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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Diversity of micro-fungi in an Antarctic dry valley

The fungal microflora of a dry valley in Southern Victoria Land near McMurdo Sound, Antarctica, was investigated. Samples were collected from introduced objects such as a mummified penguin and spent chewing tobacco in addition to the sparse soil found in rock fissures, isolated moss colonies, shoreline deposit materials, CaCO3 precipitates, and microbial mat debris obtained from the frozen surface of the lake in the basin of Taylor Valley. Using conventional media and techniques, all collection sites yielded populations of yeasts and filamentous fungi. Water samples and live microbial mats from beneath the lake ice yielded species of fungi along with an abundance of bacteria.

NASA Discipline Exobiology↗
NASA NTRSDate not supplied

Watching Without Seeing a Tool to Surveil Astronaut Health Outcomes While Maintaining Astronaut Medical Privacy

BACKGROUND The Privacy Act of 1974 regulates the use a nd disclosure of personally identifiable information by US Federal agencies. The Act applies to biographical, financial, a nd other identity-linked information, a s well a s personal health information (PHI). As such, the use of astronaut PHI is limited to authorized personnel for preapproved uses, with data reporting often limited to aggregated information about groups. These limitations on the use a nd reporting of astronaut PHI complicates surveillance efforts, wherein epidemiologists a t the National Aeronautics and Space Administration (NASA)monitor the incidence of targeted health conditions in the astronaut population, or to discover emerging trends of aging and disease. Stratification on one or more covariates –particularly time-period, sex, a nd mission participation –can lead to extremely small datasets such that the reporting of results is potentially attributable to individuals. An additional challenge is the small size of the astronaut population, both in terms of numbers of individuals a s well a s in terms of density of exposure time. Such small datasets yield volatile rate estimates that are difficult to interpret. To a id the epidemiological surveillance efforts, a surveillance tool is required that can (a) satisfy the need for rapid computation of condition-specific incidence and mortality rates; (b) improve the statistical estimates of these estimated rates; and (c) maintain astronaut privacy. Here we describe a nd demonstrate such a tool. METHODS We devised a system that models incidence a nd mortality rates rather than calculating them directly. This ha s the advantage of using all the available data to derive the estimates, lea ding to rates that a re not attributable to any one individual, a nd a re a s numerically stable a s they can be given the extremely limited data. The system models disease endpoints using a Poisson regression model with exposure density (measured in person-years) a s a n offset term. By doing so the model is estimating event counts per person-year, equivalent to modeling the rates directly. It uses a standard (pre-specified)set of covariates; the system does not engage in “model-building” as model parsimony is not the goa l. Instead, it is explicitly recognized that if a covariate is not statistically significant a nd not a confounder then it will likely have very little effect on the estimate of the incidence a nd mortality rates. Users are able to specify the disease endpoint of interest and the covariates over which they would like to stratify. The system then uses the resulting model to compute the estimated rates for the user-chosen configuration of variables as visualizes those either over an age range within a specified time-period, or over time for astronauts with a specified age range. RESULTS The first iteration of the tool computes incidence a nd mortality rates for cardiovascular conditions and cancers. Code ha s been developed to retrieve the appropriate data from the IMPALA analysis platform, compute the models for incidence a nd mortality, a nd then use those models to generate the corresponding rate curves. A companion graphical user interface allows the user to specify the curves and visualize the results. CONCLUSIONS It is important to note that the rapid surveillance tool described here is neither meant to be a definitive assessment of the incidence or mortality of any particular disease or condition in the astronaut population, nor is it meant to be used for research purposes. Rather, it is meant as an early indicator that in-depth investigation may be warranted. By automating a repetitive process and leveraging carefully curated astronaut health outcomes, the tool makes possible a rapid “first look” into known areas of concern, and, if used judiciously, may surface new areas of concern for long-term astronaut health. This work is supported in part by the Translational Research Institute for Space Health (TRISH) through NASA Cooperative Agreement NNX16AO69A.

