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Search Results: 1 - 10 of 217334 matches for " Simon L. Cotton "
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Second-Order Statistics of $κ-μ$ Shadowed Fading Channels
Simon L. Cotton
Mathematics , 2015,
Abstract: In this paper, novel closed-form expressions for the level crossing rate (LCR) and average fade duration (AFD) of $\kappa-\mu$ shadowed fading channels are derived. The new equations provide the capability of modeling the correlation between the time derivative of the shadowed dominant and multipath components of the $\kappa-\mu$ shadowed fading envelope. Verification of the new equations is performed by reduction to a number of known special cases. It is shown that as the shadowing of the resultant dominant component decreases, the signal crosses lower threshold levels at a reduced rate. Furthermore, the impact of increasing correlation between the slope of the shadowed dominant and multipath components similarly acts to reduce crossings at lower signal levels. The new expressions for the second-order statistics are also compared with field measurements obtained for cellular device-to-device and body centric communications channels which are known to be susceptible to shadowed fading.
Susceptibility to Predation Affects Trait-Mediated Indirect Interactions by Reversing Interspecific Competition
Sophie L. Mowles, Simon D. Rundle, Peter A. Cotton
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0023068
Abstract: Numerous studies indicate that the behavioral responses of prey to the presence of predators can have an important role in structuring assemblages through trait-mediated indirect interactions. Few studies, however, have addressed how relative susceptibility to predation influences such interactions. Here we examine the effect of chemical cues from the common shore crab Carcinus maenas on the foraging behavior of two common intertidal gastropod molluscs. Of the two model consumers studied, Littorina littorea is morphologically more vulnerable to crab predation than Gibbula umbilicalis, and it exhibited greater competitive ability in the absence of predation threat. However, Littorina demonstrated a greater anti-predator response when experimentally exposed to predation cues, resulting in a lower level of foraging. This reversed the competitive interaction, allowing Gibbula substantially increased access to shared resources. Our results demonstrate that the susceptibility of consumers to predation can influence species interactions, and suggest that inter-specific differences in trait-mediated indirect interactions are another mechanism through which non-consumptive predator effects may influence trophic interactions.
Secrecy Capacity Analysis over $κ-μ$ Fading Channels: Theory and Applications
Nidhi Bhargav,Simon L. Cotton,David E. Simmons
Mathematics , 2015,
Abstract: In this paper, we consider the transmission of confidential information over a $\kappa$-$\mu$ fading channel in the presence of an eavesdropper, who also observes $\kappa$-$\mu$ fading. In particular, we obtain novel analytical solutions for the probability of strictly positive secrecy capacity (SPSC) and the lower bound of secure outage probability (SOP$^L$) for channel coefficients that are positive, real, independent and non-identically distributed ($i.n.i.d.$). We also provide a closed-form expression for the probability of SPSC when the $\mu$ parameter is assumed to only take positive integer values. We then apply the derived results to assess the secrecy performance of the system in terms of the average signal-to-noise ratio (SNR) as a function of the $\kappa$ and $\mu$ fading parameters. We observed that for fixed values of the eavesdropper's average SNR, increases in the average SNR of the main channel produce a higher probability of SPSC and a lower secure outage probability (SOP). It was also found that when the main channel experiences a higher average SNR than the eavesdropper's channel, the probability of SPSC improved while the SOP was found to decrease with increasing values of $\kappa$ and $\mu$ for the legitimate channel. The versatility of the $\kappa$-$\mu$ fading model, means that the results presented in this paper can be used to determine the probability of SPSC and SOP$^L$ for a large number of other fading scenarios such as Rayleigh, Rice (Nakagami-$n$), Nakagami-$m$, One-Sided Gaussian and mixtures of these common fading models. Additionally, due to the duality of the analysis of secrecy capacity and co-channel interference, the results presented here will also have immediate applicability in the analysis of outage probability in wireless systems affected by co-channel interference and background noise.
A Stochastic Geometry Based Approach to Modeling Interference Correlation in Cooperative Relay Networks
Young Jin Chun,Simon L. Cotton,Mazen O. Hasna,Ali Ghrayeb
Mathematics , 2015,
Abstract: Future wireless networks are expected to be a convergence of many diverse network technologies and architectures, such as cellular networks, wireless local area networks, sensor networks, and device to device communications. Through cooperation between dissimilar wireless devices, this new combined network topology promises to unlock ever larger data rates and provide truly ubiquitous coverage for end users, as well as enabling higher spectral efficiency. However, it also increases the risk of co-channel interference and introduces the possibility of correlation in the aggregated interference that not only impacts the communication performance, but also makes the associated mathematical analysis much more complex. To address this problem and evaluate the communication performance of cooperative relay networks, we adopt a stochastic geometry based approach by assuming that the interfering nodes are randomly distributed according to a Poisson point process (PPP). We also use a random medium access protocol to counteract the effects of interference correlation. Using this approach, we derive novel closed-form expressions for the successful transmission probability and local delay of a relay network with correlated interference. As well as this, we find the optimal transmission probability $p$ that jointly maximizes the successful transmission probability and minimizes the local delay. Finally numerical results are provided to confirm that the proposed joint optimization strategy achieves a significant performance gain compared to a conventional scheme.
