Mathematical simulation of melting inside a square cavity with a local heat source

Numerical simulation of transient melting regimes inside an enclosure in the presence of a local heat source has been carried out. Mathematical model formulated in terms of dimensionless variables such as stream function, vorticity, and temperature has been numerically solved by finite difference method. Effects of the Rayleigh number 4·10⁵ ≤ Ra ≤ 5·10⁷, Stefan number 2.21 ≤ Ste ≤ 5.53, and dimensionless time on velocity and temperature fields as well as on the local Nusselt number along the heat source surface have been analyzed in detail. The transient effects of the considered process at high values of the Rayleigh number have been identified.     

Electron paramagnetic resonance of Ce3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Ce³⁺ impurity ions in single crystals of lead thiogallate PbGa₂S₄ have been reported. The Ce³⁺ ions substitute for Pb²⁺ ions in the crystal lattice of PbGa₂S₄. A number of paramagnetic cerium centers in lead thiogallate have been observed. The spectra are described by the spin Hamiltonian of rhombic symmetry with the effective spin S = 1/2. The g factors of the main cerium centers have been determined. A large number of paramagnetic centers are due to both nonequivalent positions of lead and local charge compensation under the substitution Ce³⁺ ?? Pb²⁺.     

The homogeneization quenching of platinum

In this paper the defect structure of platinum during homogeneization quenching has been studied by transmission electron microscopy on electropolished foils. Several black dots about 100 Å in diameter have been observed on the foils, corresponding to a density of the order of 10¹⁴ ?3. The dots have been interpreted as clusters of vacancies retained in the presence of impurities. The analysis of the number of quenched-in vacancies leads to the conclusion that the clusters are spherical and about 110 Å in diameter. In contrast to copper no dislocation density growth with the number of quenchings could be observed as the dislocation density is less than 10⁸ cm^?2, which could not be detected exactly enough by the electron microscope method.     

Nuclear reactions of medium and heavy target nuclei with high-energy projectiles II. Fragmentation ofnatAg and197Au by 3.65 AGeV12C-ions and 3.65 GeV protons

The cross sections of a number of target fragmentation products formed in nuclear reactions of 3·65 A GeV¹²C-ions and 3·65 GeV protons with^natAg and¹⁹⁷Au have been measured. The measurements have been done by direct counting of irradiated targets with Ge(Li) gamma-ray spectrometers. Comparisons between these and other data have been used to test the hypotheses of factorization and limiting fragmentation. The total cross section for residue production in both reactions indicates that target residues are formed mainly in central collisions.     

The decay of the 23min131Sb

The direct and the coincidence spectra of gamma-rays from the¹³¹Sb decay have been measured by means of different Ge(Li) detectors. The Sb sources have been prepared from mixture of²³⁵U thermal neutron fission products. The proposed level scheme of the¹³¹Te nuclei is based on the coincidence measurements, the analysis of the energy sums and the reaction data. The 49 of the total number of 64 gamma-rays observed have been placed in the present decay scheme. Properties of the some levels in¹³¹Te are compared with those observed in other oddmass Te isotopes. A probable structure of some of the excited states in¹³¹Te is discussed.     

An empirical fit to estimated neutron emission cross sections from proton induced reactions

Neutron emission cross section for various elements from⁹Be to²⁰⁹Bi have been calculated using the hybrid model code ALICE-91 for proton induced reactions in the energy range 25 MeV to 105 Me V. An empirical expression relating neutron emission cross section to target mass number and incident proton energy has been obtained. The simple expression reduces the computation time significantly. The trend in the variation of neutron emission cross sections with respect to the target mass number and incident proton energy has been discussed within the framework of the model used.     

States in 17O excited in the 13C + 9Be \rightarrow 13C + 2 \alpha + n reaction at 90 MeV

The ¹³C + ⁹Be reactions have been measured using a ¹³C beam with an incident energy of 90MeV. The ¹⁷O excitation energy spectra have been reconstructed from the detected ¹³C + $ \alpha$ coincidences. A number of the ¹⁷O states has been observed and their structure has been discussed in relation to the well-known ¹⁶O cluster states.     

