How vortices and shocks provide for a flux loop in two-dimensional compressible turbulence
Falkovich, Gregory; Kritsuk, Alexei G.
2017-09-01
Large-scale turbulence in fluid layers and other quasi-two-dimensional compressible systems consists of planar vortices and waves. Separately, wave turbulence usually produces a direct energy cascade, while solenoidal planar turbulence transports energy to large scales by an inverse cascade. Here, we consider turbulence at finite Mach numbers when the interaction between acoustic waves and vortices is substantial. We employ solenoidal pumping at intermediate scales and show how both direct and inverse energy cascades are formed starting from the pumping scale. We show that there is an inverse cascade of kinetic energy up to a scale ℓ , where a typical velocity reaches the speed of sound; this creates shock waves, which provide for a compensating direct cascade. When the system size is less than ℓ , the steady state contains a system-size pair of long-living condensate vortices connected by a system of shocks. Thus turbulence in fluid layers processes energy via a loop: Most energy first goes to large scales via vortices and is then transported by waves to small-scale dissipation.
Energy Technology Data Exchange (ETDEWEB)
Rochette, D [Laboratoire Arc Electrique et Plasmas Thermiques, CNRS UMR 6069, Universite Blaise Pascal, IUT de Montlucon, Avenue Aristide Briand, BP 2235, 03101 Montlucon Cedex (France); Clain, S [Laboratoire de Mathematiques pour l' Industrie et la Physique, CNRS UMR 5640, Universite Paul Sabatier Toulouse 3, 118 route de Narbonne, 31062 Toulouse Cedex 4 (France); Andre, P [Laboratoire Arc Electrique et Plasmas Thermiques, CNRS UMR 6069, Universite Blaise Pascal, IUT de Montlucon, Avenue Aristide Briand, BP 2235, 03101 Montlucon Cedex (France); Bussiere, W [Laboratoire Arc Electrique et Plasmas Thermiques, CNRS UMR 6069, Universite Blaise Pascal, IUT de Montlucon, Avenue Aristide Briand, BP 2235, 03101 Montlucon Cedex (France); Gentils, F [Schneider Electric-Science and Technology Division-Research Center A2, 38050 Grenoble Cedex 9 (France)
2007-05-21
Medium voltage (MV) cells have to respect standards (for example IEC ones (IEC TC 17C 2003 IEC 62271-200 High Voltage Switchgear and Controlgear-Part 200 1st edn)) that define security levels against internal arc faults such as an accidental electrical arc occurring in the apparatus. New protection filters based on porous materials are developed to provide better energy absorption properties and a higher protection level for people. To study the filter behaviour during a major electrical accident, a two-dimensional model is proposed. The main point is the use of a dedicated numerical scheme for a non-conservative hyperbolic problem. We present a numerical simulation of the process during the first 0.2 s when the safety valve bursts and we compare the numerical results with tests carried out in a high power test laboratory on real electrical apparatus.
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.
Grusche, Sascha
2014-02-01
Spatial light modulator (SLM)-based tunable sources synthesize any specified spectral power distribution. However, their complexity makes a simpler version desirable. A prism before an SLM-projector is shown to synthesize spectra at least as effectively. Moreover, this simple setup projects two-dimensional (2-D) videos onto a one-dimensional (1-D) screen. Viewed through a prism (or grating), rainbow-colored renderings of grayscale videos emerge. The semitransparent, 2-D virtual images face each viewer all around the 1-D screen. Uncannily, mirrors around the 1-D screen cannot flip the images. In hindsight, SLM-based spectral synthesis is essentially a form of spectral encoding that is applicable to video projection, and beyond.
DEFF Research Database (Denmark)
Bross, P; Jensen, T G; Andresen, B S
1994-01-01
Two-dimensional gel electrophoresis was used to study and compare wild-type medium-chain acyl-CoA dehydrogenase (MCAD; EC 1.3.99.3) and mis-sense mutant enzyme found in patients with MCAD deficiency. By comparing the patterns for wild-type and mutant MCAD expressed in Escherichia coli or in eukar......Two-dimensional gel electrophoresis was used to study and compare wild-type medium-chain acyl-CoA dehydrogenase (MCAD; EC 1.3.99.3) and mis-sense mutant enzyme found in patients with MCAD deficiency. By comparing the patterns for wild-type and mutant MCAD expressed in Escherichia coli...... of one aspartic acid residue per monomer. Comparison of pulse labeling and steady-state amounts of MCAD protein in overexpressing COS-7 cells confirms that K304E MCAD is synthesized and transported into mitochondria in amounts similar to the wild-type protein, but is degraded much more readily. For wild......-type MCAD, the spot representing the nonmodified form predominates after pulse labeling while that representing the modified form is relatively stronger in steady state, demonstrating that the modification occurs in mitochondria after the transit peptide has been removed. For K304E mutant MCAD...
Two-dimensional capillary origami
Energy Technology Data Exchange (ETDEWEB)
Brubaker, N.D., E-mail: nbrubaker@math.arizona.edu; Lega, J., E-mail: lega@math.arizona.edu
2016-01-08
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid. - Highlights: • Full solution set of the two-dimensional capillary origami problem. • Fluid does not necessarily wet the entire plate. • Global energy approach provides exact differential equations satisfied by minimizers. • Bifurcation diagrams highlight three different regimes. • Conditions for spontaneous encapsulation are identified.
Piekarski, Eve; Chitiboi, Teodora; Ramb, Rebecca; Latson, Larry A; Bhatla, Puneet; Feng, Li; Axel, Leon
2017-10-24
Residual respiratory motion degrades image quality in conventional cardiac cine MRI (CCMRI). We evaluated whether a free-breathing (FB) radial imaging CCMRI sequence with compressed sensing reconstruction [extradimensional (e.g. cardiac and respiratory phases) golden-angle radial sparse parallel, or XD-GRASP] could provide better image quality than a conventional Cartesian breath-held (BH) sequence in an unselected population of patients undergoing clinical CCMRI. One hundred one patients who underwent BH and FB imaging in a midventricular short-axis plane at a matching location were included. Visual and quantitative image analysis was performed by two blinded experienced readers, using a five-point qualitative scale to score overall image quality and visual signal-to-noise ratio (SNR) grade, with measures of noise and sharpness. End-diastolic and end-systolic left ventricular areas were also measured and compared for both BH and FB images. Image quality was generally better with the BH cines (overall quality grade for BH vs FB images 4 vs 2.9, p images regarding end-diastolic or end-systolic areas (p = 0.35 and p = 0.12). Eighteen of the 101 patients had poor BH image quality (grade 1 or 2). In this subgroup, the quality of the FB images was better (p = 0.0032), as was the SNR grade (p = 0.003), but there were no significant differences regarding noise and sharpness (p = 0.45 and p = 0.47). Although FB XD-GRASP CCMRI was visually inferior to conventional BH CCMRI in general, it provided improved image quality in the subgroup of patients with respiratory-motion-induced artifacts on BH images.
Two-dimensional flexible nanoelectronics
National Research Council Canada - National Science Library
Akinwande, Deji; Petrone, Nicholas; Hone, James
2014-01-01
.... Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps...
Two-dimensional microstrip detector for neutrons
Energy Technology Data Exchange (ETDEWEB)
Oed, A. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Because of their robust design, gas microstrip detectors, which were developed at ILL, can be assembled relatively quickly, provided the prefabricated components are available. At the beginning of 1996, orders were received for the construction of three two-dimensional neutron detectors. These detectors have been completed. The detectors are outlined below. (author). 2 refs.
Two-dimensional quantum cosmology
Energy Technology Data Exchange (ETDEWEB)
Cooper, A. (Stanford Linear Accelerator Center, CA (USA)); Susskind, L.; Thorlacius, L. (Standford Univ., CA (USA). Dept. of Physics)
1991-09-30
Two-dimensional quantum gravity coupled to conformally invariant matter with central charge c > 25 has been proposed as a toy model for quantum gravity in higher dimensions. The associated 'Wheeler-DeWitt equation' is non-linear and unstable to forming a condensate of baby universes. This will occur even in the classical c {yields} {infinity} limit. Small fluctuations about this background describe the propagation of single universes and satisfy a more conventional linear Wheeler-DeWitt equation. The resulting two-dimensional cosmology depends on details of the non-linear dynamics. In particular the existence of a large-scale cosmological constant is determined by the behavior of a string theoretic tachyon potential near its minimum. (orig.).
Two-dimensional quantum cosmology.
Cooper, A.; Susskind, L.; Thorlacius, L.
1991-09-01
Two-dimensional quantum gravity coupled to conformally invariant matter with central charge c > 25 has been proposed as a toy model for quantum gravity in higher dimensions. The associated 'Wheeler-DeWitt equation' is non-linear and unstable to forming a condensate of baby universes. This will occur even in the classical c→∞ limit. Small fluctuations about this background describe the propagation of single universes and satisfy a more conventional linear Wheeler-DeWitt equation. The resulting two-dimensional cosmology depends on details of the non-linear dynamics. In particular the existence of a large-scale cosmological constant is determined by the behavior of a string theoretic tachyon potential near its minimum.
Two-dimensional flexible nanoelectronics.
Akinwande, Deji; Petrone, Nicholas; Hone, James
2014-12-17
2014/2015 represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.
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.
Phattrawan Tongkumchum
2005-01-01
In this paper we propose a two-dimensional box plot, a simple bivariate extension of the box plot and the scatter plot. This plot comprises a pair of trapeziums oriented in the direction of a fitted straight line, with symbols denoting extreme values. The choice for the fitted straight resistant line showing the relationship between the two variables is Tukey’s resistance line. The main components of the plot are an inner box containing 50% of the projection points of the observations on the ...
A two-dimensional Dirac fermion microscope
Bøggild, Peter; Caridad, José M.; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads
2017-06-01
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
Two-Dimensional NMR Lineshape Analysis
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-04-01
NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions.
A two-dimensional Dirac fermion microscope.
Bøggild, Peter; Caridad, José M; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads
2017-06-09
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
Two-dimensional turbulent convection
Mazzino, Andrea
2017-11-01
We present an overview of the most relevant, and sometimes contrasting, theoretical approaches to Rayleigh-Taylor and mean-gradient-forced Rayleigh-Bénard two-dimensional turbulence together with numerical and experimental evidences for their support. The main aim of this overview is to emphasize that, despite the different character of these two systems, especially in relation to their steadiness/unsteadiness, turbulent fluctuations are well described by the same scaling relationships originated from the Bolgiano balance. The latter states that inertial terms and buoyancy terms balance at small scales giving rise to an inverse kinetic energy cascade. The main difference with respect to the inverse energy cascade in hydrodynamic turbulence [R. H. Kraichnan, "Inertial ranges in two-dimensional turbulence," Phys. Fluids 10, 1417 (1967)] is that the rate of cascade of kinetic energy here is not constant along the inertial range of scales. Thanks to the absence of physical boundaries, the two systems here investigated turned out to be a natural physical realization of the Kraichnan scaling regime hitherto associated with the elusive "ultimate state of thermal convection" [R. H. Kraichnan, "Turbulent thermal convection at arbitrary Prandtl number," Phys. Fluids 5, 1374-1389 (1962)].
Optimizing separations in online comprehensive two-dimensional liquid chromatography.
Pirok, Bob W J; Gargano, Andrea F G; Schoenmakers, Peter J
2017-10-13
Online comprehensive two-dimensional liquid chromatography has become an attractive option for the analysis of complex nonvolatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). Two-dimensional liquid chromatography complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. Two-dimensional liquid chromatography is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high-molecular-weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one-dimensional liquid chromatography, two-dimensional liquid chromatography provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of two-dimensional liquid chromatography with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of two-dimensional liquid chromatography experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of two-dimensional liquid chromatography separations. © 2017 The Authors. Journal of Separation Science published by WILEY-VCH Verlag GmbH & Co. KGaA.
Tunable refraction in a two dimensional quantum metamaterial
Everitt, M. J.; Samson, J. H.; Savelev, S. E.; Spiller, T. P.; Wilson, R.; Zagoskin, A. M.
2012-01-01
In this paper we consider a two-dimensional metamaterial comprising an array of qubits (two level quantum objects). Here we show that a two-dimensional quantum metamaterial may be controlled, e.g. via the application of a magnetic flux, so as to provide controllable refraction of an input signal. Our results are consistent with a material that could be quantum birefringent (beam splitter) or not dependent on the application of this control parameter. We note that quantum metamaterials as prop...
Topology optimization of two-dimensional waveguides
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard; Sigmund, Ole
2003-01-01
In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss.......In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss....
Two-Dimensional Materials for Sensing: Graphene and Beyond
Directory of Open Access Journals (Sweden)
Seba Sara Varghese
2015-09-01
Full Text Available Two-dimensional materials have attracted great scientific attention due to their unusual and fascinating properties for use in electronics, spintronics, photovoltaics, medicine, composites, etc. Graphene, transition metal dichalcogenides such as MoS2, phosphorene, etc., which belong to the family of two-dimensional materials, have shown great promise for gas sensing applications due to their high surface-to-volume ratio, low noise and sensitivity of electronic properties to the changes in the surroundings. Two-dimensional nanostructured semiconducting metal oxide based gas sensors have also been recognized as successful gas detection devices. This review aims to provide the latest advancements in the field of gas sensors based on various two-dimensional materials with the main focus on sensor performance metrics such as sensitivity, specificity, detection limit, response time, and reversibility. Both experimental and theoretical studies on the gas sensing properties of graphene and other two-dimensional materials beyond graphene are also discussed. The article concludes with the current challenges and future prospects for two-dimensional materials in gas sensor applications.
Two dimensional magnetic particle spectrometry.
Graeser, M; von Gladiss, A; Weber, M; Buzug, T M
2017-05-07
Magnetic particle spectrometry (MPS) is an excellent and straight forward method to determine the response of magnetic nanoparticles to an oscillating magnetic field. Such fields are applied in magnetic particle imaging (MPI). However, state of the art MPS devices lack the ability to excite particles in multidimensional field sequences that are present in MPI devices. Especially the particle behavior caused by Lissajous sequences cannot be measured with only one excitation direction. This work presents a new kind of MPS which features two excitation directions to overcome this limitation. Both field coils can drive AC as well as DC currents and are thereby able to emulate the field sequences for arbitrary spatial positions inside an MPI device. Since the DC currents can be switched very fast, the device can be used as system calibration unit and acquire system matrices in very short time. These are crucial for MPI image reconstruction. As the signal-to-noise-ratio provided by the MPS is approximately 1000 times higher than that of actual imaging devices, the time space analysis of particle signals is more precise and easier done. Four system matrices are presented in this paper which have been measured with the realized multidimensional MPS. Additionally, a time space comparison of the particle signal for Lissajous, radial and spiral trajectories is given.
Development of Two-Dimensional NMR
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 20; Issue 11. Development of Two-Dimensional NMR: Strucure Determination of Biomolecules in Solution. Anil Kumar. General Article Volume 20 Issue 11 November 2015 pp 995-1002 ...
Two-dimensional topological photonic systems
Sun, Xiao-Chen; He, Cheng; Liu, Xiao-Ping; Lu, Ming-Hui; Zhu, Shi-Ning; Chen, Yan-Feng
2017-09-01
The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.
Dirac cones in two-dimensional borane
Martinez-Canales, Miguel; Galeev, Timur R.; Boldyrev, Alexander I.; Pickard, Chris J.
2017-11-01
We introduce two-dimensional borane, a single-layered material of BH stoichiometry, with promising electronic properties. We show that, according to density functional theory calculations, two-dimensional borane is semimetallic, with two symmetry-related Dirac cones meeting right at the Fermi energy Ef. The curvature of the cones is lower than in graphene, thus closer to the ideal linear dispersion. Its structure, formed by a puckered trigonal boron network with hydrogen atoms connected to each boron atom, can be understood as distorted, hydrogenated borophene [Mannix et al., Science 350, 1513 (2015), 10.1126/science.aad1080]. Chemical bonding analysis reveals the boron layer in the network being bound by delocalized four-center two-electron σ bonds. Finally, we suggest high pressure could be a feasible route to synthesize two-dimensional borane.
Matching Two-dimensional Gel Electrophoresis' Spots
DEFF Research Database (Denmark)
Dos Anjos, António; AL-Tam, Faroq; Shahbazkia, Hamid Reza
2012-01-01
This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches. This ar......This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches...
Two-dimensional x-ray diffraction
He, Bob B
2009-01-01
Written by one of the pioneers of 2D X-Ray Diffraction, this useful guide covers the fundamentals, experimental methods and applications of two-dimensional x-ray diffraction, including geometry convention, x-ray source and optics, two-dimensional detectors, diffraction data interpretation, and configurations for various applications, such as phase identification, texture, stress, microstructure analysis, crystallinity, thin film analysis and combinatorial screening. Experimental examples in materials research, pharmaceuticals, and forensics are also given. This presents a key resource to resea
Two-dimensional noncommutative gravitational quantum well
Lawson, Latevi; Gouba, Laure; Avossevou, Gabriel Y.
2017-11-01
In this paper we consider two kinds of noncommutative space-time commutation relations in two-dimensional configuration space and feature the absolute value of the minimal length from the generalized uncertainty relations associated to the particular commutation relations. We study the problem of the two-dimensional gravitational quantum well in new Hermitian variables and confront the experimental results for the first lowest energy state of the neutrons in the Earth’s gravitational field to estimate the upper bounds on the noncommutativity parameters. The absolute value of the minimum length is smaller than a few nanometers.
Protein mapping by two-dimensional high performance liquid chromatography
Wagner, K.; Racaityte, K.; Unger, K.K.; Miliotis, T.; Edholm, L.E.; Bischoff, Rainer; Marko-Varga, G
2000-01-01
Current developments in drug discovery in the pharmaceutical industry require highly efficient analytical systems for protein mapping providing high resolution, robustness, sensitivity, reproducibility and a high throughput of samples. The potential of two-dimensional (2D) HPLC as a complementary
Sums of two-dimensional spectral triples
DEFF Research Database (Denmark)
Christensen, Erik; Ivan, Cristina
2007-01-01
construct a sum of two dimensional modules which reflects some aspects of the topological dimensions of the compact metric space, but this will only give the metric back approximately. At the end we make an explicit computation of the last module for the unit interval in. The metric is recovered exactly...
Two-Dimensional Bin Packing Problems
Lodi, Andrea; Martello, Silvano; Monaci, Michele; Vigo, Daniele
2014-01-01
An important variant of two-dimensional bin packing problem (2BP), which is also used in some approximation algorithms for its solution, is the strip packing problem (2SP), in which the items have to be packed in a strip of width W and infinite height, so as to minimize the height at which the strip
Analytical simulation of two dimensional advection dispersion ...
African Journals Online (AJOL)
The study was designed to investigate the analytical simulation of two dimensional advection dispersion equation of contaminant transport. The steady state flow condition of the contaminant transport where inorganic contaminants in aqueous waste solutions are disposed of at the land surface where it would migrate ...
Analytical Simulation of Two Dimensional Advection Dispersion ...
African Journals Online (AJOL)
ADOWIE PERE
ABSTRACT: The study was designed to investigate the analytical simulation of two dimensional advection dispersion equation of contaminant transport. The steady state flow condition of the contaminant transport where inorganic contaminants in aqueous waste solutions are disposed of at the land surface where it would ...
Development of Two-Dimensional NMR
Indian Academy of Sciences (India)
IAS Admin
Two-dimensional NMR, COSY,. NOESY, 2D MRI, biomolecular structure determination. The development of Fourier transform NMR in the mid. 1960's, did parallel processing of the collection of NMR data, increased the signal/noise ratio by two orders of magnitude and made it possible to record the proton NMR spectra of.
New two dimensional compounds: beyond graphene
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 Hubbard-Holstein bipolaron
Macridin, A.; Sawatzky, G. A.; Jarrell, M
We present a diagrammatic Monte Carlo study of the properties of the Hubbard-Holstein bipolaron on a two-dimensional square lattice. With a small Coulomb repulsion U and with increasing electron-phonon interaction, and when reaching a value about two times smaller than the one corresponding to the
Two-dimensional membranes in motion
Davidovikj, D.
2018-01-01
This thesis revolves around nanomechanical membranes made of suspended two - dimensional materials. Chapters 1-3 give an introduction to the field of 2D-based nanomechanical devices together with an overview of the underlying physics and the measurementtools used in subsequent chapters. The research
Analytical Simulation of Two Dimensional Advection Dispersion ...
African Journals Online (AJOL)
ADOWIE PERE
x y x. x y erfc φ... +. −... =.. ∈... (30). RESULT AND DISCUSSION. Two dimensional advection dispersion equations describing the contaminant transport are solve analytically using the change of variable method. Analytical solution of equation (9) is computed. The following figure explains contaminant.
Two-dimensional Kagome photonic bandgap waveguide
DEFF Research Database (Denmark)
Nielsen, Jens Bo; Søndergaard, Thomas; Libori, Stig E. Barkou
2000-01-01
The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes...
Piezoelectricity in Two-Dimensional Materials
Wu, Tao
2015-02-25
Powering up 2D materials: Recent experimental studies confirmed the existence of piezoelectricity - the conversion of mechanical stress into electricity - in two-dimensional single-layer MoS2 nanosheets. The results represent a milestone towards embedding low-dimensional materials into future disruptive technologies. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
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.
Vortex scaling ranges in two-dimensional turbulence
Burgess, B. H.; Dritschel, D. G.; Scott, R. K.
2017-11-01
We survey the role of coherent vortices in two-dimensional turbulence, including formation mechanisms, implications for classical similarity and inertial range theories, and characteristics of the vortex populations. We review early work on the spatial and temporal scaling properties of vortices in freely evolving turbulence and more recent developments, including a spatiotemporal scaling theory for vortices in the forced inverse energy cascade. We emphasize that Kraichnan-Batchelor similarity theories and vortex scaling theories are best viewed as complementary and together provide a more complete description of two-dimensional turbulence. In particular, similarity theory has a continued role in describing the weak filamentary sea between the vortices. Moreover, we locate both classical inertial and vortex scaling ranges within the broader framework of scaling in far-from-equilibrium systems, which generically exhibit multiple fixed point solutions with distinct scaling behaviour. We describe how stationary transport in a range of scales comoving with the dilatation of flow features, as measured by the growth in vortex area, constrains the vortex number density in both freely evolving and forced two-dimensional turbulence. The new theories for coherent vortices reveal previously hidden nontrivial scaling, point to new dynamical understanding, and provide a novel exciting window into two-dimensional turbulence.
Two-dimensional Semiconductor-Superconductor Hybrids
DEFF Research Database (Denmark)
Suominen, Henri Juhani
heterostructures, observing clear evidence of supercurrent, and the first direct spectroscopy of an induced superconducting gap in a two-dimensional electron gas. Nonetheless, these experiments reveal inhomogeneous contacts and a soft-induced superconducting gap, likely due to disorder at the Sm-S interface....... To overcome these issues we integrate the superconductor directly into the semiconducting material growth stack, depositing it in-situ in a molecular beam epitaxy system under high vacuum. We present a number of experiments on these hybrid heterostructures, demonstrating near unity interface transparency...... with previous reports of Majorana modes in semiconductor nanowires. By offering a patternable two-dimensional platform, our approach opens up the door to experiments probing the predicted topological properties in this system....
Two-dimensional ranking of Wikipedia articles
Zhirov, A. O.; Zhirov, O. V.; Shepelyansky, D. L.
2010-10-01
The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists ab aeterno. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. While PageRank highlights very well known nodes with many ingoing links, CheiRank highlights very communicative nodes with many outgoing links. In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.
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
Transmission through a two dimensional quantum metamaterial
Wilson, R. D.; Everitt, M. J.; Samson, J. H.; Salelev, S. E.; Zagoskin, A. M.; Spiller, T. P.
2013-05-01
We begin to explore the possibilities offered by two-dimensional quantum metamaterials by considering the transmission across a prototypical system, that is a square array of coupled qubits (two level quantum systems). We construct a simple model that accounts for the input and detection of propagating excitations in the system. We find that even a limited degree of control through an applied field can allow the tunability between distinctly different regimes of transmission properties.
Two-Dimensional Extreme Learning Machine
Bo Jia; Dong Li; Zhisong Pan; Guyu Hu
2015-01-01
Extreme learning machine (ELM) has achieved wide attention due to faster learning speed compared with conventional neural network models like support vector machine (SVM) and back-propagation (BP) networks. However, like many other methods, ELM is originally proposed to handle vector pattern while nonvector patterns in real applications need to be explored, such as image data. We propose the two-dimensional extreme learning machine (2DELM) based on the very natural idea to deal with matrix...
Two-dimensional silica opens new perspectives
Büchner, Christin; Heyde, Markus
2017-12-01
In recent years, silica films have emerged as a novel class of two-dimensional (2D) materials. Several groups succeeded in epitaxial growth of ultrathin SiO2 layers using different growth methods and various substrates. The structures consist of tetrahedral [SiO4] building blocks in two mirror symmetrical planes, connected via oxygen bridges. This arrangement is called a silica bilayer as it is the thinnest 2D arrangement with the stoichiometry SiO2 known today. With all bonds saturated within the nano-sheet, the interaction with the substrate is based on van der Waals forces. Complex ring networks are observed, including hexagonal honeycomb lattices, point defects and domain boundaries, as well as amorphous domains. The network structures are highly tuneable through variation of the substrate, deposition parameters, cooling procedure, introducing dopants or intercalating small species. The amorphous networks and structural defects were resolved with atomic resolution microscopy and modeled with density functional theory and molecular dynamics. Such data contribute to our understanding of the formation and characteristic motifs of glassy systems. Growth studies and doping with other chemical elements reveal ways to tune ring sizes and defects as well as chemical reactivities. The pristine films have been utilized as molecular sieves and for confining molecules in nanocatalysis. Post growth hydroxylation can be used to tweak the reactivity as well. The electronic properties of silica bilayers are favourable for using silica as insulators in 2D material stacks. Due to the fully saturated atomic structure, the bilayer interacts weakly with the substrate and can be described as quasi-freestanding. Recently, a mm-scale film transfer under structure retention has been demonstrated. The chemical and mechanical stability of silica bilayers is very promising for technological applications in 2D heterostacks. Due to the impact of this bilayer system for glass science
Two Dimensional Lattice Boltzmann Method for Cavity Flow Simulation
Panjit MUSIK; Krisanadej JAROENSUTASINEE
2004-01-01
This paper presents a simulation of incompressible viscous flow within a two-dimensional square cavity. The objective is to develop a method originated from Lattice Gas (cellular) Automata (LGA), which utilises discrete lattice as well as discrete time and can be parallelised easily. Lattice Boltzmann Method (LBM), known as discrete Lattice kinetics which provide an alternative for solving the Navier–Stokes equations and are generally used for fluid simulation, is chosen for the study. A spec...
ANALYTICITY OF TWO DIMENSIONAL FRACTIONAL FOURIER-MELLIN TRANSFORM
Sharma, V.A.; P.B. Deshmukh
2016-01-01
The Fourier-Mellin transform is a useful mathematical tool for electronic world due to its translation and scaling property. Day to day extended work of these transform has provided many applications like solving problems of the oscillation theory, hydrodynamics, the elasticity theory, and physical kinetics, algorithm, signal processing, navigation. In this paper two dimensional fractional Fourier-Mellin transform is extended in the distributional generalized sense. Analyticity...
Non-Stationary Two-Dimensional Subband Transformer Filters
Directory of Open Access Journals (Sweden)
V. Čeperković
2013-11-01
Full Text Available State-of-the-art two-dimensional subband transformation based compression methods typically require large memory size and memory bus bandwidth. This paper discloses a novel method for reducing both shortcomings, and even provides compression or decompression from the cache memory. This solution can be implemented either in software or hardware or their combination, as a front stage in either lossless or lossy image encoder or a back stage in either lossless or lossy image decoder.
Binding energy of two-dimensional biexcitons
DEFF Research Database (Denmark)
Singh, Jai; Birkedal, Dan; Vadim, Lyssenko
1996-01-01
Using a model structure for a two-dimensional (2D) biexciton confined in a quantum well, it is shown that the form of the Hamiltonian of the 2D biexciton reduces into that of an exciton. The binding energies and Bohr radii of a 2D biexciton in its various internal energy states are derived...... analytically using the fractional dimension approach. The ratio of the binding energy of a 2D biexciton to that of a 2D exciton is found to be 0.228, which agrees very well with the recent experimental value. The results of our approach are compared with those of earlier theories....
Gyroscope with two-dimensional optomechanical mirror
Davuluri, Sankar; Li, Kai; Li, Yong
2017-11-01
We propose an application of two-dimensional optomechanical oscillator as a gyroscope by detecting the Coriolis force which is modulated at the natural frequency of the optomechanical oscillator. Dependence of gyroscope's sensitivity on shot noise, back-action noise, thermal noise, and input laser power is studied. At optimal input laser power, the gyroscope's sensitivity can be improved by increasing the mass or by decreasing the temperature and decay rate of the mechanical oscillator. When the mechanical oscillator's thermal occupation number, n th, is zero, sensitivity improves with decrease in frequency of the mechanical oscillator. For {n}{{th}}\\gg 1, the sensitivity is independent of the mechanical oscillator's frequency.
Two-dimensional Hubbard-Holstein bipolaron
Macridin, Alexandru; Sawatzky, George A.; Jarrell, Mark
2004-01-01
We present a diagrammatic Monte Carlo study of the properties of the Hubbard-Holstein bipolaron on a two-dimensional square lattice. With a small Coulomb repulsion, U, and with increasing electron-phonon interaction, and when reaching a value about two times smaller than the one corresponding to the transition of light polaron to heavy polaron, the system suffers a sharp transition from a state formed by two weakly bound light polarons to a heavy, strongly bound on-site bipolaron. Aside from ...
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 give...
Extending models for two-dimensional constraints
DEFF Research Database (Denmark)
Forchhammer, Søren
2009-01-01
for models of two-dimensional constraints and as examples we apply it to the hard-square constraint and the no isolated bits (n.i.b) constraint. The iterative scaling can ensure that the entropy of the extension is optimized and that the entropy is increased compared to the initial model defined on 2 times 2...... elements. Application to a simple stationary model with hidden states is also outlined. For the n.i.b constraint, the initial model is based on elements defined by blocks of (1 times 2) binary symbols....
CORPORATE VALUATION USING TWO-DIMENSIONAL MONTE CARLO SIMULATION
Directory of Open Access Journals (Sweden)
Toth Reka
2010-12-01
Full Text Available In this paper, we have presented a corporate valuation model. The model combine several valuation methods in order to get more accurate results. To determine the corporate asset value we have used the Gordon-like two-stage asset valuation model based on the calculation of the free cash flow to the firm. We have used the free cash flow to the firm to determine the corporate market value, which was calculated with use of the Black-Scholes option pricing model in frame of the two-dimensional Monte Carlo simulation method. The combined model and the use of the two-dimensional simulation model provides a better opportunity for the corporate value estimation.
Flow transitions in two-dimensional foams.
Gilbreth, Christopher; Sullivan, Scott; Dennin, Michael
2006-11-01
For sufficiently slow rates of strain, flowing foam can exhibit inhomogeneous flows. The nature of these flows is an area of active study in both two-dimensional model foams and three dimensional foam. Recent work in three-dimensional foam has identified three distinct regimes of flow [S. Rodts, J. C. Baudez, and P. Coussot, Europhys. Lett. 69, 636 (2005)]. Two of these regimes are identified with continuum behavior (full flow and shear banding), and the third regime is identified as a discrete regime exhibiting extreme localization. In this paper, the discrete regime is studied in more detail using a model two-dimensional foam: a bubble raft. We characterize the behavior of the bubble raft subjected to a constant rate of strain as a function of time, system size, and applied rate of strain. We observe localized flow that is consistent with the coexistence of a power-law fluid with rigid-body rotation. As a function of applied rate of strain, there is a transition from a continuum description of the flow to discrete flow when the thickness of the flow region is approximately ten bubbles. This occurs at an applied rotation rate of approximately 0.07 s-1.
Procedures for two-dimensional electrophoresis of proteins
Energy Technology Data Exchange (ETDEWEB)
Tollaksen, S.L.; Giometti, C.S.
1996-10-01
High-resolution two-dimensional gel electrophoresis (2DE) of proteins, using isoelectric focusing in the first dimension and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) in the second, was first described in 1975. In the 20 years since those publications, numerous modifications of the original method have evolved. The ISO-DALT system of 2DE is a high-throughput approach that has stood the test of time. The problem of casting many isoelectric focusing gels and SDS-PAGE slab gels (up to 20) in a reproducible manner has been solved by the use of the techniques and equipment described in this manual. The ISO-DALT system of two-dimensional gel electrophoresis originated in the late 1970s and has been modified many times to improve its high-resolution, high-throughput capabilities. This report provides the detailed procedures used with the current ISO-DALT system to prepare, run, stain, and photograph two-dimensional gels for protein analysis.
Two-dimensional analysis of gait asymmetry in spastic hemiplegia
Directory of Open Access Journals (Sweden)
Marise Bueno Zonta
2010-09-01
Full Text Available Objective: Simple measures of gait for routine clinical use could be useful when the complex gait analysis systems are not available. The aim of this study was to quantify asymmetry in children with spastic hemiplegia using a two-dimensional gait analysis by videography and to relate the asymmetry to motor function. Methods: Twenty-four children with spastic hemiplegia (19 males, 5 females; mean age 49 months [SD 5 months], range from 39 to 60 months were assessed with a two-dimensional gait analysis by videography and the analyzed parameters were compared with normal values and with clinical and functional data. Results: There were significant differences in swing time (p = 0.002, stance time (p = 0.01 and stance/swing time ratio (p < 0.001. The comparison with the normal values described by Sutherland also demonstrated gait asymmetry. There was no direct relationship between the motor function and asymmetry but a score analysis for specific Gross Motor Function Measure items could quantify it in terms of age of gait acquisition. Children with more adequate muscle tone presented longer stance time in the involved limb than those with more spasticity (p = 0.03. Conclusions: These results suggest that the best performance is associated with the smallest asymmetry in this sample. Although two-dimensional gait analysis does not provide as much data as three dimensional gait analyses, we believe it can contribute significantly to the gait assessment of children with cerebral palsy.
Two-Dimensional Melting under Quenched Disorder
Deutschländer, Sven; Horn, Tobias; Löwen, Hartmut; Maret, Georg; Keim, Peter
2013-08-01
We study the influence of quenched disorder on the two-dimensional melting behavior of superparamagnetic colloidal particles, using both video microscopy and computer simulations of repulsive parallel dipoles. Quenched disorder is introduced by pinning a fraction of the particles to an underlying substrate. We confirm the occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario and observe an intermediate hexatic phase. While the fluid-hexatic transition remains largely unaffected by disorder, the hexatic-solid transition shifts to lower temperatures with increasing disorder. This results in a significantly broadened stability range of the hexatic phase. In addition, we observe spatiotemporal critical(like) fluctuations, which are consistent with the continuous character of the phase transitions. Characteristics of first-order transitions are not observed.
Strategies for Interpreting Two Dimensional Microwave Spectra
Martin-Drumel, Marie-Aline; Crabtree, Kyle N.; Buchanan, Zachary
2017-06-01
Microwave spectroscopy can uniquely identify molecules because their rotational energy levels are sensitive to the three principal moments of inertia. However, a priori predictions of a molecule's structure have traditionally been required to enable efficient assignment of the rotational spectrum. Recently, automated microwave double resonance spectroscopy (AMDOR) has been employed to rapidly generate two dimensional spectra based on transitions that share a common rotational level, which may enable automated extraction of rotational constants without any prior estimates of molecular structure. Algorithms used to date for AMDOR have relied on making several initial assumptions about the nature of a subset of the linked transitions, followed by testing possible assignments by "brute force." In this talk, we will discuss new strategies for interpreting AMDOR spectra, using eugenol as a test case, as well as prospects for library-free, automated identification of the molecules in a volatile mixture.
Two-Dimensional Distributed Inverted Files
Feuerstein, Esteban; Marin, Mauricio; Mizrahi, Michel; Gil-Costa, Veronica; Baeza-Yates, Ricardo
Term-partitioned indexes are generally inefficient for the evaluation of conjunctive queries, as they require the communication of long posting lists. On the other side, document-partitioned indexes incur in excessive overheads as the evaluation of every query involves the participation of all the processors, therefore their scalability is not adequate for real systems. We propose to arrange a set of processors in a two-dimensional array, applying term-partitioning at row level and document-partitioning at column level. Choosing the adequate number of rows and columns given the available number of processors, together with the selection of the proper ways of partitioning the index over that topology is the subject of this paper.
Engineering Two-dimensional Materials Surface Chemistry.
Shih, Chih-Jen
2016-11-30
This account reviews our recent research activities and achievements in the field of two-dimensional (2D) materials surface chemistry. 2D materials are atomically thin, so that carriers are less-restricted to move in the in-plane direction, whereas the out-of-plain motion is quantum-confined. Semiconductor quantum wells and graphene are two well-known examples. Applications of 2D materials in optoelectronics, surface modification, and complex materials must overcome engineering challenges associated with understanding and engineering surface chemistry of 2D materials, which essentially bridge multiscale physical phenomena. In my research group, we understand and engineer broad aspects of chemistry and physics at nanomaterials surfaces for advancing nanomaterials-based technologies. The three main topics covered in this account are as follows: i) colloidal synthesis of stacking-controlled 2D materials, ii) wetting properties of 2D materials, and iii) engineering electronic transport at 2D materials-semiconductor interfaces.
Two-dimensional motions of rockets
Energy Technology Data Exchange (ETDEWEB)
Kang, Yoonhwan [School of Electrical Engineering and Computer Sciences (EECS), Seoul National University, San 56-1, Sillim-dong, Gwanak-gu, Seoul 151-742 (Korea, Republic of); Bae, Saebyok [Institute for Gifted Students, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of)
2007-01-15
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.0.
Two-dimensional nuclear magnetic resonance petrophysics.
Sun, Boqin; Dunn, Keh-Jim
2005-02-01
Two-dimensional nuclear magnetic resonance (2D NMR) opens a wide area for exploration in petrophysics and has significant impact to petroleum logging technology. When there are multiple fluids with different diffusion coefficients saturated in a porous medium, this information can be extracted and clearly delineated from CPMG measurements of such a system either using regular pulsing sequences or modified two window sequences. The 2D NMR plot with independent variables of T2 relaxation time and diffusion coefficient allows clear separation of oil and water signals in the rocks. This 2D concept can be extended to general studies of fluid-saturated porous media involving other combinations of two or more independent variables, such as chemical shift and T1/T2 relaxation time (reflecting pore size), proton population and diffusion contrast, etc.
Two-dimensional fourier transform spectrometer
DeFlores, Lauren; Tokmakoff, Andrei
2013-09-03
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Two-dimensional electroacoustic waves in silicene
Zhukov, Alexander V.; Bouffanais, Roland; Konobeeva, Natalia N.; Belonenko, Mikhail B.
2018-01-01
In this letter, we investigate the propagation of two-dimensional electromagnetic waves in a piezoelectric medium built upon silicene. Ultrashort optical pulses of Gaussian form are considered to probe this medium. On the basis of Maxwell's equations supplemented with the wave equation for the medium's displacement vector, we obtain the effective governing equation for the vector potential associated with the electromagnetic field, as well as the component of the displacement vector. The dependence of the pulse shape on the bandgap in silicene and the piezoelectric coefficient of the medium was analyzed, thereby revealing a nontrivial triadic interplay between the characteristics of the pulse dynamics, the electronic properties of silicene, and the electrically induced mechanical vibrations of the medium. In particular, we uncovered the possibility for an amplification of the pulse amplitude through the tuning of the piezoelectric coefficient. This property could potentially offer promising prospects for the development of amplification devices for the optoelectronics industry.
Two-dimensional Insect Flight on an Air-Water Interface is a Chaotic Oscillator
Mukundarajan, Haripriya; Prakash, Manu
2014-01-01
Two-dimensional flapping wing insect flight on an air-water interface provides a successful foraging strategy to explore an ecological niche on the surface of a pond. However, the complex interplay of surface tension, aerodynamic forces, biomechanics and neural control that enables two-dimensional flight is unknown. Here we report the discovery of two-dimensional flight in the waterlily beetle Galerucella nymphaeae, which is the fastest reported propulsion mode for an insect on a fluid interface. Using kinematics derived from high-speed videography coupled with analytical models, we demonstrate that two-dimensional flight is a chaotic interfacial oscillator, thus significantly constraining the possible range of flight parameters. Discovery of this complex dynamics in two-dimensional flight on time scales similar to neural responses indicates the challenge of evolving active flight control on a fluid interface.
Asymptotics for Two-dimensional Atoms
DEFF Research Database (Denmark)
Nam, Phan Thanh; Portmann, Fabian; Solovej, Jan Philip
2012-01-01
We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E^{\\TF}(\\lambd......We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E......^{\\TF}(\\lambda)$ is given by a Thomas-Fermi type variational problem and $c^{\\rm H}\\approx -2.2339$ is an explicit constant. We also show that the radius of a two-dimensional neutral atom is unbounded when $Z\\to \\infty$, which is contrary to the expected behavior of three-dimensional atoms....
Seismic isolation of two dimensional periodic foundations
Energy Technology Data Exchange (ETDEWEB)
Yan, Y.; Mo, Y. L., E-mail: yilungmo@central.uh.edu [University of Houston, Houston, Texas 77004 (United States); Laskar, A. [Indian Institute of Technology Bombay, Powai, Mumbai (India); Cheng, Z.; Shi, Z. [Beijing Jiaotong University, Beijing (China); Menq, F. [University of Texas, Austin, Texas 78712 (United States); Tang, Y. [Argonne National Laboratory, Argonne, Illinois 60439 (United States)
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.
Plasmons in quasi-two-dimensional metals
da Jornada, Felipe H.; Xian, Lede; Sen, H. Sener; Rubio, Angel; Louie, Steven G.
We employ ab initio density-functional theory (DFT) and GW calculations to understand and predict the plasmon dispersion in quasi-two-dimensional (quasi-2D) metals. We show that, unlike what is found in idealized 2D electron gases, plasmons are virtually dispersionless in real quasi-2D metals for a wide range of excitation wave vectors that are experimentally accessible. We further develop a simpler model that captures this plasmon dispersion in quasi-2D metals and which depends on a single parameter: the characteristic screening length due to interband transitions. Our ab initio calculations further predict that monolayer metallic transition metal dichalcogenides are excellent candidates to explore these dispersionless (flat) plasmons: having large excitation energy that is away from the Landau damping regions makes them ideal systems to support long-lived, spatially-localized 2D plasmons which are highly tunable with substrate. This work is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division; the National Science Foundation; the European Research Council project (ERC-2015-AdG-694097), and the AFOSR Grant No. FA2386-15-1-0006 AOARD 144088.
Two-dimensional bipolar junction transistors
Gharekhanlou, Behnaz; Khorasani, Sina; Sarvari, Reza
2014-03-01
Recent development in fabrication technology of planar two-dimensional (2D) materials has introduced the possibility of numerous novel applications. Our recent analysis has revealed that by definition of p-n junctions through appropriate patterned doping of 2D semiconductors, ideal exponential I-V characteristics may be expected. However, the theory of 2D junctions turns out to be very different to that of standard bulk junctions. Based on this theory of 2D diodes, we construct for the first time a model to describe 2D bipolar junction transistors (2D-BJTs). We derive the small-signal equivalent model, and estimate the performance of a 2D-BJT device based on graphone as the example material. A current gain of about 138 and maximum threshold frequency of 77 GHz, together with a power-delay product of only 4 fJ per 1 μm lateral width is expected at an operating voltage of 5 V. In addition, we derive the necessary formulae and a new approximate solution for the continuity equation in the 2D configuration, which have been verified against numerical solutions.
Photodetectors based on two dimensional materials
Zheng, Lou; Zhongzhu, Liang; Guozhen, Shen
2016-09-01
Two-dimensional (2D) materials with unique properties have received a great deal of attention in recent years. This family of materials has rapidly established themselves as intriguing building blocks for versatile nanoelectronic devices that offer promising potential for use in next generation optoelectronics, such as photodetectors. Furthermore, their optoelectronic performance can be adjusted by varying the number of layers. They have demonstrated excellent light absorption, enabling ultrafast and ultrasensitive detection of light in photodetectors, especially in their single-layer structure. Moreover, due to their atomic thickness, outstanding mechanical flexibility, and large breaking strength, these materials have been of great interest for use in flexible devices and strain engineering. Toward that end, several kinds of photodetectors based on 2D materials have been reported. Here, we present a review of the state-of-the-art in photodetectors based on graphene and other 2D materials, such as the graphene, transition metal dichalcogenides, and so on. Project supported by the National Natural Science Foundation of China (Nos. 61377033, 61574132, 61504136) and the State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.
Perspective: Two-dimensional resonance Raman spectroscopy
Molesky, Brian P.; Guo, Zhenkun; Cheshire, Thomas P.; Moran, Andrew M.
2016-11-01
Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in complex systems. The 2DRR method can leverage electronic resonance enhancement to selectively probe chromophores embedded in complex environments (e.g., a cofactor in a protein). In addition, correlations between the two dimensions of the 2DRR spectrum reveal information that is not available in traditional Raman techniques. For example, distributions of reactant and product geometries can be correlated in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this perspective article, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide and myoglobin. We also address key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopies. Most notably, it has been shown that these two techniques are subject to a tradeoff between sensitivity to anharmonicity and susceptibility to artifacts. Overall, recent experimental developments and applications of the 2DRR method suggest great potential for the future of the technique.
Dynamics of two-dimensional dipole systems.
Golden, Kenneth I; Kalman, Gabor J; Hartmann, Peter; Donkó, Zoltán
2010-09-01
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 ϕ{D}(r)=μ{2}/r{3} repulsive interaction potential; μ is the electric dipole strength. The interest in the 2DDS is twofold. First, the quasi-long-range 1/r{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 4He . 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 4He .
Janus spectra in two-dimensional flows
Liu, Chien-Chia; Chakraborty, Pinaki
2016-01-01
In theory, large-scale atmospheric flows, soap-film flows and other two-dimensional flows may host two distinct types of turbulent energy spectra---in one, $\\alpha$, the spectral exponent of velocity fluctuations, equals $3$ and the fluctuations are dissipated at the small scales, and in the other, $\\alpha=5/3$ and the fluctuations are dissipated at the large scales---but measurements downstream of obstacles have invariably revealed $\\alpha = 3$. Here we report experiments on soap-film flows where downstream of obstacles there exists a sizable interval in which $\\alpha$ has transitioned from $3$ to $5/3$ for the streamwise fluctuations but remains equal to $3$ for the transverse fluctuations, as if two mutually independent turbulent fields of disparate dynamics were concurrently active within the flow. This species of turbulent energy spectra, which we term the Janus spectra, has never been observed or predicted theoretically. Our results may open up new vistas in the study of turbulence and geophysical flows...
