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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

The Hamiltonian formalism for scalar fields coupled to gravity in a cosmological background

A novel routine to investigate the scalar fields in a cosmological context is discussed in the framework of the Hamiltonian formalism. Starting from the Einstein–Hilbert action coupled to a Lagrangian density that contains two components–one corresponding to a scalar field Lagrangian, L{sub ϕ}, and another that depends on the scale parameter, L{sub a}–one can identify a generalized Hamiltonian density from which first-order dynamical equations can be obtained. This set up corresponds to the dynamics of Friedmann–Robertson–Walker models in the presence of homogeneous fields embedded into a generalized cosmological background fluid in a system that evolves all together isentropically. Once the generalized Hamiltonian density is properly defined, the constraints on the gravity–matter–field system are straightforwardly obtained through the first-order Hamilton equations. The procedure is illustrated for three examples of cosmological interest for studies of the dark sector: real scalar fields, tachyonic fields and generalized Born–Infeld tachyonic fields. The inclusion of some isentropic fluid component into the Friedmann equation allows for identifying an exact correspondence between the dark sector underlying scalar field and an ordinary real scalar field dynamics. As a final issue, the Hamiltonian formulation is used to set the first-order dynamical equations through which one obtains the exact analytical description of the cosmological evolution of a generalized Chaplygin gas (GCG) with dustlike matter, radiation or curvature contributions. Model stability in terms of the square of the sound velocity, c{sub s}{sup 2}, cosmic acceleration, q, and conditions for inflation are discussed. -- Highlights: •The Hamiltonian formalism for scalar fields coupled to gravity in a cosmological background is constructed. •Real scalar, tachyonic and generalized Born–Infeld tachyonic-type fields are considered. •An extended formulation of the Hamilton–Jacobi description of the dark sector dynamics driven by scalar fields is obtained.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Monte Carlo simulations for understanding the transport properties of metallic nanowires

We report the conductance calculation of metallic nanowires of different metals under the application of a tensile force. The elongation induced by the tensile force was simulated by means of the canonical Monte Carlo method combined with the embedded atom method to compute the energy of the system. We studied nanowires composed of Ag, Au, Pt and Cu. The conductance was calculated by means of the Landauer formula and the non-equilibrium Green function formalism. As previously verified experimentally and using other simulation techniques, the conductance is quantized. In addition to this, we have found that there is a strong correlation between the magnitude of the conductance and the width of the nanowire at its thinnest point. Conductance histograms were analyzed for all the different metals.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Predictive simulation of non-steady-state transport of gases through rubbery polymer membranes

In this paper, a multiscale, physically-based, reaction-diffusion kinetics model is developed for non-steady-state transport of simple gases through a rubbery polymer. Experimental data from the literature, new measurements of non-steady-state permeation and a molecular dynamics simulation of a gas-polymer sticking probability for a typical system are used to construct and validate the model framework. Using no adjustable parameters, the model successfully reproduces time-dependent experimental data for two distinct systems: (1) O 2 quenching of a phosphorescent dye embedded in poly(n-butyl(amino) thionylphosphazene), and (2) O 2 , N 2 , CH 4 and CO 2 transport through poly(dimethyl siloxane). The calculations show that in the pre-steady-state regime, permeation is only correctly described if the sorbed gas concentration in the polymer is dynamically determined by the rise in pressure. Finally, the framework is used to predict selectivity targets for two applications involving rubbery membranes: CO 2 capture from air and blocking of methane cross-over in an aged solar fuels device.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Energy benchmarks for water clusters and ice structures from an embedded many-body expansion

