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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Twofold Andreev reflections and coherent transport in ferromagnetic semiconductor/d-wave superconductor/ferromagnetic semiconductor double tunneling junctions

Coherent transport in a ferromagnetic semiconductor (FS)/d-wave superconductor (SC)/FS structure with (110) interfaces is studied by extending Bogoliubov-de Gennes equation into eight components, in which the interband coupling of heavy and light hole bands in the FS, the strengths of potential scattering at the interfaces, and the mismatches in the effective mass and Fermi vector between the FS and SC are taken into account. Twofold Andreev reflections exist due to the existence of two bands in the FS, in which the incident hole and the two Andreev-reflected electrons, belonging to the different spin subbands, form twofold spin-singlet pairing states near the FS/SC interface. It is shown that due to the interplay of the SC with unconventional d-wave pairing symmetry and FS, the differential conductance and tunneling magnetoresistance exhibit an abundant dependence on not only the interband coupling in the FS but also the strengths of potential scattering at the interfaces. More importantly, the properties are found to be quite different from those in the FS/s-wave SC/FS structure with conventional pairing symmetry for the SC.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Shock formation processes due to interactions of two plasmas in a magnetic field and modified two-stream instabilities

The study of interactions of exploding and surrounding plasmas in an external magnetic field [K. Yamauchi and Y. Ohsawa, Phys. Plasmas 14, 053110 (2007)] is verified with two-dimensional (2D) electromagnetic particle simulations, for a case in which the initial velocity of the exploding plasma is perpendicular to the external magnetic field. The 2D simulations show essentially the same shock-formation processes as those in the previous one-dimensional simulation, including penetration of exploding ions into surrounding plasma, formation of a strong magnetic-field pulse due to deceleration of the exploding ions, ion reflection by the pulse, and subsequent splitting of the pulse into two magnetosonic pulses which then develop into forward and reverse shock waves. Furthermore, the 2D structure of electromagnetic fields in the region, where the exploding and surrounding ions overlap, is investigated with particular attention to the linear and nonlinear evolution of modified two-stream instabilities in the magnetic field that is being gradually compressed. The effects of these instabilities on ion reflection and on 2D magnetic fluctuations in the two generated pulses are also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

An estimation method for echo signal energy of pipe inner surface longitudinal crack detection by 2-D energy coefficients integration

The echo signal energy is directly affected by the incident sound beam eccentricity or angle for thick-walled pipes inner longitudinal cracks detection. A method for analyzing the relationship between echo signal energy between the values of incident eccentricity is brought forward, which can be used to estimate echo signal energy when testing inside wall longitudinal crack of pipe, using mode-transformed compression wave adaptation of shear wave with water-immersion method, by making a two-dimension integration of “energy coefficient” in both circumferential and axial directions. The calculation model is founded for cylinder sound beam case, in which the refraction and reflection energy coefficients of different rays in the whole sound beam are considered different. The echo signal energy is calculated for a particular cylinder sound beam testing different pipes: a beam with a diameter of 0.5 inch (12.7mm) testing a φ279.4mm pipe and a φ79.4mm one. As a comparison, both the results of two-dimension integration and one-dimension (circumferential direction) integration are listed, and only the former agrees well with experimental results. The estimation method proves to be valid and shows that the usual method of simplifying the sound beam as a single ray for estimating echo signal energy and choosing optimal incident eccentricity is not so appropriate.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Excitation of surface waves on one-dimensional solid–fluid phononic crystals and the beam displacement effect

The possibility of surface wave generation by diffraction of pressure waves on deeply corrugated one-dimensional phononic crystal gratings is studied both theoretically and experimentally. Generation of leaky surface waves, indeed, is generally invoked in the explanation of the beam displacement effect that can be observed upon reflection on a shallow grating of an acoustic beam of finite width. True surface waves of the grating, however, have a dispersion that lies below the sound cone in water. They thus cannot satisfy the phase-matching condition for diffraction from plane waves of infinite extent incident from water. Diffraction measurements indicate that deeply corrugated one-dimensional phononic crystal gratings defined in a silicon wafer are very efficient diffraction gratings. They also confirm that all propagating waves detected in water follow the grating law. Numerical simulations however reveal that in the sub-diffraction regime, acoustic energy of a beam of finite extent can be transferred to elastic waves guided at the surface of the grating. Their leakage to the specular direction along the grating surface explains the apparent beam displacement effect.

