Suchergebnisse

Optical imaging techniques are ubiquitous for the resolution of non-uniformities in gas flows. Planar imaging techniques such as laser-induced fluorescence are well established and applied extensively in turbulent reactive flows, offering both high temporal and spatial resolutions. However, planar imaging suffers from a critical disadvantage, the requirement for spatially continuous optical access over large solid angles in both the excitation and detection paths and this precludes their application in many practical situations, for example those encountered in engine testing. Tomographic absorption spectroscopy, TAS, on the other hand, shares many of the advantages of planar imaging techniques but reduces the demands for optical access, because high quality data can be obtained with sparsely sampled volumes. The technique has unrivalled potential for imaging in harsh environments, for example for in-cylinder/in-chamber engine measurements. TAS is beginning to mature as a technique for the simultaneous imaging of temperature and species concentration, and is experiencing a surge of interest due to progress in laser technology, spectroscopy, and theoretical developments of nonlinear tomography techniques. The recent advancements in broad bandwidth, frequency-agile laser sources massively enrich the spectral information obtainable in TAS. Furthermore, nonlinear tomography enables the recovery of multiplexed information from a single tomographic inversion. The utilization of multispectral information improves the immunity of TAS to experimental noise and makes possible the simultaneous imaging of temperature, pressure, and multiple species. Nonlinear tomography can also be used to empower the imaging potential of sensitive and robust absorption techniques, such as wavelength modulation spectroscopy, for use in harsh and even optically dense environments. In combination, this greatly extends the applicability of TAS for more general and harsh scenarios in combustion technology. In this article we review basic concepts and mathematical foundations of classical absorption tomography, proceeding to more advanced recent concepts based on nonlinear tomography, and providing an extensive review of experimental demonstrations and practical applications in the context of state-of-the-art combustion research. ; European Commission under Grant No. ASHTCSC 330840; Chinese Government 'Thousand Youth Talent Program'; Engineering and Physical Sciences Research Council (EPSRC) (Grant EP/ L015889/1).

Spanish MCI Project [MTM2017-87162-P]; Spanish Government [MINECO/FEDER TIN2015-69542C2-1]; Banco de Santander; Universidad Rey Juan Carlos, Spain

The articles in this volume summarize the research results obtained in the former SFB 359 "Reactive Flow, Diffusion and Transport" which has been supported by the DFG over the period 1993-2004. The main subjects are physical-chemical processes sharing the difficulty of interacting diffusion, transport and reaction which cannot be considered separately. Typical examples are the chemical processes in flow reactors and in the catalytic combustion at surfaces. Further examples are models of star formation including diffusive mass transport, energy radiation and dust formation and the polluting transport in soil and waters. For these complex processes mathematical models are established and numerically simulated. The modeling uses multiscale techniques for nonlinear differential equations while for the numerical simulation and optimization goal-oriented mesh and model adaptivity, multigrid techniques and advanced Newton-type methods are developed combined with parallelization. This modeling and simulation is accompanied by experiments

Marked by both deep interconnectedness and polarization, the contemporary media system in the United States features news outlets and social media that are bound together, yet deeply divided along partisan lines. This article formally analyzes communication flows surrounding mass shootings in the hybrid and polarized U.S. media system. We begin by integrating media system literature with agenda setting and news framing theories and then conduct automated text analysis and time series modeling. After accounting for exogenous event characteristics, results show that (a) sympathy and gun control discourses on Twitter preceded news framing of gun policy more than the other way around, and (b) conservatives on Twitter and conservative media reacted to progressive discourse on Twitter, without their progressive counterparts exhibiting a similar reactiveness. Such results shed light on the influence of social media on political communication flows and confirm an asymmetry in the ways partisan media ecosystems respond to social events.

The concept of the "reactive state" is useful in understanding the foreign economic policy behavior of Japan and certain other middle-range powers deeply integrated in the global political economy, particularly during periods of economic turbulence when international regimes do not fully safeguard their economic interests. The essential characteristics of the reactive state are two-fold: (1) it fails to undertake major independent foreign-policy initiatives although it has the power and national incentives to do so; (2) it responds to outside pressure for change, albeit erratically, unsystematically, and often incompletely.In the Japanese case, reactive state behavior flows from domestic institutional characteristics as well as from the structure of the international system. Domestic features such as bureaucratic fragmentation, political factionalism, powerful mass media, and the lack of a strong central executive have played an especially important part in Japanese financial, energy, trade, and technology policy formation since 1971.

