TY  - JOUR
A1  - Nomdedeu, Mar Monsonis
A1  - Willen, Christine
A1  - Schieffer, Andre
A1  - Arndt, Hartmut
T1  - Temperature-dependent ranges of coexistence in a model of a two-prey-one-predator microbial food web
JF  - Marine Biology
N2  - The objective of our study was to analyze the effects of temperature on the population dynamics of a three-species food web consisting of two prey bacteria (Pedobacter sp. and Acinetobacter johnsonii) and a protozoan predator (Tetrahymena pyriformis) as model organisms. We assessed the effects of temperature on the growth rates of all three species with the objective of developing a model with four differential equations based on the experimental data. The following hypotheses were tested at a theoretical level: Firstly, temperature changes can affect the dynamic behavior of a system by temperature-dependent parameters and interactions and secondly, food web response to temperature cannot be derived from the single species temperature response. The main outcome of the study is that temperature changes affect the parameter range where coexistence is possible within all three species. This has significant consequences on our ideas regarding the evaluation of effects of global warming.
Y1  - 2012
U6  - https://doi.org/10.1007/s00227-012-1966-x
SN  - 1432-1793
VL  - 159
IS  - 11
SP  - 2423
EP  - 2430
PB  - Springer
CY  - Berlin
ER  - 
TY  - THES
A1  - Schieffer, Andre
T1  - Studies on diversity and coexistence in an experimental microbial community
N2  - Biodiversity and the coexistence of species have puzzled and fascinated biologists since decades and is a hotspot in todays’ natural sciences. Preserving this biodiversity is a great challenge as habitats and environments underlying tremendous changes like climate change and the loss of natural habitats, which are mainly due to anthropogenic influences. The coexistence of numerous species even in homogeneous environments is a stunning feature of natural communities and has been summarized under the term ‘paradox of plankton’. Up to now, there are several mechanisms discussed, which may contribute to local and global diversity of organisms. Several interspecific trade offs have been identified maintaining the coexistence of species like their abilities regarding competition and predator avoidance, their capability to disperse in space and time, and their ability to exploit variable resources. Further, micro-evolutionary dynamics supporting the coexistence of species have been added to our knowledge, and deriving from theoretical deterministic models, non-linear dynamics which describe the temporal fluctuation of abundances of organisms. Whereas competition and predation seem to be clue structural elements within interacting organisms, the intrinsic dynamic behavior – by means of temporal changes in abundance - plays an important role regarding coexistence within a community. The present work sheds light on different factors affecting the coexistence of species using experimental microbial model systems consisting of a bacterivorous ciliate as the predator and two bacteria strains as prey organism. Additionally, another experimental setup consisting of two up to five bacteria species competing for one limiting resource was investigated. Highly controllable chemostat systems were established to exclude extrinsic disturbances. According to theoretical analyses I was able to show - experimentally and theoretically - that phenotypic plasticity of one species within a microbial one-predator-two-prey food web enlarges the range of possible coexistence of all species under different dynamic conditions, compared to a food web without phenotypic plasticity. This was accompanied by non-linear (chaotic) population dynamics within all experimental systems showing phenotypic plasticity. The experiments on the interplay of competition, predation and invasion showed that all aspects have an influence on species coexistence. Under undisturbed controlled conditions all aspects were analyzed in detail and in combination. Populations showed oscillations which were shown by quasi-chaotic attractors in phase space diagrams. Competition experiments with two up to five bacteria species competing for one limiting resource showed that all organisms were able to coexist which was mediated by species oscillations entering a regime of chaos. Besides that fact it was found, that the productivity (biomass) as well as the total cell numbers – under the same nutrition supply – increased by an increasing number of species in the experimental systems. Up to now, the occurrence of non-linear dynamics in well controlled experimental studies has been recognized several times and this phenomenon seemed to be more common in natural systems than generally assumed.
