Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “activation”

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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The Effect of Material Properties on Oxygen Evolution Activity and Assessing Half-Cell Screening as a Predictive Tool in Electrolysis

Iridium-based oxygen evolution catalysts are screened in this study for activity and stability with rotating disk electrode (RDE) half-cells. This study focuses on the electrochemical and materials approaches needed to characterize oxygen evolution catalysts, and include testing for activity, stability, composition, oxide content, and structure. Findings also discuss recommendations for data interpretation and detail the difficulties of comparing catalysts across materials sets with different elemental and oxide compositions, and linking RDE activity to device-level performance. The materials evaluated are a mixture of oxides and metals, and several methods are used to quantify metal content, qualitatively assess oxide content, and determine total surface area. Oxygen evolution activities and stabilities are compared, where a wide range of results are reported. In general, higher RDE performances are found for catalysts that contained larger amounts of ruthenium and metals. Higher durability, however, is found for catalysts that only contained iridium and a higher proportion of oxides. Additionally, catalysts are evaluated for performance in membrane electrode assemblies to assess RDE as a predictive tool in electrolysis. While activity trends within individual material sets generally held between ex- and in-situ testing, RDE tends to overestimate the activity of more metallic catalysts when compared to device-level performance. These results stress the need for multiple metal/oxide baselines for mixed catalysts, to better project in-situ kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Influence of Proton Activity Gaps between Electrodes on Open-Circuit Potential of H 2 /H 2 and H 2 /Air Cells

Polymer -electrolyte-fuel-cell open-circuit voltages (OCVs) are exactly defined by equation (1), where cathode and anode proton activities [(aH+)cathode and (aH+)anode, respectively] usually are identical, so the third term in the right-hand side of equation (2) is ignored. OCV=E0+RT/2F*ln(a1/2 O2*(a2 H+)cathode/aH2O)-RT/2F*ln((a2 H+)anode/aH2) (1) =E0+RT/2F*ln(a1/2 O2*aH2/aH2O)+RT/2F*ln((a2 H+)cathode/(a2 H+)anode) (2) Water vapor pressure is a colligative property that fundamentally correlates to electrolyte concentrations in aqueous solutions. Proton activity is a function of acid concentration, such as pH, when electrolytes are acids. In polymer-electrolyte membranes, water vapor pressure and acid concentration are understood as relative humidity (RH) and water uptake (λ), respectively, where λ represents number of water molecules per sulfonic acid molecule. Several investigations have reported the relationship between RH and λ, meaning that proton activities and associated water uptakes are intimately related to RH. In actual fuel cell operation, cathode RH is determined by ambient-atmosphere and/or humidifier RH(s), and anode RH depends on hydrogen-circulator RH. Therefore, RH is not always identical at both electrodes, and the difference between electrode RHs is considerable during dry operation of polymer electrolyte fuel cells. Therefore, the third term in the right-hand side of equation (2) may be significant for dry operation. We measured OCVs when hydrogen was supplied to both electrodes at 80°C. One electrode (A) was fixed at 30% RH, while RH at the other electrode (B) was varied (0, 5, 10, 20, and 30%). Measured OCVs varied from 0 to 75 mV. For fuel cell tests, electrode A was supplied with hydrogen at 30% RH; electrode B, oxygen at 0, 5, 10, 20, and 30% RH. OCVs deviated from that measured when RH at electrode B was 30%, increasing from 0 to 60 mV with decreasing RH at electrode B. Results are also shown in Figure 1. Proton activities of both electrodes were thermodynamically calculated. The Gibbs–Duhem relation was applied to obtain molar Gibbs free energies of water and sulfonic acid, and proton activity coefficient was calculated using the Gibbs free energy of sulfonic acid and the relationship between RH and λ1–4, assuming that protons and sulfonic anions show identical ionic-activity coefficients. OCVs were estimated using the third term in the right-hand side of equation (2). Results are shown in Figure 1. Fuel-cell current–voltage performance was poor when RHs at the anode and cathode were 30 and 20%, respectively. To determine kinetic current, we measured the oxygen-reduction reaction (ORR) using a rotating-disk electrode (RDE) in concentrated-acid aqueous solutions, which modeled catalyst-layer ionomers. Kinetic currents decreased with acid concentrations. References T. A. Zawodzinski, Jr., C. Derouin, S. Radzinski, R. J. Sherman, V. T. Smith, T. E. Springer and S. Gottesfeld , J. Electrochem. Soc., 140,1041 (1993) P. K. Das and A. Z. Weber, Proceedings of the ASME 2013 11th Fuel Cell Science, Engineering and Technology Conference, Fuel Cell 18010 (2013) V. A. Sethuraman, J. W. Weidner, A. T. Haug, S. Motupally,b and L. V. Protsailo, J. Electrochem. Soc., 155, B50 (2008) A. Kusoglu and A. Z. Weber, Chem. Rev., 117, 987 (2017) Figure 1

