A stochastic probing algorithm for global optimization

Recently, simulated annealing methods have proven to be a valuable tool for global optimization. We propose a new stochastic method for locating the global optimum of a function. The proposed method begins with the subjective specification of a probing distribution. The objective function is evaluated at a few points sampled from this distribution, which is then updated using the collected information. The updating mechanism is based on the entropy of a move selecting distribution and is loosely connected to some notions in statistical thermodynamics. Examples of the use of the proposed method are presented. These indicate its superior performance as compared with simulated annealing. Preliminary considerations in applying the method to discrete problems are discussed.     

RF sputtered thin films of highT cY-Ba-Cu-O

Y-Ba-Cu-O films are grown on strontium titanate substrates by RF sputtering from a single composite target. A barium-deficient annular ring with diameter equal to that of the target dimension is repeatedly observed. Films inside this ring are deposited exclusively at the close target-substrate distance. At larger distances the films grow more in exterior regions rather than in the interior region of the ring. Stoichiometry, structural morphology and superconducting transition temperatures are studied for various regions of the film. The films are superconducting when sintered in flowing oxygen at 950°C with onset at 100 K and a broad transition width.     

Effect of cation distribution on the properties of Mn0.2ZnxNi0.8−xFe2O4

Mn_0.2Zn_xNi_0.8−xFe₂O₄ (x=0.2, 0.3, 0.4, 0.5, 0.6) are synthesized by the citrate precursor method. Effects of zinc substitution on DC resistivity, dielectric relaxation intensity, initial permeability, saturation magnetization and Curie temperature have been investigated. It is observed that resistivity increases with increase in zinc concentration up to x=0.5 and then decreases. The observed behaviour is explained in terms of hopping and site preference of ions in the lattice. The main contribution to dielectric relaxation intensity is observed to be due to space charge polarization. Initial permeability is observed to increase with increase in zinc concentration. Saturation magnetization increases up to x=0.4 and then starts decreasing. Canting effect is observed for higher zinc concentrations.     

Thermal decomposition of barium oxomolybdenum(VI) oxalate

A new molybdenum(VI) oxalato complex, Ba[MoO₃(C₂O₄)]·3H₂O (BMO), was prepared and characterized by chemical analysis and infrared spectral studies. Thermal decomposition studies were made using thermogravimetry and differential thermal analysis. Dehydration reactions take place up to 280°C in three stages with loss of one half, one and a half and one mole of water per mole of BMO, respectively. Decomposition of oxalate takes place between 280 and 435°C in a single step to give BaMoO₄ as the end product, which was characterized by chemical analysis, infrared and X-ray studies. The X-ray diffraction pattern of BMO shows that it is an amorphous compound. A chain structure containing MoO₆ octahedra linked through oxygen is proposed on the basis of the infrared absorption spectrum.     

Metal derivatives of amidoximes : II. Synthesis of 2-(tributylstannoxy)-, 2-(triphenylstannoxy)- and 2-(trimethylsiloxy)-3-hydro-4-alkyl or -4-phenyl-1,3,5,2- oxadiazaboroles

2-(Tributylstannoxy)-, 2(triphenylstannoxy)- and 2-(trimethylsiloxy)-3- hydro-4-alkyl- or -4-phenyl-1,3,5,2-oxadiazaboroles have been synthesized, and their properties examined.     

Chemistry of platinum hydrides : XXV. Preparation and characterization of platinum(II) hydridotin complexes containing bulky phosphines

Platinum(II) hydridotin complexes containing bulky phosphine ligands, trans-Pt(H)L₂(SnR₃) have been prepared from: (i) the equimolar reaction between corresponding platinum(II) dihydride complexes and HSnR₃ (Cy = cyclohexyl), P-i-Pr₃, P-t-BuPh₂, P-t-Bu₂Me; R = Ph), (ii) the oxidative addition of the corresponding zerovalent complexes, Pt⁰L₂, with HSnR₃ (L = P-i-Pr₃, P-t-BuPh₂; R = Ph), (iii) the reaction of the corresponding platinum(II) dihydride complexes with ClSnR₃ in the presence of pyridine in benzene (L = P-i-Pr₃, P-t-BuPh₂; R = CH₃, n-Bu), (iv) the sodium borohydride reduction of the corresponding hydridochloride complexes Pt(H)Cl(PR₃)₂ with ClSnR₃ in THF (L = PCy₃; R = Ph), these compounds have been characterized by their elemental analysis, infrared, ¹H and ³¹P NMR spectral data.     

Rhodium(I) derivatives of diethylbispyrazolylborate

Bis-substituted rhodium(I) polypyrazolylborates of the type L₂RhBPz₂Et₂ (L = CO or RNC where R = p-CH₃C₆H₄, t-C₄H₉ or p-CH₃C₆H₄SO₂CH₂) have been prepared and characterized and hence the analogous rhodium(III) derivatives by oxidative addition reactions with iodine, iodomethane, or mercury(II) chloride.     

Attractions, water structure, and thermodynamics of hydrophobic polymer collapse

We explore the prospects of a perturbation approach for predicting how weak attractive interactions affect collapse thermodynamics of hydrophobic polymers in water. Specifically, using molecular dynamics simulations of model polymers in explicit water, we show that the hydration structure is sensitive to the strength of the van der Waals attractions but that the hydration contribution to the potential of mean force for collapse is not. We discuss how perturbation theory ideas developed for small spherical apolar solutes need to be modified in order to account for the effect of attractions on the conformational equilibria of polymers.     

Lattice dynamics of ND4I and NH4I crystals

The phonon dispersion curves and one phonon density of states for ND₄I and NH₄I crystals in the sodium chloride structure have been calculated by making use of the deformation dipole model of Hardy incorporating general short range forces out to second neighbours. Since the electronic configuration of both the compounds is identical, we have used the input data of NH₄I to calculate the model parameters for both the crystals. The results have been compared in the three principal symmetry directions with the neutron scattering measurements available only in case of ND₄I. The theoretical results show a reasonably good agreement with the experimental data.     

A 10000 particle molecular dynamics model with long range forces

A technique is described for the computer simulation of the motion of 10000 simulated molecules. The number of computer operations per time-step is proportional to the number of simulated particles even though the force of interaction may be long range and no force cut-off is employed.