Perturbing open cavities: Anomalous resonance frequency shifts in a hybrid cavity-nanoantenna system

The influence of a small perturbation on a cavity mode plays an important role in fields like optical sensing, cavity quantum electrodynamics and cavity optomechanics. Typically, the resulting cavity frequency shift directly relates to the polarizability of the perturbation. Here we demonstrate that particles perturbing a radiating cavity can induce strong frequency shifts that are opposite to, and even exceed, the effects based on the particles' polarizability. A full electrodynamic theory reveals that these anomalous results rely on a non-trivial phase relation between cavity and nanoparticle radiation, allowing back-action via the radiation continuum. In addition, an intuitive model based on coupled mode theory is presented that relates the phenomenon to retardation. Because of the ubiquity of dissipation, we expect these findings to benefit the understanding and engineering of a wide class of systems.Comment: 15 pages, 12 figure

Dark states in the light-harvesting complex 2 revealed by two-dimensional electronic spectroscopy

Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines the selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. We suggest that Nature has used the unavoidable charge transfer processes that occur when LH pigments are concentrated to enhance and direct the flow of energy

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference

Application of optimal control theory to inverse simulation of car handling

The application of Optimal Control Theory to time-optimal inverse simulation of car handling was investigated. Time-optimal inverse simulation of car handling involves the calculation of driver actions required to perform specified manoeuvres, in as short a time as possible. Driver actions consist of time-histories of front wheel steer rate and longitudinal force. Optimal time-histories of these quantities were calculated using the Gradient method after formulating the problem as one of optimal control. Simulation results are presented for two different cars performing similar lane-changes. These results show significant differences in necessary driver actions for different cars and demonstrate the suitability of the approach taken. [Author abstract; 9 Refs; In English

Application of optimal control theory to inverse simulation of car handling

The application of Optimal Control Theory to time-optimal inverse simulation of car handling was investigated. Time-optimal inverse simulation of car handling involves the calculation of driver actions required to perform specified manoeuvres, in as short a time as possible. Driver actions consist of time-histories of front wheel steer rate and longitudinal force. Optimal time-histories of these quantities were calculated using the Gradient method after formulating the problem as one of optimal control. Simulation results are presented for two different cars performing similar lane-changes. These results show significant differences in necessary driver actions for different cars and demonstrate the suitability of the approach taken. [Author abstract; 9 Refs; In English

Metallic seed nanolayers for enhanced nucleation of nanocrystalline diamond thin films

The enhancement of the nucleation and subsequent growth of nanocrystalline diamond (NCD) films with a submicrometer thickness control on silicon substrates is demonstrated by using a sputter deposition of six different metallic (Cr, Mo, Nb, Ti, V and W) seed nanolayers. The effectiveness of altered surface morphology and surface chemistry is discussed. We show that the number density of nanodiamond particles embedded on the nanorough metallic surfaces after an ultrasonic seeding step together with the dynamic surface chemistry during hot-filament chemical vapor deposition of diamond determine the nucleation kinetics, microstructure and surface topography of the NCD films. Overall, the smoothest NCD layer (root-mean-square roughness 10 nm) was obtained with the highest seed density of diamond nanoparticles anchored to the metallic (W) surface. In particular, the rapid carbide-forming metals Mo, Nb and W showed the highest number density of diamond crystallites formed during the NCD nucleation stage, which resulted in dense, uniform and very smooth NCD films. Much rougher NCD films (17-37 nm) were obtained on the Cr, Ti, and V nanolayers that did not form carbides rapidly. Importantly, the carbon phase purity of the grown NCD films remains unaffected by the presence of different metallic seed nanolayers. Furthermore, we have assessed that the metallic nanolayer surface morphology does not play a relevant role in the enhancement of the seeding step. © 2013 American Chemical Society.J.G.B. thanks the Executive Research Agency of the European Union for funding under the Marie Curie Grant “NANODIA” (272448). This work has been partially supported by Comunidad Autónoma de Madrid (Project No. S2009/PPQ-1642, AVANSENS) and Ministerio de Economiá y Competitividad (FIS2012-38866-C05-05).Peer Reviewe