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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Parametric and sensitivity analysis of a PCM-integrated wall for optimal thermal load modulation in lightweight buildings

Load modulation in buildings is becoming increasingly important due to growing disparity in energy demand during peak and off-peak hours. Integrating phase change material (PCM) in building envelopes and using a controlled precooling strategy can provide substantial thermal load modulation; however, it may greatly increase the total energy use. Previous studies have employed PCM in building envelopes primarily for energy savings and, to some extent, peak load shedding and shifting. However, the load modulation capacity of a PCM-integrated envelope has not been well explored in the literature. In this study, we perform an extensive parametric and sensitivity analysis on PCM-integrated lightweight building walls and examine the combinatory effects of various PCM parameters on thermal load modulation and wall-related heat gains in buildings. Using numerical simulations, we investigate eight PCM parameters: PCM location in the wall, transition temperature, thickness, latent heat, transition range, density, specific heat, and thermal conductivity. Here, we evaluate their impact and relative importance to achieve maximum load modulation in buildings without compromising occupants’ thermal comfort or total energy use. The results show that the optimized PCM proposed in this study can completely invert the transient heat gain profile of the wall, providing up to 70% reduction of wall-related heat gain during peak hours without a major increase in the cumulative heat gain.

42 ENGINEERING↗
DOE OSTI2023

Multi-module-based CVAE to predict HVCM faults in the SNS accelerator

We present a multi-module framework based on Conditional Variational Autoencoder (CVAE) to detect anomalies in the power signals coming from multiple High Voltage Converter Modulators (HVCMs). We condition the model with the specific modulator type to capture different representations of the $\mathcal{normal}$ waveforms and to improve the sensitivity of the model to identify a specific type of fault when we have limited samples for a given module type. We studied several Artificial Neural Network (ANN) architectures for our CVAE model and evaluated the model performance by looking at their loss landscape for stability and generalization. Our results for the Spallation Neutron Source (SNS) experimental data show that the trained model generalizes well to detecting multiple fault types for several HVCM module types. The results of this study can be used to improve the HVCM reliability and overall SNS uptime.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Scalable semitransparent prototype organic photovoltaic module with minimal resistance loss

Semi-transparent organic photovoltaic (ST-OPV) cells are regarded as an attractive solution to building-integrated solar energy harvesting. Both the power conversion efficiency (PCE) and average photopic transmission (APT) of ST-OPVs have shown substantial increases in recent years. However, less attention has been paid to the area scaling of ST-OPV cells. In this work, we investigate the scalability of ST-OPV cells from 4 mm 2 to 1 cm 2 , as well as 9 cm 2 active area prototype module. By integrating both top and bottom metal grids onto the transparent electrodes, the series resistance loss of 1 cm 2 ST-OPV cell is significantly reduced, and is comparable to that of the grid-free 4 mm 2 cell. Nine 1 cm 2 cells are then connected in a series-parallel circuit to realize a prototype ST-OPV module. A 100% fabrication yield with only 5% PCE deviation among discrete cells is achieved. The semitransparent module shows PCE = 7.2 ± 0.1% under simulated AM 1.5G illumination at 1 sun intensity, which exhibits no connection resistance loss compared to that of the individual cells. The ST-OPV module exhibits an APT = 38.1 ± 1.1%, which enables a light utilization efficiency, LUE = 2.74 ± 0.09%. Here, the method demonstrates a promising way for ST-OPV modules to scale without compromising performance.

