Search NASA⌕ Search

SEARCH · Search NASA

Results for “CA activity”

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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Composite Analysis Solid Waste Release Data Reduction of Activity Flux from Waste Sites to the Vadose Zone for Baseline Assessment

This environmental calculation file (ECF) describes the data reduction methodology for the solid waste release datasets generated by the Composite Analysis Solid Waste Release (CASWR) model (CP-62766, Model Package Report: Composite Analysis Solid Waste Release Model [CASWR Model]) and documents the resulting reduced datasets for the updated Composite Analysis (CA) baseline assessment. This ECF is in support of the updated Hanford Site CA. The purpose of the updated Hanford Site CA is to provide an estimate of the cumulative radiological impacts from active and planned low-level radioactive waste disposals and other potentially interacting radioactive waste disposal sources that will remain following Hanford Site closure. The vadose zone modeling activities associated with the CA includes solid waste forms as contaminant sources. To support the modeling of solid waste transport from the vadose zone to the groundwater at the Hanford Site, the CASWR model was designed to generate deterministic radionuclide release rates for the Hanford Site Central Plateau solid waste disposal sites. The complete CASWR model-generated dataset for the CA Baseline Assessment consists of 2,378,831 sets of time and release rates (1,073,869 sets for the 200 East Area and 1,304,962 sets for the 200 West Area), representing a course of the simulation from year 1953 to year 12,069, 16 radiological contaminants of potential concern (COPCs), and 237 solid waste sources as documented in ECFHANFORD- 19-0112, Solid Waste Release Calculations for the Composite Analysis Baseline Assessment. For several of the STOMP vadose zone models, the number of release rate data pairs required for release at all waste sites would exceed the limitations imposed by the STOMP modelling software package used to simulate contaminant transport through the vadose zone. As a result, a data reduction of the CASWR dataset is required prior to its use as a source input for the CA vadose zone modeling activities.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

A highly oxygen reduction reaction active and CO 2 durable high-entropy cathode for solid oxide fuel cells

One big obstacle for the oxygen reduction reaction (ORR) electrode in solid oxide fuel cells (SOFCs) is the poor reaction activity and fast degradations caused by CO 2 poisoning. Here, in this study, we report our design of an active A-site Ca-rich high-entropy Pr 0.1875 Ba 0.1875 Sr 0.1875 La 0.1875 Ca 0.25 CoO 3-δ (PBSLC 25 C) electrode, guided by the O p-band theory. Here, when applied as a cathode in solid oxide fuel cells (SOFCs), it demonstrates high ORR activity and excellent CO 2 tolerance under realistic operating conditions. Ni-YSZ-based anode-supported cells with PBSLC 25 C cathodes demonstrate excellent peak power densities of 1.14 W cm -2 , 1.04 W cm -2 , and 0.77 W cm -2 in the air with 1%, 5%, and 10% CO 2 , respectively, at 750 °C. The engineered high-entropy PBSLC 25 C effectively diminishes the CO 2 poisoning effect and maintains active surfaces for fast oxygen exchange, as confirmed by the cell durability test in air containing CO 2 (5 and 10 vol%), Raman spectroscopy, and density functional theory calculations.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2004

Cloning and Characterization of an alpha-amylase Gene from the Hyperthermophilic Archaeon Thermococcus Thioreducens

The gene encoding an extracellular alpha-amylase, TTA, from the hyperthermophilic archaeon Thermococcus thioreducens was cloned and expressed in Escherichia coli. Primary structural analysis revealed high similarity with other a-amylases from the Thermococcus and Pyrococcus genera, as well as the four highly conserved regions typical for a-amylases. The 1374 bp gene encodes a protein of 457 amino acids, of which 435 constitute the mature protein preceded by a 22 amino acid signal peptide. The molecular weight of the purified recombinant enzyme was estimated to be 43 kDa by denaturing gel electrophoresis. Maximal enzymatic activity of recombinant TTA was observed at 90 C and pH 5.5 in the absence of exogenous Ca(2+), and the enzyme was considerably stable even after incubation at 90 C for 2 hours. The thermostability at 90 and 102 C was enhanced in the presence of 5 mM Ca(2+). The extraordinarily high specific activity (about 7.4 x 10(exp 3) U/mg protein at 90 C, pH 5.5 with soluble starch as substrate) together with its low pH optimum makes this enzyme an interesting candidate for starch processing applications.

