SEARCH · Engineering Papers

Results for “activation function”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53

All sources NASA NTRS DOE OSTI

NASA NTRS1983

A design procedure for active control of beam vibrations

The transverse vibrations of beams is discussed and a methodology for the design of an active damping device is given. The Bernoulli-Euler equation is used to derive a transcendental transfer function, which relates a torque applied at one end of the beam to the rotational position and velocity at that point. The active damping device consists of a wire, a linear actuator and a short torque arm attached to one end of the beam. The action of the actuator varies a tension in the wire and creates a torque which opposes the rotation of the beam and thus damps vibration. A design procedure for such an active damper is given. This procedure shows the relationships and trade-offs between the actuator stroke, power required, stress levels in the wire and beam and the geometry of the beam and wire. It is shown that by consideration of the frequency response at the beam natural frequencies, the aforementioned relationships can be greatly simplified. Similarly, a simple way of estimating the effective damping ratios and eigenvalue locations of actively controlled beams is presented.

Dickerson, S. L.↗

NASA NTRS2018

Integrating Orbital Debris Measurements and Modeling - How Observations and Laboratory Data are used to Help Make Space Operations Safer

The NASA Orbital Debris Program Office has been statistically surveying human-made resident space objects (RSOs) in geocentric orbits for several decades, using optical and infrared telescopes. The prime goal has been to understand the evolving population and characteristics of debris generated by RSOs. The debris population includes any non-functioning RSO that no longer serves a useful purpose. Any object that cannot be purposely maneuvered, including non-functioning satellites, rocket bodies, and any object generated by a collision, explosion, or fragmentation event, may pose a future collisional threat to active satellites. Key questions immediately surface from this knowledge: What can we do to protect our precious functioning satellites from collisions? How do we design our satellites to prevent them from being future sources of debris? And what can we do as a society to protect the environment surrounding Earth to preserve it for future generations? To begin to address these questions, and to better understand this population as well as break-up events contributing to it, NASA has developed a suite of models and experimental laboratory data to work in tandem with observational and laboratory measurements of RSOs. These models include the Orbital Debris Engineering Model (ORDEM), the Standard Satellite Break-up Model (SSBM), and an evolutionary model of the environment from LEO to GEO (LEGEND). Ground-based data have been collected from the infrared telescope UKIRT (UK Infrared Telescope) in Hawaii, as well as the 1.3m Eugene Stansbery Meter Class Autonomous Telescope, ES-MCAT, historically called MCAT, on Ascension Island. MCAT will be tasked to collect GEO (Geosynchronous) survey data, scanning orbits to search for uncatalogued objects (e.g. fragmentation/break-up events (SSBM)), and targeted observations of catalogued objects for more intensive studies, e.g. when a break-up or anomalous event occurs. Laboratory experimental data includes DebriSat, a satellite impacted at ~6.9 km/s in an impact laboratory on Earth, and optical photometry from the Optical Measurements Center at NASA JSC. An integrated view will be discussed of how our telescopic observations and lab measurements interplay with models to understand the current (ORDEM) and future (LEGEND) environment, the evolution of satellite breakups (SSBM), and how this knowledge can help to promote an environment that is safer for operations.

Lederer, S. M.↗

NASA NTRS1991

An investigation of the distribution of eruptive products on the shield volcanoes of the western Galapagos Islands using remotely sensed data

Recent volcanic activity in the Galapagos Islands is concentrated on the two westernmost islands, Isla Isabela and Isla Fernandina. Difficult access has thus far prevented comprehensive geological field studies, so we examine the potential of remotely sensed data as a means of studying volcanic processes in the region. Volcan Wolf is used as an example of the analysis of SPOT HRV-1 data undertaken for each volcano. Landsat TM data are analyzed in an attempt to construct a relative age sequence for the recent eruptive activity on Isla Fernandina. No systematic variation in the surface reflectance of lava flows as a function of age could be detected with these data. Thus it was not possible to complete a study of the temporal distribution of volcanic activity.

