Refine
Year of publication
Document Type
- Article (237)
- Conference Proceeding (216)
- Part of a Book (32)
- Other (31)
- video (14)
- Book (13)
- Preprint (12)
- Doctoral Thesis (4)
- Report (4)
- Working Paper (4)
- Contribution to a Periodical (2)
- Course Material (2)
- Master's Thesis (1)
Language
- English (572) (remove)
Keywords
- Robotik (8)
- Flugkörper (7)
- UAV (7)
- Rettungsrobotik (5)
- Dissipative Particle Dynamics (4)
- Polymer-Elektrolytmembran-Brennstoffzelle (4)
- adhesion (4)
- Bionik (3)
- Deep Learning (3)
- Erweiterte Realität <Informatik> (3)
Institute
- Westfälisches Institut für Gesundheit (115)
- Westfälisches Energieinstitut (61)
- Institut für Internetsicherheit (56)
- Informatik und Kommunikation (51)
- Elektrotechnik und angewandte Naturwissenschaften (50)
- Wirtschaft und Informationstechnik Bocholt (46)
- Institut für biologische und chemische Informatik (44)
- Maschinenbau Bocholt (37)
- Institut Arbeit und Technik (15)
- Wirtschaftsingenieurwesen (15)
Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, arolia must be very soft exhibiting an effective Young's modulus of below 100 kPa to adhere well to different substrates. In previous studies the effective Young´s moduli of adhesive organs were determined using indentation tests yielding their structure to be very soft indeed. However, arolia show a layered structure, thus the values measured by indentation tests comprise the effective Young´s moduli of the whole organs. In this study, a new approach is illustrated to measure the Young´s modulus of the outermost layer of the arolium, i.e. of the epicuticle, of the stick insect Carausius morosus by tensile testing. Due to the inner fibrous structure of the arolium tensile tests allow the characterisation of the overlying epicuticle.
BACKGROUND: In cartilage repair, scaffold-assisted single-step techniques are used to improve the cartilage regeneration. Nevertheless, the fixation of cartilage implants represents a challenge in orthopaedics, particularly in the moist conditions that pertain during arthroscopic surgery. Within the animal kingdom a broad range of species has developed working solutions to intermittent adhesion under challenging conditions. Using a top-down approach we identified promising mechanisms for biomimetic transfer OBJECTIVE: The tree-frog adhesive system served as a test case to analyze the adhesion capacity of a polyglycolic acid (PGA) scaffold with and without a structural modification in a bovine articular cartilage defect model. METHODS: To this end, PGA implants were modified with a simplified foot-pad structure and evaluated on femoral articular bovine cartilage lesions. Non-structured PGA scaffolds were used as control. Both implants were pressed on 20 mm × 20 mm full-thickness femoral cartilage defects using a dynamometer. RESULTS: The structured scaffolds showed a higher adhesion capacity on the cartilage defect than the non-structured original scaffolds. CONCLUSIONS: The results suggest that the adhesion ability can be increased by means of biomimetic structured surfaces without the need of additional chemical treatment and thus significantly facilitate primary fixation procedures.
Adhesive organs enable insects to reversibly adhere to substrates even during rapid locomotion. In this process a very fast but reliable change of adhesion and detachment is realised. The stick insect Carausius morosus detaches its adhesive organs by peeling them off the substrate, meaning little areas of the adhesive organs are detached one after another. For such a detachment mechanism low pulling forces are needed. A detachment mechanism as peeling seems also for artificial adhesion devices to be the easiest and the most effortless mechanism for detachment. However, artificial adhesion devices mostly exhibit a solid backing layer preventing effortless peeling. To lift up and detach a small area at the corner of an adhesion device the backing layer has to be tilted, resulting in a deformation of the whole adhesion device, which requires high forces. Subdividing the backing layer into small subunits allows a detachment of a small area at the corner of the adhesion device without deforming the rest of the adhesion device. Thereby, less force is needed to initiate and to complete detachment. To realise an easy detachment of artificial adhesion devices we constructed a holder, which gradually detaches an adhesion device from two sides off the substrate. During normal loading the subunits of the holder interlock with each other so that the pulling force is equally distributed over the whole contact area of the adhesion device ensuring maximal adhesion force. In addition, the holder can be used to increase adhesion during application of the adhesion device. When brought into contact with the substrate with lifted sides, which are lowered subsequently, air trapping is prevented and hence the area of contact can be maximised.