N2  - Biodiversität und die Koexistenz von Arten fasziniert und verblüfft Biologen seit Jahr-zehnten und stellen einen Schwerpunkt in der heutigen Umweltforschung dar. Der Schutz und die Konservierung dieser Mannigfaltigkeit stellen eine große Herausfor-derung dar, da die natürlichen Lebensräume sowie die Umwelt enormen Verände-rungen unterworfen sind, welche meist in einem anthropogenen Ursprung wurzeln. Die Koexistenz vieler Arten, auch in relativ homogenen Habitaten ist ein faszinieren-des Charakteristikum natürlicher Lebensgemeinschaften und wird als ‚Paradox des Planktons‘ bezeichnet. Gegenwärtig werden diverse Ursachen diskutiert, welche vermutlich zur lokalen und globalen Diversität von Organismen beitragen. Einige die-ser möglichen Ursachen, die zur Aufrechterhaltung der Koexistenz der Arten beitra-gen, wurden identifiziert: Das Vermögen der Konkurrenz- und Prädationsvermeidung, die Fähigkeit räumlicher sowie zeitlicher Verteilung, sowie das Vermögen variable Ressourcen zu nutzen. Des Weiteren wurden mikro-evolutionäre Phänomene und Dynamiken identifiziert, sowie, von theoretischen deterministischen Modellen ausge-hend, nichtlineare Dynamiken, welche die zeitlichen Schwankungen der Abundanzen von Organismen beschreiben. Diese Aspekte stellen die Schlüsselkomponenten zwi-schen interagierenden Organismen dar, wobei das intrinsiche, nicht lineare dynami-sche Verhalten in Form von zeitlichen Veränderungen in Abundanzen eine zusätzli-che entscheidende Rolle bezüglich der Koexistenz von Arten spielen kann. Einige dieser Aspekte wurden in der vorliegenden Arbeit untersucht. In Anlehnung an theoretische Analysen konnte experimentell sowie theoretisch gezeigt werden, dass phänotypische Plastizität in einer Bakterienart in einem mikrobiellen Ein-Räuber-zwei-Beute-Nahrungsgewebe den Bereich der möglichen Koexistenz unter sich än-dernden experimentellen Bedingungen (Änderungen der Durchflussraten der Chemostate) – im direkten Vergleich zu einem experimentellen Nahrungsgewebe ohne phänotypische Plastizität – erweitern kann. Dies wurde begleitet durch nicht lineare Abundanzschwankungen in den Populationen aller untersuchten Versuchs-ansätze. In weiteren Untersuchungen wurde das Zusammenspiel von Konkurrenz, Prädation und Invasion in einer experimentellen mikrobiellen Gemeinschaft untersucht. Unter kontrollierten Bedingungen konnten diese Aspekte detailliert untersucht werden und es konnten Aufschlüsse darüber gewonnen werden, welche Reaktionen (Interaktionen) innerhalb der untersuchten Gemeinschaften stattfinden. Im Versuchsverlauf wurden Veränderungen in den Abundanzen sowie chaotische Schwankungen der Zellzahlen festgestellt. In Konkurrenzexperimenten von zwei bis zu fünf um eine limitierende Ressource konkurrierende Bakterienarten konnte gezeigt werden, dass alle Arten – vermittelt durch chaotische Abundanzschwankungen – nebeneinander koexistieren konnten. Begleitend dazu wurde herausgefunden, dass die Produktivität (Biomasse) sowie die Gesamtzellzahl bei gleicher Nahrungsverfügbarkeit der experimentellen Systeme mit steigender Artenzahl zunehmen. Gegenwärtig ist das Auftreten von Chaos in gut kontrollierten experimentellen Studien vereinzelt beobachtet worden, wobei dieses Phänomen jedoch häufiger in der Natur aufzutreten scheint als generell vermutet.
