Gesamtliste aus der Hochschulbibliographie

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Mehler, Alexander; Néel, Nicolas; Voloshina, Elena; Dedkov, Yuriy; Kröger, Jörg;
Second floor of flatland: epitaxial growth of graphene on hexagonal boron nitride. - In: Small, ISSN 1613-6829, Bd. 17 (2021), 36, 2102747, insges. 9 S.

In the studies presented here, the subsequent growth of graphene on hexagonal boron nitride (h-BN) is achieved by the thermal decomposition of molecular precursors and the catalytic assistance of metal substrates. The epitaxial growth of h-BN on Pt(111) is followed by the deposition of a temporary Pt film that acts as a catalyst for the fabrication of the graphene sheet. After intercalation of the intermediate Pt film underneath the boron-nitride mesh, graphene resides on top of h-BN. Scanning tunneling microscopy and density functional calculations reveal that the moiré pattern of the van-der-Waals-coupled double layer is due to the interface of h-BN and Pt(111). While on Pt(111) the graphene honeycomb unit cells uniformly appear as depressions using a clean metal tip for imaging, on h-BN they are arranged in a honeycomb lattice where six protruding unit cells enframe a topographically dark cell. This superstructure is most clearly observed at small probe-surface distances. Spatially resolved inelastic electron tunneling spectroscopy enables the detection of a previously predicted acoustic hybrid phonon of the stacked materials. Its' spectroscopic signature is visible in surface regions where the single graphene sheet on Pt(111) transitions into the top layer of the stacking.
Ilchmann, Achim; Kirchhoff, Jonas;
Differential-algebraic systems are generically controllable and stabilizable. - In: Mathematics of control, signals, and systems, ISSN 1435-568X, Bd. 33 (2021), 3, S. 359-377

We investigate genericity of various controllability and stabilizability concepts of linear, time-invariant differential-algebraic systems. Based on well-known algebraic characterizations of these concepts (see the survey article by Berger and Reis (in: Ilchmann A, Reis T (eds) Surveys in differential-algebraic equations I, Differential-Algebraic Equations Forum, Springer, Berlin, pp 1-61., we use tools from algebraic geometry to characterize genericity of controllability and stabilizability in terms of matrix formats.
Scheidig, Andrea; Schütz, Benjamin; Trinh, Thanh Quang; Vorndran, Alexander; Mayfarth, Anke; Sternitzke, Christian; Röhner, Eric; Groß, Horst-Michael;
Robot-assisted gait self-training: assessing the level achieved. - In: Sensors, ISSN 1424-8220, Bd. 21 (2021), 18, 6213, insges. 15 S.

This paper presents the technological status of robot-assisted gait self-training under real clinical environment conditions. A successful rehabilitation after surgery in hip endoprosthetics comprises self-training of the lessons taught by physiotherapists. While doing this, immediate feedback to the patient about deviations from the expected physiological gait pattern during training is important. Hence, the Socially Assistive Robot (SAR) developed for this type of training employs task-specific, user-centered navigation and autonomous, real-time gait feature classification techniques to enrich the self-training through companionship and timely corrective feedback. The evaluation of the system took place during user tests in a hospital from the point of view of technical benchmarking, considering the therapists' and patients' point of view with regard to training motivation and from the point of view of initial findings on medical efficacy as a prerequisite from an economic perspective. In this paper, the following research questions were primarily considered: Does the level of technology achieved enable autonomous use in everyday clinical practice? Has the gait pattern of patients who used additional robot-assisted gait self-training for several days been changed or improved compared to patients without this training? How does the use of a SAR-based self-training robot affect the motivation of the patients?
Hirth, Matthias; Seufert, Michael; Lange, Stanislav; Meixner, Markus; Tran-Gia, Phuoc;
Performance evaluation of hybrid crowdsensing and fixed sensor systems for event detection in urban environments. - In: Sensors, ISSN 1424-8220, Bd. 21 (2021), 17, 5880, insges. 18 S.

