Statistical Mechanics of Broadcast Channels Using Low Density Parity Check Codes

We investigate the use of Gallager's low-density parity-check (LDPC) codes in a broadcast channel, one of the fundamental models in network information theory. Combining linear codes is a standard technique in practical network communication schemes and is known to provide better performance than simple timesharing methods when algebraic codes are used. The statistical physics based analysis shows that the practical performance of the suggested method, achieved by employing the belief propagation algorithm, is superior to that of LDPC based timesharing codes while the best performance, when received transmissions are optimally decoded, is bounded by the timesharing limit.Comment: 14 pages, 4 figure

Statistical Mechanics of Broadcast Channels Using Low Density Parity Check Codes

We investigate the use of Gallager's low-density parity-check (LDPC) codes in a broadcast channel, one of the fundamental models in network information theory. Combining linear codes is a standard technique in practical network communication schemes and is known to provide better performance than simple timesharing methods when algebraic codes are used. The statistical physics based analysis shows that the practical performance of the suggested method, achieved by employing the belief propagation algorithm, is superior to that of LDPC based timesharing codes while the best performance, when received transmissions are optimally decoded, is bounded by the timesharing limit.Comment: 14 pages, 4 figure

An investigation of threat types to the conservation of Pan troglodytes ellioti at Kwano forest of Gashaka-Gumti national park, Nigeria

The Nigeria-Cameroon chimpanzee has been classified on the red list of threatened species (endangered) of IUCN and It has been established that it is only when animal or plant species are subject to certain threat factors that the species can be considered as threaten. It is in view of the aforementioned that this research was carried out to determine those threat factors that mitigates against the Nigeria-Cameroon chimpanzee habitat. Transects, trails and random forest walks were the methods used for the data collection while tables, charts and mean values as well as photo plats were used to analyse the data collected. The different types of threats observed were Poaching which (11 segments; 52.4 5 %) of the habitat, illegal bush burning (16 segments; 76.6 %) of the habitat, river poisoning (1 segment; 4.8 %) of the habitat, tree felling (4 segments; 19.1 %) of the habitat and Non Timber Forest Products (NTFPs) extraction (7 segments; 33.3 %) of the habitat. Poaching activities were highest in Ngiti forest (49.4 %), followed by Yakuba forest (25.3 %) while Tounga (16.5 %) and Bakashi (8.9 %) experienced the least poaching activities. Despite the status of Kwano forest as a protected area; the sitting of a research project in the area and constant presence of researchers, some threat factors to the conservation of this forest prevails. Concerted effort from both the National Parks Service and Non-governmental organisations is highly needed to reduce or absolutely eliminate illegal activities from this area.Keywords: Chimpanzee, Habitat, Conservation, Threats and Kwan

The Structure of Screening in QED

The possibility of constructing charged particles in gauge theories has long been the subject of debate. In the context of QED we have shown how to construct operators which have a particle description. In this paper we further support this programme by showing how the screening interactions arise between these charges. Unexpectedly we see that there are two different gauge invariant contributions with opposite signs. Their difference gives the expected result.Comment: 8 pages, LaTe

A Search for Correlation of Ultra-High Energy Cosmic Rays with IRAS-PSCz and 2MASS-6dF Galaxies

We study the arrival directions of 69 ultra-high energy cosmic rays (UHECRs) observed at the Pierre Auger Observatory (PAO) with energies exceeding 55 EeV. We investigate whether the UHECRs exhibit the anisotropy signal expected if the primary particles are protons that originate in galaxies in the local universe, or in sources correlated with these galaxies. We cross-correlate the UHECR arrival directions with the positions of IRAS-PSCz and 2MASS-6dF galaxies taking into account particle energy losses during propagation. This is the first time that the 6dF survey is used in a search for the sources of UHECRs and the first time that the PSCz survey is used with the full 69 PAO events. The observed cross-correlation signal is larger for the PAO UHECRs than for 94% (98%) of realisations from an isotropic distribution when cross-correlated with the PSCz (6dF). On the other hand the observed cross-correlation signal is lower than that expected from 85% of realisations, had the UHECRs originated in galaxies in either survey. The observed cross-correlation signal does exceed that expected by 50% of the realisations if the UHECRs are randomly deflected by intervening magnetic fields by 5 degrees or more. We propose a new method of analysing the expected anisotropy signal, by dividing the predicted UHECR source distribution into equal predicted flux radial shells, which can help localise and constrain the properties of UHECR sources. We find that the 69 PAO events are consistent with isotropy in the nearest of three shells we define, whereas there is weak evidence for correlation with the predicted source distribution in the two more distant shells in which the galaxy distribution is less anisotropic.Comment: 23 pages, version published in JCA

