LES validation of urban flow, part II: eddy statistics and flow structures

Time-dependent three-dimensional numerical simulations such as large-eddy simulation (LES) play an important role in fundamental research and practical applications in meteorology and wind engineering. Whether these simulations provide a sufficiently accurate picture of the time-dependent structure of the flow, however, is often not determined in enough detail. We propose an application-specific validation procedure for LES that focuses on the time dependent nature of mechanically induced shear-layer turbulence to derive information about strengths and limitations of the model. The validation procedure is tested for LES of turbulent flow in a complex city, for which reference data from wind-tunnel experiments are available. An initial comparison of mean flow statistics and frequency distributions was presented in part I. Part II focuses on comparing eddy statistics and flow structures. Analyses of integral time scales and auto-spectral energy densities show that the tested LES reproduces the temporal characteristics of energy-dominant and flux-carrying eddies accurately. Quadrant analysis of the vertical turbulent momentum flux reveals strong similarities between instantaneous ejection-sweep patterns in the LES and the laboratory flow, also showing comparable occurrence statistics of rare but strong flux events. A further comparison of wavelet-coefficient frequency distributions and associated high-order statistics reveals a strong agreement of location-dependent intermittency patterns induced by resolved eddies in the energy-production range. The validation concept enables wide-ranging conclusions to be drawn about the skill of turbulence-resolving simulations than the traditional approach of comparing only mean flow and turbulence statistics. Based on the accuracy levels determined, it can be stated that the tested LES is sufficiently accurate for its purpose of generating realistic urban wind fields that can be used to drive simpler dispersion models

LES validation of urban flow, part I: flow statistics and frequency distributions

Essential prerequisites for a thorough model evaluation are the availability of problem-specific, quality-controlled reference data and the use of model-specific comparison methods. The work presented here is motivated by the striking lack of proportion between the increasing use of large-eddy simulation (LES) as a standard technique in micro-meteorology and wind engineering and the level of scrutiny that is commonly applied to assess the quality of results obtained. We propose and apply an in-depth, multi-level validation concept that is specifically targeted at the time-dependency of mechanically induced shear-layer turbulence. Near-surface isothermal turbulent flow in a densely built-up city serves as the test scenario for the approach. High-resolution LES data are evaluated based on a comprehensive database of boundary-layer wind-tunnel measurements. From an exploratory data analysis of mean flow and turbulence statistics, a high level of agreement between simulation and experiment is apparent. Inspecting frequency distributions of the underlying instantaneous data proves to be necessary for a more rigorous assessment of the overall prediction quality. From velocity histograms local accuracy limitations due to a comparatively coarse building representation as well as particular strengths of the model to capture complex urban flow features with sufficient accuracy are readily determined. However, the analysis shows that further crucial information about the physical validity of the LES needs to be obtained through the comparison of eddy statistics, which is focused on in part II. Compared with methods that rely on single figures of merit, the multi-level validation strategy presented here supports conclusions about the simulation quality and the model's fitness for its intended range of application through a deeper understanding of the unsteady structure of the flow

Modelling short-term maximum individual exposure from airborne hazardous releases in urban environments. Part ΙI: Validation of a deterministic model with wind tunnel experimental data

The capability to predict short-term maximum individual exposure is very important for several applications including, for example, deliberate/accidental release of hazardous substances, odour fluctuations or material flammability level exceedance. Recently, authors have proposed a simple approach relating maximum individual exposure to parameters such as the fluctuation intensity and the concentration integral time scale. In the first part of this study (Part I), the methodology was validated against field measurements, which are governed by the natural variability of atmospheric boundary conditions. In Part II of this study, an in-depth validation of the approach is performed using reference data recorded under truly stationary and well documented flow conditions. For this reason, a boundary-layer wind-tunnel experiment was used. The experimental dataset includes 196 time-resolved concentration measurements which detect the dispersion from a continuous point source within an urban model of semi-idealized complexity. The data analysis allowed the improvement of an important model parameter. The model performed very well in predicting the maximum individual exposure, presenting a factor of two of observations equal to 95%. For large time intervals, an exponential correction term has been introduced in the model based on the experimental observations. The new model is capable of predicting all time intervals giving an overall factor of two of observations equal to 100%

Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells

A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-centred transitions) which are red-shifted on going from X = H to X = I, and a broad metal-to-ligand charge transfer band with λmax in the range 387–395 nm. The ten complexes are yellow emitters in solution and yellow or yellow-orange emitters in the solid-state. For a given N^N ligand, the solution photoluminescence (PL) spectra show no significant change on going from [Cu(N^N)(POP)]+ to [Cu(N^N)(xantphos)]+; introducing the iodo-functionality into the N^N domain leads to a red-shift in λmaxem compared to the complexes with the benchmark N^N ligand 5. In the solid state, [Cu(1)(POP)][PF6] and [Cu(1)(xantphos)][PF6] (fluoro-substituent) exhibit the highest PL quantum yields (74 and 25%, respectively) with values of τ1/2 = 11.1 and 5.8 μs, respectively. Light-emitting electrochemical cells (LECs) with [Cu(N^N)(P^P)][PF6] complexes in the emissive layer have been tested. Using a block-wave pulsed current driving mode, the best performing device employed [Cu(1)(xantphos)]+ and this showed a maximum luminance (Lummax) of 129 cd m−2 and a device lifetime (t1/2) of 54 h; however, the turn-on time (time to reach Lummax) was 4.1 h. Trends in performance data reveal that the introduction of fluoro-groups is beneficial, but that the incorporation of heavier halo-substituents leads to poor devices, probably due to a detrimental effect on charge transport; LECs with the iodo-functionalized N^N ligand 4 failed to show any electroluminescence after 50 h

Characterization of final DEPFET modules for the new Pixel Vertex Detector and commissioning at the Belle II experiment

The Belle II particle physics experiment is located at the SuperKEKB e+e− collider in Japan. Its research focuses on the CP violation in B meson decays and addresses many open questions in electroweak interactions. The broad physics program also includes the search for new physics beyond the Standard Model of particle physics. An essential component of the Belle II detector for the physics mentioned above, most importantly for analyses of CP violation, is the Pixel Vertex Detector (PXD). The PXD is the innermost tracking device, surrounding the beam pipe, and provides a precise measurement of the decay vertices of B mesons and other weakly decaying particles. The PXD consists of two layers of silicon semiconductor modules with new Depleted P-channel Field Effect Transistor (DEPFET) pixels, used for the first time in a high energy physics experiment. This technology allows for an exceptionally thin active detector design of only 75 µm, achieving 15 µm impact parameter resolution and greater than 99 % detection efficiency. The PXD is an electronic device and must function properly as a subdetector of the larger Belle II electronic detector system. The first part of this thesis was the conduct of a test campaign to verify the electromagnetic compatibility (EMC) of the PXD module design. These were the first EMC measurements for a high energy physics pixel detector and also the first consideration of radiated noise from the beam pipe. After the design and prototyping phase, the module production for the final detector was started. The second part of this thesis was the development of the entire chain of test procedures and a comprehensive quality management including quality assurance software for the characterization and optimization of all production modules. The performance of 75 PXD modules was evaluated, of which 72 % achieved the highest grading after optimization. The third part of this thesis covers the assembly and commissioning of a first reduced version of the PXD at the Belle II experiment in Japan. Optimization of the module performance and operating software continued during operation. Following the occurrence of severe irradiation damage due to beam loss events, an automated detection algorithm was developed. Possible damage mechanisms were investigated and additional protection measures were implemented. The installed PXD successfully operated in the first physics data taking period of the Belle II experiment from 2019 to 2022. It reliably collected data of particular value for lifetime measurements and time-dependent CP violation analyses. During the shutdown period in 2022/23 the first PXD was replaced by PXD2, a complete successor, which will be the innermost tracking detector of Belle II for many years to come.Das Teilchenphysikexperiment Belle II befindet sich am SuperKEKB e+e− Beschleuniger in Japan. Sein Forschungsschwerpunkt liegt in der Untersuchung der CP Verletzung im Zerfall von B Mesonen. Darüber hinaus behandelt es viele offene Fragen zur elektroschwachen Wechselwirkung. Das breite Physikprogramm umfasst auch die Suche nach neuer Physik jenseits des Standardmodells der Teilchenphysik. Eine wesentliche Komponente des Belle II Teilchendetektors für das genannte Physikprogramm, insbesondere für die Analysen zur CP Verletzung, ist der Pixel Vertex Detektor (PXD). Der PXD ist der innerste Detektor für die Spurrekonstruktion. Er umschließt das Strahlrohr und liefert präzise Messungen der Zerfallsvertices von B Mesonen und anderen schwach zerfallenden Teilchen. Der PXD besteht aus zwei Lagen von Silizium-Halbleitermodulen mit neuartigen deplitierten p-Kanal-Feldeffekttransistor (DEPFET) Pixeln, die zum ersten Mal in einem Experiment der Hochenergiephysik eingesetzt werden. Diese Technologie ermöglicht ein außergewöhnlich dünnes aktives Detektordesign von nur 75 µm, wobei eine intrinsische Positionsauflösung von 15 µm und eine Detektionseffizienz von über 99 % erreicht werden. Der PXD ist ein elektronisches Gerät und muss als Teil des größeren elektronischen Detektorsystems Belle II funktionieren. Der erste Teil der vorliegenden Arbeit bestand in der Durchführung einer Messkampagne zur Überprüfung der elektromagnetischen Verträglichkeit (EMV) des PXD Moduldesigns. Dies waren die ersten EMV Messungen an einem Pixeldetektor der Hochenergiephysik und die erste Berücksichtigung von Störungen, die von einem Strahlrohr abgestrahlt werden. Nach der Design- und Prototypenphase lief die Produktion der Module für den finalen Detektor an. Der zweite Teil dieser Arbeit bestand in der Entwicklung einer vollständigen Kette von Testverfahren und eines umfassenden Qualitätsmanagements einschließlich der Qualitätssicherungssoftware für die Charakterisierung und Optimierung aller produzierten Module. Die Leistung von 75 PXD Modulen wurde evaluiert, von denen nach der Optimierung 72 % die höchste Einstufung erreichten. Der dritte Teil dieser Arbeit befasst sich mit dem Zusammenbau und der Inbetriebnahme einer ersten reduzierten Version des PXD am Belle II Experiment in Japan. Die Optimierung der Modulleistung und der Betriebssoftware wurde während des Betriebs fortgesetzt. Nach dem Auftreten gravierender Bestrahlungsschäden aufgrund von Strahlverlusten wurde ein automatischer Algorithmus zur Erkennung dieser Schäden entwickelt. Mögliche Schadensmechanismen wurden untersucht und zusätzliche Schutzmaßnahmen eingeführt. Der installierte PXD konnte in der ersten Phase der Datennahme des Belle II Experiments von 2019 bis 2022 erfolgreich betrieben werden. Er nahm zuverlässig Daten auf, die für Lebensdauermessungen und Analysen zur zeitabhängigen CP Verletzung von besonderem Wert sind. Während der Abschaltung des Beschleunigers 2022/23 wurde der erste PXD durch PXD2 ersetzt, einen vollständigen Nachfolger, der für viele kommende Jahre der innerste Detektor für die Spurrekonstruktion des Belle II Experiments sein wird