AbstractImproving the performance of proton exchange membrane fuel cells (PEMFCs) requires deep understanding of the reactive transport processes inside the catalyst layers (CLs). In this study, a particle-overlapping model is developed for accurately describing the hierarchical structures and oxygen reactive transport processes in CLs. The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness, reduces specific surface areas of ionomer and carbon, and further intensifies the local oxygen transport resistance (Rother). The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 s m-1 agrees well with the experiments. Then, a multiscale model is developed by coupling the particle-overlapping model with cell-scale models, which is validated by comparing with the polarization curves and local current density distribution obtained in experiments. The relative error of local current density distribution is below 15% in the ohmic polarization region. Finally, the multiscale model is employed to explore effects of CL structural parameters including Pt loading, I/C, ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced (PCI) flow and capillary-driven (CD) flow in CL. The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows. Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL, leading to overall higher PCI and CD rates. The maximum increase of PCI and CD rates can exceed 145%. Besides, the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface, which can occupy about 30% of the CL. The multiscale model significantly contributes to a deep understanding of reactive transport and multiphase heat transfer processes inside PEMFCs.

Recent decades have seen urban resilience becoming a more popular term internationally both within academic and policy circles. However, relatively little attention has been paid by the literature to the policy implications of striving towards more resilient urban systems and the challenges introduced by the complex, multi-level and multi-actor policy network that forms their context. The central hypothesis of this research is that resilience is a long-term goal, beyond immediate disaster planning and management, and an ongoing process that requires a proactive approach (as opposed to a reactive approach). This builds on the idea that focusing only on the immediate outcomes of extreme events keeps the city on a "catch-up mode", which is both unsustainable and inefficient in the long-term. This research proposes that in order to progress towards resilience that endures, the policies that underpin these efforts must remain effective and "survive" short-term pressures. It attempts to pinpoint the main elements that, if understood and addressed, can help policies withstand sources of stress and remain effective in delivering more enduring or sustainable forms of resilience. While there are many factors that have already been identified, this paper will explore only one aspect: Information flows. This is a topic that although is often mentioned as "important" in policy literature, it is also rarely explored. The following is the result of a qualitative meta-analysis of over 100 references relating to resilience, sustainability, and multi-actor network and complex problems policy. This paper also includes the results from the first half of a series of interviews with policy experts from industry, government and research from Australia, the UK and the USA.

Optical techniques for measuring the temperature in three-dimensional supersonic reactive flows have typically depended on lineshape measurements using single-beam laser absorption spectroscopy. However, absorption over extended path lengths in flows with symmetric, turbulent eddies can lead to systematically high extracted temperatures due to Doppler shifts resulting from flow along the absorption path. To eliminate these problems, Cross-Beam Saturation Absorption Spectroscopy (CBSAS) and Cross-Beam Inter-Modulated Fluorescence (CBIMF) have been developed which utilize two crossed and nearly copropogating laser beams.to record the spectral signal of an I2 ro-vibrational line in a small three-dimensional volume using a tunable CW dye laser. Temperature is extracted by fitting the recorded signal with a theoretical signal constructed from the Doppler-broadened hyperfine components of the ro-vibrational line. The CBIMF technique proved successful for extracting the temperature of an I2-seeded, Ar gas flow within a small, Mach 2, Laval nozzle where the overlap volume of the two 1 mm diameter laser beams was 2.4 mm3. At a test point downstream of the nozzle throat, the average temperature of 146 K ± 1.5 K extracted from measurements of the I2 P(46) 17-1 spectral line compared favorably with the 138 K temperature calculated from isentropic, one-dimensional flow theory.

