Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Homogenization”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Altered Regional Homogeneity and Functional Connectivity during Microlesion Period after Deep Brain Stimulation in Parkinson’s Disease

Background. Patients with Parkinson’s disease (PD) undergoing deep brain electrode implantation experience a temporary improvement in motor symptoms before the electrical stimulation begins. We usually call this the microlesion effect (MLE), but the mechanism behind it is not clear. Purpose. This study aimed to assess the alterations in brain functions at the regional and whole-brain levels, using regional homogeneity (ReHo) and functional connectivity (FC), during the postoperative microlesion period after deep brain stimulation (DBS) in PD patients. Method. Resting-state functional MRI data were collected from 27 PD patients before and after the first day of DBS and 12 healthy controls (HCs) in this study. The ReHo in combination with FC analysis was used to investigate the alterations of regional brain activity in all the subjects. Results. There were increased ReHo in the basal ganglia-thalamocortical circuit (left supplementary motor area and bilateral paracentral lobule), whereas decreased ReHo in the default mode network (DMN) (left angular gyrus, bilateral precuneus), prefrontal cortex (bilateral middle frontal gyrus), and the cerebello-thalamocortical (CTC) circuit (Cerebellum_crus2/1_L) after DBS. In addition, we also found abnormal FC in the lingual gyrus, cerebellum, and DMN. Conclusion. Microlesion of the thalamus caused by electrode implantation can alter the activity of the basal ganglia-thalamocortical circuit, prefrontal cortex, DMN, and CTC circuit and induce abnormal FC in the lingual gyrus, cerebellum, prefrontal cortex, and DMN among PD patients. The findings of this study contribute to the understanding of the mechanism of MLE.

Luo, Bei↗
DOE OSTI2022

Sensitivity analyses of a homogeneous model and a RZ model of the MYRRHA reactor in its critical configuration

Two homogenized models of the MYRRHA (Multi-purpose hybrid Research Reactor for High-tech Applications) reactor in its critical configuration are presented in this study. Both models will be verified by comparing the main reactor parameters (K{sub eff}, β{sub eff} and Λ) with those of the heterogeneous model and a sensitivity analysis will be performed. A sensitivity analysis of some important parameters related to reactivity, namely the vacuum coefficient, the Doppler and the power peaking factors, is also presented. The study of the vacuum coefficient has been carried out by analyzing two possible scenarios: 50% vacuum in the coolant (lead bismuth eutectic) and 100%, obtaining a list of the 10 reactions and nuclides that most affect the k{sub eff} value. With respect to the Doppler coefficient, it will be seen that a 300 degree increase in fuel temperature (starting at 800 K) results in a reduction of the total reactivity of the system by 134 pcm.. Finally, the map of the power peaking factors will be shown, as well as a sensitivity analysis. For making the sensitivity calculations Serpent-2 reactor physics Monte Carlo code has been used and JEFF-3.3 library has been chosen in order to continue with the OECD/NEA WPEC SG46 work evaluating the nuclear data of this library. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Spatial Homogeneity of Bacterial Communities Associated with the Surface Mucus Layer of the Reef-Building Coral Acropora palmata

Coral surface mucus layer (SML) microbiota are critical components of the coral holobiont and play important roles in nutrient cycling and defense against pathogens. We sequenced 16S rRNA amplicons to examine the structure of the SML microbiome within and between colonies of the threatened Caribbean reef-building coral Acropora palmata in the Florida Keys. Samples were taken from three spatially distinct colony regions—uppermost (high irradiance), underside (low irradiance), and the colony base—representing microhabitats that vary in irradiance and water flow. Phylogenetic diversity (PD) values of coral SML bacteria communities were greater than surrounding seawater and lower than adjacent sediment. Bacterial diversity and community composition was consistent among the three microhabitats. Cyanobacteria, Bacteroidetes, Alphaproteobacteria, and Proteobacteria, respectively were the most abundant phyla represented in the samples. This is the first time spatial variability of the surface mucus layer of A. palmata has been studied. Homogeneity in the microbiome of A. palmata contrasts with SML heterogeneity found in other Caribbean corals. These findings suggest that, during non-stressful conditions, host regulation of SML microbiota may override diverse physiochemical influences induced by the topographical complexity of A. palmata. Documenting the spatial distribution of SML microbes is essential to understanding the functional roles these microorganisms play in coral health and adaptability to environmental perturbations.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Fundamental absorption bandwidth to thickness limit for transparent homogeneous layers

Abstract Past work has considered the analytic properties of the reflection coefficient for a metal-backed slab. The primary result established a fundamental relationship for the minimal layer thickness to bandwidth ratio achievable for an absorber. There has yet to be establishment of a similar relationship for non-metal-backed layers, and here we present the universal result based on the Kramers–Kronig relations. Our theory is validated with transfer matrix calculations of homogeneous materials, and full-wave numerical simulations of electromagnetic metamaterials. Our results place more general fundamental limits on absorbers and thus will be important for both fundamental and applied studies.

