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DOE OSTI2025

Towards more accurate sound field verification using directional acoustic filtering

Attributing omnidirectional sound levels to a specific source in the ocean can be challenging when there are multiple competing sources of sound such as boats, or biological activity. Here, we present a method to directionally filter acoustic measurements based on vector measurements of acoustic pressure and particle velocity. The directional discrimination is applied to estimate sound energy from two marine energy sources: sound generated during the decommissioning of an oil platform and those from an operating tidal energy converter. The application of a directional mask leads to distinctly different spectra and some differences in energy, relative to the unmasked scenarios.

Barosin, Emily (ORCID:0009000765495939)↗

NASA NTRS2011

Ice Shape Characterization Using Self-Organizing Maps

A method for characterizing ice shapes using a self-organizing map (SOM) technique is presented. Self-organizing maps are neural-network techniques for representing noisy, multi-dimensional data aligned along a lower-dimensional and possibly nonlinear manifold. For a large set of noisy data, each element of a finite set of codebook vectors is iteratively moved in the direction of the data closest to the winner codebook vector. Through successive iterations, the codebook vectors begin to align with the trends of the higher-dimensional data. In information processing, the intent of SOM methods is to transmit the codebook vectors, which contains far fewer elements and requires much less memory or bandwidth, than the original noisy data set. When applied to airfoil ice accretion shapes, the properties of the codebook vectors and the statistical nature of the SOM methods allows for a quantitative comparison of experimentally measured mean or average ice shapes to ice shapes predicted using computer codes such as LEWICE. The nature of the codebook vectors also enables grid generation and surface roughness descriptions for use with the discrete-element roughness approach. In the present study, SOM characterizations are applied to a rime ice shape, a glaze ice shape at an angle of attack, a bi-modal glaze ice shape, and a multi-horn glaze ice shape. Improvements and future explorations will be discussed.

McClain, Stephen T.↗

NASA NTRS2013

Assessment of Ice Shape Roughness Using a Self-Orgainizing Map Approach

Self-organizing maps are neural-network techniques for representing noisy, multidimensional data aligned along a lower-dimensional and nonlinear manifold. For a large set of noisy data, each element of a finite set of codebook vectors is iteratively moved in the direction of the data closest to the winner codebook vector. Through successive iterations, the codebook vectors begin to align with the trends of the higher-dimensional data. Prior investigations of ice shapes have focused on using self-organizing maps to characterize mean ice forms. The Icing Research Branch has recently acquired a high resolution three dimensional scanner system capable of resolving ice shape surface roughness. A method is presented for the evaluation of surface roughness variations using high-resolution surface scans based on a self-organizing map representation of the mean ice shape. The new method is demonstrated for 1) an 18-in. NACA 23012 airfoil 2 AOA just after the initial ice coverage of the leading 5 of the suction surface of the airfoil, 2) a 21-in. NACA 0012 at 0AOA following coverage of the leading 10 of the airfoil surface, and 3) a cold-soaked 21-in.NACA 0012 airfoil without ice. The SOM method resulted in descriptions of the statistical coverage limits and a quantitative representation of early stages of ice roughness formation on the airfoils. Limitations of the SOM method are explored, and the uncertainty limits of the method are investigated using the non-iced NACA 0012 airfoil measurements.

