3,107 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 physical and structural effects of 1-MCP on four different apple cultivars during storage
The impact of the ethylene inhibitor, 1-methylcyclopropene (1-MCP), on four apple cultivars (Braeburn, Fuji, Jazz and Golden Delicious) over 150 days of storage at 2 °C was assessed. Proton transfer reaction quadrupole mass spectrometry (PTR-QUAD-MS) was used to monitor changes in VOC composition, while texture analysis and X-ray microcomputer tomography (µ-CT) scanning were used to study microstructural changes. The application of 1-MCP on apples reduced VOC emissions, concurrently maintaining a firmer texture compared to the untreated apples at each time point. The µ-CT scanning revealed how changes in specific morphological characteristics such as anisotropy, connectivity and porosity, size and shape, as well as the interconnectivity of intracellular spaces (IS) influenced texture even when porosity was similar. Additionally, this study showed that the porosity and connectivity of IS were associated with VOC emission and increased simultaneously. This study highlights how the morphological parameters of an apple can help explain their ripening process during long-term storage and how their microstructure can influence the release of VOC
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
Janzenella theia Bremer & Talamas (Platygastroidea, Janzenellidae): a new species from Baltic amber
A new species, Janzenella theia Bremer & Talamas, sp. nov., is described from Baltic amber, which is the second known species of the family Janzenellidae (Platygastroidea). Synchrotron scanning was performed to observe internal structures and external morphology that was occluded by turbidity in the amber matrix surrounding the specimen
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
The Architecture of Frederick Romberg through the Lens of Wolfgang Sievers
I examine the architecture of émigré artist Frederick Romberg (1913-1992) through the lens
of émigré photographer, Wolfgang Sievers (1913-2007). This multidisciplinary approach
of analyzing Romberg’s architecture through the photographs of Wolfgang Sievers serves
to better understand Australian migrant art and just as well, the migrant experience and
migrant identity. Romberg and Sievers fled the rise of Nazism in Germany and arrived in
Australia in 1938, bringing with them the influence of German Modernist traditions. The
professional relationship between architect and photographer resulted in a multitude
of photographs whose nature of architectural form and designs communicate not just
the physical characteristics of buildings, but also the experience of exile, constant artistic
interaction, collaboration, and active promotion of modernist aesthetics in Melbourne. Both
Romberg’s deliberate use and dependence of Sievers’ Bauhaus-trained trained photographic
practice to capture architecture, and likewise, Sievers’ selective photographic captures of
Romberg’s Modern architectural forms, provide insight as to what and whom the Modern
artist in exile depends on, engages with, and seeks once in a foreign landscape. Focusing on
Sievers’ photographs of Romberg’s designs for Stanhill Flats and Newburn flats, the paper
contends that documentary photographs further provide a historical reality of the past and
architectural practice. The photographs put us, the viewers, in the setting Romberg found
himself in and at around the time his buildings were executed; they illuminate the emerging
phenomenon of German modernism in Australia during the 1950’s. These photographs,
providing flat, almost 360-degree views of architectural forms throughout Romberg’s
artistic career, allow for an analysis of the modernist traditions that Romberg employed
in his designs. Ultimately, I hope to demonstrate how Romberg and Sievers diligently and
assertively worked together in becoming successful artists in Australia once off of the Mosel
and Comorin ships with fresh Modernism in their bags
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
Directional Soliton and Breather Beams
Solitons and breathers are nonlinear modes that exist in a wide range of
physical systems. They are fundamental solutions of a number of nonlinear wave
evolution equations, including the uni-directional nonlinear Schr\"odinger
equation (NLSE). We report the observation of slanted solitons and breathers
propagating at an angle with respect to the direction of propagation of the
wave field. As the coherence is diagonal, the scale in the crest direction
becomes finite, consequently, a beam dynamics forms. Spatio-temporal
measurements of the water surface elevation are obtained by
stereo-reconstructing the positions of the floating markers placed on a regular
lattice and recorded with two synchronized high-speed cameras. Experimental
results, based on the predictions obtained from the (2D+1) hyperbolic NLSE
equation, are in excellent agreement with the theory. Our study proves the
existence of such unique and coherent wave packets and has serious implications
for practical applications in optical sciences and physical oceanography.
Moreover, unstable wave fields in this geometry may explain the formation of
directional large amplitude rogue waves with a finite crest length within a
wide range of nonlinear dispersive media, such as Bose-Einstein condensates,
plasma, hydrodynamics and optics
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
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