1,314 research outputs found
Kelvin Helmholtz Instability and Circulation Transfer at an Isotropic-Anisotropic Superfluid Interface in a Neutron Star
A recent laboratory experiment (Blaauwgeers et al. 2003) suggests that a
Kelvin-Helmholtz (KH) instability at the interface between two superfluids, one
rotating and anisotropic, the other stationary and isotropic, may trigger
sudden spin-up of the stationary superfluid. This result suggests that a KH
instability at the crust-core (--superfluid) boundary of a
neutron star may provide a trigger mechanism for pulsar glitches. We calculate
the dispersion relation of the KH instability involving two different
superfluids including the normal fluid components and their effects on
stability, particularly entropy transport. We show that an entropy difference
between the core and crust superfluids reduces the threshold differential shear
velocity and threshold crust-core density ratio. We evaluate the wavelength of
maximum growth of the instability for neutron star parameters and find the
resultant circulation transfer to be within the range observed in pulsar
glitches.Comment: 17 pages, 8 figures, accepted for publication in MNRA
Neutrino Emission From Direct Urca Processes in Pion Condensed Quark Matter
We study neutrino emission from direct Urca processes in pion condensed quark
matter. In compact stars with high baryon density, the emission is dominated by
the gapless modes of the pion condensation which leads to an enhanced
emissivity. While for massless quarks the enhancement is not remarkable, the
emissivity is significantly larger and the cooling of the condensed matter is
considerably faster than that in normal quark matter when the mass difference
between - and -quarks is sizable.Comment: 12 pages,6 figures, published versio
Crystalline-Electric-Field Effect on the Resistivity of Ce-based Heavy Fermion Systems
The behavior of the resistivity of Ce-based heavy fermion systems is studied
using a 1/-expansion method a la Nagoya, where is the spin-orbital
degeneracy of f-electrons. The 1/-expansion is performed in terms of the
auxiliary particles, and a strict requirement of the local constraints is
fulfilled for each order of 1/N. The physical quantities can be calculated over
the entire temperature range by solving the coupled Dyson equations for the
Green functions self-consistently at each temperature. This 1/N-expansion
method is known to provide asymptotically exact results for the behavior of
physical quantities in both low- and high-energy regions when it is applied to
a single orbital periodic Anderson model (PAM). On the basis of a generalized
PAM including crystalline-electric-field splitting with a single conduction
band, the pressure dependence of the resistivity is calculated by
parameterizing the effect of pressure as the variation of the hybridization
parameter between the conduction electrons and f-electrons. The main result of
the present study is that the double-peak structure of the -dependence of
the resistivity is shown to merge into a single-peak structure with increasing
pressure.Comment: 37 pages, 22 figure
Superfluid Friction and Late-time Thermal Evolution of Neutron Stars
The recent temperature measurements of the two older isolated neutron stars
PSR 1929+10 and PSR 0950+08 (ages of and yr,
respectively) indicate that these objects are heated. A promising candidate
heat source is friction between the neutron star crust and the superfluid it is
thought to contain. We study the effects of superfluid friction on the
long-term thermal and rotational evolution of a neutron star. Differential
rotation velocities between the superfluid and the crust (averaged over the
inner crust moment of inertia) of rad s for PSR
1929+10 and rad s for PSR 0950+08 would account for their
observed temperatures. These differential velocities could be sustained by
pinning of superfluid vortices to the inner crust lattice with strengths of
1 MeV per nucleus. Pinned vortices can creep outward through thermal
fluctuations or quantum tunneling. For thermally-activated creep, the coupling
between the superfluid and crust is highly sensitive to temperature. If pinning
maintains large differential rotation ( rad s), a feedback
instability could occur in stars younger than yr causing
oscillations of the temperature and spin-down rate over a period of . For stars older than yr, however, vortex creep occurs
through quantum tunneling, and the creep velocity is too insensitive to
temperature for a thermal-rotational instability to occur. These older stars
could be heated through a steady process of superfluid friction.Comment: 26 pages, 1 figure, submitted to Ap
Confronting Neutron Star Cooling Theories with New Observations
With the successful launch of Chandra and XMM/Newton X-ray space missions
combined with the lower-energy band observations, we are in the position where
careful comparison of neutron star cooling theories with observations will make
it possible to distinguish among various competing theories. For instance, the
latest theoretical and observational developments already exclude both nucleon
and kaon direct URCA cooling. In this way we can now have realistic hope for
determining various important properties, such as the composition, degree of
superfluidity, the equation of state and steller radius. These developments
should help us obtain better insight into the properties of dense matter.Comment: 11 pages, 1 figur
Evaluating two soil carbon models within the global land surface model JSBACH using surface and spaceborne observations of atmospheric CO<sub>2</sub>
The trajectories of soil carbon (C) in the changing climate are of utmost importance, as soil carbon is a substantial carbon storage with a large potential to impact the atmospheric carbon dioxide (CO2) burden. Atmospheric CO2 observations integrate all processes affecting C exchange between the surface and the atmosphere. Therefore they provide a benchmark for carbon cycle models. We evaluated two distinct soil carbon models (CBALANCE and YASSO) that were implemented to a global land surface model (JSBACH) against atmospheric CO2 observations. We transported the biospheric carbon fluxes obtained by JSBACH using the atmospheric transport model TM5 to obtain atmospheric CO2. We then compared these results with surface observations from Global Atmosphere Watch (GAW) stations as well as with column XCO2 retrievals from the GOSAT satellite. The seasonal cycles of atmospheric CO2 estimated by the two different soil models differed. The estimates from the CBALANCE soil model were more in line with the surface observations at low latitudes (0 N–45 N) with only 1 % bias in the seasonal cycle amplitude (SCA), whereas YASSO was underestimating the SCA in this region by 32 %. YASSO gave more realistic seasonal cycle amplitudes of CO2 at northern boreal sites (north of 45 N) with underestimation of 15 % compared to 30 % overestimation by CBALANCE. Generally, the estimates from CBALANCE were more successful in capturing the seasonal patterns and seasonal cycle amplitudes of atmospheric CO2 even though it overestimated soil carbon stocks by 225 % (compared to underestimation of 36 % by YASSO) and its predictions of the global distribution of soil carbon stocks was unrealistic. The reasons for these differences in the results are related to the different environmental drivers and their functional dependencies of these two soil carbon models. In the tropical region the YASSO model showed earlier increase in season of the heterotophic respiration since it is driven by precipitation instead of soil moisture as CBALANCE. In the temperate and boreal region the role of temperature is more dominant. There the heterotophic respiration from the YASSO model had larger annual variability, driven by air temperature, compared to the CBALANCE which is driven by soil temperature. The results underline the importance of using sub-yearly data in the development of soil carbon models when they are used in shorter than annual time scales
Core-dependent changes in genomic predictions using the algorithm for proven and young in single-step genomic best linear unbiased prediction
Phase diagram at finite temperature and quark density in the strong coupling limit of lattice QCD for color SU(3)
We study the phase diagram of quark matter at finite temperature (T) and
finite chemical potential (mu) in the strong coupling limit of lattice QCD for
color SU(3). We derive an analytical expression of the effective free energy as
a function of T and mu, including baryon effects. The finite temperature
effects are evaluated by integrating over the temporal link variable exactly in
the Polyakov gauge with anti-periodic boundary condition for fermions. The
obtained phase diagram shows the first order phase transition at low
temperatures and the second order phase transition at high temperatures
separated by the tri-critical point in the chiral limit. Baryon has effects to
reduce the effective free energy and to extend the hadron phase to a larger mu
direction at low temperatures.Comment: 18 pages, 10 figure
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