322 research outputs found
Performance Analysis of Preemption Algorithms in an IDNX Circuit Switch Communications Network
Access to communication networks is increasing rapidly. The increase access to these networks results in delays and at times loss of data. At times of peak traffic or when trunks or nodes are down, very important customers\u27 communications requirements are not met. One way to combat this problem is to prioritize the network and provide different levels of grade of service (GOS) for each priority. Call preemption provides an effective method of obtaining different levels of GOS. This research seeks to design the best circuit switch communications network preemption model for the DoD by analyzing previously developed preemption algorithms. Four simulation network models are developed. The grades of service per priority are obtained as the network capacity decreases and as the calls generated in node 0 increases. The analysis of preemption network models is based on the grade of service, average number of preemptions, and average network bandwidth. The networks are simulated under the same input parameters. The analysis showed that preemption can significantly lower the grade of service for high priority customers in a congested network. The best configuration preemption model depends on the bandwidth flexibility of the network and the goals of the communications network organization
Energy bands, conductance and thermoelectric power for ballistic electrons in a nanowire with spin-orbit interaction
We calculated the effects of spin-orbit interaction (SOI) on the energy
bands, ballistic conductance and the electron-diffusion thermoelectric power of
a nanowire by varying the temperature, electron density and width of the wire.
The potential barriers at the edges of the wire are assumed to be very high. A
consequence of the boundary conditions used in this model is determined by the
energy band structure, resulting in wider plateaus when the electron density is
increased due to larger energy-level separation as the higher subbands are
occupied by electrons. The nonlinear dependence of the transverse confinement
on position with respect to the well center excludes the "pole-like feature" in
the conductance which is obtained when a harmonic potential is employed for
confinement. At low temperature, the electron diffusion thermoelectric power
increases linearly with T but deviates from the linear behavior for large
values of T.Comment: Updated corrected version of the original submissio
Epidemiological characteristics and societal burden of varicella zoster virus in the Netherlands
Background: Varicella and herpes zoster are both caused by varicella zoster virus (VZV) infection or reactivation and may lead to complications associated with a (severe) societal burden. Because the epidemiology of VZV-related diseases in the Netherlands remains largely unknown or incomplete, the main objective of this study was to study the primary care incidence, associated complications and health care resource use.Methods: We investigated the incidence of VZV complications in the Dutch general practitioner (GP) practices and pharmacies in a retrospective population-based cohort study (2004-2008) based on longitudinal GP data including free text fields, hospital referral and discharge letters from approximately 165,000 patients.Results: The average annual incidence of varicella GP-consultations was 51.5 per 10,000 (95% CI 44.4-58.7) overall; 465.5 per 10,000 for 0-1 year-olds; 610.8 per 10,000 for 1-4 year-olds; 153.5 per 10,000 for 5-9 year-olds; 8,3 per 10,000 for >10 year olds. When only ICPC coded diagnoses were analyzed the incidence was 27% lower. The proportion of complications among varicella patients was 34.9%. Most frequently complications were upper respiratory tract infections. Almost half of the varicella patients received medication. The referral rate based on GP consultations was 1.7%. The average annual incidence of herpes zoster GP-consultations was 47.5 per 10,000 (95% CI 40.6-54.4). The incidence increased with age; 32.8 per 10,000 for 65 year olds. When estimating herpes zoster incidence only on ICPC coded information, the incidence was 28% lower. The complication rate of herpes zoster was 32.9%. Post herpetic neuralgia was seen most often. Of patients diagnosed with herpes zoster 67.8% received medication. The referral rate based on GP consultations was 3.5%.Conclusions: For varicella the highest incidence of GP-consultations was found in 1-4 year-olds, for herpes zoster in the >65 years olds. The occurrence of complications was not age-dependent but varies per complication. When estimating incidence of VZV-related diseases in primary care, based on diagnostic codes only, one should be aware of a gross underestimation of the incidence. Our analysis may have important implications for the outcomes of upcoming cost-effectiveness analyses on VZV vaccination.</p
Hidden dimers and the matrix maps: Fibonacci chains re-visited
The existence of cycles of the matrix maps in Fibonacci class of lattices is
well established. We show that such cycles are intimately connected with the
presence of interesting positional correlations among the constituent `atoms'
in a one dimensional quasiperiodic lattice. We particularly address the
transfer model of the classic golden mean Fibonacci chain where a six cycle of
the full matrix map exists at the centre of the spectrum [Kohmoto et al, Phys.
