Reducing the standard deviation in multiple-assay experiments where the variation matters but the absolute value does not

You measure the value of a quantity x for a number of systems (cells, molecules, people, chunks of metal, DNA vectors, etc.). You repeat the whole set of measures in different occasions or assays, which you try to design as equal to one another as possible. Despite the effort, you find that the results are too different from one assay to another. As a consequence, some systems' averages present standard deviations that are too large to render the results statistically significant. In this work, we present a novel correction method of very low mathematical and numerical complexity that can reduce the standard deviation in your results and increase their statistical significance as long as two conditions are met: inter-system variations of x matter to you but its absolute value does not, and the different assays display a similar tendency in the values of x; in other words, the results corresponding to different assays present high linear correlation. We demonstrate the improvement that this method brings about on a real cell biology experiment, but the method can be applied to any problem that conforms to the described structure and requirements, in any quantitative scientific field that has to deal with data subject to uncertainty.Comment: Supplementary material at http://bit.ly/14I718

Conformal mapping of ultrasonic crystals: confining ultrasound and cochlear-like wave guiding

Conformal mapping of a slab of a two-dimensional ultrasonic crystal generate a closed geometrical arrangement of ultrasonic scatterers with appealing acoustic properties. This acoustic shell is able to confine ultrasonic modes. Some of these internal resonances can be induced from an external wave source. The mapping of a linear defect produces a wave-guide that exhibits a spatial-frequency selection analogous to that characteristic of a synthetic "cochlea". Both, experimental and theoretical results are reported here.Comment: 4 pages, 4 figure

Bubble size distribution resulting from the breakup of an air cavity injected into a turbulent water jet

We investigated experimentally the shape of the final size PDF(D) resulting from the breakup of an air bubble injected into the fully developed region of a high Reynolds number turbulent water jet. It is shown that the PDF(Dcirc) of the normalized bubble size Dcirc=D/D32, where D32 is the Sauter mean diameter of the distribution, has a universal single shape independent of the value of the turbulent kinetic energy of the water jet at the bubble injection point and of the air void fraction, α. The shape of the exponential tails characterizing each PDF(D) is shown to be only a function of the initial bubble size D0 and the critical bubble size Dc, defined as Dc=(1.46σ/ρ)3/5ɛ-2/5, where ɛ is the value of the dissipation rate of turbulent kinetic energy per unit mass at the air injection point

Global mode analysis of axisymmetric bluff-body wakes: Stabilization by base bleed

International audienceThe flow around a slender body with a blunt trailing edge is unstable in most situations of interest. Usually the flow instabilities are generated within the wake behind the bluff body, inducing fluctuating forces and introducing the possibility of resonance mechanisms with modes of the structure. Base bleed is a simple and well-known means of stabilizing the wake. In the present research, we investigate the global instability properties of the laminar-incompressible flow that develops behind a cylinder with sharp edges and axis aligned with the free stream using a spectral domain decomposition method. In particular, we describe the flow instability characteristics as a function of the Reynolds number, Re=?W8D/µ, and the bleed coefficient, defined as the bleed-to-free-stream velocity ratio, Cb=Wb/W8, where D is the diameter of the body and ? and µ the density and viscosity of the free stream, respectively. For a truncated cylinder of aspect ratio L/D=5, where L is the length of the body, our calculations reveal the presence of a first steady bifurcation in the wake at Re?391, as well as a second oscillatory one at Re?715 with an associated Strouhal number St?0.0905 for the most unstable azimuthal mode {pipe}m{pipe}=1. In addition, we report the existence of two critical values of the bleed coefficient Cb1*(Re,{pipe}m{pipe}) and Cb2*(Re,{pipe}m{pipe}) < Cb1*, which vary with the aspect ratio of the body, needed to stabilize both the first and second bifurcations in the range of Reynolds numbers under study, 0=Re=2200. Finally, the numerical results for the oscillatory mode obtained for a bulletlike body of aspect ratio L/D=2 without base bleed are compared with experiments performed in a wind tunnel using hot-wire anemometry, showing the limitations of using an axisymmetric basic flow at Reynolds numbers higher than the critical one corresponding to the first steady bifurcation in the global stability analysis. © 2009 American Institute of Physics

Editorial

En esta ocasión, sumamos un nuevo nutriente a la conciencia jurídica, sin descuidar que cada palabra bien emplazada proyecta conceptos pero también conciencia jurídica. Efectivamente, las sociedades reclaman rigor y honestidad a nivel normativo y doctrinario, con los cuales idóneamente se aborda y entiende la realidad. La globalización que hoy define la historia contemporánea, sobre todo con la digitación y el mundo virtual, en segundos lleva y trae conocimientos, diálogos y sobre todo resultados de la investigación científica. Cómo entonces no sentirnos satisfechos con la puntual edición de Lex, cuyo volumen 16, N° 22, hoy presentamos

Editorial

Salimos a luz con Lex 21, edad que solo se explica por la calidad, plu-ralidad temática y de enfoque de la revista que desde su política de acceso abierto tiene como objetivo la difusión y la reflexión global