Radiocarbon evidence for a smaller oceanic carbon dioxide sink than previously believed

Radiocarbon produced naturally in the upper atmosphere or artificially during nuclear weapons testing is the main tracer used to validate models of oceanic carbon cycling, in particular the exchange of carbon dioxide with the atmosphere and the mixing parameters within the ocean itself. Here we test the overall consistency of exchange fluxes between all relevant compartments in a simple model of the global carbon cycle, using measurements of the long-term tropospheric CO2 concentration and radiocarbon composition, the bomb 14C inventory in the stratosphere and a compilation of bomb detonation dates and strengths. We find that to balance the budget, we must invoke an extra source to account for 25% of the generally accepted uptake of bomb 14C by the oceans. The strength of this source decreases from 1970 onwards, with a characteristic timescale similar to that of the ocean uptake. Significant radiocarbon transport from the remote high stratosphere and significantly reduced uptake of bomb 14C by the biosphere can both be ruled out by observational constraints. We therefore conclude that the global oceanic bomb 14C inventory should be revised downwards. A smaller oceanic bomb 14C inventory also implies a smaller oceanic radiocarbon penetration depth, which in turn implies that the oceans take up 25% less anthropogenic CO2 than had previously been believed

COCAP : a carbon dioxide analyser for small unmanned aircraft systems

Unmanned aircraft systems (UASs) could provide a cost-effective way to close gaps in the observation of the carbon cycle, provided that small yet accurate analysers are available. We have developed a COmpact Carbon dioxide analyser for Airborne Platforms (COCAP). The accuracy of COCAP's carbon dioxide (CO2) measurements is ensured by calibration in an environmental chamber, regular calibration in the field and by chemical drying of sampled air. In addition, the package contains a lightweight thermal stabilisation system that reduces the influence of ambient temperature changes on the CO2 sensor by 2 orders of magnitude. During validation of COCAP's CO2 measurements in simulated and real flights we found a measurement error of 1.2 mu mol mol(-1) or better with no indication of bias. COCAP is a self-contained package that has proven well suited for the operation on board small UASs. Besides carbon dioxide dry air mole fraction it also measures air temperature, humidity and pressure. We describe the measurement system and our calibration strategy in detail to support others in tapping the potential of UASs for atmospheric trace gas measurements.Peer reviewe

Seasonal, synoptic, and diurnal-scale variability of biogeochemical trace gases and O2 from a 300-m tall tower in central Siberia

We present first results from 19 months of semicontinuous concentration measurements of biogeochemical trace gases (CO2, CO, and CH4) and O2, measured at the Zotino Tall Tower Observatory (ZOTTO) in the boreal forest of central Siberia. We estimated CO2 and O2 seasonal cycle amplitudes of 26.6 ppm and 134 per meg, respectively. An observed west-east gradient of about -7 ppm (in July 2006) between Shetland Islands, Scotland, and ZOTTO reflects summertime continental uptake of CO2 and is consistent with regional modeling studies. We found the oceanic component of the O2 seasonal amplitude (Atmospheric Potential Oxygen, or APO) to be 51 per meg, significantly smaller than the 95 per meg observed at Shetlands, illustrating a strong attenuation of the oceanic O2 signal in the continental interior. Comparison with the Tracer Model 3 (TM3) atmospheric transport model showed good agreement with the observed phasing and seasonal amplitude in CO2; however, the model exhibited greater O2 (43 per meg, 32%) and smaller APO (9 per meg, 18%) amplitudes. This seeming inconsistency in model comparisons between O2 and APO appears to be the result of phasing differences in land and ocean signals observed at ZOTTO, where ocean signals have a significant lag. In the first 2 months of measurements on the fully constructed tower (November and December 2006), we observed several events with clear vertical concentration gradients in all measured species except CO. During “cold events” (below -30°C) in November 2006, we observed large vertical gradients in CO2 (up to 22 ppm), suggesting a strong local source. The same pattern was observed in CH4 concentrations for the same events. Diurnal vertical CO2 gradients in April to May 2007 gave estimates for average nighttime respiration fluxes of 0.04 ± 0.02 mol C m-2 d-1, consistent with earlier eddy covariance measurements in 1999–2000 in the vicinity of the tower

