3,161 research outputs found
Mid-Infrared Galaxy Morphology Along the Hubble Sequence
The mid-infrared emission from 18 nearby galaxies imaged with the IRAC
instrument on Spitzer Space Telescope samples the spatial distributions of the
reddening-free stellar photospheric emission and the warm dust in the ISM.
These two components provide a new framework for galaxy morphological
classification, in which the presence of spiral arms and their emission
strength relative to the starlight can be measured directly and with high
contrast. Four mid-infrared classification methods are explored, three of which
are based on quantitative global parameters (colors, bulge-to-disk ratio)
similar to those used in the past for optical studies; in this limited sample,
all correlate well with traditional B-band classification. We suggest reasons
why infrared classification may be superior to optical classification.Comment: ApJS (in press), Spitzer Space Telescope Special Issue; 13 pages,
LaTeX (or Latex, etc); Figure 1ab is large, color plate; full-resolution
plates in .pdf format available at
http://cfa-www.harvard.edu/irac/publications
Radial HI Profiles at the Periphery of Galactic Disks: The Role of Ionizing Background Radiation
Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in
the radial density profile at some distance from the center. Using 22 galaxies
with known HI distributions as an example, we discuss the question of whether
this effect can be associated exclusively with external ionizing radiation, as
is commonly assumed. We show that before the surface density reaches
(the same for
galaxies of different types), it is hard to expect the gas to be fully ionized
by background radiation. For two of 13 galaxies with a sharp drop in the HI
profile, the "steepening" can actually be caused by ionization. At the same
time, for the remaining galaxies, the observed cutoff in the radial HI profile
is closer to the center than if it was a consequence of ionization by
background radiation and, therefore, it should be caused by other factors.Comment: 15 pages, 6 figure
"Hospital utilization by Mexican migrants returning to Mexico due to health needs"
<p>Abstract</p> <p>Background</p> <p>A total of 12.7 million Mexicans reside as migrants in the United States, of whom only 45% have health insurance in this country while access to health insurance by migrants in Mexico is fraught with difficulties. Health insurance has been shown to impact the use of health care in both countries. This paper quantifies hospitalizations by migrants who return from the US seeking medical care in public and private hospitals in the US-Mexico border area and in communities of origin. The proportion of bed utilization and the proportion of hospitalizations in Mexico out of the total expected by migrants in the US were estimated.</p> <p>Methods</p> <p>The universe included 48 Ministry of Health and 47 private hospitals serving municipalities of high or very high migration in Mexico, where 17% of remittance-receiving households are located, as well as 15 public and 159 private hospitals in 10 Mexican cities along the border with the US. Hospitals were sampled through various methods to include 27% of beds. Patients and staff were interviewed and data triangulated to quantify migrants that returned to Mexico seeking medical care. Official hospital discharge statistics and secondary data from migration databases and published statistics were analyzed to identify bed occupancy, general migrant hospitalization rates and the size of the migrant population that maintains close relationships with households in communities of origin.</p> <p>Results</p> <p>Up to 1609 migrants were admitted to public hospitals (76.6%) and 492 to private hospitals (23.4%) serving municipalities of high and very high migration intensity in 2008. Up to 0.90% of public hospital capacity was used. In the border area up to 908 and 2416 migrants were admitted to public (27.3%) and private (72.7%) hospitals, respectively. Up to 1.18% of public hospital capacity was used. Between 2.4% and 20.4% of the expected hospitalization needs of migrants with dependent households are satisfied through these services. The most common diagnostic categories mentioned across hospitals were traumatisms, complications of diabetes and elective surgery, in that order. Private hospitals mention elective surgeries as the main diagnostic category followed by complications of diabetes.</p> <p>Conclusions</p> <p>Hospitals in communities of origin in Mexico are devoting few resources to respond to hospitalization needs of migrants in the US. Currently no hospital programs exist to stimulate migrant demand or to cater to their specific needs. Registering migratory history in clinical and administrative records can be readily implemented. Developing bi-national referral networks and insuring migrants in the US within current Mexican federal programs could greatly increase migrant access to hospitals.</p
Analytic models and forward scattering from accelerator to cosmic-ray energies
Analytic models for hadron-hadron scattering are characterized by analytical
parametrizations for the forward amplitudes and the use of dispersion relation
techniques to study the total cross section and the
parameter. In this paper we investigate four aspects related to the application
of the model to and scattering, from accelerator to cosmic-ray
energies: 1) the effect of different estimations for from
cosmic-ray experiments; 2) the differences between individual and global
(simultaneous) fits to and ; 3) the role of the
subtraction constant in the dispersion relations; 4) the effect of distinct
asymptotic inputs from different analytic models. This is done by using as a
framework the single Pomeron and the maximal Odderon parametrizations for the
total cross section. Our main conclusions are the following: 1) Despite the
small influence from different cosmic-ray estimations, the results allow us to
extract an upper bound for the soft pomeron intercept: ;
2) although global fits present good statistical results, in general, this
procedure constrains the rise of ; 3) the subtraction constant as
a free parameter affects the fit results at both low and high energies; 4)
independently of the cosmic-ray information used and the subtraction constant,
global fits with the odderon parametrization predict that, above GeV, becomes greater than , and
this result is in complete agreement with all the data presently available. In
particular, we infer at GeV and
