Geert Willems

An Efficient Dense and Scale-Invariant Spatio-Temporal Interest Point Detector

Over the years, several spatio-temporal interest point detectors have been proposed. While some detectors can only extract a sparse set of scale-invariant features, others allow for the detection of a larger amount of features at user-defined scales. This paper presents for the first time spatio-temporal interest points that are at the same time scale-invariant (both spatially and temporally) and densely cover the video content. Moreover, as opposed to earlier work, the features can be computed efficiently. Applying scale-space theory, we show that this can be achieved by using the determinant of the Hessian as the saliency measure. Computations are speeded-up further through the use of approximative box-filter operations on an integral video structure. A quantitative evaluation and experimental results on action recognition show the strengths of the proposed detector in terms of repeatability, accuracy and speed, in comparison with previously proposed detectors.

Hough transform and 3D SURF for robust three dimensional classification

Most methods for the recognition of shape classes from 3D datasets focus on classifying clean, often manually generated models. However, 3D shapes obtained through acquisition techniques such as Structure-from-Motion or LIDAR scanning are noisy, clutter and holes. In that case global shape features--still dominating the 3D shape class recognition literature--are less appropriate. Inspired by 2D methods, recently researchers have started to work with local features. In keeping with this strand, we propose a new robust 3D shape classification method. It contains two main contributions. First, we extend a robust 2D feature descriptor, SURF, to be used in the context of 3D shapes. Second, we show how 3D shape class recognition can be improved by probabilistic Hough transform based methods, already popular in 2D. Through our experiments on partial shape retrieval, we show the power of the proposed 3D features. Their combination with the Hough transform yields superior results for class recognition on standard datasets. The potential for the applicability of such a method in classifying 3D obtained from Structure-from-Motion methods is promising, as we show in some initial experiments.

Voltage shift and deformation in the hysteresis loop of Pb(Zr,Ti)O3 thin film by defects

Voltage shift and deformation in the hysteresis loop of Pb(Zr,Ti)O3 (PZT) capacitors have been studied by varying the annealing temperature after patterning the top sputter‐deposited Pt electrode using reactive ion etch (RIE) with Ar gas. It was observed that the hysteresis loop of the film was seriously deformed by both sputtering and RIE induced defects. Voltage shift and polarization suppression can be explained by the charge trapping at electrode interfaces and at defect levels in the film, respectively. Space charges trapped at defect levels in the film suppress polarization parallel to poling direction, however, enhance polarization opposite to the poling direction.

Electrical conductivity in ferroelectric thin films

Abstract The possible conduction processes in Pt-PZT-Pt capacitors are analysed, based on the electronic properties of PZT and of the Pt-PZT interface. PZT behaves as an insulator, resulting in carrier-blocking Pt-PZT contacts, except when mobile ionic defects can provide the space charge to prevent full depletion. The possibilities of hole and electron injection are discussed. The current-degradation regime, while being caused by ion motion, is shown to be interface- and not bulk-controlled.

Nucleation and orientation of sol-gel PZT-films on Pt electrodes

Abstract The nucleation and preferential orientation of Lead Zirconate-Titanate (PZT) films deposited by sol-gel spin-coating on Pt bottom electrodes is discussed. The crucial role of the Ti adhesion layer is highlighted. A qualitative crystallization model is presented which can explain the nucleation behavior of PZT-films with different Zr/Ti-ratios on different electrode structures as well as the preferential orientation of the PZT-film.

Spatio-temporal features for robust content-based video copy detection

n this paper, we present a new method for robust content-based video copy detection based on local spatio-temporal features. As we show by experimental validation, the use of local spatio-temporal features instead of purely spatial ones brings additional robustness and discriminativity. Efficient operation is ensured by using the new spatio-temporal features proposed in [20]. To cope with the high-dimensionality of the resulting descriptors, these features are incorporated in a disk-based index and query system based on p-stable locality sensitive hashing. The system is applied to the task of video footage reuse detection in news broadcasts. Results are reported on 88 hours of news broadcast data from the TRECVID2006 dataset.

Exemplar-based Action Recognition in Video

In this work, we present a method for action localization and recognition using an exemplar-based approach. It starts from local dense yet scale-invariant spatio-temporal features. The most discriminative visual words are selected and used to cast bounding box hypotheses, which are then verified and further grouped into the final detections. To the best of our knowledge, we are the first to extend the exemplar-based approach using local features into the spatio-temporal domain. This allows us to avoid the problems that typically plague sliding window-based approaches - in particular the exhaustive search over spatial coordinates, time, and spatial as well as temporal scales. We report state-ofthe-art results on challenging datasets, extracted from real movies, for both classification and localization.

Elucidation of the switching processes in tetragonal pzt by hysteresis loop and impedance analysis

Abstract The switching process in tetragonal PZT films is studied. The ferroelectric capacitors show rectangular P-E hystersis loops with very abrupt switching characteristics. Small signal impedance measurements as function of DC bias voltage reveal an abrupt drop of the parallel capacitance C near the switching field EC, coinciding with a sharp peak of the equivalent parallel conductance G, different from the more gradual variation of C and G with broad peaks near EC as typically observed in materials with MPB composition. This behavior is correlated to strong 180° switching in this tetragonal material. This is further corroborated by the effects of the film orientation and of electrical and stress poling.

Integration of CMOS-electronics and particle detector diodes in high-resistivity silicon-on-insulator wafers

A new approach to monolithic pixel detectors, based on silicon on insulator (SOI) wafers with high resistivity substrate, is being pursued by the CERN RD19 collaboration. The fabrication methods and the results of the electrical evaluation of the SOI-MOSFET devices and of the detector structures fabricated in the bulk are reported. The leakage current of the high-resistivity PIN-diodes is kept of the order of 5 to 10 nA/cm/sup 2/. The SOI preparation processes employed-SIMOX (separation by implantation of oxygen) and ZMR (zone melting recrystallization)-produce working electronic circuits, and appear to be compatible with the fabrication of detectors of suitable quality. >

Influence of Zr/Ti ratios on the deformation in the hysteresis loop of Pb(Zr,Ti)O3 thin film capacitors

Electric field shift and deformation in the polarization-electric field characteristics of Pb(Zr,Ti)O3 (PZT) thin film capacitors with various Zr/Ti ratios have been studied as a function of the annealing temperature after patterning the top sputter-deposited Pt electrode using reactive ion etch with Ar gas. A large field shift and a constriction in the hysteresis loops are observed, particularly in low Zr/Ti PZT films annealed below 400 °C. A strong blocking layer effect in unannealed capacitor is found to be related to the internal field caused by trapped charges near electrodes. As the Zr/Ti ratio decreases, the field shift increases and the annealing temperature at which the internal field disappears also increases.