Two-dimensional discrete Coulomb alloy
NASA Astrophysics Data System (ADS)
Xiao, Yuqing; Thorpe, M. F.; Parkinson, J. B.
1999-01-01
We study an A1-xBx alloy on a two-dimensional triangular lattice. The ions A and B have different charges, with a background charge to ensure neutrality, and are constrained to lie at the discrete sites defined by a fixed triangular lattice. We study the various structures formed at different compositions x by doing computer simulations to find the lowest energy, using an energy minimization scheme, together with simulated annealing. Like ions try to avoid each other because of charge repulsion, which leads to structures, which are very different from those in a random alloy. At low concentrations, a triangular Wigner lattice is formed, which evolves continuously up to a concentration of x=1/3. For higher concentrations, 1/3<=x<=1/2 there are long polymer chains, with occasional branches. We show that there is a symmetry about x=1/2, which is the percolation point for nearest neighbors on the triangular lattice. At certain special stoichiometries, regular superlattices are formed, which usually have a slightly lower energy than a disordered configuration. The powder-diffraction patterns are calculated. The magnetic properties of this structure are also studied, and it is shown that the high-temperature susceptibility could be a useful diagnostic tool, in that it is very sensitive to the number of nearest-neighbor magnetic pairs. This work contributes to a better understanding of layered double hydroxides like Ni1-xAlx(OH)2(CO3)x/2.yH2O.
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.
Two-dimensional discrete solitons in rotating lattices.
Cuevas, Jesús; Malomed, Boris A; Kevrekidis, P G
2007-10-01
We introduce a two-dimensional discrete nonlinear Schrödinger (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
Brazhnyi, Valeriy A; Malomed, Boris A
2011-01-01
We study the dynamics of two-dimensional (2D) localized modes in the nonlinear lattice described by the discrete nonlinear Schrödinger equation, including a local linear or nonlinear defect. Discrete solitons pinned to the defects are investigated by means of the numerical continuation from the anticontinuum limit and also using the variational approximation, which features a good agreement for strongly localized modes. The models with the time-modulated strengths of the linear or nonlinear defect are considered too. In that case, one can temporarily shift the critical norm, below which localized 2D modes cannot exist, to a level above the norm of the given soliton, which triggers the irreversible delocalization transition.
Hysteretic Spin Crossover in Two-Dimensional (2D) Hofmann-Type Coordination Polymers.
Liu, Wei; Wang, Lu; Su, Yu-Jun; Chen, Yan-Cong; Tucek, Jiri; Zboril, Radek; Ni, Zhao-Ping; Tong, Ming-Liang
2015-09-08
Three new two-dimensional (2D) Hofmann-type coordination polymers with general formula [Fe(3-NH2py)2M(CN)4] (3-NH2py = 3-aminopyridine, M = Ni (1), Pd (2), Pt (3)) have been synthesized. Magnetic susceptibility measurements show that they exhibited cooperative spin crossover (SCO) with remarkable hysteretic behaviors. Their hysteresis widths are 25, 37, and 30 K for 1-3, respectively. The single-crystal structure of 1 suggest that the pseudo-octahedral Fe sites are equatorially bridged by [M(CN)4](2-) to form 2D grids and axially coordinated by 3-NH2py ligands. The intermolecular interactions between layers (the offset face-to-face π···π interactions, hydrogen bonds, and weak N(amino)···Ni(II) contacts) together with the covalent bonds bridged by [M(CN)4](2-) units are responsible to the significant cooperativity.
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.
A separable two-dimensional discrete Hartley transform
NASA Technical Reports Server (NTRS)
Watson, A. B.; Poirson, A.
1985-01-01
Bracewell has proposed the Discrete Hartley Transform (DHT) as a substitute for the Discrete Fourier Transform (DFT), particularly as a means of convolution. Here, it is shown that the most natural extension of the DHT to two dimensions fails to be separate in the two dimensions, and is therefore inefficient. An alternative separable form is considered, corresponding convolution theorem is derived. That the DHT is unlikely to provide faster convolution than the DFT is also discussed.
Red wine proteins: two dimensional (2-D) electrophoresis and mass spectrometry analysis.
Mainente, Federica; Zoccatelli, Gianni; Lorenzini, Marilinda; Cecconi, Daniela; Vincenzi, Simone; Rizzi, Corrado; Simonato, Barbara
2014-12-01
The aim of the present study was to optimize protein extraction from red wine (cv. Cabernet) in order to obtain a separation by two-dimensional electrophoresis (2-DE) compatible with mass spectrometry identification. Proteins were denatured by sodium dodecyl-sulphate (SDS) and precipitated as potassium salts. The potassium-DS (KDS) protein complexes obtained were treated with different solutions in order to remove the detergent. Proteins were solubilized with different buffers and separated by different electrophoretic approaches [native, urea, acid urea PAGEs and isoelectric focusing (IEF)] as the first-dimension (1-DE). The best 2D separation was achieved by using 10% saccharose in the DS removal step, and 6-cyclohexylhexyl β-d-maltoside detergent in the solubilisation buffer combined with the IEF approach. Several well focalized protein spots were obtained and analyzed through mass-spectrometry.
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.
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.
Discrete solitons and vortices in the two-dimensional Salerno model with competing nonlinearities
Gomez-Gardenes, J.; Floria, L. M.; Malomed, B. A.; Bishop, A. R.
2006-09-15
An anisotropic lattice model in two spatial dimensions, with on-site and intersite cubic nonlinearities (the Salerno model), is introduced, with emphasis on the case in which the intersite nonlinearity is self-defocusing, competing with on-site self-focusing. The model applies, for example, to a dipolar Bose-Einstein condensate trapped in a deep two-dimensional (2D) optical lattice. Soliton families of two kinds are found in the model: ordinary ones and cuspons, with peakons at the border between them. Stability borders for the ordinary solitons are found, while all cuspons (and peakons) are stable. The Vakhitov-Kolokolov criterion does not apply to cuspons, but for the ordinary solitons it correctly identifies the stability limits. In direct simulations, unstable solitons evolve into localized pulsons. Varying the anisotropy parameter, we trace a transition between the solitons in 1D and 2D versions of the model. In the isotropic model, we also construct discrete vortices of two types, on-site and intersite centered (vortex crosses and squares, respectively), and identify their stability regions. In simulations, unstable vortices in the noncompeting model transform into regular solitons, while in the model with the competing nonlinearities they evolve into localized vortical pulsons, which maintain their topological character. Bound states of regular solitons and vortices are constructed too, and their stability is identified.
PRONTO 2D: A two-dimensional transient solid dynamics program
Taylor, L.M.; Flanagan, D.P.
1987-03-01
PRONTO 2D is a two-dimensional transient solid dynamics code for analyzing large deformations of highly nonlinear materials subjected to extremely high strain rates. This Lagrangian finite element program uses an explicit time integration operator to integrate the equations of motion. Four node uniform strain quadrilateral elements are used in the finite element formulation. A number of new numerical algorithms which have been developed for the code are described in this report. An adaptive time step control algorithm is described which greatly improves stability as well as performance in plasticity problems. A robust hourglass control scheme which eliminates hourglass distortions without disturbing the finite element solution is included. All constitutive models in PRONTO are cast in an unrotated configuration defined using the rotation determined from the polar decomposition of the deformation gradient. An accurate incremental algorithm was developed to determine this rotation and is described in detail. A robust contact algorithm was developed which allows for the impact and interaction of deforming contact surfaces of quite general geometry. A number of numerical examples are presented to demonstrate the utility of these algorithms. 41 refs., 51 figs., 5 tabs.
Two-dimensional Fourier transform ESR in the slow-motional and rigid limits: 2D-ELDOR
NASA Astrophysics Data System (ADS)
Patyal, Baldev R.; Crepeau, Richard H.; Gamliel, Dan; Freed, Jack H.
1990-12-01
The two-dimensional Fourier transform ESP techniques of stimulated SECSY and 2D-ELDOR are shown to be powerful methods for the study of slow motions for nitroxides. Stimulated SECSY provides magnetization transfer rates, whereas 2D-ELDOR displays how the rotational motions spread the spins out from their initial spectral positions to new spectral positions, as a function of mixing time. The role of nuclear modulation in studies of structure and dynamics is also considered.
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.
Exact static solutions of a two-dimensional discrete ϕ4 model
NASA Astrophysics Data System (ADS)
Khare, Avinash; Suchkov, Sergey V.; Dmitriev, Sergey V.
2011-09-01
For a two-dimensional scalar discrete ϕ4 model we obtain several exact static solutions in the form of the Jacobi elliptic functions (JEF) with arbitrary shift along the lattice. The Quispel-Roberts-Thompson-type quadratic maps are identified for the considered two-dimensional model by using a JEF solution. We also show that many of the static solutions can be constructed iteratively from these quadratic maps by starting from an admissible initial value. The kink solution, having the form of tanh , is numerically demonstrated to be generically stable.
Optical properties of two-dimensional (2D) CdSe nanostructures
NASA Astrophysics Data System (ADS)
Cherevkov, S. A.; Baranov, A. V.; Fedorov, A. V.; Litvin, A. P.; Artemyev, M. V.; Prudnikau, A. V.
2013-09-01
The resonant and off-resonant Raman spectra of optical phonons in two-dimensional CdSe nanocrystals of 5, 6, and 7 monolayers are analysed. The spectra are dominated by SO and LO phonon bands of CdSe, whose frequencies are thickness-independent in the off-resonant Raman scattering but demonstrate an evident thickness dependence in the case of the resonant Raman scattering.
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..
Logarithmic discretization and systematic derivation of shell models in two-dimensional turbulence.
Gürcan, Ö D; Morel, P; Kobayashi, S; Singh, Rameswar; Xu, S; Diamond, P H
2016-09-01
A detailed systematic derivation of a logarithmically discretized model for two-dimensional turbulence is given, starting from the basic fluid equations and proceeding with a particular form of discretization of the wave-number space. We show that it is possible to keep all or a subset of the interactions, either local or disparate scale, and recover various limiting forms of shell models used in plasma and geophysical turbulence studies. The method makes no use of the conservation laws even though it respects the underlying conservation properties of the fluid equations. It gives a family of models ranging from shell models with nonlocal interactions to anisotropic shell models depending on the way the shells are constructed. Numerical integration of the model shows that energy and enstrophy equipartition seem to dominate over the dual cascade, which is a common problem of two-dimensional shell models.
Guest, Paul C
2017-01-01
This chapter describes the basics of two-dimensional difference gel electrophoresis (2D-DIGE) for multiplex analysis of up to distinct proteomes. The example given describes the analysis of undifferentiated and differentiated neural precursor cells labelled with fluorescent Cy3 and Cy5 dyes in comparison to a pooled standard labelled with Cy2. After labelling, the proteomes are mixed together and electrophoresed on the same 2D gels. Scanning the gels at wavelengths specific for each dye allows direct overlay of the two different proteomes and the differences in abundance of specific protein spots can be determined through comparison to the pooled standard.
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.
Protein profiling using two-dimensional difference gel electrophoresis (2-D DIGE).
Feret, Renata; Lilley, Kathryn S
2014-02-03
2-D DIGE relies on pre-electrophoretic labeling of samples with one of three spectrally distinct fluorescent dyes, followed by electrophoresis of all samples in one 2-D gel. The dye-labeled samples are then viewed individually by scanning the gel at different wavelengths, which circumvents problems with gel-to-gel variation and spot matching between gels. Image analysis programs are used to generate volume ratios for each spot, which essentially describe the intensity of a particular spot in each test sample, and thus enable protein abundance level changes to be identified and quantified. This unit describes the 2-D DIGE procedure including sample preparation from various cell types, labeling of proteins, and points to consider in the downstream processing of fluorescently labeled samples.
Fudge, Anthea L; Wilkinson, Kerry L; Ristic, Renata; Cozzolino, Daniel
2013-08-15
In this study, two-dimensional correlation spectroscopy (2D-COS) combined with mid-infrared (MIR) spectroscopy was evaluated as a novel technique for the identification of spectral regions associated with smoke-affected wine, for the purpose of screening taint arising from grapevine exposure to smoke. Smoke-affected wines obtained from experimental and industry sources were analysed using MIR spectroscopy and chemometrics, and calibration models developed. 2D-COS analysis was used to generate synchronous data maps for red and white cask wines spiked with guaiacol, a marker of smoke taint. Correlations were observed at wavelengths that could be attributable to aromatic C-C stretching, i.e., between 1400 and 1500 cm(-1), indicative of volatile phenols. These results demonstrate the potential of 2D-COS as a rapid, high-throughput technique for the preliminary screening of smoke tainted wine.
Two-Dimensional (2-D) Acoustic Fish Tracking at River Mile 85, Sacramento River, California
2013-06-01
7 ii Abstract Fish behavior in response to levee repairs at River Mile 85.6 of the Sacramento River was monitored using 60 VR2W 180-kHz and 45...arrays of VR2W 69-kHz receivers were installed in the river adjacent to levee repair sites and natural areas. This initial effort at 2-D tracking...a levee repair site was located on the outside of a river bend. The site was located at RM 85, just south of Knights Landing, California. The study
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)
NASA Technical Reports Server (NTRS)
Bayer, Janice I.; Varadan, V. V.; Varadan, V. K.
1991-01-01
This paper describes research into the use of discrete piezoelectric sensors and actuators for active modal control of flexible two-dimensional structures such as might be used as components for spacecraft. A dynamic coupling term is defined between the sensor/actuator and the structure in terms of structural model shapes, location and piezoelectric behavior. The relative size of the coupling term determines sensor/actuator placement. Results are shown for a clamped square plate and for a large antenna. An experiment was performed on a thin foot-square plate clamped on all sides. Sizable vibration control was achieved for first, second/third (degenerate) and fourth modes.
Neimark-Sacker bifurcation of a two-dimensional discrete-time predator-prey model.
Khan, A Q
2016-01-01
In this paper, we study the dynamics and bifurcation of a two-dimensional discrete-time predator-prey model in the closed first quadrant [Formula: see text]. The existence and local stability of the unique positive equilibrium of the model are analyzed algebraically. It is shown that the model can undergo a Neimark-Sacker bifurcation in a small neighborhood of the unique positive equilibrium and an invariant circle will appear. Some numerical simulations are presented to illustrate our theocratical results and numerically it is shown that the unique positive equilibrium of the system is globally asymptotically stable.
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.
Generalized perturbation theory using two-dimensional, discrete ordinates transport theory
Childs, R.L.
1980-06-01
Perturbation theory for changes in linear and bilinear functionals of the forward and adjoint fluxes in a critical reactor has been implemented using two-dimensional discrete ordinates transport theory. The computer program DOT IV was modified to calculate the generalized functions GAMMA and GAMMA*. Demonstration calculations were performed for changes in a reaction-rate ratio and a reactivity worth caused by system perturbations. The perturbation theory predictions agreed with direct calculations to within about 2%. A method has been developed for calculating higher lambda eigenvalues and eigenfunctions using techniques similar to those developed for generalized functions. Demonstration calculations have been performed to obtain these eigenfunctions.
2D discrete Fourier transform on sliding windows.
Park, Chun-Su
2015-03-01
Discrete Fourier transform (DFT) is the most widely used method for determining the frequency spectra of digital signals. In this paper, a 2D sliding DFT (2D SDFT) algorithm is proposed for fast implementation of the DFT on 2D sliding windows. The proposed 2D SDFT algorithm directly computes the DFT bins of the current window using the precalculated bins of the previous window. Since the proposed algorithm is designed to accelerate the sliding transform process of a 2D input signal, it can be directly applied to computer vision and image processing applications. The theoretical analysis shows that the computational requirement of the proposed 2D SDFT algorithm is the lowest among existing 2D DFT algorithms. Moreover, the output of the 2D SDFT is mathematically equivalent to that of the traditional DFT at all pixel positions.
Kevrekidis, P. G.; Malomed, Boris A.; Saxena, Avadh; ...
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
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.
NASA Astrophysics Data System (ADS)
Xin, Shihe; Le Quéré, Patrick
2012-06-01
Following our previous two-dimensional (2D) studies of flows in differentially heated cavities filled with air, we studied the stability of 2D natural convection flows in these cavities with respect to 3D periodic perturbations. The basis of the numerical methods is a time-stepping code using the Chebyshev spectral collocation method and the direct Uzawa method for velocity-pressure coupling. Newton's iteration, Arnoldi's method and the continuation method have been used in order to, respectively, compute the 2D steady-state base solution, estimate the leading eigenmodes of the Jacobian and perform linear stability analysis. Differentially heated air-filled cavities of aspect ratios from 1 to 7 were investigated. Neutral curves (Rayleigh number versus wave number) have been obtained. It turned out that only for aspect ratio 7, 3D stationary instability occurs at slightly higher Rayleigh numbers than the onset of 2D time-dependent flow and that for other aspect ratios 3D instability always takes place before 2D time-dependent flows. 3D unstable modes are stationary and anti-centro-symmetric. 3D nonlinear simulations revealed that the corresponding pitchfork bifurcations are supercritical and that 3D instability leads only to weak flow in the third direction. Further 3D computations are also performed at higher Rayleigh number in order to understand the effects of the weak 3D fluid motion on the onset of time-dependent flow. 3D flow structures are responsible for the onset of time-dependent flow for aspect ratios 1, 2 and 3, while for larger aspect ratios they do not alter the transition scenario, which was observed in the 2D cases and that vertical boundary layers become unstable to traveling waves.
Unitary implementation of the discrete two-dimensional non-separable linear canonical transform
NASA Astrophysics Data System (ADS)
Zhao, Liang; Healy, John J.; Sheridan, John T.
2014-09-01
The continuous linear canonical transforms is known to describes wave field propagation through paraxial (quadratic phase) optical systems. Digital algorithms to numerically calculate the LCT are therefore important in modelling field propagation through first order optical systems and are also of interest for many purely digital signal processing applications. Significantly the continuous LCTs are unitary, but discretization can destroy this property resulting in a loss of conservative properties. Previously we presented a sufficient condition on the sampling rates chosen during discretization to ensure that digital implementations of the 1D and 2D separable LCTs were unitary. In this paper we extend our analysis to discuss the cases of the 2D non-separable LCT which are used to describe non-orthogonal, nonaxially symmetric and anamorphic systems. We also examine the consequences of ours results.
NASA Astrophysics Data System (ADS)
Ghlaifan, Abdulatef; Tounsi, Yassine; Zada, Sara; Muhire, Desire; Nassim, Abdelkrim
2016-12-01
A method for optical phase extraction based on two-dimensional discrete wavelets transform (2-DWT) decomposition is shown. From modulated fringe pattern, phase distribution is extracted by the ratio between detail and approximation. Modulation process is realized digitally by introducing high-frequency spatial carrier, and this process needs two π/2-shifted fringe patterns. We propose to use only single fringe and generate its quadrature by spiral phase transform (SPT). After validation by computer simulation, we apply the 2-DWT algorithm on experimental speckle fringe correlation taken for hard disk surface. The extracted phase using SPT quadrature was compared with that given using this time experimental quadrature, and we show a good performance by multiscale structural similarity metric.
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.
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
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.
Flocking with discrete symmetry: The two-dimensional active Ising model.
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.
Fanchi, J.R.
1985-04-01
Under the sponsorship of the US Department of Energy, a publicly available chemical simulator has been evaluated and substantially enhanced to serve as a useful tool for projecting polymer or chemical flood performance. The program, CHEM2D, is a two-dimensional, three-phase, nine-component finite-difference numerical simulator. It can model primary depletion, waterfloods, polymer floods, and micellar/polymer floods using heterogeneous linear, areal, or cross-sectional reservoir descriptions. The user may specify well performance as either pressure or rate constrained. Both a constant time step size and a variable time step size based on extrapolation of concentration changes are available as options. A solution technique which is implicit in pressure and explicit in saturations and concentrations is used. The major physical mechanisms that are modeled include adsorption, capillary trapping, cation exchange, dilution, dispersion, interfacial tension, binary or ternary phase behavior, non-Newtonian polymer rheology, and two-phase or three-phase relative permeability. Typical components include water, oil, surfactant, polymer, and three ions (chloride, calcium, and sodium). Components may partition amongst the aqueous, oleic, and microemulsion phases. Volume I of this report provides a discussion of the formulation and algorithms used within CHEM2D. Included in Volume I are a number of validation and illustrative examples, as well as the FORTRAN code. The CHEM2D user's manual, Volume II, contains both the input data sets for the examples presented in Volume I and an example output. All appendices and a phase behavior calculation program are collected in Volume III. 20 references.
Gao, Liyan; Wang, Aili; Li, Xiaohui; Dong, Kun; Wang, Ke; Appels, Rudi; Ma, Wujun; Yan, Yueming
2009-12-01
Comparative proteomics analysis offers a new approach to identify differential proteins among different wheat genotypes and developmental stages. In this study, the non-prolamin expression profiles during grain development of two common or bread wheat cultivars (Triticum aestivum L.), Jing 411 and Sunstate, with different quality properties were analyzed using two-dimensional difference gel electrophoresis (2-D DIGE). Five grain developmental stages during the post-anthesis period were sampled corresponding to the cumulative averages of daily temperatures ( degrees C: 156 degrees C, 250 degrees C, 354 degrees C, 447 degrees C and 749.5 degrees C). More than 400 differential protein spots detected at one or more of the developmental stages of the two cultivars were monitored, among which 230 proteins were identified by MS. Of the identified proteins, more than 85% were enzymes possessing different physiological functions. A total of 36 differential proteins were characterized between the two varieties, which are likely to be related to wheat quality attributes. About one quarter of the proteins identified expressed in multiple spots with different pIs and molecular masses, implying certain post-translational modifications (PTMs) of proteins such as phosphorylations and glycosylations. The results provide new insights into biochemical mechanisms for grain development and quality.
Beura, Shradhananda; Majhi, Banshidhar; Dash, Ratnakar; Roy, Susnata
2015-04-01
An efficient approach for classification of mammograms for detection of breast cancer is presented. The approach utilises the two-dimensional discrete orthonormal S-transform (DOST) to extract the coefficients from the digital mammograms. A feature selection algorithm based the on null-hypothesis test with statistical 'two-sample t-test' method has been suggested to select most significant coefficients from a large number of DOST coefficients. The selected coefficients are used as features in the classification of mammographic images as benign or malignant. This scheme utilises an AdaBoost algorithm with random forest as its base classifier. Two standard databases Mammographic Image Analysis Society (MIAS) and Digital Database for Screening Mammography (DDSM) are used for the validation of the proposed scheme. Simulation results show an optimal classification performance with respect to accuracies of 98.3 and 98.8% and AUC (receiver operating characteristic) values of 0.9985 and 0.9992 for MIAS and DDSM, respectively. Comparative analysis shows that the proposed scheme outperforms its competent schemes.
Qi, Yiling; Zhang, Guoquan
2010-09-13
We study the linear discrete diffraction characteristics of light in two-dimensional backbone lattices. It is found that, as the refractive index modulation depth of the backbone lattice increases, high-order band gaps become open and broad in sequence, and the allowed band curves of the Floquet-Bloch modes become flat gradually. As a result, the diffraction pattern at the exit face converges gradually for both the on-site and off-site excitation cases. Particularly, when the refractive index modulation depth of the backbone lattice is high enough, for example, on the order of 0.01 for a square lattice, the light wave propagating in the backbone lattice will be localized in transverse dimension for both the on-site and off-site excitation cases. This is because only the first several allowed bands with nearly flat band curves are excited in the lattice, and the transverse expansion velocities of the Floquet-Bloch modes in these flat allowed bands approach to zero. Such a linear transverse localization of light may have potential applications in navigating light propagation dynamics and optical signal processing.
Development of a new two-dimensional Cartesian geometry nodal multigroup discrete-ordinates method
Pevey, R.E.
1982-07-01
The purpose of this work is the development and testing of a new family of methods for calculating the spatial dependence of the neutron density in nuclear systems described in two-dimensional Cartesian geometry. The energy and angular dependence of the neutron density is approximated using the multigroup and discrete ordinates techniques, respectively. The resulting FORTRAN computer code is designed to handle an arbitrary number of spatial, energy, and angle subdivisions. Any degree of scattering anisotropy can be handled by the code for either external source or fission systems. The basic approach is to (1) approximate the spatial variation of the neutron source across each spatial subdivision as an expansion in terms of a user-supplied set of exponential basis functions; (2) solve analytically for the resulting neutron density inside each region; and (3) approximate this density in the basis function space in order to calculate the next iteration flux-dependent source terms. In the general case the calculation is iterative due to neutron sources which depend on the neutron density itself, such as scattering interactions.
NASA Astrophysics Data System (ADS)
Yeom, Seungcheol; Sjoblom, Kurt
2016-12-01
The mechanical nature of crust formation as a result of raindrop impacts was simulated within a discrete element modeling environment. Simulations were conducted in two-dimensions (2D) using both linear and non-linear elastic contact models. The 2D approach was found to minimize the computational effort required and maximize the number of particles in the soil profile. For the non-linear model, the effect of the coefficient of restitution (COR) for soil-rain and soil-soil was investigated. Finally, the comparison between the linear and nonlinear elastic contact model was presented. The simulation indicated that the COR for rain-soil had negligible effect on the crust development but the computational time was exponentially increased with increasing coefficient value. In contrast, the COR for soil-soil had a dominant influence on the crust development. To validate the numerical results, a micro computerized tomography (microCT) technique was applied to characterize the changes in pore structure to a USCS SP soil after exposure under a rainfall simulator. Additionally, the effect of cyclic wetting and drying (without rainfall) on the changes in porosity was investigated. The experimental results showed that the rainfall simulator sufficiently densified the soil but the effect of cyclic wetting and drying was negligible. The numerical simulations showed similar changes in porosity along the depth of the soil profile as compared with the experimental results thus validating the DEM technique to simulate crust development.
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 Technical Reports Server (NTRS)
Pauley, Patricia M.; Wu, Xiaohua
1990-01-01
The response of the Barnes objective analysis scheme is studied as a function of wavenumber or wavelength. The first- and second-pass theoretical response functions for continuous two-dimensional fields are derived using Fourier transforms. The results are compared with Barnes' (1973) responses for one-dimensional waves. The continuous theoretical response for one- and two-dimensional waves is compared with the response for discrete applications using uniformly spaced observations for the case where interpolation points and observation points are coincident and for the case where interpolation points are midway between observation points. The actual response of an idealized discrete application of the Barnes scheme is examined, confirming the results of the analysis of the discrete theoretical response.
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.
Dual geometric worm algorithm for two-dimensional discrete classical lattice models.
Hitchcock, Peter; Sørensen, Erik S; Alet, Fabien
2004-01-01
We present a dual geometrical worm algorithm for two-dimensional Ising models. The existence of such dual algorithms was first pointed out by Prokof'ev and Svistunov [Phys. Rev. Lett. 87, 160601 (2001)
Foist, Rod B; Schulze, H Georg; Ivanov, Andre; Turner, Robin F B
2011-05-01
Two-dimensional correlation spectroscopy (2D-COS) is a powerful spectral analysis technique widely used in many fields of spectroscopy because it can reveal spectral information in complex systems that is not readily evident in the original spectral data alone. However, noise may severely distort the information and thus limit the technique's usefulness. Consequently, noise reduction is often performed before implementing 2D-COS. In general, this is implemented using one-dimensional (1D) methods applied to the individual input spectra, but, because 2D-COS is based on sets of successive spectra and produces 2D outputs, there is also scope for the utilization of 2D noise-reduction methods. Furthermore, 2D noise reduction can be applied either to the original set of spectra before performing 2D-COS ("pretreatment") or on the 2D-COS output ("post-treatment"). Very little work has been done on post-treatment; hence, the relative advantages of these two approaches are unclear. In this work we compare the noise-reduction performance on 2D-COS of pretreatment and post-treatment using 1D (wavelets) and 2D algorithms (wavelets, matrix maximum entropy). The 2D methods generally outperformed the 1D method in pretreatment noise reduction. 2D post-treatment in some cases was superior to pretreatment and, unexpectedly, also provided correlation coefficient maps that were similar to 2D correlation spectroscopy maps but with apparent better contrast.
Soliton theory of two-dimensional lattices: the discrete nonlinear schrödinger equation.
Arévalo, Edward
2009-06-05
We theoretically investigate the motion of collective excitations in the two-dimensional nonlinear Schrödinger 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
2015-01-02
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)
Fullam, Jennifer; Boye, Carol; Standaert, Theodorus; Gaudiello, John; Tomlinson, Derek; Xiao, Hong; Fang, Wei; Zhang, Xu; Wang, Fei; Ma, Long; Zhao, Yan; Jau, Jack
2011-03-01
In this paper, we tested a novel methodology of measuring critical dimension (CD) uniformity, or CDU, with electron beam (e-beam) hotspot inspection and measurement systems developed by Hermes Microvision, Inc. (HMI). The systems were used to take images of two-dimensional (2D) array patterns and measure CDU values in a custom designated fashion. Because this methodology combined imaging of scanning micro scope (SEM) and CD value averaging over a large array pattern of optical CD, or OCD, it can measure CDU of 2D arrays with high accuracy, high repeatability and high throughput.
Modeling and 2-D discrete simulation of dislocation dynamics for plastic deformation of metal
NASA Astrophysics Data System (ADS)
Liu, Juan; Cui, Zhenshan; Ou, Hengan; Ruan, Liqun
2013-05-01
Two methods are employed in this paper to investigate the dislocation evolution during plastic deformation of metal. One method is dislocation dynamic simulation of two-dimensional discrete dislocation dynamics (2D-DDD), and the other is dislocation dynamics modeling by means of nonlinear analysis. As screw dislocation is prone to disappear by cross-slip, only edge dislocation is taken into account in simulation. First, an approach of 2D-DDD is used to graphically simulate and exhibit the collective motion of a large number of discrete dislocations. In the beginning, initial grains are generated in the simulation cells according to the mechanism of grain growth and the initial dislocation is randomly distributed in grains and relaxed under the internal stress. During the simulation process, the externally imposed stress, the long range stress contribution of all dislocations and the short range stress caused by the grain boundaries are calculated. Under the action of these forces, dislocations begin to glide, climb, multiply, annihilate and react with each other. Besides, thermal activation process is included. Through the simulation, the distribution of dislocation and the stress-strain curves can be obtained. On the other hand, based on the classic dislocation theory, the variation of the dislocation density with time is described by nonlinear differential equations. Finite difference method (FDM) is used to solve the built differential equations. The dislocation evolution at a constant strain rate is taken as an example to verify the rationality of the model.
Dual geometric worm algorithm for two-dimensional discrete classical lattice models
NASA Astrophysics Data System (ADS)
Hitchcock, Peter; Sørensen, Erik S.; Alet, Fabien
2004-07-01
We present a dual geometrical worm algorithm for two-dimensional Ising models. The existence of such dual algorithms was first pointed out by Prokof’ev and Svistunov [
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, Renjie; Liu, Rong; Xu, Kexin; Yang, Yanrong
2013-12-01
A new method for discrimination analysis of adulterated milk and pure milk is proposed by combining two-dimensional correlation spectroscopy (2D-COS) with kernel orthogonal projection to latent structure (K-OPLS). Three adulteration types of milk with urea, melamine, and glucose were prepared, respectively. The synchronous 2D spectra of adulterated milk and pure milk samples were calculated. Based on the characteristics of 2D correlation spectra of adulterated milk and pure milk, a discriminant model of urea-tainted milk, melamine-tainted milk, glucose-tainted milk, and pure milk was built by K-OPLS. The classification accuracy rates of unknown samples were 85.7, 92.3, 100, and 87.5%, respectively. The results show that this method has great potential in the rapid discrimination analysis of adulterated milk and pure milk.
