50,889 research outputs found
Dynamical cluster-decay model for hot and rotating light-mass nuclear systems, applied to low-energy S + Mg Ni reaction
The dynamical cluster-decay model (DCM) is developed further for the decay of
hot and rotating compound nuclei (CN) formed in light heavy-ion reactions. The
model is worked out in terms of only one parameter, namely the neck-length
parameter, which is related to the total kinetic energy TKE(T) or effective
Q-value at temperature T of the hot CN, defined in terms of the
both the light-particles (LP), with 4, Z 2, as well as the
complex intermediate mass fragments (IMF), with , is
considered as the dynamical collective mass motion of preformed clusters
through the barrier. Within the same dynamical model treatment, the LPs are
shown to have different characteristics as compared to the IMFs. The systematic
variation of the LP emission cross section , and IMF emission
cross section , calculated on the present DCM match exactly the
statistical fission model predictions. It is for the first time that a
non-statistical dynamical description is developed for the emission of
light-particles from the hot and rotating CN. The model is applied to the decay
of Ni formed in the S + Mg reaction at two incident
energies E = 51.6 and 60.5 MeV. Both the IMFs and average
spectra are found to compare reasonably nicely with the experimental data,
favoring asymmetric mass distributions. The LPs emission cross section is shown
to depend strongly on the type of emitted particles and their multiplicities
Strong-coupling expansion for ultracold bosons in an optical lattice at finite temperatures in the presence of superfluidity
We develop a strong-coupling () expansion technique for calculating
the density profile for bosonic atoms trapped in an optical lattice with an
overall harmonic trap at finite temperature and finite on site interaction in
the presence of superfluid regions. Our results match well with quantum Monte
Carlo simulations at finite temperature. We also show that the superfluid order
parameter never vanishes in the trap due to proximity effect. Our calculations
for the scaled density in the vacuum to superfluid transition agree well with
the experimental data for appropriate temperatures. We present calculations for
the entropy per particle as a function of temperature which can be used to
calibrate the temperature in experiments. We also discuss issues connected with
the demonstration of universal quantum critical scaling in the experiments.Comment: 11 pages, 9 figure
Shell closure effects studied via cluster decay in heavy nuclei
The effects of shell closure in nuclei via the cluster decay is studied. In
this context, we have made use of the Preformed Cluster Model () of Gupta
and collaborators based on the Quantum Mechanical Fragmentation Theory. The key
point in the cluster radioactivity is that it involves the interplay of close
shell effects of parent and daughter. Small half life for a parent indicates
shell stabilized daughter and long half life indicates the stability of the
parent against the decay. In the cluster decay of trans lead nuclei observed so
far, the end product is doubly magic lead or its neighbors. With this in our
mind we have extended the idea of cluster radioactivity. We investigated decay
of different nuclei where Zirconium is always taken as a daughter nucleus,
which is very well known deformed nucleus. The branching ratio of cluster decay
and -decay is also studied for various nuclei, leading to magic or
almost doubly magic daughter nuclei. The calculated cluster decay half-life are
in well agreement with the observed data. First time a possibility of cluster
decay in nucleus is predicted
Profitable Scheduling on Multiple Speed-Scalable Processors
We present a new online algorithm for profit-oriented scheduling on multiple
speed-scalable processors. Moreover, we provide a tight analysis of the
algorithm's competitiveness. Our results generalize and improve upon work by
\textcite{Chan:2010}, which considers a single speed-scalable processor. Using
significantly different techniques, we can not only extend their model to
multiprocessors but also prove an enhanced and tight competitive ratio for our
algorithm.
In our scheduling problem, jobs arrive over time and are preemptable. They
have different workloads, values, and deadlines. The scheduler may decide not
to finish a job but instead to suffer a loss equaling the job's value. However,
to process a job's workload until its deadline the scheduler must invest a
certain amount of energy. The cost of a schedule is the sum of lost values and
invested energy. In order to finish a job the scheduler has to determine which
processors to use and set their speeds accordingly. A processor's energy
consumption is power \Power{s} integrated over time, where
\Power{s}=s^{\alpha} is the power consumption when running at speed .
Since we consider the online variant of the problem, the scheduler has no
knowledge about future jobs. This problem was introduced by
\textcite{Chan:2010} for the case of a single processor. They presented an
online algorithm which is -competitive. We provide an
online algorithm for the case of multiple processors with an improved
competitive ratio of .Comment: Extended abstract submitted to STACS 201
Obtaining pressure versus concentration phase diagrams in spin systems from Monte Carlo simulations
We propose an efficient procedure for determining phase diagrams of systems
that are described by spin models. It consists of combining cluster algorithms
with the method proposed by Sauerwein and de Oliveira where the grand canonical
potential is obtained directly from the Monte Carlo simulation, without the
necessity of performing numerical integrations. The cluster algorithm presented
in this paper eliminates metastability in first order phase transitions
allowing us to locate precisely the first-order transitions lines. We also
produce a different technique for calculating the thermodynamic limit of
quantities such as the magnetization whose infinite volume limit is not
straightforward in first order phase transitions. As an application, we study
the Andelman model for Langmuir monolayers made of chiral molecules that is
equivalent to the Blume-Emery-Griffiths spin-1 model. We have obtained the
phase diagrams in the case where the intermolecular forces favor interactions
between enantiomers of the same type (homochiral interactions). In particular,
we have determined diagrams in the surface pressure versus concentration plane
which are more relevant from the experimental point of view and less usual in
numerical studies
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