6,843 research outputs found
Double Charge Exchange And Configuration Mixing
The energy dependence of forward pion double charge exchange reactions on
light nuclei is studied for both the Ground State transition and the
Double-Isobaric-Analog-State transitions. A common characteristic of these
double reactions is a resonance-like peak around 50 MeV pion lab energy. This
peak arises naturally in a two-step process in the conventional pion-nucleon
system with proper handling of nuclear structure and pion distortion. A
comparison among the results of different nuclear structure models demonstrates
the effects of configuration mixing. The angular distribution is used to fix
the single particle wave function.Comment: Added 1 figure (now 8) corrected references and various other change
Research Revisited: Cognitive Effects of Greek Affiliation in College: Additional Evidence
Previous research found broad based negative effects of fraternity/sorority affiliation on standardized measures of cognitive development after one year of college. Following the same sample, and employing essentially the same research design and analytic model, the present study found that the negative effects of fraternity/sorority affiliation were much less pronounced during the second or third years of college
Boson mappings and four-particle correlations in algebraic neutron-proton pairing models
Neutron-proton pairing correlations are studied within the context of two
solvable models, one based on the algebra SO(5) and the other on the algebra
SO(8). Boson-mapping techniques are applied to these models and shown to
provide a convenient methodological tool both for solving such problems and for
gaining useful insight into general features of pairing. We first focus on the
SO(5) model, which involves generalized T=1 pairing. Neither boson mean-field
methods nor fermion-pair approximations are able to describe in detail
neutron-proton pairing in this model. The analysis suggests, however, that the
boson Hamiltonian obtained from a mapping of the fermion Hamiltonian contains a
pairing force between bosons, pointing to the importance of boson-boson (or
equivalently four-fermion) correlations with isospin T=0 and spin S=0. These
correlations are investigated by carrying out a second boson mapping. Closed
forms for the fermion wave functions are given in terms of the fermion-pair
operators. Similar techniques are applied -- albeit in less detail -- to the
SO(8) model, involving a competition between T=1 and T=0 pairing. Conclusions
similar to those of the SO(5) analysis are reached regarding the importance of
four-particle correlations in systems involving neutron-proton pairing.Comment: 31 pages, Latex, 3 Postscript figures, uses epsf.sty, submitted to
Physical Review
Bring a plate: facilitating experimentation in the Welcome Dinner Project
Drawing on in-depth empirical research, we explore a project called The Welcome Dinner (WDP). The WDP aims to bring together ânewly arrivedâ people and âestablished Australiansâ to meet and âshare storiesâ over a potluck meal in âthe comfort of their own homeâ. The purpose is to create meaningful connections, new friendships and social solidarities. In this paper, we focus on the micro-contexts of the dinners and the minute activities and techniques that facilitators use in hosting. Our aim is not to analyse the effects of the project but rather the design and meaning of the activities. As a form of âdesigned everyday multiculturalismâ, focused on welcoming new arrivals to Australia, it takes effort, skill and labour to manage the contact between different cultural groups over organised meals. Thus, facilitators take over the hosting of the lunches and dinners to run activities, which are imagined to lubricate social dynamics and relations, and produce convivial commensal affects and behaviours. Drawing on theories of training activities as embodied and cognitive experimentations, which enable new knowledge practices and social relations, we analyse field notes and interviews about the facilitation, structure and activities at the WDP home dinners
Local Density Approximation for proton-neutron pairing correlations. I. Formalism
In the present study we generalize the self-consistent
Hartree-Fock-Bogoliubov (HFB) theory formulated in the coordinate space to the
case which incorporates an arbitrary mixing between protons and neutrons in the
particle-hole (p-h) and particle-particle (p-p or pairing) channels. We define
the HFB density matrices, discuss their spin-isospin structure, and construct
the most general energy density functional that is quadratic in local
densities. The consequences of the local gauge invariance are discussed and the
particular case of the Skyrme energy density functional is studied. By varying
the total energy with respect to the density matrices the self-consistent
one-body HFB Hamiltonian is obtained and the structure of the resulting mean
fields is shown. The consequences of the time-reversal symmetry, charge
invariance, and proton-neutron symmetry are summarized. The complete list of
expressions required to calculate total energy is presented.Comment: 22 RevTeX page
Patterns of the ground states in the presence of random interactions: nucleon systems
We present our results on properties of ground states for nucleonic systems
in the presence of random two-body interactions. In particular we present
probability distributions for parity, seniority, spectroscopic (i.e., in the
laboratory framework) quadrupole moments and clustering in the ground
states. We find that the probability distribution for the parity of the ground
states obtained by a two-body random ensemble simulates that of realistic
nuclei: positive parity is dominant in the ground states of even-even nuclei
while for odd-odd nuclei and odd-mass nuclei we obtain with almost equal
probability ground states with positive and negative parity. In addition we
find that for the ground states, assuming pure random interactions, low
seniority is not favored, no dominance of positive values of spectroscopic
quadrupole deformation, and no sign of -cluster correlations, all in
sharp contrast to realistic nuclei. Considering a mixture of a random and a
realistic interaction, we observe a second order phase transition for the
-cluster correlation probability.Comment: 7 page
Discovery of the Acoustic Faraday Effect in Superfluid 3He-B
We report the discovery of the acoustic Faraday effect in superfluid 3He-B.
