2,808 research outputs found
Influence of nuclear physics inputs and astrophysical conditions on Th/U chronometer
The productions of thorium and uranium are key ingredients in -process
nucleo-cosmochronology. With the combination of improved nuclear and stellar
data, we have made detailed investigations on the -process abundance pattern
in the very metal-poor halo stars based on the classical -process approach.
It is found that the results are almost independent of specified simulations to
observed abundances. The influence from nuclear mass uncertainties on Th/U
chronometer can approach 2 Gyr. Moreover, the ages of the metal-poor stars HE
1523-0901, CS 31082-001, and BD +173248 are determined as , , and Gyr, respectively. The results can
serve as an independent check for age estimate of the universe.Comment: 20 pages, 5 figures. accepted by Phys. Rev.
Feasibility of the finite amplitude method in covariant density functional theory
Self-consistent relativistic random-phase approximation (RPA) in the radial
coordinate representation is established by using the finite amplitude method
(FAM). Taking the isoscalar giant monopole resonance in spherical nuclei as
example, the feasibility of the FAM for the covariant density functionals is
demonstrated, and the newly developed methods are verified by the conventional
RPA calculations. In the present relativistic RPA calculations, the effects of
the Dirac sea can be automatically taken into account in the coordinate-space
representation. The rearrangement terms due to the density-dependent couplings
can be implicitly calculated without extra computational costs in both
iterative and matrix FAM schemes.Comment: 12 pages, 5 figure
Finite-amplitude method: An extension to the covariant density functionals
The finite-amplitude method (FAM) is one of the most promising methods for
optimizing the computational performance of the random-phase approximation
(RPA) calculations in deformed nuclei. In this report, we will mainly focus on
our recent progress in the self-consistent relativistic RPA established by
using the FAM. It is found that the effects of Dirac sea can be taken into
account implicitly in the coordinate-space representation and the rearrangement
terms due to the density-dependent couplings can be treated without extra
computational costs.Comment: 5 pages, 2 figures, Proceedings of the 20th Nuclear Physics Workshop
"Marie & Pierre Curie", Kazimierz, Poland, 25-29 September, 201
Energy-Efficient Antenna Selection and Power Allocation for Large-Scale Multiple Antenna Systems with Hybrid Energy Supply
The combination of energy harvesting and large-scale multiple antenna
technologies provides a promising solution for improving the energy efficiency
(EE) by exploiting renewable energy sources and reducing the transmission power
per user and per antenna. However, the introduction of energy harvesting
capabilities into large-scale multiple antenna systems poses many new
challenges for energy-efficient system design due to the intermittent
characteristics of renewable energy sources and limited battery capacity.
Furthermore, the total manufacture cost and the sum power of a large number of
radio frequency (RF) chains can not be ignored, and it would be impractical to
use all the antennas for transmission. In this paper, we propose an
energy-efficient antenna selection and power allocation algorithm to maximize
the EE subject to the constraint of user's quality of service (QoS). An
iterative offline optimization algorithm is proposed to solve the non-convex EE
optimization problem by exploiting the properties of nonlinear fractional
programming. The relationships among maximum EE, selected antenna number,
battery capacity, and EE-SE tradeoff are analyzed and verified through computer
simulations.Comment: IEEE Globecom 2014 Selected Areas in Communications Symposium-Green
Communications and Computing Trac
Stellar electron-capture rates calculated with the finite-temperature relativistic random-phase approximation
We introduce a self-consistent microscopic theoretical framework for
modelling the process of electron capture on nuclei in stellar environment,
based on relativistic energy density functionals. The finite-temperature
relativistic mean-field model is used to calculate the single-nucleon basis and
the occupation factors in a target nucleus, and , ,
charge-exchange transitions are described by the self-consistent
finite-temperature relativistic random-phase approximation. Cross sections and
rates are calculated for electron capture on 54,56Fe and 76,78Ge in stellar
environment, and results compared with predictions of similar and complementary
model calculations.Comment: Physical Review C, accepte
GreenDelivery: Proactive Content Caching and Push with Energy-Harvesting-based Small Cells
The explosive growth of mobile multimedia traffic calls for scalable wireless
access with high quality of service and low energy cost. Motivated by the
emerging energy harvesting communications, and the trend of caching multimedia
contents at the access edge and user terminals, we propose a paradigm-shift
framework, namely GreenDelivery, enabling efficient content delivery with
energy harvesting based small cells. To resolve the two-dimensional randomness
of energy harvesting and content request arrivals, proactive caching and push
are jointly optimized, with respect to the content popularity distribution and
battery states. We thus develop a novel way of understanding the interplay
between content and energy over time and space. Case studies are provided to
show the substantial reduction of macro BS activities, and thus the related
energy consumption from the power grid is reduced. Research issues of the
proposed GreenDelivery framework are also discussed.Comment: 15 pages, 5 figures, accepted by IEEE Communications Magazin
On the Statistical Multiplexing Gain of Virtual Base Station Pools
Facing the explosion of mobile data traffic, cloud radio access network
(C-RAN) is proposed recently to overcome the efficiency and flexibility
problems with the traditional RAN architecture by centralizing baseband
processing. However, there lacks a mathematical model to analyze the
statistical multiplexing gain from the pooling of virtual base stations (VBSs)
so that the expenditure on fronthaul networks can be justified. In this paper,
we address this problem by capturing the session-level dynamics of VBS pools
with a multi-dimensional Markov model. This model reflects the constraints
imposed by both radio resources and computational resources. To evaluate the
pooling gain, we derive a product-form solution for the stationary distribution
and give a recursive method to calculate the blocking probabilities. For
comparison, we also derive the limit of resource utilization ratio as the pool
size approaches infinity. Numerical results show that VBS pools can obtain
considerable pooling gain readily at medium size, but the convergence to large
pool limit is slow because of the quickly diminishing marginal pooling gain. We
also find that parameters such as traffic load and desired Quality of Service
(QoS) have significant influence on the performance of VBS pools.Comment: Accepted by GlobeCom'1
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