R J Reynolds↗
NASA NTRS1995

Star counts from the HST Snapshot Survey. 2: Wide binaries

We report on a study of the first sample of wide binaries whose members are primarily in the old component of the Galactic disk. The binaries were discovered in 446 fields imaged with the Hubble Space Telescope (HST) Planetary Camera to an average magnitude limit of V = 2.13, as part of the Snapshot Survey for gravitational lenses. Most of the fields are at moderate to high Galactic latitude. Their total area is 0.15 deg squared. Because of the relatively faint magnitude limit, the observations are sensitive primarily to binaries in the old disk with heights above the Galactic plane of 500-1500 pc, absolute magnitudes of M(sub v) = 6-11, and physical separations of 130-4000 AU. By contrast, most previous surveys have been sensitive to binaries composed of earlier-type stars lying closer to the plane, that is, to a younger population. We find that 4% of the disk stars in the Snapshot sample have fainter companions within 1.5 mag, and separations in the range 0.13 sec is less than theta which is less than 4.0 sec. The distribution of angular separations can be fitted to a power law F(theta) is proportional to theta(exp -l), where l = 1.2 +/- 0.4, in agreement with most previous studies. The binaries in the Snapshot sample have bluer colors than would be expected for random pairs of field stars.

Gould, Andrew↗
NASA NTRS1994

Galaxy pairs in deep HST images: Evidence for evolution in the galaxy merger rate

We use four deep serendipitous fields observed with the Hubble Space Telescope (HST) Wide-Field Camera to constrain the rate of galaxy merging between the current epoch and z approximately equals 0.7. Since most mergers occur between members of bound pairs, the merger rate is given to a good approximation by (half) the rate of disappearance of galaxies in pairs. An objective criterion for pair membership shows that 34% +/- 9% of our HST galaxies with I = 18-22 belong to pairs, compared to 7% locally. This means that about 13% of the galaxy population has disappeared due to merging in the cosmic epoch corresponding to this magnitude interval (or 0.1 approximately less than z approximately less than 0.7). Our pair fraction is a lower limit: correction for pair members falling below our detection threshold might raise the fraction to approximately 50%. Since we address only two-galaxy merging, these values do not include physical systems of higher multiplicity. Incorporating I-band field-galaxy redshift distributions, the pair fraction grows with redshift as alpha(1 + z)(exp 3.5 +/- 0.5) and the merger rate as (1 + z)(exp 2.5 +/- 0.5). This may have significant implications for the interpretation of galaxy counts (disappearance of faint blue galaxies), the cosmological evolution of faint radio sources and quasars (which evolve approximately as (1 + z)(exp 3), the similarity in the power law is necessary but not sufficient evidence for a causal relation), statistics of QSO companions, the galaxy content in distant clusters, and the merging history of a 'typical' galaxy.

