Space propulsion technology overview

Chemical and electric propulsion technologies for operations beyond the shuttle's orbit with focus on future mission needs and economic effectiveness is discussed. The adequacy of the existing propulsion state-of-the-art, barriers to its utilization, benefit of technology advances, and the prognosis for advancement are the themes of the discussion. Low-thrust propulsion for large space systems is cited as a new technology with particularly high benefit. It is concluded that the shuttle's presence for at least two decades is a legitimate basis for new propulsion technology, but that this technology must be predicted on an awareness of mission requirements, economic factors, influences of other technologies, and real constraints on its utilization

ASRDI oxygen technology survey, Volume 7: Characteristics of metals that influence system safety

A literature survey and analysis of the material and process factors affecting the safety of metals in oxygen systems is presented. In addition, the practices of those who specify, build, or use oxygen systems relative to the previous is summarized. Alloys based on iron, copper, nickel, and aluminum were investigated representing the bulk of metals found in oxygen systems. Safety-related characteristics of other miscellaneous metals are summarized. It was found that factors affecting the safety of metals in oxygen systems exit in all phases of the evolutionary process, from smelting and mill techniques through end-production fabrication. The safety of a given metal in an oxygen system was determined to be influenced by the particular service requirement. The metal characteristics should favorably influence fulfillment of these requirements. Thus, no singular metal or alloy could be classified as safest for all types of oxygen service

Bibliography on aircraft fire hazards and safety. Volume 1: Hazards. Part 1: Key numbers 1 to 817

Ignition temperatures of n-hexane, n-octane, n-decane, JP-6 jet fuel, and aircraft engine oil MIL-7-7808 (0-60-18) were determined in air using heated Pyrex cylinders and Nichrome wires, rods, or tubes. Ignition temperature varied little with fuel-air ratio, but increased as the size of the heat source was decreased. Expressions are given which define the variation of the hot surface ignition temperatures of these combustibles with the radius and the surface area of the heat source. The expressions are applicable to stagnant or low velocity flow conditions (less than 0.2 in./sec.). In addition, the hot gas ignition temperatures of the combustible vapor-air mixtures were determined with jets of hot air. These ignition temperatures also varied little with fuel-air ratio and increased as the diameter of the heat sources was decreased

Bibliography on aircraft fire hazards and safety. Volume 2: Safety. Part 1: Key numbers 1 to 524

Bibliographic citations are presented to describe and define aircraft safety methods, equipment, and criteria. Some of the subjects discussed are: (1) fire and explosion suppression using whiffle balls, (2) ultraviolet flame detecting sensors, (3) evaluation of flame arrestor materials for aircraft fuel systems, (4) crash fire prevention system for supersonic commercial aircraft, and (5) fire suppression for aerospace vehicles

Vocabulary of aerospace safety terms pertaining to cryogenic safety, fires, explosions, and structure failure

This vocabulary listing characterizes the contents of over 10,000 documents of the NASA Aerospace Safety Research and Data Institute's (ASRDI) safety engineering collection. The ASRDI collection is now one of the series accessible on the NASA RECON data base. There are approximately 6,300 postable terms that describe literature in the areas of cryogenic fluid safety, specifically hydrogen, oxygen, liquified natural gas; fire and explosion technology; and the mechanics of structural failure. To facilitate the proper selection of information nonpostable, related and array terms have been included in this listing

Confirmatory testing in primary aldosteronism: extensive medication switching is not needed in all patients

Objective: Confirmatory testing of suspected primary aldosteronism (PA) requires an extensive medication switch that can be difficult for patients with severe complicated hypertension and/or refractory hypokalemia. For this reason, we investigated the effect of chronic antihypertensive medication on confirmatory testing results. To allow the results to be interpreted, the reproducibility of confirmatory testing was also evaluated. Design and methods: The study enrolled 114 individuals with suspected PA who underwent two confirmatory tests. The patients were divided into two groups. In Group A, both tests were performed on the guidelines-recommended therapy, i.e. not interfering with the renin–angiotensin–aldosterone system. In Group B, the first test was performed on chronic therapy with the exclusion of thiazides, loop diuretics, and aldosterone antagonists; and the second test was performed on guidelines-recommended therapy. Saline infusion, preceded by oral sodium loading, was used to suppress aldosterone secretion. Results: Agreement in the interpretation of the two confirmatory tests was observed in 84 and 66 % of patients in Groups A and B respectively. For all 20 individuals in Group A who ever had end-test serum aldosterone levels R240 pmol/l, aldosterone was concordantly nonsuppressible during the other test. Similarly, for all 16 individuals in Group B who had end-test serum aldosterone levels R240 pmol/l on modified chronic therapy, aldosterone remained nonsuppressible with guidelines-recommended therapy. Conclusion: Confirmatory testing performed while the patient is on chronic therapy without diuretics and aldosterone antagonists can confirm the diagnosis of PA, provided serum aldosterone remains markedly elevated at the end of saline infusion. European Journal of Endocrinology 166 679–68

Relative impact of channel symbol rate on transmission capacity

Through C+L band transmission experiments and theoretical modeling, we investigate the impact of channel symbol rate (30, 40, 60, and 85 GBd) on the performance of data center interconnection, metropolitan, and core network distances. Two different transponder architectures are investigated: (a) single-carrier receiver and (b) multi-carrier receiver, where multiple subcarriers are received together in a single wideband receiver. The architectures of both receivers experience a reduction in the achievable information rate as the channel symbol rate increases due to dominating transceiver noise; this holds over all tested transmission distances. However, the multi-carrier receiver shows a weaker performance dependency on symbol rate, as receiver-related impairments dominate. When testing the single-carrier receiver after 630 km, we find that by increasing the channel symbol rate from 40 to 85 GBd, gross capacity decreases by 16%; however, the required number of transceivers to fill the transmission window decreases by 52%. Using the multi-carrier receiver reduces receiver count further. This potentially impacts the cost and complexity of deploying fully loaded transmission systems

Phospholipid Composition of Myocardium in Children with Normoxemic and Hypoxemic Congenital Heart Diseases

Summary Samples of myocardial tissue were obtained during cardiac surgery from children operated for different types of normoxemic and hypoxemic congenital heart diseases. The phospholipid composition was analyzed by thin layer chromatography. The concentration of total phospholipids (PL), phosphatidylcholine and phosphatidylethanolamine (PE) was found lower in atrial tissue of both normoxemic and hypoxemic groups in comparison with the ventricles. When comparing the difference between hypoxemic and normoxemic defects, hypoxemia was found to increase the concentration of total PL, PE and phosphatidylserine in ventricles and total PL and PE in the atria. The increased level of particular phospholipid species may represent adaptive mechanisms to hypoxemia in children with congenital heart diseases

Recent advances of the Ti:sapphire-pumped high-repetition-rate femtosecond optical parametric oscil- lator

The details concerning the resonator configuration, crystal parameters, and operating characteristics of highrepetition-rate and high-average-power broadly tunable femtosecond optical parametric oscillators are reviewed and discussed in some detail. We also report new results on an intracavity-doubled optical parametric oscillator with tunability from 580 to 657 nm in the visible and the first, to our knowledge, high-repetition-rate femtosecond optical parametric oscillator with the new nonlinear-optical crystal In:KTiOAsO 4 , which can potentially tune to 5.3 Am