Technical University Mu Nchen
Technical University Mu Nchen
Busch P.,Jülich Research Center |
Rauscher M.,Max Planck Institute for Metals Research |
Rauscher M.,University of Stuttgart |
Moulin J.-F.,Helmholtz Center Geesthacht |
Muller-Buschbaum P.,Technical University Mu Nchen
Journal of Applied Crystallography | Year: 2011
The powder-like orientation of lamellar domains in thin films of the diblock copolymer polystyrene-block-poly(methyl methacrylate) is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence small-angle neutron scattering (GISANS). Conventional monochromatic GISANS and GISAXS measurements are compared with neutron time-of-flight GISANS. For angles of incidence and exit larger than the critical angle of total external reflection of the polymer, Debye-Scherrer rings are observed. The position of the Debye-Scherrer rings is described quantitatively based on a reduced version of the distorted-wave Born approximation. A strong distortion of the ring shape is caused by refraction and reflections from the film interfaces. Close to the critical angle, the ring shape collapses into a banana shape. © 2011 International Union of Crystallography Printed in Singapore - all rights reserved.
Mgbemere H.,University of Lagos |
Mgbemere H.,TU Hamburg - Harburg |
Schneider G.,TU Hamburg - Harburg |
Hoelzel M.,Technical University Mu nchen |
And 2 more authors.
Journal of Applied Crystallography | Year: 2016
A neutron diffraction study of (KxNa1-x)NbO3-based ceramics has been carried out from 5 K to high temperatures well above the Curie temperature. The diffraction data were analysed using Rietveld refinement. For pure KNN samples, especially at the Na-rich side of the phase diagram, the lowtemperature structure of simple rhombohedral symmetry changes to a highly complex monoclinic structure at a higher temperature. Chemical analysis on the samples showed good agreement of the expected and actual compositions. Trigonal, monoclinic, orthorhombic, tetragonal and cubic phase models as well as two-phase mixtures are observed depending on the temperature of measurement. Space groups R3c, P1m1, P11m, Amm2, P4mm, Pm3m and their combinations are used to refine the trigonal, monoclinic, orthorhombic, tetragonal, cubic and mixed phases, respectively. For the (K0.48Na0.48Li0.04)- (Nb0.86Ta0.1Sb0.04)O3 sample at temperatures between 5 and 300 K, the monoclinic P11m space group gives the best refinement fit. For the (K0.17Na0.83)NbO3 sample, a two-phase refinement using the trigonal R3c and monoclinic Pm space groups gave the best fit at 300 K, while at 5-150 K the trigonal R3c space group gives the best fit. The understanding of the structure of these lead-free ceramics will help in the optimization of their piezoelectric properties. © 2016 International Union of Crystallography.
Habel J.C.,Technical University Mu Nchen |
Mulwa R.K.,National Museums of Kenya |
Gassert F.,University of Trier |
Rodder D.,Zoologisches Forschungsmuseum Alexander Koenig |
And 4 more authors.
Heredity | Year: 2014
The Eastern Afromontane cloud forests occur as geographically distinct mountain exclaves. The conditions of these forests range from large to small and from fairly intact to strongly degraded. For this study, we sampled individuals of the forest bird species, the Montane White-eye Zosterops poliogaster from 16 sites and four mountain archipelagos. We analysed 12 polymorphic microsatellites and three phenotypic traits, and calculated Species Distribution Models (SDMs) to project past distributions and predict potential future range shifts under a scenario of climate warming. We found well-supported genetic and morphologic clusters corresponding to the mountain ranges where populations were sampled, with 43% of all alleles being restricted to single mountains. Our data suggest that large-scale and long-term geographic isolation on mountain islands caused genetically and morphologically distinct population clusters in Z. poliogaster. However, major genetic and biometric splits were not correlated to the geographic distances among populations. This heterogeneous pattern can be explained by past climatic shifts, as highlighted by our SDM projections. Anthropogenically fragmented populations showed lower genetic diversity and a lower mean body mass, possibly in response to suboptimal habitat conditions. On the basis of these findings and the results from our SDM analysis we predict further loss of genotypic and phenotypic uniqueness in the wake of climate change, due to the contraction of the species' climatic niche and subsequent decline in population size. © 2014 Macmillan Publishers Limited All rights reserved.
Mao J.,Pennsylvania State University |
Ren X.,Pennsylvania State University |
Ren X.,University of Miami |
Chen S.,Pennsylvania State University |
And 10 more authors.
