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The poor operational stability of non-fullerene electron acceptor (NFA) organic solar cells (OSCs) currently limits their commercial application. While previous studies have primarily focused on the degradation of the NFA component, we also consider here the electron donor material. We examine the stability of three representative donor polymers, PM6, D18, and PTQ10, paired with the benchmark NFA, Y6. After light soaking PM6 and D18 in air, we find an enhanced conversion of singlet excitons into trapped interchain polaron pairs on sub-100 femtosecond timescales. This process outcompetes electron transfer to Y6, significantly reducing the charge generation yield. However, this pathway is absent in PTQ10. We identify twisting in the benzo[1,2-b:4,5-b′]dithiophene (BDT)-thiophene motif shared by PM6 and D18 as the cause. By contrast, PTQ10 does not contain this structural motif and has improved stability. Thus, we show that the donor polymer can be a weak link for OSC stability, which must be addressed collectively with the NFA.

Cellulose being the most widely available biopolymer on Earth is attracting significant interest from the industry and research communities. While molecular simulations can be used to understand fundamental aspects of cellulose nanocrystal self-assembly, a model that can perform on the experimental scale is currently missing. In our study we develop a supra coarse-grained (sCG) model of cellulose nanocrystal which aims to bridge the gap between molecular simulations and experiments. The sCG model is based on atomistic molecular dynamics simulations and it is developed with the force-matching coarse-graining procedure. The validity of the model is shown through comparison with experimental and simulation results of the elastic modulus, self-diffusion coefficients and cellulose fiber twisting angle. We also present two representative case studies, self-assembly of nanocrystal during solvent evaporation and simulation of a chiral nematic phase ordering. Finally, we discuss possible future applications for our model. Graphic abstract Funding Agencies|Linkoping University; Swedish Research CouncilSwedish Research Council [2016-05990]; Knut and Alice Wallenberg foundationKnut & Alice Wallenberg Foundation; Peter Wallenberg Foundation; A forsk; Troedsson foundation; Advanced Functional Material Center at Linkoping University; SeRC (Swedish e-Science Research Center); Wallenberg Wood Science Center

The structure and dynamics of networks formed by rod-shaped particles can be indirectly investigated by measuring the diffusion of spherical tracer particles. This method was used to characterize cellulose nanofibril (CNF) networks in both dispersed and arrested states, the results of which were compared with coarse-grained Brownian dynamics simulations. At a CNF concentration of 0.2 wt% a transition was observed where, below this concentration tracer diffusion is governed by the increasing macroscopic viscosity of the dispersion. Above 0.2 wt%, the diffusion of small particles (20-40 nm) remains viscosity controlled, while particles (100-500 nm) become trapped in the CNF network. Sedimentation of silica microparticles (1-5 mu m) in CNF dispersions was also determined, showing that sedimentation of larger particles is significantly affected by the presence of CNF. At concentrations of 0.2 wt%, the sedimentation velocity of 5 mu m particles was reduced by 99 % compared to pure water. Funding Agencies|The Knut and Alice Wallenberg; Wallenberg Wood Science Center

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a conducting polymer that is used in a wide range of applications such as electronics, optoelectronics, and bio-electronics, where the fundamental understanding of the charge transport, and in particular of the electrical conductivity sigma, is a prerequisite to develop new high performance devices. There are many reports in the literature where the conductivity of archetypical conducting polymer PEDOT doped with tosylate (PEDOT:TOS) exhibits a dry negative temperature coefficient, d sigma/dT amp;lt; 0, which is strikingly different from the activated-type behavior with d sigma/dT amp;gt; 0 commonly observed in most conducting polymers. This unusual temperature dependence was attributed to the transition from the photon-assisted hopping to the metallic behavior, which is however difficult to rationalize taking into account that this transition occurs at high temperatures. In order to understand the origin of this unusual behavior, multiscale mobility calculations in PEDOT:TOS for the model of hopping transport were performed, where changes in the morphology and the density of states (DOS) with the temperature were explicitly taken into account. The morphology was calculated using the Molecular Dynamics simulations, and the hopping rates between the chains were calculated quantum-mechanically following the Miller-Abrahams formalism. Our results reproduce the observed negative temperature coefficient, where however the percolation analysis shows that this behavior mainly arises because of the changes in morphology upon heating when the system becomes less ordered. This results in a less efficient pi-pi stacking and hence lower mobility in the system. We therefore conclude that experimentally observed negative mobility temperature coefficient in conducting polymers at high temperatures is consistent with the hopping transport, and does not necessarily reflect the transition to a metallic band-like transport. Based on our multiscale modeling, we introduce a simple Gaussian Disorder Model for the efficient mobility calculations, where the DOS broadening is a function of the temperature, and where the transfer integral distribution is a bimodal distribution evolving with temperature. Funding Agencies|KAW foundation (Tail of the Sun); Swedish Research CouncilSwedish Research Council [2016-05990, 201704474]; Advanced Functional Material center at Linkoping University

