3,762 research outputs found

    Interior regularity criteria for suitable weak solutions of the Navier-Stokes equations

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    We present new interior regularity criteria for suitable weak solutions of the 3-D Navier-Stokes equations: a suitable weak solution is regular near an interior point zz if either the scaled Lx,tp,qL^{p,q}_{x,t}-norm of the velocity with 3/p+2/q≤23/p+2/q\leq 2, 1≤q≤∞1\leq q\leq \infty, or the Lx,tp,qL^{p,q}_{x,t}-norm of the vorticity with 3/p+2/q≤33/p+2/q\leq 3, 1≤q<∞1 \leq q < \infty, or the Lx,tp,qL^{p,q}_{x,t}-norm of the gradient of the vorticity with 3/p+2/q≤43/p+2/q\leq 4, 1≤q1 \leq q, 1≤p1 \leq p, is sufficiently small near zz

    Effects of submerged vegetation on water clarity across climates

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    A positive feedback between submerged vegetation and water clarity forms the backbone of the alternative state theory in shallow lakes. The water clearing effect of aquatic vegetation may be caused by different physical, chemical, and biological mechanisms and has been studied mainly in temperate lakes. Recent work suggests differences in biotic interactions between (sub)tropical and cooler lakes might result in a less pronounced clearing effect in the (sub)tropics. To assess whether the effect of submerged vegetation changes with climate, we sampled 83 lakes over a gradient ranging from the tundra to the tropics in South America. Judged from a comparison of water clarity inside and outside vegetation beds, the vegetation appeared to have a similar positive effect on the water clarity across all climatic regions studied. However, the local clearing effect of vegetation decreased steeply with the contribution of humic substances to the underwater light attenuation. Looking at turbidity on a whole-lake scale, results were more difficult to interpret. Although lakes with abundant vegetation (>30%) were generally clear, sparsely vegetated lakes differed widely in clarity. Overall, the effect of vegetation on water clarity in our lakes appears to be smaller than that found in various Northern hemisphere studies. This might be explained by differences in fish communities and their relation to vegetation. For instance, unlike in Northern hemisphere studies, we find no clear relation between vegetation coverage and fish abundance or their diet preference. High densities of omnivorous fish and coinciding low grazing pressures on phytoplankton in the (sub)tropics may, furthermore, weaken the effect of vegetation on water clarity

    Aplicação de mÊtodos quimiomÊtricos em anålises não-destrutivas de Eucalyptus grandis.

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    Este trabalho teve como objetivo a construção de uma curva de calibração utilizando a espectroscopia no infravermelho próximo (NIR) para predição de propriedades físicas como densidade båsica, retratibilidade radial, longitudinal e tangencial e anisotropia de contração de amostras de Eucalyptus grandis. A partir de anålise matemåtica multivariada dos resultados observou-se que existe correlação estatística, de acordo com o modelo proposto, com as propriedades retratibilidade radial e longitudinal

    A novel mutation in PTHLH in a family with a variable phenotype with brachydactyly, short stature, oligodontia and developmental delay

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    Mutations in PTHLH (PTH-like hormone), cause brachydactyly type E (BDE) characterized by shortening of metacarpals, metatarsals and/or phalanges with short stature. In this report we describe three siblings and their mother with a novel heterozygous mutation c.25 T &gt; C, p.Trp9Arg in exon 2 of the PTHLH gene. Beside the known clinical features of PTHLH mutations all had a delay in speech and language development, unknown if this is related to the mutation. Patients with PTHLH mutation may have a variable phenotypic presentation.</p

    Modeling approach to regime shifts of primary production in shallow coastal ecosystems

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    Pristine coastal shallow systems are usually dominated by extensive meadows of seagrass species, which are assumed to take advantage of nutrient supply from sediment. An increasing nutrient input is thought to favour phytoplankton, epiphytic microalgae, as well as opportunistic ephemeral macroalgae that coexist with seagrasses. The primary cause of shifts and succession in the macrophyte community is the increase of nutrient load to water; however temperature plays also an important role. A competition model between rooted seagrass (Zostera marina), macroalgae (Ulva sp), and phytoplankton has been developed to analyse the succession of primary producer communities in these systems. Successions of dominance states, with different resilience characteristics, are found when modifying the input of nutrients and the seasonal temperature and light intensity forcing.Comment: 33 pages, including 10 figures. To appear in Ecological Complexit

