Accommodating controller malfunctions through fault tolerant control architecture

In previous work we have proposed a supervised globalized dual heuristic programming (GDHP) controller as a solution to the fault tolerant control (FTC) problem of nonlinear plants subject to abrupt and incipient faults capable of drastically modifying the system dynamics to maintain stability and performance. The neural network (NN) based adaptive critic controller presented the best choice for the flexibility and power necessary to accomplish the task, however no success guarantees can be made for the online training of neural weights for the unrestricted fault recovery problem. Built on the existing framework, we propose a novel supervisory system capable of detecting controller malfunctions before the stability of the plant is compromised. Furthermore, due to its ability to discern between controller malfunctions and faults within the plant, the proposed supervisor acts in a specific fashion in the event of a controller malfunction to provide new avenues with a greater probability of convergence using information from a dynamic model bank. The classification and distinction of controller malfunctions from the faults in the plant itself is achieved through an advanced decision logic based on three independent quality indexes. Proof-of-the-concept simulations over a nonlinear plant demonstrate the validity of the approach.     

Loss from Approximations to Square-Law Detectors in Quadrature Systems with Postdetection Integration

The trend toward digital processing of radar and sonar signals has ledto the use of ?baseband? or bipolar video signals. The processingof both the in-phase (I) and quadrature (Q) channels generally allows an exact representation of the signals, and no loss of sensitivity need occur. However, for reasons of economy or weight only one channel is often implemented. This correspondence shows that the sensitivity loss for this case often deviates considerably from the 3-dB rule of thumb.     

Rendezvous Navigation and Guidance Using a Hand-Held Self-Powered Digital Computer

This paper describes a simplified solution of the space rendezvous problem based on optical sightings taken with a hand-held sextant entered into and processed by a small digital computer. Compared to the manual method described in [1], this approach greatly reduces the astronaut's work load. Also, the computer can provide a more accurate solution, can present more flight plan options (allowing more tradeoffs between fuel usage and time), and can allow greater freedom in the sequencing of measurements and maneuvers. Physical characteristics, input-output parameters, and logic design of the computer are briefly described.     

Understanding plant-soil relationships using controlled environment facilities.

Although soil is a component of terrestrial ecosystems, it is comprised of a complex web of interacting organisms, and therefore can be considered itself as an ecosystem. Soil microflora and fauna derive energy from plants and plant residues and serve important functions in maintaining soil physical and chemical properties, thereby affecting net primary productivity (NPP), and in the case of contained environments, the quality of the life support system. We have been using 3 controlled-environment facilities (CEF's) that incorporate different levels of soil biological complexity and environmental control, and differ in their resemblance to natural ecosystems, to study relationships among plant physiology, soil ecology, fluxes of minerals and nutrients, and overall ecosystem function. The simplest system utilizes growth chambers and specialized root chambers with organic-less media to study the physiology of plant-mycorrhizal associations. A second system incorporates natural soil in open-top chambers to study soil bacterial and fungal population response to stress. The most complex CEF incorporates reconstructed soil profiles in a "constructed" ecosystem, enabling close examination of the soil foodweb. Our results show that closed ecosystem research is important for understanding mechanisms of response to ecosystem stresses. In addition, responses observed at one level of biological complexity may not allow prediction of response at a different level of biological complexity. In closed life support systems, incorporating soil foodwebs will require less artificial manipulation to maintain system stability and sustainability.     

Some aspects of psychophysiological support of crewmember's performance reliability in space flight

Crewmembers play an important role in ensuring the efficiency of "crew-spacecraft" system. However, despite of the fact that crewmembers are well trained and highly motivated persons, extreme flight factors may influence negatively on their reliability, and lead to human error occurrence. Therefore, working out methods of human error prevention is very significant to increase crewmember's performance reliability. Human error can occur in the operation of systems for a number of reasons. Within the framework of the present investigation, with use the data collected during "Mir" station missions, the significant (p<0.05) positive correlation of crewmembers errors (CE) frequency with their psychophysiological state (PPS), and work and rest schedule (WRS) intensity has been revealed. Differently, the higher WRS intensity, the crewmember's PPS is worse, and CE frequency is higher. This finding has been based on substantiations of the approach to human reliability management. Its essence will consist of the following: reducing WRS intensity, we thus can improve a crewmember's PPS and, accordingly, reduce CE frequency. This approach is discussed in the paper.     

