groups of Crommie, Heinz, Wang, and Zhang.
Thermal Convection in a Strongly Stratified Two-dimensional Fluid
NASA Astrophysics Data System (ADS)
Zhang, Jie; Wu, X. L.; Xia, K. Q.
2004-03-01
Thermal convection occurs when a fluid becomes gravitationally unstable in the presence of a temperature gradient. While most laboratory experiments investigate convections in fluids with a uniform mass distribution, natural convections often take place in fluids whose density is stratified. In the absence of temperature gradient, a freely suspended soap film stratifies under the action of gravity and assumes a nearly exponential thickness profile similar to the distribution of air mass in atmosphere. In the presence of such a gradient, thermal plumes are generated which drives fluid flows and at the time creates two-dimensional (2D) density fluctuations. We studied thickness power spectra in soap film convection by analyzing thermal radiation signal emitting from a single spot at the center of the film. The experiments were performed at different temperature gradients (ΔT), which were imposed vertically across the film. In the buoyancy sub-range, the frequency power spectrum shows a Bolgiano-Obukhov scaling f-1.4 when ΔT ≤ 50K, and a new scaling relation f-1.0 emerges when ΔT > 50K. This latter behavior was observed to coincide with the appearance of a large-scale circulation in the film.
Lagrangian statistics in weakly forced two-dimensional turbulence.
Rivera, Michael K; Ecke, Robert E
2016-01-01
Measurements of Lagrangian single-point and multiple-point statistics in a quasi-two-dimensional stratified layer system are reported. The system consists of a layer of salt water over an immiscible layer of Fluorinert and is forced electromagnetically so that mean-squared vorticity is injected at a well-defined spatial scale ri. Simultaneous cascades develop in which enstrophy flows predominately to small scales whereas energy cascades, on average, to larger scales. Lagrangian correlations and one- and two-point displacements are measured for random initial conditions and for initial positions within topological centers and saddles. Some of the behavior of these quantities can be understood in terms of the trapping characteristics of long-lived centers, the slow motion near strong saddles, and the rapid fluctuations outside of either centers or saddles. We also present statistics of Lagrangian velocity fluctuations using energy spectra in frequency space and structure functions in real space. We compare with complementary Eulerian velocity statistics. We find that simultaneous inverse energy and enstrophy ranges present in spectra are not directly echoed in real-space moments of velocity difference. Nevertheless, the spectral ranges line up well with features of moment ratios, indicating that although the moments are not exhibiting unambiguous scaling, the behavior of the probability distribution functions is changing over short ranges of length scales. Implications for understanding weakly forced 2D turbulence with simultaneous inverse and direct cascades are discussed.
Two-Dimensional Heat Transfer in a Heterogeneous Fracture Network
NASA Astrophysics Data System (ADS)
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.
From arbitrariness to anomalies in two-dimensional perturbative calculations
NASA Astrophysics Data System (ADS)
Battistel, O. A.
2004-05-01
A very general calculational strategy is applied to the evaluation of divergent physical amplitudes which are typical of 2D perturbative calculations. With this approach, in the final results all the arbitrariness intrinsic to the calculations, due to the divergent character, is still present. We show that, concerning the arbitrariness, the regularizations can be classified into two basic classes. The consequences on adopting each such class for the symmetry relations are investigated. It is noted that if very general symmetry requirements, such as Furry's theorem or gauge invariance, are used to select a consistent regularization procedure, the possible sources of ambiguities related to the choices for the internal line momenta of loops are completely eliminated. A very transparent description of the two-dimensional anomalies emerges, allowing a clear understanding of the results obtained within the context of traditional methods. The comparison with 4D triangle anomalies reveals a completely similar situation for both cases. The very interesting phenomenon of mass generation for the gauge boson in the massless fermion theory is also obtained in agreement with the expected results.
Quantum Criticality in Quasi-Two-Dimensional Itinerant Antiferromagnets
NASA Astrophysics Data System (ADS)
Varma, C. M.
