DA495 - an aging pulsar wind nebula

We present a radio continuum study of the pulsar wind nebula (PWN) DA 495 (G65.7+1.2), including images of total intensity and linear polarization from 408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations with the Effelsberg 100-m Radio Telescope. Removal of flux density contributions from a superimposed \ion{H}{2} region and from compact extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz, with a spectral index ${\alpha}={-0.45 \pm 0.20}$ below the break and ${\alpha}={-0.87 \pm 0.10}$ above it (${S}_\nu \propto{\nu^{\alpha}}$). The spectral break is more than three times lower in frequency than the lowest break detected in any other PWN. The break in the spectrum is likely the result of synchrotron cooling, and DA 495, at an age of $\sim$20,000 yr, may have evolved from an object similar to the Vela X nebula, with a similarly energetic pulsar. We find a magnetic field of $\sim$1.3 mG inside the nebula. After correcting for the resulting high internal rotation measure, the magnetic field structure is quite simple, resembling the inner part of a dipole field projected onto the plane of the sky, although a toroidal component is likely also present. The dipole field axis, which should be parallel to the spin axis of the putative pulsar, lies at an angle of {\sim}50\degr east of the North Celestial Pole and is pointing away from us towards the south-west. The upper limit for the radio surface brightness of any shell-type supernova remnant emission around DA 495 is $\Sigma_{1 GHz} \sim 5.4 \times 10^{-23}$ OAWatt m$^{-2}$ Hz$^{-1}$ sr$^{-1}$ (assuming a radio spectral index of $\alpha = -0.5$), lower than the faintest shell-type remnant known to date.Comment: 25 pages, accepted by Ap

A Low Frequency Survey of the Galactic Plane Near l=11 degrees: Discovery of Three New Supernova Remnants

We have imaged a 1 deg^2 field centered on the known Galactic supernova remnant (SNR) G11.2-0.3 at 74, 330, and 1465 MHz with the Very Large Array radio telescope (VLA) and 235 MHz with the Giant Metrewave Radio Telescope (GMRT). The 235, 330, and 1465 MHz data have a resolution of 25 arcsec, while the 74 MHz data have a resolution of 100 arcsec. The addition of this low frequency data has allowed us to confirm the previously reported low frequency turnover in the radio continuum spectra of the two known SNRs in the field: G11.2-0.3 and G11.4-0.1 with unprecedented precision. Such low frequency turnovers are believed to arise from free-free absorption in ionized thermal gas along the lines of site to the SNRs. Our data suggest that the 74 MHz optical depths of the absorbing gas is 0.56 and 1.1 for G11.2-0.3 and G11.4-0.1, respectively. In addition to adding much needed low frequency integrated flux measurements for two known SNRs, we have also detected three new SNRs: G11.15-0.71, G11.03-0.05, and G11.18+0.11. These new SNRs have integrated spectral indices between -0.44 and -0.80. Because of confusion with thermal sources, the high resolution (compared to previous Galactic radio frequency surveys) and surface brightness sensitivity of our observations have been essential to the identification of these new SNRs. With this study we have more than doubled the number of SNRs within just a 1 deg^2 field of view in the inner Galactic plane. This result suggests that future low frequency observations of the Galactic plane of similar quality may go a long way toward alleviating the long recognized incompleteness of Galactic SNR catalogs.Comment: 31 pages, 9 figures. Figure 7 is in color. Accepted to A

Aeolian transport layer

We investigate the airborne transport of particles on a granular surface by the saltation mechanism through numerical simulation of particle motion coupled with turbulent flow. We determine the saturated flux $q_{s}$ and show that its behavior is consistent with a classical empirical relation obtained from wind tunnel measurements. Our results also allow to propose a new relation valid for small fluxes, namely, $q_{s}=a(u_{*}-u_{t})^{\alpha}$, where $u_{*}$ and $u_{t}$ are the shear and threshold velocities of the wind, respectively, and the scaling exponent is $\alpha \approx 2$. We obtain an expression for the velocity profile of the wind distorted by the particle motion and present a dynamical scaling relation. We also find a novel expression for the dependence of the height of the saltation layer as function of the wind velocity.Comment: 4 pages, 4 figure

