Determination of the valence-band offset and its temperature dependence in isotypic heterojunctions p-AlxGa1−xAs/p-AlyGa1−yAs from C-V measurements

The isotypic heterojunctions p-Al_xGa_1−x As/p-Al_yGa_1−y As, grown by MOVPE on n-GaAs substrates, have been investigated by the voltage-capacitance method at temperatures ranging from 300 to 100 K. To determine the valence-band offset ΔE _V and the built-in charge in the heterojunction, the Poisson equation was solved numerically on a nonuniform coordinate grid. The incomplete ionization of the acceptors and the different magnitude of the permittivity in different layers of the heterostructure were taken into account in the calculation. It was found that for a p-Al _0.2 a_0.8As/p-Al _0.5 Ga_0.5As heterojunction ΔE _V at room temperature is 39% (113 meV) of the total gap ΔE _g and decreases monotonically to 35% at T=120 K. Fiz. Tekh. Poluprovodn. 33, 940–944 (August 1999)     

Design and Characterization of Fabry–Pérot MEMS-Based Short-Wave Infrared Microspectrometers

Microspectrometers based on the monolithic integration of a microelectromechanical system (MEMS) Fabry–Pérot filter and a Hg _x Cd_1–x Te-based infrared detector are discussed and measured results presented. The microspectrometers are designed to operate in the 1.5 μm to 2.6 μm wavelength range. Design equations are presented which account for the mechanical and optical characteristics of the device. Measurements indicate linewidths as narrow as 55 nm, switching times of 40 μs, and a tuning range of 380 nm, which is limited by snap-down. Optical characterization of the distributed Bragg mirrors and the Fabry–Pérot filter are presented, and these are shown to be in good agreement with simple first-order analytical models. Bowing of the movable Fabry–Pérot mirror due to stress gradients is identified as the dominant source of linewidth broadening.     

Short communication: Carora cattle show high variability in alpha(s1)-casein

The objective of this study was to analyze the genetic variability of milk proteins of the Carora, a shorthorned Bos taurus cattle breed in Venezuela and in other Southern American countries that is primarily used for milk production. A total of 184 individual milk samples were collected from Carora cattle in 5 herds in Venezuela. The milk protein genes α_s1-casein (CN) (CSN1S1), β-CN (CSN2), κ-CN (CSN3), and β-lactoglobulin (LGB) were typed at the protein level by isoelectrofocusing. It was necessary to further analyze CSN1S1 at the DNA level by a PCR-based method to distinguish CSN1S1*G from B. Increased variation was found in particular at the CSN1S1 gene, where 4 variants were identified. The predominant variant was CSN1S1*B (frequency = 0.8). The second most common CSN1S1 variant was CSN1S1*G (0.101), followed by CSN1S1*C (0.082). Moreover, a new isoelectrofocusing pattern was identified, which may result from a novel CSN1S1 variant, named CSN1S1*I, migrating at an intermediate position between CSN1S1*B and CSN1S1*C. Six cows carried the variant at the heterozygous condition. For the other loci, predominance of CSN2*A² (0.764), CSN3*B (0.609), and LGB*B (0.592) was observed. Haplotype frequencies (AF) at the CSN1S1-CSN2-CSN3 complex were also estimated by taking association into account. Only 7 haplotypes showed AF values >0.05, accounting for a cumulative frequency of 0.944. The predominant haplotype was B-A²-B (frequency = 0.418), followed by B-A²-A (0.213). The occurrence of the G variant is at a rather high frequency, which is of interest for selection within the Carora breed because of the negative association of this variant with the synthesis of the specific protein. From a cheese-making point of view, this variant is associated with improved milk-clotting parameters but is negatively associated with cheese ripening. Thus, milk protein typing should be routinely carried out in the breed, with particular emphasis on using a DNA test to detect the CSN1S*G variant. The CSN1S*G allele is likely to have descended from the Brown Swiss, which contributed to the Carora breed and also carries this allele.     

Development and evaluation of an on-line hide decontamination procedure for use in a commercial beef processing plantt

The hides of cattle are the source of Escherichia coli O157:H7 that contaminates beef carcasses during commercial beef processing. Therefore, effective interventions that reduce hide contamination should reduce subsequent carcass contamination. The first objective of this study was to identify the most effective reagents for decontamination of beef hides. Cattle hides draped over barrels were used for in vitro experiments to compare the efficacy of washes using 1.6% sodium hydroxide, 4% trisodium phosphate, 4% chlorofoam, or 4% phosphoric acid, each followed by a rinse step using either water or acidified (pH 7.0) chlorine at 200 or 500 ppm. All treatments using a water rinse reduced hide coliform counts by 1.5 to 2.5 log CFU/ 100 cm2. Compared with water rinses, 200 and 500 ppm acidified chlorine rinses increased efficacy by approximately 1.0 and 2.0 log CFU/100 cm2, respectively. Vacuuming of the treated areas to remove excess liquid improved hide cleanliness by an average of an additional 1.0 log CFU/100 cm2. The second objective was to evaluate the use of an on-line hide-wash cabinet that used a sodium hydroxide wash and a chlorinated (1 ppm) water rinse. Hides sampled before entering and after exiting the cabinet had aerobic plate counts and Enterobacteriaceae counts that were reduced by 2.1 and 3.4 log CFU/100 cm2, respectively, and the prevalence of E. coli O157 on hides was reduced from 44 to 17% when the cabinet was in use. Preevisceration carcass aerobic plate counts and Enterobacteriaceae counts were both reduced by 0.8 log CFU/100 cm2, and the prevalence of E. coli O157 on preevisceration carcasses was reduced from 17 to 2% when the cabinet was in use. These results support decontamination of hides as an effective means to reduce pathogen contamination of cattle carcasses during processing.     

