Polarization singularities from unfolding an optical vortex through a birefringent crystal

Optical vortices (nodal lines and phase singularities) are the generic singularities of scalar optics but are unstable in vector optics. We investigate experimentally and theoretically the unfolding of a uniformly polarized optical vortex beam on propagation through a birefringent crystal and characterize the output field in terms of polarization singularities (C lines and points of circular polarization; L surfaces and lines of linear polarization). The field is described both in the 2-dimensional transverse plane, and in three dimensions, where the third is abstract, representing an optical path length propagated through the crystal. Many phenomena of singular optics, such as topological charge conservation and singularity reconnections, occur naturally in the description

Polarization singularities from unfolding an optical vortex through a birefringent crystal

Optical vortices (nodal lines and phase singularities) are the generic singularities of scalar optics but are unstable in vector optics. We investigate experimentally and theoretically the unfolding of a uniformly polarized optical vortex beam on propagation through a birefringent crystal and characterize the output field in terms of polarization singularities (C lines and points of circular polarization; L surfaces and lines of linear polarization). The field is described both in the 2-dimensional transverse plane, and in three dimensions, where the third is abstract, representing an optical path length propagated through the crystal. Many phenomena of singular optics, such as topological charge conservation and singularity reconnections, occur naturally in the description

The long-term outcomes of systemic vasculitis.

Patients with generalized ANCA-associated small vessel vasculitis (AAV) have a very poor outcome if the ANCA-associated vasculitis is not diagnosed, evaluated and treated properly. The introduction of treatment with immunosuppressive therapy has improved patient survival dramatically but with considerable side effects. Besides, almost 50% of surviving patients experience a relapse of vasculitis. Since 1995, the European Vasculitis Society (EUVAS) has designed and conducted several clinical trials on patients with AAV independently of pharmaceutical companies. The studies included patients with newly diagnosed AAV and were stratified according to renal function and generalized versus more localized forms. As the immediate patient survival has improved, the longer term outcome has become more important. There are several reports on outcome of patients with ANCA-associated vasculitis, but the patient groups were heterogeneous regarding diagnosis as well as treatment and follow-up. Therefore, EUVAS decided to further evaluate the effect and possible adverse events of the original randomized trials. This review presents an overview on long-term follow-up of patients with ANCA-associated vasculitis, with focus on relapse rate, patient and renal survival and development of cardiovascular disease and malignancy

Stochastic geometry and topology of non-Gaussian fields

Gaussian random fields pervade all areas of science. However, it is often the departures from Gaussianity that carry the crucial signature of the nonlinear mechanisms at the heart of diverse phenomena, ranging from structure formation in condensed matter and cosmology to biomedical imaging. The standard test of non-Gaussianity is to measure higher order correlation functions. In the present work, we take a different route. We show how geometric and topological properties of Gaussian fields, such as the statistics of extrema, are modified by the presence of a non-Gaussian perturbation. The resulting discrepancies give an independent way to detect and quantify non-Gaussianities. In our treatment, we consider both local and nonlocal mechanisms that generate non-Gaussian fields, both statically and dynamically through nonlinear diffusion.Comment: 8 pages, 4 figure

Polarization singularity anisotropy: determining monstardom

C points, that is isolated points of circular polarization in transverse fields of varying polarization, are classified morphologically into three distinct types, known as lemons, stars and monstars. These morphologies are interpreted here according to two natural parameters associated with the singularity, namely the anisotropy of the C point, and the polarization azimuth on the anisotropy axis. In addition to providing insight into singularity morphology, this observation applies to the densities of the various morphologies in isotropic random polarization speckle fields.Comment: 3 pages, 2 figures, Optics Letters styl

Critical Viscosity Exponent for Fluids: What Happend to the Higher Loops

We arrange the loopwise perturbation theory for the critical viscosity exponent $x_{\eta}$, which happens to be very small, as a power series in $x_{\eta}$ itself and argue that the effect of loops beyond two is negligible. We claim that the critical viscosity exponent should be very closely approximated by $x_{\eta}=\frac{8}{15 \pi^2}(1+\frac{8}{3 \pi^2})\simeq 0.0685$.Comment: 9 pages and 3 figure

Development of a Detailed Microphysics Cirrus Model Tracking Aerosol Particles' Histories for Interpretation of the Recent INCA Campaign

International audienceCirrus clouds play an important role in the earth's energy balance. To quantify their impact, information is needed on their microstructure and more precisely on the number and size of the ice crystals. With the anthropogenic activity, more and more aerosol particles and water vapor are released even at the altitude where cirrus clouds are formed. Cirrus clouds formed in a polluted air mass may have different microphysical properties and, therefore, a different impact on the climate system via the changed radiative properties compared to background cirrus clouds. To study this aspect, the European project called the Interhemispheric Differences in Cirrus Properties due to Anthropogenic Emissions (INCA) measured the microphysical properties of cirrus clouds together with the physical and chemicals properties of aerosol particles in clean air (at Punta Arenas, Chile) and polluted air (at Prestwick, Scotland). The goal of the present work was to develop a detailed microphysics model for cirrus clouds for the interpretation and the generalization of the INCA observations. This model considers moist aerosol particles through the Externally Mixed (EXMIX) model, so that the chemical composition of solution droplets can be followed. Ice crystal formation is described through homogeneous or heterogeneous nucleation. The crystals then grow by deposition. With this model, the interactions between the microphysical processes, simulated ice crystal concentrations, and dimensional distributions of the INCA observations were studied, and explanations were provided for the observed differences between background and polluted cirrus clouds

The politics of climate finance in Brazil. How actors and their ideas shape institutions: the case of the Amazon Fund and the ABC Programme for Low-Carbon Agriculture.

The international climate finance landscape is characterized by complexity and fragmentation (Weikmans and Roberts 2019). Navigating institutions and donor requirements is challenging for developing countries. Establishing national climate funds can be a way to meet these challenges, ensuring the targeted use of funds and strengthening ownership. This thesis examines the establishment of two national climate funds in Brazil during the administration of the Workers’ Party (2003 – 2016), the Low Carbon Agriculture Programme and the Amazon Fund. National climate funds are embedded in political and social traditions of their country and the economic and ecological context. At the same time, it is these changes and conversions that are interesting and give rise to new institutions. By asking how actors employ ideas to influence political processes and the design of climate finance institutions in Brazil the study assesses the influence of actor constellations and discourses within their political and discursive context. A drastic shift in climate policy enabled by discursive changes promoted by a coalition of government and civil society actors opened a window for political change and the establishment of new institutions. This shift allowed the Brazilian government to see the inefficiencies and unproductive aspect of deforestation (Carvalho 2012). Due to this process of sense- and meaning-making Brazil was able to reposition itself in domestic and international climate politics and gain international trust and financial support for its fight against deforestation. This development resulted in the creation of the world’s biggest national REDD+ fund and a large-scale low carbon agriculture subsidy programme. The two climate funds analysed in this thesis were created in the same period but show remarkable differences due to the actor constellations and discourses they are based upon. The study provides evidence of the power of ideas when strategically applied by actor constellations and aided by scientific knowledge

Critical light scattering in liquids

We compare theoretical results for the characteristic frequency of the Rayleigh peak calculated in one-loop order within the field theoretical method of the renormalization group theory with experiments and other theoretical results. Our expressions describe the non-asymptotic crossover in temperature, density and wave vector. In addition we discuss the frequency dependent shear viscosity evaluated within the same model and compare our theoretical results with recent experiments in microgravity.Comment: 17 pages, 12 figure