807 research outputs found
Preparation of alkali metal dispersions
A method is described for producing alkali metal dispersions of high purity. The dispersions are prepared by varying the equilibrium solubility of the alkali metal in a suitable organic solvent in the presence of aromatic hydrocarbons. The equilibrium variation is produced by temperature change. The size of the particles is controlled by controlling the rate of temperature change
Process for preparing dispersions of alkali metals
Finely divided particles of alkali metals are produced by combining alkali metals with certain aromatic compounds in selected solvents to form low-temperature soluble complexes from which the pure alkali metals precipitate quantitatively when the solutions are warmed. All operations must be carried out in an inert gas atmosphere
Polymeric compositions and their method of manufacture
Filled polymer compositions are made by dissolving the polymer binder in a suitable sublimable solvent, mixing the filler material with the polymer and its solvent, freezing the resultant mixture, and subliming the frozen solvent from the mixture from which it is then removed. The remaining composition is suitable for conventional processing such as compression molding or extruding. A particular feature of the method of manufacture is pouring the mixed solution slowly in a continuous stream into a cryogenic bath wherein frozen particles of the mixture result. The frozen individual particles are then subjected to the sublimation
Has the U.K. Violated Its International Obligations by Failing to Introduce Mandatory Sex Education in Schools?
Static electricity of polymers reduced by treatment with iodine
Treating organic polymers with iodine improves the electrical conductivity. Diffusion enables products of desired properties to be custom formulated. This eliminates a buildup of static electricity and the need for fillers or bound metal salts
Proposals For A Truth Commission And reparations Program For Victims Of Torture By US Forces Since 9/11
Since September 11, 2001, the United States has been responsible for well documented cases of torture and ill-treatment as part of its war on terror in Guantanamo, Iraq, Afghanistan and other secret sites
Has the U.K. Violated Its International Obligations by Failing to Introduce Mandatory Sex Education in Schools?
La métropole et ses relations extérieures ou l'impossible institutionnalisation des relations extra-métropolitaines
International audiencePartant du réseau des villes, en passant par l'esquisse du projet de Sillon alpin, la région urbaine de Grenoble se révèle être un puissant révélateur des questions posées par les relations inter-urbaines. La hiérarchie n'y est efficace qu'à la condition d'être reconnue et utile à chacun des membres du réseau. La gouvernance n'est acceptée que si elle repose sur un dispositif souple, sans structure ad-hoc, partageant les responsabilités en fonction des compétences et des envies. A contrario, le Sillon alpin s'est affaibli au fur et à mesure que s'esquissait la possibilité d'une structuration. Ces dynamiques laissent à douter de la possibilité d'organiser et d'institutionnaliser les relations inter-urbaine
Parallel-plate viscometer
Viscometer consists of movable vertical rod with one optical flat fixed to its lower end and centered over second optical flat held rigidly parallel to moveable flat. Two perforated diaphragms of thin metal permit limited amount of vertical movement of rod carrying movable flat, but resist lateral movement
Traces of surfactants can severely limit the drag reduction of superhydrophobic surfaces
Superhydrophobic surfaces (SHSs) have the potential to achieve large drag
reduction for internal and external flow applications. However, experiments
have shown inconsistent results, with many studies reporting significantly
reduced performance. Recently, it has been proposed that surfactants,
ubiquitous in flow applications, could be responsible, by creating adverse
Marangoni stresses. Yet, testing this hypothesis is challenging. Careful
experiments with purified water show large interfacial stresses and,
paradoxically, adding surfactants yields barely measurable drag increases. This
suggests that other physical processes, such as thermal Marangoni stresses or
interface deflection, could explain the lower performance. To test the
surfactant hypothesis, we perform the first numerical simulations of flows over
a SHS inclusive of surfactant kinetics. These simulations reveal that
surfactant-induced stresses are significant at extremely low concentrations,
potentially yielding a no-slip boundary condition on the air--water interface
(the "plastron") for surfactant amounts below typical environmental values.
These stresses decrease as the streamwise distance between plastron stagnation
points increases. We perform microchannel experiments with thermally-controlled
SHSs consisting of streamwise parallel gratings, which confirm this numerical
prediction. We introduce a new, unsteady test of surfactant effects. When we
rapidly remove the driving pressure following a loading phase, a backflow
develops at the plastron, which can only be explained by surfactant gradients
formed in the loading phase. This demonstrates the significance of surfactants
in deteriorating drag reduction, and thus the importance of including
surfactant stresses in SHS models. Our time-dependent protocol can assess the
impact of surfactants in SHS testing and guide future mitigating designs.Comment: 25 pages including supplemental information, 7 figures; videos
available on reques
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