Optimizing P300-speller sequences by RIP-ping groups apart

International audienceSo far P300-speller design has put very little emphasis on the design of optimized flash patterns, a surprising fact given the importance of the sequence of flashes on the selection outcome. Previous work in this domain has consisted in studying consecutive flashes, to prevent the same letter or its neighbors from flashing consecutively. To this effect, the flashing letters form more random groups than the original row-column sequences for the P300 paradigm, but the groups remain fixed across repetitions. This has several important consequences, among which a lack of discrepancy between the scores of the different letters. The new approach proposed in this paper accumulates evidence for individual elements, and optimizes the sequences by relaxing the constraint that letters should belong to fixed groups across repetitions. The method is inspired by the theory of Restricted Isometry Property matrices in Compressed Sensing, and it can be applied to any display grid size, and for any target flash frequency. This leads to P300 sequences which are shown here to perform significantly better than the state of the art, in simulations and online tests

Optimizing P300-speller sequences by RIP-ping groups apart

International audienceSo far P300-speller design has put very little emphasis on the design of optimized flash patterns, a surprising fact given the importance of the sequence of flashes on the selection outcome. Previous work in this domain has consisted in studying consecutive flashes, to prevent the same letter or its neighbors from flashing consecutively. To this effect, the flashing letters form more random groups than the original row-column sequences for the P300 paradigm, but the groups remain fixed across repetitions. This has several important consequences, among which a lack of discrepancy between the scores of the different letters. The new approach proposed in this paper accumulates evidence for individual elements, and optimizes the sequences by relaxing the constraint that letters should belong to fixed groups across repetitions. The method is inspired by the theory of Restricted Isometry Property matrices in Compressed Sensing, and it can be applied to any display grid size, and for any target flash frequency. This leads to P300 sequences which are shown here to perform significantly better than the state of the art, in simulations and online tests

Increase in Tomato Locule Number Is Controlled by Two Single-Nucleotide Polymorphisms Located

In tomato (Solanum lycopersicum) fruit, the number of locules (cavities containing seeds that are derived from carpels) varies from two to up to 10 or more. Locule number affects fruit shape and size and is controlled by several quantitative trait loci(QTLs). The large majority of the phenotypic variation is explained by two of these QTLs, fasciated (fas) and locule number (lc), that interact epistatically with one another. FAS has been cloned, and mutations in the gene are described as key factors leading to the increase in fruit size in modern varieties. Here, we report the map-based cloning of lc. The lc QTL includes a 1,600-bp region that is located 1,080 bp from the 3# end of WUSCHEL, which encodes a homeodomain protein that regulates stem cell fate in plants. The molecular evolution of lc showed a reduction of diversity in cultivated accessions with the exception of two single-nucleotide polymorphisms. These two single-nucleotide polymorphisms were shown to be responsible for the increase in locule number. An evolutionary model of locule number is proposed herein, suggesting that the fas mutation appeared after the mutation in the lc locus to confer the extreme high-locule-number phenotype

Numerical methods for the pricing of Swing options: a stochastic control approach

International audienceIn the natural gas market, many derivative contracts have a large degree of flexibility. These are known as Swing or Take-Or-Pay options. They allow their owner to purchase gas daily, at a fixed price and according to a volume of their choice. Daily, monthly and/or annual constraints on the purchased volume are usually incorporated. Thus, the valuation of such contracts is related to a stochastic control problem, which we solve in this paper using new numerical methods. Firstly, we extend the Longstaff–Schwarz methodology (originally used for Bermuda options) to our case. Secondly, we propose two efficient parameterizations of the gas consumption, one is based on neural networks and the other on finite elements. It allows us to derive a local optimal consumption law using a stochastic gradient ascent. Numerical experiments illustrate the efficiency of these approaches. Furthermore, we show that the optimal purchase is of bang-bang type

A call for standardised age-disaggregated health data.

The 2030 Sustainable Development Goals agenda calls for health data to be disaggregated by age. However, age groupings used to record and report health data vary greatly, hindering the harmonisation, comparability, and usefulness of these data, within and across countries. This variability has become especially evident during the COVID-19 pandemic, when there was an urgent need for rapid cross-country analyses of epidemiological patterns by age to direct public health action, but such analyses were limited by the lack of standard age categories. In this Personal View, we propose a recommended set of age groupings to address this issue. These groupings are informed by age-specific patterns of morbidity, mortality, and health risks, and by opportunities for prevention and disease intervention. We recommend age groupings of 5 years for all health data, except for those younger than 5 years, during which time there are rapid biological and physiological changes that justify a finer disaggregation. Although the focus of this Personal View is on the standardisation of the analysis and display of age groups, we also outline the challenges faced in collecting data on exact age, especially for health facilities and surveillance data. The proposed age disaggregation should facilitate targeted, age-specific policies and actions for health care and disease management

Sensitivity analysis using Itô Malliavin calculus and martingales. Application to stochastic optimal control

Abstract. We consider a multidimensional diffusion process (Xα t)0≤t≤T whose dynamics depends on a parameter α. Our first purpose is to write as an expectation the sensitivity ∇αJ(α) for the expected cost J(α) =E(f(X α T)), in order to evaluate it using Monte Carlo simulations. This issue arises, for example, from stochastic control problems (where the controller is parameterized, which reduces the control problem to a parametric optimization one) or from model misspecifications in finance. Previous evaluations of ∇αJ(α) using simulations were limited to smooth cost functions f or to diffusion coefficients not depending on α (see Yang and Kushner, SIAM J. Control Optim., 29 (1991), pp. 1216–1249). In this paper, we cover the general case, deriving three new approaches to evaluate ∇αJ(α), which we call the Malliavin calculus approach, the adjoint approach, and the martingale approach. To accomplish this, we leverage Itô calculus, Malliavin calculus, and martingale arguments. In the second part of this work, we provide discretization procedures to simulate the relevant random variables; then we analyze their respective errors. This analysis proves that the discretization error is essentially linear with respect to the time step. This result, which was already known in some specific situations, appears to be true in this much wider context. Finally, we provide numerical experiments in random mechanics and finance and compare the different methods in terms of variance, complexity, computational time, and time discretization error