Yoshida, Toshihiko↗
DOE OSTI2022

Modulation of North Atlantic Polar Low Activity and Associated Flow Patterns by Sudden Stratospheric Warmings

Abstract Polar lows (PLs) are intense maritime mesoscale cyclones that can pose hazards to coastal communities and marine operation in the Arctic. This study examines the impacts of sudden stratospheric warmings (SSWs) on PL activity in the subarctic North Atlantic. The 20 days following SSWs are characterized by tropospheric circulation anomalies resembling the negative phase of the North Atlantic Oscillation. PL activity decreases significantly over the Labrador Sea, which can be attributed to the infrequent occurrence of low static stability and strong environmental baroclinicity, as well as reduced surface turbulent heat fluxes. These results suggest that a skillful prediction of SSWs can improve the extended-range forecast of PL activity over the Labrador Sea. For the Nordic seas, the results imply that the spatial structure of an SSW event is important for the PL modulation through different tropospheric circulation patterns. Situations with increased PL frequency in the Nordic seas are characterized by SSWs centered close to northern Greenland occurring over a smaller area, and a tropospheric response featuring enhanced cold-air outbreaks over the Norwegian Sea. Conversely, PL activity is suppressed over the Nordic seas when the SSW favors the formation of a tropospheric anticyclone above Greenland and Scandinavia. Significance Statement This study investigates the relationships between polar lows (PLs) and sudden stratospheric warmings (SSWs) over the subarctic North Atlantic. A better understanding of the effect of SSWs on PL development has the potential to improve extended-range forecasts of PLs. It is shown that SSWs are responsible for the significantly suppressed regional PL activity over the Labrador Sea, suggesting that SSWs can serve as a predictor for the extended-range forecast of PLs over this region. Following SSW events, the thermodynamic state of atmosphere becomes more stable over the Labrador Sea and hinders the convective development of PLs. For the northern Nordic seas, the impacts of SSWs on PL activity are sensitive to the spatial structure of stratospheric warming.

Chang, Chuan-Chieh↗
DOE OSTI2025

In vitro activity and in vivo efficacy of omadacycline against Plasmodium species

