2,964 research outputs found
Non-tropical Cyclone Related Winter Heavy Rainfall Events over the Philippines: Climatology and Mechanisms
This study investigates non-tropical cyclone (TC) related boreal winter heavy rainfall events that lead to extensive flooding (HRF) over the Philippines through a case study and composite analysis. The HRF event examined occurred during January 16–22, 2017 over Cagayan de Oro City (CDO) in Mindanao Island (122–127°E, 5–10°N). The accumulated rainfall over CDO reached by about 180 mm from 00 UTC January 16 to 00 UTC January 17, 2017, exceeding the climatological maximum daily rainfall in January over this area. The interaction of a westward propagating cyclonic circulation over Mindanao Island (MCC) and a shearline that is associated with an eastward-propagating cyclonic and anticyclonic circulations along 20–40°N, led to enhanced moisture convergence and rainfall over CDO. The climatology of these non-TC related HRF events was examined through composite analysis of the HRF events documented in the Dartmouth Flood Observatory archive from 1979 to 2017. The authors identified 34 of such cases over the Philippines, in which 25 occurred over Mindanao Island. The composites of the circulation features of these 25 cases resemble those during the January 2017 case. A vorticity budget analysis was performed to explain the propagation tendency of the MCC. The results show that the MCC only propagated westward when the magnitudes of the stretching and advection terms of the vorticity tendency equation are almost comparable with each other, together with the weakening of the southerly winds around Mindanao Island. This study reveals how cold fronts over the north Pacific together with the MCC induces HRF events over the Philippines
On the X-ray lines in the afterglows of GRBs
The observation of X-ray lines in the afterglow of GRB 011211 has been
reported, and challenged. The lines were interpreted as blue-shifted X-rays
characteristic of a set of photoionized ``metals'', located in a section of a
supernova shell illuminated by a GRB emitted a couple of days after the
supernova explosion. We show that the most prominent reported lines coincide
with the ones predicted in the ``cannonball'' model of GRBs. In this model, the
putative signatures are Hydrogen lines, boosted by the (highly relativistic)
motion of the cannonballs (CBs). The corresponding Doppler boost can be
extracted from the fit to the observed I-, R- and V-band light-curves of the
optical afterglow of GRB 011211, so that, since the redshift is also known, the
line energies are --in the CB model-- predicted. We also discuss other GRBs of
known redshift which show spectral features generally interpreted as Fe lines,
or Fe recombination edges. The ensemble of results is very encouraging from the
CB-model's point of view, but the data on each individual GRB are not good
enough to draw (any) objectively decisive conclusions. We outline a strategy
for X-ray observers to search for lines which, in the CB model, move
predictably from higher to lower energies.Comment: Accepted for publication in Ap
Obstetric outcome of female genital mutilation in the Gambia – an observational study
Background: A 2010 survey in The Gambia among women of reproductive age put the prevalence rate of FGM/C at 76.3%. FGM/C was banned in 2015, but there is no real effort at enforcement of the ban. This study aimed to provide national data on obstetric outcomes to support advocacy and health education.A multicentre observational study to assess the obstetric and neonatal outcomes of parturient women with and without FGM/Cwas carried out across 4 healthcare facilities in The Gambia. The primary outcome was postpartum haemorrhage (>500ml) andsecondary outcomes were caesarean section, perineal tears (including episiotomy), neonatal resuscitation and perinatal death.Of the 1,569 participants recruited into the study, 23% had no FGM/C while 77% had FGM/C of varying severity. The riskof postpartum haemorrhage was doubled for women with type I FGM/C, tripled in type II FGM/C and increased by 5-foldfor those with type III and IV FGM/C. Caesarean section and perineal tears were also increased. FGM/C was associated withincreased risk for neonatal resuscitation and perinatal death.FGM/C is associated with poor obstetric and neonatal outcomes in the Gambia with degree of risk correlating with the severityof FGM/C.