14 SOLAR ENERGY↗
DOE OSTI2022

Development of a plug-and-play anti-noise module for fault diagnosis of rotating machines in nuclear power plants

The health of rotating machines is crucial to the stable operation and safety of nuclear power plants. However, research on machine learning-based fault diagnosis of rotating machines in the nuclear industry is still in its infancy. The signal noise generated in the plant may negatively affect the effectiveness of the analysis. In this paper, a plug-and-play anti-noise machine learning module is proposed to fill the knowledge and capability gap. The modules are loaded into a convolutional neural network called deep residual network (ResNet) to obtain a new model with noise reduction capability. The basic idea is that the module is able to identify noise features and include them in the subsequent analysis, effectively filtering noise at the feature level of the network. Nine variants of the new model are compared with the original ResNet as well as four classical machine learning models to test the effectiveness of the module and to examine the impact of the module's loading modes on the performance of the new model. Finally, this research helps facilitate the application of machine learning in the plant noise environment.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Printed interconnects for photovoltaic modules

Film-based photovoltaic modules employ monolithic interconnects to minimize resistance loss and enhance module voltage via series connection. Conventional interconnect construction occurs sequentially, with a scribing step following deposition of the bottom electrode, a second scribe after deposition of absorber and intermediate layers, and a third following deposition of the top electrode. This method produces interconnect widths of about 300 µm, and the area comprised by interconnects within a module (generally about 3%) does not contribute to power generation. The present work reports on an increasingly popular strategy capable of reducing the interconnect width to less than 100 µm: printing interconnects. Cost modeling projects a savings of about $0.02/watt for CdTe module production through the use of printed interconnects, with savings coming from both reduced capital expense and increased module power output. Printed interconnect demonstrations with copper-indium-gallium-diselenide and cadmium-telluride solar cells show successful voltage addition and miniaturization down to 250 µm. As a result, material selection guidelines and considerations for commercialization are discussed.

14 SOLAR ENERGY↗
DOE OSTI2018

Comparison of Photovoltaic Module Luminescence Imaging Techniques: Assessing the Influence of Lateral Currents in High-Efficiency Device Structures

We investigate the implications of using partial or patterned illumination for luminescence imaging of photovoltaic modules. Partial illumination induces local photovoltage variations that drive lateral current flow into non-illuminated cell regions, causing the average injection level to vary over the course of luminescence measurement. The extent of lateral current depends on material properties and is especially significant for high-efficiency devices such as the silicon heterojunction with intrinsic thin layer (HIT) modules that we investigate. We compare four module imaging methods including large-area illumination, scanning-laser illumination, contactless electroluminescence, and pattern-illuminated photoluminescence. By evaluating the statistical correlation among the different methods under varying laser fluences, we conclude that most methods converge to similar results at matched photon dose per cell (not laser power density) for the modules that we study, while pattern-illuminated photoluminescence yields distinct images from the other techniques regardless of the illumination power. Our combined analysis using multiple luminescence imaging techniques gives specific insight into the causes of HIT module degradation, including suspected degradation of the transparent conductive oxide and passivation layer.

14 SOLAR ENERGY↗
DOE OSTI2021

Computational design and analysis of modular cells for large libraries of exchangeable product synthesis modules

Microbial metabolism can be harnessed to produce a large library of useful chemicals from renewable resources such as plant biomass. However, it is laborious and expensive to create microbial biocatalysts to produce each new product. To tackle this challenge, we have recently developed modular cell (ModCell) design principles that enable rapid generation of production strains by assembling a modular (chassis) cell with exchangeable production modules to achieve overproduction of target molecules. Previous computational ModCell design methods are limited to analyze small libraries of around 20 products. In this study, we developed a new computational method, named ModCell-HPC, that can design modular cells for large libraries with hundreds of products with a highly-parallel and multi-objective evolutionary algorithm and enable us to elucidate modular design properties. We demonstrated ModCell-HPC to design Escherichia coli modular cells towards a library of 161 endogenous production modules. From these simulations, we identified E. coli modular cells with few genetic manipulations that can produce dozens of molecules in a growth-coupled manner with different types of fermentable sugars. These designs revealed key genetic manipulations at the chassis and module levels to accomplish versatile modular cells, involving not only in the removal of major by-products but also modification of branch points in the central metabolism. We further found that the effect of various sugar degradation on redox metabolism results in lower compatibility between a modular cell and production modules for growth on pentoses than hexoses. To better characterize the degree of compatibility, we developed a method to calculate the minimal set cover, identifying that only three modular cells are all needed to couple with up 85 compatible production modules. By determining the unknown compatibility contribution metric, we further elucidated the design features that allow an existing modular cell to be re-purposed towards production of new molecules. Altogether, ModCell-HPC is a useful tool for understanding modularity of biological systems and guiding more efficient and generalizable design of modular cells that help reduce research and development cost in biocatalysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Spectrally Selective Mirrors with Combined Optical and Thermal Benefit for Photovoltaic Module Thermal Management

