2,590 research outputs found
A 450-day light curve of the radio afterglow of GRB 970508: Fireball calorimetry
We report on the results of an extensive monitoring campaign of the radio
afterglow of GRB 970508, lasting 450 days after the burst. The spectral and
temporal radio behavior indicate that the fireball has undergone a transition
to sub-relativistic expansion at t~100 days. This allows us to perform
"calorimetry" of the explosion. The derived total energy, ~5\times 10^{50} erg,
is well below the ~5\times 10^{51} erg inferred under the assumption of
spherical symmetry from gamma-ray and early afterglow observations. A natural
consequence of this result, which can also account for deviations at t<100 days
from the spherical relativistic fireball model predictions, is that the
fireball was initially a wide-angle jet of opening angle ~30 degrees.
Our analysis also allows to determine the energy fractions carried by
electrons and magnetic field, and the density of ambient medium surrounding the
fireball. We find that during the sub-relativistic expansion electrons and
magnetic field are close to equipartition, and that the density of the ambient
medium is ~1/cm^3. The inferred density rules out the possibility that the
fireball expands into a strongly non-uniform medium, as would be expected,
e.g., in the case of a massive star progenitor.Comment: 33 pages, including 7 figures, submitted to Ap
The 1.4 GHz light curve of GRB 970508
We report on Westerbork 1.4 GHz radio observations of the radio counterpart
to -ray burst GRB~970508, between 0.80 and 138 days after this event.
The 1.4 GHz light curve shows a transition from optically thick to thin
emission between 39 and 54 days after the event. We derive the slope of the
spectrum of injected electrons () in two
independent ways which yield values very close to . This is in agreement
with a relativistic dynamically near-adiabatic blast wave model whose emission
is dominated by synchrotron radiation and in which a significant fraction of
the electrons cool fast.Comment: Paper I. Accepted for publication in the Astrophysical Journal
Letter
A bioinformatics approach to the development of immunoassays for specified risk material in canned meat products
A bioinformatics approach to developing antibodies to specific proteins has been evaluated for the production of antibodies to heat-processed specified risk tissues from ruminants (brain and eye tissue). The approach involved the identification of proteins specific to ruminant tissues by interrogation of the annotation fields within the Swissprot database. These protein sequences were then interrogated for peptide sequences that were unique to the protein. Peptides were selected that met these criteria as close as possible and that were also theoretically resistant to either pepsin or trypsin. The selected peptides were synthesised and used as immunogens to raise monoclonal antibodies. Antibodies specific for the synthetic peptides were raised to half of the selected peptides. These antibodies have each been incorporated into a competitive enzyme-linked immunosorbent assay (ELISA) and shown to be able to detect the heat-processed parent protein after digestion with either pepsin or trypsin. One antibody, specific for alpha crystallin peptide (from bovine eye tissue), was able to detect the peptide in canned meat products spiked with 10% eye tissue. These results, although preliminary in nature, show that bioinformatics in conjunction with enzyme digestion can be used to develop ELISA for proteins in high-temperature processed foods and demonstrate that the approach is worth further stud
Dynamic PRA: an Overview of New Algorithms to Generate, Analyze and Visualize Data
State of the art PRA methods, i.e. Dynamic PRA
(DPRA) methodologies, largely employ system
simulator codes to accurately model system dynamics.
Typically, these system simulator codes (e.g., RELAP5 )
are coupled with other codes (e.g., ADAPT,
RAVEN that monitor and control the simulation. The
latter codes, in particular, introduce both deterministic
(e.g., system control logic, operating procedures) and
stochastic (e.g., component failures, variable uncertainties)
elements into the simulation. A typical DPRA analysis is
performed by:
1. Sampling values of a set of parameters from the
uncertainty space of interest
2. Simulating the system behavior for that specific set of
parameter values
3. Analyzing the set of simulation runs
4. Visualizing the correlations between parameter values
and simulation outcome
Step 1 is typically performed by randomly sampling
from a given distribution (i.e., Monte-Carlo) or selecting
such parameter values as inputs from the user (i.e.,
Dynamic Event Tre
ALMA unveils wider environment of distant red protocluster core
We report observations with the Atacama Large Millimetre Array (ALMA) of six
submillimetre galaxies (SMGs) within 3 arcmin of the Distant Red Core (DRC) at
, a site of intense cluster-scale star formation, first reported by Oteo
et al. (2018). We find new members of DRC in three SMG fields; in two fields,
the SMGs are shown to lie along the line of sight towards DRC; one SMG is
spurious. Although at first sight this rate of association is consistent with
earlier predictions, associations with the bright SMGs are rarer than expected,
which suggests caution when interpreting continuum over-densities. We consider
the implications of all 14 confirmed DRC components passing simultaneously
through an active phase of star formation. In the simplest explanation, we see
only the tip of the iceberg in terms of star formation and gas available for
future star formation, consistent with our remarkable finding that the majority
of newly confirmed DRC galaxies are not the brightest continuum emitters in
their immediate vicinity. Thus while ALMA continuum follow-up of SMGs
identifies the brightest continuum emitters in each field, it does not
necessarily reveal all the gas-rich galaxies. To hunt effectively for
protocluster members requires wide and deep spectral-line imaging to uncover
any relatively continuum-faint galaxies that are rich in atomic or molecular
gas. Searching with short-baseline arrays or single-dish facilities, the true
scale of the underlying gas reservoirs may be revealed.Comment: 8 pages, 2 colour figures; MNRAS, in pres
