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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Multiwavelength infrared focal plane array detector

A multiwavelength focal plane array infrared detector is included on a common substrate having formed on its top face a plurality of In.sub.x Ga.sub.1-x As (x.ltoreq.0.53) absorption layers, between each pair of which a plurality of InAs.sub.y P.sub.1-y (y<1) buffer layers are formed having substantially increasing lattice parameters, respectively, relative to said substrate, for preventing lattice mismatch dislocations from propagating through successive ones of the absorption layers of decreasing bandgap relative to said substrate, whereby a plurality of detectors for detecting different wavelengths of light for a given pixel are provided by removing material above given areas of successive ones of the absorption layers, which areas are doped to form a pn junction with the surrounding unexposed portions of associated absorption layers, respectively, with metal contacts being formed on a portion of each of the exposed areas, and on the bottom of the substrate for facilitating electrical connections thereto.

Forrest, Stephen R.↗
NASA NTRS2011

Multi-Frequency Observations of Gamma-Ray Blazar 1633 plus 382

We perform monthly monitoring of the quasar 1633+382 (4C+38.41) within a sample of gamma-ray blazars with the VLBA at 43 GHz along with optical photometric and polarimetric observations. We construct the gamma-ray light curve of 1633+382 using data obtained by the Fermi LAT. We find that a high gamma-ray state of the quasar starting in 2009 September is simultaneous with an increase of the flux in the mm-wave VLBI core. We resolve a superluminal feature on the VLBA images that appears to be responsible for the mm-wave flux increase. We find a strong correlation between optical and gamma-ray light curves with a delay of gamma-ray variations of 5+/-3 days, as well as a strong correlation between optical flux and degree of polarization during the high gamma-ray state. Comparison between the optical polarization position angle and that in the VLBI core supports the idea that in the quasar 1633+382 a high gamma-ray state is connected with processes originating near the mm-VLBI core.

Jorstad, S. G.↗
NASA NTRS2013

Superorbital Periodic Modulation in Wind-Accretion High-Mass X-Ray Binaries from Swift Burst Alert Telescope Observations

We report the discovery using data from the Swift-Burst Alert Telescope (BAT) of superorbital modulation in the wind-accretion supergiant high-mass X-ray binaries 4U 1909+07 (= X 1908+075), IGR J16418−4532, and IGR J16479−4514. Together with already known superorbital periodicities in 2S 0114+650 and IGR J16493−4348, the systems exhibit a monotonic relationship between superorbital and orbital periods. These systems include both supergiant fast X-ray transients and classical supergiant systems, and have a range of inclination angles. This suggests an underlying physical mechanism which is connected to the orbital period. In addition to these sources with clear detections of superorbital periods, IGR J16393−4643 (= AX J16390.4−4642) is identified as a system that may have superorbital modulation due to the coincidence of low-amplitude peaks in power spectra derived from BAT, Rossi X-Ray Timing Explorer Proportional Counter Array, and International Gamma-Ray Astrophysics Laboratory light curves. 1E 1145.1−6141 may also be worthy of further attention due to the amount of low-frequency modulation of its light curve. However, we find that the presence of superorbital modulation is not a universal feature of wind-accretion supergiant X-ray binaries.

superorbital↗
NASA NTRS2019

On the Coronal Mass Ejection Detection Rate during Solar Cycles 23 and 24

The Solar and Heliospheric Observatory (SOHO) mission's white light coronagraphs have observed more than25,000 coronal mass ejections (CMEs) from 1996 January to the end of 2015 July. This period of time covers almost two solar cycles (23 and 24). The basic attributes of CMEs, reported in the SOHO/Large Angle and Spectrometric Coronagraph (LASCO) catalog, during these solar cycles were statistically analyzed. The question of the CME detection rate and its connection to the solar cycles was considered in detail. Based on the properties and detection rate, CMEs can be divided into two categories: regular and specific events. The regular events are pronounced and follow the pattern of sunspot number. On the other hand, the special events are poorer and more correlated with the general conditions of heliosphere and corona. Nevertheless, both groups of CMEs are the result of the same physical phenomenon, viz. release of magnetic energy from closed field regions. It was demonstrated that the enhanced CME rate, since the solar cycle 23 polar-field reversal, is due to a significant decrease of total(magnetic and plasma) heliospheric pressure as well as the changed magnetic pattern of solar corona. CMEs expel free magnetic energy and helicity from the Sun; therefore, they are related to complex solar magnetic field structure. It is also worth emphasizing that the CMEs listed in the SOHO/LASCO catalog are real ejections (not false identification). Their detection rate reflects the global evolution of the magnetic field on the Sun, and not only changes in the magnetic structures associated with sunspots.

