Search results for "Spect"
showing 10 items of 28650 documents
Combined Spectroscopic and TD-DFT Analysis to Elucidate Substituent and Acidochromic Effects in Organic Dyes: A Case Study on Amino- versus Nitro-Sub…
2020
Made available in DSpace on 2020-12-12T01:33:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 A combined spectroscopic and TD-DFT case study was performed, to identify a robust method to calculate the complex near UV/Vis absorption spectra of various amino- vs. nitro-substituted 2,4-diphenylquinolines, which vary strongly under neutral and successively acidic conditions. For this, different DFT functionals were tested for geometry optimization and the TD part to calculate the neutral and different protonated species in a fast screening approach, i. e. using single point calculations in an implicit solvent. Offset-corrected M06HF, hitherto only applied to polymers, was identif…
Desarrollo y evaluación de metodologías de microextracción para el análisis de volúmenes pequeños de muestra
2022
El empleo de técnicas de microextracción ha permitido el desarrollo de métodos analíticos de elevada sensibilidad. Además, ha conseguido reducir el empleo de disolventes orgánicos y otros compuestos tóxicos, permitiendo así trabajar acorde con los principios de la denominada Química Analítica ‘Verde’ en general (Green Analytical Chemistry, GAC) y, en particular, en la etapa de preparación de la muestra (Green Sample Preparation, GSP). No obstante, la miniaturización de estas técnicas, en ocasiones, descuida la miniaturización del volumen de muestra, a pesar de las múltiples ventajas que esta aporta, como son la reducción, todavía mayor, de volúmenes de disolvente, cantidad de sorbente y de …
Desarrollo de metodologías sostenibles de análisis
2017
Uno de los retos actuales en la Química Analítica reside en el desarrollo de metodologías analíticas sostenibles que respeten los principios planteados por la Química Verde, de manera su impacto sobre el entorno sea mínimo. Para conseguir este objetivo se han establecido diferentes estrategias o líneas de investigación. En primer lugar, las técnicas de microextracción están aportando numerosas ventajas, aunque todavía presentan algunas limitaciones. Por consiguiente, resulta necesario desarrollar técnicas que automaticen la etapa relativa al pretratamiento de la muestra con el fin de disminuir tanto el tiempo de análisis como la manipulación de la muestra. En segundo lugar, y atendiendo a l…
An Endemic Plant of the Mediterranean Area: Phytochemical Characterization of Strawberry Tree (Arbutus unedo L.) Fruits Extracts at Different Ripenin…
2022
This work focused on the extraction, quantification, and characterization of bioactive compounds of Arbutus unedo L. fruits, comparing the results obtained from the different ripening states. Extractions were performed by different methods (such as maceration extraction and ultrasonic extraction) and food grade solvents (aqueous and hydroalcoholic solvents) in each of the all ripening states (four states considered, associated with four different colors, i.e., green, yellow, orange, and red). The presence of (poly)phenols was quantified and characterized, and scavenging activity was determined by the Folin–Ciocâlteu reagent and the DPPH method, respectively. The content of bioactive compoun…
Theoretical investigation of paramagnetic group 13 diazabutadiene radicals: insights into the prediction and interpretation of EPR spectroscopy param…
2006
The electronic structures and the spin density distributions of the group 13 1,4-diaza(1,3)butadiene (DAB) radicals [(R-DAB)2M]˙, [(R-DAB)MX2]˙ and {[(R-DAB)MX]2}˙˙ (M = Al, Ga, In; X = F, Cl, Br, I; R = H, Me, tBu, Ph) are studied using density functional theory at both non-relativistic and relativistic levels of theory. The calculations demonstrate that all systems share a qualitatively similar electronic structure and are primarily ligand centred π-radicals. The calculated metal, nitrogen and hydrogen hyperfine couplings are found to be independent of the identity of the R-group and the halogen atom. They are, however, dependent on the geometry and oxidation state of the metal centre. Bo…
Theoretical Investigation of Paramagnetic Diazabutadiene Gallium(III)−Pnictogen Complexes: Insights into the Interpretation and Simulation of Electro…
2005
The electronic structures and the spin density distributions of the paramagnetic gallium 1,4-diaza(1,3)butadiene (DAB) model systems {(tBu-DAB)Ga(I)[Pn(SiH3)2]}• and the related dipnictogen species {(tBu-DAB)Ga[Pn(SiH3)2]2}• (Pn = N, P, As) were studied using density functional theory. The calculations demonstrate that all systems share a qualitatively similar electronic structure and are primarily ligand-centered π-radicals. The calculated electron paramagnetic resonance (EPR) hyperfine coupling constants (HFCCs) for these model systems were optimized using iterative methods and were used to create accurate spectral simulations of the parent radicals {(tBu-DAB)Ga(I)[Pn(SiMe3)2]}• (Pn = N, …
Transport and extraction of radioactive ions stopped in superfluid helium
2003
A new approach to convert a high energy beam to a low energy one, which is essential for the next generation radioactive ion beam facilities, has been proposed and tested at Jyvaskyla, Finland. An open Ra-223 alpha-decay-recoil source has been used to produce radioactive ions in superfluid helium. The alpha spectra demonstrate that the recoiling Rn-219 ions have been extracted out of liquid helium. This first observation of the extraction of heavy positive ions across the superfluid helium surface was possible thanks to the high sensitivity of radioactivity detection. An efficiency of 36% was obtained for the ion extraction out of liquid helium. (C) 2003 Elsevier Science B.V. All rights res…
Use of fragmentation beams at LNS with CHIMERA detector
2012
The recent intensity upgrade of the LNS fragmentation beam is discussed. The available beams, the tagging procedures and details on the beam quality are reported. The experimental program started with the CHIMERA detector using such beams is also discussed with preliminary results and future perspectives. © Owned by the authors, 2012.
Exploring a large dataset : typical behavior of UHF signal propagation
2020
Radioverkon suunnittelua ja käyttöä varten täytyy radio aaltojen eteneminen ymmärtää hyvin. Tässä tutkimuksessa tutustutaan laajaan mittausaineistoon hetkellisiä tehoja maanlaajuisesta UHF verkosta. Spektrianalyysillä todettiin mitatussa tehossa olevan jaksollista vaihtelua taajuuksilla kerran ja kahdesti päivässä. Myös nopeampaa vaihtelua välillä 0:1 mHz ja 1:4 mHz todettiin 34% yhteyksistä. Hierarkisella ryhmittelyllä etsittiin tyypilliset mittausten arvojakaumat. Saaduissa arvojakaumien ryhmissä oli eri levyisiä vasemmalle tai oikealle vinoja tai symmetrisiä jakaumia. The design and operation of radio networks requires good understanding of radio propagation. This study explores a datase…