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1

Optimization and improvement of Halbach cylinder design  

NASA Astrophysics Data System (ADS)

In this paper we describe the results of a parameter survey of a 16 segmented Halbach cylinder in three dimensions in which the parameters internal radius, rin, external radius, rex, and length, L, have been varied. Optimal values of rex and L were found for a Halbach cylinder with the least possible volume of magnets with a given mean flux density in the cylinder bore. The volume of the cylinder bore could also be significantly increased by only slightly increasing the volume of the magnets, for a fixed mean flux density. Placing additional blocks of magnets on the end faces of the Halbach cylinder also improved the mean flux density in the cylinder bore, especially so for short Halbach cylinders with large rex. Moreover, magnetic cooling as an application for Halbach cylinders was considered. A magnetic cooling quality parameter, ?cool, was introduced and results showed that this parameter was optimal for long Halbach cylinders with small rex. Using the previously mentioned additional blocks of magnets can improve the parameter by as much as 15% as well as improve the homogeneity of the field in the cylinder bore.

Bjørk, R.; Bahl, C. R. H.; Smith, A.; Pryds, N.

2008-07-01

2

Rock magnetic applications of Halbach cylinders  

NASA Astrophysics Data System (ADS)

Permanent magnet field sources made of NdFeB, in particular the Halbach cylinders, have not previously been used by rock magneticists. Here, their use is explored for determining saturation IRM (SIRM) and S ratio. An original "one-step" scheme is presented to obtain both parameters in one measurement and one operation of IRM acquisition using two crossed Halbach cylinders with 1.0 and 0.3 T fields. The first tests performed demonstrate the ability of Halbach cylinders to derive SIRM and S values over a wide range of coercivities using both the standard and the one-step schemes, although further improvements are needed in field homogeneity to achieve better precision. Other possible applications of Halbach cylinders are reviewed.

Rochette, P.; Vadeboin, F.; Clochard, L.

2001-10-01

3

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

4

Stability of elliptical cylinders in two-dimensional channel flow.  

PubMed

The flow around rigid cylinders of elliptical cross section placed transverse to Poiseuille flow between parallel plates was simulated to investigate issues related to the tumbling of red blood cells and other particles of moderate aspect ratio in the similar flow in a Field Flow Fractionation (FFF) channel. The torque and transverse force on the cylinder were calculated with the cylinder freely translating, but prevented from rotating, in the flow. The aspect ratios (long axis to short axis) of the elliptical cylinders were 2, 3, 4, and 5. The cylinder was placed transversely at locations of y0/H = 0.1, 0.2, 0.3, and 0.4, where y0 is the distance from the bottom of the channel and H is the height of the channel, and the orientation of the cylinder was varied from 0 to 10 deg with respect to the axis of the channel for a channel Reynolds number of 20. The results showed that equilibrium orientations (indicated by a zero net torque on the cylinder) were possible for high-aspect-ratio cylinders at transverse locations y0/H < 0.2. Otherwise, the net torque on the cylinder was positive, indicating that the cylinder would rotate. For cylinders with a stable orientation, however, a transverse lift forced existed up to about y0/H = 0.25. Thus, a cylinder of neutral or low buoyancy might be lifted with a stable orientation from an initial position near the wall until it reached y0/H < 0.2, whereupon it would begin to tumble or oscillate. The dependence of lift and torque on cylinder orientation suggested that neutral or low-buoyancy cylinders may oscillate in both transverse location and angular velocity. Cylinders more dense than the carrier fluid could be in equilibrium both in terms of orientation and transverse location if their sedimentation force matched their lift force for a location y0/H < 0.2. PMID:11091950

Zhao, Y; Sharp, M K

2000-10-01

5

Two-dimensional photonic crystal at THz frequencies constructed by metal-coated cylinders  

NASA Astrophysics Data System (ADS)

Two-dimensional photonic crystals with photonic bandgaps (PBGs) in the terahertz (THz) frequency regime have been constructed by arraying metal-coated cylinders. PBGs were observed at 2.2 and 4.7 THz for the samples with lattice constant of 140 and 70 ?m, respectively. Experimental results show that the PBGs were realized with only a small number of layers (?10 periods) and they are robust against positional disorder (about 14%). Thus, metal-coated cylinders provide us with a promising approach to create robust PBGs in the THz frequency range.

Wang, Shao-Wei; Lu, Wei; Chen, Xiao-Shuang; Li, Zhi-Feng; Shen, Xue-Chu; Wen, Weijia

2003-06-01

6

Scattering from cylinders using the two-dimensional vector plane wave spectrum.  

PubMed

The two-dimensional vector plane wave spectrum (VPWS) is scattered from parallel circular cylinders using a boundary value solution with the T-matrix formalism. The VPWS allows us to define the incident, two-dimensional electromagnetic field with an arbitrary distribution and polarization, including both radiative and evanescent components. Using the fast Fourier transform, we can quickly compute the multiple scattering of fields that have any particular functional or numerical form. We perform numerical simulations to investigate a grating of cylinders that is capable of converting an evanescent field into a set of propagating beams. The direction of propagation of each beam is directly related to a spatial frequency component of the incident evanescent field. PMID:21643402

Pawliuk, Peter; Yedlin, Matthew

2011-06-01

7

Measurement of the Rheological Properties of Magnetorheological Fluids Using a Double Concentric Halbach Cylinder Array  

NASA Astrophysics Data System (ADS)

A new experimental setup for measuring rheological properties of magnetic fluids at variable magnetic flux density B with increased homogeneity is described. The proposed setup is mounted on a commercial strain-controlled ARES rotational rheometer. The magnetic flux is generated via two concentric Halbach cylindrical arrays made from permanent NdFeB magnets. The use of permanent magnets overcomes some of the disadvantages of electromagnets (e.g., excessive heating of the coils, formation of large radial stray fields, cost of electricity, cooling, etc). The performance of the new setup is tested for a magnetorheological fluid in both steady and oscillatory shear regimes.

Barroso, Vitor C.; Raich, Hanspeter; Blümler, Peter; Wilhelm, Manfred

2008-07-01

8

Two-dimensional backscattering Mueller matrix of sphere-cylinder birefringence media  

NASA Astrophysics Data System (ADS)

We have developed a sphere-cylinder birefringence model (SCBM) for anisotropic media. The new model is based on a previously published sphere-cylinder scattering model (SCSM), but the spherical and cylindrical scatterers are embedded in a linearly birefringent medium. A Monte Carlo simulation program for SCBM was also developed by adding a new module to the SCSM program to take into account the effects of birefringence. Simulations of the backscattering Mueller matrix demonstrate that SCBM results in better agreement with experimental results than SCSM and is more suitable to characterize fibrous tissues such as skeletal muscle. Using Monte Carlo simulations, we also examined the characteristics of two-dimensional backscattering Mueller matrix of SCBM and analyzed the influence of linear birefringence.

Du, E.; He, Honghui; Zeng, Nan; Guo, Yihong; Liao, Ran; He, Yonghong; Ma, Hui

2012-12-01

9

Vortex-shedding suppression in two-dimensional mixed convective flows past circular and square cylinders  

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

Solution of particulated viscous flow over a two dimensional cylinder and in a radial inflow turbine  

NASA Astrophysics Data System (ADS)

Particle trajectories, particle fluid interaction, and erosion were studied for different solid particle sizes. The vicosity of the carrier fluid was into account and particle trajectories in viscous and inviscid fluid were systematically compared. Experiments carried out on particulated viscous flow over a two dimensional cylinder demonstrates the effect of the particles on such important flow properties as fluid steamline pattern, coefficient of drag and recirculation zone. The important effects of the solid particles on the fluid streamline pattern in a blade channel of a radial inflow turbine and a mixed flow turbine are evaluated. Results demonstrate the difference in particle trajectories, and impact locations between vicous and inviscid solutions, which would affect erosion prediction in turbomachinery. Statistical methods are used in combination with three dimensional particle trajectory calculations, the basic experimental erosion data and particle rebound characteristics, to predict erosion pattern in the turbine rotor blades.

Vittal, B. V. R.

11

Recurrent traveling waves in a two-dimensional saw-toothed cylinder and their average speed  

NASA Astrophysics Data System (ADS)

We study a curvature-dependent motion of plane curves in a two-dimensional infinite cylinder with spatially undulating boundary. The law of motion is given by V=?+A, where V is the normal velocity of the curve, ? is the curvature, and A is a positive constant. The boundary undulation is assumed to be almost periodic, or, more generally, recurrent in a certain sense. We first introduce the definition of recurrent traveling waves and establish a necessary and sufficient condition for the existence of such traveling waves. We then show that the traveling wave is asymptotically stable if it exists. Next we show that a regular traveling wave has a well-defined average speed if the boundary shape is strictly ergodic. Finally we study what we call "virtual pinning", which means that the traveling wave propagates over the entire cylinder with zero average speed. Such a peculiar situation can occur only in non-periodic environments and never occurs if the boundary undulation is periodic.

Lou, Bendong; Matano, Hiroshi; Nakamura, Ken-Ichi

12

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

Microsoft Academic Search

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

Masoud Asgari; Mehdi Akhlaghi; Seyed Mahmoud Hosseini

2009-01-01

13

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

14

Theory and Application of Spectral Methods for the Unsteady Compressible Wake Flow Past a Two-Dimensional Circular Cylinder.  

NASA Astrophysics Data System (ADS)

An unsteady compressible viscous wake flow past a two-dimensional circular cylinder has been successfully simulated using the Fourier and Chebyshev collocation methods (spectral scheme) and the mixed Fourier collocation/finite -difference method (mixed scheme). Various numerical techniques, such as the analytical grid transformation, filtering of the solution and differentiation operators etc., are employed for both numerical schemes. The number of grid points used in the spectral scheme is significantly less than other schemes. No signs of instability is indicated for integrations up to 150,000 time steps. The primary vortex shedding frequency agrees well with the results in the literature for Mach number 0.4 and Reynolds number 80. For the outer computational boundary, the characteristic boundary conditions, which are based on the extrapolation of the characteristics of the Euler equations of gas dynamics, are developed. The characteristic boundary conditions show a great improvement of the flow field when compared with the noncharacteristic one. Furthermore, the controversial secondary frequency can be artificially created and eliminated by imposing the noncharacteristic and characteristic boundary conditions respectively, in both the spectral and mixed schemes. These phenomena strongly imply that the secondary frequency is both a numerical artifact and an experimental flaw.

Don, Wai Sun

15

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

16

Lattice-Boltzmann simulation of two-dimensional flow over two vibrating side-by-side circular cylinders.  

PubMed

A numerical simulation using the multiple relaxation time lattice-Boltzmann method is carried out for the purpose of investigating fluid flow over two vibrating side-by-side circular cylinders and the effect of moving the cylinders on the wake characteristics. As a benchmark problem to assess the validity and efficiency of the model, the calculation was carried out at Reynolds number of 200 and four pitch ratios (T/D , where D is the cylinder diameter while T is the center-to-center spacing between the two cylinders) of 1.2, 1.6, 2.2, and 3.2, respectively. The calculated results indicate that the vibration of the cylinder pair has significant influence on the wake patterns. When the amplitude of vibration is big enough, the vibration locks up the vortex shedding and formation. For each cylinder vibration frequency, there exists a threshold of vibration amplitude for the lock-up phenomenon. With the vibration frequency is increased, the threshold of vibration amplitude decreases. PMID:18999533

Xu, Yousheng; Liu, Yang; Xia, Yong; Wu, Fengmin

2008-10-01

17

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

NASA Astrophysics Data System (ADS)

The incompressible Navier-Stokes equations are considered in the two-dimensional strip , 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 . This implies, after a transient period, the emergence of a laminar regime in which the solution rapidly converges to a shear flow described by the one-dimensional heat equation in an appropriate Galilean frame. The approach is constructive and provides explicit estimates on the size of the solution and the lifetime of the turbulent period in terms of the initial Reynolds number.

Gallay, Thierry; Slijep?evi?, Siniša

2015-03-01

18

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

19

Numerical analysis of the effect of radiation on laminar steady natural convection in a two-dimensional participating medium between two horizontal confocal elliptical cylinders  

SciTech Connect

Over the last two decades, natural convection in horizontal annular spaces has been studied extensively because of its numerous industrial applications, namely, nuclear reactor design, cooling of electronic equipment, study of pressurized-gas underground electric transmission cables, and solar systems. Compound parabolic collectors involve convection heat transfer in the space between the receive envelope and the surface formed by the cover and the reflector. Here, combined radiation and natural convection in a participating medium between two horizontal confocal elliptical cylinders is investigated numerically. The equations of steady, laminar two-dimensional natural convection are written by using an elliptic-cylinder coordinates system, the stream function, and the vorticity. The finite volume radiation solution method and the control volume technique are used to discretize the coupled equations of momentum, energy, and radiative transfer. Numerical solutions are obtained for Rayleigh numbers in the range 10{sup 4} to 2 {times} 10{sup 5} and the radiation-conduction parameter ranging from 0 to {infinity}. The special case corresponding to the convective flow within the annulus formed by an elliptical cylinder surrounding a flat plate is also considered.

Borjini, M.N.; Mbow, C.; Daguenet, M. [Univ. de Perpignan (France). Lab. de Thermodynanique et Energetique

1999-04-01

20

Radial Halbach Magnetic Bearings  

NASA Technical Reports Server (NTRS)

Radial 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. Radial Halbach magnetic bearings are based on the same principle as that of axial Halbach magnetic bearings, differing in geometry as the names of these two types of bearings suggest. Both radial and 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. Axial Halbach magnetic bearings were described in Axial Halbach Magnetic Bearings (LEW-18066-1), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), page 85. In the remainder of this article, the description of the principle of operation from the cited prior article is recapitulated and updated to incorporate the present radial geometry. In simplest terms, the basic principle of levitation in an axial or radial Halbach magnetic bearing is that of the repulsive electromagnetic force between (1) a moving permanent magnet and (2) an electric current induced in a stationary electrical conductor by the motion of the magnetic field. An axial or radial Halbach bearing includes multiple permanent magnets arranged in a Halbach array ("Halbach array" is defined below) in a rotor and multiple conductors in the form of wire coils in a stator, all arranged so the rotary motion produces an axial or radial repulsion that is sufficient to levitate the rotor. A basic Halbach array (see Figure 1) consists of a row of permanent magnets, each oriented so that its magnetic field is at a right angle to that of the adjacent magnet, and the right-angle turns are sequenced so as to maximize the magnitude of the magnetic flux density on one side of the row while minimizing it on the opposite side. The advantage of this configuration is that it makes it possible to approach the theoretical maximum force per unit area that could be exerted by a given amount of permanent-magnet material. The configuration is named after physicist Klaus Halbach, who conceived it for use in particle accelerators. Halbach arrays have also been studied for use in magnetic-levitation ("maglev") railroad trains. In a radial Halbach magnetic bearing, the basic Halbach arrangement is modified into a symmetrical arrangement of sector-shaped permanent magnets mounted on the outer cylindrical surface of a drum rotor (see Figure 2). The magnets are oriented to concentrate the magnetic field on their radially outermost surface. The stator coils are mounted in a stator shell surrounding the rotor.

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

2009-01-01

21

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

22

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

23

An improved discrete configuration of a cylinder magnet for portable nuclear magnetic resonance instruments  

NASA Astrophysics Data System (ADS)

The continuous magnetization profile approximated by a discrete source is the main reason for the deteriorating magnetic field homogeneity in Halbach magnet. It is identified by comparing the two-dimensional (2D) field solutions of an ideal cylinder magnet with those of a cylinder magnet constructed from several segment magnets. To improve the magnetic field homogeneity, a cylinder magnet from several crescent-shaped magnets is therefore presented. The programed 2D field solutions of the magnet from the crescent-shaped segments verify that the configuration effectively improves the homogeneity inside the cylinder magnet compared to that of a magnet built from simpler segments. For a small magnet with a required field uniformity and magnitude, the configuration has more advantages than a configuration from typical segments. Hence, the magnet is more appropriate for a portable nuclear magnetic resonance instruments.

Chen, Jizhong; Xu, Chunyan

2007-06-01

24

Magnetic field homogeneity perturbations in finite Halbach dipole magnets.  

PubMed

Halbach hollow cylinder dipole magnets of a low or relatively low aspect ratio attract considerable attention due to their applications, among others, in compact NMR and MRI systems for investigating small objects. However, a complete mathematical framework for the analysis of magnetic fields in these magnets has been developed only for their infinitely long precursors. In such a case the analysis is reduced to two-dimensions (2D). The paper details the analysis of the 3D magnetic field in the Halbach dipole cylinders of a finite length. The analysis is based on three equations in which the components of the magnetic flux density Bx, By and Bz are expanded to infinite power series of the radial coordinate r. The zeroth term in the series corresponds to a homogeneous magnetic field Bc, which is perturbed by the higher order terms due to a finite magnet length. This set of equations is supplemented with an equation for the field profile B(z) along the magnet axis, presented for the first time. It is demonstrated that the geometrical factors in the coefficients of particular powers of r, defined by intricate integrals are the coefficients of the Taylor expansion of the homogeneity profile (B(z)-Bc)/Bc. As a consequence, the components of B can be easily calculated with an arbitrary accuracy. In order to describe perturbations of the field due to segmentation, two additional equations are borrowed from the 2D theory. It is shown that the 2D approach to the perturbations generated by the segmentation can be applied to the 3D Halbach structures unless r is not too close to the inner radius of the cylinder ri. The mathematical framework presented in the paper was verified with great precision by computations of B by a highly accurate integration of the magnetostatic Coulomb law and utilized to analyze the inhomogeneity of the magnetic field in the magnet with the accuracy better than 1 ppm. PMID:24316186

Turek, Krzysztof; Liszkowski, Piotr

2014-01-01

25

Torque Production in a Halbach Machine  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

26

Acoustic metamaterials for new two-dimensional sonic devices  

Microsoft Academic Search

It has been shown that two-dimensional arrays of rigid or fluidlike cylinders in a fluid or a gas define, in the limit of large wavelengths, a class of acoustic metamaterials whose effective parameters (sound velocity and density) can be tailored up to a certain limit. This work goes a step further by considering arrays of solid cylinders in which the

Daniel Torrent; José Sánchez-Dehesa

2007-01-01

27

Two dimensional vernier  

NASA Technical Reports Server (NTRS)

A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.

Juday, Richard D. (inventor)

1992-01-01

28

Two-dimensional wind tunnel  

NASA Technical Reports Server (NTRS)

Information on the Japanese National Aerospace Laboratory two dimensional transonic wind tunnel, completed at the end of 1979 is presented. Its construction is discussed in detail, and the wind tunnel structure, operation, test results, and future plans are presented.

1982-01-01

29

Two-dimensional box plot  

Microsoft Academic Search

Tongkumchum, P. Two-dimensional box plot Songklanakarin J. Sci. Technol., 2005, 27(4) : 859-866 In this paper we propose a two-dimensional box plot, a simple bivariate extension of the box plot and the scatter plot. This plot comprises a pair of trapeziums oriented in the direction of a fitted straight line, with symbols denoting extreme values. The choice for the fitted

Phattrawan Tongkumchum

30

Two-dimensional material nanophotonics  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

31

Two dimensional radiation detecting apparatus  

SciTech Connect

A two-dimensional X-ray detecting apparatus is comprised of an amorphous silicon layer for trapping electrons in a pattern corresponding to an intensity distribution when it is receiving X-rays, and a scanning device for scanning the surface of the amorphous silicon layer with a laser beam to take out electrons trapped in the silicon layer.

Sugimoto, H.; Naruse, Y.

1985-10-15

32

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

33

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

34

Halbach array DC motor/generator  

DOEpatents

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

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

1998-01-01

35

Halbach array DC motor/generator  

DOEpatents

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

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

1998-01-06

36

Two-dimensional flexible nanoelectronics  

NASA Astrophysics Data System (ADS)

2014/2015 represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.

Akinwande, Deji; Petrone, Nicholas; Hone, James

2014-12-01

37

Two-dimensional thermofield bosonization  

SciTech Connect

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

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

2005-12-15

38

Two-Dimensional Thermofield Bosonization  

E-print Network

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

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

2005-04-01

39

Two dimensional unstable scar statistics.  

SciTech Connect

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

40

Two-Dimensional Quantum Antiferromagnets  

NASA Astrophysics Data System (ADS)

This review presents some theoretical advances in the field of quantum magnetism in two-dimensional systems, and quantum spin liquids in particular. The first version published in 2005 has been updated for the present second edition of the book: the section devoted to the kagome antiferromagnet (Sec. 7) has been completely rewritten, as well as the concluding section (Sec. 8). The other sections (Secs. 1-6) are unchanged from the first edition of the book.

Misguich, Grégoire; Lhuillier, Claire

2013-03-01

41

Two-Dimensional Colloidal Alloys  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

42

Two-dimensional colloidal alloys.  

PubMed

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

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

2011-03-25

43

Binary two-dimensional PCA.  

PubMed

Fast training and testing procedures are crucial in biometrics recognition research. Conventional algorithms, e.g., principal component analysis (PCA), fail to efficiently work on large-scale and high-resolution image data sets. By incorporating merits from both two-dimensional PCA (2DPCA)-based image decomposition and fast numerical calculations based on Haarlike bases, this technical correspondence first proposes binary 2DPCA (B-2DPCA). Empirical studies demonstrated the advantages of B-2DPCA compared with 2DPCA and binary PCA. PMID:18632407

Pang, Yanwei; Tao, Dacheng; Yuan, Yuan; Li, Xuelong

2008-08-01

44

Position sensor for linear synchronous motors employing halbach arrays  

DOEpatents

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

Post, Richard Freeman

2014-12-23

45

Two-dimensional Coulomb gas  

SciTech Connect

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

Cornu, F.; Jancovici, B.

1987-10-01

46

Two-dimensional NMR spectroscopy  

SciTech Connect

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

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

1987-01-01

47

Inverted Linear Halbach Array for Separation of Magnetic Nanoparticles  

PubMed Central

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. PMID:25382864

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

2014-01-01

48

Recent Development of Halbach Permanent Magnet Machines and Applications  

Microsoft Academic Search

Halbach magnetised PM brushless machines are novel in that their magnetisation is self-shielding. They offer many attractive features, such as sinusoidal airgap field distribution and back-emf waveform, negligible cogging torque, potentially high airgap flux density and no need of rotor back-iron. Hence, they have recently attracted many research and development interests and extensive exploitation for their applications. This paper starts

Z. Q. Zhu

2007-01-01

49

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

50

Radiation from a Line Source Placed in Two-dimensional Photonic Crystals  

Microsoft Academic Search

A novel formulation of radiation from a localized line source placed in two-dimensional photonic crystals consisting of layered\\u000a periodic arrays of parallel circular cylinders is presented. The method employs the spectral domain approach. The spectral\\u000a response of the photonic crystals to the line source excitation is calculated using the lattice sums, the T-matrix of a circular\\u000a cylinder, and the generalized

Vakhtang Jandieri; Kiyotoshi Yasumoto; Hiroshi Toyama

2007-01-01

51

Topological defects in two-dimensional crystals  

Microsoft Academic Search

By using topological current theory, we study the inner topological structure of the topological defects in two-dimensional (2D) crystal. We find that there are two elementary point defects topological current in two-dimensional crystal, one for dislocations and the other for disclinations. The topological quantization and evolution of topological defects in two-dimensional crystals are discussed. Finally, We compare our theory with

Yong Chenand; Wei-Kai Qi

2008-01-01

52

LETTER TO THE EDITOR: The Bergman spectrum of the effective dielectric constant in two-dimensional composite media  

Microsoft Academic Search

The Bergman spectrum of a two-dimensional composite with parallel cylinders immersed in the matrix was calculated and analysed. We found that the spectrum is discrete away from the percolation threshold and tends towards being continuous as the cylinders become closer and finally touch. We also calculated the effective dielectric constant and found that close to the percolation threshold the effective

Xiangting Li; H. R. Ma

1999-01-01

53

Design and Analysis of a Nested Halbach Permanent Magnet Magnetic Refrigerator  

E-print Network

Design and Analysis of a Nested Halbach Permanent Magnet Magnetic Refrigerator by Armando Tura BEng Committee Design and Analysis of a Nested Halbach Permanent Magnet Magnetic Refrigerator by Armando Tura with the potential to create efficient and compact refrigeration devices is an active magnetic regenerative

Victoria, University of

54

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

NASA Astrophysics Data System (ADS)

In order to improve the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle, a two-pole Halbach array’s permanent magnet guideway (PMG) is proposed, which is called as Halbach PMG. The finite element method (FEM) calculations indicate that Halbach PMG has a wider high-field region than the present PMG of equal PM’s transverse section. The levitation force of bulk HTSCs with the present PMG and Halbach PMG are measured. The results show that at different levitation gaps, the force ratios based on the Halbach PMG are about 2.3 times larger than that on the present PMG, which greatly increases the load capability of the system. Therefore, both the numerical analysis and experimental results have confirmed that the Halbach PMG will further enhance the performance of the vehicle and it is possible to decrease the total numbers of onboard HTSCs, reducing overall costs. So based on the Halbach PMG, we further study the width ratios between HTSCs and PMG for making the better use of the onboard HTSCs. Some preliminary results are given. These results are important for further HTS Maglev vehicle system designs using Halbach PMG.

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

2007-10-01

55

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles  

E-print Network

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles A. Sarwar targeting Optimal permanent magnet Nano-particle trapping Pushing nanoparticle Halbach array design a b to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces

Shapiro, Benjamin

56

Correspondence Quantification in Comprehensive Two-Dimensional  

E-print Network

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.

57

Two Dimensional Mechanism for Insect Hovering  

Microsoft Academic Search

Resolved computation of two dimensional insect hovering shows for the first time that a two dimen- sional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the

Z. Jane Wang

2000-01-01

58

NUMERICAL INVESTIGATION OF A TWO-DIMENSIONAL  

Microsoft Academic Search

We present here a highly efficient and accurate numerical scheme for initial and boundary value problems of a two-dimensional Boussinesq sys- tem which describes three-dimensional water waves over a moving and uneven bottom with surface pressure variation. The scheme is then used to study in details the waves generated from rectangular sources and the two-dimensional wave patterns.

59

Measuring Monotony in Two-Dimensional Samples  

ERIC Educational Resources Information Center

This note introduces a monotony coefficient as a new measure of the monotone dependence in a two-dimensional sample. Some properties of this measure are derived. In particular, it is shown that the absolute value of the monotony coefficient for a two-dimensional sample is between /"r"/ and 1, where "r" is the Pearson's correlation coefficient for…

Kachapova, Farida; Kachapov, Ilias

2010-01-01

60

Two-dimensional phased arrays of sources and detectors for depth discrimination in diffuse optical imaging  

E-print Network

Two-dimensional phased arrays of sources and detectors for depth discrimination in diffuse optical, multidetector phased-array ap- proach to diffuse optical imaging that is based on postprocessing continuous of elements. We find that the proposed phased-array method is able to separate cylinders at differ- ent depths

Fantini, Sergio

61

Photonic-band-gap structures and guide modes in two-dimensional magnetic photonic crystal heterostructures  

Microsoft Academic Search

We first investigate the band gap structures of two-dimensional magnetic photonic crystals (MPC) composed of rectangular (square) magnetic cylinders embedded in a host dielectric material in the rectangular (square) lattice, and we then study guide modes at interface of MPC heterostructures (MPCHs) by use of plane wave expansion method in combination with supercell technique. We find that both the mirror-symmetric

Yun-Song Zhou; Ben-Yuan Gu; Fu-He Wang

2003-01-01

62

RCS of two-dimensional structures consisting of both dielectrics and conductors of arbitrary cross section  

Microsoft Academic Search

The problem of determining the electromagnetic field scattered by two-dimensional structures consisting of both dielectric and conducting cylinders of arbitrary cross section is considered. The conductors may be in the form of strips and the dielectrics may be in the form of the shells. The conductors may be partially or fully covered by dielectric layers, while the dielectrics may be

Ercument Arvas; Tapan K. Sarkar

1989-01-01

63

A two-dimensional methodology to predict vertical axis wind turbine performance  

Microsoft Academic Search

An accurate two-dimensional methodology, the COIN Lambda Fast Solver, for the computation of the flow field about a vertical axis wind turbine is presented. Such a technique determines the smooth flow field by integrating the compatibility conditions along the bicharacteristic lines. The time-averaged wind turbine effects are introduced by means of an actuator porous cylinder having the same radius of

B. Fortunato; A. Dadone; V. Trifoni

1995-01-01

64

Radiation from a Line Source Embedded in Two-Dimensional Electromagnetic Crystals  

Microsoft Academic Search

The two-dimensional radiation from a localized line source embedded in electromagnetic crystals is formulated in the spectral domain, using the lattice sums, the T-matrix of a circular cylinder, and the generalized reflection and transmission matrices for the layered system. Electromagnetic crystals are periodic dielectric or metallic structures, in which any electromagnetic wave propagation is forbidden within a certain frequency range.

