bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction between Slag and Clinker during Cement Hydration Process
Authors: Zhou Sheng Bo , Shen Ai Qin , Li Geng Fei
Published: December 2013

In order to investigate the activity of different original slags and the coupled relation between the slag and the clinker, the simplified slag cement system was designed in the experiment, in which clinker was replaced by lime.The reactional degree of slag in cement was determined through using chemical combined water content method, and the hydration processs were determined through using DSC-TGA. The results showed that for the different original slags, the destruction and rebuilding process of their microstructure were important to distinguish the activity of slags. And the process of slag hydration mainly experienced two stages, including microstructure destruction at early ages and microstucture rebuilding at later ages. And the variation of Calcium hydroxide content in cement indicated the interaction between the slag and clinker, and slag may improve the clinker hydration velocity.
Characteristics for a Flow Past a Circular Cylinder with Two Types of Radial Disturbances at Re=100
Authors: Lin Li Ming , Zhong Xing Fu , Wu Ying Xiang
Published: December 2013

For better understanding physical mechanism of radial disturbances, previously proposed to disturb the wake flow and vortex-induced vibration of risers, numerical simulations are carried out for the flow around the fixed cylinder with such disturbances at a Reynolds number of 100. After introducing disturbances, specific distributions of flow and vertical vorticity near cylinder surfaces are identified and related to different vortex patterns. The spanwise variation of free shear layers is discussed and physically explained. Different characteristics for the pressure on cylinder surfaces, frequency of vortex shedding and time history of lift are also analyzed and presented in detail.
The Pre-Twisted Thin-Walled Beam Element Stiffness Matrix Considering the Saint-Venant Warping Deformation
Authors: Chen Chang Hong , Huang Ying
Published: December 2013

Based on the traditional mechanical model of thin-walled straight beam, the paper makes a systematic analysis and research on the pre-twisted thin-walled beam finite element numerical model. Firstly, based on the geometric deformation differential relationship, the paper deduces the pre-twisted thin-walled beam Saint-Venant warping strain. According to traditional thin-walled straight beam finite element mechanical model, the paper establishes its finite element stiffness matrix considering the Saint-Venant warping deformations. Finally, by calculating the pre-twisted elliptical section beam example, and contrasting three-dimensional solid finite element using ANSYS, the comparative analysis results show that pre-twisted thin-walled beam element stiffness matrix considering Saint-Venant warping deformation has good accuracy.
Thermo-Mechanical Couple Analysis of Cylinder Head Joint with Quadratic Contact
Authors: Hu Gui Chuan , Liu Jing Hua
Published: December 2013

Finite element simulation technology was applied to the steady heat transfer and thermo-mechanical coupling analysis in order to investigate the influence of thermal load on stress intensity and sealing performance. An finite element heat transfer model of cylinder head joint assembly was set up, based on which the steady heat transfer analysis was performed subsequently by applying reasonable boundary conditions and loads. The influence on cylinder head sealing performance due to thermal field under the thermal stress conditions was evaluated by using the finite element method. The results showed that the thermal load increases the bolt tensile force and the gasket pressure, which help to improve the sealing performance. Compared to the mechanical load case, the thermo-mechanical stress of the liner and the cylinder head is obviously increased, so the thermal load is not neglectable when calculating the stress intensity of the cylinder head and the cylinder liner.
A Study on Dynamic Characteristics of Hyper-Elastic Shock Programmer with Truncated Conical Shape
Authors: Yang Tae Ho , Lee Young Shin , Kim Yoon Jae , Kim Tae Hyeong , Shul Chang Won , Yang Myung Seog , An Chae Hun , Lee Gyu Sub
Published: December 2013

Polyurethane (PU) S80A was used as the material of the elastomer of the shock programmer in this paper. To validate Ogden hyper-elastic material model in simulation, the small impact test was performed. As the comparison for the time history of the acceleration between the impact test and simulation was performed. Using the cylindrical shock programmer, the constant used in Ogden hyper-elastic material model was calculated. The wave shape of the acceleration was obtained with the noised sign. To clearly obtain the wave shape of the acceleration the cylindrical shock programmer, the truncated conical shock programmer was used. Using the Ogden hyper-elastic material model, design variables of the shock programmer with the truncated conical shape was studied. Using the shock programmer with truncated conical shape the range on the level and time duration of the acceleration in simulation was from 494.9 m/s2 to 10941 m/s2 and from 1.3 msec to 23.5 msec, respectively.
Estimation of Master Curves of Relaxation Modulus and Tensile Properties for Solid Propellant
Authors: Seo Boh Wi , Kim Jae Hoon
Published: December 2013

