Quark potential in a quark–meson plasma

We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly coupled in the temperature region 1≤T/T _c≤3, with T _c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase transition point.     

Long lifetime and efficient emission from Er ions coupled to Si nanoclusters in Si-rich SiO2 layers

Reactive magnetron co-sputtering of two confocal SiO₂ and Er₂O₃ cathodes in argon-hydrogen plasma was used to deposit Er-doped Si-rich SiO₂ layers. The effects of the deposition conditions (such as RF power applied on each cathode and total plasma pressure) and annealing treatment (temperature and duration) on structural, compositional and photoluminescence (PL) properties of the layers were examined. It was found that a significant enhancement of both Er³⁺ PL intensity and emission lifetime up to 9 ms have been reached through monitoring of the conditions of both deposition process and annealing treatment. The effective absorption cross section and the fraction of Er ions coupled to Si clusters were analyzed. It was shown an increase of the fraction of Er³⁺ ions coupled to Si up to 11%.     

Langmuir probe and spectroscopic studies of RF generated helium-nitrogen mixture plasma

This paper reports the effect of helium percentage variation in a capacitive RF helium-nitrogen mixture plasma on various plasma parameters and concentration of nitrogen active species (N₂(C³Π _u) and N₂ ⁺(B²Σ _u ⁺)). Langmuir probe is used for determination of electron energy distribution functions, effective electron temperature, plasma potential and electron density. Optical emission spectroscopy is used for determination of electron temperature from Boltzmann's plot of He–I lines and the relative changes in the concentration of active species by measuring the emission intensities of nitrogen (0-0) bands of the second positive and the first negative systems. The results demonstrate that electron temperature, electron density and concentration of active species increase significantly with increase in helium percentage in the mixture and RF power.     

Role of composite MnO2 cathode on electrochemical cells based on polymer electrolyte (PEO/NaClO3)

Thin-film sodium-ion-conducting polymer electrolyte based on polyethylene oxide (PEO) system was prepared by solvent casting method. The thin-film electrolytes were characterized by X-ray diffraction (XRD), infrared (IR), cyclic voltammetry (CV) and alternating current conductivity, and Wagner’s polarization method. The complexation of salt with PEO was confirmed by XRD and IR studies. The charge transport of these electrolytes is mainly due to ions, which was confirmed by the transference number experiment. The conductivity studies show that the conductivity value of PEO/NaClO₃ complex increases with the increase of temperature as well as the addition of low molecular weight polyethylene glycol, dimethyl formamide, and propylene carbonate. The electrolyte stability and cell reversibility were analyzed by CV studies. Electrochemical cells have been fabricated with a common cell configuration Na|electrolyte|(MnO₂ + I₂ + C + electrolyte), and their discharge characteristic studies were made through a load 100 kΩ at room temperature. The measured open circuit voltage ranges from 2.80 to 2.54 V with short circuit current ranges from 667 to 1,000 μA and several other cell parameters were evaluated. Finally, the merit of the composite cathode is found with the comparison of the MnO₂ cathode.     

Speed and shape of large-amplitude solitary waves in ion-beam plasma system

Large-amplitude solitary waves are investigated in ion-beam plasma system. The Sagdeev’s pseudopotential is determined in terms of the ion speedu. It is found that there exists a critical value ofu ₀, the value ofu at (u′)² = 0, beyond which the solitary waves cease to exist. The critical value also depends on σ (the ion temperature) or σ_b (the ion beam temperature). One of the author (PC) is grateful to UGC, India for the financial support under SAP(No F.510/8/DRS/2004(SAP-1)).     

Electrochemical reactors for NO decomposition. Basic aspects and a future

The electrochemical reduction of nitric oxide in the presence of the excess oxygen was reviewed. It was shown that the selectivity and activity of the cathodes is strongly dependent on the composition and on the microstructure of the cathode material. A concept of electrochemical reactor with multilayer electro-catalytic electrode was proposed and successfully designed in Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Japan. The typical values of current efficiency in such electrochemical reactors are of the order of 10–20% at gas composition: 1,000 ppm NO and 2% O₂ balanced in He and at gas flow rate 50 ml/min. The value of current efficiency depends on the functional multi-layer electrode composition, structure, and operating temperature. Such electrochemical reactors show the value of NO/O₂ selectivity (ν _sel) higher than 5 (ν _sel > 5) at intermediate temperature and up to ν _sel = 25 at low temperature operation. It was shown that multilayer electro-catalytic electrode should consist at list from three main functional layers: cathode, electro-catalytic electrode, covering layer, in order to operate as an electrode with high selectivity.     

