Peter Pölt
Graz University of Technology
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Publication
Featured researches published by Peter Pölt.
Chemical Communications | 2007
Malene S. Thomsen; Peter Pölt; Bernd Nidetzky
A microfluidic immobilised enzyme reactor consisting of a catalytically functionalised microstructure fabricated from silicone rubber material was used for steady-state kinetic characterisation of a thermophilic beta-glycosidase under pressure-driven flow conditions and continuous conversion of lactose by this enzyme at 80 degrees C.
Macromolecular Chemistry and Physics | 2002
Thomas Kavc; Gregor Langer; Peter Pölt; Klaus Reichmann; Wolfgang Kern
Poly(4-vinylbenzyl thiocyanate) (PVBT) and a copolymer of styrene and 4-vinylbenzyl thiocyanate (PST-co-VBT) were assessed as dual-tone imaging systems. These polymers change their refractive index under deep UV irradiation as a result of the photoisomerization of SCN to NCS groups. Subsequent modification of the illuminated zones with gaseous amines grave thiourea groups via an addition reaction. The post-exposure modification of the film with gaseous amines produced large increasese of the film thickness (formation of negative images). This effect was utilized to produce surface relief gratings. Using contact lithography with λ + 193 and 248 nm, gratings with periods Λ = 300 and Λ = 600 nm were obtained. Under selected experimental conditions, a nucleophilic substitution (S N ) of the SCN units in the unirradiated zones by amines was achieved (formation of positive images). Gratings of these types are of general interest for the setup of organic lasers based upon the principle of distributed feedback (DFB) as well as for holographic recordings.
The Journal of Comparative Neurology | 2015
Stefan Wernitznig; Frances Claire Rind; Peter Pölt; Armin Zankel; Elisabeth Pritz; Dagmar Kolb; Elisabeth Bock; Gerd Leitinger
The small size of some insects, and the crystalline regularity of their eyes, have made them ideal for large‐scale reconstructions of visual circuits. In phylogenetically recent muscomorph flies, like Drosophila, precisely coordinated output to different motion‐processing pathways is delivered by photoreceptors (R cells), targeting four different postsynaptic cells at each synapse (tetrad). Tetrads were linked to the evolution of aerial agility. To reconstruct circuits for vision in the larger brain of a locust, a phylogenetically old, flying insect, we adapted serial block‐face scanning electron microscopy (SBEM). Locust lamina monopolar cells, L1 and L2, were the main targets of the R cell pathway, L1 and L2 each fed a different circuit, only L1 providing feedback onto R cells. Unexpectedly, 40% of all locust R cell synapses onto both L1 and L2 were tetrads, revealing the emergence of tetrads in an arthropod group present 200 million years before muscomorph flies appeared, coinciding with the early evolution of flight. J. Comp. Neurol. 523:298–312, 2015.
Scientific Reports | 2016
F. Claire Rind; Stefan Wernitznig; Peter Pölt; Armin Zankel; Daniel Gütl; Julieta Sztarker; Gerd Leitinger
In locusts, two lobula giant movement detector neurons (LGMDs) act as looming object detectors. Their reproducible responses to looming and their ethological significance makes them models for single neuron computation. But there is no comprehensive picture of the neurons that connect directly to each LGMD. We used high-through-put serial block-face scanning-electron-microscopy to reconstruct the network of input-synapses onto the LGMDs over spatial scales ranging from single synapses and small circuits, up to dendritic branches and total excitatory input. Reconstructions reveal that many trans-medullary-afferents (TmAs) connect the eye with each LGMD, one TmA per facet per LGMD. But when a TmA synapses with an LGMD it also connects laterally with another TmA. These inter-TmA synapses are always reciprocal. Total excitatory input to the LGMD 1 and 2 comes from 131,000 and 186,000 synapses reaching densities of 3.1 and 2.6 synapses per μm2 respectively. We explored the computational consequences of reciprocal synapses between each TmA and 6 others from neighbouring columns. Since any lateral interactions between LGMD inputs have always been inhibitory we may assume these reciprocal lateral connections are most likely inhibitory. Such reciprocal inhibitory synapses increased the LGMD’s selectivity for looming over passing objects, particularly at the beginning of object approach.
Journal of Applied Physics | 2012
Eva-Maria Steyskal; Maximilian Besenhard; Stephan Landgraf; Y. Zhong; J. Weissmüller; Peter Pölt; Mihaela Albu; Roland Würschum
The electrical resistance (R) of nanoporous platinum prepared by dealloying reversibly changes by 4% upon electrochemical surface charging in a regime where oxygen adsorption/desorption and surface oxidation/reduction occur. The variation of R with charging shows a sign inversion. Besides the usual behavior of increasing R with positive charging, a decrease of R occurs at higher potentials. Following recent studies of the sign inversion of the surface stress-charge response of porous nanophase Pt, the sign-inversion of the resistance with charging may be related to the electronic structure of the surface oxide. In addition, a charge-induced variation of the charge-carrier scattering rate at the metal–electrolyte interface is taken into account.