Vakhtang Jandieri; Kiyotoshi Yasumoto

65

Two Dimensional Mechanism for Insect Hovering  

SciTech Connect

Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient. (c) 2000 The American Physical Society.

Jane Wang, Z.

2000-09-04

66

Two-dimensional materials for electronic applications  

E-print Network

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

67

Relativity on two-dimensional spacetimes  

E-print Network

Lorentz transformation on two-dimensional spacetime is obtained without assumption of linearity. To obtain this, we use the invariance of wave equations, which is recently proved to be equivalent to the causality preservation.

Do-Hyung Kim

2013-07-26

68

Electronic properties of two-dimensional systems  

Microsoft Academic Search

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

69

Efficient Two-Dimensional-FFT Program  

NASA Technical Reports Server (NTRS)

Program computes 64 X 64-point fast Fourier transform in less than 17 microseconds. Optimized 64 X 64 Point Two-Dimensional Fast Fourier Transform combines performance of real- and complex-valued one-dimensional fast Fourier transforms (FFT's) to execute two-dimensional FFT and coefficients of power spectrum. Coefficients used in many applications, including analyzing spectra, convolution, digital filtering, processing images, and compressing data. Source code written in C, 8086 Assembly, and Texas Instruments TMS320C30 Assembly languages.

Miko, J.

1992-01-01

70

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

71

Quenched bond dilution in two-dimensional Potts models  

NASA Astrophysics Data System (ADS)

We report a numerical study of the bond-diluted two-dimensional Potts model using transfer-matrix calculations. For different numbers of states per spin, we show that the critical exponents at the random fixed point are the same as in self-dual random-bond cases. In addition, we determine the multifractal spectrum associated with the scaling dimensions of the moments of the spin-spin correlation function in the cylinder geometry. We show that the behaviour is fully compatible with the one observed in the random-bond case, confirming the general picture according to which a unique fixed point describes the critical properties of different classes of disorder: dilution, self-dual binary random bond, self-dual continuous random bond.

Chatelain, Christophe; Berche, Bertrand; Shchur, Lev N.

2001-11-01

72

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

73

Soap film flows: Statistics of two-dimensional turbulence  

SciTech Connect

Soap film flows provide a very convenient laboratory model for studies of two-dimensional (2-D) hydrodynamics including turbulence. For a gravity-driven soap film channel with a grid of equally spaced cylinders inserted in the flow, we have measured the simultaneous velocity and thickness fields in the irregular flow downstream from the cylinders. The velocity field is determined by a modified digital particle image velocimetry method and the thickness from the light scattered by the particles in the film. From these measurements, we compute the decay of mean energy, enstrophy, and thickness fluctuations with downstream distance, and the structure functions of velocity, vorticity, thickness fluctuation, and vorticity flux. From these quantities we determine the microscale Reynolds number of the flow R{sub {lambda}}{approx}100 and the integral and dissipation scales of 2D turbulence. We also obtain quantitative measures of the degree to which our flow can be considered incompressible and isotropic as a function of downstream distance. We find coarsening of characteristic spatial scales, qualitative correspondence of the decay of energy and enstrophy with the Batchelor model, scaling of energy in {ital k} space consistent with the k{sup {minus}3} spectrum of the Kraichnan{endash}Batchelor enstrophy-scaling picture, and power-law scalings of the structure functions of velocity, vorticity, vorticity flux, and thickness. These results are compared with models of 2-D turbulence and with numerical simulations. {copyright} {ital 1999 American Institute of Physics.}

Vorobieff, P.; Rivera, M.; Ecke, R.E. [Center for Nonlinear Studies and Condensed Matter and Thermal Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Center for Nonlinear Studies and Condensed Matter and Thermal Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1999-08-01

74

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

75

Improved Halbach sensor for NMR scanning of drill cores.  

PubMed

A lightweight Halbach magnet system for use in nuclear magnetic resonance (NMR) studies on drill cores was designed and built. It features an improved homogeneous magnetic field with a strength of 0.22 T and a maximum accessible sensitive volume. Additionally, it is furnished with a sliding table for automatic scans of cylindrical samples. This device is optimized for nondestructive online measurements of porosity and pore size distributions of water-saturated full cylindrical and split semicylindrical drill cores of different diameters. The porosity of core plugs with diameters from 20 to 80 mm can be measured routinely using exchangeable radiofrequency coils. Advanced NMR techniques that provide 2D T(1)-T(2) correlations with an average measurement time of 30 min and permeability estimates can be performed with a special insert suitable for small core plugs with diameter and length of 20 mm. PMID:17466767

Anferova, Sophia; Anferov, Vladimir; Arnold, Juliane; Talnishnikh, Elena; Voda, Mihai A; Kupferschläger, Klaus; Blümler, Peter; Clauser, Christoph; Blümich, Bernhard

2007-05-01

76

Experiments on Inductive Magnetic Levitation with a Circular Halbach Array  

NASA Astrophysics Data System (ADS)

Using a ring Halbach array, we are investigating a repulsive levitating force and a drag force acting on the magnet from a ring of inductors rotating below the magnet. After measuring induced currents, voltages and magnetic fields in the individual inductors (in the form of short solenoids), we investigated the dependence of lift/drag forces on the speed of relative rotation. The ratio of lift to drag increases with the angular velocity, as expected from a related theory of the induction effects in a linear motion. We are experimenting with the shape and density of inductors, and their material, in an attempt to maximize the lift at a minimal velocity of rotation. Eventually this design could have applications as frictionless bearings or as frictionless gear in a wide range of systems, especially in machinery that cannot be easily accessed.

Bean, Ian; Goncz, Doug; Raymer, Austin; Specht, Jason; Zalles, Ricardo; Majewski, Walerian

2013-03-01

77

Nitrogenated holey two-dimensional structures  

PubMed Central

Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications. PMID:25744355

Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom

2015-01-01

78

On the two-dimensional Coulomb gas  

Microsoft Academic Search

This is a sequel to a recent work of Gaudin, who studied the classical equilibrium statistical mechanics of the two-dimensional Coulomb gas on a lattice at a special value of the coupling constant? such that the model is exactly solvable. This model is briefly reviewed, and it is shown that the correlation functions obey the sum rules that characterize a

Françoise Cornu; Bernard Jancovici

1987-01-01

79

Detecting disparity in two-dimensional patterns  

Microsoft Academic Search

One can measure the disparities between two retinal images in several different ways. Experiments were conducted to identify the measure that is invariant at the threshold for detecting the disparity of two-dimensional patterns. The patterns used were stereo plaids, which permit a partial dissociation between the disparity of the pattern and the disparities of its one-dimensional compo- nents. For plaids

Bart Farell

80

Nitrogenated holey two-dimensional structures  

NASA Astrophysics Data System (ADS)

Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 107, with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications.

Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom

2015-03-01

81

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

82

Two-dimensional tunable magnetic photonic crystals  

Microsoft Academic Search

We have calculated the photonic band structure for a cubic block of magnetically saturated ferrite material having a triangular array of circular holes that is under the influence of an external static magnetic field Hex=Hexz applied in the hole direction. In this two-dimensional magnetic photonic crystal, the saturated magnetism can affect the transverse electric (TE) mode whose electric field lies

Chul-Sik Kee; Jae-Eun Kim; Hae Yong Park; H. Lim

2000-01-01

83

A Two Dimensional Car Crash Victim Simulation  

Microsoft Academic Search

The purpose of this study was to develop a two dimensional mathematical model of an unrestrained, right, front seat, passenger car occupant, subjected to frontal collision. A 10 degrees of freedom linkage system made of 8 rigid segments connected with revolute joints was used as occupant model. Relative rotation between links were constrained by torsional springs, dampers, Coulomb frictions and

M. Batman; R. Seliktar

1990-01-01

84

Two-Dimensional Cellular Automata with Memory  

Microsoft Academic Search

Standard Cellular Automata (CA) are ahistoric (memoryless), i.e., the new state of a cell depends on its neighborhood configuration only at the preceding time step. The effect of keeping ahistoric memory of all past iterations in two-dimensional CA, featuring each cell by its most frequent state is analyzed in this work.

Ramón Alonso-Sanz; Margarita Martín

2002-01-01

85

High-resolution two dimensional advective transport  

USGS Publications Warehouse

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

86

Evaporation of two-dimensional black holes  

Microsoft Academic Search

An interesting two-dimensional model theory has been proposed that allows one to consider black-hole evaporation in the semiclassical approximation. The semiclassical equations will give a singularity where the dilation field reaches a certain critical value. This singularity will be hidden behind a horizon. As the evaporation proceeds, the dilation field on the horizon will approach the critical value but the

S. W. Hawking

1992-01-01

87

Two Dimensional String Theory And Black Holes  

E-print Network

This lecture surveys a few loosely related topics, ranging from the scarcity of quantum field theories -- and the role that this has played, and still plays, in physics -- to paradoxes involving black holes in soluble two dimensional string theory and the question of whether naked singularities might be of even greater interest to string theorists than black holes.

Edward Witten

1992-06-17

88

Nitrogenated holey two-dimensional structures.  

PubMed

Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 10(7), with calculated and experimental bandgaps of approximately 1.70 and 1.96?eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications. PMID:25744355

Mahmood, Javeed; Lee, Eun Kwang; Jung, Minbok; Shin, Dongbin; Jeon, In-Yup; Jung, Sun-Min; Choi, Hyun-Jung; Seo, Jeong-Min; Bae, Seo-Yoon; Sohn, So-Dam; Park, Noejung; Oh, Joon Hak; Shin, Hyung-Joon; Baek, Jong-Beom

2015-01-01

89

Piezoelectricity in two-dimensional materials.  

PubMed

Powering up 2D materials: Recent experimental studies confirmed the existence of piezoelectricity-the conversion of mechanical stress into electricity-in two-dimensional single-layer MoS2 nanosheets. The results represent a milestone towards embedding low-dimensional materials into future disruptive technologies. PMID:25714055

Wu, Tom; Zhang, Hua

2015-04-01

90

Sound scattering by anisotropic metafluids based on two-dimensional sonic crystals  

NASA Astrophysics Data System (ADS)

Multiple-scattering theory is here employed to study the scattering of sound by a fluidlike cylinder characterized by an anisotropic mass density tensor. A derivation of the t matrix associated to such acoustic material nonexisting in nature is here comprehensively derived, and the result is employed to study the pressure field produced by plane sound waves impinging the cylinder. It is also shown that an acoustic metamaterial or metafluid can be engineered to exactly match the dynamical properties of the anisotropic fluid by using a circular cluster made of a two-dimensional sonic crystal with a nonisotropic lattice.

Torrent, Daniel; Sánchez-Dehesa, José

2009-05-01

91

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

PubMed

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

92

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

93

The two-dimensional electromagnetic inverse scattering problem for chiral media  

NASA Astrophysics Data System (ADS)

We introduce Maxwell's equations with chiral constitutive equations in the form given by Fedorov and Bokut. In the case where the scatterer is an infinitely long cylinder we derive a two-dimensional scattering problem and discuss the existence and uniqueness of solutions via an integral equation approach. Then we formulate the inverse scattering problem to find the shape of the scatterer if the far-field data are known. We give a uniqueness result and describe a numerical reconstruction scheme.

Gerlach, Thomas

1999-12-01

94

Toward two-dimensional search engines  

NASA Astrophysics Data System (ADS)

We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.

Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.

2012-07-01

95

Two-dimensional ranking of Wikipedia articles  

NASA Astrophysics Data System (ADS)

The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists ab aeterno. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. While PageRank highlights very well known nodes with many ingoing links, CheiRank highlights very communicative nodes with many outgoing links. In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.

Zhirov, A. O.; Zhirov, O. V.; Shepelyansky, D. L.

2010-10-01

96

Plasmonics with two-dimensional conductors  

PubMed Central

A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics. PMID:24567472

Yoon, Hosang; Yeung, Kitty Y. M.; Kim, Philip; Ham, Donhee

2014-01-01

97

Two-dimensional spatially developing mixing layers  

SciTech Connect

Two-dimensional, incompressible, spatially developing mixing layer simulations are performed with two classes of perturbations applied at the inlet boundary: (1) combinations of discrete modes from linear stability theory, and (2) a broad spectrum of modes derived from experimentally measured velocity spectra. The discrete modes from linear theory are obtained by solving the Orr-Sommerfeld equation, and linear stability analysis is used to investigate the effect of Reynolds number on the stability of mixing layers. Two-point spatial velocity and autocorrelations are used to estimate the size and lifetime of the resulting coherent structures and to explore possible feedback effects. It is shown that by forcing with a broad spectrum of modes derived from an experimental energy spectrum, many experimentally observed phenomena can be reproduced by a two-dimensional simulation.

Wilson, R.V.; Demuren, A.O. [Old Dominion Univ., Norfolk, VA (United States). Dept. of Mechanical Engineering

1996-04-01

98

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

99

Electronics based on two-dimensional materials.  

PubMed

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

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

2014-10-01

100

String breaking in two-dimensional QCD  

E-print Network

I present results of a numerical calculation of the effects of light quark-antiquark pairs on the linear heavy-quark potential in light-cone quantized two-dimensional QCD. I extract the potential from the Q-Qbar component of the ground-state wavefunction, and observe string breaking at the heavy-light meson pair threshold. I briefly comment on the states responsible for the breaking.

Hornbostel, K J

1999-01-01

101

Two-dimensional crosstalk avoidance codes  

Microsoft Academic Search

Global buses in deep submicron system-on-chip designs suffer from increasing crosstalk delay as the feature size shrinks. As an technology-independent solution, crosstalk avoidance coding alleviates the problem while requiring less area and power than shielding. Most previously considered crosstalk avoidance codes are one-dimensional, and have limited code rates. In this paper, we propose two-dimensional crosstalk avoidance codes (TDCAC), which achieve

Xuebin Wu; Zhiyuan Yan; Yuan Xie

2008-01-01

102

Statistical Mechanics of Two-dimensional Foams  

E-print Network

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

Marc Durand

2010-09-07

103

Fully localized two-dimensional embedded solitons  

SciTech Connect

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

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

2010-11-15

104

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles  

NASA Astrophysics Data System (ADS)

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 by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nanoparticles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm 3 volume optimal Halbach design yields a 5× greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (?1 T), size (?2000 cm 3), and number of elements (?36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ?5°), thus yielding practical designs to improve magnetic drug targeting treatment depths.

Sarwar, A.; Nemirovski, A.; Shapiro, B.

2012-03-01

105

Optimal Halbach Permanent Magnet Designs for Maximally Pulling and Pushing Nanoparticles.  

PubMed

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 depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nano-particles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm(3) volume optimal Halbach design yields a ×5 greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (? 1 Tesla), size (? 2000 cm(3)), and number of elements (? 36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ? 5°), thus yielding practical designs to improve magnetic drug targeting treatment depths. PMID:23335834

Sarwar, A; Nemirovski, A; Shapiro, B

2012-03-01

106

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

107

Loop coverings of two dimensional square lattices  

NASA Astrophysics Data System (ADS)

In a two dimensional square lattice, where all sites are covered by loops, in the past few years a classical statistical mechanics model of dense loop gas was considered for its relevance for the evaluation of observables of the quantum antiferromagnetic Heisenberg model on the resonating valence bond state. By use of transfer matrices we evaluate several observables for narrow strips with a width of two or three sites. A simple extrapolation, consistent with rigorous bounds, is conjectured for its possible use in a variational ansatz in the Hubbard model.

Cicuta, Giovanni M.; Massari, Francesco

1993-04-01

108

Analytical calculation of two-dimensional spectra.  

PubMed

We demonstrate an analytical calculation of two-dimensional (2D) coherent spectra of electronic or vibrational resonances. Starting with the solution to the optical Bloch equations for a two-level system in the 2D time domain, we show that a fully analytical 2D Fourier transform can be performed if the projection-slice and Fourier-shift theorems of Fourier transforms are applied. Results can be fit to experimental 2D coherent spectra of resonances with arbitrary inhomogeneity. PMID:25831281

Bell, Joshua D; Conrad, Rebecca; Siemens, Mark E

2015-04-01

109

Universal absorption of two-dimensional systems  

NASA Astrophysics Data System (ADS)

We discuss the optical conductivity of several noninteracting two-dimensional semiconducting systems focusing on gapped Dirac and Schrödinger fermions as well as on a system mixing these two types. Close to the band gap, we can define a universal optical conductivity quantum of ?0=1/16 e/2? for the pure systems. The effective optical conductivity then depends on the degeneracy factors gs (spin) and gv (valley) and on the curvature around the band gap ? , i.e., it generally reads ? =gsgv? ?0 . For a system composed of both types of carriers, the optical conductivity becomes nonuniversal.

Stauber, T.; Noriega-Pérez, D.; Schliemann, J.

2015-03-01

110

Cosmic Censorship in Two-Dimensional Gravity  

E-print Network

A weak version of the cosmic censorship hypothesis is implemented as a set of boundary conditions on exact semi-classical solutions of two-dimensional dilaton gravity. These boundary conditions reflect low-energy matter from the strong coupling region and they also serve to stabilize the vacuum of the theory against decay into negative energy states. Information about low-energy incoming matter can be recovered in the final state but at high energy black holes are formed and inevitably lead to information loss at the semi-classical level.

J. Russo; L. Susskind; L. Thorlacius

1992-09-22

111

Development of Halbach magnet for portable NMR device  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance (NMR) has enormous potential for various applications in industry as the on-line or at-line test/control device of process environments. Advantage of NMR is its non-destructive nature, because it does not require the measurement probe to have a contact with the tested media. Despite of the recent progress in this direction, application of NMR in industry is still very limited. This is related to the technical and analytical complications of NMR as a method, and high cost of NMR analyzers available at the market. However in many applications, NMR is a very useful technique to test various products and to monitor quantitatively industrial processes. Fortunately usually there is no need in a high-field superconducting magnets to obtain the high-resolution spectra with the detailed information on chemical shifts and coupling-constant. NMR analyzers are designed to obtain the relaxation parameters by measuring the NMR spectra in the time domain rather than in frequency domain. Therefore it is possible to use small magnetic field (and low frequency of 2-60 MHz) in NMR systems, based on permanent magnet technology, which are specially designed for specific at-line and on-line process applications. In this work we present the permanent magnet system developed to use in the portative NMR devices. We discuss the experimental parameters of the designed Halbach magnet system and compare them with results of theoretical modelling.

Do?an, N.; Topkaya, R.; Suba?i, H.; Yerli, Y.; Rameev, B.

2009-03-01

112

Flow transitions in two-dimensional foams.  

PubMed

For sufficiently slow rates of strain, flowing foam can exhibit inhomogeneous flows. The nature of these flows is an area of active study in both two-dimensional model foams and three dimensional foam. Recent work in three-dimensional foam has identified three distinct regimes of flow [S. Rodts, J. C. Baudez, and P. Coussot, Europhys. Lett. 69, 636 (2005)]. Two of these regimes are identified with continuum behavior (full flow and shear banding), and the third regime is identified as a discrete regime exhibiting extreme localization. In this paper, the discrete regime is studied in more detail using a model two-dimensional foam: a bubble raft. We characterize the behavior of the bubble raft subjected to a constant rate of strain as a function of time, system size, and applied rate of strain. We observe localized flow that is consistent with the coexistence of a power-law fluid with rigid-body rotation. As a function of applied rate of strain, there is a transition from a continuum description of the flow to discrete flow when the thickness of the flow region is approximately ten bubbles. This occurs at an applied rotation rate of approximately 0.07 s-1. PMID:17279908

Gilbreth, Christopher; Sullivan, Scott; Dennin, Michael

2006-11-01

113

Two-dimensional phonon transport in graphene.  

PubMed

Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. PMID:22562955

Nika, Denis L; Balandin, Alexander A

2012-06-13

114

Halbach array generator/motor having mechanically regulated output voltage and mechanical power output  

DOEpatents

A motor/generator has its stationary portion, i.e., the stator, positioned concentrically within its rotatable element, i.e., the rotor, along the axis of rotation of the rotor. The rotor includes a Halbach array of magnets. The voltage and power outputs are regulated by varying the radial gap in between the stator windings and the rotating Halbach array. The gap is varied by extensible and retractable supports attached to the stator windings that can move the windings in a radial direction.

Post, Richard F.

2005-06-14

115

Halbach array generator/motor having an automatically regulated output voltage and mechanical power output  

DOEpatents

A motor/generator having its stationary portion, i.e., the stator, positioned concentrically within its rotatable element, i.e., the rotor, along its axis of rotation. The rotor includes a Halbach array. The stator windings are switched or commutated to provide a DC motor/generator much the same as in a conventional DC motor/generator. The voltage and power are automatically regulated by using centrifugal force to change the diameter of the rotor, and thereby vary the radial gap in between the stator and the rotating Halbach array, as a function of the angular velocity of the rotor.

Post, Richard F.

2005-02-22

116

Two-dimensional fourier transform spectrometer  

DOEpatents

The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.

DeFlores, Lauren; Tokmakoff, Andrei

2013-09-03

117

Two-dimensional nuclear magnetic resonance petrophysics.  

PubMed

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

118

Transport in two-dimensional disordered semimetals.  

PubMed

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. PMID:25396385

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

2014-10-31

119

Gauge equivalence in two-dimensional gravity  

NASA Astrophysics Data System (ADS)

Two-dimensional quantum gravity is identified as a second-class system which we convert into a first-class system via the Batalin-Fradkin (BF) procedure. Using the extended phase space method, we then formulate the theory in the most general class of gauges. The conformal gauge action suggested by David, Distler, and Kawai is derived from first principles. We find a local, light-cone gauge action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature equation ?-R=?3-g++=0, revealing the origin of the SL(2,R) Kac-Moody symmetry. The BF degree of freedom turns out to be dynamically active as the Liouville mode in the conformal gauge, while in the light-cone gauge the conformal degree of freedom plays that role. The inclusion of the cosmological constant term in both gauges is also considered.

Fujiwara, T.; Igarashi, Y.; Kubo, J.; Tabei, T.

1993-08-01

120

Phonon hydrodynamics in two-dimensional materials.  

PubMed

The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane. PMID:25744932

Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola

2015-01-01

121

From two-dimensional materials to heterostructures  

NASA Astrophysics Data System (ADS)

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

Niu, Tianchao; Li, Ang

2015-02-01

122

Tunable two-dimensional femtosecond spectroscopy  

NASA Astrophysics Data System (ADS)

We have developed a two-dimensional (2D) Fourier-transform femtosecond spectroscopy technique for the visible spectral region. Three-pulse photon echo signals are generated in a phase-matched noncollinear four-wave mixing box geometry that employs a 3-kHz repetition-rate laser system and optical parametric amplification. Nonlinear signals are fully characterized in amplitude and phase by spectral interferometry. Unlike for previous setups, we achieve long-term phase stability by employing diffractive optics and interferometric accuracy of excitation-pulse time delays by using movable glass wedges. As an example of this technique, 2D correlation and relaxation spectra at 600 nm are shown for a solution of Nile Blue dye in acetonitrile.

Brixner, T.; Stiopkin, I. V.; Fleming, G. R.

2004-04-01

123

Two-dimensional readout of GEM detectors  

E-print Network

The recently introduced Gas Electron Multiplier (GEM) permits the amplification of electrons released by ionizing radiation in a gas by factors approaching ten thousand, larger gains can be obtained combining two GEMs in cascade. We describe methods for implementing two- and three-dimensional projective localization of radiation, with sub-millimeter accuracy, making use of specially manufactured and patterned pick-up electrodes. Easy to implement and flexible in the choice of the readout geometry, the technology has the distinctive advantage of allowing all pick-up electrodes to be kept at ground potential, thus substantially improving the system simplicity and reliability. Preliminary results demonstrating the two-dimensional imaging capability of the devices are provided and discussed, as well as future perspectives of development.

Bressan, A; Gandi, A; Labbé, J C; Ropelewski, Leszek; Sauli, Fabio; Mörmann, D; Müller, T; Simonis, H J

1999-01-01

124

Phonon hydrodynamics in two-dimensional materials  

NASA Astrophysics Data System (ADS)

The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.

Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola

2015-03-01

125

Two-Dimensional Informative Array Testing  

PubMed Central

Summary Array-based group testing algorithms for case identification are widely used in infectious disease testing, drug discovery, and genetics. In this paper, we generalize previous statistical work in array testing to account for heterogeneity among individuals being tested. We first derive closed-form expressions for the expected number of tests (efficiency) and misclassification probabilities (sensitivity, specificity, predictive values) for two-dimensional array testing in a heterogeneous population. We then propose two “informative” array construction techniques which exploit population heterogeneity in ways that can substantially improve testing efficiency when compared to classical approaches which regard the population as homogeneous. Furthermore, a useful byproduct of our methodology is that misclassification probabilities can be estimated on a per-individual basis. We illustrate our new procedures using chlamydia and gonorrhea testing data collected in Nebraska as part of the Infertility Prevention Project. PMID:22212007

McMahan, Christopher S.; Tebbs, Joshua M.; Bilder, Christopher R.

2015-01-01

126

A two dimensional piezoeletric micro-positioner  

NASA Astrophysics Data System (ADS)

A scanning probe microscope can provide very high resolution imaging, but only within a small scanning area. There is a high demand for compact long range positioners, so that distant locations on the same sample can be imaged and studied. We will present information on the design and operation of a piezoelectric driven two-dimensional micropositioner that can provide long range motion in the x- and z-directions. The z-direction motion can be used for coarse approach, while the x-direction motion can be used to scan along the sample surface. The device is build as one single unit, so it is extremely compact and rigid, and can provide a high resonance frequency platform for high performance scanning probe microscopy.

Ng, K.-W.; Nichols, John; Brill, J. W.

2009-03-01

127

Evaporation of Two Dimensional Black Holes  

E-print Network

Callan, Giddings, Harvey and Strominger have proposed an interesting two dimensional model theory that allows one to consider black hole evaporation in the semi-classical approximation. They originally hoped the black hole would evaporate completely without a singularity. However, it has been shown that the semi-classical equations will give a singularity where the dilaton field reaches a certain critical value. Initially, it seems this singularity will be hidden inside a black hole. However, as the evaporation proceeds, the dilaton field on the horizon will approach the critical value but the temperature and rate of emission will remain finite. These results indicate either that there is a naked singularity, or (more likely) that the semi-classical approximation breaks down when the dilaton field approaches the critical value.

S. W. Hawking

1992-03-18

128

Two-Dimensional Melting under Quenched Disorder  

NASA Astrophysics Data System (ADS)

We study the influence of quenched disorder on the two-dimensional melting behavior of superparamagnetic colloidal particles, using both video microscopy and computer simulations of repulsive parallel dipoles. Quenched disorder is introduced by pinning a fraction of the particles to an underlying substrate. We confirm the occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario and observe an intermediate hexatic phase. While the fluid-hexatic transition remains largely unaffected by disorder, the hexatic-solid transition shifts to lower temperatures with increasing disorder. This results in a significantly broadened stability range of the hexatic phase. In addition, we observe spatiotemporal critical(like) fluctuations, which are consistent with the continuous character of the phase transitions. Characteristics of first-order transitions are not observed.

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

2013-08-01

129

Convergence of two-dimensional Fourier series  

E-print Network

' 6 (c-a) + 2 M s + ? if n & N. 3 (c, d) Therefore ( f(x, y) sin nxdx & s ' j(a, b) The proof for cos nx is similar. 22o Vl. Ifd Il/2, 12 f, d II I 2 +I ll 2 0 Proof: Consider '0/2 r 2 +I dx = sin x 0 Ti [ 1/2 + cos Q + cos 0 ll ~it +I 't...), 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...

Kidd, Robert Henry, III

1962-01-01

130

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

131

Two-dimensional virtual impactors. Final report  

SciTech Connect

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

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

1980-12-01

132

Scattering from chiral cylinders of circular cross-sections  

Microsoft Academic Search

A semi-analytical solution is presented to the problem of electromagnetic scattering from a collection of parallel chiral cylinders of circular cross-section. The cylinders are illuminated by either a TEz or a TMz incident plane wave. The solution procedure is useful in predicting the scattering properties of arbitrary shaped two-dimensional scatterers composed of dielectric, conducting, and chiral media.