Bernhardsdotter, Eva C. M. J.↗
NASA NTRS2004

Cloning and Characterization of an Alpha-amylase Gene from the Hyperthermophilic Archaeon Thermococcus Thioreducens

The gene encoding an extracellular a-amylase, TTA, from the hyperthermophilic archaeon Thermococcus thioreducens was cloned and expressed in Escherichia coli. Primary structural analysis revealed high similarity with other a-amylases from the Thermococcus and Pyrococcus genera, as well as the four highly conserved regions typical for a-amylases. The 1374 bp gene encodes a protein of 457 amino acids, of which 435 constitute the mature protein preceded by a 22 amino acid signal peptide. The molecular weight of the purified recombinant enzyme was estimated to be 43 kDa by denaturing gel electrophoresis. Maximal enzymatic activity of recombinant TTA was observed at 90 C and pH 5.5 in the absence of exogenous Ca(2+), and the enzyme was considerably stable even after incubation at 90 C for 2 hours. The thermostability at 90 and 102 C was enhanced in the presence of 5 mM Ca(2+). The extraordinarily high specific activity (about 7.4 x 10(exp 3) U/mg protein at 90 C, pH 5.5 with soluble starch as substrate) together with its low pH optimum makes this enzyme an interesting candidate for starch processing applications.

Bernhardsdotter, Eva C. M. J.↗
NASA NTRS1994

An Arg-Gly-Asp peptide stimulates Ca2+ efflux from osteoclast precursors through a novel mechanism

We examined the effect of a peptide containing the Arg-Gly-Asp (RGD) sequence on 45Ca2+ efflux from osteoclast precursors. 45Ca(2+)-loaded osteoclast precursors were treated with GRGDSP (170 microM) for 10 min after 30 min of basal perfusion with a bicarbonate-containing buffer. GRGDSP significantly increased fractional efflux of Ca2+ from treated cells compared with vehicle-treated cells (P < 0.01) or cells treated with up to 200 micrograms/ml of a control peptide containing GRGESP. The effect of RGD was sustained for 15 min after the peptide was removed from the perfusate, but control levels of Ca2+ efflux returned by 1 h. The Ca2+ efflux effect of GRGDSP was most likely due to activation of the plasma membrane Ca(2+)-adenosinetriphosphatase (Ca(2+)-ATPase) pump, as indicated by its inhibition with vanadate and a calmodulin antagonist, N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide, and the absence of an effect of Na+/Ca2+ exchange inhibition. An inhibitor of cyclic nucleotide-dependent protein kinases, N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (0.1 mM), failed to inhibit GRGDSP-stimulated Ca2+ efflux. However, genistein and herbimycin A, inhibitors of protein-tyrosine kinases, blocked Ca2+ efflux stimulated by GRGDSP. The results indicate that RGD sequences of matrix proteins may stimulate Ca2+ efflux from osteoclasts through activation of protein-tyrosine kinases and suggest that GRGDSP-stimulated Ca2+ efflux is mediated via the plasma membrane Ca(2+)-ATPase.

NASA Discipline Musculoskeletal↗
DOE OSTI2025

Diffusion of acceptor dopants in monoclinic 𝛽−Ga 2⁢ O 3

𝛽−Ga 2 ⁢O 3 is a promising material for next-generation power electronics because of its ultrawide band gap and high critical breakdown voltage. However, realizing its full potential requires precise control over dopant incorporation and stability. In this work, we use first-principles calculations to systematically assess the diffusion behavior of eight potential deep-level substitutional acceptors (Au, Ca, Co, Cu, Fe, Mg, Mn, and Ni) in 𝛽−Ga 2 ⁢O 3 . We consider two key diffusion mechanisms: (i) interstitial diffusion under nonequilibrium conditions relevant to ion implantation, and (ii) trap-limited diffusion (TLD) under near-equilibrium thermal annealing conditions. Our results reveal a strong diffusion anisotropy along the 𝑏 and 𝑐 axes, with dopant behavior governed by competition between diffusion and incorporation (or dissociation) activation energies. Under interstitial diffusion, Ca$^{2+}_{i}$ and Mg$^{2+}_{i}$ show the most favorable combination of low migration and incorporation barriers, making them promising candidates for efficient doping along the 𝑏 and 𝑐 axes, respectively. In contrast, Au$^{+}_{i}$ diffuses readily, but exhibits an incorporation barrier that exceeds 5 eV, rendering it ineffective as a dopant. From a thermal stability perspective, Co$^{2+}_{i}$ shows poor activation but high diffusion barriers, which may suppress undesirable migration at elevated temperatures. Under trap-limited diffusion, the dissociation of dopant-host complexes controls mobility. Mg$^{2+}_{i}$ again emerges as a leading candidate, exhibiting the lowest dissociation barriers along both axes, whereas Co$^{2+}_{i}$ and Fe$^{2+}_{i}$ display the highest barriers, suggesting improved dopant retention under thermal stress. In conclusion, our findings guide dopant selection by balancing activation and thermal stability, essential for robust semi-insulating substrates.