Evolution of Brain Tumor and Stability of Geometric Invariants
K. Tawbe,F. Cotton,L. Vuillon
International Journal of Telemedicine and Applications , 2008, DOI: 10.1155/2008/210471
Abstract: This paper presents a method to reconstruct and to calculate geometric invariants on brain tumors. The geometric invariants considered in the paper are the volume, the area, the discrete Gauss curvature, and the discrete mean curvature. The volume of a tumor is an important aspect that helps doctors to make a medical diagnosis. And as doctors seek a stable calculation, we propose to prove the stability of some invariants. Finally, we study the evolution of brain tumor as a function of time in two or three years depending on patients with MR images every three or six months.
Lipodystrophy syndrome in HIV-infected children on HAART
S Innes, L Levin, M Cotton
Southern African Journal of HIV Medicine , 2009,
Abstract: Lipodystrophy syndrome (LD) is common in HIV-infected children, particularly those taking didanosine, stavudine or zidovudine. Lipo-atrophy in particular causes major stigmatisation and interferes with adherence. In addition, LD may have significant long-term health consequences, particularly cardiovascular. Since the stigmatising fat distribution changes of LD are largely permanent, the focus of management remains on early detection and arresting progression. Practical guidelines for surveillance and avoidance of LD in routine clinical practice are presented. The diagnosis of LD is described and therapeutic options are reviewed. The most important therapeutic intervention is to switch the most likely offending antiretroviral to a non-LD-inducing agent as soon as LD is recognised. Typically, when lipo-atrophy or lipohypertrophy is diagnosed the thymidine nucleoside reverse transcriptase inhibitor (NRTI) is switched to a non-thymidine agent such as abacavir (or tenofovir in adults). Where dyslipidaemia is predominant, a dietician review is helpful, and the clinician may consider switching to a protease inhibitor-sparing regimen or to atazanavir.
Clinical presentation and outcome of Tuberculosis in Human Immunodeficiency Virus infected children on anti-retroviral therapy
Elisabetta Walters, Mark F Cotton, Helena Rabie, H Simon Schaaf, Lourens O Walters, Ben J Marais
BMC Pediatrics , 2008, DOI: 10.1186/1471-2431-8-1
Abstract: We performed a comprehensive file review of all children who commenced HAART at Tygerberg Children's Hospital from January 2003 through December 2005.Data from 290 children were analyzed; 137 TB episodes were recorded in 136 children; 116 episodes occurred before and 21 after HAART initiation; 10 episodes were probably related to immune reconstitution inflammatory syndrome (IRIS). The number of TB cases per 100 patient years were 53.3 during the 9 months prior to HAART initiation, and 6.4 during post HAART follow-up [odds ratio (OR) 16.6; 95% confidence interval (CI) 12.5–22.4]. A positive outcome was achieved in 97/137 (71%) episodes, 6 (4%) cases experienced no improvement, 16 (12%) died and the outcome could not be established in 18 (13%). Mortality was less in children on HAART (1/21; 4.8%) compared to those not on HAART (15/116; 12.9%).We recorded an extremely high incidence of TB among HIV-infected children, especially prior to HAART initiation. Starting HAART at an earlier stage is likely to reduce morbidity and mortality related to TB, particularly in TB-endemic areas. Management frequently deviated from standard guidelines, but outcomes in general were good.The tuberculosis (TB) epidemic is poorly controlled in sub-Saharan Africa; the region that reports the highest TB incidence rates and highest prevalence of human immunodeficiency virus (HIV) infection [1,2]. Prevention of mother to child transmission (PMTCT) programs are poorly established in many countries and in many instances fail to use potent antiretroviral regimens, resulting in huge numbers of HIV-infected children.Childhood TB contributes significantly to the global TB case load (15–20% of cases), [3-5] especially in Africa where TB has been identified as a major respiratory cause of death in children [6]. The high disease burden results from ongoing TB transmission (poor epidemic control) and increased vulnerability as a result of HIV-induced immune compromise. Compared to HIV-uninfected childre
Emissions Mitigation Schemes in Australia—The Past, Present and Future  [PDF]
Deborah Cotton, Stefan Trück
Low Carbon Economy (LCE) , 2013, DOI: 10.4236/lce.2013.42009
Abstract:

Australia was one of the first countries in the world to adopt mandatory emissions trading schemes as part of its emissions mitigation program. To date there have been six states and one federal emissions mitigation schemes. Some state schemes operate in conjunction with other states or the federal scheme and some operate independently. This complex set of regulations and requirements for emitters has led to a deficiency in nationwide coverage with no firm target set for Australia. In July 2011 the Federal Labor Government released details of a carbon tax proposal which was passed by the two houses of Parliament by the end of 2011 and was introduced in July 2012. The Government states that an emissions trading scheme will be introduced in 2015 with a possible link to the European Emissions Trading Scheme (EU ETS). This paper provides a critical overview of Australian responses to climate change, with a particular emphasis on the numerous emissions mitigation schemes.