Burkey, Jordan M.↗
NASA NTRS1997

Cratering on Titan: A Pre-Cassini Perspective

The NASA-ESA Cassini mission, comprising a formidably instrumented orbiter and parachute-borne probe to be launched this October, promises to reveal a crater population on Titan that has been heretofore hidden by atmospheric haze. This population on the largest remaining unexplored surface in the solar system will be invaluable in comparative planetological studies, since it introduces evidence of the atmospheric effects of cratering on an icy satellite. Here, I highlight some impact features we may hope to find and could devote some modeling effort toward. Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s Atmosphere -94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface.Titan in a Nutshell: Radius= 2575 km. Density= 1880 kg/cubic m consistent with rock-ice composition. Surface pressure = 1.5 bar. Surface gravity = 1.35 m/square s; Atmosphere about 94% N2 6% CH, Surface temperature = 94K Tropopause temperature = 70K at 40 km alt. Probable liquid hydrocarbon deposits exist on or near the surface. Titan is comparable to Callisto and Ganymede for strength/gravity, Mars/Earth/Venus for atmospheric interaction, and Hyperion, Rhea, and Iapetus for impactor distribution. The leading/trailing asymmetry of crater density from heliocentric impactors is expected to be about 5-6, in the absence of resurfacing. Any Saturnocentric impactor population is likely to alter this. In particular the impact disruption of Hyperion is noted; because of the 3:4 orbital resonance with Titan, fragments from the proto-Hyperion breakup would have rapidly accreted onto Titan. Titan's resurfacing history is of course unknown. The disruption of impactors into fragments that individually create small craters is expected to occur. A crude estimate suggests a maximum separation of about 2 km (compared with 4 km on Venus, or 0.5 km on Earth). Crater chains are unlikely on Titan, since impactors must pass close enough to Saturn to be tidally disrupted; as a result, they would suffer aerodynamic disruption. Crater counting on adjacent satellites gives densities of about 200 per 10 (exp 6) square km for 20-km-diameter craters. However, the presence of a thick atmosphere leads to atmospheric shielding, depleting the relative abundance of small craters. This has been evaluated by models, and the relative abundance of small craters may be due to a diagnostic atmospheric collapse. A number of radar-dark "splotches" have been detected on Venus; these have been attributed to the interaction of the surface with the atmospheric shockwave produced by the Tunguska-like explosion of a bolide in the atmosphere. Simple analogy suggests that similar features might occur on Titan, but the shocked mass density (which controls the momentum coupling between the surface and the shockwave) of Titan's cold N2 atmosphere is about 20x smaller than that of Venus's hot CO2 atmosphere. Unless ice is much more easily turned to rubble than is rock, such features seem less probable on Titan. When the energy deposited by an impact forms a fireball with an equilibrate greater than one scale height, the fireball expands upward and can distribute ejecta. on ballistic exoatmospheric trajectories. On Venus this process is believed to be responsible for the parabolic features; the interaction of various-sized particles falling through the atmosphere with the zonal wind field winnows the particles to form a parabolic deposit. Although such a process is possible on Titan, the large scale height at higher altitudes would make it more difficult. Comparison with craters on other icy satellites suggests that craters on Titan will be fairly shallow (depth/diameter about 0.1) and craters greater than 10 km in diameter will have central peaks or domed bases, perhaps with central pits. The formation of ejecta. blankets may involve the atmosphere in a significant way, both by restraining the expansion of the ejecta cloud and by influencing the thermal history of the ejecta. Compared with Venus, Titan's atmosphere will chill an impact melt somewhat quickly, so the long ejecta flows seen on Venus seem less likely, detailed modeling needs to be performed to determine the impact melt production. Crater topography on Titan may be highlighted by the influence of liquids forming crater lakes. Craters with central peaks will typically form ring-shaped lakes, although horseshoe-shaped takes may be common; domed craters with central pits may even form bullseye lakes with islands with central ponds. If liquids have covered a substantial part of Titan's surface for a substantial period, hydroblemes and tsunami deposits may be common.

Lorenz, R. D.↗
NASA NTRS1998

Viruses in Antarctic lakes

Water samples collected from four perennially ice-covered Antarctic lakes during the austral summer of 1996-1997 contained high densities of extracellular viruses. Many of these viruses were found to be morphologically similar to double-stranded DNA viruses that are known to infect algae and protozoa. These constitute the first observations of viruses in perennially ice-covered polar lakes. The abundance of planktonic viruses and data suggesting substantial production potential (relative to bacteria] secondary and photosynthetic primary production) indicate that viral lysis may be a major factor in the regulation of microbial populations in these extreme environments. Furthermore, we suggest that Antarctic lakes may be a reservoir of previously undescribed viruses that possess novel biological and biochemical characteristics.

Non-NASA Center↗
NASA NTRS2003

Bondi Accretion and the Problem of the Missing Isolated Neutron Stars

A large number of neutron stars (NSs), approximately 10(exp 9), populate the Galaxy, but only a tiny fraction of them is observable during the short radio pulsar lifetime. The majority of these isolated NSs, too cold to be detectable by their own thermal emission, should be visible in X-rays as a result of accretion from the interstellar medium. The ROSAT All-Sky Survey has, however, shown that such accreting isolated NSs are very elusive: only a few tentative candidates have been identified, contrary to theoretical predictions that up to several thousand should be seen. We suggest that the fundamental reason for this discrepancy lies in the use of the standard Bondi formula to estimate the accretion rates. We compute the expected source counts using updated estimates of the pulsar velocity distribution, realistic hydrogen atmosphere spectra, and a modified expression for the Bondi accretion rate, as suggested by recent MHD simulations and supported by direct observations in the case of accretion around supermassive black holes in nearby galaxies and in our own. We find that, whereas the inclusion of atmospheric spectra partly compensates for the reduction in the counts due to the higher mean velocities of the new distribution, the modified Bondi formula dramatically suppresses the source counts. The new predictions are consistent with a null detection at the ROSAT sensitivity.

