Formulation of a phase space exponential operator for the Wigner transport equation accounting for the spatial variation of the effective mass

A novel numerical approximation technique for the Wigner transport equation including the spatial variation of the effective mass based on the formulation of an exponential operator within the phase space is derived. In addition, a different perspective for the discretization of the phase space is provided, which finally allows flexible discretization patterns. The formalism is presented by means of a simply structured resonant tunneling diode in the stationary and transient regime utilizing a conduction band Hamilton operator. In order to account for quantum effects within heterostructure devices adequately, the corresponding spatial variation of the effective mass is considered explicitly, which is mostly disregarded in conventional methods. The results are validated by a comparison with the results obtained from the nonequilibrium Green’s function approach within the stationary regime assuming the flatband case. Additionally, the proposed approach is utilized to perform a transient analysis of the resonant tunneling diode including the self-consistent Hartree–Fock potential

Constraining A4A_4 Leptonic Flavour Model Parameters at Colliders and Beyond

The observed pattern of mixing in the neutrino sector may be explained by the presence of a non-Abelian, discrete flavour symmetry broken into residual subgroups at low energies. Many flavour models require the presence of Standard Model singlet scalars which can promptly decay to charged leptons in a flavour-violating manner. We constrain the model parameters of a generic $A_4$ leptonic flavour model using a synergy of experimental data including limits from charged lepton flavour conversion, an 8 TeV collider analysis and constraints from the anomalous magnetic moment of the muon. The most powerful constraints derive from the MEG collaborations' limit on Br$\left(\mu\to e\gamma\right)$ and the reinterpretation of an 8 TeV ATLAS search for anomalous productions of multi-leptonic final states. We quantify the exclusionary power of each of these experiments and identify regions where the constraints from collider and MEG experimental data are complementary.Comment: v1: 28 + 9 pages, 8 figures. v2: 30 + 10 pages, 10 figures. v2 consistent with JHEP accepted version where further discussion of results and several more references were adde

Subdomain-based exponential integrators for quantum Liouville-type equations

In order to describe quantum mechanical effects, the use of the von-Neumann equation is apparent. In this work, we present a unified numerical framework so that the von-Neumann equation in center-of-mass coordinates leads to a Quantum Liouville-type equation when choosing a suitable basis. In particular, the proposed approach can be related to the conventional Wigner equation when a plane wave basis is used. The drawback of the numerical methods is the high computational cost. Our presented approach is extended to allow reducing the dimension of the basis, which leads to a computationally efficient and accurate subdomain approach. Not only the steady-state behavior is of interest, but also the dynamic behavior. In order to solve the time-dependent case, suitable approximation methods for the time-dependent exponential integrator are necessary. For this purpose, we also investigate approximations of the exponential integrator based on Faber polynomials and Krylov methods. In order to evaluate and justify our approach, various test cases, including a resonant tunnel diode as well as a double-gate field-effect transistor, are investigated and validated for the stationary and the dynamic device behavior

Calcification depth of deep-dwelling planktonic foraminifera from the eastern North Atlantic constrained by stable oxygen isotope ratios of shells from stratified plankton tows

Stable oxygen isotopes (delta O-18) of planktonic foraminifera are one of the most used tools to reconstruct environmental conditions of the water column. Since different species live and calcify at different depths in the water column, the delta O-18 of sedimentary foraminifera reflects to a large degree the vertical habitat and interspecies delta O-18 differences and can thus potentially provide information on the vertical structure of the water column. However, to fully unlock the potential of foraminifera as recorders of past surface water properties, it is necessary to understand how and under what conditions the environmental signal is incorporated into the calcite shells of individual species. Deep-dwelling species play a particularly important role in this context since their calcification depth reaches below the surface mixed layer. Here we report delta O-18 measurements made on four deep-dwelling Globorotalia species collected with stratified plankton tows in the eastern North Atlantic. Size and crust effects on the delta O-18 signal were evaluated showing that a larger size increases the delta O-18 of G. inflata and G. hirsuta, and a crust effect is reflected in a higher delta O-18 signal in G. truncatulinoides. The great majority of the delta O-18 values can be explained without invoking disequilibrium calcification. When interpreted in this way the data imply depth-integrated calcification with progressive addition of calcite with depth to about 300m for G. inflata and to about 500m for G. hirsuta. In G. scitula, despite a strong subsurface maximum in abundance, the vertical delta O-18 profile is flat and appears dominated by a surface layer signal. In G. truncatulinoides, the delta O-18 profile follows equilibrium for each depth, implying a constant habitat during growth at each depth layer. The delta O-18 values are more consistent with the predictions of the Shackleton (1974) palaeotemperature equation, except in G. scitula which shows values more consistent with the Kim and O'Neil (1997) prediction. In all cases, we observe a difference between the level where most of the specimens were present and the depth where most of their shell appears to calcify.Agência financiadora Portuguese Foundation for Science and Technology (FCT): SFRH/BD/78016/2011; UID/Multi/04326/2019 European Union Seventh Framework Programme (FP7/2007-2013): 228344-EUROFLEETS German Research Foundation (DFG): WA2175/2-1; WA2175/4-1 German Climate Modelling consortium PalMod - German Federal Ministry of Education and Research (BMBF)info:eu-repo/semantics/publishedVersio

