85 research outputs found
Kinetics in Cold Laval Nozzle Expansions: From Atmospheric Chemistry to Oxidation of Biomolecules in the Gas Phase
No full textNew developments and recent applications of pulsed and miniaturised Laval nozzle technology allowing many gas-phase molecular processes to be studied at very low temperatures are highlighted. In the present Minireview we focus on molecular energy transfer and reactions of molecular radicals (e.g. OH) with neutral molecules. We show that with the combination of pulsed laser photolysis and sensitive laser-induced fluorescence detection a large number of fast reactions of radicals with more or less complex neutral molecules can be measured in Laval nozzle expansions nowadays. It is also demonstrated that collisional energy transfer of neutral molecules can be measured via kinetically controlled selective fluorescence (KCSF) excitation down to 58 Kelvin. Finally, we show that even the primary steps in the oxidation of biomolecules or biomolecular building blocks initiated by OH radicals can be followed at low temperatures. The temperature dependence of the measured rate constants is the key for an understanding of the underlying molecular mechanisms and the Laval nozzle expansion provides a unique environment for these measurements. The experimental finding that many reactions between radicals and neutral species can be rapid at low temperatures are discussed in terms of pre-reactive complexes formed in the overall complex forming bimolecular reactions
Water catalysis of a radical-molecule gas-phase reaction
No full textThere has been considerable speculation about the role of water and water complexes in chemical gas-phase reactions, including the conjecture that water may act as a molecular catalyst through its ability to form hydrogen bonds. Here, we present kinetic studies in which the effect of water on the rate of the reaction between hydroxyl radicals and acetaldehyde has been measured directly in Laval nozzle expansions at low temperatures. An increasing enhancement of the reaction rate by added water was found with decreasing temperatures between 300 and 60 kelvin. Quantum chemical calculations and statistical rate theory support our conclusions that this observation is due to the reduction of an intrinsic reaction barrier caused by specific water aggregation. The results suggest that even single water molecules can act as catalysts in radical-molecule reactions
Primary Steps in the Reaction of OH Radicals with Amino Acids at Low Temperatures in Laval Nozzle Expansions: Perspectives from Experiment and Theory
No full textRecent work has focused on the damaging effects of free radicals on biological molecules. This study investigates the kinetics of the attack of OH radicals Oil L-alanine ethyl ester in the gas phase in cold beams of Laval nozzle expansions. Experiments and high-level theory are used to understand the preferred site of attack by the OH radical. Optimizations of L-alanine and L-alanine ethyl ester show that the essential transition state features for hydrogen abstraction off the C(alpha), C(beta), and N are similar. The energetics show that for L-alanine, the C(alpha)-site, C(beta)-site, and N-site transition states are all below the reactants level. For L-alanine ethyl ester, however, the energetics for hydrogen abstraction off the C(alpha) and N are the preferred site of reaction. These findings are Supported by the observed negative temperature dependence of the rate constants of OH with alanine ethyl ester in Laval nozzle expansion experiments. More importantly, both the experiments and theory show that L-alanine ethyl ester provides a good model For gas phase studies of the amino acids such as L-alanine.Deutsche Forschungsgemeinschaft DFG [782
Low-temperature reactions of OH radicals with propene and isoprene in pulsed laval nozzle expansions
No full textThe kinetics of the reactions of OH radicals with propene and isoprene in N 2 have been studied in the temperature range of 58-300 K in a Laval nozzle expansion. Laser-induced fluorescence of the OH radical that is formed in the photolysis of H 2O 2 at 193 nm has been detected. The determined rate constants (2 × 10 -11 to 2 × 10 -10 cm 3 molecule -1 s -1) for the OH radicals reacting with excess propene and isoprene (2-methyl-1,3-butadiene) have been found to increase when the temperature is decreased. The room temperature rate constants are in agreement with the literature data. Below 120 K, a saturation of the rate constant for the case of propene and a turnover to a formally positive temperature dependence for isoprene have been observed. The observed negative temperature dependence and the course of the temperature dependence at very low temperatures for both reactions are discussed within the framework of the loose transition-state theory and a simple two-transition-state model
Structural Optimization Of A Vertical Axis Wind Turbine With Aeroelastic Analysis
