Artificial neural networks application in thermography

In this paper, we present an application of artificial neural network (ANN) analysis in the thermovision identification of the studied thermal fields. Precise thermal field identification plays an important role in distinguished technological processes, for instance in metallurgy. Our efforts were focused in this direction. Thermovision outputs are usually thermograms with a form of a quasi-coloured imaging record of an observed temperature field. A thermogram is usually registered and presented in a form of an electronic or printed image. The character of such a document is informational only, and real temperature values are difficult to detect. The exploitation of neural networks is advantageous, if it is necessary to express complex mutual relations among sensor-based data. More accurate results of the predictions of different metallurgical parameters with the exploitation of neural networks are based on the fact that the application of neural networks enables the assignment of relations among process parameters which cannot be traced using common methods due to their mutual interactions, the considerable amount of data, dynamics and the thus ensuing time demands.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

Contactless method of specific heat capacity determination

The paper deals with theoretical and experimental aspects of the application of the lumped capacitance model (LCM) for the study of heat transport in different materials. The patented construction of the measuring chamber together with special software, the fundamental features of which are presented in this paper, enable the contactless evaluation of the specific heat capacity at the constant pressure cp. The time constant τ that determines the rate of cooling of the preheated sample is the fundamental value for determining of the cp. A new method of curve fitting was subsequently developed and implemented into the new software. All theoretical outputs were experimentally tested on a relatively large scale of materials with success.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

Quantum Hall effect in a high-mobility two-dimensional electron gas on the surface of a cylinder

The quantum Hall effect is investigated in a high-mobility two-dimensional electron gas on the surface of a cylinder. The novel topology leads to a spatially varying filling factor along the current path. The resulting inhomogeneous current-density distribution gives rise to additional features in the magneto-transport, such as resistance asymmetry and modified longitudinal resistances. We experimentally demonstrate that the asymmetry relations satisfied in the integer filling factor regime are valid also in the transition regime to non-integer filling factors, thereby suggesting a more general form of these asymmetry relations. A model is developed based on the screening theory of the integer quantum Hall effect that allows the self-consistent calculation of the local electron density and thereby the local current density including the current along incompressible stripes. The model, which also includes the so-called `static skin effect' to account for the current density distribution in the compressible regions, is capable of explaining the main experimental observations. Due to the existence of an incompressible-compressible transition in the bulk, the system behaves always metal-like in contrast to the conventional Landauer-Buettiker description, in which the bulk remains completely insulating throughout the quantized Hall plateau regime

Latest Developments from the S-DALINAC*

The S-DALINAC is a 130 MeV superconducting recirculating electron accelerator serving several nuclear and radiation physics experiments as well as driving an infrared free-electron laser. A system of normal conducting rf resonators for noninvasive beam position and current measurement was established. For the measurement of gamma-radiation inside the accelerator cave a system of Compton diodes has been developed and tested. Detailed investigations of the transverse phasespace were carried out with a tomographical reconstruction method of optical transition radiation spots. The method can be applied also to non-Gaussian phasespace distributions. The results are in good accordance with simulations. To improve the quality factor of the superconducting 3 GHz cavities, an external 2K testcryostat was commissioned. The influence of electro-chemical polishing and magnetic shielding is currently under investigation. A digital rf-feedback-system for the accelerator cavities is being developed in order to improve the energy spread of the beam of the S-DALINAC. * Supported by the BMBF under contract no. 06 DA 820, the DFG under contract no. Ri 242/12-1 and -2 and the DFG Graduiertenkolleg 'Physik und Technik von Beschleunigern

Electron-beam-induced modifications of electronic properties in GaN-based quantum well structures

The electronic properties of (In,Ga)N/GaN quantum wells fabricated by MOCVDvary significantly during investigations using low-energy electron beam irradiation (LEEBI) suchas cathodoluminescence (CL) if a certain exposure dose is exceeded. For unintentionally dopedstructures, we observe a simultaneous LEEBI-induced activation of donors and acceptors. Thus,the resistivity of the layers is not varied, while the quantum efficiency and optical transition energyincreases significantly by LEEBI. A p-n structure is turned towards flat band conditions duringLEEBI indicating an electron beam induced passivation of acceptors in the p-type layer