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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Experiments with suspended cells on the Space Shuttle
Spaceflight experiments since 1981 have demonstrated that certain cell functions are altered by micro-g. Biophysical models suggest that cell membranes and organelles should not be affected directly by gravity, however, the chemical microenvironment surrounding the cell and molecular transport could be altered by reduced gravity. Most experiments have used suspended live cells in small chambers without stirring or medium exchange. Flight results include increased attachment of anchorage-dependent human cells to collagen coated microcarriers, reduced secretion of growth hormone from pituitary cells, decreased mitogenic response of lymphocytes, increased Interferon-alpha by lymphocytes, increased Interleukin-1 and Tumor Necrosis Factor secretion by macrophages. Related experiments on cells immediately postflight and on procaryotic cells have shown significant changes in secretory capacity, cell proliferation, differentiation and development. Postulated mechanism include altered cell-cell interactions, altered calcium ion transport, effects on cell cytoskeleton, transport of transmitters and interactions with receptors. The discussion includes use of new molecular methods, considerations for cell environmental control and a preview of several experiments planned for the Shuttle and Spacelab flights to study the basic effects of microgravity on cellular physiology and potential interactions of spaceflight with radiation damage and cellular repair mechanisms.
Endurance exercise training and treatment of hypertension. The controversy
No abstract available
Imaging of the hip joint. Computed tomography versus magnetic resonance imaging
The authors reviewed the applications and limitations of computed tomography (CT) and magnetic resonance (MR) imaging in the assessment of the most common hip disorders. Magnetic resonance imaging is the most sensitive technique in detecting osteonecrosis of the femoral head. Magnetic resonance reflects the histologic changes associated with osteonecrosis very well, which may ultimately help to improve staging. Computed tomography can more accurately identify subchondral fractures than MR imaging and thus remains important for staging. In congenital dysplasia of the hip, the position of the nonossified femoral head in children less than six months of age can only be inferred by indirect signs on CT. Magnetic resonance imaging demonstrates the cartilaginous femoral head directly without ionizing radiation. Computed tomography remains the imaging modality of choice for evaluating fractures of the hip joint. In some patients, MR imaging demonstrates the fracture even when it is not apparent on radiography. In neoplasm, CT provides better assessment of calcification, ossification, and periosteal reaction than MR imaging. Magnetic resonance imaging, however, represents the most accurate imaging modality for evaluating intramedullary and soft-tissue extent of the tumor and identifying involvement of neurovascular bundles. Magnetic resonance imaging can also be used to monitor response to chemotherapy. In osteoarthrosis and rheumatoid arthritis of the hip, both CT and MR provide more detailed assessment of the severity of disease than conventional radiography because of their tomographic nature. Magnetic resonance imaging is unique in evaluating cartilage degeneration and loss, and in demonstrating soft-tissue alterations such as inflammatory synovial proliferation.
Optical remote measurement of toxic gases
Enactment of the Clean Air Act Amendments (CAAA) of 1990 has resulted in increased ambient air monitoring needs for industry, some of which may be met efficiently using open-path optical remote sensing techniques. These techniques include Fourier transform spectroscopy, differential optical absorption spectroscopy, laser long-path absorption, differential absorption lidar, and gas cell correlation spectroscopy. With this regulatory impetus, it is an opportune time to consider applying these technologies to the remote and/or path-averaged measurement and monitoring of toxic gases covered by the CAAA. This article reviews the optical remote sensing technology and literature for that application.
Environmental mycology and its importance to public health
No abstract available
Reaction cycle and thermodynamics in bacteriorhodopsin
Light causes the all-trans to 13-cis isomerization of the retinal in bacteriorhodopsin; the thermal relaxation leading back to the initial state drives proton transport first via proton transfer between the retinal Schiff base and D85 and then between the Schiff base and D96. The reaction sequence and thermodynamics of this photocycle are described by measuring time-resolved absorption changes with a gated multichannel analyzer between 100 ns and 100 ms, at six temperatures between 5 degrees C and 30 degrees C. Analysis of the energetics of the chromophore reaction sequence is on the basis of a recently proposed model (Varo & Lanyi, Biochemistry 30, 5016-5022, 1991) which consists of a single cycle and many reversible reactions: BR -hv-->K<==>L<==>M1-->M2<==>N<==>O-->BR. The existence of the M1-->M2 reaction, which functions as the switch in the proton transfer, is confirmed by spectroscopic evidence. The calculated thermodynamic parameters indicate that the exchange of free energy between the protein and the protons is at the switch step. Further, a large entropy decrease at this reaction suggests a protein conformation change which will conserve delta G for driving the completion of the reaction cycle. The results provide insights to mechanism and energy coupling in this system, with possible relevance to the general question of how ion pumps function.
Extracellular matrix and cell shape: potential control points for inhibition of angiogenesis
Capillary endothelial (CE) cells require two extracellular signals in order to switch from quiescence to growth and back to differentiation during angiogenesis: soluble angiogenic factors and insoluble extracellular matrix (ECM) molecules. Soluble endothelial mitogens, such as basic fibroblast growth factor (FGF), act over large distances to trigger capillary growth, whereas ECM molecules act locally to modulate cell responsiveness to these soluble cues. Recent studies reveal that ECM molecules regulate CE cell growth and differentiation by modulating cell shape and by activating intracellular chemical signaling pathways inside the cell. Recognition of the importance of ECM and cell shape during capillary morphogenesis has led to the identification of a series of new angiogenesis inhibitors. Elucidation of the molecular mechanism of capillary regulation may result in development of even more potent angiogenesis modulators in the future.