Electrochemical properties of carbon-coated LiFePO4 synthesized by a modified mechanical activation process

Carbon-coated lithium iron phosphate (LiFePO₄/C) composites were synthesized by conventional mechanical activation (MA) process and also by a modified MA process. Phase-pure particles were obtained of ∼100 nm size with a nano-meter thick web of carbon surrounding the particles. The composite prepared by the modified MA process shows good performance as cathode material in lithium cells at room temperature. A high performance was achieved at 0.1 C-rate with >96% utilization of the active material. A stable cycle performance even at higher C-rates was achieved with a cathode that has a total carbon content of only 12 wt%. The use of the modified MA process to synthesize LiFePO₄/C has promise to be an efficient process to decrease the total carbon content of the cathode, resulting in the enhanced energy density.     

Parameters of the discharge plasmas of surface-plasma sources of negative hydrogen ions

The main parameters of the plasma of high-current hydrogen-cesium glow discharges of surface-plasma (planotron and Penning) sources of negative hydrogen ions are determined using contact-free spectroscopic methods and compared for identical discharge current densities. The elemental and charge composition of the plasma is established. The temperature of the hydrogen atoms and the energy of the visible-range radiation of the plasma discharge are measured and estimates of the electron density in the plasma are made. The dynamics of the change in the parameters of the discharge plasma of a Penning source — the densities of hydrogen atoms, cesium atoms and ions, and molybdenum atoms — is tracked during a discharge pulse with spatial resolution along two coordinates. It is observed that cesium atoms and ions and molybdenum atoms are pent up near the cathode surface. Zh. Tekh. Fiz. 68, 32–38 (October 1998)     

Electrochemical cell with two layers cathode for NO decomposition

An electrochemical cell composed of an yttria-stabilized zirconia disk and two layers cathode was used for nitrogen monoxide decomposition. It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor (NiO) leads to enhancement of the performance of the electrochemical cell for NO_x decomposition in the presence of excess oxygen. The decomposition activity was measured for the one-compartment cell oxide|(cathode)|YSZ|(anode) by applying a DC voltage lower than 3.7 V in the temperature range 550–700 °C. The microstructure of the YSZ-NiO mixed oxide electrodes was investigated in dependence of the cell operating condition and the working electrode sintering temperature. The correlation between the microstructure of the mixed oxide electrode and conversion rate of NO was studied. The phenomenon of self-optimization of the microstructure of the NiO-YSZ working electrode during the cell operation was observed and investigated. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Exact diffusion coefficient of self-gravitating Brownian particles in two dimensions

We derive the exact expression of the diffusion coefficient of a self-gravitating Brownian gas in two dimensions. Our formula generalizes the usual Einstein relation for a free Brownian motion to the context of two-dimensional gravity. We show the existence of a critical temperature T_c at which the diffusion coefficient vanishes. For T < T_c, the diffusion coefficient is negative and the gas undergoes gravitational collapse. This leads to the formation of a Dirac peak concentrating the whole mass in a finite time. We also stress that the critical temperature T_c is different from the collapse temperature T_* at which the partition function diverges. These quantities differ by a factor 1-1/N where N is the number of particles in the system. We provide clear evidence of this difference by explicitly solving the case N = 2. We also mention the analogy with the chemotactic aggregation of bacteria in biology, the formation of “atoms” in a two-dimensional (2D) plasma and the formation of dipoles or “supervortices” in 2D point vortex dynamics.     

Experimental investigation of the anode region of a free-burning atmospheric-pressure inert-gas arc I. General characteristics of the discharge. Low-current regime

This paper reports the experimental investigation of the anode region of a free-burning inert-gas arc at atmospheric pressure in the current range from a few amperes to hundreds of amperes. The tungsten thermionic-emission cathode and the large-diameter water-cooled copper anode that were used permitted the anode arc root to assume its natural form. The general characteristics of the discharge are given and results are presented from investigations of the anode region at low currents, where the anode arc root is single and constricted, but erosion-free. Measurements of the plasma parameters as well as the current density in the arc root are reported, and a comparison is made between the values obtained and those characteristic of the region of the cathode arc root. Zh. Tekh. Fiz. 67, 35–40 (January 1997)     

Superoxide production as a stress response of wounded root cells: ESR spin-trap and acceptor methods

