160 research outputs found
P/2010A2 LINEAR - I: An impact in the Asteroid Main Belt
Comet P/2010A2 LINEAR is a good candidate for membership with the Main Belt
Comet family. It was observed with several telescopes (ESO NTT, La Silla;
Gemini North, Mauna Kea; UH 2.2m, Mauna Kea) from 14 Jan. until 19 Feb. 2010 in
order to characterize and monitor it and its very unusual dust tail, which
appears almost fully detached from the nucleus; the head of the tail includes
two narrow arcs forming a cross. The immediate surroundings of the nucleus were
found dust-free, which allowed an estimate of the nucleus radius of 80-90m. A
model of the thermal evolution indicates that such a small nucleus could not
maintain any ice content for more than a few million years on its current
orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up
and electrostatic dust levitations were also rejected, leaving an impact with a
smaller body as the favoured hypothesis, and ruling out the cometary nature of
the object.
The impact is further supported by the analysis of the tail structure.
Finston-Probstein dynamical dust modelling indicates the tail was produced by a
single burst of dust emission. More advanced models, independently indicate
that this burst populated a hollow cone with a half-opening angle alpha~40degr
and with an ejection velocity v_max ~ 0.2m/s, where the small dust grains fill
the observed tail, while the arcs are foreshortened sections of the burst cone.
The dust grains in the tail are measured to have radii between a=1-20mm, with a
differential size distribution proportional to a^(-3.44 +/- 0.08). The dust
contained in the tail is estimated to at least 8x10^8kg, which would form a
sphere of 40m radius. Analysing these results in the framework of crater
physics, we conclude that a gravity-controlled crater would have grown up to
~100m radius, i.e. comparable to the size of the body. The non-disruption of
the body suggest this was an oblique impact.Comment: 15 pages, 11 figures, in pres
Testing the Standard Model and Schemes for Quark Mass Matrices with CP Asymmetries in B Decays
The values of and , where and
are angles of the unitarity triangle, will be readily measured in a B
factory (and maybe also in hadron colliders). We study the standard model
constraints in the plane. We use the results
from recent analyses of and which take into account
heavy quark symmetry considerations. We find and
most likely \sin (2 \beta) \roughly{>} 0.6, and emphasize the strong
correlations between and . Various schemes
for quark mass matrices allow much smaller areas in the plane. We study the schemes of Fritzsch, of Dimopoulos, Hall and
Raby, and of Giudice, as well as the ``symmetric CKM'' idea, and show how CP
asymmetries in B decays will crucially test each of these schemes.Comment: 11 pages and 4 postscript figures available on request, LaTeX,
WIS-92/52/Jun-PH, LBL-3256
29P/Schwassmann-Wachmann: A Rosetta Stone for Amorphous Water Ice and CO <-> CO2 Conversion in Centaurs and Comets?
Centaur 29P/Schwassmann-Wachmann 1 (SW1) is a highly active object orbiting
in the transitional Gateway region (Sarid et al. 2019) between the Centaur and
Jupiter Family Comet regions. SW1 is unique among the Centaurs in that it
experiences quasi-regular major outbursts and produces CO emission
continuously; however, the source of the CO is unclear. We argue that due to
its very large size (approx. 32 km radius), SW1 is likely still responding, via
amorphous water ice (AWI) conversion to crystalline water ice (CWI), to the
rapid change in its external thermal environment produced by its dynamical
migration from the Kuiper belt to the Gateway Region at the inner edge of the
Centaur region at 6 au. It is this conversion process that is the source of the
abundant CO and dust released from the object during its quiescent and outburst
phases. If correct, these arguments have a number of important predictions
testable via remote sensing and in situ spacecraft characterization, including:
the quick release on Myr timescales of CO from AWI conversion for any few
km-scale scattered disk KBO transiting into the inner system; that to date SW1
has only converted between 50 to 65% of its nuclear AWI to CWI; that volume
changes upon AWI conversion could have caused subsidence and cave-ins, but not
significant mass wasting or crater loss on SW1; that SW1s coma should contain
abundant amounts of CWI CO2-rich icy dust particles; and that when SW1 transits
into the inner system within the next 10,000 years, it will be a very different
kind of JFC comet.Comment: 29 Pages, 3 Figures, 2 Tables, accepted 16-Sept-2022 by the Planetary
Science Journal Corrected proof version 26-Oct-202
Neutrino Anomalies in Gauge Mediated Model with Trilinear R violation
The structure of neutrino masses and mixing resulting from trilinear
violating interactions is studied in the presence of the gauge mediated
supersymmetry breaking. Neutrino masses arise in this model at tree level
through the RG-induced vacuum expectation values of the sneutrinos and also
through direct contribution at 1-loop. The relative importance of these
contributions is determined by the values of the strong and weak coupling
constants. In case of purely couplings, the tree contribution
dominates over the 1-loop diagram. In this case, one simultaneously obtains
atmospheric neutrino oscillations and quasi-vacuum oscillations of the solar
neutrinos if all the \l' couplings are assumed to be of similar magnitudes.
