Timing the Nearby Isolated Neutron Star RX J1856.5-3754

RX J1856.5-3754 is the X-ray brightest among the nearby isolated neutron stars. Its X-ray spectrum is thermal, and is reproduced remarkably well by a black-body, but its interpretation has remained puzzling. One reason is that the source did not exhibit pulsations, and hence a magnetic field strength--vital input to atmosphere models--could not be estimated. Recently, however, very weak pulsations were discovered. Here, we analyze these in detail, using all available data from the XMM-Newton and Chandra X-ray observatories. From frequency measurements, we set a 2-sigma upper limit to the frequency derivative of \dot\nu<1.3e-14 Hz/s. Trying possible phase-connected timing solutions, we find that one solution is far more likely than the others, and we infer a most probable value of \dot\nu=(-5.98+/-0.14)e-16 Hz/s. The inferred magnetic field strength is 1.5e13 G, comparable to what was found for similar neutron stars. From models, the field seems too strong to be consistent with the absence of spectral features for non-condensed atmospheres. It is sufficiently strong, however, that the surface could be condensed, but only if it is consists of heavy elements like iron. Our measurements imply a characteristic age of about 4 Myr. This is longer than the cooling and kinematic ages, as was found for similar objects, but at almost a factor ten, the discrepancy is more extreme. A puzzle raised by our measurement is that the implied rotational energy loss rate of about 3e30 erg/s is orders of magnitude smaller than what was inferred from the H-alpha nebula surrounding the source.Comment: 4 pages, 2 figures, 2 tables; accepted for publication in Astrophysical Journal (Letters

Probing the Crust of the Neutron Star in EXO 0748-676

X-ray observations of quiescent X-ray binaries have the potential to provide insight into the structure and the composition of neutron stars. EXO 0748-676 had been actively accreting for over 24 yr before its outburst ceased in late 2008. Subsequent X-ray monitoring revealed a gradual decay of the quiescent thermal emission that can be attributed to cooling of the accretion-heated neutron star crust. In this work, we report on new Chandra and Swift observations that extend the quiescent monitoring to ~5 yr post-outburst. We find that the neutron star temperature remained at ~117 eV between 2009 and 2011, but had decreased to ~110 eV in 2013. This suggests that the crust has not fully cooled yet, which is supported by the lower temperature of ~95 eV that was measured ~4 yr prior to the accretion phase in 1980. Comparing the data to thermal evolution simulations reveals that the apparent lack of cooling between 2009 and 2011 could possibly be a signature of convection driven by phase separation of light and heavy nuclei in the outer layers of the neutron star.Comment: 9 pages, 4 tables, 3 figures. Minor revisions according to referee report. Accepted to Ap

Measuring category intuitiveness in unconstrained categorization tasks

What makes a category seem natural or intuitive? In this paper, an unsupervised categorization task was employed to examine observer agreement concerning the categorization of nine different stimulus sets. The stimulus sets were designed to capture different intuitions about classification structure. The main empirical index of category intuitiveness was the frequency of the preferred classification, for different stimulus sets. With 169 participants, and a within participants design, with some stimulus sets the most frequent classification was produced over 50 times and with others not more than two or three times. The main empirical finding was that cluster tightness was more important in determining category intuitiveness, than cluster separation. The results were considered in relation to the following models of unsupervised categorization: DIVA, the rational model, the simplicity model, SUSTAIN, an Unsupervised version of the Generalized Context Model (UGCM), and a simple geometric model based on similarity. DIVA, the geometric approach, SUSTAIN, and the UGCM provided good, though not perfect, fits. Overall, the present work highlights several theoretical and practical issues regarding unsupervised categorization and reveals weaknesses in some of the corresponding formal models

Lentivector Transduction Improves Outcomes Over Transplantation of Human HSCs Alone in NOD/SCID/Fabry Mice

Fabry disease is a lysosomal storage disorder caused by a deficiency of a-galactosidase A (a-gal A) activity that results in progressive globotriaosylceramide (Gb(3)) deposition. We created a fully congenic nonobese diabetic (NOD)/severe combined immunodeficiency (SCID)/Fabry murine line to facilitate the in vivo assessment of human cell-directed therapies for Fabry disease. This pure line was generated after 11 generations of backcrosses and was found, as expected, to have a reduced immune compartment and background a-gal A activity. Next, we transplanted normal human CD34(+) cells transduced with a control (lentiviral vector-enhanced green fluorescent protein (LV-eGFP)) or a therapeutic bicistronic LV (LV-a-gal A/internal ribosome entry site (IRES)/hCD25). While both experimental groups showed similar engraftment levels, only the therapeutic group displayed a significant increase in plasma a-gal A activity. Gb(3) quantification at 12 weeks revealed metabolic correction in the spleen, lung, and liver for both groups. Importantly, only in the therapeutically-transduced cohort was a significant Gb(3) reduction found in the heart and kidney, key target organs for the amelioration of Fabry disease in humans.Fil: Pacienza, Natalia Alejandra. University Health Network; Canadá. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Yoshimitsu, Makoto. Kagoshima University; Japón. University Health Network; CanadáFil: Mizue, Nobuo. University Health Network; CanadáFil: Au, Bryan C. Y.. University Health Network; CanadáFil: Wang, James C. M.. University Health Network; CanadáFil: Fan, Xin. University Health Network; CanadáFil: Takenaka, Toshihiro. Kagoshima University; JapónFil: Medin, Jeffrey A. University Health Network; Canadá. University of Toronto; Canad

