Polarization Models for Rayleigh Scattering Planetary Atmospheres

We present Monte Carlo simulations for the polarization of light reflected from planetary atmospheres. We investigate dependencies of intensity and polarization on three main parameters: single scattering albedo, optical depth of a scattering layer, and albedo of a Lambert surface underneath. The main scattering process considered is Rayleigh scattering, but isotropic scattering and enhanced forward scattering on haze particles are also investigated. We discuss disk integrated results for all phase angles and radial profiles of the limb polarization at opposition. These results are useful to interpret available limb polarization measurements of solar system planets and to predict the polarization of extra-solar planets as a preparation for VLT/SPHERE. Most favorable for a detection are planets with an optically thick Rayleigh-scattering layer. The limb polarization of Uranus and Neptune is especially sensitive to the vertically stratified methane mixing ratio. From limb polarization measurements constraints on the polarization at large phase angles can be se

Frame Combination Techniques for Ultra High-Contrast Imaging

We summarize here an experimental frame combination pipeline we developed for ultra high-contrast imaging with systems like the upcoming VLT SPHERE instrument. The pipeline combines strategies from the Drizzle technique, the Spitzer IRACproc package, and homegrown codes, to combine image sets that may include a rotating field of view and arbitrary shifts between frames. The pipeline is meant to be robust at dealing with data that may contain non-ideal effects like sub-pixel pointing errors, missing data points, non-symmetrical noise sources, arbitrary geometric distortions, and rapidly changing point spread functions. We summarize in this document individual steps and strategies, as well as results from preliminary tests and simulations.Comment: 9 pages, 4 figures, SPIE conference pape

Reduction of polarimetric data using Mueller calculus applied to Nasmyth instruments

We present a method based on Mueller calculus to calibrate linear polarimetric observations. The key advantages of the proposed way of calibration are: (1) that it can be implemented in a data reduction pipeline, (2) that it is possible to do accurate polarimetry also for telescopes/instruments with polarimetric non-friendly architecture (e.g. Nasmyth instruments) and (3) that the proposed strategy is much less time consuming than standard calibration procedures. The telescope/instrument will polarimetrically be described by a train of Mueller matrices. The components of these matrices are dependent on wavelength, incident angle of the incoming light and surface properties.Comment: 2 figure

Epidemiology and impact of chronic bronchitis in chronic obstructive pulmonary disease

Research on the association between chronic bronchitis and chronic obstructive pulmonary disease (COPD) exacerbations has led to discordant results. Furthermore, the impact of chronic bronchitis on mortality in COPD subjects is unclear. Within the Rotterdam Study, a population-based cohort study of subjects aged >= 45 years, chronic bronchitis was defined as having a productive cough for >= 3 months per year for two consecutive years. Linear, logistic regression and Cox proportional hazard models were adjusted for age, sex and pack-years. Out of 972 included COPD subjects, 752 had no chronic phlegm production (CB-) and 220 had chronic phlegm production, of whom 172 met the definition of chronic bronchitis (CB+). CB+ subjects were older, more frequently current smokers and had more pack-years than CB-subjects. During a median 6.5 years of follow-up, CB+ subjects had greater decline in lung function (-38 mL.year(-1), 95% CI -61.7--14.6; p=0.024). CB+ subjects had an increased risk of frequent exacerbations (OR 4.0, 95% CI 2.7-5.9; p<0.001). In females, survival was significantly worse in CB+ subjects compared to CB-subjects. Regarding cause-specific mortality, CB+ subjects had an increased risk of respiratory mortality (hazard ratio 2.16, 95% CI 1.12-4.17; p=0.002). COPD subjects with chronic bronchitis have an increased risk of exacerbations and respiratory mortality compared to COPD subjects without chronic phlegm production

Decoherence in the cosmic background radiation

In this paper we analyze the possibility of detecting nontrivial quantum phenomena in observations of the temperature anisotropy of the cosmic background radiation (CBR), for example, if the Universe could be found in a coherent superposition of two states corresponding to different CBR temperatures. Such observations are sensitive to scalar primordial fluctuations but insensitive to tensor fluctuations, which are therefore converted into an environment for the former. Even for a free inflaton field minimally coupled to gravity, scalar-tensor interactions induce enough decoherence among histories of the scalar fluctuations as to render them classical under any realistic probe of their amplitudes.Comment: 15 pages, accepted to be published in Classical and Quantum Gravit

