Atomically Defined Rare‐Earth Scandate Crystal Surfaces

The fabrication of well‐defined, atomically sharp substrate surfaces over a wide range of lattice parameters is reported, which is crucial for atomically regulated epitaxial growth of complex oxide heterostructures. By applying a framework for controlled selective wet etching of complex oxides on the stable rare‐earth scandates (REScO₃), a_pseudocubic = 0.394 – 0.404 nm, the large chemical sensitivity of REScO₃ to basic solutions is exploited, which results in reproducible, single‐terminated surfaces. Time‐of‐flight mass‐spectroscopy measurements show that after wet etching the surfaces are predominantly ScO₂ ‐terminated. Moreover, the morphology study of SrRuO₃ thin‐film growth gives no evidence for mixed termination. Therefore, it is concluded that the REScO₃ surfaces are completely ScO₂ ‐terminated.     

Learning by Failing (and Fixing)

Unfortunately, students can graduate with a software engineering degree without learning anything about building secure systems. However, for the past two years at the Norwegian University of Science and Technology, a software security course has been giving students the theoretical foundation and practical experience necessary to start comprehending software security issues.     

Feedback–Feedforward Scheduling of Control Tasks

A scheduling architecture for real-time control tasks is proposed. The scheduler uses feedback from execution-time measurements and feedforward from workload changes to adjust the sampling periods of the control tasks so that the combined performance of the controllers is optimized. The performance of each controller is described by a cost function. Based on the solution to the optimal resource allocation problem, explicit solutions are derived for linear and quadratic approximations of the cost functions. It is shown that a linear rescaling of the nominal sampling frequencies is optimal for both of these approximations. An extensive inverted pendulum example is presented, where the performance obtained with open-loop, feedback, combined feedback and feedforward scheduling, and earliest-deadline first scheduling are compared. The performance under earliest-deadline first scheduling is explained by studying the behavior of periodic tasks under overload conditions. It is shown that the average values of the sampling periods equal the nominal periods, rescaled by the processor utilization.     

Doped CuO 2 Planes in High T c Cuprates: 2D Or Not 2D ?

The key problem in physics of underdoped cuprates is whether the doping is inhomogeneous and holes are expelled into the 1D domains (stripes). Direct comparison of the resistivity vs T curves of the recently discovered 1D spin-ladder cuprates and underdoped cuprates below the pseudogap temperature T* shows a remarkable similarity which implies that the main scattering mechanism is the same for these two classes of cuprates and therefore in the pseudogap regime the transport in underdoped cuprates is essentially 1D. All the resistivity curves in underdoped cuprates can then be fitted by the model of the 1D quantum transport with the inelastic length in charge stripes being fully controlled by the magnetic spin correlation length in even-chain spin-ladders formed in the Cu-O plane as a result of inhomogeneous doping. Knight shift data are also successfully interpreted by taking the same spin-gap value as the one found from resistivity data.     

Characterisation of Interface-Engineered Ramp-Edge Josephson Junctions by Transmission Electron Microscopy

Interface-engineered ramp-edge junctions (IEJ) have been characterised by high-resolution transmission electron microscopy, X-ray analysis and electron energy loss spectroscopy. The IEJ are prepared by plasma etching an ion-milled YBa ₂ Cu ₃ O _7- (YBCO) ramp-edge and subsequently a top YBCO layer is deposited. The results show that the YBCO at the plasma-etched interface has a modified structure. The modified barrier structure has a pseudo cubic unit cell which is rotated 45° around the [001] axis with respect to the underlying YBCO.     

On Computer-Assisted Proofs in Ordinal Number Theory

Some basic theorems about ordinal numbers were proved using McCunes computer program OTTER, building on Quaifes modification of Gödels class theory. Our theorems are based on Isbells elegant definition of ordinals. Neither the axiom of regularity nor the axiom of choice is used.     

Determination of In-Plane Anisotropy from Magnetoresistivity Measurements on YBa2Cu3O7−δ

The magnetoresistance of six untwinned YBa ₂ Cu ₃ O _7– crystals has been measured above T _c for IBc. Fluctuation theories allowing for an in-plane coherence length anisotropy ( _{a b} ) were used in the analyses. The results suggest that the anisotropy, = _b / _a , is considerably lower than that expected from the resistivity ratio, i.e., . Some magnetoresistive measurements with the field in the ab-plane are also presented.     

Structural Studies of YBCO Ramp Josephson Junctions for Rapid Single Flux Quantum Circuits

Ramp-type Josephson junctions with barrier layers of Ga doped PrBa ₂ Cu ₃ O _7- have been investigated using scanning and transmission electron microscopy. The microstructures have been correlated to the ramp geometry. The junctions exhibited low excess current. This is believed to be due to the uniform thickness of barrier layer deposited on the ion-milled edges. The uniformity of the barrier is presumed to be a result of the smooth ramp, which promoted uniform nucleation and epitaxial growth.     

热传导方程初边值问题的紧致格式

在此文内.我们给出了热传导方程紧致格式的半离散化能量估计.然后,用统一的办法分析了一族全离散格式的稳定性.在此基础上,我们讨论了紧致格式的收敛速度.最后将我们的结果推广到二维并指出在高维情形有同样的结果.