Munro, Duncan C.↗

NASA NTRS2001

Ecological physiology of Synechococcus sp. strain SH-94-5, a naturally occurring cyanobacterium deficient in nitrate assimilation

Synechococcus sp. strain SH-94-5 is a nitrate assimilation-deficient cyanobacterium which was isolated from an ammonium-replete hot spring in central Oregon. While this clone could grow on ammonium and some forms of organic nitrogen as sole nitrogen sources, it could not grow on either nitrate or nitrite, even under conditions favoring passive diffusion. It was determined that this clone does not express functional nitrate reductase or nitrite reductase and that the lack of activity of either enzyme is not due to inactivation of the cyanobacterial nitrogen control protein NtcA. A few other naturally occurring cyanobacterial strains are also nitrate assimilation deficient, and phylogenetic analyses indicated that the ability to utilize nitrate has been independently lost at least four times during the evolutionary history of the cyanobacteria. This phenotype is associated with the presence of environmental ammonium, a negative regulator of nitrate assimilation gene expression, which may indicate that natural selection to maintain functional copies of nitrate assimilation genes has been relaxed in these habitats. These results suggest how the evolutionary fates of conditionally expressed genes might differ between environments and thereby effect ecological divergence and biogeographical structure in the microbial world.

Nitrates/metabolism↗

NASA NTRSDate not supplied

Temporal Changes in Astronauts’ Muscle and Cardiorespiratory Physiology Before, During, and After Spaceflight

NASA’s planned space exploration missions will require astronauts to safely perform extravehicular activity (EVA) and to safely egress vehicles in a variety of landing scenarios. Prolonged exposure to spaceflight decreases cardiovascular and sensorimotor function, causes loss of bone mineral density, reduces muscle mass and strength, and ultimately diminishes tolerance for physical activity. Although exercise can help mitigate these spaceflight-induced physiological decrements, little is known regarding the time-course of changes in muscle and aerobic performance during spaceflight. Furthermore, these exercise countermeasures are not fully protective. For example, maximal aerobic capacity (VO2pk), lower body muscle cross-sectional area, and strength all decrease by about 10% to 15% after long-duration missions on the International Space Station (ISS). Future long-duration space missions beyond Low Earth Orbit will employ exploration vehicles with less robust exercise hardware and more constrained exercise capabilities (e.g., less operational volume, less active exercise time) than provided on the ISS. Thus, countermeasures will need to be optimized to protect crew health and performance on exploration-class missions lasting up to 3 years. This requires a more detailed understanding of the dynamic effects of spaceflight on human health and performance, the ability of exercise to protect against this deconditioning, and the interaction of exercise with interrelated factors like nutrition, sleep, and environmental conditions.

N.C. Strock↗

NASA NTRSDate not supplied

Temporal Changes in Astronauts’ Muscle and Cardiorespiratory Physiology Before, During, and After Spaceflight

N. Strock↗

NASA NTRS1984

Space Station concept development group studies

The NASA study activities in preparation for a Space Station began in the early 1970's. The early studies included many in-house NASA and contracted studies. A group of representatives from all the NASA Centers, titled the Space Station Concept Development Group (CDG) was involved in the studies which led to the initiation of the Space Station Program. The CDG studies were performed over a period of approximately one year and consisted of four phases. The initial phase had the objective to determine the functions required of the station as opposed to a configuration. The activities of the second phase were primarily concerned with a sizing of the facilities required for payloads and the resources necessary to support these mission payloads. The third phase of studies was designed to develop a philosophical approach to a number of areas related to autonomy, maintainability, operations and logistics, and verification. The fourth phase of the study was to be concerned with configuration assessment activities.

Powell, L. E.↗

NASA NTRS2016

Reconstruction of Cysteine Biosynthesis Using Engineered Cysteine-Free and Methionine-Free Enzymes

Ten of the proteinogenic amino acids can be generated abiotically while the remaining thirteen require biology for their synthesis. Paradoxically, the biosynthesis pathways observed in nature require enzymes that are made with the amino acids they produce. For example, Escherichia coli produces cysteine from serine via two enzymes that contain cysteine. Here, we substituted alternate amino acids for cysteine and also methionine, which is biosynthesized from cysteine, in serine acetyl transferase (CysE) and O-acetylserine sulfhydrylase (CysM). CysE function was rescued by cysteine-and-methionine-free enzymes and CysM function was rescued by cysteine-free enzymes. Structural modeling suggests that methionine stabilizes CysM and is present in the active site of CysM. Cysteine is not conserved among CysE and CysM protein orthologs, suggesting that cysteine is not functionally important for its own synthesis. Engineering biosynthetic enzymes that lack the amino acids being synthesized provides insights into the evolution of amino acid biosynthesis and pathways for bioengineering.

