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Report discusses factors affecting readings of hot-wire anemometer in turbulent supersonic boundary layer. Represents extension of work described in "Hot-Wire Anemometry Versus Laser-Induced Fluorescence" (ARC-11802). Presents theoretical analysis of responses of hot-wire probe to changes in flow; also compares measurements by hot-wire probe with measurements of same flows by laser-induced fluorescence (LIF).
Fluorescence is one of the most versatile and powerful tools for the study of macromolecules. While most proteins are intrinsically fluorescent, working at crystallization concentrations require the use of covalently prepared derivatives added as tracers. This approach requires derivatives that do not markedly affect the crystal packing. We have prepared fluorescent derivatives of chicken egg white lysozyme with probes bound to one of two different sites on the protein molecule. Lucifer yellow and 5-(2-aminoethyl)aminonapthalene-i-sulfonic acid (EDANS) have been attached to the side chain carboxyl of Asp(sup 101) using a carbodiimide coupling procedure. Asp(sup 101) lies within the active site cleft, and it is believed that the probes are 'buried' within that cleft. Lucifer yellow and MANS probes with iodoacetamide reactive five groups have been bound to His(sup 15), located on the 'back side' of the molecule relative to the active site. All the derivatives fluoresce in the solution and the crystalline states. Fluorescence characterization has focused on determination of binding effects on the probe quantum yield, lifetime, absorption and emission spectra, and quenching by added solutes. Quenching studies show that, as postulated, the Asp(sup 101)-bound probes are partially sheltered from the bulk solution by their location within the active site cleft. Probes bound to His(sup 15) have quenching constants about equal to those for the free probes, indicating that this site is highly exposed to the bulk solution.
During the past two decades the use of live cytoskeletal probes has increased dramatically due to the introduction of the green fluorescent protein. However, to make full use of these live cell reporters it is necessary to implement simple methods to maintain plant specimens in optimal growing conditions during imaging. To image the cytoskeleton in living Arabidopsis roots, we rely on a system involving coverslips coated with nutrient supplemented agar where the seeds are directly germinated. This coverslip system can be conveniently transferred to the stage of a confocal microscope with minimal disturbance to the growth of the seedling. For roots with a larger diameter such as Medicago truncatula, seeds are first germinated in moist paper, grown vertically in between plastic trays, and roots mounted on glass slides for confocal imaging. Parallel with our live cell imaging approaches, we routinely process fixed plant material via indirect immunofluorescence. For these methods we typically use non-embedded vibratome-sectioned and whole mount permeabilized root tissue. The clearly defined developmental regions of the root provide us with an elegant system to further understand the cytoskeletal basis of plant development.
Lunar X-ray emission measured by Lunik X lunar probe
Results are presented for supersonic molecular flow-velocity measurements using inverse Raman spectroscopy. The flow velocity, temperature, and density of flowing N2 molecules are measured because of potential wind-tunnel applications. Uncertainties of less than 5% are found for the velocity measurements, while the uncertainties are about 10% for the temperature and density measurements. The laser probe is stabilized by using I2 fluorescence, and I2 saturated absorption is utilized to provide an absolute frequency reference. Differential detection techniques are employed to reduce detection noise.
A diagnostic has been developed to measure velocity and translational temperature in the plume of an arcjet thruster. Laser induced fluorescence with a narrowband CW laser is used to probe the Balmer alpha transition of excited atomic hydrogen. The velocity is determined from the Doppler shift of the fluorescence excitation spectrum while temperature is inferred from its shape. Analysis shows that while Doppler broadening is the only significant broadening mechanism, the fine structure of the transition must be accounted for. Near the exit plane, axial velocities vary from 4 to 14 km/s; radial velocities vary from 0 to 4 km/s; and swirl velocities are shown to be relatively small. Temperatures from 1000 to 5000 K indicate high dissociation fractions.
