An Indicator of Nonlinear Gravitational Clustering

Alignment of velocity and acceleration before shell crossing, and later misalignment are used to define velocity contrast, an indicator of dynamical state of matter undergoing gravitational collapse. We use this to study bias in clustering properties of dynamically nonlinear mass.Comment: 4 pages, uuencoded postscript file. To appear in 'Clusters, Lensing, and the Future of the Universe' ed. V.Trimble and A.Reisenegge

Creating Knowledge in a High-Tech French SME.

This paper deals with organizational learning and knowledge creation in Allcapt, a high-tech French SME, through two different experiences : A technological innovation, dealing with the design of temperature sensors for Ariane V launcher, and an organizational innovation, dealing with human resource management. The paper results from a field research conducted in Allcapt’s plant between 1996-2000. The various stages and steps of the technological and organizational dimensions of problem solving are presented in order to add to existing case studies on organizational learning and knowledge creation, as they are useful to make comparative studies. The same data is also used to propose a deconstruction of the concept of organizational learning and knowledge creation in its different components according to the case in hand. For Allcapt, the proposed relevant deconstruction is the “technological” and the “organizational” aspects of learning and knowledge creation. Allcapt succeeded in the technological innovation challenge, but has been less successful in the organizational aspects, as demonstrated by attempts at innovative experiences in human resource management. This supports the notion that the success in one aspect will not guarantee success in the second aspect, and some of the reasons explaining this divergence are presented in the paper.organizational learning, knowledge creation

HI as a Probe of the Large Scale Structure in the Post-Reionization Universe

We model the distribution of neutral Hydrogen (HI hereafter) in the post-reionization universe. This model uses gravity only N-Body simulations and an ansatz to assign HI to dark matter haloes that is consistent with observational constraints and theoretical models. We resolve the smallest haloes that are likely to host HI in the simulations, care is also taken to ensure that any errors due to the finite size of the simulation box are small. We then compute the smoothed one point probability distribution function and the power spectrum of fluctuations in HI. This is compared with other predictions that have been made using different techniques. We highlight the significantly high bias for the HI distribution at small scales. This aspect has not been discussed before. We then discuss the prospects for detection with the MWA, GMRT and the hypothetical MWA5000. The MWA5000 can detect visibility correlations at large angular scales at all redshifts in the post-reionization era. The GMRT can detect visibility correlations at lower redshifts, specifically there is a strong case for a survey at z=1.3. We also discuss prospects for direct detection of rare peaks in the HI distribution using the GMRT. We show that direct detection should be possible with an integration time that is comparable to, or even less than, the time required for a statistical detection. Specifically, it is possible to make a statistical detection of the HI distribution by measuring the visibility correlation, and, direct detection of rare peaks in the HI distribution at z = 1.3 with the GMRT in less than 1000 hours of observations.Comment: 15 pages, 11 figures. Accepted for publication in the MNRAS. This is a merged manuscript also containing material covered in 0908.385

A New Statistical Indicator to Study Nonlinear Gravitational Clustering and Structure Formation

In an expanding universe, velocity field and gravitational force field are proportional to each other in the linear regime. Neither of these quantities evolve in time and these can be scaled suitably so that the constant of proportionality is unity and velocity and force field are equal. The Zeldovich approximation extends this feature beyond the linear regime, until formation of pancakes. Nonlinear clustering which takes place {\it after} the breakdown of Zeldovich approximation, breaks this relation and the mismatch between these two vectors increases as the evolution proceeds. We suggest that the difference of these two vectors could form the basis for a powerful, new, statistical indicator of nonlinear clustering. We define an indicator called velocity contrast, study its behaviour using N-Body simulations and show that it can be used effectively to delineate the regions where nonlinear clustering has taken place. We discuss several features of this statistical indicator and provide simple analytic models to understand its behaviour. Particles with velocity contrast higher than a threshold have a correlation function which is biased with respect to the original sample. This bias factor is scale dependent and tends to unity at large scales.Comment: 12 pages, 8 figures, LaTeX with uuencoded figures, uses MN.sty and epsf.sty; Discussion has been enlarged to clarify a few points. Introduction has been added. Some figures have change

Designing temperature sensors for rocket engine: Organisational change through technological innovation in a french SME.

organisational change