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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Intracranial Effects of Artificial Gravity: A 3T MRI Study

INTRODUCTION Spaceflight associated neuro-ocular syndrome (SANS) is characterized by the development of optic disc edema, posterior globe flattening, choroidal/retinal folds and hyperopic refractive errors1. SANS is hypothesized to be a result of headward fluid shifts that invariably occurs in the microgravity environment. As a countermeasure, artificial gravity (AG) through centrifugation has been proposed to reduce this headward fluid shift, however there is no current proof of benefit. The goal of this study was to determine if the application of AG can prevent or reduce known changes in brain volumetry, internal carotid artery (ICA) stroke volume and cerebral spinal fluid (CSF) flow velocity that occurs during simulated chronic headward fluid shift using head down tilt bed rest (HDTBR) methodology2 as an indicator of countermeasure efficacy. METHODS Healthy volunteers were recruited for an IRB approved HDTBR study performed at the German Aerospace Center in Cologne, Germany. Strict six-degree HDTBR was used as a spaceflight analog to induce a continuous headward fluid shift. HDTBR was carried out for 60 days for all subjects. Short-arm centrifugation was utilized to generate AG equating to ~0.3g of acceleration at the level of the eye. The subjects were divided equally into three groups: NoAG (control; n=8), daily intermittent AG (6 x 5 min iAG; n=8), and daily continuous 30 min (cAG; n=8). All studies were performed on a single dedicated 3T MRI Scanner. Pulse-gated MRI phase-contrast flow imaging was used to quantify ICA stroke volume and peak-to-peak CSF flow velocity in the mid cerebral aqueduct. 3D-SPGR was acquired for volumetric segmentation of the brain and CSF spaces. MRI acquisitions were obtained at baseline (BDC), 14 days into HDTBR (HDTBR14), 52 days into HDTBR (HDTBR52) and 3-5 days after HDTBR (recovery, R+3/5).The data were analyzed by the mixed model, which included intervention and time (BDC, HDTBR 14, HDTBR 52, R+3/5) as the fixed effects and included subject as the random effect.RESULTS24 healthy subject volunteers (16 men, 8 women, mean age = 33 years ± 9 [standard deviation] and mean BMI = 24.3 kg/m2 ± 2.0) successfully completed all phases of the study. Strict six-degree HDTBR was characterized by progressive and statistically significant (p<.01) increases in mean combined brain and CSF volumes and mean aqueductal CSF peak-to-peak flow velocity, as well as statistically significant (p<.01) progressive decrease in mean ICA stroke volume from baseline to 52 days post intervention (Figs. 1-3). Compared to baseline, only combined brain and CSF volumes did not return to baseline values in the recovery period (p=NS). Neither iAG nor cAG exerted any significant effects on the measured MRI brain parameters as compared to HDTBR alone (p=NS). CONCLUSION Our results indicate that HDTBR at 6-degrees was effective in producing alterations in ICA stroke volume, aqueductal CSF flow velocity, and combined brain and CSF volumetric change that is associated with chronic headward fluid shift. Short duration, 30-min daily exposure to either iAG or cAG appears to be insufficient in preventing or reducing the effects of chronic HDTBR and thus may not be a suitable countermeasure as currently deployed. AG protocol modifications, including increased duration and magnitude of exposure, should be considered for future research.

L A Kramer↗
NASA NTRS1968

Low density visualization

Comparison of schlieren and phase contrast methods for visualization of aerodynamic flow at hypersonic velocities

Veret, C.↗
NASA NTRS1974

Studies on Auditory and Vestibular End Organs and Brain Stem Nuclei

Cats were exposed to tones of 125, 1000, 2000, and 4000 Hz at sound pressure levels in the range 120 to 157.5 db, and for durations of one hour (1000, 2000, 4000 Hz) or four hours (125 Hz). Pure tone audiograms were obtained for each animal before and after exposure. Cochleas of animals were examined by phase-contrast microscopy. Extent of inner ear damage and range of frequencies for which hearing loss occurred increased as exposure tone was decreased in frequency. For example, exposure to 4000 Hz produced damage in a restricted region of the cochlea and hearing loss for a relatively narrow range of frequencies; exposure to 125 Hz produced wide-spread inner ear damage and hearing loss throughout the frequency range 125 to 6000 Hz.

