Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “half-life”

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.

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

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Effect of inhibitors of polyamine biosynthesis on gibberellin-induced internode growth in light-grown dwarf peas

When gibberellic acid (GA3) is sprayed on 9-day-old light-brown dwarf Progress pea (Pisum sativum) seedlings, arginine decarboxylase (ADC; EC 4.1.1.9) activity increases within 3 h and peaks at about 9 h after GA3 application. This is followed by a second lower peak at about 30 h; both peaks were higher than the corresponding peaks in the controls. In contrast, no appreciable effect of GA3 on internode length was observed until about 12 h, after which time a dramatic increase in growth rate occurred and persisted for about 12 h. Specific (DL-alpha-difluoromethylarginine) and non-specific (D-arginine and L-canavanine) inhibitors of ADC strongly inhibited ADC activity and to a lesser extent internode growth. The inhibition was reversed only slightly by the addition of polyamines. Actinomycin D and cycloheximide inhibited the rise in ADC activity induced by GA3. The half-life of the enzyme was increased by GA3 treatment. The results suggest that part of the GA3-induced increase in internode growth may result from enhanced polyamine biosynthesis through the ADC pathway. Furthermore, the GA3 induced increase in ADC activity probably requires de novo synthesis of both RNA and protein.

NASA Program Space Biology↗
NASA NTRS1991

Determination of cytoplasmic calcium concentration in Dryopteris spores: a developmentally non-disruptive technique for loading of the calcium indicator fura-2

Germination of Dryopteris spores is mediated by the physiologically active, far-red-absorbing form of phytochrome, Pfr, and external Ca2+ is necessary for the transduction of the light signal. Because knowledge about the cytoplasmic calcium ion concentration, [Ca2+]i, is of great importance for understanding the role of calcium during signal transduction, this value was measured using fura-2 in fern spores undergoing the normal developmental progression into germination. Fura-2 was loaded into the spores by electroporation, which does not disrupt the normal process of germination. The intensity of the fluorescence emission of the loaded fura-2 was analysed by a microspectrophotometric assay of single spores, and successful loading could be obtained by the application of ten electrical pulses (field strength 7.5 kV cm-1, half-life (time constant) 230 microseconds). Fura-2 was alternately excited by light of wavelengths 355 and 385 nm through an inverted fluorescence microscope, and the emitted fura-2 fluorescence was collected by a silicon-intensified video camera. The cytoplasmic calcium ion concentration was calculated from the ratio of the camera output obtained for both wavelengths and displayed by a pseudo-color technique. Spores responded to changes of the extracellular Ca2+ concentration, and this observation is considered as evidence that fura-2 is loaded into the cytoplasm. The substitution of a low external [Ca2+] (1 mM ethyleneglycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA)) by 1 mM CaCl2 caused a fast increase of [Ca2+]i from approx. 50 nM to above 500 nM. In contrast, the subsequent substitution of CaCl2 by EGTA decreased [Ca2+]i again below 100 nM within 0.5 h. Furthermore, the application of ionomycin could initiate a change in [Ca2+]i according to the Ca2+ gradient established between the extracellular medium and cytoplasm. In spores sown on a Ca(2+) -free medium, [Ca2+]i, analysed in a buffer containing EGTA, was found to be around 50 nM during the first days of cultivation, independent of the irradiation protocol. However, if spores were grown in darkness on a Ca(2+) -containing medium and analysed in EGTA, [Ca2+]i was significantly higher (> or = 500 nM). In red-light-irradiated spores, [Ca2+]i was found to decrease with increasing time after irradiation, and was determined to be less than 100 nM when analysis was done 44 h after germination was initiated by the light treatment.

