2,784 research outputs found
Stochastic Loewner evolution driven by Levy processes
Standard stochastic Loewner evolution (SLE) is driven by a continuous
Brownian motion, which then produces a continuous fractal trace. If jumps are
added to the driving function, the trace branches. We consider a generalized
SLE driven by a superposition of a Brownian motion and a stable Levy process.
The situation is defined by the usual SLE parameter, , as well as
which defines the shape of the stable Levy distribution. The resulting
behavior is characterized by two descriptors: , the probability that the
trace self-intersects, and , the probability that it will approach
arbitrarily close to doing so. Using Dynkin's formula, these descriptors are
shown to change qualitatively and singularly at critical values of and
. It is reasonable to call such changes ``phase transitions''. These
transitions occur as passes through four (a well-known result) and as
passes through one (a new result). Numerical simulations are then used
to explore the associated touching and near-touching events.Comment: Published version, minor typos corrected, added reference
Topological Insulator Nanowires and Nanoribbons
Recent theoretical calculations and photoemission spectroscopy measurements
on the bulk Bi2Se3 material show that it is a three-dimensional topological
insulator possessing conductive surface states with nondegenerate spins,
attractive for dissipationless electronics and spintronics applications.
Nanoscale topological insulator materials have a large surface-to-volume ratio
that can manifest the conductive surface states and are promising candidates
for devices. Here we report the synthesis and characterization of high quality
single crystalline Bi2Se3 nanomaterials with a variety of morphologies. The
synthesis of Bi2Se3 nanowires and nanoribbons employs Au-catalyzed
vapor-liquid-solid (VLS) mechanism. Nanowires, which exhibit rough surfaces,
are formed by stacking nanoplatelets along the axial direction of the wires.
Nanoribbons are grown along [11-20] direction with a rectangular cross-section
and have diverse morphologies, including quasi-one-dimensional, sheetlike,
zigzag and sawtooth shapes. Scanning tunneling microscopy (STM) studies on
nanoribbons show atomically smooth surfaces with ~ 1 nm step edges, indicating
single Se-Bi-Se-Bi-Se quintuple layers. STM measurements reveal a honeycomb
atomic lattice, suggesting that the STM tip couples not only to the top Se
atomic layer, but also to the Bi atomic layer underneath, which opens up the
possibility to investigate the contribution of different atomic orbitals to the
topological surface states. Transport measurements of a single nanoribbon
device (four terminal resistance and Hall resistance) show great promise for
nanoribbons as candidates to study topological surface states.Comment: Nano Letters, Article ASA
Gamow Shell Model Description of Weakly Bound Nuclei and Unbound Nuclear States
We present the study of weakly bound, neutron-rich nuclei using the nuclear
shell model employing the complex Berggren ensemble representing the bound
single-particle states, unbound Gamow states, and the non-resonant continuum.
In the proposed Gamow Shell Model, the Hamiltonian consists of a one-body
finite depth (Woods-Saxon) potential and a residual two-body interaction. We
discuss the basic ingredients of the Gamow Shell Model. The formalism is
illustrated by calculations involving {\it several} valence neutrons outside
the double-magic core: He and O.Comment: 19 pages, 20 encapsulated PostScript figure
Theoretical Aspects of Science with Radioactive Nuclear Beams
Physics of radioactive nuclear beams is one of the main frontiers of nuclear
science today. Experimentally, thanks to technological developments, we are on
the verge of invading the territory of extreme N/Z ratios in an unprecedented
way. Theoretically, nuclear exotica represent a formidable challenge for the
nuclear many-body theories and their power to predict nuclear properties in
nuclear terra incognita. It is important to remember that the lesson learned by
going to the limits of the nuclear binding is also important for normal nuclei
from the neighborhood of the beta stability valley. And, of course, radioactive
nuclei are crucial astrophysically; they pave the highway along which the
nuclear material is transported up in the proton and neutron numbers during the
complicated synthesis process in stars.Comment: 26 ReVTeX pages, 11 Postscript figures, uses epsf.sty, to be
published in: Theme Issue on Science with Beams of Radioactive Nuclei,
Philosophical Transactions, ed. by W. Gelletl
On Global Conservation Laws at Null Infinity
The ``standard'' expressions for total energy, linear momentum and also
angular momentum of asymptotically flat Bondi metrics at null infinity are also
obtained from differential conservation laws on asymptotically flat
backgrounds, derived from a quadratic Lagrangian density by methods currently
used in classical field theory. It is thus a matter of taste and commodity to
use or not to use a reference spacetime in defining these globally conserved
quantities. Backgrounds lead to N\oe ther conserved currents; the use of
backgrounds is in line with classical views on conservation laws. Moreover, the
conserved quantities are in principle explicitly related to the sources of
gravity through Einstein's equations, while standard definitions are not. The
relations depend, however, on a rule for mapping spacetimes on backgrounds
A Change in the Dark Room: The Effects of Human Factors and Cognitive Loading Issues for NextGen TRACON Air Traffic Controllers
