Analysis of a discrete-time single-server queue with bursty imputs for traffic control in ATM networks

Due to a large number of bursty traffic sources that an ATM network is expected to support, controlling network traffic becomes essential to provide a desirable level of network performance with its users. Admission control and traffic smoothing are among the most promising control techniques for an ATM network. To evaluate the performance of an ATM network when it is subject to admission control or traffic smoothing, we build a discrete-time single-server queueing model where a new call joins the existing calls.In our model. it is assumed that the cell arrivals from a new call follow a general distribution. It is also assumed that the aggregated arrivals of cells from the existing calls form batch arrivals with a general distribution for the batch size and a geometric distribution for the interarrival times of batches. We consider both finite and infinite buffer cases, and analytically obtain the waiting time distribution and cell loss probability for a new call and for existing calls. Our analysis is an exact one. Through numerical examples, we investigate how the network performance depends on the statistics of a new call (burstiness, time that a call stays in active or inactive state, etc.). We also demonstrate the effectiveness of traffic smoothing to reduce network congestion

Delay analysis for CBR traffic under static-priority scheduling

We examine the delay performance of packets from constant-bit-rate (CBR) traffic whose delay is affected by non-real-time traffic. The delay performance is analyzed by solving the nD/D/1 queue with vacations. We obtain an exact and closed form solution, hence obviating the need of any approximations or numerical Laplace inversions. We then provide various numerical results for low-bit-rate transmission links, in which packets can experience large delay. From our quantitative evaluation, we conclude that there exists an optimum packet size for a given delay bound. In extremely slow links, such as modem links, transmission control protocol (TCP) packets should be segmented to reduce the CBR delay. We therefore investigate the delay impact of TCP packet sizes as wel

Estimating the incidence of equine viral arteritis and the sensitivity of its surveillance in the French breeding stock

Equine viral arteritis (EVA) may have serious economic impact on the equine industry. For this reason, it is monitored in many countries, especially in breeding stock, to avoid its spread during breeding activities. In France, surveillance is mainly based on serological tests, since mares are not vaccinated, but difficulties in interpreting certain series of results may impair the estimation of the number of outbreaks. In this study, we propose specific rules for identifying seroconversion in order to estimate the number of outbreaks that were detected by the breeding stock surveillance component (BSSC) in France between 2006 and 2013. A consensus among multidisciplinary experts was reached to consider seroconversion as a change in antibody titer from negative to at least 32, or as an eight-fold or greater increase in antibody level. Using these rules, 239 cases and 177 outbreaks were identified. Subsequently, we calculated the BSSC's sensitivity as the ratio of the number of detected outbreaks to the total number of outbreaks that occurred in breeding stock (including unreported outbreaks) estimated using a capture-recapture model. The total number of outbreaks was estimated at 215 (95% credible interval 195-249) and the surveillance sensitivity at 82% (CrI95% 71-91). Our results confirm EVA circulation in French breeding stock, show that neutralizing antibodies can persist up to eight years in naturally infected mares and suggest that certain mares have been reinfected. This study shows that the sensitivity of the BSSC is relatively high and supports its relevance to prevent the disease spreading through mating

An evaluation of Irish cattle herds with inconclusive serological evidence of bovine brucellosis

