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1

Novel permanent magnet machines using Halbach cylinders  

Microsoft Academic Search

This paper describes various permanent magnet machines using Halbach cylinders (arrays), from using pre-magnetised anisotropic magnet segments having varying magnetisation orientations, to those moulded as bonded isotropic or anisotropic NdFeB ring magnets, which are subsequently impulse magnetised using a magnetisation fixture which produces a sinusoidal MMF distribution. Three possible magnetisation fixture designs are described. Various Halbach cylinder machine topologies are

Z. Q. Zhu; Z. P. Xia; K. Atallah; G. W. Jewell; D. Howe

2000-01-01

2

Analysis and comparison of two two-dimensional Halbach permanent magnet arrays for magnetically levitated planar motor  

NASA Astrophysics Data System (ADS)

A novel 2-D Halbach permanent magnet array which can be used in magnetically levitated planar motor is proposed in this paper. The air-gap flux density distribution of the novel 2-D Halbach permanent magnet array is solved by the scalar magnetic potential equation. In order to compare with the well-known Halbach magnet array that was used by Jansen et al. [IEEE Trans. Ind. Appl. 44(4), 1108 (2008)], harmonic analysis of the x- and z- component of the air-gap flux density are carried out by Fourier decomposition. Comparison of Bx and Bz between the two 2-D Halbach magnet arrays are made. And it is verified that the performance of the new Halbach magnet array is superior to the existing Halbach magnet arrays, its higher magnetic flux density and lower high-order harmonics will help to improve the performance of the magnetically levitated planar motor.

Zhang, Lu; Kou, Baoquan; Xing, Feng; Zhang, He

2014-05-01

3

ANALYSIS ON THE STEALTH CHARACTERISTIC OF TWO DIMENSIONAL CYLINDER PLASMA ENVELOPES  

Microsoft Academic Search

Stealth characteristic of two dimensional cylinder plasma envelopes is studied. Three cases about plasma refraction efiect, re?ection characteristic and attenuation by absorbing electromagnetic wave (EMW) are concerned synthetically. As for plasma refraction stealth, EMW traces equation in cylinder plasma is deduced; a novel concept of plasma refraction deviation angle is presented; the relation between refraction deviation angle and incidence angle

Lai-Xuan Ma; Hou Zhang; Zhong Li; Chen-Xin Zhang

2010-01-01

4

Transient heat conduction in two-dimensional functionally graded hollow cylinder with finite length  

Microsoft Academic Search

In this paper a thick hollow cylinder with finite length made of two dimensional functionally graded material (2D-FGM) subjected\\u000a to transient thermal boundary conditions is considered. The volume fraction distribution of materials, geometry and thermal\\u000a boundary conditions are assumed to be axisymmetric but not uniform along the axial direction. The finite element method with\\u000a graded material properties within each element

Masoud Asgari; Mehdi Akhlaghi

2009-01-01

5

Sound generated in laminar flow past a two-dimensional rectangular cylinder  

Microsoft Academic Search

The far-field sound generated from low Mach number flow past a two-dimensional rectangular cylinder is studied by using a two-step aeroacoustic prediction method. In the first step, the incompressible Navier–Stokes equations are solved numerically. This allows the time-dependent acoustic source to be determined from Powell's vortex sound theory. Using this information, in the second step, the inhomogeneous wave equation is

Y. S. K. Liow; B. T. Tan; M. C. Thompson; K. Hourigan

2006-01-01

6

Two-dimensional Green's tensor for gyrotropic clusters composed of circular cylinders.  

PubMed

The construction of Green's tensor for two-dimensional gyrotropic photonic clusters composed of cylinders with circular cross sections using the semi-analytic multipole method is presented. The high efficiency and accuracy of the method is demonstrated. The developed method is applied to gyrotropic clusters that support topological chiral Hall edge states. The remarkable tolerance of chiral Hall edge modes toward substantial cluster separation is revealed. The transformation of chiral Hall edge states as the cluster separation increases is also presented. The excitation of chiral Hall edge modes for different source orientations is considered. Both gyroelectric and gyromagnetic (ferrite) clusters are treated. PMID:25401258

Asatryan, Ara A; Botten, Lindsay C; Fang, Kejie; Fan, Shanhui; McPhedran, Ross C

2014-10-01

7

Two-dimensional finite difference time domain inverse scattering scheme for a perfectly conducting cylinder  

NASA Astrophysics Data System (ADS)

This paper reports a two-dimensional time-domain inverse scattering algorithm based upon the finite-difference time domain method (FDTD) for determining the shape of a perfectly conducting cylinder. FDTD is used to solve the scattering electromagnetic wave of a perfectly conducting cylinder. The inverse problem is resolved by an optimization approach and the global searching scheme asynchronous particle swarm optimization is then employed to search the parameter space. By properly processing the scattered field, some electromagnetic properties can be reconstructed. A set of representative numerical results is presented to demonstrate that the proposed approach is able to efficiently reconstruct the electromagnetic properties of metallic scatterer even when the initial guess is far away from the exact one. In addition, the effects of Gaussian noises on imaging reconstruction are also investigated.

Chen, Chien-Hung; Chiu, Chien-Ching; Sun, Chi-Hsien; Chang, Wan-Ling

2011-01-01

8

Sound generation by a two-dimensional circular cylinder in a uniform flow  

NASA Astrophysics Data System (ADS)

The sound generated by a circular cylinder in a flow at low Mach numbers is investigated by direct solution of the two-dimensional unsteady compressible Navier Stokes equations. Results show that sound pressure waves are generated primarily by vortex shedding from the cylinder surface into its wake. When a vortex is shed from one side of the cylinder, a negative pressure pulse is generated from that side whereas a positive pressure pulse is generated from the other side; alternate vortex shedding from the upper and lower sides of the cylinder produces negative and positive pulses alternately and thus produces sound pressure waves on both sides. The dipolar nature of the generated sound is confirmed; lift dipole dominates the sound field. The Doppler effect is shown to play an important role at finite Mach numbers. The direct solutions are also compared with the solutions obtained by Curle's acoustic analogy. The results show that Curle's solution describes well not only the generation mechanism of the sound but also the propagation process if we take the Doppler effect into consideration.

Inoue, Osamu; Hatakeyama, Nozomu

2002-11-01

9

Dynamic analysis of two-dimensional functionally graded thick hollow cylinder with finite length under impact loading  

Microsoft Academic Search

In this paper a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and\\u000a subjected to impact internal pressure is considered. The axisymmetric conditions are assumed for the 2D-FG cylinder. The finite\\u000a element method with graded material properties within each element is used to model the structure, and the Newmark direct\\u000a integration method is implemented to

Masoud Asgari; Mehdi Akhlaghi; Seyed Mahmoud Hosseini

2009-01-01

10

Convection in the vertical midplane of a horizontal cylinder Comparison of two-dimensional approximations with three-dimensional results  

NASA Technical Reports Server (NTRS)

Experimental results and numerical data on the flow characteristics of core-driven and boundary-layer-driven regimes (CDRs) and (BLDRs) are compared to two-dimensional solutions for heated convective flow in the vertical midplane of a horizontal cylinder. The data were obtained from laser Doppler velocimetry (LDA) measurements and from three-dimensional numerical solutions. It is shown that the approximate solutions gave the correct Rayleigh-number-dependences and distributions for the velocities in the CDR and BLDR regimes. However, the transition between the CDR and the BLDR, as well as the magnitude of the distribution of velocity components, were found to be dependent on the type of two-dimensional approximation selected. In the case of CDR, core velocities were overestimated by as much as 30 percent by the two-dimensional approximations; and in the case of BLDR, the core velocities were overestimated by 40-50 percent as compared to the measured velocities. A schematic illustration of the flow patterns in the cylinder is provided.

Bontoux, P.; Roux, B.; Schiroky, G. H.; Markham, B. L.; Rosenberger, F.

1986-01-01

11

Peak response statistics of vertical cylinders in two-dimensional irregular waves  

SciTech Connect

When dealing with the probabilistic estimation of the peak response of an offshore structure dynamically responding under excitation by unidirectional irregular waves, it becomes apparent that nonlinearities introduced by the wave-structure interaction, and principally associated with the drag contribution of the Morison force model that has been traditionally used to describe this forcing, leads to non-Gaussian statistical properties of not only the forcing, but also the response. However, it is also apparent that for lightly damped structures, the response under certain circumstances can be very narrow-banded, and hence its statistical description would then approach the Gaussian form irrespective of whether the forcing associated with the response is itself highly non-Gaussian or otherwise. This paper treats both a numerical and experimental investigation of the peak response characteristics of compliant bottom-pivoted surface-piercing cylinders subjected to hydrodynamic excitation by unidirectional Pierson-Moskowitz (P-M) irregular waves and modeled as single-degree-of-freedom (SDOF) oscillators with a fixed straight line mode shape (the result of the bottom-pivoted support condition). Conditions under which the response can reasonably be approximated as Gaussian are identified via an upcrossing investigation for the likely peak response in a storm of a nominated period of duration.

Haritos, N. [Univ. of Melbourne, Parkville, Victoria (Australia)

1996-11-01

12

Two-dimensional scattering of a plane wave from a periodic array of dielectric cylinders with arbitrary shape.  

PubMed

A two-dimensional scattering of a plane wave from a periodic array of dielectric cylinders with arbitrary shape using the multigrid-moment method is examined. The scattered field is expressed in terms of the integral form by an infinite summation of the surface integral over the cross section of the reference cylinder. The integral form is converted into the matrix equation by using the moment method. The integration in the elements of the matrix equation is evaluated by the lattice-sums technique to obtain a precise solution. The multigrid method is applied to the matrix equation to improve the CPU time. The CPU time and the residual norm are examined numerically for a given number of iterations and cycle indices. Then the effects of shape and material of the periodic structure on the power reflection coefficient of the fundamental Floquet mode are shown. In addition, the results indicate the effect of changing the relative permittivity of the dielectric coated body and the reflection coefficient. PMID:18594626

Yokota, Mitsuhiro; Sesay, Maurice

2008-07-01

13

A numerical solution of the Navier-Stokes equations for chemically nonequilibrium, merged stagnation shock layers on spheres and two-dimensional cylinders in air  

NASA Technical Reports Server (NTRS)

Results of solving the Navier-Stokes equations for chemically nonequilibrium, merged stagnation shock layers on spheres and two-dimensional cylinders are presented. The effects of wall catalysis and slip are also examined. The thin shock layer assumption is not made, and the thick viscous shock is allowed to develop within the computational domain. The results show good comparison with existing data. Due to the more pronounced merging of shock layer and boundary layer for the sphere, the heating rates for spheres become higher than those for cylinders as the altitude is increased.

Johnston, K. D.; Hendricks, W. L.

1978-01-01

14

Halbach Magnetic Rotor Development  

NASA Technical Reports Server (NTRS)

The NASA John H. Glenn Research Center has a wealth of experience in Halbach array technology through the Fundamental Aeronautics Program. The goals of the program include improving aircraft efficiency, reliability, and safety. The concept of a Halbach magnetically levitated electric aircraft motor will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels, increase efficiency and reliability, reduce maintenance and decrease operating noise levels. Experimental hardware systems were developed in the GRC Engineering Development Division to validate the basic principles described herein and the theoretical work that was performed. A number of Halbach Magnetic rotors have been developed and tested under this program. A separate test hardware setup was developed to characterize each of the rotors. A second hardware setup was developed to test the levitation characteristics of the rotors. Each system focused around a unique Halbach array rotor. Each rotor required original design and fabrication techniques. A 4 in. diameter rotor was developed to test the radial levitation effects for use as a magnetic bearing. To show scalability from the 4 in. rotor, a 1 in. rotor was developed to also test radial levitation effects. The next rotor to be developed was 20 in. in diameter again to show scalability from the 4 in. rotor. An axial rotor was developed to determine the force that could be generated to position the rotor axially while it is rotating. With both radial and axial magnetic bearings, the rotor would be completely suspended magnetically. The purpose of this report is to document the development of a series of Halbach magnetic rotors to be used in testing. The design, fabrication and assembly of the rotors will be discussed as well as the hardware developed to test the rotors.

Gallo, Christopher A.

2008-01-01

15

A detailed treatment of two-dimensional, starved lubrication in the vicinity of two counter-rotating cylinders  

NASA Technical Reports Server (NTRS)

The problem of starved lubrication in the inlet region for the case of line contact between two nondeforming, equal radii cylinders rotating in opposite directions with equal surface speeds is considered. The lubricant is assumed to be a constant density, isoviscous, Newtonian fluid. The usual approach, which involves the use of Reynolds equation everywhere, is not followed. Instead, the situation is restricted to one in which the lubricant enters the contact region in thin films which adhere to the cylinders. Using Reynolds equation only at the line of centers and a suitable thin film approximation far from that point, the intervening region is treated as a general creeping flow region. Solutions, incorporating complete free surface boundary conditions, are obtained numerically. The hitherto unobtained results due to this approach include the existence of a unique free surface location for a fixed set of operating conditions.

Medrow, R. A.; Shipers, L. R.

1982-01-01

16

Uniform Boundedness and Long-Time Asymptotics for the Two-Dimensional Navier-Stokes Equations in an Infinite Cylinder  

NASA Astrophysics Data System (ADS)

The incompressible Navier-Stokes equations are considered in the two-dimensional strip {{R} × [0,L]} , with periodic boundary conditions and no exterior forcing. If the initial velocity is bounded, it is shown that the solution remains uniformly bounded for all time, and that the vorticity distribution converges to zero as {t to infty} . This implies, after a transient period, the emergence of a laminar regime in which the solution rapidly converges to a shear flow described by the one-dimensional heat equation in an appropriate Galilean frame. The approach is constructive and provides explicit estimates on the size of the solution and the lifetime of the turbulent period in terms of the initial Reynolds number.

Gallay, Thierry; Slijep?evi?, Siniša

2014-09-01

17

On the effects of mass and momentum transfer from droplets impacting on steady two-dimensional rimming flow in a horizontal cylinder  

NASA Astrophysics Data System (ADS)

Motivated by applications in aero-engines, steady two-dimensional thin-film flow on the inside of a circular cylinder is studied when the film surface is subject to mass and momentum transfer from impacting droplets. Asymptotic analysis is used systematically to identify distinguished limits that incorporate these transfer effects at leading order and to provide a new mathematical model. Applying both analytical and numerical approaches to the model, a set of stable steady, two-dimensional solutions that fit within the rational framework is determined. A number of these solutions feature steep fronts and associated recirculating pools, which are undesirable in an aeroengine since oil may be stripped away from the steep fronts when there is a core flow external to the film, and recirculation may lead to oil degradation. The model, however, provides a means of investigating whether the formation of the steep fronts on the film surface and of internal recirculation pools can be delayed, or inhibited altogether, by designing jets to deliver prescribed distributions of oil droplets or by the judicious siting of oil sinks. Moreover, by studying pathlines, oil-residence times can be predicted and systems optimized.

Williams, J.; Hibberd, S.; Power, H.; Riley, D. S.

2012-05-01

18

Torque Production in a Halbach Machine  

NASA Technical Reports Server (NTRS)

The NASA John H. Glenn Research Center initiated the investigation of torque production in a Halbach machine for the Levitated Ducted Fan (LDF) Project to obtain empirical data in determining the feasibility of using a Halbach motor for the project. LDF is a breakthrough technology for "Electric Flight" with the development of a clean, quiet, electric propulsor system. Benefits include zero emissions, decreased dependence on fossil fuels, increased efficiency, increased reliability, reduced maintenance, and decreased operating noise levels. A commercial permanent magnet brushless motor rotor was tested with a custom stator. An innovative rotor utilizing a Halbach array was designed and developed to fit directly into the same stator. The magnets are oriented at 90deg to the adjacent magnet, which cancels the magnetic field on the inside of the rotor and strengthens the field on the outside of the rotor. A direct comparison of the commercial rotor and the Halbach rotor was made. In addition, various test models were designed and developed to validate the basic principles described, and the theoretical work that was performed. The report concludes that a Halbach array based motor can provide significant improvements in electric motor performance and reliability.

Eichenberg, Dennis J.; Gallo, Christopher A.; Thompson, William K.; Vrnak, Daniel R.

2006-01-01

19

Two-dimensional Fire codes  

Microsoft Academic Search

To improve the reliability of two-dimensional information, codes that can correct two-dimensional bursts (or spots) may be useful. In this paper a class of two-dimensional burst-correcting codes, called two-dimensional Fire codes, is proposed. The definition of these codes is a natural extension of that of the conventional Fire codes. The two-dimensional Fire code is a two-dimensional cyclic code designed for

H. Imai

1973-01-01

20

Two-Dimensional Gradiometer  

NASA Astrophysics Data System (ADS)

We developed a two-dimensional gradiometer that detects the gradient of a magnetic field in two orthogonal directions to measure the biomagnetic signal in an unshielded environment. We based the gradiometer on a low-Tc superconducting quantum interference device (SQUID) and wire-wound pickup coil. The gradiometer we developed detects both the axial-second-order and planar-first-order gradient of a magnetic field. The experimental results revealed that its noise-reduction ratio (NRR) was 54 dB from 0.5 to 49 Hz and 14 dB (5 times) larger than that of the axial-second-order gradiometer. Moreover, by using the new gradiometer, we obtained a clear magnetocardiography (MCG) waveform in real time without averaging under an unshielded environment (noise level: 3.8 nT/\\sqrt{Hz} at 1 Hz; 150 pT/\\sqrt{Hz} at 10 Hz).

Seki, Yusuke; Kandori, Akihiko

2007-06-01

21

Halbach array DC motor/generator  

DOEpatents

A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An "inside-out" design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then "switched" or "commutated" to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives.

Merritt, Bernard T. (Livermore, CA); Dreifuerst, Gary R. (Livermore, CA); Post, Richard F. (Walnut Creek, CA)

1998-01-01

22

Halbach array DC motor/generator  

DOEpatents

A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An ``inside-out`` design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then ``switched`` or ``commutated`` to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives. 17 figs.

Merritt, B.T.; Dreifuerst, G.R.; Post, R.F.

1998-01-06

23

Two-Dimensional Modulation Codes  

Microsoft Academic Search

A new class of run-length-limited codes in introduced. These codes are called two-dimensional or multitrack modulation codes. Two-dimensional modulation codes provide substantial data storage density increases for multitrack recording systems by operating on multiple tracks in parallel. Procedures for computing the capacity of these new codes are given along with fast algorithms for implementing these procedures. Examples of two-dimensional codes

Michael W. Marcellin; Harold J. Weber

1992-01-01

24

Position sensor for linear synchronous motors employing halbach arrays  

DOEpatents

A position sensor suitable for use in linear synchronous motor (LSM) drive systems employing Halbach arrays to create their magnetic fields is described. The system has several advantages over previously employed ones, especially in its simplicity and its freedom from being affected by weather conditions, accumulated dirt, or electrical interference from the LSM system itself.

Post, Richard Freeman

2014-12-23

25

A two-pole Halbach permanent magnet guideway for high temperature superconducting Maglev vehicle  

Microsoft Academic Search

In order to improve the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle, a two-pole Halbach array’s permanent magnet guideway (PMG) is proposed, which is called as Halbach PMG. The finite element method (FEM) calculations indicate that Halbach PMG has a wider high-field region than the present PMG of equal PM’s transverse section. The levitation force

H. Jing; J. Wang; S. Wang; L. Wang; L. Liu; J. Zheng; Z. Deng; G. Ma; Y. Zhang; J. Li

2007-01-01

26

Energy harvesting from electric power lines employing the Halbach arrays  

NASA Astrophysics Data System (ADS)

This paper proposes non-invasive energy harvesters to scavenge alternating magnetic field energy from electric power lines. The core body of a non-invasive energy harvester is a linear Halbach array, which is mounted on the free end of a piezoelectric cantilever beam. The Halbach array augments the magnetic flux density on the side of the array where the power line is placed and significantly lowers the magnetic field on the other side. Consequently, the magnetic coupling strength is enhanced and more alternating magnetic field energy from the current-carrying power line is converted into electrical energy. An analytical model is developed and the theoretical results verify the experimental results. A power of 566 ?W across a 196 k? resistor is generated from a single wire, and a power of 897 ?W across a 212 k? resistor is produced from a two-wire power cord carrying opposite currents at 10 A. The harvesters employing Halbach arrays for a single wire and a two-wire power cord, respectively, exhibit 3.9 and 3.2 times higher power densities than those of the harvesters employing conventional layouts of magnets. The proposed devices with strong response to the alternating currents are promising to be applied to electricity end-use environment in electric power systems.

He, Wei; Li, Ping; Wen, Yumei; Zhang, Jitao; Lu, Caijiang; Yang, Aichao

2013-10-01

27

Two-dimensional material nanophotonics  

NASA Astrophysics Data System (ADS)

Two-dimensional materials exhibit diverse electronic properties, ranging from insulating hexagonal boron nitride and semiconducting transition metal dichalcogenides such as molybdenum disulphide, to semimetallic graphene. In this Review, we first discuss the optical properties and applications of various two-dimensional materials, and then cover two different approaches for enhancing their interactions with light: through their integration with external photonic structures, and through intrinsic polaritonic resonances. Finally, we present a narrow-bandgap layered material -- black phosphorus -- that serendipitously bridges the energy gap between the zero-bandgap graphene and the relatively large-bandgap transition metal dichalcogenides. The plethora of two-dimensional materials and their heterostructures, together with the array of available approaches for enhancing the light-matter interaction, offers the promise of scientific discoveries and nanophotonics technologies across a wide range of the electromagnetic spectrum.

Xia, Fengnian; Wang, Han; Xiao, Di; Dubey, Madan; Ramasubramaniam, Ashwin

2014-12-01

28

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles  

E-print Network

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles A. Sarwar Available online 19 September 2011 Keywords: Magnetic nanoparticle Targeted drug deliver Magnetic drug targeting Optimal permanent magnet Nano-particle trapping Pushing nanoparticle Halbach array design a b

Shapiro, Benjamin

29

Two-dimensional thermofield bosonization  

SciTech Connect

The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.

Amaral, R.L.P.G. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP, 24210-340 Rio de Janeiro (Brazil)]. E-mail: rubens@if.uff.br; Belvedere, L.V. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP, 24210-340 Rio de Janeiro (Brazil); Rothe, K.D. [Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany)

2005-12-15

30

Two-Dimensional Thermofield Bosonization  

E-print Network

The main objective of this paper is to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real time formalism of Thermofield Dynamics. Formally the results parallel those of the T = 0 case. The well known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. In order to emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.

R. L. P. G. Amaral; L. V. Belvedere; K. D. Rothe

2005-04-01

31

Two-dimensional flexible nanoelectronics  

NASA Astrophysics Data System (ADS)

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.

Akinwande, Deji; Petrone, Nicholas; Hone, James

2014-12-01

32

Two-dimensional river modeling  

E-print Network

conveyance of the section would not reflect the inertial effects influencing this variation in the channel and overbank velocity. The water surface elevation is presented as water surface contours in Figure 12 and as a three-dimensional surface in Figure... OF FIGURES INTRODUCTION One-Dimensional and Two-Dimensional River Modeling Description of the Modeling System GOVERNING EQUATIONS Three-Dimensional Equations of Motion Effects of Turbulence Depth-Averaged Equations of Motion Non-conservative Equations...

Thompson, James Cameron

1988-01-01

33

Two-dimensional optical storage  

Microsoft Academic Search

With storage capacities increasing much faster than data rates, fast read-out of content is becoming a bottleneck for the convenient use of optical storage devices. Two-dimensional optical storage (TwoDOS) is a new concept that solves this data-rate problem by using a multi-spot parallel readout system. In addition, the storage capacity is increased with a factor of at least 2. Using

W. M. J. Coene; D. M. Bruls; A. H. J. Immink; A. M. van der Lee; A. P. Hekstra; J. Riani; S. van Beneden; M. Ciacci; J. W. M. Bergmans; M. Furuki

2005-01-01

34

Observability for two dimensional systems  

NASA Technical Reports Server (NTRS)

Sufficient conditions that a two-dimensional system with output is locally observable are presented. Known results depend on time derivatives of the output and the inverse function theorem. In some cases, no informaton is provided by these theories, and one must study observability by other methods. The observability problem is dualized to the controllability problem, and the deep results of Hermes on local controllability are applied to prove a theorem concerning local observability.

Hunt, L. R.; Su, R.

1981-01-01

35

Two-Dimensional Colloidal Alloys  

NASA Astrophysics Data System (ADS)

We study the structure of mixed monolayers of large (3?m diameter) and small (1?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.

Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.

2011-03-01

36

Two-dimensional colloidal alloys.  

PubMed

We study the structure of mixed monolayers of large (3 ?m diameter) and small (1 ?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations. PMID:21517357

Law, Adam D; Buzza, D Martin A; Horozov, Tommy S

2011-03-25

37

Two-dimensional Coulomb gas  

SciTech Connect

This is a sequel to a recent work of Gaudin, who studied the classical equilibrium statistical mechanics of the two-dimensional Coulomb gas on a lattice at a special value of the coupling constant Gamma such that the model is exactly solvable. This model is briefly reviewed, and it is shown that the correlation functions obey the sum rules that characterize a conductive phase. A related model in which the particles are constrained to move on an array of equidistant parallel lines has simpler mathematics, and the asymptotic behavior of its correlation functions is studied in some detail. In the low-density limit, the lattice model is expected to have the same properties as a system of charged, hard disks; the correlation functions, internal energy, and specific heat of the latter are discussed.

Cornu, F.; Jancovici, B.

1987-10-01

38

Two-dimensional NMR spectroscopy  

SciTech Connect

Written for chemists and biochemists who are not NMR spectroscopists, but who wish to use the new techniques of two-dimensional NMR spectroscopy, this book brings together for the first time much of the practical and experimental data needed. It also serves as information source for industrial, academic, and graduate student researchers who already use NMR spectroscopy, but not yet in two dimensions. The authors describe the use of 2-D NMR in a wide variety of chemical and biochemical fields, among them peptides, steroids, oligo- and poly-saccharides, nucleic acids, natural products (including terpenoids, alkaloids, and coal-derived heterocyclics), and organic synthetic intermediates. They consider throughout the book both the advantages and limitations of using 2-D NMR.

Croasmun, W.R.; Carlson, R.M.K.

1987-01-01

39

Collage of two-dimensional words  

Microsoft Academic Search

We consider a new operation on one-dimensional (resp. two-dimensional) word lan- guages, obtained by piling up, one on top of the other, words of a given recognizable language (resp. two-dimensional recognizable language) on a previously empty one- dimensional (resp. two-dimensional) array. The resulting language is the set of words \\

Christian Choffrut; Berke Durak

2005-01-01

40

Two-dimensional nozzle plume characteristics  

NASA Technical Reports Server (NTRS)

Future high performance aircraft will likely feature asymmetric or two-dimensional nozzles with or without ejectors. In order to design two-dimensional nozzle/ejector systems of minimum size and weight, the plume decay and spreading characteristics of basic two-dimensional nozzles must first be established. The present work deals with the experimental analyses of these plume characteristics and includes the effects of nozzle aspect ratio and flow conditions (jet Mach number and temperature) on the plume decay and spreading of two-dimensional nozzles. Correlations including these variables are developed in a manner similar to those previously developed successfully for conic and dual-flow plumes.

Von Glahn, Uwe H.

1987-01-01

41

Phase Transitions in Two-Dimensional Superconductors  

Microsoft Academic Search

In this thesis, we describe a number of experiments which are designed to explore the theoretically predicted phase transitions for two-dimensional superconductors. We first examine the behavior of a two-dimensional superconductor in the absence of a magnetic field, where the fluctuations in the phase of the superconducting order parameter results in the reduction of the superconducting transition temperature for a

Ali Yazdani

1995-01-01

42

Scanning of two-dimensional space groups.  

PubMed

Tables of the scanning of two-dimensional space groups are presented to determine the frieze-group symmetry of lines that transect two-dimensional crystals. It is shown how these tables can be used to predict the (001) projection symmetries of migration-related segments of coincidence site lattice tilt boundaries with [001] tilt axis. PMID:25537394

Litvin, Daniel B

2015-01-01

43

Mars Pathfinder Two-Dimensional Model  

NSDL National Science Digital Library

This activity is about the Mars Pathfinder spacecraft. Using cardboard and other materials, learners will create a two dimensional model of the spacecraft. A diagram with approximate measures of each component is provided.

2012-08-03

44

Two-Dimensional Planetary Surface Lander  

NASA Astrophysics Data System (ADS)

A systems engineering study was conducted to leverage a new two-dimensional (2D) lander concept with a low per unit cost to enable scientific study at multiple locations with a single entry system as the delivery vehicle.

Hemmati, H.; Sengupta, A.; Castillo, J.; McElrath, T.; Roberts, T.; Willis, P.

2014-06-01

45

Two-dimensional order and disorder thermofields  

SciTech Connect

The main objective of this paper was to obtain the two-dimensional order and disorder thermal operators using the Thermofield Bosonization formalism. We show that the general property of the two-dimensional world according with the bosonized Fermi field at zero temperature can be constructed as a product of an order and a disorder variables which satisfy a dual field algebra holds at finite temperature. The general correlation functions of the order and disorder thermofields are obtained.

Belvedere, L. V. [Instituto de Fisica - Universidade Federal Fluminense, Av. Litora circumflex nea S/N, Boa Viagem Niteroi, CEP 24210-340 Rio de Janeiro (Brazil)

2006-11-15

46

Modeling maglev passenger compartment static magnetic fields from linear Halbach permanent-magnet arrays  

Microsoft Academic Search

Passenger compartment magnetic field levels in a low-speed magnetic levitation (maglev) vehicle that uses linear Halbach permanent-magnet arrays for both levitation and propulsion are computed through superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. End effects due to the finite lengths of the arrays lead to fields that decay much less rapidly

James F. Hoburg

2004-01-01

47

The art and science of magnet design: Selected notes of Klaus Halbach. Volume 2  

SciTech Connect

This volume contains a compilation of 57 notes written by Dr. Klaus Halbach selected from his collection of over 1650 such documents. It provides an historic snapshot of the evolution of magnet technology and related fields as the notes range from as early as 1965 to the present, and is intended to show the breadth of Dr. Halbach`s interest and ability that have long been an inspiration to his many friends and colleagues. As Halbach is an experimental physicist whose scientific interests span many areas, and who does his most innovative work with pencil and paper rather than at the workbench or with a computer, the vast majority of the notes in this volume were handwritten and their content varies greatly--some reflect original work or work for a specific project, while others are mere clarifications of mathematical calculations or design specifications. As the authors converted the notes to electronic form, some were superficially edited and corrected, while others were extensively re-written to reflect current knowledge and notation. The notes are organized under five categories which reflect their primary content: Beam Position Monitors, (bpm), Current Sheet Electron Magnets (csem), Magnet Theory, (thry), Undulators and Wigglers (u-w), and Miscellaneous (misc). Within the category, they are presented chronologically starting from the most recent note and working backwards in time.

NONE

1995-02-01

48

Singularity-free two-dimensional cosmologies  

NASA Astrophysics Data System (ADS)

We present a class of theories of two-dimensional gravity which admits homogeneous and isotropic solutions that are nonsingular and asymptotically approach a FRW matter-dominated universe at late times. These models are generalizations of two-dimensional dilaton gravity and both vacuum solutions and those including conformally coupled matter are investigated. In each case our construction leads to an inflationary stage driven by the gravitational sector. Our work comprises a simple example of the ``nonsingular universe'' constructions of Brandenberger and co-workers.

Moessner, R.; Trodden, M.

1995-03-01

49

Singularity-free two-dimensional cosmologies  

SciTech Connect

We present a class of theories of two-dimensional gravity which admits homogeneous and isotropic solutions that are nonsingular and asymptotically approach a FRW matter-dominated universe at late times. These models are generalizations of two-dimensional dilaton gravity and both vacuum solutions and those including conformally coupled matter are investigated. In each case our construction leads to an inflationary stage driven by the gravitational sector. Our work comprises a simple example of the nonsingular universe'' constructions of Brandenberger and co-workers.

Moessner, R.; Trodden, M. (Department of Physics, Brown University, Providence, Rhode Island 02912 (United States))

1995-03-15

50

Phase Transitions in Two-Dimensional Superconductors  

NASA Astrophysics Data System (ADS)

In this thesis, we describe a number of experiments which are designed to explore the theoretically predicted phase transitions for two-dimensional superconductors. We first examine the behavior of a two-dimensional superconductor in the absence of a magnetic field, where the fluctuations in the phase of the superconducting order parameter results in the reduction of the superconducting transition temperature for a two-dimensional superconductor below the mean field transition temperature. The experimental results presented show the importance of the vortex unbinding mechanism; however they challenge some of the predictions of the current theoretical model for the normal/superconducting transition. We then turn our attention to the behavior of two-dimensional superconductors in the presence of a magnetic field. In this case, our experimental results show that vortices in weakly disordered two-dimensional superconducting films freeze into locally correlated areas at temperatures below the mean field transition temperature. The experimentally measured phase boundary between the liquid phase and the locally ordered solid phase for the vortices in our samples shows good agreement with that predicted by the dislocation unbinding melting mechanism for the two-dimensional vortex lattice. For this transition, we have also done a detailed study of the correlations in the vortex lattices as a function of the strength of pinning in our samples and established a connection between the melting theory and collective pinning theory for vortices in two dimensions. To fully examine the phase diagram of a two-dimensional superconductor we have extended our studies of the properties of this system to the limit of strong disorder, where superconductivity is weak. In this limit, we report experimental evidence for a zero temperature field-tuned superconducting-insulating phase transition driven by quantum fluctuation of the phase of the superconducting order parameter. Overall, the results of this thesis provide an experimental bases for a number of phase transitions in two-dimensional superconductors, thereby establishing a rich phase diagram for this system as a function of the temperature, the magnetic field, and the amount of disorder.

Yazdani, Ali

1995-01-01

51

Crossflow in two-dimensional asymmetric nozzles  

NASA Technical Reports Server (NTRS)

An experimental investigation of the crossflow effects in three contoured, two-dimensional asymmetric nozzles is described. The data were compared with theoretical predictions of nozzle flow by using an inviscid method of characteristics solution and two-dimensional turbulent boundary-layer calculations. The effect of crossflow as a function of the nozzle maximum expansion angle was studied by use of oil-flow techniques, static wall-pressure measurements, and impact-pressure surveys at the nozzle exit. Reynolds number effects on crossflow were investigated.

Sebacher, D. I.; Lee, L. P.

1975-01-01

52

Two-Dimensional Clifford Windowed Fourier Transform  

NASA Astrophysics Data System (ADS)

Recently several generalizations to higher dimension of the classical Fourier transform (FT) using Clifford geometric algebra have been introduced, including the two-dimensional (2D) Clifford-Fourier transform (CFT). Based on the 2D CFT, we establish the two-dimensional Clifford windowed Fourier transform (CWFT). Using the spectral representation of the CFT, we derive several important properties such as shift, modulation, a reproducing kernel, isometry, and an orthogonality relation. Finally, we discuss examples of the CWFT and compare the CFT and CWFT.

Bahri, Mawardi; Hitzer, Eckhard M. S.; Adji, Sriwulan

53

A two-dimensional Couette viscometer for Langmuir monolayers  

NASA Astrophysics Data System (ADS)

We have developed an apparatus that is capable of simultaneously measuring the viscosity of Langmuir monolayers and visualizing their flow. It consists of a circular trough with a nearly circular elastic barrier that can be rotated to generate two-dimensional Couette flow. The "inner cylinder" is a Teflon knife-edge disk that is hung by a thin wire. The torque on the inner cylinder is determined by measuring the angular displacement of the disk. A stepper motor controls the barrier rotation. Viscosity can be measured in two different ways: by oscillating the torsion pendulum and by generating Couette flow. The dynamic viscosity range of the apparatus is 10-4

Ghaskadvi, R. S.; Dennin, Michael

1998-10-01

54

A nonsingular two dimensional black hole  

NASA Astrophysics Data System (ADS)

We construct a model of gravity in 1 + 1 spacetime dimensions in which the solutions approach the Schwarzschild metric at large r and de Sitter space far inside the horizon. Our model may be viewed as a two dimensional application of the ``Limiting Curvature Construction'' of Mukhanov and Brandenberger [Phys. Rev. Lett. 68 (1992) 1969].

Trodden, M.; Mukhanov, V. F.; Brandenberger, R. H.

1993-10-01

55

High Capacity Colored Two Dimensional Codes  

Microsoft Academic Search

Barcodes enable automated work processes without human intervention, and are widely deployed because they are fast and accurate, eliminate many errors and often save time and money. In order to increase the data capacity of barcodes, two dimensional (2D) code were developed; the main challenges of 2D codes lie in their need to store more information and more character types

Antonio Grillo; Alessandro Lentini; Marco Querini; Giuseppe F. Italiano

2010-01-01

56

Spatial resource analysis of two dimensional barcodes  

Microsoft Academic Search

It cannot be denied that documents in the form of hardcopy are still being used, especially important documents such as land titles, application forms, contracts and tickets. However there are reports of forgery cases over the years and as such, it is imperative to have a mechanism for integrity verification of hardcopy document. This research proposed the usage of two-dimensional

Teoh Chin Yew; S. Mazleena; I. Subariah

2008-01-01

57

On the two-dimensional associativity equation  

E-print Network

We consider the two-dimensional associativity (or WDVV) equation u_yyy - u_xxy^2 + u_xxx u_xyy=0 and describe all integrable structures related to it (i.e., Hamiltonian, symplectic, and recursion operators). Infinite hierarchies of symmetries and conservation laws are constructed as well.

Kersten, Paul; Verbovetsky, Alexander; Vitolo, Raffaele

2011-01-01

58

Fractal two-dimensional electromagnetic bandgap structures  

Microsoft Academic Search

Fractal two-dimensional electromagnetic bandgap (EBG) materials are proposed and studied by means of a full-wave method developed for diffraction gratings. Such technique allows us to characterize, In an accurate and rapidly convergent way, the transmission and reflection properties of periodic fractal structures with an arbitrary geometry in the unit cell. Both polarization cases can be treated. A validation of the

Fabrizio Frezza; Lara Pajewski; Giuseppe Schettini

2004-01-01

59

Two-dimensional rotating heat pipe analysis  

Microsoft Academic Search

A detailed transient numerical simulation of rotating heat pipes is presented. This two-dimensional, axisymmetric formulation accounts for the thin liquid condensate film on the inner surface of the rotating pipe wall, the vapor flow in the vapor space, and the unsteady heat conduction in the pipe wall. The thin liquid film is coupled to the vapor velocity at the liquid-vapor

C. Harley; A. Faghri

1995-01-01

60

Two-Dimensional Turbulence in Magnetized Plasmas  

ERIC Educational Resources Information Center

In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…

Kendl, A.

2008-01-01

61

Two dimensional gas turbine engine exhaust nozzle  

SciTech Connect

A two-dimensional variable area gas turbine engine exhaust nozzle is described having thrust reversing capability, the nozzle including spaced apart side wall means and upper and lower flap assemblies connected to the side wall means defining an exhaust gas flow path wihtin the nozzle, the nozzle having a centerline.

Thayer, E.B.; McLafferty, G.H.

1988-06-28

62

Two-dimensional turbulence: a physicist approach  

NASA Astrophysics Data System (ADS)

Much progress has been made on two-dimensional turbulence, these last two decades, but still, a number of fundamental questions remain unanswered. The objective of the present review is to collect and organize the available information on the subject, emphasizing on aspects accessible to experiment, and outlining contributions made on simple flow configurations. Whenever possible, open questions are made explicit. Various subjects are presented: coherent structures, statistical theories, inverse cascade of energy, condensed states, Richardson law, direct cascade of enstrophy, and the inter-play between cascades and coherent structures. The review offers a physicist's view on two-dimensional turbulence in the sense that experimental facts play an important role in the presentation, technical issues are described without much detail, sometimes in an oversimplified form, and physical arguments are given whenever possible. I hope this bias does not jeopardize the interest of the presentation for whoever wishes to visit the fascinating world of Flatland.

Tabeling, Patrick

2002-05-01

63

Graphane: A two-dimensional hydrocarbon  

NASA Astrophysics Data System (ADS)

We predict the stability of an extended two-dimensional hydrocarbon on the basis of first-principles total-energy calculations. The compound that we call graphane is a fully saturated hydrocarbon derived from a single graphene sheet with formula CH. All of the carbon atoms are in sp3 hybridization forming a hexagonal network and the hydrogen atoms are bonded to carbon on both sides of the plane in an alternating manner. Graphane is predicted to be stable with a binding energy comparable to other hydrocarbons such as benzene, cyclohexane, and polyethylene. We discuss possible routes for synthesizing graphane and potential applications as a hydrogen storage material and in two-dimensional electronics.

Sofo, Jorge O.; Chaudhari, Ajay S.; Barber, Greg D.

2007-04-01

64

Graphane: a two-dimensional hydrocarbon  

NASA Astrophysics Data System (ADS)

We predict the stability of a new extended two-dimensional hydrocarbon on the basis of first-principles total energy calculations. The compound that we call graphane is a fully saturated hydrocarbon derived from a single graphene sheet with formula CH. All of the carbon atoms are in sp^3 hybridization forming a hexagonal network and the hydrogen atoms are bonded to carbon on both sides of the plane in an alternating manner. Graphane is predicted to be stable with a binding energy comparable to other hydrocarbons such as benzene, cyclohexane, and polyethylene. We discuss possible routes for synthesizing graphane and potential applications as a hydrogen storage material and in two dimensional electronics.

Sofo, Jorge; Chaudhari, Ajay; Barber, Greg

2007-03-01

65

Electronics based on two-dimensional materials  

NASA Astrophysics Data System (ADS)

The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K.; Colombo, Luigi

2014-10-01

66

Electronics based on two-dimensional materials.  

PubMed

The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments. PMID:25286272

Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K; Colombo, Luigi

2014-10-01

67

Fermions near two-dimensional surfaces  

Microsoft Academic Search

We review work on constrained systems in which (3+1)-dimensional field theories are reduced to effective (2+1)-dimensional ones. Known results are extended to encompass the Dirac equation and the nonrelativistic limit is examined. We discuss to what extent this system can really be made two dimensional and obtain a lower bound on the thickness. Some comments are made about recent theories

Mark Burgess; Bjørn Jensen

1993-01-01

68

Two-Dimensional Visual Language Grammar  

Microsoft Academic Search

\\u000a Visual language refers to the idea that communication occurs through visual symbols, as opposed to verbal symbols or words.\\u000a Contrast to a sentence construction in spoken language with a linear ordering of words, a visual language has a simultaneous\\u000a structure with a parallel temporal and spatial configuration. Inspired by Deikto [5], we propose a two-dimensional string\\u000a or sentence construction of

Siska Fitrianie; Léon J. M. Rothkrantz

2006-01-01

69

Deeply subrecoil two-dimensional Raman cooling  

SciTech Connect

We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of 30 nK (0.15T{sub rec}). This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.

Boyer, V.; Phillips, W.D. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Lising, L.J.; Rolston, S.L. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2004-10-01

70

Statistical Mechanics of Two-dimensional Foams  

E-print Network

The methods of statistical mechanics are applied to two-dimensional foams under macroscopic agitation. A new variable -- the total cell curvature -- is introduced, which plays the role of energy in conventional statistical thermodynamics. The probability distribution of the number of sides for a cell of given area is derived. This expression allows to correlate the distribution of sides ("topological disorder") to the distribution of sizes ("geometrical disorder") in a foam. The model predictions agree well with available experimental data.

Marc Durand

2010-09-07

71

Fully localized two-dimensional embedded solitons  

SciTech Connect

We report the prediction of fully localized two-dimensional embedded solitons. These solitons are obtained in a quasi-one-dimensional waveguide array which is periodic along one spatial direction and localized along the orthogonal direction. Under appropriate nonlinearity, these solitons are found to exist inside the Bloch bands (continuous spectrum) of the waveguide and thus are embedded solitons. These embedded solitons are fully localized along both spatial directions. In addition, they are fully stable under perturbations.

