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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

On the application of the expected log-likelihood gain to decision making in molecular replacement

Molecular-replacement phasing of macromolecular crystal structures is often fast, but if a molecular-replacement solution is not immediately obtained the crystallographer must judge whether to pursue molecular replacement or to attempt experimental phasing as the quickest path to structure solution. The introduction of the expected log-likelihood gain has given the crystallographer a powerful new tool to aid in making this decision. The eLLG is the log-likelihood gain on intensity expected from a correctly placed model. It is calculated as a sum over the reflections of a function dependent on the fraction of the scattering for which the model accounts, the estimated model coordinate error and the measurement errors in the data. It is shown how the eLLG may be used to answer the question 'can I solve my structure by molecular replacement?'. However, this is only the most obvious of the applications of the eLLG. It is also discussed how the eLLG may be used to determine the search order and minimal data requirements for obtaining a molecular-replacement solution using a given model, and for decision making in fragment-based molecular replacement, single-atom molecular replacement and likelihood-guided model pruning.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

A Vision–based Robust $\mathcal{H}$ ∞ Gain Scheduling Longitudinal and Lateral Following Controller for Autonomous Vehicles on Urban Curved Roads

Implementing advanced driver assistance systems (ADAS) in congested and intricate urban traffic scenarios poses significant challenges. To address the frequent stop–and–go motions exhibited by autonomous vehicles (AVs) navigating urban roads with changes in curvature, we propose a vision–based robust $\mathcal{H}$ ∞ adaptive cruise control system (ACC) for longitudinal control, plus a lane keeping assist system (LKAS) for lateral control. For the vision-based ACC, a weighted probability objective function for the vehicle following behavior is formulated. We incorporate $\mathcal{H}$ ∞ performance and gain scheduling techniques to mitigate the impact of uncertainty in visual sensor measurements. Furthermore, the optimal time headway is scheduled based on the velocity to ensure traffic flow efficiency and safety during the vehicle following process. For the LKAS, we introduce a road curvature estimation method that integrates lane and vehicle dynamics information to obtain the lateral and heading offsets. Next, the design criterion of the observer–based robust gain scheduling lateral motion controller is established by linear matrix inequality (LMI). Here, a series of experiments conducted within a camera–in–loop platform validate the proposed method.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2016

Gain Shift Corrections at Chi-Nu

Ambient conditions have the potential to cause changes in liquid scintillator detector gain that vary with time and temperature. These gain shifts can lead to poor resolution in both energy as well as pulse shape discrimination. In order to correct for these shifts in the Chi-Nu high energy array, a laser system has been developed for calibration of the pulse height signals.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

GAIN FY 2021 Walk-in Work (Summary Report)

Walk-in work (WIW) is defined as work that can benefit the nuclear industry and associated stakeholders. Throughout a fiscal year (FY), WIW projects are identified and evaluated by the Gateway for Accelerated Innovation in Nuclear (GAIN) team. Based on funding availability and industry need, the GAIN team determines whether to fund a WIW project and informs the Department of Energy Office of Nuclear Energy (DOE-NE) of these decisions.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1995

Conversion gain and noise of niobium superconducting hot-electron-mixers

A study has been done of microwave mixing at 20 GHz using the nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the nonlinear phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V-characteristic. Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3 dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for -3 dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.

CONVERSION GAIN↗
NASA NTRS1994

Enhanced Decoding for the Galileo Low-Gain Antenna Mission

Due to a malfunctioning high-gain antenna, the Galileo spacecraft is transmitting all its data through a low-gain antenna, and the data rate will seldom exceed 100 bits per second during its two-year tour of Jupiter's satellites.

decoder Viterbi decoder Reed-Solomon baseline codi↗
NASA NTRS2018

Pressure Gain Combustion 101

This presentation contains notes for a 30 minute lecture that is part of an AIAA Special Session titled, Pressure Gain Combustion Overview: Principles, Operation, and Applications. The presentation covers an introduction to Pressure Gain Combustion (PGC) and the devices used to implement it. The concept of PGC is discussed on a thermodynamic basis, the performance benefits are demonstrated, and methods of implementation are described. These include devices such as Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines.

pressure gain combustion↗
NASA NTRS1997

Air Mass Effects on the Cassini High Gain Antenna

The high gain antenna for the Cassini spacecraft is a lightweight, large surface area structural element, and therefore its dynamic characteristics are noticeably altered by air mass effects...This paper describes the method ultimately used to quantify these effects on the Cassini HGA (High Gain Antenna).

