161 research outputs found
Design and investigation of surface addressable Photonic Crystal cavity confined band edge modes for quantum photonic devices
We propose to use a localized G-point slow Bloch mode in a 2D-Photonic Crystal (PC) membrane to realize an efficient surface emitting source. This device can be used as a quantum photonic device, e.g. a single photon source. The physical mechanisms to increase the Q/V factor and to improve the directivity of the PC microcavity rely on a fine tuning of the geometry in the three directions of space. The PC lateral mirrors are first engineered in order to optimize photons confinement. Then, the effect of a Bragg mirror below the 2DPC membrane is investigated in terms of out-of-plane leakages and far field emission pattern. This photonic heterostructure allows for a strong lateral confinement of photons, with a modal volume of a few (λ/n)3 and a Purcell factor up to 80, as calculated by two different numerical methods. We finally discuss the efficiency of the single photon source for different collection set-up. © 2011 Optical Society of America
Plant RNases T2, but not Dicer-like proteins, are major players of tRNA-derived fragments biogenesis
RNA fragments deriving from tRNAs (tRFs) exist in all branches of life and the repertoire of their biological functions regularly increases. Paradoxically, their biogenesis remains unclear. The human RNase A, Angiogenin, and the yeast RNase T2, Rny1p, generate long tRFs after cleavage in the anticodon region. The production of short tRFs after cleavage in the D or T regions is still enigmatic. Here, we show that the Arabidopsis Dicer-like proteins, DCL1-4, do not play a major role in the production of tRFs. Rather, we demonstrate that the Arabidopsis RNases T2, called RNS, are key players of both long and short tRFs biogenesis. Arabidopsis RNS show specific expression profiles. In particular, RNS1 and RNS3 are mainly found in the outer tissues of senescing seeds where they are the main endoribonucleases responsible of tRNA cleavage activity for tRFs production. In plants grown under phosphate starvation conditions, the induction of RNS1 is correlated with the accumulation of specific tRFs. Beyond plants, we also provide evidence that short tRFs can be produced by the yeast Rny1p and that, in vitro, human RNase T2 is also able to generate long and short tRFs. Our data suggest an evolutionary conserved feature of these enzymes in eukaryotes
Micrometer-Thin Crystalline-Silicon Solar Cells Integrating Numerically Optimized 2-D Photonic Crystals
A 2-D photonic crystal was integrated experimentally into a thin-film
crystalline-silicon solar cell of 1-{\mu}m thickness, after numerical
optimization maximizing light absorption in the active material. The photonic
crystal boosted the short-circuit current of the cell, but it also damaged its
open-circuit voltage and fill factor, which led to an overall decrease in
performances. Comparisons between modeled and actual optical behaviors of the
cell, and between ideal and actual morphologies, show the global robustness of
the nanostructure to experimental deviations, but its particular sensitivity to
the conformality of the top coatings and the spread in pattern dimensions,
which should not be neglected in the optical model. As for the electrical
behavior, the measured internal quantum efficiency shows the strong parasitic
absorptions from the transparent conductive oxide and from the back-reflector,
as well as the negative impact of the nanopattern on surface passivation. Our
exemplifying case, thus, illustrates and experimentally confirms two
recommendations for future integration of surface nanostructures for light
trapping purposes: 1) the necessity to optimize absorption not for the total
stack but for the single active material, and 2) the necessity to avoid damage
to the active material by pattern etching.Comment: Authors' postprint version - Editor's pdf published online on Nov.
Absorbing photonic crystals for thin film photovoltaics
The absorption of thin hydrogenated amorphous silicon layers can be
efficiently enhanced through a controlled periodic patterning. Light is trapped
through coupling with photonic Bloch modes of the periodic structures, which
act as an absorbing planar photonic crystal. We theoretically demonstrate this
absorption enhancement through one or two dimensional patterning, and show the
experimental feasibility through large area holographic patterning. Numerical
simulations show over 50% absorption enhancement over the part of the solar
spectrum comprised between 380 and 750nm. It is experimentally confirmed by
optical measurements performed on planar photonic crystals fabricated by laser
holography and reactive ion etching.Comment: 6 pages. SPIE Photonics Europe pape
(16) Psyche: A mesosiderite-like asteroid?
Asteroid (16) Psyche is the target of the NASA Psyche mission. It is
considered one of the few main-belt bodies that could be an exposed
proto-planetary metallic core and that would thus be related to iron
meteorites. Such an association is however challenged by both its near- and
mid-infrared spectral properties and the reported estimates of its density.
Here, we aim to refine the density of (16) Psyche to set further constraints on
its bulk composition and determine its potential meteoritic analog.