X-Ray Observations of the supernova remnant G21.5-0.9

We present the analysis of archival X-ray observations of the supernova remnant (SNR) G21.5-0.9. Based on its morphology and spectral properties, G21.5-0.9 has been classified as a Crab-like SNR. In their early analysis of the CHANDRA calibration data, Slane et al. (2000) discovered a low-surface-brightness, extended emission. They interpreted this component as the blast wave formed in the supernova (SN) explosion. In this paper, we present the CHANDRA analysis using a total exposure of ~150 ksec. We also include ROSAT and ASCA observations. Our analysis indicates that the extended emission is non-thermal -- a result in agreement with XMM observations. The entire remnant of radius ~ 2'.5 is best fitted with a power law model with a photon index steepening away from the center. The total unabsorbed flux in the 0.5-10 keV is 1.1E-10 erg/cm2/s with an 85% contribution from the 40" radius inner core. Timing analysis of the High-Resolution Camera (HRC) data failed to detect any pulsations. We put a 16% upper limit on the pulsed fraction. We derive the physical parameters of the putative pulsar and compare them with those of other plerions (such as the Crab and 3C 58). G21.5-0.9 remains the only plerion whose size in X-rays is bigger than in the radio. Deep radio observations will address this puzzle.Comment: 23 pages including 11 figures and 3 tables; accepted by ApJ June 22, 2001; to appear in Oct 20, 2001 issue of Ap

Chandra Observations of G11.2-0.3: Implications for Pulsar Ages

We present Chandra X-ray Observatory imaging observations of the young Galactic supernova remnant G11.2-0.3. The image shows that the previously known young 65-ms X-ray pulsar is at position (J2000) RA 18h 11m 29.22s, DEC -19o 25' 27.''6, with 1 sigma error radius 0.''6. This is within 8'' of the geometric center of the shell. This provides strong confirming evidence that the system is younger, by a factor of ~12, than the characteristic age of the pulsar. The age discrepancy suggests that pulsar characteristic ages can be poor age estimators for young pulsars. Assuming conventional spin down with constant magnetic field and braking index, the most likely explanation for the age discrepancy in G11.2-0.3 is that the pulsar was born with a spin period of ~62 ms. The Chandra image also reveals, for the first time, the morphology of the pulsar wind nebula. The elongated hard-X-ray structure can be interpreted as either a jet or a Crab-like torus seen edge on. This adds to the growing list of highly aspherical pulsar wind nebulae and argues that such structures are common around young pulsars.Comment: 16 pages, 3 figures, Accepted for publication in ApJ. For a full resolution version of Fig 1, see http://www.physics.mcgill.ca/~vkaspi/G11.2-0.3/f1.ep

Scaling up proven public health interventions through a locally owned and sustained leadership development programme in rural Upper Egypt

<p>Abstract</p> <p>Introduction</p> <p>In 2002, the Egypt Ministry of Health and Population faced the challenge of improving access to and quality of services in rural Upper Egypt in the face of low morale among health workers and managers.</p> <p>From 1992 to 2000, the Ministry, with donor support, had succeeded in reducing the nationwide maternal mortality rate by 52%. Nevertheless, a gap remained between urban and rural areas.</p> <p>Case description</p> <p>In 2002, the Ministry, with funding from the United States Agency for International Development and assistance from Management Sciences for Health, introduced a Leadership Development Programme (LDP) in Aswan Governorate. The programme aimed to improve health services in three districts by increasing managers' ability to create high performing teams and lead them to achieve results.</p> <p>The programme introduced leadership and management practices and a methodology for identifying and addressing service delivery challenges. Ten teams of health workers participated.</p> <p>Discussion and evaluation</p> <p>In 2003, after participation in the LDP, the districts of Aswan, Daraw and Kom Ombo increased the number of new family planning visits by 36%, 68% and 20%, respectively. The number of prenatal and postpartum visits also rose.</p> <p>After the United States funding ended, local doctors and nurses scaled up the programme to 184 health care facilities (training more than 1000 health workers). From 2005 to 2007, the Leadership Development Programme participants in Aswan Governorate focused on reducing the maternal mortality rate as their annual goal. They reduced it from 85.0 per 100,000 live births to 35.5 per 100,000. The reduction in maternal mortality rate was much greater than in similar governorates in Egypt. Managers and teams across Aswan demonstrated their ability to scale up effective public health interventions though their increased commitment and ownership of service challenges.</p> <p>Conclusions</p> <p>When teams learn and apply empowering leadership and management practices, they can transform the way they work together and develop their own solutions to complex public health challenges. Committed health teams can use local resources to scale up effective public health interventions.</p

Influence of chitosan on the mechanical and biological properties of HDPE for biomedical applications

High density polyethylene (HDPE) is widely used in biomedical field, except when strong cell-material interactions and high mechanical properties are required. To address this pitfall, two kinds of chitosan in different amounts were used as filler in the present research. Composites were prepared by melt extrusion process and their microstructural, thermal and mechanical properties were widely investigated. Also roughness and wettability were studied, as features of paramount importance in dictating cell response. Both types of chitosan endowed HDPE with higher Young modulus and lower elongation at break. Interestingly, fibroblast adhesion and viability were enhanced when a low amount of filler was used. The interaction of HDPE/chitosan composites with biological environment was investigated for the first time in order to assess the feasibility of these composites as materials for biomedical application