In this paper, we show how an embedded many-body expansion (EMBE) can be used to calculate accurate ab initio energies of water clusters and ice structures using wavefunction-based methods. We use the EMBE described recently by Bygrave et al. [J. Chem. Phys. 137, 164102 (2012)], in which the terms in the expansion are obtained from calculations on monomers, dimers, etc., acted on by an approximate representation of the embedding field due to all other molecules in the system, this field being a sum of Coulomb and exchange-repulsion fields. Our strategy is to separate the total energy of the system into Hartree-Fock and correlation parts, using the EMBE only for the correlation energy, with the Hartree-Fock energy calculated using standard molecular quantum chemistry for clusters and plane-wave methods for crystals. Our tests on a range of different water clusters up to the 16-mer show that for the second-order Møller-Plesset (MP2) method the EMBE truncated at 2-body level reproduces to better than 0.1 mE h /monomer the correlation energy from standard methods. The use of EMBE for computing coupled-cluster energies of clusters is also discussed. For the ice structures Ih, II, and VIII, we find that MP2 energies near the complete basis-set limit reproduce very well the experimental values of the absolute and relative binding energies, but that the use of coupled-cluster methods for many-body correlation (non-additive dispersion) is essential for a full description. Possible future applications of the EMBE approach are suggested.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Potential of mean force analysis of the self-association of leucine-rich transmembrane α-helices: Difference between atomistic and coarse-grained simulations

Interaction of transmembrane (TM) proteins is important in many biological processes. Large-scale computational studies using coarse-grained (CG) simulations are becoming popular. However, most CG model parameters have not fully been calibrated with respect to lateral interactions of TM peptide segments. Here, we compare the potential of mean forces (PMFs) of dimerization of TM helices obtained using a MARTINI CG model and an atomistic (AT) Berger lipids-OPLS/AA model (AT{sup OPLS}). For helical, tryptophan-flanked, leucine-rich peptides (WL15 and WALP15) embedded in a parallel configuration in an octane slab, the AT{sup OPLS} PMF profiles showed a shallow minimum (with a depth of approximately 3 kJ/mol; i.e., a weak tendency to dimerize). A similar analysis using the CHARMM36 all-atom model (AT{sup CHARMM}) showed comparable results. In contrast, the CG analysis generally showed steep PMF curves with depths of approximately 16–22 kJ/mol, suggesting a stronger tendency to dimerize compared to the AT model. This CG > AT discrepancy in the propensity for dimerization was also seen for dilauroylphosphatidylcholine (DLPC)-embedded peptides. For a WL15 (and WALP15)/DLPC bilayer system, AT{sup OPLS} PMF showed a repulsive mean force for a wide range of interhelical distances, in contrast to the attractive forces observed in the octane system. The change from the octane slab to the DLPC bilayer also mitigated the dimerization propensity in the CG system. The dimerization energies of CG (AALALAA){sub 3} peptides in DLPC and dioleoylphosphatidylcholine bilayers were in good agreement with previous experimental data. The lipid headgroup, but not the length of the lipid tails, was a key causative factor contributing to the differences between octane and DLPC. Furthermore, the CG model, but not the AT model, showed high sensitivity to changes in amino acid residues located near the lipid-water interface and hydrophobic mismatch between the peptides and membrane. These findings may help interpret CG and AT simulation results on membrane proteins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Fully tuneable, Purcell-enhanced solid-state quantum emitters

We report the full energy control over a semiconductor cavity-emitter system, consisting of single Stark-tunable quantum dots embedded in mechanically reconfigurable photonic crystal membranes. A reversible wavelength tuning of the emitter over 7.5 nm as well as an 8.5 nm mode shift are realized on the same device. Harnessing these two electrical tuning mechanisms, a single exciton transition is brought on resonance with the cavity mode at several wavelengths, demonstrating a ten-fold enhancement of its spontaneous emission. These results open the way to bring several cavity-enhanced emitters mutually into resonance and therefore represent a key step towards scalable quantum photonic circuits featuring multiple sources of indistinguishable single photons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Tune-out wavelengths for helium atom in plasma environments

