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PubMed2005

Compact, passively Q-switched Nd:YAG laser for the MESSENGER mission to Mercury.

A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter, an instrument on the Mercury Surface, Space Environment, Geochemistry, and Ranging mission to the planet Mercury. The laser achieves 5.4% efficiency with a near-diffraction-limited beam. It passed all space-flight environmental tests at subsystem, instrument, and satellite integration testing and successfully completes a postlaunch aliveness check en route to Mercury. The laser design draws on a heritage of previous laser altimetry missions, specifically the Ice Cloud and Elevation Satellite and the Mars Global Surveyor, but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

Journal Article↗
PubMed2005

Retrieval of vertical constituents and temperature profiles from passive submillimeter wave limb observations of the Martian atmosphere: a feasibility study.

The investigation of the Martian atmosphere is of key importance for an understanding of the planets present and past. Passive limb observations of thermal radiation at submillimeter wavelengths in the 320-350-GHz range by use of a state-of-the-art satellite receiver on a low Mars orbit allow important parameters such as the mixing ratios of H2O, HDO, 12CO, 13CO, O3, and H2O2 as well as the thermal profile to be retrieved with high precision and unprecedented vertical range and resolution, providing valuable information for better understanding of the planet's water cycle, atmospheric dynamics, and photochemistry. The feasibility of these kinds of measurement is demonstrated by means of model simulations based on realistic atmospheric, spectroscopic, and instrumental parameters. Temperature can be retrieved to approximately 90 km with half-scale height vertical resolution from single-scan measurements of emission lines of the long-lived species 12CO and 13CO. The global water-vapor distribution can be measured even under dry or wet conditions with good vertical resolution from the surface to approximately 45 km, and simultaneous observations of HDO allow useful information on the D/H ratio up to an altitude of approximately 30 km to be derived. The sensitivity of the limb-sounding technique also permits information on the photochemically important minor species O3, and H2O2 to be obtained. It is shown that spectral averaging may improve precision, altitude range, and resolution of the retrieved profiles. Other frequency bands are explored, and the 435-465-GHz range is suggested as a possible alternative to the 320-350-GHz range.

Journal Article↗
PubMed2005

Imaging properties of rotating nulling interferometers.

Nulling interferometers combine on-axis suppression with high angular resolution, making them ideal instruments for the direct detection of faint planets close to their parent star. The synthesized point-spread function for a rotating nulling interferometer utilizing phase chopping is shown to consist of a main peak, satellite peaks, and their associated sidelobes, and simple analytic expressions are derived for the modulation efficiency and angular resolution. Sufficient angular resolution is vital for the detection and characterization of multiple-planet systems and requires that some configurations be substantially larger than previously thought. The corresponding increase in stellar leakage has a major effect on performance and can be a deciding factor in the choice of array configuration.

Journal Article↗
PubMed2006

Design of achromatic phase shifters for spaceborne nulling interferometry.

The designs of various achromatic phase shifters (APSs) envisaged for nulling interferometry and the search for extrasolar planets or systems from space are discussed in this Letter. It is shown that APS designs can sensibly influence the performance achieved by a simple Bracewell interferometer if they introduce a field of view (FoV) reversal and a pupil flip along one interferometer arm. Analytical and numerical simulations are presented, showing severe signal-to-noise ratio loss and a weak capacity for serendipitous discoveries. The use of FoV-reversal APS should therefore be restricted to the characterization of already known extrasolar planets rather than to their detection.

Journal Article↗
PubMed1997

Glucose homeostasis with infinite gain: further lessons from the Daisyworld parable?

A major unresolved physiological problem is how the rate of hepatic glucose production is increased to match the increased rate of glucose utilization during exercise without a change in arterial blood glucose level. A homeostat with such capabilities is said to have infinite gain. Daisyworld is an imaginary planet orbiting a variable star. The only life is black and white daisies. Black daisies retain heat, slightly warming the planet; white daisies cool it. When the two types of daisies grow best at slightly different temperatures, variations in solar luminosity (over a wide range) cause the ratio of white:black daisies to vary in a manner that keeps the planetary temperature constant. This model therefore achieves infinite gain by having two opposing but interdependent controllers. Here we suggest that the pancreatic islet alpha- and beta-cells might act as black and white daisies. For the analogy to apply, glucagon and insulin must not only have opposing effects on the blood sugar concentration, but the secretion of the one has, at some quantum level, to be at the expense of the other. Electrical coupling between heterocellular groups of alpha- and beta-cells within the pancreatic islets suggests that this might indeed be the case. alpha-Cell activity must, furthermore, promote secretory activity in other alpha-cells; similarly with beta-cells. This is probably mediated via pancreastatin and gamma-amino butyric acid (GABA) which are paracrinically co-secreted with glucagon and insulin, respectively. alpha-Cell activity spreads (at the expense of beta-cell activity) when the blood glucose level is below set point, while beta-cell activity progressively replaces alpha-cell activity above set point. At set point changes in the ratio of alpha:beta-cell activity are inhibited.