Yang Jianke [Department of Mathematics and Statistics, University of Vermont, Burlington, Vermont 05401 (United States)

2010-11-15

72

Two-dimensional arrays for medical ultrasound  

Microsoft Academic Search

The design, fabrication and evaluation of two-dimensional transducer arrays are described for medical ultrasound imaging. A 4×32, 2.8-MHz array was developed to use new signal processing techniques for improved B-scan imaging including elevation focusing, phase correction and synthetic aperture imaging. Laboratory measurements from typical array elements showed 50 ? insertion loss of -56 dB, -6 dB fractional bandwidth of 43%,

S. W. Smith; G. E. Trahey; O. T. von Ramm

1991-01-01

73

Two-dimensional dense gas dynamics  

Microsoft Academic Search

Certain polyatomic fluids with large molecular weights referred to as dense gases exhibit unusual thermodynamic and flow properties in the region of the thermodynamic critical point. A computer program developed to solve two-dimensional flow fields is used to analyze non- classical dense gas phenomena in the single-phase gas region. A two-step, flux-limited, total variation diminishing scheme solves the time-dependent Euler

Brady Polk Brown

1997-01-01

74

Two dimensional wedge/translating shroud nozzle  

NASA Technical Reports Server (NTRS)

A jet propulsion exhaust nozzle is reported for multi-engine installations which produces high internal/external, thrust-minus-drag, performance for transonic cruise or transonic acceleration as well as improved performance at subsonic and supersonic speeds. A two dimensional wedge/translating shroud provides the variable nozzle exit geometry needed to achieve high engine performance over a wide range of throttle power settings.

Maiden, D. L. (inventor)

1978-01-01

75

Two-dimensional electrophoresis of membrane proteins  

Microsoft Academic Search

One third of all genes of various organisms encode membrane proteins, emphasizing their crucial cellular role. However, due\\u000a to their high hydrophobicity, membrane proteins demonstrate low solubility and a high tendency for aggregation. Indeed, conventional\\u000a two-dimensional gel electrophoresis (2-DE), a powerful electrophoretic method for the separation of complex protein samples\\u000a that applies isoelectric focusing (IEF) in the first dimension and

Ralf J. Braun; Norbert Kinkl; Monika Beer; Marius Ueffing

2007-01-01

76

Two-Dimensional Half-Rate Codes Using Two-Dimensional Finite-Field Filter Banks  

Microsoft Academic Search

This correspondence introduces two-dimensional (2-D) filter bank codes (TDFBCs). The synthesis bank of a two-channel two-dimensional filter bank over a finite field is used to design the 2-D code, and the corresponding analysis bank is used to generate the syndrome of the code. First, we study the encoder of half-rate TDFBCs and show that these linear codes are lattice-cyclic. It

Mina Sartipi; Farshid Delgosha; Faramarz Fekri

2007-01-01

77

Two dimensional echocardiographic diagnosis of situs.  

PubMed Central

At present there is no reliable method of recognising atrial isomerism by two dimensional echocardiography. We therefore used two dimensional echocardiography to examine 158 patients including 25 with atrial isomerism and four with situs inversus. Particular attention was paid to the short and long axis subcostal scans of the abdomen. Using the position of the inferior vena cava and the aorta with respect to the spine it was possible to separate those with situs solitus from the others. Two false positives for abnormal situs had exomphalos. In situs solitus the aorta lay to the left of the spine and the inferior vena cava lay to the right. One patient with situs solitus and azygos continuation of the inferior vena cava also had inferior vena cava to right atrial connection. In the four patients with situs inversus the mirror image of the normal pattern was present. In nine patients with right isomerism the inferior vena cava and aorta ran together on one or other side of the spine. The inferior vena cava, anterior to the aorta at the level of the diaphragm, received at least the right hepatic veins (normal or partial anomalous hepatic venous connection). Of the 16 patients with left isomerism, 14 had azygos continuation of the inferior vena cava which was visualised posterior to the aorta in all but two. All patients with left isomerism had total anomalous hepatic venous connection to one or both atria via one or two separate veins. Two dimensional echocardiography therefore provides the means of detecting abnormal atrial situs and of diagnosing right or left isomerism in the great majority of patients, if not all. Images PMID:7093090

Huhta, J C; Smallhorn, J F; Macartney, F J

1982-01-01

78

Two-dimensional heat flow apparatus  

NASA Astrophysics Data System (ADS)

We have created an apparatus to quantitatively measure two-dimensional heat flow in a metal plate using a grid of temperature sensors read by a microcontroller. Real-time temperature data are collected from the microcontroller by a computer for comparison with a computational model of the heat equation. The microcontroller-based sensor array allows previously unavailable levels of precision at very low cost, and the combination of measurement and modeling makes for an excellent apparatus for the advanced undergraduate laboratory course.

McDougall, Patrick; Ayars, Eric

2014-06-01

79

Two dimensional foam rheology with viscous drag  

E-print Network

We formulate and apply a continuum model that incorporates elasticity, yield stress, plasticity and viscous drag. It is motivated by the two-dimensional foam rheology experiments of Debregeas et al. [G. Debregeas, H. Tabuteau, and J.-M. di Meglio, Phys. Rev. Lett. 87, 178305 (2001)] and Wang et al [Y. Wang, K. Krishan, and M. Dennin, Phys. Rev. E 73, 031401 (2006)], and is successful in exhibiting their principal features an exponentially decaying velocity profile and strain localisation. Transient effects are also identified.

E. Janiaud; D. Weaire; S. Hutzler

2006-07-18

80

Diffusive transport in two-dimensional nematics  

E-print Network

We discuss a dynamical theory for nematic liquid crystals describing the stage of evolution in which the hydrodynamic fluid motion has already equilibrated and the subsequent evolution proceeds via diffusive motion of the orientational degrees of freedom. This diffusion induces a slow motion of singularities of the order parameter field. Using asymptotic methods for gradient flows, we establish a relation between the Doi-Smoluchowski kinetic equation and vortex dynamics in two-dimensional systems. We also discuss moment closures for the kinetic equation and Landau-de Gennes-type free energy dissipation.

Ibrahim Fatkullin; Valeriy Slastikov

2014-03-02

81

Two-dimensional vortices in superconductors  

NASA Astrophysics Data System (ADS)

Superconductors have two key characteristics: they expel magnetic field and they conduct electrical current with zero resistance. However, both properties are compromised in high magnetic fields, which can penetrate the material and create a mixed state of quantized vortices. The vortices move in response to an electrical current, dissipating energy and destroying the zero-resistance state. One of the central problems for applications of high-temperature superconductivity is the stabilization of vortices to ensure zero electrical resistance. We find that vortices in the anisotropic superconductor Bi2Sr2CaCu2O8+? (Bi-2212) have a phase transition from a liquid state, which is inherently unstable, to a two-dimensional vortex solid. We show that at high field the transition temperature is independent of magnetic field, as was predicted theoretically for the melting of an ideal two-dimensional vortex lattice. Our results indicate that the stable solid phase can be reached at any field, as may be necessary for applications involving superconducting magnets. The vortex solid is disordered, as suggested by previous studies at lower fields. But its evolution with increasing magnetic field exhibits unexpected threshold behaviour that needs further investigation.

Chen, Bo; Halperin, W. P.; Guptasarma, Prasenjit; Hinks, D. G.; Mitrovi?, V. F.; Reyes, A. P.; Kuhns, P. L.

2007-04-01

82

Decoherence in two-dimensional quantum walks  

NASA Astrophysics Data System (ADS)

We analyze the decoherence in quantum walks in two-dimensional lattices generated by broken-link-type noise. In this type of decoherence, the links of the lattice are randomly broken with some given constant probability. We obtain the evolution equation for a quantum walker moving on two-dimensional (2D) lattices subject to this noise, and we point out how to generalize for lattices in more dimensions. In the nonsymmetric case, when the probability of breaking links in one direction is different from the probability in the perpendicular direction, we have obtained a nontrivial result. If one fixes the link-breaking probability in one direction, and gradually increases the probability in the other direction from 0 to 1, the decoherence initially increases until it reaches a maximum value, and then it decreases. This means that, in some cases, one can increase the noise level and still obtain more coherence. Physically, this can be explained as a transition from a decoherent 2D walk to a coherent 1D walk.

Oliveira, A. C.; Portugal, R.; Donangelo, R.

2006-07-01

83

Diffraction of a Cylindrical Wave by a Metamaterial Elliptic Cylinder  

NASA Astrophysics Data System (ADS)

Within the framework of two-dimensional geometry, we consider the properties of the electromagnetic fields excited by a filament source which is located near the surface of an elliptic cylinder, The cylinder is made of a metamaterial whose dielectric permittivity and magnetic permeability are equal to minus unity. The influence of the cylinder shape and the position of the source on the effects of subwavelength localization and nonresonance field enhancement is studied.

Anyutin, A. P.; Korshunov, I. P.; Shatrov, A. D.

2014-10-01

84

Rationally synthesized two-dimensional polymers.  

PubMed

Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture. PMID:23695626

Colson, John W; Dichtel, William R

2013-06-01

85

Rationally synthesized two-dimensional polymers  

NASA Astrophysics Data System (ADS)

Synthetic polymers exhibit diverse and useful properties and influence most aspects of modern life. Many polymerization methods provide linear or branched macromolecules, frequently with outstanding functional-group tolerance and molecular weight control. In contrast, extending polymerization strategies to two-dimensional periodic structures is in its infancy, and successful examples have emerged only recently through molecular framework, surface science and crystal engineering approaches. In this Review, we describe successful 2D polymerization strategies, as well as seminal research that inspired their development. These methods include the synthesis of 2D covalent organic frameworks as layered crystals and thin films, surface-mediated polymerization of polyfunctional monomers, and solid-state topochemical polymerizations. Early application targets of 2D polymers include gas separation and storage, optoelectronic devices and membranes, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.

Colson, John W.; Dichtel, William R.

2013-06-01

86

Two-Dimensional Melting under Quenched Disorder  

NASA Astrophysics Data System (ADS)

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.

Deutschländer, Sven; Horn, Tobias; Löwen, Hartmut; Maret, Georg; Keim, Peter

2013-08-01

87

Transport in Two-Dimensional Disordered Semimetals  

NASA Astrophysics Data System (ADS)

We theoretically study transport in two-dimensional semimetals. Typically, electron and hole puddles emerge in the transport layer of these systems due to smooth fluctuations in the potential. We calculate the electric response of the electron-hole liquid subject to zero and finite perpendicular magnetic fields using an effective medium approximation and a complementary mapping on resistor networks. In the presence of smooth disorder and in the limit of a weak electron-hole recombination rate, we find for small but finite overlap of the electron and hole bands an abrupt upturn in resistivity when lowering the temperature but no divergence at zero temperature. We discuss how this behavior is relevant for several experimental realizations and introduce a simple physical explanation for this effect.

Knap, Michael; Sau, Jay D.; Halperin, Bertrand I.; Demler, Eugene

2014-10-01

88

Two-dimensional fourier transform spectrometer  

DOEpatents

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.

DeFlores, Lauren; Tokmakoff, Andrei

2013-09-03

89

Inverse velocity statistics in two dimensional turbulence  

E-print Network

We present a numerical study of two-dimensional turbulent flows in the enstrophy cascade regime, with different large-scale forcings and energy sinks. In particular, we study the statistics of more-than-differentiable velocity fluctuations by means of two recently introduced sets of statistical estimators, namely {\\it inverse statistics} and {\\it second order differences}. We show that the 2D turbulent velocity field, $\\bm u$, cannot be simply characterized by its spectrum behavior, $E(k) \\propto k^{-\\alpha}$. There exists a whole set of exponents associated to the non-trivial smooth fluctuations of the velocity field at all scales. We also present a numerical investigation of the temporal properties of $\\bm u$ measured in different spatial locations.

L. Biferale; M. Cencini; A. Lanotte; D. Vergni

2002-04-10

90

Intrinsic two-dimensional features as textons  

NASA Technical Reports Server (NTRS)

We suggest that intrinsic two-dimensional (i2D) features, computationally defined as the outputs of nonlinear operators that model the activity of end-stopped neurons, play a role in preattentive texture discrimination. We first show that for discriminable textures with identical power spectra the predictions of traditional models depend on the type of nonlinearity and fail for energy measures. We then argue that the concept of intrinsic dimensionality, and the existence of end-stopped neurons, can help us to understand the role of the nonlinearities. Furthermore, we show examples in which models without strong i2D selectivity fail to predict the correct ranking order of perceptual segregation. Our arguments regarding the importance of i2D features resemble the arguments of Julesz and co-workers regarding textons such as terminators and crossings. However, we provide a computational framework that identifies textons with the outputs of nonlinear operators that are selective to i2D features.

Barth, E.; Zetzsche, C.; Rentschler, I.

1998-01-01

91

From two-dimensional materials to heterostructures  

NASA Astrophysics Data System (ADS)

Graphene, hexagonal boron nitride, molybdenum disulphide, and layered transition metal dichalcogenides (TMDCs) represent a class of two-dimensional (2D) atomic crystals with unique properties due to reduced dimensionality. Stacking these materials on top of each other in a controlled fashion can create heterostructures with tailored properties that offers another promising approach to design and fabricate novel electronic devices. In this report, we attempt to review this rapidly developing field of hybrid materials. We summarize the fabrication methods for different 2D materials, the layer-by-layer growth of various vertical heterostructures and their electronic properties. Particular interests are given to in-situ stack aforementioned 2D materials in controlled sequences, and the TMDCs heterostructures.

Niu, Tianchao; Li, Ang

2015-02-01

92

Two-dimensional layered composite photocatalysts.  

PubMed

Two-dimensional (2D) layered nanostructure composites are promising candidates for conducting high-performance energy conversion and environmental remediation. The construction of 2D layered composite photocatalysts can generate many unique properties that do not exist in other kinds of semiconductor composite photocatalyst, which are beneficial for photocatalytic performance enhancement, band gap tuning, heterojunction formation, etc. Recently, these advantages have greatly stimulated the study of 2D layered composite photocatalysts in the field of photocatalysis. This feature article summarizes the recent developments of 2D layered composite photocatalysts for photocatalytic applications, such as photocatalytic hydrogen production, bacterial disinfection, and pollutant degradation. Finally, perspectives on the challenges and opportunities for the future exploration of 2D layered composite photocatalysts are put forward. PMID:24964375

Low, Jingxiang; Cao, Shaowen; Yu, Jiaguo; Wageh, Swelm

2014-09-25

93

Two-dimensional virtual impactors. Final report  

SciTech Connect

Theoretical predictions using both potential flow analyses and solutions to Navier-Stokes equations are made for the operating characteristics of a two-dimensional virtual impactor. Experiments were performed with 2.5 ..mu..m, uranine tagged, di-octylphthalate (DOP) oil droplets for a wide range of prototype geometries to measure the magnitude of internal losses and to fully characterize the instrument response. The influence of geometry including the throat angle (38/sup 0/ less than or equal to ..beta../sub 0/ less than or equal to 58.2/sup 0/) and normalized void width (0.7 less than or equal to h/w less than or equal to 1.5) on the particle cutoff diameter, efficiency curve steepness and properties of the internal particle loss factor are presented for fixed instrument Reynolds numbers Re = 1540 and bleed flow f = 0.1. The theory, supported by trends in the empirical data, predicts that internal particle losses reduce to zero as the normalized void width increases to h/w = 1.4 +- .1 while the data show a minimum at h/w = 1.6 +- .1. Increasing the void width, however, is shown to substantially reduce the steepness of the particle efficiency curves. Visual observations of the onset of fluid separation for two-dimensional jets impinging upon a void were conducted with a scaled-up water model and correlated with theory. It was found that the limiting void width h/sub lim//w marking the onset of fluid instabilities peaked for an intermediate value of the fluid deflecting plate angle ..beta.. approx. = 80/sup 0/ with larger values of h/sub lim//w corresponding to smaller throat angles ..beta../sub 0/. The limiting void width h/sub lim//w also increased with larger bleed flows into the void. These instabilities may make it difficult to correlate experimental virtual impactor data with theory.

Forney, L.J.; Ravenhall, D.G.

1980-12-01

94

Controlling chaos in a fluid flow past a movable cylinder Juan C. Vallejo a  

E-print Network

of view, since the flow is an open flow. Hence, in this paper we analyze a fluid flow past a cylinderControlling chaos in a fluid flow past a movable cylinder Juan C. Vallejo a , Inees P. Mari of a two-dimensional fluid flow past a cylinder is a relatively simple problem with a strong impact in many

Rey Juan Carlos, Universidad

95

Two-dimensional stability of ion-acoustic solitons  

Microsoft Academic Search

Two dimensional generalizations of the Korteweg-de Vries equation appropriate to the propagation of nonlinear ion-acoustic waves are obtained. Soliton solutions are found to exist and they are shown to be stable to two dimensional perturbations.

M. Kako; G. Rowlands

1976-01-01

96

Internal tide generation by arbitrary two-dimensional topography  

E-print Network

To date, analytical models of internal tide generation by two-dimensional ridges have considered only idealized shapes. Here, we advance the Green function approach to address the generation of internal tides by two-dimensional ...

Peacock, Thomas

97

Research on Generation Algorithm of Network Two-Dimensional Code  

Microsoft Academic Search

Two-dimensional code is a new and developing code which has gradually entered people's life. In foreign countries, one-dimensional barcode has been replaced with two-dimensional code in many respects: such as ID card, driver's license, military certificate, etc. But it is not so extensive to use two-dimensional code in China. However, with the development of information technology, the use of two-dimensional

Wei Zhang

2008-01-01

98

An improved two-dimensional code encoding approach for publications  

Microsoft Academic Search

Nowadays, the publishing industry has begun to use the two-dimensional code in cell phones, but the standard is not defined. Compared with single-dimensional bar code, two-dimensional code contains more information and functions. Nowadays, two-dimensional code has been broadly used in some industries, such as mobile communication, logistics and advertising, but not in publishing. This paper introduces an improved two-dimensional code

Wang Liang; Liu Xiaodan

2010-01-01

99

????????????????????? Consideration on Two Dimensional Constraint Codes with Honeycomb Structure  

Microsoft Academic Search

Recently, two-dimensional recording system has developed in order to record information on very high density. Two-dimensional constraint codes also have stud- ied since such recording system requires the constraint with two-dimensionality. It has discussed only about the square lattice as the basic structure of a two-dimensional recording system. In this paper, we propose to use regular hexagonal as basic structure,

Shogo Usami; Akira Watanabe; Tadashi Wadayama

100

Packet Classification Using Two-Dimensional Multibit Tries  

Microsoft Academic Search

We develop fast algorithms to construct space-optimal contrained two-dimensional multibit tries for Internet packet classifier applications. Experimental evidence suggests that using the same memory budget, space-optimal two-dimensional multibit tries require 1\\/4 to 1\\/3 the memory accesses required by two-dimensional one-bit tries for table lookup. A heuristic for two-dimensional multibit tries with switch pointers also is proposed.

Wencheng Lu; Sartaj Sahni

2005-01-01

101

Two-Dimensional Weight-Constrained Codes through Enumeration Bounds  

E-print Network

Two-Dimensional Weight-Constrained Codes through Enumeration Bounds Erik Ordentlich i into An m at a rate H( );( m =m);( n =n). Keywords: Two-dimensional coding Weight-constrained codes Balanced is motivated primarily by the coding problem of two-dimensional balanced binary n m arrays, in which each row

Roth, Ronny

102

E cient Code Constructions for Certain Two-Dimensional Constraints  

E-print Network

E cient Code Constructions for Certain Two-Dimensional Constraints Roman Talyanskyy Tuvi Etzionz, there have been several results reported on two-dimensional runlength-limited coding 7], 8], coding of constraints on two- dimensional binary arrays. The rst constraint considered is that of t-conservative arrays

Roth, Ronny

103

Encorporation of Two Dimensional FrontTracking into  

E-print Network

in Computational Science (PICS) GCT code, version 1.0. This merge adds a two dimensional, discontinuity tracking is the November 92 upgrade of the Stony Brook Code. This version is a two dimensional fully parallel (node only) C­codeEncorporation of Two Dimensional Front­Tracking into PICS GCT 1.0 \\Lambda B. Bielefeld, B

New York at Stoney Brook, State University of

104

Implementations of two-dimensional liquid chromatography  

SciTech Connect

Today scientists must deal with complex samples that either cannot be adequately separated using one-dimensional chromatography or that require an inordinate amount of time for separation. For these cases we need two-dimensional chromatography because it takes far less time to generate a peak capacity n{sub c} twice in a row than to generate a peak capacity n{sub c}{sup 2} once. Liquid chromatography has been carried out successfully on thin layers of adsorbents and along tubes filled with various adsorbents. The first type of separation sorts out the sample components in a physical separation space that is the layer of packing material. The analysis time is the same for all the components of the sample while their migration distance increases with decreasing retention. The resolution between two components having a certain separation factor (a) increases with increasing migration distance, i.e., from the strongly to the weakly retained compounds. In the second type of separation, the sample components are eluted from the column and separated in the time space, their migration distances are all the same while their retention times increase from the unretained to the strongly retained compounds. Separation efficiency varies little with retention, as long as the components are eluted from the column. We call these two types of separation the chromatographic separations in space (LC{sup x}) and the chromatographic separations in time (LC{sup t}), respectively. In principle, there are four ways to combine these two modes and do two-dimensional chromatographic separations, LC{sup t} x LC{sup t}, LC{sup x} x LC{sup t}, LC{sup t} x LC{sup x}, and LC{sup x} x LC{sup x}. We review, discuss and compare the potential performance of these combinations, their advantages, drawbacks, problems, perspectives and results. Currently, column-based combinations (LC{sup t} x LC{sup t}) are the most actively pursued. We suggest that the combination LC{sup x} x LC{sup t} shows exceptional promise because it permits the simultaneous second-dimension separations of all the fractions separated in the first-dimension, thus providing remarkable time saving.

Guiochon, Georges A [ORNL; Marchetti, Nicola [University of Tennessee, Knoxville (UTK); Mriziq, Khaled S [ORNL; Shalliker, R. Andrew [University of Western Sydney, Australia

2008-01-01

105

Turbulent equipartitions in two dimensional drift convection  

SciTech Connect

Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly non-equilibrium systems such as turbulent plasmas. In turbulent systems, energy is no longer a good invariant, but one can utilize the conservation of other quantities, such as adiabatic invariants, frozen-in magnetic flux, entropy, or combination thereof, in order to derive new, turbulent quasi-equilibria. These TEP equilibria assume various forms, but in general they sustain spatially inhomogeneous distributions of the usual thermodynamic quantities such as density or temperature. This mechanism explains the effects of particle and energy pinch in tokamaks. The analysis of the relaxed states caused by turbulent mixing is based on the existence of Lagrangian invariants (quantities constant along fluid-particle or other orbits). A turbulent equipartition corresponds to the spatially uniform distribution of relevant Lagrangian invariants. The existence of such turbulent equilibria is demonstrated in the simple model of two dimensional electrostatically turbulent plasma in an inhomogeneous magnetic field. The turbulence is prescribed, and the turbulent transport is assumed to be much stronger than the classical collisional transport. The simplicity of the model makes it possible to derive the equations describing the relaxation to the TEP state in several limits.

Isichenko, M.B.; Yankov, V.V. [Univ. of California, Santa Barbara, CA (United States). Inst. for Theoretical Physics

1995-07-25

106

Seismic isolation of two dimensional periodic foundations  

NASA Astrophysics Data System (ADS)

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.

Yan, Y.; Laskar, A.; Cheng, Z.; Menq, F.; Tang, Y.; Mo, Y. L.; Shi, Z.

2014-07-01

107

Two-dimensional detector of thermal neutrons  

NASA Astrophysics Data System (ADS)

A two-dimensional detector of thermal neutrons has been designed and constructed for neutron diffraction experiments at the St. Petersburg Nuclear Physics Institute. It is based on a multiwire proportional chamber (MWPC) with cathode strip delay line readout and has a sensitive area of 170×300 mm 2 and anode wire spacing is 4 mm. It operates with a gas mixture of 1.5 bar 3He+2 bar CF 4. To improve the gas purity by a few orders of magnitude, a new technology for fabrication of the detector's electrodes has been developed. An intrinsic resolution of 0.6 mm (FWHM) and a differential nonlinearity of ±5% are achieved. It was shown that the detector, whose efficiency is about 60% for 9 Å neutrons, has a resolution of 2.5 mm along the fine axis and about 4 mm for the perpendicular discrete axis. The dependence of the measured pulse height spectra from the applied high voltage and the electric field in the drift regions has been investigated. It turns out that for thermal neutrons the measured spectra are very similar to those obtained with proportional neutron counters filled with 10 bar 3He.

Andreev, V.; Ganzha, G.; Ilyin, D.; Ivanov, E.; Kovalenko, S.; Krivshich, A.; Nadtochy, A.; Runov, V.

2007-10-01

108

An atlas of two-dimensional materials.  

PubMed

The discovery of graphene and other two-dimensional (2D) materials together with recent advances in exfoliation techniques have set the foundations for the manufacturing of single layered sheets from any layered 3D material. The family of 2D materials encompasses a wide selection of compositions including almost all the elements of the periodic table. This derives into a rich variety of electronic properties including metals, semimetals, insulators and semiconductors with direct and indirect band gaps ranging from ultraviolet to infrared throughout the visible range. Thus, they have the potential to play a fundamental role in the future of nanoelectronics, optoelectronics and the assembly of novel ultrathin and flexible devices. We categorize the 2D materials according to their structure, composition and electronic properties. In this review we distinguish atomically thin materials (graphene, silicene, germanene, and their saturated forms; hexagonal boron nitride; silicon carbide), rare earth, semimetals, transition metal chalcogenides and halides, and finally synthetic organic 2D materials, exemplified by 2D covalent organic frameworks. Our exhaustive data collection presented in this Atlas demonstrates the large diversity of electronic properties, including band gaps and electron mobilities. The key points of modern computational approaches applied to 2D materials are presented with special emphasis to cover their range of application, peculiarities and pitfalls. PMID:24825454

Miró, Pere; Audiffred, Martha; Heine, Thomas

2014-09-21

109

Compact Two-Dimensional Spectrometer Optics  

NASA Technical Reports Server (NTRS)

The figure is a simplified depiction of a proposed spectrometer optical unit that would be suitable for incorporation into a remote-sensing instrumentation system. Relative to prior spectrometer optical assemblies, this unit would be compact and simple, largely by virtue of its predominantly two-dimensional character. The proposed unit would be a combination of two optical components. One component would be an arrayed-waveguide grating (AWG) an integrated-optics device, developed for use in wavelength multiplexing in telecommunications. The other component would be a diffraction grating superimposed on part of the AWG. The function of an AWG is conceptually simple. Input light propagates along a single-mode optical waveguide to a point where it is split to propagate along some number (N) of side-by-side waveguides. The lengths of the optical paths along these waveguides differ such that, considering the paths in a sequence proceeding across the array of waveguides, the path length increases linearly. These waveguides launch quasi-free-space waves into a planar waveguide-coupling region. The waves propagate through this region to interfere onto an array of output waveguides. Through proper choice of key design parameters (waveguide lengths, size and shape of the waveguide coupling region, and lateral distances between waveguides), one can cause the input light to be channeled into wavelength bins nominally corresponding to the output waveguides.

Hong, John

2008-01-01

110

Dynamics of two-dimensional dipole systems  

SciTech Connect

Using a combined analytical/molecular dynamics approach, we study the current fluctuation spectra and longitudinal and transverse collective mode dispersions of the classical two-dimensional (point) dipole system (2DDS) characterized by the {phi}{sub D}(r)={mu}{sup 2}/r{sup 3} repulsive interaction potential; {mu} is the electric dipole strength. The interest in the 2DDS is twofold. First, the quasi-long-range 1/r{sup 3} interaction makes the system a unique classical many-body system, with a remarkable collective mode behavior. Second, the system may be a good model for a closely spaced semiconductor electron-hole bilayer, a system that is in the forefront of current experimental interest. The longitudinal collective excitations, which are of primary interest for the liquid phase, are acoustic at long wavelengths. At higher wave numbers and for sufficiently high coupling strength, we observe the formation of a deep minimum in the dispersion curve preceded by a sharp maximum; this is identical to what has been observed in the dispersion of the zero-temperature bosonic dipole system, which in turn emulates so-called roton-maxon excitation spectrum of the superfluid {sup 4}He. The analysis we present gives an insight into the emergence of this apparently universal structure, governed by strong correlations. We study both the liquid and the crystalline solid state. We also observe the excitation of combination frequencies, resembling the roton-roton, roton-maxon, etc. structures in {sup 4}He.

Golden, Kenneth I.; Kalman, Gabor J.; Hartmann, Peter; Donko, Zoltan [Department of Mathematics and Statistics, Department of Physics, University of Vermont, Burlington, Vermont 05401 (United States); Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467 (United States); Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary and Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467 (United States)

2010-09-15

111

Two-dimensional transition metal carbides.  

PubMed

Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti(2)AlC, Ta(4)AlC(3), (Ti(0.5),Nb(0.5))(2)AlC, (V(0.5),Cr(0.5))(3)AlC(2), and Ti(3)AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the "A" group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior. PMID:22279971

Naguib, Michael; Mashtalir, Olha; Carle, Joshua; Presser, Volker; Lu, Jun; Hultman, Lars; Gogotsi, Yury; Barsoum, Michel W

2012-02-28

112

Two-dimensional flow magnetophoresis of microparticles.  

PubMed

A new two-dimensional micro-flow magnetophoresis device was constructed in a superconducting magnet (10 T) using triangular shaped pole pieces, which could apply a magnetic strength, B(dB/dx), in the range of ca. 0-14,000 T(2) m(-1) across a capillary cell. Polystyrene particles with diameters of 1, 3, and 6 ?m were used as test samples in a paramagnetic medium of 1 M MnCl(2) to evaluate the performance of this method. Microparticles migrated across the capillary along the edge of the pole pieces, and then flowed through the gap in the pole piece at a position defined as the migration distance, depending on the magnetic susceptibility and the size of particles as well as the flow rate. The most effective flow rate to exhibit the largest resolution among the particles was theoretically predicted and experimentally confirmed. By this method, the magnetic susceptibilities of individual deoxygenated and non-deoxygenated red blood cells were measured from the relative migration distance. PMID:22618326

Kawano, Makoto; Watarai, Hitoshi

2012-07-01

113

Nonlinear tunneling in two-dimensional lattices  

SciTech Connect

We present a thorough analysis of the nonlinear tunneling of Bose-Einstein condensates in static and accelerating two-dimensional lattices within the framework of the mean-field approximation. We deal with nonseparable lattices, considering different initial atomic distributions in highly symmetric states. For an analytical description of the condensate before instabilities develop, we derive several few-mode models, analyzing essentially both nonlinear and quasilinear regimes of tunneling. By direct numerical simulations, we show that two-mode models provide an accurate description of tunneling when either initially two states are populated or tunneling occurs between two stable states. Otherwise, a two-mode model may give only useful qualitative hints for understanding tunneling, but does not reproduce many features of the phenomenon. This reflects the crucial role of instabilities developed due to two-body interactions resulting in a non-negligible population of the higher bands. This effect becomes even more pronounced in the case of accelerating lattices. In the latter case we show that the direction of the acceleration is a relevant physical parameter which affects the tunneling by changing the atomic rates at different symmetric states and by changing the numbers of bands involved in the atomic transfer.

Brazhnyi, V. A. [Centro de Fisica Teorica e Computacional, Universidade de Lisboa, Complexo Interdisciplinar, Avenida Professor Gama Pinto 2, Lisbon 1649-003 (Portugal); Konotop, V. V. [Centro de Fisica Teorica e Computacional, Universidade de Lisboa, Complexo Interdisciplinar, Avenida Professor Gama Pinto 2, Lisbon 1649-003 (Portugal); Departamento de Fisica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, Piso 6, Lisbon 1749-016 (Portugal); Kuzmiak, V. [Institute of Photonics and Electronics, v.v.i., Czech Academy of Sciences, Chaberska 57, 182 51 Prague 8 (Czech Republic); Shchesnovich, V. S. [Instituto de Fisica, Universidade Federal de Alagoas, Maceio AL 57072-970 (Brazil)

2007-08-15

114

Solution of the two-dimensional Euler equations with generalized coordinate transformation using flux vector splitting. [for transonic airfoil design  

NASA Technical Reports Server (NTRS)

An implicit finite difference code using flux vector splitting has been developed for solving the two-dimensional inviscid gas dynamics equations. The method is spatially second-order acurate, fully conservative, and uses body-conforming generalized coordinates for treating complex geometries. Numerical results have been obtained for transonic flow over a circular cylinder and airfoils. Steady results for a half cylinder (top and bottom symmetry-imposed) range from critical flow to a strong shock case with rotationally induced flow separation. Full cylinder solutions at freestream Mach number values of 0.5, however, show unsteady oscillation. A perturbation form of the method has also been developed and used to compute both fore and aft inviscid flow separation about a cylinder for a nonuniform incoming stream.

Buning, P. G.; Steger, J. L.

1982-01-01

115

Lamb waves in two-dimensional phononic crystal plate with anisotropic inclusions.  

PubMed

An analysis is given to the band structure of the two-dimensional phononic crystal plate constituted of a square array of elastic anisotropic, circular Pb cylinders embedded in elastic isotropic epoxy. The numerical results show that the band gap can be tuned by rotating the anisotropic material orientation. It is found that the influence of anisotropy on band gap of Lamb wave is clearly different from that on the band gap of bulk waves. The thickness of the system under study is a sensitive parameter to affect the influence of anisotropic materials on the normalized gap width. PMID:21272905

Yao, Yuanwei; Wu, Fugen; Hou, Zhilin; Xin, Zhang

2011-07-01

116

Two-Dimensional Optical Proximity Effects  

NASA Astrophysics Data System (ADS)

In projection printing the proximity effects between adjacent two-dimensional features such as concentric elbows can be the limiting factor in designing layout rules. An aerial image simulation code based on the imaging algorithms in SAMPLE has been developed and used to investigate these proximity effects. The program accepts arbitrary polygonal shapes constructed of rectangular and triangular patches. The image is calculated using Hopkins transmission cross coefficient formulation and uses rapid integral evaluation techniques. The cpu time for this FORTRAN F77 program depends on the size of the mask and the partial coherence factor as 0.25[(1 + ?) 2A(NA/?)2]2 seconds on a DEC VAX 11/780 using double precision, where A is the mask area, ? the coherence factor, NA the numerical aperture and ? the wavelength. The output intensity can be displayed with graphics tools such as UNIGRAFIX or cross-sectioned for input to SAMPLE development simulation along critical paths. Proximity effects in critical regions between features such as nested elbows, contacts near contacts and lines, and lines near large pads are studied. For small contacts studies show that a contact hole can be placed as close as 0.5?/NA microns to another contact hole. For nested elbows the critical effect is the variation in intensity in the straight regions just adjacent to the corner. This undesirable variation is primarily due to the intrafeature intensity interactions and is not greatly influenced by the proximity of another nested elbow. For general feature shapes the proximity effects are reduced by increasing the partial coherence factor to 0.5 or higher but at the cost of reducing contrast and peak intensity. For contact masks a partial coherence of 0.3 is recommended for higher edge slope and peak intensities. Proximity effects of small defects are also illustrated.

Flanner, Philip D.; Subramanian, Shankar; Neureuther, Andrew R.

1986-08-01

117

Two-dimensional material confined water.  

PubMed

Conspectus The interface between water and other materials under ambient conditions is of fundamental importance due to its relevance in daily life and a broad range of scientific research. The structural and dynamic properties of water at an interface have been proven to be significantly difference than those of bulk water. However, the exact nature of these interfacial water adlayers at ambient conditions is still under debate. Recent scanning probe microscopy (SPM) experiments, where two-dimensional (2D) materials as ultrathin coatings are utilized to assist the visualization of interfacial water adlayers, have made remarkable progress on interfacial water and started to clarify some of these fundamental scientific questions. In this Account, we review the recently conducted research exploring the properties of confined water between 2D materials and various surfaces under ambient conditions. Initially, we review the earlier studies of water adsorbed on hydrophilic substrates under ambient conditions in the absence of 2D coating materials, which shows the direct microscopic results. Subsequently, we focus on the studies of water adlayer growth at both hydrophilic and hydrophobic substrates in the presence of 2D coating materials. Ice-like water adlayers confined between hydrophobic graphene and hydrophilic substrates can be directly observed in detail by SPM. It was found that the packing structure of the water adlayer was determined by the hydrophilic substrates, while the orientation of intercalation water domains was directed by the graphene coating. In contrast to hydrophilic substrates, liquid-like nanodroplets confined between hydrophobic graphene and hydrophobic substrates appear close to step edges and atomic-scale surface defects, indicating that atomic-scale surface defects play significant roles in determining the adsorption of water on hydrophobic substrates. In addition, we also review the phenomena of confined water between 2D hydrophilic MoS2 and the hydrophilic substrate. Finally, we further discuss researchers taking advantage of 2D graphene coatings to stabilize confined water nanodroplets to manipulate nanofluidics through applying an external force by using novel SPM techniques. Moreover, for future technology application purposes, the doping effect of confined water is also discussed. The use of 2D materials as ultrathin coatings to investigate the properties of confined water under ambient conditions is developing and recognized as a profound approach to gain fundamental knowledge of water. This ideal model system will provide new opportunities in various research fields. PMID:25539031

Li, Qiang; Song, Jie; Besenbacher, Flemming; Dong, Mingdong

2015-01-20

118

Enhancement of polarizabilities of cylinders with cylinder-slab resonances.  

PubMed

If an object is very small in size compared with the wavelength of light, it does not scatter light efficiently. It is hence difficult to detect a very small object with light. We show using analytic theory as well as full wave numerical calculation that the effective polarizability of a small cylinder can be greatly enhanced by coupling it with a superlens type metamaterial slab. This kind of enhancement is not due to the individual resonance effect of the metamaterial slab, nor due to that of the object, but is caused by a collective resonant mode between the cylinder and the slab. We show that this type of particle-slab resonance which makes a small two-dimensional object much "brighter" is actually closely related to the reverse effect known in the literature as "cloaking by anomalous resonance" which can make a small cylinder undetectable. We also show that the enhancement of polarizability can lead to strongly enhanced electromagnetic forces that can be attractive or repulsive, depending on the material properties of the cylinder. PMID:25641391

Xiao, Meng; Huang, Xueqin; Liu, H; Chan, C T

2015-01-01

119

Packet Classification Using Pipelined Two-Dimensional Multibit Tries  

Microsoft Academic Search

We propose heuristics for the construction of fixed- and variable-stride two-dimensional multibit tries. These multibit tries are suitable for the classification of Internet packets using a pipelined architecture. The pipelined two-dimensional multibit tries constructed by our proposed heuristics are superior, for pipelined architectures, to two-dimensional multibit tries constructed by the best algorithms proposed for non-pipelined architectures.

Wencheng Lu; Sartaj Sahni

2006-01-01

120

Two-dimensional structures in the magnetopause  

NASA Astrophysics Data System (ADS)

A brief review is presented of a recently developed technique for reconstruction of two-dimensional structures in the magnetopause current layer. The method is based on numerical integration of the Grad-Shafranov (GS) equation, using as spatial initial conditions magnetic field and plasma velocity/pressure data measured by a single spacecraft as it traverses the structures. The method is benchmarked as follows, by use of data from the four Cluster II spacecraft: A reconstructed field map, based on data from one spacecraft, is used to predict what should be seen at the other three. These predictions are then compared with what was actually measured. The correlation coefficient between measured and predicted field components can reach values as high as 0.98. The method is then modified to allow ingestion of data from all four spacecraft, the result being field maps that no longer exactly satisfy the GS equation but produce correlation coefficients between measured and predicted field components that are substantially better: values as high as 0.994 have been reached. The reconstruction method is now used to study a few magnetopause encounters, occurring at the fairly high latitudes dictated by the Cluster orbit. Included are events that show no indications of reconnection as well as events that involve incipient reconnection and flux transfer events (FTEs). Even without any of the standard reconnection signatures, the reconstructed magnetopause maps usually display significant internal structure of the layer, in the form of magnetic islands separated by X points. The significance of such structures is discussed. Maps of FTEs indicate that, by the time they reach Cluster, they have often become fossil in the sense that reconnection activity has essentially stopped and the cross section has evolved toward a rounded final state. The axial "core" field in the FTEs is substantial, so that the FTE has the appearance of a somewhat flattened flux rope, embedded in the magnetopause. The core field and motion of the FTEs appear to require that they were generated by component merging at lower latitude and then convected past the observation site at high latitude. The orientation of the invariant axis of the FTEs is fairly well determined in the reconstruction technique, by a process of optimizing the correlation coefficient. In a test case, it shows good agreement with the orientation found from an earlier method [Khrabrov and Sonnerup, JGR, June, 1998], which technique is applicable when a spacecraft has an encounter with the external field, draped over an FTE bulge. The axis orientation of an FTE should provide an indication of the orientation of the reconnection line at which it was created. The orientations found are reasonably consistent with this expectation. The closed magnetic flux in the direction perpendicular to the FTE axis, i.e., in the reconstruction plane, can be calculated from the map and, using the time separation between FTEs, can be used to estimate the average reconnection electric field during the creation of the FTE. The results are in reasonable agreement with expectations.

Sonnerup, B.; Hasegawa, H.

121

Turbulent Flow Between Rotating Cylinders  

NASA Technical Reports Server (NTRS)

The turbulent air flow between rotating cylinders was investigated. The distributions of mean speed and of turbulence were measured in the gap between a rotating inner and a stationary outer cylinder. The measurements led to the conclusion that the turbulent flow in the gap cannot be considered two dimensional, but that a particular type of secondary motion takes place. It is shown that the experimentally found velocity distribution can be fully understood under the assumption that this secondary motion consists of three-dimensional ring-shape vortices. The vortices occur only in pairs, and their number and size depend on the speed of the rotating cylinder; the number was found to decrease with increasing speed. The secondary motion has an essential part in the transmission of the moment of momentum. In regions where the secondary motion is negligible, the momentum transfer follows the laws known for homologous turbulence. Ring-shape vortices are known to occur in the laminar flow between rotating cylinders, but it was hitherto unknown that they exist even at speeds that are several hundred times the critical limit.

Shih-I, Pai

1943-01-01

122

Silly Cylinders  

NSDL National Science Digital Library

This is a short activity where students determine the density of the human body by considering each part of the body to be a cylinder. I use this activity during the 2nd week of school, so students have already had some practice with measurement. In addition to providing students with practice in data collection and problem solving, it is a good activity that allows teachers to measure studentsâ previous knowledge in these areas.

Depalma, Darlene

2012-07-09

123

Characteristics of two-dimensional flow around a rotating circular cylinder near a plane wall  

E-print Network

the rotation rate is greater than the critical value, the Kármán vortex shedding is extinct and the flow and the wall. We quantify the effects of and h on the hydrodynamic forces and the frequency of vortex shedding depend on . The flow is steady when h hdown, while it has a wake of a regular vortex street when h hup

Luo, Li-Shi

124

A Hybrid Approach To Tandem Cylinder Noise  

NASA Technical Reports Server (NTRS)

Aeolian tone generation from tandem cylinders is predicted using a hybrid approach. A standard computational fluid dynamics (CFD) code is used to compute the unsteady flow around the cylinders, and the acoustics are calculated using the acoustic analogy. The CFD code is nominally second order in space and time and includes several turbulence models, but the SST k - omega model is used for most of the calculations. Significant variation is observed between laminar and turbulent cases, and with changes in the turbulence model. A two-dimensional implementation of the Ffowcs Williams-Hawkings (FW-H) equation is used to predict the far-field noise.

Lockard, David P.

2004-01-01

125

Demonstration of Halbach-like magnets for improving microwave window power capacity  

NASA Astrophysics Data System (ADS)

The application of a resonant magnetic field to suppress the multipactor at the vacuum/dielectric interface of a high-power microwave window was theoretically proposed by Chang et al. [Appl. Phys. Lett. 96, 111502 (2010)] and the proof-of-principle was experimentally demonstrated by Chang et al. [Appl. Phys. Lett. 97, 141501 (2010)]. However, for transmitting gigawatt power, conventional large-scale magnets have the significant drawback of a nonuniform and heterogeneous B-field, which enhances the multipactor rather than suppresses it. The Halbach-like magnets for generating the transverse homogeneous B-field in a large scale are studied for suppressing the multipactor; the underlying physics in the particle-in-cell simulation was simulated, and the window breakdown threshold was significantly enhanced at multi-gigawatt.

Chang, Chao; Liu, Yansheng; Ouyang, Xiaoping; Guo, Letian; Wu, Xiaolong; Sun, Xu; Wang, Limin

2014-09-01

126

The classical solutions of two-dimensional gravity  

E-print Network

The solutions of two-dimensional gravity following from a non-linear Lagrangian L = f(R) are classified, and their symmetry and singularity properties are described. Then a conformal transformation is applied to rewrite these solutions as analogous solutions of two-dimensional Einstein-dilaton gravity and vice versa.