We investigate the effect of plasma screening on the tune-out wavelengths for helium atom using correlated exponential wave function within the framework of Debye shielding approach. The pseudostate summation technique has been used to calculate the dynamic dipole polarizability for the states (2 {sup 1}S, 3 {sup 1}S, 2 {sup 3}S, 3 {sup 3}S) of helium embedded in plasma environments. In a free-atomic system, our calculated results are in agreement with available theoretical and experimental predictions. The tune-out wavelengths show interesting behavior as functions of screening parameter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

SIZE BIAS AND DIFFERENTIAL LENSING OF STRONGLY LENSED, DUSTY GALAXIES IDENTIFIED IN WIDE-FIELD SURVEYS

We address two selection effects that operate on samples of gravitationally lensed dusty galaxies identified in millimeter- and submillimeter-wavelength surveys. First, we point out the existence of a ''size bias'' in such samples: due to finite source effects, sources with higher observed fluxes are increasingly biased toward more compact objects. Second, we examine the effect of differential lensing in individual lens systems by modeling each source as a compact core embedded in an extended diffuse halo. Considering the ratio of magnifications in these two components, we find that at high overall magnifications, the compact component is amplified by a much larger factor than the diffuse component, but at intermediate magnifications ({approx}10) the probability of a larger magnification for the extended region is higher. Lens models determined from multi-frequency resolved imaging data are crucial to correct for this effect.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

AGES OF STAR CLUSTERS IN THE TIDAL TAILS OF MERGING GALAXIES

We study the stellar content in the tidal tails of three nearby merging galaxies, NGC 520, NGC 2623, and NGC 3256, using BVI imaging taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. The tidal tails in all three systems contain compact and fairly massive young star clusters, embedded in a sea of diffuse, unresolved stellar light. We compare the measured colors and luminosities with predictions from population synthesis models to estimate cluster ages and find that clusters began forming in tidal tails during or shortly after the formation of the tails themselves. We find a lack of very young clusters (≤10 Myr old), implying that eventually star formation shuts off in the tails as the gas is used up or dispersed. There are a few clusters in each tail with estimated ages that are older than the modeled tails themselves, suggesting that these may have been stripped out from the original galaxy disks. The luminosity function of the tail clusters can be described by a single power-law, dN/dL ∝ L{sup α}, with −2.6 < α < −2.0. We find a stellar age gradient across some of the tidal tails, which we interpret as a superposition of (1) newly formed stars and clusters along the dense center of the tail and (2) a sea of broadly distributed, older stellar material ejected from the progenitor galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Embedded EPICS server for PowerPMAC motion controllers

An embedded server layer of Experimental Physics and Industrial Control System (EPICS) for PowerPMAC motion controllers has been developed and deployed at two undulator beamlines of the National Institute of General Medical Sciences and the National Cancer Institute (GM/CA) Structural Biology Facility at the Advanced Photon Source (APS). This compact, open source solution makes the power and versatility of PowerPMAC motion controls directly accessible to distributed EPICS clients. At GM/CA the system controls about 200 servo and stepper motors — both encoded and unencoded — and multiple digital and analog I/O accessories. The server stack comprises two sublayers: a lower-level driver and database that communicates directly with PowerPMAC, and a facility-specific soft sublayer built on top. The paper describes installing EPICS on PowerPMAC, the implementation of both layers and client examples, including on-the-fly scanning.

EPICS↗
DOE OSTI2013

Influence of resonant charge exchange on the viscosity of partially ionized plasma in a magnetic field

The influence of resonant charge exchange for ion-atom interaction on the viscosity of partially ionized plasma embedded in the magnetic field is investigated. The general system of equations used to derive the viscosity coefficients for an arbitrary plasma component in the 21-moment approximation of Grad’s method is presented. The expressions for the coefficients of total and partial viscosities of a multicomponent partially ionized plasma in the magnetic field are obtained. As an example, the coefficients of the parallel and transverse viscosities for the ionic and neutral components of the partially ionized hydrogen plasma are calculated. It is shown that the account for resonant charge exchange can lead to a substantial change of the parallel and transverse viscosity of the plasma components in the region of low degrees of ionization on the order of 0.1.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Reducing AI RAG Hallucination by Optimizing Routing Techniques

