6,761 research outputs found
Thick fireballs and the steep decay in the early X-ray afterglow of gamma-ray bursts
We study the early afterglows of gamma-ray bursts produced by geometrically
thick fireballs, following the development of the external shock as energy is
continually supplied to the shocked material. We study the dependence of the
early afterglow slope on the luminosity history of the central engine. The
resulting light curves are modeled with power-law functions and the importance
of a correct choice of the reference time t_0 is investigated. We find that
deviations from a simple power-law are observed only if a large majority of the
energy is released at late times. The light curve in this case can be described
as a simple power-law if the reference time is set to be close to the end of
the burst. We applied our analysis to the cases of GRB 050219a and GRB 050315.
We show that the early steep decay of the afterglow cannot result from the
interaction of the fireball with the ambient medium. We conclude that the early
X-ray afterglow emission is associated with the prompt phase and we derive
limits on the radius at which the prompt radiation is produced.Comment: Minor revisions, accepted for publication in Ap
Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite
Most ice in nature forms thanks to impurities which boost the exceedingly low
nucleation rate of pure supercooled water. However, the microscopic details of
ice nucleation on these substances remain largely unknown. Here, we have
unraveled the molecular mechanism and the kinetics of ice formation on
kaolinite, a clay mineral playing a key role in climate science. We find that
the formation of ice at strong supercooling in the presence of this clay is
twenty orders of magnitude faster than homogeneous freezing. The critical
nucleus is substantially smaller than that found for homogeneous nucleation
and, in contrast to the predictions of classical nucleation theory (CNT), it
has a strong 2D character. Nonetheless, we show that CNT describes correctly
the formation of ice at this complex interface. Kaolinite also promotes the
exclusive nucleation of hexagonal ice, as opposed to homogeneous freezing where
a mixture of cubic and hexagonal polytypes is observed
Relativistic descriptions of final-state interactions in neutral-current neutrino-nucleus scattering at MiniBooNE kinematics
The analysis of the recent neutral-current neutrino-nucleus scattering cross
sections measured by the MiniBooNE Collaboration requires relativistic
theoretical descriptions also accounting for the role of final state
interactions. In this work we evaluate differential cross sections with the
relativistic distorted-wave impulse-approximation and with the relativistic
Green's function model to investigate the sensitivity to final state
interactions. The role of the strange-quark content of the nucleon form factors
is also discussed.Comment: 8 pages, 5 figure
Wireless communication, identification and sensing technologies enabling integrated logistics: a study in the harbor environment
In the last decade, integrated logistics has become an important challenge in
the development of wireless communication, identification and sensing
technology, due to the growing complexity of logistics processes and the
increasing demand for adapting systems to new requirements. The advancement of
wireless technology provides a wide range of options for the maritime container
terminals. Electronic devices employed in container terminals reduce the manual
effort, facilitating timely information flow and enhancing control and quality
of service and decision made. In this paper, we examine the technology that can
be used to support integration in harbor's logistics. In the literature, most
systems have been developed to address specific needs of particular harbors,
but a systematic study is missing. The purpose is to provide an overview to the
reader about which technology of integrated logistics can be implemented and
what remains to be addressed in the future
Timing as a sexually selected trait: the right mate at the right moment
Sexual selection favours the expression of traits in one sex that attract members of the opposite sex for mating. The nature of sexually selected traits such as vocalization, colour and ornamentation, their fitness benefits as well as their costs have received ample attention in field and laboratory studies. However, sexually selected traits may not always be expressed: coloration and ornaments often follow a seasonal pattern and behaviours may be displayed only at specific times of the day. Despite the widely recognized differences in the daily and seasonal timing of traits and their consequences for reproductive success, the actions of sexual selection on the temporal organization of traits has received only scant attention. Drawing on selected examples from bird and mammal studies, here we summarize the current evidence for the daily and seasonal timing of traits. We highlight that molecular advances in chronobiology have opened exciting new opportunities for identifying the genetic targets that sexual selection may act on to shape the timing of trait expression. Furthermore, known genetic links between daily and seasonal timing mechanisms lead to the hypothesis that selection on one timescale may simultaneously also affect the other. We emphasize that studies on the timing of sexual displays of both males and females from wild populations will be invaluable for understanding the nature of sexual selection and its potential to act on differences within and between the sexes in timing. Molecular approaches will be important for pinpointing genetic components of biological rhythms that are targeted by sexual selection, and to clarify whether these represent core or peripheral components of endogenous clocks. Finally, we call for a renewed integration of the fields of evolution, behavioural ecology and chronobiology to tackle the exciting question of how sexual selection contributes to the evolution of biological clocks.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'
Surrogate models for precessing binary black hole simulations with unequal masses
Only numerical relativity simulations can capture the full complexities of
binary black hole mergers. These simulations, however, are prohibitively
expensive for direct data analysis applications such as parameter estimation.
