Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae

We present spectral and long-timescale variability analyses of \textit{Chandra} ACIS-S observations of the 19 millisecond pulsars (MSPs) with precisely known positions in the globular cluster 47 Tucanae. The X-ray emission of the majority of these MSPs is well described by a thermal (blackbody or neutron star hydrogen atmosphere) spectrum with a temperature $T_{\rm eff}\sim(1-3)\times10^6$ K, emission radius $R_{\rm eff}\sim0.1-3$ km, and luminosity $L_{X}\sim10^{30-31}$ ergs s$^{-1}$. For several MSPs, there is indication that a second thermal component is required, similar to what is seen in some nearby field MSPs. The radio-eclipsing binary MSPs 47 Tuc J, O, and W show a significant non-thermal component, with photon index $\Gamma\sim 1-1.5$, which may originate in an shock formed due to interaction between the relativistic pulsar wind and matter from the stellar companion. We re-examine the X-ray--spindown luminosity relation ($L_{X}-\dot{E}$) and find that due to the large uncertainties in both parameters the result is consistent with both the linear $L_{X}-\dot{E}$ relation and the flatter $L_X\propto\dot{E}^{0.5}$ predicted by polar cap heating models. In terms of X-ray properties, we find no clear systematic differences between MSPs in globular clusters and in the field of the Galaxy.Comment: 13 pages, 6 figures, accepted for publication in the Astrophysical Journa

Chandra X-ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)

We report the detection of six discrete, low-luminosity (Lx < 10^33 erg/s) X-ray sources, located within 12 arcsec of the center of the collapsed-core globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass radius, from a 50 ksec Chandra ACIS-S exposure. Three sources lie within the very small upper limit of 1.9 arcsec on the core radius. The brightest of the three core sources has a luminosity of Lx (0.5-6 keV) = 6x10^32 erg/s and a blackbody-like soft X-ray spectrum, which are both consistent with it being a quiescent low-mass X-ray binary (qLMXB). We have identified optical counterparts to four of the six central sources and a number of the outlying sources, using deep Hubble Space Telescope and ground-based imaging. While the two proposed counterparts that lie within the core may represent chance superpositions, the two identified central sources that lie outside of the core have X-ray and optical properties consistent with being CVs. Two additional sources outside of the core have possible active binary counterparts. We discuss the X-ray source population of M30 in light of its collapsed-core status.Comment: 18 pages, 13 figures (8 color), resubmitted to ApJ after incorporating referee comment

Flow Kinematics in Variable-Height Rotating Cylinder Arrays

Experimental data are presented for large arrays of rotating, variable-height cylinders in order to study the dependence of the three-dimensional mean flows on the height heterogeneity of the array. Elements in the examined arrays were spatially arranged in the same staggered paired configuration, and the heights of each element pair varied up to ±37.5% from the mean height (kept constant across all arrays), such that the arrays were vertically structured. Four vertical structuring configurations were examined at a nominal Reynolds number (based on freestream velocity and cylinder diameter) of 600 and nominal tip-speed ratios of 0, 2, and 4. It was found that the vertical structuring of the array could significantly alter the mean flow patterns. Most notably, a net vertical flow into the array from above was observed, which was augmented by the arrays' vertical structuring, showing a 75% increase from the lowest to highest vertical flows (as evaluated at the maximum element height, at a single rotation rate). This vertical flow into the arrays is of particular interest as it represents an additional mechanism by which high streamwise momentum can be transported from above the array down into the array. An evaluation of the streamwise momentum resource within the array indicates up to a 56% increase in the incoming streamwise velocity to the elements (from the lowest to highest ranking arrays, at a single rotation rate). These arrays of rotating cylinders may provide insight into the flow kinematics of arrays of vertical axis wind turbines (VAWTs). In a physical VAWT array, an increase in incoming streamwise flow velocity to a turbine corresponds to a (cubic) increase in the power output of the turbine. Thus, these results suggest a promising approach to increasing the power output of a VAWT array

Low order physical models of vertical axis wind turbines

In order to examine the ability of low-order physical models of vertical axis wind turbines to accurately reproduce key flow characteristics, experimental data are presented for the mean flow patterns and turbulence spectra associated with pairs of rotating turbines, rotating solid cylinders, and stationary porous flat plates (of both uniform and non-uniform porosities). The experiments were conducted at a nominal model-diameter Reynolds number of 600 and rotation tip speed ratios between 0 and 6. By comparing the induced flow fields of the different models both qualitatively and quantitatively, it was concluded that the two dimensional horizontal mean flow fields induced by the porous flat plates were quantitatively similar to those induced by slowly rotating turbine models. However, over the range of the experimental parameters examined, the porous flat plates were unable to produce vertical flows similar to those associated with the slowly rotating turbine models. Conversely, the moderately rotating cylinders induced three dimensional mean flow fields quantitatively similar to those induced by rapidly rotating turbine models. These findings have implications for both laboratory experiments and numerical simulations, which have previously used analogous low order models in order to reduce experimental/computational costs. Specifically, over the range of parameters examined, the comparison between induced flow fields of the different model fidelities allows identification of the lowest cost model for which the specific goals of a study can be obtained, to within the desired accuracy. And if a lower fidelity model is used, it is possible to incorporate into the analysis of the collected data an understanding of how the results would be expected to vary from a higher fidelity case

Can the palatability of healthy, satiety-promoting foods increase with repeated exposure during weight loss?