The Superoxide generation in the plant root cells in response to wound stress has been studied by the electron spin resonance (ESR) spin-trap and epinephrine-adrenochrome acceptor methods. Tiron readily oxidized by O₂^⋅− to a rather stable free radical semiquinone was used as a spin trap. Wound stress was shown to activate the root cells inducing an increase in Superoxide production. The largest amount of Superoxide was registered in the early stage after excision of the roots from the seedlings (over 1–2 h). Further incubation of the roots for 5 and 6 h resulted in the lowering of the Superoxide level. Electron donors NADH and NADPH, nonpenetrating via plasma membrane, caused the amplification of Superoxide production in root cells, whereas oxidized nucleotide NAD did not affect the O₂^⋅− synthesis. Treatment of the roots with a water-soluble analog of naphthoquinone, vitamin K₃, led to the total disappearance of the ESR signal from Tiron semiquinone and suppression of epinephrine-adrenochrome conversion. An excessive amount of calcium ions in the root cells induced a powerful increase in the Superoxide release and disturbed the adaptation. The data obtained give us a further indication that the redox system of plasma membrane, comprising a flavoprotein, is likely involved in the production of Superoxide occurring in the response to wound stress in root cells.     

Recombination zone and efficiency in bipolar single layer light-emitting devices: a numerical study

The efficiency of organic light-emitting devices (OLEDs) is closely related to the position and width of recombination zone (RCZ) in the emission layer. Based on the drift–diffusion theory of carrier motion in semiconductors, we developed a numerical model for the position and width of the RCZ in bipolar single layer OLEDs. The calculation results show that for a given operation voltage, the position and width of the RCZ are determined by the mobility difference of electrons and holes, and the energy barrier at the two contacts. When the anode and cathode contact are both ohmic, then RCZ will be near the electrode, from which the low-mobility carriers are injected, and the smaller the mobility difference, the wider the RCZ, and the width of RCZ will be maximal when the mobility of holes and electrons are equal. When the anode contact is Schottky, while the cathode contact is ohmic, then the position and width of RCZ will be determined by both the mobility difference and hole–injection energy barrier. When μ _p<μ _n, the RCZ will be at the anode side. When μ _p>μ _n, then RCZ will move away from the anode and become wider, with the increase of the hole injection barrier. For a given hole–injection barrier and mobility of holes and electrons, the position and width of RCZ change with the applied voltage.     

Specific heat of around the glass transition

Dynamic calorimetric measurements are performed for the quaternary metallic glass Zr₆₅Al_7.5Cu_17.5Ni₁₀ in order to analyse the dependence on different heating rates for the glass transition temperature T_g. We compare two different temperature programs used for sample relaxation, to estimate the influence of the thermal history on T_g. A lower limit for the glass transition temperature T_g was calculated according to two different models based on the fact, that width and temperature of the glass transition depend on the experimental time scale set by the heating rate: One model assumes a Vogel-Fulcher-Tammann type behaviour, as used to describe more or less “fragile” glass formers and the other assumes an Arrhenius-like behaviour, which is related to “strong” glass formers. The values obtained from both models differ by about 80K. From additional absolute specific heat capacity measurements we calculate the Kauzmann temperature T_K, as a lower limit for the temperature of the glass transition from thermodynamic aspects. Comparing T_K with the temperature values obtained from the two evaluation models we can classify the quaternary metallic glass Zr₆₅Al_7.5Cu_17.5Ni₁₀, to behave more like a “strong” glass former. Received: 23 January 1998 / Received in final form and Accepted: 31 August 1998     

Linewidth studies on the Ar+ 476.5 nm and 480.6 nm lines excited in a helium-agron hollow cathode discharge

The spectral line shapes of the Ar⁺ 476.5 nm and 480.6 nm lines, excited in a He-Ar hollow cathode (HC) discharge, were measured using the Fabry-Perot technique. The collisional and Doppler linewidths were determined for the two lines. The collisional broadening constants are estimated to be (5±3) MHz/mbar and (6±3) MHz/mbar, respectively. The temperature obtained from the two Ar ion transitions was found to be 260 K higher than that expected for the rest of the gas mixture from earlier measurements. The possibility is discussed, that this excess temperature is caused by Ar ions partially created in the HC discharge by charge transfer collisions with He ₂ ⁺ molecules.     

