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NASA NTRS1954

On the three-dimensional instability of laminar boundary layers on concave walls

A study is made of the stability of laminar boundary-layer profiles on slightly curved walls relative to small disturbances that result from vortices whose axes are parallel to the principal direction of flow. The result is an eigenvalue problem by which, for a given undisturbed flow at a prescribed wall, the amplification or decay is computed for each Reynolds number and each vortex thickness. For neutral disturbances (zero amplification) a critical Reynolds number is determined for each vortex distribution. The numerical calculation produces amplified disturbances on concave walls only.

FLOW, LAMINAR↗

NASA NTRS1992

A multilayered approach to superconducting tunnel junction x ray detectors

'First generation' superconducting tunnel junction X-ray detectors (characterized by a single tunnel junction in direct contact with its substrate, with totally external amplification) remain more than an order of magnitude away from their theoretical energy resolutions which are in the order of eV's. The difficulties that first generation devices are encountering are being attacked by a 'second generation' of superconducting X-ray detector designs including quasiparticle trapping configurations and Josephson junction arrays. A second generation design concept, the multilayered superconducting tunnel junction X-ray detector, consisting of tens to hundreds of tunnel junctions stacked on top of one another (a superlattice), is presented. Some of the possibilities of this engineered materials approach include the tuning of phonon transmission characteristics of the material, suppression of parasitic quasiparticle trapping and intrinsic amplification.

Rippert, E. D.↗

NASA NTRS1993

Effects of shock strength on shock turbulence interaction

Direct numerical simulation (DNS) and linear analysis (LIA) of isotropic turbulence interacting with a shock wave are performed for several upstream shock normal Mach numbers (M(sub 1)). Turbulence kinetic energy (TKE) is amplified across the shock wave, but this amplification tends to saturate beyond M(sub 1) = 3.0. TKE amplification and Reynolds stress anisotropy obtained in DNS are consistent with LIA predictions. Rapid evolution of TKE immediate downstream of the shock wave persists for all shock strengths and is attributed to the transfer between kinetic and potential modes of turbulence energy through acoustic fluctuations. Changes in energy spectra and various length scales across the shock wave are predicted by LIA, which is consistent with DNS results. Most turbulence length scales decrease across the shock. Dissipation length scale (rho-bar q(exp 3) / epsilon), however, increases slightly for shock waves with M(sub 1) less than 1.65. Fluctuations in thermodynamic variables behind the shock wave stay nearly isentropic for M(sub 1) less than 1.2 and deviate significantly from isentropy for the stronger shock waves due to large entropy fluctuation generated through the interaction.

Lee, Sangsan↗

NASA NTRS1993

Miniaturization in x ray and gamma ray spectroscopy

The paper presents advances in two new sensor technologies and a miniaturized associated electronics technology which, when combined, can allow for very significant miniaturization and for the reduction of weight and power consumption in x-ray and gamma-ray spectroscopy systems: (1) Mercuric iodide (HgI2) x-ray technology, which allows for the first time the construction of truly portable, high-energy resolution, non-cryogenic x-ray fluorescence (XRF) elemental analyzer systems, with parameters approaching those of laboratory quality cryogenic instruments; (2) the silicon avalanche photodiode (APD), which is a solid-state light sensitive device with internal amplification, capable of uniquely replacing the vacuum photomultiplier tube in scintillation gamma-ray spectrometer applications, and offering substantial improvements in size, ruggedness, low power operation and energy resolution; and (3) miniaturized (hybridized) low noise, low power amplification and processing electronics, which take full advantage of the favorable properties of these new sensors and allow for the design and fabrication of advanced, highly miniaturized x-ray and gamma-ray spectroscopy systems. The paper also presents experimental results and examples of spectrometric systems currently under construction. The directions for future developments are discussed.

Iwanczyk, Jan S.↗

NASA NTRS1994

Measurement of very small phase fluctuations by means of the operational approach

Recently Noh, Fourgeres and Mandel (NFM) have improved the operational approach to the quantum phase problem substantially and measured the phase dispersion of coherent light down to very small means photon numbers of the order of 10(exp -2). This has prompted many other investigations and clarified some important questions in relation to what is actually measured. Although their treatment is rather general, we confine ourselves here to the case of a strong local oscillator (LO) and reproduce their measurement scheme. Surprisingly enough, this simultaneous measurement of the sine and the cosine of the phase difference is completely equivalent to an old proposal to measure the phase after strong linear amplification realized experimentally by the Welling group. The reason for this rests on the fact, that in both cases the results are determined by the Q function of the signal. This was shown for amplification in and for the measurement after beam splitting by Lai and Haus.