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format. Fil: Kaufman, Darrell. Northern Arizona University.; Estados Unidos Fil: McKay, Nicholas. Northern Arizona University.; Estados Unidos Fil: Routson, Cody. Northern Arizona University.; Estados Unidos Fil: Erb, Michael. Northern Arizona University.; Estados Unidos Fil: Davis, Basil. University Of Lausanne; Suiza Fil: Heiri, Oliver. University Of Basel; Suiza Fil: Jaccard, Samuel. University Of Bern; Suiza Fil: Tierney, Jessica. University of Arizona; Estados Unidos Fil: Dätwyler, Christoph. University Of Bern; Suiza Fil: Axford, Yarrow. Northwestern University; Estados Unidos Fil: Brussel, Thomas. University of Utah; Estados Unidos Fil: Cartapanis, Olivier. University Of Bern; Suiza Fil: Chase, Brian. Universite de Montpellier; Francia Fil: Dawson, Andria. Mount Royal University; Canadá Fil: de Vernal, Anne. Université du Québec a Montreal; Canadá Fil: Engels, Stefan. University of London; Reino Unido Fil: Jonkers, Lukas. University Of Bremen; Alemania Fil: Marsicek, Jeremiah. University of Wisconsin-Madison; Estados Unidos Fil: Moffa Sánchez, Paola. University of Durham; Reino Unido Fil: Morrill, Carrie. University of Colorado; Estados Unidos Fil: Orsi, Anais. Université Paris-Saclay; Francia Fil: Rehfeld, Kira. Heidelberg University; Alemania Fil: Saunders, Krystyna. Australian Nuclear Science And Technology Organisation; Australia Fil: Sommer, Philipp. University Of Lausanne; Suiza Fil: Thomas, Elizabeth. University At Buffalo; Estados Unidos Fil: Tonello, Marcela Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Tóth, Mónika. Balaton Limnological Institute; Hungría Fil: Vachula, Richard. Brown University; Estados Unidos Fil: Andreev, Andrei. Alfred Wegener Institut Helmholtz Centre for Polar and Marine Research; Alemania Fil: Bertrand, Sebastien. Ghent University; Bélgica Fil: Massaferro, Julieta. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format., Measurement(s)climateTechnology Type(s)digital curationFactor Type(s)temporal interval • geographic location • proxy typeSample Characteristic - Environmentclimate systemSample Characteristic - LocationEarth (planet) Machine-accessible metadata file describing the reported data: https://www.ncdc.noaa.gov/paleo/study/27330

Field ion microscopy (FIM) was the first technique to image individual atoms on the surface of a material. By a careful control of the field evaporation of surface atoms, the bulk of the material is exposed, and, through digital processing of a sequence of micrographs, an atomically-resolved three-dimensional reconstruction can be achieved. 3DFIM is particularly suited to the direct observation of crystalline defects that underpin the physical properties of materials: vacancies and vacancy clusters, interstitials, dislocations, or grain boundaries. Yet, further developments of 3DFIM are necessary to turn it into a routines technique. Here, we introduce first a protocol for 3DFIM image processing and subsequent tomographic reconstruction. Second, we propose a numerical model enabling simulation of the FIM imaging process. The model combines the meshless algorithm for field evaporation proposed by Rolland et al. (Robin–Rolland Model, or RRM) with fundamental aspects of the field ionization process of the gas image involved in FIM. The proposed model enables the simulation of imaging artefacts that are induced by non-regular field evaporation and by the disturbed electric field distribution near atomic defects. Our model enables more precise interpretation of 3DFIM characterization of structural defects.

8 p.-4 fig., Designing new high performances materials based on conducting polymers necessitates the development of multiscale models to investigate the charge transport in large realistic systems. In this work, we utilize Coarse-Grained (CG) Molecular Dynamics (MD) simulations to generate morphologies of Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with Tosylate (TOS) ions, and we develop a backmapping protocol to retrieve the atomistic details of the molecules afterwards. We demonstrate that the proposed protocol corrects for the nanostructure distortions induced by Coarse-Graining the system, namely a wrong density and an over-estimated stacking distance. Quantum chemical calculations are performed on the systems obtained after backmapping in order to calculate hopping rates for charge transport, and charge mobilities as a function of the PEDOT chain length and hydration level are then calculated by solving a master equation for transport. The results are identical to the calculations performed on PEDOT morphologies obtained by direct All-Atomistic (AA) MD simulations: the mobility increases with the chain length and decreases with the hydration level, this last effect being more pronounced for short chains. This definitely shows that the workflow CG MD backmapping mobility calculations is in position to calculate charge mobility in PEDOT based materials, paving the way for theoretical investigations of transport in more complex materials such as PEDOT doped with Polystyrene Sulfonate (PSS)., This research was funded by KAW foundation grant Tail of the Sun,and the Swedish Research Council Grant No. 2016-05990 and 2017-04474, and the Advanced Functional Material center at Linköping University.