Large Language Models (LLMs), such as ChatGPT, tend to “hallucinate”, meaning they confidently generate false information. Retrieval Augmented Generation (RAG) attempts to diminish hallucination by providing context to the LLM from data stores (indexes) containing relevant information. The LLM uses this context to formulate its response. RAG systems can still suffer from hallucination because of bad embeddings or ineffective routing. For example, a router will often return context from an irrelevant index, resulting in a hallucinated answer. In this study, we aim to minimize the frequency of routing hallucinations by optimizing Index Summary Routing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Oxide Semiconductor Sensors for Monitoring Advanced Energy Conversion and Manufacturing Processes at High Temperature

To optimize the operation and functionality of high temperature systems such as slagging gasifiers, coal boilers and glass/steel smelters, it is important to monitor temperature, corrosion and erosion of the refractory used in such systems. Both thermocouple and failure sensors (and arrays of these) would be useful to monitor the health of any refractory or coatings in these systems. Many of such type of sensors are installed into the systems through open access ports within the refractory; however, there are some disadvantages of this approach where corrosive/erosive gas and molten materials can penetrate and compromise the system. The current work presents the development and performance of refractory with embedded high temperature sensors such as thermocouples, thermistors, and various spallation/crack monitoring sensors, which may be used within a variety of refractory brick in different high temperature processes and applications. The objective of our work is to develop high-temperature sensors composed of electroceramic materials that are chemically stable at high temperatures (750°-1500°C) and high pressures (up to 1000 psi) that can be used in monitoring temperature, corrosion and erosion process in refractory used in high energy systems. The high-temperature sensors investigated in this work were composed of various oxide composites directly embedded into the refractory oxides. The composites used for this work were synthesized by a mixed-oxide route. Metal oxides were inserted within a matrix material composed of refractory oxides (Al2O3, ZrO2, etc.). The physical and electrical properties were specifically manipulated by altering the level of percolation of the conductive species (metal oxides) within the refractory constituent (refractory oxide). An example of one of these embedded sensors consisted of an electroceramic-based thermocouple fabricated with two separate oxide composite compositions which were patterned to produce a couple within the interior of a refractory matrix. The thermocouple successfully displayed thermoelectric voltage trend (as a function of temperature), and the voltage was 220.0 mV near 1400 °C. In addition, corrosion tests on the refractory embedded sensors were performed. To evaluate corrosion in the refractory was exposed to high-temperature glass compositions over a 90 h period. The penetration of the glass through the refractory could be monitored by both an amperometric and voltametric based sensor. With this experiment, it was demonstrated that the embedded sensor could dynamically monitor the corrosion process, and thus, provide real-time feedback on both temperature and the refractory health.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2013

Ultrasonic wave-based structural health monitoring embedded instrument

Piezoelectric sensors and actuators are the bridge between electronic and mechanical systems in structures. This type of sensor is a key element in the integrity monitoring of aeronautic structures, bridges, pressure vessels, wind turbine blades, and gas pipelines. In this paper, an all-in-one system for Structural Health Monitoring (SHM) based on ultrasonic waves is presented, called Phased Array Monitoring for Enhanced Life Assessment. This integrated instrument is able to generate excitation signals that are sent through piezoelectric actuators, acquire the received signals in the piezoelectric sensors, and carry out signal processing to check the health of structures. To accomplish this task, the instrument uses a piezoelectric phased-array transducer that performs the actuation and sensing of the signals. The flexibility and strength of the instrument allow the user to develop and implement a substantial part of the SHM technique using Lamb waves. The entire system is controlled using configuration software and has been validated through functional, electrical loading, mechanical loading, and thermal loading resistance tests.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

A High-Performance Embedded Hybrid Methodology for Uncertainty Quantification With Applications

