Mapping of Lattice Strain in 4H-SiC Crystals by Synchrotron Double-Crystal X-ray Topography

The presence of lattice strain in n-doped 4H-SiC substrate crystals grown by a physical vapor transport method can strongly influence the performance of related power devices that are fabricated on them. Information on the level and the variation of lattice strain in these wafer crystals is thus important. In this study, a non-destructive method is developed based on synchrotron double-crystal x-ray topography to map lattice strains in 4H-SiC wafers. Measurements are made on two 4H-SiC substrate crystals—one is an unprocessed commercial wafer while the other was subject to a post-growth high-temperature heat treatment. Maps of different strain components are generated from the equi-misorientation contour maps recorded using synchrotron monochromatic radiation. The technique is demonstrated to be a powerful tool in estimating strain fields in 4H-SiC crystals. Analysis of the strain maps also shows that the normal strain components vary much more significantly than do the shear/rotation components, indicating that lattice dilation/compression rather than lattice tilt is the major type of deformation caused by both the incorporation of nitrogen dopants and the nucleation of basal plane dislocations.     

Role of nitrogen lewis basicity in boronate affinity chromatography of nucleosides

Urinary modified nucleosides have a potential role as cancer biomarkers, and most of the methods used in their study have utilized low-pressure phenylboronate affinity chromatography materials for the purification of the cis-diol-containing nucleosides. In this study, a boronate HPLC column was surprisingly shown not to trap the nucleosides as would be expected from experience with the classic Affigel 601 resin but showed only partial selectivity toward cis-diol groups while other groups exhibited better retention. In aprotic conditions, trapping of nucleosides was possible; however, the selectivity toward cis-diol-containing compounds was lost with the Lewis basicity of available nitrogens being the main determinant of retention. The experimental findings are compared to and confirmed by DFT calculations.     

The evaluation of a PCR-based method for identification of Salmonella enterica serotypes from environmental samples and various food matrices

The most commonly used method for serotyping Salmonella spp. is based on the Kaufmann–White scheme, and is composed of serological reactions using antibodies to LPS agglutinins. The multiplex PCR used in this investigation was established by Kim et al. to serotype the 30 most common clinical Salmonella serotypes, as determined by CDC. The PCR assay consists of two five-plex reactions and a single two-plex PCR reaction, based on six genetic loci from Salmonella enterica serotype Typhimurium and four loci from S. enterica serotype Typhi. In this investigation, we further evaluated the method for serotyping Salmonella spp. using a reference collection, environmental samples collected from a Mid-Atlantic region tomato farm study, four food matrices spiked with different Salmonella serotypes and a proficiency test. The PCR assay was first evaluated using DNA isolated from pure cultures of isolates obtained from various clinical and environmental samples, and then DNA isolated from broth cultures of food matrices of “Red round” and Roma tomatoes, Romaine lettuce, green onions and Serrano peppers spiked with serotypes Newport, Typhimurium, Javiana and Saintpaul, respectively. The results showed that the PCR assay correctly serotyped Salmonella spp. from the clinical, environmental, spiked food matrices, and proficiency test samples. These findings are significant because the PCR assay was successful in the identification of Salmonella in the spiked samples in a broth culture containing other non-salmonella organism. This method may be a useful resource for the food safety community.     

Differences in the mineral composition of sound and disordered apple fruits and of sound and pitted tissue

Separation and analyses of sound Cox's Orange Pippin apples and those with disorders, after storage for 18 weeks at 3.3°C, revealed that sound apples had the lowest, apples rotted by Gloeosporium spp slightly higher, apples with bitter pit higher, and apples affected by breakdown even higher proportions of calcium in the residue after extraction with distilled water, although total concentrations of calcium in these samples were in the reverse order. Lower proportions of calcium, magnesium and potassium were extracted by 75% ethanol from fruit with breakdown than from sound apples, and similarly lower proportions of magnesium, and magnesium and potassium were extracted by water from apples with bitter pit and breakdown, respectively. Proportions of phosphorus extracted by either solvent were not obviously related to disorders. The high concentration of magnesium in pitted tissue, in relation to that in adjacent sound tissue, was evenly divided between the fractions soluble and insoluble in water, but that of calcium was mainly in the insoluble fraction.     