Atmospheric Environment | Year: 2010
Both similarities and differences in summertime atmospheric photochemical oxidation appear in the comparison of four field studies: TEXAQS2000 (Houston, 2000), NYC2001 (New York City, 2001), MCMA2003 (Mexico City, 2003), and TRAMP2006 (Houston, 2006). The compared photochemical indicators are OH and HO2 abundances, OH reactivity (the inverse of the OH lifetime), HOx budget, OH chain length (ratio of OH cycling to OH loss), calculated ozone production, and ozone sensitivity. In terms of photochemical activity, Houston is much more like Mexico City than New York City. These relationships result from the ratio of volatile organic compounds (VOCs) to nitrogen oxides (NOx), which are comparable in Houston and Mexico City, but much lower in New York City. Compared to New York City, Houston and Mexico City also have higher levels of OH and HO2, longer OH chain lengths, a smaller contribution of reactions with NOx to the OH reactivity, and NOx-sensitivity for ozone production during the day. In all four studies, the photolysis of nitrous acid (HONO) and formaldehyde (HCHO) are significant, if not dominant, HOx sources. A problematic result in all four studies is the greater OH production than OH loss during morning rush hour, even though OH production and loss are expected to always be in balance because of the short OH lifetime. The cause of this discrepancy is not understood, but may be related to the under-predicted HO2 in high NOx conditions, which could have implications for ozone production. Three photochemical indicators show particularly high photochemical activity in Houston during the TRAMP2006 study: the long portion of the day for which ozone production was NOx-sensitive, the calculated ozone production rate that was second only to Mexico City's, and the OH chain length that was twice that of any other location. These results on photochemical activity provide additional support for regulatory actions to reduce reactive VOCs in Houston in order to reduce ozone and other pollutants. © 2009 Elsevier Ltd.
Vanderelst D.,University of Antwerp |
de Mey F.,University of Antwerp |
Peremans H.,University of Antwerp |
Geipel I.,University of Ulm |
And 3 more authors.
PLoS ONE | Year: 2010
Background:Many bats vocalizing through their nose carry a prominent noseleaf that is involved in shaping the emission beam of these animals. To our knowledge, the exact role of these appendages has not been thoroughly investigated as for no single species both the hearing and the emission spatial sensitivities have been obtained. In this paper, we set out to evaluate the complete spatial sensitivity of two species of New World leaf-nosed bats: Micronycteris microtis and Phyllostomus discolor. From an ecological point of view, these species are interesting as they belong to the same family (Phyllostomidae) and their noseleaves are morphologically similar. They differ vastly in the niche they occupy. Comparing these species allows us to relate differences in function of the noseleaf to the ecological background of bat species. Methodology/Principal Findings:We simulate the spatial sensitivity of both the hearing and the emission subsystems of two species, M. microtis and P. discolor. This technique allows us to evaluate the respective roles played by the noseleaf in the echolocation system of these species. We find that the noseleaf of M. microtis focuses the radiated energy better and yields better control over the emission beam. Conclusions:From the evidence presented we conclude that the noseleaves serve quantitatively different functions for different bats. The main function of the noseleaf is to serve as an energy focusing mechanism that increases the difference between the reflected energy from objects in the focal area and objects in the periphery. However, despite the gross morphological similarities between the noseleaves of the two Phyllostomid species they focus the energy to a different extent, a capability that can be linked to the different ecological niches occupied by the two species. © 2010 Vanderelst et al.
Wyler L.,University of Zürich |
Napoli C.U.,University of Basel |
Ingold B.,University of Zürich |
Sulser T.,University of Zürich |
And 3 more authors.
British Journal of Cancer | Year: 2014
Background:The mechanisms of brain metastasis in renal cell cancer (RCC) patients are poorly understood. Chemokine and chemokine receptor expression may contribute to the predilection of RCC for brain metastasis by recruitment of monocytes/macrophages and by control or induction of vascular permeability of the blood-brain barrier.Methods:Frequency and patterns of brain metastasis were determined in 246 patients with metastatic RCC at autopsy. Expression of CXCR4, CCL7 (MCP-3), CCR2 and CD68 + tumour-associated macrophages (TAMs) were analysed in a separate series of 333 primary RCC and in 48 brain metastases using immunohistochemistry.Results:Fifteen percent of 246 patients with metastasising RCC had brain metastasis. High CXCR4 expression levels were found in primary RCC and brain metastases (85.7% and 91.7%, respectively). CCR2 (52.1%) and CCL7 expression (75%) in cancer cells of brain metastases was more frequent compared with primary tumours (15.5% and 16.7%, respectively; P<0.0001 each). The density of CD68 + TAMs was similar in primary RCC and brain metastases. However, TAMs were more frequently CCR2-positive in brain metastases than in primary RCC (P<0.001).Conclusion:Our data demonstrate that the monocyte-specific chemokine CCL7 and its receptor CCR2 are expressed in tumour cells of RCC. We conclude that monocyte recruitment by CCR2 contributes to brain metastasis of RCC. © 2014 Cancer Research UK.
