Home About us Contact
|
Home About us Contact | ||
|
|
||
Local Reduction (local + reduction)
Selected AbstractsInfluence of Low-Order Rational Surfaces on the Radial Electric Field of TJ-II ECH PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 6-7 2010O. Bondarenko Abstract Dynamic magnetic configuration scan experiments have been conducted in order to investigate the influence of the rotational transform on plasma rotation, radial electric field and turbulence. The main magnetic resonances (7/4 and 5/3 in this work) make a positive contribution to the local radial electric field, which depends on the plasma density and plasma radius. A local reduction in the level of density fluctuations due to the influence of low order rational surfaces is also observed. These results could explain local transport changes associated to low order rational surfaces observed in TJ-II ECH plasmas (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hypoxia is an inducer of vasodilator agents in peritoneal macrophages of cirrhotic patientsHEPATOLOGY, Issue 5 2002Pilar Cejudo-Martín The aim of the investigation was to assess whether hypoxia induces the production of endogenous vasoactive peptides in macrophages of cirrhotic patients with ascites because low tissue oxygenation is a relatively frequent event in these patients. Peritoneal macrophages were isolated from ascites, seeded on well plates, and cultured at different times under hypoxic (5% O2) or normoxic conditions (21% O2). Then, accumulation of vasoactive peptides sensitive to hypoxia including endothelin-1 (ET-1), vascular endothelial growth factor (VEGF), and adrenomedullin (ADM) was measured. Only VEGF and ADM were constitutively secreted, and hypoxia further stimulated the release of these vasodilator peptides. In concordance, increased messenger RNA (mRNA) levels of VEGF and ADM were found at culturing macrophages in hypoxia. This characteristic response was not observed in circulating monocytes of either cirrhotic patients or healthy subjects. Next the expression of the transcription factor, hypoxia inducible factor 1 (HIF-1), was analyzed. Expression of HIF-1, and HIF-1, messengers and HIF-1, protein subunit remained unchanged regardless of O2 tension, whereas HIF-1, protein subunit was overexpressed under hypoxic conditions. Moreover, conditioned medium from macrophages cultured under hypoxic conditions promoted a larger nitric oxide (NO) release in endothelial cells than that of normoxic macrophages. In conclusion, these data indicate that hypoxia induces the synthesis of VEGF and ADM in macrophages of cirrhotic patients, likely through HIF-1,enhanced transcriptional activity. These data suggest that a local reduction in O2 tension could enhance the synthesis of macrophage-derived vasodilators, thus aggravating the circulatory disturbance of these patients. [source] Coupled lubrication and Stokes flow finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2003Matthew S. Stay Abstract A method is developed for performing a local reduction of the governing physics for fluid problems with domains that contain a combination of narrow and non-narrow regions, and the computational accuracy and performance of the method are measured. In the narrow regions of the domain, where the fluid is assumed to have no inertia and the domain height and curvature are assumed small, lubrication, or Reynolds, theory is used locally to reduce the two-dimensional Navier,Stokes equations to the one-dimensional Reynolds equation while retaining a high degree of accuracy in the overall solution. The Reynolds equation is coupled to the governing momentum and mass equations of the non-narrow region with boundary conditions on the mass and momentum flux. The localized reduction technique, termed ,stitching,' is demonstrated on Stokes flow for various geometries of the hydrodynamic journal bearing,a non-trivial test problem for which a known analytical solution is available. The computational advantage of the coupled Stokes,Reynolds method is illustrated on an industrially applicable fully-flooded deformable-roll coating example. The examples in this paper are limited to two-dimensional Stokes flow, but extension to three-dimensional and Navier,Stokes flow is possible. Copyright © 2003 John Wiley & Sons, Ltd. [source] What controls woodland regeneration after elephants have killed the big trees?JOURNAL OF APPLIED ECOLOGY, Issue 1 2009Stein R. Moe Summary 1Top-down regulation of ecosystems by large herbivores is a topic of active debate between scientists and managers, and a prime example is the interaction between elephants Loxodonta africana and trees in African savannas. A common assumption among wildlife managers is that a local reduction in elephant numbers will ultimately allow woodland to self-restore to a desired former state. Such regeneration is, however, dependent on the survival of seedlings of impacted tree species. We conducted a field experiment to investigate seedling predation in the elephant-transformed Chobe riparian woodland of northern Botswana. 2We planted seedling gardens in (i) complete exclosures that excluded all herbivores except small rodents and invertebrates, (ii) semi-permeable exclosures that excluded ungulates but included primates, lagomorphs, all rodents, gallinaceous birds, etc, and (iii) completely open plots. Seedlings were of two tree species decreasing in the area (Faidherbia albida and Garcinia livingstonei) and two that are increasing (Combretum mossambicense and Croton megalobotrys). 3After 9 months, seedling survival ranged from >75% for all species in the complete exclosure to <20% for Faidherbia albida in the open plots. Survival of all seedlings except C. megalobotrys declined precipitously in open plots during the dry season when invertebrates are largely dormant but when impalas Aepyceros melampus (locally abundant ungulates) increase the browse components of their diets. 4Seedling survival in the open plots was negatively related to local impala density but unrelated to that of any other browser. 5Synthesis and applications. Our findings relate to the current debate about managing elephants to restore southern African savanna landscapes to desired historical states. Various seedling predators, including the ubiquitous impala Aepyceros melampus, regulate the regeneration of trees from seedlings, and our experiments support the hypothesis that tall closed-canopy woodlands originate during episodic windows of opportunity for seedling survival. To artificially recreate such a window would require the decimation of seedling predators as well as elephants, which is impractical at the landscape scale. [source] Effects of cover reduction on mulgara Dasycercus cristicauda (Marsupialia: Dasyuridae), rodent and invertebrate populations in central Australia: Implications for land managementAUSTRAL ECOLOGY, Issue 6 2003PIP MASTERS Abstract This study investigates the effect of cover reduction on the mulgara, Dasycercus cristicauda, a small marsupial classified as vulnerable to extinction, which occurs in areas of central Australia dominated by hummock grasslands. Loss or degradation of spinifex has been implicated in population declines of this species previously, but the importance of cover in maintaining quality habitat remains speculative. To determine the effect on D. cristicauda of cover reduction, caused by the harvesting of spinifex, we monitored population changes and changes in prey resources (rodents and invertebrates) before and after spinifex harvesting took place at a site near the Ayers Rock Resort, Northern Territory, Australia. Ten plots, each of 8.75 ha, were established and sampled from May 1994 to October 1995. Harvesting took place on five plots in August 1994, which reduced spinifex cover from 46 to 21% and the amount of spinifex >0.25 m high from 42 to 2%. Harvesting did not significantly affect the number of D. cristicauda known to be alive or captured despite other studies indicating that cover is an important habitat attribute. There was also no evidence that cover reduction impacted on the biomass of the invertebrate food resources. However, there was a significant reduction in the number of rodents captured. The lack of a response to cover reduction by D. cristicauda is possibly because the cover of Triodia remained high enough (above 15%) to sustain animals, and harvested areas were relatively small. This study therefore suggests that D. cristicauda can tolerate a moderate local reduction in cover of its preferred habitat. However, it remains possible that other land use practices that cause severe reduction of cover (including clearing for mining or fire prevention, grazing which may result in spinifex reduction through trampling, and fire management) will have more dramatic effects on D. cristicauda. Evaluation of such effects should be a priority for future research. [source] GATA-3 protects against severe joint inflammation and bone erosion and reduces differentiation of Th17 cells during experimental arthritisARTHRITIS & RHEUMATISM, Issue 3 2009Jan Piet van Hamburg Objective Rheumatoid arthritis is associated with the infiltration of T helper cells into the joints. It is unclear whether interferon-, (IFN,),producing Th1 cells or the novel T helper subset, interleukin-17 (IL-17),producing Th17 cells, are the pathogenic mediators of joint inflammation in chronic nonautoimmune arthritis. Therefore, this study was aimed at examining whether the Th2-specific transcription factor GATA-3 can regulate arthritis, in an experimental murine model, by modulating Th1 and/or Th17 cell polarization. Methods Arthritis was induced with methylated bovine serum albumin (mBSA) in both wild-type and CD2 T cell,specific GATA-3 (CD2,GATA-3),transgenic mice. At days 1 and 7 after the induction of arthritis, knee joints were scored macroscopically for arthritis severity and for histologic changes. Single-cell suspensions were generated from the spleens, lymph nodes, and inflamed knee joints. Cytokine expression by CD4+ T cells was determined using flow cytometry, and IL-17 expression in the inflamed knee joints was determined by enzyme-linked immunosorbent assay. Analyses of gene expression were performed for Th17-associated factors. Results Wild-type mice developed severe joint inflammation, including massive inflammatory cell infiltration and bone erosion that increased significantly over time, reaching maximal arthritis scores at day 7. In contrast, only mild joint inflammation was observed in CD2,GATA-3,transgenic mice. This mild effect was further accompanied by systemic and local reductions in the numbers of IL-17+IFN,, and IL-17+IFN,+, but not IL-17,IFN,+, CD4+ T cells, and by induction of Th2 cytokine expression. Moreover, GATA-3 overexpression resulted in reduced gene expression of the Th17-associated transcription factor retinoic acid,related orphan receptor ,t. Conclusion These results indicate that enforced GATA-3 expression protects against severe joint inflammation and bone erosion in mice, accompanied by reduced differentiation of Th17 cells, but not Th1 cells, during mBSA-induced arthritis. [source] | |||||||||||||