Characterization in MCFC conditions of high-temperature, potentiostatically deposited Co-based thin films on NiO cathode

Molten carbonate fuel cell (MCFC) is one of the most advanced high-temperature devices to convert chemical energy into electrical energy without pollution. It can be used in cogeneration as electrical and thermal generator because of its high working temperature (650 °C). Nevertheless, its commercialization is still limited. In fact, its lifetime is mostly reduced by the dissolution of the cathode into the corrosive molten carbonate electrolyte. One of the ways to overcome this problem is to modify or protect the state-of-the-art cathode. In the last case, the deposit must present conductivity as good as the classical NiO porous cathode one but a lower solubility in the electrolyte. For this reason, thin films of cobalt(III) were electrodeposited. A classical three-electrode cell was used to deposit Co-based thin films by chronoamperometry in aqueous solution, at relatively high temperature (80 °C). The deposition conditions lead to homogeneous, covering, and crystallized films. The microstructure and the crystallinity of the deposits were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. Then, their electrochemical properties were studied in the molten carbonate electrolyte under a mixture of CO₂ and air. In situ measurements such as chronopotentiometry at I = 0 (open-circuit potential) or impedance spectroscopy were carried out during 48 h. Moreover, ex situ measurements such as inductively coupled plasma atomic emission spectroscopy to evaluate the solubility, or SEM and XRD measurements were performed to characterize the thin Co-based films in such molten carbonate fuel cell working cathodic conditions.     

Cathode overpotential investigation by means of “Built-in” potential electrode

The objective of the present work is the development of a “built-in” potential electrode method for direct measurements of the cathode and anode overpotentials and the corresponding interface resistances of solid oxide fuel cells (SOFC). The studies were performed on a yttria-stabilised zirconia (YSZ) electrolyte-supported SOFC using La_0.8Sr_0.2MnO₃ as cathode, GDC as protecting layer and Ni-ScSZ cermet as anode. The mesh potential electrode was placed inside the YSZ membrane near the cathode side. Using the combination of the I-U and the impedance measurements with the built-in potential electrode technique, the temperature dependencies of the electrodes and electrolyte contributions to the total cell resistance were determined.     

Characterisation of laser-produced tungsten plasma using optical spectroscopy method

This paper describes results of spectroscopic investigation of laser-produced tungsten plasma. The laser intensity on the target surface reached up to 30 GW/cm² depending on the focusing conditions. Optical spectra emitted from plasma plumes which were formed under vacuum conditions in front of the tungsten target due to the interaction of Nd-YAG laser pulses (1.06 μm, 0.5 J), were characterised by means of an optical spectrometer (λ/Δλ= 900) in the wavelength range from 300 to 1100 nm. The spectra were recorded automatically with the use of a CCD detector with exposition time varied from 100 ns to 50 ms. On the basis of WI and WII lines it was possible to estimate electron temperature and electron density which corresponded to the expansion phase of the plasma. T_e and N_e were measured as 1.1 eV and 8×10¹⁶ cm^-3, respectively. The spectra collected by the ion energy analyser showed that the plasma included tungsten ions up to 6+ ion charge. Signals from the ion collector allowed to estimate the average value of ion energy of tungsten as 4.6 keV. Basing on this value the electron temperature corresponding to the initial stage of the plasma formation was estimated to be about 320 eV. Optical microscope investigation showed that laser irradiation caused structural changes on the surface of the target.     

Spectroscopy of the regenerative soot

The mechanisms and processes of the formation of the regenerative soot in a graphite hollow cathode discharge that produces and emits carbon clusters are presented. Mass spectrometry with a specially designed E×B velocity filter analyzes the entire range of the charged clusters from C ₁ to ∼C ₄₃₀₀. The state of the carbon vapour within the source is evaluated by using the characteristic line emissions from the carbonaceous discharge whose formative mechanisms depend upon the kinetic and potential sputtering of the sooted cathode. The carbonaceous discharge generates atomic and ionic C and its clusters C _m (m≥ 2), noble gas metastable atoms and ions, energetic electrons and photons in the cavity of the graphite hollow cathode. The parameters of soot formation and its recycling depend critically on the discharge parameters, the geometry of the hollow cathode and 3D profile of the cusp magnetic field contours. Received 2nd July 2001 and Received in final form 10 September 2001     

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采用简化阴极的一维边界层模型,将同轴磁旋转电弧等离子体发生器的阴极与弧柱耦合求解,使用FLUENT软件,数值模拟了不同锥角阴极的形状对磁分散电弧等离子体、阴极弧根和阳极弧根位形的影响.结果表明:阴极弧根具有扩散特征,其电流密度为107A·m-2量级;阴极形状的改变引起阴极弧根位形和电流密度分布变化,从而影响等离子体参数分布;随着阴极锥角的增大,阴极弧根从阴极前端移动到阴极侧面,等离子体区域向下游偏移,等离子体轴向厚度减小.