435 research outputs found
Constraints on Intervening Stellar Populations Toward the Large Magellanic Cloud
The suggestion by Zaritsky & Lin that a vertical extension of the red clump
feature in color-magnitude diagrams of the Large Magellanic Cloud (LMC) is
consistent with a significant population of foreground stars to the LMC that
could account for the observed microlensing optical depth has been challenged
by various investigators. We respond by (1) examining each of the challenges
presented and (2) presenting new photometric and spectroscopic data. We
conclude that although the CMD data do not mandate the existence of a
foreground population, they are entirely consistent with a foreground
population associated with the LMC that contributes significantly (~ 50%) to
the observed microlensing optical depth. From our new data, we conclude that <~
40% of the VRC stars are young, massive red clump stars because (1) synthetic
color-magnitude diagrams created using the star formation history derived
indepdently from HST data suggest that < 50% of the VRC stars are young,
massive red clump stars, (2) the angular distribution of the VRC stars is more
uniform than that of the young (age < 1 Gyr) main sequence stars, and (3) the
velocity dispersion of the VRC stars in the region of the LMC examined by ZL is
inconsistent with the expectation for a young disk population. Each of these
arguments is predicated on assumptions and the conclusions are uncertain.
Therefore, an exact determination of the contribution to the microlensing
optical depth by the various hypothesized foreground populations, and the
subsequent conclusions regarding the existence of halo MACHOs, requires a
detailed knowledge of many complex astrophysical issues, such as the IMF, star
formation history, and post-main sequence stellar evolution. (abridged)Comment: Scheduled for publication in AJ in May 199
An enrichment protocol and analysis pipeline for long read sequencing of the hepatitis B virus transcriptome
Hepatitis B virus (HBV) is one of the smallest human DNA viruses and its 3.2âKb genome encodes multiple overlapping open reading frames, making its viral transcriptome challenging to dissect. Previous studies have combined quantitative PCR and Next Generation Sequencing to identify viral transcripts and splice junctions, however the fragmentation and selective amplification used in short read sequencing precludes the resolution of full length RNAs. Our study coupled an oligonucleotide enrichment protocol with state-of-the-art long read sequencing (PacBio) to identify the repertoire of HBV RNAs. This methodology provides sequencing libraries where up to 25â% of reads are of viral origin and enable the identification of canonical (unspliced), non-canonical (spliced) and chimeric viral-human transcripts. Sequencing RNA isolated from de novo HBV infected cells or those transfected with 1.3âĂ overlength HBV genomes allowed us to assess the viral transcriptome and to annotate 5' truncations and polyadenylation profiles. The two HBV model systems showed an excellent agreement in the pattern of major viral RNAs, however differences were noted in the abundance of spliced transcripts. Viral-host chimeric transcripts were identified and more commonly found in the transfected cells. Enrichment capture and PacBio sequencing allows the assignment of canonical and non-canonical HBV RNAs using an open-source analysis pipeline that enables the accurate mapping of the HBV transcriptome
New Models for a Triaxial Milky Way Spheroid and Effect on the Microlensing Optical Depth to the Large Magellanic Cloud
We obtain models for a triaxial Milky Way spheroid based on data by Newberg
and Yanny. The best fits to the data occur for a spheroid center that is
shifted by 3kpc from the Galactic Center. We investigate effects of the
triaxiality on the microlensing optical depth to the Large Magellanic Cloud
(LMC). The optical depth can be used to ascertain the number of Massive Compact
Halo Objects (MACHOs); a larger spheroid contribution would imply fewer Halo
MACHOs. On the one hand, the triaxiality gives rise to more spheroid mass along
the line of sight between us and the LMC and thus a larger optical depth.
However, shifting the spheroid center leads to an effect that goes in the other
direction: the best fit to the spheroid center is_away_ from the line of sight
to the LMC. As a consequence, these two effects tend to cancel so that the
change in optical depth due to the Newberg/Yanny triaxial halo is at most 50%.
