103 research outputs found
Ferroelectricity in ultra-thin perovskite films
We report studies of ferroelectricity in ultra-thin perovskite films with
realistic electrodes. The results reveal stable ferroelectric states in thin
films less than 10 \AA thick with polarization normal to the surface. Under
short-circuit boundary conditions, the screening effect of realistic electrodes
and the influence of real metal/oxide interfaces on thin film polarization are
investigated. Our studies indicate that metallic screening from the electrodes
is affected by the difference in work functions at oxide surfaces. We
demonstrate this effect in ferroelectric PbTiO and BaTiO films.Comment: 4 pages in REVTEX4, 4 epsf figure
Clustering as a criterion for the success of modern industrial enterprises
The paper reveals the problems of the use of clusters as an important factor of innovative development of Russian enterprises and territorial entities delineated a theoretical basis for the existence of territorial formations, showing their relationship with the clusters displayed in the cluster's functioning as an open system. All the more important in the formation of innovation territorial entities in Russia acquire the cluster structure based on cooperation of enterprises, financial institutions, educational institutions etc. In the developed countries have long had and continue to have such structures in various industries. In the works of famous foreign scientists clearly defined theoretical bases of formation and functioning of clusters, use cluster models to ensure the competitiveness of the economy, their advantages and disadvantages. Foreign experience can be useful to develop a national strategy for clustering of Russia, with a comprehensive study of its socioeconomic development. These tasks at this stage be a priority for Central and local public authorities. Issues related to the principles of clusters, innovation economy, have been studied by many scientists, both Russian and foreign. In published works, the essence of cluster analysis, given the definition of "cluster" classification of clusters, the role of innovative development of economy, experience of the use of cluster models, etc
The HII region G35.673-00.847: another case of triggered star formation?
As part of a systematic study that we are performing with the aim to increase
the observational evidence of triggered star formation in the surroundings of
HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly
studied source. Using data from large-scale surveys: Two Micron All Sky Survey,
Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL,
Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky
Survey (NVSS) we performed a multiwavelength study of G35.673-00.847 and its
surroundings. The mid IR emission, shows that G35.673-00.847 has an almost
semi-ring like shape with a cut towards the galactic west. The radius of this
semi-ring is about 1.5' (~1.6 pc, at the distance of ~3.7 kpc). The distance
was estimated from an HI absorption study and from the analysis of the
molecular gas. Indeed, we find a molecular shell composed by several clumps
distributed around the HII region, suggesting that its expansion is collecting
the surrounding material. We find several YSO candidates over the molecular
shell. Finally, comparing the HII region dynamical age and the fragmentation
time of the molecular shell, we discard the collect and collapse as the
mechanism responsible for the YSOs formation, suggesting other processes such
as radiative driven implosion and/or small-scale Jeans gravitational
instabilities.Comment: Accepted for publication in A&A, 18 October 2010. Some figures were
degraded to reduce file siz
Study of the luminous blue variable star candidate G26.47+0.02 and its environment
The luminous blue variable (LBV) stars are peculiar very massive stars. The
study of these stellar objects and their surroundings is important for
understanding the evolution of massive stars and its effects on the
interstellar medium. We study the LBV star candidate G26.47+0.02. Using several
large-scale surveys in different frequencies we performed a multiwavelength
study of G26.47+0.02 and its surroundings. We found a molecular shell (seen in
the 13CO J=1-0 line) that partially surrounds the mid-infrared nebula of
G26.47+0.02, which suggests an interaction between the strong stellar winds and
the molecular gas. From the HI absorption and the molecular gas study we
conclude that G26.47+0.02 is located at a distance of ~4.8 kpc. The radio
continuum analysis shows a both thermal and non-thermal emission toward this
LBV candidate, pointing to wind-wind collision shocks from a binary system.
This hypothesis is supported by a search of near-IR sources and the Chandra
X-ray analysis. Additional multiwavelength and long-term observations are
needed to detect some possible variable behavior, and if that is found, to
confirm the binary nature of the system.Comment: accepted in A&A 01/05/201
Ptch2/Gas1 and Ptch1/Boc differentially regulate Hedgehog signalling in murine primordial germ cell migration.
