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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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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Use of a priori statistics to minimize acquisition time for RFI immune spread spectrum systems

The optimum acquisition sweep strategy was determined for a PN code despreader when the a priori probability density function was not uniform. A psuedo noise spread spectrum system was considered which could be utilized in the DSN to combat radio frequency interference. In a sample case, when the a priori probability density function was Gaussian, the acquisition time was reduced by about 41% compared to a uniform sweep approach.

Holmes, J. K.↗
NASA NTRS1983

Human cellular immune responsiveness following space flight

Peripheral circulating lymphocytes were separated from astronaut blood samples three times before and two times after the first four US Space Shuttle flights. The ability of the in vitro T lymphocytes to respond to Phytohemagglutinin by blastogenesis was found to be reduced for each crewmember following spaceflight. In addition, the astronauts experienced a postflight increase in neutrophils and a decrease in eosinophils. These postflight changes in leukocytes are shown to increase with subjectively-evaluated increases in the incidence of inflight stress, indicating that stress, and not hypogravity, is likely to be the major effector of these changes.

Taylor, G. R.↗
NASA NTRS1983

Radiation immune RAM semiconductor technology for the 80's

This paper presents current and short term future characteristics of RAM semiconductor technologies which were obtained by literature survey and discussions with cognizant Government and industry personnel. In particular, total ionizing dose tolerance and high energy particle susceptibility of the technologies are addressed. Technologies judged compatible with spacecraft applications are ranked to determine the best current and future technology for fast access (less than 60 ns), radiation tolerant RAM.

Hanna, W. A.↗
NASA NTRS1984

Prolonged weightlessness and humoral immunity

Preflight, inflight, and postflight serum samples obtained from crewmen aboard STS-9 were analyzed for immunoglobulin content. Control studies for circadian rhythm were conducted to further validate the analyses. Quantitation of immunoglobulins G, M, A, D, and E indicated relatively minor fluctuations in the concentration of each class of immunoglobulin during the experiment. Thus, microgravity effects on immunoglobulin levels during a 10-day flight were considered insignificant.

Voss, E. W., Jr.↗
NASA NTRS1986

Avionics electromagnetic interference immunity and environment

Aircraft electromagnetic spectrum and radio frequency (RF) field strengths are charted, profiling the higher levels of electromagnetic voltages encountered by the commercial aircraft wiring. Selected military, urban, and rural electromagnetic field levels are plotted and provide a comparison of radiation amplitudes. Low frequency magnetic fields and electric fields from 400 H(Z) power systems are charted versus frequency and wire separation to indicate induced voltages on adjacent or neighboring circuits. Induced EMI levels and attenuation characteristics of electric, magnetic, RF fields, and transients are plotted and graphed for common types of wire circuits. The significance of wire circuit returns and shielding is emphasized to highlight the techniques that help block the paths of electromagnetic interference and maintain avionic interface signal quality.

Clarke, C. A.↗
NASA NTRS1990

Experiment K-6-23. Effect of spaceflight on levels and function of immune cells

Two different immunology experiments were performed on samples received from rats flown on Cosmos 1887. In the first experiment, rat bone marrow cells were examined in Moscow for their response to colony stimulating factor-M. In the second experiment, rat spleen and bone marrow cells were stained in Moscow with a variety of antibodies directed against cell surface antigenic markers. These cells were preserved and shipped to the United States where they were subjected to analysis on a flow cytometer. The results of the studies indicate that bone marrow cells from flown rats showed a decreased response to colony stimulating factor than did bone marrow cells from control rats. There was a higher percentage of spleen cells from flown rats staining positively for pan-T-cell, suppressor-T-cell and innate interleukin-2 receptor antigens than from control animals. In addition, a higher percentage of cells that appeared to be part of the myelogenous population of bone marrow cells from flown rats stained positively for surface immunoglobulin than did equivalent cells from control rats.

