116 research outputs found
Renal pericytes: regulators of medullary blood flow
Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla
Scalar perturbations in conformal rolling scenario with intermediate stage
Scalar cosmological perturbations with nearly flat power spectrum may
originate from perturbations of the phase of a scalar field conformally coupled
to gravity and rolling down negative quartic potential. We consider a version
of this scenario whose specific property is a long intermediate stage between
the end of conformal rolling and horizon exit of the phase perturbations. Such
a stage is natural, e.g., in cosmologies with ekpyrosis or genesis. Its
existence results in small negative scalar tilt, statistical anisotropy of all
even multipoles starting from quardupole of general structure (in contrast to
the usually discussed single quadrupole of special type) and non-Gaussianity of
a peculiar form.Comment: 35 pages, 1 figure. Journal version. Discussion of the range of
relevant momentum scales and bounds on parameters adde
The Caravan Rolls On
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68409/2/10.1177_107554707900100103.pd
Indicadores de qualidade do solo em sistemas de cultivo orgĂąnico e convencional no semi-ĂĄrido Cearense.
A qualidade do solo pode mudar com o passar do tempo, em decorrĂȘncia de eventos naturais ou açÔes antrĂłpicas. A adoção de prĂĄticas de cultivo orgĂąnico reduz o revolvimento do solo, favorecendo a recuperação de suas propriedades
fĂsicas e quĂmicas. Este trabalho teve como objetivo comparar propriedades fĂsicas,quĂmicas e biolĂłgicas de solos cultivados com algodĂŁo em bases orgĂąnicas e no
sistema convencional, assim como identificar as que possam ser utilizadas como indicadores de qualidade do solo. Selecionaram-se seis ĂĄreas submetidas ao cultivo orgĂąnico e trĂȘs ao cultivo convencional para coleta de amostras de solo deformadas e indeformadas, nas camadas de 0â10, 10â20 e 20â30 cm. TĂ©cnicas de estatĂstica univariada e multivariada foram utilizadas para anĂĄlise dos dados. Os resultados mostraram que os indicadores fĂsicos e quĂmicos testados individualmente nĂŁo foram sensĂveis para diferenciar as ĂĄreas sob sistema de cultivo orgĂąnico daquelas sob cultivo convencional. No entanto, a aplicação de tĂ©cnicas de anĂĄlise multivariada â no caso, componentes principais e a discriminante de Anderson â permitiu a distinção entre algumas ĂĄreas cultivadas sob cultivo orgĂąnico comparativamente Ă s convencionais, atĂ© mesmo as que estavam em transição.Dos indicadores biolĂłgicos, a fauna edĂĄfica mostrou-se mais precisa na avaliação
da qualidade do solo, distinguindo de forma satisfatĂłria as ĂĄreas sob sistema de cultivo orgĂąnico das que estavam sob sistema convencional
Measuring our Peculiar Velocity by "Pre-deboosting" the CMB
It was recently shown that our peculiar velocity \beta with respect to the
CMB induces mixing among multipoles and off-diagonal correlations at all scales
which can be used as a measurement of \beta, which is independent of the
standard measurement using the CMB temperature dipole. The proposed techniques
rely however on a perturbative expansion which breaks down for \ell \gtrsim
1/(\beta) \approx 800. Here we propose a technique which consists of deboosting
the CMB temperature in the time-ordered data and show that it extends the
validity of the perturbation analysis multipoles up to \ell \sim 10000. We also
obtain accurate fitting functions for the mixing between multipoles valid in a
full non-linear treatment. Finally we forecast the achievable precision with
which these correlations can be measured in a number of current and future CMB
missions. We show that Planck could measure the velocity with a precision of
around 60 km/s, ACTPol in 4 years around 40 km/s, while proposed future
experiments could further shrink this error bar by over a factor of around 2.Comment: 14 pages, 7 figures. Revised projections for ACTPol, SPTPol and
ACBAR; included projections for BICEP2; extended conclusions; typos correcte
An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex
The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 [Dyke et al., 2003]; âQuaternary Glaciations â Extent and Chronology, Part IIâ [Dyke, 2004]). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km2, which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the worldâs largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval
Should science educators deal with the science/religion issue?
I begin by examining the natures of science and religion before looking at the ways in which they relate to one another. I then look at a number of case studies that centre on the relationships between science and religion, including attempts to find mechanisms for divine action in quantum theory and chaos theory, creationism, genetic engineering and the writings of Richard Dawkins. Finally, I consider some of the pedagogical issues that would need to be considered if the science/religion issue is to be addressed in the classroom. I conclude that there are increasing arguments in favour of science educators teaching about the science/religion issue. The principal reason for this is to help students better to learn science. However, such teaching makes greater demands on science educators than has generally been the case. Certain of these demands are identified and some specific suggestions are made as to how a science educator might deal with the science/religion issue. © 2008 Taylor & Francis
Statistical mechanics of two-dimensional vortices and stellar systems
The formation of large-scale vortices is an intriguing phenomenon in
two-dimensional turbulence. Such organization is observed in large-scale
oceanic or atmospheric flows, and can be reproduced in laboratory experiments
and numerical simulations. A general explanation of this organization was first
proposed by Onsager (1949) by considering the statistical mechanics for a set
of point vortices in two-dimensional hydrodynamics. Similarly, the structure
and the organization of stellar systems (globular clusters, elliptical
galaxies,...) in astrophysics can be understood by developing a statistical
mechanics for a system of particles in gravitational interaction as initiated
by Chandrasekhar (1942). These statistical mechanics turn out to be relatively
similar and present the same difficulties due to the unshielded long-range
nature of the interaction. This analogy concerns not only the equilibrium
states, i.e. the formation of large-scale structures, but also the relaxation
towards equilibrium and the statistics of fluctuations. We will discuss these
analogies in detail and also point out the specificities of each system.Comment: Chapter of the forthcoming "Lecture Notes in Physics" volume:
``Dynamics and Thermodynamics of Systems with Long Range Interactions'', T.
Dauxois, S. Ruffo, E. Arimondo, M. Wilkens Eds., Lecture Notes in Physics
Vol. 602, Springer (2002
Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
A41 Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study
In: Addiction Science & Clinical Practice 2017, 12(Suppl 1): A4
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