Study of the Cumulative Number Distribution of Charged Particles Produced in d<Superscript>12</Superscript>C-Interactions at 4.2 A GeV/c

In this paper the behavior of the cumulative number and also with maximum values of cumulative number distribution of protons, π⁺ and π^?-mesons, have been studied, produced in d¹²C-interctions at 4.2 A GeV/c. The experimental data has been compared with ones coming from the Dubna version of the cascade model. In the analysis we have observed; four different regions in the cumulative number distributions for all charged particle and protons and the last region is corresponding to values of cumulative number greater than 1; for pions number of regions decreased to 2 for π^±-mesons but cumulative area is absent for both mesons. Cascade cannot describe satisfactorily the distributions of the cumulative protons and cumulative π^?+-mesons, it gives less number for the all produced particles. In case of particles with maximum values of cumulative number cascade can describe the behavior of cumulative number distribution well. There exist some events with two cumulative particles which could not describe by the cascade dynamics. May be collective nucleon effect could be reasons of the observation two cumulative particles events.     

Spectroscopy of silver complexes in solutions of inorganic compounds

The absorption, photoluminescence, and photoexcitation spectra of a number of inorganic solid solutions with a silver ion impurity have been examined. The influence of the temperature on the spectral characteristics of haloid and oxygen-containing solutions activated with Ag⁺ ions has been investigated. The temperature dependences of the luminescence quantum yield of solid solutions with Ag⁺ impurity in the temperature range 77-150 K have been studied. It is shown that the spectra under observation are conditioned by electron transition between energetic levels of Ag⁺ ion which are deformed because of the interaction with environment.     

Pole and quark-counting model for form factors of light nuclei

The dispersion relation approach is applied to form factors of light nuclei. The form factor is approximated by a sum of poles. The asymptotic behaviour of form factor is assumed to be determined by quark-counting rule. Examples of³He,⁴He and⁶Li are considered. Data on form factors of these nuclei have been fitted with smaller number of parameters than usual, and corresponding charge distributions have been found which differ from conventional ones in central regions of nuclei.     

High-spin structures of the odd-A 43 97−105 Tc isotopes

The ^99?105Tc isotopes have been produced at high spin as fission fragments following the fusion reaction ³⁷Cl(170 MeV) + ¹⁷⁶Yb and studied with the Euroball3 array. The high-spin structures of ¹⁰³Tc have been identified for the first time. From the systematics of the yrast states of ^97?105Tc, the location of individual proton states can be analyzed as a function of the neutron number.     

54Cr, 54, 58Fe, 58Ni(d,p)55Cr, 55, 59Fe, 59Ni Vector analyzing power measurements

(d, p) cross sections and vector analyzing powers have been measured at 10 MeV bombarding energy for targets ⁵⁴Cr, ⁵⁴Fe, ⁵⁸Fe and ⁵⁸Ni. The systematic behaviour of the analyzing powers with Q for states of a given J^π has been observed. Spins of a number of states in ⁵⁵Cr and ⁵⁹Fe have been deduced.     

77Se and125Te nuclear magnetic resonance investigations in II–VI and IV–VI compounds

The NMR signals of⁷⁷Se or¹²⁵Te have been measured in II–VI and IV–VI-compounds ZnSe, CdSe, HgSe, PbSe and ZnTe, CdTe, HgTe, PbTe relative to aqueous solutions of Na₂SeO₃ or K₂TeO₃. The chemical shifts of about ?600 ppm for⁷⁷Se and of about ?2700 ppm for¹²⁵Te have been compared with theoretical calculations. For⁷⁷Se in hexagonal CdSe an anisotropic chemical shift has been observed and for¹²⁵Te in CdTe and PbTe linesplittings have been found. The linewidths of the⁷⁷Se and¹²⁵Te NMR signals increase with the atomic number of the counterions.     

Parametres thermodynamiques des defauts ponctuels dans le chlorure de strontium pur ou dope par des cations monovalents ou trivalents

The electrical conductivity of a great number of SrCl₂ crystals, either purified or doped with Na⁺, K⁺, Rb⁺, Gd³⁺ and Ce³⁺, has been studied. The microscopic models used for the interpretation of the results have been justified by dielectric loss measurements, ITC and EPR (for Gd³⁺). The thermodynamic parameters of point defects have been derived, over the temperature range 420–860 K, from the fitting of experimental data to the equations of the Lidiard-Debye-Hückel theory. The values of the enthalpies of Cl vacancy mobility (0.30 eV) and Cl interstitial mobility (0.76eV), association of Cl vacancy with Na⁺ (0.53 eV), K⁺ (0.42 eV), Rb⁺ (0.40 eV) and ionic Frenkel defects formation (2.20 ± 0.11 eV) have been used in the interpretation of the experimental results over a large concentration range. The solubility enthalpy of Na ⁺ is 1.2 ± 0.1 eV; the solubility of the rare earths is very small at low temperature. The thennodynamic parameters which have been found have been compared with other known experimental values and with theoretical results.     

