Biochemical constraints for survival under Martian conditions.

A wide variety of terrestrial organisms, the so-called "anhydrobiotes," has learned to survive in a state of extreme dehydration in dry environments. Strategies for survival include the accumulation of certain polyols and nonreducing saccharides, which help to prevent damage to membranes and proteins, but at low water partial pressure DNA is also progressively damaged by various lesions, including strand breaks and cross-linking to proteins. These lesions, if they are not too numerous, can be repaired before the first replication step after rehydration, but long-term exposure to dry conditions finally diminishes the chances of survival as these lesions accumulate. If an organism has no chance to repair the accumulated DNA damage during intermittent periods of active life, survival will not exceed a few decades. The restriction of survival by dryness-induced DNA lesions is corroborated by new data on conidia of Aspergillus and the free plasmid pBR 322. Our results will be discussed with respect to the chance of finding dormant life or biochemical fossils on the surface of Mars.     

Leg venous hemodynamics and leg volumes during a 42 day -6 degrees head-down bedrest

Seven healthy subjects were submitted to a 42-day head down bedrest, where leg venous compliance (venous distensibity index VDI) and leg volumes were assessed by mercury strain gauge plethysmography with venous occlusion and optoelectronic plethysmography, respectively. Plethysmographic and volometric measurements were made, before, during (at days 1, 4, 7, 14, 21, 26, 34 and 41), and after bedrest (days 1, 4, 7, 11 and 30 of the recovery period). Results showed a continuous decrease in leg volumes throughout bedrest, when VDI increased until day 26 of bedrest, and then decreased afterwards. The recovery period was characterized by a rapid return of VDI to prebedrest levels while leg volumes progressively normalised. These results showed that leg venous compliance changes are not always dependant upon skeletal muscle changes, and that factors other than size of muscle compartment are able to determine increases in leg venous compliance during long-term bedrest.     

On the correlation between individual biochemical parameters of human blood serum following space flight and their basal values

The article presents data concerning the osmolality and concentration of electrolytes and hormones regulating their balance for blood serum of 223 cosmonauts and astronauts. The obtained results allow us to judge the constancy of physicochemical parameters for the blood serum of healthy individuals and how they react to extreme conditions of space flight. The parameters used for evaluation included not just absolute values for the examined indices, but also how they responded to space flight, the dependence on baseline values and the interrelationship between ions. These data are important to predict the effect of exposure to extreme conditions and point to what extent the effect depends on the characteristics of the individual.     

Effect of potassium and calcium loading on healthy subjects under hypokinesia and physical exercise with fluid and salt supplements

The objective of this investigation was to determine the acute responses to the electrolyte challenges under hypokinesia and physical exercise (PE) of different intensities with fluid and salt supplementation (FSS). The studies were performed on 12 physically healthy male volunteers aged 19-24 years under 364 days of hypokinesia (decreased number of steps per day) with a set of PE with FSS. The volunteers were divided into two equal groups. The first group was subjected to a set of intensive PE and the second group was submitted to a set of moderate PE. Both groups of subjects consumed daily water and salt supplements that aimed to increase the body hydration level. For simulation of the hypokinetic effect all subjects were kept under an average of 3000 steps per day. Functional tests with a potassium chloride (KCl) and calcium lactate (Cal) load were performed during the hypokinetic period of 364 days and the 60-day, prehypokinetic period that served as control, while both groups of subjects consumed daily calcium and potassium supplements. The concentration of electrolyte and hormone levels in the blood and their excretion rate in urine were determined. Renal excretion of calcium and potassium and the blood concentration thereof increased markedly in both groups of subjects. With the potassium chloride load tests the increased potassium excretion was accompanied by higher aldosterone and insulin blood levels, and with the calcium lactate load tests the increased calcium excretion was accompanied by a decreased parathyroid content in the blood. FSS and PE, regardless of intensity, failed to attenuate calcium and potassium losses. Additional intake of KCl and Cal also failed to normalize potassium and calcium abnormalities. It was concluded that during the KCl and Cal loading tests, the increased losses of potassium and calcium in the hypokinetic subjects were due to the inability of their bodies to retain these electrolytes, and that electrolyte abnormalities could not be reversed by PE or rehydration in individuals subjected to prolonged restriction of motor activity.     

绿色制造中的干切削技术

冷却润滑液的存储、使用以及废弃处理需要专门的物流系统,因而费用很高;冷却润滑液处理不当会对人的健康以及环境造成危害;工件经过湿加工后必须进行清洁处理,这都费时费力,同时增加了对系统的要求.基于上述原因,近年来干切削技术受到广泛关注.     

Satellite fault diagnosis using a bank of interacting Kalman filters

The main objective of this work is development and testing of a detection, isolation, and diagnosis algorithm based on interacting multiple model (IMM) filters for both partial (soft) and total (hard) reaction wheels faults in a spacecraft. This is shown to be accomplished under a number of different faulty mode scenarios for these actuators associated with the attitude control system (ACS) of a satellite. Various operating and faulty conditions due to changes and anomalies in the temperature, the power supply line voltage, and the loss of effectiveness of the torque and the current are considered in each reaction wheel associated with the three axes of the satellite. Once a fault mode is detected and isolated the recovery procedure can subsequently be engaged by invoking appropriate switching control strategies for the ACS. The application of a bank of interacting multiple Kalman filters for detection and diagnosis of anticipated reaction wheel failures in the ACS is described and developed. Compared with other model-based fault detection, diagnosis and isolation(FDDI) strategies developed in the control systems literature, our FDDI strategy is shown, through extensive numerical simulations, to be more accurate and robust with potential for extension to a number of other application areas.     