The Tunguska event in 1908: evidence from tree-ring anatomy

We analyzed tree rings in wood samples collected from some of the few surviving trees found close to the epicenter (within 4-5 km) of the Tunguska event that occurred on the last day of June 1908. Tree-ring growth shows a depression starting in the year after the event and continuing during a 4-5-year period. The most remarkable traces of the event were found in the rings' anatomical structure: (1) formation of "light" rings and a reduction of maximum density in 1908; (2) non-thickened tracheids (the cells that make up most of the wood volume) in the transition and latewood zones (the middle and last-formed parts of the ring, respectively); and (3) deformed tracheids, which are located on the 1908 annual ring outer boundary. In the majority of samples, normal earlywood and latewood tracheids were formed in all annual rings after 1908. The observed anomalies in wood anatomy suggest two main impacts of the Tunguska event on surviving trees--(1) defoliation and (2) direct mechanical stress on active xylem tissue. The mechanical stress needed to fell trees is less than the stress needed to cause the deformation of differentiating tracheids observed in trees close to the epicenter. In order to resolve this apparent contradiction, work is suggested on possible topographic modification of the overpressure experienced by these trees, as is an experimental test of the effects of such stresses on precisely analogous growing trees.     

Haze aerosols in the atmosphere of early Earth: manna from heaven

An organic haze layer in the upper atmosphere of Titan plays a crucial role in the atmospheric composition and climate of that moon. Such a haze layer may also have existed on the early Earth, providing an ultraviolet shield for greenhouse gases needed to warm the planet enough for life to arise and evolve. Despite the implications of such a haze layer, little is known about the organic material produced under early Earth conditions when both CO(2) and CH(4) may have been abundant in the atmosphere. For the first time, we experimentally demonstrate that organic haze can be generated in different CH(4)/CO(2) ratios. Here, we show that haze aerosols are able to form at CH(4) mixing ratios of 1,000 ppmv, a level likely to be present on early Earth. In addition, we find that organic hazes will form at C/O ratios as low as 0.6, which is lower than the predicted value of unity. We also show that as the C/O ratio decreases, the organic particles produced are more oxidized and contain biologically labile compounds. After life arose, the haze may thus have provided food for biota.     

ALTEA: anomalous long term effects in astronauts. A probe on the influence of cosmic radiation and microgravity on the central nervous system during long flights.

The ALTEA project participates to the quest for increasing the safety of manned space flights. It addresses the problems related to possible functional damage to neural cells and circuits due to particle radiation in space environment. Specifically it aims at studying the functionality of the astronauts' Central Nervous Systems (CNS) during long space flights and relating it to the peculiar environments in space, with a particular focus on the particle flux impinging in the head. The project is a large international and multidisciplinary collaboration. Competences in particle physics, neurophysiology, psychophysiology, electronics, space environment, data analyses will work together to construct the fully integrated vision electrophysiology and particle analyser system which is the core device of the project: an helmet-shaped multi-sensor device that will measure concurrently the dynamics of the functional status of the visual system and passage of each particle through the brain within a pre-determined energy window. ALTEA is scheduled to fly in the International Space Station in late 2002. One part of the multi-sensor device, one of the advanced silicon telescopes, will be launched in the ISS in early 2002 and serve as test for the final device and as discriminating dosimeter for the particle fluences within the ISS.     

The first cell membranes

Organic compounds are synthesized in the interstellar medium and can be delivered to planetary surfaces such as the early Earth, where they mix with endogenous species. Some of these compounds are amphiphilic, having polar and nonpolar groups on the same molecule. Amphiphilic compounds spontaneously self-assemble into more complex structures such as bimolecular layers, which in turn form closed membranous vesicles. The first forms of cellular life required self-assembled membranes that were likely to have been produced from amphiphilic compounds on the prebiotic Earth. Laboratory simulations show that such vesicles readily encapsulate functional macromolecules, including nucleic acids and polymerases. The goal of future investigations will be to fabricate artificial cells as models of the origin of life.     

Electrification of Polymer Films in Laboratory and under Space Conditions

A simplified theory of the electrification of polymer films, which permits estimation of the internal electric fields of films irradiated by monoenergetic electrons simulating real streams of plasma electrons during magnetic substorms at a geosynchronous orbit, is suggested. To determine the depth behavior of the forward current and the dosage rate in the irradiated polymer, numerical calculations are made by the Monte Carlo technique. The appearance of electrostatic discharges in thin (5 m) mylar films is shown to be very probable in the orbit's shadow sector under magnetic substorm conditions.