13,090 research outputs found
Low-lying S-wave and P-wave Dibaryons in a Nodal Structure Analysis
The dibaryon states as six-quark clusters of exotic QCD states are
investigated in this paper. With the inherent nodal surface structure analysis,
the wave functions of the six-quark clusters (in another word, the dibaryons)
are classified. The contribution of the hidden color channels are discussed.
The quantum numbers of the low-lying dibaryon states are obtained. The States
, ,
, and the
hidden color channel states with the same quantum numbers are proposed to be
the candidates of dibaryons, which may be observed in experiments.Comment: 29 pages, 2 figure
Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
We present radio observations of 8 ultracool dwarfs with a narrow spectral
type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8
binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system
detected in radio and its trigonometric parallax pi = 67.6 mas, recently
measured by Gatewood et al., makes it the furthest ultracool system detected by
the Very Large Array to date, and the most radio-luminous outside of obvious
flaring activity or variability. With a separation of only 1.8 AU, masses of
the components of LP 349-25 can be measured precisely without any theoretical
assumptions (Forveille et al.), allowing us to clarify their fully-convective
status and hence the kind of magnetic dynamo in these components which may play
an important role to explain our detection of radio emission from these
objects. This also makes LP 349-25 an excellent target for further studies with
better constraints on the correlations between X-ray, radio emission and
stellar parameters such as mass, age, temperature, and luminosity in ultracool
dwarfs.Comment: accepted by ApJ, referee's comments included, typo in equation 1
correcte
Improvements in prevalence trend fitting and incidence estimation in EPP 2013
OBJECTIVE: Describe modifications to the latest version of the Joint United Nations Programme on AIDS (UNAIDS) Estimation and Projection Package component of Spectrum (EPP 2013) to improve prevalence fitting and incidence trend estimation in national epidemics and global estimates of HIV burden. METHODS: Key changes made under the guidance of the UNAIDS Reference Group on Estimates, Modelling and Projections include: availability of a range of incidence calculation models and guidance for selecting a model; a shift to reporting the Bayesian median instead of the maximum likelihood estimate; procedures for comparison and validation against reported HIV and AIDS data; incorporation of national surveys as an integral part of the fitting and calibration procedure, allowing survey trends to inform the fit; improved antenatal clinic calibration procedures in countries without surveys; adjustment of national antiretroviral therapy reports used in the fitting to include only those aged 15–49 years; better estimates of mortality among people who inject drugs; and enhancements to speed fitting. RESULTS: The revised models in EPP 2013 allow closer fits to observed prevalence trend data and reflect improving understanding of HIV epidemics and associated data. CONCLUSION: Spectrum and EPP continue to adapt to make better use of the existing data sources, incorporate new sources of information in their fitting and validation procedures, and correct for quantifiable biases in inputs as they are identified and understood. These adaptations provide countries with better calibrated estimates of incidence and prevalence, which increase epidemic understanding and provide a solid base for program and policy planning
Low-complexity Lattice Reduction Aided Detection for Generalised Spatial Modulation
Generalised spatial modulation (GSM) was first introduced with the maximum-likelihood (ML) optimum decoder. However, ML decoder may be infeasible for practical implementation due to its exponential complexity especially when the number of antennas or the constellation size is large. Lattice reduction (LR) aided linear decoders are known to have much lower complexity while achieving near-optimal bit-error-rate (BER) performance in MIMO V-BLAST systems. In this paper, LR-aided linear decoders are applied to GSM systems for the first time, but the simulation results demonstrate unsatisfactory BER performances. Thereby, two improved LR-aided linear decoders are proposed in this work. The proposed schemes achieve significant BER performance enhancement compared to that of conventional LR-aided linear decoders as well as linear decoders including zero forcing (ZF) detection and minimum mean square error (MMSE) detection. Compared to the ML decoder, the proposed schemes can provide fairly lower complexities with small BER performance degradation
Three Dimensional Simulation of Jet Formation in Collapsing Condensates
We numerically study the behavior of collapsing and exploding condensates
using the parameters of the experiments by E.A. Donley et al. [Nature,
412, 295, (2001)]. Our studies are based on a full three-dimensional
numerical solution of the Gross-Pitaevskii equation (GPE) including three body
loss. We determine the three body loss rate from the number of remnant
condensate atoms and collapse times and obtain only one possible value which
fits with the experimental results. We then study the formation of jet atoms by
interrupting the collapse and find very good agreement with the experiment.
Furthermore we investigate the sensitivity of the jets to the initial
conditions. According to our analysis the dynamics of the burst atoms is not
described by the GPE with three body loss incorporated.Comment: 9 pages, 10 figure
A Multi-Phase Transport Model for Relativistic Heavy Ion Collisions
We describe in detail how the different components of a multi-phase transport
(AMPT) model, that uses the Heavy Ion Jet Interaction Generator (HIJING) for
generating the initial conditions, Zhang's Parton Cascade (ZPC) for modeling
partonic scatterings, the Lund string fragmentation model or a quark
coalescence model for hadronization, and A Relativistic Transport (ART) model
for treating hadronic scatterings, are improved and combined to give a coherent
description of the dynamics of relativistic heavy ion collisions. We also
explain the way parameters in the model are determined, and discuss the
sensitivity of predicted results to physical input in the model. Comparisons of
these results to experimental data, mainly from heavy ion collisions at the
Relativistic Heavy Ion Collider (RHIC), are then made in order to extract
information on the properties of the hot dense matter formed in these
collisions.Comment: 33 pages, 38 figures, revtex. Added 9 figures, version published in
Phys. Rev. C. The full source code of the AMPT model in the Fortran 77
language and instructions for users are available from the EPAPS ftp site
(ftp://ftp.aip.org/epaps/phys_rev_c/E-PRVCAN-72-781512/) and the OSCAR
website (http://www-cunuke.phys.columbia.edu/OSCAR/
Incommensurate magnetic structure of CeRhIn5
The magnetic structure of the heavy fermion antiferromagnet CeRhIn5 is
determined using neutron diffraction. We find a magnetic wave vector
q_M=(1/2,1/2,0.297), which is temperature independent up to T_N=3.8K. A
staggered moment of 0.374(5) Bohr magneton at 1.4K, residing on the Ce ion,
spirals transversely along the c axis. The nearest neighbor moments on the
tetragonal basal plane are aligned antiferromagnetically.Comment: 4 pages, 4 figures There was an extra factor of 2 in Eq (2). This
affects the value of staggered moment. The correct staggered moment is
0.374(5) Bohr magneton at 1.4
Partial spin freezing in the quasi-two-dimensional La2(Cu,Li)O4
In conventional spin glasses, the magnetic interaction is not strongly
anisotropic and the entire spin system freezes at low temperature. In
La2(Cu,Li)O4, for which the in-plane exchange interaction dominates the
interplane one, only a fraction of spins with antiferromagnetic correlations
extending to neighboring planes become spin-glass. The remaining spins with
only in-plane antiferromagnetic correlations remain spin-liquid at low
temperature. Such a novel partial spin freezing out of a spin-liquid observed
in this cold neutron scattering study is likely due to a delicate balance
between disorder and quantum fluctuations in the quasi-two dimensional S=1/2
Heisenberg system.Comment: 4 pages, 4 figure
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