Circular depolarization ratios of single water droplets and finite ice circular cylinders: a modeling study

Computations of the phase matrix elements for single water droplets and ice crystals in fixed orientations are presented to determine if circular depolarization δ<sub>C</sub> is more accurate than linear depolarization for phase discrimination. T-matrix simulations were performed to calculate right-handed and left-handed circular depolarization ratios δ<sub>+C</sub>, respectively δ<sub>−C</sub> and to compare them with linear ones. Ice crystals are assumed to have a circular cylindrical shape where their surface-equivalent diameters range up to 5 μm. The circular depolarization ratios of ice particles were generally higher than linear depolarization and depended mostly on the particle orientation as well as their sizes. The fraction of non-detectable ice crystals (δ<0.05) was smaller considering a circular polarized light source, reaching 4.5%. However, water droplets also depolarized light circularly for scattering angles smaller than 179° and size parameters smaller than 6 at side- and backscattering regions. Differentiation between ice crystals and water droplets might be difficult for experiments performed at backscattering angles which deviate from 180° unlike LIDAR applications. Instruments exploiting the difference in the <I>P</I><sub>44</sub>/<I>P</I><sub>11</sub> ratio at a scattering angle around 115° are significantly constrained in distinguishing between water and ice because small droplets with size parameters between 5 and 10 do cause very high circular depolarizations at this angle. If the absence of the liquid phase is confirmed, the use of circular depolarization in single particle detection is more sensitive and less affected by particle orientation

Serological diagnosis of Q fever endocarditis

The diagnosis of Q fever endocarditis cannot be made by bacterial cultures and necessitates serological identification of specific antibodies to Coxiella burnetii which stimulates mainly the production of anti-phase II antibodies during the acute diséase, but primarily anti-phase I antibodies in endocarditis. Indirect micro-immunofluorescence allows rapid detection of specific IgA, IgG and IgM. The results of serological analyses of 191 acute cases of Q fever were compared with those of 8 cases of Coxiella burnetii endocarditis. All sera were evaluated by complement fixation and microimmunofluorescence tests. The highest titre differences between primary Q fever and Q fever endocarditis were observed with anti-phase IIgA and IgG antibodies measured by microimmunofluorescence followed by anti-phase I antibodies measured by complement fixation tests. Anti-phase IIgG and IgM titres were consistently higher than anti-phase II titres in endocarditis. The reverse is true in acute Q fever. In addition, anti-phase I Ig A appeared to be diagnostic for Coxiella burnetii endocarditis. Accordingly we recommend the testing of these specific IgA, IgG, and IgM by microimmunofluorescence in cases of culture-negative endocarditis. These tests could also prove useful for following the development of Coxiella burnetii endocarditis in patients under treatmen

Formation kinetics of CrSi2 films on Si substrates with and without interposed Pd2Si layer

We have measured the kinetic rate of formation of CrSi2 using 2.0-MeV 4He + backscattering spectrometry. CrSi2 was formed on single-crystal 100- and 111-oriented Si and on Pd2Si grown on 100 Si. For both Si-Cr and Si-Pd2Si-Cr samples the rate of growth of CrSi2 is linear in time with an activation energy of 1.7±0.1 eV and a value of 0.7 Å/sec at 450°C. For all annealing temperatures, the growth becomes nonlinear at long annealing times. The nonlinearity is attributed to a contaminant, probably oxygen. On Pd2Si, CrSi2 starts to form at about 400°C, while on Si, CrSi2 formation is observed at 450°C and above. The difference in formation temperatures is due to contamination at the Si-Cr interface, quite probably a thin oxide layer. The growth rate of CrSi2 in the Si-Pd2Si-Cr samples is independent of the thickness of Pd2Si

Assessment of Power Swings in Hydropower Plants through High-Order Modelling and Eigenanalysis

Power plants are subject to introduce disturbances in the power grid, resulting from interactions with the dynamical behavior of the energy source subsystem. In the case of hydropower plants when used to compensate for variations of power generation and consumption, instabilities or undesirable disturbances may arise. They may be caused by phenomena such as part load vortex rope pulsations in the draft tube of Francis turbines. This may affect the dynamical behavior of the power plant and lead to troublesome interactions with the grid. This paper presents a case study of an existing hydropower plant that illustrates the effects of pressure pulsations due to vortex rope precession on the draft tube of Francis turbines. It also showcases possible solutions to the mitigation of the effects of this disturbing hydraulic phenomenon over the operation of the generators and electrical system. The investigated system is a 1 GW hydropower plant (4 x 250 MW units). The assessment of the power swings is performed through modal analysis combined with frequency-domain and time-domain simulations, which are then compared with on-site measurements

Fluorescent nanopigments: Quantitative assessment of their quantum yield

In the last few years, an intense research effort has focused on the synthesis of fluorescent nanopigments for functional inks, light harvesting, tagging, tracing, (bio)labeling, imaging, and lighting applications. Moreover, combined with dielectric matrices, these fluorescent nanoparticles may open the way to the realization of novel optophotonic devices. In particular, due to the large variety of available organic fluorescent dyes, their encapsulation into either an inorganic or an organic host is a very promising approach to synthesize a large palette of new fluorescent nanopigments. However, since the dye encapsulation may affect the fluorescence efficiency, measuring the quantum yield of fluorescent nanopigments is of paramount importance for the development of any connected application. In this article, we present a diffuse reflectance (DR) technique that enables the quantitative assessment of the quantum yield of fluorescent nanoparticles such as zeolite L nanocrystals and poly(methyl methacrylate) nanospheres both loaded with fluorescent perylene molecules. Our method is validated by measuring a well known fluorescence standard and by comparing the results obtained for a model zeolite nanopigment with those provided by an alternative DR technique. Reliable and reproducible quantum yield values are obtained for both low- and high-efficiency fluorescent nanoparticles. Our technique can thus enable systematic and quantitative studies that may yield an important insight in the mechanisms affecting the fluorescence efficiency of a large variety of nanopigments