Padilla, Willie J.↗
DOE OSTI2012

Mechanistic Studies at the Interface Between Organometallic Chemistry and Homogeneous Catalysis

Our goal was to learn the intimate mechanistic details of reactions involved in homogeneous catalysis and to use the insight we gain to develop new and improved catalysts. Our work centered on the hydrogenation of polar functional groups such as aldehydes and ketones and on hydroformylation. Specifically, we concentrated on catalysts capable of simultaneously transferring hydride from a metal center and a proton from an acidic oxygen or nitrogen center to an aldehyde or ketone. An economical iron based catalyst was developed and patented. Better understanding of fundamental organometallic reactions and catalytic processes enabled design of energy and material efficient chemical processes. Our work contributed to the development of catalysts for the selective and mild hydrogenation of ketones and aldehydes; this will provide a modern green alternative to reductions by LiAlH 4 and NaBH 4 , which require extensive work-up procedures and produce waste streams.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

High Efficiency, Low Emissions Homogeneous Charge Compression Ignition (HCCI) Engines

This is the final report of the High Efficiency Clean Combustion (HECC) Research Program for the U.S. Department of Energy. Work under this co-funded program began in August 2005 and finished in July 2010. The objective of this program was to develop and demonstrate a low emission, high thermal efficiency engine system that met 2010 EPA heavy-duty on-highway truck emissions requirements (0.2g/bhp-hr NOx, 0.14g/bhp-hr HC and 0.01g/bhp-hr PM) with a thermal efficiency of 46%. To achieve this goal, development of diesel homogenous charge compression ignition (HCCI) combustion was the chosen approach. This report summarizes the development of diesel HCCI combustion and associated enabling technologies that occurred during the HECC program between August 2005 and July 2010. This program showed that although diesel HCCI with conventional US diesel fuel was not a feasible means to achieve the program objectives, the HCCI load range could be increased with a higher volatility, lower cetane number fuel, such as gasoline, if the combustion rate could be moderated to avoid excessive cylinder pressure rise rates. Given the potential efficiency and emissions benefits, continued research of combustion with low cetane number fuels and the effects of fuel distillation are recommended. The operation of diesel HCCI was only feasible at part-load due to a limited fuel injection window. A 4% fuel consumption benefit versus conventional, low-temperature combustion was realized over the achievable operating range. Several enabling technologies were developed under this program that also benefited non-HCCI combustion. The development of a 300MPa fuel injector enabled the development of extended lifted flame combustion. A design methodology for minimizing the heat transfer to jacket water, known as precision cooling, will benefit conventional combustion engines, as well as HCCI engines. An advanced combustion control system based on cylinder pressure measurements was developed. A Well-to-wheels analysis of the energy flows in a mobile vehicle system and a 2nd Law thermodynamic analysis of the engine system were also completed under this program.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2013

Evaluation of Technical Feasibility of Homogeneous Charge Compression Ignition (HCCI) Engine Fueled with Hydrogen, Natural Gas, and DME

The objective of the proposed project was to confirm the feasibility of using blends of hydrogen and natural gas to improve the performance, efficiency, controllability and emissions of a homogeneous charge compression ignition (HCCI) engine. The project team utilized both engine simulation and laboratory testing to evaluate and optimize how blends of hydrogen and natural gas fuel might improve control of HCCI combustion.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2014

Discussion Regarding Aqueous Homogeneous Reactor (AHR) Benchmarks

“Characteristics of Fissile Solution Systems”, LA-UR-14-21513, published by the same authors, detailed the behavior of the subject systems that distinguishes them from those employing solid fuels. This Report, a companion to the presentation by the same name published by the authors as LA-UR-14- 21529, extends that discussion to illustrate this behavior with reference to the operation of historic aqueous homogeneous reactors (AHR). In this report the term “benchmark” refers to those systems for which it is judged that sufficient experimental data exists to serve as a reference for the behavior of the class of fissile solution systems called AHR. As has been discussed in the previous report, AHR exhibit a range of modes of operation generally determined by the amount of excess reactivity inserted into the system from a steady-state condition, such as sub-critical startup, and the rate of that insertion. The amount of reactivity inserted may fall in the range of $\$0.00$ < Reactivity ≤ $\$1.00$, in the usual units of “dollars” and “cents” or > $\$1.00$. The initial region is called “delayed critical” while the latter is referenced as “super prompt critical”. Excess reactivity may be inserted in rates ranging from slow ramp to step, which drives system dynamics; however, regardless of either of these factors, amplitude or rate of insertion, the ultimate result will be steady-state operation.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Tritium Technology Program TTP-1-3089 TPBAR Homogenized Composition