Self-assembly is ubiquitous in nature and underlies the formation of many complex systems from the molecular to the macroscopic scale. Kern-Frenkel-like patchy particles are powerful models to investigate this phenomenon by computational methods such as Monte Carlo or molecular dynamics simulations. However, in these models the interactions are mediated by circular patches at the particle surface, which can be hardly mapped to realistic systems, containing for instance faceted particles with rectangular surfaces. In this paper we extend the model to take into account such geometries, and we use it to build a supra coarse-grained model of the cellulose nanocrystal where the interactions are parametrized against all-atomistic molecular dynamics simulations. The formation of cholesteric ribbons and defects in cholesteric droplets of the cellulose nanocrystal are investigated and confirm experimental behavior reported in the literature. The flexibility of this new patchy particle model makes it a powerful tool to develop supra coarse-grained models of self-assembly for large space and time scales and should find a broad range of applications for self-assembly in chemical and biological systems. Funding Agencies|Swedish Research CouncilSwedish Research Council [2016-05990]; Peter Wallenberg Foundation; Troedsson foundation; Digital Cellulose Center; Advanced Functional Material Center at Linkoping University; SeRC (Swedish e-Science Research Center); Wallenberg Wood Science Center

International audience; Atom probe tomography is unique in its ability to image in 3D at the atomic scale and measure composition in asemiconductor device with high sensitivity. However it suffers from many artefacts. The current state of the art ofnanoelectronic device analysis by atom probe is addressed and the challenges in device analysis in the next tenyears are laid out. Finally the improvements necessary in sample preparation, instrumentation and reconstructionprocedures are discussed

International audience; An analytical model describing the field evaporation dynamics of a tip made of a thin layer deposited on a substrate is presented in this paper. The difference in evaporation field between the materials is taken into account in this approach in which the tip shape is modeled at a mesoscopic scale. It was found that the non-existence of sharp edge on the surface is a sufficient condition to derive the morphological evolution during successive evaporation of the layers. This modeling gives an instantaneous and smooth analytical representation of the surface that shows good agreement with finite difference simulations results, and a specific regime of evaporation was highlighted when the substrate is a low evaporation field phase. In addition, the model makes it possible to calculate theoretically the tip analyzed volume, potentially opening up new horizons for atom probe tomographic reconstruction.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Deposition dynamics, crystallization, molecular packing, and electronic mobility of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films are affected by the nature of the substrate. Computational microscopy has been carried out to reveal the morphology-substrate dependence for PEDOT thin films doped with molecular tosylate deposited on different substrates including graphite, Si3N4, silicon, and amorphous SiO2. It is shown that the substrate is instrumental in formation of the lamellar structure. PEDOT films on the ordered substrates (graphite, Si3N4, and silicon) exhibit preferential face-on orientation, with graphite showing the most ordered and pronounced face-on packing. In contrast, PEDOT on amorphous SiO2 exhibits the dominant edge-on orientation, except in the dry state where both packings are equally presented. The role of water and the porosity of the substrate in formation of the edge-on structure on SiO2 is outlined. On the basis of the calculated morphology, the multiscale calculations of the e...

© 2018 IOP Publishing Ltd. Field ion microscopy allows for direct imaging of surfaces with true atomic resolution. The high charge density distribution on the surface generates an intense electric field that can induce ionization of gas atoms. We investigate the dynamic nature of the charge and the consequent electrostatic field redistribution following the departure of atoms initially constituting the surface in the form of an ion, a process known as field evaporation. We report on a new algorithm for image processing and tracking of individual atoms on the specimen surface enabling quantitative assessment of shifts in the imaged atomic positions. By combining experimental investigations with molecular dynamics simulations, which include the full electric charge, we confirm that change is directly associated with the rearrangement of the electrostatic field that modifies the imaging gas ionization zone. We derive important considerations for future developments of data reconstruction in 3D field ion microscopy, in particular for precise quantification of lattice strains and characterization of crystalline defects at the atomic scale.

The potential of conjugated polymers to compete with inorganic materials in the field of semiconductor is conditional on fine-tuning of the charge carriers mobility. The latter is closely related to the material morphology, and various studies have shown that the bottleneck for charge transport is the connectivity between well-ordered crystallites, with a high degree of pi-pi stacking, dispersed into a disordered matrix. However, at this time there is a lack of theoretical descriptions accounting for this link between morphology and mobility, hindering the development of systematic material designs. Here we propose a computational model to predict charge carriers mobility in conducting polymer PEDOT depending on the physicochemical properties of the system. We start by calculating the morphology using molecular dynamics simulations. Based on the calculated morphology we perform quantum mechanical calculation of the transfer integrals between states in polymer chains and calculate corresponding hopping rates using the Miller-Abrahams formalism. We then construct a transport resistive network, calculate the mobility using a mean-field approach, and analyze the calculated mobility in terms of transfer integrals distributions and percolation thresholds. Our results provide theoretical support for the recent study [Noriega et al., Nat Mater 12, 1038 (2013)] explaining why the mobility in polymers rapidly increases as the chain length is increased and then saturates for sufficiently long chains. Our study also provides the answer to the long-standing question whether the enhancement of the crystallinity is the key to designing high-mobility polymers. We demonstrate, that it is the effective pi-pi stacking, not the long-range order that is essential for the material design for the enhanced electrical performance. This generic model can compare the mobility of a polymer thin film with different solvent contents, solvent additives, dopant species or polymer characteristics, providing a general framework to design new high mobility conjugated polymer materials. Funding Agencies|Swedish Energy Agency [38332-1, 43561-1]; Knut and Alice Wallenberg Foundation through the project The Tail of the Sun; Swedish Research Council via "Research Environment grant" [2016-05990]; SeRC (Swedish e-Science Research Center)

