Verfahren zur Grundauslegung von Tragwerkstrukturen mit Hybrid-Rohren

Die vorliegende Arbeit beschäftigt sich mit der näherungsweisen Auslegung von Tragwerken aus Metall-Faserverbundkunststoffrohren zur Anwendung als Überrollschutz-Vorrichtung. Neben der Auslegung der Hybrid-Rohre soll ebenfalls die Topologie, also die Anordnung der Rohre betrachtet werden. Das Verfahren basiert auf der Berechnung der Verschiebungen und der Schnittkraftverläufe mit einem Balkenmodell. Es werden zunächst die Anforderungen an den Überrollkäfig betrachtet und ein Konzept zur Ausführung mit Hybrid-Rohren vorgestellt. Für die Berechnung der Schnittkraftverläufe werden verschiedene Verfahren wie das Übertragungsmatrizen- oder das Deformationsverfahren beschrieben und diese in einem MATLAB-Skript umgesetzt und mit einer FE-Lösung verglichen. Die Festigkeitsbewertung der Rohre erfolgt an definierten Schnittebenen. In diesen Ebenen wird der Rohrquerschnitt in Kreisringsegmente geteilt und für diese werden mittels der klassischen Laminattheorie die Versagenskriterien berechnet. Die Auswirkung des Versagens einzelner Segmente auf das globale Verhalten wird iterativ berücksichtigt. Die Auslegung der Topologie erfolgt über A-B-Vergleiche und Interpretation der Verschiebungen. Das Simulationsmodell auf Basis von Balkenelementen wird mit einem Python-Skript automatisiert in ABAQUS erstellt. Durch die Implementierung zusätzlicher Knotensteifigkeiten können Knotenverstärkungen bereits bei der Auslegung berücksichtigt werden.This thesis studies the approximatively design of structural systems consisting of metal/fibre-reinforced plastic hybrid tubes as roll cages. Besides the design of hybrid tubes, the topology, i.e. the layout of the tubes, is considered. The method is based on the computation of the displacement and strain distribution using beam theory. At first, the requirements on a roll cage are evaluated and the design of a roll cage with hybrid tubes is presented. For the computation of strain distributions, the transfer matrix method and deformation method are explained. Both methods are calculated in MATLAB and compared to a finite element solution. The strength of tubes is evaluated at defined cross-sections. At these sections, the tube cross-section is separated into annulus sector and by using classical laminate theory failure critiera are calculated. The impact of failure in single annulus sector on the global behaviour of the whole structure is evaluated iteratively. The design of the topology is done by A-B comparisons and interpretation of displacements. The creation of the simulation model consisting of beam elements is automatised via Python scripts in ABAQUS. By integrating additional joint stiffness in the design phase, joint reinforcements can be achieved

The Role of Sexual Selection in the Evolution of Chemical Signals in Insects

Chemical communication is the most ancient and widespread form of communication. Yet we are only beginning to grasp the complexity of chemical signals and the role they play in sexual selection. Focusing on insects, we review here the recent progress in the field of olfactory-based sexual selection. We will show that there is mounting empirical evidence that sexual selection affects the evolution of chemical traits, but form and strength of selection differ between species. Studies indicate that some chemical signals are expressed in relation to an individual’s condition and depend, for example, on age, immunocompetence, fertility, body size or degree of inbreeding. Males or females might benefit by choosing based on those traits, gaining resources or “good genes”. Other chemical traits appear to reliably reflect an individual’s underlying genotype and are suitable to choose a mating partner that matches best the own genotype

Frequency- adaptive control of a three-phase single-stage grid-connected photovoltaic system under grid voltage sags