The stress relaxation modulus E(t) is one of the most important properties of viscoelastic materials such as solid propellant, and it is used to define the viscoelastic behavior based on the influence of time and temperature. In this paper, stress relaxation tests are conducted under constant strain 2% for 600 seconds in the range of temperature 60°C to-60°C and tensile tests are performed for solid propellants under constant cross head rate 5 mm/min in the same temperatures as stress relaxation tests. Based on the results, time-temperature shift factors are obtainedby shifting the relaxation modulus curves horizontally and the master curve of relaxation modulus is generated. The master curve of relaxation modulus according to classical method and Williams-Landel-Ferry (WLF) method are discussed. Also, the master curve of tensile properties are drawn using predetermined shift factor and the results are discussed.
Research on the NNARX Model Identification of Hydroelectric Unit Based on Improved L-M Algorithm
Authors: Xiao Zhi Huai , An Zhou Peng , Wang Shu Qing , Zeng Shi Qi
Published: December 2013

Its hard to use traditional ways to set up a hydroelectric power plant model due to its complex, time-varying and nonlinear characteristics. This article uses the neural network autoregressive with exogenous input (NNARX) to identify and model hydro-turbine generating unit which is the key in the hydroelectric power plant modeling. The random guide vain signal is used to train NNARX in this paper and the other two working conditions are used to check its generalization ability. In order to improve identification accuracy, generalization performance and training speeds, an improved Levenberg-Marquardt algorithm is proposed in this article which is based on the L-M algorithm that widely used in artificial neural network weights adjustment. Simulation results indicate that NNARX model with improved L-M algorithm can reach high recognition accuracy and have good generalization ability. It can provide a good simulation model for intelligent controller design in the future.
A Spiral Actuated Micro In-Pipe Robot for Pipes Diameter 15mm
Authors: Jiang Tao , Luo Zi Rong , Shang Jian Zhong
Published: December 2013

Micro In-Pipe Robots are strongly demanded in the application of micro pipe failure-detection in nuclear stations and actuation systems of ships. In this essay, a micro in-pipe robot based on 15mm diameter's pipe with new spiral driving system and cage structure was developed, and the mechanics model of the micro robot was built. By utilizing virtual modeling technology, the robot's structural parameters were analyzed and optimized, and a real model was manufactured using optimized parameters with maximum traction 21.49N, maximum moving speed over 10mm/s, which met the requirements of being micro in size and large in traction.
Gear Dynamic Transmission Error Testing
Authors: Lei Dun Cai , Tang Jin Yuan , Tang Jian Jie
Published: December 2013

A measuring device for gear dynamic transmission error test is developed based on NI Labview software, and a new type eccentric bushing structure that can simulate a variety of installation errors is presented. The hardware and software design of the gear dynamic transmission error measuring device is given, and the gear dynamic transmission errors for low-speed and high-speed in different loads are gotten based on the device and the measured data. Experimental dynamic transmission error results show that the gear dynamic transmission error measuring device is a stable and friendly interface with easy operation and high accuracy, able to do real-time detection and data acquisition for gearing.
Impact of Protective Release Coatings with Nanopowders on the Quality of Bronze Castings Surface
Authors: Martyushev Nikita , Semenkov Ilya V. , Petrenko Yuriy N.
Published: December 2013

In work are submitted data of casting mold coverings with nanopowders application for molding lead bronze. Influence of a structure of used protective - separating coating of a foundry core on a microstructure of castings was investigated. For experimental work following coverings (the patent No 2297300) a mix dioxide zirconium nanopowder with industrial oil, and the same structure, but already on a basis on oxide aluminum nanopowder have been chosen. It is shown that these coverings application leads to decrease in quantity of surface defects, the roughness of a cast surface decreases. At the same time penetration of particles of a powder from a foundry covering in casting doesn't occur.
Activation of Copper and Alumina Powders in Ball Mill
Authors: Martyushev Nikita , Semenkov Ilya V.
Published: December 2013

In this work data on results of powders mix activation in a planetary spherical mill are presented at various modes of processing. For researches were chosen powders of aluminum oxide and copper. The ratio of initial powders mass and processing time in a spherical mill varied. Results showed that the increase in time of processing leads to powders particles crushing and introduction of firmer aluminum oxide powder particles in copper particles. Changes of powders phase structure in the activation course don't occur. Particles agglomerations at processing time till 5 minutes also it is not observed.
Hardening of the Surface Layer of Silumin by Electron Beam
Authors: Ivanov Yurii F. , Petrikova Elizaveta A. , Cherenda Nikolay N. , Teresov Anton D.
Published: December 2013

In the present work has been carried out the treatment of silumin by high-intensity electron beam with different density of the input energy. The structure and phase composition of surface layer have been studied by the methods of X-ray diffraction and electron microscopy both scanning and diffraction transmission. The mechanisms are responsible for improvement of properties of modified material have been revealed. It has been shown that electron beam treatment of silumin is accompanied by the formation of multilayer submicro-and nanocrystalline structure and result in increasing the microhardness of the surface layer (towards the core) is ~ 3.5 times, the Young's modulus in a ~ 1.4 times, the ultimate bending strength (in ~ 1.2 times) and tensile strength (in ~ 1.4 times), the bending plastic limit (in ~ 1.2 times) and tensile (in ~ 1.8 times).
Deposition of Biocompatible Coatings from the Ablation Plasma Produced by the Irradiation of the Hydroxyapatite Target with Powerful Ion Beams
Authors: Volokitina Tatyana L. , Tverdokhlebov Sergey Ivanovich , Remnev Gennadij , Pushkarev Alexander , Khaylov Ilya
Published: December 2013