Abstract Background Doxycycline is currently the only tetracycline-class antibiotic recommended for malaria prophylaxis. Omadacycline, a semisynthetic aminomethylcycline approved for treatment of adults with community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections, has a well-established safety profile. This study evaluated the in vitro activity of omadacycline againstPlasmodium falciparumandPlasmodium cynomolgiand its in vivo efficacy againstPlasmodium bergheiin experimental malaria models to assess its potential as an antimalarial drug. Methods Fluorescence-based assays were used to assess the in vitro blood and liver stage activity of omadacycline and doxycycline againstP. falciparumandP. cynomolgilaboratory clones. In vivo liver and early-stage blood stage efficacy were evaluated in a murine model ofP. bergheiinfection, utilizing in vivo imaging of luciferase-expressingP. berghei(ANKA strain) sporozoites in female albino C57Bl/6 mice. Parasitaemia was monitored by flow cytometry for up to 30 days post-infection. Results Omadacycline demonstrated comparable in vitro activity to doxycycline against both drug-sensitive and drug-resistantP. falciparumclones, while doxycycline showed reduced activity against two drug-resistant clones. Notably, omadacycline exhibited superior anti-schizont activity in theP. cynomolgiliver stage assay. In theP. bergheimurine model, omadacycline was efficacious in both liver and early blood stages compared to the untreated control group, and demonstrated improved survival compared to doxycycline. Conclusions Omadacycline demonstrated enhanced antimalarial efficacy over doxycycline in vitro in liver stage activity and in overcoming resistance in the blood stage, and in survival in an in vivo model ofP. bergheiinfection. These findings support further investigation of omadacycline as a potential candidate for malaria prophylaxis and treatment.

Infectious Diseases↗
DOE OSTI2026

Puget Sound Regional Council 2006 Household Activity Survey

The purpose of the 2006 Puget Sound Regional Council Household Activity Survey was to provide data for travel demand models for the Puget Sound region, for the assessment of current activity and travel patterns, and for the estimation of future activity and travel within the region under various policy scenarios. One important goal of this project is to improve planners' ability to evaluate impacts of future policies and actions on travel patterns and transportation facility use through the development of a database. This database both captures the current status of activity and travel in the region and includes attitudes, preferences, and choices about activities and travel. In the design of the 2006 survey, basic demographics, activities, and tour and travel characteristics were collected for every member (including children) of 4,746 households during a consecutive 48-hour travel period. Vehicle global positioning system (GPS) data were collected from a subsample of 220 of these households, including completed activity/travel diaries for each household member. (Up to three vehicles per household were equipped with GPS units). The final GPS tracking data contained detailed information on the travel paths of 220 households with two vehicles in the same 48-hour period recorded in the diaries.

1Hz data↗
DOE OSTI2020

Active Betweenness Cardinality: Algorithms and Applications

Centrality rankings such as degree, closeness, betweenness, Katz, PageRank, etc. are commonly used to identify critical nodes in a graph. These methods are based on two assumptions that restrict their wider applicability. First, they assume the exact topology of the network is available. Secondly, they do not take into account the activity over the network and only rely on its topology. However, in many applications, the network is autonomous, vast, and distributed, and it is hard to collect the exact topology. At the same time, the underlying pairwise activity between node pairs is not uniform and node criticality strongly depends on the activity on the underlying network. In this paper, we propose active betweenness cardinality, as a new measure, where the node criticalities are based on not the static structure, but the activity of the network. We show how this metric can be computed efficiently by using only local information for a given node and how we can find the most critical nodes starting from only a few nodes. We also show how this metric can be used to monitor a network and identify failed nodes. We present experimental results to show effectiveness by demonstrating how the failed nodes can be identified by measuring active betweenness cardinality of a few nodes in the system.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Tailoring Redox Active Ligands for Probing the Reactivity of Actinides