A. Z. Elsherbeni; M. Al Sarkawy; S. F. Mahmoud

2003-01-01

133

DARBOUX TRANSFORMATIONS FOR LINEAR OPERATORS ON TWO DIMENSIONAL REGULAR LATTICES  

E-print Network

DARBOUX TRANSFORMATIONS FOR LINEAR OPERATORS ON TWO DIMENSIONAL REGULAR LATTICES ADAM DOLIWA AND MACIEJ NIESZPORSKI Abstract. Darboux transformations for (systems of) linear operators on regular two dimensional lattices are reviewed. 1. Introduction The Darboux transformation is a well known tool

134

Two-dimensional stability of ion-acoustic solitons  

Microsoft Academic Search

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

M. Kako; G. Rowlands

1976-01-01

135

Internal tide generation by arbitrary two-dimensional topography  

E-print Network

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

Peacock, Thomas

136

ANALYSIS OF TWO-DIMENSIONAL ELECTROPHORESIS GEL IMAGES  

E-print Network

ANALYSIS OF TWO-DIMENSIONAL ELECTROPHORESIS GEL IMAGES Lars Pedersen Informatics and Mathematical of proteomics. The subject is Analysis of Two-dimensional Electrophoresis Gel Images. This work was carried out analysis of two-dimensional gel electrophoresis (2DGE) images. 2DGE is the leading technique to separate

137

A Neutrally Buoyant Elliptical Cylinder in Simple Shear  

Microsoft Academic Search

An elliptical cylinder in simple shear (i.e., 2D, zero-mean, linearly-varying) flow is a two-dimensional Lagrangian model of a fiber in a dilute sheared suspension. Simple shear flow around a neutrally buoyant cylinder is characterized by the shear-based Reynolds number ReG ? a^2G\\/nu (G is the shear rate, a is the semi-major dimension of the cylinder, and nu is the kinematic

Claudia Zettner; Minami Yoda

1999-01-01

138

Burgers approximation for two-dimensional flow past an ellipse  

NASA Technical Reports Server (NTRS)

A motivation is given for studying Burgers flow and a solution technique is outlined which works equally well for Oseen or Burgers flow past a circular cylinder. The separation behind the cylinder, the drag experienced by the cylinder, and asymptotic behavior far from the cylinder are described. It is shown that the predictions of Burgers flow near the cylinder provide a substantial improvement over those of Oseen flow. Finally, the equations of motion for Burgers flow past an ellipse are formulated and solved.

Dorrepaal, J. M.

1982-01-01

139

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

SciTech Connect

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

NONE

1995-02-01

140

A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage.  

PubMed

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force. PMID:19405690

Choi, Young-Man; Lee, Moon G; Gweon, Dae-Gab; Jeong, Jaehwa

2009-04-01

141

A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage  

NASA Astrophysics Data System (ADS)

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force.

Choi, Young-Man; Lee, Moon G.; Gweon, Dae-Gab; Jeong, Jaehwa

2009-04-01

142

Passive axial magnetic bearing with Halbach magnetized array in magnetically suspended control moment gyro application  

Microsoft Academic Search

The paper presents a special configuration of passive axial magnetic bearing with segmented Halbach magnetized array in magnetically suspended control moment gyro (MSCMG). Peculiarity of presented passive axial magnetic bearing is its ability to provide angular stiffness so that it can produce gyro moment when it is used in MSCMG. The MSCMG with this passive axial magnetic bearing can efficiently

Sun Jinji; Ren Yuan; Fang Jiancheng

2011-01-01

143

Seismic isolation of two dimensional periodic foundations  

SciTech Connect

Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5?Hz to 50?Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.

Yan, Y.; Mo, Y. L., E-mail: yilungmo@central.uh.edu [University of Houston, Houston, Texas 77004 (United States); Laskar, A. [Indian Institute of Technology Bombay, Powai, Mumbai (India); Cheng, Z.; Shi, Z. [Beijing Jiaotong University, Beijing (China); Menq, F. [University of Texas, Austin, Texas 78712 (United States); Tang, Y. [Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2014-07-28

144

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

145

Two-dimensional flow magnetophoresis of microparticles.  

PubMed

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

Kawano, Makoto; Watarai, Hitoshi

2012-07-01

146

An atlas of two-dimensional materials.  

PubMed

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

Miró, Pere; Audiffred, Martha; Heine, Thomas

2014-09-21

147

Turbulence in two dimensional visco - elastic medium  

E-print Network

The properties of decaying turbulence is studied with the help of a Generalized Hydrodynamic (GHD) fluid model in the context of two dimensional visco - elastic medium such as a strongly coupled dusty plasma system. For the incompressible case considered here however, the observations are valid for a wider class of visco - elastic systems not necessarily associated with plasmas only. Our observations show that an initial spectrum that is confined in a limited domain of wave numbers becomes broad, even when the Reynold's number is much less than the critical value required for the onset of turbulence in Newtonian fluids. This is a signature of elastic turbulence where Weissenberg's number also plays a role in the onset of turbulence. This has been reported in several experiments. It is also shown that the existence of memory relaxation time parameter and the transverse shear wave inhibit the normal process (for 2-D systems) of inverse spectral cascade in this case. A detailed simulation study has been carried ...

Tiwari, Sanat Kumar; Das, Amita; Patel, Bhavesh G; Kaw, Predhiman

2014-01-01

148

Seismic isolation of two dimensional periodic foundations  

NASA Astrophysics Data System (ADS)

Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.

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

2014-07-01

149

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

150

Vortices of Two Dimensional Guiding Center Plasmas.  

NASA Astrophysics Data System (ADS)

A system of two dimensional guiding center plasma in a square conducting boundary is used as a model to study the anomalous transport is magnetically confined plasma. An external gravitational force is introduced to simulate the curvature and gradient of the magnetic field. For finite boundaries, it is a Hamiltonian system with finite phase space and negative temperature states are allowed. The statistical equilibrium states of this system are described by the solutions of a Poisson's equation with self-consistently determined charge density. In the limit of zero gravity, it can be reduced to the sinh-Poisson equation (DEL)('2)u + (lamda)('2)sinh u = 0. Previous numerical efforts have found solutions with vortex structures. A novel method of generating general exact solutions to this nonlinear boundary value problem is presented. These solutions are given by. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). where E(,i)'s are constants and the dependence of (gamma)(,j)'s on x and y are given by a set of coupled first order nonlinear ordinary differential equations. These equations can be linearized to give u(x,y) in terms of Riemann theta functions u(x,y) = 2ln (THETA)(l + 1/2)(THETA)(l) . The phases l evolve linearly in x and y while nonlinear superposition is displayed in the solution u(x,y). The self-consistent Poisson's equation with gravity is studied numerically. Different branches of solutions are obtained and their relations to the zero gravity solutions are discussed. The thermodynamically most favored structure of the system carries the feature of a heavy ion vortex on top of the light electron vortex. Branches of solutions are found to merge into each other as parameters in the equations were smoothly varied. A critical value of gravitational force exists such that below which there is a possibility of hysteresis between different equilibrium states. With the help of the nonzero gravity solutions, we also have a clearer picture of the transition from negative to positive temperature states. Nonuniform positive temperature states with a heavy ion vortex at the bottom of the square boundary are also found when gravity is present.

Ting, Antonio Chofai

151

Two-dimensional material confined water.  

PubMed

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

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

2015-01-20

152

Front tracking and two-dimensional Riemann problems  

NASA Astrophysics Data System (ADS)

Two-dimensional Riemann problems occurring at the intersection points of discontinuous waves in a compressible, inviscid, polytropic gas are studied from both numerical and theoretical points of view using the front tracking method. The results are compared to experimental ones for two specific test problems. An example of how the motion of a two-dimensional coherent wave is determined numerically is given, and it is shown that in two-dimensional compressible gas dynamics there are only a small number of such two-dimensional coherent waves. Outstanding questions related to Riemann problems are also discussed.

Glimm, J.; Klingenberg, C.; McBryan, O.; Plohr, B.; Yaniv, S.

1985-09-01

153

Zero Potts models coupled to two-dimensional quantum gravity  

NASA Astrophysics Data System (ADS)

The critical exponents that have been calculated for the Ising and Potts models coupled to two-dimensional quantum gravity correspond to annealed averages in the language of solid state physics. Using the replica trick and the approach of DDK we calculate the critical exponents for the Ising and q = 3, 4 state Potts models coupled to quenched two-dimensional quantum gravity.

Johnston, D. A.

1992-03-01

154

Two-Dimensionally Isotropic High Index Metamaterials Yushin Kim1  

E-print Network

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

Park, Namkyoo

155

Terahertz demonstrations of effectively two-dimensional photonic bandgap structures  

E-print Network

Terahertz demonstrations of effectively two- dimensional photonic bandgap structures Yuguang Zhao March 7, 2006 (Doc. ID 67376) We demonstrate effectively two-dimensional (2D) terahertz (THz) photonic of this effectively 2D embodiment. Our observations of the strongly varying, frequency- dependent transmission through

156

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

157

New two-dimensional quantum models with shape invariance  

SciTech Connect

Two-dimensional quantum models which obey the property of shape invariance are built in the framework of polynomial two-dimensional supersymmetric quantum mechanics. They are obtained using the expressions for known one-dimensional shape invariant potentials. The constructed Hamiltonians are integrable with symmetry operators of fourth order in momenta, and they are not amenable to the conventional separation of variables.

Cannata, F. [INFN, Via Irnerio 46, 40126 Bologna (Italy); Ioffe, M. V. [Saint-Petersburg State University, 198504 St.-Petersburg (Russian Federation); Nishnianidze, D. N. [Saint-Petersburg State University, 198504 St.-Petersburg (Russian Federation); Akaki Tsereteli State University, 4600 Kutaisi (Georgia)

2011-02-15

158

Microwave tomography: a two-dimensional Newton iterative scheme  

Microsoft Academic Search

In this paper, a variant of the Newton method, which uses a fast solution of the direct problem and a dual mesh, is proposed. Computational and physical experiments with simple two-dimensional high-contrast phantoms are discussed, and a full-scaled image of a two-dimensional mathematical model of a human torso is obtained

Alexandre E. Souvorov; Alexander E. Bulyshev; Serguei Y. Semenov; Robert H. Svenson; Alexei G. Nazarov; Yuri E. Sizov; George P. Tatsis

1998-01-01

159

Plastic flow in two-dimensional solids Akira Onuki  

E-print Network

Plastic flow in two-dimensional solids Akira Onuki Department of Physics, Kyoto University, Kyoto-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow

160

A SAR processor based on two-dimensional FFT codes  

Microsoft Academic Search

A synthetic aperture radar (SAR) processor approach based on two-dimensional fast Fourier transform (FFT) codes coupled with an asymptotic evaluation of the unit response function is presented. For the latter, no approximation is made to the distance function, so that the full range of geometric aberrations is analytically considered, enabling an effective reference filter to be designed. The two-dimensional FFTs

GIORGIO FRANCESCHETTI; GILDA SCHIRINZI

1990-01-01

161

PRESSURE MEASUREMENT IN A TWO DIMENSIONAL UNSTEADY FLOW  

E-print Network

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

Patil, Mayuresh

162

Enhancement of polarizabilities of cylinders with cylinder-slab resonances.  

PubMed

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

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

2015-01-01

163

Enhancement of polarizabilities of cylinders with cylinder-slab resonances  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

164

Laboratory investigation of lateral dispersion within dense arrays of randomly distributed cylinders at transitional Reynolds number  

E-print Network

Relative (effective) lateral dispersion of a passive solute was examined at transitional Reynolds numbers within a two-dimensional array of randomly distributed circular cylinders of uniform diameter d. The present work ...

Nepf, Heidi

165

A Hybrid Approach To Tandem Cylinder Noise  

NASA Technical Reports Server (NTRS)

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

Lockard, David P.

2004-01-01

166

Silly Cylinders  

NSDL National Science Digital Library

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

Darlene DePalma

2012-07-09

167

Rotating cylinder block piston-cylinder engine  

Microsoft Academic Search

A rotating cylinder block piston-cylinder engine is described comprising: a stator means; a hollow rotor housing rotatably mounted on the stator means for rotation around a rotor housing axis of rotation; a plurality of cylinders radially positioned in the peripheral wall of the hollow rotor housing; a piston slidable in each of the cylinders and having a piston rod rigidly

Newbold

1989-01-01

168

Front tracking and two dimensional Riemann problems: a conference report  

SciTech Connect

A substantial improvement in resolution has been achieved for the computation of jump discontinuities in gas dynamics using the method of front tracking. The essential feature of this method is that a lower dimensional grid is fitted to and follows the discontinuous waves. At the intersection points of these discontinuities, two-dimensional Riemann problems occur. In this paper we study such two-dimensional Riemann problems from both numerical and theoretical points of view. Specifically included is a numerical solution for the Mach reflection, a general classification scheme for two-dimensional elementary waves, and a discussion of problems and conjectures in this area.

Glimm, J.; Klingenberg, C.; McBryan, O.; Plohr, B.; Sharp, D.; Yaniv, S.

1984-01-01

169

Front tracking and two dimensional Riemann problems: A conference report  

NASA Astrophysics Data System (ADS)

A substantial improvement in resolution was achieved for the computation of jump discontinuities in gas dynamics using the method of front tracking. The essential feature of this method is that a lower dimensional grid is fitted to and follows the discontinuous waves. At the intersection points of these discontinuities, two-dimensional Riemann problems occur. Two-dimensional Riemann problems are studied from both numerical and theoretical points of view. Specifically included is a numerical solution for the Mach reflection, a general classification scheme for two-dimensional elementary waves, and a discussion of problems and conjectures in this area.

Glimm, J.; Klingenberg, C.; McBryan, O.; Plohr, B.; Sharp, D.; Yaniv, S.

170

Spin and Valley Noise in Two-Dimensional Dirac Materials  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

171

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

PubMed

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

172

Optical properties of two-dimensional transition metal dichalcogenides  

E-print Network

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

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

2014-01-01

173

Spin-imbalanced quasi-two-dimensional fermi gases.  

PubMed

We measure the density profiles for a Fermi gas of ^{6}Li containing N_{1} spin-up atoms and N_{2} spin-down atoms, confined in a quasi-two-dimensional geometry. The spatial profiles are measured as a function of spin imbalance N_{2}/N_{1} and interaction strength, which is controlled by means of a collisional (Feshbach) resonance. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a true two-dimensional system. We find that the data for normal-fluid mixtures are reasonably well fit by a simple two-dimensional polaron model of the free energy. Not predicted by the model is a phase transition to a spin-balanced central core, which is observed above a critical value of N_{2}/N_{1}. Our observations provide important benchmarks for predictions of the phase structure of quasi-two-dimensional Fermi gases. PMID:25839246

Ong, W; Cheng, Chingyun; Arakelyan, I; Thomas, J E

2015-03-20

174

A two-dimensional Wigner crystal (Review Article)  

NASA Astrophysics Data System (ADS)

The current state of theoretical and experimental studies of the Wigner crystallization of a two-dimensional electron gas is reviewed. The Wigner crystal (WC) has first been observed experimentally in a two-dimensional electron system on the surface of liquid helium in 1979. This success was favored by the exceptional purity of the free surface of superfluid liquid and the ability to fairly accurately describe the polaronic deformation phenomena accompanying the crystallization of electrons. Very pure samples of heterostructures (GaAs/GaAlAs) and strong magnetic fields, making easier the localization of electrons in a conducting layer, were necessary in order to observe the Wigner crystallization in semiconductor two-dimensional electron systems This review discusses the basic properties of a two-dimensional WC, common to the both above-mentioned electronic systems, and also major advances in the study of transport properties of WC caused by response of the environment on motion of the electron lattice.

Monarkha, Yu. P.; Syvokon, V. E.

2012-12-01

175

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

176

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

177

Near-Surface Geophysics: Two-Dimensional Resistivity  

USGS Multimedia Gallery

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

178

Single particle spectrum of the two dimensional electron gas  

E-print Network

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

Dial, Oliver Eugene, III

2007-01-01

179

Information technologies for comprehensive two-dimensional gas chromatography  

E-print Network

there are generally available information technologies that meet requirements for routine applications. This paperReview Information technologies for comprehensive two-dimensional gas chromatography Stephen E GC) presents information technology challenges in data handling, visualization, processing, analysis

Reichenbach, Stephen E.

180

Healing of defects in a two-dimensional granular crystal  

E-print Network

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

Rice, Marie C

2014-01-01

181

Performance Analysis of Metamaterials With Two-dimensional Isotropy  

E-print Network

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

182

CHARACTERISTICS OF TWO-DIMENSIONAL PARTICLE EDDY DIFFUSION INOFFICE SPACE  

EPA Science Inventory

The paper discusses the development of a two-dimensional turbulentkinetic energy - dissipation rate (k-epsilon) turbulence model inthe form of vorticity and stream functions. his turbulence modelprovides the distribution of turbulent kinematic viscosity, used tocalculate the effe...

183

String & Sticky Tape Experiments: Two-Dimensional Collisions Using Pendulums.  

ERIC Educational Resources Information Center

Introduces a method for two-dimensional kinematics measurements by hanging marbles with long strings. Describes experimental procedures for conservation of momentum and obtaining the coefficient of restitution. Provides diagrams and mathematical expressions for the activities. (YP)

Edge, R. D.

1989-01-01

184

Two-Dimensional Sensor Integration Using Resonant Proximity Connector  

E-print Network

to be useful for inputting users' intention to a machine as well as conventional electromyography. Keywords- Two-Dimensional Communication, Networked Sensing, Man-Machine Interface, Electromyography (EMG). I

Shinoda, Hiroyuki

185

The Discontinuous Galerkin Method for Two-dimensional Hyperbolic Problems  

E-print Network

The Discontinuous Galerkin Method for Two-dimensional Hyperbolic Problems Part II: A posteriori mesh refinement for smooth and discontinuous solutions. Keywords: Discontinuous Galerkin method. They also developed the Local Discontinuous Galerkin (LDG) method for convection-diffusion problems [13

Adjerid, Slimane

186

Dynamics of quasi-two-dimensional turbulent jets  

E-print Network

and momentum flux of the flow induced by quasi-two-dimensional jets. 174 7.1 Experimental apparatus to study quasi-two-dimensional particle- laden jets (Q2DPL jets). . . . . . . . . . . . . . . . . . . . . . . . 182 7.2 Regime diagram. Three phenomenological... regimes are observed during the Q2DPL jet experiment. . . . . . . . . . . . . . . . . . 183 7.3 Illustration of the fluidization regime. . . . . . . . . . . . . . . . . 185 7.4 Illustration of the oscillatory flow regime. . . . . . . . . . . . . . . 186 7...

Landel, Julien Rémy Dominique Gérard

2012-11-13

187

Two-dimensional topological insulators in quantizing magnetic fields  

Microsoft Academic Search

Two-dimensional topological insulators are characterized by gapped bulk states and gapless helical edge states, i.e. time-reversal symmetric edge states accommodating a pair of counter-propagating electrons. An external magnetic field breaks the time-reversal symmetry. What happens to the edge states in this case? In this paper we analyze the edge-state spectrum and longitudinal conductance in a two-dimensional topological insulator subject to

G. Tkachov; E. M. Hankiewicz

2011-01-01

188

Two-dimensional thermomechanical analysis of continuous casting process  

Microsoft Academic Search

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

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

2004-01-01

189

Ground ring of two-dimensional string theory  

Microsoft Academic Search

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

Edward Witten

1992-01-01

190

Two-dimensional QCD as a string theory  

Microsoft Academic Search

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

David J. Gross

1993-01-01

191

Natural convection heat transfer from cylinders of arbitrary cross section  

Microsoft Academic Search

Analytical, numerical, and experimental studies of free convection heat transfer from the external surface of isothermal two-dimensional bodies, especially circular cylinders and vertical flat plates, have been conducted by many investigators. A review of the existing literature shows that most workers have focused mainly on experimental data of circular cylinders and vertical plates with air (Pr[approximately]0.71) as working fluid. The

A. V. Hassani

1992-01-01

192

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

PubMed

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

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

1996-03-01

193

An Investigation of Two-Dimensional CAD Generated Models with Body Decoupled Cartesian Grids for DSMC  

SciTech Connect

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

194

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

195

On the application of the Sommerfeld representation in a two-dimensional rotationally invariant anisotropic medium  

NASA Astrophysics Data System (ADS)

Sommerfeld's (1959) bundle-of-rays field representation is applied in a fictitious two-dimensional isotropic space that is mapped into a real rotationally invariant anisotropic region via a polarization-dependent coordinate transformation selected so as to obtain a field solution in the anisotropic region. Two elementary transformations are found, and the resulting representations (in the form of a modal angular spectrum or in terms of nonperiodic anisotropic ray bundles of complex trajectories) are analyzed. Field singularities are encountered and discussed in the context of their relation to the isotropic space rays. As an application, the solution to the canonical scattering problem of an anisotropically coated (ten material parameters, five for each polarization) circular cylinder is presented. Only H polarization is treated explicitly since the other (E) is obtainable via duality.

Monzon, J. Cesar

1990-07-01

196

Numerical simulations of natural convection heat transfer along a vertical cylinder  

Microsoft Academic Search

Purpose – The purpose of this paper is to present a numerical solution for the problem of steady laminar flow and heat transfer characteristics of viscous incompressible fluid. Design\\/methodology\\/approach – For this purpose a two dimensional code has been developed to simulate the natural convection heat transfer along a vertical cylinder, for four different geometries: from vertical cylinder in infinite

Muhammad Rafique; I. Ahmad; M. Abdul Basit; Romana Begum; Wajid Aziz; Muhammad Farooq; Kamran Rasheed Qureshi

2011-01-01

197

Double dipolar halbach array for rheological measurements on magnetic fluids at variable magnetic flux density B  

NASA Astrophysics Data System (ADS)

A new experimental setup for measuring rheological properties of magnetic fluids at variable magnetic flux density B with increased homogeneity is described. The proposed setup is mounted on a commercial strain-controlled ARES rotational rheometer. The magnetic flux is generated via two concentric Halbach cylindrical arrays made from permanent NdFeB magnets. The use of permanent magnets overcomes some of the disadvantages of electromagnets (e.g., excessive heating of the coils, formation of large radial stray fields, cost of electricity, cooling, etc). The performance of the new setup is tested for a magnetorheological fluid in both steady and oscillatory shear regimes.

Barroso, V. C.; Raich, H.; Blümler, P.; Wilhelm, M.

2009-02-01

198

Vortex noise from nonrotating cylinders and airfoils  

NASA Technical Reports Server (NTRS)

An experimental study of vortex-shedding noise was conducted in an acoustic research tunnel over a Reynolds-number range applicable to full-scale helicopter tail-rotor blades. Two-dimensional tapered-chord nonrotating models were tested to simulate the effect of spanwise frequency variation on the vortex-shedding mechanism. Both a tapered circular cylinder and tapered airfoils were investigated. The results were compared with data for constant-diameter cylinder and constant-chord airfoil models also tested during this study. Far-field noise, surface pressure fluctuations, and spanwise correlation lengths were measured for each configuration. Vortex-shedding noise for tapered cylinders and airfoils was found to contain many narrowband-random peaks which occurred within a range of frequencies corresponding to a predictable Strouhal number referenced to the maximum and minimum chord. The noise was observed to depend on surface roughness and Reynolds number.

Schlinker, R. H.; Amiet, R. K.; Fink, M. R.

1976-01-01

199

ORMDIN: a finite element program for two-dimensional nonlinear inverse heat conduction analysis  

SciTech Connect

The calculation of the surface temperature and surface heat flux from measured temperature transients at one or more interior points of a body is identified in the literature as the inverse heat conduction problem. Heretofore, analytical and computational methods of treating this problem have been limited to one-dimensional nonlinear or two-dimensional linear material models. This report presents, to the authors' knowledge, the first inverse solution technique applicable to the two-dimensional nonlinear model with temperature-dependent thermophysical properties. This technique, representing an extension of the one-dimensional formulation previously developed by one of the authors, utilizes a finite element heat conduction model and a generalization of Beck's one-dimensional nonlinear estimation procedure. A digital computer program ORMDIN (Oak Ridge Multi-Dimensional INverse) is developed from the formulation and applied to the cross section of a composite cylinder with temperature-dependent material properties. Results are presented to demonstrate that the inverse formulation is capable of successfully treating experimental data. An important feature of the method is that small time steps are permitted while avoiding severe oscillations or numerical instabilities due to experimental errors in measured data.

Bass, B.R.; Drake, J.B.; Ott, L.J.

1980-12-01

200

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

PubMed

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; Pištora, Jaromír

2012-05-01

201

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

202

Noninteraction of waves in two-dimensional conformal field theory  

E-print Network

In higher dimensional quantum field theory, irreducible representations of the Poincare group are associated with particles. Their counterpart in two-dimensional massless models are "waves" introduced by Buchholz. In this paper we show that waves do not interact in two-dimensional Moebius covariant theories and in- and out-asymptotic fields coincide. We identify the set of the collision states of waves with the subspace generated by the chiral components of the Moebius covariant net from the vacuum. It is also shown that Bisognano-Wichmann property, dilation covariance and asymptotic completeness (with respect to waves) imply Moebius symmetry. Under natural assumptions, we observe that the maps which give asymptotic fields in Poincare covariant theory are conditional expectations between appropriate algebras. We show that a two-dimensional massless theory is asymptotically complete and noninteracting if and only if it is a chiral Moebius covariant theory.

Yoh Tanimoto

2012-08-17

203

Rarefied gas flow through two-dimensional nozzles  

NASA Technical Reports Server (NTRS)

A kinetic theory analysis is made of the flow of a rarefied gas from one reservoir to another through two-dimensional nozzles with arbitrary curvature. The Boltzmann equation simplified by a model collision integral is solved by means of finite-difference approximations with the discrete ordinate method. The physical space is transformed by a general grid generation technique and the velocity space is transformed to a polar coordinate system. A numerical code is developed which can be applied to any two-dimensional passage of complicated geometry for the flow regimes from free-molecular to slip. Numerical values of flow quantities can be calculated for the entire physical space including both inside the nozzle and in the outside plume. Predictions are made for the case of parallel slots and compared with existing literature data. Also, results for the cases of convergent or divergent slots and two-dimensional nozzles with arbitrary curvature at arbitrary knudsen number are presented.

De Witt, Kenneth J.; Jeng, Duen-Ren; Keith, Theo G., Jr.; Chung, Chan-Hong

1989-01-01

204

Complexity and efficient approximability of two dimensional periodically specified problems  

SciTech Connect

The authors consider the two dimensional periodic specifications: a method to specify succinctly objects with highly regular repetitive structure. These specifications arise naturally when processing engineering designs including VLSI designs. These specifications can specify objects whose sizes are exponentially larger than the sizes of the specification themselves. Consequently solving a periodically specified problem by explicitly expanding the instance is prohibitively expensive in terms of computational resources. This leads one to investigate the complexity and efficient approximability of solving graph theoretic and combinatorial problems when instances are specified using two dimensional periodic specifications. They prove the following results: (1) several classical NP-hard optimization problems become NEXPTIME-hard, when instances are specified using two dimensional periodic specifications; (2) in contrast, several of these NEXPTIME-hard problems have polynomial time approximation algorithms with guaranteed worst case performance.

Marathe, M.V. [Los Alamos National Lab., NM (United States); Hunt, H.B. III; Stearns, R.E. [State Univ. of New York, Albany, NY (United States). Dept. of Computer Science

1996-09-01

205

Generation of two-dimensional plasmonic bottle beams.  

PubMed

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. PMID:23609739

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

2013-04-22

206

Bifurcation Phenomena in Two-Dimensional Piecewise Smooth Discontinuous Maps  

E-print Network

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

207

Hamiltonian formalism of two-dimensional Vlasov kinetic equation.  

PubMed

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

Pavlov, Maxim V

2014-12-01

208

Generation of two-dimensional plasmonic bottle beams  

E-print Network

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; Blanchard, Romain; She, Alan; Petit, Marlene; Cluzel, Benoit; Kats, Mikhail A; de Fornel, Frederique; Capasso, Federico

2013-01-01

209

Two-dimensional radiative heat transfer with allowance for shading  

Microsoft Academic Search

Radiative heat transfer with account taken for shading in an infinite cylinder whose contour is made up of arbitrary straight-line segments and which has variable temperature and emissivity on its two sides is examined.

V. F. Kravchenko; V. M. Yudin

1976-01-01

210

Pick's Theorem in Two-Dimensional Subspace of ?(3).  