Bandilla, Arno↗

NASA NTRS1994

Core magnetic field enhancement in single X line, multiple X line and patchy reconnection

Magnetic flux transfer events often show a significant increase of the magnetic field strength at the center of the events. Similar magnetic field observations have been reported for structures in or near the plasma sheet of the magnetotail at about 20 R(sub E). We have carried out two-dimensional (2D) and three-dimensional (3D) and simulations of single X line reconnection (SXR), multiple X line reconnection (MXR), and patchy reconnection to determine and compare the amplification of the magnetic field in the center of the developing flux tubes. The various processes are achieved by appropriate choices of 2D or 3D resistivity models. The simulations show that the increase in magnetic field strength depends on both the property of the initial configuration and the particular reconnection geometry. For the chosen initial conditions the MXR process leads to a larger increase in the core magnetic field than the patchy reconnection and SXR caused by larger magnetic tensions in the MXR process. The 3D processes always lead to a larger amplification than the corresponding 2D processes. In the 3D cases, force imbalance in the y direction will accelerate plasma out of the flux tube. This process reduces the thermal pressure and leads to a further compression of the flux rope, which yields an additional increase in the interior magnetic field strength.

Ma, Z. W.↗

NASA NTRS1994

Cyclogenesis in a saturated environment

The dynamics of baroclinic wave growth in a saturated environment is examined using linear and nonlinear models employing a parameterization of latent heat release that assumes all rising air is saturated, and saturation equivalent potential temperature is conserved on ascent. Piecewise potential vorticity (PV) diagnostics are used to interpret the results. When the stability to vertical displacements in saturated air is allowed to increase with height, as it must in an atmosphere with a constant, positive lapse rate of potential temperature, the growth rates of the most unstable modes of the Eady problem grow only marginally faster than the modes of the dry problem. The vertical variation of moist static stability produces a gradient of moist potential vorticity in the rising air, eliminating the short-wave cutoff present in the dry Eady problem. The destabilization of the short waves is shown to be associated with the interaction between surface potential temperature anomalies and diabatically generated lower-tropospheric potential vorticity anomalies. Nonlinear primitive equation simulations, starting from normal-mode initial conditions, show that while the dry wave grows at nearly the linear growth rate until maximum amplitude is reached, the moist wave grows significantly faster than the linear growth rate at finite amplitude. This enhanced growth is associated with the rapid amplification of a mesoscale PV anomaly generated by latent heat release at the warm front. The rapid amplification of the surface cyclone results from the superposition of the circulation associated with this misoscale PV anomaly upon the circulation associated with the surface and upper boundary potential temperature anomalies. Additional integrations with finite-amplitude initial conditions more typical of atmospheric conditions exhibit similar behavior. It is suggested that many of the rapid cyclogenesis events that occur as upper-troposheric PV anomalies cross the east coasts of continents may arise from the rapid generation of PV anomalies by condensational heating in the moist maritime lower troposphere.