No full textCurrently, the price per kW of offshore wind energy is 55% larger than onshore [38, 52]. Of this price, the rotor corresponds to 22%. To reduce the price of wind energy, it is necessary to investigate wind turbine concepts with scales above 10 MW. The commonly known Horizontal Axis Wind Turbine (HAWT) requires offshore a large support structure. If the turbine is designed to be floating, a deep floater is needed to limit the tilt angle. A possible concept to meet this challenges is the lift-driven Vertical Axis Wind Turbine (VAWT). This thesis aims to optimize the structural design of a VAWT rotor blade and to decrease the mass to area ratio by varying blade shape and structural layout. The choice of mass to rotor area ratio as an optimization function follows from the fact that this area is directly proportional to the energy output while mass drives production and installation costs. The VAWT is defined by an axis perpendicular to the unperturbed flow direction. The rotor geometry is described through a Troposkein shape. It is assumed that the blades carry their own weight leading to a reinforced root region. During operation the blades experience aerodynamic and inertia forces, which are deflecting the blades outwards, leading to an alternation of the aerodynamic loads.The interplay of load alternation and blade deflection could lead to a diverging flutter motion. After a fitting design is obtained, the blade motion has to be inspected for a safe use during operation. The rotor is designed with an adjusted optimizer, originally written by M. Schelbergen [62]. The optimizer uses the Matlab optimization toolbox in combination with Nastran. The modification allows a smooth transition of the thickness of skin, shear web and girder. The airfoil section is varied along the blade. The optimization is based on load cases such as a parked rotor and the maximum up- and downwind forces. These loads are simplified and assumed to vary neither by the motion nor the deflections of the blade. In addition, an aeroelastic model is required to observe the blades’ motion. Through out thisthesis two aeroelastic codes were used. The VAWT AeroElastic Multibody Panel Solver (VÆMPS) was created by coupling Sandia National Laboratories OWENS and the near wake panel solver UMPM. However, its computational performance was not satisfying and it was decided to use HAWC2 coupled with an actuator cylinder model to determine the induction.European Wind Energy Masters (EWEM
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Designing Video-Based Interactive Instructions
No full textWhen attempting to accomplish unfamiliar tasks, people often look for tutorials to follow instructions. While it is easy to access online instructions shared by domain experts, navigating step-by-step guidance using existing tools remains inefficient. In addition, producing high-quality instructions that are easy to follow requires authoring expertise and a significant time investment in editing. This dissertation introduces video-based recording, editing, and playback tools optimized for creating and consuming tutorials from author demonstrations. Our interactive systems capture videos and high-level events that are important to a learner. Using video and audio analysis techniques, we develop algorithms that automatically produce high-quality instructions, which dramatically reduce the effort required for amateur creators. By introducing novel tutorial formats combined with video content, these designs in turn improve viewers’ learning experience.We present a series of authoring tools that enable amateur authors to create effective tutorials: 1) MixT is a system that automatically generates step-by-step mixed media tutorials from software demonstrations. 2) DemoWiz is a tool that provides an increased awareness of upcoming events in a software demonstration video. 3) DemoCut is a semi-automatic video editing tool for physical tasks. 4) Kinectograph is a recording device that automatically follows an instructor for filming a physical demonstration. 5) DemoDraw is a multi-modal system to generate step-by-step motion illustrations from author’s body movements. Current authoring practices from professionals are encoded into automatic algorithms and interactive techniques. These systems are evaluated through a series of studies, which demonstrate that users can efficiently create and follow concise instructions using our tools
Major Accident Prevention - Lessons Learned and Reinforcement Initiatives Ongoing in Statoil
No full textAbstract
Statoil’s contribution to this session of the SPE HSSE Conference is to share how we have reinforced our safety culture in the way we lead and work to reduce the risk of facing high potential incidents or major accidents.
The main objective of this paper and lecture is twofold:Raise the awareness of barrier challenges that historically have caused major accidents in our industry, and still do.Present specified risk areas that Statoil have reinforced attention on based on our learning from high potential incidents and major accidents in the period of 2012-2017.
The paper is seen from an operational user perspective and founded in the author and presenter’s more than 35 years of operational experience from "sharp end" worker and management positions within offshore operations and greenfield projects.