WRF-Chem simulations in the Amazon region during wet and dry season transitions: evaluation of methane models and wetland inundation maps

The Amazon region, being a large source of methane (CH4), contributes significantly to the global annual CH4 budget. For the first time, a forward and inverse modelling framework on regional scale for the purpose of assessing the CH4 budget of the Amazon region is implemented. Here, we present forward simulations of CH4 as part of the forward and inverse modelling framework based on a modified version of the Weather Research and Forecasting model with chemistry that allows for passive tracer transport of CH4, carbon monoxide, and carbon dioxide (WRF-GHG), in combination with two different process-based bottom-up models of CH4 emissions from anaerobic microbial production in wetlands and additional datasets prescribing CH4 emissions from other sources such as biomass burning, termites, or other anthropogenic emissions. We compare WRFGHG simulations on 10 km horizontal resolution to flask and continuous CH4 observations obtained during two airborne measurement campaigns within the Balanc¸o Atmosf´erico Regional de Carbono na Amazˆonia (BARCA) project in November 2008 and May 2009. In addition, three different wetland inundation maps, prescribing the fraction of inundated area per grid cell, are evaluated. Our results indicate that the wetland inundation maps based on remote-sensing data represent the observations best except for the northern part of the Amazon basin and the Manaus area. WRF-GHG was able to represent the observed CH4 mixing ratios best at days with less convective activity. After adjusting wetland emissions to match the averaged observed mixing ratios of flights with little convective activity, the monthly CH4 budget for the Amazon basin obtained from four different simulations ranges from 1.5 to 4.8 Tg for November 2008 and from 1.3 to 5.5 Tg for May 2009. This corresponds to an average CH4 flux of 9–31 mgm−2 d−1 for November 2008 and 8–36 mgm−2 d−1 for May 2009.JRC.H.2 - Air and Climat

Influence of Fiber Volume and Alignment on Impact Resistance of Braided Carbon Fiber Epoxy Composites

The effect of axial tow alignment within a laminate ply stack on the impact penetration threshold for a series of composite panels was evaluated; specifically, the effect of a lateral shift in alignment to induce fiber nesting. Panels were fabricated from braided T700S carbon fiber and TenCate Advanced Composites's TC275-1 epoxy resin prepreg. Axial tows in each ply were aligned, offset, or rotated to evaluate the influence of such parameters on impact penetration resistance. Panel-to-panel variation in thickness, resin content, and fiber volume ratio were measured. Ultimately, process-related deviations drove penetration limits on impact. Influence of axial tow alignment was difficult to discern outside of the processing-induced variations between panels

Impact Behavior of Composite Fan Blade Leading Edge Subcomponent with Thermoplastic Polyurethane Interleave

Impact damage tolerance and damage resistance is a critical metric for application of polymer matrix composites where failure caused by impact damage could compromise structural performance and safety. As a result, several materials and/or design approaches to improve impact damage tolerance have been investigated over the past several decades. Many composite toughening methodologies impart a trade-off between increased fracture toughness and compromised in-plane strength and modulus. In large part, mechanical tests to evaluate composite damage tolerance include static methods such as Mode I, Mode II, and mixed mode failures. However, ballistic impact damage resistance does not always correlate with static properties. The intent of this paper is to evaluate the influence of a thermoplastic polyurethane veil interleave on the static and dynamic performance of composite test articles. Static coupon tests included tension, compression, double cantilever beam, and end notch flexure. Measurement of the resistance to ballistic impact damage were made to evaluate the composites response to high speed impact. The interlayer material showed a decrease of in-plane performance with only a moderate improvement to Mode I and Mode II fracture toughness. However, significant benefit to impact damage tolerance was observed through ballistic tests

Spin dependent structure function g_1 at low x and low Q^2

Theoretical description of the spin dependent structure function g_1(x,Q^2) in the region of low values of x and Q^2 is presented. It contains the Vector Meson Dominance contribution and the QCD improved parton model suitably extended to the low Q^2 domain. Theoretical predictions are compared with the recent experimental data in the low x, low Q^2 region

