58491 research outputs found
Sort by
Labor migration and commodity production in Africa: Global entanglements
No full textThis introductory article presents the objectives, scope and contents of the Special Issue titled Labor Migration and Commodity Production in Africa: Global Entanglements. By congregating a diverse team of scholars from Brazil, Turkey, Germany, France, the United States, and Cameroon, all at different stages of their careers, this Special Issue seeks to build upon current trends in the fields of Global and African History to expand our current understanding of the centrality of African subjects in the making of the contemporary, densely globalized yet deeply unequal world. This introduction sets the theoretical framework that guided our call for papers, summarizes the key findings of each article, and situate their individual contributions within the topics related to the agency of African subjects in the creation of increasingly interconnected societies. We argue that the articles in this Special Issue offer a path to further strengthen and expand both fields of African and Global History by incorporating the analysis of understudied sources from diverse linguistic backgrounds, such as Arabic, Turkish, Portuguese and German, as well as legal documents produced by contemporary African states.Este artigo introdutório apresenta os objetivos, o escopo e o conteúdo do Dossiê Temático intitulado Migração Laboral e Produção de Commodities na África: Conexões Globais. Ao congregar uma equipe diversificada de estudiosos oriundos do Brasil, Turquia, Alemanha, França, Estados Unidos, e Camarões, todos em diferentes estágios de suas carreiras, este Dossiê Temático se alicerça sobre tendências atuais nos campos da História Global e da África para expandir nossa compreensão sobre a centralidade de sujeitos africanos na formação do mundo contemporâneo – densamente globalizado, mas profundamente desigual. Esta introdução estabelece o enquadramento teórico que orientou nossa chamada de artigos, resume os principais achados de cada artigo e situa suas contribuições individuais dentro da temática relativa à agência de sujeitos africanos na criação de sociedades cada vez mais interconectadas. Argumentamos que os artigos deste Dossiê Temático oferecem um caminho para fortalecer e expandir ambos os campos da História da África e Global, incorporando a análise de fontes pouco estudadas de diferentes procedências linguísticas, como árabe, turco, português e alemão, bem como documentos legais produzidos por estados africanos contemporâneos
Odd Dynamics in Diffusion Systems
No full textOnsager reciprocal relations imply that diffusion tensors are symmetric. However, the validity of these relations is limited to systems that respect time-reversal symmetry. The motion of a charged particle in a magnetic field is a classical example of broken time-reversal symmetry. For this reason, the probability flux associated with a particle performing overdamped motion gets a specific handedness based on the charge it carries. Such a diffusion behavior, also exhibited by active chiral particles, is described by a tensor with antisymmetric or odd components.
The oddness gives rise to additional probability fluxes in diffusion systems, which we term odd-diffusive fluxes. Taking a prototype of odd-diffusive systems, which are charged Brownian particles in an external magnetic field, we investigate the importance of these fluxes on the properties of the system. These fluxes, however, are dynamical features of the system: since the Lorentz force due to an external magnetic field does not perform work on the particle, the equilibrium properties are unaffected by the odd-diffusive fluxes. In Ch. 6, we show that by stochastically resetting the Brownian particle, a nonequilibrium steady state can be created that preserves the hallmark features of dynamics under Lorentz force. As we show in Ch. 7, the physics even becomes richer when we consider charged active Brownian particles. Under stochastic resetting, an active system settles into a nontrivial stationary state with novel features with no counterpart in passive systems.
In Ch. 8, we show that in a multithermostat Brownian system, which constitutes a primitive Brownian engine composed of a gyrating Brownian particle, the magnetic field gives rise to correlations between different velocity components resulting in spatial cross-correlations. We demonstrate that these correlations persist in the stationary state. In Ch. 9, we use these correlations to propose a tunable Brownian magneto heat pump that can be operated as both a heat engine and a refrigerator.