Perna, Rosalba↗
NASA NTRS2010

Evaluation of an ATP Assay to Quantify Bacterial Attachment to Surfaces in Reduced Gravity

Aim: To develop an assay to quantify the biomass of attached cells and biofilm formed on wetted surfaces in variable-gravity environments. Methods and Results: Liquid cultures of Pseudomonas aeruginosa were exposed to 30-35 brief cycles of hypergravity (< 2-g) followed by free fall (i.e., reduced gravity) equivalent to either lunar-g (i.e., 0.17 normal Earth gravity) or micro-g (i.e., < 0.001 normal Earth gravity) in an aircraft flying a series of parabolas. Over the course of two days of parabolic flight testing, 504 polymer or metal coupons were exposed to a stationary-phase population of P. aeruginosa strain ERC1 at a concentration of 1.0 x 10(exp 5) cells per milliliter. After the final parabola on each flight test day, half of the material coupon samples were treated with either 400 micro-g/L ionic silver fluoride (microgravity-exposed cultures) or 1% formalin (lunar-gravity-exposed cultures). The remaining sample coupons from each flight test day were not treated with a fixative. All samples were returned to the laboratory for analysis within 2 hours of landing, and all biochemical assays were completed within 8 hours of exposure to variable gravity. The intracellular ATP luminescent assay accurately reflected cell physiology compared to both cultivation-based and direct-count microscopy analyses. Cells exposed to variable gravity had more than twice as much intracellular ATP as control cells exposed only to normal Earth gravity.

Birmele, Michele N.↗
NASA NTRS2000

Leonid Storm Flux Analysis From One Leonid MAC Video AL50R

A detailed meteor flux analysis is presented of a seventeen-minute portion of one videotape, collected on November 18, 1999, during the Leonid Multi-instrument Aircraft Campaign. The data was recorded around the peak of the Leonid meteor storm using an intensified CCD camera pointed towards the low southern horizon. Positions of meteors on the sky were measured. These measured meteor distributions were compared to a Monte Carlo simulation, which is a new approach to parameter estimation for mass ratio and flux. Comparison of simulated flux versus observed flux levels, seen between 1:50:00 and 2:06:41 UT, indicate a magnitude population index of r = 1.8 +/- 0.1 and mass ratio of s = 1.64 +/- 0.06. The average spatial density of the material contributing to the Leonid storm peak is measured at 0.82 +/- 0.19 particles per square kilometer per hour for particles of at least absolute visual magnitude +6.5. Clustering analysis of the arrival times of Leonids impacting the earth's atmosphere over the total observing interval shows no enhancement or clumping down to time scales of the video frame rate. This indicates a uniformly random temporal distribution of particles in the stream encountered during the 1999 epoch. Based on the observed distribution of meteors on the sky and the model distribution, recommendations am made for the optimal pointing directions for video camera meteor counts during future ground and airborne missions.

Gural, Peter S.↗
NASA NTRS2010

Lunar Meteoroid Impact Observations and the Flux of Kilogram-sized Meteoroids

Lunar impact monitoring provides useful information about the flux of meteoroids in the tens of grams to kilograms size range. The large collecting area of the night side of the lunar disk, approximately 3.4x10(exp 6) sq km in our camera field-of-view, provides statistically significant counts of the meteoroids. Nearly 200 lunar impacts have been observed by our program in roughly 3.5 years. Photometric calibration of the flashes along with the luminous efficiency (determined using meteor showers1,2,3) and assumed velocities provide their sizes. The asymmetry in the flux on the evening and morning hemispheres of the Moon is compared with sporadic and shower sources to determine their most likely origin. The asymmetry between the two hemispheres seen in Figure 1 is due to the impact rate and not to observational bias. Comparison with other measurements of the large meteoroid fluxes is consistent with these measurements as shown in Figure 2. The flux of meteoroids in this size range has important implications for the near-Earth object population and for impact risk for lunar spacecraft

Suggs, Robert M.↗
NASA NTRS1991

Acridine orange staining reaction as an index of physiological activity in Escherichia coli

The assumption that the acridine orange (AO) color reaction may be used as an index of physiological activity was investigated in laboratory grown Escherichia coli. Spectrofluorometric observations of purified nucleic acids, ribosomes and the microscopic color of bacteriophage-infected cells stained with AO confirmed the theory that single-stranded nucleic acids emit orange to red fluorescence while those that are double-stranded fluoresce green in vivo. Bacteria growing actively in a rich medium could be distinguished from cells in stationary phase by the AO reaction. Cells from log phase appeared red, whereas those in stationary phase were green. However, this differentiation was not seen when the bacteria were grown in a minimal medium or when a variation of the staining method was used. Also, shifting bacteria in stationary phase to starvation conditions rapidly changed their AO staining reaction. Boiling and exposure to lethal concentrations of azide and formalin resulted in stationary-phase cells that appeared red after staining but bacteria killed with chlorine remained green. These findings indicate that the AO staining reaction may be suggestive of physiological activity under defined conditions. However, variables in staining and fixation procedures as well as uncertainties associated with mixed bacterial populations in environmental samples may produce results that are not consistent with the classical interpretation of this reaction. The importance of validating the putative physiological implications of this staining reaction is stressed.

NASA Discipline Number 04-10↗
NASA NTRS1993

Deep imaging of high redshift QSO fields below the Lyman limit. II - Number counts and colors of field galaxies

We present an analysis of the number counts and colors of faint galaxies to about 26.5 mag in the fields of two high Galactic latitude, very-high-redshift QSOs. We concentrate on the general properties of the field galaxies at faint magnitudes. In particular, we readdress the faint galaxy number counts and colors as a function of apparent magnitude and we reexamine the possible contribution of very-high-redshift galaxies to the faint samples. We find that the number counts to R = 26 are well fitted by the relation log N(m) = 0.31R + C. The G-band counts for the same galaxies are consistent with the same slope fainter than G about 23.5, but exhibit a much steeper slope at brighter magnitudes. At R = 25.5, the differential number counts have reached about 1.2 x 10 exp 5/sq deg; the same surface density of galaxies is reached at G = 26.5. We confirm the existence of a gradual 'blueing' trend of the field galaxies toward fainter apparent magnitude; however, the blueing trend appears to extend only as faint as G about 24, fainter than which both the (G-R) and (U sub n-G) colors appear to level off. The mean colors of faint galaxies are considerably redder than flat spectrum. There are essentially no objects to R = 26 which have spectral energy distributions which are bluer than flat spectrum. The potential contribution of very-high-redshift galaxies may have been underestimated in previous analyses; the current data are consistent with the same population of relatively luminous galaxies at z about 3 as exist at z about 0.7.

Steidel, Charles C.↗
NASA NTRS1973

Survival of bacterial isolates exposed to simulated Jovian trapped radiation belt electrons and solar wind protons

With missions to Jupiter, the spacecraft will be exposed for extended durations to solar wind radiation and the Jovian trapped radiation belt. This study is designed to determine the effect of these radiation environments on spacecraft bacterial isolates. The information can be used in the probability of contamination analysis for these missions. A bacterial subpopulation from Mariner Mars 1971 spacecraft (nine spore-forming and three non-spore-forming isolates) plus two comparative organisms, Staphylococcus epidermidis ATCC 17917 and a strain of Bacillus subtilis var. niger, were exposed to 2, 12, and 25 MeV electrons at different doses with simultaneous exposure to a vacuum of 1.3 x 10(-4) N m-2 at 20 and -20 degrees C. The radioresistance of the subpopulation was dependent on the isolate, dose and energy of electrons. Temperature affected the radioresistance of only the spore-forming isolates. Survival data indicated that spores were reduced approximately 1 log/1500 J kg-1 (10 J kg-1=1 krad), while non-spore-forming isolates (micrococci) were reduced 1.5-2 logs/1500 J kg-1 with the exception of an apparent radioresistant isolate whose resistance approached that of the spores. The subpopulation was found to be less resistant to lower energy than to higher energy electrons. The bacterial isolates were exposed to 3 keV protons under the same conditions as the electrons with a total fluence of 1.5 x 10(13) p cm-2 and a dose rate of 8.6 x 10(9) p cm-2 s-1. The results showed that only 20% of S. epidermidis and 45% of B. subtilis populations survived exposure to the 3 keV protons, while the mean survival of the spacecraft subpopulation was 45% with a range from 31.8% (non-spore-former) to 64.8% (non-spore-former). No significant difference existed between spore-forming and non-spore-forming isolates.

