Sharp Transition between Coalescence and Noncoalescence of Sessile Drops

Unexpectedly, under certain conditions, sessile drops from different but completely miscible liquids do not always coalesce instantaneously upon contact: the drop bodies remain separated in a temporary state of noncoalescence, connected through a thin liquid bridge. Here we investigate the transition between the states of instantaneous coalescence and temporary noncoalescence. Experiments reveal that it is barely influenced by viscosities and absolute surface tensions. The main system control parameters for the transition are the arithmetic means of the three-phase angles, $\overline{\Theta}_a$ and the surface tension differences $\Delta\gamma$ between both liquids. These relevant parameters can be combined into a single system parameter, a speciffic Marangoni number $\widetilde{M} = 3\Delta\gamma / (2\overline{\gamma}\overline{\Theta}_a^2)$. This $\widetilde{M}$ universally characterizes the coalescence respectively transition behavior as a function of both, the physicochemical liquid properties and the shape of the liquid body in the contact region. The transition occurs at a certain threshold value $\widetilde{M}_t$ and is sharp within the experimental resolution. The experimentally observed threshold value of $\widetilde{M}_t \approx 2$ agrees quantitatively with values obtained by simulations assuming authentic real space data. The simulations indicate that the absolute value of $\widetilde{M}_t$ very weakly depends on the molecular diffusivity.Comment: 9 pages, 6 figure

Non-coalescence of sessile drops from different but miscible liquids: Hydrodynamic analysis of the twin drop contour as self stabilizing, traveling wave

Capillarity always favors drop fusion. Nevertheless sessile drops from different but completely miscible liquids often do not fuse instantaneously upon contact. Rather, intermediate non-coalescence is observed. Two separate drop bodies, connected by a thin liquid neck move over the substrate. Supported by new experimental data a thin film hydrodynamic analysis of this state is presented. Presumably advective and diffusive volume fluxes in the neck region establish a localized and temporarily stable surface tension gradient. This induces a local surface (Marangoni) flow that stabilizes a traveling wave i.e., the observed moving twin drop configuration. The theoretical predictions are in excellent agreement with the experimental findings.Comment: 5 pages, 5 figure

Critical Wetting of a Liquid/Vapor Interface by Octane

The wetting of the planar interface between air saturated with octane vapor and an aqueous solution by octane is investigated by ellipsometry and interfacial tension measurements. The interfacial interactions are varied through the concentration of the uncharged solute (glucose). We observe abrupt and continuous increases of the octane coverage with growing solute concentration. This we attribute to short- and long-range (dispersion) interactions, respectively. The continuous thickness growth is analyzed as a critical wetting transition

Controlled deposition of nanosize and microsize particles by spin-casting

The deposition of nanosize and microsize spherical particles on planar solid substrates by hydrodynamic-evaporative spin-casting is studied. The particles are dispersed in a volatile liquid, which evaporates during the process, and the particles are finally deposited on the substrate. Their coverage, Gamma, depends on the processing parameters (concentration by weight, particles size, etc.). The behavior of the particles during the spin-casting process and their final Gamma values are investigated. It is found that for up to particle diameters of a few micrometers, particle deposition can be described by a theoretical approach developed for the spin-casting of polymer solutions (Karpitschka, S.; Weber, C. M.; Riegler, H. Chem. Eng. Sci. 2015, 129, 243-248. Danglad-Flores, J.; Eickelmann, S.; Riegler, H. Chem. Eng. Sci. 2018, 179, 257-264). For large particles, this basic theory fails. The causes of this failure are analyzed, and a corrected, more general theoretical approach is presented. It takes into account particle size effects as well as particle sedimentation. In summary, we present new insights into the spin-cast process of particle dispersions, analyze the contributions affecting the final particle coverage, and present a theoretical approach which describes and explains the experimental findings

Explaining disappearances as a tool of political terror

Despite the widespread use of disappearances as a central tool of terror in recent decades, little is known about the emergence of the phenomenon or its underlying rationale. We argue that growing international accountability norms, coupled with the improved quality of reporting human rights abuses, paradoxically reshaped the repressive strategies of certain regimes and pushed them to deploy more clandestine and extrajudicial forms of repression, predominantly disappearances. We also explore the timing of disappearances: when a state decides to deploy a particular instrument of terror can greatly benefit our understanding of why it was used. We show that repressive regimes tend to use disappearances in the first period after a coup, taking advantage of the general confusion and opacity to secure strategic benefits and protect the regime from external scrutiny and future accountability. Our findings contribute to the growing literature on human rights and political repression by highlighting an ‘unintended consequence’ of international accountability norms: repressive regimes turn to clandestine crimes

Die schwierige Versöhnung

This volume is the result of collaboration between historians and scientific institutions in Austria and Italy. It covers two major topics: the bilateral contacts in the 20th century between the two neighbouring countries and the role of the South Tyrol question in this relationship. In the Rome-Vienna-Bolzano triangle, the most important intersections of this continuously maintained relationship are illuminated and central questions of recent European history are examined: the treatment of national minorities, the work of authoritarian regimes as well as democratization and the process of European integration. The aim of this volume is to map the current state of research, to open up possible new fields of research and to give new impulses to the historiographical dialogue between Rome and Vienna.; Dieser Band ist das Ergebnis der Zusammenarbeit zwischen Historikern und wissenschaftlichen Einrichtungen in Österreich und Italien. Er umfasst zwei große Themenbereiche: die bilateralen Kontakte im 20. Jahrhundert zwischen den beiden Nachbarländern sowie die Rolle der Südtirolfrage in diesem Verhältnis. Im Dreieck Rom-Wien-Bozen werden die wichtigsten Schnittpunkte dieser fortwährend aufrechterhaltenen Beziehung beleuchtet und zentrale Fragen der jüngsten europäischen Geschichte untersucht: der Umgang mit nationalen Minderheiten, das Wirken autoritärer Regimes sowie die Demokratisierung und der Prozess der europäischen Integration. Ziel dieses Bandes ist es, den derzeitigen Forschungsstand abzubilden, mögliche neue Forschungsfelder zu eröffnen und dem historiografischen Dialog zwischen Rom und Wien neue Impulse zu verleihen

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe