84,368 research outputs found
Linear magnetoresistance on the topological surface
A positive, non-saturating and dominantly linear magnetoresistance is
demonstrated to occur in the surface state of a topological insulator having a
wavevector-linear energy dispersion together with a finite positive Zeeman
energy splitting. This linear magnetoresistance shows up within quite wide
magnetic-field range in a spatially homogenous system of high carrier density
and low mobility in which the conduction electrons are in extended states and
spread over many smeared Landau levels, and is robust against increasing
temperature, in agreement with recent experimental findings in BiSe
nanoribbons.Comment: 7 pages, 4 figure
Galaxy alignment on large and small scales
Galaxies are not randomly distributed across the universe but showing
different kinds of alignment on different scales. On small scales satellite
galaxies have a tendency to distribute along the major axis of the central
galaxy, with dependence on galaxy properties that both red satellites and
centrals have stronger alignment than their blue counterparts. On large scales,
it is found that the major axes of Luminous Red Galaxies (LRGs) have
correlation up to 30Mpc/h. Using hydro-dynamical simulation with star
formation, we investigate the origin of galaxy alignment on different scales.
It is found that most red satellite galaxies stay in the inner region of dark
matter halo inside which the shape of central galaxy is well aligned with the
dark matter distribution. Red centrals have stronger alignment than blue ones
as they live in massive haloes and the central galaxy-halo alignment increases
with halo mass. On large scales, the alignment of LRGs is also from the
galaxy-halo shape correlation, but with some extent of mis-alignment. The
massive haloes have stronger alignment than haloes in filament which connect
massive haloes. This is contrary to the naive expectation that cosmic filament
is the cause of halo alignment.Comment: 4 pages, 3 figures, To appear in the proceedings of the IAU Symposium
308 "The Zeldovich Universe: Genesis and Growth of the Cosmic Web
A Large-scale Distributed Video Parsing and Evaluation Platform
Visual surveillance systems have become one of the largest data sources of
Big Visual Data in real world. However, existing systems for video analysis
still lack the ability to handle the problems of scalability, expansibility and
error-prone, though great advances have been achieved in a number of visual
recognition tasks and surveillance applications, e.g., pedestrian/vehicle
detection, people/vehicle counting. Moreover, few algorithms explore the
specific values/characteristics in large-scale surveillance videos. To address
these problems in large-scale video analysis, we develop a scalable video
parsing and evaluation platform through combining some advanced techniques for
Big Data processing, including Spark Streaming, Kafka and Hadoop Distributed
Filesystem (HDFS). Also, a Web User Interface is designed in the system, to
collect users' degrees of satisfaction on the recognition tasks so as to
evaluate the performance of the whole system. Furthermore, the highly
extensible platform running on the long-term surveillance videos makes it
possible to develop more intelligent incremental algorithms to enhance the
performance of various visual recognition tasks.Comment: Accepted by Chinese Conference on Intelligent Visual Surveillance
201
On Solving a Generalized Chinese Remainder Theorem in the Presence of Remainder Errors
In estimating frequencies given that the signal waveforms are undersampled
multiple times, Xia et. al. proposed to use a generalized version of Chinese
remainder Theorem (CRT), where the moduli are which are
not necessarily pairwise coprime. If the errors of the corrupted remainders are
within \tau=\sds \max_{1\le i\le k} \min_{\stackrel{1\le j\le k}{j\neq i}}
\frac{\gcd(M_i,M_j)}4, their schemes can be used to construct an approximation
of the solution to the generalized CRT with an error smaller than .
Accurately finding the quotients is a critical ingredient in their approach. In
this paper, we shall start with a faithful historical account of the
generalized CRT. We then present two treatments of the problem of solving
generalized CRT with erroneous remainders. The first treatment follows the
route of Wang and Xia to find the quotients, but with a simplified process. The
second treatment considers a simplified model of generalized CRT and takes a
different approach by working on the corrupted remainders directly. This
approach also reveals some useful information about the remainders by
inspecting extreme values of the erroneous remainders modulo . Both of
our treatments produce efficient algorithms with essentially optimal
performance. Finally, this paper constructs a counterexample to prove the
sharpness of the error bound
Characterisation of the transmissivity field of a fractured and karstic aquifer, Southern France
International audienceGeological and hydrological data collected at the Terrieu experimental site north of Montpellier, in a confined carbonate aquifer indicates that both fracture clusters and a major bedding plane form the main flow paths of this highly heterogeneous karst aquifer. However, characterising the geometry and spatial location of the main flow channels and estimating their flow properties remain difficult. These challenges can be addressed by solving an inverse problem using the available hydraulic head data recorded during a set of interference pumping tests.We first constructed a 2D equivalent porous medium model to represent the test site domain and then employed regular zoning parameterisation, on which the inverse modelling was performed. Because we aim to resolve the fine-scale characteristics of the transmissivity field, the problem undertaken is essentially a large-scale inverse model, i.e. the dimension of the unknown parameters is high. In order to deal with the high computational demands in such a large-scale inverse problem, a gradient-based, non-linear algorithm (SNOPT) was used to estimate the transmissivity field on the experimental site scale through the inversion of steady-state, hydraulic head measurements recorded at 22 boreholes during 8 sequential cross-hole pumping tests. We used the data from outcrops, borehole fracture measurements and interpretations of inter-well connectivities from interference test responses as initial models to trigger the inversion. Constraints for hydraulic conductivities, based on analytical interpretations of pumping tests, were also added to the inversion models. In addition, the efficiency of the adopted inverse algorithm enables us to increase dramatically the number of unknown parameters to investigate the influence of elementary discretisation on the reconstruction of the transmissivity fields in both synthetic and field studies.By following the above approach, transmissivity fields that produce similar hydrodynamic behaviours to the real head measurements were obtained. The inverted transmissivity fields show complex, spatial heterogeneities with highly conductive channels embedded in a low transmissivity matrix region. The spatial trend of the main flow channels is in a good agreement with that of the main fracture sets mapped on outcrops in the vicinity of the Terrieu site suggesting that the hydraulic anisotropy is consistent with the structural anisotropy. These results from the inverse modelling enable the main flow paths to be located and their hydrodynamic properties to be estimated
Density Matrix Renormalization Group study on incommensurate quantum Frenkel-Kontorova model
By using the density matrix renormalization group (DMRG) technique, the
incommensurate quantum Frenkel-Kontorova model is investigated numerically. It
is found that when the quantum fluctuation is strong enough, the
\emph{g}-function featured by a saw-tooth map in the depinned state will show a
different kind of behavior, similar to a standard map, but with reduced
magnitude. The related position correlations are studied in details, which
leads to a potentially interesting application to the recently well-explored
phase transitions in cold atoms loaded in optical lattices.Comment: 11 figures, submitted to Phys. Rev.
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