PubMed

In the Euclidean space ?(3), denote the set of all points with integer coordinate by ?(3). For any two-dimensional simple lattice polygon P, we establish the following analogy version of Pick's Theorem, k(I(P) + (1/2)B(P) - 1), where B(P) is the number of lattice points on the boundary of P in ?(3), I(P) is the number of lattice points in the interior of P in ?(3), and k is a constant only related to the two-dimensional subspace including P. PMID:25802889

Si, Lin

2015-01-01

211

Pick's Theorem in Two-Dimensional Subspace of ?3  

PubMed Central

In the Euclidean space ?3, denote the set of all points with integer coordinate by ?3. For any two-dimensional simple lattice polygon P, we establish the following analogy version of Pick's Theorem, k(I(P) + (1/2)B(P) ? 1), where B(P) is the number of lattice points on the boundary of P in ?3, I(P) is the number of lattice points in the interior of P in ?3, and k is a constant only related to the two-dimensional subspace including P. PMID:25802889

2015-01-01

212

Quantum Walks on Two Kinds of Two-Dimensional Models  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

213

TreePM Method for Two-Dimensional Cosmological Simulations  

E-print Network

We describe the two-dimensional TreePM method in this paper. The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid code combines the 2d Barnes and Hut Tree method and the 2d Particle-Mesh method. We describe the splitting of force between the PM and the Tree parts. We also estimate error in force for a realistic configuration. Finally, we discuss some tests of the code.

Suryadeep Ray

2004-06-01

214

Quantum walks on two kinds of two-dimensional models  

E-print Network

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

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

2015-01-08

215

Quasi-two-dimensional acoustic metamaterial with negative bulk modulus  

NASA Astrophysics Data System (ADS)

We present the experimental realization and characterization of an acoustic metamaterial with negative bulk modulus. The metamaterial consists of a two-dimensional array of cylindrical cavities, and the bulk modulus is controlled by their radius size and length. Experiments are performed in a two-dimensional waveguide where a slab of seven layers is used to extract the parameters of the metamaterial. A complete characterization of the constructed structure is reported, including the dispersion relation of the acoustic bands and the skin depth effect, which both have been measured, and the data are well supported by semianalytical models and by finite-element simulations.

García-Chocano, V. M.; Graciá-Salgado, R.; Torrent, D.; Cervera, F.; Sánchez-Dehesa, J.

2012-05-01

216

Persistence Problem in Two-Dimensional Fluid Turbulence  

NASA Astrophysics Data System (ADS)

We present a natural framework for studying the persistence problem in two-dimensional fluid turbulence by using the Okubo-Weiss parameter ? to distinguish between vortical and extensional regions. We then use a direct numerical simulation of the two-dimensional, incompressible Navier-Stokes equation with Ekman friction to study probability distribution functions (PDFs) of the persistence times of vortical and extensional regions by employing both Eulerian and Lagrangian measurements. We find that, in the Eulerian case, the persistence-time PDFs have exponential tails; by contrast, this PDF for Lagrangian particles, in vortical regions, has a power-law tail with an exponent ?=2.9±0.2.

Perlekar, Prasad; Ray, Samriddhi Sankar; Mitra, Dhrubaditya; Pandit, Rahul

2011-02-01

217

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

NASA Technical Reports Server (NTRS)

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

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

1947-01-01

218

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

NASA Technical Reports Server (NTRS)

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

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

1947-01-01

219

Calculation of flow about two-dimensional bodies by means of the velocity-vorticity formulation on a staggered grid  

NASA Technical Reports Server (NTRS)

A method for calculating the incompressible viscous flow about two-dimensional bodies, utilizing the velocity-vorticity form of the Navier-Stokes equations using a staggered-grid formulation is presented. The solution is obtained by employing an alternative-direction implicit method for the solution of the block tridiagonal matrix resulting from the finite-difference representation of the governing equations. The boundary vorticity and the conservation of mass are calculated implicitly as a part of the solution. The mass conservation is calculated to machine zero for the duration of the computation. Calculations for the flow about a circular cylinder, a 2-pct thick flat plate at 90-deg incidence, an elliptic cylinder at 45-deg incidence, and a NACA 0012, with and without a deflected flap, at - 90-deg incidence are performed and compared with the results of other numerical investigations.

Stremel, Paul M.

1991-01-01

220

Analysis of the magnetic field and force of LSM with permanent magnet Halbach array and ironless coil  

Microsoft Academic Search

The LSM, or linear synchronous motor, with permanent magnet Halbach array and ironless coil possesses the dominant advantages of direct linear movement and being energy-saving. To analytically investigate the characteristics of this innovative LSM, its magnetic field and magnetic force are analyzed in this work. Based on the magnetic field of a single surface current, the field of a single

Xiao Zhang; Yungang Li; Hengkun Liu

2011-01-01

221

Infinite conformal symmetry in two-dimensional quantum field theory  

Microsoft Academic Search

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

222

Two dimensional measurements of electrical fields in transformer oil  

Microsoft Academic Search

It is demonstrated that the electro-optical Kerr effect with field modulation can be used for angularly resolved field mapping of two-dimensional objects in transformer oils. This technique can determine the amplitude as well as the direction of the electric field in liquid insulation systems relevant for converter transformers. As an example, the technique was applied to two overlapping Macrolon barriers

U. Gafvert

1990-01-01

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 liquid crystal devices and their computer simulations  

Microsoft Academic Search

The main focus of the dissertation is design and optimization two dimensional liquid crystal devices, which means the liquid crystal director configurations vary in two dimensions. Several optimized and designed devices are discussed in the dissertation. They include long-term bistable twisted nematic liquid crystal display (BTN LCD), which is very low power consumption LCD and suitable for E-book application; wavelength

Bin Wang

2002-01-01

225

Stably Extending Two-Dimensional Bipedal Walking to Three Dimensions  

E-print Network

dynamically sta- ble bipedal walking were concerned with passive two- dimensional (2D) bipeds walking down the use of hybrid zero dynamics. I. INTRODUCTION The central goal of research in bipedal robotic walking been shown that for certain shallow slopes, these passive bipeds have stable walking gaits

Ames, Aaron

226

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

E-print Network

, they are extremely inefficient, resulting in short runtimes. The passive dynamic approach, on the other hand, models practical use. An approach in between these extremes seeks to apply passive dynamic principles two dimensional, knee-less, bipedal walking robot. After removing one of several unsuccessful control

Ruina, Andy L.

227

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

Microsoft Academic Search

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

D. Montgomery

1972-01-01

228

Two-Dimensional Vortex Dynamics With Background Vorticity  

E-print Network

vorticity. Experiments have shown that background vorticity can calm chaotic vortex motion, and cool. To appreciate the influence of background vorticity on the vortex motion, let us first consider the vortexTwo-Dimensional Vortex Dynamics With Background Vorticity David A. Schecter Advanced Study Program

Schecter, David

229

Two-dimensional vortex motion and 'negative temperatures.'  

NASA Technical Reports Server (NTRS)

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

Montgomery, D.

1972-01-01

230

Quantum Magnetoconductance of a Nondegenerate Two-Dimensional Electron Gas  

Microsoft Academic Search

Magnetoconductance measurements are reported for the low-density, two-dimensional classical electron gas formed on the surface of liquid helium. At strong magnetic fields, large deviations from the classical parabolic behaviour are observed. These deviations are described with a quantum-transport theory of scattering within broadened Landau levels.

R. W. van der Heijden; J. H. G. Surewaard; H. M. Gijsman; F. M. Peeters

1988-01-01

231

Magnetoconductivity of disordered two dimensional tight binding electrons in CPA  

Microsoft Academic Search

The magnetotransport properties of a tight binding model of electrons on a two dimensional square lattice with diagonal disorder and in a perpendicular magnetic field is investigated. The disorder is treated in the coherent potential approximation (CPA) and a quasiclassical solution of the Harper equation is used to calculate the one particle Green's function. Analytical expressions for the CPA vertex

P. Kleinert; V. V. Bryksin; H. Schlegel

1993-01-01

232

Conformal Field Theory Properties of Two-Dimensional Percolation  

E-print Network

Conformal Field Theory Properties of Two-Dimensional Percolation Michael Flohr and Annekathrin M in two dimensions has interesting features in conformal field theory such as the conformal invari- ance Network HPRN-CT-2002-00325 (EUCLID) anne@th.physik.uni-bonn.de 1 #12;conformal field theory which matches

Flohr, Michael

233

Two-dimensional readout in a liquid xenon ionisation chamber  

Microsoft Academic Search

A two-dimensional readout with metal strips deposited on both sides of a glass plate is investigated aiming to assess the possibility of its use in a liquid xenon ionisation chamber for positron emission tomography. Here, we present results obtained with an ?-source. It is shown that position resolution of ?1mm, fwhm, can be achieved for free charge depositions equivalent to

V. Solovov; V. Chepel; A. Pereira; M. I. Lopes; R. Ferreira Marques; A. J. P. L. Policarpo

2002-01-01

234

Two-dimensional ultrasonic computed tomography of growing bones.  

E-print Network

Two-dimensional ultrasonic computed tomography of growing bones. P. Lasaygues, E. Franceschini, R--This study deals with the 2-D ultrasonic qualitative and quantitative imaging of child bone. The inverse: Ultrasonic Computed Tomography, Bone imaging, Born approximation, iterative distorted method I. INTRODUCTION

Paris-Sud XI, Université de

235

FLOW AND DISPERSION OF POLLUTANTS WITHIN TWO-DIMENSIONAL VALLEYS  

EPA Science Inventory

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

236

Star discrepancy of generalized two-dimensional Hammersley point sets  

E-print Network

generalize to arbitrary bases recent results on the star discrepancy of digi- tally shifted two-dimensional Hammersley point sets in base 2 by Kritzer, Larcher and Pillichshammer. The key idea is to link our) states the link between one-dimensional sequences and two-dimentional point sets deduced from them [6, 20

Provence Aix-Marseille I, Université de

237

Numerical simulation of two?dimensional tsunami runup  

Microsoft Academic Search

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

Z. Kowalik; T. S. Murty

1993-01-01

238

condmat/9801215 Crossovers in the Two Dimensional Ising Spin Glass  

E-print Network

cond­mat/9801215 v2 26 Jan 1998 Crossovers in the Two Dimensional Ising Spin Glass of extensive computer simulations we analyze in detail the two dimen­ sional \\SigmaJ Ising spin glass with ferromagnetic next­nearest­neighbor interactions. We found a crossover from ferromagnetic to ``spin glass'' like

Roma "La Sapienza", Università di

239

Two-dimensional optimization of free-electron-laser designs  

DOEpatents

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

240

Two-dimensional optimization of free electron laser designs  

DOEpatents

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

241

Sound waves in two-dimensional ducts with sinusoidal walls  

NASA Technical Reports Server (NTRS)

The method of multiple scales is used to analyze the wave propagation in two-dimensional hard-walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.

Nayfeh, A. H.

1974-01-01

242

TWO-DIMENSIONAL ARRAY OF RECTANGULAR SLOT ANTENNAS  

E-print Network

and analysis for this class of antennas are performed using the Momentum software package of Advanced Design and a smaller size. In addition, a 2D array of this antenna is designed and presented. The numerical simulationTWO-DIMENSIONAL ARRAY OF RECTANGULAR SLOT ANTENNAS TUNED WITH PATCH STUBS FOR WIDE BANDWIDTH

Elsherbeni, Atef Z.

243

Research article Real-time two-dimensional asynchronous  

E-print Network

Research article Real-time two-dimensional asynchronous control of a computer cursor with a single the feasibility of controlling a computer cursor asynchronously in two dimensions using one subdural electrode stimulation of the primary motor cortex (MI). Interventions: Power changes in the electrocorticography signals

Popovic, Milos R.

244

Tachyon Hair for Two-Dimensional Black Holes  

E-print Network

Using a combination of analytical and numerical methods, we obtain a two-dimensional spacetime describing a black hole with tachyon hair. The physical ADM mass of the black hole is finite. The presence of tachyon hair increases the Hawking temperature.

Alan Kostelecky; Malcolm Perry

1993-11-01

245

Discrete denoising of heterogenous two-dimensional data  

E-print Network

We consider discrete denoising of two-dimensional data with characteristics that may be varying abruptly between regions. Using a quadtree decomposition technique and space-filling curves, we extend the recently developed S-DUDE (Shifting Discrete Universal DEnoiser), which was tailored to one-dimensional data, to the two-dimensional case. Our scheme competes with a genie that has access, in addition to the noisy data, also to the underlying noiseless data, and can employ $m$ different two-dimensional sliding window denoisers along $m$ distinct regions obtained by a quadtree decomposition with $m$ leaves, in a way that minimizes the overall loss. We show that, regardless of what the underlying noiseless data may be, the two-dimensional S-DUDE performs essentially as well as this genie, provided that the number of distinct regions satisfies $m=o(n)$, where $n$ is the total size of the data. The resulting algorithm complexity is still linear in both $n$ and $m$, as in the one-dimensional case. Our experimental ...

Moon, Taesup; Kim, Jae-Young

2010-01-01

246

Chaotic dynamics for two-dimensional tent maps  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

247

Two dimensional packing: the power of rotation Leah Epstein y  

E-print Network

-dimensional packing problem of packing rectangles into unit squares. However our problem is slightly di#11;er- ent are unit squares. The items are rectangles of sides bounded by 1. The items arrive one by one, each in the study of two-dimensional packing problems. In such problems the input items are rectangles which need

Epstein, Leah

248

Exploring Brain Connectivity with Two-Dimensional Neural Maps  

E-print Network

meaningful and familiar coordinates. DWI enables neural pathways in the in vivo brain to be estimatedExploring Brain Connectivity with Two-Dimensional Neural Maps Radu Jianu, Member, IEEE, C¸ agatay for exploring connectivity in the brain. For this, we create standard streamtube models from diffusion

Pratt, Vaughan

249

Two-dimensional black holes in accelerated frames: quantum aspects  

E-print Network

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

R. Balbinot; A. Fabbri

1996-07-04

250

Stationary Axisymmetric Fields as Two-Dimensional Geodesics  

E-print Network

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

D. Nunez; H. Quevedo

1993-10-08

251

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

252

Self Organization of Two-dimensional Insect Neural Networks  

E-print Network

Self Organization of Two-dimensional Insect Neural Networks Amir Ayalia , Orit Shefia> and Eshel and neural networks in particular have crossed traditional fields and disciplines of science, from computer science through physics to biology (for recent review, see [17] and references within). The neural network

Jacob, Eshel Ben

253

Two-dimensional mathematical model of evacuated tube solar collector  

Microsoft Academic Search

Analysis of an evacuated tubular solar collector is presented by developing a two-dimensional performance model. The collector uses a thin flat plate spanning its diameter as its absorbing surface. Energy balances are made on collector plate and tube, each considered as a separate unit. It has been found that a zero capacitance model is quite adequate when hourly meteorological data

F. Rahman; S. Al-Zakri; M. A. A. Rahman

1984-01-01

254

Hexagonal structures for two-dimensional photonic crystals  

Microsoft Academic Search

Periodic dielectric structures have been recently proposed to inhibit spontaneous emission in semiconductors. From this suggestion, the new concepts of photonic band gap and photonic crystal have been developed. Zero-threshold lasers, waveguides, antenna substrates, filters and polarizers are promising applications. We propose a new class of two-dimensional periodic dielectric structures with hexagonal symmetry. We study the gap opening according to

D. Cassagne; C. Jouanin; D. Bertho

1996-01-01

255

TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH  

E-print Network

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

Stockie, John

256

Physical States in Two-Dimensional Topological Gauge Theories  

E-print Network

Physical states of two-dimensional topological gauge theories are studied using the BRST formalism in the light-cone gauge. All physical states are obtained for the abelian theory. There are an infinite number of physical states with different ghost numbers. Simple examples of physical states in a non-abelian theory are also given.

Yoshiaki Tanii; Masakazu Yamashita

1993-01-09

257

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

258

Two-dimensional interaction of ion-acoustic solitons  

Microsoft Academic Search

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

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

1980-01-01

259

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals  

Microsoft Academic Search

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals (MPCs) have been studied by electromagnetic simulation and experiments in microwave frequencies. MPCs with square and hexagonal lattices are made of ferrites, and their transmission coefficients are measured in the X waveband with an applied static magnetic field. For the lattices, a stop-band and a band shift with the applied static magnetic

Jie Xu; Rui-xin Wu; Ping Chen; Yue Shi

2007-01-01

260

Sensor Networking Using Two-Dimensional Electromagnetic Wave Yasutoshi Makino*  

E-print Network

Communication (TDC)." TDC is communication in which electromagnetic wave propagates within a two dimensional medium and communication is realized be- tween the nodes which are connected to the TDC sheet. In TDC, a large number of communication nodes can connect with each other with no individual wires, while TDC has

Shinoda, Hiroyuki

261

Proximity Connector for Two-Dimensional Electromagnetic Wave Communication  

E-print Network

proposed a new physical layer of communication named "Two-Dimensional Communication (TDC)." TDC and power transmission connector that works anywhere on the TDC sheet without presice positioning. Moreover, it works as a proximity connector requiring no electrical contacts to the TDC sheet. If the surfaces

Shinoda, Hiroyuki

262

Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases  

NASA Astrophysics Data System (ADS)

We measure the density profiles for a Fermi gas of Li 6 containing N1 spin-up atoms and N2 spin-down atoms, confined in a quasi-two-dimensional geometry. The spatial profiles are measured as a function of spin imbalance N2/N1 and interaction strength, which is controlled by means of a collisional (Feshbach) resonance. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a true two-dimensional system. We find that the data for normal-fluid mixtures are reasonably well fit by a simple two-dimensional polaron model of the free energy. Not predicted by the model is a phase transition to a spin-balanced central core, which is observed above a critical value of N2/N1. Our observations provide important benchmarks for predictions of the phase structure of quasi-two-dimensional Fermi gases.

Ong, W.; Cheng, Chingyun; Arakelyan, I.; Thomas, J. E.

2015-03-01

263

Duality transformation for two-dimensional static problems  

Microsoft Academic Search

A form of duality transformation, applicable to two-dimensional static problems, is formulated. It transforms electrostatic problems into magnetostatic problems by applying, instead of the common duality between the E and H vectors, one between the vectors E and B. The transformation can be easily applied to straight TEM transmission-line geometries. Its use in teaching basic electromagnetics to electrical engineering students

Ismo Lindell

1995-01-01

264

An efficient architecture for two-dimensional discrete wavelet transform  

Microsoft Academic Search

This paper proposes an efficient architecture for the two-dimensional discrete wavelet transform (2-D DWT). The proposed architecture includes a transform module, a RAM module, and a multiplexer. In the transform module, we employ the polyphase decomposition technique and the coefficient folding technique to the decimation filters of stages 1 and 2, respectively. In comparison with other 2-D DWT architectures, the

Po-cheng Wu; Liang-gee Chen

2001-01-01

265

Dynamical properties of two-dimensional Kerr cavity solitons  

NASA Astrophysics Data System (ADS)

We present the results of our study of the dynamics of two-dimensional Kerr cavity solitons. The solitons are absolutely stable over a substantial parameter domain. We analyze their dynamics beyond the instability boundary, finding regions of stable oscillation and of fivefold or sixfold azimuthal instability. The Hopf oscillation is surprisingly robust, owing to the influence of a lower-amplitude unstable soliton.

Firth, William J.; Harkness, Graeme K.; Lord, Angus; McSloy, John M.; Gomila, Damià; Colet, Pere

2002-04-01

266

Quantum emission from two-dimensional black holes  

Microsoft Academic Search

We investigate Hawking radiation from two-dimensional dilatonic black holes using standard quantization techniques. In the background of a collapsing black-hole solution the Bogoliubov coefficients can be exactly determined. In the regime after the black hole has settled down to an equilibrium'' state but before the back reaction becomes important these give the known result of a thermal distribution of Hawking

Steven B. Giddings; William M. Nelson

1992-01-01

267

Quantum emission from two-dimensional black holes  

Microsoft Academic Search

We investigate Hawking radiation from two-dimensional dilatonic black holes using standard quantization techniques. In the background of a collapsing black-hole solution the Bogoliubov coefficients can be exactly determined. In the regime after the black hole has settled down to an ``equilibrium'' state but before the back reaction becomes important these give the known result of a thermal distribution of Hawking

Steven B. Giddings; William M. Nelson

1992-01-01

268

Investigating Coherent Structures of Quasi Two-Dimensional Flows Subject  

E-print Network

edges of the tank. An upward axial magnetic field created by permanent magnets or electromagnets. #12;L electrodes separated by 2 cm Bar magnets Permanent magnets inserted from below: Made of Neodymium. DimensionsInvestigating Coherent Structures of Quasi Two-Dimensional Flows Subject to Electromagnetic Forces

Shihadeh, Alan

269

Ventricular septal defects. Two dimensional echocardiographic and morphological correlations  

Microsoft Academic Search

To evaluate the ability of two dimensional echocardiography to identify and classify ventricular septal defects, 280 infants and children with clinically significant ventricular septal defects were studied. Multiple precordial and subcostal echocardiographic planes were scanned in each patient in an attempt to identify the defects. Defects visualised were classified on the basis of the structures which formed their margins. Subsequent

G R Sutherland; M J Godman; J F Smallhorn; P Guiterras; R H Anderson; S Hunter

1982-01-01

270

Integral invariants of two-dimensional rotational gas flows  

Microsoft Academic Search

for which Euler's equation coincides with Crocco's equation, which describes the two-dimensional rotational flow of a gas. In this paper we shall apply group theoretical methods to the study of this functional and find a group of transformations which leave tt~s functional invariant. Before we proceed to analyze the functional, we note the following property. It is known that the

K. P. Surovikhin

1965-01-01

271

Original article Two-dimensional gel electrophoresis of membrane  

E-print Network

Original article Two-dimensional gel electrophoresis of membrane proteins from ectomycorrhizal-dimensional polyacrylamide gels. Gels with limited back- ground staining and streaking and with clearly efficacité et leur compatibilité avec l'obtention de gels d'électro- phorèse bidimensionnelle. Une fraction

Paris-Sud XI, Université de

272

Anomalous Hall effect in a two-dimensional electron gas  

E-print Network

Anomalous Hall effect in a two-dimensional electron gas Tamara S. Nunner,1 N. A. Sinitsyn,2,3 Mario F. Borunda,2 V. K. Dugaev,4 A. A. Kovalev,2 Ar. Abanov,2 Carsten Timm,5 T. Jungwirth,6,7 Jun-ichiro Inoue,8 A. H. MacDonald,9 and Jairo Sinova2...

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

2007-01-01

273

Two-Dimensional Diverging Shocks in a Nonuniform Medium  

SciTech Connect

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

Roy A. Axford

1998-08-01

274

Manipulation of Dopants in a Two Dimensional Matrix  

Microsoft Academic Search

The layered dichalcogenides can be used as a matrix for incorporating and manipulating dopants in dimensionally constrained manner. The crystal structure of the dichalcogenides is formed of two-dimensional strongly bound layers separated by a van der Waals gap. Dopants can be incorporated between the layers as intercalants through a variety of methods to form a semi-ordered phase. These intercalants have

Timothy Kidd; Laura Strauss; Polina Skirtachenko; Dustin Klein

2009-01-01

275

Specific heat of two-dimensional diluted magnets  

NASA Astrophysics Data System (ADS)

Using Monte Carlo techniques, the two-dimensional site-diluted Ising model is studied. In particular, properties of the specific heat, its critical behaviour and the emergence of a non-singular maximum above the transition temperature at moderate concentration of defects, are discussed.

Selke, W.; Shchur, L. N.; Vasilyev, O. A.

276

Least-squares two-dimensional phase unwrapping using FFT's  

Microsoft Academic Search

A solution of the least-squares two-dimensional phase-unwrapping problem is presented that is simpler to understand and implement than previously published solutions. It extends the phase function to a periodic function using a mirror reflection, and the resulting equation is solved using the Fourier transform

Mark D. Pritt; Jerome S. Shipman

1994-01-01

277

Two-DIMENSIONAL WATER FLOOD AND MUDFLOW SIMULATION  

E-print Network

of flow conditions, including flow through subdivisions, street flow, and culvert or flood channelTwo-DIMENSIONAL WATER FLOOD AND MUDFLOW SIMULATION By J. S. O'Brien, 1 P. Y. Julien, 2 and W. T-water floodhazards, mudflows,and debris flowson alluvialfans and urban floodplains. Interactive flood

Julien, Pierre Y.

278

Quick release engine cylinder  

DOEpatents

A quick release engine cylinder allows optical access to an essentially unaltered combustion chamber, is suitable for use with actual combustion processes, and is amenable to rapid and repeated disassembly and cleaning. A cylinder member, adapted to constrain a piston to a defined path through the cylinder member, sealingly engages a cylinder head to provide a production-like combustion chamber. A support member mounts with the cylinder member. The support-to-cylinder mounting allows two relationships therebetween. In the first mounting relationship, the support engages the cylinder member and restrains the cylinder against the head. In the second mounting relationship, the cylinder member can pass through the support member, moving away from the head and providing access to the piston-top and head.

Sunnarborg, Duane A. (1123 Lucille St., Livermore, Alameda County, CA 94550)

2000-01-01

279

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

280

Molecular structure by two-dimensional NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Two examples are presented of the use of two-dimensional NMR spectroscopy to solve molecular structure problems. The first is called correlation spectroscopy (COSY) and it allows us to disentangle a complex network of spin-spin couplings. By dispersing the NMR information in two frequency dimensions, it facilitates the analysis of very complex spectra of organic and biochemical molecules, normally too crowded to be tractable. The second application exploits the special properties of multiple-quantum coherence to explore the molecular framework one C?C linkage at a time. The natural product panamine is used as a test example; with some supplementary evidence, the structure of this six-ringed heterocyclic molecule is elucidated from the double-quantum filtered two-dimensional spectrum.

Freeman, R.

281

Two-dimensional topological insulators in quantizing magnetic fields  

NASA Astrophysics Data System (ADS)

Two-dimensional topological insulators are characterized by gapped bulk states and gapless helical edge states, i.e. time-reversal symmetric edge states accommodating a pair of counter-propagating electrons. An external magnetic field breaks the time-reversal symmetry. What happens to the edge states in this case? In this paper we analyze the edge-state spectrum and longitudinal conductance in a two-dimensional topological insulator subject to a quantizing magnetic field. We show that the helical edge states exist also in this case. The strong magnetic field modifies the group velocities of the counter-propagating channels which are no longer identical. The helical edge states with different group velocities are particularly prone to get coupled via backscattering, which leads to the suppression of the longitudinal edge magnetoconductance.

Tkachov, G.; Hankiewicz, E. M.

2012-02-01

282

Preliminary results on two-dimensional interferometry of HL Tau  

NASA Technical Reports Server (NTRS)

Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime.

Tollestrup, Eric V.; Harvey, Paul M.

1989-01-01

283

Disordered quantum walks in two-dimensional lattices plink  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

284

Transport behavior of water molecules through two-dimensional nanopores.  

PubMed

Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ?15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules. PMID:25399193

Zhu, Chongqin; Li, Hui; Meng, Sheng

2014-11-14

285

Adaptive rezoner in a two-dimensional Lagrangian hydrodynamic code  

SciTech Connect

In an effort to increase spatial resolution without adding additional meshes, an adaptive mesh was incorporated into a two-dimensional Lagrangian hydrodynamics code along with two-dimensional flux corrected (FCT) remapper. The adaptive mesh automatically generates a mesh based on smoothness and orthogonality, and at the same time also tracks physical conditions of interest by focusing mesh points in regions that exhibit those conditions; this is done by defining a weighting function associated with the physical conditions to be tracked. The FCT remapper calculates the net transportive fluxes based on a weighted average of two fluxes computed by a low-order scheme and a high-order scheme. This averaging procedure produces solutions which are conservative and nondiffusive, and maintains positivity. 10 refs., 12 figs.

Pyun, J.J.; Saltzman, J.S.; Scannapieco, A.J.; Carroll, D.

1985-01-01

286

Two-dimensional Raman-terahertz spectroscopy of water  

PubMed Central

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

Savolainen, Janne; Ahmed, Saima; Hamm, Peter

2013-01-01

287

Two-dimensional Pauli operator in a magnetic field  

NASA Astrophysics Data System (ADS)

The two-dimensional purely magnetic Schrödinger operator for the nonrelativistic particle with a spin of ½ in a magnetic field has some remarkable properties, that were discovered in the late 70s: its strongly degenerate in the ground state and it admits supersymmetry. In the present work we investigate the special case where the magnetic flux of the periodic field through the elementary cell equals zero. This case has not been covered in the previous publications. An interesting connection with the theory of solitons, in particular with Burgers-like systems and their two-dimensional analogues, is revealed. Their linearizability properties are simpler than some famous systems, such as KdV and KP. Members of the Aharonov-Bohm-type system with quantized magnetic flux play a special role in the investigation of this case.