Ades, H. W.↗
NASA NTRS1987

Structural characterization and gas reactions of small metal particles by high resolution in-situ TEM (Transmission Electron Microscopy) and TED (Transmission Electron Diffraction)

The detection and size analysis of small metal particles supported on amorphous substrates becomes increasingly difficult when the particle size approaches that of the phase contrast background structures of the support. An approach of digital image analysis, involving Fourier transformation of the original image, filtering, and image reconstruction was studied with respect to the likelihood of unambiguously detecting particles of less than 1 nm diameter on amorphous substrates from a single electron micrograph.

Heinemann, K.↗
NASA NTRS1989

Digital image processing of nanometer-size metal particles on amorphous substrates

The task of differentiating very small metal aggregates supported on amorphous films from the phase contrast image features inherently stemming from the support is extremely difficult in the nanometer particle size range. Digital image processing was employed to overcome some of the ambiguities in evaluating such micrographs. It was demonstrated that such processing allowed positive particle detection and a limited degree of statistical size analysis even for micrographs where by bare eye examination the distribution between particles and erroneous substrate features would seem highly ambiguous. The smallest size class detected for Pd/C samples peaks at 0.8 nm. This size class was found in various samples prepared under different evaporation conditions and it is concluded that these particles consist of 'a magic number' of 13 atoms and have cubooctahedral or icosahedral crystal structure.

Soria, F.↗
NASA NTRS1953

A New Simple Interferometer for Obtaining Quantitatively Evaluable Flow Patterns

The method described in the present report makes it possible to obtain interferometer records with the aid of any one of the available Schlieren optics by the addition of very simple expedients, which fundamentally need not to be inferior to those obtained by other methods, such as the Mach-Zehnder interferometer, for example. The method is based on the fundamental concept of the phase-contrast process developed by Zernike, but which in principle has been enlarged to such an extent that it practically represents an independent interference method for general applications. Moreover, the method offers the possibility, in case of necessity, of superposing any apparent wedge field on the density field to be gauged. The theory is explained on a purely physical basis and illustrated and proved by experimental data. A number of typical cases are cited and some quantitative results reported.

INSTRUMENTS - INTERFEROMETERS↗
NASA NTRS2003

X-Ray Diffraction and Imaging Study of Imperfections of Crystallized Lysozyme with Coherent X-Rays

Phase-sensitive x-ray diffraction imaging and high angular-resolution diffraction combined with phase contrast radiographic imaging are employed to characterize defects and perfection of a uniformly grown tetragonal lysozyme crystal in symmetric Laue case. The fill width at half-maximum (FWHM) of a 4 4 0 rocking curve measured from the original crystal is approximately 16.7 arcseconds, and defects, which include point defects, line defects, and microscopic domains, have been clearly observed in the diffraction images of the crystal. The observed line defects carry distinct dislocation features running approximately along the <110> growth front, and they have been found to originate mostly at a central growth area and occasionally at outer growth regions. Individual point defects trapped at a crystal nucleus are resolved in the images of high sensitivity to defects. Slow dehydration has led to the broadening of the 4 4 0 rocking curve by a factor of approximately 2.4. A significant change of the defect structure and configuration with drying has been revealed, which suggests the dehydration induced migration and evolution of dislocations and lattice rearrangements to reduce overall strain energy. The sufficient details of the observed defects shed light upon perfection, nucleation and growth, and properties of protein crystals.

Hu, Zheng-Wei↗
NASA NTRS2004

X-ray Microscopic Characterization of Protein Crystals

The microscopic mapping of the variation in degree of perfection and in type of defects in entire protein crystals by x-rays may well be a prerequisite for better understanding causes of lattice imperfections, the growth history, and properties of protein crystals. However, x-ray microscopic characterization of bulk protein crystals, in the as-grown state, is frequently more challenging than that of small molecular crystals due to the experimental difficulties arising largely from the unique features possessed by protein crystals. In this presentation, we will illustrate ssme recent activities in employing coherence-based phase contrast x-ray imaging and high-angular-resolution diffraction techniques for mapping microdefects and the degree of perfection of protein crystals, and demonstrate a correlation between crystal perfection, diffraction phenomena., and crystallization conditions. The observed features and phenomena will be discussed in context to gain insight into the nature of defects, nucleation and growth, and the properties of protein crystals.