Hasslberger J.,Technical University Mu nchen |
Boeck L.R.,Technical University Mu nchen |
Sattelmayer T.,Technical University Mu nchen
Journal of Loss Prevention in the Process Industries | Year: 2014
A methodology for the computationally efficient CFD simulation of hydrogen-air explosions (including transition to detonation) in large volumes is presented. The model is validated by means of the largest ever conducted indoor DDT experiments in the RUT facility. A combination of models is proposed with a particular focus on the influence of flame-instabilities, especially of thermal-diffusive nature, which are crucial for very lean mixtures. Excellent agreement is achieved in terms of flame acceleration. The quality of DDT predictions itself depends on the underlying mechanism. Whereas DDT by shock-focusing is successfully simulated on under-resolved meshes, DDT by local explosions in the vicinity of the turbulent flame brush remains a challenge. Adaptive mesh refinement therefore emerges as a key technique to resolve more of the essential phenomena at reasonable computational costs affordable by industry. Finally, a generic case demonstrates the influence of mixture inhomogeneity, which can promote flame acceleration and ultimately DDT. © 2014 Elsevier Ltd.
Ru menapp C.,Technical University Mu nchen |
Wagner F.E.,Technical University Mu nchen |
Gleich B.,Technical University Mu nchen
Journal of Magnetism and Magnetic Materials | Year: 2014
Magnetic nanoparticles made of magnetite have the advantage to be biocompatible and to have a good saturation magnetisation. In this work we show that magnetite nanoparticles change their magnetic and chemical characteristics over time, depending on their storage conditions. To determine the oxidation state of the iron in the core of the nanoparticles Mo¨ssbauer spectroscopy was used at 4.2 K. This method is very accurate, especially in distinguishing maghemite and magnetite. The nanoparticles prepared by a co-precipitation method and peptized using acidic media had a core diameter of 5-7 nm. The aging process was monitored until the core was completely oxidised to maghemite and no further change occurred. The greatest change in the magnetite content of the particles was seen during the first 12. h after preparation. To preserve the good magnetic characteristics of magnetite nanoparticles a coating that prevents oxidation is therefore essential. Our results show that the point in time of the characterisation of small magnetic nanoparticles is crucial for the results. Even though magnetite nanoparticles have been formed nearly stoichiometrically, their chemical properties change over time. © 2014 Elsevier B.V.
Vuong A.-T.,Technical University Mu nchen |
Yoshihara L.,Technical University Mu nchen |
Wall W.A.,Technical University Mu nchen
Computer Methods in Applied Mechanics and Engineering | Year: 2014
In the last few decades modeling deformation and flow in porous media has been of great interest due to its possible application areas in various fields of engineering such as biomechanics, soil mechanics, geophysics, physical chemistry and material sciences. Due to the high complexity and in most cases also unknown geometry of porous media on the microscale, a fully resolved model is nearly impossible to obtain, but most of the times also not necessary to answer important questions. As a consequence, one switches to a macroscopic approach. Such a mathematical description of porous media on the macroscale leads to a volume-coupled multi-field problem, wherein the interface between the two phases is not resolved explicitly. In this work we propose a numerical approach for modeling incompressible flow through a nearly incompressible elastic matrix under finite deformations. After a short overview of physical and mathematical fundamentals, the system equations are formulated and different representations are introduced and analyzed. Based on thermodynamic principles, a general constitutive law is derived, which allows the integration of arbitrary strain energy functions for the skeleton. Discretization in space with three primary variables and discretization in time using the one-step-theta method lead to a complete discrete formulation, which includes both finite deformations as well as full coupling of structural and fluid phases. Therein, we include dynamic effects, especially a time and space dependent porosity. Due to the compressibility of the solid phase, the porosity and its time derivative is not depending on the determinant of the deformation gradient only, but also on the pore pressure, which is an effect that is neglected in many publications. Considering this and also a general version of Darcy's law, we derive two finite element formulations in a straightforward way, which, along with the numerical illustrations, provide a new numerical scheme for solving large deformation porous media problems. © 2014 Elsevier B.V.
Hoche S.,Technical University Mu nchen |
Hussein M.A.,Technical University Mu nchen |
Becker T.,Technical University Mu nchen
Ultrasonics | Year: 2014
The accuracy of density, reflection coefficient, and acoustic impedance determination via multiple reflection method was validated experimentally. The ternary system water-maltose-ethanol was used to execute a systematic, temperature dependent study over a wide range of densities and viscosities aiming an application as inline sensor in beverage industries.The validation results of the presented method and setup show root mean square errors of: 1.201E-3gcm-3 (±0.12%) density, 0.515E-3 (0.15%) reflection coefficient and 1.851E+3kgs-1 m-2 (0.12%) specific acoustic impedance. The results of the diffraction corrected absorption showed an average standard deviation of only 0.12%. It was found that the absorption change shows a good correlation to concentration variations and may be useful for laboratory analysis of sufficiently pure liquids.The main part of the observed errors can be explained by the observed noise, temperature variation and the low signal resolution of 50. MHz. In particular, the poor signal-to-noise ratio of the second reflector echo was found to be a main accuracy limitation. Concerning the investigation of liquids the unstable properties of the reference material PMMA, due to hygroscopicity, were identified to be an additional, unpredictable source of uncertainty. While dimensional changes can be considered by adequate methodology, the impact of the time and temperature dependent water absorption on relevant reference properties like the buffer's sound velocity and density could not be considered and may explain part of the observed deviations. © 2014 Elsevier B.V.