Keywords: Female genital mutilation; obstetric outcome; Gambia
Wind Energy Projection for the Philippines based on Climate Change Modeling
To complement the existing method of wind energy assessment, this study presents wind energy projection by downscaling a regional climate model, RegCM3, which is also used in predicting rainfall and temperature changes, and using a conversion method using the Weibull distribution. A couple of papers which used long-term predicting models focused on two regions, China and the US High Plains, show a decrease of about 14% and 7%-17% respectively in wind power density due to global warming over the next century. This paper focuses on a smaller grid size of 10 km x 10 km to concentrate on a specific wind farm in Pililla, Rizal, Philippines which is considered as a commercially feasible site by wind developers. Wind energy projection that considers the effects of climate change for the expected period of operation of 25 years is used because this gives wind developers an outlook on the power production during the wind farm\u27s lifetime and would contribute in determining the wind farm\u27s potential for financial returns. Percentage difference of wind power density between the baseline period of 2008-2012 and five-year projection periods from 2013-2037 are presented. Contrary to the results of studies in China and western US, the results of this research show that there is an average five-year period increase of 6% in wind power density in Pililla, Rizal over the next 25 years
Optical Behavior of GRB 061121 around its X-Ray Shallow Decay Phase
Aims. We report on a detailed study of the optical afterglow of GRB 061121
with our original time-series photometric data. In conjunction with X-ray
observations, we discuss the origin of its optical and X-ray afterglows.
Methods. We observed the optical afterglow of Swift burst GRB 061121 with the
Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers
a period just after an X-ray plateau phase. We also performed deep imaging with
the Subaru telescope in 2010 in order to estimate the contamination of the host
galaxy. Results. In the light curve, we find that the optical afterglow also
exhibited a break as in the X-ray afterglow. However, our observation suggests
a possible hump structure or a flattening period before the optical break in
the light curve. There is no sign of such a hump in the X-ray light curve.
Conclusions. This implies that the emitting region of optical was distinct from
that of X-rays. The hump in the optical light curve was possibly caused by the
passage of the typical frequency of synchrotron emission from another forward
shock distinct from the early afterglow. The observed decay and spectral
indices are inconsistent with the standard synchrotron-shock model. Hence, the
observation requires a change in microphysical parameters in the shock region
or a prior activity of the central engine. Alternatively, the emission during
the shallow decay phase may be a composition of two forward shock emissions, as
indicated by the hump structure in the light curve.Comment: 8 pages, including 4 figures and 2 tables. Accepted to A&
Two types of softening detected in X-ray afterglows of Swift bursts: internal and external shock origins?
The softening process observed in the steep decay phase of early X-ray
afterglows of Swift bursts has remained a puzzle since its discovery. The
softening process can also be observed in the later phase of the bursts and its
cause has also been unknown. Recently, it was suggested that, influenced by the
curvature effect, emission from high latitudes would shift the Band function
spectrum from higher energy band to lower band, and this would give rise to the
observed softening process accompanied by a steep decay of the flux density.
The curvature effect scenario predicts that the terminating time of the
softening process would be correlated with the duration of the process. In this
paper, based on the data from the UNLV GRB group web-site, we found an obvious
correlation between the two quantities. In addition, we found that the
softening process can be divided into two classes: the early type softening
() and the late type softening ().
The two types of softening show different behaviors in the duration vs.
terminating time plot. In the relation between the variation rates of the flux
density and spectral index during the softening process, a discrepancy between
the two types of softening is also observed. According to their time scales and
the discrepancy between them, we propose that the two types are of different
origins: the early type is of internal shock origin and the late type is of
external shock origin. The early softening is referred to the steep decay just
following the prompt emission, whereas the late decay typically conceives the
transition from flat decay to late afterglow decay. We suspect that there might
be a great difference of the Lorentz factor in two classes which is responsible
for the observed discrepancy.Comment: 20 pages, 5 figures, 2 tables, Accepted for Publication to Journal of
Cosmology and Astroparticle Physics (JCAP
The electromagnetic model of Gamma Ray Bursts
I describe electromagnetic model of gamma ray bursts and contrast its main
properties and predictions with hydrodynamic fireball model and its
magnetohydrodynamical extension. The electromagnetic model assumes that
rotational energy of a relativistic, stellar-mass central source
(black-hole--accretion disk system or fast rotating neutron star) is converted
into magnetic energy through unipolar dynamo mechanism, propagated to large
distances in a form of relativistic, subsonic, Poynting flux-dominated wind and
is dissipated directly into emitting particles through current-driven
instabilities. Thus, there is no conversion back and forth between internal and
bulk energies as in the case of fireball model. Collimating effects of magnetic
hoop stresses lead to strongly non-spherical expansion and formation of jets.
