594 research outputs found
Algebro-geometric Constructions to the Dym-type Hierarchy
Resorting to the characteristic polynomial of Lax matrix for the Dym-type
hierarchy, we define a trigonal curve, on which appropriate vector-valued
Baker-Akhiezer function and meromorphic function are introduced. Based on the
theory of trigonal curve and three kinds of Abelian differentials, we obtain
the explicit Riemann theta function representations of the meromorphic
function, from which we get the algebro-geometric constructions for the entire
Dym-type hierarch
The Novikov conjecture, the group of volume preserving diffeomorphisms and Hilbert-Hadamard spaces
We prove that the Novikov conjecture holds for any discrete group admitting
an isometric and metrically proper action on an admissible Hilbert-Hadamard
space. Admissible Hilbert-Hadamard spaces are a class of (possibly
infinite-dimensional) non-positively curved metric spaces that contain dense
sequences of closed convex subsets isometric to Riemannian manifolds. Examples
of admissible Hilbert-Hadamard spaces include Hilbert spaces, certain simply
connected and non-positively curved Riemannian-Hilbertian manifolds and
infinite\-/dimensional symmetric spaces. Thus our main theorem can be
considered as an infinite-dimensional analogue of Kasparov's theorem on the
Novikov conjecture for groups acting properly and isometrically on complete,
simply connected and non-positively curved manifolds. As a consequence, we show
that the Novikov conjecture holds for geometrically discrete subgroups of the
group of volume preserving diffeomorphisms of a closed smooth manifold. This
result is inspired by Connes' theorem that the Novikov conjecture holds for
higher signatures associated to the Gelfand-Fuchs classes of groups of
diffeormorphisms.Comment: 52 page
The diamagnetic phase transition in Magnetars
Neutron stars are ideal astrophysical laboratories for testing theories of
the de Haas-van Alphen (dHvA) effect and diamagnetic phase transition which is
associated with magnetic domain formation. The "magnetic interaction" between
delocalized magnetic moments of electrons (the Shoenberg effect), can result in
an effect of the diamagnetic phase transition into domains of alternating
magnetization (Condon's domains). Associated with the domain formation are
prominent magnetic field oscillation and anisotropic magnetic stress which may
be large enough to fracture the crust of magnetar with a super-strong field.
Even if the fracture is impossible as in "low-field" magnetar, the depinning
phase transition of domain wall motion driven by low field rate (mainly due to
the Hall effect) in the randomly perturbed crust can result in a
catastrophically variation of magnetic field. This intermittent motion, similar
to the avalanche process, makes the Hall effect be dissipative. These
qualitative consequences about magnetized electron gas are consistent with
observations of magnetar emission, and especially the threshold critical
dynamics of driven domain wall can partially overcome the difficulties of
"low-field" magnetar bursts and the heating mechanism of transient, or
"outbursting" magnetar.Comment: 15pages, 4 fiures, accepted for publication in PAS
Impulse Control of Multidimensional Jump Diffusions
This paper studies regularity property of the value function for an
infinite-horizon discounted cost impulse control problem, where the underlying
controlled process is a multidimensional jump diffusion with possibly
`infinite-activity' jumps. Surprisingly, despite these jumps, we obtain the
same degree of regularity as for the diffusion case, at least when the jump
satisfies certain integrability conditions.Comment: 15 pages, 1 figur
Pseudorapidity dependence of short-range correlations from a multi-phase transport model
Using a multi-phase transport model (AMPT) that includes both initial
partonic and hadronic interactions, we study neighboring bin multiplicity
correlations as a function of pseudorapidity in Au+Au collisions at
GeV. It is observed that for 19.6GeV Au+Au collisions, the short-range correlations of final particles have
a trough at central pseudorapidity, while for 19.6GeV AuAu
collisions, the short-range correlations of final particles have a peak at
central pseudorapidity. Our findings indicate that the pseudorapidity
dependence of short-range correlations should contain some new physical
information, and are not a simple result of the pseudorapidity distribution of
final particles. The AMPT results with and without hadronic scattering are
compared. It is found that hadron scattering can only increase the short-range
correlations to some level, but is not responsible for the different
correlation shapes for different energies. Further study shows that the
different pseudorapidity dependence of short-range correlations are mainly due
to partonic evolution and the following hadronization scheme.Comment: 5 pages, 3 figures, submitted to CP
RFP: A Remote Fetching Paradigm for RDMA-Accelerated Systems
Remote Direct Memory Access (RDMA) is an efficient way to improve the
performance of traditional client-server systems. Currently, there are two main
design paradigms for RDMA-accelerated systems. The first allows the clients to
directly operate the server's memory and totally bypasses the CPUs at server
side. The second follows the traditional server-reply paradigm, which asks the
server to write results back to the clients. However, the first method has to
expose server's memory and needs tremendous re-design of upper-layer software,
which is complex, unsafe, error-prone, and inefficient. The second cannot
achieve high input/output operations per second (IOPS), because it employs
out-bound RDMA-write at server side which is not efficient.
