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1

The application of Halbach cylinders to brushless ac servo motors

Halbach cylinders are applied to brushless ac servo motors. It is shown that a sinusoidal back-emf waveform and a low cogging torque can be achieved without recourse to conventional design features such as distributed windings and/or stator/rotor skew. A technique for imparting a multipole Halbach magnetization distribution on an isotropic permanent magnet cylinder is described, and it is shown that the torque capability of a Halbach ac servo motor can be up to 33% higher than conventional brushless permanent magnet ac motors.

Atallah, K.; Howe, D. [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering] [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering

1998-07-01

2

Two dimensional exchange NMR experiments of natural porous media with portable Halbach-Magnets

NASA Astrophysics Data System (ADS)

The characterization of pore space and connectivity in soils of different textures is one topic within Cluster A, Partial Project A1. For this purpose low field mobile NMR became a powerful tool following the development of portable NMR sensors for well logging. By now there are numerous applications of mobile NMR in materials analysis and chemical engineering where, for example, unique information about the structure, morphology and dynamics of polymers is obtained, and new opportunities are provided for geophysical investigations [1]. In particular, dynamic information can be retrieved by two-dimensional Laplace exchange NMR, where the initial NMR relaxation environment is correlated with the final relaxation environment of molecules migrating from one environment to the other within a so-called NMR mixing time tm [2]. Relaxation-relaxation exchange experiments were performed with saturated and un-saturated soil samples at low and moderately inhomogeneous magnetic field with a simple, portable Halbach-Magnet. By conducting NMR transverse relaxation exchange experiments for several mixing times and inverting the results to 2D T2 distributions (similar to joint probability densities of transverse relaxation times T2) with the help of inverse 2D Laplace Transformation (ILT), we observed characteristic exchange processes: Soils consisting mainly of silt and clay components show predominantly exchange between the smaller pores at mixing times of some milliseconds. In addition, there exists also weaker exchange with the larger pores observable for longer mixing time. In contrast to that fine sand exhibits 2D T2 distributions with no exchange processes which can be interpreted that water molecules move within pores of the same size class. These results will be compared to the exchange behaviour under unsaturated conditions. References: 1. B. Blümich, J. Mauler, A. Haber, J. Perlo, E. Danieli, F. Casanova, Mobile NMR for geophysical analysis and material testing, Petroleum Science 6 (2009) 1-7. 2. K. E. Washburn, P.T. Callaghan, Tracking pore to pore exchange using relaxation exchange spectroscopy, Phys. Rev. Lett. 97 (2006) 175502.

Haber, Agnes; Haber-Pohlmeier, Sabina; Casanova, Federico; Blümich, Bernhard

2010-05-01

3

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

4

Two-dimensional subsonic compressible flow past elliptic cylinders

NASA Technical Reports Server (NTRS)

The method of Poggi is used to calculate, for perfect fluids, the effect of compressibility upon the flow on the surface of an elliptic cylinder at zero angle of attack and with no circulation. The result is expressed in a closed form and represents a rigorous determination of the velocity of the fluid at the surface of the obstacle insofar as the second approximation is concerned. Comparison is made with Hooker's treatment of the same problem according to the method of Janzen and Rayleight and it is found that, for thick elliptic cylinders, the two methods agree very well. The labor of computation is considerably reduced by the present solution.

Kaplan, Carl

1938-01-01

5

Stick-Slip dynamics of one and two dimensional arrays of cylinders

NASA Astrophysics Data System (ADS)

We have studied the stick-slip behavior of one and two dimensional arrays of cylinders as they are pushed by a known driving force on a planar surface. We present results for the global frictional force and effective inertia as a function of confining mass, number of cylinders, and acceleration rate. We also discuss further plans to test theoretical predictions made by Radjai et al. (Farhang Radjai, Lothar Brendel and Stephane Roux, Nonsmoothness, indeterminacy and friction in two dimensional arrays of rigid particles, Phys. Rev. E, Vol. 54, no. 1, July 1996)

Nakroshis, Paul; Boss, Justin; Smith, Chris

2000-04-01

6

Numerical Simulation of Two-Dimensional Flow over Three Cylinders by Lattice Boltzmann Method

NASA Astrophysics Data System (ADS)

The numerical simulation using the multiple relaxation time lattice Boltzmann method (MRT-LBM) is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the moving cylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D = 0.5 and fv = 0.4 (where A is the forced amplitude, D is the cylinder diameter, and fv stands for the vibrating frequency, respectively). The calculated results not only indicate that the spacing ratios T/D (T is the center-to-center spacing between the two upstream cylinders) have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D (where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder).

Yang, Hong-Bing; Liu, Yang; Xu, You-Sheng; Kou, Jian-Long

2010-11-01

7

Point defect states of a hollow cylinder in two-dimensional phononic crystal

NASA Astrophysics Data System (ADS)

Point defect states in two-dimensional phononic crystal of a hollow mercury cylinder in a water host are studied. An improved plane expansion method combined with the supercell technique is used to calculate the band gaps and the pressure distribution at the defect position. The sonic pressure of defect modes shows that the waves are localized at or near the defect. As the filing fraction increases, more defect modes appear in the band gaps.

Gao, Xiao-Wei; Chen, Shi-Bo; Chen, Jian-Bing; Zheng, Qin-Hong; Yang, Hai

2012-06-01

8

The published model [Appl. Phys. Lett. 82, 4379-4381 (2003)] for the two-dimensional transient wave propagation in a cylinder is modified to avoid the inherited integration of the numerical inverse scheme. The Fourier series expansion is introduced for one spatial coordinate to resolve the transient response problem: theoretical radial displacements in either the ablation or the thermoelastic regime are obtained with little numerical noise and short computation time. The normal mode expansion method fails to deliver results with the same accuracy. Acoustic waves are fully identified by the ray trajectory analysis. These identified waves are further verified on the experimental results observed with the laser ultrasonic technique. PMID:16018463

Pan, Y; Rossignol, C; Audoin, B

2005-06-01

9

NASA Astrophysics Data System (ADS)

Vortex-shedding suppression in two-dimensional mixed convective flows past circular and square cylinders is investigated numerically at two supercritical Reynolds numbers, Re = 60 and 100, at a fixed Prandtl (Pr) number of 0.71. The Richardson number (Ri) and free-stream orientation (?) are varied in the range [0, 1.6] and [0, ?/2], respectively. The investigations involve the numerical solutions of mass, momentum, and energy equations subject to Boussinesq approximation in generalized curvilinear body-fitted coordinates. The critical Richardson numbers corresponding to the onset of suppression of vortex-shedding are determined for different free-stream orientations using the numerical data and the Stuart-Landau theory. For the case of circular cylinder, the critical Richardson number exhibits a "cosine-law" with respect to the free-stream orientation, while a non-monotonic trend is observed for the case of the square cylinder. By examining the near critical steady flow field data, two distinct components of the baroclinic vorticity generation rate are identified that appear to control the shedding suppression laws (relationships between the critical Richardson number and free-stream orientation) in theRi-? parametric space for the circular and the square cylinders. Supported by numerical experiments, the plausible roles of these baroclinic vorticity generation rate components are identified and utilized to theoretically deduce the functional forms of the shedding suppression laws that agree with the laws observed in the numerical experiments.

Hasan, Nadeem; Ali, Rashid

2013-05-01

10

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

A numerical study of two-dimensional vortex shedding from rectangular cylinders

NASA Technical Reports Server (NTRS)

An efficient time-marching, non-iterative calculation method is used to analyze time-dependent flows around rectangular cylinders. The turbulent flow in the wake region of a square section cylinder is analyzed using an anisotropic k-epsilon model. Initiation and subsequent development of the vortex shedding phenomenon is naturally captured once a perturbation is introduced in the flow. Transient calculations using standard eddy-viscosity and an anisotropic k-epsilon model averaged over an integral number of cycles to get the fluctuating energy (organized and turbulent) are compared with experimental data. It is shown that the anisotropic k-epsilon model resolves the anisotropy of the Reynolds stresses and gives mean energy distribution closer to the experiment than the standard k-epsilon model.

Hadid, A. H.; Sindir, Munir M.; Issa, R. I.

1992-01-01

12

Two-dimensional viscous flow simulation of a shock accelerated heavy gas cylinder

NASA Astrophysics Data System (ADS)

Numerical simulation of Richtmyer-Meshkov instability (RMI) is conducted using an improved localized artificial diffusivity (LAD) method, which is used to treat discontinuities in the form of material interfaces and shocks in the flow-field. The RMI occurs on a cylindrical interface between air and SF6 accelerated by a Mach 1.2 shock initially in air. Navier-Stokes simulation is conducted to accurately predict the mixing between the two fluids. The initial conditions for the two-dimensional simulations are matched to previous experimental work by C. Tomkins et al. ["An experimental investigation of mixing mechanisms in shock-accelerated flow," J. Fluid Mech. 611, 131 (2008)] and good agreement is found between the experimental data and numerical results. The study on initial condition sensitivity indicates that the initial pressure and density gradient are critical parameters that determine the primary vortex generation responsible for the flow development. A grid convergence study is carried out and the relative contribution of the artificial properties introduced by the LAD method is characterized. Novel to this study is the exploration of the effect of the third species (acetone used as a tracer particle in the experiments to obtain contour fields using planar laser induced florescence). The effect of the presence of the third species on the evolution of the RMI and mixing is shown to be non-negligible and an estimate of the amount of the tracer species that was present in the initial experimental set-up is given.

Shankar, Santhosh K.; Kawai, Soshi; Lele, Sanjiva K.

2011-02-01

13

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?, Sinia

2014-09-01

14

Axial Halbach Magnetic Bearings

NASA Technical Reports Server (NTRS)

Axial Halbach magnetic bearings have been investigated as part of an effort to develop increasingly reliable noncontact bearings for future high-speed rotary machines that may be used in such applications as aircraft, industrial, and land-vehicle power systems and in some medical and scientific instrumentation systems. Axial Halbach magnetic bearings are passive in the sense that unlike most other magnetic bearings that have been developed in recent years, they effect stable magnetic levitation without need for complex active control.

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

2008-01-01

15

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

16

Halbach arrays in precision motion control

The Halbach array was developed for use as an optical element in particle accelerators. Following up on a suggestion from Klaus Halbach, the authors have investigated the utility of such arrays as the permanent magnet structure for synchronous machines in cartesian, polar, and cylindrical geometries. Their work has focused on the design of a novel Halbach array linear motor for use in a magnetic suspension stage for photolithography. This paper presents the details of the motor design and its force and power characteristics.

Trumper, D.L.; Williams, M.E. [Massachusetts Institute of Technology, Cambridge, MA (United States)

1995-02-01

17

Two-dimensional wave processes in dispersion media

A two-dimensional expression for the flow of a nonisothermic rarefied plasma round a conductive cylinder is numerically solved. A shock wave having an oscillating structure is found to form in front of the cylinder while behind it forms a rarefied wake with focused ions on its axis.

Iu. A. Berezin; V. A. Vshivkov; V. D. Krygin

1980-01-01

18

Two Dimensional Schrodinger Equation

NSDL National Science Digital Library

The Two Dimensional Schrodinger Equation model simulates the time evolution of a two-dimensional wave packet as it moves towards a slit with an obstacle in it, both with variable widths. By changing three parameters via sliders provided, slit width, obstacle width, and initial position of the wave packet, different behaviors can be explored. These phenomena include interference, diffraction produced by a slit, a corner, and an obstacle, and bouncing of the wave packet. In addition, the angle of propagation for the diffracted part of the wave packet can be measured. This simulation is described by a paper in the European Journal of Physics, "A versatile applet to explore the wave behaviour of particles, " J I FernĂĄndez Palop, 2009 Eur. J. Phys. 30 771, which outlines the simulation and how the usefulness of the simulation has been tested in the subject of quantum physics. The Two Dimensional Schrodinger Equation model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_qm_schrodinger2d.jar file will run the program if Java is installed.

Palop, Jose I.

2010-07-16

19

Two-Dimensional Velocimetry Instrumentation.

National Technical Information Service (NTIS)

This a brief report on the acquisition and implementation of instrumentation which will be used to make two-dimensional velocimetry measurements in a study of premixed turbulent flames. Two-dimensional velocimetry. (eg)

D. A. Santavicca

1990-01-01

20

Acoustic transparency in two-dimensional sonic crystals

Acoustic transparency is studied in two-dimensional sonic crystals consisting of hexagonal distributions of cylinders with continuously varying properties. The transparency condition is achieved by selectively closing the acoustic bandgaps, which are governed by the structure factor of the cylindrical scatterers. It is shown here that cylindrical scatterers with the proposed continuously varying properties are physically realizable by using metafluids based

José Sánchez-Dehesa; Daniel Torrent; Liang-Wu Cai

2009-01-01

21

NASA Technical Reports Server (NTRS)

A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations.

Jackman, Charles H.; Douglass, Anne R.; Stolarski, Richard S.; Guthrie, Paul D.; Thompson, A. M.

1990-01-01

22

Halbach array motor/generators: A novel generalized electric machine.

National Technical Information Service (NTIS)

In August 1979, Halbach submitted a paper entitled ''Design of Permanent Multipole Magnets with Oriented Rare Earth Cobalt Material.'' In this paper, he presented a novel method of generating multipole magnetic fields using non-intuitive geometrical arran...

B. T. Merritt, R. F. Post, G. R. Dreifuerst, D. A. Bender

1994-01-01

23

NASA Astrophysics Data System (ADS)

This paper describes calculations and comparisons of eddy current losses in a cylindrical linear oscillatory actuator with a Halbach array permanent magnet mover for different voltage source waveforms. Using the magnetic vector potential and a two-dimensional cylindrical coordinate system, the paper presents an analytical procedure and obtains solutions for the eddy current losses using the Poynting theorem. To verify the proposed method, the eddy current losses obtained from the analytical solutions are compared with the results of a non-linear finite element method. Moreover, this paper shows that the eddy current losses are more significant when the actuator is driven by a square voltage waveform than when it is driven by a sinusoidal voltage waveform.

Ko, Kyoung-Jin; Choi, Ji-Hwan; Jang, Seok-Myeong; Choi, Jang-Young

2012-04-01

24

Halbach array motor/generators: A novel generalized electric machine

In August 1979, Halbach submitted a paper entitled ``Design of Permanent Multipole Magnets with Oriented Rare Earth Cobalt Material.`` In this paper, he presented a novel method of generating multipole magnetic fields using non-intuitive geometrical arrangements of permanent magnets. In subsequent publications, he further defined these concepts. Of particular interest to one of the authors (RFP) was the special magnet array that generated a uniform dipole field. In 1990 Post proposed the construction of an electric machine (a motor/generator) using a dipole field based on Klaus Halbach`s array of permanent magnets. He further proposed that such a system should be employed as an integral part of ``an electromechanical battery`` (EMB), i.e., a modular flywheel system to be used as a device for storing electrical energy, as an alternative to the electrochemical storage battery. This paper reviews Halbach`s theory for the generation of a dipole field using an array of permanent magnet bars, presents a simple analysis of a family of novel ``ironless`` electric machines designed using the dipole Halbach array, and describes the results obtained when they were tested in the laboratory.

Merritt, B.T.; Post, R.F.; Dreifuerst, G.R.; Bender, D.A.

1994-10-28

25

Two-dimensional NMR spectrometry

This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t/sub 0/; an evolution period, t/sub 1/; and a detection period, t/sub 2/.

Farrar, T.C.

1987-06-01

26

Two dimensional unstable scar statistics.

This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.

Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)

2006-12-01

27

Development and Testing of an Axial Halbach Magnetic Bearing

NASA Technical Reports Server (NTRS)

The NASA Glenn Research Center has developed and tested a revolutionary Axial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic thrust bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help to reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Axial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Axial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical systems, computer memory systems, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Axial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

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

2006-01-01

28

Development and Testing of a Radial Halbach Magnetic Bearing

NASA Technical Reports Server (NTRS)

The NASA John H. Glenn Research Center has developed and tested a revolutionary Radial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic bearing utilizing Halbach arrays for all-electric flight, and many other applications. This concept will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks, seals and friction loss. The Radial Halbach Magnetic Bearing is inherently stable and requires no active feedback control system or superconductivity as required in many magnetic bearing designs. The Radial Halbach Magnetic Bearing is useful for very high speed applications including turbines, instrumentation, medical applications, manufacturing equipment, and space power systems such as flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies developed for particle accelerators, and currently under development for maglev trains and rocket launchers, served as the basis for this application. Experimental hardware was successfully designed and developed to validate the basic principles and analyses. The report concludes that the implementation of Radial Halbach Magnetic Bearings can provide significant improvements in rotational system performance and reliability.

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

2006-01-01

29

Halbach array DC motor/generator

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

30

Correspondence Quantification in Comprehensive Two-Dimensional

Correspondence Quantification in Comprehensive Two-Dimensional Liquid Chromatography Stephen E 68588-0115 This correspondence corrects the description in a recent paper by Mondello et al., "Quantification in Comprehen- sive Two-Dimensional Liquid Chromatography" [Mon- dello, L.; Herrero, M.; Kumm, T

Reichenbach, Stephen E.

31

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

In order to improve the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle, a two-pole Halbach arrays 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 PMs 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

32

The existence of full gaps and deaf bands in two-dimensional sonic crystals

Theoretical and experimental determination of sonic band structures of two-dimensional (2-D) arrays of rigid cylinders in air is reported. We present measurements for square and triangular lattices. A variational method is employed to calculate the acoustic dispersion relation. Experimentally, a transmission technique and the analysis of the phase delay between the incident and scattered waves by the structure are used

C. Rubio; D. Caballero; J. V. Sanchez-Perez; R. Martinez-Sala; J. Sanchez-Dehesa; F. Meseguer; F. Cervera

1999-01-01

33

Both negative and positive phase velocities for acoustic waves have been experimentally established in a two-dimensional triangular sonic crystal (SC) consisting of steel cylinders embedded in air at first. With the increase of the SCs thickness layer by layer in the experiments, phase shifts decrease in the second band but increase in the first band, showing the negative and the

Ming-Hui Lu; Liang Feng; Xiao-Ping Liu; Xiao-Kang Liu; Yan-Feng Chen; Yong-Yuan Zhu; Yi-Wei Mao; Jian Zi

2007-01-01

34

Far-field imaging of acoustic waves by a two-dimensional sonic crystal

The negative refraction behavior and imaging effect for acoustic waves in two-dimensional sonic crystals consisting of hexagonal arrays of steel cylinders in air are studied in this paper. The negative refraction and left-handed behaviors are demonstrated by the simulation of a Gaussian beam through a slab of the sonic crystal. Imaging effects by the sonic crystal slab with effective refraction

Chunyin Qiu; Xiangdong Zhang; Zhengyou Liu

2005-01-01

35

Collisional diffusion in a two-dimensional point vortex gas or a two-dimensional plasma

Collisional diffusion in a two-dimensional point vortex gas or a two-dimensional plasma Daniel H. E of a multispecies two-dimensional 2D point vortex gas, or a 2D plasma, in the presence of retrograde shear of point vortices, Onsager relations require that the diffusive flux conserves the total vorticity (r

California at San Diego, University of

36

Inverted Linear Halbach Array for Separation of Magnetic Nanoparticles

A linear array of Nd-Fe-B magnets has been designed and constructed in an inverted Halbach configuration for use in separating magnetic nanoparticles. The array provides a large region of relatively low magnetic field, yet high magnetic field gradient in agreement with finite element modeling calculations. The magnet assembly has been combined with a flow channel for magnetic nanoparticle suspensions, such that for an appropriate distance away from the assembly, nanoparticles of higher moment aggregate and accumulate against the channel wall, with lower moment nanoparticles flowing unaffected. The device is demonstrated for iron oxide nanoparticles with diameters of ~ 5 and 20 nm. In comparison to other approaches, the inverted Halbach array is more amenable to modeling and to scaling up to preparative quantities of particles.

Ijiri, Y.; Poudel, C.; Williams, P.S.; Moore, L.R.; Orita, T.; Zborowski, M.

2014-01-01

37

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

38

Two-dimensional materials for electronic applications

The successful isolation of graphene in 2004 has attracted great interest to search for potential applications of this unique material and other members of the two-dimensional materials family in electronics, optoelectronics ...

Wang, Han, Ph. D. Massachusetts Institute of Technology

2013-01-01

39

Electronic properties of two-dimensional systems

The electronic properties of inversion and accumulation layers at semiconductor-insulator interfaces and of other systems that exhibit two-dimensional or quasi-two-dimensional behavior, such as electrons in semiconductor heterojunctions and superlattices and on liquid helium, are reviewed. Energy levels, transport properties, and optical properties are considered in some detail, especially for electrons at the (100) silicon-silicon dioxide interface. Other systems are discussed

Tsuneya Ando; Alan B. Fowler; Frank Stern

1982-01-01

40

Two-dimensional sonic crystals with Helmholtz resonators.

We present a type of sonic crystal composed with an array of two-dimensional Helmholtz resonators, which in the long-wave regime have both a high relative acoustic refractive index n and at the same time, a small acoustic impedance Z mismatch with air for airborne sound. We analyze the n and Z of such sonic crystals by finite-difference time-domain simulations, and by mapping our results to a corresponding electromagnetic (EM) model, and we find that our Helmholtz resonant sonic crystal has a bigger effective magnetic permeability mu than the conventional rigid-cylinder sonic crystal in its EM counterpart. As a result, a thin convergent lens with very good focusing effect is demonstrated based on our crystal. PMID:16089593

Hu, Xinhua; Chan, C T; Zi, Jian

2005-05-01

41

Burgers approximation for two-dimensional flow past an ellipse

NASA Technical Reports Server (NTRS)

A linearization of the Navier-Stokes equation due to Burgers in which vorticity is transported by the velocity field corresponding to continuous potential flow is examined. The governing equations are solved exactly for the two dimensional steady flow past an ellipse of arbitrary aspect ratio. The requirement of no slip along the surface of the ellipse results in an infinite algebraic system of linear equations for coefficients appearing in the solution. The system is truncated at a point which gives reliable results for Reynolds numbers R in the range 0 R 5. Predictions of the Burgers approximation regarding separation, drag and boundary layer behavior are investigated. In particular, Burgers linearization gives drag coefficients which are closer to observed experimental values than those obtained from Oseen's approximation. In the special case of flow past a circular cylinder, Burgers approximation predicts a boundary layer whose thickness is roughly proportional to R-1/2.

Dorrepaal, J. M.

1982-01-01

42

Effects of disorder in two-dimensional photonic crystal waveguides.

The effects of randomness on the guiding properties of waveguides embedded in disordered two-dimensional photonic crystals composed of a finite cluster of circular cylinders of infinite length are investigated for TM-polarized radiation. Different degrees of disorder in the radius, filling fraction, refractive index, and position are considered for both straight and 90 degrees bent guides. The crystals exhibit similar sensitivity to refractive index and radius disorder, with a degree of disorder from 15%-20% yielding little substantial change in the guiding properties. A smaller range of position disorder is also considered. For strong disorder in radius and refractive index, the guide effectively closes. These results were obtained by a Monte Carlo simulation method, and the performance of this method is analyzed. The method requires at least ten realizations in some cases for convergence to commence; substantially more realizations are required for moderate and strong disorder to achieve accurate results. PMID:14525137

Langtry, T N; Asatryan, A A; Botten, L C; de Sterke, C M; McPhedran, R C; Robinson, P A

2003-08-01

43

Two-dimensional nonlinear beam shaping.

We develop a technique for two-dimensional arbitrary wavefront shaping in quadratic nonlinear crystals by using binary nonlinear computer generated holograms. The method is based on transverse illumination of a binary modulated nonlinear photonic crystal, where the phase matching is partially satisfied through the nonlinear Raman-Nath process. We demonstrate the method experimentally showing a conversion of a fundamental Gaussian beam pump light into three Hermite-Gaussian and three Laguerre-Gaussian beams in the second harmonic. Two-dimensional binary nonlinear computer generated holograms open wide possibilities in the field of nonlinear beam shaping and mode conversion. PMID:22660146

Shapira, Asia; Shiloh, Roy; Juwiler, Irit; Arie, Ady

2012-06-01

44

Electromagnetic scattering of Gaussian beam by two-dimensional targets

NASA Astrophysics Data System (ADS)

On the basis of the equivalence principle and reciprocity theorem, the multiple scattering up to Nth order by N parallel two-dimensional (2-D) targets arbitrarily located in a Gaussian beam is considered. The first-order solution can be obtained by calculating the scattered field from isolated targets when illuminated by a Gaussian beam. However, it is almost impossible to find an analytical solution for the higher-order scattered field if the 2-D targets are not circular cylinders because of the difficulty in formulating the couple scattered field. In order to overcome this problem, the composite scattering field is studied by employing the technique based on the reciprocity theorem and equivalence principle, and a line integral solution up to Nth order is obtained. In this calculation, only the previous-order scattered field from scatterers and the equivalent surface electric and/or magnetic current density induced by the incident beam are required. Using the approach proposed in this paper, the bistatic and the monostatic scattering fields of a Gaussian beam by parallel inhomogeneous plasma-coated conducting circular cylinders are calculated, and the dependences of attenuation of the scattering width on the thickness of the coated layer, electron number density, collision frequency, and radar frequency are discussed in detail.

Wang, Yunhua; Guo, Lixin; Wu, Zhensen

2007-08-01

45

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

46

Two dimensional gas turbine engine exhaust nozzle

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.

E. B. Thayer; G. H. McLafferty

1988-01-01

47

Stochastic models of two-dimensional fracture

Two statistical models of (strictly two-dimensional) layer destruction are presented. The first is built as a strict percolation model with an added ``conservation law'' (conservation of mass) as physical constraint. The second allows for damped or limited fracture. Two successive fracture crack thresholds are considered. Percolation (i.e., fracture) probability and cluster distributions are studied by use of numerical simulations. Different

M. Ausloos; J. M. Kowalski

1992-01-01

48

Two-Dimensional Motions of Rockets

ERIC Educational Resources Information Center

We analyse the two-dimensional motions of the rockets for various types of rocket thrusts, the air friction and the gravitation by using a suitable representation of the rocket equation and the numerical calculation. The slope shapes of the rocket trajectories are discussed for the three types of rocket engines. Unlike the projectile motions, the

Kang, Yoonhwan; Bae, Saebyok

2007-01-01

49

High-resolution two dimensional advective transport

The paper describes a two-dimensional high-resolution scheme for advective transport that is based on a Eulerian-Lagrangian method with a flux limiter. The scheme is applied to the problem of pure-advection of a rotated Gaussian hill and shown to preserve the monotonicity property of the governing conservation law.

Smith, P.E.; Larock, B.E.

1989-01-01

50

Two-dimensional subwavelength plasmonic lattice solitons

We present a theoretical study of plasmonic lattice solitons (PLSs) formed in two-dimensional (2D) arrays of metallic nanowires embedded into a nonlinear medium with Kerr nonlinearity. We analyze two classes of 2D PLSs families, namely, fundamental and vortical PLSs in both focusing and defocusing media. Their existence, stability, and subwavelength spatial confinement are studied in detai

Ye, F; Hu, B; Panoiu, N C

2010-01-01

51

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

52

NASA Technical Reports Server (NTRS)

The dynamics of magnetic fibrils in the convective zone of a star is investigated analytically, deriving mean-field equations for the two-dimensional transverse motion of an incompressible fluid containing numerous small widely spaced circular cylinders. The equations of Parker (1982) are extended to account for the inertial effects of local flow around the cylinders. The linear field equation for the stream function at the onset of convection is then rewritten, neglecting large-scale heat transport, and used to construct a model of convective counterflow. The Kelvin impulse and fluid momentum, convective motion initiated by a horizontal impulse, and the effects of a viscous boundary layer are considered in appendices.

Parker, E. N.

1985-01-01

53

By calculating the transmission coefficients by finite-element software, the study of the tunable acoustic band gap for two-dimensional (2D) phononic crystals composed of a square array of hollow cylinders in an air background is considered. The inclusions are a dielectric elastomer cylindrical actuator, which is made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between

Wen-Pei Yang; Lien-Wen Chen

2008-01-01

54

Inductional Effects in a Halbach Magnet Motion Above Distributed Inductance

NASA Astrophysics Data System (ADS)

We experimented with attempts to levitate a linear (bar) Halbach array of five 1" Nd magnets above a linear inductive track. Next, in order to achieve a control over the relative velocity, we designed a different experiment. In it a large wheel with circumferentially positioned along its rim inducting coils rotates, while the magnet is suspended directly above the rim of the wheel on a force sensor. Faradays Law with the Lenz's Rule is responsible for the lifting and drag forces on the magnet; the horizontal drag force is measured by another force sensor. Approximating the magnet's linear relative motion over inductors with a motion along a large circle, we may use formulas derived earlier in the literature for linear inductive levitation. We measured lift and drag forces as functions of relative velocity of the Halbach magnet and the inductive ``track,'' in an approximate agreement with the existing theory. We then vary the inductance and shape of the inductive elements to find the most beneficial choice for the lift/drag ratio at the lowest relative speed.

Tchatchoua, Yves; Conrow, Ary; Kim, Dong; Morgan, Daniel; Majewski, Walerian; Zafar, Zaeema

2013-03-01

55

Magnetization study of two dimensional helium three

NASA Astrophysics Data System (ADS)

This dissertation discusses a magnetization study of a two dimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of two dimensional 3He on both GTA grafoil and ZYX Graphite substrates. Benefiting from SQUID technology, our NMR experiments were performed at very low applied magnetic field thus avoid the masking of ordering by strong external field. Monolayer 3He films adsorbed on crystalline graphite are considered a nearly ideal example of a two dimensional system of highly correlated fermions. By controlling the 3He areal density, adsorbed films exhibit a wide range of structures with different temperature- dependent magnetic properties and heat capacities. Our recent experiments on two dimensional 3He adsorbed on ZYX graphite focused on the anti-ferromagnetic 4/7 phase and the ferromagnetic incommensurate solid state of a second 3He monolayer. Ferromagnetic order was observed in two dimensional 3He films on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar field plays an important role in magnetic ordering in two dimensional spin systems. The dipole-dipole interaction leads to a frequency shift of the NMR absorption line. The resulting 3He NMR lineshape on Grafoil was a broad peak shifted towards lower frequency with a background from the randomly oriented regions extending to positive frequencies. Compared to Grafoil, ZYX graphite has a much greater structural coherence and is more highly oriented. When studying magnetism of 3He films on ZYX substrate we found that the features we observed in our original Grafoil experiment were much more pronounced on ZYX graphite. In addition, we observed some multi-peak structure on the 3He NMR lineshape, which suggest a series of spin wave resonances. We also studied the magnetic properties of the second layer of 3He films on ZYX substrate at density around 4/7 phase. To eliminate the paramagnetic signal of the first layer solid, we pre-plated a 4He layer on the ZYX that serves as a substrate for the 3He layer. In this region of density, the 3He film acts as a quantum antiferromagnet with disordered ground state (Quantum Spin Liquid). Our experimental results are reported and similar work is reviewed.

Guo, Lei

56

Negative refraction of acoustic waves in two-dimensional sonic crystals

Negative refractions of acoustic waves in a two-dimensional (2D) sonic crystal were studied both experimentally and theoretically. By calculating the acoustic band structure and equifrequency surfaces, we theoretically analyzed the acoustic single-beam negative refraction in the first band operating in the ultrasonic regime. A 2D square sonic crystal was constructed with 2.0-mm-diam steel cylinders arranged as square arrays of 2.5mm

Liang Feng; Xiao-Ping Liu; Yan-Bin Chen; Zhi-Peng Huang; Yi-Wei Mao; Yan-Feng Chen; Jian Zi; Yong-Yuan Zhu

2005-01-01

57

Transition to two-dimensionality in magnetohydrodynamic turbulent Taylor-Couette flow.

Transition from a Taylor-Couette turbulent flow to a completely two-dimensional axisymmetric turbulent state is realized numerically by increasing gradually the strength of the azimuthal magnetic field produced by electric current flowing through the axial rod. With the increase of the Hartmann number, the Taylor-vortex-like structures shrink, move closer to the inner cylinder, and turn into unsteady but perfect tori at sufficiently high Hartmann numbers. PMID:24730932

Zhao, Yurong; Tao, Jianjun; Zikanov, Oleg

2014-03-01

58

Transition to two-dimensionality in magnetohydrodynamic turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Transition from a Taylor-Couette turbulent flow to a completely two-dimensional axisymmetric turbulent state is realized numerically by increasing gradually the strength of the azimuthal magnetic field produced by electric current flowing through the axial rod. With the increase of the Hartmann number, the Taylor-vortex-like structures shrink, move closer to the inner cylinder, and turn into unsteady but perfect tori at sufficiently high Hartmann numbers.

Zhao, Yurong; Tao, Jianjun; Zikanov, Oleg

2014-03-01

59

Two-dimensional radiative heat-transfer calculations for nonequilibrium flows

The present study details the inclusion of radiative heat-transfer phenomena in the numerical simulation of reactive hypersonic and atmospheric re-entry flows. Truly two-dimensional algorithms are developed for the radiative source term in the governing equations, whereby the determination of the specific intensity field is obtained by means of a numerical integration over directions of propagation of radiation. The one-dimensional slab approximation is lifted, and the analysis presented allows the determination of the radiative characteristics of the entire flowfield, rather than being limited to the stagnation streamline, thereby providing an accurate assessment of two-dimensional relieving effects in the stagnation region. A few preliminary results are presented for the Mach 47 flow over a cylinder, including a comparison of the two-dimensional algorithm with the one-dimensional approximation and an emission-dominated case. The effects of improving the modeling of radiative heat transfer are demonstrated. 31 refs.

Elbert, G.J.; Cinnella, P. [North Carolina A& T State Univ., Greensboro, NC (United States)

1995-03-01

60

Relaxation-relaxation exchange experiments in porous media with portable Halbach-Magnets.

NASA Astrophysics Data System (ADS)

Mobile NMR became a powerful tool following the development of portable NMR sensors for well logging. By now there are numerous applications of mobile NMR in materials analysis and chemical engineering where, for example, unique information about the structure, morphology and dynamics of polymers is obtained, and new opportunities are provided for geo-physical investigations [1]. In particular, dynamic information can be retrieved by two-dimensional Laplace exchange NMR, where the initial NMR relaxation environment is correlated with the final relaxation environment of molecules migrating from one environment to the other within a so-called NMR mixing time tm [2]. Relaxation-relaxation exchange experiments of water in inorganic porous media were performed at low and moderately inhomogeneous magnetic field with a simple, portable Halbach-Magnet. By conducting NMR transverse relaxation exchange experiments for several mixing times and converting the results to 2D T2 distributions (joint probability densities of transverse relaxation times T2) with the help of the inverse 2D Laplace Transformation (ILT), we obtained characteristic exchange times for different pore sizes. The results of first experiments on soil samples are reported, which reveal information about the complex pore structure of soil and the moisture content. References: 1. B. Blümich, J. Mauler, A. Haber, J. Perlo, E. Danieli, F. Casanova, Mobile NMR for Geo-Physical Analysis and Material Testing, Petroleum Science, xx (2009) xxx - xxx. 2. K. E. Washburn, P.T. Callaghan, Tracking pore to pore exchange using relaxation exchange spectroscopy, Phys. Rev. Lett. 97 (2006) 175502.

Haber, A.; Haber-Pohlmeier, S.; Casanova, F.; Blümich, B.

2009-04-01

61

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

62

Two-dimensional fringe-pattern analysis

Two-dimensional sinusoid fitting and Fourier transform methods of analyzing fringes to determine the wave-front topography are described. The methods are easy to apply because they do not require finding fringe centers and fringe orders. Also, they are accurate. For an active optics experiment in which these techniques have been used, experimental noise exceeds the error resulting from analysis of noise-free

William W. Macy Jr.

1983-01-01

63

Two-dimensional photonic crystal microlasers

The general objective of this presentation is to demonstrate the great potential of two dimensional (2D) Photonic Crystals (PC) based on InP-membranes bonded onto silica on silicon substrates, with a special emphasis on the development of various classes of 2D PC microlasers. The basic building block consists in an InP (and related material) membrane including a 2D PC formed by

Pierre Viktorovitch; Christelle Monat; J. Mouette; Christian Seassal; Xavier Letartre; Pedro Rojo-Romeo; Marine Le Vassor d'Yerville; David Cassagne; Jean-Paul Albert; E. Jalaguier; S. Pocas; B. Aspar

2003-01-01

64

Superdiffusion in two-dimensional Yukawa liquids.