International audience; Atom probe tomography (APT) has been successfully used in materials science for several decades for probing local compositional variations. In metals, the capacity to measure reliable composition at the nanoscale in 3D was successfully demonstrated in the early nineties [I, 2]. By using a few geometric ingredients, a reconstruction recipe was proposed at this time that surprisingly produced on selected materials, 3D images with an atomic scale precision of the distribution of atoms with elemental identification [3). The ability to localize precisely the 3-D coordinates of individual atoms in direct space of materials is expected to find important applications in materials science and engineering, nanoscience, physics and chemistry. It is particularly crucial in semiconductor industry, to design optical devices or electronic devices, such as light-emitting diodes (LEDs), or transistors.This ideal picture of near-perfect 3D microscope however faces two issues. First, the precision of images may vary strongly from one material to another. Compared to an optical or an electron microscope, the spatial resolution loss is not diffraction limited, since image is produced from the inverse projection of ion trajectories, ions been produced by field evaporation of surface atoms. Precision is perturbed by slight deviations of the trajectories of ions from their initial positions at the specimen surace to the ion detector. A real understanding of this trajectory taking into account first the quantum interaction of atoms/ions with the specimen surface under the presence of the strong electric field existing on the surface is mandatory. The interplay between quantum processes, and more classical deviations induced by the distribution of the electric field close to the surface is extremely complex. In metals, most of the deviations thought to be induced by the field, as it was recently demonstrated experimentally by field ion microscopy in tungsten (fig. I). In oxides, quantum effects such as in-flight dissociation of molecules may degrade significantly the spatial precision (fig. 2) [4]. The second issue concerns the global distortions induced by the presence in the sample of phases very different in term of the critical fields required to extract surface atoms. This is a current case when analyzing devices composed of complex structures of metals, oxides and semiconductors materials. The surface of the sample ideally modelled with a constant curvature radius evolves dynamically under the process of field evaporation in a complex 3D surface. The direct consequence is the presence of distortions in the projected image. After the evaporation of each atom, the field distribution around the sample must be evaluated, to understand the projection law that should necessary be taken into account to generate an accurate reconstruction [5, 6). To overcome this cumbersome calculation, an alternative model, much simpler, was developed to reproduce the imaging process in simple configurations. In multilayers systems, it was demonstrated that most of the distortions could be reduced using a fast and efficient reconstruction algorithm that predicts the analytical shape of the emitting surface all along the evaporation process [7]. If a complementary technique can be used on the same sample to verify the morphology or provide complementary information before APT analysis, then this can also greatly…

Accuracy of atom probe tomography measurements is strongly degraded by the presence of phases that have different evaporation fields. In particular, when there are perpendicular interfaces to the tip axis in the specimen, layers thicknesses are systematically biased and the resolution is degraded near the interfaces. Based on an analytical model of field evaporated emitter end-form, a new algorithm dedicated to the 3D reconstruction of multilayered samples was developed. Simulations of field evaporation of bilayer were performed to evaluate the effectiveness of the new algorithm. Compared to the standard state-of-the-art reconstruction methods, the present approach provides much more accurate analyzed volume, and the resolution is clearly improved near the interface. The ability of the algorithm to handle experimental data was also demonstrated. It is shown that the standard algorithm applied to the same data can commit an error on the layers thicknesses up to a factor 2. This new method is not constrained by the classical hemispherical specimen shape assumption.

This study presents the results of a multi-proxy analysis of a Holocene lacustrine sediment sequence recovered from a small tundra lake in the central Canadian Arctic and links climatic variations there to the North Atlantic. Chironomid and pollen-based reconstructions of mean July air temperature (MJAT) document notable deviations at 9.3 ka and 8.2 ka. Chironomid-inferred July air temperature is depressed by 1.4 °C at 9.3 ka and 1.7 °C at 8.2 ka relative to the long-term chironomid-inferred Holocene average of 9.4 °C. These cooling events also correspond to an increase in Gramineae (Poaceae) and a decrease in Betula pollen, reflecting a decrease in the density of dwarf birch cover. Concurrent, abrupt increases in several diatom taxa, including aerophilic epiphytes, and Sphagnum indicate an expansion of moss habitats as a result of wetter conditions. The expression and timing of the cooling evidenced at TK2 during the early Holocene is consistent with abrupt climate events identified in the North Atlantic and coincides with intervals of North Atlantic cooling and weakened Atlantic Meridional Overturning Circulation (AMOC). This research, which improves our understanding of the spatial extent and magnitude of the 9.3 ka and 8.2 ka events in the central Canadian Arctic, serves as a benchmark for coupled-ocean atmosphere climate models simulating the response of the climate system to abrupt climate events and provides insight in marine-atmosphere teleconnections in the circum-North Atlantic region.