With this project, we aim to further enhance our understanding of fundamental f-element chemistry, including electronic structure and bonding behaviors. Key project goals include the characterization of actinide complexes bearing redox-active ligands, including those of lower-oxidation state uranium, and examining how structural changes to the ligand and coordination sphere affect structure and bonding. Redox-active and redox non-innocent ligands have been used widely in transition metal chemistry, but uranium complexes with redox-active ligands are surprisingly rare. We recently reported the synthesis of the redox-active ligand, “phen-BIAN” (N,N’-bis(iminophenol)acenaphthene), in an investigation of the electronic behavior of uranium and other actinides. This ligand framework borrows features from two classes of Schiff base ligands—the tetradentate O-N-N-O binding pocket from salens, and the redox-active α-diimine unit and backbone from Ar-BIANs (N,N’-bis[(aryl)imino]acenaphthenes, which can accept up to four electrons upon reduction. To continue this work, the electronics of uranyl and thorium complexes will be probed using the reduced forms of these ligands, using these in the preparation of lower-oxidation state and non-oxo uranium complexes. Additional members of the phen-BIAN family will be synthesized, including naphthol and thiol derivative. With these we can characterize the influence of substitutent groups on the redox activity, coordination geometry, and covalent interactions. The work proposed here entails extensive preparation, structural and spectroscopic characterization, of an array of actinide complexes. This will allow us to address probative questions about the nature of actinide bonding, the degree of covalency, the validity of lanthanides as models for the actinides, hard-soft interactions, magnetic interactions between metals in bimetallic complexes and what combination of electronic and steric affects produce an actinide selective ligand. The latter will assist greatly in providing a benchmark against which to compare and evaluate the distinct behaviors exhibited by 5f-element complexes. This will enable us to learn about the differences in binding between the 4f lanthanides and the 5f elements like uranium and plutonium. Such difference in binding can be exploited in separations and the development of new materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

A new active base of photomultiplier R4125 designed for the PbWO4 calorimeter

This paper presents the design, performance, and results of the radiation tests of an active base for Hamamatsu R4125 photomultiplier tube. The active base was designed at Jefferson Lab and comprises of a high voltage divider and an on-board amplifier. The photomultiplier with the active base is used to detect light from lead tungstate scintillating crystals of the forward electromagnetic calorimeter of the GlueX detector. The active base amplifier allows to operate the tube at lower high voltage and thus to limit the photomultiplier anode current to a few micro ampereres at the maximum counter rate of 1 MHz counter, while retaining the dynamic range of output signals. The performance of calorimeter modules instrumented with the active base was studied using detector prototypes positioned into the beam of photons. The key performance parameters such as the linearity, high-rate capability, and the energy resolution verified that the active base design meets the detector specifications

Somov, Alexander [Thomas Jefferson National Accele↗
DOE OSTI2025

HFIR Activity Workbook Generator (HAWK) User Guide

The HFIR Activity WorkbooK generator (HAWK) is a Python code that automates and streamlines the activity calculation of samples after irradiation in the High Flux Isotope Reactor (HFIR). HAWK’s results provide estimates of the activity and nuclide inventory of irradiated specimens before they are moved to hot cell facilities, where they undergo post-irradiation examination. The samples’ activity results guide the packing of shipping containers and inform the accountable inventories for the hot cell facilities. The toolkit was originally developed by Charles Daily, a former R&D staff member at Oak Ridge National Laboratory (ORNL). As of May 2025, HAWK is developed by the Radiation Transport & HPC Methods Group (Nuclear Energy and Fuel Cycle Division) at ORNL. Figure 1 presents HAWK’s workflow. To use HAWK, users need to: 1. Develop an Excel input workbook (i.e., XLSX extension) containing data from the experiment’s materials, irradiation history (cycles), and irradiation positions. 2. Make minor edits to an existing template JSON file (i.e., auxiliary_data.JSON) and to the Python driver. The driver sets the necessary environment variables, defines the material compositions, and ultimately calls HAWK. Once configured, HAWK runs the Oak Ridge Isotope Generation code (ORIGEN) to calculate the masses, activities, and heat load at the end of irradiation for each isotope in the specimen. ORIGEN is part of SCALE, ORNL’s in-house computational tool for performing nuclear safety and design calculations. Following this step, HAWK postprocesses the results and generates three output workbooks summarizing the activity calculations.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2021

Effect of Active Lengthening and Shortening on Small-Angle X-ray Reflections in Skinned Skeletal Muscle Fibres

