Collateral circulation: Past and present

Following an arterial occlusion outward remodeling of pre-existent inter-connecting arterioles occurs by proliferation of vascular smooth muscle and endothelial cells. This is initiated by deformation of the endothelial cells through increased pulsatile fluid shear stress (FSS) caused by the steep pressure gradient between the high pre-occlusive and the very low post-occlusive pressure regions that are interconnected by collateral vessels. Shear stress leads to the activation and expression of all NOS isoforms and NO production, followed by endothelial VEGF secretion, which induces MCP-1 synthesis in endothelium and in the smooth muscle of the media. This leads to attraction and activation of monocytes and T-cells into the adventitial space (peripheral collateral vessels) or attachment of these cells to the endothelium (coronary collaterals). Mononuclear cells produce proteases and growth factors to digest the extra-cellular scaffold and allow motility and provide space for the new cells. They also produce NO from iNOS, which is essential for arteriogenesis. The bulk of new tissue production is carried by the smooth muscles of the media, which transform their phenotype from a contractile into a synthetic and proliferative one. Important roles are played by actin binding proteins like ABRA, cofilin, and thymosin beta 4 which determine actin polymerization and maturation. Integrins and connexins are markedly up-regulated. A key role in this concerted action which leads to a 2-to-20 fold increase in vascular diameter, depending on species size (mouse versus human) are the transcription factors AP-1, egr-1, carp, ets, by the Rho pathway and by the Mitogen Activated Kinases ERK-1 and -2. In spite of the enormous increase in tissue mass (up to 50-fold) the degree of functional restoration of blood flow capacity is incomplete and ends at 30% of maximal conductance (coronary) and 40% in the vascular periphery. The process of arteriogenesis can be drastically stimulated by increases in FSS (arterio-venous fistulas) and can be completely blocked by inhibition of NO production, by pharmacological blockade of VEGF-A and by the inhibition of the Rho-pathway. Pharmacological stimulation of arteriogenesis, important for the treatment of arterial occlusive diseases, seems feasible with NO donors

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

Performance improvement of a novel combined water turbine

Nowadays, industrials and researchers are looking for renewable energy resources due to the increase of energy demand. Recently, the ability of combined turbines in harnessing energy from water current has increased their renewed interest. However, there still exist a big knowledge gap to select the optimal design of these turbines. In this paper, systematic studies of stand-alone helical Savonius and delta bladed Darrieus turbines were carried out using experimental methods as a precursor to analyze their roles in hybrid configuration. By varying the attachment angle, two hybrid configurations were tested experimentally. Using the optimal attachment angle, six hybrid configurations were investigated numerically based on the commercial software ANSYS FLUENT 17.0. From one configuration to another, only the design of the Savonius turbine was changed. The maximum power coefficient is found to be equal to 0.191 at tip-speed ratio of 0.63 using a helical bladed Savonius turbine with twist angle of 90°. However, the maximum power coefficient reaches 0.232 using a delta bladed Savonius turbine with the same twist angle. This optimization of the novel combined water turbine could be a solution to enhance the generated power

Performance study of spiral Darrieus water rotor with V-shaped blades

Because of the excessive consumption of fossil fuels, the world has begun suffering from the depleting of those sources and wide environmental problems. Hydraulic energy, considered as unlimited and non-detrimental, has become the best refuge to supply world demand while protecting the planet. Above all vertical axis water turbine, for their low cost and independency on water direction, Darrieus turbine takes the advantage to be more suitable for some implementation. Thus, various studies have been carried out to improve its efficiency. This study emphasizes on the effect of the blade chord ratio on a spiral Darrieus water rotor performance which has not been two much explored. An experimental static and dynamic tests realized in an irrigation canal were performed with a 3D printed spiral Darrieus rotor. With the intention of the performances betterment, four spiral Darrieus rotors having a chord ratio equal to 0.25, 0.5, 0.75, and 1, respectively, were tested through numerical simulations using the ANSYS FLUENT 17.0 software. Based on the numerical study, it is provided that the rotor with chord ratio of 0.5 was the optimum. In fact, it gives maximum power coefficient of 0.188 at a tip speed ratio equal to 0.71. The obtained findings present an interesting data that could provide the hydrodynamic characteristics of the water flow for the engineers and designers to improve the performance of the spiral Darrieus rotor

Multicyclic indentation on brittle glasses

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