The issue of ancient human single or multiple dispersal pathways into Eurasia is theoretically significant for understanding adaptive processes involved in peopling vacant spaces and varied, unfamiliar ecosystems, but receives mostly marginal attention. The Western Asian staging-post remains most plausible, whereas an alternative peopling directly from the Maghreb across the Gibraltar Strait into Iberia and beyond, though problematic, is proposed repeatedly. The present review discusses these issues and findings requiring interpretation, with respect to chronology, fossil human and Palaeolithic evidence, and Early Pleistocene circumstances in the Circum-Mediterranean Basin and Europe. The spatiotemporal distribution of palaeoanthropological occurrences and Ethiopian fossil mammal expansions does not support the hypothesis of a single Early Pleistocene biogeographic event originating in Subsaharan Africa, spreading throughout Western Asia and Europe. On the other hand, this spatiotemporal distribution of ancient human evidence in Europe reveals an intriguing bimodal chronological pattern. Early Pleistocene occurrences in both Eastern Europe and Western Europe prove earlier than those in West-Central Europe and the Italian Peninsula, which are dateable to the Mid-Pleistocene. This Early Pleistocene distribution cluster of occurrences in Iberia and Atlantic Europe refutes implicitly a single linked human-Ethiopian mammal biogeographic event exclusively through Western Asia, while reviving the notion of ‘sweepstake’ dispersal directly across the Strait of Gibraltar, a scenario which, however, demands independent confirmation by reviewing past circumstances favourable for a crossing, as well as suggesting a series of multiple staging-posts. The observed bimodal spatiotemporal configuration becomes more compatible with another hypothesis namely, that Europe was peopled independently by converging population movements from both the Western Asian and Ibero-Moroccan staging posts during the Early Pleistocene, between ca. 1.85–1.40 Ma.

International audience

International audience; \textcopyright 2016 IOP Publishing Ltd. The routine use of atom probe tomography (APT) as a nano-analysis microscope in the semiconductor industry requires the precise evaluation of the metrological parameters of this instrument (spatial accuracy, spatial precision, composition accuracy or composition precision). The spatial accuracy of this microscope is evaluated in this paper in the analysis of planar structures such as high-k metal gate stacks. It is shown both experimentally and theoretically that the in-depth accuracy of reconstructed APT images is perturbed when analyzing this structure composed of an oxide layer of high electrical permittivity (higher-k dielectric constant) that separates the metal gate and the semiconductor channel of a field emitter transistor. Large differences in the evaporation field between these layers (resulting from large differences in material properties) are the main sources of image distortions. An analytic model is used to interpret inaccuracy in the depth reconstruction of these devices in APT.

An alternative approach for simulating the field evaporation process in atom probe tomography is presented. The model uses the electrostatic Robin’s equation to directly calculate charge distribution over the tip apex conducting surface, without the need for a supporting mesh. The partial ionization state of the surface atoms is at the core of the method. Indeed, each surface atom is considered as a point charge, which is representative of its evaporation probability. The computational efficiency is ensured by an adapted version of the Barnes–Hut N-body problem algorithm. Standard desorption maps for cubic structures are presented in order to demonstrate the effectiveness of the method.

Although anthropogenesis reaches back to Pliocene times in Subsaharan Africa, hominid dispersals beyond began only by the Early Pleistocene, with the appearance of genus Homo with Lower Palaeolithic repertoires. Causes responsible for these events remain poorly understood. Direct evidence for environmental factors, such as prolonged aridity stress or linkage with emigrating African ungulate or carnivorous species, while plausible, remains weak or ambiguous. Bio-cultural evolutionary evidence, however, provides more compelling indications, supported by empirical findings. These are rooted in the hominid ‘dual heritage’ involving higher primate ancestry and a partly but significant zoophagous dietary shift. Several million years of evolutionary divergence separated early Homo from its pongid relatives. The consequences of an omnivorous–carnivorous shift, on the other hand, besides enabling harvesting food resources at different levels of the trophic pyramid, included ‘natural history intelligence’, observed commonly among social carnivores. It enhanced human–landscape–plant–animal relationship and knowledge. It also favoured home-ranges expansion and the eurytopic adaptability of mobile ancient foraging hominids, as well as ecological polymorphism. The latter enabled hominids to adapt and exploit an increasing range of ecosytems, from the semi-arid tropics to subtropical steppes or woodlands, Mediterranean habitats, temperate woodland/grasslands, and a diversity of tropical forest formations in Eastern Asia. This adaptive versatility, linked with encephalization, particularly the expansion and increasing complexity of the brain cortex surface, was reinforced by cultural behaviour, best documented by technological behaviour. Lower Palaeolithic toolmaking demonstrates another behavioural discontinuity or technological ‘mutation’ by a familiarity and mastery, as ‘first geologists’, in acquiring suitable minerals, and skill in producing and using tools, as ‘secondary energy traps’ for various purposes, including prey carcass processing. Intermittent fire production represents another ‘mutation’ implying that hominids were virtually unique in overcoming the genetically inherited pyrophobic response, common among mammals. Cultural behaviour, as domain of socially acquired and transmitted interpretation and meaning of events, objects or activities, for mediating the world, pervades various aspects of human life (technology, subsistence, social life, cognition). It inserted progressively a new ‘cultural environment’ to which hominids became increasingly adapted and reliant on. This African dual heritage and bio-cultural evolutionary path documents how early hominids began following a new, hitherto unexploited adaptive niche, illustrated by long-range dispersals and gradual colonization of Eurasian ecosystems throughout the Pleistocene. This expansion became increasingly non-biological and contingent on cultural repertoires.