Icing↗

NASA NTRS2000

Navigation Strategy for the Mars 2001 Lander Mission

The Mars Surveyor Program (MSP) is an ongoing series of missions designed to robotically study, map and search for signs of life on the planet Mars. The MSP 2001 project will advance the effort by sending an orbiter, a lander and a rover to the red planet in the 2001 opportunity. Each vehicle will carry a science payload that will Investigate the Martian environment on both a global and on a local scale. Although this mission will not directly search for signs of life, or cache samples to be returned to Earth, it will demonstrate certain enabling technologies that will be utilized by the future Mars Sample Return missions. One technology that is needed for the Sample Return mission is the capability to place a vehicle on the surface within several kilometers of the targeted landing site. The MSP'01 Lander will take the first major step towards this type of precision landing at Mars. Significant reduction of the landed footprint will be achieved through two technology advances. The first, and most dramatic, is hypersonic aeromaneuvering; the second is improved approach navigation. As a result, the guided entry will produce in a footprint that is only tens of kilometers, which is an order of magnitude improvement over the Pathfinder and Mars Polar Lander ballistic entries. This reduction will significantly enhance scientific return by enabling the potential selection of otherwise unreachable landing sites with unique geologic interest and public appeal. A landed footprint reduction from hundreds to tens of kilometers is also a milestone on the path towards human exploration of Mars, where the desire is to place multiple vehicles within several hundred meters of the planned landing site. Hypersonic aeromaneuvering is an extension of the atmospheric flight goals of the previous landed missions, Pathfinder and Mars Polar Lander (MPL), that utilizes aerodynamic lift and an autonomous guidance algorithm while in the upper atmosphere. The onboard guidance algorithm will control the direction of the lift vector, via bank angle modulation, to keep the vehicle on the desired trajectory. While numerous autonomous guidance algorithms have been developed for use during hypersonic flight at Earth, this will be the first flight of an autonomously directed lifting entry vehicle at Mars. However, without sufficient control and knowledge of the atmospheric entry conditions, the guidance algorithm will not perform effectively. The goal of the interplanetary navigation strategy is to deliver the spacecraft to the desired entry condition with sufficient accuracy and knowledge to enable satisfactory guidance algorithm performance. Specifically, the entry flight path angle must not exceed 0.27 deg. to a 3 sigma confidence level. Entry errors will contribute directly to the size of the landed footprint and the most significant component is entry flight path angle. The size of the entry corridor is limited on the shallow side by integrated heating constraints, and on the steep side by deceleration (g-load) and terminal descent propellant. In order to meet this tight constraint it is necessary to place a targeting maneuver seven hours prior to the time of entry. At this time the trajectory knowledge will be quite accurate, and the effects of maneuver execution errors will be small. The drawback is that entry accuracy is dependent on the success of this final late maneuver. Because propulsive maneuvers are critical events, it is desirable to minimize their occurrence and provide the flight team with as much response time as possible in the event of a spacecraft fault. A mission critical maneuver at Entry - 7 hours does not provide much fault tolerance, and it is desirable to provide a strategy that minimizes reliance on this maneuver. This paper will focus on the Improvements in interplanetary navigation that will decrease entry errors and will reduce the landed footprint, even in the absence of aeromaneuvering. The easiest to take advantage of are Improvements In the knowledge of the Mars ephemeris and gravity field due to the MGS and MSP'98 missions. Improvements In data collection and reduction techniques such as "precislon ranging' and near-simultaneous tracking will also be utilized. In addition to precise trajectory control, a robust strategy for communications and flight operations must also be demonstrated. The result Is a navigation and communications strategy on approach that utilizes optimal maneuver placement to take advantage of trajectory knowledge, minimizes risk for the flight operations team, is responsive to spacecraft hardware limitations, and achieves the entry corridor. The MSP2001 mission Is managed at JPL under the auspices of the Mars Exploration Directorate. The spacecraft flight elements are built and managed by Lockheed-Martin Astronautics in Denver, Colorado.

Mase, Robert A.↗

DOE OSTI2021

Matter-wave stripe solitons induced by helicoidal spin–orbit coupling

Highlights: • Four kinds of exact stripe soliton solutions in Bose–Einstein condensates with helicoidal spin–orbit coupling (SOC) are represented. • The influence of helicoidal SOC on the structure of stripe solitons are described in detail. • The corresponding spin polarization is expressed on the Bloch sphere. • The formation mechanism of stripe solitons and the interaction properties of moving stripe solitons are discussed. We present the exact analytical solution of stripe solitons on different backgrounds in Bose–Einstein condensates with helicoidal spin–orbit coupling (SOC). They are divided into two categories, one is stationary stripe soliton on zero background or period-wave background, the other is moving stripe soliton on zero background or plane-wave background. The period of stripe is determined by both strength and frequency of helicoidal SOC, and the oscillation amplitude of stripe is adjustable in the case of fixed total density. The corresponding spin polarization is expressed on Bloch sphere. For stationary soliton, the spin density vector take values in three directions, which is different from the Rashba–Dresslhaus coupling scheme. The spin density vectors display more complicated spatial distribution for moving stripe solitons. Meanwhile, the formation mechanism of stripe soliton and the interaction properties of moving stripe solitons are discussed. Our work enhances the understanding of stripe solitons, and is helpful for the observation of stripe phase.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1999

