Single-Electron Transport Driven by Surface Acoustic Waves: Moving Quantum Dots Versus Short Barriers

We have investigated the response of the acoustoelectric-current driven by a surface-acoustic wave through a quantum point contact in the closed-channel regime. Under proper conditions, the current develops plateaus at integer multiples of ef when the frequency f of the surface-acoustic wave or the gate voltage V_g of the point contact is varied. A pronounced 1.1 MHz beat period of the current indicates that the interference of the surface-acoustic wave with reflected waves matters. This is supported by the results obtained after a second independent beam of surface-acoustic wave was added, traveling in opposite direction. We have found that two sub-intervals can be distinguished within the 1.1 MHz modulation period, where two different sets of plateaus dominate the acoustoelectric-current versus gate-voltage characteristics. In some cases, both types of quantized steps appeared simultaneously, though at different current values, as if they were superposed on each other. Their presence could result from two independent quantization mechanisms for the acoustoelectric-current. We point out that short potential barriers determining the properties of our nominally long constrictions could lead to an additional quantization mechanism, independent from those described in the standard model of ‘moving quantum dots.’     

Conflict Resolution and Train Speed Coordination for Solving Real-Time Timetable Perturbations

During rail operations, unforeseen events may cause timetable perturbations, which ask for the capability of traffic management systems to reschedule trains and to restore the timetable feasibility. Based on an accurate monitoring of train positions and speeds, potential conflicting routes can be predicted in advance and resolved in real time. The adjusted targets (location-time-speed) would be then communicated to the relevant trains by which drivers should be able to anticipate the changed traffic circumstances and adjust the train's speed accordingly. We adopt a detailed alternative graph model for the train dispatching problem. Conflicts between different trains are effectively detected and solved. Adopting the blocking time model, we ascertain whether a safe distance headway between trains is respected, and we also consider speed coordination issues among consecutive trains. An iterative rescheduling procedure provides an acceptable speed profile for each train over the intended time horizon. After a finite number of iterations, the final solution is a conflict-free schedule that respects the signaling and safety constraints. A computational study based on a hourly cyclical timetable of the Schiphol railway network has been carried out. Our automated dispatching system provides better solutions in terms of delay minimization when compared to dispatching rules that can be adopted by a human traffic controller     

Safety against formation of through cracks of profiled fibre-reinforced cement sheets for roofing

Loads due to wind, snow or traffic on a roof determine the requirements to the strength and stiffness properties of profiled sheets for roofing. Apart from these loads, locked-in stresses can occur due to differences in temperature and moisture strains in the profiled sheets and the wooden laths supporting the sheets. These tensile and compressive stresses are induced in the sheets if they are firmly fastened to the laths with fastening screws.The purpose of this investigation was to analyse the safety of the profiled sheets in transmitting these loads without the formation of through cracks.The analysis is based on an experimental and a theoretical investigation of the strength and stiffness properties of unexposed profiled fibre-reinforced cement sheets and of sheets that had been exposed on a roof in three years.     

Development of a new electroplating process for Ni-W alloy deposits

In the present work, the effect of the complexing agents citrate, glycine and triethanolamine (TEA) on the electrodeposition of Ni-W layers from electrolytes based on NiSO₄ and Na₂WO₄, is investigated. The investigations include measurement of the current efficiencies, determination of the tungsten content in the electrodeposits (by energy dispersive X-ray analysis), voltammetry studies and characterization of complex formation by UV-spectrometry. High W content and current efficiency could be realized by using electrolytes containing all of the three complexing agents. The results show that small amounts of glycine in a citrate-triethanolamine based electrolyte positively influences both the mass-transfer and the deposition potential.     

Influence of grain size in the near-micrometre regime on the deformation microstructure in aluminium

The effect of grain size on deformation microstructure formation in the near-micrometre grain size regime has been studied using samples of aluminium prepared using a spark plasma sintering technique. Samples in a fully recrystallized grain condition with average grain sizes ranging from 5.2 to 0.8 μm have been prepared using this technique. Examination in the transmission electron microscope of these samples after compression at room temperature to approximately 20% reduction reveals that grains larger than 7 μm are subdivided by cell block boundaries similar to those observed in coarse-grained samples, with a similar dependency on the crystallographic orientation of the grains. With decreasing grain size down to approx. 1 μm there is a gradual transition from cell block structures to cell structures. At even smaller grain sizes of down to approx. 0.5 μm the dominant features are dislocation bundles and random dislocations, although at a larger compressive strain of 30% dislocation rotation boundaries may also be found in the interior of grains of this size. A standard 〈1 1 0〉 fibre texture is found for all grain sizes, with a decreasing sharpness with decreasing grain size. The structural transitions with decreasing grain size are discussed based on the general principles of grain subdivision by deformation-induced dislocation boundaries and of low-energy dislocation structures as applied to the not hitherto explored near-micrometre grain size regime.     

Model checking for E-business control and assurance

Model checking is a promising technique for the verification of complex software systems. As the use of the Internet for conducting e-business extends the reach of many organizations, well-designed software becomes the foundation of reliable implementation of e-business processes. These distributed, electronic methods of conducting transactions place reliance on the control structures embedded in the transaction processes. Deficiencies in control structures of processes that support e-business can lead to loss of physical assets, digital assets, money, and consumer confidence. Yet, assessing the reliability of e-business processes is complex and time-consuming. This paper explicates how model-checking technology can aid in the design and assurance of e-business processes in complex digital environments. Specifically, we demonstrate how model checking can be used to verify e-business requirements concerning money atomicity, goods atomicity, valid receipt, and communication-link failure. These requirements are fundamental to many e-business applications. Model checking can be used to test a broad range of systems requirements-not only for system designers, but also for auditors and security specialists. Systems that are examined by auditors need to have adequate controls built in prior to implementation and will need adequate auditing after implementation to ensure that none of the processes have been corrupted. Model checkers may also provide value in examining the processes of highly integrated applications as found in enterprise resource planning systems.     

Micro structural analysis – An essential tool for diagnosis of concrete deterioration and choice of repair strategy

The paper is a review of a 25 years long record with analyses of thin sections and fluorescein impregnated sections (slabs) as tools to characterize initial concrete quality and causes of deterioration of concrete of various qualities and suffering from various deleterious actions – primarily in Denmark. The paper demonstrates the world of opportunities and the advantages of the applied techniques by various examples from practice, covering early frost action, freeze–thaw attack, alkali‐silica reactions, acidic attack, exposure to fire, quality control of repairs, and defects in the construction phase, etc. Also the limitations of the methods are discussed.     

Solving a real-life, large-scale energy management problem

This paper introduces a three-phase hybrid heuristic for a large-scale energy management and maintenance scheduling problem. The problem is to schedule maintenance periods and refueling amounts for nuclear power plants with a time horizon of up to five years, and handling a number of scenarios for future demand and prices. The goal is to minimize the expected total production cost. The first phase of the heuristic solves a constraint programming model of a simplified version of the problem, the second performs a local search, and the third handles overproduction in a greedy fashion. This work was initiated in the context of the ROADEF/EURO Challenge 2010. In the concluding phase of the competition, our team ranked second in the junior category and sixth overall. After correcting a small implementation bug in the program that was submitted for final evaluation, our solver ranks first in the overall results from the competition.