Cassini↗
NASA NTRS2019

On-Orbit Tracking of Sub-Sample Gain Differences in SNPP and NOAA-20 VIIRS Imagery Bands

The VIIRS instruments on board the SNPP and NOAA-20 (N20) satellites have 14 reflective solar bands covering a spectral range from 412 nm to 2250 nm. Three of these are imaging bands (I bands) with a nadir spatial resolution of 375 m and 11 are moderate resolution bands (M bands) with a resolution of 750 m. The higher resolution in the I bands is achieved by a combination of more detectors, with the I bands having twice as many detectors of half the size for every M band detector, and a higher data rate, with the I bands having two sub-samples for every sample of M band data. To ensure calibration accuracy, any systematic difference in the response of the two sub-samples needs to be monitored and corrected in the calibrated products. In this paper, we use the solar diffuser calibrations to monitor the gain differences between the two sub-samples of the I bands both as a function of time and signal level. We find gain differences of about 0.1% for I1, 0.3% for I2, and <0.1% for I3 that are mostly constant over the range of signal values available in the SD calibration. These values are mostly consistent throughout the mission for both instruments. The results are remarkably similar for the two VIIRS instruments, including a slightly out-of-family behavior seen in a few detectors. We discuss possible causes for the difference and the impact on the aggregated Earth view images.

On-orbit↗
DOE OSTI2014

Sensitivity Gains, Linearity, and Spectral Reproducibility in Nonuniformly Sampled Multidimensional MAS NMR Spectra of High Dynamic Range.

Recently, we have demonstrated that considerable inherent sensitivity gains are attained in MAS NMR spectra acquired by nonuniform sampling (NUS) and introduced maximum entropy interpolation (MINT) processing that assures the linearity of transformation between the time and frequency domains. In this report, we examine the utility of the NUS/MINT approach in multidimensional datasets possessing high dynamic range, such as homonuclear 13C–13C correlation spectra. We demonstrate on model compounds and on 1–73-(U-13C,15N)/74–108-(U-15N) E. coli thioredoxin reassembly, that with appropriately constructed 50 % NUS schedules inherent sensitivity gains of 1.7–2.1-fold are readily reached in such datasets. We show that both linearity and line width are retained under these experimental conditions throughout the entire dynamic range of the signals. Furthermore, we demonstrate that the reproducibility of the peak intensities is excellent in the NUS/MINT approach when experiments are repeated multiple times and identical experimental and processing conditions are employed. Finally, we discuss the principles for design and implementation of random exponentially biased NUS sampling schedules for homonuclear 13C–13C MAS correlation experiments that yield high quality artifact-free datasets.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Spectral singularities, threshold gain, and output intensity for a slab laser with mirrors

We explore the consequences of the emergence of linear and nonlinear spectral singularities in TE modes of a homogeneous slab of active optical material that is placed between two mirrors. We use the results together with two basic postulates regarding the behavior of laser light emission to derive explicit expressions for the laser threshold condition and output intensity for these modes of the slab and discuss their physical implications. In particular, we reveal the details of the dependence of the threshold gain and output intensity on the position and properties of the mirrors and on the real part of the refractive index of the gain material.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Dietary mung bean protein reduces high-fat diet-induced weight gain by modulating host bile acid metabolism in a gut microbiota-dependent manner

Highlights: • Mung bean protein intake reduces high fat diet-induced weight gain, fat accumulation, and hepatic steatosis. . • Mung bean protein intake increases plasma GLP-1 and intestinal secondary bile acids. • The anti-obesity effects occur via a mechanism that depends on the gut microbiota. The 8-globulin-rich mung bean protein (MPI) suppresses hepatic lipogenesis in rodent models and reduces fasting plasma glucose and insulin levels in obese adults. However, its effects on mitigating high fat diet (HFD)-induced obesity and the mechanism underlying these effects remain to be elucidated. Herein, we examined the metabolic phenotype, intestinal bile acid (BA) pool, and gut microbiota of conventionally raised (CONV-R) male C57BL/6 mice and germ-free (GF) mice that were randomized to receive either regular HFD or HFD containing mung bean protein isolate (MPI) instead of the dairy protein present in regular HFD. MPI intake significantly reduced HFD-induced weight gain and adipose tissue accumulation, and attenuated hepatic steatosis. Enhancement in the secretion of intestinal glucagon-like peptide-1 (GLP-1) and an enlarged cecal and fecal BA pool of dramatically elevated secondary/primary BA ratio were observed in mice that had consumed MPI. These effects were abolished in GF mice, indicating that the effects were dependent upon the presence of the microbiota. As revealed by 16S rRNA gene sequence analysis, MPI intake also elicited dramatic changes in the gut microbiome, such as an expansion of taxa belonging to the phylum Bacteroidetes along with a reduced abundance of the Firmicutes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Modeling the gain of inner-shell X-ray laser transitions in neon, argon, and copper driven by X-ray free electron laser radiation using photo-ionization and photo-excitation processes

