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At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
NASA NTRS1956

On the Contribution of Turbulent Boundary Layers to the Noise Inside a Fuselage

The following report deals in preliminary fashion with the transmission through a fuselage of random noise generated on the fuselage skin by a turbulent boundary layer. The concept of attenuation is abandoned and instead the problem is formulated as a sequence of two linear couplings: the turbulent boundary layer fluctuations excite the fuselage skin in lateral vibrations and the skin vibrations induce sound inside the fuselage. The techniques used are those required to determine the response of linear systems to random forcing functions of several variables. A certain degree of idealization has been resorted to. Thus the boundary layer is assumed locally homogeneous, the fuselage skin is assumed flat, unlined and free from axial loads and the 'cabin' air is bounded only by the vibrating plate so that only outgoing waves are considered. Some of the details of the statistical description have been simplified in order to reveal the basic features of the problem. The results, strictly applicable only to the limiting case of thin boundary layers, show that the sound pressure intensity is proportional to the square of the free stream density, the square of cabin air density and inversely proportional to the first power of the damping constant and to the second power of the plate density. The dependence on free stream velocity and boundary layer thickness cannot be given in general without a detailed knowledge of the characteristics of the pressure fluctuations in the boundary layer (in particular the frequency spectrum). For a flat spectrum the noise intensity depends on the fifth power of the velocity and the first power of the boundary layer thickness. This suggests that boundary layer removal is probably not an economical means for decreasing cabin noise. In general, the analysis presented here only reduces the determination of cabin noise intensity to the measurement of the effect of any one of our variables (free stream velocity, boundary layer thickness, plate thickness or the characteristic velocity of propagation in the plate). The plate generates noise by vibrating in resonance over a wide range of frequencies and increasing the damping constant is consequently an effective method of decreasing noise generation. One of the main features of the results is that the relevant quantities upon which noise intensity depends are non-dimensional numbers in which boundary layer and plate properties enter as ratios. This is taken as an indication that in testing models of structures for boundary layer noise it is not sufficient to duplicate in the model the structural characteristics of the fuselage. One must match properly the characteristics of the exicitng pressure fluctuations to that of the structure.

Corcos, G. M.↗
NASA NTRS2003

Thermal Contributions to the Degradation of Ground Laboratory and Space Irradiated Teflon

The aluminized Teflon fluorinated ethylene propylene outer most layer of the multilayer insulation blankets on the Hubble Space Telescope has become embrittled resulting in severe on-orbit cracking. During the second servicing mission, a piece of aluminized fluorinated ethylene propylene was retrieved that had curled, exposing the back-surface aluminum to space. This extremely embrittled piece reached 200 C on-orbit, 150 C higher than the nominal temperature extreme. Therefore, experiments have been conducted to determine the effect of heating on the degradation of fluorinated ethylene propylene that has been irradiated in a ground laboratory facility or in space on Hubble Space Telescope. Samples of pristine, x-ray irradiated and Hubble Space Telescope retrieved fluorinated ethylene propylene were heat treated from 50 to 200 C at 25 C intervals in a high vacuum facility and tensile tested. Density measurements were also obtained. Results indicate that heating does not embrittle non-irradiated Teflon. However, there is a significant dependence of the embrittlement of irradiated Teflon on heating temperature, with near complete loss of elongation at 100 C and higher. Rate of degradation changes, which were consistent with the glass transition temperature for fluorinated ethylene propylene, were present in the data. The results support chain scission as the primary mechanism of degradation of fluorinated ethylene propylene on Hubble Space Telescope, and indicate the significance of the on-orbit temperature of fluorinated ethylene propylene with respect to its degradation in the space environment.

deGroh, Kim K.↗
NASA NTRS2003

Detection of Directions of Gravity by Organisms and Contributions to SmaggIce

Research covers the following: In the Microgravity Environment and Telescience Branch, a study wasI extended thar focused upon a flagellated alga or other swimming microbe and the effect of gravity upon its swimming direction. It has long been known that many organisms tend to swim up or down on Earth. How organisms detect the direction of gravity is a question not fully resolved. The response of such organisms to reduced gravity or the absence of gravity is also of interest, particularly because the expected modified behavior may affect the health of astronauts.