Ensuring global food security is one of the challenges of our society. Nitrogen availability is key for food production, while contributing to different environmental impacts. This paper aims firstly to assess nitrogen flows and to highlight hotspots of inefficient use of nitrogen along the European food chain, excluding primary production. Secondly, it aims to analyse the potential for reducing the identified inefficiencies and increase nitrogen circularity. A baseline and three scenarios-reflecting waste targets reported in EU legislation and technological improvements- are analysed. Results highlighted a potential to reduce reactive nitrogen emissions up to more than 45%. However, this would imply the conversion of reactive nitrogen in molecular nitrogen, such as urea, before re-entering in the food chain. Techniques to harvest reactive nitrogen directly from urine and wastewater are considered promising to increase nitrogen use efficiency along the food chain.

A climatology of new particle formation (NPF) events at high altitude in the subtropical North Atlantic is presented. A 4-year data set (June 2008–June 2012), which includes number size distributions (10–600 nm), reactive gases (SO2, NOx, and O3), several components of solar radiation and meteorological parameters, measured at Izaña Global Atmosphere Watch (GAW) observatory (2373 m above sea level; Tenerife, Canary Islands) was analysed. NPF is associated with the transport of gaseous precursors from the boundary layer by orographic buoyant upward flows that perturb the low free troposphere during daytime. On average, 30% of the days contained an NPF event. ; This study was performed within the context of several projects, supported by the Ministry of Economy and Competitiveness of Spain (POLLINDUST, CGL2011-26259), REDMAAS (CGL2011- 15008-E) and GRACCIE (CSD2007-00067) and by the European Union (FP7, ACTRIS, grant contract: 262254).

A climatology of new particle formation (NPF) events at high altitude in the subtropical North Atlantic is presented. A 4-year data set (June 2008–June 2012), which includes number size distributions (10–600 nm), reactive gases (SO2, NOx, and O3), several components of solar radiation and meteorological parameters, measured at Izaña Global Atmosphere Watch (GAW) observatory (2373 m above sea level; Tenerife, Canary Islands) was analysed. NPF is associated with the transport of gaseous precursors from the boundary layer by orographic buoyant upward flows that perturb the low free troposphere during daytime. On average, 30% of the days contained an NPF event. ; This study was performed within the context of several projects, supported by the Ministry of Economy and Competitiveness of Spain (POLLINDUST, CGL2011-26259), REDMAAS (CGL2011- 15008-E) and GRACCIE (CSD2007-00067) and by the European Union (FP7, ACTRIS, grant contract: 262254).

Any numerical subsurface model is comprised of three components: a theoretical basis to translate our understanding phenomena into partial differential equations and boundary conditions, a numerical method to approximate these governing equations and implement the boundary conditions, and a computer implementation to generate a generic code for research as well as for practical applications. Computational Subsurface Hydrology: Reactions, Transport, and Fate is organized around these themes. The fundamental processes occurring in subsurface media are rigorously integrated into governing equations using the Reynolds transport theorem and interactions of these processes with the surrounding media are sophisticatedly cast into various types of boundary conditions using physical reasoning. A variety of numerical methods to deal with reactive chemical transport are covered in Computational Subsurface Hydrology: Reactions, Transport, and Fate with a particular emphasis on the adaptive local grid refinement and peak capture using the Lagrangian-Eulerian approach. The topics on coupled fluid flows and reactive chemical transport are unique contributions of this book. They serve as a reference for research as well as for practical applications with a computer code that can be purchased from the author. Four computer codes to simulate vertically integrated horizontal solute transport (LEMA), contaminant transport in moving phreatic aquifers in three dimensions (3DLEMA), solute transport in variably saturated flows in two dimensions (LEWASTE), and solute transport under variably saturated flows in three dimensions (3DLEWASTE) are covered. These four computer codes are designed for generic applications to both research and practical problems. They could be used to simulate most of the practical, real-world field problems. Reactive chemical transport and its coupling with fluid flows are unique features in this book. Theories, numerical implementations, and example problems of coupled reactive transport and flows in variably saturated media are presented. A generic computer code, HYDROGEOCHEM 3.0, is developed. A total of eight example problems are used to illustrate the application of the computational model. These problems are intended to serve as examples for setting up a variety of simulations that one may encounter in research and field-site applications. Computational Subsurface Hydrology: Reactions, Transport, and Fate offers practicing engineers and scientists a ...