Electrons↗
NASA NTRS1992

Laboratory astrophysics under the ultraviolet, visible, and gravitational astrophysics research program: Oscillator strengths for ultraviolet atomic transitions

The conditions within astrophysical environments can be derived from observational data on atomic and molecular lines. For instance, the density and temperature of the gas are obtained from relative populations among energy levels. Information on populations comes about only when the correspondence between line strength and abundance is well determined. The conversion from line strength to abundance involves knowledge of meanlives and oscillator strengths. For many ultraviolet atomic transitions, unfortunately, the necessary data are either relatively imprecise or not available. Because of the need for more and better atomic oscillator strengths, our program was initiated. Through beam-foil spectroscopy, meanlives of ultraviolet atomic transitions are studied. In this technique, a nearly isotopically pure ion beam of the desired element is accelerated. The beam passes through a thin carbon foil (2 mg/cu cm), where neutralization, ionization, and excitation take place. The dominant process depends on the energy of the beam. Upon exiting the foil, the decay of excited states is monitored via single-photon-counting techniques. The resulting decay curve yields a meanlife. The oscillator strength is easily obtained from the meanlife when no other decay channels are presented. When other channels are present, additional measurements or theoretical calculations are performed in order to extract an oscillator strength. During the past year, three atomic systems have been studied experimentally and/or theoretically; they are Ar, I, Cl I, and N II. The results for the first two are important for studies of interstellar space, while the work on N II bears on processes occurring in planetary atmospheres.

Federman, Steven R.↗
NASA NTRS1993

Early Mars: A regional assessment of denudation chronology

Within the oldest highland units on Mars, the record of crater degradation indicates that fluvial resurfacing was responsible for modifying the Noachian through middle-Hesperian crater population. Based on crater frequency in the Noachian cratered terrain, age/elevation relations suggest that the highest exposures of Noachian dissected and plateau units became stabilized first, followed by successively lower units. In addition, studies of drainage networks indicate that the frequency of Noachian channels is greatest at high elevations. Together, these observations provide strong evidence of atmospheric involvement in volatile recycling. The long time period of crater modification also suggests that dendritic highland drainage was not simply the result of sapping by release of juvenile water, because the varied geologic units as well as the elevation dependence of stability ages makes it unlikely that subsurface recycling could provide a continuous supply of water for channel formation by sapping. While such geomorphic constraints on volatile history have been established by crater counts and stratigraphic relations using the 1:2M photomosaic series, photogeologic age relationships at the detailed level are needed to establish a specific chronology of erosion and sedimentation. Age relations for discrete erosional slopes and depositional basins will help refine ages of fluvial degradation, assess effectiveness of aeolian processes, and provide a regional chronology of fluvial events.

Maxwell, T. A.↗
NASA NTRS2002

Dynamics of cell proliferation in the adult dentate gyrus of two inbred strains of mice

The output potential of proliferating populations in either the developing or the adult nervous system is critically dependent on the length of the cell cycle (T(c)) and the size of the proliferating population. We developed a new approach for analyzing the cell cycle, the 'Saturate and Survive Method' (SSM), that also reveals the dynamic behaviors in the proliferative population and estimates of the size of the proliferating population. We used this method to analyze the proliferating population of the adult dentate gyrus in 60 day old mice of two inbred strains, C57BL/6J and BALB/cByJ. The results show that the number of cells labeled by exposure to BUdR changes dramatically with time as a function of the number of proliferating cells in the population, the length of the S-phase, cell division, the length of the cell cycle, dilution of the S-phase label, and cell death. The major difference between C57BL/6J and BALB/cByJ mice is the size of the proliferating population, which differs by a factor of two; the lengths of the cell cycle and the S-phase and the probability that a newly produced cell will die within the first 10 days do not differ in these two strains. This indicates that genetic regulation of the size of the proliferating population is independent of the genetic regulation of cell death among those newly produced cells. The dynamic changes in the number of labeled cells as revealed by the SSM protocol also indicate that neither single nor repeated daily injections of BUdR accurately measure 'proliferation.'.