The low-voltage ride-through service is carried out in this paper according to the voltage profile described by the IEC 61400-21 European normative when short-duration voltage sags happen, and some instantaneous reactive power is delivered to the grid in accordance with the Spanish grid code; the mandatory limitation of the amplitude of the three-phase inverter currents to its nominal value is carried out with a novel control strategy, in which a certain amount of instantaneous constant active power can also be delivered to the grid when small or moderate voltage sags happen. A Multiple second order generalized integrator frequency-locked loop synchronization algorithm is employed in order to estimate the system frequency without harmonic distortions, as well as to output the positive- and the negative- sequence of the αβ quantities of the three-phase grid voltages when balanced and unbalanced voltage sags happen in a frequency- adaptive scheme. The current control is carried out in the stationary reference frame, which guarantees the cancellation of the harmonic distortions in the utility grid currents using a Harmonic compensation structure, and the implementation of a constant active power control in order to protect the DC link capacitor from thermal stresses avoiding the appearance of large harmonic distortions at twice the fundamental frequency in the DC link voltage. A case study of a three-phase single-stage grid-connected PV system with a maximum apparent power about 500 kVA is tested with several simulations using MATLAB/SIMULINK firstly, and secondly, with some experiments using the Controller hardware-in-the-loop (CHIL) simulation technique for several types of voltage sags in order to do the final validation of the control algorithms.This work was supported by the project “Nuevas topologías para convertidores en MT para grandes Instalaciones Fotovoltaicas” from the Spanish Government (Ref. TEC2016-80136-P) (A. B. Rey-Boué) and the European Community’s Horizon 2020 Program (H2020/2014-2020) in project “ERIGrid” (Grant Agreement No. 654113) under the Trans-national Access (TA) User Project: 04.003-201

Frequency-adaptive control of a three-phase single-stage grid-connected photovoltaic system under grid voltage sags

The low-voltage ride-through service is carried out in this paper according to the voltage profile described by the IEC 61400-21 European normative when short-duration voltage sags happen, and some instantaneous reactive power is delivered to the grid in accordance with the Spanish grid code; the mandatory limitation of the amplitude of the three-phase inverter currents to its nominal value is carried out with a novel control strategy, in which a certain amount of instantaneous constant active power can also be delivered to the grid when small or moderate voltage sags happen. A Multiple second order generalized integrator frequency-locked loop synchronization algorithm is employed in order to estimate the system frequency without harmonic distortions, as well as to output the positive- and the negative- sequence of the {\alpha}\b{eta} quantities of the three-phase grid voltages when balanced and unbalanced voltage sags happen in a frequency-adaptive scheme. The current control is carried out in the stationary reference frame, which guarantees the cancellation of the harmonic distortions in the utility grid currents using a Harmonic compensation structure, and the implementation of a constant active power control in order to protect the DC link capacitor from thermal stresses avoiding the appearance of large harmonic distortions at twice the fundamental frequency in the DC link voltage. A case study of a three-phase single-stage grid-connected PV system with a maximum apparent power about 500 kVA is tested with several simulations using MATLAB/SIMULINK firstly, and secondly, with some experiments using the Controller hardware-in-the-loop (CHIL) simulation technique for several types of voltage sags in order to do the final validation of the control algorithms

Vectorial electron spin filtering by an all-chiral metal–molecule heterostructure

The discovery of the electrons’ chiral induced spin selective transmission (CISS) through chiral molecules has opened the pathway for manipulating spin transport in nonmagnetic structures on the nanoscale. CISS has predominantly been explored in structurally helical molecules on surfaces, where the spin selectivity affects only the spin polarization of the electrons along their direction of propagation. Here, we demonstrate a spin selective electron transmission for the point-chiral molecule 3-methylcyclohexanone (3-MCHO) adsorbed on the chiral Cu(643)R surface. Using spin- and momentum-resolved photoelectron spectroscopy, we detect a spin-dependent electron transmission through a single layer of 3-MCHO molecules that depends on all three components of the electrons’ spin. Crucially, exchanging the enantiomers alters the electrons’ spin component oriented parallel to the terraces of the Cu(643)R surface. The findings are attributed to the enantiomer-specific adsorption configuration on the surface. This opens the intriguing opportunity to selectively tune CISS by the enantiospecific molecule–surface interaction in all-chiral heterostructures

