14,944 research outputs found
Microscopic picture of aging in SiO2
We investigate the aging dynamics of amorphous SiO2 via molecular dynamics
simulations of a quench from a high temperature T_i to a lower temperature T_f.
We obtain a microscopic picture of aging dynamics by analyzing single particle
trajectories, identifying jump events when a particle escapes the cage formed
by its neighbors, and by determining how these jumps depend on the waiting time
t_w, the time elapsed since the temperature quench to T_f. We find that the
only t_w-dependent microscopic quantity is the number of jumping particles per
unit time, which decreases with age. Similar to previous studies for fragile
glass formers, we show here for the strong glass former SiO2 that neither the
distribution of jump lengths nor the distribution of times spent in the cage
are t_w-dependent. We conclude that the microscopic aging dynamics is
surprisingly similar for fragile and strong glass formers.Comment: 4 pages, 7 figure
Wind-Tunnel Investigation of an Advanced General Aviation Canard Configuration
Wind-tunnel tests of a model of an advanced canard configuration designed for general aviation were conducted in the Langley 30- by 60-Foot Tunnel. The objective of the tests was to determine the aerodynamic stability and control characteristics of the configuration for a large range of angles of attack and sideslip at several power conditions. Analysis of the aerodynamic data indicates significant effects of power and of center-of-gravity location. For forward center-of-gravity locations, the configuration had extremely stall-resistant stability and control characteristics. For aft center-of-gravity locations and high-power conditions, the combined effects of increased pitch control and reduced longitudinal stability overpowered the stall resistance provided by the canard, which led to a high-angle-of-attack, deep-stall trim condition. Other aspects of the aerodynamic characteristics studied include the following: flow-visualization study, effect of negative angles of attack, lateral-directional characteristics, and comparison of the stall characteristics with another canard configuration
Galaxy Interactions in Compact Groups II: abundance and kinematic anomalies in HCG 91c
Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS
integral field spectrograph as part of our ongoing campaign targeting the
ionized gas physics and kinematics inside star forming members of compact
groups. Here, we report the discovery of HII regions with abundance and
kinematic offsets in the otherwise unremarkable star forming spiral HCG 91c.
The optical emission line analysis of this galaxy reveals that at least three
HII regions harbor an oxygen abundance ~0.15 dex lower than expected from their
immediate surroundings and from the abundance gradient present in the inner
regions of HCG 91c. The same star forming regions are also associated with a
small kinematic offset in the form of a lag of 5-10 km/s with respect to the
local circular rotation of the gas. HI observations of HCG 91 from the Very
Large Array and broadband optical images from Pan-STARRS suggest that HCG 91c
is caught early in its interaction with the other members of HCG 91. We discuss
different scenarios to explain the origin of the peculiar star forming regions
detected with WiFeS, and show that evidence point towards infalling and
collapsing extra-planar gas clouds at the disk-halo interface, possibly as a
consequence of long-range gravitational perturbations of HCG 91c from the other
group members. As such, HCG 91c provides evidence that some of the
perturbations possibly associated with the early phase of galaxy evolution in
compact groups impact the star forming disk locally, and on sub-kpc scales.Comment: 25 pages, 21 figures, MNRAS accepted. Until publication of the
article, the interactive component of Figure 4 is available at this URL:
http://www.mso.anu.edu.au/~fvogt/website/misc.htm
Instability, Intermixing and Electronic Structure at the Epitaxial LaAlO3/SrTiO3(001) Heterojunction
The question of stability against diffusional mixing at the prototypical
LaAlO3/SrTiO3(001) interface is explored using a multi-faceted experimental and
theoretical approach. We combine analytical methods with a range of
sensitivities to elemental concentrations and spatial separations to
investigate interfaces grown using on-axis pulsed laser deposition. We also
employ computational modeling based on the density function theory as well as
classical force fields to explore the energetic stability of a wide variety of
intermixed atomic configurations relative to the idealized, atomically abrupt
model. Statistical analysis of the calculated energies for the various
configurations is used to elucidate the relative thermodynamic stability of
intermixed and abrupt configurations. We find that on both experimental and