After subtracting the spheroid contribution in the four models we consider, the
MACHO contribution (central value) to the mass of the Galactic Halo varies from
\~(8-20)% if all excess lensing events observed by the MACHO collaboration are
assumed to be due to MACHOs. Here the maximum is due to the original MACHO
collaboration results and the minimum is consistent with 0% at the 1 sigma
error level in the data.Comment: 26 pages, 2 figures. v2: minor revisions. v3: expanded discussion of
the local spheroid density and minor revisions to match version published in
Journal of Cosmology and Astroparticle Physics (JCAP
Fully differential W' production and decay at next-to-leading order in QCD
We present the fully differential production and decay of a W' boson, with
arbitrary vector and axial-vector couplings, to any final state at
next-to-leading order in QCD. We demonstrate a complete factorization of
couplings at next-to-leading order in both the partial width of the W' boson,
and in the full two-to-two cross section. We provide numerical predictions for
the contribution of a W' boson to single-top-quark production, and separate
results based on whether the mass of the right-handed neutrino (nu_R) is light
enough for the leptonic decay channel to be open. The single-top-quark analysis
will allow for an improved direct W' mass limit of 525-550 GeV using data from
run I of the Fermilab Tevatron. We propose a modified tolerance method for
estimating parton distribution function uncertainties in cross sections.Comment: 23 pages, revtex3, 13 ps fig
An enrichment protocol and analysis pipeline for long read sequencing of the hepatitis B virus transcriptome
Hepatitis B virus (HBV) is one of the smallest human DNA viruses and its 3.2âKb genome encodes multiple overlapping open reading frames, making its viral transcriptome challenging to dissect. Previous studies have combined quantitative PCR and Next Generation Sequencing to identify viral transcripts and splice junctions, however the fragmentation and selective amplification used in short read sequencing precludes the resolution of full length RNAs. Our study coupled an oligonucleotide enrichment protocol with state-of-the-art long read sequencing (PacBio) to identify the repertoire of HBV RNAs. This methodology provides sequencing libraries where up to 25â% of reads are of viral origin and enable the identification of canonical (unspliced), non-canonical (spliced) and chimeric viral-human transcripts. Sequencing RNA isolated from de novo HBV infected cells or those transfected with 1.3âĂ overlength HBV genomes allowed us to assess the viral transcriptome and to annotate 5âČ truncations and polyadenylation profiles. The two HBV model systems showed an excellent agreement in the pattern of major viral RNAs, however differences were noted in the abundance of spliced transcripts. Viral-host chimeric transcripts were identified and more commonly found in the transfected cells. Enrichment capture and PacBio sequencing allows the assignment of canonical and non-canonical HBV RNAs using an open-source analysis pipeline that enables the accurate mapping of the HBV transcriptome
Ozone in the Pacific tropical troposphere from ozonesonde observations
Ozone vertical profile measurements obtained from ozonesondes flown at Fiji, Samoa, Tahiti, and the Galapagos are used to characterize ozone in the troposphere over the tropical Pacific. There is a significant seasonal variation at each of these sites. At sites in both the eastern and western Pacific, ozone mixing ratios are greatest at almost all levels in the troposphere during the SeptemberâNovember season and smallest during MarchâMay. The vertical profile has a relative maximum at all of the sites in the midtroposphere throughout the year (the largest amounts are usually found near the tropopause). This maximum is particularly pronounced during the SeptemberâNovember season. On average, throughout the troposphere, the Galapagos has larger ozone amounts than the western Pacific sites. A trajectory climatology is used to identify the major flow regimes that are associated with the characteristic ozone behavior at various altitudes and seasons. The enhanced ozone seen in the midtroposphere during SeptemberâNovember is associated with flow from the continents. In the western Pacific this flow is usually from southern Africa (although 10âday trajectories do not always reach the continent) but also may come from Australia and Indonesia. In the Galapagos the ozone peak in the midtroposphere is seen in flow from the South American continent and particularly from northern Brazil. High ozone concentrations within potential source regions and flow characteristics associated with the ozone mixing ratio peaks seen in both the western and eastern Pacific suggest that these enhanced ozone mixing ratios result from biomass burning. In the upper troposphere, low ozone amounts are seen with flow that originates in the convective western Pacific