Radiation effects on two-dimensional materials
Energy Technology Data Exchange (ETDEWEB)
Walker, R.C. II; Robinson, J.A. [Department of Materials Science, Penn State, University Park, PA (United States); Center for Two-Dimensional Layered Materials, Penn State, University Park, PA (United States); Shi, T. [Department of Mechanical and Nuclear Engineering, Penn State, University Park, PA (United States); Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI (United States); Silva, E.C. [GlobalFoundries, Malta, NY (United States); Jovanovic, I. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI (United States)
2016-12-15
The effects of electromagnetic and particle irradiation on two-dimensional materials (2DMs) are discussed in this review. Radiation creates defects that impact the structure and electronic performance of materials. Determining the impact of these defects is important for developing 2DM-based devices for use in high-radiation environments, such as space or nuclear reactors. As such, most experimental studies have been focused on determining total ionizing dose damage to 2DMs and devices. Total dose experiments using X-rays, gamma rays, electrons, protons, and heavy ions are summarized in this review. We briefly discuss the possibility of investigating single event effects in 2DMs based on initial ion beam irradiation experiments and the development of 2DM-based integrated circuits. Additionally, beneficial uses of irradiation such as ion implantation to dope materials or electron-beam and helium-beam etching to shape materials have begun to be used on 2DMs and are reviewed as well. For non-ionizing radiation, such as low-energy photons, we review the literature on 2DM-based photo-detection from terahertz to UV. The majority of photo-detecting devices operate in the visible and UV range, and for this reason they are the focus of this review. However, we review the progress in developing 2DMs for detecting infrared and terahertz radiation. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Recent advances in electrochemical biosensors based on graphene two-dimensional nanomaterials.
Song, Yang; Luo, Yanan; Zhu, Chengzhou; Li, He; Du, Dan; Lin, Yuehe
2016-02-15
Graphene as a star among two-dimensional nanomaterials has attracted tremendous research interest in the field of electrochemistry due to their intrinsic properties, including the electronic, optical, and mechanical properties associated with their planar structure. The marriage of graphene and electrochemical biosensors has created many ingenious biosensing strategies for applications in the areas of clinical diagnosis and food safety. This review provides a comprehensive overview of the recent advances in the development of graphene based electrochemical biosensors. Special attention is paid to graphene-based enzyme biosensors, immunosensors, and DNA biosensors. Future perspectives on high-performance graphene-based electrochemical biosensors are also discussed. Copyright © 2015 Elsevier B.V. All rights reserved.
Two-dimensional crystals: managing light for optoelectronics.
Eda, Goki; Maier, Stefan A
2013-07-23
Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light-matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.
Two-dimensional microgap gas chambers on silicon
Energy Technology Data Exchange (ETDEWEB)
Marel, J. van der [Delft Univ. of Technol. (Netherlands). Fac. of Appl. Phys.]|[Delft Univ. of Technol. (Netherlands). Inst. of Microelectron. and Submicrotechnol.; Bogaard, A. van der [Delft Univ. of Technol. (Netherlands). Fac. of Appl. Phys.]|[Delft Univ. of Technol. (Netherlands). Inst. of Microelectron. and Submicrotechnol.; Eijk, C.W.E. van [Delft Univ. of Technol. (Netherlands). Fac. of Appl. Phys.]|[Delft Univ. of Technol. (Netherlands). Inst. of Microelectron. and Submicrotechnol.; Hollander, R.W. [Delft Univ. of Technol. (Netherlands). Fac. of Appl. Phys.]|[Delft Univ. of Technol. (Netherlands). Inst. of Microelectron. and Submicrotechnol.; Sarro, P.M. [Delft Univ. of Technol. (Netherlands). Fac. of Appl. Phys.]|[Delft Univ. of Technol. (Netherlands). Inst. of Microelectron. and Submicrotechnol.
1995-12-11
We are manufacturing microgap chambers (MGC) on silicon with two-dimensional read-out. They have an anode pitch of 100 {mu}m and a cathode pitch of 400 {mu}m. We obtained a maximum gas gain of 2500 and the avalanche charge collection takes place within 15 ns. The stability of the gas gain is very good. We have tested the position resolution for the detection of X-rays. It appears that the gas composition and the strength of the drift field are important parameters. A high concentration of dimethylether and a rather small drift field provide the smallst size of the total avalanche. (orig.).
Theories on Frustrated Electrons in Two-Dimensional Organic Solids
Directory of Open Access Journals (Sweden)
Chisa Hotta
2012-08-01
Full Text Available Two-dimensional quarter-filled organic solids are a promising class of materials to realize the strongly correlated insulating states called dimer Mott insulator and charge order. In their conducting layer, the molecules form anisotropic triangular lattices, harboring geometrical frustration effect, which could give rise to many interesting states of matter in the two insulators and in the metals adjacent to them. This review is concerned with the theoretical studies on such issue over the past ten years, and provides the systematic understanding on exotic metals, dielectrics, and spin liquids, which are the consequences of the competing correlation and fluctuation under frustration.
Two-dimensional carbon fundamental properties, synthesis, characterization, and applications
Yihong, Wu; Ting, Yu
2013-01-01
After a brief introduction to the fundamental properties of graphene, this book focuses on synthesis, characterization and application of various types of two-dimensional (2D) nanocarbons ranging from single/few layer graphene to carbon nanowalls and graphene oxides. Three major synthesis techniques are covered: epitaxial growth of graphene on SiC, chemical synthesis of graphene on metal, and chemical vapor deposition of vertically aligned carbon nanosheets or nanowalls. One chapter is dedicated to characterization of 2D nanocarbon using Raman spectroscopy. It provides extensive coverage for a
Method and system for determining a volume of an object from two-dimensional images
Abercrombie, Robert K [Knoxville, TN; Schlicher, Bob G [Portsmouth, NH
2010-08-10
The invention provides a method and a computer program stored in a tangible medium for automatically determining a volume of three-dimensional objects represented in two-dimensional images, by acquiring at two least two-dimensional digitized images, by analyzing the two-dimensional images to identify reference points and geometric patterns, by determining distances between the reference points and the component objects utilizing reference data provided for the three-dimensional object, and by calculating a volume for the three-dimensional object.
GPM GROUND VALIDATION TWO-DIMENSIONAL VIDEO DISDROMETER (2DVD) NSSTC V1
National Aeronautics and Space Administration — The Two-dimensional Video Disdrometer (2DVD) uses two high speed line scan cameras which provide continuous measurements of size distribution, shape and fall...
Molecular ping-pong Game of Life on a two-dimensional DNA origami array
National Research Council Canada - National Science Library
Jonoska, N; Seeman, N C
2015-01-01
.... The platform is a two-dimensional DNA origami array of tiles decorated with strands that provide both, the floating molecular tiles to attach and to pass communicating signals to neighbouring array tiles...
Enzymes are complex proteins that cause a specific chemical change in all parts of the body. For ... use them. Blood clotting is another example of enzymes at work. Enzymes are needed for all body ...
Two-dimensional grid-free compressive beamforming.
Yang, Yang; Chu, Zhigang; Xu, Zhongming; Ping, Guoli
2017-08-01
Compressive beamforming realizes the direction-of-arrival (DOA) estimation and strength quantification of acoustic sources by solving an underdetermined system of equations relating microphone pressures to a source distribution via compressive sensing. The conventional method assumes DOAs of sources to lie on a grid. Its performance degrades due to basis mismatch when the assumption is not satisfied. To overcome this limitation for the measurement with plane microphone arrays, a two-dimensional grid-free compressive beamforming is developed. First, a continuum based atomic norm minimization is defined to denoise the measured pressure and thus obtain the pressure from sources. Next, a positive semidefinite programming is formulated to approximate the atomic norm minimization. Subsequently, a reasonably fast algorithm based on alternating direction method of multipliers is presented to solve the positive semidefinite programming. Finally, the matrix enhancement and matrix pencil method is introduced to process the obtained pressure and reconstruct the source distribution. Both simulations and experiments demonstrate that under certain conditions, the grid-free compressive beamforming can provide high-resolution and low-contamination imaging, allowing accurate and fast estimation of two-dimensional DOAs and quantification of source strengths, even with non-uniform arrays and noisy measurements.
Two-dimensional Chebyshev hybrid functions and their applications to integral equations
Directory of Open Access Journals (Sweden)
Zahra JafariBehbahani
2015-06-01
Full Text Available A combination of bivariate Chebyshev polynomials and two-dimensional block-pulse functions are introduced and applied for approximating the numerical solution of two-dimensional Fredholm integral equations. All calculations in this approach would be easily implemented. The method has the advantage of reducing computational burden. The convergence analysis is given. Some numerical examples are provided to illustrate the accuracy and computational efficiency of the proposed method.
Electrical and optoelectronic properties of two-dimensional materials
Wang, Qiaoming
Electrical and optoelectronic properties of bulk semiconductor materials have been extensively explored in last century. However, when reduced to one-dimensional and two-dimensional, many semiconductors start to show unique electrical and optoelectronic behaviors. In this dissertation, electrical and optoelectronic properties of one-dimensional (nanowires) and two-dimensional semiconductor materials are investigated by various techniques, including scanning photocurrent microscopy, scanning Kelvin probe microscopy, Raman spectroscopy, photoluminescence, and finite-element simulations. In our work, gate-tunable photocurrent in ZnO nanowires has been observed under optical excitation in the visible regime, which originates from the nanowire/substrate interface states. This gate tunability in the visible regime can be used to enhance the photon absorption efficiency, and suppress the undesirable visible-light photodetection in ZnO-based solar cells. The power conversion efficiency of CuInSe2/CdS core-shell nanowire solar cells has been investigated. The highest power conversion efficiency per unit area/volume is achieved with core diameter of 50 nm and the thinnest shell thickness. The existence of the optimal geometrical parameters is due to a combined effect of optical resonances and carrier transport/dynamics. Significant current crowding in two-dimensional black phosphorus field-effect transistors has been found, which has been significantly underestimated by the commonly used transmission-line model. This current crowding can lead to Joule heating close to the contacts. New van der Waals metal-semiconductor junctions have been mechanically constructed and systematically studied. The photocurrent on junction area has been demonstrated to originate from the photothermal effect rather than the photovoltaic effect. Our findings suggest that a reasonable control of interface/surface state properties can enable new and beneficial functionalities in nanostructures. We
Photodetectors based on graphene, other two-dimensional materials and hybrid systems.
Koppens, F H L; Mueller, T; Avouris, Ph; Ferrari, A C; Vitiello, M S; Polini, M
2014-10-01
Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms. The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges. These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies. Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides.
A versatile apparatus for two-dimensional atomtronic quantum simulation
Haase, T. A.; White, D. H.; Brown, D. J.; Herrera, I.; Hoogerland, M. D.
2017-11-01
We report on the implementation of a novel optical setup for generating high-resolution customizable potentials to address ultracold bosonic atoms in two dimensions. Two key features are developed for this purpose. The customizable potential is produced with a direct image of a spatial light modulator, conducted with an in-vacuum imaging system of high numerical aperture. Custom potentials are drawn over an area of 600 ×400 μ m with a resolution of 0.9 μm. The second development is a two-dimensional planar trap for atoms with an aspect ratio of 900 and spatial extent of Rayleigh range 1.6 × 1.6 mm, providing near-ballistic in-planar movement. We characterize the setup and present a brief catalog of experiments to highlight the versatility of the system.
Effective-range dependence of two-dimensional Fermi gases
Schonenberg, L. M.; Verpoort, P. C.; Conduit, G. J.
2017-08-01
The Feshbach resonance provides precise control over the scattering length and effective range of interactions between ultracold atoms. We propose the ultratransferable pseudopotential to model effective interaction ranges -1.5 ≤kF2Reff2≤0 , where Reff is the effective range and kF is the Fermi wave vector, describing narrow to broad Feshbach resonances. We develop a mean-field treatment and exploit the pseudopotential to perform a variational and diffusion Monte Carlo study of the ground state of the two-dimensional Fermi gas, reporting on the ground-state energy, contact, condensate fraction, momentum distribution, and pair-correlation functions as a function of the effective interaction range across the BEC-BCS crossover. The limit kF2Reff2→-∞ is a gas of bosons with zero binding energy, whereas ln(kFa )→-∞ corresponds to noninteracting bosons with infinite binding energy.
Isolated structures in two-dimensional optical superlattice
Zou, Xin-Hao; Yang, Bao-Guo; Xu, Xia; Tang, Peng-Ju; Zhou, Xiao-Ji
2017-10-01
Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various "sublattice" patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal "sublattice" structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in "sublattices". Our configurations provide unique opportunities to study particle entanglement in "lattices" formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.
Intensity Coding in Two-Dimensional Excitable Neural Networks
Copelli, Mauro
2016-01-01
In the light of recent experimental findings that gap junctions are essential for low level intensity detection in the sensory periphery, the Greenberg-Hastings cellular automaton is employed to model the response of a two-dimensional sensory network to external stimuli. We show that excitable elements (sensory neurons) that have a small dynamical range are shown to give rise to a collective large dynamical range. Therefore the network transfer (gain) function (which is Hill or Stevens law-like) is an emergent property generated from a pool of small dynamical range cells, providing a basis for a "neural psychophysics". The growth of the dynamical range with the system size is approximately logarithmic, suggesting a functional role for electrical coupling. For a fixed number of neurons, the dynamical range displays a maximum as a function of the refractory period, which suggests experimental tests for the model. A biological application to ephaptic interactions in olfactory nerve fascicles is proposed.
A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy
Energy Technology Data Exchange (ETDEWEB)
El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens, E-mail: bredenbeck@biophysik.uni-frankfurt.org, E-mail: bredenbeck@biophysik.uni-frankfurt.de [Institut für Biophysik, Johann Wolfgang Goethe-Universität, Max-von-Laue-Strasse 1, 60438 Frankfurt (Germany)
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.
Perpendicular magnetic anisotropy of two-dimensional Rashba ferromagnets
Kim, Kyoung-Whan; Lee, Kyung-Jin; Lee, Hyun-Woo; Stiles, M. D.
2017-01-01
We compute the magnetocrystalline anisotropy energy within two-dimensional Rashba models. For a ferromagnetic free-electron Rashba model, the magnetic anisotropy is exactly zero regardless of the strength of the Rashba coupling, unless only the lowest band is occupied. For this latter case, the model predicts in-plane anisotropy. For a more realistic Rashba model with finite band width, the magnetic anisotropy evolves from in-plane to perpendicular and back to in-plane as bands are progressively filled. This evolution agrees with first-principles calculations on the interfacial anisotropy, suggesting that the Rashba model captures energetics leading to anisotropy originating from the interface provided that the model takes account of the finite Brillouin zone. The results show that the electron density modulation by doping or an external voltage is more important for voltage-controlled magnetic anisotropy than the modulation of the Rashba parameter. PMID:28596998
Flat Chern Band in a Two-Dimensional Organometallic Framework
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 structure, namely, the flat Chern band, has recently been proposed to spawn high-temperature fractional quantum Hall states. Despite the proposal of several theoretical lattice models, however, it remains doubtful whether such a “romance of flatland” could exist in a real material. Here, we present a first-principles design of a two-dimensional indium-phenylene organometallic framework that realizes a nearly flat Chern band right around the Fermi level by combining lattice geometry, spin-orbit coupling, and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design, in addition, provides a general strategy to synthesize topologically nontrivial materials by virtue of organic chemistry and nanotechnology.
The dynamics of cellular two-dimensional flames
Almarcha, Christophe; Quinard, Joel; Denet, Bruno; Al-Sarraf, Elias; Laugier, Jean-Marie; Villermaux, Emmanuel
2014-11-01
Premixed flames propagating in an initially quiescent medium undergo hydrodynamic instabilities that corrugate their shape, leading to non stationary cells. The shape of a flame is a critical issue as it rules its speed or the presence of incomplete reaction zones. We report here on experiments of premixed propane-air and methane-air flames freely propagating in a vertically oriented Hele-Shaw cell. In such configuration, the quasi two dimensional flames are easy to study by image analysis thanks to a high speed camera. The dynamics is favorably compared to numerical simulations of Michelson-Sivashinsky equation. The cell size distribution is analyzed and seems to be self similar whatever the gas mixture composition, provided that the dynamics is sufficiently rich, ie the flame is sufficiently unstable. We propose an explanation for this distribution.
Two Dimensional Antiferromagnetic Chern Insulator: NiRuCl6.
Zhou, P; Sun, C Q; Sun, L Z
2016-10-12
Density functional theory (DFT) and Berry curvature calculations show that quantum anomalous Hall effect (QAHE) can be realized in two-dimensional(2D) antiferromagnetic (AFM) NiRuCl6. The results indicate that NiRuCl6 behaves as an AFM Chern insulator and its spin-polarized electronic structure and strong spin-orbit coupling (SOC) are responsible for the QAHE. By tuning SOC, we found that the topological property of NiRuCl6 arises from its energy band inversion. Considering the compatibility between the AFM and insulators, AFM Chern insulator provides a new way to archive high temperature QAHE in experiments due to its different magnetic coupling mechanism from that of ferromagnetic (FM) Chern insulator.
Approaches to verification of two-dimensional water quality models
Energy Technology Data Exchange (ETDEWEB)
Butkus, S.R. (Tennessee Valley Authority, Chattanooga, TN (USA). Water Quality Dept.)
1990-11-01
The verification of a water quality model is the one procedure most needed by decision making evaluating a model predictions, but is often not adequate or done at all. The results of a properly conducted verification provide the decision makers with an estimate of the uncertainty associated with model predictions. Several statistical tests are available for quantifying of the performance of a model. Six methods of verification were evaluated using an application of the BETTER two-dimensional water quality model for Chickamauga reservoir. Model predictions for ten state variables were compared to observed conditions from 1989. Spatial distributions of the verification measures showed the model predictions were generally adequate, except at a few specific locations in the reservoir. The most useful statistics were the mean standard error of the residuals. Quantifiable measures of model performance should be calculated during calibration and verification of future applications of the BETTER model. 25 refs., 5 figs., 7 tabs.
Local Density for Two-Dimensional One-Component Plasma
Bauerschmidt, Roland; Bourgade, Paul; Nikula, Miika; Yau, Horng-Tzer
2017-11-01
We study the classical two-dimensional one-component plasma of N positively charged point particles, interacting via the Coulomb potential and confined by an external potential. For the specific inverse temperature {β=1} (in our normalization), the charges are the eigenvalues of random normal matrices, and the model is exactly solvable as a determinantal point process. For any positive temperature, using a multiscale scheme of iterated mean-field bounds, we prove that the equilibrium measure provides the local particle density down to the optimal scale of {N^{o(1)}} particles. Using this result and the loop equation, we further prove that the particle configurations are rigid, in the sense that the fluctuations of smooth linear statistics on any scale are {N^{o(1)}}.
Effective Interaction in Polarized Two-dimensional Electron Systems
Suwa, Takeshi; Takayanagi, Kazuo; Lipparini, Enrico
2004-10-01
Multiple scattering processes in two-dimensional electron systems with an arbitrary spin polarization are expressed as a spin-dependent effective interaction operator, which allows applications in various two-dimensional electron systems. Effects of the spin polarization on the correlation energy and the pair correlation function are discussed in detail in connection with the polarization-dependence of the effective interaction.
Mechanics of Apparent Horizon in Two Dimensional Dilaton Gravity
Cai, Rong-Gen
2016-01-01
In this article, we give a definition of apparent horizon in a two dimensional general dilaton gravity theory. With this definition, we construct the mechanics of the apparent horizon by introducing a quasi-local energy of the theory. Our discussion generalizes the apparent horizons mechanics in general spherically symmetric spactimes in four or higher dimensions to the two dimensional dilaton gravity case.
Two dimensional chromatographic analysis as a quality measure of ...
African Journals Online (AJOL)
The two dimensional thin layer chromatographic plate was developed in one direction using the eluent given in the GHP, the plate was then rotated 90 degrees and further developed using neat dichloromethane. Results and Conclusion: The two dimensional thin layer chromatogram for the selected sample Salvia officinalis ...
TreePM Method for Two-Dimensional Cosmological Simulations
Indian Academy of Sciences (India)
TreePM Method for Two-Dimensional Cosmological Simulations. Suryadeep Ray ... Keywords. Gravitation; methods: numerical; cosmology: large scale structure of the universe. ... The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid ...
Suzuki, H; Yaoi, T; Kawai, J; Hara, A; Kuwajima, G; Wantanabe, S
1996-01-01
We have developed a new method, designated restriction landmark cDNA scanning (RLCS), which displays many cDNA species quantitatively and simultaneously as two-dimensional gel spots. In this method cDNA species of uniform length were prepared for each mRNA species using restriction enzymes. After the restriction enzyme sites were radiolabeled as landmarks, the labeled fragments were subjected to high resolution two-dimensional gel electrophoresis. In analyses of cDNA samples from adult mouse liver and brain (cerebral cortex, cerebellum and brain stem) we detected approximately 500 and >1000 discrete gel spots respectively of various intensities at a time. The spot patterns of the three brain regions were very similar, although not identical, but were quite different from the pattern for the liver. RNA blot hybridization analysis using several cloned spot DNAs as probes showed that differences in intensity of the spots among RLCS profiles correlated well with expression levels of the corresponding mRNA species in the brain regions. Because the spots and their intensities reflect distinct mRNA species and their expression level respectively, the RLCS is a novel cDNA display system which provides a great deal of information and should be useful for systematic documentation of differentially expressed genes. PMID:8628652
Kamerlin, Shina C L; Sharma, Pankaz K; Chu, Zhen T; Warshel, Arieh
2010-03-02
One of the best systems for exploring the origin of enzyme catalysis has been the reaction of ketosteroid isomerase (KSI). Studies of the binding of phenolates to KSI have been taken as proof that the electrostatic preorganization effect only makes a minor contribution to the binding of the real, multiring, transition state (TS). However, our simulation study has determined that the difference between the phenolates and the TS arises from the fact that the nonpolar state of the phenolate can rotate freely relative to the oxyanion hole and thus loses the preorganization contribution. A recent study explored the reactivity of both small and multiring systems and concluded that their similar reactivity contradicts our preorganization idea. Herein, we establish that the available experiments in fact provide what is perhaps the best proof and clarification of the preorganization idea and its crucial role in enzyme catalysis. First, we analyze the binding energy and the pK(a) of equilenin and identify direct experimental evidence for our prediction about the differential electrostatic stabilization of the large TS and the small phenolates. Subsequently, we show that the similar reactivity of the small and large systems is also due to an electrostatic preorganization effect but that this effect only appears in the intermediate state because the TS is not free to rotate. This establishes the electrostatic origin of enzyme catalysis. We also clarify the crucial importance of having a well-defined physical concept when examining catalytic effects and the need for quantitative tools for analyzing such effects.
Tosha, Takehiko; Shiro, Yoshitsugu
2013-03-01
Respiration is an essential biological process to get bioenergy, ATP, for all kingdoms of life. Cytochrome c oxidase (COX) plays central role in aerobic respiration, catalyzing the reduction of O(2) coupled with pumping proton across the biological membrane. Nitric oxide reductase (NOR) involved in anaerobic nitrate respiration is suggested to be evolutionary related to COX and share the same progenitor with COX, on the basis of the amino acid sequence homology. Contrary to COX, NOR catalyzes the reduction of nitric oxide and shows no proton pumping ability. Thus, the respiratory enzyme acquires (or loses) proton pumping ability in addition to the conversion of the catalytic property along with the environmental change on earth. Recently, we solved the structures of two types of NORs, which provides novel insights into the functional conversion of the respiratory enzymes. In this review, we focus on the structural similarities and differences between COXs and NORs and discuss possible mechanism for the functional conversion of these enzymes during molecular evolution. Copyright © 2013 International Union of Biochemistry and Molecular Biology, Inc.
Two-dimensional materials for nanophotonics application
Directory of Open Access Journals (Sweden)
Zhao Huan
2015-05-01
Full Text Available In this article, we review the various topics on the applications of 2D materials, including both elemental and compound 2D materials, for nanophotonics application from detectors, modulators to plasmonics and light generating devices. With this review, we hope to provide an overview of the past development in this field while offering our perspectives on its future directions.
Two-Dimensional Distributed Velocity Collision Avoidance
2014-02-11
graphics libraries are used in the Multiagent 6DOF Simulation: Open Graphics Library (OpenGL), OpenGL Utility Toolkit ( GLUT ), and the OpenGL User...rendering. GLUT (Reference 13) is a library of utilities for OpenGL programs, which primarily perform system-level input/output (I/O) with the host...number of geometric primitives (both in solid and wireframe mode) are also provided, including cubes, spheres and the Utah teapot. GLUT also has
Intermittency measurement in two dimensional bacterial turbulence
Qiu, Xiang; Huang, Yongxiang; Chen, Ming; Lu, Zhiming; Liu, Yulu; Zhou, Quan
2016-01-01
In this paper, an experimental velocity database of a bacterial collective motion , e.g., \\textit{B. subtilis}, in turbulent phase with volume filling fraction $84\\%$ provided by Professor Goldstein at the Cambridge University UK, was analyzed to emphasize the scaling behavior of this active turbulence system. This was accomplished by performing a Hilbert-based methodology analysis to retrieve the scaling property without the $\\beta-$limitation. A dual-power-law behavior separated by the viscosity scale $\\ell_{\
Two-dimensional photonic crystal accelerator structures
Directory of Open Access Journals (Sweden)
Benjamin M. Cowan
2003-10-01
Full Text Available Photonic crystals provide a method of confining a synchronous speed-of-light mode in an all-dielectric structure, likely a necessary feature in any optical accelerator. We explore computationally a class of photonic crystal structures with translational symmetry in a direction transverse to the electron beam. We demonstrate synchronous waveguide modes and discuss relevant parameters of such modes. We then explore how accelerator parameters vary as the geometry of the structure is changed and consider trade-offs inherent in the design of an accelerator of this type.
Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Paul, J.; Dey, P.; Karaiskaj, D., E-mail: karaiskaj@usf.edu [Department of Physics, University of South Florida, 4202 East Fowler Ave., Tampa, Florida 33620 (United States); Tokumoto, T.; Hilton, D. J. [Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294 (United States); Reno, J. L. [CINT, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
2014-10-07
The dephasing of the Fermi edge singularity excitations in two modulation doped single quantum wells of 12 nm and 18 nm thickness and in-well carrier concentration of ∼4 × 10{sup 11} cm{sup −2} was carefully measured using spectrally resolved four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. Although the absorption at the Fermi edge is broad at this doping level, the spectrally resolved FWM shows narrow resonances. Two peaks are observed separated by the heavy hole/light hole energy splitting. Temperature dependent “rephasing” (S{sub 1}) 2DFT spectra show a rapid linear increase of the homogeneous linewidth with temperature. The dephasing rate increases faster with temperature in the narrower 12 nm quantum well, likely due to an increased carrier-phonon scattering rate. The S{sub 1} 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations. Distinct 2DFT lineshapes were observed for co-linear and cross-linear polarizations, suggesting the existence of polarization dependent contributions. The “two-quantum coherence” (S{sub 3}) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations.
Two-dimensional Minkowski causal automorphisms and conformal maps
Burgos, Juan Manuel
2013-02-01
Treating the two-dimensional Minkowski space as a Wick rotated version of the complex plane, we characterize the causal automorphisms in the two-dimensional Minkowski space as the Märzke-Wheeler maps of a certain class of observers. We also characterize the differentiable causal automorphisms of this space as the Minkowski conformal maps whose restriction to the time axis belongs to the class of observers mentioned above. We answer a recently raised question about whether causal automorphisms are characterized by their wave equation. As another application of the theory, we give a proper time formula for accelerated observers which solves the twin paradox in two-dimensional Minkowski spacetime.
ONE-DIMENSIONAL AND TWO-DIMENSIONAL LEADERSHIP STYLES
Directory of Open Access Journals (Sweden)
Nikola Stefanović
2007-06-01
Full Text Available In order to motivate their group members to perform certain tasks, leaders use different leadership styles. These styles are based on leaders' backgrounds, knowledge, values, experiences, and expectations. The one-dimensional styles, used by many world leaders, are autocratic and democratic styles. These styles lie on the two opposite sides of the leadership spectrum. In order to precisely define the leadership styles on the spectrum between the autocratic leadership style and the democratic leadership style, leadership theory researchers use two dimensional matrices. The two-dimensional matrices define leadership styles on the basis of different parameters. By using these parameters, one can identify two-dimensional styles.
Methods for two-dimensional cell confinement.
Le Berre, Maël; Zlotek-Zlotkiewicz, Ewa; Bonazzi, Daria; Lautenschlaeger, Franziska; Piel, Matthieu
2014-01-01
Protocols described in this chapter relate to a method to dynamically confine cells in two dimensions with various microenvironments. It can be used to impose on cells a given height, with an accuracy of less than 100 nm on large surfaces (cm(2)). The method is based on the gentle application of a modified glass coverslip onto a standard cell culture. Depending on the preparation, this confinement slide can impose on the cells a given geometry but also an environment of controlled stiffness, controlled adhesion, or a more complex environment. An advantage is that the method is compatible with most optical microscopy technologies and molecular biology protocols allowing advanced analysis of confined cells. In this chapter, we first explain the principle and issues of using these slides to confine cells in a controlled geometry and describe their fabrication. Finally, we discuss how the nature of the confinement slide can vary and provide an alternative method to confine cells with gels of controlled rigidity. Copyright © 2014 Elsevier Inc. All rights reserved.
Confined catalysis under two-dimensional materials
Li, Haobo; Xiao, Jianping; Bao, Xinhe
2017-01-01
Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. The microenvironment created by coating a catalyst surface with 2D material overlayer can be used to modulate surface reactivity, which has been illustrated by optimizing oxygen reduction reaction activity on Pt(111) covered by various 2D materials. We demonstrate a concept of confined catalysis under 2D cover based on a weak van der Waals interaction between 2D material overlayers and underlying catalyst surfaces. PMID:28533413
Two dimensional estimates from ocean SAR images
Directory of Open Access Journals (Sweden)
J. M. Le Caillec
1996-01-01
Full Text Available Synthetic Aperture Radar (SAR images of the ocean yield a lot of information on the sea-state surface providing that the mapping process between the surface and the image is clearly defined. However it is well known that SAR images exhibit non-gaussian statistics and that the motion of the scatterers on the surface, while the image is being formed, may yield to nonlinearities. The detection and quantification of these nonlinearities are made possible by using Higher Order Spectra (HOS methods and more specifically, bispectrum estimation. The development of the latter method allowed us to find phase relations between different parts of the image and to recognise their level of coupling, i.e. if and how waves of different wavelengths interacted nonlinearly. This information is quite important as the usual models assume strong nonlinearities when the waves are propagating in the azimuthal direction (i.e. along the satellite track and almost no nonlinearities when propagating in the range direction. In this paper, the mapping of the ocean surface to the SAR image is reinterpreted and a specific model (i.e. a Second Order Volterra Model is introduced. The nonlinearities are thus explained as either produced by a nonlinear system or due to waves propagating into selected directions (azimuth or range and interacting during image formation. It is shown that quadratic nonlinearities occur for waves propagating near the range direction while for those travelling in the azimuthal direction the nonlinearities, when present, are mostly due to wave interactions but are almost completely removed by the filtering effect coming from the surface motion itself (azimuth cut-off. An inherent quadratic interaction filtering (azimuth high pass filter is also present. But some other effects, apparently nonlinear, are not detected with the methods described here, meaning that either the usual relation developed for the Ocean-to-SAR transform is somewhat incomplete
Two-Dimensionally-Modulated, Magnetic Structure of Neodymium Metal
DEFF Research Database (Denmark)
Lebech, Bente; Bak, P.
1979-01-01
The incipient magnetic order of dhcp Nd is described by a two-dimensional, incommensurably modulated structure ("triple-q" structure). The ordering is accompanied by a lattice distortion that forms a similar pattern....
Partition function of the two-dimensional nearest neighbour Ising ...
Indian Academy of Sciences (India)
Abstract. The partition function for two-dimensional nearest neighbour Ising model in a non-zero magnetic field have been derived for a finite square lattice of 16, 25, 36 and 64 sites with the help of ...
Micromachined two dimensional resistor arrays for determination of gas parameters
van Baar, J.J.J.; Verwey, Willem B.; Dijkstra, Mindert; Dijkstra, Marcel; Wiegerink, Remco J.; Lammerink, Theodorus S.J.; Krijnen, Gijsbertus J.M.; Elwenspoek, Michael Curt
A resistive sensor array is presented for two dimensional temperature distribution measurements in a micromachined flow channel. This allows simultaneous measurement of flow velocity and fluid parameters, like thermal conductivity, diffusion coefficient and viscosity. More general advantages of
Difficulties that Students Face with Two-Dimensional Motion
Mihas, P.; Gemousakakis, T.
2007-01-01
Some difficulties that students face with two-dimensional motion are addressed. The difficulties addressed are the vectorial representation of velocity, acceleration and force, the force-energy theorem and the understanding of the radius of curvature.
Electronic Phenomena in Two-Dimensional Topological Insulators
Hart, Sean
reconstruction can be tuned by modifying the sharpness of the confining potential at the edge. In the second set of experiments, we focus on an exciting new two-dimensional system known as a quantum spin Hall insulator. Realized in quantum well heterostructures formed by layers of HgTe and HgCdTe, this material belongs to a set of recently discovered topological insulators. Like the quantum Hall effect, the quantum spin Hall effect is characterized by an insulating bulk and conducting edge states. However, the quantum spin Hall effect occurs in the absence of an external magnetic field, and contains a pair of counter propagating edge states which are the time-reversed partners of one another. It was recently predicted that a Josephson junction based around one of these edge states could host a new variety of excitation called a Majorana fermion. Majorana fermions are predicted to have non-Abelian braiding statistics, a property which holds promise as a robust basis for quantum information processing. In our experiments, we place a section of quantum spin Hall insulator between two superconducting leads, to form a Josephson junction. By measuring Fraunhofer interference, we are able to study the spatial distribution of supercurrent in the junction. In the quantum spin Hall regime, this supercurrent becomes confined to the topological edge states. In addition to providing a microscopic picture of these states, our measurement scheme generally provides a way to investigate the edge structure of any topological insulator. In further experiments, we tune the chemical potential into the conduction band of the HgTe system, and investigate the behavior of Fraunhofer interference as a magnetic field is applied parallel to the plane of the quantum well. By theoretically analyzing the interference in a parallel field, we find that Cooper pairs in the material acquire a tunable momentum that grows with the magnetic field strength. This finite pairing momentum leads to the appearance of
Two dimensional immersed boundary simulations of swimming jellyfish
Fang, Haowen
2013-01-01
The swimming behavior of jellyfish, driven by the periodic contraction of body muscles,can be modeled using a two dimensional bell-shaped membrane immersed in fluid with aperiodic contraction force exerted along the membrane. We aim to use a simple two dimensional elastic membrane to simulate the swimming behavior without imposing any given membrane configuration, in which the swimming behavior is driven naturally by the interaction between the elastic membrane and fluid and solved by the imm...
The Two-Dimensional Analogue of General Relativity
Lemos, José P. S.; Sá, Paulo M.
1993-01-01
General Relativity in three or more dimensions can be obtained by taking the limit $\\omega\\rightarrow\\infty$ in the Brans-Dicke theory. In two dimensions General Relativity is an unacceptable theory. We show that the two-dimensional closest analogue of General Relativity is a theory that also arises in the limit $\\omega\\rightarrow\\infty$ of the two-dimensional Brans-Dicke theory.
Chemical vapor deposition growth of two-dimensional heterojunctions
Cui, Yu; Li, Bo; Li, JingBo; Wei, ZhongMing
2018-01-01
The properties of two-dimensional (2D) layered materials with atom-smooth surface and special interlayer van der Waals coupling are different from those of traditional materials. Due to the absence of dangling bonds from the clean surface of 2D layered materials, the lattice mismatch influences slightly on the growth of 2D heterojunctions, thus providing a flexible design strategy. 2D heterojunctions have attracted extensive attention because of their excellent performance in optoelectronics, spintronics, and valleytronics. The transfer method was utilized for the fabrication of 2D heterojunctions during the early stage of fundamental research on these materials. This method, however, has limited practical applications. Therefore, chemical vapor deposition (CVD) method was recently developed and applied for the preparation of 2D heterojunctions. The CVD method is a naturally down-top growth strategy that yields 2D heterojunctions with sharp interfaces. Moreover, this method effectively reduces the introduction of contaminants to the fabricated heterojunctions. Nevertheless, the CVD-growth method is sensitive to variations in growth conditions. In this review article, we attempt to provide a comprehensive overview of the influence of growth conditions on the fabrication of 2D heterojunctions through the direct CVD method. We believe that elucidating the effects of growth conditions on the CVD method is necessary to help control and improve the efficiency of the large-scale fabrication of 2D heterojunctions for future applications in integrated circuits.
Thermal analysis of two-dimensional structures in fire
Directory of Open Access Journals (Sweden)
I. Pierin
Full Text Available The structural materials, as reinforced concrete, steel, wood and aluminum, when heated have their mechanical proprieties degraded. In fire, the structures are subject to elevated temperatures and consequently the load capacity of the structural elements is reduced. The Brazilian and European standards show the minimal dimensions for the structural elements had an adequate bearing capacity in fire. However, several structural checks are not contemplated in methods provided by the standards. In these situations, the knowledge of the temperature distributions inside of structural elements as function of time of exposition is required. The aim of this paper is present software developed by the authors called ATERM. The software performs the thermal transient analysis of two-dimensional structures. The structure may be formed of any material and heating is provided by means of a curve of temperature versus time. The data input and the visualization of the results is performed thought the GiD software. Several examples are compared with software Super TempCalc and ANSYS. Some conclusions and recommendations about the thermal analysis are presented
National Research Council Canada - National Science Library
Shin, Yonghee; Lee, Chiwon; Yang, Myung-Seok; Jeong, Sunil; Kim, Dongchul; Kang, Taewook
2014-01-01
Two-dimensional (2D) gold nanoparticles can possess novel physical and chemical properties, which will greatly expand the utility of gold nanoparticles in a wide variety of applications ranging from catalysis to biomedicine...
Zhu, Xudong; Zhang, Chaobo; Wu, Weimin; Li, Xiaopeng; Zhang, Chuan; Fang, Jinggui
2017-01-01
Grapes are categorized as a non-climacteric type of fruit which its ripening is not associated to important rises in respiration and ethylene synthesis. The starch metabolism shares a certain role in the carbohydrate metabolic pathways during grape berry development, and is regarded as an important transient pool in the pathway of sugar accumulation. However, the comprehensive role of starch and its contribution to the quality and flavor of grape berry have not been explored thoroughly. In this study, the expression levels of genes enzyme activities and carbohydrate concentrations related to starch metabolism, were analyzed to understand the molecular mechanism of starch accumulation during grape berry development. The results indicated that starch granules in grape berry were located at the chloroplast in the sub-epidermal tissues, acting as the temporary reserves of photosynthetic products to meet the needs for berry development, and relatively high starch contents could be detected at véraison stage. Moreover, both ADP-glucose pyrophosphorylase (EC 2.7.7.27) and sucrose phosphate synthase (EC 2.3.1.14) involved in starch synthesis displayed elevated gene expression and enzymes activities in the sub-epidermal tissue, while α- and β-amylases involved in its degradation were highly transcribed and active in the central flesh, explaining the absence of starch in this last tissue. Change in the gene expression and activities of ADP-glucose pyrophosphorylase, β-amylase and sucrose phosphate synthase revealed that they were regulated by the circadian rhythms in the fruitlets compared with those in the leaves. Both the morphological, enzymological and transcriptional data in this study provide advanced understandings on the function of starch during berry development and ripening that are so important for berry quality. This study will further facilitate our understanding of the sugar metabolism in grape berry as well as in other plant species.
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.
How two-dimensional bending can extraordinarily stiffen thin sheets
Pini, V.; Ruz, J. J.; Kosaka, P. M.; Malvar, O.; Calleja, M.; Tamayo, J.
2016-07-01
Curved thin sheets are ubiquitously found in nature and manmade structures from macro- to nanoscale. Within the framework of classical thin plate theory, the stiffness of thin sheets is independent of its bending state for small deflections. This assumption, however, goes against intuition. Simple experiments with a cantilever sheet made of paper show that the cantilever stiffness largely increases with small amounts of transversal curvature. We here demonstrate by using simple geometric arguments that thin sheets subject to two-dimensional bending necessarily develop internal stresses. The coupling between the internal stresses and the bending moments can increase the stiffness of the plate by several times. We develop a theory that describes the stiffness of curved thin sheets with simple equations in terms of the longitudinal and transversal curvatures. The theory predicts experimental results with a macroscopic cantilever sheet as well as numerical simulations by the finite element method. The results shed new light on plant and insect wing biomechanics and provide an easy route to engineer micro- and nanomechanical structures based on thin materials with extraordinary stiffness tunability.
Imaging two-dimensional mechanical waves of skeletal muscle contraction.
Grönlund, Christer; Claesson, Kenji; Holtermann, Andreas
2013-02-01
Skeletal muscle contraction is related to rapid mechanical shortening and thickening. Recently, specialized ultrasound systems have been applied to demonstrate and quantify transient tissue velocities and one-dimensional (1-D) propagation of mechanical waves during muscle contraction. Such waves could potentially provide novel information on musculoskeletal characteristics, function and disorders. In this work, we demonstrate two-dimensional (2-D) mechanical wave imaging following the skeletal muscle contraction. B-mode image acquisition during multiple consecutive electrostimulations, speckle-tracking and a time-stamp sorting protocol were used to obtain 1.4 kHz frame rate 2-D tissue velocity imaging of the biceps brachii muscle contraction. The results present novel information on tissue velocity profiles and mechanical wave propagation. In particular, counter-propagating compressional and shear waves in the longitudinal direction were observed in the contracting tissue (speed 2.8-4.4 m/s) and a compressional wave in the transverse direction of the non-contracting muscle tissue (1.2-1.9 m/s). In conclusion, analysing transient 2-D tissue velocity allows simultaneous assessment of both active and passive muscle tissue properties. Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Engineering the Kondo state in two-dimensional semiconducting phosphorene
Babar, Rohit; Kabir, Mukul
2018-01-01
Correlated interaction between dilute localized impurity electrons and the itinerant host conduction electrons in metals gives rise to the conventional many-body Kondo effect below sufficiently low temperature. In sharp contrast to these conventional Kondo systems, we report an intrinsic, robust, and high-temperature Kondo state in two-dimensional semiconducting phosphorene. While absorbed at a thermodynamically stable lattice defect, Cr impurity triggers an electronic phase transition in phosphorene to provide conduction electrons, which strongly interact with the localized moment generated at the Cr site. These manifest into the intrinsic Kondo state, where the impurity moment is quenched in multiple stages and at temperatures in the 40-200 K range. Further, along with a much smaller extension of the Kondo cloud, the predicted Kondo state is shown to be robust under uniaxial strain and layer thickness, which greatly simplifies its future experimental realization. We predict the present study will open up new avenues in Kondo physics and trigger further theoretical and experimental studies.
Two-Dimensional Solution Surface for Weighted Support Vector Machines.
Shin, Seung Jun; Wu, Yichao; Zhang, Hao Helen
2014-04-03
The support vector machine (SVM) is a popular learning method for binary classification. Standard SVMs treat all the data points equally, but in some practical problems it is more natural to assign different weights to observations from different classes. This leads to a broader class of learning, the so-called weighted SVMs (WSVMs), and one of their important applications is to estimate class probabilities besides learning the classification boundary. There are two parameters associated with the WSVM optimization problem: one is the regularization parameter and the other is the weight parameter. In this paper we first establish that the WSVM solutions are jointly piecewise-linear with respect to both the regularization and weight parameter. We then develop a state-of-the-art algorithm that can compute the entire trajectory of the WSVM solutions for every pair of the regularization parameter and the weight parameter, at a feasible computational cost. The derived two-dimensional solution surface provides theoretical insight on the behavior of the WSVM solutions. Numerically, the algorithm can greatly facilitate the implementation of the WSVM and automate the selection process of the optimal regularization parameter. We illustrate the new algorithm on various examples.
Filtering and control for classes of two-dimensional systems
Wu, Ligang
2015-01-01
This book focuses on filtering, control and model-reduction problems for two-dimensional (2-D) systems with imperfect information. The time-delayed 2-D systems covered have system parameters subject to uncertain, stochastic and parameter-varying changes. After an initial introduction of 2-D systems and the ideas of linear repetitive processes, the text is divided into two parts detailing: · general theory and methods of analysis and optimal synthesis for 2-D systems; and · application of the general theory to the particular case of differential/discrete linear repetitive processes. The methods developed provide a framework for stability and performance analysis, optimal and robust controller and filter design and model approximation for the systems considered. Solutions to the design problems are couched in terms of linear matrix inequalities. For readers interested in the state of the art in linear filtering, control and model reduction, Filtering and Control for Classes of ...
Punctured Two-Dimensional Sheets for Harvesting Blue Energy.
Aliprandi, Alessandro; Pakulski, Dawid; Ciesielski, Artur; Samorì, Paolo
2017-11-28
The challenges of global climate change and the world's growing demand for energy have brought the need for new renewable energy sources to the top of the international community's agenda. We have known for many centuries that energy is released upon mixing seawater and freshwater, yet it was just a few decades ago that it became clear how this energy can be converted into electricity instead of heat. As a result, the blue energy rush has raised and set new strategies in different science and technology sectors, leading to the construction of a new generation of plants and other technological investments. Among many approaches, pressure-retarded osmosis has emerged as a promising method to collect the largest amount of produced blue energy. In this Perspective, we highlight the advances in the development of ultrathin membranes based on two-dimensional materials. We discuss the most relevant synthetic methods devised to generate atomically thin membranes for pressure-retarded osmosis and retarded electrodialysis applications, and we provide some critical views on the greatest challenges in this thrilling research area.
Synthesis of Two-Dimensional Materials for Capacitive Energy Storage.
Mendoza-Sánchez, Beatriz; Gogotsi, Yury
2016-08-01
The unique properties and great variety of two-dimensional (2D) nanomaterials make them highly attractive for energy storage applications. Here, an insight into the progress made towards the application of 2D nanomaterials for capacitive energy storage is provided. Synthesis methods, and electrochemical performance of various classes of 2D nanomaterials, particularly based on graphene, transition metal oxides, dichalcogenides, and carbides, are presented. The factors that directly influence capacitive performance are discussed throughout the text and include nanosheet composition, morphology and texture, electrode architecture, and device configuration. Recent progress in the fabrication of 2D-nanomaterials-based microsupercapacitors and flexible and free-standing supercapacitors is presented. The main electrode manufacturing techniques with emphasis on scalability and cost-effectiveness are discussed, and include laser scribing, printing, and roll-to-roll manufacture. Various issues that prevent the use of the full energy-storage potential of 2D nanomaterials and how they have been tackled are discussed, and include nanosheet aggregation and the low electrical conductivity of some 2D nanomaterials. Particularly, the design of hybrid and hierarchical 2D and 3D structures based on 2D nanomaterials is presented. Other challenges and opportunities are discussed and include: control of nanosheets size and thickness, chemical and electrochemical instability, and scale-up of electrode films. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Development of two-dimensional interdigitated center of pressure sensor
Yoo, Byungseok; Pines, Darryll J.
