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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Culturability as an indicator of succession in microbial communities

Successional theory predicts that opportunistic species with high investment of energy in reproduction and wide niche width will be replaced by equilibrium species with relatively higher investment of energy in maintenance and narrower niche width as communities develop. Since the ability to rapidly grow into a detectable colony on nonselective agar medium could be considered as characteristic of opportunistic types of bacteria, the percentage of culturable cells may be an indicator of successional state in microbial communities. The ratios of culturable cells (colony forming units on R2A agar) to total cells (acridine orange direct microscopic counts) and culturable cells to active cells (reduction of 5-cyano-2,3-ditolyl tetrazolium chloride) were measured over time in two types of laboratory microcosms (the rhizosphere of hydroponically grown wheat and aerobic, continuously stirred tank reactors containing plant biomass) to determine the effectiveness of culturabilty as an index of successional state. The culturable cell:total cell ratio in the rhizosphere decreased from approximately 0.25 to less than 0.05 during the first 30-50 days of plant growth, and from 0.65 to 0.14 during the first 7 days of operation of the bioreactor. The culturable cell:active cell ratio followed similar trends, but the values were consistently greater than the culturable cell:total cell ratio, and even exceeded I in early samples. Follow-up studies used a cultivation-independent method, terminal restriction fragment length polymorphisms (TRFLP) from whole community DNA, to assess community structure. The number of TRFLP peaks increased with time, while the number of culturable types did not, indicating that the general decrease in culturability is associated with a shift in community structure. The ratio of respired to assimilated C-14-labeled amino acids increased with the age of rhizosphere communities, supporting the hypothesis that a shift in resource allocation from growth to maintenance occurs with time. Results from this work indicate that the percentage of culturable cells may be a useful method for assessing the successional state of microbial communities.

NASA Center KSC↗
NASA NTRS1998

Effects of starvation on physiological activity and chlorine disinfection resistance in Escherichia coli O157:H7

Escherichia coli O157:H7 can persist for days to weeks in microcosms simulating natural conditions. In this study, we used a suite of fluorescent, in situ stains and probes to assess the influence of starvation on physiological activity based on membrane potential (rhodamine 123 assay), membrane integrity (LIVE/DEAD BacLight kit), respiratory activity (5-cyano-2,3-di-4-tolyl-tetrazolium chloride assay), intracellular esterase activity (ScanRDI assay), and 16S rRNA content. Growth-dependent assays were also used to assess substrate responsiveness (direct viable count [DVC] assay), ATP activity (MicroStar assay), and culturability (R2A agar assay). In addition, resistance to chlorine disinfection was assessed. After 14 days of starvation, the DVC values decreased, while the values in all other assays remained relatively constant and equivalent to each other. Chlorine resistance progressively increased through the starvation period. After 29 days of starvation, there was no significant difference in chlorine resistance between control cultures that had not been exposed to the disinfectant and cultures that had been exposed. This study demonstrates that E. coli O157:H7 adapts to starvation conditions by developing a chlorine resistance phenotype.

NASA Discipline Environmental Health↗
NASA NTRS2008

[The Extrasolar Planetary Imaging Coronagraph]

The Extrasolar Planetary Imaging Coronagraph (EPIC) is a proposed NASA Exoplanet Probe mission to image and characterize extr asolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC will provide insights into the physical nature of a variety of planets in other solar systems complimenting radial velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets identified by radial velocity surveys, deter mine orbital inclinations and masses, characterize the atmospheres around A and F type stars which cannot be found with RV techniques, and observe the inner spatial structure and colors of debris disks. EPIC has a heliocentric Earth trailing drift-away orbit, with a 5 year mission lifetime (5 year goal). The robust mission design is simple and flexible ensuring mission success while minimizing cost and risk. The science payload consists of a heritage optical telescope assembly (OTA), and visible nulling coronagraph (VNC) instrument. The instrument achieves a contrast ratio of 10(exp 9) over a 4.84 arcsecond field-of-view with an unprecedented inner working angle of 0.14 arcseconds over the spectral range of 440-880 nm. The telescope is a 1.65 meter off-axis Cassegrain with an OTA wavefront error of /9, which when coupled to the VNC greatly reduces the requirements on the large scale optics, compressing them to stability requirements within the relatively compact VNC optical chain. The VNC features two integrated modular nullers, a spatial filter array (SFA) and an E2V-L3 photon counting CCD. Direct null control is accomplished from the science focal plane mitigating against complex wavefront and amplitude sensing and control strategies.

