No abstract available

No abstract available

[en] Observations of PHL 957 have been made with the Steward Observatory echelette spectrograph and with the Lick Observatory image-tube scanner. The stronger emission lines are found to have markedly different profiles, making emission redshift determinations rather inaccurate. No He II lambda1640 emission was detected. Wavelengths and approximate strengths of 203 absorption features are given, and two redshift systems (z/sub A/=2.3088, z/sub K/=1.7969) are shown to have a low probability of chance occurrence. Most of the lines observed shortward of emission Lα appear to be due to Lα in clouds of sufficiently low optical depth that Lβ is not detected. Systems A and K are similar in character to the absorption systems seen in 1331+170. The relative redshifts with respect to the emission systems are the same in the two QSOs and as such may provide evidence for Lyman line to Lyman continuum locking

[en] The Voltage-to-Frequency Converter (V2F) is an instrument commonly used in synchrotron beam line experiments for converting a slowly varying voltage signal representing x-ray flux to a high frequency pulse train, with each pulse representing a packet of x-ray energy. The pulses are commonly integrated with a digital counter to calculate total x-ray energy incident on a sample during an exposure. As x-ray experiment data is taken faster and faster and exposure times shrink, V2F frequencies must necessarily increase to preserve precision in measuring total x-ray energy. The APS Detector Group have designed and built two custom 50 MHz V2F instruments for APS beam line experiments. The instruments are designed according to the Nuclear Instrument Module (NIM) standard and respectively reside at APS Sector 12-BM, and in the APS Detector Pool [1].

[en] We discuss the design, fabrication and use of a custom CCD detector for x-ray powder diffraction measurements. The detector is mounted on a diffractometer arm, where line-by-line readout of the CCD is coupled to continuous motion of the arm. As the arm moves, the data from the CCD detector are accumulated and can be viewed as if it were a 'film strip' with partial powder diffraction rings. Because of the unique design of the camera, both high-resolution and rapid measurements can be performed. Powder diffraction patterns are collected with speeds of a few minutes, or less, with many of the advantages of large area position-sensitive detectors, for example amorphous silicon flat panels, such as high sensitivity, direct evidence of grainy samples and freedom from low-angle asymmetry, but with resolution better than linear position-sensitive detectors and nearly as good as the ultimate in resolution, analyser-crystal detection [2,3]

[en] The creation of thin, buried, and electrically conducting layers within an otherwise insulating diamond by annealed ion implantation damage is well known. Establishing facile electrical contact to the shallow buried layer has been an unmet challenge. We demonstrate a new method, based on laser micro-machining (laser ablation), to make reliable electrical contact to a buried implant layer in diamond. Comparison is made to focused ion beam milling.

[en] We synthesize nanoporous platinum (np-Pt) through electrochemical dealloying in aqueous HF from cosputtered Pt_xSi_1-x amorphous films for different initial composition and sputter bias conditions. We demonstrate that, in addition to the expected isotropic open cell np-Pt foam, anisotropic (columnar and Voronoi) np-Pt is obtained. There are two levels of anisotropy: on the micron scale, 100 nm columns or 1 μm Voronoi polygons form. Inside the columnar and Voronoi hyperstructures, the ligaments and pores are anisotropic ranging from 5 to 25 nm. The ligament diameter and grain size is 5 nm for all reported structures. A processing-structure map is developed that correlate np-Pt structures to processing conditions.

[en] Large fluxes of high-energy electrons are responsible for the non-thermal radio fluxes and probably the optical continua from compact sources in quasi-stellar objects. If they are accompanied by energetic fluxes of protons with energies > approximately 100 MeV, we expect that interaction with the gas will lead to spallation. Among the primary spallation products boron is the element which would be detectable in QSO spectra. The corresponding lines are absent, and by analyzing the ionization structure of the emitting and absorbing regions we find that the limit to the boron to carbon ratio is <= 1/15. Different models for explaining these results are discussed. (orig./BJ)

[en] We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emissions from high ionization lines that will not be emitted by the Crab's filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The near-NIR [Ne VI] λ7.652 μm line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV λ1549 doublet is predicted to be the strongest absorption line from the shell, which is in agreement with Hubble Space Telescope observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually ''remember'' its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level of ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion

[en] In a sub-arcsec near-infrared survey of the Crab Nebula using the new Spartan Infrared Camera, we have found several knots with high surface brightness in the H₂ 2.12 μm line and a very large H₂ 2.12 μm to Brγ ratio. The brightest of these knots has an intensity ratio I(H₂ 2.12 μm)/I(Brγ) = 18 ± 9, which we show sets a lower limit on the ratio of masses in the molecular and recombination (i.e., ionized) zones M_mol/M_rec ≥ 0.9, and a total molecular mass within this single knot M_mol ≥ 5 x 10^-5 M_sun. We argue that the knot discussed here probably is able to emit so strongly in the 2.12 μm line because its physical conditions are better tuned for such emission than is the case in other filaments. It is unclear whether this knot has an unusually large M_mol/M_rec ratio, or if many other Crab filaments also have similar amounts of molecular gas which is not emitting because the physical conditions are not so well tuned.