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At least 73 records · Page 4

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NASA NTRS1991

Gravity effects on reproduction, development, and aging

The effects of various levels of gravity force (obtained by rotation in clinostats or by centrifugation) and the near-weightlessness condition aboard orbiting spacecraft on the fertilization, embryonic development, maturation, and aging of animals are examined. Results obtained from the American and Soviet spaceborne biology experiments are presented including those on mammals, amphibians, fish, birds, invertebrates, and protozoa. Theoretical issues related to the effect of gravity on various physiological systems are discused together with the future research goals concerning human life in space. It is noted that life in space (after adaptation to near-weightlessness) might be significantly prolonged due to a reduction in metabolic rate and a concomitant decrease in oxygen radical reactions.

Miquel, Jaime↗

NASA NTRS2000

Modeling and Observations of Phase-Mask Trapezoidal Profiles with Grating-Fiber Image Reproduction

We report on an investigation of the trapezoidal design and fabrication defects in phase masks used to produce Bragg reflection gratings in optical fibers. We used a direct visualization technique to examine the nonuniformity of the interference patterns generated by several phase masks. Fringe patterns from the phase masks are compared with the analogous patterns resulting from two-beam interference. Atomic force microscope imaging of the actual phase gratings that give rise to anomalous fringe patterns is used to determine input parameters for a general theoretical model. Phase masks with pitches of 0.566 and 1.059 microns are modeled and investigated.

Lyons, Donald R.↗

NASA NTRS2002

Experimental Reproduction of Type 1B Chondrules

We have replicated type 1B chondrule textures and compositions with crystallization experiments in which UOC material was melted at 1400 deg.C and cooled at 5-1000 deg.C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment. Additional information is contained in the original extended abstract.

Lofgren, G. E.↗

NASA NTRS2002

Who or What? Self-Replication and Function-Reproduction in the Origin of Life

In this presentation, we will present results on the fundamental properties of two classes of replicating systems: autocatalytic replicators that reproduce exact copies of a template molecule, and function reproducers that maintain a set of essential functions without replicating the identities of the functional moieties. We will describe the stability and behavior in-the-large of autocatalytic replicators. Most importantly, we have found no sharp distinction between an autocatalytic and a non-autocatalytic domain. We will also present a new derivation of von Kiedrowski's square-root rate law. Function - reproducers are proposed as an important component of protocells and we will present theoretical results on a simple model system that incorporates known peptide biophysics. For a wide range of parameters, we have shown that this type of system can improve its overall performance, even in the absence of any method for information storage. This type of system improvement is defined to be non-genomic evolution.

New, Michael H.↗

NASA NTRS2003

Dynamic Crystallization Experiments on LEW97008: Experimental Reproduction of Chondroid Textures

Dynamic crystallization experiments were conducted using LEW97008 (L3.4) as starting material. Experiments were melted at temperatures well below its liquidus (1250-1450 C) in order to document the textural and compositional changes that occur in UOC material with modest amounts of partial melting and subsequent crystallization. The textures of the experimental products compare very well to natural chondroids (partially melted nebular particles that would become chondrules if more completely melted). Thus it is possible to use the textures in these experiments as a guide to unraveling the melting and cooling histories of natural chondroids. The Antarctic meteorite LEW97008 was chosen as the starting material for our experiments. As an L3.4 it is slightly more metamorphosed than would ordinarily be preferred, but this meteorite is unusually fresh for an Antarctic meteorite, which made it attractive.

Nettles, J. W.↗

NASA NTRS2003

Common endocrine control of body weight, reproduction, and bone mass

Bone mass is maintained constant between puberty and menopause by the balance between osteoblast and osteoclast activity. The existence of a hormonal control of osteoblast activity has been speculated for years by analogy to osteoclast biology. Through the search for such humoral signal(s) regulating bone formation, leptin has been identified as a strong inhibitor of bone formation. Furthermore, intracerebroventricular infusion of leptin has shown that the effect of this adipocyte-derived hormone on bone is mediated via a brain relay. Subsequent studies have led to the identification of hypothalamic groups of neurons involved in leptin's antiosteogenic function. In addition, those neurons or neuronal pathways are distinct from neurons responsible for the regulation of energy metabolism. Finally, the peripheral mediator of leptin's antiosteogenic function has been identified as the sympathetic nervous system. Sympathomimetics administered to mice decreased bone formation and bone mass. Conversely, beta-blockers increased bone formation and bone mass and blunted the bone loss induced by ovariectomy.

NASA Discipline Regulatory Physiology↗

NASA NTRS2005

Experimental Reproduction of Olivine rich Type-I Chondrules

Ordinary chondritic meteorites are an abundant type of stony meteorite characterized by the presence of chondrules. Chondrules are small spheres consisting of silicate, metal, and sulfide minerals that experienced melting in the nebula before incorporation into chondritic meteorite parent bodies. Therefore, chondrules record a variety of processes that occurred in the early solar nebula. Two common types of unequilibrated chondrules with porphyritic textures include FeO-poor (type I) and FeO-rich (type II) each subdivided into an A (SiO2-poor) and B (SiO2-rich) series. Type IA chondrules include those with high proportions of olivine phenocrysts (>80% olivine) and type IB chondrules include those with high proportions of pyroxene phenocrysts (<20% olivine). An intermediate composition, type IAB chondrules include those chondrules in which the proportion of olivine phenocrysts is between 20-80%. We conducted high-temperature laboratory experiments (melting at 1550 C) to produce type I chondrules from average unequilibrated ordinary chondrite (UOC) material mixed with small amounts of additional olivine. The experiments were conducted by adding forsteritic rich olivine (San Carlos olivine, Fo 91) to UOC material (GRO 95544) in a 30/70 ratio, respectively. Results of these high temperature experiments suggest that we have replicated type IA chondrule textures and compositions with dynamic crystallization experiments in which a heterogeneous mixture of UOC (GRO 95544) and olivine (San Carlos olivine) were melted at 1550 C for 1 hr. and cooled at 5-1000 C/hr using graphite crucibles in evacuated silica tubes to provide a reducing environment.

