39,852 research outputs found
The fundamental theorem of affine geometry in
Let be the algebra of equivalence classes of real valued random
variables on a probability space. For each integer , we consider
--the -ary Cartesian power of --as a free -module and
establish the fundamental theorem of affine geometry in : an injective
map which has local property and maps each -line
onto an -line must be an -affine linear map.Comment: 10 page
Energy-Efficient Offloading in Mobile Edge Computing with Edge-Cloud Collaboration
Multiple access mobile edge computing is an emerging technique to bring
computation resources close to end mobile users. By deploying edge servers at
WiFi access points or cellular base stations, the computation capabilities of
mobile users can be extended. Existing works mostly assume the remote cloud
server can be viewed as a special edge server or the edge servers are willing
to cooperate, which is not practical. In this work, we propose an edge-cloud
cooperative architecture where edge servers can rent for the remote cloud
servers to expedite the computation of tasks from mobile users. With this
architecture, the computation offloading problem is modeled as a mixed integer
programming with delay constraints, which is NP-hard. The objective is to
minimize the total energy consumption of mobile devices. We propose a greedy
algorithm as well as a simulated annealing algorithm to effectively solve the
problem. Extensive simulation results demonstrate that, the proposed greedy
algorithm and simulated annealing algorithm can achieve the near optimal
performance. On average, the proposed greedy algorithm can achieve the same
application completing time budget performance of the Brute Force optional
algorithm with only 31\% extra energy cost. The simulated annealing algorithm
can achieve similar performance with the greedy algorithm.Comment: Accepted by the 18th International Conference on Algorithms and
Architectures for Parallel Processing (ICA3PP 2018
Seeing Permeability From Images: Fast Prediction with Convolutional Neural Networks
Fast prediction of permeability directly from images enabled by image
recognition neural networks is a novel pore-scale modeling method that has a
great potential. This article presents a framework that includes (1) generation
of porous media samples, (2) computation of permeability via fluid dynamics
simulations, (3) training of convolutional neural networks (CNN) with simulated
data, and (4) validations against simulations. Comparison of machine learning
results and the ground truths suggests excellent predictive performance across
a wide range of porosities and pore geometries, especially for those with
dilated pores. Owning to such heterogeneity, the permeability cannot be
estimated using the conventional Kozeny-Carman approach. Computational time was
reduced by several orders of magnitude compared to fluid dynamic simulations.
We found that, by including physical parameters that are known to affect
permeability into the neural network, the physics-informed CNN generated better
results than regular CNN, however improvements vary with implemented
heterogeneity.Comment: 17 pages, 8 figure
Convergence Analysis for A Class of Iterative Methods for Solving Saddle Point Systems
Convergence analysis of a nested iterative scheme proposed by Bank,Welfert
and Yserentant (BWY) ([Numer. Math., 666: 645-666, 1990]) for solving saddle
point system is presented. It is shown that this scheme converges under weaker
conditions: the contraction rate for solving the block matrix is bound
by . Similar convergence result is also obtained for a class of
inexact Uzawa method with even weaker contraction bound .
Preconditioned generalized minimal residual method using BWY method as a
preconditioner is shown to converge with realistic assumptions
A protocol to estimate the average fidelity of the bipartite system
In present work, we shall develope a protocol to estimate the average
fidelity for the bipartite system. We show that the average fidelity should be
known if the three measurable quantities, the average survive probability of
the product state and the the average survive probablity of each subsystem,
have been decided. Our protocol can be also applied to decide the selected
element of the quantum proess matrix.Comment: 10 pages, 4 figure
ENGINE:Cost Effective Offloading in Mobile Edge Computing with Fog-Cloud Cooperation
Mobile Edge Computing (MEC) as an emerging paradigm utilizing cloudlet or fog
nodes to extend remote cloud computing to the edge of the network, is foreseen
as a key technology towards next generation wireless networks. By offloading
computation intensive tasks from resource constrained mobile devices to fog
nodes or the remote cloud, the energy of mobile devices can be saved and the
computation capability can be enhanced. For fog nodes, they can rent the
resource rich remote cloud to help them process incoming tasks from mobile
devices. In this architecture, the benefit of short computation and computation
delay of mobile devices can be fully exploited. However, existing studies
mostly assume fog nodes possess unlimited computing capacity, which is not
practical, especially when fog nodes are also energy constrained mobile
devices. To provide incentive of fog nodes and reduce the computation cost of
mobile devices, we provide a cost effective offloading scheme in mobile edge
computing with the cooperation between fog nodes and the remote cloud with task
dependency constraint. The mobile devices have limited budget and have to
determine which task should be computed locally or sent to the fog. To address
this issue, we first formulate the offloading problem as a task finish time
inimization problem with given budgets of mobile devices, which is NP-hard. We
then devise two more algorithms to study the network performance. Simulation
results show that the proposed greedy algorithm can achieve the near optimal
performance. On average, the Brute Force method and the greedy algorithm
outperform the simulated annealing algorithm by about 28.13% on the application
finish time.Comment: 10 pages, 9 figures, Technical Repor
Perturbative scattering in chiral effective field theory
Within the framework of chiral effective field theory, perturbative
calculation for scattering is carried out in partial waves with orbital
angular momentum . The primary goal is to identify the lowest
angular momenta at which perturbative treatment of chiral forces can apply.
