Liquid-grain mixing suppresses droplet spreading and splashing during impact

Would a raindrop impacting on a coarse beach behave differently from that impacting on a desert of fine sand? We study this question by a series of model experiments, where the packing density of the granular target, the wettability of individual grains, the grain size, the impacting liquid, and the impact speed are varied. We find that by increasing the grain size and/or the wettability of individual grains the maximum droplet spreading undergoes a transition from a capillary regime towards a viscous regime, and splashing is suppressed. The liquid-grain mixing is discovered to be the underlying mechanism. An effective viscosity is defined accordingly to quantitatively explain the observations

Crater formation during raindrop impact on sand

After a raindrop impacts on a granular bed, a crater is formed as both drop and target deform. After an initial, transient, phase in which the maximum crater depth is reached, the crater broadens outwards until a final steady shape is attained. By varying the impact velocity of the drop and the packing density of the bed, we find that avalanches of grains are important in the second phase and hence, affect the final crater shape. In a previous paper, we introduced an estimate of the impact energy going solely into sand deformation and here we show that both the transient and final crater diameter collapse with this quantity for various packing densities. The aspect ratio of the transient crater is however altered by changes in the packing fraction.Comment: 9 pages, 9 figure

Exploring droplet impact near a millimetre-sized hole: comparing a closed pit with an open-ended pore

We investigate drop impact dynamics near both closed pits and open- ended pores experimentally. The resulting impact phenomena differ greatly for a pit or a pore. For the first, we observe three phenomena: a splash, a jet and an air bubble, whose appearance depends on the distance between impact location and pit. Furthermore, we found that splash velocities can reach up to seven times the impact velocity. Drop impact near a pore, however, results solely in splashing. Surprisingly, two distinct and disconnected splashing regimes occur, with a region of plain spreading in-between. For pores, splashes are less pronounced than in the pit case. We state that, for the pit case, the presence of air inside the pit plays a crucial role: it promotes splashing and allows for air bubbles to appear.Comment: 17 pages, 11 figures, 1 supplementary movie, submitted to JF

How Does It Fit? Exploring the Congruence Between Organizations and Their Corporate Social Responsibility (CSR) Activities

Several studies have focused on the effects of corporate social responsibility (CSR) fit on external stakeholders’ evaluations of CSR activities, attitudes towards companies or brands, and behaviors. The results so far have been contradictory. A possible reason may be that the concept of CSR fit is more complicated than previously assumed. Researchers suggest that there may be different types of CSR fit, but so far no empirical research has focused on a typology of CSR fit. This study fills this gap, describing a qualitative content analysis of the congruence between six organizations and their various CSR activities. Ten annual reports and CSR reports were analyzed, and 102 specific CSR activities were identified. The results show that two levels of fit must be distinguished: based on the means for and the intended ends of the CSR activity. Furthermore, six different types of fit were found, focusing on (1) products and services, (2) production processes, (3) environmental impact, (4) employees, (5) suppliers, and (6) geographical location. Considering the above variety of fit possibilities, the findings emphasize the role of CSR communication as a means of creating fit perception

Microbubble shape oscillations excited through ultrasonic parametric driving\ud

An air bubble driven by ultrasound can become shape-unstable through a parametric instability. We report time-resolved optical observations of shape oscillations (mode n=2 to 6) of micron-sized single air bubbles. The observed mode number n was found to be linearly related to the ambient radius of the bubble. Above the critical driving pressure threshold for shape oscillations, which is minimal at the resonance of the volumetric radial mode, the observed mode number n is independent of the forcing pressure amplitude. The microbubble shape oscillations were also analyzed numerically by introducing a small nonspherical linear perturbation to a Rayleigh-Plesset-type equation, capturing the experimental observations in detail.\ud \u

Modeling Human Cardiac Hypertrophy in Stem Cell-Derived Cardiomyocytes

Cardiac hypertrophy accompanies many forms of cardiovascular diseases. The mechanisms behind the development and regulation of cardiac hypertrophy in the human setting are poorly understood, which can be partially attributed to the lack of a human cardiomyocyte-based preclinical test system recapitulating features of diseased myocardium. The objective of our study is to determine whether human embryonic stem cell-derived cardiomyocytes (hESC-CMs) subjected to mechanical stretch can be used as an adequate in vitro model for studying molecular mechanisms of cardiac hypertrophy. We show that hESC-CMs subjected to cyclic stretch, which mimics mechanical overload, exhibit essential features of a hypertrophic state on structural, functional, and gene expression levels. The presented hESC-CM stretch approach provides insight into molecular mechanisms behind mechanotransduction and cardiac hypertrophy and lays groundwork for the development of pharmacological approaches as well as for discovering potential circulating biomarkers of cardiac dysfunction. In this article, Berezikov, van der Meer, and colleagues used stem cell-derived cardiomyocytes to model human cardiac hypertrophy. Their approach provides novel insights into molecular mechanisms behind mechanotransduction and cardiac hypertrophy and lays groundwork for the development of new pharmacological approaches as well as for discovering new potential circulating biomarkers of cardiac dysfunction

Microbubble Surface Modes

We have investigated surface vibrations generated by ultrasound excitation of individual unencapsulated micron-sized bubbles. In addition, we present surface modes (n=2 and 3) observed for phospholipid-coated ultrasound contrast agents excited through excitation of radial modes at frequencies between 1 and 4 MHz. Even higher modes of vibration (up to mode 5) are observed for coated microbubbles at insonation frequencies of 10 and 19 MHz. The potential relevance of surface modes for medical ultrasound is discussed, including the possible implications for current theoretical models of ultrasound contrast agents

Patient-reported outcome measures after 8 weeks of mepolizumab treatment and long-term outcomes in patients with severe asthma:an observational study

Background The novel anti-IL-5 drug mepolizumab improves asthma outcomes in the majority but not all patients with severe eosinophilic asthma. Currently it is difficult to predict an individuals' chance of being a responder. Early changes in patient-reported outcome measures may contribute to the prediction of long-term outcomes. Aim To compare early changes in patient-reported outcome measures after 8 weeks and long-term response to mepolizumab treatment. Method 22 severe eosinophilic asthma patients starting mepolizumab therapy in a severe asthma centre in the Netherlands were evaluated on baseline, 8 weeks and 52 weeks, collecting questionnaire scores and asthma-related parameters. Well-controlled asthma was defined as an asthma control questionnaire score ≤ 0.75. Long-term treatment response was defined as continuing mepolizumab therapy at 52 weeks. Results Nine patients (41%) had well-controlled asthma at 8 weeks and all were mepolizumab responders at 52 weeks (positive predictive value = 100%, 95%CI 66-100), versus only 5 responders out of 13 patients with not well-controlled asthma at 8 weeks (negative predictive value = 62%, 95%CI 32-86). Conclusion The results in this study suggest that patients receiving mepolizumab therapy with an ACQ-score ≤ 0.75 at 8 weeks are unlikely to need extensive monitoring, for they are very likely to be long-term responders