Our purpose was to use small-angle X-ray diffraction to investigate the structural changes within sarcomeres at steady-state isometric contraction following active lengthening and shortening, compared to purely isometric contractions performed at the same final lengths. We examined force, stiffness, and the 1,0 and 1,1 equatorial and M3 and M6 meridional reflections in skinned rabbit psoas bundles, at steady-state isometric contraction following active lengthening to a sarcomere length of 3.0 µm (15.4% initial bundle length at 7.7% bundle length/s), and active shortening to a sarcomere length of 2.6 µm (15.4% bundle length at 7.7% bundle length/s), and during purely isometric reference contractions at the corresponding sarcomere lengths. Compared to the reference contraction, the isometric contraction after active lengthening was associated with an increase in force (i.e., residual force enhancement) and M3 spacing, no change in stiffness and the intensity ratio I 1,1 /I 1,0 , and decreased lattice spacing and M3 intensity. Compared to the reference contraction, the isometric contraction after active shortening resulted in decreased force, stiffness, I 1,1 /I 1,0 , M3 and M6 spacings, and M3 intensity. This suggests that residual force enhancement is achieved without an increase in the proportion of attached cross-bridges, and that force depression is accompanied by a decrease in the proportion of attached cross-bridges. Furthermore, the steady-state isometric contraction following active lengthening and shortening is accompanied by an increase in cross-bridge dispersion and/or a change in the cross-bridge conformation compared to the reference contractions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Antiviral Activity and Crystal Structures of HIV-1 gp120 Antagonists

As part of our effort to discover drugs that target HIV-1 entry, we report the antiviral activity and crystal structures of two novel inhibitors in a complex with a gp120 core. NBD-14204 showed similar antiviral activity against all the clinical isolates tested. The IC50 values were in the range of 0.24–0.9 µM with an overall mean of 0.47 ± 0.03 µM, showing slightly better activity against the clinical isolates than against the lab-adapted HIV-1 HXB2 (IC 50 = 0.96 ± 0.1 µM). Moreover, the antiviral activity of NBD-14208 was less consistent, showing a wider range of IC 50 values (0.66–5.7 µM) with an overall mean of 3 ± 0.25 µM and better activity against subtypes B and D (Mean IC 50 2.2–2.5 µM) than the A, C and Rec viruses (Mean IC 50 2.9–3.9 µM). SI of NBD-14204 was about 10-fold higher than NBD-14208, making it a better lead compound for further optimization. In addition, we tested these compounds against S375Y and S375H mutants of gp120, which occurred in some clades and observed these to be sensitive to NBD-14204 and NBD-14208. These inhibitors also showed modest activity against HIV-1 reverse transcriptase. Furthermore, we determined the crystal structures of both inhibitors in complexes with gp120 cores. As expected, both NBD-14204 and NBD-14208 bind primarily within the Phe43 cavity. It is noteworthy that the electron density of the thiazole ring in both structures was poorly defined due to the flexibility of this scaffold, suggesting that these compounds maintain substantial entropy, even when bound to the Phe43 cavity.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

EpiPro, a Novel, Synthetic, Activity-Regulated Promoter That Targets Hyperactive Neurons in Epilepsy for Gene Therapy Applications

Epileptogenesis is characterized by intrinsic changes in neuronal firing, resulting in hyperactive neurons and the subsequent generation of seizure activity. These alterations are accompanied by changes in gene transcription networks, first with the activation of early-immediate genes and later with the long-term activation of genes involved in memory. Our objective was to engineer a promoter containing binding sites for activity-dependent transcription factors upregulated in chronic epilepsy (EpiPro) and validate it in multiple rodent models of epilepsy. First, we assessed the activity dependence of EpiPro: initial electrophysiology studies found that EpiPro-driven GFP expression was associated with increased firing rates when compared with unlabeled neurons, and the assessment of EpiPro-driven GFP expression revealed that GFP expression was increased ~150× after status epilepticus. Following this, we compared EpiPro-driven GFP expression in two rodent models of epilepsy, rat lithium/pilocarpine and mouse electrical kindling. In rodents with chronic epilepsy, GFP expression was increased in most neurons, but particularly in dentate granule cells, providing in vivo evidence to support the “breakdown of the dentate gate” hypothesis of limbic epileptogenesis. Finally, we assessed the time course of EpiPro activation and found that it was rapidly induced after seizures, with inactivation following over weeks, confirming EpiPro’s potential utility as a gene therapy driver for epilepsy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Time-domain Modulation of HD 189733 Activities by Its Planet