Boriskina, Svetlana V; Sewell, Phillip; Benson, Trevor M; Nosich, Alexander I
2004-03-01
A fast and accurate method is developed to compute the natural frequencies and scattering characteristics of arbitrary-shape two-dimensional dielectric resonators. The problem is formulated in terms of a uniquely solvable set of second-kind boundary integral equations and discretized by the Galerkin method with angular exponents as global test and trial functions. The log-singular term is extracted from one of the kernels, and closed-form expressions are derived for the main parts of all the integral operators. The resulting discrete scheme has a very high convergence rate. The method is used in the simulation of several optical microcavities for modern dense wavelength-division-multiplexed systems.
Brûlé, Yoann; Demésy, Guillaume; Gralak, Boris; Popov, Evgeny
2015-04-06
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.
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.
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.
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.
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)
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).
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.
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 assessed as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.
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
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).
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}.
Lü, Chengxu; Chen, Longjian; Yang, Zengling; Liu, Xian; Han, Lujia
2014-01-01
This article presents a novel method for combining auto-peak and cross-peak information for sensitive variable selection in synchronous two-dimensional correlation spectroscopy (2D-COS). This variable selection method is then applied to the case of near-infrared (NIR) microscopy discrimination of meat and bone meal (MBM). This is of important practical value because MBM is currently banned in ruminate animal compound feed. For the 2D-COS analysis, a set of NIR spectroscopy data of compound feed samples (adulterated with varying concentrations of MBM) was pretreated using standard normal variate and detrending (SNVD) and then mapped to the 2D-COS synchronous matrix. For the auto-peak analysis, 12 main sensitive variables were identified at 6852, 6388, 6320, 5788, 5600, 5244, 4900, 4768, 4572, 4336, 4256, and 4192 cm(-1). All these variables were assigned their specific spectral structure and chemical component. For the cross-peak analysis, these variables were divided into two groups, each group containing the six sensitive variables. This grouping resulted in a correlation between the spectral variables that was in accordance with the chemical-component content of the MBM and compound feed. These sensitive variables were then used to build a NIR microscopy discrimination model, which yielded a 97% correct classification. Moreover, this method detected the presence of MBM when its concentration was less than 1% in an adulterated compound feed sample. The concentration-dependent 2D-COS-based variable selection method developed in this study has the unique advantages of (1) introducing an interpretive aspect into variable selection, (2) substantially reducing the complexity of the computations, (3) enabling the transferability of the results to discriminant analysis, and (4) enabling the efficient compression of spectral data.
1-kHz two-dimensional coherent anti-Stokes Raman scattering (2D-CARS) for gas-phase thermometry.
Miller, Joseph D; Slipchenko, Mikhail N; Mance, Jason G; Roy, Sukesh; Gord, James R
2016-10-31
Two-dimensional gas-phase coherent anti-Stokes Raman scattering (2D-CARS) thermometry is demonstrated at 1 kHz in a heated jet. A hybrid femtosecond/picosecond CARS configuration is used in a two-beam phase-matching arrangement with a 100-femtosecond pump/Stokes pulse and a 107-picosecond probe pulse. The femtosecond pulse is generated using a mode-locked oscillator and regenerative amplifier that is synchronized to a separate picosecond oscillator and burst-mode amplifier. The CARS signal is spectrally dispersed in a custom imaging spectrometer and detected using a high-speed camera with image intensifier. 1-kHz, single-shot planar measurements at room temperature exhibit error of 2.6% and shot-to-shot variations of 2.6%. The spatial variation in measured temperature is 9.4%. 2D-CARS temperature measurements are demonstrated in a heated O_{2} jet to capture the spatiotemporal evolution of the temperature field.
Qu, Lei; Chen, Jian-Bo; Zhang, Gui-Jun; Sun, Su-Qin; Zheng, Jing
2017-03-05
As a kind of expensive perfume and valuable herb, Aquilariae Lignum Resinatum (ALR) is often adulterated for economic motivations. In this research, Fourier transform infrared (FT-IR) spectroscopy is employed to establish a simple and quick method for the adulteration screening of ALR. First, the principal chemical constituents of ALR are characterized by FT-IR spectroscopy at room temperature and two-dimensional correlation infrared (2D-IR) spectroscopy with thermal perturbation. Besides the common cellulose and lignin compounds, a certain amount of resin is the characteristic constituent of ALR. Synchronous and asynchronous 2D-IR spectra indicate that the resin (an unstable secondary metabolite) is more sensitive than cellulose and lignin (stable structural constituents) to the thermal perturbation. Using a certified ALR sample as the reference, the infrared spectral correlation threshold is determined by 30 authentic samples and 6 adulterated samples. The spectral correlation coefficient of an authentic ALR sample to the standard reference should be not less than 0.9886 (p=0.01). Three commercial adulterated ALR samples are identified by the correlation threshold. Further interpretation of the infrared spectra of the adulterated samples indicates the common adulterating methods - counterfeiting with other kind of wood, adding ingredient such as sand to increase the weight, and adding the cheap resin such as rosin to increase the content of resin compounds. Results of this research prove that FT-IR spectroscopy can be used as a simple and accurate quality control method of ALR.
NASA Astrophysics Data System (ADS)
Qu, Lei; Chen, Jian-bo; Zhang, Gui-Jun; Sun, Su-qin; Zheng, Jing
2017-03-01
As a kind of expensive perfume and valuable herb, Aquilariae Lignum Resinatum (ALR) is often adulterated for economic motivations. In this research, Fourier transform infrared (FT-IR) spectroscopy is employed to establish a simple and quick method for the adulteration screening of ALR. First, the principal chemical constituents of ALR are characterized by FT-IR spectroscopy at room temperature and two-dimensional correlation infrared (2D-IR) spectroscopy with thermal perturbation. Besides the common cellulose and lignin compounds, a certain amount of resin is the characteristic constituent of ALR. Synchronous and asynchronous 2D-IR spectra indicate that the resin (an unstable secondary metabolite) is more sensitive than cellulose and lignin (stable structural constituents) to the thermal perturbation. Using a certified ALR sample as the reference, the infrared spectral correlation threshold is determined by 30 authentic samples and 6 adulterated samples. The spectral correlation coefficient of an authentic ALR sample to the standard reference should be not less than 0.9886 (p = 0.01). Three commercial adulterated ALR samples are identified by the correlation threshold. Further interpretation of the infrared spectra of the adulterated samples indicates the common adulterating methods - counterfeiting with other kind of wood, adding ingredient such as sand to increase the weight, and adding the cheap resin such as rosin to increase the content of resin compounds. Results of this research prove that FT-IR spectroscopy can be used as a simple and accurate quality control method of ALR.
Peng, Rui; Liang, Liangbo; Hood, Zachary D.; ...
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
Kenfack Tsobnang, Patrice; Wenger, Emmanuel; Biache, Coralie; Lambi Ngolui, John; Ponou, Siméon; Dahaoui, Slimane; Lecomte, Claude
2014-10-01
The stacked two-dimensional supramolecular compound catena-{Co(amp)3Cr(ox)3·6H2O} (amp = 2-picolylamine, ox = oxalate) has been synthesized from the bimolecular approach using hydrogen bonds. It is built from layers in which both Co(amp)(3+) (D) and Cr(ox)(3-) (A) ions are bonded in a repeating DADADA… pattern along the a and c axes by multiple hydrogen bonds. These layers host a well resolved R12 dodecameric discrete ring of water clusters built by six independent molecules located around the 2c centrosymmetric Wyckoff positions of the P21/n space group in which the compound crystallizes. These clusters are ranged along the [001] direction, occupy 733.5 Å(3) (22.0%) of the unit cell and have a chair conformation via 12 hydrogen bonds. The water molecules of the cluster are linked with stronger hydrogen bonds than those between the cluster and its host, which explains the single continuous step of the dehydration process of the compound.
Cook, Daniel W; Rutan, Sarah C; Stoll, Dwight R; Carr, Peter W
2015-02-15
Comprehensive two-dimensional liquid chromatography (LC×LC) is rapidly evolving as the preferred method for the analysis of complex biological samples owing to its much greater resolving power compared to conventional one-dimensional (1D-LC). While its enhanced resolving power makes this method appealing, it has been shown that the precision of quantitation in LC×LC is generally not as good as that obtained with 1D-LC. The poorer quantitative performance of LC×LC is due to several factors including but not limited to the undersampling of the first dimension and the dilution of analytes during transit from the first dimension ((1)D) column to the second dimension ((2)D) column, and the larger relative background signals. A new strategy, 2D assisted liquid chromatography (2DALC), is presented here. 2DALC makes use of a diode array detector placed at the end of each column, producing both multivariate (1)D and two-dimensional (2D) chromatograms. The increased resolution of the analytes provided by the addition of a second dimension of separation enables the determination of analyte absorbance spectra from the (2)D detector signal that are relatively pure and can be used to initiate the treatment of data from the first dimension detector using multivariate curve resolution-alternating least squares (MCR-ALS). In this way, the approach leverages the strengths of both separation methods in a single analysis: the (2)D detector data is used to provide relatively pure analyte spectra to the MCR-ALS algorithm, and the final quantitative results are obtained from the resolved (1)D chromatograms, which has a much higher sampling rate and lower background signal than obtained in conventional single detector LC×LC, to obtain accurate and precise quantitative results. It is shown that 2DALC is superior to both single detector selective or comprehensive LC×LC and 1D-LC for quantitation of compounds that appear as severely overlapped peaks in the (1)D chromatogram - this is
Peng, Rui; Liang, Liangbo; Hood, Zachary D.; Boulesbaa, Abdelaziz; Puretzky, Alexander; Ievlev, Anton V.; Come, Jeremy; Ovchinnikova, Olga S.; Wang, Hui; Ma, Cheng; Chi, Miaofang; Sumpter, Bobby G.; Wu, Zili
2016-08-30
Two-dimensional (2D) single-layer MoS_{2} nanosheets are demonstrated as efficient photocatalysts for hydrogen evolution reaction (HER) from water reduction, thanks to specific in-plane heterojunctions constructed in the MoS_{2} monolayer. These functional heterojunctions are formed among the different phases of chemically exfoliated MoS_{2} monolayers: semiconducting 2H, metallic 1T, and quasi-metallic 1T' phases. The proportion of the three MoS_{2} 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 to shed light on the role of the multiphases of MoS_{2} and reveal that optimum photocatalytic HER activity results from the formation of the in-plane heterojunctions between 1T' MoS_{2} and 2H MoS_{2}. 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' MoS_{2}. Furthermore, our work manifests how the confluence of the optical, electronic and chemical properties of 2D MoS_{2} monolayers can be fully captured for efficient photocatalytic water reduction.
Mazella, Anaïs; Albaret, Jean-Michel; Picard, Delphine
2016-01-01
To fill an important gap in the psychometric assessment of children and adolescents with impaired vision, we designed a new battery of haptic tests, called Haptic-2D, for visually impaired and sighted individuals aged five to 18 years. Unlike existing batteries, ours uses only two-dimensional raised materials that participants explore using active touch. It is composed of 11 haptic tests, measuring scanning skills, tactile discrimination skills, spatial comprehension skills, short-term tactile memory, and comprehension of tactile pictures. We administered this battery to 138 participants, half of whom were sighted (n=69), and half visually impaired (blind, n=16; low vision, n=53). Results indicated a significant main effect of age on haptic scores, but no main effect of vision or Age × Vision interaction effect. Reliability of test items was satisfactory (Cronbach's alpha, α=0.51-0.84). Convergent validity was good, as shown by a significant correlation (age partialled out) between total haptic scores and scores on the B101 test (rp=0.51, n=47). Discriminant validity was also satisfactory, as attested by a lower but still significant partial correlation between total haptic scores and the raw score on the verbal WISC (rp=0.43, n=62). Finally, test-retest reliability was good (rs=0.93, n=12; interval of one to two months). This new psychometric tool should prove useful to practitioners working with young people with impaired vision.
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.
Coloured computational imaging with single-pixel detectors based on a 2D discrete cosine transform
NASA Astrophysics Data System (ADS)
Liu, Bao-Lei; Yang, Zhao-Hua; Liu, Xia; Wu, Ling-An
2017-02-01
We propose and demonstrate a computational imaging technique that uses structured illumination based on a two-dimensional discrete cosine transform to perform imaging with a single-pixel detector. A scene is illuminated by a projector with two sets of orthogonal patterns, then by applying an inverse cosine transform to the spectra obtained from the single-pixel detector a full-color image is retrieved. This technique can retrieve an image from sub-Nyquist measurements, and the background noise is easily canceled to give excellent image quality. Moreover, the experimental setup is very simple.
A Polar Discrete Ordinate Radiation Transport Method for 2D ALE Meshes in HYDRA
NASA Astrophysics Data System (ADS)
Chang, Britton; Marinak, Marty; Weber, Chris; Peterson, Luc
2016-10-01
The Polar Discrete Ordinate Radiation Transport Method in HYDRA has been extended to handle general 2D r-z meshes. Previously the method was only for orthogonal 2D meshes. The new method can be employed with the ALE methodology for managing mesh motion that is used to simulate Rayleigh-Taylor and Richtmyer-Meshkov instabilities on NIF capsule implosions. The results of an examination of this kind will be compared to those obtained by the corresponding diffusion method. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.
Raufaste, C; Cox, S J; Marmottant, P; Graner, F
2010-03-01
We study the elasto-plastic behavior of materials made of individual (discrete) objects such as a liquid foam made of bubbles. The evolution of positions and mutual arrangements of individual objects is taken into account through statistical quantities such as the elastic strain of the structure, the yield strain, and the yield function. The past history of the sample plays no explicit role except through its effect on these statistical quantities. They suffice to relate the discrete scale with the collective global scale. At this global scale, the material behaves as a continuous medium; it is described with tensors such as elastic strain, stress, and velocity gradient. We write the differential equations which predict their elastic and plastic behavior in both the general case and the case of simple shear. An overshoot in the shear strain or shear stress is interpreted as a rotation of the deformed structure, which is a purely tensorial effect that exists only if the yield strain is at least of order 0.3. We suggest practical applications including the following: when to choose a scalar formalism rather than a tensorial one; how to relax trapped stresses; and how to model materials with a low, or a high, yield strain.
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.
Majumdar, A.K.; Agrawal, N.K.; Keeton, L.W.; Singhal, A.K.
1985-07-01
Cooling towers that do not meet design performance standards can add millions of dollars to the long-term operating costs of generating plants. The VERA2D-84 code offers a reliable method for predicting the performance of natural-draft and mechanical-draft towers on the basis of physical design information.
Kondo, Tadashi; Hirohashi, Setsuo
2006-01-01
Proteome data combined with histopathological information provides important, novel clues for understanding cancer biology and reveals candidates for tumor markers and therapeutic targets. We have established an application of a highly sensitive fluorescent dye (CyDye DIGE Fluor saturation dye), developed for two-dimensional difference gel electrophoresis (2D-DIGE), to the labeling of proteins extracted from laser microdissected tissues. The use of the dye dramatically decreases the protein amount and, in turn, the number of cells required for 2D-DIGE; the cells obtained from a 1 mm2 area of an 8-12 microm thick tissue section generate up to 5,000 protein spots in a large-format 2D gel. This protocol allows the execution of large-scale proteomics in a more efficient, accurate and reproducible way. The protocol can be used to examine a single sample in 5 d or to examine hundreds of samples in large-scale proteomics.
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.
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
A new stationary gridline artifact suppression method based on the 2D discrete wavelet transform
Tang, Hui; Tong, Dan; Bao, Xudong; Dillenseger, Jean-Louis
2015-01-01
Purpose In digital X-ray radiography, an anti-scatter grid is inserted between the patient and the image receptor to reduce scattered radiation. If the anti-scatter 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 sub-images using a multi-scale 2D discrete wavelet transform (DWT). The decomposition process stops when the gridline signal is found to be greater than a threshold in one or several of these sub-images using a gridline detection module. An automatic Gaussian band-stop filter is then applied to the detected sub-images to remove the gridline signal. Finally, the restored image is achieved using the corresponding 2D inverse discrete wavelet transform (IDWT). Results The processed images show that the proposed method can remove the gridline signal efficiently while maintaining the image details. The spectra of a 1-dimensional 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. PMID:25832061
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.
Conservative discontinuous Galerkin discretizations of the 2D incompressible Euler equation
NASA Astrophysics Data System (ADS)
Waelbroeck, Francois; Michoski, Craig; Bernard, Tess
2016-10-01
Discontinuous Galerkin (DG) methods provide local high-order adaptive numerical schemes for the solution of convection-diffusion problems. They combine the advantages of finite element and finite volume methods. In particular, DG methods automatically ensure the conservation of all first-order invariants provided that single-valued fluxes are prescribed at inter-element boundaries. For the 2D incompressible Euler equation, this implies that the discretized fluxes globally obey Gauss' and Stokes' laws exactly, and that they conserve total vorticity. Liu and Shu have shown that combining a continuous Galerkin (CG) solution of Poisson's equation with a central DG flux for the convection term leads to an algorithm that conserves the principal two quadratic invariants, namely the energy and enstrophy. Here, we present a discretization that applies the DG method to Poisson's equation as well as to the vorticity equation while maintaining conservation of the quadratic invariants. Using a DG algorithm for Poisson's equation can be advantageous when solving problems with mixed Dirichlet-Neuman boundary conditions such as for the injection of fluid through a slit (Bickley jet) or during compact toroid injection for tokamak startup.
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.
Multirate-based fast parallel algorithms for 2-D DHT-based real-valued discrete Gabor transform.
Tao, Liang; Kwan, Hon Keung
2012-07-01
Novel algorithms for the multirate and fast parallel implementation of the 2-D discrete Hartley transform (DHT)-based real-valued discrete Gabor transform (RDGT) and its inverse transform are presented in this paper. A 2-D multirate-based analysis convolver bank is designed for the 2-D RDGT, and a 2-D multirate-based synthesis convolver bank is designed for the 2-D inverse RDGT. The parallel channels in each of the two convolver banks have a unified structure and can apply the 2-D fast DHT algorithm to speed up their computations. The computational complexity of each parallel channel is low and is independent of the Gabor oversampling rate. All the 2-D RDGT coefficients of an image are computed in parallel during the analysis process and can be reconstructed in parallel during the synthesis process. The computational complexity and time of the proposed parallel algorithms are analyzed and compared with those of the existing fastest algorithms for 2-D discrete Gabor transforms. The results indicate that the proposed algorithms are the fastest, which make them attractive for real-time image processing.
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.
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.
NASA Astrophysics Data System (ADS)
Hladowski, Lukasz; Galkowski, Krzysztof; Cai, Zhonglun; Rogers, Eric; Freeman, Chris T.; Lewin, Paul L.
2011-07-01
In this article a new approach to iterative learning control for the practically relevant case of deterministic discrete linear plants with uniform rank greater than unity is developed. The analysis is undertaken in a 2D systems setting that, by using a strong form of stability for linear repetitive processes, allows simultaneous consideration of both trial-to-trial error convergence and along the trial performance, resulting in design algorithms that can be computed using linear matrix inequalities (LMIs). Finally, the control laws are experimentally verified on a gantry robot that replicates a pick and place operation commonly found in a number of applications to which iterative learning control is applicable.
Analytical calculation of two-dimensional spectra.
Bell, Joshua D; Conrad, Rebecca; Siemens, Mark E
2015-04-01
We demonstrate an analytical calculation of two-dimensional (2D) coherent spectra of electronic or vibrational resonances. Starting with the solution to the optical Bloch equations for a two-level system in the 2D time domain, we show that a fully analytical 2D Fourier transform can be performed if the projection-slice and Fourier-shift theorems of Fourier transforms are applied. Results can be fit to experimental 2D coherent spectra of resonances with arbitrary inhomogeneity.
Carbonate fracture stratigraphy: An integrated outcrop and 2D discrete element modelling study
NASA Astrophysics Data System (ADS)
Spence, Guy; Finch, Emma
2013-04-01
Constraining fracture stratigraphy is important as natural fractures control primary fluid flow in low matrix permeability naturally fractured carbonate hydrocarbon reservoirs. Away from the influence of folds and faults, stratigraphic controls are known to be the major control on fracture networks. The fracture stratigraphy of carbonate nodular-chert rhythmite successions are investigated using a Discrete Element Modelling (DEM) technique and validated against observations from outcrops. Comparisons are made to the naturally fractured carbonates of the Eocene Thebes Formation exposed in the west central Sinai of Egypt, which form reservoir rocks in the nearby East Ras Budran Field. DEM allows mechanical stratigraphy to be defined as the starting conditions from which forward numerical modelling can generate fracture stratigraphy. DEM can incorporate both stratigraphic and lateral heterogeneity, and enable mechanical and fracture stratigraphy to be characterised separately. Stratally bound stratified chert nodules below bedding surfaces generate closely spaced lateral heterogeneity in physical properties at stratigraphic mechanical interfaces. This generates extra complexity in natural fracture networks in addition to that caused by bed thickness and lithological physical properties. A series of representative geologically appropriate synthetic mechanical stratigraphic models were tested. Fracture networks generated in 15 DEM experiments designed to isolate and constrain the effects of nodular chert rhythmites on carbonate fracture stratigraphy are presented. The discrete element media used to model the elastic strengths of rocks contain 72,866 individual elements. Mechanical stratigraphies and the fracture networks generated are placed in a sequence stratigraphic framework. Nodular chert rhythmite successions are shown to be a distinct type of naturally fractured carbonate reservoir. Qualitative stratigraphic rules for predicting the distribution, lengths, spacing
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.
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.
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.
Soliton nanoantennas in two-dimensional arrays of quantum dots
NASA Astrophysics Data System (ADS)
Gligorić, G.; Maluckov, A.; Hadžievski, Lj; Slepyan, G. Ya; Malomed, B. A.
2015-06-01
We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schrödinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D soliton-based nano-antenna, which is stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.
Two-dimensional photonic crystal surfactant detection.
Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A
2012-08-07
We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants.
2014-09-26
linear electronic specific heat disappears in strong magnetic fields if Landau levels are not broadened. Thus, the amplitude of the magnetothermal...Molec. Crys. Liq. Crys. 121, 169 (1984). In consideration of mixing of low-lying Landau levels, the magneto- conductance of two-dimensional electrons...and narrowing can be explained when the Landau level filling factor v is larger than 1. Actually, we have shown that the resonance phenomena are
One and Two Dimensional Discrete Wavelet Transforms
1992-09-01
dimensional case in Chapter IV. Chapter V proposes another method for decomposing the data at the expense of physical memory , the so-called multiple-phase...more efficient. Practically, this savings in memory is very insignificant, since the number of practical resolution levels is approximately [log2( I...filters, N, and the current resolution level, m: Ie.1 = Ic0I + (N-1)(2`-1) (43) So enough memory must be allocated if we desire lower and lower
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.
NASA Astrophysics Data System (ADS)
Palha, A.; Gerritsma, M.
2017-01-01
In this work we present a mimetic spectral element discretization for the 2D incompressible Navier-Stokes equations that in the limit of vanishing dissipation exactly preserves mass, kinetic energy, enstrophy and total vorticity on unstructured triangular grids. The essential ingredients to achieve this are: (i) a velocity-vorticity formulation in rotational form, (ii) a sequence of function spaces capable of exactly satisfying the divergence free nature of the velocity field, and (iii) a conserving time integrator. Proofs for the exact discrete conservation properties are presented together with numerical test cases on highly irregular triangular grids.
Two-dimensional Quantum Gravity
NASA Astrophysics Data System (ADS)
Rolf, Juri
1998-10-01
This Ph.D. thesis pursues two goals: The study of the geometrical structure of two-dimensional quantum gravity and in particular its fractal nature. To address these questions we review the continuum formalism of quantum gravity with special focus on the scaling properties of the theory. We discuss several concepts of fractal dimensions which characterize the extrinsic and intrinsic geometry of quantum gravity. This work is partly based on work done in collaboration with Jan Ambjørn, Dimitrij Boulatov, Jakob L. Nielsen and Yoshiyuki Watabiki (1997). The other goal is the discussion of the discretization of quantum gravity and to address the so called quantum failure of Regge calculus. We review dynamical triangulations and show that it agrees with the continuum theory in two dimensions. Then we discuss Regge calculus and prove that a continuum limit cannot be taken in a sensible way and that it does not reproduce continuum results. This work is partly based on work done in collaboration with Jan Ambjørn, Jakob L. Nielsen and George Savvidy (1997).
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.
Zhu, Zongxiao; Wang, Guoyou; Liu, Jianguo; Chen, Zhong
2013-12-01
This paper initially develops the discrete-point sampling operator's concept, model, and parameters that we have previously proposed, and makes its belt-shaped regions in a discrete-point sampling map more salient and appropriate for centerline extraction. The cross-sectional features of these belt-shaped regions are then analyzed and seven types of feature points are defined to facilitate descriptions of such features. Based on these feature points, a three-level detection system is proposed, including feature points, line segments, and centerlines, to extract centerlines from the belt-shaped regions. Eight basic types of centerlines and five types of relationships among the centerlines are defined by computational geometry algorithms, and Gestalt laws are used to cluster them into groupings. If some prior information about a desired shape is available, retrieval grouping may be carried out by a discrete-point sampling map, the purpose of which is to find centerlines by best matching with prior information. Discrete-point sampling effectually overcomes the influences of interference from noise, textures, and uneven illumination, and greatly reduces the difficulty of centerline extraction. Centerline clustered groupings and retrieval grouping can offer a strong anti-interference ability with nonlinear deformations such as articulation and occlusion. This method can extract large-scale complex shapes combined of lines and planes from complex images. The wheel location results of noise test and other shape extraction experiments show that our method has a strong capability to persist with nonlinear deformations.
NASA Astrophysics Data System (ADS)
Hematiyan, M. R.
2007-03-01
A robust method is presented to evaluate 2D and 3D domain integrals without domain discretization. Each domain integral is transformed into a double integral, a boundary integral and a 1D integral. Both integrals are evaluated by adaptive Simpson quadrature method. The method can be used to evaluate domain integrals over simply or multiply connected regions with any arbitrary form of integrands. As an application of the method, domain integrals produced in boundary element formulation of potential and elastostatic problems are analyzed. Several examples are provided to show the validity and accuracy of the method.
NASA Astrophysics Data System (ADS)
Mei, Hong-Xin; Zhang, Ting; Huang, Hua-Qi; Huang, Rong-Bin; Zheng, Lan-Sun
2016-03-01
Three mix-ligand Ag(I) coordination compounds, namely, {[Ag10(tpyz) 5(L1) 5(H2 O)2].(H2 O)4}n (1, tpyz = 2,3,4,5-tetramethylpyrazine, H2 L1 = phthalic acid), [Ag4(tpyz) 2(L2) 2(H2 O)].(H2 O)5}n (2, H2 L2 = isophthalic acid) {[Ag2(tpyz) 2(L3) (H2 O)4].(H2 O)8}n (3, H2 L3 = terephthalic acid), have been synthesized and characterized by elemental analysis, IR, PXRD and X-ray single-crystal diffraction. 1 exhibits a 2D layer which can be simplified as a (4,4) net. 2 is a 3D network which can be simplified as a (3,3)-connected 2-nodal net with a point symbol of {102.12}{102}. 3 consists of linear [Ag(tpyz) (H2 O)2]n chain. Of particular interest, discrete hexamer water clusters were observed in 1 and 2, while a 2D L10(6) water layer exists in 3. The results suggest that the benzene dicarboxylates play pivotal roles in the formation of the different host architectures as well as different water aggregations. Moreover, thermogravimetric analysis (TGA) and emissive behaviors of these compounds were investigated.
Rationally synthesized two-dimensional polymers.
Colson, John W; Dichtel, William R
2013-06-01
Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.
Rationally synthesized two-dimensional polymers
NASA Astrophysics Data System (ADS)
Colson, John W.; Dichtel, William R.
2013-06-01
Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.
No-hair conjecture in two-dimensional dilaton supergravity
NASA Astrophysics Data System (ADS)
Gamboa, J.; Georgelin, Y.
1993-11-01
We study two-dimensional (2D) dilaton gravity and supergravity following Hamiltonian methods. First, we consider the structure of constraints of 2D dilaton gravity, and then the 2D dilaton supergravity theory is obtained taking the square root of the bosonic constraints. We integrate exactly the equations of motion in both cases, and we show that the solutions of the equation of motion of 2D dilaton supergravity differ from the solutions of 2D dilaton gravity only by boundary conditions on the fermionic variables; i.e., the black holes of 2D dilaton supergravity theory are exactly the same black holes of 2D bosonic dilaton gravity modulo supersymmetry transformations. This result is the two-dimensional analogue of the no-hair theorem for supergravity.
NASA Astrophysics Data System (ADS)
Orso, Giuliano
2017-03-01
We investigate the metal-insulator transition occurring in two-dimensional (2D) systems of noninteracting atoms in the presence of artificial spin-orbit interactions and a spatially correlated disorder generated by laser speckles. Based on a high order discretization scheme, we calculate the precise position of the mobility edge and verify that the transition belongs to the symplectic universality class. We show that the mobility edge depends strongly on the mixing angle between Rashba and Dresselhaus spin-orbit couplings. For equal couplings a non-power-law divergence is found, signaling the crossing to the orthogonal class, where such a 2D transition is forbidden.
Kirigami for Two-Dimensional Electronic Membranes
NASA Astrophysics Data System (ADS)
Qi, Zenan; Bahamon, Dario; Campbell, David; Park, Harold
2015-03-01
Two-dimensional materials have recently drawn tremendous attention because of their unique properties. In this work, we introduce the notion of two-dimensional kirigami, where concepts that have been used almost exclusively for macroscale structures are applied to dramatically enhance their stretchability. Specifically, we show using classical molecular dynamics simulations that the yield and fracture strains of graphene and MoS2 can be enhanced by about a factor of three using kirigami as compared to standard monolayers. Finally, using graphene as an example, we demonstrate that the kirigami structure may open up interesting opportunities in coupling to the electronic behavior of 2D materials. Authors acknowledge Mechanical Engineering and Physics departments at Boston University, and Mackgrafe at Mackenzie Presbyterian University.
Spatially resolved two-dimensional Fourier transform electron spin resonance
NASA Astrophysics Data System (ADS)
Ewert, Uwe; Crepeau, Richard H.; Lee, Sanghyuk; Dunnam, Curt R.; Xu, Dajiang; Freed, Jack H.
1991-09-01
Fourier transform ESR methods have been extended to permit spatially resolved two-dimensional (2D)-ESR experiments. This is illustrated for the case of 2D-electron-electron double resonance (2D-ELDOR) spectra of nitroxides in a liquid that exhibits appreciable cross-peaks due to Heisenberg spin exchange. The use of spin-echo decays in spatially resolved FT-ESR is also demonstrated.
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.
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.
Dynamics of two-dimensional and quasi-two-dimensional polymers
NASA Astrophysics Data System (ADS)
Sung, Bong June; Yethiraj, Arun
2013-06-01
The dynamic properties of dense two-dimensional (2D) polymer melts are studied using discontinuous molecular dynamics simulations. Both strictly 2D and quasi-2D systems are investigated. The strictly 2D model system consists of a fluid of freely jointed tangent hard disc chains. The translational diffusion coefficient, D, is strongly system size dependent with D ˜ ln L where L is the linear dimension of the square simulation cell. The rotational correlation time, τrot, is, however, independent of system size. The dynamics is consistent with Rouse behavior with D/ln L ˜ N-1 and τrot ˜ N2 for all area fractions. Analysis of the intermediate scattering function, Fs(k, t), shows that the dynamics becomes slow for N = 256 and the area fraction of 0.454 and that there might be a glass transition for long polymers at sufficiently high area fractions. The polymer mobility is not correlated with the conformation of the molecules. In the quasi-2D system hard sphere chains are confined between corrugated surfaces so that chains cannot go over each other or into the surfaces. The conformational properties are identical to the 2D case, but D and τrot are independent of system size. The scaling of D and τrot with N is similar to that of strictly 2D systems. The simulations suggest that 2D polymers are never entangled and follow Rouse dynamics at all densities.