Photoassociation of heteronuclear lithium

Photoassociation of ultracold heteronuclear ⁶Li⁷Li molecules is observed inside a combined magneto-optical trap for ⁶Li and ⁷Li. The trapped atomic cloud is illuminated by a tunable single-mode laser and the number of trapped ⁷Li atoms is monitored by absorption spectroscopy. Characteristic hyperfine resolved spectra have been recorded for singlet spin orientation. Interesting saturation effects have been observed. Received: 12 July 2001 / Revised version: 1 October 2001 / Published online: 23 November 2001     

Dynamic effects in iron phthalocyanine-like compounds

⁵⁷Fe isotope-enriched iron phthalocyanine has been synthesized and studied by the Mössbauer spectroscopic method. The samples were investigated in the temperature range 100–350 K. Some peculiarities in atomic and molecular electronic structure fluctuations were observed. The intermediate Fe oxidation states are observed and it has been found that the rate of charge redistribution is temperature-dependent. The correlation between the temperature behavior of the isomeric shift and quadrupole splitting has been demonstrated. At elevated temperatures above 300 K, the Fe²⁺ oxidation number is quasistable. The alteration of Fe oxidation number is associated with fluctuations of electron charges, and the electron-accepting and electron-donating properties of surrounding ligands. The energy barriers separating Fe oxidation states have been determined. The possibility of modeling Mössbauer spectra of electron-transfer systems has been shown.     

Comparative study for nucleus-nucleus interactions and modified cascade evaporation model at (4.1 – 4.5) AGeV/c

The characteristics of the nucleus-nucleus collisions at high energy for the interactions of ¹H, ⁴He, ¹²C, ¹⁶O, ²²Ne, ²⁸Si and ³²S with emulsion at momentum (4.1 – 4.5) AGeV/c have been investigated. It has been found that the multiplicity distributions of the different emitted particles and their average values can be described by the modified cascade evaporation model. The model reproduces satisfactorily the multiplicity distributions of the shower, grey and black particles and the correlations between their multiplicities. It has been seen that the number of the produced shower particles increases with the increase of the projectile mass number. From the correlation between the average multiplicity of the evaporation particles and the number of the produced particles, it was found that a phase transition in the target system may occur. The calculated pseudo-rapidity distributions of the produced shower particles are typically Gaussian shaped in the mid-rapidity region and agree well with the experimental data. Also, the angular distributions of the grey and black particles have been investigated. The angular distributions of the grey particles show a universal shape independent of the type of projectile. The angular distributions of the black particles are nearly isotropic with a small asymmetry in the forward direction. The modified cascade evaporation model, reproduces the general characteristics of the nucleus-nucleus interactions and gives an explanation for the multiparticle production process.     

Effect of Sm3+ concentration on electroluminescence excitation mechanism in (Zn,Cd) S phosphors

(Zn, Cd)S phosphors activated with varying concentrations of Sm³⁺ have been prepared in argon atmosphere, and their voltage dependence of EL-brightness, current-voltage characteristics and SEM measurements have been carried out. The nature of variation of EL-brightness with voltage is found to depend on Sm³⁺ concentration. The result is interpreted as an effect of increase in number and effectiveness of Mott-Schottky type potential barriers which probably exist at the grain boundaries.     

Core-level shifts,isomer shifts and the electron distribution of iron

The radial integrals of 1/r and 1/r³ have been calculated for a number of ion states of Fe. Correlations involving different inner-shell binding energies and atomic charges have been studied and a method for estimating effective valence-electron populations is discussed.     

Observations on Some New Separated Flames in Analytical Emission Spectroscopy

The renewed interest in flame emission spectroscopy (FES) in recent years has lead a number of workers to investigate the potential of the mechanically separated or the gas sheathed flame as a low background, high temperature atom reservoir in analytical spectroscopy. The work reported so far has been reviewed elsewhere^2,3, and will not be considered here, other than to indicate that only acetylene has been extensively investigated as a fuel for separated flames in FES. Separated hydrogen flames have been applied only to atomic fluorescence spectroscopy (AFS)^4-6 particularly when non-dispersive detector systems have been used⁶. The object of the present investigation was to examine the potential application of the separation of some recently proposed flames^7-11 in emission spectroscopy, including the nitrous oxide-hydrogen flame, the merits of which have recently been the subject of controversial discussion^7,8, and the air and nitrous oxide MAPP Gas flames, which have been tentatively suggested^9-11 as safer alternatives to the equivalent acetylene flames. (MAPP Gas is a registered trademark of the A i r Reduction Company.)