Evapotranspiration and water use efficiency in relation to climate and canopy nitrogen in U.S. forests

Understanding relations among forest carbon (C) uptake and water use is critical for predicting forest-climate interactions. Although the basic properties of tree-water relations have long been known, our understanding of broader-scale patterns is limited by several factors including (1) incomplete understanding of drivers of change in coupled C and water fluxes and water use efficiency (WUE), (2) difficulty in reconciling WUE estimates obtained at different scales, and (3) uncertainty in how evapotranspiration (ET) and WUE vary with other important resources such as nitrogen (N). To address these issues, we examined ET, gross primary production (GPP), and WUE at 11 AmeriFlux sites across North America. Our analysis spanned leaf and ecosystem scales and included foliar δ13C, δ18O, and %N measurements; eddy covariance estimates of GPP and ET; and remotely sensed estimates of canopy %N. We used flux data to derive ecosystem WUE (WUEe) and foliar δ13C to infer intrinsic WUE. We found that GPP, ET, and WUEe scaled with canopy %N, even when environmental variables were considered, and discuss the implications of these relationships for forest-atmosphere-climate interactions. We observed opposing patterns of WUE at leaf and ecosystem scales and examined uncertainties to help explain these opposing patterns. Nevertheless, significant relationship between C isotope-derived ci/ca and GPP indicates that δ13C can be an effective predictor of forest GPP. Finally, we show that incorporating species functional traits—wood anatomy, hydraulic strategy, and foliar %N—into a conceptual model improved the interpretation of Δ13C and δ18O vis-à-vis leaf to canopy water-carbon fluxes

Herstellung und Bewertung von elektrophoretisch abgeschiedenen keramischen 3D-Strukturen