Grinevich, P. G.; Mironov, A. E.; Novikov, S. P.

2011-10-01

288

Robust L1-norm two-dimensional linear discriminant analysis.  

PubMed

In this paper, we propose an L1-norm two-dimensional linear discriminant analysis (L1-2DLDA) with robust performance. Different from the conventional two-dimensional linear discriminant analysis with L2-norm (L2-2DLDA), where the optimization problem is transferred to a generalized eigenvalue problem, the optimization problem in our L1-2DLDA is solved by a simple justifiable iterative technique, and its convergence is guaranteed. Compared with L2-2DLDA, our L1-2DLDA is more robust to outliers and noises since the L1-norm is used. This is supported by our preliminary experiments on toy example and face datasets, which show the improvement of our L1-2DLDA over L2-2DLDA. PMID:25721558

Li, Chun-Na; Shao, Yuan-Hai; Deng, Nai-Yang

2015-05-01

289

Polaronic aspects of the two-dimensional ferromagnetic Kondo model  

NASA Astrophysics Data System (ADS)

The two-dimensional ferromagnetic Kondo model with classical core spins is studied via unbiased Monte Carlo simulations for a hole doping up to x = 12.5%. A canonical algorithm for finite temperatures is developed. We show that, with realistic parameters for the manganites and at low temperatures, the double-exchange mechanism does not lead to phase separation on a two-dimensional lattice but rather stabilizes individual ferromagnetic polarons for this doping range. A detailed analysis of unbiased Monte Carlo results reveals that the polarons can be treated as independent particles for these hole concentrations. It is found that a simple polaron model describes the physics of the ferromagnetic Kondo model amazingly well. The ferromagnetic polaron picture provides an obvious explanation for the pseudogap in the one-particle spectral function Ak(ohgr) observed in the ferromagnetic Kondo model.

Daghofer, M.; Koller, W.; Evertz, H. G.; von der Linden, W.

2004-08-01

290

Revisiting freely decaying two-dimensional turbulence at millennial resolution  

NASA Astrophysics Data System (ADS)

We study the evolution of vortex statistics in freely decaying two-dimensional turbulence at very large Reynolds number. The results obtained here confirm that the peak vorticity inside vortex cores is conserved and that the number of vortices as a function of time, N(t), decreases as a power law. In addition, the numerical findings are consistent with the predictions of the scaling theories proposed by Carnevale et al. [Phys. Rev. Lett. 66, 2735 (1991)] and Weiss and McWilliams [Phys. Fluids A 5, 608 (1993)]. We also obtain new evidence for a self-similar distribution of vortex radii and circulations, that suggests the possibility of a generic statistical behavior of the decaying phase of two-dimensional turbulence at high Reynolds number.

Bracco, A.; McWilliams, J. C.; Murante, G.; Provenzale, A.; Weiss, J. B.

2000-11-01

291

Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas  

SciTech Connect

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

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

2001-07-05

292

Tunable refraction in a two dimensional quantum metamaterial  

E-print Network

In this paper we consider a two-dimensional metamaterial comprising an array of qubits (two level quantum objects). Here we show that a two-dimensional quantum metamaterial may be controlled, e.g. via the application of a magnetic flux, so as to provide controllable refraction of an input signal. Our results are consistent with a material that could be quantum birefringent (beam splitter) or not dependent on the application of this control parameter. We note that quantum metamaterials as proposed here may be fabricated from a variety of current candidate technologies from superconducting qubits to quantum dots. Thus the ideas proposed in this work would be readily testable in existing state of the art laboratories.

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

2012-08-22

293

Transport behavior of water molecules through two-dimensional nanopores  

SciTech Connect

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

Zhu, Chongqin; Li, Hui; Meng, Sheng, E-mail: smeng@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2014-11-14

294

Automatic measurement method of two-dimensional complex geometric features  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

295

Two-dimensional time dependent Riemann solvers for neutron transport  

SciTech Connect

A two-dimensional Riemann solver is developed for the spherical harmonics approximation to the time dependent neutron transport equation. The eigenstructure of the resulting equations is explored, giving insight into both the spherical harmonics approximation and the Riemann solver. The classic Roe-type Riemann solver used here was developed for one-dimensional problems, but can be used in multidimensional problems by treating each face of a two-dimensional computation cell in a locally one-dimensional way. Several test problems are used to explore the capabilities of both the Riemann solver and the spherical harmonics approximation. The numerical solution for a simple line source problem is compared to the analytic solution to both the P{sub 1} equation and the full transport solution. A lattice problem is used to test the method on a more challenging problem.

Brunner, Thomas A. [Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1186 (United States)]. E-mail: tabrunn@sandia.gov; Holloway, James Paul [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2014 (United States)

2005-11-20

296

Talbot image of two-dimensional fractal grating  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

297

Multiple Potts models coupled to two-dimensional quantum gravity  

NASA Astrophysics Data System (ADS)

We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.

Baillie, C. F.; Johnston, D. A.

1992-07-01

298

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

299

Two-Dimensional Proportional Chamber Readout Using Digital Techniques  

Microsoft Academic Search

Two systems of two-dimensional proportional chamber readout are presented, using digital hardware techniques. Centre-of-cluster readout is simple, cheap and very fast: 100 nsec dead-time. Centre-of-gravity readout is slower, with a dead-time of 1 ¿sec, but capable of considerable electronic spatial resolution: 10 ¿m FWHM from 3 mm spaced channels. With this resolution the asymmetry of avalanche formation on anode wires

A. P. Jeavons; N. Ford; B. Lindberg; C. Parkman; Z. Hajduk

1976-01-01

300

Two-dimensional black hole and singularities of CY manifolds  

Microsoft Academic Search

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

Hirosi Ooguri; Cumrun Vafa

1996-01-01

301

A Calculation Procedure for Two-Dimensional Elliptic Situations  

Microsoft Academic Search

A calculation method based on the control-volume approach has been developed for solving two-dimensional elliptic problems involving fluid flow and heat and mass transfer. The main features of the method include a power-law formulation for the combined convection-diffusion influence, an equation-solving scheme that consists of a block-correction method coupled with a line-by-line procedure, and a new algorithm for handling the

Suhas Patankar

1981-01-01

302

Modeling and Simulating for Two Dimensional Infrared Photonic Crystal Devices  

Microsoft Academic Search

In order to design infrared devices efficiently, dispersive properties of two dimensional photonic crystal is studied in this paper. A model of eigenfrequencies is created by combining the variational expression with the conformal finite-difference time-domain (C-FDTD) technique. Useful data obtained by presentation can be applied to the analysis of the dispersion curves and design of the near-infrared waveguides.

Hong-Xing Zheng; Dao-Yin Yu

2004-01-01

303

Two-dimensional process simulation using verified phenomenological models  

Microsoft Academic Search

Two-dimensional (2-D) effects are becoming increasingly important in the diffusion of impurities in submicrometer silicon devices. The authors describe a 2-D process simulator, PREDICT2, that handles implant damage effects, annealing, and lateral diffusion. PREDICT2 simulates the diffusion of impurities in silicon by using phenomenological diffusion coefficients. The phenomenological models are verified by comparing simulated and experimental results. This approach is

Richard B. Fair; Carl L. Gardner; Michael J. Johnson; Stephen W. Kenkel; Donald J. Rose; John E. Rose; Ravi Subrahmanyan

1991-01-01

304

Suspended two-dimensional electron and hole gases  

SciTech Connect

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

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

2013-12-04

305

Two-dimensional gravitation and Sine-Gordon-Solitons  

E-print Network

Some aspects of two-dimensional gravity coupled to matter fields, especially to the Sine-Gordon-model are examined. General properties and boundary conditions of possible soliton-solutions are considered. Analytic soliton-solutions are discovered and the structure of the induced space-time geometry is discussed. These solutions have interesting features and may serve as a starting point for further investigations.

Bernd Stoetzel

1995-07-07

306

Dilute bose gas in a quasi-two dimensional trap  

Microsoft Academic Search

We investigate the behavior of a dilute quasi two-dimensional, harmonically confined, weakly interacting Bose gas within the finite-temperature Thomas-Fermi approximation. We find that the thermodynamic properties of the system are markedly different for repulsive and attractive interactions. Specifically, in contrast to the repulsive case, there appears to be a phase transition when the atoms interact with an attractive pseudo-potential, in

Brandon Peter van Zyl; Rajat Kumar Bhaduri; Justin Sigetich

2002-01-01

307

Dilute Bose gas in a quasi-two-dimensional trap  

Microsoft Academic Search

We investigate the behaviour of a dilute quasi-two-dimensional, harmonically confined, weakly interacting Bose gas within the finite-temperature Thomas-Fermi approximation. We find that the thermodynamic properties of the system are markedly different for repulsive and attractive interactions. Specifically, in contrast to the repulsive case, there appears to be a phase transition when the atoms interact with an attractive pseudo-potential, in the

Brandon P. van Zyl; R. K. Bhaduri; Justin Sigetich

2002-01-01

308

Two-Dimensional Polynomial Phase Signals: Parameter Estimation and Bounds  

Microsoft Academic Search

This paper considers the problem of parametric modeling and estimation of nonhomogeneous two-dimensional (2-D) signals. In particular, we focus our study on the class of constant modulus polynomial-phase 2-D nonhomogeneous signals. We present two different phase models and develop computationally efficient estimation algorithms for the parameters of these models. Both algorithms are based on phase differencing operators. The basic properties

Joseph M. Francos; Benjamin Friedlander

1998-01-01

309

Palmprint Recognition Based on Two-dimensional Fisher Linear Discriminant  

Microsoft Academic Search

(Abstract)In the FLD-based recognition, the within-class scatter matrix is always singular. To overcome the above problem, a new way is to directly project the image matrix based on Two-Dimensional FLD(2DFLD). In PolyU palmprint database, this paper applies PCA, PCA+FLD and 2DFLD to extract the palmprint feature subspace. The images to be recognized are projected on small dimension subspace. A classifier

GUO Jin-yu; YUAN Wei-qi

310

Exact analytic flux distributions for two-dimensional solar concentrators.  

PubMed

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

311

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

312

Glassy behavior of two-dimensional stripe-forming systems  

NASA Astrophysics Data System (ADS)

We study two-dimensional frustrated but nondisordered systems applying a replica approach to a stripe-forming model with competing interactions. The phenomenology of the model is representative of several well-known systems, like high-Tc superconductors and ultrathin ferromagnetic films, which have been the subject of intense research. We establish the existence of a glass transition to a nonergodic regime accompanied by an exponential number of long-lived metastable states, responsible for slow dynamics and nonequilibrium effects.

Ribeiro Teixeira, Ana C.; Stariolo, Daniel A.; Barci, Daniel G.

2013-06-01

313

Two-dimensional color-code quantum computation  

SciTech Connect

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

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

2011-04-15

314

The Study of Two-dimensional Polytropic Stars  

E-print Network

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

315

Two-dimensional Hazard Estimation for Longevity Analysis  

Microsoft Academic Search

We investigate developments in Danish mortality based on data from 1974–1998 working in a two-dimensional model with chronological time and age as the two dimensions. The analyses are done with non-parametric kernel hazard estimation techniques. The only assumption is that the mortality surface is smooth. Cross-validation is applied for optimal bandwidth selection to ensure the proper amount of smoothing to

Peter Fledelius; Montserrat Guillen; Jens Perch Nielsen; Michael Vogelius

2004-01-01

316

Two-dimensional analysis of a dielectric waveguide mirror  

Microsoft Academic Search

We present the two-dimensional (2-D) mode numerical analysis of a dielectric waveguide mirror with arbitrary structure angle. This work is an extension of a previously reported one-dimensional (1-D) mode analysis which accounts for the transverse variation, in addition to the lateral, of the waveguide modes. Inclusion of the transverse confinement is very important and has a significant effect on the

S. T. Lau; J. M. Ballantyne

1997-01-01

317

Two-dimensional void reconstruction by neutron transmission  

Microsoft Academic Search

Contemporary algebraic reconstruction methods are utilized in investigating the two-dimensional void distribution in a water analog from neutron transmission measurements. It is sought to ultimately apply these techniques to the determination of time-averaged void distribution in two-phase flow systems as well as for potential usage in neutron radiography. Initially, projection data were obtained from a digitized model of a hypothetical

G. D. Zakaib; A. A. Harms; J. Vlachopoulos

1978-01-01

318

Coll Positioning systems: a two-dimensional approach  

E-print Network

The basic elements of Coll positioning systems (n clocks broadcasting electromagnetic signals in a n-dimensional space-time) are presented in the two-dimensional case. This simplified approach allows us to explain and to analyze the properties and interest of these relativistic positioning systems. The positioning system defined in flat metric by two geodesic clocks is analyzed. The interest of the Coll systems in gravimetry is pointed out.

Joan Josep Ferrando

2006-01-27

319

Two-dimensional correlation spectroscopy in polymer study  

PubMed Central

This review outlines the recent works of two-dimensional correlation spectroscopy (2DCOS) in polymer study. 2DCOS is a powerful technique applicable to the in-depth analysis of various spectral data of polymers obtained under some type of perturbation. The powerful utility of 2DCOS combined with various analytical techniques in polymer studies and noteworthy developments of 2DCOS used in this field are also highlighted.

Park, Yeonju; Noda, Isao; Jung, Young Mee

2015-01-01

320

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

321

Signal processing and coding for two-dimensional optical storage  

Microsoft Academic Search

The paper introduces the concept of two-dimensional optical storage (TwoDOS). In this concept, bits are written in a broad spiral consisting of a number of bit-rows stacked together in a hexagonal packing. Bits with a value '1' are represented physically as circular pit-holes on the disc, while bits with a value '0' are characterized by the absence of such a

A. H. J. Immink; W. M. J. Coene; A. M. van der Lee; C. Busch; A. P. Hekstra; J. W. M. Bergmans; J. Riani; S. J. L. V. Beneden; T. Conway

2003-01-01

322

Chebyshev approximation for two-dimensional nonrecursive digital filters  

Microsoft Academic Search

The Remez exchange algorithm is extended for the design of two-dimensional nonrecursive digital filters approximating circularly symmetrical low-pass specifications according to a weighted Chebyshev error norm. Since the approximating function does not satisfy the Haar condition, the optimal solution is not necessarily unique and a straightforward extension of the one-dimensional exchange method may fail to converge. It is shown how

Y. Kamp; J. Thiran

1975-01-01

323

Easy interpretation of optical two-dimensional correlation spectra.  

PubMed

We demonstrate that the value of the underlying frequency-frequency correlation function can be retrieved from a two-dimensional optical correlation spectrum through a simple relationship. The proposed method yields both intuitive clues and a quantitative measure of the dynamics of the system. The technique is applied to studying the effects of temperature and phase changes on liquid-glass solvent dynamics. PMID:17072421

Lazonder, Kees; Pshenichnikov, Maxim S; Wiersma, Douwe A

2006-11-15

324

Accelerating universe in two-dimensional noncommutative dilaton cosmology  

E-print Network

We show that the phase transition from the decelerating universe to the accelerating universe, which is of relevance to the cosmological coincidence problem, is possible in the semiclassically quantized two-dimensional dilaton gravity by taking into account the noncommutative field variables during the finite time. Initially, the quantum-mechanically induced energy from the noncommutativity among the fields makes the early universe decelerate and subsequently the universe is accelerating because the dilaton driven cosmology becomes dominant later.

Wontae Kim; Myung Seok Yoon

2006-12-01

325

Two-Dimensional Black Hole and Nonperturbative String Theory  

E-print Network

We discuss the interpertation of the $c=1$ matrix model as two-dimensional string theory in a dilaton-black hole background. The nonperturbative formulation of $c=1$ matrix model in terms of an integrable model of nonrelativistic fermions enables us to study the quantum fate of the classical black hole singularity. We find that the classical singularity is wiped out by quantum corrections when summed to all orders.

Avinash Dhar

1993-08-04

326

A two-dimensional computer-controlled visual stimulator  

Microsoft Academic Search

A computer-controlled instrument that creates complex two-dimensional patterns on a CRT monitor is described. These patterns\\u000a are used to elicit visual evoked responses. Patterns are produced on a raster that is rotatable about its center. It is possible\\u000a to assign to arbitrary regions in the raster any of four independent one-dimensional spatial-temporal functions. For each\\u000a spatial-temporal function, the experimenter can

Norman Milkman; Gary Schick; Michelangelo Rossetto; Floyd Ratliff; Robert Shapley; Jonathan Victor

1980-01-01

327

Confinement-deconfinement transitions for two-dimensional Dirac particles  

E-print Network

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

Josef Mehringer; Edgardo Stockmeyer

2014-05-27

328

Two-dimensional detector arrays for gamma spectroscopy  

Microsoft Academic Search

We have developed a pixel detector hybrid called DANA-2 (Detector Array for Nuclear Applications). DANA-2 consists of a two-dimensional, monolithic Cadmium Zinc Telluride (CZT) detector array flip-chip bonded directly to a readout IC designed for high energy resolution. Both the detector and the IC have 16 × 16 pixels with a pitch of 0.5 mm × 0.5 mm; the detector

Martin Clajus; Victoria B. Cajipe; Tumay O. Tumer; Alexander Volkovskii

2008-01-01

329

Two-Dimensional-Three-Dimensional Correspondence in Mammography  

Microsoft Academic Search

We present a framework for the registration and correspondence of magnetic resonance (MR) (three-dimensional data, 3D, data) and x-ray (two-dimensional data, 2D, data) mammographic images. The robustness of this work relies on the development of a novel method to establish nonlinear correspondence between modalities of different dimensionality, which also represent different physical tissue aspects. The correspondence is based on a

Robert Marti; Reyer Zwiggelaar; Caroline M. E. Rubin; Erika R. E. Denton

2004-01-01

330

Matrix models of two-dimensional gravity and Toda theory  

Microsoft Academic Search

Recurrent relations for orthogonal polynomials, arising in the study of the one-matrix model of two-dimensional gravity, are shown to be equivalent to the equations of the Toda-chain hierarchy supplemented by additional Virasoro constraints. This is the case even before the continuum limit is taken. When the odd times are suppressed, the Volterra hierarchy arises, its continuum limit being the KdV

A. Gerasimov; A. Marshakov; A. Mironov; A. Morozov; A. Orlov

1991-01-01

331

Molecular interconversion behaviour in comprehensive two-dimensional gas chromatography  

Microsoft Academic Search

Comprehensive two-dimensional gas chromatography (GC×GC) is shown to provide information on dynamic molecular behaviour (interconversion), with the interconversion process occurring on both columns in the coupled-column experiment. The experiment requires suitable adjustment of both experimental conditions and relative dimensions of each of the columns. In this case, a longer column than normally employed in GC×GC allows sufficient retention duration on

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

2004-01-01

332

Two-dimensional evolution of an ion-acoustic soliton  

SciTech Connect

The two-dimensional evolution of an ion-acoustic soliton from a grid with regular or random perturbations in the direction transverse to the direction of the soliton propagation is experimentally examined. The soliton initially follows the contour of the exciting grid but evolves into a planar structure. These experimental results are compared with a model based on the higher dimensional Kadomtsev--Petviashvili equation. Both the theoretical and numerical predictions agree with the experiment.

Chang, H.; Lien, C.; Hill, J.; Raychaudhuri, S.; Lonngren, K.E.; Gabl, E.F.

1986-11-01

333

Magnetotransport in two-dimensional electron gas in helical nanomembranes.  

PubMed

Heterostructures containing high-mobility two-dimensional electron gas were rolled into freestanding helically shaped contacted Hall bars. Magnetotransport measurements in these structures at high magnetic fields revealed minima in the longitudinal magnetoresistance corresponding to integer and fractional filling factors. A strong asymmetry of the longitudinal magnetoresistance with respect to the external magnetic field direction was observed. For this new type of structures, an edge state picture was considered, and calculations based on the Landauer-Büttiker formalism are performed. PMID:25650698

Vorobyova, Julia S; Vorob'ev, Alexander B; Prinz, Victor Y; Toropov, Alexander I; Maude, Duncan K

2015-03-11

334

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

335

Two-dimensional DNA fingerprinting of human individuals  

SciTech Connect

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

336

The Number of States of Two Dimensional Critical String Theory  

E-print Network

We discuss string theory vacua which have the wrong number of spacetime dimensions, and give a crude argument that vacua with more than four large dimensions are improbable. We then turn to two dimensional vacua, which naively appear to violate Bekenstein's entropy principle. A classical analysis shows that the naive perturbative counting of states is unjustified. All excited states of the system have strong coupling singularities which prevent us from concluding that they really exist. A speculative interpretation of the classical solutions suggests only a finite number of states will be found in regions bounded by a finite area. We also argue that the vacuum degeneracy of two dimensional classical string theory is removed in quantum mechanics. The system appears to be in a Kosterlitz-Thouless phase. This leads to the conclusion that it is also improbable to have only two large spacetime dimensions in string theory. However, we note that, unlike our argument for high dimensions, our conclusions about the ground state have neglected two dimensional quantum gravitational effects, and are at best incomplete.

T. Banks; L. Susskind

1995-11-27

337

Number of states of two-dimensional critical string theory  

SciTech Connect

We discuss string theory vacua which have the wrong number of spacetime dimensions, and give a crude argument that vacua with more than four large dimensions are improbable. We then turn to two-dimensional vacua, which naively appear to violate Bekenstein{close_quote}s entropy principle. A classical analysis shows that the naive perturbative counting of states is unjustified. All excited states of the system have strong coupling singularities which prevent us from concluding that they really exist. A speculative interpretation of the classical solutions suggests only a finite number of states will be found in regions bounded by a finite area. We also argue that the vacuum degeneracy of two-dimensional classical string theory is removed in quantum mechanics. The system appears to be in a Kosterlitz-Thouless phase. This leads to the conclusion that it is also improbable to have only two large spacetime dimensions in string theory. However, we note that, unlike our argument for high dimensions, our conclusions about the ground state have neglected two-dimensional quantum gravitational effects, and are at best incomplete. {copyright} {ital 1996 The American Physical Society.}

Banks, T. [Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855-0849 (United States)] [Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855-0849 (United States); Susskind, L. [Physics Department, Stanford University, Stanford, California 94305 (United States)] [Physics Department, Stanford University, Stanford, California 94305 (United States)

1996-07-01

338

Two dimensional liquid crystal devices and their computer simulations  

NASA Astrophysics Data System (ADS)

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

Wang, Bin

339

Procedures for two-dimensional electrophoresis of proteins  

SciTech Connect

High-resolution two-dimensional gel electrophoresis (2DE) of proteins, using isoelectric focusing in the first dimension and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) in the second, was first described in 1975. In the 20 years since those publications, numerous modifications of the original method have evolved. The ISO-DALT system of 2DE is a high-throughput approach that has stood the test of time. The problem of casting many isoelectric focusing gels and SDS-PAGE slab gels (up to 20) in a reproducible manner has been solved by the use of the techniques and equipment described in this manual. The ISO-DALT system of two-dimensional gel electrophoresis originated in the late 1970s and has been modified many times to improve its high-resolution, high-throughput capabilities. This report provides the detailed procedures used with the current ISO-DALT system to prepare, run, stain, and photograph two-dimensional gels for protein analysis.

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

1996-10-01

340

Two-dimensional potential double layers and discrete auroras  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

341

Two-dimensional map for impact oscillator with drift.  

PubMed

An impact oscillator with drift is considered. The model accounts for viscoelastic impacts and is capable of mimicking the dynamics of progressive motion, which is important in many applications. To simplify the analysis of this system, a transformation decoupling the original coordinates is introduced. As a result, the bounded oscillations are separated from the drift motion. To study the bounded dynamics, a two-dimensional analytical map is developed and analyzed. In general, the dynamic state of the system is fully described by four variables: time tau , relative displacement p and velocity y of the mass, and relative displacement q of the slider top. However, this number can be reduced to two if the beginning of the progression phase is being monitored. The lower and upper bounds of the map domain are approximated. A graphical method of iteration of the two-dimensional map, similar to the cobweb method used in the one-dimensional case, is proposed. The results of numerical iterations of this two-dimensional map are presented, and a comparison is given between bifurcation diagrams calculated for this map and for the original system of differential equations. PMID:15524606

Pavlovskaia, Ekaterina; Wiercigroch, Marian; Grebogi, Celso

2004-09-01

342

Quasi-two-dimensional dynamics of plasmas and fluids.  

PubMed

In the lowest order of approximation quasi-two-dimensional dynamics of planetary atmospheres and of plasmas in a magnetic field can be described by a common convective vortex equation, the Charney and Hasegawa-Mima (CHM) equation. In contrast to the two-dimensional Navier-Stokes equation, the CHM equation admits "shielded vortex solutions" in a homogeneous limit and linear waves ("Rossby waves" in the planetary atmosphere and "drift waves" in plasmas) in the presence of inhomogeneity. Because of these properties, the nonlinear dynamics described by the CHM equation provide rich solutions which involve turbulent, coherent and wave behaviors. Bringing in nonideal effects such as resistivity makes the plasma equation significantly different from the atmospheric equation with such new effects as instability of the drift wave driven by the resistivity and density gradient. The model equation deviates from the CHM equation and becomes coupled with Maxwell equations. This article reviews the linear and nonlinear dynamics of the quasi-two-dimensional aspect of plasmas and planetary atmosphere starting from the introduction of the ideal model equation (CHM equation) and extending into the most recent progress in plasma turbulence. PMID:12780102

Horton, Wendell; Hasegawa, Akira

1994-06-01

343

Two-dimensional oxides: multifunctional materials for advanced technologies.  

PubMed

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

Pacchioni, Gianfranco

2012-08-13

344

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

345

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

346

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

PubMed

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 5mm 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. PMID:21036637

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

2011-01-01

347

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

SciTech Connect

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

Furman, M.A.

2007-05-29

348

The unsteady structure of two-dimensional steady laminar separation  

NASA Astrophysics Data System (ADS)

The two-dimensional unsteady incompressible Navier-Stokes equations, solved by a fractional time-step method, were used to investigate separation due to the application of an adverse pressure gradient to a low-Reynolds number boundary layer flow. The inviscid pressure distribution of Gaster [AGARD CP 4, 813 (1966)] was applied in the present computations to study the development of a laminar separation bubble. In all cases studied, periodic vortex shedding occurred from the primary separation region. The shed vortices initially lifted from the boundary layer and then returned towards the surface downstream. The shedding frequency nondimensionalized by the momentum thickness was found to be independent of Reynolds number. The value of the nondimensional Strouhal number, however, was found to differ from the results of Pauley et al. [J. Fluid Mech. 220, 397 (1990)], indicating that the shedding frequency varies with the nondimensional pressure distribution, Cp. The computational results were time averaged over several shedding cycles and the results were compared with Gaster. The numerical study accurately reproduced the major characteristics of the separation found in Gaster's study such as the separation point, the pressure plateau within the upstream portion of the separation bubble, and the reattachment point. The similarity between the experimental results and the time-averaged two-dimensional computational results indicates that the low-frequency velocity fluctuations detected by Gaster are primarily due to the motion of large vortex structures. This suggests that large-scale two-dimensional structures control bubble reattachment and small-scale turbulence contributes a secondary role.

Ripley, Matthew D.; Pauley, Laura L.

1993-12-01

349

Drift modes of a quasi-two-dimensional current sheet  

SciTech Connect

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

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

2012-03-15

350

Correction-to-scaling exponent for two-dimensional percolation  

SciTech Connect

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

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

2011-02-15

351

Coherent forward scattering in two-dimensional disordered systems  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

352

Two-Dimensional Spectroscopy with the Cosmic Origins Spectrograph  

NASA Astrophysics Data System (ADS)

The circular aperture of HSTs' Cosmic Origins Spectrograph (COS) is 2.5" in diameter, but transmission extends out to a 4" diameter. The NUV MAMA and the FUV microchannel plates image the sky over the full extent of the transmission. The cross-dispersion plate scale of the NUV channel is 0.02" and is 0.1" for the FUV channel. In this presentation we will discuss the capabilities and limitations of performing two-dimensional spectroscopy, in the cross-dispersion direction, with COS. In particular, we will discuss FUV detector effects, such as fixed pattern noise, gain sag, and Y walk, and the latest techniques for their correction.

Penton, Steven V.; Sahnow, D.; France, K.

2011-05-01

353

Solving time-dependent two-dimensional eddy current problems  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

354

Two-dimensional homogeneous isotropic fluid turbulence with polymer additives  

NASA Astrophysics Data System (ADS)

We carry out an extensive and high-resolution direct numerical simulation of homogeneous, isotropic turbulence in two-dimensional fluid films with air-drag-induced friction and with polymer additives. Our study reveals that the polymers (a) reduce the total fluid energy, enstrophy, and palinstrophy; (b) modify the fluid energy spectrum in both inverse- and forward-cascade régimes; (c) reduce small-scale intermittency; (d) suppress regions of high vorticity and strain rate; and (e) stretch in strain-dominated regions. We compare our results with earlier experimental studies and propose new experiments.

