177 research outputs found
A Mining-Based System Framework for Deploying Knowledge Maps of Composite E-Services
Providing e-services and composite e-services on the Internet is an important trend of e-business. Composite e-services are complex processes which consist of various e-services provided by different e-service providers. In such complex environments, the flexibility and success of e-business depend on effective knowledge supports to access related information and resources of composite e-services. This work proposes a knowledge map platform to provide an effective knowledge support for utilizing composite e-services. A mining-based system framework is proposed to construct the knowledge map. Moreover, the proposed knowledge map is integrated with recommendation capability to provide users customized decision support in utilizing composite e-services
Power-Law Decay of Standing Waves on the Surface of Topological Insulators
We propose a general theory on the standing waves (quasiparticle interference
pattern) caused by the scattering of surface states off step edges in
topological insulators, in which the extremal points on the constant energy
contour of surface band play the dominant role. Experimentally we image the
interference patterns on both BiTe and BiSe films by measuring
the local density of states using a scanning tunneling microscope. The observed
decay indices of the standing waves agree excellently with the theoretical
prediction: In BiSe, only a single decay index of -3/2 exists; while in
BiTe with strongly warped surface band, it varies from -3/2 to -1/2 and
finally to -1 as the energy increases. The -1/2 decay indicates that the
suppression of backscattering due to time-reversal symmetry does not
necessarily lead to a spatial decay rate faster than that in the conventional
two-dimensional electron system. Our formalism can also explain the
characteristic scattering wave vectors of the standing wave caused by
non-magnetic impurities on BiTe.Comment: 4 pages, 3 figure
Low-Quality Training Data Only? A Robust Framework for Detecting Encrypted Malicious Network Traffic
Machine learning (ML) is promising in accurately detecting malicious flows in
encrypted network traffic; however, it is challenging to collect a training
dataset that contains a sufficient amount of encrypted malicious data with
correct labels. When ML models are trained with low-quality training data, they
suffer degraded performance. In this paper, we aim at addressing a real-world
low-quality training dataset problem, namely, detecting encrypted malicious
traffic generated by continuously evolving malware. We develop RAPIER that
fully utilizes different distributions of normal and malicious traffic data in
the feature space, where normal data is tightly distributed in a certain area
and the malicious data is scattered over the entire feature space to augment
training data for model training. RAPIER includes two pre-processing modules to
convert traffic into feature vectors and correct label noises. We evaluate our
system on two public datasets and one combined dataset. With 1000 samples and
45% noises from each dataset, our system achieves the F1 scores of 0.770,
0.776, and 0.855, respectively, achieving average improvements of 352.6%,
284.3%, and 214.9% over the existing methods, respectively. Furthermore, We
evaluate RAPIER with a real-world dataset obtained from a security enterprise.
RAPIER effectively achieves encrypted malicious traffic detection with the best
F1 score of 0.773 and improves the F1 score of existing methods by an average
of 272.5%
Electron interaction-driven insulating ground state in Bi2Se3 topological insulators in the two dimensional limit
We report a transport study of ultrathin Bi2Se3 topological insulators with
thickness from one quintuple layer to six quintuple layers grown by molecular
beam epitaxy. At low temperatures, the film resistance increases
logarithmically with decreasing temperature, revealing an insulating ground
state. The sharp increase of resistance with magnetic field, however, indicates
the existence of weak antilocalization, which should reduce the resistance as
temperature decreases. We show that these apparently contradictory behaviors
can be understood by considering the electron interaction effect, which plays a
crucial role in determining the electronic ground state of topological
insulators in the two dimensional limit.Comment: 4 figure
Visualizing the elongated vortices in -Ga nanostrips
We study the magnetic response of superconducting -Ga via low
temperature scanning tunneling microscopy and spectroscopy. The magnetic vortex
cores rely substantially on the Ga geometry, and exhibit an unexpectedly-large
axial elongation with aspect ratio up to 40 in rectangular Ga nano-strips
(width 100 nm). This is in stark contrast with the isotropic circular
vortex core in a larger round-shaped Ga island. We suggest that the unusual
elongated vortices in Ga nanostrips originate from geometric confinement effect
probably via the strong repulsive interaction between the vortices and Meissner
screening currents at the sample edge. Our finding provides novel conceptual
insights into the geometrical confinement effect on magnetic vortices and forms
the basis for the technological applications of superconductors.Comment: published in Phys. Rev. B as a Rapid Communicatio
Generation of high-density high-polarization positrons via single-shot strong laser-foil interaction
We put forward a novel method for producing ultrarelativistic high-density
high-polarization positrons through a single-shot interaction of a strong laser
with a tilted solid foil. In our method, the driving laser ionizes the target,
and the emitted electrons are accelerated and subsequently generate abundant
photons via the nonlinear Compton scattering, dominated by the laser.
These photons then generate polarized positrons via the nonlinear
Breit-Wheeler process, dominated by a strong self-generated quasi-static
magnetic field . We find that placing the foil at an
appropriate angle can result in a directional orientation of , thereby polarizing positrons. Manipulating the laser polarization
direction can control the angle between the photon polarization and
, significantly enhancing the positron polarization degree.
Our spin-resolved quantum electrodynamics particle-in-cell simulations
demonstrate that employing a laser with a peak intensity of about
W/cm can obtain dense ( 10 cm) polarized positrons
with an average polarization degree of about 70\% and a yield of above 0.1 nC
per shot. Moreover, our method is feasible using currently available or
upcoming laser facilities and robust with respect to the laser and target
parameters. Such high-density high-polarization positrons hold great
significance in laboratory astrophysics, high-energy physics and new physics
beyond the Standard Model
Experimental demonstration of the topological surface states protected by the time-reversal symmetry
We report direct imaging of standing waves of the nontrivial surface states
of topological insulator BiTe by using a low temperature scanning
tunneling microscope. The interference fringes are caused by the scattering of
the topological states off Ag impurities and step edges on the
BiTe(111) surface. By studying the voltage-dependent standing wave
patterns, we determine the energy dispersion , which confirms the Dirac
cone structure of the topological states. We further show that, very different
from the conventional surface states, the backscattering of the topological
states by nonmagnetic impurities is completely suppressed. The absence of
backscattering is a spectacular manifestation of the time-reversal symmetry,
which offers a direct proof of the topological nature of the surface states
- …