Repeated exposure to sugary, fatty, and salty foods often enhances their appeal. However, it is unknown if exposure influences learned palatability of foods typically promoted as part of a healthy diet. We tested whether the palatability of pulse containing foods provided during a weight loss intervention which were particularly high in fiber and low in energy density would increase with repeated exposure. At weeks 0, 3, and 6, participants (n = 42; body mass index (BMI) 31.2 ± 4.3 kg/m²) were given a test battery of 28 foods, approximately half which had been provided as part of the intervention, while the remaining half were not foods provided as part of the intervention. In addition, about half of each of the foods (provided as part or not provided as part of the intervention) contained pulses. Participants rated the taste, appearance, odor, and texture pleasantness of each food, and an overall flavor pleasantness score was calculated as the mean of these four scores. Linear mixed model analyses showed an exposure type by week interaction effect for taste, texture and overall flavor pleasantness indicating statistically significant increases in ratings of provided foods in taste and texture from weeks 0 to 3 and 0 to 6, and overall flavor from weeks 0 to 6. Repeated exposure to these foods, whether they contained pulses or not, resulted in a ~4% increase in pleasantness ratings. The long-term clinical relevance of this small increase requires further study.T32 AT000815 - NCCIH NIH HH

Chandra observations of the accretion-driven millisecond X-ray pulsars XTE J0929-314 and XTE J1751-305 in quiescence

(Abridge) We observed the accreting millisecond X-ray pulsars XTE J0929-314 and XTE J1751-305 in their quiescent states using Chandra. From XTE J0929-314 we detected 22 photons (0.3-8 keV) in 24.4 ksec, resulting in a count rate of 9 x 10^{-4} c/s. The small number of photons detected did not allow for a detailed spectral analysis, but we can demonstrate that the spectrum is harder than simple thermal emission which is what is usually presumed to arise from a cooling neutron star that has been heated during the outbursts. Assuming a power-law model for the spectrum, we obtain a power-law index of ~1.8 and an unabsorbed flux of 6 x 10^{-15} ergs/s/cm^2 (0.5-10 keV), resulting in a luminosity of 7 x 10^{31} (d/10 kpc)^2 ergs/s, with d in kpc. No thermal component could be detected; such a component contributed at most 30% to the 0.5-10 keV flux. Variability in the count rate of XTE J0929-314 was observed at the 95% confidence level. We did not conclusively detect XTE J1751-305 in our 43 ksec observation, with 0.5-10 keV flux upper limits between 0.2 and 2.7 x 10^{-14} ergs/s/cm^2 depending on assumed spectral shape, resulting in luminosity upper limits of 0.2 - 2 x 10^{32} (d/8 kpc)^2 ergs/s. We compare our results with those obtained for other neutron-star X-ray transients in their quiescent state. Using simple accretion disk physics in combination with our measured quiescent luminosity of XTE J0929-314 and the luminosity upper limits of XTE J1751-305, and the known spin frequency of the neutron stars, we could constrain the magnetic field of the neutron stars in XTE J0929-314 and XTE J1751-305 to be less than 3 x 10^9 (d/10 kpc) and 3 - 7 x 10^8 (d/8 kpc) Gauss (depending on assumed spectral shape of the quiescent spectrum), respectively.Comment: Accepted for publication in ApJ, 29 September 2004. Added spectral variability search for the data of XTE J0929-314 and added the non-detection with Chandra of XTE J1751-30

Evolution of displacements and strains in sheared amorphous solids

The local deformation of two-dimensional Lennard-Jones glasses under imposed shear strain is studied via computer simulations. Both the mean squared displacement and mean squared strain rise linearly with the length of the strain interval $\Delta \gamma$ over which they are measured. However, the increase in displacement does not represent single-particle diffusion. There are long-range spatial correlations in displacement associated with slip lines with an amplitude of order the particle size. Strong dependence on system size is also observed. The probability distributions of displacement and strain are very different. For small $\Delta \gamma$ the distribution of displacement has a plateau followed by an exponential tail. The distribution becomes Gaussian as $\Delta \gamma$ increases to about .03. The strain distributions consist of sharp central peaks associated with elastic regions, and long exponential tails associated with plastic regions. The latter persist to the largest $\Delta \gamma$ studied.Comment: Submitted to J. Phys. Cond. Mat. special volume for PITP Conference on Mechanical Behavior of Glassy Materials. 16 Pages, 8 figure