Crowdsensing offers a cost-effective way to collect large amounts of environmental sensor data; however, the spatial distribution of crowdsensing sensors can hardly be influenced, as the participants carry the sensors, and, additionally, the quality of the crowdsensed data can vary significantly. Hybrid systems that use mobile users in conjunction with fixed sensors might help to overcome these limitations, as such systems allow assessing the quality of the submitted crowdsensed data and provide sensor values where no crowdsensing data are typically available. In this work, we first used a simulation study to analyze a simple crowdsensing system concerning the detection performance of spatial events to highlight the potential and limitations of a pure crowdsourcing system. The results indicate that even if only a small share of inhabitants participate in crowdsensing, events that have locations correlated with the population density can be easily and quickly detected using such a system. On the contrary, events with uniformly randomly distributed locations are much harder to detect using a simple crowdsensing-based approach. A second evaluation shows that hybrid systems improve the detection probability and time. Finally, we illustrate how to compute the minimum number of fixed sensors for the given detection time thresholds in our exemplary scenario.
Zhang, Yan; Müller, Steffen; Stephan, Benedict; Groß, Horst-Michael; Notni, Gunther;
Point cloud hand-object segmentation using multimodal imaging with thermal and color data for safe robotic object handover. - In: Sensors, ISSN 1424-8220, Bd. 21 (2021), 16, 5676, insges. 16 S.
Žuraulis, Vidas; Sivilevičius, Henrikas; Šabanovič, Eldar; Ivanov, Valentin; Skrickij, Viktor;
Variability of gravel pavement roughness: an analysis of the impact on vehicle dynamic response and driving comfort. - In: Applied Sciences, ISSN 2076-3417, Bd. 11 (2021), 16, 7582, insges. 18 S.

Gravel pavement has lower construction costs but poorer performance than asphalt surfaces on roads. It also emits dust and deforms under the impact of vehicle loads and ambient air factors; the resulting ripples and ruts constantly deepen, and therefore increase vehicle vibrations and fuel consumption, and reduce safe driving speed and comfort. In this study, existing pavement quality evaluation indexes are analysed, and a methodology for adapting them for roads with gravel pavement is proposed. We report the measured wave depth and length of gravel pavement profile using the straightedge method on a 160 m long road section at three stages of road utilization. The measured pavement elevation was processed according to ISO 8608, and the frequency response of a vehicle was investigated using simulations in MATLAB/Simulink. The international roughness index (IRI) analysis showed that a speed of 30-45 km/h instead of 80 km/h provided the objective results of the IRI calculation on the flexible pavement due to the decreasing velocity of a vehicles unsprung mass on a more deteriorated road pavement state. The influence of the corrugation phenomenon of gravel pavement was explored, identifying specific driving safety and comfort cases. Finally, an increase in the dynamic load coefficient (DLC) at a low speed of 30 km/h on the most deteriorated pavement and a high speed of 90 km/h on the middle-quality pavement demonstrated the demand for timely gravel pavement maintenance and the complicated prediction of a safe driving speed for drivers. The main relevant objectives of this study are the adaptation of a road roughness indicator to gravel pavement, including the evaluation of vehicle dynamic responses at different speeds and pavement deterioration states.
Cretu, Andrea; Mattea, Carlos; Stapf, Siegfried;
Low-field and variable-field NMR relaxation studies of H2O and D2O molecular dynamics in articular cartilage. - In: PLOS ONE, ISSN 1932-6203, Bd. 16 (2021), 8, e0256177, insges. 34 S.
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Supreeti, Shraddha; Schienbein, Ralf; Feßer, Patrick; Fern, Florian; Hoffmann, Martin; Sinzinger, Stefan;
Development and implementation of a rotating nanoimprint lithography tool for orthogonal imprinting on edges of curved surfaces. - In: Nanomanufacturing and metrology, ISSN 2520-8128, Bd. 4 (2021), 3, S. 175-180

