Formation mechanism of InxGa1−xAs ohmic contacts to n-type GaAs prepared by radio frequency sputtering

The formation mechanisms of InAs/Ni/W ohmic contacts to n-type GaAs prepared by radio-frequency (rf) sputtering were studied by measuring contact resistances (R_c) using a transmission line method and by analyzing the interfacial structure mainly by x-ray diffraction and transmission electron microscopy. Current-voltage characteristics of the InAs/Ni/W contacts after annealing at temperatures above 600°C showed “ohmic-like behavior.” In order to obtain the “ohmic” behavior in the contacts, pre-heating at 300°C prior to high temperature annealing was found to be essential. The contacts showed ohmic behavior after annealing at temperatures in the range of 500∼850°C and contact resistance values of as low as ∼0.3Ω-mm were obtained. By analyzing the interfacial structures of these contacts, In_xGa_1−xAs layers with low density of misfit dislocations at the In_xGa_1−xAs and GaAs interface were observed to grow epitaxially on the GaAs substrate upon heating at high temperatures. This intermediate In_xGa_1−xAs layer is believed to divide the high energy barrier at the contact metal and GaAs interface into two low barriers, resulting in reduction of the contact resistance. In addition, Ni was found to play a key role to relax a strain in the In_xGa_1−xAs layer (introduced due to lattice mismatch between the In_xGa_1−xAs and GaAs) by forming an intermediate Ni_xGaAs layer on the GaAs surface prior to formation of the In_xGa_1−xxAs layer.     

Melt spinning and metal chloride vapor curing process on polymethylsilsesquioxane as Si?O?C fiber precursor

Melt spinning process of polymethylsilsesquioxane (PMSQ) at 403–453 K was investigated as a Si? O? C fiber precursor in terms of averages and distributions of spun fiber diameters. Because of fusible character of PMSQ at low temperature, the spun fibers were exposed to vapors of various metal chlorides (SiCl₄, Si(CH₃)Cl₃, TiCl₄, and BCl₃) to promote the fiber curing. Cured fibers were investigated by FTIR and TG analyses. In a case of the fiber synthesized with SiCl₄ curing, tensile tests on the pyrolyzed fibers were performed. Exposure of the synthesized fiber at high temperature with a flame of an oxygen‐gas burner was examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Spray Pyrolysis of Fe3O4–BaTiO3 Composite Particles

Fe₃O₄–BaTiO₃ composite particles were successfully prepared by ultrasonic spray pyrolysis. A mixture of iron(III) nitrate, barium acetate and titanium tetrachloride aqueous solution were atomized into the mist, and the mist was dried and pyrolyzed in N₂ (90%) and H₂ (10%) atmosphere. Fe₃O₄–BaTiO₃ composite particle was obtained between 900° and 950°C while the coexistence of FeO was detected at 1000°C. Transmission electron microscope observation revealed that the composite particle is consisted of nanocrystalline having primary particle size of 35 nm. Lattice parameter of the Fe₃O₄–BaTiO₃ nanocomposite particle was 0.8404 nm that is larger than that of pure Fe₃O₄. Coercivity of the nanocomposite particle (390 Oe) was much larger than that of pure Fe₃O₄ (140 Oe). These results suggest that slight diffusion of Ba into Fe₃O₄ occurred.     

Resistance to aerobic deterioration of total mixed ration silage: effect of ration formulation,air infiltration and storage period on fermentation characteristics and aerobic stability

BACKGROUND: High aerobic stability can be expected when wet brewers' grains are stored as a total mixed ration (TMR) silage. To understand the factors affecting the stability, the effects of ration formulation, air infiltration and storage period were studied. RESULTS: A TMR containing wet brewers' grains, hay, maize, wheat bran, beet pulp and molasses was ensiled in laboratory silos for 14 and 56 days. The effects of hay species (lucerne or sudangrass) and air infiltration (Exp. 1) and of excluding one, two or three items from the six ingredients (Exp. 2) were examined. Ethanol was the main fermentation product in all TMR silages in this study. Aerobic deterioration occurred in 14 day silages prepared with sudangrass hay along with air infiltration (Exp. 1), and with the simplest recipe where three items (hay, maize and wheat bran) were excluded (Exp. 2). No deterioration occurred in 56 day silages regardless of ration formulation and air infiltration. Yeasts receded in 56 day silages, except with the simplest recipe, to the 10² cfu g^?1 level and remained undetectable in the presence of air (Exp. 2). CONCLUSION: TMR silage can resist aerobic deterioration provided that a sufficient ensiling period has elapsed. Silages stored for only a few weeks may be susceptible to deterioration when air is infiltrated or where fewer ingredients are used in the TMR mixture. Copyright © 2007 Society of Chemical Industry     

