79 research outputs found

    Venous hemodynamics in neurological disorders: an analytical review with hydrodynamic analysis.

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    Venous abnormalities contribute to the pathophysiology of several neurological conditions. This paper reviews the literature regarding venous abnormalities in multiple sclerosis (MS), leukoaraiosis, and normal-pressure hydrocephalus (NPH). The review is supplemented with hydrodynamic analysis to assess the effects on cerebrospinal fluid (CSF) dynamics and cerebral blood flow (CBF) of venous hypertension in general, and chronic cerebrospinal venous insufficiency (CCSVI) in particular.CCSVI-like venous anomalies seem unlikely to account for reduced CBF in patients with MS, thus other mechanisms must be at work, which increase the hydraulic resistance of the cerebral vascular bed in MS. Similarly, hydrodynamic changes appear to be responsible for reduced CBF in leukoaraiosis. The hydrodynamic properties of the periventricular veins make these vessels particularly vulnerable to ischemia and plaque formation.Venous hypertension in the dural sinuses can alter intracranial compliance. Consequently, venous hypertension may change the CSF dynamics, affecting the intracranial windkessel mechanism. MS and NPH appear to share some similar characteristics, with both conditions exhibiting increased CSF pulsatility in the aqueduct of Sylvius.CCSVI appears to be a real phenomenon associated with MS, which causes venous hypertension in the dural sinuses. However, the role of CCSVI in the pathophysiology of MS remains unclear

    Outsourcing and its implications for market success : negative curvilinearity, firm resources, and competition

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    Over the past few decades, outsourcing has become a widely discussed and researched means for firms to change their performance. In this article, we attempt to link outsourcing to the market success of firms, specifically their market share. We argue that although firms may be able to increase their market share through outsourcing, this is only true up to a point, beyond which market share actually decreases as a consequence of further outsourcing. There is, in other words, a negatively curvilinear (inverted U) relationship between outsourcing and market share. We also hypothesize that the outsourcing–market share relationship is moderated negatively by both the strength of firm resources and the extent of competition in a firm‘s market. We empirically confirm these arguments through a panel data analysis containing over 19,000 observations on manufacturing firms, and offer some case examples to illustrate the mechanisms driving these results. We discuss implications for marketing research and practice

    Dynamics of open DNA sliding clamps

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    A range of enzymes in DNA replication and repair bind to DNA-clamps: torus-shaped proteins that encircle double-stranded DNA and act as mobile tethers. Clamps from viruses (such as gp45 from the T4 bacteriophage) and eukaryotes (PCNAs) are homotrimers, each protomer containing two repeats of the DNA-clamp motif, while bacterial clamps (pol III β) are homodimers, each protomer containing three DNA-clamp motifs. Clamps need to be flexible enough to allow opening and loading onto primed DNA by clamp loader complexes. Equilibrium and steered molecular dynamics simulations have been used to study DNA-clamp conformation in open and closed forms. The E. coli and PCNA clamps appear to prefer closed, planar conformations. Remarkably, gp45 appears to prefer an open right-handed spiral conformation in solution, in agreement with previously reported biophysical data. The structural preferences of DNA clamps in solution have implications for understanding the duty cycle of clamp-loaders
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