10,298 research outputs found
Deep Reinforcement Learning for Resource Allocation in V2V Communications
In this article, we develop a decentralized resource allocation mechanism for
vehicle-to-vehicle (V2V) communication systems based on deep reinforcement
learning. Each V2V link is considered as an agent, making its own decisions to
find optimal sub-band and power level for transmission. Since the proposed
method is decentralized, the global information is not required for each agent
to make its decisions, hence the transmission overhead is small. From the
simulation results, each agent can learn how to satisfy the V2V constraints
while minimizing the interference to vehicle-to-infrastructure (V2I)
communications
Progenitor delay-time distribution of short gamma-ray bursts: Constraints from observations
Context. The progenitors of short gamma-ray bursts (SGRBs) have not yet been
well identified. The most popular model is the merger of compact object
binaries (NS-NS/NS-BH). However, other progenitor models cannot be ruled out.
The delay-time distribution of SGRB progenitors, which is an important property
to constrain progenitor models, is still poorly understood. Aims. We aim to
better constrain the luminosity function of SGRBs and the delay-time
distribution of their progenitors with newly discovered SGRBs. Methods. We
present a low-contamination sample of 16 Swift SGRBs that is better defined by
a duration shorter than 0.8 s. By using this robust sample and by combining a
self-consistent star formation model with various models for the distribution
of time delays, the redshift distribution of SGRBs is calculated and then
compared to the observational data. Results. We find that the power-law delay
distribution model is disfavored and that only the lognormal delay distribution
model with the typical delay tau >= 3 Gyr is consistent with the data.
Comparing Swift SGRBs with T90 > 0.8 s to our robust sample (T90 < 0.8 s), we
find a significant difference in the time delays between these two samples.
Conclusions. Our results show that the progenitors of SGRBs are dominated by
relatively long-lived systems (tau >= 3 Gyr), which contrasts the results found
for Type Ia supernovae. We therefore conclude that primordial NS-NS systems are
not favored as the dominant SGRB progenitors. Alternatively, dynamically formed
NS-NS/BH and primordial NS-BH systems with average delays longer than 5 Gyr may
contribute a significant fraction to the overall SGRB progenitors.Comment: 8 pages, 6 figures, Astron. Astrophys. in pres
Energy-storage properties and electrocaloric effects of Pb(1-3x/2)LaxZr0.85Ti0.15O3 antiferroelectric thick films
1-µm-Pb(1-3x/2)LaxZr0.85Ti0.15O3 (PLZT) antiferroelectric (AFE) thick films with x = 0.08,
0.10, 0.12, and 0.14 were deposited on LaNiO3/Si (100) substrates by a sol-gel method. The
dielectric properties, energy-storage performance, electrocaloric effect, and leakage current behavior
were investigated in detail. With increasing La content, dielectric constant and saturated polarizations
of the thick films were gradually decreased. A maximum recoverable energy-storage density of 38
J/cm3 and efficiency of 71% were achieved in the thick films with x = 0.12 at room temperature.
Moreover, a large reversible adiabatic temperature change ∆T = 25.0
o
C was presented in the thick
films with x = 0.08 at 127
o
C at 990 kV/cm. All the samples had a lower leakage current density
below 10-
6
A/cm2 at room temperature. These results indicated that the PLZT AFE thick films could
be a potential candidate for applications in high energy-storage density capacitors and cooling
devices
A giant electrocaloric effect of a Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3 antiferroelectric thick film at room temperature
A 2-µm-Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3 (PLZST) antiferroelectric (AFE) thick film with tetragonal structure was deposited on LaNiO3/Si (100) substrates via a sol-gel technique. The electrocaloric effect (ECE) of the PLZST thick film is investigated under the functions of external electric field and temperature. Giant ECEs (∆T = 53.8 oC and ∆S = 63.9 J·K-1·kg-1) are received at 5 oC, which is attributed to a field-induced AFE to ferroelectric (FE) phase transition. Moreover, a large ∆T of above 30 oC is remains at temperature range from 5 oC to 25 oC. The maximum electrocaloric coefficient (ξmax = 0.060 K·cm/kV) and refrigeration efficiency (COP = 18) of the film are also obtained at 5 oC. At room temperature, the values of ∆T, ∆S, COP and ξmax are 35.0 oC, 39.0 J·K-1·kg-1, 14 and 0.039 K·cm/kV at 900 kV/cm, respectively. The AFE thick films with giant ECEs are promising candidates for applications in cooling systems at room temperature
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