Optical emission spectroscopic studies on laser ablated TiO2 plasma

Optical emission spectroscopic investigations of the plasma produced during Nd:YAG laser ablation of sintered TiO₂ targets, in oxygen and argon gas environments are reported. The spatial variations of electron temperature (T_e) and electron number density (N_e) are studied. The effect of oxygen/argon pressure on electron temperature (T_e) and electron number density (N_e) is presented. The kinematics of the emitted particles and expansion of plume edge are discussed. Spatio-temporal variations of various species in TiO₂ plasma were recorded and corresponding velocities were calculated. The effect of oxygen pressure on intensity of neutral/ion species and their corresponding velocities is also reported.     

Analysis of the method for studying the zenith-angle EAS distribution

The methodical problems related to analysis of the zenith-angle distribution of extensive air showers with N _e > 10⁷ particles are discussed. The effect of the array geometry on the angle measurement error is considered. Possible distortions of angular distribution due to errors have been calculated. The presence of excess showers detected at large zenith angles is shown.     

Study of the hadronic component of extensive air showers at the Carpet-2 EAS array

A method for the detection of hadrons with a muon detector at the Carpet-2 EAS array (Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences) has been described. Events induced by cosmic-ray hadrons have a signature that makes it possible to reliably distinguish them from muons. The characteristics of the hadronic component of extensive air showers with N _e ≥ 10⁵ have been presented.     

Spectroscopic study of plasma during electrolytic oxidation of magnesium- and aluminium-alloy

We present the results of an optical emission spectroscopy study of Plasma during Electrolytic Oxidation (PEO) of magnesium- and aluminum-alloy. Plasma electron number density N_e diagnostics is performed either from the H_β line shape or from the width or shift of non-hydrogenic ion lines of aluminum and magnesium. The line profile analysis of the H_β suggests presence of two PEO processes characterized by relatively low electron number densities N_e≈1.2×10¹⁵ cm^?3 and N_e≈2.3×10¹⁶  cm^?3. Apart from these two low N_e processes, there is the third one related to the ejection of evaporated anode material through micro-discharge channels. This process is characterized by larger electron density N_e=(1.2–1.6)10¹⁷ cm^?3, which is detected from the shape and shift of aluminum and magnesium singly charged ion lines. Two low N_e values detected from the H_β and large N_e measured from the widths and shift of ion lines suggest presence of three types of discharges during PEO with aluminum- and magnesium-alloy anode. On the basis of present and earlier results one can conclude that low N_e processes do not depend upon anode material or electrolyte composition.The electron temperature of 4000 K and 33,000 K are determined from relative intensities of Mg I and O II lines, respectively. The attention is drawn to the possibility of N_e application for T_e evaluation using Saha equation what is of importance for PEO metal plasma characterization. During the course of this study, difficulties in the analysis of spectral line shapes are encountered and the ways to overcome some of the obstacles are demonstrated.     

PHOBOS at RHIC: Some global observations

Particle production in Au+Au collisions has been measured in the PHOBOS experiment at RHIC for a range of collision energies for a large span of pseudorapidities, |η| < 5.4. Three empirical observations have emerged from this data set which require theoretical examination. First, there is clear evidence of limiting fragmentation. Namely, particle production in central Au + Au collisions, when expressed as dN/dη′ ( η′ ≡ – y_beam), becomes energy independent at high energy for a broad region of η′ around η′ = 0. This energy-independent region grows with energy, allowing only a limited region (if any) of longitudinal boost-invariance. Second, there is a striking similarity between particle production in e⁺e⁻and Au + Au collisions (scaled by the number of participating nucleon pairs). Both the total number of produced particles and the longitudinal distribution of produced particles are approximately the same in e⁺e⁻and in scaled Au + Au. This observation This presentation is based in large part on the PHOBOS summary talk by M Baker at the16th Int. Conf. on Ultrarelativistic Nucleus- Nucleus Collisions, Quark Matter 2002, Nantes, France was not predicted and has not been explained. Finally, particle production has been found to scale approximately with the number of participating nucleon pairs for (N _part ) > 65. This scaling occurs both for the total multiplicity and for highp _T particles (3 <p _T < 4.5 GeV/c). This presentation is based in large part on the PHOBOS summary talk by M Baker at the16th Int. Conf. on Ultrarelativistic Nucleus-Nucleus Collisions, Quark Matter 2002, Nantes, France     

Nuclear composition of 1-to 20-PeV primary cosmic rays according to lateral features of the electron-photon component of all extensive air showers and of extensive air showers accompanying high-energy gamma rays and hadrons in x-ray emulsion chambers at the Tien Shan level