Star–planet interaction can be studied by analyzing exoplanetary orbit and stellar rotation modulations of the transit emissions from exoplanetary systems. Here we carry out a time-domain analysis of the multiband activities of the HD 189733 star–planet system observed in X-ray, atomic lines, and broadband spectra reported in the literature. We find that the number of activities occuring at beat angles (of the planetary orbit and the stellar rotation) concentrating on a sector with a width of 108° are significantly larger than expected from a uniform distribution of activities, which indicates the existence of a major stellar active magnetic field region. The concentration of activities in this active magnetic field region shows their possible origins from the magnetic field interaction between HD 189733 and its close planet HD 189733 b.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Magnitude-squared Coherence: A Powerful Tool for Disentangling Doppler Planet Discoveries from Stellar Activity

Abstract If Doppler searches for Earth-mass, habitable planets are to succeed, observers must be able to identify and model out stellar activity signals. Here we demonstrate how to diagnose activity signals by calculating the magnitude-squared coherence C ˆ xy 2 ( f ) between an activity-indicator time series x t and the radial-velocity (RV) time series y t . Since planets only cause modulation in RV, not in activity indicators, a high value of C ˆ xy 2 ( f ) indicates that the signal at frequency f has a stellar origin. We use Welch’s method to measure coherence between activity indicators and RVs in archival observations of GJ 581, α Cen B, and GJ 3998. High RV-H α coherence at the frequency of GJ 3998 b and high RV-S index coherence at the frequency of GJ 3998c, indicate that the planets may actually be stellar signals. We also replicate previous results showing that GJ 581 d and g are rotation harmonics and demonstrate that α Cen B has activity signals that are not associated with rotation. Welch’s power spectrum estimates have cleaner spectral windows than Lomb–Scargle periodograms, improving our ability to estimate rotation periods. We find that the rotation period of GJ 581 is 132 days, with no evidence of differential rotation. Welch’s method may yield unacceptably large bias for data sets with N < 75 observations and works best on data sets with N > 100. Tapering the time-domain data can reduce the bias of the Welch’s power spectrum estimator, but observers should not apply tapers to data sets with extremely uneven observing cadence. A software package for calculating magnitude-squared coherence and Welch’s power spectrum estimates is available on github.

Dodson-Robinson, Sarah E. (ORCID:0000000287964974)↗
DOE OSTI2026

Investigating the Effects of Bars on Star Formation and Nuclear Activity of Galaxies Using DESI Survey Data

We present a statistical analysis of the connections between galactic bars, star formation, and active galactic nucleus (AGN) activity using 33,201 disk galaxies (0.01 < z < 0.05) from Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1) cross-matched with Galaxy Zoo DESI. Based on morphological classifications, we identify 3508 strongly barred and 8335 weakly barred systems. We find that barred galaxies exhibit a clear bimodal distribution in color–mass space: weak bars are preferentially found in bluer, lower-mass disks, whereas strong bars are more common in massive, redder systems. Strongly barred galaxies are on average more massive and metal rich than unbarred systems. In addition, strong bars enhance central star formation rates (SFRs) in low-mass galaxies but reduce specific SFRs in massive systems, reflecting a dual role where bars initially trigger central star formation but eventually promote quenching by accelerating gas consumption. In terms of nuclear activity, barred galaxies display a higher incidence of AGN activity. The presence of a bar is also associated with an increased fraction of powerful AGN, with the highest proportions found in strongly barred systems. However, the correlations between AGN activity and detailed bar structural parameters are weak, suggesting that the link between bars and nuclear activity is indirect and regulated by multiple factors. Overall, our results support a scenario in which bars facilitate angular momentum transport and gas inflow, thereby driving central star formation and fueling supermassive black hole accretion while operating alongside other processes that shape galaxy evolution.