2017-12-01
This paper presents the development of a two-dimensional (2D) flexible patch sensor to detect and monitor the center of pressure (CoP) location and the total magnitude of a spatially distributed pressure to the specific surface areas of engineering structures. The CoP sensor with the contact mode induced by a pressure distribution was formulated by force sensitive resistor technology and was mainly composed of a thin conductive polymer layer, adhesive spacers, and two interdigitated patterned electrode films with unique sensing aperture shadings. By properly mapping the interdigitated electrode patterns to the top and bottom surfaces of the conductive polymer, the proposed sensor ideally enables to measure an overall applied pressure level and its centroid location within a predetermined sensing region in real-time. The CoP sensor containing 36 sensing sections within a dimension of around 3 × 3 inches was prototyped and experimentally investigated to verify its capability to identify the CoP location and magnitude due to the presence of a permanent magnet-based local pressure distribution. Only five electric wires connected to the CoP sensor to inspect the pressure-sensing positions of 36 segments. The evaluation results of the measured sensor data demonstrate good agreements with the actual test parameters such as the total pressure and its centroid position with about 5% locational error. However, to provide accurate information on the overall pressure range, the compensation factors must be determined and applied to the individual sensing sections of the sensor.
Photon management in two-dimensional disordered media
Vynck, Kevin; Burresi, Matteo; Riboli, Francesco; Wiersma, Diederik S.
2012-12-01
Elaborating reliable and versatile strategies for efficient light coupling between free space and thin films is of crucial importance for new technologies in energy efficiency. Nanostructured materials have opened unprecedented opportunities for light management, notably in thin-film solar cells. Efficient coherent light trapping has been accomplished through the careful design of plasmonic nanoparticles and gratings, resonant dielectric particles and photonic crystals. Alternative approaches have used randomly textured surfaces as strong light diffusers to benefit from their broadband and wide-angle properties. Here, we propose a new strategy for photon management in thin films that combines both advantages of an efficient trapping due to coherent optical effects and broadband/wide-angle properties due to disorder. Our approach consists of the excitation of electromagnetic modes formed by multiple light scattering and wave interference in two-dimensional random media. We show, by numerical calculations, that the spectral and angular responses of thin films containing disordered photonic patterns are intimately related to the in-plane light transport process and can be tuned through structural correlations. Our findings, which are applicable to all waves, are particularly suited for improving the absorption efficiency of thin-film solar cells and can provide a new approach for high-extraction-efficiency light-emitting diodes.
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. Copyright © 2015 Elsevier Ltd. All rights reserved.
Photonics and optoelectronics of two-dimensional materials beyond graphene
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.
Exciton Band Structure in Two-Dimensional Materials.
Cudazzo, Pierluigi; Sponza, Lorenzo; Giorgetti, Christine; Reining, Lucia; Sottile, Francesco; Gatti, Matteo
2016-02-12
Low-dimensional materials differ from their bulk counterparts in many respects. In particular, the screening of the Coulomb interaction is strongly reduced, which can have important consequences such as the significant increase of exciton binding energies. In bulk materials the binding energy is used as an indicator in optical spectra to distinguish different kinds of excitons, but this is not possible in low-dimensional materials, where the binding energy is large and comparable in size for excitons of very different localization. Here we demonstrate that the exciton band structure, which can be accessed experimentally, instead provides a powerful way to identify the exciton character. By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane and single-layer hexagonal boron nitride, we draw a general picture of the exciton dispersion in two-dimensional materials, highlighting the different role played by the exchange electron-hole interaction and by the electronic band structure. Our interpretation is substantiated by a prediction for phosphorene.
Nonvolatile resistance switching on two-dimensional electron gas.
Joung, Jin Gwan; Kim, Shin-Ik; Moon, Seon Young; Kim, Dai-Hong; Gwon, Hyo Jin; Hong, Seong-Hyeon; Chang, Hye Jung; Hwang, Jin-Ha; Kwon, Beom Jin; Kim, Seong Keun; Choi, Ji-Won; Yoon, Seok-Jin; Kang, Chong-Yun; Yoo, Kwang Soo; Kim, Jin-Sang; Baek, Seung-Hyub
2014-10-22
Two-dimensional electron gas (2DEG) at the complex oxide interfaces have brought about considerable interest for the application of the next-generation multifunctional oxide electronics due to the exotic properties that do not exist in the bulk. In this study, we report the integration of 2DEG into the nonvolatile resistance switching cell as a bottom electrode, where the metal-insulator transition of 2DEG by an external field serves to significantly reduce the OFF-state leakage current while enhancing the on/off ratio. Using the Pt/Ta2O5-y/Ta2O5-x/SrTiO3 heterostructure as a model system, we demonstrate the nonvolatile resistance switching memory cell with a large on/off ratio (>10(6)) and a low leakage current at the OFF state (∼10(-13) A). Beyond exploring nonvolatile memory, our work also provides an excellent framework for exploring the fundamental understanding of novel physics in which electronic and ionic processes are coupled in the complex heterostructures.
Characterization of the Human Pancreatic Islet Proteome by Two-Dimensional LC/MS/MS
Energy Technology Data Exchange (ETDEWEB)
Metz, Thomas O.; Jacobs, Jon M.; Gritsenko, Marina A.; Fontes, Ghislaine; Qian, Weijun; Camp, David G.; Poitout, Vincent J.; Smith, Richard D.
2006-12-01
Research to elucidate the pathogenesis of type 1 diabetes mellitus has traditionally focused on the genetic and immunological factors associated with the disease, and, until recently, has not considered the target cell. While there have been reports detailing proteomic analyses of established islet cell lines or isolated rodent islets, the information gained is not always easily extrapolated to humans. Therefore, extensive characterization of the human islet proteome could result in better understanding of islet biology and lead to more effective treatment strategies. We have applied a two-dimensional LC-MS/MS-based analysis to the characterization of the human islet proteome, resulting in the detection of 29,021 unique peptides corresponding to 4,925 proteins. As expected, major islet hormones (insulin, glucagon, somatostatin), beta-cell enriched secretory products (IAPP), ion channels (K-ATP channel), and transcription factors (PDX-1, Nkx 6.1, HNF-1 beta) were detected. In addition, significant proteome coverage of metabolic enzymes and cellular pathways was obtained, including the insulin signaling cascade and the MAP kinase, NF-κβ, and JAK/STAT pathways. This work represents the most extensive characterization of the human islet proteome to date and provides a peptide reference library that may be utilized in future studies of islet biology and type 1 diabetes.
Two-dimensional analytic weighting functions for limb scattering
Zawada, D. J.; Bourassa, A. E.; Degenstein, D. A.
2017-10-01
Through the inversion of limb scatter measurements it is possible to obtain vertical profiles of trace species in the atmosphere. Many of these inversion methods require what is often referred to as weighting functions, or derivatives of the radiance with respect to concentrations of trace species in the atmosphere. Several radiative transfer models have implemented analytic methods to calculate weighting functions, alleviating the computational burden of traditional numerical perturbation methods. Here we describe the implementation of analytic two-dimensional weighting functions, where derivatives are calculated relative to atmospheric constituents in a two-dimensional grid of altitude and angle along the line of sight direction, in the SASKTRAN-HR radiative transfer model. Two-dimensional weighting functions are required for two-dimensional inversions of limb scatter measurements. Examples are presented where the analytic two-dimensional weighting functions are calculated with an underlying one-dimensional atmosphere. It is shown that the analytic weighting functions are more accurate than ones calculated with a single scatter approximation, and are orders of magnitude faster than a typical perturbation method. Evidence is presented that weighting functions for stratospheric aerosols calculated under a single scatter approximation may not be suitable for use in retrieval algorithms under solar backscatter conditions.
Traditional Semiconductors in the Two-Dimensional Limit
Lucking, Michael C.; Xie, Weiyu; Choe, Duk-Hyun; West, Damien; Lu, Toh-Ming; Zhang, S. B.
2018-02-01
Interest in two-dimensional materials has exploded in recent years. Not only are they studied due to their novel electronic properties, such as the emergent Dirac fermion in graphene, but also as a new paradigm in which stacking layers of distinct two-dimensional materials may enable different functionality or devices. Here, through first-principles theory, we reveal a large new class of two-dimensional materials which are derived from traditional III-V, II-VI, and I-VII semiconductors. It is found that in the ultrathin limit the great majority of traditional binary semiconductors studied (a series of 28 semiconductors) are not only kinetically stable in a two-dimensional double layer honeycomb structure, but more energetically stable than the truncated wurtzite or zinc-blende structures associated with three dimensional bulk. These findings both greatly increase the landscape of two-dimensional materials and also demonstrate that in the double layer honeycomb form, even ordinary semiconductors, such as GaAs, can exhibit exotic topological properties.
Phase diagram of two-dimensional hard rods from fundamental mixed measure density functional theory.
Wittmann, René; Sitta, Christoph E; Smallenburg, Frank; Löwen, Hartmut
2017-10-07
A density functional theory for the bulk phase diagram of two-dimensional orientable hard rods is proposed and tested against Monte Carlo computer simulation data. In detail, an explicit density functional is derived from fundamental mixed measure theory and freely minimized numerically for hard discorectangles. The phase diagram, which involves stable isotropic, nematic, smectic, and crystalline phases, is obtained and shows good agreement with the simulation data. Our functional is valid for a multicomponent mixture of hard particles with arbitrary convex shapes and provides a reliable starting point to explore various inhomogeneous situations of two-dimensional hard rods and their Brownian dynamics.
Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.
Wang, Qing Hua; Kalantar-Zadeh, Kourosh; Kis, Andras; Coleman, Jonathan N; Strano, Michael S
2012-11-01
The remarkable properties of graphene have renewed interest in inorganic, two-dimensional materials with unique electronic and optical attributes. Transition metal dichalcogenides (TMDCs) are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Although TMDCs have been studied for decades, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. TMDCs such as MoS(2), MoSe(2), WS(2) and WSe(2) have sizable bandgaps that change from indirect to direct in single layers, allowing applications such as transistors, photodetectors and electroluminescent devices. We review the historical development of TMDCs, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.
Two-Dimensional Electronic Spectroscopy Using Incoherent Light: Theoretical Analysis
Turner, Daniel B; Sutor, Erika J; Hendrickson, Rebecca A; Gealy, M W; Ulness, Darin J
2012-01-01
Electronic energy transfer in photosynthesis occurs over a range of time scales and under a variety of intermolecular coupling conditions. Recent work has shown that electronic coupling between chromophores can lead to coherent oscillations in two-dimensional electronic spectroscopy measurements of pigment-protein complexes measured with femtosecond laser pulses. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pulses with physiological illumination conditions. Noisy-light spectroscopy can begin to address this question. In this work we present the theoretical analysis of incoherent two-dimensional electronic spectroscopy, I(4) 2D ES. Simulations reveal diagonal peaks, cross peaks, and coherent oscillations similar to those observed in femtosecond two-dimensional electronic spectroscopy experiments. The results also expose fundamental differences between the femtosecond-pulse and noisy-light techniques; the differences lead to new challenges and opp...
Two dimensional convolute integers for machine vision and image recognition
Edwards, Thomas R.
1988-01-01
Machine vision and image recognition require sophisticated image processing prior to the application of Artificial Intelligence. Two Dimensional Convolute Integer Technology is an innovative mathematical approach for addressing machine vision and image recognition. This new technology generates a family of digital operators for addressing optical images and related two dimensional data sets. The operators are regression generated, integer valued, zero phase shifting, convoluting, frequency sensitive, two dimensional low pass, high pass and band pass filters that are mathematically equivalent to surface fitted partial derivatives. These operators are applied non-recursively either as classical convolutions (replacement point values), interstitial point generators (bandwidth broadening or resolution enhancement), or as missing value calculators (compensation for dead array element values). These operators show frequency sensitive feature selection scale invariant properties. Such tasks as boundary/edge enhancement and noise or small size pixel disturbance removal can readily be accomplished. For feature selection tight band pass operators are essential. Results from test cases are given.
Control Operator for the Two-Dimensional Energized Wave Equation
Directory of Open Access Journals (Sweden)
Sunday Augustus REJU
2006-07-01
Full Text Available This paper studies the analytical model for the construction of the two-dimensional Energized wave equation. The control operator is given in term of space and time t independent variables. The integral quadratic objective cost functional is subject to the constraint of two-dimensional Energized diffusion, Heat and a source. The operator that shall be obtained extends the Conjugate Gradient method (ECGM as developed by Hestenes et al (1952, [1]. The new operator enables the computation of the penalty cost, optimal controls and state trajectories of the two-dimensional energized wave equation when apply to the Conjugate Gradient methods in (Waziri & Reju, LEJPT & LJS, Issues 9, 2006, [2-4] to appear in this series.
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-06-22
Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials.
Directory of Open Access Journals (Sweden)
Manuel M Müller
Full Text Available The contemporary proteinogenic repertoire contains 20 amino acids with diverse functional groups and side chain geometries. Primordial proteins, in contrast, were presumably constructed from a subset of these building blocks. Subsequent expansion of the proteinogenic alphabet would have enhanced their capabilities, fostering the metabolic prowess and organismal fitness of early living systems. While the addition of amino acids bearing innovative functional groups directly enhances the chemical repertoire of proteomes, the inclusion of chemically redundant monomers is difficult to rationalize. Here, we studied how a simplified chorismate mutase evolves upon expanding its amino acid alphabet from nine to potentially 20 letters. Continuous evolution provided an enhanced enzyme variant that has only two point mutations, both of which extend the alphabet and jointly improve protein stability by >4 kcal/mol and catalytic activity tenfold. The same, seemingly innocuous substitutions (Ile→Thr, Leu→Val occurred in several independent evolutionary trajectories. The increase in fitness they confer indicates that building blocks with very similar side chain structures are highly beneficial for fine-tuning protein structure and function.
Critical Behaviour of a Two-Dimensional Random Antiferromagnet
DEFF Research Database (Denmark)
Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.
1976-01-01
A neutron scattering study of the order parameter, correlation length and staggered susceptibility of the two-dimensional random antiferromagnet Rb2Mn0.5Ni0.5F4 is reported. The system is found to exhibit a well-defined phase transition with critical exponents identical to those of the isomorphou...... pure materials K2NiF4 and K2MnF4. Thus, in these systems, which have the asymptotic critical behaviour of the two-dimensional Ising model, randomness has no measurable effect on the phase-transition behaviour....
Chaotic dynamics in two-dimensional noninvertible maps
Mira, Christian; Cathala, Jean-Claude; Gardini, Laura
1996-01-01
This book is essentially devoted to complex properties (Phase plane structure and bifurcations) of two-dimensional noninvertible maps, i.e. maps having either a non-unique inverse, or no real inverse, according to the plane point. They constitute models of sets of discrete dynamical systems encountered in Engineering (Control, Signal Processing, Electronics), Physics, Economics, Life Sciences. Compared to the studies made in the one-dimensional case, the two-dimensional situation remained a long time in an underdeveloped state. It is only since these last years that the interest for this resea
Experiments in the stability of basic two-dimensional flows
Fontana, Paul W.; Titmus, Edward C.; Kirn, Adrian
2010-11-01
Two-dimensional flows have different stability behavior than their three-dimensional counterparts due to enstrophy conservation, but they have not been studied as thoroughly in experiments. We present data from quasi-two-dimensional flow experiments suggesting that basic shear flows show instability not predicted by theory, while square-votex-lattice flows are more stable than predicted by linear theory. To allow proper quantitative comparisons between experiments and theory we have developed new techniques for quantifying and distinguishing kinematic viscosity and Ekman friction.
Dynamics of vortex interactions in two-dimensional flows
DEFF Research Database (Denmark)
Juul Rasmussen, J.; Nielsen, A.H.; Naulin, V.
2002-01-01
The dynamics and interaction of like-signed vortex structures in two dimensional flows are investigated by means of direct numerical solutions of the two-dimensional Navier-Stokes equations. Two vortices with distributed vorticity merge when their distance relative to their radius, d/R-0l. is below...... a critical value, a(c). Using the Weiss-field, a(c) is estimated for vortex patches. Introducing an effective radius for vortices with distributed vorticity, we find that 3.3 ... with the formation of "vortex crystals"....
Quantum melting of a two-dimensional Wigner crystal
Dolgopolov, V. T.
2017-10-01
The paper reviews theoretical predictions about the behavior of two-dimensional low-density electron systems at nearly absolute zero temperatures, including the formation of an electron (Wigner) crystal, crystal melting at a critical electron density, and transitions between crystal modifications in more complex (for example, two-layer) systems. The paper presents experimental results obtained from real two-dimensional systems in which the nonconducting (solid) state of the electronic system with indications of collective localization is actually realized. Experimental methods for detecting a quantum liquid–solid phase interface are discussed.
Two-dimensional superconductors with atomic-scale thickness
Uchihashi, Takashi
2017-01-01
Recent progress in two-dimensional superconductors with atomic-scale thickness is reviewed mainly from the experimental point of view. The superconducting systems treated here involve a variety of materials and forms: elemental metal ultrathin films and atomic layers on semiconductor surfaces; interfaces and superlattices of heterostructures made of cuprates, perovskite oxides, and rare-earth metal heavy-fermion compounds; interfaces of electric-double-layer transistors; graphene and atomic sheets of transition metal dichalcogenide; iron selenide and organic conductors on oxide and metal surfaces, respectively. Unique phenomena arising from the ultimate two dimensionality of the system and the physics behind them are discussed.
Molecular dynamics simulation of a two-dimensional system
Directory of Open Access Journals (Sweden)
S. M. Huseini
2001-06-01
Full Text Available The study of a two-dimensional (2-D system started nearly half a century ago when Peierls and Landau showed the lack of long range translational order in a two-dimensional solid. In 1968, Mermin proved that despite the absence of long range translational order. Two-dimensional solids can still exhibit a different kind of long range bond orientation. During the last decade, fascinating theories were put forward to explain the role of topological defects in the melting of two-dimensional solids, starting with Kosterlitz and Thouless. Recent surge of interest in melting is also due to the theoretical ideas of Halperin, Nelson and Young. They have suggested that the transition may be fundamentally different from that observed in ordinary three-dimensional systems. Computer simulations suggest that the transition is of the usual first-order type observed in a three-dimensional system. A large body of experimental and simulation research into the two-dimensional melting followed the announcement of the KTHNY theory. In spite of all this effort, the question as to the nature of two dimensional melting remains unresolved. Recent experimental work supporting the existence of continuous melting transitions in some two-dimentsional systems indicates the need for further theoretical and computational work to lead to an understanding of the experimental results. In this paper we intend to summarze and clarify the current situation with regard to research in the two-dimensional melting with an emphasis on computer simulations. The paper begins with an overview of the current status of relevant theoretical, experimental and simulation research, then a two-dimensional simulation of an ionic salt system is studied in detail. This simulation has been done by using the molecular dynamics method. The most important parameters that have been determined are ,The trnsition temperature, the total energy of the system, the mean square displacement and the bond
Finite element solution of two dimensional time dependent heat equation
Maa
1999-01-01
A Microsoft Windows based computer code, named FHEAT, has been developed for solving two dimensional heat problems in Cartesian and Cylindrical geometries. The programming language is Microsoft Visual Basic 3.0. The code makes use of Finite element formulation for spatial domain and Finite difference formulation for time domain. Presently the code is capable of solving two dimensional steady state and transient problems in xy- and rz-geometries. The code is capable excepting both triangular and rectangular elements. Validation and benchmarking was done against hand calculations and published results.
Absolute negative conductivity in two-dimensional electron systems under microwave radiation
Ryzhii, Victor
2004-01-01
We overview mechanisms of absolute negative conductivity in two-dimensional electron systems in a magnetic field irradiated with microwaves and provide plausible explanations of the features observed in recent experiments related to the so-called zero-resistance (zero-conductance) states.
Jansen, Thomas la Cour; Knoester, Jasper
2007-01-01
We combine numerical Langevin simulations with numerical integration of the Schrodinger equation to calculate two-dimensional infrared spectra of ultrafast chemical exchange. This provides a tool to model and interpret such spectra of molecules undergoing chemical processes, such as isomerization
Specification of a Two-Dimensional Test Case
DEFF Research Database (Denmark)
Nielsen, Peter Vilhelm
This paper describes the geometry and other boundary conditions for a test case which can be used to test different two-dimensional CFD codes in the lEA Annex 20 work. The given supply opening is large compared with practical openings. Therefore, this geometry will reduce the need for a high number...
CUDA application on two-dimensional CFD problems
Tsivinskaya, Yu. S.
2017-10-01
Parallel computations based on CUDA technology are applied for solving two-dimensional problems. Heat distribution and velocity field calculation in a liquid is considered. Various iterative methods are used to solve simultaneous linear equations with sparse matrices, obtained by the initial equations approximation. The efficiency of using GPUs to accelerate calculations is estimated, which grows with the unknowns number increase.
Magnetoelectronic transport of the two-dimensional electron gas in ...
Indian Academy of Sciences (India)
Abstract. Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of. CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal ...
Easy interpretation of optical two-dimensional correlation spectra
Lazonder, K.; Pshenichnikov, M.S.; Wiersma, D.A.
2006-01-01
We demonstrate that the value of the underlying frequency-frequency correlation function can be retrieved from a two-dimensional optical correlation spectrum through a simple relationship. The proposed method yields both intuitive clues and a quantitative measure of the dynamics of the system. The
Types of two-dimensional N = 4 superconformal field theories
Indian Academy of Sciences (India)
This should also complete the classification of all two-dimensional linear superconformal theories because N = 4 symmetries are the highest ones which can have non-vanishing central charges without requiring operators of negative dimensions. Classification of N = 4 superconformal symmetries is very interesting because ...
Influence of index contrast in two dimensional photonic crystal lasers
DEFF Research Database (Denmark)
Jørgensen, Mette Marie; Petersen, Sidsel Rübner; Christiansen, Mads Brøkner
2010-01-01
The influence of index contrast variations for obtaining single-mode operation and low threshold in dye doped polymer two dimensional photonic crystal (PhC) lasers is investigated. We consider lasers made from Pyrromethene 597 doped Ormocore imprinted with a rectangular lattice PhC having a cavity...
An anionic two-dimensional indium carboxylate framework derived ...
Indian Academy of Sciences (India)
The framework solid has been characterized by elemental analysis, FT-IR spectroscopy, TGA, PXRD and single crystal X-ray diffraction studies. DMF undergoes cleavage to dimethyl ammonium and formate ions, which are incorporated in the framework. A slipped stacking of the two dimensional sheets along -axis in 1 ...
An anionic two-dimensional indium carboxylate framework derived ...
Indian Academy of Sciences (India)
1385–1391. c Indian Academy of Sciences. An anionic two-dimensional indium carboxylate framework derived from a pseudo C3-symmetric semi-flexible tricarboxylic acid. PRATAP VISHNOI, ALOK CH KALITA and RAMASWAMY MURUGAVEL. ∗. Department of Chemistry, Indian Institute of Technology Bombay, Powai, ...
Optical properties of two-dimensional magnetoelectric point scattering lattices
DEFF Research Database (Denmark)
Hansen, Per Lunnemann; Sersic, Ivana; Koenderink, A. Femius
2013-01-01
We explore the electrodynamic coupling between a plane wave and an infinite two-dimensional periodic lattice of magnetoelectric point scatterers, deriving a semianalytical theory with consistent treatment of radiation damping, retardation, and energy conservation. We apply the theory to arrays of...
Stress and mixed boundary conditions for two-dimensional ...
Indian Academy of Sciences (India)
For plate bending and stretching problems in two-dimensional (2D) dodecagonal quasi-crystal (QC) media, the reciprocal theorem and the general solution for QCs are applied in a novel way to obtain the appropriate stress and mixed boundary conditions accurate to all order. The method developed by Gregory and Wan is ...
Avoiding acidic region streaking in two-dimensional gel ...
Indian Academy of Sciences (India)
2014-07-21
Jul 21, 2014 ... Acidic region streaking (ARS) is one of the lacunae in two-dimensional gel electrophoresis (2DE) of bacterial proteome. This streaking is primarily caused by nucleic acid (NuA) contamination and poses major problem in the downstream processes like image analysis and protein identification. Although ...
521 Image Making in Two Dimensional Art; Experiences with Straw ...
African Journals Online (AJOL)
User
Online). Image Making in Two Dimensional Art; Experiences with. Straw and Fabric (Straw Appliqué Technique) (Pp. 521-528). Enenajor Marshall Eniwo - Department of Fine Arts and Design,. University of Port Harcourt, P.O.Box 106 Uniport, ...
Algebra and two-dimensional quasiexactly solvable Hamiltonian ...
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 83; Issue 1. 2 Algebra and two-dimensional ... Then, by choosing an appropriate set of coefficients and making a gauge rotation, we show that this Hamiltonian leads to the solvable Poschl–Teller model on an open infinite strip. Finally, we assign 2 hidden algebra ...
Divorticity and dihelicity in two-dimensional hydrodynamics
DEFF Research Database (Denmark)
Shivamoggi, B.K.; van Heijst, G.J.F.; Juul Rasmussen, Jens
2010-01-01
A framework is developed based on the concepts of divorticity B (≡×ω, ω being the vorticity) and dihelicity g (≡vB) for discussing the theoretical structure underlying two-dimensional (2D) hydrodynamics. This formulation leads to the global and Lagrange invariants that could impose significant...
Longitudinal and transverse modes dispersion in two-dimensional ...
African Journals Online (AJOL)
... two-dimensional Yukawa fluids in the domain of weak and intermediate coupling parameters were analyzed through molecular dynamics (MD) simulation. The dispersion relation for both the longitudinal and transverse modes were obtained and compared with random phase approximation (RPA) and harmonic phonons ...
Vibrations of thin piezoelectric shallow shells: Two-dimensional ...
Indian Academy of Sciences (India)
In this paper we consider the eigenvalue problem for piezoelectric shallow shells and we show that, as the thickness of the shell goes to zero, the eigensolutions of the three-dimensional piezoelectric shells converge to the eigensolutions of a two-dimensional eigenvalue problem.
Vibrations of thin piezoelectric shallow shells: Two-dimensional ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
of the three-dimensional piezoelectric shells converge to the eigensolutions of a two- dimensional eigenvalue problem. Keywords. Vibrations; piezoelectricity; shallow shells. 1. Introduction. Lower dimensional models of shells are preferred in numerical computations to three- dimensional models when the thickness of the ...
Breakdown of Optical Phonons' Splitting in Two-Dimensional Materials.
Sohier, Thibault; Gibertini, Marco; Calandra, Matteo; Mauri, Francesco; Marzari, Nicola
2017-06-14
We investigate the long-wavelength dispersion of longitudinal and transverse optical phonon modes in polar two-dimensional materials, multilayers, and their heterostructures. Using analytical models and density-functional perturbation theory in a two-dimensional framework, we show that at variance with the three-dimensional case these modes are degenerate at the zone center but the macroscopic electric field associated with the longitudinal-optical modes gives rise to a finite slope at the zone center in their corresponding phonon dispersions. This slope increases linearly with the number of layers and it is determined solely by the Born effective charges of the material and the dielectric properties of the surrounding media. Screening from the environment can greatly reduce the slope splitting between the longitudinal and transverse optical modes and can be seen in the experimentally relevant case of boron nitride-graphene heterostructures. As the phonon momentum increases, the intrinsic screening properties of the two-dimensional material dictate the transition to a momentum-independent splitting similar to that of three-dimensional materials. These considerations are essential to understand electrical transport and optical coupling in two-dimensional systems.
Sound waves in two-dimensional ducts with sinusoidal walls
Nayfeh, A. H.
1974-01-01
The method of multiple scales is used to analyze the wave propagation in two-dimensional hard-walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.
Dislocation climb in two-dimensional discrete dislocation dynamics
Davoudi, K.M.; Nicola, L.; Vlassak, J.J.
2012-01-01
In this paper, dislocation climb is incorporated in a two-dimensional discrete dislocation dynamics model. Calculations are carried out for polycrystalline thin films, passivated on one or both surfaces. Climb allows dislocations to escape from dislocation pile-ups and reduces the strain-hardening
Topology optimization of two-dimensional elastic wave barriers
DEFF Research Database (Denmark)
Van Hoorickx, C.; Sigmund, Ole; Schevenels, M.
2016-01-01
Topology optimization is a method that optimally distributes material in a given design domain. In this paper, topology optimization is used to design two-dimensional wave barriers embedded in an elastic halfspace. First, harmonic vibration sources are considered, and stiffened material is insert...
A two-dimensional electrophoresis protocol suitable for Medicago ...
African Journals Online (AJOL)
The gels were stained with Coomassie Brilliant Blue G-250 and digitalized gels were analyzed using the PDquest 8.0.1 software. The results indicated that 931 protein dots were detected in the gel. A technology suitable for the M. truncatula leaves protein extraction by TCA/acetone and a protocol for two-dimensional ...
Dynamical instability of a two-dimensional quantum black hole
Itoh, Y.; Hotta, M.; Morikawa, M.; Futamase, T.
1998-04-01
We investigate the dynamical instability of the two-dimensional quantum black hole model considered by Lowe in his study of Hawking evaporation. The model is supposed to express a black hole in equilibrium with a bath of Hawking radiation. It turns out that the model has at least one instability mode for a wide range of parameters, and thus it is unstable.
Stress and mixed boundary conditions for two-dimensional ...
Indian Academy of Sciences (India)
Abstract. For plate bending and stretching problems in two-dimensional (2D) do- decagonal quasi-crystal (QC) media, the reciprocal theorem and the general solution for. QCs are applied in a novel way to obtain the appropriate stress and mixed boundary conditions accurate to all order. The method developed by Gregory ...
Magnetic order in two-dimensional nanoparticle assemblies
Georgescu, M
2008-01-01
This thesis involves a fundamental study of two-dimensional arrays of magnetic nanoparticles using non-contact Atomic Force Microscopy, Magnetic Force Microscopy, and Atomic Force Spectroscopy. The goal is to acquire a better understanding of the interactions between magnetic nanoparticles and the
Low-frequency scattering from two-dimensional perfect conductors
DEFF Research Database (Denmark)
Hansen, Thorkild; Yaghjian, A.D
1991-01-01
Exact expressions have been obtained for the leading terms in the low-frequency expansions of the far fields scattered from three different types of two-dimensional perfect conductors: a cylinder with finite cross section, a cylindrical bump on an infinite ground plane, and a cylindrical dent...
Nonlinear dynamic characterization of two-dimensional materials
Davidovikj, D.; Alijani, F.; Cartamil Bueno, S.J.; van der Zant, H.S.J.; Amabili, M.; Steeneken, P.G.
2017-01-01
Owing to their atomic-scale thickness, the resonances of two-dimensional (2D) material membranes show signatures of nonlinearities at forces of only a few picoNewtons. Although the linear dynamics of membranes is well understood, the exact relation between the nonlinear response and the resonator's
Two Dimensional Potential Mapping–Monte Carlo Simulation
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 10; Issue 7. Two Dimensional Potential Mapping – Monte Carlo Simulation. J Meena Devi K Ramachandran. Classroom Volume 10 Issue 7 July 2005 pp 73-84. Fulltext. Click here to view fulltext PDF. Permanent link:
Non-Integrability of Two-Dimensional QCD
Krauth, W; Krauth, Werner; Staudacher, Matthias
1996-01-01
In this paper we numerically demonstrate that massless two-dimensional QCD is not integrable. To this aim, we explicitly solve the 't Hooft integral equation for bound states by an adaptive spline procedure, and compute the decay amplitudes. These amplitudes significantly differ from zero except in all cases in which the decay also produces a pion.
Discrete Dynamics of Two-Dimensional Nonlinear Hybrid Automata
L. Sella (Lorenzo); P.J. Collins (Pieter)
2008-01-01
htmlabstractIn this paper, we develop an algorithm to compute under- and over-approximations to the discrete dynamics of a hybrid automaton. We represent the approximations to the dynamics as \\emph{sofic shifts}, which can be generated by a discrete automaton. We restrict to two-dimensional
Magnetoelectronic transport of the two-dimensional electron gas in ...
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 72; Issue 2 ... CdSe quantum wells; 2D electron gas; magneto-electronic transport. Abstract. Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are ...
Non perturbative methods in two dimensional quantum field theory
Abdalla, Elcio; Rothe, Klaus D
1991-01-01
This book is a survey of methods used in the study of two-dimensional models in quantum field theory as well as applications of these theories in physics. It covers the subject since the first model, studied in the fifties, up to modern developments in string theories, and includes exact solutions, non-perturbative methods of study, and nonlinear sigma models.
Two-dimensional manifold with point-like defects
Gani, Vakhid A; Rubin, Sergei G
2014-01-01
We study a class of two-dimensional extra spaces isomorphic to the $S^2$ sphere in the framework of the multidimensional gravitation. We show that there exists a family of stationary metrics that depend on the initial (boundary) conditions. All these geometries have a singular point. We also discuss the possibility for these deformed extra spaces to be considered as dark matter candidates.
Two-dimensional manifold with point-like defects
Gani, Vakhid A; Rubin, Sergey G
2015-01-01
We study a class of two-dimensional compact extra spaces isomorphic to the sphere $S^2$ in the framework of multidimensional gravitation. We show that there exists a family of stationary metrics that depend on the initial (boundary) conditions. All these geometries have a singular point. We also discuss the possibility for these deformed extra spaces to be considered as dark matter candidates.
Two-dimensional static deformation of an anisotropic medium
Indian Academy of Sciences (India)
The problem of two-dimensional static deformation of a monoclinic elastic medium has been studied using the eigenvalue method, following a Fourier transform. We have obtained expressions for displacements and stresses for the medium in the transformed domain. As an application of the above theory, the particular ...
Cryptanalysis of the Two-Dimensional Circulation Encryption Algorithm
Directory of Open Access Journals (Sweden)
Bart Preneel
2005-07-01
Full Text Available We analyze the security of the two-dimensional circulation encryption algorithm (TDCEA, recently published by Chen et al. in this journal. We show that there are several flaws in the algorithm and describe some attacks. We also address performance issues in current cryptographic designs.
Two-dimensional NMR studies of allyl palladium complexes of ...
Indian Academy of Sciences (India)
Administrator
h3-Allyl complexes are intermediates in organic synthetic reactions such as allylic alkylation and amination. There is growing interest in understanding the structures of chiral h3-allyl intermediates as this would help to unravel the mechanism of enantioselective C–C bond forming reactions. Two-dimensional NMR study is a.
Surface hopping modeling of two-dimensional spectra
Tempelaar, Roel; Vegte, Cornelis P. van der; Knoester, Jasper; Jansen, Thomas L.C.
2013-01-01
Recently, two-dimensional (2D) electronic spectroscopy has become an important tool to unravel the excited state properties of complex molecular assemblies, such as biological light harvesting systems. In this work, we propose a method for simulating 2D electronic spectra based on a surface hopping
Colloidal interactions in two-dimensional nematic emulsions
Indian Academy of Sciences (India)
Abstract. We review theoretical and experimental work on colloidal interactions in two- dimensional (2D) nematic emulsions. We pay particular attention to the effects of (i) the nematic elastic constants, (ii) the size of the colloids, and (iii) the boundary conditions at the particles and the container. We consider the interactions ...
Solitary wave solutions of two-dimensional nonlinear Kadomtsev ...
Indian Academy of Sciences (India)
2017-09-13
Sep 13, 2017 ... Home; Journals; Pramana – Journal of Physics; Volume 89; Issue 3. Solitary wave solutions of two-dimensional nonlinear Kadomtsev–Petviashvili dynamic equation in dust-acoustic ... Keywords. Magnetized plasma; dust-acoustic solitary waves; Kadomtsev–Petviashvili equation; mathematical methods ...
Fermi liquid of two-dimensional polar molecules
Lu, Z.K; Shlyapnikov, G.V.
2012-01-01
We study Fermi-liquid properties of a weakly interacting two-dimensional gas of single-component fermionic polar molecules with dipole moments d oriented perpendicularly to the plane of their translational motion. This geometry allows the minimization of inelastic losses due to chemical reactions
Directory of Open Access Journals (Sweden)
Steven Carberry
2013-12-01
Full Text Available In this article, we illustrate the application of difference in-gel electrophoresis for the proteomic analysis of dystrophic skeletal muscle. The mdx diaphragm was used as a tissue model of dystrophinopathy. Two-dimensional gel electrophoresis is a widely employed protein separation method in proteomic investigations. Although two-dimensional gels usually underestimate the cellular presence of very high molecular mass proteins, integral membrane proteins and low copy number proteins, this method is extremely powerful in the comprehensive analysis of contractile proteins, metabolic enzymes, structural proteins and molecular chaperones. This gives rise to two-dimensional gel electrophoretic separation as the method of choice for studying contractile tissues in health and disease. For comparative studies, fluorescence difference in-gel electrophoresis has been shown to provide an excellent biomarker discovery tool. Since aged diaphragm fibres from the mdx mouse model of Duchenne muscular dystrophy closely resemble the human pathology, we have carried out a mass spectrometry-based comparison of the naturally aged diaphragm versus the senescent dystrophic diaphragm. The proteomic comparison of wild type versus mdx diaphragm resulted in the identification of 84 altered protein species. Novel molecular insights into dystrophic changes suggest increased cellular stress, impaired calcium buffering, cytostructural alterations and disturbances of mitochondrial metabolism in dystrophin-deficient muscle tissue.
TDIGG - TWO-DIMENSIONAL, INTERACTIVE GRID GENERATION CODE
Vu, B. T.
1994-01-01
TDIGG is a fast and versatile program for generating two-dimensional computational grids for use with finite-difference flow-solvers. Both algebraic and elliptic grid generation systems are included. The method for grid generation by algebraic transformation is based on an interpolation algorithm and the elliptic grid generation is established by solving the partial differential equation (PDE). Non-uniform grid distributions are carried out using a hyperbolic tangent stretching function. For algebraic grid systems, interpolations in one direction (univariate) and two directions (bivariate) are considered. These interpolations are associated with linear or cubic Lagrangian/Hermite/Bezier polynomial functions. The algebraic grids can subsequently be smoothed using an elliptic solver. For elliptic grid systems, the PDE can be in the form of Laplace (zero forcing function) or Poisson. The forcing functions in the Poisson equation come from the boundary or the entire domain of the initial algebraic grids. A graphics interface procedure using the Silicon Graphics (GL) Library is included to allow users to visualize the grid variations at each iteration. This will allow users to interactively modify the grid to match their applications. TDIGG is written in FORTRAN 77 for Silicon Graphics IRIS series computers running IRIX. This package requires either MIT's X Window System, Version 11 Revision 4 or SGI (Motif) Window System. A sample executable is provided on the distribution medium. It requires 148K of RAM for execution. The standard distribution medium is a .25 inch streaming magnetic IRIX tape cartridge in UNIX tar format. This program was developed in 1992.
Two-dimensional silicon: the advent of silicene
Grazianetti, Carlo; Cinquanta, Eugenio; Molle, Alessandro
2016-03-01
Silicene is sometimes thought of as the Si alter ego of graphene. However, experimental evidence indicates that silicene is substantially different from graphene in terms of its stability, atomic structure, electronic properties, and device process issues. Some of these aspects hamper the feasibility of silicene for practical application, but at the same time they may offer routes to engineer or functionalize silicene as a complementary material to graphene if a good control of the material can be achieved. As such, the research on silicene runs along the cutting edge between unsurmountable limitation and pioneering opportunities. In the present review, we examine the issues that are representative of this dual edge and try to make a preliminary balance of the state-of-the-art features of this material. Each relevant topic will be explored in a dedicated section. We start with the introduction of ‘experimental’ silicene in the so-called ’flatland’ from the point of view of technology drivers and of its conceptual precursor, freestanding silicene. We then explore the following: specific aspects of the silicene on substrates; the tendency of silicene to have multiple structural forms (what we call the polymorphic nature of silicene) the role of the strong hybridization with the substrate in the electronic band structure of silicene; the Raman spectrum of silicene, and silicene processing and integration into a transistor. Finally we conclude by proposing an investigation into silicene’s emerging contemporaries in the realm of elementary two-dimensional materials. Mindful of ongoing discussions and current issues, we try to go to the heart of the problems by treating each topic objectively and scientifically and we then provide our personal views in the discussion.
The amyloid architecture provides a scaffold for enzyme-like catalysts.
Al-Garawi, Z S; McIntosh, B A; Neill-Hall, D; Hatimy, A A; Sweet, S M; Bagley, M C; Serpell, L C
2017-08-03
Natural biological enzymes possess catalytic sites that are generally surrounded by a large three-dimensional scaffold. However, the proportion of the protein molecule that participates in the catalytic reaction is relatively small. The generation of artificial or miniature enzymes has long been a focus of research because enzyme mimetics can be produced with high activity at low cost. These enzymes aim to mimic the active sites without the additional architecture contributed by the protein chain. Previous work has shown that amyloidogenic peptides are able to self-assemble to create an active site that is capable of binding zinc and catalysing an esterase reaction. Here, we describe the structural characterisation of a set of designed peptides that form an amyloid-like architecture and reveal that their capability to mimic carbonic anhydrase and serve as enzyme-like catalysts is related to their ability to self-assemble. These amyloid fibril structures can bind the metal ion Zn 2+ via a three-dimensional arrangement of His residues created by the amyloid architecture. Our results suggest that the catalytic efficiency of amyloid-like assembly is not only zinc-dependent but also depends on an active centre created by the peptides which is, in turn, dependent on the ordered architecture. These fibrils have good esterase activity, and they may serve as good models for the evolution of modern-day enzymes. Furthermore, they may be useful in designing self-assembling fibrils for applications as metal ion catalysts. This study also demonstrates that the ligands surrounding the catalytic site affect the affinity of the zinc-binding site to bind the substrate contributing to the enzymatic activity of the assembled peptides.
Recombination in one- and two-dimensional fitness landscapes.
Avetisyan, Zh; Saakian, David B
2010-05-01
We consider many-site mutation-recombination models of molecular evolution, where fitness is a function of a Hamming distance from one (one-dimensional case) or two (two-dimensional case) sequences. For the one-dimensional case, we calculate the population distribution dynamics for a model with zero fitness and an arbitrary symmetric initial distribution and find an error threshold transition point in the single-peak fitness model for a given initial symmetric distribution. We calculate the recombination period in the case of a single-peak fitness function, when the original population is located at one sequence, at some Hamming distance from the peak configuration. Steady-state fitness is calculated with finite genome length corrections. We derive analytical equations for the two-dimensional mutation-recombination model.
Entanglement Entropy in Two-Dimensional String Theory.
Hartnoll, Sean A; Mazenc, Edward A
2015-09-18
To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space.
Explorative data analysis of two-dimensional electrophoresis gels
DEFF Research Database (Denmark)
Schultz, J.; Gottlieb, D.M.; Petersen, Marianne Kjerstine
2004-01-01
Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening...... of gels is presented. First, an approach is demonstrated in which no prior knowledge of the separated proteins is used. Alignment of the gels followed by a simple transformation of data makes it possible to analyze the gels in an automated explorative manner by principal component analysis, to determine...... if the gels should be further analyzed. A more detailed approach is done by analyzing spot volume lists by principal components analysis and partial least square regression. The use of spot volume data offers a mean to investigate the spot pattern and link the classified protein patterns to distinct spots...
A two-dimensional dam-break flood plain model
Hromadka, T.V.; Berenbrock, C.E.; Freckleton, J.R.; Guymon, G.L.
1985-01-01
A simple two-dimensional dam-break model is developed for flood plain study purposes. Both a finite difference grid and an irregular triangle element integrated finite difference formulation are presented. The governing flow equations are approximately solved as a diffusion model coupled to the equation of continuity. Application of the model to a hypothetical dam-break study indicates that the approach can be used to predict a two-dimensional dam-break flood plain over a broad, flat plain more accurately than a one-dimensional model, especially when the flow can break-out of the main channel and then return to the channel at other downstream reaches. ?? 1985.
Numerical analysis of a two-dimensional nonsteady detonations
Taki, S.; Fujiwara, T.
1976-01-01
In the present work a system of two-dimensional nonsteady hydrodynamic and chemical kinetic equations was numerically integrated for an exothermic system. Assumed two-step reaction model simulates practically an oxyhydrogen mixture. The calculation starts from a plane Chapman-Jouguet detonation as an initial condition. Two-dimensional disturbances are generated by artificially placing nonuniformities ahead of the detonation front. Regardless of the difference of the given initial disturbances, a fixed number of triple shock waves were produced for a fixed combination of mixture model and geometry when the transition period was over. This shows that for a given detonation tube geometry any exothermic system has its own characteristic multidimensional structure. The obtained number of triple shock waves contained in the detonation front was in agreement with existing experimental observations under the same condition.
Directional detection of dark matter with two-dimensional targets
Directory of Open Access Journals (Sweden)
Yonit Hochberg
2017-09-01
Full Text Available We propose two-dimensional materials as targets for direct detection of dark matter. Using graphene as an example, we focus on the case where dark matter scattering deposits sufficient energy on a valence-band electron to eject it from the target. We show that the sensitivity of graphene to dark matter of MeV to GeV mass can be comparable, for similar exposure and background levels, to that of semiconductor targets such as silicon and germanium. Moreover, a two-dimensional target is an excellent directional detector, as the ejected electron retains information about the angular dependence of the incident dark matter particle. This proposal can be implemented by the PTOLEMY experiment, presenting for the first time an opportunity for directional detection of sub-GeV dark matter.
Robust L1-norm two-dimensional linear discriminant analysis.
Li, Chun-Na; Shao, Yuan-Hai; Deng, Nai-Yang
2015-05-01
In this paper, we propose an L1-norm two-dimensional linear discriminant analysis (L1-2DLDA) with robust performance. Different from the conventional two-dimensional linear discriminant analysis with L2-norm (L2-2DLDA), where the optimization problem is transferred to a generalized eigenvalue problem, the optimization problem in our L1-2DLDA is solved by a simple justifiable iterative technique, and its convergence is guaranteed. Compared with L2-2DLDA, our L1-2DLDA is more robust to outliers and noises since the L1-norm is used. This is supported by our preliminary experiments on toy example and face datasets, which show the improvement of our L1-2DLDA over L2-2DLDA. Copyright © 2015 Elsevier Ltd. All rights reserved.
Negative differential Rashba effect in two-dimensional hole systems
Habib, B.; Tutuc, E.; Melinte, S.; Shayegan, M.; Wasserman, D.; Lyon, S. A.; Winkler, R.
