Non-interacting electrons and the metal-insulator transition in 2D with correlated impurities

While standard scaling arguments show that a system of non-interacting electrons in two dimensions and in the presence of uncorrelated disorder is insulating, in this work we discuss the case where inter-impurity correlations are included. We find that for point-like impurities and an infinite inter-impurity correlation length a mobility edge exists in 2D even if the individual impurity potentials are random. In the uncorrelated system we recover the scaling results, while in the intermediate regime for length scales comparable to the correlation length, the system behaves like a metal but with increasing fluctuations, before strong localization eventually takes over for length scales much larger than the correlation length. In the intermediate regime, the relevant length scale is not given by the elastic scattering length but by the inter-impurity correlation length, with important consequences for high mobility systems.Comment: 4 page

Simulation model for cost estimation of integrated care concepts of heart failure patients

BACKGROUND: As a direct result of the population growing older the total number of chronic illnesses increases. The future expenditure for care of chronically ill patients is an ever-present challenge for the health care system. New solutions based on integrated care or the inclusion of telemedical systems in the treatment procedure can be essential for reducing the future financial burden. Therefore a detailed economic model was developed, which enables the comparison of health and cost outcomes for conventional medical care and different integrated care concepts in heart failure treatment. METHODS: F0r modelling, the discrete event technique was used. The model takes outpatient care as well as inpatient care into account to estimate the total occurring costs. It enables the treatment of patients by a physician, a specialist or a clinical ambulance for the simulation of the outpatient care. For inpatient care the model considers the total-costs of the hospitalization and rate of re-admission and furthermore the costs which occur because of special medical treatments or necessary stay at intensive care units. To rate the severity of symptoms patients can be classified using NYHA groups. To outline some of the potential model results, two scenarios have been simulated to compare both methods of care regarding overall costs. RESULTS: The developed simulation model allows comparing health and cost outcomes of different integrated care concepts for the treatment of heart failure patients. Additionally to the simulation of standard outpatient and inpatient care procedures in Austria the approach of a telemedical monitoring system for heart failure patients was implemented in this economic model. With the simulated scenarios it could be shown that under the given simulation parameters the telemedical system can lead to cost savings of up to 8% within the first three years. CONCLUSIONS: The developed model represents a comprehensive tool, which opens a wide field of possible simulation scenarios for the treatment of heart failure patients with special focus on overall cost estimations and reimbursement strategies. The simulated scenarios show that telemedical care has the potential of improved health outcomes and economic benefits

Analyzing WLCG File Transfer Errors Through Machine Learning: An Automatic Pipeline to Support Post-mortem Distributed Data Management

The increasingly growing scale of modern computing infrastructures solicits more ingenious and automatic solutions to their management. Our work focuses on file transfer failures within the Worldwide Large Hadron Collider Computing Grid and proposes a pipeline to support distributed data management operations by suggesting potential issues to investigate. Specifically, we adopt an unsupervised learning approach leveraging Natural Language Processing and Machine Learning tools to automatically parse error messages and group similar failures. The results are presented in the form of a summary table containing the most common textual patterns and time evolution charts. This approach has two main advantages. First, the joint elaboration of the error string and the transfer’s source/destination enables more informative and compact trouble- shooting, as opposed to inspecting each site and checking unique messages separately. As a by-product, this also reduces the number of errors to check by some orders of magnitude (from unique error strings to unique categories or patterns). Second, the time evolution plots allow operators to immediately filter out secondary issues (e.g. transient or in resolution) and focus on the most serious problems first (e.g. escalating failures). As a preliminary assessment, we compare our results with the Global Grid User Support ticketing system, showing that most of our suggestions are indeed real issues (direct association), while being able to cover 89% of reported incidents (inverse relationship)