Hans - Juergen Schmidt

1999-05-15

127

Completeness through Flatness in Two-Dimensional Temporal Logic  

E-print Network

] for an overview) to develop two-dimensional modal logics taking care of the linguistic phenomenon that the truth (Venema [26]) which is based on the idea that in its semantics, transitions (arrows) do not link the possible worlds, they are the possible worlds. Two-dimensional arrow logic arises if we see transitions

Venema, Yde

128

Two-dimensional simulation of the polarization switching in ferroelectrics  

NASA Astrophysics Data System (ADS)

The main switching properties in ferroelectrics are simulated within the framework of the extended Ishibashi dipole-lattice model including the dipole-dipole interaction in a two-dimensional case. The mechanism of the polarization reversal is modeled in the two-dimensional case. The results of the modeling are in a good agreement with experimental data for the set of materials.

Bakaleinikov, L. A.; Gordon, A.

2009-12-01

129

Automatic identification technology — Application of two-dimensional code  

Microsoft Academic Search

With the modern development of intelligent information society, automatic identification technology will be a research priority. This article focuses on one field of automatic identification technology - two-dimensional code technology. By studying the application of two-dimensional codes, the application of certain areas could be promoted, so as to improve the development of automatic identification technology in China, promote China's economic

Tao Sun; Di Zhou

2011-01-01

130

Two-Dimensionally Isotropic High Index Metamaterials Yushin Kim1  

E-print Network

Two-Dimensionally Isotropic High Index Metamaterials Yushin Kim1 , Muhan Choi1,2 , Seung Hoon Lee1 of Korea bmin@kaist.ac.kr Abstract: We fabricated two-dimensionally isotropic high index metamaterials indices in the terahertz frequency range. OCIS codes: (160.3918) Metamaterials; (300.6495) Spectroscopy

Park, Namkyoo

131

Two-dimensional wavelet compression of ion mobility spectra  

Microsoft Academic Search

A two-dimensional wavelet compression method has been developed as a tool for portable ion mobility sensors. Ion mobility spectrometry (IMS) offers chemical sensors with low detection limits and rapid response for many compounds. Two-dimensional wavelet compression yields compressions greater than 99% without significant loss of information. A method has also been developed and evaluated to optimize the compression. The compression

Aaron A. Urbas; Peter B. Harrington

2001-01-01

132

Adiabatic Single Scan Two-Dimensional NMR Spectrocopy Philippe Pelupessy*,  

E-print Network

on the use adiabatic pulses, for single scan two-dimensional NMR experiments (Frydman et al., Proc. Nat. Acad- and heteronuclear experiments are presented. Introduction The introduction of two-dimensional (2D) experiments has revolutionized the field of nuclear magnetic resonance (NMR).1,2 Unfortunately, these experiments are inherently

133

Two-Dimensional Signal Transmission for Networked Sensing  

E-print Network

Transmission (2DST)" for connecting a large number of devices, using microwave propagation localized in a thin in which signals are conveyed by microwave propagation localized within a two-dimensional signal. In this paper, first we analyze two dimensional propagation of electromagnetic wave in a thin layer. We show

Shinoda, Hiroyuki

134

PRESSURE MEASUREMENT IN A TWO DIMENSIONAL UNSTEADY FLOW  

E-print Network

PRESSURE MEASUREMENT IN A TWO DIMENSIONAL UNSTEADY FLOW William Walker Virginia Polytechnic to obtain unsteady aerodynamic data from a two dimensional wing, and analyzing the pressure variations with time over the wing surface. The data was gathered by using electronic pressure transducers

Patil, Mayuresh

135

Information technologies for comprehensive two-dimensional gas chromatography  

E-print Network

Review Information technologies for comprehensive two-dimensional gas chromatography Stephen E December 2003 Available online 8 March 2004 Abstract Comprehensive two-dimensional gas chromatography (GC Ã?-dimensional gas chromatography; GCÃ?GC; Information technology; Image processing; Visualization; Computer

Reichenbach, Stephen E.

136

Spin and Valley Noise in Two-Dimensional Dirac Materials  

NASA Astrophysics Data System (ADS)

We develop a theory for optical Faraday rotation noise in two-dimensional Dirac materials. In contrast to spin noise in conventional semiconductors, we find that the Faraday rotation fluctuations are influenced not only by spins but also the valley degrees of freedom attributed to intervalley scattering processes. We illustrate our theory with two-dimensional transition-metal dichalcogenides and discuss signatures of spin and valley noise in the Faraday noise power spectrum. We propose optical Faraday noise spectroscopy as a technique for probing both spin and valley relaxation dynamics in two-dimensional Dirac materials.

Tse, Wang-Kong; Saxena, A.; Smith, D. L.; Sinitsyn, N. A.

2014-07-01

137

Two-dimensional array codes correcting rectangular burst errors  

Microsoft Academic Search

Two-dimensional array codes correcting rectangular burst errors are considered. We give a construction and examples of linear\\u000a two-dimensional array codes correcting rectangular burst errors of size b\\u000a 1 b\\u000a 2 with minimum redundancy r = 2b\\u000a 1\\u000a b\\u000a 2. We present constructions of cyclic two-dimensional array codes correcting phased and arbitrary rectangular burst errors;\\u000a their encoding and decoding algorithms are

I. M. Boyarinov

2006-01-01

138

Local curvature and stability of two-dimensional systems  

E-print Network

We propose a fast method to determine the local curvature in two-dimensional (2D) systems with arbitrary shape. The curvature information, combined with elastic constants obtained for a planar system, provides an accurate ...

Guan, Jie

139

Quasiparticle Energy and Excitons in Two-Dimensional Structures.  

E-print Network

??Two-dimensional materials, such as graphene-related structures, transition metal dichalcogenides, are attracting enormous interest in nowadays condensed matter physics. They not only serve as ideal testbeds… (more)

Liang, Yufeng

2014-01-01

140

Single particle spectrum of the two dimensional electron gas  

E-print Network

Accurate spectroscopy has driven advances in chemistry, materials science, and physics. However, despite their importance in the study of highly correlated systems, two-dimensional systems (2DES) have proven difficult to ...

Dial, Oliver Eugene, III

2007-01-01

141

Optical properties of two-dimensional transition metal dichalcogenides  

E-print Network

The re-discovery of the atomically thin transition metal dichalcogenides (TMDs), which are mostly semiconductors with a wide range of band gaps, has diversified the family of two-dimensional materials and boosted the ...

Lin, Yuxuan, S.M. Massachusetts Institute of Technology

2014-01-01

142

Design and analysis of a two-dimensional camera array  

E-print Network

I present the design and analysis of a two-dimensional camera array for virtual studio applications. It is possible to substitute conventional cameras and motion control devices with a real-time, light field camera array. ...

Yang, Jason C. (Jason Chieh-Sheng), 1977-

2005-01-01

143

Model of a Negatively Curved Two-Dimensional Space.  

ERIC Educational Resources Information Center

Describes the construction of models of two-dimensional surfaces with negative curvature that are used to illustrate differences in the triangle sum rule for the various Big Bang Theories of the universe. (JRH)

Eckroth, Charles A.

1995-01-01

144

Healing of defects in a two-dimensional granular crystal  

E-print Network

Using a macroscopic analog for a two dimensional hexagonal crystal, we perform an experimental investigation of the self-healing properties of circular grain defects with an emphasis on defect orientation. A circular grain ...

Rice, Marie C

2014-01-01

145

Two-dimensional signal processing with application to image restoration  

NASA Technical Reports Server (NTRS)

A recursive technique for modeling and estimating a two-dimensional signal contaminated by noise is presented. A two-dimensional signal is assumed to be an undistorted picture, where the noise introduces the distortion. Both the signal and the noise are assumed to be wide-sense stationary processes with known statistics. Thus, to estimate the two-dimensional signal is to enhance the picture. The picture representing the two-dimensional signal is converted to one dimension by scanning the image horizontally one line at a time. The scanner output becomes a nonstationary random process due to the periodic nature of the scanner operation. Procedures to obtain a dynamical model corresponding to the autocorrelation function of the scanner output are derived. Utilizing the model, a discrete Kalman estimator is designed to enhance the image.

Assefi, T.

1974-01-01

146

Near-Surface Geophysics: Two-Dimensional Resistivity  

USGS Multimedia Gallery

USGS hydrologist conducts a two-dimensional (2D) resistivity survey to investigate and characterize the shallow subsurface. The survey was conducted as part of an applied research effort by the USGS Office of Groundwater Branch of Geophysics in 2006....

147

Difficulties that Students Face with Two-Dimensional Motion  

ERIC Educational Resources Information Center

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.

Mihas, P.; Gemousakakis, T.

2007-01-01

148

Quantization of two-dimensional gravity with dynamical torsion  

NASA Astrophysics Data System (ADS)

We consider two-dimensional gravity with dynamical torsion in the BV (Batalin-Vilkovisky) and BLT (Batalin-Lavrov-Tyutin) formalisms of gauge theory quantization, as well as in the background field method.

Lavrov, P. M.; Moshin, P. Yu

1999-07-01

149

Two-dimensional hydrodynamic model of St. Lucie Estuary  

SciTech Connect

A two-dimensional hydrodynamic model of St. Lucie Estuary was developed to assess the impact of drainage canal discharge and storm water runoff. Water surface elevation, two-dimensional velocity field and salinity are collected during 1998--1998 ENSO episode. The data sets cover an eight months period that includes both wet ad dry weather conditions. The model has been applied to St. Lucie Estuary salinity study. It will also provide flow fields to a water quality model.

Hu, G.G.

1999-07-01

150

Shell Model of Two-dimensional Turbulence in Polymer Solutions  

E-print Network

We address the effect of polymer additives on two dimensional turbulence, an issue that was studied recently in experiments and direct numerical simulations. We show that the same simple shell model that reproduced drag reduction in three-dimensional turbulence reproduces all the reported effects in the two-dimensional case. The simplicity of the model offers a straightforward understanding of the all the major effects under consideration.

Roberto Benzi; Nizan Horesh; Itamar Procaccia

2003-10-13

151

Sensor Networking based on Two-Dimensional Signal Transmission Technology  

Microsoft Academic Search

This paper introduces our project of sensor networking technology called two-dimensional signal transmission (2DST). 2DST is a new form of room-size communication, in which the signal energy is confined in thin sheets. The sheet is composed of a dielectric layer sandwiched between a conductive mesh and a continuous conductive layer, typically. Signals are sent by microwaves propagating in the two-dimensional

Hiroyuki Shinoda

2006-01-01

152

The Two-Dimensional Bar Code Application in Book Management  

Microsoft Academic Search

Two-dimensional bar code is one of the most basic and key technologies to achieve the process of identifying information technology for the Internet of things. This paper focuses on book management based on two-dimensional bar code through Visual Basic.NET and SQL Server databases. It can achieve anti-counterfeiting, automatic book information entry, reader identification and library lending management. It can also

He Xuechen

2010-01-01

153

Two-dimensional QCD as a string theory  

Microsoft Academic Search

I explore the possibility of finding an equivalent string representation of\\u000atwo dimensional QCD. I develop the large N expansion of the ${\\\\rm QCD_2}$\\u000apartition function on an arbitrary two dimensional Euclidean manifold. If this\\u000ais related to a two-dimensional string theory then many of the coefficients of\\u000athe ${1\\\\over N}$ expansion must vanish. This is shown to be true

David J. Gross

1993-01-01

154

Ground ring of two-dimensional string theory  

Microsoft Academic Search

String theories with two-dimensional space-time target spaces are characterized by the existence of a ``ground ring'' of operators of spin (0, 0). By understanding this ring, one can understand the symmetries of the theory and illuminate the relation of the critical string theory to matrix models. The symmetry groups that arise are, roughly, the area-preserving diffeomorphisms of a two-dimensional phase

Edward Witten

1992-01-01

155

Numerical modeling of two-dimensional confined flows  

NASA Technical Reports Server (NTRS)

A numerical model of two-dimensional confined flows is presented. The flow in the duct is partitioned into finite streams. The difference equations are then obtained by applying conservation principles directly to the individual streams. A listing of a computer code based on this approach in FORTRAN 4 language is presented. The code computes two dimensional compressible turbulent flows in ducts when the duct area along the flow is specified and the pressure gradient is unknown.

Greywall, M. S.

1979-01-01

156

On GID-testable two-dimensional iterative arrays  

Microsoft Academic Search

A new approach is presented for easily testable two-dimensional iterative arrays. It is an improvement on GI-testability (Group\\u000a Identical testability) and is referred to as GID-testability (Group Identical and Different testability). In a GID-testable\\u000a two-dimensional array, the primaryx andy outputs are organized into groups and every group has more than one output. This is similar to the GI-testable arrays. However,

Weikang Huang; F. Lombard

1994-01-01

157

Two-dimensional thermomechanical analysis of continuous casting process  

Microsoft Academic Search

In this work the two-dimensional analysis of continuous casting of low carbon steel was presented. The interaction between moved ingot, copper mould and transport rolls was modeling. The influence of liquid steel ferrostatic pressure and coupled between temperature and deformation fields were taken into consideration.For thermal analysis (with phase change), the two-dimensional unsteady-state heat conduction equation with enthalpy convention was

M. Janik; H. Dyja; S. Berski; G. Banaszek

2004-01-01

158

C-Testability of Two-Dimensional Iterative Arrays  

Microsoft Academic Search

The issue of testing two-dimensional iterative arrays with a constant number of test vectors independent of the array size (C-testability) is discussed in this paper. Sufficient conditions for C-testability are stated. It is shown that any two-dimensional array can be modified to become C-testable. An extension to systolic (synchronous) arrays is made. The approach simplifies testing systolic arrays by using

Hasan Elhuni; Anastasios Vergis; Larry L. Kinney

1986-01-01

159

Two-dimensional ionization chamber arrays for IMRT plan verification  

SciTech Connect

In this paper we describe a concept for dosimetric treatment plan verification using two-dimensional ionization chamber arrays. Two different versions of the 2D-ARRAY (PTW-Freiburg, Germany) will be presented, a matrix of 16x16 chambers (chamber cross section 8 mmx8 mm; the distance between chamber centers, 16 mm) and a matrix of 27x27 chambers (chamber cross section 5 mmx5 mm; the distance between chamber centers is 10 mm). The two-dimensional response function of a single chamber is experimentally determined by scanning it with a slit beam. For dosimetric plan verification, the expected two-dimensional distribution of the array signals is calculated via convolution of the planned dose distribution, obtained from the treatment planning system, with the two-dimensional response function of a single chamber. By comparing the measured two-dimensional distribution of the array signals with the expected one, a distribution of deviations is obtained that can be subjected to verification criteria, such as the gamma index criterion. As an example, this verification method is discussed for one sequence of an IMRT plan. The error detection capability is demonstrated in a case study. Both versions of two-dimensional ionization chamber arrays, together with the developed treatment plan verification strategy, have been found to provide a suitable and easy-to-handle quality assurance instrument for IMRT.

Poppe, Bjoern; Blechschmidt, Arne; Djouguela, Armand; Kollhoff, Ralf; Rubach, Antje; Willborn, Kay C.; Harder, Dietrich [Klinik fuer Strahlentherapie und Internistische Onkologie, Pius-Hospital, Oldenburg, Germany, and Carl-von-Ossietzky-Universitaet Oldenburg, Oldenburg (Germany); Carl-von-Ossietzky-Universitaet Oldenburg, Oldenburg (Germany); Klinik fuer Strahlentherapie und Internistische Onkologie, Pius-Hospital, Oldenburg (Germany); Georg-August-Universitaet Goettingen, Goettingen (Germany)

2006-04-15

160

Federated two-dimensional electrophoresis database: a simple means of publishing two-dimensional electrophoresis data.  

PubMed

While a two-dimensional electrophoresis (2-DE) database is a relatively old concept, in recent years it generated renewed interest within the 2-DE community due to two main factors: (i) The high reproducibility of the current 2-DE method allows 2-DE images to be exchanged and compared between laboratories. (ii) The recent development of faster and more powerful techniques for protein identification such as microsequencing, matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) and amino acid composition makes the production of reference protein maps and 2-DE databases cost- and time-effective. Additionally, the Internet network's current increase in popularity, combined with the rapid growth of Internet-connected laboratories, provides a straightforward means of publishing and sharing 2-DE data. While a small number of laboratories have already successfully published their data over the net, the increasing number of 2-DE database servers that are currently being set up will sooner or later require some kind of standardization. Unfortunately, standardization can be a long and cumbersome process inevitably leading to undesirable compromises. A federated database offers a simple and efficient way to publish and share 2-DE data without the need for standardization. Taking advantage of Internet protocols such as World Wide Web, they allow each laboratory to maintain their own database and to interconnect it with other similar databases through the use of active cross-references. This paper first presents guidelines for building a federated 2-DE database that may easily be followed by most laboratories. It then briefly reviews the state-of-the-art in networked 2-DE databases, and finally describes the SWISS-2DPAGE database which fully implements the concept of a federated 2-DE database. PMID:8740178

Appel, R D; Bairoch, A; Sanchez, J C; Vargas, J R; Golaz, O; Pasquali, C; Hochstrasser, D F

1996-03-01

161

Two-Dimensional Grammars And Their Applications To Artificial Intelligence  

NASA Astrophysics Data System (ADS)

During the past several years, the concepts and techniques of two-dimensional grammars1,2 have attracted growing attention as promising avenues of approach to problems in picture generation as well as in picture description3 representation, recognition, transformation and manipulation. Two-dimensional grammar techniques serve the purpose of exploiting the structure or underlying relationships in a picture. This approach attempts to describe a complex picture in terms of their components and their relative positions. This resembles the way a sentence is described in terms of its words and phrases, and the terms structural picture recognition, linguistic picture recognition, or syntactic picture recognition are often used. By using this approach, the problem of picture recognition becomes similar to that of phrase recognition in a language. However, describing pictures using a string grammar (one-dimensional grammar), the only relation between sub-pictures and/or primitives is the concatenation; that is each picture or primitive can be connected only at the left or right. This one-dimensional relation has not been very effective in describing two-dimensional pictures. A natural generaliza-tion is to use two-dimensional grammars. In this paper, two-dimensional grammars and their applications to artificial intelligence are presented. Picture grammars and two-dimensional grammars are introduced and illustrated by examples. In particular, two-dimensional grammars for generating all possible squares and all possible rhombuses are presented. The applications of two-dimensional grammars to solving region filling problems are discussed. An algorithm for region filling using two-dimensional grammars is presented together with illustrative examples. The advantages of using this algorithm in terms of computation time are also stated. A high-level description of a two-level picture generation system is proposed. The first level is the picture primitive generation using two-dimensional grammars. The second level is picture generation using either string description or entity-relationship (ER) diagram description. Illustrative examples are also given. The advantages of ER diagram description together with its comparison to string description are also presented. The results obtained in this paper may have useful applications in artificial intelligence, robotics, expert systems, picture processing, pattern recognition, knowledge engineering and pictorial database design. Furthermore, examples related to satellite surveillance and identifications are also included.

Lee, Edward T.

1987-05-01

162

Backscatter RCS for TE and TM excitations of dielectric-filled cavity-backed apertures in two-dimensional bodies  

NASA Technical Reports Server (NTRS)

Transverse electric (TE) and transverse magnetic (TM) scattering from dielectric-filled, cavity-backed apertures in two-dimensional bodies are treated using the method of moments technique to solve a set of combined-field integral equations for the equivalent induced electric and magnetic currents on the exterior of the scattering body and on the associated aperture. Results are presented for the backscatter radar cross section (RCS) versus the electrical size of the scatterer for two different dielectric-filled cavity-backed geometries. The first geometry is a circular cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the cylinder is dielectric filled and is also of circular cross section. The two cylinders (external and internal) are of different radii and their respective longitudinal axes are parallel but not collocated. The second is a square cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the square cylinder is dielectric-filled and is also of square cross section.

Goggans, Paul M.; Shumpert, Thomas H.

1991-01-01

163

Read\\/Write Channel Modeling and Two-Dimensional Neural Network Equalization for Two-Dimensional Magnetic Recording  

Microsoft Academic Search

An accurate medium modeling method of discretized granular medium with non-magnetic grain boundaries using a discrete Voronoi diagram is proposed for two-dimensional magnetic recording. A simple closed-form representation of a double-shielded reader sensitivity function is also proposed for modeling the reading process. Moreover, a two-dimensional neural network equalizer (2D-NNE) is proposed to mitigate the influence of intertrack interference and jitter-like

Masato Yamashita; Hisashi Osawa; Yoshihiro Okamoto; Yasuaki Nakamura; Yoshio Suzuki; Kenji Miura; Hiroaki Muraoka

2011-01-01

164

High resolution, two-dimensional imaging, microchannel plate detector for use on a sounding rocket experiment  

NASA Technical Reports Server (NTRS)

We discuss a high resolution microchannel plate (MCP) imaging detector to be used in measurements of Doppler-shifted hydrogen Lyman-alpha line emission from Jupiter and the interplanetary medium. The detector is housed in a vacuum-tight stainless steel cylinder (to provide shielding from magnetic fields) with a MgF2 window. Operating at nominal voltage, the four plate configuration provides a gain of 1.2 x 10 exp 7 electrons per incident photon. The wedge-and-strip anode has two-dimensional imaging capabilities, with a resolution of 40 microns FWHM over a one centimeter diameter area. The detector has a high quantum efficiency while retaining a low background rate. A KBr photocathode is used to enhance the quantum efficiency of the bare MCPs to a value of 35 percent at Lyman-alpha.

Bush, Brett C.; Cotton, Daniel M.; Siegmund, Oswald H.; Chakrabarti, Supriya; Harris, Walter; Clarke, John

1991-01-01

165

Three-Dimensional Field Solutions for Multi-Pole Cylindrical Halbach Arrays in an Axial Orientation  

NASA Technical Reports Server (NTRS)

This article presents three-dimensional B field solutions for the cylindrical Halbach array in an axial orientation. This arrangement has applications in the design of axial motors and passive axial magnetic bearings and couplers. The analytical model described here assumes ideal magnets with fixed and uniform magnetization. The field component functions are expressed as sums of 2-D definite integrals that are easily computed by a number of mathematical analysis software packages. The analysis is verified with sample calculations and the results are compared to equivalent results from traditional finite-element analysis (FEA). The field solutions are then approximated for use in flux linkage and induced EMF calculations in nearby stator windings by expressing the field variance with angular displacement as pure sinusoidal function whose amplitude depends on radial and axial position. The primary advantage of numerical implementation of the analytical approach presented in the article is that it lends itself more readily to parametric analysis and design tradeoffs than traditional FEA models.

Thompson, William K.

2006-01-01

166

Two-dimensional alignment of imogolite on a solid surface.  

PubMed

Surface modified imogolite fiber, hydrated aluminium silicate that has the shape of a rigid hollow cylinder, was aligned with consistent nano spacing and was visualized by scanning tunneling microscopy. PMID:17622430

Park, Sungjin; Lee, Yunha; Kim, Bumjung; Lee, Jisun; Jeong, Youngdo; Noh, Jaegeun; Takahara, Atsushi; Sohn, Daewon

2007-07-28

167

Hamiltonian formalism of two-dimensional Vlasov kinetic equation.  

PubMed

In this paper, the two-dimensional Benney system describing long wave propagation of a finite depth fluid motion and the multi-dimensional Russo-Smereka kinetic equation describing a bubbly flow are considered. The Hamiltonian approach established by J. Gibbons for the one-dimensional Vlasov kinetic equation is extended to a multi-dimensional case. A local Hamiltonian structure associated with the hydrodynamic lattice of moments derived by D. J. Benney is constructed. A relationship between this hydrodynamic lattice of moments and the two-dimensional Vlasov kinetic equation is found. In the two-dimensional case, a Hamiltonian hydrodynamic lattice for the Russo-Smereka kinetic model is constructed. Simple hydrodynamic reductions are presented. PMID:25484603

Pavlov, Maxim V

2014-12-01

168

Two dimensional convolute integers for machine vision and image recognition  

NASA Technical Reports Server (NTRS)

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.

Edwards, Thomas R.

1988-01-01

169

Quantum Walks on Two Kinds of Two-Dimensional Models  

NASA Astrophysics Data System (ADS)

In this paper, we numerically study quantum walks on two kinds of two-dimensional graphs: cylindrical strip and Mobius strip. The two kinds of graphs are typical two-dimensional topological graph. We study the crossing property of quantum walks on these two models. Also, we study its dependence on the initial state, size of the model. At the same time, we compare the quantum walk and classical walk on these two models to discuss the difference of quantum walk and classical walk.

Li, Dan; Mc Gettrick, Michael; Zhang, Wei-Wei; Zhang, Ke-Jia

2015-01-01

170

A two-dimensional nematic phase of magnetic nanorods  

NASA Astrophysics Data System (ADS)

We report a hybrid mesophase consisting of magnetic nanorods confined between the non-ionic surfactant bilayers of a lamellar phase. The magnetic field-induced ordering of the nanorods was measured experimentally and modeled by a two-dimensional Onsager theory including the third virial coefficient. The nanorods are strongly confined in layers, with no orientational coupling from one layer to the next. At high volume concentration they exhibit spontaneous in-plane orientational ordering and form a stack of independent two-dimensional nematic systems. This isotropic-nematic transition is first-order.

Slyusarenko, Kostyantyn; Constantin, Doru; Davidson, Patrick

2014-03-01

171

A two-dimensional nematic phase of magnetic nanorods.  

PubMed

We report a hybrid mesophase consisting of magnetic nanorods confined between the non-ionic surfactant bilayers of a lamellar phase. The magnetic field-induced ordering of the nanorods was measured experimentally and modeled by a two-dimensional Onsager theory including the third virial coefficient. The nanorods are strongly confined in layers, with no orientational coupling from one layer to the next. At high volume concentration they exhibit spontaneous in-plane orientational ordering and form a stack of independent two-dimensional nematic systems. This isotropic-nematic transition is first-order. PMID:24628202

Slyusarenko, Kostyantyn; Constantin, Doru; Davidson, Patrick

2014-03-14

172

[A two-dimensional double dispersed hadamard transform spectrometer].  

PubMed

A kind of two-dimensional hadamard transform spectrometer was developed. A grating was used for chromatic dispersion of orders and a prism was used for spectral dispersion. Quite different from traditional CCD detection method, a digital micromirror device (DMD) was applied for optical modulation, and a simple point detector was used as the sensor. Compared with traditional two-dimensional spectrometer, it has the advantage of high resolution and signal-noise-ratio, which was proved by theoretical calculation and computer simulation. PMID:22870674

Liu, Jia; Shi, Lei; Li, Kai; Zheng, Xin-Wen; Zeng, Li-Bo; Wu, Qiong-Shui

2012-06-01

173

Stabilization of two-dimensional spatial solitons in dissipative media  

NASA Astrophysics Data System (ADS)

This work analyzes the dynamics of two-dimensional spatial solitons in dissipative media. Stable solitons are formed in a two-dimensional medium with constant dissipation due to the balancing between dissipation and the instabilities due to nonlinearity. The dynamics have also been studied for linear, quadratic and exponential loss profiles. When a beam propagates in media with dissipation, where dissipation is a function of distance, it becomes compressed. A linear loss profile results in higher compression, while compression is minimal for an exponential profile.

Aysha Muhsina, K.; Subha, P. A.

2014-07-01

174

Application of the Analogy Between Water Flow with a Free Surface and Two-dimensional Compressible Gas Flow  

NASA Technical Reports Server (NTRS)

The theory of hydraulic analogy, that is, the analogy between water flow with a free surface and two-dimensional compressible gas flow and the limitations and conditions of the analogy are discussed. A test run was made using the hydraulic analogy as applied to the flow about circular cylinders at various diameters at subsonic velocities extending to the super critical range. The apparatus and techniques used in this application are described and criticized. Reasonably satisfactory agreement of pressure distributions and flow fields existed between water and airflow about corresponding bodies. This agreement indicated the possibility of extending experimental compressibility research by new methods.

Orlin, W James; Lindner, Norman J; Bitterly, Jack G

1947-01-01

175

Electro-optical resonant switching in two-dimensional side-coupled waveguide-cavity photonic crystal systems  

NASA Astrophysics Data System (ADS)

Photonic crystals have many potential applications because of their ability to control lightwave propagation. We have investigated the electro-optical resonant switching in two-dimensional photonic crystal structures. The optical microcavity side coupled with a waveguide composed of a dielectric cylinder in air is studied by solving Maxwell's equations using the plane wave expansion method and finite-difference time-domain method. The switching mechanism is a change in the conductance of the microcavity and hence modulating the resonant mode and eventually resonant switching is achieved. Such a mechanism of switching should open up a new application for designing components in photonic integrated circuits.

Liu, Cheng-Yang

2011-10-01

176

A two-dimensional Helmhotlz equation solution for the multiple ...  

E-print Network

Feb 1, 2013 ... inlet ducts or cavity-backed antennas can dominate the total radar cross section. .... We focus on a two-dimensional geometry by assuming that the ... Here j2 ¼ x2el0, where x is the angular frequency and j is known as the wavenumber. ...... by micro strip patch antennas and arrays residing in a cavity, IEEE.

Peijun Li

2013-02-19

177

Two-dimensional interaction of ion-acoustic solitons  

Microsoft Academic Search

The two-dimensional nonlinear interaction of two planar ion-acoustic solitons has been studied experimentally. When the angle between the wave vectors of the two interacting solitons is small and the soliton amplitudes approach a critical value, a resonant three-soliton interaction occurs.

P. A. Folkes; H. Ikezi; R. Davis

1980-01-01

178

Matrix characteristics for two dimensional nongroup Cellular Automata  

Microsoft Academic Search

In this paper we explore the properties of two dimensional Cellular Automata based on its matrix characteristics. In general, Cellular Automata is divided into two classes: group and nongroup Cellular Automata, each of which has its own matrix characteristics with the different properties. In this paper we restrict our study to nongroup Cellular Automata because of its uniqueness properties. The

J. Santoso; O. Slamet Santoso; B. Riyanto Trilaksono

2011-01-01

179

Statistical Transmutation and Phases of Two-Dimensional Quantum Matter  

E-print Network

After surveying the quantum kinematics and dynamics of statistical transmutation, I show how this concept suggests a phase diagram for the two-dimensional matter in a magnetic field, as a function of quantum statistics. I discuss the fundamental properties of quasiparticles in the different phases, and briefly suggest {\\it gedanken\\/} -- but not manifestly infeasible -- experiments to show up these properties.

Frank Wilczek

1995-09-14

180

CHAPTER 6 COMPREHENSIVE TWO-DIMENSIONAL GAS CHROMATOGRAPHY ( GC × GC )  

Microsoft Academic Search

Comprehensive two-dimensional gas chromatography (GC × GC) is one of the most powerful analytical tools for the analysis of organic compounds in complex matrices. The technique is based on continuous collection of the effluent from a GC column and periodic reinjection of small portions of the effluent to a second column of different properties. The process is repeated at a

Tadeusz Górecki; James Harynuk

181

Quantum of optical absorption in two-dimensional semiconductors  

E-print Network

Quantum of optical absorption in two-dimensional semiconductors Hui Fanga,b,c , Hans A. Bechteld semiconductor, where is the fine structure con- stant and nc is an optical local field correction factor quantitative examination of the intrinsic absorption properties of free-standing 2D semiconductor thin films

California at Irvine, University of

182

Defects activated photoluminescence in two-dimensional semiconductors  

E-print Network

Defects activated photoluminescence in two-dimensional semiconductors: interplay between bound of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, People's Republic of China, 3, Berkeley, California 94720, United States. Point defects in semiconductors can trap free charge carriers

Wu, Junqiao

183

Stationary Axisymmetric Fields as Two-Dimensional Geodesics  

E-print Network

Einstein's equations for stationary axisymmetric fields are reformulated as the equations for affine geodesics in a two--dimensional space. The affine collineations of this space are investigated and used to relate explicit solutions of Einstein's equations with different physical properties. Particularly, the solutions describing the exterior fields of a dyon and a slowly rotating body are discussed.

D. Nunez; H. Quevedo

1993-10-08

184

Two-dimensional black holes in accelerated frames: quantum aspects  

E-print Network

By considering charged black hole solutions of a one parameter family of two dimensional dilaton gravity theories, one finds the existence of quantum mechanically stable gravitational kinks with a simple mass to charge relation. Unlike their Einsteinian counterpart (i.e. extreme Reissner-Nordstr\\"om), these have nonvanishing horizon surface gravity.

R. Balbinot; A. Fabbri

1996-07-04

185

Coherent addition of two dimensional array of fiber lasers  

E-print Network

Configurations for efficient free space coherent addition of four separate fiber lasers arranged in two dimensional array are presented. They include compact and robust interferometric combiners that can be inserted either inside or outside the cavity of the combined lasers system. The results reveal that over 85% combining efficiency can be obtained.

Fridman, Moti; Davidson, Nir; Friesem, Asher A; Luria, Elena; Krupkin, Vladimir

2008-01-01

186

Sound waves in two-dimensional ducts with sinusoidal walls  

NASA Technical Reports Server (NTRS)

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.

Nayfeh, A. H.

1974-01-01

187

Two-dimensional structure of auroral poleward boundary intensifications  

Microsoft Academic Search

We investigate the two-dimensional structure of auroral poleward boundary intensifications (PBIs). PBIs are a nightside auroral intensification that has been studied primarily with ground-based meridian scanning photometers (MSPs). They have a signature that in the MSP data, appears as an increase in intensity at or near the magnetic separatrix and is often seen to extend equatorward. They are also associated

E. Zesta; E. Donovan; L. Lyons; G. Enno; J. S. Murphree; L. Cogger

2002-01-01

188

The Two-Dimensional Lattice Gas with Nearest Neighbor Interaction  

Microsoft Academic Search

The transfer matrix for the two-dimensional lattice gas with nearest neighbor interaction u is investigated. After some preliminary work, it is shown that the transfer matrix can be partially diagonalized, not only when the number of rows is prime, but also when it is non-prime. Equations are given for computing the size of the transfer matrix, and the largest submatrix

James Lawrence Bighouse

1988-01-01

189

Chaotic dynamics for two-dimensional tent maps  

NASA Astrophysics Data System (ADS)

For a two-dimensional extension of the classical one-dimensional family of tent maps, we prove the existence of an open set of parameters for which the respective transformation presents a strange attractor with two positive Lyapounov exponents. Moreover, periodic orbits are dense on this attractor and the attractor supports a unique ergodic invariant probability measure.

Pumariño, Antonio; Ángel Rodríguez, José; Carles Tatjer, Joan; Vigil, Enrique

2015-02-01

190

A two-dimensional ideal gas finite element  

Microsoft Academic Search

The formulation of a family of two-dimensional finite elements that model an ideal gas is presented. The elements support nonlinear analysis and represent either a plane strain or axisymmetric condition. The family of elements is intended for use with conventional elasticity-type elements to perform structural analysis of insulated glass units, pressure vessels, and other systems for which the interaction between

Richard J. Schmidt; Keith R. Fulton

2001-01-01

191

Resonant Proximity Connector for Two-Dimensional Sensor Implantation  

Microsoft Academic Search

In this paper, we propose a stable proximity connector RFC (resonant proximity connector) to TDC (two-dimensional communication) sheet. RFC is an electrode whose length is a quarter of the electromagnetic wavelength. The induced resonance around the electrode reduces the impedance between the connector and TDC sheet, which allows sensor chips to communicate with TDC sheet stably. Since the resonance depends

Hiromasa Chigusa; Yasutoshi Makino; Hiroyuki Shinoda

2006-01-01

192

Two-Dimensional Ratchets with Non-Conservative Impulsive Force  

Microsoft Academic Search

We discuss the directed motion of overdamped Brownian particles based on a two-dimensional ratchet model with a non-conservative impulsive force field. We consider the combined effects on the stationary current due to local spatial asymmetry in the longitudinal direction as well as the constrained harmonic force in the transverse direction. We notice that the current reversal is induced by the

Tong-Jun Zhao; Yi-Zhong Zhuo; Yong Zhan; Qing Ji; Tian-Guang Cao

2002-01-01

193

A survey of two-dimensional codes for optical CDMA  

Microsoft Academic Search

The paper presents the implementation of an optical CDMA system with two-dimensional coding using wavelength channels and time chips to create the codeword. Computer simulations have been performed in order to analyze and optimize the electronic circuits. The experimental work has been designed in order to investigate and evaluate the capabilities ofthe implemented optical CDMA system.

Petre Stroica; Marian Vladescu; Ovidiu Iancu

2007-01-01

194

Two-Dimensional Computational Fluid Dynamics and Conduction  

E-print Network

Two-Dimensional Computational Fluid Dynamics and Conduction Simulations of Heat Transfer were performed, two with a CFD code and four with a building- component thermal-simulation tool using) simulations with detailed radiation modeling are used as a reference. Four different frames were studied. Two

195

Potential for two-dimensional codes in automated manufacturing  

Microsoft Academic Search

Linear barcodes have found wide acceptance in all sectors of industry as machine-readable part identifiers, but their low data density limits practical data capacity to some 20 characters. Two-dimensional codes, however, have a much higher data density, and can contain significant volumes of data in compact symbols that can be printed or marked directly on to small parts. When used

Keith A. Osman; Anthony Furness

2000-01-01

196

Random and guided generation of coherent two-dimensional codes  

Microsoft Academic Search

Two-dimensional codes play a central role for many optical applications. Such codes are distributions of weighted points; a code is good if its autocorrelation closely approximates a multiple of the delta-function. This paper treats coherent codes with weights +1 and -1, shows their significant improvement compared with the incoherent codes which have only weights of +1, and outlines a method

K. Pasedach; E. Haase

1981-01-01

197

Image transmission by two-dimensional contour coding  

Microsoft Academic Search

The results of a computer simulation of an image transmission system are reported. A reduction in the total number of bits required to describe a picture by a factor of 4 to 23 is possible as compared with 6-bit PCM. In this system an image is treated as a two-dimensional signal of the spatial coordinates x and y. The large

DONALD NORMAN GRAHAM

1967-01-01

198

Towards a two dimensional code of anisotropic Godunov type  

Microsoft Academic Search

A two dimensional code of Godunov type is developed for solving gas dynamic equations. In the Godunov type code interaction between neighbor meshes are analyzed by using a Riemann problem solution. Special attention is given to the problem of anisotropy: the scheme gives different responses depending on the orientation of the meshes. The analysis is performed under Lagrangian concepts for

B. Meltz; J. K. Dukowicz

1987-01-01

199

Two-dimensional coded classification schemes in wireless sensor networks  

Microsoft Academic Search

This work proposes a novel fault-tolerant classification system based on distributed detection and two-dimensional channel coding. A rule is then derived to reduce the search space such that the optimal code matrix can be found. Simulation results reveal that the proposed scheme has higher classification reliability and better capability of fault tolerance than previous methods. Moreover, a code matrix using

Hung-ta Pai; Yunghsiang S. Han; Jing-tian Sung

2008-01-01

200

Two-dimensional vortex motion and 'negative temperatures.'  

NASA Technical Reports Server (NTRS)

Explanation of the novel phenomenon, tentatively identified as the 'ergodic boundary' in a space of initial conditions for turbulent flow, suggested by the recent numerical integration of the two-dimensional Navier-Stokes equations at high Reynolds numbers reported by Deem and Zabusky (1971). The proposed explanation is presented in terms of negative temperatures for a point vortex model.

Montgomery, D.

1972-01-01

201

Two-dimensional vortex motion and ``negative temperatures''  

Microsoft Academic Search

A recent numerical integration of the two-dimensional Navier-Stokes equations has tentatively identified an ``ergodic boundary'' in the space of initial conditions for the turbulent flow. An explanation is suggested in terms of negative temperatures, for a point vortex model. The author acknowledges valuable discussions with Drs. F. Tapert and R. Hardin.

D. Montgomery

1972-01-01

202

Algebraic analysis of a model of two-dimensional gravity  

E-print Network

An algebraic analysis of the Hamiltonian formulation of the model two-dimensional gravity is performed. The crucial fact is an exact coincidence of the Poisson brackets algebra of the secondary constraints of this Hamiltonian formulation with the SO(2,1)-algebra. The eigenvectors of the canonical Hamiltonian $H_{c}$ are obtained and explicitly written in closed form.

A. M. Frolov; N. Kiriushcheva; S. V. Kuzmin

2009-01-22

203

FLOW AND DISPERSION OF POLLUTANTS WITHIN TWO-DIMENSIONAL VALLEYS  

EPA Science Inventory

Wind-tunnel experiments and a theoretical model concerning the flow structure and pollutant diffusion over two-dimensional valleys of varying aspect ratio are described and compared. hree model valleys were used, having small, medium, and steep slopes. Measurements of mean and tu...

204

A fast two-dimensional median filtering algorithm  

Microsoft Academic Search

We present a fast algorithm for two-dimensional median filtering. It is based on storing and updating the gray level histogram of the picture elements in the window. The algorithm is much faster than conventional sorting methods. For a window size of m × n, the computer time required is 0(n).

Thomas S. Huang; George J. Yang; Gregory Y. Tang

1979-01-01

205

Distributions of the Two-Dimensional DCT Coefficients for Images  

Microsoft Academic Search

For a two-dimensional discrete cosine transform (DCT) image coding system, there have been different assumptions concerning the distributions of the transform coefficients. This paper presents results of distribution tests that indicate that for many images the statistics of the coefficients are best approximated by a Gaussian distribution for the DC coefficient and a Laplacian distribution for the other coefficients. Furthermore,

R. Reininger; J. Gibson

1983-01-01

206

Exact two-dimensional superconformal R symmetry and c extremization.  

PubMed

We uncover a general principle dubbed c extremization, which determines the exact R symmetry of a two-dimensional unitary superconformal field theory with N=(0,2) supersymmetry. To illustrate its utility, we study superconformal theories obtained by twisted compactifications of four-dimensional N=4 super-Yang-Mills theory on Riemann surfaces and construct their gravity duals. PMID:23432232

Benini, Francesco; Bobev, Nikolay

2013-02-01

207

Light absorption by a two-dimensional quantum dot superlattice  

Microsoft Academic Search

The monochromatic light absorption in an ideal two-dimensional quantum dot superlattice (QDSL) is considered theoretically. Calculations of the absorption coefficient are done in both the absence and presence of a homogeneous DC electric field with rational and irrational orientations. The explicit dependencies of the absorption coefficient on the frequency of the light, the QDSL parameters and the strength of the

Manuk G. Barseghyan; Albert A. Kirakosyan

2005-01-01

208

Kubo conductivity of a strongly magnetized two-dimensional plasma.  

NASA Technical Reports Server (NTRS)

The Kubo formula is used to evaluate the bulk electrical conductivity of a two-dimensional guiding-center plasma in a strong dc magnetic field. The particles interact only electrostatically. An ?anomalous' electrical conductivity is derived for this system, which parallels a recent result of Taylor and McNamara for the coefficient of spatial diffusion.

Montgomery, D.; Tappert, F.

1971-01-01

209

Adapting Grids For Computing Two-Dimensional Flows  

NASA Technical Reports Server (NTRS)

SAGE2D is two-dimensional implementation of Self Adaptive Grid Evolution computer program that intelligently redistributes initial grid points on basis of initial flow-field solution. Grids modified according to initial computed flows enabling recomputation at greater accuracy. Written in FORTRAN 77.

Davies, Carol B.; Venkatapathy, Ethiraj

1992-01-01

210

Two-Dimensional Diverging Shocks in a Nonuniform Medium  

SciTech Connect

An analytic solution is derived from the time evolution of a two- dimensional diverging shock in r - z geometry. The shock propagates through a condensed medium characterized by a Mie-Gruneisen equation of state with a nonzero density gradient in the axial direction.

Roy A. Axford

1998-08-01

211

A two-dimensional global study of tropospheric ozone production  

Microsoft Academic Search

The ozone production in the troposphere has been studied by means of a zonally averaged model which consists of a two-dimensional transport model, a description of the emissions, wet and dry deposition, and chemical processes of importance for the ozone production in the troposphere. The transport model describes a closed circulation in the meridional plane below 10 hPa and has

Asbjørn Strand; Ø. Hov

1994-01-01

212

Two-dimensional NMR spectroscopy with temperature-sweep.  

PubMed

Two-dimensional nuclear magnetic resonance (NMR) spectroscopy is useful for studying temperature-dependent effects on molecular structure. However, experimental time is usually long, because sampling is repeated at several temperatures. A novel solution to the problem is proposed, in which signal sampling is performed in parallel to the linear temperature-sweep. PMID:24863674

Bermel, Wolfgang; Dass, Rupashree; Neidig, Klaus-Peter; Kazimierczuk, Krzysztof

2014-08-01

213

Two-dimensional group lattices with a twist  

NASA Astrophysics Data System (ADS)

We study a statistical mechanics system defined on a particular two-dimensional group lattice. The lattice has local abstract dislocation defects. The partition function is explicitly computed and the phase transition points are enumerated. We consider several applications to physical systems.