Biocompatible calcium phosphate coatings were formed from the ablation plasma fusion produced by irradiation of natural and synthetic hydroxyapatite target with power ion beams. The experimental work to increase the energy efficiency of coatings deposition by high-power ion beams method is carried on the TEMP 4M accelerator
Mechanical and Tribotechnical Characteristics of Nanocomposites Based on Mixture of Ultrahigh Molecular Weight Polyethylene and Polypropylene
Authors: Panin Sergey V. , Kornienko Lyudmila А. , Poltaranin М.A. , Маndoung Т. , Ivanova L.R.
Published: December 2013

The aim of the study is to design wear-resistant and extrudable polymeric composites based on mixture of UHMWPE+PP with increased tribotechnical characteristics for the wide application in friction units of machine parts and mechanisms as well as using the polymeric resin developed for obtaining nanocomposites. Adding of block copolymer PP-b LLDPE to UHMWPE is motivated by the necessity to increase the adhesion between the incompatible polymeric components of the mixture. It is shown that wear intensity of the polymer-polymeric composites UHMWPE+n wt.% PP-b-LLDPE is reduced at filling UHMWPE by the block copolymer. In doing so, an important technological characteristic of UHMWPE specific extrusion pressure (proportional to the melt flow index) is improved (is lowered). Nanocomposites on the basis of the given matrix have shown wear resistance of 3-4 times higher in contrast with pure UHMWPE. Permolecular structure and wear track surfaces of nanocomposites on the basis of polymer-polymeric matrix (UHMWPE+10 wt.% PP-b-LLDPE) were investigated. The mechanism of the wear of nanocomposites is discussed.
Properties of Silver Nanoparticles Prepared by the Electric Spark Dispersion Method
Authors: Zhuravkov S.P. , Plotnikov Evgeny , Martemiyanov Dmitry , Yavorovsky Nikolay A. , Hasse Ulrich , Zander Stefan
Published: December 2013

The morphological and structural characteristics of nanoscale silver particles obtained by the method of electric spark dispersion of metal granules in the liquid aprotic medium were obtained using atomic force microscopy, transmission electron microscopy, and dynamic light scattering spectroscopy. The specific surface, morphology, structure and the distribution by size of the particles are presented.
Venation-Inspired Growth Technique for Stiffener Layout Design of Plate and Shell Structures
Authors: Xue Kai , Li Lei , Li Qiu Hong
Published: December 2013

A novel design method for stiffener layout of plate and shell structures is proposed in this paper. The method is inspired by the morphogenesis mechanism of dicotyledonous venation which is featured by hierarchy and functional adaptivity. It is expected that a optimal stiffener layout can be gradually achieved if the stiffeners extend by obeying a similar growth rule as the venation. Starting from the so called “seeds”, the stiffeners grow and branch off towards the direction that optimizes the structural performance. And the stiffeners with the minimum effectiveness to the structural performance are degenerated simultaneously. During the design process, the relative density of each element is treated as the design variable. The growth and degeneration of the stiffeners are determined by the nodal and elemental sensitivity numbers respectively. The design algorithm is programmed in Python and integrated with Abaqus software which is used as the FEA preprocessor and solver. To validate the effectiveness of the proposed method, it is applied to design the stiffener layouts of some typical structures with the objective of maximizing the overall stiffness with a volume constraint.
Mn Blended Hydroxyapatite Nanoceramic: Bioactivity, Dielectric and Luminescence Studies
Authors: Mahabole Megha , Bahir Manjushree , Khairnar Rajendra
Published: December 2013

Abstract: In this study, in-vitro bioactivity of manganese blended hydroxyapatite (Mn-HAp) pellets is carried out using simulated body fluid (SBF) solution. The incubated Mn-HAp samples are characterized by XRD, FTIR and SEM/EDAX. Dielectric and photoluminescence properties of Mn-HAp samples are studied as a function of incubation period in SBF. XRD profiles show that hexagonal apatite structure remains intact after partial replacement of calcium ions by manganese ions and even after incubation. The change in absorption due to phosphate group, depicted in FTIR spectra, for incubated samples confirms growth of apatite on Mn-HAp surface. SEM/ EDAX studies suggest that Mn-HAp surface promotes the growth of apatite without changing its structure due to apatite nucleation and growth on the surface of Mn-HAp. The value of dielectric constant of Mn-HAp increases after incubation. Increase in period of immersion in m-SBF leads to decrease in dielectric constant of manganese exchanged hydroxyapatite. The photoluminescence (PL) study reveals that the Mn-HAp can be used stable and efficient blue luminescent material.
Optimal Design and Experimental Investigations of Aluminium Extrusion Profiles for Lightweight of Car Bumper
Authors: Zhou Jia , Wan X.M. , Li Y. , Zhao Q.J.
Published: December 2013

