Wetting behaviour of 5CB and 8CB and their binary mixtures above the isotropic transition

High resolution optical microscopy techniques have been employed to study the wetting properties of (5CB)_x/(8CB)_100-x (x=0, 10, 30, 50, 70, 90, and 100 wt %) binary mixture liquid crystal thin films above the isotropic transitions. Dewetting is found to occurr at T_w=65 and 42.5°C for the 5CB and 8CB samples, respectively, and to depend strongly on the 5CB content in the mixtures. First-order wetting transitions were seen for pure 5CB and 8CB samples; a higher order wetting transitions were obtained for the mixtures. For thin film 5CB, a large hysteresis (ΔT=30°C) between wetting and dewetting during the heating and cooling is obtained. This hysteresis is compared with the corresponding values obtained for pure 8CB and mixture samples. Evidence of the formation of nematic layers on the surface of isotropic droplets was found. Attempts to extract values of the contact line tension for these materials are made. In this respect the applicability of the modified Young's equation is questionable.     

A dynamical model of storm surges along island coasts

A time-independent dynamical model of storm surge along island coasts using orthogonal curvilinear coordinates is presented. The curved annulus between an island coast and an arbitrary deep-water boundary is mapped conformally onto a rectangular image. Two configurations of island coasts are investigated; circular and elliptic coasts. The corresponding coordinates are circular polar and elliptic respectively. The linearized vertically-integrated equations of motion are used to model storm surges with two assumptions: (i) bottom stress is proportional to horizontal transport, and (ii) storm forces are shear stresses on water surface. Analytical solutions are presented for three dynamical cases: (i) a constant-depth basin acted upon by a uniform storm stress, (ii) variable-depth basin acted upon by a uniform-direction variable-magnitude stress, and. (iii) a basin with closed depth contours acted upon by vortex-shaped storm stress. The obtained solutions clarify the relative importance of the various parameters and variables that affect surge height distribution along island coasts. These solutions may be used to test a time-dependent, numerical dynamical storm model.     

Normal coordinate treatment and assignment of fundamental vibrations of vinyl fluoride and the seven deuterovinyl fluorides

The results of a unified normal coordinate treatment for vinyl fluoride and the seven deuterated species are presented. Our calculation confirms the out-of-plane assignment of Scherer and Potts. For the in-plane vibrations, we have used a modified valence-force type of potential function and, on the basis of the results, we are presenting a satisfactory assignment for most of the fundamentals. Investigation of the liquid spectra is recommended to resolve the ambiguity of the remaining few undecided in-plane fundamentals.The authors wish to thank both the Data Processing Center of Texas A & M University for the generous allotment of computer time during the early part of this investigation and the Bartlesville Petroleum Research Center of the Bureau of Mines for the key punch facilities during the latter part of this research. Thanks are also due Dr. Donald W. Scott of the Bartlesville Petroleum Research Center for stimulating discussions. This work was supported in part by the Thermodynamics Research Center Data Project (formerly the Manufacturing Chemists Association Research Project) and the National Bureau of Standards Office of Standard Reference Data.     

Structural Elucidation and Antimicrobial Evaluation of Novel [1,2,4]Triazolo[4,3‐a]pyrimidines and Pyrido[2,3‐d][1,2,4]triazolo[4,3‐a]pyrimidinones

1,3‐Di(thiophen‐2‐yl)prop‐2‐en‐1‐one ( 1 ) was utilized in the synthesis of 4,6‐di(thiophen‐2‐yl)‐3,4‐dihydropyrimidine‐2(1H)‐thione ( 2 ) and 5,7‐di(thiophen‐2‐yl)‐2‐thioxo‐2,3‐dihydropyrido[2,3‐d]pyrimidin‐4(1H)‐one ( 4 ). The latter thiones were used in the synthesis of two new series of [1,2,4]triazolo[4,3‐a]pyrimidines 10a – i and pyrido[2,3‐d][1,2,4]triazolo[4,3‐a]pyrimidinones 5a – i via reaction with the appropriate hydrazonoyl halides using triethylamine as a basic catalyst in dioxane. The mechanism of formation of the synthesized compounds was discussed, and the assigned structure was established via microanalysis, spectral data (infrared, ¹H NMR, and Mass), and density functional calculations. Moreover, the newly synthesized products were evaluated for their antimicrobial activities, and the results show that some derivatives have been well with mild activities. Finally, quantum chemistry calculations confirmed the mechanism and structure of the products.     

