5,848 research outputs found
Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian
The complete exact solution of the T=1 neutron-proton pairing Hamiltonian is
presented in the context of the SO(5) Richardson-Gaudin model with
non-degenerate single-particle levels and including isospin-symmetry breaking
terms. The power of the method is illustrated with a numerical calculation for
Ge for a model space which is out of reach of modern
shell-model codes.Comment: To be published by Physical Review Letter
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
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
Methodological challenges in online trials: an update and insights from the REACT trial
There has been a growth in the number of web-based trials of web-based interventions, adding to an increasing evidence base for their feasibility and effectiveness. However, there are challenges associated with such trials, which researchers must address. This discussion paper follows the structure of the Down Your Drink trial methodology paper, providing an update from the literature for each key trial parameter (recruitment, registration eligibility checks, consent and participant withdrawal, randomization, engagement with a web-based intervention, retention, data quality and analysis, spamming, cybersquatting, patient and public involvement, and risk management and adverse events), along with our own recommendations based on designing the Relatives Education and Coping Toolkit randomized controlled trial for relatives of people with psychosis or bipolar disorder. The key recommendations outlined here are relevant for future web-based and hybrid trials and studies using iterative development and test models such as the Accelerated Creation-to-Sustainment model, both within general health research and specifically within mental health research for relatives. Researchers should continue to share lessons learned from conducting web-based trials of web-based interventions to benefit future studies
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
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
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
Neutrino Pair Bremsstrahlung in Neutron Star Crusts: a Reappraisal
We demonstrate that band-structure effects suppress bremsstrahlung of
neutrino pairs by electrons in the crusts of neutron stars at temperatures of
the order of and below. Taking this into account,
together with the fact that recent work indicates that the masses of neutron
star crusts are considerably smaller than previously estimated, we find
neutrino pair bremsstrahlung to be much less important for the thermal
evolution of neutron stars than earlier calculations suggested.Comment: 11 plain LaTeX pages, 3 figures available on request, NORDITA-93/72
A/S/
Optical-chemical-microphysical relationships and closure studies for mixed carbonaceous aerosols observed at Jeju Island; 3-laser photoacoustic spectrometer, particle sizing, and filter analysis
Transport of aerosols in pollution plumes from the mainland Asian continent was observed in situ at Jeju, South Korea during the Cheju Asian Brown Cloud Plume-Asian Monsoon Experiment (CAPMEX) field campaign throughout August and September 2008 using a 3-laser photoacoustic spectrometer (PASS-3), chemical filter analysis, and size distributions. The PASS-3 directly measures the effects of morphology (e.g. coatings) on light absorption that traditional filter-based instruments are unable to address. Transport of mixed sulfate, carbonaceous, and nitrate aerosols from various Asian pollution plumes to Jeju accounted for 74% of the deployment days, showing large variations in their measured chemical and optical properties. Analysis of eight distinct episodes, spanning wide ranges of chemical composition, optical properties, and source regions, reveals that episodes with higher organic carbon (OC)/sulfate (SO 2-4 ) and nitrate (NO-3 )/SO2-4 composition ratios exhibit lower single scatter albedo at shorter wavelengths (!405). We infer complex refractive indices (n-ik) as a function of wavelength for the high, intermediate, and low OC/SO2-4 pollution episodes by using the observed particle size distributions and the measured optical properties. The smallest mean particle diameter corresponds to the high OC/SO2-4 aerosol episode. The imaginary part of the refractive index (k) is greater for the high OC/SO2- 4 episode at all wavelengths. A distinct, sharp increase in k at short wavelength implies enhanced light absorption by OC, which accounts for 50% of the light absorption at 405 nm, in the high OC/SO2-4 episode. Idealized analysis indicates increased absorption at 781 nm by factors greater than 3 relative to denuded black carbon in the laboratory. We hypothesize that coatings of black carbon cores are the mechanism of this enhancement. This implies that climate warming and atmospheric heating rates from black carbon particles can be significantly larger than have been estimated previously. The results of this study demonstrate ways in which atmospheric processing and mixing can amplify particle light absorption for carbonaceous aerosol, significantly at short wavelength, underscoring the need to understand and predict chemical composition effects on optical properties to accurately estimate the climate radiative forcing by mixed carbonaceous aerosols
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