NASA Discipline Plant Biology↗
NASA NTRS1998

Differential regulation of protease activated receptor-1 and tissue plasminogen activator expression by shear stress in vascular smooth muscle cells

Recent studies have demonstrated that vascular smooth muscle cells are responsive to changes in their local hemodynamic environment. The effects of shear stress on the expression of human protease activated receptor-1 (PAR-1) and tissue plasminogen activator (tPA) mRNA and protein were investigated in human aortic smooth muscle cells (HASMCs). Under conditions of low shear stress (5 dyn/cm2), PAR-1 mRNA expression was increased transiently at 2 hours compared with stationary control values, whereas at high shear stress (25 dyn/cm2), mRNA expression was decreased (to 29% of stationary control; P<0.05) at all examined time points (2 to 24 hours). mRNA half-life studies showed that this response was not due to increased mRNA instability. tPA mRNA expression was decreased (to 10% of stationary control; P<0.05) by low shear stress after 12 hours of exposure and was increased (to 250% of stationary control; P<0.05) after 24 hours at high shear stress. The same trends in PAR-1 mRNA levels were observed in rat smooth muscle cells, indicating that the effects of shear stress on human PAR-1 were not species-specific. Flow cytometry and ELISA techniques using rat smooth muscle cells and HASMCs, respectively, provided evidence that shear stress exerted similar effects on cell surface-associated PAR-1 and tPA protein released into the conditioned media. The decrease in PAR-1 mRNA and protein had functional consequences for HASMCs, such as inhibition of [Ca2+] mobilization in response to thrombin stimulation. These data indicate that human PAR-1 and tPA gene expression are regulated differentially by shear stress, in a pattern consistent with their putative roles in several arterial vascular pathologies.

NASA Discipline Cell Biology↗
NASA NTRS1997

COL1A1 transgene expression in stably transfected osteoblastic cells. Relative contributions of first intron, 3'-flanking sequences, and sequences derived from the body of the human COL1A1 minigene

Collagen reporter gene constructs have be used to identify cell-specific sequences needed for transcriptional activation. The elements required for endogenous levels of COL1A1 expression, however, have not been elucidated. The human COL1A1 minigene is expressed at high levels and likely harbors sequence elements required for endogenous levels of activity. Using stably transfected osteoblastic Py1a cells, we studied a series of constructs (pOBColCAT) designed to characterize further the elements required for high level of expression. pOBColCAT, which contains the COL1A1 first intron, was expressed at 50-100-fold higher levels than ColCAT 3.6, which lacks the first intron. This difference is best explained by improved mRNA processing rather than a transcriptional effect. Furthermore, variation in activity observed with the intron deletion constructs is best explained by altered mRNA splicing. Two major regions of the human COL1A1 minigene, the 3'-flanking sequences and the minigene body, were introduced into pOBColCAT to assess both transcriptional enhancing activity and the effect on mRNA stability. Analysis of the minigene body, which includes the first five exons and introns fused with the terminal six introns and exons, revealed an orientation-independent 5-fold increase in CAT activity. In contrast the 3'-flanking sequences gave rise to a modest 61% increase in CAT activity. Neither region increased the mRNA half-life of the parent construct, suggesting that CAT-specific mRNA instability elements may serve as dominant negative regulators of stability. This study suggests that other sites within the body of the COL1A1 minigene are important for high expression, e.g. during periods of rapid extracellular matrix production.