Superdiffusion of two-dimensional (2D) liquids was studied using an equilibrium molecular dynamics simulation. At intermediate temperatures, the mean-squared displacement, probability distribution function (PDF), and velocity autocorrelation function (VACF) all indicate superdiffusion; the VACF has a long-time tail; and the PDF indicates no Lévy flights. These effects are predicted to occur in 2D dusty plasmas and other 2D liquids that can be modeled with a long-range repulsive potential. PMID:17358266

Liu, Bin; Goree, J

2007-01-01

65

The unramified two-dimensional Langlands correspondence

NASA Astrophysics Data System (ADS)

We describe the unramified Langlands correspondence for two-dimensional local fields and construct a categorical analogue of the unramified principal series representation and study its properties. The main tool for this description is the construction of a certain central extension. For this and other central extensions, we prove non-commutative reciprocity laws (that is, splitting of the central extensions over certain subgroups) for arithmetic surfaces and projective surfaces over finite fields. These reciprocity laws connect central extensions constructed locally and globally.

Osipov, D. V.

2013-08-01

66

Diamagnetism of quasi-two-dimensional graphites

The temperature dependence of the diamagnetic susceptibility of quasi-two-dimensional graphites is studied in the temperature interval 4.2-1000 K. At low temperatures, the large diamagnetic susceptibility, in comparison with the exponentially small value predicted by current theories, is attributable to the effect of scattering of electrons by the structural defects on the smearing of the energy spectrum near a conic singularity. 8 references.

Kotosonov, A.S.

1986-01-01

67

Two-dimensional orthogonal complete complementary codes

Two families of two-dimensional orthogonal complete complementary codes (2D-OCCC) are presented They can be constructed, for example, over binary or complex symbols. The new 2D-OCCC retain most of the properties of the 1D-OCCC. The autocorrelation function is equal to zero for all nonzero shifts in both dimensions of any signature selected from the code. The cross-correlation for any pair of

P. Farkas; M. Turcsany

2003-01-01

68

Statistical Mechanics of Two-dimensional Foams

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

69

Two-dimensional structured illumination microscopy.

In widefield fluorescence microscopy, images from all but very flat samples suffer from fluorescence emission from layers above or below the focal plane of the objective lens. Structured illumination microscopy provides an elegant approach to eliminate this unwanted image contribution. To this end a line grid is projected onto the sample and phase images are taken at different positions of the line grid. Using suitable algorithms 'quasi-confocal images' can be derived from a given number of such phase-images. Here, we present an alternative structured illumination microscopy approach, which employs two-dimensional patterns instead of a one-dimensional one. While in one-dimensional structured illumination microscopy the patterns are shifted orthogonally to the pattern orientation, in our two-dimensional approach it is shifted at a single, pattern-dependent angle, yet it already achieves an isotropic power spectral density with this unidirectional shift, which otherwise would require a combination of pattern-shift and -rotation. Moreover, our two-dimensional approach also yields a better signal-to-noise ratio in the evaluated image. PMID:25113075

Schropp, M; Uhl, R

2014-10-01

70

NASA Astrophysics Data System (ADS)

Flow past a spinning circular cylinder placed in a uniform stream is investigated via two-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and free-stream speed of the flow is 200. The non-dimensional rotation rate, [alpha] (ratio of the surface speed and freestream speed), is varied between 0 and 5. The time integration of the flow equations is carried out for very large dimensionless time. Vortex shedding is observed for [alpha] < 1.91. For higher rotation rates the flow achieves a steady state except for 4.34 < [alpha] < 4:70 where the flow is unstable again. In the second region of instability, only one-sided vortex shedding takes place. To ascertain the instability of flow as a function of [alpha] a stabilized finite element formulation is proposed to carry out a global, non-parallel stability analysis of the two-dimensional steady-state flow for small disturbances. The formulation and its implementation are validated by predicting the Hopf bifurcation for flow past a non-rotating cylinder. The results from the stability analysis for the rotating cylinder are in very good agreement with those from direct numerical simulations. For large rotation rates, very large lift coefficients can be obtained via the Magnus effect. However, the power requirement for rotating the cylinder increases rapidly with rotation rate.

Mittal, Sanjay; Kumar, Bhaskar

2003-02-01

71

The eddy current, Joule heat and input electrical power of a permanent magnet type eddy current heater based on cylindrical Halbach arrays to reduce the viscosity of crude oil in oil wells were analysed and studied by means of a three-dimensional finite-element method. The results show that when Halbach arrays generate a 0.9 T sinusoidal static field and the annulus

L. Z. Zhao; Y. Peng; C. W. Sha; R. Li; Y. Y. Xu

2010-01-01

72

A method is proposed for measuring either the solidliquid contact angle or the liquid surface tension. The method applies the geometrical instability of a liquid meniscus. When a circular cylinder as a test solid is horizontally immersed into a liquid bath and lifted up gradually, a pair of two-dimensional meniscuses is formed under the side wall. At a certain critical

Kenji Katoh; Yu Tsao; Masayoshi Yamamoto; Tsuneo Azuma; Hideomi Fujita

1998-01-01

73

Two-Dimensional Synthetic-Aperture Radiometer

NASA Technical Reports Server (NTRS)

A two-dimensional synthetic-aperture radiometer, now undergoing development, serves as a test bed for demonstrating the potential of aperture synthesis for remote sensing of the Earth, particularly for measuring spatial distributions of soil moisture and ocean-surface salinity. The goal is to use the technology for remote sensing aboard a spacecraft in orbit, but the basic principles of design and operation are applicable to remote sensing from aboard an aircraft, and the prototype of the system under development is designed for operation aboard an aircraft. In aperture synthesis, one utilizes several small antennas in combination with a signal processing in order to obtain resolution that otherwise would require the use of an antenna with a larger aperture (and, hence, potentially more difficult to deploy in space). The principle upon which this system is based is similar to that of Earth-rotation aperture synthesis employed in radio astronomy. In this technology the coherent products (correlations) of signals from pairs of antennas are obtained at different antenna-pair spacings (baselines). The correlation for each baseline yields a sample point in a Fourier transform of the brightness-temperature map of the scene. An image of the scene itself is then reconstructed by inverting the sampled transform. The predecessor of the present two-dimensional synthetic-aperture radiometer is a one-dimensional one, named the Electrically Scanned Thinned Array Radiometer (ESTAR). Operating in the L band, the ESTAR employs aperture synthesis in the cross-track dimension only, while using a conventional antenna for resolution in the along-track dimension. The two-dimensional instrument also operates in the L band to be precise, at a frequency of 1.413 GHz in the frequency band restricted for passive use (no transmission) only. The L band was chosen because (1) the L band represents the long-wavelength end of the remote- sensing spectrum, where the problem of achieving adequate spatial resolution is most critical and (2) imaging airborne instruments that operate in this wavelength range and have adequate spatial resolution are difficult to build and will be needed in future experiments to validate approaches for remote sensing of soil moisture and ocean salinity. The two-dimensional instrument includes a rectangular array of patch antennas arranged in the form of a cross. The ESTAR uses analog correlation for one dimension, whereas the two-dimensional instrument uses digital correlation. In two dimensions, many more correlation pairs are needed and low-power digital correlators suitable for application in spaceborne remote sensing will help enable this technology. The two-dimensional instrument is dual-polarized and, with modification, capable of operating in a polarimetric mode. A flight test of the instrument took place in June 2003 and it participated in soil moisture experiments during the summers of 2003 and 2004.

LeVine, David M.

2010-01-01

74

Bubbles in sheared two-dimensional foams

Oscillatory shear on two-dimensional monodisperse liquid foams was performed. We show that the effect of the oscillatory shear is to cause the migration of bubbles which size is greater than that of a typical bubble of the foam. These so-called flaws move towards the periphery of the foam in a non random motion, thus realizing size segregation in a system which is by construction gravity insensitive. We also show that elongated cavities in the foam could be relaxed towards a more isotropic form with oscillatory shear, and we discuss the pertinent parameters of this relaxation.

C. Quilliet; M. A. P. Idiart; B. Dollet; L. Berthier; A. Yekini

2005-02-18

75

Two-dimensional Clustering for Text Categorization

We propose a new method to improve the accuracy of Text Categorization using twodimensional clustering. In a number of previous probabilistic approaches, texts in the same category are implicitly assumed to be generated from an identical distribution. We empirically show that this assumption is not accurate, and propose a new framework based on twodimensional clustering to alleviate this problem. In our method, training texts are clustered so that the assumption is more likely to be true, and at the same time, features are also clustered in order to tackle the data sparseness problem. We conduct some experiments to validate the proposed two-dimensional clustering method.

Hiroya Takamura; Yuji Matsumoto

2002-01-01

76

Two-dimensional Hubbard-Holstein model

NASA Astrophysics Data System (ADS)

The interplay of electron-phonon coupling and strong electronic correlations is studied in the frame of the two-dimensional Hubbard-Holstein model. Static and dynamic properties are determined by quantum Monte Carlo simulations and by Migdal-Eliashberg theory. The comparison allows us to assess the diagrammatic approach. The competition between the phonon-mediated electron-electron attraction and the local Coulomb repulsion leads to a rich phase diagram, which we study in detail for a wide range of parameters. We address the question, to which extent the systems can be described by an effective negative-U Hubbard model.

Berger, E.; Valáek, P.; von der Linden, W.

1995-08-01

77

Two-Dimensional Low-Turbulence Tunnel

NASA Technical Reports Server (NTRS)

Construction of the wood frame for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

1938-01-01

78

Two-Dimensional Low-Turbulence Tunnel

NASA Technical Reports Server (NTRS)

Construction of the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

1937-01-01

79

Two-Dimensional Low-Turbulence Tunnel

NASA Technical Reports Server (NTRS)

Manometer for the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

1938-01-01

80

Graphene: the new two-dimensional nanomaterial.

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties. PMID:19784976

Rao, C N R; Sood, A K; Subrahmanyam, K S; Govindaraj, A

2009-01-01

81

Breathers in Two-Dimensional Neural Media

NASA Astrophysics Data System (ADS)

In this Letter we show how nontrivial forms of spatially localized oscillations or breathers can occur in two-dimensional excitable neural media with short-range excitation and long-range inhibition. The basic dynamical mechanism involves a Hopf bifurcation of a stationary pulse solution in the presence of a spatially localized input. Such an input could arise from external stimuli or reflect changes in the excitability of local populations of neurons as a precursor for epileptiform activity. The resulting dynamical instability breaks the underlying radial symmetry of the stationary pulse, leading to the formation of a nonradially symmetric breather. The number of breathing lobes is consistent with the order of the dominant unstable Fourier mode associated with perturbations of the stationary pulse boundary

Folias, S. E.; Bressloff, P. C.

2005-11-01

82

Two dimensional nanomaterials for flexible supercapacitors.

Flexible supercapacitors, as one of most promising emerging energy storage devices, are of great interest owing to their high power density with great mechanical compliance, making them very suitable as power back-ups for future stretchable electronics. Two-dimensional (2D) nanomaterials, including the quasi-2D graphene and inorganic graphene-like materials (IGMs), have been greatly explored to providing huge potential for the development of flexible supercapacitors with higher electrochemical performance. This review article is devoted to recent progresses in engineering 2D nanomaterials for flexible supercapacitors, which survey the evolution of electrode materials, recent developments in 2D nanomaterials and their hybrid nanostructures with regulated electrical properties, and the new planar configurations of flexible supercapacitors. Furthermore, a brief discussion on future directions, challenges and opportunities in this fascinating area is also provided. PMID:24614864

Peng, Xu; Peng, Lele; Wu, Changzheng; Xie, Yi

2014-05-21

83

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

84

Two-dimensional structure of slow shocks

NASA Technical Reports Server (NTRS)

The two-dimensional (2-D) structure of switch-off slow magnetosonic shocks is investigated using an electromagnetic hybrid (fluid electrons, kinetic ions) code. It is shown that the basic physical processes occurring at 1-D slow shocks are also operative in 2-D. Specifically, the interaction between the upstream ions and those streaming away from the shock results in the excitation of Alfven/ions-cyclotron (AIC) waves. Depending on the plasma parameters, these waves may either stay in the upstream or convect back into the shock resulting in a non-steady shock behavior which prevents the formation of a trailing wave train. Despite this similarity, some slow shocks which are steady in 1-D are found to be non-steady in 2-D. Fourier analysis of the waves downstream of non-steady shocks identifies them as AIC, demonstrating that the waves remain on the same branch as they convect from upstream into the downstream region.

Omidi, N.; Johnson, M.; Krauss-Varban, D.; Karimabadi, H.

1995-01-01

85

Localization of two-dimensional quantum walks

NASA Astrophysics Data System (ADS)

The Grover walk, which is related to Grovers search algorithm on a quantum computer, is one of the typical discrete time quantum walks. However, a localization of the two-dimensional Grover walk starting from a fixed point is strikingly different from other types of quantum walks. The present paper explains the reason why the walker who moves according to the degree-four Grover operator can remain at the starting point with a high probability. It is shown that the key factor for the localization is due to the degeneration of eigenvalues of the time evolution operator. In fact, the global time evolution of the quantum walk on a large lattice is mainly determined by the degree of degeneration. The dependence of the localization on the initial state is also considered by calculating the wave function analytically.

Inui, Norio; Konishi, Yoshinao; Konno, Norio

2004-05-01

86

Two-dimensional horn imaging arrays (abstract)

NASA Astrophysics Data System (ADS)

A two-dimensional horn imaging array has been demonstrated at 242 and 93 GHz. In this configuration, a dipole is suspended in a pyramidal horn, fabricated by an anisotropic chemical etch technique, on a 1-?m silicon-oxynitride membrane. This approach leaves room for low-frequency lines and processing electronics. Pattern measurements on a 1.45-? imaging array agree well with theory, show no sidelobes, and a 3-dB beamwidth of 35° and 46° for the E and H planes, respectively. Application areas include a superconducting tunnel-junction receiver for radio astronomy and imaging arrays for real-time electron density mapping in fusion plasmas. Support for this project was provided by DOE contract DE-FG03-86-ER-53225 (subcontracted from U.C.L.A.).

Rebeiz, Gabriel M.; Guo, Yong; Stimson, P. A.; Rutledge, David B.; Kasilingan, Dayalan P.

1988-08-01

87

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

88

Two-dimensional nuclear magnetic resonance petrophysics.

Two-dimensional nuclear magnetic resonance (2D NMR) opens a wide area for exploration in petrophysics and has significant impact to petroleum logging technology. When there are multiple fluids with different diffusion coefficients saturated in a porous medium, this information can be extracted and clearly delineated from CPMG measurements of such a system either using regular pulsing sequences or modified two window sequences. The 2D NMR plot with independent variables of T2 relaxation time and diffusion coefficient allows clear separation of oil and water signals in the rocks. This 2D concept can be extended to general studies of fluid-saturated porous media involving other combinations of two or more independent variables, such as chemical shift and T1/T2 relaxation time (reflecting pore size), proton population and diffusion contrast, etc. PMID:15833623

Sun, Boqin; Dunn, Keh-Jim

2005-02-01

89

Two-dimensional Gel Electrophoresis (2DE)

NASA Astrophysics Data System (ADS)

The chemical compounds, which are present in the environment, increasingly cause bad effects on health. The most serious effects are tumors and various mutations at the cellular level. Such compounds, from the analytical point of view, can serve the function of biomarkers, constituting measurable changes in the organism's cells and biochemical processes occurring therein. The challenge of the twenty-first century is therefore searching for effective and reliable methods of identification of biomarkers as well as understanding bodily functions, which occur in living organisms at the molecular level. The irreplaceable tool for these examinations is proteomics, which includes both quality and quantity analysis of proteins composition, and also makes it possible to learn their functions and expressions. The success of proteomics examinations lies in the usage of innovative analytical techniques, such as electromigration technique, two-dimensional electrophoresis in polyacrylamide gel (2D PAGE), liquid chromatography, together with high resolution mass spectrometry and bio-informatical data analysis. Proteomics joins together a number of techniques used for analysis of hundreds or thousands of proteins. Its main task is not the examination of proteins inside the particular tissue but searching for the differences in the proteins' profile between bad and healthy tissues. These differences can tell us a lot regarding the cause of the sickness as well as its consequences. For instance, using the proteomics analysis it is possible to find relatively fast new biomarkers of tumor diseases, which in the future will be used for both screening and foreseeing the course of illness. In this chapter we focus on two-dimensional electrophoresis because as it seems, it may be of enormous importance when searching for biomarkers of cancer diseases.

K?odzi?ska, Ewa; Buszewski, Bogus?aw

90

Two-dimensional stability of ion-acoustic solitons

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

91

Two-dimensional QCD is a string theory

The partition function of two-dimensional QCD on a Riemann surface of area A is expanded as a power series in 1\\/N and A. It is shown that the coefficients of this expansion are precisely determined by a sum over maps from a two-dimensional surface onto the two-dimensional target space. Thus two-dimensional QCD has a simple interpretation as a closed string

David J. Gross; Washington Taylor

1993-01-01

92

Two-dimensional surface emitting photonic crystal laser with hybrid

modeling and an experimental investigation of two-dimensional photonic crystal microlasers: defect stateTwo-dimensional surface emitting photonic crystal laser with hybrid triangular-graphite structure at room temperature. A two-dimensional photonic crystal lattice conformed in a hybrid triangular- graphite

93

Implementations of two-dimensional liquid chromatography

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

94

Tunable filtering and demultiplexing in phononic crystals with hollow cylinders Y. Pennec,1,2

Tunable filtering and demultiplexing in phononic crystals with hollow cylinders Y. Pennec,1,2 B composed of a row of hollow cylinders in a two-dimensional 2D phononic crystal made of filled steel. By selectively filling the cylinders with water or mercury we have created an active device that permits

Deymier, Pierre

95

Convective heat transfer around a triangular cylinder in an air cross flow

Two dimensional laminar forced convection heat transfer around horizontal triangular cylinder in air is investigated numerically. Equilateral triangular cylinder of different side dimensions and configurations are examined under laminar conditions (Re?200). Two configurations of the triangular cylinders are considered; one when the vertex of the triangle facing the flow and the other when the base of the triangle facing the

O. Zeitoun; Mohamed Ali; A. Nuhait

2011-01-01

96

An atlas of two-dimensional materials.

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

97

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 ą5% are achieved. It was shown that the detector, whose efficiency is about 60% for 9 Ĺ 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

98

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

99

Two-dimensional boron monolayer sheets.

Boron, a nearest-neighbor of carbon, is possibly the second element that can possess free-standing flat monolayer structures, evidenced by recent successful synthesis of single-walled and multiwalled boron nanotubes (MWBNTs). From an extensive structural search using the first-principles particle-swarm optimization (PSO) global algorithm, two boron monolayers (?(1)- and ?(1)-sheet) are predicted to be the most stable ?- and ?-types of boron sheets, respectively. Both boron sheets possess greater cohesive energies than the state-of-the-art two-dimensional boron structures (by more than 60 meV/atom based on density functional theory calculation using PBE0 hybrid functional), that is, the ?-sheet previously predicted by Tang and Ismail-Beigi and the g(1/8)- and g(2/15)-sheets (both belonging to the ?-type) recently reported by Yakobson and co-workers. Moreover, the PBE0 calculation predicts that the ?-sheet is a semiconductor, while the ?(1)-, ?(1)-, g(1/8)-, and g(2/15)-sheets are all metals. When two ?(1) monolayers are stacked on top each other, the bilayer ?(1)-sheet remains flat with an optimal interlayer distance of ~3.62 Ĺ, which is close to the measured interlayer distance (~3.2 Ĺ) in MWBNTs. PMID:22816319

Wu, Xiaojun; Dai, Jun; Zhao, Yu; Zhuo, Zhiwen; Yang, Jinlong; Zeng, Xiao Cheng

2012-08-28

100

Order Parameters for Two-Dimensional Networks

NASA Astrophysics Data System (ADS)

We derive methods that explain how to quantify the amount of order in ``ordered'' and ``highly ordered'' porous arrays. Ordered arrays from bee honeycomb and several from the general field of nanoscience are compared. Accurate measures of the order in porous arrays are made using the discrete pair distribution function (PDF) and the Debye-Waller Factor (DWF) from 2-D discrete Fourier transforms calculated from the real-space data using MATLAB routines. An order parameter, OP3, is defined from the PDF to evaluate the total order in a given array such that an ideal network has the value of 1. When we compare PDFs of man-made arrays with that of our honeycomb we find OP3=0.399 for the honeycomb and OP3=0.572 for man's best hexagonal array. The DWF also scales with this order parameter with the least disorder from a computer-generated hexagonal array and the most disorder from a random array. An ideal hexagonal array normalizes a two-dimensional Fourier transform from which a Debye-Waller parameter is derived which describes the disorder in the arrays. An order parameter S, defined by the DWF, takes values from [0, 1] and for the analyzed man-made array is 0.90, while for the honeycomb it is 0.65. This presentation describes methods to quantify the order found in these arrays.

Kaatz, Forrest; Bultheel, Adhemar; Egami, Takeshi

2007-10-01

101

Convergence of two-dimensional Fourier series

), then the two-dimensional Fourier series equivalent to f(x, y) is Co CO Co Co f(x, y) = L' L' A sin(nx) sin (my) + Z Z B sin(@x)cos(my) n=l m=1 n=l m=1 1 CG Co co + ? F, B sin(nx) + Z Z C cos (nx) sin(my) + ? Z C sin(my) 2 1 n, o n, m 2 I OIm Co Co OO... 1 + g P D cos(nx)cos(my)+ ? Z D cos(nx) ? g D cos(my) n, m 2 1 n 0 2 o, m + ? D 1 4 o, o where A 1 n, m ? w B 1 n, m 2 w B 1 n, o 2 w C 1 n, m 2 w (w, w) f(x, y) sin (nx) sin(my) d(x, y) (-w, -w) (w, w) f(x, y) sin (nx) cos...

Kidd, Robert Henry, III

2012-06-07

102

Laminar free convection over two-dimensional bodies with uniform surface heat flux

NASA Technical Reports Server (NTRS)

A general analysis is presented of the steady nondissipative constant-property laminar boundary layer flow over a two-dimensional body of uniform surface heat flux situated in an infinite ambient fluid of undisturbed temperature. The analysis is then applied to a long horizontal circular cylinder. Numerical solutions to the universal functions associated with the first two terms in the derived series are given for Prandtl numbers 0.7, 1, 3, 5, 7, and 10. The results are compared with those obtained by Koh (1964) whose method is patterned after the Blasius-Frossling procedure for forced convection flow. The study reveals that Wilks' (1972) analysis concerning the external natural convection about two-dimensional bodies with constant heat flux is in error.

Lin, F. N.

1976-01-01

103

Structural parameter optimization design for Halbach permanent maglev rail

NASA Astrophysics Data System (ADS)

Maglev rail is an important part of the magnetic levitation launch system. Reducing the manufacturing cost of magnetic levitation rail is the key problem for the development of magnetic levitation launch system. The Halbach permanent array has an advantage that the fundamental spatial field is cancelled on one side of the array while the field on the other side is enhanced. So this array used in the design of high temperature superconducting permanent maglev rail could improve the surface magnetic field and the levitation force. In order to make the best use of Nd-Fe-B (NdFeB) material and reduce the cost of maglev rail, the effect of the rails structural parameters on levitation force and the utilization rate of NdFeB material are analyzed. The optimal ranges of these structural parameters are obtained. The mutual impact of these parameters is also discussed. The optimization method of these structure parameters is proposed at the end of this paper.

Guo, F.; Tang, Y.; Ren, L.; Li, J.

2010-11-01

104

Computed Flow around an Oscillating Circular Cylinder

NASA Astrophysics Data System (ADS)

The oscillation of a circular cylinder in a uniform flow is not only one of the basic subjects of fluid dynamics, but is also a very important problem in fluids engineering. In the present paper, the cross-flow and in-line vibrations of a two-dimensional circular cylinder were studied numerically. Both the forced and free vibrations were examined. Vortex shedding became synchronized with the forced cross-flow vibration at a frequency close to that of the Strouhal number of a stationary cylinder. With forced in-line vibration, vortex shedding began to synchronize with the frequency and also one half that of a circular cylinder at a higher vibration rate. With free vibration, the cross-flow vibration was excited when the natural frequency of the cylinder was near the stationary Strouhal number, and in-line vibration was observed near the natural frequency at around twice the stationary Strouhal number.

Asano, Hiroyoshi; Morishita, Etsuo

105

Shear-wave band gaps tuned in two-dimensional phononic crystals with magnetorheological material

NASA Astrophysics Data System (ADS)

The shear-wave (S-wave) band structure of a two-dimensional phononic crystals (PCs) was studied. The PCs consist of lead cylinders in a magnetorheological elastomer matrix with square lattice. Numerical results showed that S-wave band gaps can be obtained and tuned as frequency-selective filters by application of an external contactless magnetic field. This magnetic field can be rotated or possesses a variable magnitude. These approaches can be potentially applied in the design of S-wave band gap-tunable devices.

Xu, Zhenlong; Wu, Fugen; Guo, Zhongning

2013-01-01

106

NASA Astrophysics Data System (ADS)

Spontaneous Raman Scattering was used for quantitative, two-dimensional, single-shot measurements of species concentration in optically accessible confinements and in an experimental single-cylinder internal combustion engine. The study comprised three parts. In the first part, the technique was used for methane concentration measurements in a laminar jet issuing into compressed nitrogen (10 bar, 293 K). The injection Reynolds number was 550. Initial results showed unexpected structures in the acquired concentration profiles. Thus, the steadiness of the laminar flow was confirmed with high speed shadowgraph movies and laser induced fluorescence measurements. Eventually, it was proven that the structures were due to characteristics of the camera system. A technique was then devised for the proper acquisition and processing of data and spatial resolution of 500 mum was achieved. Methane number density equal to 12% of the number density of pure methane (0.247E+26 molecules/msp3) was then measured with a signal-to-noise ratio of approximately 3. The measurements were compared with the results of direct numerical simulation of the flow field. In the second part, measurements in a laminar hydrogen jet were taken. Because of the reduced Raman signal of hydrogen, the incident laser power was increased by installing the pressurized chamber within the laser cavity. This yielded an increase in power by a factor of 2.5. For the measurement of the laser sheet intensity in the laser cavity, insertion of a fluorescent dye cell and Rayleigh scattering were used and evaluated comparatively. The precise location of the waist of the laser sheet was determined by trial and error. The spatial resolution of the measurements was 650 mum and a number density of 0.371E+26 hydrogen molecules/msp3 was measured with a signal-to-noise ratio of 3. The measurements were again compared with results of direct numerical simulation. In the third part, the feasibility of two-dimensional single-shot Spontaneous Raman measurements in an engine cylinder was established. Measurements of methane concentration after direct injection in the cylinder of an experimental single-cylinder engine were taken. The engine was not fired to avoid laser induced incandescence interference. The spatial resolution was limited to 800 mum by the thickness of the laser sheet. Fast mixing of the methane jet was documented but a precise evaluation of the equivalence ratio was beyond the resolution of this first attempt. Finally, existing hardware for data acquisition and algorithms for two dimensional data reduction were reviewed and recommendations were made for the extraction of quantitative information from two-dimensional, single-shot Spontaneous Raman signals which are weak and noisy.

Kyritsis, Dimitrios Constantinou

107

Two-dimensional dense gas dynamics

NASA Astrophysics Data System (ADS)

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 equations for supersonic steady flow fields and mixed subsonic and supersonic transient flow fields. Two non- ideal gas models are incorporated into the numerical scheme in order to simulate dense gas effects. The van der Waals model, which is the simplest gas model that will show dense gas behavior, is employed to economically demonstrate qualitative trends in dense gas flows. The more complex Martin-Hou model is incorporated for cases where quantitative accuracy becomes more important. Simulated flows over simple geometries such as wedges, arcs, ramps, and steps using both the van der Waals gas model and the perfect gas model demonstrate significant differences in wave field configurations between dense gases and ideal gases. Results are also computed using the Martin-Hou equation of state which is more conservative in predicting dense gas effects than the van der Waals model. In addition to exploring the basic nature of dense gas flows for simple geometries, the utilization of dense gas properties to improve the efficiency of organic Rankine- cycle engines is investigated. Simulations of supersonic dense gas flows through impulse turbine cascades demonstrate improvements in flow quality through the cascades by reducing losses due to shock waves.

Brown, Brady Polk

108

On the stability of rimming flows to two-dimensional disturbances

NASA Astrophysics Data System (ADS)

It is well known that a variety of qualitatively different flows is realisable when a horizontal cylinder containing a small amount of highly viscous liquid is rotated about its axis at constant speed. A mathematical model first proposed by Moffatt and based on lubrication analysis has proved very fertile ground for basing the study of these flows. In this study we develop, using kinetic-wave theory, the two-dimensional stability results of Benjamin et al. reported in an unpublished paper and bring new insights into this now-classical problem. Moreover, we find fascinating new results by extending the class of flows to incorporate the effects of constant traction at the free surface of the liquid film. In particular, we describe a novel weak solution where the stable surface profile contains a shock at any location around the cylinder.

Villegas-Díaz, M.; Power, H.; Riley, D. S.

2003-07-01

109

NASA Astrophysics Data System (ADS)

The characteristics of the permanent magnets composing the guideway in superconducting magnetic levitation devices are very important for their performance in terms of levitation force and stability. From a model based on minimizing the magnetic energy in the superconductor and considering realistic parameters of actual maglev devices, we calculate the levitation and guidance forces and stability arising from both conventional arrangements and recently proposed Halbach-like arrangements. When a comparison is carefully made under similar conditions, we conclude that not always complicated arrangements based on Halbach arrays bring significant improvements with respect to some simpler arrangements that also provide large force. These results may help improving the design of actual maglev devices.

Del-Valle, Nuria; Sanchez, Alvaro; Navau, Carles; Chen, Du-Xing

2011-01-01

110

Two dimensional electron gas at oxide interfaces

NASA Astrophysics Data System (ADS)

Extraordinary phenomena can occur at the interface between two oxide materials. A spectacular example is a formation of a two-dimensional electron gas (2DEG) at the SrTiO3/LaAlO3 interface. In this dissertation the properties of the 2DEG are investigated from first principles. The spatial extent of the 2DEG formed at the SrTiO3/LaAlO 3 n-type interface is studied. It is shown that the confinement of the 2DEG is controlled by metal induced gap states formed in the band gap of SrTiO 3. The confinement width is then determined by the attenuation length of the metal induced gap states into SrTiO3 which is governed by the lowest decay rate evanescent states of bulk SrTiO3 which in turn can be found from the complex band structure of bulk SrTiO3. Magnetic properties of the 2DEG formed at the n-type interface of the SrTiO3/LaAlO3 superlattices are investigated. It is found that for a thin SrTiO3 film the interface is ferromagnetic but for a thicker SrTiO3 film the magnetic moment decreases and eventually disappears. This is a result of delocalization of the 2DEG that spreads over thicker SrTiO3 film which leads to violation of the Stoner criterion. Further, it is shown that inclusion of the Hubbard U interaction enhances the Stoner parameter and stabilizes the magnetism. The effect of the 2DEG and the polar interfaces for the thin film ferroelectricity is investigated using both first principles and model calculations. Using a TiO2-terminated BaTiO3 film with LaO monolayers at the two interfaces it is shown that the intrinsic electric field produced by the polar interface forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO 3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. It is found that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric.

Janicka, Karolina

111

Path integration in two-dimensional topological quantum field theory

NASA Astrophysics Data System (ADS)

A positive, diffeomorphism-invariant generalized measure on the space of metrics of a two-dimensional smooth manifold is constructed. We use the term generalized measure analogously with the generalized measures of Ashtekar and Lewandowski and of Baez. A family of actions is presented which, when integrated against this measure gives the two-dimensional axiomatic topological quantum field theories, or TQFTs, in terms of which Durhuus and Jonsson decompose every two-dimensional unitary TQFT as a direct sum.

Sawin, Stephen

1995-11-01

112

On two-dimensional adaptive channel estimation in OFDM systems

In orthogonal frequency division multiplexing (OFDM) systems, two-dimensional (both time and frequency) minimum mean square error (2D-MMSE) channel estimation is optimum. However, accurate channel statistics are required to realize it, which are often unavailable in practice. In contrast, two-dimensional adaptive channel estimation based on a two-dimensional least mean square (2D-LMS) algorithm does not require any channel statistics, and at the

Xiaolin Hou; Shubo Li; Danpu Liu; Changchuan Yin; Guangxin Yue

2004-01-01

113

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles

Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at a depth

A. Sarwar; A. Nemirovski; B. Shapiro

114

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

115

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

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

116

An asymmetric pair of vortices adjacent to a spinning cylinder

NASA Astrophysics Data System (ADS)

The two-dimensional flow field over a spinning circular cylinder is analyzed using an extension of the Foeppl method. Equilibrium equations for two asymmetric point vortices in the wake of the cylinder are solved for a case when both vortices are equidistant from the cylinder. The two Foeppl solutions for the cylinder are presented. It is observed that the spin does not affect the angle between the two vortices; however, it displaces the vortex pair in the spin direction and the sinus of the displacement angle is proportional to the spin rate.

Iosilevskii, G.; Seginer, A.

117

Information technologies for comprehensive two-dimensional gas chromatography

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 Ă?-dimensional gas chromatography; GCĂ?GC; Information technology; Image processing; Visualization; Computer

Reichenbach, Stephen E.

118

Completeness through Flatness in Two-Dimensional Temporal Logic

] 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

119

Two-dimensional equations for electroelastic plates under biasing fields

Two-dimensional equations for piezoelectric plates have been very effective in modeling piezoelectric resonators. To predict the behavior of resonators under environmental effects like temperature change or acceleration, the theory of incremental motions in an electroelastic body under biasing fields is necessary. Existing two-dimensional equations for electroelastic plates under biasing fields employ various simplifying assumptions. For example, electroelastic couplings are often

Y. T. Hu; Q. Jiang; J. S. Yang; X. Zhang

2001-01-01

120

Multilinear Constraints in Two-dimensional Vision and Isogonal Conjugacy

problem in three-dimensional vision is the analysis of object shape and camera motion from images: The structure and motion problem for two-dimensional calibrated vision. Fig. 2.A: Three images or setsMultilinear Constraints in Two-dimensional Vision and Isogonal Conjugacy Kalle AÂ° stroÂ¨m Dept

Lunds Universitet

121

q Discretization of the two-dimensional Toda equations

q-Discrete versions of the two-dimensional Toda molecule equation and the two-dimensional Toda lattice equation are proposed through the direct method. The Bäcklund transformation and the Lax pair of the former are obtained. Moreover, the reduction to theq-discrete cylindrical Toda equations is also discussed.

K. Kajiwara; Ya. Ohta; J. Satsuma

1994-01-01

122

Solution of the two-dimensional spectral factorization problem

NASA Technical Reports Server (NTRS)

An approximation theorem is proven which solves a classic problem in two-dimensional (2-D) filter theory. The theorem shows that any continuous two-dimensional spectrum can be uniformly approximated by the squared modulus of a recursively stable finite trigonometric polynomial supported on a nonsymmetric half-plane.

Lawton, W. M.

1985-01-01

123

Beginning Introductory Physics with Two-Dimensional Motion

ERIC Educational Resources Information Center

During the session on "Introductory College Physics Textbooks" at the 2007 Summer Meeting of the AAPT, there was a brief discussion about whether introductory physics should begin with one-dimensional motion or two-dimensional motion. Here we present the case that by starting with two-dimensional motion, we are able to introduce a considerable

Huggins, Elisha

2009-01-01

124

TWO-DIMENSIONAL NMR SIGNAL ANALYSIS WITH AN ADAPTED SUBBAND

: This paper presents a methodology allowing to estimate the parameters of two-dimensional damped frequency estimator based on the Prony model. At each node resulting from the decomposition, a stopping rule. [2002]). In this paper, we consider the problem of estimat- ing the parameters of two-dimensional NMR

Boyer, Edmond

125

A two-dimensional technique for frequency-wavenumber estimation

A simple two-dimensional technique for frequency-wavenumber estimation is presented which is a direct extension of a previously proposed one-dimensional frequency estimation technique. The proposed method is computationally efficient and is shown to be superior to the two-dimensional Fourier transform method in resolving signals closely spaced in frequency and wavenumber.