at 500 GeV (BNL RHIC energies).Comment: 16 pages, 7 figures, aps-revtex, wording changes, corrected typos, to
appear in Physical Review
The Bacterial Chemotactic Response Reflects a Compromise Between Transient and Steady State Behavior
Swimming bacteria detect chemical gradients by performing temporal
comparisons of recent measurements of chemical concentration. These comparisons
are described quantitatively by the chemotactic response function, which we
expect to optimize chemotactic behavioral performance. We identify two
independent chemotactic performance criteria: in the short run, a favorable
response function should move bacteria up chemoattractant gradients, while in
the long run, bacteria should aggregate at peaks of chemoattractant
concentration. Surprisingly, these two criteria conflict, so that when one
performance criterion is most favorable, the other is unfavorable. Since both
types of behavior are biologically relevant, we include both behaviors in a
composite optimization that yields a response function that closely resembles
experimental measurements. Our work suggests that the bacterial chemotactic
response function can be derived from simple behavioral considerations, and
sheds light on how the response function contributes to chemotactic
performance.Comment: 19 pages, 5 figure
UV-Optical Pixel Maps of Face-On Spiral Galaxies -- Clues for Dynamics and Star Formation Histories
UV and optical images of the face-on spiral galaxies NGC 6753 and NGC 6782
reveal regions of strong on-going star formation that are associated with
structures traced by the old stellar populations. We make NUV--(NUV-I) pixel
color-magnitude diagrams (pCMDs) that reveal plumes of pixels with strongly
varying NUV surface brightness and nearly constant I surface brightness. The
plumes correspond to sharply bounded radial ranges, with (NUV-I) at a given NUV
surface brightness being bluer at larger radii. The plumes are parallel to the
reddening vector and simple model mixtures of young and old populations, thus
neither reddening nor the fraction of the young population can produce the
observed separation between the plumes. The images, radial surface-brightness,
and color plots indicate that the separate plumes are caused by sharp declines
in the surface densities of the old populations at radii corresponding to disk
resonances. The maximum surface brightness of the NUV light remains nearly
constant with radius, while the maximum I surface brightness declines sharply
with radius. An MUV image of NGC 6782 shows emission from the nuclear ring. The
distribution of points in an (MUV-NUV) vs. (NUV-I) pixel color-color diagram is
broadly consistent with the simple mixture model, but shows a residual trend
that the bluest pixels in (MUV-NUV) are the reddest pixels in (NUV-I). This may
be due to a combination of red continuum from late-type supergiants and [SIII]
emission lines associated with HII regions in active star-forming regions. We
have shown that pixel mapping is a powerful tool for studying the distribution
and strength of on-going star formation in galaxies. Deep, multi-color imaging
can extend this to studies of extinction, and the ages and metallicities of
composite stellar populations in nearby galaxies.Comment: LaTeX with AASTeX style file, 29 pages with 12 figures (some color,
some multi-part). Accepted for publication in The Astrophysical Journa
Cultivo do milho em sistema de corte e trituração da capoeira na região Nordeste do Pará efeito da época do preparo de área.
bitstream/item/48947/1/Boletim-PD-19-AMAZ-ORIENTAL.pd
The Distribution of Bar and Spiral Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamental property
of the galaxy population that has only begun to be explored. We have applied
the bar/spiral separation method of Buta, Block, and Knapen to derive the
distribution of maximum relative gravitational bar torques, Q_b, for 147 spiral
galaxies in the statistically well-defined Ohio State University Bright Galaxy
Survey (OSUBGS) sample. Our goal is to examine the properties of bars as
independently as possible of their associated spirals. We find that the
distribution of bar strength declines smoothly with increasing Q_b, with more
than 40% of the sample having Q_b <= 0.1. In the context of recurrent bar
formation, this suggests that strongly-barred states are relatively short-lived
compared to weakly-barred or non-barred states. We do not find compelling
evidence for a bimodal distribution of bar strengths. Instead, the distribution
is fairly smooth in the range 0.0 <= Q_b < 0.8. Our analysis also provides a
first look at spiral strengths Q_s in the OSU sample, based on the same torque
indicator. We are able to verify a possible weak correlation between Q_s and
Q_b, in the sense that galaxies with the strongest bars tend also to have
strong spirals.Comment: Accepted for publication in the Astronomical Journal, August 2005
issue (LaTex, 23 pages + 11 figures, uses aastex.cls
Hadronic Cross-sections in two photon Processes at a Future Linear Collider
In this note we address the issue of measurability of the hadronic
cross-sections at a future photon collider as well as for the two-photon
processes at a future high energy linear collider. We extend, to
higher energy, our previous estimates of the accuracy with which the \gamgam\
cross-section needs to be measured, in order to distinguish between different
theoretical models of energy dependence of the total cross-sections. We show
that the necessary precision to discriminate among these models is indeed
possible at future linear colliders in the Photon Collider option. Further we
note that even in the option a measurement of the hadron production
cross-section via \gamgam processes, with an accuracy necessary to allow
discrimination between different theoretical models, should be possible. We
also comment briefly on the implications of these predictions for hadronic
backgrounds at the future TeV energy collider CLIC.Comment: 20 pages, 5 figures, LaTeX. Added an acknowledgemen
Fine Structure Discussion of Parity-Nonconserving Neutron Scattering at Epithermal Energies
The large magnitude and the sign correlation effect in the parity
non-conserving resonant scattering of epithermal neutrons from Th is
discussed in terms of a non-collective local doorway model. General
conclusions are drawn as to the probability of finding large parity violation
effects in other regions of the periodic table.Comment: 6 pages, Tex. CTP# 2296, to appear in Z. Phys.
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