NASA Discipline Cell Biology↗
NASA NTRS1997

A mathematical model of diurnal variations in human plasma melatonin levels

Studies in animals and humans suggest that the diurnal pattern in plasma melatonin levels is due to the hormone's rates of synthesis, circulatory infusion and clearance, circadian control of synthesis onset and offset, environmental lighting conditions, and error in the melatonin immunoassay. A two-dimensional linear differential equation model of the hormone is formulated and is used to analyze plasma melatonin levels in 18 normal healthy male subjects during a constant routine. Recently developed Bayesian statistical procedures are used to incorporate correctly the magnitude of the immunoassay error into the analysis. The estimated parameters [median (range)] were clearance half-life of 23.67 (14.79-59.93) min, synthesis onset time of 2206 (1940-0029), synthesis offset time of 0621 (0246-0817), and maximum N-acetyltransferase activity of 7.17(2.34-17.93) pmol x l(-1) x min(-1). All were in good agreement with values from previous reports. The difference between synthesis offset time and the phase of the core temperature minimum was 1 h 15 min (-4 h 38 min-2 h 43 min). The correlation between synthesis onset and the dim light melatonin onset was 0.93. Our model provides a more physiologically plausible estimate of the melatonin synthesis onset time than that given by the dim light melatonin onset and the first reliable means of estimating the phase of synthesis offset. Our analysis shows that the circadian and pharmacokinetics parameters of melatonin can be reliably estimated from a single model.

NASA Discipline Number 70-10↗
NASA NTRS1994

Extracellular matrix controls tubulin monomer levels in hepatocytes by regulating protein turnover

Cells have evolved an autoregulatory mechanism to dampen variations in the concentration of tubulin monomer that is available to polymerize into microtubules (MTs), a process that is known as tubulin autoregulation. However, thermodynamic analysis of MT polymerization predicts that the concentration of free tubulin monomer must vary if MTs are to remain stable under different mechanical loads that result from changes in cell adhesion to the extracellular matrix (ECM). To determine how these seemingly contradictory regulatory mechanisms coexist in cells, we measured changes in the masses of tubulin monomer and polymer that resulted from altering cell-ECM contacts. Primary rat hepatocytes were cultured in chemically defined medium on bacteriological petri dishes that were precoated with different densities of laminin (LM). Increasing the LM density from low to high (1-1000 ng/cm2), promoted cell spreading (average projected cell area increased from 1200 to 6000 microns2) and resulted in formation of a greatly extended MT network. Nevertheless, the steady-state mass of tubulin polymer was similar at 48 h, regardless of cell shape or ECM density. In contrast, round hepatocytes on low LM contained a threefold higher mass of tubulin monomer when compared with spread cells on high LM. Furthermore, similar results were obtained whether LM, fibronectin, or type I collagen were used for cell attachment. Tubulin autoregulation appeared to function normally in these cells because tubulin mRNA levels and protein synthetic rates were greatly depressed in round cells that contained the highest level of free tubulin monomer. However, the rate of tubulin protein degradation slowed, causing the tubulin half-life to increase from approximately 24 to 55 h as the LM density was lowered from high to low and cell rounding was promoted. These results indicate that the set-point for the tubulin monomer mass in hepatocytes can be regulated by altering the density of ECM contacts and changing cell shape. This finding is consistent with a mechanism of MT regulation in which the ECM stabilizes MTs by both accepting transfer of mechanical loads and altering tubulin degradation in cells that continue to autoregulate tubulin synthesis.

Non-NASA Center↗
NASA NTRS1957

Steady Nuclear Combustion in Rockets

The astrophysical theory of stationary nuclear reactions in stars is applied to the conditions that would be met in the practical engineering cases that would differ from the former, particularly with respect to the much lower combustion pressures, dimensions of the reacting volume, and burnup times. This application yields maximum rates of hear production per unit volume of reacting gas occurring at about 10(exp 8) K in the cases of reactions between the hydrogen isotopes, but yields higher rates for heavier atoms. For the former, with chamber pressures of the order of 100 atmospheres, the energy production for nuclear combustion reaches values of about 10(exp 4) kilocalories per cubic meter per second, which approaches the magnitude for the familiar chemical fuels. The values are substantially lower for heavier atoms, and increase with the square of the combustion pressure. The half-life of the burnup in the fastest reactions may drop to values as low as those for chemical fuels so that, despite the high temperature, the radiated energy can remain smaller than the energy produced, particularly if an inefficiently radiating (i.e., easily completely ionized reacting material like hydrogen), is used. On the other hand, the fraction of completely ionized particles in the gases undergoing nuclear combustion must not exceed a certain upper limit because the densities (approximately 10(exp -10) grams per cubic centimeter)) lie in the range of high vacua and only for the previously mentioned fraction of nonionized particles can mean free paths be retained small enough so that the chamber diameters of several dozen meters will suffice. Under these conditions it appears that continuously maintained stable nuclear reactions at practical pressures and dimensions are fundamentally possible and their application can be visualized as energy sources for power plants and propulsion units.