Synthesis and Luminescence Modulation of Pyrazine-Based Gold(III) Pincer Complexes

The first examples of pyrazine-based gold(III) pincer complexes have been synthesized; their intense photoemissions can be modified by interactions with the non-coordinating pyrazine-N atom. Luminescence modulation is possible without the need for altering the ligand framework. Emissions shift from red (77 K) to blue (298 K) due to thermally activated delayed fluorescence (TADF

Highly photoluminescent copper carbene complexes based on prompt rather than delayed fluorescence

Linear two-coordinate copper complexes of cyclic (alkyl)(amino)-carbenes (CAAC)CuX (X = halide) show photoluminescence with solid-state quantum yields of up to 96%; in contrast to previously reported Cu photoemitters the emission is independent of temperature over the range T = 4 – 300 K and occurs very efficiently by prompt rather than delayed fluorescence, with lifetimes in the sub-nanosecond range

Development and validation of tools for the implementation of european air quality policy in Germany (Project VALIUM)

International audienceIn the framework of the German Atmospheric Research Program AFO-2000 a system of consistent coupled numerical models has been developed. The purpose of the model system is to serve as a tool for the execution of European urban air quality regulations. A consortium with the acronym VALIUM was formed, which consisted of German research institutes, environmental consultancies and an environmental agency. A substantial part of the VALIUM program was devoted to the generation of a set of high quality data for the validation of the numerical model system. The validation data are based on a combination of field studies, tracer experiments and corresponding wind tunnel experiments. The field experiments were carried out inside and around a street canyon in a city district of Hanover/Germany. After a brief introduction to the VALIUM project a summary of the main results will be given

Sustained pain-related depression of behavior: effects of intraplantar formalin and complete freund’s adjuvant on intracranial self-stimulation (ICSS) and endogenous kappa opioid biomarkers in rats

Background: Intraplantar administration of complete Freund's adjuvant (CFA) and formalin are two noxious stimuli commonly used to produce sustained pain-related behaviors in rodents for research on neurobiology and treatment of pain. One clinically relevant manifestation of pain is depression of behavior and mood. This study compared effects of intraplantar CFA and formalin on depression of positively reinforced operant behavior in an assay of intracranial self-stimulation (ICSS) in rats. Effects of CFA and formalin on other physiological and behavioral measures, and opioid effects on formalin-induced depression of ICSS, were also examined. Results: There were four main findings. First, consistent with previous studies, both CFA and formalin produced similar paw swelling and mechanical hypersensitivity. Second, CFA produced weak and transient depression of ICSS, whereas formalin produced a more robust and sustained depression of ICSS that lasted at least 14 days. Third, formalin-induced depression of ICSS was reversed by morphine doses that did not significantly alter ICSS in saline-treated rats, suggesting that formalin effects on ICSS can be interpreted as an example of pain-related and analgesic-reversible depression of behavior. Finally, formalin-induced depression of ICSS was not associated with changes in central biomarkers for activation of endogenous kappa opioid systems, which have been implicated in depressive-like states in rodents, nor was it blocked by the kappa antagonist norbinaltorphimine. Conclusions: These results suggest differential efficacy of sustained pain stimuli to depress brain reward function in rats as assessed with ICSS. Formalin-induced depression of ICSS does not appear to engage brain kappa opioid systems. Electronic supplementary material The online version of this article (doi:10.1186/1744-8069-10-62) contains supplementary material, which is available to authorized users