57 research outputs found
Impact of internal heating on the thermal evolution of neutron stars
The impact of various competing heating processes on the thermal evolution of
neutron stars is investigated. We show that internal heating leads to
significantly enhanced surface temperatures for pulsars of middle and old age.
The heating due to thermal creep of pinned vortices and due to outward motion
of proton vortices in the interior of the star leads to a better agreement with
the observed data in the case of enhanced cooling. The strong pinning models
are ruled out by a comparison with the cooling data on the old pulsars. For
millisecond pulsars, the heating due to thermal creep of pinned vortices and
chemical heating of the core have the largest impact on the surface
temperatures. The angular dependence of the heating rates require two
dimensional cooling simulations in general. Such a simulation is performed for
a selected case in order to check the applicability of one-dimensional codes
used in the past.Comment: 18 pages, to be published in A & A. Postscript and additional tables
at http://www.physik.uni-muenchen.de/sektion/suessmann/astro/cool/schaab.109
Implications of Hyperon Pairing for Cooling of Neutron Stars
The implications of hyperon pairing for the thermal evolution of neutron
stars containing hyperons are investigated. The outcome of cooling simulations
are compared for neutron star models composed only of nucleons and leptons,
models including hyperons, and models including pairing of hyperons. We show
that lambda and neutron pairing suppresses all possible fast neutrino emission
processes in not too massive neutron stars. The inclusion of lambda pairing
yields better agreement with X-ray observations of pulsars. Particularly, the
surface temperatures deduced from X-ray observations within the hydrogen
atmosphere model are more consistent with the thermal history of neutron stars
containing hyperons, if the critical temperature for the onset of lambda and
nucleon pairing is not too small.Comment: 7 pages, 3 figures. To be published in ApJL. The postscript and
additional tables can be found at
http://www.physik.uni-muenchen.de/sektion/suessmann/astro/cool/schaab.089
Differences in the Cooling Behavior of Strange Quark Matter Stars and Neutron Stars
The general statement that hypothetical strange (quark matter) stars cool
more rapidly than neutron stars is investigated in greater detail. It is found
that the direct Urca process could be forbidden not only in neutron stars but
also in strange stars. In this case, strange stars are slowly cooling, and
their surface temperatures are more or less indistinguishable from those of
slowly cooling neutron stars. Furthermore the case of enhanced cooling is
reinvestigated. It shows that strange stars cool significantly more rapidly
than neutron stars within the first years after birth. This feature
could become particularly interesting if continued observation of SN 1987A
would reveal the temperature of the possibly existing pulsar at its center.Comment: 9 pages, LaTeX (aas-style file), 2 ps-figures. To be published in ApJ
Letter
Probing Teichoic Acid Genetics with Bioactive Molecules Reveals New Interactions among Diverse Processes in Bacterial Cell Wall Biogenesis
SummaryThe bacterial cell wall has been a celebrated target for antibiotics and holds real promise for the discovery of new antibacterial chemical matter. In addition to peptidoglycan, the walls of Gram-positive bacteria contain large amounts of the polymer teichoic acid, covalently attached to peptidoglycan. Recently, wall teichoic acid was shown to be essential to the proper morphology of Bacillus subtilis and an important virulence factor for Staphylococcus aureus. Additionally, recent studies have shown that the dispensability of genes encoding teichoic acid biosynthetic enzymes is paradoxical and complex. Here, we report on the discovery of a promoter (PywaC), which is sensitive to lesions in teichoic acid synthesis. Exploiting this promoter through a chemical-genetic approach, we revealed surprising interactions among undecaprenol, peptidoglycan, and teichoic acid biosynthesis that help explain the complexity of teichoic acid gene dispensability. Furthermore, the new reporter assay represents an exciting avenue for the discovery of antibacterial molecules
Thermal Evolution of Compact Stars
A collection of modern, field-theoretical equations of state is applied to
the investigation of cooling properties of compact stars. These comprise
neutron stars as well as hypothetical strange matter stars, made up of
absolutely stable 3-flavor strange quark matter. Various uncertainties in the
behavior of matter at supernuclear densities, e.g., hyperonic degrees of
freedom, behavior of coupling strengths in matter, pion and meson condensation,
superfluidity, transition to quark matter, absolute stability of strange quark
matter, and last but not least the many-body technique itself are tested
against the body of observed cooling data.Comment: 41 pages, revised versio
Integrated genomics and proteomics define huntingtin CAG length-dependent networks in mice.
To gain insight into how mutant huntingtin (mHtt) CAG repeat length modifies Huntington's disease (HD) pathogenesis, we profiled mRNA in over 600 brain and peripheral tissue samples from HD knock-in mice with increasing CAG repeat lengths. We found repeat length-dependent transcriptional signatures to be prominent in the striatum, less so in cortex, and minimal in the liver. Coexpression network analyses revealed 13 striatal and 5 cortical modules that correlated highly with CAG length and age, and that were preserved in HD models and sometimes in patients. Top striatal modules implicated mHtt CAG length and age in graded impairment in the expression of identity genes for striatal medium spiny neurons and in dysregulation of cyclic AMP signaling, cell death and protocadherin genes. We used proteomics to confirm 790 genes and 5 striatal modules with CAG length-dependent dysregulation at the protein level, and validated 22 striatal module genes as modifiers of mHtt toxicities in vivo
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