Mandel, A. D.↗
NASA NTRS1991

Designs for surge immunity in critical electronic facilities

In recent years, Federal Aviation Administration (FAA) embarked on a program replacing older tube type electronic equipment with newer solid state equipment. This replacement program dramatically increased the susceptibility of the FAA's facilities to lightning related damages. The proposal is presented of techniques which may be employed to lessen the susceptibility of new FAA electronic facility designs to failures resulting from lightning related surges and transients as well as direct strikes. The general concept espoused is one of a consistent system approach employing both perimeter and internal protection. It compares the technique presently employed to reduce electronic noise with other techniques which reduce noise while lowering susceptibility to lightning related damage. It is anticipated that these techniques will be employed in the design of an Air Traffic Control Tower in a high isokeraunic area. This facility would be subjected to rigorous monitoring over a multi-year period to provide quantitative data hopefully supporting the advantage of this design.

Roberts, Edward F., Jr.↗
NASA NTRS1992

Spaceflight alters immune cell function and distribution

Experiments are described which were performed onboard Cosmos 2044 to determine spaceflight effects on immunologically important cell function and distribution. Results indicate that bone marrow cells from flown and suspended rats exhibited a decreased response to a granulocyte/monocyte colony-stimulating factor compared with the bone marrow cells from control rats. Bone marrow cells showed an increase in the percentage of cells expressing markers for helper T-cells in the myelogenous population and increased percentages of anti-asialo granulocyte/monocyte-1-bearing interleulin-2 receptor bearing pan T- and helper T-cells in the lymphocytic population.

Sonnenfeld, Gerald↗
NASA NTRS1992

Low power SEU immune CMOS memory circuits

The authors report a design improvement for CMOS static memory circuits hardened against single event upset (SEU) using a recently proposed logic/circuit design technique. This improvement drastically reduces static power consumption, reduces the number of transistors required in a D flip-flop design, and eliminates the possibility of capturing an upset state in the slave section during a clock transition.

Liu, M. N.↗
NASA NTRS1994

Constant current loop impedance measuring system that is immune to the effects of parasitic impedances

A constant current loop measuring system is provided for measuring a characteristic of an environment. The system comprises a first impedance positionable in the environment, a second impedance coupled in series with said first impedance and a parasitic impedance electrically coupled to the first and second impedances. A current generating device, electrically coupled in series with the first and second impedances, provides a constant current through the first and second impedances to produce first and second voltages across the first and second impedances, respectively, and a parasitic voltage across the parasitic impedance. A high impedance voltage measuring device measures a voltage difference between the first and second voltages independent of the parasitic voltage to produce a characteristic voltage representative of the characteristic of the environment.

Anderson, Karl F.↗
NASA NTRS1994

Experiment K-7-23: Effect of Spaceflight on Level and Function of Immune Cells: Proliferation and Cytokines - Part 2

Lymphocytes from the superficial inguinal lymph nodes of rats flown on the Cosmos 2044 space mission were tested for proliferation in response to polyclonal activators. Cells were cultured with T or B cell mitogens, phorbol ester and calcium ionophore, or T cell mitogen and the lymphokines interleukin-1 (IL-1) or interleukin-2 (IL-2), and assayed for DNA synthesis by (3)H-thymidine incorporation. Lymphocytes also were incubated with concanavalin A (Con A), a T cell mitogen, and tested for IL-2 production. Mitogen-stimulated proliferation of lymphocytes from rats exposed to microgravity was not significantly different from synchronous or vivarium controls. Responses to Con A and IL-2, and Con A and IL-1 likewise were unaffected by space flight. Lymphocytes from all of these groups responded well to phorbol ester and calcium ionophore stimulation. Furthermore, lymph node cells (LNC) from control rats and rats flown on Cosmos 2044 produced similar amounts of IL-2. The results obtained using hindlimb suspended rats were notably different from those of flight and control animals. LNC from suspended rats generally had greater proliferative responses to T cell mitogens than did lymphocytes from other groups. Responsiveness to a B cell mitogen was not enhanced. Con A-stimulated LNC from hindlimb suspended rats also produced more IL-2 than did lymphocytes from the other groups. This difference was statistically significant at both IL-2 induction times tested.

Nash, P. V.↗
NASA NTRS1997

Role of Dendritic Cells in Immune Dysfunction

Specific aims include: (1) Application of the bioreactor to enhance cytokine-regulated proliferation and maturation of dendritic cells (DC); (2) Based on clues from spaceflight: compare the frequency and function of DC in normal donors and immunocompromised cancer patients; and (3) Initiate studies on the efficiency of cytokine therapy and DC-assisted immunotherapy (using bioreactor-expanded DC) in animal models of experimental fungal infections.