R. Kumaresan; D. W. Tufts

1981-01-01

126

Casimir forces between cylinders and plates

NASA Astrophysics Data System (ADS)

We study collective interaction effects that result from the change of free quantum electrodynamic field fluctuations by one- and two-dimensional perfect metal structures. The Casimir interactions in geometries containing plates and cylinders is explicitly computed using partial wave expansions of constrained path integrals. We generalize previously obtained results and provide a more detailed description of the technical aspects of the approach. We find that the interactions involving cylinders have a weak logarithmic dependence on the cylinder radius, reflecting that one-dimensional perturbations are marginally relevant in 4D space time. For geometries containing two cylinders and one or two plates, we confirm a previously found nonmonotonic dependence of the interaction on the objects separations which does not follow from pairwise summation of two-body forces. Qualitatively, this effect is explained in terms of fluctuating charges and currents and their mirror images.

Rahi, Sahand Jamal; Emig, Thorsten; Jaffe, Robert L.; Kardar, Mehran

2008-07-01

127

Hydroelastic wave diffraction by a vertical cylinder.

A linear three-dimensional problem of hydroelastic wave diffraction by a bottom-mounted circular cylinder is analysed. The fluid is of finite depth and is covered by an ice sheet, which is clamped to the cylinder surface. The ice stretches from the cylinder to infinity in all lateral directions. The hydroelastic behaviour of the ice sheet is described by linear elastic plate theory, and the fluid flow by a potential flow model. The two-dimensional incident wave is regular and has small amplitude. An analytical solution of the coupled problem of hydroelasticity is found by using a Weber transform. We determine the ice deflection and the vertical and horizontal forces acting on the cylinder and analyse the strain in the ice sheet caused by the incident wave. PMID:21690136

Brocklehurst, Paul; Korobkin, Alexander; P?r?u, Emilian I

2011-07-28

128

As a prelude of three-dimensional modeling of a submarine, an analysis of degaussing of a two-dimensional magnetic cylinder is presented in this paper. The cylinder is of infinite length and may be of arbitrary cross section. As the first step of determining the degaussing current needed for minimizing the magnetic field of the cylinder, a free surface current is assumed

X. B. Xu; L. Zeng

1998-01-01

129

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

130

Spin and valley noise in two-dimensional Dirac materials.

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. PMID:25105640

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

2014-07-25

131

Dynamics of two-dimensional and quasi-two-dimensional polymers.

The dynamic properties of dense two-dimensional (2D) polymer melts are studied using discontinuous molecular dynamics simulations. Both strictly 2D and quasi-2D systems are investigated. The strictly 2D model system consists of a fluid of freely jointed tangent hard disc chains. The translational diffusion coefficient, D, is strongly system size dependent with D ? ln?L where L is the linear dimension of the square simulation cell. The rotational correlation time, ?rot, is, however, independent of system size. The dynamics is consistent with Rouse behavior with D?ln?L ? N(-1) and ?rot ? N(2) for all area fractions. Analysis of the intermediate scattering function, Fs(k, t), shows that the dynamics becomes slow for N = 256 and the area fraction of 0.454 and that there might be a glass transition for long polymers at sufficiently high area fractions. The polymer mobility is not correlated with the conformation of the molecules. In the quasi-2D system hard sphere chains are confined between corrugated surfaces so that chains cannot go over each other or into the surfaces. The conformational properties are identical to the 2D case, but D and ?rot are independent of system size. The scaling of D and ?rot with N is similar to that of strictly 2D systems. The simulations suggest that 2D polymers are never entangled and follow Rouse dynamics at all densities. PMID:23802982

Sung, Bong June; Yethiraj, Arun

2013-06-21

132

Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy

NASA Astrophysics Data System (ADS)

The dephasing of the Fermi edge singularity excitations in two modulation doped single quantum wells of 12 nm and 18 nm thickness and in-well carrier concentration of 4 × 1011 cm-2 was carefully measured using spectrally resolved four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. Although the absorption at the Fermi edge is broad at this doping level, the spectrally resolved FWM shows narrow resonances. Two peaks are observed separated by the heavy hole/light hole energy splitting. Temperature dependent "rephasing" (S1) 2DFT spectra show a rapid linear increase of the homogeneous linewidth with temperature. The dephasing rate increases faster with temperature in the narrower 12 nm quantum well, likely due to an increased carrier-phonon scattering rate. The S1 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations. Distinct 2DFT lineshapes were observed for co-linear and cross-linear polarizations, suggesting the existence of polarization dependent contributions. The "two-quantum coherence" (S3) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations.

Paul, J.; Dey, P.; Tokumoto, T.; Reno, J. L.; Hilton, D. J.; Karaiskaj, D.

2014-10-01

133

Dynamics of two-dimensional and quasi-two-dimensional polymers

NASA Astrophysics Data System (ADS)

The dynamic properties of dense two-dimensional (2D) polymer melts are studied using discontinuous molecular dynamics simulations. Both strictly 2D and quasi-2D systems are investigated. The strictly 2D model system consists of a fluid of freely jointed tangent hard disc chains. The translational diffusion coefficient, D, is strongly system size dependent with D ln L where L is the linear dimension of the square simulation cell. The rotational correlation time, ?rot, is, however, independent of system size. The dynamics is consistent with Rouse behavior with D/ln L N-1 and ?rot N2 for all area fractions. Analysis of the intermediate scattering function, Fs(k, t), shows that the dynamics becomes slow for N = 256 and the area fraction of 0.454 and that there might be a glass transition for long polymers at sufficiently high area fractions. The polymer mobility is not correlated with the conformation of the molecules. In the quasi-2D system hard sphere chains are confined between corrugated surfaces so that chains cannot go over each other or into the surfaces. The conformational properties are identical to the 2D case, but D and ?rot are independent of system size. The scaling of D and ?rot with N is similar to that of strictly 2D systems. The simulations suggest that 2D polymers are never entangled and follow Rouse dynamics at all densities.

Sung, Bong June; Yethiraj, Arun

2013-06-01

134

Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy.

The dephasing of the Fermi edge singularity excitations in two modulation doped single quantum wells of 12 nm and 18 nm thickness and in-well carrier concentration of ?4 × 10(11) cm(-2) was carefully measured using spectrally resolved four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. Although the absorption at the Fermi edge is broad at this doping level, the spectrally resolved FWM shows narrow resonances. Two peaks are observed separated by the heavy hole/light hole energy splitting. Temperature dependent "rephasing" (S1) 2DFT spectra show a rapid linear increase of the homogeneous linewidth with temperature. The dephasing rate increases faster with temperature in the narrower 12 nm quantum well, likely due to an increased carrier-phonon scattering rate. The S1 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations. Distinct 2DFT lineshapes were observed for co-linear and cross-linear polarizations, suggesting the existence of polarization dependent contributions. The "two-quantum coherence" (S3) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations. PMID:25296819

Paul, J; Dey, P; Tokumoto, T; Reno, J L; Hilton, D J; Karaiskaj, D

2014-10-01

135

Two-Dimensional Bulk Acoustic Wave Correlator-Convolver.

National Technical Information Service (NTIS)

The present invention concerns an extension of data processing concepts and apparatus. For a most important application of these concepts, i.e., performance of two-dimensional correlations and convolutions, it has heretofore been necessary to have two com...

B. A. Auld

1983-01-01

136

A CLASS OF OPTIMAL TWO-DIMENSIONAL MULTIMATERIAL CONDUCTING LAMINATES

A CLASS OF OPTIMAL TWO-DIMENSIONAL MULTIMATERIAL CONDUCTING LAMINATES NATHAN ALBIN1, ANDREJ, polyconvexity, rank-one convexity, multiwell variational problem . 1 #12;2 N. ALBIN, A. CHERKAEV, AND V. NESI

Cherkaev, Andrej

137

Performance Analysis of Metamaterials With Two-dimensional Isotropy

A two-dimensional isotropic metamaterials formed by crossed split-ring resonators (CSRRs) are studied in this paper. The effective characteristic parameters of this media are determined by quasi-static Lorentz theory. The ...

Yao, Hai-Ying

138

Two-Dimensional Inlet Simulation Using a Diagonal Implicit Algorithm.

National Technical Information Service (NTIS)

A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. T...

D. S. Chaussee, T. H. Pulliam

1981-01-01

139

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

140

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

141

Single particle spectrum of the two dimensional electron gas

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

142

Dynamics of spin vortices in two-dimensional planar magnets

We investigate the dynamics of a dilute gas of free spin vortices in a two-dimensional planar magnet. An equation of motion for the spin vortex is presented and compared with the corresponding equation for a vortex in a superfluid film. Exploiting a similar analogy with the dynamics of a two-dimensional plasma in a perpendicular magnetic field we calculate the mean-square

D. L. Huber

1982-01-01

143

Dynamics of Vortices in Two-Dimensional Magnets

Theories, simulations and experiments on vortex dynamics in quasi-two-dimensional magnetic materials are reviewed. These materials can be modelled by the classical two-dimensional anisotropic Heisenberg model with XY (easy-plane) symmetry. There are two types of vortices, characterized by their polarization (a second topological charge in addition to the vorticity): Planar vortices have Newtonian dynamics (even-order equations of motion) and exhibit strong

Franz G. Mertens; Alan R. Bishop

2000-01-01

144

Dynamics of Vortices in Two-Dimensional Magnets

Theories, simulations and experiments on vortex dynamics in quasi-two-dimensional magnetic materials are reviewed. These materials\\u000a can be modelled by the classical two-dimensional anisotropic Heisenberg model with XY (easy-plane) symmetry. There are two types of vortices, characterized by their polarization (a second topological charge\\u000a in addition to the vorticity): Planar vortices have Newtonian dynamics (evenorder equations of motion) and exhibit strong

Franz G. Mertens; Alan R. Bishop

145

Light evolution in arbitrary two-dimensional waveguide arrays

We introduce an analytical formula for the dynamics of light propagation in a two-dimensional waveguide lattice including diagonal coupling. A superposition of infinite arrays created by imaginary sources is used to derive an expression for boundary reflections. It is shown analytically that for large propagation distances the propagating field reaches uniformity. Furthermore, periodic field recovery is studied and discrete anomalous refraction and diffraction are investigated in arbitrary two-dimensional lattices.

Szameit, Alexander; Pertsch, Thomas; Dreisow, Felix; Nolte, Stefan; Tuennermann, Andreas; Peschel, Ulf; Lederer, Falk [Institute of Applied Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Institute of Optics, Information and Photonics, Friedrich-Alexander-University Erlangen-Nuremberg, G.-Scharowsky-Strasse 1, 91058 Erlangen (Germany); Institute for Condensed Matter Theory and Optics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena (Germany)

2007-05-15

146

Diagnosis of left ventricular thrombi by two-dimensional echocardiography.

Sixteen patients had two-dimensional echocardiographic diagnosis of the presence or absence of left ventricular thrombi and anatomical, radiological, or clinical confirmation of the diagnosis. Eleven patients had positive diagnoses, which were confirmed in 10 and possibly incorrect in one. Five other records were reviewed because the patients had undergone aneurysmectomy after two-dimensional echocardiograms: three were true negative and two were false negative studies. Images PMID:508446

Meltzer, R S; Guthaner, D; Rakowski, H; Popp, R L; Martin, R P

1979-01-01

147

Two-Dimensional Systolic Array For Kalman-Filter Computing

NASA Technical Reports Server (NTRS)

Two-dimensional, systolic-array, parallel data processor performs Kalman filtering in real time. Algorithm rearranged to be Faddeev algorithm for generalized signal processing. Algorithm mapped onto very-large-scale integrated-circuit (VLSI) chip in two-dimensional, regular, simple, expandable array of concurrent processing cells. Processor does matrix/vector-based algebraic computations. Applications include adaptive control of robots, remote manipulators and flexible structures and processing radar signals to track targets.

Chang, Jaw John; Yeh, Hen-Geul

1988-01-01

148

Ground ring of two-dimensional string theory

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

149

Two-dimensional QCD as a string theory

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

150

Dynamics of supersonic two-dimensional plasma jets

A high-speed photographic recording device has been used to investigate divergence and reflection by a wall of a two-dimensional impulse plasma jet within a closed gas-filled cylindrical container. It is shown that in an electric discharge source, a two-dimensional jet is formed by a number of individual streams. The gas-dynamic structure of the individual plasma streams is examined. Plasma temperature

V. N. Fedorishchev; A. G. Gridnev

1982-01-01

151

Two-dimensional impurity profiling with emission computed tomography techniques

A technique for the determination of two-dimensional impurity profiles in silicon using methods for emission computed tomography is presented. Several one-dimensional impurity profiles obtained for different directions through the sample are used to reconstruct the two-dimensional profile. A simulation study of the experiment is described, and effects of various experimental and reconstruction parameters are discussed. Reconstructions of an area of

Scott H. Goodwin-johansson; Ravi Subrahmanyan; Carey E. Floyd; Hisham Z. Massoud

1989-01-01

152

Nicked-sleeve interface for two-dimensional capillary electrophoresis

We report an improved interface for two-dimensional capillary electrophoresis. This interface is based on capillary tubing and a Plexiglas chip, both of which were milled using a micro-dicing saw. The interface was evaluated and compared to a traditional interface design for both pseudo one-dimensional and two-dimensional capillary electrophoresis. We observe less than 70% transfer efficiency for the traditional design and greater than 90% transfer efficiency with this new interface. PMID:23702824

Flaherty, Ryan J.; Huge, Bonnie J.; Bruce, Spencer M.; Dada, Oluwatosin O.; Dovichi, Norman J.

2013-01-01

153

A Synchronization Problem in Two-Dimensional Cellular Automata

NASA Astrophysics Data System (ADS)

The firing squad synchronization problem on cellular automata has been studied extensively for more than forty years, and a rich variety of synchronization algorithms have been proposed so far. In the present paper, we give a survey on recent developments in firing squad synchronization algorithms for large-scale two-dimensional cellular automata. Several state-efficient implementations of the two-dimensional synchronization algorithms are given.

Umeo, Hiroshi

154

Two dimensional properties of methane adsorbed on porous silicon

TWO DIMENSIONAL PROPERTIES OF METHANE ADSORBED ON POROUS SILICON A Thesis by RICHARD FRANKLIN TENNIS Submitted to the Office of Graduate Studies of Texas ASM University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE May 1989 Major Subject: Physics TWO DIMENSIONAL PROPERTIES OF METHANE ADSORBED ON POROUS SILICON A Thesis by RICHARD FRANKLIN TENNIS Approved as to style and content by: P. Kirk (C ir of Committee) Glenn olet (M er) Da J. Ernst...

Tennis, Richard Franklin

2012-06-07

155

Three superintegrable two-dimensional oscillators: Superintegrability, nonlinearity, and curvature

The superintegrability of three different two-dimensional oscillators is studied: (i) a nonlinear oscillator dependent on a parameter {lambda} (two-dimensional version of the oscillator of Lakshmanan and Mathews), (ii) a nonlinear oscillator related to the Riccati equation, and (iii) the standard harmonic oscillator on constant curvature spaces. They can be considered as nonlinear deformations, or curvature-dependent versions, of the linear harmonic oscillator.

Carinena, J. F., E-mail: jfc@unizar.es; Ranada, M. F. [Universidad de Zaragoza, Departamento de Fisica Teorica, Facultad de Ciencias (Spain)], E-mail: mfran@unizar.es; Santander, M. [Universidad de Valladolid, Departamento de Fisica Teorica, Facultad de Ciencias (Spain)], E-mail: msn@fta.uva.es

2007-03-15

156

Statistical Mechanics of Two-Dimensional Vortices and Stellar Systems

The formation of large-scale vortices is an intriguing phenomenon in two-dimensional turbulence. Such organization is observed\\u000a in large-scale oceanic or atmospheric flows, and can be reproduced in laboratory experiments and numerical simulations. A\\u000a general explanation of this organization was first proposed by Onsager (1949) by considering the statistical mechanics for\\u000a a set of point vortices in two-dimensional hydrodynamics. Similarly, the

Pierre-Henri Chavanis

2002-01-01

157

Terahertz demonstrations of effectively two-dimensional photonic bandgap structures

by the 160 m lat- tice constant, the 65 m diameter, and the dielectric constant of the cylinders waveguides (PPWG). The 2D-PBG structures consisting of square arrays of dielectric cylinders were characterized by THz time- domain spectroscopy (THz-TDS). THz photonic bandgaps were observed, as determined

158

Enhancement of polarizabilities of cylinders with cylinder-slab resonances

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 pro...

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

2014-01-01

159

Magnetomechanics of internal-dipole, Halbach-array motor\\/generators

The magnetomechanical behavior of internal-dipole, Halbach-type magnet arrays is analyzed for application as a motor\\/generator (M\\/G) with an energy-storage flywheel that is suspended by low-stiffness bearings. Scaling laws for the maximization of torque are derived as a function of geometry. The optimal geometry is relatively insensitive to gap and stator design and occurs approximately at a ratio of inner to

John R. Hull; Larry R. Turner

2000-01-01

160

A low-field, low-cost Halbach magnet array for open-access NMR

NASA Astrophysics Data System (ADS)

A working prototype of a novel low-cost Halbach-array-based NMR system is described. The new design provides open access to the sample relative to conventional NMR magnet designs and this facilitates the simultaneous use of multi-sensor techniques on the same sample, in which NMR/MRI can potentially be combined with other spectroscopies such as impedance spectroscopy, laser scattering and rheological experiments.

Hills, B. P.; Wright, K. M.; Gillies, D. G.

2005-08-01

161

A comprehensive two-dimensional (2D) retention time alignment algorithm was developed using a novel indexing scheme. The algorithm is termed comprehensive because it functions to correct the entire chromatogram in both dimensions and it preserves the separation information in both dimensions. Although the algorithm is demonstrated by correcting comprehensive two-dimensional gas chromatography (GC x GC) data, the algorithm is designed to

Karisa M. Pierce; Lianna F. Wood; Bob W. Wright; Robert E. Synovec

2005-01-01

162

Halbach array type focusing actuator for small and thin optical data storage device

NASA Astrophysics Data System (ADS)

The small form factor optical data storage devices are developing rapidly nowadays. Since it is designed for portable and compatibility with flesh memory, its components such as disk, head, focusing actuator, and spindle motor should be assembled within 5 mm. The thickness of focusing actuator is within 2 mm and the total working range is +/-100um, with the resolution of less than 1?m. Since the thickness is limited tightly, it is hard to place the yoke that closes the magnetic circuit and hard to make strong flux density without yoke. Therefore, Halbach array is adopted to increase the magnetic flux of one side without yoke. The proposed Halbach array type focusing actuator has the advantage of thin actuation structure with sacrificing less flex density than conventional magnetic array. The optical head unit is moved on the swing arm type tracking actuator. Focusing coil is attached to swing arm, and Halbach magnet array is positioned at the bottom of deck along the tracking line, and focusing actuator exerts force by the Fleming's left hand rule. The dynamics, working range, control resolution of focusing actuator are analyzed and performed.

Lee, Sung Q.; Park, Kang-Ho; Paek, Mun Chul

2004-09-01

163

Magnetic nanoparticles for therapy and diagnosis are at the leading edge of the rapidly developing field of bionanotechnology. In this study, we have theoretically studied motion of magnetic nano- as well as micro-particles in the field of cylindrical Halbach array of permanent magnets. Magnetic flux density was modeled as magnetostatic problem by finite element method and particle motion was described using system of ordinary differential equations--Newton law. Computations were done for nanoparticles Nanomag-D with radius 65 nm, which are often used in magnetic drug targeting, as well as microparticles DynaBeads-M280 with radius 1.4 microm, which can be used for magnetic separation. Analyzing snapshots of trajectories of hundred magnetite particles of each size in the water as well as in the air, we have found that optimally designed magnetic circuits of permanent magnets in quadrupolar Halbach array have substantially shorter capture time than simple blocks of permanent magnets commonly used in experiments, therefore, such a Halbach array may be useful as a potential source of magnetic field for magnetic separation and targeting of magnetic nanoparticles as well as microparticles for delivery of drugs, genes, and cells in various biomedical applications. PMID:20517710

Babinec, Peter; Krafcík, Andrej; Babincová, Melánia; Rosenecker, Joseph

2010-08-01

164

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

Tunable two-dimensional photonic crystal couplers made of dielectric elastomer inclusions.

We propose a tunable directional coupler based on a two-dimensional photonic crystal made of dielectric elastomer rods embedded in air background. In the interaction region, the inclusions are a dielectric elastomer cylindrical actuator made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between the compliant electrodes, the radial strain of the silicon-made actuator and the coupling characteristics of the photonic crystal coupler are investigated. The coupling length of the photonic crystal coupler depends on the voltage applied between the electrodes, which is analyzed by the plane wave expansion method. Due to the radial strain of the dielectric elastomer under external voltage, the tunable photonic crystal coupler is realized. Numerical simulations obtained by the finite-difference time-domain method confirmed the feasibility of the tunable photonic crystal coupler. PMID:20563196

Wang, Chun-Chih; Chen, Lien-Wen

2010-06-20

166

Evanescent modes in out-of-plane band structure for two-dimensional photonic crystals.

Reflection, diffraction and transmission of optical waves at the interface between a photonic crystal and the surrounding air can be described by propagating and evanescent Bloch modes. We have found such modes for one of the canonical two-dimensional photonic crystals, identical circular cylinders in a square pattern. We present computed out-of-plane band diagrams for propagating as well as evanescent modes, obtained with a numerical method based on Fourier-Bessel expansions. For a given frequency, all the modes are evanescent, except for a few low-order propagating modes. We find that most of the evanescent modes have a purely imaginary z-component of the Bloch wave vector, but many of the modes have a complex z-component. PMID:19399093

Blad, Jakob; Sudbř, Aasmund S

2009-04-27

167

NASA Astrophysics Data System (ADS)

The presence of extreme material properties and undesired scattering make practical implementation of transformation optics based cloaks an extremely challenging issue. To overcome these problems, a simplified quadratic cloak has been proposed which provides finite material properties at the inner radius of the cloak and impedance match with the free space at the outer radius of the cloak simultaneously. The simultaneous occurrence of finite material properties and impedance match with the free space at the respective boundaries reduces the scattering cross section significantly. The material properties of the proposed simplified quadratic cloak can be realized with two dimensional (2D) metamaterials. The performance of the proposed cloak is examined by plotting the normalized total scattering cross section (SCSt,norm), and the scattering patterns in azimuthal plane. The proposed simplified quadratic cloak shows 10 dB reduction of the scattered field in both the forward and backward directions with respect to the perfect electric conductor (PEC) cylinder.

Rajput, Archana; Srivastava, Kumar Vaibhav

2014-09-01

168

This paper presents an investigation of a technique for using two-dimensional bodies composed of simple polygons with a body decoupled uniform Cmtesian grid in the Direct Simulation Monte Carlo method (DSMC). The method employs an automated grid pre-processing scheme beginning form a CAD geometry definition file, and is based on polygon triangulation using a trapezoid algorithm. A particle-body intersection time comparison is presented between the Icarus DSMC code using a body-fitted structured grid and using a structured body-decoupled Cartesian grid with both linear and logarithmic search techniques. A comparison of neutral flow over a cylinder is presented using the structured body fitted grid and the Cartesian body de-coupled grid.

OTAHAL,THOMAS J.; GALLIS,MICHAIL A.; BARTEL,TIMOTHY J.

2000-06-27

169

For an optimal design of degaussing system of a submarine, a thorough understanding of magnetization of a submarine in the earth's magnetic field is required. As a prelude of three-dimensional modeling of a submarine, in this paper is presented an analysis of magnetization of a two-dimensional magnetizable cylinder placed in the earth's magnetic field. The cylinder is of infinite length

X. B. Xu; L. Zeng

1998-01-01

170

An efficient numerical method is developed for computing the transmission and reflection spectra of finite two-dimensional photonic crystals composed of circular cylinders in a triangular lattice. Our method manipulates a pair of operators defined on a set of curves and it remains effective when the radius of the cylinders is larger than ? 3\\/4 of the lattice constant a

Yumao Wu; Ya Yan Lu

2008-01-01

171

Chaotic Rotation of a Towed Elliptical Cylinder

In this paper I consider the self-excited rotation of an elliptical cylinder towed through a viscous fluid as a canonical model of nonlinear fluid structure interactions with possible applications in the design of sensors and energy extraction devices. Remarkably, it is shown that this system demonstrates chaotic trajectories with only one structural degree of freedom in a two-dimensional laminar flow. First, this self-excited system is shown to be analogous to the forced bistable oscillators studied in classic chaos theory. Next, fully coupled computational fluid dynamics simulations of the motion of the cylinder demonstrate limit cycle, period doubling, intermittently chaotic, and fully chaotic dynamics as the distance between the pivot and the centroid is varied. The viscous wake behind the cylinder is presented for the limit cycle cases and new types of stable wakes are characterized. The wake in the chaotic case demonstrates a strong history effect, with a variety of wake types possible for a given struc...

Weymouth, G D

2013-01-01

172

Accurate analysis of electromagnetic scattering from periodic circular cylinder array with defects.

This paper considers the two-dimensional electromagnetic scattering from periodic array of circular cylinders in which some cylinders are removed, and presents a formulation based on the recursive transition-matrix algorithm (RTMA). The RTMA was originally developed as an accurate approach to the scattering problem of a finite number of cylinders, and an approach to the problem of periodic cylinder array was then developed with the help of the lattice sums technique. This paper introduces the concept of the pseudo-periodic Fourier transform to the RTMA with the lattice sums technique, and proposes a spectral-domain approach to the problem of periodic cylinder array with defects. PMID:22565690

Watanabe, Koki; Nakatake, Yoshimasa; Pitora, Jaromír

2012-05-01

173

Scale-by-scale turbulent energy budget in the intermediate wake of two-dimensional generators

NASA Astrophysics Data System (ADS)

It is first established, on the basis of new X-wire measurements, that the equilibrium similarity of the terms in the scale-by-scale (s-b-s) budget of the turbulent energy overline{q^2} is reasonably well approximated on the axis of the intermediate wake of a circular cylinder. The similarity, which scales on the Taylor microscale ? and overline{q^2}, is then used to determine s-b-s energy budgets from the data of Antonia, Zhou, and Romano ["Small-scale turbulence characteristics of two-dimensional bluff body wakes," J. Fluid Mech. 459, 67-92 (2002)] for 5 different two-dimensional wake generators. In each case, the budget is reasonably well closed, using the locally isotropic value of the mean energy dissipation rate, except near separations comparable to the wavelength of the coherent motion (CM). The influence of the initial conditions is first felt at a separation Lc identified with the cross-over between the energy transfer and large scale terms of the s-b-s budget. When normalized by overline{q^2} and Lc, the mean energy dissipation rate is found to be independent of the Taylor microscale Reynolds number. The CM enhances the maximum value of the energy transfer, the latter exceeding that predicted from models of decaying homogeneous isotropic turbulence.

Thiesset, F.; Antonia, R. A.; Danaila, L.

2013-11-01

174

Electric field-induced motion of solid particles in two-dimensional fluids

NASA Astrophysics Data System (ADS)

Electric field induced motion of spherical and cylindrical glass particles were studied in a smectic A liquid crystal octyl cyanobiphenyl (8CB) medium. The particles were dispersed in the smectic A medium, sandwiched between to glass plates with conductive inner surfaces. Under DC fields the smectic layers become parallel to the glass substrates. Such configuration corresponds to a two dimensional isotropic fluid structure along the film surface: the motion of solid particles results viscous forces along the substrates, whereas the motion across the layers is opposed by elastic permeation forces. Under DC fields above a threshold instability occurs and the particles move with constant speed in arbitrary directions normal to the electric field. The moving spheres and the cylinders rotate about their symmetry axis along the layers. When air bubbles are present in the film the, spheres tend to stick to the bubbles, and rotate collectively with a field- dependent speed that is independent of the radius of the bubbles (the angular velocity is inversely proportional to the radius). The details of the motion and the underlying physical mechanism will be discussed. The studies may have relevance of understanding particle motions in cell membranes under electric actuations and will contribute to our understanding of the hydrodynamic properties of two-dimensional fluid systems.

Jackli, Antal; Liao, Guangxun; Kelly, Jack R.

2004-03-01

175

Generation of two-dimensional plasmonic bottle beams

NASA Astrophysics Data System (ADS)

By analogy to the three dimensional optical bottle beam, we introduce the plasmonic bottle beam: a two dimensional surface wave which features a lattice of plasmonic bottles, i.e. alternating regions of bright focii surrounded by low intensities. The two-dimensional bottle beam is created by the interference of a non-diffracting beam, a cosine-Gaussian beam, and a plane wave, thus giving rise to a non-diffracting complex intensity distribution. By controlling the propagation constant of the cosine-Gauss beam, the size and number of plasmonic bottles can be engineered. The two dimensional lattice of hot spots formed by this new plasmonic wave could have applications in plasmonic trapping.

Genevet, Patrice; Dellinger, Jean; Blanchard, Romain; She, Alan; Petit, Marlene; Cluzel, Benoit; Kats, Mikhail A.; de Fornel, Frederique; Capasso, Federico

2013-04-01

176

Bifurcation Phenomena in Two-Dimensional Piecewise Smooth Discontinuous Maps

In recent years the theory of border collision bifurcations has been developed for piecewise smooth maps that are continuous across the border, and has been successfully applied to explain nonsmooth bifurcation phenomena in physical systems. However, many switching dynamical systems have been found to yield two-dimensional piecewise smooth maps that are discontinuous across the border. The theory for understanding the bifurcation phenomena in such systems is not available yet. In this paper we present the first approach to the problem of analysing and classifying the bifurcation phenomena in two-dimensional discontinuous maps, based on a piecewise linear approximation in the neighborhood of the border. We explain the bifurcations occurring in the static VAR compensator used in electrical power systems, using the theory developed in this paper. This theory may be applied similarly to other systems that yield two-dimensional discontinuous maps.

Biswambhar Rakshit; Manjul Apratim; Parag Jain; Soumitro Banerjee

2008-09-18

177

Two-dimensional convolute integers for analytical instrumentation

NASA Technical Reports Server (NTRS)

As new analytical instruments and techniques emerge with increased dimensionality, a corresponding need is seen for data processing logic which can appropriately address the data. Two-dimensional measurements reveal enhanced unknown mixture analysis capability as a result of the greater spectral information content over two one-dimensional methods taken separately. It is noted that two-dimensional convolute integers are merely an extension of the work by Savitzky and Golay (1964). It is shown that these low-pass, high-pass and band-pass digital filters are truly two-dimensional and that they can be applied in a manner identical with their one-dimensional counterpart, that is, a weighted nearest-neighbor, moving average with zero phase shifting, convoluted integer (universal number) weighting coefficients.

Edwards, T. R.

1982-01-01

178

Two-dimensional temperature mapping using thermographic phosphors

We have demonstrated the feasibility of extending a point-temperature measurement method to two-dimensional mapping of temperature distributions on surfaces. The point-measurement method used the temperature-dependant characteristics of sharp emission lines from thermographic phosphors to measure temperature. The two-dimensional extrusion uses an ultraviolet light source to illuminate the phosphor-coated surface and a high-grain video camera filtered to select the desired emission line. By changing filters, we acquire video data that are over-laid and analyzed by a video processor, then displayed in contour or pseudocolor maps of the temperature distribution. 13 refs., 14 figs., 1 tabs.

Noel, B.W. (Los Alamos National Lab., NM (USA)); Turley, W.D. (EG and G Energy Measurements, Inc., Goleta, CA (USA)); Cates, M.R.; Tobin, K.W. (Oak Ridge National Lab., TN (USA))

1990-01-01

179

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

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

180

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

181

Equilibrium state of a trapped two-dimensional Bose gas

We study experimentally and numerically the equilibrium density profiles of a trapped two-dimensional {sup 87}Rb Bose gas and investigate the equation of state of the homogeneous system using the local density approximation. We find a clear discrepancy between in situ measurements and quantum Monte Carlo simulations, which we attribute to a nonlinear variation of the optical density of the atomic cloud with its spatial density. However, good agreement between experiment and theory is recovered for the density profiles measured after time of flight, taking advantage of their self-similarity in a two-dimensional expansion.

Rath, Steffen P.; Yefsah, Tarik; Guenter, Kenneth J.; Cheneau, Marc; Desbuquois, Remi; Dalibard, Jean [Laboratoire Kastler Brossel, CNRS, Universite Pierre et Marie Curie, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France); Holzmann, Markus [Laboratoire de Physique Theorique de la Matiere Condensee, CNRS, Universite Pierre et Marie Curie, 4 Place Jussieu, F-75005 Paris, France, and Laboratoire de Physique et Modelisation des Milieux Condenses, CNRS, Universite Joseph Fourier, BP 166, F-38042 Grenoble (France); Krauth, Werner [Laboratoire de Physique Statistique, CNRS, Universite Pierre et Marie Curie, Universite Paris Diderot, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France)

2010-07-15

182

Two-Dimensional Inlet Simulation Using a Diagonal Implicit Algorithm

NASA Technical Reports Server (NTRS)

A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. The modification transforms the coupled system of equations Into an uncoupled diagonal form which requires less computation work. For steady-state applications the resulting diagonal algorithm retains the stability and accuracy characteristics of the original algorithm. Solutions are given for inviscid and laminar flow about a two-dimensional wedge inlet configuration. Comparisons are made between computed results and exact theory.

Chaussee, D.S.; Pulliam, T. H.

1981-01-01

183

Field analysis of two-dimensional focusing grating couplers

NASA Astrophysics Data System (ADS)

A different technique was developed by which several two-dimensional dielectric optical gratings, consisting 100 or more corrugations, were treated in a numerical reliable approach. The numerical examples that were presented were restricted to gratings made up of sequences of waveguide sections symmetric about the x = 0 plane. The newly developed method was effectively used to investigate the field produced by a two-dimensional focusing grating coupler. Focal-region fields were determined for three symmetrical gratings with 19, 50, and 124 corrugations. For focusing grating coupler with limited length, high-frequency intensity variations were noted in the focal region.

Borsboom, P.-P.; Frankena, H. J.

1995-05-01

184

NASA Astrophysics Data System (ADS)

Two-dimensional dielectric photonic crystals (PCs) having periodic air hole cylinders, when designed properly, exhibit near-zero effective refractive index and the wave impedance is dependent on local observation points. The incident wave is mostly reflected at the PC-air interface due to large impedance mismatch. We show, analytically and numerically, that even in the near-zero effective refractive index case the reflection can be suppressed by utilizing an antireflection structure consisting of a PC with the same lattice constant but a different radius for the periodic air hole cylinders. The antireflection PC must be truncated at properly selected cross sections in order to possess the same impedance at cross sections with the host PC and with the air structure. An analytical model combined with the plane-wave expansion method captures the antireflection behavior obtained by the full wave simulations.

Iizuka, Hideo; Engheta, Nader

2014-09-01

185

Two-dimensional gas vortices and twisted gas jets

This paper studies an invariant solution of rank one of the equations of motion of a polytropic gas that describes two-dimensional\\u000a gas vortices and twisted gas jets. Flow types are classified according to the governing parameter: vortices in the form of\\u000a sources and sinks, unlimited expansion, and collapse.

A. P. Chupakhin

2009-01-01

186

Two-dimensional gas vortices and twisted gas jets

This paper studies an invariant solution of rank one of the equations of motion of a polytropic gas that describes two-dimensional gas vortices and twisted gas jets. Flow types are classified according to the governing parameter: vortices in the form of sources and sinks, unlimited expansion, and collapse.

A. P. Chupakhin

2009-01-01

187

Dynamics of vortices in quasi-two-dimensional planar magnets

The dynamics of the vortex gas associated with the Kosterlitz-Thouless transition in quasi-two-dimensional planar magnets is discussed. It is pointed out that there is a central peak in the Fourier transform of the longitudinal spin autocorrelation function whose width is determined by the vortex velocity autocorrelation function and whose intensity is proportional to the density of mobile vortices.