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.
NASA Technical Reports Server (NTRS)
Jackman, Charles H.; Douglass, Anne R.; Stolarski, Richard S.; Guthrie, Paul D.; Thompson, A. M.
1990-01-01
A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations.
Polaritons in layered two-dimensional materials
NASA Astrophysics Data System (ADS)
Low, Tony; Chaves, Andrey; Caldwell, Joshua D.; Kumar, Anshuman; Fang, Nicholas X.; Avouris, Phaedon; Heinz, Tony F.; Guinea, Francisco; Martin-Moreno, Luis; Koppens, Frank
2016-11-01
In recent years, enhanced light-matter interactions through a plethora of dipole-type polaritonic excitations have been observed in two-dimensional (2D) layered materials. In graphene, electrically tunable and highly confined plasmon-polaritons were predicted and observed, opening up opportunities for optoelectronics, bio-sensing and other mid-infrared applications. In hexagonal boron nitride, low-loss infrared-active phonon-polaritons exhibit hyperbolic behaviour for some frequencies, allowing for ray-like propagation exhibiting high quality factors and hyperlensing effects. In transition metal dichalcogenides, reduced screening in the 2D limit leads to optically prominent excitons with large binding energy, with these polaritonic modes having been recently observed with scanning near-field optical microscopy. Here, we review recent progress in state-of-the-art experiments, and survey the vast library of polaritonic modes in 2D materials, their optical spectral properties, figures of merit and application space. Taken together, the emerging field of 2D material polaritonics and their hybrids provide enticing avenues for manipulating light-matter interactions across the visible, infrared to terahertz spectral ranges, with new optical control beyond what can be achieved using traditional bulk materials.
Buckled two-dimensional Xene sheets
NASA Astrophysics Data System (ADS)
Molle, Alessandro; Goldberger, Joshua; Houssa, Michel; Xu, Yong; Zhang, Shou-Cheng; Akinwande, Deji
2017-01-01
Silicene, germanene and stanene are part of a monoelemental class of two-dimensional (2D) crystals termed 2D-Xenes (X = Si, Ge, Sn and so on) which, together with their ligand-functionalized derivatives referred to as Xanes, are comprised of group IVA atoms arranged in a honeycomb lattice -- similar to graphene but with varying degrees of buckling. Their electronic structure ranges from trivial insulators, to semiconductors with tunable gaps, to semi-metallic, depending on the substrate, chemical functionalization and strain. More than a dozen different topological insulator states are predicted to emerge, including the quantum spin Hall state at room temperature, which, if realized, would enable new classes of nanoelectronic and spintronic devices, such as the topological field-effect transistor. The electronic structure can be tuned, for example, by changing the group IVA element, the degree of spin-orbit coupling, the functionalization chemistry or the substrate, making the 2D-Xene systems promising multifunctional 2D materials for nanotechnology. This Perspective highlights the current state of the art and future opportunities in the manipulation and stability of these materials, their functions and applications, and novel device concepts.
Polaritons in layered two-dimensional materials.
Low, Tony; Chaves, Andrey; Caldwell, Joshua D; Kumar, Anshuman; Fang, Nicholas X; Avouris, Phaedon; Heinz, Tony F; Guinea, Francisco; Martin-Moreno, Luis; Koppens, Frank
2017-02-01
In recent years, enhanced light-matter interactions through a plethora of dipole-type polaritonic excitations have been observed in two-dimensional (2D) layered materials. In graphene, electrically tunable and highly confined plasmon-polaritons were predicted and observed, opening up opportunities for optoelectronics, bio-sensing and other mid-infrared applications. In hexagonal boron nitride, low-loss infrared-active phonon-polaritons exhibit hyperbolic behaviour for some frequencies, allowing for ray-like propagation exhibiting high quality factors and hyperlensing effects. In transition metal dichalcogenides, reduced screening in the 2D limit leads to optically prominent excitons with large binding energy, with these polaritonic modes having been recently observed with scanning near-field optical microscopy. Here, we review recent progress in state-of-the-art experiments, and survey the vast library of polaritonic modes in 2D materials, their optical spectral properties, figures of merit and application space. Taken together, the emerging field of 2D material polaritonics and their hybrids provide enticing avenues for manipulating light-matter interactions across the visible, infrared to terahertz spectral ranges, with new optical control beyond what can be achieved using traditional bulk materials.
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.
Fiber-optic localization by geometric space coding with a two-dimensional gray code
NASA Astrophysics Data System (ADS)
Zheng, Yunhui; Brady, David J.; Sullivan, Michaell E.; Guenther, Bob D.
2005-07-01
With the objective of monitoring motion within a room, we segment the two-dimensional (2D) floor space into discrete cells and encode each cell with a binary code word generated by a fiber. We design a set of k-neighbor-local codes to localize an extended object and, particularly when k=2, employ a 2D gray code to localize a human by tracking his or her footsteps. Methods for implementing the codes in a fiber web are discussed, and we demonstrate the experimental result with the fiber mat. The observed system performance confirms the theoretical analysis. The space coding technique is a promising low-cost candidate not only for human tracking but also for other applications such as human gait analysis.
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
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 NMR spectrometry
Farrar, T.C.
1987-06-01
This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t/sub 0/; an evolution period, t/sub 1/; and a detection period, t/sub 2/.
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.
NASA Technical Reports Server (NTRS)
Juday, Richard D.
1992-01-01
Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.
Two-Dimensional Potential Flows
NASA Technical Reports Server (NTRS)
Schaefer, Manfred; Tollmien, W.
1949-01-01
Contents include the following: Characteristic differential equations - initial and boundary conditions. Integration of the second characteristic differential equations. Direct application of Meyer's characteristic hodograph table for construction of two-dimensional potential flows. Prandtl-Busemann method. Development of the pressure variation for small deflection angles. Numerical table: relation between deflection, pressure, velocity, mach number and mach angle for isentropic changes of state according to Prandtl-Meyer for air (k = 1.405). References.
Manning’s equation and two-dimensional flow analogs
NASA Astrophysics Data System (ADS)
Hromadka, T. V., II; Whitley, R. J.; Jordan, N.; Meyer, T.
2010-07-01
SummaryTwo-dimensional (2D) flow models based on the well-known governing 2D flow equations are applied to floodplain analysis purposes. These 2D models numerically solve the governing flow equations simultaneously or explicitly on a discretization of the floodplain using grid tiles or similar tile cell geometry, called "elements". By use of automated information systems such as digital terrain modeling, digital elevation models, and GIS, large-scale topographic floodplain maps can be readily discretized into thousands of elements that densely cover the floodplain in an edge-to-edge form. However, the assumed principal flow directions of the flow model analog, as applied across an array of elements, typically do not align with the floodplain flow streamlines. This paper examines the mathematical underpinnings of a four-direction flow analog using an array of square elements with respect to floodplain flow streamlines that are not in alignment with the analog's principal flow directions. It is determined that application of Manning's equation to estimate the friction slope terms of the governing flow equations, in directions that are not coincident with the flow streamlines, may introduce a bias in modeling results, in the form of slight underestimation of flow depths. It is also determined that the maximum theoretical bias, occurs when a single square element is rotated by about 13°, and not 45° as would be intuitively thought. The bias as a function of rotation angle for an array of square elements follows approximately the bias for a single square element. For both the theoretical single square element and an array of square elements, the bias as a function of alignment angle follows a relatively constant value from about 5° to about 85°, centered at about 45°. This bias was first noted about a decade prior to the present paper, and the magnitude of this bias was estimated then to be about 20% at about 10° misalignment. An adjustment of Manning's n is
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.
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.
Physical Mechanisms of Two-Dimensional Turbulence
NASA Astrophysics Data System (ADS)
Ecke, Robert
2004-03-01
Turbulence has slowly yielded its mysteries through over 100 years of persistent effort. Recently experimental techniques and computation power have reached the stage where significant progress has been made on this very challenging problem. Two dimensional turbulence offers some real advantages in terms of reduced degrees of freedom such that the problem can now be thoroughly explored from many perspectives. Further, two-dimensional turbulence exhibits the basic phenomena of direct-enstrophy and inverse-energy cascades thought to apply to oceanic and atmospheric systems. We have investigated the properties of turbulence in two spatial dimensions using experimental measurements of the grid turbulence in a flowing soap film^1 and of the electromagnetically-forced turbulence in a thin salt layer floating on a dense immiscible fluid underlayer. We have also explored 2D turbulence using several different direct numerical simulations of homogeneous, isotropic turbulence in a periodic box^2. The data for both consist of high resolution fields of velocity; some are statistically independent sets and others are temporally resolved for dynamics. From this data we construct conventional Eulerian statistics, directly measure energy and enstrophy transfer^1, identify coherent structures in the flow, determine Lagrangian quantities, and calculate stretching fields. This comprehensive experimental and numerical characterization elucidates the physical mechanisms of two-dimensional turbulence. ^1 M.K. Rivera, W.B. Daniel and R.E. Ecke, Phys. Rev. Lett. 90, 104502 (2003). ^2 S. Chen, R.E. Ecke, G. Eyink, X. Wang, and Z. Xiao, Phys. Rev. Lett. 91, 214501 (2003).
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; ...
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.
Molecular assembly on two-dimensional materials.
Kumar, Avijit; Banerjee, Kaustuv; Liljeroth, Peter
2017-02-24
Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging from
Molecular assembly on two-dimensional materials
NASA Astrophysics Data System (ADS)
Kumar, Avijit; Banerjee, Kaustuv; Liljeroth, Peter
2017-02-01
Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule–substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging
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 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
2016-10-25
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Two-dimensional fourier transform spectrometer
DeFlores, Lauren; Tokmakoff, Andrei
2013-09-03
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Surface chemistry and catalysis confined under two-dimensional materials.
Fu, Qiang; Bao, Xinhe
2016-10-07
Two-dimensional (2D) materials are characterised by their strong intraplanar bonding but weak interplanar interaction. Interfaces between neighboring 2D layers or between 2D overlayers and substrate surfaces provide intriguing confined spaces for chemical processes, which have stimulated a new area of "chemistry under 2D cover". In particular, well-defined 2D material overlayers such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have been deposited on solid surfaces, which can be used as model systems to understand the new chemistry. In the present review, we first show that many atoms and molecules can intercalate ultrathin 2D materials supported on solid surfaces and the space under the 2D overlayers has been regarded as a 2D nanocontainer. Moreover, chemical reactions such as catalytic reactions, surface adlayer growth, chemical vapor deposition, and electrochemical reactions occur in the 2D confined spaces, which further act as 2D nanoreactors. It has been demonstrated that surface chemistry and catalysis are strongly modulated by the 2D covers, resulting in weakened molecule adsorption and enhanced surface reactions. Finally, we conclude that the confinement effect of the 2D cover leads to new chemistry in a small space, such as "catalysis under cover" and "electrochemistry under cover". These new concepts enable us to design advanced nanocatalysts encapsulated with 2D material shells which may present improved performance in many important processes of heterogeneous catalysis, electrochemistry, and energy conversion.
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 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.
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
Ultrafast two dimensional infrared chemical exchange spectroscopy
NASA Astrophysics Data System (ADS)
Fayer, Michael
2011-03-01
The method of ultrafast two dimensional infrared (2D IR) vibrational echo spectroscopy is described. Three ultrashort IR pulses tuned to the frequencies of the vibrational transitions of interest are directed into the sample. The interaction of these pulses with the molecular vibrational oscillators produces a polarization that gives rise to a fourth pulse, the vibrational echo. The vibrational echo pulse is combined with another pulse, the local oscillator, for heterodyne detection of the signal. For fixed time between the second and third pulses, the waiting time, the first pulse is scanned. Two Fourier transforms of the data yield a 2D IR spectrum. The waiting time is increased, and another spectrum is obtained. The change in the 2D IR spectra with increased waiting time provides information on the time evolution of the structure of the molecular system under observation. In a 2D IR chemical exchange experiment, two species A and B, are undergoing chemical exchange. A's are turning into B's, and B's are turning into A's, but the overall concentrations of the species are not changing. The kinetics of the chemical exchange on the ground electronic state under thermal equilibrium conditions can be obtained 2D IR spectroscopy. A vibration that has a different frequency for the two species is monitored. At very short time, there will be two peaks on the diagonal of the 2D IR spectrum, one for A and one for B. As the waiting time is increased, chemical exchange causes off-diagonal peaks to grow in. The time dependence of the growth of these off-diagonal peaks gives the chemical exchange rate. The method is applied to organic solute-solvent complex formation, orientational isomerization about a carbon-carbon single bond, migration of a hydrogen bond from one position on a molecule to another, protein structural substate interconversion, and water hydrogen bond switching between ions and water molecules. This work was supported by the Air Force Office of Scientific
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.
Elastic models of defects in two-dimensional crystals
NASA Astrophysics Data System (ADS)
Kolesnikova, A. L.; Orlova, T. S.; Hussainova, I.; Romanov, A. E.
2014-12-01
Elastic models of defects in two-dimensional (2D) crystals are presented in terms of continuum mechanics. The models are based on the classification of defects, which is founded on the dimensionality of the specification region of their self-distortions, i.e., lattice distortions associated with the formation of defects. The elastic field of an infinitesimal dislocation loop in a film is calculated for the first time. The fields of the center of dilatation, dislocation, disclination, and circular inclusion in planar 2D elastic media, namely, nanofilms and graphenes, are considered. Elastic fields of defects in 2D and 3D crystals are compared.
Melting behavior of single two-dimensional crystal
NASA Astrophysics Data System (ADS)
Zheng, X. H.; Grieve, R.
2006-02-01
In an experimental system millimeter-sized steel balls repel each other through the Coulomb force to imitate a two-dimensional (2D) atomic lattice in a vacuum both topologically and dynamically. Care has been taken to avoid the formation of grain boundaries. This 2D single crystal melts into a liquid via the hexatic state consistent with the Kosterlitz-Thouless-Halperin-Nelson-Young scenario. Initially in the melting process defects of the 2D lattice tend to emerge from the edge of the crystal. These defects are found to be close to the liquid state according to the Lindemann and Born criteria, confirming the idea of edge melting.
Perspective: Two-dimensional resonance Raman spectroscopy
NASA Astrophysics Data System (ADS)
Molesky, Brian P.; Guo, Zhenkun; Cheshire, Thomas P.; Moran, Andrew M.
2016-11-01
Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in complex systems. The 2DRR method can leverage electronic resonance enhancement to selectively probe chromophores embedded in complex environments (e.g., a cofactor in a protein). In addition, correlations between the two dimensions of the 2DRR spectrum reveal information that is not available in traditional Raman techniques. For example, distributions of reactant and product geometries can be correlated in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this perspective article, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide and myoglobin. We also address key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopies. Most notably, it has been shown that these two techniques are subject to a tradeoff between sensitivity to anharmonicity and susceptibility to artifacts. Overall, recent experimental developments and applications of the 2DRR method suggest great potential for the future of the technique.
Parallel Stitching of Two-Dimensional Materials
NASA Astrophysics Data System (ADS)
Ling, Xi; Lin, Yuxuan; Dresselhaus, Mildred; Palacios, Tomás; Kong, Jing; Department of Electrical Engineering; Computer Science, Massachusetts Institute of Technology Team
Large scale integration of atomically thin metals (e.g. graphene), semiconductors (e.g. transition metal dichalcogenides (TMDs)), and insulators (e.g. hexagonal boron nitride) is critical for constructing the building blocks for future nanoelectronics and nanophotonics. However, the construction of in-plane heterostructures, especially between two atomic layers with large lattice mismatch, could be extremely difficult due to the strict requirement of spatial precision and the lack of a selective etching method. Here, we developed a general synthesis methodology to achieve both vertical and in-plane ``parallel stitched'' heterostructures between a two-dimensional (2D) and TMD materials, which enables both multifunctional electronic/optoelectronic devices and their large scale integration. This is achieved via selective ``sowing'' of aromatic molecule seeds during the chemical vapor deposition growth. MoS2 is used as a model system to form heterostructures with diverse other 2D materials. Direct and controllable synthesis of large-scale parallel stitched graphene-MoS2 heterostructures was further investigated. Unique nanometer overlapped junctions were obtained at the parallel stitched interface, which are highly desirable both as metal-semiconductor contact and functional devices/systems, such as for use in logical integrated circuits (ICs) and broadband photodetectors.
Superloop equations and two-dimensional supergravity
Alvarez-Guame, L.; Itoyama, H.; Manes, J.L.; Zadra, A. )
1992-08-20
In this paper, the authors propose a discrete model whose continuum limit reproduces the string susceptibility and the scaling dimensions of (2, 4m) minimal superconformal models coupled to 2D supergravity. The basic assumption in their presentation is a set of super-Virasoro constraints imposed on the partition function. The authors recover the Neveu-Schwarz and Ramond sectors of the theory, and they are also able to evaluate all planar loop correlation functions in the continuum limit. The authors find evidence to identify the integrable hierarchy of nonlinear equations describing the double scaling limit as a supersymmetric generalization of KP studied by Rabin.
Two-dimensional quantum repeaters
NASA Astrophysics Data System (ADS)
Wallnöfer, J.; Zwerger, M.; Muschik, C.; Sangouard, N.; Dür, W.
2016-11-01
The endeavor to develop quantum networks gave rise to a rapidly developing field with far-reaching applications such as secure communication and the realization of distributed computing tasks. This ultimately calls for the creation of flexible multiuser structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multiuser applications. To address this challenge, we propose a two-dimensional quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and imperfect local control operations. The scheme is based on the creation of self-similar multiqubit entanglement structures at growing scale, where variants of entanglement swapping and multiparty entanglement purification are combined to create high-fidelity entangled states. We show how such networks can be implemented using trapped ions in cavities.
Two-dimensional capillary origami
NASA Astrophysics Data System (ADS)
Brubaker, N. D.; Lega, J.
2016-01-01
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.
Flow of rarefied gases over two-dimensional bodies
NASA Technical Reports Server (NTRS)
Jeng, Duen-Ren; De Witt, Kenneth J.; Keith, Theo G., Jr.; Chung, Chan-Hong
1989-01-01
A kinetic-theory analysis is made of the flow of rarefied gases over two-dimensional bodies of arbitrary curvature. The Boltzmann equation simplified by a model collision integral is written in an arbitrary orthogonal curvilinear coordinate system, and solved by means of finite-difference approximation with the discrete ordinate method. A numerical code is developed which can be applied to any two-dimensional submerged body of arbitrary curvature for the flow regimes from free-molecular to slip at transonic Mach numbers. Predictions are made for the case of a right circular cylinder.
A two-dimensional adaptive mesh generation method
NASA Astrophysics Data System (ADS)
Altas, Irfan; Stephenson, John W.
1991-05-01
The present, two-dimensional adaptive mesh-generation method allows selective modification of a small portion of the mesh without affecting large areas of adjacent mesh-points, and is applicable with or without boundary-fitted coordinate-generation procedures. The cases of differential equation discretization by, on the one hand, classical difference formulas designed for uniform meshes, and on the other the present difference formulas, are illustrated through the application of the method to the Hiemenz flow for which the Navier-Stokes equation's exact solution is known, as well as to a two-dimensional viscous internal flow problem.
NASA Astrophysics Data System (ADS)
Borodich, Feodor M.; Galanov, Boris A.
2016-11-01
Contact probing is the preferable method for studying mechanical properties of thin two-dimensional (2D) materials. These studies are based on analysis of experimental force-displacement curves obtained by loading of a stretched membrane by a probe of an atomic force microscope or a nanoindenter. Both non-adhesive and adhesive contact interactions between such a probe and a 2D membrane are studied. As an example of the 2D materials, we consider a graphene crystal monolayer whose discrete structure is modelled as a 2D isotropic elastic membrane. Initially, for contact between a punch and the stretched circular membrane, we formulate and solve problems that are analogies to the Hertz-type and Boussinesq frictionless contact problems. A general statement for the slope of the force-displacement curve is formulated and proved. Then analogies to the JKR (Johnson, Kendall and Roberts) and the Boussinesq-Kendall contact problems in the presence of adhesive interactions are formulated. General nonlinear relations among the actual force, displacements and contact radius between a sticky membrane and an arbitrary axisymmetric indenter are derived. The dimensionless form of the equations for power-law shaped indenters has been analysed, and the explicit expressions are derived for the values of the pull-off force and corresponding critical contact radius.
Galanov, Boris A.
2016-01-01
Contact probing is the preferable method for studying mechanical properties of thin two-dimensional (2D) materials. These studies are based on analysis of experimental force–displacement curves obtained by loading of a stretched membrane by a probe of an atomic force microscope or a nanoindenter. Both non-adhesive and adhesive contact interactions between such a probe and a 2D membrane are studied. As an example of the 2D materials, we consider a graphene crystal monolayer whose discrete structure is modelled as a 2D isotropic elastic membrane. Initially, for contact between a punch and the stretched circular membrane, we formulate and solve problems that are analogies to the Hertz-type and Boussinesq frictionless contact problems. A general statement for the slope of the force–displacement curve is formulated and proved. Then analogies to the JKR (Johnson, Kendall and Roberts) and the Boussinesq–Kendall contact problems in the presence of adhesive interactions are formulated. General nonlinear relations among the actual force, displacements and contact radius between a sticky membrane and an arbitrary axisymmetric indenter are derived. The dimensionless form of the equations for power-law shaped indenters has been analysed, and the explicit expressions are derived for the values of the pull-off force and corresponding critical contact radius. PMID:27956879
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 magnetohydrodynamic studies of implosion modes of nested wire array z-pinches
Huang, Jun; Ding, Ning Xue, Chuang; Sun, Shunkai
2014-07-15
Implosion dynamics of nested wire arrays in (r, θ) geometry was studied with two-dimensional magnetohydrodynamic (2D MHD) simulations. Three different implosion modes are obtained by just changing the wire number of the outer array, when the other conditions, such as the initial radius, length, mass of each array, the wire number of the inner array, and the discharge voltage waveform, are fixed. Simulation results show that the effect of discrete wires, which cannot be described by the thin shell inductive model, will influence the distribution of current between the outer and inner arrays at the early stage, and the discrepancy between results from MHD and thin shell model increases with the interwire gap of the outer array.
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.
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.
Emergent elemental two-dimensional materials beyond graphene
NASA Astrophysics Data System (ADS)
Zhang, Yuanbo; Rubio, Angel; Le Lay, Guy
2017-02-01
Two-dimensional (2D) materials may offer the ultimate scaling beyond the 5 nm gate length. The difficulty of reliably opening a band gap in graphene has led to the search for alternative, semiconducting 2D materials. Emerging classes of elemental 2D materials stand out for their compatibility with existing technologies and/or for their diverse, tunable electronic structures. Among this group, black phosphorene has recently shown superior semiconductor performances. Silicene and germanene feature Dirac-type band dispersions, much like graphene. Calculations show that most group IV and group V elements have one or more stable 2D allotropes, with properties potentially suitable for electronic and optoelectronic applications. Here, we review the advances in these fascinating elemental 2D materials and discuss progress and challenges in their applications in future opto- and nano-electronic devices.
Vibrational Properties of a Two-Dimensional Silica Kagome Lattice
2016-01-01
Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two-dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon–phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2. PMID:28024359
Vibrational Properties of a Two-Dimensional Silica Kagome Lattice.
Björkman, Torbjörn; Skakalova, Viera; Kurasch, Simon; Kaiser, Ute; Meyer, Jannik C; Smet, Jurgen H; Krasheninnikov, Arkady V
2016-12-27
Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two-dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon-phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2.
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.
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.
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.
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.
Two-dimensional dynamic fluid bowtie attenuators
Hermus, James R.; Szczykutowicz, Timothy P.
2016-01-01
Abstract. 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
Two-dimensional wavelength demultiplexing employing multilevel arrayed waveguides.
Yang, Jianyi; Jiang, Xiaoqing; Wang, Minghua; Wang, Yuelin
2004-03-22
Two-dimensional (2D) optical wavelength demultiplexing is demonstrated by employing multilevel arrayed waveguides as a 2D diffraction grating, named the 2D arrayed waveguide grating (2D-AWG). Since the monochromatic lightwave is diffracted by the 2D-AWG to a series of periodic spots with 2D diffraction orders in both x and y directions while the dispersion direction is never parallel to the x or y direction, we can obtain 2D wavelength demultiplexing exploiting diffraction orders of either the x or y direction. One of the two dispersion components is designed much larger than the other, and the correspondent spatial free spectral range component is set properly to ensure high diffraction efficiency. The input and output ports can also be designed based on the multilevel lightwave circuit (MLC), and their level planes can be tuned parallel to that of the MLC-based 2D-AWG, which makes it feasible to integrate the 2D-AWG with the input port and/or the output port. It provides a promising way to realize large-scale and high-density optical multiplexers/demultiplexers.
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.
Two-dimensional convective turbulence
Gruzinov, A.V.; Kukharkin, N.; Sudan, R.N.
1996-02-01
We show that 2D {bold E{times}B} ionospheric turbulence of the electron density in the equatorial electrojet is isomorphic to the viscous convection of an ordinary fluid in a porous medium due to temperature gradients. Numerical simulations reveal the strong anisotropy in the turbulence, which consists of rising hot bubbles and falling cool bubbles. These bubbles break up into fingers leading to the formation of stable shear flows. After reaching a quasisteady state, the omnidirectional energy spectrum approaches a {ital k}{sup {minus}2} behavior, rather than {ital k}{sup {minus}5/3} as expected from isotropic turbulence. Physical mechanisms that lead to anisotropy are analyzed. {copyright} {ital 1996 The American Physical Society.}
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.
Two-Dimensional Simulation of Truckee River Hydrodynamics
2006-09-01
ANALYSIS: The Truckee River originates from Lake Tahoe , flowing 140 miles (225 km) through Reno, NV, to Pyramid Lake . The downstream boundary of the...riverine restoration design. A two-dimensional (2-D) hydrodynamic model was applied to the McCarran Ranch reach of the Truckee River to evaluate...existing condition and future restoration plan condition hydraulics. The impact of the restoration design is presented in terms of the difference in the
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.
Femtosecond phase-coherent two-dimensional spectroscopy.
Tian, Peifang; Keusters, Dorine; Suzaki, Yoshifumi; Warren, Warren S
2003-06-06
Femtosecond phase-coherent two-dimensional (2D) spectroscopy has been experimentally demonstrated as the direct optical analog of 2D nuclear magnetic resonance. An acousto-optic pulse shaper created a collinear three-pulse sequence with well-controlled and variable interpulse delays and phases,which interacted with a model atomic system of rubidium vapor. The desired nonlinear polarization was selected by phase cycling (coadding experimental results obtained with different interpulse phases). This method may enhance our ability to probe the femtosecond structural dynamics of macromolecules.
High-Tc superconductors in the two-dimensional limit:
Choy; Kwon; Park
1998-06-05
The free modulation of interlayer distance in a layered high-transition temperature (high-Tc) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-Tc superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-Tc cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-Tc superconductivity.
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.
Two-dimensional assemblies from crystallizable homopolymers with charged termini.
He, Xiaoming; Hsiao, Ming-Siao; Boott, Charlotte E; Harniman, Robert L; Nazemi, Ali; Li, Xiaoyu; Winnik, Mitchell A; Manners, Ian
2017-04-01
The creation of shaped, uniform and colloidally stable two-dimensional (2D) assemblies by bottom-up methods represents a challenge of widespread current interest for a variety of applications. Herein, we describe the utilization of surface charge to stabilize self-assembled planar structures that are formed from crystallizable polymer precursors by a seeded growth approach. Addition of crystallizable homopolymers with charged end-groups to seeds generated by the sonication of block copolymer micelles with crystalline cores yields uniform platelet micelles with controlled dimensions. Significantly, the seeded growth approach is characterized by a morphological memory effect whereby the origin of the seed, which can involve a quasi-hexagonal or rectangular 2D platelet precursor, dictates the observed 2D platelet shape. This new strategy is illustrated using two different polymer systems, and opens the door to the construction of 2D hierarchical structures with broad utility.
Proposed two-dimensional topological insulator in SiTe
NASA Astrophysics Data System (ADS)
Ma, Yandong; Kou, Liangzhi; Dai, Ying; Heine, Thomas
2016-11-01
The two-dimensional (2D) crystal SiTe is identified to be a 2D topological insulator (TI) with bulk band gap of 220 meV by means of first-principles calculations. The synthesis of 2D SiTe has been reported earlier [Phys. Status Solidi RRL 8, 302 (2014), 10.1002/pssr.201409013] as part of a three-dimensional superlattice. The freestanding monolayer is thermally and dynamically stable and only weakly bound within the layered superlattice, offering the possibility of mechanical exfoliation. Our discovery of a topological signature with large band gap raises the expectation that the most apparent showstopper in experimental 2D TI research, the lack of stable materials exposing a quantum spin Hall effect at room temperature, can be overcome. This offers many laboratories an opportunity to participate in investigating exciting new phenomena in condensed matter physics, such as new quasiparticles and dissipationless spin transport.
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.
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.
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
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. 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.
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
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.
Two-dimensional gallium nitride realized via graphene encapsulation
NASA Astrophysics Data System (ADS)
Al Balushi, Zakaria Y.; Wang, Ke; Ghosh, Ram Krishna; Vilá, Rafael A.; Eichfeld, Sarah M.; Caldwell, Joshua D.; Qin, Xiaoye; Lin, Yu-Chuan; Desario, Paul A.; Stone, Greg; Subramanian, Shruti; Paul, Dennis F.; Wallace, Robert M.; Datta, Suman; Redwing, Joan M.; Robinson, Joshua A.
2016-11-01
The spectrum of two-dimensional (2D) and layered materials `beyond graphene’ offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (~5.0-6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices. A gap, however, remains between the theoretical prediction of 2D nitrides `beyond hBN’ and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.
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.
Two-dimensional Brownian vortices
NASA Astrophysics Data System (ADS)
Chavanis, Pierre-Henri
2008-12-01
We introduce a stochastic model of 2D Brownian vortices associated with the canonical ensemble. The point vortices evolve through their usual mutual advection but they experience in addition a random velocity and a systematic drift generated by the system as a whole. The statistical equilibrium state of this stochastic model is the Gibbs canonical distribution. We consider a single species system and a system made of two types of vortices with positive and negative circulations. At positive temperatures, like-sign vortices repel each other (“plasma” case) and at negative temperatures, like-sign vortices attract each other (“gravity” case). We derive the stochastic equation satisfied by the exact vorticity field and the Fokker-Planck equation satisfied by the N-body distribution function. We present the BBGKY-like hierarchy of equations satisfied by the reduced distribution functions and close the hierarchy by considering an expansion of the solutions in powers of 1/N, where N is the number of vortices, in a proper thermodynamic limit. For spatially inhomogeneous systems, we derive the kinetic equations satisfied by the smooth vorticity field in a mean field approximation valid for N→+∞. For spatially homogeneous systems, we study the two-body correlation function, in a Debye-Hückel approximation valid at the order O(1/N). The results of this paper can also apply to other systems of random walkers with long-range interactions such as self-gravitating Brownian particles and bacterial populations experiencing chemotaxis. Furthermore, for positive temperatures, our study provides a kinetic derivation, from microscopic stochastic processes, of the Debye-Hückel model of electrolytes.
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.
Two-dimensional treatment of the level shift and decay rate in photonic crystals
NASA Astrophysics Data System (ADS)
Fussell, D. P.; McPhedran, R. C.; Martijn de Sterke, C.