Data from the Tien Shan array Adron on the dependence of the lateral distributions of the electron-photon component (age parameter S) in extensive air showers of cosmic rays on the number of electrons, N _e , which is a quantity that characterizes the primary-nucleus energy E₀, are subjected to a comparative analysis. The distributions in question are given both for all showers and for showers accompanying high-energy gamma rays and hadrons in x-ray emulsion chambers. According to calculations, events associated with the latter are generated predominantly by primary protons, and this makes it possible to assess their role at various values of E₀. The distributions with respect to S suggest a significant fraction of light nuclei, predominantly protons, in the region after the knee in the spectrum for N _e >10⁶, at least up to N _e =5.6×10⁶ (E₀ ～ 10 PeV).     

Fragment-ion appearance-potential spectroscopy

Nitrogen K-shell excitation in NH₃, NO, N₂, N₂O and NF₃ has been measured. The excitation thresholds were identified by mass-spectroscopic detection of positive ions produced in the course of decay of the highly excited species. The threshold energies for the N1s core level show a pattern similar to ESCA chemical shifts. In the N₂O data, the abundances of fragment ions having m/e = 14 and m/e = 16 correlate with the location of the primary K-shell vacancy. This may indicate a new approach to molecular structure determinations.     

A test of ν stability using a 200 GeV narrow-band neutrino beam at BEBC

ν_e induced events obtained in a 200 GeV narrow-band beam have been studied and compared to the number expected from K_e3⁺ decay. Agreement is found between the expected and observed numbers allowing limits to be set on ν_e → ν_x mixing.     

(e, 2e) spectroscopy of N2—valence momentum distributions and configuration interaction

The noncoplanar symmetric (e, 2e) reaction has been applied to N₂ at 1200, 600 and 400 eV. Separation energy spectra are obtained in the valence region, the observed structure extending to above 60 eV. Electron momentum profiles are measured at a number of separation energies. They agree very well with the momentum distributions for valence orbitals given by SCF calculations. Considerable configuration interaction structure is observed, being primarily due to configuration interaction in the 2σ_g hole state. At 1200 eV the spectroscopic sum rule is satisfied within experimental error, confirming the validity of the analysis.     

Antiferromagnetic resonance studies in molecular magnetic materials

EPR spectroscopy has become an increasingly powerful tool to examine the spin states and dynamics of single-molecule magnets, but has not been exploited to probe bulk magnetically ordered phases of molecular magnets. In this article, we review the EPR spectra of antiferromagnets and canted antiferromagnets below T_N with particular reference to our own studies on the canted antiferromagnet, p-NCC₆F₄CNSSN (T_N=36 K). The antiferromagnetic resonance experiment allows the saturation of the sublattice magnetisation to be probed. In addition, the exchange and anisotropy fields (H_e and H_a), the spin-flop field (H_sf) and for canted antiferromagnets, the Dzyaloshinskii-Moriya field (H_DM), which gives rise to the spontaneous moment, can be determined.     

Optical emission studies of sulphur plasma using laser induced breakdown spectroscopy

We present the optical emission studies of sulphur (S) plasma generated by the first (1064 nm) and second (532 nm) wavelengths of a Q-switched Nd:YAG laser. The target material was placed in front of laser beam in air at atmospheric pressure. The experimentally observed line profiles of neutral sulphur have been used to extract the electron temperature (T _e ) using the Boltzmann plot method, whereas the electron number density (N _e ) has been determined from the Stark broadening. The electron temperature is calculated by varying, distance from, the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser irradiance is increased.     

Absolute photonic band gaps in a two-dimensional photonic crystal with hollow anisotropic rods

The plane-wave expansion method is used to calculate photonic band gaps for two structures with hollow anisotropic tellurium (Te) rods. Both structures are found to have absolute band gaps at the low- and high-frequency regions. Compared with the photonic crystal with solid Te rods, the photonic crystal with hollow Te rods has a large absolute band gap at the high-frequency region: for the triangular lattice of oval hollow Te rods, there is an absolute band gap of 0.058w_e (w_e=2πc/a), and for the square lattice of square hollow Te rods, there is an absolute band gap of 0.056w_e.     

Studying the muon and hadron components of extensive air showers with the Carpet-2 array

The method of separating muons and hadrons recorded by the Muon Detector of the Carpet-2 air shower array of Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) is described. The results of studying characteristics of the muon and hadron components of extensive air showers (EAS) with N _e ≥ 10⁵ are presented. For the range of distances 40–55 m from shower axes the numbers of hadrons with energies higher than 30 GeV and muons with energies above 1 GeV are obtained as functions of the shower size N _e .     