Defects↗
NASA NTRS1986

UBV photometry of ten southern hemisphere active-chromosphere stars

High-precision UBV photometry of ten southern hemisphere active-chromosphere stars with strong Ca II H and K and/or H-alpha emission has been obtained. Eight of these stars showed variability during June 1985. Complete or partial light curves are presented for the stars, and these data, as well as mean V magnitudes and colors, are compared with the results of other investigators. In a number of cases, significant changes in photometric amplitude are found, which may serve to track the formation and evolution of active regions on these stars.

Bopp, Bernard W.↗
DOE OSTI2021

Portlandite solubility and Ca2+ activity in presence of gluconate and hexitols

The current paper investigates the impact of gluconate, D-sorbitol, d-mannitol and D-galactitol on calcium speciation at high pH values by i) solubility measurements of portlandite (Ca(OH){sub 2}) and ii) potentiometric titration measurements of calcium salt solutions. Thermodynamic modelling was used to fit the chemical activities of Ca{sup 2+} and OH{sup −} ions and thus to determine the strength and kind of the different Ca-organic-hydroxide complexes. The strength of complex formation with Ca{sup 2+} decreases in the order gluconate ≫ sorbitol > mannitol > galactitol, which follows the same order as sorption on portlandite. Heteropolynuclear gluconate complexes with calcium and hydroxide dominate the Ca-speciation in the presence of portlandite, while for sorbitol ternary CaSorbOH{sup +} complexes were dominant under alkaline conditions. We expect that these results will help in better understanding the influence of gluconate and hexitols on the hydration of alite and Portland cement.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Selective posttranslational inhibition of Ca V β 1 -associated voltage-dependent calcium channels with a functionalized nanobody

Ca 2+ influx through high-voltage-activated calcium channels (HVACCs) controls diverse cellular functions. A critical feature enabling a singular signal, Ca 2+ influx, to mediate disparate functions is diversity of HVACC pore-forming α1 and auxiliary Ca V β 1 –Ca V β 4 subunits. Selective Ca V α 1 blockers have enabled deciphering their unique physiological roles. By contrast, the capacity to post-translationally inhibit HVACCs based on Ca V β isoform is non-existent. Conventional gene knockout/shRNA approaches do not adequately address this deficit owing to subunit reshuffling and partially overlapping functions of Ca V β isoforms. Here, we identify a nanobody (nb.E8) that selectively binds Ca V β 1 SH3 domain and inhibits Ca V β 1 -associated HVACCs by reducing channel surface density, decreasing open probability, and speeding inactivation. Functionalizing nb.E8 with Nedd4L HECT domain yielded Chisel-1 which eliminated current through Ca V β 1 -reconstituted Ca V 1/Ca V 2 and native Ca V 1.1 channels in skeletal muscle, strongly suppressed depolarization-evoked Ca 2+ influx and excitation-transcription coupling in hippocampal neurons, but was inert against Ca V β 2 -associated Ca V 1.2 in cardiomyocytes. The results introduce an original method for probing distinctive functions of ion channel auxiliary subunit isoforms, reveal additional dimensions of Ca V β 1 signaling in neurons, and describe a genetically-encoded HVACC inhibitor with unique properties.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1989

Relations between the photospheric magnetic field and the emission from the outer atmospheres of cool stars. I - The solar Ca II K line core emission

Observations of a solar active region complex and its surroundings are used to establish a quantitative relation between the Ca II K line core intensity and magnetic flux density. The Ca II K line core intensity is transformed to a Ca II H + K line core flux density to facilitate a comparison of solar and stellar data. A new absolute calibration for the Mount Wilson Ca II H + K fluxes for G-type dwarfs is derived. The minimum Ca II K flux, found in the centers of supergranulation cells in quiet regions on the sun, is identical to the minimum flux that is observed for solar-type stars. An expression is presented for the nonlinear trend between the Ca II H + K line core excess flux density and the absolute value of the magnetic flux density. Models that explain the nonlinearity of the mean trend and the large intrinsic scatter about it are discussed. The solar data define a relation that is similar to the relation between stellar hemisphere-average magnetic flux densities and Ca II H + K excess flux densities.

