Vortex transport and voltage noise in disordered superconductors

We study, by means of three-dimensional Monte Carlo simulations, the current-voltage (IV) characteristics and the voltage noise spectrum at low temperatures of driven magnetic flux lines interacting with randomly placed point or columnar defects, as well as with periodically arranged linear pinning centers. Near the depinning current J_c, the voltage noise spectrum S(w) universally follows a 1/w^a power law. For currents J > J_c, distinct peaks appear in S(w) which are considerably more pronounced for extended as compared to point defects, and reflect the spatial distribution of the correlated pinning centers.Comment: 8 pages, latex, Elsevier style file and figures include

A Suzaku Observation of NGC 4593: Illuminating the Truncated Disk

We report results from a 2007 Suzaku observation of the Seyfert 1 AGN NGC 4593. The narrow Fe K alpha emission line has a FWHM width ~4000 km/s, indicating emission from >~ 5000 Rg. There is no evidence for a relativistically broadened Fe K line, consistent with the presence of a radiatively efficient outer disk which is truncated or transitions to an interior radiatively inefficient flow. The Suzaku observation caught the source in a low-flux state; compared to a 2002 XMM observation, the hard X-ray flux decreased by 3.6, while the Fe K alpha line intensity and width each roughly halved. Two model-dependent explanations for the changes in Fe line profile are explored. In one, the Fe line width has decreased from ~10000 to ~4000 km/s from 2002 to 2007, suggesting that the thin disk truncation/transition radius has increased from 1000-2000 to >~5000 Rg. However, there are indications from other compact accreting systems that such truncation radii tend to be associated only with accretion rates relative to Eddington much lower than that of NGC 4593. In the second (preferred) model, the line profile in the XMM observation consists of a time-invariant narrow component plus a broad component originating from the inner part of the truncated disk (~300 Rg) which has responded to the drop in continuum flux. The Compton reflection component strength R is ~1.1, consistent with the measured Fe K alpha line total EQW with an Fe abundance 1.7 times solar. The modest soft excess has fallen by a factor of ~20 from 2002 to 2007, ruling out emission from a region 5 lt-yr in size.Comment: Accepted for publication in The Astrophysical Journal. 17 pages, 10 figure

Forest fragmentation impacts the seasonality of Amazonian evergreen canopies

Predictions of the magnitude and timing of leaf phenology in Amazonian forests remain highly controversial. Here, we use terrestrial LiDAR surveys every two weeks spanning wet and dry seasons in Central Amazonia to show that plant phenology varies strongly across vertical strata in old-growth forests, but is sensitive to disturbances arising from forest fragmentation. In combination with continuous microclimate measurements, we find that when maximum daily temperatures reached 35 °C in the latter part of the dry season, the upper canopy of large trees in undisturbed forests lost plant material. In contrast, the understory greened up with increased light availability driven by the upper canopy loss, alongside increases in solar radiation, even during periods of drier soil and atmospheric conditions. However, persistently high temperatures in forest edges exacerbated the upper canopy losses of large trees throughout the dry season, whereas the understory in these light-rich environments was less dependent on the altered upper canopy structure. Our findings reveal a strong influence of edge effects on phenological controls in wet forests of Central Amazonia.Peer reviewe

Forest fragmentation impacts the seasonality of Amazonian evergreen canopies

Predictions of the magnitude and timing of leaf phenology in Amazonian forests remain highly controversial. Here, we use terrestrial LiDAR surveys every two weeks spanning wet and dry seasons in Central Amazonia to show that plant phenology varies strongly across vertical strata in old-growth forests, but is sensitive to disturbances arising from forest fragmentation. In combination with continuous microclimate measurements, we find that when maximum daily temperatures reached 35 °C in the latter part of the dry season, the upper canopy of large trees in undisturbed forests lost plant material. In contrast, the understory greened up with increased light availability driven by the upper canopy loss, alongside increases in solar radiation, even during periods of drier soil and atmospheric conditions. However, persistently high temperatures in forest edges exacerbated the upper canopy losses of large trees throughout the dry season, whereas the understory in these light-rich environments was less dependent on the altered upper canopy structure. Our findings reveal a strong influence of edge effects on phenological controls in wet forests of Central Amazonia

Lysophosphatidic Acid Induces Migration of Human Lung‐Resident Mesenchymal Stem Cells Through the β‐Catenin Pathway

Mesenchymal stem cells (MSCs) have been demonstrated to reside in human adult organs. However, mechanisms of migration of these endogenous MSCs within their tissue of origin are not well understood. Here, we investigate migration of human adult lung‐resident (LR) mesenchymal progenitor cells. We demonstrate that bioactive lipid lysophosphatidic acid (LPA) plays a principal role in the migration of human LR‐MSCs through a signaling pathway involving LPA1‐induced β‐catenin activation. LR‐MSCs isolated from human lung allografts and lungs of patients with scleroderma demonstrated a robust migratory response to LPA in vitro. Furthermore, LPA levels correlated with LR‐MSC numbers in bronchoalveolar lavage (BAL), providing demonstration of the in vivo activity of LPA in human adult lungs. Migration of LR‐MSCs was mediated via LPA1 receptor ligation and LPA1 silencing significantly abrogated the migratory response of LR‐MSCs to LPA as well as human BAL. LPA treatment of LR‐MSCs induced protein kinase C‐mediated glycogen synthase kinase‐3β phosphorylation, with resulting cytoplasmic accumulation and nuclear translocation of β‐catenin. TCF/LEF dual luciferase gene reporter assay demonstrated a significant increase in transcriptional activity after LPA treatment. LR‐MSC migration and increase in reporter gene activity in the presence of LPA were abolished by transfection with β‐catenin small interfering RNA demonstrating that β‐catenin is critical in mediating LPA‐induced LR‐MSC migration. These data delineate a novel signaling pathway through which ligation of a G protein‐coupled receptor by a biologically relevant lipid mediator induces migration of human tissue‐resident mesenchymal progenitors. S tem C ells 2012;30:2010–2019Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93548/1/1171_ftp.pd

A Review of Bondi--Hoyle--Lyttleton Accretion

If a point mass moves through a uniform gas cloud, at what rate does it accrete material? This is the question studied by Bondi, Hoyle and Lyttleton. This paper draws together the work performed in this area since the problem was first studied. Time has shown that, despite the simplifications made, Bondi, Hoyle and Lyttleton made quite accurate predictions for the accretion rate. Bondi--Hoyle--Lyttleton accretion has found application in many fields of astronomy, and these are also discussed.Comment: 25 pages Accepted by New Astronomy Reviews Revision corrects a rather important typo about timescales in the stability sectio

Starobinsky Model in Schroedinger Description

In the Starobinsky inflationary model inflation is driven by quantum corrections to the vacuum Einstein equation. We reduce the Wheeler-DeWitt equation corresponding to the Starobinsky model to a Schroedinger form containing time. The Schroedinger equation is solved with a Gaussian ansatz. Using the prescription for the normalization constant of the wavefunction given in our previous work, we show that the Gaussian ansatz demands Hawking type initial conditions for the wavefunction of the universe. The wormholes induce randomness in initial states suggesting a basis for time-contained description of the Wheeler-DeWitt equation.Comment: 19 Pages, LaTeX, no figure, gross typographical mistake