2004-01-01
We demonstrate experimentally and theoretically that two-dimensional (2D) heavy hole systems in single heterostructures exhibit a \\emph{decrease} in spin-orbit interaction-induced spin splitting with an increase in perpendicular electric field. Using front and back gates, we measure the spin splitting as a function of applied electric field while keeping the density constant. Our results are in contrast to the more familiar case of 2D electrons where spin splitting increases with electric field.
Effective interaction in two-dimensional electron systems
Suwa, Takeshi; Takayanagi, Kazuo; Lipparini, Enrico
2004-03-01
A fully microscopic derivation is proposed for an effective interaction operator between electrons in the two-dimensional electron gas (2DEG), which represents multiple-scattering processes in the medium. The obtained interaction features short-range behaviors between electrons, and is presented in a simple form which allows applications in various systems. Short-range correlation in the 2DEG is discussed in detail in terms of the effective interaction with special emphasis on the nonlocal aspect of the correlation.
Excitonic condensation in quasi-two-dimensional systems
Energy Technology Data Exchange (ETDEWEB)
Crisan, M. [Department of Theoretical Physics, University of Cluj, 400084 Cluj-Napoca (Romania)]. E-mail: mcrisan@phys.ubbcluj.ro; Tifrea, I. [Department of Theoretical Physics, University of Cluj, 400084 Cluj-Napoca (Romania); Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)
2005-10-17
We present a low energy model for the Bose-Einstein condensation in a quasi-two-dimensional excitonic gas. Using the flow equations of the renormalization group and a {phi}{sup 4} model with the dynamical critical exponent z=2 we calculate the temperature dependence of the critical density, coherence length, magnetic susceptibility, and specific heat. The model can be relevant for the macroscopic coherence observed in GaAs/AlGaAs coupled quantum wells.
Chemical signal amplification in two-dimensional paper networks
Fu, Elain; Kauffman, Peter; Lutz, Barry; Yager, Paul
2010-01-01
Two-dimensional paper networks (2DPNs) hold great potential for extending the utility of paper-based chemical and biochemical diagnostics at a cost and ease-of-use that is comparable to conventional lateral flow strips. 2DPNs enable the automated sequential delivery of multiple reagents to a detection region with a single user activation step, and therefore have the potential to extend the processing capabilities of inexpensive paper-based assays with comparable ease of use to conventional la...
The problem of friction in two-dimensional relative motion
Grech, Dariusz; Mazur, Zygmunt
2000-01-01
We analyse a mechanical system in two-dimensional relative motion with friction. Although the system is simple, the peculiar interplay between two kinetic friction forces and gravity leads to the wide range of admissible solutions exceeding most intuitive expectations. In particular, the strong qualitative dependence between behaviour of the system, boundary conditions and parameters involved in its description is emphasised. The problem is intended to be discussed in theoretical framework an...
Analysis of two dimensional signals via curvelet transform
Lech, W.; Wójcik, W.; Kotyra, A.; Popiel, P.; Duk, M.
2007-04-01
This paper describes an application of curvelet transform analysis problem of interferometric images. Comparing to two-dimensional wavelet transform, curvelet transform has higher time-frequency resolution. This article includes numerical experiments, which were executed on random interferometric image. In the result of nonlinear approximations, curvelet transform obtains matrix with smaller number of coefficients than is guaranteed by wavelet transform. Additionally, denoising simulations show that curvelet could be a very good tool to remove noise from images.
Magneto-static vortices in two dimensional Abelian gauge theories
Bellazzini, J.; Bonanno, C.; Siciliano, G
2008-01-01
We study the existence of vortices of the Klein-Gordon-Maxwell equations in the two dimensional case. In particular we find sufficient conditions for the existence of vortices in the magneto-static case, i.e when the electric potential $\\phi=0$. This result, due to the lack of suitable embedding theorems for the vector potential $\\A$ is achieved with the help of a penalization method.
Two-dimensional correlation spectroscopy in polymer study
Park, Yeonju; Noda, Isao; Jung, Young Mee
2015-01-01
This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted. PMID:25815286
Minor magnetization loops in two-dimensional dipolar Ising model
Energy Technology Data Exchange (ETDEWEB)
Sarjala, M. [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland); Seppaelae, E.T., E-mail: eira.seppala@nokia.co [Nokia Research Center, Itaemerenkatu 11-13, FI-00180 Helsinki (Finland); Alava, M.J., E-mail: mikko.alava@tkk.f [Aalto University, Department of Applied Physics, P.O. Box 14100, FI-00076 Aalto (Finland)
2011-05-15
The two-dimensional dipolar Ising model is investigated for the relaxation and dynamics of minor magnetization loops. Monte Carlo simulations show that in a stripe phase an exponential decrease can be found for the magnetization maxima of the loops, M{approx}exp(-{alpha}N{sub l}) where N{sub l} is the number of loops. We discuss the limits of this behavior and its relation to the equilibrium phase diagram of the model.
Interior design of a two-dimensional semiclassic black hole
Levanony, Dana; 10.1103/PhysRevD.80.084008
2009-01-01
We look into the inner structure of a two-dimensional dilatonic evaporating black hole. We establish and employ the homogenous approximation for the black-hole interior. The field equations admit two types of singularities, and their local asymptotic structure is investigated. One of these singularities is found to develop, as a spacelike singularity, inside the black hole. We then study the internal structure of the evaporating black hole from the horizon to the singularity.
Acoustic transparency in two-dimensional sonic crystals
Energy Technology Data Exchange (ETDEWEB)
Sanchez-Dehesa, Jose; Torrent, Daniel [Wave Phenomena Group, Department of Electronic Engineering, Polytechnic University of Valencia, C/ Camino de Vera s/n, E-46022 Valencia (Spain); Cai Liangwu [Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506 (United States)], E-mail: jsdehesa@upvnet.upv.es
2009-01-15
Acoustic transparency is studied in two-dimensional sonic crystals consisting of hexagonal distributions of cylinders with continuously varying properties. The transparency condition is achieved by selectively closing the acoustic bandgaps, which are governed by the structure factor of the cylindrical scatterers. It is shown here that cylindrical scatterers with the proposed continuously varying properties are physically realizable by using metafluids based on sonic crystals. The feasibility of this proposal is analyzed by a numerical experiment based on multiple scattering theory.
Particle transport in a two-dimensional septate channel
Energy Technology Data Exchange (ETDEWEB)
Borromeo, M. [Dipartimento di Fisica, Universita di Perugia, I-06123 Perugia (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); Marchesoni, F., E-mail: fabio.marchesoni@pg.infn.it [Dipartimento di Fisica, Universita di Camerino, I-62032 Camerino (Italy); Department of Physics, Boston University, Boston, MA 02215 (United States)
2010-10-05
Graphical abstract: {open_square}{open_square}{open_square}. - Abstract: We analyze the transport properties of a Brownian particle diffusing along a two-dimensional septate channel, namely, a channel formed by equal rectangular cavities separated by narrow pores, subjected to an external longitudinal drive. We determine analytical formulas for the dependence of the particle mobility and diffusivity on the geometric channel parameters at zero and large applied drives. Finally, we rule out anomalous negative mobility for pointlike particles in a septate channel.
Dilanian, Ruben A; Varghese, Jose N; Wilkins, Steve W; Oka, Toshihiko; Yagi, Naoto; Quiney, Harry M; Nugent, Keith A
2010-01-01
The application of powder diffraction methods in two-dimensional crystallography is regarded as intractable because of the uncertainties associated with overlapping reflections. Here, we report an approach that resolves these ambiguities and provides reliable low-resolution phase information directly from powder diffraction data. We apply our method to the recovery of the structure of the bacteriorhodopsin (bR) molecule to a resolution of 7 angstroms using only powder diffraction data obtained from two-dimensional purple membrane (PM) crystals.
Two-Dimensional Identification of Fetal Tooth Germs.
Seabra, Mariana; Vaz, Paula; Valente, Francisco; Braga, Ana; Felino, António
2017-03-01
To demonstrate the efficiency and applicability of two-dimensional ultrasonography in the identification of tooth germs and in the assessment of potential pathology. Observational, descriptive, cross-sectional study. Prenatal Diagnosis Unit of Centro Hospitalar de Vila Nova de Gaia / Espinho-Empresa Pública in Portugal. A total of 157 white pregnant women (median age, 32 years; range, 14 to 47 years) undergoing routine ultrasound exams. Description of the fetal tooth germs, as visualized by two-dimensional ultrasonography, including results from prior fetal biometry and detailed screening for malformations. In the first trimester group, ultrasonography identified 10 tooth germs in the maxilla and 10 tooth germs in the mandible in all fetuses except for one who presented eight maxillary tooth germs. This case was associated with a chromosomal abnormality (trisomy 13) with a bilateral cleft palate. In the second and third trimesters group, ultrasonography identified a larger range of tooth germs: 81.2% of fetuses showed 10 tooth germs in the maxilla and 85.0% of fetuses had 10 tooth germs in the mandible. Hypodontia was more prevalent in the maxilla than in the mandible, which led us to use qualitative two-dimensional ultrasonography to analyze the possible association between hypodontia and other variables such as fetal pathology, markers, head, nuchal, face, and spine. We recommend using this method as the first exam to evaluate fetal morphology and also to help establish accurate diagnosis of abnormalities in pregnancy.
Experimental realization of two-dimensional boron sheets
Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui
2016-06-01
A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp2 hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.
Electromagnetically induced two-dimensional grating assisted by incoherent pump
Energy Technology Data Exchange (ETDEWEB)
Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang, E-mail: wrg@snnu.edu.cn
2017-04-25
We propose a scheme for realizing electromagnetically induced two-dimensional grating in a double-Λ system driven simultaneously by a coherent field and an incoherent pump field. In such an atomic configuration, the absorption is suppressed owing to the incoherent pumping process and the probe can be even amplified, while the refractivity is mainly attributed to the dynamically induced coherence. With the help of a standing-wave pattern coherent field, we obtain periodically modulated refractive index without or with gain, and therefore phase grating or gain-phase grating which diffracts a probe light into high-order direction efficiently can be formed in the medium via appropriate manipulation of the system parameters. The diffraction efficiency attainable by the present gratings can be controlled by tuning the coherent field intensity or the interaction length. Hence, the two-dimensional grating can be utilized as all-optical splitter or router in optical networking and communication. - Highlights: • Two-dimensional grating is coherently induced in four-level atoms. • Phase and gain-phase gratings are obtained assisted by incoherent pump. • The diffraction power is improved due to the enhanced refraction modulation. • The gratings can be utilized as multi-channel all-optical splitter and router.
Quantum oscillations in quasi-two-dimensional conductors
Galbova, O
2002-01-01
The electronic absorption of sound waves in quasi-two-dimensional conductors in strong magnetic fields, is investigated theoretically. A longitudinal acoustic wave, propagating along the normal n-> to the layer of quasi-two-dimensional conductor (k-> = left brace 0,0,k right brace; u-> = left brace 0,0,u right brace) in magnetic field (B-> = left brace 0, 0, B right brace), is considered. The quasiclassical approach for this geometry is of no interest, due to the absence of interaction between electromagnetic and acoustic waves. The problem is of interest in strong magnetic field when quantization of the charge carriers energy levels takes place. The quantum oscillations in the sound absorption coefficient, as a function of the magnetic field, are theoretically observed. The experimental study of the quantum oscillations in quasi-two-dimensional conductors makes it possible to solve the inverse problem of determining from experimental data the extrema closed sections of the Fermi surface by a plane p sub z = ...
Directory of Open Access Journals (Sweden)
D. A. Fetisov
2015-01-01
Full Text Available The controllability conditions are well known if we speak about linear stationary systems: a linear stationary system is controllable if and only if the dimension of the state vector is equal to the rank of the controllability matrix. The concept of the controllability matrix is extended to affine systems, but relations between affine systems controllability and properties of this matrix are more complicated. Various controllability conditions are set for affine systems, but they deal as usual either with systems of some special form or with controllability in some small neighborhood of the concerned point. An affine system is known to be controllable if the system is equivalent to a system of a canonical form, which is defined and regular in the whole space of states. In this case, the system is said to be feedback linearizable in the space of states. However there are examples, which illustrate that a system can be controllable even if it is not feedback linearizable in any open subset in the space of states. In this article we deal with such systems.Affine systems with two-dimensional control are considered. The system in question is assumed to be equivalent to a system of a quasicanonical form with two-dimensional zero dynamics which is defined and regular in the whole space of states. Therefore the controllability of the original system is equivalent to the controllability of the received system of a quasicanonical form. In this article the sufficient condition for an available solution of the terminal problem is proven for systems of a quasicanonical form with two-dimensional control and two-dimensional zero dynamics. The condition is valid in the case of an arbitrary time interval and arbitrary initial and finite states of the system. Therefore the controllability condition is set for systems of a quasicanonical form with two-dimensional control and two-dimensional zero dynamics. An example is given which illustrates how the proved
Chemistry of Two-Dimensional Transition Metal Carbides (MXenes)
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
Park, Sungjoon; Yang, Bohm-Jung
2017-09-01
We classify all possible gap-closing procedures which can be achieved in two-dimensional time-reversal invariant noncentrosymmetric systems. For exhaustive classification, we examine the space-group symmetries of all 49 layer groups lacking inversion, taking into account spin-orbit coupling. Although a direct transition between two insulators is generally predicted to occur when a band crossing happens at a general point in the Brillouin zone, we find that a variety of stable semimetal phases with point or line nodes can also arise due to the band crossing in the presence of additional crystalline symmetries. Through our theoretical study, we provide the complete list of nodal semimetals created by a band inversion in two-dimensional noncentrosymmetric systems with time-reversal invariance. The transition from an insulator to a nodal semimetal can be grouped into three classes depending on the crystalline symmetry. First, in systems with a twofold rotation about the z axis (normal to the system), a band inversion at a generic point generates a two-dimensional Weyl semimetal with point nodes. Second, when the band crossing happens on the line invariant under a twofold rotation (mirror) symmetry with the rotation (normal) axis lying in the two-dimensional plane, a Weyl semimetal with point nodes can also be obtained. Finally, when the system has a mirror symmetry about the plane embracing the whole system, a semimetal with nodal lines can be created. Applying our theoretical framework, we identify various two-dimensional materials as candidate systems in which stable nodal semimetal phases can be induced via doping, applying electric field, or strain engineering, etc.
Dissipation of coherent structures in confined two-dimensional turbulence
Clercx, H. J. H.; van Heijst, G. J. F.
2017-11-01
Since the seminal article "Inertial ranges in two-dimensional turbulence" by Kraichnan in 1967, our understanding of the dynamics and transport properties of two-dimensional turbulence is largely built on the assumption of homogeneity and isotropy of statistically steady or decaying turbulence. In the last two decades, more attention has been paid to the presence of lateral walls, either with stress-free or no-slip boundary conditions, and also considering a variety of geometries such as square, rectangular, or circular domains. The impact of confining boundaries on the dynamics of two-dimensional turbulence is important. This is in sharp contrast with three-dimensional turbulence, where homogeneity and isotropy are locally restored due to the cascade process in the inertial range. The impact of confining boundaries is therefore limited in three-dimensional turbulence. The presence of an inverse energy cascade in two-dimensional turbulence, however, will continuously generate large-scale energy-containing eddies, and their vigorous interaction with, in particular, no-slip walls generates large amounts of vorticity and contributes significantly to the dissipation of kinetic energy of the flow. The dissipation is even strongly enhanced compared with the unbounded case. In this review, we will focus on one of the elementary structures observed in two-dimensional turbulent flows: the dipolar vortex. With its self-induced velocity, it propagates easily through the domain and is hence likely to interact with domain boundaries. Standard vortex generation mechanisms allow to create well-defined dipoles and to investigate the collision of such structures with rigid domain boundaries in detail. Relevant aspects of the collision process concern the dynamics and stability of the generated boundary layers, the vorticity, and vorticity gradients contained in these boundary layers, and the dissipation of kinetic energy when dipoles collide with walls. Some of these aspects will
Directory of Open Access Journals (Sweden)
Dinesh Kumar
2013-11-01
Full Text Available This paper deals with the study of two-dimensional Saigo-Maeda operators of Weyl type associated with Aleph function defined in this paper. Two theorems on these defined operators are established. Some interesting results associated with the H-functions and generalized Mittag-Leffler functions are deduced from the derived results. One dimensional analog of the derived results is also obtained.
Graphene as a Prototypical Model for Two-Dimensional Continuous Mechanics
Directory of Open Access Journals (Sweden)
Philippe Lambin
2017-08-01
Full Text Available This paper reviews a few problems where continuous-medium theory specialized to two-dimensional media provides a qualitatively correct picture of the mechanical behavior of graphene. A critical analysis of the parameters involved is given. Among other results, a simple mathematical description of a folded graphene sheet is proposed. It is also shown how the graphene–graphene adhesion interaction is related to the cleavage energy of graphite and its C 33 bulk elastic constant.
Modelling Altitude Information in Two-Dimensional Traffic Networks for Electric Mobility Simulation
Diogo Santos; José Pinto; Rossetti, Rosaldo J. F.; Eugénio Oliveira
2016-01-01
Elevation data is important for electric vehicle simulation. However, traffic simulators are often two-dimensional and do not offer the capability of modelling urban networks taking elevation into account. Specifically, SUMO - Simulation of Urban Mobility, a popular microscopic traffic simulator, relies on networks previously modelled with elevation data as to provide this information during simulations. This work tackles the problem of adding elevation data to urban network models - particul...
Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots
Energy Technology Data Exchange (ETDEWEB)
Cundiff, Steven T. [Univ. of Colorado, Boulder, CO (United States)
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.
Pollaris, H.; Braekers, K.; Caris, A.; Janssens, G.K.; S Limbourg
2014-01-01
A mixed integer linear programming model for a two-dimensional capacitated vehicle routing problem (2L-CVRP) with sequence based loading and axle weight restrictions is provided. To the authors’ knowledge, it is the first time that axle weight restrictions are incorporated in a VRP. Axle weight limits impose a great challenge for transportation companies. Trucks with overloaded axles represent a significant threat for traffic safety and may cause serious damage to the road surface. Transpor...
Trushin, Maxim
2017-01-01
We find that intrinsic graphene provides efficient photocarrier transport across a two-dimensional graphene-semiconductor Schottky junction as a linear response to monochromatic light with excitation energy well below the semiconductor bandgap. The operation mechanism relies both on zero-bias photoexcited and thermionic emission contributing to photoresponsivity, enabled by the extended photocarrier thermalization time in intrinsic graphene. The photoresponsivity rapidly increases with excita...
Two-Dimensional, Time-Dependent Plasma Structures of a Hall Effect Thruster
2011-09-01
This ultra-high speed imaging capability provides a two-dimensional description of the plasma field with time-resolved information. Moreover, this...47 3.7 Relative spectral response of the Shimadzu HPV -2 ultra-high speed camera taken from Shimadzu HPV -2 Spectral Response . 48 3.8 Sample...magnetic field. Operational characteristics of the thruster, such as a description of the parts and the fuel types, will also be discussed. Chapter II will
Observation of two-dimensional Faraday waves in extremely shallow depth.
Li, Xiaochen; Yu, Zhengyue; Liao, Shijun
2015-09-01
A family of two-dimensional Faraday waves in extremely shallow depth (1 mm to 2 mm) of absolute ethanol are observed experimentally using a Hele-Shaw cell that vibrates vertically. The same phenomena are not observed by means of water, ethanol solution, and silicone oil. These Faraday waves are quite different from the traditional ones. These phenomena are helpful to deepen and enrich our understandings about Faraday waves, and besides provide a challenging problem for computational fluid dynamics.
Guiding of elastic waves in a two-dimensional graded phononic crystal plate
Guo, Yuning; Hettich, Mike; Dekorsy, Thomas
2017-01-01
The guiding of elastic waves in a two-dimensional graded phononic crystal plate is investigated. This effect is induced by the resonance coupling of attachments and matrix in a silicon pillar-substrate system and the resonance frequencies of guided surface modes can be tuned by tailoring the geometry and material properties of the pillars. The resonance frequencies increase with radius and Young's modulus, and decrease with height and density of the pillars, which provides several possibiliti...
Magnetism and pairing of two-dimensional trapped fermions.
Chiesa, Simone; Varney, Christopher N; Rigol, Marcos; Scalettar, Richard T
2011-01-21
The emergence of local phases in a trapped two-component Fermi gas in an optical lattice is studied using quantum Monte Carlo simulations. We treat temperatures that are comparable to or lower than those presently achievable in experiments and large enough systems that both magnetic and paired phases can be detected by inspection of the behavior of suitable short-range correlations. We use the latter to suggest the interaction strength and temperature range at which experimental observation of incipient magnetism and d-wave pairing are more likely and evaluate the relation between entropy and temperature in two-dimensional confined fermionic systems.
Nonlinear excitations in two-dimensional molecular structures with impurities
DEFF Research Database (Denmark)
Gaididei, Yuri Borisovich; Rasmussen, Kim; Christiansen, Peter Leth
1995-01-01
We study the nonlinear dynamics of electronic excitations interacting with acoustic phonons in two-dimensional molecular structures with impurities. We show that the problem is reduced to the nonlinear Schrodinger equation with a varying coefficient. The latter represents the influence...... excitations. Analytical results are in good agreement with numerical simulations of the nonlinear Schrodinger equation....... of the impurity. Transforming the equation to the noninertial frame of reference coupled with the center of mass we investigate the soliton behavior in the close vicinity of the impurity. With the help of the lens transformation we show that the soliton width is governed by an Ermakov-Pinney equation. We also...
Two-dimensional metamaterial transparent metal electrodes for infrared optoelectronics.
Clark, Samuel M; Han, Sang Eon
2014-06-15
We examine the optical properties of two-dimensionally nanostructured metals in the metamaterial regime for infrared applications. Compared with straight nanowires and nanogrids, serpentine structures exhibit much lower optical losses of less than 7% even at a large metal area fraction of 0.3. The low loss is primarily due to a small effective conductivity of the meandering structures, and self-inductance plays a modest role in reducing losses in these structures. The high transparency at a large metal area coverage would be useful for transparent electrodes in optoelectronic devices.
Two-Dimensional Pulse Propagation without Anomalous Dispersion
Bender, Carl M.; Rodríguez-Fortuño, Francisco J.; Sarkar, Sarben; Zayats, Anatoly V.
2017-09-01
Anomalous dispersion is a surprising phenomenon associated with wave propagation in an even number of space dimensions. In particular, wave pulses propagating in two-dimensional space change shape and develop a tail even in the absence of a dispersive medium. We show mathematically that this dispersion can be eliminated by considering a modified wave equation with two geometric spatial dimensions and, unconventionally, two timelike dimensions. Experimentally, such a wave equation describes pulse propagation in an optical or acoustic medium with hyperbolic dispersion, leading to a fundamental understanding and new approaches to ultrashort pulse shaping in nanostructured metamaterials.
Graphene and Two-Dimensional Materials for Optoelectronic Applications
Directory of Open Access Journals (Sweden)
Andreas Bablich
2016-03-01
Full Text Available This article reviews optoelectronic devices based on graphene and related two-dimensional (2D materials. The review includes basic considerations of process technology, including demonstrations of 2D heterostructure growth, and comments on the scalability and manufacturability of the growth methods. We then assess the potential of graphene-based transparent conducting electrodes. A major part of the review describes photodetectors based on lateral graphene p-n junctions and Schottky diodes. Finally, the progress in vertical devices made from 2D/3D heterojunctions, as well as all-2D heterostructures is discussed.
Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs
Energy Technology Data Exchange (ETDEWEB)
Mannix, A. J.; Zhou, X. -F.; Kiraly, B.; Wood, J. D.; Alducin, D.; Myers, B. D.; Liu, X.; Fisher, B. L.; Santiago, U.; Guest, J. R.; Yacaman, M. J.; Ponce, A.; Oganov, A. R.; Hersam, M. C.; Guisinger, N. P.
2015-12-17
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.
Negative-refraction imaging with two-dimensional phononic crystals
Ke, Manzhu; Liu, Zhengyou; Qiu, Chunyin; Wang, Wengang; Shi, Jing; Wen, Weijia; Sheng, Ping
2005-08-01
We report negative refraction imaging for acoustic waves in a two-dimensional phononic crystal. The sample consists of a triangular array of steel rods immersed in water. Both the observed negative refraction behavior and imaging effect are in excellent agreement with numerical simulations by the multiple scattering theory method. The existence of nearly circular dispersion surfaces for the phonic crystal sample means that the negative refraction is well defined for all angles of incidence, and very robust in its realization and application to focusing and imaging.
Mass/Count Variation: A Mereological, Two-Dimensional Semantics
Directory of Open Access Journals (Sweden)
Peter R Sutton
2016-12-01
Full Text Available We argue that two types of context are central to grounding the semantics for the mass/count distinction. We combine and develop the accounts of Rothstein (2010 and Landman (2011, which emphasize (non-overlap at a context. We also adopt some parts of Chierchia’s (2010 account which uses precisifying contexts. We unite these strands in a two-dimensional semantics that covers a wide range of the puzzling variation data in mass/count lexicalization. Most importantly, it predicts where we should expect to find such variation for some classes of nouns but not for others, and also explains why.
The Penalty Cost Functional for the Two-Dimensional
Directory of Open Access Journals (Sweden)
Victor Onomza WAZIRI
2006-07-01
Full Text Available This paper constructs the penalty cost functional for optimizing the two-dimensional control operator of the energized wave equation. In some multiplier methods such as the Lagrange multipliers and Pontrygean maximum principle, the cost of merging the constraint equation to the integral quadratic objective functional to obtain an unconstraint equation is normally guessed or obtained from the first partial derivatives of the unconstrained equation. The Extended Conjugate Gradient Method (ECGM necessitates that the penalty cost be sequentially obtained algebraically. The ECGM problem contains a functional which is completely given in terms of state and time spatial dependent variables.
Dynamics of Saturated Energy Condensation in Two-Dimensional Turbulence
Chan, Chi-kwan; Brandenburg, Axel
2011-01-01
We derive and numerically confirm that the saturation of energy condensation in two-dimensional turbulence is governed by the balance between forcing and small-scale dissipation. The time scale of saturation is inversely proportional to the viscosity but the saturation energy level is determined by both viscosity and the forcing scale. It is shown that, because the energy dissipation is proportional to the enstrophy, which itself is a conserved quantity in the ideal case, it is necessary to resolve the enstrophy spectrum to achieve numerical consistency. We also find that the movement of the condensate vortices can be described as Brownian motion of an inertial particle.
Two-Dimensional Fractional Order Generalized Thermoelastic Porous Material
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Ibrahim A. Abbas
Full Text Available AbstractIn the work, a two-dimensional problem of a porous material is considered within the context of the fractional order generalized thermoelasticity theory with one relaxation time. The medium is assumed initially quiescent for a thermoelastic half space whose surface is traction free and has a constant heat flux. The normal mode analysis and eigenvalue approach techniques are used to solve the resulting non-dimensional coupled equations. The effect of the fractional order of the temperature, displacement components, the stress components, changes in volume fraction field and temperature distribution have been depicted graphically.
Two-Dimensional Electron System in Electromagnetic Radiation Field
Lungu, Radu Paul; Manolescu, Andrei
We consider a two-dimensional electron gas in the presence of a monochromatic linear polarized electromagnetic field, within the Floquet formalism. The Floquet states have a simple relation with the energy eigenstates in the absence of the field. Therefore the single-particle and the two-particle Green functions of the many-body system with Coulomb interactions, in the radiation field, can be formally calculated by the standard diagrammatic techniques, as for the conservative system. We derive the elementary excitations of quasi-particle type, the plasma dispersion relation, and the ground state quasi-energy, and we relate them to the corresponding results for the conservative system.
Spin dynamics in a two-dimensional quantum gas
DEFF Research Database (Denmark)
Pedersen, Poul Lindholm; Gajdacz, Miroslav; Deuretzbacher, Frank
2014-01-01
We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions...... with superimposed angular density modulations. The density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We show that the two clouds are anticorrelated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source...
Free fermions in two-dimensional Ising model (in English)
Plechko, V. N.
The two--dimensional (2D) Ising model is reviewed as a theory of free fermions on a lattice. The discussion includes the fermionization procedure based on the mirror--ordered factorization of the density matrix, Gaussian fermionic integral representation for partition function, the momentum--space analysis and Onsager's result, the effective continuum--limit field theories and the critical--point singularities. The emergence of long--range fermionic correlations in a nonzero magnetic field and the behaviour of the specific heat along the critical isotherm are commented. Attention is given to the choice of rational computational devices.
Investigation of a traffic modelling inspired two dimensional map
McCartney, Mark; Mooney, Helen; Stretch, Chris
2010-09-01
Commencing with a class of differential equation based car following models for traffic flow a simplified discrete time model on a closed loop is found. A two dimensional map, containing two free parameters, and corresponding to the behaviour of two vehicles on the loop is investigated. Bounds on the prisoner set of the map are determined, and a number of strange attractors are presented. The variation of largest Lyapunov exponent over a range of parameter space is considered. The resulting behaviour of the map is considered within a traffic flow context.
Optimum high temperature strength of two-dimensional nanocomposites
Energy Technology Data Exchange (ETDEWEB)
Monclús, M. A.; Molina-Aldareguía, J. M., E-mail: jon.molina@imdea.org [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Zheng, S. J.; Mayeur, J. R.; Beyerlein, I. J.; Mara, N. A. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Polcar, T. [Czech Technical University in Prague, Technická 2, Prague 6 (Czech Republic); Llorca, J. [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Department of Materials Science, Polytechnic University of Madrid, E. T. S. de Ingenieros de Caminos, 28040 Madrid (Spain)
2013-11-01
High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.
Optimum high temperature strength of two-dimensional nanocomposites
Directory of Open Access Journals (Sweden)
M. A. Monclús
2013-11-01
Full Text Available High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.
Smoothed Particle Hydrodynamics Method for Two-dimensional Stefan Problem
Tarwidi, Dede
2016-01-01
Smoothed particle hydrodynamics (SPH) is developed for modelling of melting and solidification. Enthalpy method is used to solve heat conduction equations which involved moving interface between phases. At first, we study the melting of floating ice in the water for two-dimensional system. The ice objects are assumed as solid particles floating in fluid particles. The fluid and solid motion are governed by Navier-Stokes equation and basic rigid dynamics equation, respectively. We also propose a strategy to separate solid particles due to melting and solidification. Numerical results are obtained and plotted for several initial conditions.
A Two-Dimensional Improvement for Farr-Gao Algorithm
Dong, Tian
2010-01-01
Farr-Gao algorithm is a state-of-the-art algorithm for reduced Gr\\"{o}bner bases of vanishing ideals of finite points, which has been implemented in Maple$^\\circledR$ as a build-in command. In this paper, we present a two-dimensional improvement for it that employs a preprocessing strategy for computing reduced Gr\\"{o}bner bases associated with tower subsets of given point sets. Experimental results show that the preprocessed Farr-Gao algorithm is more efficient than the classical one.
Sample solublization buffers for two-dimensional electrophoresis.
Weiss, Walter; Görg, Angelika
2008-01-01
Before two-dimensional electrophoresis (2-DE), proteins of the sample must be denatured, reduced, disaggregated, and solubilized. Sample solubilization is usually carried out in a buffer containing chaotropes (typically 9.5 M urea, or 5-8 M urea and 2 M thiourea), 2-4% nonionic and/or zwitterionic detergent(s), reducing agent(s), carrier ampholytes and, depending on the type of sample, protease inhibitors. In this chapter, the major constituents of sample solubilization/lysis buffers will be briefly reviewed, some general sample preparation guidelines will be given, and the most common protein solubilization cocktails will be described.
Anisotropic mass density by two-dimensional acoustic metamaterials
Energy Technology Data Exchange (ETDEWEB)
Torrent, Daniel; Sanchez-Dehesa, Jose [Wave Phenomena Group, Department of Electronic Engineering, Polytechnic University of Valencia, C/Camino de Vera s/n, E-46022 Valencia (Spain)], E-mail: jsdehesa@upvnet.upv.es
2008-02-15
We show that specially designed two-dimensional arrangements of full elastic cylinders embedded in a nonviscous fluid or gas define (in the homogenization limit) a new class of acoustic metamaterials characterized by a dynamical effective mass density that is anisotropic. Here, analytic expressions for the dynamical mass density and the effective sound velocity tensors are derived in the long wavelength limit. Both show an explicit dependence on the lattice filling fraction, the elastic properties of cylinders relative to the background, their positions in the unit cell, and their multiple scattering interactions. Several examples of these metamaterials are reported and discussed.
Two-dimensional Bose and Fermi gases beyond weak coupling
França, Guilherme; LeClair, André; Squires, Joshua
2017-07-01
Using a formalism based on the two-body S-matrix we study two-dimensional Bose and Fermi gases with both attractive and repulsive interactions. Approximate analytic expressions, valid at weak coupling and beyond, are developed and applied to the Berezinskii-Kosterlitz-Thouless (BKT) transition. We successfully recover the correct logarithmic functional form of the critical chemical potential and density for the Bose gas. For fermions, the BKT critical temperature is calculated in BCS and BEC regimes through consideration of Tan’s contact.
The Two-Dimensional Prouhet-Tarry-Escott Problem
Alpers, A. and R. Tijdeman
2017-01-01
In this paper we generalize the Prouhet–Tarry–Escott problem (PTE) to any dimension. The onedimensional PTE problem is the classical PTE problem. We concentrate on the two-dimensional version which asks, given parameters n, k ∈ N, for two different multi-sets {(x1, y1), . . . , (xn, yn)}, {(x1, y1), . . . , (x n, y n)} of points from Z2 such that n i=1 xj i y d−j i = n i=1 xj i yd−j i for all d,j ∈ {0,...,k} with j d. We present parametric solutions for n ∈ {2, 3, 4, 6} with optimal...
Network patterns in exponentially growing two-dimensional biofilms
Zachreson, Cameron; Yap, Xinhui; Gloag, Erin S.; Shimoni, Raz; Whitchurch, Cynthia B.; Toth, Milos
2017-10-01
Anisotropic collective patterns occur frequently in the morphogenesis of two-dimensional biofilms. These patterns are often attributed to growth regulation mechanisms and differentiation based on gradients of diffusing nutrients and signaling molecules. Here, we employ a model of bacterial growth dynamics to show that even in the absence of growth regulation or differentiation, confinement by an enclosing medium such as agar can itself lead to stable pattern formation over time scales that are employed in experiments. The underlying mechanism relies on path formation through physical deformation of the enclosing environment.
Solution-Based Processing of Monodisperse Two-Dimensional Nanomaterials.
Kang, Joohoon; Sangwan, Vinod K; Wood, Joshua D; Hersam, Mark C
2017-04-18
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
Azcatl Zacatzi, Angelica
Two-dimensional transition metal dichalcogenides (TMDs) are considered potential channel materials for emerging electronic devices in the roadmap beyond Si-CMOS technology. Layered TMDs offer intrinsically an ultrathin body without compromising the semiconducting properties. For the implementation of TMDs in electronic device structures, the understanding of their surface properties is essential. This work combines a variety of materials characterization techniques such as in-situ X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, and Raman spectroscopy to investigate the chemistry and structure of TMDs upon different surface treatments. In addition, first-principle calculations are presented to give insights on the mechanism involved in the surface modification of TMD. The impact of the TMDs surface modification on processes for gate-oxide integration by atomic layer deposition and covalent doping are investigated here. This work provides a comprehensive understanding of the surface chemistry of TMDs for two-dimensional electronic device applications.
Magnetism in atomically thin quasi two-dimensional materials: Renormalized spin wave theory
Li, Zhenglu; Cao, Ting; Louie, Steven G.
In this work, we apply renormalized spin wave theory to the magnetic behavior of atomically thin two-dimensional crystals. We find that magnon-magnon interaction plays an important role in renormalizing the magnetic transition temperature, and the magnetic behavior is largely dependent on the magnetic anisotropy and the thickness of the crystal in the two-dimensional limit. Our method is applicable to general magnetic crystals with input spin interaction parameters mapped out from either ab initio calculations or extracted from experiments. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, and by the National Science Foundation. Computational resources have been provided by NERSC and XSEDE.
Ocular Proteomics with Emphasis on Two-Dimensional Gel Electrophoresis and Mass Spectrometry
Directory of Open Access Journals (Sweden)
Honoré Bent
2010-01-01
Full Text Available Abstract The intention of this review is to provide an overview of current methodologies employed in the rapidly developing field of ocular proteomics with emphasis on sample preparation, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE and mass spectrometry (MS. Appropriate sample preparation for the diverse range of cells and tissues of the eye is essential to ensure reliable results. Current methods of protein staining for 2D-PAGE, protein labelling for two-dimensional difference gel electrophoresis, gel-based expression analysis and protein identification by MS are summarised. The uses of gel-free MS-based strategies (MuDPIT, iTRAQ, ICAT and SILAC are also discussed. Proteomic technologies promise to shed new light onto ocular disease processes that could lead to the discovery of strong novel biomarkers and therapeutic targets useful in many ophthalmic conditions.
Ocular Proteomics with Emphasis on Two-Dimensional Gel Electrophoresis and Mass Spectrometry
Directory of Open Access Journals (Sweden)
Mandal Nakul
2009-12-01
Full Text Available Abstract The intention of this review is to provide an overview of current methodologies employed in the rapidly developing field of ocular proteomics with emphasis on sample preparation, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE and mass spectrometry (MS. Appropriate sample preparation for the diverse range of cells and tissues of the eye is essential to ensure reliable results. Current methods of protein staining for 2D-PAGE, protein labelling for two-dimensional difference gel electrophoresis, gel-based expression analysis and protein identification by MS are summarised. The uses of gel-free MS-based strategies (MuDPIT, iTRAQ, ICAT and SILAC are also discussed. Proteomic technologies promise to shed new light onto ocular disease processes that could lead to the discovery of strong novel biomarkers and therapeutic targets useful in many ophthalmic conditions.
Numerically exact correlations and sampling in the two-dimensional Ising spin glass.
Thomas, Creighton K; Middleton, A Alan
2013-04-01
A powerful existing technique for evaluating statistical mechanical quantities in two-dimensional Ising models is based on constructing a matrix representing the nearest-neighbor spin couplings and then evaluating the Pfaffian of the matrix. Utilizing this technique and other more recent developments in evaluating elements of inverse matrices and exact sampling, a method and computer code for studying two-dimensional Ising models is developed. The formulation of this method is convenient and fast for computing the partition function and spin correlations. It is also useful for exact sampling, where configurations are directly generated with probability given by the Boltzmann distribution. These methods apply to Ising model samples with arbitrary nearest-neighbor couplings and can also be applied to general dimer models. Example results of computations are described, including comparisons with analytic results for the ferromagnetic Ising model, and timing information is provided.
A reliable way of mechanical exfoliation of large scale two dimensional materials with high quality
Yuan, Lin; Ge, Jun; Peng, Xianglin; Zhang, Qian; Wu, Zefei; Jian, Yu; Xiong, Xiaolu; Yin, Hongxing; Han, Junfeng
2016-12-01
In this work, we have developed a modified way of mechanical exfoliation for making two-dimensional materials by introducing a home-designed exfoliation machine. Optical microscopy was employed to identify the thin-layer (mono- and few-layer) flakes primarily. To testify the high efficiency of our modified exfoliation method, we did a simple statistical work on the exfoliation of graphene and WSe2. Further, we used the Raman spectroscopy and the Atomic Force Microscopy (AFM) to characterize the samples. The results indicated the high quality of the as-fabricated samples. Finally, we developed an exfoliation technique for working with easily oxidizing samples. Our modified exfoliation method would be intriguing and innovative for fabricating two dimensional materials, providing a facile way for making electronic and optoelectronic devices.
A reliable way of mechanical exfoliation of large scale two dimensional materials with high quality
Directory of Open Access Journals (Sweden)
Lin Yuan
2016-12-01
Full Text Available In this work, we have developed a modified way of mechanical exfoliation for making two-dimensional materials by introducing a home-designed exfoliation machine. Optical microscopy was employed to identify the thin-layer (mono- and few-layer flakes primarily. To testify the high efficiency of our modified exfoliation method, we did a simple statistical work on the exfoliation of graphene and WSe2. Further, we used the Raman spectroscopy and the Atomic Force Microscopy (AFM to characterize the samples. The results indicated the high quality of the as-fabricated samples. Finally, we developed an exfoliation technique for working with easily oxidizing samples. Our modified exfoliation method would be intriguing and innovative for fabricating two dimensional materials, providing a facile way for making electronic and optoelectronic devices.
Direct correlation functions in two-dimensional anisotropic fluids
Chamoux, Antoine; Perera, Aurelien
1998-08-01
A geometrical approximation for the direct correlation of two-dimensional multicomponent fluids is introduced herein. This approximation is semianalytical and involves the knowledge of elementary geometrical properties of a single particle. The formalism is applied to anisotropic two-dimensional fluids of various particle shapes such as hard ellipses, diskorectangles, and cut disks of various size ratios. The particular case of the hard needles fluid is also investigated. The accuracy of the approximation is tested by comparing the equation of state and the correlation functions to those obtained by integral equation techniques and Monte Carlo simulations. In almost all cases these comparisons are found to be quite satisfactory and even excellent in the case of moderate size ratios. Both the isotropic and orientationally ordered phases are investigated and particular attention is paid to the orientational stability of the isotropic phase. The cut disk fluid has a particularly interesting long-range order for thicknesses around 0.3, which is very much reminiscent of the cubatic order observed in the corresponding three-dimensional case of cut spheres. This feature observable by both the simulations and the hypernetted chain integral equation is also predicted by the present geometrical theory, but at larger thicknesses.
Reliability of a two-dimensional footprint measurement approach.
Reel, Sarah; Rouse, Simon; Vernon, Wesley; Doherty, Patrick
2010-09-01
Although footprint evidence can be taken from the scene of a crime, the science underpinning such measurement in forensic science has not been fully explored. A literature search revealed various measuring approaches, all of which demonstrated either little or no measurement rigour in terms of reliability. The aim of this study was to apply a robust measurement approach for testing the reliability of two-dimensional footprint impressions. Three dynamic and three static footprints were taken from the right foot of thirty female and thirty one male volunteers using the 'Inkless Shoeprint Kit'. The images were digitised. Lengths, widths and angles were measured using a selection of currently employed methods. An investigation of the reliability of the chosen measuring method suggested high intra-rater agreement: for example, the length measurement suggested an intraclass correlation coefficient (ICC) 0.99, 95% Confidence Interval (CI) -0.28 to 0.01, standard error of measurement (SEM) 0.07, Limits of Agreement (LOA) -0.91 to 0.65. Inter-rater reliability between three operators was also high: SEM ranged from 0.05 mm to 0.07 mm, ICC 0.99. Our study has established a reliable two-dimensional measuring technique that could be used for footprint comparison in further research. Copyright © 2009 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
Morphological arrangement of two-dimensional aggregated colloid
Promkotra, Sarunya; Kangsadan, Tawiwan
2017-07-01
Two-dimensional aggregate morphologies can be controlled by adjusting the suspending alcohol and the composition of the substrate solution. Water-glycerol substrates were used in these experiments because their high viscosity minimizes vibration in floating 2D aggregates. The polystyrene microspheres, 4.0 µm in diameter, were suspended in alcohol-water solutions at 0.1 vol% solid fraction by adding appropriate amounts of the as-received dispersion to the alcohol. The resulting suspending phase contained 12 vol% water. Methanol and ethanol were used as the suspension medium for the particles. The substrate composition and the suspending medium alcohol were varied, leading to a better understanding of the effect of these variables on 2Daggregate morphology. Light alcohols, methanol and ethanol, formed the two-dimensional(2D) aggregated monolayers at the air-liquid interface. Also, high acidity in the liquid substrate (pH values below 6) was required for formation of 2D aggregates. Similarly, salt additions also induced particle aggregation. The 2D morphologies were classified by their fractal dimension, which increased with the concentration of glycerol and acid in the substrateliquid. In addition, both aggregates and isolated particles in the ethanol system showed anovel circular ring structure, which disappeared over time. Morphology diagrams for the 2D aggregates were developed; these diagrams showed the fractal dimension of the clusteras a function of the formation conditions.
Two-Dimensional Impact Reconstruction Method for Rail Defect Inspection
Directory of Open Access Journals (Sweden)
Jie Zhao
2014-01-01
Full Text Available The safety of train operating is seriously menaced by the rail defects, so it is of great significance to inspect rail defects dynamically while the train is operating. This paper presents a two-dimensional impact reconstruction method to realize the on-line inspection of rail defects. The proposed method utilizes preprocessing technology to convert time domain vertical vibration signals acquired by wireless sensor network to space signals. The modern time-frequency analysis method is improved to reconstruct the obtained multisensor information. Then, the image fusion processing technology based on spectrum threshold processing and node color labeling is proposed to reduce the noise, and blank the periodic impact signal caused by rail joints and locomotive running gear. This method can convert the aperiodic impact signals caused by rail defects to partial periodic impact signals, and locate the rail defects. An application indicates that the two-dimensional impact reconstruction method could display the impact caused by rail defects obviously, and is an effective on-line rail defects inspection method.
Two dimensional kinetic analysis of electrostatic harmonic plasma waves
Energy Technology Data Exchange (ETDEWEB)
Fonseca-Pongutá, E. C.; Ziebell, L. F.; Gaelzer, R. [Instituto de Física, UFRGS, 91501-970 Porto Alegre, RS (Brazil); Yoon, P. H. [IPST, University of Maryland, College Park, Maryland 20742 (United States); SSR, Kyung Hee University, Yongin, Gyeonggi 446-701 (Korea, Republic of)
2016-06-15
Electrostatic harmonic Langmuir waves are virtual modes excited in weakly turbulent plasmas, first observed in early laboratory beam-plasma experiments as well as in rocket-borne active experiments in space. However, their unequivocal presence was confirmed through computer simulated experiments and subsequently theoretically explained. The peculiarity of harmonic Langmuir waves is that while their existence requires nonlinear response, their excitation mechanism and subsequent early time evolution are governed by essentially linear process. One of the unresolved theoretical issues regards the role of nonlinear wave-particle interaction process over longer evolution time period. Another outstanding issue is that existing theories for these modes are limited to one-dimensional space. The present paper carries out two dimensional theoretical analysis of fundamental and (first) harmonic Langmuir waves for the first time. The result shows that harmonic Langmuir wave is essentially governed by (quasi)linear process and that nonlinear wave-particle interaction plays no significant role in the time evolution of the wave spectrum. The numerical solutions of the two-dimensional wave spectra for fundamental and harmonic Langmuir waves are also found to be consistent with those obtained by direct particle-in-cell simulation method reported in the literature.
