bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hot Spot Formation on different Tokamak Wall Materials
Authors: Nedospasov A. V. , Bezlyudny I. V. 
Published: July 2007

AbstractThe thermal contraction phenomenon and generation of ‘hot spots’ due to thermoemission were described in [1–3]. The paper consider non‐linear stages of heat contraction on the graphite, beryllium, tungsten and vanadium wall. It is shown that on the beryllium surface hot spot can't appear due to strong cooling by sublimation. For other materials the conditions of hot spot appearance due to local superheating of the wall have been calculated and their parameters were found: critical surface temperature, size of spots and their temperature profiles, heat fluxes from plasma to the spots. It have been calculated fluxes of sublimating materials from spots to the plasma. It is noticed that nominal temperature of the grafite divertor plate, accepted in ITER's project to being equal 1500°C, is lower then critical temperature of the development heat contraction due to thermoemission.
One‐Particle Spectral Function of Electrons in a Hot and Dense Plasma
Authors: Wierling A. , Röpke G. 
Published: July 2007

AbstractA self‐consistent determination of the spectral function and the self‐energy of electrons in a hot and dense plasma is reported. The self‐energy is determined within the approximation of the screened potential (GW approximation). The rigorous self‐consistent calculation of the spectral function is compared with the quasi‐particle approximation. Results are presented for the solar core plasma as well as for ICF plasmas. It is shown, that the quasi‐particle concept is not an adequate concept for these plasmas. For the sake of comparison an effective quasi‐particle picture is introduced.
Time ‐ Dependent Multi ‐ Term Treatment of Plasma Electrons Acted upon by RF Electric Fields
Authors: Loffhagen D. , Braglia G. L. , Winkler R. 
Published: July 2007

AbstractUsing a new method for solving the time‐dependent electron Boltzmann equation in higher order accuracy, studies of the temporal behaviour of electrons in weakly ionized, collision‐dominated plasmas under the action of rf fields have been performed. The method is based upon a multi‐term approximation of the Legendre polynomial expansion of electron velocity distribution function and is applied to investigate the established periodic behaviour of the electron velocity distribution in helium, argon and CO plasmas.The results obtained in various approximation orders are discussed. The analysis has shown that the simplified treatment using only two terms of the velocity distribution expansion can fail in several conditions. In general, the four‐term approximation gives already a good representation of the convergent solution of the electron Boltzmann equation at each instant of the rf period. The discrepancies between two‐term and convergent results are found to depend sensitively on the specific atomic data, in particular on the magnitude of the various electron collision cross sections involved.Furthermore, the results obtained in the multi‐term approximation are compared with corresponding ones obtained by accurate Monte Carlo simulations. Very good agreement between convergent eight‐term Boltzmann and Monte Carlo calculations is found.
Nonlinear Ion‐Acoustic Solitary Waves and Double Layers in Multicomponent Plasmas
Authors: Das G. C. , Talukdar Madhuri , Sarma Jnanjyoti 
Published: July 2007

AbstractIn sequel to earlier observations on soliton dynamics in the plasmas, a few more features on solitons and double layers have been studied in a nonisothermal plasma conceiving multi‐temperature electrons. The basic equations governing the plasma dynamics, based on quasipotential analysis, are first reduced to an energy integral equation known as Sagdeev potential equation, to elucidates the salient features plasma of acoustic modes associating to those furthered in laboratory and space plasmas. The Sagdeev potential equation, under small amplitude approximation derives various kinds of Korteweg de Vries (K‐dV) equations in nonisothermal plasma and is solved by employing a modified approach of simple wave solution technique called as tanh‐method. The analyses show, under certain conditions, the remarkable properties of soliton propagation and double layers of compressive and rarefactive nature in the plasmas. The outcome of the observations could be of interest further in understanding the features of various plasma acoustic waves in laboratory and space plasmas.
Quasiparticle Boltzmann Equation for Nonlocal Binary Collisons
Authors: Morawetz K. , Špička V. , Lipavský P. 
Published: July 2007