Fluorescence in situ hybridization with a composite probe for human chromosome 4 and a probe that stained all centromeres was used to study gamma-ray induced breakage, rejoining and misrejoining in prematurely condensed chromosomes in human lymphocytes. Dose-response curves for the induction of all types of aberrations in prematurely condensed human chromosomes 4 were determined immediately after irradiation and after 8 h postirradiation incubation. In addition, aberrations were measured after various incubation times from 0 to 18 h after a dose of 7 Gy. Unrejoined chromosome breaks were the most frequent type of aberration observed immediately after irradiation. Approximately 15% of total aberrations observed were chromosome exchanges. After 8 h postirradiation incubation, the frequency of breaks in prematurely condensed chromosomes declined to about 20% of the initial value, and chromosomal exchanges became the most frequent aberration. Results of metaphase analysis were similar to those for prematurely condensed chromosomes after 8 h incubation with the exception that a significantly lower frequency of fragments was observed. Symmetrical and asymmetrical interchanges were found at similar frequencies at all doses. No complex exchanges were observed in lymphocyte chromosomes immediately after exposure. They accounted for about 1% of total exchanges in metaphase chromosomes at doses <3 Gy and about 14% at 7 Gy. Incomplete exchanges amounted to approximately 15% of total exchanges at all doses. The kinetics of break rejoining was exponential, and the frequency of exchanges increased with kinetics similar to that observed for the rejoining of the breaks. This increase in the total exchanges as a function of the time between irradiation and fusion was due to a rapid increase in reciprocal interchanges, and a slower increase in complex exchanges; the frequency of incomplete exchanges increased initially, then decreased with prolonged incubation to the level observed in metaphase. It is concluded that the formation of each kind of chromosome aberrations follows different kinetics.
Meteoritic ablation in the upper atmosphere is the commonly accepted source of the mesospheric metals between 80 and 105 km. The vertical and temporal behavior of some of these metals can be probed with high accuracy and resolution using resonance fluorescence lidar techniques. Of considerable interest in recent years has been the sporadic and rapid formation of thin, dense enhancements in these metallic layers. Since late Mar. 1991, the UIUC CEDAR lidar system, located at the Urbana Atmospheric Observatory, has been routinely operating at the Fe resonance line of 372 nm in order to probe the mesospheric Fe layer. In Nov. 1991, the capability to investigate mesospheric Ca(+) at the resonance line of 393.4 nm was added. The lidar's eximer-pumped dye laser uses Exciton QUI laser dye dissolved in p-dioxane, which can lase at both the Fe and Ca(+) frequencies. Various aspects of this investigation are discussed.
Experiments and modelling have been undertaken to clarify the role of metal catalysts during single-wall carbon nanotube formation. For instance, we wonder whether the metal catalyst is active as an atom, a cluster, a liquid or solid nanoparticle [1]. A reactor has been developed for synthesis by continuous CO2-laser vaporisation of a carbon-nickel-cobalt target in laminar helium flow. The laser induced fluorescence technique [2] is applied for local probing of gaseous Ni, Co and CZ species throughout the hot carbon flow of the target heated up to 3500 K. A rapid depletion of C2 in contrast to the spatial extent of metal atoms is observed in the plume (Fig. 1). This asserts that C2 condenses earlier than Ni and Co atoms.[3, 4]. The depletion is even faster when catalysts are present. It may indicate that an interaction between metal atoms and carbon dimers takes place in the gas as soon as they are expelled from the target surface. Two methods of modelling are used: a spatially I-D calculation developed originally for the arc process [5], and a zero-D time dependent calculation, solving the chemical kinetics along the streamlines [6]. The latter includes Ni cluster formation. The peak of C2 density is calculated close to the target surface where the temperature is the highest. In the hot region, C; is dominant. As the carbon products move away from the target and mix with the ambient helium, they recombine into larger clusters, as demonstrated by the peak of C5 density around 1 mm. The profile of Ni-atom density compares fairly well with the measured one (Fig. 2). The early increase is due to the drop of temperature, and the final decrease beyond 6 mm results from Ni cluster formation at the eutectic temperature (approx.1600 K).