Selected Performance Measurements of the F-15 ACTIVE Axisymmetric Thrust-Vectoring Nozzle

Flight tests recently completed at the NASA Dryden Flight Research Center evaluated performance of a hydromechanically vectored axisymmetric nozzle onboard the F-15 ACTIVE. A flight-test technique whereby strain gages installed onto engine mounts provided for the direct measurement of thrust and vector forces has proven to be extremely valuable. Flow turning and thrust efficiency, as well as nozzle static pressure distributions were measured and analyzed. This report presents results from testing at an altitude of 30,000 ft and a speed of Mach 0.9. Flow turning and thrust efficiency were found to be significantly different than predicted, and moreover, varied substantially with power setting and pitch vector angle. Results of an in-flight comparison of the direct thrust measurement technique and an engine simulation fell within the expected uncertainty bands. Overall nozzle performance at this flight condition demonstrated the F100-PW-229 thrust-vectoring nozzles to be highly capable and efficient.

Orme, John S.↗

NASA NTRS1998

Selected Performance Measurements of the F-15 Active Axisymmetric Thrust-vectoring Nozzle

Orme, John S.↗

DOE OSTI2019

Magnetic structure of Nd in NdFeAsO studied by x-ray resonant magnetic scattering

The magnetic structure of Nd in NdFeAsO compound has been explored by x-ray resonant magnetic scattering at the Nd L 2 edge ( E = 6.725 keV) at 1.7 ≤ T ≤ 15 K. At T = 1.7 K we find that the Nd moments are aligned along the crystallographic c direction with the (1, 0, 0) propagation vector, and are arranged antiferromagnetically along the a direction and ferromagnetically along the b and c directions. At 1.7 < T ≤ 15 K, we observe an unusual temperature dependence of the magnetic Bragg peaks that appear differently at Q = ( h , 0 , l ) and ( 0 , k , l ) . From the changes of magnetic intensities and our representation analysis, we find that the Nd moments are reoriented toward the a direction with a gradual decrease of the moment component in the c direction with increasing temperature. We postulate that the reorientation of the Nd moment is due to a strong interplay with the Fe moment which is fully ordered in this temperature range.

36 MATERIALS SCIENCE↗

NASA NTRS1998

EMG responses to maintain stance during multidirectional surface translations

To characterize muscle synergy organization underlying multidirectional control of stance posture, electromyographic activity was recorded from 11 lower limb and trunk muscles of 7 healthy subjects while they were subjected to horizontal surface translations in 12 different, randomly presented directions. The latency and amplitude of muscle responses were quantified for each perturbation direction. Tuning curves for each muscle were examined to relate the amplitude of the muscle response to the direction of surface translation. The latencies of responses for the shank and thigh muscles were constant, regardless of perturbation direction. In contrast, the latencies for another thigh [tensor fascia latae (TFL)] and two trunk muscles [rectus abdominis (RAB) and erector spinae (ESP)] were either early or late, depending on the perturbation direction. These three muscles with direction-specific latencies may play different roles in postural control as prime movers or as stabilizers for different translation directions, depending on the timing of recruitment. Most muscle tuning curves were within one quadrant, having one direction of maximal activity, generally in response to diagonal surface translations. Two trunk muscles (RAB and ESP) and two lower limb muscles (semimembranosus and peroneus longus) had bipolar tuning curves, with two different directions of maximal activity, suggesting that these muscle can play different roles as part of different synergies, depending on translation direction. Muscle tuning curves tended to group into one of three regions in response to 12 different directions of perturbations. Two muscles [rectus femoris (RFM) and TFL] were maximally active in response to lateral surface translations. The remaining muscles clustered into one of two diagonal regions. The diagonal regions corresponded to the two primary directions of active horizontal force vector responses. Two muscles (RFM and adductor longus) were maximally active orthogonal to their predicted direction of maximal activity based on anatomic orientation. Some of the muscles in each of the synergic regions were not anatomic synergists, suggesting a complex central organization for recruitment of muscles. The results suggest that neither a simple reflex mechanism nor a fixed muscle synergy organization is adequate to explain the muscle activation patterns observed in this postural control task. Our results are consistent with a centrally mediated pattern of muscle latencies combined with peripheral influence on muscle magnitude. We suggest that a flexible continuum of muscle synergies that are modifiable in a task-dependent manner be used for equilibrium control in stance.

