1,876 research outputs found

    Analytical Modeling of a Large Local Area Network - Part I: Internet Traffic Characterization

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    The goal of both IP network operators and the end users is to get the highest performance from the system for a given cost. This makes Performance a key criterion in the design, procurement, and use of computer and communication systems. In order to address problems associated with performance degradation of operational communicationssystems, over the last decade, traffic engineering techniques have emerged in an attempt to optimize communication systems’ performance and ensure more efficient use of their resources. One of these techniques is analytical modeling. Analytic performance models are an excellent tool for quickly evaluating the performance of operational or new systems. They are also well suited to comparing the performance of several alternative designs. However, analytical models can only be developed once detailed knowledge of characteristics of trafficcarried by a network is available. In Part I of this paper, traffic characterization of traffic carried by the largest Local Area Network (LAN) in Tanzania, University of Dar es Salaam Network (UDSMNET) is carried out. In Part II of this paper, an analytical model based on the Discrete Time Markov Modulated Poisson Process is proposed and validated for performance analysis of IP networks

    Strong "quantum" chaos in the global ballooning mode spectrum of three-dimensional plasmas

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    The spectrum of ideal magnetohydrodynamic (MHD) pressure-driven (ballooning) modes in strongly nonaxisymmetric toroidal systems is difficult to analyze numerically owing to the singular nature of ideal MHD caused by lack of an inherent scale length. In this paper, ideal MHD is regularized by using a kk-space cutoff, making the ray tracing for the WKB ballooning formalism a chaotic Hamiltonian billiard problem. The minimum width of the toroidal Fourier spectrum needed for resolving toroidally localized ballooning modes with a global eigenvalue code is estimated from the Weyl formula. This phase-space-volume estimation method is applied to two stellarator cases.Comment: 4 pages typeset, including 2 figures. Paper accepted for publication in Phys. Rev. Letter

    Masswe Colonic Haemorrhage from a Solitary Caecal Varix

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    A 51 year old lady with chronic active hepatitis presented with massive lower gastrointestinal tract bleeding. Angiography demonstrated a solitary varix in the caecum which was found at laparotomy to be entering the bowel wall at the site ofadhesions from a previous appendicectomy. The portal pressure was found to be raised. Aright hemicolectomy stopped the blood loss, but she subsequently died ofliver failure. Solitary colonic varices associated with adhesions are extremely rare and their optimal management has not been established

    Genetic diversity and population structure of three native cattle populations in Mozambique

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    In the present work, the population diversity and structure of three populations of native Mozambican cattle were studied, to develop knowledge that is required for sound conservation and genetic improvement programs of these genetic resources. A total of 228 animals (Landim, Angone, and Tete) were genotyped using the International Dairy and Beef version three (IDBV3) SNP BeadChip array. Population parameters varied within a limited scope, with the average minor allele frequency (MAF) ranging from 0.228 ± 0.154 in the Angone to 0.245 ± 0.145 in the Tete population, while estimates of expected heterozygosities varied from 0.304 ± 0.166 in the Angone to 0.329 ± 0.148 in the Tete population. Low positive (0.065 ± 0.109) inbreeding rates were detected in the three cattle groups. Population structure and admixture analyses indicated low genetic differentiation and various degrees of admixture among the populations. The effective population size has decreased over time and at 12 generations ago ranged between 349 (Tete) and 929 (Landim). The average linkage disequilibrium (LD) of the studied populations ranged from 0.400 ± 0.213 (Tete) to 0.434 ± 0.232 (Landim). The findings of this study will be valuable for formulating management and conservation strategies for indigenous Mozambican cattle populations.The Ministry of Science, Technology, and Higher Education of Mozambique.http://link.springer.com/journal/11250hj2022Animal and Wildlife Science