Two-dimensional nuclear magnetic resonance of quadrupolar systems
Energy Technology Data Exchange (ETDEWEB)
Wang, Shuanhu [Univ. of California, Berkeley, CA (United States)
1997-09-01
This dissertation describes two-dimensional nuclear magnetic resonance theory and experiments which have been developed to study quadruples in the solid state. The technique of multiple-quantum magic-angle spinning (MQMAS) is extensively reviewed and expanded upon in this thesis. Specifically, MQMAS is first compared with another technique, dynamic-angle spinning (DAS). The similarity between the two techniques allows us to extend much of the DAS work to the MQMAS case. Application of MQMAS to a series of aluminum containing materials is then presented. The superior resolution enhancement through MQMAS is exploited to detect the five- and six-coordinated aluminum in many aluminosilicate glasses. Combining the MQMAS method with other experiments, such as HETCOR, greatly expands the possibility of the use of MQMAS to study a large range of problems and is demonstrated in Chapter 5. Finally, the technique switching-angle spinning (SAS) is applied to quadrupolar nuclei to fully characterize a quadrupolar spin system in which all of the 8 NMR parameters are accurately determined. This dissertation is meant to demonstrate that with the combination of two-dimensional NMR concepts and new advanced spinning technologies, a series of multiple-dimensional NMR techniques can be designed to allow a detailed study of quadrupolar nuclei in the solid state.
A microprocessor based on a two-dimensional semiconductor
Wachter, Stefan; Polyushkin, Dmitry K.; Bethge, Ole; Mueller, Thomas
2017-04-01
The advent of microcomputers in the 1970s has dramatically changed our society. Since then, microprocessors have been made almost exclusively from silicon, but the ever-increasing demand for higher integration density and speed, lower power consumption and better integrability with everyday goods has prompted the search for alternatives. Germanium and III-V compound semiconductors are being considered promising candidates for future high-performance processor generations and chips based on thin-film plastic technology or carbon nanotubes could allow for embedding electronic intelligence into arbitrary objects for the Internet-of-Things. Here, we present a 1-bit implementation of a microprocessor using a two-dimensional semiconductor--molybdenum disulfide. The device can execute user-defined programs stored in an external memory, perform logical operations and communicate with its periphery. Our 1-bit design is readily scalable to multi-bit data. The device consists of 115 transistors and constitutes the most complex circuitry so far made from a two-dimensional material.
Bielectron vortices in two-dimensional Dirac semimetals.
Downing, C A; Portnoi, M E
2017-10-12
Searching for new states of matter and unusual quasi-particles in emerging materials and especially low-dimensional systems is one of the major trends in contemporary condensed matter physics. Dirac materials, which host quasi-particles which are described by ultrarelativistic Dirac-like equations, are of a significant current interest from both a fundamental and applied physics perspective. Here we show that a pair of two-dimensional massless Dirac-Weyl fermions can form a bound state independently of the sign of the inter-particle interaction potential, as long as this potential decays at large distances faster than Kepler's inverse distance law. This leads to the emergence of a new type of energetically favorable quasiparticle: bielectron vortices, which are double-charged and reside at zero-energy. Their bosonic nature allows for condensation and may give rise to Majorana physics without invoking a superconductor. These novel quasi-particles arguably explain a range of poorly understood experiments in gated graphene structures at low doping.Two-dimensional Dirac semimetals are known to host fermionic excitations which can mimic physics usually found in ultrarelativistic quantum mechanics. Here, the authors unveil the existence of another type of quasiparticle, bielectron vortices, which are bosonic and may give rise to new types of condensates.
Quantum creep in a highly crystalline two-dimensional superconductor
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.
Two-dimensional fluorescence spectroscopy of laser-produced plasmas
Energy Technology Data Exchange (ETDEWEB)
Harilal, Sivanandan S.; LaHaye, Nicole L.; Phillips, Mark C.
2016-08-01
We use a two-dimensional laser-induced fluorescence spectroscopy technique to measure the coupled absorption and emission properties of atomic species in plasmas produced via laser ablation of solid aluminum targets at atmospheric pressure. Emission spectra from the Al I 394.4 nm and Al I 396.15 nm transitions are measured while a frequency-doubled, continuous-wave, Ti:Sapphire laser is tuned across the Al I 396.15 nm transition. The resulting two-dimensional spectra show the energy coupling between the two transitions via increased emission intensity for both transitions during resonant absorption of the continuous-wave laser at one transition. Time-delayed and gated detection of the emission spectrum is used to isolate the resonantly-excited fluorescence emission from the thermally-excited emission from the plasma. In addition, the tunable continuous-wave laser measures the absorption spectrum of the Al transition with ultra-high resolution after the plasma has cooled, resulting in narrower spectral linewidths than observed in emission spectra. Our results highlight that fluorescence spectroscopy employing continuous-wave laser re-excitation after pulsed laser ablation combines benefits of both traditional emission and absorption spectroscopic methods.
Magnetic field correlations in kinematic two-dimensional magnetohydrodynamic turbulence
Schumacher, J; Schumacher, Joerg; Eckhardt, Bruno
1999-01-01
The scaling properties of the second order magnetic structure function $D_2^{(B)}(r)$ and the corresponding magnetic correlation function $C_2^{(B)}(r)$ are derived for two-dimensional magnetohydrodynamic turbulence in the kinematic regime where the ratio of kinetic energy to magnetic energy is much larger than one. In this regime the magnetic flux function $\\psi$ can be treated as a passive scalar advected in a two-dimensional turbulent flow. Its structure function $D_2^{(\\psi)}(r)$ and the one for the magnetic field $D_2^{(B)}(r)$ are connected by an exact relation. We calculate $D_2^{(\\psi)}(r)$ and thus $D_2^{(B)}(r)$ within geometric measure theory over a wide range of scales $r$ and magnetic Prandtl numbers $Pr_m$. The magnetic field correlations follow a $r^{-4/3}$--scaling law and show an anticorrelation at the beginning of the Batchelor regime indicative of the formation of strongly filamented current sheets. Differences to the full dynamic regime, where the ratio of kinetic to magnetic energies is s...
On Space Efficient Two Dimensional Range Minimum Data Structures
DEFF Research Database (Denmark)
Brodal, Gerth Stølting; Davoodi, Pooya; Rao, S. Srinivasa
2012-01-01
The two dimensional range minimum query problem is to preprocess a static m by n matrix (two dimensional array) A of size N=m⋅n, such that subsequent queries, asking for the position of the minimum element in a rectangular range within A, can be answered efficiently. We study the trade-off betwee...... structure of optimal size O(N) bits. For the case where queries can not probe A, we give a data structure of size O(N⋅min {m,log n}) bits with O(1) query time, assuming m≤n. This leaves a gap to the space lower bound of Ω(Nlog m) bits for this version of the problem...... the space and query time of the problem. We show that every algorithm enabled to access A during the query and using a data structure of size O(N/c) bits requires Ω(c) query time, for any c where 1≤c≤N. This lower bound holds for arrays of any dimension. In particular, for the one dimensional version...
One-dimensional metallic wires at phase-engineered boundaries in two-dimensional materials
Gibertini, Marco; Marzari, Nicola
At the interfaces between systems with different electric polarization, free carriers appear in order to screen the resulting polarization charges associated with the resulting polar discontinuity. This mechanism is believed to be at the origin of the two-dimensional electron gas emerging at oxide interfaces and provides the basis for manifold exciting novel phenomena. Recently, it has been shown that similar processes take place also in two-dimensional materials, where one-dimensional wires of free carriers are induced at planar interfaces between materials with different in-plane polarization or at the edges of polar nanoribbons. Here we show by first-principles simulations that some two-dimensional polar materials can display a metastable non-polar phase, so that boundaries between the stable and metastable phases support a polar discontinuity and the resulting one-dimensional metallic wires. We provide several approaches to engineer such phase boundaries by locally inducing metastable phases in a single parent crystal. We finally show how this novel strategy to engineer polar discontinuities in two dimensions offers unprecedented opportunities to efficiently manipulate and reconfigure the emerging one-dimensional metallic wires or switch their conducting state.
Berezinskii–Kosterlitz–Thouless transition and two-dimensional melting
Ryzhov, V. N.; Tareyeva, E. E.; Fomin, Yu D.; Tsiok, E. N.
2017-12-01
The main aspects of the theory of phase transitions in two-dimensional degenerate systems (Berezinskii–Kosterlitz–Thouless, or BKT, transitions) are reviewed in detail, including the transition mechanism, the renormalization group as a tool for describing the transition, and how the transition scenario can possibly depend on the core energy of topological defects (in particular, in thin superconducting films). Various melting scenarios in two-dimensional systems are analyzed, and the current status of actual experiments and computer simulations in the field is examined. Whereas in three dimensions melting always occurs as a single first-order transition, in two dimensions, as shown by Halperin, Nelson, and Young, melting via two continuous BKT transitions with an intermediate hexatic phase characterized by quasi-long-range orientational order is possible. But there is also a possibility for a first-order phase transition to occur. Recently, one further melting scenario, different from that occurring in the Berezinskii–Kosterlitz–Thouless–Halperin–Nelson–Young theory, has been proposed, according to which a solid can melt in two stages: a continuous BKT-type solid–hexatic transition and then a first-order hexatic-phase–isotropic-liquid phase transition. Particular attention is given to the melting scenario as a function of the potential shape and to the random pinning effect on two-dimensional melting. In particular, it is shown that random pinning can alter the melting scenario fundamentally in the case of a first-order transition. Also considered is the melting of systems with potentials having a negative curvature in the repulsion region–potentials that are successfully used in describing the anomalous properties of water in two dimensions. This review is an extended version of the report “Old and new in the physics of phase transitions” presented at the scientific session of the Physical Sciences Division of the Russian Academy of
Optimal Padding for the Two-Dimensional Fast Fourier Transform
Dean, Bruce H.; Aronstein, David L.; Smith, Jeffrey S.
2011-01-01
One-dimensional Fast Fourier Transform (FFT) operations work fastest on grids whose size is divisible by a power of two. Because of this, padding grids (that are not already sized to a power of two) so that their size is the next highest power of two can speed up operations. While this works well for one-dimensional grids, it does not work well for two-dimensional grids. For a two-dimensional grid, there are certain pad sizes that work better than others. Therefore, the need exists to generalize a strategy for determining optimal pad sizes. There are three steps in the FFT algorithm. The first is to perform a one-dimensional transform on each row in the grid. The second step is to transpose the resulting matrix. The third step is to perform a one-dimensional transform on each row in the resulting grid. Steps one and three both benefit from padding the row to the next highest power of two, but the second step needs a novel approach. An algorithm was developed that struck a balance between optimizing the grid pad size with prime factors that are small (which are optimal for one-dimensional operations), and with prime factors that are large (which are optimal for two-dimensional operations). This algorithm optimizes based on average run times, and is not fine-tuned for any specific application. It increases the amount of times that processor-requested data is found in the set-associative processor cache. Cache retrievals are 4-10 times faster than conventional memory retrievals. The tested implementation of the algorithm resulted in faster execution times on all platforms tested, but with varying sized grids. This is because various computer architectures process commands differently. The test grid was 512 512. Using a 540 540 grid on a Pentium V processor, the code ran 30 percent faster. On a PowerPC, a 256x256 grid worked best. A Core2Duo computer preferred either a 1040x1040 (15 percent faster) or a 1008x1008 (30 percent faster) grid. There are many industries that
Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures
Kang, Kibum; Lee, Kan-Heng; Han, Yimo; Gao, Hui; Xie, Saien; Muller, David A.; Park, Jiwoong
2017-10-01
High-performance semiconductor films with vertical compositions that are designed to atomic-scale precision provide the foundation for modern integrated circuitry and novel materials discovery. One approach to realizing such films is sequential layer-by-layer assembly, whereby atomically thin two-dimensional building blocks are vertically stacked, and held together by van der Waals interactions. With this approach, graphene and transition-metal dichalcogenides--which represent one- and three-atom-thick two-dimensional building blocks, respectively--have been used to realize previously inaccessible heterostructures with interesting physical properties. However, no large-scale assembly method exists at present that maintains the intrinsic properties of these two-dimensional building blocks while producing pristine interlayer interfaces, thus limiting the layer-by-layer assembly method to small-scale proof-of-concept demonstrations. Here we report the generation of wafer-scale semiconductor films with a very high level of spatial uniformity and pristine interfaces. The vertical composition and properties of these films are designed at the atomic scale using layer-by-layer assembly of two-dimensional building blocks under vacuum. We fabricate several large-scale, high-quality heterostructure films and devices, including superlattice films with vertical compositions designed layer-by-layer, batch-fabricated tunnel device arrays with resistances that can be tuned over four orders of magnitude, band-engineered heterostructure tunnel diodes, and millimetre-scale ultrathin membranes and windows. The stacked films are detachable, suspendable and compatible with water or plastic surfaces, which will enable their integration with advanced optical and mechanical systems.
Influence of disorder and magnetic field on conductance of “sandwich” type two dimensional system
Directory of Open Access Journals (Sweden)
Long LIU
2017-04-01
Full Text Available In order to discuss the transport phenomena and the physical properties of the doping of the disorder system under magnetic field, the electron transport in a two-dimensional system is studied by using Green function and scattering matrix theory. Base on the two-dimensional lattice model, the phenomenon of quantized conductance of the "sandwich" type electronic system is analyzed. The contact between the lead and the scatterer reduce the system's conductance, and whittle down the quantum conductance stair-stepping phenomenon; when an external magnetic field acts on to the system, the conductance presents a periodicity oscillation with the magnetic field. The intensity of this oscillation is related to the energy of the electron;with the increase of the impurity concentration, the conductance decreases.In some special doping concentration, the conductance of the system can reach the ideal step value corresponding to some special electron energy. The result could provide reference for further study of the conductance of the "sandwich" type two dimensional system.
Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.
Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil
2017-11-07
Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.
Sun, Yongfu; Gao, Shan; Xie, Yi
2014-01-21
Atomically-thick two-dimensional crystals can provide promising opportunities to satisfy people's requirement of next-generation flexible and transparent nanodevices. However, the characterization of these low-dimensional structures and the understanding of their clear structure-property relationship encounter many great difficulties, owing to the lack of long-range order in the third dimensionality. In this review, we survey the recent progress in fine structure characterization by X-ray absorption fine structure spectroscopy and also overview electronic structure modulation by density-functional calculations in the ultrathin two-dimensional crystals. In addition, we highlight their structure-property relationship, transparent and flexible device construction as well as wide applications in photoelectrochemical water splitting, photodetectors, thermoelectric conversion, touchless moisture sensing, supercapacitors and lithium ion batteries. Finally, we outline the major challenges and opportunities that face the atomically-thick two-dimensional crystals. It is anticipated that the present review will deepen people's understanding of this field and hence contribute to guide the future design of high-efficiency energy-related devices.
Dynamics of saturated energy condensation in two-dimensional turbulence.
Chan, Chi-kwan; Mitra, Dhrubaditya; Brandenburg, Axel
2012-03-01
In two-dimensional forced Navier-Stokes turbulence, energy cascades to the largest scales in the system to form a pair of coherent vortices known as the Bose condensate. We show, both numerically and analytically, that the energy condensation saturates and the system reaches a statistically stationary state. The time scale of saturation is inversely proportional to the viscosity and the saturation energy level is determined by both the viscosity and the force. We further show that, without sufficient resolution to resolve the small-scale enstrophy spectrum, numerical simulations can give a spurious result for the saturation energy level. We also find that the movement of the condensate is similar to the motion of an inertial particle with an effective drag force. Furthermore, we show that the profile of the saturated coherent vortices can be described by a Gaussian core with exponential wings.
Diffusion in the two-dimensional necklace model for reptation.
Terranova, G; Aldao, C M; Mártin, H O
2007-09-01
An extension of a recently introduced one-dimensional model, the necklace model, is used to study the reptation of a chain of N particles in a two-dimensional square lattice. The mobilities of end and middle particles of a chain are governed by three free parameters. This new model mimics the behavior of a long linear and flexible polymer in a gel. Noninteracting and self-avoiding chains are considered. For both cases, analytical approximations for the diffusion coefficient of the center of mass of the chain, for all values of N , are proposed. The validity of these approximations for different values of the free parameters is verified by means of Monte Carlo simulations. Extensions to higher dimensions are also discussed.
Proximity Induced Superconducting Properties in One and Two Dimensional Semiconductors
DEFF Research Database (Denmark)
Kjærgaard, Morten
This report is concerned with the properties of one and two dimensional semiconducting materials when brought into contact with a superconductor. Experimentally we study the 2D electron gas in an InGaAs/InAs heterostructure with aluminum grown in situ on the surface, and theoretically we show...... that a superconducting 1D nanowire can harbor Majorana bound states in the absence of spin–orbit coupling. We fabricate and measure micrometer–sized mesoscopic devices demonstrating the inheritance of superconducting properties in the 2D electron gas. By placing a quantum point contact proximal to the interface between...... a voltage is passed through the Josephson junction, we observe multiple Andreev reflections and preliminary results point to a highly transmissive interface between the 2D electron gas and the superconductor. In the theoretical section we demonstrate analytically and numerically, that in a 1D nanowire...
The cleft ion fountain - A two-dimensional kinetic model
Horwitz, J. L.; Lockwood, M.
1985-01-01
The transport of ionospheric ions from a source in the polar cleft ionosphere through the polar magnetosphere is investigated using a two-dimensional, kinetic, trajectory-based code. The transport model includes the effects of gravitation, longitudinal magnetic gradient force, convection electric fields, and parallel electric fields. Individual ion trajectories as well as distribution functions and resulting bulk parameters of density, parallel average energy, and parallel flux for a presumed cleft ionosphere source distribution are presented for various conditions to illustrate parametrically the dependences on source energies, convection electric field strengths, ion masses, and parallel electric field strengths. The essential features of the model are consistent with the concept of a cleft-based ion fountain supplying ionospheric ions to the polar magnetosphere, and the resulting plasma distributions and parameters are in general agreement with recent low-energy ion measurements from the DE 1 satellite.
Multipair excitations in the two-dimensional electron gas
Pederiva, F.; Emperador, A.; Lipparini, E.
2002-10-01
We present a sum-rule study of spin multipair excitations in the two-dimensional electron gas. The cubic-energy-weighted sum rule m3=∫S(q,ω)ω3dω is microscopically calculated taking into account the effect of dynamical correlations. The comparison among exact sum rules and the ones derived within Landau theory allows us to give a proper estimate of the average spin multipair excitation energy and a rigorous lower bound for the multipair contribution to the static form factor in the low-q limit. The relative importance of spin multipair excitations in two- and three-dimensional electron gases is discussed. Finally, numerical results of the contribution of multipair excitations to the m3 sum rule in the density channel are given.
Electromagnetic two-dimensional analysis of trapped-ion eigenmodes
Energy Technology Data Exchange (ETDEWEB)
Kim, D.; Rewoldt, G.
1984-11-01
A two-dimensional electromagnetic analysis of the trapped-ion instability for the tokamak case with ..beta.. not equal to 0 has been made, based on previous work in the electrostatic limit. The quasineutrality condition and the component of Ampere's law along the equilibrium magnetic field are solved for the perturbed electrostatic potential and the component of the perturbed vector potential along the equilibrium magnetic field. The general integro-differential equations are converted into a matrix eigenvalue-eigenfunction problem by expanding in cubic B-spline finite elements in the minor radius and in Fourier harmonics in the poloidal angle. A model MHD equilibrium with circular, concentric magnetic surfaces and large aspect ratio is used which is consistent with our assemption that B << 1. The effect on the trapped-ion mode of including these electromagnetic extensions to the calculation is considered, and the temperature (and ..beta..) scaling of the mode frequency is shown and discussed.
Two-dimensional wave propagation in layered periodic media
Quezada de Luna, Manuel
2014-09-16
We study two-dimensional wave propagation in materials whose properties vary periodically in one direction only. High order homogenization is carried out to derive a dispersive effective medium approximation. One-dimensional materials with constant impedance exhibit no effective dispersion. We show that a new kind of effective dispersion may arise in two dimensions, even in materials with constant impedance. This dispersion is a macroscopic effect of microscopic diffraction caused by spatial variation in the sound speed. We analyze this dispersive effect by using highorder homogenization to derive an anisotropic, dispersive effective medium. We generalize to two dimensions a homogenization approach that has been used previously for one-dimensional problems. Pseudospectral solutions of the effective medium equations agree to high accuracy with finite volume direct numerical simulations of the variable-coeffi cient equations.
Structural and collective properties of two-dimensional Yukawa liquids
Murillo, M S
2003-01-01
The radial distribution function of two-dimensional Yukawa systems has been computed with the hypernetted chain equations and compared with molecular dynamics simulations. A comparison is also made with similar quantities in three-dimensional systems. The importance of the bridge function in two dimensions is illustrated. Collective behaviour is described in terms of the dynamic structure factor S(q, omega); inclusion of the local field correction G(q, omega) incorporates physics beyond the random phase approximation. Simulation results are compared with renormalized mean-field approximations G(q, omega) approx G(q, 0) and G(q, omega) approx G(q, infinity). These approximations fail to capture details of the spectrum.
Soliton nanoantennas in two-dimensional arrays of quantum dots
Gligorić, G; Hadžievski, Lj; Slepyan, G Ya; Malomed, B A
2015-01-01
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 Schr\\"{o}dinger 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 \\textit{% soliton-based nano-antenna}, which should be 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 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.
A two-dimensional model for gamma-ray bursts
Fryxell, B. A.; Woosley, S. E.
1982-07-01
The spherically symmetric calculations of a thermonuclear explosion on a neutron star is extended to two dimensions. Assuming a simple dipolar field, accretion will be focused onto a small region at the polar cap. For a suitable accretion rate hydrogen burns stably by the beta-limited CNO cycle, forming a layer of helium; a thermonuclear runaway initiates at a point at the base of the helium layer. The detonation model is hydrodynamically calculated using a two-dimensional hydrodynamic code. The wave is found to propagate across the helium lake at 9000 km/s without dying out, igniting all the helium and liberating 2.4 x 10 to the 39th ergs. The rise time of the burst, determined by the time required to propagate the detonation across the helium layer, is about 50 microseconds.
Two dimensional fractional projectile motion in a resisting medium
Rosales, Juan; Guía, Manuel; Gómez, Francisco; Aguilar, Flor; Martínez, Juan
2014-07-01
In this paper we propose a fractional differential equation describing the behavior of a two dimensional projectile in a resisting medium. In order to maintain the dimensionality of the physical quantities in the system, an auxiliary parameter k was introduced in the derivative operator. This parameter has a dimension of inverse of seconds (sec)-1 and characterizes the existence of fractional time components in the given system. It will be shown that the trajectories of the projectile at different values of γ and different fixed values of velocity v 0 and angle θ, in the fractional approach, are always less than the classical one, unlike the results obtained in other studies. All the results obtained in the ordinary case may be obtained from the fractional case when γ = 1.
Thinnest two-dimensional nanomaterial-graphene for solar energy.
Hu, Yun Hang; Wang, Hui; Hu, Bo
2010-07-19
Graphene is a rapidly rising star in materials science. This two-dimensional material exhibits unique properties, such as low resistance, excellent optical transmittance, and high mechanical and chemical stabilities. These exceptional advantages possess great promise for its potential applications in photovoltaic devices. In this Review, we present the status of graphene research for solar energy with emphasis on solar cells. Firstly, the preparation and properties of graphene are described. Secondly, applications of graphene as transparent conductive electrodes and counter electrodes are presented. Thirdly, graphene-based electron- (or hole) accepting materials for solar energy conversion are evaluated. Fourthly, the promoting effect of graphene on photovoltaic devices and the photocatalytic property of graphene-semiconductor composites are discussed. Finally, the challenges to increase the power conversion efficiency of graphene-based solar cells are explored.
Structure and computation of two-dimensional incompressible extended MHD
Grasso, D; Abdelhamid, H M; Morrison, P J
2016-01-01
A comprehensive study of a reduced version of Lust's equations, the extended magnetohydrodynamic (XMHD) model obtained from the two-fluid theory for electrons and ions with the enforcement of quasineutrality, is given. Starting from the Hamiltonian structure of the fully three-dimensional theory, a Hamiltonian two-dimensional incompressible four-field model is derived. In this way energy conservation along with four families of Casimir invariants are naturally obtained. The construction facilitates various limits leading to the Hamiltonian forms of Hall, inertial, and ideal MHD, with their conserved energies and Casimir invariants. Basic linear theory of the four-field model is treated, and the growth rate for collisionless reconnection is obtained. Results from nonlinear simulations of collisionless tearing are presented and interpreted using, in particular normal fields, a product of the Hamiltonian theory that gives rise to simplified equations of motion.
Plasmon excitations in two-dimensional atomic cluster systems
Energy Technology Data Exchange (ETDEWEB)
Yu, Yan-Qin; Yu, Ya-Bin, E-mail: apybyu@hnu.edu.cn; 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.
Equation of State of the Two-Dimensional Hubbard Model.
Cocchi, Eugenio; Miller, Luke A; Drewes, Jan H; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael
2016-04-29
The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0≲U/t≲20 and temperatures, down to k_{B}T/t=0.63(2) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches.
Two Dimensional Projection Pursuit Applied to Gaussian Mixture Model Fitting
Directory of Open Access Journals (Sweden)
Natella Likhterov
2003-08-01
Full Text Available In this paper we seek a Gaussian mixture model (GMM of an n-variate probability density function. Usually the parameters of GMMs are determined by a maximum likelihood (ML criterion. A practical deficiency of ML fitting of GMMs is poor performance when dealing with high-dimensional data since a large sample size is needed to match the accuracy that is possible in low dimensions. We propose a method to fit the GMM to multivariate data which is based on the two-dimensional projection pursuit (PP method. By means of simulations we compare the proposed method with a one-dimensional PP method for GMM. We conclude that a combination of one- and twodimensional PP methods could be useful in some applications.
Entanglement branes in a two-dimensional string theory
Donnelly, William; Wong, Gabriel
2017-09-01
What is the meaning of entanglement in a theory of extended objects such as strings? To address this question we consider the spatial entanglement between two intervals in the Gross-Taylor model, the string theory dual to two-dimensional Yang-Mills theory at large N . The string diagrams that contribute to the entanglement entropy describe open strings with endpoints anchored to the entangling surface, as first argued by Susskind. We develop a canonical theory of these open strings, and describe how closed strings are divided into open strings at the level of the Hilbert space. We derive the modular Hamiltonian for the Hartle-Hawking state and show that the corresponding reduced density matrix describes a thermal ensemble of open strings ending on an object at the entangling surface that we call an entanglement brane, or E-brane.
Confinement and dynamical regulation in two-dimensional convective turbulence
DEFF Research Database (Denmark)
Bian, N.H.; Garcia, O.E.
2003-01-01
In this work the nature of confinement improvement implied by the self-consistent generation of mean flows in two-dimensional convective turbulence is studied. The confinement variations are linked to two distinct regulation mechanisms which are also shown to be at the origin of low......-frequency bursting in the fluctuation level and the convective heat flux integral, both resulting in a state of large-scale intermittency. The first one involves the control of convective transport by sheared mean flows. This regulation relies on the conservative transfer of kinetic energy from tilted fluctuations...... to the mean component of the flow. Bursting can also result from the quasi-linear modification of the linear instability drive which is the mean pressure gradient. For each bursting process the relevant zero-dimensional model equations are given. These are finally coupled in a minimal model of convection...
Topological Valley Transport in Two-dimensional Honeycomb Photonic Crystals.
Yang, Yuting; Jiang, Hua; Hang, Zhi Hong
2018-01-25
Two-dimensional photonic crystals, in analogy to AB/BA stacking bilayer graphene in electronic system, are studied. Inequivalent valleys in the momentum space for photons can be manipulated by simply engineering diameters of cylinders in a honeycomb lattice. The inequivalent valleys in photonic crystal are selectively excited by a designed optical chiral source and bulk valley polarizations are visualized. Unidirectional valley interface states are proved to exist on a domain wall connecting two photonic crystals with different valley Chern numbers. With the similar optical vortex index, interface states can couple with bulk valley polarizations and thus valley filter and valley coupler can be designed. Our simple dielectric PC scheme can help to exploit the valley degree of freedom for future optical devices.
Hysteresis in Two-Dimensional Liquid Crystal Models
Directory of Open Access Journals (Sweden)
Slavko Buček
2015-01-01
Full Text Available We make a numerical study of hysteresis loop shapes within a generalized two-dimensional Random Anisotropy Nematic (RAN model at zero temperature. The hysteresis loops appear on cycling a static external ordering field. Ordering in these systems is history dependent and involves interplay between the internal coupling constant J, the anisotropy random field D, and the ordering external field H. Here the external field is represented by a traceless tensor, analogous to extension-type fields in continuum mechanics. The calculations use both a mean field approach and full lattice simulations. Our analysis suggests the existence of two qualitatively different solutions, which we denote as symmetric and symmetry breaking. For the set of parameters explored, only the symmetric solutions are stable. Both approaches yield qualitatively similar hysteresis curves, which are manifested either by single or double loops. But the quantitative differences indicate that mean field estimates are only of limited predictive value.
Critical behavior of dissipative two-dimensional spin lattices
Rota, R.; Storme, F.; Bartolo, N.; Fazio, R.; Ciuti, C.
2017-04-01
We explore critical properties of two-dimensional lattices of spins interacting via an anisotropic Heisenberg Hamiltonian that are subject to incoherent spin flips. We determine the steady-state solution of the master equation for the density matrix via the corner-space renormalization method. We investigate the finite-size scaling and critical exponent of the magnetic linear susceptibility associated with a dissipative ferromagnetic transition. We show that the von Neumann entropy increases across the critical point, revealing a strongly mixed character of the ferromagnetic phase. Entanglement is witnessed by the quantum Fisher information, which exhibits a critical behavior at the transition point, showing that quantum correlations play a crucial role in the transition.
Patched Green's function techniques for two-dimensional systems
DEFF Research Database (Denmark)
Settnes, Mikkel; Power, Stephen; Lin, Jun
2015-01-01
We present a numerically efficient technique to evaluate the Green's function for extended two-dimensional systems without relying on periodic boundary conditions. Different regions of interest, or “patches,” are connected using self-energy terms which encode the information of the extended parts...... of the system. The calculation scheme uses a combination of analytic expressions for the Green's function of infinite pristine systems and an adaptive recursive Green's function technique for the patches. The method allows for an efficient calculation of both local electronic and transport properties, as well...... as the inclusion of multiple probes in arbitrary geometries embedded in extended samples. We apply the patched Green's function method to evaluate the local densities of states and transmission properties of graphene systems with two kinds of deviations from the pristine structure: bubbles and perforations...
Efficient two-dimensional compressive sensing in MIMO radar
Shahbazi, Nafiseh; Abbasfar, Aliazam; Jabbarian-Jahromi, Mohammad
2017-12-01
Compressive sensing (CS) has been a way to lower sampling rate leading to data reduction for processing in multiple-input multiple-output (MIMO) radar systems. In this paper, we further reduce the computational complexity of a pulse-Doppler collocated MIMO radar by introducing a two-dimensional (2D) compressive sensing. To do so, we first introduce a new 2D formulation for the compressed received signals and then we propose a new measurement matrix design for our 2D compressive sensing model that is based on minimizing the coherence of sensing matrix using gradient descent algorithm. The simulation results show that our proposed 2D measurement matrix design using gradient decent algorithm (2D-MMDGD) has much lower computational complexity compared to one-dimensional (1D) methods while having better performance in comparison with conventional methods such as Gaussian random measurement matrix.
Creating an artificial two-dimensional Skyrmion crystal by nanopatterning.
Sun, L; Cao, R X; Miao, B F; Feng, Z; You, B; Wu, D; Zhang, W; Hu, An; Ding, H F
2013-04-19
A Skyrmion crystal typically arises from helical spin structures induced by the Dzyaloshinskii-Moriya interaction. Experimentally its physical exploration has been impeded because it is a rarity and is found only within a narrow temperature and magnetic field range. We present a method for the assembly of a two-dimensional Skyrmion crystal based upon a combination of a perpendicularly magnetized film and nanopatterned arrays of magnetic vortices that are geometrically confined within nanodisks. The practical feasibility of the method is validated by micromagnetic simulations and computed Skyrmion number per unit cell. We also quantify a wide range in temperature and field strength over which the Skyrmion crystal can be stabilized without the need for any intrinsic Dzyaloshinskii-Moriya interactions, which otherwise is needed to underpin the arrangement as is the case in the very few known Skyrmion crystal cases. Thus, our suggested scheme involves a qualitative breakthrough that comes with a substantial quantitative advance.
Epi-two-dimensional flow and generalized enstrophy
Yoshida, Zensho
2016-01-01
The conservation of the enstrophy ($L^2$ norm of the vorticity $\\omega$) plays an essential role in the physics and mathematics of two-dimensional (2D) Euler fluids. Generalizing to compressible ideal (inviscid and barotropic) fluids, the generalized enstrophy $\\int_{\\Sigma(t)} f(\\omega/\\rho)\\rho\\, d^2 x$, ($f$ an arbitrary smooth function, $\\rho$ the density, and $\\Sigma(t)$ an arbitrary 2D domain co-moving with the fluid) is a constant of motion, and plays the same role. On the other hand, for the three-dimensional (3D) ideal fluid, the helicity $\\int_{M} {V}\\cdot\\omega\\,d^3x$, ($V$ the flow velocity, $\\omega=\
Two-dimensional electronic spectroscopy with birefringent wedges
Energy Technology Data Exchange (ETDEWEB)
Réhault, Julien; Maiuri, Margherita; Oriana, Aurelio; Cerullo, Giulio [IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)
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.
Surface Ship Shock Modeling and Simulation: Two-Dimensional Analysis
Directory of Open Access Journals (Sweden)
Young S. Shin
1998-01-01
Full Text Available The modeling and simulation of the response of a surface ship system to underwater explosion requires an understanding of many different subject areas. These include the process of underwater explosion events, shock wave propagation, explosion gas bubble behavior and bubble-pulse loading, bulk and local cavitation, free surface effect, fluid-structure interaction, and structural dynamics. This paper investigates the effects of fluid-structure interaction and cavitation on the response of a surface ship using USA-NASTRAN-CFA code. First, the one-dimensional Bleich-Sandler model is used to validate the approach, and second, the underwater shock response of a two-dimensional mid-section model of a surface ship is predicted with a surrounding fluid model using a constitutive equation of a bilinear fluid which does not allow transmission of negative pressures.
The first principle calculation of two-dimensional Dirac materials
Lu, Jin
2017-12-01
As the size of integrated device becoming increasingly small, from the last century, semiconductor industry is facing the enormous challenge to break the Moore’s law. The development of calculation, communication and automatic control have emergent expectation of new materials at the aspect of semiconductor industrial technology and science. In spite of silicon device, searching the alternative material with outstanding electronic properties has always been a research point. As the discovery of graphene, the research of two-dimensional Dirac material starts to express new vitality. This essay studied the development calculation of 2D material’s mobility and introduce some detailed information of some approximation method of the first principle calculation.
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. Copyright © 2015, American Association for the Advancement of Science.
Review—Two-Dimensional Layered Materials for Energy Storage Applications
Kumar, Pushpendra
2016-07-02
Rechargeable batteries are most important energy storage devices in modern society with the rapid development and increasing demand for handy electronic devices and electric vehicles. The higher surface-to-volume ratio two-dimensional (2D) materials, especially transition metal dichalcogenides (TMDCs) and transition metal carbide/nitrite generally referred as MXene, have attracted intensive research activities due to their fascinating physical/chemical properties with extensive applications. One of the growing applications is to use these 2D materials as potential electrodes for rechargeable batteries and electrochemical capacitors. This review is an attempt to summarize the research and development of TMDCs, MXenes and their hybrid structures in energy storage systems. (C) The Author(s) 2016. Published by ECS. All rights reserved.
Self-organized defect strings in two-dimensional crystals.
Lechner, Wolfgang; Polster, David; Maret, Georg; Keim, Peter; Dellago, Christoph
2013-12-01
Using experiments with single-particle resolution and computer simulations we study the collective behavior of multiple vacancies injected into two-dimensional crystals. We find that the defects assemble into linear strings, terminated by dislocations with antiparallel Burgers vectors. We show that these defect strings propagate through the crystal in a succession of rapid one-dimensional gliding and rare rotations. While the rotation rate decreases exponentially with the number of defects in the string, the diffusion constant is constant for large strings. By monitoring the separation of the dislocations at the end points, we measure their effective interactions with high precision beyond their spontaneous formation and annihilation, and we explain the double-well form of the dislocation interaction in terms of continuum elasticity theory.
Seismic isolation of buildings on two dimensional phononic crystal foundation
Han, Lin; Li, Xiao-mei; Zhang, Yan
2017-11-01
In order to realize the seismic isolation of buildings, we establish the two dimensional phononic crystal (PC) foundation which has the cell with the size close to the regular concrete test specimens, and is composed of the concrete base, rubber coating and lead cylindrical core. We study the in-plane band gap (BG) characteristics in it, through the analysis of the frequency dispersion relation and frequency response result. To lower the start BG frequency to the seismic frequency range, we also study the influences of material parameters (the elastic modulus of coating and density of cylindrical core) and geometry parameters (the thickness of coating, radius of cylindrical core and lattice constant) on BG ranges. The study could help to design the PC foundation for seismic isolation of building.
Probing Mechanics of Rippled Two-Dimensional Materials
Nicholl, Ryan; Conely, Hiram; Lavrik, Nickolay; Vlassiouk, Ivan; Bolotin, Kirill
2015-03-01
Two-dimensional materials such as graphene tend to ripple in the out of plane direction. These ripples arise both due to thermal fluctuations and uneven stress forces at the boundary. In this work, we study the effect of the rippling on the effective mechanical properties of graphene: Young's modulus and bending rigidity. To accomplish this, we developed a non-contact technique that allows probing mechanical properties of graphene at temperatures between 4K and 400K. We use a high voltage electrostatic force to pull on graphene and high-resolution optical interferometric profilometery to measure its mechanical response. We find that the effective Young's modulus of graphene is significantly softened and the bending rigidity is increased due to rippling.
Atlas for the properties of elemental two-dimensional metals
Nevalaita, Janne; Koskinen, Pekka
2018-01-01
Common two-dimensional (2D) materials have a layered three-dimensional (3D) structure with covalently bonded, atomically thin layers held together by weak van der Waals forces. However, in a recent transmission electron microscopy experiment, atomically thin 2D patches of iron were discovered inside a graphene nanopore. Motivated by this discovery, we perform a systematic density-functional study on atomically thin elemental 2D metal films, using 45 metals in three lattice structures. Cohesive energies, equilibrium distances, and bulk moduli in 2D are found to be linearly correlated to the corresponding 3D bulk properties, enabling the quick estimation of these values for a given 2D metal and lattice structure. In-plane elastic constants show that most 2D metals are stable in hexagonal and honeycomb, but unstable in square 2D structures. Many 2D metals are surprisingly stable against bending.
Acoustic resonances in two-dimensional radial sonic crystal shells
Energy Technology Data Exchange (ETDEWEB)
Torrent, Daniel; Sanchez-Dehesa, Jose, E-mail: jsdehesa@upvnet.upv.e [Wave Phenomena Group, Departamento de Ingenieria Electronica, Universidad Politecnica de Valencia, C/Camino de Vera s.n., E-46022 Valencia (Spain)
2010-07-15
Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sanchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts.
Acoustic metamaterials for new two-dimensional sonic devices
Energy Technology Data Exchange (ETDEWEB)
Torrent, Daniel; Sanchez-Dehesa, Jose [Wave Phenomena Group, Department of Electronic Engineering, Polytechnic University of Valencia, C/Camino de Vera sn, E-46022 Valencia (Spain)
2007-09-15
It has been shown that two-dimensional arrays of rigid or fluidlike cylinders in a fluid or a gas define, in the limit of large wavelengths, a class of acoustic metamaterials whose effective parameters (sound velocity and density) can be tailored up to a certain limit. This work goes a step further by considering arrays of solid cylinders in which the elastic properties of cylinders are taken into account. We have also treated mixtures of two different elastic cylinders. It is shown that both effects broaden the range of acoustic parameters available for designing metamaterials. For example, it is predicted that metamaterials with perfect matching of impedance with air are now possible by using aerogel and rigid cylinders equally distributed in a square lattice. As a potential application of the proposed metamaterial, we present a gradient index lens for airborne sound (i.e. a sonic Wood lens) whose functionality is demonstrated by multiple scattering simulations.
Acoustic resonances in two-dimensional radial sonic crystal shells
Torrent, Daniel; Sánchez-Dehesa, José
2010-07-01
Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sánchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts.
Two-dimensional random arrays for real time volumetric imaging
DEFF Research Database (Denmark)
Davidsen, Richard E.; Jensen, Jørgen Arendt; Smith, Stephen W.
1994-01-01
beams. A random array with Gaussian distribution of transmitters and uniform distribution of receivers was found to have better resolution and depth-of-field than both a Mills cross array and a random array with uniform distribution of both transmit and receive elements. The Gaussian random array......Two-dimensional arrays are necessary for a variety of ultrasonic imaging techniques, including elevation focusing, 2-D phase aberration correction, and real time volumetric imaging. In order to reduce system cost and complexity, sparse 2-D arrays have been considered with element geometries...... selected ad hoc, by algorithm, or by random process. Two random sparse array geometries and a sparse array with a Mills cross receive pattern were simulated and compared to a fully sampled aperture with the same overall dimensions. The sparse arrays were designed to the constraints of the Duke University...
Two dimensional radiated power diagnostics on Alcator C-Moda)
Reinke, M. L.; Hutchinson, I. H.
2008-10-01
The radiated power diagnostics for the Alcator C-Mod tokamak have been upgraded to measure two dimensional structure of the photon emissivity profile in order to investigate poloidal asymmetries in the core radiation. Commonly utilized unbiased absolute extreme ultraviolet (AXUV) diode arrays view the plasma along five different horizontal planes. The layout of the diagnostic set is shown and the results from calibrations and recent experiments are discussed. Data showing a significant, 30%-40%, inboard/outboard emissivity asymmetry during ELM-free H-mode are presented. The ability to use AXUV diode arrays to measure absolute radiated power is explored by comparing diode and resistive bolometer-based emissivity profiles for highly radiative L-mode plasmas seeded with argon. Emissivity profiles match in the core but disagree radially outward resulting in an underprediction of Prad of nearly 50% by the diodes compared to Prad determined using resistive bolometers.
Parametric pumping of the two-dimensional quantum spin liquid
Zvyagin, A. A.
2017-02-01
With the help of the exact solution of the Kitaev model the parametric pumping of the two-dimensional quantum spin liquid under the action of the ac magnetic field is studied. In the dynamical regime the field produces oscillations of the magnetization with the field's frequency, modulated by the Rabi-like oscillations. In the steady-state regime, the Rabi-like oscillations are damped. The absorption of the ac field by the Kitaev spin model is finite and manifests resonance features. Such a behavior is generic for quantum spin liquids with fermionic excitations, and it is different from the linear spin-wave response of magnetically ordered systems to such a parametric pumping.
The encoding complexity of two dimensional range minimum data structures
DEFF Research Database (Denmark)
Brodal, Gerth Stølting; Brodnik, Andrej; Davoodi, Pooya
2013-01-01
of the encoding variant of the problem where queries have access to the constructed data structure but can not access the input matrix A, i.e. all information must be encoded in the data structure. Previously it was known how to solve the problem with space O(mn min {m,logn}) bits (and with constant query time......In the two-dimensional range minimum query problem an input matrix A of dimension m ×n, m ≤ n, has to be preprocessed into a data structure such that given a query rectangle within the matrix, the position of a minimum element within the query range can be reported. We consider the space complexity...
Acoustic resonances in two dimensional radial sonic crystals shells
Torrent, Daniel
2010-01-01
Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction. They have been recently introduced and are only possible thanks to the anisotropy of specially designed acoustic metamaterials [see Phys. Rev. Lett. {\\bf 103} 064301 (2009)]. We present here a comprehensive analysis of two-dimensional RSC shells, which consist of a cavity defect centered at the origin of the crystal and a finite thickness crystal shell surrounded by a fluidlike background. We develop analytic expressions demonstrating that, like for other type of crystals (photonic or phononic) with defects, these shells contain Fabry-Perot like resonances and strongly localized modes. The results are completely general and can be extended to three dimensional acoustic structures and to their photonic counterparts, the radial photonic crystals.
Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.
Kokkin, Damian L.; Steimle, Timothy
2014-06-01
Determining the physical properties (bond lengths, angles, dipole moments, etc) of transition metal oxides and dioxides is relevant to catalysis, high temperature chemistry, materials science and astrophysics. Analysis of optical spectra is a convenient method for extraction of physical properties, but can be difficult because of the density of electronic states and in the case of the dioxides, presence of both the oxide and superoxide forms. Here we demonstrate the application of two dimensional fluorescence spectroscopy for aiding in the assignment and analysis. Particular attention will be paid to the spectroscopy of first row transition metal monoxides and dioxides of Nickel, NiO and NiO_2, and Manganese, MnO. Furthermore, the application of this technique to discovering the spectrum of other transition metal systems such as Metal-dicarbides will be outlined. N.J. Reilly, T.W. Schmidt, S.H. Kable, J. Phys. Chem. A., 110(45), 12355-12359, 2006
Nematic Equilibria on a Two-Dimensional Annulus
Lewis, A. H.
2017-01-16
We study planar nematic equilibria on a two-dimensional annulus with strong and weak tangent anchoring, in the Oseen–Frank theoretical framework. We analyze a radially invariant defect-free state and compute analytic stability criteria for this state in terms of the elastic anisotropy, annular aspect ratio, and anchoring strength. In the strong anchoring case, we define and characterize a new spiral-like equilibrium which emerges as the defect-free state loses stability. In the weak anchoring case, we compute stability diagrams that quantify the response of the defect-free state to radial and azimuthal perturbations. We study sector equilibria on sectors of an annulus, including the effects of weak anchoring and elastic anisotropy, giving novel insights into the correlation between preferred numbers of boundary defects and the geometry. We numerically demonstrate that these sector configurations can approximate experimentally observed equilibria with boundary defects.
Oscillation of Two-Dimensional Neutral Delay Dynamic Systems
Directory of Open Access Journals (Sweden)
Xinli Zhang
2013-01-01
Full Text Available We consider a class of nonlinear two-dimensional dynamic systems of the neutral type (x(t-a(tx(τ1(tΔ=p(tf1(y(t, yΔ(t=-q(tf2(x(τ2(t. We obtain sufficient conditions for all solutions of the system to be oscillatory. Our oscillation results when a(t=0 improve the oscillation results for dynamic systems on time scales that have been established by Fu and Lin (2010, since our results do not restrict to the case where f(u=u. Also, as a special case when =ℝ, our results do not require an to be a positive real sequence. Some examples are given to illustrate the main results.