Samuel, Stuart

1991-08-01

214

A recursive exact algorithm for weighted two-dimensional cutting  

Microsoft Academic Search

Gilmore and Gomory's algorithm is one of the better actually known exact algorithms for solving unconstrained guillotine two-dimensional cutting problems. Herz's algorithm is more effective, but only for the unweighted case. We propose a new exact algorithm adequate for both weighted and unweighted cases, which is more powerful than both algorithms. The algorithm uses dynamic programming procedures and one-dimensional knapsack

M. Hifi; V. Zissimopoulos

1996-01-01

215

Two-Dimensional Fourier Transform Analysis of Helicopter Flyover Noise  

NASA Technical Reports Server (NTRS)

A method to separate main rotor and tail rotor noise from a helicopter in flight is explored. Being the sum of two periodic signals of disproportionate, or incommensurate frequencies, helicopter noise is neither periodic nor stationary. The single Fourier transform divides signal energy into frequency bins of equal size. Incommensurate frequencies are therefore not adequately represented by any one chosen data block size. A two-dimensional Fourier analysis method is used to separate main rotor and tail rotor noise. The two-dimensional spectral analysis method is first applied to simulated signals. This initial analysis gives an idea of the characteristics of the two-dimensional autocorrelations and spectra. Data from a helicopter flight test is analyzed in two dimensions. The test aircraft are a Boeing MD902 Explorer (no tail rotor) and a Sikorsky S-76 (4-bladed tail rotor). The results show that the main rotor and tail rotor signals can indeed be separated in the two-dimensional Fourier transform spectrum. The separation occurs along the diagonals associated with the frequencies of interest. These diagonals are individual spectra containing only information related to one particular frequency.

SantaMaria, Odilyn L.; Farassat, F.; Morris, Philip J.

1999-01-01

216

Numerical simulation of two?dimensional tsunami runup  

Microsoft Academic Search

The hydrodynamic and mathematical problems connected with discontinuity between wet and dry domains, nonlinearity, friction, and computational instability are the main problems that have to be sorted out in the runup computation. A variety of runup models are analyzed, including the boundary conditions used to move the shoreline. Based on the initial experiments one?dimensional and two?dimensional algorithms are constructed. These

Z. Kowalik; T. S. Murty

1993-01-01

217

Numerical Modelling of induction heating for two dimensional geometries.  

E-print Network

Numerical Modelling of induction heating for two dimensional geometries. P. Dreyfuss J. Rappaz Summary We present both a mathematical model and a numerical method for simulating induction heating and infinite in one direction. Thus the induction heating problem can be studied in a plane perpendicular

Dreyfuss, Pierre

218

TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH  

E-print Network

TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH by Haowen Fang B.Eng., Nanjing Simulations Of Swim- ming Jellyfish Examining Committee: Dr. Weiran Sun, Assistant Professor Chair Dr. John iii #12;Abstract The swimming behavior of jellyfish, driven by the periodic contraction of body

Stockie, John

219

Disorder and Magnetism in Two Dimensional Quantum Systems  

E-print Network

Introduction 1 References 10 2 Kondo Lattice Scenario in Semiconductor Heterostructures 11 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Two dimensional Kondo model . . . . . . . . . . . . . . . . . . . . . 17 2.2.1 One impurity . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2.3 Lattice of impurity spins . . . . . . . . . . . . . . . . . . . . . 25 2.3 Summary

220

Area two-dimensional converging\\/diverging nozzle  

Microsoft Academic Search

A two-dimensional variable area exhaust nozzle assembly is described for a gas turbine engine, the engine having an axis and comprising: exhaust duct means having opposed, fixed, side walls; variable position exhaust nozzle means disposed within the exhaust duct means, the nozzle means including upper flap means and lower flap means opposed to the upper flap means, the upper and

1986-01-01

221

Vessel Segmentation and Tracking Using a Two-Dimensional Model  

Microsoft Academic Search

The segmentation and analysis of blood vessels in retinal images is of immense interest for study of diseases involving vasculature changes. An algorithm to segment blood vessels in colour retinal images by tracking of vessels is described. This algorithm proceeds by fitting a physically inspired two-dimensional model of the vessel profile to a local region of the vessel. By fitting

M. J. Cree; D. Cornforth; H. F. Jelinek

222

Two-dimensional parallel thinning algorithms based on critical kernels  

E-print Network

Two-dimensional parallel thinning algorithms based on critical kernels G. Bertrand and M. Couprie complexes for the study of parallel thinning in any dimension. The most fundamental result in this framework to simple local characterizations, we are able to express thinning algorithms by the way of sets of masks

Boyer, Edmond

223

Symmetries in two-dimensional dilaton gravity with matter  

Microsoft Academic Search

The symmetries of generic two-dimensional (2D) dilaton models of gravity with (and without) matter are studied in some detail. It is shown that delta2, one of the symmetries of the matterless models, can be generalized to the case where matter fields of any kind are present. The general (classical) solution for some of these models, in particular, those coupled to

Miguel Navarro; F ´ õsica; Teorica y Computacional

1997-01-01

224

Higgs algebraic symmetry in the two-dimensional Dirac equation  

E-print Network

The dynamical symmetry algebra of the two-dimensional Dirac Hamiltonian with equal scalar and vector Smorodinsky-Winternitz potentials is constructed. It is the Higgs algebra, a cubic polynomial generalization of SU(2). With the help of the Casimir operators, the energy levels are derived algebraically.

Fu-Lin Zhang; Bo Fu; Jing-Ling Chen

2009-07-04

225

Compact Analytic Expression for the Electric Field of a 2DElliptical Charge Distribution Inside a Perfectly Conducting CircularCylinder  

SciTech Connect

By combining the method of images with calculus of complex variables, we provide a simple expression for the electric field of a two-dimensional (2D) static elliptical charge distribution inside a perfectly conducting cylinder. The charge distribution need not be concentric with the cylinder.

Furman, M.A.

2007-05-29

226

Strong localization effect in magnetic two-dimensional hole systems  

SciTech Connect

We report an extensive study of the magnetotransport properties of magnetically doped two-dimensional hole systems. Inverted manganese modulation doped InAs quantum wells with localized manganese ions providing a magnetic moment of S=5/2 were grown by molecular beam epitaxy. Strong localization effect found in low-field magnetotransport measurements on these structures can either be modified by the manganese doping density or by tuning the two-dimensional hole density p via field effect. The data reveal that the ratio between p and manganese ions inside or in close vicinity to the channel enlarges the strong localization effect. Moreover, asymmetric broadening of the doping layer due to manganese segregation is significantly influenced by strain in the heterostructure.

Wurstbauer, U. [Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg (Germany); Institute of Applied Physics, University of Hamburg, 20355 Hamburg (Germany); Knott, S.; Zolotaryov, A.; Hansen, W. [Institute of Applied Physics, University of Hamburg, 20355 Hamburg (Germany); Schuh, D. [Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg (Germany); Wegscheider, W. [Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg (Germany); Solid State Physics Laboratory, ETH Zurich, 8093 Zurich (Switzerland)

2010-01-11

227

Multigrid Navier-Stokes calculation for two dimensional cascades  

NASA Astrophysics Data System (ADS)

A fast and accurate numerical method for solving the two dimensional Reynolds averaged Navier-Stokes is applied to calculate the internal fluid of turbines and compressors. The code is based on an explicit, time-marching, finite volume technique. In order to accelerate convergence, local time stepping, multigrid method is employed. Four stage Runge-Kutta method is implemented to extend the stability domain. Test cases of Hobson’s impulse cascade, NASA Rotor 37 and Sanz’s supercritical compressor cascade are presented. Results of Mach number distribution on blade surfaces and Mach number contour plots indicate good agreement with experimental data. Compared with full three 3D Navier-Stokes (N-S) codes, the two dimensional code only takes a short time to obtain predicted results. This code can be used widely in practical engineering design.

Yang, Ce; Lao, Dazhong; Jiang, Zikang

1998-03-01

228

Two-dimensional Raman-terahertz spectroscopy of water  

PubMed Central

Two-dimensional Raman-terahertz (THz) spectroscopy is presented as a multidimensional spectroscopy directly in the far-IR regime. The method is used to explore the dynamics of the collective intermolecular modes of liquid water at ambient temperatures that emerge from the hydrogen-bond networks water forming. Two-dimensional Raman-THz spectroscopy interrogates these modes twice and as such can elucidate couplings and inhomogeneities of the various degrees of freedoms. An echo in the 2D Raman-THz response is indeed identified, indicating that a heterogeneous distribution of hydrogen-bond networks exists, albeit only on a very short 100-fs timescale. This timescale appears to be too short to be compatible with more extended, persistent structures assumed within a two-state model of water. PMID:24297930

Savolainen, Janne; Ahmed, Saima; Hamm, Peter

2013-01-01

229

Automatic measurement method of two-dimensional complex geometric features  

NASA Astrophysics Data System (ADS)

To realize automatic measurement of two-dimensional complex geometric features on parts with high-precision, the characteristics and advantages of five types of machine vision measurement methods are analyzed. The technological challenges that each method faces in dealing with high-precise automatic measurement of complex geometric features are indicated. To solve the problem, a machine vision measurement method with cooperation of multi field of view, which has a hierarchical structure, is proposed. Its principle and procedures are introduced. The experimental results show that the relative error is less than 0.025% using the method to gauge conventional scale parts. Its outstanding advantage is that the measuring accuracy is NOT influenced by ambient temperature and the precision of machine systems compared with traditional CMM. Therefore, it is an effective method that can be applied in industrial spot to automatically measure normal and large scale two-dimensional complex geometric characteristics with high-precision.

He, Boxia; He, Yong; Ren, Fu-long; Xue, Rong

2013-01-01

230

Overlap distributions in two-dimensional spin glasses  

NASA Astrophysics Data System (ADS)

Numerical results are presented for overlaps of configurations of two-dimensional Ising spin glasses. At low temperatures, the correlation length greatly exceeds the system size, so that spin-spin correlations are relatively long range and domain wall energies exhibit sensitive dependence to temperature,as seen in the low temperature phase of three-dimensional spin glasses. Exact sampling algorithms are used so that there is no doubt of equilibration. High statistics runs are carried out, with tens of thousands of samples of size L^2=256^2 simulated. The results of the size-dependent spin overlap distribution P(q) are evaluated using statistics recently developed by Yucesoy, Katzgraber and Machta. The statistics for two-dimensional models at low temperature are found to be quite similar to those of three-dimensional spin glasses at finite temperatures below the spin-glass transition.

Middleton, A. Alan

2013-03-01

231

Silicon-based two dimensional tunable photonic crystal devices  

NASA Astrophysics Data System (ADS)

Photonic crystal devices are capable of controlling the flow of light in ultra compact scales. Silicon two dimensional (2D) nanostructures are well developed in the integrated circuit (IC) industry. Silicon is transparent to infrared light and has high refractive index which makes silicon an ideal material for photonic crystals in the infrared spectrum. Silicon 2D photonic crystals have attracted a lot of interest for showing feasibility of photonic integrated circuits. Typical photonic crystal devices are waveguides or cavities, which were developed as mostly passive devices. Various methods can be used to make photonic crystals tunable. In this work, silicon 2D tunable photonic crystal devices are studied using thermo-optic effect of silicon. In addition, this research presents one-step lithography to form micro and nano combined structures for the two-dimensional slab photonic crystals.

Choi, Kyung-Hak

232

Disordered quantum walks in two-dimensional lattices plink  

NASA Astrophysics Data System (ADS)

The properties of the two-dimensional quantum walk with point, line, and circle disorders in phase are reported. Localization is observed in the two-dimensional quantum walk with certain phase disorder and specific initial coin states. We give an explanation of the localization behavior via the localized stationary states of the unitary operator of the walker + coin system and the overlap between the initial state of the whole system and the localized stationary states. Project supported by the National Natural Science Foundation of China (Grant No. 11174052), the National Basic Research Program of China (Grant No. 2011CB921203), and the Open Fund from the State Key Laboratory of Precision Spectroscopy of East China Normal University.

Zhang, Rong; Xu, Yun-Qiu; Xue, Peng

2015-01-01

233

High-speed, two-dimensional filtering using residue arithmetic  

NASA Astrophysics Data System (ADS)

An operation common to many applications of high-speed, real-time signal processing is two-dimensional filtering. Recent advances in memory technology and residue arithmetic allow high-speed implementation. A two-dimensional five-by-five matrix convolution filter for pulse matching was implemented in residue arithmetic using programmable read only memory (PROM). The simple architecture of this all-PROM filter permits easy pipeline design and the inherent modular structure of residue arithmetic minimized the design overhead. The filter operates at 20 million operations per second with emitter coupled logic (ECL) PROMs. This filter has options such as elementary error detection, multiple patterns matching and adaptive filtering. An Intel 8086 microproprocessor was used as a controller to the filter.

Huang, C. H.

1980-01-01

234

Talbot image of two-dimensional fractal grating  

NASA Astrophysics Data System (ADS)

Talbot effect of two-dimensional fractal grating built by square aperture arrays is studied theoretically and experimentally in this paper. The amplitude fractal gratings are produced by use of the spatial light modulator, and the diffraction intensity distributions of fractal gratings with different fractal level in Fresnel diffraction field are measured with the help of the two-dimensional CCD. Talbot images of fractal gratings with 1-level and 2-level fractal are obtained in practical experiment. The analytic expression of Fresnel diffraction intensity of the fractal gratings is derived through decomposing fractal gratings into the sum of many periodic gratings. Theoretic results predict the self-image of fractal grating reappears at some certain distance. The numerical calculations also show the Talbot image and the fractional Talbot image of fractal grating. These results may extend the application of fractal grating in the optical processing of information and laser measurement.

Teng, Shuyun; Wang, Junhong; Li, Furui; Zhang, Wei

2014-03-01

235

Two-dimensional turbulence in the inverse cascade range.  

PubMed

Numerical and physical experiments on forced two-dimensional Navier-Stokes equations show that transverse velocity differences are described by "normal" Kolmogorov scaling <(deltav)(2n)> proportional r(2n/3) and obey Gaussian statistics. Since nontrivial scaling is a sign of the strong nonlinearity of the problem, these two results seem to contradict each other. A theory explaining these observations is presented in this paper. The derived self-consistent expression for the pressure gradient contributions leads to the conclusion that small-scale transverse velocity differences are governed by a linear Langevin-like equation, stirred by a nonlocal, universal, solution-dependent Gaussian random force. This explains the experimentally observed Gaussian statistics of transverse velocity differences and their Kolmogorov scaling. The solution for the PDF of longitudinal velocity differences is based on the numerical smallness of the energy flux in two-dimensional turbulence. The theory makes a few quantitative predictions that can be tested experimentally. PMID:11970429

Yakhot, V

1999-11-01

236

Tunable refraction in a two dimensional quantum metamaterial  

E-print Network

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 proposed here may be fabricated from a variety of current candidate technologies from superconducting qubits to quantum dots. Thus the ideas proposed in this work would be readily testable in existing state of the art laboratories.

M. J. Everitt; J. H. Samson; S. E. Savelev; T. P. Spiller; R. Wilson; A. M. Zagoskin

2012-08-22

237

Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas  

SciTech Connect

A two-dimensional wave propagation code, developed specifically to simulate correlation reflectometry in large-scale fusion plasmas is described. The code makes use of separate computational methods in the vacuum, underdense and reflection regions of the plasma in order to obtain the high computational efficiency necessary for correlation analysis. Simulations of Tokamak Fusion Test Reactor (TFTR) plasma with internal transport barriers are presented and compared with one-dimensional full-wave simulations. It is shown that the two-dimensional simulations are remarkably similar to the results of the one-dimensional full-wave analysis for a wide range of turbulent correlation lengths. Implications for the interpretation of correlation reflectometer measurements in fusion plasma are discussed.

E.J. Valeo; G.J. Kramer; R. Nazikian

2001-07-05

238

A two-dimensional dam-break flood plain model  

USGS Publications Warehouse

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.

Hromadka, T.V., II; Berenbrock, C.E.; Freckleton, J.R.; Guymon, G.L.

1985-01-01

239

On comparing helioseismic two-dimensional inversion methods  

NASA Technical Reports Server (NTRS)

We consider inversion techniques for investigating the structure and dynamics of the solar interior as functions of radius and latitude. In particular, we look at the problem of inferring the radial and latitudinal dependence of the Sun's internal rotation, using a fully two-dimensional least-squares inversion algorithm. Concepts such as averaging kernels, measures of resolution, and trade-off curves, which have previously been used in the one-dimensional case, are generalized to facilitate a comparison of two-dimensional methods. We investigate the weighting given to different modes and discuss the implications of this for observational strategies. As an illustration we use a mode set whose properties are similar to those expected for data from the GONG network.

Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.

1994-01-01

240

Two-dimensional semi-parametric alignment of chromatograms.  

PubMed

We present a comprehensive alignment algorithm that extends the semi-parametric approach to two dimensions. The algorithm is based on modeling shifts with a two-dimensional "warp function" such that the sample chromatogram - its shifts corrected with the warp function - is adjusted to the reference chromatogram by minimizing the squared intensity difference. A warp function approach has the advantage that overlapping peaks are easily dealt with compared to other proposed two-dimensional algorithms. Another advantage is that missing peaks are allowed if the absence of these peaks has little numerical effect on the warp function computation and if these peaks occur between existing peaks. Performance of the algorithm is demonstrated using GC×GC data from three batches of three diesel oil samples and LC-MS data from a mouse breast cancer data set. PMID:24794941

de Boer, Wim P H; Lankelma, Jan

2014-06-01

241

Wavelength scale terahertz two-dimensional photonic crystal waveguides.  

PubMed

A terahertz-scale two-dimensional photonic-crystal waveguide based on a silicon-on-insulator was fabricated, and the optical transmission spectrum was measured. Terahertz beam propagation characteristics were observed using a thermal imaging camera, with incident light in the 10.1-10.7 microm range. The measured transmission spectrum was in good agreement with a three-dimensional finite-difference time-domain calculation. PMID:19488208

Lin, Chunchen; Chen, Caihua; Schneider, Garrett; Yao, Peng; Shi, Shouyuan; Sharkawy, Ahmed; Prather, Dennis

2004-11-15

242

Suspended two-dimensional electron and hole gases  

SciTech Connect

We report on the fabrication of fully suspended two-dimensional electron and hole gases in III-V heterostructures. Low temperature transport measurements verify that the properties of the suspended gases are only slightly degraded with respect to the non-suspended gases. Focused ion beam technology is used to pattern suspended nanostructures with minimum damage from the ion beam, due to the small width of the suspended membrane.

Kazazis, D.; Bourhis, E.; Gierak, J.; Gennser, U. [Laboratoire de Photonique et de Nanostructures, CNRS-LPN, Route de Nozay, 91460 Marcoussis (France); Bourgeois, O. [Institut Néel, CNRS-UJF, BP 166, 38042 Grenoble Cedex 9 (France); Antoni, T. [Laboratoire de Photonique et de Nanostructures, CNRS-LPN, Route de Nozay, 91460 Marcoussis, France and Laboratoire Kastler Brossel, Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris (France)

2013-12-04

243

Two-dimensional high temperature strain measurement system  

NASA Technical Reports Server (NTRS)

Two-dimensional optical strain measurements on high temperature test specimens are presented. This two-dimensional capability is implemented through a rotatable sensitive strain axis. Three components of surface strain can be measured automatically, from which the first and second principal strains are calculated. One- and two-dimensional strain measurements at temperatures beyond 750 C with a resolution of 15 microstrain are demonstrated. The system is based on a one-dimensional speckle shift technique. The speckle shift technique makes use of the linear relationship between surface strain and the differential shift of laser speckle patterns in the diffraction plane. Laser speckle is a phase effect that occurs when spatially coherent light interacts with an optically rough surface. Since speckle is generated by any diffusely reflecting surface, no specimen preparation is needed to obtain a good signal. Testing was done at room temperature on a flat specimen of Inconel 600 mounted in a fatigue testing machine. A load cell measured the stress on the specimen before and after acquiring the speckle data. Strain components were measured at 0 C (parallel to the load axis) and at plus or minus 45 C, and plots indicate the calculated values of the first and second principal strains. The measured values of Young's modulus and Poisson's ratio are in good agreement with handbook values. Good linearity of the principal strain moduli at high temperatures indicate precision and stability of the system. However, a systematic error in the high-temperature test setup introduced a scale factor in the slopes of the two-dimensional stress-strain curves. No high temperature effects, however, have been observed to degrade speckle correlation.

Lant, Christian T.; Barranger, John P.

1989-01-01

244

Acousto-optic efficiency of two-dimensional photonic crystals  

NASA Astrophysics Data System (ADS)

The Bragg regime of the acousto-optic (AO) interaction in two-dimensional (2D) photonic crystals (PhCs) is considered. Approximate formulas for the AO figures of merit of PhCs are obtained and their frequency dependences for 2D PhC of the Si-SiO2 system are calculated. It is shown that the figures of merit of a composite PhC can exceed the values of these parameters for the components.

Pyatakova, Z. A.; Belokopytov, G. V.

2011-01-01

245

Rectangles and Squares Recognized by Two-Dimensional Automata  

Microsoft Academic Search

We consider sets of rectangles and squares recognized by deterministic and non-deterministic two-dimensional finite-state automata. We show that NFAs are strictly more powerful than DFAs, even for pictures over a one-symbol alphabet. In the process, we show that the pitcure languages recognized by NFAs are not closed under complement, resolving a long-standing open question. We also show that NFAs can

Jarkko Kari; Cristopher Moore

2000-01-01

246

Solvable quantum mechanical model in two-dimensional space  

Microsoft Academic Search

A one-particle non-relativistic quantum mechanical solvable model in two-dimensional space is given. The Hamiltonian is the sum of kinetic and interaction parts. Interactions are separable and can be centred at n arbitrary points of the plane. Conditions for the existence and for the number of bound states in finite linear chains are formulated in terms of the parameters of the

E. de Prunelé

2006-01-01

247

Two-dimensional quantum mechanical modeling of nanotransistors  

Microsoft Academic Search

Quantization in the inversion layer and phase coherent transport are anticipated to have significant impact on device performance in ``ballistic'' nanoscale transistors. While the role of some quantum effects have been analyzed qualitatively using simple one-dimensional ballistic models, two-dimensional (2D) quantum mechanical simulation is important for quantitative results. In this paper, we present a framework for 2D quantum mechanical simulation

A. Svizhenko; M. P. Anantram; T. R. Govindan; B. Biegel; R. Venugopal

2002-01-01

248

A Two-Dimensional Lattice Model with Exact Supersymmetry  

E-print Network

Starting from a simple discrete model which exhibits a supersymmetric invariance we construct a local, interacting, two-dimensional Euclidean lattice theory which also admits an exact supersymmetry. This model is shown to correspond to the Wess-Zumino model with extended N=2 supersymmetry in the continuum. We have performed dynamical fermion simulations to check the spectrum and supersymmetric Ward identities and find good agreement with theory.

S. Catterall; S. Karamov

2001-10-12

249

Error-correcting two-dimensional modulation codes  

Microsoft Academic Search

Digital magnetic recording\\/playback systems usually require both runlength-limited (RLL) coding and error correction coding (ECC), and these two steps have typically been performed independently, although various methods of combining them have recently appeared. The recent development of two-dimensional modulation codes, which meet runlength constraints using several parallel recording tracks, has significantly increased the capacity of such channels. In this paper,

Wayne H. Erxleben; Michael W. Marcellin

1994-01-01

250

Two-dimensional code acquisition in fixed multipath channels  

Microsoft Academic Search

Analytical performance results of a two-dimensional code acquisition process are obtained for a multipath fixed channel where L equal-amplitude delay- or angle-contiguous components are present. The performance measure used here is the worst-case mean acquisition time. Two basic search strategies are used in the acquisition process, namely an angle-delay and delay-angle search approaches. Optimal threshold setting is employed while interference

M. Katz; J. Iinatti; S. Glisic

2000-01-01

251

Two-dimensional color-code quantum computation  

SciTech Connect

We describe in detail how to perform universal fault-tolerant quantum computation on a two-dimensional color code, making use of only nearest neighbor interactions. Three defects (holes) in the code are used to represent logical qubits. Triple-defect logical qubits are deformed into isolated triangular sections of color code to enable transversal implementation of all single logical qubit Clifford group gates. Controlled-NOT (CNOT) is implemented between pairs of triple-defect logical qubits via braiding.

Fowler, Austin G. [Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Victoria 3010 (Australia)

2011-04-15

252

Multilength two-dimensional codes for optical CDMA system  

Microsoft Academic Search

A newe class of multilength, constant-weight and two-dimensional multiwavelength optical orthogonal code (2D MWOOCs) with\\u000a large capacity and good correlation properties is constructed based on multilength one-dimensional (1D) OOCs. The performance\\u000a of these newe MWOOCs in an OCDMA network with double-services is analyzed. The result shows that media with the shorter codeword\\u000a performs much better than the media with longer

Xiu-Li Zhou; Yu Hu

2005-01-01

253

Penny-Packing and Two-Dimensional Codes  

Microsoft Academic Search

We consider the problem of packingn equal circles (i.e., pennies) in the plane so as to minimize the second momentU about their centroid. These packings are also minimal-energy two-dimensional codes. Adding one penny at a time according to the greedy algorithm produces a unique sequence of packings for the first 75 pennies, and appears to produce optimal packings for infinitely

Ronald L. Graham; Neil J. A. Sloane

1990-01-01

254

Bounds on the capacity of constrained two-dimensional codes  

Microsoft Academic Search

Bounds on the capacity of constrained two-dimensional (2-D) codes are presented. The bounds of Calkin and Wilf (see SIAM J. Discr. Math., vol.11, no.1, p.54-60, 1998) apply to first-order symmetric constraints. The bounds are generalized in a weaker form to higher order and nonsymmetric constraints. Results are given for constraints specified by run-length limits or a minimum distance between pixels

Søren Forchhammer; Jørn Justesen

2000-01-01

255

Two-dimensional code acquisition using antenna arrays  

Microsoft Academic Search

An extension of conventional (delay domain) code acquisition to the delay-angle domain is studied. The two-dimensional uncertainty region is serially searched in an angle-delay or delay-angle fashion. Under the assumption that the signal is seen from one out of m possible angular directions and the interference can be modeled as temporarily and spatially white we show that there exist an

Marcos Katz; Jari Iinatti; Savo Glisic

2000-01-01

256

A numerical method for two dimensional unsteady reacting flows  

Microsoft Academic Search

The paper presents a method that numerically solves the full two-dimensional time-dependent Navier-Stokes equations with species transport, mixing, and chemical reaction between species. The generality of the formulation permits solution of problems involving flows in which deflagrations, detonations, or transitions from deflagration to detonation are found. The solution procedure, embodied in the RICE computer program, an Eulerian finite difference computer

T. D. Butler; P. J. Orourke

1977-01-01

257

Numerical method for two-dimensional unsteady reacting flows  

Microsoft Academic Search

A method that numerically solves the full two-dimensional, time-dependent Navier-Stokes equations with species transport, mixing, and chemical reaction between species is presented. The generality of the formulation permits the solution of flows in which deflagrations, detonations, or transitions from deflagration to detonation are found. The solution procedure is embodied in the RICE computer program. RICE is an Eulerian finite difference

T. D. Butler; P. J. Orourke

1976-01-01

258

Dynamics of Clusters in Two-dimensional Potts Model  

E-print Network

Dynamical behavior of the clusters during relaxation is studied in two-dimensional Potts model using cluster algorithm. Average cluster size and cluster formation velocity are calculated on two different lattice sizes for different number of states during initial stages of the Monte Carlo simulation. Dependence of these quantities on the order of the transition provides an efficient method to study nature of the phase transitions occuring in similar models.

Yigit Gunduc; Meral Aydin

1996-05-11

259

Two-dimensional black hole and singularities of CY manifolds  

Microsoft Academic Search

We study the degenerating limits of superconformal theories for compactifications on singular K3 and Calabi-Yau threefolds. We find that in both cases the degeneration involves creating an Euclidean two-dimensional black hole coupled weakly to the rest of the system. Moreover we find that the conformal theory of An singularities of K3 are the same as that of the symmetric fivebrane.

Hirosi Ooguri; Cumrun Vafa

1996-01-01

260

Dynamics of the two-dimensional gonihedric spin model  

Microsoft Academic Search

In this paper, we study dynamical aspects of the two-dimensional (2D) gonihedric spin model using both numerical and analytical methods. This spin model has vanishing microscopic surface tension and it actually describes an ensemble of loops living on a 2D surface. The self-avoidance of loops is parametrized by a parameter kappa . The kappa=0 model can be mapped to one

D. Espriu; A. Prats

2004-01-01

261

Localization of vibration propagation in two-dimensional systems  

Microsoft Academic Search

In this paper, a method of regular perturbation for a linear algebraic system is applied to study localization of vibration propagation in randomly disordered weakly coupled two-dimensional cantilever-spring arrays under external harmonic excitations. Localization factors, which characterize the average exponential rates of decay of the amplitudes of vibration, are defined in terms of the angles of orientation. First-order approximate results

Wei-Chau Xie

2000-01-01

262

Inferring three-dimensional shapes from two-dimensional silhouettes  

Microsoft Academic Search

Although an infinity of three-dimensional (3-D) objects could generate any given silhouette, we usually infer only one 3-D object from its two-dimensional (2-D) projection. What are the constraints that restrict this infinity of choices? We identify three mathematical properties of smooth surfaces plus one simple viewing constraint that seem to drive our preferred interpretation of 3-D shape from 2-D contour.

W. A. Richards; Jan J. Koenderink; D. D. Hoffman

1987-01-01

263

Two-dimensional model for twin-roll continuous casting  

Microsoft Academic Search

A numerical algorithm for the two-dimensional solidification problem in the twin-roll continuous casting system is presented\\u000a in this paper. Attention is focused on the elucidation of heat transfer and flow characteristics in both the liquid and the\\u000a solid phases. The present mathematical model can be applied to general full Navier-Stokes and energy equations, thereby covering\\u000a the wide range of twin-roll

T. Saitoh; H. Hojo; H. Yaguchi; C. G. Kang

1989-01-01

264

Two-dimensional Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

It has been recognized that the magnetic reconnection process is of great importance in high-energy astrophysics. We develop a new two-dimensional relativistic resistive magnetohydrodynamic (R2MHD) code and carry out numerical simulations of magnetic reconnection. We find that the outflow velocity reaches the Alfvén velocity in the inflow region and that a higher Alfvén velocity provides a higher reconnection rate. We also find that Lorentz contraction plays an important role in enhancement of the reconnection rate.

Watanabe, Naoyuki; Yokoyama, Takaaki

2006-08-01

265

Unsteady two-dimensional theory of a flapping wing  

NASA Astrophysics Data System (ADS)

An analytical evaluation of the hydrodynamic force on a single flapping wing is presented, based on the two-dimensional inviscid theory, with the addition of an attached leading-edge vortex. The explicit expression of the force is given and compared with some of the measurements by Dickinson et al. [Science 284, 1954 (1999)] and Sane and Dickinson [J. Expl. Biol. 204, 2607 (2001)] for a fruit fly model wing.

Minotti, F. O.

2002-11-01

266

Equations for the design of two-dimensional supersonic nozzles  

NASA Technical Reports Server (NTRS)

Equations are presented for obtaining the wall coordinates of two-dimensional supersonic nozzles. The equations are based on the application of the method of characteristics to irrotational flow of perfect gases in channels. Curves and tables are included for obtaining the parameters required by the equations for the wall coordinates. A brief discussion of characteristics as applied to nozzle design is given to assist in understanding and using the nozzle-design method of this report. A sample design is shown.

Pinkel, I Irving

1948-01-01

267

Hall conductivity of a two-dimensional graphite system  

Microsoft Academic Search

Within a self-consistent Born approximation, the Hall conductivity of a two-dimensional graphite system in the presence of a magnetic field is studied by quantum transport theory. The Hall conductivity is calculated for short- and long-range scatterers. It is calculated analytically in the limit of strong magnetic fields and in the Boltzmann limit in weak magnetic fields. The numerical calculation shows

Yisong Zheng; Tsuneya Ando

2002-01-01

268

Melting of two-dimensional tunable-diameter colloidal crystals  

Microsoft Academic Search

Melting of two-dimensional colloidal crystals is studied by video microscopy. The samples were composed of microgel spheres whose diameters could be temperature tuned, and whose pair potentials were measured to be short ranged and repulsive. We observed two-step melting from the crystal to a hexatic phase and from the hexatic to the liquid phase as a function of the temperature-tunable

Y. Han; N. Y. Ha; A. M. Alsayed; A. G. Yodh

2008-01-01

269

Numerical simulation of two-dimensional snowflake growth  

Microsoft Academic Search

We develop an efficient numerical scheme for integrating the equations of two-dimensional dendritic growth in the thermal-diffusion-limiting region. We use a Green's function representation to recast the problem as an essentially one-dimensional integro-differential equation which is solved numerically. We find that anisotropic surface tension is required to produce the stable tip behavior and repeated sidebranching of snowflakelike shapes.

David A. Kessler; Joel Koplik; Herbert Levine

1984-01-01

270

Excitons in anisotropic two-dimensional semiconducting crystals  

NASA Astrophysics Data System (ADS)

The excitonic behavior of anisotropic two-dimensional crystals is investigated using numerical methods. We employ a screened potential arising due to the system polarizability to solve the central-potential problem using the Numerov approach. The dependence of the exciton energies on the interaction strength and mass anisotropy is demonstrated. We use our results to obtain the exciton binding energy in phosphorene as a function of the substrate dielectric constant.

Rodin, A. S.; Carvalho, A.; Castro Neto, A. H.

2014-08-01

271

Two-dimensional drive characteristics by circular-shaped motor  

Microsoft Academic Search

An induction-type motor with a toroidal core, called a surface induction motor (SIM), is proposed for any directional motion in a two-dimensional plane. In the case of small size, the SIM has large thrust compared with a linear induction motor (LIM) because the slots in the SIM can be used effectively. For practical use, a conventional double-layer winding and ordinary

Nobuo Fujii; Masashi Fujitake

1999-01-01

272

A foveated silicon retina for two-dimensional tracking  

Microsoft Academic Search

A silicon retina chip with a central foveal region for smooth-pursuit tracking and a peripheral region for saccadic target acquisition is presented. The foveal region contains a 9×9 dense array of large dynamic range photoreceptors and edge detectors. Two-dimensional direction of foveal motion is computed outside the imaging array. The peripheral region contains a sparse array of 19×17 similar, but

Ralph Etienne-Cummings; Jan Van der Spiegel; Paul Mueller; Mao-Zhu Zhang

2000-01-01

273

Molecular Dynamics Simulation of a Two-Dimensional Heisenberg Fluid  

NASA Astrophysics Data System (ADS)

In this work we use numerical Monte Carlo and molecular dynamics to study a classical two-dimensional compressible magnetic fluid. The magnetic interactions are realized through a Yukawa-like potential while particles interact through Lenard-Jones forces. Our preliminary results point to a very rich phase transition picture. At high density the system seems to undergoes a transition, as suggested by the magnetization and susceptibility results.

Correa, Eberth; Lima, A. B.; Costa, B. V.

2012-04-01

274

Molecular Dynamics Simulation of a Two Dimensional Heisenberg Fluid  

NASA Astrophysics Data System (ADS)

In this work we use numerical Monte Carlo and Molecular Dynamics to study a classical two-dimensional compressible magnetic fluid. The magnetic interactions are realized through a Yukawa-like potential while particles interact through Lenard-Jones forces. Our preliminary results point to a very rich phase transition picture. At high density the system seems to undergo a magnetic transition, as suggested by the magnetization and susceptibility results.

Costa, B. V.; Lima, A. B.; Correa, E.

2012-02-01

275

Finite difference methods for two-dimensional fractional dispersion equation  

Microsoft Academic Search

Fractional order partial differential equations, as generalizations of classical integer order partial differential equations, are increasingly used to model problems in fluid flow, finance and other areas of application. In this paper we discuss a practical alternating directions implicit method to solve a class of two-dimensional initial-boundary value fractional partial differential equations with variable coefficients on a finite domain. First-order

Mark M. Meerschaert; Hans-Peter Scheffler; Charles Tadjeran

2006-01-01

276

Boundary element methods for two-dimensional, coupled, thermoviscous flow  

Microsoft Academic Search

Boundary element methods are developed for various forms of two-dimensional, coupled, thermoviscous flow. The coupling arises from the nonlinear convective terms in the Navier-Stokes equations, from the thermal buoyancy effect, from non-Newtonian fluid models, and from the viscous heating effect. Theoretical and numerical details are presented. Both steady and transient problems are considered, as well as linear and nonlinear problems.

Keith Alan Honkala

1992-01-01

277

Dirac Points in Two-Dimensional Inverse Opals  

NASA Astrophysics Data System (ADS)

The electron energy states and energy bands are calculated for a two-dimensional inverse opal structure. Assume that the opal structure is closed-packed circles, the inverse opal has the honeycomb lattice. The honeycomb lattice in two dimensions has a Dirac point. Its properties can be manipulated by altering the structure of the inverse opal: the radius of the circle, and the small gap between circles.

Mahan, G. D.

2013-10-01

278

A Two-dimensional Magnetoseismic Network in the United States  

NASA Astrophysics Data System (ADS)

Supported through several projects a series of ground magnetometers deployed in the past few years have formed a two-dimensional magnetoseismic network in the United States. This network includes the nine-station Mid-continent MAgnetoseismic Chain (McMAC) along the 330th magnetic meridian and the Falcon chain spanning from Maryland to Alaska. Sampling at 2 Hz the high-resolution fluxgate magnetometers located at these ground stations detect magnetospheric perturbations in the ULF frequencies and transmit the data through the Internet for analysis. In this presentation we focus on the ULF wave activities, including the resonances of magnetospheric field lines and the impulsive signals, observed by this two-dimensional magnetoseismic network in conjunction with other magnetometer arrays in North America. In sounding the plasmaspheric density, the gradient method can make use of the two-dimensional array to identify field line resonance (FLR) signatures from station pairs that are not strictly aligned in the same meridian but are separated by up to 20 degrees in longitude. Using the observations from the two-dimensional magnetoseismic network we found the spatial variations of plasmaspheric density in local time that would otherwise be unidentifiable by only the data from a single meridian chain. In timing the substorm onsets in the magnetotail, the magnetometer network can measure the different arrival times of magnetic impulses induced by substorm onsets and infer the start time and location of the associated reconnection in the magnetotail. A future plan on enhancing the capability of this magnetoseismic network in space weather monitoring and the coordination with space missions will be discussed.

Chi, P. J.; Bristow, W. A.; Chun, F. K.; Engebretson, M. J.; Hairston, M. R.; Jorgensen, A. M.; McHarg, M. G.; Mynatt, D.; Petit, N.; Russell, C. T.; Scherrer, D. K.; Takahashi, K.; Wing, S.; Winkler, L. I.; Cruz-Abeyro, J. L.

2010-12-01

279

Two-dimensional amorphous silicon image sensor arrays  

Microsoft Academic Search

Large two-dimensional amorphous silicon image sensor arrays offer an advantage for high speed document scanning and medical X-ray imaging. We describe our page sized 200 spot per inch imager and the accompanying high speed readout electronics. The spatial resolution performance for white light and X-ray imaging is illustrated. We discuss how the important issues of noise and resolution depend on

X. D. Wu; R. Weisfield; S. Ready; R. Apte; M. Ngyuen; W. B. Jackson; P. Nylen

1996-01-01

280

Two dimensional prolate spheroidal wave functions for MRI  

Microsoft Academic Search

The tradeoff between spatial and temporal resolution is often used to increase data acquisition speed for dynamic MR imaging. Reduction of the k-space sampling area, however, leads to stronger partial volume and truncation effects. A two dimensional prolate spheroidal wave function (2D-PSWF) method is developed to address these problems. Utilizing prior knowledge of a given region of interest (ROI) and

Qing X. Yang; Martin A Lindquist; Lawrence Shepp; Cun-Hui Zhang; Jianli Wang; Michael B Smith

2002-01-01

281

Confinement-deconfinement transitions for two-dimensional Dirac particles  

E-print Network

We consider a two-dimensional massless Dirac operator coupled to a magnetic field $B$ and an electric potential $V$ growing at infinity. We find a characterization of the spectrum of the resulting operator $H$ in terms of the relation between $B$ and $V$ at infinity. In particular, we give a sharp condition for the discreteness of the spectrum of $H$ beyond which we find dense pure point spectrum.

Josef Mehringer; Edgardo Stockmeyer

2012-10-18

282

Two-dimensional density currents in a confined basin  

Microsoft Academic Search

We present new experimental results on the mechanisms through which steady two-dimensional density currents lead to the formation of a stratification in a closed basin. A motivation for this work is to test the underlying assumptions in a diffusive “filling box” model that describes the oceanic thermohaline circulation (Hughes, G.O. and Griffiths, R.W., A simple convective model of the global

M. G. Wells; J. S. Wettlaufer

2005-01-01

283

Two-dimensional density currents in a confined basin  

Microsoft Academic Search

We present new experimental results on the mechanisms through which steady two-dimensional density currents lead to the formation of a stratification in a closed basin. A motivation for this work is to test the underlying assumptions in a diffusive ``filling box'' model that describes the oceanic thermohaline circulation (Hughes, G.O. and Griffiths, R.W., A simple convective model of the global

M. G. Wells; J. S. Wettlaufer

2005-01-01

284

Natural convection on a vertical stretching cylinder  

NASA Astrophysics Data System (ADS)

The flow and natural (or mixed) convection due to a vertical stretching cylinder is studied. Using similarity transforms, the Navier-Stokes and energy equations reduce to a set of nonlinear ordinary differential equations. Asymptotic analysis for large Reynolds numbers shows the relation between axisymmetric flow and two-dimensional flow. Due to the algebraic decay of the similarity functions, numerical integration is performed using a compressed coordinate. The axial velocity is composed of forced convection due to stretching and natural convection from the heated cylinder. The heat transfer increases with both the Reynolds number and the Prandtl number. The result is also a rare similarity solution of the free convection and Navier-Stokes equations.

Wang, C. Y.

2012-03-01

285

Two dimensional liquid crystal devices and their computer simulations  

NASA Astrophysics Data System (ADS)

The main focus of the dissertation is design and optimization two dimensional liquid crystal devices, which means the liquid crystal director configurations vary in two dimensions. Several optimized and designed devices are discussed in the dissertation. They include long-term bistable twisted nematic liquid crystal display (BTN LCD), which is very low power consumption LCD and suitable for E-book application; wavelength tunable liquid crystal Fabry-Perot etalon filter, which is one of the key components in fiber optic telecommunications; high speed refractive index variable devices, which can be used in infrared beam steering and telecommunications; high density polymer wall diffractive liquid crystal on silicon (PWD-LCoS) light valve, which is a promising candidate for larger screen projection display and also can be used in other display applications. Two dimensional liquid crystal director simulation program (relaxation method) and two dimensional optical propagation simulation program (finite-difference time-domain, FDTD method) are developed. The algorithms of these programs are provided. It has been proved that they are the very efficient tools that used in design and optimization the devices described above.

Wang, Bin

286

Two-dimensional potential double layers and discrete auroras  

NASA Technical Reports Server (NTRS)

This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

1979-01-01

287

Procedures for two-dimensional electrophoresis of proteins  

SciTech Connect

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.

Tollaksen, S.L.; Giometti, C.S.

1996-10-01

288

Two-dimensional oxides: multifunctional materials for advanced technologies.  