2005-10-01
We present a comprehensive treatment of the level shift and decay rate of a model line source in a two-dimensional photonic crystal (2D PC) composed of circular cylinders. The quantities in this strictly two-dimensional system are determined by the two-dimensional local density of states (2D LDOS), which we compute using Rayleigh-multipole methods. We extend the critical point analysis that is traditionally applied to the 2D DOS (or decay rate) to the level shift. With this, we unify the crucial quantity for experiment—the 2D LDOS in a finite PC—with the band structure and the 2D DOS, 2D LDOS, and level shift in infinite PC’s. Consistent with critical point analysis, large variations in the level shift are associated with large variations in the 2D DOS (and 2D LDOS), corroborating a giant anomalous Lamb shift. The boundary of a finite 2D PC can produce resonances that cause the 2D LDOS in a finite 2D PC to differ markedly from the 2D LDOS in an infinite 2D PC.
Two-dimensional treatment of the level shift and decay rate in photonic crystals
Fussell, D.P.; McPhedran, R.C.; Martijn de Sterke, C.
2005-10-01
We present a comprehensive treatment of the level shift and decay rate of a model line source in a two-dimensional photonic crystal (2D PC) composed of circular cylinders. The quantities in this strictly two-dimensional system are determined by the two-dimensional local density of states (2D LDOS), which we compute using Rayleigh-multipole methods. We extend the critical point analysis that is traditionally applied to the 2D DOS (or decay rate) to the level shift. With this, we unify the crucial quantity for experiment - the 2D LDOS in a finite PC - with the band structure and the 2D DOS, 2D LDOS, and level shift in infinite PC's. Consistent with critical point analysis, large variations in the level shift are associated with large variations in the 2D DOS (and 2D LDOS), corroborating a giant anomalous Lamb shift. The boundary of a finite 2D PC can produce resonances that cause the 2D LDOS in a finite 2D PC to differ markedly from the 2D LDOS in an infinite 2D PC.
Two-dimensional treatment of the level shift and decay rate in photonic crystals.
Fussell, D P; McPhedran, R C; Martijn de Sterke, C
2005-10-01
We present a comprehensive treatment of the level shift and decay rate of a model line source in a two-dimensional photonic crystal (2D PC) composed of circular cylinders. The quantities in this strictly two-dimensional system are determined by the two-dimensional local density of states (2D LDOS), which we compute using Rayleigh-multipole methods. We extend the critical point analysis that is traditionally applied to the 2D DOS (or decay rate) to the level shift. With this, we unify the crucial quantity for experiment--the 2D LDOS in a finite PC--with the band structure and the 2D DOS, 2D LDOS, and level shift in infinite PC's. Consistent with critical point analysis, large variations in the level shift are associated with large variations in the 2D DOS (and 2D LDOS), corroborating a giant anomalous Lamb shift. The boundary of a finite 2D PC can produce resonances that cause the 2D LDOS in a finite 2D PC to differ markedly from the 2D LDOS in an infinite 2D PC.
Hur, Jin; Jung, Ka-Young; Jung, Young Mee
2011-04-01
The spectral responses of a leaf litter derived humic substance (LLHS) and Suwannee River fulvic acid (SRFA) upon ultraviolet (UV) A irradiation were characterized using two-dimensional correlation spectroscopy (2D-COS) based on the absorption and the synchronous fluorescence spectra at different irradiation times. A 12 day irradiation on the humic substances (HS) resulted in higher reduction of the absorbance relative to the dissolved organic carbon concentration, suggesting that aromatic chromophores were preferentially oxidized and/or non UV-absorbing compounds were generated by the photobleaching. Synchronous fluorescence spectra revealed the preferential removal of fulvic-like and humic-like fluorophores and delayed response of protein-like fluorescence upon the irradiation. The spectral features at long wavelengths (>430 nm) appear to be affected by intra-molecular interactions of the individual chromophores associated with shorter wavelengths. Absorption-based 2D-COS demonstrated that there are three types of absorption bands for the two HS, which changed sequentially in the order of 290-400 nm → 200-250 nm → 250-290 nm. In addition, two or three distinctive fluorescence bands in response to the irradiation were identified from 2D-COS. The sequential orders and the associated wavelength bands were possibly explained by the irradiation wavelengths and the differences between direct and indirect photochemical reactions. The interpretation of the 2D-COS results was very consistent with the kinetic rate constants individually calculated at several discrete wavelengths. Our study demonstrated that 2D-COS could be used as a powerful tool in identifying distinctive bands of HS that have dissimilar behavior and the associated sequential orders by visualizing the spectral changes at continuous wavelengths.
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.
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…
Electronic transport in two-dimensional high dielectric constant nanosystems
Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; Baturina, T. I.
2015-01-01
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. PMID:25860804
Electronic transport in two-dimensional high dielectric constant nanosystems
Ortuño, M.; Somoza, A. M.; Vinokur, V. M.; ...
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
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.
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.
Interaction of two-dimensional magnetoexcitons
NASA Astrophysics Data System (ADS)
Dumanov, E. V.; Podlesny, I. V.; Moskalenko, S. A.; Liberman, M. A.
2017-04-01
We study interaction of the two-dimensional magnetoexcitons with in-plane wave vector k→∥ = 0 , taking into account the influence of the excited Landau levels (ELLs) and of the external electric field perpendicular to the surface of the quantum well and parallel to the external magnetic field. It is shown that the account of the ELLs gives rise to the repulsion between the spinless magnetoexcitons with k→∥ = 0 in the Fock approximation, with the interaction constant g decreasing inverse proportional to the magnetic field strength B (g (0) ∼ 1 / B) . In the presence of the perpendicular electric field the Rashba spin-orbit coupling (RSOC), Zeeman splitting (ZS) and nonparabolicity of the heavy-hole dispersion law affect the Landau quantization of the electrons and holes. They move along the new cyclotron orbits, change their Coulomb interactions and cause the interaction between 2D magnetoexcitons with k→∥ = 0 . The changes of the Coulomb interactions caused by the electrons and by the holes moving with new cyclotron orbits are characterized by some coefficients, which in the absence of the electric field turn to be unity. The differences between these coefficients of the electron-hole pairs forming the magnetoexcitons determine their affinities to the interactions. The interactions between the homogeneous, semihomogeneous and heterogeneous magnetoexcitons forming the symmetric states with the same signs of their affinities are attractive whereas in the case of different sign affinities are repulsive. In the heterogeneous asymmetric states the interactions have opposite signs in comparison with the symmetric states. In all these cases the interaction constant g have the dependence g (0) 1 /√{ B} .
Linkage analysis by two-dimensional DNA typing
Meerman, G.J. te; Meulen, M.A. van der ); Mullaart, E.; Morolli, B.; Uitterlinden, A.G. ); Daas, J.H.G. den ); Vijg, J. Beth Israel Hospital, Boston, MA )
1993-12-01
In two-dimensional (2-D) DNA typing, genomic DNA fragments are separated, first according to size by electrophoresis in a neutral polyacrylamide gel and second according to sequence by denaturing gradient gel electrophoresis, followed by hybridization analysis using micro- and minisatellite core probes. The 2-D DNA typing method generates a large amount of information on polymorphic loci per gel. Here, the authors demonstrate the potential usefulness of 2-D DNA typing in an empirical linkage study on the red factor in cattle, and the authors show an example of the 2-D DNA typing analysis of a human pedigree. The power efficiency of 2-D DNA typing in general is compared with that of single-locus typing by simulation. The results indicate that, although 2-D DNA typing is very efficient in generating data on polymorphic loci, its power to detect linkage is lower than single-locus typing, because it is not obvious whether a spot represents the presence of one or two alleles. It is possible to compensate for this lower informativeness by increasing the sample size. Genome scanning by 2-D DNA typing has the potential to be more efficient than current genotyping methods in scoring polymorphic loci. Hence, it could become a method of choice in mapping genetic traits in humans and animals. 13 refs., 5 figs., 4 tabs.
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.
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.
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
Two-dimensional electronic spectroscopy of molecular excitons.
Milota, Franz; Sperling, Jaroslaw; Nemeth, Alexandra; Mancal, Tomás; Kauffmann, Harald F
2009-09-15
Understanding of the nuclear and electronic structure and dynamics of molecular systems has advanced considerably through probing the nonlinear response of molecules to sequences of pulsed electromagnetic fields. The ability to control various degrees of freedom of the excitation pulses-such as duration, sequence, frequency, polarization, and shape-has led to a variety of time-resolved spectroscopic methods. The various techniques that researchers use are commonly classified by their dimensionality, which refers to the number of independently variable time delays between the pulsed fields that induce the signal. Though pico- and femtosecond time-resolved spectroscopies of electronic transitions have come of age, only recently have researchers been able to perform two-dimensional electronic spectroscopy (2D-ES) in the visible frequency regime and correlate transition frequencies that evolve in different time intervals. The two-dimensional correlation plots and their temporal evolution allow one to access spectral information that is not exposed directly in other one-dimensional nonlinear methods. In this Account, we summarize our studies of a series of increasingly complex molecular chromophores. We examine noninteracting dye molecules, a monomer-dimer equilibrium of a prototypical dye molecule, and finally a supramolecular assembly of electronically coupled absorbers. By tracing vibronic signal modulations, differentiating line-broadening mechanisms, analyzing distinctly different relaxation dynamics, determining electronic coupling strengths, and directly following excitation energy transfer pathways, we illustrate how two-dimensional electronic spectroscopy can image physical phenomena that underlie the optical response of a particular system. Although 2D-ES is far from being a "turn-key" method, we expect that experimental progress and potential commercialization of instrumentation will make 2D-ES accessible to a much broader scientific audience, analogous to
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.
A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy
NASA Astrophysics Data System (ADS)
El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens
2015-08-01
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.
Two-dimensional optical splitters with polymer optical fibre arrays
NASA Astrophysics Data System (ADS)
Wen, Fung Jacky; Sheun Chung, Po
2007-07-01
A novel approach for optical beam distribution into two-dimensional (2D) fibre arrays using 2D Dammann gratings is investigated. We report for the first time experimental results of a 2D optical power distribution into 2 × 2 polymer optical fibre arrays using a Dammann grating. This paper focuses on the design and fabrication of the diffractive optical element (DOE) along with investigating the coupling performance of the system. This grating may be applicable to a fibre to the home (FTTH) network as it can support sufficient channels with good output uniformity together with low polarization-dependent loss (PDL). Using an appropriate optimization algorithm, the optimum profile for the Dammann gratings can be calculated. The gratings are then fabricated on indium-doped tin oxide (ITO) glass using electron-beam lithography. This method shows that it can achieve low PDL and good uniformity together with acceptable insertion loss.
Separation of colloidal two dimensional materials by density gradient ultracentrifugation
NASA Astrophysics Data System (ADS)
Kuang, Yun; Song, Sha; Huang, Jinyang; Sun, Xiaoming
2015-04-01
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.
Adsorption of C20 on two-dimensional materials
NASA Astrophysics Data System (ADS)
Hussain, M. B.; Xu, L. H.; Xu, Y. X.; Wu, S. Q.; Zhu, Z. Z.
2017-03-01
We considered the geometric and electronic properties of C20 molecule adsorbed on various two-dimensional (2D) substrates surfaces, such as graphene, silicene, germanene, stanene, BN and MoS2 by using first-principles calculations based on the density functional theory. For each case, we have considered three adsorption configurations of C20 molecule, i.e. top-site (T), hallow-site (H) and bridge site (B), respectively. Our results show that C20's are strongly bound to silicene, germanene and stanene, however, the adsorbed C20 molecules have only weak interactions with graphene, BN and MoS2 substrates. Moreover, charge density plot implies substantial charge transfer taking place between the constituents of C20 and the substrate of silicene, germanene and stanene. Results indicate that the buckling structure of the 2D material plays important role in determining the reactivity of a 2D substrate.
A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy.
El Khoury, Youssef; Van Wilderen, Luuk J G W; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens
2015-08-01
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.
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.
An n-channel two-dimensional covalent organic framework.
Ding, Xuesong; Chen, Long; Honsho, Yoshihito; Feng, Xiao; Saengsawang, Oraphan; Guo, Jingdong; Saeki, Akinori; Seki, Shu; Irle, Stephan; Nagase, Shigeru; Parasuk, Vudhichai; Jiang, Donglin
2011-09-21
Co-condensation of metallophthalocyanine with an electron-deficient benzothiadiazole (BTDA) block leads to the formation of a two-dimensional covalent organic framework (2D-NiPc-BTDA COF) that assumes a belt shape and consists of AA stacking of 2D polymer sheets. Integration of BTDA blocks at the edges of a tetragonal metallophthalocyanine COF causes drastic changes in the carrier-transport mode and a switch from a hole-transporting skeleton to an electron-transporting framework. 2D-NiPc-BTDA COF exhibits broad and enhanced absorbance up to 1000 nm, shows panchromatic photoconductivity, is highly sensitive to near-infrared photons, and has excellent electron mobility as high as 0.6 cm(2) V(-1) s(-1).
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.
Quasi-two-dimensional Fermi gases at finite temperatures
NASA Astrophysics Data System (ADS)
Fischer, Andrea M.; Parish, Meera M.
2014-12-01
We consider a Fermi gas with short-range attractive interactions that is confined along one direction by a tight harmonic potential. For this quasi-two-dimensional (quasi-2D) Fermi gas, we compute the pressure equation of state, radiofrequency spectrum, and the superfluid critical temperature Tc using a mean-field theory that accounts for all the energy levels of the harmonic confinement. Our calculation for Tc provides a natural generalization of the Thouless criterion to the quasi-2D geometry, and it correctly reduces to the 3D expression derived from the local density approximation in the limit where the confinement frequency ωz→0 . Furthermore, our results suggest that Tc can be enhanced by relaxing the confinement and perturbing away from the 2D limit.
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.
Two-dimensional fluorescence spectroscopy for application in biotechnology
NASA Astrophysics Data System (ADS)
Lindemann, Carsten; Marose, S.; Scheper, Thomas-Helmut; Nielsen, Hans O.; Hitzmann, Bernd; Belgardt, K.-H.
1999-02-01
A wide range of excitation and emission wavelengths is measured using the technique of two-dimensional (2D-) fluorescence spectroscopy. In a single, so called, two- dimensional fluorescence spectrum several biogenic fluorophors like proteins, vitamins and coenzymes can be detected simultaneously. This can give important information for bioprocess monitoring and control. An optical sensor (BioViewR) for on line fluorescence measurements at industrial (bio)-processes was used to get the results presented in this paper. This BioViewR-sensor is optimized to work in the harsh environment of production sites in biotechnological industry and -- using an optical light guide system with open-end detection -- it is very well suited for in vivo measurements, because it is non-invasive and the on line data can be performed in-situ.
Two-dimensional Raman-terahertz spectroscopy of water
Savolainen, Janne; Ahmed, Saima; Hamm, Peter
2013-01-01
Two-dimensional Raman-terahertz (THz) spectroscopy is presented as a multidimensional spectroscopy directly in the far-IR regime. The method is used to explore the dynamics of the collective intermolecular modes of liquid water at ambient temperatures that emerge from the hydrogen-bond networks water forming. Two-dimensional Raman-THz spectroscopy interrogates these modes twice and as such can elucidate couplings and inhomogeneities of the various degrees of freedoms. An echo in the 2D Raman-THz response is indeed identified, indicating that a heterogeneous distribution of hydrogen-bond networks exists, albeit only on a very short 100-fs timescale. This timescale appears to be too short to be compatible with more extended, persistent structures assumed within a two-state model of water. PMID:24297930
Extension of modified power method to two-dimensional problems
Zhang, Peng; Lee, Hyunsuk; Lee, Deokjung
2016-09-01
In this study, the generalized modified power method was extended to two-dimensional problems. A direct application of the method to two-dimensional problems was shown to be unstable when the number of requested eigenmodes is larger than a certain problem dependent number. The root cause of this instability has been identified as the degeneracy of the transfer matrix. In order to resolve this instability, the number of sub-regions for the transfer matrix was increased to be larger than the number of requested eigenmodes; and a new transfer matrix was introduced accordingly which can be calculated by the least square method. The stability of the new method has been successfully demonstrated with a neutron diffusion eigenvalue problem and the 2D C5G7 benchmark problem. - Graphical abstract:.
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 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.
Face recognition based on the band fusion of generalized phase spectrum of 2D-FrFT
NASA Astrophysics Data System (ADS)
Wang, Xu; Qi, Lin; Tie, Yun; Chen, Enqing; Sun, Huijing
2017-02-01
In this paper, we propose a novel feature extraction method for face recognition based on two dimensional fractional Fourier transform (2D-FrFT). First, we extract the phase information of facial image in 2D-FrFT, which is called the generalized phase spectra (GPS). Then, we present an improved two-dimensional separability judgment (I2DSJ) to select appropriate order parameters for discrete fractional Fourier transform. Finally, multiple orders' generalized phase spectrum bands (MGPSB) fusion is proposed. In order to make full use of the discriminative information from different orders for face recognition, the proposed approach merges different orders' generalized phase spectra (GPS) of 2D-FrFT. The proposed method is no need to construct the subspace through the feature extraction methods and has less computation cost. Experimental results on the public face databases demonstrate that our method outperforms the representative methods.
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.
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.
Two-dimensional correlation analysis of near-infrared spectral intensity variations of ground wheat
Technology Transfer Automated Retrieval System (TEKTRAN)
Generalized two-dimensional (2D) correlation analysis was applied to characterize the NIR spectral intensity fluctuations among many spectra of ground wheat with multi-variable variations. Prior to 2D analysis, the spectra having neighboring protein / SDSS reference values were averaged and then new...
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…
Two-dimensional multiferroics in monolayer group IV monochalcogenides
NASA Astrophysics Data System (ADS)
Wang, Hua; Qian, Xiaofeng
2017-03-01
Low-dimensional multiferroic materials hold great promises in miniaturized device applications such as nanoscale transducers, actuators, sensors, photovoltaics, and nonvolatile memories. Here, using first-principles theory we predict that two-dimensional (2D) monolayer group IV monochalcogenides including GeS, GeSe, SnS, and SnSe are a class of 2D semiconducting multiferroics with giant strongly-coupled in-plane spontaneous ferroelectric polarization and spontaneous ferroelastic lattice strain that are thermodynamically stable at room temperature and beyond, and can be effectively modulated by elastic strain engineering. Their optical absorption spectra exhibit strong in-plane anisotropy with visible-spectrum excitonic gaps and sizable exciton binding energies, rendering the unique characteristics of low-dimensional semiconductors. More importantly, the predicted low domain wall energy and small migration barrier together with the coupled multiferroic order and anisotropic electronic structures suggest their great potentials for tunable multiferroic functional devices by manipulating external electrical, mechanical, and optical field to control the internal responses, and enable the development of four device concepts including 2D ferroelectric memory, 2D ferroelastic memory, and 2D ferroelastoelectric nonvolatile photonic memory as well as 2D ferroelectric excitonic photovoltaics.
First-Principles Predication of Two-Dimensional Electrides
NASA Astrophysics Data System (ADS)
Ming, Wenmei; Yoon, Mina
Two-dimensional (2D) electrides have recently received increasing interest due to its promise for electron emitter, surface catalyst and high-mobility electronic devices. However, they are very limited in a few layered alkaline-earth nitrides and rare-earth carbides. Here, we extend the possibility of 2D electrides by structure predication, using density functional theory calculation in conjunction with particle swarm optimization algorithm. Simple-element compounds A2B (A/B = alkali metals/halogen, or A/B = alkaline-earth metals/VA, VIA, VIIA nonmetals) and AB (A/B = alkaline-earth metals/halogen), which have nominal imbalanced oxidation numbers, were investigated. We find several new 2D electrides out of 90 candidates, and uncover that the stabilization of the 2D layered structure, which is required for the success of 2D electrides, strongly depends on the relative size of cation, in such a way that it has to be of similar or larger size than the anion in order to sufficiently screen the repulsion between the excess electrons and anions. We additionally identify the experimental conditions of temperature and chemical potential where the predicted 2D electrides are stabilized against the decomposition into compounds with balanced oxidation numbers. Funding support from LDRD program at ORNL.
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.
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.
Soluble, Exfoliated Two-Dimensional Nanosheets as Excellent Aqueous Lubricants.
Zhang, Wenling; Cao, Yanlin; Tian, Pengyi; Guo, Fei; Tian, Yu; Zheng, Wen; Ji, Xuqiang; Liu, Jingquan
2016-11-30
Dispersion in water of two-dimensional (2D) nanosheets is conducive to their practical applications in fundamental science communities due to their abundance, low cost, and ecofriendliness. However, it is difficult to achieve stable aqueous 2D material suspensions because of the intrinsic hydrophobic properties of the layered materials. Here, we report an effective and economic way of producing various 2D nanosheets (h-BN, MoS2, MoSe2, WS2, and graphene) as aqueous dispersions using carbon quantum dots (CQDs) as exfoliation agents and stabilizers. The dispersion was prepared through a liquid phase exfoliation. The as-synthesized stable 2D nanosheets based dispersions were characterized by UV-vis, HRTEM, AFM, Raman, XPS, and XRD. The solutions based on CQD decorated 2D nanosheets were utilized as aqueous lubricants, which realized a friction coefficient as low as 0.02 and even achieved a superlubricity under certain working conditions. The excellent lubricating properties were attributed to the synergetic effects of the 2D nanosheets and CQDs, such as good dispersion stability and easy-sliding interlayer structure. This work thus proposes a novel strategy for the design and preparation of high-performance water based green lubricants.
Two-dimensional generalized Toda lattice
NASA Astrophysics Data System (ADS)
Mikhailov, A. V.; Olshanetsky, M. A.; Perelomov, A. M.
1981-12-01
The zero curvature representation is obtained for the two-dimensional generalized Toda lattices connected with semisimple Lie algebras. The reduction group and conservation laws are found and the mass spectrum is calculated.
Two-dimensional function photonic crystals
NASA Astrophysics Data System (ADS)
Liu, Xiao-Jing; Liang, Yu; Ma, Ji; Zhang, Si-Qi; Li, Hong; Wu, Xiang-Yao; Wu, Yi-Heng
2017-01-01
In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.
Two Dimensional Plasmonic Cavities on Moire Surfaces
NASA Astrophysics Data System (ADS)
Balci, Sinan; Kocabas, Askin; Karabiyik, Mustafa; Kocabas, Coskun; Aydinli, Atilla
2010-03-01
We investigate surface plasmon polariton (SPP) cavitiy modes on two dimensional Moire surfaces in the visible spectrum. Two dimensional hexagonal Moire surface can be recorded on a photoresist layer using Interference lithography (IL). Two sequential exposures at slightly different angles in IL generate one dimensional Moire surfaces. Further sequential exposure for the same sample at slightly different angles after turning the sample 60 degrees around its own axis generates two dimensional hexagonal Moire cavity. Spectroscopic reflection measurements have shown plasmonic band gaps and cavity states at all the azimuthal angles (omnidirectional cavity and band gap formation) investigated. The plasmonic band gap edge and the cavity states energies show six fold symmetry on the two dimensional Moire surface as measured in reflection measurements.
Two-dimensional 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.
Dissipative vortex solitons in two-dimensional lattices
Mejia-Cortes, C.; Soto-Crespo, J. M.; Molina, Mario I.; Vicencio, Rodrigo A.
2010-12-15
We report the existence of stable symmetric vortex-type solutions for two-dimensional nonlinear discrete dissipative systems governed by a cubic-quintic complex Ginzburg-Landau equation. We construct a whole family of vortex solitons with a topological charge S=1. Surprisingly, the dynamical evolution of unstable solutions of this family does not significantly alter their profile, but instead their phase distribution completely changes; they transform into two-charge swirl-vortex solitons. We dynamically excite this structure showing its experimental feasibility.
Magnetic quantum dot in two-dimensional topological insulators
NASA Astrophysics Data System (ADS)
Li, Guo; Zhu, Jia-Lin; Yang, Ning
2017-03-01
Magnetic quantum dots in two-dimensional band and topological insulators are studied by solving the modified Dirac model under nonuniform magnetic fields. The Landau levels split into discrete states with certain angular momentum. The states splitting from the zero Landau levels lie in the energy gap for topological insulators but are out of the gap for band insulators. It is found that the ground states oscillate between the spin-up and spin-down states when the magnetic field or the dot size changes. The oscillation manifests itself as changes of sign and strength of charge currents near the dot's edge.
Investigation of Membrane Peptides by Two-Dimensional Infrared Spectroscopy
NASA Astrophysics Data System (ADS)
Blanco, Emily Ann; Zanni, Martin T.
2009-06-01
Two-dimensional infrared spectroscopy (2D IR) is a useful tool for studying the structure of membrane peptides. Isotope labeling individual amino acids with 13C=18O decouples the isotope labeled amide I from the other amide I modes in the peptide. Work has been done on both the M2 ion channel and ovispirin antimicrobial peptide, studying the diagonal linewidths of the isotope labeled amide I. The diagonal linewidth of the isotope labeled amide I gives information about the local environment of that residue, which in turn gives structural information about the membrane peptide.
25th anniversary article: hybrid nanostructures based on two-dimensional nanomaterials.
Huang, Xiao; Tan, Chaoliang; Yin, Zongyou; Zhang, Hua
2014-04-09
Two-dimensional (2D) nanomaterials, such as graphene and transition metal dichalcogenides (TMDs), receive a lot of attention, because of their intriguing properties and wide applications in catalysis, energy-storage devices, electronics, optoelectronics, and so on. To further enhance the performance of their application, these 2D nanomaterials are hybridized with other functional nanostructures. In this review, the latest studies of 2D nanomaterial-based hybrid nanostructures are discussed, focusing on their preparation methods, properties, and applications.
Band alignment of two-dimensional lateral heterostructures
NASA Astrophysics Data System (ADS)
Zhang, Junfeng; Xie, Weiyu; Zhao, Jijun; Zhang, Shengbai
2017-03-01
Recent experimental synthesis of two-dimensional (2D) heterostructures opens a door to new opportunities in tailoring the electronic properties for novel 2D devices. Here, we show that a wide range of lateral 2D heterostructures could have a prominent advantage over the traditional three-dimensional (3D) heterostructures, because their band alignments are insensitive to the interfacial conditions. They should be at the Schottky-Mott limits for semiconductor-metal junctions and at the Anderson limits for semiconductor junctions, respectively. This fundamental difference from the 3D heterostructures is rooted in the fact that, in the asymptotic limit of large distance, the effect of the interfacial dipole vanishes for 2D systems. Due to the slow decay of the dipole field and the dependence on the vacuum thickness, however, studies based on first-principles calculations often failed to reach such a conclusion. Taking graphene/hexagonal-BN and MoS2/WS2 lateral heterostructures as the respective prototypes, we show that the converged junction width can be order of magnitude longer than that for 3D junctions. The present results provide vital guidance to high-quality transport devices wherever a lateral 2D heterostructure is involved.
Generalized non-separable two-dimensional Dammann encoding method
NASA Astrophysics Data System (ADS)
Yu, Junjie; Zhou, Changhe; Zhu, Linwei; Lu, Yancong; Wu, Jun; Jia, Wei
2017-01-01
We generalize for the first time, to the best of our knowledge, the Dammann encoding method into non-separable two-dimensional (2D) structures for designing various pure-phase Dammann encoding gratings (DEGs). For examples, three types of non-separable 2D DEGs, including non-separable binary Dammann vortex gratings, non-separable binary distorted Dammann gratings, and non-separable continuous-phase cubic gratings, are designed theoretically and demonstrated experimentally. Correspondingly, it is shown that 2D square arrays of optical vortices with topological charges proportional to the diffraction orders, focus spots shifting along both transversal and axial directions with equal spacings, and Airy-like beams with controllable orientation for each beam, are generated in symmetry or asymmetry by these three DEGs, respectively. Also, it is shown that a more complex-shaped array of modulated beams could be achieved by this non-separable 2D Dammann encoding method, which will be a big challenge for those conventional separable 2D Dammann encoding gratings. Furthermore, the diffractive efficiency of the gratings can be improved around ∼10% when the non-separable structure is applied, compared with their conventional separable counterparts. Such improvement in the efficiency should be of high significance for some specific applications.
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.
Two-dimensional topological insulators with large bulk energy gap
NASA Astrophysics Data System (ADS)
Yang, Z. Q.; Jia, Jin-Feng; Qian, Dong
2016-11-01
Two-dimensional (2D) topological insulators (TIs, or quantum spin Hall insulators) are special insulators that possess bulk 2D electronic energy gap and time-reversal symmetry protected one-dimensional (1D) edge state. Carriers in the edge state have the property of spin-momentum locking, enabling dissipation-free conduction along the 1D edge. The existence of 2D TIs was confirmed by experiments in semiconductor quantum wells. However, the 2D bulk gaps in those quantum wells are extremely small, greatly limiting potential application in future electronics and spintronics. Despite this limitation, 2D TIs with a large bulk gap attracted plenty of interest. In this paper, recent progress in searching for TIs with a large bulk gap is reviewed briefly. We start by introducing some theoretical predictions of these new materials and then discuss some recent important achievements in crystal growth and characterization. Project supported by the National Natural Science Foundation of China (Grant Nos. U1632272, 11574201, and 11521404). D. Q. acknowledges support from the Changjiang Scholars Program, China and the Program for Professor of Special Appointment (Eastern Scholar), China.
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.
a First Cryptosystem for Security of Two-Dimensional Data
NASA Astrophysics Data System (ADS)
Mishra, D. C.; Sharma, Himani; Sharma, R. K.; Kumar, Naveen
In this paper, we present a novel technique for security of two-dimensional data with the help of cryptography and steganography. The presented approach provides multilayered security of two-dimensional data. First layer security was developed by cryptography and second layer by steganography. The advantage of steganography is that the intended secret message does not attract attention to itself as an object of scrutiny. This paper proposes a novel approach for encryption and decryption of information in the form of Word Data (.doc file), PDF document (.pdf file), Text document, Gray-scale images, and RGB images, etc. by using Vigenere Cipher (VC) associated with Discrete Fourier Transform (DFT) and then hiding the data behind the RGB image (i.e. steganography). Earlier developed techniques provide security of either PDF data, doc data, text data or image data, but not for all types of two-dimensional data and existing techniques used either cryptography or steganography for security. But proposed approach is suitable for all types of data and designed for security of information by cryptography and steganography. The experimental results for Word Data, PDF document, Text document, Gray-scale images and RGB images support the robustness and appropriateness for secure transmission of these data. The security analysis shows that the presented technique is immune from cryptanalytic. This technique further provides security while decryption as a check on behind which RGB color the information is hidden.
Two-dimensional 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.
Two-dimensional graphitic carbon nitride nanosheets for biosensing applications.
Xiong, Mengyi; Rong, Qiming; Meng, Hong-Min; Zhang, Xiao-Bing
2017-03-15
Two-dimensional graphitic carbon nitride nanosheets (CNNSs) with planar graphene-like structure have stimulated increasingly research interest in recent years due to their unique physicochemical properties. CNNSs possess superior stability, high fluorescence quantum yield, low-toxicity, excellent biocompatibility, unique electroluminescent and photoelectrochemical properties, which make them appropriate candidates for biosensing. In this review, we first introduce the preparation and unique properties of CNNSs, with emphasis on their superior properties for biosensing. Then, recent advances of CNNSs in photoelectrochemical biosensing, electrochemiluminescence biosensing and fluorescence biosensing are highlighted. An additional attention is paid to the marriage of CNNSs and nucleic acids, which exhibits great potentials in both biosensing and intracellular imaging. Finally, current challenges and opportunities of this 2D material are outlined. Inspired by the unique properties of CNNSs and their advantages in biological applications, we expect that more attention will be drawn to this promising 2D material and extensive applications can be found in bioanalysis and diseases diagnosis.