36 MATERIALS SCIENCE↗
NASA NTRS2008

On-Orbit Noise Characterization for MODIS Reflective Solar Bands

Since launch, the Moderate Resolution Imaging Spectroradiometer (MODIS) has operated successfully on-board the NASA Earth Observing System (EOS) Terra and EOS Aqua spacecraft. MODIS is a passive cross-track scanning radiometer that makes observations in 36 spectral bands with spectral wavelengths from visible (VIS) to long-wave infrared. MODIS bands 1-19 and 26 are the reflective solar bands (RSB) with wavelengths from 0.41 to 2.2 micrometers. They are calibrated on-orbit using an on-board solar diffuser (SD) and a SD stability monitor (SDSM) system. For MODIS RSB, the level 1B calibration algorithm produces top of the atmosphere reflectance factors and radiances for every pixel of the Earth view. The sensor radiometric calibration accuracy, specified at each spectral band's typical scene radiance, is 2% for the RSB reflectance factors and 5% for the RSB radiances. Also specified at the typical scene radiance is the detector signal-to-noise ratio (SNR), a key sensor performance parameter that directly impacts its radiometric calibration accuracy and stability, as well as the image quality. This paper describes an on-orbit SNR characterization approach developed to evaluate and track MODIS RSB detector performance. In order to perform on-orbit SNR characterization, MODIS RSB detector responses to the solar illumination reflected from the SD panel must be corrected for factors due to variations of the solar angles and the SD bi-directional reflectance factor. This approach enables RSB SNR characterization to be performed at different response levels for each detector. On-orbit results show that both Terra and Aqua MODIS RSB detectors have performed well since launch. Except for a few noisy or inoperable detectors which were identified pre-launch, most RSB detectors continue to meet the SNR design requirements and are able to maintain satisfactory short-term stability. A comparison of on-orbit noise characterization results with results derived from pre-launch calibration and characterization are also provided.

Xiong, X.↗
DOE OSTI2020

Imitation of spin density wave order in Cu 3 Nb 2 O 8

Spin density waves, based on modulated local moments, are usually associated with metallic materials, but have recently been reported in insulators which display coupled magnetic and structural order parameters. Here, we discuss one such example, the multiferroic Cu 3 Nb 2 O 8 , which is reported to undergo two magnetic phase transitions, first to an unknown antiferromagnetic phase at $T_N$ ≈ 26.5 K , and then to a helicoidal structure coupled to an electric polarization below $T_2$ ≈ 24 K which breaks the crystallographic inversion symmetry. By analogy with other complex oxides, one might naturally expect this intermediate phase to be a spin density wave phase. We apply spherical polarimetry to confirm the low-temperature magnetic structure, yet only observe a single magnetic phase transition to helicoidal order. We argue that the reported unknown phase actually supports an imitation spin density wave which originates from a decoupling of the components of the magnetic order parameter, as allowed by symmetry and driven by thermal fluctuations. This provides a mechanism for the magnetic, but not nuclear, structure to break inversion symmetry thereby creating an intermediate phase in the proximity of $T_N$ which imitates a spin density wave. As the temperature is reduced, this intermediate structure destabilizes the crystal such that a structural chirality is induced, as reflected by the emergence of the electric polarization, and the imitation spin density wave relaxes into a generic helicoid. This scenario in which critical fluctuations allow the magnetic structure to break inversion symmetry while the crystal structure remains centrosymmetric might be relevant to other complex multiferroics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

On the broadband vibration isolation performance of nonlocal total-internal-reflection metasurfaces