NASA Discipline Neuroscience↗

NASA NTRS1994

Independent pixel and Monte Carlo estimates of stratocumulus albedo

Monte Carlo radiative transfer methods are employed here to estimate the plane-parallel albedo bias for marine stratocumulus clouds. This is the bias in estimates of the mesoscale-average albedo, which arises from the assumption that cloud liquid water is uniformly distributed. The authors compare such estimates with those based on a more realistic distribution generated from a fractal model of marine stratocumulus clouds belonging to the class of 'bounded cascade' models. In this model the cloud top and base are fixed, so that all variations in cloud shape are ignored. The model generates random variations in liquid water along a single horizontal direction, forming fractal cloud streets while conserving the total liquid water in the cloud field. The model reproduces the mean, variance, and skewness of the vertically integrated cloud liquid water, as well as its observed wavenumber spectrum, which is approximately a power law. The Monte Carlo method keeps track of the three-dimensional paths solar photons take through the cloud field, using a vectorized implementation of a direct technique. The simplifications in the cloud field studied here allow the computations to be accelerated. The Monte Carlo results are compared to those of the independent pixel approximation, which neglects net horizontal photon transport. Differences between the Monte Carlo and independent pixel estimates of the mesoscale-average albedo are on the order of 1% for conservative scattering, while the plane-parallel bias itself is an order of magnitude larger. As cloud absorption increases, the independent pixel approximation agrees even more closely with the Monte Carlo estimates. This result holds for a wide range of sun angles and aspect ratios. Thus, horizontal photon transport can be safely neglected in estimates of the area-average flux for such cloud models. This result relies on the rapid falloff of the wavenumber spectrum of stratocumulus, which ensures that the smaller-scale variability, where the radiative transfer is more three-dimensional, contributes less to the plane-parallel albedo bias than the larger scales, which are more variable. The lack of significant three-dimensional effects also relies on the assumption of a relatively simple geometry. Even with these assumptions, the independent pixel approximation is accurate only for fluxes averaged over large horizontal areas, many photon mean free paths in diameter, and not for local radiance values, which depend strongly on the interaction between neighboring cloud elements.

Cahalan, Robert F.↗

NASA NTRS1991

Particle displacement tracking applied to air flows

Electronic Particle Image Velocimeter (PIV) techniques offer many advantages over conventional photographic PIV methods such as fast turn around times and simplified data reduction. A new all electronic PIV technique was developed which can measure high speed gas velocities. The Particle Displacement Tracking (PDT) technique employs a single cw laser, small seed particles (1 micron), and a single intensified, gated CCD array frame camera to provide a simple and fast method of obtaining two-dimensional velocity vector maps with unambiguous direction determination. Use of a single CCD camera eliminates registration difficulties encountered when multiple cameras are used to obtain velocity magnitude and direction information. An 80386 PC equipped with a large memory buffer frame-grabber board provides all of the data acquisition and data reduction operations. No array processors of other numerical processing hardware are required. Full video resolution (640x480 pixel) is maintained in the acquired images, providing high resolution video frames of the recorded particle images. The time between data acquisition to display of the velocity vector map is less than 40 sec. The new electronic PDT technique is demonstrated on an air nozzle flow with velocities less than 150 m/s.

Wernet, Mark P.↗

NASA NTRS1991

Particle displacement tracking applied to air flows

Electronic Particle Image Velocimetric (PIV) techniques offer many advantages over conventional photographic PIV methods such as fast turn around times and simplified data reduction. A new all electronic PIV technique was developed which can measure high speed gas velocities. The Particle Displacement Tracking (PDT) technique employs a single CW laser, small seed particles (1 micron), and a single intensified, gated CCD array frame camera to provide a simple and fast method of obtaining two-dimensional velocity vector maps with unambiguous direction determination. Use of a single CCD camera eliminates registration difficulties encountered when multiple cameras are used to obtain velocity magnitude and direction information. An 80386 PC equipped with a large memory buffer frame-grabber board provides all of the data acquisition and data reduction operations. No array processors of other numerical processing hardware are required. Full video resolution (640 x 480 pixel) is maintained in the acquired images, providing high resolution video frames of the recorded particle images. The time between data acquisition to display of the velocity vector map is less than 40 sec. The new electronic PDT technique is demonstrated on an air nozzle flow with velocities less than 150 m/s.

