Quasi Periodic Oscillations in Low Mass X-Ray Binaries and Constraints on the Equation of State of Neutron Star Matter

Recently discovered quasi periodic oscillations in the X-ray brightness of low mass X-ray binaries are used to derive constraints on the mass of the neutron star component and the equation of state of neutron star matter. The observations are compared with models of rapidly rotating neutron stars which are calculated by means of an exact numerical method in full relativity. For the equations of state we select a broad collection of models representing different assumptions about the many-body structure and the complexity of the composition of super dense matter. The mass constraints differ from their values in the approximate treatment by \sim 10%. Under the assumption that the maximum frequency of the quasi periodic oscillations originates from the innermost stable orbit the mass of the neutron star is in the range: $M\sim 1.92-2.25 M_\odot$. Especially the quasi periodic oscillation in the Atoll-source 4U 1820-30 is only consistent with equations of state which are rather stiff at high densities which is explainable, so far, only with pure nucleonic/leptonic composition. This interpretation contradicts the hypothesis that the protoneutron star formed in SN 1987A collapsed to a black hole, since this would demand a maximum neutron star mass below $1.6 M_\odot$. The recently suggested identification of quasi periodic oscillations with frequencies around 10 Hz with the Lense-Thirring precession of the accretion disk is found to be inconsistent with the models studied in this work, unless it is assumed that the first overtone of the precession is observed.Comment: 12 pages including figures, to be published in MNRA

Neutron star properties in the Thomas-Fermi model

The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to the properties of finite nuclei, the parameters of the mass formula, and the behavior of the optical potential is used to calculate the properties of $\beta$--equilibrated neutron star matter, and to study the impact of this equation of state on the properties of (rapidly rotating) neutron stars and their cooling behavior. The results are in excellent agreement with the outcome of calculations performed for a broad collection of sophisticated nonrelativistic as well as relativistic models for the equation of state.Comment: 23 pages, LaTeX, 15 ps-figure

A SILAC-based Approach Identifies Substrates of Caspase-dependent Cleavage upon TRAIL-induced Apoptosis

The extracellular ligand-induced extrinsic pathway of apoptosis is executed via caspase protease cascades that activate downstream effectors by means of site-directed proteolysis. Here we identify proteome changes upon the induction of apoptosis by the cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in a Jurkat T cell line. We detected caspase-dependent cleavage substrates by quantifying protein intensities before and after TRAIL induction in SDS gel slices. Apoptotic protein cleavage events are identified by a characteristic stable isotope labeling with amino acids in cell culture (SILAC) ratio pattern across gel slices that results from differential migration of the cleaved and uncleaved proteins. We applied a statistical test to define apoptotic substrates in the proteome. Our approach identified more than 650 of these cleaved proteins in response to TRAIL-induced apoptosis, including many previously unknown substrates and cleavage sites. Inhibitor treatment combined with triple SILAC demonstrated that the detected cleavage events were caspase dependent. Proteins located in the lumina of organelles such as mitochondria and endoplasmic reticulum were significantly underrepresented in the substrate population. Interestingly, caspase cleavage is generally observed in not only one but several members of stable complexes, but often with lower stoichiometry. For instance, all five proteins of the condensin I complex were cleaved upon TRAIL treatment. The apoptotic substrate proteome data can be accessed and visualized in the MaxQB database and might prove useful for basic and clinical research into TRAIL-induced apoptosis. The technology described here is extensible to a wide range of other proteolytic cleavage events

Rearrangement of the Fermi Surface of Dense Neutron Matter and Direct Urca Cooling of Neutron Stars

It is proposed that a rearrangement of single-particle degrees of freedom may occur in a portion of the quantum fluid interior of a neutron star. Such a rearrangement is associated with the pronounced softening of the spin-isospin collective mode which, under increasing density, leads to pion condensation. Arguments and estimates based on fundamental relations of many-body theory show that one realization of this phenomenon could produce very rapid cooling of the star via a direct nucelon Urca process displaying a $T^5$ dependence on temperature.Comment: 8 pages, 2 figure

Electronic bulk and domain wall properties in B-site doped hexagonal ErMnO3_3

Acceptor and donor doping is a standard for tailoring semiconductors. More recently, doping was adapted to optimize the behavior at ferroelectric domain walls. In contrast to more than a century of research on semiconductors, the impact of chemical substitutions on the local electronic response at domain walls is largely unexplored. Here, the hexagonal manganite ErMnO$_3$ is donor doped with Ti$^{4+}$. Density functional theory calculations show that Ti$^{4+}$ goes to the B-site, replacing Mn$^{3+}$. Scanning probe microscopy measurements confirm the robustness of the ferroelectric domain template. The electronic transport at both macro- and nanoscopic length scales is characterized. The measurements demonstrate the intrinsic nature of emergent domain wall currents and point towards Poole-Frenkel conductance as the dominant transport mechanism. Aside from the new insight into the electronic properties of hexagonal manganites, B-site doping adds an additional degree of freedom for tuning the domain wall functionality

S-wave Pairing of Λ\Lambda Hyperons in Dense Matter

In this work we calculate the $^1S_0$ gap energies of $\Lambda$ hyperons in neutron star matter. The calculation is based on a solution of the BCS gap equation for an effective G-matrix parameterization of the $\Lambda-\Lambda$ interaction with a nuclear matter background, presented recently by Lanskoy and Yamamoto. We find that a gap energy of a few tenths of MeV is expected for $\Lambda$ Fermi momenta up to about 1.3 fm$^{-1}$. Implications for neutron star matter are examined, and suggest the existence of a $\Lambda$ $^1S_0$ superfluid between the threshold baryon density for $\Lambda$ formation and the baryon density where the $\Lambda$ fraction reaches $15-20$.Comment: 16 pages, Revtex, 9 figures, 33 reference