Hu, Z. W.↗
NASA NTRS2004

Diffraction and Imaging Study of Imperfections of Protein Crystals with Coherent X-rays

High angular-resolution x-ray diffraction and phase contrast x-ray imaging were combined to study defects and perfection of protein crystals. Imperfections including line defects, inclusions and other microdefects were observed in the diffraction images of a uniformly grown lysozyme crystal. The observed line defects carry distinct dislocation features running approximately along the <110> growth front and have been found to originate mostly in a central growth area and occasionally in outer growth regions. Slow dehydration led to the broadening of a fairly symmetric 4 4 0 rocking curve by a factor of approximately 2.6, which was primarily attributed to the dehydration-induced microscopic effects that are clearly shown in diffraction images. X-ray imaging and diffraction characterization of the quality of apoferritin crystals will also be discussed in the presentation.

Hu, Z. W.↗
NASA NTRS2002

Tetracycline rapidly reaches all the constituent cells of uropathogenic Escherichia coli biofilms

We have developed a method for visualizing Escherichia coli cells that are exposed to tetracycline in a biofilm, based on a previous report that liposomes containing the E. coli TetR(B) protein fluoresce when exposed to this antibiotic. By our method, cells devoid of TetR(B) also exhibited tetracycline-dependent fluorescence. At 50 microg of tetracycline ml(-1), planktonic cells of a uropathogenic E. coli (UPEC) strain developed maximal fluorescence after 7.5 to 10 min of exposure. A similar behavior was exhibited by cells in a 24- or 48-h UPEC biofilm, as examined by confocal laser microscopy, regardless of whether they lined empty spaces or occupied densely packed regions. Further, a comparison of phase-contrast and fluorescent images of corresponding biofilm zones showed that all the cells fluoresced. Thus, all the biofilm cells were exposed to tetracycline and there were no pockets within the biofilm where the antibiotic failed to reach. It also appeared unlikely that niches of reduced exposure to the antibiotic existed within the biofilms.

Non-NASA Center↗
NASA NTRS1999

Devescovinid trichomonad with axostyle-based rotary motor ("Rubberneckia"): taxonomic assignment as Caduceia versatilis sp. nov

An amitochondriate trichomonad cell of the family Devescovinidae (Class Parabasalia), helped demonstrate the fluid model of lipoprotein cell membranes. This wood-ingesting symbiont in the hindgut of the dry wood-eating termite Cryptotermes cavifrons is informally known to cell biologists as "Rubberneckia". As the microtubular axo-style complex generates force causing clockwise movement of the entire anterior portion of the cell at the shear zone the protist displays "head" rotation. Studies by phase contrast and videomicroscopy of live cells, of whole mounts by scanning, and thin sections by transmission electron microscopy extend the observations of Tamm and Tamm [24-26] and Tamm [19-23]. Habitat, cell shape, size, nuclear features, parabasal apparatus and other morphological details permit the assignment of "Rubberneckia" to Kirby's cosmopolitan genus Caduceia. This large-sized devescovinid has distinctive parabasal gyres, an axostylar rotary, motor, and regularly-associated nonflagellated, fusiform and flagellated rod epibiotic surface bacteria. In addition to regularly aligned epibionts intranuclear and endocytoplasmic bacteria are abundant and hydrogenosomes are Present. "Rubberneckia" is compared here to the other seven species of Caduceia. Since it is clearly sufficiently distinctive to warrant new species status, we named it C. versatilis.

Non-NASA Center↗
NASA NTRS1989

Ecology and life history of an amoebomastigote, Paratetramitus jugosus, from a microbial mat: new evidence for multiple fission

Five microbial habitats (gypsum crust, gypsum photosynthetic community, Microcoleus mat, Thiocapsa scum, and black mud) were sampled for the presence of the euryhaline, rapidly growing amoebomastigote, Paratetramitus jugosus. Field investigations of microbial mats from Baja California Norte, Mexico, and Salina Bido near Matanzas, Cuba, reveal that P. jugosus is most frequently found in the Thiocapsa layer of microbial mats. Various stages of the life history were studied using phase-contrast, differential-interference, and transmission electron microscopy. Mastigote stages were induced and studied by electron microscopy; mastigotes that actively feed on bacteria bear two or more undulipodia. A three-dimensional drawing of the kinetid ("basal apparatus") based on electron micrographs is presented. Although promitoses were occasionally observed, it is unlikely that they can account for the rapid growth of P. jugosus populations on culture media. Dense, refractile, spherical, and irregular-shaped bodies were seen at all times in all cultures along with small mononucleate (approximately 2-7 micrometers diameter) amoebae. Cytochemical studies employing two different fluorescent stains for DNA (DAPI, mithramycin) verified the presence of DNA in these small bodies. Chromatin-like material seen in electron micrographs within the cytoplasm and blebbing off nuclei were interpreted to the chromatin bodies. Our interpretation, consistent with the data but not proven, is that propagation by multiple fission of released chromatin bodies that become small amoebae may occur in Paratetramitus jugosus. These observations are consistent with descriptions of amoeba propagules in the early literature (Hogue, 1914).

