Kelvin Probe Spectroscopy of a Two-Dimensional Electron Gas Below 300 mK

A scanning force microscope with a base temperature below 300 mK is used for measuring the local electron density of a two-dimensional electron gas embedded in an Ga[Al]As heterostructure. At different separations between AFM tip and sample, a dc-voltage is applied between the tip and the electron gas while simultaneously recording the frequency shift of the oscillating tip. Using a plate capacitor model the local electron density can be extracted from the data. The result coincides within 10% with the data obtained from transport measurements.Comment: 3 pages, 3 figure

Resistance effects due to magnetic guiding orbits

The Hall and magnetoresistance of a two dimensional electron gas subjected to a magnetic field barrier parallel to the current direction is studied as function of the applied perpendicular magnetic field. The recent experimental results of Nogaret {\em et al.} [Phys. Rev. Lett. {\bf 84}, 2231 (2000)] for the magneto- and Hall resistance are explained using a semi-classical theory based on the Landauer-B\"{u}ttiker formula. The observed positive magnetoresistance peak is explained as due to a competition between a decrease of the number of conducting channels as a result of the growing magnetic field, from the fringe field of the ferromagnetic stripe as it becomes magnetized, and the disappearance of snake orbits and the subsequent appearance of cycloidlike orbits.Comment: 7 pages, 7 figure

Transformation kinetics of selected steel grades after plastic deformation

The aim of this article was to assess the impact of previous plastic deformation on the kinetics of transformations of four selected steels. The research was conducted with use of the universal plastometer GLEEBLE 3800, when Continuous Cooling Transformation (CCT) and Deformation Continuous Cooling Transformation (DCCT) diagrams of selected steels were constructed on the basis of dilatometric tests. The research confirmed that the strain accelerates the particularly the transformations controlled by diffusion. Bainitic transformation was accelerated in three of the four steels. In the case of martensitic transformation the effect of the previous deformation was relatively small, but with clearly discernible trend

Hot flow stress models of the steel C45

Flows stress of the steel C45 were predicted on the basis of experimentally obtained flow stress curves, using uniaxial hot compression tests on the plastometer HDS-20, by two completely different types of mathematical models, moreover with comparison to a model comprised in the FEM database of the FORGE software. The tests were carried out within the temperature range from 900 to 1 280 °C, at the strain rate from 0,1 to 100 s^-1 and deformations up to 1,0. It follows from the results of flow stress prediction that models designed on the basis of experimental measurements have much better information capability than the generated model implemented into the database of the FORGE software, however, their extrapolation for larger deformations is limited