Long and short GRBs may develop in a qualitatively similar way, except that in
case of long bursts ejecta expansion has a relatively short, non-relativistic,
strongly dissipative stage inside the star. Electromagnetic and fireball models
(as well as strongly and weakly magnetized fireballs) lead to different early
afterglow dynamics, before deceleration time. Finally, I discuss the models in
view of latest observational data in the Swift era.Comment: solicited contribution to Focus Issue of New Journal of Physics, 27
pages, 4 figure
GRB Fireball Physics: Prompt and Early Emission
We review the fireball shock model of gamma-ray burst prompt and early
afterglow emission in light of rapid follow-up measurements made and enabled by
the multi-wavelength Swift satellite. These observations are leading to a
reappraisal and expansion of the previous standard view of the GRB and its
fireball. New information on the behavior of the burst and afterglow on minutes
to hour timescales has led, among other results, to the discovery and follow-up
of short GRB afterglows, the opening up of the z>6 redshift range, and the
first prompt multi-wavelength observations of a long GRB-supernova. We discuss
the salient observational results and some associated theoretical issues.Comment: 23 pages. Published in the New Journal of Physics Focus Issue, "Focus
on Gamma-Ray Bursts in the Swift Era" (Eds. D. H. Hartmann, C. D. Dermer & J.
Greiner). V2: Minor change
Absolute electron and positron fluxes from PAMELA/Fermi and Dark Matter
We extract the positron and electron fluxes in the energy range 10 - 100 GeV
by combining the recent data from PAMELA and Fermi LAT. The {\it absolute
positron and electron} fluxes thus obtained are found to obey the power laws:
and respectively, which can be confirmed by the
upcoming data from PAMELA. The positron flux appears to indicate an excess at
energies E\gsim 50 GeV even if the uncertainty in the secondary positron flux
is added to the Galactic positron background. This leaves enough motivation for
considering new physics, such as annihilation or decay of dark matter, as the
origin of positron excess in the cosmic rays.Comment: Accepted by JCA
The Spectrum of Electromagnetic Jets from Kerr Black Holes and Naked Singularities in the Teukolsky Perturbation Theory
We give a new theoretical basis for examination of the presence of the Kerr
black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of
different astrophysical objects around which astrophysical jets are typically
formed: X-ray binary systems, gamma ray bursts (GRBs), active galactic nuclei
(AGN), etc. Our method is based on the study of the exact solutions of the
Teukolsky master equation for electromagnetic perturbations of the Kerr metric.
By imposing original boundary conditions on the solutions so that they describe
a collimated electromagnetic outflow, we obtain the spectra of possible {\em
primary jets} of radiation, introduced here for the first time. The theoretical
spectra of primary electromagnetic jets are calculated numerically. Our main
result is a detailed description of the qualitative change of the behavior of
primary electromagnetic jet frequencies under the transition from the KBH to
the KNS, considered here as a bifurcation of the Kerr metric. We show that
quite surprisingly the novel spectra describe linearly stable primary
electromagnetic jets from both the KBH and the KNS. Numerical investigation of
the dependence of these primary jet spectra on the rotation of the Kerr metric
is presented and discussed.Comment: 18 pages, 35 figures, LaTeX file. Final version. Accepted for
publication in Astrophysics and Space Science. Amendments. Typos corrected.
Novel notion -"primary jet" is introduced. New references and comments adde
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