theoretical fronts, the tendency toward intermixing is very strong. We have
also measured and calculated key electronic properties such as the presence of
electric fields and the value of the valence band discontinuity at the
interface. We find no measurable electric field in either the LaAlO3 or SrTiO3,
and that the valence band offset is near zero, partitioning the band
discontinuity almost entirely to the conduction band edge. Moreover, we find
that it is not possible to account for these electronic properties
theoretically without including extensive intermixing in our physical model of
the interface. The atomic configurations which give the greatest electrostatic
stability are those that eliminate the interface dipole by intermixing, calling
into question the conventional explanation for conductivity at this interface -
electronic reconstruction. Rather, evidence is presented for La indiffusion and
doping of the SrTiO3 below the interface as being the cause of the observed
conductivity
Effect of Water Management on Interannual Variation in Bulk Soil Properties from the Eastern Coastal Everglades
We examined interannual variation in soil properties from wetlands occurring in adjacent drainage basins from the southeastern Everglades. Triplicate 10-cm soil cores were collected, homogenized, and analyzed during the wet season 2006–2010 from five freshwater sawgrass wetland marshes and three estuarine mangrove forests. Soil bulk density from the Taylor Slough basin ranged from 0.15 gm-cm−3 to 0.5 gm-cm−3, was higher than from the Panhandle basin every year, and generally increased throughout the study period. Organic matter as a percent loss on ignition ranged from 7 % to 12 % from freshwater marshes and from 13 % to 56 % from estuarine mangroves. Extractable iron in soils was similar among drainage basins and wetland types, typically ranging from 0.6 to 2.0 g Fe kg−1. In contrast, inorganic sulfur was on average over four times higher from estuarine soils relative to freshwater, and was positively correlated with soil organic matter. Finally total soil phosphorus (P) was lower in freshwater soils relative to estuarine soils (84 ± 5 versus 326 ± 32 mg P kg−1). Total P from the freshwater marshes in the Panhandle basin rose throughout the study period from 54.7 ± 8.4 to 107 ± 17 mg P kg−1, a possible outcome of differences in water management between drainage basins
Crystallization of the oligopeptide-binding protein AppA from Bacillus subtilis
AppA is the membrane-anchored extracellular receptor component of an ABC transporter responsible for the uptake of oligopeptides into Bacillus subtilis. AppA has been overexpressed as a cleavable maltose-binding protein fusion in Escherichia coli. Following removal of the fusion portion, AppA has been crystallized from morpholino-ethanesulfonic acid-buffered solutions at pH 6.5 containing polyethylene glycol and zinc acetate. A complete X-ray diffraction data set extending to 2.3 Angstrom spacing has been collected
Health beliefs and compliance with inhaled corticosteroids by asthmatic patients in primary care practices
AbstractThe aim of this study was to determine factors associated with regular use of inhaled corticosteroids (ICS) by asthmatic patients in primary care practices. A cross-sectional survey was carried out over 12 family practices in the Philadelphia greater Metropolitan area. A total of 394 patients aged 18–49 years, who received medical care for asthma from their primary care physician and had been prescribed ICS between 1 January 1995 and 31 December 1996, were included.The study measured self-reported demographics, experience with asthma, use of and attitudes about ICS, and health beliefs in six domains.Only 38% of patients reported using ICS at least twice a day almost every day. The most frequently cited reasons for inconsistent or non-use of ICS were related to a belief that ICS were unnecessary during asymptomatic periods and to a general concern about side-effects. By logistic regression, factors associated with regular use of ICS were two patient health beliefs, namely the health belief of ‘Active’ participation in clinical decision-making with their physician (OR=4·6, 95% CI 2·8, 7·5), and the health belief that asthma was a ‘Serious’ health problem (OR=2·3, 95% CI 1·4, 3·7), and hospitalization for asthma within the previous 12 months (OR=2·3, 95% CI 1·6, 4·6).Patients were more likely to report regular use of ICS if they saw themselves as active participants in their treatment planning and conceptualized asthma as a potentially serious illness. These results support the themes of patient education and shared decision-making between patients and physicians that are promoted by the Asthma Guidelines from the National Heart, Lung and Blood Institute (NHLBI)
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