1,733 research outputs found
The Possible Interstellar Anion CH2CN-: Spectroscopic Constants, Vibrational Frequencies, and Other Considerations
It is hypothesized that the A ^1B_1 <- X ^1A' excitation into the
dipole-bound state of the cyanomethyl anion (CH2CN-) is proposed as the carrier
for one diffuse interstellar band. However, this particular molecular system
has not been detected in the interstellar medium even though the related
cyanomethyl radical and the isoelectronic ketenimine molecule have been found.
In this study we are employing the use of proven quartic force fields and
second-order vibrational perturbation theory to compute accurate spectroscopic
constants and fundamental vibrational frequencies for ^1A' CH2CN- in order to
assist in laboratory studies and astronomical observations
Diagrammatic Coupled Cluster Monte Carlo
We propose a modified coupled cluster Monte Carlo algorithm that
stochastically samples connected terms within the truncated
Baker--Campbell--Hausdorff expansion of the similarity transformed Hamiltonian
by construction of coupled cluster diagrams on the fly. Our new approach --
diagCCMC -- allows propagation to be performed using only the connected
components of the similarity-transformed Hamiltonian, greatly reducing the
memory cost associated with the stochastic solution of the coupled cluster
equations. We show that for perfectly local, noninteracting systems, diagCCMC
is able to represent the coupled cluster wavefunction with a memory cost that
scales linearly with system size. The favorable memory cost is observed with
the only assumption of fixed stochastic granularity and is valid for arbitrary
levels of coupled cluster theory. Significant reduction in memory cost is also
shown to smoothly appear with dissociation of a finite chain of helium atoms.
This approach is also shown not to break down in the presence of strong
correlation through the example of a stretched nitrogen molecule. Our novel
methodology moves the theoretical basis of coupled cluster Monte Carlo closer
to deterministic approaches.Comment: 31 pages, 6 figure
The effect of lens-induced anisometropia on sterolocalization
Little research has been done to study the effect of anisometropia on the ability of subjects to localize an object in space using binocular depth cues. Rendering a patient artificially anisometropic is similar to prescribing an unbalanced refraction or inducing anisometropia in a monovision contact lens fit. We investigated the effect of induced anisometropia on stereolocalization. Spectacle lenses were used to create the anisometropic conditions and all subjects were pretested for isometropia while wearing their best distance refractive corrections. Thirty-eight subjects judged the distance of a floating vectographic Quoit\u27s Ring target under varying amounts of anisometropia in a featureless field. The amounts of anisometropia induced ranged between 0.50 D and 1.75 D. The results indicate that there is no statistically significant difference in the ability to stereolocalize with up to 1.00 D of anisometropia, however, beyond this limit a statistically significant decrease in performance clearly exists
Determinants of Farm Productivity in Africa: A Synthesis of Four Case Studies
Productivity Analysis, Downloads July 2008 - July 2009: 20,
Vibrational Frequencies and Spectroscopic Constants for 1(sup 3)A' HNC and 1(sup 3)A' HOC+ from High-Accuracy Quartic Force Fields
The spectroscopic constants and vibrational frequencies for the 1(sup 3)A' states of HNC, DNC, HOC+, and DOC+ are computed and discussed in this work. The reliable CcCR quartic force field based on high-level coupled cluster ab initio quantum chemical computations is exclusively utilized to provide the anharmonic potential. Then, second order vibrational perturbation theory and vibrational configuration interaction methods are employed to treat the nuclear Schroedinger equation. Second-order perturbation theory is also employed to provide spectroscopic data for all molecules examined. The relationship between these molecules and the corresponding 1(sup 3)A' HCN and HCO+ isomers is further developed here. These data are applicable to laboratory studies involving formation of HNC and HOC+ as well as astronomical observations of chemically active astrophysical environments
The Velocity Distribution of the Nearest Interstellar Gas
The bulk flow velocity for the cluster of interstellar cloudlets within about
30 pc of the Sun is determined from optical and ultraviolet absorption line
data, after omitting from the sample stars with circumstellar disks or variable
emission lines and the active variable HR 1099. Ninety-six velocity components
towards the remaining 60 stars yield a streaming velocity through the local
standard of rest of -17.0+/-4.6 km/s, with an upstream direction of l=2.3 deg,
b=-5.2 deg (using Hipparcos values for the solar apex motion). The velocity
dispersion of the interstellar matter (ISM) within 30 pc is consistent with
that of nearby diffuse clouds, but present statistics are inadequate to
distinguish between a Gaussian or exponential distribution about the bulk flow
velocity. The upstream direction of the bulk flow vector suggests an origin
associated with the Loop I supernova remnant. Groupings of component velocities
by region are seen, indicating regional departures from the bulk flow velocity
or possibly separate clouds. The absorption components from the cloudlet
feeding ISM into the solar system form one of the regional features. The
nominal gradient between the velocities of upstream and downstream gas may be