D. L. Huber

1980-01-01

188

Ballistic two-dimensional electrons in a random magnetic field

We report excess longitudinal resistivity of a high-mobility two-dimensional electron gas (2DEG) in a random distribution of submicrometer magnetic-flux tubes (vortices) which are formed at the 2DEG by a superconducting gate layer. The results are explained in terms of small-angle scattering of ballistic electrons by the magnetic-field inhomogeneities.

A. K. Geim; S. J. Bending; I. V. Grigorieva; M. G. Blamire

1994-01-01

189

Ultrafast two-dimensional nuclear magnetic resonance spectroscopy of

.Frydman@weizmann.ac.il Published online: 22 April 2007; doi:10.1038/nphys597 Two-dimensional (2D) NMR is an important tool to NMR techniques, resulting in typical acquisition times for 2D NMR spectra ranging from minutes transient, making it a poor starting point for conventional 2D NMR acquisitions. Here, we show

Loss, Daniel

190

Ultrafast two-dimensional NMR spectroscopy using constant acquisition gradients

and on continuously flowing samples, as well as the utilization of 2D NMR to follow dynamic biophysical and metabolicUltrafast two-dimensional NMR spectroscopy using constant acquisition gradients Yoav Shrot NMR spectroscopy plays an important role in the characterization of molecular structure and dynamics

Frydman, Lucio

191

Two-Dimensional Fourier Transform Applied to 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, but possibly harmonizable. 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 show helicopter noise as harmonizable. 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.

Santa Maria, Odilyn L.

1999-01-01

192

Numerical simulation of two-dimensional nonlinear standing acoustic waves

NASA Astrophysics Data System (ADS)

In this paper the behavior of strongly nonlinear waves in two-dimensional resonators filled with thermoviscous fluid is studied. For this purpose a set of differential equations, written in Lagrangian coordinates, is proposed and a time-domain numerical scheme is developed for solving them. Full nonlinear equations are derived from the conservation laws and state equation by assuming an irrotational fluid. Auxiliary conditions are written by considering a rigid-walled cavity, excitation at some points of the boundary, and rest at the outset. Finite differences are applied in the space and time domains, and lead to an implicit scheme. The numerical model solves the problem in terms of displacement vector field. The pressure field is then obtained from the displacement values. The algorithm allows us to analyze the evolution of the behavior of complex standing waves. The nonlinear characteristics of standing waves, well known in one-dimensional chambers, are now apparent in two-dimensional resonators by means of this new computational model. Some numerical experiments are carried out, a validation of the model is achieved, and results are given at a complex mode for which plane wave approximation is not appropriate. Several aspects of the nonlinear pressure field inside two-dimensional resonators are presented, such as harmonic distortion and nonlinear attenuation effects. In particular the quasi-standing character of such waves is detected and described. The effect of redistribution of rms pressure inside a two-dimensional cavity is commented.

Vanhille, Christian; Campos-Pozuelo, Cleofé

2004-07-01

193

Numerical Modelling of induction heating for two dimensional geometries.

://dmawww.epfl.ch/rappaz.mosaic/index.html 1 #12;(3) The heat source is the Joule power density which is related to through a non linearNumerical 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

Dreyfuss, Pierre

194

Heterogeneous slow dynamics in a two dimensional doped classical antiferromagnet

We introduce a lattice model for a classical doped two dimensional antiferromagnet which has no quenched disorder, yet displays slow dynamics similar to those observed in supercooled liquids. We calculate two-time spatial and spin correlations via Monte Carlo simulations and find that for sufficiently low temperatures, there is anomalous diffusion and stretched-exponential relaxation of spin correlations. The relaxation times associated

Malcolm P. Kennett; Claudio Chamon; Leticia F. Cugliandolo

2005-01-01

195

Critical dynamics in the two-dimensional XY-model

NASA Astrophysics Data System (ADS)

We present the first high resolution spin dynamics simulation of critical dynamics in the classical, two-dimensional XY-model. Using square lattices as large as 204 × 204 with periodic boundaries, we integrate coupled equations of motion and determine the scattering function S( q, ?). At the critical temperature we find a rich structure which is not adequately described by existing theory.

Landau, D. P.; Gerling, R. W.

1992-02-01

196

A maximum likelihood approach to two-dimensional crystals

Maximum likelihood (ML) processing of transmission electron microscopy images of protein particles can produce reconstructions of superior resolution due to a reduced reference bias. We have investigated a ML processing approach to images centered on the unit cells of two-dimensional (2D) crystal images. The implemented software makes use of the predictive lattice node tracking in the MRC software, which is

Xiangyan Zeng; Henning Stahlberg; Nikolaus Grigorieff

2007-01-01

197

Stably Extending Two-Dimensional Bipedal Walking to Three Dimensions

In this paper we develop a feedback control law that results in stable walking gaits on flat ground for a three-dimensional bipedal robotic walker given stable walking gaits for a two-dimensional bipedal robotic walker. This is achieved by combining disparate techniques that have been employed in the bipedal robotic community: controlled symmetries, geometric reduction and hybrid zero dynamics. Controlled symmetries

Aaron D. Ames; Robert D. Gregg

2007-01-01

198

Electronic Control of a Two-Dimensional, Knee-less,

, specifically in the robustness and consistency of an efficient powered walker and the agreement between roboticElectronic Control of a Two- Dimensional, Knee-less, Bipedal Robot Final Report for MAE 490 under Walking Robot successfully demonstrates a stable walking cycle using the same control components

Ruina, Andy L.

199

Stably Extending Two-Dimensional Bipedal Walking to Three Dimensions

on flat ground for a three- dimensional bipedal robotic walker given stable walking gaits for a two-dimensional bipedal robotic walker. This is achieved by combining disparate techniques that have been employed in the bipedal robotic community: controlled symmetries, geomet- ric reduction and hybrid zero dynamics

Ames, Aaron

200

A two-dimensional model for relativistic gas jets

Many extragalactic radio sources contain jets of plasma moving away from a central source at relativistic velocities. A two dimensional, cylindrically symmetric, relativistic hydrodynamics model was created to address the issue of jet stability. A description of the model is presented. The derivation of the relativistic fluid dynamics equations, in both conservative and characteristic forms, with specialization to the two

K. W. Thompson

1985-01-01

201

Shear induced anisotropy in two-dimensional liquids

The behavior of a dense two-dimensional soft disc liquid under shear is studied via nonequilibrium molecular dynamics. The structure factor for the liquid at a given shear rate is evaluated directly by plotting the particle positions, taken at random from the NEMD simulation at that shear, onto photographic film and using light scattering to obtain a diffraction pattern. The pair

H. J. M. Hanley; G. P. Morriss; T. R. Welberry; D. J. Evans

1988-01-01

202

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

203

Comparison of two-dimensional periodic and finite absorber structures

The study of absorber structures and shielding screens remains an important topic in EMC. A general two-dimensional boundary integral equation (BIE) technique has been implemented to handle both finite and periodic absorber structures. The generality of the method is twofold: the geometry of the structure may be chosen arbitrary finite or one-dimensional periodic, and the materials being used are uniaxial

B. Baekelandt; F. Olyslager; D. De Zutter

1995-01-01

204

Research article Real-time two-dimensional asynchronous

two-dimensional control using one subdural electrode was developed. Keywords: Spinal cord injuries palsy, and spinal cord injury.1 The types of signals used to implement BMI systems are as diverse.Marquez@uhn.ca ÂŠ The Academy of Spinal Cord Injury Professionals, Inc. 2012 DOI 10.1179/2045772312Y.0000000043 The Journal

Popovic, Milos R.

205

Self-similar dynamic quasi-two-dimensional sand fronts

We report on a study of advancing quasi-two-dimensional sand fronts on an inclined flat and thin strip confined between two vertical plates. These fronts form when a thin initial stream of sand running down the flat obstacle gets trapped at some distance from the injection point. Right after this trapping, the front starts to advance upstream and grow in time.

J.-F. Boudet; S. Gauthier; Y. Amarouchene; H. Kellay

2003-01-01

206

Plasmonics with Two-Dimensional Conductors Hosang Yoon1

As/AlGaAs heterostructure, two-dimensional electron gas, plasmonics, metamaterials, terahertz. Author for correspondence to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, due, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former

Ham, Donhee

207

An approach to two-dimensional cutting stock problems

One of the resource utilization problems is the location of two-dimensional patterns onto stock sheets with finite dimensions. Stock sheets, in this respect, are depletable resources to be used and the remaining material which is known as the scrap (or trim loss) cannot usually be used later for allocating patterns. Thus, a decrease in the amount of scrap yields a

C?HAN H. DAGLI; M. YALÇIN TATOGLU

1987-01-01

208

Two-Dimensional Bit-Stuffing Schemes with Multiple Transformers

and applied to the class of 2-D (d, ) constraints. Analytical lower bounds on the rate of these encoders were-dimensional (1-D) track model [1]. This approach gives rise to new types of error patterns, constraints and encoding algorithms. Two- dimensional constraints can be defined over different 2-D lattices, depending

Siegel, Paul H.

209

Suzuki phase in two-dimensional sonic crystals

In analogy with the structures discovered by Suzuki in alkali halides, in this article we introduce a two-dimensional acoustic system consisting of a periodic distribution of impurities (vacancies) in a host array. A triangular lattice of cylindrical sound scatterers is chosen as the host. The sonic crystal, called the Suzuki phase, shows extraordinary sound transmission properties: it holds the attenuation

D. Caballero; J. Sánchez-Dehesa; R. Martínez-Sala; C. Rubio; J. V. Sánchez-Pérez; L. Sanchis; F. Meseguer

2001-01-01

210

Two-dimensional nanohybridization of gold nanorods and polystyrene colloids

Two-dimensional nanohybridization of gold nanorods and polystyrene colloids Dong Kee Yi,1 Jin hybrid nanomaterials. The process is demonstrated using 0D polystyrene colloids and 1D Au nanorods-dimensional 2D hexagonally ar- rayed submicron sized polystyrene and silica colloids form regularly ordered

Rogers, John A.

211

Two-dimensional Euler flows in slowly deforming domains

We consider the evolution of an incompressible two-dimensional perfect fluid as the boundary of its domain is deformed in a prescribed fashion. The flow is taken to be initially steady, and the boundary deformation is assumed to be slow compared to the fluid motion. The Eulerian flow is found to remain approximately steady throughout the evolution. At leading order, the

J. Vanneste; D. Wirosoetisno

2008-01-01

212

Fluid Flows Through Two-Dimensional Channels of Composite Materials

The present analysis relates to the study of the full two-dimensional Brinkman equation representing the fluid flow through porous medium. The steady, incompressible fluid flow, with a negligible gravitational force, is constrained to flow in an infinitely long channel in which the height assumes a series of piecewise constant values. The control volume method is used to solve the Brinkman

A. K. Al-Hadhrami; L. Elliott; D. B. Ingham; X. Wen

2001-01-01

213

Two Dimensional Incompressible Ideal Flow Around a Small Obstacle

In this article we study the asymptotic behavior of incompressible, ideal, time-dependent two dimensional flow in the exterior of a single smooth obstacle when the size of the obstacle becomes very small. Our main purpose is to identify the equation satisfied by the limit flow. We will see that the asymptotic behavior depends on ?, the circulation around the obstacle.

D. Iftimie; M. C. Lopes Filho; H. J. Nussenzveig Lopes

2003-01-01

214

Contour Dynamics of Two-Dimensional Incompressible Systems

Studying models of incompressible systems is very important as there are many sytems in dierent areas of physics that may be regarded as incompress- ible. Two particular examples are vortex patches in ideal fluids (1) and two- dimensional electrons systems in the presense of a magnetic eld (2) . Since these systems are incompressible, they are easier to study because

Christina Skowronski; Alan Dorsey; Carlos Wexler

215

Resolution Limits Of A Two Dimensional Antenna Array

NASA Astrophysics Data System (ADS)

We propose two novel algorithms for signal processing of data from a rectangular (two dimensional) antenna array for which the number of complex operations necessary to Implement the algorithms is significantly less than that for the naive extension of the MUSIC algorithm. We present simulation results for both algorithms and discuss these in relation to the information content of the data.

Clarke, Ira J.; de Villiers, Geoffrey D.; Mather, John L.

1986-01-01

216

Compressor noise control with a two-dimensional enclosure

This paper is concerned with the use of a two-dimensional enclosure with masonry block wall to mitigate compressor noise in a northern California location for consistency with city standards. Sensitive receptors consist of a duplex and single residences across the street from the source. Background sound is provided primarily by a nearby highway that is elevated. Noise reduction is accomplished

Ballard W. George

2003-01-01

217

Nonlinear elastic behavior of two-dimensional molybdenum disulfide

NASA Astrophysics Data System (ADS)

This research explores the nonlinear elastic properties of two-dimensional molybdenum disulfide. We derive a thermodynamically rigorous nonlinear elastic constitutive equation and then calculate the nonlinear elastic response of two-dimensional MoS2 with first-principles density functional theory (DFT) calculations. The nonlinear elastic properties are used to predict the behavior of suspended monolayer MoS2 subjected to a spherical indenter load at finite strains in a multiple-length-scale finite element analysis model. The model is validated experimentally by indenting suspended circular MoS2 membranes with an atomic force microscope. We find that the two-dimensional Young's modulus and intrinsic strength of monolayer MoS2 are 130 and 16.5 N/m, respectively. The results approach Griffith's predicted intrinsic strength limit of ?int(E)/(9), where E is the Young's modulus. This study reveals the predictive power of first-principles density functional theory in the derivation of nonlinear elastic properties of two-dimensional MoS2. Furthermore, the study bridges three main gaps that hinder understanding of material properties: DFT to finite element analysis, experimental results to DFT, and the nanoscale to the microscale. In bridging these three gaps, the experimental results validate the DFT calculations and the multiscale constitutive model.

Cooper, Ryan C.; Lee, Changgu; Marianetti, Chris A.; Wei, Xiaoding; Hone, James; Kysar, Jeffrey W.

2013-01-01

218

Infinite conformal symmetry in two-dimensional quantum field theory

We present an mvestlgaUon of the massless, two-dimensional, interacting field theories Their basic property is their invanance under an lnfimte-dlmenslonal group of conformal (analytic) transformations It is shown that the local fields forlmng the operator algebra can be classified according to the irreducible representations of Vtrasoro algebra, and that the correlation functions are bmlt up of the \\

A A Belavin; A M Polyakov; A B Zamolodchikov

1984-01-01

219

Two-dimensional interaction of ion-acoustic solitons

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

220

Symmetry relations of two-dimensional photonic crystal cavity modes

Degeneracy of resonant modes in two-dimensional (2-D) photonic crystal cavities are investigated using the symmetry relations. The 2-D photonic crystal cavity tends to have either a pair of doubly degenerate modes or nondegenerate modes. We de- rive simple relations between degenerate modes without using a rigorous group theory. These relations are useful for classifying the resonant modes into degenerate pairs

Se-Heon Kim; Yong-Hee Lee

2003-01-01

221

Two-dimensional temperature estimation using diagnostic ultrasound

A two-dimensional temperature estimation method was developed based on the detection of shifts in echo location of backscattered ultrasound from a region of tissue undergoing thermal therapy. The echo shifts are due to the combination of the local temperature dependence of speed of sound and thermal expansion in the heated region. A linear relationship between these shifts and the underlying

Claudio Simon; Philip VanBaren; Emad S. Ebbini

1998-01-01

222

Two-dimensional Yukawa liquids: structure and collective excitations

NASA Astrophysics Data System (ADS)

The paper reports molecular dynamics (MD) simulations on two-dimensional, strongly-coulped Yukawa liquids. An effective coupling coefficient ?* for the liquid phase is identified; thermodynamic properties such as internal energy, pressure and compressibility, as well as longitudinal and transverse mode dispersions are analysed.

Hartmann, P.; Kalman, G. J.; Donkó, Z.

2006-04-01

223

Two-Dimensional Grids About Airfoils and Other Shapes

NASA Technical Reports Server (NTRS)

GRAPE computer program generates two-dimensional finite-difference grids about airfoils and other shapes by use of Poisson differential equation. GRAPE can be used with any boundary shape, even one specified by tabulated points and including limited number of sharp corners. Numerically stable and computationally fast, GRAPE provides aerodynamic analyst with efficient and consistant means of grid generation.

Sorenson, R.

1982-01-01

224

Two-dimensional materials with Dirac cones: Graphynes containing heteroatoms

NASA Astrophysics Data System (ADS)

Two graphynes, 6(H2),14,18 graphyne and 6BN,6,12 graphyne, that contain the heteroatoms hydrogen or boron and nitrogen, respectively, are shown to feature Dirac points in their band structure according to first-principles electronic structure calculations. This shows that the existence of Dirac points in the band structure of two-dimensional materials is neither restricted to graphene nor to other two-dimensional all-carbon materials. 6(H2),14,18 graphyne and 6BN,6,12 graphyne belong to the rectangular two-dimensional space groups pmm and pm, respectively, and thus exhibit completely different symmetries than graphene. 6BN,6,12 graphyne features a Dirac cone with a band gap originating from an avoided crossing of its valence and conduction band at the Dirac point due to missing reflection symmetry. The examples of 6(H2),14,18 graphyne and 6BN,6,12 graphyne suggest that a wealth of two-dimensional materials with various chemical compositions and with electronic properties equally amazing as those of graphene is awaiting discovery.

Malko, Daniel; Neiss, Christian; Görling, Andreas

2012-07-01

225

Spinvalley phase diagram of the two-dimensional metalinsulator transition

temperature dependence (d/dT > 0) of the resistivity, , in low-disorder, dilute 2DESs in Si metalÂ oxide temperatures in low-disorder, dilute, two-dimensional (2D) carrier systems is of considerable interest of freedom, namely the valley polarization. Using symmetry-breaking strain together with an in-plane magnetic

Loss, Daniel

226

Two-dimensional dilaton gravity coupled to massless spinors

NASA Astrophysics Data System (ADS)

We derive exact solutions of two-dimensional dilaton gravity coupled to massless spinors for some particular choices of the dilatonic potential. For constant dilatonic potential the model turns out to be completely solvable and the general solution is found. For linear and exponential dilatonic potentials we present the class of exact solutions with a Killing vector.

Cavagliŕ, Marco; Fatibene, Lorenzo; Francaviglia, Mauro

1998-11-01

227

Two-dimensional dilaton gravity coupled to massless spinors

We derive exact solutions of two-dimensional dilaton gravity coupled to massless spinors for some particular choices of the dilatonic potential. For constant dilatonic potential the model turns out to be completely solvable and the general solution is found. For linear and exponential dilatonic potentials we present the class of exact solutions with a Killing vector.

Marco Cavagliŕ; Lorenzo Fatibene; Mauro Francaviglia

1998-01-01

228

Optical implementability of the two-dimensional Quantum Walk

We propose an optical cavity implementation of the two-dimensional coined quantum walk on the line. The implementation makes use of only classical resources, and is tunable in the sense that a large number of different unitary transformations can be implemented by tuning some parameters of the device.

Eugenio Roldan; J. C. Soriano

2005-03-07

229

Towards a two dimensional lattice gas with dynamical geometry

We report on simulations using a lattice gas automaton in which the lattice is replaced by a triangulation of an arbitrary two-dimensional manifold. If the manifold is 2D Euclidean space the particles move on the Kagome lattice. We report results of simulations of channel flow for the flat space model and of simulations in which the particle state can change

Anna Klales; Donato Cianci; Zachary Needell; Peter Love

2009-01-01

230

Comprehensive two-dimensional chromatography in food analysis

Comprehensive two-dimensional (2D) chromatographic techniques can be considered innovative methods, only quite recently developed. Since their introduction to the chromatographic community, these techniques have been used in several fields and have gained an excellent reputation as valuable and powerful analytical tools. The revolutionary aspect of comprehensive multidimensional (MD) techniques, in respect to classical MD chromatography, is that the entire sample

Peter Quinto Tranchida; Paola Dugo; Giovanni Dugo; Luigi Mondello

2004-01-01

231

Two-dimensional optimization of free-electron-laser designs

Off-axis, two-dimensional designs for free electron lasers are described that maintain correspondence of a light beam with a synchronous electron at an optimal transverse radius r > 0 to achieve increased beam trapping efficiency and enhanced laser beam wavefront control so as to decrease optical beam diffraction and other deleterious effects.

Prosnitz, D.; Haas, R.A.

1982-05-04

232

Two-dimensional optimization of free electron laser designs

Off-axis, two-dimensional designs for free electron lasers that maintain correspondence of a light beam with a "synchronous electron" at an optimal transverse radius r>0 to achieve increased beam trapping efficiency and enhanced laser beam wavefront control so as to decrease optical beam diffraction and other deleterious effects.

Prosnitz, Donald (Walnut Creek, CA); Haas, Roger A. (Pleasanton, CA)

1985-01-01

233

Vertical spreading of two-dimensional crystalline colloidal arrays

evaporation and LangmuirÂBlodget deposition, etc. have been used to prepare 2-D colloidal arrays on planarVertical spreading of two-dimensional crystalline colloidal arrays Jian-Tao Zhang,a Luling Wang-dimensional (2-D) ordered monolayer crystalline colloidal arrays (CCAs). This phenom- enon can be used to rapidly

Asher, Sanford A.

234

Lattice Boltzmann simulation for forced two-dimensional turbulence

NASA Astrophysics Data System (ADS)

The direct numerical simulations of forced two-dimensional turbulent flow are presented by using the lattice Boltzmann method. The development of an energy-enstrophy double cascade is investigated in the two cases of external force of two-dimensional turbulence, Gaussian force and Kolmogorov force. It is found that the friction force is a necessary condition of the occurrence of a double cascade. The energy spectrum k-3 in the enstrophy inertial range is in accord with the classical Kraichnan theory for both external forces. The energy spectrum of the Gaussian force case in an inverse cascade is k-2; however, the Kolmogorov force drives the k-5/3 energy in a backscatter cascade. The result agrees with Scott's standpoint, which describes nonrobustness of the two-dimensional turbulent inverse cascade. Also, intermittency is found for the enstrophy cascade in two cases of the external force form. Intermittency refers to the nonuniform distribution of saddle points in the two-dimensional turbulent flow.

Xia, YuXian; Qian, YueHong

2014-08-01

235

Two-Dimensional Chirality in Three-Dimensional Chemistry.

ERIC Educational Resources Information Center

The concept of two-dimensional chirality is used to enhance students' understanding of three-dimensional stereochemistry. This chirality is used as a key to teaching/understanding such concepts as enaniotropism, diastereotopism, pseudoasymmetry, retention/inversion of configuration, and stereochemical results of addition to double bonds. (JN)

Wintner, Claude E.

1983-01-01

236

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

237

A two-dimensional Prony's method for spectral estimation

The problem of estimating the parameters of a model for bidimensional data made up by a linear combination of damped two-dimensional sinusoids is considered. Frequencies, amplitudes, phases, and damping factors are estimated by applying a generalization of the monodimensional Prony's method to spatial data. This procedure finds the desired quantities after an autoregressive model fitting to the data, a polynomial

M. M. Barbieri; P. Barone

1992-01-01

238

Two-dimensional Prony modeling and parameter estimation

A new method for estimating the two-dimensional (2D) exponential modes and amplitude coefficients in a Prony model is presented. This method involves two parts, each utilizing a 1D singular value decomposition-based technique, and is capable of locating frequencies anywhere in the 2D frequency plane. Simulations are shown which demonstrate the performance of the algorithm

Joseph J. Sacchini; William M. Steedly; Randolph L. Moses

1993-01-01

239

Two-dimensional Prony modeling and parameter estimation

A new method for estimating two-dimensional (2-D) poles and amplitude coefficients in a Prony model is presented. This method involves two parts, each utilizing a 1-D singular-value-decomposition-based technique, and is capable of locating frequencies anywhere in the 2-D frequency plane. Simulations are shown which demonstrate the performance of the algorithm

Joseph J. Sacchini; Williuni M. Steedly; R. L. Moses

1992-01-01

240

THERMOPOWER AND MAGNETORESISTANCE STUDIES IN A TWO-DIMENSIONAL

three-dimensional (3D) and two-dimensional (2D) interface phonons can contribute to this effect. The TEP (Rxy) does not develop into quantized plateau. The first derivative of Hall resistance with respect a sharp, strongly temperature-dependent minimum cen- tered at = 1/2, whereas concomitant Hall resistance

Natelson, Douglas

241

HOMOGENIZATION OF TWO DIMENSIONAL LINEAR FLOWS WITH INTEGRAL INVARIANCE1

HOMOGENIZATION OF TWO DIMENSIONAL LINEAR FLOWS WITH INTEGRAL INVARIANCE1 Tamir Tassa Abstract We study the homogenization of 2D linear transport equations, ut + a(x/) Âˇ xu = 0, where a is a non in the special cases of incompressible flows and shear flows. When the flow on T2 is non-ergodic, the homogenized

Beimel, Amos

242

condmat/9801215 Crossovers in the Two Dimensional Ising Spin Glass

numerical evidence for a spin glass transition at finite temperature simulating intermediate lattice sizescondÂmat/9801215 v2 26 Jan 1998 Crossovers in the Two Dimensional Ising Spin Glass of extensive computer simulations we analyze in detail the two dimenÂ sional \\SigmaJ Ising spin glass

Roma "La Sapienza", UniversitĂ di

243

Federal Register 2010, 2011, 2012, 2013

...of Biomolecules In a Two- Dimensional Array;'' U.S...of Biomolecules In a Two-Dimensional Array;'' U.S...foreign counterparts to 2-D Bio, LLC, having...parallel analysis and two dimensional analyses of...

2011-04-05

244

Two-dimensional phononic crystals: Examples and applications

NASA Astrophysics Data System (ADS)

Phononic crystals are composite materials made of periodic distributions of inclusions embedded in a matrix. Due to their periodic structure, these materials may exhibit under certain conditions, absolute acoustic band gaps i.e. forbidden bands that are independent of the direction of propagation of the incident elastic wave. In the first part of this review paper, we present some examples of two-dimensional bulk phononic crystals i.e. two-dimensional arrays of inclusions assumed of infinite extent along the three spatial directions. We show that the bandwidth of the forbidden band depends strongly on the nature of the constituent materials (solid or fluid), as well as the contrast between the physical characteristics (density and elastic moduli) of the inclusions and of the matrix, the geometry of the array of inclusions, the inclusion shape and the filling factor of inclusions. The second part of this review paper is devoted to some possible applications of these composite materials. In particular, we show that defect modes (cavities, waveguides, stubs, etc.) inserted inside the two-dimensional periodic structure may lead to very selective frequency filters and efficient devices for the wavelength demultiplexing. We present also the possibility of sonic insulators for frequencies of the order of kHz with relatively small thicknesses of phononic crystal samples. Finally we report on the vibration modes of a two-dimensional phononic crystal plate i.e. a phononic crystal of finite thickness along the axis of the inclusions. We discuss guided modes which may occur in the band structure of the plate. Surface acoustic waves propagating in two-dimensional phononic crystals should open new perspectives in high-frequency radio-frequency devices. Throughout the paper, the methods of calculation are presented with some details and some experimental results complete the numerical predictions.

Pennec, Yan; Vasseur, Jérôme O.; Djafari-Rouhani, Bahram; Dobrzy?ski, Leonard; Deymier, Pierre A.

2010-08-01

245

Two-Dimensional Mathematical Modeling of the Pack Carburizing Process

NASA Astrophysics Data System (ADS)

Pack carburization is the oldest method among the case-hardening treatments, and sufficient attempts have not been made to understand this process in terms of heat and mass transfer, effect of alloying elements, dimensions of the sample, etc. Thus, a two-dimensional mathematical model in cylindrical coordinate is developed for simulating the pack carburization process for chromium-bearing steel in this study. Heat and mass balance equations are solved simultaneously, where the surface temperature of the sample varies with time, but the carbon potential at the surface during the process remains constant. The fully implicit finite volume technique is used to solve the governing equations. Good agreement has been found between the predicted and published data. The effect of temperature, carburizing time, dimensions of the sample, etc. on the pack carburizing process shows some interesting results. It is found that the two-dimensional model gives better insight into understanding the carburizing process.

Sarkar, S.; Gupta, G. S.

2008-10-01

246

Two-dimensional flow through large numbers of circular inhomogeneities

NASA Astrophysics Data System (ADS)

An implicit analytic solution is presented for two-dimensional groundwater flow through a large number of non-intersecting circular inhomogeneities in the hydraulic conductivity. The locations, sizes and conductivity of the inhomogeneities may be arbitrarily selected. The influence of each inhomogeneity is expanded in a series that satisfies the Laplace equation exactly. The unknown coefficients in this expansion are related to the coefficients in the expansion of the combined discharge potential from all other elements. Using a least squares formulation for the boundary conditions and an iterative algorithm, solutions can be obtained for a very large number of inhomogeneities (e.g. 10,000) on a personal computer to any desired precision, up to the machine's limit. Such precision and speed allows the development of a numerical laboratory for investigating two-dimensional flow and convective transport.

Barnes, R.; Jankovi?, I.

1999-12-01

247

Strong localization effect in magnetic two-dimensional hole systems

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

248

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

249

Tunable refraction in a two dimensional quantum metamaterial

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

250

Unshielded fetal magnetocardiography system using two-dimensional gradiometers

NASA Astrophysics Data System (ADS)

We developed a fetal magnetocardiography (fMCG) system that uses a pair of two-dimensional gradiometers to achieve high signal-to-noise ratio. The gradiometer, which is based on a low-Tc superconducting quantum interference device, detects the gradient of a magnetic field in two orthogonal directions. Gradiometer position is easy to adjust by operating the gantry to drive the cryostat in both the swinging and axial directions. As a result, a fMCG waveform for 25weeks' gestation was measured under an unshielded environment in real time. Moreover, the P and T waves for 25 and 34weeks' gestation, respectively, were obtained by averaging. These results indicate that this two-dimensional gradiometer is one of the most promising techniques for measuring fetal heart rate and diagnosing fetal arrhythmia.

Seki, Yusuke; Kandori, Akihiko; Kumagai, Yukio; Ohnuma, Mitsuru; Ishiyama, Akihiko; Ishii, Tetsuko; Nakamura, Yoshiyuki; Horigome, Hitoshi; Chiba, Toshio

2008-03-01

251

On two-dimensional flows of compressible fluids

NASA Technical Reports Server (NTRS)

This report is devoted to the study of two-dimensional steady motion of a compressible fluid. It is shown that the complete flow pattern around a closed obstacle cannot be obtained by the method of Chaplygin. In order to overcome this difficulty, a formula for the stream-function of a two-dimensional subsonic flow is derived. The formula involves an arbitrary function of a complex variable and yields all possible subsonic flow patterns of certain types. Conditions are given so that the flow pattern in the physical plane will represent a flow around a closed curve. The formula obtained can be employed for the approximate determination of a subsonic flow around an obstacle. The method can be extended to partially supersonic flows.

Bergman, Stefan

1945-01-01

252

A two-dimensional dam-break flood plain model

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

253

Transport behavior of water molecules through two-dimensional nanopores

NASA Astrophysics Data System (ADS)

Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ?15 Ĺ water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.

Zhu, Chongqin; Li, Hui; Meng, Sheng

2014-11-01

254

Coarsening of Two Dimensional Foams on a Curved Surface

NASA Astrophysics Data System (ADS)

We report on foam coarsening and statistics of bubble distributions in a closed, two dimensional, hemispheric cell of constant curvature. Using this cell it is possible to observe individual bubbles and measure their coarsening rates. Our results are consistent with the modification to von Neumann's law predicted by Avron and Levine. We observed the relative frequencies of bubbles with a given number of sides and found a shortage of bubbles with few sides as compared to a flat two dimensional cell. We also measured the value of m(n), the average number of sides of an n sided bubble, and found general agreement with the Aboav-Weaire law, although there was greater deviation than for a flat cell.

Roth, Adam; Jones, Chris; Durian, Doug

2012-02-01

255

Two-Dimensional Computational Model for Wave Rotor Flow Dynamics

NASA Technical Reports Server (NTRS)

A two-dimensional (theta,z) Navier-Stokes solver for multi-port wave rotor flow simulation is described. The finite-volume form of the unsteady thin-layer Navier-Stokes equations are integrated in time on multi-block grids that represent the stationary inlet and outlet ports and the moving rotor passages of the wave rotor. Computed results are compared with three-port wave rotor experimental data. The model is applied to predict the performance of a planned four-port wave rotor experiment. Two-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified. The performance impact of rounding the inlet port wall, to inhibit separation during passage gradual opening, is assessed.

Welch, Gerard E.

1996-01-01

256

Grain boundary segregation, two dimensional compound formation, and precipitation

Although not able to account for structural properties of the grain-boundaries -at least without the help of statistical mechanics-the formalism of classical equilibrium thermodynamics can be a powerful tool in understanding equilibrium segregation, i.e. chemical properties of the essentially two-dimensional (2D) grain boundaries and their relation to bulk material (3D) properties, in particular precipitation. This is exemplified by the case

Michel Guttmann

1977-01-01

257

Two dimensional thermal and charge mapping of power thyristors

NASA Technical Reports Server (NTRS)

The two dimensional static and dynamic current density distributions within the junction of semiconductor power switching devices and in particular the thyristors were obtained. A method for mapping the thermal profile of the device junctions with fine resolution using an infrared beam and measuring the attenuation through the device as a function of temperature were developed. The results obtained are useful in the design and quality control of high power semiconductor switching devices.

Hu, S. P.; Rabinovici, B. M.

1975-01-01

258

In vivo two-dimensional NMR correlation spectroscopy

NASA Astrophysics Data System (ADS)

The poor resolution of in-vivo one- dimensional nuclear magnetic resonance spectroscopy (NMR) has limited its clinical potential. Currently, only the large singlet methyl resonances arising from N-acetyl aspartate (NAA), choline, and creatine are quantitated in a clinical setting. Other metabolites such as myo- inositol, glutamine, glutamate, lactate, and ?- amino butyric acid (GABA) are of clinical interest but quantitation is difficult due to the overlapping resonances and limited spectral resolution. To improve the spectral resolution and distinguish between overlapping resonances, a series of two- dimensional chemical shift correlation spectroscopy experiments were developed for a 1.5 Tesla clinical imaging magnet. Two-dimensional methods are attractive for in vivo spectroscopy due to their ability to unravel overlapping resonances with the second dimension, simplifying the interpretation and quantitation of low field NMR spectra. Two-dimensional experiments acquired with mix-mode line shape negate the advantages of the second dimension. For this reason, a new experiment, REVOLT, was developed to achieve absorptive mode line shape in both dimensions. Absorptive mode experiments were compared to mixed mode experiments with respect to sensitivity, resolution, and water suppression. Detailed theoretical and experimental calculations of the optimum spin lock and radio frequency power deposition were performed. Two-dimensional spectra were acquired from human bone marrow and human brain tissue. The human brain tissue spectra clearly reveal correlations among the coupled spins of NAA, glutamine, glutamate, lactate, GABA, aspartate and myo-inositol obtained from a single experiment of 23 minutes from a volume of 59 mL. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Kraft, Robert A.

1999-10-01

259

Efficient Method for ECG Compression Using Two Dimensional Multiwavelet Transform

? AbstractIn this paper we introduce an effective ECG compression algorithm based on two dimensional multi- wavelet transform. Multi-wavelets offer simultaneous orthogonality, symmetry and short support, which is not possible with scalar two-channel wavelet systems. These features are known to be important in signal processing. Thus multiwavelet offers the possibility of superior performance for image processing applications. The SPIHT algorithm

Morteza Moazami-Goudarzi; Mohammad H. Moradi; Ali Taheri

2005-01-01

260

Structural transitions in laterally compressed two-dimensional Coulomb clusters

We model structural transitions of small-size Wigner crystals in laterally compressed two-dimensional traps. Ground and metastable configurations are calculated and their transformations are linked to conspicuous changes in the heat capacity of the system. We show that various types of structural transitions are reflected by characteristic features in the behavior of the heat capacity. For deeper understanding, results produced by the Monte Carlo numerical calculations are compared to predictions of simple one-dimensional models.

