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981.
Advanced Genetic Programming Based Machine Learning 总被引:1,自引:0,他引:1
Stephan Winkler Michael Affenzeller Stefan Wagner 《Journal of Mathematical Modelling and Algorithms》2007,6(3):455-480
A Genetic Programming based approach for solving classification problems is presented in this paper. Classification is understood
as the act of placing an object into a set of categories, based on the object’s properties; classification algorithms are
designed to learn a function which maps a vector of object features into one of several classes. This is done by analyzing
a set of input-output examples (“training samples”) of the function. Here we present a method based on the theory of Genetic
Algorithms and Genetic Programming that interprets classification problems as optimization problems: Each presented instance
of the classification problem is interpreted as an instance of an optimization problem, and a solution is found by a heuristic
optimization algorithm. The major new aspects presented in this paper are advanced algorithmic concepts as well as suitable
genetic operators for this problem class (mainly the creation of new hypotheses by merging already existing ones and their
detailed evaluation). The experimental part of the paper documents the results produced using new hybrid variants of Genetic
Algorithms as well as investigated parameter settings. Graphical analysis is done using a novel multiclass classifier analysis
concept based on the theory of Receiver Operating Characteristic curves.
The work described in this paper was done within the Translational Research Project L282 “GP-Based Techniques for the Design
of Virtual Sensors” sponsored by the Austrian Science Fund (FWF). 相似文献
982.
We investigate a novel concept to efficiently generate multiphoton induced fluorescence from organic molecules. The concept is based on frustrating the energy transfer between a fluorescent donor and one or more acceptors in conjugated molecules. The nonlinearity is not based on higher order molecular susceptibilities but entirely on their linear properties. Therefore, in contrast to nonresonant multiphoton absorption, this method does not require high local intensities. Likewise, the production of visible fluorescence does not require an infrared excitation wavelength. Hence, when applied to scanning microscopy this property is predicted to increase spatial resolution. Instead of the ∼10 GW/cm2 required in non-resonant multiphoton excitation, focal intensities ∼10 MW/cm2 are expected to produce an equally strong nonlinear signal. The predicted resolution is up to 30% greater than that of an ideal confocal microscope operating at the same fluorescence wavelength. The resolution improvement over non-resonant two-photon absorption microscopes is about two-fold in all directions. 相似文献
983.
Density stratification has a strong impact on turbulence in geophysical flows. Stratification changes the spatial turbulence spectrum and the energy transport and conversion within the spectrum. We analyze these effects based on a series of direct numerical simulations (DNS) of stratified turbulence. To facilitate simulations of real-world problems, which are usually beyond the reach of DNS, we propose a subgrid-scale turbulence model for large eddy simulations of stratified flows based on the Adaptive Local Deconvolution Method (ALDM). Flow spectra and integral quantities predicted by ALDM are in excellent agreement with direct numerical simulation. ALDM automatically adapts to strongly anisotropic turbulence and is thus a suitable tool for studying turbulent flow phenomena in atmosphere and ocean. 相似文献
984.
Dr. James R. Frost Prof. Dr. Stefan M. Huber Dr. Stefan Breitenlechner M. Sc. Christoph Bannwarth Prof. Dr. Thorsten Bach 《Angewandte Chemie (International ed. in English)》2015,54(2):691-695
Spirocyclic oxindoles undergo an enantioselective oxygenation reaction (nine examples; e.r. up to 97:3) upon catalysis by a chiral ruthenium porphyrin complex (1 mol %). The catalyst exhibits a lactam ring, which is responsible for substrate association through hydrogen bonds, and an active ruthenium center, which is in a defined spatial relationship to the oxygenation substrate. DFT calculations illustrate the perfect alignment of the active site with the reactive C? H bond and suggest—in line with the kinetic isotope effect—an oxygen rebound mechanism for the reaction. 相似文献
985.
986.
987.
Michael Johlitz Stefan Diebels Wulff Possart 《Archive of Applied Mechanics (Ingenieur Archiv)》2012,82(8):1089-1102
In the present contribution, a phenomenological material model is presented describing the viscoelastic behaviour of polyurethane bonds under finite deformations. The model includes the temperature dependency of the material behaviour close to the glass transition temperature. Experimentally observed size effects can also be described. It is known from previous investigations that the bonds show an effective behaviour that is influenced by the layer thickness. The physical reason for this behaviour can be found in the formation of boundary layers in the polymer which are located close to the substrate. In these boundary layers, the material behaviour differs from the bulk behaviour. The effective properties of bonds of different thickness are experimentally investigated in isothermal shear tests performed at different temperatures. In order to model the observed effects, a previously developed approach of viscoelasticity is extended including the temperature dependency. Furthermore, a supplementary parameter field is introduced, taking the formation of the boundary layers into account. This field is determined by a partial differential equation in form of a reaction–diffusion equation containing the boundary conditions. The local properties of the polymer are linked to the distribution of this additional field. It is shown that the model parameters can be identified and that the model is able to describe the complex experimentally observed behaviour. 相似文献
988.