Saenger, E.↗
NASA NTRS2004

Bioavailability and Pharmacodynamics of Promethazine in Human Subjects

The acute effects of exposure to microgravity include the development of space motion sickness, which usually requires therapeutic intervention. The current drug of choice, promethazine (PMZ), is available to astronauts in three different dosage forms during space flight; its side effects include nausea, dizziness, sedation and impaired psychomotor performance. This ground-based study is designed to validate flight-suitable methods for pharmacodynamic evaluation of PMZ and to estimate bioavailability and pharmacodynamics of PMZ. Experimental design consists of intramuscular administration of three doses of PMZ (12.5,25 and 50 mg) and placebo in a randomized double blind fashion to human subjects and collecting blood, urine and saliva samples for 72 h. Subjects also complete cognitive performance test batteries, WinSCAT (Windows based Space Cognitive Assessment Test) and ARES (ANAM Readiness Evaluation System). Preliminary results indicate a significant relationship (p=9.88e-05) between circulating PMZ levels and cognitive performance parameters. Time to accurately complete memory tasks increases significantly with concentrations; higher concentrations also increase response time and decrease accuracy of substitution and matching tasks. AUC and half-life estimates for PMZ ranged between 0.12 and 1.7 mg.h/L and 15 and 50 h, respectively. These preliminary results indicate that PMZ may exhibit dose-dependent pharmacokinetics in humans; also, WinSCAT and ARES are sensitive for pharmacodynamic assessment of PMZ, and may be applicable for assessing the pharmacodynamics of other neurocognitive drugs.

Boyd, J. L.↗
NASA NTRS2006

What Happens to bone health during and after spaceflight?

Weightless conditions of space flight accelerate bone loss. There are no reports to date that address whether the bone that is lost during spaceflight could ever be recovered. Spaceinduced bone loss in astronauts is evaluated at the Johnson Space Center (JSC) by measurement of bone mineral density (BMD) by Dual-energy x-ray absorptiometry (DXA) scans. Astronauts are routinely scanned preflight and at various time points postflight (greater than or equal to Return+2 days). Two sets of BMD data were used to model spaceflight-induced loss and skeletal recovery in crewmembers following long-duration spaceflight missions (4-6 months). Group I was from astronauts (n=7) who were systematically scanned at multiple time points during the postflight period as part of a research protocol to investigate skeletal recovery. Group II came from a total of 49 sets of preflight and postflight data obtained by different protocols. These data were from 39 different crewmembers some of whom served on multiple flights. Changes in BMD (between pre- and postflight BMD) were plotted as a function of time (days-after-landing); plotted data were fitted to an exponential equation which enabled estimations of i) BMD change at day 0 after landing and ii) the number of days by which 50% of the lost bone is recovered (half-life). These fits were performed for BMD of the lumbar spine, trochanter, pelvis, femoral neck and calcaneus. There was consistency between the models for BMD recovery. Based upon the exponential model of BMD restoration, recovery following long-duration missions appears to be substantially complete in crewmembers within 36 months following return to Earth.

