Optical Kerr effect in supercooled water

We present molecular dynamics simulations of the optical Kerr effect in liquid and supercooled water and compare with recent time-resolved Kerr spectroscopy measurements [R. Torre, Nature (London) 428, 296 (2004)]. The short time features of the Kerr response, characterized by peaks near 15, 60, and 160 fs, are weakly temperature dependent. The long-time decay is well described by a stretched exponential with a nearly constant stretch parameter and relaxation times that follow a power law approximately (T-T(S))(-gamma), with T(S)=198.3 K and gamma=2.35. Our findings are discussed in the light of the spectroscopy data and previous simulation analyzes of the structural relaxation in supercooled water.     

Possible one-dimensional 3He quantum fluid formed in nanopores

Heat capacity measurements have been made down to 5 mK for 3He fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 A in diameter, preplated with 4He of 1.47 atomic layers. At low 3He density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures. The peak behavior is attributed to the crossover from a 2D gas to a 1D state at low temperatures. The degenerate state of the 1D 3He fluid is indicated by a predominantly linear temperature dependence below about 30 mK.     

Determination of molecular parameters for 1,3-butadiene and propylene using infrared tunable diode laser absorption spectroscopy

A technique has been developed for the determination of molecular parameters, including infrared absorption line positions, strengths, and nitrogen-broadened half-widths for 1,3-butadiene (C(4)H(6)) and propylene (C(3)H(6)). The parameters for these two molecules are required for quantitation using Tunable Diode Laser Absorption Spectroscopy (TDLAS). These molecules have populations of highly overlapping infrared absorption lines in their room temperature spectra. The technique reported here provides a procedure for estimating the molecular parameters for these overlapping absorption lines from quantitative reference spectra taken with the TDLAS instrument at different pressures and concentrations. The system was developed for the quantitation of gaseous constituents in a single puff of cigarette smoke and this paper will describe the procedure and some of the factors that influence the accuracy of quantitation for 1,3-butadiene, including the approach taken to minimize the adverse effects of the absorption due to propylene in the same spectral region.     

The EC networking on elemental speciation revisited

In Europe, the EC-funded Thematic Network Speciation 21 was instrumental in disseminating the existing knowledge about chemical speciation of trace elements. It created a forum in which analytical chemists working in method development were mixed with potential users from industry and representatives of legislative bodies. This endeavour is continuing in the currently established European Virtual Institute for Speciation Analysis (EVISA). Although there already exists substantial know-how in Europe for the speciation of a number of substances, such as organo-arsenic, organo-tin and organo-mercury compounds, to name just these three groups, there is an urgent need to enforce the analytical potential in speciation analysis on a much wider scope of compounds capable of providing data of a suitable quality. The ensuing need for quality assurance of the analytical procedures requires the analysis of representative reference materials, certified for the relevant species. Last but not least, where applicable, the European-wide legislation should be adapted to focus on toxic species of the elements, rather than the total element.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, June 15–19, 2003, Berlin, Germany. Disclaimer The opinions expressed in the present article are entirely those of the authors. They do not represent the opinion of the European Community.     

Design and synthesis of organochalcogen (Se or Te) based multifunctional derivatives: structural determination and dynamic behavior of 2-chloro-4,6-bis(phenylselenoethylamino)-1,3,5-triazines

A novel class of multifunctional and multinucleate chalcogen (selenium and tellurium) containing derivatives (1-10) has been developed based on sequential chloride substitution of 2,4,6-trichloro-1,3,5-triazine with chalcogen-bearing amines. The structure of compound 1 has been determined in the solid state by X-ray crystallography.     

Rapid two-step synthesis of mitrin from heparosan: a replacement for heparin

We have engineered a two-step enzymatic synthesis of Mitrin which is a more potent and homogeneous anticoagulant than the current animal-derived heparin. This engineered heparin may have advantages of being free from animal-derived pathogens and may also have reduced side effects such as heparin induced thrombocytopenia. This approach can also be extended to tailor heparin-based drugs with improved therapeutic characteristics to treat other disorders or infections in which heparin-like molecules play a major role.     

Reversal of diastereoselectivities in intra- and intermolecular reactions of 2-adamantanylidenes primarily caused by electron-donating and electron- withdrawing substituents on C5

[reaction: see text] A reversal of diastereoselectivity was observed for novel 5-(trimethylsilyl)adamantan-2-ylidene (1c) with regard to 5-hydroxyadamantan-2-ylidene (1a). Ostensibly in intermolecular reactions, 5-substituted 2-adamantanylidenes (1) are sterically unbiased. However, inductive effects originating from the pendant group bend the divalent carbon bridge of 1 either toward (ERG's, e.g., -Si(CH(3))(3)) or away from (EWG's, e.g., -OH) the gamma-position. Hence, the more exposed side is more susceptible to intermolecular reaction and the other side concomitantly undergoes intramolecular 1,3-CH insertions more readily.     

Local completeness I

An infinite algebra is locally complete if its local closure is the set of all finitary operations. We give a local completeness criterion in terms of a system R of finitary relations on A such that the polymorph Pol of each R is locally incomplete and for every locally incomplete algebra A; F we have F Pol for some R. This system consists of (i) certain natural relations whose polymorphs are best possible in the sense that they are co-atoms in the lattice of locally closed incomplete algebras, (ii) five types of binary relations, (iii) one type of ternary relations and (iv) at least ternary totally reflexive and symmetric relations that are not locally central.Presented by K. A. Baker.     

Instrumental neutron activation analysis of rock samples from Ugep area of Cross River State,Nigeria

The theory and analytical procedures in Instrumental Neutron Activation Analysis (INAA) are discussed. Application of the method to the determination of sixteen trace elements: Na, K, Mn, Sm, La, Fe, Th, Sc, Co, Ba, Rb, Br, Sb, Cs and Ta in some rock samples from Ugep in the Lower Benue Region of Nigeria, is described. The high radioactivity observed in some of the samples analyzed has been associated with the higher-than-normal concentrations of Th and K in the samples. Also, Ba and Fe concentrations in some of the samples were found to be anomalous when compared with average expected values in normal sedimentary rocks.