PubMed

The last decade has seen spectacular progress in the design, preparation, and characterization down to the atomic scale of oxide ultrathin films of few nanometers thickness grown on a different material. This has paved the way towards several sophisticated applications in advanced technologies. By playing around with the low-dimensionality of the oxide layer, which sometimes leads to truly two-dimensional systems, one can exploit new properties and functionalities that are not present in the corresponding bulk materials or thick films. In this review we provide some clues about the most recent advances in the design of these systems based on modern electronic structure theory and on their preparation and characterization with specifically developed growth techniques and analytical methods. We show how two-dimensional oxides can be used in mature technologies by providing added value to existing materials, or in new technologies based on completely new paradigms. The fields in which two-dimensional oxides are used are classified based on the properties that are exploited, chemical or physical. With respect to chemical properties we discuss use of oxide ultrathin films in catalysis, solid oxide fuel cells, gas sensors, corrosion protection, and biocompatible materials; regarding the physical properties we discuss metal-oxide field effect transistors and memristors, spintronic devices, ferroelectrics and thermoelectrics, and solar energy materials. PMID:22847915

Pacchioni, Gianfranco

2012-08-13

289

Two-dimensional optical beam deflector operated by wavelength tuning  

NASA Astrophysics Data System (ADS)

A new method based on an optical delay line structure is proposed for two-dimensional raster optical beam steering. For one-dimensional beam steering, the laser beam to be deflected is split into N co-directional sub-beams of equal intensity with the aid of a plane-parallel plate. These sub-beams experience a relative time delay, which translates into a phase difference, thus forming a phased array. When the laser wavelength is tuned, the relative phase varies and the far-field interference footprint can be steered across a receive plane. By employing two plane-parallel plates in series, the described scheme can be extended to produce a two-dimensional N × N array of sub-beams, allowing two-dimensional beam steering via wavelength tuning. In this case, wavelength tuning over a larger range leads to a linear deflection which repeats itself in a raster-like fashion. One direction of deflection repeats itself multiple times as wavelength is scanned over larger range, that is, a raster effect. In this paper, the principle is theoretically derived and formulated, and the preliminary experimental results with four sub-beams are presented.

Toyoshima, Morio; Fidler, Franz; Pfennigbauer, Martin; Leeb, Walter R.

2006-05-01

290

Enhanced diffraction radiation from two dimensional periodical structure  

NASA Astrophysics Data System (ADS)

Stronger surface plasmon polaritons (SPPs) enhanced diffraction radiation will be obtained on rectangular metallic bigrating comparing to one dimensional grating excited by a uniformly parallel moving electron beam, the stronger enhancement comes from the interaction effect of two SPPs excited simultaneously along the orthogonal period structure of rectangular metallic bigrating. Based on the advantage of rectangular bigrating, we presented and explored a novel metal film attached two-dimensional periodical lattice structure by reducing the thickness of the bigrating substrate to tens of nanometers. In this structure, with the excitation of uniform electron beam moving above the metal film surface, SPPs are firstly excited on the metal film, which will couple with the electromagnetic fields in the two-dimensional periodical lattice, and then transformed into enhanced radiation wave by diffracting of the rectangular lattice. The radiation power can reach 2.7 times that of the bigrating with dramatically decreased exciting beam energy, the fields can radiate to the whole space comparing to only the upper half space for the bigrating. To obtain better radiation behavior, double metal films sandwiched two-dimensional periodical lattice structure is proposed, which provides radiation power over 10 times that of bigrating. The results will be beneficial to electromagnetic radiation source based on SPPs in ultraviolet region.

Zhao, Tao; Zhong, Renbin; Gong, Sen; Zhang, Ping; Chen, Xiaoxing; Hu, Min; Liu, Shenggang

2014-10-01

291

H? sensing properties of two-dimensional zinc oxide nanostructures.  

PubMed

In this work we have grown particular zinc oxide two-dimensional nanostructures which are essentially a series of hexagonal very thin sheets. The hexagonal wurtzite crystal structure gives them their peculiar shape, whose dimensions are few microns wide, with a thickness in the order of 25 nm. Such kind of nanostructure, grown by thermal oxidation of evaporated metallic zinc on a silica substrate, has been used to fabricate conductometric gas sensors, investigated then for hydrogen gas detection. The "depletion layer sensing mechanism" is clarified, explaining how the geometrical factors of one- and two-dimensional nanostructures affect their sensing parameters. The comparison with one-dimensional ZnO nanowires based structures shows that two-dimensional nanostructures are ideal for gas sensing, due to their tiny thickness, which is comparable to the depletion-layer thickness, and their large cross-section, which increases the base current, thus lowering the limit of detection. The response to H? has been found good even to sub-ppm concentrations, with response and recovery times shorter than 18s in the whole range of H? concentrations investigated (500 ppb-10 ppm). The limit of detection has been found around 200 ppb for H? gas even at relatively low working temperature (175 °C). PMID:24720984

Tonezzer, Matteo; Iannotta, Salvatore

2014-05-01

292

Cylinder Test Specification  

SciTech Connect

The purpose of the cylinder testis two-fold: (1) to characterize the metal-pushing ability of an explosive relative to that of other explosives as evaluated by the E{sub 19} cylinder energy and the G{sub 19} Gurney energy and (2) to help establish the explosive product equation-of-state (historically, the Jones-Wilkins-Lee (JWL) equation). This specification details the material requirements and procedures necessary to assemble and fire a typical Los Alamos National Laboratory (LANL) cylinder test. Strict adherence to the cylinder. material properties, machining tolerances, material heat-treatment and etching processes, and high explosive machining tolerances is essential for test-to-test consistency and to maximize radial wall expansions. Assembly and setup of the cylinder test require precise attention to detail, especially when placing intricate pin wires on the cylinder wall. The cylinder test is typically fired outdoors and at ambient temperature.

Richard Catanach; Larry Hill; Herbert Harry; Ernest Aragon; Don Murk

1999-10-01

293

Flow of an aqueous foam through a two-dimensional porous medium: a pore scale investigation  

NASA Astrophysics Data System (ADS)

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 foam into a two-dimensional porous medium consisting of cylinders that have been positioned randomly between the two plates of the Hele-Shaw cell described above. Intermittent flow and non-stationarity of the velocity field are observed under permanent controlled inlet flow. Flow channeling is also different from what would be expected for a Newtonian fluid, which allows a different part of the pore population to be visited. Foam flow in a two-dimensional porous medium;

Meheust, Y.; Jones, S. A.; Dollet, B.; Cox, S.; Cantat, I.

2012-12-01

294

Microwave propagation in two-dimensional dielectric lattices  

Microsoft Academic Search

The properties of X-band microwaves propagating in a 2D array of low-loss high-dielectric constant cylinders are calculated and measured. Transmission bands and photonic band gaps are conclusively identified in excellent agreement with the theoretical predictions. Detailed data on the properties of isolated defect states are also presented. It is concluded that studies of this model scattering system allow the quantitative

S. L. McCall; P. M. Platzman; R. Dalichaouch; David Smith; S. Schultz

1991-01-01

295

Interacting two dimensional systems with a discrete degree of freedom  

NASA Astrophysics Data System (ADS)

This thesis considers several two dimensional and quasi-two dimensional systems in AlAs and GaAs with discrete electronic degrees of freedom, such as spin, valley, and layer indices. Each discrete degree of freedom responds to an externally applied field, allowing us control over the occupation of the levels. Each also enables a new measurement technique, with which we can probe these strongly interacting systems. We confine holes in closely spaced bilayer GaAs quantum well (QW) samples. In this system the holes possess a layer degree of freedom, which we easily manipulate using electric fields from electrostatic gates on the surface and substrate of the sample. Tunneling through the narrow insulating barrier between the QWs couples the two layers, and allows us to use tunneling measurements to probe the energetics of the two dimensional hole system above and below the Fermi energy. By applying a large magnetic field parallel to the system, we probe the in-plane dispersion of strongly interacting holes. We find a striking departure from the expected dispersion for large magnetic fields. Electrons in wide AlAs QWs occupy two degenerate minima in the conduction band, called valleys. We break the degeneracy of these valleys with applied strain in the plane of the QW, applied in-situ using a piezoelectric stack. It is well known that changing valley occupation shows clearly in the changing strength of integer quantum Hall resistance minima. We find analogous behavior in the fractional quantum Hall effect (FQHE) minima around Landau level filling factor nu = 32 . In light of the composite fermion model of the FQHE, we deduce that composite fermions in AlAs have a valley degree of freedom, and determine the valley susceptibility and valley polarization energy.

Bishop, Nathaniel

296

Memory device for two-dimensional radiant energy array computers  

NASA Technical Reports Server (NTRS)

A memory device for two dimensional radiant energy array computers was developed, in which the memory device stores digital information in an input array of radiant energy digital signals that are characterized by ordered rows and columns. The memory device contains a radiant energy logic storing device having a pair of input surface locations for receiving a pair of separate radiant energy digital signal arrays and an output surface location adapted to transmit a radiant energy digital signal array. A regenerative feedback device that couples one of the input surface locations to the output surface location in a manner for causing regenerative feedback is also included

Schaefer, D. H.; Strong, J. P., III (inventors)

1977-01-01

297

Vortex annihilation and inverse cascades in two dimensional superfluid turbulence  

E-print Network

We study two dimensional superfluid turbulence by employing an effective description valid in the limit where the density of superfluid vortices is parametrically small. At sufficiently low temperatures the effective description yields an inverse cascade with Kolmogorov energy spectrum $E(k) \\sim k^{-5/3}$. Denoting the number of vortices as a function of time by $N(t)$, we find that the vortex annihilation rate scales like $\\dot N \\sim N^{5/3}$ in states with an inverse cascade and $\\dot N \\sim N^2$ for laminar flow.

Paul M. Chesler; Andrew Lucas

2014-11-10

298

Kinetic analysis of two dimensional metallic grating Cerenkov maser  

SciTech Connect

The dispersion relation of two dimensional metallic grating Cerenkov maser has been given by using kinetic analysis, in which the influence of electron movement is directly considered without using an equivalent dielectric medium assumption. The effects of structural parameters and beam state on the interaction gain and synchronous frequency have also been investigated in detail by numerical calculations. To an illustrative case, the quantitative relations produced from varying the gap distance between electron beam and metallic grating, beam current, electron transverse to axial velocity ratio, and electron axial velocity spread have been obtained. The developed method can be used to predict the real interaction system performances.

Zhao Ding [Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China)

2011-08-15

299

Anomalous Hall effect in a two-dimensional electron gas  

E-print Network

Anomalous Hall effect in a two-dimensional electron gas Tamara S. Nunner,1 N. A. Sinitsyn,2,3 Mario F. Borunda,2 V. K. Dugaev,4 A. A. Kovalev,2 Ar. Abanov,2 Carsten Timm,5 T. Jungwirth,6,7 Jun-ichiro Inoue,8 A. H. MacDonald,9 and Jairo Sinova2...,6 1Institut f?r Theoretische Physik, Freie Universit?t Berlin, Arnimallee 14, 14195 Berlin, Germany 2Department of Physics, Texas A&M University, College Station, Texas 77843-4242, USA 3CNLS/CCS-3, Los Alamos National Laboratory, Los Alamos, New...

Nunner, Tamara S.; Sinitsyn, N. A.; Borunda, Mario F.; Dugaev, V. K.; Kovalev, A. A.; Abanov, Artem; Timm, Carsten; Jungwirth, T.; Inoue, Jun-ichiro; MacDonald, A. H.; Sinova, Jairo.

2007-01-01

300

Quasi Two-Dimensional Turbulent Flow Over Discontinuous Topography  

NASA Astrophysics Data System (ADS)

Decaying turbulent flows with topography are studied by means of laboratory experiments in a rotating tank and by numerical simulations based on a quasi-two-dimensional model. The basic configuration is a step-like topography dividing the flow domain in deep and shallow regions. The main objectives are: to prove that different domain geometries influence the long-term flow evolution; to show the generation of a final flow configuration; and to examine the physical mechanisms behind the main interactions of simple structures with the topography, like dipoles, in order to explain the final flow distribution.

Tenreiro, M.; Zavala Sansón, L.

2007-05-01

301

Drift modes of a quasi-two-dimensional current sheet  

SciTech Connect

Stability of a plasma configuration consisting of a thin one-dimensional current sheet embedded into a two-dimensional background current sheet is studied. Drift modes developing in plasma as unstable waves along the current direction are considered. Dispersion relations for kink and sausage perturbation modes are obtained depending on the ratio of parameters of thin and background current sheets. It is shown that the existence of the background sheet results in a decrease in the instability growth rates and a significant increase in the perturbation wavelengths. The role of drift modes in the excitation of oscillations observed in the current sheet of the Earth's magnetotail is discussed.

Artemyev, A. V.; Malova, Kh. V.; Popov, V. Yu.; Zelenyi, L. M. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2012-03-15

302

Quantum control in two-dimensional Fourier-transform spectroscopy  

SciTech Connect

We present a method that harnesses coherent control capability to two-dimensional Fourier-transform optical spectroscopy. For this, three ultrashort laser pulses are individually shaped to prepare and control the quantum interference involved in two-photon interexcited-state transitions of a V-type quantum system. In experiments performed with atomic rubidium, quantum control for the enhancement and reduction of the 5P{sub 1/2}{yields} 5P{sub 3/2} transition was successfully tested in which the engineered transitions were distinguishably extracted in the presence of dominant one-photon transitions.

Lim, Jongseok; Lee, Han-gyeol; Lee, Sangkyung; Ahn, Jaewook [Department of Physics, KAIST, Daejeon 305-701 (Korea, Republic of)

2011-07-15

303

Seabed disposal project two-dimensional axisymmetric penetrometer simulations  

SciTech Connect

Preliminary two-dimensional, one-constituent hole closure analyses of an experimental apparatus and the flow of in situ ocean sediments following a penetrometer explacement have been performed. Boundary conditions associated with the experimental apparatus were found to greatly affect cavity response. Difficulties were encountered in modelling penetrometer-sediment interfaces and in obtaining smooth stress histories. The use of a different computer code in later analyses led to more realistic penetrometer-sediment interface models and to improved success in obtaining stress histories. These results along with some recommendations for future work are presented.

Chavez, P.F.; Dawson, P.R.; Schuler, K.W.

1980-03-01

304

Optical interleavers based on two-dimensional photonic crystals.  

PubMed

An ultrasmall device size optical interleaver based on directional coupler waveguides in two-dimensional photonic crystals (PCs) is proposed. The numerical results show that the proposed PCs waveguide structure could really function as an interleaver with the central wavelength 1550 nm and the channel spacing 0.8 nm (frequency spacing of 100 GHz) of the dense wavelength division multiplexing (DWDM) specification. It can be widely used as the wavelength selective element for multiplexer-demultiplexer to lower or raise channel densities in DWDM optical fiber communication systems. PMID:17932532

Wu, Yaw-Dong; Huang, Min-Lin; Shih, Tien-Tsorng

2007-10-10

305

Coexistence of two Bose-Einstein condensates of two dimensional  

NASA Astrophysics Data System (ADS)

The theoretical investigations of the Bose -Einstein Condensation (BEC) of the two-dimensional (2D) magnetoexcitons are shortly reviewed. New details and more arguments in the favour of the possible coexistence of two BEC-tes with and without motional dipole moments in the case of an ideal 2D layer are revealed. The luminescence of the superfluid magnetoexcitons on the surface of the disk in the presence of a radial electric field strength is discussed. The new results concerning the energy spectrum of nine types of magnetoexcitons related with first three Landau levels for electrons and holes are presented.

Moskalenko, S. A.; Dumanov, E. V.; Podlesny, I. V.; Shmigliuk, M. I.

2003-06-01

306

Two-dimensional carbon semiconductor: Density functional theory calculations  

NASA Astrophysics Data System (ADS)

We show that patterned defects can be used to disrupt the sublattice symmetry of graphene so as to open up a band gap. This way of modifying graphene’s electronic structure does not rely on external agencies, the addition of new elements or special boundaries. The method is used to predict a planar, low energy, graphene allotrope with a band gap of 1.2 eV. This defect engineering also allows semiconducting ribbons of carbon to be fabricated within graphene. Linear arrangements of defects lead to naturally embedded ribbons of the semiconducting material in graphene, offering the prospect of two-dimensional circuit logic composed entirely of carbon.

Appelhans, David J.; Lin, Zhibin; Lusk, Mark T.

2010-08-01

307

Thermodynamics of the Two-Dimensional Hubbard Model  

NASA Astrophysics Data System (ADS)

The application of a numerically exact continuous time impurity solver with the DCA dynamical mean field theory has allowed us to study the thermodynamics of the two-dimensional Hubbard model for finite, but large cluster sizes. Variation in cluster size, upwards of 50-sites, allows for extrapolation to the thermodynamic limit. We present results relevant to cold gas systems, such as entropy, double occupancy and nearest-neighbour spin correlations as well as discuss the implications of these calculations on pseudogap physics of the High-Tc Cuprate superconductors away from half filling.

Leblanc, James; Gull, Emanuel

2013-03-01

308

Coherent forward scattering in two-dimensional disordered systems  

NASA Astrophysics Data System (ADS)

We present a detailed numerical and theoretical analysis of the recently discovered phenomenon of coherent forward scattering. This effect manifests itself as a macroscopic interference peak in the forward direction of the momentum distribution of a matter wave launched with finite velocity in a random potential. Focusing on the two-dimensional case, we show that coherent forward scattering generally arises due the confinement of the wave in a finite region of space, and explain under which conditions it can be seen as a genuine signature of Anderson localization.

Ghosh, S.; Cherroret, N.; Grémaud, B.; Miniatura, C.; Delande, D.

2014-12-01

309

Two-dimensional solitons in a quintic-septimal medium  

NASA Astrophysics Data System (ADS)

We report an observation of spatial solitons in a medium managed to present fifth-seventh (focusing-defocusing) refractive nonlinearities with suppressed third-order nonlinearity. Propagation of two-dimensional bright spatial solitons for ˜10 Rayleigh lengths was observed and characterized in a suspension of silver nanoparticles in acetone using the scattered light imaging method. Numerical calculations based on a nonlinear Schrödinger-type equation, including contributions up to the seventh-order susceptibility, were performed showing good agreement with the experimental results.

Reyna, Albert S.; Jorge, Kelly C.; de Araújo, Cid B.

2014-12-01

310

Optimum high temperature strength of two-dimensional nanocomposites  

SciTech Connect

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.

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

311

A zonal flow analysis method for two-dimensional airfoils  

NASA Technical Reports Server (NTRS)

A closed-loop, overlapped, velocity-coupling procedure has been utilized to combine a two-dimensional potential flow panel code and a Navier-Stokes code. The fully coupled, two-zone code has been used to compute the flow past a NACA 0012 airfoil. For this case, the zonal method has shown that the grid domain size can be reduced to 0.14 chord lengths with less than 1 percent loss in accuracy. Further, the required computation time is reduced by a factor of approximately four.

Summa, J. Michael; Strash, Daniel J.; Yoo, Sungyul

1990-01-01

312

Two-dimensional random walk in a bounded domain  

E-print Network

In a recent Letter Ciftci and Cakmak [EPL 87, 60003 (2009)] showed that the two dimensional random walk in a bounded domain, where walkers which cross the boundary return to a base curve near origin with deterministic rules, can produce regular patterns. Our numerical calculations suggest that the cumulative probability distribution function of the returning walkers along the base curve is a Devil's staircase, which can be explained from the mapping of these walks to a non-linear stochastic map. The non-trivial probability distribution function(PDF) is a universal feature of CCRW characterized by the fractal dimension d=1.75(0) of the PDF bounding curve.

Basu, Mahashweta

2010-01-01

313

Two-dimensional random walk in a bounded domain  

E-print Network

In a recent Letter Ciftci and Cakmak [EPL 87, 60003 (2009)] showed that the two dimensional random walk in a bounded domain, where walkers which cross the boundary return to a base curve near origin with deterministic rules, can produce regular patterns. Our numerical calculations suggest that the cumulative probability distribution function of the returning walkers along the base curve is a Devil's staircase, which can be explained from the mapping of these walks to a non-linear stochastic map. The non-trivial probability distribution function(PDF) is a universal feature of CCRW characterized by the fractal dimension d=1.75(0) of the PDF bounding curve.

Mahashweta Basu; P. K. Mohanty

2010-03-09

314

Two-dimensional laminar incompressible separated flow past airfoils  

NASA Technical Reports Server (NTRS)

A method is proposed to treat the problem of steady, two-dimensional, laminar, incompressible high Reynolds number separated flow past thin airfoils. An integral form of the boundary layer equations with interaction is used and the interaction between the inviscid and viscous flow fields is provided for by use of a thin-airfoil integral. Documentation of the attempts at obtaining a solution is presented. A survey of the current state-of-the-art of problems involving viscous-inviscid interactions in flow fields with separation is given.

Plotkin, A.

1973-01-01

315

Elastic models of defects in two-dimensional crystals  

NASA Astrophysics Data System (ADS)

Elastic models of defects in two-dimensional (2D) crystals are presented in terms of continuum mechanics. The models are based on the classification of defects, which is founded on the dimensionality of the specification region of their self-distortions, i.e., lattice distortions associated with the formation of defects. The elastic field of an infinitesimal dislocation loop in a film is calculated for the first time. The fields of the center of dilatation, dislocation, disclination, and circular inclusion in planar 2D elastic media, namely, nanofilms and graphenes, are considered. Elastic fields of defects in 2D and 3D crystals are compared.

Kolesnikova, A. L.; Orlova, T. S.; Hussainova, I.; Romanov, A. E.

2014-12-01

316

Stable dilute supersolid of two-dimensional dipolar bosons  

E-print Network

We consider two-dimensional bosonic dipoles oriented perpendicularly to the plane. On top of the usual two-body contact and long-range dipolar interactions we add a contact three-body repulsion as expected, in particular, for dipoles in the bilayer geometry with tunneling. We show that this model allows for stable continuous space supersolid states in the dilute regime and calculate the zero-temperature phase diagram. The three-body repulsion is crucial for stabilizing the system and, combined with the two-body attraction, can lead to self-trapped supersolid droplets.

Zhen-Kai Lu; D. S. Petrov; G. V. Shlyapnikov

2014-09-26

317

Wake-induced bending of two-dimensional plasma crystals  

SciTech Connect

It is shown that the wake-mediated interactions between microparticles in a two-dimensional plasma crystal affect the shape of the monolayer, making it non-flat. The equilibrium shape is calculated for various distributions of the particle number density in the monolayer. For typical experimental conditions, the levitation height of particles in the center of the crystal can be noticeably smaller than at the periphery. It is suggested that the effect of wake-induced bending can be utilized in experiments, to deduce important characteristics of the interparticle interaction.

Röcker, T. B., E-mail: tbr@mpe.mpg.de; Ivlev, A. V., E-mail: ivlev@mpe.mpg.de; Zhdanov, S. K.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany); Couëdel, L. [CNRS, Aix-Marseille-Université, Laboratoire de Physique des Interactions Ioniques et Moléculaires, UMR 7345, 13397 Marseille Cedex 20 (France)

2014-07-15

318

Semiclassical statistical mechanics of a two-dimensional fluid  

NASA Astrophysics Data System (ADS)

Expansions are obtained for the radial distribution function and free energy for a two-dimensional hard-core fluid in the semiclassical limit, using the ``modified'' Wigner-Kirkwood expansion method. These results are used to obtain expressions for the density-independent part of the radial distribution function and the first-order density correction to it. Quantum corrections to the second and third virial coefficients are discussed in detail. Explicit results are given for the Sutherland, Yukawa-tail, Wood-Saxan, square-well, and Lennard-Jones (12-6) pair potential models.

Sinha, S. K.; Sainger, Y. S.; Singh, Y.

1982-12-01

319

Two-dimensional hybrid simulation of a curved bow shock  

NASA Technical Reports Server (NTRS)

Results are presented from two-dimensional hybrid simulations of curved collisionless supercritical shocks, retaining both quasi-perpendicular and quasi-parallel sections of the shock in order to study the character and origin of the foreshock ion population. The simulations demonstrate that the foreshock ion population is dominated by ions impinging upon the quasi-parallel side of the shock, while nonlocal transport from the quasi-perpendicular side of the shock into the foreshock region is minimal. Further, it is shown that the ions gain energy by drifting significantly in the direction of the convection electric field through multiple shock encounters.

Thomas, V. A.; Winske, D.

1990-01-01

320

Condensate fraction of a two-dimensional attractive Fermi gas  

SciTech Connect

We investigate the Bose-Einstein condensation of fermionic pairs in a two-dimensional uniform two-component Fermi superfluid obtaining an explicit formula for the condensate density as a function of the chemical potential and the energy gap. By using the mean-field extended Bardeen-Cooper-Schrieffer theory, we analyze, as a function of the bound-state energy, the off-diagonal long-range order in the crossover from the Bardeen-Cooper-Schrieffer state of weakly bound Cooper pairs to the Bose-Einstein condensate of strongly-bound molecular dimers.

Salasnich, Luca [CNR-INFM and CNISM, Dipartimento di Fisica 'Galileo Galilei', Universita di Padova, Via Marzolo 8, 35131 Padova (Italy)

2007-07-15

321

Creating arbitrary arrays of two-dimensional topological defects  

NASA Astrophysics Data System (ADS)

An atomic force microscope was used to scribe a polyimide-coated substrate with complex patterns that serve as an alignment template for a nematic liquid crystal. By employing a sufficiently large density of scribe lines, two-dimensional topological defect arrays of arbitrary defect strength were patterned on the substrate. When used as the master surface of a liquid crystal cell, in which the opposing slave surface is treated for planar degenerate alignment, the liquid crystal adopts the pattern's alignment with a disclination line emanating at the defect core on one surface and terminating at the other surface.

Murray, Bryce S.; Pelcovits, Robert A.; Rosenblatt, Charles

2014-11-01

322

Dynamics of the two-dimensional gonihedric spin model  

E-print Network

In this paper we study dynamical aspects of the two-dimensional gonihedric spin model using both numerical and analytical methods. This spin model has vanishing microscopic surface tension and it actually describes an ensemble of loops living on a 2D surface. The self-avoidance of loops is parametrized by a parameter $\\kappa$. The $\\kappa=0$ model can be mapped to one of the six-vertex models discussed by Baxter and it does not have critical behavior. We have found that $\\kappa\

D. Espriu; A. Prats

2005-11-15

323

Dynamic ground effects on a two-dimensional flat plate  

NASA Technical Reports Server (NTRS)

The effect of time-variant vortex shedding is simulated by a sequence of discrete vortices convecting downstream in the wake of a two-dimensional flat plate whose lifting condition is modeled by means of the quasi-vortex lattice method. The boundary condition of this problem is specified in such a way that the tangency condition on the surface of the flat plate is satisfied; the boundary condition also takes into account the effect of airfoil motion relative to the ground. Significant lift changes are shown to occur, due to the dynamic ground effect, that are crucial in aircraft takeoff and landing transitions.

Chen, Y.-S.; Schweikhard, W. G.

1985-01-01

324

High order hybrid numerical simulations of two dimensional detonation waves  

NASA Technical Reports Server (NTRS)

In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.

Cai, Wei

1993-01-01

325

A fractal transition in the two dimensional shear layer  

NASA Technical Reports Server (NTRS)

The dependence of product generation with the Peclet and Reynolds number in a numerically simulated, reacting, two dimensional, temporally growing mixing layer is used to compute the fractal dimension of passive scalar interfaces. A transition from a low dimension of 4/3 to a higher one of 5/3 is identified and shown to be associated to the kinematic distortion on the flow field during the first pairing interaction. It is suggested that the structures responsible for this transition are non-deterministic, non-random, inhomogeneous fractals. Only the large scales are involved. No further transition is found for Reynolds numbers up to 20,000.

Jimenez, Javier; Martel, Carlos

1990-01-01

326

Solving time-dependent two-dimensional eddy current problems  

NASA Technical Reports Server (NTRS)

Results of transient eddy current calculations are reported. For simplicity, a two-dimensional transverse magnetic field which is incident on an infinitely long conductor is considered. The conductor is assumed to be a good but not perfect conductor. The resulting problem is an interface initial boundary value problem with the boundary of the conductor being the interface. A finite difference method is used to march the solution explicitly in time. The method is shown. Treatment of appropriate radiation conditions is given special consideration. Results are validated with approximate analytic solutions. Two stringent test cases of high and low frequency incident waves are considered to validate the results.

Lee, Min Eig; Hariharan, S. I.; Ida, Nathan

1988-01-01

327

Solving time-dependent two-dimensional eddy current problems  

NASA Technical Reports Server (NTRS)

Transient eddy current calculations are presented for an EM wave-scattering and field-penetrating case in which a two-dimensional transverse magnetic field is incident on a good (i.e., not perfect) and infinitely long conductor. The problem thus posed is of initial boundary-value interface type, where the boundary of the conductor constitutes the interface. A potential function is used for time-domain modeling of the situation, and finite difference-time domain techniques are used to march the potential function explicitly in time. Attention is given to the case of LF radiation conditions.

Lee, Min Eig; Hariharan, S. I.; Ida, Nathan

1990-01-01

328

Domain engineering of physical vapor deposited two-dimensional materials  

NASA Astrophysics Data System (ADS)

Physical vapor deposited two-dimensional (2D) materials span larger areas compared to exfoliated flakes, but suffer from very small grain or domain sizes. In this letter, we fabricate freestanding molybdenum disulfide (MoS2) and amorphous boron nitride (BN) specimens to expose both surfaces. We performed in situ heating in a transmission electron microscope to observe the domain restructuring in real time. The freestanding MoS2 specimens showed up to 100× increase in domain size, while the amorphous BN transformed in to polycrystalline hexagonal BN (h-BN) at temperatures around 600 °C much lower than the 850-1000 °C range cited in the literature.

Alam, Tarek; Wang, Baoming; Pulavarthy, Raghu; Haque, M. A.; Muratore, Christopher; Glavin, Nicholas; Roy, Ajit K.; Voevodin, Andrey A.

2014-11-01

329

Two-dimensional conformal field theory and the butterfly effect  

E-print Network

We study chaotic dynamics in two-dimensional conformal field theory through out-of-time order thermal correlators of the form $\\langle W(t)VW(t)V\\rangle$. We reproduce bulk calculations similar to those of [1], by studying the large $c$ Virasoro identity block. The contribution of this block to the above correlation function begins to decrease exponentially after a delay of $\\sim t_* - \\frac{\\beta}{2\\pi}\\log \\beta^2E_w E_v$, where $t_*$ is the scrambling time $\\frac{\\beta}{2\\pi}\\log c$, and $E_w,E_v$ are the energy scales of the $W,V$ operators.

Daniel A. Roberts; Douglas Stanford

2014-12-16

330

Two-dimensional global manifolds of vector fields.  

PubMed

We describe an efficient algorithm for computing two-dimensional stable and unstable manifolds of three-dimensional vector fields. Larger and larger pieces of a manifold are grown until a sufficiently long piece is obtained. This allows one to study manifolds geometrically and obtain important features of dynamical behavior. For illustration, we compute the stable manifold of the origin spiralling into the Lorenz attractor, and an unstable manifold in zeta(3)-model converging to an attracting limit cycle. (c) 1999 American Institute of Physics. PMID:12779872

Krauskopf, Bernd; Osinga, Hinke

1999-09-01

331

Disordered two-dimensional electron systems with chiral symmetry  

NASA Astrophysics Data System (ADS)

We review the results of our recent numerical investigations on the electronic properties of disordered two dimensional systems with chiral unitary, chiral orthogonal, and chiral symplectic symmetry. Of particular interest is the behavior of the density of states and the logarithmic scaling of the smallest Lyapunov exponents in the vicinity of the chiral quantum critical point in the band center at E=0. The observed peaks or depressions in the density of states, the distribution of the critical conductances, and the possible non-universality of the critical exponents for certain chiral unitary models are discussed.

Markoš, P.; Schweitzer, L.

2012-10-01

332

Focused two-dimensional antiscatter grid for mammography.  

SciTech Connect

We are developing freestanding high-aspect-ratio, focused, two-dimensional antiscatter grids for mammography using deep x-ray lithography and copper electroforming. The exposure is performed using x-rays from bending magnet beamline 2-BM at the Advanced Photon Source (APS) of Argonne National Laboratory. A 2.8-mm-thick prototype freestanding copper antiscatter grid with 25 {micro}m-wide parallel cell walls and 550 {micro}m periodicity has been fabricated. The progress in developing a dynamic double-exposure technique to create the grid with the cell walls aligned to a point x-ray source of the mammography system is discussed.

Makarova, O. V.; Moldovan, N.; Tang, C.-M.; Mancini, D. C.; Divan, R.; Zyryanov, V. N.; Ryding, D. C.; Yaeger, J.; Liu, C.; Creatv MicroTech Inc.

2002-09-01

333

Numerical calculations of two dimensional, unsteady transonic flows with circulation  

NASA Technical Reports Server (NTRS)

The feasibility of obtaining two-dimensional, unsteady transonic aerodynamic data by numerically integrating the Euler equations is investigated. An explicit, third-order-accurate, noncentered, finite-difference scheme is used to compute unsteady flows about airfoils. Solutions for lifting and nonlifting airfoils are presented and compared with subsonic linear theory. The applicability and efficiency of the numerical indicial function method are outlined. Numerically computed subsonic and transonic oscillatory aerodynamic coefficients are presented and compared with those obtained from subsonic linear theory and transonic wind-tunnel data.

Beam, R. M.; Warming, R. F.

1974-01-01

334

Correction-to-scaling exponent for two-dimensional percolation  

SciTech Connect

We show that the correction-to-scaling exponents in two-dimensional percolation are bounded by {Omega}{<=}72/91, {omega}=D{Omega}{<=}3/2, and {Delta}{sub 1}={nu}{omega}{<=}2, based upon Cardy's result for the crossing probability on an annulus. The upper bounds are consistent with many previous measurements of site percolation on square and triangular lattices and new measurements for bond percolation, suggesting that they are exact. They also agree with exponents for hulls proposed recently by Aharony and Asikainen, based upon results of den Nijs. A corrections scaling form evidently applicable to site percolation is also found.

Ziff, Robert M. [Center for the Study of Complex Systems and Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2011-02-15

335

From Weak to Strong Coupling in Two-Dimensional Gravity  

E-print Network

The strong coupling physics of two dimensional gravity at C=7, 13, 19 is deciphered, by building up on previous works along the same line (for a recent review, of the background material, see hep-th/9408069). It is shown that chirality becomes deconfined. The string suceptibility is derived, and found to be real contrary to the continuation of the KPZ formula. Topological Liouville string theories (without transverse degree of freedom) are explicitely solved. Altough they involve strongly coupled gravity, they share many features with the standard matrix models.

Jean-Loup Gervais; Jean-François Roussel

1994-08-12

336

Operational manual for two-dimensional transonic code TSFOIL  

NASA Technical Reports Server (NTRS)

This code solves the two-dimensional, transonic, small-disturbance equations for flow past lifting airfoils in both free air and various wind-tunnel environments by using a variant of the finite-difference method. A description of the theoretical and numerical basis of the code is provided, together with complete operating instructions and sample cases for the general user. In addition, a programmer's manual is also presented to assist the user interested in modifying the code. Included in the programmer's manual are a dictionary of subroutine variables in common and a detailed description of each subroutine.

Stahara, S. S.

1978-01-01

337

Nongalvanic primary thermometry of a two-dimensional electron gas  

NASA Astrophysics Data System (ADS)

We report the experimental realization of a nongalvanic, primary thermometer capable of measuring the electron temperature of a two-dimensional electron gas with negligible thermal load. Such a thermometer consists of a quantum dot whose temperature-dependent, single-electron transitions are detected by means of a quantum-point-contact electrometer. Its operating principle is demonstrated for a wide range of electron temperatures from 40 to 800 mK. This noninvasive thermometry can find application in experiments addressing the thermal properties of micrometer-scale mesoscopic electron systems, where heating or cooling electrons require relatively low thermal budgets.

Torresani, P.; Martínez-Pérez, M. J.; Gasparinetti, S.; Renard, J.; Biasiol, G.; Sorba, L.; Giazotto, F.; De Franceschi, S.

2013-12-01

338

Local curvature and stability of two-dimensional systems  

NASA Astrophysics Data System (ADS)

We propose a fast method to determine the local curvature in two-dimensional (2D) systems with arbitrary shape. The curvature information, combined with elastic constants obtained for a planar system, provides an accurate estimate of the local stability in the framework of continuum elasticity theory. Relative stabilities of graphitic structures including fullerenes, nanotubes, and schwarzites, as well as phosphorene nanotubes, calculated using this approach, agree closely with ab initio density functional calculations. The continuum elasticity approach can be applied to all 2D structures and is particularly attractive in complex systems with known structure, where the quality of parameterized force fields has not been established.

Guan, Jie; Jin, Zhongqi; Zhu, Zhen; Chuang, Chern; Jin, Bih-Yaw; Tománek, David

2014-12-01

339

Optical and electronic properties of two dimensional graphitic silicon carbide  

E-print Network

Optical and electronic properties of two dimensional few layers graphitic silicon carbide (GSiC), in particular monolayer and bilayer, are investigated by density functional theory and found different from that of graphene and silicene. Monolayer GSiC has direct bandgap while few layers exhibit indirect bandgap. The bandgap of monolayer GSiC can be tuned by an in-plane strain. Properties of bilayer GSiC are extremely sensitive to the interlayer distance. These predictions promise that monolayer GSiC could be a remarkable candidate for novel type of light-emitting diodes utilizing its unique optical properties distinct from graphene, silicene and few layers GSiC.

Lin, Xiao; Lin, Shisheng; Hakro, Ayaz Ali; Cao, Te; Chen, Hongsheng; Zhang, Baile

2012-01-01

340

Highly directional thermal emission from two-dimensional silicon structures.  

PubMed

We simulate, fabricate, and characterize near perfectly absorbing two-dimensional grating structures in the thermal infrared using heavily doped silicon (HdSi) that supports long wave infrared surface plasmon polaritons (LWIR SPP's). The devices were designed and optimized using both finite difference time domain (FDTD) and rigorous coupled wave analysis (RCWA) simulation techniques to satisfy stringent requirements for thermal management applications requiring high thermal radiation absorption over a narrow angular range and low visible radiation absorption over a broad angular range. After optimization and fabrication, characterization was performed using reflection spectroscopy and normal incidence emissivity measurements. Excellent agreement between simulation and experiment was obtained. PMID:23546065

Ribaudo, Troy; Peters, David W; Ellis, A Robert; Davids, Paul S; Shaner, Eric A

2013-03-25

341

Inverse methods in two-dimensional NMR spectral analysis  

NASA Astrophysics Data System (ADS)

Solid-state NMR is a valuable technique for the study of disordered materials. Analysis of such spectra usually involves solution of so-called ill-posed inverse problems. Here we present a strategy for the analysis of two-parameter two-dimensional NMR problems and test it on 2D DECODER and DOQSY experiments. Using Monte Carlo tests, constraints are determined for the resolution and accuracy of the analysis for both experiments. The methods are finally applied to spectra of spider dragline silk, a heterogeneous solid fibrous protein.

van Beek, Jacco D.; Meier, Beat H.; Schäfer, Hartmut

2003-05-01

342

Inviscid dynamics of two-dimensional shear layers  

NASA Astrophysics Data System (ADS)

The dynamics of unconfined, spatially developing shear layers is studied by numerical solutions of the time-dependent Euler equations using a second-order Godunov scheme. Effects of density and velocity variations between the two streams of the shear layer are studied and color graphics is used to show more clearly the entrainment process of the surrounding streams. The calculations demonstrated that the evolution of the mean flow was dominated by two-dimensional, inviscid effects. The rms fluctuating velocity and density profiles were found to be in good agreement with the measurements of Oster and Wygnanski and of Konrad, except for the peak value of the v-prime profile.

Chien, Kuei-Yuan; Ferguson, Ralph E.; Kuhl, Allen L.; Glaz, Harland M.; Colella, Philip

1991-06-01

343

Statistical Mechanics of Unbound Two Dimensional Self-Gravitating Systems  

E-print Network

We study, using both theory and molecular dynamics simulations, the relaxation dynamics of a microcanonical two dimensional self-gravitating system. After a sufficiently large time, a gravitational cluster of N particles relaxes to the Maxwell-Boltzmann distribution. The time to reach the thermodynamic equilibrium, however, scales with the number of particles. In the thermodynamic limit, $N\\to\\infty$ at fixed total mass, equilibrium state is never reached and the system becomes trapped in a non-ergodic stationary state. An analytical theory is presented which allows us to quantitatively described this final stationary state, without any adjustable parameters.

Tarcísio N. Teles; Yan Levin; Renato Pakter; Felipe B. Rizzato

2010-04-01

344

Testability of non-autonomous two dimensional iterative logic array  

E-print Network

' SCIENCE August III91 Major Subject: Electrical Engineering TESTABILITY OF NON-AUTONOMOUS T'A'0 DIMENSIONAL ITERATIVE LOGIC ARRAY A Thesis by HIDEO NAGUMO Approved as to style and content by: . . ed~ I(aran L. watson (Chair of Committee) Mi Lu... (Member) William G. Bliss (Member) Donald K. Friesen (Member) Jo Howze (Head of Department) August 1991 ABSTRACT Testability of i%on-Autonomous Two-Dimensional Iterative Logic Array. (August 1991) Hideo iX'agumo, B. S. , Shinshu University...

Nagumo, Hideo

2012-06-07

345

Birth and Growth of Two-dimensional Universe  

E-print Network

A master equation for the evolution of two-dimensional universe is derived based on the simplicial quantum gravity regarding the evolution as the Markov process of a space-time lattice. Three typical phases, expanding, elongating and collapsing phase, which have been found in the numerical simulation, are studied together with their boundaries, analytically. Asymptotic solutions of the evolution equation for statistical quantities, such as averaged area, boundary length, and correlation of fluctuations, are obtained for each phase and boundary.After introducing a physical time the cosmological significance of each phase is discussed.

Tetsuyuki Yukawa

2011-11-30

346

Phase Separation in the Two-Dimensional Hubbard Model  

NASA Astrophysics Data System (ADS)

In this paper, we study phase separation in the two-dimensional single-band Hubbard model with the unrestricted Hartree-Fock(UHF) method and the restricted Hartree-Fock (RHF) method. We perform the calculation for square lattices and rectangle lattices. It is observed that the stripe phase exists and it depends on three aspects: geometry of the lattice, Coulomb interaction U and band filling n. To gain more physical insights, we consider the Hubbard model with spin dependent hoppings: t? and t?, and study the effect of varying (t?)/(t?) on the phase separation.

Yu, M.; Lin, H. Q.

347

Two-dimensional nodal model using legendre expansions  

SciTech Connect

A two-dimensional diffusion theory nodal model has been developed in which Legendre polynomials are used as the expansion functions. The minimization for these trial functions is done in a least-squares sense over the individual nodes. Interface conditions are matched as averaged conditions over one-half of each node interface. This method is an extension of the one-dimensional model. A sample problem was developed to compare with the International Atomic Energy Agency light water reactor (IAEA LWR) benchmark problem.

Rohach, A.F.

1986-01-01

348

Application of two dimensional periodic molecular dynamics to interfaces.  

NASA Astrophysics Data System (ADS)

We have applied two-dimensional molecular dynamics to the surface of a crystalline aspartame and the interface between the crystal face and a solvent (water). This has allowed us to look at the dynamic processes at the surface. Understanding the surface structure and properties are important to controlling the crystal morphology. The thermodynamic ensemble was constant Number, surface Area and Temperature (NAT). The calculations have been carried out using a 2D Ewald summation and 2D periodic boundary conditions for the short range potentials. The equations of motion integration has been carried out using the standard velocity Verlet algorithm.

Gay, David H.; Slater, Ben; Catlow, C. Richard A.

1997-08-01

349

Path-integral solubility of two-dimensional models  

SciTech Connect

We apply the technique of Fujikawa to solve for simple two-dimensional models by looking at the nontrivial transformation properties of the fermion measure in the path-integral formalism. We obtain the most general solution for the massless Thirring model and point out how the one-parameter solution reduces to that of Johnson and Sommerfield in a particular limit. We present the most general solution for the massive vector model indicating how it reduces to the solutions of Brown and Sommerfield for different values of the parameter. The solution of a gradient-coupling model is also discussed.

Das, Ashok K.; Mathur, Vishnu S.

