Behavior of self-propelled acetone droplets in a Leidenfrost state on liquid substrates

It is demonstrated that non-coalescent droplets of acetone can be formed on liquid substrates. The fluid flows around and in an acetone droplet hovering on water are recorded to shed light on the mechanisms which might lead to non-coalescence. For sufficiently low impact velocities, droplets undergo a damped oscillation on the surface of the liquid substrate but at higher velocities clean bounce-off occurs. Comparisons of experimentally observed static configurations of floating droplets to predictions from a theoretical model for a small non-wetting rigid sphere resting on a liquid substrate are made and a tentative strategy for determining the thickness of the vapor layer under a small droplet on a liquid is proposed. This strategy is based on the notion of effective surface tension. The droplets show self-propulsion in straight line trajectories in a manner which can be ascribed to a Marangoni effect. Surprisingly, self-propelled droplets can become immersed beneath the undisturbed water surface. This phenomenon is reasoned to be drag-inducing and might provide a basis for refining observations in previous work

Two dimensional Leidenfrost Droplets in a Hele Shaw Cell

We experimentally and theoretically investigate the behavior of Leidenfrost droplets inserted in a Hele-Shaw cell. As a result of the confinement from the two surfaces, the droplet has the shape of a flattened disc and is thermally isolated from the surface by the two evaporating vapor layers. An analysis of the evaporation rate using simple scaling arguments is in agreement with the experimental results. Using the lubrication approximation we numerically determine the shape of the droplets as a function of its radius. We furthermore find that the droplet width tends to zero at its center when the radius reaches a critical value. This prediction is corroborated experimentally by the direct observation of the sudden transition from a flattened disc into an expending torus. Below this critical size, the droplets are also displaying capillary azimuthal oscillating modes reminiscent of a hydrodynamic instability

Cascaded Blended Mentoring. Unterstützung von Studienanfängerinnen und Studienanfängern in der Studieneingangsphase

Die Studiensituation in einem Massenstudium wie dem Diplomstudium Psychologie an der Universität Wien ist für Studierende und Lehrende alles andere als optimal. Vor allem der Studieneinstieg stellt eine schwer bewältigbare Herausforderung für viele Studienanfänger(innen) dar, die Betreuungssituation ist zudem extrem angespannt. Mit dem Projekt Cascaded Blended Mentoring wird ein Konzept vorgestellt, das bisher ungenutzte Kompetenzen und Erfahrungen von fortgeschrittenen Studierenden zur Unterstützung von Studienanfänger(inne)n in der Studieneingangsphase einbindet. Auf Blended-Learning-Basis werden die Studienanfänger(innen) in Kleingruppen virtuell und präsent von fortgeschrittenen Studierenden beim Erwerb von Schlüsselkompetenzen, die für ein erfolgreiches Studium wichtig sind, unterstützt. Die erstmalige Erprobung dieses Modells findet mit Studienanfänger(inne)n des Sommersemesters 2007 statt. (DIPF/Orig.

Reshaping and Capturing Leidenfrost drops with a magnet

Liquid oxygen, which is paramagnetic, also undergoes Leidenfrost effect at room temperature. In this article, we first study the deformation of oxygen drops in a magnetic field and show that it can be described via an effective capillary length, which includes the magnetic force. In a second part, we describe how these ultra-mobile drops passing above a magnet significantly slow down and can even be trapped. The critical velocity below which a drop is captured is determined from the deformation induced by the field.Comment: Published in Physics of Fluids (vol. 25, 032108, 2013) http://pof.aip.org/resource/1/phfle6/v25/i3/p032108_s1?isAuthorized=n

Film boiling heat transfer and vapour film collapse on spheres, cylinders and plane surfaces

Copyright @ 2009 Elsevier B.V. The final version of this article may be viewed at the link below.An experimental study of transient film boiling was conducted, with different coolant velocities, on two spheres with different diameters, two cylindrical specimens of different lengths in parallel flow, a cylinder in cross flow and two flat plates with different lengths. A frame by frame photographic study on the nature of the vapour/liquid interface and the collapse modes has revealed a new mode for film collapse, in which an explosive liquid–solid contact is followed by film re-formation and the motion of a quench front over the hot surface. Steady state tests were carried out on a plate similar to the short plate used in the transient experiments and the heat transfer, film stability and collapse results are compared with those of the transient investigation. Heat transfer coefficients and heat fluxes during film boiling were found essentially to depend on specimen temperature and water subcooling. In contrast, the influences on heat transfer of specimen size and water velocity were relatively small for the ranges studied. A theoretical model predicted heat transfer coefficients to within 10% of experimental values for water subcoolings above 10 K and within 30% in all cases

How I do it: Minimally invasive Cox-Maze IV procedure

Clinical vignette Our patient is a 66-year-old female with a 2-year history of atrial fibrillation (AF) and mitral valve prolapse who presented with dyspnea on exertion. She was found to be in AF upon her admission electrocardiogram. A transthoracic echocardiogram was performed demonstrating moderate-to-severe mitral regurgitation (MR) with a left atrial (LA) diameter of 5.1 cm and normal left ventricular (LV) function. After completion of her workup, it was decided that the patient would best be treated by a minimally invasive Cox-Maze IV (CMIV) and concomitant mitral valve procedure given her significant MR and symptoms. This article and accompanying video will discuss how the minimally invasive CMIV procedure is performed. Surgical technique

Support for Freshmen at a Mass-University Program - The Cascaded Blended Mentoring Project

This paper describes a new mentoring project that is being carried out at the Faculty of Psychology at the University of Vienna. The general objective of this project is to help freshmen to manage the demands that come with mass-studies like Psychology. Senior students act as mentors for a group of freshmen by sharing the experiences and knowledge they already gained in their studies. The project is currently in its pilot phase and will start for the main test phase in fall 2007

Viva Survivors – the effect of peer-mentoring on pre-viva anxiety in early-years students

Viva voce exams are used in many disciplines as a test of students’ knowledge and skills. Whilst acknowledged as a useful form of assessment, vivas commonly lead to a great deal of anxiety for students. This anxiety is also apparent for vivas in phonetics, where students must produce and recognise sounds drawn from across the world’s languages, and pervious work has shown that viewing a video of a mock-viva does not reduce this anxiety. To address anxiety prior to phonetics vivas, 63 students, across three cohorts, engaged in a brief, isolated, peer-mentoring session with previously successful students (‘viva survivors’). Anxiety about the viva was measured before and after the mentoring experience, using the short form of the State Trait Anxiety Inventory. There was a significant reduction in anxiety after mentoring, and a significant correlation between anxiety before mentoring and the decrease in anxiety after mentoring. Short-term mentoring is posited as a time- and cost-effective method to decrease viva-related anxiety across disciplines

Maine Monthly Overdose Report for November 2021

During November there were a total of 773 fatal and nonfatal overdoses, including 64 (8%) confirmed and suspected fatal overdoses and 709 (92%) nonfatal overdoses. The proportion of fatal to nonfatal overdoses decreased from 9% to 7% between January and November. Deduplicated data derived from multiple statewide sources were compiled to reach these totals. These sources include nonfatal overdose incidents reported by hospital emergency rooms (ED), emergency medical service (EMS) responses without transport to the ED; overdose reversals reported by law enforcement; and overdose reversals reported by community members or agencies receiving state-distributed naloxone. There are an unknown number of private overdose reversals that were not reported and an unknown number of the community-reported reversals that may have overlapped with emergency response by EMS or law enforcement