The concept of a nonlocal elastic metasurface has been recently proposed and experimentally demonstrated in Zhu et al. (2020). When implemented in the form of a total-internal-reflection (TIR) interface, the metasurface can act as an elastic wave barrier that is impenetrable to deep subwavelength waves over an exceptionally wide frequency band. The underlying physical mechanism capable of delivering this broadband subwavelength performance relies on an intentionally nonlocal design that leverages long-range connections between the units forming the fundamental supercell. This paper explores the design and application of a nonlocal TIR metasurface to achieve broadband passive vibration isolation in a structural assembly made of multiple dissimilar elastic waveguides. The specific structural system comprises shell, plate, and beam waveguides, and can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. The study also reports the results of an experimental investigation that confirms the significant vibration isolation capabilities afforded by the embedded nonlocal TIR metasurface. We report these results are particularly remarkable because they show that the performance of the nonlocal metasurface is preserved when applied to a complex structural assembly and under non-ideal incidence conditions of the incoming wave, hence significantly extending the validity of the results presented in Zhu et al. (2020). Results also confirm that, under proper conditions, the original concept of a planar metasurface can be morphed into a curved interface while still preserving full wave control capabilities.

42 ENGINEERING↗
NASA NTRS1991

An ultrasonic technique to measure the depth of burn wounds in humans

Whenever ultrasound encounters discontinuity in its medium of propagation, some energy is reflected from the interface. Such reflections or echoes occur when incident energy encounters the front skin, viable/necrotic, and dermis/fat skin tissue interfaces. It was shown that the most probable cause of the viable/necrotic interface is the uncoiling of collagen in the necrotic tissue, which can cause a reflection at the viable/necrotic interface of approximately 10 percent of the wave amplitude, and is approximately the same as that from the other two interfaces noted. The instrument, still in the prototype stage, was designed to detect the various reflections from within the skin layer. It is shown that, by studying the timing between the various echoes, one can use ultrasound as an aid in diagnosing the depth of burned skin tissue in humans. The instrument is a 60-MHz A-scan unit, modified to more easily identify the echoes occurring within the short time interval during which the reflections are received from the skin layers. A high frequency unit was selected so that various transducers could be utilized to optimize the system. Signal conditioning circuits were modified and added to provide an adequate display of the principle reflections expected. The unit was successful in studying burned tissue in pigs and was recently used to study burn wounds in humans. Measurement techniques and preliminary results are presented.

Yost, William T.↗
DOE OSTI2013

Characteristics of surface photorefractive waves in a nonlinear SBN-75 crystal coated with a metal film

Based on the calculation of the electrostatic field potential of space charges, we have analysed the characteristic features of light-induced scattering of extraordinary polarised light in photorefractive (PR) crystals (for example, an SBN-75 crystal). Using the method of images, the electrostatic field is analysed for surface (aperiodic) waves along the crystal - dielectric (air) interface. It is shown that the field distributions satisfying the boundary conditions can emerge only upon accumulation of a screening electric charge in a narrow transition layer of thickness {approx}1 mm, the sign of the charge being opposite that of the space charge in the illuminated region of the crystal. A model is proposed to explain the observed features of the surface PR waves in a metal-film coated PR crystal. In considering the contact potential difference at the PR crystal - film interface it is shown that in the crystal layer (adjacent to the film) enriched with charge carriers, i.e., electrons, the refractive index can be significantly reduced. In the case of small excitation angles (0 - 1.5deg ), this layer can act as an optical barrier, the reflection from which can result in near-surface waves; a characteristic difference from the previously observed oscillatory surface waves is the presence of a broadened intensity distribution shifted inside the crystal. (nonlinear optical phenomena)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1989

Evaluation of reflection and transmission coefficients for multi-layered chiral structures

The paper examines a structure consisting of an arbitrary number of layers of different chiral materials, backed by either a perfect conductor or a penetrable half-space. A plane electromagnetic wave of arbitrary polarization is obliquely incident on the structure. The reflection and transmission coefficients of the structure can be determined by a chain-matrix algorithm.