用X射线激光M-Z干涉仪诊断点聚焦CH等离子体电子密度

在神光Ⅱ装置上，用软X射线激光Mach-Zehnder干涉仪诊断了点聚焦CH等离子体电子密度N_e分布，介绍了实验结果. 通过Abel变换进行了密度反演， 给出了N_e的2D分布，测得的最高N_e为3.2×10²¹cm^-3. 通过同1.5维JB19程序以及二维XRL2D程序的模拟结果的比较，发现高密度区，限流因子取0.05的理论结果同实验相符，但是低密度区实验得到的N_e分布下降得更快，而且理论模拟的N_e二维分布同实验结果在细节上有比较大的差别. 粗略的误差分析显示，干涉仪面型误差是实验误差的主要来源. 关键词： 类镍银X射线激光 Mach-Zehnder干涉仪 密度反演 Abel变换     

A Monte Carlo method for calculating strength functions in many-fermion systems

The calculation of moments is an essential first step in the calculation of strength functions for operators. A method for calculating approximate moments of a variety of operators in large vector spaces (dimension N_e) based on the use of sets of random multiparticle vectors (dimension N_d<N_e) is described and applied to the calculation of hamiltonian moments 〈Hⁿ〉 in two nuclear cases: ${}^{21}\text{Ne}\text{(n=1}\text{to}\text{10)}\text{and}{}^{28}\text{Si}\text{(nm=1}\text{to}\text{3)}$. The random vectors, which we call RRV's (random representative vectors), are constructed by statistically sampling a fraction f=N_d/N_e of the full space. Useful results are obtained with f?10^?6(case of ²⁸Si, N_e = 5.5 × 10⁷). For N_d=N_e case of ²¹Ne, N_e=1935) our results for the dispersions of the sets of the moments closely approximate the predictions of Porter.     

Random walks and diameter of finite scale-free networks

Dynamical scalings for the end-to-end distance R_ee and the number of distinct visited nodes N_v of random walks (RWs) on finite scale-free networks (SFNs) are studied numerically. 〈R_ee〉 shows the dynamical scaling behavior , where is the average minimum distance between all possible pairs of nodes in the network, N is the number of nodes, γ is the degree exponent of the SFN and t is the step number of RWs. Especially, in the limit t→∞ satisfies the relation , where d is the diameter of network with for γ≥3 or for γ<3. Based on the scaling relation 〈R_ee〉, we also find that the scaling behavior of the diameter of networks can be measured very efficiently by using RWs.     

Doping strategies for increased performance in BiFeO3

Investigation of crystal structure, dielectric, magnetic and local ferroelectric properties of the diamagnetically substituted Bi_1−xA_xFeO_3−x/2 (A=Ca, Sr, Pb, Ba; x=0.2, 0.3) polycrystalline samples has been carried out. It has been shown that the heterovalent A²⁺ substitution result in the formation of oxygen vacancies in the host lattice. The solid solutions have been found to possess a rhombohedrally distorted perovskite structure described by the space group R3c. Piezoresponse force microscopy has revealed signs of existence of the ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO₃ giving rise to the appearance of room-temperature weak ferromagnetism.     

Microwave diagnostics of a deuterium afterglow plasma

The electron number density, N_e, was measured by interferrometry with a signal of 9.531 GHz. The time decay of N_e indicated that electron-ion recombination was important with a recombination coefficient α_r = 1.1 X 10^-6cm³sec^-1.     

Automatic 3D scanning surface generation for microphone array acoustic imaging

This work presents a new technique for automatically generating the 3D scanning surface for acoustic imaging using microphone arrays. Acoustic images, or maps, of sound coming from spatially distributed sources, may be generated from microphone array data using algorithms such as beamforming. Traditional 2D acoustic maps can contain errors in the near-field if the object being imaged has a 3D shape. It has been shown that using the 3D surface geometry of an object as a scanning surface for beamforming can provide more accurate results. The methods used previously to generate this 3D scanning surface have either required existing CAD (Computer-Aided Design) models of the object being acoustically imaged or have required separate equipment which is generally bulky and expensive. The new method uses one or more cameras in the array, a data projector, and structured light code to automatically generate the 3D scanning surface. This has the advantage that it is inexpensive, can be incorporated as an add-onto existing microphone arrays, has short scan time, and is capable of being extended to imaging dynamic scenes. This technique is tested using beamforming and CLEAN-SC (CLEAN based on spatial Source Coherence) algorithms for a spherical array and an Underbrink multi-arm spiral array. For sound sources located about 1.2 m from the array, the mean position errors obtained are 6 mm. This is a quarter of the diameter of the mini-speakers being used as a sound sources.