7,188 research outputs found
V2PSense: Enabling Cellular-based V2P Collision Warning Service Through Mobile Sensing
The C-V2X (Cellular Vehicle-to-Everything) technology
is developing in full swing. One of its mainstream services
can be the Vehicle-to-Pedestrian (V2P) service. It can protect
pedestrians who are mostly vulnerable on the road. In this
work, we seek to enable a V2P service that can identify which
pedestrians may be nearby a dangerous driving event and then
notify them of warning messages. To enable this V2P service,
there are two major challenges. First, a low-latency V2P message
transport is required for this infrastructure-based service.
Second, the pedestrian’s smartphone requires an energy-efficient
outdoor positioning method instead of power-hungry GPS due
to its limited battery life. We thus propose a novel solution,
V2PSense, which trades off positioning precision for energy
savings while achieving low-latency message transport with LTE
high-priority bearers. It does a coarse-grained positioning by
leveraging intermittent GPS information and mobile sensing data,
which includes step count from the pedometer and cellular signal
strength changes. Though the V2PSense’s positioning is not as
precise as the GPS, it can still ensure that all the pedestrians
nearby dangerous spots can be notified. Our results show that
it can achieve the average precision ratio 92.6% for estimating
where the pedestrian is while saving 20.8% energy, compared
with the GPS always-on case.This work was partially supported by the Ministry of Science and Tech-nology, Taiwan, under grant numbers 106-2622-8-009-017 and 106-2218-E-009-018, and by the H2020 collaborative Europe/Taiwan research project 5G-CORAL (grant num. 761586
A Three-Dimensional Tight-Binding Model and Magnetic Instability of KFe2e2
For a newly discovered iron-based high T_c superconducting parent material
KFe2Se2, we present an effective three-dimensional five-orbital tight-binding
model by fitting the band structures. The three t2g-symmetry orbitals of the
five Fe 3d orbitals mainly contribute to the electron-like Fermi surface, in
agreement with recent angle-resolved photoemission spectroscopy experiments. To
understand the groundstate magnetic structure, the two- and three-dimensional
dynamical spin susceptibilities within the random phase approximation are
investigated. It obviously shows a sharp peak at wave vector
(, ), indicating the magnetic instability of {\it
Nel}-type antiferromagnetic rather than (/2, /2)-type
antiferromagnetic ordering. While along \emph{c} axis, it exhibits a
ferromagnetic coupling between the nearest neighboring FeSe layers. The
difference between the present results and the experimental observation in
KxFe2-ySe2 is attributed to the presence of Fe vacancy in the latter.Comment: 14 pages, 8 figure
Oxygen Vacancy Induced Ferromagnetism in VO
{\it Ab initio} calculations within density functional theory with
generalized gradient approximation have been performed to study the effects of
oxygen vacancies on the electronic structure and magnetism in undoped
VO (). It is found that the introduction of oxygen
vacancies would induce ferromagnetism in VO with the magnetization
being proportional to the O vacancy concentration . The calculated
electronic structure reveals that the valence electrons released by the
introduction of oxygen vacancies would occupy mainly the neighboring V
-dominant band which then becomes spin-polarized due to intra-atomic
exchange interaction, thereby giving rise to the half-metallic ferromagnetism.Comment: To be published as a Letter in J. Phys. Soc. Japa
Theoretical Limits on the Equation-of-State Parameter of Phantom Cosmology
We investigate the restrictions on the equation-of-state parameter of phantom
cosmology, due to the minimum quantum gravitational requirements. We find that
for all the examined -parametrizations and for arbitrary phantom
potentials and spatial curvature, the phantom equation-of-state parameter is
not restricted at all. This is in radical contrast with the quintessence
paradigm, and makes phantom cosmology more robust and capable of constituting
the underlying mechanism for dark energy.Comment: 7 pages, 7 figure
Holographic dark energy and cosmic coincidence
In this Letter we demonstrate that any interaction of pressureless dark
matter with holographic dark energy, whose infrared cutoff is set by the Hubble
scale, implies a constant ratio of the energy densities of both components thus
solving the coincidence problem. The equation of state parameter is obtained as
a function of the interaction strength. For a variable degree of saturation of
the holographic bound the energy density ratio becomes time dependent which is
compatible with a transition from decelerated to accelerated expansion.Comment: 9 pages, no figures, references updated, typos eliminated. To be
published in Physics Letters
Constraints on holographic dark energy from X-ray gas mass fraction of galaxy clusters
We use the Chandra measurements of the X-ray gas mass fraction of 26 rich
clusters released by Allen et al. to perform constraints on the holographic
dark energy model. The constraints are consistent with those from other
cosmological tests, especially with the results of a joint analysis of
supernovae, cosmic microwave background, and large scale structure data. From
this test, the holographic dark energy also tends to behave as a quintom-type
dark energy.Comment: 5 pages, 3 figures; to appear in Phys. Lett.
Possible theoretical limits on holographic quintessence from weak gravity conjecture
The holographic dark energy model is one of the important ways for dealing
with the dark energy problems in the quantum gravity framework. In this model,
the dimensionless parameter plays an essential role in determining the
evolution of the holographic dark energy. In particular, the holographic dark
energy with can be effectively described by a quintessence
scalar-field. However, according to the requirement of the weak gravity
conjecture the variation of the quintessence scalar-field should be less than
the Planck mass, which would give theoretic constraints on the parameters
and . Therefore, we get the possible theoretical limits
on the parameter for the holographic quintessence model.Comment: LaTex, 13 pages and 4 figures, revised versio
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