Wernet, Mark P.↗

NASA NTRS1974

V/STOL flying qualities research using the X-22A

The X-22A has four ducted propellers and four engines. The engines are connected to a common system of rotating shafts which distribute propulsive power to the four propellers. Changes in the direction of the thrust vector are accomplished by rotating the ducts, which are interconnected so that all rotate through the same angle. Thrust magnitude is determined by a collective pitch lever, very similar to a helicopter. There are four variable stability system (VSS) controllers: thrust, pitch, roll, and yaw, and three artificial feel servos for the evaluation pilot cockpit controls, each employing electrohydraulic servos. Longitudinal flying qualities for STOL landing approach, and lateral-directional flying qualities and control power requirements for STOL landing approach are discussed. Attention is given to the data acquisition and processing system.

Smith, R. E.↗

DOE OSTI2020

Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model: Implications for spin waves of detwinned iron pnictides

Elucidating the nature of spin excitations is important to understanding the mechanism of superconductivity in the iron pnictides. Motivated by recent inelastic neutron scattering measurements in the nearly 100% detwinned BaFe 2 As 2 , we study the spin dynamics of an $\textit{S}$ = 1 frustrated bilinear-biquadratic Heisenberg model in the antiferromagnetic phase with wave vector (π, 0). The biquadratic interactions are treated in a dynamical way using a flavor-wave theory in an $\textit{SU}$(3) representation. Besides the dipolar spin wave (magnon) excitations, the biquadratic interactions give rise to quadrupolar excitations at high energies. In this work, we find that the quadrupolar wave significantly influences, in an energy dependent way, the anisotropy between the spin excitation spectra along the (π, 0) and (0, π) directions in the wave vector space. Our theoretical results capture the essential behavior of the spin dynamics measured in the antiferromagnetic phase of the detwinned BaFe 2 As 2 . More generally, our results underscore the importance of electron correlation effects for the microscopic physics of the iron pnictides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1995

The underlying magnetic field direction in Ulysses observations of the southern polar heliosphere

Between May 1993 and January 1995, the Ulysses spacecraft has probed the southern polar heliosphere at latitudes greater than 30 deg S, reaching a maximum latitude of 80.2 deg S in September 1994. Using hourly averages of the data obtained by the magnetometer experiment on Ulysses we have studied the underlying direction of the magnetic field threading this region of the heliosphere, away from the influence of the magnetic sector structure which complicates similar analyses in the ecliptic plane. We have constructed histograms of the measured magnetic field direction using the simple Parker spiral model field direction as a reference. We find that throughout this region the meridional angle between the field vector and the Parker model direction has a distribution which is symmetric and has a most probable value consistent with the model. At latitudes below about 60 deg S the azimuthal angle distribution also has a most probable value consistent with the model but this distribution is highly asymmetric with a greater number of observations of field lines less tightly wound than the expected spiral direction. At latitudes greater than 60 deg S the most probable value of the azimuthal angle is found to have become nearly 30 more tightly wound than the expected direction, but due to the asymmetric distribution still with a greater number of observations less tightly wound than expected. We consider possible causes of both the asymmetry in the distributions and the shift in the most probable value at the highest latitudes, one of which may be the presence of large amplitude, long period Alfven waves in the magnetic field originating from the Sun's southern polar coronal hole.