Michalek, Grzegorz↗
NASA NTRS2023

A Sensitive Search for Supernova Emission Associated with the Extremely Energetic and Nearby GRB 221009A

We report observations of the optical counterpart of the long gamma-ray burst GRB 221009A. Due to the extreme rarity of being both nearby (z = 0.151) and highly energetic (E ϒ,iso ≥ 10 54 erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of γ-ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated supernova (SN) contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence (K Bayes =10 1.2 for the presence of an additional component arising from an associated SN, SN 2022xiw, and find that it must be substantially fainter (<67% as bright at the 99% confidence interval) than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the SN parameters (M Ni , M ej and E KE ) under several different assumptions with respect to the host galaxy's extinction. We find properties that are broadly consistent with previous GRB-associated SNe: M Ni = 0.05–0.25 M ⊙ , M ej = 3.5–11.1 M ⊙ , and E KE = (1.6–5.2) × 10 52 erg. We note that these properties are weakly constrained due to the faintness of the SN with respect to the afterglow and host emission, but we do find a robust upper limit on M Ni of M Ni < 0.36 M ⊙ . Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (seven orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.

Core-collapse supernovae↗
DOE OSTI2019

Optimization of switch diagnostics on the MAIZE linear transformer driver

The MAIZE Linear Transformer Driver is made of 40 capacitor-switch-capacitor `bricks' connected in parallel. When these 40 bricks are charged to 100-kV and then discharged synchronously, the MAIZE facility generates a 1-MA current pulse with a 100-ns rise time into a matched load impedance. Discharging each of the capacitors in a brick is carried out by the breakdown of a spark-gap switch, a process which results in the emission of light. Monitoring this output light with a fiber optic coupled to a photomultiplier tube (PMT) and an oscilloscope channel provides information on switch performance and timing jitter– whether a switch red early, late, or in phase with the other switches. However, monitoring each switch with a dedicated detector- oscilloscope channel can be problematic for facilities where the number of switches to be monitored (e.g., 40 on MAIZE) greatly exceeds the number of detector-oscilloscope channels available. The technique of using fibers to monitor light emission from switches can be optimized by treating a PMT as a binary digit or bit and using a combinatorial encoding scheme, where each switch is monitored by a unique combination of fiber- PMT-oscilloscope channels simultaneously. By observing the unique combination of ber-PMT-oscilloscope channels that are turned on, the pre-firing or late-firing of a single switch on MAIZE can be identified by as few as six PMT-oscilloscope channels. The number of PMT-oscilloscope channels, N , required to monitor X switches can be calculated by 2 N = X + 1, where the number '2' is selected because the PMT-oscilloscope acts as a bit. Here, we demonstrate the use of this diagnostic technique on MAIZE. In conclusion, we also present an analysis of how this technique could be scaled to monitor the tens of thousands of switches proposed for various next generation pulsed power facilities.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Over 8 hours of continuous operation of a free-electron laser driven by a laser-plasma accelerator

Since the emergence of laser-plasma accelerators (LPAs), substantial work has been dedicated to using LPAs to drive free-electron lasers (FELs) for a broad range of applications. Despite recent breakthroughs, which have proven the fundamental feasibility of operating FELs with an LPA source, stable FEL operation over multiple hours without operator input had yet to be achieved. In this work, we report significant improvements to the stability of a hundred terawatt laser system, resulting in successful demonstration of reliable, long-term operation of an LPA-driven FEL in the self-amplified spontaneous emission (SASE) regime at 420 nm. The LPA source delivered 100 MeV electron beams at 1 Hz with high stability over more than 10 h, enabling over 8 h of continuous FEL operation without operator input. The acquired data were subsequently used to investigate correlations between the measured undulator radiation and parameters of the drive laser, plasma source, and electron beam. The revealed connections between LPA and FEL performance gave important additional insights into ways to further improve and stabilize the system, thus demonstrating the capability of our setup to serve as a powerful platform for future studies of LPA-driven FEL operation. The one-of-a-kind integration of multiple stabilization concepts onto the LPA facility discussed in this manuscript yielded significant accelerator and light source improvements (with residual correlations suggesting even more is possible), which will positively impact LPA applications at large.