Clampin, Mark↗
NASA NTRS2012

Non-Equilibrium Properties from Equilibrium Free Energy Calculations

Calculating free energy in computer simulations is of central importance in statistical mechanics of condensed media and its applications to chemistry and biology not only because it is the most comprehensive and informative quantity that characterizes the eqUilibrium state, but also because it often provides an efficient route to access dynamic and kinetic properties of a system. Most of applications of equilibrium free energy calculations to non-equilibrium processes rely on a description in which a molecule or an ion diffuses in the potential of mean force. In general case this description is a simplification, but it might be satisfactorily accurate in many instances of practical interest. This hypothesis has been tested in the example of the electrodiffusion equation . Conductance of model ion channels has been calculated directly through counting the number of ion crossing events observed during long molecular dynamics simulations and has been compared with the conductance obtained from solving the generalized Nernst-Plank equation. It has been shown that under relatively modest conditions the agreement between these two approaches is excellent, thus demonstrating the assumptions underlying the diffusion equation are fulfilled. Under these conditions the electrodiffusion equation provides an efficient approach to calculating the full voltage-current dependence routinely measured in electrophysiological experiments.

Pohorille, Andrew↗
NASA NTRS1969

Direct measurement of carbon-14 in carbon dioxide by liquid scintillation counting

Liquid scintillation counting technique is applied to the direct measurement of carbon-14 in carbon dioxide. This method has high counting efficiency and eliminates many of the basic problems encountered with previous techniques. The technique can be used to achieve a percent substitution reaction and is of interest as an analytical technique.

Horrocks, D. L.↗
NASA NTRS1981

Results of a new approach to determining the density function in the galactic plane - The local system

Star counts in the directions of 15 opaque CO clouds of known distance are used to determine the density function in the galactic plane of the local system of apparently enhanced stellar density. Counts were made on Palomar Sky Survey blue prints in the directions of the highest opacity portions of 15 molecular clouds. Average values of the density functions obtained are found to be significantly less than unity for clouds more distant than 800 pc regardless of galactic longitude, confirming the presence of the local mass density enhancement. Data suggest that the local system represents a density enhancement of a factor of 2 over a region of approximately 500 pc. An empirical relationship is also determined between the distance to a molecular cloud and the number of foreground stars projected on it, which may be useful in determining distances to clouds nearer than 3 kpc. The potential of the Space Telescope for complete stellar mass determinations out to a distance of 1 kpc is pointed out.

Herbst, W.↗
NASA NTRS1981

Analysis of GOES imagery and digitized data for the SEV-UPS period, August 1979

In support of the Southeastern Virginia Urban Plume Study (SEV-UPS), GOES satellite imagery was analyzed for the month of August 1979. The analyzed GOES images provide an additional source of meteorological input useful in the evaluation of air quality data collected during the month long period of the SEV-UPS experiment. In addition to the imagery analysis, GOES digitized data were analyzed for the period of August 6 to 11, during which a regional haze pattern was detectable in the imagery. The results of the study indicate that the observed haze patterns correspond closely with areas shown in surface based measurements to have reduced visibilities and elevated pollution levels. Moreover, the results of the analysis of digitized data indicate that digital reflectance counts can be directly related to haze intensity both over land and ocean. The model results agree closely with the observed GOES digital reflectance counts, providing further indication that satellite remote sensing can be a useful tool for monitoring regional elevated pollution episodes.

Bowley, C. J.↗
NASA NTRS1981

Stratospheric CCN sampling program

When Mt. St. Helens produced several major eruptions in the late spring of 1980, there was a strong interest in the characterization of the cloud condensation nuclei (CCN) activity of the material that was injected into the troposphere and stratosphere. The scientific value of CCN measurements is two fold: CCN counts may be directly applied to calculations of the interaction of the aerosol (enlargement) at atmospherically-realistic relative humidities or supersaturations; and if the chemical constituency of the aerosol can be assumed, the number-versus-critical supersaturation spectrum may be converted into a dry aerosol size spectrum covering a size region not readily measured by other methods. The sampling method is described along with the instrumentation used in the experiments.

Rogers, C. F.↗
NASA NTRS1984

LANDSAT 4 band 6 data evaluation

A series of images of a portion of a TM frame of Lake Ontario are presented. The top left frame is the TM Band 6 image, the top right image is a conventional contrast stretched image. The bottom left image is a Band 5 to Band 3 ratio image. This image is used to generate a primitive land cover classificaton. Each land cover (Water, Urban, Forest, Agriculture) is assigned a Band 6 emissivity value. The ratio image is then combined with the Band 6 image and atmospheric propagation data to generate the bottom right image. This image represents a display of data whose digital count can be directly related to estimated surface temperature. The resolution appears higher because the process cell is the size of the TM shortwave pixels.