Finally, we show that odd-diffusivity can be used to stabilize Brownian systems which are subjected to a vortex flow. We study the escape dynamics in diffusion systems subjected to Lorentz forces. In Ch. 10, we study the escape dynamics in an anisotropically driven Brownian magneto-system. We show that the spatial correlations induced by the Lorentz force help to restore the broken spatial symmetry by the anisotropy. Chapter 11 presents the investigation of the escape dynamics of a Brownian magneto-system when combined with a vortex flow. Combining the vortex flow and the magnetic field can effectively help the particle escape
Das CXCL12-System kontrolliert die Migration humaner Tumorzellen über EGFR-abhängige Signalwege
No full textDas Chemokin CXCL12 (stromal cell derived-factor, SDF-1) bindet an die Rezeptoren CXCR4 und CXCR7 und kontrolliert damit unter anderem das Wachstum sowie die Metastasierung von Tumoren in unterschiedlichen Organen. Interessanterweise werden diese protumorogenen Einflüsse abhängig vom Zelltyp und der jeweiligen zellulären Antwort entweder von CXCR4, CXCR7 oder der Kombination beider Rezeptoren vermittelt. CXCR4 ist ein klassischer G-Protein-gekoppelter Rezeptor, der nach Ligandenbindung zur Aktivierung von Gi, Gq sowie G12/G13 führt. Demgegenüber steht der CXCR7, welcher primär als Scavenger Rezeptor betrachtet wird und über Bildung eines extrazellulären CXCL12-Gradienten vor allem die CXCR4-abhängige Zellmigration kontrolliert. Neuere Arbeiten belegen allerdings, dass auch CXCR7 zu einem eigenständigen Signalverhalten in der Lage ist und ähnlich wie CXCR4 die Migration, Proliferation sowie Invasion von (Tumor)zellen beeinflusst. Die Aktivierung der beteiligten Signalwege erfolgt dabei im Regelfall über Arrestine. Ausnahmen bilden bislang Astrozyten und bestimmte Gliomzellen, in denen CXCR7 als klassischer G-Protein-gekoppelter Rezeptor wirkt. Eine weitere, bislang vor allem für CXCR4 gezeigte Möglichkeit, zelluläre Signalwege zu aktivieren, ist über die Transaktivierung des EGFRs (engl.: epidermal growth factor receptor). Diese Arbeit zeigt, dass die Src-Kinase-vermittelte und G-Protein-abghängige Transaktivierung des EGFRs einen generellen Mechanismus darstellt, über den CXCL12 die Migration in den Tumorzelllinien steuert und damit zur Tumormetastasierung führen kann. Untersucht wurden dabei die Tumorzelllinien A549 (nichtkleinzelliges Lungenkarzinom), C33A (Zervixkarzinom), DLD‑1 (kolorektales Karzinom), MDA‑MB‑231 (Mammakarzinom) und PC‑3 (Prostatakarzinom), in denen die CXCL12-induzierte Zellmigration entweder über CXCR4, CXCR7 oder beide Rezeptoren vermittelt wird. Tatsächlich unterblieb die CXCL12-abhängige Migration aller Tumorzellen in Anwesenheit sowohl des Src-Kinase-Inhibitors Src-I1 als auch des EGFR-Inhibitors AG1478, nicht aber nach Hemmung der Arrestin-Expression mittels RNA-Interferenz. Das zelluläre Migrationsverhalten wurde mittels der Boyden-Kammer analysiert. Die Expression des EGFRs sowie β-Arrestin 1/2 wurde im Western Blot nachgewiesen. Die bereits früher gezeigte unterschiedliche Verwendung von CXCR4 und/oder CXCR7 für die Vermittlung des CXCL12-Signals in den verschiedenen Tumorzellen wurde unter Zuhilfenahme spezifischer Rezeptor-Antagonisten (AMD3100, CCX771) bestätigt. Die erhaltenen Befunde identifizieren den EGFR als einen möglichen therapeutischen Ansatzpunktpunkt zur Unterbindung der von CXCL12 induzierten Metastasierung von Tumoren. Im Vergleich zu CXCR4- oder CXCR7-Rezeptorantagonisten hat dieser Ansatz den Vorteil, dass keine Kenntnis darüber notwendig ist, über welchen CXCL12-Rezeptor das Metastasierungsverhalten des jeweiligen Tumors gesteuert wird
Politico-Theological Debates in Ghadames between the 1770s and the 1850s from a Global Perspective
No full textThis article aims to shed light on the history of politico-theological debates in Ghadames, focusing on two distinct case studies through discourse analysis. The particular geographical location of Ghadames, situated between two prominent states—Morocco and the Ottoman Empire—each with their respective caliphal claims, has historically enabled the scholars of the city to formulate and substantiate their own political stances. As a result, a substantial body of written materials, including chronicles, biographies, and letters, has emerged from Ghadames, reflecting the political discourse as articulated by its scholars, who adapted their perspectives in response to shifts in regional power dynamics. Notably, this adaptation was facilitated by the active intellectual engagement of the city’s scholars. In this context, the article investigates the politico-theological discussions in Ghadames from the 1750s to the 1850s, analysing the persistent yet varied arguments and justifications, as well as the intellectual milieu that intersected with them