Y1  - 2012
N1  - Köln, Univ., Diss., 2012
ER  - 
TY  - JOUR
A1  - Alexopoulos, Spiros
T1  - Biogas systems: basics, biogas multifunction, principle of fermentation and hybrid application with a solar tower for the treatment of waste animal manure
JF  - Journal of Engineering Science and Technology Review
N2  - Two of the main environmental problems of today’s society are the continuously increasing production of organic wastes as well as the increase of carbon dioxide in the atmosphere and the related green house effect. A way to solve these problems is the production of biogas. Biogas is a combustible gas consisting of methane, carbon dioxide and small amounts of other gases and trace elements. Production of biogas through anaerobic digestion of animal manure and slurries as well as of a wide range of digestible organic wastes and agricultural residues, converts these substrates into electricity and heat and offers a natural fertiliser for agriculture. The microbiological process of decomposition of organic matter, in the absence of oxygen takes place in reactors, called digesters. Biogas can be used as a fuel in a gas turbine or burner and can be used in a hybrid solar tower system offering a solution for waste treatment of agricultural and animal residues. A solar tower system consists of a heliostat field, which concentrates direct solar irradiation on an open volumetric central receiver. The receiver heats up ambient air to temperatures of around 700°C. The hot air’s heat energy is transferred to a steam Rankine cycle in a heat recovery steam generator (HRSG). The steam drives a steam turbine, which in turn drives a generator for producing electricity. In order to increase the operational hours of a solar tower power plant, a heat storage system and/ or hybridization may be considered. The advantage of solar-fossil hybrid power plants, compared to solar-only systems, lies in low additional investment costs due to an adaptable solar share and reduced technical and economical risks. On sunny days the hybrid system operates in a solar-only mode with the central receiver and on cloudy days and at night with the gas turbine only. As an alternative to methane gas, environmentally neutral biogas can be used for operating the gas turbine. Hence, the hybrid system is operated to 100% from renewable energy sources
Y1  - 2012
SN  - 1791-2377
N1  - Special Issue on Renewable Energy Systems
VL  - 5
IS  - 4
SP  - 48
EP  - 55
ER  - 
TY  - CHAP
A1  - Streun, M.
A1  - Al-Kaddoum, R.
A1  - Parl, C.
A1  - Pietrzyk, U.
A1  - Ziemons, Karl
A1  - Waasen, S. van
T1  - Simulation studies of optical photons in monolithic block scintillators
T2  - 2011 IEEE Nuclear Science Symposium Conference Record (NSS/MIC)
N2  - The interest in PET detectors with monolithic block scintillators is growing. In order to obtain high spatial resolutions dedicated positioning algorithms are required. But even an ideal algorithm can only deliver information which is provided by the detector. In this simulation study we investigated the light distribution on one surface of cuboid LSO scintillators of different size. Scintillators with a large aspect ratio (small footprint and large height) showed significant position information only for a minimum interaction depth of the gamma particle. The results allow a quantitative estimate for a useful aspect ratio.
Y1  - 2012
SN  - 978-1-4673-0120-6 (electronic ISBN)
SN  - 978-1-4673-0118-3 (print ISBN)
U6  - https://doi.org/10.1109/NSSMIC.2011.6154621
SP  - 1380
EP  - 1382
PB  - IEEE
CY  - New York
ER  - 
TY  - CHAP
A1  - Frotscher, Ralf
A1  - Raatschen, Hans-Jürgen
A1  - Staat, Manfred
ED  - Holzapfel, Gerhard A.
T1  - Effectiveness of the edge-based smoothed finite element method applied to soft biological tissues
T2  - ESMC-2012 - 8th European Solid Mechanics Conference, Graz, Austria, July 9-13, 2012
Y1  - 2012
SN  - 978-3-85125-223-1
PB  - Verlag d. Technischen Universität Graz
CY  - Graz
ER  - 
TY  - CHAP
A1  - Duong, Minh Tuan
A1  - Nguyen, Nhu Hunyh
A1  - Staat, Manfred
T1  - Finite Element Implementation of a 3D Fung-type Model
T2  - ESMC-2012 - 8th European Solid Mechanics Conference, Graz, Austria, July 9-13, 2012
Y1  - 2012
SN  - 978-3-85125-223-1
PB  - Verlag d. Technischen Universität Graz
CY  - Graz
ER  - 
TY  - JOUR
A1  - Lustfeld, H.
A1  - Pithan, C.