Gas1 and Boc/Cdon act as co-receptors in the vertebrate Hedgehog signalling pathway, but the nature of their interaction with the primary Ptch1/2 receptors remains unclear. Here we demonstrate, using primordial germ cell migration in mouse as a developmental model, that specific hetero-complexes of Ptch2/Gas1 and Ptch1/Boc mediate the process of Smo de-repression with different kinetics, through distinct modes of Hedgehog ligand reception. Moreover, Ptch2-mediated Hedgehog signalling induces the phosphorylation of Creb and Src proteins in parallel to Gli induction, identifying a previously unknown Ptch2-specific signal pathway. We propose that although Ptch1 and Ptch2 functionally overlap in the sequestration of Smo, the spatiotemporal expression of Boc and Gas1 may determine the outcome of Hedgehog signalling through compartmentalisation and modulation of Smo-downstream signalling. Our study identifies the existence of a divergent Hedgehog signal pathway mediated by Ptch2 and provides a mechanism for differential interpretation of Hedgehog signalling in the germ cell niche
Discovery of a Radio Source following the 27 December 2004 Giant Flare from SGR 1806-20
Over a decade ago it was established that the remarkable high energy
transients, known as soft gamma-ray repeaters (SGRs), are a Galactic population
and originate from neutron stars with intense (<~ 10^15 G) magnetic fields
("magnetars"). On 27 December 2004 a giant flare (fluence >~ 0.3 erg/cm^2) was
detected from SGR 1806-20. Here we report the discovery of a fading radio
counterpart. We began a monitoring program from 0.2GHz to 250GHz and obtained a
high resolution 21-cm radio spectrum which traces the intervening interstellar
neutral Hydrogen clouds. Analysis of the spectrum yields the first direct
distance measurement of SGR 1806-20. The source is located at a distance
greater than 6.4 kpc and we argue that it is nearer than 9.8 kpc. If true, our
distance estimate lowers the total energy of the explosion and relaxes the
demands on theoretical models. The energetics and the rapid decay of the radio
source are not compatible with the afterglow model that is usually invoked for
gamma-ray bursts. Instead we suggest that the rapidly decaying radio emission
arises from the debris ejected during the explosion.Comment: 16 pages, 2 figures, submitted to Nature (substantial revisions
MALT90 Kinematic Distances to Dense Molecular Clumps
Using molecular-line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90), we have estimated kinematic distances to 1905 molecular clumps identified in the ATLASGAL 870 μm continuum survey over the longitude range 295° < l < 350°. The clump velocities were determined using a flux-weighted average of the velocities obtained from Gaussian fits to the HCO+, HNC, and N2H+ (1–0) transitions. The near/far kinematic distance ambiguity was addressed by searching for the presence or absence of absorption or self-absorption features in 21 cm atomic hydrogen spectra from the Southern Galactic Plane Survey. Our algorithm provides an estimation of the reliability of the ambiguity resolution. The Galactic distribution of the clumps indicates positions where the clumps are bunched together, and these locations probably trace the locations of spiral arms. Several clumps fall at the predicted location of the far side of the Scutum–Centaurus arm. Moreover, a number of clumps with positive radial velocities are unambiguously located on the far side of the Milky Way at galactocentric radii beyond the solar circle. The measurement of these kinematic distances, in combination with continuum or molecular-line data, now enables the determination of fundamental parameters such as mass, size, and luminosity for each clump
The Bolocam Galactic Plane Survey V: HCO+ and N2H+ Spectroscopy of 1.1 mm Dust Continuum Sources
We present the results of observations of 1882 sources in the Bolocam
Galactic Plane Survey (BGPS) at 1.1 mm with the 10m Heinrich Hertz Telescope
simultaneously in HCO+ J=3-2 and N2H+ J=3-2. We detect 77% of these sources in
HCO^+ and 51% in N2H+ at greater than 3. We find a strong correlation
between the integrated intensity of both dense gas tracers and the 1.1 mm dust
emission of BGPS sources. We determine kinematic distances for 529 sources (440
in the first quadrant breaking the distance ambiguity and 89 in the second
quadrant) We derive the size, mass, and average density for this subset of
clumps. The median size of BGPS clumps is 0.75 pc with a median mass of 330
M (assuming T_{Dust}=20 K). The median HCO+ linewidth is 2.9 km
s indicating that BGPS clumps are dominated by supersonic turbulence or
unresolved kinematic motions. We find no evidence for a size-linewidth
relationship for BGPS clumps. We analyze the effects of the assumed dust
temperature on the derived clump properties with a Monte Carlo simulation and
we find that changing the temperature distribution will change the median
source properties (mass, volume-averaged number density, surface density) by
factors of a few. The observed differential mass distribution has a power-law
slope that is intermediate between that observed for diffuse CO clouds and the
stellar IMF. BGPS clumps represent a wide range of objects (from dense cores to
more diffuse clumps) and are typically characterized by larger sizes and lower
densities than previously published surveys of high-mass star-forming regions.
