Capacitively coupled radio-frequency hydrogen discharges : the role of kinetics

This paper presents a systematic characterization of capacitively coupled radio-frequency hydrogen, discharges, produced within a parallel plate cylindrical setup at different rf applied voltages (Vrf=50–600 V), frequencies (f =13.56–40.68 MHz), and pressures (p=0.2–1 torr). A two-dimensional, time-dependent fluid model for charged particle transport is self-consistently solved coupled to a homogeneous kinetic model for hydrogen, including vibrationally excited molecular species and electronically excited atomic species. Numerical simulations are compared with experimental measurements of various plasma parameters. A good quantitative agreement is found between simulations and experiment for the coupled electrical power and the plasma potential. The model underestimates the values of the electron density, the self-bias potential, and the H(n=1) atom density with respect to measurements, but agrees with experiment when predicting that all these parameters increase with either Vrf, f, or p. The dissociation degree is about 10^−3 for the work conditions considered. Simulations adopt a wall recombination probability for H atoms that was experimentally measured, thus accounting for surface modification with discharge operating conditions. Results show the key role played by the atomic wall recombination mechanism in plasma description

Capacitively coupled hydrogen discharges : modeling vs. experiment

This paper presents a systematic characterization of hydrogen capacitively coupled very high frequency discharges, produced within a parallel plate cylindrical setup, by comparing numerical simulations to experimental measurements for various plasma parameters. A good quantitative agreement is found between calculation and experiment for the coupled electrical power and the plasma potential, at various frequencies, pressures and applied voltages. However, the model generally underestimates the electron density and the self-bias potential with respect to measured values. Model predictions for the absolute density of H(n=1) atoms are compared to first diagnostic results, obtained by two-photon absorption laser-induced fluorescence diagnostics at various pressures and frequencies.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/5012/200

Modelling the influence of frequency in a low pressure capacitively coupled hydrogen discharge

This paper investigates the dependence of plasma density and self-bias voltage with excitation frequency (13.56-40.68 MHz) using a two-dimensional (2D) fluid model in a low pressure (300 mTorr) radio frequency (RF) capacitively coupled hydrogen discharge. A comparison with experimental results reveals that the model predicts the correct trends of density and self-bias voltage variation with driving frequenc

Fluorine negative ion density measurement in a dual frequency capacitive plasma etch reactor by cavity ring-down spectroscopy

F⁻ negative ions were detected by direct observation of the weak photodetachmentabsorption continuum below 364.5nm by cavity ring-down spectroscopy. The negative ions were generated in a modified industrial dielectricplasmaetch reactor, with 2+27MHz dual frequency capacitive excitation in Ar∕CF₄∕O₂ and Ar∕C₄F₈∕O₂ gas mixtures. The F⁻ signal was superimposed on an unidentified absorption continuum, which was diminished by O₂ addition. The F⁻ densities were in the range of (0.5–3)×10¹¹cm⁻³, and were not significantly different for single (27MHz) or dual (2+27MHz) frequency excitation, not confirming recent modeling predictions.The authors wish to thank Lam Research Corporation for donation of equipment and financial support

THE COOPERATIVE FIRM AS MONITORED CREDIT

Abstract. We develop a nancial-contracting theory of the cooperative rm where production requires three generic tasks: working, managing, and monitoring. Workers provide an intermediate input (or labor directly); managers convert the workers' input into a nal output; and directors monitor managers. We model the cooperative rm by letting the workers act also as directors. We show how bundling the labor and monitoring tasks can expand the scope for equilibrium market activity, even when doing so results in a strictly positive deadweight loss. Our theory provides new insight with respect to a substantial theoretical and empirical literature on the life cycle of worker-managed rms, and with respect to a complementary body of anecdotal evidence on the causes of worker buyouts and cooperative degeneration. Our theory is also consistent with dierences between the board compensation policies of cooperative rms, where members typically receive little more than travel and per-diem reimbursements, and of investor-owned rms, where members receive substantial pay often based in part on rm nancial performance

VARIATIONS DEPUIS 10000 ANS DE LA REPARTITION ET DE LA PRODUCTIVITE DES FORETS D'ALTITUDE DANS LES ALPES ET LE JURA ET SIMULATION DES CHANGEMENTS FUTURS

