Revisiting Complex Moments For 2D Shape Representation and Image Normalization

When comparing 2D shapes, a key issue is their normalization. Translation and scale are easily taken care of by removing the mean and normalizing the energy. However, defining and computing the orientation of a 2D shape is not so simple. In fact, although for elongated shapes the principal axis can be used to define one of two possible orientations, there is no such tool for general shapes. As we show in the paper, previous approaches fail to compute the orientation of even noiseless observations of simple shapes. We address this problem. In the paper, we show how to uniquely define the orientation of an arbitrary 2D shape, in terms of what we call its Principal Moments. We show that a small subset of these moments suffice to represent the underlying 2D shape and propose a new method to efficiently compute the shape orientation: Principal Moment Analysis. Finally, we discuss how this method can further be applied to normalize grey-level images. Besides the theoretical proof of correctness, we describe experiments demonstrating robustness to noise and illustrating the method with real images.Comment: 69 pages, 20 figure

Credit where credit is due: an approach to education returns based on Shapley values

We propose the use of methods based on the Shapley value to assess the fact that private returns to lower levels of educational attainment should be credited with part of the returns from higher attainment levels, since achieving primary education is a necessary condition to enter secondary and tertiary educational levels. We apply the proposed adjustment to a global dataset of private returns to different educational attainment levels and find that the corrected returns to education imply a large shift of returns from tertiary to primary schooling in countries at all income levels

Heterogeneous immunological landscapes and medieval plague : an invitation to a new dialogue between historians and immunologists.

Efforts to understand the differential mortality caused by plague must account for many factors, including human immune responses. In this essay we are particularly interested in those people who were exposed to the Yersinia pestis pathogen during the Black Death, but who had differing fates—survival or death—that could depend on which individuals (once infected) were able to mount an appropriate immune response as a result of biological, environmental, and social factors. The proposed model suggests that historians of the medieval world could make a significant contribution to the study of human health, and especially the role of human immunology in past environments and societies, by helping to reconstruct these conditions

Windows through the Dusty Disks Surrounding the Youngest Low Mass Protostellar Objects

The formation and evolution of young low mass stars are characterized by important processes of mass loss and accretion ocurring in the innermost regions of their placentary circumstellar disks. Because of the large obscuration of these disks at optical and infrared wavelengths in the early protostellar stages (Class 0 Sources), they were previously detected only at radio wavelengths using interferometric techniques. We have detected with the Infrared Space Observatory (ISO) the mid-infrared emission associated with the Class 0 protostar VLA1 in the HH1-2 region located in the Orion nebula. The emission arises in the three wavelength windows at 5.3, 6.6 and 7.5 micras where the absorption due to ices and silicates has a local minimum that exposes the central parts of the youngest protostellar systems to mid-infrared investigations. The mid-infrared emission arises from a central source with 4 AU diameter at an averaged temperature of 700 K, deeply embedded in a dense region with a visual extinction of Av=80-100mag.Comment: The article is here and on pres

Continuous spectra in high-harmonic generation driven by multicycle laser pulses

We present observations of the emission of XUV continua in the 20-37 eV region by high harmonic generation (HHG) with $4$-$7\ \mathrm{fs}$ pulses focused onto a Kr gas jet. The underlying mechanism relies on coherent control of the relative delays and phases between individually generated attosecond pulse, achievable by adjusting the chirp of the driving pulses and the interaction geometry. Under adequate negative chirp and phase matching conditions, the resulting interpulse interference yields a continuum XUV spectrum, which is due to both microscopic and macroscopic (propagation) contributions. This technique opens the route for modifying the phase of individual attosecond pulses and for the coherent synthesis of XUV continua from multicycle driving laser pulses without the need of an isolated attosecond burst.Comment: 14 pages, 5 figures. Submitted to Physical Review

High magnification crack-tip field characterisation under biaxial conditions

This work presents a novel methodology for characterising fatigue cracks under biaxial conditions.The methodology uses high magnification Digital Image Correlation (DIC) technique for measuringdisplacement and strain crack-tip fields. By applying micro-speckle pattern on the metal surface it is possible toachieve high magnification for DIC technique. The speckles were created by electro-spray technique. Thevalidity of this novel technique is demonstrated by direct comparison with standard extensometermeasurements, under tension-compression and torsion conditions. In order to image the correct region, thenotch effect on the fatigue life was also evaluated