By 2020 all aircraft in United States airspace must use ADS-B (Automatic Dependent Surveillance-Broadcast) Out. This is a key component of the Next Generation (NextGen) Air Transportation System, which marks the first time all aircraft will be tracked continuously using satellites instead of ground-based radar. Standard Terminal Automation Replacement System (STARS) in the Terminal Radar Approach Control (TRACON) is a primary NextGen upgrade where digitized automation/information surrounds STARS controllers while controlling aircraft. Applying the SHELL model, the authors analyze human factors changes affecting TRACON controllers from pre-STARS technology through NextGen technologies on performance. Results of an informal survey of STARS controllers assessed cognitive processing issues and indicates the greatest concern is with movements to view other displays and added time to re-engage STARS
Associations of Serum 25-Hydroxyvitamin D, Parathyroid Hormone and Calcium with Cardiovascular Risk Factors: Analysis of 3 NHANES Cycles (2001–2006)
Increasing evidence suggests a role for mineral metabolism in cardiovascular disease risk. 25-hydroxyvitamin D (25(OH)D), parathyroid hormone (PTH), and calcium may be directly associated with cardiovascular risk factors or mediated by each other.We combined data for adult participants in three cycles of the National Health and Nutrition Examination Survey (2001-2, 2003-4, 2005-6), a representative sample of the civilian, non-institutionalized US population (N = 3,958). Using this data we examined joint associations of 25(OH)D, PTH and calcium with a range of cardiovascular risk factors. 25(OH)D was inversely associated with fasting insulin (mean difference in insulin per 1 standard deviation 25(OH)D: -0.053 (95%CI: -0.091, -0.015)), glucose (-0.046 95%CI: -0.081, -0.012) and systolic blood pressure (SBP) (-0.032 95%CI: -0.062, -0.001), and positively associated with high density lipoprotein cholesterol HDL-c (0.088 95%CI: 0.044, 0.148), after adjustment for ethnicity, smoking, socio-economic status and waist circumference. PTH was positively associated with diastolic blood pressure (0.110, 95%CI: 0.055, 0.164) in confounder adjusted models, but was not associated with other cardiovascular risk factors. Albumin adjusted calcium was associated with triglycerides (0.102 95%CI: 0.063, 0.141), postload glucose (0.078, 95%CI: 0.025, 0.130), fasting insulin (0.074, 95%CI: 0.044, 0.104), HbA1c (0.070, 95%CI: 0.036, 0.105), SBP (0.064, 95%CI: 0.028, 0.100), fasting glucose (0.055, 95%CI: 0.018, 0.092) and low density lipoprotein cholesterol (0.052, 95%CI: 0.014, 0.091). With mutual adjustment for each other, these associations remained essentially unchanged.Lower levels of 25(OH)D and higher levels of calcium and PTH appear to be associated with different cardiovascular risk factors and may therefore affect cardiovascular disease risk through different mechanisms
Redox proteomics of the inflammatory secretome identifies a common set of redoxins and other glutathionylated proteins released in inflammation, influenza virus infection and oxidative stress
Protein cysteines can form transient disulfides with glutathione (GSH), resulting in the production of glutathionylated proteins, and this process is regarded as a mechanism by which the redox state of the cell can regulate protein function. Most studies on redox regulation of immunity have focused on intracellular proteins. In this study we have used redox proteomics to identify those proteins released in glutathionylated form by macrophages stimulated with lipopolysaccharide (LPS) after pre-loading the cells with biotinylated GSH. Of the several proteins identified in the redox secretome, we have selected a number for validation. Proteomic analysis indicated that LPS stimulated the release of peroxiredoxin (PRDX) 1, PRDX2, vimentin (VIM), profilin1 (PFN1) and thioredoxin 1 (TXN1). For PRDX1 and TXN1, we were able to confirm that the released protein is glutathionylated. PRDX1, PRDX2 and TXN1 were also released by the human pulmonary epithelial cell line, A549, infected with influenza virus. The release of the proteins identified was inhibited by the anti-inflammatory glucocorticoid, dexamethasone (DEX), which also inhibited tumor necrosis factor (TNF)-α release, and by thiol antioxidants (N-butanoyl GSH derivative, GSH-C4, and N-acetylcysteine (NAC), which did not affect TNF-α production. The proteins identified could be useful as biomarkers of oxidative stress associated with inflammation, and further studies will be required to investigate if the extracellular forms of these proteins has immunoregulatory functions
Characteristics of DNA-binding proteins determine the biological sensitivity to high-linear energy transfer radiation
Non-homologous end-joining (NHEJ) and homologous recombination repair (HRR), contribute to repair ionizing radiation (IR)-induced DNA double-strand breaks (DSBs). Mre11 binding to DNA is the first step for activating HRR and Ku binding to DNA is the first step for initiating NHEJ. High-linear energy transfer (LET) IR (such as high energy charged particles) killing more cells at the same dose as compared with low-LET IR (such as X or γ rays) is due to inefficient NHEJ. However, these phenomena have not been demonstrated at the animal level and the mechanism by which high-LET IR does not affect the efficiency of HRR remains unclear. In this study, we showed that although wild-type and HRR-deficient mice or DT40 cells are more sensitive to high-LET IR than to low-LET IR, NHEJ deficient mice or DT40 cells are equally sensitive to high- and low-LET IR. We also showed that Mre11 and Ku respond differently to shorter DNA fragments in vitro and to the DNA from high-LET irradiated cells in vivo. These findings provide strong evidence that the different DNA DSB binding properties of Mre11 and Ku determine the different efficiencies of HRR and NHEJ to repair high-LET radiation induced DSBs
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