Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “OV”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The Dependence of Convective Core Overshooting on Stellar Mass: A Semi-empirical Determination Using the Diffusive Approach with Two Different Element Mixtures

Convective core overshooting has a strong influence on the evolution of stars of moderate and high mass. Studies of double-lined eclipsing binaries and stellar oscillations have renewed interest in the possible dependence of overshooting on stellar mass, which has been poorly constrained by observations so far. Here, we have used a sample of 29 well-studied double-lined eclipsing binaries in key locations of the H–R diagram to establish the explicit dependence of f{sub ov} on mass, where f{sub ov} is the free parameter in the diffusive approximation to overshooting. Measurements of the masses, radii, and temperatures of the binary components were compared against stellar evolution calculations based on the MESA code to infer semi-empirical values of f{sub ov} for each component. We find a clear mass-dependence such that f{sub ov} rises sharply from zero in the range 1.2--2.0 M{sub ⊙}, and levels off thereafter up to the 4.4 M{sub ⊙} limit of our sample. Tests with two different element mixtures indicate the trend is the same, and we find it to also be qualitatively similar to the one established in our previous study with the classical step-function implementation of overshooting characterized by the free parameter α{sub ov}. Based on these measurements, we infer an approximate relationship between the two overshooting parameters of α{sub ov}/f{sub ov}=11.36±0.22, with a possible dependence on stellar properties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Does Renal Artery Supply Indicate Treatment Success of Renal Denervation?

PurposeRenal denervation (RDN) emerged as an innovative interventional antihypertensive therapy. With the exception of pretreatment blood pressure (BP) level, no other clear predictor for treatment efficacy is yet known. We analyzed whether the presence of multiple renal arteries has an impact on BP reduction after RDN.MethodsFifty-three patients with treatment-resistant hypertension (office BP {>=} 140/90 mmHg and 24-h ambulatory BP monitoring ({>=}130/80 mmHg) underwent bilateral catheter-based RDN. Patients were stratified into one-vessel (OV) (both sides) and at least multivessel (MV) supply at one side. Both groups were treated on one vessel at each side; in case of multiple arteries, only the dominant artery was treated on each side.ResultsBaseline clinical characteristics (including BP, age, and estimated glomerular filtration rate) did not differ between patients with OV (n = 32) and MV (n = 21). Office BP was significantly reduced in both groups at 3 months (systolic: OV -15 {+-} 23 vs. MV -16 {+-} 20 mmHg; diastolic: OV -10 {+-} 12 vs. MV -8 {+-} 11 mmHg, both p = NS) as well as 6 months (systolic: OV -18 {+-} 18 vs. MV -17 {+-} 22 mmHg; diastolic: OV -10 {+-} 10 vs. -10 {+-} 12 mmHg, both p = NS) after RDN. There was no difference in responder rate (rate of patients with office systolic BP reduction of at least 10 mmHg after 6 months) between the groups.ConclusionIn patients with multiple renal arteries, RDN of one renal artery-namely, the dominant one-is sufficient to induce BP reduction in treatment-resistant hypertension.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Determination of contact maps in proteins: A combination of structural and chemical approaches

Contact map selection is a crucial step in structure-based molecular dynamics modelling of proteins. The map can be determined in many different ways. We focus on the methods in which residues are represented as clusters of effective spheres. One contact map, denoted as overlap (OV), is based on the overlap of such spheres. Another contact map, named Contacts of Structural Units (CSU), involves the geometry in a different way and, in addition, brings chemical considerations into account. We develop a variant of the CSU approach in which we also incorporate Coulombic effects such as formation of the ionic bridges and destabilization of possible links through repulsion. In this way, the most essential and well defined contacts are identified. The resulting residue-residue contact map, dubbed repulsive CSU (rCSU), is more sound in its physico-chemical justification than CSU. It also provides a clear prescription for validity of an inter-residual contact: the number of attractive atomic contacts should be larger than the number of repulsive ones — a feature that is not present in CSU. However, both of these maps do not correlate well with the experimental data on protein stretching. Thus, we propose to use rCSU together with the OV map. We find that the combined map, denoted as OV+rCSU, performs better than OV. In most situations, OV and OV+rCSU yield comparable folding properties but for some proteins rCSU provides contacts which improve folding in a substantial way. We discuss the likely residue-specificity of the rCSU contacts. Finally, we make comparisons to the recently proposed shadow contact map, which is derived from different principles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Crystal structure of N-terminally hexahistidine-tagged Onchocerca volvulus macrophage migration inhibitory factor-1