Socio-cultural dynamics in spatial policy: explaining the on-going success of cluster politics
(2013)
The two-state two-path model is introduced as a minimized model to describe the quantum dynamics of an electronic wave packet in the vicinity of a conical intersection. It involves two electronic potential energy surfaces each of which hosts a pair of quasi-classical trajectories over which the wave packet is assumed to be delocalized. When both trajectories evolve dynamically either diabatically or adiabatically, the full wave packet dynamics shows only features of the dynamics around avoided level crossings in the vicinity of the conical intersection. When one trajectory evolves adiabatically whereas the other trajectory follows a diabatic evolution, quantum mechanical interference of the wave packet components on each path generates Stueckelberg oscillations in the transition probability. These are surprisingly robust against a dissipative environment and, thus, should be a marker for conical intersections.
We present a scheme for cooling a vibrational mode of a magnetic molecular nanojunction by a spin-polarized charge current upon exploiting the interaction between its magnetic moment and the vibration. The spin-polarized charge current polarizes the magnetic moment of the nanoisland, thereby lowering its energy. A small but finite coupling between the vibration and the magnetic moment permits a direct exchange of energy such that vibrational energy can be transferred into the magnetic state. For positive bias voltages, this generates an effective cooling of the molecular vibrational mode. We determine parameter regimes for the cooling of the vibration to be optimal. Although the flowing charge current inevitably heats up the vibrational mode via Ohmic energy losses, we show that due to the magnetomechanical coupling, the vibrational energy (i.e, the effective phonon temperature) can be lowered below 50% of its initial value, when the two leads are polarized anti-parallel. In contrast to the cooling effect for positive bias voltages, net heating of the vibrational mode occurs for negative bias voltages. The cooling effect is enhanced for a stronger anti-parallel magnetic polarization of the leads, while the heating is stronger for a larger parallel polarization. Yet, dynamical cooling is also possible with parallel lead alignments when the two tunneling barriers are asymmetric.
Commonly, nanosystems are characterized by their response to time-dependent external fields in the presence of inevitable environmental fluctuations. The direct impact of the external driving on the environment is generally neglected. While this approach is satisfactory for macroscopic systems, on the nanoscale, an interaction of external fields with the environment is often unavoidable on principle. We extend the standard linear response theory of quantum dissipative systems to strongly driven baths. Significant modifications are found for two paradigm examples. First, we evaluate the polarizability of a molecule immersed in a strongly polarizable medium that responds to terahertz radiation. We find an increase of the molecular polarizability by about 30%. Second, we determine the response of a semiconductor quantum dot in close proximity to a metallic nanoparticle. Both are placed in a polarizable medium and exposed to electromagnetic irradiation. We show that the response of the quantum dot is qualitatively modified by the driven nanoparticle, including the generation of an additional channel of stimulated emission.
When an open quantum system is driven by an external time-dependent force, the coupling of the driving to the central system is usually included, whereas the impact of the driving field on the bath is neglected. We investigate the effect of a quantum bath of linearly driven harmonic oscillators on the relaxation dynamics of a quantum two-level system which is not directly driven. In particular, we calculate the frequency-dependent response of the system when the bath is subject to Dirac and Gaussian driving pulses. We show that a time-retarded effective force on the system is induced by the driven bath which depends on the full history of the perturbation and the spectral characteristics of the underlying bath. In particular, when a structured Ohmic bath with a pronounced Lorentzian peak is considered, the dynamical response of the system to a driven bath is qualitatively different than that of the undriven bath. Specifically, additional resonances appear which can be directly associated with a Jaynes-Cummings-like effective energy spectrum.