A1  - Reißel, Martin
T1  - Metallic electrolyte composites in the framework of the brick-layer model
JF  - Journal of the European Ceramic Society
N2  - It is well known that the already large dielectric constants of some electrolytes like BaTiO₃ can be enhanced further by adding metallic (e.g. Ni, Cu or Ag) nanoparticles. The enhancement can be quite large, a factor of more than 1000 is possible. The consequences for the properties will be discussed in the present paper applying a brick-layer model (BLM) for calculating dc-resistivities of thin layers and a modified one (PBLM) that includes percolation for calculating dielectric properties of these materials. The PBLM results in an at least qualitative description and understanding of the physical phenomena: This model gives an explanation for the steep increase of the dielectric constant below the percolation threshold and why this increase is connected to a dramatic decrease of the breakdown voltage as well as the ability of storing electrical energy. We conclude that metallic electrolyte composites like BaTiO₃ are not appropriate for energy storage.
Y1  - 2012
U6  - https://doi.org/10.1016/j.jeurceramsoc.2011.10.017
SN  - 0955-2219
VL  - 32
IS  - 4
SP  - 859
EP  - 864
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - CHAP
A1  - Reisert, Steffen
A1  - Geissler, H.
A1  - Flörke, R.
A1  - Weiler, C.
A1  - Wagner, P.
A1  - Schöning, Michael Josef
ED  - Abdelghani, Adnane
ED  - Schöning, Michael Josef
T1  - Characterisation of aseptic sterilisation processes using an electronic nose
T2  - Nanoscale Science and Technology (NS&T´12) : Proceedings Book Humboldt Kolleg ; Tunisia, 17-19 March, 2012
Y1  - 2012
SP  - 45
EP  - 45
ER  - 
TY  - CHAP
A1  - Schusser, Sebastian
A1  - Leinhos, Marcel
A1  - Poghossian, Arshak
A1  - Wagner, Patrick
A1  - Schöning, Michael Josef
ED  - Abdelghani, Adnane
ED  - Schöning, Michael Josef
T1  - Biopolymer-degradation monitoring by chip-­based impedance spectroscopy technique
T2  - Nanoscale Science and Technology (NS&T´12) : Proceedings Book Humboldt Kolleg ; Tunisia, 17-19 March, 2012
Y1  - 2012
SP  - 47
EP  - 47
ER  - 
TY  - JOUR
A1  - Abouzar, Maryam H.
A1  - Poghossian, Arshak
A1  - Cherstvy, Andrey G.
A1  - Pedraza, Angela M.
A1  - Ingebrandt, Sven
A1  - Schöning, Michael Josef
T1  - Label-free electrical detection of DNA by means of field-effect nanoplate capacitors: Experiments and modeling
JF  - Physica Status Solidi (a)
N2  - Label-free electrical detection of consecutive deoxyribonucleic acid (DNA) hybridization/denaturation by means of an array of individually addressable field-effect-based nanoplate silicon-on-insulator (SOI) capacitors modified with gold nanoparticles (Au-NP) is investigated. The proposed device detects charge changes on Au-NP/DNA hybrids induced by the hybridization or denaturation event. DNA hybridization was performed in a high ionic-strength solution to provide a high hybridization efficiency. On the other hand, to reduce the screening of the DNA charge by counter ions and to achieve a high sensitivity, the sensor signal induced by the hybridization and denaturation events was measured in a low ionic-strength solution. High sensor signals of about 120, 90, and 80 mV were registered after the DNA hybridization, denaturation, and re-hybridization events, respectively. Fluorescence microscopy has been applied as reference method to verify the DNA immobilization, hybridization, and denaturation processes. An electrostatic charge-plane model for potential changes at the gate surface of a nanoplate field-effect sensor induced by the DNA hybridization has been developed taking into account both the Debye length and the distance of the DNA charge from the gate surface.