Sediment cores were recovered from Stella Lake and Baker Lake, sub-alpine lakes located in Great Basin National Park, NV, in 2005 and 2007, respectively. The cores were analyzed for subfossil chironomid (Insecta: Diptera: Chironomidae) remains. Chronologies for the sediment cores, developed using 210Pb, indicate the cores span the 20th century. The midge communities present in the lakes experience muted compositional change through much of the 20th century; however, the post-AD 1980 interval is notable due to rapid lake-specific faunal turnover. The recently deposited sediment in Baker Lake is characterized by decreases in the relative of abundance of Psectrocladius semicirculatus/sordillelus, Cladotanytarsus mancus group and Procladius, the local extirpation of Chironomus, and an increase the proportion of Sergentia, Tanytarsus type G and Tanytarsus type B. The Stella Lake midge community experienced a shift post-AD 1990 from an assemblage dominated by Tanytarsus type G to a P. semicirculatus/sordillelus dominated community. Application of a chironomid-based inference model for mean July air temperature (MJAT), based on a calibration set developed for the Inter-Mountain West of the United States consisting of 79 lakes and 54 midge taxa (rjack2 = 0.55 °C, RMSEP = 0.9 °C, maximum bias = 1.66 °C), provided a means to reconstruct the 20th century temperature regime for the region. Stella Lake and Baker Lake experience large fluctuations in MJAT during the early to mid-20th century and consistently above average temperature during the late-20th century. The chironomid-inferred MJAT reconstructions for Stella Lake and Baker Lake track observed July temperature in the region encompassed by Nevada Climate Division #2 during the late-20th century.

This study presents the Late-Holocene evolution of a northern Southampton Island (Nunavut, Canada) lake, using fossil chironomids supported by sedimentological evidences (XRF, grain size and CNS). All proxies revealed a relatively stable environment during the last millennium with short-lived events driving changes in the entire lake ecosystem. The chironomid-based paleotemperatures revealed variations of significant amplitude coincident with changes in the sediment density and chemical composition of the core. Higher temperature intervals were generally correlated to lower sediment density with higher chironomid concentration and diversity. Higher temperatures were recorded from cal yr AD 1160 to AD 1360, which may correspond to the Medieval Warm Period. Between cal yr AD 1360 and AD 1700, lower temperatures were probably related to a Little Ice Age event. This study presents new information on the timing of known climatic events which will refine our knowledge of the paleoclimate and climatic models of the Foxe Basin region. It also provides a new framework for the evolution of such freshwater ecosystems under the “Anthropocene” and underlines the importance of including sedimentological proxies when interpreting chironomid remains as this combined approach provides an extended overview of the past hydrological and geochemical changes and their impacts on lake biota.

Sieving samples for chironomid analysis with a 150μm mesh was shown to greatly reduce sample preparation time, and use of only larger specimens did not affect chironomid-inferred salinities in African lakes. Here, we tested if this method is suitable for temperature reconstruction in colder lakes at higher latitudes. Removal of specimens 150μm) than those obtained with the full model (all specimens >100μm). General patterns of temperature change were also altered. For Lake 7 on Southampton Island, Canada, a cooling trend was reconstructed with the full Canadian model while the modified Canadian model yielded a warming trend. When only specimens >150μm were used, two to three times more wet sediment was needed to obtain a sufficient number of head capsules. These results indicate that, in cold lakes (mean July/August air temperature ≤11°C), large proportions of head capsules are

Instrumental climate records from the central Canadian treeline zone display a pattern of variation similar to general Northern Hemisphere temperature trends. To examine whether this general correspondence extends back beyond the instrumental record, we obtained a sediment core from Lake S41, a small lake in the Northwest Territories of Canada at 63°43.11′ N, 109°19.07′ W. A radiocarbon-based chronology was developed for the core. The sediments were analyzed for organic-matter content by loss-on-ignition (LOI), biogenic-silica content (BSi), and chironomid community composition to reconstruct July air temperature and summer water temperature. The paleolimnological records were compared with records of atmospheric CO2 concentration, solar variability, and hemispheric temperature variations over the past 2000 years. The results of the analyses suggest that widely-documented long-term variations in Northern Hemisphere temperature associated with radiative forcing, namely the cooling following the medieval period during the Little Ice Age (LIA), and twentieth century warming, are represented in the central Canadian treeline zone. There is also evidence of a brief episode of warming during the eighteenth century. As evidenced by LOI and BSi, the twentieth century warming is typified by increased lake productivity relative to the LIA. Depending upon the measure, the increased productivity of the twentieth century nearly equals or exceeds that of any other period in the past 2000 years. In contrast, the rate of chironomid head capsule accumulation decreased and remained low during the twentieth century. Although the chironomid-inferred temperature reconstructions indicate cooling during the LIA, they present no evidence of greatly increased temperatures during the twentieth century. Warming during the twentieth century might have enhanced lake stratification, and the response of the chironomid fauna to warming was attenuated by decreased oxygen and lower temperatures in the hypolimnion of the more stratification-prone lake.

A lake sediment core recovered from Lake V57 on Victoria Island, Nunavut, Canada, spanning the last 2000 years, was analyzed for sub-fossil midge remains and organic-matter content (estimated by loss-on-ignition (LOI)). Significant changes in midge community composition occurred during the last 2000 years, with a distinct midge community appearing after 1600 AD. The chironomid community between 0 and 1600 AD was dominated by Heterotrissocladius, Tanytarsus, Abiskomyia, and Paracladius. At approximately 1600 AD, Heterotrissocladius decreased in relative abundance and taxa such as Corynocera ambigua, C. oliveri, Psectrocladius sordidellus type, and Pentanneurini increased in relative abundance. Previously published midge-based inference models for average July air temperature (AJAT) and summer surface–water temperature (SSWT) were applied to the subfossil midge stratigraphy. The AJAT reconstruction indicates relatively cool conditions existed between 1100 and 1600 AD, with exceptional warming occuring after 1600 AD, as lake productivity inferred from organic-matter content increased concomitantly with midge-inferred AJAT and SSWT. The cooler conditions between 1200 and 1600 AD, and the pattern of warming over recent centuries inferred from Lake V57 is broadly consistent with temperature-sensitive biogenic silica records from other sites in the central Canadian Arctic and the treeline zone to the south suggesting a regionally synchronous response to climate forcing.