proteinogenic amino acids↗

NASA NTRS1999

Anticipatory Postural Activity During Long-Duration Space Flight

Somatosensory input has been used to modify motor output in many contexts. During space flight, the use of the lower limb musculature is much less than during activities in 1g. Consequently the neuromuscular activity of the legs is also reduced during space flight. This decrease in muscle activity contributes to muscle atrophy. Furthermore, adaptations to weightlessness contribute to posture and locomotion problems upon the return to Earth. Providing techniques to counter the negative effects of weightlessness on the neuromuscular system is an important goal, particularly during a long-duration mission. Previous work by our group has shown that lower limb neuromuscular activation that normally precedes arm movements in 1g is absent or greatly reduced during similar movements made while freefloating. However, preliminary evidence indicates that applying pressure to the feet results in enhanced neuromuscular activation during rapid arm movements performed while freefloating. This finding suggests that sensory input can be used to "drive" the motor system to increase neuromuscular functioning throughout a mission. The purpose of this investigation was to quantify the increase in neuromuscular activation resulting from the application of pressure to the feet.

Layne, C. S.↗

NASA NTRS1989

Contributions of low-luminosity sources to the X-ray background

We have exploited the HEAO 1 A-2 data base to determine hard X-ray fluxes, or upper limits, for complete optically selected samples of active and normal galaxies, in order to estimate or to constrain their local X-ray luminosity functions. We find that the luminosity function of Seyfert nuclei must flatten down drastically shortly below the observational limit of Piccinotti et al.; little can be added by dwarf active nuclei hidden in otherwise normal galaxies. We also analyze the possible contribution to the X-ray background from galaxies with strong star formation activity, in the light of the possibility of a substantial cosmological evolution suggested by recent radio and IRAS data.

Nuclei galaxies↗

NASA NTRS1979

A tethering system for direct measurement of cardiovascular function in the caged baboon

A device suitable for the continuous measurement of physiological activity in large, conscious monkeys has permitted the direct recording of systemic arterial blood pressure and heart rate in caged baboons. The device comprises a lightweight fiberglass backpack, retained in place on the baboon by a thoracic elastic band and shoulder straps, and a flexible stainless steel tether connecting the pack to an electrocannular slip-ring in the top center of the baboon's cage. A chronically indwelling arterial catheter inserted retrograde into the abdominal aorta via the internal iliac artery and connected to a small pressure transducer on the pack provides direct measurement of blood pressure and heart rate. Body fluids can be sampled or drugs administered via an indwelling catheter in the inferior vena cava. Electrical and fluid connections between the fiberglass pack and recording and infusion equipment located outside the cage pass through the flexible tether and remain protected from the subject. The reliability of the tethering system has been demonstrated in physiological, pharmacological, and behavioral experiments with baboons.

Byrd, L. D.↗

NASA NTRS1999

Effect of Space Flight on Adrenal Medullary Function

We hypothesize that microgravity conditions during space flight alter the expression and specific activities of the adrenal medullary CA synthesizing enzymes (CASE). Previously, we examined adrenals from six rats flown for six days aboard STS 54 and reported that microgravity induced a decrease in the expression and specific activity of rat adrenal medullary tyrosine hydroxylase, the rate limiting enzyme of CA synthesis, without affecting the expression of other CASE. In the past, we analyzed some of the > 300 adrenals from two previous Space Shuttle missions (PARE 03 and SLS 2). The preliminary results (a) attest to the good state of tissue preservation, thus proving the feasibility of subsequent large-scale evaluation, and (b) confirm and extend our previous findings. With this grant we will be able to expeditiously analyze all our specimens and to complete our studies in a timely fashion.

Lelkes, Peter I.↗

NASA NTRS2001

The Effect of Cytidine on the Structure and Function of an RNA Ligase Ribozyme

A cytidine-free ribozyme with RNA ligase activity was obtained by in vitro evolution, starting from a pool of random- sequence RNAs that contained only guanosine, adenosine, and uridine. This ribozyme contains 74 nt and catalyzes formation of a 3',5' -phosphodiester linkage with a catalytic rate of 0.016/min. The RNA adopts a simple secondary structure based on a three-way junction motif, with ligation occurring at the end of a stem region located several nucleotides away from the junction. Cytidine was introduced to the cytidine-free ribozyme in a combinatorial fashion and additional rounds of in vitro evolution were carried out to allow the molecule to adapt to this added component. The resulting cytidine-containing ribozyme formed a 3',5' linkage with a catalytic rate of 0.32/min. The improved rate of the cytidine-containing ribozyme was the result of 12 mutations, including seven added cytidines, that remodeled the internal bulge loops located adjacent to the three-way junction and stabilized the peripheral stem regions.