Results up to the order where the subleading two-pion exchange appears are
shown. It is concluded that perturbation theory applies to all partial waves
but , , and . Where it is applicable,
perturbation theory with the delta-less chiral forces produces good agreement
with the empirical phase shifts up to MeV.Comment: Matches published version; suppression of TPEs accounted for at
referee's suggestion; main conclusion unchanged, that most P waves and higher
waves are perturbativ
Exact zero modes in a quantum compass chain under inhomogeneous transverse fields
We study the emergence of exact Majorana zero modes (EMZMs) in a
one-dimensional quantum transverse compass model with both the nearest-neighbor
interactions and transverse fields varying over space. By transforming the spin
system into a quadratic Majorana-fermion model, we derive an exact formula for
the number of the emergent EMZMs, which is found to depend on the partition
nature of the lattice sites on which the magnetic fields vanish. We also derive
explicit expressions for the wavefunctions of these EMZMs and show that they
indeed depend on fine features of the foregoing partition of site indices.
Based on the above rigorous results about the EMZMs, we provide an
interpretation for the interesting dependence of the eigenstate-degeneracy on
the transverse fields observed in prior literatures. As a special case, we
employ a plane-wave ansatz to exactly solve an open compass chain with
alternating nearest-neighbor interactions and staggered magnetic fields.
Explicit forms of the canonical Majorana modes diagonalizing the model are
given even for finite chains. We show that besides the possibly existing EMZMs,
no almost Majorana zero modes exist unless the fields on both the two
sublattices are turned off. Our results might shed light on the control of
ground-state degeneracies by solely tuning the external fields in related
systems.Comment: 17 pages, 4 figures; to appear in Physical Review
Topological Properties of Electrons in Honeycomb Lattice with Kekul\'{e} Hopping Textures
Honeycomb lattice can support electronic states exhibiting Dirac energy
dispersion, with graphene as the icon. We propose to derive nontrivial topology
by grouping six neighboring sites of honeycomb lattice into hexagons and
enhancing the inter-hexagon hopping energies over the intra-hexagon ones. We
reveal that this manipulation opens a gap in the energy dispersion and drives
the system into a topological state. The nontrivial topology is characterized
by the index associated with a pseudo time-reversal symmetry
emerging from the symmetry of the Kekul\'{e} hopping texture, where the
angular momentum of orbitals accommodated on the hexagonal "artificial atoms"
behaves as the pseudospin. The size of topological gap is proportional to the
hopping-integral difference, which can be larger than typical spin-orbit
couplings by orders of magnitude and potentially renders topological electronic
transports available at high temperatures.Comment: 7 pages, 7 figure
Scheme to Achieve Silicon Topological Photonics
We derive in the present work topological photonic states purely based on
silicon, a conventional dielectric material, by deforming a honeycomb lattice
of silicon cylinders into a triangular lattice of cylinder hexagons. The
photonic topology is associated with a pseudo time reversal (TR) symmetry
constituted by the TR symmetry respected in general by the Maxwell equations
and the crystal symmetry upon design, which renders the Kramers doubling
in the present photonic system with the role of pseudo spin played by the
circular polarization of magnetic field in the transverse magnetic mode. We
solve Maxwell equations, and demonstrate new photonic topology by revealing
pseudo spin-resolved Berry curvatures of photonic bands and helical edge states
characterized by Poynting vectors.Comment: 5 pages, 5 figure
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