9,886 research outputs found
Convergence to the Self-similar Solutions to the Homogeneous Boltzmann Equation
The Boltzmann H-theorem implies that the solution to the Boltzmann equation
tends to an equilibrium, that is, a Maxwellian when time tends to infinity.
This has been proved in varies settings when the initial energy is finite.
However, when the initial energy is infinite, the time asymptotic state is no
longer described by a Maxwellian, but a self-similar solution obtained by
Bobylev-Cercignani. The purpose of this paper is to rigorously justify this for
the spatially homogeneous problem with Maxwellian molecule type cross section
without angular cutoff.Comment: 23 page
Entanglement Preserving in Quantum Copying of Three-qubit Entangled State
We study the degree to which quantum entanglement survives when a three-qubit
entangled state is copied by using local and non-local processes, respectively,
and investigate iterating quantum copying for the three-qubit system. There may
exist inter-three-qubit entanglement and inter-two-qubit entanglement for the
three-qubit system. We show that both local and non-local copying processes
degrade quantum entanglement in the three-particle system due to a residual
correlation between the copied output and the copying machine. We also show
that the inter-two-qubit entanglement is preserved better than the
inter-three-qubit entanglement in the local cloning process. We find that
non-local cloning is much more efficient than the local copying for
broadcasting entanglement, and output state via non-local cloning exhibits the
fidelity better than local cloning.Comment: 6 pages, 3 figure
Global solutions to the Vlasov-Poisson-Landau System
Based on the recent study on the Vlasov-Poisson-Boltzmann system with general
angular cutoff potentials [3, 4], we establish in this paper the global
existence of classical solutions to the Cauchy problem of the
Vlasov-Poisson-Landau system that includes the Coulomb potential. This then
provides a different approach on this topic from the recent work [8].Comment: 10 page
Adaptive Stochastic Alternating Direction Method of Multipliers
The Alternating Direction Method of Multipliers (ADMM) has been studied for
years. The traditional ADMM algorithm needs to compute, at each iteration, an
(empirical) expected loss function on all training examples, resulting in a
computational complexity proportional to the number of training examples. To
reduce the time complexity, stochastic ADMM algorithms were proposed to replace
the expected function with a random loss function associated with one uniformly
drawn example plus a Bregman divergence. The Bregman divergence, however, is
derived from a simple second order proximal function, the half squared norm,
which could be a suboptimal choice.
In this paper, we present a new family of stochastic ADMM algorithms with
optimal second order proximal functions, which produce a new family of adaptive
subgradient methods. We theoretically prove that their regret bounds are as
good as the bounds which could be achieved by the best proximal function that
can be chosen in hindsight. Encouraging empirical results on a variety of
real-world datasets confirm the effectiveness and efficiency of the proposed
algorithms.Comment: 13 page
Fast and Accurate Graph Stream Summarization
A graph stream is a continuous sequence of data items, in which each item
indicates an edge, including its two endpoints and edge weight. It forms a
dynamic graph that changes with every item in the stream. Graph streams play
important roles in cyber security, social networks, cloud troubleshooting
systems and other fields. Due to the vast volume and high update speed of graph
streams, traditional data structures for graph storage such as the adjacency
matrix and the adjacency list are no longer sufficient. However, prior art of
graph stream summarization, like CM sketches, gSketches, TCM and gMatrix,
either supports limited kinds of queries or suffers from poor accuracy of query
results. In this paper, we propose a novel Graph Stream Sketch (GSS for short)
to summarize the graph streams, which has the linear space cost (O(|E|), E is
the edge set of the graph) and the constant update time complexity (O(1)) and
supports all kinds of queries over graph streams with the controllable errors.