AbstractVirial corrections to the Boltzmann equation for quasiparticles are obtained from non‐equilibrium Green's functions. These corrections are expressed in terms of shifts in space and time that characterize non‐locality of scattering integrals. The space shifts parallel finite‐diameter corrections to collisions of hard spheres. The time shift is identified as the collision delay. All shifts are given by derivatives of the phase shift in a binary collision.
Stopping Power of Proton Beam in a Weakly Non‐ideal Xenon Plasma
Authors: Mintsev V. , Gryaznov V. , Kulish M. , Filimonov A. , Fortov V. , Sharkov B. , Golubev A. , Fertman A. , Turtikov V. , Vishnevskiy A. , Kozodaev A. , Hoffmann D. H. H. , Funk U. , Stoewe S. , Geisel M. , Jacoby J. , Gardes D. , Chabot M. 
Published: July 2007

AbstractExperimental equipment for the investigations of stopping power of proton beam in explosively driven plasma is described. A 3 MeV 60 μs duration proton beam pulses delivered by 148.5 MHz ISTRA‐36 RFQ linac at ITEP and compact metallic vacuum pumped chamber for explosions up to 150 g TNT were the main unit of this set‐up. Differential pumping and fast valves proved to be sufficient for the protection of high vacuum beam line from the high pressure detonation products. Compact explosively driven cumulative shock tubes were worked out to generate uniform plasma slug behind powerful shock waves with the velocities of 10 km/s at the initial pressure of Xenon 50‐200 kPa. Plasma parameters were: pressure 15–100 MPa, electron concentration 1E+19 ‐ 1E+20 1/cc, nonideality parameter 0.2–0.5. Stopping power of proton beam was defined by the displacement of the position of the spot image of the beam on the scintillator screen after it's passing through the analyzing magnet and by time of flight method. The measured values of proton beam energy losses were 100–300 keV in dependence on plasma parameters. Comparison of the experimental data with the theoretical models was carried out.
A Semirelativistic Equation of State for Stellar Interiors
Authors: Stolzmann W. , Blöcker T. 
Published: July 2007

AbstractUsing the technique of Padé Approximants for the correlation contributions of charged particles we are able to reproduce complex mathematical expressions by simple algebraic formulas. The Padé formulas are analytical expressions, which interpolate between certain density‐temperature regions and are characterized by exact asymptotics. We present a semi‐relativistic description of the thermodynamics applicable for stellar interiors. Comparisons with equation‐of‐state data obtained by other calculational schemes are presented.
Electrical Conductivity of Fully‐Ionized Multicomponent Real and Model Plasmas
Authors: Tkachenko I. M. , De Córdoba P. Fernández 
Published: July 2007

AbstractA self‐consistent field theory of transport properties of strongly coupled, fully ionized, multicomponent plasmas is successfully applied to real and model plasmas. In addition, a soft interpolation is found between the Monte‐Carlo OCP equation of state and the low‐density exact expansion by Abe.
Landau and Collisional Damping in Nonideal Plasmas
Authors: Kaklyugin A. S. 
Published: July 2007

AbstractTaking into account collisional damping as a diffusion of nonuniformity of space distribution of the charges allows to present plasma polarization as a regular integral. Estimates of permittivity can be drawn from the proposed regular integral for both large and small frequences compared to wave number multiplied by thermal velocity of charges. It is shown that in nonideal plasmas: (1) plasma wave decrement decreases as nonideality grows, (2) negative dispersion appears for large wave number, (3) ion‐sound waves appear to be possible even in isothermal plasmas and their frequency turns out to be greater than the standard value about 1.5 times.
The Influences of the Magnetic Field Strength on the Magnetic Confinement of Primary Electrons in an Ion Source
Authors: Sandonato G. M. , Lima P. E. , Maciel H. S. , Otani C. 
Published: July 2007