Kohrell, Finn [Lawrence Berkeley National Laborato↗
NASA NTRS1974

Ontogenesis of receptive fields in the rabbit striate cortex

The development of receptive fields in rabbit pups was investigated by measuring their responses to various light stimuli and to electric shock delivered to the optic nerve head. The pups ranged in age from three to twenty-five days, allowing correlation of findings with maturation. The data, classified according to relation with symmetric or asymmetric field types, strongly suggest that retina maturation is the key factor in the rate of development in central visual pathways, and that central synaptic connections are made before the onset of retinal activity.

Mathers, L. H.↗
NASA NTRS1975

Magnetic effects of shock and their implications for magnetism of lunar samples

The principal problem in lunar magnetism is to account for the surprisingly large magnitude of the remanent magnetism of lunar surface material. Experiments conducted in this connection have shown that shock is an important mechanism of both magnetization and demagnetization. A description is presented of new experimental results in the low-shock range. An attempt is made to assess the effect of shock upon estimates of the ancient lunar field intensity. The results are used as a basis for a reconsideration of the present lunar field models in the light of intensity estimates and other new results. It is found that the central questions in lunar magnetism have not yet been answered to everyone's satisfaction.

Cisowski, S. M.↗
DOE OSTI2021

A Novel Fiber-Bragg-Grating-Based Unique Identifier for Use in Tags and Seals

Tags and seals are important tools used in safeguards regimes for the control of nuclear materials. Vital to a successful tag or seal is the ability to securely, uniquely, and positively distinguish it from others of the same kind. This allows one to validate that items entered into an inspection regime to which the tag or seal is affixed are as claimed. We are developing a new type of unique identifier (UID) for such applications that is based on fiber-Bragg grating (FBG) technology. The index of refraction of the core glass of a fiber optic can be locally and permanently altered if sensitized fibers are exposed to intense ultraviolet light. This can be used to create index modulations with a regular periodicity comparable to the wavelengths of light with which the fiber is used. If broadband illumination is sent down the fiber, any light that is in resonance with the modulations will be reflected back to the input end of the fiber where it can be detected. The shape of the returned spectrum can be set by the modulation pattern written into the fiber’s core. We take advantage of these properties to create a compact UID that contains several FBGs potted into a monolithic body. By connecting the UID to an optical interrogator, the complex spectral return can be uniquely identified with a short measurement, providing a robust identification. As a device based on narrowband spectral returns, FBGs are inherently radiation tolerant, making them ideal for use with nuclear materials. Further, they can be read out remotely via a long fiber optic or locally via brief connection to a portable optical interrogator. Because the spectral signature of FBGs is sensitive to external mechanical perturbations, we are exploring the ability to reversibly alter the signature obtained from the UID by applying controlled mechanical forces with a simple device. Such a “key” will allow different stakeholders to obtain their own unique signature from the device, providing a new level of surety to safeguards inspections.

Ziock, Klaus-Peter↗
DOE OSTI2025

Probing substrate water access through the O1 channel of Photosystem II by single site mutations and membrane inlet mass spectrometry

Abstract Light-driven water oxidation by photosystem II sustains life on Earth by providing the electrons and protons for the reduction of CO 2 to carbohydrates and the molecular oxygen we breathe. The inorganic core of the oxygen evolving complex is made of the earth-abundant elements manganese, calcium and oxygen (Mn 4 CaO 5 cluster), and is situated in a binding pocket that is connected to the aqueous surrounding via water-filled channels that allow water intake and proton egress. Recent serial crystallography and infrared spectroscopy studies performed with PSII isolated fromThermosynechococcus vestitus(T. vestitus) support that one of these channels, the O1 channel, facilitates water access to the Mn 4 CaO 5 cluster during its S 2 →S 3 and S 3 →S 4 →S 0 state transitions, while a subsequent CryoEM study concluded that this channel is blocked in the cyanobacteriumSynechocystis sp.PCC 6803, questioning the role of the O1 channel in water delivery. Employing site-directed mutagenesis we modified the two O1 channel bottleneck residues D1-E329 and CP43-V410 (T. vestitusnumbering) and probed water access and substrate exchange via time resolved membrane inlet mass spectrometry. Our data demonstrates that water reaches the Mn 4 CaO 5 cluster via the O1 channel in both wildtype and mutant PSII. In addition, the detailed analysis provides functional insight into the intricate protein-water-cofactor network near the Mn 4 CaO 5 cluster that includes the pentameric, near planar ‘water wheel’ of the O1 channel.

