Search results for "Roca"
showing 10 items of 1893 documents
The electromagnetic and Proca fields revisited: A unified quantization
1997
Quantizing the electromagnetic field with a group formalism faces the difficulty of how to turn the traditional gauge transformation of the vector potential, Aμ(x) → Aμ(x) + ∂μφ(x), into a group law. In this paper, it is shown that the problem can be solved by looking at gauge transformations in a slightly different manner which, in addition, does not require introducing any BRST-like parameter. This gauge transformation does not appear explicitly in the group law of the symmetry but rather as the trajectories associated with generalized equations of motion generated by vector fields with null Noether invariants. In the new approach the parameters of the local group, U(1)(x, t), acquire dyn…
A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitrones with strained allenes
2017
Indexación: Scopus. The [3 + 2] cycloaddition (32CA) reaction of C-phenyl-N-tert-butylnitrone with 1,2-cyclohexadiene (CHDE), a strained allene, has been studied within Molecular Electron Density Theory (MEDT) at the DFT B3LYP/6-311G(d,p) computational level. This non-polar 32CA reaction, which takes place through a non-concerted two-stage one-step mechanism, proceeds with a moderate Gibbs free activation energy of 22.7 kcal mol-1, and presents low stereo- and regioselectivities. The reaction begins by the creation of a pseudoradical center at the central carbon of the strained allene with a relatively low energy cost, which immediately promotes the formation the first C-C single bond. This…
The hydration shell of myoglobin.
1992
The space in the unit cell of a metmyoglobin crystal not occupied by myoglobin atoms was filled with water using Monte Carlo calculations. Independent calculations with different amounts of water have been performed. Structure factors were calculated using the water coordinates thus obtained and the known coordinates of the myoglobin atoms. A comparison with experimental structure factors showed that both the low and the high resolution regime could be well reproduced with 814 Monte Carlo water molecules per unit cell with a B-value of 50 A2. The Monte Carlo water molecules yield a smaller standard R-value (0.166) than using a homogeneous electron density for the simulation of the crystal w…
Acoustic manipulation of electron-hole pairs in GaAs at room temperature
2004
We demonstrate the optically detected long-range (>100 μm) ambipolar transport of photogenerated electrons and holes at room temperature by surface acoustic waves (SAWs) in (In,Ga)As-based quantum well structures coupled to an optical microcavity. We also show the control of the propagation direction of the carriers by a switch composed of orthogonal SAW beams, which can be used as a basic control gate for information processing based on ambipolar transport.
T-wave alternans analysis improvement by means of curve alignment prior to distance calculation.
2007
Tracking of repolarization instabilities in the ECG, such as T-wave alternans (TWA), has become a popular non-invasive method to assess the vulnerability to malignant arrhythmic events. These instabilities are usually characterized by small amplitude changes and their measurement is difficult due to the presence of noise and artifacts. Several methods have been recently proposed to address this problem. Most of them are based on amplitude analysis of beat-to-beat alternation of the T wave. This paper describes a preprocessing stage intended to be used prior to amplitude analysis and aimed at improving the alignment between consecutive T waves. This increases the accuracy of the difference c…
A crystalline radical cation derived from Thiele’s hydrocarbon with redox range beyond 1 V
2021
Thiele’s hydrocarbon occupies a central role as an open-shell platform for new organic materials, however little is known about its redox behaviour. While recent synthetic approaches involving symmetrical carbene substitution of the CPh2 termini yield isolable neutral/dicationic analogues, the intervening radical cations are much more difficult to isolate, due to narrow compatible redox ranges (typically 1 V), permitting its isolation in crystalline form. Further single-electron oxidation affords borenium dication 12+, thereby establishing an organoboron redox system fully characterized in all three redox states. We perceive that this strategy can be extended to other transient organic rad…
Biomimetic oxidation of pyrene and related aromatic hydrocarbons. Unexpected electron accepting abilities of pyrenequinones
2014
We present a mild catalytic method to oxidize PAHs and, in particular, pyrene. The pyrenediones are much better electron acceptors than benzoquinone in the gas phase and present similar accepting abilities in solution.
La capilla de la Virgen de los Ojos Grandes de la Catedral de Lugo, un espacio de exaltación mariana
1991
LA CAPILLA DE LOS OJOS GRANDES DE LA CATEDRAL DE LUGO ES UNA OBRA CUMBRE DEL BARROCO GALLEGO. LA CAPILLA EN SU CONJUNTO, SI BIEN SU PROGRAMA NO HA SIDO TOTALMENTE DESCIFRADO, ES UN EJEMPLO DEL SENTIDO TOTALIZADOR DEL ESPACIO MARIANO QUE ES LA CAPILLA BARROCA, Y ES UNA EXALTACION DE LA VIRGEN MARIA. EN EL PUDIERON INFLUIR DOS LIBROS CON GRABADOS: FARFAN Y SU OBRA SOBRE LAS FIESTAS DE CANONIZACION DE FERNANDO III (SEVILLA, 1671), Y P. LAIGLESIA Y SU OBRA FLORES DE MIRAFLORES (BURGOS, 1659). (A.B.C./L.A.G.)
La imagen alegórico-emblemática de los lugares geográficos: el catafalco de María de Borbón.
1993
EL LENGUAJE ALEGORICO FUE MUY APROPIADO PARA REPRESENTAR LAS REALIDADES GEOGRAFICAS, NO TANTO DESDE EL PUNTO DE VISTA FISICO, SINO SOBRE TODO POR SUS CONTENIDOS MORALES Y SIMBOLICOS. FECHA CLAVE PARA LAS REPRESENTACIONES ALEGORICAS FUE EL AÑO 1593 EN EL QUE SE PUBLICA LA "ICONOLOGIA" DE CESARE RIPA. ESTA OBRA ES BASICA PARA LA INTERPRETACION DE LAS IMAGENES ALEGORICO-EMBLEMATICAS DE CARACTER GEOGRAFICO DEL CATAFALCO O MONUMENTO EFIMERO LEVANTADO EN 1689 EN LA CATEDRAL DE PALERMO CON MOTIVO DE LA MUERTE DE LA PRIMERA ESPOSA DE CARLOS II, MARIA LUISA DE ORLEANS; CATAFALCO DESCRITO POR FRAY FRANCISCO DE MONTALVO EN SU OBRA "NOTICIAS FUNEBRES DE LAS MAGESTUOSAS EXEQUIAS QUE HIZO LA FELICISIMA C…
Reciprocal Effects: Toward a Theory of Mass Media Effects on Decision Makers
2007
The article presents a framework for the analysis of reciprocal effects of mass media—in this case, their impact on subjects of media reports, especially on decision makers in areas of politics and business. It outlines a feedback model with three sets of variables referring to (1) media coverage and media as institutions, (2) awareness and processing of information, and (3) observable effects on subjects and others.The article presents several theories that explain effects on decision makers and illustrate the relevance of this approach with empirical data from a broad range of quantitative studies. In the final section, theoretical and methodological problems of such an approach are discu…