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.
Two-Dimensional Hexagonal Transition-Metal Oxide for Spintronics.
Kan, Erjun; Li, Ming; Hu, Shuanglin; Xiao, Chuanyun; Xiang, Hongjun; Deng, Kaiming
2013-04-04
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.
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.
2015-01-01
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. PMID:24663470
Interferometric Diagnosis of Two-Dimensional Plasma Expansion
Smith, R F; Moon, S; Dunn, J; Nilsen, J; Shlyaptsev, V N; Hunter, J R; Rocca, J; Filevich, J; Marconi, M C
2002-07-31
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 within the plasma. In this paper we present experimentally measured density profiles from an Al plasma and make comparisons with 1.5-D and 2-D code simulations. The results are discussed along with an analysis of the underlying mechanisms driving the plasma expansion.
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 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.
Thermal conductivity of disordered two-dimensional binary alloys.
Zhou, Yang; Guo, Zhi-Xin; Cao, Hai-Yuan; Chen, Shi-You; Xiang, Hong-Jun; Gong, Xin-Gao
2016-10-20
Using non-equilibrium molecular dynamics simulations, we have studied the effect of disorder on the thermal conductivity of two-dimensional (2D) C1-xNx alloys. We find that the thermal conductivity not only depends on the substitution concentration of nitrogen, but also strongly depends on the disorder distribution. A general linear relationship is revealed between the thermal conductivity and the participation ratio of phonons in 2D alloys. Localization mode analysis further indicates that the thermal conductivity variation in the ordered alloys can be attributed to the number of inequivalent atoms. As for the disordered alloys, we find that the thermal conductivity variation can be described by a simple linear formula with the disorder degree and the substitution concentration. The present study suggests some general guidance for phonon manipulation and thermal engineering in low dimensional alloys.
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).
On final states of two-dimensional decaying turbulence
NASA Astrophysics Data System (ADS)
Yin, Z.
2004-12-01
Numerical and analytical studies of final states of two-dimensional (2D) decaying turbulence are carried out. The first part of this work is trying to give a definition for final states of 2D decaying turbulence. The functional relation of ω-ψ, which is frequently adopted as the characterization of those final states, is merely a sufficient but not necessary condition; moreover, it is not proper to use it as the definition. It is found that the method through the value of the effective area S covered by the scatter ω-ψ plot, initially suggested by Read, Rhines, and White ["Geostrophic scatter diagrams and potential vorticity dynamics," J. Atmos. Sci. 43, 3226 (1986)] is more general and suitable for the definition. Based on this concept, a definition is presented, which covers all existing results in late states of decaying 2D flows (including some previous unexplainable weird double-valued ω-ψ scatter plots). The remaining part of the paper is trying to further study 2D decaying turbulence with the assistance of this definition. Some numerical results, leading to "bar" final states and further verifying the predictive ability of statistical mechanics [Yin, Montgomery, and Clercx, "Alternative statistical-mechanical descriptions of decaying two-dimensional turbulence in terms of patches and points," Phys. Fluids 15, 1937 (2003)], are reported. It is realized that some simulations with narrow-band energy spectral initial conditions result in some final states that cannot be very well interpreted by the statistical theory (meanwhile, those final states are still in the scope of the definition).
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.
Materials synthesis: Two-dimensional gallium nitride
NASA Astrophysics Data System (ADS)
Koratkar, Nikhil A.
2016-11-01
Graphene is used as a capping sheet to synthesize 2D gallium nitride by means of migration-enhanced encapsulation growth. This technique may allow the stabilization of 2D materials that are not amenable to synthesis by traditional methods.
Mobility anisotropy of two-dimensional semiconductors
NASA Astrophysics Data System (ADS)
Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong
2016-12-01
The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.
MAGNUM2D. Radionuclide Transport Porous Media
Langford, D.W.; Baca, R.G.
1989-03-01
MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water/rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and interconnecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculations assume local thermodynamic equilibrium between the rock and groundwater, nonisothermal Darcian flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER postprocessor interpolates nonregularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH postprocessor plots flow paths and computes the corresponding travel times.
MAGNUM2D. Radionuclide Transport Porous Media
Langford, D.W.; Baca, R.G.
1988-08-01
MAGNUM2D was developed to analyze thermally driven fluid motion in the deep basalts below the Paco Basin at the Westinghouse Hanford Site. Has been used in the Basalt Waste Isolation Project to simulate nonisothermal groundwater flow in a heterogeneous anisotropic medium and heat transport in a water/rock system near a high level nuclear waste repository. Allows three representations of the hydrogeologic system: an equivalent porous continuum, a system of discrete, unfilled, and interconnecting fractures separated by impervious rock mass, and a low permeability porous continuum with several discrete, unfilled fractures traversing the medium. The calculation assumes local thermodynamic equilibrium between the rock and groundwater, nonisothermal Darcian flow in the continuum portions of the rock, and nonisothermal Poiseuille flow in discrete unfilled fractures. In addition, the code accounts for thermal loading within the elements, zero normal gradient and fixed boundary conditions for both temperature and hydraulic head, and simulation of the temperature and flow independently. The Q2DGEOM preprocessor was developed to generate, modify, plot and verify quadratic two dimensional finite element geometries. The BCGEN preprocessor generates the boundary conditions for head and temperature and ICGEN generates the initial conditions. The GRIDDER postprocessor interpolates nonregularly spaced nodal flow and temperature data onto a regular rectangular grid. CONTOUR plots and labels contour lines for a function of two variables and PARAM plots cross sections and time histories for a function of time and one or two spatial variables. NPRINT generates data tables that display the data along horizontal or vertical cross sections. VELPLT differentiates the hydraulic head and buoyancy data and plots the velocity vectors. The PATH postprocessor plots flow paths and computes the corresponding travel times.
Novel Two-Dimensional Silicon Dioxide with in-Plane Negative Poisson's Ratio.
Gao, Zhibin; Dong, Xiao; Li, Nianbei; Ren, Jie
2017-02-08
Silicon dioxide or silica, normally existing in various bulk crystalline and amorphous forms, was recently found to possess a two-dimensional structure. In this work, we use ab initio calculation and evolutionary algorithm to unveil three new two-dimensional (2D) silica structures whose thermal, dynamical, and mechanical stabilities are compared with many typical bulk silica. In particular, we find that all three of these 2D silica structures have large in-plane negative Poisson's ratios with the largest one being double of penta graphene and three times of borophenes. The negative Poisson's ratio originates from the interplay of lattice symmetry and Si-O tetrahedron symmetry. Slab silica is also an insulating 2D material with the highest electronic band gap (>7 eV) among reported 2D structures. These exotic 2D silica with in-plane negative Poisson's ratios and widest band gaps are expected to have great potential applications in nanomechanics and nanoelectronics.
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.
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…
New two dimensional compounds: beyond graphene
NASA Astrophysics Data System (ADS)
Lebegue, Sebastien
2015-03-01
In the field of nanosciences, the quest for materials with reduced dimensionality is only at its beginning. While a lot of effort has been put initially on graphene, the focus has been extended in the last past years to functionalized graphene, boron nitride, silicene, and transition metal dichalcogenides in the form of single layers. Although these two-dimensional compounds offer a larger range of properties than graphene, there is a constant need for new materials presenting equivalent or superior performances to the ones already known. Here I will present an approach that we have used to discover potential new two-dimensional materials. This approach corresponds to perform datamining in the Inorganic Crystal Structure Database using simple geometrical criterias, and allowed us to identify nearly 40 new materials that could be exfoliated into two-dimensional sheets. Then, their electronic structure (density of states and bandstructure) was obtained with density functional theory to predict whether the two-dimensional material is metallic or insulating, as well as if it undergoes magnetic ordering at low temperatures. If time allows, I will also present some of our recent results concerning the electronic structure of transition metal dichalcogenides bilayers.
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…
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; ...
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
Two-dimensional fluorescence intensity distribution analysis: theory and applications.
Kask, P; Palo, K; Fay, N; Brand, L; Mets, U; Ullmann, D; Jungmann, J; Pschorr, J; Gall, K
2000-04-01
A method of sample analysis is presented which is based on fitting a joint distribution of photon count numbers. In experiments, fluorescence from a microscopic volume containing a fluctuating number of molecules is monitored by two detectors, using a confocal microscope. The two detectors may have different polarizational or spectral responses. Concentrations of fluorescent species together with two specific brightness values per species are determined. The two-dimensional fluorescence intensity distribution analysis (2D-FIDA), if used with a polarization cube, is a tool that is able to distinguish fluorescent species with different specific polarization ratios. As an example of polarization studies by 2D-FIDA, binding of 5'-(6-carboxytetramethylrhodamine) (TAMRA)-labeled theophylline to an anti-theophylline antibody has been studied. Alternatively, if two-color equipment is used, 2D-FIDA can determine concentrations and specific brightness values of fluorescent species corresponding to individual labels alone and their complex. As an example of two-color 2D-FIDA, binding of TAMRA-labeled somatostatin-14 to the human type-2 high-affinity somatostatin receptors present in stained vesicles has been studied. The presented method is unusually accurate among fluorescence fluctuation methods. It is well suited for monitoring a variety of molecular interactions, including receptors and ligands or antibodies and antigens.
Photonics and optoelectronics of two-dimensional materials beyond graphene
NASA Astrophysics Data System (ADS)
Ponraj, Joice Sophia; Xu, Zai-Quan; Chander Dhanabalan, Sathish; Mu, Haoran; Wang, Yusheng; Yuan, Jian; Li, Pengfei; Thakur, Siddharatha; Ashrafi, Mursal; Mccoubrey, Kenneth; Zhang, Yupeng; Li, Shaojuan; Zhang, Han; Bao, Qiaoliang
2016-11-01
Apart from conventional materials, the study of two-dimensional (2D) materials has emerged as a significant field of study for a variety of applications. Graphene-like 2D materials are important elements of potential optoelectronics applications due to their exceptional electronic and optical properties. The processing of these materials towards the realization of devices has been one of the main motivations for the recent development of photonics and optoelectronics. The recent progress in photonic devices based on graphene-like 2D materials, especially topological insulators (TIs) and transition metal dichalcogenides (TMDs) with the methodology level discussions from the viewpoint of state-of-the-art designs in device geometry and materials are detailed in this review. We have started the article with an overview of the electronic properties and continued by highlighting their linear and nonlinear optical properties. The production of TIs and TMDs by different methods is detailed. The following main applications focused towards device fabrication are elaborated: (1) photodetectors, (2) photovoltaic devices, (3) light-emitting devices, (4) flexible devices and (5) laser applications. The possibility of employing these 2D materials in different fields is also suggested based on their properties in the prospective part. This review will not only greatly complement the detailed knowledge of the device physics of these materials, but also provide contemporary perception for the researchers who wish to consider these materials for various applications by following the path of graphene.
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
Line shape analysis of two-dimensional infrared spectra
Guo, Qi; Pagano, Philip; Li, Yun-Liang; Kohen, Amnon; Cheatum, Christopher M.
2015-01-01
Ultrafast two-dimensional infrared (2D IR) spectroscopy probes femtosecond to picosecond time scale dynamics ranging from solvation to protein motions. The frequency-frequency correlation function (FFCF) is the quantitative measure of the spectral diffusion that reports those dynamics and, within certain approximations, can be extracted directly from 2D IR line shapes. A variety of methods have been developed to extract the FFCF from 2D IR spectra, which, in principle, should give the same FFCF parameters, but the complexity of real experimental systems will affect the results of these analyses differently. Here, we compare five common analysis methods using both simulated and experimental 2D IR spectra to understand the effects of apodization, anharmonicity, phasing errors, and finite signal-to-noise ratios on the results of each of these analyses. Our results show that although all of the methods can, in principle, yield the FFCF under idealized circumstances, under more realistic experimental conditions they behave quite differently, and we find that the centerline slope analysis yields the best compromise between the effects we test and is most robust to the distortions that they cause. PMID:26049447
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.
Two dimensional electron spin resonance: Structure and dynamics of biomolecules
NASA Astrophysics Data System (ADS)
Saxena, Sunil; Freed, Jack H.
1998-03-01
The potential of two dimensional (2D) electron spin resonance (ESR) for measuring the structural properties and slow dynamics of labeled biomolecules will be presented. Specifically, it will be shown how the recently developed method of double quantum (DQ) 2D ESR (S. Saxena and J. H. Freed, J. Chem. Phys. 107), 1317, (1997) can be used to measure large interelectron distances in bilabeled peptides. The need for DQ ESR spectroscopy, as well as the challenges and advantages of this method will be discussed. The elucidation of the slow reorientational dynamics of this peptide (S. Saxena and J. H. Freed, J. Phys. Chem. A, 101) 7998 (1997) in a glassy medium using COSY and 2D ELDOR ESR spectroscopy will be demonstrated. The contributions to the homogeneous relaxation time, T_2, from the overall and/or internal rotations of the nitroxide can be distinguished from the COSY spectrum. The growth of spectral diffusion cross-peaks^2 with mixing time in the 2D ELDOR spectra can be used to directly determine a correlation time from the experiment which can be related to the rotational correlation time.
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.
Photonics and optoelectronics of two-dimensional materials beyond graphene.
Ponraj, Joice Sophia; Xu, Zai-Quan; Dhanabalan, Sathish Chander; Mu, Haoran; Wang, Yusheng; Yuan, Jian; Li, Pengfei; Thakur, Siddharatha; Ashrafi, Mursal; Mccoubrey, Kenneth; Zhang, Yupeng; Li, Shaojuan; Zhang, Han; Bao, Qiaoliang
2016-11-18
Apart from conventional materials, the study of two-dimensional (2D) materials has emerged as a significant field of study for a variety of applications. Graphene-like 2D materials are important elements of potential optoelectronics applications due to their exceptional electronic and optical properties. The processing of these materials towards the realization of devices has been one of the main motivations for the recent development of photonics and optoelectronics. The recent progress in photonic devices based on graphene-like 2D materials, especially topological insulators (TIs) and transition metal dichalcogenides (TMDs) with the methodology level discussions from the viewpoint of state-of-the-art designs in device geometry and materials are detailed in this review. We have started the article with an overview of the electronic properties and continued by highlighting their linear and nonlinear optical properties. The production of TIs and TMDs by different methods is detailed. The following main applications focused towards device fabrication are elaborated: (1) photodetectors, (2) photovoltaic devices, (3) light-emitting devices, (4) flexible devices and (5) laser applications. The possibility of employing these 2D materials in different fields is also suggested based on their properties in the prospective part. This review will not only greatly complement the detailed knowledge of the device physics of these materials, but also provide contemporary perception for the researchers who wish to consider these materials for various applications by following the path of graphene.
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.
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 material electronics and photonics (Presentation Recording)
NASA Astrophysics Data System (ADS)
Zhu, Wenjuan
2015-09-01
Two-dimensional (2D) materials has attracted intense interest in research in recent years. As compared to their bulk counterparts, these 2D materials have many unique properties due to their reduced dimensionality and symmetry. A key difference is the band structures, which lead to distinct electronic and photonic properties. The 2D nature of the materials also plays an important role in defining their exceptional properties of mechanical strength, surface sensitivity, thermal conductivity, tunable band-gap and interaction with light. These unique properties of 2D materials open up broad territories of applications in computing, communication, energy, and medicine. In this talk, I will present our work on understanding the electrical properties of graphene and MoS2, in particular current transport and band-gap engineering in graphene, interface between gate dielectrics and graphene, and gap states in MoS2. I will also present our work on the nano-scale electronic devices (RF and logic devices) and photonic devices (plasmonic devices and photo-detectors) based on graphene and transition metal dichalcogenides.
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.
Solution-Based Processing of Monodisperse Two-Dimensional Nanomaterials.
Kang, Joohoon; Sangwan, Vinod K; Wood, Joshua D; Hersam, Mark C
2017-02-27
Exfoliation of single-layer graphene from bulk graphite and the subsequent discovery of exotic physics and emergent phenomena in the atomically thin limit has motivated the isolation of other two-dimensional (2D) layered nanomaterials. Early work on isolated 2D nanomaterial flakes has revealed a broad range of unique physical and chemical properties with potential utility in diverse applications. For example, the electronic and optical properties of 2D nanomaterials depend strongly on atomic-scale variations in thickness, enabling enhanced performance in optoelectronic technologies such as light emitters, photodetectors, and photovoltaics. Much of the initial research on 2D nanomaterials has relied on micromechanical exfoliation, which yields high-quality 2D nanomaterial flakes that are suitable for fundamental studies but possesses limited scalability for real-world applications. In an effort to overcome this limitation, solution-processing methods for isolating large quantities of 2D nanomaterials have emerged. Importantly, solution processing results in 2D nanomaterial dispersions that are amenable to roll-to-roll fabrication methods that underlie lost-cost manufacturing of thin-film transistors, transparent conductors, energy storage devices, and solar cells. Despite these advantages, solution-based exfoliation methods typically lack control over the lateral size and thickness of the resulting 2D nanomaterial flakes, resulting in polydisperse dispersions with heterogeneous properties. Therefore, post-exfoliation separation techniques are needed to achieve 2D nanomaterial dispersions with monodispersity in lateral size, thickness, and properties. In this Account, we survey the latest developments in solution-based separation methods that aim to produce monodisperse dispersions and thin films of emerging 2D nanomaterials such as graphene, boron nitride, transition metal dichalcogenides, and black phosphorus. First, we motivate the need for precise thickness
NASA Astrophysics Data System (ADS)
Dorozhkin, S. I.
1990-02-01
Recent experimental results of Das et al. and of Luo et al. on the Shubnikov-de Haas oscillation beatings in two-dimensional electron systems (2D ES) are quantitatively described in terms of a model based on the energy spectrum of a 2D ES with strong spin-orbit coupling. Values of the energy spectrum parameters, including the g factor, are obtained for two-dimensional electrons in InxGa1-xAs/In0.52Al0.48As (x~=0.6) heterostructures.
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 graphene analogues for biomedical applications.
Chen, Yu; Tan, Chaoliang; Zhang, Hua; Wang, Lianzhou
2015-05-07
The increasing demand of clinical biomedicine and fast development of nanobiotechnology has substantially promoted the generation of a variety of organic/inorganic nanosystems for biomedical applications. Biocompatible two-dimensional (2D) graphene analogues (e.g., nanosheets of transition metal dichalcogenides, transition metal oxides, g-C3N4, Bi2Se3, BN, etc.), which are referred to as 2D-GAs, have emerged as a new unique family of nanomaterials that show unprecedented advantages and superior performances in biomedicine due to their unique compositional, structural and physicochemical features. In this review, we summarize the state-of-the-art progress of this dynamically developed material family with a particular focus on biomedical applications. After the introduction, the second section of the article summarizes a range of synthetic methods for new types of 2D-GAs as well as their surface functionalization. The subsequent section provides a snapshot on the use of these biocompatible 2D-GAs for a broad spectrum of biomedical applications, including therapeutic (photothermal/photodynamic therapy, chemotherapy and synergistic therapy), diagnostic (fluorescent/magnetic resonance/computed tomography/photoacoustic imaging) and theranostic (concurrent diagnostic imaging and therapy) applications, especially on oncology. In addition, we briefly present the biosensing applications of these 2D-GAs for the detection of biomacromolecules and their in vitro/in vivo biosafety evaluations. The last section summarizes some critical unresolved issues, possible challenges/obstacles and also proposes future perspectives related to the rational design and construction of 2D-GAs for biomedical engineering, which are believed to promote their clinical translations for benefiting the personalized medicine and human health.
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
Defect Characterization Using Two-Dimensional Arrays
NASA Astrophysics Data System (ADS)
Velichko, A.; Wilcox, P. D.
2011-06-01
2D arrays are able to `view' a given defect from a range of angles leading to the possibility of obtaining richer characterization detail than possible with 1D arrays. In this paper a quantitative comparison of 2D arrays with different element layouts is performed. A technique for extracting the scattering matrix of a defect from the raw 2D array data is also presented. The method is tested on experimental data for characterization of various volumetric defects.
Magnetization study of two dimensional helium three
NASA Astrophysics Data System (ADS)
Guo, Lei
This dissertation discusses a magnetization study of a two dimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of two dimensional 3He on both GTA grafoil and ZYX Graphite substrates. Benefiting from SQUID technology, our NMR experiments were performed at very low applied magnetic field thus avoid the masking of ordering by strong external field. Monolayer 3He films adsorbed on crystalline graphite are considered a nearly ideal example of a two dimensional system of highly correlated fermions. By controlling the 3He areal density, adsorbed films exhibit a wide range of structures with different temperature- dependent magnetic properties and heat capacities. Our recent experiments on two dimensional 3He adsorbed on ZYX graphite focused on the anti-ferromagnetic 4/7 phase and the ferromagnetic incommensurate solid state of a second 3He monolayer. Ferromagnetic order was observed in two dimensional 3He films on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar field plays an important role in magnetic ordering in two dimensional spin systems. The dipole-dipole interaction leads to a frequency shift of the NMR absorption line. The resulting 3He NMR lineshape on Grafoil was a broad peak shifted towards lower frequency with a background from the randomly oriented regions extending to positive frequencies. Compared to Grafoil, ZYX graphite has a much greater structural coherence and is more highly oriented. When studying magnetism of 3He films on ZYX substrate we found that the features we observed in our original Grafoil experiment were much more pronounced on ZYX graphite. In addition, we observed some multi-peak structure on the 3He NMR lineshape, which suggest a series of spin wave resonances. We also studied the magnetic properties of the second layer of 3He films on ZYX substrate at density around 4/7 phase. To eliminate the paramagnetic signal of the first layer solid, we pre-plated a 4He layer on the
Novel symmetries in the modified version of two dimensional Proca theory
NASA Astrophysics Data System (ADS)
Bhanja, T.; Shukla, D.; Malik, R. P.
2013-08-01
By exploiting Stueckelberg's approach, we obtain a gauge theory for the two-dimensional, that is, (1+1)-dimensional (2D) Proca theory and demonstrate that this theory is endowed with, in addition to the usual Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetries, the on-shell nilpotent (anti-)co-BRST symmetries, under which the total gauge-fixing term remains invariant. The anticommutator of the BRST and co-BRST (as well as anti-BRST and anti-co-BRST) symmetries define a unique bosonic symmetry in the theory, under which the ghost part of the Lagrangian density remains invariant. To establish connections of the above symmetries with the Hodge theory, we invoke a pseudo-scalar field in the theory. Ultimately, we demonstrate that the full theory provides a field theoretic example for the Hodge theory where the continuous symmetry transformations provide a physical realization of the de Rham cohomological operators and discrete symmetries of the theory lead to the physical realization of the Hodge duality operation of differential geometry. We also mention the physical implications and utility of our present investigation.
Synthesis of two-dimensional materials by selective extraction.
Naguib, Michael; Gogotsi, Yury
2015-01-20
CONSPECTUS: Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials. The most common synthesis approach in general is by reacting different elements or compounds to form a new compound. However, this approach does not necessarily work well for low-dimensional structures, since it favors formation of energetically preferred 3D (bulk) solids. Many 2D materials are produced by exfoliation of van der Waals solids, such as graphite or MoS2, breaking large particles into 2D layers. However, these approaches are not universal; for example, 2D transition metal carbides cannot be produced by any of them. An alternative but less studied way of material synthesis is the selective extraction process, which is based on the difference in reactivity and stability between the different components (elements or structural units) of the original material. It can be achieved using thermal, chemical, or electrochemical processes. Many 2D materials have been synthesized using selective extraction, such as graphene from SiC, transition metal oxides (TMO) from layered 3D salts, and transition metal carbides or carbonitrides (MXenes) from MAX phases. Selective extraction synthesis is critically important when the bonds between the building blocks of the material are too strong (e.g., in carbides) to be broken mechanically in order to form nanostructures. Unlike extractive metallurgy, where the extracted metal is the goal of the process, selective extraction of one or more elements from
Two-Dimensional Plasmonics in Massive and Massless Electron Gases
NASA Astrophysics Data System (ADS)
Yoon, Hosang
Plasmonic waves in solid-state are caused by collective oscillation of mobile charges inside or at the surface of conductors. In particular, surface plasmonic waves propagating at the skin of metals have recently attracted interest, as they reduce the wavelength of electromagnetic waves coupled to them by up to ˜10 times, allowing one to create miniaturized wave devices at optical frequencies. In contrast, plasmonic waves on two-dimensional (2D) conductors appear at much lower infrared and THz-GHz frequencies, near or in the electronics regime, and can achieve far stronger wavelength reduction factor reaching well above 100. In this thesis, we study the unique machinery of 2D plasmonic waves behind this ultra-subwavelength confinement and explore how it can be used to create various interesting devices. To this end, we first develop a physically intuitive theoretical formulation of 2D plasmonic waves, whose two main components---the Coulomb restoration force and inertia of the collectively oscillating charges---are combined into a transmission-line-like model. We then use this formulation to create various ultra-subwavelength 2D plasmonic devices. For the 2D conductor, we first choose GaAs/AlGaAs heterostructure---a 2D electron gas consisting of massive (m* > 0) electrons---demonstrating plasmonic bandgap crystals, interferometers, and negatively refracting metamaterials. We then examine a 2D plasmonic device based on graphene, a 2D electron gas consisting of effectively massless (m* = 0) electrons. We theoretically show and experimentally demonstrate that the massless electrons in graphene can surprisingly exhibit a collective mass when subjected to a collective excitation, providing the inertia that is essential for the propagation of 2D plasmonic waves. Lastly, we theoretically investigate the thermal current fluctuation behaviors in massive and massless electron gases. While seemingly unrelated on first sight, we show that the thermal current fluctuation is
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
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
NASA Astrophysics Data System (ADS)
Hidema, R.
2014-08-01
In order to study the effects of extensional viscosities on turbulent drag reduction, experimental studies using two-dimensional turbulence have been made. Anisotropic structures and variations of energy transfer induced by polymers are considered. Polyethyleneoxide and hydroxypropyl cellulose having different flexibility, which is due to different characteristics of extensional viscosity, are added to 2D turbulence. Variations of the turbulence were visualized by interference patterns of 2D flow, and were analysed by an image processing. The effects of polymers on turbulence in the streamwise and normal directions were also analysed by 2D Fourier transform. In addition, characteristic scales in 2D turbulence were analysed by wavelet transform.
Cooperative two-dimensional directed transport
NASA Astrophysics Data System (ADS)
Zheng, Zhigang; Chen, Hongbin
2010-11-01
A mechanism for the cooperative directed transport in two-dimensional ratchet potentials is proposed. With the aid of mutual couplings among particles, coordinated unidirectional motion along the ratchet direction can be achieved by transforming the energy from the transversal rocking force (periodic or stochastic) to the work in the longitude direction. Analytical predictions on the relation between the current and other parameters for the ac-driven cases are given, which are in good agreement with numerical simulations. Stochastic driving forces can give rise to the resonant directional transport. The effect of the free length, which has been explored in experiments on the motility of bipedal molecular motors, is investigated for both the single- and double-channel cases. The mechanism and results proposed in this letter may both shed light on the collective locomotion of molecular motors and open ways on studies in two-dimensional collaborative ratchet dynamics.
Toward two-dimensional search engines
NASA Astrophysics Data System (ADS)
Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.
2012-07-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.
Electronics based on two-dimensional materials.
Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K; Colombo, Luigi
2014-10-01
The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.
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 plasmonic nanosurface for photovoltaics
NASA Astrophysics Data System (ADS)
Polemi, Alessia; Shuford, Kevin L.
2011-12-01
In this paper, we investigate a two-dimensional corrugated plasmonic nanosurface for efficient light trapping in a photovoltaic cell. Inspired by a well-known one-dimensional grating nanosurface, the present configuration is composed of two perpendicular gratings in the metal film that intersect to yield cross-shaped nanoelements. The surface corrugation is then covered by a silicon film. An additional degree of freedom can be introduced into the design by interrupting the grid in both directions. We show that this extra spacing between the array elements can be used to tune the absorption properties of the nanosurface. By including the effect of the solar spectrum, we demonstrate how this two-dimensional configuration is more efficient than its one-dimensional counterpart in terms of the actual short circuit photocurrent density. Finally, we propose possible extensions of this structure design, which can further enhance the solar cell performance.
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.
Two-Dimensional NMR Lineshape Analysis
NASA Astrophysics Data System (ADS)
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-04-01
NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions.
Two-Dimensional 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
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
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.
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.
Two dimensional echocardiographic detection of intraatrial masses.
DePace, N L; Soulen, R L; Kotler, M N; Mintz, G S
1981-11-01
With two dimensional echocardiography, a left atrial mass was detected in 19 patients. Of these, 10 patients with rheumatic mitral stenosis had a left atrial thrombus. The distinctive two dimensional echocardiographic features of left atrial thrombus included a mass of irregular nonmobile laminated echos within an enlarged atrial cavity, usually with a broad base of attachment to the posterior left atrial wall. Seven patients had a left atrial myxoma. Usually, the myxoma appeared as a mottled ovoid, sharply demarcated mobile mass attached to the interatrial septum. One patient had a right atrial angiosarcoma that appeared as a nonmobile mass extending from the inferior vena caval-right atrial junction into the right atrial cavity. One patient had a left atrial leiomyosarcoma producing a highly mobile mass attached to the lateral wall of the left atrium. M mode echocardiography detected six of the seven myxomas, one thrombus and neither of the other tumors. Thus, two dimensional echocardiography appears to be the technique of choice in the detection, localization and differentiation of intraatrial masses.
van Agthoven, Maria A; Barrow, Mark P; Chiron, Lionel; Coutouly, Marie-Aude; Kilgour, David; Wootton, Christopher A; Wei, Juan; Soulby, Andrew; Delsuc, Marc-André; Rolando, Christian; O'Connor, Peter B
2015-12-01
Two-dimensional Fourier transform ion cyclotron resonance mass spectrometry is a data-independent analytical method that records the fragmentation patterns of all the compounds in a sample. This study shows the implementation of atmospheric pressure photoionization with two-dimensional (2D) Fourier transform ion cyclotron resonance mass spectrometry. In the resulting 2D mass spectrum, the fragmentation patterns of the radical and protonated species from cholesterol are differentiated. This study shows the use of fragment ion lines, precursor ion lines, and neutral loss lines in the 2D mass spectrum to determine fragmentation mechanisms of known compounds and to gain information on unknown ion species in the spectrum. In concert with high resolution mass spectrometry, 2D Fourier transform ion cyclotron resonance mass spectrometry can be a useful tool for the structural analysis of small molecules. Graphical Abstract ᅟ.
NASA Astrophysics Data System (ADS)
van Agthoven, Maria A.; Barrow, Mark P.; Chiron, Lionel; Coutouly, Marie-Aude; Kilgour, David; Wootton, Christopher A.; Wei, Juan; Soulby, Andrew; Delsuc, Marc-André; Rolando, Christian; O'Connor, Peter B.
2015-12-01
Two-dimensional Fourier transform ion cyclotron resonance mass spectrometry is a data-independent analytical method that records the fragmentation patterns of all the compounds in a sample. This study shows the implementation of atmospheric pressure photoionization with two-dimensional (2D) Fourier transform ion cyclotron resonance mass spectrometry. In the resulting 2D mass spectrum, the fragmentation patterns of the radical and protonated species from cholesterol are differentiated. This study shows the use of fragment ion lines, precursor ion lines, and neutral loss lines in the 2D mass spectrum to determine fragmentation mechanisms of known compounds and to gain information on unknown ion species in the spectrum. In concert with high resolution mass spectrometry, 2D Fourier transform ion cyclotron resonance mass spectrometry can be a useful tool for the structural analysis of small molecules.