Sibonga, Jean D.↗
NASA NTRS2006

Skeletal Recovery Following Long-Duration Spaceflight Missions as Determined by Preflight and Postflight DXA Scans of 45 Crew Members

Introduction: The loss of bone mineral in astronauts during spaceflight has been investigated throughout the more than 40 years of bone research in space. Consequently, it is a medical requirement at NASA that changes in bone mass be monitored in crew members by measurements of bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA). This report is the first to evaluate medical data to address the recovery of bone mineral that is lost during spaceflight. Methods: DXA scans are performed before and after flight in astronauts who serve on long-duration missions (4-6 months) to ensure that medical standards for flight certification are met, to evaluate the effects of spaceflight and to monitor the restoration to preflight BMD status after return to Earth. Through cooperative agreements with the Russian Space Agency, the Bone and Mineral Lab at NASA Johnson Space Center (Houston, TX), also had access to BMD data from cosmonauts who had flown on long-duration missions yielding data from a total of 45 individual crew members. Changes in BMD (between 56 different sets of pre- and postflight measurements) were plotted as a function of time (days after landing); plotted data were fitted to an exponential mathematical model that determined i) BMD change at day 0 after landing and ii) the number of days after which 50% of the lost bone was recovered ("Recovery Half-Life"). These fits were performed for BMD of the lumbar spine, trochanter, pelvis, femoral neck and calcaneus. Results: In sum, averaged losses of bone mineral after spaceflight ranged between 2-9% for sites in the axial and appendicular skeleton. The fitted postflight BMD values predicted a 50% recovery of bone loss for all sites within 9 months.

Sibonga, J. D.↗
NASA NTRS2007

Determination of Scopolamine in Human Saliva Using Solid Phase Extraction and LC/MS/MS

Purpose: Scopolamine is the preferred treatment for motion sickness during space flight because of its quick onset of action, short half-life and favorable side-effect profile. The dose administered depends on the mode of administration and usually ranges between 0.1 and 0.8 mg. Such small doses make it difficult to detect concentrations of scopolamine in biological fluids by using conventional HPLC methods. To measure scopolamine in saliva and thereby to evaluate the pharmacokinetics of scopolamine, we developed an LC/MS/MS method using off-line solid phase extraction. Method: Samples (0.5mL) were loaded onto Waters Oasis HLB co-polymer cartridges (10 mg, 1 mL) and eluted with 0.5 mL methanol without evaporation and reconstitution. HPLC separation of the eluted sample was performed using an Agilent Zorbax SB-CN column (50 x 2.1 mm) at a flow rate of 0.2 mL/min for 4 minutes. The mobile phase for separation was 90:10 (v/v) methanol: ammonium acetate (2 mM) in water, pH 5.0 +/- 0.1. Concentrations of scopolamine were determined using a Micromass Quattro Micro(TM) mass spectrometer with electrospray ionization (ESI). ESI mass spectra were acquired in positive ion mode with multiple reaction monitoring for the determination of scopolamine m/z = 304.2 yields 138.1 and internal standard (IS) hyoscyamine m/z = 290.2 yields 124.1. Results: The method is rapid, reproducible, specific and has the following parameters: scopolamine and the IS are eluted at 1.7 and 3.2 min respectively. The linear range is 50-5000 pg/mL for scopolamine in saliva with correlation coefficients > 0.99 with a CV < 0.5 %. The intra-day and inter-day CVs are < 15 % for quality control samples with concentrations of 75, 300, 750 and 3000 pg/mL of scopolamine in human saliva. Conclusion: Solid phase extraction allows more rapid sample preparation and greater precision than liquid extraction. Furthermore, we increased the sensitivity and specificity by adjusting the LC mobile phase and using an MS/MS detector.

