22,041 research outputs found
Moduli Stabilization in Type IIB Flux Compactifications
In the present paper, we reexamine the moduli stabilization problem of the
Type IIB orientifolds with one complex structure modulus in a modified two-step
procedure. The full superpotential including both the 3-form fluxes and the
non-perturbative corrections is used to yield a F-term potential. This
potential is simplified by using one optimization condition to integrate the
dilaton field out. It is shown that having a locally stable supersymmetric
Anti-deSitter vacuum is not inevitable for these orientifolds, which depend
strongly upon the details of the flux parameters. For those orientifolds that
have stable/metastable supersymmetry-broken minima of the F-term potential, the
deSitter vacua might emerge even without the inclusion of the uplifting
contributions.Comment: 10 pages, LaTeX2e style. The paper is rewritten in ver3 with more
references adde
A Tri-band-notched UWB Antenna with Low Mutual Coupling between the Band-notched Structures
A compact printed U-shape ultra-wideband (UWB) antenna with triple band-notched characteristics is presented. The proposed antenna, with compact size of 24Ă—33 mm2, yields an impedance bandwidth of 2.8-12GHz for VSWR<2, except the notched bands. The notched bands are realized by introducing two different types of slots. Two C-shape half-wavelength slots are etched on the radiating patch to obtain two notched bands in 3.3-3.7GHz for WiMAX and 7.25-7.75GHz for downlink of X-band satellite communication systems. In order to minimize the mutual coupling between the band-notched structures, the middle notched band in 5-6GHz for WLAN is achieved by using a U-slot defected ground structure. The parametric study is carried out to understand the mutual coupling. Surface current distributions and equivalent circuit are used to illustrate the notched mechanism. The performance of this antenna both by simulation and by experiment indicates that the proposed antenna is suitable and a good candidate for UWB applications
"Virus hunting" using radial distance weighted discrimination
Motivated by the challenge of using DNA-seq data to identify viruses in human
blood samples, we propose a novel classification algorithm called "Radial
Distance Weighted Discrimination" (or Radial DWD). This classifier is designed
for binary classification, assuming one class is surrounded by the other class
in very diverse radial directions, which is seen to be typical for our virus
detection data. This separation of the 2 classes in multiple radial directions
naturally motivates the development of Radial DWD. While classical machine
learning methods such as the Support Vector Machine and linear Distance
Weighted Discrimination can sometimes give reasonable answers for a given data
set, their generalizability is severely compromised because of the linear
separating boundary. Radial DWD addresses this challenge by using a more
appropriate (in this particular case) spherical separating boundary.
Simulations show that for appropriate radial contexts, this gives much better
generalizability than linear methods, and also much better than conventional
kernel based (nonlinear) Support Vector Machines, because the latter methods
essentially use much of the information in the data for determining the shape
of the separating boundary. The effectiveness of Radial DWD is demonstrated for
real virus detection.Comment: Published at http://dx.doi.org/10.1214/15-AOAS869 in the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Sub-Nanosecond Time of Flight on Commercial Wi-Fi Cards
Time-of-flight, i.e., the time incurred by a signal to travel from
transmitter to receiver, is perhaps the most intuitive way to measure distances
using wireless signals. It is used in major positioning systems such as GPS,
RADAR, and SONAR. However, attempts at using time-of-flight for indoor
localization have failed to deliver acceptable accuracy due to fundamental
limitations in measuring time on Wi-Fi and other RF consumer technologies.
While the research community has developed alternatives for RF-based indoor
localization that do not require time-of-flight, those approaches have their
own limitations that hamper their use in practice. In particular, many existing
approaches need receivers with large antenna arrays while commercial Wi-Fi
nodes have two or three antennas. Other systems require fingerprinting the
environment to create signal maps. More fundamentally, none of these methods
support indoor positioning between a pair of Wi-Fi devices
without~third~party~support.
In this paper, we present a set of algorithms that measure the time-of-flight
to sub-nanosecond accuracy on commercial Wi-Fi cards. We implement these
algorithms and demonstrate a system that achieves accurate device-to-device
localization, i.e. enables a pair of Wi-Fi devices to locate each other without
any support from the infrastructure, not even the location of the access
points.Comment: 14 page
Local vertical measurements and violation of Bell inequality
For two qubits belonging to Alice and Bob, we derive an approach to setup the
bound of Bell operator in the condition that Alice and Bob continue to perform
local vertical measurements. For pure states we find that if the entanglement
of the two qubits is less than 0.2644 (measured with von Neumann entropy) the
violation of the Bell inequality will never be realized, and only when the
entanglement is equal to 1 the maximal violation () can occur. For
specific form of mixed states, we prove that the bound of the Bell inequality
depends on the concurrence. Only when the concurrence is greater than 0.6 the
violation of the Bell inequality can occur, and the maximal violation can never
be achieved. We suggest that the bound of the Bell operator in the condition of
local vertical measurements may be used as a measure of the entanglement.Comment: 4 pages, 3 figure
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