Effect of skimmed milk and its fractions on the inactivation of Escherichia coli K12 by high hydrostatic pressure treatment

We investigated the effects of skimmed milk and its protein fractions (casein, whey, globulin, and albumin) on the injury and inactivation of Escherichia coli K-12 by high hydrostatic pressure (HHP) treatment. The protective effect of skimmed milk on HHP-mediated inactivation and injury of E. coli increased with increases in the skimmed milk concentration. However, protein fractions derived from skimmed milk did not exhibit this protective effect. Microscopy analysis by DAPI/PI staining indicated that some cells were localized in the solid portion of skimmed milk, and some of these cells were alive. The coagulated fraction derived from the autoclaved whey fraction also showed a significant protective effect. We speculate that the solid portion in skimmed milk could provide the protective effect to bacterial cells.     

Design of energy‐efficient train speed profiles considering fixed‐block signaling system

In dense traffic railway networks, trains may often slow down or stop between stations owing to previous train delays. If preceding train trajectory can be predicted, energy‐efficient driving can be achieved by suppressing unnecessary speed changes. In this paper, we propose an algorithm to find energy‐efficient driving considering fixed‐block signaling (FBS) system by using dynamic programming (DP). DP is suitable for use because it can optimize the control inputs with discrete and state constraints. In this paper, we discuss energy‐efficient driving by considering a FBS system using some case studies of simulation. In the simulation, we examine a technique to drive an express train in an energy‐efficient way when the preceding local train is running toward the station with passing loops. The results show that the proposed method can derive complex speed profiles for energy‐efficient driving and the train can be operated with a maximum reduced energy consumption of 8.3%.     

Investigation on the Interactions between Self-Assembled β-Sheet Peptide Nanofibers and Model Cell Membranes

Self-assembled peptide nanofibers (NFs) obtained from β-sheet peptides conjugated with drugs, including antigenic peptides, have recently attracted significant attention. However, extensive studies on the interactions of β-sheet peptide NFs with model cell membranes have not been reported. In this study, we investigated the interactions between three types of NFs, composed of PEG-peptide conjugates with different ethylene glycol (EG) lengths (6-, 12- and 24-mer), and dipalmitoylphosphatidylcholine (DPPC) Langmuir membranes. When increasing the EG chain length, those interactions significantly decreased considering measurements in the presence of the NFs of: (i) changes in surface pressure of the DPPC Langmuir monolayers and (ii) surface pressure–area (π–A) compression isotherms of DPPC. Because the observed trend was similar to the EG length dependency with regard to cellular association and cytotoxicity of the NFs that was reported previously, the interaction of NFs with phospholipid membranes represented a crucial factor to determine the cellular association and toxicity of the NFs. In contrast to NFs, no changes were observed with varying EG chain length on the interaction of the building block peptide with the DPPC membrane. The results obtained herein can provide a design guideline on the formulation of β-sheet peptide NFs, which may broaden its potential.     

Dimeric C34 Derivatives Linked through Disulfide Bridges as New HIV-1 Fusion Inhibitors

C34, a 34-mer fragment peptide, is contained in the HIV-1 envelope protein gp41. A dimeric derivative of C34 linked through a disulfide bridge at its C terminus was synthesized and found to display potent anti-HIV activity, comparable with that of a previously reported PEGylated dimer of C34REG. The reduction in the size of the linker moiety for dimerization was thus successful, and this result might shed some light on the mechanism of the suppression of six-helix bundle formation by these C34 dimeric derivatives. Addition of a Gly-Cys(CH₂CONH₂)-Gly-Gly motif at the N-terminal position of a C34 monomeric derivative significantly increased the anti-HIV-1 activity. This moiety functions as a new pharmacophore, and this might provide a useful insight into the design of potent HIV-1 fusion inhibitors.     

Quantitative Elemental Analysis of a Single Cell by Using Inductively Coupled Plasma-Mass Spectrometry in Fast Time-Resolved Analysis Mode

The elemental composition of a single yeast, green alga, or red blood cell (RBC) was precisely determined by using inductively coupled plasma-mass spectrometry (ICP-MS) operating in fast time-resolved analysis (TRA) mode. The technique is known as single-cell (SC)-ICP-MS. Phosphorus, sulfur, magnesium, zinc, and iron were detected in the three types of cell. The elemental composition of yeast and green alga obtained by SC-ICP-MS was consistent with results obtained from conventional ICP-MS measurements following acid digestion of the cells. Slight differences were found in the measured values between SC-ICP-MS and the conventional ICP-MS results for RBC. However, the SC-ICP-MS results for S and Fe in RBC were closer to the estimated values for these elements that were calculated from the level of hemoglobin in RBCs. The data suggest that SC-ICP-MS is suitable for the analysis of various cell types, namely, fungus, plant, and animal cells.