Two-dimensional computer simulation of high intensity proton beams
Lapostolle, Pierre M
1972-01-01
A computer program has been developed which simulates the two- dimensional transverse behaviour of a proton beam in a focusing channel. The model is represented by an assembly of a few thousand 'superparticles' acted upon by their own self-consistent electric field and an external focusing force. The evolution of the system is computed stepwise in time by successively solving Poisson's equation and Newton's law of motion. Fast Fourier transform techniques are used for speed in the solution of Poisson's equation, while extensive area weighting is utilized for the accurate evaluation of electric field components. A computer experiment has been performed on the CERN CDC 6600 computer to study the nonlinear behaviour of an intense beam in phase space, showing under certain circumstances a filamentation due to space charge and an apparent emittance growth. (14 refs).
Analysis of Two-Dimensional Electrophoresis Gel Images
DEFF Research Database (Denmark)
Pedersen, Lars
2002-01-01
for parametric modelling of several spots that may also be overlapping is proposed. To enable comparison of protein patterns between different samples, it is necessary to match the patterns so that homologous spots are identified. Protein spot patterns, represented by the spot centre coordinates can be regarded......This thesis describes and proposes solutions to some of the currently most important problems in pattern recognition and image analysis of two-dimensional gel electrophoresis (2DGE) images. 2DGE is the leading technique to separate individual proteins in biological samples with many biological...... methods based on image analysis techniques in order to significantly accelerate this key technology. The methods described and developed fall into three categories: image segmentation, point pattern matching, and a unified approach simultaneously segmentation the image and matching the spots. The main...
High Performance Palmprint Identification System Based On Two Dimensional Gabor
Directory of Open Access Journals (Sweden)
Erdiawan
2010-12-01
Full Text Available Palmprint is a relatively new in physiological biometrics. Palmprint region of interest (ROI segmentation and feature extraction are two important issues in palmprint recognition. The main problem in palmprint recognition system is how to extract the region of interest (ROI and the features of palmprint. This paper introduces two steps in center of mass moment method for ROI segmentation and then applied the Gabor two dimensional (2D filters to obtain palm code as palmprint feature vector. Normalized Hamming distance is used to measure the similarity degrees of two feature vectors of palmprint. The system has been tested by using database 1000 palmprint images, are generated from 5 samples from each of the 200 persons randomly selected. Experiment results show that this system can achieve a high performance with success rate about 98.7% (FRR=1.1667%, FAR=0.1111%, T=0.376.
On dynamical behaviour of two-dimensional biological reactors
Lara-Cisneros, Gerardo; Femat, Ricardo; Pérez, Elías
2012-03-01
The dynamical behaviour for a generic two-dimensional model of a continuous bioreactor is studied in this article. The state variables for the bio-reacting system are restricted to concentrations of substrate and biomass, where the specific growth rate is a smooth function of the substrate concentration, which can be a kinetic function, monotone or non-monotone (as Monod, Haldane, Teissier, etc.). The effect of input (dilution rate) on multiplicity and bifurcation of equilibrium is shown in open-loop configuration. The absence of limit cycles on open-loop configuration and through state-feedback on the dilution rate are demonstrated. The aim of analysing oscillations under state feedback control is related to the possible improvement of reactor yields under this operation regime. An example for a cell-producing bioreactor illustrates the analytical results.
Electronic nanobiosensors based on two-dimensional materials
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.
On final states of two-dimensional decaying turbulence
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).
Performance Characteristics of Plane-Wall Two-Dimensional Diffusers
Reid, Elliott G
1953-01-01
Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery
On Space Efficient Two Dimensional Range Minimum Data Structures
DEFF Research Database (Denmark)
Davoodi, Pooya; Brodal, Gerth Stølting; Rao, S. Srinivasa
2010-01-01
The two dimensional range minimum query problem is to preprocess a static two dimensional m by n array A of size N = m · n, such that subsequent queries, asking for the position of the minimum element in a rectangular range within A, can be answered efficiently. We study the trade-off between the...... optimal O(N) bits additional space. For the case where queries can not probe A, we give a data structure of size O(N· min {m,logn}) bits with O(1) query time, assuming m ≤ n. This leaves a gap to the lower bound of Ω(Nlogm) bits for this version of the problem....... the space and query time of the problem. We show that every algorithm enabled to access A during the query and using O(N/c) bits additional space requires Ω(c) query time, for any c where 1 ≤ c ≤ N. This lower bound holds for any dimension. In particular, for the one dimensional version of the problem......, the lower bound is tight up to a constant factor. In two dimensions, we complement the lower bound with an indexing data structure of size O(N/c) bits additional space which can be preprocessed in O(N) time and achieves O(clog2 c) query time. For c = O(1), this is the first O(1) query time algorithm using...
The two-dimensional code image recognition based on wavelet transform
Wan, Hao; Peng, Cheng
2017-01-01
With the development of information technology, two-dimensional code is more and more widely used. In the technology of two-dimensional code recognition, the noise reduction of the two-dimensional code image is very important. Wavelet transform is applied to the noise reduction of two-dimensional code, and the corresponding Matlab experiment and simulation are made. The results show that the wavelet transform is simple and fast in the noise reduction of two-dimensional code. And it can commendably protect the details of the two-dimensional code image.
Directory of Open Access Journals (Sweden)
M.A.R. Feliciano
2007-10-01
Full Text Available Gestational period in a bitch, after natural mating with a normal dog, was evaluated by two-dimensional conventional, high-resolution two-dimensional and three-dimensional ultrasonography. High-resolution two-dimensional ultrasonography show better image and provides early diagnosis of pregnancy (15 days in comparison to conventional one (20 days. Three-dimensional ultrasonography was use to evaluate fetal morphology during late gestation period, however its application is still limited.
Hogge, Jerome W. III
1991-01-01
This research addresses a two-dimensional stock cutting problem encountered at the New River Valley Workshop (NRV), Inc. in Radford, VA. This research considers recent literature on two-dimensional stock cutting techniques, pattern generating methods, solution approaches, and practical problem considerations in addressing the NRV cutting problem. Linear Programming analysis is applied to NRV's two-dimensional cutting problem. A computer-based implementation of the LP s...
Wang, Donglin; Yu, Zhongyuan; Liu, Yumin; Guo, Xiaotao; Shu, Changgan; Zhou, Shuai
2013-09-10
A two-dimensional photonic crystal waveguide structure is designed for both TE- and TM-mode slow light propagation. The minimum group index of the waveguide for TE and TM modes can reach to 137.8 and 126.4, and the two polarizations have the same slow light frequency region. The designed structure can provide a large bandwidth range with very low group velocity dispersion for both TE and TM modes. The transmission property investigation for a suspended two-dimensional slab photonic crystal waveguide (PCW) indicates that such slow light character may be retained when perfect reflectors can be fixed on the horizontal surfaces of the slab. Such high group index for both TE and TM modes in two-dimensional PCWs is, to the best of our knowledge, first reported here, and may provide some useful guides for slow light research in theory.
Laser-sub-cycle two-dimensional electron momentum mapping using orthogonal two-color fields
Zhang, Li; Roither, Stefan; Kartashov, Daniil; Wang, YanLan; Wang, ChuanLiang; Schöffler, Markus; Shafir, Dror; Corkum, Paul; Baltuška, Andrius; Ivanov, Igor; Kheifets, Anatoli; Liu, XiaoJun; Staudte, André; Kitzler, Markus
2014-01-01
The two-dimensional sub-cycle-time to electron momentum mapping provided by orthogonal two-color laser fields is applied to photoelectron spectroscopy. Using neon as the example we gain experimental access to the dynamics of emitted electron wave packets in electron momenta spectra measured by coincidence momentum imaging. We demonstrate the opportunities provided by this time-to-momentum mapping by investigating the influence of the parent ion on the emitted electrons on laser-sub-cycle times. It is found that depending on their sub-cycle birth time the trajectories of photoelectrons are affected differently by the ion's Coulomb field.
Sahin, A; Ozaktas, H M; Mendlovic, D
1998-04-10
We provide a general treatment of optical two-dimensional fractional Fourier transforming systems. We not only allow the fractional Fourier transform orders to be specified independently for the two dimensions but also allow the input and output scale parameters and the residual spherical phase factors to be controlled. We further discuss systems that do not allow all these parameters to be controlled at the same time but are simpler and employ a fewer number of lenses. The variety of systems discussed and the design equations provided should be useful in practical applications for which an optical fractional Fourier transforming stage is to be employed.
From two-dimensional to three-dimensional turbulence through two-dimensional three-component flows
Biferale, L.; Buzzicotti, M.; Linkmann, M.
2017-11-01
The relevance of two-dimensional three-component (2D3C) flows goes well beyond their occurrence in nature, and a deeper understanding of their dynamics might also be helpful in order to shed further light on the dynamics of pure two-dimensional (2D) or three-dimensional (3D) flows and vice versa. The purpose of the present paper is to make a step in this direction through a combination of numerical and analytical work. The analytical part is mainly concerned with the behavior of 2D3C flows in isolation and the connection between the geometry of the nonlinear interactions and the resulting energy transfer directions. Special emphasis is given to the role of helicity. We show that a generic 2D3C flow can be described by two stream functions corresponding to the two helical sectors of the velocity field. The projection onto one helical sector (homochiral flow) leads to a fully 3D constraint and to the inviscid conservation of the total (three-dimensional) enstrophy and hence to an inverse cascade of the kinetic energy of the third component also. The coupling between several 2D3C flows is studied through a set of suitably designed direct numerical simulations, where we also explore the transition between 2D and fully 3D turbulence. In particular, we find that the coupling of three 2D3C flows on mutually orthogonal planes subject to small-scale forcing leads to stationary 3D out-of-equilibrium dynamics at the energy containing scales. The transition between 2D and 3D turbulence is then explored through adding a percentage of fully 3D Fourier modes in the volume.
Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals
Energy Technology Data Exchange (ETDEWEB)
Foteinopoulou, Stavroula [Iowa State Univ., Ames, IA (United States)
2003-01-01
In this dissertation, they have undertaken the challenge to understand the unusual propagation properties of the photonic crystal (PC). The photonic crystal is a medium where the dielectric function is periodically modulated. These types of structures are characterized by bands and gaps. In other words, they are characterized by frequency regions where propagation is prohibited (gaps) and regions where propagation is allowed (bands). In this study they focus on two-dimensional photonic crystals, i.e., structures with periodic dielectric patterns on a plane and translational symmetry in the perpendicular direction. They start by studying a two-dimensional photonic crystal system for frequencies inside the band gap. The inclusion of a line defect introduces allowed states in the otherwise prohibited frequency spectrum. The dependence of the defect resonance state on different parameters such as size of the structure, profile of incoming source, etc., is investigated in detail. For this study, they used two popular computational methods in photonic crystal research, the Finite Difference Time Domain method (FDTD) and the Transfer Matrix Method (TMM). The results for the one-dimensional defect system are analyzed, and the two methods, FDTD and TMM, are compared. Then, they shift their attention only to periodic two-dimensional crystals, concentrate on their band properties, and study their unusual refractive behavior. Anomalous refractive phenomena in photonic crystals included cases where the beam refracts on the ''wrong'' side of the surface normal. The latter phenomenon, is known as negative refraction and was previously observed in materials where the wave vector, the electric field, and the magnetic field form a left-handed set of vectors. These materials are generally called left-handed materials (LHM) or negative index materials (NIM). They investigated the possibility that the photonic crystal behaves as a LHM, and how this behavior relates
GPM GROUND VALIDATION TWO-DIMENSIONAL VIDEO DISDROMETER (2DVD) NSSTC V1
National Aeronautics and Space Administration — The GPM Ground Validation Two-Dimensional Video Disdrometer (2DVD) NSSTC dataset was collected by the Two-Dimensional Video Disdrometer (2DVD), which uses two high...
GPM GROUND VALIDATION TWO-DIMENSIONAL VIDEO DISDROMETER (2DVD) GCPEX V1
National Aeronautics and Space Administration — The GPM Ground Validation Two-Dimensional Video Disdrometer (2DVD) GCPEX dataset was collected by the Two-Dimensional Video Disdrometer (2DVD) data, which was...
Two-dimensional electronic spectroscopy of anharmonic molecular potentials.
Anda, André; Abramavičius, Darius; Hansen, Thorsten
2018-01-17
Two-dimensional electronic spectroscopy (2DES) is a powerful tool in the study of coupled electron-phonon dynamics, yet very little is known about how nonlinearities in the electron-phonon coupling, arising from anharmonicities in the nuclear potentials, affect the spectra. These become especially relevant when the coupling is strong. From the linear spectroscopies, anharmonicities are known to give structure to the zero-phonon line and to break mirror-symmetry between absorption and emission, but the 2D analogues of these effects have not been identified. Using a simple two-level model where the electronic states are described by (displaced) harmonic oscillators with differing curvatures or displaced Morse oscillators, we find that the zero-phonon line shape is essentially transferred to the diagonal in 2DES spectra, and that anharmonicities break a horizontal mirror-symmetry in the infinite waiting time limit. We also identify anharmonic effects that are only present in 2DES spectra: twisting of cross-peaks stemming from stimulated emission signals; and oscillation period mismatch between ground state bleach and stimulated emission (for harmonic oscillators with differing curvatures), or inherently chaotic oscillations (for Morse oscillators). Our findings will facilitate an improved understanding of 2DES spectra and aid the interpretation of signals that are more realistic than those arising from simple models.
Two-dimensional topological order of kinetically constrained quantum particles
Kourtis, Stefanos
2015-03-01
Motivated by recent experimental and theoretical work on driven optical lattices, we investigate how imposing kinetic restrictions on quantum particles that would otherwise hop freely on a two-dimensional lattice can lead to topologically ordered states. The kinetically constrained models introduced here are derived as an approximate generalization of strongly interacting particles hopping on Haldane and equivalent lattices and are pertinent to systems irradiated by circularly polarized light. After introducing a broad class of models, we focus on particular realizations and show numerically that they exhibit topological order, by observing topological ground-state degeneracies and the quantization of corresponding invariants. Apart from potentially being crucial for the interpretation of forthcoming cold-atom experiments, our results also hint at unexplored possibilities for the realization of topologically ordered matter. A further implication, relevant to fractional quantum Hall (FQH) physics, is that the correlations responsible for FQH-like states can arise from processes other than density-density interactions. Financial support from EPSRC (Grant No. EP/K028960/1) and ICAM Branch Contributions.
Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures
Energy Technology Data Exchange (ETDEWEB)
Azad, Abul K [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Han, Jiaguang [OSU; Lu, Xinchao [OSU; Zhang, Weili [OSU
2009-01-01
The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.
New ideas for two dimensional position sensitive silicon drift detectors
Energy Technology Data Exchange (ETDEWEB)
Hijzen, E.A.; Schooneveld, E.M.; Eijk, C.W.E. van; Hollander, R.W.; Sarro, P.M.; Bogaard, A. van den (Delft Univ. of Technology (Netherlands))
1994-08-01
In this paper the authors present two new ideas for drift detectors with two dimensional position resolution. The first idea is based on the regular drift detector, but has a slightly different design in order to deal with diffusion problems. The second idea embodies a completely new type of drift detector that uses drift time measurements for both dimensions. The design consists of concentric quadrilateral closed strips with a small collecting anode in the center. At first electrons travel perpendicular to the strips until they reach a diagonal. Then they proceed along this diagonal until they are collected at the centre. Position resolution in two dimensions can be obtained when both the time the electrons need to reach the diagonal and the time they need to reach the centre are measured. The latter is obtained from the collecting anode, the former form a diagonal strip present at the back side of the detector. Compared to common 2D drift detectors this detector offers the advantage of a small amount of read out electronics. It also has the advantage of having just one small collecting anode with a very low capacitance, resulting in low noise and therefore in a good energy resolution.
Spin-orbit torque in two dimensional antiferromagnetic topological insulators
Ghosh, Sumit; Manchon, Aurelien
Topological insulators (TI) have been found to be a source of huge spin-orbit torque (SOT) that originates from their surface states. However, the proximity of a ferromagnetic layer can destroy the surface states which makes the exact nature of the SOT quite argumentative. Recently it has been found that in presence of an antiferromagnetic magnetization, a TI can preserve its gapless states. We conduct a systematic study on two-dimensional antiferromagnetic TI and find that they are more robust compared to a ferromagnetic TI against impurity scattering. It can facilitate a field like SOT due to the intrinsic spin-orbit coupling and an antidamping SOT via scattering by scalar impurity. Interestingly, a moderate amount of impurity enhances the staggered spin density at the edges resulting in a uniform antidamping torque with the conductance remaining finite. It is, therefore, possible to manipulate the magnetization either by using a pulse via field like SOT or by a dc current via antidamping SOT. This work was supported by the King Abdullah Uni- versity of Science and Technology (KAUST) through the Office of Sponsored Research (OSR) [Grant Number OSR-2015- CRG4-2626].
Emerging terahertz photodetectors based on two-dimensional materials
Yang, Jie; Qin, Hua; Zhang, Kai
2018-01-01
Inspired by the innovations in photonics and nanotechnology, the remarkable properties of two-dimensional (2D) materials have renewed interest for the development of terahertz (THz) photodetectors. The versatility of these materials enables ultrafast and ultrasensitive photodetection of THz radiation at room temperature. The atomically thin characteristic together with van der Waals interactions among the layers make it easy to scaling down and integrate with other 2D materials based devices, as well as silicon chips. Efforts have increased fast in the past decade in developing proof-of-concept and the further prospective THz photodetectors based on 2D materials. Here, the recent progress on the exploring of THz photodetectors based on 2D materials is reviewed. We summarized the THz photodetectors under different physical mechanism and introduced the state-of-the-art THz photodetectors based on various promising 2D materials, such as graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP) and topological insulators (TIs). A brief discussion on the remaining challenges and a perspective of the 2D materials based THz photodetectors are also given.
Tunable states of interlayer cations in two-dimensional materials
Energy Technology Data Exchange (ETDEWEB)
Sato, K.; Numata, K. [Department of Environmental Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501 (Japan); Dai, W. [Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071 (China); Hunger, M. [Institute of Chemical Technology, University of Stuttgart, 70550 Stuttgart (Germany)
2014-03-31
The local state of cations inside the Ångstrom-scale interlayer spaces is one of the controlling factors for designing sophisticated two-dimensional (2D) materials consisting of 2D nanosheets. In the present work, the molecular mechanism on how the interlayer cation states are induced by the local structures of the 2D nanosheets is highlighted. For this purpose, the local states of Na cations in inorganic 2D materials, in which the compositional fluctuations of a few percent are introduced in the tetrahedral and octahedral units of the 2D nanosheets, were systematically studied by means of {sup 23}Na magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and {sup 23}Na multiple-quantum MAS (MQMAS) NMR spectroscopy. In contrast with an uniform distribution of Na cations expected so far, various well-defined cation states sensitive to the local structures of the 2D nanosheets were identified. The tunability of the interlayer cation states along with the local structure of the 2D nanosheets, as the smallest structural unit of the 2D material, is discussed.
On the critical behaviour of two-dimensional liquid crystals
Directory of Open Access Journals (Sweden)
A.l. Fariñas-Sánchez
2010-01-01
Full Text Available The Lebwohl-Lasher (LL model is the traditional model used to describe the nematic-isotropic transition of real liquid crystals. In this paper, we develop a numerical study of the temperature behaviour and of finite-size scaling of the two-dimensional (2D LL-model. We discuss two possible scenarios. In the first one, the 2D LL-model presents a phase transition similar to the topological transition appearing in the 2D XY-model. In the second one, the 2D LL-model does not exhibit any critical transition, but its low temperature behaviour is rather characterized by a crossover from a disordered phase to an ordered phase at zero temperature. We realize and discuss various comparisons with the 2D XY-model and the 2D Heisenberg model. Having added finite-size scaling behaviour of the order parameter and conformal mapping of order parameter profile to previous studies, we analyze the critical scaling of the probability distribution function, hyperscaling relations and stiffness order parameter and conclude that the second scenario (no critical transition is the most plausible.
Screw dislocation-driven growth of two-dimensional nanoplates.
Morin, Stephen A; Forticaux, Audrey; Bierman, Matthew J; Jin, Song
2011-10-12
We report the dislocation-driven growth of two-dimensional (2D) nanoplates. They are another type of dislocation-driven nanostructure and could find application in energy storage, catalysis, and nanoelectronics. We first focus on nanoplates of zinc hydroxy sulfate (3Zn(OH)(2)·ZnSO(4)·0.5H(2)O) synthesized from aqueous solutions. Both powder X-ray and electron diffraction confirm the zinc hydroxy sulfate (ZHS) crystal structure as well as their conversion to zinc oxide (ZnO). Scanning electron, atomic force, and transmission electron microscopy reveal the presence of screw dislocations in the ZHS nanoplates. We further demonstrate the generality of this mechanism through the growth of 2D nanoplates of α-Co(OH)(2), Ni(OH)(2), and gold that can also follow the dislocation-driven growth mechanism. Finally, we propose a unified scheme general to any crystalline material that explains the growth of nanoplates as well as different dislocation-driven nanomaterial morphologies previously observed through consideration of the relative crystal growth step velocities at the dislocation core versus the outer edges of the growth spiral under various supersaturations.
The planiverse computer contact with a two-dimensional world
Dewdney, Alexander Keewatin
2000-01-01
When The Planiverse ?rst appeared 16 years ago, it caught more than a few readers off guard. The line between willing suspension of dis- lief and innocent acceptance, if it exists at all, is a thin one. There were those who wanted to believe, despite the tongue-in-cheek subtext, that we had made contact with a two-dimensional world called Arde, a di- shaped planet embedded in the skin of a vast, balloon-shaped space called the planiverse. It is tempting to imagine that those who believed, as well as those who suspended disbelief, did so because of a persuasive consistency in the cosmology and physics of this in?nitesimally thin universe, and x preface to the millennium edition in its bizarre but oddly workable organisms. This was not just your r- of-the-mill universe fashioned out of the whole cloth of wish-driven imagination. The planiverse is a weirder place than that precisely - cause so much of it was “worked out” by a virtual team of scientists and technologists. Reality, even the pseudoreality of su...
Dirac Dispersion in Two-Dimensional Photonic Crystals
Directory of Open Access Journals (Sweden)
C. T. Chan
2012-01-01
Full Text Available We show how one may obtain conical (Dirac dispersions in photonic crystals, and in some cases, such conical dispersions can be used to create a metamaterial with an effective zero refractive index. We show specifically that in two-dimensional photonic crystals with C4v symmetry, we can adjust the system parameters to obtain accidental triple degeneracy at Γ point, whose band dispersion comprises two linear bands that generate conical dispersion surfaces and an additional flat band crossing the Dirac-like point. If this triply degenerate state is formed by monopole and dipole excitations, the system can be mapped to an effective medium with permittivity and permeability equal to zero simultaneously, and this system can transport wave as if the refractive index is effectively zero. However, not all the triply degenerate states can be described by monopole and dipole excitations and in those cases, the conical dispersion may not be related to an effective zero refractive index. Using multiple scattering theory, we calculate the Berry phase of the eigenmodes in the Dirac-like cone to be equal to zero for modes in the Dirac-like cone at the zone center, in contrast with the Berry phase of π for Dirac cones at the zone boundary.
Classifying two-dimensional orbits using pattern recognition
Faber, N. T.; Flitti, F.; Boily, C. M.; Collet, C.; Patsis, P. A.; Portegies Zwart, S.
2013-12-01
We present a fast algorithm to identify both regular and irregular orbits that map out a sustained shape in configuration space. The method, which we dub 'pattern autocorrelation' (PACO), detects a repeating pattern in time-series constructed from binary sign changes in phase-space coordinates reduced to two dimensions. This is achieved by computing the autocorrelation function of the time-series, and by retrieving a pattern and a pattern-to-signal ratio. We apply the method to two-dimensional orbits in the logarithmic potential in an application to spiral galaxies with an asymptotically flat rotation curve; the general case of three-dimensional orbits is sketched. We find that irregular orbits can yet sustain the smooth morphological features of a galaxy for a substantial fraction of a Hubble time: this fraction is quantified through the pattern-to-signal ratio. In the case where a central supermassive black hole is added to the potential, we find that up to ≈16% of initial conditions space yields irregular motion that may sustain long-lived regular features. The method further detects and distinguishes orbits that are not based on Lissajous theory of resonant motion.
Helical rays in two-dimensional resonant wave conversion
Energy Technology Data Exchange (ETDEWEB)
Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.
2004-09-14
The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model will exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.
Helical rays in two-dimensional resonant wave conversion
Energy Technology Data Exchange (ETDEWEB)
Kaufman, Allan N.; Tracy, Eugene R.; Brizard, Alain J.
2004-12-08
The process of resonant wave conversion (often called linear mode conversion) has traditionally been analyzed with a spatially one-dimensional slab model, for which the rays propagate in a two-dimensional phase space. However, it has recently been shown [E.R. Tracy and A.N. Kaufman, Phys. Rev. Lett. 91, 130402 (2003)] that multidimensional rays have a helical structure for conversion in two or more spatial dimensions (if their dispersion matrix is generic). In that case, a one-dimensional model is inadequate; a correct analysis requires two spatial dimensions and, thus, four-dimensional phase space. In this paper we show that a cold plasma model will exhibit ray helicity in conversion regions where the density and magnetic field gradients are significantly non-parallel. For illustration, we examine a model of the poloidal plane of a deuterium-tritium tokamak plasma, and identify such a region. In this region, characterized by a six-sector topology, rays in the sector for incident and reflected magnetosonic waves exhibit significant helicity. We introduce a ''symmetric-wedge'' model, to develop a detailed analytic and numerical study of helical rays in this sector.
Anomalous electron doping independent two-dimensional superconductivity
Zhou, Wei; Xing, Xiangzhuo; Zhao, Haijun; Feng, Jiajia; Pan, Yongqiang; Zhou, Nan; Zhang, Yufeng; Qian, Bin; Shi, Zhixiang
2017-07-01
Transition metal (Co and Ni) co-doping effects are investigated on an underdoped Ca0.94La0.06Fe2As2 compound. It is discovered that electron doping from substituting Fe with transition metal (TM = Co, Ni) can trigger high-{T}{{c}} superconductivity around 35 K, which emerges abruptly before the total suppression of the innate spin-density-wave/anti-ferromagnetism (SDW/AFM) state. Remarkably, the critical temperature for the high-{T}{{c}} superconductivity remains constant against a wide range of TM doping levels. And the net electron doping density dependence of the superconducting {T}{{c}} based on the rigid band model can be nicely scaled into a single curve for Co and Ni substitutions, in stark contrast to the case of Ba(Fe1-x TM x )2As2. This carrier density independent superconductivity and the unusual scaling behavior are presumably resulted from the interface superconductivity based on the similarity with the interface superconductivity in a La2-x Sr x CuO4-La2CuO4 bilayer. Evidence of the two-dimensional character of the superfluid by angle-resolved magneto-resistance measurements can further strengthen the interface nature of the high-{T}{{c}} superconductivity.
Hyperbolic Covariant Coherent Structures in Two Dimensional Flows
Directory of Open Access Journals (Sweden)
Giovanni Conti
2017-09-01
Full Text Available A new method to describe hyperbolic patterns in two-dimensional flows is proposed. The method is based on the Covariant Lyapunov Vectors (CLVs, which have the properties of being covariant with the dynamics, and thus, being mapped by the tangent linear operator into another CLVs basis, they are norm independent, invariant under time reversal and cannot be orthonormal. CLVs can thus give more detailed information about the expansion and contraction directions of the flow than the Lyapunov vector bases, which are instead always orthogonal. We suggest a definition of Hyperbolic Covariant Coherent Structures (HCCSs, which can be defined on the scalar field representing the angle between the CLVs. HCCSs can be defined for every time instant and could be useful to understand the long-term behavior of particle tracers. We consider three examples: a simple autonomous Hamiltonian system, as well as the non-autonomous “double gyre” and Bickley jet, to see how well the angle is able to describe particular patterns and barriers. We compare the results from the HCCSs with other coherent patterns defined on finite time by the Finite Time Lyapunov Exponents (FTLEs, to see how the behaviors of these structures change asymptotically.
Sub-Nanometer Channels Embedded in Two-Dimensional Materials
Han, Yimo
2017-07-31
Two-dimensional (2D) materials are among the most promising candidates for next-generation electronics due to their atomic thinness, allowing for flexible transparent electronics and ultimate length scaling1. Thus far, atomically-thin p-n junctions2-7, metal-semiconductor contacts8-10, and metal-insulator barriers11-13 have been demonstrated. While 2D materials achieve the thinnest possible devices, precise nanoscale control over the lateral dimensions are also necessary. Although external one-dimensional (1D) carbon nanotubes14 can be used to locally gate 2D materials, this adds a non-trivial third dimension, complicating device integration and flexibility. Here, we report the direct synthesis of sub-nanometer 1D MoS2 channels embedded within WSe2 monolayers, using a dislocation-catalyzed approach. The 1D channels have edges free of misfit dislocations and dangling bonds, forming a coherent interface with the embedding 2D matrix. Periodic dislocation arrays produce 2D superlattices of coherent MoS2 1D channels in WSe2. Molecular dynamics (MD) simulations have identified other combinations of 2D materials that could form 1D channels. Density function theory (DFT) calculation predicts these 1D channels display type II band alignment needed for carrier confinement and charge separation to access the ultimate length scales necessary for future electronic applications.
Sub-nanometre channels embedded in two-dimensional materials
Han, Yimo
2017-12-04
Two-dimensional (2D) materials are among the most promising candidates for next-generation electronics due to their atomic thinness, allowing for flexible transparent electronics and ultimate length scaling1. Thus far, atomically thin p–n junctions2,3,4,5,6,7,8, metal–semiconductor contacts9,10,11, and metal–insulator barriers12,13,14 have been demonstrated. Although 2D materials achieve the thinnest possible devices, precise nanoscale control over the lateral dimensions is also necessary. Here, we report the direct synthesis of sub-nanometre-wide one-dimensional (1D) MoS2 channels embedded within WSe2 monolayers, using a dislocation-catalysed approach. The 1D channels have edges free of misfit dislocations and dangling bonds, forming a coherent interface with the embedding 2D matrix. Periodic dislocation arrays produce 2D superlattices of coherent MoS2 1D channels in WSe2. Using molecular dynamics simulations, we have identified other combinations of 2D materials where 1D channels can also be formed. The electronic band structure of these 1D channels offers the promise of carrier confinement in a direct-gap material and the charge separation needed to access the ultimate length scales necessary for future electronic applications.
Image encryption using the two-dimensional logistic chaotic map
Wu, Yue; Yang, Gelan; Jin, Huixia; Noonan, Joseph P.
2012-01-01
Chaos maps and chaotic systems have been proved to be useful and effective for cryptography. In our study, the two-dimensional logistic map with complicated basin structures and attractors are first used for image encryption. The proposed method adopts the classic framework of the permutation-substitution network in cryptography and thus ensures both confusion and diffusion properties for a secure cipher. The proposed method is able to encrypt an intelligible image into a random-like one from the statistical point of view and the human visual system point of view. Extensive simulation results using test images from the USC-SIPI image database demonstrate the effectiveness and robustness of the proposed method. Security analysis results of using both the conventional and the most recent tests show that the encryption quality of the proposed method reaches or excels the current state-of-the-art methods. Similar encryption ideas can be applied to digital data in other formats (e.g., digital audio and video). We also publish the cipher MATLAB open-source-code under the web page https://sites.google.com/site/tuftsyuewu/source-code.
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. Copyright © 2016 Elsevier B.V. All rights reserved.
Design and fabrication of two-dimensional superconducting bolometer arrays
Benford, Dominic J.; Staguhn, Johannes G.; Stacey, Gordon J.; Page, Lyman; Moseley, S. H., Jr.; Irwin, Kent D.; Chervenak, James A.; Allen, Christine A.
2004-10-01
We have been developing an architecture for producing large format, two-dimensional arrays of close-packed bolometers, which will enable far-infrared to millimeter wavelength (lambda=100µm-2mm) cameras and spectrometers to obtain images and spectra orders of magnitude faster than present instruments. The low backgrounds achieved in these instruments require very sensitive detectors with NEPs ranging from 10-17 to 10-19 W/(Hz-1/2). Superconducting transition edge sensor bolometers can be close-packed using the Pop-Up Detector (PUD) format, and SQUID multiplexers operating at the detector base temperature can be intimately coupled to them. The array unit cell is 8x32 pixels, using 32-element detector and multiplexer components. We have fabricated an engineering model array with this technology featuring a very compact, modular approach for large format arrays. We report on the production of the 32-element components for the arrays. Planned instruments using this array architecture include the Submillimeter and Far-InfraRed Experiment (SAFIRE) on the SOFIA airborne observatory, the South Pole Imaging Fabry-Perot Interferometer (SPIFI) for the AST/RO observatory, the Millimeter Bolometer Camera for the Atacama Cosmology Telescope (MBC/ACT), and the Redshift "Z" Early Universe Spectrometer (ZEUS).
Two Dimensional Heat Transfer around Penetrations in Multilayer Insulation
Johnson, Wesley L.; Kelly, Andrew O.; Jumper, Kevin M.
2012-01-01
The objective of this task was to quantify thermal losses involving integrating MLI into real life situations. Testing specifically focused on the effects of penetrations (including structural attachments, electrical conduit/feedthroughs, and fluid lines) through MLI. While there have been attempts at quantifying these losses both analytically and experimentally, none have included a thorough investigation of the methods and materials that could be used in such applications. To attempt to quantify the excess heat load coming into the system due to the integration losses, a calorimeter was designed to study two dimensional heat transfer through penetrated MLI. The test matrix was designed to take as many variables into account as was possible with the limited test duration and system size. The parameters varied were the attachment mechanism, the buffer material (for buffer attachment mechanisms only), the thickness of the buffer, and the penetration material. The work done under this task is an attempt to measure the parasitic heat loads and affected insulation areas produced by system integration, to model the parasitic loads, and from the model produce engineering equations to allow for the determination of parasitic heat loads in future applications. The methods of integration investigated were no integration, using a buffer to thermally isolate the strut from the MLI, and temperature matching the MLI on the strut. Several materials were investigated as a buffer material including aerogel blankets, aerogel bead packages, cryolite, and even an evacuated vacuum space (in essence a no buffer condition).
Two-dimensional multiferroics in monolayer group IV monochalcogenides
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.
Compact design for two-dimensional electronic spectroscopy
Huang, Zheng; Wang, Peng; Shen, Xiong; Yan, Tian-Min; Zhang, Yizhu; Liu, Jun
2016-03-01
We present a passively phase-stabilized two-dimensional electronic spectroscopy (2DES) with a compact size, and the ease of implementation and maintenance. Our design relies on a mask beam-splitter with four holes to form non-collinear box geometry, and a homebuilt stacked retroreflector, which introduces the phase-locked pulse sequence, remedying the instability of commonly used translation stages. The minimized size of the setup suppresses the influences of optical path-length fluctuations during measurements, improving the phase stability and precise timing of pulse sequences. In our 2DES, only few conventional optical components are used, which make this sophisticated instrumentation convenient to establish and particularly easy to conduct alignment. In data analysis, the self-referencing spectral interferometry (SRSI) method is first introduced to extract the complex-valued signal from spectral interferometry in 2DES. The alternative algorithm achieves the improvement of the signal-to-noise ratio (SNR) and considerable reduction of data acquisition time. The new setup is suitable over a tunable range of spectroscopic wavelength, from ultraviolet (UV) to the near-infrared (NIR) regime, and for ultra-broadband bandwidth, few-cycle laser pulses.
Structure function of passive scalars in two-dimensional turbulence
Eckhardt, B; Eckhardt, Bruno; Schumacher, Joerg
1999-01-01
The structure function of a scalar $\\theta({\\bf x},t)$, passively advected in a two-dimensional turbulent flow ${\\bf u}({\\bf x},t)$, is discussed by means of the fractal dimension $\\delta^{(1)}_g$ of the passive scalar graph. A relation between $\\delta^{(1)}_g$, the scaling exponent $\\zeta_1^{(\\theta)}$ of the scalar structure function $D_1^{(\\theta)}(r)$, and the structure function $D_2(r)$ of the underlying flow field is derived. Different from the 3-d case, the 2-d structure function also depends on an additional parameter, characteristic of the driving of the passive scalar. In the enstrophy inertial subrange a mean field approximation for the velocity structure function gives a scaling of the passive scalar graph with $\\delta^{(1)}_g<2$ for intermediate and large values of the Prandtl number $Pr$. In the energy inertial subrange a model for the energy spectrum and thus $D_2(r)$ gives a passive scalar graph scaling with exponent $\\delta^{(1)}_g=5/3$. Finally, we discuss an application to recent observa...
Clogging of soft particles in two-dimensional hoppers
Hong, Xia; Kohne, Meghan; Morrell, Mia; Wang, Haoran; Weeks, Eric R.
2017-12-01
Using experiments and simulations, we study the flow of soft particles through quasi-two-dimensional hoppers. The first experiment uses oil-in-water emulsion droplets in a thin sample chamber. Due to surfactants coating the droplets, they easily slide past each other, approximating soft frictionless disks. For these droplets, clogging at the hopper exit requires a narrow hopper opening only slightly larger than the droplet diameter. The second experiment uses soft hydrogel particles in a thin sample chamber, where we vary gravity by changing the tilt angle of the chamber. For reduced gravity, clogging becomes easier and can occur for larger hopper openings. Our simulations mimic the emulsion experiments and demonstrate that softness is a key factor controlling clogging: with stiffer particles or a weaker gravitational force, clogging is easier. The fractional amount a single particle is deformed under its own weight is a useful parameter measuring particle softness. Data from the simulation and hydrogel experiments collapse when compared using this parameter. Our results suggest that prior studies using hard particles were in a limit where the role of softness is negligible, which causes clogging to occur with significantly larger openings.
Hilbert Statistics of Vorticity Scaling in Two-Dimensional Turbulence
Tan, H S; Meng, Jianping
2014-01-01
In this paper, the scaling property of the inverse energy cascade and forward enstrophy cascade of the vorticity filed $\\omega(x,y)$ in two-dimensional (2D) turbulence is analyzed. This is accomplished by applying a Hilbert-based technique, namely Hilbert-Huang Transform, to a vorticity field obtained from a $8192^2$ grid-points direct numerical simulation of the 2D turbulence with a forcing scale $k_f=100$ and an Ekman friction. The measured joint probability density function $p(C,k)$ of mode $C_i(x)$ of the vorticity $\\omega$ and instantaneous wavenumber $k(x)$ is separated by the forcing scale $k_f$ into two parts, which corresponding to the inverse energy cascade and the forward enstrophy cascade. It is found that all conditional pdf $p(C\\vert k)$ at given wavenumber $k$ has an exponential tail. In the inverse energy cascade, the shape of $p(C\\vert k)$ does collapse with each other, indicating a nonintermittent cascade. The measured scaling exponent $\\zeta_{\\omega}^I(q)$ is linear with the statistical ord...
Subsurface imaging of two-dimensional materials at the nanoscale
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.
Layers dependent dielectric properties of two dimensional hexagonal boron nitridenanosheets
Directory of Open Access Journals (Sweden)
Liang Wang
2016-12-01
Full Text Available Two dimensional (2D boron nitride (h-BN nanosheets are well known as their tunable electric properties and well compatible with graphene. Studying the dielectric properties carefully is essential for their promised applications. Most previous first principle studies treated 2D h-BN as a strict 2D system, where the contribution of ion polarization is neglected. The results show obvious deviation from experimental values, and the situations are worse with the stacking layer increasing. Thus, in present works, the dielectric properties of 2D h-BN nanosheets are studied with involving the ion contributions appropriately. The evolution of dielectric performance with stacking layers varying is also studied. Obvious layer dependent anisotropic dielectric properties are predicted, which reaches the bulk h-BN level as the thickness approaching 5.8nm (20L. There should be a balance between dielectric properties and the thickness (stacking layers for the dielectric applications of 2D h-BN nanosheets.
First-Principles Predication of Two-Dimensional Electrides
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.
Extension of the T-bridge method for measuring the thermal conductivity of two-dimensional materials
Kim, Jungwon; Seo, Dong-Jea; Park, Hwanjoo; Kim, Hoon; Choi, Heon-Jin; Kim, Woochul
2017-05-01
In this paper, the T-bridge method is extended to measure the thermal properties of two-dimensional nanomaterials. We present an analysis of the measureable positions, width, and thermal resistance of two-dimensional materials. For verification purposes, the thermal conductivity of a SiO2 nanoribbon was measured. To enhance the thermal contact between the nanoribbon and the heater in the setup, the nanoribbon was dipped into either isopropanol or water in order to promote a sticking force. Also, focused ion beam deposition was used to deposit the nanoribbon onto the contact. The thermal conductivities of all three cases were identical, showing that water dipping could be used to enhance the thermal contact. Due to the simple structure of this method and the analysis provided herein, the T-bridge method can be widely used for measuring the thermal conductivity of two-dimensional materials.
van Zyl, B. P.; Berkane, K.; Bencheikh, K.; Farrell, A.
2011-05-01
We examine the leading-order semiclassical gradient corrections to the noninteracting kinetic-energy density functional of a two-dimensional Fermi gas by applying the extended Thomas-Fermi theory at finite temperature. We find a nonzero von Weizsäcker-like gradient correction, which in the high-temperature limit goes over to the functional form (ℏ2/24m)(∇ρ)2/ρ. Our work provides a theoretical justification for the inclusion of gradient corrections in applications of density-functional theory to inhomogeneous two-dimensional Fermi systems at any finite temperature.
Directory of Open Access Journals (Sweden)
Ke Liang
2017-06-01
Full Text Available An optimization method is introduced to design the aerodynamic parameters of a dual-spin two-dimensional guided projectile with the canards for trajectory correction. The nose guidance component contains two pairs of canards which can provide lift and despin with the projectile for stability. The optimal design algorithm is developed to decide the profiles both of the steering and spinning canards, and their deflection angles are also simulated to meet the needs of trajectory correction capabilities. Finally, the aerodynamic efficiency of the specific canards is discussed according to the CFD simulations. Results that obtained here can be further applied to the exterior ballistics design.
Landi, Gregorio
2003-01-01
The center of gravity as an algorithm for position measurements is analyzed for a two-dimensional geometry. Several mathematical consequences of discretization for various types of detector arrays are extracted. Arrays with rectangular, hexagonal, and triangular detectors are analytically studied, and tools are given to simulate their discretization properties. Special signal distributions free of discretized error are isolated. It is proved that some crosstalk spreads are able to eliminate the center of gravity discretization error for any signal distribution. Simulations, adapted to the CMS em-calorimeter and to a triangular detector array, are provided for energy and position reconstruction algorithms with a finite number of detectors.
Energy Technology Data Exchange (ETDEWEB)
Rucker, S.P.
1991-07-01
Magnetic couplings between protons, such as through-space dipole couplings, and scalar J-couplings depend sensitively on the structure of the molecule. Two dimensional nuclear magnetic resonance experiments provide a powerful tool for measuring these couplings, correlating them to specific pairs of protons within the molecule, and calculating the structure. This work discusses the development of NMR methods for examining two such classes of problems -- determination of the secondary structure of flexible molecules in anisotropic solutions, and primary structure of large biomolecules in aqueous solutions. 201 refs., 84 figs., 19 tabs.
Nonlinear kinetic modeling and simulations of Raman scattering in a two-dimensional geometry
Directory of Open Access Journals (Sweden)
Bénisti Didier
2013-11-01
Full Text Available In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering (SRS by the means of envelope equations, whose coefficients have been derived using a mixture of perturbative and adiabatic calculations. First examples of the numerical resolution of these envelope equations in a two-dimensional homogeneous plasma are given, and the results are compared against those of particle-in-cell (PIC simulations. These preliminary comparisons are encouraging since our envelope code provides threshold intensities consistent with those of PIC simulations while requiring computational resources reduced by 4 to 5 orders of magnitude compared to full-kinetic codes.
Conformal mapping technique for two-dimensional porous media and jet impingement heat transfer
Siegel, R.
1974-01-01
Transpiration cooling and liquid metals both provide highly effective heat transfer. Using Darcy's law in porous media and the inviscid approximation for liquid metals, the local fluid velocity in these flows equals the gradient of a potential. The energy equation and flow region are simplified when transformed into potential plane coordinates. In these coordinates, the present problems are reduced to heat conduction solutions which are mapped into the physical geometry. Results are obtained for a porous region with simultaneously prescribed surface temperature and heat flux, heat transfer in a two-dimensional porous bed, and heat transfer for two liquid metal slot jets impinging on a heated plate.
Zhong, Zhi-Rong
2016-12-05
We construct shortcuts to adiabatic passage to achieve controllable and fast quantum-information transfer (QIT) between arbitrary two distant nodes in a two-dimensional (2D) quantum network. Through suitable designing of time-dependent Rabi frequencies, we show that perfect QIT between arbitrary two distant nodes can be rapidly achieved. Numerical simulations demonstrate that the proposal is robust to the decoherence caused by atomic spontaneous emission and cavity photon leakage. Additionally, the proposed scheme is also insensitive to the variations of the experimental parameters. Thus, the proposed scheme provides a new perspective on robust quantum information processing in 2D quantum networks.
Mathematical description of the two-dimensional Gabor transform. Application to image encryption
Perez, Ronal; Vilardy, Juan M.; Torres, Cesar O.
2017-01-01
Information security with optical processing, such as the double random phase encoding and the Gabor transform (GT) has been investigated by various researchers. We present a two-dimensional (2-D) generalization of the one-dimensional GT. This 2-D GT is applied to encrypt digital images in this paper. The scaling factors of the GT can be used as new keys, providing a new encryption system with a high security characteristics. This method can encrypt and protect the information of the digital images with a high security for information processing systems.
Two-dimensional fluorescence spectroscopy of uranium isotopes in femtosecond laser ablation plumes.
Phillips, Mark C; Brumfield, Brian E; LaHaye, Nicole; Harilal, Sivanandan S; Hartig, Kyle C; Jovanovic, Igor
2017-06-19
We demonstrate measurement of uranium isotopes in femtosecond laser ablation plumes using two-dimensional fluorescence spectroscopy (2DFS). The high-resolution, tunable CW-laser spectroscopy technique clearly distinguishes atomic absorption from 235U and 238U in natural and highly enriched uranium metal samples. We present analysis of spectral resolution and analytical performance of 2DFS as a function of ambient pressure. Simultaneous measurement using time-resolved absorption spectroscopy provides information on temporal dynamics of the laser ablation plume and saturation behavior of fluorescence signals. The rapid, non-contact measurement is promising for in-field, standoff measurements of uranium enrichment for nuclear safety and security.
