570 research outputs found
Compression load failure of aluminum plates due to fire
An experimental study was performed to quantify the response and failure of 5083-H116 and 6082-T6 aluminum plates under compression load while being subjected to a constant heat flux representing a fire exposure. Using an intermediate scale loading frame with integrated heating, the study evaluated the effects of geometry, aluminum type, fire exposure, load, and fire protection. Intermediate scale aluminum panels which were more than 0.7 m high and 0.2 m wide were used to gain insights into the structural behavior of large structural sections exposed to fire. Failure temperatures were measured to range from 100 to 480 C and were dependent on applied stress and aluminum type. This indicates that the use of a single temperature criterion in fire resistance without load as typically done is not sufficient for evaluating structural response during fire. An empirical failure model was developed to account for fire exposure conditions, aluminum type, and geometr
Isospin-rich nuclei in neutron star matter
Stability of nuclei beyond the drip lines in the presence of an enveloping
gas of nucleons and electrons, as prevailing in the inner crust of a neutron
star, is studied in the temperature-dependent Thomas-Fermi framework. A
limiting asymmetry in the isospin space beyond which nuclei cannot exist
emerges from the calculations. The ambient conditions like temperature, baryon
density and neutrino concentration under which these exotic nuclear systems can
be formed are studied in some detail.Comment: Submitted to Phy. Rev. C: Revtex version of manuscript 22 pages and
10 PS-files for figure
A numerical study of the r-mode instability of rapidly rotating nascent neutron stars
The first results of numerical analysis of classical r-modes of {\it rapidly}
rotating compressible stellar models are reported. The full set of linear
perturbation equations of rotating stars in Newtonian gravity are numerically
solved without the slow rotation approximation. A critical curve of
gravitational wave emission induced instability which restricts the rotational
frequencies of hot young neutron stars is obtained. Taking the standard cooling
mechanisms of neutron stars into account, we also show the `evolutionary
curves' along which neutron stars are supposed to evolve as cooling and
spinning-down proceed. Rotational frequencies of stars suffering
from this instability decrease to around 100Hz when the standard cooling
mechanism of neutron stars is employed. This result confirms the results of
other authors who adopted the slow rotation approximation.Comment: 4 pages, 2 figures; MNRAS,316,L1(2000
Isospin-rich nuclei in neutron star matter
Stability of nuclei beyond the drip lines in the presence of an enveloping
gas of nucleons and electrons, as prevailing in the inner crust of a neutron
star, is studied in the temperature-dependent Thomas-Fermi framework. A
limiting asymmetry in the isospin space beyond which nuclei cannot exist
emerges from the calculations. The ambient conditions like temperature, baryon
density and neutrino concentration under which these exotic nuclear systems can
be formed are studied in some detail.Comment: Submitted to Phy. Rev. C: Revtex version of manuscript 22 pages and
10 PS-files for figure
A phenomenological equation of state for isospin asymmetric nuclear matter
A phenomenological momentum-independent (MID) model is constructed to
describe the equation of state (EOS) for isospin asymmetric nuclear matter,
especially the density dependence of the nuclear symmetry energy
. This model can reasonably describe the general
properties of the EOS for symmetric nuclear matter and the symmetry energy
predicted by both the sophisticated isospin and momentum dependent MDI model
and the Skyrme-Hartree-Fock approach. We find that there exists a nicely linear
correlation between and as well as between and , where and represent, respectively, the
slope and curvature parameters of the symmetry energy at the normal nuclear
density while and are, respectively, the
incompressibility and the third-order derivative parameter of symmetric nuclear
matter at . These correlations together with the empirical
constraints on , and lead to an
estimation of -477 MeV MeV for the
second-order isospin asymmetry expansion coefficient for the incompressibility
of asymmetric nuclear matter at the saturation point.Comment: 9 pages, 4 figures, contribution to Special Topic on Large-Scale
Scientific Facilities (LSSF) in Science in China Series G: Physics, Mechanics
& Astronom
Diffuse supernova neutrinos: oscillation effects, stellar cooling and progenitor mass dependence
We estimate the diffuse supernova neutrino background (DSNB) using the recent
progenitor-dependent, long-term supernova simulations from the Basel group and
including neutrino oscillations at several post-bounce times. Assuming
multi-angle matter suppression of collective effects during the accretion
phase, we find that oscillation effects are dominated by the matter-driven MSW
resonances, while neutrino-neutrino collective effects contribute at the 5-10%
level. The impact of the neutrino mass hierarchy, of the time-dependent
neutrino spectra and of the diverse progenitor star population is 10% or less,
