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Search Results: 1 - 10 of 11833 matches for " Olaf Andreas; "
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LC-Circuit Calorimetry
Olaf Bossen,Andreas Schilling
Physics , 2011, DOI: 10.1063/1.3632116
Abstract: We present a new type of calorimeter in which we couple an unknown heat capacity with the aid of Peltier elements to an electrical circuit. The use of an electrical inductance and an amplifier in the circuit allows us to achieve autonomous oscillations, and the measurement of the corresponding resonance frequency makes it possible to accurately measure the heat capacity with an intrinsic statistical error that decreases as ~t^{-3/2} with measuring time t, as opposed to a corresponding error ~t^{-1/2} in the conventional alternating current (a.c.) method to measure heat capacities. We have built a demonstration experiment to show the feasibility of the new technique, and we have tested it on a gadolinium sample at its transition to the ferromagnetic state.
Estimates for the thermodynamic signatures of vortex-lattice melting in conventional superconductors
Olaf Bossen,Andreas Schilling
Physics , 2012, DOI: 10.1016/j.physc.2012.08.005
Abstract: The first-order nature of the vortex-lattice melting transition in copper-based layered high-Tc superconductors is well established. The associated discontinuities in magnetization have been extensively studied, for example, in YBa2Cu3O7 and Bi2Sr2CaCu2O8, while the respective latent heats have been systematically investigated only in YBa2Cu3O7 and related compounds. The apparent absence of such signatures in conventional superconductors such as Nb raises the question whether or not the concept of vortex-lattice melting is applicable at all in such materials. Based on available literature to describe the vortex-state and using the Lindemann criterion, we estimate quantitatively the order of magnitude for the expected latent heats of melting and the associated discontinuities in magnetization, respectively, as functions of a few known material parameters. It turns out that both thermodynamic quantities are not strictly vanishing even in isotropic materials as long as $\kappa > 1/\sqrt{2}$, but they are small and may often be beyond the available experimental resolution.
Dynamics of molecular clouds under the influence of ionizing radiation from young massive stars
Olaf Kessel Deynet,Andreas Burkert
Revista mexicana de astronomía y astrofísica , 2002,
Abstract: Presentamos simulaciones num ericas sobre la implosi on radiativa de inhomogeneidades en n ucleos de nubes moleculares debido a la radiaci on ionizante de estrellas masivas. Hicimos c alculos SPH con una distribuci on Gaussiana de perturbaciones en la densidad. Encontramos que las pertubaciones a gran escala con un espectro de potencias de
Learning About Hydroelectric Power Plants Using a Model and Utilising a Game Scenario
Olaf Hallan Graven,Dag Andreas Hals Samuelsen
International Journal of Online Engineering (iJOE) , 2013, DOI: 10.3991/ijoe.v9i1.2403
Abstract: The system described in this paper is focused on the challenge of engaging and motivating pupils in secondary schools and further education for STEM education in general, and demonstration of how energy conversion is done in hydroelectric power plants in particular. The method selected in order to engage and motivate the user is a games based approach. The implementation created to encourage the pupils to use the system and not only be passive viewers of a demonstration of the principles involved. The paper describes the design and implementation of the system. The system has been used by multiple groups of pupils over a period of two years.
Highly configurable low cost remote laboratory with integrated support for learning - Software and learning support
Olaf Hallan Graven,Dag Andreas Hals Samuelsen
International Journal of Online Engineering (iJOE) , 2013, DOI: 10.3991/ijoe.v9is3.2534
Abstract: A highly configurable remote laboratory system has been create by the authors as a long running project. This paper presents the current version of the software and automated learning support facilities that are parts of this system. The software for the remote laboratory system is created in order to facilitate initially simple, but later on more complex pedagogic support for students using remote laboratories. Current version of the software system includes facilities to limit unwanted behaviour, particularly where students utilise a trial and error approach. The system utilise a batch processing where the aim of the system is to complete all requests within seconds, giving the students the feeling that they have full control over the experiment all the time even when they share it with ten, twenty or more other students.