Ready for robots? Assessment of autonomous delivery robot operative accessibility in German cities
No full textUnlike autonomous car applications, the operational area of urban service autonomous robots like autonomous delivery robots (ADRs) is not clearly defined at the moment. Due to large variations in the different robot designs, specific local infrastructure and regulation, assessing the feasibility of different operational scenarios is difficult. This paper presents a prototype evaluation methodology based on Open Street Map data for the assessment of ADR deployments considering one-to-many delivery schemes. Four different robot configurations and potential operational specifications are modeled and evaluated in a sample of German cities. The bandwidth of considered robot types ranges from large ADRs operating on roadways down to small size systems operating on sidewalks. The performance of the first category is limited by the reduced accessibility in areas with higher traffic. On the contrary, small ADRs present a higher detour time but increased accessibility. The evaluated operational scenarios show very diverse performance depending on the considered metrics and cities. For all the metrics considered in the paper, sidewalk ADRs show poor performance when compared to other potential ADR deployments
Modifizierung des langfristigen Leistungsaufbaus im Sportschwimmen unter den Bedingungen der Sportförderung Ägyptens mit besonderer Berücksichtigung des Grundlagentrainings
No full textTätigkeitsbericht der Beauftragten für Integration und Migration / Landkreis Sächsische Schweiz-Osterzgebirge
No full textFuture power markets: Impacts of consumer response and dynamic retail prices on electricity markets
No full textIn this article we discuss the impact of the increasingly higher dynamics and transparency on future electricity markets due to a higher degree of automation along the energy supply chain. As part of the SESAM (Self Organization and Spontaneity in Liberalized and Harmonized Markets) project, we analyze the consequences of the customers’ higher willingness to change their supplier. In addition, we evaluate the major changes in load profiles caused by the use of load management systems in combination with dynamic retail electricity prices. We demonstrate that not only the consumer load but also the application of decentralized combined heat and power plants can be rescheduled. Finally, we outline further research activities
A Model-Based Approach for Online Optimization of Pneumatic Drives
No full textThis article presents an online monitoring and setup strategy to optimize the operating conditions of pneumatic drives. The strategy integrates a model-based optimization approach with a hybrid machine learning (HML) model designed to assess the loading conditions and improve the performance of pneumatic actuators. Employing the operating point method, a model-based approach, the HML model seeks an optimal balance between energy efficiency and robustness. A strategy based on the chambers’ pressures is applied on the HML model to assess in real-time the actual load being applied on the cylinder, establishing a reference pair of pressure ratios, and making it suitable for nonconstant load force applications. A sensitivity analysis is performed to evaluate the impact of the uncertainties associated with the operating point parameters on the HML model output. Experimental results under several load conditions demonstrated its ability to significantly reduce air consumption in underloaded scenarios. Furthermore, the HML approach improved system robustness in overloaded cases, mitigating the impact on displacement time due to possible load variations. Comparative evaluations with a conventional architecture and a commercially available energy-saving device highlight the capabilities of the proposed online monitoring strategy of cost-effectively enhancing the operation of pneumatic drives