Wang, Zuwei↗
NASA NTRS2008

A Modified LC/MS/MS Method with Enhanced Sensitivity for the Determination of Scopolamine in Human Plasma

Intranasal scopolamine is a choice drug for the treatment of motion sickness during space flight because of its quick onset of action, short half-life and favorable sideeffects profile. The dose administered usually ranges between 0.1 and 0.4 mg. Such small doses make it difficult to detect concentrations of scopolamine in biological fluids using existing sensitive LC/MS/MS method, especially when the biological sample volumes are limited. To measure scopolamine in human plasma to facilitate pharmacokinetic evaluation of the drug, we developed a sensitive LC/MS/MS method using 96 well micro elution plates for solid phase extraction (SPE) of scopolamine in human plasma. Human plasma (100-250 micro L) were loaded onto Waters Oasis HLB 96 well micro elution plate and eluted with 50 L of organic solvent without evaporation and reconstitution. HPLC separation of the eluted sample was performed using an Agilent Zorbax SB-CN column (50 x 2.1 mm) at a flow rate of 0.2 mL/min for 3 minutes. The mobile phase for separation was 80:20 (v/v) methanol: ammonium acetate (30 mM) in water. Concentrations of scopolamine were determined using a Micromass Quattro Micro(TM) mass spectrometer with electrospray ionization (ESI). ESI mass spectra were acquired in positive ion mode with multiple reaction monitoring for the determination of scopolamine m/z = 304.2 right arrow 138.1 and internal standard hyoscyamine m/z = 290.2 right arrow 124.1. The method is rapid, reproducible, specific and has the following parameters: scopolamine and the IS are eluted at about 1.1 and 1.7 min respectively. The linear range is 25-10000 pg/mL for scopolamine in human plasma with correlation coefficients greater than 0.99 and CV less than 0.5%. The intra-day and inter-day CVs are less than 15% for quality control samples with concentrations of 75,300, and 750 pg/mL of scopolamine in human plasma. SPE using 96 well micro elution plates allows rapid sample preparation and enhanced sensitivity for the LC/MS/MS determination of scopolamine in a small volume of biological samples. The new method is also cost effective since it uses a small volume of organic solvents compared to the methods using SPE cartridges or regular 96 well SPE plates. This method can be successfully used for bioavailability and pharmacokinetic evaluations of scopolamine, especially when volumes of biological samples are limited. Further investigation to use automated SPE system with 96 well micro elution plates is planned.

Wang, Zuwei↗
NASA NTRS2009

Lunar Dust and Lunar Simulant Activation, Monitoring, Solution and Cellular Toxicity Properties

During the Apollo missions, many undesirable situations were encountered that must be mitigated prior to returning humans to the moon. Lunar dust (that part of the lunar regolith less than 20 m in diameter) was found to produce several problems with astronaut s suits and helmets, mechanical seals and equipment, and could have conceivably produced harmful physiological effects for the astronauts. For instance, the abrasive nature of the dust was found to cause malfunctions of various joints and seals of the spacecraft and suits. Additionally, though efforts were made to exclude lunar dust from the cabin of the lunar module, a significant amount of material nonetheless found its way inside. With the loss of gravity correlated with ascent of the lunar module from the lunar surface to rendezvous with the command module, much of the major portions of the contaminating soil and dust began to float, irritating the astronaut s eyes and being inhaled into their lungs. Our goal has been to understand some of the properties of lunar dust that could lead to possible hazards for humans. Due to the lack of an atmosphere, there is nothing to protect the lunar soil from ultraviolet radiation, solar wind, and meteorite impacts. These processes could all serve to activate the soil, or produce reactive surface species. In order to understand the possible toxic effects of the reactive dust, it is necessary to reactivate the dust, as samples returned during the Apollo missions were exposed to the atmosphere of the Earth. We have used grinding and UV exposure to mimic some of the processes occurring on the Moon. The level of activation has been monitored using two methods: fluorescence spectroscopy and electron paramagnetic resonance spectroscopy (EPR). These techniques allow the monitoring of hydroxyl radical production in solution. We have found that grinding of lunar dust produces 2-3 times the concentration of hydroxyl radicals as lunar simulant and 10 times that of quartz. Exposure of the lunar dust to UV radiation under vacuum was also found to lead to hydroxyl radical production. After grinding, we have also monitored loss of reactivity of the dusts by exposing them to conditions of known humidity and temperature. From these tests, it was found that the reactivity half-life of lunar simulant is approximately 3 hours, while that of quartz is approximately 2 hours. Placing lunar dust in solution could lead to effects on mechanical and physiological systems, as well as other biological systems. For instance, while it is known that lunar dust is highly abrasive and caused a variety of problems with suits and equipment during Apollo, it is unknown as to how these properties might be affected in the presence of water or other liquids. It is possible that the dust may release minerals (e.g., metallic nanophase Fe) into solution that could speed corrosion or rust. Also, as lunar dust produces hydroxyl radicals (and possibly other reactive oxygen species) in solution, these radicals could also lead to the breakdown of suit or habitat materials. In the body (i.e., in lung solution), the effects could be two-fold. First, if the lunar dust dissolves, it may release an excess of elements (such as zero-valence metallic Fe) that are necessary for bodily functions but only in certain concentration ranges. For lunar dust, the presence of nanophase iron being released into the body is a concern. Secondly, the hydroxyl radicals or other reactive oxygen species produced by the dust in solution could conceivably interact with cells, leading to various problems. We have studied the dissolution of both ground and unground lunar simulant in buffer solutions of different pH. The concentration of a number of species was determined using mass spectrometry. These studies showed that lowering the pH of the solution causes a dramatic increase in the amount of each element released into solution and that grinding also produces higher concentrations. Finally, we have perfmed initial tests aimed at understanding the effects of lunar simulant on cellular systems. Alveolar epithelial cells were cultured and exposed to different concentrations of dust suspended in cell culture media. After predetermined amounts of time, the media was removed and the concentrations of important inflammatory cytokines (IL6, IL8, and TNF-alpha ) were measured. The results of these tests are being used to develop the correct protocols for tests to be performed using lunar dust samples.

