Search query: University of Bremen

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abstract: Strain engineering vanadium dioxide thin films is one way to alter this material's characteristic first order transition from semiconductor to metal. In this study we extend the exploitable strain
author_names: Simon Fischer

Jon-Olaf Krisponeit

Michael Foerster

Lucia Aballe

Jens Falta

Jan Ingo Flege
title: Massively Strained VO2 Thin Film Growth on RuO2
year: 2020

abstract: We have investigated the toroidal analog of ellipsoidal shells of matter, which are of great significance in Astrophysics. The exact formula for the gravitational potential \Psi(R,Z) of a shell with a circular section at the pole of toroidal coordinates is first established. It depends on the mass of the shell, its main radius and axis ratio $e$ (i.e. core to main radius ratio) and involves the product of the complete elliptic integrals of the first and second kinds. Next, we show that successive partial derivatives \partial^{n +m} \Psi/\partial_{R^n} \partial_{Z^m} are also accessible by analytical means at that singular point, thereby enabling the expansion of the interior potential as a bivariate series. Then, we have generated approximations at orders $0$ $1$ $2$ and $3$ corresponding to increasing accuracy. Numerical experiments confirm the great reliability of the approach, in particular for small to moderate axis ratios $e^2 \lesssim 0.1$ typically) In contrast with the ellipsoidal case (Newton's theorem) the potential is not uniform inside the shell cavity as a consequence of the curvature. We explain how to construct the interior potential of toroidal shells with a thick edge (i.e. tubes) and how a core stratification can be accounted for. This is a new step towards the full description of the gravitating potential and forces of tori and rings. Applications also concern electrically charged systems, and thus go beyond the context of gravitation.
author_names: Jean-Marc Hur'e

Audrey Trova

Vladim R Karas

CNRSUniv Bordeaux

University of Bremen

Center of Applied Space Technology

Microgravity Germany

A -M Dumont Astronomical Institute

Academy of Sciences

Czech Republic
title: Interior potential of a toroidal shell from pole values
venue: Monthly Notices of the Royal Astronomical Society
year: 2019

abstract: Real time electron microscopy observation on morphological changes in gold nanostructures deposited on Si (1?0?0) surfaces as a function of annealing temperatures has been reported. Two types of interfaces with silicon substrates were used prior to gold thin film deposition: (i) without native oxide and on ultra clean reconstructed Si surfaces and (ii) with native oxide covered Si surfaces. For ?2.0?nm thick Au films deposited on reconstructed Si (1?0?0) surfaces using the molecular beam epitaxy method under ultra high vacuum conditions, aligned four fold symmetric nanogold silicide structures formed at relatively lower temperatures (compared with the one with native oxide at the interface) For this system, 82% of the nanostructures were found to be nanorectangle like structures with an average length of ?27?nm and aspect ratio of 1.13 at ?700??C. For ?5.0?nm thick Au films deposited on Si (1?0?0) surface with native oxide at the interface, the formation of a rectangular structure was observed at higher temperatures ?850??C) At these high temperatures, desorption of gold silicide followed the symmetry of the substrate. Native oxide at the interface was found to act like a barrier for the inter diffusion phenomena. Structural characterization was carried out using advanced electron microscopy methods.
author_names: Ashutosh Rath

Jatis Kumar Dash

Raghavendra Rao Juluri

Andreas Rosenauer

P V Satyam Institute of Physics

Sachivalaya Marg

India Department of Physics

University of Bremen
title: Temperature dependent electron microscopy study of Au thin films on Si (1 0 0) with and without a native oxide layer as barrier at the interface
year: 2011

abstract: We report on the formation of oriented gold nanostructures on Si(100) substrate by annealing procedures in low vacuum (10 2 mbar) and at high temperature (975 degC) Various thicknesses of gold films have been deposited with SiOx (using high vacuum thermal evaporation) and without SiOx (using molecular beam epitaxy) at the interface on Si(100) Electron microscopy measurements were performed to determine the morphology, orientation of the structures and the nature of oxide layer. Interfacial oxide layer, low vacuum and high temperature annealing conditions are found to be necessary to grow oriented gold structures. These gold structures can be transferred by simple scratching method.
author_names: Ashutosh Rath

Jatis Kumar Dash

Raghavendra Rao Juluri

Andreas Rosenauer

Marcos Schoewalter

P V Satyam Institute of Physics

Sachivalaya Marg

India Department of Physics

University of Bremen
title: Growth of oriented Au nanostructures: Role of oxide at the interface
year: 2012

abstract: We report on the phase separation in Au Ge system leading to the formation of lobe lobe (bi lobed) Au Ge nanostructures under ultra high vacuum (UHV) conditions (3 x 10 10 mbar) on clean Si(100) surfaces. For this study, 2.0 nm thick Au samples were grown on the substrate surface by molecular beam epitaxy. Thermal annealing was carried out inside the UHV chamber at temperature 500 degC and following this, nearly square shaped AuxSi1 x nano structures of average length 48 nm were formed. A 2 nm Ge film was further deposited on the above surface while the substrate was kept at a temperature of 500 degC. Well ordered Au Ge nanostructures where Au and Ge residing side by side (lobe lobe structures) were formed. In our systematic studies, we show that, gold silicide nanoalloy formation at the substrate (Si) surface is necessary for forming phase separated Au Ge bilobed nanostructures. These results show that the Au Ge bonding is unstable in nature. Electron microscopy (TEM, STEM EDS, SEM) studies were carrie.
author_names: Ashutosh Rath

