A New Unconditionally Stable Algorithm for Steady-State Fluid Simulation of High Density Plasma Discharge

A new unconditionally stable algorithm for steady-state fluid simulation of high density plasma discharge is suggested. The physical origin of restriction on simulation time step is discussed and a new method to overcome it is explained. To compare the new method with previous other methods, a one-dimensional fluid simulation of inductively coupled plasma discharge is performed.     

Nonlinear Landau Damping in Spherically Symmetric Vlasov Poisson Systems

The Vlasov Poisson system is a partial differential equation widely used to describe collisionless plasma. It is formulated in a six-dimensional phase space, this prohibits a numerical solution on a complete phase space grid. In some applications, however, spherical symmetry is given, which introduces singularities into the Vlasov Poisson equation. We focus on such problems and propose a stable algorithm using accommodating boundaries. At first, the method is tested in the linear regime, where analytical solutions are available. Thereafter it is applied to large disturbances from equilibrium.     

Solitonic mechanism of structural transformations in a nondegenerate chain of particles with anharmonic and competing interactions

A new type of dynamics of an infinite atomic chain of particles with anharmonic and competing interactions is investigated in the general case when its homogeneous equilibrium states have different energies. Cooperative transformations realized by topological and nontopological solitons are revealed. The soliton velocity spectrum is calculated in the framework of an approximate continuous second-order theory. Solitons with vanishing velocity are shown to be in good asymptotical correspondence with the exact static solutions of the Reichert-Schilling model.     

Electron scattering by a ring-shaped barrier in magnetic fields

We investigate the transport phenomena through a region containing a ring-shaped barrier in a quasi-one-dimensional quantum wire in magnetic fields. The calculated magnetoconductance curve shows a periodic dip structure, which is superimposed upon by another quasi-periodic dip structure. The current distributions for resonant states and the magnetoconductance features are well explained on the basis of the magnetic field dependence of the eigenvalue in the two-dimensional system.     

Investigation of transmit and receive performance at the fundamental and third harmonic resonance frequency of a medical ultrasound transducer

In this study, the phenomenon of higher harmonic thickness resonance of a piezoelectric transducer was used to investigate potentially additional sensitivity at the third harmonic frequency for conventional medical transducers. The motivation for this research is that some applications in medical ultrasound (e.g. third harmonic transmit phasing and contrast imaging) need probes which are sensitive around both the fundamental and third harmonic frequencies, and that these higher harmonic thickness modes, although often considered as undesired, might be used beneficially. The novelty aspect in this study is the presented transmit and receive potential at both the fundamental and third harmonic of a conventional cardiac probe with modified electrical tuning. Elements of an experimental PZT-based phased-array probe (f_c = 3 MHz, 64 elements, element width = 0.3 mm, elevation aperture = 13 mm) were electrically retuned with series inductors around the third harmonic resonance frequency at 10 MHz. Hydrophone measurements with 10-MHz-tuned elements showed that, as compared to a conventionally tuned element, the transmit transfer function at the third harmonic increased more than 23 dB, while the sensitivity at the fundamental frequency was only 6 dB lower. Pulse-echo measurements showed that the two-way transfer function of a 10-MHz-tuned element resulted in 20 dB increased sensitivity around the third harmonic as compared to an untuned element. Simulated transfer functions, from both a 1D KLM and 2D finite element model of an element of the experimental array transducer, confirmed the measured sensitivity peaks at the fundamental and third harmonic. In conclusion, this study demonstrated the effect of changing the electrical tuning on a conventional array transducer which increased the sensitivity around the third harmonic resonance frequency, while maintaining good sensitivity at the fundamental frequency.     

A Roe Scheme for Ideal MHD Equations on 2D Adaptively Refined Triangular Grids

In this paper we present a second order finite volume method for the resolution of the bidimensional ideal MHD equations on adaptively refined triangular meshes. Our numerical flux function is based on a multidimensional extension of the Roe scheme proposed by Cargo and Gallice for the 1D MHD system. If the mesh is only composed of triangles, our scheme is proved to be weakly consistent with the condition …B=0. This property fails on a cartesian grid. The efficiency of our refinement procedure is shown on 2D MHD shock capturing simulations. Numerical results are compared in case of the interaction of a supersonic plasma with a cylinder on the adapted grid and several non-refined grids. We also present a mass loading simulation which corresponds to a 2D version of the interaction between the solar wind and a comet.     

The beam propagation factors and the kurtosis parameters of a Lorentz beam

Based on the second-order moments, the beam propagation factors and the kurtosis parameters of a Lorentz beam have been investigated. The M² value of a Lorentz beam is verified to be . The analytical expressions of the kurtosis parameters have been derived. The kurtosis parameter varies upon the propagation, and it is decided by two ratios z/z_rx and z/z_ry. The kurtosis parameter versus the two ratios z/z_rx and z/z_ry is plotted and discussed in detail. This work is of benefit to the practical application of laser sources that produce highly divergent beams.     