Jeevarajan, A.S.↗
NASA NTRS2009

Bioavailability of Promethazine during Spaceflight

Promethazine (PMZ) is the choice anti-motion sickness medication for treating space motion sickness (SMS) during flight. The side effects associated with PMZ include dizziness, drowsiness, sedation, and impaired psychomotor performance which could impact crew performance and mission operations. Early anecdotal reports from crewmembers indicate that these central nervous system side effects of PMZ are absent or greatly attenuated in microgravity, potentially due to changes in pharmacokinetics (PK) and pharmacodynamics in microgravity. These changes could also affect the therapeutic effectiveness of drugs in general and PMZ, in particular. In this investigation, we examined bioavailability and associated pharmacokinetics of PMZ in astronauts during and after space flight. Methods. Nine astronauts received, per their preference, PMZ (25 or 50 mg as intramuscular injection, oral tablet, or rectal suppository) on flight day one for the treatment of SMS and subsequently collected saliva samples and completed sleepiness scores for 72 h post dose. Thirty days after the astronauts returned to Earth, they repeated the protocol. Bioavailability and PK parameters were calculated and compared between flight and ground. Results. Maximum concentration (Cmax) was lower and time to reach Cmax (tmax) was longer in flight than on the ground. Area under the curve (AUC), a measure of bioavailability, was lower and biological half-life (t1/2) was longer in flight than on the ground. Conclusion. Results indicate that bioavailability of PMZ is reduced during spaceflight. Number of samples, sampling method, and sampling schedule significantly affected PK parameter estimates.

Boyd, Jason L.↗
NASA NTRS2004

Photophysics of Laser Dye-Doped Polymer Membranes for Laser-Induced Fluorescence Photogrammetry

Laser-induced fluorescence target generation in dye-doped polymer films has recently been introduced as a promising alternative to more traditional photogrammetric targeting techniques for surface profiling of highly transparent or reflective membrane structures. We investigate the photophysics of these dye-doped polymers to help determine their long-term durability and suitability for laser-induced fluorescence photogrammetric targeting. These investigations included experimental analysis of the fluorescence emission pattern, spectral content, temporal lifetime, linearity, and half-life. Results are presented that reveal an emission pattern wider than normal Lambertian diffuse surface scatter, a fluorescence time constant of 6.6 ns, a pump saturation level of approximately 20 micro J/mm(exp 2), and a useful lifetime of more than 300,000 measurements. Furthermore, two demonstrations of photogrammetric measurements by laser-induced fluorescence targeting are presented, showing agreement between photogrammetric and physically measured dimensions within the measurement scatter of 100 micron.

