37,477 research outputs found

### Monopole Excitation to Cluster States

We discuss strength of monopole excitation of the ground state to cluster
states in light nuclei. We clarify that the monopole excitation to cluster
states is in general strong as to be comparable with the single particle
strength and shares an appreciable portion of the sum rule value in spite of
large difference of the structure between the cluster state and the
shell-model-like ground state. We argue that the essential reasons of the large
strength are twofold. One is the fact that the clustering degree of freedom is
possessed even by simple shell model wave functions. The detailed feature of
this fact is described by the so-called Bayman-Bohr theorem which tells us that
SU(3) shell model wave function is equivalent to cluster model wave function.
The other is the ground state correlation induced by the activation of the
cluster degrees of freedom described by the Bayman-Bohr theorem. We
demonstrate, by deriving analytical expressions of monopole matrix elements,
that the order of magnitude of the monopole strength is governed by the first
reason, while the second reason plays a sufficient role in reproducing the data
up to the factor of magnitude of the monopole strength. Our explanation is made
by analysing three examples which are the monopole excitations to the $0^+_2$
and $0^+_3$ states in $^{16}$O and the one to the $0^+_2$ state in $^{12}$C.
The present results imply that the measurement of strong monopole transitions
or excitations is in general very useful for the study of cluster states.Comment: 11 pages, 1 figure: revised versio

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### Full-Densification of SLS Parts by Re-Melting

Among commercially available rapid prototyping processes, SLS is the most effective in
terms of adaptability of various materials. However, rapid prototyped parts by the process are
always porous and the physical properties of the parts are different from dense parts which is to
be used in final product. This paper introduces a post process that can densify SLS processed
plastic parts to almost 100%. An SLS processed polystyrene part is densified and, resultantly, a
much stronger and transparent part is obtained.Mechanical Engineerin

### Electrical switching in cadmium boracite single crystals

Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed

### Crystal-field-induced magnetostrictions in the spin reorientation process of Nd$_2$Fe$_{14}$B-type compounds

Volume expansion $\Delta V / V$ associated with the spin reorientation
process of Nd$_2$Fe$_{14}$B-type compounds has been investigated in terms of
simple crystalline-electric-field (CEF) model. In this system, $\Delta V / V$
is shown to be a direct measure of second order CEF energy. Calculated
anomalies in $\Delta V / V$ associated with the first-order magnetization
process of Nd$_2$Fe$_{14}$B are presented, which well reproduced the
observations.Comment: 2 pages, 2 figures, to appear in J. Magn. Magn. Mate

### Chiral dynamics of $\Sigma$-hyperons in the nuclear medium

Using SU(3) chiral perturbation theory we calculate the density-dependent
complex mean field $U_\Sigma(k_f)+ i W_\Sigma(k_f)$ of a $\Sigma$-hyperon in
isospin-symmetric nuclear matter. The leading long-range $\Sigma N$-interaction arises from one-kaon exchange and from two-pion exchange with a
$\Sigma$- or a $\Lambda$-hyperon in the intermediate state. We find from the
$\Sigma N\to \Lambda N$ conversion process at nuclear matter saturation density
$\rho_0 = 0.16$fm$^{-3}$ an imaginary single-particle potential of
$W_\Sigma(k_{f0}) =-21.5$ MeV, in fair agreement with existing empirical
determinations. The genuine long-range contributions from iterated (second
order) one-pion exchange with an intermediate $\Sigma$- or $\Lambda$-hyperon
sum up to a moderately repulsive real single-particle potential of
$U_\Sigma(k_{f0})= 59$ MeV. Recently measured $(\pi^-,K^+$) inclusive spectra
related to $\Sigma^-$-formation in heavy nuclei give evidence for a
$\Sigma$-nucleus repulsion of similar size. Our results suggest that the net
effect of the short-range $\Sigma N$-interaction on the $\Sigma$-nuclear mean
field could be small.Comment: 7 pages, 2 figures, published in: Phys. Rev. C 71, 068201 (2005

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### Preliminary Study for Transparentization of SLS Parts by Resin Infiltration

Since opacity of SLS processed parts are derived from random reflection and refraction at
boundaries of refractive indices between the air and plastic, infiltration of resin that shares the
same index with the plastic can increase transparency of the parts. In this paper, desirable
characteristics for the infiltrant were investigated first, and transparentization test of SLS
processed parts out of CastFormTM was carried out. The highest transmittance of 80% and the
lowest haze of 55% were obtained. However, exact match of refractive indices of powder for SLS
and infiltrant did not give the best transparency. The reasons were considered in discussions.Mechanical Engineerin

### On the Genus Expansion in the Topological String Theory

A systematic formulation of the higher genus expansion in topological string
theory is considered. We also develop a simple way of evaluating genus zero
correlation functions. At higher genera we derive some interesting formulas for
the free energy in the $A_1$ and $A_2$ models. We present some evidence that
topological minimal models associated with Lie algebras other than the A-D-E
type do not have a consistent higher genus expansion beyond genus one. We also
present some new results on the $CP^1$ model at higher genera.Comment: 36 pages, phyzzx, UTHEP-27

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