Jatis Kumar Dash

Raghavendra Rao Juluri

Marco Schowalter

K N Mueller

Andreas Rosenauer

P V Satyam Institute of Physics

Sachivalaya Marg

India Department of Physics

University of Bremen
title: Nano scale phase separation in Au Ge system on ultra clean Si(100) surfaces
year: 2012

abstract: Two questions on the topology of compact energy surfaces of natural two degrees of freedom Hamiltonian systems in a magnetic field are discussed. We show that the topology of this 3 manifold (if it is not a unit tangent bundle) is uniquely determined by the Euler characteristic of the accessible region in configuration space. In this class of 3 manifolds for most cases there does not
author_names: Alexey Bolsinov

Holger R Dullin

Andrea E Schweitzer Ohio State University

University of Bremen
title: Topology of energy surfaces and existence of transversal Poincare sections
year: 1996

abstract: "Inquiry based learning" is set to be promoted as a trendy concept. Numerous institutions of higher learning are involved in projects relating to inquiry based learning and declare it a distinguishing feature of their teaching. This applies in particular to research intensive universities. What does inquiry based learning mean for higher education development? Is inquiry based learning suited to serve as the strategic orientation of the entire institution? And how can this be implemented beyond a guiding principle and mere announcements at an institute of higher learning? How can the greatest possible number of actors be involved in these processes? And what should be taken into consideration in so doing? The following article addresses these questions and refers by way of example to activities and experiences in the profile development for inquiry based learning at the University of Bremen.
author_names: Margrit E Kaufmann

Heidi Schelhowe
title: Inquiry Based Learning as a Teaching Profile at Institutions of Higher Learning The Example of the University of Bremen
year: 2019

abstract: The Geosciences Collection of the University of Bremen is a midsize collection of estimated about 800,000 specimens that are housed at the Faculty of Geosciences of Bremen University, focused on the field of paleontology. Nevertheless, the collections include more than 300,000 individual neontological specimens; most of these are gastropods, a focal point that fits well into the mollusk focus of the paleontology collection. Among the recent gastropods, the most important part are species of the unranked clade Stylommatophora, terrestrial gastropods comprising about one third of the total number of specimens in the collection. The gastropod collection contains originals to the nineteenth century collections of Borcherding, Gerhard von dem Busch, Hartmann, Jantzen, and Schmacker among others, including important historical collections of achatinellids from Hawaii and clausilids from China. A few hundred types or potential types are registered in the database; to illustrate the research potencies, some type material is presented exemplarily. Technically, the material and the collection are in an excellent condition, and thus preconditions for scientific revisions are excellent. A permanent preservation and curation are ensured by a contract between the Ubersee Museum, the institution formerly holding these city owned collections, and the University of Bremen. As a consequence the collection has a good staffing today, including one technical assistant and one scientist handling collection affairs. The lively exhibition projects include major exceptional exhibits on inland water vessel and shopping centers, with the conceptional focus to present zoological specimens in comparison with fossil representatives with respect to constructional morphology, evolution, and diversity.
author_names: Jens Lehmann
title: BREMEN: Geosciences Collection of the University of Bremen: The Recent Mollusk Compilation
year: 2018

abstract: The Geosciences Collection of the University of Bremen is a mid size collection of estimated about 800,000 specimens that are housed at the Faculty of Geosciences of the University of Bremen. It is focused on the field of research in paleontology. The collections include more than 500,000 individual fossils, most of these are ammonoids, a focus that is flanked by the mollusk focus of the neontological collection comprising many type specimens. The ammonoid focus is developed fairly recently as well as a very comprising research collection on the Lower Cretaceous (lower Aptian) of North Germany. The research focus of the collection is furthermore underlined by various new collections mainly from the Cretaceous of England, France, North Africa, North America and Tibet. Nevertheless the collection includes important historical material. Examples are the type of the Baltic amber tick Ixodes succineus, a topotype of the largest ammonoid species recorded, Parapuzosia seppenradensis from the late Cretaceous of North Germany, and a complete skeleton of a giant deer, Megaloceros giganteus, from the late Pleistocene of Ireland. Technically, the material and the collection are in an excellent condition today and thus precondition for the further scientific development is very well. The collection is also housing an established working group of the geoscientific department of the university intensively incorporating student education. A long lasting preservation and curation is ensured by a contract between the Ubersee Museum, the institution formerly holding these city owned collections, and the University of Bremen. As a consequence the collection has a good staffing today. Permanent positions include one technical assistant and one scientist handling collection affairs. The lively exhibition projects comprise exceptional exhibits on inland water vessel and shopping centers, with a conceptional focus to present aspects of evolution, diversity and constructional morphology.
author_names: Jens Lehmann
title: BREMEN: The Paleontological Research Collection of the Geosciences Collection of the University of Bremen
year: 2018

abstract: The Zoological Collection of the University of Bremen is a very young collection of arthropod and vertebrate material collected in different ecological research projects between 1960 and 2010. Carabid and staphylinid beetle and spider communities of bogs and salt marshes are the greatest part of the collections which includes time series within different habitats and documented communities of formerly undisturbed bogs. Other arthropod groups are included as far as pitfall traps will get them. As climate change was one aspect of most salt marsh projects, the material was collected as baseline documents for further studies.
author_names: Hans Konrad Nettmann
title: BREMEN: Zoological Collection of the University of Bremen
year: 2018