Nurturing lifelong learning in communities through the National University of Lesotho: prospects and challenges

This paper analyses one aspect of a pan-African action research project called ITMUA (Implementing the Third Mission of Universities in Africa). This particular paper draws on the data from that project to explore the National University of Lesotho’s contribution to lifelong learning in its communities. It provides background information on the ITMUA initiative and analyses interview and focus group responses to two case studies in terms of their contribution to lifelong learning. It uses, as its analytical framework, a modified version of Mbigi’s African perspective on the four De Lors’ ‘pillars’, by adding a fifth pillar, courtesy of Torres. The paper argues that community engagement is a two-way process between universities and their wider constituencies with opportunities for mutual lifelong learning. But there are also challenges of understanding and process which must be addressed if the full range of these lifelong learning pillars is to be accommodated within African contexts. The paper provides an introduction to the history of community engagement in Africa as a university mission, followed by a brief discussion of lifelong learning within African perspectives. After describing the particular context of Lesotho, the concept of community service and community engagement in contemporary African contexts introduces the action research project and the case studies. The final part of the paper presents and discusses the research findings

Estudo duplo-cego, randômico comparando indinavir, zidovudina e indinavir mais zidovudina na terapia anti-retroviral de indivíduos HIV+ sem tratamento anterior, com contagem de células CD4 entre 50 e 250/mm3

Treatment with indinavir has been shown to result in marked decreases in viral load and increases in CD4 cell counts in HIV-infected individuals. A randomized double-blind study to evaluate the efficacy of indinavir alone (800 mg q8h), zidovidine alone (200 mg q8h) or the combination was performed to evaluate progression to AIDS. 996 antiretroviral therapy-naive patients with CD4 cell counts of 50-250/mm3 were allocated to treatment. During the trial the protocol was amended to add lamivudine to the zidovudine-containing arms. The primary endpoint was time to development of an AIDS-defining illness or death. The study was terminated after a protocol-defined interim analysis demonstrated highly significant reductions in progression to a clinical event in the indinavir-containing arms, compared to the zidovudine arm (p<0.0001). Over a median follow-up of 52 weeks (up to 99 weeks), percent reductions in hazards for the indinavir plus zidovudine and indinavir groups compared to the zidovudine group were 70% and 61%, respectively. Significant reductions in HIV RNA and increases in CD4 cell counts were also seen in the indinavir-containing groups compared to the zidovudine group. Improvement in both CD4 cell count and HIV RNA were associated with reduced risk of disease progression. All three regimens were generally well tolerated.Foi demonstrado que o tratamento com indinavir resulta em importante redução da carga viral e aumentos das células CD4 em pacientes infectados pelo HIV. Foi realizado um estudo duplo-cego, randômico para avaliar a eficácia do indinavir isoladamente (800 mg cada 8h), zidovudina isoladamente (200 mg cada 8h) ou a combinação, para avaliar a progressão para AIDS. Foram distribuidos para tratamento 996 pacientes virgens de tratamento antiretroviral, com contagens de CD4 entre 50 e 250 células/mm3. Durante o estudo, o protocolo foi modificado para adicionar lamivudina aos braços contendo zidovudina. O "endpoint" primário foi o tempo para o desenvolvimento de uma doença-definidora de AIDS ou morte. O estudo foi interrompido após uma análise preliminar definida no protocolo ter demonstrado reduções significativas na progressão para um evento clínico nos grupos contendo indinavir, comparado ao grupo da zidovudina (p< 0,0001). Após uma mediana de seguimento de 52 semanas (chegando a 99 semanas), as reduções percentuais nas ocorrências para indinavir+zidovudina e indinavir, comparado com zidovudina foram de 70% e 61%, respectivamente. Reduções significativas na medida do RNA viral e aumentos nas contagens de CD4 também foram observadas nos grupos contendo indinavir, em relação ao da zidovudina. A melhora nas células CD4 e RNA viral foram ambas associadas a risco reduzido de progressão da doença. Os três tratamentos foram geralmente bem tolerados