Dill, Loren H.↗
NASA NTRS2003

Bermuda Contribution to a North Atlantic Aerobiology Study

The primary aim of this project, a 6-month effort that commenced October 1 2002 (with no-cost extension until September 30 2003) was to collect a weekly time series of marine aerosol samples at Bermuda for the enumeration, culture and characterization of microbes, particularly those associated with soil dust and other aerosol particles originating from North Africa, North America, and Asia. Such airborne microbes may play important roles as pathogens, and also in the large-scale biogeochemical exchange between land, atmosphere and ocean.

Source record↗
NASA NTRS2004

Contributions of Spherical Harmonics to Magnetic and Gravitational Fields

Gravitational forces are of cardinal importance in the dynamics of spacecraft; magnetic attractions sometime play a significant role also, as was the case with the Long Duration Exposure Facility, and as is now true for the first segment of Space Station Freedom. Both satellites depend on gravitational moment and a device known as a magnetic damper to stabilize their orientation. Magnetic fields are mathematically similar to gravitational fields in one important respect: each can be regarded as a gradient of a potential function that, in turn, can be described as an infinite series of spherical harmonics. Consequently, the two fields can be computed, in part, with quantities that need only be evaluated once, resulting in a savings of time when both fields are needed. The objective of this material is to present magnetic field and gravitational force expressions, and point out the terms that belong to both this is accomplished in Section 1 and 2. Section 3 contains the deductive reasoning with which one obtains the expressions of interest. Finally, examples in Section 4 show these equations can be used to reproduce others that arise in connection with special cases such as the magnetic field produced by a tilted dipole, and gravitational force exerted by an oblate spheroid. The mathematics are discussed in the context of terrestrial fields; however, by substituting appropriate constants, the results can be made applicable to fields belonging to other celestial bodies. The expressions presented here share the characteristics of algorithms set forth for computing gravitational force. In particular, computation is performed speedily by means of recursion formulae, and the expressions do not suffer from the shortcoming of a singularity when evaluated at points that lie on the polar axis.

Roithmayr, Carlos M.↗
NASA NTRS2004

Stimulated Mid-Infrared Luminescence Experiment: Contribution to the Study of Pre-Earthquake Phenomena and UV Absorption by Interstellar Dust

The work performed under this proposal is based on the experimentally supported observation - or inference - that a small fraction of the oxygen anions in silicate minerals in igneous and high-grade metamorphic rocks on Earth may not be in the usual 2- oxidation state, O(sup 2-), but in a higher oxidation state, as O(sup -). If this is true, the same would likely apply to the fine dust that fills the diffuse interstellar medium. An (sup -) in a matrix of O(sup 2-) represents a defect electron in the valence band, also known as positive hole or p-hole for short. When two O(sup -) combine, they undergo spin-pairing and form a positive hole pair, PHP. Chemically speaking a PHP is a peroxy bond. In an oxide matrix a peroxy bond takes the form of a peroxy anion, O2(sup 2-). In a silicate matrix it probably exists in the form of peroxy links between adjacent [SiO4] tetrahedral, O3Si00\SiO3. From a physics perspective a PHP is an electrically inactive point defect, which contains dormant electronic charge carriers. When the peroxy bond breaks, p-hole charge carriers are released. These p-holes are diffusively mobile and spread through the O 2p-dominated valence band of the otherwise insulating mineral matrix.

Freund, Friedemann↗
NASA NTRS2004

Contribution of TOMS to Earth Science- An Overview

The TOMS instrument was launched on the Nimbus-7 satellite in Oct 1978 with the goal of understanding the meteorological influences on the ozone column. The nominal lifetime of the instrument was 1 year. However, in response to the concern over possible man-made influences on the ozone layer NASA continued to nurse the instrument for 13.5 years and launched a major program to produce accurate trend quality dataset of ozone. Despite severe optical degradation and other significant anomalies that developed in the instrument over its lifetime, the effort turned out to be a tremendous success. In 1984, TOMS took center stage as the primary provider of Antarctic ozone hole maps to the world community; it continues to play that role until today. An unexpected benefit of the close attention paid to improving the TOMS data quality was that several atmospheric constituents that interfere with ozone measurement were also identified and meticulously converted into long-term datasets of their own. These constituents include clouds, volcanic S02, aerosols, and ocean phytoplankton. In addition, the high quality of the basic datasets made it possible to produce global maps of surface UV and tropospheric ozone. In most cases there are no other sources of these data sets. Advanced UV instruments currently under development in the US and Europe will continue to exploit the TOMS-developed techniques for several decades.