Chromogranin A↗
PubMed2003

[An encounter with extraterrestrial intelligence].

It is much easier to find extraterrestrial intelligence than to detect simple organisms living on other planets. However, it is hard to communicate with such intelligence without the mutual understanding of inter-stellar communication protocol. The radio SETI (The Search for Extra-Terrestrial Intelligence) was initiated with the pioneering work of F. Drake in 1960, one year after the historical SETI paper by Cocconi and Morrison. This talk explains that SETI evolves with two bases of science; the understanding of our universe and the development of technology. Since SETI has had strong connection with radio astronomy from its early beginning, the impacts of radio astronomical findings and technological breakthrough can be seen in many aspects of the SETI history. Topics of this talk include the detection of microwave 3 K background radiation in the universe. Interstellar atomic and molecular lines found in radio-wave spectra provide the evidence of pre-biotic chemical evolution in such region. Radio telescope imaging and spectral technique are closely associated with methodology of SETI. Topics of the talk extend to new Allen Telescope Array and projected Square Kilometer Array. Recent optical SETI and the discoveries of extra solar planets are also explained. In the end, the recent understanding of our universe is briefly introduced in terms of matter, dark matter and dark energy. Even our understanding of the universe has been evolutionarily revolved and accumulated after 1960, we must recognize that our universe is still poorly understood and that astronomy and SETI are required to proceed hand in hand.

Astronomy↗
PubMed1993

The effects of prolonged weightlessness and reduced gravity environments on human survival.

The manned exploration of the solar system and the surfaces of some of the smaller planets and larger satellites requires that we are able to keep the adverse human physiological response to long term exposure to near zero and greatly reduced gravity environments within acceptable limits consistent with metabolic function. This paper examines the physiological changes associated with microgravity conditions with particular reference to the weightless demineralizatoin of bone (WDB). It is suggested that many of these changes are the result of physical/mechanical processes and are not primarily a medical problem. There are thus two immediately obvious and workable, if relatively costly, solutions to the problem of weightlessness. The provision of a near 1 g field during prolonged space flights, and/or the development of rapid transit spacecraft capable of significant acceleration and short flight times. Although these developments could remove or greatly ameliorate the effects of weightlessness during long-distance space flights there remains a problem relating to the long term colonization of the surfaces of Mars, the Moon, and other small solar system bodies. It is not yet known whether or not there is a critical threshold value of 'g' below which viable human physiological function cannot be sustained. If such a threshold exists permanent colonization may only be possible if the threshold value of 'g' is less than that at the surface of the planet on which we wish to settle.

Adaptation, Physiological↗
PubMed2000

Extremophiles in astrobiology: per Ardua ad Astra.

As we consider the possibilities of finding life on other planets, it behooves us to evaluate what we know about the limits for life on planet Earth. In our continued exploration of Earth, we are finding microbes in a variety of unexpected habitats. In geothermal hot springs, we have discovered organisms thriving at temperatures near the boiling point of water and at pH values down to 0.5; in the deepest parts of the oceans, those that grow optimally at pressures above 1000 bars and die at pressures below 500 bars; and at the poles, those that grow below the freezing point of water and die at temperatures above 10 degrees C. All of these organisms are living proof that the biochemical "machinery" of life can be adapted to conditions that, from our anthropocentric perspective, appear to be extreme. By studying the molecular adaptations of extremophiles, we begin to identify the critical cellular components that expand the envelope for life. As an example, I will discuss what we have learned about the role of the proteins we call "heat shock proteins" in pushing the upper temperature limit of life and how our studies have provided a new perspective on the function of these proteins.

Adaptation, Physiological↗
PubMed1964

Problems in sterilization of unmanned space vehicles.