Non-NASA Center↗
NASA NTRS2002

Size distribution of retrovirally marked lineages matches prediction from population measurements of cell cycle behavior

Mechanisms that regulate neuron production in the developing mouse neocortex were examined by using a retroviral lineage marking method to determine the sizes of the lineages remaining in the proliferating population of the ventricular zone during the period of neuron production. The distribution of clade sizes obtained experimentally in four different injection-survival paradigms (E11-E13, E11-E14, E11-E15, and E12-E15) from a total of over 500 labeled lineages was compared with that obtained from three models in which the average behavior of the proliferating population [i.e., the proportion of cells remaining in the proliferative population (P) vs. that exiting the proliferative population (Q)] was quantitatively related to lineage size distribution. In model 1, different proportions of asymmetric, symmetric terminal, and symmetric nonterminal cell divisions coexisted during the entire developmental period. In model 2, the developmental period was divided into two epochs: During the first, asymmetric and symmetric nonterminal cell divisions occurred, but, during the second, asymmetric and symmetric terminal cell divisions occurred. In model 3, the shifts in P and Q are accounted for by changes in the proportions of the two types of symmetric cell divisions without the inclusion of any asymmetric cell divisions. The results obtained from the retroviral experiments were well accounted for by model 1 but not by model 2 or 3. These findings demonstrate that: 1) asymmetric and both types of symmetric cell divisions coexist during the entire period of neurogenesis in the mouse, 2) neuron production is regulated in the proliferative population by the independent decisions of the two daughter cells to reenter S phase, and 3) neurons are produced by both asymmetric and symmetric terminal cell divisions. In addition, the findings mean that cell death and/or tangential movements of cells in the proliferative population occur at only a low rate and that there are no proliferating lineages "reserved" to make particular laminae or cell types. Copyright 2002 Wiley-Liss, Inc.

NASA Discipline Developmental Biology↗
NASA NTRSDate not supplied

Microbiological Analysis of Mizuna Grown in the Veggie Hardware to Define Critical Control Points and Ensure the Safety of Space Grown Crops

The Veggie facility on the International Space Station has been utilized as a “pick and eat” plant growth system to provide fresh produce for crew consumption. The VEG-04 experiments completed in 2019 examined the effect of red-rich and blue-rich light treatments on the growth of mizuna as well as harvest method and resulting yield. Analysis was performed on plant tissues and associated hardware to evaluate the influence of these experimental variables on the microbial population. VEG-04A plant pillows with pre-planted Mizuna mustard seeds were launched on SpaceX-16 in December 2018. The pillows were initiated, and a single 35-day harvest was performed. Veg 04B pillows were pre-planted with Mizuna seeds and launched on SpaceX-18 in July 2019, initiated and subsequently harvested at days 29, 43 and 58. The crew consumed approximately half of the produce, and the remainder was frozen and returned for analysis. Leaves, swabs, wicking material, substrate, and roots were processed and plated on media for the enumeration and isolation of bacteria and fungi. Isolated bacterial colonies were identified using Biolog Micro ID system or MicroSEQ16S rDNA sequencing technique. Fungal colonies were identified using the MicroSEQ D2 rDNA kit. Sample extracts were plated onto specialized media to identify Escherichia coli/coliforms, Staphylococcus aureus and Salmonella sp. Results indicate that bacterial and fungal counts were higher in plants grown in red-rich lightin VEG-04A, while the opposite was true in the Veg-04B third harvest. Microbial counts increased with the repeated harvest method used in Veg-04B. These data support the understanding of environmental and horticultural practices that can affect the microbiological quality of space-grown produce grown and aid in identification of critical control points for the development of a hazard analysis critical control point plan for ISS-grown crops. This research was co-funded by the NASA’s Human Research Program and Space Biology.

Mary E Hummerick↗