Source record↗
NASA NTRS1986

X-ray properties of optically selected QSOs

The dependence of the X-ray-to-optical luminosity ratio on optical luminosity and redshift for optically selected QSOs is studied, largely on the basis of two, complete, magnitude-limited samples (Bright Quasar Survey /1983/ and Braccesi Faint /1984/) which were observed with the Einstein Observatory. Heterogeneous samples are established as adequate for the study of that dependence. Optimal choices for increasing the size of the data set for such a study are pointed out. The previous results of Avni and Tananbaum for alpha sub 0, x(z, L sub opt) are confirmed and strengthened, and the numerical sensitivity to changes in the values of q sub 0 and of the optical spectral index is evaluated. It is shown that the large majority, probably all, of optically selected QSOs are X-ray loud; no more than a few percent can be X-ray quiet. Thus X-ray emission appears to be a universal property of QSOs. It is shown that comparisons of optically selected QSOs with X-ray selected QSOs are numerically sensitive to the details of the input ingredients. A residual discrepancy of about a factor of 2 between calculated and observed X-ray number counts is found. Directions for further research that are important for understanding the full bivariate optical-X-ray evolution and luminosity function for QSOs are discussed.

Avni, Y.↗
NASA NTRS1992

The stellar content of LH 9 and 10 (N11) in the LMC - A case for sequential star formation

The young OB associations Lucke-Hodge 9 and 10 are studied with UBV photometry that is independent of reddening to determine the IMF directly from star counts. The temperature and reddening of the stars are determined which, in conjunction with the spectroscopic classification of the earliest stars, is employed to place the stellar groups on the theoretical H-R diagram. Observations are also presented of the highly compact H II region/knot N11A and the multiple system HD 32228, and LH 9 and 10 are compared. The Lyman ionizing flux calculated at 4.9-7.2 x 10 exp 50/s agrees well with flux required to generate the H-alpha luminosity of the H II region. LH 10 has a much flatter slope, a higher ratio of higher-mass to lower-mass stars, and greater reddening than LH 9, and LH 10 contains all of the O stars earlier than O6. It is concluded that LH 9 is older than LH 10 and probably contributed to the initiation of star formation in LH 10.

Parker, Joel WM.↗
NASA NTRS1992

Model reduction for Space Station Freedom

Model reduction is an important practical problem in the control of flexible spacecraft, and a considerable amount of work has been carried out on this topic. Two of the best known methods developed are modal truncation and internal balancing. Modal truncation is simple to implement but can give poor results when the structure possesses clustered natural frequencies, as often occurs in practice. Balancing avoids this problem but has the disadvantages of high computational cost, possible numerical sensitivity problems, and no physical interpretation for the resulting balanced 'modes'. The purpose of this work is to examine the performance of the subsystem balancing technique developed by the investigator when tested on a realistic flexible space structure, in this case a model of the Permanently Manned Configuration (PMC) of Space Station Freedom. This method retains the desirable properties of standard balancing while overcoming the three difficulties listed above. It achieves this by first decomposing the structural model into subsystems of highly correlated modes. Each subsystem is approximately uncorrelated from all others, so balancing them separately and then combining yields comparable results to balancing the entire structure directly. The operation count reduction obtained by the new technique is considerable: a factor of roughly r(exp 2) if the system decomposes into r equal subsystems. Numerical accuracy is also improved significantly, as the matrices being operated on are of reduced dimension, and the modes of the reduced-order model now have a clear physical interpretation; they are, to first order, linear combinations of repeated-frequency modes.

Williams, Trevor↗
NASA NTRS1999

The Special Sensor Microwave Imager Wind Dataset: A Source of Quantitative Information for the Ocean-to-Land Advection

