The study of chemical reactions on the molecular (femtosecond) timescale typically uses pump laser pulses to excite molecules and subsequent probe pulses to interrogate them. The ultrashort pump ...pulse can excite only a small fraction of molecules, and the probe wavelength must be carefully chosen to discriminate between excited and unexcited molecules. The past decade has seen the emergence of new methods that are also aimed at imaging chemical reactions as they occur, based on X-ray diffraction, electron diffraction or laser-induced recollision-with spectral selection not available for any of these new methods. Here we show that in the case of high-harmonic spectroscopy based on recollision, this apparent limitation becomes a major advantage owing to the coherent nature of the attosecond high-harmonic pulse generation. The coherence allows the unexcited molecules to act as local oscillators against which the dynamics are observed, so a transient grating technique can be used to reconstruct the amplitude and phase of emission from the excited molecules. We then extract structural information from the amplitude, which encodes the internuclear separation, by quantum interference at short times and by scattering of the recollision electron at longer times. The phase records the attosecond dynamics of the electrons, giving access to the evolving ionization potentials and the electronic structure of the transient molecule. In our experiment, we are able to document a temporal shift of the high-harmonic field of less than an attosecond (1 as = 10−18 s) between the stretched and compressed geometry of weakly vibrationally excited Br2 in the electronic ground state. The ability to probe structural and electronic features, combined with high time resolution, make high-harmonic spectroscopy ideally suited to measuring coupled electronic and nuclear dynamics occurring in photochemical reactions and to characterizing the electronic structure of transition states.
Silicon spin qubits have emerged as a promising path to large-scale quantum processors. In this prospect, the development of scalable qubit readout schemes involving a minimal device overhead is a ...compelling step. Here we report the implementation of gate-coupled rf reflectometry for the dispersive readout of a fully functional spin qubit device. We use a p-type double-gate transistor made using industry-standard silicon technology. The first gate confines a hole quantum dot encoding the spin qubit, the second one a helper dot enabling readout. The qubit state is measured through the phase response of a lumped-element resonator to spin-selective interdot tunneling. The demonstrated qubit readout scheme requires no coupling to a Fermi reservoir, thereby offering a compact and potentially scalable solution whose operation may be extended above 1 K.
•We provide an eXtended Conditional Auto-Regressive Expected Shortfall model.•We estimate a regularized network of US financial companies based on this model.•We propose a calibration approach for ...uncovering relevant edges of the network.•Our approach is shown to provide useful information for portfolio risk management.
In this article, we first generalize the Conditional Auto-Regressive Expected Shortfall (CARES) model by introducing the loss exceedances of all (other) listed companies in the Expected Shortfall related to each firm, thus proposing the CARES-X model (where the ‘X’, as usual, stands for eXtended in the case of large-dimensional problems). Second, we construct a regularized network of US financial companies by introducing the Least Absolute Shrinkage and Selection Operator in the estimation step. Third, we also propose a calibration approach for uncovering the relevant edges between the network nodes, finding that the estimated network structure dynamically evolves through different market risk regimes. We ultimately show that knowledge of the extreme risk network links provides useful information, since the intensity of these links has strong implications on portfolio risk. Indeed, it allows us to design effective risk management mitigation allocation strategies.
For years, Value-at-Risk and Expected Shortfall have been well established measures of market risk and the Basel Committee on Banking Supervision recommends their use when controlling risk. But their ...computations might be intractable if we do not rely on simplifying assumptions, in particular on distributions of returns. One of the difficulties is linked to the need for Integral Constrained Optimizations. In this article, two new stochastic optimization-based Simulated Annealing algorithms are proposed for addressing problems associated with the use of statistical methods that rely on extremizing a non-necessarily differentiable criterion function, therefore facing the problem of the computation of a non-analytically reducible integral constraint. We first provide an illustrative example when maximizing an integral constrained likelihood for the stress-strength reliability that confirms the effectiveness of the algorithms. Our results indicate no clear difference in convergence, but we favor the use of the problem approximation strategy styled algorithm as it is less expensive in terms of computing time. Second, we run a classical financial problem such as portfolio optimization, showing the potential of our proposed methods in financial applications.
In this review, recent developments and future prospects of obtaining a better understanding of the regulation of nitrogen use efficiency in the main crop species cultivated in the world are ...presented. In these crops, an increased knowledge of the regulatory mechanisms controlling plant nitrogen economy is vital for improving nitrogen use efficiency and for reducing excessive input of fertilizers, while maintaining an acceptable yield. Using plants grown under agronomic conditions at low and high nitrogen fertilization regimes, it is now possible to develop whole-plant physiological studies combined with gene, protein, and metabolite profiling to build up a comprehensive picture depicting the different steps of nitrogen uptake, assimilation, and recycling to the final deposition in the seed. A critical overview is provided on how understanding of the physiological and molecular controls of N assimilation under varying environmental conditions in crops has been improved through the use of combined approaches, mainly based on whole-plant physiology, quantitative genetics, and forward and reverse genetics approaches. Current knowledge and prospects for future agronomic development and application for breeding crops adapted to lower fertilizer input are explored, taking into account the world economic and environmental constraints in the next century.
► Influence of climatic factors on beverage and the volatile fingerprint in green Arabica coffee. ► Coffee produced at high elevations displayed high quality attributes such as fruity character. ► ...Two alcohols were closely correlated with an increase in earthy and green flavours. ► Climate change will probably negatively impact lowlands coffee quality.
Coffee grown at high elevations fetches a better price than that grown in lowland regions. This study was aimed at determining whether climatic conditions during bean development affected sensory perception of the coffee beverage and combinations of volatile compounds in green coffee. Green coffee samples from 16 plots representative of the broad range of climatic variations in Réunion Island were compared by sensory analysis. Volatiles were extracted by solid phase micro-extraction and the volatile compounds were analysed by GC–MS. The results revealed that, among the climatic factors, the mean air temperature during seed development greatly influenced the sensory profile. Positive quality attributes such as acidity, fruity character and flavour quality were correlated and typical of coffees produced at cool climates. Two volatile compounds (ethanal and acetone) were identified as indicators of these cool temperatures. Among detected volatiles, most of the alcohols, aldehydes, hydrocarbons and ketones appeared to be positively linked to elevated temperatures and high solar radiation, while the sensory profiles displayed major defects (i.e. green, earthy flavour). Two alcohols (butan-1,3-diol and butan-2,3-diol) were closely correlated with a reduction in aromatic quality, acidity and an increase in earthy and green flavours. We assumed that high temperatures induce accumulation of these compounds in green coffee, and would be detected as off-flavours, even after roasting. Climate change, which generally involves a substantial increase in average temperatures in mountainous tropical regions, could be expected to have a negative impact on coffee quality.
Soft x-ray excitonics Moulet, A.; Bertrand, J. B.; Klostermann, T. ...
Science,
09/2017, Volume:
357, Issue:
6356
Journal Article
Peer reviewed
Open access
The dynamic response of excitons in solids is central to modern condensed-phase physics, material sciences, and photonic technologies. However, study and control have hitherto been limited to photon ...energies lower than the fundamental band gap. Here we report application of attosecond soft x-ray and attosecond optical pulses to study the dynamics of core-excitons at the L2,3 edge of Si in silicon dioxide (SiO₂). This attosecond x-ray absorption near-edge spectroscopy (AXANES) technique enables direct probing of the excitons’ quasiparticle character, tracking of their subfemtosecond relaxation, the measurement of excitonic polarizability, and observation of dark core-excitonic states. Direct measurement and control of core-excitons in solids lay the foundation of x-ray excitonics.
Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers a compact and scalable readout with high fidelity, however, ...further improvements in sensitivity are required to meet the fidelity thresholds and measurement timescales needed for the implementation of fast feedback in error correction protocols. Here, we combine radio-frequency gate-based sensing at 622 MHz with a Josephson parametric amplifier, that operates in the 500-800 MHz band, to reduce the integration time required to read the state of a silicon double quantum dot formed in a nanowire transistor. Based on our achieved signal-to-noise ratio, we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 μs, well below the requirements for fault-tolerant readout and 30 times faster than without the Josephson parametric amplifier. Additionally, the Josephson parametric amplifier allows operation at a lower radio-frequency power while maintaining identical signal-to-noise ratio. We determine a noise temperature of 200 mK with a contribution from the Josephson parametric amplifier (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the readout speed.
L’estimation de l’âge au décès de sujets adultes découverts en contexte médico-légal ou archéologique est un sujet fondamental. La cémentochronologie, fondée sur le dépôt annuel de cément, est une ...technique parmi les plus performantes dont l’exactitude est appréciée dans de nombreuses publications. Cependant, le manque de standardisation ralentit l’adoption de cette méthode et freine l’étude de la précision qui demeure méconnue tout comme l’impact des conditions taphonomiques. L’objectif de ce travail est de mesurer la concordance des estimations, donc la précision, puis d’évaluer l’exactitude, donc la qualité de l’accord entre l’âge estimé et l’âge chronologique, en appliquant un protocole standardisé pour s’affranchir des biais inhérents à la préparation. L’étude porte sur 2 000 lames histologiques réalisées à partir de 400 canines. Deux cents canines sont issues de collections de référence dont l’âge, le sexe, l’intervalle post mortem et la durée d’inhumation des sujets sont connus. Afin d’étudier l’applicabilité de la méthode à du matériel ancien, 200 canines extraites de sujets archéologiques datés entre les XII
e
et XVIII
e
siècles sont intégrées à l’étude. Les résultats démontrent que l’analyse cémentochronologique peut permettre une estimation fiable de l’âge au décès mais révèlent également une diminution significative de la lisibilité des dépôts cémentaires avec l’âge et une moindre efficacité pour les sujets de plus de 50 ans.
Adult age at death estimation is a fundamental component of biological profiles in forensic and archaeological contexts. Cementochronology based on annual deposition of acellular cementum is one of the most effective ageing techniques, and its accuracy, i.e., the agreement between estimated and chronological age, is acknowledged in many publications. However, a lack of standardization has led to the method not being widely adopted. This has also hindered the evaluation of its precision, currently unknown, as well as of the impact taphonomical processes may have on the method. The aim of this study is to measure the agreement between cementum estimates, i.e,. the precision, and to assess the accuracy of the estimates, that is how close is the estimated age to the chronological age, by applying a standardized protocol to overcome bias inherent to sample preparation. This study is based on 2000 histological slices from 400 canines. Two hundred canines are derived from reference collections with documented age, sex, post mortem interval and burial duration. In order to investigate the applicability of this method on ancient material, 200 canines extracted from archaeological assemblages dated between the 12
th
and 18
th
Centuries are included in the study. Results show that cementochronological analysis can provide a reliable estimate of age at death, but also reveal a significant decrease of cementum readability with age and a decreased efficiency for individuals over 50 years old.
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