Effects of photon reabsorption phenomena in confocal micro-photoluminescence measurements in crystalline silicon

Confocal micro-photoluminescence (PL) spectroscopy has become a powerful characterization technique for studying novel photovoltaic (PV) materials and structures at the micrometer level. In this work, we present a comprehensive study about the effects and implications of photon reabsorption phenomena on confocal micro-PL measurements in crystalline silicon (c-Si), the workhorse material of the PV industry. First, supported by theoretical calculations, we show that the level of reabsorption is intrinsically linked to the selected experimental parameters, i.e., focusing lens, pinhole aperture, and excitation wavelength, as they define the spatial extension of the confocal detection volume, and therefore, the effective photon traveling distance before collection. Second, we also show that certain sample properties such as the reflectance and/or the surface recombination velocity can also have a relevant impact on reabsorption. Due to the direct relationship between the reabsorption level and the spectral line shape of the resulting PL emission signal, reabsorption phenomena play a paramount role in certain types of micro-PL measurements. This is demonstrated by means of two practical and current examples studied using confocal PL, namely, the estimation of doping densities in c-Si and the study of back-surface and/or back-contacted Si devices such as interdigitated back contact solar cells, where reabsorption processes should be taken into account for the proper interpretation and quantification of the obtained PL data.Peer ReviewedPostprint (published version

Methods to Monitor and Quantify Autophagy in the Social Amoeba Dictyostelium discoideum

Autophagy is a eukaryotic catabolic pathway that degrades and recycles cellular components to maintain homeostasis. It can target protein aggregates, superfluous biomolecular complexes, dysfunctional and damaged organelles, as well as pathogenic intracellular microbes. Autophagy is a dynamic process in which the different stages from initiation to final degradation of cargo are finely regulated. Therefore, the study of this process requires the use of a palette of techniques, which are continuously evolving and whose interpretation is not trivial. Here, we present the social amoeba Dictyostelium discoideum as a relevant model to study autophagy. Several methods have been developed based on the tracking and observation of autophagosomes by microscopy, analysis of changes in expression of autophagy genes and proteins, and examination of the autophagic flux with various techniques. In this review, we discuss the pros and cons of the currently available techniques to assess autophagy in this organism

A low-pass filter with automatic frequency tuning for a bluetooth receiver

A third-order Gm-C Chebyshev low-pass filter with high linearity and automatic frequency programmability has been designed. The filter is intended to be used as a channel-select filter for a zero-IF Bluetooth receiver. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. The filter bandwidth is 0.5 MHz and the overall scheme dissipates 1.1 mA from a 1.8-V supply. The third-order intermodulation (IM3) distortion of the filter for a 1Vpp two-tone signal centered at 350 kHz is -67dB.Ministerio de Ciencia y Tecnología TEC2007-67460-C03-02

Mechanical behavior of tungsten-vanadium-lanthana alloys as function of temperature

The mechanical behavior of three tungsten (W) alloys with vanadium (V) and lanthana (La2O3) additions (W–4%V, W–1%La2O3, W–4%V–1%La2O3) processed by hot isostatic pressing (HIP) have been compared with pure-W to analyze the influence of the dopants. Mechanical characterization was performed by three point bending (TPB) tests in an oxidizing air atmosphere and temperature range between 77 (immersion tests in liquid nitrogen) and 1273 K, through which the fracture toughness, flexural strength, and yield strength as function of temperature were obtained. Results show that the V and La2O3 additions improve the mechanical properties and oxidation behavior, respectively. Furthermore, a synergistic effect of both dopants results in an extraordinary increase of the flexure strength, fracture toughness and resistance to oxidation compared to pure-W, especially at higher temperatures. In addition, a new experimental method was developed to obtain a very small notch tip radius (around 5–7 μm) and much more similar to a crack through the use of a new machined notch. The fracture toughness results were lower than those obtained with traditional machining of the notch, which can be explained with electron microscopy, observations of deformation in the rear part of the notch tip. Finally, scanning electron microscopy (SEM) examination of the microstructure and fracture surfaces was used to determine and analyze the relationship between the macroscopic mechanical properties and the micromechanisms of failure involved, depending on the temperature and the dispersion of the alloy

KLaF4 nanocrystallisation in oxyfluoride glass-ceramics

Nanocrystallisation of the cubic and hexagonal polymorphs of KLaF 4 in a 70SiO2-7Al2O3-16K 2O-7LaF3 (mol%) glass has been achieved by heat treatment above the glass transition temperature. For treatment at 580°C, only the cubic structure crystallises, with a maximum crystallite size of ~9 nm. At higher temperatures, crystallisation of the hexagonal structure also takes place. The crystallisation process has been analysed using several thermal and structural techniques and is revealed to occur from a constant number of nuclei. The formation of a viscous barrier which inhibits further crystal growth and limits the crystal size to the nanometric range is observed. The title materials doped with lanthanide ions may be good candidates for optical applications