2015-10-01
Quasi-two-dimensional itinerant fermions in the antiferromagnetic (AFM) quantum-critical region of their phase diagram, such as in the Fe-based superconductors or in some of the heavy-fermion compounds, exhibit a resistivity varying linearly with temperature and a contribution to specific heat or thermopower proportional to T ln T . It is shown, here, that a generic model of itinerant anti-ferromagnet can be canonically transformed so that its critical fluctuations around the AFM-vector Q can be obtained from the fluctuations in the long wavelength limit of a dissipative quantum X Y model. The fluctuations of the dissipative quantum X Y model in 2D have been evaluated recently, and in a large regime of parameters, they are determined, not by renormalized spin fluctuations, but by topological excitations. In this regime, the fluctuations are separable in their spatial and temporal dependence and have a spatial correlation length which is proportional to the logarithm of the temporal correlation length, i.e., for some purposes, the effective dynamic exponent z =∞ . The time dependence gives ω /T scaling at criticality. The observed resistivity and entropy then follow. Several predictions to test the theory are also given.
Fast, comprehensive two-dimensional liquid chromatography
Stoll, Dwight R.; Li, Xiaoping; Wang, Xiaoli; Carr, Peter W.; Porter, Sarah E. G.; Rutan, Sarah C.
2011-01-01
The absolute need to improve the separating power of liquid chromatography, especially for multi-constituent biological samples, is becoming increasingly evident. In response, over the past few years, there has been a great deal of interest in the development of two dimension liquid chromatography (2DLC). Just as 1DLC is preferred to 1DGC based on its compatibility with biological materials we believe that ultimately 2DLC will be preferred to the much more highly developed 2DGC for such samples. The huge advantage of 2D chromatographic techniques over 1D methods is inherent in the tremendous potential increase in peak capacity (resolving power). This is especially true of comprehensive 2D chromatography wherein it is possible, under ideal conditions, to obtain a total peak capacity equal to the product of the peak capacities of the first and second dimension separations. However, the very long timescale (typically several hours to tens of hours) of comprehensive 2DLC is clearly its chief drawback. Recent advances in the use of higher temperatures to speed up isocratic and gradient elution liquid chromatography have been used to decrease the time needed to do the second dimension LC separation of 2DLC to about 20 seconds for a full gradient elution run. Thus fast, high temperature LC is becoming a very promising technique. Peak capacities of over 2000 and rates of peak capacity production of nearly 1 peak/s have been achieved. In consequence, many real samples showing more than 200 peaks with signal to noise ratios of better than 10:1 have been run in total times of under 30 minutes. This report is not intended to be a comprehensive review of 2DLC, but is deliberately focused on the issues involved in doing fast 2DLC by means of elevating the column temperature; however, many issues of broader applicability will be discussed. PMID:17888443
Bicubic B-spline interpolation method for two-dimensional heat equation
NASA Astrophysics Data System (ADS)
Hamid, Nur Nadiah Abd.; Majid, Ahmad Abd.; Ismail, Ahmad Izani Md.
2015-10-01
Two-dimensional heat equation was solved using bicubic B-spline interpolation method. An arbitrary surface equation was generated by bicubic B-spline equation. This equation was incorporated in the heat equation after discretizing the time using finite difference method. An under-determined system of linear equation was obtained and solved to obtain the approximate analytical solution for the problem. This method was tested on one example.
Two-dimensional optical tomography of hemodynamic changes in a preterm infant brain
NASA Astrophysics Data System (ADS)
Gao, Feng; Xue, Yuan; Zhao, Huijuan; Kusaka, Takashi; Ueno, Masanori; Yamada, Yukio
2007-08-01
Our preliminary results on two-dimensional (2D) optical tomographic imaging of hemodynamic changes in a preterm infant brain are reported. We use the established 16-channel time-correlated single photon counting system for the detection and generalized pulse spectrum technique based algorithm for the image reconstruction. The experiments demonstrate that diffuse optical tomography may be a potent means for investigating brain functions and neural development of infant brains in the perinatal period.
Quantitative 2D liquid-state NMR.
