6,477 research outputs found
Nucleon Superfluidity vs Observations of Cooling Neutron Stars
Cooling simulations of neutron stars (NSs) are performed assuming that
stellar cores consist of neutrons, protons and electrons and using realistic
density profiles of superfluid critical temperatures and
of neutrons and protons. Taking a suitable profile of
with maximum K one can obtain smooth
transition from slow to rapid cooling with increasing stellar mass. Adopting
the same profile one can explain the majority of observations of thermal
emission from isolated middle--aged NSs by cooling of NSs with different masses
either with no neutron superfluidity in the cores or with a weak superfluidity,
K. The required masses range from for (young
and hot) RX J0822-43 and (old and warm) PSR 1055-52 and RX J1856-3754 to
for the (colder) Geminga and Vela pulsars. Observations
constrain the and profiles with respect to the
threshold density of direct Urca process and maximum central density of NSs.Comment: 4 pages, 2 figures, AA Letters, accepte
Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter
The bulk viscosity of the neutron star matter due to the direct Urca
processes involving nucleons, electrons and muons is studied taking into
account possible superfluidity of nucleons in the neutron star cores. The cases
of singlet-state pairing or triplet-state pairing (without and with nodes of
the superfluid gap at the Fermi surface) of nucleons are considered. It is
shown that the superfluidity may strongly reduce the bulk viscosity. The
practical expressions for the superfluid reduction factors are obtained. For
illustration, the bulk viscosity is calculated for two models of dense matter
composed of neutrons, protons,electrons and muons. The presence of muons
affects the bulk viscosity due to the direct Urca reactions involving electrons
and produces additional comparable contribution due to the direct Urca
reactions involving muons. The results can be useful for studying damping of
vibrations of neutron stars with superfluid cores.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy
and Astrophysic
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/
Nuclear Effects on Bremsstrahlung Neutrino Rates of Astrophysical Interest
We calculate in this work the rates for the neutrino pair production by
nucleon-nucleon bremsstrahlung taking into account the full contribution from a
nuclear one-pion-exchange potential. It is shown that if the temperatures are
low enough (), the integration over the nuclear part can be done
for the general case, ranging from the completely degenerate (D) to the
non-degenerate (ND) regime. We find that the inclusion of the full nuclear
contribution enhances the neutrino pair production by and
bremsstrahlung by a factor of about two in both the D and ND limits when
compared with previous calculations. This result may be relevant for the
physical conditions of interest in the semitransparent regions near the
neutrinosphere in type II supernovae, cooling of neutron stars and other
astrophysical situations.Comment: 11 pages, no figures, LaTex file. submitted to PR
New records and combinations for Neotropical Leptophlebiidae (Ephemeroptera)
Several species of Leptophlebiidae (Atalophlebiinae) from South and Central America are given new generic combinations based on improved knowledge of the Leptophlebiidae of the region. These are Tikuna bilineata (Needham & Murphy, 1924, Choroterpes) comb. nov.; Terpides vinculum (Traver, 1947, Choroterpes) comb. n.; Hermanella costalis (Navas, 1934, Thraulus) comb. n.; Hermanella costalis (Navas, 1934, Thraulus) comb.n.; Ulmeritoides haarupi (Esben-Petersen, 1912, Thraulus) comb. n. (synonyms Deleatidium vittatum, Thew syn. n. and Ulmeritoides fidalgoi Dominguez, 1995, syn. n.). In addition, we give new distribution records for Tikuna bilineata, report Choroterpes from Colombia, and describe Hagenulus marshal sp. n. from Ecuador based on two male imagos.Fil: Peters, J. G.. Florida A&M University; Estados UnidosFil: Flowers, R. W.. Florida A&M University; Estados UnidosFil: Hubbard, M. D.. Florida A&M University; Estados UnidosFil: Dominguez, Eduardo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - TucumĂĄn; Argentina. Universidad Nacional de TucumĂĄn. Facultad de Ciencias Naturales e Instituto Miguel Lillo; ArgentinaFil: Savage, H. M.. Centers for Disease Control and Prevention; Estados Unidos. Florida A&M University; Estados Unido
Three Types of Cooling Superfluid Neutron Stars: Theory and Observations
Cooling of neutron stars (NSs) with the cores composed of neutrons, protons,
and electrons is simulated assuming S pairing of neutrons in the NS
crust, and also S pairing of protons and weak P pairing of
neutrons in the NS core, and using realistic density profiles of the superfluid
critical temperatures . The theoretical cooling models of
isolated middle-aged NSs can be divided into three main types. (I) {\it
Low-mass}, {\it slowly cooling} NSs where the direct Urca process of neutrino
emission is either forbidden or almost fully suppressed by the proton
superfluidity. (II) {\it Medium-mass} NSs which show {\it moderate} cooling via
the direct Urca process suppressed by the proton superfluidity. (III) {\it
Massive} NSs which show {\it fast} cooling via the direct Urca process weakly
suppressed by superfluidity. Confronting the theory with observations we treat
RX J0822--43, PSR 1055--52 and RX J1856--3754 as slowly cooling NSs. To explain
these sufficiently warm sources we need a density profile in
the crust with a rather high and flat maximum and sharp wings. We treat 1E
1207--52, RX J0002+62, PSR 0656+14, Vela, and Geminga as moderately cooling
NSs. We can determine their masses for a given model of proton superfluidity,
, and the equation of state in the NS core. No rapidly
cooling NS has been observed so far.Comment: 12 pages, 10 figures, Astron. Astrophys., submitte
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
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A cancer rainbow mouse for visualizing the functional genomics of oncogenic clonal expansion.
Field cancerization is a premalignant process marked by clones of oncogenic mutations spreading through the epithelium. The timescales of intestinal field cancerization can be variable and the mechanisms driving the rapid spread of oncogenic clones are unknown. Here we use a Cancer rainbow (Crainbow) modelling system for fluorescently barcoding somatic mutations and directly visualizing the clonal expansion and spread of oncogenes. Crainbow shows that mutations of Ă-catenin (Ctnnb1) within the intestinal stem cell results in widespread expansion of oncogenes during perinatal development but not in adults. In contrast, mutations that extrinsically disrupt the stem cell microenvironment can spread in adult intestine without delay. We observe the rapid spread of premalignant clones in Crainbow mice expressing oncogenic Rspondin-3 (RSPO3), which occurs by increasing crypt fission and inhibiting crypt fixation. Crainbow modelling provides insight into how somatic mutations rapidly spread and a plausible mechanism for predetermining the intratumor heterogeneity found in colon cancers
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
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