Onchocerca volvulus causes blindness, onchocerciasis, skin infections and devastating neurological diseases such as nodding syndrome. New treatments are needed because the currently used drug, ivermectin, is contraindicated in pregnant women and those co-infected with Loa loa . The Seattle Structural Genomics Center for Infectious Disease (SSGCID) produced, crystallized and determined the apo structure of N-terminally hexahistidine-tagged O. volvulus macrophage migration inhibitory factor-1 (His- Ov MIF-1). Ov MIF-1 is a possible drug target. His- Ov MIF-1 has a unique jellyfish-like structure with a prototypical macrophage migration inhibitory factor (MIF) trimer as the `head' and a unique C-terminal `tail'. Deleting the N-terminal tag reveals an Ov MIF-1 structure with a larger cavity than that observed in human MIF that can be targeted for drug repurposing and discovery. Removal of the tag will be necessary to determine the actual biological oligomer of Ov MIF-1 because size-exclusion chomatographic analysis of His- Ov MIF-1 suggests a monomer, while PISA analysis suggests a hexamer stabilized by the unique C-terminal tails.

Kimble, Amber D. (ORCID:0000000167851596)↗
DOE OSTI2018

Correlating DFT Calculations with CO Oxidation Reactivity on Ga-Doped Pt/CeO2 Single-Atom Catalysts

Pt/CeO2 single-atom catalysts have recently attracted increasing interest due to excellent thermal stability, high atom efficiency, and high activity in catalysis. In this study, by means of density functional theory (DFT) calculations, we systematically compare the stability and CO oxidation reactivity of Pt single atoms supported on CeO2(111) (Pt/CeO2) and Ga-doped CeO2(111) (Pt/Ga–CeO2). It was found that the formation of an oxygen vacancy (OV) is very facile near a surface Ga-doping site (Pt/Ga–CeO2–OV). Significantly, the stability of Pt single atoms anchored on the Ga site was enhanced compared with those on the bare ceria surface. In addition, our DFT results suggest a CO oxidation mechanism on Pt/Ga–CeO2–OV that differs from that on Pt/CeO2. In particular, the OV site plays an important role in activating the oxygen molecule, which then reacts with CO preadsorbed on Pt. The calculated energy barrier on Pt/Ga–CeO2–OV is about 0.43 eV lower than that on the undoped catalyst, suggesting an enhanced reactivity for CO oxidation. Experiments on CO oxidation and in situ diffuse reflectance infrared Fourier transform spectroscopy are performed to corroborate the results obtained from the DFT calculations, and a good agreement is achieved. The combination between calculations and experiments sheds light on the influence of support doping on atomically dispersed Pt/CeO2 catalysts.

Feng, Yingxin↗
DOE OSTI2016

Regulation of oxygen vacancy types on SnO{sub 2} (110) surface by external strain

In tin dioxide nanostructures, oxygen vacancies (OVs) play an important role in their optical properties and thus regulation of both OV concentration and type via external strain is crucial to exploration of more applications. First-principle calculations of SnO{sub 2} (110) surface disclose that asymmetric deformations induced by external strain not only lead to its intrinsic surface elastic changes, but also result in different OV formation energy. In the absence of external strain, the energetically favorable oxygen vacancies(EFOV) appear in the bridging site of second layer. When -3.5% external strain is applied along y direction, the EFOV moves into plane site. This can be ascribed that the compressed deformation gives rise to redistribution of electronic wave function near OVs, therefore, formation of newly bond structures. Our results suggest that different type OVs in SnO{sub 2} surface can be controlled by strain engineering.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Oxygen vacancy induced electronic structure modification of KTaO 3

