Amplitude of solar gravity modes generated by penetrative plumes

The detection of gravity modes is expected to give us unprecedented insights into the inner dynamics of the Sun. Within this framework, predicting their amplitudes is essential to guide future observational strategies and seismic studies. In this work, we predict the amplitude of low-frequency asymptotic gravity modes generated by penetrative convection at the top of the radiative zone. The result is found to depend critically on the time evolution of the plumes inside the generation region. Using a solar model, we compute the GOLF apparent surface radial velocity of low-degree gravity modes in the frequency range $10~\mu H_z\le \nu \le 100~\mu H_z$. In case of a Gaussian plume time evolution, gravity modes turn out to be undetectable because of too small surface amplitudes. This holds true despite a wide range of values considered for the parameters of the model. In the other limiting case of an exponential time evolution, plumes are expected to drive gravity modes in a much more efficient way because of a much higher temporal coupling between the plumes and the modes than in the Gaussian case. Using reasonable values for the plume parameters based on semi-analytical models, the apparent surface velocities in this case turn out to be one order of magnitude smaller than the 22-years GOLF detection threshold and than the previous estimates considering turbulent pressure as the driving mechanism, with a maximum value of $0.05$ cm s${}^{-1}$ for $\ell =1$ and $\nu\approx 100~\mu H_z$. When accounting for uncertainties on the plume parameters, the apparent surface velocities in the most favorable plausible case become comparable to those predicted with turbulent pressure, and the GOLF observation time required for a detection at $\nu \approx100~\mu H_z$ and $\ell=1$ is reduced to about 50 yrs.Comment: 18 pages, Accepted for publication in A&

A comparison of wave mode identification techniques

The four point measurements available from the Cluster mission enable spatiotemporal effects in data sets to be resolved. One application of these multipoint measurements is the determination of the wave vectors and hence the identification of wave modes that exist within the plasma. Prior to multi-satellite missions, wave identification techniques were based upon the interpretation of observational data using theoretically defined relations. However, such techniques are limited by the quality of the data and the type of plasma model employed. With multipoint measurements, wave modes can be identified and their wave directions determined purely from the available observations. This paper takes two such methods, a phase differencing technique and k-filtering and compares their results. It is shown that both methods can resolve the k vector for the dominant mirror mode present in the data. The phase differencing method shows that the nature of the wave environment is constantly changing and as such both methods result in an average picture of the wave environment in the period analysed. The k-filtering method is able to identify other modes that are present

Thorough characterisation of the 16 Cygni system

Context. The advent of space-based photometry observations provided high-quality asteroseismic data for a large number of stars. These observations enabled the adaptation of advanced analyses techniques, until then restricted to the field of helioseismology, to study the best asteroseismic targets. Amongst these, the 16Cyg binary system holds a special place, as they are the brightest solar twins observed by the Kepler mission. For this specific system, modellers have access to high-quality asteroseismic, spectroscopic and interferometric data, making it the perfect testbed for the limitations of stellar models. Aims. We aim to further constrain the internal structure and fundamental parameters of 16CygA&B using linear seismic inversion techniques of both global indicators and localised corrections of the hydrostatic structure. Methods. We start from the models defined by detailed asteroseismic modelling in our previous paper and extend our analysis by applying variational inversions to our evolutionary models. We carried out inversions of so-called seismic indicators and attempted to provide local corrections of the internal structure of the two stars. Results. Our results indicate that linear seismic inversions alone are not able to discriminate between standard and non-standard models for 16CygA&B. We confirm the results of our previous studies that used linear inversion techniques, but consider that the observed differences could be linked to small fundamental parameters variations rather than to a missing process in the models. Conclusions. We confirm the robustness and reliability of the results of the modelling we performed in our previous paper. We conclude that non-linear inversions are likely required to further investigate the properties of 16CygA&B from a seismic point of view, but that these inversions have to be coupled to analyses of the depletion of light elements such as lithium and beryllium to constrain the macroscopic transport of chemicals in these stars and also to constrain potential non-standard evolutionary paths

