Ionospheric E-region Irregularities Produced by Non-linear Coupling of Unstable Plasma Waves

Ionospheric E region irregularities produced by nonlinear coupling of unstable plasma wave

A Hybrid Analysis for Security Protocols with State

Cryptographic protocols rely on message-passing to coordinate activity among principals. Each principal maintains local state in individual local sessions only as needed to complete that session. However, in some protocols a principal also uses state to coordinate its different local sessions. Sometimes the non-local, mutable state is used as a means, for example with smart cards or Trusted Platform Modules. Sometimes it is the purpose of running the protocol, for example in commercial transactions. Many richly developed tools and techniques, based on well-understood foundations, are available for design and analysis of pure message-passing protocols. But the presence of cross-session state poses difficulties for these techniques. In this paper we provide a framework for modeling stateful protocols. We define a hybrid analysis method. It leverages theorem-proving---in this instance, the PVS prover---for reasoning about computations over state. It combines that with an "enrich-by-need" approach---embodied by CPSA---that focuses on the message-passing part. As a case study we give a full analysis of the Envelope Protocol, due to Mark Ryan

ALMA observations of the supergiant B[e] star Wd1-9

Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible – radiatively driven winds, impulsive ejection and/or binary interaction – remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (∼100 km s-1 ) ionized wind, with an extreme mass-loss rate ≳6.4 × 105(d/5 kpc)1.5 Mȯyr-1. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they – and by extension the wider class of supergiant B[e] stars – may provide a unique window into the physics of a process that shapes the life-cycle of ∼70 per cent of massive stars found in binary systems

The Liquidus Temperature for Methanol-Water Mixtures at High Pressure and Low Temperature, with Application to Titan

Methanol is a potentially important impurity in subsurface oceans on Titan and Enceladus. We report measurements of the freezing of methanol-water samples at pressures up to 350~MPa using a volumetric cell with sapphire windows. For low concentrations of methanol, the liquidus temperature is typically a few degrees below the corresponding ice freezing point, while at high concentrations it follows the pure methanol trend. In the Ice-III regime, we observe several long-lived metastable states. The results suggest that methanol is a more effective antifreeze than previously estimated, and might have played an important role in the development of Titan's subsurface ocean

High resolution radio observations of the colliding-wind binary WR140

Milli-arcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype WR+O star colliding-wind binary (CWB) system WR140 are presented for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that rotates as the orbit progresses. We interpret this rotation as due to the O star moving from SE to approximately E of the WR star, which leads to solutions for the orbit inclination of 122+/-5 deg, the longitude of the ascending node of 353+/-3 deg, and an orbit semi-major axis of 9.0+/-0.5 mas. The distance to WR140 is determined to be 1.85+/-0.16 kpc, which requires the O star to be a supergiant. The inclination implies the mass of the WR and O star to be 20+/-4 and 54+/-10 solar masses respectively. We determine a wind-momentum ratio of 0.22, with an expected half-opening angle for the WCR of 63 deg, consistent with 65+/-10 deg derived from the VLBA observations. Total flux measurements from Very Large Array (VLA) observations show the radio emission from WR140 is very closely the same from one orbit to the next, pointing strongly toward emission, absorption and cooling mechanism(s) that are controlled largely by the orbital motion. The synchrotron spectra evolve dramatically through the orbital phases observed, exhibiting both optically thin and optically thick emission. We discuss a number of absorption and cooling mechanisms that may determine the evolution of the synchrotron spectrum with orbital phase.Comment: Accepted by ApJ, to appear in v623, April 20, 2005. 14 pages, 13 figs, requires emulateapj.cls. A version with full resolution figs can be obtained from http://www.drao.nrc.ca/~smd/preprint/wr140_data.pd

An X-Ray Jet from a White Dwarf - Detection of the Collimated Outflow from CH Cygni with Chandra

Most symbiotic stars consist of a white dwarf accreting material from the wind of a red giant. An increasing number of these objects have been found to produce jets. Analysis of archival Chandra data of the symbiotic system CH Cygni reveals faint extended emission to the south, aligned with the optical and radio jets seen in earlier HST and VLA observations. CH Cygni thus contains only the second known white dwarf with an X-ray jet, after R Aquarii. The X-rays from symbiotic-star jets appear to be produced when jet material is shock-heated following collision with surrounding gas, as with the outflows from some protostellar objects and bipolar planetary nebulae.Comment: 4 & a bit pages, 4 figures, accepted by ApJL; uses emulateapj.cls and revtex4. Minor changes following referees report, & shortened to meet page limi

One hundred twenty-five concomitant endovascular and open procedures for lower extremity arterial disease

AbstractObjective: Although the results of staged endovascular and open surgical reconstructions have been well documented, the safety and efficacy of concomitant procedures in the operating room are less well defined. Suboptimal performance of endovascular procedures in an operative setting, or inappropriate reliance on endovascular techniques, might theoretically compromise graft patency. We questioned whether late graft thrombosis is frequently attributable to failure at the endovascularly treated site in this setting. Materials and Methods: Between May 1, 1993, and June 30, 2001, we performed 125 concomitant endovascular and open arterial reconstructions (73 primary reconstructions, 52 graft revisions) in 106 patients. Endovascular techniques were used to treat inflow lesions in 72 cases, outflow lesions in 14 cases, both in four cases, and the graft itself in 35 cases. Fifty-five iliac, 18 femoral, 13 popliteal, six tibial, and 35 graft lesions were treated. For primary bypasses, 33 were to the popliteal level (21 prosthetic, 12 autogenous), 19 were to the tibial or pedal arteries (16 autogenous, three prosthetic or composite), and 12 were to the femoral arteries (one autogenous, 11 prosthetic). Nine patch angioplasties (eight femoral, one popliteal) were performed. For graft revisions, endovascular intervention was for inflow in 13 cases, outflow in three cases, both in one case, and of the graft itself in 35 cases. Surgical revisions involved segmental grafts in 33 cases, patch angioplasty in 18 cases, and both in one case. Results: In the primary group, the initial technical success rate of the endovascular procedure was 93% (68/73), with five patients needing open conversion. The 30-day mortality rate was 1.4%, and the morbidity rate was 11.0%. Of the 19 grafts in the primary group that occluded during the follow-up period (mean, 11.9 months), five thromboses could possibly be attributed to failure at the endovascular site. In the revision group, the initial technical success rate of the endovascular procedure was 88% (46/52), with six patients undergoing conversion to open procedure. The 30-day mortality rate was 0%, and the morbidity rate was 15.4%. Of 22 late graft occlusions in the revision group, only three were attributed to failure at the endovascular site. Conclusion: This largest report to date of concomitant lower extremity endovascular and open revascularization procedures shows the approach to be safe. Few late graft occlusions were attributable to failure at the endovascularly treated site. The concomitant approach offers the efficiency and convenience of single stage therapy and allows immediate treatment for inadequate endovascular results or their complications and potential cost savings. (J Vasc Surg 2003;37:316-22.