1986-01-01

350

Two-dimensional manifolds with metrics of revolution  

SciTech Connect

This is a study of the topological and metric structure of two-dimensional manifolds with a metric that is locally a metric of revolution. In the case of compact manifolds this problem can be thoroughly investigated, and in particular it is explained why there are no closed analytic surfaces of revolution in R{sup 3} other than a sphere and a torus (moreover, in the smoothness class C{sup {infinity}} such surfaces, understood in a certain generalized sense, exist in any topological class)

Sabitov, I Kh [M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2000-10-31

351

Two-dimensional density currents in a confined basin  

NASA Astrophysics Data System (ADS)

We present new experimental results on the mechanisms through which steady two-dimensional density currents lead to the formation of a stratification in a closed basin. A motivation for this work is to test the underlying assumptions in a diffusive “filling box” model that describes the oceanic thermohaline circulation (Hughes, G.O. and Griffiths, R.W., A simple convective model of the global overturning circulation, including effects of entrainment into sinking regions, Ocean Modeling, 2005, submitted.). In particular, they hypothesized that a non-uniform upwelling velocity is due to weak along-slope entrainment in density currents associated with a large horizontal entrainment ratio of Eeq?~?0.1. We experimentally measure the relationship between the along-slope entrainment ratio, E, of a density current to the horizontal entrainment ratio, Eeq, of an equivalent vertical plume. The along-slope entrainment ratios show the same quantitative decrease with slope as observed by Ellison and Turner (Ellison, T.H. and Turner, J.S., Turbulent entrainment in stratified flows, J. Fluid Mech., 1959, 6, 423-448.), whereas the horizontal entrainment ratio Eeq appears to asymptote to a value of Eeq?=?0.08 at low slopes. Using the measured values of Eeq we show that two-dimensional density currents drive circulations that are in good agreement with the two-dimensional filling box model of Baines and Turner (Baines, W.D. and Turner, J.S., Turbulent buoyant convection from a source in a confined region, J. Fluid. Mech., 1969, 37, 51-80.). We find that the vertical velocities of density fronts collapse onto their theoretical prediction that U =-2-2/3B1/3Eeq2/3 (H/R) ?, where U is the velocity, H the depth, B the buoyancy flux, R the basin width, Eeq the horizontal entrainment ratio and???= z/H the dimensionless depth. The density profiles are well fitted with???= 2-1/3B2/3Eeq-2/3H-1 [ln(? )?+?t ], where?t?is the dimensionless time. Finally, we provide a simple example of a diffusive filling box model, where we show how the density stratification of the deep Caribbean waters (below 1850?m depth) can be described by a balance between a steady two-dimensional entraining density current and vertical diffusion in a triangular basin.

Wells, M. G.; Wettlaufer, J. S.

2005-03-01

352

Engine Cylinder Temperature Control  

DOEpatents

A method and apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine. The cylinder is fluidly connected to an intake manifold and an exhaust manifold. The method and apparatus includes increasing a back pressure associated with the exhaust manifold to a level sufficient to maintain a desired quantity of residual exhaust gas in the cylinder, and varying operation of an intake valve located between the intake manifold and the cylinder to an open duration sufficient to maintain a desired quantity of fresh air from the intake manifold to the cylinder, wherein controlling the quantities of residual exhaust gas and fresh air are performed to maintain the temperature in the cylinder at a desired level.

Kilkenny, Jonathan Patrick (Peoria, IL); Duffy, Kevin Patrick (Metamora, IL)

2005-09-27

353

Dirac spectra of two-dimensional QCD-like theories  

NASA Astrophysics Data System (ADS)

We analyze Dirac spectra of two-dimensional QCD-like theories both in the continuum and on the lattice and classify them according to random matrix theories sharing the same global symmetries. The classification is different from QCD in four dimensions because the antiunitary symmetries do not commute with ?5. Therefore, in a chiral basis, the number of degrees of freedom per matrix element are not given by the Dyson index. Our predictions are confirmed by Dirac spectra from quenched lattice simulations for QCD with two or three colors with quarks in the fundamental representation as well as in the adjoint representation. The universality class of the spectra depends on the parity of the number of lattice points in each direction. Our results show an agreement with random matrix theory that is qualitatively similar to the agreement found for QCD in four dimensions. We discuss the implications for the Mermin-Wagner-Coleman theorem and put our results in the context of two-dimensional disordered systems.

Kieburg, Mario; Verbaarschot, Jacobus J. M.; Zafeiropoulos, Savvas

2014-10-01

354

Two-dimensional gas of massless Dirac fermions in graphene.  

PubMed

Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment. PMID:16281030

Novoselov, K S; Geim, A K; Morozov, S V; Jiang, D; Katsnelson, M I; Grigorieva, I V; Dubonos, S V; Firsov, A A

2005-11-10

355

Matter waves in two-dimensional arbitrary atomic crystals  

NASA Astrophysics Data System (ADS)

We present a general scheme to realize a cold-atom quantum simulator of bidimensional atomic crystals. Our model is based on the use of two independently trapped atomic species: the first one, subject to a strong in-plane confinement, constitutes a two-dimensional matter wave which interacts only with atoms of the second species, deeply trapped around the nodes of a two-dimensional optical lattice. By introducing a general analytic approach we show that the system Green function can be exactly determined, allowing for the investigation of the matter-wave transport properties. We propose some illustrative applications to both Bravais (square, triangular) and non-Bravais (graphene, kagomé) lattices, studying both ideal periodic systems and experimental-size and disordered ones. Some remarkable spectral properties of these atomic artificial lattices are pointed out, such as the emergence of single and multiple gaps, flat bands, and Dirac cones. All these features can be manipulated via the interspecies interaction, which proves to be widely tunable due to the interplay between scattering length and confinements.

Bartolo, Nicola; Antezza, Mauro

2014-09-01

356

Two-dimensional visualization of cluster beams by microchannel plates  

E-print Network

An advanced technique for a two-dimensional real time visualization of cluster beams in vacuum as well as of the overlap volume of cluster beams with particle accelerator beams is presented. The detection system consists of an array of microchannel plates (MCP) in combination with a phosphor screen which is read out by a CCD camera. This setup together with the ionization of a cluster beam by an electron or ion beam allows for spatial resolved investigations of the cluster beam position, size, and intensity. Moreover, since electrically uncharged clusters remain undetected, the operation in an internal beam experiment opens the way to monitor the overlap region and thus the position and size of an accelerator beam crossing an originally electrically neutral cluster jet. The observed intensity distribution of the recorded image is directly proportional to the convolution of the spatial ion beam and cluster beam intensities and is by this a direct measure of the two-dimensional luminosity distribution. This inf...

Khoukaz, Alfons; Grieser, Silke; Hergemöller, Ann-Katrin; Köhler, Esperanza; Täschner, Alexander

2013-01-01

357

Two-dimensional visualization of cluster beams by microchannel plates  

E-print Network

An advanced technique for a two-dimensional real time visualization of cluster beams in vacuum as well as of the overlap volume of cluster beams with particle accelerator beams is presented. The detection system consists of an array of microchannel plates (MCP) in combination with a phosphor screen which is read out by a CCD camera. This setup together with the ionization of a cluster beam by an electron or ion beam allows for spatial resolved investigations of the cluster beam position, size, and intensity. Moreover, since electrically uncharged clusters remain undetected, the operation in an internal beam experiment opens the way to monitor the overlap region and thus the position and size of an accelerator beam crossing an originally electrically neutral cluster jet. The observed intensity distribution of the recorded image is directly proportional to the convolution of the spatial ion beam and cluster beam intensities and is by this a direct measure of the two-dimensional luminosity distribution. This information can directly be used for the reconstruction of vertex positions as well as for an input for numerical simulations of the reaction zone. The spatial resolution of the images are dominated by the granularity of the complete MCP device and was found to be in the order of \\sigma~100 \\mu m.

Alfons Khoukaz; Daniel Bonaventura; Silke Grieser; Ann-Katrin Hergemöller; Esperanza Köhler; Alexander Täschner

2013-07-23

358

Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions  

NASA Astrophysics Data System (ADS)

Two-dimensional layered semiconductors such as MoS2 and WSe2 have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS2–MoSe2 and WS2–WSe2 lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe2–WS2 heterojunctions form lateral p–n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics.

Duan, Xidong; Wang, Chen; Shaw, Jonathan C.; Cheng, Rui; Chen, Yu; Li, Honglai; Wu, Xueping; Tang, Ying; Zhang, Qinling; Pan, Anlian; Jiang, Jianhui; Yu, Ruqing; Huang, Yu; Duan, Xiangfeng

2014-12-01

359

Two-dimensional phased array probe shape corrections  

NASA Astrophysics Data System (ADS)

The availability of non-destructive testing hardware capable of controlling large numbers of elements has made possible forays into two-dimensional ultrasonic arrays. Here, we explore two such arrays. The first is a conical matrix array for three-dimensional imaging of fastener holes in aircraft wing structures, and the second is an annular-sectorial array with a compound radius of curvature for the inspection of aircraft engine grade billets. In both prototypes, significant departures of the true shape of the probe face from its ideal value are observed. Since the shape aberrations are many wavelengths in magnitude, it is impossible to arrive at the desired beam profile using the beamforming parameters for the ideal probe shape. We detail our approach for correcting the beamforming process. It is based on a combination of parametric representations of probe shape families and experimental measurements with specially designed targets. While exposing current limitations in the probe manufacturing process, our results demonstrate that complicated probe malformations of many wavelengths in magnitude can easily be corrected and that the spatially disjoint nature of two-dimensional arrays becomes an opportunity for such corrections.

Lupien, Vincent; Cancre, Fabrice; Lacroix, Benolt; Miller, Ted; Selman, John; Kinney, Andy; Duffy, Tim; Herzog, Pamela G.

2002-05-01

360

Two-dimensional interpreter for field-reversed configurations  

SciTech Connect

An interpretive method is developed for extracting details of the fully two-dimensional (2D) “internal” structure of field-reversed configurations (FRC) from common diagnostics. The challenge is that only external and “gross” diagnostics are routinely available in FRC experiments. Inferring such critical quantities as the poloidal flux and the particle inventory has commonly relied on a theoretical construct based on a quasi-one-dimensional approximation. Such inferences sometimes differ markedly from the more accurate, fully 2D reconstructions of equilibria. An interpreter based on a fully 2D reconstruction is needed to enable realistic within-the-shot tracking of evolving equilibrium properties. Presented here is a flexible equilibrium reconstruction with which an extensive data base of equilibria was constructed. An automated interpreter then uses this data base as a look-up table to extract evolving properties. This tool is applied to data from the FRC facility at Tri Alpha Energy. It yields surprising results at several points, such as the inferences that the local ? (plasma pressure/external magnetic pressure) of the plasma climbs well above unity and the poloidal flux loss time is somewhat longer than previously thought, both of which arise from full two-dimensionality of FRCs.

Steinhauer, Loren, E-mail: lstein@uw.edu [Tri Alpha Energy, Rancho Santa Margarita, California 92688 (United States)

2014-08-15

361

A Two-Dimensional Linear Bicharacteristic Scheme for Electromagnetics  

NASA Technical Reports Server (NTRS)

The upwind leapfrog or Linear Bicharacteristic Scheme (LBS) has previously been implemented and demonstrated on one-dimensional electromagnetic wave propagation problems. This memorandum extends the Linear Bicharacteristic Scheme for computational electromagnetics to model lossy dielectric and magnetic materials and perfect electrical conductors in two dimensions. This is accomplished by proper implementation of the LBS for homogeneous lossy dielectric and magnetic media and for perfect electrical conductors. Both the Transverse Electric and Transverse Magnetic polarizations are considered. Computational requirements and a Fourier analysis are also discussed. Heterogeneous media are modeled through implementation of surface boundary conditions and no special extrapolations or interpolations at dielectric material boundaries are required. Results are presented for two-dimensional model problems on uniform grids, and the Finite Difference Time Domain (FDTD) algorithm is chosen as a convenient reference algorithm for comparison. The results demonstrate that the two-dimensional explicit LBS is a dissipation-free, second-order accurate algorithm which uses a smaller stencil than the FDTD algorithm, yet it has less phase velocity error.

Beggs, John H.

2002-01-01

362

Two-dimensional nuclear magnetic resonance of quadrupolar systems  

SciTech Connect

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.

Wang, Shuanhu

1997-09-17

363

Buoyant plane plumes from heated horizontal confined wires and cylinders  

Microsoft Academic Search

Two-dimensional computations are reported for time-dependent laminar buoyancy-induced flows above a horizontal heated source\\u000a immersed in an air-filled vessel. Two kinds of heated source were considered: a line heat source, modelled as a heat source\\u000a term in the energy equation, and a heat-flux cylinder of small diameter. First, comparisons are presented for the results\\u000a obtained for these two heated sources.

Guy Lauriat; Gilles Desrayaud

1994-01-01

364

Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics  

NASA Astrophysics Data System (ADS)

We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system.

Ackerman, Paul J.; Trivedi, Rahul P.; Senyuk, Bohdan; van de Lagemaat, Jao; Smalyukh, Ivan I.

2014-07-01

365

Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics.  

PubMed

We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system. PMID:25122322

Ackerman, Paul J; Trivedi, Rahul P; Senyuk, Bohdan; van de Lagemaat, Jao; Smalyukh, Ivan I

2014-07-01

366

Optical properties of two-dimensional metamaterial photonic crystals  

SciTech Connect

In the present work, we theoretically study a 2D photonic crystal (PC) comprised by double negative (DNG) metamaterial cylinders, showing that such a system presents a superior light-matter interaction when compared with their single negative (SNG) plasmonic PC counterparts, suggesting a route to enhance the performance of sensors and photovoltaic cells. On the other hand, we have observed that depending on the frequency, the mode symmetry resembles either the case of SNG electric (SNG-E) or SNG magnetic (SNG-M) PC, suggesting that either the electric or magnetic character of the DNG metamaterial dominates in each case.

Mejía-Salazar, J. R. [Departamento de Física, Universidad del Valle, AA 25360, Cali, Colombia and Instituto de Física, UNICAMP, Campinas-SP 13083-859 (Brazil)

2013-12-14

367

Optimal Padding for the Two-Dimensional Fast Fourier Transform  

NASA Technical Reports Server (NTRS)

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 can benefit from this algorithm, including optics, image-processing, signal-processing, and engineering applications.

Dean, Bruce H.; Aronstein, David L.; Smith, Jeffrey S.

2011-01-01

368

Two-dimensional Electronic Double-Quantum Coherence Spectroscopy  

PubMed Central

CONSPECTUS The theory of electronic structure of many-electron systems like molecules is extraordinarily complicated. A lot can be learned by considering how electron density is distributed, on average, in the average field of the other electrons in the system. That is, mean field theory. However, to describe quantitatively chemical bonds, reactions, and spectroscopy requires consideration of the way that electrons avoid each other by the way they move; this is called electron correlation (or in physics, the many-body problem for fermions). While great progress has been made in theory, there is a need for incisive experimental tests that can be undertaken for large molecular systems in the condensed phase. Here we report a two-dimensional (2D) optical coherent spectroscopy that correlates the double excited electronic states to constituent single excited states. The technique, termed two-dimensional double-coherence spectroscopy (2D-DQCS), makes use of multiple, time-ordered ultrashort coherent optical pulses to create double- and single-quantum coherences over time intervals between the pulses. The resulting two-dimensional electronic spectrum maps the energy correlation between the first excited state and two-photon allowed double-quantum states. The principle of the experiment is that when the energy of the double-quantum state, viewed in simple models as a double HOMO to LUMO excitation, equals twice that of a single excitation, then no signal is radiated. However, electron-electron interactions—a combination of exchange interactions and electron correlation—in real systems generates a signal that reveals precisely how the energy of the double-quantum resonance differs from twice the single-quantum resonance. The energy shift measured in this experiment reveals how the second excitation is perturbed by both the presence of the first excitation and the way that the other electrons in the system have responded to the presence of that first excitation. We compare a series of organic dye molecules and find that the energy offset for adding a second electronic excitation to the system relative to the first excitation is on the order of tens of milli-electronvolts, and it depends quite sensitively on molecular geometry. These results demonstrate the effectiveness of 2D-DQCS for elucidating quantitative information about electron-electron interactions, many-electron wavefunctions, and electron correlation in electronic excited states and excitons. PMID:19552412

Kim, Jeongho; Mukamel, Shaul

2009-01-01

369

Two-dimensional radiant energy array computers and computing devices  

NASA Technical Reports Server (NTRS)

Two dimensional digital computers and computer devices operate in parallel on rectangular arrays of digital radiant energy optical signal elements which are arranged in ordered rows and columns. Logic gate devices receive two input arrays and provide an output array having digital states dependent only on the digital states of the signal elements of the two input arrays at corresponding row and column positions. The logic devices include an array of photoconductors responsive to at least one of the input arrays for either selectively accelerating electrons to a phosphor output surface, applying potentials to an electroluminescent output layer, exciting an array of discrete radiant energy sources, or exciting a liquid crystal to influence crystal transparency or reflectivity.

Schaefer, D. H.; Strong, J. P., III (inventors)

1976-01-01

370

Dirac Cones in two-dimensional conjugated polymer networks.  

PubMed

Linear electronic band dispersion and the associated Dirac physics has to date been limited to special-case materials, notably graphene and the surfaces of three-dimensional (3D) topological insulators. Here we report that it is possible to create two-dimensional fully conjugated polymer networks with corresponding conical valence and conduction bands and linear energy dispersion at the Fermi level. This is possible for a wide range of polymer types and connectors, resulting in a versatile new family of experimentally realisable materials with unique tuneable electronic properties. We demonstrate their stability on substrates and possibilities for doping and Dirac cone distortion. Notably, the cones can be maintained in 3D-layered crystals. Resembling covalent organic frameworks, these materials represent a potentially exciting new field combining the unique Dirac physics of graphene with the structural flexibility and design opportunities of organic-conjugated polymer chemistry. PMID:25519052

Adjizian, Jean-Joseph; Briddon, Patrick; Humbert, Bernard; Duvail, Jean-Luc; Wagner, Philipp; Adda, Coline; Ewels, Christopher

2014-01-01

371

Dirac Cones in two-dimensional conjugated polymer networks  

NASA Astrophysics Data System (ADS)

Linear electronic band dispersion and the associated Dirac physics has to date been limited to special-case materials, notably graphene and the surfaces of three-dimensional (3D) topological insulators. Here we report that it is possible to create two-dimensional fully conjugated polymer networks with corresponding conical valence and conduction bands and linear energy dispersion at the Fermi level. This is possible for a wide range of polymer types and connectors, resulting in a versatile new family of experimentally realisable materials with unique tuneable electronic properties. We demonstrate their stability on substrates and possibilities for doping and Dirac cone distortion. Notably, the cones can be maintained in 3D-layered crystals. Resembling covalent organic frameworks, these materials represent a potentially exciting new field combining the unique Dirac physics of graphene with the structural flexibility and design opportunities of organic-conjugated polymer chemistry.

Adjizian, Jean-Joseph; Briddon, Patrick; Humbert, Bernard; Duvail, Jean-Luc; Wagner, Philipp; Adda, Coline; Ewels, Christopher

2014-12-01

372

Electronic properties of two-dimensional covalent organic frameworks.  

PubMed

The electronic properties of a number of two-dimensional covalent organic frameworks are studied using a combination of density functional theory and quasiparticle theory calculations. The effect of composition and system size on the electronic band gap is systematically considered for a series of systems, using van der Waals corrected density functional theory calculations to determine the effect of a graphene substrate on deposited covalent frameworks. We predict that covalent organic frameworks' (COFs') electronic properties, such as their band gap can be fine tuned by appropriate modifications of their structures, specifically by increasing organic chain-links in the framework. The effect of strain on the electronic properties is also studied. The graphene substrate is shown to not significantly alter the properties of COFs, thereby indicating the robustness of COFs' intrinsic properties for practical applications. PMID:23277948

Zhu, P; Meunier, V

2012-12-28

373

Electronic properties of two-dimensional covalent organic frameworks  

NASA Astrophysics Data System (ADS)

The electronic properties of a number of two-dimensional covalent organic frameworks are studied using a combination of density functional theory and quasiparticle theory calculations. The effect of composition and system size on the electronic band gap is systematically considered for a series of systems, using van der Waals corrected density functional theory calculations to determine the effect of a graphene substrate on deposited covalent frameworks. We predict that covalent organic frameworks' (COFs') electronic properties, such as their band gap can be fine tuned by appropriate modifications of their structures, specifically by increasing organic chain-links in the framework. The effect of strain on the electronic properties is also studied. The graphene substrate is shown to not significantly alter the properties of COFs, thereby indicating the robustness of COFs' intrinsic properties for practical applications.

Zhu, P.; Meunier, V.

2012-12-01

374

Two-dimensional soft nanomaterials: a fascinating world of materials.  

PubMed

The discovery of graphene has triggered great interest in two-dimensional (2D) nanomaterials for scientists in chemistry, physics, materials science, and related areas. In the family of newly developed 2D nanostructured materials, 2D soft nanomaterials, including graphene, Bx Cy Nz nanosheets, 2D polymers, covalent organic frameworks (COFs), and 2D supramolecular organic nanostructures, possess great advantages in light-weight, structural control and flexibility, diversity of fabrication approaches, and so on. These merits offer 2D soft nanomaterials a wide range of potential applications, such as in optoelectronics, membranes, energy storage and conversion, catalysis, sensing, biotechnology, etc. This review article provides an overview of the development of 2D soft nanomaterials, with special highlights on the basic concepts, molecular design principles, and primary synthesis approaches in the context. PMID:25155302

Zhuang, Xiaodong; Mai, Yiyong; Wu, Dongqing; Zhang, Fan; Feng, Xinliang

2015-01-01

375

A multiple devil's staircase in a two-dimensional map  

NASA Astrophysics Data System (ADS)

We found a multiple devil's staircase in a two-dimensional discontinuous map that can be viewed as a simplified model of an impact oscillator. The staircase loses monotonicity and self-similarity and shows a very complicated structure. In some parts of the staircase one can see tower-like structures. Each tower is consisted of two branches. They are conventional devil's staircases. Each phase-locked plateau in the staircase is confined by conditions created by the collision between a periodic orbit and a point located on the discontinuous boundary of the system. The collision points of the phase-locked plateau in a conventional devil's staircase moves linearly along the boundary when the winding number changes. While the collision points of the plateau in different branches do not obey this rule. This observation may suggest that multiple devil's staircase can be found widely in higher-dimensional discontinuous maps.

Wang, Wen-Xiu; Wang, Xu-Ming; He, Da-Ren; Mao, Jian-Shan

2001-03-01

376

A two-dimensional tidal model for the Mediterranean Sea  

NASA Astrophysics Data System (ADS)

The tidal propagation in the Mediterranean Sea is described through a high-resolution, two-dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the Strait of Gibraltar. The four most significant constituents, M2, S2, K1, and O1, are included in the model. Good agreement with a set of 63 coastal gauges is achieved. The significance of the equilibrium tide and the forcing at the open boundary is investigated. The incoming wave from the Strait of Gibraltar is important in tuning the tides in the whole of the Mediterranean. For the north Aegean Sea the solution without the forcing at Gibraltar results in a doubling of the amplitudes of the semidiurnal tides. The estimated energy dissipation due to bottom friction is 8.8×108 W. The major area of dissipation is the Gulf of Gabes. Energy fluxes through the major straits are calculated.

Tsimplis, M. N.; Proctor, R.; Flather, R. A.

1995-08-01

377

Improved parallel implementation of the two-dimensional Ising model  

NASA Astrophysics Data System (ADS)

Some simulations we would like to perform in computational physics require so much computation time that it is not possible to finish them in reasonable length of time on any nowadays available computer. If it is possible to decompose a compute intensive problem into smaller independent tasks one possibility is to shorten the calculation time is to apply a parallel algorithm. Java, a platform independent programming language changed the way of software design by using Jini and JavaSpaces, new technologies that have been introduced recently. By applying JavaSpaces, a virtual, network accessible space can be used to store Java objects but also for effective parallel processing. In this paper, we report a novel, parallel implementation of the two-dimensional Ising model using the JavaSpaces technology. Our new approach was implemented on standard computer equipment and results in significant improvement of computation time.

Knoll, P.; Mirzaei, S.

2001-12-01

378

Numerically simulated two-dimensional auroral double layers  

NASA Technical Reports Server (NTRS)

A magnetized 2 1/2-dimensional particle-in-cell system which is periodic in one direction and bounded by reservoirs of Maxwellian plasma in the other is used to numerically simulate electrostatic plasma double layers. For the cases of both oblique and two-dimensional double layers, the present results indicate periodic instability, Debye length rather than gyroradii scaling, and low frequency electrostatic turbulence together with electron beam-excited electrostatatic electron-cyclotron waves. Estimates are given for the thickness of auroral doule layers, as well as the separations within multiple auroral arcs. Attention is given to the temporal modulation of accelerated beams, and the possibilities for ion precipitation and ion conic production by the double layer are hypothesized. Simulations which include the atmospheric backscattering of electrons imply the action of an ionospheric sheath which accelerates ionospheric ions upward.

Borovsky, J. E.; Joyce, G.

1983-01-01

379

Two-dimensional atom localization via Raman-driven coherence  

NASA Astrophysics Data System (ADS)

A scheme for two-dimensional (2D) atom localization via Raman-driven coherence in a four-level diamond-configuration system is suggested. The atom interacts with two orthogonal standing-wave fields where each standing-wave field is constructed from the superposition of the two-standing wave fields along the corresponding directions. Due to the position-dependent atom-field interaction, the frequency of the spontaneously emitted photon carries the position information about the atom. We investigate the effect of the detunings and phase shifts associated with standing-wave fields. Unique position information of the single atom is obtained by properly adjusting the system parameters. This is an extension of our previous proposal for one-dimensional atom localization via Raman-driven coherence [1].

Rahmatullah; Qamar, Sajid

2014-02-01

380

Point vortices in two dimensional-plasma hydrodynamics  

SciTech Connect

An exact theory of point vortices in two dimensional (2D) electron-ion plasma hydrodynamics is presented. This theory is a logical generalization of the classical theory of point vortices in a 2D Euler equation. The existence of two types of point vortices is shown: ion and electron, and their structure is described in detail. Ion vortices interact over long distances, while electron vortices interact over short distances. A dynamic system is obtained, which describes the common motion of an arbitrary number of electron and ion vortices. The proposed theory can be used to construct finite dimensional dynamical models of plasma motion, as well as for the construction of finite dimensional statistical models of turbulence, transport processes and filaments.

Tur, Anatoly [CNRS, Centre d'Etude Spatiale des Rayonnements, Universite de Toulouse (UPS), 9 Avenue du Colonel Roche, BP 4346, 31028 Toulouse Cedex 4 (France); Yanovsky, Vladimir [Institute for Single Crystals, National Academy of Science Ukraine, Kharkov 31001 (Ukraine)

2010-11-15

381

Microwave near-field imaging of two-dimensional semiconductors.  

PubMed

Optimizing new generations of two-dimensional devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS2 and n- and p-doped WSe2. By controlling the sample charge carrier concentration through the applied tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effects of surface contaminants. By further performing tip bias-dependent point spectroscopy together with finite element simulations, we distinguish the effects of the quantum capacitance and determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials to image, identify, and study electronic defects. PMID:25625509

Berweger, Samuel; Weber, Joel C; John, Jimmy; Velazquez, Jesus M; Pieterick, Adam; Sanford, Norman A; Davydov, Albert V; Brunschwig, Bruce; Lewis, Nathan S; Wallis, Thomas M; Kabos, Pavel

2015-02-11

382

Two-dimensional fruit ripeness estimation using thermal imaging  

NASA Astrophysics Data System (ADS)

Some green fruits do not change their color from green to yellow when being ripe. As a result, ripeness estimation via color and fluorescent analytical approaches cannot be applied. In this article, we propose and show for the first time how a thermal imaging camera can be used to two-dimensionally classify fruits into different ripeness levels. Our key idea relies on the fact that the mature fruits have higher heat capacity than the immature ones and therefore the change in surface temperature overtime is slower. Our experimental proof of concept using a thermal imaging camera shows a promising result in non-destructively identifying three different ripeness levels of mangoes Mangifera indica L.

Sumriddetchkajorn, Sarun; Intaravanne, Yuttana

2013-06-01

383

Quasi-two-dimensional Fermi gases at finite temperatures  

NASA Astrophysics Data System (ADS)

We consider a Fermi gas with short-range attractive interactions that is confined along one direction by a tight harmonic potential. For this quasi-two-dimensional (quasi-2D) Fermi gas, we compute the pressure equation of state, radiofrequency spectrum, and the superfluid critical temperature Tc using a mean-field theory that accounts for all the energy levels of the harmonic confinement. Our calculation for Tc provides a natural generalization of the Thouless criterion to the quasi-2D geometry, and it correctly reduces to the 3D expression derived from the local density approximation in the limit where the confinement frequency ?z?0 . Furthermore, our results suggest that Tc can be enhanced by relaxing the confinement and perturbing away from the 2D limit.

Fischer, Andrea M.; Parish, Meera M.

2014-12-01

384

Two-dimensional photonic crystal based sensor for pressure sensing  

NASA Astrophysics Data System (ADS)

In this paper, a two-dimensional photonic crystal (2DPC) based pressure sensor is proposed and designed, and the sensing characteristics such as the sensitivity and dynamic range are analyzed over the range of pressure from 0 GPa to 7 GPa. The sensor is based on 2DPC with the square array of silicon rods surrounded by air. The sensor consists of two photonic crystal quasi waveguides and L3 defect. The L3 defect is placed in between two waveguides and is formed by modifying the radius of three Si rods. It is noticed that through simulation, the resonant wavelength of the sensor is shifted linearly towards the higher wavelength region while increasing the applied pressure level. The achieved sensitivity and dynamic range of the sensor is 2 nm/GPa and 7 Gpa, respectively.

Vijaya Shanthi, Krishnan; Robinson, Savarimuthu

2014-09-01

385

Thermal stability of two-dimensional gold nanocrystal superlattices.  

SciTech Connect

The thermal stability of highly ordered two-dimensional superlattices consisting of dodecanethiol-ligated Au nanoparticles has been investigated using in situ grazing incidence small-angle x-ray scattering in air and in vacuum. In the lower temperature region (<70 C), annealing in air results in a minimal change of superlattice structure, whereas annealing in vacuum leads to a considerable lattice contraction and a decrease in long-range order. At higher temperatures (>100 C), ligand desorption causes nanocrystals to sinter locally, destroying quasi-long-range order. The sintering process is significantly enhanced in vacuum compared to the case in air due to the increased desorption rate of thiol ligands under low pressure.

Robel, I.; Lin, X.-M.; Sprung, M.; Wang, J.

2009-07-01

386

Two-dimensional heterostructures: fabrication, characterization, and application.  

PubMed

Two-dimensional (2D) materials such as graphene, hexagonal boron nitrides (hBN), and transition metal dichalcogenides (TMDs, e.g., MoS2) have attracted considerable attention in the past few years because of their novel properties and versatile potential applications. These 2D layers can be integrated into a monolayer (lateral 2D heterostructure) or a multilayer stack (vertical 2D heterostructure). The resulting artificial 2D structures provide access to new properties and applications beyond their component 2D atomic crystals and hence, they are emerging as a new exciting field of research. In this article, we review recent progress on the fabrication, characterization, and applications of various 2D heterostructures. PMID:25219598

Wang, Hong; Liu, Fucai; Fu, Wei; Fang, Zheyu; Zhou, Wu; Liu, Zheng

2014-11-01

387

Spin susceptibility of two-dimensional transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

We have obtained analytical expressions for the q-dependent static spin susceptibility of monolayer transition-metal dichalcogenides, considering both the electron-doped and hole-doped cases. Our results are applied to calculate spin-related physical observables of monolayer MoS2, focusing especially on in-plane/out-of-plane anisotropies. We find that the hole-mediated Ruderman-Kittel-Kasuya-Yosida exchange interaction for in-plane impurity-spin components decays with the power law R-5/2 as a function of distance R, which deviates from the R-2 power law normally exhibited by a two-dimensional Fermi liquid. In contrast, the out-of-plane spin response shows the familiar R-2 long-range behavior. We also use the spin susceptibility to define a collective g factor for hole-doped MoS2 systems and discuss its density-dependent anisotropy.

Hatami, H.; Kernreiter, T.; Zülicke, U.

2014-07-01

388

Polycrystalline graphene and other two-dimensional materials.  

PubMed

Graphene, a single atomic layer of graphitic carbon, has attracted intense attention because of its extraordinary properties that make it a suitable material for a wide range of technological applications. Large-area graphene films, which are necessary for industrial applications, are typically polycrystalline - that is, composed of single-crystalline grains of varying orientation joined by grain boundaries. Here, we present a review of the large body of research reported in the past few years on polycrystalline graphene. We discuss its growth and formation, the microscopic structure of grain boundaries and their relations to other types of topological defect such as dislocations. The Review further covers electronic transport, optical and mechanical properties pertaining to the characterizations of grain boundaries, and applications of polycrystalline graphene. We also discuss research, still in its infancy, performed on other two-dimensional materials such as transition metal dichalcogenides, and offer perspectives for future directions of research. PMID:25152238

Yazyev, Oleg V; Chen, Yong P

2014-10-01

389

Electron capture imaging of two-dimensional materials  

NASA Astrophysics Data System (ADS)

We demonstrate that electron transfer induced by fast ion impact can be used as an imaging technique of two-dimensional materials. Applied to a keV proton beam passing through a graphene surface, it is shown that coherent single-electron capture gives a sub-ångström-scale spatial resolution image of the electronic structure of a single sheet. This imaging scheme is shown to be particularly effective, resolving missing atoms (vacancies) in the lattice, in a narrow projectile 5-10-keV energy region, where the capture probability exhibits a minimum at the center of the hexagonal cells. This geometry-dependent phenomenon is caused by the coupling dynamic between the initial state and a multi-electron entangled one-hole state and is therefore highly sample selective.

Labaigt, G.; Dubois, A.; Hansen, J. P.

2014-06-01

390

Self-organized defect strings in two-dimensional crystals.  

PubMed

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. PMID:24483371

Lechner, Wolfgang; Polster, David; Maret, Georg; Keim, Peter; Dellago, Christoph

2013-12-01

391

Two-dimensional random walk in a bounded domain  

NASA Astrophysics Data System (ADS)

In a recent letter Ciftci and Cakmak (EPL, 87 (2009) 60003) showed that the two-dimensional random walk in a bounded domain, where walkers which cross the boundary return to a base curve near the origin with deterministic rules, can produce regular patterns. Our numerical calculations suggest that the cumulative probability distribution function of the returning walkers along the base curve is a Devil's staircase, which can be explained from the mapping of these walks to a non-linear stochastic map. The non-trivial probability distribution function (PDF) is a universal feature of CCRW characterized by the fractal dimension d=1.75(0) of the curve which bounds this distribution.

Basu, Mahashweta; Mohanty, P. K.

2010-06-01

392

A ballistic two-dimensional-electron-gas Andreev interferometer  

NASA Astrophysics Data System (ADS)

We report the realization and investigation of a ballistic Andreev interferometer based on an InAs two dimensional electron gas coupled to a superconducting Nb loop. We observe strong magnetic modulations in the voltage drop across the device due to quasiparticle interference within the weak-link. The interferometer exhibits flux noise down to ˜80 ??0/?Hz and a robust behavior in temperature with voltage oscillations surviving up to ˜7 K. Besides this remarkable performance, the device represents a crucial first step for the realization of a fully-tunable ballistic superconducting magnetometer and embodies a potential advanced platform for the investigation of Majorana bound states, non-local entanglement of Cooper pairs, as well as the manipulation and control of spin triplet correlations.

Amado, M.; Fornieri, A.; Biasiol, G.; Sorba, L.; Giazotto, F.

2014-06-01

393

Two-dimensional optical thermal ratchets based on Fibonacci spirals.  

PubMed

An ensemble of symmetric potential energy wells arranged at the vertices of a Fibonacci spiral can serve as the basis for an irreducibly two-dimensional thermal ratchet. Periodic rotation of the potential energy landscape through a three-step cycle drives trapped Brownian particles along spiral trajectories through the pattern. Which spiral is selected depends on the angular displacement at each step, with transitions between selected spirals arising at rational proportions of the golden angle. Fibonacci spiral ratchets therefore display an exceptionally rich range of transport properties, including inhomogeneous states in which different parts of the pattern induce motion in different directions. Both the radial and angular components of these trajectories can undergo flux reversal as a function of the scale of the pattern or the rate of rotation. PMID:21867137

Xiao, Ke; Roichman, Yael; Grier, David G

2011-07-01

394

Two-dimensional nonlinear map characterized by tunable Lévy flights.  

PubMed

After recognizing that point particles moving inside the extended version of the rippled billiard perform Lévy flights characterized by a Lévy-type distribution P(l)?l(-(1+?)) with ?=1, we derive a generalized two-dimensional nonlinear map M? able to produce Lévy flights described by P(l) with 0

Méndez-Bermúdez, J A; de Oliveira, Juliano A; Leonel, Edson D

2014-10-01

395

Dynamics of a Two-Dimensional System of Quantum Dipoles  

SciTech Connect

A detailed microscopic analysis of the dynamic structure function S(k,{omega}) of a two-dimensional Bose system of dipoles polarized along the direction perpendicular to the plane is presented and discussed. Starting from ground-state quantities obtained using a quantum diffusion Monte Carlo algorithm, the density-density response is evaluated in the context of the correlated basis functions (CBF) theory. CBF predicts a sharp peak and a multiexcitation component at higher energies produced by the decay of excitations. We discuss the structure of the phonon-roton peak and show that the Feynman and Bogoliubov predictions depart from the CBF result already at low densities. We finally discuss the emergence of a roton in the spectrum, but find the roton energy not low enough to make the system unstable under density fluctuations up to the highest density considered that is close to the freezing point.

Mazzanti, F.; Astrakharchik, G. E.; Boronat, J. [Departament de Fisica i Enginyeria Nuclear, Campus Nord B4-B5, Universitat Politecnica de Catalunya, E-08034 Barcelona (Spain); Zillich, R. E. [Institut fuer Theoretische Physik, Johannes-Kepler Universitaet, Altenbergerstr. 69, 4040 Linz (Austria)

2009-03-20

396

Pairwise interactions of colloids in two-dimensional geometric confinement.  

PubMed

We present the pairwise interaction behaviour of colloids confined to two-dimensional (2D) colloidal cages using optical laser tweezers. A single probe particle inside hexagonal cage particles at a planar oil-water interface is allowed to diffuse freely and the spring constant is extracted from its trajectories. To evaluate the effect of multibody interactions, the pair interactions between the probe particle and each cage particle are directly measured by using optical tweezers. Based on pairwise additivity, Monte Carlo simulations are used to compare the values of the spring constant obtained from experiments and simulations. We find that the multibody interactions negligibly occur and thus the particle interactions confined to such colloidal cages are highly pairwise. This work demonstrates that the use of the pairwise assumption in numerical simulations is rational when interparticle repulsive interactions are sufficiently strong, such as the particle interactions at fluid-fluid interfaces. PMID:25363564

Park, Bum Jun; Lee, Bomsock; Yu, Taekyung

2014-11-19

397

Phase diagram of two-dimensional hard ellipses  

E-print Network

We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [PRL 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i. e. isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios.

Gustavo Bautista-Carbajal; Gerardo Odriozola

2014-05-09

398

The two-dimensional derivative-coupling model revisited  

NASA Astrophysics Data System (ADS)

Using the operator approach we reexamine the two-dimensional model describing a massive Fermi field interacting via derivative couplings with two massless Bose fields, one scalar and the other pseudoscalar. Performing a canonical transformation on the Bose field algebra, the Fermi field operator is written in terms of the Mandelstam soliton operator and the derivative-coupling (DC) model is mapped into the massive Thirring model with two vector-current-scalar-derivative interactions (Schroer-Thirring model). The DC model with massless fermions can be mapped into the massless Rothe-Stamatescu model with a Thirring interaction (massless Rothe-Stamatescu-Thirring model). Within the present approach the weak equivalence between the fermionic sector of the DC model and the massive Thirring model is exhibited compactly.

Belvedere, L. V.; Rodrigues, A. F.

2007-05-01

399

Two-dimensional turbulence of dilute polymer solutions  

E-print Network

We investigate theoretically and numerically the effect of polymer additives on two-dimensional turbulence by means of a viscoelastic model. We provide compelling evidence that at vanishingly small concentrations, such that the polymers are passively transported, the probability distribution of polymer elongation has a power law tail: its slope is related to the statistics of finite-time Lyapunov exponents of the flow, in quantitative agreement with theoretical predictions. We show that at finite concentrations and sufficiently large elasticity the polymers react on the flow with manifold consequences: velocity fluctuations are drastically depleted, as observed in soap film experiments; the velocity statistics becomes strongly intermittent; the distribution of finite-time Lyapunov exponents shifts to lower values, signalling the reduction of Lagrangian chaos.

G. Boffetta; A. Celani; S. Musacchio

2003-03-05

400

Higgs mode in a two-dimensional superfluid.  

PubMed

We present solid evidence for the existence of a well-defined Higgs amplitude mode in two-dimensional relativistic field theories based on analytically continued results from quantum Monte Carlo simulations of the Bose-Hubbard model in the vicinity of the superfluid-Mott insulator quantum critical point, featuring emergent particle-hole symmetry and Lorentz invariance. The Higgs boson, seen as a well-defined low-frequency resonance in the spectral density, is quickly pushed to high energies in the superfluid phase and disappears by merging with the broad secondary peak at the characteristic interaction scale. Simulations of a trapped system of ultracold (87)Rb atoms demonstrate that the low-frequency resonance is lost for typical experimental parameters, while the characteristic frequency for the onset of a strong response is preserved. PMID:23031091

Pollet, L; Prokof'ev, N

2012-07-01

401

Bond Order Solid of Two-Dimensional Dipolar Fermions  

NASA Astrophysics Data System (ADS)

Cold atoms provide a promising platform to solve problems that, although computationally infeasible, are of immense importance to condensed matter physics and material science. Ultra-cold bosonic atoms have been quite successful in emulating the Bose-Hubbard model. Experiments are now underway towards mapping out the unknown phase diagram of the Fermi-Hubbard model. Recent experimental advances in cooling dipolar gases to quantum degeneracy provide an unprecedented opportunity to engineer Hubbard- like models with long range interactions. Here, with the aid of functional renormalization group technique, we show that two new and exotic types of order emerge generically in dipolar fermion systems: bond order solids of p- and d-wave symmetry. Similar, but manifestly different, phases of two-dimensional correlated electronic systems have previously only been hypothesized. Our results suggest that these phases can be constructed flexibly with dipolar fermions, using currently available experimental techniques, providing detectable experimental signatures.

Bhongale, Satyan; Mathey, Ludwig; Tsai, Shan-Wen; Clark, Charles; Zhao, Erhai

2012-02-01

402

An investigation of a two-dimensional propulsive lifting system  

NASA Technical Reports Server (NTRS)

Several aspects of the nonhomogeneous flow associated with a system combining lifting and propulsive requirements of an aircraft are considered by analytical and experimental methods. The basic geometry of the problem is that of two lifting surfaces with an actuator disk located between them. The principles governing flow with energy addition are examined. Basic equations and boundary conditions are developed for the complete inviscid and incompressible analysis for the two-dimensional case. The corresponding flow singularities are discussed and the integral equations which completely specify the system are derived. The two special cases of small and large energy addition are considered in detail including solutions. A numerical procedure is developed to solve the full problem including allowance for the wake deflection. Appropriate vorticity forms are used to represent the entire system. An iterative scheme is presented which rapidly converges to a solution for the magnitude and location of the system vorticity distributions. Forces and moments are evaluated on the propulsive lift system.

Shollenberger, C. A.

1973-01-01

403

Two-dimensional pixel readout of wire chambers  

NASA Astrophysics Data System (ADS)

We describe a new concept for two-dimensional position readout of wire chambers. The cathode is divided into small electrodes (pads) with approximately the size of the desired position resolution. The pulse height in each pad is compared with a threshold. A particle hit will always result in a cluster of three neighbouring pads fired, thus providing a very high noise immunity in spite of the simple threshold readout. Test results for single particles are reported. The results are used as the input for a simulation of the two track separation power. The simulations indicate that the concept will show excellent performance at the very high particle multiplicities prevailing in heavy ion collisions at RHIC and LHC.

Carlén, L.; Garpman, S.; Gustafsson, H.-Å.; Oskarsson, A.; Otterlund, I.; Stenlund, E.; Svensson, T.; Söderström, K.

1997-02-01

404

Two-dimensional plasma photonic crystals in dielectric barrier discharge  

SciTech Connect

A series of two-dimensional plasma photonic crystals have been obtained by filaments' self-organization in atmospheric dielectric barrier discharge with two water electrodes, which undergo the transition from square to square superlattice and finally to the hexagon. The spatio-temporal behaviors of the plasma photonic crystals in nanosecond scale have been studied by optical method, which show that the plasma photonic crystal is actually an integration of different transient sublattices. The photonic band diagrams of the transverse electric (TE) mode and transverse magnetic mode for each sublattice of these plasma photonic crystals have been investigated theoretically. A wide complete band gap is formed in the hexagonal plasma photonic crystal with the TE mode. The changes of the band edge frequencies and the band gap widths in the evolvement of different structures are studied. A kind of tunable plasma photonic crystal which can be controlled both in space and time is suggested.

Fan Weili; Dong Lifang [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Zhang Xinchun [School of Energy and Power Engineering, North China Electric Power University, Baoding 071003 (China)

2010-11-15

405

Two-dimensional electronic spectroscopy with birefringent wedges  

NASA Astrophysics Data System (ADS)

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.