AbstractThis paper deals with the simulation of trajectories of energetic electrons under the influence of a multi‐cusp magnetic field produced by a permanent magnet assembly in a ring cusp geometry which is designed for supporting a plasma based ion source. The primary electrons are assumed as being emitted from a cathode located coaxially with the cylindrical discharge chamber. The volume of the region occupied by the electron trajectories and the magnetic trapping time were evaluated and plots are presented showing the effects of the surface magnetic field strength of the magnets on the volume and the mean confinement time of primary electrons in the ion source.
Dielectric Function and Diffusivity of Nonideal Plasmas
Authors: Röpke G. , Redmer R. , Wierling A. , Reinholz H. 
Published: July 2007

AbstractThe dielectric function for a two‐component (hydrogen) plasma at arbitrary degeneracies is considered in the entire (k, w)‐space. Collisions are treated in Born approximation leading to a (k, w)‐dependent collision integral. Two possible limits are considered: (1) k → 0 (first), w → 0 (second) leading to the dc conductivity σ. (2) w → 0 (first), k → 0 (second) leading to the diffusivity D. The relation between σ and D is discussed.
Some Basic Physics Results for Plasma Spectroscopy and Modelling
Authors: Behringer K. , Fantz U. 
Published: July 2007

AbstractSpectroscopic diagnostics and modelling of technical or divertor plasmas require many results from basic physics research. Reasonable simplifications must be introduced and information is necessary about atomic and molecular processes in the plasma volume and at the walls. As a first approximation, the corona model is presented, which is applicable for excitation and ionisation at low densities. This model requires cross sections and rate coefficients for electron impact. Many of these can be found in the literature, but it is also shown, how they can be estimated from the optical f‐values. Consideration of competing processes is often required, as e.g. dissociative excitation, excitation transfer, charge exchange or quenching. Some examples are reported. At higher electron densities, collisional‐radiative models must be used, which are available for electron impact collisions. Redistribution by neutral particles can present a major problem in low density discharges and many questions are still open. Heavy particle reaction rates are published in the literature, but must sometimes be taken with caution. The optical thickness of resonance lines is discussed, which may considerably affect line emission also in the visible spectral range. Models and programs are described for taking into account opacity and the results are shown. In addition to reaction cross sections, the electron energy distribution function must be known, which is often non‐Maxwellian. It is demonstrated, how deviations can be recognised in spectroscopic criteria with different energy thresholds and how the high‐energy tail may be reconstructed for further use in diagnostics or modelling. Eventually, a self‐consistent model of these plasmas is highly desirable calculating electrical and magnetic fields, all chemical reaction rates and the consequent distribution functions.
Modern Applications of Plasma Etching and Patterning in Silicon Process Technology
Authors: Engelhardt M. 
Published: July 2007

AbstractBesides plasma etching of through‐wafer interconnects in wafer stacks for vertical integration of chips, fabrication of platinum (Pt) electrodes with non‐tapered sidewalls for the storage node in modern memories (DRAMs and FeRAMs) is one of the most challenging tasks of plasma process technology today.This paper describes the achievement of vertical integration of chips by plasma etching of high aspect ratio interchip vias. The etching processes for dielectrics, single crystal silicon, and the organic glue layer were all optimized for minimum reactive ion etching (RIE) lag i.e. for minimum decrease of etch rate with increasing etch depth.Furthermore the fabrication of perfect Pt electrodes for modern DRAMs and FeRAMs is reported. Vertical Pt profiles were achieved by plasma processing with resist mask. In this novel approach, the build‐up of thin redepositions of Pt onto the sidewalls of the resist, obtained as a result of processing in pure Ar plasmas, is utilized to achieve a sidewall steepness of the patterned Pt film which is determined by the steepness of the pre‐etch resist profile. After pattern transfer and resist stripping, the portion of the redepositions protruding above the fabricated storage node was completely removed by chemical mechanical polishing.
A time and wavelength division fiber loop distribution system with acousto‐optic tunable filters
Authors: Shimazu Yoshihiro , Kikuchi Shiro 
Published: July 2007