This collection of objects is a less-biased sample of star-forming regions in
the Milky Way that likely span a wide range of evolutionary states.Comment: 48 pages, 25 figures, Accepted for publicatio
Fungal enzyme sets for plant polysaccharide degradation
Enzymatic degradation of plant polysaccharides has many industrial applications, such as within the paper, food, and feed industry and for sustainable production of fuels and chemicals. Cellulose, hemicelluloses, and pectins are the main components of plant cell wall polysaccharides. These polysaccharides are often tightly packed, contain many different sugar residues, and are branched with a diversity of structures. To enable efficient degradation of these polysaccharides, fungi produce an extensive set of carbohydrate-active enzymes. The variety of the enzyme set differs between fungi and often corresponds to the requirements of its habitat. Carbohydrate-active enzymes can be organized in different families based on the amino acid sequence of the structurally related catalytic modules. Fungal enzymes involved in plant polysaccharide degradation are assigned to at least 35 glycoside hydrolase families, three carbohydrate esterase families and six polysaccharide lyase families. This mini-review will discuss the enzymes needed for complete degradation of plant polysaccharides and will give an overview of the latest developments concerning fungal carbohydrate-active enzymes and their corresponding families
Fluid challenges in intensive care: the FENICE study A global inception cohort study
Fluid challenges (FCs) are one of the most commonly used therapies in critically ill patients and represent the cornerstone of hemodynamic management in intensive care units. There are clear benefits and harms from fluid therapy. Limited data on the indication, type, amount and rate of an FC in critically ill patients exist in the literature. The primary aim was to evaluate how physicians conduct FCs in terms of type, volume, and rate of given fluid; the secondary aim was to evaluate variables used to trigger an FC and to compare the proportion of patients receiving further fluid administration based on the response to the FC.This was an observational study conducted in ICUs around the world. Each participating unit entered a maximum of 20 patients with one FC.2213 patients were enrolled and analyzed in the study. The median [interquartile range] amount of fluid given during an FC was 500 ml (500-1000). The median time was 24 min (40-60 min), and the median rate of FC was 1000 [500-1333] ml/h. The main indication for FC was hypotension in 1211 (59 %, CI 57-61 %). In 43 % (CI 41-45 %) of the cases no hemodynamic variable was used. Static markers of preload were used in 785 of 2213 cases (36 %, CI 34-37 %). Dynamic indices of preload responsiveness were used in 483 of 2213 cases (22 %, CI 20-24 %). No safety variable for the FC was used in 72 % (CI 70-74 %) of the cases. There was no statistically significant difference in the proportion of patients who received further fluids after the FC between those with a positive, with an uncertain or with a negatively judged response.The current practice and evaluation of FC in critically ill patients are highly variable. Prediction of fluid responsiveness is not used routinely, safety limits are rarely used, and information from previous failed FCs is not always taken into account
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