Y1  - 2012
U6  - https://doi.org/10.1002/pssa.201100710
SN  - 1862-6319
VL  - 209
SP  - 925
EP  - 934
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - CHAP
A1  - Yoshinobu, Tatsuo
A1  - Miyamoto, Ko-Ichiro
A1  - Wagner, Torsten
A1  - Schöning, Michael Josef
ED  - Yamaguchi, Takami
T1  - Miniaturized and high-speed chemical imaging systems
T2  - Nano-Biomedical Engineering 2012. Proceedings of the Tohoku University Global Centre of Excellence Programme, Sakura Hall, Tohoku University, Sendai Japan, 5 – 6 March 2012
Y1  - 2012
U6  - https://doi.org/10.1142/9781848169067_0045
SP  - 386
EP  - 395
PB  - World Scientific
CY  - Singapur
ER  - 
TY  - JOUR
A1  - Leurs, Ulrike
A1  - Mezo, Gabor
A1  - Öhlschläger, Peter
A1  - Orban, Erika
A1  - Marquard, Andrea
A1  - Manea, Marilena
T1  - Design, synthesis, in vitro stability and cytostatic effect of multifunctional anticancer drug-bioconjugates containing GnRH-III as a targeting moiety
JF  - Peptide Science
N2  - Bioconjugates containing the GnRH-III hormone decapeptide as a targeting moiety are able to deliver chemotherapeutic agents specifically to cancer cells expressing GnRH receptors, thereby increasing their local efficacy while limiting the peripheral toxicity. However, the number of GnRH receptors on cancer cells is limited and they desensitize under continuous hormone treatment. A possible approach to increase the receptor mediated tumor targeting and consequently the cytostatic effect of the bioconjugates would be the attachment of more than one chemotherapeutic agent to one GnRH-III molecule. Here we report on the design, synthesis and biochemical characterization of multifunctional bioconjugates containing GnRH-III as a targeting moiety and daunorubicin as a chemotherapeutic agent. Two different drug design approaches were pursued. The first one was based on the bifunctional [4Lys]-GnRH-III (Glp-His-Trp-Lys-His-Asp-Trp-Lys-Pro-Gly-NH2) containing two lysine residues in positions 4 and 8, whose ϵ-amino groups were used for the coupling of daunorubicin. In the second drug design, the native GnRH-III (Glp-His-Trp-Ser-His-Asp-Trp-Lys-Pro-Gly-NH2) was used as a scaffold; an additional lysine residue was coupled to the ϵ-amino group of 8Lys in order to generate two free amino groups available for conjugation of daunorubicin. The in vitro stability/degradation of all synthesized compounds was investigated in human serum, as well as in the presence of rat liver lysosomal homogenate. Their cellular uptake was determined on human breast cancer cells and the cytostatic effect was evaluated on human breast, colon and prostate cancer cell lines. Compared with a monofunctional compound, both drug design approaches resulted in multifunctional bioconjugates with increased cytostatic effect.
Y1  - 2012
U6  - https://doi.org/10.1002/bip.21640
SN  - 1097-0282
VL  - 98
IS  - 1
SP  - 1
EP  - 10
PB  - Wiley
CY  - New York, NY
ER  - 
TY  - JOUR
A1  - Grinsven, Bart van
A1  - Bon, Natalie vanden
A1  - Strauven, Hannelore
A1  - Grieten, Lars
A1  - Murib, Mohammed
A1  - Jiménez Monroy, Kathia L.
A1  - Janssens, Stoffel D.
A1  - Haenen, Ken
A1  - Schöning, Michael Josef
A1  - Vermeeren, Veronique
A1  - Ameloot, Marcel
A1  - Michiels, Luc
A1  - Thoelen, Ronald
A1  - Ceuninck, Ward de
A1  - Wagner, Patrick
T1  - Heat-Transfer Resistance at Solid-Liquid Interfaces: A Tool for The Detection of Single Nucleotide Polymorphisms in DNA.