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 discre-tized 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.
Optoelectronics in two-dimensional semiconductor alloys (Presentation Recording)
NASA Astrophysics Data System (ADS)
Léonard, François
2015-08-01
Two -dimensional transition-metal dichalcogenides (2D-TMDs) have attracted attention for applications in electronics and photonics, as well as for the wealth of new scientific phenomena that arise at low dimensionality. Recently, the ability to grow 2D-TMDs by chemical vapor deposition has opened the path to large area devices, but also to the synthesis of semiconductor alloys with tunable bandgaps. In this presentation, I will discuss our recent experimental work in exploring the optoelectronic properties of 2D MoS_2(1-x)Se_2x alloys spanning the compositional range. In particular, we report the observation of a new regime of operation where the photocurrent depends superlinearly on light intensity. We use spatially-resolved photocurrent measurements on devices consisting of CVD-grown monolayers to show the photoconductive nature of the photoresponse, with the photocurrent dominated by recombination and field-induced carrier separation in the channel. Time-dependent photoconductivity measurements show the presence of persistent photoconductivity for the S-rich alloys, while photocurrent measurements at fixed wavelength for devices of different alloy compositions show a systematic decrease of the responsivity with increasing Se content associated with increased linearity of the current-voltage characteristics. A model based on the presence of different types of recombination centers is presented to explain the origin of the superlinear dependence on light intensity, which emerges when the non-equilibrium occupancy of initially empty fast recombination centers becomes comparable to that of slow recombination centers.
Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films.
Halim, Joseph; Lukatskaya, Maria R; Cook, Kevin M; Lu, Jun; Smith, Cole R; Näslund, Lars-Åke; May, Steven J; Hultman, Lars; Gogotsi, Yury; Eklund, Per; Barsoum, Michel W
2014-04-08
Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm(2) Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films' resistivity increases with decreasing temperature and they exhibit negative magnetoresistance-both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.
Interactions between lasers and two-dimensional transition metal dichalcogenides.
Lu, Junpeng; Liu, Hongwei; Tok, Eng Soon; Sow, Chorng-Haur
2016-05-03
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.
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.
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 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.
Theory of two-dimensional ESR with nuclear modulation
NASA Astrophysics Data System (ADS)
Gamliel, Dan; Freed, Jack H.
A formalism for computing 2D ESR lineshapes with nuclear modulation is developed in a form which is useful for planning phase cycles for particular purposes. A simple method of processing spectra, utilizing quadrature detection, is shown to enhance the selectivity of the phase cycling techniques. Computed ESR-COSY, ESR-SECSY, and 2D ELDOR lineshapes are presented for several kinds of polycrystalline and single-crystal samples which exhibit nuclear modulation, due to one or several nuclei. The two-dimensional methods are found to give more detailed structural information than the corresponding ESEEM spectra. New phase cycles are found to eliminate completely all transverse and axial peaks in 2D ELDOR and in ESR-COSY, and at the same time eliminate all artifacts arising from incomplete image rejection. Other phase cycles are presented for selecting in those experiments only axial peaks, for measuring T1. It is also shown how selective phase cycles may help to distinguish between coherent and exchange cross peaks. In the special case of nitroxides in typical Zeeman fields, there are no significant nuclear modulation effects from the 14N nuclear spin interaction, but those from the protons (or deuterons) will, in general, be significant.
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.}
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.
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.
Gaynor, James D; Courtney, Trevor L; Balasubramanian, Madhumitha; Khalil, Munira
2016-06-15
The development of coherent Fourier transform two-dimensional electronic-vibrational (2D EV) spectroscopy with acousto-optic pulse-shaper-generated near-UV pump pulses and an octave-spanning broadband mid-IR probe pulse is detailed. A 2D EV spectrum of a silicon wafer demonstrates the full experimental capability of this experiment, and a 2D EV spectrum of dissolved hexacyanoferrate establishes the viability of our 2D EV experiment for studying condensed phase molecular ensembles.
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
2016-01-01
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
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.
Lou, C.; Zhou, H.C.
2005-10-01
This paper presents a novel instrumentation system for deducing the two-dimensional (2-D) distribution of temperature across a cross section of a furnace fired with pulverized coal. The system consisted of four flame image detectors, a frame-maker, and a microcomputer with a frame-grabber. Four colored images were captured by the four detectors, which were mounted in the four corners of a tangentially fired furnace. A radiation model was established to relate the flame images with the 2-D temperature distribution. A revised Tikhonov regularization method was used to reconstruct the 2-D temperature distribution from the flame radiation images. The experiment was done in a 1025 t/h boiler furnace of a 300-MW power generation unit. The 2-D temperature distribution in 100 discrete meshes in the cross section above the burner zone was deduced continuously using this instrumentation. The experimental results show that the 2-D temperature distribution appears typically to have single-peak shape with temperatures higher in the center and lower near the wall. Results obtained over a range of combustion conditions demonstrated that the average temperature of the cross section changed in direct proportion to the load of the furnace. The method is practically suitable for the on-line monitoring of combustion in a furnace.
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
Automated grid handling and image acquisition for two-dimensional crystal screening.
Cheng, Anchi
2013-01-01
Routine large-scale two-dimensional (2D) crystallization trials are good candidates for automation. For imaging the large number of grids prepared from 2D crystallization trials, a two-pass imaging protocol using Leginon and a grid handling robot is described. A manual target selection bridges the two imaging passes. The two passes can be combined into one if objects of interests at different stages of trials can be reliably found using automated methods.
NASA Astrophysics Data System (ADS)
Wang, Xiaoan; Xiang, Kewei; Zhang, Dian; Wu, Jinrong; Huang, Guangsu
The practical computation process of 2D correlation spectra and the influence of pretreatment factors such as noise reduction, peak position shift have been discussed in this paper. The excessive noise reduction and peak position shift would lead to erroneous interpretation of 2D spectra. Two-dimensional correlation dynamic mechanical spectroscopy is suitable for the analysis of relaxation processes if with appropriate external perturbation.
Two-Dimensional Isotope Imaging of Radiation Shielded Materials Using Nuclear Resonance Fluorescence
NASA Astrophysics Data System (ADS)
Toyokawa, Hiroyuki; Ohgaki, Hideaki; Hayakawa, Takehito; Kii, Toshiteru; Shizuma, Toshiyuki; Hajima, Ryoichi; Kikuzawa, Nobuhiro; Masuda, Kai; Kitatani, Fumito; Harada, Hideo
2011-10-01
A novel method for two-dimensional (2D) imaging of a specific isotope in a material, which is hidden by a thick radiation shield is presented. Nuclear resonance fluorescence and the laser Compton scattering are used in the present method. We measured γ-rays of 5512 keV from the nuclear resonance fluorescence of 208Pb at several points, and obtained a 2D image of isotope distribution.
Two dimensional turbulence in inviscid fluids or guiding center plasmas
NASA Technical Reports Server (NTRS)
Seyler, C. E., Jr.; Salu, Y.; Montgomery, D.; Knorr, G.
1975-01-01
Analytic theory for two-dimensional turbulent equilibria for the inviscid Navier-Stokes equations is examined mathematically. Application of the technique to electrostatic guiding center plasma is discussed. A good fit is demonstrated for the approach to a predicted energy per Fourier mode obtained from a two-temperature canonical ensemble. Negative as well as positive temperature regimes are explored. Fluctuations about the mean energy per mode also compare well with theory. In the regime of alpha less than zero, beta greater than zero, with the minimum value of alpha plus beta times k squared near zero, contour plots of the stream function reveal macroscopic vortex structures similar to those seen previously in discrete vortex simulations. Eulerian direct interaction equations, which can be used to follow the approach to inviscid equilibrium, are derived.
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 relaxation 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.
Mixing times in quantum walks on two-dimensional grids
Marquezino, F. L.; Portugal, R.; Abal, G.
2010-10-15
Mixing properties of discrete-time quantum walks on two-dimensional grids with toruslike boundary conditions are analyzed, focusing on their connection to the complexity of the corresponding abstract search algorithm. In particular, an exact expression for the stationary distribution of the coherent walk over odd-sided lattices is obtained after solving the eigenproblem for the evolution operator for this particular graph. The limiting distribution and mixing time of a quantum walk with a coin operator modified as in the abstract search algorithm are obtained numerically. On the basis of these results, the relation between the mixing time of the modified walk and the running time of the corresponding abstract search algorithm is discussed.
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.
Algebraic construction of a Nambu bracket for the two-dimensional vorticity equation.
Sommer, M; Brazda, K; Hantel, M
2011-08-29
So far fluid mechanical Nambu brackets have mainly been given on an intuitive basis. Alternatively an algorithmic construction of such a bracket for the two-dimensional vorticity equation is presented here. Starting from the Lie-Poisson form and its algebraic properties it is shown how the Nambu representation can be explicitly constructed as the continuum limit from the structure preserving Zeitlin discretization.
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.
2-d Finite Element Code Postprocessor
Sanford, L. A.; Hallquist, J. O.
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 forces 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.
Towards automated screening of two-dimensional crystals.
Cheng, Anchi; Leung, Albert; Fellmann, Denis; Quispe, Joel; Suloway, Christian; Pulokas, James; Abeyrathne, Priyanka D; Lam, Joseph S; Carragher, Bridget; Potter, Clinton S
2007-12-01
Screening trials to determine the presence of two-dimensional (2D) protein crystals suitable for three-dimensional structure determination using electron crystallography is a very labor-intensive process. Methods compatible with fully automated screening have been developed for the process of crystal production by dialysis and for producing negatively stained grids of the resulting trials. Further automation via robotic handling of the EM grids, and semi-automated transmission electron microscopic imaging and evaluation of the trial grids is also possible. We, and others, have developed working prototypes for several of these tools and tested and evaluated them in a simple screen of 24 crystallization conditions. While further development of these tools is certainly required for a turn-key system, the goal of fully automated screening appears to be within reach.
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.
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
Solvent minimization in two-dimensional liquid chromatography.
Horváth, Krisztián; Sepsey, Annamária; Hajós, Péter
2015-01-23
An algorithm was developed for the minimization of consumption of organic solvent in comprehensive two-dimensional liquid chromatography (2DLC). It was shown that one can reach higher peak capacities only by using more eluent. The equilibration volume of the second dimension, however, did not affect the solvent consumption significantly. Calculations confirmed that the same target peak capacity could be achieved by consuming significantly different volume of organic modifier depending on the number of fractions analyzed in the second dimension suggesting that 2D separations can be optimized for eluent consumption. It was shown that minimization of eluent usage requires the use of small and high efficient columns in the second dimension. A simple equation was derived for the calculation of the optimal number of collected fractions from the first dimension that allowed the minimization of eluent usage, cost and environmental impact of comprehensive 2DLC separations.
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.
Li, Zhenyu; Abramavicius, Darius; Zhuang, Wei; Mukamel, Shaul
2007-11-15
The two dimensional (2D) photon echo spectrum of the amide ultraviolet (UV) bands of proteins are simulated. Two effective exciton Hamiltonian parameter sets developed by Woody and Hirst, which predict similar CD spectra, may be distinguished by their very different 2DUV spectra. These differences are enhanced in specific configurations of pulse polarizations which provide chirality-induced signals.
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...
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…
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...
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.
Jiang, Ming; Kulsing, Chadin; Nolvachai, Yada; Marriott, Philip J
2015-06-02
Comprehensive two-dimensional gas chromatography hyphenated with accurate mass time-of-flight mass spectrometry (GC × GC-accTOFMS) was applied for improved analytical accuracy of saffron analysis, by using retention indices in the two-dimensional separation. This constitutes 3 dimensions of identification. In addition to accTOFMS specificity, and first dimension retention indices ((1)I), a simple method involving direct multiple injections with stepwise isothermal temperature programming is described for construction of isovolatility curves for reference alkane series in GC × GC. This gives access to calculated second dimension retention indices ((2)I). Reliability of the calculated (2)I was evaluated by using a Grob test mixture, and saturated alkanes, revealing good correlation between previously reported I values from the literature, with R(2) correlation being 0.9997. This essentially recognizes the retention property of peaks in the GC × GC 2D space as being reducible to a retention index in each dimension, which should be a valuable tool supporting identification. The benefit of (2)I data, in supplementing (1)I and MS library matching, was clearly demonstrated by the progressive reduction of the number of possible compound matches for peaks observed in saffron. 114 analytes were assessed according to (1)I and (2)I values within ±20 index unit of reference values, and by MS spectrum matching above a match statistic of 750 (including mass accuracy of the molecular ion <20 ppm) and their possible identities derived. The described method provides a new avenue to utilize the full capability of the two-dimensional separation (GC × GC), in combination with MS library matching in complex sample analysis, to provide improved component identification.
Two dimensional thick center vortex model
Rafibakhsh, Shahnoosh; Ahmadi, Alireza
2016-01-22
The potential between static color source is calculated in the SU (3) gauge group by introducing a two dimensional vortex flux. To generalize the model, the length of the Wilson loop is equal to R oriented along the x axis, and the vortex flux is considered as a function of x and y. The comparison between the generalized model and the original one shows that the intermediate linear regime is increased significantly and better agreement with Casimir scaling is achieved. Furthermore, the model is applied to calculate the potential between baryons.
Universal absorption of two-dimensional systems
NASA Astrophysics Data System (ADS)
Stauber, T.; Noriega-Pérez, D.; Schliemann, J.
2015-03-01
We discuss the optical conductivity of several noninteracting two-dimensional semiconducting systems focusing on gapped Dirac and Schrödinger fermions as well as on a system mixing these two types. Close to the band gap, we can define a universal optical conductivity quantum of σ0=1/16 e/2ℏ for the pure systems. The effective optical conductivity then depends on the degeneracy factors gs (spin) and gv (valley) and on the curvature around the band gap ν , i.e., it generally reads σ =gsgvν σ0 . For a system composed of both types of carriers, the optical conductivity becomes nonuniversal.
One- and two-dimensional hydrogen atoms
NASA Astrophysics Data System (ADS)
Hassoun, G. Q.
1981-02-01
Certain one- and two-dimensional reductions of the three-dimensional Schrödinger equation of the hydrogen atom are considered. These reductions are carried out from the point of view of the two common sets of space coordinates: Cartesian and spherical. The resulting systems have features that relate more readily to the old quantum theory models of Bohr and Sommerfeld than the general three-dimensional hydrogen atom. Furthermore, the considerations yield interesting insights into the quantum mechanics of the hydrogen atom and may serve as helpful intermediary preparation, in an introductory presentation of the subject, for the unreduced three-dimensional case.
Study of two-dimensional squeezed magnetopolarons
NASA Astrophysics Data System (ADS)
Zhang, Yanmin; Cheng, Ze; Wu, Zixia; Wang, Junfeng
2006-11-01
In this Letter, some properties of two-dimensional squeezed magnetopolarons are investigated. The Hamiltonian of magnetopolarons is dealt with by using squeezed state transformation, which is based on the Lee Low Pines and Huybrechts (LLP H) canonical transformations. This method makes it possible to consider bilinear terms of the phonon operators as well as linear terms arising from the LLP H transformations. Some exact results are obtained, such as the energies of ground and excited states for squeezed magnetopolarons and renormalized cyclotron masses for some possible transitions.
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.
Dynamics of film. [two dimensional continua theory
NASA Technical Reports Server (NTRS)
Zak, M.
1979-01-01
The general theory of films as two-dimensional continua are elaborated upon. As physical realizations of such a model this paper examines: inextensible films, elastic films, and nets. The suggested dynamic equations have enabled us to find out the characteristic speeds of wave propagation of the invariants of external and internal geometry and formulate the criteria of instability of their shape. Also included herein is a detailed account of the equation describing the film motions beyond the limits of the shape stability accompanied by the formation of wrinkles. The theory is illustrated by examples.
Two-dimensional meniscus in a wedge
Kagan, M.; Pinczewski, W.V.; Oren, P.E.
1995-03-15
This paper presents a closed-form analytical solution of the augmented Young-Laplace equation for the meniscus profile in a two-dimensional wedge-shaped capillary. The solution is valid for monotonic forms of disjoining pressure which are repulsive in nature. In the limit of negligible disjoining pressure, it is shown to reduce to the classical solution of constant curvature. The character of the solution is examined and examples of practical interest which demonstrate the application of the solution to the computation of the meniscus profile in a wedge-shaped capillary are discussed.
Two-dimensional Rayleigh model of vapor bubble evolution
Amendt, P; Friedman, M; Glinsky, M; Gurewitz, E; London, R A; Strauss, M
1999-01-14
The understanding of vapor bubble generation in an aqueous tissue near a fiber tip has required advanced two dimensional (2D) hydrodynamic simulations. For 1D spherical bubble expansion a simplified and useful Rayleigh-type model can be applied. For 2D bubble evolution, such a model does not exist. The present work proposes a Rayleigh-type model for 2D bubble expansion that is faster and simpler than the 2D hydrodynamic simulations. The model is based on a flow potential representation of the hydrodynamic motion controlled by a Laplace equation and a moving boundary condition. We show that the 1D Rayleigh equation is a specific case of our model. The Laplace equation is solved for each time step by a finite element solver using a triangulation of the outside bubble region by a fast unstructured mesh generator. Two problems of vapor bubbles generated by short-pulse lasers near a fiber tip-are considered: (a) the outside region has no boundaries except the fiber, (b) the fiber and the bubble are confined in a long channel, which simulates a fiber in a vessel wall. Our simulations for problems of type (a) include features of bubble evolution as seen in experiments, including a collapse away from the fiber tip. A different behavior was obtained for problems of type (b) when the channel boundary is close to the fiber. In this case the bubble's expansion and collapse are both extremely slow in the direction normal to this boundary and distortion of the bubble is observed.
Two-Dimensional Electron-Spin Resonance
NASA Astrophysics Data System (ADS)
Freed, Jack H.
2000-03-01
The extension of the concepts of 2D-NMR to ESR posed significant technological challenges, especially for liquids. ESR relaxation times are very short, as low as 10-15 ns. for T_2's. Spectral bandwidths are 100-250 MHz for nitroxide spin labels. Adequate coverage is obtained with 3-5 ns. π/2 (9-17 GHz) microwave pulses into a small low Q resonator. Dead-times are currently 25-30 ns. Additional requirements are rapid phase shifting for phase cycling, nsec. data acquisition, and fast repetition rates (10-100 kHz). 2D-ELDOR (electron-electron double resonance), which is a 3-pulse 2D-exchange experiment, takes about 30 minutes with just 0.5 nanomole spin-probe in solution (SNR 200). 2D-ELDOR is very useful in studies of molecular dynamics and local structure in complex fluids. For such media, the slow rotational dynamics requires a theory based upon the stochastic Liouville equation which enables quantitative interpretation of 2D-ELDOR experiments. In studies of spin-probes in a liquid crystal new insights could be obtained on the dynamic structure in different phases. One obtains, in addition to ordering and reorientation rates of the probes, details of the local dynamic cage: its orienting potential and (slow) relaxation rate. 2D-ELDOR overcomes the loss of resolution resulting from microscopically ordered but macroscopically disordered complex fluids. This is illustrated by studies of the dynamic structure of lipid membrane vesicles, and the effects of adding a peptide. The short dead times enable the observation of both the bulk lipids and the more immobilized lipids that coat (or are trapped) by the (aggregates of) peptides. Also, new developments of multi-quantum (2D) FT-ESR from nitroxide spin labels interacting by dipolar interactions show considerable promise in measuring distances of ca. 15-70A in macromolecules.
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 Dirac carbon allotropes from graphene.
Xu, Li-Chun; Wang, Ru-Zhi; Miao, Mao-Sheng; Wei, Xiao-Lin; Chen, Yuan-Ping; Yan, Hui; Lau, Woon-Ming; Liu, Li-Min; Ma, Yan-Ming
2014-01-21
Using a structural search method in combination with first-principles calculations, we found lots of low energy 2D carbon allotropes and examined all possible Dirac points around their Fermi levels. Three amazing 2D Dirac carbon allotropes have been discovered, named as S-graphene, D-graphene and E-graphene. By analyzing the topology correlations among S-, T, net W graphene and graphene, we found that a general rule is valuable for constructing 2D carbon allotropes that are keen to possess Dirac cones in their electronic structures. Based on this rule, we have successfully designed many new 2D carbon allotropes possessing Dirac cones. Their energy order can be well described by an Ising-like model, and some allotropes are energetically more stable than those recently reported. The related electronic structures of these Dirac allotropes are anisotropy distinguished from those of graphene. Moreover, the fact that D- and E-graphene present Dirac cones suggests that sp hybridization or sp(3) hybridization could not suppress the emerging of Dirac features. Our results demonstrate that the Dirac cone and carrier linear dispersion is a very common feature in 2D carbon allotropes and can exist beyond the limitations of fundamental structure features of graphene.
Wang, C.; Theocharis, G.; Kevrekidis, P. G.; Whitaker, N.; Law, K. J. H.; Frantzeskakis, D. J.; Malomed, B. A.
2009-10-15
We study the existence and stability of localized modes in the two-dimensional (2D) nonlinear Schroedinger/Gross-Pitaevskii (NLS/GP) equation with a symmetric four-well potential. Using the corresponding four-mode approximation, we trace the parametric evolution of the trapped stationary modes, starting from the linear limit, and thus derive a complete bifurcation diagram for families of the stationary modes. This provides the picture of spontaneous symmetry breaking in the fundamental 2D setting. In a broad parameter region, the predictions based on the four-mode decomposition are found to be in good agreement with full numerical solutions of the NLS/GP equation. Stability properties of the stationary states coincide with those suggested by the corresponding discrete model in the large-amplitude limit. The dynamics of unstable modes is explored by means of direct simulations. Finally, in addition to the full analysis for the case of the self-attractive nonlinearity, the bifurcation diagram for the case of self-repulsion is briefly considered too.
Wang, C; Theocharis, G; Kevrekidis, P G; Whitaker, N; Law, K J H; Frantzeskakis, D J; Malomed, B A
2009-10-01
We study the existence and stability of localized modes in the two-dimensional (2D) nonlinear Schrödinger/Gross-Pitaevskii (NLS/GP) equation with a symmetric four-well potential. Using the corresponding four-mode approximation, we trace the parametric evolution of the trapped stationary modes, starting from the linear limit, and thus derive a complete bifurcation diagram for families of the stationary modes. This provides the picture of spontaneous symmetry breaking in the fundamental 2D setting. In a broad parameter region, the predictions based on the four-mode decomposition are found to be in good agreement with full numerical solutions of the NLS/GP equation. Stability properties of the stationary states coincide with those suggested by the corresponding discrete model in the large-amplitude limit. The dynamics of unstable modes is explored by means of direct simulations. Finally, in addition to the full analysis for the case of the self-attractive nonlinearity, the bifurcation diagram for the case of self-repulsion is briefly considered too.
Technology Transfer Automated Retrieval System (TEKTRAN)
Two-dimensional (2D) correlation analysis was applied to characterize the ATR spectral intensity fluctuations of native cotton fibers with various water contents. Prior to 2D analysis, the spectra were leveled to zero at the peak intensity of 1800 cm-1 and then were normalized at the peak intensity ...
Optoelectronics with 2D semiconductors
NASA Astrophysics Data System (ADS)
Mueller, Thomas
2015-03-01
Two-dimensional (2D) atomic crystals, such as graphene and layered transition-metal dichalcogenides, are currently receiving a lot of attention for applications in electronics and optoelectronics. In this talk, I will review our research activities on electrically driven light emission, photovoltaic energy conversion and photodetection in 2D semiconductors. In particular, WSe2 monolayer p-n junctions formed by electrostatic doping using a pair of split gate electrodes, type-II heterojunctions based on MoS2/WSe2 and MoS2/phosphorene van der Waals stacks, 2D multi-junction solar cells, and 3D/2D semiconductor interfaces will be presented. Upon optical illumination, conversion of light into electrical energy occurs in these devices. If an electrical current is driven, efficient electroluminescence is obtained. I will present measurements of the electrical characteristics, the optical properties, and the gate voltage dependence of the device response. In the second part of my talk, I will discuss photoconductivity studies of MoS2 field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photoconductive gain. A model will be presented that reproduces our experimental findings, such as the dependence on optical power and gate voltage. We envision that the efficient photon conversion and light emission, combined with the advantages of 2D semiconductors, such as flexibility, high mechanical stability and low costs of production, could lead to new optoelectronic technologies.
Eigenstate thermalization in the two-dimensional transverse field Ising model.
Mondaini, Rubem; Fratus, Keith R; Srednicki, Mark; Rigol, Marcos
2016-03-01
We study the onset of eigenstate thermalization in the two-dimensional transverse field Ising model (2D-TFIM) in the square lattice. We consider two nonequivalent Hamiltonians: the ferromagnetic 2D-TFIM and the antiferromagnetic 2D-TFIM in the presence of a uniform longitudinal field. We use full exact diagonalization to examine the behavior of quantum chaos indicators and of the diagonal matrix elements of operators of interest in the eigenstates of the Hamiltonian. An analysis of finite size effects reveals that quantum chaos and eigenstate thermalization occur in those systems whenever the fields are nonvanishing and not too large.
Quantum dots derived from two-dimensional materials and their applications for catalysis and energy.
Wang, Xuewan; Sun, Gengzhi; Li, Nan; Chen, Peng
2016-04-21
Quantum dots (QDs) derived from the atomically-thin two-dimensional (2D) sheets (graphene, transition metal dichalcogenide, graphitic carbon nitride, hexagonal boron nitride, and phosphorene) are emerging extraordinary zero-dimensional materials. Covering a broad spectrum of interesting optical, catalytic, electronic, chemical and electrochemical properties, these 2D-QDs promise a wide range of novel applications including imaging, sensing, cancer therapy, optoelectronics, display, catalysis, and energy. In this article, we discuss the synthesis methods and the properties of these 2D-QDs and emphasize their applications in electrocatalysis, photocatalysis, supercapacitors, batteries, and photovoltaics.
Photodetecting and light-emitting devices based on two-dimensional materials
NASA Astrophysics Data System (ADS)
Yu, Yuanfang; Miao, Feng; He, Jun; Ni, Zhenhua
2017-03-01
Two dimensional (2D) materials, e.g. graphene, transition metal dichalcogenides (TMDs), black phosphorus (BP), have demonstrated fascinating electrical and optical characteristics and exhibited great potential in optoelectronic applications. High performance and multifunctional devices were achieved by employing diverse designs of architectures, such as hybrid systems with nanostructured materials, bulk semiconductors and organics, forming 2D heterostructures. In this review, we mainly discuss the recent progresses of 2D materials in high responsive photodetectors, light-emitting devices and single photon emitters. Hybrid systems and van der Waals heterostructures based devices are emphasized, which exhibit great potential in state-of-the-art applications.
Two-dimensional Fibonacci grating for far-field super-resolution imaging
Wu, Kedi; Wang, Guo Ping
2016-01-01
A two-dimensional (2D) Fibonacci grating is used to transform evanescent waves into propagating waves for far-field super-resolution imaging. By detecting far-field intensity distributions of light field through objects in front of the 2D Fibonacci grating in free space at once, we can retrieve the image of objects with beyond λ/7 spatial resolution. We also find that the coherent illumination case can give a better resolution than incoherent illumination case by such 2D grating-assisted imaging system. The analytical results are verified by numerical simulation. PMID:27934906
Cavity-enhanced ultrafast two-dimensional spectroscopy using higher order modes
NASA Astrophysics Data System (ADS)
Allison, Thomas K.
2017-02-01
We describe methods using frequency combs and optical resonators for recording two-dimensional (2D) ultrafast spectroscopy signals with high sensitivity. By coupling multiple frequency combs to higher-order modes of one or more optical cavities, background-free, cavity-enhanced 2D spectroscopy signals are naturally generated via phase cycling. As in cavity-enhanced ultrafast transient absorption spectroscopy, the signal to noise is enhanced by a factor proportional to the cavity finesse squared, so even using cavities of modest finesse, a very high sensitivity is expected, enabling ultrafast 2D spectroscopy experiments in dilute molecular beams.
Two-dimensional Fibonacci grating for far-field super-resolution imaging
NASA Astrophysics Data System (ADS)
Wu, Kedi; Wang, Guo Ping
2016-12-01
A two-dimensional (2D) Fibonacci grating is used to transform evanescent waves into propagating waves for far-field super-resolution imaging. By detecting far-field intensity distributions of light field through objects in front of the 2D Fibonacci grating in free space at once, we can retrieve the image of objects with beyond λ/7 spatial resolution. We also find that the coherent illumination case can give a better resolution than incoherent illumination case by such 2D grating-assisted imaging system. The analytical results are verified by numerical simulation.
Melting in three-dimensional and two-dimensional Yukawa systems
NASA Astrophysics Data System (ADS)
Vaulina, O. 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.
Electron compound nature in a surface atomic layer of a two-dimensional hexagonal lattice
NASA Astrophysics Data System (ADS)
Matsuda, Iwao; Nakamura, Fumitaka; Kubo, Keisuke; Hirahara, Toru; Yamazaki, Shiro; Choi, Won Hoon; Yeom, Han Woong; Narita, Hisashi; Fukaya, Yuki; Hashimoto, Mie; Kawasuso, Atsuo; Ono, Masanori; Hasegawa, Yukio; Hasegawa, Shuji; Kobayashi, Katsuyoshi
2010-10-01
The two-dimensional (2D) ordered phase of monovalent metal alloy, 21×21 , is formed on the Si(111) surface with the constant electron/atom ratio, indicating electron compound nature. Two conventional theories of the Hume-Rothery compounds, Jones model (nearly-free-electron model), and pseudopotential model (interionic interaction model), were applied to examine stability of the 2D phase. We found breakdown of the former and confirmation of the latter approaches with importance of medium-range interatomic interaction, mediated by the 2D surface-state electrons, in the latter approach.
Two-dimensional Fibonacci grating for far-field super-resolution imaging.
Wu, Kedi; Wang, Guo Ping
2016-12-09
A two-dimensional (2D) Fibonacci grating is used to transform evanescent waves into propagating waves for far-field super-resolution imaging. By detecting far-field intensity distributions of light field through objects in front of the 2D Fibonacci grating in free space at once, we can retrieve the image of objects with beyond λ/7 spatial resolution. We also find that the coherent illumination case can give a better resolution than incoherent illumination case by such 2D grating-assisted imaging system. The analytical results are verified by numerical simulation.
Plasmid DNA topology assayed by two-dimensional agarose gel electrophoresis.
Schvartzman, Jorge B; Martínez-Robles, María-Luisa; Hernández, Pablo; Krimer, Dora B
2013-01-01
Two-dimensional (2D) agarose gel electrophoresis is nowadays one of the best methods available to analyze DNA molecules with different masses and shapes. The possibility to use nicking enzymes and intercalating agents to change the twist of DNA during only one or in both runs, improves the capacity of 2D gels to discern molecules that apparently may look alike. Here we present protocols where 2D gels are used to understand the structure of DNA molecules and its dynamics in living cells. This knowledge is essential to comprehend how DNA topology affects and is affected by all the essential functions that DNA is involved in: replication, transcription, repair and recombination.
Subsurface imaging of two-dimensional materials at the nanoscale.