an artifact of the Sun's location near the edge of the local cloud complex. The
Sun may emerge from the surrounding gas-patch within several thousand years.Comment: Typographical errors corrected; Five tables, seven figures;
Astrophysical Journal, in pres
High-Resolution Observations of Interstellar Ca I Absorption -- Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM ~ 0.3-1.5 km/s) spectra of interstellar Ca I
absorption toward 30 Galactic stars. Comparisons of the column densities of Ca
I, Ca II, K I, and other species -- for individual components identified in the
line profiles and also when integrated over entire lines of sight -- yield
information on relative electron densities and depletions. There is no obvious
relationship between the ratio N(Ca I)/N(Ca II) [equal to n_e/(Gamma/alpha_r)
for photoionization equilibrium] and the fraction of hydrogen in molecular form
f(H2) (often taken to be indicative of the local density n_H). For a smaller
sample of sightlines for which the thermal pressure (n_H T) and local density
can be estimated via analysis of the C I fine-structure excitation, the average
electron density inferred from C, Na, and K (assuming photoionization
equilibrium) seems to be independent of n_H and n_H T. While the n_e obtained
from the ratio N(Ca I)/N(Ca II) is often significantly higher than the values
derived from other elements, the patterns of relative n_e derived from
different elements show both similarities and differences for different lines
of sight -- suggesting that additional processes besides photoionization and
radiative recombination commonly and significantly affect the ionization
balance of heavy elements in diffuse IS clouds. Such additional processes may
also contribute to the (apparently) larger than expected fractional ionizations
(n_e/n_H) found for some lines of sight with independent determinations of n_H.
In general, inclusion of ``grain-assisted'' recombination does reduce the
inferred n_e, but it does not reconcile the n_e estimated from different
elements. The depletion of calcium may have a much weaker dependence on density
than was suggested by earlier comparisons with CH and CN.Comment: aastex, 70 pages, accepted to ApJ
Lifelong behavioral and neuropathological consequences of repetitive mild traumatic brain injury
Objective:
Exposure to repetitive concussion, or mild traumatic brain injury (mTBI), has been linked with increased risk of long-term neurodegenerative changes, specifically chronic traumatic encephalopathy (CTE). To date, preclinical studies largely have focused on the immediate aftermath of mTBI, with no literature on the lifelong consequences of mTBI in these models. This study provides the first account of lifelong neurobehavioral and histological consequences of repetitive mTBI providing unique insight into the constellation of evolving and ongoing pathologies with late survival.
Methods:
Male C57BL/6J mice (aged 2–3 months) were exposed to either single or repetitive mild TBI or sham procedure. Thereafter, animals were monitored and assessed at 24 months post last injury for measures of motor coordination, learning deficits, cognitive function, and anxiety-like behavior prior to euthanasia and preparation of the brains for detailed neuropathological and protein biochemical studies.
Results:
At 24 months survival animals exposed to r-mTBI showed clear evidence of learning and working memory impairment with a lack of spatial memory and vestibule-motor vestibulomotor deficits compared to sham animals. Associated with these late behavioral deficits there was evidence of ongoing axonal degeneration and neuroinflammation in subcortical white matter tracts. Notably, these changes were also observed after a single mTBI, albeit to a lesser degree than repetitive mTBI.
Interpretation:
In this context, our current data demonstrate, for the first time, that rather than an acute, time limited event, mild TBI can precipitate a lifelong degenerative process. These data therefore suggest that successful treatment strategies should consider both the acute and chronic nature of mTBI
An X-ray Selected Galaxy Cluster at z=1.26
We report the discovery of an X-ray luminous galaxy cluster at z=1.26.
RXJ0848.9+4452 was selected as an X-ray cluster candidate in the ROSAT Deep
Cluster Survey, on the basis of its spatial extent. Deep optical and near-IR
imaging have revealed a galaxy overdensity around the peak of the X-ray
emission, with a significant excess of red objects with J-K colors typical of
elliptical galaxies at z>1. Spectroscopic observations at the Keck II telescope
have secured 6 galaxy redshifts in the range 1.257=1.261), within
a 35 arcsec radius around the peak X-ray emission. This system lies only 4.2
arcmin away (5.0 h^{-1}_{50} comoving Mpc, q_0=0.5) from the galaxy cluster ClG
J0848+4453, which was identified by Stanford et al. (1997) at z=1.273 in a
near-IR field galaxy survey, and is also known to be X-ray luminous. Assuming
that the X-ray emission is entirely due to hot intra-cluster gas, both these
systems have similar rest frame luminosities L_x ~=1x10^{44} ergs/s (0.5-2.0
keV band). In combination with our spectrophotometric data for the entire 30
arcmin^2 field, this suggests the presence of a superstructure, consisting of
two collapsed, possibly virialized clusters, the first detected to date at z>1.Comment: To appear in The Astronomical Journal, 24 pages, 8 figures, 1 color
jpg plate (fig.7), see http://www.eso.org/~prosati/lynx/plate_fig7.jp
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