Interacting effects of tillage method,nitrogen fertiliser and secondary drainage on winter wheat production on a calcareous clay soil

The response of winter wheat to nitrogen fertiliser within the range 0–200 kg ha^?1 in 40 kg increments applied either in April or in May in two consecutive seasons (1976–77 and 1977–78) was tested in a field experiment on a calcareous clay soil that was either direct-drilled, shallow tine cultivated (5–8 cm), or mouldboard ploughed (23 cm). These cultivation methods had been used on the same plots in the four preceding seasons (1973 to 1976) in a comparison of cultivation systems. A comparison was also made with direct-drilling on land that had been deep tine cultivated (17 cm) during the 1973–76 experiment. In the second season (1977–78) effects were examined of newly drawn mole drains, on land that had been direct-drilled or ploughed. In both seasons the effect of cultivation method on grain yield was small when nitrogen fertiliser was applied at 80–120 kg N ha^?1. Nitrogen top dressings in April gave heavier yields than the equivalent dressings in May, partly because of dry weather after the May applications in both years. There was no interaction between method of cultivation and amount of nitrogen applied in 1976–77, but a significant interaction was detected in 1977–78 which was probably associated with less nitrogen being available in the uncultivated soil during the winter and spring. The results show that the potential yield of direct-drilled crops may have been underestimated in some earlier comparisons of different methods of cultivation where small uniform top dressings of nitrogen were applied to each cultivation treatment. Mole drainage increased yield especially at low rates of nitrogen and after direct drilling, These results indicate that direct-drilled and ploughed land may differ in their drainage requirements.     

Redistribution of minerals in apple fruit during storage: Effects of storage temperature,varietal differences and orchard management

Transverse calcium redistribution from the cores to the outer zones of the fruit was interrupted for a short period when calcium was imported by the cores of both Cox and Spartan apples, especially at 3.5°C. Bitter pit lesions developed in mid and outer cortical tissues of Cox fruit stored at 3.5°C 2 to 4 weeks after calcium concentrations in these zones were reduced. Redistribution of magnesium from the outer zones to the cores of Spartan apples occurred during storage at 3.5°C but was inhibited at 0°C. Redistribution of magnesium in Cox's Orange Pippin apples was mainly from inner cortex to the core and outer zones at 3.5°C and from central to outer zones at 0°C, but immediately low temperature breakdown become evident at 0°C, magnesium was transferred from the peel and core to the affected zones. The redistribution of phosphorus to the cores, which occurred in Spartan apples (resistant to low temperature breakdown) stored at either 3.5°C or 0°C was barely evident in Cox fruit (susceptible to low temperature breakdown) stored at 3.5°C and did not occur at 0°C. Irrigated grass compared with overall herbicide soil management increased the proportion of calcium in the core zones of both Cox and Spartan apples and the proportion of magnesium in the core zone of Spartan apples at harvest. Irrigated grass management also increased the rate of calcium redistribution in Cox and Spartan fruit during storage and altered magnesium redistribution in Spartan apples stored at 0°C.     

Complete characterization of terahertz pulse trains generated fromnonlinear processes in optical fibers

The measurement technique of frequency-resolved optical gating (FROG) is used to characterize the intensity and phase of terahertz pulse trains generated from nonlinear and dispersive interactions in optical fibers. We show that existing FROG retrieval algorithms are easily adapted to allow the retrieval of periodic pulse characteristics and, using synthetic pulse trains generated from numerical simulations, we demonstrate how FROG can differentiate between periodic pulse trains with fundamentally different intensity and phase characteristics, yet qualitatively similar autocorrelation functions and spectra. Experimental results are presented for the FROG characterization of a 0.3-THz sinusoidal beat signal from a dual wavelength laser source, a 2.5-THz train of dark solitons generated in a high-birefringence fiber, and a 0.6-THz bright polarization domain wall soliton train generated in an ultra-low birefringence fiber. These results are shown to be in good agreement with nonlinear Schrodinger equation simulations     

Surface plasmon resonance biosensor for rapid label-free detection of microribonucleic acid at subfemtomole level

Microribonucleic acids (miRNAs) have been linked with various regulatory functions and disorders, such as cancers and heart diseases. They, therefore, present an important target for detection technologies for future medical diagnostics. We report here a novel method for rapid and sensitive miRNA detection and quantitation using surface plasmon resonance (SPR) sensor technology and a DNA*RNA antibody-based assay. The approach takes advantage of a novel high-performance portable SPR sensor instrument for spectroscopy of surface plasmons based on a special diffraction grating called a surface plasmon coupler and disperser (SPRCD). The surface of the grating is functionalized with thiolated DNA oligonucleotides which specifically capture miRNA from a liquid sample without amplification. Subsequently, an antibody that recognizes DNA*RNA hybrids is introduced to bind to the DNA*RNA complex and enhance sensor response to the captured miRNA. This approach allows detection of miRNA in less than 30 min at concentrations down to 2 pM with an absolute amount at high attomoles. The methodology is evaluated for analysis of miRNA from mouse liver tissues and is found to yield results which agree well with those provided by the quantitative polymerase chain reaction (qPCR).     

Microwave power amplifiers for space systems

This paper addresses both solid state power amplifiers (sspas) and travelling wave tube amplifiers (twtas), highlighting their capabilities, drawbacks and future developments, for space systems. These two technologies are complementary and will coexist in future pay loads.