Since 1998, there has been a steady decline in herd restrictions and de-populations in Ireland due to bovine brucellosis. There is concern that the interpretation of laboratory results may become increasingly problematic, as brucellosis prevalence falls in Ireland. Therefore, the purpose of the current study was to evaluate the infection status of Irish herds and animals with inconclusive serological evidence of bovine brucellosis. During 12 months from September 1, 2004, laboratory and observational epidemiological data were collected from all Irish herds where animal testing identified at least one animal with a complement fixation test (CFT) reading greater than zero and/or a positive result to the indirect enzyme-linked immunosorbent assay (iELISA). Due to the observational nature of the study, we have robust estimates of the relative, but not the absolute, performance of the CFT, iELISA and brucellin skin test (BST). Herds were divided into three categories (Group A, B or C) on the basis of test results at initial assessment. A total of 639 herds were enrolled into the study, and observed for at least two years following enrolment. A rising CFT titre, with a CFT reading of 111 International CFT Units (IU) or greater at the subsequent blood test, was generally associated with herds where other evidence of infection was also available. Knowledge of the CFT reading at the initial and a subsequent blood test proved useful in distinguishing false-positive and true-positive brucellosis results. There was poor correlation between the CFT and iELISA results, and between the CFT and BST results. As a result of this study, national policy has been modified to include re-sampling of all animals with CFT readings of 20 IU or greater. This project has also led to a reduction in the number of herds restricted, as well as restriction duration. It has also contributed to a reduction in the number of herds listed for contiguous tests, and therefore the potential for contiguity testing of false positive results

The read-across hypothesis and environmental risk assessment of pharmaceuticals

This article is made available through the Brunel Open Access Publishing Fund. Copyright © 2013 American Chemical Society.Pharmaceuticals in the environment have received increased attention over the past decade, as they are ubiquitous in rivers and waterways. Concentrations are in sub-ng to low μg/L, well below acute toxic levels, but there are uncertainties regarding the effects of chronic exposures and there is a need to prioritise which pharmaceuticals may be of concern. The read-across hypothesis stipulates that a drug will have an effect in non-target organisms only if the molecular targets such as receptors and enzymes have been conserved, resulting in a (specific) pharmacological effect only if plasma concentrations are similar to human therapeutic concentrations. If this holds true for different classes of pharmaceuticals, it should be possible to predict the potential environmental impact from information obtained during the drug development process. This paper critically reviews the evidence for read-across, and finds that few studies include plasma concentrations and mode of action based effects. Thus, despite a large number of apparently relevant papers and a general acceptance of the hypothesis, there is an absence of documented evidence. There is a need for large-scale studies to generate robust data for testing the read-across hypothesis and developing predictive models, the only feasible approach to protecting the environment.BBSRC Industrial Partnership Award BB/ I00646X/1 and BBSRC Industrial CASE Partnership Studentship BB/I53257X/1 with AstraZeneca Safety Health and Environment Research Programme

Residential exposure to plasticizers and its possible role in the pathogenesis of asthma.

The plasticizer di(2-ethylhexyl) phthalate (DEHP) is widely used in building materials. DEHP is identified as the major plasticizer exposure in dwellings. We provide evidence that inhalation exposure to DEHP as aerosols adsorbed to particulate matter is as important, or more important, than vapor phase exposure. The particulate inhalation exposure to DEHP is considered to be significant due to its low clearance and extensive penetration into the pulmonary region. DEHP is capable of creating high local concentrations in the airways at the deposition site with subsequent local effects. The proposed mechanism of effect states that mono(2-ethylhexyl) phthalate (MEHP), the primary hydrolysis product of DEHP, mimics the inducing prostaglandins (PG) PGD(2), 9alpha,11betaPGF2, and PGF2alpha, and thromboxanes in the lungs, thereby increasing the risk of inducing inflammation in the airways, which is a characteristic of asthma

Impact of Vaccination and Pathogen Exposure Dosage on Shedding Kinetics of Infectious Hematopoietic Necrosis Virus (IHNV) in Rainbow Trout

Vaccine efficacy in preventing clinical disease has been well characterized. However, vaccine impacts on transmission under diversefied conditions, such as variable pathogen exposure dosages, are not fully understood. We evaluated the impacts of vaccination on disease-induced host mortality and shedding of infectious hematopoietic necrosis virus (IHNV) in Rainbow Trout Oncorhynchus mykiss. Fish, in up to three different genetic lines, were exposed to different dosages of IHNV to simulate field variability. Mortality and viral shedding of each individual fish were quantified over the course of infection. As the exposure dosage increased, mortality, number offish shedding virus,daily virus quantity shed, and total amount of virus shed also increased. Vaccination significantly reduced mortality but had a much smaller impact on shedding, such that vaccinated fish still shed significant amounts of virus, particularly at higher viral exposure dosages. These studies demonstrate that the consideration of pathogen exposure dosage and transmission are critical for robust inference of vaccine efficacy