Rogers, Jeff↗

NASA NTRS2002

A site-directed mutagenesis analysis of tNOX functional domains

Constitutive NADH oxidase proteins of the mammalian cell surface exhibit two different activities, oxidation of hydroquinones (or NADH) and protein disulfide-thiol interchange which alternate to yield oscillatory patterns with period lengths of 24 min. A drug-responsive tNOX (tumor-associated NADH oxidase) has a period length of about 22 min. The tNOX cDNA has been cloned and expressed. These two proteins are representative of cycling oxidase proteins of the plant and animal cell surface. In this report, we describe a series of eight amino acid replacements in tNOX which, when expressed in Escherichia coli, were analyzed for enzymatic activity, drug response and period length. Replacement sites selected include six cysteines that lie within the processed plasma membrane (34 kDa) form of the protein, and amino acids located in putative drug and adenine nucleotide (NADH) binding domains. The latter, plus two of the cysteine replacements, resulted in a loss of enzymatic activity. The recombinant tNOX with the modified drug binding site retained activity but the activity was no longer drug-responsive. The four remaining cysteine replacements were of interest in that both activity and drug response were retained but the period length for both NADH oxidation and protein disulfide-thiol interchange was increased from 22 min to 36 or 42 min. The findings confirm the correctness of the drug and adenine nucleotide binding motifs within the tNOX protein and imply a potential critical role of cysteine residues in determining the period length.

Non-NASA Center↗

NASA NTRS2000

Microsphere Integration in Active and Passive Photonics Devices

An important step towards integration of microspheres in compact functional photonics devices, we demonstrate direct efficient coupling of light in and out of high-Q whispering-gallery (WG) modes in silica microspheres using angle-polished single mode fibers.

photonics↗

NASA NTRS1995

Assessing potential targets of calcium action in light-modulated gravitropism

Light, through the mediation of the pigment phytochrome, modulates the gravitropic response of the shoots and roots of many plants. The transduction of both light and gravity stimuli appears to involve Ca(2+)-regulated steps, one or more of which may represent points of intersection between the two transduction chains. To be confident that Ca2+ plays a critical role in stimulus-response coupling for gravitropism, it will be important to identify specific targets of Ca2+ action whose function can be clearly linked to the regulation of growth. Calcium typically exerts its influence on cell metabolism through binding to and activating key regulatory proteins. The three best characterized of these proteins in plants are the calmodulins, calcium-dependent protein kinases, and annexins. In this review we summarize what is known about the structure and function of these proteins and speculate on how their activation by Ca2+ could influence the differential growth response of gravitropism.

Review, Tutorial↗

NASA NTRS1992

The real world and lunar base activation scenarios

A lunar base or a network of lunar bases may have highly desirable support functions in a national or international program to explore and settle Mars. In addition, He-3 exported from the Moon could be the basis for providing much of the energy needs of humankind in the twenty-first century. Both technical and managerial issues must be addressed when considering the establishment of a lunar base that can serve the needs of human civilization in space. Many of the technical issues become evident in the consideration of hypothetical scenarios for the activation of a network of lunar bases. Specific and realistic assumptions must be made about the conduct of various types of activities in addition to the general assumptions given above. These activities include landings, crew consumables, power production, crew selection, risk management, habitation, science station placement, base planning, science, agriculture, resource evaluation, readaptation, plant activation and test, storage module landings, resource transport module landings, integrated operations, maintenance, Base 2 activation, and management. The development of scenarios for the activation of a lunar base or network of bases will require close attention to the 'real world' of space operations. That world is defined by the natural environment, available technology, realistic objectives, and common sense.

Schmitt, Harrison H.↗

NASA NTRS1984

Age-rotation relationship for late-type main-sequence stars

With advancing spectral type and increasing age, late main-sequence stars exhibit monotonic decrease in rotational velocity. It is of great interest to extend the rotation-age relationship to stars of later spectral type. In recent times it has become possible to measure directly the rotational periods from the photometric modulation by Ca II H and K line emission. There have also been successful attempts to relate the chromospheric activity as manifested through Ca II H and K lines to the rotation period, and it was shown that the fraction of total stellar luminosity in Ca II H and K lines, corrected for photospheric contribution, is a function of a single parameter related to P and B-V. In the present investigation, this rotation-activity relation is utilized to infer the rotation periods as a function of spectral type. The period versus B-V plot is employed as a basis to infer that the rotational period of main-sequence stars is a single-valued function of mass (B-V color) and age.

Rengarajan, T. N.↗