A local and global tour on MOMoT

Software and Systems Modeling - Many model transformation scenarios require flexible execution strategies as they should produce models with the highest possible quality. At the same time,...     

Multiple widths yield reliable finite differences [computer vision]

A finite difference edge finder in which the finite difference is computed at a range of widths, i.e. a range of distances between data points, is introduced. Wide operators report low-amplitude responses more reliably than narrow operators, so if wide operators are used to fill gaps in narrow operator responses, each operator can be restricted to report only statistically reliable responses without losing many real features. This sharply reduces the noise in the final output. Theoretical bounds on spurious responses in the finite difference outputs, given only weak assumptions about the signal and noise, are presented. The expected response of the edge finder to an ideal straight step edge is also analyzed. These performance measures are compared with those of a standard algorithm based on Gaussian smoothing and those of a second algorithm that also considers the spatial structure of noise. The algorithms prove equally good at suppressing noise, but are better able to detect faint or blurred features. These predictions are confirmed by empirical tests on real images     

The failure of composite tubes due to combined compression and torsion

The strength of unidirectional carbon-fibre epoxy laminates has been measured for combined compression and shear loading. Failure was by plastic microbuckling. The axial compressive strength decreased linearly to zero as the shear stress parallel to the fibres was increased from zero to the shear strength. These experimental results support the predictions of Budiansky and Fleck and suggest an average fibre misalignment angle of 2°–3°.     

Randomized multicenter comparison of conventional anticoagulation versus antiplatelet therapy in unplanned and elective coronary stenting. The full anticoagulation versus aspirin and ticlopidine (fantastic) study

BACKGROUND: Dual therapy with ticlopidine and aspirin has been shown to be as effective as or more effective than conventional anticoagulation in patients with an optimal result after implantation of intracoronary metallic stents. However, the safety and efficacy of antiplatelet therapy alone in an unselected population has not been evaluated. METHODS: Patients were randomized to conventional anticoagulation or to treatment with antiplatelet therapy alone. Indications for stenting were classified as elective (decided before the procedure) or unplanned (to salvage failed angioplasty or to optimize the results of balloon angioplasty). After stenting, patients received aspirin and either ticlopidine or conventional anticoagulation (heparin or oral anticoagulant). The primary end point was the occurrence of bleeding or peripheral vascular complications; secondary end points were cardiac events (death, infarction, or stent occlusion) and duration of hospitalization. RESULTS: In 13 centers, 236 patients were randomized to anticoagulation and 249 to antiplatelet therapy. Stenting was elective in 58% of patients and unplanned in 42%. Stent implantation was successfully achieved in 99% of patients. A primary end point occurred in 33 patients (13.5%) in the antiplatelet group and 48 patients (21%) in the anticoagulation group (odds ratio=0.6 [95% CI 0.36 to 0.98], P=0.03). Major cardiac-related events in electively stented patients were less common (odds ratio=0.23 [95% CI 0.05 to 0.91], P=0.01) in the antiplatelet group (3 of 123, 2.4%) than the anticoagulation group (11 of 111, 9.9%). Hospital stay was significantly shorter in the antiplatelet group (4.3+/-3.6 versus 6. 4+/-3.7 days, P=0.0001). CONCLUSIONS: Antiplatelet therapy after coronary stenting significantly reduced rates of bleeding and subacute stent occlusion compared with conventional anticoagulation.     

Processing and interactive editing of huge point clouds from 3D scanners

This paper describes a new out-of-core multi-resolution data structure for real-time visualization, interactive editing and externally efficient processing of large point clouds. We describe an editing system that makes use of the novel data structure to provide interactive editing and preprocessing tools for large scanner data sets. Using the new data structure, we provide a complete tool chain for 3D scanner data processing, from data preprocessing and filtering to manual touch-up and real-time visualization. In particular, we describe an out-of-core outlier removal and bilateral geometry filtering algorithm, a toolset for interactive selection, painting, transformation, and filtering of huge out-of-core point-cloud data sets and a real-time rendering algorithm, which all use the same data structure as storage backend. The interactive tools work in real-time for small model modifications. For large scale editing operations, we employ a two-resolution approach where editing is planned in real-time and executed in an externally efficient offline computation afterwards. We evaluate our implementation on example data sets of sizes up to 63 GB, demonstrating that the proposed technique can be used effectively in real-world applications.     

Cyclic Nanoindentation for Local High Cycle Fatigue Investigations: A Methodological Approach Accounting for Thermal Drift

Cyclic nanoindentation allows characterizing the influence of single phases and their interactions on fatigue mechanisms. Herein, a method for high cycle fatigue testing by nanoindentation is presented. By combining high- and low-frequency indentation modes, high cycle numbers are achieved while obtaining sufficient data points to reconstruct force–displacement hysteresis loops. A challenge is the stochastic course of thermal drift which is addressed by measuring drift rate in regular low-force holding segments. Drift rates are used to correct the displacement values, yielding reproducible cyclic deformation data as it is shown for two very different materials, a ductile metal and a brittle ceramic.     

Thermo‐responsive polymers for drag reduction in turbulent Taylor–Couette flow

The addition of a small amount of high molecular weight polymer to a solvent can substantially decrease friction losses by approximately 80%. This phenomenon known as drag reduction (DR) is used extensively in oil recovery during hydraulic fracturing and in many other applications to reduce the pumping costs. However, because of long chain length, these polymers get adsorbed on the surface of reservoir, diminishing the effectiveness of fracking. In the current study, a thermo‐responsive polymer, i.e., poly(N‐isopropylacrylamide) (PNIPAM) is investigated as a drag reducing agent (DRA), which collapses reversibly above 33 °C known as lower critical solution temperature (LCST), thereby preventing it from getting adsorbed beyond this temperature. Free radical polymerization was used to synthesize the PNIPAM and a Taylor–Couette (TC) setup with a rotating inner cylinder was utilized for measuring the DR. The effect of concentration, Reynolds number (Re), and temperature on DR were studied and a maximum of 50% DR was observed at 400 PPM concentration. PNIPAM demonstrated significant decrease in DR beyond LCST, validating its thermo‐responsive nature that could be beneficial for DR in oil recovery or in providing a control modality to DR technologies.DR versus temperature for PNIPAM solution (500 PPM) at Re = 100,000 demonstrating responsive behavior with temperature © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44191.     

Prediction of the dynamic response of composite sandwich beams under shock loading

Finite element calculations are reported for the dynamic shock response of fully clamped monolithic and sandwich beams, with elastic face sheets and a compressible elastic–plastic core. Predictions of the peak mid-span deflections and deflected shapes of the beams are compared with the previously reported measured response of end-clamped sandwich beams, made from face sheets of glass fibre reinforced vinyl ester and a core of PVC foam or balsa wood [1]. Good agreement is observed, and the maximum sustainable impulse is also predicted adequately upon assuming a tensile failure criterion for the face sheets. The finite element calculations can also be used to bound the response by considering the extremes of a fully intact core and a fully damaged core. It is concluded that the shock resistance of a composite sandwich beam is maximised by selecting a composite with fibres of high failure strain.     

Optical Properties of Doped Antiferromagnets

We investigate the consequences of an incommensurate magnetic order in doped La_2–x Sr _x CuO₄ using dynamical mean-field theory for the effective single-band model. The high-energy optical transitions are due to high-energy excitations across large Mott–Hubbard gap, while low-energy excitations involve a pseudogap induced by the local spin order. The latter lead to a strong drop in the scattering rate at low , in qualitative agreement with the experimental data.