Plant Sciences↗
NASA NTRS2000

New Human-Computer Interface Concepts for Mission Operations

The current climate of budget cuts has forced the space mission operations community to reconsider how it does business. Gone are the days of building one-of-kind control centers with teams of controllers working in shifts 24 hours per day, 7 days per week. Increasingly, automation is used to significantly reduce staffing needs. In some cases, missions are moving towards lights-out operations where the ground system is run semi-autonomously. On-call operators are brought in only to resolve anomalies. Some operations concepts also call for smaller operations teams to manage an entire family of spacecraft. In the not too distant future, a skeleton crew of full-time general knowledge operators will oversee the operations of large constellations of small spacecraft, while geographically distributed specialists will be assigned to emergency response teams based on their expertise. As the operations paradigms change, so too must the tools to support the mission operations team's tasks. Tools need to be built not only to automate routine tasks, but also to communicate varying types of information to the part-time, generalist, or on-call operators and specialists more effectively. Thus, the proper design of a system's user-system interface (USI) becomes even more importance than before. Also, because the users will be accessing these systems from various locations (e.g., control center, home, on the road) via different devices with varying display capabilities (e.g., workstations, home PCs, PDAS, pagers) over connections with various bandwidths (e.g., dial-up 56k, wireless 9.6k), the same software must have different USIs to support the different types of users, their equipment, and their environments. In other words, the software must now adapt to the needs of the users! This paper will focus on the needs and the challenges of designing USIs for mission operations. After providing a general discussion of these challenges, the paper will focus on the current efforts of creatin(y an effective USI for one specific suite of tools, SERS (The Spacecraft Emergency Response System), which has been built to enable lights-out operations. SERS is a Web-based collaborative environment that enables secure distributed fault management.

Fox, Jeffrey A.↗
DOE OSTI2021

Possible Superconductivity with a Bogoliubov Fermi Surface in a Lightly Doped Kagome U(1) Spin Liquid

Whether the doped t-J model on the Kagome lattice supports exotic superconductivity has not been decisively answered. In this paper, we propose a new class of variational states for this model and perform large-scale variational Monte Carlo simulation on it. The proposed variational states are parameterized by the SU(2)-gauge-rotation angles, as the SU(2)-gauge structure hidden in the Gutzwiller-projected mean-field ansatz for the undoped model is broken upon doping. These variational doped states smoothly connect to the previously studied U(1) π-flux or 0-flux states, and energy minimization among them yields a chiral noncentrosymmetric nematic superconducting state with 2 × 2-enlarged unit cell. Moreover, this pair density wave state possesses a finite Fermi surface for the Bogoliubov quasi particles. We further study experimentally relevant properties of this intriguing pairing state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Unraveling the Correlation between Raman and Photoluminescence in Monolayer MoS 2 through Machine‐Learning Models

Abstract 2D transition metal dichalcogenides (TMDCs) with intense and tunable photoluminescence (PL) have opened up new opportunities for optoelectronic and photonic applications such as light‐emitting diodes, photodetectors, and single‐photon emitters. Among the standard characterization tools for 2D materials, Raman spectroscopy stands out as a fast and non‐destructive technique capable of probing material's crystallinity and perturbations such as doping and strain. However, a comprehensive understanding of the correlation between photoluminescence and Raman spectra in monolayer MoS 2 remains elusive due to its highly nonlinear nature. Here, the connections between PL signatures and Raman modes are systematically explored, providing comprehensive insights into the physical mechanisms correlating PL and Raman features. This study's analysis further disentangles the strain and doping contributions from the Raman spectra through machine‐learning models. First, a dense convolutional network (DenseNet) to predict PL maps by spatial Raman maps is deployed. Moreover, a gradient boosted trees model (XGBoost) with Shapley additive explanation (SHAP) to bridge the impact of individual Raman features in PL features is applied. Last, a support vector machine (SVM) to project PL features on Raman frequencies is adopted. This work may serve as a methodology for applying machine learning to characterizations of 2D materials.

