QSAR modelling of the toxicity to Tetrahymena pyriformis by balance of correlations

Balance of correlations is an approach to build up quantitative structure–property/activity relationships (QSPR/QSAR). This approach is based on a split into the subtraining, calibration and test sets instead of classic split into training and test sets. The function of the calibration set is the preliminary check up of the model. In other words, the calibration set is like a preliminary test set. Computational experiments (with the Monte Carlo method) have shown that the statistical characteristics of the prediction for the toxicity to Tetrahymena pyriformis (the 50% growth inhibition concentration, IGC₅₀) based on the balance of correlations are better than the statistical characteristics of the prediction based on the classic scheme.     

On the investigation of nucleon-nucleon correlations by means of high-energy scattering

The possible effects of short-range dynamical nucleon-nucleon correlations on high-energy hadron scattering on ⁴He are examined. The Glauber theory of multiple scattering is used as the basis for the computations. The conclusion is that very small effects are to be expected for elastic and sum total inelastic scattering of commonly available projectiles.     

Synthesis of superconducting compounds by thermolysis of volatile hydrides and organometallic compounds on glowing wires

The synthesis of high temperature superconducting phases in the NbGe, NbSn, VSi, VGe, VSn, NbC and MoC systems is described by method consisting in the thermolysis of volatile hydrides or organometallic compounds on resistively heated wires. For face-centred cubic NbC a higher transition temperature than previously reported was obtained. The A15 phase boundary of NbGe is extended towards the stoichiometric 3:1 composition, affording samples of Nb₃ Ge with a T_c onset of 15.8°K.     

Determination of the Planck constant by means of a watt balance

The kilogram is the only base unit of the Système International d’unités (SI) still defined by a material artefact. Regarding the past evolution of the SI and the poor knowledge of the stability of the international prototype, its definition is not satisfactory. In the long term, it would be better to move to a definition based either on atomic properties or on fundamental constants. Among the various researches in progress in metrology laboratories, one of the most promising ways seems to be the watt balance. Its principle consists in comparing a mechanical power to an electromagnetic power. This comparison results from a measurement performed in two steps: a static measurement during which the Laplace force acting on a coil driven by a DC current and subjected to an induction field is compared to the weight of a standard mass, and a dynamic measurement where the induced voltage at the terminals of the same coil is determined when it is moved in the same field at a known velocity. The measurement of electrical quantities in terms of the Josephson and the quantum Hall effects then allows the mass unit be linked to the Planck constant. Although the principle of the experiment remains simple and direct, obtaining sufficiently low uncertainty ( 10^-8) implies that devices relevant of various fields of physics must be implemented at their best level. In this paper, a review of the present developments at international level is presented.     

Derivation of the classical theory of correlations in fluids by means of functional differentiation

The k-particle, infinite-volume distribution functions $\text{n}\text{?}{}_{\mathrm{k}}\text{(}\text{r}{}_1\text{, …,}\text{r}{}_{\mathrm{k?1}}\text{, γ)}$ and modified Ursell correlation functions $\text{U}\text{?}{}_{\mathrm{k}}\text{(}\text{r}{}_1\text{, …,}\text{r}{}_{\mathrm{k?1}}\text{, γ)}$ of a classical system of particles with the two-body potential $\text{q(}\text{r}\text{) + γ}{}^{\mathrm{\nu }}\text{K(γ}\text{r}\text{)}$ are considered. The limiting values of the functions $\text{n}\text{?}{}_{\mathrm{k}}\text{(}\text{r}{}_1\text{, …,}\text{r}{}_{\mathrm{k?1}}\text{, γ),}\text{n}\text{?}{}_{\mathrm{k}}\text{(}\text{S}{}_1\text{/γ, …,}\text{S}{}_{\mathrm{k?1}}\text{/γ, γ)}$ and $\text{γ(}{}^{\mathrm{1?k}}\text{)ν}\text{U}\text{?}{}_{\mathrm{k}}\text{(}\text{S}{}_1\text{/γ, …,}\text{S}{}_{\mathrm{k?1}}\text{/γ, γ)}$ in the limit γ → 0 are calculated, under fairly weak conditions on q and K, by a method involving functional differentiation. These limiting functions are used to describe the molecular structure of the various states of the system both in the range of the potential q(r) and in the rage of the potential γ^νK(γr). The direct correlation function c? (r, γ) is also considered and it is shown that for $\text{S}\text{≠ 0}$, $\text{lim}{}_{\mathrm{\gamma \to 0}}\text{γ}{}^{\mathrm{?\nu }}\text{c}\text{?}\text{(}\text{S}\text{γ}\text{, γ) = ?βK (}\text{S}\text{)}$, for all one-phase states, where β is the reciprocal temperature. Special cases of our results confirm those of other authors, including the well-known results of Ornstein and Zernike.     

Lattice defects in ion-implanted aluminium studied by means of perturbed angular correlations

Migration and clustering of lattice defects after implantation of¹¹¹In in Al and subsequent annealing at temperatures in the range from 80 to 800 K were investigated applying the DPAC technique. The effects of implantation dose, implantation temperature, laser irradiation, and plastic deformation were studied. The measurements on plastically deformed Al were complemented by positron lifetime measurements. We observed four In-defect clusters that can be flagged by well-defined hyperfine interaction parameters, and we determined their symmetry properties by using single-crystal samples. Important conclusions are: (i) monovacancies are not trapped by In-atoms, (ii) small In-defect clusters are formed by direct trapping of divacancies and/or trivacancies, and (iii) extended In-defect clusters are very stable and anneal in the temperature range 600–700 K. Consequences for the interpretation of other measurements on dilute Al(In) alloys are discussed.On leave from Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India.     