CoAdapt P300 speller: optimized flashing sequences and online learning

International audienceThis paper presents a series of recent improvements made on the P300 speller paradigm in the context of the CoAdapt project. The flashing sequence is elicited by a new design called RIPRAND, in which the flashing rate of elements can be controlled independently of grid cardinality. Element-based evidence accumulation allows early-stopping of the flashes as soon as the symbol has been detected with confidence. No calibration session is nec-essary, thanks to a mixture-of-experts method which makes the initial predictions. When sufficient data can be buffered, subject-specific spatial and temporal filters are learned, with which the interface seamlessly makes its predictions, and the classifiers are adapted online. This paper, which presents results of three online sessions totalling 26 subjects, is the first to report online performance of a P300 speller with no calibration. 1 Material and Methods The P300 speller presented in this work was implemented in C++ with OpenViBE [7], and a dedicated stimulating software controlled the keyboard display. The software is opensource and part of OpenViBE release 0.18 We used a single Windows laptop to run all software components. The P300 speller keyboard was displayed on a separate LCD screen. A TMSi Refa8 amplifier, synchronized via hardware to the laptop, was used to record from 12 actively shielded electrodes. The visual stimulations consisted of briefly flashing "smiley" pictures. The P300 wave was detected via 3 channels of an xDAWN spatial filter [8], combined with a Regularized LDA classifier hereforth called RDA, which incorporates a regularisation of the common covariance matrix. The output of the classifier at each flashing time t is denote y(t). To save time, elements are always flashed in groups. Initial design of P300 speller groups involved rows and columns of a square matrix [2] or their randomizations [1]. The target element is then found at the intersection of the groups eliciting a P300 response. But repetitively flashing the same groups causes elements within the target groups to be wrongly selected, because of visual attention effects, and because of the contamination of all group elements by classification errors. Element-wise evidence accumulation avoids these two effects. A different random per-mutation can then be performed at each repetition of the flashes, effectively changing elements' group membership across repetitions. At each flash t, let the binary vector a(t) represent the set of n flashed elements within the grid of cardinality N . The score α(t) of each element (initialized to 0 at time 0) is updated with the following scheme, in which both target and non-target flashes contribute to the accumulation: α(t) = α(t − 1) + lo

The ecologically relevant genetics of plant-plant interactions

International audienceInteractions among plants have been long recognized as a major force driving plant community dynamics and crop yield. Surprisingly, our knowledge of the ecological genetics associated with variation of plant-plant interactions remains limited. In this opinion article by scientists from complementary disciplines, the international PLANTCOM network identified four timely questions to foster a better understanding of the mechanisms mediating plant assemblages. We propose that by identifying the key relationships among phenotypic traits involved in plant-plant interactions and the underlying adaptive genetic and molecular pathways, while considering environmental fluctuations at diverse spatial and time scales, we can improve predictions of genotype-by-genotype-by-environment interactions and modeling of productive and stable plant assemblages in wild habitats and crop fields

Temporal Trends in Transcatheter Aortic Valve Replacement in France: FRANCE 2 to FRANCE TAVI

International audienceBackground - Transcatheter aortic valve replacement (TAVR) is standard therapy for patients with severe aortic stenosis who are at high surgical risk. However, national data regarding procedural characteristics and clinical outcomes over time are limited. Objectives - The aim of this study was to assess nationwide performance trends and clinical outcomes of TAVR during a 6-year period. Methods - TAVRs performed in 48 centers across France between January 2013 and December 2015 were prospectively included in the FRANCE TAVI (French Transcatheter Aortic Valve Implantation) registry. Findings were further compared with those reported from the FRANCE 2 (French Aortic National CoreValve and Edwards 2) registry, which captured all TAVRs performed from January 2010 to January 2012 across 34 centers. Results - A total of 12,804 patients from FRANCE TAVI and 4,165 patients from FRANCE 2 were included in this analysis. The median age of patients was 84.6 years, and 49.7% were men. FRANCE TAVI participants were older but at lower surgical risk (median logistic European System for Cardiac Operative Risk Evaluation [EuroSCORE]: 15.0% vs. 18.4%; p < 0.001). More than 80% of patients in FRANCE TAVI underwent transfemoral TAVR. Transesophageal echocardiography guidance decreased from 60.7% to 32.3% of cases, whereas more recent procedures were increasingly performed in hybrid operating rooms (15.8% vs. 35.7%). Rates of Valve Academic Research Consortium-defined device success increased from 95.3% in FRANCE 2 to 96.8% in FRANCE TAVI (p < 0.001). In-hospital and 30-day mortality rates were 4.4% and 5.4%, respectively, in FRANCE TAVI compared with 8.2% and 10.1%, respectively, in FRANCE 2 (p < 0.001 for both). Stroke and potentially life-threatening complications, such as annulus rupture or aortic dissection, remained stable over time, whereas rates of cardiac tamponade and pacemaker implantation significantly increased. Conclusions - The FRANCE TAVI registry provided reassuring data regarding trends in TAVR performance in an all-comers population on a national scale. Nonetheless, given that TAVR indications are likely to expand to patients at lower surgical risk, concerns remain regarding potentially life-threatening complications and pacemaker implantation. (Registry of Aortic Valve Bioprostheses Established by Catheter [FRANCE TAVI]; NCT01777828)