2,441 research outputs found
Microstructure Effects on Daily Return Volatility in Financial Markets
We simulate a series of daily returns from intraday price movements initiated
by microstructure elements. Significant evidence is found that daily returns
and daily return volatility exhibit first order autocorrelation, but trading
volume and daily return volatility are not correlated, while intraday
volatility is. We also consider GARCH effects in daily return series and show
that estimates using daily returns are biased from the influence of the level
of prices. Using daily price changes instead, we find evidence of a significant
GARCH component. These results suggest that microstructure elements have a
considerable influence on the return generating process.Comment: 15 pages, as presented at the Complexity Workshop in Aix-en-Provenc
Embedded Stellar Clusters in the W3/W4/W5 Molecular Cloud Complex
We analyze the embedded stellar content in the vicinity of the W3/W4/W5 HII
regions using the FCRAO Outer Galaxy 12CO(J=1-0) Survey, the IRAS Point Source
Catalog, published radio continuum surveys, and new near-infrared and molecular
line observations. Thirty-four IRAS Point Sources are identified that have
far-infrared colors characteristic of embedded star forming regions, and we
have obtained K' mosaics and 13CO(J=1-0) maps for 32 of them. Ten of the IRAS
sources are associated with an OB star and 19 with a stellar cluster, although
three OB stars are not identified with a cluster. Half of the embedded stellar
population identified in the K' images is found in just the 5 richest clusters,
and 61% is contained in IRAS sources associated with an embedded OB star. Thus
rich clusters around OB stars contribute substantially to the stellar
population currently forming in the W3/W4/W5 region. Approximately 39% of the
cluster population is embedded in small clouds with an average mass of ~130 Mo
that are located as far as 100 pc from the W3/W4/W5 cloud complex. We speculate
that these small clouds are fragments of a cloud complex dispersed by previous
episodes of massive star formation. Finally, we find that 4 of the 5 known
embedded massive star forming sites in the W3 molecular cloud are found along
the interface with the W4 HII region despite the fact that most of the
molecular mass is contained in the interior regions of the cloud. These
observations are consistent with the classical notion that the W4 HII region
has triggered massive star formation along the eastern edge of the W3 molecular
cloud.Comment: to appear in ApJS, see http://astro.caltech.edu/~jmc/papers/w
First Passage Properties of the Erdos-Renyi Random Graph
We study the mean time for a random walk to traverse between two arbitrary
sites of the Erdos-Renyi random graph. We develop an effective medium
approximation that predicts that the mean first-passage time between pairs of
nodes, as well as all moments of this first-passage time, are insensitive to
the fraction p of occupied links. This prediction qualitatively agrees with
numerical simulations away from the percolation threshold. Near the percolation
threshold, the statistically meaningful quantity is the mean transit rate,
namely, the inverse of the first-passage time. This rate varies
non-monotonically with p near the percolation transition. Much of this behavior
can be understood by simple heuristic arguments.Comment: 10 pages, 9 figures, 2-column revtex4 forma
Shared understanding in psychiatrist–patient communication: Association with treatment adherence in schizophrenia
Objective
Effective doctor–patient communication, including a shared understanding, is associated with treatment adherence across medicine. However, communication is affected by a diagnosis of schizophrenia and reaching a shared understanding can be challenging. During conversation, people detect and deal with possible misunderstanding using a conversational process called repair. This study tested the hypothesis that more frequent repair in psychiatrist–patient communication is associated with better treatment adherence in schizophrenia.
Methods
Routine psychiatric consultations involving patients with (DSM-IV) schizophrenia or schizoaffective disorder were audio-visually recorded. Consultations were coded for repair and patients’ symptoms and insight assessed. Adherence was assessed six months later. A principal components analysis reduced the repair data for further analysis. Random effects models examined the association between repair and adherence, adjusting for symptoms, consultation length and the amount patients spoke.
Results
138 consultations were recorded, 118 were followed up. Patients requesting clarification of the psychiatrist's talk and the clarification provided by the psychiatrist was associated with adherence six months later (OR 5.82, 95% CI 1.31–25.82, p = 0.02).
Conclusion
The quality of doctor–patient communication also appears to influence adherence in schizophrenia.
