Chemical bond approach to determining conductivity band gaps in amorphous chalcogenides and pnictides

The minimum energy required for the formation of conjugate pair of charged defects is found to be approximately equal to the experimental activation energy for d.c. conductivity in a number of amorphous chalcoganides and pnictides. This observation implies that the defect pair formation energy represents an intrinsic gap for transport in amorphous chalcogenides.

Structure of 5-Bromo-2',3'-O-isopropylideneuridine, C12H15BrN206

Mr= 363.17, orthorhombic, P21212 ~, a= 5.251(4), b=14.962(5), c=19.112(5)A, U= 1501.41/k 3, Z=4, Dx=1.61Mgm -3, /t(CuKa)= 3.02 mm -1, 2(Cu Ka)= 1.5418/~, final R = 7.0% for 1091 reflections with Fo> 2e(Fo). The glycosidic torsion angle ZCN is 13"1 (12) °. The ribose has a C (3')-exo,C (4)-endo twist geometry. The dioxolane ring assumes an envelope conformation with 0(3') displaced by 0.453 (10)/k from the plane of the other four atoms. The conformation about the C(4')-C(5') bond is gauche-gauche. The structure is stabilized by two hydrogen bonds between screw-axis-related molecules. The crystal packing and the conformation of the molecule are very similar to those found in the structure of 2',3'-O-isopropylideneuridine which lacks the Br atom at the 5-position.

Estimation of cosmological parameters from neutral hydrogen observations of the post-reionization epoch

The emission from neutral hydrogen (HI) clouds in the post-reionization era (z <= 6), too faint to be individually detected, is present as a diffuse background in all low frequency radio observations below 1420MHz. The angular and frequency fluctuations of this radiation (similar to 1 mK) are an important future probe of the large-scale structures in the Universe. We show that such observations are a very effective probe of the background cosmological model and the perturbed Universe. In our study we focus on the possibility of determining the redshift-space distortion parameter beta, coordinate distance r(nu), and its derivative with redshift r(nu)('). Using reasonable estimates for the observational uncertainties and configurations representative of the ongoing and upcoming radio interferometers, we predict parameter estimation at a precision comparable with supernova Ia observations and galaxy redshift surveys, across a wide range in redshift that is only partially accessed by other probes. Future HI observations of the post-reionization era present a new technique, complementing several existing ones, to probe the expansion history and to elucidate the nature of the dark energy.

Volumetric behavior of ethylene and ethylene-hydrogen mixtures

A Burnett apparatus deslgned and fabrlcated was used to collect volumetric data for ethylene and ethylene-hydrogen mixtures. Measurements were made In the temperature range 298.15-423.15 K at Intervals of 25 K and In the pressure range 0.3-7.0 MPa. Vlrlal coefflclents derlved from the compresslblllty data are tabulated. The data are fltted to different equations of state.

Modeling growth of hydrogen bubbles in aluminum castings using the level-set method

A new approach is proposed to solve for the growth as well as the movement of hydrogen bubbles during solidification in aluminum castings. A level-set methodology has been adopted to handle this multiphase phenomenon. A microscale domain is considered and the growth and movement of hydrogen bubbles in this domain has been studied. The growth characteristics of hydrogen bubbles have been evaluated under free growth conditions in a melt having a hydrogen input caused b solidification occurring around the microdomain.

Cyclic Peptide Disulfides - Solution And Solid-State Conformation Of Boc-Cys-Pro-Aib-Cys-S-S-Bridge-Nhme,A Disulfide-Bridged Peptide Helix