The observation of a metallic interface between band insulators LaAlO 3 and SrTiO 3 has led to massive efforts to understand the origin of the phenomenon as well as to search for other systems hosting such two-dimensional electron gases (2-DEGs). However, the understanding of the origin of the 2-DEG is very often hindered as several possible mechanisms such as polar catastrophe, cationic intermixing, and oxygen vacancy (OV) can be operative simultaneously. The presence of a heavy element makes the KTaO 3 (KTO) based 2-DEG a potential platform to investigate spin-orbit coupling driven novel electronic and magnetic phenomena. In this work, we investigate the sole effect of OV in KTO, which makes KTO metallic. O K-edge x-ray absorption spectroscopy measurements find that OV dopes electrons in Ta t * 2g antibonding states. Photoluminescence measurements reveal the existence of a highly localized deep midgap state in oxygen-deficient KTO. Our detailed ab initio calculations demonstrate that such deep midgap state arises due to the linear clustering of OVs around Ta. Finally, our present work emphasizes that we must pay attention to the possible presence of OVs in interpreting emergent behavior of KTO-based heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1986

Comparison of solar hard X-ray and UV line and continuum bursts with high time resolution

The close temporal correlation between the ultraviolet line emission from OV (lambda 1371A) and hard X-rays above 30 keV has been previously established from a comparison of data sets from the Ultraviolet Spectrometer and Polarimeter (UVSP) and Hard X-Ray Burst Spectrometer (HXRBS) instruments on Solar Maximum Mission (SMM). Corresponding features were found to be coincident to within 1 s. Following the SMM repair, similar measurements were made for a flare occurring on May 20, 1984, at 0259 UT, this time with UVSP observing in the continuum near 1600A with much higher time resolution (75ms). The simultaneity of several features in this flare were established to better than 0.1 s, thus reinforcing the close relationship between hard X-ray and UV emission. Following the repair of the UVSP wavelength drive, similar measurements were repeated for a flare occurring at 0148 UT on April 24, 1985. This event was observed simultaneously in the OV line, the UV continuum and in hard X-rays by the same SMM instruments. Temporal comparisons of the three data sets show that, for a few selected features, simultaneity of the hard X-ray and UV emissions does exist. However, cross-correlation analyses of the entire data sets indicate that there is a trend for the fastest OV emission features to be delayed with respect to the hard X-rays by approx. 260 ms. On the other hand the fast OV and UV continuum features are simultaneous to within the instrumental uncertainty. The combined results have established the close relationship of the impulsive phase hard X-ray and UV continuum and OV line emissions. They lend support to the argument that both the hard X-ray and UV radiations originate low in the solar atmosphere.

Orwig, L. E.↗
NASA NTRS1991

Hubble Space Telescope high speed photometer orbital verification

The purpose of this report is to provide a summary of the results of the HSP (High Speed Photometer) Orbital Verification (OV) tests and to report conclusions and lessons learned from the initial operations of the HSP. The HSP OV plan covered the activities through fine (phase 3) alignment. This report covers all activities (OV, SV, and SAO) from launch to the completion of phase 3 alignment. Those activities in this period that are not OV tests are described to the extent that they relate to OV activities.