Waste heat generated during daytime operation of a solar module will raise its temperature and reduce cell efficiency. In addition to thermalization and carrier recombination, one major source of excess heat in modules is the parasitic absorption of light with sub-bandgap energy. Parasitic absorption can be prevented if sub-bandgap radiation is reflected away from the module. We report on the design considerations and projected changes to module energy yield for photonic reflectors capable of reflecting a portion of sub-bandgap radiation while maintaining or improving transmission of light with energy greater than the semiconductor bandgap. Using a previously developed, self-consistent opto-electro-thermal finite-element simulation, we calculate the total additional energy generated by a module, including various photonic reflectors, and decompose these benefits into thermal and optical effects. We show that the greatest total energy yield improvement comes from photonic mirrors designed for the outside of the glass, but that mirrors placed between the glass and the encapsulant can have significant thermal benefit. We then show that optimal photonic mirror design requires consideration of all angles of incidence, despite unequal amounts of radiation arriving at each angle. We find that optimized photonic mirrors will be omnidirectional in the sense that they have beneficial performance, regardless of the angle of incidence of radiation. By fulfilling these criteria, photonic mirrors can be used at different geographic locations or different tilt angles than their original optimization conditions with only marginal changes in performance. We show designs that improve energy output in Golden, Colorado by 3.7% over a full year. This work demonstrates the importance of considering real-world irradiance and weather conditions when designing optical structures for solar applications.

14 SOLAR ENERGY↗
DOE OSTI2011

Modulating the Neutron Flux from a Mirror Neutron Source

A 14-MeV neutron source based on a Gas-Dynamic Trap will provide a high flux of 14 MeV neutrons for fusion materials and sub-component testing. In addition to its main goal, the source has potential applications in condensed matter physics and biophysics. In this report, the author considers adding one more capability to the GDT-based neutron source, the modulation of the neutron flux with a desired frequency. The modulation may be an enabling tool for the assessment of the role of non-steady-state effects in fusion devices as well as for high-precision, low-signal basic science experiments favoring the use of the synchronous detection technique. A conclusion is drawn that modulation frequency of up to 1 kHz and modulation amplitude of a few percent is achievable. Limitations on the amplitude of modulations at higher frequencies are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Femtosecond measurements of near-infrared pulse induced mid-infrared transmission modulation of quantum cascade lasers

We temporally resolved the ultrafast mid-infrared transmission modulation of quantum cascade lasers (QCLs) using a near-infrared pump/mid-infrared probe technique at room temperature. Two different femtosecond wavelength pumps were used with photon energy above and below the quantum well (QW) bandgap. The shorter wavelength pump modulates the mid-infrared probe transmission through interband transition assisted mechanisms, resulting in a high transmission modulation depth and several nanoseconds recovery lifetime. In contrast, pumping with a photon energy below the QW bandgap induces a smaller transmission modulation depth but much faster (several picoseconds) recovery lifetime, attributed to intersubband transition assisted mechanisms. The latter ultrafast modulation (>60 GHz) could provide a potential way to realize fast QCL based free space optical communication.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Phase control and fast start-up of a magnetron using modulation of an addressable faceted cathode