The solution and solid-state conformations of the peptide disulfide Boc-Cys-Pro-Aib-Cys-NHMe have been determined by NMR spectroscopy and X-ray diffraction. The Cys(4) and methylamide NH groups are solvent shielded in CDCI3 and (CD,),SO, suggesting their involvement in intramolecular hydrogen bonding. On the basis of known stereochemical preferences of Pro and Aib residues, a consecutive @-turn structure is favored in solution. X-ray diffraction analysis reveals a highly folded 310 helical conformation for the peptide, with the S-S bridge lying approximately parallel to the helix axis, linking residues 1 and 4. The backbone conformational angles are Cys(1) 4 = -121.1', $ = 65.6"; Pro(2) 4 = -58.9', 4 = -34.0'; Aib(3) 4 = -61.8', $ = -17.9'; Cys(4) 4 = -70.5', $ = -18.6'. Two intramolecular hydrogen bonds are observed between Cys(1) CO--HN Cys(4) and Pro(2) CO--HNMe. The disulfide bond has a right-handed chirality, with a dihedral angle (xss) of 82'.

A gravimetric procedure for the determination of wet precipitated sulphur, dissolved sulphur, soluble sulphides and hydrogen sulphide

Elemental sulphur (in wet precipitated form or dissolved in organic solvents) and hydrogen sulphide have been determined gravimetrically at room temperature by conversion into copper sulphide by elemental copper in presence of an organic solvent such as benzene or acetonitrile. Any solvent in which sulphur is soluble can be used. The black copper sulphide formed can be weighed or determined iodometrically. Analysis indicates the black compound to be Cu1.8S. This room temperature method is a versatile one-step procedure sensitive to microgram or macro amounts of sulphur. It has been used for determining the solubility of sulphur in tetrahydrofuran and dioxan. The apparent heat of solution indicates that sulphur dissolves in these solvents without any marked solute—solvent interactions.

Mossbauer Effect Study of the Thermal Decomposition in Hydrogen of Homogeneously Mixed Ferrous Nickel Oxalates with Different Iron to Nickel Ratios

Mossbauer effect and X-ray measurements are carried out on product samples of the thermogravimetric analysis (TGA) and isothermal decomposition in hydrogen of homogeneously mixed ferrous nickel oxalates with different iron to nickel ratios. The formation of Fe-Ni alloy is obtained at considerably lower temperatures (z 300 "C) in each case. The Fe-Ni alloys obtained shift from iron-rich to nickel-rich composition as the nickel ratio in the mixed metal oxalates is increased. The formation of Pe-Ni Invar from mixed metal oxalate with Fe:Ni = 1:l is indicated in the early stages but not from those with Fe:Ni = 2: 1 or 64:36. An Produktproben von homogen verteilten Eisen-Nickeloxalaten mit unterschiedlichem Eisen- Nickel-Verhaltnis nach thermogravimetrischer Analyse (TGA) und isothermem Zerfall in Wasserstoff werden Mollbauereffekt- und Rontgenmessnngen durchgefuhrt. In allen Fiillen wird die Bildung der Fe-Ni-Legierung bei betriichtlich niedrigeren Temperaturen (= 300 "C) erhalten. Die erhaltenen Fe-Ni-Legierungen verschieben sich von der eisenreichen zur nickelreichen Zusrtmmensetzung, wenn das Nickelverhaltnis in dem BIetall-Mischoxalat erhoht wird. Die Bildung der Fe-Ni-lnvar-Legierung aus dem Metall-Mischoxalat mit Fe:Ni = 1 : 1 wird in fruhen Zustanden beobachtet, iedoch nicht aus Oxalaten mit Fe:Ni = 2:1 oder 64:36.

Bond Characteristics of Strengthened and Retrofitted Steel by Smart CFRP Technique

Usage of new smart materials in retrofitting of structures has become popular within last decade. Carbon fiber reinforced polymer (CFRP) has been widely used in retrofitting and strengthening of concrete structures and its usage in metallic structures is still in the developing stage. The variation of mechanical properties of CFRP and the consequent effects on strengthening and retrofitting CFRP systems are yet to be investigated under different loading and environmental conditions. This paper presents the results of CFRP strengthened and retrofitted corroded steel plate double strap joints under tension. An accelerated corrosion cell has been developed to accelerate the corrosion of the steel samples and CFRP strengthened samples. The results show a direct comparison of bond characteristics of CFRP strengthened and retrofitted steel double strap joints.