Gupta, Anupam; Perlekar, Prasad; Pandit, Rahul

2015-03-01

355

Nanocavity absorption enhancement for two-dimensional material monolayer systems.  

PubMed

Here we propose a strategy to enhance the light-matter interaction of two-dimensional (2D) material monolayers based on strong interference effect in planar nanocavities, and overcome the limitation between optical absorption and the atomically-thin thickness of 2D materials. By exploring the role of spacer layers with different thicknesses and refractive indices, we demonstrate that a nanocavity with an air spacer layer placed between a graphene monolayer and an aluminum reflector layer will enhance the exclusive absorption in the graphene monolayer effectively, which is particularly useful for the development of atomically-thin energy harvesting/conversion devices. PMID:25837057

Song, Haomin; Jiang, Suhua; Ji, Dengxin; Zeng, Xie; Zhang, Nan; Liu, Kai; Wang, Chu; Xu, Yun; Gan, Qiaoqiang

2015-03-23

356

Three-Particle Complexes in Two-Dimensional Semiconductors  

NASA Astrophysics Data System (ADS)

We evaluate binding energies of trions X±, excitons bound by a donor or acceptor charge XD (A ) , and overcharged acceptors or donors in two-dimensional atomic crystals by mapping the three-body problem in two dimensions onto one particle in a three-dimensional potential treatable by a purposely developed boundary-matching-matrix method. We find that in monolayers of transition metal dichalcogenides the dissociation energy of X± is typically much larger than that of localized exciton complexes, so that trions are more resilient to heating, despite the fact that their recombination line in optics is less redshifted from the exciton line than the line of XD (A ) .

Ganchev, Bogdan; Drummond, Neil; Aleiner, Igor; Fal'ko, Vladimir

2015-03-01

357

Conformal invariance in two-dimensional discrete field theory  

SciTech Connect

A discretized massless wave equation in two dimensions, on an appropriately chosen square lattice, exactly reproduces the solutions of the corresponding continuous equations. We show that the reason for this exact solution property is the discrete analogue of conformal invariance present in the model, and find more general field theories on a two-dimensional lattice that exactly solve their continuous limit equations. These theories describe in general nonlinearly coupled bosonic and fermionic fields and are similar to the Wess-Zumino-Witten model. {copyright} {ital 1997} {ital The American Physical Society}

Winitzki, S. [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155 (United States)] [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155 (United States)

1997-05-01

358

Superfluid transition in quasi-two-dimensional Fermi gases  

SciTech Connect

We show that atomic Fermi gases in quasi-two-dimensional (2D) geometries are promising for achieving superfluidity. In the regime of BCS pairing for weak attraction, we calculate the critical temperature T{sub c} and analyze possibilities of increasing the ratio of T{sub c} to the Fermi energy. In the opposite limit, where a strong coupling leads to the formation of weakly bound quasi-2D dimers, we find that their Bose-Einstein condensate will be stable on a long time scale.

Petrov, D.S. [FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam (Netherlands); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Baranov, M.A. [Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover (Germany); Shlyapnikov, G.V. [FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam (Netherlands); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Laboratoire Kastler Brossel, 24 rue Lhomond, F-75231 Paris Cedex 05 (France)

2003-03-01

359

Stable dilute supersolid of two-dimensional dipolar bosons  

E-print Network

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

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

2014-09-26

360

Condensate fraction of a two-dimensional attractive Fermi gas  

SciTech Connect

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

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

2007-07-15

361

Kinetic analysis of two dimensional metallic grating Cerenkov maser  

SciTech Connect

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

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

2011-08-15

362

Carbon dioxide separation with a two-dimensional polymer membrane.  

PubMed

Carbon dioxide gas separation is important for many environmental and energy applications. Molecular dynamics simulations are used to characterize a two-dimensional hydrocarbon polymer, PG-ES1, that uses a combination of surface adsorption and narrow pores to separate carbon dioxide from nitrogen, oxygen, and methane gases. The CO2 permeance is 3 × 10(5) gas permeation units (GPU). The CO2/N2 selectivity is 60, and the CO2/CH4 selectivity exceeds 500. The combination of high CO2 permeance and selectivity surpasses all known materials, enabling low-cost postcombustion CO2 capture, utilization of landfill gas, and horticulture applications. PMID:22734516

Schrier, Joshua

2012-07-25

363

Transport in two dimensional electronic micro-emulsions  

SciTech Connect

In two dimensional electron systems with Coulomb or dipolar interactions, a direct transition, whether first or second order, from a liquid to a crystalline state is forbidden. As a result, between these phases there must be other (micro-emulsion) phases which can be viewed as a meso-scale mixture of the liquid and crystalline phases. We investigate the transport properties of these new electronic phases and present arguments that they are responsible for the various transport anomalies that have been seen in experiments on the strongly correlated 2DEG in high mobility semiconductor devices with low electron densities.

Spivak, Boris [Department of Physics, University of Washington, Seattle, WA 98195 (United States)]. E-mail: spivak@u.washington.edu; Kivelson, Steven A. [Department of Physics, Stanford University, Stanford, CA 94305-4045 (United States)

2006-09-15

364

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

365

Measuring system for two-dimensional testing of electrical steel  

NASA Astrophysics Data System (ADS)

The measuring system for two-dimensional testing of electrical steel is proposed. In this system the sample in the form of a sheet can be magnetised along arbitrary direction. The magnetizing conditions, the dimensions of the yoke and sheet, the methods of detection of magnetic field strength and flux density are discussed. Both components of magnetic field strength Hx and Hy and flux density Bx and By with respect to the rolling direction or the magnetizing direction can be measured. The examples of tests of grain-oriented steel are presented. The variation of special directions of B and H and the spatial phase shift between these values has been determined.

Tumanski, Slawomir; Bakon, Tomasz

2001-02-01

366

Steady thermocapillary flows in two-dimensional slots  

NASA Technical Reports Server (NTRS)

Liquid in a slot flows owing to a temperature gradient applied along its free surface. The thermal variation of surface tension induces a steady viscous flow directed on the surface from hot to cold, and recirculating below. For small aspect ratios A, giving flow in thin, two-dimensional slots, an asymptotic theory valid for A yields to 0 is used to obtain the fluid and thermal fields as well as the interfacial shapes. Solutions are obtained for both fixed lines and fixed angles at the contact between the interface and the solid side walls.

Sen, A. K.; Davis, S. H.

1982-01-01

367

Instabilities and mixing in two-dimensional Kolmogorov flow  

E-print Network

This paper presents results of a theoretical investigation of transport in a numerical model of a two-dimensional Kolmogorov flow. We investigate the changes in its mixing properties associated with transition from laminar regime to turbulence. It is found that significant changes in the flow do not always lead to comparable changes in its transport properties. On the other hand, some very subtle changes in the flow can dramatically alter the degree of mixing. We show that interaction of multiple resonances can provide an explanation for many of these seemingly paradoxical results.

Radford Mitchell Jr; Roman O. Grigoriev

2012-12-12

368

A zonal flow analysis method for two-dimensional airfoils  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

369

Improved bends for two-dimensional photonic crystal waveguides  

NASA Astrophysics Data System (ADS)

For two-dimensional photonic crystals involving infinitely long dielectric rods or air-holes on square or triangular lattices, a number of high performance 60° and 90° waveguide bends are obtained by solving optimization problems involving the radii of a few rods or air-holes as the degrees of freedom. In particular, the proposed 60° bends significantly outperform previous designs that insert three or five identical air-holes in the bend. The optimization problems are solved using a recently developed method based on the so-called Dirichlet-to-Neumann (DtN) maps of the unit cells.

Hu, Zhen; Lu, Ya Yan

2011-06-01

370

Friedel theorem for two dimensional relativistic spin-½ systems  

NASA Astrophysics Data System (ADS)

The Friedel sum rule is generalized to relativistic systems of spin-1/2 particles in two dimensions. The change in energy due to the presence of an impurity is studied. The relation of the sum rule with the relativistic Levinson theorem is presented. Density oscillations in such systems are discussed. Since the Friedel theorem has been of major importance in understanding the impurity scattering in materials, the present results may be useful to explain some phenomena in two dimensional fermionic many body systems.

Lin, De-Hone

2006-04-01

371

Basics and recent advances of two dimensional- polyacrylamide gel electrophoresis  

PubMed Central

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

372

Phonon dispersion in hypersonic two-dimensional phononic crystal membranes  

NASA Astrophysics Data System (ADS)

We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significantly modify the propagation of thermally activated GHz phonons. We use numerical modeling based on the finite element method to analyze the experimental results and determine polarization, symmetry, or three-dimensional localization of observed modes.

Graczykowski, B.; Sledzinska, M.; Alzina, F.; Gomis-Bresco, J.; Reparaz, J. S.; Wagner, M. R.; Sotomayor Torres, C. M.

2015-02-01

373

Cyclotron resonance in a two-dimensional semimetal  

NASA Astrophysics Data System (ADS)

Cyclotron resonance in a two-dimensional semimetal has been studied theoretically, keeping in mind recent experiments reported in Z. D. Kvon, S. N. Pamilov, S. D. Ganichev, et al., in Proceedings of the 14th International Conference on Narrow Gap Semiconductors and Systems (Sendai, Japan, 2009). Since the size of the sample is finite, the exciting microwave inhomogeneous and there is a plasma shift of resonance frequency. There are two magnetoplasmon branches in a two-component system, which undergo pseudocrossing under the found criterion. Resonance frequencies and intensities of absorption peaks have been found. The latter are complicated functions of the electron and hole densities.

Vitlina, R. Z.; Magarill, L. I.; Chaplik, A. V.

2011-04-01

374

Statistical Mechanics of Unbound Two Dimensional Self-Gravitating Systems  

E-print Network

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

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

2010-04-19

375

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

376

Two-dimensional approach to relativistic positioning systems  

E-print Network

A relativistic positioning system is a physical realization of a coordinate system consisting in four clocks in arbitrary motion broadcasting their proper times. The basic elements of the relativistic positioning systems are presented in the two-dimensional case. This simplified approach allows to explain and to analyze the properties and interest of these new systems. The positioning system defined by geodesic emitters in flat metric is developed in detail. The information that the data generated by a relativistic positioning system give on the space-time metric interval is analyzed, and the interest of these results in gravimetry is pointed out.

Bartolomé Coll; Joan Josep Ferrando; Juan Antonio Morales

2006-05-22

377

Two-dimensional metamaterial transparent metal electrodes for infrared optoelectronics.  

PubMed

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

378

Two-dimensional solitons in a quintic-septimal medium  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

379

Two-dimensional conformal field theory and the butterfly effect  

E-print Network

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

Daniel A. Roberts; Douglas Stanford

2015-02-04

380

Optimum high temperature strength of two-dimensional nanocomposites  

SciTech Connect

High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

Monclús, M. A.; Molina-Aldareguía, J. M., E-mail: jon.molina@imdea.org [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Zheng, S. J.; Mayeur, J. R.; Beyerlein, I. J.; Mara, N. A. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Polcar, T. [Czech Technical University in Prague, Technická 2, Prague 6 (Czech Republic); Llorca, J. [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Department of Materials Science, Polytechnic University of Madrid, E. T. S. de Ingenieros de Caminos, 28040 Madrid (Spain)

2013-11-01

381

Testability of non-autonomous two dimensional iterative logic array  

E-print Network

) of Theorem 6. Theorem 8: A homogeneous non-autonon&ous ILA is & -controllable if every subgraph (connecte&1 graph) of the state graph is Eulerian (i. e. , the directecl graph has a circuit &chief contains every edge exact ll oner) [13]. Proof: Suppose..., condition A &vill be satisf&ed only if every z-state appears as an i-entry aud every y-state as a 1)-cntiy in the flow table. Thcoiern '&: For a two-dimensional ILA, condition 8 ivill be satisfied only if no two rows of the flow table are alike and no two...

Nagumo, Hideo

1991-01-01

382

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals  

NASA Astrophysics Data System (ADS)

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals (MPCs) have been studied by electromagnetic simulation and experiments in microwave frequencies. MPCs with square and hexagonal lattices are made of ferrites, and their transmission coefficients are measured in the X waveband with an applied static magnetic field. For the lattices, a stop-band and a band shift with the applied static magnetic field are observed. The experimental results are in good agreement with those of electromagnetic simulations when magnetic anisotropy of ferrites is represented by a tensor but deviate from the simulation results when the anisotropy is modelled by an effective permeability of TMz mode.

Xu, Jie; Wu, Rui-xin; Chen, Ping; Shi, Yue

2007-02-01

383

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

384

Highly directional thermal emission from two-dimensional silicon structures.  

PubMed

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

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

2013-03-25

385

Birth and Growth of Two-dimensional Universe  

E-print Network

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

Tetsuyuki Yukawa

2011-11-30

386

Approximation algorithms for maximum two-dimensional pattern matching  

SciTech Connect

We introduce the following optimization version of the classical pattern matching problem (referred to as the maximum pattern matching problem). Given a two-dimensional rectangular text and a 2- dimensional rectangular pattern find the maximum number of non- overlapping occurrences of the pattern in the text. Unlike the classical 2-dimensional pattern matching problem, the maximum pattern matching problem is NP - complete. We devise polynomial time approximation algorithms and approximation schemes for this problem. We also briefly discuss how the approximation algorithms can be extended to include a number of other variants of the problem.

Arikati, S.R. [Memphis Univ., TN (United States); Dessmark, A.; Lingas, A. [Lund Univ. (Sweden); Marathe, M.

1996-07-01

387

Exact results at the two-dimensional percolation point  

NASA Astrophysics Data System (ADS)

We derive exact expressions for the excess number of clusters b and the excess cumulants bn of a related quantity at the two-dimensional percolation point. High-accuracy computer simulations are in accord with our predictions. The parameter b is a finite-size correction to the Temperley-Lieb or Baxter-Temperley-Ashley formula for the number of clusters per site nc in the infinite system limit; the bn correct bulk cumulants. Both b and bn are universal, and thus depend only on the system's shape. Higher-order corrections show no apparent dependence on fractional powers of the system size.

Kleban, P.; Ziff, R. M.

1998-04-01

388

Thermodynamics of interfacial oscillations in two-dimensional systems  

SciTech Connect

The quiescent two-phase interface density profile and its capillary wave broadening are obtained heuristically. In two-dimensional space, the drumhead model in an arbitrary external field is transformed into a pair of Bloch equations and solved in special cases. It is extended to encompass a fixed liquid volume change. The original model is then solved completely and expressed as a free energy density functional, which is likewise extended. Finally, the genesis of the singular structure of the free energy is discussed. 14 references, 1 figure.

Percus, J.K.

1984-12-20

389

Fractional-step method for two-dimensional estuarine transport  

USGS Publications Warehouse

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

390

Reentrant miscibility in two-dimensional symmetrical mixtures  

NASA Astrophysics Data System (ADS)

The Monte Carlo simulation method in the grand canonical ensemble is used to study the phase behavior of two-dimensional symmetrical binary mixtures of Lennard-Jones particles with negative nonadditivity and the weaker interaction between the pairs of unlike than between the pairs of like particles. We have determined the evolution of the phase diagram topology when the parameters describing the interaction between unlike particles vary. It has been found that such systems may exhibit reentrant miscibility in the liquid and the solid phases.

Materniak, S.; Patrykiejew, A.; R?ysko, W.

2013-06-01

391

Seabed disposal project two-dimensional axisymmetric penetrometer simulations  

SciTech Connect

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

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

1980-03-01

392

Two-dimensional simulations of magnetically-driven instabilities  

SciTech Connect

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

393

Domain engineering of physical vapor deposited two-dimensional materials  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

394

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

395

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

396

Optical and electronic properties of two dimensional graphitic silicon carbide  

E-print Network

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

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

2012-01-01

397

SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.  

USGS Publications Warehouse

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

398

Reentrant miscibility in two-dimensional symmetrical mixtures.  

PubMed

The Monte Carlo simulation method in the grand canonical ensemble is used to study the phase behavior of two-dimensional symmetrical binary mixtures of Lennard-Jones particles with negative nonadditivity and the weaker interaction between the pairs of unlike than between the pairs of like particles. We have determined the evolution of the phase diagram topology when the parameters describing the interaction between unlike particles vary. It has been found that such systems may exhibit reentrant miscibility in the liquid and the solid phases. PMID:23848674

Materniak, S; Patrykiejew, A; R?ysko, W

2013-06-01

399

Two-dimensional complex parity-time-symmetric photonic structures  

NASA Astrophysics Data System (ADS)

We propose a simple realistic two-dimensional complex parity-time-symmetric photonic structure that is described by a non-Hermitian potential but possesses real-valued eigenvalues. The concept is developed from basic physical considerations to provide asymmetric coupling between harmonic wave components of the electromagnetic field. The structure results in a nonreciprocal chirality and asymmetric transmission between in- and out-coupling channels into the structure. The analytical results are supported by a numerical study of the Bloch-like mode formations and calculations of a realistic planar semiconductor structure.

Turduev, M.; Botey, M.; Giden, I.; Herrero, R.; Kurt, H.; Ozbay, E.; Staliunas, K.

2015-02-01

400

Two-dimensional manifolds with metrics of revolution  

SciTech Connect

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

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

2000-10-31

401

Nonlinear Cascades in Two-Dimensional Turbulent Magnetoconvection  

SciTech Connect

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

402

Effective theory of chiral two-dimensional superfluids  

E-print Network

We construct, to leading orders in the momentum expansion, an effective theory of a chiral $p_x + ip_y$ two-dimensional fermionic superfluid at zero temperature that is consistent with nonrelativistic general coordinate invariance. This theory naturally incorporates the parity and time reversal violating effects such as the Hall viscosity and the edge current. The particle number current and stress tensor are computed and their linear response to electromagnetic and gravitational sources is calculated. We also consider an isolated vortex in a chiral superfluid and identify the leading chirality effect in the density depletion profile.

Carlos Hoyos; Sergej Moroz; Dam Thanh Son

2014-05-12

403

Diffusion in a two-dimensional periodic potential  

SciTech Connect

We report a numerical study of the self-diffusion of a single-point particle in a two-dimensional periodic potential of triangular symmetry. The self-diffusion coefficient is obtained via computer simulations for several values of the particle energy. We find that the self-diffusion process is complicated due to the existence of correlated motions involving two or more cells. A random-walk model which takes into account the effects of correlated motions involving only the nearest-neighbor cells is constructed, and compared with the experimental results.

Bagchi, B.; Zwanzig, R.; Cristina Marchetti, M.

1985-02-01

404

Human muscle proteins: analysis by two-dimensional electrophoresis  

SciTech Connect

Proteins from single frozen sections of human muscle were separated by two-dimensional gel electrophoresis and detected by fluorography or Coomassie Blue staining. The major proteins were identical in different normal muscles obtained from either sex at different ages, and in Duchenne and myotonic dystrophy samples. Congenital myopathy denervation atrophy, polymyositis, and Becker's muscular dystrophy samples, however, showed abnormal myosin light chain compositions, some with a decrease of fast-fiber myosin light chains and others with a decrease of slow-fiber light chains. These protein alterations did not correlate with any specific disease, and may be cause by generalized muscle-fiber damage.

Giometti, C.S.; Danon, M.J.; Anderson, N.G.

1983-09-01

405

Two-dimensional Effects in High Power Microwave Breakdown  

NASA Astrophysics Data System (ADS)

A major limiting factor in transmission of high power microwave radiation is dielectric window breakdown. A one-dimensional particle-in-cell/Monte Carlo collision (PIC/MCC) model was used to study dielectric window breakdown from vacuum multipactor to collisional microwave discharge for noble gases [1]. It showed that multipactor on the dielectric window drives breakdown at low pressure, and volumetric collisional ionization is the main mechanism for breakdown at high pressure. A Monte Carlo (MC) model was also used to investigate dielectric window breakdown in two-dimensionals, including spatial variation of the microwave electric field in transverse direction [2]. The breakdown times were consistent with their experiment data and also showed the interesting feature of electron clusters above the window. MC, however, is not self-consistent and neglects the space charge effect resulting from the charge build-up. In this work, two-dimensional PIC/MCC was employed to investigate the breakdown in oxygen including the space charge effect. [1] H.C. Kim, and J.P. Verboncoeur, Phys. Plasmas, 13, 123506(2006). [2] J.T. Krile, A.A. Neuber, and H. G. Krompholz, Appl. Phys. Lett., 89, 201501(2006).

Nam, Sang Ki; Lim, Chul-Hyun; Verboncoeur, John

2008-10-01

406

Phonons in two-dimensional soft colloidal crystals  

E-print Network

The vibrational modes of pristine and polycrystalline monolayer colloidal crystals composed of thermosensitive microgel particles are measured using video microscopy and covariance matrix analysis. At low frequencies, the Debye relation for two dimensional harmonic crystals is observed in both crystal types; at higher frequencies, evidence for van Hove singularities in the phonon density of states is significantly smeared out by experimental noise and measurement statistics. The effects of these errors are analyzed using numerical simulations. We introduce methods to correct for these limitations, which can be applied to disordered systems as well as crystalline ones, and we show that application of the error correction procedure to the experimental data leads to more pronounced van Hove singularities in the pristine crystal. Finally, quasi-localized low-frequency modes in polycrystalline two-dimensional colloidal crystals are identified and demonstrated to correlate with structural defects such as dislocations, suggesting that quasi-localized low-frequency phonon modes may be used to identify local regions vulnerable to rearrangements in crystalline as well as amorphous solids.

Ke Chen; Tim Still; Samuel Schoenholz; Kevin B. Aptowicz; Michael Schindler; A. C. Maggs; Andrea J. Liu; A. G. Yodh

2013-09-11

407

Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

408

Electron fractionalization in two-dimensional graphenelike structures  

NASA Astrophysics Data System (ADS)

Electron fractionalization is intimately related to topology. In one-dimensional systems, such as polyacetelene, fractionally charged states exist at domain walls between degenerate vacua. In two-dimensional systems, fractionalization exists in quantum Hall fluids, where time-reversal symmetry is broken by a large external magnetic field. Recently, there has been a tremendous effort in the search for examples of fractionalization in two-dimensional systems with time-reversal symmetry. Here we show that fractionally charged topological excitations exist in tight-biding systems where time-reversal symmetry is respected. These systems are described, in the continuum approximation, by the Dirac equation in two space dimensions. The topological zero-modes are mathematically similar to fractional vortices in p-wave superconductors. They correspond to a twist in the phase in the mass of the Dirac fermions, akin to cosmic strings in particle physics. The quasiparticle excitations can carry irrational charge and irrational exchange statistics. These excitations can be deconfined at zero temperature, but when they are, the charge re-rationalizes to the value 1/2. REFS.:Chang-Yu Hou, Claudio Chamon, Christopher Mudry, Phys. Rev. Lett. 98, 186809 (2007); Claudio Chamon, Chang-Yu Hou, Roman Jackiw, Christopher Mudry, So-Young Pi, Andreas P. Schnyder, Phys. Rev. Lett, 100, 110405 (2008); Claudio Chamon, Chang-Yu Hou, Roman Jackiw, Christopher Mudry, So-Young Pi, Gordon Semenoff, Phys. Rev. B 77, 235431 (2008)

Chamon, Claudio

2009-03-01

409

Two-dimensional fluorescence lifetime correlation spectroscopy. 1. Principle.  

PubMed

Fluorescence correlation spectroscopy (FCS) is a unique tool for investigating microsecond molecular dynamics of complex molecules in equilibrium. However, application of FCS in the study of molecular dynamics has been limited, owing to the complexity in the extraction of physically meaningful information. In this work, we develop a new method that combines FCS and time-correlated single photon counting (TCPSC) to extract unambiguous information about equilibrium dynamics of complex molecular systems. In this method, which we name two-dimensional fluorescence lifetime correlation spectroscopy (2D FLCS), we analyze the correlation of the fluorescence photon pairs, referring to the fluorescence lifetime. We first obtain the correlations of the photon pairs with respect to the excitation-emission delay times in the form of a two-dimensional (2D) map. Then, the 2D map is converted to the correlations between different species that have distinct fluorescence lifetimes using inverse Laplace transformation. This 2D FLCS is capable of visualizing the equilibration dynamics of complex molecules with microsecond time resolution at the single-molecule level. We performed a kinetic Monte Carlo simulation of a TCPSC-FCS experiment as a proof-of-principle example. The result clearly shows the validity of the proposed method and its high potential in analyzing the photon data of dynamic systems. PMID:23977832

Ishii, Kunihiko; Tahara, Tahei

2013-10-01

410

Modeling two-dimensional detonations with detonation shock dynamics  

SciTech Connect

In any explosive device, the chemical reaction of the explosive takes place in a thin zone just behind the shock front. The finite size of the reaction zone is responsible for: the pressure generated by the explosive being less near the boundaries, for the detonation velocity being lower near a boundary than away from it, and for the detonation velocity being lower for a divergent wave than for a plane wave. In computer models that are used for engineering design calculations, the simplest treatment of the explosive reaction zone is to ignore it completely. Most explosive modeling is still done this way. The neglected effects are small when the reaction zone is very much smaller than the explosive's physical dimensions. When the ratio of the explosive's detonation reaction-zone length to a representative system dimension is of the order of 1/100, neglecting the reaction zone is not adequate. An obvious solution is to model the reaction zone in full detail. At present, there is not sufficient computer power to do so economically. Recently we have developed an alternative to this standard approach. By transforming the governing equations to the proper intrinsic-coordinate frame, we have simplified the analysis of the two-dimensional reaction-zone problem. When the radius of curvature of the detonation shock is large compared to the reaction-zone length, the calculation of the two-dimensional reaction zone can be reduced to a sequence of one-dimensional problems. 9 refs., 5 figs.

Bdzil, J.B.; Stewart, D.S.

1988-01-01

411

Two-Dimensional, Optical Ellipsometric Studies of Polymer Orientation  

NASA Astrophysics Data System (ADS)

Crystalline or liquid crystalline polymers exhibit optical birefringence as a result of formation of superstructures, such as spherulites, axialites, dendrites or liquid crystalline phases. Our method of choice for optical characterization is a variation of ellipsometry based on Stokes analysis. We use ellipsometry to measure the retardation and azimuthal angle of optically anisotropic polymeric materials. In addition, the embodiment of the method provides two-dimensional, i.e., spatially resolved, information about the optical parameters across the field of view. Monochromatic, incoherent light is polarized through states of differing ellipticity using liquid crystal variable retarders as universal compensator, as suggested by the method of Oldenbourg and Mei. After transmission through the polymer sample, the state of ellipticity of the polymer is quantitatively determined at every pixel in the two-dimensional optical image. To date we have investigated zone drawn polyethylene tapes, electrically activated liquid crystal display cells, and several thermotropic liquid crystalline polymers including Vectra. We aim to provide fundamental information about the formation of optically anisotropic structure, including measurement of phase transformation kinetics and development of textures.

Georgiev, Georgi; Berns, David; Cebe, Peggy

2001-03-01

412

High reproducibility of large-gel two-dimensional electrophoresis.  

PubMed

Two-dimensional gel electrophoresis (2-DE) facilitates the separation of thousands of proteins from highly complex protein mixtures and has become a central method in proteomics in recent years. In the present study, we examined the technical variability of large 2-DE gels with respect to sample preparation, electrophoresis procedure, data acquisition, and biological variation by analyzing a disease (Huntington's disease) and control state with a commercially available software package, PROTEOMWEAVER trade mark. Scatter plots and correlation coefficients were obtained to quantify both technical and biological variation. Even 2-DE gels run separately in both dimensions yielded correlation coefficients around 0.88 and deviations from the mean close to 20% for low-intensity spots. This indicates a high technical reproducibility of the 2-DE procedure developed in our laboratory. Variability within a biological condition was low and comparable to technical variation (at least 0.87). Two-dimensional (2-D) gels obtained from samples of different biological conditions (health vs. disease) achieved a variability similar to intracondition and technical variability. These findings highlight the importance of multiple gel and spot-by-spot comparisons to identify biological significant changes. Minor errors introduced by technical and biological variation allow a comparison of all gels within a study which facilitates the tackling of complex biological problems. PMID:15349946

Challapalli, Kiran Kumar; Zabel, Claus; Schuchhardt, Johannes; Kaindl, Angela M; Klose, Joachim; Herzel, Hanspeter

2004-09-01

413

Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions.  