PurposeThis paper illustrates, on the basis of a case study of a multinational corporation, the positive impact of intra‐organizational networking on the capacity to sustain competitive advantage in a highly volatile environment. It aims to provide researchers, consultants and managers with insights on how to design an organization leveraging internal resources and capabilities.Design/methodology/approachOne original case is presented, along with a series of analytical points drawn from this study. The research design is based on action research methods (one author participated in designing and implementing the “networking attitude” project) as well as primary (interviews) and secondary data (internal documents). The paper makes several basic points on the relationship between inter‐unit knowledge sharing and renewing competitive advantage in multinational corporations.FindingsThe critical findings relate to the importance of creating effective inter‐personal networks for enhancing knowledge sharing, and to the direct positive impact on overall strategic performance of transferring knowledge across organizational units. The bottom line is that knowledge is detained by people and it cannot be coordinated in a top‐down centralized manner, but rather requires organizational designs based on greater autonomy, efficient incentive systems and strategically coherent organizational cultures.Research limitations/implicationsThe findings of the paper are based on a single case study of a firm that successfully managed to create intra‐organizational knowledge‐sharing networks that resulted in significant improvements in overall performance, and hence generalization and robustness of the results would require the analysis of additional – successful and unsuccessful cases.Practical implicationsThe paper provides insights on the creation of effective knowledge‐sharing networks in multinational corporations.Originality/valueThe data, approach, and analysis are all original. This paper enriches the existing theory on knowledge management and strategy formation by highlighting the direct link between leveraging internal resources and improved performance. It addresses the problem of knowledge sharing in multinational corporations and emphasizes the importance of interpersonal links and autonomy in organizations. The model of knowledge sharing described in the paper can easily be adapted in different contexts and should therefore be of value to managers. To researchers it offers a comprehensive framework integrating internal capabilities and strategy implementation perspectives.

Concerns about the effects of global warming on Arctic environments have stimulated multidisciplinary research into the history of their long-term climatic and environmental variability to improve future predictions of climate in these remote areas. Here we present the first palaeolimnological study for Southampton Island using analyses of chironomids supported by sedimentological analyses, carried out on a 1 m long core retrieved from a lake located in the northeastern part of the island. This core was made up of marine sediments underneath 65 cm of freshwater lake sediments. A marine shell, humic-acids and chironomid head capsules were used to date this sequence. The Holocene environmental history of the lake consisted of two major contrasting periods. The first one, between about 5570 and 4360 cal. yr BP, was climatically unstable, with common postglacial chironomid taxa such as Corynocera oliveri-type, Paracladius and Microspectra radialis-type. This period also corresponded to the highest chironomid-inferred August air temperature (10°C) for the whole record and to significant increases in major chemical elements as detected by x-ray fluorescence. During the second period, which lasted from about 3570 cal. yr BP until the present, limnological conditions seemed to stabilize after a change to cold oligotrophic chironomid taxa, such as Heterotrissocladius subpilosus-group, with no major variations in the abundance of chemical elements. Inferred August air temperatures ranged between 8 and 9°C. This study provided unique information on the timing of the Holocene Thermal Maximum in the Foxe Basin area, a region with very little information available on long-term climate change. This region showed, so far, relatively few signs of recent climatic change, as opposed to other regions in the High Arctic.

PurposeThis paper seeks to take up the challenges of examining the issues of knowledge transfer in an organization operating across Europe, the Middle East, Africa and Latin America. The purpose is directed to understanding whether knowledge management efforts can lead to the improvement of knowledge transfer.Design/methodology/approachThe paper adopts a qualitative analysis based on a case study whose aim is to evaluate the effectiveness of a global knowledge management programme in achieving best practices transfer in sales and marketing practices throughout business units of Europe, Middle East, Africa and Latin America. The principal data‐gathering method is a structured interview conducted with senior staff from within 28 markets.FindingsThe study's findings reveal that there is a level of complexity and non‐linear interconnectivity within and between business units, which confirms that knowledge transfer is a complex, multifactor process relying on a number of interacting variables.Research limitations/implicationsThe results of a case study are somewhat limited in terms of their generalizability. Also, reflecting on the findings, it is useful to think of the challenge of achieving knowledge transfer across countries and cultures as a journey.Originality/valueThe value‐added of this paper is to give emphasis to the factors impacting knowledge transfer on a global scale.

