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Stabilization of transverse beam parameters at the S-DALINAC
No full textElectron-induced fission reactions will be deployed and studied at the S-DALINAC. For these experiments, it is desirable to limit the transverse displacements of the electron beam due to drifts and distortions to below 200μm. Prior to the present work, this requirement was not met at the S-DALINAC. A total of three systems have been developed, implemented and interconnected to monitor and improve the transverse beam stability: (i) The beam position monitoring system based on high-speed cameras provides transverse beam parameters with micrometer resolution at a kilohertz rate. (ii) A newly designed compensator device mitigates longitudinal and transverse perturbations from the mains frequency on the electron beam. (iii) Finally, an active beam stabilization system ensures high beam stability at the intended interaction point of the electron beam and the fission target. The design and implementation of these systems as well as performance measurements will be presented in this paper
Influence of reinforcement and its omission on trial‐by‐trial changes of response bias in perceptual decision making
No full textDiscrimination performance in perceptual choice tasks is known to reflect both sensory discriminability and nonsensory response bias. In the framework of signal detection theory, these aspects of discrimination performance are quantified through separate measures, sensitivity ( d′ ) for sensory discriminability and decision criterion ( c ) for response bias. However, it is unknown how response bias (i.e., criterion) changes at the single‐trial level as a consequence of reinforcement history. We subjected rats to a two‐stimulus two‐response conditional discrimination task with auditory stimuli and induced response bias through unequal reinforcement probabilities for the two responses. We compared three signal‐detection‐theory‐based criterion learning models with respect to their ability to fit experimentally observed fluctuations of response bias on a trial‐by‐trial level. These models shift the criterion by a fixed step (1) after each reinforced response or (2) after each nonreinforced response or (3) after both. We find that all three models fail to capture essential aspects of the data. Prompted by the observation that steady‐state criterion values conformed well to a behavioral model of signal detection based on the generalized matching law, we constructed a trial‐based version of this model and find that it provides a superior account of response bias fluctuations under changing reinforcement contingencies
Thermodynamisch‐analytische Modellierung der Karbonatisierung in Betonen aus klinkerreduzierten Zementen
No full textDas Bestreben, die Umwelteinwirkungen von Zement und Beton zu verringern, wird zukünftig zum vermehrten Einsatz klinkerreduzierter Zemente führen. Etablierte Modelle zur Vorhersage der Karbonatisierungstiefe (xc) sind aber häufig auf Betone aus handelsüblichem Zement beschränkt. In diesem Beitrag werden die Karbonatisierungsraten von Beton aus Zement mit bis zu 60 Gew.‐% Kalksteinmehl (LS) und w/z‐Werten von 0,3 bis 0,75 untersucht. Zur Abschätzung der xc wurde ein gekoppeltes analytisch‐thermodynamisches Modell entwickelt. Der vorgeschlagene Modellierungsansatz beinhaltet die thermodynamische Berechnung der effektiven CO2‐Bindekapazität und einen analytischen Ansatz zur Abschätzung des CO2‐Diffusionskoeffizienten. Die gute Übereinstimmung zwischen berechneten und experimentell (XRD und TGA) ermittelten Phasenzusammensetzungen zeigt, dass thermodynamische Teilmodelle eine Möglichkeit bieten die Vorhersagegenauigkeit der xc zu verbessern. Die größten Abweichungen zwischen simulierten und tatsächlichen xc wurden bei dichtem Beton beobachtet. Die Untersuchungen und Modellierungen ergaben, dass die betontechnologisch optimierten, klinkerreduzierten Betone mit bis zu 60 Gew.‐% Kalksteinmehl ähnlich hohe Karbonatisierungswiderstände aufweisen können wie Beton aus CEM I 52.5 R
Enabling Natural Zero-Shot Prompting on Encoder Models via Statement-Tuning
No full textWhile Large Language Models (LLMs) exhibit remarkable capabilities in zero-shot and few-shot scenarios, they often require computationally prohibitive sizes. Conversely, smaller Masked Language Models (MLMs) like BERT and RoBERTa achieve state-of-the-art results through fine-tuning but struggle with extending to few-shot and zero-shot settings due to their architectural constraints. Hence, we propose Statement-Tuning, a technique that models discriminative tasks as a set of finite statements and trains an encoder model to discriminate between the potential statements to determine the label. We do Statement-Tuning on multiple tasks to enable cross-task generalization. Experimental results demonstrate that Statement-Tuning achieves competitive performance compared to state-of-the-art LLMs with significantly fewer parameters. Furthermore, we compare with previous encoder-based methodology and show that our method is more accurate and more robust to spurious patterns. Moreover, the study investigates the impact of several design choices on few-shot and zero-shot generalization, revealing that Statement-Tuning can achieve strong performance with modest training data and benefits from task and statement diversity for unseen task generalizability. We release all the code used to generate statement data, train and evaluate our Statement-Tuned models
