RESUMO
Estimating the speed of sound for the dense vapor phase of D6 (dodecamethylcyclohexasiloxane, C12H36O6Si6) is particularly relevant to the study of nonideal compressible fluid dynamics (NICFD), the gas dynamics of fluids whose properties depart significantly from those related by the ideal gas model. If molecular complexity is sufficiently large, dense vapor flows may exhibit so-called nonclassical gasdynamic effects, and D6 is a candidate for experimental studies aimed at proving for the first time the existence of these exotic phenomena. More in general, speed of sound measurements in the dense vapor phase are important for NICFD applications: for example, complex organic compounds are employed as working fluids in organic Rankine cycle power plants and the correct prediction of the dense-vapor speed of sound is of paramount importance for the design of the supersonic turbines equipping these systems. This type of measurements is challenging and thus rare, especially in the case of complex organic molecules, given the high temperature at which they must be performed, close to the temperature at which the molecule thermally decomposes. Therefore, a new prismatic resonator (the OVAR, organic vapor acoustic resonator) has been conceived, designed, and realized. It is suitable for speed of sound measurements in the vapor phase of organic compounds at temperatures up to approximately 670 K and pressures up to about 1.5 MPa. The speed of sound of D6 (97.4% pure) has been measured along eight isotherms between 555 and 645 K and from nearly saturated density to densities close to ideal gas conditions (compressibility factor Z ≈ 0.95). The estimated relative uncertainty of these sound speed measurements is 0.14%. In addition, corresponding density values have been obtained with an estimated uncertainty between 0.2 kg·m-3 and 1.2 kg·m-3.
RESUMO
The Dunning-Kruger premise assumes that unqualified people are unaware of their limited skills. We tested this hypothesis in the context of the coronavirus disease 2019 (COVID-19) pandemic. In this cross-sectional study, 2487 participants had to self-estimate their knowledge about COVID-19 in a questionnaire on the topic. Poor performers were more likely to use mass media and social networks as sources of information and had lower levels of education. The mean self-assessment (SD) was 6.88 (2.06) and was not linked to actual level of knowledge. This observation should prompt regulatory agencies and media to apply rules that limit dissemination of "infodemics" during global health crises.
RESUMO
Rayleigh scattering of a laser beam can be used for time-resolved local measurements of density in flows. A key-point of the approach lies in extracting flow density statistics from the measurement of the scattered-light power. Complex hardware equipment and software procedures are involved in this process. The present paper offers a method to assess the entire chain of acquisition of a typical setup in realistic conditions, and an analysis of its dynamic performances with respect to the theoretical expectations. This is achieved by simulating the light intensity fluctuations typically observed with a Rayleigh scattering setup, by use of a known light intensity fluctuation signal generated using a light-emitting diode modulated in output power. The tested Rayleigh scattering setup is shown to perfectly satisfy the theoretical predictions, meaning that it allows us to measure the spectrum of light intensity variations with an outstanding linearity within a dynamic range proportional to the square-root of the measurement time.
RESUMO
An asymptomatic pelvic tumor was incidentally found in a 27-year-old man. A CT-guided needle biopsy with a pathologic examination confirmed the diagnosis of a benign schwannoma. We describe the complete robotic resection with the conservation of normal fascicles. The postoperative course was uneventful. No neurological deficit occurred, and the electromyogram was normal 6 weeks and 7 months later.
