2,314 research outputs found
A fireworks model for Gamma-Ray Bursts
The energetics of the long duration GRB phenomenon is compared with models of
a rotating Black Hole (BH) in a strong magnetic field generated by an accreting
torus. A rough estimate of the energy extracted from a rotating BH with the
Blandford-Znajek mechanism is obtained with a very simple assumption: an
inelastic collision between the rotating BH and the torus. The GRB energy
emission is attributed to an high magnetic field that breaks down the vacuum
around the BH and gives origin to a e+- fireball. Its subsequent evolution is
hypothesized, in analogy with the in-flight decay of an elementary particle, to
evolve in two distinct phases. The first one occurs close to the engine and is
responsible of energizing and collimating the shells. The second one consists
of a radiation dominated expansion, which correspondingly accelerates the
relativistic photon--particle fluid and ends at the transparency time. This
mechanism simply predicts that the observed Lorentz factor is determined by the
product of the Lorentz factor of the shell close to the engine and the Lorentz
factor derived by the expansion. An anisotropy in the fireball propagation is
thus naturally produced, whose degree depends on the bulk Lorentz factor at the
end of the collimation phase.Comment: Accepted for publication in MNRA
Methemoglobinemia Associated with Late-Onset Neonatal Sepsis: A Single-Center Experience
Objective â Methemoglobinemia (MetHb) is a rare congenital or acquired cause of infantile cyanosis. We examined the role of MetHb in a neonatal intensive care unit (NICU). Study Design â A retrospective observational study was conducted reviewing blood gas analyses of hospitalized newborns over a 2-year period. MetHb-positive patients (MetHb >1.8%) were matched with a control group for gestational age, weight, disease, and illness severity at admission. Maternal, neonatal, clinical, and laboratory parameters were collected and analyzed in both groups. Results â MetHb incidence was 6%. The mean MetHb in the case group was 7.2%, and the first positive samples were observed at a mean of 22 days of life, 6 days prior to clinical or culture-proven sepsis. We identified low maternal age (31 vs. 34 years; p = 0.038), sepsis (90 vs. 45%; p = 0.022), and protracted parenteral nutrition (46 vs. 23 days; p = 0.013) as risk factors for MetHb, and early minimal enteral feeding as protective factor (12th vs. 9th day; p = 0.038). Conclusion â MetHb has a high occurrence in NICU and can be a helpful prognostic indicator of an infectious process. Understanding and prompt identification of MetHb can allow pediatricians to implement a life-saving therapy
The Energy Dependence of Neutron Star Surface Modes and X-ray Burst Oscillations
We calculate the photon energy dependence of the pulsed amplitude of neutron
star (NS) surface modes. Simple approximations demonstrate that it depends most
strongly on the bursting NS surface temperature. This result compares well with
full integrations that include Doppler shifts from rotation and general
relativistic corrections to photon propagation. We show that the energy
dependence of type I X-ray burst oscillations agrees with that of a surface
mode, lending further support to the hypothesis that they originate from
surface waves. The energy dependence of the pulsed emission is rather
insensitive to the NS inclination, mass and radius, or type of mode, thus
hindering constraints on these parameters. We also show that, for this
energy-amplitude relation, the majority of the signal (relative to the noise)
comes in the 2-25 keV band, so that the current burst oscillation searches with
the Rossi X-Ray Timing Explorer are close to optimal. The critical test of the
mode hypothesis for X-ray burst oscillations would be a measurement of the
energy dependence of burst oscillations from an accreting millisecond pulsar.Comment: Accepted for publication in The Astrophysical Journal, 6 pages, 5
figures (revised version: no changes to text, just edited author list
Virus diseases of the grapevine in a Sicilian herbarium of the past century
Dried grapevine specimens, collected in Sicily between 1880 and 1886, and showing different morphological and chromatic modifications, were found in a herbarium established in 1830 by Dr. FRANCESCO MINA PALUMBO, a physician of Castelbuono (Palermo). On the basis of symptoms still visible on the specimens and of the herbarium's original explanatory notes, the diseased material was identified as being affected by fanleaf, yellow mosaic and leafroll.Rebvirosen in einem sizilianischen Herbarium aus dem letzten JahrhundertGetrocknete Exemplare von Reben, die zwischen 1880 und 1886 in Sizilien für ein von Dr. FRANCESCO MINA PALUMBO, einem Arzt aus Castelbuono (Palermo), begründetes Herbarium gesammelt worden waren, zeigten verschiedene morphologische und farbliche Modifikationen. Die noch sichtbaren Symptome an den Herbarexemplaren erlauben zusammen mit den erläuternden Originalnotizen eine Diagnose auf Befall durch Reisigkrankheit, Gelbmosaik und Blattrollkrankheit
On Spectral and Temporal Variability in Blazars and Gamma Ray Bursts
A simple model for variability in relativistic plasma outflows is studied, in
which nonthermal electrons are continuously and uniformly injected in the
comoving frame over a time interval dt. The evolution of the electron
distribution is assumed to be dominated by synchrotron losses, and the energy-
and time-dependence of the synchrotron and synchrotron self-Compton (SSC)
fluxes are calculated for a power-law electron injection function with index s
= 2. The mean time of a flare or pulse measured at photon energy E with respect
to the onset of the injection event varies as E^{-1/2} and E^{-1/4} for
synchrotron and SSC processes, respectively, until the time approaches the
limiting intrinsic mean time (1+z)dt/(2 D), where z is the redshift and D is
the Doppler factor. This dependence is in accord with recent analyses of blazar
and GRB emissions, and suggests a method to discriminate between external
Compton and SSC models of high-energy gamma radiation from blazars and GRBs.
