High-resolution 3D optical microscopy inside the beating zebrafish heart using prospective optical gating

3D fluorescence imaging is a fundamental tool in the study of functional and developmental biology, but effective imaging is particularly difficult in moving structures such as the beating heart. We have developed a non-invasive real-time optical gating system that is able to exploit the periodic nature of the motion to acquire high resolution 3D images of the normally-beating zebrafish heart without any unnecessary exposure of the sample to harmful excitation light. In order for the image stack to be artefact-free, it is essential to use a synchronization source that is invariant as the sample is scanned in 3D. We therefore describe a scheme whereby fluorescence image slices are scanned through the sample while a brightfield camera sharing the same objective lens is maintained at a fixed focus, with correction of sample drift also included. This enables us to maintain, throughout an extended 3D volume, the same standard of synchronization we have previously demonstrated in and near a single 2D plane. Thus we are able image the complete beating zebrafish heart exactly as if the heart had been artificially stopped, but sidestepping this undesirable interference with the heart and instead allowing the heart to beat as normal

Baryon polarization in low-energy unpolarized meson-baryon scattering

We compute the polarization of the final-state baryon, in its rest frame, in low-energy meson--baryon scattering with unpolarized initial state, in Unitarized BChPT. Free parameters are determined by fitting total and differential cross-section data (and spin-asymmetry or polarization data if available) for $pK^-$, $pK^+$ and $p\pi^+$ scattering. We also compare our results with those of leading-order BChPT

The excluded volume of two-dimensional convex bodies: shape reconstruction and non-uniqueness

In the Onsager model of one-component hard-particle systems, the entire phase behaviour is dictated by a function of relative orientation, which represents the amount of space excluded to one particle by another at this relative orientation. We term this function the excluded volume function. Within the context of two-dimensional convex bodies, we investigate this excluded volume function for one-component systems addressing two related questions. Firstly, given a body can we find the excluded volume function? Secondly, can we reconstruct a body from its excluded volume function? The former is readily answered via an explicit Fourier series representation, in terms of the support function. However we show the latter question is ill-posed in the sense that solutions are not unique for a large class of bodies. This degeneracy is well characterised however, with two bodies admitting the same excluded volume function if and only if the Fourier coefficients of their support functions differ only in phase. Despite the non-uniqueness issue, we then propose and analyse a method for reconstructing a convex body given its excluded volume function, by means of a discretisation procedure where convex bodies are approximated by zonotopes with a fixed number of sides. It is shown that the algorithm will always asymptotically produce a best least-squares approximation of the trial function, within the space of excluded volume functions of centrally symmetric bodies. In particular, if a solution exists, it can be found. Results from a numerical implementation are presented, showing that with only desktop computing power, good approximations to solutions can be readily found

Numerical simulation of rivulet evolution on a horizontal cable subject to an external aerodynamic field

On wet and windy days, the inclined cables of cable-stayed bridges may experience a large amplitude oscillation known as rain-wind-induced vibration (RWIV). It has previously been shown by in situ and wind-tunnel studies that the formation of rain-water accumulations or ‘rivulets’ at approximately the separation points of the external aerodynamic flow field and the resulting effect that these rivulets have on this field may be one of the primary mechanisms for RWIV. A numerical method has been developed to undertake simulations of certain aspects of RWIV, in particular, rivulet formation and evolution. Specifically a two-dimensional model for the evolution of a thin film of water on the outer surface of a horizontal circular cylinder subject to the pressure and shear forces that result from the external flow field is presented. Numerical simulations of the resulting evolution equation using a bespoke pseudo-spectral solver capture the formation of two-dimensional rivulets, the geometry, location and growth rate of which are all in good agreement with previous studies. Examinations of how the distribution and magnitude of aerodynamic loading and the Reynolds number influence the rivulet temporal evolution are undertaken, the results of which indicate that while all three affect the temporal evolution, the distribution of the loading has the greatest effect

New developments in rain–wind-induced vibrations of cables

On wet and windy days, the inclined cables of cable stayed bridges can experience large amplitude, potentially damaging oscillations known as rain-wind-induced vibration (RWIV). RWIV is believed to be the result of a complicated non-linear interaction between rivulets of rain water that run down the cables and the wind loading on the cables from the unsteady aerodynamics; however, despite a considerable international research effort, the underlying physical mechanism that governs this oscillation is still not satisfactorily understood. An international workshop on RWIV was held in April 2008, hosted at the University of Strathclyde. The main outcomes of this workshop are summarised in the paper. A numerical method to investigate aspects of the RWIV phenomenon has recently been developed by the authors, which couples an unsteady aerodynamic solver to a thin-film model based on lubrication theory for the flow of the rain water to ascertain the motion of the rivulets owing to the unsteady aerodynamic field. This novel numerical technique, which is still in the relatively early stages of development, has already provided useful information on the coupling between the external aerodynamic flow and the rivulet, and a summary of some of the key results to date is presented