Equivalence of star products on a symplectic manifold; an introduction to Deligne''s ech cohomology classes

These notes grew out of the Quantisation Seminar 1997–1998 on Deligne's paper [P. Deligne, Déformations de l'algèbre des fonctions d'une variété symplectique: Comparison entre Fedosov et De Wilde, Lecomte, Selecta Math. (New Series) 1 (1995) 667–697] and the lecture of the first author in the Workshop on Quantisation and Momentum Maps at the University of Warwich in December 1997.We recall the definitions of the cohomology classes introduced by Deligne for equivalence classes of differential star products on a symplectic manfold and show the properties of the relations between these classes by elementary methods based on ech cohomology.     

Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007： a New s- and r-Process Paradigm

The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity [Fe/H] = -2.0, which is just at the upper limit of the metallicity for the observed double-enhanced stars. Using a parametric model, we find that almost all s-elements were made in a single neutron exposure. This star should be a member of a post-commonenvelope binary. After the s-process material has experienced only one neutron exposure in the nucleosynthesis region and is dredged-up to its envelope, the AGB evolution is terminated by the onset of common-envelope evolution. Based on the high radial-velocity of HE 1305-0007, we speculate that the star could be a runaway star from a binary system, in which the AIC event has occurred and produced the r-process elements.     

Robust profilometer for the measurement of 3-D object shapes based on a regularized phase tracker

A robust profilometer is proposed to measure 3-D object shapes based on a regularized phase tracker that is capable of demodulating fringe patterns with a high noise presence and broad bandwidth due to the object shape. As shown herein, the technique acts as an adaptive filter and is capable of giving the detected phase continuously so that no further unwrapping process is required. Experimental results of real surface profiles are presented.     

Design and implementation of a protection system for NMR spectrometers

We have implemented a scheme, SPECMON, for monitoring various parameters of a spectrometer, such as nitrogen pressure and sample temperature, and taking corrective action. The scheme is based on considerations of protection management which are of general application. Evaluation of the spectrometer state is incorporated in macros of the application software (VNMR) and is therefore very flexible. In contrast, corrective action is limited to the single one which is deemed fully safe: complete shutdown of the spectrometer and logging. Shutdown is implemented by a minor hardware modification of the spectrometer: the introduction of a second input to a relay already present for protection of the spectrometer power supply. Monitoring is handled by the host computer, and the shutdown command is transmitted via control lines of its series port, independent of the standard connection between the host computer and the NMR system console. The monitoring system (software and hardware) is unobtrusive in normal conditions, and it can be tested without affecting the operation of the spectrometer.     

Signal-to-noise ratio enhancement based on wavelet filtering in ultrasonic testing

In ultrasonic non-destructive testing of materials with a coarse-grained structure the scattering from the grains causes backscattering noise, which masks flaw echoes in the measured signal. Several filtering methods have been proposed for improving the signal-to-noise ratio. In this paper we present a comparative study of methods based on the wavelet transform. Experiments with stationary, discrete and wavelet packet de-noising are evaluated by means of signal-to-noise ratio enhancement. Measured and simulated ultrasonic signals are used to verify the proposed de-noising methods. For comparison, we use signal-to-noise ratio enhancement related to fault echo amplitudes and filtering efficiency specific for ultrasonic signals. The best results in our setup were achieved with the wavelet packet de-noising method.     

Model Photosphere of a Magnetic White Dwarf

We consider a self-consistent model of an isothermal photosphere of a magnetic white dwarf, in which the effect of the cyclotron radiation pressure on the plasma distribution is taken into account. We determine the values of the magnetic field and temperature of the star at which the scale height of the plasma density in the upper photosphere becomes comparable to the size of gyroresonance layer, and thus conditions favoring the outflow of the photospheric plasma into the magnetosphere are realized.     

Modeling Three-Dimensional Multiphase Flow Using a Level Contour Reconstruction Method for Front Tracking without Connectivity

Three-dimensional multiphase flow and flow with phase change are simulated using a simplified method of tracking and reconstructing the phase interface. The new level contour reconstruction technique presented here enables front tracking methods to naturally, automatically, and robustly model the merging and breakup of interfaces in three-dimensional flows. The method is designed so that the phase surface is treated as a collection of physically linked but not logically connected surface elements. Eliminating the need to bookkeep logical connections between neighboring surface elements greatly simplifies the Lagrangian tracking of interfaces, particularly for 3D flows exhibiting topology change. The motivation for this new method is the modeling of complex three-dimensional boiling flows where repeated merging and breakup are inherent features of the interface dynamics. Results of 3D film boiling simulations with multiple interacting bubbles are presented. The capabilities of the new interface reconstruction method are also tested in a variety of two-phase flows without phase change. Three-dimensional simulations of bubble merging and droplet collision, coalescence, and breakup demonstrate the new method's ability to easily handle topology change by film rupture or filamentary breakup. Validation tests are conducted for drop oscillation and bubble rise. The susceptibility of the numerical method to parasitic currents is also thoroughly assessed.     

