A Phase-Change Model with a Zone of Coexistence of Phases

A mathematical model for change of phase is presented, accountingfor the presence of regions in which liquid and solid coexist.The basic variables are temperature and solid fraction v. Westart from a relationship of the type =(v), supposed valid inthermodynamical equilibrium. Then for dynamical processes weintroduce a perturbation causing v to be less than its equilibriumvalue in any solidification process. This solid fraction deficiencyis governed by an ordinary differential equation containing_t, in the forcing term. The heat-balance equation is in turncoupled to the ordinary differential equation through the termv_t, ( is latent heat). Some existence and uniqueness resultsare proved and some monotonicity properties are described forpure melting or pure solidification processes.     

CYTOTOXIC AND MUTAGENIC EFFECTS OF THE PHOTODYNAMIC ACTION OF CHLOROALUMINUM PHTHALOCYANINE AND VISIBLE LIGHT IN L5178Y CELLS

Abstract The cytotoxic and mutagenic effects of chloroaluminum phthalocyanine (CAPC) plus red light have been measured in strains of L5178Y mouse lymphoma cells which differ in their DNA repair capacities. Strain LY-R, deficient in the excision repair of UV-induced dimers, was found to be relatively more sensitive to the cytotoxic effects of CAPC plus light, whereas strain LY-S, deficienl in the repair of DNA double-strand breaks, was more sensitive than strain LY-R to the mutagenic effects of the treatment. Mutation frequencies were measured in LY-S and LY-R sub-strains which were heterozygous or hemizygous at the thymidine kinase (tk) locus. The mutation frequency at the tk locus induced in the heterozygous strain LY-SI by CAPC plus light was lower than that induced by an equitoxic dose of ionizing radiation but similar to that induced by an equitoxic dose of UVC radiation: The mutation frequency at the F., dose of CAPC plus light was approximately 1100 per 10⁶ surviving cells. The induced frequency in strain LY-S1 was much higher than in either tk+l-heterozygous or ik+10 hemizygous strains of LY-R. The rate and extent of incorporation of CAPC by the LY-R strains was somewhat greater than for strain LY-S1 at early times after CAPC addition, but by the time the cells were irradiated (18 h after CAPC addition) the difference was not great enough to account for the difference in cytotoxicity. It is possible that the cytotoxic and mutagenic lesions differ and that either the quantities of the respective lesions induced or the efficiencies of repair of the respective lesions differ inversely in the two strains. light have been measured in strains of L5178Y mouse lymphoma cells which differ in their DNA repair capacities. Strain LY-R, deficient in the excision repair of UV-induced dimers, was found to be relatively more sensitive to the cytotoxic effects of CAPC plus light, whereas strain LY-S, deficienl in the repair of DNA double-strand breaks, was more sensitive than strain LY-R to the mutagenic effects of the treatment. Mutation frequencies were measured in LY-S and LY-R sub-strains which were heterozygous or hemizygous at the thymidine kinase (tk) locus. The mutation frequency at the tk locus induced in the heterozygous strain LY-SI by CAPC plus light was lower than that induced by an equitoxic dose of ionizing radiation but similar to that induced by an equitoxic dose of UVC radiation: The mutation frequency at the F., dose of CAPC plus light was approximately 1100 per 10⁶ surviving cells. The induced frequency in strain LY-S1 was much higher than in either tk+l-heterozygous or ik+10 hemizygous strains of LY-R. The rate and extent of incorporation of CAPC by the LY-R strains was somewhat greater than for strain LY-S1 at early times after CAPC addition, but by the time the cells were irradiated (18 h after CAPC addition) the difference was not great enough to account for the difference in cytotoxicity. It is possible that the cytotoxic and mutagenic lesions differ and that either the quantities of the respective lesions induced or the efficiencies of repair of the respective lesions differ inversely in the two strains.     

The interaction of Cr(CO)3 on the (n, 0) nanotube side-walls: a density functional study through a cluster model approach

Density functional calculations have been performed to investigate the functionalization of single-wall carbon nanotubes (SWNTs) with the Cr(CO)₃ metal fragment, employing extended molecular models. A circumcoronene molecule (C₅₄H₁₈), made by the fusion of 19 hexagonal carbon rings, can be regarded as a fragment of a graphene sheet. To reproduce the curvature of the SWNT surface, suitable geometric constraints have been imposed on the C₅₄H₁₈ model, freezing the positions of the outer hydrogens along the directions of the nanotube C-C bonds. Geometry optimizations have then been performed under this constraint on the Cr(CO)₃-C₅₄H₁₈ complexes, pointing out the most favourable coordination sites on the hexagonal rings of the carbon atom surface and the electronic properties of the resulting system. The effect of the curvature on the metal coordination to nanotubes has been analysed by investigating the interaction of the Cr(CO)₃ metal complex with the C₅₄H₁₈ molecules, modelling (n, 0) nanotubes with different degrees of curvature, i.e. with various values of the chiral vector (n, 0).     

Effects of molecular geometry on liquid crystalline phase behaviour: isotropic-nematic transition

The effects of range and geometry of a simple attractive square-well on the phase diagram of hard ellipsoids and hard spherocylinders is systematically studied using a simple van der Waals type theory. The orientational single particle distribution function is approximated using the Onsager trial function. The quantitative errors introduced by this are thought to be considerably smaller than the use of the van der Waals approximation, which has been shown to give qualitatively correct phase diagrams for similar models. The phase diagrams obtained for hard ellipsoids and hard spherocylinders of aspect ratios ranging between 3 and 10 with a variety of square-well attractions are found to fall into three general types. The first type shows liquid-vapour coexistence and an isotropic-nematic transition, which meet at a liquid-vapour-nematic triple point. The second type shows a marked widening of the isotropic-nematic biphasic region which pre-empts the liquid-vapour coexistence. The final phase diagram shows a strong destabilization of the nematic phase with respect to the isotropic, which results in a shift of the phase transition to higher densities and pressures as the temperature is lowered.     