If R parity violation arises from the trilinear \l couplings, then the loop
induced contribution dominates over the tree level. One cannot simultaneously
explain the solar and atmospheric deficit in this case if all the \l
couplings are of similar magnitude. This however becomes possible with
hierarchical \l and we give a specific example of this.Comment: 26 pages Latex, 2 figures, certain sections rewritten, improved
discussion about derivations added. To appear in Physical Review
The Astropy Problem
The Astropy Project (http://astropy.org) is, in its own words, "a community
effort to develop a single core package for Astronomy in Python and foster
interoperability between Python astronomy packages." For five years this
project has been managed, written, and operated as a grassroots,
self-organized, almost entirely volunteer effort while the software is used by
the majority of the astronomical community. Despite this, the project has
always been and remains to this day effectively unfunded. Further, contributors
receive little or no formal recognition for creating and supporting what is now
critical software. This paper explores the problem in detail, outlines possible
solutions to correct this, and presents a few suggestions on how to address the
sustainability of general purpose astronomical software
Maternal Perception of Reduced Fetal Movements Is Associated with Altered Placental Structure and Function
Maternal perception of reduced fetal movement (RFM) is associated with increased risk of stillbirth and fetal growth restriction (FGR). DFM is thought to represent fetal compensation to conserve energy due to insufficient oxygen and nutrient transfer resulting from placental insufficiency. To date there have been no studies of placental structure in cases of DFM.To determine whether maternal perception of reduced fetal movements (RFM) is associated with abnormalities in placental structure and function.Placentas were collected from women with RFM after 28 weeks gestation if delivery occurred within 1 week. Women with normal movements served as a control group. Placentas were weighed and photographs taken. Microscopic structure was evaluated by immunohistochemical staining and image analysis. System A amino acid transporter activity was measured as a marker of placental function. Placentas from all pregnancies with RFM (irrespective of outcome) had greater area with signs of infarction (3.5% vs. 0.6%; p<0.01), a higher density of syncytial knots (p<0.001) and greater proliferation index (p<0.01). Villous vascularity (p<0.001), trophoblast area (p<0.01) and system A activity (p<0.01) were decreased in placentas from RFM compared to controls irrespective of outcome of pregnancy.This study provides evidence of abnormal placental morphology and function in women with RFM and supports the proposition of a causal association between placental insufficiency and RFM. This suggests that women presenting with RFM require further investigation to identify those with placental insufficiency
Cytomegalovirus antibodies in dried blood spots: a minimally invasive method for assessing stress, immune function, and aging
<p>Abstract</p> <p>Background</p> <p>Cytomegalovirus (CMV) is a prevalent herpesvirus with links to both stress and aging. This paper describes and validates a minimally invasive method for assessing antibodies against CMV in finger stick whole blood spot samples for use as an indirect marker of an aspect of cell-mediated immunity.</p> <p>Results</p> <p>Analysis of CMV in dried blood spot samples (DBS) was based on modifications of a commercially available protocol for quantifying CMV antibodies in serum or plasma. The method was evaluated through analysis of precision, reliability, linearity, and correlation between matched serum and DBS samples collected from 75 volunteers. Correlation between DBS and plasma values was linear and high (Pearson correlation <it>R </it>= .96), and precision, reliability, and linearity of the DBS assay were within acceptable ranges.</p> <p>Conclusions</p> <p>The validity of a DBS assay for CMV antibodies will enable its inclusion in population-based surveys and other studies collecting DBS samples in non-clinical settings, increasing scientific understanding of the interaction of social and biological stress and immune function.</p
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