Savary, Cherylyn A.↗
NASA NTRS1999

Update on the Effects of Space Flight on Development of Immune Responses

This study has been completed, and the following is an update of the results as published. Pregnant rats were flown on the Space Shuttle in the NIH.R I mission for 11 days, and pregnant control rats were maintained in animal enclosure modules in a ground-based chamber under conditions approximating those in flight. Additional controls were in standard housing. The effects of the flight on immunological parameters (including blastogenesis, interferon-gamma production, response to colony stimulating factor and total immunoglobulin levels) of dams, fetuses, and pups was determined.

Sonnenfeld, G.↗
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 NTRS1992

Glucocorticoid effects on immune cell activation by staphylococcal exotoxins and lipopolysaccharide

Experiments were conducted to determine the effects of physiologically elevated corticosterone on the activation of macrophages and T cells. These studies find that the elevation of corticosterone does not affect the expression of membrane receptors on macrophages and does not affect the activation of macrophages to produce cytokines. In contrast, elevated corticosterone levels correlate with enhanced T cell proliferation to both mitogens and superantigens.

NASA Discipline Cell Biology↗
NASA NTRS2001

Complex expression patterns of lymphocyte-specific genes during the development of cartilaginous fish implicate unique lymphoid tissues in generating an immune repertoire

Cartilaginous fish express canonical B and T cell recognition genes, but their lymphoid organs and lymphocyte development have been poorly defined. Here, the expression of Ig, TCR, recombination-activating gene (Rag)-1 and terminal deoxynucleosidase (TdT) genes has been used to identify roles of various lymphoid tissues throughout development in the cartilaginous fish, Raja eglanteria (clearnose skate). In embryogenesis, Ig and TCR genes are sharply up-regulated at 8 weeks of development. At this stage TCR and TdT expression is limited to the thymus; later, TCR gene expression appears in peripheral sites in hatchlings and adults, suggesting that the thymus is a source of T cells as in mammals. B cell gene expression indicates more complex roles for the spleen and two special organs of cartilaginous fish-the Leydig and epigonal (gonad-associated) organs. In the adult, the Leydig organ is the site of the highest IgM and IgX expression. However, the spleen is the first site of IgM expression, while IgX is expressed first in gonad, liver, Leydig and even thymus. Distinctive spatiotemporal patterns of Ig light chain gene expression also are seen. A subset of Ig genes is pre-rearranged in the germline of the cartilaginous fish, making expression possible without rearrangement. To assess whether this allows differential developmental regulation, IgM and IgX heavy chain cDNA sequences from specific tissues and developmental stages have been compared with known germline-joined genomic sequences. Both non-productively rearranged genes and germline-joined genes are transcribed in the embryo and hatchling, but not in the adult.

Non-NASA Center↗
NASA NTRS2000

Acute effects of whole-body proton irradiation on the immune system of the mouse

The acute effects of proton whole-body irradiation on the distribution and function of leukocyte populations in the spleen and blood were examined and compared to the effects of photons derived from a (60)Co gamma-ray source. Adult female C57BL/6 mice were exposed to a single dose (3 Gy at 0.4 Gy/min) of protons at spread-out Bragg peak (SOBP), protons at the distal entry (E) region, or gamma rays and killed humanely at six different times thereafter. Specific differences were noted in the results, thereby suggesting that the kinetics of the response may be variable. However, the lack of significant differences in most assays at most times suggests that the RBE for both entry and peak regions of the Bragg curve was essentially 1.0 under the conditions of this study. The greatest immunodepression was observed at 4 days postexposure. Flow cytometry and mitogenic stimulation analyses of the spleen and peripheral blood demonstrated that lymphocyte populations differ in radiosensitivity, with B (CD19(+)) cells being most sensitive, T (CD3(+)) cells being moderately sensitive, and natural killer (NK1.1(+)) cells being most resistant. B lymphocytes showed the most rapid recovery. Comparison of the T-lymphocyte subsets showed that CD4(+) T helper/inducer cells were more radiosensitive than the CD8(+) T cytotoxic/suppressor cells. These findings should have an impact on future studies designed to maximize protection of normal tissue during and after proton-radiation exposure.

NASA Discipline Radiation Health↗