PubMed

Two-dimensional layered semiconductors such as MoS? and WSe? have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS?-MoSe? and WS?-WSe? lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe?-WS? heterojunctions form lateral p-n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics. PMID:25262331

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

2014-12-01

414

Nonlocal transport in a hybrid two-dimensional topological insulator  

NASA Astrophysics Data System (ADS)

We study nonlocal resistance in an H-shaped two-dimensional HgTe/CdTe quantum well consisting of an injector and a detector, both of which can be tuned in the quantum spin Hall or metallic spin Hall regime. Because of strong spin-orbit interaction, there always exists the spin Hall effect and nonlocal resistance in the HgTe/CdTe quantum well. We find that when both the detector and the injector are in the quantum spin Hall regime, the nonlocal resistance is quantized at 0.25he2, which is robust against weak disorder scattering and small magnetic field. When the detector or injector is beyond this regime, the nonlocal resistance decreases rapidly and will be strongly suppressed by disorder and magnetic field. In the presence of a strong magnetic field, the quantum spin Hall regime will be switched into the quantum Hall regime, and the nonlocal resistance will disappear. The nonlocal signal and its various manifestations in different hybrid regimes originate from the special band structure of the HgTe/CdTe quantum well, and they can be considered as the fingerprint of the helical quantum spin Hall edge states in a two-dimensional topological insulator.

Xing, Yanxia; Sun, Qing-feng

2014-02-01

415

Human lymphocyte polymorphisms detected by quantitative two-dimensional electrophoresis  

SciTech Connect

A survey of 186 soluble lymphocyte proteins for genetic polymorphism was carried out utilizing two-dimensional electrophoresis of /sup 14/C-labeled phytohemagglutinin (PHA)-stimulated human lymphocyte proteins. Nineteen of these proteins exhibited positional variation consistent with independent genetic polymorphism in a primary sample of 28 individuals. Each of these polymorphisms was characterized by quantitative gene-dosage dependence insofar as the heterozygous phenotype expressed approximately 50% of each allelic gene product as was seen in homozygotes. Patterns observed were also identical in monozygotic twins, replicate samples, and replicate gels. The three expected phenotypes (two homozygotes and a heterozygote) were observed in each of 10 of these polymorphisms while the remaining nine had one of the homozygous classes absent. The presence of the three phenotypes, the demonstration of gene-dosage dependence, and our own and previous pedigree analysis of certain of these polymorphisms supports the genetic basis of these variants. Based on this data, the frequency of polymorphic loci for man is: P . 19/186 . .102, and the average heterozygosity is .024. This estimate is approximately 1/3 to 1/2 the rate of polymorphism previously estimated for man in other studies using one-dimensional electrophoresis of isozyme loci. The newly described polymorphisms and others which should be detectable in larger protein surveys with two-dimensional electrophoresis hold promise as genetic markers of the human genome for use in gene mapping and pedigree analyses.

Goldman, D.; Merril, C.R.

1983-09-01

416

Analytical study of two-dimensional degenerate metamaterial antennas  

NASA Astrophysics Data System (ADS)

Dispersion curves of metamaterial steerable antennas composed of two-dimensional arrays of metallic unit structures with the C4v and C6v symmetries are calculated both qualitatively by the tight-binding approximation and quantitatively by the finite-difference time-domain method. Special attention is given to the case of eigenmodes of the E symmetry of the C4v point group and those of the E1 and E2 symmetries of the C6v point group, since they are doubly degenerate on the ? point of the Brillouin zone so that they naturally satisfy the steerability condition. We show that their dispersion curves have quadratic dependence on the wave vector in the vicinity of the ? point. To get a linear dispersion, which is advantageous for steerable antennas, we propose a method of controlled symmetry reduction. The present theory is an extension of our previous one [Opt. Express 18, 27371 (2010)] to two-dimensional systems, for which we can achieve the deterministic degeneracy due to symmetry and the controlled symmetry reduction becomes available. This design of metamaterial steerable antennas is advantageous in the optical frequency.

Sakoda, Kazuaki; Zhou, Haifeng

2011-07-01

417

Two-dimensional nuclear magnetic resonance of quadrupolar systems  

SciTech Connect

This dissertation describes two-dimensional nuclear magnetic resonance theory and experiments which have been developed to study quadruples in the solid state. The technique of multiple-quantum magic-angle spinning (MQMAS) is extensively reviewed and expanded upon in this thesis. Specifically, MQMAS is first compared with another technique, dynamic-angle spinning (DAS). The similarity between the two techniques allows us to extend much of the DAS work to the MQMAS case. Application of MQMAS to a series of aluminum containing materials is then presented. The superior resolution enhancement through MQMAS is exploited to detect the five- and six-coordinated aluminum in many aluminosilicate glasses. Combining the MQMAS method with other experiments, such as HETCOR, greatly expands the possibility of the use of MQMAS to study a large range of problems and is demonstrated in Chapter 5. Finally, the technique switching-angle spinning (SAS) is applied to quadrupolar nuclei to fully characterize a quadrupolar spin system in which all of the 8 NMR parameters are accurately determined. This dissertation is meant to demonstrate that with the combination of two-dimensional NMR concepts and new advanced spinning technologies, a series of multiple-dimensional NMR techniques can be designed to allow a detailed study of quadrupolar nuclei in the solid state.

Wang, Shuanhu

1997-09-17

418

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

419

Face recognition using two-dimensional nonnegative principal component analysis  

NASA Astrophysics Data System (ADS)

Although two-dimensional principal component analysis (2DPCA) extracts image features directly from 2D image matrices rather than one dimensional vectors, 2DPCA is only based on the whole images to preserve total variances by maximizing the trace of feature covariance matrix. Thus, 2DPCA cannot extract localized components, which are usually important for face recognition. Inspired by nonnegative matrix factorization (NMF), which is based on localized features, we propose a novel algorithm for face recognition called two-dimensional nonnegative principal component analysis (2DNPCA) to extract localized components and maintain the maximal variance property of 2DPCA. 2DNPCA is a matrix-based algorithm to preserve the local structure of facial images and has the nonnegative constraint to learn localized components. Therefore, 2DNPCA has both advantages of 2DPCA and NMF. Furthermore, 2DNPCA solves the time-consuming problem by removing the restriction of minimizing the cost function and extracting only the base matrix. The nearest neighbor (NN) classifier and linear regression (LR) classifier are used for classification and extensive experimental results show that 2DNPCA plus NN and 2DNPCA plus LR are both very efficient approaches for face recognition.

Ma, Peng; Yang, Dan; Ge, Yongxin; Zhang, Xiaohong; Qu, Ying

2012-07-01

420

Simulated ship recognition using two-dimensional PCA  

NASA Astrophysics Data System (ADS)

This paper proposes a fast and robust algorithm for classification and recognition of ships based on the two-dimensional Principal Component Analysis (2DPCA) method. The three-dimensional ship models achieve by modeling software of MultiGen, and then they are projected by Vega simulating software for two-dimensional ship silhouettes. The 2DPCA method as against conventional PCA method for simulated ship recognition using training and testing experiments, as the training and testing sample size is large, and there are great variations in different azimuth and elevation for ship viewpoints. The experiment of ship recognition using the global feature of ships is not satisfied with us, so we proposed an improved 2DPCA method based on the local feature of ships. Some recognition results from simulated data are presented, it shows that the improved 2DPCA method outperform PCA in ship recognition and also superior to PCA in terms of computational efficiency for feature extraction. So our method is more preferable for ship classification and recognition.

Zhao, Guangzhou; Zhu, Guangxi; Peng, Feng; Wang, Shuwen; Xu, Huazhong

2007-11-01

421

Electronic transport in two-dimensional high dielectric constant nanosystems.  

PubMed

There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screening length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials. PMID:25860804

Ortuño, M; Somoza, A M; Vinokur, V M; Baturina, T I

2015-01-01

422

Cylinder Test Specification  

SciTech Connect

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

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

1999-10-01

423

The Cylinder Problem  

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.

The Math Forum

2001-01-01

424

SCAPS, a two-dimensional ion detector for mass spectrometer  

NASA Astrophysics Data System (ADS)

Faraday Cup (FC) and electron multiplier (EM) are of the most popular ion detector for mass spectrometer. FC is used for high-count-rate ion measurements and EM can detect from single ion. However, FC is difficult to detect lower intensities less than kilo-cps, and EM loses ion counts higher than Mega-cps. Thus, FC and EM are used complementary each other, but they both belong to zero-dimensional detector. On the other hand, micro channel plate (MCP) is a popular ion signal amplifier with two-dimensional capability, but additional detection system must be attached to detect the amplified signals. Two-dimensional readout for the MCP signals, however, have not achieve the level of FC and EM systems. A stacked CMOS active pixel sensor (SCAPS) has been developed to detect two-dimensional ion variations for a spatial area using semiconductor technology [1-8]. The SCAPS is an integrated type multi-detector, which is different from EM and FC, and is composed of more than 500×500 pixels (micro-detectors) for imaging of cm-area with a pixel of less than 20 µm in square. The SCAPS can be detected from single ion to 100 kilo-count ions per one pixel. Thus, SCAPS can be accumulated up to several giga-count ions for total pixels, i.e. for total imaging area. The SCAPS has been applied to stigmatic ion optics of secondary ion mass spectrometer, as a detector of isotope microscope [9]. The isotope microscope has capabilities of quantitative isotope images of hundred-micrometer area on a sample with sub-micrometer resolution and permil precision, and of two-dimensional mass spectrum on cm-scale of mass dispersion plane of a sector magnet with ten-micrometer resolution. The performance has been applied to two-dimensional isotope spatial distribution for mainly hydrogen, carbon, nitrogen and oxygen of natural (extra-terrestrial and terrestrial) samples and samples simulated natural processes [e.g. 10-17]. References: [1] Matsumoto, K., et al. (1993) IEEE Trans. Electron Dev. 40, 82-85. [2] Takayanagi et al. (1999) Proc. 1999 IEEE workshop on Charge-Coupled Devices and Advanced Image Sensors, 159-162. [3] Kunihiro et al. (2001) Nucl. Instrum. Methods Phys. Res. Sec. A 470, 512-519. [4] Nagashima et al. (2001) Surface Interface Anal. 31, 131-137. [5] Takayanagi et al. (2003) IEEE Trans. Electron Dev. 50, 70- 76. [6] Sakamoto and Yurimoto (2006) Surface Interface Anal. 38, 1760-1762. [7] Yamamoto et al. (2010) Surface Interface Anal. 42, 1603-1605. [8] Sakamoto et al. (2012) Jpn. J. Appl. Phys. 51, 076701. [9] Yurimoto et al. (2003) Appl. Surf. Sci. 203-204, 793-797. [10] Nagashima et al. (2004) Nature 428, 921-924. [11] Kunihiro et al. (2005) Geochim. Cosmochim. Acta 69, 763-773. [12] Nakamura et al. (2005) Geology 33, 829-832. [13] Sakamoto et al. (2007) Science 317, 231-233. [14] Greenwood et al. (2008) Geophys. Res. Lett., 35, L05203. [15] Greenwood et al. (2011) Nature Geoscience 4, 79-82. [16] Park et al. (2012) Meteorit. Planet. Sci. 47, 2070-2083. [17] Hashiguchi et al. (2013) Geochim. Cosmochim. Acta. 122, 306-323.

Yurimoto, Hisayoshi

2014-05-01

425

A solution-adaptive lattice Boltzmann method for two-dimensional incompressible viscous flows  

NASA Astrophysics Data System (ADS)

A stencil adaptive lattice Boltzmann method (LBM) is developed in this paper. It incorporates the stencil adaptive algorithm developed by Ding and Shu [26] for the solution of Navier-Stokes (N-S) equations into the LBM calculation. Based on the uniform mesh, the stencil adaptive algorithm refines the mesh by two types of 5-points symmetric stencils, which are used in an alternating sequence for increased refinement levels. The two types of symmetric stencils can be easily combined to form a 9-points symmetric structure. Using the one-dimensional second-order interpolation recently developed by Wu and Shu [27] along the straight line and the D2Q9 model, the adaptive LBM calculation can be effectively carried out. Note that the interpolation coefficients are only related to the lattice velocity and stencil size. Hence, the simplicity of LBM is not broken down and the accuracy is maintained. Due to the use of adaptive technique, much less mesh points are required in the simulation as compared to the standard LBM. As a consequence, the computational efficiency is greatly enhanced. The numerical simulation of two dimensional lid-driven cavity flows is carried out. Accurate results and improved efficiency are reached. In addition, the steady and unsteady flows over a circular cylinder are simulated to demonstrate the capability of proposed method for handling problems with curved boundaries. The obtained results compare well with data in the literature.

Wu, J.; Shu, C.

2011-03-01

426

Two-Dimensional Fractal Characteristics of the Martian Surface  

NASA Astrophysics Data System (ADS)

We present global maps of two-dimensional fractal statistics for Mars topography calculated by applying the two-dimensional Fourier spectral approach to MOLA altimetry measurements over spatial scales extending from approximately 450 meters to 15 kilometers. Three global maps were generated: 1) surface (two-dimensional) fractal dimension, 2) roughness amplitude at a scale of one kilometer, and 3) linear model fit error in the log-log relation of mean power spectral density to radial wavenumber. The linear model fit error is a convenient way to judge the appropriateness of the fractal model. Examination of the fractal dimension and model error maps reveals that a majority of the surface is well modeled by fractal geometry. This is evidenced by minimal systematic spatial variation in fractal dimension and low model fit errors, with the northern plains exhibiting slightly higher overall error than the cratered highlands. There are also several spatially coherent regions in the fractal dimension map that have enhanced values. These regions include Amazonis Planitia and southeast Elysium Planitia. On the other hand, Isidis Planitia and portions of the Olympus Mons aureole exhibit high model fit errors which imply a lower applicability of fractal geometry to these terrains. The one kilometer roughness amplitude map exhibits a tremendous amount of spatial detail and clearly delineates differing roughness terrains. The portions of Amazonis Planitia and southeast Elysium Planitia with enhanced fractal dimension have roughness amplitudes significantly below the global mean, while the Valles Marineris system, the circum-Argyre region, and the chaotic and heavily eroded terrains located along the crustal dichotomy boundary exhibit elevated roughness values. The Tharsis region is particularly rich in detail, displaying a wide range of spatially contiguous roughness provinces that are traceable to known surface units. Comparison of the roughness amplitude map to the MOLA pulse width-derived roughness data (75 meter baseline) reveals a strong correlation with a few notable exceptions. The circum-polar debris mantle located 30 to 45 degrees bilaterally from the equator and a small yet distinct terrain located northwest of Olympus Mons are both evident in the 75 m pulse width data but are not expressed in the longer wavelength roughness amplitude map. This implies that the surface processes responsible for producing these terrains are dominant only at shorter length scales.

Seelos, F. P.; Deal, K. S.; Arvidson, R. E.; Neumann, G. A.

2003-12-01

427

Optimal Padding for the Two-Dimensional Fast Fourier Transform  

NASA Technical Reports Server (NTRS)

One-dimensional Fast Fourier Transform (FFT) operations work fastest on grids whose size is divisible by a power of two. Because of this, padding grids (that are not already sized to a power of two) so that their size is the next highest power of two can speed up operations. While this works well for one-dimensional grids, it does not work well for two-dimensional grids. For a two-dimensional grid, there are certain pad sizes that work better than others. Therefore, the need exists to generalize a strategy for determining optimal pad sizes. There are three steps in the FFT algorithm. The first is to perform a one-dimensional transform on each row in the grid. The second step is to transpose the resulting matrix. The third step is to perform a one-dimensional transform on each row in the resulting grid. Steps one and three both benefit from padding the row to the next highest power of two, but the second step needs a novel approach. An algorithm was developed that struck a balance between optimizing the grid pad size with prime factors that are small (which are optimal for one-dimensional operations), and with prime factors that are large (which are optimal for two-dimensional operations). This algorithm optimizes based on average run times, and is not fine-tuned for any specific application. It increases the amount of times that processor-requested data is found in the set-associative processor cache. Cache retrievals are 4-10 times faster than conventional memory retrievals. The tested implementation of the algorithm resulted in faster execution times on all platforms tested, but with varying sized grids. This is because various computer architectures process commands differently. The test grid was 512 512. Using a 540 540 grid on a Pentium V processor, the code ran 30 percent faster. On a PowerPC, a 256x256 grid worked best. A Core2Duo computer preferred either a 1040x1040 (15 percent faster) or a 1008x1008 (30 percent faster) grid. There are many industries that can benefit from this algorithm, including optics, image-processing, signal-processing, and engineering applications.

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

2011-01-01

428

Optical properties of two-dimensional metamaterial photonic crystals  

SciTech Connect

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

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

2013-12-14

429

Soliton nanoantennas in two-dimensional arrays of quantum dots  

E-print Network

We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schr\\"{o}dinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D \\textit{% soliton-based nano-antenna}, which should be stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.

Gligori?, G; Hadžievski, Lj; Slepyan, G Ya; Malomed, B A

2015-01-01

430

Topological gauged WZW model and two-dimensional gravity  

NASA Astrophysics Data System (ADS)

We study the "topological gauged WZW model associated with SU(2)/U(1)", which is defined as the twisted version of the corresponding supersymmetric gauged WZW model. It is shown that this model is equivalent to a topological conformal field theory characterized by two independent topological conformal algebras, one of which is the "twisted Kazama-Suzuki type" and the other is the "twisted Coulomb gas type". We further show that our formalism of this gauged WZW model naturally reduces to the well-known formulations of two-dimensional gravity coupled with conformal matter; one of the gauge choices leads to Li's theory, and the alternative choices lead to the KPZ theory or the DDK (Liouville) theory. In the appendix we argue on a possibility of deriving such topological conformal models from the G/G-gauged WZW models.

Nakatsu, Toshio; Sugawara, Yuji

1992-10-01

431

Higgs mode in a two-dimensional superfluid.  

PubMed

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

Pollet, L; Prokof'ev, N

2012-07-01

432

Two-dimensional electronic spectroscopy with birefringent wedges  

NASA Astrophysics Data System (ADS)

We present a simple experimental setup for performing two-dimensional (2D) electronic spectroscopy in the partially collinear pump-probe geometry. The setup uses a sequence of birefringent wedges to create and delay a pair of phase-locked, collinear pump pulses, with extremely high phase stability and reproducibility. Continuous delay scanning is possible without any active stabilization or position tracking, and allows to record rapidly and easily 2D spectra. The setup works over a broad spectral range from the ultraviolet to the near-IR, it is compatible with few-optical-cycle pulses and can be easily reconfigured to two-colour operation. A simple method for scattering suppression is also introduced. As a proof of principle, we present degenerate and two-color 2D spectra of the light-harvesting complex 1 of purple bacteria.

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

2014-12-01

433

Two-dimensional electronic spectroscopy with birefringent wedges.  

PubMed

We present a simple experimental setup for performing two-dimensional (2D) electronic spectroscopy in the partially collinear pump-probe geometry. The setup uses a sequence of birefringent wedges to create and delay a pair of phase-locked, collinear pump pulses, with extremely high phase stability and reproducibility. Continuous delay scanning is possible without any active stabilization or position tracking, and allows to record rapidly and easily 2D spectra. The setup works over a broad spectral range from the ultraviolet to the near-IR, it is compatible with few-optical-cycle pulses and can be easily reconfigured to two-colour operation. A simple method for scattering suppression is also introduced. As a proof of principle, we present degenerate and two-color 2D spectra of the light-harvesting complex 1 of purple bacteria. PMID:25554272

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

2014-12-01

434

General stability criterion of two-dimensional inviscid parallel flow  

E-print Network

General stability criterions of two-dimensional inviscid parallel flow are obtained analytically for the first time. First, a criterion for stability is found as $\\frac{U''}{U-U_s}>-\\mu_1$ everywhere in the flow, where $U_s$ is the velocity at inflection point, $\\mu_1$ is eigenvalue of Poincar\\'{e}'s problem. Second, we also prove a principle that the flow is stable, if and only if all the disturbances with $c_r=U_s$ are neutrally stable. Finally, following this principle, a criterion for instability is found as $\\frac{U''}{U-U_s}<-\\mu_1$ everywhere in the flow. These results extend the former theorems obtained by Rayleigh, Tollmien and Fj{\\o}rtoft and will lead future works to investigate the mechanism of hydrodynamic instability.

Liang Sun

2005-12-27

435

Application of Two Dimensional Flourescence Spectroscopy to Transition Metal Clusters.  

NASA Astrophysics Data System (ADS)

Determining the physical properties (bond lengths, angles, dipole moments, etc) of transition metal oxides and dioxides is relevant to catalysis, high temperature chemistry, materials science and astrophysics. Analysis of optical spectra is a convenient method for extraction of physical properties, but can be difficult because of the density of electronic states and in the case of the dioxides, presence of both the oxide and superoxide forms. Here we demonstrate the application of two dimensional fluorescence spectroscopy for aiding in the assignment and analysis. Particular attention will be paid to the spectroscopy of first row transition metal monoxides and dioxides of Nickel, NiO and NiO_2, and Manganese, MnO. Furthermore, the application of this technique to discovering the spectrum of other transition metal systems such as Metal-dicarbides will be outlined. N.J. Reilly, T.W. Schmidt, S.H. Kable, J. Phys. Chem. A., 110(45), 12355-12359, 2006

Kokkin, Damian L.; Steimle, Timothy

2014-06-01

436

Monitoring intracellular protein profiles with two-dimensional gel electrophoresis.  

PubMed

Two-dimensional polyacrylamide gel electrophoresis (2D PAGE) is a method of separating complex protein mixtures, such as whole cell extracts, on the basis of protein isoelectric point and molecular weight. In bioprocess engineering, conventional 2D PAGE has tremendous potential to yield detailed information on the intracellular effect of various process conditions. It has been used in our work to examine global intracellular changes occurring in a typical cycloheximide fermentation and to look at the feedback regulatory behavior of cycloheximide biosynthesis. Application of the technique for bioprocess monitoring will require that the time necessary for preparation of a 2D electropherogram be substantially shortened. This may be accomplished by performing the separation on a miniature scale or eventually by use of capillary electrophoresis for one or more of the separations. Advantages and disadvantages of these two approaches are discussed. PMID:1368457

Dykstra, K H; Wang, H Y

1992-01-01

437

Symmetry breaking of solitons in two-dimensional complex potentials  

NASA Astrophysics Data System (ADS)

Symmetry breaking is reported for continuous families of solitons in the nonlinear Schrödinger equation with a two-dimensional complex potential. This symmetry breaking is forbidden in generic complex potentials. However, for a special class of partially parity-time-symmetric potentials, it is allowed. At the bifurcation point, two branches of asymmetric solitons bifurcate out from the base branch of symmetry-unbroken solitons. Stability of these solitons near the bifurcation point are also studied, and two novel properties for the bifurcated asymmetric solitons are revealed. One is that at the bifurcation point, zero and simple imaginary linear-stability eigenvalues of asymmetric solitons can move directly into the complex plane and create oscillatory instability. The other is that the two bifurcated asymmetric solitons, even though having identical powers and being related to each other by spatial mirror reflection, can possess different types of unstable eigenvalues and thus exhibit nonreciprocal nonlinear evolutions under random-noise perturbations.

Yang, Jianke

2015-02-01

438

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

439

Two-dimensional heterostructures: fabrication, characterization, and application  

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

440

Two-dimensional nonlinear map characterized by tunable Lévy flights.  

PubMed

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

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

2014-10-01

441

Extracting joint weak values from two-dimensional spatial displacements  

E-print Network

The joint weak value is a counterfactual quantity related to quantum correlations and quantum dynamics, which can be retrieved via weak measurements, as initiated by Aharonov and colleagues. In this Rapid Communication, we provide a full analytical extension of the method described by Puentes et al. [Phys. Rev. Lett. 109, 040401 (2012)], to extract the joint weak values of single-particle operators from two-dimensional spatial displacements of Laguerre-Gauss probe states, for the case of azimuthal index |l|>1. This method has a statistical advantage over previous ones since information about the conjugate observable, i.e., the momentum displacement of the probe, is not required. Moreover, we demonstrate that under certain conditions, the joint weak value can be extracted directly from spatial displacements without any additional data processing.

Hirokazu Kobayashi; Graciana Puentes; Yutaka Shikano

2012-11-06

442

Two-dimensional skyrmion lattice in a nanopatterned magnetic film  

NASA Astrophysics Data System (ADS)

We study the possibility of a two-dimensional (2D) skyrmion crystal stabilization in a magnetic film with perpendicular anisotropy in the absence of Dzyaloshinskii-Moriya interaction by creating the regular array of blind holes or stubs. By micromagnetic simulation we demonstrate that skyrmions can be stable in the patterned films with the parameters of ordinary materials such as CoPt, FePt, or FePd. The skyrmion lattices can be initialized in the system by simple magnetization in the uniform external magnetic field. At the zero external field the skyrmion helicity depends on the geometry of the blind hole or stub but also can be tuned by applying the field. The suggested method makes it possible to create dense enough (with the period less than 100 nm) skyrmion lattices which are important to carry out transport measurements.

Sapozhnikov, M. V.; Ermolaeva, O. L.

2015-01-01

443

Random diffusion and cooperation in continuous two-dimensional space.  

PubMed

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

444

Superfluid response of two-dimensional parahydrogen clusters in confinement.  

PubMed

We study by computer simulations the effect of confinement on the superfluid properties of small two-dimensional (2D) parahydrogen clusters. For clusters of fewer than twenty molecules, the superfluid response in the low temperature limit is found to remain comparable in magnitude to that of free clusters, within a rather wide range of depth and size of the confining well. The resilience of the superfluid response is attributable to the "supersolid" character of these clusters. We investigate the possibility of establishing a bulk 2D superfluid "cluster crystal" phase of p-H2, in which a global superfluid response would arise from tunnelling of molecules across adjacent unit cells. The computed energetics suggests that for clusters of about ten molecules, such a phase may be thermodynamically stable against the formation of the equilibrium insulating crystal, for values of the cluster crystal lattice constant possibly allowing tunnelling across adjacent unit cells. PMID:25854239

Idowu, Saheed; Boninsegni, Massimo

2015-04-01

445

Exit Time Distribution in Spherically Symmetric Two-Dimensional Domains  

NASA Astrophysics Data System (ADS)

The distribution of exit times is computed for a Brownian particle in spherically symmetric two-dimensional domains (disks, angular sectors, annuli) and in rectangles that contain an exit on their boundary. The governing partial differential equation of Helmholtz type with mixed Dirichlet-Neumann boundary conditions is solved analytically. We propose both an exact solution relying on a matrix inversion, and an approximate explicit solution. The approximate solution is shown to be exact for an exit of vanishing size and to be accurate even for large exits. For angular sectors, we also derive exact explicit formulas for the moments of the exit time. For annuli and rectangles, the approximate expression of the mean exit time is shown to be very accurate even for large exits. The analysis is also extended to biased diffusion. Since the Helmholtz equation with mixed boundary conditions is encountered in microfluidics, heat propagation, quantum billiards, and acoutics, the developed method can find numerous applications beyond exit processes.

Rupprecht, J.-F.; Bénichou, O.; Grebenkov, D. S.; Voituriez, R.

2015-01-01

446

The Absorbing Properties of Two-Dimensional Plasma Photonic Crystals  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

447

Spontaneous motion on two-dimensional continuous attractors.  

PubMed

Attractor models are simplified models used to describe the dynamics of firing rate profiles of a pool of neurons. The firing rate profile, or the neuronal activity, is thought to carry information. Continuous attractor neural networks (CANNs) describe the neural processing of continuous information such as object position, object orientation, and direction of object motion. Recently it was found that in one-dimensional CANNs, short-term synaptic depression can destabilize bump-shaped neuronal attractor activity profiles. In this article, we study two-dimensional CANNs with short-term synaptic depression and spike frequency adaptation. We found that the dynamics of CANNs with short-term synaptic depression and CANNs with spike frequency adaptation are qualitatively similar. We also found that in both kinds of CANNs, the perturbative approach can be used to predict phase diagrams, dynamical variables, and speed of spontaneous motion. PMID:25602773

Fung, C C Alan; Amari, S-I

2015-03-01

448

Tachyon hair on two-dimensional black holes  

SciTech Connect

Static black holes in two-dimensional string theory can carry tachyon hair. Configurations which are nonsingular at the event horizon have a nonvanishing asymptotic energy density. Such solutions can be smoothly extended through the event horizon and have a nonvanishing energy flux emerging from the past singularity. Dynamical processes will not change the amount of tachyon hair on a black hole. In particular, there will be no tachyon hair on a black hole formed in gravitational collapse if the initial geometry is the linear dilaton vacuum. There also exist static solutions with a finite total energy, which have singular event horizons. Simple dynamical arguments suggest that black holes formed in gravitational collapse will not have tachyon hair of this type.