We observed (16) Psyche with ESO VLT/SPHERE/ZIMPOL as part of our large
program (ID 199.C-0074). We used the high angular resolution of these
observations to refine Psyche's three-dimensional (3D) shape model and
subsequently its density when combined with the most recent mass estimates. In
addition, we searched for potential companions around the asteroid. We derived
a bulk density of 3.99\,\,0.26\,gcm for Psyche. While such
density is incompatible at the 3-sigma level with any iron meteorites
(7.8\,gcm), it appears fully consistent with that of
stony-iron meteorites such as mesosiderites (density
4.25\,cm). In addition, we found no satellite in our images
and set an upper limit on the diameter of any non-detected satellite of
1460\,\,200}\,m at 150\,km from Psyche (0.2\%\,\,R, the
Hill radius) and 800\,\,200\,m at 2,000\,km (3\%\,\,).
Considering that the visible and near-infrared spectral properties of
mesosiderites are similar to those of Psyche, there is merit to a
long-published initial hypothesis that Psyche could be a plausible candidate
parent body for mesosiderites.Comment: 16 page
Collapse of the N=28 shell closure in Si
The energies of the excited states in very neutron-rich Si and
P have been measured using in-beam -ray spectroscopy from the
fragmentation of secondary beams of S at 39 A.MeV. The low 2
energy of Si, 770(19) keV, together with the level schemes of
P provide evidence for the disappearance of the Z=14 and N=28
spherical shell closures, which is ascribed mainly to the action of
proton-neutron tensor forces. New shell model calculations indicate that
Si is best described as a well deformed oblate rotor.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. let
Nucleic Acids Res
In plants, the voltage-dependent anion-selective channel (VDAC) is a major component of a pathway involved in transfer RNA (tRNA) translocation through the mitochondrial outer membrane. However, the way in which VDAC proteins interact with tRNAs is still unknown. Potato mitochondria contain two major mitochondrial VDAC proteins, VDAC34 and VDAC36. These two proteins, composed of a N-terminal α-helix and of 19 ÎČ-strands forming a ÎČ-barrel structure, share 75% sequence identity. Here, using both northwestern and gel shift experiments, we report that these two proteins interact differentially with nucleic acids. VDAC34 binds more efficiently with tRNAs or other nucleic acids than VDAC36. To further identify specific features and critical amino acids required for tRNA binding, 21 VDAC34 mutants were constructed and analyzed by northwestern. This allowed us to show that the ÎČ-barrel structure of VDAC34 and the first 50 amino acids that contain the α-helix are essential for RNA binding. Altogether the work shows that during evolution, plant mitochondrial VDAC proteins have diverged so as to interact differentially with nucleic acids, and this may reflect their involvement in various specialized biological functions
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High-speed optical mapping of heart and brain voltage activities in zebrafish larvae exposed to environmental contaminants
Data availability: Data will be made available on request.Supplementary data are available online at https://www.sciencedirect.com/science/article/pii/S235218642300192X?via%3Dihub#appSB .Copyright © 2023 The Author(s). Environmental contaminants represent a poorly understood ecotoxicological and health risk. Here, we advanced a high-speed optical mapping (OM) technique to non-invasively track voltage dynamics in living zebrafish larvaeâs heart and brain and investigate the effects of selected pesticides.
OM allowed high resolution (
17x) and fast acquisition (100 to 200 frames/s) of the voltage signal generated in the heart and brain after immersion of the zebrafish larvae in a voltage-sensitive dye. First, we used varying temperatures (20 °C to 25 °C) to test the adequacy of OM in capturing cardiac and brain voltage changes. Then, we tested the effects of glyphosate or a selected pesticide cocktail (2 to 120 h post-fertilization), accounting for their environmental thresholds and mimicking high-level exposure. Glyphosate (0.1 and 1000
g/L) and the pesticide cocktail (0.1 and 10
g/L) did not alter cardiac activity, except for a trend increase in heart rate variability at high glyphosate dose. Fourier transform (FT) analyses indicated that glyphosate reduced the abundance of low-amplitude voltage activities in the brain at the target low-frequency range of 0.2â15 Hz. The anatomical fragmentation of the brain into four regions, right and left diencephalon (RD and LD) and right and left optic tectum (ROT and LOT), confirmed the impact of glyphosate on the larvae brain and revealed a specific adaptation to the pesticide cocktail in the RD and ROT regions.
In summary, OM captured heart and brain voltage changes in zebrafish larvae, with discrete patterns of brain depolarization in the presence of specific water contaminants. Here we discuss the relevance of these findings to ecotoxicology and exposome research.This work was supported by ANR-Hepatobrain and Epidimicmac ANSES to NM, and âSoutien Ă la Recherche 2021â of the University of Montpellier and Fondation pour la Recherche sur le Cerveau, France: Espoir en tĂȘte 2022/23 to AGT. Partially funded by OptoFish ANSES, ANR-EpiCatcher, ANR/Era-Net Neu-Vasc to NM and the Fondation pour la Recherche MĂ©dicale, France (FRM, grant DPC2017 to M.E.M)
The \u3cem\u3eChlamydomonas\u3c/em\u3e Genome Reveals the Evolution of Key Animal and Plant Functions
Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the âŒ120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella
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