690 research outputs found
Hoping to Help: The Promises and Pitfalls of Global Health Volunteering
Volunteers and the organizations that send them for short periods to poorer countries often describe the trips as “missions” or “brigades.” Both words describe organized, purposeful ventures to accomplish a goal. “Mission” has been used in religious contexts; “brigade” is primarily a military term. In whatever use, both words denote a group with a purpose, a calling, and a common cause.
What I am exploring here is the purpose of these missions and brigades and whether these hundreds of weekly arrivals really bring hope (or housing or health benefits) to Haiti or to the thousands of other poor communities around the world that receive international volunteers every year. It may seem obvious that the goal is to accomplish good for the communities visited, to “make a difference,” and often to “give back.” Whether this actually happens, and what other objectives might be involved in these volunteer trips, is rarely considered. These issues motivate this book. Do volunteers help or hurt? In what ways? Can these missions be handled more effectively
Forecasting Volatility of Dhaka Stock Exchange: Linear Vs Non-linear Models
Prior information about a financial market is very essential for investor to invest money on parches share from the stock market which can strengthen the economy. The study examines the relative ability of various models to forecast daily stock indexes future volatility. The forecasting models that employed from simple to relatively complex ARCH-class models. It is found that among linear models of stock indexes volatility, the moving average model ranks first using root mean square error, mean absolute percent error, Theil-U and Linex loss function criteria. We also examine five nonlinear models. These models are ARCH, GARCH, EGARCH, TGARCH and restricted GARCH models. We find that nonlinear models failed to dominate linear models utilizing different error measurement criteria and moving average model appears to be the best. Then we forecast the next two months future stock index price volatility by the best (moving average) model
MultiFit: a web server for fitting multiple protein structures into their electron microscopy density map
Advances in electron microscopy (EM) allow for structure determination of large biological assemblies at increasingly higher resolutions. A key step in this process is fitting multiple component structures into an EM-derived density map of their assembly. Here, we describe a web server for this task. The server takes as input a set of protein structures in the PDB format and an EM density map in the MRC format. The output is an ensemble of models ranked by their quality of fit to the density map. The models can be viewed online or downloaded from the website. The service is available at; http://salilab.org/multifit/ and http://bioinfo3d.cs.tau.ac.il/
The investigation of absolute proper motions of the XPM Catalogue
The XPM-1.0 is the regular version of the XPM catalogue. In comparison with
XPM the astrometric catalogue of about 280 millions stars covering entire sky
from -90 to +90 degrees in declination and in the magnitude range 10^m<B<22^m
is something improved. The general procedure steps were followed as for XPM,
but some of them are now performed on a more sophisticated level. The XPM-1.0
catalogue contains star positions, proper motions, 2MASS and USNO photometry of
about 280 millions of the sources. We present some investigations of the
absolute proper motions of XPM-1.0 catalogue and also the important information
for the users of the catalogue. Unlike previous version, the XPM-1.0 contains
the proper motions over the whole sky without gaps. In the fields, which cover
the zone of avoidance or which contain less than of 25 galaxies a quasi
absolute calibration was performed. The proper motion errors are varying from 3
to 10 mas/yr, depending on a specific field. The zero-point of the absolute
proper motion frame (the absolute calibration) was specified with more than 1
million galaxies from 2MASS and USNO-A2.0. The mean formal error of absolute
calibration is less than 1 mas/yr.Comment: 11 pages, 9 figures, accepte
Memberships and CM Diagrams of the Open Cluster NGC 7243
The results of astrometric and photometric investigations of the open cluster
NGC 7243 are presented. Proper motions of 2165 stars with root-mean-square
error of 1.1 mas/yr were obtained by means of PDS scanning of astrometric
plates covering the time interval of 97 years. A total of 211 cluster members
down to V=15.5 mag have been identified. V and B magnitudes have been
determined for 2118 and 2110 stars respectively. Estimations of mass (348Mo < M
< 522Mo), age (t=2.5x10^8 yr), distance (r=698 pc) and reddening (E(B-V)=0.24)
of the cluster NGC 7243 have been made.Comment: 24 pages, 15 figures. Submitted to Astronomy and Astrophysic
Cosmic Optical Background: the View from Pioneer 10/11
We present the new constraints on the cosmic optical background (COB)
obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter (IPP)
data. After careful examination of data quality, the usable measurements free
from the zodiacal light are integrated into sky maps at the blue (~0.44 um) and
red (~0.64 um) bands. Accurate starlight subtraction is achieved by referring
to all-sky star catalogs and a Galactic stellar population synthesis model down
to 32.0 mag. We find that the residual light is separated into two components:
one component shows a clear correlation with thermal 100 um brightness, while
another betrays a constant level in the lowest 100 um brightness region.
