Comparative study of membranes of Streptococcus faecalis and Micrococcus lysodeikticus

A comparative study of ultrastructure and IR-spectroscopy of osmotic shock membranes from cells of glycolyzing (Streptococcus faecalis) and respiring (Micrococcus lysodeikticus) bacteria, was made. The S. faecalis and M. lysodeikticus membranes differ in their cross-section. Treatment of the preliminary washed membranes of S. faecalis and M. lysodeikticus with a low ionic strength solution removes 40% and 70% of their proteins respectively, decreases the membrane cross-section but does not change their fracture faces. Pre-cooling of the membrane suspensions within the temperature range of +5 degrees-10 degrees results in the appearance of large smooth areas on S. faecalis membrane fracture faces, but does not affect the ones of M. lysodeikticus membrane. Treatment of the washed suspensions with Triton X-100 results in the appearance of drastic changes of S. faecalis membrane fracture faces and does not change the fracture faces of M. lysodeikticus membranes; treatment by the detergent does not alter the IR-spectroscopy of membranes of both bacteria. Treatment of S. faecalis and M. lysodeikticus membranes with high temperature irreversibly changes the structure of 20% and 40% of protein components respectively,, but does not affect the distribution of the subparticles on their fracture faces. It is assumed that the differences found are determined by the composition of lipid components of the membranes studied and that the amount of proteins closely bound with lipids in the membranes of S. faecalis is likely to be greater than that of M. lysodeikticus membranes.     

Electron microscopy study of ion beam synthesized β-FeSi2

β-FeSi₂ embedded in a Si matrix was prepared by ion beam synthesis (IBS). Two step implantation, with energies 60 and 20 keV, of two different doses of the iron ions, 5 × 10¹⁵ and 5 × 10¹⁶ cm⁻¹, was performed. After the implantation, the samples were subjected to rapid thermal annealing (RTA) at 900 °C. The crystal structure of the resulting material was studied using cross-sectional transmission electron microscopy (XTEM), including high-resolution electron microscopy (HREM). The comparison of the XTEM images with the initial iron ions implantation profiles, simulated by SRIM (Stopping and Range of Ions in Matter) demonstrate that the process of IBS, followed by RTA, preserves the initial implantation profile, implying a negligible Fe atoms diffusion velocity in comparison with the one of the chemical reaction between Fe and Si. The XTEM images show that continuous β-FeSi₂ layers are fabricated when there is a stoichiometric region in the initial implantation profile. Fe concentration lower than the stoichiometric one in the whole implantation range results in formation of β-FeSi₂ nanocrystallites embedded in the Si matrix. The behavior of the absorption coefficient energy dependences, obtained from the optical transmittance and reflectance measurements, reflects the different crystal structures forming in the two types of samples.     

Formaldehyde levels in FEMA‐supplied travel trailers,park models,and mobile homes in Louisiana and Mississippi

In 2006, area physicians reported increases in upper respiratory symptoms in patients living in U.S. Federal Emergency Management Agency (FEMA)‐supplied trailers following Hurricanes Katrina and Rita. One potential etiology to explain their symptoms included formaldehyde; however, formaldehyde levels in these occupied trailers were unknown. The objectives of our study were to identify formaldehyde levels in occupied trailers and to determine factors or characteristics of occupied trailers that could affect formaldehyde levels. A disproportionate random sample of 519 FEMA‐supplied trailers was identified in Louisiana and Mississippi in November 2007. We collected and tested an air sample from each trailer for formaldehyde levels and administered a survey. Formaldehyde levels among all trailers in this study ranged from 3 parts per billion (ppb) to 590 ppb, with a geometric mean (GM) of 77 ppb [95% confidence interval (CI): 70–85; range: 3–590 ppb]. There were statistically significant differences in formaldehyde levels between trailer types (P < 0.01). The GM formaldehyde level was 81 ppb (95% CI: 72–92) among travel trailers (N = 360), 57 ppb (95% CI: 49–65) among mobile homes (N = 57), and 44 ppb (95% CI: 38–53) among park models (N = 44). Among travel trailers, formaldehyde levels varied significantly by brand. While formaldehyde levels varied by trailer type, all types tested had some levels ≥100 ppb.     

Liquid‐selenium‐enhanced grain growth of nanoparticle precursor layers for CuInSe2 solar cell absorbers

Large‐grained CuInSe₂ absorber layers are synthesized using a non‐vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide‐based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H₂ or H₂Se gasses. Lateral grain sizes up to 4 µm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe₂ enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low‐cost, non‐vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes. Copyright © 2014 John Wiley & Sons, Ltd.