Non-NASA Center↗
NASA NTRS1992

Rapid in situ hybridization technique using 16S rRNA segments for detecting and differentiating the closely related gram-positive organisms Bacillus polymyxa and Bacillus macerans

A rapid, sensitive, inexpensive in situ hybridization technique, using 30-mer 16S rRNA probes, can specifically differentiate two closely related Bacillus spp., B. polymyxa and B. macerans. The 16S rRNA probes were labeled with a rhodamine derivative (Texas Red), and quantitative fluorescence measurements were made on individual bacterial cells. The microscopic fields analyzed were selected by phase-contrast microscopy, and the fluorescence imaging analyses were performed on 16 to 67 individual cells. The labeled 16S rRNA probe, POL, whose sequence was a 100% match with B. polymyxa 16S rRNA but only a 60% match with B. macerans 16S rRNA, gave quantitative fluorescence ratio measurements that were 34.8-fold higher for B. polymyxa cells than for B. macerans cells. Conversely, the labeled probe, MAC, which matched B. polymyxa 16S rRNA in 86.6% of its positions and B. macerans 16S rRNA in 100% of its positions, gave quantitative fluorescence measurements that were 59.3-fold higher in B. macerans cells than in B. polymyxa cells. Control probes, whose 16S rRNA sequence segment (P-M) was present in both B. polymyxa and B. macerans as well as a panprokaryotic probe (16S), having a 100% match with all known bacteria, hybridized equally well with both organisms. These latter hybridizations generated very high fluorescence signals, but their comparative fluorescence ratios (the differences between two organisms) were low. The control paneukaryotic probe (28S), which had less than 30% identity for both B. macerans and B. polymyxa, did not hybridize with either organism.

Non-NASA Center↗
NASA NTRS2005

Morphology and Elemental Composition of Recent and Fossil Cyanobacteria

Cyanobacteria (cyanophyta, cyanoprokaryota, and blue-green algae) are an ancient, diverse and abundant group of photosynthetic oxygenic microorganisms. Together with other bacteria and archaea, the cyanobacteria have been the dominant life forms on Earth for over 3.5 billion years. Cyanobacteria occur in some of our planets most extreme environments - hot springs and geysers, hypersaline and alkaline lakes, hot and cold deserts, and the polar ice caps. They occur in a wide variety of morphologies. Unlike archaea and other bacteria, which are typically classified in pure culture by their physiological, biochemical and phylogenetic properties, the cyanobacteria have historically been classified based upon their size and morphological characteristics. These include the presence or absence of heterocysts, sheath, uniseriate or multiseriate trichomes, true or false branching, arrangement of thylakoids, reproduction by akinetes, binary fission, hormogonia, fragmentation, presence/absence of motility etc. Their antiquity, distribution, structural and chemical differentiation, diversity, morphological complexity and large size compared to most other bacteria, makes the cyanobacteria ideal candidates for morphological biomarkers in returned Astromaterials. We have obtained optical (nomarski and phase contrast)/fluorescent (blue and green excitation) microscopy images using an Olympus BX60 compound microscope and Field Emission Scanning Electron Microscopy images and EDAX elemental compositions of living and fossil cyanobacteria. The S-4000 Hitachi Field Emission Scanning Electron Microscope (FESEM) has been used to investigate microfossils in freshly fractured interior surfaces of terrestrial rocks and the cells, hormogonia, sheaths and trichomes of recent filamentous cyanobacteria. We present Fluorescent and FESEM Secondary and Backscattered Electron images and associated EDAX elemental analyses of recent and fossil cyanobacteria, concentrating on representatives of the genera Calothnx, Leptolyngbya, Lyngbya, Planktolyngbya and Oscillatoria.

SaintAmand, Ann↗
NASA NTRS2005

Nondestructive Visualization of Defects and Crack Propagation of Shuttle-Foam

Shuttle insulating foam is a low-density closed-cell solid-gas composite. A chief barrier to understanding foam loss has been extreme difficulties in nondestructively visualizing defects of the foam that is almost transparent to x-rays. Here we show that defects, crack propagation, and cell structure can be clearly and nondestructively observed by turning the density inhomogeneity across foam structures into a source for phase contrast imaging. This provides a new powerful way to help understand foam loss.

Hu, Zheng-Wei↗