Inclusion of interparticle correlations in the collision integral by means of continuous integration. II

Representation of the causal two-body Green's function in the form of a double (with respect to the external fields and the trajectories) continuous integral with a subsequent density expansion and termwise integration with respect to the external fields is used to consider correlation corrections to the collision integral for charged quantum particles in the field of the compensating background. The first-order coupling approximation leads to a nonlinear dependence of the collision integral on the two-particle Green's function, and in developing different approximations for the latter, collision integrals associated with the ring and ladder diagrams of Silin and Balescu that allow for a slow time delay, as in [1, 2], are obtained, as is a collision integral with an exponential cutoff for small distances.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 118–121, April, 1976.The author is grateful to L. Ya. Kobelev for suggesting the topic and his interest in the work, and to B. N. Shalaev for useful discussions.     

Analysis of Mg-B compounds by means of Auger electron microprobe

For the development of a low-cost MgB₂ superconductor the “powder-in-tube” (PIT) technique is investigated. Mechanically alloyed MgB₂ powder provides a favorable microstructure and phase composition for the low temperature preparation of MgB₂ tapes with superconducting properties. The composition of sintered bulk samples and Fe-clad MgB₂ tapes made of mechanically alloyed MgB₂ has been investigated by Auger micro-analysis. Due to the process the samples contain about 15% oxygen. Pure MgB₂ crystallites were investigated as standard for stoichiometry and peak shape analysis.     

UV excimer laser photochemistry of hybrid organometallic compounds of gallium

The gas phase ultraviolet (UV) excimer laser induced photolysis of the gallium-alkyls Ga(t-C₄H₉) _n ^– (CH₃)_3–n (n=0, 1, 2, 3) was studied, using photolysis wavelengths of 308, 248, and 193 nm. The photofragments Ga, GaH, and GaCH₃ were detected by laser ionization time-of-flight mass spectroscopy, while the hydrocarbon products CH₄, C₂H₆, HC(CH₃)₃ and H₂C=C(CH₃)₂ were identified using Fourier transform infrared (FTIR) spectroscopy. The formation of the GaH photofragment, and a high olefin-to-alkane product ratio, for Ga(t-C₄H₉)₂(CH₃) and Ga(t-C₄H₉)₃ are interpreted to indicate a -hydrogen elimination process. However, -hydrogen elimination only occurs after fission of the weakest Ga-C bond, thus no -hydride elimination is observed for Ga(t-C₄H₉)(CH₃)₂. Detection of C₂H₆ for Ga(CH₃)₃ and Ga(t-C₄H₉)(CH₃)₂, but not for Ga(t-C₄H₉)₂(CH₃), shows that under our experimental conditions the formation of ethane is as a result of the reductive elimination of the methyl groups, and is not due to the recombination of two free methyl radicals.     

Molecular spectroscopy by means of ESCA: V. Boron compounds

The B 1s binding energies of 23 compounds, including boron hydrides and carboranes have been measured in the vapor state. Correlations with Pauling charges and with shifts, calculated from the potential model using CNDO charges, are presented. The B 1s binding energies are subsequently discussed in terms of the chemical reactivity of the compounds. The iodomethanes have also been studied, and an electronegativity value for iodine suitable for ESCA correlations is given.     

The nonlinear optical response of new organometallic compounds under picosecond excitation

The nonlinear optical response of three new organometallic compounds was studied by z-scan method under picosecond excitation at 1064 and 532 nm. The compounds showed self-focus effect at both wavelengths, and effective reverse saturation absorption at 532 nm and strong two-photon absorption at 1064 nm occurred. Through calculating and comparing the nonlinear optical indexes of the compounds, we found that the third-order nonlinear susceptibility was enhanced by two-fold for one photon transition resonant effect, and incorporating different heavy metal atoms in the delocalized organic system slightly influenced the nonlinear optical indexes.     

The comparison of the ability for induction of antiferroelectric phase of cyanoterminated compounds by means of miscibility studies

Ability for an induction of the antiferroelectric phase in compounds with a cyano group in a terminal position has been tested by comparison of phase diagrams of their mixtures. Most of the tested compounds do not cause the induction by themselves but they support an antiferroelectric ordering in mixtures. The core comprising biphenylate fragment has a higher tendency to support the antiferroelectric order.     

An ESCA study of Sn organometallic compounds: Solid state broadening effects

X-ray photoelectron spectra have been recorded for a number of solid and gaseous organotin compounds. Solid-state charging effects (such as differential charge broadening) can be large, though we have almost eliminated them by subliming very thin films onto platinum metal. In this way, we have obtained solid-state Sn 3d line widths that are within 10% of the analogous gas-phase values. The quality and reproducibility of the solid-state spectra likewise approach those of gases.The general correlation between ESCA Sn 3d line widths and Mössbauer quadrupole splittings indicates that the broadening of the Sn 3d lines is due to crystal-field splitting from the C₂⁰ term (the quadrupole term) in the crystal-field expansion. There is a general correlation between ESCA binding energies and Mössbauer isomer shifts for the solids.