Homologous recombination in animal mitochondria
James Cotton
Genome Biology , 2001, DOI: 10.1186/gb-2001-2-10-reports0034
Abstract: This is rather surprising, as this paradigm is based on indirect evidence and is challenged by a growing body of data. The original observation that paternal mitochondria do not penetrate the egg is now known to be in error, with paternal organelles persisting for several hours after fertilization. It is also known that mammalian mitochondria contain the necessary enzymatic machinery for homologous recombination, and mitochondrial fusion is well known in Drosophila. Non-homologous recombination (unequal crossing-over) has been held responsible for variation in the number of tandem repeats in a number of animal mitochondrial genomes, and has been directly observed in a nematode. Two recent population studies have also suggested that recombination has occurred in human mtDNA.With all this evidence, it would seem likely that homologous recombination does occur in animal mitochondria, but the publication of human population studies last year provoked considerable debate, emphasizing that there is much interest in whether animal mtDNA does show homologous recombination, and considerable skepticism. Many authors will no doubt remain skeptical, despite the results of this paper, in which Ladoukakis and Zouros have exploited the unusual genetic system of the mussel to uncover direct evidence for homologous recombination within animal mitochondria.The unusual biparental inheritance of mitochondria in mussels of the families Unionidea and Mytilidaehas been known for about a decade, and is an interesting exception to the otherwise universal rule of maternal inheritance for animal mtDNA. Normally, female (F) and male (M) mitochondrial sequences differ by 20% - too great an amount to expect to observe homologous recombination. Luckily, a quirk of the Mytilus system allows a unique opportunity to observe mtDNA recombination in action. Occasionally, F genomes become 'masculinized', invading the M transmission route in sperm (see Figure 1). These MF genomes can now diverge from the
A new profusion of planktonic eukaryotes
James Cotton
Genome Biology , 2001, DOI: 10.1186/gb-2001-2-7-reports0016
Abstract: These methods have been very little used on eukaryotic microorganisms, however. Despite a growing sense of our ignorance of the extent of biodiversity, the feeling seems to have been that the largest branches of the tree of eukaryotic life are largely described. Recent culture-based studies have, however, identified two new groups of marine planktonic eukaryotes, raising expectations that tiny plankton may harbor more surprises. Moon-van der Staay and colleagues report one of the first large-scale molecular studies of marine picoplankton (microorganisms of < 3 μm diameter), revealing for the first time the true diversity of eukaryotes in this environment.Moon-van der Staay et al. used primers to regions of the 18S rRNA gene conserved across most, but not all, eukaryotes, to clone 103 and sequence 35 almost full-length 18S sequences derived from picoplankton of the equatorial Pacific. Only two of the sequences showed 99% identity to known organisms, but phylogenetic analysis revealed that most of the sequences are either from new members of known eukaryotic lineages or are related to known organisms. The results confirm the importance of autotrophic groups such as haptophytes and prasinophytes in this environment. Among the more arresting discoveries is a new lineage that appears to be very common among the picoplankton: 6 out of 35 sequenced clones belong to a lineage related to both the dinoflagellates and the parasitic Perkinsozoa. This clade could be related to the currently unsequenced heterotroph Oxyrrhis. Also well represented are acantharians, stramenopiles and dinoflagellates. In most cases, it is unclear whether the divergent environmental clones belong to auto- or heterotrophic clades within these groups, although the majority of dinoflagellate sequences seem, rather surprisingly, to form a lineage with a parasitic organism, Amoebophrya.The full text of Moon-van der Staay et al's article together with a similar article on Antarctic picoplankton by a differ
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