The fate and transport of RDX, HMX, TNT and DNT in the volcanic soils of Hawaii: a laboratory and modeling study

The adsorption and degradation behavior of RDX, HMX, TNT and DNT and the impact of pH, ionic strength and dissolved organic matter on sorption were examined for two volcanic soils of a former military training area on Hawaii Island, Hawaii, USA. The transport of these chemicals in the soil was also studied in small packed columns and simulated using a water-flow and solute-transport model, HYDRUS_1D. The results show that HMX and RDX are both significantly more mobile than TNT and DNT. The adsorbability of the four chemicals was ranked as: RDXRDX>DNT>TNT. No significant trend was observed for the effect of ionic strength, pH and dissolved organic carbon (DOC) on the adsorption of explosive compounds within the concentrations and pH ranges evaluated. The simulation results show that TNT and DNT would not leach beyond a depth of 30cm soil profile whereas a significant amount of HMX and RDX would pass the 30cm depth. It seems that the risk for contamination of groundwater is much higher for both HMX and RDX than for DNT and TNT as the substratum in this area consists of highly permeable lavas.     

On the Possibility of Retaining the Microporous Structure of the LSX Zeolite During Ion Exchage of K+,Na+ → $${\text{NH}}_{4}^{ + }$$

Protection of Metals and Physical Chemistry of Surfaces - By means of elemental and X-ray powder diffraction analysis, N2 adsorption at –196°C and CO2 adsorption at 0°C the textural...     

Creation of a functional polysiloxane layer on the surface of magnetic nanoparticles using the sol-gel method

The developed methods using tetraethoxysilane and trifunctional silanes were applied to obtain Fe₃O₄ magnetic particles that contain amino groups with compositions of ≡Si(CH₂)₃NH₂, ≡Si(CH₂)₃NH(CH₂)₂NH₂, and [≡Si(CH₂)₃]₂NH. The XRD data show that the nuclei of nanoparticles in the obtained materials preserve the structure of the primary carrier, namely, that of Fe₃O₄ magnetite. The thermograms show a high thermal stability of the applied surface layers, i.e., their destruction was found to start at temperature above 250°C. The DRIFT spectra indicate the formation of the silica bond framework in the surface layers of nanoparticles and also the existence of hydrogen bonds between amino groups and silanol groups with the participation of water molecules aided. All of the obtained materials exhibit magnetic properties and offer promising application in medicine.     

Stability of carotenoid pigments in foods

Carotenoids are responsible for the colour of a wide variety of both vegetable and animal foods. Several studies published recently have shown that these compounds have a beneficial effect in human health, thus, from a nutritional point of view, it is important to know the factors related to their degradation, because carotenoid losses, not only produce changes in food colour, but also decrease their nutritional value. The instability of carotenoids is due to the fact that they are highly unsaturated compounds, thus degradation is due mainly to oxidation. Other factors, such as temperature, light or pH can produce important qualitative changes in these compounds by means of isomerization reactions.     

High temperature performance of soy-based adhesives

We studied the high temperature performance of soy meal processed to different protein concentrations (flour, concentrate, and isolate), as well as formulated soy-based adhesives, and commercial nonsoy adhesives for comparison. No thermal transitions were seen in phenol-resorcinol-formaldehyde (PRF) or soy-phenol-formaldehyde (SoyPF) or in as-received soy flour adhesive during differential scanning calorimetry scans heating at 10?°C/min between 35 and 235?°C. Heat flow rates decreased in the order soy flour (as received)?>?SoyPF?>?PRF?>?emulsion polymer isocyanate (EPI). In thermogravimetric analysis (TGA) scans from 110 to 300?°C at 2?°C/min, total weight loss decreased in the order soy flour (as-received)>SoyPF?>?PRF?>?casein?>?maple?>?EPI. For bio-based materials, the total weight loss (TGA) decreased in the order soy flour (as-received) > concentrate, casein?>?isolate. Dynamic mechanical analysis from 35 to 235?°C at 5?°C/min of two veneers bonded by cured adhesive showed 30–40% decline in storage modulus for maple compared to 45–55% for the adhesive made from soy flour in water (Soy Flour) and 70–80% for a commercial poly(vinyl acetate) modified for heat resistance. DMA on glass fiber mats showed thermal softening temperatures increasing in the order Soy Flour?<?casein?<?isolate?<?concentrate. We suggest that the low molecular weight carbohydrates plasticize the flour product. When soy-based adhesives were tested in real bondlines in DMA and creep tests in shear, they showed less decrease in storage modulus than the glass fiber-supported specimens. This suggests that interaction with the wood substrate improved the heat resistance property of the adhesive. Average hot shear strengths (ASTM D7247) were 4.6 and 3.1?MPa for SoyPF and Soy Flour compared to 4.7 and 0.8?MPa for PRF and EPI and 4.7 for solid maple. As a whole, these data suggest that despite indications of heat sensitivity when tested neat, soy-based adhesives are likely to pass the heat resistance criterion required for structural adhesives.