Simulations of the Kelvin-Helmholtz instability driven by coronal mass ejections in the turbulent corona

Recent high resolution AIA/SDO images show evidence of the development of the Kelvin-Helmholtz instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is inferred, both on the CME and on the background sides. However, the magnetic field component along the shear flow is not strong enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the criteria for the development of the instability are a-priori expected to differ from the laminar case. To study the evolution of the Kelvin-Helmholtz instability with a turbulent background, we perform three-dimensional simulations of the incompressible magnetohydrodynamic equations. The instability is driven by a velocity profile tangential to the CME-corona interface, which we simulate through a hyperbolic tangent profile. The turbulent background is generated by the application of a stationary stirring force. We compute the instability growth-rate for different values of the turbulence intensity, and find that the role of turbulence is to attenuate the growth. The fact that the Kelvin-Helmholtz instability is observed, sets an upper limit to the correlation length of the coronal background turbulence

Lepton-Flavor Violation with Non-universal Soft Terms

We study the lepton-flavor violation processes tau ->mu gamma and mu->e gamma in two different examples of models with non-universal soft breaking terms derived from strings. We show that the predictions are quite different from those of universal scenarios. Non-universal A-terms provide an interesting framework to enhance the supersymmetric contributions to CP violation effects. We observe that in the case of the lepton-flavor violation we study, the non-universality of the scalar masses enhances the branching ratios more significantly than the non-universality of the A-terms. We find that the current experimental bounds on these processes restrict both the parameter space of the models and the texture of the Yukawa couplings which predicts the lepton masses, providing at the same time an interesting experimental test for physics beyond the Standard Model.Comment: 15 pages, 6 figures minor change

Hot Carrier extraction with plasmonic broadband absorbers

Hot charge carrier extraction from metallic nanostructures is a very promising approach for applications in photo-catalysis, photovoltaics and photodetection. One limitation is that many metallic nanostructures support a single plasmon resonance thus restricting the light-to-charge-carrier activity to a spectral band. Here we demonstrate that a monolayer of plasmonic nanoparticles can be assembled on a multi-stack layered configuration to achieve broad-band, near-unit light absorption, which is spatially localised on the nanoparticle layer. We show that this enhanced light absorbance leads to $\sim$ 40-fold increases in the photon-to-electron conversion efficiency by the plasmonic nanostructures. We developed a model that successfully captures the essential physics of the plasmonic hot-electron charge generation and separation in these structures. This model also allowed us to establish that efficient hot carrier extraction is limited to spectral regions where the photons possessing energies higher than the Schottky junctions and the localised light absorption of the metal nanoparticles overlap.Comment: submitte

Direct frequency comb measurements of absolute optical frequencies and population transfer dynamics

A phase-stabilized femtosecond laser comb is directly used for high-resolution spectroscopy and absolute optical frequency measurements of one- and two-photon transitions in laser-cooled \rb atoms. Absolute atomic transition frequencies, such as the 5S$_{1/2}$ F=2 \ra 7S$_{1/2}$ F"=2 two-photon resonance measured at 788 794 768 921(44) kHz, are determined without \textit{a priori} knowledge about their values. Detailed dynamics of population transfer driven by a sequence of pulses are uncovered and taken into account for the measurement of the 5P states via resonantly enhanced two-photon transitions.Comment: 5 pages, 4 figures, submitte

Eternal Sunshine of the Solar Panel

The social dynamics of residential solar panel use within a theoretical population are studied using a compartmental model. In this study we consider three solar power options commonly available to consumers: the community block, leasing, and buying. In particular we are interested in studying how social influence affects the dynamics within these compartments. As a result of this research a threshold value is determined, beyond which solar panels persist in the population. In addition, as is standard in this type of study, we perform equilibrium analysis, as well as uncertainty and sensitivity analyses on the threshold value. We also perform uncertainty analysis on the population levels of each compartment. The analysis shows that social influence plays an important role in the adoption of residential solar panels

Divergent modulation of nociception by glutamatergic and GABAergic neuronal subpopulations in the periaqueductal gray

The ventrolateral periaqueductal gray (vlPAG) constitutes a major descending pain modulatory system and is a crucial site for opioid-induced analgesia. A number of previous studies have demonstrated that glutamate and GABA play critical opposing roles in nociceptive processing in the vlPAG. It has been suggested that glutamatergic neurotransmission exerts antinociceptive effects, whereas GABAergic neurotransmission exert pronociceptive effects on pain transmission, through descending pathways. The inability to exclusively manipulate subpopulations of neurons in the PAG has prevented direct testing of this hypothesis. Here, we demonstrate the different contributions of genetically defined glutamatergic and GABAergic vlPAG neurons in nociceptive processing by employing cell type-specific chemogenetic approaches in mice. Global chemogenetic manipulation of vlPAG neuronal activity suggests that vlPAG neural circuits exert tonic suppression of nociception, consistent with previous pharmacological and electrophysiological studies. However, selective modulation of GABAergic or glutamatergic neurons demonstrates an inverse regulation of nociceptive behaviors by these cell populations. Selective chemogenetic activation of glutamatergic neurons, or inhibition of GABAergic neurons, in vlPAG suppresses nociception. In contrast, inhibition of glutamatergic neurons, or activation of GABAergic neurons, in vlPAG facilitates nociception. Our findings provide direct experimental support for a model in which excitatory and inhibitory neurons in the PAG bidirectionally modulate nociception

On stratification control of the velocity fluctuations in sedimentation

International audienceWe have tested whether stratification can govern local velocity fluctuations in suspensions of sedimenting spheres. Comparison of the proposed scaling for local control of fluctuations by stratification to experimental data demonstrates that this mechanism cannot account for the reduction of the observed velocity fluctuations