AbstractA time and wavelength division fiber loop distribution system with acousto‐optic tunable filters is proposed. This system can provide a large number of 150 Mb/s HDTV channels with a reliable technology. A theoretical analysis by Gaussian beam approximation shows that one system can distribute 320 HDTV channels to 256 subscribers with a minimum wavelength spacing of 2 nm. An experimental 12 channel (4 time division × 3 wavelength division) system with a wavelength spacing of 20 nm in the 1.3 μm region demonstrates a data rate of 1.2 Gb/s with only −4dB loss and −20 dB crosstalk at the tunable filter. The experimental loss and crosstalk characteristics agree well with the theoretical analysis.
Traffic characteristics and a congestion control scheme for an ATM network
Authors: Hirano Miki , Watanabe Naoya 
Published: July 2007

AbstractIn this paper, the cell loss rate and delay time of a cell multiplexer handling bursty input traffic are analysed, and the relation between these characteristics and burstiness is shown. Then, a buffer design guideline when input traffic characteristics are given is introduced for determining the queue size which satisfies permissible loss rate and delay time. Next, input traffic management and congestion control are discussed. For a congestion control, the marking method, which marks cells exceeding the bandwidth, allocated when the call is established, at a user/network interface, and discards those marked cells only at congested nodes, is evaluated. Simulation results show that the marking method can improve service quality and network throughput by allowing cells exceeding the allocated bandwidth into the network instead of discarding them.
Prototyping an ATM adaptation layer in a multimedia terminal
Authors: Armitage G. J. , Adams K. M. 
Published: July 2007

AbstractThis paper describes the implementation of a prototype ATM adaptation layer (AAL) within the kernels of two machines running Sun Operating System 4.1.1. The implementation is achieved by using the STREAMS paradigm and an Ethernet link between the two machines as a surrogate optical fibre link. The flexibility of the STREAMS facility for building layered protocols, and the real‐time performance limitations of the STREAMS scheduling system are identified. STREAMS is shown to be no less susceptible to naïve buffer utilization than earlier paradigms. It is necessary to minimize message passing and copying of data to achieve high throughput. This study has clarified several key issues in the functional design of AALs.
The JAK/STAT pathway regulates proximo‐distal patterning in Drosophila
Authors: Ayala‐Camargo Aidee , Ekas Laura A. , Flaherty Maria Sol , Baeg Gyeong‐Hun , Bach Erika A. 
Published: July 2007

AbstractJAK/STAT signaling is thought to control growth and proliferation. However, here we show a novel role for this pathway in the patterning of Drosophila appendages. Loss of Stat92E function results mainly in ventralizations and multiplications of the proximo‐distal axis in leg and antenna, primarily through the ectopic misexpression of wingless. We also show that the pathway ligand Unpaired is expressed in two domains in leg and antenna that abuts those of wingless and decapentaplegic. We report that JAK/STAT signaling represses both wingless and decapentaplegic, restricting them to their respective domains in leg and antenna. In a reciprocal manner, we show that wingless and decapentaplegic restrict unpaired to its two domains. Thus, a main function of the JAK/STAT pathway in leg and antennal development is to promote the formation of a single proximo‐distal axis per disc by constraining the intersection of wingless and decapentaplegic to the center of the disc. Developmental Dynamics 236:2721–2730, 2007. © 2007 Wiley‐Liss, Inc.
A method of estimating the irregularity of scattering medium using characteristics of ultrasonic speckle
Authors: Ohya Akihisa , Kashioka Junji , Nakajima Masato 
Published: July 2007

AbstractWhen examining a random group of scatterers, random granular patterns called speckle appear on echograms obtained by pulse echo ultrasonic diagnostic equipment. In living body organs such as the liver, there is a profound connection between the irregularity of the tissue structure and the severity of the disease. Therefore, if the degree of the irregularity can be estimated through analysis of the echogram, the possibility exists that the properties of the tissues can be diagnosed quantitatively.This paper considers a medium that grouped scatterers as the model of the object and investigates the relationship between the statistics of interference pattern such as the speckle that appears on the ultrasonic echogram and the irregularity of the scattering medium. Also examined is the possibility of estimating the degree of irregularity of the medium from the echogram.From the results of a computer simulation, it is found that if the density of the scatterers is known, the degree of irregularity of the medium can be determined from the value of the signal‐to‐noise ratio (SNR) statistic of the echogram. In addition, it is learned that by using the SNR as the statistics together with the skewness of the brightness histogram of the image, it is possible to estimate the degree of irregularity and the density of the scatterers.
A generalized principal component analysis for mixed measurement level data
Authors: Yaguchi Hiroyuki , Ichino Manabu 
Published: July 2007