Giraudeau, Patrick
2014-06-01
Two-dimensional (2D) liquid-state NMR has a very high potential to simultaneously determine the absolute concentration of small molecules in complex mixtures, thanks to its capacity to separate overlapping resonances. However, it suffers from two main drawbacks that probably explain its relatively late development. First, the 2D NMR signal is strongly molecule-dependent and site-dependent; second, the long duration of 2D NMR experiments prevents its general use for high-throughput quantitative applications and affects its quantitative performance. Fortunately, the last 10 years has witnessed an increasing number of contributions where quantitative approaches based on 2D NMR were developed and applied to solve real analytical issues. This review aims at presenting these recent efforts to reach a high trueness and precision in quantitative measurements by 2D NMR. After highlighting the interest of 2D NMR for quantitative analysis, the different strategies to determine the absolute concentrations from 2D NMR spectra are described and illustrated by recent applications. The last part of the manuscript concerns the recent development of fast quantitative 2D NMR approaches, aiming at reducing the experiment duration while preserving - or even increasing - the analytical performance. We hope that this comprehensive review will help readers to apprehend the current landscape of quantitative 2D NMR, as well as the perspectives that may arise from it.
Vortices of Two Dimensional Guiding Center Plasmas.
NASA Astrophysics Data System (ADS)
Ting, Antonio Chofai
A system of two dimensional guiding center plasma in a square conducting boundary is used as a model to study the anomalous transport is magnetically confined plasma. An external gravitational force is introduced to simulate the curvature and gradient of the magnetic field. For finite boundaries, it is a Hamiltonian system with finite phase space and negative temperature states are allowed. The statistical equilibrium states of this system are described by the solutions of a Poisson's equation with self-consistently determined charge density. In the limit of zero gravity, it can be reduced to the sinh-Poisson equation (DEL)('2)u + (lamda)('2)sinh u = 0. Previous numerical efforts have found solutions with vortex structures. A novel method of generating general exact solutions to this nonlinear boundary value problem is presented. These solutions are given by. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). where E(,i)'s are constants and the dependence of (gamma)(,j)'s on x and y are given by a set of coupled first order nonlinear ordinary differential equations. These equations can be linearized to give u(x,y) in terms of Riemann theta functions u(x,y) = 2ln (THETA)(l + 1/2)(THETA)(l) . The phases l evolve linearly in x and y while nonlinear superposition is displayed in the solution u(x,y). The self-consistent Poisson's equation with gravity is studied numerically. Different branches of solutions are obtained and their relations to the zero gravity solutions are discussed. The thermodynamically most favored structure of the system carries the feature of a heavy ion vortex on top of the light electron vortex. Branches of solutions are found to merge into each other as parameters in the equations were smoothly varied. A critical value of gravitational force exists such that below which there is a possibility of hysteresis between different equilibrium states. With the help of the nonzero gravity solutions, we also have a clearer picture of the transition from
Non-Hermitian engineering of single mode two dimensional laser arrays
Teimourpour, Mohammad H.; Ge, Li; Christodoulides, Demetrios N.; El-Ganainy, Ramy
2016-01-01
A new scheme for building two dimensional laser arrays that operate in the single supermode regime is proposed. This is done by introducing an optical coupling between the laser array and lossy pseudo-isospectral chains of photonic resonators. The spectrum of this discrete reservoir is tailored to suppress all the supermodes of the main array except the fundamental one. This spectral engineering is facilitated by employing the Householder transformation in conjunction with discrete supersymmetry. The proposed scheme is general and can in principle be used in different platforms such as VCSEL arrays and photonic crystal laser arrays. PMID:27698355
Exact two-body solutions and quantum defect theory of two-dimensional dipolar quantum gas
NASA Astrophysics Data System (ADS)
Jie, Jianwen; Qi, Ran
2016-10-01
In this paper, we provide the two-body exact solutions of the two-dimensional (2D) Schrödinger equation with isotropic +/- 1/{r}3 interactions. An analytic quantum defect theory is constructed based on these solutions and it is applied to investigate the scattering properties as well as two-body bound states of an ultracold polar molecules confined in a quasi-2D geometry. Interestingly, we find that for the attractive case, the scattering resonance happens simultaneously in all partial waves, which has not been observed in other systems. The effect of this feature on the scattering phase shift across such resonances is also illustrated.
Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou
2015-01-01
Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold–gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon–hydrogen bonds with molecular oxygen. PMID:25902034
NASA Astrophysics Data System (ADS)
Rossi, Enrico; Triola, Christopher; Badiane, Driss; Balatsky, Alexander V.
We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity-coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling will exhibit odd-frequency superconducting pairing. Work supported by US DOE BES E304, KAW, ACS-PRF-53581-DNI5, and NSF-DMR-1455233.