Bhartia, P. K.↗
NASA NTRS2004

Decreased Estrogen May Contribute to Osteopenia in Unloaded Bones

Progressive loss of weight-bearing bone in astronauts is one of the most serious impediments to long-duration spaceflight. Estrogen deficiency in women is an established factor in bone loss. Reduced sex hormone levels have been reported in male astronauts, but no data is available regarding spaceflight effects on female sex hormones. The objective of our study was to determine the role of estrogen in disuse osteopenia. The NASA developed hindlimb suspension (HLS) model was used to simulate the unloading disuse of weight-bearing bones experienced in space. Female Sprague-Dawley rats (age 77d; n = 20/group) were HLS or kept ambulatory (AMB) for 38 d and endocrine and bone indices determined. HLS of rats resulted in lower (p less than 0.01) bone mass (9%0), bone mineral content (BMC 13%) and mechanical strength (28%) compared to AMB animals. Plasma estradiol (E2) was lower (p = 0.03) in HLS (10.1 +/- 1.4 pg/ml) compared to AMB rats (16.7 +/- 2.6 pg/ml). E2 was positively correlated to BMC r(sup 2) = 0.67 and mechanical strength r(sup 2) = 0.61. These results suggest that reduced E2 plays a role in disuse osteopenia induced by HLS. Plasma or pituitary lutenizing hormone (LH) and follicle stimulating hormone (FSH) levels were not different in HLS versus AMB rats. However, pituitary LH was correlated to E2 (r(sup 2) = 0.57), suggesting changes in E2 were exerted at the level of the hypothalamus-pituitary axis. Understanding the role of estrogen in disuse osteopenia is necessary to the development of efficacious therapies for female astronauts, bed rest patients and the increasing number of individuals in our sedentary population suffering bone loss.

Tou, Janet↗
NASA NTRS2004

A Reply to Diem et al.'s Commentary on a Recent Literature Contribution Focused on Urban-Induced Rainfall in Atlanta

A response is provided to Diem and colleagues discussion on the whether urbanization-enhanced precipitation should be maximized in the South-Southeast of Atlanta, Georgia as documented in Shepherd et al. (2003). Diem and colleagues have offered a critical response to Shepherd et al. (2002). The response herein offers both general and specific responses to issues raised by Diem and colleagues.

Shepherd, J. Marshall↗
NASA NTRS2004

Can Assimilation of Satellite Ozone Data Contribute to the Understanding of the Lower Stratospheric Ozone?

We study the quality of lower stratospheric ozone fields from a three- dimensional global ozone assimilation system. Ozone in this region is important for the forcing of climate, but its global distribution is not fully known because of its large temporal and vertical variability. Modeled fields often have biases due to the inaccurate representation of transport processes in this region with strong gradients. Accurate ozonesonde or satellite occultation measurements have very limited coverage. Nadir measurements, such as those from the Solar Backscatter Ultraviolet/2 (SBUV/2) instrument that provide wide latitudinal coverage, lack the vertical resolution needed to represent sharp vertical features. Limb measurements, such as those from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), provide a finer vertical resolution. We show that assimilation of MIPAS data in addition to SBUV/2 data leads to better estimates of ozone in comparison with independent high quality satellite, aircraft, and ozone sonde measurements. Other modifications to the statistical analysis that have an impact on the lower stratospheric ozone will be mentioned: error covariance modeling and data selection. Direct and indirect impacts of transport and chemistry models will be discussed. Implications for multi-year analyses and short-tern prediction will be addressed.

Stajner, I.↗
NASA NTRS1999

Contributions to Active Buffeting Alleviation Programs by the NASA Langley Research Center

Buffeting is an aeroelastic phenomenon which plagues high performance aircraft, especially those with twin vertical tails like the F/A-18, at high angles of attack. This buffeting is a concern from fatigue and inspection points of view. By means of wind-tunnel and flight tests, this phenomenon is well studied to the point that buffet loads can be estimated and fatigue life can be increased by structural enhancements to the airframe. In more recent years, buffeting alleviation through active control of smart materials has been highly researched in wind-tunnel proof-of-concept demonstrations and full-scale ground tests using the F/A-18 as a test bed. Because the F/A-18 resides in fleets outside as well as inside the United States, these tests have evolved into international collaborative research activities with Australia and Canada, coordinated by the Air Force Research Laboratory (AFRL) and conducted under the auspices of The Technical Cooperation Program (TTCP). With the recent successes and advances in smart materials, the main focus of these buffeting alleviation tests has also evolved to a new level: utilize the F/A-18 as a prototype to mature smart materials for suppressing vibrations of aerospace structures. The role of the NASA Langley Research Center (LaRC) in these programs is presented.