Rancova, O.; Anisimovas, E.; Varanavicius, T. [Department of Theoretical Physics, Vilnius University, Sauletekio 9, LT-10222 Vilnius (Lithuania)

2011-03-15

261

Two-dimensional protein crystals for solar energy conversion.

Two-dimensional photosynthetic protein crystals provide a high density of aligned reaction centers. We reconstitute the robust light harvesting protein Photosystem I into a 2D crystal with lipids and integrate the crystals into a photo-electrochemical device. A 4-fold photocurrent enhancement is measured by incorporating conjugated oligoelectrolytes to form a supporting conductive bilayer in the device which produces a high photocurrent of ?600 ?A per mg PSI deposited. PMID:25155990

Saboe, Patrick O; Lubner, Carolyn E; McCool, Nicholas S; Vargas-Barbosa, Nella M; Yan, Hengjing; Chan, Stanley; Ferlez, Bryan; Bazan, Guillermo C; Golbeck, John H; Kumar, Manish

2014-11-01

262

Superradiance in a Two-Dimensional Photonic Bandgap Structure

In this paper, we study the superradiant decay of an ensemble of inverted two-level atoms embedded into a continuous dielectric and a two-dimensional (2-D) photonic crystal with lateral confinement of the radiation. The nonlinear superradiance pulse characteristics are calculated using a Green's-function-based model. Specifically, we predict fast phase synchronization across the ensemble that builds up a distributed feedback structure responsible

Igor V. Mel'nikov; Joseph W. Haus; J. Stewart Aitchison

2006-01-01

263

Augmented Reality Simulator for Training in Two-Dimensional Echocardiography

In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of

M. Weidenbach; C. Wick; S. Pieper; K. J. Quast; T. Fox; G. Grunst; D. A. Redel

2000-01-01

264

Orthorhombic Two-Dimensional Crystal form of Purple Membrane

A new two-dimensional crystal form of purple membrane has been obtained in vitro. It is produced by the joint use of a cationic detergent, dodecyltrimethylammonium chloride, and the nonionic detergent, Triton X-100. It primarily forms large, rolled-up sheets that look like needles in the light microscope. Liposomes and tubes are also observed. The absorption maximum of the new form of

Hartmut Michel; Dieter Oesterhelt; Richard Henderson

1980-01-01

265

Heterogeneous slow dynamics in a two dimensional doped classical antiferromagnet

We introduce a lattice model for a classical doped two-dimensional antiferromagnet that has no quenched disorder, yet displays slow dynamics similar to those observed in supercooled liquids. We calculate two-time spatial and spin correlations via Monte Carlo simulations and find that for sufficiently low temperatures, there is anomalous diffusion and stretched-exponential relaxation of spin correlations. The relaxation times associated with

Malcolm P. Kennett; Claudio Chamon; Leticia F. Cugliandolo

2005-01-01

266

Two Dimensional Velocity Fields of Low Surface Brightness Galaxies

We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for LCDM.

Rachel Kuzio de Naray; Stacy S. McGaugh; W. J. G. de Blok; Albert Bosma

2005-09-22

267

Constant rate shearing on two-dimensional cohesive discs

We performed two-dimensional molecular dynamics simulations of cohesive discs under shear. The cohesion between the discs is added by the action of springs between very next neighbouring discs, modelling capillary forces. The geometry of the cell allows disc-disc shearing and not disc-cell wall shearing as is commonly found in the literature. Does a stick-slip phenomenon happen though the upper cover

N. Olivi-Tran; O. Pozo; N. Fraysse

2005-01-01

268

Peierls transition in two-dimensional metallic monophosphate tungsten bronzes

The two-dimensional metallic bronzes made of ReO3-type layers of MoO6 or WO6 octahedra present quasi-one-dimensional (1D) electronic structures along three directions of preferential overlap of the t2g transition metal orbitals. They exhibit a Peierls instability towards the formation of charge density waves (CDW) at the 2kF critical wave vector allowing to nest simultaneously the Fermi surfaces associated to two quasi-1D

P. Foury-Leylekian; J.-P. Pouget

2002-01-01

269

Acoustic Bloch oscillations in a two-dimensional phononic crystal.

We report the observation of acoustic Bloch oscillations at megahertz frequency in a two-dimensional phononic crystal. By creating periodically arrayed cavities with a decreasing gradient in width along one direction in the phononic crystal, acoustic Wannier-Stark ladders are created in the frequency domain. The oscillatory motion of an incident Gaussian pulse inside the sample is demonstrated by both simulation and experiment. PMID:18233780

He, Zhaojian; Peng, Shasha; Cai, Feiyan; Ke, Manzhu; Liu, Zhengyou

2007-11-01

270

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

271

Two-dimensional sonic crystals with Helmholtz resonators

We present a type of sonic crystal composed with an array of two-dimensional Helmholtz resonators, which in the long-wave regime have both a high relative acoustic refractive index n and at the same time, a small acoustic impedance Z mismatch with air for airborne sound. We analyze the n and Z of such sonic crystals by finite-difference time-domain simulations, and

Xinhua Hu; C. T. Chan; Jian Zi

2005-01-01

272

Two-dimensional high-resolution stepper image monitor

A two-dimensional image monitor with high resolution has been implemented on a deep-UV 0.6 NA stepper. The aerial intensity sensor uses a photodiode which is integrated in the wafer chuck and a chromium coated quartz wafer with an array of 0.2 micrometers pinholes. The aerial image is scanned by the sensor which is positioned by the stepper stage. The image

Anton K. Pfau; Richard Hsu; William G. Oldham

1992-01-01

273

Trochoidal Solutions to the Incompressible Two-Dimensional Euler Equations

. Within the Lagrangian framework we present an approach yielding some explicit solutions to the incompressible two-dimensional\\u000a Euler equations, generalizing the celebrated Gerstner flow. The solutions so obtained, for which explicit formulas of each\\u000a particle trajectory are provided, represent either flows in domains with a rigid boundary or free-surface flows for a fluid\\u000a of infinite depth. For some of these solutions

Adrian Constantin; Walter A. Strauss

2010-01-01

274

Two-dimensional polaron coherence in Poly(3-hexylthiophene)

NASA Astrophysics Data System (ADS)

The two-dimensional coherence function corresponding to positively charged polarons ("holes") in poly(3- hexylthiophene) ?-stacks is calculated based on a Holstein-style Hamiltonian which treats electronic coupling, vibronic coupling and disorder on equal footing. Assuming a model of isotropic site-energy disorder, the hole is found to be delocalized between 1-2 nm along the polymer chain and between 0.5-1 nm along the stacking axis.

Pochas, C. M.; Yamagata, Hajime; Spano, F. C.

2014-09-01

275

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

276

Optical conductivity of the two-dimensional Hubbard model

The optical conductivity sigma1(omega) of the two-dimensional Hubbard model on finite clusters of 4×4 and &surd;10 × &surd;10 sites is reported. Experimental features found in the high-Tc cuprate superconductors can be qualitatively reproduced by this model including the presence of mid-infrared spectral weight, a Drude peak whose intensity grows with doping and a total spectral weight that varies slowly as

E. Dagotto; A. Moreo; F. Ortolani; J. Riera; D. J. Scalapino

1992-01-01

277

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

278

Exact analytic flux distributions for two-dimensional solar concentrators.

A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the method's versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers. PMID:23842256

Fraidenraich, Naum; Henrique de Oliveira Pedrosa Filho, Manoel; Vilela, Olga C; Gordon, Jeffrey M

2013-07-01

279

Two-dimensional magnetic ordering in a multilayer structure

The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of research for almost 100 years. The role of dipolar interactions and anisotropy are important to obtain, the otherwise forbidden, ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monolayers). We have demonstrated that conventional low-temperature magnetometry

M. K. Mukhopadhyay; M. K. Sanyal

2006-01-01

280

Two-dimensional magnetic ordering in a multilayer structure

The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of\\u000a research for almost 100 years. The role of dipolar interactions and anistropy are important to obtain, the otherwise forbidden,\\u000a ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monlayers). We have demonstrated\\u000a that conventional low-temperature magnetometry

M K Mukhopadhyay; M K Sanyal

2006-01-01

281

Solitonic Bloch oscillations in two-dimensional optical lattices

NASA Astrophysics Data System (ADS)

A theoretical description for nonlinear beam propagation in a two-dimensional optical lattice in the presence of a refractive-index gradient has been developed. This problem is associated with nonlinear Bloch oscillations; it has been reduced to a nonlinear Schrödinger equation with a varying dispersion coefficient. It is shown that, if the periodicity of longitudinal modulation coincides with the transverse gradient of the refractive index, a stationary oscillatory picture emerges in the nonlinear regime.

Khomeriki, Ramaz

2010-09-01

282

Two-Dimensional Dilaton-Gravity Coupled to Massless Spinors

We apply a global and geometrically well-defined formalism for spinor-dilaton-gravity to two-dimensional manifolds. We discuss the general formalism and focus attention on some particular choices of the dilatonic potential. For constant dilatonic potential the model turns out to be completely solvable and the general solution is found. For linear and exponential dilatonic potentials we present the class of exact solutions with a Killing vector.

Marco Cavaglia; Lorenzo Fatibene; Mauro Francaviglia

1998-01-23

283

Suspended two-dimensional electron and hole gases

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

284

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

285

Two-dimensional quasi orthogonal complete complementary codes

Construction of a new family of two-dimensional quasi orthogonal complete complementary codes (2D-QOCCC) is presented The new 2D-QOCCC retain most of the properties of the 2D-OCCC except the ideal sum of correlation values within the zero horizontal shift. The benefit is a several times larger number of signatures for a given number of elements, thus the enlargement of a maximum

M. Turcsany; Peter FarkaS

2003-01-01

286

Magnetic levitation in two-dimensional geometry with translational invariance

NASA Astrophysics Data System (ADS)

The development of activities in space and of the corresponding technologies requires research on the behavior of both matter and biological organisms under weightless conditions. Various methods have been invented in order to simulate weightlessness, for example, drop towers, sounding rockets, or parabolic flights. Magnetic field ground-based devices have also been developed. This paper introduces an optimization method of the magnetic field so as to obtain magnetic levitation in a two-dimensional cylindrical geometry.

Lorin, C.; Mailfert, A.

2008-11-01

287

Finite difference methods for two-dimensional fractional dispersion equation

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

288

Itinerant ferromagnetism in a two-dimensional atomic gas

Motivated by the first experimental evidence of ferromagnetic behavior in a three-dimensional ultracold atomic gas, we explore the possibility of itinerant ferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a formalism that demonstrates how quantum fluctuations drive the ferromagnetic reconstruction first order, and consider the consequences of an imposed population imbalance. Secondly, we adapt this formalism to elucidate the key experimental signatures of ferromagnetism in a realistic trapped geometry.

Conduit, G. J. [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel) and Physics Department, Ben Gurion University, Beer Sheva 84105 (Israel)

2010-10-15

289

Conductivity of a two-dimensional guiding center plasma.

NASA Technical Reports Server (NTRS)

The Kubo method is used to calculate the electrical conductivity of a two-dimensional, strongly magnetized plasma. The particles interact through (logarithmic) electrostatic potentials and move with their guiding center drift velocities (Taylor-McNamara model). The thermal equilibrium dc conductivity can be evaluated analytically, but the ac conductivity involves numerical solution of a differential equation. Both conductivities fall off as the inverse first power of the magnetic field strength.

Montgomery, D.; Tappert, F.

1972-01-01

290

Mesoscopic diffusion thermopower in two-dimensional electron gases

NASA Astrophysics Data System (ADS)

The diffusion of energy that is locally deposited into two-dimensional electron gases by Joule heating generates transverse voltages across devices with broken symmetry. For mesoscopic structures characterized by device dimensions comparable to the energy diffusion length, the resulting thermopower strongly depends on details of the potential profile defined by electric gates. We discuss these mesoscopic features within a diffusion thermopower model and propose schemes to measure the energy diffusion length and its dependence on gate voltage.

Rojek, Stephan; König, Jürgen

2014-09-01

291

FRACTURE ROUGHNESS FOR THE TWO-DIMENSIONAL CENTRAL FORCE MODEL

We study the fracture roughness for a two-dimensional central force model by nu- merical simulations to check the conjecture that the fracture roughness is due to the fracture process being a stress-weighted percolation process. The simulations are done on a triangular lattice and the fracture process is quasi-static. The simulations are done in mode I and the elastic equilibrium equations

Jan Ř; H. Bakke; Thomas Ramstad; Alex Hansen

292

The Study of Two-dimensional Polytropic Stars

In this article we have studied the structure of hypothetical two-dimensional polytropic stars. Considering some academic interest, we have developed a formalism to investigate some of the gross properties of such stellar objects. However, we strongly believe that the formalism developed here may be prescribed as class problem for post-graduate level students in physics or a post-graduate dissertation project work in physics.

Sanchari De; Somenath Chakrabarty

2014-04-28

293

On the invariants of two dimensional linear parabolic equations

NASA Astrophysics Data System (ADS)

We consider the most general two dimensional linear parabolic equations. Motivated by the recent work of Ibragimov et al. [1-3] we construct differential invariants, semi-invariants and invariant equations. These results are achieved with the employment of the equivalence group admitted by this class of parabolic equations. We derive those variable coefficient equations of this class of linear parabolic equations that can be mapped into constant coefficient equations. Further applications are presented.

Tsaousi, C.; Sophocleous, C.; Tracinŕ, R.

2012-09-01

294

Two-dimensional electrons on KTaO3 surfaces

NASA Astrophysics Data System (ADS)

The two-dimensional electron gas systems at the interface of polar/non-polar oxides interfaces, e.g. LaAlO3(LAO)/SrTiO3(STO), have received considerable attention due to interesting phenomena stemming from strong electron-electron interactions. A recent experiment [1] showed that the (001) surface of KTaO3 (KTO) can induce two-dimensional electron gas even without external doping. KTO differs from widely studied STO in that KTO has more than 20 times stronger spin-orbit coupling. We carried out density functional theory calculations of vacuum-cleaved KTO surface structure to study the electronic and spin properties of the two-dimensional electrons. The electric field that arises from the surface polarization makes the conduction electrons near the surface, resulting in an orbital ordering similar to LAO/STO interface. Despite the strong spin-orbit coupling, about 400 meV, our result shows the Rashba spin splitting in this perovskite oxide is much smaller than that of conventional semiconductors, which is a good agreement with the angle-resolved photoemission measurement.[1] P. D. C. King, et al. Phys. Rev. Lett. 108, 117602 (2012).

Park, Pumsuk; Lee, Byounghak

2013-03-01

295

The critical properties of two-dimensional oscillator arrays

NASA Astrophysics Data System (ADS)

We present a renormalization group study of two-dimensional oscillator arrays, with dissipative, short-range interactions. We consider the case of non-identical oscillators, with distributed intrinsic frequencies within the array and study the steady-state properties of the system. In two dimensions no macroscopic mutual entrainment is found but, for identical oscillators, critical behaviour of the Berezinskii-Kosterlitz-Thouless (BKT) type is shown to be present. We then discuss the stability of BKT order in the physical case of distributed quenched random frequencies. In order to do that, we show how the steady-state dynamical properties of the two-dimensional array of non-identical oscillators are related to the equilibrium properties of the XY model with quenched randomness, which has already been studied in the past. We propose a novel set of recursion relations to study this system within the Migdal-Kadanoff (MK) renormalization group scheme, by means of a discrete clock state formulation. For identical oscillators, we compute the phase diagram in the presence of random dissipative coupling, at finite values of the clock state parameter. Possible experimental applications in two-dimensional arrays of microelectromechanical oscillators are briefly suggested. This work is devoted to Professor David Sherrington, in occasion of his 65th birthday.

Migliorini, Gabriele

2008-08-01

296

The Critical Properties of Two-dimensional Oscillator Arrays

NASA Astrophysics Data System (ADS)

We present a renormalization group study of two dimensional arrays of oscillators, with dissipative, short range interactions. We consider the case of non-identical oscillators, with distributed intrinsic frequencies within the array and study the steady-state properties of the system. In two dimensions no macroscopic mutual entrainment is found but, for identical oscillators, critical behavior of the Berezinskii-Kosterlitz-Thouless type is shown to be present. We then discuss the stability of (BKT) order in the physical case of distributed quenched random frequencies. In order to do that, we show how the steady-state dynamical properties of the two dimensional array of non-identical oscillators are related to the equilibrium properties of the XY model with quenched randomness, that has been already studied in the past. We propose a novel set of recursion relations to study this system within the Migdal Kadanoff renormalization group scheme, by mean of the discrete clock-state formulation. We compute the phase diagram in the presence of random dissipative coupling, at finite values of the clock state parameter. Possible experimental applications in two dimensional arrays of microelectromechanical oscillators are briefly suggested.

Migliorini, Gabriele

2008-03-01

297

Two-dimensional DNA fingerprinting of human individuals

The limiting factor in the presently available techniques for the detection of DNA sequence variation in the human genome is the low resolution of Southern blot analysis. To increase the analytical power of this technique, the authors applied size fractionation of genomic DNA restriction fragments in conjunction with their sequence-dependent separation in denaturing gradient gels; the two-dimensional separation patterns obtained were subsequently transferred to nylon membranes. Hybridization analysis using minisatellite core sequences as probes resulted in two-dimensional genomic DNA fingerprints with a resolution of up to 625 separated spots per probe per human individual; by conventional Southern blot analysis, only 20-30 bands can be resolved. Using the two-dimensional DNA fingerprinting technique, they demonstrate in a small human pedigree the simultaneous transmission of 37 polymorphic fragments (out of 365 spots) for probe 33.15 and 105 polymorphic fragments (out of 625 spots) for probe 33.6. In addition, a mutation was detected in this pedigree by probe 33.6. They anticipate that this method will be of great use in studies aimed at (i) measuring human mutation frequencies, (ii) associating genetic variation with disease, (iii) analyzing genomic instability in relation to cancer and aging, and (iv) linkage analysis and mapping of disease genes.

Uitterlinden, A.G.; Slagboom, P.E.; Knook, D.L.; Vijg, J. (TNO Institute for Experimental Gerontology, Rijswijk (Netherlands))

1989-04-01

298

One-to-two dimensional transition in small Debye clusters

NASA Astrophysics Data System (ADS)

We study the transition from one-dimensional to two-dimensional configurations of small clusters of monodisperse dust particles levitated in plasma. Particles are confined by a highly-anisotropic two-dimensional potential well in the Dusty ONU experimenT (DONUT). The well anisotropy, as determined by measuring the center-of-mass oscillation frequencies in the x and y directions using Brownian motion, is found to be ?0y^2/?0x^2=30.7. For n<=9 particles, the cluster is in a linear, one-dimensional configuration. The addition of one more particle (n=10) causes a zig-zag transition to a two-dimensional ``barred-elliptical'' configuration with an ``elliptical'' nucleus and linear tails. As more particles are added the nucleus grows and the tails decline until the cluster becomes an oval. These results are found to be in good agreement with Monte Carlo calculations of particle configurations. The Monte Carlo calculations show that in a linear configuration normal modes are either longitudinal or transverse, so that for low energies the cluster dynamics are one-dimensional.

Sheridan, T. E.; Wells, K. D.

2008-11-01

299

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

300

Two-dimensional open resonators with cylindrical mirrors

The results of a theoretical analysis of the spectral characteristics of twodimensional open resonators are presented. The resonators are formed by a finite number of nonclosed screens coinciding with parts of surfaces of circular cylinders. The analysis is done for the case when the resonance wavelength is comparable to the characteristic dimension of the structure. Methods of increasing the quality

V. N. Koshparenok; P. N. Melezhik; A. E. Poedinchuk; V. P. Shestopalov

1984-01-01

301

On Two-Dimensional Modeling Of Magnetotelluric Field Data

NASA Astrophysics Data System (ADS)

In this paper, some recent topics on the modeling of magnetotelluric data are introduced. The focus is on the handling of real field data for two-dimensional resistivity modeling. First, the removal of the effects of near surface heterogeneity is reviewed. It covers telluric distortions (phase mixing and static shift) and magnetic distortions using conventional Groom-Bailey type 3D/2D model (three-dimensional local anomaly underlain by regional two-dimensional structure). The extension of a 3D/2D distortion model for multi-site, multi-frequency is a new development. Magnetic distortion seems to be less significant for land observations, but significant for sea floor data, where the regional magnetic field is weak due to seawater. In special cases involving for example, distortion due to topography and bathymetry, explicit removal is possible. There are some schemes proposed for a 3D/3D model (three-dimensional local anomaly underlain by regional three-dimensional structure). Along with the removal of the distortion, it is important to recognize the dimensionality of the dataset prior to modeling. A property using strike estimates for each site is an indicator for dimensionality which is unaffected by local distortion. Mapping the local strike or a rose diagram is an effective visualization of the dimensionality.Two-dimensional inversion is becoming routine. For the fast calculation of derivatives, approximate calculation, reciprocity or conjugate gradient methods are used. In order to incorporate a priori information and to overcome the intrinsic ill-posed nature of the inversion problem, imposing constraints on the model structure is important. A proper tradeoff between the data fit and constraints should be optimized to obtain minimum structures that are required by the field data. However, the choice of constraints is rather subjective and depends on the geological situations. For field data, two-dimensional inversion has limits on modes, area, and period range. Special care must be taken for the structure outside the profile. Two-dimensional inversion incorporating anisotropy is interesting and becoming popular, but the structure may not be unique. Future development in three-dimensional inversion for real datasets should take the above points into consideration.

Ogawa, Yasuo

302

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

303

The invention discloses a cylinder de-activator system for an internal combustion engine having a block, an engine head, a plurality of engine cylinders in the block, intake and exhaust valves for each engine cylinder spring-loaded to their closed positions, a cam operated valve train operating each of the valves with the valve train having a rocker lever that is rockingly

H. T. Jr

1979-01-01

304

Effects induced by Mie resonance in two-dimensional photonic crystals.

The effects of Mie resonance on the photonic band-gap structure of two-dimensional photonic crystals are investigated in detail. Firstly, we demonstrate the correlation between the band-gap structure and Mie resonance, such as the midgap frequency and the changes in gap width with different cylinder radii. We find that the midgap frequency and the gap width increase linearly and then saturate, before and after the Mie resonance frequency crosses the midgap frequency. The radius value at the crossing point between the midgap frequency and the Mie resonance frequency becomes smaller with the increase in the refractive contrast. For large radius, all the Mie resonance frequencies fall into the corresponding bands. Secondly, the changes in the gap width are studied with increasing index of the cylinders. Changing rules of the gap width are found depending on the position of the Mie resonance frequency. For example, when the Mie resonance falls inside the gap the gap width increases most rapidly and reaches its maximum value when the Mie resonance is leaving the gap range (around the lower edge of the gap). After that the gap width decreases very steeply with increase in the refractive contrast. Thirdly, we investigate the effect of Mie resonance on the band width for the 'heavy-photon band', which is the third band of our system. We find that, quite different from other bands, the band widths of such bands are determined by the overlapping integral of the Mie resonance states. All these results can be explained by the Mie resonance based on two physical pictures, i.e. the scattering picture and the hopping picture. According to these analyses and results, we may understand more clearly how the Mie resonances influence the formation of the band-gap structure. The Mie resonance effects on photonic band-gap structure presented in this paper would be valuable in designing various kinds of photonic crystals. PMID:21690959

Shi, Lina; Jiang, Xunya; Li, Chengfang

2007-04-30

305

Vortices in the two-dimensional dipolar Bose gas

We present vortex solutions for the homogeneous two-dimensional Bose-Einstein condensate featuring dipolar atomic interactions, mapped out as a function of the dipolar interaction strength (relative to the contact interactions) and polarization direction. Stable vortex solutions arise in the regimes where the fully homogeneous system is stable to the phonon or roton instabilities. Close to these instabilities, the vortex profile differs significantly from that of a vortex in a nondipolar quantum gas, developing, for example, density ripples and an anisotropic core. Meanwhile, the vortex itself generates a mesoscopic dipolar potential which, at distance, scales as 1/r^2 and has an angular dependence which mimics the microscopic dipolar interaction.

B. C. Mulkerin; D. H. J. O'Dell; A. M. Martin; N. G. Parker

2013-12-15

306

Thermally induced rotons in two-dimensional dilute Bose gases

We show that rotonlike excitations are thermally induced in a two-dimensional dilute Bose gas as a consequence of the strong phase fluctuations in two dimensions. At low momentum, the rotonlike excitations lead for small enough temperatures to an anomalous phonon spectrum with a temperature-dependent exponent reminiscent of the Kosterlitz-Thouless transition. Despite the anomalous form of the energy spectrum, it is shown that the corresponding effective theory of vortices describes the usual Kosterlitz-Thouless transition. The possible existence of an anomalous normal state in a small temperature interval is also discussed.

Nogueira, Flavio S.; Kleinert, Hagen [Institut fuer Theoretische Physik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin (Germany)

2006-03-01

307

Vortices in the two-dimensional dipolar Bose gas

NASA Astrophysics Data System (ADS)

We present vortex solutions for the homogeneous two-dimensional Bose-Einstein condensate featuring dipolar atomic interactions, mapped out as a function of the dipolar interaction strength (relative to the contact interactions) and polarization direction. Stable vortex solutions arise in the regimes where the fully homogeneous system is stable to the phonon or roton instabilities. Close to these instabilities, the vortex profile differs significantly from that of a vortex in a nondipolar quantum gas, developing, for example, density ripples and an anisotropic core. Meanwhile, the vortex itself generates a mesoscopic dipolar potential which, at distance, scales as 1/?2 and has an angular dependence which mimics the microscopic dipolar interaction.

Mulkerin, B. C.; O'Dell, D. H. J.; Martin, A. M.; Parker, N. G.

2014-04-01

308

Ballistic spin transport in a two-dimensional electron gas

NASA Astrophysics Data System (ADS)

We explore electrically injected, spin-polarized transport in a ballistic two-dimensional electron gas. We augment the Büttiker-Landauer picture with a simple, but realistic model for spin-selective contacts to describe multimode reservoir-to-reservoir transport of ballistic spin-1/2 particles. Clear and unambiguous signatures of spin transport are established in this regime, for the simplest measurement configuration that demonstrates them directly. These effects originate from spin precession of ballistic carriers; they exhibit a strong dependence upon device geometry, and vanish in the diffusive limit. Our results have important implications for prospective ``spin transistor'' devices.

Tang, H. X.; Monzon, F. G.; Lifshitz, Ron; Cross, M. C.; Roukes, M. L.

2000-02-01

309

Drift modes of a quasi-two-dimensional current sheet

NASA Astrophysics Data System (ADS)

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.

2012-03-01

310

Optical and electronic properties of two dimensional graphitic silicon carbide

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

311

Two-Dimensional Polymers with Random Short-Range Interactions

We use complete enumeration and Monte Carlo techniques to study two-dimensional self-avoiding polymer chains with quenched ``charges'' $\\pm 1$. The interaction of charges at neighboring lattice sites is described by $q_i q_j$. We find that a polymer undergoes a collapse transition at a temperature $T_{\\theta}$, which decreases with increasing imbalance between charges. At the transition point, the dependence of the radius of gyration of the polymer on the number of monomers is characterized by an exponent $\

Ido Golding; Yacov Kantor

1997-04-30

312

Some two-dimensional flows with couple stresses

NASA Astrophysics Data System (ADS)

The effect of couple stresses on some two-dimensional flows is considered. The numerical solutions are obtained by the shooting method using the Runge-Kutta algorithm in the four flow problems for a couple stress fluid, namely, for the Blasius, Sakiadis, stretching, and stagnation-point flows. The obtained solutions are nonsimilar for the Blasius and Sakiadis flows. The results are interpreted concerning the influence of the couple stress parameter which is a measure of the polarity of a fluid. It is shown that for large values of this parameter the solution converges to the solution for a Newtonian fluid.

Sajid, M.; Ali, N.; Abbas, Z.; Javed, T.; Imran, M.

2012-05-01

313

Condensate fraction of a two-dimensional attractive Fermi gas

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

314

Optimum high temperature strength of two-dimensional nanocomposites

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

315

Two-Dimensional X-Ray Beam Phase Sensing

NASA Astrophysics Data System (ADS)

We present a new method to analyze quantitatively the wave front of a partially coherent x-ray beam. The technique is based on the use of two-dimensional speckle patterns combined with digital image correlation algorithms and offers a pixel size resolution, a high accuracy, and a reduced sensitivity to mechanical vibrations thanks to a very simple setup. The requirements on transverse and longitudinal coherence are also low. Finally, we show how the method can be used for phase contrast imaging applications by a single sample exposure process.

Bérujon, Sébastien; Ziegler, Eric; Cerbino, Roberto; Peverini, Luca

2012-04-01

316

Two-dimensional x-ray beam phase sensing.

We present a new method to analyze quantitatively the wave front of a partially coherent x-ray beam. The technique is based on the use of two-dimensional speckle patterns combined with digital image correlation algorithms and offers a pixel size resolution, a high accuracy, and a reduced sensitivity to mechanical vibrations thanks to a very simple setup. The requirements on transverse and longitudinal coherence are also low. Finally, we show how the method can be used for phase contrast imaging applications by a single sample exposure process. PMID:22587288

Bérujon, Sébastien; Ziegler, Eric; Cerbino, Roberto; Peverini, Luca

2012-04-13

317

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

318

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

319

Highly directional thermal emission from two-dimensional silicon structures.

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

320

Two-dimensional simulations of magnetically-driven instabilities

A two-dimensional Eulerian MHD code is used to study the evolution of magnetically-driven instabilities in cylindrical geometry. The code incorporates an equation of state, resistivity, and radiative cooling model appropriate for an aluminum plasma. The simulations explore the effects of initial perturbations, electrical resistivity, and radiative cooling on the growth and saturation of the instabilities. Comparisons are made between the 2-D simulations, previous 1-D simulations, and results from the Pioneer experiments of the Los Alamos foil implosion program.

Peterson, D.; Bowers, R.; Greene, A.E.; Brownell, J.

1986-01-01

321

Correction-to-scaling exponent for two-dimensional percolation

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

322

Aerodynamics of two-dimensional slotted bluff bodies

Aerodynamic characteristics of two-dimensional, slotted bluff bodies were experimentally investigated. Flow visualizations, base pressure measurements, mean velocity vector measurements, and drag force measurements were conducted to analyze effects of spacing ratio (i.e., porosity), curvature, and vent. Low porosity model configurations produced stable near-wake patterns with enhanced vortex sheddings of overall wake formations. Model curvature reduced drag forces and weakened the vortex sheddings. Stabilizing effect of curvature on the near-wake patterns was also found. A vent combined with large model curvature was found to control drag force effectively, as well as suppressing vortex sheddings. 10 refs., 52 figs., 1 tab.

Takahashi, F.; Higuchi, H.

1988-04-30

323

Nonlinear Cascades in Two-Dimensional Turbulent Magnetoconvection

The dynamics of spectral transport in two-dimensional turbulent convection of electrically conducting fluids is studied by means of direct numerical simulations in the frame of the magnetohydrodynamic Boussinesq approximation. The system performs quasioscillations between two different regimes of small-scale turbulence: one dominated by nonlinear magnetohydrodynamic interactions; the other governed by buoyancy forces. The self-excited change of turbulent states is reported here for the first time. The process is controlled by the ideal invariant cross helicity, H{sup C}=SdSv{center_dot}b. The observations are explained by the interplay of convective driving with the nonlinear spectral transfer of total magnetohydrodynamic energy and cross helicity.

Skandera, Dan; Mueller, Wolf-Christian [Max-Planck-Institut fuer Plasmaphysik, 85748 Garching (Germany)

2009-06-05

324

Two-dimensional quantum black holes: numerical methods

NASA Astrophysics Data System (ADS)

We present details of a new numerical code designed to study the formation and evaporation of two-dimensional black holes within the Callan-Giddings-Harvey-Strominger model. We explain several elements of the scheme that are crucial to resolve the late-time behavior of the spacetime, including regularization of the field variables, compactification of the coordinates, the algebraic form of the discretized equations of motion and the use of a modified Richardson extrapolation scheme to achieve high-order convergence. Physical interpretation of our results will be discussed in detail elsewhere.

Ramazano?lu, Fethi M.; Pretorius, Frans

2010-12-01

325

Two-dimensional metamaterial transparent metal electrodes for infrared optoelectronics.

We examine the optical properties of two-dimensionally nanostructured metals in the metamaterial regime for infrared applications. Compared with straight nanowires and nanogrids, serpentine structures exhibit much lower optical losses of less than 7% even at a large metal area fraction of 0.3. The low loss is primarily due to a small effective conductivity of the meandering structures, and self-inductance plays a modest role in reducing losses in these structures. The high transparency at a large metal area coverage would be useful for transparent electrodes in optoelectronic devices. PMID:24978563

Clark, Samuel M; Han, Sang Eon

2014-06-15

326

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

327

Drift modes of a quasi-two-dimensional current sheet

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

328

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

329

Self-similar dynamic quasi-two-dimensional sand fronts.

We report on a study of advancing quasi-two-dimensional sand fronts on an inclined flat and thin strip confined between two vertical plates. These fronts form when a thin initial stream of sand running down the flat obstacle gets trapped at some distance from the injection point. Right after this trapping, the front starts to advance upstream and grow in time. The shapes at successive times are found to be self-similar in time. The stability conditions for the obtained fronts are also outlined. A simple model for interface dynamics gives reasonable predictions for the observed shapes. PMID:12636479

Boudet, J-F; Gauthier, S; Amarouchene, Y; Kellay, H

2003-01-01

330

Self-similar dynamic quasi-two-dimensional sand fronts

NASA Astrophysics Data System (ADS)

We report on a study of advancing quasi-two-dimensional sand fronts on an inclined flat and thin strip confined between two vertical plates. These fronts form when a thin initial stream of sand running down the flat obstacle gets trapped at some distance from the injection point. Right after this trapping, the front starts to advance upstream and grow in time. The shapes at successive times are found to be self-similar in time. The stability conditions for the obtained fronts are also outlined. A simple model for interface dynamics gives reasonable predictions for the observed shapes.

Boudet, J.-F.; Gauthier, S.; Amarouchene, Y.; Kellay, H.

2003-01-01

331

Laminar flame and acoustic waves in two-dimensional flow

The complete system of fluid dynamics equations describing the development of instability of a reaction front in a two-dimensional flow in reversed time are reduced to a closed system of equations of front dynamics by using Lagrangian variables and integrals of motion. The system can be used to analyze processes behind the front without solving the complete system of fluid dynamics and chemical kinetics equations. It is demonstrated how the gas density disturbances induced by the moving front can be described in the adiabatic approximation.

Zaytsev, M. L., E-mail: mlzaytsev@gmail.com; Akkerman, V. B., E-mail: slava.akkerman@gmail.com [Russian Academy of Sciences, Nuclear Safety Institute (Russian Federation)

2011-03-15

332

Two-dimensional macroscopic quantum dynamics in YBCO Josephson junctions

We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBCO Josephson junction coupled with an LC circuit. The TA and MQT escape rate are calculated by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling leads to the slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson junctions.

Shiro Kawabata; Takeo Kato; Floriana Lombardi; Thilo Bauch

2009-11-06

333

Dissipative vortex solitons in two-dimensional lattices

We report the existence of stable symmetric vortex-type solutions for two-dimensional nonlinear discrete dissipative systems governed by a cubic-quintic complex Ginzburg-Landau equation. We construct a whole family of vortex solitons with a topological charge S=1. Surprisingly, the dynamical evolution of unstable solutions of this family does not significantly alter their profile, but instead their phase distribution completely changes; they transform into two-charge swirl-vortex solitons. We dynamically excite this structure showing its experimental feasibility.

