The Switched Local Area Networks’ Delay Problem: Issues and a Deterministic Solution Approach

A large number of installed local area networks are sluggish in terms of speed of uploading and down- loading of information. Researchers have, therefore, proposed the need for such networks to be designed with specified maximum end-to-end delay. This is because, if the maximum packet delay between any two nodes of a network is not known, it is impossible to provide a deterministic guarantee of worst case response times of packets’ flows. Therefore, the need for analytic and formal basis for designing such networks becomes very imperative. In this regard, this chapter has discussed the switched local area networks’ delay problem and related issues. It compared the two principal approaches for determining the end-to-end response times of flows in communication networks – stochastic approach and determin- istic approach. The chapter goes on to demonstrate the superiority of the latter approach by using it to develop and validate the goodness of a general maximum delay packet switch model

A Formal Structure of Separation of Duty and Trust in Modelling Delegation Policy

There are considerable number of approaches to policy specification both for security management and policy driven network management purposes as reported in [20]. This specification sort security policies into two basic types: authorization and obligation policies. Most of the researches in security policies specification over the years focus on authorization policy modelling. In this paper, we report our approach in the design and Modelling of obligation Policy as delegation in information security by considering separation of duty and trust as pre-requisite conditions for delegation. The formal structures of the Delegation models developed was adapted from the Mathematical structures of Separation of duty (both Static and Dynamic SoD) in RBAC environment as described in [8] and [16]. Three factors of Properties, Experiences and Recommendation as described in [22] were used for the Trust Modelling. Future works proposed include the development of a formal model for revocation after delegation and integration of appropriate authorization policy with the model.Facultad de Informátic

Return interval distribution of extreme events and long term memory

The distribution of recurrence times or return intervals between extreme events is important to characterize and understand the behavior of physical systems and phenomena in many disciplines. It is well known that many physical processes in nature and society display long range correlations. Hence, in the last few years, considerable research effort has been directed towards studying the distribution of return intervals for long range correlated time series. Based on numerical simulations, it was shown that the return interval distributions are of stretched exponential type. In this paper, we obtain an analytical expression for the distribution of return intervals in long range correlated time series which holds good when the average return intervals are large. We show that the distribution is actually a product of power law and a stretched exponential form. We also discuss the regimes of validity and perform detailed studies on how the return interval distribution depends on the threshold used to define extreme events.Comment: 8 pages, 6 figure

Essential Medicines at the National Level : The Global Asthma Network's Essential Asthma Medicines Survey 2014

Patients with asthma need uninterrupted supplies of affordable, quality-assured essential medicines. However, access in many low- and middle-income countries (LMICs) is limited. The World Health Organization (WHO) Non-Communicable Disease (NCD) Global Action Plan 2013-2020 sets an 80% target for essential NCD medicines' availability. Poor access is partly due to medicines not being included on the national Essential Medicines Lists (EML) and/or National Reimbursement Lists (NRL) which guide the provision of free/subsidised medicines. We aimed to determine how many countries have essential asthma medicines on their EML and NRL, which essential asthma medicines, and whether surveys might monitor progress. A cross-sectional survey in 2013-2015 of Global Asthma Network principal investigators generated 111/120 (93%) responses41 high-income countries and territories (HICs); 70 LMICs. Patients in HICs with NRL are best served (91% HICs included ICS (inhaled corticosteroids) and salbutamol). Patients in the 24 (34%) LMICs with no NRL and the 14 (30%) LMICs with an NRL, however no ICS are likely to have very poor access to affordable, quality-assured ICS. Many LMICs do not have essential asthma medicines on their EML or NRL. Technical guidance and advocacy for policy change is required. Improving access to these medicines will improve the health system's capacity to address NCDs.Peer reviewe

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Rural farmers' perception of climate variabilities in Benue State of Nigeria

Climate change and severe weather events such as temperature shocks and declining rainfall often strongly impede sustainable farming development, especially where agriculture is rain fed and when other external shocks such as poverty, poor access to inputs and credit are common. This is the context in which rural farmers carry out their farming and other livelihoods activities. This study compares rural farmers’ perception of temperature and rainfall with the result of 30 years (1980-2009) meteorological records of temperature and rainfall, examines the farmers adaptation practices in response to climate change and the constraints to their adaptation. The study found an increasing trend in minimum and maximum temperature as well as rainfall amount. This validates the farmers’ perception of temperature and rainfall. Bush burning and Tree cutting were the perceived leading causes of climate change. Farmers mostly engaged in changing planting dates and change in house construction in response to climate change. Efforts that address poverty and provide access to agricultural support services like access to credit; farm inputs and weather forecasting service will help enhance farmers’ adaptive capacity to climate change. Farmers’ adaptive capacity could be enhanced through agricultural support services such as access to credit, farm inputs and weather forecastin