Homogenized TPBAR number densities contained herein have been derived for unclassified core physics calculations. The use of this information may not provide accurate, conservative or representative results and must be evaluated for applicability to the specific problem.

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

New Homogeneous Chromophore/Catalyst Concepts for the Solar-Driven Reduction of Carbon Dioxide

One of the major scientific and technical challenges of this century is to develop chemical means to store solar energy in the form of fuels. This can be accomplished by developing light-absorbing and catalytic compounds that function cooperatively to rearrange the chemical bonds of feedstocks in a way that allows solar energy to be stored and released on demand. The research conducted during this project was directed toward addressing fundamental questions that underlie the conversion of CO 2 to a solar fuel using homogeneous molecular systems. The research focused particularly on developing methods for extracting the reducing equivalents for these photochemical conversions from H 2 , which is a renewable molecule sourced to water. The research followed two main lines. One effort focused on understanding the general principles that govern how light-absorbing molecules interact with independent H 2 oxidation and CO 2 reduction catalysts to produce a functional cycle for driving the energy-storing reverse water-gas-shift reaction with light. The second effort centered on developing the excited-state properties and H 2 activation chemistry of tungsten–alkylidyne complexes. These chromophores were found to be powerful excited-state reducing agents, which could be incorporated into light-light-harvesting assemblies, and to hold the potential to be regenerated using H 2 .

14 SOLAR ENERGY↗
DOE OSTI2016

Request for Information from entities interested in commercializing Laboratory-developed homogeneous catalyst technology

Many industrial catalysts used for homogeneous hydrogenation and dehydrogenation of unsaturated substrates are derived from metal complexes that include (air-sensitive) ligands that are often expensive and difficult to synthesize. In particular, catalysts used for many hydrogenations are based on phosphorus containing ligands (in particular PNP pincer systems). These ligands are often difficult to make, are costly, are constrained to having two carbon atoms in the ligand backbone and are susceptible to oxidation at phosphorus, making their use somewhat complicated. Los Alamos researchers have recently developed a new and novel set of ligands that are based on a NNS (ENENES) skeleton (i.e. no phosphorus donors, just nitrogen and sulfur).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

(U) Analytic First and Second Derivatives of the Uncollided Leakage for a Homogeneous Sphere

The second-order adjoint sensitivity analysis methodology (2nd-ASAM), developed by Cacuci, has been applied by Cacuci to derive second derivatives of a response with respect to input parameters for uncollided particles in an inhomogeneous transport problem. In this memo, we present an analytic benchmark for verifying the derivatives of the 2nd-ASAM. The problem is a homogeneous sphere, and the response is the uncollided total leakage. This memo does not repeat the formulas given in Ref. 2. We are preparing a journal article that will include the derivation of Ref. 2 and the benchmark of this memo.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Eutectoid Transformation in U10Mo Alloy: Effect of Deformation History and Homogenization Heat Treatment

In the United States, uranium 10 wt.% molybdenum (U10Mo) alloy has been selected as the nuclear fuel that will be used when transitioning research reactors and radioisotope production facilities from highly enriched uranium (>85% 235 U) fuel to low-enriched uranium (<20% 235 U) fuel. The fabrication steps for producing U10Mo fuel foil involve multiple hot-rolling/cold-rolling/intermediate annealing steps. The U10Mo alloy, which can retain the desirable high-temperature body-centered cubic γ-U (A2) structure at room temperature as a metastable phase for optimum in-reactor performance, goes through a eutectoid reaction below ~560°C and forms a-U as a reaction product, which is highly undesirable. Because the fabrication steps are carried out in the temperature range of 500 to 700°C, it is critical to understand the eutectoid reaction kinetics as a function of rolling/annealing steps. In this study, we determined the eutectoid transformation behavior of various rolled/annealed U10Mo coupons at 450, 500, and 525°C. The results show that the highest degree of phase transformation occurs when the U10Mo billet is rolled down from the as-cast condition without any prior homogenization treatment. Further, we observed that mechanical deformation (in the form of hot-rolling/cold-rolling) leads to increased eutectoid transformation compared to the billets that were not deformed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Homogeneity, Heterogeneity and Uncertainty in Epic Shadow exercises [Slides]

High precision analyses demonstrate the ability to measure very small differences between sample aliquots. Is it appropriate for us to assume a homogenous sample in ES exercises? When running aliquots in triplicate should the data be averaged? If averaged what uncertainty should be applied, and what does the uncertainty describe? What is the most appropriate uncertainty to apply on single measurements?

