60 research outputs found
Early afterglow, magnetized central engine, and a quasi-universal jet configuration for long GRBs
Two separate topics are discussed. (1) We describe the classifications of the
long GRB early afterglow lightcurves within the framework of the fireball shock
model, focusing on the interplay between the reverse and forward shock emission
components. We will also provide evidence that the central engine of at least
two bursts are entrained with strong magnetic fields, and discuss the
implications of this result for our understanding of the GRB phenomenon; (2) We
argue that the current gamma-ray burst (GRB) and X-ray flash (XRF) data are
consistent with a picture that all GRB-XRF jets are structured and
quasi-universal, with a typical Gaussian-like jet structure.Comment: 5 pages, 8 figures, to appear in the Proceedings of Santa Fe GRB
Conference (talk by Zhang at the meeting
The SOS Pilot Study: a RCT of routine oxygen supplementation early after acute strokeâeffect on recovery of neurological function at one week
Mild hypoxia is common after stroke and associated with poor long-term outcome. Oxygen supplementation could prevent hypoxia and improve recovery. A previous study of routine oxygen supplementation showed no significant benefit at 7 and 12 months. This pilot study reports the effects of routine oxygen supplementation for 72 hours on oxygen saturation and neurological outcomes at 1 week after a stroke
Light-Driven Nanoscale Vectorial Currents
Controlled charge flows are fundamental to many areas of science and
technology, serving as carriers of energy and information, as probes of
material properties and dynamics, and as a means of revealing or even inducing
broken symmetries. Emerging methods for light-based current control offer
promising routes beyond the speed and adaptability limitations of conventional
voltage-driven systems. However, optical manipulation of currents at nanometer
spatial scales remains a basic challenge and a key step toward scalable
optoelectronic systems and local probes. Here, we introduce vectorial
optoelectronic metasurfaces as a new class of metamaterial in which ultrafast
charge flows are driven by light pulses, with actively-tunable directionality
and arbitrary patterning down to sub-diffractive nanometer scales. In the
prototypical metasurfaces studied herein, asymmetric plasmonic nanoantennas
locally induce directional, linear current responses within underlying
graphene. Nanoscale unit cell symmetries are read out via polarization- and
wavelength-sensitive currents and emitted terahertz (THz) radiation. Global
vectorial current distributions are revealed by spatial mapping of the THz
field polarization, also demonstrating the direct generation of elusive
broadband THz vector beams. We show that a detailed interplay between
electrodynamic, thermodynamic, and hydrodynamic degrees of freedom gives rise
to these currents through rapidly-evolving nanoscale forces and charge flows
under extreme spatial and temporal localization. These results set the stage
for versatile patterning and optical control over nanoscale currents in
materials diagnostics, nano-magnetism, microelectronics, and ultrafast
information science
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs
(Abridged) The two high-redshift gamma-ray bursts, GRB 080913 at z=6.7 and
GRB 090423 at z=8.3, recently detected by Swift appear as intrinsically short,
hard GRBs. They could have been recognized by BATSE as short/hard GRBs should
they have occurred at z <= 1. We perform a more thorough investigation on two
physically distinct types (Type I/II) of cosmological GRBs and their
observational characteristics. We reiterate the definitions of Type I/II GRBs
and review the observational criteria and their physical motivations. Contrary
to the traditional approach of assigning the physical category based on the
gamma-ray properties (duration, hardness, and spectral lag), we take an
alternative approach to define the Type I and Type II Gold Samples using
several criteria that are more directly related to the GRB progenitors, and
study the properties of the two Gold Samples and compare them with the
traditional long/soft and short/hard samples. We find that the Type II Gold
Sample reasonably tracks the long/soft population, although it includes several
intrinsically short (shorter than 1s in the rest frame) GRBs. The Type I Gold
Sample only has 5 GRBs, 4 of which are not strictly short but have extended
emission. Other short/hard GRBs detected in the Swift era represent the BATSE
short/hard sample well, but it is unclear whether all of them belong to Type I.
We suggest that some (probably even most) high-luminosity short/hard GRBs
instead belong to Type II. We suggest that GRB 080913 and GRB 090423 are more
likely Type II events. We re-emphasize the importance of invoking multiple
observational criteria, and cautiously propose an operational procedure to
infer the physical origin of a given GRB with available multiple observational
criteria, with various caveats laid out.Comment: 32 pages, ApJ, in press. The strengths and weaknesses of physical
classification and its relation to phenomenological classification are fully
discussed in a newly added section 3. Discussions on GRBs 090423, 090426, and
090510 are include
Astrophysics with the Laser Interferometer Space Antenna
Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy as it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and other space-based instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed: ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or intermediate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help make progress in the different areas. New research avenues that LISA itself, or its joint exploitation with studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe
AI is a viable alternative to high throughput screening: a 318-target study
: High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that our AtomNetÂź convolutional neural network successfully finds novel hits across every major therapeutic area and protein class. We address historical limitations of computational screening by demonstrating success for target proteins without known binders, high-quality X-ray crystal structures, or manual cherry-picking of compounds. We show that the molecules selected by the AtomNetÂź model are novel drug-like scaffolds rather than minor modifications to known bioactive compounds. Our empirical results suggest that computational methods can substantially replace HTS as the first step of small-molecule drug discovery
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