Calibration and Evaluation of Blackbeard Time Tagging Capability

The Blackbeard instrument is a broadband radio receiver on the ALEXIS (Array of Low Energy X-ray Imaging Sensors) satellite. It detects and records transient VHF radio signals. During November and December of 1996, the Los Alamos Portable Pulser (LAPP) facility was used to transmit 31 broadband pulses to Blackbeard to evaluate the instrument\u27s time tagging accuracy. LAPP firing times were used in conjunction with propagation delays to compute estimated times of arrival (ETOAs) for pulses reaching Blackbeard. ETOAs were compared to Blackbeard reported times of arrival (RTOAs), which were computed using information returned by Blackbeard and an algorithm presented in this paper. For the 31 pulser shots received by Blackbeard, the mean difference between ETOA and RTOA was 1.97 milliseconds, with RTOAs occurring later than ETOAs. The standard deviation of the difference was 0.43 milliseconds. As a result of the study, the algorithm used for accurate Blackbeard time tag studies has been modified to subtract 1.97 milliseconds from reported times of arrival. The 0.43 ms error standard deviation is now used to describe the uncertainty of Blackbeard time tags

Four years of operations and results with FORTE

The FORTE (Fast Onboard Recording of Transient Events) satellite was launched on 29 August 1997 and has been in continuous operation since that time. FORTE was placed in a nearly circular, 825-km-altitude, 70 degrees inclination orbit by a Pegasus rocket funded by Air Force Space Test Program. The Department of Energy funded the FORTE satellite, which was designed and built at Los Alamos. FORTE's successful launch and engineered robustness were a result of several years of dedicated work by the joint Los Alamos National Laboratory/Sandia National Laboratory project team, led through mission definition, payload and satellite development, and launch by Dr. Stephen Knox. The project is now led by Dr. Abram Jacobson. FORTE carries a suite of instruments, an optical system and a rf system, for the study of lightning and anthropogenic signals. As a result of this effort, new understandings of lightning events have emerged as well as a more complete understanding of the relationship between optical and rf lightning events. This paper will provide an overview of the FORTE satellite and will discuss the on orbit performance of the subsystems

Second asymptomatic carotid surgery trial (ACST-2) : a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86-1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91-1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable