Simple Scalings for Various Regimes of Electron Acceleration in Surface Plasma Waves

Different electron acceleration regimes in the evanescent field of a surface plasma wave are studied by considering the interaction of a test electron with the high-frequency electromagnetic field of a surface wave. The non-relativistic and relativistic limits are investigated. Simple scalings are found demonstrating the possibility to achieve an efficient conversion of the surface wave field energy into electron kinetic energy. This mechanism of electron acceleration can provide a high-frequency pulsed source of relativistic electrons with a well defined energy. In the relativistic limit, the most energetic electrons are obtained in the so-called electromagnetic regime for surface waves. In this regime the particles are accelerated to velocities larger than the wave phase velocity, mainly in the direction parallel to the plasma-vacuum interface

Optical properties of an ensemble of G-centers in silicon

We addressed the carrier dynamics in so-called G-centers in silicon (consisting of substitutional-interstitial carbon pairs interacting with interstitial silicons) obtained via ion implantation into a silicon-on-insulator wafer. For this point defect in silicon emitting in the telecommunication wavelength range, we unravel the recombination dynamics by time-resolved photoluminescence spectroscopy. More specifically, we performed detailed photoluminescence experiments as a function of excitation energy, incident power, irradiation fluence and temperature in order to study the impact of radiative and non-radiative recombination channels on the spectrum, yield and lifetime of G-centers. The sharp line emitting at 969 meV ($\sim$1280 nm) and the broad asymmetric sideband developing at lower energy share the same recombination dynamics as shown by time-resolved experiments performed selectively on each spectral component. This feature accounts for the common origin of the two emission bands which are unambiguously attributed to the zero-phonon line and to the corresponding phonon sideband. In the framework of the Huang-Rhys theory with non-perturbative calculations, we reach an estimation of 1.6$\pm$0.1 \angstrom for the spatial extension of the electronic wave function in the G-center. The radiative recombination time measured at low temperature lies in the 6 ns-range. The estimation of both radiative and non-radiative recombination rates as a function of temperature further demonstrate a constant radiative lifetime. Finally, although G-centers are shallow levels in silicon, we find a value of the Debye-Waller factor comparable to deep levels in wide-bandgap materials. Our results point out the potential of G-centers as a solid-state light source to be integrated into opto-electronic devices within a common silicon platform

Atmospheric methane, record from greenland ice core over the last 1000 years

The atmospheric methane concentration in ancient times can be reconstructed by analysing air entrapped in bubbles of polar ice sheets. We present results from an ice core from Central Greenland (Eurocore) covering the last 1000 years. We observe variations of about 70 ppbv around the mean pre-industrial level, which is confirmed at about 700 ppbv on a global average. According to our data, the beginning of the anthropogenic methane increase can be set between 1750 and 1800. Changes in the oxidizing capacity of the atmosphere may contribute significantly to the pre-industrial methane concentration variations, but changes in methane emissions probably play a dominant role. Since methane release depends on a host of influences it is difficult to specify clearly the reasons for these emission changes. Methane concentrations correlate only partially with proxy-data of climatic factors which influence the wetland release (the main source in pre-industrial times). A good correlation between our data and a population record from China suggests that man may already have influenced the CH4-cycle significantly before industrialisation

A characterization of cardiac-induced noise in R2* maps of the brain.

Cardiac pulsation increases the noise level in brain maps of the transverse relaxation rate R <sub>2</sub> *. Cardiac-induced noise is challenging to mitigate during the acquisition of R <sub>2</sub> * mapping data because its characteristics are unknown. In this work, we aim to characterize cardiac-induced noise in brain maps of the MRI parameter R <sub>2</sub> *. We designed a sampling strategy to acquire multi-echo 3D data in 12 intervals of the cardiac cycle, monitored with a fingertip pulse-oximeter. We measured the amplitude of cardiac-induced noise in this data and assessed the effect of cardiac pulsation on R <sub>2</sub> * maps computed across echoes. The area of k-space that contains most of the cardiac-induced noise in R <sub>2</sub> * maps was then identified. Based on these characteristics, we introduced a tentative sampling strategy that aims to mitigate cardiac-induced noise in R <sub>2</sub> * maps of the brain. In inferior brain regions, cardiac pulsation accounts for R <sub>2</sub> * variations of up to 3 s <sup>-1</sup> across the cardiac cycle (i.e., ∼35% of the overall variability). Cardiac-induced fluctuations occur throughout the cardiac cycle, with a reduced intensity during the first quarter of the cycle. A total of 50% to 60% of the overall cardiac-induced noise is localized near the k-space center (k < 0.074 mm <sup>-1</sup> ). The tentative cardiac noise mitigation strategy reduced the variability of R <sub>2</sub> * maps across repetitions by 11% in the brainstem and 6% across the whole brain. We provide a characterization of cardiac-induced noise in brain R <sub>2</sub> * maps that can be used as a basis for the design of mitigation strategies during data acquisition

Hypercontractivity on the qq-Araki-Woods algebras

Extending a work of Carlen and Lieb, Biane has obtained the optimal hypercontractivity of the $q$-Ornstein-Uhlenbeck semigroup on the $q$-deformation of the free group algebra. In this note, we look for an extension of this result to the type III situation, that is for the $q$-Araki-Woods algebras. We show that hypercontractivity from $L^p$ to $L^2$ can occur if and only if the generator of the deformation is bounded.Comment: 17 page

Instanton bundles on Fano threefolds

We introduce the notion of an instanton bundle on a Fano threefold of index 2. For such bundles we give an analogue of a monadic description and discuss the curve of jumping lines. The cases of threefolds of degree 5 and 4 are considered in a greater detail.Comment: 31 page, to appear in CEJ

Contribuições da pesquisa agropecuária pública para as indicações geográficas: estudo de caso do Institut National de la Recherche Agronomique (INRA).

A Indicação Geográfica (IG) é uma forma de proteger o uso do nome geográfico de origem de bens diferenciados. Sua evolução institucional e disseminação no mundo teve a França como protagonista. Esse é um tipo de inovação organizacional, de mercado e institucional, de natureza distinta daquela que geralmente envolve a pesquisa agropecuária pública. O objetivo deste trabalho é analisar como a pesquisa agropecuária, na França, vem interagindo com as IGs. O estudo de caso do Institut National de la Recherche Agronomique (INRA) analisa sua interação com a evolução das IGs (AOC e IGP) na França e em seus rebatimentos internacionais. Procedeu-se a análises dos projetos executados, das parcerias e da produção de CT&I gerada pelo instituto no tema. Distinguiram-se as contribuições do INRA em diferentes domínios institucionais relevantes para o desenvolvimento das IGs. A análise baseada em dados secundários identifica a evolução e o tipo de conhecimentos gerados pela pesquisa agropecuária que contribuem aos fatores de desempenho dos domínios institucionais relacionados às IGs. Os resultados mostram interações do INRA com diversos processos de evolução dos domínios institucionais, revelando o papel da pesquisa agropecuária pública no processo de inovação organizacional relacionado aos sinais de qualidade de bens territoriais.Título em inglês Public agricultural research contributions to Geographical Indications: case study of the Institut National de la Recherche Agronomique (INRA)

Regulator constants and the parity conjecture

The p-parity conjecture for twists of elliptic curves relates multiplicities of Artin representations in p-infinity Selmer groups to root numbers. In this paper we prove this conjecture for a class of such twists. For example, if E/Q is semistable at 2 and 3, K/Q is abelian and K^\infty is its maximal pro-p extension, then the p-parity conjecture holds for twists of E by all orthogonal Artin representations of Gal(K^\infty/Q). We also give analogous results when K/Q is non-abelian, the base field is not Q and E is replaced by an abelian variety. The heart of the paper is a study of relations between permutation representations of finite groups, their "regulator constants", and compatibility between local root numbers and local Tamagawa numbers of abelian varieties in such relations.Comment: 50 pages; minor corrections; final version, to appear in Invent. Mat