Temperature dependence of crystal growth of hexagonal ice (I(h))

The transformations between water and ice have many implications across numerous fields of study. A better understanding of this process would benefit many areas of science and technology such as medicine, biology, and atmospheric and material sciences. In the present work the temperature dependence of the rate of growth (melting) of the basal face of hexagonal ice I(h) and the effect of system size are investigated in molecular dynamics simulations. Using an effective pair potential model of water, systems are studied over temperatures ranging from T(M) - 40 to T(M) + 16 K, where T(M) is the melting temperature of the model. It is found that the growth rates reach a maximum value of 0.7 ? ns(-1) (7 cm s(-1)) at about 12 K below the melting temperature. A noticeable effect of the system size on the melting temperature and ice growth rates is observed; it is shown that the size effect arises in smaller systems due to the artificial ordering under periodic conditions. The decrease in melting entropy in the smallest system by 0.4 J (mol K)(-1) relative to the largest system results in an up-shift in the melting temperature by about 2 K. An almost 60% increase in the maximum growth rate is observed for the smallest system.     

Crystal growth simulations of methane hydrates in the presence of silica surfaces

We present a molecular dynamics simulation study of the crystal growth of methane hydrates in the presence of model silica (SiO(2)) surfaces. The crystal growth under apparent steady-state conditions shows a clear preference for bulk solution. We observe rather disordered water arrangements very close to the silica surface within about 5 ? in both liquid and crystalline regions of the system. These disordered structures have dynamic and structural properties intermediate between those exhibited by molecules in bulk liquid and crystalline phases. The presence of methane molecules appears to help stabilize these structures. We observe that under appropriate conditions, the hydroxylated silica surfaces can serve as a source of methane molecules which can help promote hydrate growth near the surfaces.     

Mirror symmetry for Del Pezzo surfaces: Vanishing cycles and coherent sheaves

We study homological mirror symmetry for Del Pezzo surfaces and their mirror Landau-Ginzburg models. In particular, we show that the derived category of coherent sheaves on a Del Pezzo surface X _k obtained by blowing up ℂℙ² at k points is equivalent to the derived category of vanishing cycles of a certain elliptic fibration W _k :M _k →ℂ with k+3 singular fibers, equipped with a suitable symplectic form. Moreover, we also show that this mirror correspondence between derived categories can be extended to noncommutative deformations of X _k , and give an explicit correspondence between the deformation parameters for X _k and the cohomology class [B+iω]∈H ²(M _k ,ℂ).     

Completeness and orthogonality of the null plane of one class of solutions of the relativistic wave equations

Possible redefinitions of the scalar product are analyzed for relativistic wave fields of the Klein-Gordon and Dirac types. It is shown that for an entire class of new exact solutions, for which it was previously not possible to define the usual scalar product on the x⁰=const plane, it is possible to find a correct scalar product on the null plane x⁰?x³=const. Orthogonality and completeness relations are proved for this scalar product. Possible applications of the results are discussed.     

Electrophoresis in capillary cells with detection gap

A novel design of the detection zone in multicapillary arrays used for electrophoretic separation is presented. The use of a detection gap (DG), in which the reflective surfaces separating the channels of the array are eliminated, is proposed to improve the illumination and detection of the separated DNA fragments. The electric field compression in the DG is achieved by optimization of the gap geometry. The results of the computer simulation and experiment demonstrate no substantial band-broadening in the DG. We believe that the proposed method will be useful for application in the microfabricated devices.     

Unconventional zigzag indium phosphide single-crystalline and twinned nanowires

Unconventional zigzag indium phosphide (InP) single-crystalline and twinned nanowires were produced via thermal evaporation of indium phosphide in the presence of zinc selenide. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that two type of nanowires exist in the products, namely, the periodic-rhombus-decorated single-crystalline InP (type I) nanowires and jagged twinned InP (type II) nanowires. Both of them have preferential 111 growth directions. The optical properties were also investigated at room temperature, and they show that the nanowires display a strong emission at approximately 750 nm, which is quite different from that observed in all previous reports related to the InP nanostructures.