The present study aimed at developing an aluminium car bumper unit to replace the steel ones by using optimization based on experimental and FEM simulation results. The topology optimization method and response surface methodology (RSM) were applied in order to achieve an optimized design for the cross section of the crossbeam and the crash box, respectively. The three-points bending test and crash test for bumper unit were simulated to evaluate the optimization processes. The 6061 and 6063 aluminium alloy bumper unit has a weight reduction of 67% compared to the steel ones. The new extrusion dies were manufactured to produce profiles for the crossbeam and the crash box, respectively. Then the optimized extrusion profiles of crossbeam and crash box were verified by experimental studies. The performance tests were arranged to validate the experimental product. The mechanical properties of extruded aluminium crossbeam and crash box can satisfy the design requirements of products. The results indicate that the new designed unit can change the whole design of automotive parts for crash energy absorption, and definitely contribute to drastic weight reduction of steel parts.
Simulation of Material Flow Coupled with Die Analysis in Complex Shape Extrusion
Authors: Biba Nikolay , Stebunov Sergei , Lishny Andrey
Published: December 2013

The paper presents recent studies in simulation of thin profile extrusion technology with the emphasis on interaction between the material flow and the state of the tooling set. To take into consideration die deflection and gradient of the temperature across the die and mandrel during the entire process cycle a transient coupled thermo-mechanical model has been built on the basis of QForm-Extrusion program. The paper explains the background for this model and some tests to verify its accuracy. Practical implementation of this model at several die making and extrusion companies has shown it to be of higher accuracy compared to the results of rigid die simulation.
Finite Element Based Determination and Optimization of Seam Weld Positions in Porthole Die Extrusion of Double Hollow Profile with Asymmetric Cross Section
Authors: Schwane Martin , Kloppenborg Thomas , Khalifa Nooman Ben , Jäger Andreas , Tekkaya A. Erman
Published: December 2013

Finite elemente analysis (FEA) allows to reduce development time during the die design stage as well as costly extrusion trials with prototypes. Therefore, it is essential that FEA computation provides reliable results. Among other output quantities such as temperature, load, or die stress, the prediction of material flow is one of the most essential ones. Especially in porthole dies, the material flow can be very complex and thus the position of the seam welds in the profile may be uncertain. In this study the particle tracing method was utilized to determine and finally adjust the seam weld positions in a double hollow profile with varying wall thicknesses over the cross section. The seam weld positions resulting from the original die design were determined by Eulerian FEA computation in the first step. Subsequently, the seam weld positions were adjusted by changing the die geometry. The simulation results were verified by means of extrusion tests, which were conducted under industrial conditions. In addition, Lagrangian and Eulerian FEA was utilized to analyze the evolution of the seam weld positions by evaluation of material flow as well as pressure distribution during the transient initial stage and the steady-state stage of the extrusion process.
It was demonstrated that steady state process simulation and the particle tracing method can be used for the prediction of seam weld positions in complex hollow cross sections.
Functional diversity and seasonal activity of dung beetles (Coleoptera: Scarabaeoidea) on native grasslands in southern Alberta, Canada
Authors: Kadiri N. , Lumaret J.-P. , Floate K.D.
Published: December 2013

To characterise their functional diversity and seasonal activity, dung beetles (Coleoptera: Scarabaeoidea) were collected with baited pitfall traps at three sites for three years on a native grassland in southern Alberta, Canada. The total collection of 125 820 beetles comprised 12 species of which eight were of European origin. For each combination of site and year, assemblages were dominated by two or three core species of European origin that represented 70–95% of total beetles and more than 75% of total biomass, but only 10–30% of species richness. Core species consistently includedOnthophagus nuchicornis(Linnaeus) and occasionallyChilothorax distinctus(Müller) andColobopterus erraticus(Linnaeus). Coexistence of these core species appears to be facilitated by differences in their size, seasonal activity, and life history traits.
A preliminary examination of an in situ dual dye approach to measuring light fluxes in lotic systems
Authors: Minor Elizabeth C. , James Elizabeth , Austin Jay A. , Nelson Veronica , Lusk Ryan , Mopper Kenneth
Published: December 2013