Mejia-Cortes, C.; Soto-Crespo, J. M. [Instituto de Optica, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid (Spain); Molina, Mario I.; Vicencio, Rodrigo A. [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Center for Optics and Photonics, Universidad de Concepcion, Casilla 4016, Concepcion (Chile)

2010-12-15

334

Linear and nonlinear viscous flow in two-dimensional fluids

We report on molecular dynamics simulations of shear viscosity {eta} of a dense two-dimensional fluid as a function of the shear rate {gamma}. We find an analytic dependence of {eta} on {gamma}, and do not find any evidence whatsoever of divergence in the Green-Kubo (GK) value that would be caused by the well-known long-time tail for the shear-stress autocorrelation function, as predicted by the mode-coupling theory. In accordance with the linear response theory, the GK value of {eta} agrees remarkably well with nonequilibrium values at small shear rates. (c) 1995 The American Physical Society

Gravina, D.; Ciccotti, G.; Holian, B.L. [Dipartimento di Fisica, Universita di Roma ``La Sapienza,`` piazzale Aldo Moro 2, 00185 Roma (Italy)] [Dipartimento di Fisica, Universita di Roma ``La Sapienza,`` piazzale Aldo Moro 2, 00185 Roma (Italy); [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1995-12-01

335

Hydrometeor classification from two-dimensional video disdrometer data

NASA Astrophysics Data System (ADS)

The first hydrometeor classification technique based on two-dimensional video disdrometer (2DVD) data is presented. The method provides an estimate of the dominant hydrometeor type falling over time intervals of 60 s during precipitation, using the statistical behavior of a set of particle descriptors as input, calculated for each particle image. The employed supervised algorithm is a support vector machine (SVM), trained over 60 s precipitation time steps labeled by visual inspection. In this way, eight dominant hydrometeor classes can be discriminated. The algorithm achieved high classification performances, with median overall accuracies (Cohen's K) of 90% (0.88), and with accuracies higher than 84% for each hydrometeor class.

Grazioli, J.; Tuia, D.; Monhart, S.; Schneebeli, M.; Raupach, T.; Berne, A.

2014-09-01

336

Merging of Dirac points in a two-dimensional crystal

NASA Astrophysics Data System (ADS)

We study under which general conditions a pair of Dirac points in the electronic spectrum of a two-dimensional crystal may merge into a single one. The merging signals a topological transition between a semimetallic phase and a band insulator. We derive a universal Hamiltonian that describes the physical properties of the transition, which is controlled by a single parameter, and analyze the Landau-level spectrum in its vicinity. This merging may be observed in the organic salt ?-(BEDT-TTF)2I3 or in an optical lattice of cold atoms simulating deformed graphene.

Montambaux, G.; Piéchon, F.; Fuchs, J.-N.; Goerbig, M. O.

2009-10-01

337

Two-dimensional symmetrical inlets with external compression

NASA Technical Reports Server (NTRS)

The purpose of inlets like, for instance, those of air-cooled radiators and scoops is to take a certain air quantity out of the free stream and to partly convert the free-stream velocity into pressure. In the extreme case this pressure conversion may occur either entirely in the interior of the inlet (inlet with internal compression) or entirely in the free stream ahead of the inlet (inlet with external compression). In this report a theory for two-dimensional inlets with external compression is developed and illustrated by numerical examples. Intermediary forms between inlets with internal and external compression which can be derived from the latter are briefly discussed.

Ruden, P

1950-01-01

338

Two-dimensional Lagrangian simulation of suspended sediment

A two-dimensional laterally averaged model for suspended sediment transport in steady gradually varied flow that is based on the Lagrangian reference frame is presented. The layered Lagrangian transport model (LLTM) for suspended sediment performs laterally averaged concentration. The elevations of nearly horizontal streamlines and the simulation time step are selected to optimize model stability and efficiency. The computational elements are parcels of water that are moved along the streamlines in the Lagrangian sense and are mixed with neighboring parcels. Three applications show that the LLTM can accurately simulate theoretical and empirical nonequilibrium suspended sediment distributions and slug injections of suspended sediment in a laboratory flume.

Schoellhamer, David H.

1988-01-01

339

SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.

A simplification of the two-dimensional (2-D) continuity and momentum equations is the diffusion equation. To investigate its capability, the numerical model using the diffusion approach is applied to a hypothetical failure problem of a regional water reservoir. The model is based on an explicit, integrated finite-difference scheme, and the floodplain is simulated by a popular home computer which supports 64K FORTRAN. Though simple, the 2-D model can simulate some interesting flooding effects that a 1-D full dynamic model cannot.

Hromadka, T.V., II; Lai, Chintu

1985-01-01

340

Fractional-step method for two-dimensional estuarine transport

The fractional-step method was used in this study to split the longitudinal advective transport term from the other terms in the two-dimensional, laterally-averaged equation for estuarine mass transport. The method of characteristics with spline interpolations was used to approximate the longitudinal advective transport. A general discussion of the fractional-step method, the specific algorithm developed in this investigation, and results of numerical tests are presented. Application of the fractional-step method in conjunction with the characteristic-spline scheme offers the potential for improved simulations of transport for situations in which concentration gradients are steep.

Bales, Jerad D.; Holley, Edward R.

1988-01-01

341

Two-Dimensional Two-Component Plasma with Adsorbing Impurities

NASA Astrophysics Data System (ADS)

We study the behavior of the two-dimensional two-component plasma in the presence of some adsorbing impurities. Using a solvable model, we find analytic expressions for the thermodynamic properties of the plasma such as the n-body densities, the grand potential, and the pressure. We specialize in the case where there are one or two adsorbing point impurities in the plasma, and in the case where there are one or two parallel adsorbing lines. In the former case we study the effective interaction between the impurities, due to the charge redistribution around them. The latter case is a model for electrodes with adsorbing sticky sites on their surface.

Ferrero, Alejandro; Téllez, Gabriel

2007-11-01

342

Vortex properties of two-dimensional superconducting Pb films.

Using low temperature scanning tunnelling microscopy/spectroscopy (STM/STS) we have investigated the vortex behaviours of two-dimensional superconducting Pb films at different thicknesses. STS at the vortex core shows an evolution of electronic states with film thickness. Transition from the clean limit to the dirty limit of superconductivity is identified, which can be ascribed to the decreased electronic mean free path induced by stronger scattering from the disordered interface at smaller thicknesses. A magnetic field dependent vortex core size is observed even for such a low- ? superconductor. The weak pinning induced by surface defects leads to the formation of a distorted hexagonal vortex lattice. PMID:21389372

Ning, Y X; Song, C L; Wang, Y L; Chen, Xi; Jia, J F; Xue, Q K; Ma, X C

2010-02-17

343

Ion focusing by an expanding, two-dimensional plasma sheath

NASA Astrophysics Data System (ADS)

The temporal evolution of the collisionless, pulsed plasma sheath around a square bar is studied using a two-dimensional particle-in-cell code. It is found that the incident ion dose is peaked near to, but not on, the corner. This effect is explained physically by considering ion trajectories across the sheath, yielding an estimate for the dose in good agreement with the simulation results. The present results are compared to those from a fluid simulation [T. E. Sheridan and M. J. Alport, Appl. Phys. Lett. 64, 1783 (1994)], and it is found that the fluid simulation erroneously underestimates the ion dose near the corner of the bar.

Sheridan, T. E.

1996-04-01

344

Surface gravity waves over a two-dimensional random seabed.

We extend homogenization theory to study the two-dimensional evolution of weakly nonlinear waves in a sea where the bathymetry is random over a large area. A deterministic nonlinear Schrödinger equation is derived for the envelope of a nearly sinusoidal progressive wave train. Randomness is shown to yield a linear term with a complex coefficient depending on a certain statistical average of the bathymetry. Numerical solutions are discussed for the diffraction of a Stokes wave in head-sea incidence towards a bathymetry of given plan form. Effects of the height and plan form of the randomness, as well as wave nonlinearity are examined analytically and numerically. PMID:12241504

Pihl, Jřrgen H; Mei, Chiang C; Hancock, Matthew J

2002-07-01

345

Local contact numbers in two dimensional packings of frictional disks

We analyze the local structure of two dimensional packings of frictional disks numerically. We focus on the fractions x_i of particles that are in contact with i neighbors, and systematically vary the confining pressure p and friction coefficient \\mu. We find that for all \\mu, the fractions x_i exhibit powerlaw scaling with p, which allows us to obtain an accurate estimate for x_i at zero pressure. We uncover how these zero pressure fractions x_i vary with \\mu, and introduce a simple model that captures most of this variation. We also probe the correlations between the contact numbers of neighboring particles.

Silke Henkes; Kostya Shundyak; Wim van Saarloos; Martin van Hecke

2009-11-27

346

Quantum control in two-dimensional Fourier-transform spectroscopy

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

347

On Two-Dimensional Sonic-Subsonic Flow

NASA Astrophysics Data System (ADS)

A compensated compactness framework is established for sonic-subsonic approximate solutions to the two-dimensional Euler equations for steady irrotational flows that may contain stagnation points. Only crude estimates are required for establishing compactness. It follows that the set of subsonic irrotational solutions to the Euler equations is compact; thus flows with sonic points over an obstacle, such as an airfoil, may be realized as limits of sequences of strictly subsonic flows. Furthermore, sonic-subsonic flows may be constructed from approximate solutions. The compactness framework is then extended to self-similar solutions of the Euler equations for unsteady irrotational flows.

Chen, Gui-Qiang; Dafermos, Constantine M.; Slemrod, Marshall; Wang, Dehua

2007-05-01

348

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

349

Two-dimensional phononic-photonic bandgap optomechanical crystal cavity

We present the fabrication and characterization of an artificial crystal structure formed from a thin-film of silicon which has a full phononic bandgap for microwave X-band phonons and a two-dimensional pseudo-bandgap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the bandgap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large vacuum coupling rate of 220kHz between the fundamental optical cavity resonance at 195THz and a co-localized mechanical resonance at 9.3GHz.

Safavi-Naeini, Amir H; Meenehan, Sean; Chan, Jasper; Groeblacher, Simon; Painter, Oskar

2014-01-01

350

Statistical Mechanics of Unbound Two Dimensional Self-Gravitating Systems

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

351

Lagrangian statistics in forced two-dimensional turbulence.

We report on simulations of two-dimensional turbulence in the inverse energy cascade regime. Focusing on the statistics of Lagrangian tracer particles, scaling behavior of the probability density functions of velocity fluctuations is investigated. The results are compared to the three-dimensional case. In particular an analysis in terms of compensated cumulants reveals the transition from a strong non-Gaussian behavior with large tails to Gaussianity. The reported computation of correlation functions for the acceleration components sheds light on the underlying dynamics of the tracer particles. PMID:18851157

Kamps, O; Friedrich, R

2008-09-01

352

Optical interleavers based on two-dimensional photonic crystals.

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

353

Ultra-subwavelength two-dimensional plasmonic circuits.

We report electronics regime (GHz) two-dimensional (2D) plasmonic circuits, which locally and nonresonantly interface with electronics, and thus offer to electronics the benefits of their ultrasubwavelength confinement, with up to 440,000-fold mode-area reduction. By shaping the geometry of 2D plasmonic media 80 nm beneath an unpatterned metallic gate, plasmons are routed freely into various types of reflections and interferences, leading to a range of plasmonic circuits, e.g., plasmonic crystals and plasmonic-electromagnetic interferometers, offering new avenues for electronics. PMID:22494364

Andress, William F; Yoon, Hosang; Yeung, Kitty Y M; Qin, Ling; West, Ken; Pfeiffer, Loren; Ham, Donhee

2012-05-01

354

Decoherence in Two-Dimensional Quantum Random Walks with Traps

Quantum random walk in a two-dimensional lattice with randomly distributed traps is investigated. Distributions of quantum walkers are evaluated dynamically for the cases of Hadamard, Fourier, and Grover coins, and quantum to classical transition is examined as a function of the density of the traps. It is shown that traps act as a serious and additional source of quantum decoherence. Furthermore, non-trivial temporal dependence of the standard deviation of the probability distribution of the walker is found when the trapping imperfections are introduced.

Meltem Gonulol; Ekrem Aydiner; Ozgur E. Mustecaplioglu

2009-09-07

355

Two-dimensional random walk in a bounded domain

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

2009-10-30

356

Counterpropagating surface solitons in two-dimensional photonic lattices.

We study interaction of counterpropagating beams in truncated two-dimensional photonic lattices induced optically in photorefractive crystals, and demonstrate the existence of counterpropagating surface solitons localized in the lattice corners and at the edges. We display intriguing dynamical properties of such composite optical beams and reveal that the lattice surface provides a strong stabilization effect on the beam propagation. We also observe dynamical instabilities for stronger coupling and longer propagation distances in the form of beam splitting. No such instabilities exist in the single beam surface propagation. PMID:19997392

Jovi?, Dragana; Kivshar, Yuri S; Jovanovi?, Raka; Beli?, Milivoj

2009-11-23

357

Beam propagation in two-dimensional media with spatial dispersion

NASA Astrophysics Data System (ADS)

We theoretically investigate the propagation of a paraxial beam in two-dimensional media with spatial dispersion. Based on the spatial dispersion theory and the (1+1)-dimensional paraxial wave equation, we get an expression which determines the diffraction of the beam. By fitting the dispersion surface of a typical spatial dispersion medium (a photonic crystal) calculated by the plane-wave-expansion method, the value of the diffraction term is determined, with which one can predict the diffraction of the paraxial beam that propagates in such media. Numerical simulations based on the finite-difference time-domain method confirm the theoretical results.

Dai, Zhiping; Xu, Yi; Guo, Qi; Chi, Sien

2013-05-01

358

Two-dimensional carbon allotrope with strong electronic anisotropy

NASA Astrophysics Data System (ADS)

Two two-dimensional carbon allotropes comprised of octagons and pentagons are proposed based on the first-principles calculations. The two carbon allotropes, named OPG-L and OPG-Z, are found to have distinct properties. OPG-L is metallic, while OPG-Z is a gapless semimetal. Remarkably, OPG-Z exhibits pronounced electronic anisotropy with highly anisotropic Dirac points at the Fermi level. A tight-binding model is suggested to describe the low-energy quasiparticles, which clarifies the origin of the anisotropic Dirac points. The electronic anisotropy of OPG-Z is expected to have interesting potential applications in electronic devices.

Su, Cong; Jiang, Hua; Feng, Ji

2013-02-01

359

Two-dimensional dynamics of relativistic solitons in cold plasmas

The two-dimensional dynamics of solitons appearing during relativistic laser-plasma interaction is investigated. The analysis starts from known soliton models in one space-dimension (1D). Some of the soliton solutions are already unstable in 1D, and all suffer from transverse instability in two dimensions (2D). The most unstable modes are calculated. They give a hint to the 2D structures which appear because of transversal effects. The linear stability considerations are supplemented by full 2D nonlinear simulations.

Lehmann, G.; Laedke, E. W.; Spatschek, K. H. [Institut fuer Theoretische Physik, Heinrich-Heine-Universitaet Duesseldorf, D-40225 Duesseldorf (Germany)

2008-07-15

360

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

361

Basics and recent advances of two dimensional- polyacrylamide gel electrophoresis

Gel- based proteomics is one of the most versatile methods for fractionating protein complexes. Among these methods, two dimensional- polyacrylamide gel electrophoresis (2-DE) represents a mainstay orthogonal approach, which is popularly used to simultaneously fractionate, identify, and quantify proteins when coupled with mass spectrometric identification or other immunological tests. Although 2-DE was first introduced more than three decades ago, several challenges and limitations to its utility still exist. This review discusses the principles of 2-DE as well as both recent methodological advances and new applications. PMID:24735559

2014-01-01

362

NSDL National Science Digital Library

This lesson plan begins with two rectangular pieces of paper -- one forming a cylinder by joining the long sides, the other forming a second cylinder by joining the short sides. Which of these two cylinders will have greater volume? or will they hold the same amount? Students will build a family of cylinders and discover the relation between the dimensions of the generating rectangle and the resulting pair of cylinders. They will also order the cylinders by the amount they hold, and draw a conclusion about the relation between the cylinder's dimensions and the amount it holds. Watch video clips of different classrooms' experiments with this classic conservation problem from Piagetian psychology; see reflections from teachers; read predictions collated from 667 different students.

Forum, The M.

2001-01-01

363

Construction of a two-dimensional thermal neutron detector

NASA Astrophysics Data System (ADS)

China Spallation Neutron Source (CSNS) was under construction since 2008. A two-dimensional thermal neutron detector with sensitive area of 200mm×200mm was constructed for the Reflect Spectrometer of CSNS. The detector was based on two-dimensional cathode strip readout MWPC, using 5.5atm3He+2.5atmC3H8 mixture as working gas, and the thickness of the gas volume was 16mm. A readout electronics system was also developed for the detector, which mainly consists of charge-sensitive preamplifiers, amplifiers, charge measurement modules and a 6U VME64x crate. The design maximum neutron count rate of the detector was 105 events per second and the calculated neutron detection efficiency was about 70% for A2 neutrons. A prototype of the detector had been constructed at first, which own an energy resolution (FWHM) of about 23% for 55Fe 5.9keV X-ray, and its spatial resolution (FWHM) along the anode wire direction was about 300?m in X-ray test. The detector was then tested by an Am-Be neutron source. The pulse height spectrum of the neutron signal was studied. The detector can work normally and has a good performance in neutron-gamma ray discrimination.

Wang, Xiao-hu; Chen, Yuan-bo; Sheng, Huan-yi; Zhao, Yu-bin; Zhang, Hong-yu; Zhu, Qi-ming; Liu, Rong-guang; Zhang, Jian; Xu, Pin

2009-07-01

364

Two-dimensional nuclear magnetic resonance of quadrupolar systems

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

365

Detection of chemicals in mixed, two-dimensional Raman spectra

NASA Astrophysics Data System (ADS)

Recently, researchers at the Naval Research Laboratory have developed the SWORrD system for measuring two-dimensional Raman Spectra. The device consists of a tunable 2d ultraviolet laser that illuminates the sample at various wavelengths (210-300 nm) and collects a single Raman spectrum at each laser wavelength. The single spectra are combined to form a two-dimensional spectrum (laser wavelength by scattered wavenumber). In this paper we introduce a novel method for the detection of known agents ('targets') within measured 2d spectra. Our method is bases on 'linear mixed pixel' techniques from hyperspectral imagery; in particular, we generalize the Adaptive Subspace Detector (ASD) to a form suitable for SWORrD samples. Our detector uses the individual laser runs to define a set of points within wavenumber space; the set of points corresponding to a 2d spectra defines a particular subspace that contains each material. These subspaces are then used with ASD to identify targets. We include experimental results using real-world data to illustrate our results.

Gillis, David; Grun, Jacob; Bowles, Jeffrey; Lunsford, Robert; Nikitin, Sergei; Manka, Charles

2010-04-01

366

Aspects of Jamming in Two-Dimensional Frictionless Systems

In this work we provide an overview of jamming transitions in two dimensional systems focusing on the limit of frictionless particle interactions in the absence of thermal fluctuations. We first discuss jamming in systems with short range repulsive interactions, where the onset of jamming occurs at a critical packing density and where certain quantities show a divergence indicative of critical behavior. We describe how aspects of the dynamics change as the jamming density is approached and how these dynamics can be explored using externally driven probes. Different particle shapes can produce jamming densities much lower than those observed for disk-shaped particles, and we show how jamming exhibits fragility for some shapes while for other shapes this is absent. Next we describe the effects of long range interactions and jamming behavior in systems such as charged colloids, vortices in type-II superconductors, and dislocations. We consider the effect of adding obstacles to frictionless jamming systems and discuss connections between this type of jamming and systems that exhibit depinning transitions. Finally, we discuss open questions such as whether the jamming transition in all these different systems can be described by the same or a small subset of universal behaviors, as well as future directions for studies of jamming transitions in two dimensional systems, such as jamming in self-driven or active matter systems.

C. Reichhardt; C. J. Olson Reichhardt

2013-12-18

367

The Convective Urca Process with Implicit Two-Dimensional Hydrodynamics

Consideration of the role of the convective flux in the thermodymics of the convective Urca neutrino loss process in degenerate, convective, quasi-static, carbon-burning cores shows that the convective Urca process slows down the convective current around the Urca-shell, but, unlike the "thermal" Urca process, does not reduce the entropy or temperature for a given convective volume. Here we demonstrate these effects with two-dimensional numerical hydrodynamical calculations. These two-dimensional implicit hydrodynamics calculations invoke an artificial speeding up of the nuclear and weak rates. They should thus be regarded as indicative, but still qualitative. We find that, compared to a case with no Urca-active nuclei, the case with Urca effects leads to a higher entropy in the convective core because the energy released by nuclear burning is confined to a smaller volume by the effective boundary at the Urca shell. All else being equal, this will tend to accelerate the progression to dynamical runaway. We discuss the open issues regarding the impact of the convective Urca process on the evolution to the "smoldering phase" and then to dynamical runaway.

Josef Stein; J. Craig Wheeler

2005-12-22

368

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

369

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

370

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

371

Effective complex permittivity tensor of a periodic array of cylinders

We determine the effective complex permittivity of a two-dimensional composite, consisting of an arbitrary doubly periodic array of identical circular cylinders in a homogeneous matrix, and whose dielectric properties are complex-valued. Efficient formulas are provided to determine the effective complex permittivity tensor which are in excellent agreement with numerical calculations. We also show that in contrast to the real-valued case, the real and imaginary parts of the effective complex-valued tensor can exhibit non-monotonic behavior as functions of volume fraction of cylinders, and can be either greater or less than that of the constituents.

Yuri A. Godin

2013-01-01

372

Wavelength dependence of focusing properties of two-dimensional photonic quasicrystal flat lens.

We investigated the wavelength dependence of the focusing properties of a germanium-cylinder-based two-dimensional (2D) decagonal Penrose-type photonic quasicrystal (PQC) flat lens for the first time, to the best of our knowledge. We found that near the second bandgap and in the high-frequency side (between the bandgap boundary and the first light intensity peak) of the pass band, the flat lens can exhibit a focusing effect for a point light source and that the focusing wavelengths can directly be drawn from the photonic band structure. For all the focusing wavelengths, the summation of the object distance and the image distance is less than the thickness of the flat lens when the object distance is half the thickness of the flat lens. As the wavelength increases, the image distance, the image quality, and the effective refractive index of the flat lens increase, whereas the image power of the point light source decreases. The effective refractive index of the flat lens is less than -1. PMID:22627552

Liu, Jianjun; Fan, Zhigang; Hu, Haili; Yang, Maohua; Guan, Chunying; Yuan, Libo; Guo, Hao; Zhang, Xiong

2012-05-15

373

NASA Astrophysics Data System (ADS)

Coupled effect of horizontal seepage and gravity modulation on the onset and nonlinear regimes of two-dimensional thermal buoyancy convection in horizontal fluid-saturated porous cylinder of rectangular cross section with perfectly conductive boundaries is studied. It is shown that gravity modulation makes destabilizing effect. Null-dimensional dynamical system describing supercritical convective regimes is derived. Conditions for existence of stable periodical regimes are defined. It is found that system demonstrates dynamics on a torus which can be either resonant or non-resonant depending on the parameters. Synchronization domains which correspond to the resonant torus existence in the parameter space are determined by the rotation number technique. It is found that at certain values of the ratio of the cross section height to width, degeneracy takes place. In this case different stable periodical regimes forming one-parametric family coexist. Linear stability and nonlinear dynamics of the system at finite values of the parameters are studied numerically by finite difference method.

Maryshev, Boris; Lyubimova, Tatyana; Lyubimov, Dmitriy

2013-08-01

374

Mobility and Diffusion-Ordered Two-Dimensional NMR Spectroscopy

NASA Astrophysics Data System (ADS)

Mobility and diffusion-ordered two-dimensional nuclear magnetic resonance spectroscopy experiments have been developed for the analysis of mixtures. In the mobility -ordered experiments, the full range of positive and negative electrophoretic mobilities is displayed in one dimension and chemical shifts are displayed in the other. A concentric cylindrical tube electrophoresis chamber was designed to reduce the effective pathlength for current and to provide unidirectional flow for ions of interest. Techniques based upon the reverse precession method were also implemented to recover the signs of the mobilities and improved resolution in the mobility dimension was obtained by replacing Fourier transformation of truncated data sets with a linear prediction analysis. In the diffusion-ordered two-dimensional NMR experiments, the conventional chemical shift spectrum is resolved in one dimension and spectra of diffusion rates or molecular radii are resolved in the other. Diffusion dependent pulsed field gradient NMR data sets were inverted by means of the computer programs SPLMOD or DISCRETE, when discrete diffusion coefficients were present, and CONTIN when continuous distributions were present. Since the inversion is ill -conditioned, it was necessary to introduce additional information to limit the range of the solutions. In addition to prior knowledge of the decay kernels and non-negativity of amplitudes and damping constants, a set of rejection criteria was constructed for the discrete analysis case that took into account physical limits on diffusion coefficients, experimentally accessible values, and variations in effective decay kernels resulting from instrumental non-linearities. Examples of analyses of simulated data and experimental data for mixtures are presented as well as two-dimensional spectra generated by CONTIN for polydisperse polymer samples. Also, resolution in the diffusion dimension was increased by performing experiments on hydrophobic molecules in the presence of surfactant micelles. Finally, the diffusion-ordered experiment was used to study the polymer induced breakdown of micelles consisting of cetyltrimethylammonium bromide and sodium salicylate. Addition of the polymer poly(vinyl methyl ether) resulted in an increase in the micelle diffusion coefficient and at high polymer concentrations and elevated temperatures the polymer and micelle were observed to diffuse at the same rate.

Morris, Kevin Freeman

375

Airfoil model in Two-Dimensional Low-Turbulence Tunnel

NASA Technical Reports Server (NTRS)

Airfoil model with pressure taps inside the test section of the Two-Dimensional Low-Turbulence Tunnel. The Two-Dimensional Low-Turbulence Tunnel was originally called the Refrigeration or 'Ice' tunnel because it was intended to support research on aircraft icing. The tunnel was built of wood, lined with sheet steel, and heavily insulated on the outside. Refrigeration equipment was installed to generate icing conditions inside the test section. The NACA sent out a questionnaire to airline operators, asking them to detail the specific kinds of icing problems they encountered in flight. The replies became the basis for a comprehensive research program begun in 1938 when the tunnel commenced operation. Research quickly focused on the concept of using exhaust heat to prevent ice from forming on the wing's leading edge. This project was led by Lewis Rodert, who later would win the Collier Trophy for his work on deicing. By 1940, aircraft icing research had shifted to the new Ames Research Laboratory, and the Ice tunnel was refitted with screens and honeycomb. Researchers were trying to eliminate all turbulence in the test section. From TN 1283: 'The Langley two-dimensional low-turbulence pressure tunnel is a single-return closed-throat tunnel.... The tunnel is constructed of heavy steel plate so that the pressure of the air may be varied from approximately full vacuum to 10 atmospheres absolute, thereby giving a wide range of air densities. Reciprocating compressors with a capacity of 1200 cubic feet of free air per minute provide compressed air. Since the tunnel shell has a volume of about 83,000 cubic feet, a compression rate of approximately one atmosphere per hour is obtained. ... The test section is rectangular in shape, 3 feet wide, 7 1/2 feet high, and 7 1/2 feet long. ... The over-all size of the wind-tunnel shell is about 146 feet long and 58 feet wide with a maximum diameter of 26 feet. The test section and entrance and exit cones are surrounded by a 22-foot diameter section of the shell to provide a space to house much of the essential equipment.

1939-01-01

376

Optical properties of two-dimensional metamaterial photonic crystals

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

377

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

378

A portable Halbach magnet that can be opened and closed without force: The NMR-CUFF

NASA Astrophysics Data System (ADS)

Portable equipment for nuclear magnetic resonance (NMR) is becoming increasingly attractive for use in a variety of applications. One of the main scientific challenges in making NMR portable is the design of light-weight magnets that possess a strong and homogeneous field. Existing NMR magnets can provide such magnetic fields, but only for small samples or in small regions, or are rather heavy. Here we show a simple yet elegant concept for a Halbach-type permanent magnet ring, which can be opened and closed with minimal mechanical force. An analytical solution for an ideal Halbach magnet shows that the magnetic forces cancel if the structure is opened at an angle of 35.3° relative to its poles. A first prototype weighed only 3.1 kg, and provided a flux density of 0.57 T with a homogeneity better than 200 ppm over a spherical volume of 5 mm in diameter without shimming. The force needed to close it was found to be about 20 N. As a demonstration, intact plants were imaged and water (xylem) flow measured. Magnets of this type (NMR-CUFF = Cut-open, Uniform, Force Free) are ideal for portable use and are eminently suited to investigate small or slender objects that are part of a larger or immobile whole, such as branches on a tree, growing fruit on a plant, or non-metallic tubing in industrial installations. This new concept in permanent-magnet design enables the construction of openable, yet strong and homogeneous magnets, which aside from use in NMR or MRI could also be of interest for applications in accelerators, motors, or magnetic bearings.

Windt, Carel W.; Soltner, Helmut; Dusschoten, Dagmar van; Blümler, Peter

2011-01-01

379

Two-dimensional photonic quasicrystal flat lens with three scatterers

NASA Astrophysics Data System (ADS)

A two-dimensional (2-D) photonic quasicrystal (PQC) flat lens with three scatterers is proposed, and its focusing characteristics for a point source are analyzed for the case of a continuously changing scatterer radius. The results show that a super-lens can be formed by three scatterers, and there is a threshold for scatterer radius. The focusing characteristics of the flat lens within the focusing radius are changed with regularity. It is reported for the first time that best image quality and the stability of perfect imaging in this 2-D PQC flat lens with three scatterers are superior to those in 2-D PQC or periodic photonic crystal flat lenses with multiple scatterers.

Liu, Jianjun; Fan, Zhigang

2014-07-01

380

Vortices in the classical two-dimensional anisotropic Heisenberg model

The structure and dynamics of vortex spin configurations are considered for a two-dimensional classical Heisenberg model with easy-plane anisotropy. Using both approximate analytic methods based on a continuum description and direct numerical simulations on a discrete lattice, two types of static vortices (planar and out-of-plane) are identified. Planar (out-of-plane) vortices are stable below (above) a critical anisotropy. The structure of moving vortices is calculated approximately in a continuum limit. Vortex-vortex interactions are investigated numerically. A phenomenology for dynamic structure factors is developed based on a dilute gas of mobile vortices above the Kosterlitz-Thouless transition. This yields a central peak scattering whose form is compared with the results of a large-scale Monte Carlo--molecular-dynamics simulation.

Gouvat /reat; xa, M. E.; Wysin, G. M.; Bishop, A. R.; Mertens, F. G.

1989-06-01

381

Two-dimensional NQR using ultra-broadband electronics

NASA Astrophysics Data System (ADS)

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 14N) by using multi-frequency excitation and a single RF coil. Experimental results on pure samples and mixtures are also presented.

Mandal, S.; Song, Y.-Q.

2014-03-01

382

Two-dimensional lattice-fluid model with waterlike anomalies

NASA Astrophysics Data System (ADS)

We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the Mercedes Benz type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed.

Buzano, C.; de Stefanis, E.; Pelizzola, A.; Pretti, M.

2004-06-01

383

Two-dimensional lattice-fluid model with waterlike anomalies.

We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed. PMID:15244571

Buzano, C; De Stefanis, E; Pelizzola, A; Pretti, M

2004-06-01

384

On two-dimensional packets of capillary-gravity waves

NASA Technical Reports Server (NTRS)

The motion of a two-dimensional packet of capillary-gravity waves on water of finite depth is studied. The evolution of a packet is described by two partial differential equations: the nonlinear Schroedinger equation with a forcing term and a linear equation, which is of either elliptic or hyperbolic type depending on whether the group velocity of the capillary-gravity wave is less than or greater than the velocity of long gravity waves. These equations are used to examine the stability of the Stokes capillary-gravity wave train. The analysis reveals the existence of a resonant interaction between a capillary-gravity wave and a long gravity wave. The interaction requires that the liquid depth be small in comparison with the wavelength of the (long) gravity waves and the evolution equations describing the dynamics of this interaction are derived.

Djordjevic, V. D.; Redekopp, L. G.

1977-01-01

385

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

386

Two-dimensional NQR using ultra-broadband electronics.

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

387

Dislocations and grain boundaries in two-dimensional boron nitride.

A new dislocation structure-square-octagon pair (4|8) is discovered in two-dimensional boron nitride (h-BN), via first-principles calculations. It has lower energy than corresponding pentagon-heptagon pairs (5|7), which contain unfavorable homoelemental bonds. On the basis of the structures of dislocations, grain boundaries (GB) in BN are investigated. Depending on the tilt angle of grains, GB can be either polar (B-rich or N-rich), constituted by 5|7s, or unpolar, composed of 4|8s. The polar GBs carry net charges, positive at B-rich and negative at N-rich ones. In contrast to GBs in graphene which generally impede the electronic transport, polar GBs have a smaller bandgap compared to perfect BN, which may suggest interesting electronic and optical applications. PMID:22780217

Liu, Yuanyue; Zou, Xiaolong; Yakobson, Boris I

2012-08-28

388

Two-dimensional polymers with random short-range interactions

We use complete enumeration and Monte Carlo techniques to study two-dimensional self-avoiding polymer chains with quenched {open_quotes}charges{close_quotes} {plus_minus}1. The interaction of charges at neighboring lattice sites is described by q{sub i}q{sub j}. We find that a polymer undergoes a collapse transition at a temperature T{sub {theta}}, which decreases with increasing imbalance between charges. At the transition point, the dependence of the radius of gyration of the polymer on the number of monomers is characterized by an exponent {nu}{sub {theta}}=0.60{plus_minus}0.02, which is slightly larger than the similar exponent for homopolymers. We find no evidence of freezing at low temperatures. {copyright} {ital 1997} {ital The American Physical Society}

Golding, I.; Kantor, Y. [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69 978 (Israel)] [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69 978 (Israel)

1997-08-01

389

Pair correlations in the two-dimensional Fermi gas.

We consider the two-dimensional Fermi gas at finite temperature with attractive short-range interactions. Using the virial expansion, which provides a controlled approach at high temperatures, we determine the spectral function and contact for the normal state. Our calculated spectra are in qualitative agreement with recent photoemission measurements [M. Feld et al., Nature (London) 480, 75 (2011).], thus suggesting that the observed pairing gap is a feature of the high-temperature gas rather than being evidence of a pseudogap regime just above the superfluid transition temperature. We further argue that the strong pair correlations result from the fact that the crossover to bosonic dimers occurs at weaker interactions than previously assumed. PMID:24483801

Ngampruetikorn, Vudtiwat; Levinsen, Jesper; Parish, Meera M

2013-12-27

390

Bound states in a quasi-two-dimensional Fermi gas.

We consider the problem of N identical fermions of mass m(?) and one distinguishable particle of mass m(?) interacting via short-range interactions in a confined quasi-two-dimensional (quasi-2D) geometry. For N=2 and mass ratios m(?)/m(?)<13.6, we find non-Efimov trimers that smoothly evolve from 2D to 3D. In the limit of strong 2D confinement, we show that the energy of the N+1 system can be approximated by an effective two-channel model. We use this approximation to solve the 3+1 problem and we find that a bound tetramer can exist for mass ratios m(?)/m(?) as low as 5 for strong confinement, thus providing the first example of a universal, non-Efimov tetramer involving three identical fermions. PMID:23414030

Levinsen, Jesper; Parish, Meera M

2013-02-01

391

Two-dimensional nonlinear map characterized by tunable Lévy flights

NASA Astrophysics Data System (ADS)

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

392

Electronic properties of two-dimensional covalent organic frameworks.

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

393

Two-dimensional Fermi liquid with fixed chemical potential

de Haas-van Alphen measurements made on the organic metal {beta}{sup ''}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} reveal the existence of an ideal two-dimensional (2D) Fermi surface, but rather than having the conventional sawtooth wave form that is normally observed in all other 2D electron gases, instead, an ''inverse sawtooth'' wave form is observed, which is to be expected when the chemical potential is pinned at a constant value. While this proves the existence of the theoretically predicted quasi-one-dimensional band, it further implies that this band has an exceptionally large density of states. (c) 2000 The American Physical Society.