Triola, Christopher; Badiane, Driss M; Balatsky, Alexander V; Rossi, E
2016-06-24
We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling exhibits odd-frequency superconducting pairing. Our results allow the identification of a new class of systems among van der Waals heterostructures in which odd-frequency superconductivity should be present. PMID:27391743
Bonilla-Musoles, F.; Raga, F.; Bonilla, F.; Blanes, J.; Osborne, N. G.
1998-01-01
Transvaginal three-dimensional (3-D) and color Doppler ultrasound were used to establish a first-trimester definitive diagnosis and classification of thoracoomphalopagus conjoined twins following two-dimensional (2-D) transabdominal and transvaginal scans that indicated twin gestation of uncertain classification. Color Doppler in combination with 3-D ultrasound can be a useful complement to 2-D ultrasound to confirm early diagnosis and determine the extent of organ sharing and definitive classification of conjoined twins. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 PMID:9770956
Particle mesh Ewald method for three-dimensional systems with two-dimensional periodicity
NASA Astrophysics Data System (ADS)
Kawata, Masaaki; Nagashima, Umpei
2001-05-01
A particle mesh Ewald method for calculating Coulomb interactions in three-dimensional (3D) systems with two-dimensional (2D) periodicity was developed. Computational efficiency and accuracy of this method were evaluated for a TIP3P water system with 2928 particles in a cubic box with 2D periodicity. The accuracy of this method for calculating Coulomb interactions is comparable to our previous method that uses Fourier integral. For calculations with maximum errors in the Coulomb force of 0.4- 20.0 kJ mol -1 nm-1, the current method was up to five times faster than the previous method.
Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors
NASA Astrophysics Data System (ADS)
Padhiyar, Ashvin; Patel, A. J.; Oza, A. T.
2007-12-01
It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.
Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou
2015-04-22
Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold-gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon-hydrogen bonds with molecular oxygen.
Effective viscosity of dilute bacterial suspensions : a two-dimensional model.
Haines, B. M.; Aranson, I. S.; Berlyand, L.; Karpeev, D. A.; Pennsylvania State Univ.
2008-01-01
Suspensions of self-propelled particles are studied in the framework of two-dimensional (2D) Stokesean hydrodynamics. A formula is obtained for the effective viscosity of such suspensions in the limit of small concentrations. This formula includes the two terms that are found in the 2D version of Einstein's classical result for passive suspensions. To this, the main result of the paper is added, an additional term due to self-propulsion which depends on the physical and geometric properties of the active suspension. This term explains the experimental observation of a decrease in effective viscosity in active suspensions.
Two-dimensional single-pixel imaging by cascaded orthogonal line spatial modulation.
Winters, David G; Bartels, Randy A
2015-06-15
Two-dimensional (2D) images are taken using a single-pixel detector by temporally multiplexing spatial frequency projections from orthogonal, time varying spatial line modulation gratings. Unique temporal frequencies are applied to each point in 2D space, applying a continuous spread of frequencies to one dimension, and an offset frequency applied to each line in the orthogonal dimension. The object contrast information can then be recovered from the electronic spectrum of the single pixel, and through simple processing be reformed into a spatial image. PMID:26076259
Generic Weyl phase in the vortex state of quasi-two-dimensional chiral superconductors
NASA Astrophysics Data System (ADS)
Yoshida, Tomohiro; Udagawa, Masafumi
2016-08-01
We study the collective behavior of Majorana modes in the vortex state of chiral p -wave superconductors. Away from the isolated vortex limit, the zero-energy Majorana states communicate with each other on a vortex lattice, and form a coherent band structure with a nontrivial topological character. We reveal that the topological nature of Majorana bands changes sensitively via quantum phase transitions in two-dimensional (2D) systems, by sweeping magnetic field or Fermi energy. Through the idea of dimensional reduction, we show the existence of a generic superconducting Weyl phase in a low magnetic field region of quasi-2D chiral superconductors.
Electron- and photon-induced plasmonic excitations in two-dimensional silver nanostructures
Hoang, C. V.; Rana, M.; Nagao, T.
2014-06-23
Plasmons are the quasi particles of collective oscillations of electrons and form the basis of plasmonics and optical metamaterials. We combined electron spectroscopy and optical spectroscopy techniques to study plasmons in atomically smooth Ag films and in epitaxial Ag nanodisks to map the momentum-energy dispersion curves of the two-dimensional (2D) sheet plasmon and the quasi-2D plasmons to clarify the essential differences between them. Our experimental results combined with the results of numerical electromagnetic simulations showed that the bulk-like nature of the silver plasmon starts in layers that are only two atoms thick.