Richards, Evan E.↗
DOE OSTI2011

The Targeted Synthesis of Single Site Vanadyl Species on the Surface and in the Framework of Silicate Building Block Materials

A new synthetic methodology for the targeted preparation of single site, atomically dispersed vanadyl groups in silicate matrices is described. This methodology requires functionalized silicate building blocks Si{sub 8}O{sub 20}(OSnMe{sub 3}){sub 8} that become linked together through vanadyl ({triple_bond}V=O) groups in the matrix. A sequential addition strategy is illustrated which allows the targeting of specific connectivities for the vanadyl group to the silicate building block matrix (i.e. the number of V-O-Si bonds linking the vanadyl unit). Silicate matrices containing exclusively 3-connected (OV(OSi{sub cube}){sub 3}), 2-connected (OV(OR)(OSi{sub cube}){sub 2}) or 1-connected (OVCl{sub 2}(OSi{sub cube})) vanadyl sites are described and characterized via a wide variety spectroscopic and physical techniques (gravimetric analysis, EXAFS, AA and solid state NMR ({sup 51}V, {sup 29}Si, and {sup 17}O)). We demonstrate how the combination of gravimetric, solid state NMR (SSNMR) and EXAFS data can be used to uniquely define the vanadyl sites in these matrices. Furthermore, the use of {sup 17}O SSNMR (1D and MQMAS) is illustrated as an indirect spectroscopic probe to follow changes in the ligands bound to vanadium atom within the vanadyl groups in these matrices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A statistical mechanics approach to macroscopic limits of car-following traffic dynamics

Herein we study the derivation of macroscopic traffic models from car-following vehicle dynamics by means of hydrodynamic limits of an Enskog-type kinetic description. We consider the superposition of Follow-the-Leader (FTL) interactions and relaxation towards a traffic-dependent Optimal Velocity (OV) and we show that the resulting macroscopic models depend on the relative frequency between these two microscopic processes. If FTL interactions dominate then one gets an inhomogeneous Aw–Rascle–Zhang model, whose (pseudo) pressure and stability of the uniform flow are precisely defined by some features of the microscopic FTL and OV dynamics. Conversely, if the rate of OV relaxation is comparable to that of FTL interactions then one gets a Lighthill–Whitham–Richards model ruled only by the OV function. We further confirm these findings by means of numerical simulations of the particle system and the macroscopic models. Unlike other formally analogous results, our approach builds the macroscopic models as physical limits of particle dynamics rather than assessing the convergence of microscopic to macroscopic solutions under suitable numerical discretisations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2013

Mechanical relaxation in thermoelectric oxide Ca{sub 3−x}Sr{sub x}Co{sub 4}O{sub 9+δ} (x=0, 0.25, 0.5, 1.0) associated with oxygen vacancies

Ca{sub 3}Co{sub 4}O{sub 9+δ} has a unique structure that leads to exceptionally good thermoelectric (TE) properties. To change the concentration of oxygen vacancies (OVs) of the sample, the same sintered Ca{sub 3}Co{sub 4}O{sub 9+δ} polycrystalline ceramic suffered treating in 30 wt% oxydol (H{sub 2}O{sub 2}) solution and then annealing at 600 °C in pure N{sub 2}-gas atmosphere. Before and after each treatment, we performed dynamic mechanical analysis (DMA) with different frequencies, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) on the sample. A relaxation peak was observed at the temperature range from 90 °C to 150 °C, and the relaxation process is most likely caused by the migration of single OVs. The consistency in the results from TGA and XPS could well support the conclusion that the OVs of Ca{sub 3}Co{sub 4}O{sub 9+δ} are located on the O site of CoO layer in Ca{sub 2}CoO{sub 3} subsystem. Further DMA investigations on the Ca{sub 3−x}Sr{sub x}Co{sub 4}O{sub 9+δ} (x=0, 0.25, 0.5, 1.0) ceramic indicated that Sr substitution of Ca could suppress the relaxation peak, suggesting the migration of single OVs mainly processes between CoO and CaO layers of Ca{sub 2}CoO{sub 3} subsystem. - Graphical abstract: A relaxation peak and a transition peak could be observed in the internal friction spectra of Ca{sub 3}Co{sub 4}O{sub 9+δ}. The calculated activation energy indicates the relaxation process is associated with migration of oxygen vacancies. Highlights: ► We performed dynamic mechanical analysis on the thermoelectric oxide Ca{sub 3}Co{sub 4}O{sub 9+δ}. ► We observed a relaxation peak and a transition peak. ► The oxygen vacancies are located in CoO layer of Ca{sub 2}CoO{sub 3} subsystem. ► The relaxation peak originates from migration of single oxygen vacancies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Binding Interactions between Receptor-Binding Domain of Spike Protein and Human Angiotensin Converting Enzyme-2 in Omicron Variant

