Nonlinear dynamics of inclined films under low-frequency forcing

The evolution of an inclined liquid film, subjected to regular inlet disturbances of small frequency, f, is studied experimentally and computationally. The fluorescence imaging method is used to quantitatively document film thickness at a downstream window of the flow channel, and a Galerkin finite-element solution of the Navier-Stokes equation of motion is invoked to predict the entire spatio-temporal dynamics of the free surface. Experiments confirm that, below a certain frequency, f(p), the regular wave train is destroyed by the appearance of one or more parasitic crests behind each major wave. Experiments and simulations indicate that parasitic crests are not the result of spatially unlocalized instabilities in the substrate, but originate in a regular way from a depression developing at the tails of growing solitary waves. Their downstream fate is dictated by the proximity of the next major wave, and thus different scenarios are predicted and observed for fapproximate tof(p) and f<f(p). A theoretical explanation of the phenomenon is suggested in terms of the radiation properties of growing solitary crests, as described by Chang, Demekhin, and Kalaidin [SIAM (Soc. Ind. Appl. Math.) J. Appl. Math. 58, 1246 (1998)]. (C) 2004 American Institute of Physics

Solitary waves on inclined films: their characteristics and the effects on wall shear stress

The properties of solitary waves, developing from inlet disturbances of controlled frequency along an inclined film flow, are systematically studied experimentally and computationally. Time-variations of film height and wall shear stress are measured, using respectively a capacitance probe and an electrodiffusion sensor. Computational data are provided from simulations performed by a Galerkin finite element scheme. The height and spacing of solitary humps, their phase velocity and the wavelength of the preceding capillary ripples are reported as functions of the Reynolds number (10 < Re < 100) and the inlet frequency (0.5 Hz < f < 2.5 Hz). The wall shear stress modulation imposed by the passage of solitary waves is studied experimentally and computationally as a function of Re. Distinct nonlinear characteristics are noted, including a steep maximum and a negative minimum, with the effects intensifying at intermediate Re. All computer predictions are found to be in good quantitative agreement with the experimental data

Experimental study of inclined film flow along periodic corrugations: The effect of wall steepness

Gravity-driven film flow along an inclined periodic wall with transverse rectangular corrugations is studied experimentally. The effect of corrugation steepness (=height/length) is considered in detail and an interesting contrast emerges between properties of the flow that are apparently independent of corrugation steepness and properties that are strongly affected by it. The steady interaction between the wall and the flow leads to a statically deformed free surface, whose amplitude is independent of the corrugation heights tested. Beyond the maximum steady free-surface amplitude, a three-dimensional pattern is established (consisting of transverse arrays of depressions along corrugation valleys), again at conditions independent of corrugation height. On the contrary, steep corrugations expand significantly the stable region of steady flow. Also, fully developed traveling waves (emerging from ambient noise under unsteady conditions) are significantly larger and more regular than under the same conditions along a flat wall. This difference is attributed to the continuous interaction of traveling pulses with the steadily deformed substrate

Assessment of COVID-19 Fear in Five European Countries before Mass Vaccination and Key Predictors among Nurses and Nursing Students

Background: Levels of fear have increased since the COVID-19 pandemic outbreak. The absence of a safe and effective vaccine for mass-vaccination deteriorates this situation, which has a significant impact on mental health. This study aimed to assess the feelings of fear among nurses and nursing students in five European countries. Methods: A multicenter cross-sectional study was conducted in five European countries (Greece, Albania, Cyprus, Spain, and Kosovo) before the start of mass vaccination in Europe. Data collection was conducted in December 2020–January 2021 using an online questionnaire for nursing students and professional nurses. Fear of COVID-19 Scale (FCV-19S) was used for measuring levels of fear. IBM SPSS version 21.0 was used for statistical analysis. Results: The study population included 1135 nurses and 1920 nursing students from Kosovo (n = 1085), Spain (n = 663), Greece (n = 534), Albania (n = 529), and Cyprus (n = 244). According to multivariable analysis, females (OR = 2.53, 95% CI = 1.89–3.15), married (OR = 0.86, 95% CI = 0.24–1.48), nurses (OR = 0.87, 95% CI = 0.28–1.45) and those with a chronic disease (OR = 0.86, 95% CI = 0.11–1.62) were more fearful of COVID-19. Conclusions: It is important to decrease fear in the population of nurses who are at the frontlines of the pandemic. The provision of appropriate education and training activities for nurses and students to manage their stress levels is of high importance. Future studies should focus on levels of fear after the administration of several safe and effective vaccines worldwide. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Assessment of COVID-19 Fear in Five European Countries before Mass Vaccination and Key Predictors among Nurses and Nursing Students

Background: Levels of fear have increased since the COVID-19 pandemic outbreak. The absence of a safe and effective vaccine for mass-vaccination deteriorates this situation, which has a significant impact on mental health. This study aimed to assess the feelings of fear among nurses and nursing students in five European countries. Methods: A multicenter cross-sectional study was conducted in five European countries (Greece, Albania, Cyprus, Spain, and Kosovo) before the start of mass vaccination in Europe. Data collection was conducted in December 2020\u2013January 2021 using an online questionnaire for nursing students and professional nurses. Fear of COVID-19 Scale (FCV-19S) was used for measuring levels of fear. IBM SPSS version 21.0 was used for statistical analysis. Results: The study population included 1135 nurses and 1920 nursing students from Kosovo (n = 1085), Spain (n = 663), Greece (n = 534), Albania (n = 529), and Cyprus (n = 244). According to multivariable analysis, females (OR = 2.53, 95% CI = 1.89\u20133.15), married (OR = 0.86, 95% CI = 0.24\u20131.48), nurses (OR = 0.87, 95% CI = 0.28\u20131.45) and those with a chronic disease (OR = 0.86, 95% CI = 0.11\u20131.62) were more fearful of COVID-19. Conclusions: It is important to decrease fear in the population of nurses who are at the frontlines of the pandemic. The provision of appropriate education and training activities for nurses and students to manage their stress levels is of high importance. Future studies should focus on levels of fear after the administration of several safe and effective vaccines worldwide

Electrified film flow over step topography at zero Reynolds number.

The flow of a liquid film over step topography under the influence of an electric field is considered in the limit of zero Reynolds number. The particular topographies considered include a flat wall with a downward step or an upward step, or a flat wall which is indented with a rectangular trench. A uniform electric field is imposed at infinity in the direction normal to the flatwall. The air above the film is treated as a perfect dielectric. The liquid in the film is assumed to behave either as a perfect conductor or as a perfect dielectric whose dielectric constant in general differs from that in the air. Asymptotic results are derived on the assumption of small step height, and formulas are presented for the first-order correction to the free-surface deformation due to the topography. It is demonstrated that, in an appropriate long-wave limit, the solutions approach those obtained using the lubrication approximation. Finally, the small-step asymptotics are favourably compared with numerical solutions for Stokes flow over steps of arbitrary height computed using the boundary-element method. In summary, it is shown that asymptotic models based on small-amplitude step topography provide simple formulas which are effective in describing the flow even for moderate step amplitudes, making them an efficient analytical tool for solving practical film-flow problems