Uspostava nadnacionalnih autoriteta regulacije banaka izravno je pridonijela boljem razumijevanju ponašanja i utjecaja bankovnog sektora na ekonomske tokove u cjelini. Institucionalna povezanost nacionalnih regulatornih tijela u kontekstu globalizacijskih odnosa pridonosi željenoj standardizaciji podataka koji su temelj za svaku validnu ekonomsku analizu. Napose, tržišna disciplina kao uporište suvremene regulacije reducira prostor neprozirnosti bankovne tvrtke, dok s druge strane dostupnost relevantnih baza podataka širi horizonte modelskog pristupa analize bankovnog sektora. Dominacija istog sektora kao izvora eksternog financiranja na zajedničkom europskom tržištu ishodište je traženja rješenja izlaska iz stagnacijskih pritisaka na gospodarska kretanja. Dinamičnost kauzalnih ekonomskih odnosa nameće potrebu sve veće pouzdanosti u izvore podataka, stoga reprezentativnost uzorka ne samo da usmjerava pojedino istraživanje već i determinira spoznajni proces. Analiza javno dostupnih podataka bankovnih tvrtki suvremenim ekonometrijskim alatima svakako je velik iskorak u pokušaju uspostave jasnog i transparentnog metodološkog okvira monitoringa reaktivnog djelovanja bankarskog sektora na nužnu promjenu regulatornih uvjeta u funkciji postkriznog pokretanja kreditnog ciklusa. Model empirijske analize usklađivanja bankarskog sektora s novim kapitalnim zahtjevima ovim će se radom testirati na uzorku od 35 bankovnih grupacija koje posluju na području EU-a za razdoblje od 2000. do 2016. godine, odabranih po veličini aktive. Analizom panel modela izvršen je odabir dinamičkog panela generaliziranom metodom momenata (engl. Generalized Method of Moments – GMM) jednim korakom. Rezultati istraživanja dali su dokaze da najava povećanja regulatornog kapitala utječe na rast ukupnih bankovnih aktiva odnosno dolazi do značajnog porasta udjela bezrizičnih aktiva u imovini banaka, dok s druge strane dolazi do kreditne kontrakcije koja olakšava zadovoljenje regulatornih zahtjeva. Konačno, upravljačke strukture preko neto kamatne marže kao instrumenta kreditno-depozitne politike, realociraju vlastita i tuđa sredstva u funkciji očuvanja likvidnosti i solventnosti banke u cjelini. ; The establishment of supranational banks regulatory authorities has directly contributed to a better understanding of the behaviour and impact of the banking sector on economic flows comprehensively. Institutional linkage of national regulatory bodies in the context of globalization relations contributes to the desired standardization of data, which are the basis for every valid economic analysis. The market discipline as the backbone of modern regulation reduces especially the banking firm opacity area, while on the other hand the availability of relevant databases expands the horizons of the model approach to banking sector analysis. The dominance of the same sector as a source of external financing on a common European market is the starting point in seeking solutions of emersion from stagnant pressures on economic trends. The dynamism of causative economic relationships imposes the need for ever greater reliability in data sources, hence the representativeness of the sample not only directs an individual research but also determines the cognitive process itself. The analysis of publicly available banking firm data using modern econometric tools is certainly a significant step forward in the attempt to establish a clear and transparent methodological framework for monitoring the reactive activity of the banking sector to the necessary change of regulatory terms in the function of post-crisis launch of the credit cycle. The empirical analysis of the banking sector alignment with new capital requirements will be tested in this paper on a sample of 35 banking groups operating in the EU area for the period from 2000 to 2016, selected by size of assets. The selection of the dynamic panel was performed through panel modelling analysis using Generalized Method of Moments (GMM). The research results have provided evidence that the announcement of the increase in regulatory capital affects the growth of total banking assets, namely there is a significant increase in the share of non-risky assets in bank assets, while on the other hand there is a credit contraction that facilitates the regulatory requirements compliance. Finally, the management structures over the net interest margin as a credit and deposit policy instrument reallocate their own and other resources in the function of preserving the liquidity and solvency of the bank in general.