Skalak's extended theory of water hammer

Half a century ago Richard Skalak [see T.C. Skalak, A dedication in memoriam of Dr. Richard Skalak, Annual Review of Biomedical Engineering 1 (1999) 1-18] published a paper with the title "An extension of the theory of water hammer" [R. Skalak, An Extension of the Theory of Water Hammer, PhD Thesis, Faculty of Pure Science, Columbia University, New York, USA, 1954; R. Skalak, An extension of the theory of water hammer, Water Power 7/8 (1955/1956) 458-462/17-22; R. Skalak, An extension of the theory of water hammer, Transactions of the ASME 78 (1956) 105-116], which has been the basis of much subsequent work on hydraulic transients with fluid-structure interaction (FSI). The paper considers the propagation of pressure waves in liquid-filled pipes and the coupled radial/axial response of the pipe walls. In a tribute to Skalak's work, his paper is revisited and some of his less-known results are used to assess the dispersion of pressure waves in long-distance pipelines. Skalak's theory predicts that the spreading of wave fronts due to FSI is small, at most of the order of 10 pipe diameters. © 2007 Elsevier Ltd. All rights reserved.Arris S. Tijsseling, Martin F. Lambert, Angus R. Simpson, Mark L. Stephens, John P. Vítkovský, and Anton Berganthttp://www.elsevier.com/wps/find/journaldescription.cws_home/622899/description#descriptio

Selective self-assembly and light emission tuning of layered hybrid perovskites on patterned graphene

The emission of light in two-dimensional (2-D) layered hybrid organic lead halide perovskites, namely (R-NH3)2PbX4, can be effectively tuned using specific building blocks for the perovskite formation. Herein this behaviour is combined with a non-covalent graphene functionalization allowing excellent selectivity and spatial resolution of the perovskite film growth, promoting the formation of hybrid 2-D perovskite : graphene heterostructures with uniform coverage of up to centimeter scale graphene sheets and arbitrary shapes down to 5 μm. Using cryo-Raman microspectroscopy, highly resolved spectra of the perovskite phases were obtained and the Raman mapping served as a convenient spatially resolved technique for monitoring the distribution of the perovskite and graphene constituents on the substrate. In addition, the stability of the perovskite phase with respect to the thermal variation was inspected in situ by X-ray diffraction. Finally, time-resolved photoluminescence characterization demonstrated that the optical properties of the perovskite films grown on graphene are not hampered. Our study thus opens the door to smart fabrication routes for (opto)-electronic devices based on 2-D perovskites in contact with graphene with complex architectures

Mastering the Wrinkling of Self-supported Graphene

Abstract We present an approach that allows for the preparation of well-defined large arrays of graphene wrinkles with predictable geometry. Chemical vapor deposition grown graphene transferred onto hexagonal pillar arrays of SiO2 with sufficiently small interpillar distance forms a complex network of two main types of wrinkle arrangements. The first type is composed of arrays of aligned equidistantly separated parallel wrinkles propagating over large distances, and originates from line interfaces in the graphene, such as thin, long wrinkles and graphene grain boundaries. The second type of wrinkle arrangement is composed of non-aligned short wrinkles, formed in areas without line interfaces. Besides the presented hybrid graphene topography with distinct wrinkle geometries induced by the pre-patterned substrate, the graphene layers are suspended and self-supporting, exhibiting large surface area and negligible doping effects from the substrate. All these properties make this wrinkled graphene a promising candidate for a material with enhanced chemical reactivity useful in nanoelectronic applications