Carrier transport properties in the vicinity of single seld-assembled quantum dots determined by low-voltage cathodoluminescence imaging

Abstract : We propose a method to investigate the carrier transport properties in the ultrathin wetting layer of a self-assembled quantum dot (QD) structure using low-voltage cathodoluminescence (CL) imaging. Measurements are performed on diluted InAs/InP QDs in order to spatially resolve them on CL images at temperature ranging from 5 to 300 K. The mean ambipolar diffusion length extracted from CL intensity profiles across different isolated bright spots is about 300 nm at 300 K. This gives an ambipolar carrier mobility of about 110 cm2/(V s)110 cm2/(V s). Temperature investigation reveals a maximum diffusion length near 120 K

Responses to Pheromones in a Complex Odor World: Sensory Processing and Behavior

Insects communicating with pheromones, be it sex- or aggregation pheromones, are confronted with an olfactory environment rich in a diversity of volatile organic compounds of which plants are the main releaser. Certain of these volatiles can represent behaviorally relevant information, such as indications about host- or non-host plants; others will provide essentially a rich odor background out of which the behaviorally relevant information needs to be extracted. In an attempt to disentangle mechanisms of pheromone communication in a rich olfactory environment, which might underlie interactions between intraspecific signals and a background, we will summarize recent literature on pheromone/plant volatile interactions. Starting from molecular mechanisms, describing the peripheral detection and central nervous integration of pheromone-plant volatile mixtures, we will end with behavioral output in response to such mixtures and its plasticity

Orbital Parameter Determination for Wide Stellar Binary Systems in the Age of Gaia

The orbits of binary stars and planets, particularly eccentricities and inclinations, encode the angular momentum within these systems. Within stellar multiple systems, the magnitude and (mis)alignment of angular momentum vectors among stars, disks, and planets probes the complex dynamical processes guiding their formation and evolution. The accuracy of the \textit{Gaia} catalog can be exploited to enable comparison of binary orbits with known planet or disk inclinations without costly long-term astrometric campaigns. We show that \textit{Gaia} astrometry can place meaningful limits on orbital elements in cases with reliable astrometry, and discuss metrics for assessing the reliability of \textit{Gaia} DR2 solutions for orbit fitting. We demonstrate our method by determining orbital elements for three systems (DS Tuc AB, GK/GI Tau, and Kepler-25/KOI-1803) using \textit{Gaia} astrometry alone. We show that DS Tuc AB's orbit is nearly aligned with the orbit of DS Tuc Ab, GK/GI Tau's orbit might be misaligned with their respective protoplanetary disks, and the Kepler-25/KOI-1803 orbit is not aligned with either component's transiting planetary system. We also demonstrate cases where \textit{Gaia} astrometry alone fails to provide useful constraints on orbital elements. To enable broader application of this technique, we introduce the python tool \texttt{lofti\_gaiaDR2} to allow users to easily determine orbital element posteriors.Comment: 18 pages, 10 figures, accepted for publication in Ap

Trends in recovery of mediterranean soil chemical properties and microbial activities after infrequent and frequent wildfires

Since the 1970s, increase in fire frequency has been observed in all European Mediterranean regions. The objectives of this study were (1) to determine the effects of wildfire frequency on the recovery at short- and long-term of soil chemical and microbial properties and (2) to identify the mechanisms underlying the recovery of these sites properties. Soils from 17 plots (Maures mountains range, Var, France) were classified into 5 wildfire regimes (i.e. not burned since at least 57 years ago, infrequently and frequently burned-with time since fire between 4 and 17 years). Soil samples from these plots were analysed for their nutrient content, chemical functions of soil organic matter (SOM) using FT-MIR spectroscopy and microbial mineralising activities. Our results showed that the frequent wildfire regime slowed down the recovery in the short term of SOM spectroscopic properties and nutrient availability. Both low quantity and low quality (i.e. high percentage of aromatic and phenolic organic forms) of soil organic matter were found to be related to soil microbial recovery at 4 years after frequent wildfires. The frequent wildfires improved the recovery in net nitrification and nitrate content, leading to an increase in catabolic evenness and a recovery in microbial C-substrate utilisation profiles between 4 and 17 years. However, frequent wildfires slowed down the recovery of hydrolytic enzyme pool (i.e. FDA hydrolases) and phenol oxidase activity, both involved in soil C cycling. Overall, our observations suggest that 4 fires in 50 years is a threshold beyond which soil quality may be endangered

Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

We study the ionization energy, electron affinity, and the \u3c0 \u2192 \u3c0- (1La) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO \u2192 LUMO one, which underlies the 1La excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in \u3c0-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral 1La excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account. \ua9 2015 AIP Publishing LLC