Réhault, Julien; Maiuri, Margherita; Oriana, Aurelio; Cerullo, Giulio

2014-12-01

406

A Vortex Particle Method for Two-Dimensional Compressible Flow  

NASA Astrophysics Data System (ADS)

A vortex particle method is developed for simulating two-dimensional, unsteady compressible flow. The method uses the Helmholtz decomposition of the velocity field to separately treat the irrotational and solenoidal portions of the flow, and the particles are allowed to change volume to conserve mass. In addition to having vorticity and dilatation properties, the particles also carry density, enthalpy, and entropy. The resulting evolution equations contain terms that are computed with techniques used in some incompressible methods. Truncation of unbounded domains via a nonreflecting boundary condition is also considered. The fast multipole method is adapted to compressible particles in order to make the method computationally efficient. The new method is applied to several problems, including sound generation by corotating vortices and generation of vorticity by baroclinic torque.

Eldredge, Jeff D.; Colonius, Tim; Leonard, Anthony

2002-07-01

407

Fractional impurity moments in two-dimensional noncollinear magnets.  

PubMed

We study dilute magnetic impurities and vacancies in two-dimensional frustrated magnets with noncollinear order. Taking the triangular-lattice Heisenberg model as an example, we use quasiclassical methods to determine the impurity contributions to the magnetization and susceptibility. Most importantly, each impurity moment is not quantized but receives nonuniversal screening corrections due to local relief of frustration. At finite temperatures, where bulk long-range order is absent, this implies an impurity-induced magnetic response of Curie form, with a prefactor corresponding to a fractional moment per impurity. We also discuss the behavior in an applied magnetic field, where we find a singular linear-response limit for overcompensated impurities. PMID:22026900

Wollny, Alexander; Fritz, Lars; Vojta, Matthias

2011-09-23

408

Method and apparatus for two-dimensional absolute optical encoding  

NASA Technical Reports Server (NTRS)

This invention presents a two-dimensional absolute optical encoder and a method for determining position of an object in accordance with information from the encoder. The encoder of the present invention comprises a scale having a pattern being predetermined to indicate an absolute location on the scale, means for illuminating the scale, means for forming an image of the pattern; and detector means for outputting signals derived from the portion of the image of the pattern which lies within a field of view of the detector means, the field of view defining an image reference coordinate system, and analyzing means, receiving the signals from the detector means, for determining the absolute location of the object. There are two types of scale patterns presented in this invention: grid type and starfield type.

Leviton, Douglas B. (Inventor)

2004-01-01

409

Two dimensional fractional projectile motion in a resisting medium  

NASA Astrophysics Data System (ADS)

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 ? and different fixed values of velocity v 0 and angle ?, 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 ? = 1.

Rosales, Juan J.; Guía, Manuel; Gómez, Francisco; Aguilar, Flor; Martínez, Juan

2014-07-01

410

Two-Dimensional Quantum Model of a Nanotransistor  

NASA Technical Reports Server (NTRS)

A mathematical model, and software to implement the model, have been devised to enable numerical simulation of the transport of electric charge in, and the resulting electrical performance characteristics of, a nanotransistor [in particular, a metal oxide/semiconductor field-effect transistor (MOSFET) having a channel length of the order of tens of nanometers] in which the overall device geometry, including the doping profiles and the injection of charge from the source, gate, and drain contacts, are approximated as being two-dimensional. The model and software constitute a computational framework for quantitatively exploring such device-physics issues as those of source-drain and gate leakage currents, drain-induced barrier lowering, and threshold voltage shift due to quantization. The model and software can also be used as means of studying the accuracy of quantum corrections to other semiclassical models.

Govindan, T. R.; Biegel, B.; Svizhenko, A.; Anantram, M. P.

2009-01-01

411

Sample preparation guidelines for two-dimensional electrophoresis.  

PubMed

Sample preparation is one of the key technologies for successful two-dimensional electrophoresis (2DE). Due to the great diversity of protein sample types and sources, no single sample preparation method works with all proteins; for any sample the optimum procedure must be determined empirically. This review is meant to provide a broad overview of the most important principles in sample preparation in order to avoid a multitude of possible pitfalls. Sample preparation protocols from the expert in the field were screened and evaluated. On the basis of these protocols and my own comprehensive practical experience important guidelines are given in this review. The presented guidelines will facilitate straightforward protocol development for researchers new to gel-based proteomics. In addition the available choices are rationalized in order to successfully prepare a protein sample for 2DE separations. The strategies described here are not limited to 2DE and can also be applied to other protein separation techniques. PMID:25211021

Posch, Anton

2014-12-01

412

Search for conformal invariance in compressible two-dimensional turbulence  

E-print Network

We present a search for conformal invariance in vorticity isolines of two-dimensional compressible turbulence. The vorticity is measured by tracking the motion of particles that float at the surface of a turbulent tank of water. The three-dimensional turbulence in the tank has a Taylor microscale $Re_\\lambda \\simeq 160$. The conformal invariance theory being tested here is related to the behavior of equilibrium systems near a critical point. This theory is associated with the work of L\\"owner, Schramm and others and is usually referred to as Schramm-L\\"owner Evolution (SLE). The system was exposed to several tests of SLE. The results of these tests suggest that zero-vorticity isolines exhibit noticeable departures from this type of conformal invariance.

S. Stefanus; J. Larkin; W. I. Goldburg

2011-10-11

413

Circle-map scaling in a two-dimensional setting  

NASA Astrophysics Data System (ADS)

Hopf bifurcations in two-dimensional maps give rise to closed invariant curves and circle maps induced on these curves. It is not obvious whether the induced maps will exhibit the full array of scaling phenomena familiar from the study of one-dimensional maps. In the present work we numerically study a variable Jacobian map (the coupled logistic map). A detailed investigation along its critical line shows an excellent agreement of the map with the critical scaling predictions for a circle map with a smooth cubic inflection point. This occurs in spite of the fact that within mode-locking intervals on the critical line, which together occupy a set of full measure, the induced map has no cubic inflection point.

Wang, Xiaowu; Mainieri, Ronnie; Lowenstein, J. H.

1989-11-01

414

Analysis of cancellation exponents in two-dimensional Vlasov turbulence  

SciTech Connect

Statistical properties of plasma turbulence are investigated by means of two-dimensional Vlasov simulations. In particular, a classical technique called signed measure is used to characterize the scaling behavior and the topology of sign-oscillating structures in simulations of the hybrid Vlasov-Maxwell model. Exploring different turbulence regimes, varying both the plasma ? and the level of fluctuations, it is observed that Vlasov turbulence manifests two ranges with different exponents, the transition being observed near the ion skin depth. These results, which may have applications to both laboratory and astrophysical systems, further confirm the singular nature of small scale fluctuations in a plasma, mainly classified as intermittent, narrow, and intense current sheets.

De Vita, G.; Valentini, F.; Servidio, S.; Primavera, L.; Carbone, V.; Veltri, P. [Dipartimento di Fisica, Università della Calabria, 87036 Rende, CS (Italy); Sorriso-Valvo, L. [CNR-IPCF - U.O.S. di Cosenza, 87036 Rende, CS (Italy); Space Sciences Laboratory, University of California, Berkeley, California 94720 (United States)

2014-07-15

415

Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence  

SciTech Connect

The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.

Donato, S.; Servidio, S.; Carbone, V. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET, Buenos Aires (Argentina); Shay, M. A.; Matthaeus, W. H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)

2012-09-15

416

Two-dimensional quantum gas in a hybrid surface trap  

NASA Astrophysics Data System (ADS)

We demonstrate the realization of a two-dimensional (2D) quantum gas in a smooth optical surface trap. Using a combination of evanescent wave, standing wave, and magnetic potentials, we create a long-lived quantum gas deep in the 2D regime at a distance of a few microns from a glass surface. To realize a system suitable for many-body quantum simulation, we introduce methods such as broadband “white” light to create evanescent and standing waves to realize a smooth potential with a trap frequency aspect ratio of 300:1:1. We are able to detect phase fluctuations and vortices, and we demonstrate cooling to degeneracy and low disorder in the 2D configuration.

Gillen, J. I.; Bakr, W. S.; Peng, A.; Unterwaditzer, P.; Fölling, S.; Greiner, M.

2009-08-01

417

Kinetic theory of a two-dimensional magnetized plasma.  

NASA Technical Reports Server (NTRS)

Several features of the equilibrium and nonequilibrium statistical mechanics of a two-dimensional plasma in a uniform dc magnetic field are investigated. The charges are assumed to interact only through electrostatic potentials. The problem is considered both with and without the guiding-center approximation. With the guiding-center approximation, an appropriate Liouville equation and BBGKY hierarchy predict no approach to thermal equilibrium for the spatially uniform case. For the spatially nonuniform situation, a guiding-center Vlasov equation is discussed and solved in special cases. For the nonequilibrium, nonguiding-center case, a Boltzmann equation, and a Fokker-Planck equation are derived in the appropriate limits. The latter is more tractable than the former, and can be shown to obey conservation laws and an H-theorem, but contains a divergent integral which must be cut off on physical grounds. Several unsolved problems are posed.

Vahala, G.; Montgomery, D.

1971-01-01

418

Global geometry of two-dimensional charged black holes  

SciTech Connect

The semiclassical geometry of charged black holes is studied in the context of a two-dimensional dilaton gravity model where effects due to pair-creation of charged particles can be included in a systematic way. The classical mass-inflation instability of the Cauchy horizon is amplified and we find that gravitational collapse of charged matter results in a spacelike singularity that precludes any extension of the spacetime geometry. At the classical level, a static solution describing an eternal black hole has timelike singularities and multiple asymptotic regions. The corresponding semiclassical solution, on the other hand, has a spacelike singularity and a Penrose diagram like that of an electrically neutral black hole. Extremal black holes are destabilized by pair-creation of charged particles. There is a maximally charged solution for a given black hole mass but the corresponding geometry is not extremal. Our numerical data exhibits critical behavior at the threshold for black hole formation.

Frolov, Andrei V.; Kristjansson, Kristjan R.; Thorlacius, Larus [KIPAC/SITP, Stanford University, Stanford, California 94305-4060 (United States); NORDITA, Blegdamsvej 17, 2100 Copenhagen (Denmark); University of Iceland, Science Institute, Dunhaga 3, 107 Reykjavik (Iceland)

2006-06-15

419

Exciton spectra in two-dimensional graphene derivatives  

NASA Astrophysics Data System (ADS)

The energy spectra and wave functions of bound excitons in important two-dimensional (2D) graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter modified hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a candidate for intriguing energy and biomedical applications.

Huang, Shouting; Liang, Yufeng; Yang, Li

2013-08-01

420

Solvent minimization in two-dimensional liquid chromatography.  

PubMed

An algorithm was developed for the minimization of consumption of organic solvent in comprehensive two-dimensional liquid chromatography (2DLC). It was shown that one can reach higher peak capacities only by using more eluent. The equilibration volume of the second dimension, however, did not affect the solvent consumption significantly. Calculations confirmed that the same target peak capacity could be achieved by consuming significantly different volume of organic modifier depending on the number of fractions analyzed in the second dimension suggesting that 2D separations can be optimized for eluent consumption. It was shown that minimization of eluent usage requires the use of small and high efficient columns in the second dimension. A simple equation was derived for the calculation of the optimal number of collected fractions from the first dimension that allowed the minimization of eluent usage, cost and environmental impact of comprehensive 2DLC separations. PMID:25555411

Horváth, Krisztián; Sepsey, Annamária; Hajós, Péter

2015-01-23

421

The Two-Dimensional Euler Equations on Singular Domains  

NASA Astrophysics Data System (ADS)

We establish the existence of global weak solutions of the two-dimensional incompressible Euler equations for a large class of non-smooth open sets. Loosely, these open sets are the complements (in a simply connected domain) of a finite number of obstacles with positive Sobolev capacity. Existence of weak solutions with L p vorticity is deduced from a property of domain continuity for the Euler equations that relates to the so-called ?-convergence of open sets. Our results complete those obtained for convex domains in Taylor (Progress in Nonlinear Differential Equations and their Applications, Vol. 42, 2000), or for domains with asymptotically small holes (I ftimie et al. in Commun Partial Differ Equ 28(1-2), 349-379, 2003; Lopes Filho in SIAM J Math Anal 39(2), 422-436, 2007).

Gérard-Varet, David; Lacave, Christophe

2013-07-01

422

Investigation of Turbulent Flow in a Two-Dimensional Channel  

NASA Technical Reports Server (NTRS)

A detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 12,300, 30,800, and 61,600, based on the half width of the channel and the maximum mean velocity. A channel of 5-inch width and 12:1 aspect ratio was used for the investigation. Mean-speed and axial-fluctuation measurements were made well within the laminar sublayer. The semitheoretical predictions concerning the extent of the laminar sublayer were confirmed. The distribution of the velocity fluctuations in the direction of mean flow u' shows that the influence of the viscosity extends farther from the wall than indicated by the mean velocity profile, the region of influence being approximately four times as wide.

Laufer, John

1951-01-01

423

Bond order solid of two-dimensional dipolar fermions.  

PubMed

The recent experimental realization of dipolar Fermi gases near or below quantum degeneracy provides an opportunity to engineer Hubbard-like models with long-range interactions. Motivated by these experiments, we chart out the theoretical phase diagram of interacting dipolar fermions on the square lattice at zero temperature and half filling. We show that, in addition to p-wave superfluid and charge density wave order, two new and exotic types of bond order emerge generically in dipolar fermion systems. These phases feature homogeneous density but periodic modulations of the kinetic hopping energy between nearest or next-nearest neighbors. Similar, but manifestly different, phases of two-dimensional correlated electrons have previously only been hypothesized and termed "density waves of nonzero angular momentum." Our results suggest that these phases can be constructed flexibly with dipolar fermions, using currently available experimental techniques. PMID:22540802

Bhongale, S G; Mathey, L; Tsai, Shan-Wen; Clark, Charles W; Zhao, Erhai

2012-04-01

424

Waves in two-dimensional superparamagnetic dusty plasma liquids.  

PubMed

Wave dispersion relations in the strongly coupled liquid phase of a two-dimensional system of dust grains interacting via both Yukawa and dipole interactions are investigated. The model system comprises a layer of charged superparamagnetic grains in a plasma in an external, uniform magnetic field B whose magnitude and direction can be varied. Because the induced magnetic dipole moments of the grains lie along B, the interaction between the grains becomes anisotropic as B is tilted with respect to the layer. The theoretical approach uses a reformulated quasilocalized charge approximation that can treat dipole interactions, combined with molecular dynamics simulations. The mode dispersion relations are found to depend on the relative strengths of the Yukawa and dipole interactions and the direction of wave propagation in the plane. PMID:24827350

Hartmann, Peter; Donkó, Zoltán; Rosenberg, Marlene; Kalman, Gabor J

2014-04-01

425

Polycrystalline graphene and other two-dimensional materials  

NASA Astrophysics Data System (ADS)

Graphene, a single atomic layer of graphitic carbon, has attracted intense attention because of its extraordinary properties that make it a suitable material for a wide range of technological applications. Large-area graphene films, which are necessary for industrial applications, are typically polycrystalline -- that is, composed of single-crystalline grains of varying orientation joined by grain boundaries. Here, we present a review of the large body of research reported in the past few years on polycrystalline graphene. We discuss its growth and formation, the microscopic structure of grain boundaries and their relations to other types of topological defect such as dislocations. The Review further covers electronic transport, optical and mechanical properties pertaining to the characterizations of grain boundaries, and applications of polycrystalline graphene. We also discuss research, still in its infancy, performed on other two-dimensional materials such as transition metal dichalcogenides, and offer perspectives for future directions of research.

Yazyev, Oleg V.; Chen, Yong P.

2014-10-01

426

Nonlinear compressional waves in a two-dimensional Yukawa lattice.  

PubMed

A modified Korteweg-de Vries (KdV) equation is obtained for studying the propagation of nonlinear compressional waves and pulses in a chain of particles including the effect of damping. Suitably altering the linear phase velocity makes this equation useful also for the problem of phonon propagation in a two-dimensional (2D) lattice. Assuming a Yukawa potential, we use this method to model compressional wave propagation in a 2D plasma crystal, as in a recent experiment. By integrating the modified KdV equation the pulse is allowed to evolve, and good agreement with the experiment is found. It is shown that the speed of a compressional pulse increases with its amplitude, while the speed of a rarefactive pulse decreases. It is further discussed how the drag due to the background gas has a crucial role in weakening nonlinear effects and preventing the emergence of a soliton. PMID:14683049

Avinash, K; Zhu, P; Nosenko, V; Goree, J

2003-10-01

427

Two-dimensional models for an electrode with adsorption sites  

NASA Astrophysics Data System (ADS)

Through a new method, the following model is solved exactly in the framework of classical equilibrium statistical mechanics of two-dimensional Coulomb systems, for the special value ?=2 of the coupling constant: the mobile charges of a one-component plasma are attracted by a line of equidistant sticky adsorption sites embedded in a background, the density of which varies in the direction orthogonal to the line. First the general expressions are given for the densities and correlation functions of nonadsorbed and adsorbed particles. Then these results are used to investigate two models of electrodes with localized adsorption: the externally charged hard wall and the impermeable polarized membrane. In each case the influence of the adsorption upon macroscopic features is studied: the potential drop across the interface, the contact theorem, and the Lippmann equation, which involves the surface free energy.

Cornu, Françoise

1989-02-01

428

Noise correlations of two-dimensional Bose gases  

E-print Network

We analyze density-density correlations of expanding clouds of weakly interacting two-dimensional Bose gases below and above the Berezinskii-Kosterlitz-Thouless transition, with particular focus on short-time expansions. During time-of-flight expansion, phase fluctuations of the trapped system translate into density fluctuations, in addition to the density fluctuations that exist in in-situ. We calculate the correlations of these fluctuations both in real space and in momentum space, and derive analytic expressions in momentum space. Below the transition, the correlation functions show an oscillatory behavior, controlled by the scaling exponent of the quasi-condensed phase, due to constructive interference. We argue that this can be used to extract the scaling exponent of the quasi-condensate experimentally. Above the transition, the interference is rapidly suppressed when the atoms travel an average distance beyond the correlation length. This can be used to distinguish the two phases qualitatively.

Vijay Pal Singh; Ludwig Mathey

2014-03-17

429

Nanoelectronic circuits based on two-dimensional atomic layer crystals.  

PubMed

Since the discovery of graphene and related forms of two-dimensional (2D) atomic layer crystals, numerous studies have reported on the fundamental material aspects, such as the synthesis, the physical properties, and the electrical properties on the transistor level. With the advancement in large-area synthesis methods, system level integration to exploit the unique applications of these materials is close at hand. The main purpose of this review is to focus on the current progress and the prospect of circuits and systems based on 2D material that go beyond the single-transistor level studies. Both analog and digital circuits based on graphene and related 2D atomic layer crystals will be discussed. PMID:25268929

Lee, Seunghyun; Zhong, Zhaohui

2014-11-21

430

Waves in two-dimensional superparamagnetic dusty plasma liquids  

NASA Astrophysics Data System (ADS)

Wave dispersion relations in the strongly coupled liquid phase of a two-dimensional system of dust grains interacting via both Yukawa and dipole interactions are investigated. The model system comprises a layer of charged superparamagnetic grains in a plasma in an external, uniform magnetic field B whose magnitude and direction can be varied. Because the induced magnetic dipole moments of the grains lie along B, the interaction between the grains becomes anisotropic as B is tilted with respect to the layer. The theoretical approach uses a reformulated quasilocalized charge approximation that can treat dipole interactions, combined with molecular dynamics simulations. The mode dispersion relations are found to depend on the relative strengths of the Yukawa and dipole interactions and the direction of wave propagation in the plane.

Hartmann, Peter; Donkó, Zoltán; Rosenberg, Marlene; Kalman, Gabor J.

2014-04-01

431

Non-monotonic magnetoresistivity in two-dimensional electron systems  

NASA Astrophysics Data System (ADS)

The connection being studied is the one between the non-monotonic magnetoresistivity (MR) and the electron-electron interaction (EEI) correction in weakly-disordered two-dimensional electron systems (2DESs) in the ballistic region k B T ? / ? > 1, where k B , T, ?, and ? are the Boltzmann constant, the temperature, the scattering time, and the reduced Planck constant, respectively. At zero magnetic field, a transition of the resistivity ?( T) from the insulating region d?/ dT < 0 to the metallic region d?/ dT > 0 is observed. The MR shows a maximum, and with increasing T, the position of the MR maximum in B increases for both GaAs-based (sample A) and GaN-based (sample B) 2DESs. Our data suggest that the EEI plays an important role in such a non-monotonic MR effect and in the temperature dependence of the resistivity.

Wang, Yi-Ting; Woo, Tak-Pong; Lo, Shun-Tsung; Kim, Gil-Ho; Liang, Chi-Te

2014-11-01

432

Towards automated screening of two-dimensional crystals.  

PubMed

Screening trials to determine the presence of two-dimensional (2D) protein crystals suitable for three-dimensional structure determination using electron crystallography is a very labor-intensive process. Methods compatible with fully automated screening have been developed for the process of crystal production by dialysis and for producing negatively stained grids of the resulting trials. Further automation via robotic handling of the EM grids, and semi-automated transmission electron microscopic imaging and evaluation of the trial grids is also possible. We, and others, have developed working prototypes for several of these tools and tested and evaluated them in a simple screen of 24 crystallization conditions. While further development of these tools is certainly required for a turn-key system, the goal of fully automated screening appears to be within reach. PMID:17977016

Cheng, Anchi; Leung, Albert; Fellmann, Denis; Quispe, Joel; Suloway, Christian; Pulokas, James; Abeyrathne, Priyanka D; Lam, Joseph S; Carragher, Bridget; Potter, Clinton S

2007-12-01

433

The Absorbing Properties of Two-Dimensional Plasma Photonic Crystals  

NASA Astrophysics Data System (ADS)

Plasma photonic crystals composed of periodic plasma and dielectric materials have attracted considerable attention because of their tunable photonic band gaps, but only their band structures or negative refractive index properties have been addressed in previous works. In this paper, through studying the transmission and reflection characteristics of two types of two-dimensional plasma photonic crystals, it is found that plasma photonic crystals play an important role in absorbing waves, and they show broader band and higher amplitude absorption characteristics than bulk plasmas. Also, the absorption of plasma photonic crystals can be tuned via plasma parameters; varying the collision frequency can make the bandwidth and amplitude tunable, but cannot change the central frequency, whereas varying the plasma frequency would control both the location and the amplitude of the absorbers. These features of plasma photonic crystals have potential for terahertz tunable absorber applications.

Qi, Limei; Li, Chao; Fang, Guangyou; Gao, Xiang

2015-01-01

434

Superconductivity of the Two-Dimensional Penson--Kolb Model  

NASA Astrophysics Data System (ADS)

Two-dimensional (d=2) Penson--Kolb model, i.e. the tight-binding model with the pair-hopping (intersite charge exchange) interaction, is considered and the effects of phase fluctuations on the s-wave superconductivity of this system are discussed within the Kosterlitz--Thouless scenario. The London penetration depth ? at T= 0, the Kosterlitz-Thouless critical temperature Tc, and the Hartree--Fock approximation critical temperature Tp are determined as a function of particle concentration and interaction. The Uemura type plots (Tc vs. ?-2(0)) are derived. Beyond weak coupling and for low concentrations they show the existence of universal scaling: Tc~1/?2(0), as it was previously found for the attractive Hubbard model and for the models with intersite electron pairing.

Czart, W. R.; Robaszkiewicz, S.

1998-12-01

435

A ballistic two-dimensional-electron-gas Andreev interferometer  

SciTech Connect

We report the realization and investigation of a ballistic Andreev interferometer based on an InAs two dimensional electron gas coupled to a superconducting Nb loop. We observe strong magnetic modulations in the voltage drop across the device due to quasiparticle interference within the weak-link. The interferometer exhibits flux noise down to ?80???{sub 0}/?(Hz) and a robust behavior in temperature with voltage oscillations surviving up to ?7?K. Besides this remarkable performance, the device represents a crucial first step for the realization of a fully-tunable ballistic superconducting magnetometer and embodies a potential advanced platform for the investigation of Majorana bound states, non-local entanglement of Cooper pairs, as well as the manipulation and control of spin triplet correlations.

Amado, M., E-mail: mario.amadomontero@sns.it; Fornieri, A.; Sorba, L.; Giazotto, F., E-mail: f.giazotto@sns.it [NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy); Biasiol, G. [CNR-IOM, Laboratorio TASC, Area Science Park, I-34149 Trieste (Italy)

2014-06-16

436

Density of states in two-dimensional colloidal system  

NASA Astrophysics Data System (ADS)

The vibrational density of states (VDOS) of particles in a two-dimensional binary colloidal system was investigated using video microscopy. Our ultimate goal is to explore how the VDOS varies near the jamming transition [1]. Various distributions of NIPA particles, whose diameters can be tuned by small temperature variations, were loaded into parallel-plate microscope cells, and their motions tracked with video microscopy. This approach permits in-situ observation over a wide range of particle packing fractions, from colloidal fluids to colloidal glasses. A search for excess VDOS at low frequencies in colloidal glass is ongoing. 1. N. Xu, M. Wyart, A. J. Liu, and S. R. Nagel, Phys. Rev. Lett. 98, 175502 (2007) This work is supported by NSF DMR-080488, MRSEC DMR-0520020

Chen, Ke; Zhang, Zexin; Yunker, Peter; Yodh, Arjun

2009-03-01

437

Two-dimensional NQR using ultra-broadband electronics.  

PubMed

We have recently developed an ultra-broadband instrument that can effectively excite and detect NMR and NQR signals over a wide frequency range. Our current system operates between 100 kHz and 3.2 MHz using an un-tuned sample coil. The major benefits of this instrument compared to conventional NQR/NMR systems include increased robustness, ease of use (in particular for multi-frequency experiments), and elimination of the need for tuning adjustments in the hardware. Here we describe its use for performing two-dimensional (2D) scans, which allow improved interpretation of complex NQR spectra by detecting the connected resonances. Our method relies on population transfers between the three energy levels of spin-1 nuclei (such as (14)N) by using multi-frequency excitation and a single RF coil. Experimental results on pure samples and mixtures are also presented. PMID:24495675

Mandal, S; Song, Y-Q

2014-03-01

438

Two dimensional prolate spheroidal wave functions for MRI  

NASA Astrophysics Data System (ADS)

The tradeoff between spatial and temporal resolution is often used to increase data acquisition speed for dynamic MR imaging. Reduction of the k-space sampling area, however, leads to stronger partial volume and truncation effects. A two dimensional prolate spheroidal wave function (2D-PSWF) method is developed to address these problems. Utilizing prior knowledge of a given region of interest (ROI) and the spatial resolution requirement as constraints, this method tailors the k-space sampling area with a matching 2D-PSWF filter so that optimal signal concentration and minimal truncation artifacts are achieved. The k-space sampling area is reduced because the shape and size of the sampling area match the resolution posed by the non-rectangular shape of a convex ROI. The 2D-PSWF method offers an efficient way for spatial and temporal tradeoff with minimal penalty due to truncation, and thus, it promises a wide range of applications in MRI research.

Yang, Qing X.; Lindquist, Martin A.; Shepp, Lawrence; Zhang, Cun-Hui; Wang, Jianli; Smith, Michael B.

2002-09-01

439

Efficient solutions of two-dimensional incompressible steady viscous flows  

NASA Technical Reports Server (NTRS)

A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.

Morrison, J. H.; Napolitano, M.

1988-01-01

440

Efficient solutions of two-dimensional incompressible steady viscous flows  

NASA Technical Reports Server (NTRS)

A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.

Morrison, J. H.; Napolitano, M.

1986-01-01

441

Two-dimensional electronic spectroscopy with birefringent wedges.  

PubMed

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. PMID:25554272

Réhault, Julien; Maiuri, Margherita; Oriana, Aurelio; Cerullo, Giulio

2014-12-01

442

Transport of Electrons in Two-Dimensional Systems  

NASA Astrophysics Data System (ADS)

The present thesis is a contribution to the theory of linear and nonlinear electron transport in quasi-two -dimensional (Q2D) semiconductor systems. The nonlinear transport in a low density two-dimensional electron gas (2DEG) was studied in the presence of only scattering with longitudinal-optical (LO) phonons. The results form our Monte Carlo simulation were used as a test for different approximation schemes: (i) the analytic solution of the Boltzmann equation at zero-temperature; (ii) the momentum and energy balance equations; (iii) the diffusion-to-streaming model; and (iv) the streaming-to -accumulation model. In the weak electric field limit, we studied the warm-electron transport and we confirmed that the mobility is a non-analytic function of the electric field. In the absence of a magnetic field, two different types of quantum resonances were studied in a Q2D system where several subbands are occupied: (i) the electro-phonon resonances, which occur each time the energy separation between two subbands equals the energy of the LO-phonon, were studied in the linear and the nonlinear response regimes; (ii) at low temperature the resonance effect, which is analogous to the Shubnikov-de Haas effect, was studied and good agreement was found between our theoretical results and the recent experimental results from the Technical University of Eindhoven. The magneto-transport in heterostructures at high temperature and in the presence of a high magnetic field was investigated. The results of our calculation were compared with recent experimental data from the Clarendon Laboratory (U.K.) and good agreement with experiment was found. We were able to explain the increase of the inverse magneto-resistivity with temperature for T < 80 K which occurs for B = 9 T. This is a consequence of the electron-impurity scattering mechanism.

Xu, Wen

1992-06-01

443

High Resolution Two-Dimensional Electrophoresis of Proteins*  

PubMed Central

Summary A technique has been developed for the separation of proteins by two-dimensional polyacrylamide gel electrophoresis. Due to its resolution and sensitivity, this technique is a powerful tool for the analysis and detection of proteins from complex biological sources. Proteins are separated according to isoelectric point by isoelectric focusing in the first dimension, and according to molecular weight by sodium dodecyl sulfate electrophoresis in the second dimension. Since these two parameters are unrelated, it is possible to obtain an almost uniform distribution of protein spots across a two-dimensional gel. This technique has resolved 1100 different components from Escherichia coli and should be capable of resolving a maximum of 5000 proteins. A protein containing as little as one disintegration per min of either 14C or 35S can be detected by autoradiography. A protein which constitutes 10?4 to 10?5% of the total protein can be detected and quantified by autoradiography. The reproducibility of the separation is sufficient to permit each spot on one separation to be matched with a spot on a different separation. This technique provides a method for estimation (at the described sensitivities) of the number of proteins made by any biological system. This system can resolve proteins differing in a single charge and consequently can be used in the analysis of in vivo modifications resulting in a change in charge. Proteins whose charge is changed by missense mutations can be identified. A detailed description of the methods as well as the characteristics of this system are presented. PMID:236308

O'Farrell, Patrick H.

2010-01-01

444

Dynamics of entanglement in a two-dimensional spin system  

NASA Astrophysics Data System (ADS)

We consider the time evolution of entanglement in a finite two-dimensional transverse Ising model. The model consists of a set of seven localized spin-(1)/(2) particles in a two-dimensional triangular lattice coupled through nearest-neighbor exchange interaction in the presence of an external time-dependent magnetic field. The magnetic field is applied in different function forms: step, exponential, hyperbolic, and periodic. We found that the time evolution of the entanglement shows an ergodic behavior under the effect of the time-dependent magnetic fields. Also, we found that while the step magnetic field causes great disturbance to the system, creating rapid oscillations, the system shows great controllability under the effects of the other magnetic fields where the entanglement profile follows closely the shape of the applied field even with the same frequency for periodic fields. This follow-up trend breaks down as the strength of the field, the transition constant for the exponential and hyperbolic forms, or the frequency for periodic field increase leading to rapid oscillations. We observed that the entanglement is very sensitive to the initial value of the applied periodic field: the smaller the initial value is, the less distorted the entanglement profile is. Furthermore, the effect of thermal fluctuations is very devastating to the entanglement, which decays very rapidly as the temperature increases. Interestingly, although a large value of the magnetic field strength may yield a small entanglement, the magnetic field strength was found to be more persistent against thermal fluctuations than the small field strengths.

Xu, Qing; Sadiek, Gehad; Kais, Sabre

2011-06-01

445

Two-dimensional electrons with valley degree of freedom  

NASA Astrophysics Data System (ADS)

The purpose of this thesis is to explore some of the consequences of the valley degree of freedom for the properties of AlAs two-dimensional electron systems. We start by demonstrating our ability to tune the relative valley occupancy in wide AlAs quantum wells by applying a shear, in-plane strain. We continue by characterizing the piezoresistance of AlAs 2DES at both zero and finite magnetic fields. We then proceed to show that, unlike the single-particle predictions, the perpendicular (but not parallel) magnetic field couples to the valley degree of freedom. This suggests that electron-electron interaction is the origin of the observed field-induced valley splitting. We then focus on the role of electron-electron interaction by measuring the energy gap of the quantum Hall state at filling factor nu = 1 as a function of valley splitting. We find that at nu = 1 valleys are strongly coupled through the electronelectron interaction, and that the lowest energy charged excitations of the nu = 1 quantum Hall state are valley Skyrmions. Finally, we explore the interplay between the valley and the spin degrees of freedom by measuring the spin-susceptibility of the AlAs two-dimensional electrons as a function of valley occupancy. At a given density, when two AlAs valleys are equally populated, the measured spin-susceptibility is smaller than when only one valley is occupied. This observation, which is counter to the single-particle prediction, suggests that the valley and spin degrees of freedom are also coupled.

Shkolnikov, Yakov Pyotr

446

Two-dimensional nanoarchitectonics: organic and hybrid materials  

NASA Astrophysics Data System (ADS)

Programmed molecular assemblies with molecular-level precision have always intrigued mankind in the quest to master the art of molecular engineering. In this regard, our review seeks to highlight the state of the art in supramolecular engineering. Herein we describe two-dimensional (2D) nanoarchitectonics of organic and organic-inorganic based hybrid materials. Molecular systems ranging from simpler hydrogen bonding driven bis-acylurea and cyclic dipeptide derivatives to complex peptoids, arylenes, cucurbiturils, biphenyls, organosilicons and organometallics, which involve a delicate interplay of multiple noncovalent interactions are discussed. These specifically chosen examples illustrate the molecular design principles and synthetic protocols to realize 2D nanosheets. The description also emphasizes the wide variety of functional properties and technological implications of these 2D nanomaterials besides an outlook for future progress.Programmed molecular assemblies with molecular-level precision have always intrigued mankind in the quest to master the art of molecular engineering. In this regard, our review seeks to highlight the state of the art in supramolecular engineering. Herein we describe two-dimensional (2D) nanoarchitectonics of organic and organic-inorganic based hybrid materials. Molecular systems ranging from simpler hydrogen bonding driven bis-acylurea and cyclic dipeptide derivatives to complex peptoids, arylenes, cucurbiturils, biphenyls, organosilicons and organometallics, which involve a delicate interplay of multiple noncovalent interactions are discussed. These specifically chosen examples illustrate the molecular design principles and synthetic protocols to realize 2D nanosheets. The description also emphasizes the wide variety of functional properties and technological implications of these 2D nanomaterials besides an outlook for future progress. Dedicated to Prof. C. N. R. Rao, FRS on the occasion of his 78th birthday.

Govindaraju, T.; Avinash, M. B.

2012-09-01

447

Two-dimensional fast marching for geometrical optics.  

PubMed

We develop an approach for the fast and accurate determination of geometrical optics solutions to Maxwell's equations in inhomogeneous 2D media and for TM polarized electric fields. The eikonal equation is solved by the fast marching method. Particular attention is paid to consistently discretizing the scatterers' boundaries and matching the discretization to that of the computational domain. The ray tracing is performed, in a direct and inverse way, by using a technique introduced in computer graphics for the fast and accurate generation of textured images from vector fields. The transport equation is solved by resorting only to its integral form, the transport of polarization being trivial for the considered geometry and polarization. Numerical results for the plane wave scattering of two perfectly conducting circular cylinders and for a Luneburg lens prove the accuracy of the algorithm. In particular, it is shown how the approach is capable of properly accounting for the multiple scattering occurring between the two metallic cylinders and how inverse ray tracing should be preferred to direct ray tracing in the case of the Luneburg lens. PMID:25401818

Capozzoli, Amedeo; Curcio, Claudio; Liseno, Angelo; Savarese, Salvatore

2014-11-01

448

Statistical mechanics of two-dimensional shuffled foams: prediction of the correlation between geometry and topology  

E-print Network

Statistical mechanics of two-dimensional shuffled foams: prediction of the correlation between for the statistical mechanics of shuffled two-dimensional foams with moderate bubble size polydispersity. It predicts

Cox, Simon

449

Levitation Force Investigation of Bulk HTSC Above Halbach PMG with Different Cross-Section Physical Dimensions by 3D-Modeling Numerical Method  

NASA Astrophysics Data System (ADS)

The levitation force of a bulk high temperature superconductor (HTSC) over Halbach permanent magnet guideways (PMG) with different cross-section configuration is studied by numerical method. The Halbach PMG is composed of three host permanent magnets (HPMs) and two slave permanent magnets (SPMs). One cylindrical bulk HTSC with a diameter of 30 mm and height of 15 mm is used. The 3D-modeling is formulated by the H-method. The numerical resolving codes are practiced using finite element method (FEM). The E-J power law is used to describe the electric current nonlinear characteristics of bulk HTSC. By the method, the influence of the cross-section physical dimensions of Halbach PMG on the levitation forces of bulk HTSC levitated above the PMG is studied. The simulation results show that increasing the width of SPM ( can enhance the bulk HTSC levitation performance immediately under the condition of keeping the ratio of ( : the width of HPM) to between 1.6 and 1.8, the ratio of td (the height of the PMG) to between 1.2 and 1.4. By the method, the bulk HTSC better levitation performance can be expected.

Lu, Yiyun; Liu, Guoliang; Qin, Yujie

2014-10-01

450

Numerical simulation of the flow induced by an oscillating cylinder  

NASA Astrophysics Data System (ADS)

The problem of unsteady, laminar flow past a circular cylinder which performs recti-linear oscillations at an arbitrary angle with respect to the oncoming uniform flow is considered.The flow is incompressible and two-dimensional, and the cylinder oscillations are harmonic. The motion is governed by the Navier-Stokes equations and the method of solution is based on the use of truncated Fourier series representations for the stream function and vorticity in the angular polar coordinate. A non-inertial coordinate transformation is used so that the grid mesh remains fixed relative to the accelerating cylinder. The Navier-Stokes equations are reduced to ordinary differential equations in the spatial variable and these sets of equations are solved by using finite difference methods, but with the boundary vorticity calculated using integral conditions rather than local finite-difference approximations.

Kocabiyik, Serpil

2002-11-01

451

Numerical Study of the Unsteady Flow Over AN Oscillating Cylinder  

NASA Astrophysics Data System (ADS)

The problem of unsteady, laminar flow past a circular cylinder which performs recti-linear oscillations at an arbitrary angle with respect to the oncoming uniform flow is investigated numerically for the first time.The flow is incompressible and two-dimensional, and the cylinder oscillations are harmonic. The investigation is based on an implicit finite difference scheme for integrating the unsteady Navier-Stokes equations together with the mass conservation equation in their vorticity stream function formulation. The boundary vorticity is calculated using integral conditions rather than local finite-difference approximations. The near wake structure as well as the hydrodynamic forces acting on the cylinder under different oscillation conditions are presented. The primary focus is to examine the effect of increase of the forced oscillation amplitude.

Lawrence, Karl; Kocabiyik, Serpil

2003-11-01

452

Scattering by a homogeneous anisotropic-coated conducting elliptic cylinder  

NASA Astrophysics Data System (ADS)

A solution to the two-dimensional scattering properties of a conducting elliptic cylinder coated with a homogeneous anisotropic elliptical shell is obtained. The conducting elliptic cylinder and the shell have the same eccentricity. The transmitted and scattered fields of the anisotropic shell are expressed as Mathieu functions in elliptic coordinates. The unknown coefficients of the scattered and transmitted fields are solved with the aid of the boundary conditions and the Galerkin's method. Only the transverse magnetic (TM) polarization is presented and the transverse electric (TE) polarization can be obtained in the same way. Some numerical results are presented and discussed. As expected the result is in agreement with that available when the coated elliptic cylinder degenerates to a coated circular one.

Mao, Shi-Chun; Wu, Zhen-Sen; Jin, Zhao; Wang, Fan

2011-03-01

453

Two--Dimensional Mesh Design Pattern Template for Steve MacDonald  

E-print Network

on the application--specific code since the structure is provided. 2 Intent The Two--Dimensional Mesh patternTwo--Dimensional Mesh Design Pattern Template for CO 2 P 3 S Steve MacDonald Email: stevem@cs.ualberta.ca 1 Introduction This report details the Two--Dimensional Mesh design pattern template for CO 2 P 3

MacDonald, Steve

454

Powder Technology, 72 (1992) 255-267 Force distribution in a two dimensional sandpile  

E-print Network

-particle interactions. As a first example we have applied the code to a two dimensional triangular pile of discretePowder Technology, 72 (1992) 255-267 Force distribution in a two dimensional sandpile 255 Kurt particles. We take this to be a two dimensional analogue of a conical pile of particulate material

Chan, Derek Y C

455

Large Families of Asymptotically Optimal Two-Dimensional Optical Orthogonal Codes  

E-print Network

1 Large Families of Asymptotically Optimal Two-Dimensional Optical Orthogonal Codes Reza Omrani codes are provided. Index Terms--Optical orthogonal codes, optical CDMA, OCDMA, two-dimensional codes, 2 two-dimensional optical orthogonal codes (2-D OOCs) that spread in both time and wavelength domain

Gesbert, David

456

Quantization of Systems with Internal Degrees of Freedom in Two-Dimensional Manifolds  

NASA Astrophysics Data System (ADS)

Presented is a primary step towards quantization of infinitesimal rigid body moving in a two-dimensional manifold. The special stress is laid on spaces of constant curvature like the two-dimensional sphere and pseudosphere (Lobachevsky space). Also two-dimensional torus is briefly discussed as an interesting algebraic manifold.

Ro?ko, Ewa Eliza; Gobcewicz, Ewa

2014-06-01

457

Reliable Peak Selection for Multisample Analysis with Comprehensive Two-Dimensional Chromatography  

E-print Network

Reliable Peak Selection for Multisample Analysis with Comprehensive Two-Dimensional Chromatography with samples of complex bio-oils analyzed by comprehensive two-dimensional gas chromatography (GCxGC) coupled-dimensional gas chromatography (GCxGC) and comprehensive two-dimensional liquid chroma- tography (LCxLC), hold

Reichenbach, Stephen E.

458

Tandem Cylinder Noise Predictions  

NASA Technical Reports Server (NTRS)

In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.

2007-01-01

459

Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals  

SciTech Connect

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 with the observed negatively refractive phenomena. They found that in the PC system, negative refraction is neither a prerequisite nor guarantees left-handed behavior. They examined carefully the condition to obtain left-handed behavior in the PC. They proposed a wedge type of experiment, in accordance with the experiment performed on the traditional LHM, to test these conditions. They found that for certain frequencies the PC shows left-handed behavior and acts in some respects like a homogeneous medium with a negative refractive index. they used the realistic PC system for this case to show how negative refraction occurs at the interface between a material with a positive and a material with a negative refractive index. Their findings indicate that the formation of the negatively refracted beam is not instantaneous and involves a transient time. With this time-dependent analysis, they were able to address previous controversial issues about negative refraction concerning causality and the speed of light limit. Finally, they attempt a systematic study of anomalous refractive phenomena that can occur at the air-PC interface. They observe cases where only a single refracted beam (in the positive or negative direction) is present, as well as cases with birefringence. they classify these different effects according to their origin and type of propagation (left-handed or not). For a complete study of the system, they also obtain expressions for the energy and group velocities, and show their equality. For cases with very low index contrast, band folding becomes an artificiality. They discuss the validity of their findings when they move to the limit of photonic crystals with a low index modulation.