Multiphysics processes modeled by a system of unsteady differential equations are naturally suited for partitioned (modular) solution strategies. We consider such a model where probabilistic uncertainties are present in each module of the system and represented as a set of random input parameters. A straightforward approach in quantifying uncertainties in the predicted solution would be to sample all the input parameters into a single set, and treat the full system as a black-box. Although this method is easily parallelizable and requires minimal modifications to deterministic solver, it is blind to the modular structure of the underlying multiphysical model. On the other hand, using spectral representations polynomial chaos expansions (PCE) can provide richer structural information regarding the dynamics of these uncertainties as they propagate from the inputs to the predicted output, but can be prohibitively expensive to implement in the high-dimensional global space of uncertain parameters. Therefore, we investigated hybrid methodologies wherein each module has the flexibility of using sampling or PCE based methods of capturing local uncertainties while maintaining accuracy in the global uncertainty analysis. For the latter case, we use a conditional PCE model which mitigates the curse of dimension associated with intrusive Galerkin or semi-intrusive Pseudospectral methods. After formalizing the theoretical framework, we demonstrate our proposed method using a numerical viscous flow simulation and benchmark the performance against a solely Monte-Carlo method and solely spectral method.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

CYDRES: CYber Defense and REsilient System for securing grid-interactive efficient buildings

Smart buildings, especially Grid-interactive Efficient Buildings (GEBs), suffer from cyber-attacks and physical faults due to the integration of a large number of sensors and controls, connected devices, and associated communication networks. This study demonstrated a real-time advanced building resilient platform, called CYber Defense and REsilient System (CYDRES), which is deployable for existing and emerging Building Automation Systems (BASs). CYDRES aims to empower GEBs with cyber-attack-immune capabilities through multi-layer prevention and adaptation mechanisms to monitor, detect, and respond to cyber-attacks and physical operational faults. CYDRES is demonstrated through real-time experiments in a Hardware-in-the-Loop (HIL) testbed.

Building automation system, Cyber-attacks, Physica↗
DOE OSTI2021

Reduced-order modeling of advection-dominated systems with recurrent neural networks and convolutional autoencoders

A common strategy for the dimensionality reduction of nonlinear partial differential equations (PDEs) relies on the use of the proper orthogonal decomposition (POD) to identify a reduced subspace and the Galerkin projection for evolving dynamics in this reduced space. However, advection-dominated PDEs are represented poorly by this methodology since the process of truncation discards important interactions between higher-order modes during time evolution. In this study, we demonstrate that encoding using convolutional autoencoders (CAEs) followed by a reduced-space time evolution by recurrent neural networks overcomes this limitation effectively. We demonstrate that a truncated system of only two latent space dimensions can reproduce a sharp advecting shock profile for the viscous Burgers equation with very low viscosities, and a six-dimensional latent space can recreate the evolution of the inviscid shallow water equations. Additionally, the proposed framework is extended to a parametric reduced-order model by directly embedding parametric information into the latent space to detect trends in system evolution. Furthermore, our results show that these advection-dominated systems are more amenable to low-dimensional encoding and time evolution by a CAE and recurrent neural network combination than the POD-Galerkin technique.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Three-dimensional stable lithium metal anode with nanoscale lithium islands embedded in ionically conductive solid matrix

Significance Lithium metal anode holds great promises for next-generation high-energy lithium battery systems. This work introduces an electrolyte-proof design of three-dimensional lithium metal anode where most of the lithium domains are embedded in a lithium-ion conductive matrix. In this architecture, the lithium-ion conductive matrix can isolate the embedded lithium domains from liquid electrolyte and thus prevent severe initial side reactions, while the matrix can simultaneously transport lithium ion and maintain the electrochemical activity of the embedded lithium. The design principle enables highly stable, high-power, and safe lithium metal anodes with minimal side reactions and negligible volume variation during cycling, which paves the way for viable lithium metal batteries in the future.

Lin, Dingchang↗