A Cloud Tracking Tool for Planetary Orbiter Images

During their operations phase, planetary missions continuously produce a wealth of data that tend to overwhelm research teams. Spectral imagers, in particular, produce data cubes in which the wavelength dimension adds to the two spatial dimensions. Tracking of atmospheric features in order to derive winds and the construction of global maps from such large data volumes becomes particularly time-consuming if done manually. This highlights the importance of automated procedures capable of analysing sequences of data cubes with minimal user interaction. A tool for cloud tracking for such a purpose is currently under development in our group. In its present state it is based on synthetic images and uses a simple method of multiple matrix comparison to derive wind components. Deriving winds from data from the Venus Express - Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) instrument will be a possible application. We shall present an overview of the method, its benchmarking and the current status and future development of the project

Localization transition in one dimension using Wegner flow equations

The flow equation method was proposed by Wegner as a technique for studying interacting systems in one dimension. Here, we apply this method to a disordered one dimensional model with power-law decaying hoppings. This model presents a transition as function of the decaying exponent $\alpha$. We derive the flow equations, and the evolution of single-particle operators. The flow equation reveals the delocalized nature of the states for $\alpha<1/2$. Additionally, in the regime, $\alpha>1/2$, we present a strong-bond renormalization group structure based on iterating the three-site clusters, where we solve the flow equations perturbatively. This renormalization group approach allows us to probe the critical point $\left(\alpha=1\right)$. This method correctly reproduces the critical level-spacing statistics, and the fractal dimensionality of the eigenfunctions.Comment: 19 pages, 16 figure

DEoptim: An R Package for Global Optimization by Differential Evolution

This article describes the R package DEoptim, which implements the differential evolution algorithm for global optimization of a real-valued function of a real-valued parameter vector. The implementation of differential evolution in DEoptim interfaces with C code for efficiency. The utility of the package is illustrated by case studies in fitting a Parratt model for X-ray reflectometry data and a Markov-switching generalized autoregressive conditional heteroskedasticity model for the returns of the Swiss Market Index.

Weber blockade theory of magnetoresistance oscillations in superconducting strips

Recent experiments on the conductance of thin, narrow superconducting strips have found periodic fluctuations, as a function of the perpendicular magnetic field, with a period corresponding to approximately two flux quanta per strip area [A. Johansson et al., Phys. Rev. Lett. {\bf 95}, 116805 (2005)]. We argue that the low-energy degrees of freedom responsible for dissipation correspond to vortex motion. Using vortex/charge duality, we show that the superconducting strip behaves as the dual of a quantum dot, with the vortices, magnetic field, and bias current respectively playing the roles of the electrons, gate voltage and source-drain voltage. In the bias-current vs. magnetic-field plane, the strip conductance displays what we term `Weber blockade' diamonds, with vortex conductance maxima (i.e., electrical resistance maxima) that, at small bias-currents, correspond to the fields at which strip states of $N$ and $N+1$ vortices have equal energy.Comment: 4+a bit pages, 3 figures, 1 tabl

DEoptim: An R Package for Global Optimization by Differential Evolution

This article describes the R package DEoptim, which implements the differential evolution algorithm for global optimization of a real-valued function of a real-valued parameter vector. The implementation of differential evolution in DEoptim interfaces with C code for efficiency. The utility of the package is illustrated by case studies in fitting a Parratt model for X-ray reflectometry data and a Markov-switching generalized autoregressive conditional heteroskedasticity model for the returns of the Swiss Market Index

The planetary nebula IC 4776 and its post-common-envelope binary central star

We present a detailed analysis of IC 4776, a planetary nebula displaying a morphology believed to be typical of central star binarity. The nebula is shown to comprise a compact hourglass-shaped central region and a pair of precessing jet-like structures. Time-resolved spectroscopy of its central star reveals periodic radial velocity variability consistent with a binary system. While the data are insufficient to accurately determine the parameters of the binary, the most likely solutions indicate that the secondary is probably a low-mass main sequence star. An empirical analysis of the chemical abundances in IC 4776 indicates that the common-envelope phase may have cut short the AGB evolution of the progenitor. Abundances calculated from recombination lines are found to be discrepant by a factor of approximately two relative to those calculated using collisionally excited lines, suggesting a possible correlation between low abundance discrepancy factors and intermediate-period post-common-envelope central stars and/or Wolf-Rayet central stars. The detection of a radial velocity variability associated with binarity in the central star of IC 4776 may be indicative of a significant population of (intermediate-period) post-common-envelope binary central stars which would be undetected by classic photometric monitoring techniques.Comment: Accepted for publication in MNRA

Uveal Hematocysts in a Golden Retriever Dog

Case Description. A 7-year-old neutered male golden retriever presented for examination 1 month following the observation of multifocal round brown structures in the anterior chamber of the left eye and similar, but blood-filled, structures in the right eye. Clinical Findings. Ophthalmic examination revealed bilateral iris hyperpigmentation, pigment deposition on the anterior lens capsule, and uveal cysts. The uveal cysts in the right eye were partially blood filled. Clinical findings were consistent with pigmentary uveitis of golden retrievers. Treatment and Outcome. The patient has been maintained on topical anti-inflammatories and no progression of the disease has occurred in eight months. Clinical Relevance. This paper emphasizes the importance of recognizing the unique clinical signs of pigmentary uveitis and highlights uveal hematocysts, a rare manifestation of the disease