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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Myogenic regulatory factors during regeneration of skeletal muscle in young, adult, and old rats

Myogenic factor mRNA expression was examined during muscle regeneration after bupivacaine injection in Fischer 344/Brown Norway F1 rats aged 3, 18, and 31 mo of age (young, adult, and old, respectively). Mass of the tibialis anterior muscle in the young rats had recovered to control values by 21 days postbupivacaine injection but in adult and old rats remained 40% less than that of contralateral controls at 21 and 28 days of recovery. During muscle regeneration, myogenin mRNA was significantly increased in muscles of young, adult, and old rats 5 days after bupivacaine injection. Subsequently, myogenin mRNA levels in young rat muscle decreased to postinjection control values by day 21 but did not return to control values in 28-day regenerating muscles of adult and old rats. The expression of MyoD mRNA was also increased in muscles at day 5 of regeneration in young, adult, and old rats, decreased to control levels by day 14 in young and adult rats, and remained elevated in the old rats for 28 days. In summary, either a diminished ability to downregulate myogenin and MyoD mRNAs in regenerating muscle occurs in old rat muscles, or the continuing myogenic effort includes elevated expression of these mRNAs.

Non-NASA Center↗
NASA NTRS1994

Transcription factor IID in the Archaea: sequences in the Thermococcus celer genome would encode a product closely related to the TATA-binding protein of eukaryotes

The first step in transcription initiation in eukaryotes is mediated by the TATA-binding protein, a subunit of the transcription factor IID complex. We have cloned and sequenced the gene for a presumptive homolog of this eukaryotic protein from Thermococcus celer, a member of the Archaea (formerly archaebacteria). The protein encoded by the archaeal gene is a tandem repeat of a conserved domain, corresponding to the repeated domain in its eukaryotic counterparts. Molecular phylogenetic analyses of the two halves of the repeat are consistent with the duplication occurring before the divergence of the archael and eukaryotic domains. In conjunction with previous observations of similarity in RNA polymerase subunit composition and sequences and the finding of a transcription factor IIB-like sequence in Pyrococcus woesei (a relative of T. celer) it appears that major features of the eukaryotic transcription apparatus were well-established before the origin of eukaryotic cellular organization. The divergence between the two halves of the archael protein is less than that between the halves of the individual eukaryotic sequences, indicating that the average rate of sequence change in the archael protein has been less than in its eukaryotic counterparts. To the extent that this lower rate applies to the genome as a whole, a clearer picture of the early genes (and gene families) that gave rise to present-day genomes is more apt to emerge from the study of sequences from the Archaea than from the corresponding sequences from eukaryotes.

NASA Discipline Exobiology↗
NASA NTRS1992

The Ribosomal Database Project

The Ribosomal Database Project (RDP) complies ribosomal sequences and related data, and redistributes them in aligned and phylogenetically ordered form to its user community. It also offers various software packages for handling, analyzing and displaying sequences. In addition, the RDP offers (or will offer) certain analytic services. At present the project is in an intermediate stage of development.

Non-NASA Center↗
NASA NTRS2006

Grism Performance for Mid-IR (5-40 microns) Spectroscopy

Grisms provide a straightforward method to transform an imager into a spectrometer with little change to the original imaging optics. This paper addresses the performance of a suite of grisms as part of an Astrobiology Science and Instrument Development (ASTID) Program to implement a moderate resolution spectroscopic capability to the mid/far-IR facility instrument FORCAST for the Stratospheric Observatory For Infrared Astronomy (SOFIA) [see accompanying abstract by Adams et al.]. A moderate resolution mid-IR spectrometer on SOFIA will offer advantages not available to either ground or space-based instruments after the Spitzer Space Telescope ceases operation in approx. 2007. SOFIA will begin operations in 2007 and will have an operational lifetime of approx. 20 years. From aircraft altitudes, it will be possible to cover a range of wavelengths, particularly in the critical 5-9 micron band, where detection of astrobiologically interesting molecules have key spectral signatures, that are not accessible from the ground. This grism suite consists of six grisms: four monolithic Si grisms [see accompanying abstract by Mar et al.] and two KRS-5 grisms. These devices will allow long slit low-resolution and short slit, cross-dispersed high-resolution spectroscopic modes selectable by simply moving the camera filter wheels. This configuration will enable observing programs to gather images and spectra in a single SOFIA flight. The four silicon grisms, whose performance is highlighted in this paper, will operate in the following wavelength ranges: 5-8, 17-28, and 28-37 microns. In the 5-8 micron range, R=1200 is achievable for a 2 arcsecond slit using the grism as a cross-disperser. For the 17-28 and 28-37 micron ranges, the resolving powers are R approx. 130, 250 when used in low orders with a slit of 3 arcseconds. The silicon grisms demonstrate a new family of dispersive elements with good optical performance for spectroscopy from 1.2-8 micron and beyond 18 microns. Furthermore, the FORCAST grism modes are close in wavelength coverage and resolving power to the Spitzer Infrared Spectrograph (IRS), so that among other possible observations, SOFIA can now enable follow-up studies of the brighter objects that Spitzer has observed and enable studies of sources that were too bright for observation with Spitzer.

Ennico, K. A.↗
NASA NTRS1996

The Astronomical Low-Frequency Array

An array of satellites is proposed to make astronomic observations in the low frequency range of a few tens of MHz down to roughly 100 kHz, a range that cannot be observed through the ionosphere. The array would be in a solar orbit to avoid radio interference from Earth and to simplify trajectory tracking and control.

low-frequency array radio astronomy microsats↗
NASA NTRS1994

A Search for Low V Earth-to-Moon Trajectories

A search for low V Earth-to-Moon trajectories has been initiated. Numerical integration of the equations of motion from the circular restricted three-body problem has resulted in the computation of a trajectory that saves more that 100 m/s over a Hohmann transfer, although the flight time is almost ten months.

trajectory↗
NASA NTRS1996

Full-Sky Imaging at Low Frequencies

Exploring the frequency range from a few tens of MHZ down to a few tens of kHz commonly requires multiple antennas operating as an aperture synthesis interferometer to obtain angular resolution. This design must overcome the corrupting effects of interplanetary scintillation, interfering signals and nearly isotropic antennas that see strong sources such as the Sun and Jupiter at all times.

Jones, D. L.↗