The use of an addressable, faceted cathode has been proposed as a method of modulating current injection in a magnetron to improve performance and control phase. To implement the controllable electron emission, five-sided and ten-sided faceted planar cathodes employing gated field emitters are considered as these emitters could be fabricated on flat substrates. For demonstration, the conformal finite-difference time-domain particle-in-cell simulation, as implemented in VORPAL, has been used to model a ten-cavity, rising sun magnetron using the modulated current sources and benchmarked against a typical continuous current source. For the modulated, ten-sided faceted cathode case, the electrons are injected from three emitter elements on each of the ten facets. Each emitter is turned ON and OFF in sequence at the oscillating frequency with five emitters ON at one time to drive the five electron spokes of the π-mode. The emitter duty cycle is then 1/6th the Radio-Frequency (RF) period. Simulations show a fast start-up time as low as 35 ns for the modulated case compared to 100 ns for the continuous current cases. Analysis of the RF phase using the electron spoke locations and the RF magnetic field components shows that the phase is controlled for the modulated case while it is random, as typical, for the continuous current case. Active phase control during oscillation was demonstrated by shifting the phase of the electron injection 180° after oscillations started. The 180° phase shift time was approximately 25 RF cycles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Strain-modulation of spin-dependent transport in graphene

We investigate strain modulation of the spin-dependent electron transport in a graphene junction using the transfer matrix method. As an analogy to optics, we define the modulation depth in the electron optics domain. Additionally, we discuss the transport properties and show that the modulation depth and the conductance depend on the spin-orbit coupling strength, the strain magnitude, the width of the strained area, and the energy of the incident electron. The conductances of the spin-down and spin-up electrons have opposite and symmetrical variations, which results in the analogous features of their modulation depths. The maximum conditions for both the modulation depth and the electron spin upset rate are also analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Modulation-mediated unlocking of a parametrically phase-locked spin torque oscillator

Modulation of an oscillator is crucial for its application in communication devices. While the output power and linewidth of single magnetic tunnel junction-based spin-torque oscillators (MTJ-STO) are not yet adequate for practical uses, the synchronization of such devices can overcome these limitations. Here, we investigate the modulation behavior of a parametrically synchronized MTJ-STO and show experimentally that modulation of the synchronized state preserves synchronization as long as the modulation frequency, f{sub mod}, is above a characteristic frequency, f{sub unlock}. The unlocking frequency increases with the modulation amplitude in agreement with analytical estimates and numerical simulations. These phenomena are described as a non-resonant unlocking mechanism, whose characteristics are directly related to inherent parameters of the oscillator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Control of the repetition rate and reduction of the jitter of the pulses of passively Q-switched solid-state miniature lasers using periodic diode-pump modulation

Based on an extended point laser model, the lasing of passively Q-switched Nd : YAG minilasers has been numerically analysed. We have shown that periodically modulated diode pump may be used to control the pulse repetition rate and substantially reduce the timing pulse jitter. When the pump is modulated with rectangular pulses, switching from a high pump level to a low one upon generation of a successive laser pulse improves the stability of the pulse repetition rate relative to variations of the average pump level and broadens the range of repetition frequencies whereby they may be locked to the pulse modulation frequency. The feasibility of lowering the timing jitter and locking the pulse repetition frequency to the pump modulation frequency has been confirmed experimentally. For repetition rates {approx}1 kHz, the relative standard deviation of the pulse-repetition period is reduced from several percent for a continuous pumping to 0.06 % by applying ''truncation'' of modulation pulses. The experimental results agree well with simulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Parametric excitation of relaxation oscillations at the subharmonic of the external modulating signal in a ring Nd : YAG laser

The dynamics of solid-state ring laser (SSRL) radiation with periodic pump modulation is studied experimentally and simulated numerically in the case of parametric excitation of relaxation oscillations at the subharmonic of a modulating signal. Parametric processes are investigated by modulating the pump in two regimes of the SSRL operation: steady-state regime of unidirectional lasing and self-modulation regime of the first kind. Significant differences in the dynamics of radiation for these regimes are found. It is established that when the laser operates in the self-modulation regime, a first-order parametric instability can result in the appearance of the dynamic chaos regime. (control of laser radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