Schrijver, C. J.↗
NASA NTRS1993

Evolution in vitro: analysis of a lineage of ribozymes

Background: Catalytic RNAs, or ribozymes, possessing both a genotype and a phenotype, are ideal molecules for evolution experiments in vitro. A large, heterogeneous pool of RNAs can be subjected to multiple rounds of selection, amplification and mutation, leading to the development of variants that have some desired phenotype. Such experiments allow the investigator to correlate specific genetic changes with quantifiable alterations of the catalytic properties of the RNA. In addition, patterns of evolutionary change can be discerned through a detailed examination of the genotypic composition of the evolving RNA population. Results: Beginning with a pool of 10(13) variants of the Tetrahymena ribozyme, we carried out in vitro evolution experiments that led to the generation of ribozymes with the ability to cleave an RNA substrate in the presence of Ca2+ ions, an activity that does not exist for the wild-type molecule. Over the course of 12 generations, a seven-error variant emerged that has substantial Ca(2+)-dependent RNA-cleavage activity. Advantageous mutations increased in frequency in the population according to three distinct dynamics--logarithmic, linear and transient. Through a comparative analysis of 31 individual variants, we infer how certain mutations influence the catalytic properties of the ribozyme. Conclusions: In vitro evolution experiments make it possible to elucidate important aspects of both evolutionary biology and structural biochemistry on a reasonable short time scale.

Non-NASA Center↗
NASA NTRS2002

The plasma membrane-associated NADH oxidase of spinach leaves responds to blue light

The plasma membrane-associated NADH oxidase (NOX) of spinach leaf disks is characterized by oscillations in activity with a regular period length of ca. 24 min. Within a single population of plants exposed to light at the same time, NOX activities of all plants function synchronously. Exposure of plants transferred from darkness to blue light (495 nm, 2 min, 50 micromoles m-2 s-1) resulted in a complex response pattern but with a new maximum in the rate of NOX activity 36 (24+12) min after illumination and then with maxima in the rate of NOX activity every 24 min thereafter. Transient maxima in NOX activity were observed as well after 9.3 + /- 1.4 and 20.7 +/- 2.1 min. The blue light response differed from the response to red (650 nm, 10 min, 50 micromoles m-2 s-1) or white light where activity maxima were initiated 12 min after the light exposure followed by maxima every 24 min thereafter. Green or yellow light was ineffective. The light response was independent of the time in the 24-min NOX cycle when the light was given. The net effects of blue and red light were ultimately the same with a new maximum in the rate of NOX activity at 12+24=36 min (and every 24 min thereafter), but the mechanisms appear to be distinct.

NASA Discipline Cell Biology↗
DOE OSTI2025

2,4,6-Triphenylpyridinium-Substituted Neutral Nickel Catalysts: Ethylene Polymerization, Influence of Activator, Catalyst Decomposition, and End-Group Analysis

The reactivity of 2,4,6-triphenylpyridinium-substituted nickel(II)-salicyliminato catalysts in ethylene polymerization has been explored. Here, the known complex 6a equipped with a 2,6-diisopropylphenyl group affords polyethylene with M n = 10-12 kDa at 19 ⁰C, while 8a possessing the bulkier 2,6-diphenylphenyl moiety gives polymer with M n = 270-310 kDa. The stability of catalyst 6a depends on the borane activator. If B(C 6 F 5 ) 3 is employed, enhanced stability is observed compared with using 3H 2 O·B(C 6 F 5 ) 3 activator. Catalyst 6a decomposes forming a hydroxyl-bridged dimer 14 which may be reac-tivated, albeit inefficiently, by excess borane activator. Polymer formed by 6a contains ca. 3-6% of 2-trifluoromethylphenyl, pentafluorophenyl, and 3,5-bis(trifluoromethyl)phenyl end groups combined. The pentafluoro-phenyl end group originates from reaction of 6a with borane activator, and from reactivation of hydroxyl-bridged dimer 14. 3,5-Bis(trifluoromethyl)phenyl end groups are likely formed in a reaction sequence initiated by protonation of one aryl group in NaBArF which creates B[C 6 H 3 (CF 3 ) 2 ] 3 . The triarylborane can then react with 6a or 14 transferring the 3,5-bis(trifluoromethyl)phenyl group to nickel.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

An investigation of the physical and chemical changes of Pd nanoparticles on carbon supports in response to the release of hydrogen from aqueous formate solutions

Palladium nanoparticles on carbon supports (Pd/C) are effective for catalyzing hydrogen release from aqueous formate solutions but typically suffer from a gradual decrease of activity. This study finds two primary factors influencing activity: (i) the number of available surface Pd sites, and (ii) metal-support interactions which depend on the nature of the C support. We propose that the Pd/C catalyst is structure insensitive and undergoes Ostwald ripening to yield an active ‘conditioned’ catalyst with dispersion plateauing between ca. 15–20 %. Contrary to earlier studies, in-situ XANES experiments show that PdO is not an active catalyst for formate dehydrogenation. Calcination of Pd/C before dehydrogenation increases the catalytic activity which suggests a beneficial, albeit temporary, modification of the metal support interaction. N-containing supports minimize nanoparticle growth and also increase activity through a metal-support interaction. In conclusion, these findings advance our understanding of catalyst evolution and stability in formate dehydrogenation systems.