Langmuir | 2016
Eva-Maria Steyskal; Zhen Qi; Peter Pölt; Mihaela Albu; J. Weissmüller; Roland Würschum
The extremely high surface-to-volume ratio of nanoporous platinum (np-Pt) produced by dealloying was applied for tuning electrical resistance by surface charging. In the as-dealloyed state, a characteristic sign-inversion of the charging-induced resistance variation occurs, which can be associated with the electronic structure of PtO. After electrochemical reduction, the relative resistance variations of np-Pt of up to 58% could be generated by electrochemically induced adsorption and desorption, which was 1 order of magnitude larger compared with that of cluster-assembled nanocrystalline Pt. Although the maximum resistance variation was also higher than that of dealloyed nanoporous gold (np-Au), the resistance variation related to the imposed charge was reduced owing to the higher bulk resistance of Pt compared with that of Au. The sign-inversion behavior of the resistance could be recovered by re-oxidation.
International Journal of Materials Research | 2017
Jaromir Anatol Kotzurek; Wolfgang Sprengel; Maciej Krystian; Sanja Simic; Peter Pölt; Anton Hohenwarter; Reinhard Pippan; Roland Würschum
Abstract Structural anisotropy and excess volume in ultra-fine grained high-purity nickel prepared by equal-channel angular pressing (ECAP) is studied by means of dilatometry and compared with the processing route of high-pressure torsion. Both routes exhibit qualitatively similar three-stage behavior in length change upon defect annealing with a characteristic dependence on the measuring direction related to the deformation axes. Taking into account shape anisotropy of the crystallites, the length change in various directions can be quantitatively analyzed yielding direct access to the concentration of deformation-induced lattice vacancies, the vacancy relaxation, and the grain boundary expansion. The routes A12 and BC12 of ECAP are compared.
Journal of Neuroscience Methods | 2016
Stefan Wernitznig; Mariella Sele; Martin Urschler; Armin Zankel; Peter Pölt; F. Claire Rind; Gerd Leitinger
BACKGROUND Elucidating the anatomy of neuronal circuits and localizing the synaptic connections between neurons, can give us important insights in how the neuronal circuits work. We are using serial block-face scanning electron microscopy (SBEM) to investigate the anatomy of a collision detection circuit including the Lobula Giant Movement Detector (LGMD) neuron in the locust, Locusta migratoria. For this, thousands of serial electron micrographs are produced that allow us to trace the neuronal branching pattern. NEW METHOD The reconstruction of neurons was previously done manually by drawing cell outlines of each cell in each image separately. This approach was very time consuming and troublesome. To make the process more efficient a new interactive software was developed. It uses the contrast between the neuron under investigation and its surrounding for semi-automatic segmentation. RESULTS For segmentation the user sets starting regions manually and the algorithm automatically selects a volume within the neuron until the edges corresponding to the neuronal outline are reached. Internally the algorithm optimizes a 3D active contour segmentation model formulated as a cost function taking the SEM image edges into account. This reduced the reconstruction time, while staying close to the manual reference segmentation result. COMPARISON WITH EXISTING METHODS Our algorithm is easy to use for a fast segmentation process, unlike previous methods it does not require image training nor an extended computing capacity. CONCLUSION Our semi-automatic segmentation algorithm led to a dramatic reduction in processing time for the 3D-reconstruction of identified neurons.
Archive | 2017
Manfred Nachtnebel; Armin Zankel; C. Mayrhofer; M. Gahleitner; Peter Pölt
The fracture behaviour of ethylene–propylene rubber (EPR) and linear low-density polyethylene (PE-LLD)-modified polypropylene was investigated. Most interpretations of the fracture behaviour of such polymers are based on results gained from completely fractured samples. To gain deeper insight into the fracture mechanisms the focus was put on the very early stages of the fracturing process. For this purpose tensile tests of the samples were stopped at predefined forces far below the yield. Subsequently 3D reconstructions of the already damaged regions were performed, using serial block-face scanning electron microscopy to get the image stacks. In a comprehensive discussion of the sample preparation the limitations of this method are disclosed. The EPR- and PE-LLD-modified samples showed completely different fracture behaviour, at least at the crack initiation and at low stresses. The results also seem to prove that the interparticle distance is a decisive parameter in the interpretation of the results.
Philosophical Magazine Letters | 2017
Jaromir Anatol Kotzurek; M. Hofmann; Sanja Simic; Peter Pölt; Anton Hohenwarter; Reinhard Pippan; Wolfgang Sprengel; Roland Würschum
Abstract A combined study of neutron diffraction and difference dilatometry on submicrocrystalline Ni prepared by high pressure torsion aims at studying the anisotropic behaviour during dilatometry and its relation to internal stress and structural anisotropy. Macroscopic stresses were undetectable in the dilatometer samples. Along with specific tests such as post cold-rolling, this shows that an observed anisotropic length change upon annealing is not caused by internal stress, but can be explained by the inherent microstructure, i.e. the anisotropic annealing of relaxed vacancies at grain boundaries of shape-anisotropic crystallites.