X-ray excited photoelectron spectra of LiNbO3: A quantitative analysis

X-ray excited photoelectron spectra (XPS) using monochromatized Al — K radiation ( =1,486.7 eV) have been analysed quantitatively. The intensities of the various core lines (Li(1s), O(1s), O(2s), Nb(3s), Nb(3p), Nb(3d), Nb(4s), Nb(4p)) normalized to the intensity of the Nb (3d _5/2)-line, show good agreement with those calculated with theoretical values for the photoabsorption cross section of the free atoms and the theoretical estimates of the dependance of the electron escape depth on the electron kinetic energy. From the energy loss spectra observed at the high binding energy side of the XPS core lines the energy loss function Im {–1/()} is calculated and compared to published optical data. This comparison yields directly the total electron escape depth as function of the electron energy over a large energy range.     

Medium-spin excitations of the neutron-rich 84Se isotope: Possible decrease in energy of the N = 50 neutron-core excitation

The ⁸⁴Se nucleus has been produced as fission fragment in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Medium-spin states of this neutron-rich isotope have been identified for the first time. Its level scheme has been obtained up to 4.9MeV excitation energy and spin I 7. Its structure is interpreted by analogy with those of the stable heavier isotones. The evolution of the energy of the N = 50 neutron-core excitation is discussed as a function of the proton number.     

Grain Boundary Wetting Statistic in Zn/Ga System and its Application to Grain Boundary Energy Spectrum Estimation

The grain boundary statistic in zinc polycrystals in contact with saturated Ga(Zn) melt has been studied. The misorientation angle distributions for zinc thin foil and zinc plates were obtained. The influence of the misorientation angle value on the wetting probability p of grain boundaries was observed. The grain boundary energy distribution parameters were obtained by using the p() relationship. The dihedral angles in triple lines of non-wetted zinc samples were also measured and their distribution was used to obtain the grain boundary energy distribution function. The parameters obtained by two different methods correspond to one other.     

3He–HeII Mixtures in the Static Approximation

We have applied, for the first time, the so-called static approximation (SA) on the ³He–HeII mixtures to calculate their thermodynamic properties under different conditions. For that, we have first obtained the so-called self-consistent long-range-equation. The essence of this approximation is to replace the true quantum-mechanical spectrum of the local-field operator with a distribution around the expectation value of the local-field operator. The distribution function of the fermionic particles has been found to be almost a step function up to 0.1 K. The chemical potential, pressure, and the mean internal energy per unit volume have been calculated in this temperature range with different values for the volume differential coefficient and the effective mass m ₃*. We have found that the thermodynamic properties of this system are temperature independent.     

Inelastic interactions of protons with photoemulsion nuclei at 4·5 GeV/c

In inelastic collisions of protons with photoemulsion nuclei at 4·5 GeV/c, data have been obtained on multiplicity of shower particles, energy spectrum of fast secondary protons with (2·5±0·1) GeV average energy, and energy spectrum of produced charged pions with (640±±50) MeV average energy. The multiplicity, angular distributions, and energy of particles arising from splitting target-nuclei are also determined: the proton spectrum is approximated by the power dependenceE ^- with=1·4±0·1. The distribution of protons and-mesons over rapiditiesy=0·5 In[(E+p)/(E–p)] have been obtained. The average multiplicity for secondary particles coincide with the predicted values given by the cascade-evaporation model.Dedicated to the 25th anniversary of the Joint Institute for Nuclear Research.The authors would like to express their gratitude to the synchrophasotron group of JINR and to the group of S. J. Ljubomilov for the assistance in the experiment, to V. S. Barashenkov and V. V. Ivanov for the assistance in the cascade-evaporation model calculations, and also to the laboratories which took part in the scanning and measurement.     

The influence of temperature on superplasticity of Zn-Al-Cd alloy

Experimental results of the study of superplastic behaviour in Zn-0·35 wt. % Al-0·25 wt. % Cd alloy are presented. The attention has been paid to the influence of temperature on stress-strain curves, ductility, strain rate sensitivy parameterm and activation energy of superplastic flow. The best superplastic properties have been established at temperatures T370 K (0·53 T_m): ductilityA=600% and parameterm=0·56. A fast grain growth observed at temperaturesT 380 K has been suggested to be responsible both for the decrease in ductility and parameterm values and for the origin of an anomaly in the decreasing temperature dependence of flow stress. The measurements of activation energy have shown an expected decrease in activation energy at the transition from the non-superplastic region at lower temperatures to the superplastic region at higher temperatures. Significant transient effects after strain rate changes have been observed. The experimental results obtained in the Zn-Al-Cd alloy have been compared with those obtained in binary Zn-1·1 wt. % Al alloy and discussed from the point of view of possible models of structural superplasticity.     

Equations of fluctuating nonlinear hydrodynamics for normal fluids

The full set of fluctuating nonlinear hydrodynamic equations for normal fluids is derived from the conventional Langevin equations extended to include multiplicative noise. The equations describing the set of conserved variables (the mass density, the momentum densityg, the energy density) agree with those found by Morozov for a case of a driving free energy which is a local function of the hydrodynamic variables. We show here that if the standard form of the hydrodynamic equations is to hold in the absence of noise, then the driving free energy must be a local function ofg and, but it may have to be a nonlocal function of the mass density.     

