419 research outputs found
Rods are less fragile than spheres: Structural relaxation in dense liquids composed of anisotropic particles
We perform extensive molecular dynamics simulations of dense liquids composed
of bidisperse dimer- and ellipse-shaped particles in 2D that interact via
repulsive contact forces. We measure the structural relaxation times obtained
from the long-time decay of the self-part of the intermediate scattering
function for the translational and rotational degrees of freedom (DOF) as a
function of packing fraction \phi, temperature T, and aspect ratio \alpha. We
are able to collapse the \phi and T-dependent structural relaxation times for
disks, and dimers and ellipses over a wide range of \alpha, onto a universal
scaling function {\cal F}_{\pm}(|\phi-\phi_0|,T,\alpha), which is similar to
that employed in previous studies of dense liquids composed of purely repulsive
spherical particles in 3D. {\cal F_{\pm}} for both the translational and
rotational DOF are characterized by the \alpha-dependent scaling exponents \mu
and \delta and packing fraction \phi_0(\alpha) that signals the crossover in
the scaling form {\cal F}_{\pm} from hard-particle dynamics to super-Arrhenius
behavior for each aspect ratio. We find that the fragility at \phi_0,
m(\phi_0), decreases monotonically with increasing aspect ratio for both
ellipses and dimers. Moreover, the results for the slow dynamics of dense
liquids composed of dimer- and ellipse-shaped particles are qualitatively the
same, despite the fact that zero-temperature static packings of dimers are
isostatic, while static packings of ellipses are hypostatic.Comment: 10 pages, 17 figures, and 1 tabl
Observation of the non-Hermitian skin effect and Fermi skin on a digital quantum computer
Non-Hermitian physics has attracted considerable attention in the recent
years, in particular the non-Hermitian skin effect (NHSE) for its extreme
sensitivity and non-locality. While the NHSE has been physically observed in
various classical metamaterials and even ultracold atomic arrays, its
highly-nontrivial implications in many-body dynamics have never been
experimentally investigated. In this work, we report the first observation of
the NHSE on a universal quantum processor, as well as its characteristic but
elusive Fermi skin from many-fermion statistics. To implement NHSE dynamics on
a quantum computer, the effective time-evolution circuit not only needs to be
non-reciprocal and non-unitary, but must also be scaled up to a sufficient
number of lattice qubits to achieve spatial non-locality. We show how such a
non-unitary operation can be systematically realized by post-selecting multiple
ancilla qubits, as demonstrated through two paradigmatic non-reciprocal models
on a noisy IBM quantum processor, with clear signatures of asymmetric spatial
propagation and many-body Fermi skin accumulation. To minimize errors from
inevitable device noise, time evolution is performed using a trainable
optimized quantum circuit produced with variational quantum algorithms. Our
study represents a critical milestone in the quantum simulation of
non-Hermitian lattice phenomena on present-day quantum computers, and can be
readily generalized to more sophisticated many-body models with the remarkable
programmability of quantum computers.Comment: 24 pages and 13 figure
A Novel Autonomous Robotics System for Aquaculture Environment Monitoring
Implementing fully automatic unmanned surface vehicles (USVs) monitoring
water quality is challenging since effectively collecting environmental data
while keeping the platform stable and environmental-friendly is hard to
approach. To address this problem, we construct a USV that can automatically
navigate an efficient path to sample water quality parameters in order to
monitor the aquatic environment. The detection device needs to be stable enough
to resist a hostile environment or climates while enormous volumes will disturb
the aquaculture environment. Meanwhile, planning an efficient path for
information collecting needs to deal with the contradiction between the
restriction of energy and the amount of information in the coverage region. To
tackle with mentioned challenges, we provide a USV platform that can perfectly
balance mobility, stability, and portability attributed to its special
round-shape structure and redundancy motion design. For informative planning,
we combined the TSP and CPP algorithms to construct an optimistic plan for
collecting more data within a certain range and limiting energy restrictions.We
designed a fish existence prediction scenario to verify the novel system in
both simulation experiments and field experiments. The novel aquaculture
environment monitoring system significantly reduces the burden of manual
operation in the fishery inspection field. Additionally, the simplicity of the
sensor setup and the minimal cost of the platform enables its other possible
applications in aquatic exploration and commercial utilization
Spectral Efficiency Analysis of Uplink-Downlink Decoupled Access in C-V2X Networks
The uplink (UL)/downlink (DL) decoupled access has been emerging as a novel
access architecture to improve the performance gains in cellular networks. In
this paper, we investigate the UL/DL decoupled access performance in cellular
vehicle-to-everything (C-V2X). We propose a unified analytical framework for
the UL/DL decoupled access in C-V2X from the perspective of spectral efficiency
(SE). By modeling the UL/DL decoupled access C-V2X as a Cox process and
leveraging the stochastic geometry, we obtain the joint association
probability, the UL/DL distance distributions to serving base stations and the
SE for the UL/DL decoupled access in C-V2X networks with different association
cases. We conduct extensive Monte Carlo simulations to verify the accuracy of
the proposed unified analytical framework, and the results show a better system
average SE of UL/DL decoupled access in C-V2X.Comment: 6pagaes,5 figures, globecom 202
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