It is well recognized that advection from the North Atlantic has a profound effect on the climatic conditions in central Europe. A new dataset of the ocean-surface winds, derived from the Special Sensor Microwave Imager, SSM/1, is now available. This satellite instrument measures the wind speed, but not the direction. However, variational analysis developed at the Data Assimilation Office, NASA Goddard Space Flight Center, by combining the SSM/I measurements with wind vectors measured from ships, etc., produced global maps of the ocean surface winds suitable for climate analysis. From this SSM/I dataset, a specific index I(sub na) of the North Atlantic surface winds has been developed, which pertinently quantifies the low-level advection into central Europe. For a selected time-period, the index I(sub na) reports the average of the amplitude of the wind, averaging only the speed when the direction is from the southwest (when the wind is from another direction, the contribution counts to the average as zero speed). Strong correlations were found between February I(sub na) and the surface air temperatures in Europe 50-60 deg N. In the present study, we present the correlations between I(sub na) and temperature I(sub s), and also the sensitivity of T(sub s), to an increase in I(sub na), in various seasons and various regions. We specifically analyze the flow of maritime-air from the North Atlantic that produced two extraordinary warm periods: February 1990, and early-winter 2000/2001. The very cold December 2001 was clearly due to a northerly flow. Our conclusion is that the SSM/I dataset is very useful for providing insight to the forcing of climatic fluctuations in Europe.

Otterman, J.↗
NASA NTRS2013

Fiber Treatment Effects on Bioreactor Bulk Fluid Trends

In order to facilitate the exploration of worlds beyond the borders of our planet, it is necessary to maintain sustainable levels of clean water. The remediation of water via Membrane Aerated Bioreactors (MABRs) is one such method, and the focus of this study. MARRs rely on healthy biofilms grown on hollow fiber membranes to clean non-potable water. These biofilms can take weeks to months to establish. Therefore, various fiber treatments and two inoculums were evaluated for their effect on rapid biofilm formation. Fiber treatments are as follows: sanding of the fibers with 1500 and 8000 grit sandpaper, immersion of the fibers in a 1% hydrofluoric acid solution for 12 seconds and 15 minutes, and the immersion of the fibers in a Fluoroetch® solution for 18 seconds and 5 minutes. The two inoculums utilized were sourced from healthy, established MARRs; Texas Tech University (TTU) MABR "TRL5" and Kennedy Space Center (KSC) MABR "R3". Data attained from direct bacterial cell counts of the reactor bulk fluids via fluorescent microscopy, suggests that the fluoroetching treatment combined with the TTU inoculum show the greatest biofilm creation.

Ellis, Ronald II↗
NASA NTRS1973

Lidar Observations of Raman Scattering from S02 in a Power Plant Stack Plume

LIDAR techniques have been successfully applied to the detection of the Raman backscatter from S02 in the plume of a 200 megawatt coal-burning electrical- generating plant from a distance of 210 meters. The LIDAR system used consists of a 61-centimeter-diameter, f /4 Newtonian telescope and a 1.0-1.5-joules per pulse, 1-pulse-per-second ruby laser. Narrow band interference filters are used to select the 7546-angstrom v (sub 1) vibrational line of S02. The signal from a photomultiplier tube was sequentially applied to each 254-nanosecond-wide channel of a 15-cihannel photon counting system, resulting in a direct correlation between channel number and range increment. Photon counts were accumulated from the backscatter of a number of laser pulses (typically 50 or 100), and the accumulated counts per channel printed on paper tape. One sequence of measurements was made during a two-hour period while the plant electrical output was being reduced by approximately 50 percent. Although the Raman system had not been quantitatively calibrated, the LIDAR data correlated well with the varying plant electrical output. N2 scattering observations were also made and an approximate quantitative S02 concentration obtained by ratioing the S02 data to N2 data. This ratio compared well to the in-situ measurements made during the same period by Environmental Protection Agency sampling instruments.

Brumfield, M. L.↗
NASA NTRS1969

Direct determination of lead-210 by liquid-scintillation counting

Soft betas, the internal conversion electrons, and unconverted gamma rays from lead-210 are efficiently detected in a liquid scintillation counting system with efficiency of 97 percent. The counter is interfaced with a multichannel pulse height analyzer. The spectra obtained is stored on paper tape and plotted on an x-y plotter.

Fairman, W. D.↗
NASA NTRS1981

Predicted star counts in selected fields and photometric bands Applications to galactic structure, the disk luminosity function, and the detection of a massive halo

Tables are presented of predicted star counts in 17 selected directions on the sky as a function of apparent B, V, R, and I magnitudes and absolute visual magnitudes calculated from the Bahcall-Soneira Galaxy model. It is noted that eight of the fields were selected ab initio for their usefulness in determining from star counts either parameters of galactic structure, the faint end of the disk luminosity function, or the detection of a massive stellar halo. Star counts in specified fields to m sub I = 19 mag are able to reveal the faint end of the disk luminosity function down to the end of the hydrogen-burning main sequence. It is thought that star counts at high galactic latitudes to m sub I = 22 mag should reveal the stellar constituents of a massive halo if they are massive enough to be on the hydrogen-burning main sequence.

Bahcall, J. N.↗