Radiation Hardness of Thin Low Gain Avalanche Detectors

Low Gain Avalanche Detectors (LGAD) are based on a n++-p+-p-p++ structure where an appropriate doping of the multiplication layer (p+) leads to high enough electric fields for impact ionization. Gain factors of few tens in charge significantly improve the resolution of timing measurements, particularly for thin detectors, where the timing performance was shown to be limited by Landau fluctuations. The main obstacle for their operation is the decrease of gain with irradiation, attributed to effective acceptor removal in the gain layer. Sets of thin sensors were produced by two different producers on different substrates, with different gain layer doping profiles and thicknesses (45, 50 and 80 um). Their performance in terms of gain/collected charge and leakage current was compared before and after irradiation with neutrons and pions up to the equivalent fluences of 5e15 cm-2. Transient Current Technique and charge collection measurements with LHC speed electronics were employed to characterize the detectors. The thin LGAD sensors were shown to perform much better than sensors of standard thickness (~300 um) and offer larger charge collection with respect to detectors without gain layer for fluences <2e15 cm-2. Larger initial gain prolongs the beneficial performance of LGADs. Pions were found to be more damaging than neutrons at the same equivalent fluence, while no significant difference was found between different producers. At very high fluences and bias voltages the gain appears due to deep acceptors in the bulk, hence also in thin standard detectors

Dengue virus downregulates TNFR1- and TLR3-stimulated NF-kB activation by targeting RIPK1

Dengue virus (DENV) infection is the most prevalent arthropod-borne virus disease and is endemic in more than 100 countries. Several DENV proteins have been shown to target crucial human host proteins to evade innate immune responses and establish a productive infection. Here we report that the DENV NS3 protein targets RIPK1 (Receptor Interacting Protein Kinase I), a central mediator of inflammation and cell death, and decreases intracellular RIPK1 levels during DENV infection. The interaction of NS3 with RIPK1 results in the inhibition of NF-κB activation in response to TNFR or TLR3 stimulation. Also, we observed that the effects of NS3 on RIPK1 were independent of NS3 protease activity. Our data demonstrate a novel mechanism by which DENV suppresses normal cellular functions to evade host innate immune response

Feature integration in natural language concepts

Two experiments measured the joint influence of three key sets of semantic features on the frequency with which artifacts (Experiment 1) or plants and creatures (Experiment 2) were categorized in familiar categories. For artifacts, current function outweighed both originally intended function and current appearance. For biological kinds, appearance and behavior, an inner biological function, and appearance and behavior of offspring all had similarly strong effects on categorization. The data were analyzed to determine whether an independent cue model or an interactive model best accounted for how the effects of the three feature sets combined. Feature integration was found to be additive for artifacts but interactive for biological kinds. In keeping with this, membership in contrasting artifact categories tended to be superadditive, indicating overlapping categories, whereas for biological kinds, it was subadditive, indicating conceptual gaps between categories. It is argued that the results underline a key domain difference between artifact and biological concepts

Mutational analysis of active site residues of human adenosine deaminase

Adenosine deaminase was overexpressed in a baculovirus system. The pure recombinant and native enzymes were identical in size, Zn2+ content, and activity. Five amino acids, in proximity to the active site, were replaced by mutagenesis. The altered enzymes were purified to homogeneity and compared to wild-type adenosine deaminase with respect to zinc content, enzymatic activity, and kinetic parameters. All but one of the alterations produced significant activity perturbations. Replacement of Cys262 produced a protein that retained at least 30-40% of wild-type activity. In contrast, replacements of His17, His214, His238, and Glu217 resulted in dramatic losses of enzyme activity. None of these mutants exhibited large variations in Km. The proteins produced from alterations of amino acids implicated in metal coordination were slightly activated by inclusion of Zn2+ throughout purification. These experiments confirm that in the active enzyme Zn2+ plays a critical role in catalysis, that a histidine or glutamate residue plays a mechanistic role in the hydrolytic deamination step, and that cysteine is not involved in the catalytic mechanism of adenosine deaminase. These data support the roles for these amino acid residues suggested from the x-ray structure of murine adenosine deaminase (Wilson, D. K., Rudolf, F. B., and Quicho, F. A. (1991) Science 252, 1278-1284)

Stratigraphic context and paleoenvironmental significance of minor taxa (Pisces, Reptilia, Aves, Rodentia) from the late Early Pleistocene palaeoanthropological site of Buia (Eritrea)

none13noneL. Rook; M. Ghinassi; G. Carnevale; M. Delfino; M. Pavia; L. Bondioli ; F. Candilio; A. Coppa; B. Martínez-Navarro; T. Medin; M. Papini; C. Zanolli; Y. LibsekalL., Rook; Ghinassi, Massimiliano; G., Carnevale; M., Delfino; M., Pavia; L., Bondioli; F., Candilio; A., Coppa; B., Martínez Navarro; T., Medin; M., Papini; C., Zanolli; Y., Libseka