High-T c superconducting magnetic bearings for rotation-based devices

Summary A Modified-Melt-Powder-Melt-Growth (MMPMG) technique has been developed for the preparation of melt-textured Y-Ba−Cu−O pellets. To test their performances, the samples were characterized with respect to their microstructure, pinning strength and interaction force with permanent magnets. A superconducting magnetic bearing was built and integrated in a levitating flywheel system for energy storage. Paper presented at the “VII Congresso SATT?, Torino, 4–7 October 1994. Under a Fondazione Confalonieri grant.     

The effect of nano-scale interaction forces on the premature pull-in of real-life Micro-Electro-Mechanical Systems

A new experimental device has been designed and produced with the purpose of investigating the possible effect of nano-scale interaction forces on the reliability issue related to pull-in of uncharged plates. This paper reports the outcomes of the experimental tests carried out on the aforementioned micro-structure, which presents the essential features of real-life MEMS and is produced using the same technology as standard commercial devices. The experiments show, with a high degree of repeatability, a premature failure of the structure, as a consequence of pull-in instability. The results of the tests are critically evaluated by comparison with theoretical predictions, in order to assess the role played by nano-scale interaction forces caused by, e.g., parasitic charging, contact and patch potentials, Casimir force.     

Computer modelling and analysis of the photodegradation effect in a-Si:H p-i-n solar cell

Using a previous model, which was developed to describe the light-induced creation of the defect density in the a-Si:H gap states, we present in this work a numerical modelling of the photodegradation effect in the a-Si:H p-i-n solar cell under continuous illumination. We first considered the simple case of a monochromatic light beam with a wavelength λ between 530-540 nm non uniformly absorbed, then the global standard solar spectrum (AM 1.5) illumination is taken into account. The photodegradation is analysed on the basis of the resulting changes in the free carrier's densities, recombination rate, band structure, electrical potential and field, space charge, and current densities. Changes in the cell's external parameters: the open circuit voltage V_oc, the short circuit current density J_sc, the fill factor FF and the maximum power density P_max are also presented.     

Automatic construction of multiple-object three-dimensional statistical shape models: application to cardiac modeling

A novel method is introduced for the generation of landmarks for three-dimensional (3-D) shapes and the construction of the corresponding 3-D statistical shape models. Automatic landmarking of a set of manual segmentations from a class of shapes is achieved by 1) construction of an atlas of the class, 2) automatic extraction of the landmarks from the atlas, and 3) subsequent propagation of these landmarks to each example shape via a volumetric nonrigid registration technique using multiresolution B-spline deformations. This approach presents some advantages over previously published methods: it can treat multiple-part structures and requires less restrictive assumptions on the structure's topology. In this paper, we address the problem of building a 3-D statistical shape model of the left and right ventricle of the heart from 3-D magnetic resonance images. The average accuracy in landmark propagation is shown to be below 2.2 mm. This application demonstrates the robustness and accuracy of the method in the presence of large shape variability and multiple objects.     

A registration-based approach to quantify flow-mediated dilation (FMD) of the brachial artery in ultrasound image sequences

Flow-mediated dilation (FMD) offers a mechanism to characterize endothelial function and, therefore, may play a role in the diagnosis of cardiovascular diseases. Computerized analysis techniques are very desirable to give accuracy and objectivity to the measurements. Virtually all methods proposed up to now to measure FMD rely on accurate edge detection of the arterial wall, and they are not always robust in the presence of poor image quality or image artifacts. A novel method for automatic dilation assessment based on a global image analysis strategy is presented. We model interframe arterial dilation as a superposition of a rigid motion and a scaling factor perpendicular to the artery. Rigid motion can be interpreted as a global compensation for patient and probe movements, an aspect that has not been sufficiently studied before. The scaling factor explains arterial dilation. The ultrasound sequence is analyzed in two phases using image registration to recover both transformation models. Temporal continuity in the registration parameters along the sequence is enforced with a Kalman filter since the dilation process is known to be a gradual physiological phenomenon. Comparing automated and gold standard measurements (average of manual measurements) we found a negligible bias (0.05%FMD) and a small standard deviation (SD) of the differences (1.05%FMD). These values are comparable with those obtained from manual measurements (bias = 0.23%FMD, SD(intra-obs) = 1.13%FMD, SD(inter-obs) 1.20%FMD). The proposed method offers also better reproducibility (CV = 0.40%) than the manual measurements (CV = 1.04%).     

Backbone curves,Neimark-Sacker boundaries and appearance of quasi-periodicity in nonlinear oscillators: application to 1:2 internal resonance and frequency combs in MEMS

Meccanica - Quasi-periodic solutions can arise in assemblies of nonlinear oscillators as a consequence of Neimark-Sacker bifurcations. In this work, the appearance of Neimark-Sacker bifurcations is...     

Influence of a presintering treatment on melt-textured Y−Ba−Cu−O growth

Summary The influence of a presintering treatment on Y-Ba-Cu-O prepared by a modified MPMG process was investigated. The sinterization, reducing the material porosity, was found to enhance the homogeneity of the Y₂BaCuO₅ (Y-211) particles distribution during the partial melting at 1100°C. As a consequence, the melttextured YBa₂Cu₃O_7−x (Y-123) grows more uniformly producing oriented domain up to 3cm in size. Microstructural and diffractometrical analyses were performed on samples quenched at different stages during the thermal treatment. Paper presented at the ?VII Congresso SATT? Torino, 4–7 October 1994. Under a Fondazione Confalonieri grant.