Light is a critical parameter in aquatic ecosystems, affecting primary production and in situ photochemistry. However, measuring light exposure for suspended particles or dissolved components in a dynamic water column can be challenging with existing Eulerian approaches. Here, we assess the simultaneous deployment of two dyes differing in photolability (rhodamine WT and fluorescein) as a Lagrangian measure of sunlight exposure in a lotic system. Fluorescein is sensitive to light exposure; rhodamine WT is relatively photostable. We examined dye fluorescence at various pH, salinity, and temperature conditions. We also tested dye photolability as a function of pH and wavelength range. In conjunction with this laboratory work, we performed initial field testing of the dual‐dye approach in a stream on the north shore of Lake Superior, USA. Irradiation of the dyes using long‐pass filters identified wavelengths ≥ 420 nm as responsible for the vast majority of the loss of fluorescein fluorescence, with rhodamine appearing relatively photostable in these short‐term studies across the wave‐length ranges tested. Dye response to irradiation is pH‐sensitive; the dual‐dye approach will require additional calibration for acidic or basic waters and should be used with caution in aquatic systems undergoing strong (several pH unit) changes in pH. Field testing showed that the fluorescein to rhodamine WT ratio decreased approximately linearly with light exposure. The dual‐dye methodology shows promise as an in situ light sensor applicable to water column species in lotic systems if temperature is recorded, and the pH range is measured and relatively stable (e.g., varies by < 1 unit).
Size-resolved measurements of brown carbon in water and methanol extracts and estimates of their contribution to ambient fine-particle light absorption
Authors: Liu J. , Bergin M. , Guo H. , King L. , Kotra N. , Edgerton E. , Weber R. J.
Published: December 2013

Abstract. Light absorbing organic carbon, often called brown carbon, has the potential to significantly contribute to the visible light-absorption budget, particularly at shorter wavelengths. Currently, the relative contributions of particulate brown carbon to light absorption, as well as the sources of brown carbon, are poorly understood. With this in mind size-resolved direct measurements of brown carbon were made at both urban (Atlanta), and rural (Yorkville) sites in Georgia. Measurements in Atlanta were made at both a representative urban site and a road-side site adjacent to a main highway. Fine particle absorption was measured with a multi-angle absorption photometer (MAAP) and seven-wavelength Aethalometer, and brown carbon absorption was estimated based on Mie calculations using direct size-resolved measurements of chromophores in solvents. Size-resolved samples were collected using a cascade impactor and analyzed for water-soluble organic carbon (WSOC), organic and elemental carbon (OC and EC), and solution light-absorption spectra of water and methanol extracts. Methanol extracts were more light-absorbing than water extracts for all size ranges and wavelengths. Absorption refractive indices of the organic extracts were calculated from solution measurements for a range of wavelengths and used with Mie theory to predict the light absorption by fine particles comprised of these components, under the assumption that brown carbon and other aerosol components were externally mixed. For all three sites, chromophores were predominately in the accumulation mode with an aerodynamic mean diameter of 0.5 μm, an optically effective size range resulting in predicted particle light absorption being a factor of 2 higher than bulk solution absorption. Mie-predicted brown carbon absorption at 350 nm contributed a significant fraction (20 to 40%) relative to total light absorption, with the highest contributions at the rural site where organic to elemental carbon ratios were highest. Brown carbon absorption, however, was highest by the roadside site due to vehicle emissions. The direct size-resolved measurement of brown carbon in solution definitively shows that it is present and optically important in the near-UV range in both a rural and urban environment during the summer when biomass burning emissions are low. These results allow estimates of brown carbon aerosol absorption from direct measurements of chromophores in aerosol extracts.
Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer
Authors: Kupiszewski P. , Leck C. , Tjernström M. , Sjogren S. , Sedlar J. , Graus M. , Müller M. , Brooks B. , Swietlicki E. , Norris S. , Hansel A.
Published: December 2013

Abstract. Unique measurements of vertical size-resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from on board the Swedish icebreaker Oden, and provided both ship- and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Within the lowermost couple hundred metres, transport from the marginal ice zone (MIZ), condensational growth and cloud processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and therefore long-range transport plumes are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, such plumes can influence the radiative balance of the planetary boundary layer (PBL) by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles could be in biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary-layer transport of precursor gases from the MIZ, are considered to constitute the origin of cloud condensation nuclei (CCN) particles and thus be of importance for the formation of interior Arctic low-level clouds during summer, and subsequently, through cloud influences, for the melting and freezing of sea ice.
Growth of climate change commitments from HFC banks and emissions
Authors: Velders G. J. M. , Solomon S. , Daniel J. S.
Published: December 2013

Abstract. Chlorofluorocarbons (CFCs) are the primary cause of ozone depletion, and they also contribute to global climate change. With the global phaseout of CFCs and the coming phaseout of hydrochlorofluorocarbons (HCFCs), the substitute hydrofluorocarbons (HFCs) are increasingly used. While CFCs were originally used mainly in applications such as spray cans and were released within a year after production, concern about the ozone layer led to reductions in rapid-release applications, and the relative importance of slower-release applications grew. HFCs are now mainly used in refrigerators and air-conditioners (AC) and are released over years to a decade after production. Their containment in such equipment represents banks, which are building up as production grows. A key finding of our work is that the increases of HFC banks represent a substantial unseen commitment to further radiative forcing of climate change after production of the chemicals ceases. We show that earlier phaseouts of HFCs would provide greater benefits for climate protection than previously recognized, due to the avoided buildup of the banks. If, for example, HFC production were to be phased out in 2020 instead of 2050, not only would about 91–146 GtCO2eq of cumulative emission be avoided from 2020 to 2050, but an additional bank of about 39–64 GtCO2eq is also avoided in 2050. Choices of later phaseout dates lead to larger commitments to climate change unless growing banks of HFCs from millions of dispersed locations are collected and destroyed.
Sources and geographical origins of fine aerosols in Paris (France)
Authors: Bressi M. , Sciare J. , Ghersi V. , Mihalopoulos N. , Petit J.-E. , Nicolas J. B. , Moukhtar S. , Rosso A. , Féron A. , Bonnaire N. , Poulakis E. , Theodosi C.
Published: December 2013

