A.J. Sims

Observations of single-event upsets in non-hardened high-density SRAMs in Sun-synchronous orbit

Observations of single-event upset (SEU) activity in nonhardened static and dynamic RAMs of both low (16-kb) and high (256-kb, 1-Mb), density are presented for a family of small spacecraft in low-earth, near-polar, Sun-synchronous orbits. The observation of single-event multiple-bit upset (MBU) in these devices is discussed, and the implications of such events for error-protection coding schemes are examined. Contrary to expectations, the 1-Mb static RAMs (SRAMs) are more resilient to SEU than the 256-kb SRAMs, and one type of commercial 1-Mb SRAM shows a particularly low error rate. >

Measurements of solar flare enhancements to the single event upset environment in the upper atmosphere (avionics)

The Cosmic Radiation Environment Monitor has flown regularly on a supersonic airliner over a period of 18 months in order to explore the extent of single-event phenomena in the upper atmosphere. Data presented are from flights occurring between November 1988 and May 1990. The detector system used is briefly described. Quiet-time data now have good statistical precision and are compared with predictions of environment models. A number of increases and decreases were observed during the solar flare events of September and October 1989. >

An algorithm to distinguish ischaemic and non-ischaemic ST changes in the Holter ECG

Changes in the ECG ST segment are often observed in patients with myocardial ischaemia. However, non-ischaemic changes in ST level are also common thereby limiting ischaemia detection accuracy. The aim of this study was to devise an algorithm and determine its accuracy in distinguishing between ischaemic and non-ischaemic changes in the ECG ST-segment, using expertly annotated ECG data sets as a gold standard reference. The algorithm considered only the change in ST relative to a baseline ST level (/spl Delta/ST) provided by the PhysioNet database, and based on simple level thresholding within specified time windows. An initial score of 82.3% (accuracy 91.1%, with sensitivity 99.0% and specificity 88.8%) was achieved for the learning set. By making slight modifications to the algorithm and introducing principal components of ST it was not possible to improve the original algorithm. The original algorithm was therefore left as our challenge entry achieving an accuracy of 90.7% for the test data set (score of 81.4%, entry 1, 1 May 2003).

The single event upset environment for avionics at high latitude

Measurements of the high latitude SEU environment at avionics altitude have been made on board a commercial airliner. Results are compared with models of primary and secondary cosmic rays and atmospheric neutrons. Ground based SEU tests of static RAMs are used to predict rates in flight. >

Measurements of the SEU environment in the upper atmosphere

Regular flights of a cosmic radiation environment monitor on board the supersonic Concorde have allowed mapping of the atmospheric environment to 60000 feet. Results show the importance of secondary particles produced by nuclear reactions in the atmosphere. Thus far there have been no upset recorded in the microprocessor or memory incorporated in the experiment. Based on the environment data obtained to date and limited data on upset cross-sections for similar devices, it is estimated that upsets will occur at a rate of approximately one per 50000 flight hours. >

Secondary radiation environments in heavy space vehicles and instruments

Secondary radiations produced by the interactions of primary cosmic rays and trapped protons with spacecraft materials and detectors provides an important, and sometimes dominant, radiation environment for sensitive scientific instruments and biological systems. In this paper the success of a number of calculations in predicting a variety of effects will be examined. The calculation techniques include Monte Carlo transport codes and semi-empirical fragmentation calculations. Observations are based on flights of the Cosmic Radiation Environment and Activation Monitor at a number of inclinations and altitudes on Space Shuttle. The Shuttle experiments included an active cosmic-ray detector as well as metal activation foils and passive detector crystals of sodium iodide which were counted for induced radioactivity soon after return to earth. Results show that cosmic-ray secondaries increase the fluxes of particles of linear energy transfer less than 200 MeV/(gm cm-2), while the activation of the crystals is enhanced by about a factor of three due to secondary neutrons. Detailed spectra of induced radioactivity resulting from spallation products have been obtained. More than a hundred significant radioactive nuclides are included in the calculation and overall close agreement with the observations is obtained.

Oscillometric blood pressure devices and simulators: measurements of repeatability and differences between models.

Primary objective: To measure the repeatability and pressure pulse envelope of simulators used for testing oscillometric non-invasive blood pressure (NIBP) devices; to study the effect of different envelopes on NIBP devices, and to measure the difference between NIBP devices due to different oscillometric algorithms.Methods: Three different models of NIBP simulator and 18 different patient monitors with NIBP function were studied. We developed a pressure measurement system (accuracy 0.048?mmHg) to measure the repeatability of simulators. The effect of changing the envelope was measured by using three simulators with one NIBP device. Differences between 18 NIBP devices were measured using one simulator at seven blood pressure settings.Main outcomes and results: Simulators generate repeatable pressure pulse envelopes (?<?0.2?mmHg) but the magnitude and shape depends on the model of simulator. Oscillometric NIBP devices are highly repeatable (?<?2?mmHg) when presented with a repeatable pressure pulse envelope, but different devices employ different algorithms and give different results. For a simulated standard blood pressure setting of 120/80?mmHg, estimates of systolic pressure ranged from 112.6 to 126.6?mmHg (sd of 3.0?mmHg), and diastolic pressure ranged from 74.8 to 86.9?mmHg (sd of 3.5?mmHg).Conclusions: Simulators and NIBP devices are sufficently repeatable for clinical use, but further systematic clinical studies are required to better characterize the pressure pulse envelope for different patient groups.

Measurements of the SEE environment from sea level to GEO using the CREAM and CREDO experiments

The cosmic radiation environment and activation monitor (CREAM) and cosmic radiation environment and dosimetry (CREDO) experiments have now been employed in a wide range of flight situations including aircraft, Space Shuttle, UOSAT spacecraft, and most recently the advanced photovoltaics and electronics experiment (APEX) and Space Technology Research Vehicle (STRV) satellites. Results from this unique coverage of the environment will be given ranging from the atmosphere, through the radiation belts to geostationary orbit. Collateral data on upsets have also been obtained for a number of situations. Comparisons are made with standard environment and SEE models and show significant deficiencies and discrepancies. These include time variations in the trapped particles, new radiation belts, secondary particle effects in both heavy spacecraft and the atmosphere, and overestimates of cosmic ray and solar flare heavy ions. The need for both further developments in the models and a comprehensive programme of flight experiments is emphasized.

Morphological Assessment of the Soft Palate in Habitual Snoring Using Image Analysis

Objectives: Define differences in palatal and uvular dimensions between habitual snorers and healthy nonsnoring control subjects. Document the changes in palatal configuration after different types of palatoplasty.

The low Earth orbit radiation environment and its evolution from measurements using the CREAM and CREDO experiments

The new regime of trapped protons centered around L=2.5 and observed by CRRES (Combined Release and Radiation Effects Satellite) between March and October 1991 has been observed by CREAM (Cosmic Radiation Environment and Activation Monitor) on Shuttle missions at an altitude of 569 km in September 1991 (STS-48) and at altitudes of 385 km and 326 km in December 1992 on STS-53. CREDO (Cosmic Radiation Environment and Dosimetry instrument) on UOSAT-3 at 800 km observed the decay of the belt from March 1991 to March 1992. At high latitudes cosmic-ray fluxes have increases by a factor of two between June 1991 and March 1993. The effect of Shuttle shielding on cosmic rays is to increase the fluxes of low LET (linear energy transfer) secondaries and neutrons. Trapped protons and their dose contribution are attenuated, but again significant fluxes of secondary neutrons are produced. >