    Early warning of climate tipping points from critical slowing down: comparing methods to improve robustness

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    We address whether robust early warning signals can, in principle, be provided before a climate tipping point is reached, focusing on methods that seek to detect critical slowing down as a precursor of bifurcation. As a test bed, six previously analysed datasets are reconsidered, three palaeoclimate records approaching abrupt transitions at the end of the last ice age and three models of varying complexity forced through a collapse of the Atlantic thermohaline circulation. Approaches based on examining the lag-1 autocorrelation function or on detrended fluctuation analysis are applied together and compared. The effects of aggregating the data, detrending method, sliding window length and filtering bandwidth are examined. Robust indicators of critical slowing down are found prior to the abrupt warming event at the end of the Younger Dryas, but the indicators are less clear prior to the Bølling-Allerød warming, or glacial termination in Antarctica. Early warnings of thermohaline circulation collapse can be masked by inter-annual variability driven by atmospheric dynamics. However, rapidly decaying modes can be successfully filtered out by using a long bandwidth or by aggregating data. The two methods have complementary strengths and weaknesses and we recommend applying them together to improve the robustness of early warnings

    Serum Differentially Modulates the Clonal Growth and Differentiation of Cultured Limbal and Corneal Epithelium

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    Purpose. The stem cell-containing limbal epithelium is in proximity with highly vascularized tissue, as opposed to the transient amplifying cell-containing corneal basal epithelium, which resides on top of avascular corneal stroma. We therefore speculate that limbal stem cells are preferentially under the modulation of serum-derived factors. Methods. Using a previously reported serum-free, chemically defined culture system for ocular surface epithelium, a culture condition primarily supporting transient amplifying cells of both corneal and limbal epithelia, we compared the clonal growth measured by colony-forming efficiency (CFE), colony size, and BrdU labeling, as well as colony differentiation measured by colony morphology and immunofluorescence staining, with the monoclonal antibody AE-5 against keratin K3 when fetal bovine serum (FBS) was added at different concentrations. Results. The addition of 1% FBS decreased CFE and colony size in peripheral corneal cultures but had no effect in limbal cultures. Both cultures showed no obvious difference in colony morphology or BrdU labeling and AE-5 staining. In contrast, at 10% or 20% FBS, CFE and colony size increased in limbal cultures, but dose dependently decreased in peripheral corneal cultures. The presence of a unique subpopulation of progenitor cells in limbal cultures different from transient amplifying cells in corneal cultures was further supported by the emergence of a higher proportion of a unique type (B) colonies in limbal cultures that had high BrdU labeling and heterogeneous or negative AE-5 staining, indicative of their being in a proliferating, undifferentiated state. These colonies showed continuous growth in late cultures and could be passaged into serum-free medium. Conclusio

    Intention of preserving forest remnants among landowners in the Atlantic Forest: The role of the ecological context via ecosystem services

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    Unravelling the psychological processes determining landowners' support towards forest conservation is crucial, particularly in rural areas of the tropics, where most forest remnants are within private lands. As human–nature connections are known to shape pro‐environmental behaviours, the intention of preserving forest remnants should ultimately be determined by the ecological context people live in. Here, we investigate the pathways through which the ecological context (forest cover), via direct contact with forests and ecosystem services and disservices, influence the psychological antecedents of conservation behaviour (beliefs, attitude and intention of preserving forest remnants). We conceptualized a model based on the Reasoned Action Approach, using the ecological context and these three forest experiences as background factors, and tested the model using Piecewise Structural Equation Modelling. Data were collected through an interview‐based protocol applied to 106 landowners across 13 landscapes varying in forest cover in a consolidated rural region in the Brazilian Atlantic Forest. Our results indicate that: (a) ecosystem services are more important than disservices for shaping intention of preserving forests, particularly non‐provisioning services; (b) contact with forest has an indirect effect on intention, by positively influencing the frequency of receiving ecosystem services; (c) people living in more forested ecological contexts have more contact with forests, receive ecosystem services more frequently and, ultimately, have stronger intention of preserving forests. Hence, our study suggests a dangerous positive feedback loop between deforestation, the extinction of forest experiences and impairment of human–nature connections. Local demands across the full range of ecosystem services, the balance between services and disservices and the ecological context people live in should be considered when developing conservation initiatives in tropical rural areas
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