Two-dimensional fluorescence spectroscopy of uranium isotopes in femtosecond laser ablation plumes
Energy Technology Data Exchange (ETDEWEB)
Phillips, Mark C.; Brumfield, Brian E.; LaHaye, Nicole L.; Harilal, Sivanandan S.; Hartig, Kyle C.; Jovanovic, Igor
2017-06-19
We demonstrate measurement of uranium isotopes in femtosecond laser ablation plumes using two-dimensional fluorescence spectroscopy (2DFS). The high-resolution, tunable CW-laser spectroscopy technique clearly distinguishes atomic absorption from 235U and 238U in natural and highly enriched uranium metal samples. We present analysis of spectral resolution and analytical performance of 2DFS as a function of ambient pressure. Simultaneous measurement using time-resolved absorption spectroscopy provides information on temporal dynamics of the laser ablation plume and saturation behavior of fluorescence signals. The rapid, non-contact measurement is promising for in-field, standoff measurements of uranium enrichment for nuclear safety and security applications.
Guiding of elastic waves in a two-dimensional graded phononic crystal plate
Guo, Yuning; Hettich, Mike; Dekorsy, Thomas
2017-01-01
The guiding of elastic waves in a two-dimensional graded phononic crystal plate is investigated. This effect is induced by the resonance coupling of attachments and matrix in a silicon pillar-substrate system and the resonance frequencies of guided surface modes can be tuned by tailoring the geometry and material properties of the pillars. The resonance frequencies increase with radius and Young’s modulus, and decrease with height and density of the pillars, which provides several possibilities for the guiding of elastic waves. These devices show the capability of spatially selecting different frequencies into designed channels, thus acting as a phononic multi-channel filter.
Schimming, C. D.; Durian, D. J.
2017-09-01
For dry foams, the transport of gas from small high-pressure bubbles to large low-pressure bubbles is dominated by diffusion across the thin soap films separating neighboring bubbles. For wetter foams, the film areas become smaller as the Plateau borders and vertices inflate with liquid. So-called "border-blocking" models can explain some features of wet-foam coarsening based on the presumption that the inflated borders totally block the gas flux; however, this approximation dramatically fails in the wet or unjamming limit where the bubbles become close-packed spheres and coarsening proceeds even though there are no films. Here, we account for the ever-present border-crossing flux by a new length scale defined by the average gradient of gas concentration inside the borders. We compute that it is proportional to the geometric average of film and border thicknesses, and we verify this scaling by numerical solution of the diffusion equation. We similarly consider transport across inflated vertices and surface Plateau borders in quasi-two-dimensional foams. And we show how the d A /d t =K0(n -6 ) von Neumann law is modified by the appearance of terms that depend on bubble size and shape as well as the concentration gradient length scales. Finally, we use the modified von Neumann law to compute the growth rate of the average bubble area, which is not constant.
Two-dimensional materials based transparent flexible electronics
Yu, Lili; Ha, Sungjae; El-Damak, Dina; McVay, Elaine; Ling, Xi; Chandrakasan, Anantha; Kong, Jing; Palacios, Tomas
2015-03-01
Two-dimensional (2D) materials have generated great interest recently as a set of tools for electronics, as these materials can push electronics beyond traditional boundaries. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. These thin, lightweight, bendable, highly rugged and low-power devices may bring dramatic changes in information processing, communications and human-electronic interaction. In this report, for the first time, we demonstrate two complex transparent flexible systems based on molybdenum disulfide (MoS2) grown by chemical vapor method: a transparent active-matrix organic light-emitting diode (AMOLED) display and a MoS2 wireless link for sensor nodes. The 1/2 x 1/2 square inch, 4 x 5 pixels AMOLED structures are built on transparent substrates, containing MoS2 back plane circuit and OLEDs integrated on top of it. The back plane circuit turns on and off the individual pixel with two MoS2 transistors and a capacitor. The device is designed and fabricated based on SPICE simulation to achieve desired DC and transient performance. We have also demonstrated a MoS2 wireless self-powered sensor node. The system consists of as energy harvester, rectifier, sensor node and logic units. AC signals from the environment, such as near-field wireless power transfer, piezoelectric film and RF signal, are harvested, then rectified into DC signal by a MoS2 diode. CIQM, CICS, SRC.
Stable small bubble clusters in two-dimensional foams.
Zhang, Kai; Kuo, Chin-Chang; See, Nathaniel; O'Hern, Corey; Dennin, Michael
2017-06-21
Key features of the mechanical response of amorphous particulate materials, such as foams, emulsions, and granular media, to applied stress are determined by the frequency and size of particle rearrangements that occur as the system transitions from one mechanically stable state to another. This work describes coordinated experimental and computational studies of bubble rafts, which are quasi-two dimensional systems of bubbles confined to the air-water interface. We focus on small mechanically stable clusters of four, five, six, and seven bubbles with two different sizes with diameter ratio σL/σS ≃ 1.4. Focusing on small bubble clusters, which can be viewed as subsystems of a larger system, allows us to investigate the full ensemble of clusters that form, measure the respective frequencies with which the clusters occur, and determine the form of the bubble-bubble interactions. We emphasize several important results. First, for clusters with N > 5 bubbles, we find using discrete element simulations that short-range attractive interactions between bubbles give rise to a larger ensemble of distinct mechanically stable clusters compared to that generated by long-range attractive interactions. The additional clusters in systems with short-range attractions possess larger gaps between pairs of neighboring bubbles on the periphery of the clusters. The ensemble of bubble clusters observed in experiments is similar to the ensemble of clusters with long-range attractive interactions. We also compare the frequency with which each cluster occurs in simulations and experiments. We find that the cluster frequencies are extremely sensitive to the protocol used to generate them and only weakly correlated to the energy of the clusters.
Green's function for a generalized two-dimensional fluid.
Iwayama, Takahiro; Watanabe, Takeshi
2010-09-01
A Green's function for a generalized two-dimensional (2D) fluid in an unbounded domain (the so-called α turbulence system) is discussed. The generalized 2D fluid is characterized by a relationship between an advected quantity q and the stream function ψ : namely, q=-(-Δ){α/2}ψ . Here, α is a real number and q is referred to as the vorticity. In this study, the Green's function refers to the stream function produced by a delta-functional distribution of q , i.e., a point vortex with unit strength. The Green's function has the form G{(α)}(r)∝r{α-2} , except when α is an even number, where r is the distance from the point vortex. This functional form is known as the Riesz potential. When α is a positive even number, the logarithmic correction to the Riesz potential has the form G(r){(α)}∝r{α-2} ln r . In contrast, when α is a negative even number, G{(α)} is given by the higher-order Laplacian of the delta function. The transition of the small-scale behavior of q at α=2 , a well-known property of forced and dissipative α turbulence, is explained in terms of the Green's function. Moreover, the azimuthal velocity around the point vortex is derived from the Green's function. The functional form of the azimuthal velocity indicates that physically realizable systems for the generalized 2D fluid exist only when α≤3 . The Green's function and physically realizable systems for an anisotropic generalized 2D fluid are presented as an application of the present study.
A Laboratory Model of two-dimensional Granular Collisions
Burton, J. C.; Nagel, S.
2011-12-01
Many astrophysical and geophysical processes involve repeated inelastic collisions between discrete granular particles in large-scale flows. Every time the particles collide with one another they lose kinetic energy so that the system cools over time. Examples include the clustering of particles in a granular gas [1], flow in avalanches [2], and the catastrophic collapse of Antarctic ice-shelves [3]. In order to investigate such inelastic, many-particle, systems, we have studied ~2000 particles moving on a two-dimensional, 90 cm x 90 cm, anodized aluminum plate. Our particles are composed of dry ice (solid carbon dioxide) pellets with diameter ~0.5 cm. When placed on a heated flat surface, the pellets float on a cushion of sublimated gas, so that they move in two dimensions essentially without friction. Over time (~ 1 minute), the particles slowly lose mass until they have completely disappeared. Collisions with the plate boundaries are made elastic by sloping the plate's edges slightly upward. The experiment is filmed from above with a high-speed digital camera, so that translational and rotational kinetic energy of each particle can be tracked over time. Our results show qualitative clustering of pellets into regions where many collisions occur, as expected from models of inelastic gases [4]. We will show the results for different initial conditions including "clouds" of pellets colliding with each other at different initial impact velocities. [1] I. Goldhirsch and G. Zanetti, Phys. Rev. Lett. 70, 1619 (1993); S. McNamara and W.R. Young. Phys. Rev. E 50, R28 (1994). [2] P. Bartelt and O. Buser, Ann. Glaciol. 51, 98 (2010). [3] N. Guttenberg et al., Ann. Glaciol. 52, 51 (2011). [4] For a review see: I. Goldhirsch, Annu. Rev. Fluid Mech. 35, 267 (2003).
Electronic, Spin and Valley Transport in Two Dimensional Dirac Systems
Xu, Hongya
This dissertation aims to study and understand relevant issues related to the electronic, spin and valley transport in two-dimensional Dirac systems for different given physical settings. In summary, four key findings are achieved. First, studying persistent currents in confined chaotic Dirac fermion systems with a ring geometry and an applied Aharonov-Bohm flux, unusual whispering-gallery modes with edge-dependent currents and spin polarization are identified. They can survive for highly asymmetric rings that host fully developed classical chaos. By sustaining robust persistent currents, these modes can be utilized to form a robust relativistic quantum two-level system. Second, the quantized topological edge states in confined massive Dirac fermion systems exhibiting a remarkable reverse Stark effect in response to an applied electric field, and an electrically or optically controllable spin switching behavior are uncovered. Third, novel wave scattering and transport in Dirac-like pseudospin-1 systems are reported. (a), for small scatterer size, a surprising revival resonant scattering with a peculiar boundary trapping by forming unusual vortices is uncovered. Intriguingly, it can persist in arbitrarily weak scatterer strength regime, which underlies a superscattering behavior beyond the conventional scenario. (b), for larger size, a perfect caustic phenomenon arises as a manifestation of the super-Klein tunneling effect. (c), in the far-field, an unexpected isotropic transport emerges at low energies. Fourth, a geometric valley Hall effect (gVHE) originated from fractional singular Berry flux is revealed. It is shown that gVHE possesses a nonlinear dependence on the Berry flux with asymmetrical resonance features and can be considerably enhanced by electrically controllable resonant valley skew scattering. With the gVHE, efficient valley filtering can arise and these phenomena are robust against thermal fluctuations and disorder averaging.
Quantum holographic encoding in a two-dimensional electron gas
Energy Technology Data Exchange (ETDEWEB)
Moon, Christopher
2010-05-26
The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.
HASHING ALGORITHM BASED ON TWO-DIMENSIONAL CHAOTIC MAPPINGS
Directory of Open Access Journals (Sweden)
A. V. Sidorenko
2017-01-01
Full Text Available A new hashing algorithm based on dynamic chaos is proposed. Owing to the use of chaotic mappings, this algorithm is irreversible and a search for two messages with identical hash-values becomes computationally difficult. The proposed algorithm consists of the stages: selection of the variables and of the parameters of two-dimensional chaotic mappings; realization of iterations of the chaotic mappings with the addition of the original-message elements to the variables; realization of iterations of the chaotic mappings without the addition of the original-message elements to the variables; the hash-value formation. The formation of the two hash-values h1 and h2realized with different orders of the variables. The resultant hash-value is obtained by the modulo-2 addition operation applied to the hash-values h1 and h2. The proposed algorithm has been tested. It has been found that this algorithm is characterized by the avalanche effect. The statistical characteristics of the sequence formed of hash-values are identical to those of the sequence with the randomly obtained values of the elements, pointing to the adequate performance of this algorithm. The computational experiment has been realized using the Chirikov, «Arnold’s cat» and Henon maps. It is demonstrated that, with the use of Henon and «Arnold’s cat» maps for the messages exceeding 4 KB, the proposed algorithm outperforms «Keccak» algorithm, being faster by 20% and more.The proposed hashing algorithm may be used in solving the problems of data integrity in modern telecommunication systems.
DEFF Research Database (Denmark)
Harbo, Anders La-Cour
2004-01-01
in the same two-dimensional plane. The model is based on geometrical observations and provides a mapping of the measured reflected intensities to spatial position. The mapping is derived from intersection sets of prolate spheroids with emitters and receivers in the focal points, and it is shown...
DEFF Research Database (Denmark)
Chen, Yunzhong; Green, Robert J.; Sutarto, Ronny
2017-01-01
Polar discontinuities and redox reactions provide alternative paths to create two-dimensional electron liquids (2DELs) at oxide interfaces. Herein, we report high mobility 2DELs at interfaces involving SrTiO3 (STO) achieved using polar La7/8Sr1/8MnO3 (LSMO) buffer layers to manipulate both...
Efremov, MA; Petropavlovsky, SV; Fedorov, MV; Schleich, WP; Yakovlev, VP
The formation of two-dimensional nonspreading atomic wave packets produced in the interaction of a beam of two-level atoms with two standing light waves polarised in the same plane is considered. The mechanism providing a dispersionless particle dynamics is the balance of two processes: a rapid
Consistent two-dimensional visualization of protein-ligand complex series
Directory of Open Access Journals (Sweden)
Stierand Katrin
2011-06-01
Full Text Available Abstract Background The comparative two-dimensional graphical representation of protein-ligand complex series featuring different ligands bound to the same active site offers a quick insight in their binding mode differences. In comparison to arbitrary orientations of the residue molecules in the individual complex depictions a consistent placement improves the legibility and comparability within the series. The automatic generation of such consistent layouts offers the possibility to apply it to large data sets originating from computer-aided drug design methods. Results We developed a new approach, which automatically generates a consistent layout of interacting residues for a given series of complexes. Based on the structural three-dimensional input information, a global two-dimensional layout for all residues of the complex ensemble is computed. The algorithm incorporates the three-dimensional adjacencies of the active site residues in order to find an universally valid circular arrangement of the residues around the ligand. Subsequent to a two-dimensional ligand superimposition step, a global placement for each residue is derived from the set of already placed ligands. The method generates high-quality layouts, showing mostly overlap-free solutions with molecules which are displayed as structure diagrams providing interaction information in atomic detail. Application examples document an improved legibility compared to series of diagrams whose layouts are calculated independently from each other. Conclusions The presented method extends the field of complex series visualizations. A series of molecules binding to the same protein active site is drawn in a graphically consistent way. Compared to existing approaches these drawings substantially simplify the visual analysis of large compound series.
Interfacial engineering of two-dimensional nano-structured materials by atomic layer deposition
Energy Technology Data Exchange (ETDEWEB)
Zhuiykov, Serge, E-mail: serge.zhuiykov@ugent.be [Ghent University Global Campus, Department of Applied Analytical & Physical Chemistry, Faculty of Bioscience Engineering, 119 Songdomunhwa-ro, Yeonsu-Gu, Incheon 406-840 (Korea, Republic of); Kawaguchi, Toshikazu [Global Station for Food, Land and Water Resources, Global Institution for Collaborative Research and Education, Hokkaido University, N10W5 Kita-ku, Sapporo, Hokkaido 060-0810 (Japan); Graduate School of Environmental Science, Hokkaido University, N10W5 Kita-ku, Sapporo, Hokkaido 060-0810 (Japan); Hai, Zhenyin; Karbalaei Akbari, Mohammad; Heynderickx, Philippe M. [Ghent University Global Campus, Department of Applied Analytical & Physical Chemistry, Faculty of Bioscience Engineering, 119 Songdomunhwa-ro, Yeonsu-Gu, Incheon 406-840 (Korea, Republic of)
2017-01-15
Highlights: • Advantages of atomic layer deposition technology (ALD) for two-dimensional nano-crystals. • Conformation of ALD technique and chemistry of precursors. • ALD of semiconductor oxide thin films. • Ultra-thin (∼1.47 nm thick) ALD-developed tungsten oxide nano-crystals on large area. - Abstract: Atomic Layer Deposition (ALD) is an enabling technology which provides coating and material features with significant advantages compared to other existing techniques for depositing precise nanometer-thin two-dimensional (2D) nanostructures. It is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. ALD is especially advantageous when the film quality or thickness is critical, offering ultra-high aspect ratios. ALD provides digital thickness control to the atomic level by depositing film one atomic layer at a time, as well as pinhole-free films even over a very large and complex areas. Digital control extends to sandwiches, hetero-structures, nano-laminates, metal oxides, graded index layers and doping, and it is perfect for conformal coating and challenging 2D electrodes for various functional devices. The technique’s capabilities are presented on the example of ALD-developed ultra-thin 2D tungsten oxide (WO{sub 3}) over the large area of standard 4” Si substrates. The discussed advantages of ALD enable and endorse the employment of this technique for the development of hetero-nanostructure 2D semiconductors with unique properties.
The application of digital image recognition to the analysis of two-dimensional fingerprints.
Zhai, Hong Lin; Hu, Fang Di; Huang, Xiao Yan; Chen, Jun Hui
2010-01-11
High-performance liquid chromatography (HPLC) fingerprint has been commonly used in the quality control and assessment of herbal medicines, and two-dimensional (2D) fingerprint obtained by means of HPLC-diode array detector (HPLC/DAD) can provide higher reliability. In this paper, an approach to the analysis of the 2D HPLC/DAD fingerprints, which was based on digital image recognition techniques, was developed for the first time. First, wavelet transform was employed to eliminate noise signal in the 2D fingerprint, and then the 2D fingerprint was converted into grayscale image. Second, several features of the image were calculated, and hierarchical clustering. This approach was applied to the qualitative analysis of the different samples of coptis chinensis, and the clustering result of samples was all highly consistent with the real situation. Based on the densities in grayscale image, three components in standard samples were quantitative analyzed, and the obtained correlation coefficients between concentration and grayscale density were more than 0.999. Our study indicated that the analysis of the 2D HPLC/DAD fingerprint was successful based on the idea and techniques of digital image recognition techniques, and this proposed approach provided a new pathway for the analysis of two-dimensional spectrums.
Error compensation of IQ modulator using two-dimensional DFT
Energy Technology Data Exchange (ETDEWEB)
Ohshima, Takashi, E-mail: ohshima@spring8.or.jp [RIKEN, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Maesaka, Hirokazu [RIKEN, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Matsubara, Shinichi [Japan Synchrotron Radiation Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Otake, Yuji [RIKEN, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan)
2016-06-01
It is important to precisely set and keep the phase and amplitude of an rf signal in the accelerating cavity of modern accelerators, such as an X-ray Free Electron Laser (XFEL) linac. In these accelerators an acceleration rf signal is generated or detected by an In-phase and Quadrature (IQ) modulator, or a demodulator. If there are any deviations of the phase and the amplitude from the ideal values, crosstalk between the phase and the amplitude of the output signal of the IQ modulator or the demodulator arises. This causes instability of the feedback controls that simultaneously stabilize both the rf phase and the amplitude. To compensate for such deviations, we developed a novel compensation method using a two-dimensional Discrete Fourier Transform (DFT). Because the observed deviations of the phase and amplitude of an IQ modulator involve sinusoidal and polynomial behaviors on the phase angle and the amplitude of the rf vector, respectively, the DFT calculation with these basis functions makes a good approximation with a small number of compensation coefficients. Also, we can suppress high-frequency noise components arising when we measure the deviation data. These characteristics have advantages compared to a Look Up Table (LUT) compensation method. The LUT method usually demands many compensation elements, such as about 300, that are not easy to treat. We applied the DFT compensation method to the output rf signal of a C-band IQ modulator at SACLA, which is an XFEL facility in Japan. The amplitude deviation of the IQ modulator after the DFT compensation was reduced from 15.0% at the peak to less than 0.2% at the peak for an amplitude control range of from 0.1 V to 0.9 V (1.0 V full scale) and for a phase control range from 0 degree to 360 degrees. The number of compensation coefficients is 60, which is smaller than that of the LUT method, and is easy to treat and maintain.
Manning’s equation and two-dimensional flow analogs
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
Converting Panax ginseng DNA and chemical fingerprints into two-dimensional barcode.
Cai, Yong; Li, Peng; Li, Xi-Wen; Zhao, Jing; Chen, Hai; Yang, Qing; Hu, Hao
2017-07-01
In this study, we investigated how to convert the Panax ginseng DNA sequence code and chemical fingerprints into a two-dimensional code. In order to improve the compression efficiency, GATC2Bytes and digital merger compression algorithms are proposed. HPLC chemical fingerprint data of 10 groups of P. ginseng from Northeast China and the internal transcribed spacer 2 (ITS2) sequence code as the DNA sequence code were ready for conversion. In order to convert such data into a two-dimensional code, the following six steps were performed: First, the chemical fingerprint characteristic data sets were obtained through the inflection filtering algorithm. Second, precompression processing of such data sets is undertaken. Third, precompression processing was undertaken with the P. ginseng DNA (ITS2) sequence codes. Fourth, the precompressed chemical fingerprint data and the DNA (ITS2) sequence code were combined in accordance with the set data format. Such combined data can be compressed by Zlib, an open source data compression algorithm. Finally, the compressed data generated a two-dimensional code called a quick response code (QR code). Through the abovementioned converting process, it can be found that the number of bytes needed for storing P. ginseng chemical fingerprints and its DNA (ITS2) sequence code can be greatly reduced. After GTCA2Bytes algorithm processing, the ITS2 compression rate reaches 75% and the chemical fingerprint compression rate exceeds 99.65% via filtration and digital merger compression algorithm processing. Therefore, the overall compression ratio even exceeds 99.36%. The capacity of the formed QR code is around 0.5k, which can easily and successfully be read and identified by any smartphone. P. ginseng chemical fingerprints and its DNA (ITS2) sequence code can form a QR code after data processing, and therefore the QR code can be a perfect carrier of the authenticity and quality of P. ginseng information. This study provides a theoretical
Mehlenbacher, Randy D; McDonough, Thomas J; Grechko, Maksim; Wu, Meng-Yin; Arnold, Michael S; Zanni, Martin T
2015-04-13
Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Förster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap separation, whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.
Boundary Layer Receptivity to Three-Dimensional Freestream Disturbances at Two-Dimensional Roughness
Dietz, Anthony; Sheehan, Daniel; Davis, Sanford (Technical Monitor)
1997-01-01
The receptivity of a laminar boundary layer to an isolated three-dimensional convected disturbance is investigated in a low-speed wind tunnel experiment. The disturbance is created by the short-duration pulsed displacement of a small low-aspect-ratio wing located upstream of a flat plate. The height of the wing is set so that the convected disturbance grazes the edge of the flat-plate boundary layer. A receptivity site is provided by a two-dimensional roughness strip on the surface of the plate. The different propagation speeds of acoustic, convected and instability waves cause the various wave packets from the pulsed displacement to arrive at a downstream measurement station at different times, separating the phenomena and allowing them to be studied independently. Ensemble- averaged measurements are made with and without roughness on the plate. Preliminary analysis of the measurements suggest the presence of a two-dimensional T-S wave packet arising from an interaction between an acoustic wave and the roughness, and a three-dimensional T-S wave packet arising from an interaction between the localized convected disturbance and the roughness strip. The growth rates and spatial characteristics of the disturbances and the instability wave packets are measured as they propagate downstream.
Two-dimensional concentrated-stress low-frequency piezoelectric vibration energy harvesters
Sharpes, Nathan; Abdelkefi, Abdessattar; Priya, Shashank
2015-08-01
Vibration-based energy harvesters using piezoelectric materials have long made use of the cantilever beam structure. Surmounting the deficiencies in one-dimensional cantilever-based energy harvesters has been a major focus in the literature. In this work, we demonstrate a strategy of using two-dimensional beam shapes to harvest energy from low frequency excitations. A characteristic Zigzag-shaped beam is created to compare against the two proposed two-dimensional beam shapes, all of which occupy a 25.4 × 25.4 mm2 area. In addition to maintaining the low-resonance bending frequency, the proposed beam shapes are designed with the goal of realizing a concentrated stress structure, whereby stress in the beam is concentrated in a single area where a piezoelectric layer may be placed, rather than being distributed throughout the beam. It is shown analytically, numerically, and experimentally that one of the proposed harvesters is able to provide significant increase in power production, when the base acceleration is set equal to 0.1 g, with only a minimal change in the resonant frequency compared to the current state-of-the-art Zigzag shape. This is accomplished by eliminating torsional effects, producing a more pure bending motion that is necessary for high electromechanical coupling. In addition, the proposed harvesters have a large effective beam tip whereby large tip mass may be placed while retaining a low-profile, resulting in a low volume harvester and subsequently large power density.
Reichenbach, Stephen E.; Ni, Mingtian; Kottapalli, Visweswara; Visvanathan, Arvind; Ledford, Edward B., Jr.; Oostdijk, John; Trap, Henk C.
2003-08-01
Comprehensive two-dimensional gas chromatography (GCxGC) is an emerging technology for chemical separation that provides an order-of-magnitude increase in separation capacity over traditional gas chromatography. GCxGC separates chemical species with two capillary columns interfaced by two-stage thermal desorption. Because GCxGC is comprehensive and has high separation capacity, it can perform multiple traditional analytical methods with a single analysis. GCxGC has great potential for a wide variety of environmental sensing applications, including detection of chemical warfare agents (CWA) and other harmful chemicals. This paper demonstrates separation of nerve agents sarin and soman from a matrix of gasoline and diesel fuel. Using a combination of an initial column separating on the basis of boiling point and a second column separating on the basis of polarity, GCxGC clearly separates the nerve agents from the thousands of other chemicals in the sample. The GCxGC data is visualized, processed, and analyzed as a two-dimensional digital image using a software system for GCxGC image processing developed at the University of Nebraska - Lincoln.
Camargo, Franco V A; Anderson, Harry L; Meech, Stephen R; Heisler, Ismael A
2015-01-08
In this work we present experimental and calculated two-dimensional electronic spectra for a 5,15-bisalkynyl porphyrin chromophore. The lowest energy electronic Qy transition couples mainly to a single 380 cm(-1) vibrational mode. The two-dimensional electronic spectra reveal diagonal and cross peaks which oscillate as a function of population time. We analyze both the amplitude and phase distribution of this main vibronic transition as a function of excitation and detection frequencies. Even though Feynman diagrams provide a good indication of where the amplitude of the oscillating components are located in the excitation-detection plane, other factors also affect this distribution. Specifically, the oscillation corresponding to each Feynman diagram is expected to have a phase that is a function of excitation and detection frequencies. Therefore, the overall phase of the experimentally observed oscillation will reflect this phase dependence. Another consequence is that the overall oscillation amplitude can show interference patterns resulting from overlapping contributions from neighboring Feynman diagrams. These observations are consistently reproduced through simulations based on third order perturbation theory coupled to a spectral density described by a Brownian oscillator model.
Philen, Michael K.; Wang, K. W.
2004-04-01
A substantial amount of research exists concerning shape control of two-dimensional optical mirror structures with attached piezoelectric ceramic sheet actuators. Researchers have investigated the optimal placement, size, and electrode pattern of the piezoceramic actuators for maximizing the system performance. In many situations, the performance could be further improved with tailoring of the actuator configuration. For example, it was found that to avoid 'exciting' higher order deformation modes (the wrinkling effect) in two-dimensional structures, the ideal actuator would be one that is directionally decoupled, i.e., only actuates in one direction when controlling certain deformation modes of interest. The active stiffener (AS) concept has been proposed to realize such an effect, where a stiffener is inserted between a host structure and the piezoelectric ceramic actuator patch. The objective of the research presented in this paper is to develop a local analysis of the AS actuator to gain good insight into its characteristics and determine parameters that can best achieve the decoupling actions. Using a three-dimensional finite element model, analyses of a single active stiffener attached to rigid and flexible host structures are presented. The effects of various material and system parameters on the bending moments applied to the host structure are illustrated. It is shown that, with proper design, the active stiffener can significantly reduce the bending moment (active authority) in a selected direction while maintaining sufficient authority in the orthogonal direction. The results of this investigation should provide valuable guidelines for the design of effective AS actuators.
Energy Technology Data Exchange (ETDEWEB)
Kocharian, Armen N. [Department of Physics, California State University, Los Angeles, CA 90032 (United States); Fernando, Gayanath W.; Fang, Kun [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Palandage, Kalum [Department of Physics, Trinity College, Hartford, Connecticut 06106 (United States); Balatsky, Alexander V. [AlbaNova University Center Nordita, SE-106 91 Stockholm (Sweden)
2016-05-15
Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges and opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.
Directory of Open Access Journals (Sweden)
Armen N. Kocharian
2016-05-01
Full Text Available Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges and opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.
Two-dimensional correlation spectroscopy in protein science, a summary for past 20years.
Wu, Yuqing; Zhang, Liping; Jung, Young Mee; Ozaki, Yukihiro
2018-01-15
Two-dimensional correlation spectroscopy (2DCOS) has been widely used to Infrared, Raman, Near IR, Optical Activity (ROA), Vibrational Circular Dichroism (VCD) and Fluorescence spectroscopy. In addition, several new developments, such as 2D hetero-correlation analysis, moving-window two-dimensional (MW2D) correlation, model based correlation (βν and kν correlation analyses) have also well incorporated into protein research. They have been used to investigate secondary structure, denaturation, folding and unfolding changes of protein, and have contributed greatly to the field of protein science. This review provides an overview of the applications of 2DCOS in the field of protein science for the past 20 year, especially to memory our old friend, Dr. Boguslawa Czarnik-Matusewicz, for her great contribution in this research field. The powerful utility of 2DCOS combined with various analytical techniques in protein studies is summarized. The noteworthy developments and perspective of 2DCOS in this field are highlighted finally. Copyright © 2017 Elsevier B.V. All rights reserved.
Two-dimensional Kikuchi patterns of Si as measured using an electrostatic analyser
Energy Technology Data Exchange (ETDEWEB)
Vos, Maarten, E-mail: maarten.vos@anu.edu.au [Electronic Materials Engineering Department, Research School of Physics and Engineering, The Australian National University, Canberra 2601 (Australia); Winkelmann, Aimo [Bruker Nano GmbH, Am Studio 2D, Berlin 12489 (Germany)
2016-12-15
We present Kikuchi patterns of Si single crystals measured with an electrostatic analyser, where the kinetic energy of the diffracted electron is known with sub-eV precision. Two-dimensional patterns are acquired by rotating the crystal under computer control. This makes detailed comparison of calculated and measured distributions possible with precise knowledge of the energy of the scattered electrons. The case of Si is used to validate the method, and these experiments provide a detailed comparison of measured and calculated Kikuchi patterns. In this way, we can gain more insight on Kikuchi pattern formation in non-energy resolved measurements of conventional electron backscatter diffraction (EBSD) and electron channeling patterns (ECP). It was possible to identify the influence of channeling of the incoming beam on the measured Kikuchi pattern. The effect of energy loss on the Kikuchi pattern was established, and it is demonstrated that, under certain conditions, the channeling features have a different dependence on the energy loss compared to the Kikuchi lines. - Highlights: • Two-dimensional Kikuchi patterns measured for Silicon with electrostatic analyser. • Good agreement obtained with dynamical theory of diffraction. • Channeling effects of the incoming beam are identified.
Two-dimensional thermal analysis of a fuel rod by finite volume method
Energy Technology Data Exchange (ETDEWEB)
Costa, Rhayanne Y.N.; Silva, Mario A.B. da; Lira, Carlos A.B. de O., E-mail: ryncosta@gmail.com, E-mail: mabs500@gmail.com, E-mail: cabol@ufpe.br [Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Departamaento de Energia Nuclear
2015-07-01
In a nuclear reactor, the amount of power generation is limited by thermal and physic limitations rather than by nuclear parameters. The operation of a reactor core, considering the best heat removal system, must take into account the fact that the temperatures of fuel and cladding shall not exceed safety limits anywhere in the core. If such considerations are not considered, damages in the fuel element may release huge quantities of radioactive materials in the coolant or even core meltdown. Thermal analyses for fuel rods are often accomplished by considering one-dimensional heat diffusion equation. The aim of this study is to develop the first paper to verify the temperature distribution for a two-dimensional heat transfer problem in an advanced reactor. The methodology is based on the Finite Volume Method (FVM), which considers a balance for the property of interest. The validation for such methodology is made by comparing numerical and analytical solutions. For the two-dimensional analysis, the results indicate that the temperature profile agree with expected physical considerations, providing quantitative information for the development of advanced reactors. (author)
Pursuing two-dimensional nanomaterials for flexible lithium-ion batteries
Energy Technology Data Exchange (ETDEWEB)
Liu, Bin; Zhang, Ji-Guang; Shen, Guozhen
2016-02-01
Stretchable/flexible electronics provide a foundation for various emerging applications that beyond the scope of conventional wafer/circuit board technologies due to their unique features that can satisfy a broad range of applications such as wearable devices. Stretchable electronic and optoelectronics devices require the bendable/wearable rechargeable Li-ion batteries, thus these devices can operate without limitation of external powers. Various two-dimensional (2D) nanomaterials are of great interest in flexible energy storage devices, especially Li-ion batteries. This is because 2D materials exhibit much more exposed surface area supplying abundant Li-insertion channels and shortened paths for fast lithium ion diffusion. Here, we will review the recent developments on the flexible Li-ion batteries based on two dimensional nanomaterials. These researches demonstrated advancements in flexible electronics by incorporating various 2D nanomaterials into bendable batteries to achieve high electrochemical performance, excellent mechanical flexibility as well as electrical stability under stretching/bending conditions.
Li, Zejun; Zhao, Yingcheng; Mu, Kejun; Shan, Huan; Guo, Yuqiao; Wu, Jiajing; Su, Yueqi; Wu, Qiran; Sun, Zhe; Zhao, Aidi; Cui, Xuefeng; Wu, Changzheng; Xie, Yi
2017-11-15
Superconductivity is mutually exclusive with ferromagnetism, because the ferromagnetic exchange field is often destructive to superconducting pairing correlation. Well-designed chemical and physical methods have been devoted to realize their coexistence only by structural integrity of inherent superconducting and ferromagnetic ingredients. However, such coexistence in freestanding structure with nonsuperconducting and nonferromagnetic components still remains a great challenge up to now. Here, we demonstrate a molecule-confined engineering in two-dimensional organic-inorganic superlattice using a chemical building-block approach, successfully realizing first freestanding coexistence of superconductivity and ferromagnetism originated from electronic interactions of nonsuperconducting and nonferromagnetic building blocks. We unravel totally different electronic behavior of molecules depending on spatial confinement: flatly lying Co(Cp)2 molecules in strongly confined SnSe2 interlayers weaken the coordination field, leading to spin transition to form ferromagnetism; meanwhile, electron transfer from cyclopentadienyls to the Se-Sn-Se lattice induces superconducting state. This entirely new class of coexisting superconductivity and ferromagnetism generates a unique correlated state of Kondo effect between the molecular ferromagnetic layers and inorganic superconducting layers. We anticipate that confined molecular chemistry provides a newly powerful tool to trigger exotic chemical and physical properties in two-dimensional matrixes.
Spatially Resolved Two-Dimensional Infrared Spectroscopy via Wide-Field Microscopy.
Ostrander, Joshua S; Serrano, Arnaldo L; Ghosh, Ayanjeet; Zanni, Martin T
2016-07-20
We report the first wide-field microscope for measuring two-dimensional infrared (2D IR) spectroscopic images. We concurrently collect more than 16 000 2D IR spectra, made possible by a new focal plane array detector and mid-IR pulse shaping, to generate hyperspectral images with multiple frequency dimensions and diffraction-limited spatial resolution. Both frequency axes of the spectra are collected in the time domain by scanning two pairs of femtosecond pulses using a dual acousto-optic modulator pulse shaper. The technique is demonstrated by imaging a mixture of metal carbonyl absorbed polystyrene beads. The differences in image formation between FTIR and 2D IR microscopy are also explored by imaging a patterned USAF test target. We find that our 2D IR microscope has diffraction-limited spatial resolution and enhanced contrast compared to FTIR microscopy because of the nonlinear scaling of the 2D IR signal to the absorptivity coefficient for the vibrational modes. Images generated using off-diagonal peaks, created from vibrational anharmonicities, improve the molecular discrimination and eliminate noise. Two-dimensional wide-field IR microscopy provides information on vibrational lifetimes, molecular couplings, transition dipole orientations, and many other quantities that can be used for creating image contrast to help disentangle and interpret complex and heterogeneous samples. Such experiments made possible could include the study of amyloid proteins in tissues, protein folding in heterogeneous environments, and structural dynamics in devices employing mid-IR materials.
A simple, robust orthogonal background correction method for two-dimensional liquid chromatography.
Filgueira, Marcelo R; Castells, Cecilia B; Carr, Peter W
2012-08-07
Background correction is a very important step that must be performed before peak detection or any quantification procedure. When successful, this step greatly simplifies such procedures and enhances the accuracy of quantification. In the past, much effort has been invested to correct drifting baseline in one-dimensional chromatography. In fast online comprehensive two-dimensional liquid chromatography (LC×LC) coupled with a diode array detector (DAD), the change in the refractive index (RI) of the mobile phase in very fast gradients causes extremely serious baseline disturbances. The method reported here is based on the use of various existing baseline correction methods of one-dimensional (1D) liquid chromatography to correct the two-dimensional (2D) background in LC×LC. When such methods are applied orthogonally to the second dimension ((2)D), background correction is dramatically improved. The method gives an almost zero mean background level and it provides better background correction than does simple subtraction of a blank. Indeed, the method proposed does not require running a blank sample.
A binary motor imagery tasks based brain-computer interface for two-dimensional movement control
Xia, Bin; Cao, Lei; Maysam, Oladazimi; Li, Jie; Xie, Hong; Su, Caixia; Birbaumer, Niels
2017-12-01
Objective. Two-dimensional movement control is a popular issue in brain–computer interface (BCI) research and has many applications in the real world. In this paper, we introduce a combined control strategy to a binary class-based BCI system that allows the user to move a cursor in a two-dimensional (2D) plane. Users focus on a single moving vector to control 2D movement instead of controlling vertical and horizontal movement separately. Approach. Five participants took part in a fixed-target experiment and random-target experiment to verify the effectiveness of the combination control strategy under the fixed and random routine conditions. Both experiments were performed in a virtual 2D dimensional environment and visual feedback was provided on the screen. Main results. The five participants achieved an average hit rate of 98.9% and 99.4% for the fixed-target experiment and the random-target experiment, respectively. Significance. The results demonstrate that participants could move the cursor in the 2D plane effectively. The proposed control strategy is based only on a basic two-motor imagery BCI, which enables more people to use it in real-life applications.
Ferroelectric FET for nonvolatile memory application with two-dimensional MoSe2 channels
Wang, Xudong; Liu, Chunsen; Chen, Yan; Wu, Guangjian; Yan, Xiao; Huang, Hai; Wang, Peng; Tian, Bobo; Hong, Zhenchen; Wang, Yutao; Sun, Shuo; Shen, Hong; Lin, Tie; Hu, Weida; Tang, Minghua; Zhou, Peng; Wang, Jianlu; Sun, Jinglan; Meng, Xiangjian; Chu, Junhao; Li, Zheng
2017-06-01
Graphene and other two-dimensional materials have received considerable attention regarding their potential applications in nano-electronics. Here, we report top-gate nonvolatile memory field-effect transistors (FETs) with different layers of MoSe2 nanosheets channel gated by ferroelectric film. The conventional gate dielectric of FETs was replaced by a ferroelectric thin film that provides a ferroelectric polarization electric field, and therefore defined as an Fe-FET where the poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was used as the gate dielectric. Among the devices with MoSe2 channels of different thicknesses, the device with a single layer of MoSe2 exhibited a large hysteresis of electronic transport with an over 105 write/erase ratio, and displayed excellent retention and endurance performance. The possible mechanism of the device’s good properties was qualitatively analyzed using band theory. Additionally, a comprehensive study comparing the memory properties of MoSe2 channels of different thicknesses is presented. Increasing the numbers of MoSe2 layers was found to cause a reduced memory window. However, MoSe2 thickness of 5 nm yielded a write/erase ratio of more than 103. The results indicate that, based on a Fe-FET structure, the combination of two-dimensional semiconductors and organic ferroelectric gate dielectrics shows good promise for future applications in nonvolatile ferroelectric memory.
The origin of two-dimensional electron gases at oxide interfaces: insights from theory.
Bristowe, N C; Ghosez, Philippe; Littlewood, P B; Artacho, Emilio
2014-04-09
The response of oxide thin films to polar discontinuities at interfaces and surfaces has generated enormous activity due to the variety of interesting effects that it gives rise to. A case in point is the discovery of the electron gas at the interface between LaAlO3 and SrTiO3, which has since been shown to be quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite these findings, the origin of the two-dimensional electron gas is highly debated and several possible mechanisms remain. Here we review the main proposed mechanisms and attempt to model expected effects in a quantitative way with the ambition of better constraining what effects can/cannot explain the observed phenomenology. We do it in the framework of a phenomenological model constructed to provide an understanding of the electronic and/or redox screening of the chemical charge in oxide heterostructures. We also discuss the effect of intermixing, both conserving and not conserving the total stoichiometry.
Results from laboratory tests of the two-dimensional Time-Encoded Imaging System.
Energy Technology Data Exchange (ETDEWEB)
Marleau, Peter; Brennan, James S.; Brubaker, Erik; Gerling, Mark D; Le Galloudec, Nathalie Joelle
2014-09-01
A series of laboratory experiments were undertaken to demonstrate the feasibility of two dimensional time-encoded imaging. A prototype two-dimensional time encoded imaging system was designed and constructed. Results from imaging measurements of single and multiple point sources as well as extended source distributions are presented. Time encoded imaging has proven to be a simple method for achieving high resolution two-dimensional imaging with potential to be used in future arms control and treaty verification applications.
Two-dimensional imaginary lobachevsky space. Separation of variables and contractions
Energy Technology Data Exchange (ETDEWEB)
Pogosyan, G. S., E-mail: pogosyan@theor.jinr.ru; Yakhno, A. [Universidad de Guadalajara, Departamento de Matematicas, CUCEI (Mexico)
2011-07-15
The Inoenue-Wigner contraction from the SO(2, 1) group to the E(1, 1) group is used to relate the separation of variables in Laplace-Beltrami (Helmholtz) equations for the corresponding two-dimensional homogeneous spaces: two-dimensional one sheeted hyperboloid and two-dimensional pseudo-Euclidean space. Here we consider the contraction limits of some basis functions for the subgroup coordinates only.
Two-dimensional gel proteomic analysis of Dermatophagoides farinae feces.
Erban, Tomas; Hubert, Jan
2015-01-01
Dermatophagoides farinae fecal allergens are a major source of immunogens in home environments; however, as the source of mite fecal allergen is considered spent growth medium extract that can only mimic the pure fecal extract. In this study, we prepared and using proteomic methods analyzed a D. farinae fecal extract for the first time. The preparation approach used D. farinae feces that were produced within 8 weeks of initiating cultivation in minimized growth media. The feces were collected via adhesion to the tissue culture flask surfaces after removing the SGM and mites. This study contains in-depth proteomic mapping of the allergenic isoforms from the D. farinae fecal extract. Despite extensive analysis, MALDI TOF/TOF spectrometry showed that only six proteins/allergens, Der f1, Der f2, Der f3, Der f6, Der f15 and ferritin, originated from D. farinae. No other analyzed proteins were exactly assigned to Dermatophagoides or to similar invertebrate species by sequence similarity. The remaining proteins were assigned mostly to yeasts or cereals (originally dietary proteins); however, many of the proteins were not successfully identified in the current NCBInr. The numerous dietary proteins identified in the feces suggest that these proteins remained highly stable after passing through the gut. Isoforms of the allergens Der f1, Der f3 and Der f15 were identified in more MWs indicating the presence of zymogens and active-enzyme forms. The identified fecal allergens accumulate in the environment during the life of the mite and represent quantitatively greater amounts of mite immunogens than those that were missed in the 2D-E. The results contribute to our understanding of D. farinae digestive physiology with regard to the enzymes/proteins present in the feces.
Directory of Open Access Journals (Sweden)
J. Liang
2005-12-01
Full Text Available Multi-instrument observations of a small substorm event on 9 October 2000 provide, with high time resolution, two-dimensional information about substorm dynamics. A sequence of three optical intensifications, each associated with a Pi2 burst, were found, in which the third auroral intensification marked the onset of a small substorm. All three intensifications originated close to midnight, but evolved progressively eastward. Within each of the three optical intensifications, a few azimuthally-spaced patches appeared, the first one near midnight and the subsequent patches successively eastward in the postmidnight sector, providing evidence for drift wave activity in the near-geosynchronous-orbit plasma sheet (NGOPS. The SuperDARN measurements reveal the development of eastward electric fields at NGOPS latitude within each Pi2 burst interval. These observations can be interpreted as supporting the drift-Alfvén-ballooning (DAB mode instability and its role in substorm expansion at NGOPS.
Two dimensional recursive digital filters for near real time image processing
Olson, D.; Sherrod, E.
1980-01-01
A program was designed toward the demonstration of the feasibility of using two dimensional recursive digital filters for subjective image processing applications that require rapid turn around. The concept of the use of a dedicated minicomputer for the processor for this application was demonstrated. The minicomputer used was the HP1000 series E with a RTE 2 disc operating system and 32K words of memory. A Grinnel 256 x 512 x 8 bit display system was used to display the images. Sample images were provided by NASA Goddard on a 800 BPI, 9 track tape. Four 512 x 512 images representing 4 spectral regions of the same scene were provided. These images were filtered with enhancement filters developed during this effort.
Heterostructures based on two-dimensional layered materials and their potential applications
Li, Ming-yang
2015-12-04
The development of two-dimensional (2D) layered materials is driven by fundamental interest and their potential applications. Atomically thin 2D materials provide a wide range of basic building blocks with unique electrical, optical, and thermal properties which do not exist in their bulk counterparts. The van der Waals interlayer interaction enables the possibility to exfoliate and reassemble different 2D materials into arbitrarily and vertically stacked heterostructures. Recently developed vapor phase growth of 2D materials further paves the way of directly synthesizing vertical and lateral heterojunctions. This review provides insights into the layered 2D heterostructures, with a concise introduction to preparative approaches for 2D materials and heterostructures. These unique 2D heterostructures have abundant implications for many potential applications.
Korolkov, Vladimir V.; Baldoni, Matteo; Watanabe, Kenji; Taniguchi, Takashi; Besley, Elena; Beton, Peter H.
2017-12-01
Two-dimensional (2D) supramolecular arrays provide a route to the spatial control of the chemical functionality of a surface, but their deposition is in almost all cases limited to a monolayer termination. Here we investigated the sequential deposition of one 2D array on another to form a supramolecular heterostructure and realize the growth—normal to the underlying substrate—of distinct ordered layers, each of which is stabilized by in-plane hydrogen bonding. For heterostructures formed by depositing terephthalic acid or trimesic acid on cyanuric acid/melamine, we have determined, using atomic force microscopy under ambient conditions, a clear epitaxial arrangement despite the intrinsically distinct symmetries and/or lattice constants of each layer. Structures calculated using classical molecular dynamics are in excellent agreement with the orientation, registry and dimensions of the epitaxial layers. Calculations confirm that van der Waals interactions provide the dominant contribution to the adsorption energy and registry of the layers.
