12,233 research outputs found
The Scattered Disk as the source of the Jupiter Family comets
The short period Jupiter family comets (JFCs) are thought to originate in the
Kuiper Belt; specifically, a dynamical subclass of the Kuiper Belt known as the
`scattered disk' is argued to be the dominant source of JFCs. However, the best
estimates from observational surveys indicate that this source may fall short
by more than two orders of magnitude the estimates obtained from theoretical
models of the dynamical evolution of Kuiper belt objects into JFCs. We
re-examine the scattered disk as a source of the JFCs and make a rigorous
estimate of the discrepancy. We find that the uncertainties in the dynamical
models combined with a change in the size distribution function of the
scattered disk at faint magnitudes (small sizes) beyond the current
observational limit offer a possible but problematic resolution to the
discrepancy. We discuss several other possibilities: that the present
population of JFCs is a large fluctuation above their long term average, that
larger scattered disk objects tidally break-up into multiple fragments during
close planetary encounters as their orbits evolve from the trans-Neptune zone
to near Jupiter, or that there are alternative source populations that
contribute significantly to the JFCs. Well-characterized observational
investigations of the Centaurs, objects that are transitioning between the
trans-Neptune Kuiper belt region and the inner solar system, can test the
predictions of the non-steady state and the tidal break-up hypotheses. The
classical and resonant classes of the Kuiper belt are worth re-consideration as
significant additional or alternate sources of the JFCs.Comment: 33 pages, 6 figures. Revised Content. To be published in The
Astrophysical Journa
The origin of planetary impactors in the inner solar system
New insights into the history of the inner solar system are derived from the
impact cratering record of the Moon, Mars, Venus and Mercury, and from the size
distributions of asteroid populations. Old craters from a unique period of
heavy bombardment that ended 3.8 billion years ago were made by asteroids
that were dynamically ejected from the main asteroid belt, possibly due to the
orbital migration of the giant planets. The impactors of the past 3.8
billion years have a size distribution quite different from the main belt
asteroids, but very similar to the population of near-Earth asteroids.Comment: 12 pages (including 4 figures
Assessing the pros and cons of vaginal birth after caesarean relative to elective repeat caesarean section
Background: Recent years have witnessed a rise in rate of primary caesarean section (CS). No. of women reporting with a previous CS scar is also increasing. Judicious trial of labor in such patients can prevent repeat caesarean section. Aim of this study was to assessing the safety and success rate of vaginal birth after caesarean (VBAC) in selected cases of patients who have undergone previous lower segment CS (LSCS) is the main aim of this study.Methods: In this prospective observational study carried out in a tertiary care teaching hospital over a period of 1 year. 375 pregnant women with a history of one previous LSCS for non-recurrent indications were enrolled. The statistical technique of t-test was administered for relative comparison with respect to maternal and neonatal complications across the two groups, i.e. repeat LSCS and vaginal delivery.Results: Out of 375 patients 187 patients (49.9%) underwent elective LSCS for recurrent indication and for non-recurrent indication associated with some complicating factor. Trial of labor in 188 (50.10%) was given out of which 59.3% had spontaneous vaginal delivery,7.20% had instrumental delivery and 33.50% landed into emergency CS. Commonest cause of Em. LSCS being Fetal distress. As regards maternal complications, no statistically significant difference was found between the Repeat LSCS and Vaginal delivery groups (t = 0.779, p > 0.05). On similar lines, there was no statistically significant difference across both groups as regards neonatal complications (t = 0.632, p > 0.05).Conclusions: Taking into account the increased trend of primary CS, trial of VBAC in selected cases is very important. It can be concluded that VBAC has chances of success in cases with previous one LSCS but it must be carefully investigated and monitored
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Increasing compliance with low tidal volume ventilation in the ICU with two nudge-based interventions: evaluation through intervention time-series analyses
Objectives: Low tidal volume (TVe) ventilation improves outcomes for ventilated patients, and the majority of clinicians state they implement it. Unfortunately, most patients never receive low TVes. ‘Nudges’ influence decision-making with subtle cognitive mechanisms and are effective in many contexts. There have been few studies examining their impact on clinical decision-making. We investigated the impact of 2 interventions designed using principles from behavioural science on the deployment of low TVe ventilation in the intensive care unit (ICU).
Setting: University Hospitals Bristol, a tertiary, mixed medical and surgical ICU with 20 beds, admitting over 1300 patients per year.
Participants: Data were collected from 2144 consecutive patients receiving controlled mechanical ventilation for more than 1 hour between October 2010 and September 2014. Patients on controlled mechanical ventilation for more than 20 hours were included in the final analysis.