The qualititative behavior of the X-ray spectral index/flux relation observed
from BL Lac objects can be explained with this model. This demonstrates that
synchrotron losses are primarily responsible for the X-ray variability behavior
and strengthens a new test for beaming from correlated hard X-ray/TeV
observations.Comment: 10 pages, 2 figures, accepted for publication in Astrophysical
Journal Letters; uses aaspp4.sty, epsf.st
Fireballs Loading and the Blast Wave Model of Gamma Ray Bursts
A simple function for the spectral power
is proposed to model, with 9 parameters, the spectral and temporal evolution of
the observed nonthermal synchrotron power flux from GRBs in the blast wave
model. Here mc is the observed dimensionless photon
energy and is the observing time. Assumptions and an issue of lack of
self-consistency are spelled out. The spectra are found to be most sensitive to
the baryon loading, expressed in terms of the initial bulk Lorentz factor
, and an equipartition term which is assumed to be constant in
time and independent of . Expressions are given for the peak spectral
power at the photon energy of the spectral power peak. A general rule is that the total
fireball particle kinetic energy , where is the deceleration time scale and is the maximum measured bolometric
power output in radiation, during which it is carried primarily by photons with
energy .Comment: 26 pages, including 4 figures, uses epsf.sty, rotate.sty; submitted
to ApJ; revised version with extended introduction, redrawn figures, and
correction
Microcephaly and macrocephaly. A study on anthropometric and clinical data from 308 subjects
Head circumference is the auxological parameter that most correlates with developmental anomalies in childhood. Head circumference (HC) two standard deviations (SD) below or above the mean defines microcephaly and macrocephaly, respectively. The aim of this retrospective study was to explore anthropometric parameters and clinical characteristics among subjects with abnormalities in HC who had been referred for developmental assessment. One hundred and sixty four subjects with microcephaly and 144 subjects with macrocephaly were enrolled from birth to 18 months of age. Head circumference at birth and the association with variables related to maternal health status, gestational age, growth pattern, brain imaging and clinical characteristics were analyzed. In some cases, an etiological diagnosis was made. In the two considered conditions, we found different anthropometric and clinical associations, some of which were statistically significant, with implications for ongoing neurodevelopmental surveillance
Recognizable neonatal clinical features of aplasia cutis congenita
Background: Aplasia cutis congenita (ACC), classified in nine groups, is likely to be underreported, since milder isolated lesions in wellbeing newborns could often be undetected, and solitary lesions in the context of polymalformative syndromes could not always be reported. Regardless of form and cause, therapeutic options have in common the aim to restore the deficient mechanical and immunological cutaneous protection and to limit the risk of fluid leakage or rupture of the exposed organs. We aimed to review our institutional prevalence, comorbidities, treatment and outcome of newborns with ACC. Methods: We conducted a retrospective study including all newborns affected by ACC and admitted at the University Mother-Child Department from October 2010 to October 2019. Anthropometric and clinical characteristics of ACC1 versus a non-isolated ACC group were analyzed. Results: We encountered 37 newborns, 16 with ACC1 versus 21 with non-isolated ACC. The incidence rate of 0.1% in ACC1 was higher than expected, while 19% of cases showed intrafamilial autosomal dominant transmission. Higher birth weight centile, though lower than reference population, being adequate for gestational age, normal Apgar score and euglycemia characterizing ACC1 resulted associated to a rapid tissue regeneration. Non-isolated ACC, in relation to concomitant congenital anomalies and higher prematurity rate, showed more surgical and medical complications along with the risk of neonatal death. Specifically, newborns with ACC4 were characterized by the frequent necessity of abdominal wall defect repair, responsible for the occurrence of an abdominal compartment syndrome. Conclusion: Prompt carefully assessment of the newborn with ACC in order to exclude concomitant other congenital malformations, provides clues to the underlying pathophysiology, and to the short-term prognosis. Family should be oriented toward identification of other family members affected by similar pathology, while obstetric history should exclude initial multiple pregnancy with death of a co-twin, placental anomalies and drug assumption. Molecular-genetic diagnosis and genetic counseling are integrative in individualized disease approach
Broad band spectral properties of Seyfert 1 galaxies observed with BeppoSAX
We will present some results on the broad--band observations of BeppoSAX of
the bright Seyfert galaxies NGC 4151 and NGC 5548.Comment: 5 pages, 4 figures, Proc. of the 32 COSPAR Ass., Session E1.1 "Broad
Band X-Ray Spectra of Cosmic Sources, ed.s K. Makishima, L. Piro, T.
Takahashi, Advances in Space Research, in pres
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