90,059 research outputs found
Off-Shell NN Potential and Triton Binding Energy
The NONLOCAL Bonn-B potential predicts 8.0 MeV binding energy for the triton
(in a charge-dependent 34-channel Faddeev calculation) which is about 0.4 MeV
more than the predictions by LOCAL NN potentials. We pin down origin and size
of the nonlocality in the Bonn potential, in analytic and numeric form. The
nonlocality is due to the use of the correct off-shell Feynman amplitude of
one-boson-exchange avoiding the commonly used on-shell approximations which
yield the local potentials. We also illustrate how this off-shell behavior
leads to more binding energy. We emphasize that the increased binding energy is
not due to on-shell differences (differences in the fit of the NN data or phase
shifts). In particular, the Bonn-B potential reproduces accurately the
mixing parameter up to 350 MeV as determined in the recent
Nijmegen multi-energy NN phase-shift analysis. Adding the relativistic effect
from the relativistic nucleon propagators in the Faddeev equations, brings the
Bonn-B result up to 8.2 MeV triton binding. This leaves a difference of only
0.3 MeV to experiment, which may possibly be explained by refinements in the
treatment of relativity and the inclusion of other nonlocalities (e.~g.,
quark-gluon exchange at short range). Thus, it is conceivable that a realistic
NN potential which describes the NN data up to 300 MeV correctly may explain
the triton binding energy without recourse to 3-N forces; relativity would play
a major role for this result.Comment: 5 pages LaTeX and 2 figures (hardcopies, available upon reqest),
UI-NTH-940
An intelligent genetic algorithm for PAPR reduction in a multi-carrier CDMA wireless system
Abstractâ A novel intelligent genetic algorithm (GA), called Minimum Distance guided GA (MDGA) is proposed for peak-average-power ratio (PAPR) reduction based on partial transmit sequence (PTS) scheme in a synchronous Multi-Carrier Code Division Multiple Access (MC-CDMA) system. In contrast to traditional GA, our MDGA starts with a balanced ratio of exploration and exploitation which is maintained throughout the process. It introduces a novel replacement strategy which increases significantly the convergence rate and reduce dramatically computational complexity as compared to the conventional GA. The simulation results demonstrate that, if compared to the PAPR reduction schemes using exhaustive search and traditional GA, our scheme achieves 99.52% and 50+% reduction in computational complexity respectively
Inconsistences in Interacting Agegraphic Dark Energy Models
It is found that the origin agegraphic dark energy tracks the matter in the
matter-dominated epoch and then the subsequent dark-energy-dominated epoch
becomes impossible. It is argued that the difficulty can be removed when the
interaction between the agegraphic dark energy and dark matter is considered.
In the note, by discussing three different interacting models, we find that the
difficulty still stands even in the interacting models. Furthermore, we find
that in the interacting models, there exists the other serious inconsistence
that the existence of the radiation/matter-dominated epoch contradicts the
ability of agegraphic dark energy in driving the accelerated expansion. The
contradiction can be avoided in one of the three models if some constraints on
the parameters hold.Comment: 12 pages, no figure; analysis is added; conclusion is unchange
Geometric Phase, Hannay's Angle, and an Exact Action Variable
Canonical structure of a generalized time-periodic harmonic oscillator is
studied by finding the exact action variable (invariant). Hannay's angle is
defined if closed curves of constant action variables return to the same curves
in phase space after a time evolution. The condition for the existence of
Hannay's angle turns out to be identical to that for the existence of a
complete set of (quasi)periodic wave functions. Hannay's angle is calculated,
and it is shown that Berry's relation of semiclassical origin on geometric
phase and Hannay's angle is exact for the cases considered.Comment: Submitted to Phys. Rev. Lett. (revised version
Diversity gain for DVB-H by using transmitter/receiver cyclic delay diversity
The objective of this paper is to investigate different diversity techniques for broadcast networks that will minimize the complexity and improve received SNR of broadcast systems.
Resultant digital broadcast networks would require fewer transmitter sites and thus be more cost-effective and have less environmental impact. The techniques can be applied to DVB-T,
DVB-H and DAB systems that use Orthogonal Frequency Division Multplexing (OFDM). These are key radio broadcast network technologies, which are expected to complement emerging technologies
such as WiMAX and future 4G networks for delivery
of broadband content. Transmitter and receiver diversity technologies can increase the frequency and time selectivity of the resulting channel transfer function at the receiver. Diversity exploits the statistical nature of fading due to multipath and reduces the likelihood of deep fading by providing a diversity of transmission signals. Multiple signals are transmitted in such
a way as to ensure that several signals reach the receiver each with uncorrelated fading. Transmit diversity is more practical than receive diversity due to the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here comply with existing DVB standards and can be incorporated into existing systems without change. The diversity techniques introduced in this paper are applied to the DVB-H system. Bit error performance investigations were conducted by
simulation for different DVB-H and diversity parameters
Liver segmentation using automatically defined patient specific B-Spline surface models
This paper presents a novel liver segmentation algorithm. This is a model-driven approach; however, unlike previous techniques which use a statistical model obtained from a training set, we initialize patient-specific models directly from their own pre-segmentation. As a result, the non-trivial problems such as landmark correspondences, model registration etc. can be avoided. Moreover, by dividing the liver region into three sub-regions, we convert the problem of building one complex shape model into constructing three much simpler models, which can be fitted independently, greatly improving the computation efficiency. A robust graph-based narrow band optimal surface fitting scheme is also presented. The proposed approach is evaluated on 35 CT images. Compared to contemporary approaches, our approach has no training requirement and requires significantly less processing time, with an RMS error of 2.440.53mm against manual segmentation
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