Moses, Robert W.↗
NASA NTRS2003

Monosodium glutamate-sensitive hypothalamic neurons contribute to the control of bone mass

Using chemical lesioning we previously identified hypothalamic neurons that are required for leptin antiosteogenic function. In the course of these studies we observed that destruction of neurons sensitive to monosodium glutamate (MSG) in arcuate nuclei did not affect bone mass. However MSG treatment leads to hypogonadism, a condition inducing bone loss. Therefore the normal bone mass of MSG-treated mice suggested that MSG-sensitive neurons may be implicated in the control of bone mass. To test this hypothesis we assessed bone resorption and bone formation parameters in MSG-treated mice. We show here that MSG-treated mice display the expected increase in bone resorption and that their normal bone mass is due to a concomitant increase in bone formation. Correction of MSG-induced hypogonadism by physiological doses of estradiol corrected the abnormal bone resorptive activity in MSG-treated mice and uncovered their high bone mass phenotype. Because neuropeptide Y (NPY) is highly expressed in MSG-sensitive neurons we tested whether NPY regulates bone formation. Surprisingly, NPY-deficient mice had a normal bone mass. This study reveals that distinct populations of hypothalamic neurons are involved in the control of bone mass and demonstrates that MSG-sensitive neurons control bone formation in a leptin-independent manner. It also indicates that NPY deficiency does not affect bone mass.

NASA Discipline Regulatory Physiology↗
NASA NTRS2002

Does the vestibular system contribute to head direction cell activity in the rat?

Head direction cells (HDC) located in several regions of the brain, including the anterior dorsal nucleus of the thalamus (ADN), postsubiculum (PoS), and lateral mammillary nuclei (LMN), provide the neural substrate for the determination of head direction. Although activity of HDC is influenced by various sensory signals and internally generated cues, lesion studies and some anatomical and physiological evidence suggest that vestibular inputs are critical for the maintenance of directional sensitivity of these cells. However, vestibular inputs must be transformed considerably in order to signal head direction, and the neuronal circuitry that accomplishes this signal processing has not been fully established. Furthermore, it is unclear why the removal of vestibular inputs abolishes the directional sensitivity of HDC, as visual and other sensory inputs and motor feedback signals strongly affect the firing of these neurons and would be expected to maintain their directional-related activity. Further physiological studies will be required to establish the role of vestibular system in producing HDC responses, and anatomical studies are needed to determine the neural circuitry that mediates vestibular influences on determination of head direction.

Review, Tutorial↗
NASA NTRS2003

Genetic models in applied physiology: selected contribution: effects of spaceflight on immunity in the C57BL/6 mouse. I. Immune population distributions

There are several aspects of the spaceflight environment that may lead to changes in immunity: mission-related psychological stress, radiation, and changes in gravity. On December 5, 2001, the space shuttle Endeavor launched for a 12-day mission to examine these effects on C57BL/6 mice for the first time. On their return, assays were performed on the spleen, blood, and bone marrow. In response to flight, there were no significant differences in the general circulating leukocyte proportions. In contrast, there was an increase in splenic lymphocyte percentages, with a corresponding decrease in granulocytes. There was an overall shift in splenic lymphocytes away from T cells toward B cells, and a decrease in the CD4-to-CD8 ratios due to a decrease in T helpers. In contrast, there were proportional increases in bone marrow T cells, with decreases in B cells. Although the blast percentage and count were decreased in flight mice, the CD34(+) population was increased. The data were more consistent with a shift in bone marrow populations rather than a response to changes in the periphery. Many of the results are similar to those using other models. Clearly, spaceflight can influence immune parameters ranging from hematopoiesis to mature leukocyte mechanisms.