Alkali metal oxides: Occupied,unoccupied and excited states

The occupied and unoccupied electronic states of NaO₂ and KO₂ have been investigated by UV photoemission spectroscopy and inverse photoemission spectroscopy, respectively. In addition single electron excitations from occupied into empty levels have been probed by x-ray absorption and electron energy loss spectroscopy. The experimental data are augmented by LCGTO-X model cluster calculations. A detailed assignment of initial and final states is given. The excitation cross sections and an inversion of the ligand field induced3d level splitting in NaO₂ are discussed.     

Spectral‐Luminescent Properties of Oxazoles and Oxadiazoles in a Gas Phase on Excitation by Electrons

The energyloss spectra of electrons, fluorescence excitation functions, and the fluorescence spectra on excitation of the vapors of a number of oxazoles and oxadiazoles by monokinetic beams of electrons of various energies are determined. In contrast to optical absorption spectra, in the energyloss spectra of a number of studied substances a band associated with the S ₀–T ₁ singlettriplet transition is observed. The –^*type transitions are fixed up to S ₀–S ₅ on excitation of molecules by highenergy electrons, including the region of vacuum ultraviolet. The cross sections of elastic and inelastic collisions of electrons of different energies with POPOP molecules have been measured. The dependences obtained differ substantially from those calculated in the Born approximation. The cross section of elastic scattering is in a rather good correspondence with the geometric section of the molecule.     

New FTS measurements, optimized energy levels and refined VUV standards in the Ne III spectrum

All observed spectral lines of Ne III in the range 204 ? to 36 μm (277 cm^-1 to 490000 cm^-1) have been compiled and critically evaluated. 57 visible and ultraviolet lines of Ne III have been precisely measured using Fourier transform spectroscopy. An optimized level scheme has been derived from the total list of observed lines. Relative positions of about 180 out of a total of 226 previously known energy levels of Ne III have been determined with improved accuracy compared to previous studies. Excitation energies of almost all excited levels have been revised by (1.5–2.0) cm^-1. 127 precise wavelength standards in the region 210 ? to 2900 ? have been derived. Concepts of error current and covariance matrix have been implemented in a computational algorithm that permits one to derive the uncertainties of Ritz wavelength standards obtained from a set of least-squares-optimized energy levels. Nine new energy levels have been found, and 16 new transitions have been identified in the extreme ultraviolet region. The ionization potential has been increased by 4.5 cm^-1. The new value is ( ( ).     

Role of the Medium in Radiationless Conversion of the Energy of the Excited S 1 State in Equilibrium Systems with Intramolecular Charge Transfer

Using the Onsager model, the effect of molecular orientation interactions in solutions on the rate constant of radiationless conversion of the energy of the excited S ₁ state has been calculated for equilibrium systems with intramolecular charge transfer. The rate constant of the radiationless conversion of energy S ₁ — X _n is represented as a function of the polarity of the medium f() = ( – 1)/(2 + 1), where is the permittivity of a solvent. The results obtained are compared with the Marcus theory and are also used to explain the well-known literature data on the influence of a solvent on the lifetime of the S ₁ state of some carotenoids.     

Temperature and composition dependence of the energy band gap of Pb1−x Mn x S solid solution

Photovoltaicp-n junctions inn-type Pb_1–xMn _x Sx0.04, have been made by sulphur diffusion. Current-voltage and resistance-voltage characteristics have been examined at various temperatures. The spectral responses of the diodes have been measured within the temperature range from 5 to 300 K at a zero bias. From these measurements the energy band gap of Pb_1–x Mn _x S solid solution has been determined as a function of temperature and manganese content. A phenomenological expression describing the variation of the energy gap of Pb_1–x Mn _x S with temperature and alloy composition has been proposed.     

The structure of28Si above 10 MeV excitation energy II: Assignments of quantum numbers

New assignments of quantum numbers have been obtained for more than 50 levels in²⁸Si between 8953 and 15915 keV excitation energy. They are based on the measurement of -ray angular distributions or anisotropies on 29 resonances of the²⁷Al(p, ) reaction and on the²⁴Mg(a, ) resonance atE =3355 keV. A total of 15 high-spin states withI=5–7 has been obtained and the spectrum ofT=1 states has been identified up to 15915 keV excitation energy and a maximum spinI=6.     

Low-lying levels in103Rh from Coulomb excitation

Five low-lying negative parity states of¹⁰³Rh up to 1277 keV excitation energy were observed to be Coulomb excited with 2·5–4·5 MeV protons. The de-excitation gamma rays from these levels were identified in the singles spectra recorded with a 57 cc Ge(Li) detector. The level energies, branching ratios, reduced transition probabilitiesB(E2) and the multipole mixing ratios () were obtained. The 880, 1106 and 1277 keV levels have been Coulomb excited with protons for the first time. The ambiguity in theJ values for 803 and 1106 keV levels have been resolved using ²-fits, the assigned spin values are 1/2^– and 5/2^–, respectively. The-values for 474·1 and 811·2 keV transitions were obtained for the first time. The results have been discussed in the light of previously reported results.The authors wish to thank Professor I. M. Govil for his active interest at various stages of this work. One of us (DCT) acknowledges the financial support from U.G.C., New Delhi, under Faculty Improvement Programme.     

