Simple approach to include external resistances in the Monte Carlo simulation of MESFETs and HEMTs

The contact and external series resistances play an important role in the performance of modern 0.1-0.2 μm HEMT's. It is not possible to include these resistances directly into the Monte Carlo simulations. Here we describe a simple and efficient way to include the external series resistances into the Monte Carlo results of the intrinsic device simulations. Examples of simulation results are given for a 0.2 μm pseudomorphic HEMT

Effect of Temperature on in vitro Survival of some Bradyrhizobium Strains

Evaluating Rhizobium survival in inoculants exposed to high temperature may be considered the first stage in identifying potential inoculant strains that would withstand temperature stress on inoculated seeds in the field. High temperatures may adversely affect the survival of Rhizobium in packaged inoculants during storage and inoculation (Somasegaran et al., 1984), and the viability of rhizobia in inoculants may be lost in a few weeks at temperatures of 350C or higher (Smith, 1987). Low storage temperature, however, is not always better than room temperature, as some slow growing bradyrhizobia were found to survive better at 260C than at 40C (Vincent, 1982). Soil temperature is also an important environmental variable that affects general biological activity. Nodulation and N2-fixation were observed under a wide range of temperatures with an optimum range between 20 and 300C. Elevated temperatures affect nodule initiation and development in temperate legumes, whereas, in tropical legumes it is mainly N2 fixation efficiency that is affected (Somasegaran et al., 1984). Temperature changes affect the competitive ability of Rhizobium strains and there are also specific temperature-sensitive Rhizobium legume combinations e.g. R. Legumino- sarum biovar-trifolii that forms nodules with Trifolium subterranium (Lewis-Henderson and Djordjevic, 1991(

Utility of Lymph Node Aspiration in the Diagnosis of Visceral Leishmaniasis in Sudan.

We evaluated lymph node aspiration (LNA) as a simple diagnostic procedure for visceral leishmaniasis (VL). Lymph node aspiration was compared with the direct agglutination test (DAT) using a diagnostic titer > or = 1:6,400 in 7,880 suspected VL patients in eastern Sudan. Compared with DAT, LNA had a sensitivity of 65.1% (95% confidence interval = 63.5-66.6%). Parasite density in LNA correlated strongly with DAT titers (P < 0.0001), and low parasite density accounted for 78.1% of positive LNA results with DAT titers < 1:6,400 (n = 782). Risk factors predictive of a positive LNA result were an age of 1-29 years, male sex, a hemoglobin level < 10.0 g/dL, a DAT titer > or = 1:800, and a location with a higher prevalence of VL. Lymph node and splenic aspirations were similarly accurate as tests of cure after treatment of 50 VL patients in southern Sudan. Pre-treatment LNA results were negative in 20 cases of severe post kala-azar dermal leishmaniasis

DETERMINATION OF TOTAL PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF DICHROSTACHYS CINERA, GUIERA SENEGALENSIS AND VITEX DONIANA

The present work was undertaken to determine the phenolic content and antioxidant capacity of three plants used in Sudanese folk medicine.The total phenolic content was measured by Folin Ciocalteau method using gallic acid as standard while the antioxidant capacity was based on the ability of these plant extracts to scavenge DPPH radical.High total phenolic content was detected in Dichrostachys cinera followed by Guiera senegalensis and Vitex doniana. Dichrostachys cinera exhibited the strongest antioxidant capacity with EC50 6.63 μg/ml, followed by Guiera senegalensis (7.74 μg/ml) and Vitex doniana (22.72 μg/ml). A significant linear correlation between total phenolic content and antioxidant capacity(R2=0.9957) confirmed that the phenolic phytoconstituents are responsible for the antioxidant activity.It can be concluded that the three surveyed plants could be potential sources of antioxidant agent

Population inversion in optically pumped asymmetric quantum well terahertz lasers

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga(1 – x)Al(x)As quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. © 1997 American Institute of Physics

The genetic variation of lactase persistence alleles in northeast Africa

Lactase persistence (LP) is a well-studied example of a Mendelian trait under selection in some human groups due to gene-culture co-evolution. We investigated the frequencies of genetic variants linked to LP in Sudanese and South Sudanese populations. These populations have diverse subsistence patterns, and some are dependent on milk to various extents, not only from cows, but also from other livestock such as camels and goats. We sequenced a 316bp region involved in regulating the expression of the LCT gene on chromosome 2, which encompasses five polymorphisms that have been associated with LP. Pastoralist populations showed a higher frequency of LP-associated alleles compared to non-pastoralist groups, hinting at positive selection also in northeast African pastoralists. There was no incidence of the East African LP allele (−14010:C) in the Sudanese groups, and only one heterozygote individual for the European LP allele (−13910:T), suggesting limited recent admixture from these geographic regions. Among the LP variants, the −14009:G variant occurs at the highest frequency among the investigated populations, followed by the −13915:G variant, which is likely of Middle Eastern origin, consistent with Middle Eastern gene-flow to the Sudanese populations. The Beja population of the Beni Amer show three different LP-variants at substantial and similar levels, resulting in one of the greatest frequencies of LP-variants among all populations across the world.Competing Interest StatementThe authors have declared no competing interest.Introduction Results and Discussion - Allele frequencies - Haplotype Structure - Selection Scan Conclusion Materials and Methods - Phasing and imputation to analyze haplotype structure - Locus specific branch length (LSBL

Effect of nitrogen and phosphorus on growth and yield of irrigated sunflower (Helianthus annuus L.)*

&nbsp;&nbsp;&nbsp;&nbsp; Experiments were conducted in winter (2000 2001) and summer (2001) seasons at Elrahad Research Station to investigate the influe- nce of four levels of nitrogen and two levels of phosphorus on growth characters and seed yield of two sunflower cultivars, viz Rodio and Hysun 33. Experiments were arranged in a randomized complete block design with four replications. Rodio and Hysun 33 varied in their growth characters. Differences between the two cultivars. Were highly significant for plant height, leaf area index, days to 50% flowering, days to maturity, head diameter, number of seeds per head, 1000-seed weight and empty seeds percentage. The two cultivars were siY1ificantly different in their seed yield. Nitrogen application significantly increased all growth characters and seed yield of the two cultivars, in both seasons, however, it decreased days to 50% flowering and days to maturity. Nitrogen fertilizer had no significant effect on empty seeds percentage. Phosphorus application signific- antly increased leaf area index, head diameter, number of seeds per head and 1000-seed weight. However, plant height, days to maturity and percentage of empty seeds were not affected. Application of phosphorus had no significant effect on seed yield

Complete Monte Carlo RF analysis of 'real' short-channel compound FET's

A comprehensive RF analysis technique based on ensemble Monte Carlo (EMC) simulation of compound FET's with realistic device geometry is presented. Y-parameters are obtained through Fourier transformation of the EMC transients in response to small changes in the terminal voltages. The terminal currents are statistically enhanced and filtered to allow for reliable y-parameters extraction. Improved analytic procedure for extracting the intrinsic device small-signal circuit components is described. As a result, stable y-parameters and reliable circuit components can he extracted for the whole range of device operation voltages. Parasitic components like contact and gate resistances are included in the y-parameters at a post processing stage to facilitate the forecast of the performance figures of merit of real devices. The developed RF technique has been applied in the EMC simulation of pseudomorphic HEMT's (pHEMT's) fabricated at the Glasgow Nanoelectronics Research Center. Good agreement has been achieved between the simulated and measured small-signal circuit components and performance figures of meri