Both theoretical analysis and experiment results confirm the superiority of our
solution with regard to the time/space complexity and query results' precision
compared with the state-of-the-art
The Vlasov-Maxwell-Boltzmann system near Maxwellians in the whole space with very soft potentials
Since the work [13] by Guo [Invent. Math. 153 (2003), no. 3, 593--630], how
to establish the global existence of perturbative classical solutions around a
global Maxwellian to the Vlasov-Maxwell-Boltzmann system with the whole range
of soft potentials has been an open problem. This is mainly due to the complex
structure of the system, in particular, the degenerate dissipation at large
velocity, the velocity-growth of the nonlinear term induced by the Lorentz
force, and the regularity-loss of the electromagnetic fields. This paper aims
to resolve this problem in the whole space provided that initial perturbation
has sufficient regularity and velocity-integrability.Comment: 41 page
One-dimensional Compressible Navier-Stokes Equations with Temperature Dependent Transport Coefficients and Large Data
This paper is concerned with the global smooth non-vacuum solutions with
large data to the Cauchy problem of the one-dimensional compressible
Navier-Stokes equations with degenerate temperature dependent transport
coefficients which satisfy conditions from the consideration in kinetic theory.
A Nishida-Smoller type result is obtained.Comment: 36 page
Deep Compressive Autoencoder for Action Potential Compression in Large-Scale Neural Recording
Understanding the coordinated activity underlying brain computations requires
large-scale, simultaneous recordings from distributed neuronal structures at a
cellular-level resolution. One major hurdle to design high-bandwidth,
high-precision, large-scale neural interfaces lies in the formidable data
streams that are generated by the recorder chip and need to be online
transferred to a remote computer. The data rates can require hundreds to
thousands of I/O pads on the recorder chip and power consumption on the order
of Watts for data streaming alone. We developed a deep learning-based
compression model to reduce the data rate of multichannel action potentials.
The proposed model is built upon a deep compressive autoencoder (CAE) with
discrete latent embeddings. The encoder is equipped with residual
transformations to extract representative features from spikes, which are
mapped into the latent embedding space and updated via vector quantization
(VQ). The decoder network reconstructs spike waveforms from the quantized
latent embeddings. Experimental results show that the proposed model
consistently outperforms conventional methods by achieving much higher
compression ratios (20-500x) and better or comparable reconstruction
accuracies. Testing results also indicate that CAE is robust against a diverse
range of imperfections, such as waveform variation and spike misalignment, and
has minor influence on spike sorting accuracy. Furthermore, we have estimated
the hardware cost and real-time performance of CAE and shown that it could
support thousands of recording channels simultaneously without excessive
power/heat dissipation. The proposed model can reduce the required data
transmission bandwidth in large-scale recording experiments and maintain good
signal qualities. The code of this work has been made available at
https://github.com/tong-wu-umn/spike-compression-autoencoderComment: 19 pages, 13 figure
Excited states of holographic superconductors
In this paper we re-investigate the model of the anti-de Sitter gravity
coupled to Maxwell and charged scalar fields, which has been studied as the
gravitational dual to a superconductor for a long time since the famous work
[Phys.\ Rev.\ Lett.\ {\bf 101}, 031601 (2008)]. By numerical method, we present
a novel family of solutions of holographical superconductor with excited
states, and find there exists a lower critical temperature in the corresponding
excited state. Moreover, we study the condensate and conductivity in the
excited states. It is very interesting that the conductivity of each
excited state has an additional pole in and a delta
function in arising at the low temperature inside the gap,
which is just the evidence of the existence of excited states.Comment: 13 pages, 3 figures; V2: discussions and references added, accepted
for publication in JHE
Strong magnetization and Chern insulators in compressed graphene/CrI van der Waals heterostructures
Graphene-based heterostructures are a promising material system for designing
the topologically nontrivial Chern insulating devices. Recently, a
two-dimensional (2D) monolayer ferromagnetic insulator CrI was
successfully synthesized in experiments [Huang et al., Nature 546, 270 (2017)].
Here, these two interesting materials are proposed to build a heterostructure
(Gr/CrI). Our first-principles calculations show that the system forms a
van der Waals (vdW) heterostructure, relatively facilely fabricated in
experiments. A Chern insulating state is acquired in the Gr/CrI
heterostructure if the vdW gap is compressed to certain extents by applying an
external pressure. Amazingly, very strong magnetization (about 150 meV) is
found in graphene, induced by the substrate CrI, despite the vdW
interactions between them. A low-energy effective model is employed to
understand the mechanism. The work functions, contact types, and band
alignments of the Gr/CrI heterostructure system are also studied. Our
work demonstrates that the Gr/CrI heterostructure is a promising system
to observe the quantum anomalous Hall effect at high temperatures (up to 45 K)
in experiments.Comment: 9 pages, 5 figure
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