Hierarchical design in mesoporous silica using functional templates and digital light processing
No full textThe aim of this work was to achieve precise local control of structural and functional hierarchy in mesoporous silica along all length scales by combining 3D printing with light-induced sol-gel chemistry. Stimuli-responsive block copolymers (BCPs) should be used to define the localization of functionalities within the mesoporous silica. Thus, the first part of this work was to synthesize BCPs as functional mesopore templates and characterize their ability to act as structure-directing agents during the EISA process to obtain in situ functionalized mesopores. PEO-b-PNBA BCPs were synthesized with different molecular weights, block lengths, and block length ratios, and their use as mesopore template resulted in highly filled hybrid mesoporous silica films with adjustable pore sizes between 5 nm and 12 nm, varying porosities between 31 vol% and 53 vol%, different orientations of pore domains and different polymer chain sequences within the mesopores. The BCP filled pores were obtained by only varying the BCPs in the sol-gel solution while other components and preparation conditions were kept constant. It was concluded, that with increasing hydrophobic PNBA block length and constant PEO block length, pore size and porosity increased. Increasing the PEO block length resulted in ink-bottle shaped mesopores. In addition to the mesoporous film structure, the degree of pore filling and the light-induced cleavage of the PNBA block leading to the irradiation time-dependent release of pH-responsive carboxylic acid groups had a considerable influence on the ionic mesopore accessibility. Thus, a direct polymer functionalization was achieved, which allowed gradual charge control in mesopores.
A second BCP, PDMAEMA-b-PAA, was synthesized with different block compositions and molecular weight, and was successfully integrated into mesoporous silica films as functional templates. By using these PDMAEMA-b-PAA BCPs, mesoporous silica films with varying pore sizes between 7 nm and 16 nm, and porosities between 18 vol% and 41 vol% were obtained. The ionic mesopore accessibility of PDMAEMA-b-PAA BCPs filled mesoporous silica films was selective towards negatively charged molecules at pH 3 which corresponds to the expected positive charge inside the BCP filled mesopores. Contrary to expectations, PDMAEMA-b-PAA filled mesopores were even accessible to positively and negatively charged molecules at pH 10, which suggested a complex charge distribution or spatially separated charged volumes inside the mesopores. Although the pH-dependent charge distribution is not fully understood yet, it was demonstrated that PDMAEMA-b-PAA functionalized mesoporous silica films were favoring the access of negatively charged molecules as compared to free pore spaces of the calcined silica films with silanol groups on the surface.
To conclude, the library of reported functional mesopore templates was extended by the light- and pH-responsive PEO-b-PNBA and the pH-responsive PDMAEMA-b-PAA. The resulting ionic mesopore accessibility is caused by a complex interplay between mesopore structure, porosity, pore filling and charge distribution. The approach of in situ functionalization represents an important step towards multifunctional, hierarchical and complex mesoporous materials, as the placement of functionalities is directed by the use of the respective sol-gel solution.
In order to extend the structural control from the nm-scale to the µm- and mm-scale, the light-induced sol-gel solution was adapted to match the light source of the 3D printer. The developed composition of the LISA solution enabled a simple and fast two-step process for printing various mesoporous silica shapes, such as filled or hollow circles and squares with sizes between 0.27 mm and 6 mm, which were obtained from thin film deposition and subsequent irradiation using DLP in a 3D printer. The DLP defined the irradiation patterns within which the LISA solution solidified. The mesoporosity of the printed Pluronic® P123 filled silica shapes was then achieved simply by calcination. The resulting mesoporous shapes had specific surface areas of 127-155 m2 g-1 and pore sizes of ~5 nm according to gas adsorption measurements. A reduction of the required irradiation time from 500 s to 25 s and an increase of shape accuracy was achieved upon further optimization of the solution composition. To functionalize these printed mesoporous silica shapes, two approaches were carried out successfully. Instead of the commercially available Pluronic® P123 the synthesized light- and pH-responsive PEO-b-PNBA BCP was used in the LISA solution to directly print BCP filled mesoporous silica shapes. Besides in situ polymer functionalization using functional mesopore templates, the printed mesoporous silica shapes were successfully shape-selectively functionalized to allow component identification by shape detection or by fluorescence imaging based on their respective functionality. Taking advantage of both characteristic recognition methods, relatively large amounts of analytes are envisioned to be tested simultaneously.
