Search results for "element"
showing 10 items of 13601 documents
Problemas multiplicativos relacionados con la división de fracciones : un estudio sobre su enseñanza y aprendizaje
2013
Los estudiantes tienen dificultades para asociar el enunciado de un problema multiplicativo con la operación que permite resolverlo; esta investigación identifica los tipos de problemas multiplicativos que los estudiantes reconocen como de división de fracciones. Mediante el análisis histórico-epistemológico de textos de enseñanza sobre tres épocas históricas y ocho períodos diferentes, se obtiene un listado de variables de enseñanza (algoritmos, sentidos de uso de fracción y de división de fracciones, representaciones, problemas), así como los valores de dichas variables. Se localizan en los textos consultados algunas reglas particulares y seis algoritmos generales, cuyo predominio ha vari…
Effects of an incremental maximal endurance exercise stress-induced cortisol on cognitive performance
2019
Exercise; Cognitive functions; Cortisol Ejercicio físico; Funciones cognitivas; Cortisol Exercici físic; Funcions cognitives; Cortisol Objectives: It can be hypothesized that cognitive performance decreases after fatigue protocol when it coincides with the maximum peak of cortisol. The first aim of this study was to elucidate the effects of a single bout of high intensity exercise on behavioural (i.e., attention and memory) and physiological (i.e., salivary cortisol) responses. The second objective was to evaluate the effect of the performance of the cognitive tasks on cortisol levels. Methods: Thirty-four physically active men (at least 5 days/week of physical activity practice) 38.11 (1.5…
A TWO-COMPONENT MANTLE EXTENDING FROM MT. ETNA TO HYBLEAN PLATEAU (EASTERN SICILY) AS INFERRED BY AN INTEGRATED APPROACH WITH NOBLE GASES, TRACE ELEM…
2012
Humusvielu izcelsmes – īpašību izpēte izmantojot to multiparametru raksturojumu
2019
Humusvielu izcelsmes-īpašību izpēte izmantojot to multiparametru raksturojumu. Upska K., zinātniskais vadītājs prof., Dr. habil. chem. Kļaviņš M. prof. Dr.chem. Vīksna A. un, Kursa darbs, 62 lappuses, 22 attēli, 11 tabulas, 37 literatūras avoti, 2 pielikumi. Latviešu valodā. Bakalaura darbā tika apkopota zinātniskā literatūra par humusvielām, to izcelsmi, funkcijām biosfērā, ražošanas, izdalīšanas un pētīšanas metodēm. Tika noteikts humusvielu organiskais un neorganiskais elementsastāvs, kas sniedz informāciju par rūpnieciski ražotu humusvielas produktu kvalitāti. Izmantojot UV-Vis un FTIR molekulārās absorbcijas metodi tika uzņemti un analizēti humusvielu absorbcijas spektri. Izmantojot fl…
V2O5 nanowires with an intrinsic peroxidase-like activity
2010
V2O5 nanowires exhibit an intrinsic catalytic activity towards classical peroxidase substrates such as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 3,3,5,5,-tetramethylbenzdine (TMB) in the presence of H2O2. These V2O5 nanowires show an optimum reactivity at a pH of 4.0 and the catalytic activity is dependent on the concentration. The Michaelis-Menten kinetics of the ABTS oxidation over these nanowires reveals a behavior similar to that of their natural vanadium-dependent haloperoxidase (V-HPO) counterparts. The V2O5 nanowires mediate the oxidation of ABTS in the presence of H2O2 with a turnover frequency (k(cat)) of 2.5 x 10(3) s(-1). The K-M values of the V2O5 nanowire…
Considering syntrophic acetate oxidation and ionic strength improves the performance of models for food waste anaerobic digestion.
2021
Current mechanistic anaerobic digestion (AD) models cannot accurately represent the underlying processes occurring during food waste (FW) AD. This work presents an update of the Anaerobic Digestion Model no. 1 (ADM1) to provide accurate estimations of free ammonia concentrations and related inhibition thresholds, and model syntrophic acetate oxidation as acetate-consuming pathway. A modified Davies equation predicted NH3 concentrations and pH more accurately, and better estimated associated inhibitory limits. Sensitivity analysis results showed the importance of accurate disintegration kinetics and volumetric mass transfer coefficients, as well as volatile fatty acids (VFAs) and hydrogen up…
Pyrithione-based ruthenium complexes as inhibitors of aldo-keto reductase 1C enzymes and anticancer agents.
2016
Four ruthenium complexes of clinically used zinc ionophore pyrithione and its oxygen analog 2-hydroxypyridine N-oxide were prepared and evaluated as inhibitors of enzymes of the aldo–keto reductase subfamily 1C (AKR1C). A kinetic study assisted with docking simulations showed a mixed type of inhibition consisting of a fast reversible and a slow irreversible step in the case of both organometallic compounds 1A and 1B. Both compounds also showed a remarkable selectivity towards AKR1C1 and AKR1C3 which are targets for breast cancer drug design. The organoruthenium complex of ligand pyrithione as well as pyrithione itself also displayed toxicity on the hormone-dependent MCF-7 breast cancer cell…
Firefly Algorithm for Structural Optimization Using ANSYS
2021
In the mid-1980s, several metaheuristic methods began to be developed for solving a very large class of computational problems with the aim of obtaining more robust and efficient procedures. Among them, many metaheuristic methods use bio-inspired intelligent algorithms. In recent years, these methods are becoming increasingly important and they can be used in various subject areas for solving complex problems. Firefly Algorithm is a nature-inspired optimization algorithm proposed by Yang to solve multimodal optimization problems. In particular, the method is inspired by the nature of fireflies to emit a light signal to attract other individuals of this species. In this work, a numerical stu…
Mikrozaļumu ķīmiskais sastāvs atkarībā no fotoperioda audzēšanas laikā
2020
Literatūras apskatā ir aprakstīts augu ķīmiskais sastāvs un gaismas ietekme uz to. Apkopotas paraugu sagatavošanas un analīzes metodes. Darbā ir veikta četru dažādu ģiņšu mikrozaļumu diedzēšana pie 4, 8 un 12 stundu ilgiem fotoperiodiem. Spektrometriski ir noteikta kopējā hlorofila un karotenoīdu koncentrācija, kopējā polifenolu koncentrācija un antiradikālā aktivitāte augos. Noteica mikroelementu un makroelementu sastāvu augos ar ICP-MS metodi. Noteica brīvo aminoskābju koncentrāciju augos ar HPLC-MS metodi. Iegūtie dati salīdzināti savā starpā, kā arī tika salīdzināts ķīmiskais sastāvs atkarībā no fotoperioda.
Revised rates for the stellar triple-alpha process from measurement of C-12 nuclear resonances
2005
4 pages, 3 figures.-- PMID: 15650733 [PubMed].