AbstractThe principal component analysis is well known as a method to summarize the phenomenon described by the quantitative features. The quantification theory III is known as a method to summarize the phenomenon described by the mixed qualitative and quantitative features. However, several problems are pointed out in the quantification theory III, e.g., the manipulation containing an arbitrariness to divide the quantitative feature into intervals or the increase of the number of features due to the use of the dummy variables.This paper proposes a generalization of the principal component analysis for the mixed qualitative and quantitative data. A model is considered which can handle the mixed qualitative and quantitative data, and the quantification of the information is executed on the model using the distance function. Then the principal component analysis is applied. The proposed method is a natural extension of the ordinary principal component analysis and has the advantages that the resolution for the score is high, the number of features is less, and the interpretation of the result of analysis is easy. Using two simple examples, the proposed method is compared to the quantification theory III and the effectiveness of the proposed method is demonstrated.
A method of selecting HDTV test pictures for subjective quality assessments
Authors: Tachi Takeshi , Iai Satoru , Kitawaki Nobuhiko 
Published: July 2007

AbstractThis paper presents a quantitative selection method for still images for use in assessment tests to obtain reasonable assessment results for high‐quality images in subjective assessment tests of high‐definition television (HDTV) signals. First, based on the selection criterion which is to select images that exhibit the characteristic of high quality, it was clarified that the three elementary psychological factors of vividness, comfortableness, and sharpness constituted the characteristics of high‐quality images and that the amplitudes of these psychological factors could be quantified by means of the statistics of the HVC signal distribution in the Munsell color space of the image.Next, based on the selection criterion where images can be evaluated accurately even when slightly degraded, subjective assessment tests were performed for random additive noise, high‐frequency cutoff, and adaptive DCT coding distortion. The results showed clearly that images suited for use in the assessment test of each degradation could be selected based on the statistics of the image HVC signal distribution. By performing assessment tests using the smallest possible number of images selected by the guidelines presented here, assessment results can easily be obtained efficiently and reliably.
Stability analysis of periodic solutions in nonautonomous systems with hysteretic elements
Authors: Matsuo Tetsuji , Kishima Akira 
Published: July 2007

AbstractThis paper considers the case where hysteresis is given by the Preisach model and discusses the stability analysis for the periodic solution in the nonautonomous system containing hysteretic elements. The behavior of the system containing hysteretic elements is affected by the history of the system until it arrives at the steady state.In this paper, it is shown first that even periodic solutions with the same hysteretic loop may have different variational systems for the steady‐state solution if the histories until arriving at the steady state are different. Next, two kinds of stability criteria are considered based on the difference of the history up to the steady state and the stability against the external disturbance is investigated. The dependence of the stability of the solution on the bifurcation of the periodic solution also is discussed. Finally, examples of numerical analysis are presented to verify the result of discussions.
Synchronized quasi‐periodic oscillations in a ring of coupled oscillators with hard characteristics
Authors: Yoshinaga Tetsuya , Kawakami Hiroshi 
Published: July 2007

AbstractThis paper considers properties of quasi‐periodic oscillations in a ring of mutually coupled oscillators and investigates phenomena such that envelopes of wave‐forms observed in the oscillators are synchronized dynamically.Several properties derived from analysis using a perturbation method are discussed, and the following results are obtained: It is necessary for the stability of double‐mode oscillations that oscillators have hard characteristic nonlinearity; phase relations among envelopes depend on oscillatory mode combinations; and so on. It is shown that all quasi‐periodic oscillations, whose stability is suggested by the theoretical analysis, are observed numerically in up to four‐coupled oscillators. Moreover, the system parameter regions in which quasi‐periodic oscillations exist are given for two‐coupled oscillators and it is shown that an out‐of‐phase synchronization of envelopes can be explained by using the bifurcation theory of periodic oscillations.