Interventions: (1) Default ventilator settings were adjusted to comply with low TVe targets from the initiation of ventilation unless actively changed by a clinician. (2) A large dashboard was deployed displaying TVes in the format mL/kg ideal body weight (IBW) with alerts when TVes were excessive.
Primary outcome measure: TVe in mL/kg IBW.
Findings: TVe was significantly lower in the defaults group. In the dashboard intervention, TVe fell more quickly and by a greater amount after a TVe of 8 mL/kg IBW was breached when compared with controls. This effect improved in each subsequent year for 3 years.
Conclusions: This study has demonstrated that adjustment of default ventilator settings and a dashboard with alerts for excessive TVe can significantly influence clinical decision-making. This offers a promising strategy to improve compliance with low TVe ventilation, and suggests that using insights from behavioural science has potential to improve the translation of evidence into practice
A narrow-band search for Ly alpha emitting galaxies at z = 8.8
Aims: The first star forming galaxies in the early universe should be copious
Ly alpha emitters, and may play a significant role in ionizing the
intergalactic medium (IGM). It has been proposed that the luminosity function
of Lya emitting galaxies beyond z~6 may be used to constrain the neutral
fraction of the IGM during this epoch. In this work we report on a search for
Ly alpha emitters at redshift 8.8.
Methods: We performed a narrow band imaging programme using ISAAC at the ESO
VLT. Seven fields, covering a total area of 31sq. arcmin and for which optical
and broad band infra-red images have been obtained in the GOODS survey, were
imaged to a limiting flux (respectively luminosity) of ~ 1.3 x 10^{-17}
ergs.s^{-1}.cm^{-2} (respectively ~ 1.3 x 10^{43} ergs.s^{-1} in a narrow band
filter centered in a region of low OH sky emission at 1.19 micron. Candidate
Lyman alpha emitters are objects that are detected in the ISAAC NB images and
undetected in the visible broad band images.
Results: No z=8.8 Ly alpha emitting galaxies were detected to a limit
approaching recent estimates of the luminosity function at z ~ 6. Our results
do suggest, however, that detections or substantial constraints could be
achieved by this method in the near future with larger field instruments
planned for various telescopes.Comment: 7 pages, accepted for publication in A&
The Size Distribution of Trans-Neptunian Bodies
[Condensed] We search 0.02 deg^2 for trans-Neptunian objects (TNOs) with
m<=29.2 (diameter ~15 km) using the ACS on HST. Three new objects are
discovered, roughly 25 times fewer than expected from extrapolation of the
differential sky density Sigma(m) of brighter objects. The ACS and other recent
TNO surveys show departures from a power law size distribution. Division of the
TNO sample into ``classical Kuiper belt'' (CKB) and ``Excited'' samples reveals
that Sigma(m) differs for the two populations at 96% confidence. A double power
law adequately fits all data. Implications include: The total mass of the CKB
is ~0.010 M_Earth, only a few times Pluto's mass, and is predominately in the
form of ~100 km bodies. The mass of Excited objects is perhaps a few times
larger. The Excited class has a shallower bright-end size distribution; the
largest objects, including Pluto, comprise tens of percent of the total mass
whereas the largest CKBOs are only ~2% of its mass. The predicted mass of the
largest Excited body is close to the Pluto mass; the largest CKBO is ~60 times
less massive. The deficit of small TNOs occurs for sizes subject to disruption
by present-day collisions, suggesting extensive depletion by collisions. Both
accretion and erosion appearing to have proceeded to more advanced stages in
the Excited class than the CKB. The absence of distant TNOs implies that any
distant (60 AU) population must have less than the CKB mass in the form of
objects 40 km or larger. The CKB population is sparser than theoretical
estimates of the required precursor population for short period comets, but the
Excited population could be a viable precursor population.Comment: Revised version accepted to the Astronomical Journal. Numerical
results are very slightly revised. Implications for the origins of
short-period comets are substantially revised, and tedious material on
statistical tests has been collected into a new Appendi
Efficacy of Certain Essential Oils and Insect Repellents Against Land Leeches
Relative efficacy of six essential oils, viz., Cinnamon, Citronella, Eucalyptus, Orange, Pine, Spearmint and four insect repellents i.e, Dimethyl phthalate (DMP), Dibutyl phthalate (DBP), Expel and Mylol was investigated against landleeches,Haemadipsa zeylanica montivindicis Moore, under laboratory conditions. Cinnamon oil was found to be the best among the essential oils and out of repellents, Mylol and DMP were effective equally
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