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Poisson Equation for a (General) Homogeneous d-Dimensional Ellipsoid with Applications to Beam Envelope Tracking

This note describes the solution of the free-space Poisson equation in the interior of a $d$-dimensional homogeneous ellipsoid, and the associated space charge fields. An explicit formula (\ref{Sformula}) is provided that relates the $d\times d$ matrix describing the space charge (quadratic) potential to the $d\times d$ covariance matrix of the ellipsoid. For the cases $d=2$ and $d=3$, this result is used to determine the linear map corresponding to a space charge kick, that may be used to push the beam $6\times 6$ covariance matrix during envelope tracking. The treatment of upright ellipsoids for $d=2$ and $d=3$ is well-represented in the literature. However, the approach taken here emphasizes a general ellipsoid with arbitrary correlations in any dimension. The Appendix provides a general solution of the free-space Poisson equation in dimension $d$ for a source distribution with ellipsoidal symmetry.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Dual Readout in Homogenous Inorganic Scintillators for Precision Calorimeters

Homogeneous inorganic scintillator-based calorimeters are the gold standard for electromagnetic energy resolution, but often degrade the hadronic energy resolution achievable at colliders. By incorporating the dual readout technique, we seek to improve the hadronic energy resolution of these calorimeters through the measurement and separation of the scintillation and Cherenkov light in hadronic showers. In April 2024, CalVision performed single-crystal tests using the electron test beam at DESY. Using a single delay line technique for waveform analysis, sufficient cerenkov light can be extracted to fully capitalize on the dual readout technique. This talk will present the results of PWO, BGO, BSO, PbF2, and two novel scintillating glasses.

Anderson, Thomas [Virginia U.]↗
DOE OSTI2019

Bridging the Homogeneous-Heterogeneous Divide: Modeling Spin for Reactivity in Single Atom Catalysis

Single atom catalysts (SACs) are emergent catalytic materials that have the promise of merging the scalability of heterogeneous catalysts with the high activity and atom economy of homogeneous catalysts. Computational, first-principles modeling can provide essential insight into SAC mechanism and active site configuration, where the sub-nm-scale environment can challenge even the highest-resolution experimental spectroscopic techniques. Nevertheless, the very properties that make SACs attractive in catalysis, such as localized d electrons of the isolated transition metal center, make them challenging to study with conventional computational modeling using density functional theory (DFT). For example, Fe/N-doped graphitic SACs have exhibited spin-state dependent reactivity that remains poorly understood. However, spin-state ordering in DFT is very sensitive to the nature of the functional approximation chosen. In this work, we develop accurate benchmarks from correlated wavefunction theory (WFT) for relevant octahedral complexes. We use those benchmarks to evaluate optimal DFT functional choice for predicting spin state ordering in small octahedral complexes as well as models of pyridinic and pyrrolic nitrogen environments expected in larger SACs. Using these guidelines, we determine Fe/N-doped graphene SAC model properties and reactivity as well as their sensitivities to DFT functional choice. Finally, we conclude with broad recommendations for computational modeling of open-shell transition metal single-atom catalysts.

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

Optimized Slurries for Spray Drying: Different Approaches to Obtain Homogeneous and Deformable Alumina-Zirconia Granules

Spray drying is widely used for producing granulated feed materials for compaction process, which is the current industrial method for manufacturing alumina-zirconia femoral heads. The optimization of the granules compaction behavior requires the control of the slurry rheology. Moreover, for a dual-phase ceramic suspension, the even phase distribution has to be kept through the atomization step. Here we present two approaches addressing the key issues involved in the atomization of a composite system. Alumina-10 vol % zirconia powders were prepared by either a powder mixing route, or by the surface modification of a commercial α-alumina powder with a zirconium salt. Slurries from both powders were spray dried. The correlation between slurry rheology and pH, granules morphology and sintered microstructures was here investigated and discussed on the ground of the two feed materials characteristics. The processing conditions were optimized to obtain dense and homogeneous alumina-zirconia micro-nano composites by both processing routes.

36 MATERIALS SCIENCE↗