4,631 research outputs found
High-energy Neutrinos from Merging Stellar-mass Black Holes in Active Galactic Nuclei Accretion Disk
A population of binary stellar-mass black hole (BBH) mergers are believed to
occur embedded in the accretion disk of active galactic nuclei (AGNs). In this
{\em Letter}, we demonstrate that the jets from these BBH mergers can propagate
collimatedly within the disk atmosphere along with a forward shock and a
reverse shock forming at the jet head. Efficient proton acceleration by these
shocks is usually expected before the breakout, leading to the production of
TeVPeV neutrinos through interactions between these protons and
electron-radiating photons via photon-meson production. AGN BBH mergers
occurring in the outer regions of the disk are more likely to produce more
powerful neutrino bursts. Taking the host AGN properties of the potential
GW190521 electromagnetic (EM) counterpart as an example, one expects
neutrino events detectable by IceCube if the jet is on-axis and the radial
location of the merger is , where is the
gravitational radius of the supermassive BH. Neutrino bursts from AGN BBH
mergers could be detected by IceCube following the observation of gravitational
waves (GWs), serving as precursor signals before the detection of EM breakout
signals. AGN BBH mergers are potential target sources for future joint GW,
neutrino, and EM multi-messenger observations.Comment: Accepted by MNRAS Letters. Comments are welcome. 8 pages, 1 table, 3
figures, and 1 beautiful schematic figure in the appendi
Design of a multiple bloom filter for distributed navigation routing
Unmanned navigation of vehicles and mobile robots can be greatly simplified by providing environmental intelligence with dispersed wireless sensors. The wireless sensors can work as active landmarks for vehicle localization and routing. However, wireless sensors are often resource scarce and require a resource-saving design. In this paper, a multiple Bloom-filter scheme is proposed to compress a global routing table for a wireless sensor. It is used as a lookup table for routing a vehicle to any destination but requires significantly less memory space and search effort. An error-expectation-based design for a multiple Bloom filter is proposed as an improvement to the conventional false-positive-rate-based design. The new design is shown to provide an equal relative error expectation for all branched paths, which ensures a better network load balance and uses less memory space. The scheme is implemented in a project for wheelchair navigation using wireless camera motes. © 2013 IEEE
The long-lasting optical afterglow plateau of short burst GRB 130912A
The short burst GRB 130912A was detected by Swift, Fermi satellites and
several ground-based optical telescopes. Its X-ray light curve decayed with
time normally. The optical emission, however, displayed a long term plateau,
which is the longest one in current short GRB observations. In this work we
examine the physical origin of the X-ray and optical emission of this peculiar
event. We find that the canonical forward shock afterglow emission model can
account for the X-ray and optical data self-consistently and the energy
injection model that has been widely adopted to interpret the
shallowly-decaying afterglow emission is not needed. We also find that the
burst was born in a very-low density interstellar medium, consistent with the
compact object merger model. Significant fractions of the energy of the forward
shock have been given to accelerate the non-thermal electrons and amplify the
magnetic fields (i.e., and , respectively), which are much larger than those inferred in most short
burst afterglow modeling and can explain why the long-lasting optical afterglow
plateau is rare in short GRBs.Comment: 5 pages, 2 figure
Transmission resonance in a composite plasmonic structure
The design, fabrication, and optical properties of a composite plasmonic
structure, a two-dimentional array of split-ring resonators inserted into
periodic square holes of a metal film, have been reported. A new type of
transmission resonance, which makes a significant difference from the
conventional peaks, has been suggested both theoretically and experimentally.
To understand this effect, a mechanism of ring- resonance induced dipole
emission is proposed.Comment: 14 pages, 4 figure
High-energy Neutrino Productions from AGN Disk Transients Impacted by Circum-disk Medium
Various supernovae (SN), compact object coalescences, and tidal disruption
events are widely believed to occur embedded in active galactic nuclei (AGN)
accretion disks and generate detectable electromagnetic (EM) signals. We
collectively refer to them as \emph{AGN disk transients}. The inelastic
hadronuclear () interactions between shock-accelerated cosmic rays and AGN
disk materials shortly after the ejecta shock breaks out of the disk can
produce high-energy neutrinos. However, the expected efficiency of neutrino
production would decay rapidly by adopting a pure Gaussian density atmosphere
profile applicable for stable gas-dominated disks. On the other hand, AGN
outflows and disk winds are commonly found around AGN accretion disks. In this
paper, we present that the circum-disk medium would further consume the shock
kinetic energy to more efficiently produce high-energy neutrinos, especially
for \,TeVPeV neutrinos that IceCube is interested in. Thanks to the
existence of the circum-disk medium, we find that the neutrino production will
be enhanced significantly and make a much higher contribution to the diffuse
neutrino background. Optimistically, diffuse neutrino background can
be contributed from AGN disk transients.Comment: 10 Pages, 3 figurs and 2 tables; Submitted to ApJ
Studying newborn neutron stars by the transient emission after stellar collapses and compact binary mergers
The formation of neutron stars (NSs), both from collapses of massive stars
and mergers of compact objects, can be usually indicated by bright transients
emitted from explosively-ejected material. In particular, if the newborn NSs
can rotate at a millisecond period and have a sufficiently high magnetic field,
then the spin-down of the NSs would provide a remarkable amount of energy to
the emitting material. As a result, super-luminous supernovae could be produced
in the massive stellar collapse cases, while some unusual fast evolving and
luminous optical transients could arise from the cases of NS mergers and
accretion-induced collapses of white dwarfs. In all cases, if the dipolar
magnetic fields of the newborn NSs can be amplified to be as high as
G, a relativistic jet could be launched and then a gamma-ray burst can be
produced as the jet successfully breaks out from the surrounding
nearly-isotropic ejected material.Comment: 10 pages, 9 pictures, to appear in the AIP Proceedings of the
Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era
of Gravitational Wave Astronomy, Jan. 3-7, Xiamen, Chin
A mosaic of eyes
Autonomous navigation is a traditional research topic in intelligent robotics and vehicles, which requires a robot to perceive its environment through onboard sensors such as cameras or laser scanners, to enable it to drive to its goal. Most research to date has focused on the development of a large and smart brain to gain autonomous capability for robots. There are three fundamental questions to be answered by an autonomous mobile robot: 1) Where am I going? 2) Where am I? and 3) How do I get there? To answer these basic questions, a robot requires a massive spatial memory and considerable computational resources to accomplish perception, localization, path planning, and control. It is not yet possible to deliver the centralized intelligence required for our real-life applications, such as autonomous ground vehicles and wheelchairs in care centers. In fact, most autonomous robots try to mimic how humans navigate, interpreting images taken by cameras and then taking decisions accordingly. They may encounter the following difficulties
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