Abstract. The present study aims at identifying and apportioning the major sources of fine aerosols in Paris (France) – the second largest megacity in Europe –, and determining their geographical origins. It is based on the daily chemical composition of PM2.5 characterised during one year at an urban background site of Paris (Bressi et al., 2013). Positive Matrix Factorization (EPA PMF3.0) was used to identify and apportion the sources of fine aerosols; bootstrapping was performed to determine the adequate number of PMF factors, and statistics (root mean square error, coefficient of determination, etc.) were examined to better model PM2.5 mass and chemical components. Potential Source Contribution Function (PSCF) and Conditional Probability Function (CPF) allowed the geographical origins of the sources to be assessed; special attention was paid to implement suitable weighting functions. Seven factors named ammonium sulfate (A.S.) rich factor, ammonium nitrate (A.N.) rich factor, heavy oil combustion, road traffic, biomass burning, marine aerosols and metals industry were identified; a detailed discussion of their chemical characteristics is reported. They respectively contribute 27, 24, 17, 14, 12, 6 and 1% of PM2.5 mass (14.7 μg m−3) on the annual average; their seasonal variability is discussed. The A.S. and A.N. rich factors have undergone north-eastward mid- or long-range transport from Continental Europe, heavy oil combustion mainly stems from northern France and the English Channel, whereas road traffic and biomass burning are primarily locally emitted. Therefore, on average more than half of PM2.5 mass measured in the city of Paris is due to mid- or long-range transport of secondary aerosols stemming from continental Europe, whereas local sources only contribute a quarter of the annual averaged mass. These results imply that fine aerosols abatement policies conducted at the local scale may not be sufficient to notably reduce PM2.5 levels at urban background sites in Paris, suggesting instead more coordinated strategies amongst neighbouring countries. Similar conclusions might be drawn in other continental urban background sites given the transboundary nature of PM2.5 pollution.
Temperature influence on the natural aerosol budget over boreal forests
Authors: Liao L. , Kerminen V.-M. , Boy M. , Kulmala M. , Dal Maso M.
Published: December 2013

Abstract. We investigated the natural aerosol evolution from biogenic monoterpene emissions among northern boreal forest area as function of temperature, using long-term field measurements of aerosol size distributions and back trajectories at two stations SMEAR I and SMEAR II in Finland. Particles were formed via nucleation through the clean ocean to land transition of air parcels, and continuously grew to larger sizes during air mass transport. Both the travelling hour over land and temperature influences the evolution of the particle number size distribution and the average aerosol mass yield from BVOC emissions. Average concentrations of nucleation mode particles were higher at lower temperatures, whereas the opposite was true for accumulation mode particles, thus more CCN may be formed at higher temperature. The overall apparent aerosol yield derived from the aerosol masses against accumulated monoterpene emissions ranges 13–37% with a minor yet complicating temperature dependence.
Characterization of uncertainties in atmospheric trace gas inversions using hierarchical Bayesian methods
Authors: Ganesan A. L. , Rigby M. , Zammit-Mangion A. , Manning A. J. , Prinn R. G. , Fraser P. J. , Harth C. M. , Kim K.-R. , Krummel P. B. , Li S. , Mühle J. , O'Doherty S. J. , Park S. , Salameh P. K. , Steele L. P. , Weiss R. F.
Published: December 2013

Abstract. We present a hierarchical Bayesian method for atmospheric trace gas inversions. This method is used to estimate emissions of trace gases as well as "hyper-parameters" that characterize the probability density functions (PDF) of the a priori emissions and model-measurement covariances. By exploring the space of "uncertainties in uncertainties", we show that the hierarchical method results in a more complete estimation of emissions and their uncertainties than traditional Bayesian inversions, which rely heavily on expert judgement. We present an analysis that shows the effect of including hyper-parameters, which are themselves informed by the data, and show that this method can serve to reduce the effect of errors in assumptions made about the a priori emissions and model-measurement uncertainties. We then apply this method to the estimation of sulfur hexafluoride (SF6) emissions over 2012 for the regions surrounding four Advanced Global Atmospheric Gases Experiment (AGAGE) stations. We find that improper accounting of model representation uncertainties, in particular, can lead to the derivation of emissions and associated uncertainties that are unrealistic and show that those derived using the hierarchical method are likely to be more representative of the true uncertainties in the system. We demonstrate through this SF6 case study that this method is less sensitive to outliers in the data and to subjective assumptions about a priori emissions and model-measurement uncertainties, than traditional methods.
Contiguous polarisation spectra of the Earth from 300–850 nm measured by GOME-2 onboard MetOp-A
Authors: Tilstra L. G. , Lang R. , Munro R. , Aben I. , Stammes P.
Published: December 2013