Using an X-ray free electron laser (XFEL) at 960 eV to photo-ionize the 1s electron in neutral neon followed by lasing on the 2p-1s transition in singly-ionized neon, an inner-shell X-ray laser was demonstrated at 849 eV in singly-ionized neon gas several years ago. It took decades to demonstrate this scheme, because it required a very strong X-ray source that could photo-ionize the 1s (K shell) electron in neon on a timescale comparable to the intrinsic Auger lifetime in neon of 2 fs. In this paper, we model the neon inner shell X-ray laser under similar conditions to those used in the XFEL experiments at the SLAC Linac Coherent Light Source (LCLS), and show how we can improve the efficiency of the neon laser and reduce the drive requirements by tuning the XFEL to the 1s-3p transition in neutral neon in order to create gain on the 2p-1s line in neutral neon. We also show how the XFEL could be used to photo-ionize L-shell electrons to drive gain on n = 3–2 transitions in singly-ionized Ar and Cu plasmas. These bright, coherent, and monochromatic X-ray lasers may prove very useful for doing high-resolution spectroscopy and for studying non-linear process in the X-ray regime.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Combination of two Gas Electron Multipliers and a Micromegas as gain elements for a time projection chamber

We measured the properties of a novel combination of two Gas Electron Multipliers with a Micromegas for use as amplification devices in high-rate gaseous time projection chambers. The goal of this design is to minimize the buildup of space charge in the drift volume of such detectors in order to eliminate the standard gating grid and its resultant dead time, while preserving good tracking and particle identification performance. To characterize this micro-pattern gas detector configuration, we measured the positive ion back-flow and energy resolution at various element gains and electric fields, using a variety of gases, and additionally studied crosstalk effects and discharge rates. At a gain of 2000, this configuration achieves an ion back-flow below 0.4% and an energy resolution better than σ / E = 12 % for 55 Fe X-rays.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Studies of uniformity of 50 μ m low-gain avalanche detectors at the Fermilab test beam

In this study, we report measurements of the uniformity of time resolution, signal amplitude, and charged particle detection efficiency across the sensor surface of low-gain avalanche detectors (LGAD). Comparisons of the performance of sensors with different doping concentrations and different active thicknesses are presented, as well as their temperature dependence and radiation tolerance up to 6 x 10 14 n/cm 2 . Results were obtained at the Fermilab test beam facility using 120 GeV proton beams, and a high precision pixel tracking detector. LGAD sensors manufactured by the Centro Nacional de Microelectrónica (CNM) and Hamamatsu Photonics (HPK) were studied. The uniformity of the sensor response in pulse height before irradiation was found to have a 2% spread. The signal detection efficiency and timing resolution in the sensitive areas before irradiation were found to be 100% and 30–40 ps, respectively. A “no-response” area between pads was measured to be about 130 μm for CNM and 170μm for HPK sensors. After a neutron fluence of 6 x 10 14 n/cm 2 the CNM sensor exhibits a large gain variation of up to a factor of 2.5 when comparing metalized and non-metalized sensor areas. An irradiated CNM sensor achieved a time resolution of 30 ps for the metalized area and 40 ps for the non-metalized area, while a HPK sensor irradiated to the same fluence achieved a 30 ps time resolution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Characterization of 4H-SiC Low Gain Avalanche Detectors (LGADs)

4H-SiC Low Gain Avalanche Detectors (LGADs) have been fabricated and characterized. The devices employ a circular mesa design with low-resistivity contacts and an SiO 2 passivation layer. The I–V and C–V characteristics of the 4H-SiC LGADs are compared with complementary 4H-SiC PiN diodes to confirm a high breakdown voltage and low leakage current. Both LGADs and PiN diodes were irradiated with alpha particles from a $^{210}_{84}$Po source. The charge collected by each device was compared, and it was observed that low-gain charge carrier multiplication is achieved in the 4H-SiC LGAD.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Methodology to predict annual yield losses and gains caused by solar module design and materials under field exposure

Solar cells and modules are usually optimized separately under standard test conditions (STC). However, the actual performance under field exposure depends on module design, installation and environmental conditions. This work therefore presents a methodology to predict the annual yield of crystalline silicon solar modules for varying module configurations and environments using a time step simulation approach. We define and quantify 12 effects that affect the annual module performance, starting with solar cells in air under STC to a complete module under realistic conditions. We consider the interaction of optical, thermal and electrical effects in the module and combine it with an angular, spectral and time resolved light source. The model enables understanding the impact of the module environment, such as regions with high wind speeds or high diffuse light, on the annual output of a particular module type. We validate our model with measured power and temperature data for crystalline silicon heterojunction solar cell modules and find an agreement of the annual yield within 0.7%. We quantify the annual gains and losses for this module and identify that major losses are caused by elevated operating temperatures (2.3%) and reflection losses at the front glass (2.6%). Critically, the coupling gains at the cell surface increase significantly by 1.5% when considering angular light irradiance compared to normal incidence. To conclude, we apply our Cell-to-Module-Yield method to a 72-cell mono-crystalline PERC module, where the main annual yield losses are caused by reflection at the front glass and ohmic losses in the connector ribbons.

14 SOLAR ENERGY↗