Study of the Local Interstellar Medium using Pulsar Scintillation

We present here the results from an extensive scintillation study of twenty pulsars in the dispersion measure (DM) range 3 - 35 pc cm^-3 carried out using the Ooty Radio Telescope, to investigate the distribution of ionized material in the local interstellar medium (LISM). Our analysis reveals several anomalies in the scattering strength, which suggest that the distribution of scattering material in the Solar neighborhood is not uniform. Our model suggests the presence of a low density bubble surrounded by a shell of much higher density fluctuations. We are able to put some constraints on geometrical and scattering properties of such a structure, and find it to be morphologically similar to the Local Bubble known from other studies.Comment: 5 pages, 3 figure

Genèse du monde, architectonique de la pensée

Nous apportons dans cette contribution de nouvelles réflexions au champ ouvert par celles conduites à partir de l\u27étude du texte biblique de la Genèse.1 Nous avions considéré la parole divine face à l\u27informe de la matière et rapporté le principe à l\u27œuvre dans ce récit de la Création au tracé d\u27une ligne délimitant des formes. Nous avions reconnu trois pouvoirs à ce principe : un pouvoir de séparation (le pouvoir sécant), un pouvoir de regroupement (de rassemblement), un pouvoir de gouvernement (de gouvernance). Nous avions examiné comment des formes parfaites surviennent, sur la seule injonction divine, dans une immédiateté saisissante, ignorant tout des lois de la successivité et par là de la séquence "aspectuelle" classique (début-développement-fin). Avec la naissance de l\u27"organisé", nous avions assisté à la naissance concomitante de la "perfectivité".2 Nous reprenons ici cette immédiateté qui suspend toute considération de temps, annulant la distinction, aussi infime fût-elle, entre un "avant" et un "après". Cette immédiateté dans laquelle fusionnent et co-ïncident le vouloir-désir de Dieu et la Création de ses formes, nous voulons la questionner à même la parole divine : qu\u27en est-il de l\u27immédiateté, que nous avions constatée dans l\u27œuvre, dès lors que nous l\u27interrogeons du côté de la pensée de l\u27"organisateur" ? Et que signifie que notre questionnement s\u27adresse au Créateur, et non plus à la Création ? Nous inversons les pôles de l\u27agir divin — Schelling dirait que nous considérons maintenant le principe "affirmant" et non plus l\u27"affirmé", le principe "affirmant" étant conçu comme étant en avance sur le principe "affirmé", l\u27être.3 Notes : 1 Cf. Daviet-Taylor, F., "Du tracé de la ligne dans la Genèse : naissance du nombre, de la limite et de la perfectivité ", Dumas, Ch., Gangl, M. (éds), Le théâtre du monde, Mélanges offerts à Manfred Eggert, Université d\u27Angers, 2006, p. 67-85) 2 Ibid. 3 Cf. Daviet-Taylor, 1993, 49. Nous avions découvert dans cet article des considérations étrangement jumelles entre le philosophe F. W. J. Schelling et le linguiste Gustave Guillaume dans leur approfondissement du rapport entre la puissance (le virtuel) et l\u27acte (le réel actualisé). Ces considérations éclairent également cette contribution. Citons cet aphorisme de Schelling : "L\u27affirmatif (le concept) est toujours plus grand que l\u27affirmé (la chose)."  In Œuvres métaphysiques, p. 33, aphorisme 58

De la systémicité fonctionnelle de la particule gotique ga-

Nous aborderons la question du système comme une formation (Gebilde) résultant d’une opération de pensée, opération créatrice sur laquelle la langue nous renseigne pour peu qu’en soient questionnés les “précipités” produits, déposés et recueillis en elle. Comme matériau d’illustration, nous convoquons l’un de ces précipités exemplaires qu’est la systémicité fonctionnelle1 propre à une particule, la particule gotique ga-, particule de phrase d’origine indo-européenne et qui apparaît en gotique dans une véritable constellation, celle des composés verbaux et nominaux. Cette particule est en effet la trace d’une opération d’“englobement”, qu’elle soit de portée spatiale ou temporelle. Le repérage de cette systémicité et son étude appliquée aux composés verbaux nous avait permis de rapporter toute occurrence de forme verbale composée en ga- à l’une des quatre valeurs dégagées et indexées sur un continuum fonctionnel, chacune des valeurs se laissant obtenir par déboîtement de la précédente : la valeur sociative, la valeur complexive (résultative), la valeur d’incidence et la valeur jonctive.