Trafficking of Mononuclear Phagocytes in Healthy Arteries and Atherosclerosis

Monocytes and macrophages play essential roles in all stages of atherosclerosis – from early precursor lesions to advanced stages of the disease. Intima-resident macrophages are among the first cells to be confronted with the influx and retention of apolipoprotein B-containing lipoproteins at the onset of hypercholesterolemia and atherosclerosis development. In this review, we outline the trafficking of monocytes and macrophages in and out of the healthy aorta, as well as the adaptation of their migratory behaviour during hypercholesterolemia. Furthermore, we discuss the functional and ontogenetic composition of the aortic pool of mononuclear phagocytes and its link to the atherosclerotic disease process. The development of mouse models of atherosclerosis regression in recent years, has enabled scientists to investigate the behaviour of monocytes and macrophages during the resolution of atherosclerosis. Herein, we describe the dynamics of these mononuclear phagocytes upon cessation of hypercholesterolemia and how they contribute to the restoration of tissue homeostasis. The aim of this review is to provide an insight into the trafficking, fate and disease-relevant dynamics of monocytes and macrophages during atherosclerosis, and to highlight remaining questions. We focus on the results of rodent studies, as analysis of cellular fates requires experimental manipulations that cannot be performed in humans but point out findings that could be replicated in human tissues. Understanding of the biology of macrophages in atherosclerosis provides an important basis for the development of therapeutic strategies to limit lesion formation and promote plaque regression

Numerische Methoden für die Analyse von Quantenbauelementen auf Grundlage der Liouville-von-Neumann-Gleichung

Heutzutage ist die numerische Modellierung des Transportverhaltens innerhalb von Quantenbauelementen für die Analyse und das Design moderner Komponenten der Nanoelektronik, Hochfrequenztechnik und Terahertz-Technik unabdingbar. Neben der Analyse des stationären Regimes erlangt dabei insbesondere die Erfassung transienter Phänomene unter Berücksichtigung von Wechselwirkungsmechanismen eine große Bedeutung. Während sich Ansätze auf Basis von Greenschen-Funktionen mittlerweile zur Analyse des stationären Transportverhaltens als erfolgreich erwiesen haben, ist ihr Einsatz im transienten Regime aufgrund der hohen Anforderungen an Rechenressourcen zur Analyse von ingenieurmäßigen Anwendungen zu aufwendig. Eine numerisch zielgerichtete Analyse des transienten Transportverhaltens auf Basis der statistischen Dichtematrix erscheint vor diesem Hintergrund sinnvoll. Hierzu wird vor allem die Wigner-Transportgleichung herangezogen. Die korrespondierende numerische Approximation auf Basis von Finiten-Differenzen ist jedoch mit einer Vielzahl von Problemen behaftet. Stark oszillierende Integralkerne im Phasenraum innerhalb der Wigner- Transportgleichung bereiten Schwierigkeiten bei der Approximation. Kohärente Effekte und nichtlokale Randbedingungen werden im Grundsatz nicht erfasst. Oberflächenterme infolge eines abgeschlossenen Rechengebiets werden nicht berücksichtigt. Als Konsequenz kommt es zu unphysikalischen Reflexionen an den Rändern. Die Ergebnisse weichen bereits stark im stationären Regime von anerkannten Referenzlösungen auf Grundlage Greenscher-Funktionen ab. In dieser Arbeit werden neu konzipierte Formalismen zur numerischen Approximation der Transportgleichungen vorgestellt, mit denen die genannten Probleme vermieden werden können. Grundlage für dieses Vorhaben ist einerseits eine semi-analytische Lösung auf Basis eines Exponentialoperators und andererseits die Einführung eines komplexen Potenzials hinsichtlich der Einbindung der Oberflächenterme. Unter Verwendung der Liouville-von-Neumann-Gleichung in Schwerpunkt- und Relativkoordinaten wird ein weiteres Feld zur Analyse des Transportverhaltens eröffnet. Hiermit gelingt nicht nur die Kombination der Vorteile einer Ortsraumdiskretisierung mit denen einer Phasenraumdarstellung, sondern auch die Formulierung eines numerisch effizienten Unterraum-Verfahrens. Die entwickelten Formalismen werden anhand von Intra-, Inter- und Multisubbandtransportmodellen im stationären und transienten Regime untersucht. Im Vergleich zu den ursprünglich eingesetzten Methoden wird eine hervorragende Übereinstimmung mit anerkannten Verfahren im stationären Regime erzielt und somit der Grundstein für die ingenieurmäßige Analyse von zeitabhängigen Phänomenen in Quantenbauelementen gelegt

