8,077 research outputs found
Quantum Monte-Carlo method applied to Non-Markovian barrier transmission
In nuclear fusion and fission, fluctuation and dissipation arise due to the
coupling of collective degrees of freedom with internal excitations. Close to
the barrier, both quantum, statistical and non-Markovian effects are expected
to be important. In this work, a new approach based on quantum Monte-Carlo
addressing this problem is presented. The exact dynamics of a system coupled to
an environment is replaced by a set of stochastic evolutions of the system
density. The quantum Monte-Carlo method is applied to systems with quadratic
potentials. In all range of temperature and coupling, the stochastic method
matches the exact evolution showing that non-Markovian effects can be simulated
accurately. A comparison with other theories like Nakajima-Zwanzig or
Time-ConvolutionLess ones shows that only the latter can be competitive if the
expansion in terms of coupling constant is made at least to fourth order. A
systematic study of the inverted parabola case is made at different
temperatures and coupling constants. The asymptotic passing probability is
estimated in different approaches including the Markovian limit. Large
differences with the exact result are seen in the latter case or when only
second order in the coupling strength is considered as it is generally assumed
in nuclear transport models. On opposite, if fourth order in the coupling or
quantum Monte-Carlo method is used, a perfect agreement is obtained.Comment: 10 pages, 6 figures, to be published in Phys. Rev.
Non-Markovian effects in quantum system: an exact stochastic mean-field treatment
A quantum Monte-Carlo is proposed to describe fusion/fission processes when
fluctuation and dissipation, with memory effects, are important. The new theory
is illustrated for systems with inverted harmonic potentials coupled to a
heat-bath.Comment: Proceedings of the international conference: "Nuclear Structure and
related topics, Dubna, June (2009
Polarization of the nuclear surface in deformed nuclei
The density profiles of around 750 nuclei are analyzed using the Skyrme
energy density functional theory. Among them, more than 350 nuclei are found to
be deformed. In addition to rather standard properties of the density, we
report a non-trivial behavior of the nuclear diffuseness as the system becomes
more and more deformed. Besides the geometric effects expected in rigid body,
the diffuseness acquires a rather complex behavior leading to a reduction of
the diffuseness along the main axis of deformation simultaneously with an
increase of the diffuseness along the other axis. The possible isospin
dependence of this polarization is studied. This effect, that is systematically
seen in medium- and heavy-nuclei, can affect the nuclear dynamical properties.
A quantitative example is given with the fusion barrier in the Ca+
U reaction.Comment: 8 pages, 13 figure
Using datasets from the Internet for hydrological modeling: an example from the Kntnk Menderes Basin, Turkey
River basin development / Water resources / Data collection / Models / Hydrology / Land classification / Water management / Water scarcity / Water allocation / Stream flow / Water demand / Turkey / Kntnk Menderes Basin
The effect of metacognitive strategy instruction on L2 learner beliefs and listening skills
This pilot study investigated the effect of semester-long strategy-based instruction on
learner beliefs and skills in the processing of aural input by adult learners of English as a
second language at metacognitive and procedural levels. The study addressed two
frequently encountered learner beliefs thought to impede L2 processing of aural input:
The little words aren’t important; intonation is merely decorative. Working on the
premise that learner beliefs underpin learner strategies for processing aural input and are
reflected in learner productive and receptive skills, pre- and post-instruction instruments
measured both learners’ awareness of connected speech processes and the functions of
intonation, and their ability to segment a continuous speech stream, and to process
utterances for speaker intent. Findings using repeated measures analysis of variance
support strategy-based metacognitive training in connected speech and stress and
intonation to promote listening skills awareness, aid word segmentation, and facilitate
understanding utterance content and intended meaning.Published versio
Non-Markovian dynamics with fermions
Employing the quadratic fermionic Hamiltonians for the collective and
internal subsystems with a linear coupling, we studied the role of fermionic
statistics on the dynamics of the collective motion. The transport coefficients
are discussed as well as the associated fluctuation-dissipation relation. Due
to different nature of the particles, the path to equilibrium is slightly
affected. However, in the weak coupling regime, the time-scale for approaching
equilibrium is found to be globally unchanged. The Pauli-blocking effect can
modify the usual picture in open quantum system. In some limits, contrary to
boson, this effect can strongly hinder the influence of the bath by blocking
the interacting channels.Comment: 13 pages, 6 figures. Submitted to PR
Neutron pair transfer in sub-barrier capture process
The sub-barrier capture reactions following the neutron pair transfer are
proposed to be used for the indirect study of neutron-neutron correlation in
the surface region of nucleus. The strong effect of the dineutron-like clusters
transfer stemming from the surface of magic and non-magic nuclei O,
Ca, Ni, Mo, Ru, Pd, and
Sn is demonstrated. The dominance of
two-neutron transfer channel at the vicinity of the Coulomb barrier is further
supported by time-dependent mean-field approaches.Comment: 17 pages, 7 figures, accepted in PR
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