KLaF4 nanocrystallisation in oxyfluoride glass-ceramics

Nanocrystallisation of the cubic and hexagonal polymorphs of KLaF 4 in a 70SiO2-7Al2O3-16K 2O-7LaF3 (mol%) glass has been achieved by heat treatment above the glass transition temperature. For treatment at 580°C, only the cubic structure crystallises, with a maximum crystallite size of ~9 nm. At higher temperatures, crystallisation of the hexagonal structure also takes place. The crystallisation process has been analysed using several thermal and structural techniques and is revealed to occur from a constant number of nuclei. The formation of a viscous barrier which inhibits further crystal growth and limits the crystal size to the nanometric range is observed. The title materials doped with lanthanide ions may be good candidates for optical applications

The 8Li + 2H reaction studied in inverse kinematics at 3.15 MeV/nucleon using the REX-ISOLDE post-accelerator

The reaction 8Li + 2H has been studied in inverse kinematics at the incident energy of 3.15 MeV/nucleon, using the REX-ISOLDE post-accelerator. The reaction channels corresponding to (d,p), (d,d), and (d,t) reactions populating ground states and low-lying excited states in 7 -9Li have been identified and the related angular distributions extracted and compared with coupled-channels, distorted-wave Born approximation (DWBA), and coupled-reaction-channels calculations. For the inelastic and (d,t) channels we find that higher order effects are very important and hence one needs to go beyond the simple DWBA to extract reliable structure information from these processes.Ministerio de Ciencia e Innovación FPA2006-13807-C02-01 FPA2009-08848 FPA2009-07653 FPA2009-07387 FPA2010-17142Unión Europea RII3-EURONS 50606

Circadian rhythms regulate the environmental responses of net CO2 exchange in bean and cotton canopies

Studies on the dependence of the rates of ecosystem gas exchange on environmental parameters often rely on the up-scaling of leaf-level response curves ('bottom-up' approach), and/or the down-scaling of ecosystem fluxes ('top-down' approach), where one takes advantage of the natural diurnal covariation between the parameter of interest and photosynthesis rates. Partly independent from environmental variation, molecular circadian clocks drive ∼24 h oscillations in leaf-level photosynthesis, stomatal conductance and other physiological processes in plants under controlled laboratory conditions. If present and of sufficient magnitude at ecosystem scales, circadian regulation could lead to different results when using the bottom-up approach (where circadian regulation exerts a negligible influence over fluxes because the environment is modified rapidly) relative to the top-down approach (where circadian regulation could affect fluxes as it requires the passage of a few hours). Here we dissected the drivers of diurnal net CO2 exchange in canopies of an annual herb (bean) and of a perennial shrub (cotton) through a set of experimental manipulations to test for the importance of circadian regulation of net canopy CO2 exchange, relative to that of temperature and vapor pressure deficit, and to understand whether circadian regulation could affect the derivation of environmental flux dependencies. Contrary to conventional wisdom, we observed how circadian regulation exerted controls over net CO2 exchange that were of similar magnitude to the controls exerted by direct physiological responses to temperature and vapor pressure deficit. Diurnal patterns of net CO2 exchange could only be explained by considering effects of environmental responses combined with circadian effects. Consequently, we observed significantly different results when inferring the dependence of photosynthesis over temperature and vapor pressure deficit when using the top-down and the bottom up approaches.We remain indebted to E. Gerardeau, D. Dessauw, J. Jean, P. Prudent (Aïda CIRAD), J.-J. Drevon, C. Pernot (Eco&Sol INRA), B. Buatois, A. Rocheteau (CEFE CNRS), A. Pra, A. Mokhtar and the full Ecotron team, in particular C. Escape, for outstanding technical assistance during experiment set-up, plant cultivation and measurements. Earlier versions of the manuscript benefitted from comments by M. Dietze, B. Medlyn, R. Duursma and Y.-S. Lin. This study benefited from the CNRS human and technical resources allocated to the ECOTRONS Research Infrastructures as well as from the state allocation ‘Investissement d'Avenir’ ANR-11-INBS-0001, ExpeER Transnational Access program, Ramón y Cajal fellowships (RYC-2012-10970 to VRD and RYC-2008-02050 to JPF), the Erasmus Mundus Master Course Mediterranean Forestry and Natural Resources Management (MEDfOR) and internal grants from UWS-HIE to VRD and ZALF to AG. We thank the Associate Editor T. Vesala and two anonymous reviewers for their help to improve this manuscript

IKs Computational Modeling to Enforce the Investigation of D242N, a KV7.1 LQTS Mutation

A KCNQ1 mutation, D242N, was found in a pair of twins and characterized at the cellular level. To investigate whether and how the mutation causes the clinically observed lost adaptation to fast heart rate, we performed a computational study. Firstly, we identified a new I Ks model based on voltage clamp experimental data. Then we included this formulation in the human action potential model of O'Hara Rudy (ORd) and simulate d the effects of the mutation. We also included adrenergic stimulation to the action potential, since the basal adrenergic tone is likely to affect the influence of I Ks on QTc in vivo. Finally, we simulated the pseudo-ECG, taking into account the heterogeneity of the cardiac wall. At the basal rate (60bpm), the mutation had negligible effects for all cell types, whereas at the high rate (180bpm), with concomitant β-adrenergic stimulation (mimicking exercise conditions), the mutant AP failed to adapt its duration to the same extent as the wild-type AP (e.g. 281ms vs. 267ms in M cells), due to a smaller amount of I Ks current. Pseudo-ECG results show only a slight rate adaptation, and the simulated QTc was significantly prolonged from 387ms to 493ms, similar to experimental recordings