45 research outputs found
Symplectic structure and monopole strength in 12C
The relation between the monopole transition strength and existence of
cluster structure in the excited states is discussed based on an algebraic
cluster model. The structure of C is studied with a 3 model, and
the wave function for the relative motions between clusters are
described by the symplectic algebra , which corresponds to the
linear combinations of states with different multiplicities.
Introducing algebra works well for reducing the number of the basis
states, and it is also shown that states connected by the strong monopole
transition are classified by a quantum number of the
algebra.Comment: Phys. Rev. C in pres
Formation and decay of resonance state in Be and B nuclei. Microscopic three-cluster model investigations
We study nature of the low-lying resonance states in mirror nuclei Be
and B. Investigations are performed within a three-cluster model. The
model makes use of the hyperspherical harmonics, which provides convenient
description of three-cluster continuum. The dominant three-cluster
configurations and in Be and B,
respectively, are taken into account. Dominant decay channels for all resonance
states in Be and B are explored. Much attention is paid to the
controversial resonance states in both nuclei. We study effects of
the Coulomb interaction on energy and width of three-cluster resonances in the
mirror nuclei Be and B. We also search for the Hoyle-analogue state
which is a key step for alternative way of Be and B syntheses in a
triple collision of clusters in a stellar environment.Comment: 17 pages, 16 figures, submitted to Phys. Rev.
Decoherence suppression via environment preparation
To protect a quantum system from decoherence due to interaction with its
environment, we investigate the existence of initial states of the environment
allowing for decoherence-free evolution of the system. For models in which a
two-state system interacts with a dynamical environment, we prove that such
states exist if and only if the interaction and self-evolution Hamiltonians
share an eigenstate. If decoherence by state preparation is not possible, we
show that initial states minimizing decoherence result from a delicate
compromise between the environment and interaction dynamics.Comment: 4 pages, 2 figure
Particle-unstable nuclei in the Hartree-Fock theory
Ground state energies and decay widths of particle unstable nuclei are
calculated within the Hartree-Fock approximation by performing a complex
scaling of the many-body Hamiltonian. Through this transformation, the wave
functions of the resonant states become square integrable. The method is
implemented with Skyrme effective interactions. Several Skyrme parametrizations
are tested on four unstable nuclei: 10He, 12O, 26O and 28O.Comment: 5 pages, LaTeX, submitted to Phys. Rev. Let
Towards a More Complete and Accurate Experimental Nuclear Reaction Data Library (EXFOR): International Collaboration Between Nuclear Reaction Data Centres (NRDC)
The International Network of Nuclear Reaction Data Centres (NRDC) coordinated
by the IAEA Nuclear Data Section (NDS) is successfully collaborating in the
maintenance and development of the EXFOR library. As the scope of published
data expands (e.g., to higher energy, to heavier projectile) to meet the needs
from the frontier of sciences and applications, it becomes nowadays a hard and
challenging task to maintain both completeness and accuracy of the whole EXFOR
library. The paper describes evolution of the library with highlights on recent
developments.Comment: 4 pages, 2 figure
Shell Model in the Complex Energy Plane
This work reviews foundations and applications of the complex-energy
continuum shell model that provides a consistent many-body description of bound
states, resonances, and scattering states. The model can be considered a
quasi-stationary open quantum system extension of the standard configuration
interaction approach for well-bound (closed) systems.Comment: Topical Review, J. Phys. G, Nucl. Part. Phys, in press (2008
Few-body resonances in light nuclei
We have localized several few-body resonances in light nuclei, using methods which can properly handle two- or three-body resonant states. Among other results, we predict the existence of a three-neutron resonance, small spin-orbit splittings between the low-lying states in He-5 and Li-5, the nonexistence of the soft dipole resonance in He-6, new 1+ states in Li-8 and B-8, and the presence of a nonlinear amplification phenomenon in the 0+_2 state of C-12
Impact of network structure and cellular response on spike time correlations
Novel experimental techniques reveal the simultaneous activity of larger and
larger numbers of neurons. As a result there is increasing interest in the
structure of cooperative -- or correlated -- activity in neural populations,
and in the possible impact of such correlations on the neural code. A
fundamental theoretical challenge is to understand how the architecture of
network connectivity along with the dynamical properties of single cells shape
the magnitude and timescale of correlations. We provide a general approach to
this problem by extending prior techniques based on linear response theory. We
consider networks of general integrate-and-fire cells with arbitrary
architecture, and provide explicit expressions for the approximate
cross-correlation between constituent cells. These correlations depend strongly
on the operating point (input mean and variance) of the neurons, even when
connectivity is fixed. Moreover, the approximations admit an expansion in
powers of the matrices that describe the network architecture. This expansion
can be readily interpreted in terms of paths between different cells. We apply
our results to large excitatory-inhibitory networks, and demonstrate first how
precise balance --- or lack thereof --- between the strengths and timescales of
excitatory and inhibitory synapses is reflected in the overall correlation
structure of the network. We then derive explicit expressions for the average
correlation structure in randomly connected networks. These expressions help to
identify the important factors that shape coordinated neural activity in such
networks