Uniform molding and demolding of structures on highly curved surfaces through conformal contact is a crucial yet often-overlooked aspect of nanoimprint lithography (NIL). This study describes the development of a NIL tool and its integration into a nanopositioning and nanomeasuring machine to achieve high-precision orthogonal molding and demolding for soft ultraviolet-assisted NIL (soft UV-NIL). The process was implemented primarily on the edges of highly curved plano-convex substrates to demonstrate structure uniformity on the edges. High-resolution nanostructures of sub-200-nm lateral dimension and microstructures in the range of tens of microns were imprinted. However, the nanostructures on the edges of the large, curved substrates were difficult to characterize precisely. Therefore, microstructures were used to measure the structure fidelity and were characterized using profilometry, white light interferometry, and confocal laser scanning microscopy. Regardless of the restricted imaging capabilities at high inclinations for high-resolution nanostructures, the scanning electron microscope (SEM) imaging of the structures on top of the lens substrate and at an inclination of 45˚ was performed. The micro and nanostructures were successfully imprinted on the edges of the plano-convex lens at angles of 45˚, 60˚,and 90˚ from the center of rotation of the rotating NIL tool. The method enables precise imprinting at high inclinations, thereby presenting a different approach to soft UV-NIL on curved surfaces.
Prem, Nina; Schale, Florian; Zimmermann, Klaus; Gowda, Darshan Kare; Odenbach, Stefan;
Synthesis and characterization of the properties of thermosensitive elastomers with thermoplastic and magnetic particles for application in soft robotics. - In: Journal of applied polymer science, ISSN 1097-4628, Bd. 138 (2021), 44, 51296, insges. 14 S.

In the currently rapidly developing field of soft robots, smart materials with controllable properties play the central role. Thermosensitive elastomers are soft, smart materials whose material properties can be controlled by changing their temperature. The aim of this work is to investigate the mechanical properties, to analyze the surface, the inner structure, and the heat transfer within the thermosensitive elastomer materials. This should provide a knowledge base for new combinations, such as a combination of thermosensitive and the well-known magneto sensitive elastomers, in order to realize new applications. Thermoplastic polycaprolactone particles were incorporated into a flexible polydimethylsiloxane matrix to produce thermosensitive elastomer samples. With a low melting point in the range of 58-60˚C, polycaprolactone offers good application potential compared to other thermoplastic materials such as polymethamethylacrylate with a melting point above 160˚C. Test samples of different material compositions and geometries were made to examine temperature-depending material properties. Two useful effects were identified: temperature-dependent change in stiffness and the shape memory effect. In certain examinations, carbonyl iron particles were also included to find out if the two particle systems are compatible with each other and can be combined in the polydimethylsiloxane matrix without disadvantages. Changes in shore hardness before and after the influence of temperature were investigated. Micro computed tomography images and scanning electron microscopy images of the respective samples were also obtained in order to detect the temperature influence on the material internally as well as on the surface of the thermosensitive elastomers in combination with carbonyl iron particles. In order to investigate the heat transfer within the samples, heating tests were carried out and the influence of different particle concentrations of the thermosensitive elastomers with and without carbonyl iron particles was determined. Further work will focus on comprehensive investigations of thermo-magneto-sensitive elastomers, as this will enable the functional integration in the material to be implemented with increased efficiency. By means of the different investigations, the authors see future applications for this class of materials in adaptive sensor and gripper elements in soft robotics.
Zeußel, Lisa; Mai, Patrick; Sharma, Sanjay; Schober, Andreas; Ren, Shizhan; Singh, Sukhdeep;
Colorimetric method for instant detection of lysine and arginine using novel Meldrum's acid-furfural conjugate. - In: ChemistrySelect, ISSN 2365-6549, Bd. 6 (2021), 27, S. 6834-6840

In the past few years Meldrum's acid furfural conjugate (MAFC) have been extensively explored as starting material for the synthesis of photo switchable donor acceptor stenhouse adducts (DASA). Hereby, we have explored the interaction of MAFC with various amino acids. To our surprise, nitrogen rich amino acids like lysine and arginine interact spontaneously with MAFC to give colored adduct immediately, whereas other amino acids, including nitrogen rich histidine, didn't show any coloration. Naked eye detection of lysine in benign solvent make this reagent an attractive new entry to the collection of chemosensors for the colorimetric detection of lysine and arginine. Intense coloration corresponds to the absorption at 514 nm under UV-Vis spectrometer. Lowest concentration of 100 m can be detected with UV-Vis spectrometer. NMR titrations reveals that the appearance of color is due to ring opening of a furfural that leads to the formation of conjugated triene species. Compared to previously reported chemosensors for lysine and arginine, MAFC offers advantages including simple synthesis, easy handling, high speed, low cost, good sensitivity/selectivity.