Formate dehydrogenation↗
NASA NTRS1990

Partial purification and characterization of a Ca(2+)-dependent protein kinase from the green alga, Dunaliella salina

A calcium-dependent protein kinase was partially purified and characterized from the green alga Dunaliella salina. The enzyme was activated at free Ca2+ concentrations above 10(-7) molar. and half-maximal activation was at about 3 x 10(-7) molar. The optimum pH for its Ca(2+)-dependent activity was 7.5. The addition of various phospholipids and diolein had no effects on enzyme activity and did not alter the sensitivity of the enzyme toward Ca2+. The enzyme was inhibited by calmodulin antagonists, N-(6-aminohexyl)-1-naphthalene sulfonamide and N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide in a dose-dependent manner while the protein kinase C inhibitor, sphingosine, had little effect on enzyme activity up to 800 micromolar. Immunoassay showed some calmodulin was present in the kinase preparations. However, it is unlikely the kinase was calmodulin regulated, since it still showed stimulation by Ca2+ in gel assays after being electrophoretically separated from calmodulin by two different methods. This gel method of detection of the enzyme indicated that a protein band with an apparent molecular weight of 40,000 showed protein kinase activity at each one of the several steps in the purification procedure. Gel assay analysis also showed that after native gel isoelectric focusing the partially purified kinase preparations had two bands with calcium-dependent activity, at isoelectric points 6.7 and 7.1. By molecular weight, by isoelectric point, and by a comparative immunoassay, the Dunaliella kinase appears to differ from at least some of the calcium-dependent, but calmodulin and phospholipid independent kinases described from higher plants.

Non-NASA Center↗
DOE OSTI2024

Multivariate Bayesian Optimization of CoO Nanoparticles for CO 2 Hydrogenation Catalysis

The hydrogenation of CO 2 holds promise for transforming the production of renewable fuels and chemicals. However, the challenge lies in developing robust and selective catalysts for this process. Transition metal oxide catalysts, particularly cobalt oxide, have shown potential for CO 2 hydrogenation, with performance heavily reliant on crystal phase and morphology. Achieving precise control over these catalyst attributes through colloidal nanoparticle synthesis could pave the way for catalyst and process advancement. Yet, navigating the complexities of colloidal nanoparticle syntheses, governed by numerous input variables, poses a significant challenge in systematically controlling resultant catalyst features. We present a multivariate Bayesian optimization, coupled with a data-driven classifier, to map the synthetic design space for colloidal CoO nanoparticles and simultaneously optimize them for multiple catalytically relevant features within a target crystalline phase. The optimized experimental conditions yielded small, phase-pure rock salt CoO nanoparticles of uniform size and shape. These optimized nanoparticles were then supported on SiO 2 and assessed for thermocatalytic CO 2 hydrogenation against larger, polydisperse CoO nanoparticles on SiO 2 and a conventionally prepared catalyst. The optimized CoO/SiO 2 catalyst consistently exhibited higher activity and CH 4 selectivity (ca. 98%) across various pretreatment reduction temperatures as compared to the other catalysts. This remarkable performance was attributed to particle stability and consistent H* surface coverage, even after undergoing the highest temperature reduction, achieving a more stable catalytic species that resists sintering and carbon occlusion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1984

The sun as a star - 1982 June 14-August 13

During a 60-day period in the summer of 1982, a joint observing project between the High Altitude Observatory and the University of Hawaii was undertaken to collect a set of solar photospheric, chromospheric, and coronal data. From these data, the relationships between quantities recognized to be related to solar activity are specified. The amplitude of rotational modulation of the diagnostic parameters derived for the full disk was approximately equal to the modulation observed over an entire solar cycle. Those integrated solar data have been used as diagnostics of generalized stellar activity. A relationship between the Ca II line K flux and total inferred coronal mass of the sun existed during this observation period, and this fact leads to the hypothesis that ca II flux modulation in other stars may be used to infer stellar coronal conditions.

Fisher, R.↗