Whitaker, Jeffrey S.↗

NASA NTRS1994

Modeling of the hydrogen maser disk in MWC 349

Maser amplification in a Keplerian circumstellar disk seen edge on-the idea put forward by Gordon (1992), Martin-Pintado, & Serabyn (1992), and Thum, Martin-Pintado, & Bachiller (1992) to explain the millimeter hydrogen recombination lines in MWC 349-is further justified and developed here. The double-peaked (vs. possible triple-peaked) form of the observed spectra is explained by the reduced emission from the inner portion of the disk, the portion responsible for the central ('zero velocity') component of a triple-peaked spectrum. Radial gradient of electron density and/or free-free absorption within the disk are identified as the probable causes of this central 'hole' in the disk and of its opacity. We calculate a set of synthetic maser spectra radiated by a homogeneous Keplerian ring seen edge-on and compare them to the H30-alpha observations of Thum et al., averaged over about 1000 days. We used a simple graphical procedure to solve an inverse problem and deduced the probable values of some basic disk and maser parameters. We find that the maser is essentially unsaturated, and that the most probable values of electron temperature. Doppler width of the microturbulence, and electron density, all averaged along the amplification path are, correspondingly, T(sub e) less than or equal to 11,000 K, V(sub micro) less than or equal to 14 km/s, n(sub e) approx. = (3 +/- 2) x 10(exp 7)/cu cm. The model shows that radiation at every frequency within the spectrum arises in a monochromatic 'hot spot.' The maximum optical depth within the 'hot spot' producing radiation at the spectral peak maximum is tau(sub max) approx. = 6 +/- 1; the effective width of the masing ring is approx. = 0.4-0.7 times its outer diameter; the size of the 'hot spot' responsible for the radiation at the spectral peak frequency is approx. = 0.2-0.3 times the distance between the two 'hot spots' corresponding to two peaks. An important derivation of our model is the dynamical mass of the central star, M(sub *) approx. = 26 solar masses (D/1.2 kpc), D being the distance to the star. Prospects for improving the model are discussed.

Ponomarev, Victor O.↗

NASA NTRS1995

Programmable Iterative Optical Image And Data Processing

Proposed method of iterative optical image and data processing overcomes limitations imposed by loss of optical power after repeated passes through many optical elements - especially, beam splitters. Involves selective, timed combination of optical wavefront phase conjugation and amplification to regenerate images in real time to compensate for losses in optical iteration loops; timing such that amplification turned on to regenerate desired image, then turned off so as not to regenerate other, undesired images or spurious light propagating through loops from unwanted reflections.

Jackson, Deborah J.↗

NASA NTRS1997

Design of a Minimum Surface-Effect Tendon-Based Microactuator for Micromanipulation

A piezoelectric (PZT) stack-based actuator was developed to provide a means of actuation with dynamic characteristics appropriate for small-scale manipulation. In particular, the design incorporates a highly nonlinear, large-ratio transmission that provides approximately two orders of magnitude motion amplification from the PZT stack. In addition to motion amplification, the nonlinear transmission was designed via optimization methods to distort the highly non-uniform properties of a piezoelectric actuator so that the achievable actuation force is nearly constant throughout the actuator workspace. The package also includes sensors that independently measure actuator output force and displacement, so that a manipulator structure need not incorporate sensors nor the associated wires. Specifically, the actuator was designed to output a maximum force of at least one Newton through a stroke of at least one millimeter. For purposes of small-scale precision position and/or force control, the actuator/sensor package was designed to eliminate stick-slip friction and backlash. The overall dimensions of the actuator/sensor package are approximately 40 x 65 x 25 mm.

Goldfarb, Michael↗

NASA NTRS1997

Enantiomeric Cross-Inhibition in the Synthesis of Oligonucleotides on a Nonchiral Template

Prebiotic syntheses of chiral monomers always yield racemic mixtures. Living systems, however, utilize L-amino acids and D-nucleotides in their biopolymers. The generation of optical asymmetry by selection and amplification in an autocatalytic process is, therefore, an important element in many theories of the origin of life. Replication of polynucleotides in template-directed syntheses is an obvious candidate for such an amplification step in a pre-'RNA world'. A serious objection to this suggestion is the observation that the efficiency of template-directed syntheses of RNA is limited by enantiomeric cross-inhibition. Peptide Nucleic Acids (PNAs), amide-linked, nonchiral analogues of RNA, have been 'copied' into RNA and constitute an alternative to chiral polynucleotides as an informational replicating system. Here, we use PNA as model for a hypothetical, nonchiral precursor of RNA in experiments re-examining enantiomeric cross-inhibition. We find that enantiomeric cross-inhibition is as serious in the polymerization of nucleotides on a PNA template as it is on a conventional RNA or DNA template.