Compton Large Area Silicon Timing Tracker for Cosmic Vision M3

International audienceProposed in response to the ESA call for the third Medium size mission (M3), CAPSiTT is a small mission designed for a 3-year survey of the non-thermal high energy sky from an equatorial LEO orbit. With a large effective area and a very wide field of view, its single instrument, a silicon tracker, provides good imaging, spectroscopic and polarimetric capabilities with a sensitivity 10-100 times better than COMPTEL. Nucleosynthesis and particle acceleration mechanisms in various sites are the main scientific topics addressed by CAPSiTT

Architecture, symbolic capital and elite mobilizations: The case of the Royal Bank of Scotland corporate campus

In this article, we apply the conceptual framework of Pierre Bourdieu, in particular forms of capital, social fields, field of power and modes of domination, to demonstrate how the study of a symbolically powerful building can provide insights into what are often opaque elite interactions. In order to do this, we focus on the corporate campus headquarters of a powerful financial institution, the Royal Bank of Scotland in the context of Scotland in the period 2000–2009. We pose the following questions: What is the relationship between corporate space and the field of power? What role does a corporate building play in circuits of capital conversion? What does this case tell us about the role of architecture in elite mobilisations? In addressing these questions, we contribute to critical organisation studies by identifying and theorising the role of corporate space in inter-elite dynamics and circuits of capital conversion. This approach, we argue, provides a methodological lever which could be applied to other symbolically important buildings in order to understand the nature and role of inter-field interactions in the conception and realisation of such buildings

Identification and thermochemical analysis of high-lignin feedstocks for biofuel and biochemical production

Background - Lignin is a highly abundant biopolymer synthesized by plants as a complex component of plant secondary cell walls. Efforts to utilize lignin-based bioproducts are needed. Results - Herein we identify and characterize the composition and pyrolytic deconstruction characteristics of high-lignin feedstocks. Feedstocks displaying the highest levels of lignin were identified as drupe endocarp biomass arising as agricultural waste from horticultural crops. By performing pyrolysis coupled to gas chromatography-mass spectrometry, we characterized lignin-derived deconstruction products from endocarp biomass and compared these with switchgrass. By comparing individual pyrolytic products, we document higher amounts of acetic acid, 1-hydroxy-2-propanone, acetone and furfural in switchgrass compared to endocarp tissue, which is consistent with high holocellulose relative to lignin. By contrast, greater yields of lignin-based pyrolytic products such as phenol, 2-methoxyphenol, 2-methylphenol, 2-methoxy-4-methylphenol and 4-ethyl-2-methoxyphenol arising from drupe endocarp tissue are documented. Conclusions - Differences in product yield, thermal decomposition rates and molecular species distribution among the feedstocks illustrate the potential of high-lignin endocarp feedstocks to generate valuable chemicals by thermochemical deconstruction

Establishing causal order in longitudinal studies combining binary and continuous dependent variables

Longitudinal studies with a mix of binary outcomes and continuous variables are common in organizational research. Selecting the dependent variable is often difficult due to conflicting theories and contradictory empirical studies. In addition, organizational researchers are confronted with methodological challenges posed by latent variables relating to observed binary outcomes and within-subject correlation. We draw on Dueker’s (2005) qualitative vector autoregression (QVAR) and Lunn et al.’s (2014) multivariate probit model to develop a solution to these problems in the form of a qualitative short panel vector autoregression (QSP-VAR). The QSP-VAR combines binary and continuous variables into a single vector of dependent variables, making every variable endogenous a priori. The QSP-VAR identifies causal order, reveals within-subject correlation and accounts for latent variables. Using a Bayesian approach, the QSP-VAR provides reliable inference for short time dimension longitudinal research. This is demonstrated through analysis of the durability of elite corporate agents, social networks and firm performance in France. We provide our OpenBUGS code to enable implementation of the QSP-VAR by other researchers