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Several large (at least 0.°5 diameter) supernova remnants (SNR) located at 2. °5 or more from the galactic plane have been mapped with the Westerbork Synthesis Radio Telescope (WSRT) at 49 cm. The sample, which includes IC443, DA530, VR042.05.01, CTA1 and OA184, is particularly suitable for complementary studies in other spectral regimes. By choosing objects at relatively high galactic latitudes we have consciously selected SNR which are likely to suffer less than average extinction and are probably nearer to the sun than most. This makes them particularly attractive for optical and X-ray studies which, along with IR and further radio observations, are either in progress or being planned. These are summarized in Table 1.
The extended cloud complex containing members of the Gem OB1 association, the supernova remnant IC443, and the H II region S249 has been studied with IRAS observations at 12,25,60 and 100 microns and WSRT observations at 327 and 1400 MHz and in the 21-cm H I line. A skeleton-like framework of cool dust delineates the boundaries of the region, and physical parameters have been derived for the entire complex, individual H II regions and the shocked and recombined gas within IC443 using the radio and infrared data. IC443 is shown to consist of three interconnected, roughly spherical subshells of vastly different radii and centroids. The geometry is fully constrained by the structural and kinematic data. Two of the subshells together define the usually assumed boundaries of IC443, while the third includes the optical filaments which extend beyond the northeastern rim and which are shown to have well-correlated nonthermal radio components. The available evidence implies that the SNR shock has encountered a pre-existing high density shell. It is shown that the system of subshells is fully consistent with formation by stellar wind driven bubbles generated by association members within the inhomogeneous environment of the complex.
The remnant of Tycho's supernova of 1572 has been polarimetrically imaged using the 4 configurations of the VLA at wavelengths of 22 and 6 cm. A few data were also obtained at wavelengths of 21, 19, and 18 cm in the B configuration to check for any ambiguities in the Faraday rotation measurements and to look for deviations from the λ2 dependence of the Faraday rotation which would indicate significant internal Faraday effects. Although the total intensity shows structure on a scale of about 1 arcsecond the polarized emission appears to be resolved into cells of perhaps 10-arcsec size (1 arcsec corresponds to 0.011 pc at the 2.2 kpc distance to Tycho's SNR). We have therefore convolved the map shown in Figure 1 to a resolution of 4 arcsec to improve the signal-to-noise ratio. The contours represent the total intensity at 6-cm wavelength and the vectors show the position angle of the magnetic field with a length corresponding to the polarized intensity at 6 cm. In order to be seen, the vectors have a separation of 6 arcsec but no significant information is lost on this spacing.
Based on our examination of the characteristics of about 280 known pulsars and 40 millisecond pulsars (MSPs), we have derived selection criteria for MSP candidates: steep spectrum, highly linearly polarized point sources. The first sample of 14 candidates from the NVSS at 1.4 GHz and the WENSS at 325 MHz has been observed by the WSRT using PuMa at both 92 and 21 cm in May 1999. We have finished processing all data and find no evidence for MSPs for a dispersion measure range of 0 —- 200 cm−3 pc in this first sample.
We have compiled data from the literature on rotational velocities and/or periods for > 1000 K & M stars in 10 young clusters ranging in age from Orion to the IC 1391/2602. These data show that most PMS stars < 3 Myr do not appear to spin up in response to contraction, but there is a suggestion of slight spinup by ~8 Myr. These results extend and reinforce our earlier study (Rebull et al. 2002), based on observations of ~300 stars in the Orion Flanking Fields, NGC 2264, and the Orion Nebula Cluster (ONC), which showed that the majority of PMS stars in these three groups apparently do not conserve stellar angular momentum as they contract, but instead evolve at nearly constant angular velocity. This result applies both to stars with and without near-IR I – K excesses indicative of disks.
We first very briefly introduce the major radio facilities for astronomical research in China, and then report on the present interference situation at major radio observatories. Some of the radio interference problems are caused by paging services, mobile phone satellites, telemetry services for power supply, waterpower and earthquake activity, or radar systems, but some causes are unknown. In the worst case, harmful to radio astronomy, the Sesan VLBI station has not been able to do any observations at 92 cm due to serious radio interference problems since 1992. Still more serious interference coming from satellites can be expected in the next decade. International efforts on frequency protection should be urgently pursued if ground-based radio astronomy is to survive.