Tamirisa, P.↗
DOE OSTI2024

Anti-reflection coating with mullite and Duroid for large-diameter cryogenic sapphire and alumina optics

We developed a broadband two-layer anti-reflection (AR) coating for use on a sapphire half-wave plate (HWP) and an alumina infrared (IR) filter for the cosmic microwave background (CMB) polarimetry. Measuring the faint CMB B-mode signals requires maximizing the number of photons reaching the detectors and minimizing spurious polarization due to reflection with an off-axis incident angle. Sapphire and alumina have high refractive indices of 3.1 and are highly reflective without an AR coating. This paper presents the design, fabrication, quality control, and measured performance of an AR coating using thermally sprayed mullite and Duroid 5880LZ. This technology enables large optical elements with diameters of 600 mm. We also present a thermography-based nondestructive quality control technique, which is key to assuring good adhesion and preventing delamination when thermal cycling. We demonstrate the average reflectance of about 2.6% (0.9%) for two observing bands centered at 90/150 (220/280) GHz. At room temperature, the average transmittance of a 105 mm square test sample at 220/280 GHz is 83%, and it will increase to 90% at 100 K, attributed to reduced absorption losses. Therefore, our developed layering technique has proved effective for 220/280 GHz applications, particularly in addressing dielectric loss concerns. This AR coating technology has been deployed in the cryogenic HWP and IR filters of the Simons Array and the Simons observatory experiments and applies to future experiments such as CMB-S4.

Sakaguri, Kana (ORCID:0000000156678118)↗
NASA NTRS1993

Voyager Photometry of Saturn's A Ring

Saturn's A Ring samples a wide range of dynamical environments, from the relatively unperturbed, optically thick inner region to the outer part of the ring, which contains numerous density waves. We analyze Voyager images of the A Ring to determine how the reflectivity of different radial regions varies with lighting and viewing geometry. We model our data with a classical radiative transfer code that includes the illumination of the rings by the Sun and Saturn. The particles in the inner and mid-A Ring have Bond albedos near 0.5 and are more backscattering than satellites of comparable albedo. The region outside the Encke Gap becomes progressively less backscattering with increasing radius. Particle properties change abruptly outside the Keeler Gap; particles here have an albedo near 0.6 and a Lambert-like phase function. In contrast with previous suggestions, the abundance of free, submicrometer "dust" is small throughout the entire A Ring; this conclusion holds even in the outermost A Ring, which is strongly perturbed by density waves. Models derived from low-phase data, assuming only macroscopic particles, correctly predict the highphase reflectivity of the outer A Ring and individual strong density waves in the mid-A Ring. However, the inner and mid-A Ring are typically darker at high phase by a factor of two than our models predict. This discrepancy may be due to the reduced multiple scattering from a layer in which the particles are more closely packed. We have also studied the quadrupole azimuthal brightness asymmetry of the A Ring. The asymmetry has a full amplitude of 35% in the mid-A Ring in low-phase Voyager 2 images. We present results on its behavior and possible implications for the structure of the rings. Finally, we compare our results with studies using other data sets to synthesize our current understanding of the nature of the A Ring.

Dones, Luke↗
DOE OSTI2024

Optical second harmonic generation in anisotropic multilayers with complete multireflection of linear and nonlinear waves using ♯SHAARP.ml package

Abstract Optical second harmonic generation (SHG) is a nonlinear optical effect widely used for nonlinear optical microscopy and laser frequency conversion. Closed-form analytical solution of the nonlinear optical responses is essential for evaluating materials whose optical properties are unknown a priori. A recent open-source code, ♯SHAARP. si , can provide such closed form solutions for crystals with arbitrary symmetries, orientations, and anisotropic properties at a single interface. However, optical components are often in the form of slabs, thin films on substrates, and multilayer heterostructures with multiple reflections of both the fundamental and up to ten different SHG waves at each interface, adding significant complexity. Many approximations have therefore been employed in the existing analytical approaches, such as slowly varying approximation, weak reflection of the nonlinear polarization, transparent medium, high crystallographic symmetry, Kleinman symmetry, easy crystal orientation along a high-symmetry direction, phase matching conditions and negligible interference among nonlinear waves, which may lead to large errors in the reported material properties. To avoid these approximations, we have developed an open-source package named Second Harmonic Analysis of Anisotropic Rotational Polarimetry in Multilayers (♯SHAARP. ml ). The reliability and accuracy are established by experimentally benchmarking with both the SHG polarimetry and Maker fringes using standard and commonly used nonlinear optical materials as well as twisted 2-dimensional heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The lateral variation of P n velocity gradient under Eurasia