The observation of this effect provides the first direct evidence for
propagating transverse acoustic waves in liquid 3He, a mode first predicted by
Landau in 1957. The Faraday rotation is large and observable because of
spontaneously broken spin-orbit symmetry in 3He-B. We compare the experimental
observations with a simulation of the transverse acoustic impedance that
includes the field-induced circular birefringence of transverse waves.Comment: 4 pages in RevTex plus 3 postscript figures; new version includes:
minor corrections to the text and an updated of list of reference
Contribution of the massive photon decay channel to neutrino cooling of neutron stars
We consider massive photon decay reactions via intermediate states of
electron-electron-holes and proton-proton-holes into neutrino-antineutrino
pairs in the course of neutron star cooling. These reactions may become
operative in hot neutron stars in the region of proton pairing where the photon
due to the Higgs-Meissner effect acquires an effective mass that
is small compared to the corresponding plasma frequency. The contribution of
these reactions to neutrino emissivity is calculated; it varies with the
temperature and the photon mass as
for . Estimates show that these processes appear as extra
efficient cooling channels of neutron stars at temperatures K.Comment: accepted to publication in Zh. Eksp. Teor. Fiz. (JETP
Deformations of the fermion realization of the sp(4) algebra and its subalgebras
With a view towards future applications in nuclear physics, the fermion
realization of the compact symplectic sp(4) algebra and its q-deformed versions
are investigated. Three important reduction chains of the sp(4) algebra are
explored in both the classical and deformed cases. The deformed realizations
are based on distinct deformations of the fermion creation and annihilation
operators. For the primary reduction, the su(2) sub-structure can be
interpreted as either the spin, isospin or angular momentum algebra, whereas
for the other two reductions su(2) can be associated with pairing between
fermions of the same type or pairing between two distinct fermion types. Each
reduction provides for a complete classification of the basis states. The
deformed induced u(2) representations are reducible in the action spaces of
sp(4) and are decomposed into irreducible representations.Comment: 28 pages, LaTeX 12pt article styl
Fully general relativistic simulation of coalescing binary neutron stars: Preparatory tests
We present our first successful numerical results of 3D general relativistic
simulations in which the Einstein equation as well as the hydrodynamic
equations are fully solved. This paper is especially devoted to simulations of
test problems such as spherical dust collapse, stability test of perturbed
spherical stars, and preservation of (approximate) equilibrium states of
rapidly rotating neutron star and/or corotating binary neutron stars. These
test simulations confirm that simulations of coalescing binary neutron stars
are feasible in a numerical relativity code. It is illustrated that using our
numerical code, simulations of these problems, in particular those of
corotating binary neutron stars, can be performed stably and fairly accurately
for a couple of dynamical timescales. These numerical results indicate that our
formulation for solving the Einstein field equation and hydrodynamic equations
are robust and make it possible to perform a realistic simulation of coalescing
binary neutron stars for a long time from the innermost circular orbit up to
formation of a black hole or neutron star.Comment: 36 pages, to be published in PRD 15, erase unnecessary figure
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