Abstract. In this paper we present the first contiguous high-resolution spectra of the Earth's polarisation observed by a satellite instrument. The measurements of the Stokes fraction Q/I are performed by the spectrometer GOME-2 onboard the MetOp-A satellite. Polarisation measurements by GOME-2 are performed by onboard polarisation measurement devices (PMDs) and the high-resolution measurements discussed in this paper are taken in the special "PMD RAW" mode of operation. The spectral resolution of these PMD RAW polarisation measurements varies from 3 nm in the ultraviolet (UV) to 35 nm in the near-infrared wavelength range. We first compare measurements of the polarisation from cloud-free scenes with radiative transfer calculations for a number of cases. We find good agreement but also a spectral discrepancy at 800 nm, which we attribute to remaining imperfections in the calibration key data. Secondly, we study the polarisation of scenes with special scattering geometries that normally lead to near-zero Q/I. The GOME-2 polarisation spectra indeed show this behaviour and confirm the existence of the small discrepancy found earlier. Thirdly, we study the Earth polarisation for a variety of scenes. This provides a blueprint of Q/I over land and sea surfaces for various degrees of cloud cover. Fourthly, we compare the spectral dependence of measurements of Q/I in the UV with the generalised distribution function that was proposed in the past (Schutgens and Stammes, 2002) to describe the shape of the UV polarisation spectrum. The GOME-2 data confirm that these functions match the spectral behaviour captured by the GOME-2 PMD RAW mode.
A reduced fraction of plant N derived from atmospheric N (%Ndfa) and reduced rhizobial nifH gene numbers indicate a lower capacity for nitrogen fixation in nodules of white clover exposed to long-term CO2 enrichment
Authors: Watanabe T. , Bowatte S. , Newton P. C. D.
Published: December 2013

Abstract. Using the δ15N natural abundance method, we found that the fraction of nitrogen derived from atmospheric N (%Ndfa) in field-grown white clover (Trifolium repens L.) plants was significantly lower (72.0% vs. 89.8%, p = 0.047 in a grassland exposed to elevated CO2 for 13 yr using free air carbon dioxide enrichment (FACE). Twelve months later we conducted an experiment to investigate the reasons behind the reduced N fixation. We took cuttings from white clover plants growing in the FACE and established individual plants in a glasshouse using soil from the appropriate ambient or elevated CO2 treatments. The established plants were then transplanted back into their "rings of origin" and sampled over a 6-week period. We used molecular ecological analyses targeting nifH genes and transcripts of rhizobia in symbiosis with white clover (Trifolium repens L.) to understand the potential mechanisms. Shoot biomass was significantly lower in eCO2, but there was no difference in nodule number or mass per plant. The numbers of nifH genes and gene transcripts per nodule were significantly reduced under eCO2, but the ratio of gene to transcript number and the strains of rhizobia present were the same in both treatments. We conclude that the capacity for biological nitrogen fixation was reduced by eCO2 in white clover and was related to the reduced rhizobia numbers in nodules. We discuss the finding of reduced gene number in relation to factors controlling bacteroid DNA amount, which may imply an influence of nitrogen as well as phosphorus.
Relationships between substrate, surface characteristics, and vegetation in an initial ecosystem
Authors: Biber P. , Seifert S. , Zaplata M. K. , Schaaf W. , Pretzsch H. , Fischer A.
Published: December 2013

Abstract. We investigated surface and vegetation dynamics in the artificial initial ecosystem "Chicken Creek" (Lusatia, Germany) in the years 2006–2011 across a wide spectrum of empirical data. We scrutinized three overarching hypotheses concerning (1) the relations between initial geomorphological and substrate characteristics with surface structure and terrain properties, (2) the effects of the latter on the occurrence of grouped plant species, and (3) vegetation density effects on terrain surface change. Our data comprise and conflate annual vegetation monitoring results, biennial terrestrial laser scans (starting in 2008), annual groundwater levels, and initially measured soil characteristics. The empirical evidence mostly confirms the hypotheses, revealing statistically significant relations for several goal variables: (1) the surface structure properties, local rill density, local relief energy and terrain surface height change; (2) the cover of different plant groups (annual, herbaceous, grass-like, woody, Fabaceae), and local vegetation height; and (3) terrain surface height change showed significant time-dependent relations with a variable that proxies local plant biomass. Additionally, period specific effects (like a calendar-year optimum effect for the occurrence of Fabaceae) were proven. Further and beyond the hypotheses, our findings on the spatiotemporal dynamics during the system's early development grasp processes which generally mark the transition from a geo-hydro-system towards a bio-geo-hydro system (weakening geomorphology effects on substrate surface dynamics, while vegetation effects intensify with time), where pure geomorphology or substrate feedbacks are changing into vegetation–substrate feedback processes.
The role of ocean acidification in Emiliania huxleyi coccolith thinning in the Mediterranean Sea
Authors: Meier K. J. S. , Beaufort L. , Heussner S. , Ziveri P.
Published: December 2013