STATE-DEPENDENT ORBITAL MODULATION OF X-RAYS IN CYG X-3

We analyze all of the available RXTE observations of Cyg X-3 in order to investigate the connection between the central X-ray source and its surrounding environment. The hardness-intensity diagram of Cyg X-3 displays a 'shoe' shape rather than the Q-type shape commonly seen in other black hole X-ray binary, and exhibits no apparent hysteresis effect. During the {gamma}-ray outbursts, no existing data are located in the hard and intermediate states, which suggest the absence of a significant population of non-thermal electrons when the source is in these states. For the first time, we present the orbital modulation of the X-ray light curve (LC) of all five states. The different energy band LCs are in phase with each other in all five states, and the modulation amplitude of both soft and hard X-ray LCs monotonously increases with decreasing hardness from hard to soft non-thermal states. We confirm that the modulation depth decreases with increasing energy in the hard, intermediate, and very high states, as originally reported by Zdziarski et al. However, in the soft non-thermal state, the hard X-ray modulation strength significantly increases and is even larger than the soft X-ray one. Our results rule out both wind absorption and jet origins of the hard X-ray LC modulation in the soft non-thermal state, and challenge our understanding of the states of Cyg X-3.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SCIENTIFIC VERIFICATION OF FARADAY ROTATION MODULATORS: DETECTION OF DIFFUSE POLARIZED GALACTIC EMISSION

The design and performance of a wide bandwidth linear polarization modulator based on the Faraday effect is described. Faraday Rotation Modulators (FRMs) are solid-state polarization switches that are capable of modulation up to 10 kHz. Six FRMs were utilized during the 2006 observing season in the Background Imaging of Cosmic Extragalactic Polarization (BICEP) experiment; three FRMs were used at each of BICEP's 100 and 150 GHz frequency bands. The technology was verified through high signal-to-noise detection of Galactic polarization using two of the six FRMs during four observing runs in 2006. The features exhibit strong agreement with BICEP's measurements of the Galaxy using non-FRM pixels and with the Galactic polarization models. This marks the first detection of high signal-to-noise mm-wave celestial polarization using fast, active optical modulation. The performance of the FRMs during periods when they were not modulated was also analyzed and compared to results from BICEP's 43 pixels without FRMs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

SOLAR ENERGETIC PARTICLE MODULATIONS ASSOCIATED WITH COHERENT MAGNETIC STRUCTURES

In situ observations of solar energetic particles (SEPs) often show rapid variations of their intensity profile, affecting all energies simultaneously, without time dispersion. A previously proposed interpretation suggests that these modulations are directly related to the presence of magnetic structures with a different magnetic topology. However, no compelling evidence of local changes in magnetic field or in plasma parameters during SEP modulations has been reported. In this paper, we performed a detailed analysis of SEP events and we found several signatures in the local magnetic field and/or plasma parameters associated with SEP modulations. The study of magnetic helicity allowed us to identify magnetic boundaries, associated with variations of plasma parameters, which are thought to represent the borders between adjacent magnetic flux tubes. It is found that SEP dispersionless modulations are generally associated with such magnetic boundaries. Consequently, we support the idea that SEP modulations are observed when the spacecraft passes through magnetic flux tubes, filled or devoid of SEPs, which are alternatively connected and not connected with the flare site. In other cases, we found SEP dropouts associated with large-scale magnetic holes. A possible generation mechanism suggests that these holes are formed in the high solar corona as a consequence of magnetic reconnection. This reconnection process modifies the magnetic field topology, and therefore, these holes can be magnetically isolated from the surrounding plasma and could also explain their association with SEP dropouts.

79 ASTRONOMY AND ASTROPHYSICS↗