Interatomic interactions and the Cotton—Mouton effect for helium

We report calculations of the interaction-induced polarizability (δα^anis), magnetizability (δξ^anis;) and hypermagnetizability (δη^anis) anisotropies for the helium gas as a function of the interatomic separation. From these data we determine the virial coefficients for the Cotton—Mouton effect and the hypermagnetizability anisotropy of helium. We also find the mean polarizability and magnetizability as a function of the interatomic separation and the virial coefficients for these properties. The results for the Cotton—Mouton effect indicate that pressure affects the Cotton—Mouton constant to the same extent as it does the second hyperpolarizability (γ) and the virial coefficient b^CME(ω, T) lies in the range of ?1.6 to ?1.8 cm³ mol^?1. This means that pressure effects for the Cotton-Mouton constant could be detected with modern experimental techniques. All calculations were carried out using the full configuration interaction technique and large basis sets of London atomic orbitals. The polarizability calculations were performed both for relevant optical frequencies as well as the static case.     

Pt/Ce0.75Zr0.25O2的催化性能及其氧移动性的 18O 同位素交换表征

 采用浸渍法制备了Pt/Ce0.75Zr0.25O2催化剂,考察了催化剂对乙醇及CO的氧化活性,并采用 18O 同位素交换、乙醇程序升温表面反应(C2H5OH-TPSR)、一氧化碳程序升温脱附(CO-TPD)和程序升温还原(H2-TPR)等技术对催化剂进行了表征. 结果表明, Pt/Ce0.75Zr0.25O2催化剂表现出较高的乙醇和CO氧化活性,其催化活性随着Pt负载量的增加而提高. 当Pt负载量为3%时,活性最高. 继续增加Pt负载量,催化剂活性下降. C2H5OH-TPSR和CO-TPD结果表明,催化剂对乙醇或CO的氧化活性与从催化剂表面脱附出来的CO2量有对应关系, CO2脱附量越大,催化剂活性越高. 18O 同位素交换结果表明,表面氧交换能力与其氧化活性有一定对应关系,催化剂的表面氧交换能力越高,氧化活性越高.     

AN ESR STUDY OF THE VISIBLE LIGHT PHOTOCHEMISTRY OF GILVOCARCIN V

Photolysis of gilvocarcin (GV) at 405 nm in argon saturated dimethylsulfoxide (DMSO) or 50% DMSO-water solutions in the presence of the sodium salt of 3,5-dibromo-2,6-dideutero-4-nitrosobenzene sulfonic acid (DBNBS-d2) generates the CH3-DBNBS-d2.spin adduct. It is postulated that this spin adduct is produced by photoreduction of DMSO by GV and the consequent formation and trapping of the generated methyl radicals. Gilvocarcin V also photoreduces oxygen and methyl viologen with quantum yields of 0.019 and 0.0012 respectively. The quantum yield for singlet oxygen formation by GV in DMSO, determined by measuring the rate of production of the nitroxyl radical produced by the reaction of 2,2,6,6-tetramethylpiperidinol with singlet oxygen, was found to be 0.15. Thus, GV photochemistry proceeds by both Type I and Type II pathways which could contribute to the reported GV phototoxicity in biological systems.     

Ternary oil—water—amphiphile systems: self-assembly and phase equilibria

The micellization properties and phase behaviour of model ternary surfactant—oil—water systems were studied by grand canonical Monte Carlo simulations assisted by histogram reweighting techniques. Larson's lattice model was used for a symmetrical H₄T₄ surfactant, where H represents hydrophilic and T hydrophobic groups. In contrast to earlier studies, oil chains of variable length, from T to T₄, were studied and the effect of added oil on the critical micelle concentration (cmc) was determined quantitatively. It was found that the cmc decreases as the volume fraction of oil in the aqueous phase is increased. Longer oil chains have a stronger effect than shorter chains for the same volume fraction. The oil, tail and head density profiles were obtained for typical micelles. Simulation results for the density profiles indicate that long chain oils are almost exclusively located within the micellar aggregates, in agreement with single-chain mean-field theory predictions. Ternary phase diagrams were obtained both by simulations and by quasichemical theory. The results suggest that the critical micelle concentration line is directed towards the oil-lean corner of the three-phase triangle, if there is one present in the system. It was also found that the amount of oil that can be dissolved in the ternary system increases sharply at the surfactant critical micelle concentration, indicating that micellization greatly enhances oil solubility.     

Density dependence of the electric-field-gradient induced birefringence of the helium,neon and argon gases

An ab initio investigation of the density dependence of the electric-field-gradient induced birefringence (EFGB) for the noble gases helium, neon and argon is presented. To determine the second coefficient in the virial expansion of the molecular EFGB constant _mQ, the effect of two-body interactions has been studied by computing the internuclear dependence of the molecular quadrupole moment and of the dipole-dipole-quadrupole and dipole-magnetic dipole-dipole hyperpolarizabilities of the van der Waals dimers. A full-configuration-interaction approach as well as the coupled cluster singles and doubles and the coupled cluster singles and doubles plus perturbative triples approximations have been adopted, and extended basis sets including midbond functions have been employed. A semi-classical integration yields the virial coefficients. The effect of density for standard experimental conditions is found to be of the order of a few tens of parts per million for helium and neon, and of the order of a few parts per thousands for argon at low temperatures, and thus not detectable with present apparatus.