1,116 research outputs found
Resection Margins for Colorectal Metastases to The Liver: Do They Make A Difference?
Objective: The authors determined an appropriate surgical treatment for liver metastases from
colorectal cancers. Clinicopathologic featuresof metastatic lesions of colorectal cancers
were studied
The metallicity range of variables in M3
The recently published spectroscopic metallicities of RR Lyrae stars in M3
(Sandstrom, K., Pilachowski, C. A., and Saha, A. 2001, AJ 122, 3212) though
show a relatively wide range of the [Fe/H] values, the conclusion that no
metallicity spread is real has been drawn, as no dependence on either minimum
temperature or period was detected. Comparing these spectroscopic metallicities
with [Fe/H] calculated from the Fourier parameters of the light curves of the
variables a correlation between the [Fe/H] values appears. As a consequence of
the independence of the spectroscopic and photometric metallicities, this
correlation points to the reality of a metallicity spread. The absolute
magnitudes of these stars follow a similar trend along both the spectroscopic
and photometric metallicities as the general relation
predicts, which strengthens that the detected metallicity range is real.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Dust in the diffuse ISM as revealed by DIRBE observations
The weekly averaged DIRBE full sky images have been processed to separate the various components contributing to the total brightness in the various bands. The zodiacal emission, which dominates at 12 and 25 μm and the zodiacal dust scattering at λ<5 μm are both accounted for using an empirical fit to the data. The diffuse stellar emission which dominates at λ<5 μm is determined using the shortest DIRBE photometric bands at 1.25 and 2.2 μm and a standard NIR extinction law. Preliminary results based on the first release of the DIRBE data have been presented in Bernard et al. 1994. When the zodiacal light and stellar emission are subtracted, significant emission remains above 2.2 μm, which follows the general distribution of the dust emission as seen in the IRAS bands. The DIRBE images therefore allow to extend our knowledge of the dust emission spectrum below 12 μm and above 100 μm. In the L(3.5 μm) and M(4.9 μm) bands, the dust emission can be seen not only toward the galactic plane but also in diffuse regions above the plane as well as toward closeby molecular complexes (ρ‐Ophiuchi, Orion, Taurus,...). The existence of NIR dust emission in cold and diffuse regions strongly suggests transiently heated small dust particles as the carrier. The dust NIR spectrum is generally consistent with the dust model of Désert et al. 1990. In particular, the dust emission increases from 4.9 to 3.5 μm, which can be attributed to the contribution of the 3.3 μm emission feature of Polycyclic Aromatic Hydrocarbons (PAH). Significant continuum emission, or other feature emission, is also required to explain the observed brightness in the L band and the AROME ballon experiment results at low galactic latitude
Dark gas in the solar neighnorhood from extinction data
When modeling infrared or gamma-ray data as a linear combination of observed
gas tracers, excess emission has been detected compared to expectations from
known neutral and atomic gas as traced by HI and CO measurements, respectively.
This excess might correspond to an additional gas component. This so-called
"dark gas" (DG) has been observed in our Galaxy, as well as the Magellanic
Clouds. For the first time, we investigate the correlation between visible
extinction (Av) data and gas tracers on large scales in the solar neighborhood.
Our work focuses on both the solar neighborhood (|b|>10\degr), and the inner
and outer Galaxy, as well as on four individual regions: Taurus, Orion,
Cepheus-Polaris and Aquila-Ophiuchus. Thanks to the recent production of an
all-sky Av map, we first perform the correlation between Av and both HI and CO
emission over the most diffuse regions, to derive the optimal (Av/NH)^(ref)
ratio. We then iterate the analysis over the entire regions to estimate the
CO-to-H2 conversion factor as well as the DG mass fraction. The average
extinction to gas column-density ratio in the solar neighborhood is found to be
(Av/NH)^(ref)=6.53 10^(-22) mag. cm^2, with significant differences between the
inner and outer Galaxy. We derive an average XCO value of 1.67 10^(20) H2
cm^(-2)/(K km s^(-1)). In the solar neighborhood, the gas mass in the dark
component is found to be 19% relative to that in the atomic component and
164 relative to the one traced by CO. These results are compatible with the
recent analysis using Planck data within the uncertainties of our measurements.
We estimate the ratio of dark gas to total molecular gas to be 0.62 in the
solar neighborhood. The HI-to-H2 and H2-to-CO transitions appear for Av
0.2 mag and Av mag, respectively, in agreement with
theoretical models of dark-H2 gas.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in A&A (in
press
Low Energy Leptogenesis in Left-Right Symmetric Models
We propose a new mechanism for baryogenesis. We study the effective potential
of left-right extension of the standard model and show that there can be a
first order phase transition at the left-right symmetry breaking and hence
symmetry breaking scale, which is around TeV in our scenario. As a
result, although violating interactions are in equilibrium at this
scale, enough asymmetry may be generated. This asymmetry is
then converted to baryon asymmetry during the anomalous electroweak process. If
right handed gauge bosons are seen in the TeV scale, then we argue that this
will be the only consistent mechanism to generate baryon asymmetry of the
universe.Comment: 16 pages (Latex file) - 1 postscript figure appende
Persistent spins in the linear diffusion approximation of phase ordering and zeros of stationary gaussian processes
The fraction r(t) of spins which have never flipped up to time t is studied
within a linear diffusion approximation to phase ordering. Numerical
simulations show that, even in this simple context, r(t) decays with time like
a power-law with a non-trival exponent which depends on the space
dimension. The local dynamics at a given point is a special case of a
stationary gaussian process of known correlation function and the exponent
is shown to be determined by the asymptotic behavior of the
probability distribution of intervals between consecutive zero-crossings of
this process. An approximate way of computing this distribution is proposed, by
taking the lengths of the intervals between successive zero-crossings as
independent random variables. The approximation gives values of the exponent
in close agreement with the results of simulations.Comment: 10 pages, 2 postscript files. Submitted to PRL. Reference screwup
correcte
Exact first-passage exponents of 1D domain growth: relation to a reaction diffusion model
In the zero temperature Glauber dynamics of the ferromagnetic Ising or
-state Potts model, the size of domains is known to grow like .
Recent simulations have shown that the fraction of spins which have
never flipped up to time decays like a power law with a non-trivial dependence of the exponent on
and on space dimension. By mapping the problem on an exactly soluble
one-species coagulation model (), we obtain the exact
expression of in dimension one.Comment: latex,no figure
Can We Trust the Dust? Evidence of Dust Segregation in Molecular Clouds
Maps of estimated dust column density in molecular clouds are usually assumed
to reliably trace the total gas column density structure. In this work we
present results showing a clear discrepancy between the dust and the gas
distribution in the Taurus molecular cloud complex. We compute the power
spectrum of a 2MASS extinction map of the Taurus region and find it is much
shallower than the power spectrum of a 13CO map of the same region previously
analyzed. This discrepancy may be explained as the effect of grain growth on
the grain extinction efficiency. However, this would require a wide range of
maximum grain sizes, which is ruled out based on constraints from the
extinction curve and the available grain models. We show that major effects due
to CO formation and depletion are also ruled out. Our result may therefore
suggest the existence of intrinsic spatial fluctuations of the dust to gas
ratio, with amplitude increasing toward smaller scales. Preliminary results of
numerical simulations of trajectories of inertial particles in turbulent flows
illustrate how the process of clustering of dust grains by the cloud turbulence
may lead to observable effects. However, these results cannot be directly
applied to large scale supersonic and magnetized turbulence at present.Comment: 10 pages, 8 figures included, ApJ, in pres
- …