Differential postural effects of plantar-flexor muscles fatigue under normal, altered and improved vestibular and neck somatosensory conditions

The aim of the present study was to assess the effects of plantar-flexor muscles fatigue on postural control during quiet standing under normal, altered and improved vestibular and neck somatosensory conditions. To address this objective, young male university students were asked to stand upright as still as possible with their eyes closed in two conditions of No Fatigue and Fatigue of the plantar-flexor muscles. In Experiment 1 (n=15), the postural task was executed in two Neutral head and Head tilted backward postures, recognized to degrade vestibular and neck somatosensory information. In Experiment 2 (n=15), the postural task was executed in two conditions of No tactile and Tactile stimulation of the neck provided by the application of strips of adhesive bandage to the skin over and around the neck. Centre of foot pressure displacements were recorded using a force platform. Results showed that (1) the Fatigue condition yielded increased CoP displacements relative to the No Fatigue condition (Experiment 1 and Experiment 2), (2) this destabilizing effect was more accentuated in the Head tilted backward posture than Neutral head posture (Experiment 1) and (3) this destabilizing effect was less accentuated in the condition of Tactile stimulation than that of No tactile stimulation of the neck (Experiment 2). In the context of the multisensory control of balance, these results suggest an increased reliance on vestibular and neck somatosensory information for controlling posture during quiet standing in condition of altered ankle neuromuscular function

Genetic characterization of 2008 reassortant influenza A virus (H5N1), Thailand

In January and November 2008, outbreaks of avian influenza have been reported in 4 provinces of Thailand. Eight Influenza A H5N1 viruses were recovered from these 2008 AI outbreaks and comprehensively characterized and analyzed for nucleotide identity, genetic relatedness, virulence determinants, and possible sites of reassortment. The results show that the 2008 H5N1 viruses displayed genetic drift characteristics (less than 3% genetic differences), as commonly found in influenza A viruses. Based on phylogenetic analysis, clade 1 viruses in Thailand were divided into 3 distinct branches (subclades 1, 1.1 and 1.2). Six out of 8 H5N1 isolates have been identified as reassorted H5N1 viruses, while other isolates belong to an original H5N1 clade. These viruses have undergone inter-lineage reassortment between subclades 1.1 and 1.2 and thus represent new reassorted 2008 H5N1 viruses. The reassorted viruses have acquired gene segments from H5N1, subclade 1.1 (PA, HA, NP and M) and subclade 1.2 (PB2, PB1, NA and NS) in Thailand. Bootscan analysis of concatenated whole genome sequences of the 2008 H5N1 viruses supported the reassortment sites between subclade 1.1 and 1.2 viruses. Based on estimating of the time of the most recent common ancestors of the 2008 H5N1 viruses, the potential point of genetic reassortment of the viruses could be traced back to 2006. Genetic analysis of the 2008 H5N1 viruses has shown that most virulence determinants in all 8 genes of the viruses have remained unchanged. In summary, two predominant H5N1 lineages were circulating in 2008. The original CUK2-like lineage mainly circulated in central Thailand and the reassorted lineage (subclades 1.1 and 1.2) predominantly circulated in lower-north Thailand. To prevent new reassortment, emphasis should be put on prevention of H5N1 viruses circulating in high risk areas. In addition, surveillance and whole genome sequencing of H5N1 viruses should be routinely performed for monitoring the genetic drift of the virus and new reassorted strains, especially in light of potential reassortment between avian and mammalian H5N1 viruses