Ce travail repose sur les charbons de bois enfouis dans les sols et les autres macrorestes ont été datés par 14C et identifiés botaniquement, et pour un site particulier (lac Cristol), sur les analyses de pollens, d'insectes, de macro-restes végétaux, charbons de bois et tronc d'arbres ont été combinés en une « approche multi-proxy » afin de mieux comprendre les variations de la forêt de montagne en réponse aux changements climatiques globaux et à l'activité anthropique. Les variations de la limite de la forêt sont de plus de 500 m durant l'Holocène. La période la plus chaude semble avoir été 9000-8000 ans cal B.P. (années calendaires avant le présent). Les hauts niveaux lacustres du début et de la fin de l'Holocène sont de natures en fait assez différentes. Au début de l'Holocène ils sont principalement dus à une évapotranspiration plus faible, et à la fin de l'Holocène à des précipitations plus élevées. L'ensemble de ces informations a permis de tester un modèle de végétation (Biome3) par une utilisation en mode inverse et à essayer de prédire l'évolution de la végétation. Un doublement de CO2 permet à la végétation d'évoluer vers des conditions plus tempérées. Une « forêt mixte tempérée », pourra devenir une forêt décidue tempérée grâce à des hivers nettement plus doux et à une meilleure efficacité dans l'utilisation de l'eau en été. Ces sites d'altitude ont connu une telle végétation entre 9000 et 8000 ans cal B.P

Writing in Britain and Ireland, c. 400 to c. 800

No abstract available

Reimagining Development 3.0 for a Changing Planet

This working paper argues we need to reimagine development tactics to fashion Development 3.0, to match what business analysts now call World 3.0, a global system characterized by high turbulence and new threats. It begins by contrasting our former classification of countries spatially into First, Second and Third worlds with a new division of development epochs in sequence since the end of World War II. World 1.0 emphasized industrialization, urbanization, and modernization, lasting from 1945 to 1980. World 2.0 emphasized global trade, and a shift to private actors doing the work of development, from 1980 to the early 2000s. World 3.0 can be seen as superceding globalization by concern with emergent threats. World 1.0 privileged state actions to accelerate “nation building” within former colonies, whereas World 2.0 privileged private capital and free trade as engines for economic growth. Now, following wars, disasters, and the near meltdown of the global financial system in 2007/08, we enter World 3.0 as depicted by Ghemawat and others. We review thirteen major changes not recognized within World 2.0 or its accompanying Development 2.0 regime. The major changes include the rise of homeless capital, the Conservative counter-revolution of the 1980s, the implosion of the USSR, rise of modern China, emergence of BRIC nations, a pan-urban world, rise of identity politics, reemergence of Africa, shift to non-state warfare, growing threat of climate change, MENA nations experience Arab Spring, digital worlds expand, and velocity increases. They suggest coming turbulence and unexpected outcomes, or “mashups” (Ramo). These changes suggest a different emergent system, becoming World 3.0 which has profound differences from how we view our planet’s political economy (World 2.0). If so, the paper outlines implications which suggest the time has come to “take on board” our changed planetary circumstances, and thus begin crafting Development 3.0. “Where the wild things are”, introduces metaphors to change the ‘meta-narratives’ used for viewing World 3.0: “herding elephants,” “taming feral capital”, “swimming with tides” and “avoiding mashups”. They help us realize that long recognized problems (or “elephants”) may show unexpected behaviors to pose new threats within World 3.0. The main argument of the paper then lays out a baker’s dozen changes needed if we hope to fashion more effective ways to promote development for us all. We must “rebalance society” (ala Mintzberg), refashion aid, privilege sustainability, emphasize fair trade, tame feral capital, devise better metrics, include all nations & peoples, seat G-20 not G-8, recognize semi-sovereigns, focus on a pan-urban world, build coalitions in networks, involve women & youth, and rebuild community leadership. All of which assumes we can offset a strong tide towards return to the excesses of World 2.0

Le tuf calcaire de La Celle-sur-Seine (Seine et Marne) : nouvelles données sur un site clé du stade 11 dans le Nord de la France