Gas-discharge XeF* (B→X) laser with high specific output energy

The discharge characteristics of the XeF* (BX) laser are investigated. The NF₃ and Xe partial pressure of the laser gas mixture and the total gas pressure have been varied. A highest specific output energy of 4.7 J/l with an efficiency of 0.5% was obtained from a X-ray preionized Ne/Xe/NF₃ gas mixture at 6 bar with single-pulse excitation through a multichannel spark gap.     

Xenon: Oscillator strengths and photoionization

Electron energy loss spectra of Xe have been analyzed by means of Fano and Lu's collision theory of spectra. A new and improved set of empirical parameters has been determined,eigenquantum defects, orthogonal transformation matrix, anddipole matrix elements. These data have been used to calculate the autoionized profile and the asymmetry parameter of the angular distribution of photoelectrons. The autoionization profile is in agreement with the measurements of Huffman, Tanaka, and Larrabee. In addition, the theory predicts a distinct interference effect betweens andd excitation. The energetic shifting between the measured and calculated asymmetry parameter observed previously is removed. Nevertheless, deviations concerning the magnitude of nears state excitation are still left unexplained. They are probably due to insufficient resolution of the photoelectron measurement.     

Analytic solution of the covariant shell model of three dirac fermions with harmonic forces

A covariant shell model of three Dirac fermions in the center-of-mass frame is analytically solved for a particular spin-dependent harmonic-oscillator potential. Three equal-mass quarks are all assumed to be in states with identical quantum numbers ofj =1/2⁺ for the shell-model ground state. The sixtyfour-component composite wave function for three Dirac fermions is reduced to a set of four coupled differential equations for the four independent composite radial components. Hyperspherical coordinates are used. The two-body potential used vanish in the small component of the composite wave function. The various components of the composite wave function are found to have a ^l exp(– ² ) hyperradial dependence, where is the hyperradius, andl is the sum of the orbital angular momentum acting in the various components of the composite wave function. For an eigenergy equal to the proteon rest-mass energy, the root-mean-square radius calculated is about 0.84 fermi, about 80% of that calculated in an independent-particle harmonic-oscillator model with the same rest-mass energy for the system. A sixth-order polynomial equation is found for the rest-mass energy of the system in terms of the potential-strength parameter, and the quark mass, For a quark mass of zero, a quadratic equation inE ³ is obtained. One solution agrees with earlier work, and the other can be rejected on physical grounds. The various components of the composite three-body wave function are dominated by thel=0s-state component as the quark mass approaches one third of the system rest-mass energy. For zero quark mass thes-wave component is about 29% of the normalization, thep wave about 44%, thed wave about 22%, and thef wave 4% of the normalization.     

The 2-site Hubbard and $\mathsf{t}$-$\mathsf{J}$ models

The fermionic and bosonic sectors of the 2-site Hubbard model have been exactly solved by means of the equation of motion and Greens function formalism. The exact solution of the t-J model has been also reported to investigate the low-energy dynamics. We have successfully searched for the exact eigenoperators, and the corresponding eigenenergies, having in mind the possibility to use them as an operatorial basis on the lattice. Many local, single-particle, thermodynamical and response properties have been studied as functions of the external parameters and compared between the two models and with some numerical and exact results. It has been shown that the 2-site Hubbard model already contains the most relevant energy scales of the Hubbard model: the local Coulomb interaction U and the spin-exchange one . As a consequence of this, for some relevant properties (kinetic energy, double occupancy, energy, specific heat and entropy) and as regards the metal-insulator transition issue, it has resulted possible to almost exactly mime the behavior of larger systems, sometimes using a higher temperature to get a comparable level spacing. The 2-site models have been also used as toy models to test the efficiency of the Greens function formalism for composite operators. The capability to reproduce the exact solutions, obtained by the exact diagonalization technique, gives a firm ground to the approximate treatments based on this formalism.Received: 16 July 2003, Published online: 30 January 2004PACS: 71.10.-w Theories and models of many-electron systems - 71.10.Fd Lattice fermion models (Hubbard model, etc.)     

Distribution for fermionic discrete lattice gas within the canonical ensemble

The distinct deviations from the Fermi-Dirac statistics ascertained recently at low temperatures for a one-dimensional, spinless fermionic discrete lattice gas with conserved number of noninteracting particles hopping on the non-degenerated, well-separated single-particle energy levels are studied in numerical and theoretical terms. The generalized distribution is derived in the formn(h)={Y _h exp [(_h–)]+1{su–1 valid even in the thermodynamic limit, when the discreteness of the energy levels is kept. This distribution demonstrates good agreement with the data obtained numerically both by the canonical partition function technique and by Monte Carlo simulation.