Dorrington, Adrian A.↗
NASA NTRS2006

Alpha-Voltaic Sources Using Diamond as Conversion Medium

A family of proposed miniature sources of power would exploit the direct conversion of the kinetic energy of a particles into electricity in diamond semiconductor diodes. These power sources would function over a wide range of temperatures encountered in terrestrial and outer-space environments. These sources are expected to have operational lifetimes of 10 to 20 years and energy conversion efficiencies >35 percent. A power source according to the proposal would include a pair of devices like that shown in the figure. Each device would contain Schottky and p/n diode devices made from high-band-gap, radiation-hard diamond substrates. The n and p layers in the diode portion would be doped sparsely (<1014 cm-3) in order to maximize the volume of the depletion region and thereby maximize efficiency. The diode layers would be supported by an undoped diamond substrate. The source of a particles would be a thin film of 244Cm (half-life 18 years) sandwiched between the two paired devices. The sandwich arrangement would force almost every a particle to go through the active volume of at least one of the devices. Typical a particle track lengths in the devices would range from 20 to 30 microns. The a particles would be made to stop only in the undoped substrates to prevent damage to the crystalline structures of the diode portions. The overall dimensions of a typical source are expected to be about 2 by 2 by 1 mm. Assuming an initial 244Cm mass of 20 mg, the estimated initial output of the source is 20 mW (a current of 20 mA at a potential of 1 V).

Patel, Jagadish U.↗
NASA NTRS2006

On Release of Microbe-Laden Particles from Mars Landers

A paper presents a study in which rates of release of small particles from Mars lander spacecraft into the Martian atmosphere were estimated from first principles. Because such particles can consist of, or be laden with, terrestrial microbes, the study was undertaken to understand their potential for biological contamination of Mars. The study included taking account of forces and energies involved in adhesion of particles and of three mechanisms of dislodgement of particles from the surface of a Mars lander: wind shear, wind-driven impingement of suspended dust, and impingement of wind-driven local saltating sand particles. Wind shear was determined to be effective in dislodging only particles larger than about 10 microns and would probably be of limited interest because such large particles could be removed by pre-flight cleaning of the spacecraft, and their number on the launched spacecraft would thus be relatively small. Dislodgement by wind-driven dust was found to be characterized by an adhesion half-life of the order of 10,000 years judged to be too long to be of concern. Dislodgement by saltating sand particles, including skirts of dust devils, was found to be of potential importance, depending on the sizes of the spacecraft-attached particles and characteristics of both Mars sand-particle and spacecraft surfaces.

Bellan, Josette↗
NASA NTRS2004

Miniature Radioisotope Thermoelectric Power Cubes

Cube-shaped thermoelectric devices energized by a particles from radioactive decay of Cm-244 have been proposed as long-lived sources of power. These power cubes are intended especially for incorporation into electronic circuits that must operate in dark, extremely cold locations (e.g., polar locations or deep underwater on Earth, or in deep interplanetary space). Unlike conventional radioisotope thermoelectric generators used heretofore as central power sources in some spacecraft, the proposed power cubes would be small enough (volumes would range between 0.1 and 0.2 cm3) to play the roles of batteries that are parts of, and dedicated to, individual electronic-circuit packages. Unlike electrochemical batteries, these power cubes would perform well at low temperatures. They would also last much longer: given that the half-life of Cm-244 is 18 years, a power cube could remain adequate as a power source for years, depending on the power demand in its particular application.

Patel, Jagdish U.↗