The probability of achieving and maintaining sterility of an unmanned spacecraft with varied suggested procedures is examined in detail, as are alternative techniques for avoiding biological contamination of the planets. The required degree of assurance against contamination of Mars, Venus and the Moon with Earth organisms is also considered. For Mars landers and orbiters, sterilization of the spacecraft or capsule by dry heat, with no subsequent access, is found to be desirable. For the present, sterilization of Venus landers still seems desirable. For Mars flybys, and for Venus orbiters and flybys, control of the trajectory to minimize the chance of unintentionally entering the planetary atmosphere appears the method of choice. For the Moon, sterilization seems unnecessary, but microbial counts should be kept low. Sterilization lowers spacecraft and system reliability. It reduces the chance of launching within periods fixed by astronomical constraints and increases costs. The gain which should be achieved through spacecraft sterilization, in return of significant biological information about the planets, must be balanced against these losses. In particular, one should keep in mind the loss in return of biological data occasioned by failure of a spacecraft to fulfill its mission; the probability of such failure is increased by sterilization.

Containment of Biohazards↗
PubMed1973

Organic analysis of lunar samples and the Martian surface.

In addition to the organogenic elements (H, C, N, O, S, P) which are necessary for the synthesis of organic molecules, the lunar samples from Apollo 11, 12, 14 and 15 contain substantial amounts (approximately equal to 10 to 100 microgram/g) of CO, N2 and CO2, which are released at relatively high temperatures and smaller amounts (approximately equal to 0.1 to 10 microgram/g) of more complex organic compounds (e.g. benzene). Most of these analyses have been performed by mass spectrometry or by combined gas chromatography-mass spectrometry after appropriate volatilization. The release of very small amounts of water has also been observed and is consistent with the findings of goethite (FeO.OH) and with measurements by the suprathermal ion detector. The lunar surface provides one of the less favorable solar system models for the synthesis of organic compounds yet small amounts of these compounds have been detected in the returned samples. It is reasonable to assume that the different physical and developmental features of the planet Mars (increased gravitational field, presence of an atmosphere with CO2, CO and H2O, recent volcanic and tectonic activity, etc.) would favor an increased organic content of the surface of this planet relative to the moon. Therefore the organic molecules present in the Martian soil should be measurable by miniaturized mass spectrometers after fractional distillation or gas chromatographic separation of the volatiles released by moderate heating.

Carbon Dioxide↗
PubMed1963

Perspectives for the development of exobiology.

In the majority of the papers dealing with the status and prospects of the development of exobiology a theoretical analysis predominates. More attention should be given to the discussion of methods and experiments carried out at the present time or planned for the near future. In investigating life in the cosmos, we attach considerable interest to detection of compounds specific to living beings, in particular, organic compounds of phosphorus, porphyrins, amino nitrogen and others. In searching for microorganisms on other planets and in interplanetary space the greatest danger is that, as a result of errors in technique, the investigator will detect earthly microorganisms which have invaded and reproduced in the nutrient mediums used. Information on the vitality of microbes detected in the ground taken in the zone of eternal frigidity, in big pieces of rock salt, in meteorites, etc. confirms these apprehensions. Initially, search for heterotrophic bacteria should be carried out, then for phototrophic, denitrifying, sulfate-reducing, nitrogen-fixing microorganisms, as well as bacteria oxydizing sulfur, iron, methane and hydrogen. Instruments for detection of cosmobionts can be based on nephelometry, potentiometry, manometry and on the use of carbon labelled compounds and added to the nutrient medium. Investigations elucidating the influence of low and high temperatures, vacuum, and radiation on living cells are possible to carry out on earth and therefore are most accessible to exobiology. They give interesting results and in some degree make it possible to approach the study of the conditions to which life would be exposed in space. The sterilization of space ships is of paramount importance for further exobiological investigations. Under space conditions microbes will not completely perish on the space ship surface and, therefore, careful sterilization is necessary. The assertion that earth microbes, having reached the lunar surface, will not be able to develop is not free of objections. To carry out sterilization so that space ships will not contain dead bodies of microbes is impossible. Therefore, the wish expressed sometimes that "carcasses" of microbes should not be conveyed onto other planets is practically unrealizable.

Containment of Biohazards↗
PubMed1971

Theoretical and experimental decisions in the creation of an artificial ecosystem for human life support in space.

All of man's former space flights were not real ventures into space in the biological sense, as his life was supported with unregenerated earth supplies. The coming stage of space exploration requires man's long existence in the cosmos and on the other planets. This stage of man's activity outside the earth become possible only by creating small man-made ecosystems, permitting the support of his metabolism by the recycling of substances of the terrestrial biosphere. Creation of such systems is a new scientific and technical task. Man-made ecosystems are a new product of man's activity, which have no complete analogy, either in nature, or in technology. Stochastic mechanisms, which stabilize biogeocenosis, cannot be effective in small ecosystems. A technique of parametric control over biosynthesis made it possible to calculate, and put to practice, an ecosystem for man with a cyclic regeneration of the atmosphere, water and, partially, food. The specific bio-technological properties of small man-made ecosystems are being analysed. The possibility of their application for man's excursions into space and for the settlement of other planets is being considered.