The radio to X-ray spectrum of GRB 970508 on May 21.0 UT
We have reconstructed the spectrum of the afterglow of GRB 970508, on May
21.0 UT (12.1 days after the GRB), on the basis of observations spanning the
X-ray to radio range. The low-frequency power law index of the spectrum,
(), is in agreement with the
expected value for optically thin synchrotron radiation. The 1.4
GHz emission is self-absorbed. We infer constraints on the break frequecies
and on May 21.0 UT from a spectral transition from to in the optical passband around
1.4 days. A model of an adiabatically expanding blast wave, emitting
synchrotron radiation, in which a significant fraction of the electrons cool
rapidly provides a successful and consistent description of the afterglow
observations over nine decades in frequency, ranging in time from trigger until
several months later.Comment: Paper II. Accepted for publication in the Astrophysical Journal
Letter
Coreâshell catalyst pellets for effective reaction heat management
Catalyst research is concerned with synthesizing increasingly active materials, leading to safety issues at reactor scale, unless the reaction heat release is controllable. Computational studies predict that coreâshell pellets with catalytically active core and inert shell are beneficial for this purpose, compared to established concepts such as catalyst pellet dilution. At high temperatures, reactant diffusion through the shell becomes rate-determining, resulting in a well-controllable heat release rate, which prevents further temperature increase. Here, industrial catalyst pellets were coated in a fluidized-bed pilot plant, demonstrating large-scale production feasibility. The obtained pellets were characterized via Dynamic Image Analysis, Scanning Electron Microscopy and X-ray Computed Tomography. Conducted CO2 methanation experiments confirm the predicted trends, if the applied shell is fully closed. Furthermore, mathematical and experimental studies demonstrate, that the inert shell shifts selectivity. Based on this work, safer and yet economical reactor operation is anticipated also for other reaction systems
Finite Action in d5 Gauged Supergravity and Dilatonic Conformal Anomaly for Dual Quantum Field Theory
Gauged supergravity (SG) with single scalar (dilaton) and arbitrary scalar
potential is considered. Such dilatonic gravity describes special RG flows in
extended SG where scalars lie in one-dimensional submanifold of total space.
The surface counterterm and finite action for such gauged SG in three-, four-
and five-dimensional asymptotically AdS space are derived. Using finite action
and consistent gravitational stress tensor (local surface counterterm
prescription) the regularized expressions for free energy, entropy and mass of
d4 dilatonic AdS black hole are found. The same calculation is done within
standard reference background subtraction.
The dilaton-dependent conformal anomaly from d3 and d5 gauged SGs is
calculated using AdS/CFT correspondence. Such anomaly should correspond to two-
and four-dimensional dual quantum field theory which is classically (not
exactly) conformally invariant, respectively. The candidate c-functions from d3
and d5 SGs are suggested. These c-functions which have fixed points in
asymptoticaly AdS region are expressed in terms of dilatonic potential and they
are positively defined and monotonic for number of potentials.Comment: LaTeX file, 46 pages, two appendixes and some clarifications are
adde
Condensates formed by prion-like low-complexity domains have small-world network structures and interfaces defined by expanded conformations
Biomolecular condensates form via coupled associative and segregative phase transitions of multivalent associative macromolecules. Phase separation coupled to percolation is one example of such transitions. Here, we characterize molecular and mesoscale structural descriptions of condensates formed by intrinsically disordered prion-like low complexity domains (PLCDs). These systems conform to sticker-and-spacers architectures. Stickers are cohesive motifs that drive associative interactions through reversible crosslinking and spacers affect the cooperativity of crosslinking and overall macromolecular solubility. Our computations reproduce experimentally measured sequence-specific phase behaviors of PLCDs. Within simulated condensates, networks of reversible inter-sticker crosslinks organize PLCDs into small-world topologies. The overall dimensions of PLCDs vary with spatial location, being most expanded at and preferring to be oriented perpendicular to the interface. Our results demonstrate that even simple condensates with one type of macromolecule feature inhomogeneous spatial organizations of molecules and interfacial features that likely prime them for biochemical activity
"All-fiber" tunable laser in the 2 mu m region, designed for CO2 detection
A stable and tunable thulium-doped âall-fiberâ laser offering a narrow linewidth has been created specifically to act as a compact and simple laser source for gaseous CO2 detection. This has been done through a careful design to match the laser output wavelengths to the CO2 absorption lines at 1.875 and 1.997 ÎŒm, respectively. A sustainable output power of 11 mW over a tuning range of 7 nm has been obtained by using a combination of a high-reflective fiber Bragg grating with a low-reflective broadband mirror, fabricated at the end of the fiber through silver film deposition. The tuning was achieved using the relaxation-compression mechanism of the fiber Bragg grating, which formed an integral part of the laser resonant cavity. A fiber Bragg grating at 1.548 ÎŒm was utilized as a wavelength reference to monitor the tuning of the laser output over the 2 ÎŒm wavelength range with a simple and inexpensive interrogator, to avoid the use of an expensive optical spectrum analyzer and to facilitate âin-the-fieldâ operation. This âall-fiberâ laser resonator has been shown to be superior in terms of laser tuning range, output power, and linewidth compared to that created with a fiber Bragg grating pair, which was limited by the nonuniform strain transfer to both fiber Bragg gratings
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