Discrete-time observability and estimability analysis for bearings-only target motion analysis

Observability in the context of bearings-only tracking (BOT) is still the subject of important literature. Different from previous approaches, where continuous-time analysis was considered, our approach relies on discrete-time analysis. It is then shown that this allows us to use directly and efficiently the simple formalisms of linear algebra. Using the direct approach, observability analysis is essentially reduced to basic considerations about subspace dimensions. Even if this approach is conceptually quite direct, it becomes more and more complex as the source-encounter scenario complexity increases. For complex scenarios, the dual approach may present some advantages essentially due to the direct use of multilinear algebra. New results about BOT observability for maneuvering sources are thus obtained. Observability analysis is then extended to unknown instants of source velocity changes. Even if observability analysis provides thorough insights about the algebraic structure of the BOT problem, the optimization of the observer maneuvers is essentially a control problem. Basic algebraic considerations prove that a relevant cost functional for this control problem is the determinant of the Fisher information matrix (FIM). So, a large part of this work is devoted to the analysis of this cost functional. Using multilinear algebra, general approximations of this functional are given. In order to involve only directly estimable parameters, the source bearing-rates are examined. Using these approximations, a general framework for optimizing the observer trajectory is derived which allow us to approximate the optimal sequence of controls. It is worth stressing that our approach does not require the knowledge of the source trajectory parameters and is still valid for a maneuvering source.     

Specification and Performance of Passive Sonar Spectral Estimators

The application of existing estimation theory to the problem of specification and performance of passive sonar spectral estimators is considered. The classification function is addressed, so that the signal is assumed to be present, and so that the energy arrival angle is known. The spatial filter considered is a line array of M equally spaced omnidirectional hydrophones. Signal and ambient noise are both zero-mean, wide-sense, stationary Gaussian random processes that differ in their spatial correlation across the face of the array. The signal is a plane wave that can be made totally spacially corrected between array elements by inserting delays between sensors to invert the signal propagation delay. The noise correlation is a function of frequency, bandwidth, element separation, and the relative time delay between sensors. Under these assumptions, the Cramer-Rao lower bound is derived for the class of unbiased estimates of signal power in a narrow frequency band at the hydrophone in the presence of correlated ambient noise of known power. The bound is examined numerically, resulting in a threshold phenomenon with M that constitutes a new design consideration. In addition, there is a striking insensitivity to realistic values of ambient noise correlation, and there are ranges in signal-to-noise ratio for which one gains more by increasing M than by increasing the bandwidth-time product. Specific processors, including a new unbiased estimator when noise power is unknown, are developed.     

A gentle process for the formation of Algols

This work is concerned with binary systems that we call ‘moderately close’. These are systems in which the primary (by which we mean the initially more massive star) fills its Roche lobe when it is on the giant branch with a deep convective envelope but before helium ignition (late case B). We find that if the mass ratio q(= M ₁/M ₂) < q _crit = 0.7 when the primary fills its Roche lobe positive feedback will lead to a rapid hydrodynamic phase of mass transfer which will probably lead to common envelope evolution and thence to either coalescence or possibly to a close binary in a planetary nebula. Although most Algols have probably filled their Roche lobes before evolving off the main-sequence we find that some could not have and are therefore ‘moderately close’. Since rapid overflow is unlikely to lead to an Algol-like system there must be some way of avoiding it. The most likely possibility is that the primary can lose sufficient mass to reduce q below q _crit before overflow begins. Ordinary mass loss rates are insufficient but evidence that enhanced mass loss does take place is provided by RS CVn systems that have inverted mass ratios but have not yet begun mass transfer. We postulate that the cause of enhanced mass loss lies in the heating of the corona by by magnetic fields maintained by an α — ω dynamo which is enhanced by tidal effects associated with corotation. In order to model the the effects of enhanced mass loss we ignore the details and adopt an empirical approach calibrating a simple formula with the RS CVn system Z Her. Using further empirical relations (deduced from detailed stellar models) that describe the evolution of red giants we have investigated the effect on a large number of systems of various initial mass ratios and periods. These are notable in that some systems can now enter a much gentler Algol-like overflow phase and others are prevented from transferring mass altogether. We have also investigated the effects of enhanced angular momentum loss induced by corotation of the wind in the strong magnetic fields and consider this in relation to observed period changes. We find that a typical ‘moderately close’ Algol-like system evolves through an RS CVn like system and then possibly a symbiotic state before becoming an Algol and then goes on through a red giant-white dwarf state which may become symbiotic before ending up as a double white dwarf system in either a close or wide orbit depending on how much mass is lost before the secondary fills its Roche lobe.