JF  - ACS Nano
N2  - In this article, we report on the heat-transfer resistance at interfaces as a novel, denaturation-based method to detect single-nucleotide polymorphisms in DNA. We observed that a molecular brush of double-stranded DNA grafted onto synthetic diamond surfaces does not notably affect the heat-transfer resistance at the solid-to-liquid interface. In contrast to this, molecular brushes of single-stranded DNA cause, surprisingly, a substantially higher heat-transfer resistance and behave like a thermally insulating layer. This effect can be utilized to identify ds-DNA melting temperatures via the switching from low- to high heat-transfer resistance. The melting temperatures identified with this method for different DNA duplexes (29 base pairs without and with built-in mutations) correlate nicely with data calculated by modeling. The method is fast, label-free (without the need for fluorescent or radioactive markers), allows for repetitive measurements, and can also be extended toward array formats. Reference measurements by confocal fluorescence microscopy and impedance spectroscopy confirm that the switching of heat-transfer resistance upon denaturation is indeed related to the thermal on-chip denaturation of DNA.
Y1  - 2012
U6  - https://doi.org/10.1021/nn300147e
SN  - 1936-086X
VL  - 6
IS  - 3
SP  - 2712
EP  - 2721
PB  - ACS Publications
CY  - Washington, DC
ER  - 
TY  - CHAP
A1  - Fredebeul-Krein, Markus
A1  - Steingröver, Markus
T1  - Wholesale Broadband Access to IPTV in an NGA environment : how to deal with it from a regulatory perspective?
Y1  - 2012
N1  - Regional ITS Conference of the international Telecommunications Society , February 22-24, 2012 New Delhi, India
SP  - 1
EP  - 16
ER  - 
TY  - CHAP
A1  - Poghossian, Arshak
A1  - Abouzar, Maryam H.
A1  - Schöning, Michael Josef
ED  - Abdelghani, Adnane
ED  - Schöning, Michael Josef
T1  - (Bio-­)chemical sensor array based on nanoplate SOI capacitors
T2  - Nanoscale Science and Technology (NS&T´12) : Proceedings Book Humboldt Kolleg ; Tunisia, 17-19 March, 2012
Y1  - 2012
SP  - 31
EP  - 31
ER  - 
TY  - CHAP
A1  - Bohrn, U.
A1  - Stütz, E.
A1  - Fleischer, M.
A1  - Schöning, Michael Josef
A1  - Wagner, P.
ED  - Abdelghani, Adnane
ED  - Schöning, Michael Josef
T1  - Towards a paradigm change – mammalian cells as sensitive biosensor layers for the detection of unexpected toxic substances in air
T2  - Nanoscale Science and Technology (NS&T´12) : Proceedings Book Humboldt Kolleg ; Tunisia, 17-19 March, 2012
Y1  - 2012
SP  - 44
EP  - 44
ER  - 
TY  - JOUR
A1  - Bäcker, Matthias
A1  - Raue, Markus
A1  - Schusser, Sebastian
A1  - Jeitner, C.
A1  - Breuer, L.
A1  - Wagner, P.
A1  - Poghossian, Arshak
A1  - Förster, Arnold
A1  - Mang, Thomas
A1  - Schöning, Michael Josef
T1  - Microfluidic chip with integrated microvalves based on temperature- and pH-responsive hydrogel thin films
JF  - Physica Status Solidi  (a)
N2  - Two types of microvalves based on temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) and pH-responsive poly(sodium acrylate) (PSA) hydrogel films have been developed and tested. The PNIPAAm and PSA hydrogel films were prepared by means of in situ photopolymerization directly inside the fluidic channel of a microfluidic chip fabricated by combining Si and SU-8 technologies. The swelling/shrinking properties and height changes of the PNIPAAm and PSA films inside the fluidic channel were studied at temperatures of deionized water from 14 to 36 °C and different pH values (pH 3–12) of Titrisol buffer, respectively. Additionally, in separate experiments, the lower critical solution temperature (LCST) of the PNIPAAm hydrogel was investigated by means of a differential scanning calorimetry (DSC) and a surface plasmon resonance (SPR) method. Mass-flow measurements have shown the feasibility of the prepared hydrogel films to work as an on-chip integrated temperature- or pH-responsive microvalve capable to switch the flow channel on/off.