Liu, Jianfei [Chinese Academy of Sciences (CAS), B↗
DOE OSTI2025

Activation of propane on Ag–PdO(101) model surfaces

Oxidation of alkanes remains a central challenge in catalysis due to the high activation barriers of C–H bonds and the thermodynamic favorability of complete oxidation. Palladium oxide (PdO), particularly its (101) facet, is known for its high reactivity in alkane oxidation, which is attributed to its coordinatively unsaturated palladium (Pd) and O atoms. In this study, we investigate the effect of silver (Ag) incorporation on the oxidation behavior of propane over PdO(101) using temperature-programmed reaction spectroscopy (TPRS) under controlled conditions. While pristine PdO(101) exhibits complete oxidation of propane with CO₂ and H₂O desorption at high temperatures (approximately 475 K), Ag incorporation induces a new CO₂ desorption peak at significantly lower temperatures (approximately 330 K). This shift is attributed to the formation of new active sites at the Ag–PdO(101) interface. Quantitative analysis reveals that low-temperature activity correlates with Ag coverage, while overall CO₂ production decreases, suggesting a redistribution of reactivity rather than an increase in active surface area. Activation energy estimations using the Redhead method confirm that C–H bond activation becomes more facile at the interface, with a 46 kJ/mol reduction compared to pristine PdO(101). These findings demonstrate that incorporating a less reactive metal such as Ag into PdO surfaces not only modifies the reaction energetics but also enables the design of bimetallic catalysts with improved selectivity for partial oxidation reactions.

Chemistry↗
NASA NTRS1973

The activation energy for creep of columbium /niobium/.

The activation energy for creep of nominally pure columbium (niobium) was determined in the temperature range from 0.4 to 0.75 T sub M by measuring strain rate changes induced by temperature shifts at constant stress. A peak in the activation energy vs temperature curve was found with a maximum value of 160 kcal/mole. A pretest heat treatment of 3000 F for 30 min resulted in even higher values of activation energy (greater than 600 kcal/mole) in this temperature range. The activation energy for the heat-treated columbium (Nb) could not be determined near 0.5 T sub M because of unusual creep curves involving negligible steady-state creep rates and failure at less than 5% creep strain. It is suggested that the anomalous activation energy values and the unusual creep behavior in this temperature range are caused by dynamic strain aging involving substitutional atom impurities and that this type of strain aging may be in part responsible for the scatter in previously reported values of activation energy for creep of columbium (Nb) near 0.5 T sub M.

Klein, M. J.↗
NASA NTRS1974

Flutter suppression and gust alleviation using active controls

The effects of active controls on the suppression of flutter and gust alleviation of two different types of subsonic aircraft (the Arava, twin turboprop STOL transport, and the Westwind twin-jet business transport) are investigated. The active controls are introduced in pairs which include, in any chosen wing strip, a leading-edge (LE) control and a trailing-edge (TE) control. Each control surface is allowed to be driven by a combined linear-rotational sensor system, located on the activated strip. The control law, which translates the sensor signals into control surface rotations, is based on the concept of aerodynamic energy. The results indicate the extreme effectiveness of the active systems in controlling flutter. A single system spanning 10% of the wing semispan made the Arava flutter-free, and a similar active system, for the Westwind aircraft, yielded a reduction of 75% in the maximum bending moment of the wing and a reduction of 90% in the acceleration of the cg of the aircraft. Results for simultaneous activation of several LE - TE systems are presented. Further work needed to bring the investigation to completion is also discussed.

Nissim, E.↗