Stavroula Foteinopoulou

2003-12-12

460

Cracked semi-infinite cylinder and finite cylinder problems  

Microsoft Academic Search

This work considers the analysis of a cracked semi-infinite cylinder and a finite cylinder. Material of the cylinder is assumed to be linearly elastic and isotropic. One end of the cylinder is bonded to a fixed support while the other end is subjected to axial tension. Solution of this problem can be obtained by superposition of solutions for an infinite

Mete Onur Kaman; Mehmet Rusen Gecit

2006-01-01

461

Two-Dimensional Nonlinear Finite Element Analysis of CMC Microstructures  

NASA Technical Reports Server (NTRS)

A research program has been developed to quantify the effects of the microstructure of a woven ceramic matrix composite and its variability on the effective properties and response of the material. In order to characterize and quantify the variations in the microstructure of a five harness satin weave, chemical vapor infiltrated (CVI) SiC/SiC composite material, specimens were serially sectioned and polished to capture images that detailed the fiber tows, matrix, and porosity. Open source quantitative image analysis tools were then used to isolate the constituents, from which two dimensional finite element models were generated which approximated the actual specimen section geometry. A simplified elastic-plastic model, wherein all stress above yield is redistributed to lower stress regions, is used to approximate the progressive damage behavior for each of the composite constituents. Finite element analyses under in-plane tensile loading were performed to examine how the variability in the local microstructure affected the macroscopic stress-strain response of the material as well as the local initiation and progression of damage. The macroscopic stress-strain response appeared to be minimally affected by the variation in local microstructure, but the locations where damage initiated and propagated appeared to be linked to specific aspects of the local microstructure.

Mital, Subodh K.; Goldberg, Robert K.; Bonacuse, Peter J.

2012-01-01

462

Dynamic testing of a two-dimensional box truss beam  

NASA Technical Reports Server (NTRS)

Testing to determine the effects of joint freeplay and pretensioning of diagonal members on the dynamic characteristics of a two-dimensional box truss beam was conducted. The test article was ten bays of planar truss suspended by long wires at each joint. Each bay measured 2 meters per side. Pins of varying size were used to simulate various joint freeplay conditions. Single-point random excitation was the primary method of test. The rational fraction polynomial method was used to extract modal characteristics from test data. A finite element model of the test article was generated from which modal characteristics were predicted. These were compared with those obtained from tests. With the exception of the fundamental mode, correlation of theoretical and experimental results was poor, caused by the resonant coupling of local truss member bending modes with global truss beam modes. This coupling introduced many modes in the frequency range of interest whose frequencies were sensitive to joint boundary conditions. It was concluded that local/global coupling must be avoided in the frequency range where accurate modal characteristics are required.

White, Charles W.

1987-01-01

463

Localization phase diagram of two-dimensional quantum percolation  

NASA Astrophysics Data System (ADS)

We examine quantum percolation on a square lattice with random dilution up to q = 38% and energy 0.001 ? E ? 1.6 (measured in units of the hopping matrix element), using numerical calculations of the transmission coefficient at a much larger scale than previously. Our results confirm the previous finding that the two dimensional quantum percolation model exhibits localization-delocalization transitions, where the localized region splits into an exponentially localized region and a power-law localization region. We determine a fuller phase diagram confirming all three regions for energies as low as E = 0.1, and the delocalized and exponentially localized regions for energies down to E = 0.001. We also examine the scaling behavior of the residual transmission coefficient in the delocalized region, the power law exponent in the power-law localized region, and the localization length in the exponentially localized region. Our results suggest that the residual transmission at the delocalized to power-law localized phase boundary may be discontinuous, and that the localization length is likely not to diverge with a power-law at the exponentially localized to power-law localized phase boundary. However, further work is needed to definitively assess the characters of the two phase transitions as well as the nature of the intermediate power-law regime.

Dillon, Brianna S.; Nakanishi, Hisao

2014-12-01

464

Two-dimensional transition metal dichalcogenide nanosheet-based composites.  

PubMed

Ultrathin two-dimensional (2D) nanosheets of layered transition metal dichalcogenides (TMDs), such as MoS2, TiS2, TaS2, WS2, MoSe2, WSe2, etc., are emerging as a class of key materials in chemistry and electronics due to their intriguing chemical and electronic properties. The ability to prepare these TMD nanosheets in high yield and large scale via various methods has led to increasing studies on their hybridization with other materials to create novel functional composites, aiming to engineer their chemical, physical and electronic properties and thus achieve good performance for some specific applications. In this critical review, we will introduce the recent progress in hybrid nanoarchitectures based on 2D TMD nanosheets. Their synthetic strategies, properties and applications are systematically summarized and discussed, with emphasis on those new appealing structures, properties and functions. In addition, we will also give some perspectives on the challenges and opportunities in this promising research area. PMID:25292209

Tan, Chaoliang; Zhang, Hua

2014-10-01

465

Two-dimensional CFD modeling of wave rotor flow dynamics  

NASA Technical Reports Server (NTRS)

A two-dimensional Navier-Stokes solver developed for detailed study of wave rotor flow dynamics is described. The CFD model is helping characterize important loss mechanisms within the wave rotor. The wave rotor stationary ports and the moving rotor passages are resolved on multiple computational grid blocks. The finite-volume form of the thin-layer Navier-Stokes equations with laminar viscosity are integrated in time using a four-stage Runge-Kutta scheme. Roe's approximate Riemann solution scheme or the computationally less expensive advection upstream splitting method (AUSM) flux-splitting scheme is used to effect upwind-differencing of the inviscid flux terms, using cell interface primitive variables set by MUSCL-type interpolation. The diffusion terms are central-differenced. The solver is validated using a steady shock/laminar boundary layer interaction problem and an unsteady, inviscid wave rotor passage gradual opening problem. A model inlet port/passage charging problem is simulated and key features of the unsteady wave rotor flow field are identified. Lastly, the medium pressure inlet port and high pressure outlet port portion of the NASA Lewis Research Center experimental divider cycle is simulated and computed results are compared with experimental measurements. The model accurately predicts the wave timing within the rotor passages and the distribution of flow variables in the stationary inlet port region.

Welch, Gerard E.; Chima, Rodrick V.

1994-01-01

466

Two-dimensional NMR spectroscopy. Applications for chemists and biochemists  

SciTech Connect

Two-dimensional nuclear magnetic resonance spectroscopy (2-D NMR) has become a very powerful class of experiments (in the hands of an adept scientist) with broad adaptability to new situations. It is the product of a happy marriage between modern pulse FT-NMR technology, with its large memory and high-speed computers, and the physicists and chemists who love to manipulate spin systems. Basic 2-D experiments are now a standard capability of modern NMR spectrometers, and this timely book intends to make 2-D NMR users of those who are familiar with normal 1-D NMR. The 2-D NMR goal is correlation of the lines of the observed NMR spectrum with other properties of the system. This book deals with applications to high-resolution spectrum analysis, utilizing either coupling between the NMR-active nuclei or chemical exchange to perform the correlation. The coupling can be scalar (through bonds) or direct through space (within 5 A). The coupling may be homonuclear (between like nuclei) or heteronuclear.

Croasmun, W.R.; Carlson, R.M.K.

1987-01-01

467

Fluctuoscopy spectroscopy of disordered two-dimensional superconductors.  

SciTech Connect

We revise the long-studied problem of fluctuation conductivity (FC) in disordered two-dimensional superconductors placed in a perpendicular magnetic field by finally deriving the complete solution in the temperature-magnetic field phase diagram. The obtained expressions allow both to perform straightforward (numerical) calculation of the FC surface {delta}{sigma}{sub xx}{sup (tot)}(T,H) and to get asymptotic expressions in all its qualitatively different domains. This surface becomes in particular nontrivial at low temperatures, where it is trough-shaped with {delta}{sigma}{sub xx}{sup (tot)}(T,H) < 0. In this region, close to the quantum-phase transition, {delta}{sigma}{sub xx}{sup (tot)}(T,H = const) is nonmonotonic, in agreement with experimental findings. We reanalyzed and present comparisons to several experimental measurements. Based on our results we derive a qualitative picture of superconducting fluctuations close to H{sub c2}(0) and T=0 where fluctuation Cooper pairs rotate with cyclotron frequency {omega}{sub c}-{Delta}{sub BCS}{sup -1} and Larmor radius {approx}{zeta}{sub BCS}, forming some kind of quantum liquid with long coherence length {zeta}{sub QF} >> {zeta}{sub BCS} and slow relaxation {tau}{sub QF} >> {h_bar}{Delta}{sub BCS}{sup -1}.

Glatz, A.; Varlamov, A. A.; Vinokur, V. M. (Materials Science Division); (CNR-SPIN)

2011-01-01

468

Freely decaying turbulence in two-dimensional electrostatic gyrokinetics  

SciTech Connect

In magnetized plasmas, a turbulent cascade occurs in phase space at scales smaller than the thermal Larmor radius ('sub-Larmor scales') [Tatsuno et al., Phys. Rev. Lett. 103, 015003 (2009)]. When the turbulence is restricted to two spatial dimensions perpendicular to the background magnetic field, two independent cascades may take place simultaneously because of the presence of two collisionless invariants. In the present work, freely decaying turbulence of two-dimensional electrostatic gyrokinetics is investigated by means of phenomenological theory and direct numerical simulations. A dual cascade (forward and inverse cascades) is observed in velocity space as well as in position space, which we diagnose by means of nonlinear transfer functions for the collisionless invariants. We find that the turbulence tends to a time-asymptotic state, dominated by a single scale that grows in time. A theory of this asymptotic state is derived in the form of decay laws. Each case that we study falls into one of three regimes (weakly collisional, marginal, and strongly collisional), determined by a dimensionless number D{sub *}, a quantity analogous to the Reynolds number. The marginal state is marked by a critical number D{sub *}=D{sub 0} that is preserved in time. Turbulence initialized above this value become increasingly inertial in time, evolving toward larger and larger D{sub *}; turbulence initialized below D{sub 0} become more and more collisional, decaying to progressively smaller D{sub *}.

Tatsuno, T. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Department of Communication Engineering and Informatics, University of Electro-Communications, Chofu, Tokyo 182-8585 (Japan); Plunk, G. G. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Max-Planck-Institut fuer Plasmaphysik, 17491 Greifswald (Germany); Barnes, M. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Dorland, W. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States); Numata, R. [Department of Physics and IREAP, University of Maryland, College Park, Maryland 20742 (United States); Graduate School of Simulation Studies, University of Hyogo, Kobe, Hyogo 650-0047 (Japan)

2012-12-15

469

Two-Dimensional Axisymmetric Collapse of Thermally Unstable Primordial Clouds  

E-print Network

We have performed two-dimensional hydrodynamic simulations of the collapse of isolated axisymmetric clouds condensing via radiative cooling in a primordial background gas. In order to study the development of the so-called ``shape-instability'', we have considered two types of axisymmetric clouds, oblate and prolate clouds of various sizes and with axial ratios of $0.5 \\leq {R_{\\rm c,R}} /{R_{\\rm c,z}} \\leq 2$. We find that the degree of oblateness or prolateness is enhanced during the initial cooling phase. But it can be reversed later, if the initial contrast in cooling times between the cloud gas and the background gas is much greater than one. In such cases an oblate cloud collapses to a structure composed of an outer thin disk and a central prolate component. A prolate cloud, on the other hand, becomes a thin cigar-shape structure with a central dense oblate component. The reversal of shape in the central part of the cooled clouds is due to supersonic motions either along the disk plane in the case of ob...

Baek, C H; Ryu, D; Baek, Chang Hyun; Kang, Hyesung; Ryu, Dongsu

2003-01-01

470

Swelling of two-dimensional polymer rings by trapped particles  

E-print Network

The mean area of a two-dimensional Gaussian ring of $N$ monomers is known to diverge when the ring is subject to a critical pressure differential, $p_c \\sim N^{-1}$. In a recent publication [Eur. Phys. J. E 19, 461 (2006)] we have shown that for an inextensible freely jointed ring this divergence turns into a second-order transition from a crumpled state, where the mean area scales as $ \\sim N$, to a smooth state with $ \\sim N^2$. In the current work we extend these two models to the case where the swelling of the ring is caused by trapped ideal-gas particles. The Gaussian model is solved exactly, and the freely jointed one is treated using a Flory argument, mean-field theory, and Monte Carlo simulations. For fixed number $Q$ of trapped particles the criticality disappears in both models through an unusual mechanism, arising from the absence of an area constraint. In the Gaussian case the ring swells to such a mean area, $ \\sim NQ$, that the pressure exerted by the particles is at $p_c$ for any $Q$. In the freely jointed model the mean area is such that the particle pressure is always higher than $p_c$, and $$ consequently follows a single scaling law, $ \\sim N^2 f(Q/N)$, for any $Q$. By contrast, when the particles are in contact with a reservoir of fixed chemical potential, the criticality is retained. Thus, the two ensembles are manifestly inequivalent in these systems.

Emir Haleva; Haim Diamant

2008-04-27

471

Intermittency in Two-Dimensional Turbulence with Drag  

E-print Network

We consider the enstrophy cascade in forced two-dimensional turbulence with a linear drag force. In the presence of linear drag, the energy wavenumber spectrum drops with a power law faster than in the case without drag, and the vorticity field becomes intermittent, as shown by the anomalous scaling of the vorticity structure functions. Using a previous theory, we compare numerical simulation results with predictions for the power law exponent of the energy wavenumber spectrum and the scaling exponents of the vorticity structure functions $\\zeta_{2q}$ obtained in terms of the distribution of finite time Lyapunov exponents. We also study, both by numerical experiment and theoretical analysis, the multifractal structure of the viscous enstrophy dissipation in terms of its R\\'{e}nyi dimension spectrum $D_q$ and singularity spectrum $f(\\alpha)$. We derive a relation between $D_q$ and $\\zeta_{2q}$, and discuss its relevance to a version of the refined similarity hypothesis. In addition, we obtain and compare theoretically and numerically derived results for the dependence on separation $r$ of the probability distribution of $\\delta_{\\V{r}}\\omega$, the difference between the vorticity at two points separated by a distance $r$. Our numerical simulations are done on a $4096 \\times 4096$ grid.

Yue-Kin Tsang; Edward Ott; Thomas M. Antonsen; Parvez N. Guzdar

2005-03-22

472

Contact and Friction of One- and Two-Dimensional Nanostructures  

NASA Astrophysics Data System (ADS)

Because their thickness dimension is very small compared with other dimensions, the one-dimensional (1D) nanostructures (such as nanowire, nanotube, and nanobelt) and two-dimensional (2D) nanostructures (such as graphene) are highly prone to bend. Because of their large bending flexurality, the 1D and 2D nanostructures exhibit different contact behavior from those chunky ones. Without considering the flexurality effect, the analysis on the experimental data of 1D and 2D nanostructures can lead to different and even contradicting results/conclusions on their mechanical properties. One focus of this chapter is on what can go wrong in the indentation and three-point bending tests of 1D nanostructures if the flexurality effect is not accounted. At the same time, the 1D and 2D nanostructures also exhibit abnormal friction behavior. The assumptions of the classical contact are reviewed, and their possible deficiencies and difficulties of being used to analyze the contact and friction of 1D/2D nanostructures are also discussed.

Zhang, Yin; Zhao, Ya-pu

473

Passive hydrodynamic synchronization of two-dimensional swimming cells  

NASA Astrophysics Data System (ADS)

Spermatozoa flagella are known to synchronize when swimming in close proximity. We use a model consisting of two-dimensional sheets propagating transverse waves of displacement to demonstrate that fluid forces lead to such synchronization passively. Using two distinct asymptotic descriptions (small amplitude and long wavelength), we derive the synchronizing dynamics analytically for arbitrarily shaped waveforms in Newtonian fluids, and show that phase-locking will always occur for sufficiently asymmetric shapes. We characterize the effect of the geometry of the waveforms and the separation between the swimmers on the synchronizing dynamics, the final stable conformations, and the energy dissipated by the cells. For two closely swimming cells, synchronization always occurs at the in-phase or opposite-phase conformation, depending solely on the geometry of the cells. In contrast, the work done by the swimmers is always minimized at the in-phase conformation. As the swimmers get further apart, additional fixed points arise at intermediate values of the relative phase. In addition, computations for large amplitude waves using the boundary integral method reveal that the two asymptotic limits capture all the relevant physics of the problem. Our results provide a theoretical framework to address other hydrodynamic interactions phenomena relevant to populations of self-propelled organisms.

Elfring, Gwynn J.; Lauga, Eric

2011-01-01

474

Two-Dimensional Crystals of Icosahedral Viruses at Liquid interfaces  

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) assembly of turnip yellow mosaic virus (TYMV) on cationic lipid monolayers is investigated at the air-water interface. TYMV, an icosahedral virus with a diameter of 28 nm, exhibits well-defined roughness, charge distribution, and hydrophilic/hydrophobic patches on its surface. The electrostatic attraction to the lipid-coated aqueous interface provides means to impose a specific virus orientation and hence reduce the number of possible inter-particle interactions. The 2D geometry is particularly advantageous in dissecting the role of anisotropy in aqueous-media assembly, which involves various types of similarly weak interactions. We show that the assembly approach used not only facilitates crystallization but also provides insights on how complex anisotropic interactions can be exploited to generate long-range order. Specifically, we report an in situ x-ray scattering observation of novel 2D crystal forms of TYMV that reflect the virus' icosahedral symmetry. The symmetry, shape, and surface heterogeneities of TYMV suggest a mechanism by which these crystals are stabilized by a combination of hydrophobic, electrostatic, and steric interactions.

Fukuto, Masafumi; Yang, Lin; Checco, Antonio; Kuzmenko, Ivan; Nguyen, Quyen; Mank, Nick; Wang, Qian

2012-02-01

475

Diamagnetic phase transitions in two-dimensional conductors  

NASA Astrophysics Data System (ADS)

A theory describing the susceptibility amplitude and the magnetic induction bifurcation near the dHvA driven diamagnetic phase transitions in quasi two-dimensional (2D) organic conductors of the (ET)2X with X=Cu(NCS)2, KHg(SCN)4, I3, AuBr2, IBr2, etc. is presented. We show that there is a drastic increase in the temperature and magnetic field dependence of the susceptibility amplitude on approaching the diamagnetic phase transition point. Near the phase transition point the temperature and magnetic field dependences are fitted by the ones typical of the mean-field phase transition theory. These dependences confirm the long-range character of the magnetic interactions among the conduction electrons leading to diamagnetic phase transitions. We demonstrate that the magnetic induction splitting of nuclear magnetic resonance (NMR) and muon spin-rotation spectroscopy (?SR) lines due to two Condon domains decreases tending to zero on approaching the diamagnetic phase transition. This decrease is fitted by the temperature and magnetic field dependence of the susceptibility characteristic of the mean-field theory of phase transitions. Performing new susceptibility, NMR and ?SR experiments will enable to detect diamagnetic phase transitions and Condon domains in quasi 2D metals.

Bakaleinikov, L. A.; Gordon, A.

2014-11-01

476

Two-dimensional packing in prolate granular materials.  

PubMed

We investigate the two-dimensional packing of extremely prolate (aspect ratio alpha=L/D>10) granular materials, comparing experiments with Monte Carlo simulations. The average packing fraction of particles with aspect ratio alpha=12 is 0.68+/-0.03. We quantify the orientational correlation of particles and find a correlation length of two particle lengths. The functional form of the orientational correlation is the same in both experiments and simulations which three orders of magnitude in aspect ratio, all decaying over a distance of two particle lengths. It is possible to identify voids in the pile with sizes ranging over two orders of magnitude. The experimental void distribution function is a power law with exponent -beta=-2.43+/-0.08. Void distributions in simulated piles do not decay as a power law, but do show a broad tail. We extend the simulation to investigate the scaling at very large aspect ratios. A geometric argument predicts the pile number density to scale as alpha(-2). Simulations do indeed scale this way, but particle alignment complicates the picture, and the actual number densities are quite a bit larger than predicted. PMID:12786141

Stokely, K; Diacou, A; Franklin, Scott V

2003-05-01

477

Dragging two-dimensional discrete solitons by moving linear defects  

SciTech Connect

We study the mobility of small-amplitude solitons attached to moving defects which drag the solitons across a two-dimensional (2D) discrete nonlinear Schroedinger lattice. Findings are compared to the situation when a free small-amplitude 2D discrete soliton is kicked in a uniform lattice. In agreement with previously known results, after a period of transient motion the free soliton transforms into a localized mode pinned by the Peierls-Nabarro potential, irrespective of the initial velocity. However, the soliton attached to the moving defect can be dragged over an indefinitely long distance (including routes with abrupt turns and circular trajectories) virtually without losses, provided that the dragging velocity is smaller than a certain critical value. Collisions between solitons dragged by two defects in opposite directions are studied too. If the velocity is small enough, the collision leads to a spontaneous symmetry breaking, featuring fusion of two solitons into a single one, which remains attached to either of the two defects.

Brazhnyi, Valeriy A.; Malomed, Boris A. [Centro de Fisica do Porto, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre 687, Porto P-4169-007 (Portugal); Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel) and ICFO-Institut de Ciencies Fotoniques and Universitat Politecnica de Catalunya, Mediterranean Technology Park, E-08860 Castelldefels, Barcelona (Spain)

2011-07-15

478

pentahexoctite: A new two-dimensional allotrope of carbon  

NASA Astrophysics Data System (ADS)

The ability of carbon to exist in many forms across dimensions has spawned search in exploring newer allotropes consisting of either, different networks of polygons or rings. While research on various 3D phases of carbon has been extensive, 2D allotropes formed from stable rings are yet to be unearthed. Here, we report a new sp2 hybridized two-dimensional allotrope consisting of continuous 5-6-8 rings of carbon atoms, named as ``pentahexoctite''. The absence of unstable modes in the phonon spectra ensures the stability of the planar sheet. Furthermore, this sheet has mechanical strength comparable to graphene. Electronically, the sheet is metallic with direction-dependent flat and dispersive bands at the Fermi level ensuring highly anisotropic transport properties. This sheet serves as a precursor for stable 1D nanotubes with chirality-dependent electronic and mechanical properties. With these unique properties, this sheet becomes another exciting addition to the family of robust novel 2D allotropes of carbon.

Sharma, Babu Ram; Manjanath, Aaditya; Singh, Abhishek K.

2014-11-01

479

Imperfections in a two-dimensional hierarchical structure  

NASA Astrophysics Data System (ADS)

Hierarchical and fractal designs have been shown to yield high mechanical efficiency under a variety of loading conditions. Here a fractal frame is optimized for compressive loading in a two-dimensional space. We obtain the dependence of volume required for stability against loading for which the structure is optimized and a set of scaling relationships is found. We evaluate the dependence of the Hausdorff dimension of the optimal structure on the applied loading and establish the limit to which it tends under gentle loading. We then investigate the effect of a single imperfection in the structure through both analytical and simulational techniques. We find that a single asymmetric perturbation of beam thickness, increasing or decreasing the failure load of the individual beam, causes the same decrease in overall stability of the structure. A scaling relationship between imperfection magnitude and decrease in failure loading is obtained. We calculate theoretically the limit to which the single perturbation can effect the overall stability of higher generation frames.

Rayneau-Kirkhope, Daniel; Mao, Yong; Farr, Robert

2014-02-01

480

Kolmogorov flow in two dimensional strongly coupled dusty plasma  

SciTech Connect

Undriven, incompressible Kolmogorov flow in two dimensional doubly periodic strongly coupled dusty plasma is modelled using generalised hydrodynamics, both in linear and nonlinear regime. A complete stability diagram is obtained for low Reynolds numbers R and for a range of viscoelastic relaxation time ?{sub m} [0?

Gupta, Akanksha; Ganesh, R., E-mail: ganesh@ipr.res.in; Joy, Ashwin [Institute for Plasma Research, Bhat Gandhinagar, Gujarat 382 428 (India)

2014-07-15

481

Two-dimensional imaging of fast intracellular Ca2+ release.  

PubMed

Asynchronous release of calcium (Ca(2+))-for example, the generation of Ca(2+) alternans in cardiac myocytes-is a phenomenon important in the development of cardiac arrhythmogenesis. The development of a failure to release Ca(2+) at individual release sites can be regarded as a major contributor to cardiac pathologies such as hypertrophy. Although confocal linescans provide sufficient temporal resolution to investigate the physiological and pathological cardiac excitation-contraction (EC) coupling, linescans can only image ?1.5% of the cross section of myocytes, which raises doubts about how representative such recordings are, especially in light of nonhomogeneous uncoupling of Ca(2+) channels and ryanodine receptors. Nowadays, the speed of confocal microscopes has been greatly improved, enabling two-dimensional (2D) imaging at sufficient image rates (>100 frames/sec). To understand better the physiological and pathophysiological EC coupling of cardiomyocytes, we describe here a protocol to monitor fast intracellular Ca(2+) signals using fast 2D confocal scanning. PMID:25447280

Tian, Qinghai; Kaestner, Lars; Lipp, Peter

2014-01-01

482

Two dimensional kicked quantum Ising model: dynamical phase transitions  

NASA Astrophysics Data System (ADS)

Using an efficient one and two qubit gate simulator operating on graphical processing units, we investigate ergodic properties of a quantum Ising spin 1/2 model on a two-dimensional lattice, which is periodically driven by a ?-pulsed transverse magnetic field. We consider three different dynamical properties: (i) level density, (ii) level spacing distribution of the Floquet quasienergy spectrum, and (iii) time-averaged autocorrelation function of magnetization components. Varying the parameters of the model, we found transitions between ordered (non-ergodic) and quantum chaotic (ergodic) phases, but the transitions between flat and non-flat spectral density do not correspond to transitions between ergodic and non-ergodic local observables. Even more surprisingly, we found good agreement of level spacing distribution with the Wigner surmise of random matrix theory for almost all values of parameters except where the model is essentially non-interacting, even in regions where local observables are not ergodic or where spectral density is non-flat. These findings question the versatility of the interpretation of level spacing distribution in many-body systems and stress the importance of the concept of locality.

Pineda, C.; Prosen, T.; Villaseñor, E.

2014-12-01

483

Kolmogorov flow in two dimensional strongly coupled dusty plasma  

NASA Astrophysics Data System (ADS)

Undriven, incompressible Kolmogorov flow in two dimensional doubly periodic strongly coupled dusty plasma is modelled using generalised hydrodynamics, both in linear and nonlinear regime. A complete stability diagram is obtained for low Reynolds numbers R and for a range of viscoelastic relaxation time ?m [0 < ?m < 10]. For the system size considered, using a linear stability analysis, similar to Navier Stokes fluid (?m = 0), it is found that for Reynolds number beyond a critical R, say Rc, the Kolmogorov flow becomes unstable. Importantly, it is found that Rc is strongly reduced for increasing values of ?m. A critical ? m c is found above which Kolmogorov flow is unconditionally unstable and becomes independent of Reynolds number. For R < Rc, the neutral stability regime found in Navier Stokes fluid (?m = 0) is now found to be a damped regime in viscoelastic fluids, thus changing the fundamental nature of transition of Kolmogorov flow as function of Reynolds number R. A new parallelized nonlinear pseudo spectral code has been developed and is benchmarked against eigen values for Kolmogorov flow obtained from linear analysis. Nonlinear states obtained from the pseudo spectral code exhibit cyclicity and pattern formation in vorticity and viscoelastic oscillations in energy.

Gupta, Akanksha; Ganesh, R.; Joy, Ashwin

2014-07-01

484

Vortex merger and topological changes in two-dimensional turbulence.  

PubMed

On the basis of the critical point analysis, we study the reconnection process of vorticity contours associated with coherent vortices in two-dimensional turbulence. After checking topological integrity by the Euler index theorem, we make use of the critical points and their connectivity (so-called surface networks) to characterize topological changes of vorticity contours. We quantify vortex merger by computing the number of centers and saddles of the vorticity field systematically. Surface networks are topological graphs consisting of the critical points and edges connecting them. They can tell in particular which vortices are going to merge in near future. Moreover, we show how this method can remarkably distinguish the dynamics of the vorticity field in the Navier-Stokes equations and that of the Charney-Hasegawa-Mima equation. The relationship between the number of the critical points and hyperpalinstrophy is discussed by deriving the so-called generalized Rice theorem in the spirit of S. Goto and J. C. Vassilicos [Phys. Fluids 21, 035104-1 (2009)]. The Okubo-Weiss' conditional sampling is used to compare reconnection in elliptic and hyperbolic regions. A comparison has been made between topological changes of the vorticity and that of a passive scalar. A study in inviscid flows with different resolutions is also given. PMID:23005527

Al Sulti, Fayeza; Ohkitani, Koji

2012-07-01

485

Strongly bound excitons in gapless two-dimensional structures  

NASA Astrophysics Data System (ADS)

Common wisdom asserts that bound excitons cannot form in high-dimensional (d>1) metallic structures because of their overwhelming screening and the unavoidable resonance with nearby continuous bands. Strikingly we illustrate that this prevalent assumption is not quite true. A key ingredient has been overlooked: Destructive coherent effects are capable of thwarting the formation of resonance. As an example of this general mechanism, we focus on an experimentally relevant material and predict bound excitons in twisted bilayer graphene, which is a two-dimensional gapless structure that exhibits metallic screening. The binding energies calculated by first-principles simulations are surprisingly large. The low-energy effective model reveals that these bound states are produced by a unique destructive coherence between two alike subband resonant excitons. In particular, this coherent effect is not sensitive to the screening and dimensionality, and hence may persist as a general mechanism for creating bound excitons in various metallic structures, opening the door for excitonic applications based on metallic structures.

Liang, Yufeng; Soklaski, Ryan; Huang, Shouting; Graham, Matthew W.; Havener, Robin; Park, Jiwoong; Yang, Li

2014-09-01

486

Two-dimensional analytical model of dry air thermal convection  

NASA Astrophysics Data System (ADS)

In the present work, the steady-state stationary dry air thermal convection in a lower atmosphere has been studied theoretically. The thermal convection was considered without accounting for the Coriolis force, and with only the vertical temperature gradient. The stream function has been analytically obtained within the framework of two-dimensional thermal convection model in the Boussinesq approximation with velocity divergence taken as zero. It has been shown that the stream function is symmetrical about the horizontal and vertical. The expressions for the horizontal and vertical air velocity components have been obtained. The maximal vertical velocities level is in the center of the convective cell where the horizontal air velocity component is equal to zero. It has been shown that the air parcel's rotation period during the thermal convection is determined by the Brunt-Väisälä frequency. The expression for the maximal air velocity vertical component has been found. The dependence of the maximal air velocity vertical component on the overheat function at ground surface and on the atmosphere instability has been demonstrated. The expression for the pressure disturbance has been obtained. It has been demonstrated that at the points with maximal pressure disturbance the vertical velocity is equal to zero and the horizontal velocity is maximal. It has been found that the convection cell size depends on the atmosphere stability state.

Zakinyan, R. G.; Zakinyan, A. R.; Lukinov, A. A.

2015-01-01

487

From arbitrariness to anomalies in two-dimensional perturbative calculations  

NASA Astrophysics Data System (ADS)

A very general calculational strategy is applied to the evaluation of divergent physical amplitudes which are typical of 2D perturbative calculations. With this approach, in the final results all the arbitrariness intrinsic to the calculations, due to the divergent character, is still present. We show that, concerning the arbitrariness, the regularizations can be classified into two basic classes. The consequences on adopting each such class for the symmetry relations are investigated. It is noted that if very general symmetry requirements, such as Furry's theorem or gauge invariance, are used to select a consistent regularization procedure, the possible sources of ambiguities related to the choices for the internal line momenta of loops are completely eliminated. A very transparent description of the two-dimensional anomalies emerges, allowing a clear understanding of the results obtained within the context of traditional methods. The comparison with 4D triangle anomalies reveals a completely similar situation for both cases. The very interesting phenomenon of mass generation for the gauge boson in the massless fermion theory is also obtained in agreement with the expected results.

Battistel, O. A.

2004-05-01

488

Two Dimensional Heat Transfer around Penetrations in Multilayer Insulation  

NASA Technical Reports Server (NTRS)

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).

Johnson, Wesley L.; Kelly, Andrew O.; Jumper, Kevin M.

2012-01-01

489

Photocatalytic reaction centers in two-dimensional titanium oxide crystals.  

PubMed

Co-catalysts play an important role in photocatalytic water splitting. The co-catalyst is generally deposited in the form of nanoparticles on the catalyst surface, and is believed to provide water oxidation and reduction sites. However, the minimum size of a co-catalyst that can function as a reaction site and the detailed local environment of the photocatalytic reaction centers are not yet fully understood. Here, we show that even isolated single-atom Rh dopants in two-dimensional titanium oxide crystals can effectively act as co-catalysts for the water-splitting reaction. At an optimal doping concentration, the hydrogen production rate is increased substantially in comparison to that found with the undoped crystals. We also present first-principles simulations based on density functional theory to provide insights into the atomic-scale mechanism by which the isolated Rh dopants induce changes to the dissociation reaction energy landscape. These results provide new insights for better understanding the role of the co-catalyst in the photocatalytic reaction. PMID:25479408

Ida, Shintaro; Kim, Namhoon; Ertekin, Elif; Takenaka, Sakae; Ishihara, Tatsumi

2015-01-14

490

Thermodynamics of the two-dimensional Heisenberg classical honeycomb lattice  

NASA Astrophysics Data System (ADS)

In this article we adapt a previous work concerning the two-dimensional (2D) Heisenberg classical square lattice [Physica B 245, 263 (1998)] to the case of a honeycomb lattice. Closed-form expressions of the main thermodynamic functions of interest are derived in the zero-field limit. Notably, near absolute zero (i.e., the critical temperature), we derive the values of the critical exponents ?=0, ?=-1, ?=3, and ?=1, as for the square lattice, thus proving their universal character. A very simple model allows one to give a good description of the low-temperature behaviors of the product ?T. For a 2D-compensated antiferromagnet, we derive simple relations between the characteristics of the maximum of the susceptibility curve T(?max) and ?max and the involved exchange energies. Therefore, owing to the knowledge of T(?max) and ?max, one can directly obtain the respective values of these energies. Finally, we show that the theoretical model allows one to fit correctly experimental susceptibility data of the recently synthetized compound Mn2(bpm)(ox)2.6H2O characterized by a 2D classical honeycomb lattice (where ``bpm'' and ``ox'' are the abbreviations for the ligands bipyrimidine and oxalate, respectively).

Curély, Jacques; Lloret, Francesc; Julve, Miguel

1998-11-01

491

Phase diagram of two-dimensional hard ellipses.  

PubMed

We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [E. P. Bernard and W. Krauth, Phys. Rev. Lett. 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i.e., isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios. PMID:24880296

Bautista-Carbajal, Gustavo; Odriozola, Gerardo

2014-05-28

492

Two dimensional simulation of high power laser-surface interaction  

SciTech Connect

For laser intensities in the range of 10{sup 8}--10{sup 9} W/cm{sup 2}, and pulse lengths of order 10 {micro}sec or longer, the authors have modified the inertial confinement fusion code Lasnex to simulate gaseous and some dense material aspects of the laser-matter interaction. The unique aspect of their treatment consists of an ablation model which defines a dense material-vapor interface and then calculates the mass flow across this interface. The model treats the dense material as a rigid two-dimensional mass and heat reservoir suppressing all hydrodynamic motion in the dense material. The computer simulations and additional post-processors provide predictions for measurements including impulse given to the target, pressures at the target interface, electron temperatures and densities in the vapor-plasma plume region, and emission of radiation from the target. The authors will present an analysis of some relatively well diagnosed experiments which have been useful in developing their modeling. The simulations match experimentally obtained target impulses, pressures at the target surface inside the laser spot, and radiation emission from the target to within about 20%. Hence their simulational technique appears to form a useful basis for further investigation of laser-surface interaction in this intensity, pulse-width range. This work is useful in many technical areas such as materials processing.

Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P. [Los Alamos National Lab., NM (United States); Busch, G.E. [KMS Fusion, Inc., Ann Arbor, MI (United States)

1998-08-01

493

Acoustic dispersion in a two-dimensional dipole system  

SciTech Connect

We calculate the full density response function and from it the long-wavelength acoustic dispersion for a two-dimensional system of strongly coupled point dipoles interacting through a 1/r{sup 3} potential at arbitrary degeneracy. Such a system has no random-phase-approximation (RPA) limit and the calculation has to include correlations from the outset. We follow the quasilocalized charge (QLC) approach, accompanied by molecular-dynamics (MD) simulations. Similarly to what has been recently reported for the closely spaced classical electron-hole bilayer [G. J. Kalman et al., Phys. Rev. Lett. 98, 236801 (2007)] and in marked contrast to the RPA, we report a long-wavelength acoustic phase velocity that is wholly maintained by particle correlations and varies linearly with the dipole moment p. The oscillation frequency, calculated both in an extended QLC approximation and in the Singwi-Tosi-Land-Sjolander approximation [Phys. Rev. 176, 589 (1968)], is invariant in form over the entire classical to quantum domains all the way down to zero temperature. Based on our classical MD-generated pair distribution function data and on ground-state energy data generated by recent quantum Monte Carlo simulations on a bosonic dipole system [G. E. Astrakharchik et al., Phys. Rev. Lett. 98, 060405 (2007)], there is a good agreement between the QLC approximation kinetic sound speeds and the standard thermodynamic sound speeds in both the classical and quantum domains.

Golden, Kenneth I.; Kalman, Gabor J.; Donko, Zoltan; Hartmann, Peter [Department of Mathematics and Statistics, College of Engineering and Mathematical Sciences, University of Vermont, Burlington, Vermont 05401-1455 (United States); Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467 (United States); Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary)

2008-07-15

494

Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence  

NASA Technical Reports Server (NTRS)

Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence.The se features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo.Recently, the origin of broken ergodicity in 3-D MHD turbulence that is manifest in the lowest wavenumbers was explained. Here, a detailed description of the origins of broken ergodicity in 2-D MHD turbulence is presented. It will be seen that broken ergodicity in ideal 2-D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions.T he origins of broken ergodicity in ideal 2-D homogeneous MHD turbulence are found through an eigen analysis of the covariance matrices of the modal probability density functions.It will also be shown that when the lowest wavenumber magnetic field becomes quasi-stationary, the higher wavenumber modes can propagate as Alfven waves on these almost static large-scale magnetic structures

Shebalin, John V.

2010-01-01

495

On small insect flight -- a two-dimensional study  

NASA Astrophysics Data System (ADS)

Small insect flight is characterized by very small Reynolds numbers and relatively simple wing motions. In this study, a two-dimensional approximation of small insect flight is calculated with a newly developed high-order immersed boundary incompressible Navier-Stokes flow solver. The simulated motion of the model wing is a simplification of the flight of Drosophila melanogaster, and was done in line with previous experimental and numerical simulations available in the literature. Calculations were carried out until a time-periodic steady-state was achieved. Changes in lift generation and vortex dynamics are studied for Reynolds numbers spanning two orders of magnitude, in order to accurately find the critical Re number above which flapping flight is possible. Above the critical Reynolds number, vortices are alternately shed during translation. Below the critical Reynolds number, vortices are formed but not shed during translation, creating two attached and almost identical vortices. This transition is significant because, below it, an important mechanism of lift generation no longer applies, effectively indicating a lower bound for insect flight to occur.

Ferreira de Sousa, Paulo

2006-03-01

496

Molecular interconversion behaviour in comprehensive two-dimensional gas chromatography.  

PubMed

Comprehensive two-dimensional gas chromatography (GC x GC) is shown to provide information on dynamic molecular behaviour (interconversion), with the interconversion process occurring on both columns in the coupled-column experiment. The experiment requires suitable adjustment of both experimental conditions and relative dimensions of each of the columns. In this case, a longer column than normally employed in GC x GC allows sufficient retention duration on the second column, which permits the typical plateau-shape recognised for the interconversion process to be observed. The extent of interconversion depends on prevailing temperature, retention time, and the phase type. Polyethylene glycol-based phases were found to result in high interconversion kinetics, although terephthalic acid-terminated polyethylene glycol had a lesser extent of interconversion. Much less interconversion was seen for phenyl-methylpolysiloxane and cyclodextrin phases. This suggests that for the oximes, interconversion largely occurs in the stationary phase. Examples of different extents of interconversion in both dimensions are shown, including peak coalescence on the first column with little interconversion on the second column. PMID:15072298

Marriott, Philip; Aryusuk, Kornkanok; Shellie, Robert; Ryan, Danielle; Krisnangkura, Kanit; Schurig, Volker; Trapp, Oliver

2004-04-01

497

Impact of heterocirculene molecular symmetry upon two-dimensional crystallization  

PubMed Central

Despite the development of crystal engineering, it remains a great challenge to predict the crystal structure even for the simplest molecules, and a clear link between molecular and crystal symmetry is missing in general. Here we demonstrate that the two-dimensional (2D) crystallization of heterocirculenes on a Au(111) surface is greatly affected by the molecular symmetry. By means of ultrahigh vacuum scanning tunneling microscopy, we observe a variety of 2D crystalline structures in the coverage range from submonolayer to monolayer for D8h-symmetric sulflower (C16S8), whereas D4h-symmetric selenosulflower (C16S4Se4) forms square and rectangular lattices at submonolayer and monolayer coverages, respectively. No long-range ordered structure is observed for C1h-symmetric selenosulflower (C16S5Se3) self-assembling at submonolayer coverage. Such different self-assembly behaviors for the heterocirculenes with reduced molecular symmetries derive from the tendency toward close packing and the molecular symmetry retention in 2D crystallization due to van der Waals interactions. PMID:24957140

Xiao, W. D.; Zhang, Y. Y.; Tao, L.; Aït-Mansour, K.; Chernichenko, K. Y.; Nenajdenko, V. G.; Ruffieux, P.; Du, S. X.; Gao, H.-J.; Fasel, R.

2014-01-01

498

Atmospheric flow over two-dimensional bluff surface obstructions  

NASA Technical Reports Server (NTRS)

The phenomenon of atmospheric flow over a two-dimensional surface obstruction, such as a building (modeled as a rectangular block, a fence or a forward-facing step), is analyzed by three methods: (1) an inviscid free streamline approach, (2) a turbulent boundary layer approach using an eddy viscosity turbulence model and a horizontal pressure gradient determined by the inviscid model, and (3) an approach using the full Navier-Stokes equations with three turbulence models; i.e., an eddy viscosity model, a turbulence kinetic-energy model and a two-equation model with an additional transport equation for the turbulence length scale. A comparison of the performance of the different turbulence models is given, indicating that only the two-equation model adequately accounts for the convective character of turbulence. Turbulence flow property predictions obtained from the turbulence kinetic-energy model with prescribed length scale are only insignificantly better than those obtained from the eddy viscosity model. A parametric study includes the effects of the variation of the characteristics parameters of the assumed logarithmic approach velocity profile. For the case of the forward-facing step, it is shown that in the downstream flow region an increase of the surface roughness gives rise to higher turbulence levels in the shear layer originating from the step corner.

Bitte, J.; Frost, W.

1976-01-01

499

Two-dimensional Potts model with aperiodic interactions: numerical simulation  

NASA Astrophysics Data System (ADS)

The uniform two-dimensional Potts model presents first-order transitions for q (number of states) greater than 4. The introduction of aperiodic modulations on its interactions may change the universality class or the nature of the transition. Previous results for the q=8 Potts model on the square lattice suggest that the Harris-Luck criterion is satisfied also for first-order transitions [1]. However, for random disorder, the new universality class that may emerge depends on the number of states of the Potts model [2]. In order to test this possibility for aperiodic modulations, we have made extensive numerical simulations on the q=6 Potts model on the square lattice, for three aperiodic sequence. Our results show that the Harris-Luck criterion is obeyed and that the new universality class that may emerge is the same as for the q=8 Potts model. Therefore, we stablish that, contrarily to random disorder, the introduction of relevant aperiodic modulation leads the system to a new universality class, irrespective number of states of the Potts model.[4pt] [1] C. Chatelain, B. Berche, Phys. Rev. Lett. 80, 1670 (1998).[0pt] [2] J.L. Jacobsen and J. Cardy, Phys. Rev. Lett. 79, 4063 (1997).

Branco, Nilton; Girardi, Daniel

2010-03-01

500

Two-Dimensional Nonlinear Finite Element Analysis of CMC Microstructures  

NASA Technical Reports Server (NTRS)

Detailed two-dimensional finite element analyses of the cross-sections of a model CVI (chemical vapor infiltrated) SiC/SiC (silicon carbide fiber in a silicon carbide matrix) ceramic matrix composites are performed. High resolution images of the cross-section of this composite material are generated using serial sectioning of the test specimens. These images are then used to develop very detailed finite element models of the cross-sections using the public domain software OOF2 (Object Oriented Analysis of Material Microstructures). Examination of these images shows that these microstructures have significant variability and irregularity. How these variabilities manifest themselves in the variability in effective properties as well as the stress distribution, damage initiation and damage progression is the overall objective of this work. Results indicate that even though the macroscopic stress-strain behavior of various sections analyzed is very similar, each section has a very distinct damage pattern when subjected to in-plane tensile loads and this damage pattern seems to follow the unique architectural and microstructural details of the analyzed sections.

Mital, Subodh K.; Goldberg, Robert K.; Bonacuse, Peter J.

2011-01-01