Schmidt, Jurgen G.↗

NASA NTRS1997

Receptivity of Flat-Plate Boundary Layer in a Non-Uniform Free Stream (Vorticity Normal to the Plate)

Work is devoted to study of free-stream vorticity normal to leading edge interaction with boundary layer over plate and resulting flow distortion influence on laminar-turbulent transition. In experiments made the wake behind the vertically stretched wire was used as a source of vortical disturbances and its effect on the boundary layer over the horizontally mounted plate with various leading edge shapes was investigated. The purpose of experiments was to check the predictions of theoretical works of M.E. Goldstein, et. al. This theory shows that small free-stream inhomogeneity interacting with leading edge produces considerable distortion of boundary layer flow. In general, results obtained confirms predictions of Goldstein's theory, i.e., the amplification of steady vortical disturbances in boundary layer caused by vortex lines stretching was observed. Experimental results fully coincide with predictions of theory for large Reynolds number, relatively sharp leading edge and small disturbances. For large enough disturbances the flow distortion caused by symmetric wake unexpectedly becomes antisymmetric in spanwise direction. If the leading edge is too blunt the maximal distortion takes place immediately at the nose and no further amplification was observed. All these conditions and results are beyond the scope of Goldstein's theory.

Kogan, M. N.↗

NASA NTRS1995

A DNA enzyme with Mg(2+)-Dependent RNA Phosphoesterase Activity

Previously we demonstrated that DNA can act as an enzyme in the Pb(2+)-dependent cleavage of an RNA phosphoester. This is a facile reaction, with an uncatalyzed rate for a typical RNA phosphoester of approx. 10(exp -4)/ min in the presence of 1 mM Pb(OAc)2 at pH 7.0 and 23 C. The Mg(2+) - dependent reaction is more difficult, with an uncatalyzed rate of approx. 10(exp -7)/ min under comparable conditions. Mg(2+) - dependent cleavage has special relevance to biology because it is compatible with intracellular conditions. Using in vitro selection, we sought to develop a family of phosphoester-cleaving DNA enzymes that operate in the presence of various divalent metals, focusing particularly on the Mg(2+) - dependent reaction. Results: We generated a population of greater than 10(exp 13) DNAs containing 40 random nucleotides and carried out repeated rounds of selective amplification, enriching for molecules that cleave a target RNA phosphoester in the presence of 1 mM Mg(2+), Mn(2+), Zn(2+) or Pb(2+). Examination of individual clones from the Mg(2+) lineage after the sixth round revealed a catalytic motif comprised of a three-stem junction.This motif was partially randomized and subjected to seven additional rounds of selective amplification, yielding catalysts with a rate of 0.01/ min. The optimized DNA catalyst was divided into separate substrate and enzyme domains and shown to have a similar level of activity under multiple turnover conditions. Conclusions: We have generated a Mg(2+) - dependent DNA enzyme that cleaves a target RNA phosphoester with a catalytic rate approx. 10(exp 5) - fold greater than that of the uncatalyzed reaction. This activity is compatible with intracellular conditions, raising the possibility that DNA enzymes might be made to operate in vivo.

Breaker, Ronald R.↗

NASA NTRS1998

Traveling-Wave Tubes

The traveling-wave tube (TWT) is a vacuum device invented in the early 1940's used for amplification at microwave frequencies. Amplification is attained by surrendering kinetic energy from an electron beam to a radio frequency (RF) electromagnetic wave. The demand for vacuum devices has been decreased largely by the advent of solid-state devices. However, although solid state devices have replaced vacuum devices in many areas, there are still many applications such as radar, electronic countermeasures and satellite communications, that require operating characteristics such as high power (Watts to Megawatts), high frequency (below 1 GHz to over 100 GHz) and large bandwidth that only vacuum devices can provide. Vacuum devices are also deemed irreplaceable in the music industry where musicians treasure their tube-based amplifiers claiming that the solid-state and digital counterparts could never provide the same "warmth" (3). The term traveling-wave tube includes both fast-wave and slow-wave devices. This article will concentrate on slow-wave devices as the vast majority of TWTs in operation fall into this category.

Kory, Carol L.↗

NASA NTRS1999

Simulations of the Surface Pressure Tides on Mars Incorporating New MOLA Topography Data

Simulations of surface pressure tides on Mars have been conducted previously with the NASA Ames Mars General Circulation Model (MGCM), as well as by Wilson and Hamilton. In the case of the MGCM, annual simulations with realistic (Viking-derived) dust loading have been reasonably successful at reproducing observed tides at the Viking Lander sites. One obvious discrepancy between observed and simulated tides is the amplification found in the model's diurnal tidal amplitude around L(sub s) 90. The observations show no such amplification. We report here on recent simulations of the surface pressure tide on Mars conducted with the MGCM and with the newly acquired MOLA topography data. The data is provided at 1deg x 1deg resolution, and is used by the MGCM at 7.5deg x 9deg resolution. The vertical domain of the MGCM extends to around 80 km. In the simulations reported in, the vertical domain extended to around 50 km, and the Consortium topography dataset was used. Additional information is contained in the original extended abstract.