Quantum diffusion wave-function approach to two-dimensional vibronic spectroscopy
Wehner, Johannes; Falge, Mirjam; Engel, Volker; Strunz, Walter T.
2014-10-07
We apply the quantum diffusion wavefunction approach to calculate vibronic two-dimensional (2D) spectra. As an example, we use a system consisting of two electronic states with harmonic oscillator potentials which are coupled to a bath and interact with three time-delayed laser pulses. The first- and second-order perturbative wave functions which enter into the expression for the third-order polarization are determined for a sufficient number of stochastic runs. The wave-packet approach, besides being an alternative technique to calculate the spectra, offers an intuitive insight into the dissipation dynamics and its relation to the 2D vibronic spectra.
A compact chaotic laser device with a two-dimensional external cavity structure
Sunada, Satoshi Adachi, Masaaki; Fukushima, Takehiro; Shinohara, Susumu; Arai, Kenichi; Harayama, Takahisa
2014-06-16
We propose a compact chaotic laser device, which consists of a semiconductor laser and a two-dimensional (2D) external cavity for delayed optical feedback. The overall size of the device is within 230 μm × 1 mm. A long time delay sufficient for chaos generation can be achieved with the small area by the multiple reflections at the 2D cavity boundary, and the feedback strength is controlled by the injection current to the external cavity. We experimentally demonstrate that a variety of output properties, including chaotic output, can be selectively generated by controlling the injection current to the external cavity.
NASA Astrophysics Data System (ADS)
Kaufman, George K.; Reches, Meital; Thomas, Samuel W.; Feng, Ji; Shaw, Bryan F.; Whitesides, George M.
2009-01-01
This letter describes the formation of two-dimensional (2D) crystals of dipolar particles (TN) made of electrostatically charged, joined, millimeter-scale Teflon (T) and nylon-6,6 (N) spheres, and the separation of these crystals, as a distinct phase, from a mixture of TN and similar, capacitively charged particles that were coated with gold (Au2). The extent of separation increased with increasing amplitude of agitation, and with decreasing density of particles. Above a threshold in the amplitude of agitation, the crystals broke apart and the particles remixed. This system is a 2D model of the nucleation of crystals of polar molecules in a polarizable liquid.
Two-dimensional femtosecond optical spectroscopy of trapping dynamics in a charge-transfer process
NASA Astrophysics Data System (ADS)
Keß, Martin; Engel, Volker
2016-04-01
We study charge-transfer dynamics monitored by two-dimensional (2D) optical spectroscopy. The often used model consisting of two coupled diabatic electronic states in a single reaction coordinate is used to demonstrate the relation between the vibronic dynamics and the 2D-spectra. Within the employed wave-function approach, dissipation is included via a quantum-jump algorithm with explicit treatment of dephasing. States with long lifetimes which decay slowly due to the interaction with the environment are identified. Using filtered Fourier transforms, energy and time resolved information about the dissipative system dynamics can be obtained.
Nunomura, S; Goree, J; Hu, S; Wang, X; Bhattacharjee, A
2002-06-01
Dispersion relations of longitudinal and transverse waves in two-dimensional (2D) screened-Coulomb crystals were investigated. The waves were excited in 2D crystals made from complex plasmas, i.e., dusty plasmas, by applying radiation pressure of laser light. The dependencies of the dispersion relation on the shielding parameter, the damping rate, and the wave propagation direction were experimentally measured. The measured dispersion relations agree reasonably with a recently developed theory, and the comparison yields the shielding parameter and the charge on particles.
Boron based two-dimensional crystals: theoretical design, realization proposal and applications.
Li, Xian-Bin; Xie, Sheng-Yi; Zheng, Hui; Tian, Wei Quan; Sun, Hong-Bo
2015-12-01
The successful realization of free-standing graphene and the various applications of its exotic properties have spurred tremendous research interest for two-dimensional (2D) layered materials. Besides graphene, many other 2D materials have been successfully produced by experiment, such as silicene, monolayer MoS2, few-layer black phosphorus and so on. As a neighbor of carbon in the periodic table, element boron is interesting and many researchers have contributed their efforts to realize boron related 2D structures. These structures may be significant both in fundamental science and future technical applications in nanoelectronics and nanodevices. In this review, we summarize the recent developments of 2D boron based materials. The theoretical design, possible experimental realization strategies and their potential technical applications are presented and discussed. Also, the current challenges and prospects of this area are discussed. PMID:26523799
The two-dimensional character of spin-up in a rectangular container
NASA Astrophysics Data System (ADS)
Zavala Sansón, L.