On Wigner functions and a damped star product in dissipative phase-space quantum mechanics

Dito and Turrubiates recently introduced an interesting model of the dissipative quantum mechanics of a damped harmonic oscillator in phase space. Its key ingredient is a non-Hermitian deformation of the Moyal star product with the damping constant as deformation parameter. We compare the Dito-Turrubiates scheme with phase-space quantum mechanics (or deformation quantization) based on other star products, and extend it to incorporate Wigner functions. The deformed (or damped) star product is related to a complex Hamiltonian, and so necessitates a modified equation of motion involving complex conjugation. We find that with this change the Wigner function satisfies the classical equation of motion. This seems appropriate since non-dissipative systems with quadratic Hamiltonians share this property.     

Kaon and antikaon optical potentials in isospin asymmetric hyperonic matter

The medium modifications of the energies of kaons and antikaons in isospin asymmetric hyperonic matter are investigated using a chiral SU(3) model. The isospin-dependent medium effects are important for asymmetric heavy-ion collision experiments, as well as relevant for the neutron star phenomenology as the bulk matter in the interior of the neutron star is highly isospin asymmetric. The effects of hyperons on the medium modifications of the kaons and antikaons in the strange hadronic matter are investigated in the present work and are seen to be appreciable for hadronic matter with large strangeness fractions. The study of the K -mesons in the asymmetric strange hadronic matter can be especially relevant for the compressed strange baryonic matter which can result from asymmetric heavy-ion collision experiments in the future accelerator facility FAIR at GSI.     

The weak electroproduction of Σ in electron–proton scattering

We obtain differential cross sections for the reaction e⁻+p→Σ⁰+ν_e, for incident electron energies from 0.5 GeV to 6.0 GeV. This calculation is phenomenologically based and makes use of SU(3) and SU(2) relations. We obtain contributions of the individual form factors to the differential cross section and show that the vector current form factor dominates in the region of observability. We also obtain reaction rates for a standard set of conditions. Finally we compare this case with that for Λ production and discuss what might be learned from this reaction concerning the structure of the weak, strangeness changing, hadronic current.     

An azo-isomerization-induced Freedericksz transition of a nematic liquid crystal

We observed an azo-isomerization-induced Freedericksz transition of the 5CB liquid crystal doped with 1% double-azo. In experiment, we found that the Freedericksz transition threshold occurred at optical intensity level of 0.3 mW/mm² for the 12.5 μm-thickness planar alignment doped 5CB, which is four orders of magnitude lower as that for the pure 5CB. Using optical phase retardation, we measured the relations between the Freedericksz transition threshold and the pump beam polarization. The maximum twist angle of liquid crystal molecules under different pump beam intensity is given. The experiment indicated that trans–cis isomerization plays an important role in the decrease of the Freedericksz transition threshold.     

Implementation Aspects of 3D Lattice-BGK: Boundaries, Accuracy, and a New Fast Relaxation Method

In many realistic fluid-dynamical simulations the specification of the boundary conditions, the error sources, and the number of time steps to reach a steady state are important practical considerations. In this paper we study these issues in the case of the lattice-BGK model. The objective is to present a comprehensive overview of some pitfalls and shortcomings of the lattice-BGK method and to introduce some new ideas useful in practical simulations. We begin with an evaluation of the widely used bounce-back boundary condition in staircase geometries by simulating flow in an inclined tube. It is shown that the bounce-back scheme is first-order accurate in space when the location of the non-slip wall is assumed to be at the boundary nodes. Moreover, for a specific inclination angle of 45 degrees, the scheme is found to be second-order accurate when the location of the non-slip velocity is fitted halfway between the last fluid nodes and the first solid nodes. The error as a function of the relaxation parameter is in that case qualitatively similar to that of flat walls. Next, a comparison of simulations of fluid flow by means of pressure boundaries and by means of body force is presented. A good agreement between these two boundary conditions has been found in the creeping-flow regime. For higher Reynolds numbers differences have been found that are probably caused by problems associated with the pressure boundaries. Furthermore, two widely used 3D models, namelyD₃Q₁₅andD₃Q₁₉, are analysed. It is shown that theD₃Q₁₅model may induce artificial checkerboard invariants due to the connectivity of the lattice. Finally, a new iterative method, which significantly reduces the saturation time, is presented and validated on different benchmark problems.