We have carried out a series of measurements at some locations in Guizhou Province and one additional site at the Urumqi Astronomical Station in the Xinjiang autonomous region, to check on their suitability, from the point of view of interference, for the construction of a Five-hundred-meter Aperture Spherical Telescope (FAST). This large facility will in some sense act as a prototype for the Square Kilometer Array (SKA). Measurements were made using a commercial receiver in the frequency range 25–1500 MHz. The results in Guizhou look quite promising. A protected radio quiet zone in Guizhou would make it an ideal location for an international radio astronomical facility, and would establish the FAST site as a natural SKA location.
The last triennium marked the 50th anniversary of the paper describing the first observations of cosmic radio emission by Karl Jansky in 1933. Sullivan (82 Classics in Radio Astronomy, Reidel) has published a collection of the major historical papers in radio astronomy, and collections of papers discussing the historical development have been published by Sullivan (84 Early Years of Radio Astronomy, Cambridge Univ. Press) and by Kellermann and Sheets (84 Serendipitous Discoveries in Radio Astronomy, NRAO).
Seven millisecond pulsars (MSPs) have been identified from the NVSS by positional coincidence. Our examination of the characteristics of about, 280 known pulsars and 40 MSPs has shown that they have high polarization and a steep spectrum. We identify likely MSP candidates from both the NVSS at 1.4 GHz and the WENSS at 325 MHz. The first sample of 14 candidates has been observed by the WSRT using PuMa at both 92 and 21 cm in May 1999. From our preliminary analysis of the 382 MHz data, we find no evidence for MSPs in the first sample.
The 39.5 ms pulsar PSR 1951+32 and the remnant with which it is associated, CTB 80, have both been observed with the recently upgraded Westerbork synthesis array (WSRT). Parts of CTB 80 have been observed over the frequency coverage from 0.3 to 8 GHz, while PSR 1951+32 has been observed from 0.3 to 1.6 GHz. The results are described and discussed in the context of the pulsar-remnant association.
The Westerbork Synthesis Radio Telescope (WSRT) has now been used to make source surveys at frequencies of 610 and 1415 MHz. This paper summarizes the results concerning source counts and anisotropies in the distribution of sources from those surveys not concerned with clusters of galaxies.
NGC 6251, a 14th mag elliptical galaxy, was shown by Waggett et al. (1977) to have large-scale radio emission features with a total angular extent of ∼ 1.1°, which corresponds to a projected linear size of about 1.7 Mpc (HO = 75 km s−1 Mpc−1). A bright radio jet links a central core source embedded in NGC 6251 to the extended emission on the northwest side of the galaxy.
Continuum observations of IC 443 were made at 21 cm with a resolution of 23″×59″. The appearance in the radio continuum is very similar to the optical appearance. Since the radio emission is nonthermal, this requires a mechanism that can enhance the synchrotron volume emissivity within thermal filaments, which emit strong optical radiation. We suggest compression of gas and magnetic fields in a shock.
Tycho's remnant has been observed both at 21 cm (resolution 24″ × 27″) and at 6 cm (resolution 7″ × 8″). Most of the fine scale structure is resolved. The similarity at the two wavelengths indicates a remarkable constancy in the spectral index of features down to a scale of 20″.
To quantify and characterize overall antimicrobial use, including appropriateness of indication, among patients receiving chronic hemodialysis.
Retrospective and prospective observational study.
Two outpatient hemodialysis units.
All patients receiving chronic hemodialysis.
The rate of parenteral antimicrobial use (number of doses per 100 patient-months) was calculated retrospectively from September 2008 through July 2011. Indication and appropriateness of antimicrobial doses were characterized prospectively from August 2010 through July 2011. Inappropriate administration was defined as occasions when criteria for infection based on national guidelines were not met, failure to choose a more narrow-spectrum antimicrobial on the basis of culture data, or occasions when indications for surgical prophylaxis were not met.