Aircraft-engine rotating equipment usually operates at high temperature and stress. Non-invasive inspection of microcracks in those components poses a challenge for the non-destructive evaluation community. A low-profile ultrasonic guided wave sensor can detect cracks in situ. The key feature of the sensor is that it should withstand high temperatures and excite strong surface wave energy to inspect surface/subsurface cracks. As far as the innovators know at the time of this reporting, there is no existing sensor that is mounted to the rotor disks for crack inspection; the most often used technology includes fluorescent penetrant inspection or eddy-current probes for disassembled part inspection. An efficient, high-temperature, low-profile surface acoustic wave transducer design has been identified and tested for nondestructive evaluation of structures or materials. The development is a Sol-Gel bismuth titanate-based surface-acoustic-wave (SAW) sensor that can generate efficient surface acoustic waves for crack inspection. The produced sensor is very thin (submillimeter), and can generate surface waves up to 540 C. Finite element analysis of the SAW transducer design was performed to predict the sensor behavior, and experimental studies confirmed the results. One major uniqueness of the Sol-Gel bismuth titanate SAW sensor is that it is easy to implement to structures of various shapes. With a spray coating process, the sensor can be applied to surfaces of large curvatures. Second, the sensor is very thin (as a coating) and has very minimal effect on airflow or rotating equipment imbalance. Third, it can withstand temperatures up to 530 C, which is very useful for engine applications where high temperature is an issue.
The mechanisms contributing to the erosion of the inner magnetic pole of a 6-kW magnetically shielded Hall thruster are experimentally and numerically investigated. Sputtering from ion bombardment is believed to be the cause of this wear, but the nature and source of the responsible ions remains unknown. Laser induced fluorescence and translating and surface-mounted probes are employed to characterize the flux and energy distribution of ions incident at the inner pole. It is found that the bulk population is comprised of ions originating from the cathode plume and the near field immediately adjacent to the inner pole. These ions have a low average kinetic energy, < 5 eV kinetic, but a high thermal spread in velocity, Ti = 10 eV. Calculations for the erosion at the pole from experimental measurements indicate that the bulk population only accounts for 10-25% of the observed erosion. It is postulated that the remainder of the erosion results from a separate population of ions with sufficiently high energy (> 150 V) to cause high sputtering but too low density to be detected experimentally by the plasma diagnostics in this region. The existence for this high energy population is shown to be a consequence of the high plasma potentials downstream of the thruster exit plane that are characteristic of a magnetically-shielded topography. A simulation validated by experimental measurements of the thruster provides further evidence that a high energy ion populations exists with sufficient density to explain the observed erosion.
Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields, solvent-polarity- dependent fluorescence behavior, susceptibility to quenching by certain chemical species, and/or two-photon fluorescence, none of them has the combination of all of these attributes. Because the present dyes do have all of these attributes, they have potential utility as molecular probes in a variety of applications. Examples include (1) monitoring curing and deterioration of polymers; (2) monitoring protein expression; (3) high-throughput screening of drugs; (4) monitoring such chemical species as glucose, amines, amino acids, and metal ions; and (5) photodynamic therapy of cancers and other diseases.
