10,660 research outputs found
Mass-to-Radius Ratio for the Millisecond Pulsar J0437-4715
Properties of X-ray radiation emitted from the polar caps of a radio pulsar
depend not only on the cap temperature, size, and position, but also on the
surface chemical composition, magnetic field, and neutron star's mass and
radius. Fitting the spectra and the light curves with neutron star atmosphere
models enables one to infer these parameters. As an example, we present here
results obtained from the analysis of the pulsed X-ray radiation of a nearby
millisecond pulsar J0437-4715. In particular, we show that stringent
constraints on the mass-to-radius ratio can be obtained if orientations of the
magnetic and rotation axes are known, e.g., from the radio polarization data.Comment: 2 figures, aasms4.sty; accepted for publication in ApJLetter
X-ray emission from the old pulsar B0950+08
We present the timing and spectral analyses of theXMM-newton data on the
17-Myr-old, nearby radio pulsar B0950+08. This observation revealed pulsations
of the X-ray flux of the pulsar at its radio period. The pulse shape and pulsed
fraction are apparently different at lower and higher energies of the observed
0.2-10 keV energy range, which suggests that the radiation cannot be explained
by a single emission mechanism. The X-ray spectrum of the pulsar can be fitted
with a power-law model with a photon index about 1.75 and an (isotropic)
luminosity about 9.8e29 erg/s in the 0.2-10 keV. Better fits are obtained with
two-component, power-law plus thermal, models with index of 1.30 and 9.7e29
erg/s for the power-law component that presumably originates from the pulsar's
magnetosphere. The thermal component, dominating at E>0.7 keV, can be
interpreted as radiation from heated polar caps on the neutron star surface
covered with a hydrogen atmosphere. The inferred effective temperature, radius,
and bolometric luminosity of the polar caps are about 1 MK, 250 m, and 3e29
erg/s. Optical through X-ray nonthermal spectrum of the pulsar can be described
as a single power-law with index 1.3-1.4 for the two-component X-ray fit. The
ratio of the nonthermal X-ray (1-10 keV) luminosity to the nonthermal optical
(4000-9000 \AA) luminosity is within the range of 1e2-1e3 observed for younger
pulsars, which suggests that the magnetospheric X-ray and optical emissions are
powered by the same mechanism in all pulsars. An upper limit on the temperature
of the bulk of the neutron star surface, inferred from the optical and X-ray
data, is about 0.15 MK. We also analyze X-ray observations of several other old
pulsars, B2224+65, J2043+2740, B0628-28, B1813-36, B1929+10, and B0823+26.Comment: To be published in ApJ. Nonthermal optical and X-ray luminosities of
seven radio pulsars are updated and presented in a new Table. Figure 6
showing the ratios of the luminosities vs. spin-down energy is also update
A five year record of high-frequency in situ measurements of non-methane hydrocarbons at Mace Head, Ireland
Continuous high-frequency in situ measurements of a range of non-methane hydrocarbons have been made at Mace Head since January 2005. Mace Head is a background Northern Hemispheric site situated on the eastern edge of the Atlantic. Five year measurements (2005–2009) of six C<sub>2</sub>–C<sub>5</sub> non-methane hydrocarbons have been separated into baseline Northern Hemispheric and European polluted air masses, among other sectors. Seasonal cycles in baseline Northern Hemispheric air masses and European polluted air masses arriving at Mace Head have been studied. Baseline air masses show a broad summer minima between June and September for shorter lived species, longer lived species show summer minima in July/August. All species displayed a winter maxima in February. European air masses showed baseline elevated mole fractions for all non-methane hydrocarbons. Largest elevations (of up to 360 ppt for ethane maxima) from baseline data were observed in winter maxima, with smaller elevations observed during the summer. Analysis of temporal trends using the Mann-Kendall test showed small (<6 % yr<sup>&minus;1</sup>) but statistically significant decreases in the butanes and <i>i</i>-pentane between 2005 and 2009 in European air. No significant trends were found for any species in baseline air
Sustainable business investment to advance livestock health and productivity in Sub-Saharan Africa: the African Livestock Productivity & Health Advancement (A.L.P.H.A.) initiative
