Interfacial tension and critical wetting phenomena of the binary liquid mixture cyclohexane-acetonitrile near the critical solution temperature

The determination of the capillary parameter for the partially miscible binary liquid system acetonitrile + cyclohexane has been reported. The system has closely matched densities and the data points are affected by gravity only when the fractional change of the temperature from the critical temperature is about 10^–6. The system also exhibits very interesting wetting properties. The interfacial tension has been fitted to a power law =0.061 (T_c-T)^1.26. The effect of doping with water and the instability of the wetting layer, which crucially depends on the interfacial tension, are studied.     

On the mechanism of the ion-molecule reaction CH3+ + CH4 = C2H5+ + H2

Experimental evidence supporting the “direct” reaction model and the “intermediate complex” model for the reaction CH₃⁺(CH₄, H₂)C₂H₅⁺ are analysed. It is shown that the evidence for the former can equally well be interpreted in terms of a proposed model of persistent complex formation and decay. The plausibility of a “direct” mechanism is discussed and is found to be poor.     

Infra red quantum dot photolithography

CdS quantum dots were fabricated photolithographically on the surface and in the bulk of silica hydrogels, as well as on the surface of planar substrates. Silica hydrogels were prepared with a standard base-catalyzed route, and the solvent was exchanged with a cold aqueous solution of Cd(NO₃)₂, NH₄OH, thiourea, and a capping agent, e.g., 2-mercaptoethanol. The samples were then exposed to a focused infrared beam produced by a continuous-wave Nd:YAG laser. The precursors reacted upon heating, and CdS nanoparticles formed in the illuminated regions. Use of capping agents allowed to control the mean particle size, while focusing of the beam inside hydrogel monoliths generated nanoparticles in their bulk, but not at the surface. Planar substrates were patterned by illuminating a precursor solution spin-coated on the substrates. The average size of the CdS nanoparticles could be varied between about 1.5 and 4.5 nm by varying the type and the concentration of the capping agents.     

Fatigue life prediction of welded cruciform joints using strain energy density factor approach

The influences of two welding processes, namely, shielded metal arc welding (SMAW) and flux cored arc welding (FCAW), on fatigue life of cruciform joints containing lack of penetration (LOP) defects have been analyzed by using the strain energy density factor (SEDF) approach. Load carrying cruciform joints were fabricated from ASTM 517 ‘F’ grade steel. Fatigue crack growth experiments were carried out in a mechanical resonance vertical pulsator (SCHENCK 200 kN capacity) with a frequency of 30 Hz under constant amplitude loading (R=0). It was found that the fatigue lives of the cruciform joints fabricated by SMAW process were relatively higher than the FCAW counterpart. Moreover, fracture mechanics equations have been developed to predict the fatigue life of the cruciform joints fabricated by the above-mentioned two processes.     

3-[4-Bromo-α(<Emphasis Type="Italic">R</Emphasis>*)-methoxybenzyl]-6-chloro-3(<Emphasis Type="Italic">S</Emphasis>*),4(<Emphasis Type="Italic">S</Emphasis>*)-dihydroxychroman: X-ray and DFT Studies

Sodium borohydride reduction of E-3-benzylidenechromanone epoxides in dry methanol has afforded 3(S*), 4(S*)-dihydroxy-3-[α(R*)-methoxybenzyl]chromans as an interesting class of products, the structures of which have been assigned mainly from spectral data and consideration of the mechanistic aspects. X-ray diffraction study of one of them, 3-[4-bromo-α(R*)-methoxybenzyl]-6-chloro-3(S*),4(S*)- dihydroxychroman, is performed. The title compound crystallizes in the monoclinic sp. gr. P2₁/n, with a = 13.336(6) Å, b = 10.866(5) Å, c = 27.166(11) Å, β = 95.193(6)°, V = 3920(3) ų, and Z = 8. Supramolecular construction of the compound involves O–H···O intermolecular hydrogen bonds as well as three other types of non-covalent interactions which are responsible for crystal packing. Density functional theory was applied for geometry optimization, molecular orbital calculations, and prediction of UV spectral features. The geometric parameters (bond lengths, bond angles, and dihedral angles) for the representative compound obtained from density functional theory with B3LY6-31G basis set were in good agreement with experimental values.     

Ligational behaviour of two biologically active N−S donors towards cobalt(III), iron(III), iron(II) and rhodium(III)

Summary The chelating behaviour of two biologically active ligands, pyridine-2-carboxaldehyde(4-phenyl) thiosemicarbazone(L₁H) and pyridine-2-carboxaldehyde thiosemicarbazone(LH), towards Fe^III, Co^III, Fe^II and Rh^III has been investigated. The ligands act as tridentate N–N–S donors, resulting in the formation of bis-chelate complexes of the type M^III(A)₂X·nH₂O (A=L₁ or L; X=Cl, ClO₄; M=Co^III, Rh^III, Fe^III), Fe^II(L₁H)₂SO₄·2H₂O and Fe^II(L₁)₂·H₂O. Biological activity of the ligands and the metal complexes in the form ofin vitro antibacterial activities towardsE. coli has been evaluated and the possible reasons for enhancement of the activity of ligands on coordination to metal ion is discussed.     

Metallic nonsuperconducting phase and D-wave superconductivity in Zn-substituted La1.85Sr0.15CuO4

Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La1.85Sr0.15CuO4, with up to 12 at. % of Zn substituted for the Cu. The results show that the quadratic temperature dependence of the inverse square of the penetration depth, indicative of d-wave superconductivity, is not affected by doping. The suppression of superconductivity leads to a metallic nonsuperconducting phase, as expected for a pairing mechanism related to spin fluctuations. The metal-insulator transition occurs in the vicinity of k(F)l approximately 1, and appears to be disorder driven, with the carrier concentration unaffected by doping.     

The large N limit of the O(N) Heisenberg spin system in two dimensions

The large N limit of the O(N) Heisenberg spin system in two dimensions (a lattice version of the non-linear σ-model) is analysed by the collective field technique. A compact expression for the mass gap and the β-function is obtained for arbitrary but fixed gN. The strong and weak coupling limits of this expression correctly reproduce the known results.     

Parametric excitation of acoustohelicon waves in a piezoelectric semiconductor

The parametric excitation of acoustohelicon waves has been studied in a piezoelectric semiconductor in the presence of a strong high frequency oscillatory electric field. The threshold electric field amplitude and the growth rate of the unstable mode have been obtained analytically and for n-InSb at 77 K the unstable mode is found to be propagating with a growth rate ～10³ s^?1 when the crystal is irradiated with a 10.6 μm CO₂ laser.