Lu, Ang‐Yu↗
DOE OSTI2025

Comparing Machine Learning and Physics-Based Nanoparticle Geometry Determinations Using Far-Field Spectral Properties

Anisotropic metal nanostructures exhibit polarization-dependent light scattering, a property which has been widely studied and exploited to determine orientations of subwavelength structures using far-field microscopy. Here we explore the use of variational autoencoders (VAEs) to determine the geometries of gold nanorods (NRs) such as in-plane orientation and aspect ratio under linearly polarized dark-field illumination in an optical microscope. We enforce a shared latent space to connect two VAEs trained separately with polarized dark-field scattering spectra and electron microscopy images and achieve image prediction (shape, orientation, and size) of Au NRs using only polarized dark-field scattering spectra. We determine the geometrical parameters of orientational angle and aspect ratio quantitatively via both our dual-VAE and physics-based analysis on the input scattering spectra. We show that orientational angle prediction by dual-VAE performs well with only a small (~300 particle) training set, yielding a mean absolute error (MAE) of 14.4° and a concordance correlation coefficient (CCC) of 0.95. This performance is only marginally worse than the physics-based cos(2?) fitting approach between the scattering intensity and the polarizing angle, which achieves MAE of 8.78° and CCC of 0.99. Aspect ratio determination is also comparable for the dual-VAE and physics-based fitting comparison (MAE of 0.21 vs. 0.23 and CCC of 0.53 vs. 0.68). Here, this dual encoder-decoder architecture effectively exploits the structure-property relationships of plasmonic nanostructures to construct a cross-modal machine learning (ML) approach, providing a pathway to employ ML approaches to address other structure-property relationships in materials science.

Dark-field scattering↗
DOE OSTI2020

Structural basis of the activation of a metabotropic GABA receptor

Metabotropic γ-aminobutyric acid receptors (GABA B ) are involved in the modulation of synaptic responses in the central nervous system and have been implicated in neuropsychological conditions that range from addiction to psychosis. GABA B belongs to class C of the G-protein-coupled receptors, and its functional entity comprises an obligate heterodimer that is composed of the GB1 and GB2 subunits. Each subunit possesses an extracellular Venus flytrap domain, which is connected to a canonical seven-transmembrane domain. In this paper we present four cryo-electron microscopy structures of the human full-length GB1–GB2 heterodimer: one structure of its inactive apo state, two intermediate agonist-bound forms and an active form in which the heterodimer is bound to an agonist and a positive allosteric modulator. The structures reveal substantial differences, which shed light on the complex motions that underlie the unique activation mechanism of GABA B . Our results show that agonist binding leads to the closure of the Venus flytrap domain of GB1, triggering a series of transitions, first rearranging and bringing the two transmembrane domains into close contact along transmembrane helix 6 and ultimately inducing conformational rearrangements in the GB2 transmembrane domain via a lever-like mechanism to initiate downstream signalling. This active state is stabilized by a positive allosteric modulator binding at the transmembrane dimerization interface.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Temperature Dependence of Structural Relaxation in Glass-Forming Liquids and Polymers

Understanding the microscopic mechanism of the transition of glass remains one of the most challenging topics in Condensed Matter Physics. What controls the sharp slowing down of molecular motion upon approaching the glass transition temperature T g , whether there is an underlying thermodynamic transition at some finite temperature below T g , what the role of cooperativity and heterogeneity are, and many other questions continue to be topics of active discussions. This review focuses on the mechanisms that control the steepness of the temperature dependence of structural relaxation (fragility) in glass-forming liquids. We present a brief overview of the basic theoretical models and their experimental tests, analyzing their predictions for fragility and emphasizing the successes and failures of the models. Special attention is focused on the connection of fast dynamics on picosecond time scales to the behavior of structural relaxation on much longer time scales. A separate section discusses the specific case of polymeric glass-forming liquids, which usually have extremely high fragility. We emphasize the apparent difference between the glass transitions in polymers and small molecules. We also discuss the possible role of quantum effects in the glass transition of light molecules and highlight the recent discovery of the unusually low fragility of water. At the end, we formulate the major challenges and questions remaining in this field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

Differential optoacoustic absorption detector

A differential optoacoustic absorption detector employed two tapered cells in tandem or in parallel. When operated in tandem, two mirrors were used at one end remote from the source of the beam of light directed into one cell back through the other, and a lens to focus the light beam into the one cell at a principal focus half way between the reflecting mirror. Each cell was tapered to conform to the shape of the beam so that the volume of one was the same as for the other, and the volume of each received maximum illumination. The axes of the cells were placed as close to each other as possible in order to connect a differential pressure detector to the cells with connecting passages of minimum length. An alternative arrangement employed a beam splitter and two lenses to operate the cells in parallel.

Shumate, M. S.↗