Non-NASA Center↗
NASA NTRS2003

Genetic models in applied physiology: selected contribution: effects of spaceflight on immunity in the C57BL/6 mouse. II. Activation, cytokines, erythrocytes, and platelets

This portion of the study quantified the effects of a 12-day space shuttle mission (Space Transport System-108/UF-1) on body and lymphoid organ masses, activation marker expression, cytokine secretion, and erythrocyte and thrombocyte characteristics in C57BL/6 mice. Animals in flight (Flt group) had 10-12% lower body mass compared with ground controls housed either in animal enclosure modules or under standard vivarium conditions (P < 0.001) and the smallest thymus and spleen masses. Percentages of CD25(+) lymphocytes, CD3(+)/CD25(+) T cells, and NK1.1(+)/CD25(+) natural killer cells from Flt mice were higher compared with both controls (P < 0.05). In contrast, CD71 expression was depressed in the Flt and animal enclosure module control mice compared with vivarium control animals (P < 0.001). Secretion of interferon-gamma, IL-2, and IL-4, but not tumor necrosis factor-alpha and IL-5, by splenocytes from Flt mice was decreased relative to either one or both ground controls (P < 0.05). Flt mice also had high red blood cell and thrombocyte counts compared with both sets of controls; low red blood cell volume and distribution width, percentage of reticulocytes, and platelet volume were also noted (P < 0.05) and were consistent with dehydration. These data indicate that relatively short exposure to the spaceflight environment can induce profound changes that may become significant during long-term space missions.

Flight Experiment↗
NASA NTRS2002

Cell prestress. II. Contribution of microtubules

The tensegrity model hypothesizes that cytoskeleton-based microtubules (MTs) carry compression as they balance a portion of cell contractile stress. To test this hypothesis, we used traction force microscopy to measure traction at the interface of adhering human airway smooth muscle cells and a flexible polyacrylamide gel substrate. The prediction is that if MTs balance a portion of contractile stress, then, upon their disruption, the portion of stress balanced by MTs would shift to the substrate, thereby causing an increase in traction. Measurements were done first in maximally activated cells (10 microM histamine) and then again after MTs had been disrupted (1 microM colchicine). We found that after disruption of MTs, traction increased on average by approximately 13%. Because in activated cells colchicine induced neither an increase in intracellular Ca(2+) nor an increase in myosin light chain phosphorylation as shown previously, we concluded that the observed increase in traction was a result of load shift from MTs to the substrate. In addition, energy stored in the flexible substrate was calculated as work done by traction on the deformation of the substrate. This result was then utilized in an energetic analysis. We assumed that cytoskeleton-based MTs are slender elastic rods supported laterally by intermediate filaments and that MTs buckle as the cell contracts. Using the post-buckling equilibrium theory of Euler struts, we found that energy stored during buckling of MTs was quantitatively consistent with the measured increase in substrate energy after disruption of MTs. This is further evidence supporting the idea that MTs are intracellular compression-bearing elements.

Non-NASA Center↗
NASA NTRS2001

Contribution of perfusion pressure to vascular resistance response during head-up tilt

We measured brachial and femoral artery flow velocity in eight subjects and peroneal and median muscle sympathetic nerve activity (MSNA) in five subjects during tilt testing to 40 degrees. Tilt caused similar increases in MSNA in the peroneal and median nerves. Tilt caused a fall in femoral artery flow velocity, whereas no changes in flow velocity were seen in the brachial artery. Moreover, with tilt, the increase in the vascular resistance employed (blood pressure/flow velocity) was greater and more sustained in the leg than in the arm. The ratio of the percent increase in vascular resistance in leg to arm was 2.5:1. We suggest that the greater vascular resistance effects in the leg were due to an interaction between sympathetic nerve activity and the myogenic response.

NASA Discipline Cardiopulmonary↗
NASA NTRS2001

Stromal cells can contribute oncogenic signals

The majority of studies of neoplastic transformation have focused attention on events that occur within transformed cells. These cell autonomous events result in the disruption of molecular pathways that regulate basic activities of the cells such as proliferation, death, movement and genomic integrity. Other studies have addressed the microenvironment of tumor cells and documented its importance in supporting tumor progression. Recent work has begun to expand on these initial studies of tumor microenvironment and now provide novel insights into the possible initiation and progression of malignant cells. This review will address the transforming effect of stromal cells on epithelial components. Copyright 2001 Academic Press.

Review↗