International audience; Since Atom Probe Tomography reconstruction is based on ion back projection onto the emitter surface, understanding of the evolution dynamics of the tip shape is essential to get an accurate picture of the initial sample. In this article, an analytical approach is presented to dynamically describe the morphology evolution of complex multilayer structures during field evaporation. The model is mostly founded on the common continuity hypothesis, except for the classical hemispherical description of the tip apex, which is extended to a wider class of a constant mean curvature surface of revolution, the Delaunay surfaces. The results obtained from this approach are comparable with standard numerical simulations, but the analytical character of the model gives more insight into the principles driving the emitter morphology. In particular, a complete picture of curvature evolution during the transition from one layer to another is provided. Additionally, a field evaporation threshold for tip fracture in a bilayer sample is highlighted.

We describe the design, semantics, and implementation of a probabilistic programming language where programs are spreadsheet queries. Given an input database consisting of tables held in a spreadsheet, a query constructs a probabilistic model conditioned by the spreadsheet data, and returns an output database determined by inference. This work extends probabilistic programming systems in three novel aspects: (1) embedding in spreadsheets, (2) dependently typed functions, and (3) typed distinction between random and query variables. It empowers users with knowledge of statistical modelling to do inference simply by editing textual annotations within their spreadsheets, with no other coding.

International audience; The analysis of a same sample using nanometre or atomic-scale techniques is fundamental to fully understand device properties. This is especially true for the dopant distribution within last generation nano-transistors such as MOSFET or FINFETs. In this work, the spatial distribution of boron in a nano-transistor at the atomic scale has been investigated using a correlative approach combining electron and atom probe tomography. The distortions present in the reconstructed volume using atom probe tomography have been discussed by simulations of surface atoms using a cylindrical symmetry taking into account the evaporation fields. Electron tomography combined with correction of atomic density was used so that to correct image distortions observed in atom probe tomography\backslashnreconstructions. These corrected atom probe tomography\backslashnreconstructions then enable a detailed boron\backslashndoping analysis of the device.

Kerosene, a grade mineral oil, is commonly used to extract beetles from sediment. Here, the use of kerosene to extract chironomid head capsules was tested on 10 samples from sediment of different lakes, with different organic matter content as measured by loss on ignition, and estimated ages. Our results revealed that this flotation tool is very effective in extracting either full or half chironomid head capsules. The mean extraction efficiency was 89.3 ± 8.0% with an estimated relative abundance error ranging from −1% to 1% for 46 of the 57 identified taxa. Larger chironomids (400–500 µm width), which are often full of sediment particles, have the highest relative abundance error, with a maximum of 4.3% for Corynocera oliveri-type. A canonical correspondence analysis showed that, despite this small bias, samples retrieved with the kerosene flotation do not differ from the whole sample assemblages. These results give us confidence in the use of this flotation technique for chironomid sample preparation.

The effect of 33 environmental variables on the distribution of chironomids was studied in 60 lakes of northwestern Quebec (Canada). A detrended canonical correspondence analysis detected linearity in the chironomid assemblages, thus redundancy analysis was used to identify the variables affecting the chironomid communities. Lake depth, dissolved organic carbon (DOC), mean August air temperature, and surface water temperature were the four variables that best explained the distribution of chironomids. Partial least squares analysis was used to develop new inference models. Among models, the one for mean August air temperature had the highest coefficient of determination (r[Formula: see text] = 0.67) and the lowest root mean square error of prediction (= 1.17 °C). The results indicated that for downcore temperature reconstructions, it might be hard to dissociate the combined effects of temperature, DOC, and depth. Changes in taxa such as Heterotrissocladius brundini-type, Heterotrissocladius subpilosus-type, Heterotrissocladius grimshawi-type, Micropsectra radialis-type, Tanytarsus lugens-type, and Microtendipes can be attributed to changes in lake depth and (or) temperature. Changes in Heterotanytarsus, Dicrotendipes, Cryptotendipes, and Cryptochironomus might be attributed to shifts in temperature and DOC. Relationships among temperature, DOC, and lake depth should be studied in a "neo-ecology" design to better understand their impact on chironomid assemblage composition.

The concept of a home-based land use strategy is fundamental for studying recent and prehistoric foraging populations. A proposed datum for the emergence of this behavior is set during later Middle Pleistocene times, around 400–350 kya, and temporally linked with the first established evidence for domestic fire making. Precise causes for this dual appearance remain obscure. Surveying the known Paleolithic record and contexts serves to identify possible factors and processes leading to this development. The emphasis here is on fire technology, particularly domestic fire making and uses, and fire's relationship with home base sensu lato characteristics, as contrasted with a previous land use system that reflects earlier primate patterns. Intentional bush and grassland burning could be components of this home base and domestic fire system. The issue of domestic fire and home base at Locality 1 in Zhoukoudian Cave is evaluated from the perspective of contemporaneous hominid behavior in Eurasia and Africa.

We propose a new kind of probabilistic programming language for machine learning. We write programs simply by annotating existing relational schemas with probabilistic model expressions. We describe a detailed design of our language, Tabular, complete with formal semantics and type system. A rich series of examples illustrates the expressiveness of Tabular. We report an implementation, and show evidence of the succinctness of our notation relative to current best practice. Finally, we describe and verify a transformation of Tabular schemas so as to predict missing values in a concrete database. The ability to query for missing values provides a uniform interface to a wide variety of tasks, including classification, clustering, recommendation, and ranking.

Middle Palaeolithic tool assemblages have a long history of controversy. This new analysis employing principal components addresses the recurrent issues of comparing tool assemblages from different sites, whilst retaining support from the seminal study of Bordes.