Dinelli, Franco; Pingue, Pasqualantonio; Kay, Nicholas D; Kolosov, Oleg V
2017-02-24
Scanning probe microscopy (SPM) represents a powerful tool that, in the past 30 years, has allowed for the investigation of material surfaces in unprecedented ways at the nanoscale level. However, SPM has shown very little capability for depth penetration, which several nanotechnology applications require. Subsurface imaging has been achieved only in a few cases, when subsurface features influence the physical properties of the surface, such as the electronic states or the heat transfer. Ultrasonic force microscopy (UFM), an adaption of the contact mode atomic force microscopy, can dynamically measure the stiffness of the elastic contact between the probing tip and the sample surface. In particular, UFM has proven highly sensitive to the near-surface elastic field in non-homogeneous samples. In this paper, we present an investigation of two-dimensional (2D) materials, namely flakes of graphite and molybdenum disulphide placed on structured polymeric substrates. We show that UFM can non-destructively distinguish suspended and supported areas and localise defects, such as buckling or delamination of adjacent monolayers, generated by residual stress. Specifically, UFM can probe small variations in the local indentation induced by the mechanical interaction between the tip and the sample. Therefore, any change in the elastic modulus within the volume perturbed by the applied load or the flexural bending of the suspended areas can be detected and imaged. These investigation capabilities are very promising in order to study the buried interfaces of nanostructured 2D materials such as in graphene-based devices.
Two-dimensional electronic spectroscopy signatures of the glass transition
Lewis, K. L. .. M.; Myers, J. A.; Fuller, F.; ...
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
Subsurface imaging of two-dimensional materials at the nanoscale
NASA Astrophysics Data System (ADS)
Dinelli, Franco; Pingue, Pasqualantonio; Kay, Nicholas D.; Kolosov, Oleg V.
2017-02-01
Scanning probe microscopy (SPM) represents a powerful tool that, in the past 30 years, has allowed for the investigation of material surfaces in unprecedented ways at the nanoscale level. However, SPM has shown very little capability for depth penetration, which several nanotechnology applications require. Subsurface imaging has been achieved only in a few cases, when subsurface features influence the physical properties of the surface, such as the electronic states or the heat transfer. Ultrasonic force microscopy (UFM), an adaption of the contact mode atomic force microscopy, can dynamically measure the stiffness of the elastic contact between the probing tip and the sample surface. In particular, UFM has proven highly sensitive to the near-surface elastic field in non-homogeneous samples. In this paper, we present an investigation of two-dimensional (2D) materials, namely flakes of graphite and molybdenum disulphide placed on structured polymeric substrates. We show that UFM can non-destructively distinguish suspended and supported areas and localise defects, such as buckling or delamination of adjacent monolayers, generated by residual stress. Specifically, UFM can probe small variations in the local indentation induced by the mechanical interaction between the tip and the sample. Therefore, any change in the elastic modulus within the volume perturbed by the applied load or the flexural bending of the suspended areas can be detected and imaged. These investigation capabilities are very promising in order to study the buried interfaces of nanostructured 2D materials such as in graphene-based devices.
Two-dimensional transition metal dichalcogenide nanosheet-based composites.
Tan, Chaoliang; Zhang, Hua
2015-05-07
Ultrathin two-dimensional (2D) nanosheets of layered transition metal dichalcogenides (TMDs), such as MoS2, TiS2, TaS2, WS2, MoSe2, WSe2, etc., are emerging as a class of key materials in chemistry and electronics due to their intriguing chemical and electronic properties. The ability to prepare these TMD nanosheets in high yield and large scale via various methods has led to increasing studies on their hybridization with other materials to create novel functional composites, aiming to engineer their chemical, physical and electronic properties and thus achieve good performance for some specific applications. In this critical review, we will introduce the recent progress in hybrid nanoarchitectures based on 2D TMD nanosheets. Their synthetic strategies, properties and applications are systematically summarized and discussed, with emphasis on those new appealing structures, properties and functions. In addition, we will also give some perspectives on the challenges and opportunities in this promising research area.
Synthesis and Electrochemical Properties of Two-Dimensional Hafnium Carbide.
Zhou, Jie; Zha, Xianhu; Zhou, Xiaobing; Chen, Fanyan; Gao, Guoliang; Wang, Shuwei; Shen, Cai; Chen, Tao; Zhi, Chunyi; Eklund, Per; Du, Shiyu; Xue, Jianming; Shi, Weiqun; Chai, Zhifang; Huang, Qing
2017-04-06
We demonstrate fabrication of a two-dimensional Hf-containing MXene, Hf3C2Tz, by selective etching of a layered parent Hf3[Al(Si)]4C6 compound. A substitutional solution of Si on Al sites effectively weakened the interfacial adhesion between Hf-C and Al(Si)-C sublayers within the unit cell of the parent compound, facilitating the subsequent selective etching. The underlying mechanism of the Si-alloying-facilitated etching process is thoroughly studied by first-principles density functional calculations. The result showed that more valence electrons of Si than Al weaken the adhesive energy of the etching interface. The MXenes were determined to be flexible and conductive. Moreover, this 2D Hf-containing MXene material showed reversible volumetric capacities of 1567 and 504 mAh cm(-3) for lithium and sodium ions batteries, respectively, at a current density of 200 mAg(-1) after 200 cycles. Thus, Hf3C2Tz MXenes with a 2D structure are candidate anode materials for metal-ion intercalation, especially for applications where size matters.
Two-dimensional Fourier transform ESR correlation spectroscopy
NASA Astrophysics Data System (ADS)
Gorcester, Jeff; Freed, Jack H.
1988-04-01
We describe our pulsed two-dimensional Fourier transform ESR experiment and demonstrate its applicabilty for the double resonance of motionally narrowed nitroxides. Multiple pulse irradiation of the entire nitroxide spectrum enables the correlation of two precessional periods, allowing observation of cross correlations between hyperfine lines introduced by magnetization transfer in the case of a three-pulse experiment (2D ELDOR), or coherence transfer in the case of a two-pulse experiment (COSY). Cross correlations are revealed by the presence of cross peaks which connect the autocorrelation lines appearing along the diagonal ω1=ω2. The amplitudes of these cross peaks are determined by the rates of magnetization transfer in the 2D ELDOR experiment. The density operator theory for the experiment is outlined and applied to the determination of Heisenberg exchange (HE) rates in 2,2,6,6-tetramethyl-4-piperidone-N-oxyl-d15 (PD-tempone) dissolved in toluene-d8. The quantitative accuracy of this experiment is established by comparison with the HE rate measured from the dependence of the spin echo T2 on nitroxide concentration.
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
2016-02-07
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.
Orthogonal grid generation in two dimensional space
NASA Astrophysics Data System (ADS)
Theodoropoulos, T.; Bergeles, G.; Athanassiadis, N.
A generalization of a numerical technique for orthogonal mapping, used by Ryskin and Leal (1983) for the construction of boundary-fitted curvilinear coordinate systems in two-dimensional space, is proposed. The boundary-fitted orthogonal curvilinear coordinates are assumed to transform to Cartesian coordinates by Laplace equations. The scale factors involved in the Laplace equations are computed on boundaries and estimated on internal points by means of an interpolation formula. Three types of boundary conditions have been tested: Dirichlet, Cauchy-Riemann, and pseudo-Dirichlet. It is shown that, using this method, grids appropriate for the calculation of flow fields over sharp edges, complex boundary shapes, etc., can be easily constructed. Examples on various geometries are presented, together with a convenient method to check the orthogonality of the resulting meshes.
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.
Two-dimensional motions of rockets
NASA Astrophysics Data System (ADS)
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 descending parts of the trajectories tend to be gentler and straighter slopes than the ascending parts for relatively large launching angles due to the non-vanishing thrusts. We discuss the ranges, the maximum altitudes and the engine performances of the rockets. It seems that the exponential fuel exhaustion can be the most potent engine for the longest and highest flights.
Two-Dimensional Informative Array Testing
McMahan, Christopher S.; Tebbs, Joshua M.; Bilder, Christopher R.
2015-01-01
Summary Array-based group testing algorithms for case identification are widely used in infectious disease testing, drug discovery, and genetics. In this paper, we generalize previous statistical work in array testing to account for heterogeneity among individuals being tested. We first derive closed-form expressions for the expected number of tests (efficiency) and misclassification probabilities (sensitivity, specificity, predictive values) for two-dimensional array testing in a heterogeneous population. We then propose two “informative” array construction techniques which exploit population heterogeneity in ways that can substantially improve testing efficiency when compared to classical approaches which regard the population as homogeneous. Furthermore, a useful byproduct of our methodology is that misclassification probabilities can be estimated on a per-individual basis. We illustrate our new procedures using chlamydia and gonorrhea testing data collected in Nebraska as part of the Infertility Prevention Project. PMID:22212007
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.
Methods of Two-Dimensional Spectroscopy
NASA Astrophysics Data System (ADS)
Kneer, F.
One of the main fields of solar research is the study of dynamic processes of small-scale structures. For this purpose, time sequences of spectroscopic and polarimetric information in two spatial dimensions with best achievable quality are needed. The present contribution deals with the ways to obtain images in small wavelength bands. Among these are image scanners and the MSDP (Multi-Channel Subtractive Double Pass Spectrograph). Further potential instruments are scanning Fabry-Perot interferometers (FPI). The principles of such instruments are discussed. The results obtained hitherto from the FPI in the Vacuum Tower Telescope at the Observatorio del Teide are promising. Small-band, two-dimensional spectroscopy with spatial resolution close to the telescopic diffraction limit seems possible in the near future.
Phonon hydrodynamics in two-dimensional materials
NASA Astrophysics Data System (ADS)
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-03-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.
Two-dimensional 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.
[Research in two-dimensional critical phenomena and conformal field theory]. Final report
Not Available
1990-12-31
A very theoretical description is given of research in two- dimensional critical phenomena and conformal field theory. Major progress is reported in the field of fluctuating two-dimensional surfaces. A discretized representation of fluctuating geometry is used where surfaces are represented by triangulations; continuum surfaces are recovered by taking the size of the triangles to zero. One of the central goals of the theory of critical phenomena is to find all possible universality classes of n-dimensional critical phenomena; this goal has been translated into the problem of clasifying all possible scale-invariant euclidean quantum field theories. (RWR)
Two-dimensional angularly selective optical properties of gold nanoshell with holes.
Qian, Jun; Chen, Zongqiang; Chen, Jing; Li, Yudong; Xu, Jingjun; Sun, Qian
2012-06-18
We studied the optical extinction properties of Au nanoshell with two holes by the discrete-dipole approximation method. We found that the extinction spectra of the nanoparticles are sensitive to the angle between the polarization vector of the incident light and either symmetrical axis of the hole on nanoshell and also the sizes of two holes. The nanostructure we proposed provides the additional dimensional angularly selectivity of the optical properties and the plasmon resonances redshift comparing with the nanocup. In addition, the conception of the "two-dimensional" symmetry breaking of the nanoparticle is suggested which can induce the two-dimensional spatial asymmetry of optical properties of nanoparticles.
Two-dimensional polymers: concepts and perspectives.
Payamyar, Payam; King, Benjamin T; Öttinger, Hans Christian; Schlüter, A Dieter
2016-01-04
Creation of polymers comprised of repeat units that can create topologically planar macromolecules (rather than linear) has been the topic of several recent studies in the field of synthetic polymer chemistry. Such novel macromolecules, known as 2D polymers, are the result of advanced synthetic methodology which allows creation of monolayer sheets with a periodic internal structure and functional groups placed at predetermined sites under mild conditions. Given the promising potentials of 2D polymers, this feature paper aims at discussing the concept of these novel macromolecules from a topological viewpoint in Section 1. This is followed by spotlighting the expected behavior of 2D polymers in the context of polymer physics (entropy elasticity, strength, percolation, and persistence) and polymer chemistry (copolymers and growth kinetics) in Section 2. Section 3 delineates synthetic and analytical matters associated with 2D polymers followed by a brief final section highlighting the potential of these sheet-like macromolecules for application purposes. We hope this article will trigger the interest of chemists, physicists and engineers to help develop this encouraging new class of materials further such that societally relevant applications will be accessible in the market soon.
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.
Theory and application of the RAZOR two-dimensional continuous energy lattice physics code
Zerkle, M.L.; Abu-Shumays, I.K.; Ott, M.W.; Winwood, J.P.
1997-04-01
The theory and application of the RAZOR two-dimensional, continuous energy lattice physics code are discussed. RAZOR solves the continuous energy neutron transport equation in one- and two-dimensional geometries, and calculates equivalent few-group diffusion theory constants that rigorously account for spatial and spectral self-shielding effects. A dual energy resolution slowing down algorithm is used to reduce computer memory and disk storage requirements for the slowing down calculation. Results are presented for a 2D BWR pin cell depletion benchmark problem.
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.
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
The two-dimensional transport solution within CASMO-4
Knott, D.; Edenius, M. )
1993-01-01
First-generation lattice physics codes, such as CASMO-1 through CASMO-3 (Ref. 1), were developed in an effort to analyze relatively short fuel cycles of [approximately]12 months. Fuel designs for these cycles were only mildly heterogeneous, containing a narrow range of enrichments and small loadings of burnable absorbers. The transport methods in these earlier codes, such as transmission probabilities for homogeneous cells, were more than adequate for such fuel designs. As utilities strive for longer cycle lengths, fuel designs have become far more heterogeneous, The current generation of boiling water reactor (BWR) fuel designs may contain nearly 100 fuel pins, with enrichments ranging from 2 to 5% and gadolinia loadings upward of 10% in as many as a dozen pins. In addition, these designs contain large islands of water in and around the center of the assembly and varying amounts of box wall material around the corners of the channel. Such heterogeneities require a more accurate representation at the level of the two-dimensional transport calculation, and this need has fueled interest in a new generation of lattice physics codes. In the most recent version of CASMO (i.e., CASMO-4), the two-dimensional homogeneous transmission probability module from earlier CASMO versions has been replaced with a heterogeneous characteristics solution. Although not entirely integral in nature, the characteristics method combines the most desirable features of integral transport theory (i.e., heterogeneous geometry, explicit representation of streaming, and the capability of generating an exact solution for a given set of data) with those of discrete ordinates (i.e., easy representation of anisotropic scattering and execution time that is directly proportional to problem size).
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.
Chemistry of Two-Dimensional Transition Metal Carbides (MXenes)
NASA Astrophysics Data System (ADS)
Mashtalir, Olha
With consumer trends pushing toward smaller, faster, more flexible, multitasking devices, researchers striving to meet these needs have targeted two-dimensional (2D) materials---and graphene in particular---as holding the most promise for use in advanced applications. But in 2011, a significant interest has been triggered by a newly discovered family of novel 2D materials---layered transitional metal carbides and carbonitrides, named MXenes. Those compounds were of general formula Mn+1 XnTx, where M stands for metal atom, X is C and/or N, n = 1, 2 or 3, and Tx represents surface groups. Being initially suggested as a material for electrical energy storage systems, MXenes' properties and their potential applications have not been explored. This work is the first complete study of MXenes' chemistry that sheds light on the chemical composition, structure and properties of these novel materials and possible routes of its modification. The research was focused on 2D titanium carbide, Ti3C2Tx, chosen as the representative of the MXene family. The kinetic study of Ti 3C2Tx synthesis discovered the main synthesis parameters, viz. temperature, time and particle size, that affect the etching process and define the quality of final product. MXenes were found to be able to spontaneously accommodate various ions and small organic molecules between the layers leading to preopening of the structure. A major challenge of large scale production of delaminated, atomically thin 2D MXene layers was solved with two delamination techniques involving dimethyl sulfoxide and isopropyl amine pre-intercalation followed by sonication in water. Ti3C2Tx was also found to possess adsorptive and photocatalytic properties, revealing its potential for environmental applications. It also showed limited stability in water and in the presence of oxygen, providing important practical information on proper handling and storage of MXene materials. Completion of this work allowed the performance of energy
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.
Ionic solutions of two-dimensional materials
NASA Astrophysics Data System (ADS)
Cullen, Patrick L.; Cox, Kathleen M.; Bin Subhan, Mohammed K.; Picco, Loren; Payton, Oliver D.; Buckley, David J.; Miller, Thomas S.; Hodge, Stephen A.; Skipper, Neal T.; Tileli, Vasiliki; Howard, Christopher A.
2016-11-01
Strategies for forming liquid dispersions of nanomaterials typically focus on retarding reaggregation, for example via surface modification, as opposed to promoting the thermodynamically driven dissolution common for molecule-sized species. Here we demonstrate the true dissolution of a wide range of important 2D nanomaterials by forming layered material salts that spontaneously dissolve in polar solvents yielding ionic solutions. The benign dissolution advantageously maintains the morphology of the starting material, is stable against reaggregation and can achieve solutions containing exclusively individualized monolayers. Importantly, the charge on the anionic nanosheet solutes is reversible, enables targeted deposition over large areas via electroplating and can initiate novel self-assembly upon drying. Our findings thus reveal a unique solution-like behaviour for 2D materials that enables their scalable production and controlled manipulation.
Two-Dimensional Depth-Averaged Hydrodynamic Model for Meandering Channels
NASA Astrophysics Data System (ADS)
Yu, C.; Duan, J. G.
2013-12-01
This research is to simulate meandering channel processes using a two-dimensional depth-averaged hydrodynamic model. The complex interactions among unsteady flow, turbulence, secondary flow, sediment transport and bank erosion are simulated in the model. The governing equations are the two-dimensional depth-averaged Reynolds-averaged Navier-Stokes (2D-RANS) equations and the Exner equation for bed elevation changes. The k-ɛ turbulence model is coupled into the governing equations to calculate the Reynolds stresses in terms of the eddy viscosity concept. The effect of secondary flow, which represents the discrepancy between depth-averaged velocity and actual velocity, is expressed as the dispersion terms in momentum equations. Non-equilibrium sediment transport algorithm is adapted which accounts for the spatial lag between the instantaneous flow properties and the rate of sediment transport. During the process of adaptation, the sediment transport rate gradually develops into the transport capacity of a given flow condition. The model adopts the nonequilibrium total load sediment transport equation that uses the adaptation length to calculate the actual rate of sediment transport. The evolution of channel bed and bank is modeled by the general Exner equation which accounts for both vertical deformation of bed elevation as well as lateral migration of bank. The system of governing equations is solved by the Godunov-type finite volume method on a rectangular grid. The Harten-Lax-van Leer-Contact (HLLC) approximate Riemann solver is adapted to this system of seven equations and the advective fluxes across each cell interface are simultaneously calculated by the extended HLLC solver. At each time step, the diffusion terms in the governing equations are solved by the implicit Euler scheme which is more stable than explicit scheme for the diffusion terms. The source terms are discretized in a well-balanced way to retain the C-property of the proposed hydrodynamic model
Two-dimensional semiconductors for transistors
NASA Astrophysics Data System (ADS)
Chhowalla, Manish; Jena, Debdeep; Zhang, Hua
2016-11-01
In the quest for higher performance, the dimensions of field-effect transistors (FETs) continue to decrease. However, the reduction in size of FETs comprising 3D semiconductors is limited by the rate at which heat, generated from static power, is dissipated. The increase in static power and the leakage of current between the source and drain electrodes that causes this increase, are referred to as short-channel effects. In FETs with channels made from 2D semiconductors, leakage current is almost eliminated because all electrons are confined in atomically thin channels and, hence, are uniformly influenced by the gate voltage. In this Review, we provide a mathematical framework to evaluate the performance of FETs and describe the challenges for improving the performances of short-channel FETs in relation to the properties of 2D materials, including graphene, transition metal dichalcogenides, phosphorene and silicene. We also describe tunnelling FETs that possess extremely low-power switching behaviour and explain how they can be realized using heterostructures of 2D semiconductors.
Color two-dimensional barcode patterns for extra encrypting sinusoidal-function scrambled data
NASA Astrophysics Data System (ADS)
Yeh, Sheng Lih; Lin, Kuang Tsan; Lin, Shyh-Tsong
2016-06-01
Conventional two-dimensional (2-D) barcode patterns are printed with black and white squares to encode texts. A few papers have proposed special 2-D barcode patterns with extra encrypted data, but the security of extra encrypted data is not emphasized usually. Therefore, this paper proposes color 2-D barcode patterns composed of black, blue, white, and yellow subsquares to extra encrypt binary data with higher security. Because blue looks like black and yellow looks like white, a color 2-D barcode pattern performs like a conventional 2-D barcode pattern. On the other hand, black, blue, white, and yellow subsquares are used to denote binary data. The security of extra encrypted data depends on an image scrambling algorithm by using the sinusoidal function, and the image scrambling algorithm can make a scrambled image have a high image scrambling degree percentage even after image scrambling is operated only one time.
Unitary-quantum-lattice algorithm for two-dimensional quantum turbulence
NASA Astrophysics Data System (ADS)
Zhang, Bo; Vahala, George; Vahala, Linda; Soe, Min
2011-10-01
Quantum vortex structures and energy cascades are examined for two-dimensional quantum turbulence (2D QT) at zero temperature. A special unitary evolution algorithm, the quantum lattice algorithm, is employed to simulate the Bose-Einstein condensate governed by the Gross-Pitaevskii (GP) equation. A parameter regime is uncovered in which, as in 3D QT, there is a short Poincaré recurrence time. It is demonstrated that such short recurrence times are destroyed by stronger nonlinear interaction. The similar loss of Poincaré recurrence is also seen in the 3D GP equation. Various initial conditions are considered in an attempt to discern if 2D QT exhibits inverse cascades as is seen in 2D classical turbulence (CT). In our simulation parameter regimes, no dual cascade spectra were observed for 2D QT—unlike that seen in 2D CT.
Two-Dimensional Semiconductor Optoelectronics Based on van der Waals Heterostructures
Lee, Jae Yoon; Shin, Jun-Hwan; Lee, Gwan-Hyoung; Lee, Chul-Ho
2016-01-01
Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDCs) and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW) heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structures of 2D semiconducting TMDCs and their exceptional optical properties, and further discuss the fabrication and distinctive features of vdW heterostructures assembled from different kinds of 2D materials with various physical properties. We then focus on reviewing the recent progress on the fabrication of 2D semiconductor optoelectronic devices based on vdW heterostructures including photodetectors, solar cells, and light-emitting devices. Finally, we highlight the perspectives and challenges of optoelectronics based on 2D semiconductor heterostructures. PMID:28335321
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)
Novel two-dimensional DOA estimation with L-shaped array
NASA Astrophysics Data System (ADS)
Xiaofei, Zhang; Jianfeng, Li; Lingyun, Xu
2011-12-01
Two-dimensional (2D) direction-of-arrival (DOA) estimation has played an important role in array signal processing. In this article, we address a problem of bind 2D-DOA estimation with L-shaped array. This article links the 2D-DOA estimation problem to the trilinear model. To exploit this link, we derive a trilinear decomposition-based 2D-DOA estimation algorithm in L-shaped array. Without spectral peak searching and pairing, the proposed algorithm employs well. Moreover, our algorithm has much better 2D-DOA estimation performance than the estimation of signal parameters via rotational invariance technique algorithms and propagator method. Simulation results illustrate validity of the algorithm.
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.
2015-01-01
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. While 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. PMID:26323616
Two-dimensional solid solution alloy of Bi-Pb binary films on Rh(111)
NASA Astrophysics Data System (ADS)
Yuhara, J.; Yokoyama, M.; Matsui, T.
2011-10-01
We studied the atomic arrangements and phase diagrams of two-dimensional (2D) Bi-Pb binary films on a Rh(111) surface with low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy. The 2D binary films exhibited incommensurate (4 × 4) LEED patterns with any compositional ratio of Bi:Pb. Atomically resolved STM images revealed that the binary films formed hexagonal, close-packed structures in a 2D solid solution alloy. We found that the 2D binary films followed the Hume-Rothery rule. The interatomic distance decreased linearly from 0.359 nm to 0.342 nm with increasing proportions of Pb. This indicated that the lattice constant of the 2D binary films followed Vegard's law.
A Ternary Solvent Method for Large-Sized Two-Dimensional Perovskites.
Chen, Junnian; Gan, Lin; Zhuge, Fuwei; Li, Huiqiao; Song, Jizhong; Zeng, Haibo; Zhai, Tianyou
2017-02-20
Recent reports demonstrate that a two-dimensional (2D) structural characteristic can endow perovskites with both remarkable photoelectric conversion efficiency and high stability, but the synthesis of ultrathin 2D perovskites with large sizes by facile solution methods is still a challenge. Reported herein is the controlled growth of 2D (C4 H9 NH3 )2 PbBr4 perovskites by a chlorobenzene-dimethylformide-acetonitrile ternary solvent method. The critical factors, including solvent volume ratio, crystallization temperature, and solvent polarity on the growth dynamics were systematically studied. Under optimum reaction condition, 2D (C4 H9 NH3 )2 PbBr4 perovskites, with the largest lateral dimension of up to 40 μm and smallest thickness down to a few nanometers, were fabricated. Furthermore, various iodine doped 2D (C4 H9 NH3 )2 PbBrx I4-x perovskites were accessed to tune the optical properties rationally.
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.
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.
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.
Two-dimensional hexagonal semiconductors beyond graphene
NASA Astrophysics Data System (ADS)
Nguyen, Bich Ha; Hieu Nguyen, Van
2016-12-01
The rapid and successful development of the research on graphene and graphene-based nanostructures has been substantially enlarged to include many other two-dimensional hexagonal semiconductors (THS): phosphorene, silicene, germanene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs) such as MoS2, MoSe2, WS2, WSe2 as well as the van der Waals heterostructures of various THSs (including graphene). The present article is a review of recent works on THSs beyond graphene and van der Waals heterostructures composed of different pairs of all THSs. One among the priorities of new THSs compared to graphene is the presence of a non-vanishing energy bandgap which opened up the ability to fabricate a large number of electronic, optoelectronic and photonic devices on the basis of these new materials and their van der Waals heterostructures. Moreover, a significant progress in the research on TMDCs was the discovery of valley degree of freedom. The results of research on valley degree of freedom and the development of a new technology based on valley degree of freedom-valleytronics are also presented. Thus the scientific contents of the basic research and practical applications os THSs are very rich and extremely promising.
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
Nonlinear tunneling in two-dimensional lattices
Brazhnyi, V. A.; Konotop, V. V.; Kuzmiak, V.; Shchesnovich, V. S.
2007-08-15
We present a thorough analysis of the nonlinear tunneling of Bose-Einstein condensates in static and accelerating two-dimensional lattices within the framework of the mean-field approximation. We deal with nonseparable lattices, considering different initial atomic distributions in highly symmetric states. For an analytical description of the condensate before instabilities develop, we derive several few-mode models, analyzing essentially both nonlinear and quasilinear regimes of tunneling. By direct numerical simulations, we show that two-mode models provide an accurate description of tunneling when either initially two states are populated or tunneling occurs between two stable states. Otherwise, a two-mode model may give only useful qualitative hints for understanding tunneling, but does not reproduce many features of the phenomenon. This reflects the crucial role of instabilities developed due to two-body interactions resulting in a non-negligible population of the higher bands. This effect becomes even more pronounced in the case of accelerating lattices. In the latter case we show that the direction of the acceleration is a relevant physical parameter which affects the tunneling by changing the atomic rates at different symmetric states and by changing the numbers of bands involved in the atomic transfer.
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.
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.
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.
Elucidation of Chemical Reactions by Two-Dimensional Resonance Raman Spectroscopy
NASA Astrophysics Data System (ADS)
Moran, Andrew
Two-dimensional (2D) Raman spectroscopies were proposed by Mukamel and Loring in1985 as a method for resolving line broadening mechanisms of vibrational motions in liquids. Significant technical issues challenged the development of both five- and seven-pulse 2D Raman spectroscopies. For this reason, 2D Raman experiments were largely abandoned in 2002 following the first demonstrations of 2D infrared spectroscopies (i.e., an alternate approach for obtaining similar information). We have recently shown that 2D Raman experiments conducted under electronically resonant conditions are much less susceptible to the problems encountered in the earlier 2D Raman work, which was carried out off-resonance. In effect, Franck-Condon activity obviates the problematic selection rules encountered under electronically off-resonant conditions. In this presentation, I will discuss applications of 2D resonance Raman spectroscopies to photodissocation reactions of triiodide and myoglobin. It will be shown that vibrational resonances of the reactants and products can be displayed in separate dimensions of a 2D resonance Raman spectrum when the photo-dissociation reaction is fast compared to the vibrational period. Such 2D spectra expose correlations between the nonequilibrium geometry of the reactant and the distribution of vibrational quanta in the product, thereby yielding insight in the photo-dissociation mechanism. Our results suggest that the ability of 2D resonance Raman spectroscopy to detect correlations between reactants and products will generalize to other ultrafast processes such as electron transfer and energy transfer.
Two-Dimensional Nanomaterials for Biomedical Applications: Emerging Trends and Future Prospects.
Chimene, David; Alge, Daniel L; Gaharwar, Akhilesh K
2015-12-02
Two-dimensional (2D) nanomaterials are ultrathin nanomaterials with a high degree of anisotropy and chemical functionality. Research on 2D nanomaterials is still in its infancy, with the majority of research focusing on elucidating unique material characteristics and few reports focusing on biomedical applications of 2D nanomaterials. Nevertheless, recent rapid advances in 2D nanomaterials have raised important and exciting questions about their interactions with biological moieties. 2D nanoparticles such as carbon-based 2D materials, silicate clays, transition metal dichalcogenides (TMDs), and transition metal oxides (TMOs) provide enhanced physical, chemical, and biological functionality owing to their uniform shapes, high surface-to-volume ratios, and surface charge. Here, we focus on state-of-the-art biomedical applications of 2D nanomaterials as well as recent developments that are shaping this emerging field. Specifically, we describe the unique characteristics that make 2D nanoparticles so valuable, as well as the biocompatibility framework that has been investigated so far. Finally, to both capture the growing trend of 2D nanomaterials for biomedical applications and to identify promising new research directions, we provide a critical evaluation of potential applications of recently developed 2D nanomaterials.
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.
Quasi two-dimensional astigmatic solitons in soft chiral metastructures.
Laudyn, Urszula A; Jung, Paweł S; Karpierz, Mirosław A; Assanto, Gaetano
2016-03-15
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.
Quasi two-dimensional astigmatic solitons in soft chiral metastructures
NASA Astrophysics Data System (ADS)
Laudyn, Urszula A.; Jung, Paweł S.; Karpierz, Mirosław A.; Assanto, Gaetano
2016-03-01
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.
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.
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
An Implicit 2-D Shallow Water Flow Model on Unstructured Quadtree Rectangular Mesh
2011-01-01
Hanson, H.; Wamsley, T., and Zundel, A. K., 2006. Two-dimensional depth-averaged circulation model CMS- M2D : Version 3.0, Report 2: Sediment...Militello, A.; Reed, C.W.; Zundel, A.K. and Kraus, N.C., 2004. Two-dimensional depth-averaged circulation model M2D : Version 2.0, Report 1, Technical
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.
Two-Dimensional Optical Proximity Effects
NASA Astrophysics Data System (ADS)
Flanner, Philip D.; Subramanian, Shankar; Neureuther, Andrew R.
1986-08-01
In projection printing the proximity effects between adjacent two-dimensional features such as concentric elbows can be the limiting factor in designing layout rules. An aerial image simulation code based on the imaging algorithms in SAMPLE has been developed and used to investigate these proximity effects. The program accepts arbitrary polygonal shapes constructed of rectangular and triangular patches. The image is calculated using Hopkins transmission cross coefficient formulation and uses rapid integral evaluation techniques. The cpu time for this FORTRAN F77 program depends on the size of the mask and the partial coherence factor as 0.25[(1 + σ) 2A(NA/λ)2]2 seconds on a DEC VAX 11/780 using double precision, where A is the mask area, σ the coherence factor, NA the numerical aperture and λ the wavelength. The output intensity can be displayed with graphics tools such as UNIGRAFIX or cross-sectioned for input to SAMPLE development simulation along critical paths. Proximity effects in critical regions between features such as nested elbows, contacts near contacts and lines, and lines near large pads are studied. For small contacts studies show that a contact hole can be placed as close as 0.5λ/NA microns to another contact hole. For nested elbows the critical effect is the variation in intensity in the straight regions just adjacent to the corner. This undesirable variation is primarily due to the intrafeature intensity interactions and is not greatly influenced by the proximity of another nested elbow. For general feature shapes the proximity effects are reduced by increasing the partial coherence factor to 0.5 or higher but at the cost of reducing contrast and peak intensity. For contact masks a partial coherence of 0.3 is recommended for higher edge slope and peak intensities. Proximity effects of small defects are also illustrated.