The emergence of new SARS-CoV-2 Omicron variant of concern (OV) has exacerbated the COVID-19 pandemic because of a large number of mutations in the spike protein, particularly in the receptor-binding domain (RBD), resulting in highly contagious and/or vaccine-resistant strains. Herein, we present a systematic analysis based on detailed molecular dynamics (MD) simulations in order to understand how the OV RBD mutations affect the ACE2 binding. We show that the OV RBD binds to ACE2 more efficiently and tightly predominantly because of strong electrostatic interactions, thereby promoting increased infectivity and transmissibility compared to other strains. Some of the OV RBD mutations are predicted to affect the antibody neutralization either through their role in the S-protein conformational changes, such as S371L, S373P, and S375F, or through changing its surface charge distribution, such as G339D, N440K, T478K, and E484A. Other mutations, such as K417N, G446S, and Y505H, decrease the ACE2 binding, whereas S447N, Q493R, G496S, Q498R, and N501Y tend to increase it.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Room temperature alcohol sensing by oxygen vacancy controlled TiO{sub 2} nanotube array

Oxygen vacancy (OV) controlled TiO{sub 2} nanotubes, having diameters of 50–70 nm and lengths of 200–250 nm, were synthesized by electrochemical anodization in the mixed electrolyte comprising NH{sub 4}F and ethylene glycol with selective H{sub 2}O content. The structural evolution of TiO{sub 2} nanoforms has been studied by field emission scanning electron microscopy. Variation in the formation of OVs with the variation of the structure of TiO{sub 2} nanoforms has been evaluated by photoluminescence and X-ray photoelectron spectroscopy. The sensor characteristics were correlated to the variation of the amount of induced OVs in the nanotubes. The efficient room temperature sensing achieved by the control of OVs of TiO{sub 2} nanotube array has paved the way for developing fast responding alcohol sensor with corresponding response magnitude of 60.2%, 45.3%, and 36.5% towards methanol, ethanol, and 2-propanol, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

ON CARBON BURNING IN SUPER ASYMPTOTIC GIANT BRANCH STARS

We explore the detailed and broad properties of carbon burning in Super Asymptotic Giant Branch (SAGB) stars with 2755 MESA stellar evolution models. The location of first carbon ignition, quenching location of the carbon-burning flames and flashes, angular frequency of the carbon core, and carbon core mass are studied as a function of the zero-age main sequence (ZAMS) mass, initial rotation rate, and mixing parameters such as convective overshoot, semiconvection, thermohaline, and angular momentum transport. In general terms, we find that these properties of carbon burning in SAGB models are not a strong function of the initial rotation profile, but are a sensitive function of the overshoot parameter. We quasi-analytically derive an approximate ignition density, ρ{sub ign} ≈ 2.1 × 10{sup 6} g cm{sup −3}, to predict the location of first carbon ignition in models that ignite carbon off-center. We also find that overshoot moves the ZAMS mass boundaries where off-center carbon ignition occurs at a nearly uniform rate of ΔM{sub ZAMS}/Δf{sub ov} ≈ 1.6 M{sub ⊙}. For zero overshoot, f{sub ov} = 0.0, our models in the ZAMS mass range ≈8.9–11 M{sub ⊙} show off-center carbon ignition. For canonical amounts of overshooting, f{sub ov} = 0.016, the off-center carbon ignition range shifts to ≈7.2–8.8 M{sub ⊙}. Only systems with f{sub ov} ≥ 0.01 and ZAMS mass ≈7.2–8.0 M{sub ⊙} show carbon burning is quenched a significant distance from the center. These results suggest a careful assessment of overshoot modeling approximations on claims that carbon burning quenches an appreciable distance from the center of the carbon core.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Continuous, edge localized ion heating during non-solenoidal plasma startup and sustainment in a low aspect ratio tokamak

