Electrical Properties of Boron Nitride Matrix Composites: III, Observations near the Percolation Threshold in BN–B4C Composites

In this third paper of the series, we discuss the electrical resistivity of BN–B₄C composites with compositions ranging from 0% to 100% B₄C. After establishing the response of samples whose compositions lie far away from the percolation region, where effective medium models apply, we focus attention on samples with compositions at or near the percolation threshold (∼60% BN–40% B₄C). The large differences in electrical properties among samples with the same nominal composition can be explained by invoking a connectivity parameter. Since the difference in the electrical resistivity of BN and B₄C is about 9 orders of magnitude, the degree of connectivity of the two components at the percolation threshold determines the resultant composite resistivity. Connectivity in these composites was quantified by taking BN peak height ratios in X-ray diffraction patterns of all samples containing 60% BN–40% B₄C. The degree of preferred orientation of the BN platelets can be correlated with systematic increases in the electrical resistivity of the composites.     

Wideband mobile radio channel characterization

Wideband mobile radio channel characterization has generally been carried out by employing sounders. These systems transmit either narrow periodic pulses or pseudo random binary sequences (prbs) with either matched filters or cross-correlators for compression at the receiver. Recently, frequency modulated continous wave (fmcw or chirp) sounders have been applied to wideband mobile radio channel characterization. The paper briefly reviews the theory of wideband channel characterization and relates the known analytical expressions to the necessary processing to extract the mobile radio channel parameters. Different architectures of chirp sounders are compared and the implementation advantages of the heterodyne detector of chirp sounders are highlighted. These are demonstrated by presenting indoor and outdoor wideband measurements.     

Construction of Phase Diagrams for Al<Subscript>x</Subscript>HfNbTaTiZr Refractory High Entropy Alloy

This work involves construction of phase diagrams of Al_xHfNbTaTiZr refractory high entropy alloy (RHEA) with an objective to understand the phase stability of the alloy at different concentrations of Al, which is expected to stabilize the body-centred cubic (BCC) structure. The constructed hexanal phase diagrams of Al_xHfNbTaTiZr RHEA shows that continuous BCC solid solution forms up to 1.5 mol of initial concentration of Al and any further increase in the Al concentration results in the formation of intermetallic phases. Further, the phase stability of Al_xHfNbTaTiZr RHEA as a function of Al concentration has been discussed in correlation with the concerned Valence Electron Concentration parameter.     

Seasonal variations in the chemical composition of camel milk in Jordan

The principal chemical components of milk from the Arabian camel (Camelus dromedarius) were monitored in Jordan over one year. The analyses included total solids, fat, protein, vitamins, minerals and organic acids. Large seasonal variations in total solids and fat were apparent, with maxima in mid-winter of 139 and 39.0 g/l, respectively, and minima in August of 102 and 25.0 g/l. These differences may be sufficient to alter the sensory properties of the milk, and the fat: casein ratio may need standardisation for cheesemaking. The mean values of trace elements like zinc (5.8 mg/l), iron (4.4 mg/l) and manganese (0.05 mg/l) in Jordanian camel milk could provide valuable additions to the diet of urban populations, as could the mean concentration of vitamin C (33 mg/l). The levels of organic acids were generally higher than in bovine milk and, as with all the constituents of the milk, there were discernible patterns linking concentration and season of the year.     

Protein expression by Listeria monocytogenes grown on a RTE-meat matrix

Little is known about whether the growth of L. monocytogenes on a ready-to-eat (RTE) meat matrix has an impact on the bacterium's pathogenic capabilities. In this report, we examined protein expression by L. monocytogenes grown on RTE sliced turkey meat, using L. monocytogenes grown on brain-heart-infusion agar as a control. Total protein fractions of L. monocytogenes from both growth conditions were extracted and compared by two-dimensional gel electrophoresis. Seventy-seven proteins expressed by turkey meat-grown L. monocytogenes were identified by MALDI-TOF/TOF mass spectrometry analysis. The identified proteins include proteins known to be involved in virulence and stress adaptation such as ClpB, ClpC, ClpP, and surface antigen. This is the first report describing the proteome expressed by L. monocytogenes grown on a meat matrix. Our results suggest that certain proteins that are expressed by RTE meat-grown L. monocytogenes may contribute to the virulence of the bacterium.     

IGIF does not drive Th1 development but synergizes with IL-12 for interferon-gamma production and activates IRAK and NFkappaB

In these studies, IFN gamma-inducing factor (IGIF), unlike IL-12, did not drive Th1 development in BALB/c or C57BL/6 mice, but like IL-1alpha, potentiated IL-12-driven Th1 development in BALB/c mice. IGIF and IL-12 synergized for IFN gamma production from Th1 cells. Unlike IL-1alpha, IGIF had no effect on Th2 cells. IGIF signaled through IRAK, IL-1 receptor-associated kinase, to induce nuclear translocation of p65/p50 NFkappaB in Th1 cells. IL-1alpha had no effect on proliferation, cytokine production, or NFkappaB activation in Th1 cells but activated NFkappaB and proliferation in Th2 cells. Thus, Th1 and Th2 cells may differ in responsiveness and receptor expression for IL-1 family molecules. IGIF and IL-1alpha may differentially amplify Th1 and Th2 effector responses, respectively.     

Correlation between menstrual cycle and cognitive performance in a chimpanzee (Pan troglodytes).

Extensive research on human subjects has tried to investigate whether there is a correlation between cognitive performance and the menstrual cycle. Less is known about the relationship between the menstrual cycle and task performance in other cognitive animals. We test whether the secretion of a sex hormone [luteinizing hormone(LH)] influences the performance of cognitive tasks by a female chimpanzee (Pan troglodytes) who is part of a long-term cognition research program. We focus on two cognitive tasks: an “easy task,” which consists of simple numerical ordering, and a “difficult task,” which combines numerical ordering with memorizing the numerals' spatial location. Data on the performance of these cognitive tasks, urine samples, and sexual swelling over six menstrual cycles showed that the chimpanzee's performance accuracy decreased and that the intertrial interval was longer during the LH-surge of the menstrual cycle, but only for the performance of the difficult task. These performance attributes seem to reflect a decrease in attention or motivation during ovulation. In summary, the cognitive performance of a chimpanzee was disturbed by hormonal changes despite her long-term experience in the tasks. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Multi-radio multi-channel routing metrics in IEEE 802.11s based wireless mesh networks

IEEE 802.11s is one of the emerging standards designed to build wireless mesh networks which may serve to extend the coverage of access networks. The default IEEE 802.11s path selection protocol Hybrid Wireless Mesh Protocol (HWMP) is based on the radio-aware airtime link metric (ALM) that outperforms the hop-count metric in single channel multi-hop wireless networks. However, this metric may lead to capacity degradation when multiple channels and/or multi-radio are used. To fully exploit the capacity gain of multiple channels use, new routing metrics have been proposed such as weighted cumulative expected transmission time, metric of interference and channel switching, interference aware routing metric, exclusive expected transmission time, and normalized bottleneck link capacity. These metrics distribute the data traffic load among channels and/or radios to reach the final destination. In this paper, we provide a qualitative comparison study that considers the characteristics of these metrics. Indeed, we substitute ALM by these different metrics, and we evaluate the performance of HWMP through simulation. Obtained results allow us to identify the appropriate use case of each metric.