Eine gesunde, ausgewogene Lebensweise und ein gutes soziales Standing sind bedingt durch funktionsfähigen, hochästhetischen Zahnersatz. Auch das steigende Bewusstsein für den eigenen Körper erhöht die Forderungen der Patienten nach hochästhetischem und metallfreiem Zahnersatz. Aktuell wird die vollkeramische Versorgung durch CAD/CAM basierte Fertigung von Monolithen und Gerüsten, die nachfolgend mit einer Verblendkeramik individualisiert werden müssen, erreicht. Es kommt immer noch zu Chipping und Gerüstfrakturen. Um dem entgegenzuwirken, hat sich diese Arbeit damit befasst, monolithische und hierarchisch geschichtete Käppchen unter Verwendung der Elektrophorese herzustellen und zu untersuchen. Es wurden verschiedene Setups mit individuellen Parametern erstellt, bei denen unterschiedliche Suspensionen zum Einsatz kamen. Es war dadurch möglich Monolithe, zu denen auch gesteuert poröse Käppchen zählen, aus verschiedenen Suspensionen zu produzieren. Anschließend wurden hierarchische Käppchen elektrophoretisch erzeugt, deren jeweilige Innen- bzw. Außenschicht auf die weitere strukturelle Funktion, wie zum Beispiel das adhäsive Befestigen zum Zahn oder ein verbesserter Haftverbund zur Verblendkeramik, abgestimmt wurde. Für die Suspensionen kamen nanoskalige Oxidkeramikpulver (Zirkoniumdioxid und Aluminiumoxid) zum Einsatz. Diese wurden mit absolutem Ethanol und Benzoesäure dispergiert. Teilweise wurden verschiedene Zusätze und Binder wie Butvar B 98, Tulopur 4000 oder Optapix PAF 46 hinzugefügt. Unter Anwendung der Nanoindentation konnte eine literaturbeschriebene Festigkeit des elektrophoretisch erzeugten Zirkongerüstes belegt werden. Es konnte ein druckknopfartiger Verbund von Zirkoniumdioxid und Aluminiumoxid nach dem Sintern im Rasterelektronenmikroskop beschrieben werden. Die einzelnen hierarchischen Schichten waren fest mit einander verbunden und es kam zu keinen strukturellen Trennungen bzw. Ablösungen der jeweiligen Schichten. Ein gesteigerter Haftverbund von 37,1 % von Zirkoniumdioxidgerüst und Verblendkeramik konnte unter Durchführung eines Druck-Scher-Versuches nachgewiesen werden. Der Test nach ISO 9693-2 belegt, dass unter Anwendung des neuentwickelten Bonders zuerst die Verblendkeramik nachgibt, während der Haftverbund noch intakt ist. Somit konnte gezeigt werden, dass eine hierarchische Strukturierung von dreidimensionalen Gerüstkeramiken möglich und umsetzbar ist. Modifizierte Schichten von Oxidkeramiken sind an ihrer Oberfläche ätzbar und sorgen somit für einen besseren Haftverbund zum Zahn und einer festeren Verbindung zur Verblendung. Auch die Einlagerung von Poren in die Gerüstkeramik konnte in Ansätzen gezeigt werden.A healthy, balanced way of life and well positioned social standing are both based on functional, high esthetic dental prosthesis. Even the raising awareness of the own body increases the patients request for high esthetic and crowns and bridges, which are free of alloys. The most popular possibility of all-ceramic dental care is the CAD/CAM-method. Monoliths and framework for dental covering are the products of this technology. Literature gives us a reference for the problem, called chipping and framework fracture. This work is based on the possibility of producing monolithic and hierachically structured frameworks, which were realized with Electrophoretic Deposition. Different setups were introduced with individual parameters and different suspensions. Caused on this, it was possible to produce monolithic dense and controlled porous frameworks. Afterwards 3D-frameworks with different hierarchical levels were investigated. The inner and outer layers were coordinated with their following function (for example the adhesiv cementation on a teeth or the increasing bond to the covering feldspar ceramic). Nanoscaled oxyd ceramic (circonia and aluminia) powder were used for the suspensions. They were dispersed in absolut ethanol and added with benzoic acid. Sometimes additives like Butvar B 98, Optapix PAF 46 and Tulopur 4000 were used. With the use of a nanoindenter it was documented, that the hardness of electrophoretic depositioned circonia is as high as it is mentioned in the literature. In the REM could be found a special bonding like a press button between circonia an aluminia after sintering. All hierarchically structures were straight bonded to each other. No cracks between the layers could be observed. With the results of pressure-shear-trials an increased bonding toughness of +37.1 % could be proved between the circonia framework and the added ceramic feldspar layer. The testing in the dependence on ISO 9693-2 had shown, that there is a delamination between the feldspar ceramic itself, while the bonding is still intact.So, it was demonstrated, that hierarchically structuring of dental frameworks with nanoscaled circonia and aluminia powder by using the epd technic is possible and realizable. Modified oxyd ceramic layers are on one hand etchable for a better framework-teeth-bonding and on the other hand for an increased toughness between framework and the feldspar ceramic layer. Even the inclusion of controlled pores in the framework could be shown

Strong radiative effect induced by clouds and smoke on forest net ecosystem productivity in central Siberia

Aerosols produced by wildfires are a common phenomenon in boreal regions. For the Siberian taiga, it is still an open question if the effects of aerosols on atmospheric conditions increase net CO2 uptake or photosynthesis. We investigated the factors controlling forest net ecosystem productivity (NEP) and explored how clouds and smoke modulate radiation as a major factor controlling NEP during fire events in the years 2012 and 2013. To characterize the underlying mechanisms of the NEP response to environmental drivers, Artificial Neural Networks (ANNs) were trained by eddy covariance flux measurements nearby the Zotino Tall Tower Observatory (ZOTTO). Total photosynthetically active radiation, vapour pressure deficit, and diffuse fraction explain at about 54-58% of NEP variability. NEP shows a strong negative sensitivity to VPD, and a small positive to f(dlf). A strong diffuse radiation fertilization effect does not exist at ZOTTO forest due to the combined effects of low light intensity, sparse canopy and low leaf area index. Results suggests that light intensity and canopy structure are important factors of the overall diffuse radiation fertilization effect.Peer reviewe