Forsyth, R. J.↗

NASA NTRS1998

Mechanotransduction molecules in the plant gravisensory response: amyloplast/statolith membranes contain a beta 1 integrin-like protein

It has been hypothesized that the sedimentation of amyloplasts within root cap cells is the primary event in the plant gravisensory-signal transduction cascade. Statolith sedimentation, with its ability to generate weighty mechanical signals, is a legitimate means for organisms to discriminate the direction of the gravity vector. However, it has been demonstrated that starchless mutants with reduced statolith densities maintain some ability to sense gravity, calling into question the statolith sedimentation hypothesis. Here we report on the presence of a beta 1 integrin-like protein localized inside amyloplasts of tobacco NT-1 suspension culture, callus cells, and whole-root caps. Two different antibodies to the beta 1 integrin, one to the cytoplasmic domain and one to the extracellular domain, localize in the vicinity of the starch grains within amyloplasts of NT-1. Biochemical data reveals a 110-kDa protein immunoprecipitated from membrane fractions of NT-1 suspension culture indicating size homology to known beta 1 integrin in animals. This study provides the first direct evidence for the possibility of integrin-mediated signal transduction in the perception of gravity by higher plants. An integrin-mediated pathway, initiated by starch grain sedimentation within the amyloplast, may provide the signal amplification necessary to explain the gravitropic response in starch-depleted cultivars.

NASA Discipline Plant Biology↗

NASA NTRS1972

Change in transmittance of fused silica as a means of detecting material sputtered from components on a 5-cm ion thruster

Two endurance tests of a 5-cm mercury bombardment thruster are reported. Both tests used a translational screen-grid system with the beam vectored 10 degrees. The first test lasted 141 hours and the second test operated for 2026 hours. In each test two fused silica samples (solar cell covers), 2.0 cm by 2.1 cm, were placed in shielded holders to detect materials sputtered from the thruster. Spectral optical properties between 0.398 and 2.16 microns were measured on each sample, both before and after the endurance tests. The deposition on each sample was spectrographically analyzed to determine the type of materials sputtered from the thruster. It was found that sputtering from the neutralizer is highly dependent on its position with respect to the beam edge. The sputtering from the accelerator grid of the translational screen-grid system of the 2026 hour test was sufficient to form an opaque film on the sample located in the direction opposite to the vectored beam.

Weigand, A. J.↗

NASA NTRS1999

Experimental Studies of the Interaction Between a Parallel Shear Flow and a Directionally-Solidifying Front

It has long been recognized that flow in the melt can have a profound influence on the dynamics of a solidifying interface and hence the quality of the solid material. In particular, flow affects the heat and mass transfer, and causes spatial and temporal variations in the flow and melt composition. This results in a crystal with nonuniform physical properties. Flow can be generated by buoyancy, expansion or contraction upon phase change, and thermo-soluto capillary effects. In general, these flows can not be avoided and can have an adverse effect on the stability of the crystal structures. This motivates crystal growth experiments in a microgravity environment, where buoyancy-driven convection is significantly suppressed. However, transient accelerations (g-jitter) caused by the acceleration of the spacecraft can affect the melt, while convection generated from the effects other than buoyancy remain important. Rather than bemoan the presence of convection as a source of interfacial instability, Hurle in the 1960s suggested that flow in the melt, either forced or natural convection, might be used to stabilize the interface. Delves considered the imposition of both a parabolic velocity profile and a Blasius boundary layer flow over the interface. He concluded that fast stirring could stabilize the interface to perturbations whose wave vector is in the direction of the fluid velocity. Forth and Wheeler considered the effect of the asymptotic suction boundary layer profile. They showed that the effect of the shear flow was to generate travelling waves parallel to the flow with a speed proportional to the Reynolds number. There have been few quantitative, experimental works reporting on the coupling effect of fluid flow and morphological instabilities. Huang studied plane Couette flow over cells and dendrites. It was found that this flow could greatly enhance the planar stability and even induce the cell-planar transition. A rotating impeller was buried inside the sample cell, driven by an outside rotating magnet, in order to generate the flow. However, it appears that this was not a well-controlled flow and may also have been unsteady. In the present experimental study, we want to study how a forced parallel shear flow in a Hele-Shaw cell interacts with the directionally solidifying crystal interface. The comparison of experimental data show that the parallel shear flow in a Hele-Shaw cell has a strong stabilizing effect on the planar interface by damping the existing initial perturbations. The flow also shows a stabilizing effect on the cellular interface by slightly reducing the exponential growth rate of cells. The left-right symmetry of cells is broken by the flow with cells tilting toward the incoming flow direction. The tilting angle increases with the velocity ratio. The experimental results are explained through the parallel flow effect on lateral solute transport. The phenomenon of cells tilting against the flow is consistent with the numerical result of Dantzig and Chao.

Zhang, Meng↗