Let’s Get This Show on the Road: Driverless Cars Have Arrived and It’s Time to Advance the Regulatory Framework

The potential benefits that driverless automobile technology will provide to the U.S. and its roadways are vast. Greatly enhanced safety of American citizens is chief among these benefits. Congressional and administrative support will be required if these benefits are to be completely realized by American society. However, lawmakers are dragging their feet on passing legislation that will allow driverless cars to hit the road in full force. This comment examines the legislative proposals put forth by the House of Representatives and Senate. It argues that the differences between the two versions are inconsequential and urges lawmakers to act in order to save American lives and keep pace with other nations

Bianisotropic Effective Parameters of Optical Metamagnetics and Negative-Index Materials

Approaches to the adequate homogenization of optical metamaterials are becoming more and more complex, primarily due to an increased understanding of the role of asymmetric electrical and magnetic responses, in addition to the nonlocal effects of the surrounding medium, even in the simplest case of plane-wave illumination. The current trend in developing such advanced homogenization descriptions often relies on utilizing bianisotropic models as a base on top of which novel optical characterization techniques can be built. In this paper, we first briefly review general principles for developing a bianisotropic homogenization approach. Second, we present several examples validating and illustrating our approach using single-period passive and active optical metamaterials. We also show that the substrate may have a significant effect on the bianisotropic characteristics of otherwise symmetric passive and active metamaterials

Numerical Modeling of Plasmonic Nanoantennas with Realistic 3D Roughness and Distortion

Nanostructured plasmonic metamaterials, including optical nanoantenna arrays, are important for advanced optical sensing and imaging applications including surface-enhanced fluorescence, chemiluminescence, and Raman scattering. Although designs typically use ideally smooth geometries, realistic nanoantennas have nonzero roughness, which typically results in a modified enhancement factor that should be involved in their design. Herein we aim to treat roughness by introducing a realistic roughened geometry into the finite element (FE) model. Even if the roughness does not result in significant loss, it does result in a spectral shift and inhomogeneous broadening of the resonance, which could be critical when fitting the FE simulations of plasmonic nanoantennas to experiments. Moreover, the proposed approach could be applied to any model, whether mechanical, acoustic, electromagnetic, thermal, etc, in order to simulate a given roughness-generated physical phenomenon

Simplified model for periodic nanoantennae: linear model and inverse design

We determine and use a minimal set of numerical simulations to create a simplified model for the spectral response of nanoantennae with respect to their geometric and modeling parameters. The simplified model is then used to rapidly obtain best-fit modeling parameters to match experimental results, accurately predict the spectral response for various geometries, and inversely design antennae to have a desired performance. This method is structure and model independent, and is applied here to both nanoantenna pair arrays and strips modeled using a 3D finite-element method and 2D spatial harmonic analysis, respectively. Typical numerical simulations may need hours per model, whereas this method, after the initial time to obtain a baseline set of simulations, requires only seconds to analyze and generate spectra for new geometries

Engineered nonlinear materials using gold nanoantenna array

Gold dipole nanoantennas embedded in an organic molecular film provide strong local electromagnetic fields to enhance both the nonlinear refractive index (n(2)) and two-photon absorption (2PA) of the molecules. An enhancement of 53x for 2PA and 140x for nonlinear refraction is observed for BDPAS (4,4'-bis(diphenylamino) stilbene) at 600 nm with only 3.7% of gold volume fraction. The complex value of the third-order susceptibility enhancement results in a sign change of n(2) for the effective composite material relative to the pure BDPAS film. This complex nature of the enhancement and the tunability of the nanoantenna resonance allow for engineering the effective nonlinear response of the composite film8119Agências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

The Origin Recognition Complex Interacts with a Subset of Metabolic Genes Tightly Linked to Origins of Replication

The origin recognition complex (ORC) marks chromosomal sites as replication origins and is essential for replication initiation. In yeast, ORC also binds to DNA elements called silencers, where its primary function is to recruit silent information regulator (SIR) proteins to establish transcriptional silencing. Indeed, silencers function poorly as chromosomal origins. Several genetic, molecular, and biochemical studies of HMR-E have led to a model proposing that when ORC becomes limiting in the cell (such as in the orc2-1 mutant) only sites that bind ORC tightly (such as HMR-E) remain fully occupied by ORC, while lower affinity sites, including many origins, lose ORC occupancy. Since HMR-E possessed a unique non-replication function, we reasoned that other tight sites might reveal novel functions for ORC on chromosomes. Therefore, we comprehensively determined ORC “affinity” genome-wide by performing an ORC ChIP–on–chip in ORC2 and orc2-1 strains. Here we describe a novel group of orc2-1–resistant ORC–interacting chromosomal sites (ORF–ORC sites) that did not function as replication origins or silencers. Instead, ORF–ORC sites were comprised of protein-coding regions of highly transcribed metabolic genes. In contrast to the ORC–silencer paradigm, transcriptional activation promoted ORC association with these genes. Remarkably, ORF–ORC genes were enriched in proximity to origins of replication and, in several instances, were transcriptionally regulated by these origins. Taken together, these results suggest a surprising connection among ORC, replication origins, and cellular metabolism

Optical metamaterials: Linear and nonlinear characterization and application to optical limiting

Recent developments in metamaterials, or nanostructured materials with engineered optical properties, enable the creation of previously impossible devices. Optical cloaks, superlenses, optical black holes, and more are now theoretically possible, but robust methods to characterize the linear and nonlinear optical properties of these materials are critical to the evaluation and development of devices. First, this work is concerned with the linear optical characterization of general sub-wavelength periodic metal-dielectric nanostructures - optical metamagnetics - capable of producing magnetic responses in the visible. Then, nonlinear characterization of a nanoantenna type metamaterial is examined in the context of the optimal design of a thin-film optical limiting device. Optical limiting, or the ability to maintain high low intensity transmission and yet significantly attenuate or ‘limit’ high intensity throughput, has a wide variety of applications, most significantly for sensor protection or protective eyeware. In this work, the high local fields present in plasmonically resonant metamaterials are used to enhance the nonlinear response of a dye, resulting in a higher nonlinear absorption relative to the incident intensity, and a significant increase in the ‘effective’ nonlinear absorption coefficient. This work provides a foundation of linear and nonlinear characterization tools applicable to all metamaterials, but which is focused on optical limiting optimization

Let’s Get This Show on the Road: Driverless Cars Have Arrived and It’s Time to Advance the Regulatory Framework

The potential benefits that driverless automobile technology will provide to the U.S. and its roadways are vast. Greatly enhanced safety of American citizens is chief among these benefits. Congressional and administrative support will be required if these benefits are to be completely realized by American society. However, lawmakers are dragging their feet on passing legislation that will allow driverless cars to hit the road in full force. This comment examines the legislative proposals put forth by the House of Representatives and Senate. It argues that the differences between the two versions are inconsequential and urges lawmakers to act in order to save American lives and keep pace with other nations

Optical Dispersion Models for Time-Domain Modeling of Metal-Dielectric Nanostructures

We discuss second-order complex Pade approximants which give a systematic approach to time-domain modeling of dispersive dielectric functions. These approximants, which also reduce to the classical Drude, Lorentz, Sellmeier, critical points and other models upon appropriate truncation, are used to compare frequency domain (FD) versus time-domain (TD) simulations of local optical responses and the transmission-reflection spectra for a plasmonic nanostructure. A comparison is also made using auxiliary differential equations (ADE), and second order recursive convolution (RC) formulations embedded in finite-difference, finite-volume, and finite-element time-domain solvers