Practice implications
Future research should investigate how patient clarification can be encouraged among patients and facilitated by psychiatrists’ communication
Water and ammonia abundances in S140 with the Odin satellite
We have used the Odin satellite to obtain strip maps of the ground-state
rotational transitions of ortho-water and ortho-ammonia, as well as CO(5-4) and
13CO(5-4) across the PDR, and H218O in the central position. A physi-chemical
inhomogeneous PDR model was used to compute the temperature and abundance
distributions for water, ammonia and CO. A multi-zone escape probability method
then calculated the level populations and intensity distributions. These
results are compared to a homogeneous model computed with an enhanced version
of the RADEX code. H2O, NH3 and 13CO show emission from an extended PDR with a
narrow line width of ~3 kms. Like CO, the water line profile is dominated by
outflow emission, however, mainly in the red wing. The PDR model suggests that
the water emission mainly arises from the surfaces of optically thick, high
density clumps with n(H2)>10^6 cm^-3 and a clump water abundance, with respect
to H2, of 5x10^-8. The mean water abundance in the PDR is 5x10^-9, and between
~2x10^-8 -- 2x10^-7 in the outflow derived from a simple two-level
approximation. Ammonia is also observed in the extended clumpy PDR, likely from
the same high density and warm clumps as water. The average ammonia abundance
is about the same as for water: 4x10^-9 and 8x10^-9 given by the PDR model and
RADEX, respectively. The similarity of water and ammonia PDR emission is also
seen in the almost identical line profiles observed close to the bright rim.
Around the central position, ammonia also shows some outflow emission although
weaker than water in the red wing. Predictions of the H2O(110-101) and
(111-000) antenna temperatures across the PDR are estimated with our PDR model
for the forthcoming observations with the Herschel Space Observatory.Comment: 13 pages, 14 figures, 10 tables. Accepted for publication in
Astronomy & Astrophysics 14 November 200
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Stabilization of electron beam spot size by self bias potential
In high resolution flash x-ray imaging technology the electric field developed between the electron beam and the converter target is large enough to draw ions from the target surface. The ions provide fractional neutralization and cause the electron beam to focus radially inward, and the focal point subsequently moves upstream due to the expansion of the ion column. A self-bias target concept is proposed and verified via computer simulation that the electron charge deposited on the target can generate an electric potential, which can effectively limit the ion motion and thereby stabilize the growth of the spot size. A target chamber using the self bias target concept was designed and tested in the Integrated Test Stand (ITS). The authors have obtained good agreement between computer simulation and experiment
One-carbon metabolism in cancer
Cells require one-carbon units for nucleotide synthesis, methylation and reductive metabolism, and these pathways support the high proliferative rate of cancer cells. As such, anti-folates, drugs that target one-carbon metabolism, have long been used in the treatment of cancer. Amino acids, such as serine are a major one-carbon source, and cancer cells are particularly susceptible to deprivation of one-carbon units by serine restriction or inhibition of de novo serine synthesis. Recent work has also begun to decipher the specific pathways and sub-cellular compartments that are important for one-carbon metabolism in cancer cells. In this review we summarise the historical understanding of one-carbon metabolism in cancer, describe the recent findings regarding the generation and usage of one-carbon units and explore possible future therapeutics that could exploit the dependency of cancer cells on one-carbon metabolism
An Ultra-High-Resolution Survey of the Interstellar ^7Li-to-^6Li Isotope Ratio in the Solar Neighborhood
In an effort to probe the extent of variations in the interstellar ^7Li/^6Li
ratio seen previously, ultra-high-resolution (R ~ 360,000), high
signal-to-noise spectra of stars in the Perseus OB2 and Scorpius OB2
Associations were obtained. These measurements confirm our earlier findings of
an interstellar ^7Li/^6Li ratio of about 2 toward o Per, the value predicted
from models of Galactic cosmic ray spallation reactions. Observations of other
nearby stars yield limits consistent with the isotopic ratio ~ 12 seen in
carbonaceous chondrite meteorites. If this ratio originally represented the gas
toward o Per, then to decrease the original isotope ratio to its current value
an order of magnitude increase in the Li abundance is expected, but is not
seen. The elemental K/Li ratio is not unusual, although Li and K are formed via
different nucleosynthetic pathways. Several proposals to account for the low
^7Li/^6Li ratio were considered, but none seems satisfactory.
Analysis of the Li and K abundances from our survey highlighted two sight
lines where depletion effects are prevalent. There is evidence for enhanced
depletion toward X Per, since both abundances are lower by a factor of 4 when
compared to other sight lines. Moreover, a smaller Li/H abundance is observed
toward 20 Aql, but the K/H abundance is normal, suggesting enhanced Li
depletion (relative to K) in this direction. Our results suggest that the
^7Li/^6Li ratio has not changed significantly during the last 4.5 billion years
and that a ratio ~ 12 represents most gas in the solar neighborhood. In
addition, there appears to be a constant stellar contribution of ^7Li,
indicating that one or two processes dominate its production in the Galaxy.Comment: 54 pages, accepted for publication in the Astrophysical Journa
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