A Two-Dimensional Cloud Model for Condition Assessment of HVDC Converter Transformers
Directory of Open Access Journals (Sweden)
Linjie Zhao
2012-01-01
Full Text Available Converter transformers are the key and the most important components in high voltage direct current (HVDC power transmission systems. Statistics show that the failure rate of HVDC converter transformers is approximately twice of that of transformers in AC power systems. This paper presents an approach integrated with a two-dimensional cloud model and an entropy-based weight model to evaluate the condition of HVDC converter transformers. The integrated approach can describe the complexity of HVDC converter transformers and achieve an effective assessment of their condition. Data from electrical testing, DGA, oil testing, and visual inspection were chosen to form the double-level assessment index system. Analysis results show that the integrated approach is capable of providing a relevant and effective assessment which in turn, provides valuable information for the maintenance of HVDC converter transformers.
2014-05-07
Advanced Distillation Data using Comprehensive Two- Dimensional Gas Chromatography coupled with Time-of-Flight Mass Spectrometry and Partial Least Squares...that included comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry (GC × GC –TOFMS) to analyze RP-1 fuels...secondary dimensions, respectively, to separate the chemical compound classes ( alkanes , cycloalkanes, aromatics, etc), providing a significant level of
Hehemann, Jan-Hendrik; Smyth, Leo; Yadav, Anuj; Vocadlo, David J; Boraston, Alisdair B
2012-04-20
Agars are abundant polysaccharides from marine red algae, and their chemical structure consists of alternating D-galactose and 3,6-anhydro-L-galactose residues, the latter of which are presumed to make the polymer recalcitrant to degradation by most terrestrial bacteria. Here we study a family 117 glycoside hydrolase (BpGH117) encoded within a recently discovered locus from the human gut bacterium Bacteroides plebeius. Consistent with this locus being involved in agarocolloid degradation, we show that BpGH117 is an exo-acting 3,6-anhydro-α-(1,3)-L-galactosidase that removes the 3,6-anhydrogalactose from the non-reducing end of neoagaro-oligosaccharides. A Michaelis complex of BpGH117 with neoagarobiose reveals the distortion of the constrained 3,6-anhydro-L-galactose into a conformation that favors catalysis. Furthermore, this complex, supported by analysis of site-directed mutants, provides evidence for an organization of the active site and positioning of the catalytic residues that are consistent with an inverting mechanism of catalysis and suggests that a histidine residue acts as the general acid. This latter feature differs from the vast majority of glycoside hydrolases, which use a carboxylic acid, highlighting the alternative strategies that enzymes may utilize in catalyzing the cleavage of glycosidic bonds.
Decoding human motor activity from EEG single trials for a discrete two-dimensional cursor control
Huang, Dandan; Lin, Peter; Fei, Ding-Yu; Chen, Xuedong; Bai, Ou
2009-08-01
This study aims to explore whether human intentions to move or cease to move right and left hands can be decoded from spatiotemporal features in non-invasive EEG in order to control a discrete two-dimensional cursor movement for a potential multidimensional brain-computer interface (BCI). Five naïve subjects performed either sustaining or stopping a motor task with time locking to a predefined time window by using motor execution with physical movement or motor imagery. Spatial filtering, temporal filtering, feature selection and classification methods were explored. The performance of the proposed BCI was evaluated by both offline classification and online two-dimensional cursor control. Event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were observed on the contralateral hemisphere to the hand moved for both motor execution and motor imagery. Feature analysis showed that EEG beta band activity in the contralateral hemisphere over the motor cortex provided the best detection of either sustained or ceased movement of the right or left hand. The offline classification of four motor tasks (sustain or cease to move right or left hand) provided 10-fold cross-validation accuracy as high as 88% for motor execution and 73% for motor imagery. The subjects participating in experiments with physical movement were able to complete the online game with motor execution at an average accuracy of 85.5 ± 4.65%; the subjects participating in motor imagery study also completed the game successfully. The proposed BCI provides a new practical multidimensional method by noninvasive EEG signal associated with human natural behavior, which does not need long-term training.
Decoding human motor activity from EEG single trials for a discrete two-dimensional cursor control.
Huang, Dandan; Lin, Peter; Fei, Ding-Yu; Chen, Xuedong; Bai, Ou
2009-08-01
This study aims to explore whether human intentions to move or cease to move right and left hands can be decoded from spatiotemporal features in non-invasive EEG in order to control a discrete two-dimensional cursor movement for a potential multidimensional brain-computer interface (BCI). Five naïve subjects performed either sustaining or stopping a motor task with time locking to a predefined time window by using motor execution with physical movement or motor imagery. Spatial filtering, temporal filtering, feature selection and classification methods were explored. The performance of the proposed BCI was evaluated by both offline classification and online two-dimensional cursor control. Event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were observed on the contralateral hemisphere to the hand moved for both motor execution and motor imagery. Feature analysis showed that EEG beta band activity in the contralateral hemisphere over the motor cortex provided the best detection of either sustained or ceased movement of the right or left hand. The offline classification of four motor tasks (sustain or cease to move right or left hand) provided 10-fold cross-validation accuracy as high as 88% for motor execution and 73% for motor imagery. The subjects participating in experiments with physical movement were able to complete the online game with motor execution at an average accuracy of 85.5 +/- 4.65%; the subjects participating in motor imagery study also completed the game successfully. The proposed BCI provides a new practical multidimensional method by noninvasive EEG signal associated with human natural behavior, which does not need long-term training.
Optical Studies of Excitonic Effects at Two-Dimensional Nanostructure Interfaces
Ajayi, Obafunso Ademilolu
Atomically thin two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have seen a rapid growth of exploration since the isolation of monolayer graphene. These materials provide a rich field of study for physics and optoelectronics applications. Many applications seek to combine a two dimensional (2D) material with another nanomaterial, either another two dimensional material or a zero (0D) or one dimensional (1D) material. The work in this thesis explores the consequences of these interactions from 0D to 2D. We begin in Chapter 2 with a study of energy transfer at 0D-2D interfaces with quantum dots and graphene. In our work we seek to maximize the rate of energy transfer by reducing the distance between the materials. We observe an interplay with the distance-dependence and surface effects from our halogen terminated quantum dots that affect our observed energy transfer. In Chapter 3 we study supercapacitance in composite graphene oxide-carbon nanotube electrodes. At this 2D-1D interface we observe a compounding effect between graphene oxide and carbon nanotubes. Carbon nanotubes increase the accessible surface area of the supercapacitors and improve conductivity by forming a conductive pathway through electrodes. In Chapter 4 we investigate effective means of improving sample quality in TMDCs and discover the importance of the monolayer interface. We observe a drastic improvement in photoluminescence when encapsulating our TMDCs with Boron Nitride. We measure spectral linewidths approaching the intrinsic limit due to this 2D-2D interface. We also effectively reduce excess charge and thus the trion-exciton ratio in our samples through substrate surface passivation. In Chapter 5 we briefly discuss our investigations on chemical doping, heterostructures and interlayer decoupling in ReS2. We observe an increase in intensity for p-doped MoS2 samples. We investigated the charge transfer exciton previously identified in
A two-dimensional protein map of Pleurotus ostreatus microsomes-proteome dynamics.
Petráčková, Denisa; Halada, Petr; Bezoušková, Silvia; Křesinová, Zdena; Svobodová, Kateřina
2016-01-01
Recent studies documented that several processes in filamentous fungi are connected with microsomal enzyme activities. In this work, microsomal subproteomes of Pleurotus ostreatus were analyzed by two-dimensional (2-D) polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry analysis. To assess proteome dynamics, microsomal proteins were isolated from fungal cultures after 7 and 12 days of cultivation. Additionally, 10 mg/L of 17α-ethinylestradiol (EE2) was treated with the cultures during 2 days. Despite the EE2 degradation by the fungus reached 97 and 76.3 % in 7- and 12-day-old cultures, respectively, only a minor effect on the composition of microsomal proteins was observed. The changes in protein maps related to ageing prevailed over those induced by EE2. Epoxide hydrolase, known to metabolize EE2, was detected in 12-day-old cultures only which suggests differences in EE2 degradation pathways utilized by fungal cultures of different age. The majority (32 %) of identified microsomal proteins were parts of mitochondrial energy metabolism.
Vibrational two-dimensional correlation spectroscopy (2DCOS) study of proteins
Noda, Isao
2017-12-01
A tutorial is provided for the generalized two-dimensional correlation spectroscopy (2DCOS), which is applicable to the vibrational spectroscopic study of proteins and related systems. In 2DCOS, similarity or dissimilarity among variations of spectroscopic intensities, which are induced by applying an external perturbation to the sample, is examined by constructing correlation spectra defined by two independent spectral variable axes. By spreading congested or overlapped peaks along the second dimension, apparent spectral resolution is enhanced and interpretation of complex spectra becomes simplified. A set of simple rules for the intensities and signs of correlation peaks is used to extract insightful information. Simulated IR spectra for a model protein are used to demonstrate the specific utility of 2DCOS. Additional tools useful in the 2DCOS analysis of proteins, such as data segmentation assisted with moving-window analysis, 2D codistribution analysis, Pareto scaling, and null-space projection are also discussed.
Thermodynamics of strongly interacting fermions in two-dimensional optical lattices
Energy Technology Data Exchange (ETDEWEB)
Khatami, Ehsan; Rigol, Marcos [Department of Physics, Georgetown University, Washington DC, 20057 (United States); Kavli Institute for Theoretical Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States)
2011-11-15
We study finite-temperature properties of strongly correlated fermions in two-dimensional optical lattices by means of numerical linked cluster expansions, a computational technique that allows one to obtain exact results in the thermodynamic limit. We focus our analysis on the strongly interacting regime, where the on-site repulsion is of the order of or greater than the band width. We compute the equation of state, double occupancy, entropy, uniform susceptibility, and spin correlations for temperatures that are similar to or below the ones achieved in current optical lattice experiments. We provide a quantitative analysis of adiabatic cooling of trapped fermions in two dimensions, by means of both flattening the trapping potential and increasing the interaction strength.
Thermodynamics of strongly interacting fermions in two-dimensional optical lattices
Khatami, Ehsan; Rigol, Marcos
2011-11-01
We study finite-temperature properties of strongly correlated fermions in two-dimensional optical lattices by means of numerical linked cluster expansions, a computational technique that allows one to obtain exact results in the thermodynamic limit. We focus our analysis on the strongly interacting regime, where the on-site repulsion is of the order of or greater than the band width. We compute the equation of state, double occupancy, entropy, uniform susceptibility, and spin correlations for temperatures that are similar to or below the ones achieved in current optical lattice experiments. We provide a quantitative analysis of adiabatic cooling of trapped fermions in two dimensions, by means of both flattening the trapping potential and increasing the interaction strength.
Holt, Ian J; Kazak, Lawrence; Reyes, Aurelio; Wood, Stuart R
2016-01-01
Our understanding of the mechanisms of DNA replication in a broad range of organisms and viruses has benefited from the application of two-dimensional agarose gel electrophoresis (2D-AGE). The method resolves DNA molecules on the basis of size and shape and is technically straightforward. 2D-AGE sparked controversy in the field of mitochondria when it revealed replicating molecules with lengthy tracts of RNA, a phenomenon never before reported in nature. More recently, radioisotope labeling of the DNA in the mitochondria has been coupled with 2D-AGE. In its first application, this procedure helped to delineate the "bootlace mechanism of mitochondrial DNA replication," in which processed mitochondrial transcripts are hybridized to the lagging strand template at the replication fork as the leading DNA strand is synthesized. This chapter provides details of the method, how it has been applied to date and concludes with some potential future applications of the technique.
Qi, Jingshan; Li, Xiao; Qian, Xiaofeng
2016-06-01
Electrically controlled band gap and topological electronic states are important for the next-generation topological quantum devices. In this letter, we study the electric field control of band gap and topological phase transitions in multilayer germanane. We find that although the monolayer and multilayer germananes are normal insulators, a vertical electric field can significantly reduce the band gap of multilayer germananes owing to the giant Stark effect. The decrease of band gap eventually leads to band inversion, transforming them into topological insulators with nontrivial Z2 invariant. The electrically controlled topological phase transition in multilayer germananes provides a potential route to manipulate topologically protected edge states and design topological quantum devices. This strategy should be generally applicable to a broad range of materials, including other two-dimensional materials and ultrathin films with controlled growth.
Strong coupling between Tamm plasmon polariton and two dimensional semiconductor excitons
Hu, Tao; Wang, Yafeng; Wu, Lin; Zhang, Long; Shan, Yuwei; Lu, Jian; Wang, Jun; Luo, Song; Zhang, Zhe; Liao, Liming; Wu, Shiwei; Shen, Xuechu; Chen, Zhanghai
2017-01-01
Two dimensional (2D) semiconductor materials of transition-metal dichalcogenides (TMDCs) manifest many peculiar physical phenomena in the light-matter interaction. Due to their ultrathin property, strong interaction with light and the robust excitons at room temperature, they provide a perfect platform for studying the physics of strong coupling in low dimension and at room temperature. Here we report the strong coupling between 2D semiconductor excitons and Tamm plasmon polaritons (TPPs). We observe a Rabi splitting of about 54 meV at room temperature by measuring the angle resolved differential reflectivity spectra and simulate the theoretical results by using the transfer matrix method. Our results will promote the realization of the TPP based ultrathin polariton devices at room temperature.
Using FDFD Technique in Two-Dimensional TE Analysis for Modeling Clutter in Wall Penetrating Radar
Directory of Open Access Journals (Sweden)
David Insana
2014-01-01
Full Text Available Finite difference frequency domain (FDFD computational electromagnetic modeling is implemented to perform a two-dimensional TEz analysis for the application of wall penetrating radar (WPR. Resolving small targets of interest, embedded in a strong clutter environment of unknown configuration, is difficult. Field interaction between clutter elements will dominate the received fields back-scattered from the scene. Removing the effects of clutter ultimately relies on the accuracy of the model. Analysis starts with a simple model that continues to build based on the dominant scattering features of the scene. FDFD provides a steady state frequency response to a discrete excitation. Taking the fast Fourier transform of the wideband response of the scene, at several external transmit/receive locations, produces 2D images of the clutter, which are used to mature the model.
Shi, Li; Ouyang, Yixin; Wang, Jinlan
2016-01-01
Two-dimensional (2D) boron monolayers have been successfully synthesized on silver substrate very recently. Their potential application is thus of great significance. In this work, we explore the possibility of boron monolayers (BMs) as electrocatalysts for hydrogen evolution reaction (HER) by first-principle method. Our calculations show that the BMs are active catalysts for HER with nearly zero free energy of hydrogen adsorption, metallic conductivity and plenty of active sites in the basal plane. The effect of the substrate on the HER activity is further assessed. It is found that the substrate has a positive effect on the HER performance caused by the competitive effect of mismatch strain and charge transfer. The indepth understanding of the structure dependent HER activity is also provided.
Panman, Matthijs R; Vos, Jannie; Bocokić, Vladica; Bellini, Rosalba; de Bruin, Bas; Reek, Joost H N; Woutersen, Sander
2013-12-16
Catalytic transition-metal complexes often occur in several conformations that exchange rapidly (
Energy Technology Data Exchange (ETDEWEB)
Bagchi, Bijan, E-mail: bbagchi123@gmail.com [Department of Applied Mathematics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009 (India); Marquette, Ian, E-mail: i.marquette@uq.edu.au [School of Mathematics and Physics, The University of Queensland, Brisbane, QLD 4072 (Australia)
2015-08-14
We derive a one-step extension of the well known Swanson oscillator that describes a specific type of pseudo-Hermitian quadratic Hamiltonian connected to an extended harmonic oscillator model. Our analysis is based on the use of the techniques of supersymmetric quantum mechanics and addresses various representations of the ladder operators starting from a seed solution of the harmonic oscillator expressed in terms of a pseudo-Hermite polynomial. The role of the resulting chain of Hamiltonians related to similarity transformation is then exploited. In the second part we write down a two dimensional generalization of the Swanson Hamiltonian and establish superintegrability of such a system. - Highlights: • We show that the Swanson system admits a 1-step rational extension. • We provide a flow-chart linking the Swanson model to its generalized counterpart. • We examine superintegrability of the Hermitian equivalence of the Swanson oscillator.
Plasmon-exciton polaritons in two-dimensional semiconductor/metal interfaces
Gonçalves, P. A. D.; Bertelsen, L. P.; Xiao, Sanshui; Mortensen, N. Asger
2018-01-01
The realization and control of polaritons is of paramount importance in the prospect of novel photonic devices. Here, we investigate the emergence of plasmon-exciton polaritons in hybrid structures consisting of a two-dimensional transition-metal dichalcogenide (TMDC) deposited onto a metal substrate or coating a metallic thin film. We determine the polaritonic spectrum and show that, in the former case, the addition of a top dielectric layer and, in the latter case, the thickness of the metal film can be used to tune and promote plasmon-exciton interactions well within the strong-coupling regime. Our results demonstrate that Rabi splittings exceeding 100 meV can readily be achieved in planar dielectric/TMDC/metal structures under ambient conditions. We thus believe that this Rapid Communication provides a simple and intuitive picture to tailor strong coupling in plexcitonics with potential applications for engineering compact photonic devices with tunable optical properties.
Johansson, Annika; Henk, Jürgen; Mertig, Ingrid
2016-05-01
A charge current driven through a two-dimensional electron gas (2DEG) with Rashba spin-orbit coupling generates a spatially homogeneous spin polarization perpendicular to the applied electric field. This phenomenon is the Aronov-Lyanda-Geller-Edelstein (ALGE) effect. For selected model systems, we consider the ALGE effect within the semiclassical Boltzmann transport theory. Its energy dependence is investigated, in particular the regime below the Dirac point of the 2DEG. In addition to an isotropic 2DEG, we analyze systems with anisotropic Fermi contours. We predict that the current-induced spin polarization vanishes if the Fermi contour passes through a Lifshitz transition. Further, we corroborate that topological insulators (TI) provide a very efficient charge-to-spin conversion.
Anomalous Nonlocal Resistance and Spin-Charge Conversion Mechanisms in Two-Dimensional Metals
Huang, Chunli; Chong, Y. D.; Cazalilla, Miguel A.
2017-09-01
We uncover two anomalous features in the nonlocal transport behavior of two-dimensional metallic materials with spin-orbit coupling. First, the nonlocal resistance can have negative values and oscillate with distance, even in the absence of a magnetic field. Second, the oscillations of the nonlocal resistance under an applied in-plane magnetic field (the Hanle effect) can be asymmetric under field reversal. Both features are produced by direct magnetoelectric coupling, which is possible in materials with broken inversion symmetry but was not included in previous spin-diffusion theories of nonlocal transport. These effects can be used to identify the relative contributions of different spin-charge conversion mechanisms. They should be observable in adatom-functionalized graphene, and they may provide the reason for discrepancies in recent nonlocal transport experiments on graphene.
A two-dimensional volatility basis set – Part 3: Prognostic modeling and NOx dependence
Directory of Open Access Journals (Sweden)
W. K. Chuang
2016-01-01
Full Text Available When NOx is introduced to organic emissions, aerosol production is sometimes, but not always, reduced. Under certain conditions, these interactions will instead increase aerosol concentrations. We expanded the two-dimensional volatility basis set (2D-VBS to include the effects of NOx on aerosol formation. This includes the formation of organonitrates, where the addition of a nitrate group contributes to a decrease of 2.5 orders of magnitude in volatility. With this refinement, we model outputs from experimental results, such as the atomic N : C ratio, organonitrate mass, and nitrate fragments in Aerosol Mass Spectrometer (AMS measurements. We also discuss the mathematical methods underlying the implementation of the 2D-VBS and provide the complete code in the Supplement. A developer version is available on Bitbucket, an online community repository.
A two-dimensional volatility basis set - Part 3: Prognostic modeling and NOx dependence
Chuang, W. K.; Donahue, N. M.
2016-01-01
When NOx is introduced to organic emissions, aerosol production is sometimes, but not always, reduced. Under certain conditions, these interactions will instead increase aerosol concentrations. We expanded the two-dimensional volatility basis set (2D-VBS) to include the effects of NOx on aerosol formation. This includes the formation of organonitrates, where the addition of a nitrate group contributes to a decrease of 2.5 orders of magnitude in volatility. With this refinement, we model outputs from experimental results, such as the atomic N : C ratio, organonitrate mass, and nitrate fragments in Aerosol Mass Spectrometer (AMS) measurements. We also discuss the mathematical methods underlying the implementation of the 2D-VBS and provide the complete code in the Supplement. A developer version is available on Bitbucket, an online community repository.
Two-dimensional dynamics of a trapped active Brownian particle in a shear flow.
Li, Yunyun; Marchesoni, Fabio; Debnath, Tanwi; Ghosh, Pulak K
2017-12-01
We model the two-dimensional dynamics of a pointlike artificial microswimmer diffusing in a harmonic trap subject to the shear flow of a highly viscous medium. The particle is driven simultaneously by the linear restoring force of the trap, the drag force exerted by the flow, and the torque due to the shear gradient. For a Couette flow, elliptical orbits in the noiseless regime, and the correlation functions between the particle's displacements parallel and orthogonal to the flow are computed analytically. The effects of thermal fluctuations (translational) and self-propulsion fluctuations (angular) are treated separately. Finally, we discuss how to extend our approach to the diffusion of a microswimmer in a Poiseuille flow. These results provide an accurate reference solution to investigate, both numerically and experimentally, hydrodynamics corrections to the diffusion of active matter in confined geometries.
Limits to the Optical Response of Graphene and Two-Dimensional Materials.
Miller, Owen D; Ilic, Ognjen; Christensen, Thomas; Reid, M T Homer; Atwater, Harry A; Joannopoulos, John D; Soljačić, Marin; Johnson, Steven G
2017-09-13
Two-dimensional (2D) materials provide a platform for strong light-matter interactions, creating wide-ranging design opportunities via new-material discoveries and new methods for geometrical structuring. We derive general upper bounds to the strength of such light-matter interactions, given only the optical conductivity of the material, including spatial nonlocality, and otherwise independent of shape and configuration. Our material figure-of-merit shows that highly doped graphene is an optimal material at infrared frequencies, whereas single-atomic-layer silver is optimal in the visible. For quantities ranging from absorption and scattering to near-field spontaneous-emission enhancements and radiative heat transfer, we consider canonical geometrical structures and show that in certain cases the bounds can be approached, while in others there may be significant opportunity for design improvement. The bounds can encourage systematic improvements in the design of ultrathin broadband absorbers, 2D antennas, and near-field energy harvesters.
The PLSI Method of Stabilizing Two-Dimensional Nonsymmetric Half-Plane Recursive Digital Filters
Directory of Open Access Journals (Sweden)
Gangatharan N
2003-01-01
Full Text Available Two-dimensional (2D recursive digital filters find applications in image processing as in medical X-ray processing. Nonsymmetric half-plane (NSHP filters have definitely positive magnitude characteristics as opposed to quarter-plane (QP filters. In this paper, we provide methods for stabilizing the given 2D NSHP polynomial by the planar least squares inverse (PLSI method. We have proved in this paper that if the given 2D unstable NSHP polynomial and its PLSI are of the same degree, the PLSI polynomial is always stable, irrespective of whether the coefficients of the given polynomial have relationship among its coefficients or not. Examples are given for 2D first-order and second-order cases to prove our results. The generalization is done for the th order polynomial.
Functional Two-Dimensional Coordination Polymeric Layer as a Charge Barrier in Li–S Batteries
Huang, Jing-Kai
2018-01-04
Ultrathin two-dimensional (2D) polymeric layers are capable of separating gases and molecules based on the reported size exclusion mechanism. What is equally important but missing today is an exploration of the 2D layers with charge functionality, which enables applications using the charge exclusion principle. This work demonstrates a simple and scalable method of synthesizing a free-standing 2D coordination polymer Zn2(benzimidazolate)2(OH)2 at the air–water interface. The hydroxyl (−OH) groups are stoichiometrically coordinated and implement electrostatic charges in the 2D structures, providing powerful functionality as a charge barrier. Electrochemical performance of the Li–S battery shows that the Zn2(benzimidazolate)2(OH)2 coordination polymer layers efficiently mitigate the polysulfide shuttling effects and largely enhance the battery capacity and cycle performance. The synthesis of the proposed coordination polymeric layers is simple, scalable, cost saving, and promising for practical use in batteries.
Two-dimensional salt and temperature DNA denaturation analysis using a magnetoresistive sensor
DEFF Research Database (Denmark)
Rizzi, Giovanni; Dufva, Martin; Hansen, Mikkel Fougt
2017-01-01
We present a microfluidic system and its use to measure DNA denaturation curves by varying the temperature or salt (Na+) concentration. The readout is based on real-time measurements of DNA hybridization using magnetoresistive sensors and magnetic nanoparticles (MNPs) as labels. We report the first...... melting curves of DNA hybrids measured as a function of continuously decreasing salt concentration at fixed temperature and compare them to the corresponding curves obtained vs. temperature at fixed salt concentration. The magnetoresistive sensor platform provided reliable results under varying...... temperature as well as salt concentration. The salt concentration melting curves were found to be more reliable than temperature melting curves. We performed a two-dimensional mapping of the melting profiles of a target to probes targeting its wild type (WT) and mutant type (MT) variants in the temperature...
Two-Dimensional Photonic Crystals for Sensitive Microscale Chemical and Biochemical Sensing
Miller, Benjamin L.
2015-01-01
Photonic crystals – optical devices able to respond to changes in the refractive index of a small volume of space – are an emerging class of label-free chemical-and bio-sensors. This review focuses on one class of photonic crystal, in which light is confined to a patterned planar material layer of sub-wavelength thickness. These devices are small (on the order of tens to 100s of microns square), suitable for incorporation into lab-on-a-chip systems, and in theory can provide exceptional sensitivity. We introduce the defining characteristics and basic operation of two-dimensional photonic crystal sensors, describe variations of their basic design geometry, and summarize reported detection results from chemical and biological sensing experiments. PMID:25563402
Evaluation of several two-dimensional gel electrophoresis techniques in cardiac proteomics.
Li, Zhao Bo; Flint, Paul W; Boluyt, Marvin O
2005-09-01
Two-dimensional gel electrophoresis (2-DE) is currently the best method for separating complex mixtures of proteins, and its use is gradually becoming more common in cardiac proteome analysis. A number of variations in basic 2-DE have emerged, but their usefulness in analyzing cardiac tissue has not been evaluated. The purpose of the present study was to systematically evaluate the capabilities and limitations of several 2-DE techniques for separating proteins from rat heart tissue. Immobilized pH gradient strips of various pH ranges, parameters of protein loading and staining, subcellular fractionation, and detection of phosphorylated proteins were studied. The results provide guidance for proteome analysis of cardiac and other tissues in terms of selection of the isoelectric point separating window for cardiac proteins, accurate quantitation of cardiac protein abundance, stabilization of technical variation, reduction of sample complexity, enrichment of low-abundant proteins, and detection of phosphorylated proteins.
Yaqoob, Zahid; Arain, Muzammil A; Riza, Nabeel A
2003-09-10
A high-speed free-space wavelength-multiplexed optical scanner with high-speed wavelength selection coupled with narrowband volume Bragg gratings stored in photothermorefractive (PTR) glass is reported. The proposed scanner with no moving parts has a modular design with a wide angular scan range, accurate beam pointing, low scanner insertion loss, and two-dimensional beam scan capabilities. We present a complete analysis and design procedure for storing multiple tilted Bragg-grating structures in a single PTR glass volume (for normal incidence) in an optimal fashion. Because the scanner design is modular, many PTR glass volumes (each having multiple tilted Bragg-grating structures) can be stacked together, providing an efficient throughput with operations in both the visible and the infrared (IR) regions. A proof-of-concept experimental study is conducted with four Bragg gratings in independent PTR glass plates, and both visible and IR region scanner operations are demonstrated.
Self-assembly of two-dimensional binary quasicrystals: A possible route to a DNA quasicrystal
Reinhardt, Aleks; Romano, Flavio; Doye, Jonathan P K
2016-01-01
We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta- and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm `star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms. We explore several possible design strategies and conclude that DNA star tiles that are designed to interact with one another in a specific but not overly constrained way could potentially be used to construct soft quasicrystals in experiment. We verify that such star tiles can form stable dodecagonal motifs using oxDNA, a realistic coarse-grained model of DNA.
Smoothing two-dimensional Malaysian mortality data using P-splines indexed by age and year
Kamaruddin, Halim Shukri; Ismail, Noriszura
2014-06-01
Nonparametric regression implements data to derive the best coefficient of a model from a large class of flexible functions. Eilers and Marx (1996) introduced P-splines as a method of smoothing in generalized linear models, GLMs, in which the ordinary B-splines with a difference roughness penalty on coefficients is being used in a single dimensional mortality data. Modeling and forecasting mortality rate is a problem of fundamental importance in insurance company calculation in which accuracy of models and forecasts are the main concern of the industry. The original idea of P-splines is extended to two dimensional mortality data. The data indexed by age of death and year of death, in which the large set of data will be supplied by Department of Statistics Malaysia. The extension of this idea constructs the best fitted surface and provides sensible prediction of the underlying mortality rate in Malaysia mortality case.
González-Tudela, A.; Cirac, J. I.
2017-10-01
The interaction of quantum emitters with structured baths modifies both their individual and collective dynamics. In A. González-Tudela and J. I. Cirac, Phys. Rev. Lett. 119, 143602 (2017), 10.1103/PhysRevLett.119.143602, we show how exotic quantum dynamics emerges when quantum emitters are spectrally tuned around the middle of the band of a two-dimensional structured reservoir, where we predict the failure of perturbative treatments, anisotropic non-Markovian interactions, and remarkable superradiant and subradiant behavior. In this work, we provide further analysis of that situation, together with a complete analysis for the quantum emitter dynamics in spectral regions different from the center of the band.
Force signature of the unzipping transition for strip confined two-dimensional polymers
Owczarek, Aleksander L.; Rechnitzer, Andrew
2017-12-01
We find and analyse the exact solution of two friendly walks, modelling polymers, confined between two parallel walls in a two-dimensional strip (or slit) where the polymers interact with each other via an attractive contact interaction. In the bulk, where the polymers are always far from any walls, there is an unzipping transition between phases where the two walks drift away for low attractive fugacity (high temperatures) and bind together for high attractive fugacities (low temperatures). Previously this has been used to model the denaturation of DNA. In a strip the transition is not sharp. However, we demonstrate that there is an abrupt change in the repulsive force exerted on the walls of the strip that can be calculated exactly. We suggest that this change in the force could be exploited to provide an experimental signature of the unzipping transition.
Two-dimensional dielectric nanosheets: novel nanoelectronics from nanocrystal building blocks.
Osada, Minoru; Sasaki, Takayoshi
2012-01-10
Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness and infinite planar lengths, are regarded as the thinnest functional nanomaterials. The recent development of methods for manipulating graphene (carbon nanosheet) has provided new possibilities and applications for 2D systems; many amazing functionalities such as high electron mobility and quantum Hall effects have been discovered. However, graphene is a conductor, and electronic technology also requires insulators, which are essential for many devices such as memories, capacitors, and gate dielectrics. Along with graphene, inorganic nanosheets have thus increasingly attracted fundamental research interest because they have the potential to be used as dielectric alternatives in next-generation nanoelectronics. Here, we review the progress made in the properties of dielectric nanosheets, highlighting emerging functionalities in electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanoelectronics. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Directory of Open Access Journals (Sweden)
Dongkyun IM
2011-12-01
Full Text Available River corridors, even if highly modified or degraded, still provide important habitats for numerous biological species, and carry high aesthetic and economic values. One of the keys to urban stream restoration is recovery and maintenance of ecological flows sufficient to sustain aquatic ecosystems. In this study, the Hongje Stream in the Seoul metropolitan area of Korea was selected for evaluating a physically-based habitat with and without habitat structures. The potential value of the aquatic habitat was evaluated by a weighted usable area (WUA using River2D, a two-dimensional hydraulic model. The habitat suitability for Zacco platypus in the Hongje Stream was simulated with and without habitat structures. The computed WUA values for the boulder, spur dike, and riffle increased by about 2%, 7%, and 131%, respectively, after their construction. Also, the three habitat structures, especially the riffle, can contribute to increasing hydraulic heterogeneity and enhancing habitat diversity.
Two-dimensional structure-embedded acoustic lenses based on periodic acoustic black holes
Zhu, Hongfei; Semperlotti, Fabio
2017-08-01
Recent studies have introduced a new class of two-dimensional acoustic metamaterials whose dispersion and propagation properties result from the use of geometric inhomogeneities in the form of Acoustic Black Holes (ABH). The ABH is an element able to smoothly bend acoustic rays and slow down elastic bending waves, therefore providing a variety of unconventional dispersion and propagation properties that are typically observed in more complex multi-material and locally resonant designs. Our approach enables full integration of acoustic lenses in thin-walled structural elements while preserving the structural character. The lenses are capable of different high-level functionalities such as focusing, collimation, and negative refraction. Numerical and experimental results show that such structures exhibit broadband operating conditions that span both the metamaterial and the phononic range.
Watching Proteins Wiggle: Mapping Structures with Two-Dimensional Infrared Spectroscopy.
Ghosh, Ayanjeet; Ostrander, Joshua S; Zanni, Martin T
2017-08-23
Proteins exhibit structural fluctuations over decades of time scales. From the picosecond side chain motions to aggregates that form over the course of minutes, characterizing protein structure over these vast lengths of time is important to understanding their function. In the past 15 years, two-dimensional infrared spectroscopy (2D IR) has been established as a versatile tool that can uniquely probe proteins structures on many time scales. In this review, we present some of the basic principles behind 2D IR and show how they have, and can, impact the field of protein biophysics. We highlight experiments in which 2D IR spectroscopy has provided structural and dynamical data that would be difficult to obtain with more standard structural biology techniques. We also highlight technological developments in 2D IR that continue to expand the scope of scientific problems that can be accessed in the biomedical sciences.
Digital chaos-masked optical encryption scheme enhanced by two-dimensional key space
Liu, Ling; Xiao, Shilin; Zhang, Lu; Bi, Meihua; Zhang, Yunhao; Fang, Jiafei; Hu, Weisheng
2017-09-01
A digital chaos-masked optical encryption scheme is proposed and demonstrated. The transmitted signal is completely masked by interference chaotic noise in both bandwidth and amplitude with analog method via dual-drive Mach-Zehnder modulator (DDMZM), making the encrypted signal analog, noise-like and unrecoverable by post-processing techniques. The decryption process requires precise matches of both the amplitude and phase between the cancellation and interference chaotic noises, which provide a large two-dimensional key space with the help of optical interference cancellation technology. For 10-Gb/s 16-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) signal over the maximum transmission distance of 80 km without dispersion compensation or inline amplifier, the tolerable mismatch ranges of amplitude and phase/delay at the forward error correction (FEC) threshold of 3.8×10-3 are 0.44 dB and 0.08 ns respectively.
Modelling Altitude Information in Two-Dimensional Traffic Networks for Electric Mobility Simulation
Directory of Open Access Journals (Sweden)
Diogo Santos
2016-06-01
Full Text Available Elevation data is important for electric vehicle simulation. However, traffic simulators are often two-dimensional and do not offer the capability of modelling urban networks taking elevation into account. Specifically, SUMO - Simulation of Urban Mobility, a popular microscopic traffic simulator, relies on networks previously modelled with elevation data as to provide this information during simulations. This work tackles the problem of adding elevation data to urban network models - particularly for the case of the Porto urban network, in Portugal. With this goal in mind, a comparison between different altitude information retrieval approaches is made and a simple tool to annotate network models with altitude data is proposed. The work starts by describing the methodological approach followed during research and development, then describing and analysing its main findings. This description includes an in-depth explanation of the proposed tool. Lastly, this work reviews some related work to the subject.
A Kalman filter for a two-dimensional shallow-water model
Parrish, D. F.; Cohn, S. E.
1985-01-01
A two-dimensional Kalman filter is described for data assimilation for making weather forecasts. The filter is regarded as superior to the optimal interpolation method because the filter determines the forecast error covariance matrix exactly instead of using an approximation. A generalized time step is defined which includes expressions for one time step of the forecast model, the error covariance matrix, the gain matrix, and the evolution of the covariance matrix. Subsequent time steps are achieved by quantifying the forecast variables or employing a linear extrapolation from a current variable set, assuming the forecast dynamics are linear. Calculations for the evolution of the error covariance matrix are banded, i.e., are performed only with the elements significantly different from zero. Experimental results are provided from an application of the filter to a shallow-water simulation covering a 6000 x 6000 km grid.
Rashetnia, Reza; Hallaji, Milad; Smyl, Danny; Seppänen, Aku; Pour-Ghaz, Mohammad
2017-11-01
This paper studies the feasibility of applying electrical resistance tomography (ERT) to detect changes in two-dimensional (2D) temperature distributions with potential applications in sensor development. The proposed sensor consists of a thin layer of porous metal film manufactured by spraying colloidal copper paint to a solid surface. A change of the temperature distribution on the surface changes the 2D distributed electrical conductivity of the metal film. The change of the electrical conductivity is localized and quantified with ERT, and further, to convert the estimated conductivity change of the sensor to temperature change, an experimentally developed model is used. The proposed temperature sensor is evaluated experimentally by applying it to a polymeric substrate, and exposing it to known temperature changes using heat sources of different shapes. The results demonstrate that the proposed sensor is capable of detecting and localizing temperature changes, and provides at least qualitative information on the magnitude of the temperature change.
A Short Note on the Scaling Function Constant Problem in the Two-Dimensional Ising Model
Bothner, Thomas
2017-12-01
We provide a simple derivation of the constant factor in the short-distance asymptotics of the tau-function associated with the 2-point function of the two-dimensional Ising model. This factor was first computed by Tracy (Commun Math Phys 142:297-311, 1991) via an exponential series expansion of the correlation function. Further simplifications in the analysis are due to Tracy and Widom (Commun Math Phys 190:697-721, 1998) using Fredholm determinant representations of the correlation function and Wiener-Hopf approximation results for the underlying resolvent operator. Our method relies on an action integral representation of the tau-function and asymptotic results for the underlying Painlevé-III transcendent from McCoy et al. (J Math Phys 18:1058-1092, 1977).
Two-dimensional phase unwrapping using the transport of intensity equation.
Pandey, Neeraj; Ghosh, Amitava; Khare, Kedar
2016-03-20
We report a method for two-dimensional phase unwrapping based on the transport of intensity equation (TIE). Given a wrapped phase profile, we generate an auxiliary complex field and propagate it to small distances to simulate two intensity images on closely spaced planes. Using the longitudinal intensity derivative of the auxiliary field as an input, the TIE is solved by employing the regularized Fourier-transform-based approach. The resultant phase profile is automatically in the unwrapped form, as it has been obtained as a solution of a partial differential equation rather than as an argument of a complex-valued function. Our simulations and experimental results suggest that this approach is fast and accurate and provides a simple and practical solution for routine phase unwrapping tasks in interferometry and digital holography.
Two-dimensional patterning of thin coatings for the control of tissue outgrowth
DEFF Research Database (Denmark)
Thissen, H.; Johnson, G.; Hartley, P.G.
2006-01-01
boundaries of tissue growth on surfaces in two dimensions. The method relies on the generation of a spatially defined surface chemistry comprising protein adsorbing and non-adsorbing areas that allow control over the adsorption of cell-adhesive glycoproteins. Surface modification was carried out...... by deposition of thin acetaldehyde and allylamine plasma polymer coatings on silicon wafer and FEP substrates, followed by grafting of a protein resistant layer of poly(ethylene oxide). Spatially controlled patterning of the surface chemistry was achieved by masking during plasma polymerization. XPS and AFM...... were used to provide evidence of successful surface modifications. Adsorption of the extracellular matrix protein collagen I followed by tissue outgrowth experiments with bovine corneal epithelial tissue for up to 21 days showed that two-dimensional control over tissue outgrowth is achievable with our...
Vibrational relaxation in simulated two-dimensional infrared spectra of two amide modes in solution
Dijkstra, Arend G.; Jansen, Thomas la Cour; Bloem, Robbert; Knoester, Jasper
2007-01-01
Two-dimensional infrared spectroscopy is capable of following the transfer of vibrational energy between modes in real time. We develop a method to include vibrational relaxation in simulations of two-dimensional infrared spectra at finite temperature. The method takes into account the correlated
Electron cryomicroscopy of two-dimensional crystals of the H+-ATPase from chloroplasts
Böttcher, Bettina; Gräber, Peter; Boekema, Egbert J.; Lücken, Uwe
1995-01-01
The H+-ATPase from spinach chloroplasts was isolated and purified. Two-dimensional crystals were obtained from the protein/lipid/detergent micelles by treatment with phospholipase and simultaneous removal of detergent and fatty acids by Biobeads. The resulting two-dimensionally ordered arrays were
Bedani, F.; Schoenmakers, P.J.; Janssen, H.-G.
2012-01-01
On-line comprehensive two-dimensional liquid chromatography techniques promise to resolve samples that current one-dimensional liquid chromatography methods cannot adequately deal with. To make full use of the potential of two-dimensional liquid chromatography, optimization is required. Optimization
Schäpers, Th.; Guzenko, V.A.; Müller, R.P.; Golubov, Alexandre Avraamovitch; Brinkman, Alexander; Crecelius, G.; Kaluza, A.; Lüth, H.
2003-01-01
We study the suppression of the critical current in a multi-terminal superconductor/two-dimensional electron gas/superconductor Josephson junction by means of hot carrier injection. As a superconductor Nb is used, while the two-dimensional electron gas is located in a strained InGaAs/InP
Park, Hee-June; Cha, Wonjae; Kim, Geun-Hyo; Jeon, Gye-Rok; Lee, Byung Joo; Shin, Bum-Joo; Choi, Yang-Gyu; Wang, Soo-Geun
2016-05-01
Laryngeal videokymography and high-speed digital kymography are the currently available techniques for studying aperiodic vibration of the vocal folds. However, videokymography has a fundamental limitation that only linear portions of the vocal fold mucosa can be visualized, whereas high-speed digital kymography has the disadvantages of lack of immediate feedback during examination and considerable waiting time before kymographic visualization. We developed a new system, two-dimensional (2D) scanning videokymography, that provides a possible alternative for evaluation of the vibratory pattern of the vocal folds. Herein, we report the application of 2D scanning videokymography for visualization of vocal fold vibration in humans and an analysis of its parameters. Two young healthy volunteers (one man and one woman) took part in this study. The vibratory patterns of their vocal folds were evaluated using 2D scanning videokymography and laryngeal stroboscopy. Two-dimensional scanning videokymography provided a high-definition image of the vibratory movements of the vocal folds. In analysis of the images acquired by the device, various parameters including fundamental frequency; ratio of the vibratory phases; phase, amplitude, and glottal area symmetry; and cycle-to-cycle variability were extracted. Our results indicate that 2D scanning videokymography is a useful and promising tool for visualization of the vibratory movement of the vocal folds. This new technique might improve our understanding of the mechanism of vocal fold vibration and contribute to voice research as well as clinical practice. Copyright © 2016 The Voice Foundation. Published by Elsevier Inc. All rights reserved.
Flow of an aqueous foam through a two-dimensional porous medium: a pore scale investigation
Meheust, Y.; Jones, S. A.; Dollet, B.; Cox, S.; Cantat, I.
2012-12-01
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soil: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that might be of benefit to the application. We address here this physical aspect of the topic. As a precursor to the study of foam flow through a complex porous material, we first study the behavior of an aqueous two-dimensional foam flowing through a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow velocity, and hence flux, in each channel is measured by analyzing images of the flowing foam. It is then compared to a theoretical model, the basic assumption of which is that the pressure drop along a channel is identical for both channels. This pressure drop both consists of (i) a dynamic pressure drop, which is controlled by bubble-wall friction and depends on the foam velocity in the channel, and (ii) a capillary pressure drop over the bubble films that emerge at the channel outlet, the latter pressure drop being controlled by the radius of curvature of the bubble film. Based on this assumption, the dependence of the ratio of the foam velocities in the two channels is inferred as a function of the channel width ratio. It compares well to the measurements and shows that the flow behavior is highly dependent on the foam structure within the narrowest of the two channels, especially when a "bamboo" structure is obtained. Consequently, the flux in a channel is found to have a more complicated relation to the channel width than expected for the flow of a standard Newtonian fluid in the same geometry. We provide a comparison to this reference configuration. We then study the flow of the same
Huang, Norden E. (Inventor)
2001-01-01
A computer implemented method of processing two-dimensional physical signals includes five basic components and the associated presentation techniques of the results. The first component decomposes the two-dimensional signal into one-dimensional profiles. The second component is a computer implemented Empirical Mode Decomposition that extracts a collection of Intrinsic Mode Functions (IMF's) from each profile based on local extrema and/or curvature extrema. The decomposition is based on the direct extraction of the energy associated with various intrinsic time scales in the profiles. In the third component, the IMF's of each profile are then subjected to a Hilbert Transform. The fourth component collates the Hilbert transformed IMF's of the profiles to form a two-dimensional Hilbert Spectrum. A fifth component manipulates the IMF's by, for example, filtering the two-dimensional signal by reconstructing the two-dimensional signal from selected IMF(s).
DEFF Research Database (Denmark)
Chen, Yunzhong; Trier, Felix; Wijnands, T.
2015-01-01
The discovery of two-dimensional electron gases (2DEGs) at the interface between two insulating complex oxides, such as LaAlO3 (LAO) or gamma-Al2O3 (GAO) epitaxially grown on SrTiO3 (STO), provides an opportunity for developing all-oxide electronic devices. These 2DEGs at complex oxide interfaces...... than two orders of magnitude. Our in-situ and resonant x-ray spectroscopic in addition to transmission electron microscopy results indicate that the manganite layer undergoes unambiguous electronic reconstruction and leads to modulation doping of such atomically engineered complex oxide......The discovery of two-dimensional electron gases (2DEGs) at the interface between two insulating complex oxides, such as LaAlO3 (LAO) or gamma-Al2O3 (GAO) epitaxially grown on SrTiO3 (STO), provides an opportunity for developing all-oxide electronic devices. These 2DEGs at complex oxide interfaces...
Mah, Kenneth; Binik, Yitzchak M
2002-05-01
The characteristics common to all human orgasm experiences and potential gender and contextual factors affecting these experiences were investigated in two studies. A two-dimensional descriptive model of the orgasm experience was evaluated by testing hypotheses concerning (a) fit of the model to adjective-ratings data describing male and female orgasm experiences, and (b) sexual context effects on the importance of model components. In the first model-evaluation study, 888 university students (523 women) provided adjective ratings to convey orgasm experiences attained through both solitary masturbation and sex with a partner. In a cross-validation study, 798 university students (503 women) provided similar ratings to convey orgasm experiences attained either through solitary masturbation or through sex with a partner. Overall, findings supported the utility of a two-dimensional model of the orgasm experience, an adjective-rating approach in comparing male and female orgasm, and the importance of examining sexual context effects on the orgasm experience.