Plasmas in the Pegasus spherical tokamak are initiated and grown by the non-solenoidal local helicity injection (LHI) current drive technique. The LHI system consists of three adjacent electron current sources that inject multiple helical current filaments that can reconnect with each other. Anomalously high impurity ion temperatures are observed during LHI with T i,OV ≤ 650 eV, which is in contrast to T i,OV ≤ 70 eV from Ohmic heating alone. Spatial profiles of T i,OV indicate an edge localized heating source, with T i,OV ~ 650 eV near the outboard major radius of the injectors and dropping to ~150 eV near the plasma magnetic axis. Experiments without a background tokamak plasma indicate the ion heating results from magnetic reconnection between adjacent injected current filaments. In these experiments, the HeII T i perpendicular to the magnetic field is found to scale with the reconnecting field strength, local density, and guide field, while ${{T}_{\text{i},\parallel}}$ experiences little change, in agreement with two-fluid reconnection theory. In conclusion, this ion heating is not expected to significantly impact the LHI plasma performance in Pegasus, as it does not contribute significantly to the electron heating. However, estimates of the power transfer to the bulk ion are quite large, and thus LHI current drive provides an auxiliary ion heating mechanism to the tokamak plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

TU-AB-BRA-12: Impact of Image Registration Algorithms On the Prediction of Pathological Response with Radiomic Textures

Purpose: Tumor regions-of-interest (ROI) can be propagated from the pre-onto the post-treatment PET/CT images using image registration of their CT counterparts, providing an automatic way to compute texture features on longitudinal scans. This exploratory study assessed the impact of image registration algorithms on textures to predict pathological response. Methods: Forty-six esophageal cancer patients (1 tumor/patient) underwent PET/CT scans before and after chemoradiotherapy. Patients were classified into responders and non-responders after the surgery. Physician-defined tumor ROIs on pre-treatment PET were propagated onto the post-treatment PET using rigid and ten deformable registration algorithms. One co-occurrence, two run-length and size zone matrix textures were computed within all ROIs. The relative difference of each texture at different treatment time-points was used to predict the pathologic responders. Their predictive value was assessed using the area under the receiver-operating-characteristic curve (AUC). Propagated ROIs and texture quantification resulting from different algorithms were compared using overlap volume (OV) and coefficient of variation (CoV), respectively. Results: Tumor volumes were better captured by ROIs propagated by deformable rather than the rigid registration. The OV between rigidly and deformably propagated ROIs were 69%. The deformably propagated ROIs were found to be similar (OV∼80%) except for fast-demons (OV∼60%). Rigidly propagated ROIs with run-length matrix textures failed to significantly differentiate between responders and non-responders (AUC=0.65, p=0.07), while the differentiation was significant with other textures (AUC=0.69–0.72, p<0.03). Among the deformable algorithms, fast-demons was the least predictive (AUC=0.68–0.71, p<0.04). ROIs propagated by all other deformable algorithms with any texture significantly predicted pathologic responders (AUC=0.71–0.78, p<0.01) despite substantial variation in texture quantification (CoV>70%). Conclusion: Propagated ROIs using deformable registration for all textures can lead to accurate prediction of pathologic response, potentially expediting the temporal texture analysis process. However, rigid and fast-demons deformable algorithms are not recommended due to their inferior performance compared to other algorithms. The project was supported in part by a Kaye Scholar Award.

60 APPLIED LIFE SCIENCES↗