Photoinduced Dynamics with Constrained Vibrational Motion: FrozeNM Algorithm.

Ab initio molecular dynamics (AIMD) simulation, analyzed in terms of vibrational normal modes, is a widely used technique that facilitates understanding of complex structural motions and coupling between electronic and nuclear degrees of freedom. Usually, only a subset of vibrations is directly involved in the process of interest. The impact of these vibrations can be evaluated by performing AIMD simulations by selectively freezing certain motions. Herein, we present frozen normal mode (FrozeNM), a new algorithm to apply normal-mode constraints in AIMD simulations, as implemented in the nonadiabatic excited state molecular dynamics code. We further illustrate its capacity by analyzing the impact of normal-mode constraints on the photoinduced energy transfer between polyphenylene ethynylene dendrimer building blocks. Our results show that the electronic relaxation can be significantly slowed down by freezing a well-selected small subset of active normal modes characterized by their contributions in the direction of energy transfer. The application of these constraints reduces the nonadiabatic coupling between electronic excited states during the entire dynamical simulations. Furthermore, we validate reduced dimensionality models by freezing all the vibrations, except a few active modes. Altogether, we consider FrozeNM as a useful tool that can be broadly used to underpin the role of vibrational motion in a studied process and to formulate reduced models that describe essential physical phenomena.

Photoexcited energy relaxation and vibronic couplings in π-conjugated carbon nanorings.

Conjugated carbon nanorings exhibit unique photophysical properties that, combined with their tunable sizes and conformations, make them suitable for a variety of practical applications. These properties are intimately associated to their strained, bent and sterically hindered cyclic structures. Herein we perform a comparative analysis of the photoinduced dynamics in carbon nanorings composed of nine phenyl units([9]CPP) and nine naphthyl units ([9]CN) respectively. The sterically demanding naphthyl units lead to large dihedral angles between neighboring units. Nevertheless, the ultrafast electronic and vibrational energy relaxation and redistribution is found to be similar for both systems. We observe that vibronic couplings, introduced by nonadiabatic energy transfer between electronic excited states, ensure the intramolecular vibrational energy redistribution through specific vibrational modes. The comparative impact of the internal conversion process on the exciton spatial localization and intra-ring migration indicates that naphthyl units in [9]CN achieve more efficient but less dynamical self-trapping compared to that of phenyl units in [9]CPP. That is, during the photoinduced process, the exciton in [9]CN is more static and localized than the exciton in [9]CPP. The internal conversion processes take place through a specific set of middle- to high-frequency normal modes, which directly influence the spatial exciton redistribution during the internal conversion, self-trapping and intra-ring migration.

Invasión de viento sahariano y su impacto en la asistencia sanitaria urgente / Saharian wind invasion and impact on emergency health care

Objetivo: Evaluar la influencia que el polvo sahariano en suspensión ejerce sobre la demanda asistencial urgente. Método: Diseño: Estudio descriptivo longitudinal. Ámbito: Servicio de Urgencias de Hospital Universitario de 3er nivel. Sujetos: Todos los pacientes (n=705) mayores de 14 años que solicitaron asistencia urgente por patología médica y que estuvieron expuestos al polvo en suspensión; como grupo control, todos los pacientes (n=662) que la solicitaron en el mismo período del año anterior sin haber estado expuestos a dicho fenómeno atmosférico. Mediciones: La variable principal dependiente fue el diagnóstico del paciente al alta; edad y sexo eran las variables secundarias. Se realizó análisis de la distribución de frecuencias, tablas de contingencia y Chi-cuadrado con nivel de significación del 5 por ciento. Resultados: En días de polución la frecuencia de crisis asmática fue 8,9 por ciento, cerca de 10 veces más que en el grupo control (p<0,05). Tras dos días de exposición, la atención por broncopatía crónica reagudizada fue 1,5 veces mayor que en el período control (p<0.05). Durante el periodo estudiado, los trastornos de ansiedad y dolor torácico atípico fueron 5 y 7,4 veces más frecuentes, respectivamente (p<0,05). No se observó un aumento significativo de casos de cardiopatía isquémica. Conclusiones: La presencia de polvo sahariano en suspensión condiciona un aumento de la demanda asistencial urgente por patología respiratoria, trastornos de ansiedad y dolores torácicos atípicos. Deberían proponerse medidas para detección precoz e información a la población de riesgo sobre medidas preventivas (AU)