Bacteria↗
PubMedDate not supplied

The real problem.

I really was dismayed to see the basic cause of all our planet's problems buried in the September/October 96 issue: "...religious zealots might wreck the family planning needs of a billion people...." Let's face hard facts: all these problems would go away if the planet's population were small enough. What we really need to establish is what the population of the earth should be, and then set out to achieve that population as soon as possible. All of our efforts to reduce automobile pollution, the amount of reactor waste, the number of species being obliterated, etc., are just postponing the inevitable. What we need to look at, and keep track of, are those factors that encourage expanding population and discourage population control. For example, most businesses like to see the population expand so they can have a growing customer base. I truly appreciate your efforts. But if we are going to get anywhere we have to clearly identify the real problem. And then we have to break it down into manageable pieces and go to work on them. Otherwise we are going to keep looking at the graphs and wringing our hands as this accumulation of problems builds until it sweeps over us like a giant tsunami.

Conservation of Natural Resources↗
PubMed2003

Circadian light input in plants, flies and mammals.

The rotation of our planet results in daily changes in light and darkness, as well as seasons with characteristic photoperiods. Adaptation to these daily and seasonal changes in light properties (and associated changes in the environment) is important to the sustained survival of higher life forms on our planet. Many organisms use their intrinsic circadian oscillator or clock to orchestrate daily rhythms in behaviour and physiology to adapt to diurnal changes. Some higher organisms use the same oscillator to monitor day length in selecting the appropriate season for reproductive behaviour. Organisms have developed irradiance measurement mechanisms to ignore photic noise (lightning, moonlight), and use the light of dusk and dawn for circadian photoentrainment. They have also devised multiple photoreceptors and signalling cascades to buffer against changes in the spectral composition of natural light. The interaction of the clock with ambient light is, therefore, quite intricate.

Animals↗
PubMed2004

[The pegasys using and HCV genotype were the independent predictors of the response to antiviral therapy in chronic hepatitis C].

OBJECTIVE: To investigate the predictors of IFN therapy in patients with chronic hepatitis C through making the multivariate logistic regression analysis. METHODS: The patients in the opened, randomized and controlled trial were enrolled into two group, pegasys and Roferon-A group, and were given 24 weeks of pegasys (injection of 180 microg a week), and Roferon-A (injection three times of Roferon-A 3 MU a week) therapy, and followed 24 weeks. The HCV RNA content was determined at the time before, end of treatment and at the followed-up. The association of the response to the treatment with the clinical characteristics including age, gender, way of HCV infection, history of IFN treatment, planet count, AST/ALT ratio, HCV RNA level, HCV genotype and treatment drugs was made trough multivariate logistic regression analysis. RESULTS: The PP population containing 197 cases was analyzed. After controlling for age, gender, way of HCV infection, history of IFN treatment, planet count, AST/ALT ratio, HCV RNA level and treatment, the HCV genotype was not predictor of the end of treatment viral response (ETVR) to IFN therapy (OR 0.604, 95% CI 0.271-1.349, P = 0.219), but was the independent predictor of sustained viral response (SVR) (OR 0.408, 95% CI 0.189-0.881, P = 0.023). After controlling for other characteristics, the treatment drug was the predictors of ETVR (OR 0.105, 95% CI 0.052-0.212, P < 0.001) and SVR (OR 0.255, 95% CI 0.123-0.529, P < 0.001). CONCLUSION: The pegasys using and HCV genotype were the independent predictors of the response to antiviral therapy in chronic hepatitis C.

Adolescent↗
PubMed2006

Swimming upstream: faculty and staff members from urban middle schools in low-income communities describe their experience implementing nutrition and physical activity initiatives.