Thermal decomposition of hydrazinium hydrogen oxalate and dihydrazinium oxalate

Thermal decompositions of hydrazinium hydrogen oxalate (HHOX) and dihydrazinium oxalate (DOX) have been studied. DOX on heating is converted into HHOX and thereafter both follow the same pattern of decomposition.

Pyridinium poly(hydrogen fluoride). A versatile fluorinating reagent preparation and characterization of nonmetal and metal complex fluoro salts

Abstract is not available.

The nature of hydrogen induced amorphization of SmNi2 laves compound

Abstract is not available.

Hydrogen utilising bacteria from the forestomach of eastern grey (Macropus giganteus) and red (Macropus rufus) kangaroos

Reductive acetogenesis is an alternative to methanogenesis for removing hydrogen produced during enteric fermentation. In Australia, kangaroos have evolved an enlarged forestomach analogous to the rumen of sheep and cattle. However, unlike sheep and cattle, kangaroos produce very little methane from enteric fermentation. From samples of gut contents from five eastern grey and three red kangaroos, we were not able to detect methanogens using a PCR protocol, but did detect the formyltetrahydrofolate synthetase (FTHFS) gene (likely to be used for reductive acetogenesis) in all animals. Isolations to recover acetogens resulted in two different classes of hydrogen consuming bacteria being isolated. The first class consisted of acetogens that possessed the FTHFS gene, which except for Clostridium glycolicum, were not closely related to any previously cultured bacteria. The second class were not acetogens but consisted of enterobacteria (Escherichia coli and Shigella) that did not possess FTHFS genes but did utilise hydrogen and produce acetate. Enumeration of the acetogens containing the FTHFS gene by real-time PCR indicated that bacteria of the taxa designated YE257 were common to all the kangaroos whereas YE266/YE273 were only detected in eastern grey kangaroos. When present, both species occurred at densities above *106 cell equivalents per mL. C. glycolicum was not detected in the kangaroos and, unlike YE257 and YE266/273, is unlikely to play a major role in reductive acetogenesis in the foregut of kangaroos.

NMR studies of phase transition in ammonium hydrogen bischloroacetate, NH4H(CH2ClCOOO)2

Proton second moment (M2) and spin-lattice relaxation time (T1) of Ammonium Hydrogen Bischloroacetate (ABCA) have been measured in the range 77-350 K. A value of 6.5 G2 has been observed for the second moment at room temperature, which is typical of NH4+ reorientation and also a second moment transition in the range 170-145 K indicates the freezing of NH4+ motion. The NMR signal disappears dicontinuously at 128 K. Proton spin-lattice relaxation time (T1) Vs temperature, yielded only one sharp miniumum of 1.9 msec which is again typical of NH4+ reorientation. A slope change at 250 K is also observed, prbably due to CH2 motion. Further, the FID signal disappears at 128 K. Thus the Tc appears to be 128 K (of two reported values 120 K and 128 K). Activation energies have been calculated and the mechanism of the phase transition is discussed.

Hydrogen- 1 and Carbon- 13 Magnetic Resonance Studies of Nonactin-Calcium Complex

For an understanding of the cation selectivity and general binding characteristics of macrotetralide antibiotic nonactin (NA) with ions of different sizes and charges, the nature of binding of divalent cation, Ca2+, to NA and conformation of the NA-Ca2+ complex have been studied by use of 270-MHz proton nuclear magnetic resonance ('H NMR) and carbon-13 nuclear magnetic resonance (13C NMR). The calcium ion induced significantly large changes in chemical shifts for H7, H2, H3, and H5 protons of NA and relatively small changes for H18 and H2' protons. Changes in I3C chemical shift were quite large for carbonyl carbon, C,; it is noteworthy that in the NA-K+ complex, H2 and H2' protons practically do not show any change during complexation and carbonyl carbon shows a much smaller chemical shift change.