Livestock are an essential asset to rural communities, and the health of livestock is critical for achieving food security in regions where there is exceptionally high incidence of livestock and human disease. Sub-Saharan Africa (SSA) has amongst the highest human population growth rates in the world, with five-fold growth in Tanzania projected by 2100. Livestock productivity therefore must be improved by overcoming existing constraints to the livestock health sector, including: lack of access to quality veterinary medicines and products, poor rural extension services, limited sustainability of diagnostics services, and low education regarding animal health. Zoetis, the global animal health leader, partnered with the Bill & Melinda Gates Foundation through a $14.4M business development grant with a key focus on sustainable improvement of livestock production in SSA. In the focal countries of Nigeria, Uganda, and now Tanzania and Ethiopia, the African Livestock Health and Productivity Advancement (A.L.P.H.A.) initiative centres around three central pillars namely; Veterinary Medicines & Services, Training & Education, and Veterinary Laboratory networks. Empowerment of the veterinary profession is a key component of our aim to demonstrate the value of animal health to farmers, particularly through encouraging business acumen and highlighting the importance of correct and responsible use of veterinary medicines. After successful launch activities in Nigeria and Uganda, we seek to continue our approach in Tanzania to focus on partnerships with important distributors, veterinary laboratories, and other key contributors to the supply chain to work towards common goals engineered for future growth and longevity.
Keywords: Productivity, Sub-Saharan Africa, livestock, sustainability, diagnostic
Superintegrability on the two-dimensional hyperboloid
In this work we examine the basis functions for classical and quantum mechanical systems on the two-dimensional hyperboloid that admit separation of variables in at least two coordinate systems. We present all of these cases from a unified point of view. In particular, all of the special functions that arise via variable separation have their essential features expressed in terms of their zeros. The principal new results are the details of the polynomial bases for each of the nonsubgroup bases, not just the subgroup spherical coordinate cases, and the details of the structure of the quadratic symmetry algebras
Rate dependent shear bands in a shear transformation zone model of amorphous solids
We use Shear Transformation Zone (STZ) theory to develop a deformation map
for amorphous solids as a function of the imposed shear rate and initial
material preparation. The STZ formulation incorporates recent simulation
results [Haxton and Liu, PRL 99 195701 (2007)] showing that the steady state
effective temperature is rate dependent. The resulting model predicts a wide
range of deformation behavior as a function of the initial conditions,
including homogeneous deformation, broad shear bands, extremely thin shear
bands, and the onset of material failure. In particular, the STZ model predicts
homogeneous deformation for shorter quench times and lower strain rates, and
inhomogeneous deformation for longer quench times and higher strain rates. The
location of the transition between homogeneous and inhomogeneous flow on the
deformation map is determined in part by the steady state effective
temperature, which is likely material dependent. This model also suggests that
material failure occurs due to a runaway feedback between shear heating and the
local disorder, and provides an explanation for the thickness of shear bands
near the onset of material failure. We find that this model, which resolves
dynamics within a sheared material interface, predicts that the stress weakens
with strain much more rapidly than a similar model which uses a single state
variable to specify internal dynamics on the interface.Comment: 10 pages, 13 figures, corrected typos, added section on rate
strengthening vs. rate weakening material
Dynamics of Counterion Condensation
Using a generalization of the Poisson-Boltzmann equation, dynamics of
counterion condensation is studied. For a single charged plate in the presence
of counterions, it is shown that the approach to equilibrium is diffusive. In
the far from equilibrium case of a moving charged plate, a dynamical counterion
condensation transition occurs at a critical velocity. The complex dynamic
behavior of the counterion cloud is shown to lead to a novel nonlinear
force-velocity relation for the moving plate.Comment: 5 pages, 1 ps figure included using eps
Interaction of Bearing and Tensile Loads on Creep Properties of Joints
The interaction of bearing and tensile loads on the creep behavior of joints was studied. A specimen was designed for this study which possessed some of the general features of pin and rivet joint connections and an apparatus was constructed to apply both bearing and tensile loads to the joint model. Deformation measurements were made by use of a photogrid printed on the joint model
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