Datenübertragung mittels MQTT

Das Internet der Dinge bezeichnet die Vernetzung unterschiedlicher Geräte über das Internet. Die Wahl eines geeigneten Nachrichtenprotokolls ist aufgrund der hohen Anforderungen nicht einfach. Um eine möglichst breite Vernetzung zu ermöglichen, muss das Protokoll für so viele Gerätetypen wie möglich verwendbar sein. Hierzu gehören auch Geräte mit schlechter Hardware und Geräte in Gebieten mit schlechter Netzanbindung. Da wir uns im Bereich des Internets bewegen, darf natürlich auch die Sicherheit und Zuverlässigkeit des Protokolls nicht vernachlässigt werden. Ziel dieser Arbeit ist die Präsentation des Nachrichtenprotokolls MQTT, das im Internet der Dinge weite Verbreitung findet. Zunächst wird die genaue Funktionsweise des Protokolls erläutert. Nachdem die Sicherheit des Protokolls genau betrachtet wurde, werden die Vor- und Nachteile des Protokolls herausgearbeitet. Anhand einer Beispielimplementierung wird zudem dessen Verwendung erläutert. Anschließend werden alternative Protokolle des Internets der Dinge vorgestellt und mit dem MQTT Protokoll verglichen. Am Ende der Arbeit wird ein Fazit gezogen, das das MQTT Protokoll für die Verwendung im Internet der Dinge bewertet

Digital orientation and environmental performance in times of technological change

Digitalization is increasingly seen as a strategic means for firms to yield competitive and environmental advantages. Still, current empirical research does not yet provide ample evidence on how a firm's strategic posture towards digitalization connects to environmental performance. This study examines the link between digital orientation and environmental performance as well as the moderating role of technological turbulence. The natural-resource-based view and literature on strategic orientations provide the conceptual foundations. The hypotheses are tested with data from 515 U.S. Standard and Poor's 500 companies with 2,800 firm observations from 2009 to 2019. The results indicate that, first, a firm's digital orientation has a significant and positive effect on environmental performance and, second, this effect is even more pronounced in technologically turbulent business environments. In sum, our findings suggest that managers can improve their firm's environmental performance and competitive position by increasing the digital orientation within their organizations. We thus add to the literature on the natural-resource-based view by identifying digital orientation as a strategy aligned with the natural environment. Finally, we derive practical implications for managers and policymakers aiming to bring together digitalization and green strategies

Cycloaddition of Alkenes and Alkynes to the P-centered Singlet Biradical [P(μ-NTer)]2

The reaction of biradical [P(μ-NTer)]2 (1, Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl) towards different alkenes (R = 2,3-dimethyl–butadiene, 2,5-dimethyl-2,4-hexadiene, 1,7-octadiene, 1,4-cyclohexadiene) and alkynes (R = 1,4-diphenyl-1,3-butadiyne) was studied experimentally. Although these olefins can react in different ways, only [2+2] cycloaddition products (1R) were observed. The reaction with 2,3-dimethylbutadiene also led to the [2+2] product (1dmb). Thermal treatment of 1dmb above 140 °C resulted in the recovery of biradical 1 upon homolytic bond cleavage of the two P–C bonds and the release of 2,3-dimethylbutadiene. In contrast to this reaction, all other [2+2] additions products (1R, R = 1,7-octadiene, 1,4-cyclohexadiene, 1,4-diphenyl-1,3-butadiyne) began to decompose at temperatures between 200 °C and 300 °C. Only unidentified products were obtained but no temperature-controlled equilibrium reactions were observed. Computations were carried out to shed light into the formal [2+2] as well as the possible [4+2] addition reaction

A 60 kW Power Hardware-in-the-Loop Test Bench for grid emulation based on a Series Hybrid Cascaded H-Bridge Converter

In this paper the requirements for a Power Hardware-In-the-Loop (PHIL) system for the emulation of grids and grid faults are discussed. Solutions for all parts of the PHIL system – the power electronics, the signal processing system and the software structure – are presented. Subsequently, an analysis of the accuracy, bandwidth and stability of the PHIL testbench is done and the effects of different interface algorithms are shown. Concluding, measurement results of emulated highly dynamic grid faults such as voltage dips and spikes, distorted grids and weak grid situations are shown, which prove the performance of the PHIL system