Evolution of thickness dependent buckle geometries

Interfaces determine the overall reliability of multi-material components since they have to bear the distinct physical and chemical properties of the different adhering materials. In microelectronic applications, where several materials are implemented at small length scales, the main interest is on identifying the weakest interface, since it dictates the overall reliability of the implemented packages. The focus of the present study is set on a multi-layer stack composed of a rigid Si substrate with dielectric borophosphosilicate glass (BPSG) and a thin TiW film acting as adhesion promoter and diffusion barrier to the copper film, which are finally covered with 6 µm of polyimide (PI). Of main interest is a thorough characterization of the delamination of the various interfaces, which allow for a better understanding of the adhesion and the stress states present in the complex material stack. As a first step to study the interfacial behaviour, a peeling test was carried out to reveal the weakest interfaces resulting in three different delamination zones. Zone 1 delaminated at the BPSG-TiW interface and Zone 2 delaminated at the copper-PI interface (Fig 1a). An intermediate Zone 3 (Fig 1a) was identified, where straight buckles formed in the Cu-TiW layer parallel to the peeling direction at the TiW-BPSG interface (Fig 1b). Using these Zone 3 delaminations, the evolution of the buckle shape as a function of film thickness and layer stress was investigated using atomic force microscopy and X-ray diffraction. Of great interest is that with the Cu layer the buckles have a straight geometry (Fig 1b) indicating an isotropic stress. However, when the Cu layer is removed with chemical etching, the buckle morphology changes to a telephone cord geometry (Fig. 1c), maintaining the outer boundaries from the previous straight buckles shape. The change in geometry could be due to the change in film stress from isotropic to biaxial as well as the fact that the out of plane plasticity is constrained while the copper film is present. Both topics will be further discussed along with how the interfacial adhesion measurements may also be influenced by the change in buckle geometry. Please click Additional Files below to see the full abstract

Role of film microstructure on interface stability: in-situ and ex-situ investigations

Thin film adhesion is an important measure to quantify the stability of thin film – substrate interfaces. Film thickness, film microstructure, residual stresses as well as chemical reactions at the interface determine this value and it is often difficult to decouple each individual factor to study their influence on interface adhesion. In the following study the role of grain size on the interface stability was investigated for a model system at constant film thickness with comparable residual stresses. Therefore, 100 nm thin Cu films were sputtered on glass substrates. The film microstructure was tuned by a change of Argon pressure during deposition and by isothermal heat treatments post-deposition. To quantify the adhesion of the obtained Cu films, 500 nm thick, highly stressed Mo overlayers were deposited on the films leading to a spontaneous delamination at the Cu-glass interface in the shape of straight and telephone cord buckles. The model of Hutchinson & Suo could then be extended to a bilayer problem, allowing to determine adhesion for each Cu-glass system. The small grained films revealed improved adhesion compared to the large grained films. Detailed characterizations of the Cu film microstructures as well as the particular interfaces were conducted by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Finally, to study the plasticity mechanisms upon delamination, cyclic bending experiments were conducted in-situ in the TEM to observe the crack propagation towards the Cu-glass interface as a function of the film microstructure. Please click Additional Files below to see the full abstract

Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields

A self-consistent treatment of exchange and correlation interactions in a quantum wire (QW) subject to a strong perpendicular magnetic field is presented using a modified local-density approximation (MLDA). The influence of many-body interactions on the spin-splitting between the two lowest Landau levels (LLs) is calculated within the screened Hartree-Fock approximation (SHFA), for filling factor \nu=1, and the strong spatial dependence of the screening properties of electrons is taken into account. In comparison with the Hartree-Fock result, the spatial behavior of the occupied LL in a QW is strongly modified when correlations are included. Correlations caused by screening at the edges strongly suppress the exchange splitting and smoothen the energy dispersion at the edges. The theory accounts well for the experimentally observed strong suppression of the spin-splitting pertinent to the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures, submitted to Physical Review

Anomalous Rashba spin splitting in two-dimensional hole systems

It has long been assumed that the inversion asymmetry-induced Rashba spin splitting in two-dimensional (2D) systems at zero magnetic field is proportional to the electric field that characterizes the inversion asymmetry of the confining potential. Here we demonstrate, both theoretically and experimentally, that 2D heavy hole systems in accumulation layer-like single heterostructures show the opposite behavior, i.e., a decreasing, but nonzero electric field results in an increasing Rashba coefficient.Comment: 4 pages, 3 figure