small compared to the uncertainty of at least 25% of the normalization of the
supernova rate. Therefore, assuming that the sign of the neutrino mass
hierarchy will be determined within the next decade, the future detection of
the DSNB will deliver approximate information on the MSW-oscillated neutrino
spectra. With a reliable model for neutrino emission, its detection will be a
powerful instrument to provide complementary information on the star formation
rate and for learning about stellar physics.Comment: 19 pages, including 4 figures and 1 table. Clarifying paragraphs
added; results unchanged. Matches published version in JCA
Dirac-Neutrino Magnetic Moment and the Dynamics of a Supernova Explosion
The double conversion of the neutrino helicity
has been analyzed for supernova conditions, where the first stage is due to the
interaction of the neutrino magnetic moment with plasma electrons and protons
in the supernova core, and the second stage, due to the resonance spin flip of
the neutrino in the magnetic field of the supernova envelope. It is shown that,
in the presence of the neutrino magnetic moment in the range and a magnetic field of G
between the neutrinosphere and the shock-stagnation region, an additional
energy of about erg, which is sufficient for a supernova explosion,
can be injected into this region during a typical shock-stagnation time.Comment: 10 pages, LaTeX, 4 EPS figures, accepted to JETP Letter
Neutron Star Structure and the Neutron Radius of 208Pb
We study relationships between the neutron-rich skin of a heavy nucleus and
the properties of neutron-star crusts. Relativistic effective field theories
with a thicker neutron skin in Pb have a larger electron fraction and a
lower liquid-to-solid transition density for neutron-rich matter. These
properties are determined by the density dependence of the symmetry energy
which we vary by adding nonlinear couplings between isoscalar and isovector
mesons. An accurate measurement of the neutron radius in Pb---via
parity violating electron scattering---may have important implications for the
structure of neutron stars.Comment: 5 pages 3 figures, added additional evidence of model independence,
Phys. Rev. Letters in pres
Implementing telephone triage in general practice: a process evaluation of a cluster randomised controlled trial
Background: Telephone triage represents one strategy to manage demand for face-to-face GP appointments in primary care. However, limited evidence exists of the challenges GP practices face in implementing telephone triage. We conducted a qualitative process evaluation alongside a UK-based cluster randomised trial (ESTEEM) which compared the impact of GP-led and nurse-led telephone triage with usual care on primary care workload, cost, patient experience, and safety for patients requesting a same-day GP consultation. The aim of the process study was to provide insights into the observed effects of the ESTEEM trial from the perspectives of staff and patients, and to specify the circumstances under which triage is likely to be successfully implemented. Here we report perspectives of staff. Methods: The intervention comprised implementation of either GP-led or nurse-led telephone triage for a period of 2-3 months. A qualitative evaluation was conducted using staff interviews recruited from eight general practices (4 GP triage, 4 Nurse triage) in the UK, implementing triage as part of the ESTEEM trial. Qualitative interviews were undertaken with 44 staff members in GP triage and nurse triage practices (16 GPs, 8 nurses, 7 practice managers, 13 administrative staff). Results: Staff reported diverse experiences and perceptions regarding the implementation of telephone triage, its effects on workload, and on the benefits of triage. Such diversity were explained by the different ways triage was organised, the staffing models used to support triage, how the introduction of triage was communicated across practice staff, and by how staff roles were reconfigured as a result of implementing triage. Conclusion: The findings from the process evaluation offer insight into the range of ways GP practices participating in ESTEEM implemented telephone triage, and the circumstances under which telephone triage can be successfully implemented beyond the context of a clinical trial. Staff experiences and perceptions of telephone triage are shaped by the way practices communicate with staff, prepare for and sustain the changes required to implement triage effectively, as well as by existing practice culture, and staff and patient behaviour arising in response to the changes made. Trial registration: Current Controlled Trials ISRCTN20687662. Registered 28 May 2009
Rapid cooling of magnetized neutron stars
The neutrino emissivities resulting from direct URCA processes in neutron
stars are calculated in a relativistic Dirac-Hartree approach in presence of a
magnetic field. In a quark or a hyperon matter environment, the emissivity due
to nucleon direct URCA processes is suppressed relative to that from pure
nuclear matter. In all the cases studied, the magnetic field enhances
emissivity compared to the field-free cases.Comment: 9 pages; Revtex; figure include
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