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.
Two-dimensional materials and their prospects in transistor electronics.
Schwierz, F; Pezoldt, J; Granzner, R
2015-05-14
During the past decade, two-dimensional materials have attracted incredible interest from the electronic device community. The first two-dimensional material studied in detail was graphene and, since 2007, it has intensively been explored as a material for electronic devices, in particular, transistors. While graphene transistors are still on the agenda, researchers have extended their work to two-dimensional materials beyond graphene and the number of two-dimensional materials under examination has literally exploded recently. Meanwhile several hundreds of different two-dimensional materials are known, a substantial part of them is considered useful for transistors, and experimental transistors with channels of different two-dimensional materials have been demonstrated. In spite of the rapid progress in the field, the prospects of two-dimensional transistors still remain vague and optimistic opinions face rather reserved assessments. The intention of the present paper is to shed more light on the merits and drawbacks of two-dimensional materials for transistor electronics and to add a few more facets to the ongoing discussion on the prospects of two-dimensional transistors. To this end, we compose a wish list of properties for a good transistor channel material and examine to what extent the two-dimensional materials fulfill the criteria of the list. The state-of-the-art two-dimensional transistors are reviewed and a balanced view of both the pros and cons of these devices is provided.
Two dimensional layered materials: First-principle investigation
NASA Astrophysics Data System (ADS)
Tang, Youjian
Two-dimensional layered materials have emerged as a fascinating research area due to their unique physical and chemical properties, which differ from those of their bulk counterparts. Some of these unique properties are due to carriers and transport being confined to 2 dimensions, some are due to lattice symmetry, and some arise from their large surface area, gateability, stackability, high mobility, spin transport, or optical accessibility. How to modify the electronic and magnetic properties of two-dimensional layered materials for desirable long-term applications or fundamental physics is the main focus of this thesis. We explored the methods of adsorption, intercalation, and doping as ways to modify two-dimensional layered materials, using density functional theory as the main computational methodology. Chapter 1 gives a brief review of density functional theory. Due to the difficulty of solving the many-particle Schrodinger equation, density functional theory was developed to find the ground-state properties of many-electron systems through an examination of their charge density, rather than their wavefunction. This method has great application throughout the chemical and material sciences, such as modeling nano-scale systems, analyzing electronic, mechanical, thermal, optical and magnetic properties, and predicting reaction mechanisms. Graphene and transition metal dichalcogenides are arguably the two most important two-dimensional layered materials in terms of the scope and interest of their physical properties. Thus they are the main focus of this thesis. In chapter 2, the structure and electronic properties of graphene and transition metal dichalcogenides are described. Alkali adsorption onto the surface of bulk graphite and metal intecalation into transition metal dichalcogenides -- two methods of modifying properties through the introduction of metallic atoms into layered systems -- are described in chapter 2. Chapter 3 presents a new method of tuning
Parrondo Games with Two-Dimensional Spatial Dependence
NASA Astrophysics Data System (ADS)
Ethier, S. N.; Lee, Jiyeon
Parrondo games with one-dimensional (1D) spatial dependence were introduced by Toral and extended to the two-dimensional (2D) setting by Mihailović and Rajković. MN players are arranged in an M × N array. There are three games, the fair, spatially independent game A, the spatially dependent game B, and game C, which is a random mixture or non-random pattern of games A and B. Of interest is μB (or μC), the mean profit per turn at equilibrium to the set of MN players playing game B (or game C). Game A is fair, so if μB ≤ 0 and μC > 0, then we say the Parrondo effect is present. We obtain a strong law of large numbers (SLLN) and a central limit theorem (CLT) for the sequence of profits of the set of MN players playing game B (or game C). The mean and variance parameters are computable for small arrays and can be simulated otherwise. The SLLN justifies the use of simulation to estimate the mean. The CLT permits evaluation of the standard error of a simulated estimate. We investigate the presence of the Parrondo effect for both small arrays and large ones. One of the findings of Mihailović and Rajković was that “capital evolution depends to a large degree on the lattice size.” We provide evidence that this conclusion is partly incorrect. A paradoxical feature of the 2D game B that does not appear in the 1D setting is that, for fixed M and N, the mean function μB is not necessarily a monotone function of its parameters.
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.
Note: Unshielded bilateral magnetoencephalography system using two-dimensional gradiometers.
Seki, Yusuke; Kandori, Akihiko; Ogata, Kuniomi; Miyashita, Tsuyoshi; Kumagai, Yukio; Ohnuma, Mitsuru; Konaka, Kuni; Naritomi, Hiroaki
2010-09-01
Magnetoencephalography (MEG) noninvasively measures neuronal activity with high temporal resolution. The aim of this study was to develop a new type of MEG system that can measure bilateral MEG waveforms without a magnetically shielded room, which is an obstacle to reducing both the cost and size of an MEG system. An unshielded bilateral MEG system was developed using four two-dimensional (2D) gradiometers and two symmetric cryostats. The 2D gradiometer, which is based on a low-T(c) superconducting quantum interference device and wire-wound pickup coil detects a magnetic-field gradient in two orthogonal directions, or ∂/∂x(∂(2)B(z)/∂z(2)), 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.
Lift evaluation of a two-dimensional pitching flat plate
NASA Astrophysics Data System (ADS)
Xia, X.; Mohseni, K.
2013-09-01
Several previous experimental and theoretical studies have shown that a leading edge vortex (LEV) on an airfoil or wing can provide lift enhancement. In this paper, unsteady two-dimensional (2D) potential flow theory is employed to model the flow field of a pitching flat plate wing. A multi-vortices model is developed to model both the leading edge and trailing edge vortices (TEVs), which offers improved accuracy compared with using only single vortex at each separation location. The lift is obtained by integrating the unsteady Blasius equation. It is found that the motion of vortices contributes significantly to the overall aerodynamic force on the flat plate. A Kutta-like condition is used to determine the vortex intensity and location at the leading edge for large angle of attack cases; however, it is proposed to relax this condition for small angle of attack cases and apply a 2D shear layer model to calculate the circulation of the new added vortex. The results of the simulation are then compared with classical numerical, theoretical, and experimental data for canonical unsteady flat plat problems. Good agreement with these data is observed. Moreover, these results suggested that the leading edge vortex shedding for small angles of attack should be modeled differently than that for large angles of attack. Finally, the results of vortex motion vs. lift indicate that the slow convection of the LEV creates less negative lift while the rapid shedding of the TEV creates more positive lift. The difference between these two contributions of lift results in a total positive lift that lasts for about two chord-length travel of the plate. It is therefore concluded that the lift enhancement during the LEV "stabilization" above the wing is a combined effect of both the LEV and TEV motion. This also provides the insights for future active flow control of micro aerial vehicles (MAVs) that the formation and shedding process of LEVs and TEVs can be manipulated to provide lift
Monolithic multigrid methods for two-dimensional resistive magnetohydrodynamics
Adler, James H.; Benson, Thomas R.; Cyr, Eric C.; ...
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
Convergence study of Rattlesnake solutions for the two-dimensional C5G7 MOX benchmark
Wang, Yaqi; DeHart, Mark David; Gaston, Derek Ray; Gleicher, Frederick Nathan; Martineau, Richard Charles; Peterson, John William; Schunert, Sebastian
2015-04-01
This paper presents the convergence study of a specific transport scheme, self-adjoint angular flux (SAAF) formulation with the discrete ordinates (SN) method and continuous finite element method (CFEM), implemented with Rattlesnake, on solving the well known two-dimensional C5G7 MOX benchmark. Both the convergence in space and angle are studied. Numerical results show the convergence of the spatial and angular refinements.
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.
Host-guest chemistry in two-dimensional supramolecular networks.
Teyssandier, Joan; Feyter, Steven De; Mali, Kunal S
2016-09-20
Nanoporous supramolecular networks physisorbed on solid surfaces have been extensively used to immobilize a variety of guest molecules. Host-guest chemistry in such two-dimensional (2D) porous networks is a rapidly expanding field due to potential applications in separation technology, catalysis and nanoscale patterning. Diverse structural topologies with high crystallinity have been obtained to capture molecular guests of different sizes and shapes. A range of non-covalent forces such as hydrogen bonds, van der Waals interactions, coordinate bonds have been employed to assemble the host networks. Recent years have witnessed a surge in the activity in this field with the implementation of rational design strategies for realizing controlled and selective guest capture. In this feature article, we review the development in the field of surface-supported host-guest chemistry as studied by scanning tunneling microscopy (STM). Typical host-guest architectures studied on solid surfaces, both under ambient conditions at the solution-solid interface as well as those formed at the ultrahigh vacuum (UHV)-solid interface, are described. We focus on isoreticular host networks, hosts functionalized pores and dynamic host-guest systems that respond to external stimuli.
A two-dimensional electrophoresis database of rat heart proteins.
Li, X P; Pleissner, K P; Scheler, C; Regitz-Zagrosek, V; Salnikow, J; Jungblut, P R
1999-01-01
More than 3000 myocardial protein species of Wistar Kyoto rat, an important animal model, were separated by high-resolution two-dimensional gel electrophoresis (2-DE) and characterized in terms of isoelectric point (pI) and molecular mass (Mr). Currently, the 2-DE database contains 64 identified proteins; forty-three were identified by peptide mass fingerprinting (PMF) using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), nine by exclusive comparison with other 2-DE heart protein databases, and in only 12 cases of 60 attempts N-terminal sequencing was successful. We used the Make2ddb software package downloaded from the ExPASy server for the construction of a rat myocardial 2-DE database. The Make2ddb package simplifies the creation of a new 2-DE database if the Melanie II software and a Sun workstation under Solaris are available. Our 2-DE database of rat heart proteins can be accessed at URL http://gelmatching.inf.fu-berlin.de/pleiss/2d.
Two dimensional discriminant neighborhood preserving embedding in face recognition
NASA Astrophysics Data System (ADS)
Pang, Meng; Jiang, Jifeng; Lin, Chuang; Wang, Binghui
2015-03-01
One of the key issues of face recognition is to extract the features of face images. In this paper, we propose a novel method, named two-dimensional discriminant neighborhood preserving embedding (2DDNPE), for image feature extraction and face recognition. 2DDNPE benefits from four techniques, i.e., neighborhood preserving embedding (NPE), locality preserving projection (LPP), image based projection and Fisher criterion. Firstly, NPE and LPP are two popular manifold learning techniques which can optimally preserve the local geometry structures of the original samples from different angles. Secondly, image based projection enables us to directly extract the optimal projection vectors from twodimensional image matrices rather than vectors, which avoids the small sample size problem as well as reserves useful structural information embedded in the original images. Finally, the Fisher criterion applied in 2DDNPE can boost face recognition rates by minimizing the within-class distance, while maximizing the between-class distance. To evaluate the performance of 2DDNPE, several experiments are conducted on the ORL and Yale face datasets. The results corroborate that 2DDNPE outperforms the existing 1D feature extraction methods, such as NPE, LPP, LDA and PCA across all experiments with respect to recognition rate and training time. 2DDNPE also delivers consistently promising results compared with other competing 2D methods such as 2DNPP, 2DLPP, 2DLDA and 2DPCA.
Statistical properties of two-dimensional magnetohydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Biskamp, D.; Welter, H.; Walter, M.
1990-12-01
The statistical properties of two-dimensional (2-D) magnetohydrodynamic (MHD) turbulence are studied by means of high-resolution numerical simulations. As a theoretical point of reference, the β model of intermittent turbulence is adapted to the MHD case. Comparison of simulation results for energy spectra with the β-model predictions shows intermittency corrections to be small, δ<0.2, while fourth-order correlation functions exhibit a stronger effect δ≂0.35, consistent with the numerically observed Reynolds-number dependence of the flatness factor F∝R1/2λ. An argument is given that this scaling valid for Rλ˜102 is, however, not characteristic of the asymptotic regime Rλ→∞, where a constant value of F is to be expected. The probability distributions of the field difference δv(x,t), δB(x,t) are Gaussian for large separation x or t, approaching an approximately exponential distribution for x, t→0. This behavior can be understood by a simple probabilistic argument. The probability distribution of the local energy dissipation rate ɛ is roughly consistent with a log-normal distribution at larger ɛ but shows a different behavior at small ɛ.
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.
Initial- value problem for the two-dimensional growing wake
NASA Astrophysics Data System (ADS)
Scarsoglio, S.; Tordella, D.; Criminale, W. O.
2006-11-01
A general three-dimensional initial-value perturbation problem is investigated as to effects in a two-dimensional but growing wake. The linearized perturbation analysis considers both the early transient as well as the asymptotic behavior of the disturbance (Blossey, Criminale & Fisher, JFM 2006 submitted). The representation of the mean flow is physically accurate, since it has been obtained by considering the lateral entrainment process and associated streamwise evolution of mass flow (increase) and kinetic energy (decrease) (Tordella & Belan, PoF 2003). This base model is combined with a change of coordinate (moving coordinate trasform) (Criminale & Drazin, Stud. Appl. Math, 1990). The evolution analysis considers inviscid disturbances that are expanded in terms of small values of the wavenumber. The long time behavior is represented by means of a multiple spatial and temporal scale description of the velocity and vorticity perturbations. The limit for small wavenumbers has been studied. It is seen that an increase of the entrainment in the base flow yields instability and grows algebraically in time. This result is also obtained when considering a more general problem where larger wavenumbers, wavelengths of the order of the thickness of the variable shear region, are allowed. Comparison with a recent spatio-temporal multiscale Orr-Sommerfeld analysis of the 2D wake instability (Tordella, Scarsoglio & Belan, PoF 2006). is presented. The perturbation dynamics is examined for different base flow configurations.
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.
Direct Imaging of a Two-Dimensional Silica Glass on Graphene
NASA Astrophysics Data System (ADS)
Huang, P. Y.; Kurasch, S.; Srivastava, A.; Skakalova, V.; Kotakoski, J.; Krasheninnikov, A. V.; Hovden, R. M.; Mao, Q.; Meyer, J. C.; Smet, J.; Muller, D. A.; Kaiser, U.
2012-02-01
Large-area graphene substrates [1] are a promising lab bench for synthesizing and characterizing novel low-dimensional materials such as two-dimensional (2D) glasses. Unlike 2D crystals such as graphene, 2D glasses are almost entirely unexplored--yet they have enormous applicability for understanding amorphous structures, which are difficult to probe in 3D. We report direct observations of the structure of an amorphous 2D silica supported on graphene. To our knowledge, these results represent the first discovery of an extended 2D glass. The 2D glass enables aberration-corrected scanning transmission electron microscopy and spectroscopy, producing the first atomically-resolved experimental images of a glass. The images strikingly resemble Zachariasen's seminal 1932 cartoons of a 2D continuous random network glass [2] and allow direct structural analyses not possible in 3D glassy materials. DFT calculations indicate that van der Waals interactions with graphene energetically favor the 2D structure over bulk SiO2, suggesting that graphene can be instrumental in stabilizing new 2D materials. [1] J. C. Meyer et al., Nature 454, 319--322 (2008). [2] W. H. Zachariasen, J. Am. Chem. Soc. 54, 3841--3851 (1932).
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
Two dimensional electron gas at oxide interfaces
NASA Astrophysics Data System (ADS)
Janicka, Karolina
2011-12-01
Extraordinary phenomena can occur at the interface between two oxide materials. A spectacular example is a formation of a two-dimensional electron gas (2DEG) at the SrTiO3/LaAlO3 interface. In this dissertation the properties of the 2DEG are investigated from first principles. The spatial extent of the 2DEG formed at the SrTiO3/LaAlO 3 n-type interface is studied. It is shown that the confinement of the 2DEG is controlled by metal induced gap states formed in the band gap of SrTiO 3. The confinement width is then determined by the attenuation length of the metal induced gap states into SrTiO3 which is governed by the lowest decay rate evanescent states of bulk SrTiO3 which in turn can be found from the complex band structure of bulk SrTiO3. Magnetic properties of the 2DEG formed at the n-type interface of the SrTiO3/LaAlO3 superlattices are investigated. It is found that for a thin SrTiO3 film the interface is ferromagnetic but for a thicker SrTiO3 film the magnetic moment decreases and eventually disappears. This is a result of delocalization of the 2DEG that spreads over thicker SrTiO3 film which leads to violation of the Stoner criterion. Further, it is shown that inclusion of the Hubbard U interaction enhances the Stoner parameter and stabilizes the magnetism. The effect of the 2DEG and the polar interfaces for the thin film ferroelectricity is investigated using both first principles and model calculations. Using a TiO2-terminated BaTiO3 film with LaO monolayers at the two interfaces it is shown that the intrinsic electric field produced by the polar interface forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO 3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. It is found that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric
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
Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots
Cundiff, Steven T.
2016-05-03
This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.
He, Chunyong; Tao, Juzhou
2016-07-07
A novel highly active and stable HER catalyst containing two-dimensional TaC nanosheets hybridized with reduced graphene oxide (2D TaC-RGO) was prepared as an efficient and stable hydrogen evolution reaction catalyst.
NASA Astrophysics Data System (ADS)
Koo, Keunhwi; Kim, Soo-Yong; Jeong, Jae Jin; Kim, Sang Woo
2014-09-01
This study introduces a two-dimensional (2D) partial response maximum likelihood (PRML) method to reconstruct a degraded data page having 2D inter-symbol interference for holographic data storage. The proposed 2D PRML method consists of 2D partial response (PR) target, 2D equalizer using least mean square algorithm, and 2D soft output Viterbi algorithm (SOVA) having just two one-dimensional (1D) SOVAs in horizontal and vertical directions. To accurately organize a trellis diagram of the 1D SOVA in structural accordance with the 2D PR target, this study proposes the self-reference process for the extrinsic information in the 1D SOVA. Finally, simulation results show that the proposed method has bit error rate performance similar to that of modified 2D SOVA having four 1D SOVAs despite the relatively low computational complexity. Moreover, parallel processing is possible in the two 1D SOVAs through the self-reference process.
NASA Astrophysics Data System (ADS)
Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou
2015-04-01
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.
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
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.
NASA Astrophysics Data System (ADS)
Armigliato, A.; Balboni, R.; Carnevale, G. P.; Pavia, G.; Piccolo, D.; Frabboni, S.; Benedetti, A.; Cullis, A. G.
2003-03-01
A method of obtaining quantitative two-dimensional (2D) maps of strain by the convergent beam electron diffraction technique in a transmission electron microscope is described. It is based on the automatic acquisition of a series of diffraction patterns generated from digital rastering the electron spot in a matrix of points within a selected area of the sample. These patterns are stored in a database and the corresponding strain tensor at each point is calculated, thus yielding a 2D strain map. An example of application of this method to cross-sectioned cells fabricated for the 0.15 μm technology of flash memories is reported.
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.
Pan, Jeng-Jong
1989-01-01
An equation to compute the gravity anomalies of two-dimensional (2-D) bodies with density contrast varying with depth (z axis) was developed by Murthy and Rao (1979). I develop an equation for computing the gravity anomalies of 2-D bodies with constant horizontal density gradient. By combining this equation with the equation of Murthy and Rao, I estimate the depth of the sedimentary basin which is adjacent to the master fault associated with the Rio Grande rift in New Mexico, where the density is assumed to decrease basinward from the fault (Cordell, 1979).
Hydrostatic pressure response of an oxide-based two-dimensional electron system
NASA Astrophysics Data System (ADS)
Zabaleta, J.; Borisov, V. S.; Wanke, R.; Jeschke, H. O.; Parks, S. C.; Baum, B.; Teker, A.; Harada, T.; Syassen, K.; Kopp, T.; Pavlenko, N.; Valentí, R.; Mannhart, J.
2016-06-01
Two-dimensional electron systems with fascinating properties exist in multilayers of standard semiconductors, on helium surfaces, and in oxides. Compared to the two-dimensional (2D) electron gases of semiconductors, the 2D electron systems in oxides are typically more strongly correlated and more sensitive to the microscopic structure of the hosting lattice. This sensitivity suggests that the oxide 2D systems are highly tunable by hydrostatic pressure. Here we explore the effects of hydrostatic pressure on the well-characterized 2D electron system formed at LaAlO3-SrTiO3 interfaces [A. Ohtomo and H. Y. Hwang, Nature (London) 427, 423 (2004), 10.1038/nature02308] and measure a pronounced, unexpected response. Pressure of ˜2 GPa reversibly doubles the 2D carrier density ns at 4 K. Along with the increase of ns, the conductivity and mobility are reduced under pressure. First-principles pressure simulations reveal the same behavior of the carrier density and suggest a possible mechanism of the mobility reduction, based on the dielectric properties of both materials and their variation under external pressure.
Large-quantity and continuous preparation of two-dimensional nanosheets
NASA Astrophysics Data System (ADS)
Zhao, Gang; Wu, Yongzhong; Shao, Yongliang; Hao, Xiaopeng
2016-03-01
With the increasing demand for two-dimensional (2D) nanosheets, such as graphene, hexagonal boron nitride (h-BN), and MoS2 and WS2 nanosheets, finding a simple and feasible method to obtain nanosheets is crucial. Here, we present a high-efficiency exfoliation method to obtain abundant and superior graphene, h-BN, MoS2, and WS2 nanosheets in aqueous solution. The obtained 2D nanosheets are very thin, especially MoS2 and WS2 nanosheets which are below 1 nm.With the increasing demand for two-dimensional (2D) nanosheets, such as graphene, hexagonal boron nitride (h-BN), and MoS2 and WS2 nanosheets, finding a simple and feasible method to obtain nanosheets is crucial. Here, we present a high-efficiency exfoliation method to obtain abundant and superior graphene, h-BN, MoS2, and WS2 nanosheets in aqueous solution. The obtained 2D nanosheets are very thin, especially MoS2 and WS2 nanosheets which are below 1 nm. Electronic supplementary information (ESI) available: SEM images of large quantities of exfoliation of layered nanosheets; SEM images of raw materials; the experimental instrument; specific preparation time of exfoliation of 2D materials; solvents influence at the same exfoliation time. See DOI: 10.1039/c5nr07950k
Difference between fracture of thin brittle sheets and two-dimensional fracture.
Aström, J A
2009-10-01
Recently there has been some suggestions that fragmentation of thin brittle sheets is qualitatively different from pure two-dimensional fragmentation. The obvious reason for such a discrepancy is the possibility of the sheet to deform out of plane. There is a generic crack-branching mechanism that creates power-law fragment size distribution in the small fragment range for two-dimensional (2D) and three-dimensional bulk fragmentation with the power exponent (2D-1)/D. For thin sheets, the power exponent seems to be close to 1.2 which differs from the D=2 exponent 1.5. In order to make a distinct separation between sheet and 2D fragmentation, high-resolution fragment size distributions are required for fragmentation models with minimal differencies other than dimensionality. Here a very efficient numerical model which can be switched from 2D fragmentation to out-of-plane sheet fragmentation with minimal changes is used to produce high-resolution fragment size distribution for the two cases. The model results cast some doubt on the existence of separate universality classes for sheet and 2D fragmentation.
Difference between fracture of thin brittle sheets and two-dimensional fracture
NASA Astrophysics Data System (ADS)
Åström, J. A.
2009-10-01
Recently there has been some suggestions that fragmentation of thin brittle sheets is qualitatively different from pure two-dimensional fragmentation. The obvious reason for such a discrepancy is the possibility of the sheet to deform out of plane. There is a generic crack-branching mechanism that creates power-law fragment size distribution in the small fragment range for two-dimensional (2D) and three-dimensional bulk fragmentation with the power exponent (2D-1)/D . For thin sheets, the power exponent seems to be close to 1.2 which differs from the D=2 exponent 1.5. In order to make a distinct separation between sheet and 2D fragmentation, high-resolution fragment size distributions are required for fragmentation models with minimal differencies other than dimensionality. Here a very efficient numerical model which can be switched from 2D fragmentation to out-of-plane sheet fragmentation with minimal changes is used to produce high-resolution fragment size distribution for the two cases. The model results cast some doubt on the existence of separate universality classes for sheet and 2D fragmentation.
Topological events in two-dimensional grain growth: Experiments and simulations
Fradkov, V.E.; Glicksman, M.E.; Palmer, M.; Rajan, K. . Materials Engineering Dept.)
1994-08-01
Grain growth in polycrystals is a process that occurs as a result of the vanishing of small grains. The mean topological class of vanishing two-dimensional (2-D) grains was found experimentally to be about 4.5. This result suggests that most vanishing grains are either 4- or 5-sided. A recent theory of 2-D grain growth is explicitly based on this fact, treating the switching as random events. The process of shrinking of 4- and 5-sided two-dimensional grains was observed experimentally on polycrystalline films of transparent, pure succinonitrile (SCN). Grain shrinking was studied theoretically and simulated by computer (both dynamic and Monte Carlo). It was found that most shrinking grains are topologically stable and remain within their topological class until they are much smaller than their neighbors. They discuss differences which were found with respect to the behavior of 2-D polycrystals, a 2-D ideal soap froth, and a 2-D section of a 3-D grain structure.
Two-dimensional synthetic aperture laser optical feedback imaging using galvanometric scanning.
Witomski, Arnaud; Lacot, Eric; Hugon, Olivier; Jacquin, Olivier
2008-02-20
We have improved the resolution of our laser optical feedback imaging (LOFI) setup by using a synthetic aperture (SA) process. We report a two-dimensional (2D) SA LOFI experiment where the unprocessed image (i.e., the classical LOFI image) is obtained point by point, line after line using full 2D galvanometric scanning. The 2D superresolved image is then obtained by successively computing two angular SA operations while a one-dimensional angular synthesis is preceded by a frequency synthesis to obtain a 2D superresolved image conventionally in the synthetic aperture radar (SAR) method and their corresponding laser method called synthetic aperture ladar. The numerical and experimental results are compared.
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.
The development of two dimensional group IV chalcogenides, blocks for van der Waals heterostructures
NASA Astrophysics Data System (ADS)
Sa, Baisheng; Sun, Zhimei; Wu, Bo
2015-12-01
In this work, we introduce a series of two dimensional (2D) group IV chalcogenides (AX)2 with the building block X-A-A-X (A = Si, Ge, Sn, and Pb, and X = Se and Te) on the basis of ab initio calculations. The analysis of energy evaluation, lattice vibration as well as the chemical bonding demonstrate the good stability of these 2D materials. Furthermore, the pictures for the chemical bonding and electronic features of the 2D (AX)2 are drawn. Their narrow gapped semiconducting nature is unraveled. Especially, strong interactions between the electrons and phonons as well as the topological insulating nature in (SiTe)2 are observed. The present results indicate that such remarkable artificial 2D (AX)2 are building blocks for van der Waals heterostructure engineering, which shows potential applications in nanoscaled electronics and optoelectronics.
Boron based two-dimensional crystals: theoretical design, realization proposal and applications
NASA Astrophysics Data System (ADS)
Li, Xian-Bin; Xie, Sheng-Yi; Zheng, Hui; Tian, Wei Quan; Sun, Hong-Bo
2015-11-01
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.
NASA Astrophysics Data System (ADS)
Kong, Gyuyeol; Choi, Sooyong
2012-08-01
An effective two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for holographic data storage (HDS) systems is proposed. The proposed scheme adopts the simplified trellis diagram, uses a priori information, and detects the data in two directions from the previously proposed detection schemes. The simplified trellis diagram which has 4 states and 8 branches yields a dramatic complexity reduction while the simplified 2D PRML detector shows serious performance degradation in the high density HDS channels. To prevent performance degradation, the proposed detector uses a priori information in order to give higher reliability to the branch metric. Furthermore, the proposed scheme detects the data in the vertical and horizontal directions to fully utilize the characteristics of the channel detection with a 2D partial response target. By effective combination of these three techniques, the proposed scheme with a simple structure has more than 2 dB gains compared to the conventional detection schemes.
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.
NASA Astrophysics Data System (ADS)
Ogilvie, Jennifer
2010-03-01
Two-dimensional (2D) Fourier transform electronic spectroscopy has recently emerged as a powerful tool for the study of energy transfer in complex condensed-phase systems. Its experimental implementation is challenging but can be greatly simplified by implementing a pump-probe geometry, where the two phase-stable collinear pump pulses are created with an acousto-optic pulse-shaper. This approach also allows the use of a continuum probe pulse, expanding the available frequency range of the detection axis and allowing studies of energy transfer and electronic coupling over a broad range of frequencies. We discuss several benefits of 2D electronic spectroscopy and present 2D data on the D1-D2 reaction center complex of Photosystem II from spinach. We discuss the ability of 2D spectroscopy to distinguish between current models of energy and charge transfer in this system.
NASA Astrophysics Data System (ADS)
Heisler, Ismael A.; Moca, Roberta; Camargo, Franco V. A.; Meech, Stephen R.
2014-06-01
We report an improved experimental scheme for two-dimensional electronic spectroscopy (2D-ES) based solely on conventional optical components and fast data acquisition. This is accomplished by working with two choppers synchronized to a 10 kHz repetition rate amplified laser system. We demonstrate how scattering and pump-probe contributions can be removed during 2D measurements and how the pump probe and local oscillator spectra can be generated and saved simultaneously with each population time measurement. As an example the 2D-ES spectra for cresyl violet were obtained. The resulting 2D spectra show a significant oscillating signal during population evolution time which can be assigned to an intramolecular vibrational mode.
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
2015-12-07
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.
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.
Two Dimensional Synthetic Electron Cyclotron Emission Imaging
NASA Astrophysics Data System (ADS)
Shi, Lei; Valeo, Ernest J.; Tobias, Benjamin J.; Kramer, Gerrit J.; Liu, Chang; Tang, William M.
2016-10-01
Electron Cyclotron Emission (ECE) has been widely used as a measurement of the electron temperature profile in magnetically confined plasmas. The ECE Imaging (ECEI) system provides additional vertical resolutions, and is used to measure the electron temperature fluctuations. The vertical resolution is typically a few centi-meters which is sometimes comparable to the vertical wave length of the underlying fluctuations. The ray-tracing technique used in most synthetic ECE codes to determine the origin and spatial extent of the ECE radiations is not accurate when the refraction and diffraction due to the fluctuations are important. In this presentation, we introduce a new synthetic ECEI code which solves the wave propagation up to the 2nd order of the WKB approximation, and provides full 2D information of the ECE source. We'll show that when the ECE frequency is near the cutoff, the refraction due to the fluctuations is important. A ``trapping'' of the ECE source by the density fluctuations is identified, and is potentially useful for determining the cross phase between electron temperature and density fluctuations. The new formalism is also used to study the Runaway Electrons contribution to the ECE signal, and provides insights to the measured ECE spectrum on DIII-D. This work has been funded by the US Department of Energy under Contract Number DE-AC02-09CH11466.
Elliptic Length Scales in Laminar, Two-Dimensional Supersonic Flows
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AFRL-RQ-WP-TP-2015-0109 ELLIPTIC LENGTH SCALES IN LAMINAR, TWO- DIMENSIONAL SUPERSONIC FLOWS James H. Miller Vehicle Technology Branch...SUBTITLE ELLIPTIC LENGTH SCALES IN LAMINAR, TWO-DIMENSIONAL SUPERSONIC FLOWS 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...ANSI Std. Z39-18 1 Approved for public release; distribution unlimited. Elliptic Length Scales in Laminar, Two-Dimensional Supersonic Flows
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