Epidemiology and impact of chronic bronchitis in chronic obstructive pulmonary disease

Research on the association between chronic bronchitis and chronic obstructive pulmonary disease (COPD) exacerbations has led to discordant results. Furthermore, the impact of chronic bronchitis on mortality in COPD subjects is unclear. Within the Rotterdam Study, a population-based cohort study of subjects aged ≥45 years, chronic bronchitis was defined as having a productive cough for ≥3 months per year for two consecutive years. Linear, logistic regression and Cox proportional hazard models were adjusted for age, sex and pack-years. Out of 972 included COPD subjects, 752 had no chronic phlegm production (CB-) and 220 had chronic phlegm production, of whom 172 met the definition of chronic bronchitis (CB+). CB+ subjects were older, more frequently current smokers and had more pack-years than CB- subjects. During a median 6.5 years of followup, CB+ subjects had greater decline in lung function (-38 mL·year-1, 95% CI -61.7 - -14.6; p=0.024). CB+ subjects had an increased risk of frequent exacerbations (OR 4.0, 95% CI 2.7-5.9; p<0.001). In females, survival was significantly worse in CB+ subjects compared to CB- subjects. Regarding cause-specific mortality, CB+ subjects had an increased risk of respiratory mortality (hazard ratio 2.16, 95% CI 1.12-4.17; p=0.002). COPD subjects with chronic bronchitis have an increased risk of exacerbations and respiratory mortality compared to COPD subjects without chronic phlegm production

On the Schwinger Model on Riemann Surfaces

In this paper, the massless Schwinger model or two dimensional quantum electrodynamics is exactly solved on a Riemann surface. The partition function and the generating functional of the correlation functions involving the fermionic currents are explicitly derived using a method of quantization valid for any abelian gauge field theory and explained in the recent references [F. Ferrari, {\it Class. Quantum Grav.} {\bf 10} (1993), 1065], [F. Ferrari, hep-th 9310024]. In this sense, the Schwinger model is one of the few examples of interacting and nontopological field theories that are possible to quantize on a Riemann surface. It is also shown here that the Schwinger model is equivalent to a nonlocal integrable model which represents a generalization of the Thirring model. Apart from the possible applications in string theory and integrable models, we hope that this result can be also useful in the study of quantum field theories in curved space-times.Comment: 22 pages, plain TeX + harvmac, Preprint MPI-Ph/93-71, LMU-TPW 93-2

Topologically Nontrivial Sectors of the Maxwell Field Theory on Algebraic Curves

In this paper the Maxwell field theory is considered on the $Z_n$ symmetric algebraic curves. As a first result, a large family of nondegenerate metrics is derived for general curves. This allows to treat many differential equations arising in quantum mechanics and field theory on Riemann surfaces as differential equations on the complex sphere. The examples of the scalar fields and of an electron immersed in a constant magnetic field will be briefly investigated. Finally, the case of the Maxwell equations on curves with $Z_n$ group of automorphisms is studied in details. These curves are particularly important because they cover the entire moduli space spanned by the Riemann surfaces of genus $g\le 2$. The solutions of these equations corresponding to nontrivial values of the first Chern class are explicitly constructed.Comment: 24 pages, latex file + 3 ps figure

The Benefits of Financial Statement Comparability

Investors, regulators, academics, and researchers all emphasize the importance of financial statement comparability. However, an empirical construct of comparability is typically not specified. In addition, little evidence exists on the benefits of comparability to users. This study attempts to fill these gaps by developing a measure of financial statement comparability. Empirically, this measure is positively related to analyst following and forecast accuracy, and negatively related to analysts’ dispersion in earnings forecasts. These results suggest that financial statement comparability lowers the cost of acquiring information, and increases the overall quantity and quality of information available to analysts about the firm