Wosnitza, J. [Physikalisches Institut, Universitaet Karlsruhe, 76128 Karlsruhe, (Germany)] [Physikalisches Institut, Universitaet Karlsruhe, 76128 Karlsruhe, (Germany); Wanka, S. [Physikalisches Institut, Universitaet Karlsruhe, 76128 Karlsruhe, (Germany)] [Physikalisches Institut, Universitaet Karlsruhe, 76128 Karlsruhe, (Germany); Hagel, J. [Physikalisches Institut, Universitaet Karlsruhe, 76128 Karlsruhe, (Germany)] [Physikalisches Institut, Universitaet Karlsruhe, 76128 Karlsruhe, (Germany); Balthes, E. [Grenoble High Magnetic Field Laboratory, MPI and C.N.R.S., 38042 Grenoble, (France)] [Grenoble High Magnetic Field Laboratory, MPI and C.N.R.S., 38042 Grenoble, (France); Harrison, N. [National High Magnetic Field Laboratory, LANL Los Alamos, New Mexico 87545 (United States)] [National High Magnetic Field Laboratory, LANL Los Alamos, New Mexico 87545 (United States); Schlueter, J. A.; Kini, A.M.; Geiser, U. [Chemistry and Materials Science Divisions, Argonne National Laboratory, Argonne, Ilinois 60439 (United States)] [Chemistry and Materials Science Divisions, Argonne National Laboratory, Argonne, Ilinois 60439 (United States); Mohtasham, J.; Winter, R. W. [Department of Chemistry, Portland State University, Portland, Oregon 97207 (United States)] (and others) [Department of Chemistry, Portland State University, Portland, Oregon 97207 (United States)

2000-03-15

394

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

395

Random diffusion and cooperation in continuous two-dimensional space.

This work presents a systematic study of population games of the Prisoner's Dilemma, Hawk-Dove, and Stag Hunt types in two-dimensional Euclidean space under two-person, one-shot game-theoretic interactions, and in the presence of agent random mobility. The goal is to investigate whether cooperation can evolve and be stable when agents can move randomly in continuous space. When the agents all have the same constant velocity cooperation may evolve if the agents update their strategies imitating the most successful neighbor. If a fitness difference proportional is used instead, cooperation does not improve with respect to the static random geometric graph case. When viscosity effects set-in and agent velocity becomes a quickly decreasing function of the number of neighbors they have, one observes the formation of monomorphic stable clusters of cooperators or defectors in the Prisoner's Dilemma. However, cooperation does not spread in the population as in the constant velocity case. PMID:24316109

Antonioni, Alberto; Tomassini, Marco; Buesser, Pierre

2014-03-01

396

Two dimensional radiated power diagnostics on Alcator C-Mod

The radiated power diagnostics for the Alcator C-Mod tokamak have been upgraded to measure two dimensional structure of the photon emissivity profile in order to investigate poloidal asymmetries in the core radiation. Commonly utilized unbiased absolute extreme ultraviolet (AXUV) diode arrays view the plasma along five different horizontal planes. The layout of the diagnostic set is shown and the results from calibrations and recent experiments are discussed. Data showing a significant, 30%-40%, inboard/outboard emissivity asymmetry during ELM-free H-mode are presented. The ability to use AXUV diode arrays to measure absolute radiated power is explored by comparing diode and resistive bolometer-based emissivity profiles for highly radiative L-mode plasmas seeded with argon. Emissivity profiles match in the core but disagree radially outward resulting in an underprediction of P{sub rad} of nearly 50% by the diodes compared to P{sub rad} determined using resistive bolometers.

Reinke, M. L.; Hutchinson, I. H. [Massachusetts Institute of Technology, 77 Massachusetts Avenue, NW17-225, Cambridge, Massachusetts 02139 (United States)

2008-10-15

397

Silicon two-dimensional phononic crystal resonators using alternate defects

NASA Astrophysics Data System (ADS)

We present the numerical and experimental investigations of micromechanical resonators made by creating alternate defects with different central-hole radii (r') in a two-dimensional (2-D) phononic crystal (PnC) slab. The PnC structures were fabricated by etching a square array of cylindrical air holes in a 10 ?m thick free-standing silicon plate using a CMOS-compatible process. Preliminary experimental results show that the performance of the PnC resonators in terms of resonant frequency, Q factor, and insertion loss (IL) is highly dependent on r'. A Q factor of more than 3000 is achieved for the case of r' = 6 ?m while all the designed resonators with alternate defects have higher Q factor and lower IL than the resonators based on the normal Fabry-Perot structure due to the reduction in the mode mismatch.

Wang, Nan; Hsiao, Fu-Li; Palaniapan, Moorthi; Lee, Chengkuo

2011-12-01

398

Multiple plasmon excitations in adsorbed two-dimensional systems.

Using monolayer graphene as a model system for a purely two-dimensional (2D) electron gas, we show by energy electron loss spectroscopy, highly resolved both in energy and momentum, that there is a significant probability for the excitation of not only one but two dispersing losses. The appearance of both losses is independent of the substrate (we tested graphene on the Si face of 6H-SiC(0001), and on Ir(111) without and with an intercalated Na layer), and the ratio of the slope in the dispersion curves varies between 1.4 (SiC) and 2. While the lower dispersion curve can be attributed to the excitation of the sheet plasmon, in agreement with theoretical model calculations, the upper dispersion branch has not been identified before for plasmonic excitations in a 2D electron gas, and we assign it tentatively to the excitation of a multipole sheet plasmon. PMID:21358038

Pfnür, H; Langer, T; Baringhaus, J; Tegenkamp, C

2011-03-23

399

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

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

2014-10-01

400

Acoustic resonances in two dimensional radial sonic crystals shells

Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction. They have been recently introduced and are only possible thanks to the anisotropy of specially designed acoustic metamaterials [see Phys. Rev. Lett. {\\bf 103} 064301 (2009)]. We present here a comprehensive analysis of two-dimensional RSC shells, which consist of a cavity defect centered at the origin of the crystal and a finite thickness crystal shell surrounded by a fluidlike background. We develop analytic expressions demonstrating that, like for other type of crystals (photonic or phononic) with defects, these shells contain Fabry-Perot like resonances and strongly localized modes. The results are completely general and can be extended to three dimensional acoustic structures and to their photonic counterparts, the radial photonic crystals.

Torrent, Daniel

2010-01-01

401

Acoustic resonances in two-dimensional radial sonic crystal shells

NASA Astrophysics Data System (ADS)

Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sánchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts.

Torrent, Daniel; Sánchez-Dehesa, José

2010-07-01

402

Topological states in two-dimensional optical lattices

We present a general analysis of two-dimensional optical lattice models that give rise to topologically nontrivial insulating states. We identify the main ingredients of the lattice models that are responsible for the nontrivial topological character and argue that such states can be realized within a large family of realistic optical lattice Hamiltonians with cold atoms. We focus our quantitative analysis on the properties of topological states with broken time-reversal symmetry specific to cold-atom settings. In particular, we analyze finite-size effects, multiorbital phenomena that give rise to a variety of distinct topological states and transitions between them, the dependence on the trap geometry, and, most importantly, the behavior of the edge states for different types of soft and hard boundaries. Furthermore, we demonstrate the possibility of experimentally detecting the topological states through light Bragg scattering of the edge and bulk states.

Stanescu, Tudor D. [Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States); Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Galitski, Victor; Das Sarma, S. [Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)

2010-07-15

403

Holographic entanglement entropy for excited states in two dimensional CFT

NASA Astrophysics Data System (ADS)

We use holographic methods to study the entanglement entropy for excited states in a two dimensional conformal field theory. The entangling area is a single interval and the excitations are produced by in and out vertex operators with given scaling dimensions. On the gravity side we provide the excitations by turning on a scalar field with an appropriate mass. The calculation amounts to using the gravitational background, with a singular boundary, to find the one point function of the vertex operators. The singular boundary is taken care of by introducing a nontrivial UV regulator surface to calculate gravitational partition functions. By means of holographic methods we reproduce the field theory results for primary excitations.

Astaneh, Amin Faraji; Mosaffa, Amir Esmaeil

2013-03-01

404

Semimetallic Two-Dimensional Boron Allotrope with Massless Dirac Fermions

NASA Astrophysics Data System (ADS)

It has been widely accepted that planar boron structures, composed of triangular and hexagonal motifs are the most stable two-dimensional (2D) phases and likely precursors for boron nanostructures. Here we predict, based on an ab initio evolutionary structure search, a novel 2D boron structure with nonzero thickness, which is considerably, by 50 meV/atom, lower in energy than the recently proposed ?-sheet structure and its analogues. In particular, this phase is identified for the first time to have a distorted Dirac cone, after graphene and silicene the third elemental material with massless Dirac fermions. The buckling and coupling between the two sublattices not only enhance the energetic stability, but also are the key factors for the emergence of the distorted Dirac cone.

Zhou, Xiang-Feng; Dong, Xiao; Oganov, Artem R.; Zhu, Qiang; Tian, Yongjun; Wang, Hui-Tian

2014-02-01

405

Optical conductivity of the two-dimensional Hubbard model

NASA Astrophysics Data System (ADS)

The optical conductivity ?1(?) of the two-dimensional Hubbard model on finite clusters of 4×4 and ?10 × ?10 sites is reported. Experimental features found in the high-Tc cuprate superconductors can be qualitatively reproduced by this model including the presence of mid-infrared spectral weight, a Drude peak whose intensity grows with doping and a total spectral weight that varies slowly as the system is doped away from half filling. We find that to reproduce qualitatively the main experimental features of ?1(?), we need to work with a coupling constant of the order of the bandwidth, i.e., U/t~8-10. Results for the negative-U Hubbard model are included for comparison.

Dagotto, E.; Moreo, A.; Ortolani, F.; Riera, J.; Scalapino, D. J.

1992-05-01

406

Optical conductivity of the two-dimensional Hubbard model

The optical conductivity {sigma}{sub 1}({omega}) of the two-dimensional Hubbard model on finite clusters of 4{times}4 and {radical}10 {times} {radical}10 sites is reported. Experimental features found in the high-{ital T}{sub {ital c}} cuprate superconductors can be qualitatively reproduced by this model including the presence of mid-infrared spectral weight, a Drude peak whose intensity grows with doping and a total spectral weight that varies slowly as the system is doped away from half filling. We find that to reproduce qualitatively the main experimental features of {sigma}{sub 1}({omega}), we need to work with a coupling constant of the order of the bandwidth, i.e., {ital U}/{ital t}{similar to}8--10. Results for the negative-{ital U} Hubbard model are included for comparison.

Dagotto, E.; Moreo, A.; Ortolani, F.; Riera, J.; Scalapino, D.J. (Institute for Theoretical Physics and Department of Physics, University of California at Santa Barbara, Santa Barbara, California 93106 (United States))

1992-05-01

407

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

408

Numerical Computation of Two Dimensional Wind Accretion of Isothermal Gas

A new numerical algorithm for calculating isothermal wind accretion flows has been developed and is applied here to the analysis of the hydrodynamics of two-dimensional plane symmetric accretion flows in wind-fed sources. Polar coordinates are used to ensure fine resolution near the object. It is found that a thin accretion column is formed which shows wave-like oscillations. Small accretion disks are formed temporarily around the object. Mass accretion rate and angular momentum accretion rate exhibit quasi-periodic oscillations. The amplitudes of the oscillations depend on the size of the inner boundary, the number of grid points and the method of calculation. For a smaller size of the inner boundary, finer grids and more accurate numerical schemes, the amplitudes of the oscillation become larger.

Eiji Shima; Takuya Matsuda; Ulrich Anzer; Gerhard Borner; Henri M. J. Boffin

1998-05-28

409

Noise correlations of two-dimensional Bose gases

NASA Astrophysics Data System (ADS)

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 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 quasicondensed phase, due to constructive interference. We argue that this can be used to extract the scaling exponent of the quasicondensate 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.

Singh, V. P.; Mathey, L.

2014-05-01

410

Noise correlations of two-dimensional Bose gases

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

411

Higgs mode in a two-dimensional superfluid.

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

412

The development of two-dimensional object identification techniques

NASA Technical Reports Server (NTRS)

This report marks the end of the first year of an anticipated three year effort to study methods for numerically identifying objects according to shape in two dimensions. The method is based upon comparing the unit gradient of an observed object and the unit gradient of a standard object over a specified range of points. The manner in which the gradients are compared forms the basis of a shape recognition scheme, which is then applied to simple closed plane figures. The gradient based method is calibrated by using various distorted objects in comparison with a set of standard reference objects. The use of pattern recognition techniques for computer identification of two-dimensional figures will be investigated during the second and third years of this project.

Lebby, Gary; Sherrod, Earnest E.

1989-01-01

413

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

414

Bosonization and the Berry connection in two-dimensional QED

The dynamical effects of topological charge in two-dimensional QED can be expressed in terms of a topological order parameter via a Berry phase construction. The Berry phase describes the electric charge polarization of the vacuum in a manner similar to the theory of polarization in topological insulators. The topological order parameter labels discrete vacua which differ by units of electric flux. Here the associated Berry connection is explicitly constructed from the Dirac Hamiltonian eigenstates by introducing a small attractive Thirring coupling, so that there is still a stable boson in the limit of zero EM coupling. The Berry connection arises from the analytic structure of the Bethe ansatz states in complex rapidity near the free fermion point.

H. B. Thacker; Gabriel Wong

2014-09-02

415

Bosonization and the Berry connection in two-dimensional QED

The dynamical effects of topological charge in two-dimensional QED can be expressed in terms of a topological order parameter via a Berry phase construction. The Berry phase describes the electric charge polarization of the vacuum in a manner similar to the theory of polarization in topological insulators. The topological order parameter labels discrete vacua which differ by units of electric flux. Here the associated Berry connection is explicitly constructed from the Dirac Hamiltonian eigenstates by introducing a small attractive Thirring coupling, so that there is still a stable boson in the limit of zero EM coupling. The Berry connection arises from the analytic structure of the Bethe ansatz states in complex rapidity near the free fermion point.

Thacker, H B

2014-01-01

416

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

417

Nanoelectronic circuits based on two-dimensional atomic layer crystals.

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

2014-10-24

418

Two-dimensional angular transmission characterization of CPV modules.

This paper proposes a fast method to characterize the two-dimensional angular transmission function of a concentrator photovoltaic (CPV) system. The so-called inverse method, which has been used in the past for the characterization of small optical components, has been adapted to large-area CPV modules. In the inverse method, the receiver cell is forward biased to produce a Lambertian light emission, which reveals the reverse optical path of the optics. Using a large-area collimator mirror, the light beam exiting the optics is projected on a Lambertian screen to create a spatially resolved image of the angular transmission function. An image is then obtained using a CCD camera. To validate this method, the angular transmission functions of a real CPV module have been measured by both direct illumination (flash CPV simulator and sunlight) and the inverse method, and the comparison shows good agreement. PMID:21165081

Herrero, R; Domínguez, C; Askins, S; Antón, I; Sala, G

2010-11-01

419

Coherent angular momentum states for the two-dimensional oscillator

NASA Astrophysics Data System (ADS)

Coherent angular momentum states are defined for the two-dimensional isotropic harmonic oscillator. They share many attractive properties with the familiar (Cartesian) coherent states, but are in general distinct from those states. The probabilities of obtaining particular values for the radial and angular momentum quantum numbers follow independent Poisson distributions in the new states, but not in the old. In a quasiclassical description of the oscillator, corresponding to a given classical trajectory, the uncertainty in the angular momentum of the system is smaller if the new states are used rather than the old. The new states are the natural analogs of the coherent angular momentum states introduced for the three-dimensional oscillator by Bracken and Leemon [A. J. Bracken and H. I. Leemon, J. Math. Phys. 22, 719 (1981)].

Bracken, A. J.; McAnally, D. S.; Ódúndún, O. A.

1987-02-01

420

Two-dimensional optical thermal ratchets based on Fibonacci spirals.

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

421

Optical two-dimensional coherent spectroscopy of semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Our recent work on optical two-dimensional coherent spectroscopy (2DCS) of semiconductor materials is reviewed. We present and compare two approaches that are appropriate for the study of semiconductor nanostructures. The first one is based on a non-collinear geometry, where the Four-Wave-Mixing (FWM) signal is detected in the form of a radiated optical field. This approach works for samples with translational symmetry, such as Quantum Wells (QWs), or large and dense ensembles of Quantum Dots (QDs). The second method is based on a collinear geometry, where the FWM is detected in the form of a photocurrent. This second approach enables 2DCS of samples where translational symmetry is broken, such as single QDs, nanowires, or nanotubes, and small ensembles thereof. For each method, we provide an example of experimental results obtained on semiconductor QWs. In particular, it is shown how 2DCS can reveal coherent excitonic coupling between adjacent QWs.

Nardin, Gaël.; Autry, Travis M.; Moody, Galan; Singh, Rohan; Li, Hebin; Cundiff, Steven T.

2014-09-01

422

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

423

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

424

Temperature profile retrieval by two-dimensional filtering

NASA Technical Reports Server (NTRS)

A two-dimensional spatial filter, optimum in the minimum-mean-square error sense, has been used to retrieve atmospheric temperature profiles from TIROS-N and NOAA-6 Microwave Sounding Unit measurements. This approach considers correlations both in the vertical and horizontal (along the orbital track) directions. It is found that lower retrieval errors result from the 2-D technique, compared with the 1-D technique, especially in the troposphere. The additional horizontal information used in the 2-D formulation substantially improves temperature retrievals over a severe cold front where vertical correlations are lessened. The improved results of the 2-D filter in the upper troposphere point to the presence of profile components in the null space of the weighting functions that are horizontally correlated with the observed data.

Nathan, K. S.; Rosenkranz, P. W.; Staelin, D. H.

1985-01-01

425

Finite volume model for two-dimensional shallow environmental flow

This paper presents the development of a two-dimensional, depth integrated, unsteady, free-surface model based on the shallow water equations. The development was motivated by the desire of balancing computational efficiency and accuracy by selective and conjunctive use of different numerical techniques. The base framework of the discrete model uses Godunov methods on unstructured triangular grids, but the solution technique emphasizes the use of a high-resolution Riemann solver where needed, switching to a simpler and computationally more efficient upwind finite volume technique in the smooth regions of the flow. Explicit time marching is accomplished with strong stability preserving Runge-Kutta methods, with additional acceleration techniques for steady-state computations. A simplified mass-preserving algorithm is used to deal with wet/dry fronts. Application of the model is made to several benchmark cases that show the interplay of the diverse solution techniques. ?? 2011 ASCE.

Simoes, F.J.M.

2011-01-01

426

Intertwined Hamiltonians in two-dimensional curved spaces

The problem of intertwined Hamiltonians in two-dimensional curved spaces is investigated. Explicit results are obtained for Euclidean plane, Minkowski plane, Poincare half plane (AdS{sub 2}), de Sitter plane (dS{sub 2}), sphere, and torus. It is shown that the intertwining operator is related to the Killing vector fields and the isometry group of corresponding space. It is shown that the intertwined potentials are closely connected to the integral curves of the Killing vector fields. Two problems are considered as applications of the formalism presented in the paper. The first one is the problem of Hamiltonians with equispaced energy levels and the second one is the problem of Hamiltonians whose spectrum is like the spectrum of a free particle.

Aghababaei Samani, Keivan [Department of Physics, Isfahan University of Technology (IUT), Isfahan 84156 (Iran, Islamic Republic of)]. E-mail: samani@cc.iut.ac.ir; Zarei, Mina [Department of Physics, Isfahan University of Technology (IUT), Isfahan 84156 (Iran, Islamic Republic of)

2005-04-01

427

Nonlinear screening in large two-dimensional Coulomb clusters

NASA Astrophysics Data System (ADS)

The distortion due to a fixed point impurity with variable charge placed in the center of a classical harmonically confined two-dimensional (2D) large Coulomb cluster is studied. We find that the net topological charge (N--N+) of the system is always equal to six independent of the position and charge of the impurity. In comparison with a 2D cluster without impurity charge, only the breathing mode remains unchanged. The screening length is found to be a highly nonlinear function of the impurity charge. For values of the impurity charge smaller than the charge of the other particles, the system has almost the same screening strength. When the impurity charge is larger, the screening length is strongly enhanced. This result can be explained by the competition between the different forces active in the system.

Kong, Minghui; Vagov, A.; Partoens, B.; Peeters, F. M.; Ferreira, W. P.; Farias, G. A.

2004-11-01

428

Two-dimensional autocorrelation function analysis of smoked foil patterns

NASA Astrophysics Data System (ADS)

Digital image processing techniques have been applied to the analysis of cellular smoked foil patterns from gaseous detonations. In particular, the two-dimensional autocorrelation function is applied to digital cell pattern images and an orientational correlation parameter is calculated. Taking line profiles along the directions of highest correlation provides an unbiased method of determining the mean cell size in each of the two principal directions. By analyzing the width, amplitude and angular position of the orientational correlation plots, information can be extracted concerning the cellular pattern regularity, the relative angular correlation between two sets of transverse waves in two directions, and the mean shape or elongation of the cells within the pattern. The technique is applied to smoked foils from oxyacetylene mixtures with argon dilutions ranging from 0 to 75% to quantify the increase in regularity with argon dilution. This method provides a simple and useful way of analyzing cellular patterns and constitutes a promising technique for improving smoked foil diagnostics.

Lee, J. J.; Garinis, D.; Frost, D. L.; Lee, J. H. S.; Knystautas, R.

1995-10-01

429

Mixing times in quantum walks on two-dimensional grids

NASA Astrophysics Data System (ADS)

Mixing properties of discrete-time quantum walks on two-dimensional grids with toruslike boundary conditions are analyzed, focusing on their connection to the complexity of the corresponding abstract search algorithm. In particular, an exact expression for the stationary distribution of the coherent walk over odd-sided lattices is obtained after solving the eigenproblem for the evolution operator for this particular graph. The limiting distribution and mixing time of a quantum walk with a coin operator modified as in the abstract search algorithm are obtained numerically. On the basis of these results, the relation between the mixing time of the modified walk and the running time of the corresponding abstract search algorithm is discussed.

Marquezino, F. L.; Portugal, R.; Abal, G.

2010-10-01

430

Two-dimensional plasma photonic crystals in dielectric barrier discharge

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

431

Spin chirality on a two-dimensional frustrated lattice.

The collective behaviour of interacting magnetic moments can be strongly influenced by the topology of the underlying lattice. In geometrically frustrated spin systems, interesting chiral correlations may develop that are related to the spin arrangement on triangular plaquettes. We report a study of the spin chirality on a two-dimensional geometrically frustrated lattice. Our new chemical synthesis methods allow us to produce large single-crystal samples of KFe3(OH)6(SO4)2, an ideal Kagomé lattice antiferromagnet. Combined thermodynamic and neutron scattering measurements reveal that the phase transition to the ordered ground-state is unusual. At low temperatures, application of a magnetic field induces a transition between states with different non-trivial spin-textures. PMID:15793572

Grohol, Daniel; Matan, Kittiwit; Cho, Jin-Hyung; Lee, Seung-Hun; Lynn, Jeffrey W; Nocera, Daniel G; Lee, Young S

2005-04-01

432

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-ĺngström-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

433

Dissipative, forced turbulence in two-dimensional magnetohydrodynamics

NASA Technical Reports Server (NTRS)

The equations of motion for turbulent two-dimensional magnetohydrodynamic flows are solved in the presence of finite viscosity and resistivity, for the case in which external forces (mechanical and/or magnetic) act on the fluid. The goal is to verify the existence of a magnetohydrodynamic dynamo effect which is represented mathematically by a substantial back-transfer of mean square vector potential to the longest allowed Fourier wavelengths. External forces consisting of a random part plus a fraction of the value at the previous time step are employed, after the manner of Lilly for the Navier-Stokes case. The regime explored is that for which the mechanical and magnetic Reynolds numbers are in the region of 100 to 1000. The conclusions are that mechanical forcing terms alone cannot lead to dynamo action, but that dynamo action can result from either magnetic forcing terms or from both mechanical and magnetic forcing terms simultaneously.

Fyfe, D.; Montgomery, D.; Joyce, G.

1976-01-01

434

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

435

Waveguiding through a two-dimensional metallic photonic crystal.

We present a two-dimensional (2D) finite-difference time domain simulation of the propagation of light through linear and bent channels in metallic photonic crystals. We took as a starting point the Bozhevolnyi experiment, consisting of the scattering of surface plasmons by a 2D structure of finitely sized periodic gold dots arranged in a triangular lattice of 400-nm period. We model injection and propagation of light through linear channels of different widths. We also study the behaviour of light in the presence of a 90 degrees bent line defect made in the structure. We show that the confinement depends on the orientation of the input and output line defects. The two cases of GammaM and GammaK orientations are considered and a spectral study for five different wavelengths is carried out. PMID:14731297

Baida, F I; Van Labeke, D; Pagani, Y; Guizal, B; Al Naboulsi, M

2004-02-01

436

Towards Automated Screening of Two-dimensional Crystals

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; Carragher, Bridget; Potter, Clinton S.

2007-01-01

437

Modulational instabilities in two-dimensional magnetized dust-lattice

The transverse oscillations of paramagnetic dust grains in hexagonal dusty plasma crystal are discussed. The nonlinearity, which is related to the sheath electric/magnetic field(s) and to the weak inter grain interactions (magnetic dipole), is shown to lead to the generation of phase harmonics. In the case of propagating two-dimensional transverse dust-lattice modes in an arbitrary direction, it is shown the modulational instability of the carrier wave is due to self-interaction. The stability depends on the form of the electric field, the magnetic field, and the magnetic permeability of dust particles. The long term evolution of the modulated wave packet is described by a discrete nonlinear Schrodinger equation and it is solved numerically by Adomian decomposition method.

Farokhi, B.; Abdikian, A. [Department of Physics, Faculty of Science, Arak-University, 38156-8-8349 Arak (Iran, Islamic Republic of)

2011-11-15

438

Self-organized defect strings in two-dimensional crystals.

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

439

Two-dimensional freezing criteria for crystallizing colloidal monolayers

Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Loewen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At the freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing.

Wang Ziren; Han Yilong [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay (Hong Kong); Alsayed, Ahmed M. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, Pennsylvania 19104 (United States); Complex Assemblies of Soft Matter, CNRS/UPENN/Rhodia UMI 3254, Bristol, Pennsylvania 19007 (United States); Yodh, Arjun G. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, Pennsylvania 19104 (United States)

2010-04-21

440

Search for conformal invariance in compressible two-dimensional turbulence

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

2011-06-10

441

Pairwise interactions of colloids in two-dimensional geometric confinement.

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

442

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

443

Cylinders containing depleted uranium hexafluoride (UF{sub 6}) in storage at the Department of Energy (DOE) gaseous diffusion plants, managed by Martin Marietta Energy Systems, Inc., are being evaluated to determine their expected storage life. Cylinders evaluated recently have been in storage service for 30 to 40 years. In the present environment, the remaining life for these storage cylinders is estimated to be 30 years or greater. The group of cylinders involved in recent tests will continue to be monitored on a periodic basis, and other storage cylinders will be observed as on a statistical sample population. The program has been extended to all types of large capacity UF{sub 6} cylinders.

Alderson, J.H. [Martin Marietta Energy Systems, Inc., Paducah, KY (United States)

1991-12-31

444

Nanoscale insights on one- and two-dimensional material structures

NASA Astrophysics Data System (ADS)

The race for smaller, faster and more efficient devices has led researchers to explore the possibilities of utilizing nanostructures for scaling. These one-dimensional and two-dimensional materials have properties that are attractive for this purpose but are still not well controlled. Control comes with a complete understanding of the materials' electrical, thermal, optical and structural characteristics but is difficult to obtain due to their small scale. This work is intended to help researchers overcome the difficulty in studying nanostructures by providing techniques for analysis and insights of nanostructures that have not been previously available. Two nanostructures were studied: silicon nanowires and graphene. The nanowires were prepared for cross-section transmission electron microscopy (TEM) to discover the effects that controlled oxidation has on the dimensions and shape of the nanowires. Since cross-section TEM is not able to provide information about surface structure, a method for manipulating the wires with orientation control was developed. With this ability, all three orthogonal views of the nanowire were compiled for a comprehensive study on its structure in terms of shape and surface roughness. Graphene was used for a two-dimensional analytical technique that took advantage of customized computer programs for data acquisition, measurement and display. With the information provided, distinctions between grain boundary types in polycrystalline graphene were made and supported by statistical information from the software's output. It was also applied to a growth series of graphene samples in conjunction with scanning electron microscopy (SEM) images and electron backscatter diffraction (EBSD) maps. The results help point to origins of graphene's polycrystalline nature. This dissertation concludes with a thought towards the future by highlighting a method that can help analyze nanostructures, which may become incorporated into the structures of large devices. The fold-out method is a TEM sample preparation technique utilizing a focused ion beam (FIB) for site specific thinning across a large sample area. Its process is demonstrated along with advantages over conventional methods.

Floresca, Herman Carlo

445

Dynamics of entanglement in a two-dimensional spin system

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 [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Sadiek, Gehad [Department of Physics, King Saud University, Riyadh 11451 (Saudi Arabia); Department of Physics, Ain Shams University, Cairo 11566 (Egypt); Kais, Sabre [Department of Physics, King Saud University, Riyadh 11451 (Saudi Arabia); Department of Chemistry and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

2011-06-15

446

Effect of a circular cylinder on separated forced convection at a backward-facing step

The current study investigates the augmentation in the laminar forced convection characteristics of the backward-facing step flow in a two-dimensional channel by means of introducing an adiabatic circular cylinder in the domain. The effects of various cross-stream positions (i.e., yc = 01.5) of the circular cylinder on the flow and heat transfer characteristics of the backward-facing step flow has been numerically explored

Ankit Kumar; Amit K. Dhiman

447

In this paper, we have demonstrated the existence of surface acoustic waves in two-dimensional phononic crystals with fluid matrix, which is composed of a square array of steel cylinders put in air background. By using the supercell method, we investigate the dispersion relation and the eigenfield distribution of surface modes. Surface waves can be easily excited at the surface of a finite size phononic crystal by line source or Gaussian beam placed in or launched from the background medium, and they propagate along the surface with the form of 'beat.' Taking advantage of these surface modes, we can obtain a highly directional emission wave beam by introducing an appropriate corrugation layer on the surface of a waveguide exit.

Zhao Degang; Liu Zhengyou; Qiu Chunyin; He Zhaojian; Cai Feiyan; Ke Manzhu [Key Laboratory of Acoustic and Photonic Materials and Devices of Ministry of Education and Department of Physics, Wuhan University, Wuhan 430072 (China)

2007-10-01

448

NASA Astrophysics Data System (ADS)

A two-dimensional (2D) phononic crystal (PC), including a type of linear defect that is composed of third component materials, is proposed in this paper. The sonic guided characteristics of the structure are investigated by combining the plane-wave expansion method and a supercell technique. The results show that there are guided modes in the original band gap when third material-based linear defects are introduced in the two-component PC. The frequency of the guided modes changes with the rotational angle and filling fraction of the linear defect. The frequency distribution is symmetric to the (0, 1) direction. The sonic waveguide characteristics of the PC do not change with the orientation and the type of cross-section of the defect cylinders when the filling fraction is very small. This property has potential application in controlling the guided modes in a 2D PC.

Yan-Cheng, Zhao; Lian-Zhi, Deng; Li-Bo, Yuan

2012-02-01

449

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

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.

450

Two-dimensional models of the magnetic-field enhancement at pit and bump

Formulae of magnetic field enhancement at a two-dimensional semi-elliptical bump and a two-dimensional pit with chamfered edges are derived by using the method of conformal mapping. The latter can be regarded as an approximated model of the two-dimensional pit with round edges.

Kubo, Takayuki

2014-01-01

451

ERIC Educational Resources Information Center

Hoping to develop in her students an understanding of mathematics as a way of thinking more than a way of doing, the author of this article describes how her students worked on a spatial reasoning problem stemming from an iteratively constructed sequence of cylinders. She presents an activity of making cylinders out of paper models, and for every

Johnson, Erica

2006-01-01

452

of Technology, Pasadena, California 91125 Joel W. Burdickc) Department of Mechanical Engineering, 104-44, California Institute of Technology, Pasadena, California 91125 Scott D. Kellyd) Department of Mechanical the irrotational region traversed by CR , Eq. A18 ... .'' There is no negative sign in front of the last term in Eq

Shashikanth, Banavara N.

453

The acoustical performances of regular arrays of cylindrical elements, with their axes aligned and parallel to a ground plane, have been investigated through predictions and laboratory experiments. Semi-analytical predictions based on multiple scattering theory and numerical simulations based on a boundary element formulation have been made. Measurements have been made in an anechoic chamber using arrays of (a) cylindrical acoustically-rigid scatterers (PVC pipes) and (b) thin elastic shells. Insertion loss (IL) spectra due to the arrays have been measured without and with ground planes for several receiver heights. Data and predictions have been compared. The minima in the excess attenuation spectrum i.e., attenuation maxima due to the ground alone resulting from destructive interference between direct and ground-reflected sound waves, tend to have an adverse influence on the band gaps (BG) related to a periodic array in the free field when these two effects coincide. On the other hand, the presence of rigid ground may result in an IL for an array near the ground similar to or, in the case of the first BG, greater than that resulting from a double array, equivalent to the original array plus its ground plane mirror image, in the free field.

Anton Krynkin; Olga Umnova; Juan Vicente Sanchez-Perez; Alvin Y. B. Chong; Shahram Taherzadeh; Keith Attenborough

2011-02-15

454

, Illinois 61801 Received 8 May 2001; accepted 27 November 2001 This paper studies the dynamical fluid plus to study the linear and nonlinear stability of the moving FoÂ¨ppl equilibrium solutions using the energy of these interactions has for a long time, however, ruled out the possibility of sophis- ticated mathematical modeling

Shashikanth, Banavara N.

455

Modulation of trapped waves giving approximate two-dimensional solitions

NASA Astrophysics Data System (ADS)

In a previous paper, F. Calogero and the author studied the non-linear modulation of dispersive trapped water-waves in a channel or along a beach (edge waves). They showed that the signal envelope, (which is studied with convenient time scale and length scale) obeys Nonlinear Schrödinger Equation. The result is extended here to waves trapped by the bottom geometry of a basin which is infinitely extended into all horizontal directions. One can obtain along the guided path, envelope solitons of Nonlinear Schrödinger Equation for a signal whose amplitude exponentially decreases in transverse directions. These bidimensional solitons are thus shown as asymptotic features for a large class of problems. This class is narrower than in the finite case or in the semiinfinite case because strong conditions must be set either on the linear part or on the nonlinear part of the operator in order to guarantee an exponentially decreasing behavior on both sides. In addition, the envelope solitons are in most cases unstable features, because of side-band instabilities. Nevertheless, the result suggests that the exact bidimensional solitons recently derived by Boiti et al. for special Equations are not an exceptional physical feature of two-dimensional evolutions.

Sabatier, P. C.

456

Electromagnetic scattering from two-dimensional thick material junctions

NASA Technical Reports Server (NTRS)

The problem of the plane wave diffraction is examined by an arbitrary symmetric two dimensional junction, where Generalized Impedance Boundary Conditions (GIBCs) and Generalized Sheet Transition Conditions (GSTCs) are employed to simulate the slabs. GIBCs and GSTCs are constructed for multilayer planar slabs of arbitrary thickness and the resulting GIBC/GSTC reflection coefficients are compared with exact counterparts to evaluate the GIBCs/GSTCs. The plane wave diffraction by a multilayer material slab recessed in a perfectly conducting ground plane is formulated and solved via the Generalized Scattering Matrix Formulation (GDMF) in conjunction with the dual integral equation approach. Various scattering patterns are computed and validated with exact results where possible. The diffraction by a material discontinuity in a thick dielectric/ferrite slab is considered by modelling the constituent slabs with GSTCs. A non-unique solution in terms of unknown constants is obtained, and these constants are evaluated for the recessed slab geometry by comparison with the solution obtained therein. Several other simplified cases are also presented and discussed. An eigenfunction expansion method is introduced to determine the unknown solution constants in the general case. This procedure is applied to the non-unique solution in terms of unknown constants; and scattering patterns are presented for various slab junctions and compared with alternative results where possible.

Ricoy, M. A.; Volakis, John L.

