On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

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Microfluidics: Fluid physics at the nanoliter scale

I. the origin of species by means of natural selection

The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

The stability of the steady flow of a viscous liquid through a thick-wall, three-layer, viscoelastic tube with different rheological parameters for each layer is studied. The temporal and spatial eigenvalues of the system are found. Influence of the material parameters of the layers and the Reynolds number on the spatial and temporal amplification rate of the most unstable mode is investigated. It is shown that the system can be in both absolute and convective unstable states. Effects of the rheological parameters of each layer on the amplification rate of the most unstable mode that represents an absolute instability are examined. It is shown that the absolute instability of the system can be converted into a convective instability, and in some cases the system can even be stabilized with an appropriate choice of the rheological parameters. The rheological parameters of the tube layers influence the system stability in different ways. While some of those parameters destabilize the system, others stabilize it. It is found that an anisotropic tube composed of layers possessing distinct rheological values can completely eliminate all absolute instability modes. The present model can be applied to blood vessels that are composed of three viscoelastic layers with distinct rheological properties and to distensible tubes conveying fluids in different technical devices. Copyright © 2009 John Wiley & Sons, Ltd.

Suppression of absolute instabilities in the flow inside a compliant tube

Flow Control: Reynolds Number Effects

Molecular Dynamic Simulations of Fibrous Distillation Membranes

Laboratory experiments were conducted in a wind-wave tank to study the turbulent characteristics in the water boundary-layers under the action of wind and waves and to study the oil dispersion characteristics under the action of breaking waves Effects of an oil slick on the wind-waves or mechanically-generated waves with wind were also investigated The objective was to understand by means of laboratory experiments the behavior of oil dispersion in the upper ocean Two new instruments, a laser Doppler velocimeter and a photodiode wave guage, have been developed to measure remotely the velocity and the vertical displacement of the water surface The two new techniques and the experimental results are described in detail For field application, empirical formulas were derived from the laboratory results (Author)

A study to conduct experiments concerning turbulent dispersion of oil slicks

The purpose of this article is to review some of the novel flow visualization techniques that are particularly suited for studying unsteady flows. While many of these techniques were originally developed for steady flow fields, the present paper will emphasize applications to time-dependent flows. The flow visualization methods presented include those that make use of scattered light from small particles or foreign additives as well as those that make use of changes in the index of refraction.

Mohamed Gad-el-Hak

Papers

Suppression of absolute instabilities in the flow inside a compliant tube

Flow Control: Reynolds Number Effects

Molecular Dynamic Simulations of Fibrous Distillation Membranes

A study to conduct experiments concerning turbulent dispersion of oil slicks

Review of flow visualization techniques for unsteady flows