    AAC Congress Durum Wheat

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    Congress durum wheat (Triticum turgidum L. subsp. durum (Desf.) Husn.) is adapted to the durum production area of the Canadian prairies. Averaged over three years, AAC Congress yielded significantly more grain than Strongfield and AC Navigator. AAC Congress had protein concentration significantly lower than Strongfield but significantly higher than Brigade. AAC Congress is eligible for grades of Canada Western Amber Durum. It has lower grain cadmium concentration and higher yellow pigment concentration than the check cultivars, except AAC Cabri

    AAC Penhold Canada Prairie Spring Red Wheat

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    AAC Penhold, an awned hard red spring wheat (Triticum aestivum L.) cultivar, yielded significantly more grain than 5700PR while maturing 2 days earlier, and 7.5 cm shorter stature. The seed size was significantly larger than 5700PR and 5701PR, with a test weight significantly heavier than both checks. AAC Penhold expressed resistance to prevalent races of leaf rust and common bunt, and moderate resistance to fusarium head blight and stem rust. AAC Penhold had higher grain and flour protein than the checks and improved Hagberg Falling Number, amylograph viscosity, and water absorption. AAC Penhold is eligible for grades of the market class, Canada Prairie Spring Red wheat

    AAC W1876 hard red spring wheat

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    AAC W1876 hard red spring wheat (Triticum aestivum L.) has grain yield and time to maturity within the range of the check cultivars: Katepwa, Laura, Lillian, Carberry, and CDC Kernen. AAC W1876 has an awned spike, a low lodging score indicative of strong straw, and a short plant stature typical of a semidwarf wheat. AAC W1876 expressed resistance to prevalent races of leaf rust, moderate resistance to stem rust, intermediate resistance to fusarium head blight, yellow rust, common bunt, and loose smut. Compared to the Canada Western Red Spring check cultivars, AAC W1876 had improved flour yield and lower flour ash. AAC W1876 is eligible for grades of Canada Western Red Spring

    Optical Detection of a Single Nuclear Spin

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    We propose a method to optically detect the spin state of a 31-P nucleus embedded in a 28-Si matrix. The nuclear-electron hyperfine splitting of the 31-P neutral-donor ground state can be resolved via a direct frequency discrimination measurement of the 31-P bound exciton photoluminescence using single photon detectors. The measurement time is expected to be shorter than the lifetime of the nuclear spin at 4 K and 10 T.Comment: 4 pages, 3 figure

    Characterizing groundwater-surface water interactions in idealized ephemeral stream systems

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    Transmission losses from the beds of ephemeral streams are thought to be a widespread mechanism of groundwater recharge in arid and semi‐arid regions and support a range of dryland hydro‐ecology. Dryland areas cover ~40% of the Earth's land surface and groundwater resources are often the main source of freshwater. It is commonly assumed that where an unsaturated zone exists beneath a stream, the interaction between surface water and groundwater is unidirectional and that groundwater does not exert a significant feedback on transmission losses. To test this assumption, we conducted a series of numerical model experiments using idealized two‐dimensional channel‐transects to assess the sensitivity and degree of interaction between surface and groundwater for typical dryland ephemeral stream geometries, hydraulic properties and flow regimes. We broaden the use of the term “stream‐aquifer interactions” to refer not just to fluxes and water exchange but also to include the ways in which the stream and aquifer have a hydraulic effect on one another. Our results indicate that deep water tables, less frequent streamflow events, and/or highly permeable sediments tend to result in limited bi‐directional hydraulic interaction between the stream and the underlying groundwater which, in turn, results in high amounts of infiltration. With shallower initial depth to the water table, higher streamflow frequency, and/or lower bed permeability, greater “negative” hydraulic feedback from the groundwater occurs which in turn results in lower amounts of infiltration. Streambed losses eventually reach a constant rate as initial water table depths increase, but only at depths of 10s of metres in some of the cases studied. Our results highlight that bi‐directional stream‐aquifer hydraulic interactions in ephemeral streams may be more widespread than is commonly assumed. We conclude that groundwater and surface water should be considered as connected systems for water resource management unless there is clear evidence to the contrary
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