Key risks to be covered: Plant vibrations Plant corrosion Overdue/backlog of safety critical maintenance Diffuse gas leakages Transport of risks between an onshore planning party and offshore executing party Last minute change of plans Compliance with safe work requirements Competence
A film is developed to support the lecture in plenary.</jats:p
Development of Optimized Test Planning Procedures for Stabilizing Ramp-up Processes by Means of Design Science Research
No full textAbstractUnplanned engineering changes represent a major field of disturbance during production ramp-up. They require time-consuming qualification and approval procedures for product- or process-related redesign. Numerous engineering changes during production ramp-up can be traced back to lack of product maturity, not sufficiently increased during the precedent stage of product development. By applying effective and efficient product testing processes, product maturity can be measured and enhanced at an early stage. As a consequence, unplanned engineering changes can be avoided. Nevertheless, contemporary test management procedures lack of methodological support, especially in the field of test planning. To date, the successful evaluation of testing demand and selection of necessary test specifications mainly depends on the expert knowledge of the test management team. The present paper focuses on the development of optimized test planning procedures in order to accelerate early product maturity enhancement for stabilizing production ramp-up processes. Following design science research methodology, the relevance of the problem statement in the application environment of production ramp-up will be assessed. Furthermore, approaches of the knowledge base related to test management will be analyzed in order to constitute rigor of the applied research approach. Based on the evaluation of business needs from the relevant environment as well as the investigation of application knowledge, a research framework for deriving optimized test planning procedures is presented
How much randomness is needed for statistics?
No full textIn algorithmic randomness, when one wants to define a randomness notion with respect to some non-computable measure λ, a choice needs to be made. One approach is to allow randomness tests to access the measure λ as an oracle
(which we call the \classical approach"). The other approach is the opposite one, where the randomness tests are completely effective and do not have access to the information contained in λ (we call this approach \Hippocratic"). While the Hippocratic approach is in general much more restrictive, there are cases
where the two coincide. The first author showed in 2010 that in the particular case where the notion of randomness considered is Martin-Löf randomness and the measure λ is a Bernoulli measure, classical randomness and Hippocratic randomness coincide. In this paper, we prove that this result no longer holds for
other notions of randomness, namely computable randomness and stochasticity
Integrating catchment properties in small scale species distribution models of stream macroinvertebrates
No full textSpecies distribution models are increasingly applied to freshwater ecosystems. Most applications use large scales, coarse resolutions and anthropocentric modelling extents, thus not being able to consider important environmental predictors and ecological processes detectable within a catchment and at finer scales. Moreover, high resolution predictions of species distribution in streams can help improve our understanding of how environmental variables within a catchment affect the distribution of stream macroinvertebrates. We built models at a resolution of 25 m x 25 m for a 488 km(2) catchment in northern Germany to determine whether the spatial approach in which environmental predictors are implemented in the model affects the overall performance. We used predictors from four different categories relevant to freshwater ecosystems: bioclimatic, topographic, hydrologic and land use. Two spatial approaches were tested: a local one, or grid based and a cumulative for the upstream area, or subcatchment specific. Models were evaluated in terms of model performance and accuracy in order to identify the approach best suited for each category, as well as the most important predictor in each. In the case of the land use category, the subcatchment approach made a significant difference, increasing performance. A final model, calibrated with the selected predictors, resulted in the highest model performance and accuracy. Our results indicate that species distribution models perform well and are accurate at high resolutions, within small catchments. We conclude that catchment wide models, especially when using predictors from multiple categories, have the potential to significantly improve modelling framework of species distribution in freshwater ecosystems. The information produced by accurate, small scale, species distribution models can guide managers and conservation practitioners, by predicting the effects of management decisions within a catchment. We suggest that highly resolved predictors be applied in models using the catchment approach. (C) 2014 Elsevier B.V. All rights reserved.Species distribution models are increasingly applied to freshwater ecosystems. Most applications use large scales, coarse resolutions and anthropocentric modelling extents, thus not being able to consider important environmental predictors and ecological processes detectable within a catchment and at finer scales. Moreover, high resolution predictions of species distribution in streams can help improve our understanding of how environmental variables within a catchment affect the distribution of stream macroinvertebrates. We built models at a resolution of 25 m x 25 m for a 488 km(2) catchment in northern Germany to determine whether the spatial approach in which environmental predictors are implemented in the model affects the overall performance. We used predictors from four different categories relevant to freshwater ecosystems: bioclimatic, topographic, hydrologic and land use. Two spatial approaches were tested: a local one, or grid based and a cumulative for the upstream area, or subcatchment specific. Models were evaluated in terms of model performance and accuracy in order to identify the approach best suited for each category, as well as the most important predictor in each. In the case of the land use category, the subcatchment approach made a significant difference, increasing performance. A final model, calibrated with the selected predictors, resulted in the highest model performance and accuracy. Our results indicate that species distribution models perform well and are accurate at high resolutions, within small catchments. We conclude that catchment wide models, especially when using predictors from multiple categories, have the potential to significantly improve modelling framework of species distribution in freshwater ecosystems. The information produced by accurate, small scale, species distribution models can guide managers and conservation practitioners, by predicting the effects of management decisions within a catchment. We suggest that highly resolved predictors be applied in models using the catchment approach. (C) 2014 Elsevier B.V. All rights reserved
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