Presence of the second component is significant after all the uncertainties and
possible residual light in the Galaxy are taken into account, thus it most
likely has the extragalactic origin (i.e., the COB). The derived COB brightness
is (1.8 +/- 0.9) x 10^(-9) and (1.2 +/- 0.9) x 10^(-9) erg/s/cm2/sr/A at the
blue and red band, respectively, or 7.9 +/- 4.0 and 7.7 +/- 5.8 nW/m2/sr. Based
on a comparison with the integrated brightness of galaxies, we conclude that
the bulk of the COB is comprised of normal galaxies which have already been
resolved by the current deepest observations. There seems to be little room for
contributions of other populations including "first stars" at these
wavelengths. On the other hand, the first component of the IPP residual light
represents the diffuse Galactic light (DGL) - scattered starlight by the
interstellar dust. We derive the mean DGL-to-100 um brightness ratios of 2.1 x
10^(-3) and 4.6 x 10^(-3) at the two bands, which are roughly consistent with
the previous observations toward denser dust regions. Extended red emission in
the diffuse interstellar medium is also confirmed.Comment: Accepted for publication in the Astrophysical Journal; Typos
correcte
A low luminosity state in the massive X-ray binary SAX J0635+0533
The X-ray pulsar SAX J0635+0533 was repeatedly observed with the XMM-Newton
satellite in 2003-2004. The precise localization provided by these observations
confirms the association of SAX J0635+0533 with a Be star. The source was
found, for the first time, in a low intensity state, a factor ~30 lower than
that seen in all previous observations. The spectrum, well fitted by an
absorbed power law with photon index ~1.7 and N_H = 1.2x10^22 cm^-2, was
compatible with that of the high state. The low flux did not allow the
detection of the pulsations at 33.8 ms seen BeppoSAX and RXTE data. In view of
the small luminosity observed in 2003-2004, we reconsider the peculiarities of
this source in both the accretion and rotation powered scenarios.Comment: Accepted for publication on Astronomy and Astrophysic
Pictor A (PKS 0518-45) - From Nucleus to Lobes
We present radio and optical imaging and kinematic data for the radio galaxy
Pictor A, including HST continuum and [OIII], emission-line images (at a
resolution of 25 - 100 mas) and ground-based imaging and spectroscopy (at a
resolution of ~ 1.5". The radio data include 3 cm Australia Telescope images of
the core, at a resolution comparable to that of the optical, ground-based
images, and a VLBI image of a jet in the compact core (at a resolution of 2 -
25 mas), which seems to align with a continuum ``jet'' found in the HST images.
The core radio jet, the HST optical continuum ``jet'', and the NW H-alpha
filaments all appear to point toward the optical-synchrotron hot-spot in the NW
lobe of this object and are associated with a disrupted velocity field in the
extended ionized gas. The ground-based spectra which cover this trajectory also
yield line ratios for the ionized gas which have anomalously low [NII] (6564),
suggesting either a complex, clumpy structure in the gas with a higher
cloud-covering factor at larger radii and with denser clouds than is found in
the nuclear regions of most NLRG and Seyfert 2 galaxies, or some other,
unmodeled, mechanism for the emergent spectrum from this region. The H-alpha
emission-line filaments to the N appear to be associated with a 3 cm radio
continuum knot which lies in a gap in the filaments ~ 4" from the nucleus.
Altogether, the data in this paper provide good circumstantial evidence for
non-disruptive redirection of a radio jet by interstellar gas clouds in the
host galaxy.Comment: 19 pages, 6 ps.gz fig pages, to appear in the Ap.J. Supp
Constraining the optical emission from the double pulsar system J0737-3039
We present the first optical observations of the unique system J0737-3039
(composed of two pulsars, hereafter PSR-A and PSR-B). Ultra-deep optical
observations, performed with the High Resolution Camera of the Advanced Camera
for Surveys on board the Hubble Space Telescope could not detect any optical
emission from the system down to m_F435W=27.0 and m_F606W=28.3. The estimated
optical flux limits are used to constrain the three-component (two thermal and
one non-thermal) model recently proposed to reproduce the XMM-Newton X-ray
spectrum. They suggest the presence of a break at low energies in the
non-thermal power law component of PSR-A and are compatible with the expected
black-body emission from the PSR-B surface. The corresponding efficiency of the
optical emission from PSR-A's magnetosphere would be comparable to that of
other Myr-old pulsars, thus suggesting that this parameter may not dramatically
evolve over a time-scale of a few Myr.Comment: 16 pages, 3 figures, ApJ accepte
The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant
We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at
Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young
oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the
resultant data cube, we have been able to reconstruct the full 3D structure of
the system of [O III] filaments. The majority of the ejecta form a ring of
~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We
conclude that SNR N132D is approaching the end of the reverse shock phase
before entering the fully thermalized Sedov phase of evolution. We speculate
that the ring of oxygen-rich material comes from ejecta in the equatorial plane
of a bipolar explosion, and that the overall shape of the SNR is strongly
influenced by the pre-supernova mass loss from the progenitor star. We find
tantalizing evidence of a polar jet associated with a very fast oxygen-rich
knot, and clear evidence that the central star has interacted with one or more
dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8
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