Flight test evaluation of an RAF high altitude partial pressure protective assembly

A partial pressure suit was evaluated during tests in an F-104 and F-15 as a protective garment for emergency descents. The garment is an pressure jerkin and modified anti-g suit combined with an oronasal mask. The garment can be donned and doffed at the aircraft to minimize thermal buildup. The oronasal mask was favored by the pilots due to its immobility on the face during high g-loading. The garment was chosen to provide optimum dexterity for the pilot, which is not available in a full pressure suit, while protecting the pilot at altitudes up to 18,288 meters, during a cabin decompression, and subsequent aircraft descent. During cabin decompressions in the F-104 and F-15, cabin pressure altitude was measured at various aircraft angles of attack, Mach numbers, and altitudes to determine the effect of the aerodynamic slipstream on the cabin altitude

Noether Currents of Charged Spherical Black Holes

We calculate the Noether currents and charges for Einstein-Maxwell theory using a version of the Wald approach. In spherical symmetry, the choice of time can be taken as the Kodama vector. For the static case, the resulting combined Einstein-Maxwell charge is just the mass of the black hole. Using either a classically defined entropy or the Iyer-Wald selection rules, the entropy is found to be just a quarter of the area of the trapping horizon. We propose identifying the combined Noether charge as an energy associated with the Kodama time. For the extremal black hole case, we discuss the problem of Wald's rescaling of the surface gravity to define the entropy.Comment: 4 page

Chandra Detection of the Forward and Reverse Shocks in Cassiopeia-A

We report the localization of the forward and reversed shock fronts in the young supernova remnant Cas-A using X-ray data obtained with the Chandra Observatory. High resolution X-ray maps resolve a previously unseen X-ray feature encompassing the extremity of the remnant. This feature consists of thin, tangential wisps of emission bordering the outer edge of the thermal X-ray and radio remnant, forming a circular rim, approx. 2.7 in radius. Radio images show a sharp rise in brightness at this X-ray rim, along with a large jump in the synchrotron polarization angle. These characteristics suggest that these wisps are the previously unresolved signature of the forward, or outer, shock. Similarly, we identify the sharp rise in emissivity of the bright shell for both the radio and X-ray line emission associated with the reverse shock. The derived ratio of the averaged forward and reverse shock radii of approx. 3:2 constrains the remnant to have swept up roughly the same amount of mass as was ejected; this suggests that Cas-A is just entering the Sedov phase. Comparison of the X-ray spectra from the two shock regions shows that the equivalent widths of prominent emission lines are significantly lower exterior to the bright shell, as expected if they are respectively identified with the shocked circumstellar material and shocked ejecta. Furthermore, the spectrum of the outer rim itself is dominated by power-law emission, likely the counterpart of the non-thermal component previously seen at energies above 10 keV.Comment: 7 pages with 5 figures, LaTex, emulateapj.sty. To appear in the Astrophysical Journal Letter

Toward a simulation approach for alkene ring-closing metathesis : scope and limitations of a model for RCM

A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of di-Et diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications. Unfortunately, the model is too flexible and the published rate consts. do not agree with exptl. studies in the literature. However, by fixing the values of important rate consts. and restricting the concn. ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concn. can be simulated accurately and the effect of precatalyst loading can be anticipated. Progress has also been made toward applying the model to precatalyst evaluation, but further modifications to the model are necessary to achieve much broader aims

On Ignorant Voters and Busy Politicians

We show that a large electorate of ignorant voters can succeed in establishing high levels of electoral accountability. In our model an incumbent politician is confronted with a large number of voters who receive very noisy signals about her performance. We find that the accountability problem can be solved well in the sense that the incumbent exerts effort as if she faced a social planner who receives a perfect signal about her performance. Our results thus shed light on another potential blessing of large electorates in addition to information aggregation as postulated by the jury theorem

Thorium Energy Futures

The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options – liquid or solid, with or without an accelerator – can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice

Factors affecting metal mobilisation during oxidation of sulphidic, sandy wetland substrates