1990-01-01

457

Vortex Formation in Two-Dimensional Bose Gas

We discuss the stability of a homogeneous two-dimensional Bose gas at finite temperature against formation of isolated vortices. We consider a patch of several healing lengths in size and compute its free energy using the Euclidean formalism. Since we deal with an open system, which is able to exchange particles and angular momentum with the rest of the condensate, we use the symmetry-breaking (as opposed to the particle number conserving) formalism, and include configurations with all values of angular momenta in the partition function. At finite temperature, there appear sphaleron configurations associated to isolated vortices. The contribution from these configurations to the free energy is computed in the dilute gas approximation. We show that the Euclidean action of linearized perturbations of a vortex is not positive definite. As a consequence the free energy of the 2D Bose gas acquires an imaginary part. This signals the instability of the gas. This instability may be identified with the Berezinskii, Kosterlitz and Thouless (BKT) transition.

Esteban Calzetta; Kwan-yuet Ho; B. L. Hu

2009-10-22

458

Vortex pairing in two-dimensional Bose gases

Recent experiments on ultracold Bose gases in two dimensions have provided evidence for the existence of the Berezinskii-Kosterlitz-Thouless (BKT) phase via analysis of the interference between two independent systems. In this work we study the two-dimensional quantum degenerate Bose gas at finite temperature using the projected Gross-Pitaevskii equation classical field method. Although this describes the highly occupied modes of the gas below a momentum cutoff, we have developed a method to incorporate the higher momentum states in our model. We concentrate on finite-sized homogeneous systems in order to simplify the analysis of the vortex pairing. We determine the dependence of the condensate fraction on temperature and compare this to the calculated superfluid fraction. By measuring the first order correlation function we determine the boundary of the Bose-Einstein condensate and BKT phases, and find it is consistent with the superfluid fraction decreasing to zero. We reveal the characteristic unbinding of vortex pairs above the BKT transition via a coarse-graining procedure. Finally, we model the procedure used in experiments to infer system correlations [Hadzibabic et al., Nature 441, 1118 (2006)], and quantify its level of agreement with directly calculated in situ correlation functions.

Foster, Christopher J.; Davis, Matthew J. [University of Queensland, School of Mathematics and Physics, ARC Centre of Excellence for Quantum-Atom Optics, Queensland 4072 (Australia); Blakie, P. Blair [Jack Dodd Centre for Quantum Technology, Department of Physics, University of Otago, Dunedin (New Zealand)

2010-02-15

459

Quantum tunneling of vortices in two-dimensional condensates

The tunneling rate t{sub v}/({Dirac_h}/2{pi}) of a vortex between two pinning sites (of strength V separated by d) is computed using the Bogoliubov expansion of vortex wave-functions overlap. For BCS vortices, tunneling is suppressed beyond a few Fermi wavelengths. For Bose condensates, t{sub v}=V exp(-{pi}n{sub s}d{sup 2}/2), where n{sub s} is the boson density. The analogy between vortex hopping in a superconducting film and two-dimensional electrons in a perpendicular magnetic field is exploited. We derive the variable range hopping temperature, below which vortex tunneling contributes to magnetoresistance. Using the 'quantum Hall insulator' analogy we argue that the Hall conductivity (rather than the inverse Hall resistivity) measures the effective carrier density in domains of mobile vortices. Details of vortex wave functions and overlap calculations, and a general derivation of the Magnus coefficient for any wave function on the sphere, are provided in appendixes.

Auerbach, Assa [Physics Department, Technion, Haifa 32000 (Israel); Arovas, Daniel P. [Department of Physics, University of California at San Diego, La Jolla, California 92093 (United States); Ghosh, Sankalpa [Physics Department, Okayama University, Okayama-700-8530 (Japan)

2006-08-01

460

Mechanical Stress Inference for Two Dimensional Cell Arrays

Many morphogenetic processes involve mechanical rearrangements of epithelial tissues that are driven by precisely regulated cytoskeletal forces and cell adhesion. The mechanical state of the cell and intercellular adhesion are not only the targets of regulation, but are themselves the likely signals that coordinate developmental process. Yet, because it is difficult to directly measure mechanical stress in vivo on sub-cellular scale, little is understood about the role of mechanics in development. Here we present an alternative approach which takes advantage of the recent progress in live imaging of morphogenetic processes and uses computational analysis of high resolution images of epithelial tissues to infer relative magnitude of forces acting within and between cells. We model intracellular stress in terms of bulk pressure and interfacial tension, allowing these parameters to vary from cell to cell and from interface to interface. Assuming that epithelial cell layers are close to mechanical equilibrium, we use the observed geometry of the two dimensional cell array to infer interfacial tensions and intracellular pressures. Here we present the mathematical formulation of the proposed Mechanical Inverse method and apply it to the analysis of epithelial cell layers observed at the onset of ventral furrow formation in the Drosophila embryo and in the process of hair-cell determination in the avian cochlea. The analysis reveals mechanical anisotropy in the former process and mechanical heterogeneity, correlated with cell differentiation, in the latter process. The proposed method opens a way for quantitative and detailed experimental tests of models of cell and tissue mechanics. PMID:22615550

Chiou, Kevin K.; Hufnagel, Lars; Shraiman, Boris I.

2012-01-01

461

Dissipation in quasi-two-dimensional flowing foams

NASA Astrophysics Data System (ADS)

The dissipation between two-dimensional (2D) monolayers of bubbles, the so-called quasi-2D foams, and a wall is investigated in two setups: a "liquid pool" system, where the foam is confined between a soap solution and a glass coverslip, and a Hele-Shaw cell, where the foam occupies the narrow gap between two plates. This experimental study reports dissipation measurements for mobile gas/liquid interfaces (free shear boundary condition) over a large range of parameters: in the liquid pool system, velocity and bubble area; in the Hele-Shaw cell, velocity and liquid fraction. The effect of the latter quantity is measured for the first time over more than three orders of magnitude. A full comparison between our results and other experimental studies is proposed and enables to rescale all measurements on a single master curve. It shows that for mobile gas/liquid interfaces, the existing models systematically underestimate the dissipation in flowing foams. This is quantified by a discrepancy factor ?, ratio of the experimental dissipation measurements to the theoretical predictions, which scales as ? =1.4(RP/?A )-0.5 with RP the Plateau border radius and A the bubble area, showing that the discrepancy is higher for dry foams.

Raufaste, Christophe; Foulon, Amandine; Dollet, Benjamin

2009-05-01

462

Novel Phases and Reentrant Melting of Two Dimensional Colloidal Crystals

We investigate two-dimensional (2d) melting in the presence of a one-dimensional (1d) periodic potential as, for example, realized in recent experiments on 2d colloids subjected to two interfering laser beams. The topology of the phase diagram is found to depend primarily on two factors: the relative orientation of the 2d crystal and the periodic potential troughs, which select a set of Bragg planes running parallel to the troughs, and the commensurability ratio p= a'/d of the spacing a' between these Bragg planes to the period d of the periodic potential. The complexity of the phase diagram increases with the magnitude of the commensurabilty ratio p. Rich phase diagram, with ``modulated liquid'', ``floating'' and ``locked floating'' solid and smectic phases are found. Phase transitions between these phases fall into two broad universality classes, roughening and melting, driven by the proliferation of discommensuration walls and dislocations, respectively. We discuss correlation functions and the static structure factor in these phases and make detailed predictions of the universal features close to the phase boundaries. We predict that for charged systems with highly screened short-range interactions these melting transitions are generically reentrant as a function of the strength of the periodic potential, prediction that is in accord with recent 2d colloid experiments. Implications of our results for future experiments are also discussed.

Leo Radzihovsky; Erwin Frey; David R. Nelson

2000-08-11

463

Impact of heterocirculene molecular symmetry upon two-dimensional crystallization

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.; Ait-Mansour, K.; Chernichenko, K. Y.; Nenajdenko, V. G.; Ruffieux, P.; Du, S. X.; Gao, H.-J.; Fasel, R.

2014-01-01

464

Two-dimensional carbon leading to new photoconversion processes.

Two-dimensional (2D) carbon allotropes, which are atomic thick layers made of network carbon atoms with hexagonal structured lattices, have been neglected until the direct investigation of mechanically exfoliated graphene by Novoselov et al. in 2004. Graphene is a 2D carbon allotrope with a unique structure of hexagonally arranged atoms that give it unparalleled electrical conductivity and carrier mobility, in addition to excellent mechanical flexibility and extremely high specific surface area. Graphene and its derivatives have been extensively studied for photovoltaic and photocatalytic applications due to their inherent nature to extract and transport charges from photon-absorbing semiconductors and conjugated polymers. Graphyne and graphdiyne, 2D carbon allotropes like graphene but containing not only doubly but also triply bonded carbon atoms, are predicted to possess intrinsic semiconductor bandgap and even more superior electrical properties than graphene. The current theoretical understanding and experimental status of graphyne and graphdiyne will be discussed in contrast of graphene, demonstrating those promising competitors to graphene in further lightening a new photoconversion. This review addresses the recent successes and current challenges of graphene, graphyne and graphdiyne, and provides insightful perspectives for the future applications of 2D carbon materials in photoelectric conversion and photocatalysis. PMID:24654006

Tang, Hongjie; Hessel, Colin M; Wang, Jiangyan; Yang, Nailiang; Yu, Ranbo; Zhao, Huijun; Wang, Dan

2014-07-01

465

Tunable states of interlayer cations in two-dimensional materials

NASA Astrophysics Data System (ADS)

The local state of cations inside the Ĺngstrom-scale interlayer spaces is one of the controlling factors for designing sophisticated two-dimensional (2D) materials consisting of 2D nanosheets. In the present work, the molecular mechanism on how the interlayer cation states are induced by the local structures of the 2D nanosheets is highlighted. For this purpose, the local states of Na cations in inorganic 2D materials, in which the compositional fluctuations of a few percent are introduced in the tetrahedral and octahedral units of the 2D nanosheets, were systematically studied by means of 23Na magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and 23Na multiple-quantum MAS (MQMAS) NMR spectroscopy. In contrast with an uniform distribution of Na cations expected so far, various well-defined cation states sensitive to the local structures of the 2D nanosheets were identified. The tunability of the interlayer cation states along with the local structure of the 2D nanosheets, as the smallest structural unit of the 2D material, is discussed.

Sato, K.; Numata, K.; Dai, W.; Hunger, M.

2014-03-01

466

Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.

Azad, Abul K [Los Alamos National Laboratory; Chen, Houtong [Los Alamos National Laboratory; Taylor, Antoinette [Los Alamos National Laboratory; O' Hara, John F [Los Alamos National Laboratory; Han, Jiaguang [OSU; Lu, Xinchao [OSU; Zhang, Weili [OSU

2009-01-01

467

Two-dimensional state in driven magnetohydrodynamic turbulence

The dynamics of the two-dimensional (2D) state in driven three-dimensional (3D) incompressible magnetohydrodynamic turbulence is investigated through high-resolution direct numerical simulations and in the presence of an external magnetic field at various intensities. For such a flow the 2D state (or slow mode) and the 3D modes correspond, respectively, to spectral fluctuations in the plane k{sub ||}=0 and in the area k{sub ||}>0. It is shown that if initially the 2D state is set to zero it becomes nonnegligible in few turnover times, particularly when the external magnetic field is strong. The maintenance of a large-scale driving leads to a break for the energy spectra of 3D modes; when the driving is stopped, the previous break is removed and a decay phase emerges with Alfvenic fluctuations. For a strong external magnetic field the energy at large perpendicular scales lies mainly in the 2D state, and in all situations a pinning effect is observed at small scales.

Bigot, Barbara [Space Science Center, University of New Hampshire, Durham, New Hampshire 03824 (United States); Center for Integrated Computation and Analysis of Reconnection And Turbulence (United States); Galtier, Sebastien [Universite Paris-Sud, Institut d'Astrophysique Spatiale, bat. 121, F-91405 Orsay (France); Institut universitaire de France (France)

2011-02-15

468

Nonvolatile resistance switching on two-dimensional electron gas.

Two-dimensional electron gas (2DEG) at the complex oxide interfaces have brought about considerable interest for the application of the next-generation multifunctional oxide electronics due to the exotic properties that do not exist in the bulk. In this study, we report the integration of 2DEG into the nonvolatile resistance switching cell as a bottom electrode, where the metal-insulator transition of 2DEG by an external field serves to significantly reduce the OFF-state leakage current while enhancing the on/off ratio. Using the Pt/Ta2O5-y/Ta2O5-x/SrTiO3 heterostructure as a model system, we demonstrate the nonvolatile resistance switching memory cell with a large on/off ratio (>10(6)) and a low leakage current at the OFF state (?10(-13) A). Beyond exploring nonvolatile memory, our work also provides an excellent framework for exploring the fundamental understanding of novel physics in which electronic and ionic processes are coupled in the complex heterostructures. PMID:25243475

Joung, Jin Gwan; Kim, Shin-Ik; Moon, Seon Young; Kim, Dai-Hong; Gwon, Hyo Jin; Hong, Seong-Hyeon; Chang, Hye Jung; Hwang, Jin-Ha; Kwon, Beom Jin; Kim, Seong Keun; Choi, Ji-Won; Yoon, Seok-Jin; Kang, Chong-Yun; Yoo, Kwang Soo; Kim, Jin-Sang; Baek, Seung-Hyub

2014-10-22

469

Epoxy nanocomposites with two-dimensional transition metal dichalcogenide additives.

Emerging two-dimensional (2D) materials such as transition metal dichalcogenides offer unique and hitherto unavailable opportunities to tailor the mechanical, thermal, electronic, and optical properties of polymer nanocomposites. In this study, we exfoliated bulk molybdenum disulfide (MoS2) into nanoplatelets, which were then dispersed in epoxy polymers at loading fractions of up to 1% by weight. We characterized the tensile and fracture properties of the composite and show that MoS2 nanoplatelets are highly effective at enhancing the mechanical properties of the epoxy at very low nanofiller loading fractions (below 0.2% by weight). Our results show the potential of 2D sheets of transition metal dichalcogenides as reinforcing additives in polymeric composites. Unlike graphene, transition metal dichalcogenides such as MoS2 are high band gap semiconductors and do not impart significant electrical conductivity to the epoxy matrix. For many applications, it is essential to enhance mechanical properties while also maintaining the electrical insulation properties and the high dielectric constant of the polymer material. In such applications, conductive carbon based fillers such as graphene cannot be utilized. This study demonstrates that 2D transition metal dichalcogenide additives offer an elegant solution to such class of problems. PMID:24754702

Eksik, Osman; Gao, Jian; Shojaee, S Ali; Thomas, Abhay; Chow, Philippe; Bartolucci, Stephen F; Lucca, Don A; Koratkar, Nikhil

2014-05-27

470

Two-dimensional axisymmetric Child-Langmuir scaling law

The classical one-dimensional (1D) Child-Langmuir law was previously extended to two dimensions by numerical calculation in planar geometries. By considering an axisymmetric cylindrical system with axial emission from a circular cathode of radius r, outer drift tube radius R>r, and gap length L, we further examine the space charge limit in two dimensions. Simulations were done with no applied magnetic field as well as with a large (100 T) longitudinal magnetic field to restrict motion of particles to 1D. The ratio of the observed current density limit J{sub CL2} to the theoretical 1D value J{sub CL1} is found to be a monotonically decreasing function of the ratio of emission radius to gap separation r/L. This result is in agreement with the planar results, where the emission area is proportional to the cathode width W. The drift tube in axisymmetric systems is shown to have a small but measurable effect on the space charge limit. Strong beam edge effects are observed with J(r)/J(0) approaching 3.5. Two-dimensional axisymmetric electrostatic particle-in-cell simulations were used to produce these results.

Ragan-Kelley, Benjamin [Applied Science and Technology, University of California, Berkeley, California 94720 (United States); Verboncoeur, John; Feng Yang [Nuclear Engineering, University of California, Berkeley, California 94720 (United States)

2009-10-15

471

A two dimensional phase-shifting method for deflectometry

NASA Astrophysics Data System (ADS)

Deflectometry is widely used to measure three-dimensional profile of a specular free-form surface because of its high accuracy and short inspection time. With phase data obtained by observing the fringe patterns reflected via the surface, we can measure the shape, specifically normal vector of the surface. In order to obtain the shape of specular free-form surfaces, two different phases have to be computed for a single area. Two phases are calculated by using two sets of the phase-shifting patterns with different direction, and usually eight images are needed. In this paper, we propose a two dimensional phase-shifting method, called 2D phase-shifting method, to compute two phases with different direction with a single set of 2D phase with only five images. Therefore, the proposed method is expected to have a strong impact on measurement industry where reducing the number of acquired images is desirable for increasing measurement speed. The proposed method is verified by both simulation and experiments, in which phase information is successfully extracted with 2D phase-shifting method.

Park, Heechan; Hong, Deokhwa; Cho, Hyungsuck

2008-11-01

472

Two dimensional simulation of high power laser-surface interaction

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

473

Two-dimensional gas flow in an electrode assembly

The interface between a source of positive or negative ions and a multichannel MEQALAC accelerator will be the Low-Energy Beam Transport (LEBT) consisting of a lattice of quadrupole focusing electrodes transporting the beam while the gas pressure is reduced from the high-pressure ion source to the low-pressure accelerator. Gas emitted from the ion source will flow through the LEBT electrode lattice to a pumping volume. It is necessary to analyze the two-dimensional gas flow to ascertain the gas densities throughout the LEBT and to design the system so that only a small fraction of the ion beam is lost by gas collisions. The analysis uses the fact that the gas-flow rate is proportional to the density gradient if the mean free path of the low-pressure gas is greater than the inter-electrode spacing. Consequently the mathematics developed for conductivity of heat or electric current can be used. The practical result of this analysis is to determine the maximum width of the LEBT so that the beam loss by gas collisions is tolerable. The maximum width is a function of beam density, gas efficiency, and electrode spacing. The beam current per unit length of module will be somewhat greater than 75 mA/cm. Electrode dimensions should be chosen to fit the characteristics of the ion source.

Hamilton, G.W.; Willmann, P.A.

1980-04-08

474

Structure of self - assembled two-dimensional spherical crystals

NASA Astrophysics Data System (ADS)

Dense spherical particles on a flat surface usually pack into a simple triangular lattice, similar to billiard balls at the start of a game. The minimum energy configuration for interacting particles on the curved surface of a sphere, however, presents special difficulties, as recognized already by J.J. Thomson. We describe experimental investigations of the structure of two-dimensional spherical crystals. The crystals, formed by beads self-assembled on water droplets in oil, serve as model systems for exploring very general theories about the minimum energy configurations of particles with arbitrary repulsive interactions on curved surfaces. Above a critical system size we find that crystals develop distinctive high-angle grain boundaries or "scars" not found in planar crystals. The number of excess defects in a scar is shown to grow linearly with the dimensionless system size. First experiments where the melting of the crystal structure was observable will be discussed. Dynamic triangulation methods allow the analysis of the dynamics of the defects. Possible modifications towards mechanically stabilized self assembly structures result in so called Colloidosomes, which are promising for many different encapsulation purposes.

Bausch, Andreas R.

2004-03-01

475

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

476

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

477

Two-dimensional imaging velocity interferometry: Data analysis techniques

NASA Astrophysics Data System (ADS)

We describe data analysis procedures for an emerging interferometric technique for measuring target motion across a two-dimensional image at a moment in time, i.e., a snapshot 2D-VISAR. Conventional VISARs (velocity interferometer system for any reflector) are commonly used in shock physics to measure velocity history at a single point or many points across a line on target. These however are not recorded in two-dimensions and cannot be used with ultrashort pulsed illumination because the coherence length is smaller than the interferometer delay, preventing fringe formation. In our scheme, dual matched interferometers allow use of low- or incoherent illumination such as ultrashort laser pulses to freeze motion of target, allowing use of slow CCD imaging detectors. Quadrature phase recording and push-pull data analysis simultaneously produces an ordinary nonfringing reflectivity image and a fringing image. The latter is converted into a 2D-phase map which is proportional to target velocity. Example data on shocked crystalline [111] Si shows incipient features of 50 ?m scale.

Erskine, David J.; Smith, R. F.; Bolme, C. A.; Celliers, P. M.; Collins, G. W.

2012-04-01

478

Peierls transition in two-dimensional metallic monophosphate tungsten bronzes

NASA Astrophysics Data System (ADS)

The two-dimensional metallic bronzes made of ReO 3-type layers of MoO 6 or WO 6 octahedra present quasi-one-dimensional (1D) electronic structures along three directions of preferential overlap of the t 2g transition metal orbitals. They exhibit a Peierls instability towards the formation of charge density waves (CDW) at the 2 kF critical wave vector allowing to nest simultaneously the Fermi surfaces associated to two quasi-1D band structures out of three. The Peierls transition is achieved through a periodic lattice distortion (PLD), that we analyse, in the present work, for the monophosphate tungsten bronzes. The Peierls critical temperature decreases in presence of disorder, which breaks the electron-hole pairs forming the CDW condensate, and in presence of misfit between the PLD wave vector and the 2 kF nesting wave vector. The pair breaking effect accounts for the drop of the Peierls transition in the Na xP 4W 12O 44 ( x<1) bronzes while the misfit effect, associated to a variation of the band filling, explains quantitatively the phase diagram of the K xP 4W 8O 32 (1< x<2) bronzes.

Foury-Leylekian, P.; Pouget, J.-P.

2002-03-01

479

Two-dimensional echocardiography during percutaneous transluminal coronary angioplasty.

In order to study myocardial and clinical events during transient coronary occlusion in humans, two-dimensional echocardiography was continuously performed in 15 patients undergoing 49 balloon inflations during percutaneous transluminal coronary angioplasty (PTCA). Transient segmental asynergy developed in all patients 8 +/- 3 seconds after balloon inflation and returned to baseline 19 +/- 8 seconds after balloon deflation. Segmental dyskinesis was seen in only 8 of 11 patients undergoing PTCA of the left anterior descending artery (LAD). A wall motion score, based on degree of asynergy of 13 segments of the left ventricle, was significantly higher during LAD than during right coronary artery inflation (7.9 +/- 1.3 vs 4.0 +/- 1.4, p less than 0.01). Left ventricular size index increased significantly during balloon inflation, from 179 +/- 9 to 196 +/- 10 mm (p less than 0.01). Four patients developed transient ST segment changes in the extremity leads of the ECG and five patients had angina pectoris. The very first sign of ischemia in three patients, who developed all of these symptoms together, was consistently asynergy, followed by ECG changes, and last, angina pectoris. Thus during PTCA, transient asynergy and left ventricular dilatation develop, which are often clinically silent. PMID:2940852

Visser, C A; David, G K; Kan, G; Romijn, K H; Meltzer, R S; Koolen, J J; Dunning, A J

1986-06-01

480

Exploratory data analysis in two-dimensional electrophoresis.

The use of computerized matching of proteins in the analysis of multiple two-dimensional electrophoresis (2DE) gels creates volumes of data that are readily accessible for exploratory analysis. When these data are used in health-effects studies or in studies to identify factors associated with particular diseases, hundreds or even thousands of hypotheses can be tested. Interpreting so many hypothesis tests requires some preliminary statistical evaluations of the data. In addition, prior to the preliminary statistical evaluations and subsequent hypothesis tests, accurate protein quantification and correct protein matching must be verified. In this report we present an approach used at the Centers for Disease Control to address these issues. This approach consists of a randomized experimental design incorporating replicate gels for each specimen, gel image analysis, protein matching, editing, Boolean unions of all gels to obtain correspondences and contradictions of match identification numbers, resolution of correspondences and contradictions, statistical tests to identify outliers, and finally an assessment of statistical and practical significance to focus attention on the proteins most likely to be associated with the effects under study. We illustrate our approach with data from an exploratory exposure-response study. PMID:8512943

Caudill, S P; Myrick, J E; Robinson, M K

1993-01-01

481

Phase diagram of two-dimensional hard ellipses.

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

482

Broken ergodicity in two-dimensional homogeneous magnetohydrodynamic turbulence

Two-dimensional (2D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3D) homogeneous MHD turbulence. These features include several ideal (i.e., nondissipative) invariants along with the phenomenon of broken ergodicity (defined as nonergodic behavior over a very long time). 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 3D MHD turbulence that is manifest in the lowest wavenumbers was found. Here, we study the origin of broken ergodicity in 2D MHD turbulence. It will be seen that broken ergodicity in ideal 2D 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. The origins of broken ergodicity in an ideal 2D homogeneous MHD turbulence are found through an eigenanalysis of the covariance matrices of the probability density function and by an examination of the associated entropy functional. When the values of ideal invariants are kept fixed and grid size increases, it will be shown that the energy in a few large modes remains constant, while the energy in any other mode is inversely proportional to grid size. Also, as grid size increases, we find that broken ergodicity becomes manifest at more and more wavenumbers.

Shebalin, John V. [Astromaterials Research and Exploration Science Office, NASA Johnson Space Center, Houston, Texas 77058-3696 (United States)

2010-09-15

483

Grain boundaries in hybrid two-dimensional materials

NASA Astrophysics Data System (ADS)

In two-dimensional (2D) materials, bisector grain boundaries (GBs) are energetically favorable as they allow perfect match of neighbor grains. We demonstrate here a contrasting behavior for GBs in hybrid 2D materials, which tend to be non-bisector and obey a universal law to optimally match the heterogeneous grains: the ratio of cosines of the rotation angles of two neighbor grains equals the ratio of constituent's lattice parameters, reminiscent of Snell's law for light refraction. Details of the optimal GB structures are further formulated in terms of tilt angle, lattice mismatch strain and deviation angle from the bisector line, in good agreement with comprehensive numerical analyses. The ground state structures of the GBs manifest as a series of laterally misaligned bisector segments, which are verified by intensive first-principle calculations. Our findings not only provide a general guidance for exploring GBs in various hybrid 2D materials but also serve as an important stepping stone for understanding mechanical and electronic behaviors in these 2D nanoscale patchworks.

Zhang, Zhuhua; Yang, Yang; Yakobson, Boris I.

2014-10-01

484

Two-Dimensional Gas of Massless Dirac Fermions in Graphene

Electronic properties of materials are commonly described by quasiparticles that behave as non-relativistic electrons with a finite mass and obey the Schroedinger equation. Here we report a condensed matter system where electron transport is essentially governed by the Dirac equation and charge carriers mimic relativistic particles with zero mass and an effective "speed of light" c* ~10^6m/s. Our studies of graphene - a single atomic layer of carbon - have revealed a variety of unusual phenomena characteristic of two-dimensional (2D) Dirac fermions. In particular, we have observed that a) the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; b) graphene's conductivity never falls below a minimum value corresponding to the conductance quantum e^2/h, even when carrier concentrations tend to zero; c) the cyclotron mass m of massless carriers with energy E in graphene is described by equation E =mc*^2; and d) Shubnikov-de Haas oscillations in graphene exhibit a phase shift of pi due to Berry's phase.

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

2005-09-13

485

Tunable Plasmonic Crystals Induced from a Two Dimensional Electron Gas

NASA Astrophysics Data System (ADS)

A two dimensional electron gas (2DEG) with periodic variation of its screening,^1 geometry,^2 or carrier density^3 provides an electromagnetic medium for the formation of a broadly tunable plasmonic crystal (PC). By using a periodic gate to control the 2DEG density in GaAs/AlGaAs heterostructures, we have induced terahertz (THz) PCs consisting of several bipartite crystal units cells. The PC band structure, Tamm states, and electromagnetically induced transparency phenomena are observed utilizing a gate-controlled defect adjacent to the PC to generate a plasmonic mixing photovoltage. These integrated PCs have potential applications in the areas of frequency selective THz detection, strong light-matter interaction, and planar metamaterials. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. The work at Sandia National Laboratories was supported by the DOE Office of Basic Energy Sciences. ^1U. Mackens, et. al., Phys. Rev. Lett. 53, 1485 (1984). ^2V. M. Muravev, et. al., Phys. Rev. Lett. 101, 216801 (2008). ^3G. C. Dyer, et. al., Phys. Rev. Lett. 109, 126803 (2012).

Dyer, Gregory; Aizin, Gregory; Allen, S. James; Grine, Albert; Bethke, Don; Reno, John; Shaner, Eric

2013-03-01

486

Rearrangements in a two-dimensional packing of disks.

Several aspects of the dynamics of a granular two-dimensional (2D) packing of disks slowly tilted until the system loses stability and an avalanche takes place are discussed. The evolution of the system, constructed with monodisperse disks placed on a thin cell, is studied by image analysis. As in the 3D case (packing of spheres), the system undergoes several rearrangements of different magnitude before the avalanche takes place. For thick systems, not only are small rearrangements detected but also displacements of large clusters of disks are observed in the bulk and on the free surface of the packing. In particular, characteristic angles and the avalanche mass were determined for samples of different heights. On thick systems, velocity fields of large rearrangements are presented and changes in the internal structure of the packing produced by these rearrangements are analyzed. It is found that the main effects of rearrangements is to increase the disorder of the system. Also, as the disorder of the system increases its stability threshold decreases. PMID:16711793

Aguirre, M A; Calvo, A; Ippolito, I; Medus, A; Mancuso, M

2006-04-01

487

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. The Roe approximate Riemann solution scheme or the computationally less expensive Advection Upstream Splitting Method (AUSM) flux-splitting scheme are 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 passage and the distribution of flow variables in the stationary inlet port region.

Welch, Gerard E.; Chima, Rodrick V.

1993-01-01

488

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

489

The new skinny in two-dimensional nanomaterials.

While the advent of graphene has focused attention on the extraordinary properties of two-dimensional (2D) materials, graphene's lack of an intrinsic band gap and limited amenability to chemical modification has sparked increasing interest in its close relatives and in other 2D layered nanomaterials. In this issue of ACS Nano, Bianco et al. report on the production and characterization of one of these related materials: germanane, a one-atom-thick sheet of hydrogenated puckered germanium atoms structurally similar to graphane. It is a 2D nanomaterial generated via mechanical exfoliation from GeH. Germanane has been predicted to have technologically relevant properties such as a direct band gap and high electron mobility. Monolayer 2D materials like germanane, in general, have attracted enormous interest for their potential technological applications. We offer a perspective on the field of 2D layered nanomaterials and the exciting growth areas and discuss where the new development of germanane fits in, now and in the foreseeable future. PMID:23678956

Koski, Kristie J; Cui, Yi

2013-05-28

490

Helicity modulus in the two-dimensional Hubbard model

The helicity modulus, which is the stiffness associated with a twisted order parameter, for the two-dimensional Hubbard model is calculated for the equivalent cases of (i) attractive on-site interaction (negative [ital U]) with arbitrary strength, arbitrary electron density, and zero magnetic field and (ii) repulsive on-site interaction (positive [ital U]) with arbitrary strength, at half-filling and in an arbitrary magnetic field. An explicit formula for the helicity modulus is derived using the Bogoliubov-Hartree-Fock approximation. An improved value for the helicity modulus is obtained by performing variational Monte Carlo calculations using a Gutzwiller projected trial wave function. To within a small correction term the helicity modulus is found to be given by [minus]1/8 the average kinetic energy. The variational Monte Carlo calculation is found to increase the value of the helicity modulus by a small amount (about 5% for intermediate values of the interaction strength) compared to the results from the Bogoliubov-Hartree-Fock approximation. In the case of attractive interaction, from a comparison with the Kosterlitz-Thouless relation between critical temperature and helicity modulus, the critical temperature for a Kosterlitz-Thouless transition is calculated and a phase diagram is obtained. An optimal critical temperature is found for an intermediate value of [ital U]. We discuss connections of our results with results in the literature on the Hubbard model using the random-phase approximation and quantum Monte Carlo calculations.

Denteneer, P.J.H.; An, G.; van Leeuwen, J.M.J. (Instituut-Lorentz, University of Leiden, P.O. Box 9506, 2300 RA Leiden (Netherlands))

1993-03-15

491

Linkage analysis by two-dimensional DNA typing.

In two-dimensional (2-D) DNA typing, genomic DNA fragments are separated, first according to size by electrophoresis in a neutral polyacrylamide gel and second according to sequence by denaturing gradient gel electrophoresis, followed by hybridization analysis using micro- and minisatellite core probes. The 2-D DNA typing method generates a large amount of information on polymorphic loci per gel. Here we demonstrate the potential usefulness of 2-D DNA typing in an empirical linkage study on the red factor in cattle, and we show an example of the 2-D DNA typing analysis of a human pedigree. The power efficiency of 2-D DNA typing in general is compared with that of single-locus typing by simulation. The results indicate that, although 2-D DNA typing is very efficient in generating data on polymorphic loci, its power to detect linkage is lower than single-locus typing, because it is not obvious whether a spot represents the presence of one or two alleles. It is possible to compensate for this lower informativeness by increasing the sample size. Genome scanning by 2-D DNA typing has the potential to be more efficient than current genotyping methods in scoring polymorphic loci. Hence, it could become a method of choice in mapping genetic traits in humans and animals. Images Figure 3 Figure 2 Figure 4 PMID:8250045

te Meerman, G J; Mullaart, E; van der Meulen, M A; den Daas, J H; Morolli, B; Uitterlinden, A G; Vijg, J

1993-01-01

492

Transport Studies in Parallel Two-Dimensional Electron Gases

NASA Astrophysics Data System (ADS)

This thesis presents electron transport studies in GaAs-AlAs double quantum wells (DQW's) where a system of nearby parallel two-dimensional electron gases is formed. It starts from a systematic modeling of the system from a circuit level down to a microscopic quantum mechanical level based on a single electron model. A new concept of "virtual separation of node", in which different circuit nodes represent energies at the Fermi level and at the subband edge of the quantum well, enables the hierarchical modeling of the system, significantly reducing the computation time of the transient analysis. Then, two experiments, done in low temperature, demonstrate physics beyond the above framework. The first experiment shows a sudden charge transfer, when the wells are biased, associated with strong inter-layer Coulomb scattering. The other finds a strong temperature dependence of the resonant tunneling between the two wells in contrast to ordinary electron tunneling process in metal-insulator-metal junctions or semiconductors. It is argued that the electron-electron correlation originating from the small inter-layer electron spacing comparable to the intra-layer electron spacing is responsible for the former and the interaction with the external phonon bath usually neglected at low temperature for the latter. Finally, a couple of possibilities to make device building blocks out of DQW systems are discussed. In particular, a new type of junction, dubbed SD-junction, which consists of an abrupt interface between double- to single-QW interface, is proposed.

Katayama, Yasunao

493

Initial- value problem for the two-dimensional growing wake

NASA Astrophysics Data System (ADS)

A general three-dimensional initial-value perturbation problem is investigated as to effects in a two-dimensional but growing wake. The linearized perturbation analysis considers both the early transient as well as the asymptotic behavior of the disturbance (Blossey, Criminale & Fisher, JFM 2006 submitted). The representation of the mean flow is physically accurate, since it has been obtained by considering the lateral entrainment process and associated streamwise evolution of mass flow (increase) and kinetic energy (decrease) (Tordella & Belan, PoF 2003). This base model is combined with a change of coordinate (moving coordinate trasform) (Criminale & Drazin, Stud. Appl. Math, 1990). The evolution analysis considers inviscid disturbances that are expanded in terms of small values of the wavenumber. The long time behavior is represented by means of a multiple spatial and temporal scale description of the velocity and vorticity perturbations. The limit for small wavenumbers has been studied. It is seen that an increase of the entrainment in the base flow yields instability and grows algebraically in time. This result is also obtained when considering a more general problem where larger wavenumbers, wavelengths of the order of the thickness of the variable shear region, are allowed. Comparison with a recent spatio-temporal multiscale Orr-Sommerfeld analysis of the 2D wake instability (Tordella, Scarsoglio & Belan, PoF 2006). is presented. The perturbation dynamics is examined for different base flow configurations.

Scarsoglio, S.; Tordella, D.; Criminale, W. O.

2006-11-01

494

Two-dimensional magnetic ordering in a multilayer structure

NASA Astrophysics Data System (ADS)

The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of research for almost 100 years. The role of dipolar interactions and anisotropy are important to obtain, the otherwise forbidden, ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monolayers). We have demonstrated that conventional low-temperature magnetometry and polarized neutron scattering measurements can be performed to study short-range ferromagnetic ordering of in-plane spins in 2D systems using a multilayer stack of non-interacting monolayers of gadolinium ions formed by Langmuir-Blodgett (LB) technique. The spontaneous magnetization could not be detected in the heterogeneous magnetic phase observed here and the saturation value of the net magnetization was found to depend on the sample temperature and applied magnetic field. The net magnetization rises exponentially with lowering temperatur