Peet, A.; Susskind, L.; Thorlacius, L. (Department of Physics, Stanford University, Stanford, California 94305 (United States))

1993-09-15

449

Dirac Cones in two-dimensional conjugated polymer networks  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

450

Wave propagation in two-dimensional periodic lattices.  

PubMed

Plane wave propagation in infinite two-dimensional periodic lattices is investigated using Floquet-Bloch principles. Frequency bandgaps and spatial filtering phenomena are examined in four representative planar lattice topologies: hexagonal honeycomb, Kagomé lattice, triangular honeycomb, and the square honeycomb. These topologies exhibit dramatic differences in their long-wavelength deformation properties. Long-wavelength asymptotes to the dispersion curves based on homogenization theory are in good agreement with the numerical results for each of the four lattices. The slenderness ratio of the constituent beams of the lattice (or relative density) has a significant influence on the band structure. The techniques developed in this work can be used to design lattices with a desired band structure. The observed spatial filtering effects due to anisotropy at high frequencies (short wavelengths) of wave propagation are consistent with the lattice symmetries. PMID:16642813

Phani, A Srikantha; Woodhouse, J; Fleck, N A

2006-04-01

451

Unsteady Shear Disturbances Within a Two Dimensional Stratified Flow  

NASA Technical Reports Server (NTRS)

The origin and evolution of shear disturbances within a stratified, inviscid, incompressible flow are investigated numerically by a Clebsch/Weber decomposition based scheme. In contrast to homogeneous flows, within which vorticity can be redistributed but not generated, the presence of a density stratification can render an otherwise irrotational flow vortical. In this work, a kinematic decomposition of the unsteady Euler equations separates the unsteady velocity field into rotational and irrotational components. The subsequent evolution of these components is used to study the influence various velocity disturbances have on both stratified and homogeneous flows. In particular, the flow within a two-dimensional channel is used to investigate the evolution of rotational disturbances, generated or convected, downstream from an unsteady inflow condition. Contrasting simulations of both stratified and homogeneous flows are used to distinguish between redistributed inflow vorticity and that which is generated by a density stratification.

Yokota, Jeffrey W.

1992-01-01

452

Collisionless reconnection in two-dimensional magnetotail equilibria  

NASA Technical Reports Server (NTRS)

A two-dimensional particle simulation model based on the Darwin approximation to Maxwell's equations for studying collisionless reconnection in the magnetotail has been developed. Simulations of the pure ion tearing mode in a thin current sheet with normal B(z) field component demonstrate that in this limit this mode grows more slowly than expected based on previous analytic estimates. The saturation level of the tearing instability greatly surpasses estimates based on a simple trapping argument. The effect of the normal field component on the evolution of the tearing instability is considered. It is found that a normal field of even a few percent on axis strongly inhibits the growth of the instability.

Pritchett, P. L.; Coroniti, F. V.; Pellat, R.; Karimabadi, H.

1991-01-01

453

Self-organized defect strings in two-dimensional crystals.  

PubMed

Using experiments with single-particle resolution and computer simulations we study the collective behavior of multiple vacancies injected into two-dimensional crystals. We find that the defects assemble into linear strings, terminated by dislocations with antiparallel Burgers vectors. We show that these defect strings propagate through the crystal in a succession of rapid one-dimensional gliding and rare rotations. While the rotation rate decreases exponentially with the number of defects in the string, the diffusion constant is constant for large strings. By monitoring the separation of the dislocations at the end points, we measure their effective interactions with high precision beyond their spontaneous formation and annihilation, and we explain the double-well form of the dislocation interaction in terms of continuum elasticity theory. PMID:24483371

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

2013-12-01

454

Topological Hofstadter insulators in a two-dimensional quasicrystal  

NASA Astrophysics Data System (ADS)

We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.

Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre

2015-02-01

455

A renormalization group analysis of two-dimensional magnetohydrodynamic turbulence  

NASA Technical Reports Server (NTRS)

The renormalization group (RNG) method is used to study the physics of two-dimensional (2D) magnetohydrodynamic (MHD) turbulence. It is shown that, for a turbulent magnetofluid in two dimensions, no RNG transformation fixed point exists on account of the coexistence of energy transfer to small scales and mean-square magnetic flux transfer to large scales. The absence of a fixed point renders the RNG method incapable of describing the 2D MHD system. A similar conclusion is reached for 2D hydrodynamics, where enstrophy flows to small scales and energy to large scales. These analyses suggest that the applicability of the RNG method to turbulent systems is intrinsically limited, especially in the case of systems with dual-direction transfer.

Liang, Wenli Z.; Diamond, P. H.

1993-01-01

456

Nanoelectronic circuits based on two-dimensional atomic layer crystals  

NASA Astrophysics Data System (ADS)

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.

Lee, Seunghyun; Zhong, Zhaohui

2014-10-01

457

Bosonization and the Berry connection in two-dimensional QED  

NASA Astrophysics Data System (ADS)

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.; Wong, Gabriel

2015-03-01

458

Two-dimensional NQR using ultra-broadband electronics.  

PubMed

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

Mandal, S; Song, Y-Q

2014-03-01

459

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

PubMed

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

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

2015-01-21

460

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

461

Time-evolving bubbles in two-dimensional stokes flow  

NASA Technical Reports Server (NTRS)

A general class of exact solutions is presented for a time evolving bubble in a two-dimensional slow viscous flow in the presence of surface tension. These solutions can describe a bubble in a linear shear flow as well as an expanding or contracting bubble in an otherwise quiescent flow. In the case of expanding bubbles, the solutions have a simple behavior in the sense that for essentially arbitrary initial shapes the bubble will asymptote an expanding circle. Contracting bubbles, on the other hand, can develop narrow structures ('near-cusps') on the interface and may undergo 'break up' before all the bubble-fluid is completely removed. The mathematical structure underlying the existence of these exact solutions is also investigated.

Tanveer, Saleh; Vasconcelos, Giovani L.

1994-01-01

462

Two dimensional heteronuclear complexes with cyanide and 4-aminomethylpyridine ligands  

NASA Astrophysics Data System (ADS)

Two new cyano-bridged two-dimensional heteronuclear complexes, [Cd(NH3)2(?-ampy)Ni(?-CN)2(CN)2]n (1) and [Cd(H2O)2(?-ampy)Pt(?-CN)2(CN)2]n (2) (ampy = 4-aminomethylpyridine), were synthesized and characterized by FT-IR and Raman spectroscopic, thermal (TG, DTG and DTA) and elemental analyses and single crystal X-ray diffraction techniques. They crystallize in the triclinic system and P-1 space group. The Ni(II) or Pt(II) ions are four coordinate with four cyanide-carbon atoms in a square planar geometry and the Cd(II) ion exhibits a distorted octahedral coordination by two different N-atoms from two symmetrically equivalent ampy ligands, two ammine or aqua ligands and two bridging cyano groups.The most important features of the complexes are the presence of obvious M⋯? (M = Ni(II) or Pt(II)) interactions.

Karaa?aç, Dursun; Kürkçüo?lu, Güne? Süheyla; Ye?ilel, Okan Zafer; MuratTa?

2014-09-01

463

Search for conformal invariance in compressible two-dimensional turbulence  

E-print Network

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

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

2011-10-11

464

Exciton spectra in two-dimensional graphene derivatives  

NASA Astrophysics Data System (ADS)

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

Huang, Shouting; Liang, Yufeng; Yang, Li

2013-08-01

465

Ultrasonic transducer with a two-dimensional Gaussian field profile  

NASA Technical Reports Server (NTRS)

A transducer is described which generates a two-dimensional Gaussian field by controlling both the position of multiple circular electrodes and the voltage applied to each electrode. The transducer is constructed by depositing concentric rings electrodes onto one flat surface of a circular piezoelectric crystal disk and attaching the rings to an impedance matching network which acts as a voltage divider. Geometrical inter-ring separations and electrical inter-ring impedances are designed to minimize the error between the generated acoustic field, modeled as a piecewise linear function, and the desired Gaussian distribution. Total mean squared error between the averaged far-field data and a Gaussian shape is less than two percent.

Claus, R. O.; Zerwekh, P. S.

1983-01-01

466

Shock wave in a two-dimensional dusty plasma crystal  

SciTech Connect

Two-dimensional (2D) shock structures of longitudinal dust lattice wave (LDLW) in a hexagonal Yukawa crystal are studied. The nonlinear evolution equation derived for dusty plasma crystal is found to be a 2D Burgers' equation, where the Burgers' term, i.e., the dissipation is provided by ''hydrodynamic damping'' due to irreversible processes that take place within the system. Analytical and numerical solutions of this equation on the basis of crystal experimental parameters show the development of compressional shock structures of LDLW in 2D dusty plasma crystal. The shock strength decreases (increases) with the increase in lattice parameter {kappa} (angle of propagation of the nonlinear wave). The results are discussed in the context of 2D monolayer hexagonal dusty plasma crystal experiments.

Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009 (India)

2009-10-15

467

Spin precession in inversion-asymmetric two-dimensional systems  

NASA Astrophysics Data System (ADS)

We present a theoretical method to calculate the expectation value of spin in an inversion-asymmetric two-dimensional (2D) system with respect to an arbitrarily spin-polarized electron state, injected via an ideal point contact. The 2D system is confined in a [0 0 1]-grown quantum well, where both the Rashba and the Dresselhaus spin-orbit couplings are taken into account. The obtained analytical results allow more concrete description of the spatial behaviors of the spin precession caused individually by the Rashba and the Dresselhaus terms. Applying the calculation on the Datta-Das spin-FET, whose original design considers only the Rashba effect inside the channel, we investigate the possible influence due to the Dresselhaus spin-orbit coupling. Concluded solution is the choice of ±[1±10], in particular [1 1 0], as the channel direction.

Liu, Ming-Hao; Chang, Ching-Ray

2006-09-01

468

Two-dimensional modeling of nickel electrodeposition in LIGA microfabrication.  

SciTech Connect

Two-dimensional processes of nickel electrodeposition in LIGA microfabrication were modeled using the finite-element method and a fully coupled implicit solution scheme via Newtons technique. Species concentrations, electrolyte potential, flow field, and positions of the moving deposition surfaces were computed by solving the species-mass, charge, and momentum conservation equations as well as pseudo-solid mesh-motion equations that employ an arbitrary Lagrangian-Eulerian (ALE) formulation. Coupling this ALE approach with repeated re-meshing and re-mapping makes it possible to track the entire transient deposition processes from start of deposition until the trenches are filled, thus enabling the computation of local current densities that influence the microstructure and functional/mechanical properties of the deposit.

Evans, Gregory Herbert (Sandia National Laboratories, Livermore, CA); Chen, Ken Shuang

2003-07-01

469

Two-dimensional plasma photonic crystals in dielectric barrier discharge  

SciTech Connect

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

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

2010-11-15

470

Two dimensional radiated power diagnostics on Alcator C-Mod  

SciTech Connect

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

471

Experimental implementations of two-dimensional fourier transform electronic spectroscopy.  

PubMed

Two-dimensional electronic spectroscopy (2DES) reveals connections between an optical excitation at a given frequency and the signals it creates over a wide range of frequencies. These connections, manifested as cross-peak locations and their lineshapes, reflect the underlying electronic and vibrational structure of the system under study. How these spectroscopic signatures evolve in time reveals the system dynamics and provides a detailed picture of coherent and incoherent processes. 2DES is rapidly maturing and has already found numerous applications, including studies of photosynthetic energy transfer and photochemical reactions and many-body interactions in nanostructured materials. Many systems of interest contain electronic transitions spanning the ultraviolet to the near infrared and beyond. Most 2DES measurements to date have explored a relatively small frequency range. We discuss the challenges of implementing 2DES and compare and contrast different approaches in terms of their information content, ease of implementation, and potential for broadband measurements. PMID:25664841

Fuller, Franklin D; Ogilvie, Jennifer P

2015-04-01

472

Dispersion-free continuum two-dimensional electronic spectrometer  

PubMed Central

Electronic dynamics span broad energy scales with ultrafast time constants in the condensed phase. Two-dimensional (2D) electronic spectroscopy permits the study of these dynamics with simultaneous resolution in both frequency and time. In practice, this technique is sensitive to changes in nonlinear dispersion in the laser pulses as time delays are varied during the experiment. We have developed a 2D spectrometer that uses broadband continuum generated in argon as the light source. Using this visible light in phase-sensitive optical experiments presents new challenges in implementation. We demonstrate all-reflective interferometric delays using angled stages. Upon selecting an ~180 nm window of the available bandwidth at ~10 fs compression, we probe the nonlinear response of broadly absorbing CdSe quantum dots and electronic transitions of Chlorophyll a. PMID:24663470

Zheng, Haibin; Caram, Justin R.; Dahlberg, Peter D.; Rolczynski, Brian S.; Viswanathan, Subha; Dolzhnikov, Dmitriy S.; Khadivi, Amir; Talapin, Dmitri V.; Engel, Gregory S.

2015-01-01

473

Self-organized defect strings in two-dimensional crystals  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

474

A simple self-propelled two-dimensional micropositioner  

NASA Astrophysics Data System (ADS)

A quartz tube is propelled horizontally along a quartz track by the stick-slip inertial slider method, activated by the longitudinal mode of a piezoelectric tube mounted inside the quartz tube. Two-dimensional motion is achieved by rotation of the quartz tube, activated by the bending mode of the piezo. With a sample attached to the quartz tube, the device is an excellent replacement for the electrostatic-clamp type of walker used as the coarse approach mechanism in scanning probe microscopes (SPMs). Alternatively, by attaching the tip (or sample) to the piezo tube, the device can function as a very simple SPM in which the same piezo tube is used for coarse approach and for scanning. The device performs reliably in air and high vacuum, and is ultrahigh vacuum compatible. Step sizes from 10 to 1000 nm, and speeds up to 0.2 mm/s are possible.

Blackford, B. L.

1993-05-01

475

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

476

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

477

Quantum Emission from Two-Dimensional Black Holes  

E-print Network

We investigate Hawking radiation from two-dimensional dilatonic black holes using standard quantization techniques. In the background of a collapsing black hole solution the Bogoliubov coefficients can be exactly determined. In the regime after the black hole has settled down to an `equilibrium' state but before the backreaction becomes important these give the known result of a thermal distribution of Hawking radiation at temperature lambda/(2pi). The density matrix is computed in this regime and shown to be purely thermal. Similar techniques can be used to derive the stress tensor. The resulting expression agrees with the derivation based on the conformal anomaly and can be used to incorporate the backreaction. Corrections to the thermal density matrix are also examined, and it is argued that to leading order in perturbation theory the effect of the backreaction is to modify the Bogoliubov transformation, but not in a way that restores information lost to the black holes.

Steven B. Giddings; W. M. Nelson

2009-11-27

478

Two-dimensional freezing criteria for crystallizing colloidal monolayers  

SciTech Connect

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

479

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

480

The Two-Dimensional Euler Equations on Singular Domains  

NASA Astrophysics Data System (ADS)

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

Gérard-Varet, David; Lacave, Christophe

2013-07-01

481

Two-dimensional hexagonal V2O nanosheet and nanoribbons  

NASA Astrophysics Data System (ADS)

A novel two-dimensional hexagonal V2O was proposed and investigated through first-principles calculations. The hexagonal V2O nanosheet exhibited a V–O–V sandwich structure. The stability of monolayer V2O was verified by formation energy and phonon frequency calculations. The calculations of electronic properties using a hybrid density functional method indicate that monolayer V2O is a nonmagnetic metal. However, the zigzag nanoribbon exhibited robust edge magnetism, while the armchair nanoribbon was found to be a nonmagnetic semiconductor with a direct band gap. The variety of electronic properties of monolayer V2O nanosheets and nanoribbons opens up tremendous opportunities for nano-electronic and spintronic devices.

Tang, Zhen-Kun; Geng, Wei; Zhang, Yan-Ning; Zhang, Deng-Yu; Liu, Li-Min

2015-03-01

482

Electrical resistance of complex two-dimensional structures of loops  

NASA Astrophysics Data System (ADS)

This work presents a study of the dc electrical resistance of a recently discovered hierarchical two-dimensional system which has a complex topology consisting of a distribution of disordered macroscopic loops with no characteristic size and a distribution of several types of contacts between loops. In addition to its intrinsic interest in the important context of low-dimensional systems and crumpled systems, the structures under study are of relevance in a number of areas including soft condensed matter and packing of DNA in viral capsids. In the particular case discussed here, the loops are made of layers of graphite with a height of tens of nanometers deposited on a substrate of cellulose. Experiments with these systems indicate an anomalous electrical resistance of sub-diffusive type. The results reported here are explained with scaling arguments and computer simulation. A comparison with the dc electrical properties of percolation clusters is made, and some other experimental issues as future prospects are commented.

Gomes, M. A. F.; Hora, R. R.; Brito, V. P.

2011-06-01

483

Analysis of cancellation exponents in two-dimensional Vlasov turbulence  

SciTech Connect

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

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

2014-07-15

484

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

485

Topological states in two-dimensional optical lattices  

SciTech Connect

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

486

Magnetotunneling spectroscopy of chiral two-dimensional electron systems  

NASA Astrophysics Data System (ADS)

We present a theoretical study of momentum-resolved tunneling between parallel two-dimensional conductors whose charge carriers have a (pseudo)spin-1/2 degree of freedom that is strongly coupled to their linear orbital momentum. Specific examples are single- and bilayer graphene as well as single-layer molybdenum disulfide. Resonant behavior of the differential tunneling conductance exhibited as a function of an in-plane magnetic field and bias voltage is found to be strongly affected by the (pseudo)spin structure of the tunneling matrix. We discuss ramifications for the direct measurement of electronic properties such as Fermi surfaces and dispersion curves. Furthermore, using a graphene double-layer structure as an example, we show how magnetotunneling transport can be used to measure the pseudospin structure of tunneling matrix elements, thus enabling electronic characterization of the barrier material.

Pratley, L.; Zülicke, U.

2013-12-01

487

Remarks on the KLB theory of two-dimensional turbulence  

E-print Network

We study the inverse energy transfer in forced two-dimensional (2D) Navier--Stokes turbulence in a doubly periodic domain. It is shown that an inverse energy cascade that carries a nonzero fraction of the injected energy to the large scales via a power-law energy spectrum $\\propto k^{-\\alpha}$ requires that $\\alpha\\ge5/3$. This result is consistent with the classical theory of 2D turbulence that predicts a $k^{-5/3}$ inverse-cascading range, thus providing for the first time a rigorous basis for this important feature of the theory. We derive bounds for the Kolmogorov constant $C$ in the classical energy spectrum $E(k)=C\\epsilon^{2/3}k^{-5/3}$, where $\\epsilon$ is the energy injection rate. Issues related to Kraichnan's conjecture of energy condensation and to power-law spectra as the quasi-steady dynamics become steady are discussed.

Chuong V. Tran; Theodore G. Shepherd

2004-12-10

488

Dynamics of saturated energy condensation in two-dimensional turbulence  

NASA Astrophysics Data System (ADS)

In two-dimensional forced Navier-Stokes turbulence, energy cascades to the largest scales in the system to form a pair of coherent vortices known as the Bose condensate. We show, both numerically and analytically, that the energy condensation saturates and the system reaches a statistically stationary state. The time scale of saturation is inversely proportional to the viscosity and the saturation energy level is determined by both the viscosity and the force. We further show that, without sufficient resolution to resolve the small-scale enstrophy spectrum, numerical simulations can give a spurious result for the saturation energy level. We also find that the movement of the condensate is similar to the motion of an inertial particle with an effective drag force. Furthermore, we show that the profile of the saturated coherent vortices can be described by a Gaussian core with exponential wings.

Chan, Chi-kwan; Mitra, Dhrubaditya; Brandenburg, Axel

2012-03-01

489

Spectral energy transport in two-dimensional quantum vortex dynamics  

NASA Astrophysics Data System (ADS)

We explore the possible regimes of decaying two-dimensional quantum turbulence, and elucidate the nature of spectral energy transport by introducing a dissipative point-vortex model with phenomenological vortex-sound interactions. The model is valid for a large system with weak dissipation, and also for systems with strong dissipation, and allows us to extract a meaningful and unambiguous spectral energy flux associated with quantum vortex motion. For weak dissipation and large system size we find a regime of hydrodynamic vortex turbulence in which energy is transported to large spatial scales, resembling the phenomenology of the transient inverse cascade observed in decaying turbulence in classical incompressible fluids. For strong dissipation the vortex dynamics are dominated by dipole recombination and exhibit no appreciable spectral transport of energy.

Billam, T. P.; Reeves, M. T.; Bradley, A. S.

2015-02-01

490

Two-dimensional electron cyclotron emission imaging diagnostic for TEXTOR  

SciTech Connect

A two-dimensional electron cyclotron emission imaging (ECEI) diagnostic has been developed in which broad bandwidth radiation is collected by a vertically aligned mixer array and separated by frequency band. Using a 16 element array, and an 8 band receiver attached to each array element, time-resolved 16x8 images of electron temperature profiles and fluctuations of the TEXTOR plasma are acquired with vertical and horizontal channel spacings of 11 and 8 mm, and spot sizes of 13 and 9 mm, respectively. The system is wideband tunable from 95 to 130 GHz, and the focus location may be shifted horizontally via translation of one of the optical imaging elements. System design and laboratory testing details of the ECE Imaging optics and multichannel wideband electronics are presented, together with TEXTOR plasma data.

Wang, J.; Domier, C.W.; Xia, Z.G.; Liang, Y.; Luhmann, N.C. Jr.; Park, H.; Munsat, T.; Mazzucato, E.; Pol, M.J. van de; Classen, I.G.J.; Donne, A.J.H. [Department of Applied Science, 3001 Engineering Unit III, University of California, Davis, California 95616 (United States); Plasma Physics Laboratory, P.O. Box 451, Princeton University, Princeton, New Jersey 08543 (United States); FOM-Institute for Plasma Physics Rijnhuizen, Associatie EURATOM-FOM, Trilateral Euregio Cluster, 3430 BE, Nieuwegein (Netherlands)

2004-10-01

491

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

492

Two dimensional condensing flow in transonic turbine cascades  

NASA Astrophysics Data System (ADS)

A method for predicting spontaneous condensation in nozzles is presented. The conservation laws are formulated separately for each phase, and the vapor phase equations are integrated with a time marching scheme. An analytical solution of the liquid phase equations provides the droplet growth model. Calculations suggest that the two dimensional character of the flow plays a decisive role in the appearance of the liquid phase. The first droplets appear along the suction side where reversion to thermodynamic equilibrium can take place before the flow reaches the trailing edge. This is not so along the pressure side, where the steam remains subcooled because of the lower expansion rate. The heat released by the droplets affects the blade pressure distribution. When an aerodynamic shock impinges on the suction side in dry conditions, its strength can be substantially reduced by condensation. The outlet flow angle variation can reach several degrees with respect to the value computed for the same pressure ratio and superheated steam.

Snoeck, J.

493

Experimental observations of two dimensional blade-vortex interaction  

NASA Technical Reports Server (NTRS)

Blade-vortex interaction (BVI) is the source mechanism for a prominent impulsive noise created by rotorcraft. An experimental study of two dimensional BVI, a simplified case representing the most intense and impulsive noise generation condition, was performed to explore the fundamental physics associated with the blade-vortex interaction process. The purpose of this paper is to report cumulative results from this experimental study. The interaction process is shown to involve a combination of effects on the vortex including changes in trajectory and distortion of the vortex core shape. The blade involved undergoes significant transient loading. The effects of the interaction process on the blade and the vortex are shown to be increased by both reduction of blade-to-vortex spacing and increase in blade loading. Calculations of the acoustic field produced by the interaction using measured unsteady blade surface pressure data are presented and show acoustic waveforms similar to those obtained from model helicopter acoustic tests.

Booth, E. R., Jr.

1987-01-01

494

Microphase morphology in two dimensional fluids under lateral confinement  

E-print Network

We study the effects of confinement between two parallel walls on a two dimensional fluid with competing interactions which lead to the formation of particle micro-domains at the thermodynamic equilibrium (microphases or microseparation). The possibility to induce structural changes of the morphology of the micro-domains is explored, under different confinement conditions and temperatures. In presence of neutral walls, a switch from stripes of particles to circular clusters (droplets) occurs as the temperature decreases, which does not happen in bulk. While the passage from droplets to stripes, as the density increases, is a well known phenomenon, the change of the stripes into droplets as an effect of temperature is rather unexpected. Depending on the wall separation and on the wall-fluid interaction parameters, the stripes can switch from parallel to perpendicular to the walls and also a mixed morphology can be stable.

A. Imperio; L. Reatto

2007-09-13

495

Dynamics of a Two-Dimensional System of Quantum Dipoles  

SciTech Connect

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

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

2009-03-20

496

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

497

Dynamics of entanglement in a two-dimensional spin system  

NASA Astrophysics Data System (ADS)

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

Xu, Qing; Sadiek, Gehad; Kais, Sabre

2011-06-01

498

A two-dimensional global study of tropospheric ozone production  

SciTech Connect

The ozone production in the troposphere has been studied by means of a zonally averaged model which consists of a two-dimensional transport model, a description of the emissions, wet and dry deposition, and chemical processes of importance for the ozone production in the troposphere. The transport model describes a closed circulation in the meridional plane below 10 hPa and has a resolution and a numerical solution which compares favorable with earlier two-dimensional studies. The transport model also takes into account the fast vertical mixing in convective clouds and in frontal circulation. The production of nitrogen oxides by lightning has been coupled to the convection parameterization by assuming that the nitrogen oxides are transported vertically in the thunder clouds and released at the altitudes where boundary layer air entrained in the convective cells is released. Comparisons with observations indicate that the model is able to reproduce the seasonal variation of ozone in the meridional plane quite realistically. The calculated distributions of the chemical species which determine tropospheric ozone also compare well with measurements. The model estimated an annually averaged production of ozone in the troposphere over the northern hemisphere of 16.6 x 10(exp 10) molecules/sq cm/sec and over the southern hemisphere of 5.1 x 10(exp 10) molecules/sq cm/sec. The annually and globally averaged dry deposition is 14.9 x 10(exp 10) molecules/sq cm/sec, and the corresponding injection from the stratosphere is 4.1 x 10(exp 10) molecules/sq cm/sec. A 50% reduction of the man-made emissions from the industrialized society of nitrogen oxides resulted in a reduction in the ozone production of 2.9 x 10(exp 10) molecules/sq cm/sec in the lower troposphere over the northern hemisphere during the period of maximum photochemical production, June-August.

Strand, A.; Hov, O. [Nansen Environmental and Remote Sensing Center, Bergen (Norway)]|[Univ. of Bergen, Bergen (Norway)

1994-11-01

499

Performance Characteristics of Plane-Wall Two-Dimensional Diffusers  

NASA Technical Reports Server (NTRS)

Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery

Reid, Elliott G

1953-01-01

500

Two-dimensional Imaging Velocity Interferometry: Technique and Data Analysis  

SciTech Connect

We describe the data analysis procedures for an emerging interferometric technique for measuring motion across a two-dimensional image at a moment in time, i.e. a snapshot 2d-VISAR. Velocity interferometers (VISAR) measuring target motion to high precision have been an important diagnostic in shockwave physics for many years Until recently, this diagnostic has been limited to measuring motion at points or lines across a target. We introduce an emerging interferometric technique for measuring motion across a two-dimensional image, which could be called a snapshot 2d-VISAR. If a sufficiently fast movie camera technology existed, it could be placed behind a traditional VISAR optical system and record a 2d image vs time. But since that technology is not yet available, we use a CCD detector to record a single 2d image, with the pulsed nature of the illumination providing the time resolution. Consequently, since we are using pulsed illumination having a coherence length shorter than the VISAR interferometer delay ({approx}0.1 ns), we must use the white light velocimetry configuration to produce fringes with significant visibility. In this scheme, two interferometers (illuminating, detecting) having nearly identical delays are used in series, with one before the target and one after. This produces fringes with at most 50% visibility, but otherwise has the same fringe shift per target motion of a traditional VISAR. The 2d-VISAR observes a new world of information about shock behavior not readily accessible by traditional point or 1d-VISARS, simultaneously providing both a velocity map and an 'ordinary' snapshot photograph of the target. The 2d-VISAR has been used to observe nonuniformities in NIF related targets (polycrystalline diamond, Be), and in Si and Al.

Erskine, D J; Smith, R F; Bolme, C; Celliers, P; Collins, G

2011-03-23