Effect of contact angle hysteresis on thermocapillary droplet actuation

Open microfluidic devices based on actuation techniques such as electrowetting, dielectrophoresis, or thermocapillary stresses require controlled motion of small liquid droplets on the surface of glass or silicon substrates. In this article we explore the physical mechanisms affecting thermocapillary migration of droplets generated by surface temperature gradients on the supporting substrate. Using a combination of experiment and modeling, we investigate the behavior of the threshold force required for droplet mobilization and the speed after depinning as a function of the droplet size, the applied thermal gradient and the liquid material parameters. The experimental results are well described by a hydrodynamic model based on earlier work by Ford and Nadim. The model describes the steady motion of a two-dimensional droplet driven by thermocapillary stresses including contact angle hysteresis. The results of this study highlight the critical role of chemical or mechanical hysteresis and the need to reduce this retentive force for minimizing power requirements in microfluidic devices

Fault Slip and Exhumation History of the Willard Thrust Sheet, Sevier Fold‐Thrust Belt, Utah: Relations to Wedge Propagation, Hinterland Uplift, and Foreland Basin Sedimentation

Zircon (U‐Th)/He (ZHe) and zircon fission track thermochronometric data for 47 samples spanning the areally extensive Willard thrust sheet within the western part of the Sevier fold‐thrust belt record enhanced cooling and exhumation during major thrust slip spanning approximately 125–90 Ma. ZHe and zircon fission track age‐paleodepth patterns along structural transects and age‐distance relations along stratigraphic‐parallel traverses, combined with thermo‐kinematic modeling, constrain the fault slip history, with estimated slip rates of ~1 km/Myr from 125 to 105 Ma, increasing to ~3 km/Myr from 105 to 92 Ma, and then decreasing as major slip was transferred onto eastern thrusts. Exhumation was concentrated during motion up thrust ramps with estimated erosion rates of ~0.1 to 0.3 km/Myr. Local cooling ages of approximately 160–150 Ma may record a period of regional erosion, or alternatively an early phase of limited... (see full abstract in article)

Symmetric Edit Lenses: A New Foundation for Bidirectional Languages

Lenses are bidirectional transformations between pairs of connected structures capable of translating an edit on one structure into an edit on the other. Most of the extensive existing work on lenses has focused on the special case of asymmetric lenses, where one structures is taken as primary and the other is thought of as a projection or view. Some symmetric variants exist, where each structure contains information not present in the other, but these all lack the basic operation of composition. Additionally, existing accounts do not represent edits carefully, making incremental operation difficult or producing unsatisfactory synchronization candidates. We present a new symmetric formulation which works with descriptions of changes to structures, rather than with the structures themselves. We construct a semantic space of edit lenses between “editable structures”—monoids of edits with a partial monoid action for applying edits—with natural laws governing their behavior. We present generalizations of a number of known constructions on asymmetric lenses and settle some longstanding questions about their properties—in particular, we prove the existence of (symmetric monoidal) tensor products and sums and the non-existence of full categorical products and sums in a category of lenses. Universal algebra shows how to build iterator lenses for structured data such as lists and trees, yielding lenses for operations like mapping, filtering, and concatenation from first principles. More generally, we provide mapping combinators based on the theory of containers. Finally, we present a prototype implementation of the core theory and take a first step in addressing the challenge of translating between user gestures and the internal representation of edits

Equilibrium, Disequilibrium, and the General Possibility of a Science of Politics

In recent years important theoretical contributions have shown that majority rule is a very badly behaved collective choice mechanism. In the absence of artificial restraints on preferences majority rule processes are almost always in disequilibrium. Moreover, the extent of the disequilibrium is pervasive, as captured by the observation that "anything can happen". What are the implications of such nihilistic results for the study of democratic political processes? Some authors believe that the implications are major, that they in fact preclude the development of a science of politics. Other authors take a more sanguine view. This essay argues that equilibrium notions, as presently formulated, are neither necessary nor sufficient for the development of a scientific study of politics. The newly proved disequilibrium results do suggest a change in the research agenda facing political scientists. The broad outlines of that agenda, and a general strategy for proceeding are discussed

Post retention with mineral trioxide aggregate and accelerated Portland cement

Perforations occurring during post placement are problematic. Mineral trioxide aggregate (MTA) is slow to set. A trial demonstrated that CaCl2 accelerated the set of Portland cement. Forty single-rooted teeth were sectioned, treated with endodontic therapy and post prepared. The first group contained 20 teeth, evaluated at 72 hours. MTA, Portland cement with 10% CaCl2, 15% CaCl2 and zinc phosphate were used as post cements. The second group was evaluated at 28 days. The posts were cemented with either MTA or zinc phosphate. Instron mechanical testing was used to determine forces needed for post dislodgement. The 72 hour group showed statistically significant higher resistance to dislodgement with zinc phosphate. (p\u3c.05) No significance was found between resistance in the experimental groups. The 28 day group posts seated with zinc phosphate had a higher resistance to dislodgement than those with MTA. (p\u3c.05) At 28 days, MTA was found to be 28 % weaker than zinc phosphate

Guidelines for ethical nudging in password authentication

Nudging has been adopted by many disciplines in the last decade in order to achieve behavioural change. Information security is no exception. A number of attempts have been made to nudge end-users towards stronger passwords. Here we report on our deployment of an enriched nudge displayed to participants on the system enrolment page, when a password has to be chosen. The enriched nudge was successful in that participants chose significantly longer and stronger passwords. One thing that struck us as we designed and tested this nudge was that we were unable to find any nudge-specific ethical guidelines to inform our experimentation in this context. This led us to reflect on the ethical implications of nudge testing, specifically in the password authentication context. We mined the nudge literature and derived a number of core principles of ethical nudging. We tailored these to the password authentication context, and then show how they can be applied by assessing the ethics of our own nudge. We conclude with a set of preliminary guidelines derived from our study to inform other researchers planning to deploy nudge-related techniques in this context