Immunity of intersubband polaritons to inhomogeneous broadening

We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous effects originating from the presence of multiple quantum wells (MQWs). In a series of samples that exhibit mid-infrared ISB absorption transitions with broadenings varying by a factor of 5 (from 4 meV to 20meV), we have observed polariton linewidths always lying in the 4 - 7 meV range only. We have experimentally verified the dominantly inhomogeneous origin of the broadening of the ISB transition, and that the linewidth reduction effect of the polariton modes persists up to room-temperature. This immunity to inhomogeneous broadening is a direct consequence of the coupling of the large number of ISB oscillators to a single photonic mode. It is a precious tool to gauge the natural linewidth of the ISB plasmon , that is otherwise masked in such MQWs system , and is also beneficial in view of perspective applications such as intersubband polariton lasers

Theory of coherent optical nonlinearities of intersubband transitions in semiconductor quantum wells

We theoretically study the coherent nonlinear response of electrons confined in semiconductor quantum wells under the effect of an electromagnetic radiation close to resonance with an intersubband transition. Our approach is based on the time-dependent Schr\"odinger-Poisson equation stemming from a Hartree description of Coulomb-interacting electrons. This equation is solved by standard numerical tools and the results are interpreted in terms of approximated analytical formulas. For growing intensity, we observe a redshift of the effective resonance frequency due to the reduction of the electric dipole moment and the corresponding suppression of the depolarization shift. The competition between coherent nonlinearities and incoherent saturation effects is discussed. The strength of the resulting optical nonlinearity is estimated across different frequency ranges from mid-IR to THz with an eye to ongoing experiments on Bose-Einstein condensation of intersubband polaritons and to the speculative exploration of quantum optical phenomena such as single-photon emission in the mid-IR and THz windows

RPANDA: an R package for macroevolutionary analyses on phylogenetic trees

A number of approaches for studying macroevolution using phylogenetic trees have been developed in the last few years. Here, we present RPANDA, an R package that implements model‐free and model‐based phylogenetic comparative methods for macroevolutionary analyses. The model‐free approaches implemented in RPANDA are recently developed approaches stemming from graph theory that allow summarizing the information contained in phylogenetic trees, computing distances between trees, and clustering them accordingly. They also allow identifying distinct branching patterns within single trees. RPANDA also implements likelihood‐based models for fitting various diversification models to phylogenetic trees. It includes birth–death models with i) constant, ii) time‐dependent and iii) environmental‐dependent speciation and extinction rates. It also includes models with equilibrium diversity derived from the coalescent process, as well as a likelihood‐based inference framework to fit the individual‐based model of Speciation by Genetic Differentiation, which is an extension of Hubbell's neutral theory of biodiversity. RPANDA can be used to (i) characterize trees by plotting their spectral density profiles (ii) compare trees and cluster them according to their similarities, (iii) identify and plot distinct branching patterns within trees, (iv) compare the fit of alternative diversification models to phylogenetic trees, (v) estimate rates of speciation and extinction, (vi) estimate and plot how these rates have varied with time and environmental variables and (vii) deduce and plot estimates of species richness through geological time. RPANDA provides investigators with a set of tools for exploring patterns in phylogenetic trees and fitting various models to these trees, thereby contributing to the ongoing development of phylogenetics in the life sciences

Pseudomonas cannabina pv. cannabina pv. nov., and Pseudomonas cannabina pv. alisalensis (Cintas Koike and Bull, 2000) comb. nov., are members of the emended species Pseudomonas cannabina (ex Šutič & Dowson 1959) Gardan, Shafik, Belouin, Brosch, Grimont

Sequence similarity in the 16S rDNA gene confirmed that crucifer pathogen Pseudomonas syringae pv. alisalensis belongs to P. syringae sensu lato. In reciprocal DNA/DNA hybridization experiments, DNA relatedness was high (69–100%) between P. syringae pv. alisalensis strains and the type strain of P. cannabina (genomospecies 9). In contrast, DNA relatedness was low (below 48%) between P. syringae pv. alisalensis and reference strains from the remaining genomospecies of P. syringae including the type strain of P. syringae and reference strain of genomospecies 3 (P. syringae pv. tomato) although the well-known crucifer pathogen, P. syringae pv. maculicola, also belongs to genomospecies 3. Additional evidence that P. syringae pv. alisalensis belongs to P. cannabina was sequence similarity in five gene fragments used in multilocus sequence typing, as well as similar rep-PCR patterns when using the BOX-A1R primers. The description of P. cannabina has been emended to include P. syringae pv. alisalensis. Host range testing demonstrated that P. syringae pv. alisalensis strains, originally isolated from broccoli, broccoli raab or arugula, were not pathogenic on Cannabis sativa (family Cannabinaceae). Additionally, P. cannabina strains, originally isolated from the C. sativa were not pathogenic on broccoli raab or oat while P. syringae pv. alisalensis strains were pathogenic on these hosts. Distinct host ranges for these two groups indicate that P. cannabina emend. consists of at least two distinct pathovars, P. cannabina pv. cannabina pv. nov., and P. cannabina pv. alisalensis comb. nov. Pseudomonas syringae pv. maculicola strain CFBP 1637 is a member of P. cannabina