Preparation and characterization of polyaniline/manganese dioxide composites and their catalytic activity

This paper is devoted to the preparation of polyaniline/MnO2 (PANI/MnO2) composites via chemical oxidation of aniline in H2SO4 medium using beta-MnO2 as an oxidant. The parameters affecting the polymerization reaction are considered. These parameters are [aniline], amount of beta-MnO2, stirring time, and polymerization temperature. SEM, FT-IR, XRD, and TGA techniques are used to characterize the resulting composites. XRD measurements reveal the distortion of the crystal structure of beta-MnO2 after the polymerization reaction. Thus, the XRD pattern of PANI is predominating. The crystalline composites are obtained using higher molar ratio of [Ox]/[ANI] and at higher temperature. Increasing the amount of beta-MnO2 led to an increase in the acidic character of the obtained composites due to adsorption of excess H+ on the oxide surface. The thermal stability of the composites decreased with increasing both [aniline] and stirring time, while it increased with increasing amount of beta-MnO2. The applications of the composites in the oxidative degradation of Direct Red 81, Acid Blue 92, and Indigo Carmine dyes exhibited good catalytic activity in the presence of H2O2 as an oxidant. The reactions followed first-order kinetics and the rate constants were determined. The degradation reaction involved the catalytic action of the PANI counterpart of the composite toward H2O2 decomposition, which can lead to the generation of HO radicals as a highly efficient oxidant attacking the target dyes. The detailed kinetic studies and the mechanism of these catalytic reactions are under consideration in our group.     

Nanocarriers for cytoplasmic delivery: cellular uptake and intracellular fate of chitosan and hyaluronic acid-coated chitosan nanoparticles in a phagocytic cell model

The cellular uptake of hyaluronic-acid-coated, negatively charged chitosan/triphosphate nanoparticles and that of uncoated, positively charged ones is investigated by studying cellular localization, uptake kinetics and mechanism of internalization in J774.2 macrophages, using non-phagocytic L929 fibroblasts as a control for uncoated nanoparticles. Both kinds of nanoparticles undergo endosomal escape and adopt a similar clathrin-based endocytic mechanism. The surface decoration with HA profoundly influences the kinetics of cellular uptake, with an at least two orders of magnitude slower kinetics, but also the nature of the binding on the cellular surface.     

Reactions of Hydrazonoyl Halides 41: 1 Synthesis of 1,2,4-Triazoles, 2,3-Dihydro-1,3,4-thiadiazoles,and Triazolo[4, 3-a]pyrimidines

Triazoles, thiadiazoles, and triazolo[4, 3-a]pyrimidines were synthesized via reaction of hydrazonoyl halides with each of 3-methyl-4-(methylthiothioxomethyl)-2-pyrazolin-5-one, 3-methyl-4-[methylthio(phenylamino)methyl]-2-pyrazolin-5-one, and pyrimidine-2-thiones. Structures of the newly synthesized compounds were elucidated on the basis of elemental analysis, spectral data, and alternative-methods synthesis whenever possible.     

Protonation of 5‐methylhydantoin and its thio derivatives in the gas phase: A theoretical study

The gas phase proton affinities of 5‐methylhydantoin and its thio derivatives were theoretically studied through the use of high‐level density functional theory calculations. The structure of all possible tautomers and their conformers were optimized at the B3LYP/6‐311+(d,p) level of theory. Final energies were obtained at the B3LYP/6‐311+(2df,2p) level. The imidazolidone derivatives 5‐methyl‐2,4‐dioxo imidazolidine, 5‐methyl‐2‐oxo‐4‐thio imidazolidine, 5‐methyl‐2‐thio‐4‐oxo imidazolidine, and 5‐methyl‐2,4‐dithio imidazolidine possess moderately strong proton affinities. Protonation at sulfur would be larger than protonation at oxygen. The most stable protonated forms of 2O4O and 2S4O have the proton attached to the heteroatom in position 2, whereas protonation of 2O4S and 2S4S preferentially takes place at position 4. The barriers for proton migration between the different tautomers are rather large. The energy decomposition analysis analysis of the O? H⁺ and S? H⁺ interactions suggests that the bonding interactions come mainly from the covalent bond formation. The contribution of the Coulomb attraction is rather small. © 2012 Wiley Periodicals, Inc.     

等离子辅助分子束外延技术研究生长在Si(111)衬底的氮化镓pn结

利用等离子辅助分子束外延系统研究了生长在硅(111)衬底的氮化镓pn结,并将其应用于光学器件．硅和镁分别用做n和p掺杂,反射高能电子衍射图像显示氮化镓pn结层具有良好的表面形貌,结层厚度约为0.705 nm,且为六方结构．室温下X射线衍射对称摇摆曲线中(0002)面的ω/2θ显示,半峰宽为0.340,说明氮化镓pn结质量高．另外,在硅和镁掺杂样品中没有A1峰淬灭．光致发光光谱表明pn结样品具有良好的光学性能．镍和铝作为分别作为正面和背面的电极接触应用于光学器件,该器件的电流电压特性显示了典型的异质结整流特性．正向接触镍经过氮气中退火处理10 min,结果表明,600 oC处理的样品比400 oC处理和未经处理的样品具有更高的增益．     

Collisional effect on the Weibel instability in the limit of high plasma temperature

The Weibel instability (WI) of relativistic electron beam (REB) penetrating an infinite collisional plasma was studied in the following models: (i) REB model, where the total equilibrium distribution function f ₀($ \vec p $ \vec p ) is approximated by nonrelativistic background electron and REB distribution functions and (ii) relativistic monoenergetic beam (RMB) model, where f ₀($ \vec p $ \vec p ) is approximated by nonrelativistic background electrons and RMB distribution functions.