Smith, Robert K.↗

NASA NTRS2005

Reproductive Ecology Of The Florida Scrub-Jay (Aphelocoma Coerulescens) On John F. Kennedy Space Center/Merritt Island National Wildlife Refuge: A Long-Term Study

From 1988 to 2002 we studied the breeding ecology of Florida Scrub-Jays (Aphelocoma coerulescens) on John F. Kennedy Space Center/Merritt Island National Wildlife Refuge. We examined phenology, clutch size, hatching failure rates, fledgling production, nest success, predation rates, sources egg and nestling mortality, and the effects of helpers on these measures. Nesting phenology was similar among sites. Mean clutch size at Titan was significantly larger than at HC or T4. Pairs with helpers did not produce larger clutches than pairs without helpers. Fledgling production at T4 was significantly greater than at HC and similar to Titan. Pairs with helpers at HC produced significantly more fledglings than pairs without helpers; helpers did not influence fledgling production at the other sites. Nest success at HC and Titan was low, 19% and 32% respectively. Nest success at T4 was 48% and was significantly greater than at HC. Average predation rates at all sites increased with season progression. Predation rates at all sight rose sharply by early June. The main cause of nest failure at all sites was predation, 93%.

Carter, Geoffry M.↗

NASA NTRS2006

JSC Materials Laboratory Reproduction and Failure Analysis of Cracked Orbiter Reaction Control System Niobium Thruster Injectors

In April 2004 a Space Shuttle Orbiter Reaction Control System (RCS) thruster was found to be cracked while undergoing a nozzle (niobium/C103 alloy) retrofit. As a failure resulting from an in-flight RCS thruster burn-through (initiated from a crack) could be catastrophic, an official Space Shuttle Program flight constraint was issued until flight safety could be adequately demonstrated. This paper describes the laboratory test program which was undertaken to reproduce the cracking in order to fully understand and bound the driving environments. The associated rationale developed to justify continued safe flight of the Orbiter RCS system is also described. The laboratory testing successfully reproduced the niobium cracking, and established specific bounding conditions necessary to cause cracking in the C103 thruster injectors. Each of the following conditions is necessary in combination together: 1) a mechanically disturbed / cold-worked free surface, 2) an externally applied sustained tensile stress near yield strength, 3) presence of fluorine-containing fluids on exposed tensile / cold-worked free surfaces, and 4) sustained exposure to temperatures greater than 400 F. As a result of this work, it was concluded that fluorine-containing materials (e.g. HF acid, Krytox , Brayco etc.) should be carefully controlled or altogether eliminated during processing of niobium and its alloys.

Castner, Willard L.↗

NASA NTRS1995

Adaptive noise reduction circuit for a sound reproduction system

A noise reduction circuit for a hearing aid having an adaptive filter for producing a signal which estimates the noise components present in an input signal. The circuit includes a second filter for receiving the noise-estimating signal and modifying it as a function of a user's preference or as a function of an expected noise environment. The circuit also includes a gain control for adjusting the magnitude of the modified noise-estimating signal, thereby allowing for the adjustment of the magnitude of the circuit response. The circuit also includes a signal combiner for combining the input signal with the adjusted noise-estimating signal to produce a noise reduced output signal.

Engebretson, A. Maynard↗

NASA NTRS1998

Adaptive gain and filtering circuit for a sound reproduction system

Adaptive compressive gain and level dependent spectral shaping circuitry for a hearing aid include a microphone to produce an input signal and a plurality of channels connected to a common circuit output. Each channel has a preset frequency response. Each channel includes a filter with a preset frequency response to receive the input signal and to produce a filtered signal, a channel amplifier to amplify the filtered signal to produce a channel output signal, a threshold register to establish a channel threshold level, and a gain circuit. The gain circuit increases the gain of the channel amplifier when the channel output signal falls below the channel threshold level and decreases the gain of the channel amplifier when the channel output signal rises above the channel threshold level. A transducer produces sound in response to the signal passed by the common circuit output.

Engebretson, A. Maynard↗

NASA NTRS1998

Adaptive gain and filtering circuit for a sound reproduction system

Engebretson, A. Maynard↗

NASA NTRSDate not supplied

Experimental reproduction of space weathering of C-type asteroids by He exposure: irradiation-energy and physical-property dependence

Visible and near-infrared observations of C-type asteroid 162173 Ryugu suggest that the surface color variation seems to have resulted from a surface-correlated process which changed the color from blue to red, but the mechanism for the change is not yet identified. Space weathering is one possible mechanism responsible for the color variation, but the spectral changes of C-type asteroids from space weathering are not yet fully understood. We have carried out He exposure experiments on hydrous carbonaceous chondrites in order to understand the irradiation-energy and the physical-property dependence of space weathering of C-type asteroids. He exposure to different porosities of the same meteorite samples results in different behavior of spectral changes. In addition, the meteorite samples with the same porosity and the same surface roughness show different spectral changes when the samples are exposed to He ions with different energies. Therefore, our experiments indicate that spectral changes by space weathering of C-type asteroids depend not only on the asteroid types but also on the physical properties of the regolith surface and the solar-wind He energy.

Michael E Zolensky↗

NASA NTRSDate not supplied