A contribution with review to the description of mineralization of bone and other calcified tissues in vivo
This manuscript considers certain aspects of mineral deposition in bone and other vertebrate calcifying tissues in order to examine physical, chemical, and biological factors important in the mineralization process. The paper in a discussion format principally presents a new data and the formulation of concepts based on such data as well as a summary of background material as necessary review. Mineralization is found to occur at spatially independent sites throughout the organic extracellular tissue matrices. Matrix vesicles and collagen fibrils each may serve as independent nucleation centers for mineral with vesicle mineralization being local and collagen mineralization dominating the tissues as a whole. Collagen fibril organization is suggested to be such that hole zones are aligned in three dimensions, creating extensive channels for mineral accommodation. Nucleation occurs initially in hole zones and crystal growth leads to the development of plate-like mineral particles whose orientation, disposition, and sizes within fibrils are detailed. Effects of diffusion, crystallinity, and critical nucleation and growth events are described with respect to their influence on mineral deposition in bulk and local regions of tissue matrices.
Molecular and cellular adaptation of muscle in response to exercise: perspectives of various models
No abstract available
Physical and psychosocial effects of antepartum hospital bedrest: a review of the literature
No abstract available
A model for diurnal patterns of carbon fixation in a Precambrian microbial mat based on a modern analog
Microbial mat communities are one of the first and most prevalent biological communities known from the Precambrian fossil record. These fossil mat communities are found as laminated sedimentary rock structures called stromatolites. Using a modern microbial mat as an analog for Precambrian stromatolites, a study of carbon fixation during a diurnal cycle under ambient conditions was undertaken. The rate of carbon fixation depends primarily on the availability of light (consistent with photosynthetic carbon fixation) and inorganic carbon, and not nitrogen or phosphorus. Atmospheric PCO2 is thought to have decreased from 10 bars at 4 Ga (10(9) years before present) to approximately 10(-4) bars today, implying a change in the availability of inorganic carbon for carbon fixation. Experimental manipulation of levels of inorganic carbon to levels that may have been available to Precambrian mat communities resulted in increased levels of carbon fixation during daylight hours. Combining these data with models of daylength during the Precambrian, models are derived for diurnal patterns of photosynthetic carbon fixation in a Precambrian microbial mat community. The models suggest that, even in the face of shorter daylengths during the Precambrian, total daily carbon fixation has been declining over geological time, with most of the decrease having occurred during the Precambrian.
Determinants of the mechanical properties of bones
The mechanical properties of bones are governed by the same principles as those of man-made load-bearing structures, but the organism is able to adapt its bone structure to changes in skeletal loading. In this overview of the determinants of the strength and stiffness of bone, a continuum approach has been taken, in which the behavior of a macroscopic structure depends on its shape and size, and on the mechanical properties of the material within. The latter are assumed to depend on the composition (porosity and mineralization) and organization (trabecular or cortical bone architecture, collagen fiber orientation, fatigue damage) of the bone. The effects of each of these factors are reviewed. Also, the possible means of non-invasively estimating the strength or other mechanical properties of a bone are reviewed, including quantitative computed tomography, photon absorptiometry, and ultrasonic measurements. The best estimates of strength have been obtained with photon absorptiometry and computed tomography, which at best are capable of accounting for 90% of the strength variability in a simple in vitro test, but results from different laboratories have been highly variable.
Properties of calcium channels isolated with spider toxin, FTX
No abstract available
Metabolic consequences of resistive-type exercise
This brief review concerns acute and chronic metabolic responses to resistive-type exercise (RTE) (i.e., Olympic/power weight lifting and bodybuilding). Performance of RTE presents power output substantially greater (10-15-fold) than that evident with endurance-type exercise. Accordingly, RTE relies heavily on the anaerobic enzyme machinery of skeletal muscle for energy supply, with alterations in the rate of aerobic metabolism being modest. Hydrolysis of high energy phosphate compounds (PC, ATP), glycogenolysis, and glycolysis are evident during an acute bout of RTE as indicated by metabolic markers in mixed fiber type skeletal muscle samples. The type of RTE probably influences the magnitude of these responses since the increase in blood lactate is much greater during a typical "bodybuilding" than "power lifting" session. The influence of RTE training on acute metabolic responses to RTE has received little attention. An individual's inherent metabolic characteristics are apparently sufficient to meet the energy demands of RTE as training of this type does not increase VO2max or substantially alter the content of marker enzymes in mixed fiber type skeletal muscle. Analyses of pools of fast- vs slow-twitch fibers, however, indicate that RTE-induced changes may be fiber type specific. Future studies should better delineate the metabolic responses to RTE and determine whether these are related to the enhanced performance associated with such training.
Environmental stressors during space flight: potential effects on body temperature
1. Organisms may be affected by many environmental factors during space flight, e.g., acceleration, weightlessness, decreased pressure, changes in oxygen tension, radiofrequency radiation and vibration. 2. Previous studies of change in body temperature--one response to these environmental factors--are reviewed. 3. Conditions leading to heat stress and hypothermia are discussed.