Near-Infrared Surface Photometry of Bulges and Disks of Spiral Galaxies. The Data

We present optical and near-infrared (NIR) surface brightness and colour profiles,in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 degrees. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and real-colour images are presented, as well as colour index maps. This data set, tailored for the study of the population characteristics of galaxy bulges, provides useful information on the colours of inner disks as well. In related papers, we have used them to quantify colour gradients in bulges, and age differentials between bulge and inner disk.Comment: 18 pages Latex with 2 postscript figures. Accepted for New Astronomy. This is an electronic paper; a complete preprint, including all of the tables and figures can be found at ftp://www.astro.rug.nl/peletier/newast/newast.htm

Upscaling of dislocation walls in finite domains

We wish to understand the macroscopic plastic behaviour of metals by upscaling the micro-mechanics of dislocations. We consider a highly simplified dislocation network, which allows our microscopic model to be a one dimensional particle system, in which the interactions between the particles (dislocation walls) are singular and non-local. As a first step towards treating realistic geometries, we focus on finite-size effects rather than considering an infinite domain as typically discussed in the literature. We derive effective equations for the dislocation density by means of \Gamma-convergence on the space of probability measures. Our analysis yields a classification of macroscopic models, in which the size of the domain plays a key role

An Internet Portal based on 'Twenty Questions'

An efficient Internet portal should contain a search engine or maybe even a decision support system to supply the user with the information (s)he may be looking for. In this report an intelligent agent is suggested that relates different sites to each other, based on the answers supplied by the users looking for certain information. For this purpose a self-learning system has been made, based on the neural network of the game Twenty Questions, but with a strategy that relates different objects or sites by correlating the list of answers to the questions

Thermal Modeling in Polymer Extrusion

In this paper we consider thermal effects of polymer flows through a cylindrical die. First, we derive a model for the oscillatory behavior of polymer flow in an extruder given a functional relation between the pressure and flow rate. A simple isothermal but temperature dependent model is constructed to find this relation. Unfortunately, the model is shown to be invalid in the physical regime of interest. We present several arguments to suggest that the isothermal assumption is reasonable but that a more detailed understanding of the small-scale molecular dynamics near the boundary may be required. Second, we show that a simplified model for thermoflow multiplicity in a cooled tube is inconsistent, when the stationary non-Newtonian flow is assumed to be incompressible without radial pressure gradients and without radial velocity. This inconsistency can be removed by allowing for weak compressibility effects in the down-steam area

Quantification of coarse-graining error in Langevin and overdamped Langevin dynamics

In molecular dynamics and sampling of high dimensional Gibbs measures coarse-graining is an important technique to reduce the dimensionality of the problem. We will study and quantify the coarse-graining error between the coarse-grained dynamics and an effective dynamics. The effective dynamics is a Markov process on the coarse-grained state space obtained by a closure procedure from the coarse-grained coefficients. We obtain error estimates both in relative entropy and Wasserstein distance, for both Langevin and overdamped Langevin dynamics. The approach allows for vectorial coarse-graining maps. Hereby, the quality of the chosen coarse-graining is measured by certain functional inequalities encoding the scale separation of the Gibbs measure. The method is based on error estimates between solutions of (kinetic) Fokker-Planck equations in terms of large-deviation rate functionals

A consistent treatment of link and writhe for open rods, and their relation to end rotation

We combine and extend the work of Alexander & Antman \cite{alexander.82} and Fuller \cite{fuller.71,fuller.78} to give a framework within which precise definitions can be given of topological and geometrical quantities characterising the contortion of open rods undergoing large deformations under end loading. We use these definitions to examine the extension of known results for closed rods to open rods. In particular, we formulate the analogue of the celebrated formula $Lk=Tw+Wr$ (link equals twist plus writhe) for open rods and propose an end rotation, through which the applied end moment does work, in the form of an integral over the length of the rod. The results serve to promote the variational analysis of boundary-value problems for rods undergoing large deformations.Comment: 17 pages, 4 figure

Star formation in the central regions of galaxies

Massive star formation in the central regions of spiral galaxies plays an important role in the dynamical and secular evolution of their hosts. Here, we summarise a number of recent investigations of the star formation history and the physical conditions of the gas in circumnuclear regions, to illustrate not only the detailed results one can achieve, but also the potential of using state-of-the-art spectroscopic and analysis techniques in researching the central regions of galaxies in general. We review how the star formation history of nuclear rings confirms that they are long-lived and stable configurations. Gas flows in from the disk, through the bar, and into the ring, where successive episodes of massive star formation occur. Analysing the ring in NGC 7742 in particular, we determine the physical conditions of the line emitting gas using a combination of ionisation and stellar population modelling, concluding that the origin of the nuclear ring in this non-barred galaxy lies in a recent minor merger with a small gas-rich galaxy.Comment: Invited contribution, to appear in "Mapping the Galaxy and other galaxies", Eds. K. Wada and F. Combes, Springer, in pres

A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology

We present a detailed study of the bar fraction in the CfA sample of Seyfert galaxies, and in a carefully selected control sample of non-active galaxies, to investigate the relation between the presence of bars and of nuclear activity. To avoid the problems related to bar classification in the RC3, e.g., subjectivity, low resolution and contamination by dust, we have developed an objective bar classification method, which we conservatively apply to our new sub-arcsecond resolution near-infrared imaging data set (Peletier et al. 1999). We are able to use stringent criteria based on radial profiles of ellipticity and major axis position angle to determine the presence of a bar and its axial ratio. Concentrating on non-interacting galaxies in our sample for which morphological information can be obtained, we find that Seyfert hosts are barred more often (79% +/- 7.5%) than the non-active galaxies in our control sample (59% +/- 9%), a result which is at the 2.5 sigma significance level. The fraction of non-axisymmetric hosts becomes even larger when interacting galaxies are taken into account. We discuss the implications of this result for the fueling of central activity by large-scale bars. This paper improves on previous work by means of imaging at higher spatial resolution and by the use of a set of stringent criteria for bar presence, and confirms that the use of NIR is superior to optical imaging for detection of bars in disk galaxies.Comment: Latex, 3 figures, includes aaspptwo.sty, accepted for publication in the Astrophysical Journa