Abstract. Ocean acidification is a result of the uptake of anthropogenic CO2 from the atmosphere into the ocean and has been identified as a major environmental and economic threat. The release of several thousands of petagrams of carbon over a few hundred years will overwhelm the capacity of the surface ocean reservoirs to absorb carbon. The recorded and anticipated changes in seawater carbonate chemistry will presumably affect the global oceanic carbonate production. Coccolithophores as the primary calcifying phytoplankton group, and especially Emiliania huxleyi as the most abundant species have shown a reduction of calcification at increased CO2 concentrations for the majority of strains tested in culture experiments. A reduction of calcification is associated with a decrease in coccolith weight. However, the effect in monoclonal cultures is relatively small compared to the strong variability displayed in natural E. huxleyi communities, as these are a mix of genetically and sometimes morphologically distinct types. Average coccolith weight is likely influenced by the variability in seawater carbonate chemistry in different parts of the worlds' oceans and on glacial/interglacial time scales due to both physiological effects and morphotype selectivity. An effect of the ongoing ocean acidification on E. huxleyi calcification has so far not been documented in situ. Here, we analyze E. huxleyi coccolith weight from the NW Mediterranean Sea in a 12 yr sediment trap series, and surface sediment and sediment core samples using an automated recognition and analyzing software. Our findings clearly show (1) a continuous decrease in the average coccolith weight of E. huxleyi from 1993 to 2005, reaching levels below pre-industrial Holocene and industrial 20th century values recorded in the sedimentary record, and (2) seasonal variability in coccolith weight that is linked to the coccolithophore production. The observed long-term decrease in coccolith weight is most likely a result of the changes in the surface ocean carbonate system. Our results provide first indications of an in situ impact of ocean acidification on coccolithophore weight in a natural E. huxleyi population even in the highly alkaline Mediterranean Sea.
Forcing mechanisms behind variations in total organic carbon (TOC) concentration of lake waters during the past eight centuries – palaeolimnological evidence from southern Sweden
Authors: Bragée P. , Mazier F. , Rosén P. , Fredh D. , Broström A. , Granéli W. , Hammarlund D.
Published: December 2013

Abstract. Decadal-scale variations in total organic carbon (TOC) concentration in lake water since AD 1200 in two small lakes in southern Sweden were reconstructed based on visible-near infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts of local land-use changes and regional variations in sulphur deposition and climate on the inferred changes in TOC concentration, the same sediment records were subjected to multi-proxy palaeolimnological analyses. Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical records provided information on catchment-scale environmental changes, and comparisons were made with available records of climate and population density. Our long-term reconstructions reveal that TOC concentrations were generally high prior to AD 1900, with second-order variations coupled mainly to changes in agricultural land-use intensity. The last century showed significant changes, and unusually low TOC concentrations were recorded in 1930–1990, followed by a recent increase. Variations in sulphur emissions, with an increase in the early 1900s to a peak around AD 1980 and a subsequent decrease, were most likely the main driver of these dynamics, although processes related to the introduction of modern forestry and recent increases in precipitation and temperature may have contributed. The increase in lake-water TOC concentration from around AD 1980 may therefore reflect a recovery process. Given that the effects of sulphate deposition now subside, other forcing mechanisms related to land management and climate change will possibly become the main drivers of TOC concentration changes in boreal lake waters in the future.
Accuracy of the zeroth- and second-order shallow-ice approximation – numerical and theoretical results
Authors: Ahlkrona J. , Kirchner N. , Lötstedt P.
Published: December 2013

Abstract. In ice sheet modelling, the shallow-ice approximation (SIA) and second-order shallow-ice approximation (SOSIA) schemes are approaches to approximate the solution of the full Stokes equations governing ice sheet dynamics. This is done by writing the solution to the full Stokes equations as an asymptotic expansion in the aspect ratio ε, i.e. the quotient between a characteristic height and a characteristic length of the ice sheet. SIA retains the zeroth-order terms and SOSIA the zeroth-, first-, and second-order terms in the expansion. Here, we evaluate the order of accuracy of SIA and SOSIA by numerically solving a two-dimensional model problem for different values of ε, and comparing the solutions with afinite element solution to the full Stokes equations obtained from Elmer/Ice. The SIA and SOSIA solutions are also derived analytically for the model problem. For decreasing ε, the computed errors in SIA and SOSIA decrease, but not always in the expected way. Moreover, they depend critically on a parameter introduced to avoid singularities in Glen's flow law in the ice model. This is because the assumptions behind the SIA and SOSIA neglect a thick, high-viscosity boundary layer near the ice surface. The sensitivity to the parameter is explained by the analytical solutions. As a verification of the comparison technique, the SIA and SOSIA solutions for a fluid with Newtonian rheology are compared to the solutions by Elmer/Ice, with results agreeing very well with theory.