We report that mantle lid P wave velocity gradient, or P n velocity gradient, reflects the depth and lateral variations of thermal and rheological state of the uppermost mantle. Mapping the P n velocity gradient and its lateral variation helps us gain insight into the temperature, composition, and dynamics of the uppermost mantle. In addition, because P n velocity gradient has profound influence on P n propagation behavior, an accurate mapping of P n velocity gradient also improves the modeling and prediction of P n travel times and amplitudes. In this study, I used measured P n travel times to derive path-specific P n velocity gradients. I then inverted these velocity gradients for two-dimensional (2-D) P n velocity-gradient models for Eurasia based on the assumption that a path-specific Pn velocity gradient is the mean of laterally varying P n velocity gradients along the P n path. Result from a Monte Carlo simulation indicates that the assumption is appropriate. The 2-D velocity-gradient models show that most of Eurasia has positive velocity gradients. High velocity gradients exist mainly in tectonically active regions. Most tectonically stable regions show low and more uniform velocity gradients. In conclusion, strong velocity-gradient variations occur largely along convergent plate boundaries, particularly under overriding plates.

58 GEOSCIENCES↗
DOE OSTI2017

Characterization of the structure of low-e substrates and consequences for IR transflection measurements

Spectral distortions caused by the electric field standing wave effect were investigated for two commonly used reflective substrates: low-emissivity glass and gold-coated glass. Our analytical calculations showed that spectral distortions may arise for both incoherent and coherent light sources when performing transflectance measurements. We experimentally confirmed our predictions using a commercial mid-infrared quantum cascade laser microscope and an interferometric infrared imaging system.

infrared spectroscopy↗
DOE OSTI2013

Tunable nanostructured composite with built-in metallic wire-grid electrode

In this paper, the authors report an experimental demonstration of microwave reflection tuning in carbon nanostructure-based composites by means of an external voltage supplied to the material. DC bias voltages are imparted through a metal wire-grid. The magnitude of the reflection coefficient is measured upon oblique plane-wave incidence. Increasing the bias from 13 to 700 V results in a lowering of ∼20 dB, and a “blueshift” of ∼600 MHz of the material absorption resonance. Observed phenomena are ascribed to a change of the dielectric response of the carbon material. Inherently, the physical role of tunneling between nanofillers (carbon nanotubes) is discussed. Achievements aim at the realization of a tunable absorber. There are similar studies in literature that focus on tunable metamaterials operating at either optical or THz wavelengths.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Optics learning through affordable kit

An affordable kit which helps to understand some of the optical phenomena qualitatively and quantitatively is presented in this paper. It supplements optics taught in classes. The kit consists of equipments which are available in the market at nominal cost such as laser pointer, lenses, glass plates, razor blades, coins, ball bearing etc. Experiments which come under wave optics (interference and diffraction) and ray optics (reflection and refraction) are explained using this kit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Particle size effect on microwave absorbing of La{sub 0.67}Ba{sub 0.33}Mn{sub 0.94}Ti{sub 0.06}O{sub 3} powders prepared by mechanical alloying with the assistance of ultrasonic irradiation

Doped manganites have attracted substantial interest due to their unique chemical and physics properties, which makes it possible to be used for microwave absorbing materials. In this paper we report synthesizes and characterization of La{sub 0.67}Ba{sub 0.33}Mn{sub 0.94}Ti{sub 0.06}O{sub 3} powders prepared by mechanical alloying with the assistance of a high power ultrasonic treatment. After solid state reaction, the presence of single phase was confirmed by X-ray Diffraction (XRD). Refinement results showed that samples are single phase with monoclinic structure. It was found that powder materials derived from mechanical alloying results in large variation in the particle size. A significant improvement was obtained upon subjecting the mechanically milled powder materials to an ultrasonication treatment for a relatively short period of time. As determined by particle size analyzer (PSA), the mean particle size gradually decreased from the original size of 5.02 µm to 0.36 µm. Magnetic properties were characterized by VSM, and hysteresis loops results showed that samples are soft magnetic. It was found that when the mean particle size decreases, saturation was increases and coersitivity was decreases. Microwave absorption properties were investigated in the frequency range of 8-12 GHz using vector network analyzer. An optimal reflection loss of 24.44 dB is reached at 11.4 GHz.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