Bridger, A. F. C.↗

NASA NTRS2000

Microwave Driven Actuators Power Allocation and Distribution

Design, fabrication and test of a power allocation and distribution (PAD) network for microwave driven actuators is presented in this paper. Development of a circuit that would collect power from a rectenna array amplify and distribute the power to actuators was designed and fabricated for space application in an actuator array driven by a microwave. A P-SPICE model was constructed initially for data reduction purposes, and was followed by a working real-world model. A voltage up - converter (VUC) is used to amplify the voltage from the individual rectenna. The testing yielded a 26:1 voltage amplification ratio with input voltage at 9 volts and a measured output voltage 230VDC. Future work includes the miniaturization of the circuitry, the use of microwave remote control, and voltage amplification technology for each voltage source. The objective of this work is to develop a model system that will collect DC voltage from an array of rectenna and propagate the voltage to an array of actuators.

Forbes, Timothy↗

NASA NTRS2001

Transition In Supersonic Flows With Corners

It is proposed to investigate the effect of sudden change in the slope of the surface on the stability and transition onset point in supersonic and hypersonic boundary layers. Since we can not use the linear stability theory in flows where there are discontinuities we have to solve the full Navier-Stokes equations to determine the amplification of the disturbances across the oblique shock which exists at the corner. We will use the Navier-Stokes code which was developed by Dr. Harold Atkins in the aerodynamic and acoustic methods branch. The code is developed using the higher order ENO scheme and is currently set up for two-dimensional flows. In the first year of our investigation, we will investigate the evolution of small amplitude two-dimensional disturbances and determine the N-factors for the most amplified disturbances. We will perform the analysis for the parameter similar to X-31 model and flight experiment conditions. From these computation we will infer what is the maximum amplification rate possible in quite environments without any tripping devices. In the second part of the investigation, we will perform nonlinear computations to determine what is the minimum amplitudes necessary to cause the transition at a designed location. In the third part, we have to determine what kind of trip devices necessary to excite the required disturbances. The principal investigator of this project is Dr. P. Balakumar, Associate Professor of Department of Aerospace Engineering, Old Dominion University. We will actively collaborate with research scientists in the Aero-Thermodynamics Branch at NASA/Langley Research Center. A half-time graduate student will also participate in the project.

Balakumar, P.↗

NASA NTRS2002

Aeroheating Predictions for the X-43 Cowl-Closed Configuration at Mach 7 and 10

A pre-flight analysis was conducted for the Mach 7 and Mach 10 X-43 cowl-closed configurations to evaluate three-dimensional flow-field effects on localized heating in the vicinity of the closed cowl flap and sidewall. First, engineering-level analyses based on documented laminar and turbulent surface heating database were used to estimate localized heating amplification factors to account for turbulent flow effects, corner flow effects and the presence of forebody boundary layer trip devices. These estimated factors were applied to 2-D computational predictions to develop surface heat loads. Second, thin-film gauge surface heating data were obtained for a Mach 10 cowl-closed configuration in a reflected shock tunnel at simulated flight conditions. Third, computational fluid dynamics (CFD) flow-field predictions were obtained at Mach 10 ground test conditions to provide comparisons with the engineering database predictions and experimental measurements. Similarly, a CFD solution was also obtained at Mach 7 flight conditions to provide qualitative comparisons with engineering predictions. The Mach 10 CFD predictions compare favorably with the experimental measurements and the engineering estimates for surface heating amplification on the closed cowl. However, experimental measurements were not of sufficient quantity on the sidewall surface to capture the highest localized heating rates, and also the Mach 10 CFD predictions suggest higher peak heating on the sidewall compared to the engineering estimates. Also, the Mach 7 CFD predictions indicate qualitative agreement with the database estimates in terms of flow-field structure and peak heating locations on the closed-cowl flap and sidewall surfaces.

Cockrell, Charles E., Jr.↗