Backpropagation Imaging in Nonlinear Harmonic Holography in the Presence of Measurement and Medium Noises

In this paper, the detection of a small reflector in a randomly heterogenous medium using second-harmonic generation is investigated. The medium is illuminated by a time-harmonic plane wave at frequency omega. It is assumed that the reflector has a non-zero second-order nonlinear susceptibility, and thus emits a wave at frequency two omega in addition to the fundamental frequency linear scattering. It is shown how the fundamental frequency signal and the second-harmonic signal propagate in the medium. A statistical study of the images obtained by migrating the boundary data is performed. It is proved that the second-harmonic image is more stable with respect to medium noise than the one obtained with the fundamental signal. Moreover, the signal-to-noise ratio for the second-harmonic image does not depend neither on the second-order susceptibility tensor nor on the volume of the particle.Comment: 36 pages, 18 figure

Morphological Evolution Is Accelerated among Island Mammals

Dramatic evolutionary changes occur in species isolated on islands, but it is not known if the rate of evolution is accelerated on islands relative to the mainland. Based on an extensive review of the literature, I used the fossil record combined with data from living species to test the hypothesis of an accelerated morphological evolution among island mammals. I demonstrate that rates of morphological evolution are significantly greater—up to a factor of 3.1—for islands than for mainland mammal populations. The tendency for faster evolution on islands holds over relatively short time scales—from a few decades up to several thousands of years—but not over larger ones—up to 12 million y. These analyses form the first empirical test of the long held supposition of accelerated evolution among island mammals. Moreover, this result shows that mammal species have the intrinsic capacity to evolve faster when confronted with a rapid change in their environment. This finding is relevant to our understanding of species' responses to isolation and destruction of natural habitats within the current context of rapid climate warming

Financial Fair Play in European football

This thesis deals with the matter of competitive balance in European club football. Its starting point is UEFA’s new set of regulations known as Financial Fair Play. These new rules officially started to be active for the season 2013-2014. The ground rule for FFP as I will call it further on, is the so-called “break-even” criterion, and cancels the possibility for clubs to make losses at the end of each season. This new regulation is important since it cancels the possibility for so called “sugar-daddy” club owners to make money injections into the club as a mean to buy players and pay high wages. This should impact well-known clubs such as Manchester City or Paris Saint-Germain for example, at least theoretically. The purpose of this study is to analyze whether or not these regulations will have a real impact on the competitive balance within and between leagues, in terms of fairness of the competition means. I first consider the consequences for the competitive balance in the short-term to then analyze consequences in the medium-term. Since these regulations have only been active for a few months my study is presented in the form of a prediction and reflects the expected outcome. This outcome shows that FFP will indeed improve the competitive balance between clubs. Especially because clubs will compete with similar and fairer means after FFP is introduced. However, big clubs will still have an advantage on smaller clubs mainly because of a bigger market size. But the fact that FFP will force clubs towards better management incentives should benefit the smaller ones that already focused on ”healthy” and “smart” management before FFP came into force. In the end those two effects might compensate each other

A mathematical and numerical framework for ultrasonically-induced Lorentz force electrical impedance tomography

We provide a mathematical analysis and a numerical framework for Lorentz force electrical conductivity imaging. Ultrasonic vibration of a tissue in the presence of a static magnetic field induces an electrical current by the Lorentz force. This current can be detected by electrodes placed around the tissue; it is proportional to the velocity of the ultrasonic pulse, but depends nonlinearly on the conductivity distribution. The imaging problem is to reconstruct the conductivity distribution from measurements of the induced current. To solve this nonlinear inverse problem, we first make use of a virtual potential to relate explicitly the current measurements to the conductivity distribution and the velocity of the ultrasonic pulse. Then, by applying a Wiener filter to the measured data, we reduce the problem to imaging the conductivity from an internal electric current density. We first introduce an optimal control method for solving such a problem. A new direct reconstruction scheme involving a partial differential equation is then proposed based on viscosity-type regularization to a transport equation satisfied by the current density field. We prove that solving such an equation yields the true conductivity distribution as the regularization parameter approaches zero. We also test both schemes numerically in the presence of measurement noise, quantify their stability and resolution, and compare their performance

Modal expansion for plasmonic resonators in the time domain

We study the electromagnetic field scattered by a metallic nanoparticle with dispersive material parameters placed in a homogeneous medium in a low frequency regime. We use asymptotic analysis and spectral theory to diagonalise a singular integral operator, which allows us to write the field inside and outside the particle in the form of a complete and orthogonal modal expansion. We find the eigenvalues of the volume operator to be associated, via a non-linear relation, to the resonant frequencies of the problem. We prove that all resonances lie in a bounded region near the origin. Finally we use complex analysis to compute the Fourier transform of the scattered field and obtain its modal expansion in the time domain

How Context Shapes our Concerns: Investigating the Causal Effects of Social Identity Threat Concerns using the SITC Inventory”

The Social Identity Threat Concerns (SITC) Inventory measures people’s concerns about being devalued because of their important social identities (e.g., being stereotyped, disrespected, marginalized, etc.). So far, research examining the validity of the SITC Inventory has been correlational. The objective of the present study is to examine the causal effects of social identity and context on social identity threat concerns, as measured by the SITC Inventory. We Predicted that people exposed to threatening social contexts would report greater social identity threat concerns than people exposed to non-threatening social contexts. Participants (N=###) were placed in either a threatening or a non-threatening discussion group, based on their political or racial identity. Then social identity threat concerns were assessed. As Predicted, when people were placed in threatening (vs. non-threatening) contexts, they reported greater social identity threat concerns. Taken all together, these results further support the validity and utility of the SITC Inventory as a threat assessment tool