Varying importance of cuticular hydrocarbons and iridoids in the species-specific mate recognition pheromones of three closely related Leptopilina species

Finding a suitable mate for reproduction is one of the most important tasks for almost all animals. In insects this task is often facilitated by pheromone-mediated communication. While insect pheromones in general show enormous chemical diversity, closely related species often use structurally similar compounds in their pheromones. Despite this similarity, pheromones of congeneric species living in sympatry need to be species specific. We investigated the pheromone-mediated mate recognition by males of three closely related species of Leptopilina, a genus of parasitoid wasps that utilize the larvae of Drosophila as hosts. The study species, L. heterotoma, L. boulardi, and L. victoriae, occur sympatrically and have a similar ecology and life history. We have found that mate recognition is species specific in all three species. This species specificity is achieved by a differing importance of cuticular hydrocarbons (CHCs) and iridoids in the female mate recognition pheromones. In L. heterotoma the iridoids are of major importance while CHCs play a negligible role. In L. boulardi, however, the CHCs are as important as the iridoids, while in L. victoriae, the CHCs alone elicit a full behavioral response of males. Our results provide novel insights into pheromone evolution in insects by showing that selection on two completely different classes of chemical compounds may generate conditions where compounds from both classes contribute to a varying degree to the chemical communication of closely related species and that this variation also generates the species specificity of the signals

β-Catenin Promotes the Differentiation of Epidermal Langerhans Dendritic Cells

The epithelial signaling protein and transcriptional regulator β-catenin has recently been implicated in hematopoietic dendritic cell (DC) differentiation as well as in DC-mediated tolerance. We here observed that epidermal Langerhans cells (LCs) but not interstitial/dermal DCs express detectable β-catenin. LCs are unique among the DC family members in that LC networks critically depend on epithelial adhesion molecules as well as on the cytokine transforming growth factor-β1 (TGF-β1). However, despite the important functions of LCs in the immune system, the molecular mechanisms governing LC differentiation and maintenance remain poorly defined. We found that TGF-β1 induces β-catenin in progenitor cells undergoing LC differentiation and that β-catenin promotes LC differentiation. Vitamin D, another epidermal signal, enhanced TGF-β1-mediated β-catenin induction and promoted the expression of multiple epithelial genes by LCs. Moreover, full-length vitamin D receptor (VDR) promoted, whereas a truncated VDR diminished, the positive effects of ectopic β-catenin on LC differentiation. Therefore, we here identified β-catenin as a positive regulator of LC differentiation in response to TGF-β1 and identified a functional interaction between β-catenin and VDR in these cells

Ultrafast charge-transfer exciton dynamics in C60_{60} thin films

The high flexibility of organic molecules offers great potential for designing the optical properties of light-active materials for the next generation of optoelectronic and photonic applications. However, despite successful implementations of molecular materials in todays' display and photovoltaic technology, many fundamental aspects of the light-to-charge conversion have still to be uncovered. Here, we focus on the ultrafast dynamics of optically excited excitons in C$_{60}$ thin films depending on the molecular coverage and the light-polarization of the optical excitons. Using time- and momentum-resolved photoemission with fs-XUV radiation, we follow the depopulation dynamics in the excited states while simultaneously monitoring the signatures of the excitonic charge character in the molecular valence states. Optical excitation with visible light results in the instantaneous formation of charge-transfer (CT) excitons, which transform stepwise into energetically lower Frenkel-like excitons. While the number and energetic position of energy levels within this cascade process are independent of the molecular coverage and the light polarization of the optical excitation, we find quantitative differences in the depopulation times and the optical excitation efficiency. Our comprehensive study reveals the crucial role of CT excitons for the excited state dynamics of homo-molecular fullerene materials and thin films

ProMeQuaLab - Projeto de Melhoria da Qualidade Laboratorial para Países de Língua Portuguesa: trabalhos realizados e em curso 2017

Apresentação sobre os trabalhos realizados e em curso no âmbito do projeto de Melhoria da Qualidade Laboratorial para Países de Língua Portuguesa (ProMeQuaLab).N/