Kai Pielhop Carmen Schmidt Stefan Zholtovski Michael Klaas Wolfgang Schröder 《Experiments in fluids》2014,55(10):1-13
Fluid–structure interaction phenomena are extremely important when laminar flows through elastic vessels such as in biomedical flow problems are considered. In general, such elastic vessels are curved which is why an elastic 180° bend at a curvature ratio \(\delta = D/D_{\rm C} = 0.\bar{2}\) defines the reference geometry in this study. It is the purpose of this study to compare the results with the steady flow through a 180° rigid pipe bend and to quantify the impact of the fluid–structure interaction on the overall flow pattern and the vessel deformation at oscillating fully developed entrance flow. The findings comprise velocity, pressure, and structure deformation measurements. The vessel dilatation amplitude was varied between 3.75 % and 7 % of the vessel diameter at Dean De and Womersley number Wo ranges of \(327\,\le\,De\,\le\,350\) and \(7\,\le\,Wo\,\le\,8.\) The flow is investigated by time-resolved stereoscopic particle-image velocimetry in five radial cross sections located in the elastic 180° bend and in the inlet pipes. The unsteady static vessel pressure is measured synchronously at these cross sections. The comparison of the steady with the unsteady flow field shows a strong change in the axial and secondary velocity distributions at periods of transition between the centrifugal forces and the unsteady inertia forces dominated regimes. These changes are characterized by asymmetric fluctuations of the centers of the counter-rotating vortex pair. The investigation of the impact of the structure deformation amplitude on these fluctuations reveals a significant attenuation at high deformation amplitudes. The spatial motion of the elastic vessel due to the forces applied by the flow exhibits amplitudes up to 15 % of the vessel diameter. Considering the fluid–structure interaction, an amplification of the volume flux amplitude by a factor of 2.1 at the vessel outlet and phase lags up to 30° occur. The static pressure distribution is characterized by a pronounced asymmetry between forward and backward flow with a 40 % higher peak magnitude at backward flow and phase lags of 35°. The results evidence that a strong distortion of the velocity distribution in the bend, which is caused by the oscillating nature of the flow, is reduced as a result of the fluid–structure interaction. 相似文献
989.
Zhen Li Chen Stefan Hickel Antoine Devesa Julien Berland Nikolaus A. Adams 《Theoretical and Computational Fluid Dynamics》2014,28(1):1-21
We propose and analyze a wall model based on the turbulent boundary layer equations (TBLE) for implicit large-eddy simulation (LES) of high Reynolds number wall-bounded flows in conjunction with a conservative immersed-interface method for mapping complex boundaries onto Cartesian meshes. Both implicit subgrid-scale model and immersed-interface treatment of boundaries offer high computational efficiency for complex flow configurations. The wall model operates directly on the Cartesian computational mesh without the need for a dual boundary-conforming mesh. The combination of wall model and implicit LES is investigated in detail for turbulent channel flow at friction Reynolds numbers from Re τ = 395 up to Re τ =100,000 on very coarse meshes. The TBLE wall model with implicit LES gives results of better quality than current explicit LES based on eddy viscosity subgrid-scale models with similar wall models. A straightforward formulation of the wall model performs well at moderately large Reynolds numbers. A logarithmic-layer mismatch, observed only at very large Reynolds numbers, is removed by introducing a new structure-based damping function. The performance of the overall approach is assessed for two generic configurations with flow separation: the backward-facing step at Re h = 5,000 and the periodic hill at Re H = 10,595 and Re H = 37,000 on very coarse meshes. The results confirm the observations made for the channel flow with respect to the good prediction quality and indicate that the combination of implicit LES, immersed-interface method, and TBLE-based wall modeling is a viable approach for simulating complex aerodynamic flows at high Reynolds numbers. They also reflect the limitations of TBLE-based wall models. 相似文献
990.
Turbulence,dynamic similarity and scale effects in high-velocity free-surface flows above a stepped chute 总被引:2,自引:0,他引:2
In high-velocity free-surface flows, air entrainment is common through the interface, and intense interactions take place
between turbulent structures and entrained bubbles. Two-phase flow properties were measured herein in high-velocity open channel
flows above a stepped chute. Detailed turbulence measurements were conducted in a large-size facility, and a comparative analysis
was applied to test the validity of the Froude and Reynolds similarities. The results showed consistently that the Froude
similitude was not satisfied using a 2:1 geometric scaling ratio. Lesser number of entrained bubbles and comparatively greater
bubble sizes were observed at the smaller Reynolds numbers, as well as lower turbulence levels and larger turbulent length
and time scales. The results implied that small-size models did underestimate the rate of energy dissipation and the aeration
efficiency of prototype stepped spillways for similar flow conditions. Similarly a Reynolds similitude was tested. The results
showed also some significant scale effects. However a number of self-similar relationships remained invariant under changes
of scale and confirmed the analysis of Chanson and Carosi (Exp Fluids 42:385-401, 2007). The finding is significant because self-similarity may provide a picture general enough to be used to characterise the
air–water flow field in large prototype channels. 相似文献