The Raman spectra of the three varieties of hydrated calcium carbonate, monohydrate, hexahydrate and 'amorphous,' are reported for the first time and discussed according to the already known crystal structures. The transformation by dehydration of these hydrated phases into the usual anhydrous forms was followed by in situ micro-Raman spectroscopy. It is shown that the dehydration of the hexahydrate proceeds through the formation of the 'amorphous' phase. The latter is better described as microcrystalline monohydrate.

The aim of this study was to estimate the incidence of COVID-19 disease in the French national population of dialysis patients, their course of illness and to identify the risk factors associated with mortality. Our study included all patients on dialysis recorded in the French REIN Registry in April 2020. Clinical characteristics at last follow-up and the evolution of COVID-19 illness severity over time were recorded for diagnosed cases (either suspicious clinical symptoms, characteristic signs on the chest scan or a positive reverse transcription polymerase chain reaction) for SARS-CoV-2. A total of 1,621 infected patients were reported on the REIN registry from March 16th, 2020 to May 4th, 2020. Of these, 344 died. The prevalence of COVID-19 patients varied from less than 1% to 10% between regions. The probability of being a case was higher in males, patients with diabetes, those in need of assistance for transfer or treated at a self-care unit. Dialysis at home was associated with a lower probability of being infected as was being a smoker, a former smoker, having an active malignancy, or peripheral vascular disease. Mortality in diagnosed cases (21%) was associated with the same causes as in the general population. Higher age, hypoalbuminemia and the presence of an ischemic heart disease were statistically independently associated with a higher risk of death. Being treated at a selfcare unit was associated with a lower risk. Thus, our study showed a relatively low frequency of COVID-19 among dialysis patients contrary to what might have been assumed.

Electrochemical noise (EN) measurements have been carried out on several corroding systems, utilizing the technique of simultaneous recording of current and voltage fluctuations, and calculating the frequency dependent spectral noise impedance R,(f) as the square root of the ratio of the power spectral densities (PSD) of the voltage to current noise. The results are compared with the theoretical predictions stemming from an analysis of the technique, which is presented in the preceding paper.' It is shown that, over a quite large range of conditions, coincides with the impedance modulus of the electrodes under study. From the relationship between R,,, and the noise resistance R, which is usually obtained calculating the ratio of the standard deviations of the voltage and current fluctuations, it is shown that the latter quantity can be equal to the zero frequency limit of the impedance only if certain conditions are satisfied.