Rev. B 35, 1020 (1987)], and for which no simple physical picture has so far
been provided, to the best of our knowledge. In addition, we show that our
prescription leads to a determination of other energy values for a mixed model
of the Fibonacci chain, for which the full matrix map may have similar cyclic
behaviour. Apart from the standard transfer-model of a golden mean Fibonacci
chain, we address a variant of it and the silver mean lattice, where the
existence of four cycles of the matrix map is already known to exist. The
underlying positional correlations for all such cases are discussed in details.Comment: 14 pages, 2 figures. Submitted to Physical Review
Magneto-infrared modes in InAs-AlSb-GaSb coupled quantum wells
We have studied a series of InAs/GaSb coupled quantum wells using
magneto-infrared spectroscopy for high magnetic fields up to 33T within
temperatures ranging from 4K to 45K in both Faraday and tilted field
geometries. This type of coupled quantum wells consists of an electron layer in
the InAs quantum well and a hole layer in the GaSb quantum well, forming the
so-called two dimensional electron-hole bilayer system. Unlike the samples
studied in the past, the hybridization of the electron and hole subbands in our
samples is largely reduced by having narrower wells and an AlSb barrier layer
interposed between the InAs and the GaSb quantum wells, rendering them weakly
hybridized. Previous studies have revealed multiple absorption modes near the
electron cyclotron resonance of the InAs layer in moderately and strongly
hybridized samples, while only a single absorption mode was observed in the
weakly hybridized samples. We have observed a pair of absorption modes
occurring only at magnetic fields higher than 14T, which exhibited several
interesting phenomena. Among which we found two unique types of behavior that
distinguishes this work from the ones reported in the literature. This pair of
modes is very robust against rising thermal excitations and increasing magnetic
fields alligned parallel to the heterostructures. While the previous results
were aptly explained by the antilevel crossing gap due to the hybridization of
the electron and hole wavefunctions, i.e. conduction-valence Landau level
mixing, the unique features reported in this paper cannot be explained within
the same concept. The unusual properties found in this study and their
connection to the known models for InAs/GaSb heterostructures will be
disccused; in addition, several alternative ideas will be proposed in this
paper and it appears that a spontaneous phase separation can account for most
of the observed features
Anomalous Photon-Assisted Tunneling in Graphene
We investigated the Dirac electrons transmission through a potential barrier
in the presence of circularly polarized light. An anomalous photon-assisted
enhanced transmission is predicted and explained in a comparison with the
well-known Klein paradox. It is demonstrated that the perfect transmission for
nearly-head-on collision in an infinite graphene is suppressed in gapped
dressed states of electrons, which is further accompanied by shift of peaks as
a function of the incident angle away from the head-on collision. In addition,
the perfect transmission in the absence of potential barrier is partially
suppressed by a photon-induced gap in illuminated graphene. After the effect of
rough edges of the potential barrier or impurity scattering is included, the
perfect transmission with no potential barrier becomes completely suppressed
and the energy range for the photon-assisted perfect transmission is reduced at
the same time
Global priorities for conservation of reptilian phylogenetic diversity in the face of human impacts
Phylogenetic diversity measures are increasingly used in conservation planning to represent aspects of biodiversity beyond that captured by species richness. Here we develop two new metrics that combine phylogenetic diversity and the extent of human pressure across the spatial distribution of species — one metric valuing regions and another prioritising species. We evaluate these metrics for reptiles, which have been largely neglected in previous studies, and contrast these results with equivalent calculations for all terrestrial vertebrate groups. We find that regions under high human pressure coincide with the most irreplaceable areas of reptilian diversity, and more than expected by chance. The highest priority reptile species score far above the top mammal and bird species, and reptiles include a disproportionate number of species with insufficient extinction risk data. Data Deficient species are, in terms of our species-level metric, comparable to Critically Endangered species and therefore may require urgent conservation attention
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