Optically Implemented Broadband Blueshift Switch in the Terahertz Regime

Cataloged from PDF version of article.We experimentally demonstrate, for the first time, an optically implemented blueshift tunable metamaterial in the terahertz (THz) regime. The design implies two potential resonance states, and the photoconductive semiconductor (silicon) settled in the critical region plays the role of intermediary for switching the resonator from mode 1 to mode 2. The observed tuning range of the fabricated device is as high as 26% (from 0.76 THz to 0.96 THz) through optical control to silicon. The realization of broadband blueshift tunable metamaterial offers opportunities for achieving switchable metamaterials with simultaneous redshift and blueshift tunability and cascade tunable devices. Our experimental approach is compatible with semiconductor technologies and can be used for other applications in the THz regime

Monolithic echo-less photoconductive switches for high-resolution terahertz time-domain spectroscopy

Interdigitated photoconductive (IPC) switches are convenient sources and detectors for terahertz (THz) time domain spectroscopy. However, reflection of the emitted or detected radiation within the device substrate can lead to echoes that inherently limits the spectroscopic resolution achievable. In this work, we design and realize low-temperature-grown-GaAs (LT-GaAs) IPC switches for THz pulse generation and detection that suppresses such unwanted echoes. This is realized through a monolithic geometry of an IPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector, and coupling it to an echo-less IPC source, enables echo-free THz-TDS and high-resolution spectroscopy, with a resolution limited only by the temporal length of the measurement governed by the mechanical delay line used

Room temperature strong light-matter coupling in three dimensional terahertz meta-atoms

We demonstrate strong light-matter coupling in three dimensional terahertz meta-atoms at room temperature. The intersubband transition of semiconductor quantum wells with a parabolic energy potential is strongly coupled to the confined circuital mode of three-dimensional split-ring metal-semiconductor-metal resonators that have an extreme sub-wavelength volume (λ/10). The frequency of these lumped-element resonators is controlled by the size and shape of the external antenna, while the interaction volume remains constant. This allows the resonance frequency to be swept across the intersubband transition and the anti-crossing characteristic of the strong light-matter coupling regime to be observed. The Rabi splitting, which is twice the Rabi frequency (2ΩRabi), amounts to 20% of the bare transition at room temperature, and it increases to 28% at low-temperatur

Coupled-cavity terahertz quantum cascade lasers for single mode operation

We demonstrate the operation of coupled-cavity terahertz frequency quantum-cascade lasers composed of two sub-cavities separated by an air gap realized by optical lithography and dry etching. This geometry allows stable, single mode operation with typical side mode suppression ratios in the 30-40 dB range. We employ a transfer matrix method to model the mode selection mechanism. The obtained results are in good agreement with the measurements and allow prediction of the operating frequency

Guidance on the environmental risk assessment of plant pests

The European Food Safety Authority (EFSA) requested the Panel on Plant Health to develop a methodology for assessing the environmental risks posed by harmful organisms that may enter, establish and spread in the European Union. To do so, the Panel first reviewed the methods for assessing the environmental risks of plant pests that have previously been used in pest risk assessment. The limitations identified by the review led the Panel to define the new methodology for environmental risk assessment which is described in this guidance document. The guidance is primarily addressed to the EFSA PLH Panel and has been conceived as an enhancement of the relevant parts of the “Guidance on a harmonised framework for pest risk assessment and the identification and evaluation of pest risk management options by EFSA”. Emphasizing the importance of assessing the consequences on both the structural (biodiversity) and the functional (ecosystem services) aspects of the environment, this new approach includes methods for assessing both aspects for the first time in a pest risk assessment scheme. A list of questions has been developed for the assessor to evaluate the consequences for structural biodiversity and for ecosystem services in the current area of invasion and in the risk assessment area. To ensure the consistency and transparency of the assessment, a rating system has also been developed based on a probabilistic approach with an evaluation of the degree of uncertainty. Finally, an overview of the available risk reduction options for pests in natural environments is presented, minimum data requirements are described, and a glossary to support the common understanding of the principles of this opinion is provided

Scientific opinion on a quantitative pathway analysis of the likelihood of Tilletia indica M. introduction into EU with importation of US wheat

The European Commission requested EFSA to provide a scientific opinion on the USDA APHIS quantitative pathway analysis on likelihood of Karnal bunt introduction with importation of US wheat for grain into EU and desert durum wheat for grain into Italy. EFSA was also requested to indicate whether the US bunted kernel standard would provide equivalent protection against introduction of Tilletia indica into EU, compared to the existing EU import requirement. The Panel on Plant Health reviewed pathway scenarios, model and parameters and found several shortcomings regarding model equations and parameter values, particularly a lack of scientific evidence for the infection threshold. Simulations were computed, for importations of US wheat into EU and desert durum wheat into Italy, based on original model and an updated model with revised parameter values. Model output was teliospores number per hectare on soil surface of each EU country. Simulated teliospores numbers entering EU were lower with the updated than with the original model. These results showed a high uncertainty, underestimated with the original model, over the number of teliospores entering each EU country. Sensitivity analysis showed several key parameters (proportion of bunted kernels in Arizona regulated counties, number of Arizona positive hectares and number of teliospores per bunted kernel) strongly influencing number of teliospores entering the EU. In addition, high sensitivity indices were obtained with the updated wheat model for several parameters related to EU country characteristics. Further research is needed to refine parameter values, to reduce uncertainty and to determine relationship between teliospores number on soil surface and number of bunted kernels resulting from infection of a wheat plant. The Panel concluded that the US bunted kernel standard does not provide a level of protection equivalent to EU requirements and that such level of protection could only be warranted by measures which include testing at harvest and before shipment to detect T. indica teliospores