2,688 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
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
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Experimental evidence of a dynamic Jahn-Teller effect in C+60.
Detailed analysis of the highest occupied molecular orbital band shape in the photoelectron spectrum of gaseous C60 reveals a dynamic Jahn-Teller effect in the ground state of C+60. The direct observation of three tunneling states asserts a D3d geometry for the isolated cation, originating from a strong vibronic coupling. These results show that the ionic motion plays an important role in the electron-phonon interaction
Mental Health Treatment Seeking Patterns and Preferences of Appalachian Women with Depression
This qualitative study explored social-cultural factors that shape treatment seeking behaviors among depressed rural, low-income women in Appalachia—a region with high rates of depression and a shortage of mental health services. Recent research shows that increasingly rural women are receiving some form of treatment and identifying their symptoms as depression. Using purposive sampling, investigators recruited 28 depressed low-income women living in Appalachian Kentucky and conducted semistructured interviews on participants’ perceptions of depression and treatment seeking. Even in this sample of women with diverse treatment behaviors (half reported current treatment), participants expressed ambivalence about treatment and its potential to promote recovery. Participants stressed that poor treatment quality—not merely access—limited their engagement in treatment and at times reinforced their depression. While women acknowledged the stigma of depression, they indicated that their resistance to seek help for their depression was influenced by the expectation of women’s self-reliance in the rural setting and the gendered taboo against negative thinking. Ambivalence and stigma led women to try to cope independently, resulting in further isolation. This study’s findings reiterate the need for improved quality and increased availability of depression treatment in rural areas. In addition, culturally appropriate depression interventions must acknowledge rural cultural values of self-reliance and barriers to obtaining social support that lead many women to endure depression in isolation
Water Abundance in Molecular Cloud Cores
We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the
1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud
cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL
2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and
B335. We also present a small map of the water emission in S140. Observations
of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission
was detected. The abundance of ortho-water relative to H_2 in the giant
molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five
of the cloud cores in our sample have previous water detections; however, in
all cases the emission is thought to arise from hot cores with small angular
extents. The water abundance estimated for the hot core gas is at least 100
times larger than in the gas probed by SWAS. The most stringent upper limit on
the ortho-water abundance in dark clouds is provided in TMC-1, where the
3-sigma upper limit on the ortho-water fractional abundance is 7x10^{-8}.Comment: 5 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty
(included), and apjfonts.sty (included
The Distribution of Water Emission in M17SW
We present a 17-point map of the M17SW cloud core in the 1_{10}-1_{01}
transition of ortho-water at 557 GHz obtained with the Submillimeter Wave
Astronomy Satellite. Water emission was detected in 11 of the 17 observed
positions. The line widths of the water emission vary between 4 and 9 km
s^{-1}, and are similar to other emission lines that arise in the M17SW core. A
direct comparison is made between the spatial extent of the water emission and
the ^{13}CO J = 5\to4 emission; the good agreement suggests that the water
emission arises in the same warm, dense gas as the ^{13}CO emission. A spectrum
of the H_2^{18}O line was also obtained at the center position of the cloud
core, but no emission was detected. We estimate that the average abundance of
ortho-water relative to H_2 within the M17 dense core is approximately
1x10^{-9}, 30 times smaller than the average for the Orion core. Toward the H
II region/molecular cloud interface in M17SW the ortho-water abundance may be
about 5 times larger than in the dense core.Comment: 4 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty
(included), and apjfonts.sty (included
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Distribution ofWater Vapor in Molecular Clouds
We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water vapor measured toward 77 spatial positions along the face-on Orion ridge, excluding positions surrounding the outflow associated with BN/KL and IRc2, display integrated intensities that correlate strongly with known cloud surface tracers such as CN, C2H, 13CO J = 5-4, and HCN, and less well with the volume tracer N2H+. Moreover, at total column densities corresponding to A V\u3c 15 mag, the ratio of H2O to C18O integrated intensities shows a clear rise approaching the cloud surface. We show that this behavior cannot be accounted for by either optical depth or excitation effects, but suggests that gas-phase water abundances fall at large A V. These results are important as they affect measures of the true water-vapor abundance in molecular clouds by highlighting the limitations of comparing measured water-vapor column densities with such traditional cloud tracers as 13CO or C18O. These results also support cloud models that incorporate freeze out of molecules as a critical component in determining the depth-dependent abundance of water vapor
Chemical sensitivity to the ratio of the cosmic-ray ionization rates of He and H2 in dense clouds
Aim: To determine whether or not gas-phase chemical models with homogeneous
and time-independent physical conditions explain the many observed molecular
abundances in astrophysical sources, it is crucial to estimate the
uncertainties in the calculated abundances and compare them with the observed
abundances and their uncertainties. Non linear amplification of the error and
bifurcation may limit the applicability of chemical models. Here we study such
effects on dense cloud chemistry. Method: Using a previously studied approach
to uncertainties based on the representation of rate coefficient errors as log
normal distributions, we attempted to apply our approach using as input a
variety of different elemental abundances from those studied previously. In
this approach, all rate coefficients are varied randomly within their log
normal (Gaussian) distribution, and the time-dependent chemistry calculated
anew many times so as to obtain good statistics for the uncertainties in the
calculated abundances. Results: Starting with so-called ``high-metal''
elemental abundances, we found bimodal rather than Gaussian like distributions
for the abundances of many species and traced these strange distributions to an
extreme sensitivity of the system to changes in the ratio of the cosmic ray
ionization rate zeta\_He for He and that for molecular hydrogen zeta\_H2. The
sensitivity can be so extreme as to cause a region of bistability, which was
subsequently found to be more extensive for another choice of elemental
abundances. To the best of our knowledge, the bistable solutions found in this
way are the same as found previously by other authors, but it is best to think
of the ratio zeta\_He/zeta\_H2 as a control parameter perpendicular to the
''standard'' control parameter zeta/n\_H.Comment: Accepted for publicatio
Probing the molecular environment using spin-resolved photoelectron spectroscopy.
Angle- and spin-resolved photoelectron spectroscopy with linearly and circularly polarized synchrotron radiation were used to study the electronic structure of model triatomic molecules, hydrogen sulfide, and carbonyl sulfide. The spin-polarization measurements of the molecular field split components of the S 2p photolines revealed a strong effect of the different molecular environments. The validity of simple atomic models to explain the results is discussed
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