Nevertheless, the printed mesoporous silica shapes were still produced from one layer of LISA solution. In order to print larger 3D mesoporous silica objects, especially with more structural control and flexibility in the z-direction, the LISA solution was mixed with different commercially available photocurable resins that can undergo radical polymerization, thus enabling even faster solidification to print 3D silica-resin objects. While the light-induced self-assembly process of the mesopore template in the LISA solution contributed to the structural control on the nm-scale, the polymerized monomer of the commercial resin could provide additional control in the µm-range of the printed object upon calcination. Thus, hierarchically porous silica objects consisting of ordered mesopores with diameters around 5 nm and high specific surface areas of ~400 m2 g-1 were successfully printed. 3D printing enabled the fabrication of different geometries of the mesoporous silica, such as cylinders or gyroids, with sizes up to 10 mm and a fast and easy post-processing.
This approach of combining light-induced self-assembly in sol-gel chemistry with 3D printing resulted in the first example of shaping of purely mesoporous silica macroscopically while maintaining control on the nanometer scale. When adding a photocurable monomer to the LISA solution, 3D hierarchically structured porous silica from the nanoscale to macroscopic object geometry was obtained. The in situ functionalization of single-layered mesoporous silica shapes with PEO-b-PNBA demonstrated the great potential of this approach combining light-induced sol-gel chemistry, functional mesopore templates and 3D printing to create multifunctional, hierarchically porous, and geometrically complex mesoporous silica objects by using different printing solutions in a multi-material printer setup.
To achieve this, further improvements on the fidelity of the printed mesoporous silica shapes and objects, as well as a larger library of BCPs for in situ functionalization of the mesopores are expected to be beneficial. The presented approach, which combines light-induced sol-gel chemistry and 3D printing, offers advanced structural control and a direct pathway to polymer-functionalized mesoporous silica object, and is therefore expected to open new possibilities for future applications in sensing, separation, and catalysis
Finite-Element Simulation of Homogenized Field Models for Foil Windings
No full textIn electrical engineering, foil windings are used in various application areas, such as transformers or magnet systems.
A foil winding is a coil that is built from winding a conducting foil that is insulated at its surface.
There exists a standard model that allows to efficiently simulate foil windings in a low to medium frequency range.
It uses a homogenization technique that prevents the resolution of the typically very thin foil and rather models the foil winding as a whole.
Currently, the switching frequency in power electronics components is increasing as higher frequencies allow to build smaller devices with better performance.
At higher frequencies, capacitive effects become relevant for foil windings.
They can drastically change the behavior of foil windings because above a certain frequency, a foil winding behaves like a capacitor and no longer like a coil.
Until now, there did not exist a general homogenization model for the simulation of foil windings that includes capacitive effects.
The standard model only considers resistive and inductive effects but neglects capacitive effects.
At the same time, a brute force simulation with a full resolution of the details in the foil winding is infeasible due to very high computational costs.
This dissertation develops a finite element model for foil windings that includes capacitive effects at moderate computational costs.
The model consists of two parts.
First, it uses a homogenization of the materials in the foil winding domain that allows to reduce the spatial resolution of the mesh, thereby reducing the computational costs immensely.
Second, it defines conditions that ensure the correct current to flow through the foil winding.
These conditions enforce conductive currents to flow through the turns and displacement currents to flow across the insulation between the turns.
Both parts of the model are implemented into the finite element solver Pyrit in Python.
The homogenization is validated and verified with high-resolution reference simulations.
Simulation results with the entire model are compared to measurement results for two distinct foil windings, showing the capability of the developed model to predict the behavior of foil windings for a large frequency range.