De nouvelles études morphostratigraphiques et biostratigraphiques ainsi que des datations ont été entreprises sur le célèbre dépôt de tuf calcaire de La Celle-sur-Seine afin d'obtenir une reconstruction détaillée des successions paléoenvironnementales et climatiques enregistrées dans cette formation interglaciaire du Pléistocène moyen. L'approche développée a privilégié l'aspect pluridisciplinaire afin d'exploiter la richesse paléontologique du gisement, de mieux appréhender ses caractères morphostratigraphiques et de préciser sa position chronologique. Les premiers résultats obtenus à partir des études malacologiques montrent que le dépôt, composé de tufs et de niveaux limono-argileux, s'est construit en progradant le long du versant. Ainsi l'épaisseur totale de la formation atteint près de 9 mètres. Les malacofaunes permettent de reconstituer une évolution paléoenvironnementale correspondant au début puis à l'optimum d'une phase climatique interglaciaire. Les niveaux sommitaux sont, eux, caractérisés par un net recul de la couverture forestière.La création de nouveaux profils stratigraphiques a permis la découverte dans un niveau de limon gris tufacé d'une abondante faune de mammifères accompagnée par quelques silex taillés. Cet horizon appartient à la malacozone la plus riche en taxons thermophiles qui est interprétée comme la phase optimum de l'Interglaciaire. La signification environnementale et climatique du cortège mammalogique, qui comprend en particulier de l'hippopotame et du macaque, corrobore les résultats malacologiques. L'industrie lithique est de type bifaciale en cohérence avec les récoltes de bifaces acheuléens effectuées à la fin du 19ème siècle. La composition du cortège de mollusques permet de rapprocher la faune de La Celle de "l'assemblage à Lyrodiscus", caractéristique des tufs du stade 11 dans le nord-ouest de l'Europe. Cette attribution chronologique est confirmée par les premières mesures radiométriques obtenus par U-Th sur des échantillons de tuf induré et par RPE/U-Th sur une dent de cheval. Enfin la révision des collections paléontologiques d'empreintes foliaires permet, en conjonction avec les données malacologiques, d'initier la discussion sur l'interprétation paléoclimatique du biome à Lyrodiscus. L'association floristique et faunique de La Celle qui comprend quelques taxons arboréens méditerranéens et nombre de gastéropodes éteints ou de répartition actuelle centre-européenne et océanique rend compte d'un environnement tempéré de forêt humide. La présence de ces espèces allochtones dans le nord de la France est mise en parallèle avec la durée exceptionnellement longue du Stade Isotopique Marin (SIM) 11 et de faibles amplitudes de températures saisonnières, qui auraient permis à plusieurs taxons méridionaux de coloniser cette zone septentrionale, plutôt qu'avec un climat plus tempéré que l'actuel.New morpho and biostratigraphical studies have been undertaken at the famous calcareous tufa deposit of La Celle-sur-Seine in order to obtain a detailed paleoenvironmental and climatic reconstruction from this Middle Pleistocene Interglacial formation. Multiproxy approach allows to study palaeontological contain of the tufa as well as its morphostratigraphical aspects and chronological allocation. First results from malacological study show that the tufa edificated downwards the slope reaching a total thickness of 9 metres high. Moreover molluscs show palaeoenvironmental succession corresponding to the early part of an Interglacial period followed by an optimum phase. Finally, at the top of the deposit faunas clearly indicate decrease of forest biotopes.Excavation of new profiles have allowed to discover a grey silty tufa horizon (lgt) yielding abundant mammal remains and a few lithic artefacts. This level is part of the molluscs zone 3 corresponding to the climatic optimum. Palaeoenvironmental and climatic conditions inferred from mammal assemblage (including Hippopotamus and Macaca) strengthened the malacological interpretation. The lithic industry is identified as Acheulean and appears in agreement with earliest handaxes discoveries during the late 19th century.La Celle malacological fauna belongs to the well-known MIS 11 "Lyrodiscus assemblage" in north-west Europe. This chronological allocation is confirmed by first U-series radiometric measures. Finally reappraisal of leaf print collections allows together with malacological data to discuss palaeoclimatic interpretation of the "Lyrodiscus biome". Flora and fauna from La Celle include a few mediterranean trees and several extinct gastropods together with few molluscs of central Europe modern range, allowing to describe a forest and humid lanscape. Presence of these peculiar species in northern France is thought to be related with the long length of MIS 11 and lower seasonal temperature contrast, that have allowed northern colonisation by southern species, rather than with occurrence of temperature higher than today