Presupernova Structure of Massive Stars

Issues concerning the structure and evolution of core collapse progenitor stars are discussed with an emphasis on interior evolution. We describe a program designed to investigate the transport and mixing processes associated with stellar turbulence, arguably the greatest source of uncertainty in progenitor structure, besides mass loss, at the time of core collapse. An effort to use precision observations of stellar parameters to constrain theoretical modeling is also described.Comment: Proceedings for invited talk at High Energy Density Laboratory Astrophysics conference, Caltech, March 2010. Special issue of Astrophysics and Space Science, submitted for peer review: 7 pages, 3 figure

Treatment of post-cholecystectomy biliary strictures with fully-covered self-expanding metal stents - results after 5 years of follow-up

BACKGROUND: Endoscopic treatment of post-cholecystectomy biliary strictures (PCBS) with multiple plastic biliary stents placed sequentially is a minimally invasive alternative to surgery but requires multiple interventions. Temporary placement of a single fully-covered self-expanding metal stent (FCSEMS) may offer safe and effective treatment with fewer re-interventions. Long-term effectiveness of treatment with FCSEMS to obtain PCBS resolution has not yet been studied. METHODS: In this prospective multi-national study in patients with symptomatic benign biliary strictures (N = 187) due to various etiologies received a FCSEMS with scheduled removal at 6-12 months and were followed for 5 years. We report here long-term outcomes of the subgroup of patients with PCBS (N = 18). Kaplan Meier analyses assessed long-term freedom from re-stenting. Adverse events were documented. RESULTS: Endoscopic removal of the FCSEMS was achieved in 83.3% (15/18) of patients after median indwell of 10.9 (range 0.9-13.8) months. In the remaining 3 patients (16.7%), the FCSEMS spontaneously migrated and passed without complications. At the end of FCSEMS indwell, 72% (13/18) of patients had stricture resolution. At 5 years after FCSEMS removal, 84.6% (95% CI 65.0-100.0%) of patients who had stricture resolution at FCSEMS removal remained stent-free. In addition, at 75 months after FCSEMS placement, the probability of remaining stent-free was 61.1% (95% CI 38.6-83.6%) for all patients. Stent or removal related serious adverse events occurred in 38.9% (7/18) all resolved without sequalae. CONCLUSIONS: In patients with symptomatic PCBS, temporary placement of a single FCSEMS intended for 10-12 months indwell is associated with long-term stricture resolution up to 5 years. Temporary placement of a single FCSEMS may be considered for patients with PCBS not involving the main hepatic confluence. TRIAL REGISTRATION NUMBERS: NCT01014390; CTRI/2012/12/003166; Registered 17 November 2009

Propagation of ultra-high energy protons in regular extragalactic magnetic fields

We study the proton flux expected from sources of ultra high energy cosmic rays (UHECR) in the presence of regular extragalactic magnetic fields. It is assumed that a local source of ultra-high energy protons and the magnetic field are all in a wall of matter concentration with dimensions characteristic of the supergalactic plane. For a single source, the observed proton flux and the local cosmic ray energy spectrum depend strongly on the strength of the field, the position of the observer, and the orientation of the field relative to the observer's line of sight. Regular fields also affect protons emitted by sources outside the local magnetic fields structure. We discuss the possibility that such effects could contribute to an explanation of the excess of UHECR above $5.10^{19}$ eV, and the possibility that sources of such particles may be missed if such magnetic fields are not taken into account.Comment: 6 pages, 4 figures Comments for revised version: 12 pages, 12 figures. Enlarged discussion of effects on cosmic ray spectrum. Additional discussion focussing on spatial and temporal boundary condition