We find that the performance of out-bound RDMA-write and in-bound RDMA-read
is asymmetric and the latter is 5 times faster than the former. Based on this
observation, we propose a novel design paradigm named Remote Fetching Paradigm
(RFP). In RFP, the server is still responsible for processing requests from the
clients. However, counter-intuitively, instead of sending results back to the
clients through out-bound RDMA-write, the server only writes the results in
local memory buffers, and the clients use in-bound RDMA-read to remotely fetch
these results. Since in-bound RDMA-read achieves much higher IOPS than
out-bound RDMA-write, our model is able to bring higher performance than the
traditional models.
In order to prove the effectiveness of RFP, we design and implement an
RDMA-accelerated in-memory key-value store following the RFP model. To further
improve the IOPS, we propose an optimization mechanism that combines status
checking and result fetching. Experiment results show that RFP can improve the
IOPS by 160%~310% against state-of-the-art models for in-memory key-value
stores.Comment: 11 pages, 10 figures; Key Words: RDMA and InfiniBand, Remote Fetching
Paradigm, IOPS, and Small Dat
Singularities of plane gravitational waves and their memory effects
Similar to the Schwarzschild coordinates for spherical black holes, the
Baldwin, Jeffery and Rosen (BJR) coordinates for plane gravitational waves are
often singular, and extensions beyond such singularities are necessary, before
studying asymptotic properties of such spacetimes at the null infinity of the
plane, on which the gravitational waves propagate. The latter is closely
related to the studies of memory effects and soft graviton theorems. In this
paper, we point out that in the BJR coordinates all the spacetimes are singular
physically at the focused point , except for the two cases: (1)
; and (2) , where are the coefficients in the expansion \chi \equiv
\left[{\mbox{det}}\left(g_{ab}\right) \right]^{1/4} = \left(u -
u_s\right)^{\alpha}\sum_{n = 0}^{\infty}\chi_n \left(u - u_s\right)^n with
, the constant characterizes the strength
of the singularities, and denotes the reduced metric on the
two-dimensional plane orthogonal to the propagation direction of the wave.
Therefore, the hypersurfaces already represent the boundaries of such
spacetimes, and the null infinity does not belong to them. As a result, they
cannot be used to study properties of plane gravitational waves at null
infinities, including memory effects and soft graviton theorems.Comment: revtex4-1, one figure. Corrected some typos. Gen. Relativ. Grav. 52
(2020) 2
Question Answering over Knowledge Base with Neural Attention Combining Global Knowledge Information
With the rapid growth of knowledge bases (KBs) on the web, how to take full
advantage of them becomes increasingly important. Knowledge base-based question
answering (KB-QA) is one of the most promising approaches to access the
substantial knowledge. Meantime, as the neural network-based (NN-based) methods
develop, NN-based KB-QA has already achieved impressive results. However,
previous work did not put emphasis on question representation, and the question
is converted into a fixed vector regardless of its candidate answers. This
simple representation strategy is unable to express the proper information of
the question. Hence, we present a neural attention-based model to represent the
questions dynamically according to the different focuses of various candidate
answer aspects. In addition, we leverage the global knowledge inside the
underlying KB, aiming at integrating the rich KB information into the
representation of the answers. And it also alleviates the out of vocabulary
(OOV) problem, which helps the attention model to represent the question more
precisely. The experimental results on WEBQUESTIONS demonstrate the
effectiveness of the proposed approach
How does the electric current propagate through the fully-hydrogenated borophene?
We study the electronic transport properties of two-dimensional (2D)
fully-hydrogenated borophene (namely, borophane), using the density functional
theory and non-equilibrium Green's function approaches. Borophane shows a
perfect electrical transport anisotropy and is promising for applications.
Along the peak- or equivalently the valley-parallel direction, the 2D borophane
exhibits a metallic characteristic and its current-voltage (I-V) curve shows a
linear behavior, corresponding to the ON state in borophane-based nano-switch.
In this case, electrons mainly propagate via the B-B bonds along the linear
boron chains. In contrast, the electron transmission is almost forbidden along
the perpendicular buckled direction (i.e., the OFF state), due to its
semi-conductor property. Our work demonstrates that 2D borophane could combine
the metal and semiconductor features and can be a promising candidate of
nano-switching materials with stable structure and high ON/OFF ratio
Ultrafast Electronic Dynamics of a Weyl Semimetal MoTe Revealed by Time and Angle Resolved Photoemission Spectroscopy
A Weyl semimetal is a new type of topological quantum phase with intriguing
physics near the Weyl nodes. Although the equilibrium state of Weyl semimetals
has been investigated, the ultrafast dynamics near the Weyl node in the
nonequilibrium state is still missing. Here by performing time and angle
resolved photoemission spectroscopy on type-II Weyl semimetal MoTe, we
reveal the dispersion of the unoccupied states and identify the Weyl node at 70
meV above E. Moreover, by tracking the ultrafast relaxation dynamics near
the Weyl node upon photo-excitation with energy, momentum and temporal
resolution, two intrinsic recovery timescales are observed, a fast one of 430
fs and a slow one of 4.1 ps, which are associated with hot electron cooling by
optical phonon cascade emission and anharmonic decay of hot optical phonons
respectively. The electron population shows a metallic response, and the two
temperature model fitting of the transient electronic temperature gives an
electron-phonon coupling constant of
. Our work provides important dynamic information for
understanding the relaxation mechanism of a Weyl semimetal and for exploiting
potential applications using ultrafast optical control.Comment: Submitted on 09/12/2017, including 16 pages, 4 figure
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