We present two new fast and accurate surrogate models for the outputs of these
simulations: the first model, NRSur7dq4, predicts the gravitational waveform
and the second model, \RemnantModel, predicts the properties of the remnant
black hole. These models extend previous 7-dimensional, non-eccentric
precessing models to higher mass ratios, and have been trained against 1528
simulations with mass ratios and spin magnitudes , with generic spin directions. The waveform model, NRSur7dq4, which begins
about 20 orbits before merger, includes all spin-weighted
spherical harmonic modes, as well as the precession frame dynamics and spin
evolution of the black holes. The final black hole model, \RemnantModel, models
the mass, spin, and recoil kick velocity of the remnant black hole. In their
training parameter range, both models are shown to be more accurate than
existing models by at least an order of magnitude, with errors comparable to
the estimated errors in the numerical relativity simulations. We also show that
the surrogate models work well even when extrapolated outside their training
parameter space range, up to mass ratios .Comment: Matches published version. Models publicly available at
https://zenodo.org/record/3455886#.XZ9s1-dKjBI and
https://pypi.org/project/surfinB
Processing and characterization of dual phase steel foam
Porous materials featuring cellular structures are known to have many interesting combinations of physical and mechanical properties. Some of them have been extensively used in the transportation field (i.e. balsa wood). Steel foams presented promising theoretical properties for both functional and structural applications in transportation, but processing of such a kind of foams is complex due to their high melting point. Recently a technique for processing Cu-based alloys open-cell foams through the molten metal infiltration of a leachable bed of amorphous SiO2 particles was proposed. A variation of the proposed technique that uses SiC particles as space holder is now presented and was recently successfully applied for dual phase steel foam processing. Results from a processing of dual phase DP500 steel foams, including some morphological, micro-structural and mechanical characterization, are here presented
Mechanisms of 2n potato pollen formation in dihaploid Solanum tuberosum L. x S. chacoense Bitt. hybrid clones.
The backcrosses of dihaploid Solanum tuberosum with wild species hybrids generating tetraploids progenies require the formation of non-reduced pollen. In this work, the mechanisms responsible for the formation of 2n pollen in 28 dihaploid Solanum tuberosum x Solanum chacoense hybrids were studied. Four mechanisms were found: parallelspindles (ps), fused spindles (fs), premature cytokinesis-1 (pc-1) and premature cytokinesis-2 (pc-2). The ps mechanism was the most frequent, being found in 23 of the 28 assessed clones. The ps and fs mechanisms led to the formation of dyads by first division restitution (FDR), transferring about 80% of the heterozygosity to the progenies. The pc-1 and pc-2 mechanisms also led to the formation of dyads, but they were genetically equivalent to second division restitution (SDR), transferring only 40% of the heterozygosity to the progenies. Occurrence of FDR and SDR were shown to be associated in 12 clones, indicating that the clones can produce non-reduced microspores by more than one mechanism. However, only one mechanism is functional in a single pollen-grain mother-cell. Clones 9-2, 9-3, 9-6 and 15-15 are recommended for use in 4x x 2x matings
Deep Chandra and multicolor HST observations of the jets of 3C 371 and PKS 2201+044
This paper presents multiwavelength imaging and broad-band spectroscopy of
the relativistic jets in the two nearby radio galaxies 3C 371 and PKS 2201+044,
acquired with Chandra, HST, VLA, and Merlin. Radio polarization images are also
available. The two sources stand out as "intermediate'' between FRIs and FRIIs;
their cores are classified as BL Lacs, although broad and narrow optical
emission lines were detected at times. The multiwavelength images show jet
morphologies with the X-ray emission peaking closer to the nucleus than the
longer wavelengths. The jets are resolved at all wavelengths in a direction
perpendicular to the jet axis. The jets SEDs are consistent with a single
spectral component from radio to X-rays, interpreted as synchrotron emission.
The SEDs show a progressive softening from the inner to the outer regions of
the jet, indicating that the electron break energy moves to lower energies with
distance from the core. Overall, the X-ray and multiwavelength properties of
the jets of 3C 371 and PKS 2201+044 appear intermediate between those of FRIs
and FRIIs.Comment: Accepted for publication in ApJ; 28 pages (emulateapj5), 17 figure
Anomalous Aharonov--Bohm gap oscillations in carbon nanotubes
The gap oscillations caused by a magnetic flux penetrating a carbon nanotube
represent one of the most spectacular observation of the Aharonov-Bohm effect
at the nano--scale. Our understanding of this effect is, however, based on the
assumption that the electrons are strictly confined on the tube surface, on
trajectories that are not modified by curvature effects. Using an ab-initio
approach based on Density Functional Theory we show that this assumption fails
at the nano-scale inducing important corrections to the physics of the
Aharonov-Bohm effect. Curvature effects and electronic density spilled out of
the nanotube surface are shown to break the periodicity of the gap
oscillations. We predict the key phenomenological features of this anomalous
Aharonov-Bohm effect in semi-conductive and metallic tubes and the existence of
a large metallic phase in the low flux regime of Multi-walled nanotubes, also
suggesting possible experiments to validate our results.Comment: 7 figure
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