Low Cost Robots as Target System for Students Training Using Java
Dag Andreas Hals Samuelsen,Olaf Hallan Graven
International Journal of Online Engineering (iJOE) , 2009, DOI: 10.3991/ijoe.v5i4.1120
Abstract: The topic of this paper is a cost efficient programming environment designed with a focus on enhancing the students’ engagement and effort to complete the assignments. The environment is designed to give the students an approach that is similar to a professional work situation with respect to hardware-software interaction, documentation and complexity. The system presented is based on low-cost, off-the-shelf equipment for easy implementation on mass in an educational institution. As part of the system a low-cost positioning system for mobile robots in an indoor application is included, giving further opportunities for engaging task for the students.
Offering Students a Selection of Multiple Class B/AB Power Amplifiers as a Remote Laboratory
Olaf Hallan Graven,Dag Andreas Hals Samuelsen
International Journal of Online Engineering (iJOE) , 2011, DOI: 10.3991/ijoe.v7is1.1722
Abstract: In this paper a remote laboratory setup for conducting experiments on a class B/AB power amplifier is presented, addressing the problems related to running experiments requiring temperature matching between transistors and bias diodes, in order to avoid thermal runaway in the transistors. In addition there is an option for the student to quickly examine a range of different transistors in both class B and class AB setups.
Radiation Driven Implosion of Molecular Cloud Cores
Olaf Kessel-Deynet,Andreas Burkert
Physics , 2002, DOI: 10.1046/j.1365-8711.2003.05737.x
Abstract: We present the first three-dimensional calculations of Radiation Driven Implosion of Molecular Clouds including self-gravity and ionization. We discuss the effects of initial density perturbations on the dynamics of ionizing globules and show that the onset of gravitational collapse can be significantly delayed for a multiple of the implosion timescale. We demonstrate that Radiation Driven Implosion could be an efficient process for injecting disordered kinetic energy into molecular clouds in the vicinity of massive stars.
Ac-magnetic susceptibility in the peak-effect region of Nb$_3$Sn
Olaf Bossen,Andreas Schilling,Naoki Toyota
Physics , 2013, DOI: 10.1016/j.physc.2013.05.028
Abstract: We performed a systematic study of the ac magnetic-susceptibility on a Nb3Sn single crystal which displays a strong peak effect near the upper critical field Hc2. In external magnetic fields above 3 T, the peak effect manifests itself in a single, distinct peak in the real part of the ac susceptibility as a function of temperature T, the size of which continuously increases with increasing magnetic field H. In the imaginary part of the ac susceptibility, on the other hand, a single peak initially grows with increasing H up to a well-defined value, and then splits into two sharp peaks which separate when H is further increased. We explain this surprising behavior by a flux-creep model and taking into account the enhancement of the critical-current density in the peak-effect region near Tc in which Bean's critical-state model seems to apply. Outside this region, the crystal is clearly in a flux-creep regime with finite creep exponent n.
Sigma-model limit of Yang-Mills instantons in higher dimensions
Andreas Deser,Olaf Lechtenfeld,Alexander D. Popov
Mathematics , 2014, DOI: 10.1016/j.nuclphysb.2015.03.009
Abstract: We consider the Hermitian Yang-Mills (instanton) equations for connections on vector bundles over a 2n-dimensional K\"ahler manifold X which is a product Y x Z of p- and q-dimensional Riemannian manifold Y and Z with p+q=2n. We show that in the adiabatic limit, when the metric in the Z direction is scaled down, the gauge instanton equations on Y x Z become sigma-model instanton equations for maps from Y to the moduli space M (target space) of gauge instantons on Z if q>= 4. For q<4 we get maps from Y to the moduli space M of flat connections on Z. Thus, the Yang-Mills instantons on Y x Z converge to sigma-model instantons on Y while Z shrinks to a point. Put differently, for small volume of Z, sigma-model instantons on Y with target space M approximate Yang-Mills instantons on Y x Z.
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