1,950 research outputs found
Gamma-Ray Bursts as a Probe of the Very High Redshift Universe
We show that, if many GRBs are indeed produced by the collapse of massive
stars, GRBs and their afterglows provide a powerful probe of the very high
redshift (z > 5) universe.Comment: To appear in Proc. of the 5th Huntsville Gamma-Ray Burst Symposium, 5
pages, LaTe
Longboard classification using Machine Learning
There are several techniques a rider can choose from that they can perform being distributed along the long-board ride. This research aims to create a machine-learning model that can efficiently classify these techniques at different periods of time using raw acceleration data. This paper presents the complete workflow of the application. This application involves analytical geometry, multidimensional calculus, and linear algebra and can be used to visualize and normalize time-invariant object paths. This model focuses on displacement data calculated from raw acceleration data and gyro sensor data from a smartphone application called Physics Toolbox Sensor Suite . We extracted features from each dynamic window of time in the displacement data and then fed them into machine learning algorithms with various statistical features, including supervised learning classifiers and Long short-term memory. We found that the Decision Tree with post-pruning produces a performance 93.4%, and the Random Forest produces a performance 96.8%. Although Decision Tree works faster than Random Forest, we ultimately used Random Forest classifier in our application, since the application does not perform prediction and classification in real-time
Anakinra treats fulminant myocarditis from Neisseria meningitidis septicaemia and haemophagocytic lymphohistiocytosis: a case report
Background: Fulminant myocarditis is a life-threatening condition characterized by acute cardiac dysfunction requiring pharmacological or mechanical circulatory support. Haemophagocytic lymphohistiocytosis (HLH) is an uncommon state of immune dysregulation and overactivation. Inflammation mediated by interleukin-1 (IL-1) is thought to play a role in the pathogenesis of myocarditis and HLH, and there is some evidence that the IL-1 receptor antagonist Anakinra may play a role in treating both these conditions.
Case summary: A 26-year-old previously healthy male presented to the Emergency Department with a 3-day history of malaise, headache, vomiting, diarrhoea, and fever. He was profoundly hypotensive on arrival, diagnosed with septic shock, and commenced on broad-spectrum antibiotics and vasopressors. Blood tests showed lymphopenia, thrombocytopenia, low fibrinogen and elevated high sensitivity troponin T, ferritin, and C-reactive protein. Echocardiography demonstrated severely impaired biventricular systolic function and a diagnosis of fulminant myocarditis was made. His condition deteriorated and he required intubation and additional inotropic support. A diagnosis of HLH was made and he was commenced on Anakinra and Methylprednisolone. His condition improved rapidly thereafter. Polymerase chain reaction testing subsequently confirmed infection with Neisseria meningitidis.
Discussion: In this case, fulminant myocarditis and HLH were life-threatening manifestations of meningococcal septicaemia, and the patient’s condition improved rapidly following administration of the IL-1 receptor antagonist Anakinra. These complications should be borne in mind in septic patients with marked haemodynamic instability and multiorgan dysfunction, and treatment with Anakinra should be considered in those who fail to respond to conventional therapy
An Evolving Stellar Initial Mass Function and the Gamma-Ray Burst Redshift Distribution
Recent studies suggest that Swift gamma-ray bursts (GRBs) may not trace an
ordinary star formation history. Here we show that the GRB rate turns out to be
consistent with the star formation history with an evolving stellar initial
mass function (IMF). We first show that the latest Swift sample of GRBs reveals
an increasing evolution in the GRB rate relative to the ordinary star formation
rate at high redshifts. We then assume only massive stars with masses greater
than the critical value to produce GRBs, and use an evolving stellar IMF
suggested by Dav\'{e} (2010) to fit the latest GRB redshift distribution. This
evolving IMF would increase the relative number of massive stars, which could
lead to more GRB explosions at high redshifts. We find that the evolving IMF
can well reproduce the observed redshift distribution of Swift GRBs.Comment: 13 pages, 4 figures, accepted for publication in ApJ
Toward high-precision values of the self energy of non-S states in hydrogen and hydrogen-like ions
The method and status of a study to provide numerical, high-precision values
of the self-energy level shift in hydrogen and hydrogen-like ions is described.
Graphs of the self energy in hydrogen-like ions with nuclear charge number
between 20 and 110 are given for a large number of states. The self-energy is
the largest contribution of Quantum Electrodynamics (QED) to the energy levels
of these atomic systems. These results greatly expand the number of levels for
which the self energy is known with a controlled and high precision.
Applications include the adjustment of the Rydberg constant and atomic
calculations that take into account QED effects.Comment: Minor changes since previous versio
High-redshift star formation rate up to z~8.3 derived from gamma-ray bursts and influence of background cosmology
The high-redshift star formation rate (SFR) is difficult to measure directly
even by modern approaches. Long-duration gamma-ray bursts (GRBs) can be
detected to the edge of the visible universe because of their high
luminorsities. The collapsar model of long gamma-ray bursts indicates that they
may trace the star formation history. So long gamma-ray bursts may be a useful
tool of measuring the high-redshift SFR. Observations show that long gamma-ray
bursts prefer to form in a low-metallicity environment. We study the
high-redshift SFR up to z~8.3 considering the Swift GRBs tracing the star
formation history and the cosmic metallicity evolution in different background
cosmological models including CDM, quintessence, quintessence with a
time-varying equation of state, and brane-world model. We use latest Swift GRBs
including two highest- GRBs, GRB 080913 at and GRB 090423 at
. We find that the SFR at shows a steep decay with a slope of
in CDM. In the other three models, the high-redshift SFR
is slightly different from CDM model, and also shows a steep decay.Comment: 5 pages, 5 figures, 2 tables, two references adde
Host Galaxies of Gamma-Ray Bursts and their Cosmological Evolution
We use numerical simulations of large scale structure formation to explore
the cosmological properties of Gamma-Ray Burst (GRB) host galaxies. Among the
different sub-populations found in the simulations, we identify the host
galaxies as the most efficient star-forming objects, i.e. galaxies with high
specific star formation rates. We find that the host candidates are low-mass,
young galaxies with low to moderate star formation rate. These properties are
consistent with those observed in GRB hosts, most of which are sub-luminous,
blue galaxies. Assuming that host candidates are galaxies with high star
formation rates would have given conclusions inconsistent with the
observations. The specific star formation rate, given a galaxy mass, is shown
to increase as the redshift increases. The low mass of the putative hosts makes
them difficult to detect with present day telescopes and the probability
density function of the specific star formation rate is predicted to change
depending on whether or not these galaxies are observed.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
The Star Formation Rate in the Reionization Era as Indicated by Gamma-ray Bursts
High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to
study aspects of the early Universe, including the cosmic star formation rate
(SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and
GRB 090423 at z = 8.1, and more than four years of Swift observations, we first
confirm that the GRB rate does not trace the SFR in an unbiased way. Correcting
for this, we find that the implied SFR to beyond z = 8 is consistent with
LBG-based measurements after accounting for unseen galaxies at the faint end of
the UV luminosity function. We show that this provides support for the
integrated star formation in the range 6 < z < 8 to have been alone sufficient
to reionize the Universe.Comment: 4 pages, 4 figures; modified to match version accepted for
publication in ApJ Letter
Elliptic Curves over Real Quadratic Fields are Modular
We prove that all elliptic curves defined over real quadratic fields are
modular.Comment: 38 pages. Magma scripts available as ancillary files with this arXiv
versio
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