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud
For seven years, the EROS-2 project obtained a mass of photometric data on
variable stars. We present a peculiar Cepheid-like star, in the direction of
the Small Magellanic Cloud, which demonstrates unusual photometric behaviour
over a short time interval. We report on data of the photometry acquired by the
MARLY telescope and spectroscopy from the EFOSC instrument for this star,
called EROS2 J005135-714459(sm0060n13842), which resembles the unusual Cepheid
HR 7308. The light curve of our target is analysed using the Analysis of
Variance method to determine a pulsational period of 5.5675 days. A fit of
time-dependent Fourier coefficients is performed and a search for proper motion
is conducted. The light curve exhibits a previously unobserved and spectacular
change in both mean magnitude and amplitude, which has no clear theoretical
explanation. Our analysis of the spectrum implies a radial velocity of 104 km
s and a metallicity of -0.40.2 dex. In the direction of right
ascension, we measure a proper motion of 17.46.0 mas yr using EROS
astrometry, which is compatible with data from the NOMAD catalogue. The nature
of EROS2 J005135-714459(sm0060n13842) remains unclear. For this star, we may
have detected a non-zero proper motion for this star, which would imply that it
is a foreground object. Its radial velocity, pulsational characteristics, and
photometric data, however, suggest that it is instead a Cepheid-like object
located in the SMC. In such a case, it would present a challenge to
conventional Cepheid models.Comment: Correction of typos in the abstrac
Pixel lensing observations towards globular clusters
It has been suggested that a monitoring program employing the pixel lensing
method to search for microlensing events towards galactic globular clusters may
increase the statistics and discriminate among different halo models.
Stimulated by this proposal, we evaluate an upper limit to the pixel lensing
event rate for such a survey. Four different dark halo models have been
considered changing both the flattening and the slope of the mass density
profile. The lenses mass function has been modelled as a homogenous power - law
for and both the mass limits and the slope of the mass
function have been varied to investigate their effect on the rate. The target
globular clusters have been selected in order to minimize the disk contribution
to the event rate. We find that a pixel lensing survey towards globular
clusters is unable to discriminate among different halo models since the number
of detectable events is too small to allow any reliable statistical analysis.Comment: 10 pages, accepted for publication on A&
Foreign body granuloma in the anterior abdominal wall mimicking an acute appendicular lump and induced by a translocated copper-T intrauterine contraceptive device: a case report
<p>Abstract</p> <p>Introduction</p> <p>Intrauterine contraceptive devices may at times perforate and migrate to adjacent organs. Such uterine perforation usually passes unnoticed with development of potentially serious complications.</p> <p>Case presentation</p> <p>A 25-year-old woman of North Indian origin presented with an acute tender lump in the right iliac fossa. The lump was initially thought to be an appendicular lump and treated conservatively. Resolution of the lump was incomplete. On exploratory laparotomy, a hard suspicious mass was found in the anterior abdominal wall of the right iliac fossa. Wide excision and bisection of the mass revealed a copper-T embedded inside. Examination of the uterus did not show any evidence of perforation. The next day, the patient gave a history of past copper-T Intrauterine contraceptive device insertion.</p> <p>Conclusions</p> <p>Copper-T insertion is one of the simplest contraceptive methods but its neglect with inadequate follow-up may lead to uterine perforation and extra-uterine migration. Regular self-examination for the "threads" supplemented with abdominal X-ray and/or ultrasound in the follow-up may detect copper-T migration early. To the best of our knowledge, this is the first report of intrauterine contraceptive device migration to the anterior abdominal wall of the right iliac fossa.</p
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