Most metals accumulate as sulphides under anoxic conditions in wetland substrates, reducing their bioavailability due to the solubility of metal sulphides. However, upon oxidation of these sulphides when the substrate is occasionally oxidised, metals can be released from the solid phase to the pore water or overlaying surface water. This release can be affected by the presence of carbonates, organic matter and clay. We compared changes of Cd, Cu and Zn mobility (CaCl2 extraction) during oxidation of a carbonate-rich and a carbonate-poor sulphidic, sandy wetland substrate. In addition, we studied how clay with low and high cation sorption capacity (bentonite and kaolinite, respectively) and organic matter (peat) can counteract Cd, Cu and Zn release during oxidation of both carbonate-rich and carbonate-poor sulphidic sediments. CaCl2-extractability of Cu, a measure for its availability, is low in both carbonate-poor and carbonate-rich substrates, whereas its variability is high. The availability of Cd and Zn is much higher and increases when peat is supplied to carbonate-poor substrates. A strong reduction of Cd and Zn extractability is observed when clay is added to carbonate-poor substrates. This reduction depends on the clay type. Most observations could be explained taking into account pH differences between treatments, with kaolinite resulting in a lower pH in comparison to bentonite. These pH differences affect the presence and characteristics of dissolved organic carbon and the metal speciation, which in turns affects the interaction of metals with the solid soil phase. In carbonate-rich substrates, Cd and Zn availability is lower and the effects of peat and clay amendment are less clear. The latter can also be attributed to the high pH and lack of pH differences between treatments

Upper Limits On Periodic, Pulsed Radio Emission from the X-Ray Point Source in Cassiopeia A

The Chandra X-ray Observatory recently discovered an X-ray point source near the center of Cassiopeia A, the youngest known Galactic supernova remnant. We have conducted a sensitive search for radio pulsations from this source with the Very Large Array, taking advantage of the high angular resolution of the array to resolve out the emission from the remnant itself. No convincing signatures of a dispersed, periodic source or of isolated dispersed pulses were found, whether for an isolated or a binary source. We derive upper limits of 30 and 1.3 mJy at 327 and 1435 MHz for the phase-averaged pulsed flux density from this source. The corresponding luminosity limits are lower than those for any pulsar with age less than 10^4 years. The sensitivities of our search to single pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsar emits roughly 80 pulses per minute with flux densities greater than 100 Jy at 327 MHz and 8 pulses per minute with flux densities greater than 50 Jy at 1435 MHz. These limits are consistent with the suggestion that the X-ray point source in Cas A adds to the growing number of neutron stars which are not radio pulsars.Comment: accepted by ApJ Letter

The Central X-Ray Point Source in Cassiopeia A

The spectacular first light observation by the Chandra X-Ray Observatory revealed an X-ray point source near the center of the 300 yr old Cas A supernova remnant. We present an analysis of the public X-ray spectral and timing data. No coherent pulsations were detected in the Chandra/HRC data. The 3-sigma upper limit on the pulsed fraction is 20 ms. The Chandra/ACIS spectrum of the point source may be fit with an ideal blackbody (kT=0.5 keV), or with BB models modified by the presence of a NS atmosphere (kT=0.25-0.35 keV), but the temperature is higher and the inferred emitting area lower than expected for a 300 yr old NS according to standard cooling models. The spectrum may also be fit with a power law model (photon index 2.8-3.6). Both the spectral properties and the timing limits of the point source are inconsistent with a young Crab-like pulsar, but are quite similar to the properties of the anomalous X-ray pulsars. The spectral parameters are also very similar to those of the other radio-quiet X-ray point sources in the supernova remnants Pup A, RCW 103, and PKS 1209-52. Current limits on an optical counterpart for the Cas A point source rule out models that invoke fallback accretion onto a compact object if fallback disk properties are similar to those in quiescent low-mass X-ray binaries. However, the optical limits are marginally consistent with plausible alternative assumptions for a fallback disk. In this case, accreting NS models can explain the X-ray data, but an accreting BH model is not promising.Comment: 17 pages including 2 figs. To appear in ApJ, Vol. 546 (Jan 10, 2001). Minor revisions per referee. Pulsation limits revised in light of HRC wiring problem. Typos correcte