The simulations confirm the transition from a resistive behavior at low frequencies via an inductive behavior at medium frequencies to a capacitive behavior at high frequencies
Investigation on THz response of dielectric substrates for integration and packaging of direct THz detectors
No full textWithin this work, we investigated the response of dielectric materials used in high-frequency laminates, such as Rogers laminates and quartz substrates. A free-space, frequency-domain, non-destructive technique using a continuous-wave THz source was employed in these experiments to provide insights into the material parameters from the experimental results with a focus on the losses induced by these materials in the THz domain (0.02 to 2.5 THz). We extracted the material parameters from the experimental results. The results on the broadband response of materials provide valuable insights for designing novel frequency-selective passive components, which can be used for packaging and integration of THz detectors
Polyhedral Embeddings of Triangular Regular Maps of Genus g, 2 ⩽ g ⩽ 14, and Neighborly Spatial Polyhedra
No full textThis article provides a survey of polyhedral embeddings of triangular regular maps of genus g, 2⩽g⩽14, and of neighborly spatial polyhedra. An old conjecture of Grünbaum from 1967, although disproved in 2000, lies behind this investigation. We discuss all duals of these polyhedra as well, whereby we accept, e.g., the Szilassi torus with its non-convex faces to be a dual of the Möbius torus. A numerical optimization approach by the second author for finding such embeddings was first applied to finding (unsuccessfully) a dual polyhedron of one of the 59 closed oriented surfaces with the complete graph of 12 vertices as their edge graph. The same method has been successfully applied for finding polyhedral embeddings of triangular regular maps of genus g, 2⩽g⩽14. The effectiveness of the new method has led to ten additional new polyhedral embeddings of triangular regular maps and their duals. There do exist symmetrical polyhedral embeddings of all triangular regular maps with genus g, 2⩽g⩽14, except in a single undecided case of genus 13. Among these results, there are three new Leonardo polyhedra, each with 156 vertices, 546 edges, and 364 triangular faces, based on the Hurwitz triplet of genus 14 with Conder notation R14.1, R14.2, and R14.3
Sample coverage affects diversity measures of bird communities along a natural recovery gradient of abandoned agriculture in tropical lowland forests
No full textTropical old‐growth forests continue to decline worldwide, resulting in a huge loss of biodiversity. The extent to which the expansion of second‐growth forests can counteract biodiversity loss is context‐dependent and controversial.
To test the recovery of bird communities along a gradient from active pastures and cacao plantations, through regenerating forest on land last used for agriculture between 1 and 38 years ago, to old‐growth forest, we sampled simultaneous audio recordings from 66 plots, from which an expert identified all bird species detected at fixed time points throughout the day. The study area is characterized by typical small‐scale agriculture with remnant trees in the Ecuadorian Chocó Forest. To quantify different aspects of biodiversity, we used incidence‐based Hill numbers focusing on infrequent, frequent and highly frequent species in taxonomic, functional and phylogenetic diversity, considering sample coverage (an objective measure of sample completeness).
Bird community composition changed with the regrowth gradient represented on the first axis of the ordination. Differences in bird communities were also very robust to changes in sample coverage.
The sample coverage decreased significantly along the recovery gradient and affected the different measures of alpha diversity. Although the results controlled by sample coverage showed no change in taxonomic and phylogenetic diversity, the functional diversity of infrequent, frequent and highly frequent species decreased along the recovery gradient.
Cacao plantations exhibited particularly high diversity values, highlighting the potential of these patches to support woodland and shrubland species in agriculture. Furthermore, several forest species regularly used the agricultural areas, attracted by remnant trees characteristic of the small‐scale agricultural landscape in our study region.
Synthesis and applications. Our results highlight the importance of standardizing biodiversity measures and incorporating beta diversity in biodiversity monitoring. We demonstrate that taxonomic, phylogenetic and functional bird diversity can be high in secondary forests within smallholder agricultural landscapes. This underscores the potential for natural forest recovery, particularly when recovery patches are embedded within a forest matrix that includes old‐growth stands
Muscular responses to upper body mediolateral angular momentum perturbations during overground walking
No full textAdaptive motor control and seamless coordination of muscle actions in response to external perturbations are crucial to maintaining balance during bipedal locomotion. There is an ongoing debate about the specific roles of individual muscles and underlying neural control circuitry that humans employ to maintain balance in different perturbation scenarios. To advance our understanding of human motor control in perturbation recovery, we conducted a study using a portable Angular Momentum Perturbator (AMP). Unlike other push/pull perturbation systems, the AMP can generate perturbation torques on the upper body while minimizing the perturbing forces at the center of mass. In this study, ten participants experienced trunk perturbations during either the mid-stance or touchdown phase in two frontal plane directions (ipsilateral and contralateral). We recorded and analyzed the electromyography (EMG) activity of eight lower-limb muscles from both legs to examine muscular responses in different phases and directions. Based on our findings, individuals primarily employ long-latency hip strategies to effectively counteract perturbation torques, with the occasional use of ankle strategies. Furthermore, it was found that proximal muscles, particularly the biarticular Rectus Femoris, consistently exhibited higher activation levels than other muscles. Additionally, in instances where a statistically significant difference was noted, we observed that the fastest reactions generally stem from muscles in close proximity to the perturbation site. However, the temporal sequence of muscles’ activation depends on the timing and direction of the perturbation. These findings enhance reflex response modeling, aiding the development of simulation tools for accurately predicting exogenous disturbances. Additionally, they hold the potential to shape the development of assistive devices, with implications for clinical interventions, particularly for the elderly