Carbon nanotubes, elongated molecular tubes with diameters of nanometers and lengths in microns, hold great promise for material science. Hopes for super strong light-weight material to be used in spacecraft design is the driving force behind nanotube work at JSC. The molecular nature of these materials requires the appropriate tools for investigation of their structure, properties, and formation. The mechanism of nanotube formation is of particular interest because it may hold keys to controlling the formation of different types of nanotubes and allow them to be produced in much greater quantities at less cost than is currently available. This summer's work involved the interpretation of data taken last summer and analyzed over the academic year. The work involved diagnostic studies of carbon nanotube formation processes occurring in a laser-produced plume. Laser ablation of metal doped graphite to produce a plasma plume in which carbon nanotubes self assemble is one method of making carbon nanotube. The laser ablation method is amenable to applying the techniques of laser spectroscopy, a powerful tool for probing the energies and dynamics of atomic and molecular species. The experimental work performed last summer involved probing one of the metal catalysts, nickel, by laser induced fluorescence. The nickel atom was studied as a function of oven temperature, probe laser wavelength, time after ablation, and position in the laser produced plume. This data along with previously obtained data on carbon was analyzed over the academic year. Interpretations of the data were developed this summer along with discussions of future work. The temperature of the oven in which the target is ablated greatly influences the amount of material ablated and the propagation of the plume. The ablation conditions and the time scale of atomic and molecular lifetimes suggest that initial ablation of the metal doped carbon target results in atomic and small molecular species. The metal atoms survive for several milliseconds while the gaseous carbon atoms and small molecules nucleate more rapidly. Additional experiments and the development of in situ methods for carbon nanotube detection would allow these results to be interpreted from the perspective of carbon nanotube formation.
The mechanisms underlying the hyper-radiosensitivity of AT cells were investigated by analyzing chromosome aberrations in the G(2) and M phases of the cell cycle using a combination of chemically induced premature chromosome condensation (PCC) and fluorescence in situ hybridization (FISH) with chromosome painting probes. Confluent cultures of normal fibroblast cells (AG1522) and fibroblast cells derived from an individual with AT (GM02052) were exposed to gamma rays and allowed to repair at 37 degrees C for 24 h. At doses that resulted in 10% survival, GM02052 cells were approximately five times more sensitive to gamma rays than AG1522 cells. For a given dose, GM02052 cells contained a much higher frequency of deletions and misrejoining than AG1522 cells. For both cell types, a good correlation was found between the percentage of aberrant cells and cell survival. The average number of color junctions, which represent the frequency of chromosome misrejoining, was also found to correlate well with survival. However, in a similar surviving population of GM02052 and AG1522 cells, induced by 1 Gy and 6 Gy, respectively, AG1522 cells contained four times more color junctions and half as many deletions as GM02052 cells. These results indicate that both repair deficiency and misrepair may be involved in the hyper-radiosensitivity of AT cells.
Production of electronic ground state NO(sub 2) from 248 nm photolysis of HNO(sub 3) was detected by laser induced fluorescence (LIF). A growth in the LIF signal was observed following the photolysis and has been interpreted as the relaxation of NO(sub 2) through the higher vibrational levels of the X state; an energy region where the probe laser photodissociates the NO(sub 2) instead of inducing fluorescence.
Electron microprobe for X-ray fluorescence chemical analysis
A device for the calibration of a tunable excimer laser is currently under development. The laser provides UV radiation at three principal wavelengths, 193, 248, and 308 nm and is tunable over a range of 1 nm at each of these wavelengths. The laser is used as a non-intrusive optical probe to excite electronic transitions, and thereby induce fluorescence, of the principle molecules or atoms of interest in supersonic flowfields, both reacting and nonreacting. The fluorescence resulting from the excitation is observed with an intensified camera. Over the range of tunability at the three wavelengths are a number of transitions that can be observed. The intensity of the fluorescence depends in part on the local temperature and density. The nature of this thermodynamic dependence is variable among transitions; thus, identification of the transition under observation is required. The specific transition excited corresponds directly to the wavelength of the radiation. The present technique used for transition identification consists of scanning the laser across the range of tunability and observing the fluorescence resulting from various molecular transitions.
Some of our recent work on molecular band emissions from recombination of molecular dimer ions (N4(+) and CO(+) CO) is discussed. Much of the experimental work was done by Y. S. Cao; the results on N4(+) recombination have been published. A brief progress report is given on our ongoing measurements of neutral products of recombination using the flowing-afterglow Langmuir-probe technique in conjunction with laser-induced fluorescence.