Y1  - 2012
U6  - https://doi.org/10.1002/pssa.201100763
SN  - 1862-6319
VL  - 209
IS  - 5
SP  - 839
EP  - 845
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Olaru, Alexandra Maria
A1  - Kowalski, Julia
A1  - Sethi, Vaishali
A1  - Blümich, Bernhard
T1  - Exchange relaxometry of flow at small Péclet numbers in a glass bead pack
JF  - Journal of Magnetic Resonance (JMR)
N2  - In this paper we consider low Péclet number flow in bead packs. A series of relaxation exchange experiments has been conducted and evaluated by ILT analysis. In the resulting correlation maps, we observed a collapse of the signal and a translation towards smaller relaxation times with increasing flow rates, as well as a signal tilt with respect to the diagonal. In the discussion of the phenomena we present a mathematical theory for relaxation exchange experiments that considers both diffusive and advective transport. We perform simulations based on this theory and discuss them with respect to the conducted experiments.
KW  - NMR exchange relaxometry
KW  - Low-field NMR
Y1  - 2012
U6  - https://doi.org/10.1016/j.jmr.2012.04.015
SN  - 1096-0856
VL  - 220
SP  - 32
EP  - 44
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Fischer, Jan-Thomas
A1  - Kowalski, Julia
A1  - Pudasaini, Shiva P.
T1  - Topographic curvature effects in applied avalanche modelling
JF  - Cold Regions Science and Technology
N2  - This paper describes the implementation of topographic curvature effects within the RApid Mass MovementS (RAMMS) snow avalanche simulation toolbox. RAMMS is based on a model similar to shallow water equations with a Coulomb friction relation and the velocity dependent Voellmy drag. It is used for snow avalanche risk assessment in Switzerland. The snow avalanche simulation relies on back calculation of observed avalanches. The calibration of the friction parameters depends on characteristics of the avalanche track. The topographic curvature terms are not yet included in the above mentioned classical model. Here, we fundamentally improve this model by mathematically and physically including the topographic curvature effects. By decomposing the velocity dependent friction into a topography dependent term that accounts for a curvature enhancement in the Coulomb friction, and a topography independent contribution similar to the classical Voellmy drag, we construct a general curvature dependent frictional resistance, and thus propose new extended model equations. With three site-specific examples, we compare the apparent frictional resistance of the new approach, which includes topographic curvature effects, to the classical one. Our simulation results demonstrate substantial effects of the curvature on the flow dynamics e.g., the dynamic pressure distribution along the slope. The comparison of resistance coefficients between the two models demonstrates that the physically based extension presents an improvement to the classical approach. Furthermore a practical example highlights its influence on the pressure outline in the run out zone of the avalanche. Snow avalanche dynamics modeling natural terrain curvature centrifugal force friction coefficients.
KW  - Snow
KW  - Avalanche
Y1  - 2012
U6  - https://doi.org/10.1016/j.coldregions.2012.01.005
SN  - 1872-7441
VL  - 74-75
SP  - 21
EP  - 30
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Pieper, Martin
A1  - Klein, Peter
T1  - Application of simple, periodic homogenization techniques to non-linear heat conduction problems in non-periodic, porous media
JF  - Heat mass transfer
N2  - Often, detailed simulations of heat conduction in complicated, porous media have large runtimes. Then homogenization is a powerful tool to speed up the calculations by preserving accurate solutions at the same time. Unfortunately real structures are generally non-periodic, which requires unpractical, complicated homogenization techniques. We demonstrate in this paper, that the application of simple, periodic techniques to realistic media, that are just close to periodic, gives accurate, approximative solutions. In order to obtain effective parameters for the homogenized heat equation, we have to solve a so called “cell problem”. In contrast to periodic structures it is not trivial to determine a suitable unit cell, which represents a non-periodic media. To overcome this problem, we give a rule of thumb on how to choose a good cell. Finally we demonstrate the efficiency of our method for virtually generated foams as well as real foams and compare these results to periodic structures.
Y1  - 2012
U6  - https://doi.org/10.1007/s00231-011-0879-4
SN  - 0947-7411
VL  - 48
IS  - 2
SP  - 291
EP  - 300
PB  - Springer
CY  - Berlin
ER  -