An Approach to A 1-Oxacephem Skeleton from D-Galactose

Abstract

2,4,6-Tri-O-benzyl-D-galactal (1) was transformed into a 1-oxacephem skeleton. The sequence of reaction involved: [2+2]cycloaddition, N-alkylation, glycolic cleavage of the vic-diol grouping, reduction of dialdehyde and cyclization to the title skeleton.     

Triphenylamine derivatized phenylacetylene macrocycle with large two-photon absorption cross-section

A phenylacetylene macrocycle (PAM) derivative containing triphenylamine as the framework was synthesized in one-step Sonogashira coupling. The photophysical and electrochemical properties were investigated in details. This hexamer shows significant enhancement in two-photon absorption cross-section relative to reported PAM derivatives.     

Time-resolved streak camera system with solid state laser and optical parametric generator in different spectroscopic applications

Apparatus to study time-evolution of emission spectra over very wide time and spectral range is described. Excitation part of the equipment consists of solid state Nd:YAG laser and optical parametric generator. The heart of the detection system consists of spectrograph and streak camera. The significance of optics and electronics built in the system for proper, fast and convenient measurements is underlined. The results of donor-acceptor energy transfer in a rigid polyvinyl alcohol matrix serve here as an example of application our equipment to study complex systems.     

Forbidden Gap Argument for Phase Transitions Proved by Means of Chessboard Estimates

Chessboard estimates are one of the standard tools for proving phase coexistence in spin systems of physical interest. In this note we show that the method not only produces a point in the phase diagram where more than one Gibbs states coexist, but that it can also be used to rule out the existence of shift-ergodic states that differ significantly from those proved to exist. For models depending on a parameter (say, the temperature), this shows that the values of the conjugate thermodynamic quantity (the energy) inside the ``transitional gap'' are forbidden in all shift-ergodic Gibbs states. We point out several models where our result provides useful additional information concerning the set of possible thermodynamic equilibria.     

Properties of reachable sets in the sub-Lorentzian geometry

The aim of this paper is to develop local theory of future timelike, nonspacelike and null reachable sets from a given point _q0$q_0$ in the sub-Lorentzian geometry. In particular, we prove that if U$U$ is a normal neighbourhood of _q0$q_0$ then the three reachable sets, computed relative to U$U$, have identical interiors and boundaries with respect to U$U$. Further, among other things, we show that for Lorentzian metrics on contact distributions on R²ⁿ⁺¹${\mathbb{R}}^{2n+1}$, n≥1$n\ge 1$, the boundary of reachable sets from _q0$q_0$ is, in a neighbourhood of _q0$q_0$, made up of null future directed curves starting from _q0$q_0$. Every such curve has only a finite number of non-smooth points; smooth pieces of every such curve are Hamiltonian geodesics. For general sub-Lorentzian structures, contrary to the Lorentzian case, timelike curves may appear on the boundary. It turns out that such curves are always Goh curves. We also generalize a classical result on null Lorentzian geodesics: every null future directed Hamiltonian sub-Lorentzian geodesic initiating at _q0$q_0$ is contained, at least to a certain moment of time, in the boundary of the reachable set from _q0$q_0$.     

Observation of transcrystalline growth of PLA crystals on sisal fibre bundles and the effect of crystal structure on interfacial shear strength

Hot-stage microscopy was used to characterise crystal growth at the interface between sisal fibre bundles and a polylactic acid (PLA) matrix in order to better understand the mechanical properties of sisal fibre–PLA composites. Cooling rates and crystallisation temperatures and times were varied to influence crystalline morphology at the interface. Single sisal fibre bundles were evaluated in their as received state or treated with 6 wt.% caustic soda solution for 48?h at room temperature. A microbond shear test was used to characterise the shear strength of the interface as a function of fibre surface treatment. These tests were performed on sisal fibre bundles carefully embedded in flat films of PLA supported on card mounts. Fibre bundles in a PLA matrix were cooled from 180?°C at rates from 2 to 9?°C/min and then crystallised isothermally. For as received fibre bundles uneven growth of PLA spherulites occurred at all cooling rates and crystallisation temperatures. For caustic soda treated fibres, uneven spherulitic growth was observed at crystallisation temperatures at and above 125?°C. In contrast, transcrystalline growth was observed for samples cooled to 120?°C at cooling rates from 2 to 6?°C/min and then allowed to crystallise. The microbond shear strengths of untreated and caustic soda treated fibre bundles were evaluated using Weibull statistics and the caustic soda treated fibres exhibited higher interfacial shear strengths in comparison to untreated fibres, reflecting the development of a transcrystalline layer at the fibre to matrix interface.     

Silicon solar cells with Al2O3 antireflection coating

The paper presents the possibility of using Al₂O₃ antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al₂O₃ thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al₂O₃ antireflection coating by ALD method. Results and their analysis allow to conclude that the Al₂O₃ antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al₂O₃ the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al₂O₃ on the bulk passivation of the silicon.