Hydrogen-helium scattering cross-sections for transmission elastic recoil detection analysis

¹H(,p) ⁴He scattering cross-sections were determined for the 6.5–13 MeV (incident energy) range, thereby extending the energy range for such data beyond that available in the literature. These values are essential for the further development of hydrogen concentration profiling by the transmission elastic recoil detection technique, of particular interest in the design of surface-engineered hydrogen contamination barriers for steels.     

Direct evidence for chain orientation in poly(acetylene)

Two conflicting structural models (platelet and fibril) have been proposed in the literature for pristine cis-poly(acetylene). The respective models have separate, distinct implications for the chemical, physical and electrical properties of the material, in particular, the cis-trans isomerization, doping and conduction mechanisms. Luttinger-type cis-poly(acetylene) was prepared and studied in the transmission electron microscope (TEM) by low-dose conventional imaging, in dark-field mode and by electron diffraction. Thin ‘films’ of the material were shown to consist of fibrillar nets, having fibrils of diameter 5–25 nm. Combined electron diffraction and dark-field observations in the TEM indicated the structural arrangement within the fibrils as that having polymer molecular chains aligned parallel to fibril axes.     

Kinetic parameters during the tempering of low-alloy steel through the non-isothermal dilatometry

The kinetic study of the tempering reactions of a low-alloy steel (AISI 1050) was carried out through non-isothermal dilatometry. The kinetic parameters of the first and third stages on tempering (here referred to as processes I and II) are calculated by procedures which assume that the nucleation and growth reactions obey a Kolmogorov–Johnson–Mehl–Avrami (KJMA) kinetic model. The recipes to obtain the kinetic parameters (E, K ₀, n) of the reactions on tempering are presented. The first stage of tempering is characterized by the growth of the transition carbide nuclei formed during the quenching, n = 1 (site saturation situation). This stage is controlled by the pipe diffusion of the iron atoms. The third stage of tempering is characterized by the cementite nucleation on dislocations due to the gradual dissolution of the transition carbide, n = 0.66. The cementite growth is controlled by diffusion of the iron atoms through dislocations and in the matrix.     

A membrane-bound NAD(P)+-reducing hydrogenase provides reduced pyridine nucleotides during citrate fermentation by Klebsiella pneumoniae

During anaerobic growth of Klebsiella pneumoniae on citrate, 9.4 mmol of H2/mol of citrate (4-kPa partial pressure) was formed at the end of growth besides acetate, formate, and CO2. Upon addition of NiCl2 (36 microM) to the growth medium, hydrogen formation increased about 36% to 14.8 mmol/mol of citrate (6 kPa), and the cell yield increased about 15%. Cells that had been harvested and washed under anoxic conditions exhibited an H2-dependent formation of NAD(P)H in vivo. The reduction of internal NAD(P)+ was also achieved by the addition of formate. In crude extracts, the H2:NAD+ oxidoreductase activity was 0.13 micromol min-1 mg-1, and 76% of this activity was found in the washed membrane fraction. The highest specific activities of the membrane fraction were observed in 50 mM potassium phosphate, with 1.6 micromol of NADPH formed min-1 mg-1 at pH 7.0 and 1.7 micromol of NADH formed min-1 mg-1 at pH 9.5. In the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone and the Na+/H+ antiporter monensin, the H2-dependent reduction of NAD+ by membrane vesicles decreased only slightly (about 16%). The NADP+- or NAD+-reducing hydrogenases were solubilized from the membranes with the detergent lauryldimethylamine-N-oxide or Triton X-100. NAD(P)H formation with H2 as electron donor, therefore, does not depend on an energized state of the membrane. It is proposed that hydrogen which is formed by K. pneumoniae during citrate fermentation is recaptured by a novel membrane-bound, oxygen-sensitive H2:NAD(P)+ oxidoreductase that provides reducing equivalents for the synthesis of cell material.     

Incorporation of crystallographic temperature factors in the statistical analysis of protein tertiary structures

A method to identify statistically significant differences betweenequivalent atoms in two closely related protein X-ray crystallographicstructures is described. This method uses the linear relationshipfound between the logarithm of the distance between equivalentatoms and their mean temperature factor to determine, by linearregression, the expected difference and variance.     

The effect of anticipatory strategies on the first day of smoking cessation.

The authors tested a model hypothesizing the predictors and the effects of anticipatory strategy use on the 1st day of smoking cessation using data from 63 participants in an ecological momentary assessment study of smoking cessation. Remaining abstinent on the 1st day of cessation was not associated with mean level of urges to smoke during tempting situations but was associated with anticipatory strategy use, which accounted for 18% of the variance. Getting rid of cigarettes contributed the most to this effect (β?=?-.397). Getting rid of cigarettes was itself predicted by 2 variables, lower nicotine dependence (β?=?-.264) and attending a formal smoking cessation class (β?=?.305), which accounted for 15% of its variance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oxygen diffusion through a developing biofilm of pseudomonas fluorescens

Using a specially designed miniature probe mounted into a plate across which water contaminated with the bacterium Pseudomonas fluorescens was flowing, oxygen levels at the biofilm/substrate interface have been determined. The experimental results show a rapid fall in the amount of oxygen available to the micro-organisms in the layers near the interface. As the biofilm approached 300 μm in thickness higher flow velocities across the biofilm had little effect on oxygen availability in the regions near the interface.     

An Alternative Cu-Based Bond Layer for Electric Arc Coating Process

A Cu-Al alloy has been used as bond coat between a carbon steel substrate and a final coating deposit obtained by applying the twin wire electric arc spraying coating technique. The presence of a copper-based material in the composite system can change the overall temperature profile during deposition because copper exhibits a thermal conductivity several times higher than that of the normally recommended bond coat materials (such as nickel-aluminum alloys or nickel-chromium alloys). The microstructures of 420 and 304 stainless steels deposited by the electric arc spray process have been investigated, focusing attention on the deposit homogeneity, porosity, lamellar structure, and microhardness. The nature of the local temperature gradient during deposition can strongly influence the formation of the final coating deposit. This study presents a preliminary study, undertaken to investigate the changes in the temperature profile which occur when a Cu-Al alloy is used as bond coat, and the possible consequences of these changes on the microstructure and adhesion of the final coating deposit. The influence of the thickness of the bond layer on the top coating temperature has also been also evaluated.