INTRODUCTION: Addressing childhood overweight has become a top priority in the United States. Modification of school policies and practices has been used in an attempt to address the overweight epidemic among children and adolescents. Culturally diverse urban schools in low-income communities attempting to improve nutrition and increase physical activity may face unique challenges in the school environment. A better understanding is needed about school environments and how they may affect the implementation, efficacy, and sustainability of initiatives designed to improve nutrition and physical activity. METHODS: We carried out a qualitative study in five urban middle schools in low-income communities that had recently implemented Planet Health, a nutrition and physical activity intervention, to assess which aspects of the schools' physical, social, and policy environments were facilitating or impeding the implementation of health promotion initiatives. Thirty-five faculty and staff members participated. We conducted one focus group per school, with an average of seven participants per group. We analyzed focus group transcripts using the thematic analysis technique to identify key concepts, categories, and themes. RESULTS: Teachers and staff members in our study identified many school-related environmental barriers to successful implementation of nutrition and physical activity initiatives in their schools. School personnel recommended that classroom-based nutrition interventions such as Planet Health be coordinated with school food services so that the healthy messages taught in the classroom are reinforced by the availability of healthy, culturally appropriate cafeteria food. They identified household food insufficiency and overly restrictive eligibility criteria of the federally subsidized meal program as critical barriers to healthy nutritional behaviors. They also identified weight-related teasing and bullying and unhealthy weight-control behaviors as challenges to promotion of healthy nutrition and physical activity. CONCLUSION: To maximize intervention efforts, researchers and practitioners must consider the effects of school environments on nutrition and physical activity initiatives.

Adolescent↗
PubMed1990

The early development and evolution of the human brain.

THE CHEMISTRY OF THE BRAIN: The brain and nervous system is characterised by a heavy investment in lipid chemistry which accounts for up to 60% of its structural material. In the different mammalian species so far studied, only the 20 and 22 carbon chain length polyenoic fatty acids were present and the balance of the n-3 to n-6 fatty acids was consistently 1:1. The difference observed between species, was not in the chemistry but in the extent to which the brain is developed. This paper discusses the possibility that essential fatty acids may have played a part in it evolution. THE ORIGIN OF AIR BREATHING ANIMALS: The first phase of the planet's existence indulged in high temperature reactions in which oxygen combined with everything feasible: from silicon to make rocks to hydrogen to make water. Once the planet's temperature dropped to a point at which water could condense on the surface allowing chemical reactions to take place in it. The atmosphere was at that time devoid of oxygen so life evolved in a reducing atmosphere. Oxygen was liberated by photolysis of water and as a by-product of the blue-green algae through photosynthesis. When the point was reached at which oxidative metabolism became thermodynamically possible, animal life evolved with all the principle phyla establishing themselves within a relatively short space of geological time. (Bernal 1973). DHA and nerve cell membranes DHA AND NERVE CELL MEMBRANES: From the chemistry of contemporary algae it is likely that animal life evolved in an n-3 rich environment although not exclusively so as smaller amounts of n-6 fatty acids would have been present. A key feature of the first animals was the evolution of the photoreceptor: in examples of marine, amphibian and modern mammalian species, it has been found to use docosahexaenoic acid (DHA) as the principle membrane fatty acid in the phosphoglycerides. It is likely that the first animals did so as well. Coincidentally, the synaptic membranes involved in signal transduction also use high proportions of n-3 fatty acids. However, the n-6 fatty acids also find a place, in the inositol phosphoglyceride (IPG) which appears to be involved with calcium ion transport and hence signal activation and reception. Even in the photoreceptor, the IPG is an arachidonic acid rich phosphoglyceride. THE EVOLUTION OF MAMMALS AND THE LARGE BRAIN: The dominance of n-3 fatty acids in the food chain, persisted until the end of the Cretaceous period when the flowering plants followed on the disappearance of the giant cycads and ferns. A new set of species, the mammals, then evolved with a requirement for n-6 fatty acids for reproduction. This dependance was coincident with the flowering plants which for the first time produced protected seeds: these introduced a rich source of n-6 fatty acids. The brain size of the mammals tended to be relatively larger (that is in relation to body size) by comparison with the previous reptilian or egg laying systems. This process led to the large human brain. A crucial difference between man and other animals, is undoubtedly the extent to which the brain and its peripheral attributes have been developed. This paper will address the possibility that the potential for the evolution of the large human brain may have been released by the evolving human primate occupying an ecological niche which offered a rich source of those nutrients specifically required for the brain. That niche is at the land/water interface.

Animals↗
PubMed1990

[Progress and new environmental emergencies: the earth at the limits of survival?].

This paper highlights the risks to which our planet as well as mankind are exposed as a result of the fast and dyshomogenous technological progress. Although this progress has permitted, on the one hand, greater prosperity (however not equally distributed among different peoples), on the other, it has changed the balance between the forces of Nature, thus threatening both our the planet's chances of survival. We are already on the alert; therefore, if we want to avoid dangerous consequences for future generations, we needs to ponder on this problem. We have to stop the "culture of arms", that every year dissipates the resources of industrialized countries. Consequently, let us aim at world peace in order to solve our problems and to guarantee healthy progress for the rising generations, without endangering the capability of the future ones.

Acid Rain↗