Over the 35-month retrospective study period, the rate of parenteral antimicrobial use was 32.9 doses per 100 patient-months. Vancomycin was the most commonly prescribed antimicrobial, followed by cefazolin and third- or fourth-generation cephalosporins. Over the 12-month prospective study, 1,003 antimicrobial doses were prescribed. Among the 926 (92.3%) doses for which an indication for administration was available, 276 (29.8%) were classified as inappropriate. Of these, a total of 146 (52.9%) did not meet criteria for infection, 74 (26.8%) represented failure to choose a more narrow-spectrum antimicrobial, and 56 (20.3%) did not meet criteria for surgical prophylaxis. The most common inappropriately prescribed antimicrobials were vancomycin and third- or fourth- generation cephalosporins.
Parenteral antimicrobial use was extensive, and as much as one-third was categorized as inappropriate. The findings of this study provide novel information toward minimizing inappropriate antimicrobial use.
We have observed giant Magnetoresistance (GMR) in Ni81Fe19/Ag granular structures synthesized by the annealing of artificial multilayers made by sputtering. The size and morphology of the magnetic precipitates can be controlled by adjusting the magnetic layer thickness in the initial stage. Magnetoresistance as large as 30% was found at 4.2 K with a rather small saturation field. Giant Magnetoresistance in this alloy system essentially depends on the magnetic precipitate size, annealing temperature and the Ni81Fe19 concentration. The temperature dependence of the magnetoresistance in these films is discussed.
Quasicrystalline materials have been investigated for application as thermoelectric materials due to their inherently low thermal conductivity. With the discovery of a new stable, binary Cd5.7Yb quasicrystal, thermal and electrical transport measurements have been performed on these materials. It is found that the electronic contribution to the thermal conductivity calculated from the Wiedemann-Franz relationship is comparable to or greater than the total measured thermal conductivity, leaving the appearance of a “negligible lattice contribution.” In addition, no semblance of the lattice contribution appears in the temperature dependence of the thermal conductivity. The thermal conductivity increases linearly with temperature above 75K and proportional to T3/4 between 2 K and 75 K.
We report room temperature thermopower values and the temperature dependence for several AlPdMn based quasicrystals. In an effort to further understand the complexities of electrical transport in quasicrystalline systems, thermopower data for icosahedral Al71Pd21Mn8-XReX will be presented and discussed. A relation of room temperature thermopower to the curvature of the thermopower is demonstrated. We propose an empirical fit to the thermopower data, utilizing three free variables. The physical significance of the fit parameters is discussed. These results are discussed in brief concerning the relation to the application of quasicrystals for use as thermoelectric materials.
Reversible structural relaxation has been studied in (Fe1-xNix)80B10Si10 by differential scanning calorimetry and X-ray diffraction. It is found that surface crystallization plays a major role in inhibiting reversibility. In consequence previously published data have presented a misleading picture about the composition dependence of the reversible effect in Fe-Ni-B-Si, which simply increases monotonically with Ni composition. There is no evidence that chemical short range order plays any role in reversibility.
The effects of adding small amounts of phosphorus to amorphous Fe78Si9B13 alloys have been investigated. Substituting boron atoms by phosphorus improves the thermal stability of the glassy alloys. The optimum stability is reached at about 1.2 at. % phosphorus concentration. With respect to the soft ferromagnetic properties, the saturation induction increases rapidly with increasing phosphorus concentration, reaches a maximum around 0.1–0.2 at. % and then decreases upon further addition. The highest induction value was achieved with 0.1 at. % phosphorus after field annealing for 2 hours around 633K. The mechanical strength of the amorphous alloy is greatly reduced for phosphorus concentrations larger than 0.4 at. %.
Nanocrystalline and amorphous Fe-Ti at or close to the equiatomic composition have been prepared by ball milling, starting either from the elemental components or from the pre-melted intermetallic. The final structure, whose evolution has been monitored by Xray diffraction and transmission electron microscopy, is found to be critically dependent on milling conditions and contamination level.
Hydrogen absorption properties of both the amorphous and nanocrystalline alloys have been investigated. These properties are substantially modified by the reduction in grain size. We will also discuss the influence of the activation process and repeated hydrogen charging on substitutional disorder and grain size.