2003-06-01
This study presents two-dimensional (2D) numerical simulations of the spin-up of a homogeneous fluid in a rectangular container, compared with the corresponding three-dimensional (3D) simulation presented by other authors. A 2D simulation is based on a recently derived model [Zavala Sansón and van Heijst, J. Fluid Mech. 412, 75 (2000)] including nonlinear Ekman friction effects, in addition to the well-known linear damping term. It is found that the inclusion of nonlinear Ekman terms provides a remarkable agreement between 2D and 3D simulations for times comparable with the Ekman timescale, which implies that this formulation is able to capture the essential viscous features of the 3D situation. In contrast, a simulation based on a 2D model with conventional linear friction is not able to represent the 3D case correctly.
Rajan, Arunkumar Chitteth; Rezapour, Mohammad Reza; Yun, Jeonghun; Cho, Yeonchoo; Cho, Woo Jong; Min, Seung Kyu; Lee, Geunsik; Kim, Kwang S
2014-02-25
Laser-driven molecular spectroscopy of low spatial resolution is widely used, while electronic current-driven molecular spectroscopy of atomic scale resolution has been limited because currents provide only minimal information. However, electron transmission of a graphene nanoribbon on which a molecule is adsorbed shows molecular fingerprints of Fano resonances, i.e., characteristic features of frontier orbitals and conformations of physisorbed molecules. Utilizing these resonance profiles, here we demonstrate two-dimensional molecular electronics spectroscopy (2D MES). The differential conductance with respect to bias and gate voltages not only distinguishes different types of nucleobases for DNA sequencing but also recognizes methylated nucleobases which could be related to cancerous cell growth. This 2D MES could open an exciting field to recognize single molecule signatures at atomic resolution. The advantages of the 2D MES over the one-dimensional (1D) current analysis can be comparable to those of 2D NMR over 1D NMR analysis.
Epitaxy and photoresponse of two-dimensional GaSe crystals on flexible transparent mica sheets.
Zhou, Yubing; Nie, Yufeng; Liu, Yujing; Yan, Kai; Hong, Jinhua; Jin, Chuanhong; Zhou, Yu; Yin, Jianbo; Liu, Zhongfan; Peng, Hailin
2014-02-25
We present the controlled synthesis of high-quality two-dimensional (2D) GaSe crystals on flexible transparent mica substrates via a facile van der Waals epitaxy method. Single- and few-layer GaSe nanoplates with the lateral size of up to tens of micrometers were produced. The orientation and nucleation sites of GaSe nanoplates were well-controlled. The 2D GaSe crystal-based photodetectors were demonstrated on both mechanically rigid SiO2/Si and flexible mica substrates. Efficient photoresponse was observed in 2D GaSe crystal devices on transparent flexible mica substrates, regardless of repeated bending with different radii. The controlled growth of 2D GaSe crystals with efficient photoresponsivity opens up opportunities for both fundamental aspects and new applications in photodetectors.
Two-dimensional excitons in three-dimensional hexagonal boron nitride
Cao, X. K.; Lin, J. Y. Jiang, H. X.; Clubine, B.; Edgar, J. H.
2013-11-04
The recombination processes of excitons in hexagonal boron nitride (hBN) have been probed using time-resolved photoluminescence. It was found that the theory for two-dimensional (2D) exciton recombination describes well the exciton dynamics in three-dimensional hBN. The exciton Bohr radius and binding energy deduced from the temperature dependent exciton recombination lifetime is around 8 Å and 740 meV, respectively. The effective masses of electrons and holes in 2D hBN deduced from the generalized relativistic dispersion relation of 2D systems are 0.54m{sub o}, which are remarkably consistent with the exciton reduced mass deduced from the experimental data. Our results illustrate that hBN represents an ideal platform to study the 2D optical properties as well as the relativistic properties of particles in a condensed matter system.