Multi-electrode nerve cuff recording - model analysis of the effects of finite cuff length

The effect of finite cuff length on the signals recorded by electrodes at different positions along the nerve was analysed in a model study. Relations were derived using a one-dimensional model. These were evaluated in a more realistic axially symmetric 3D model. This evaluation indicated that the cuff appeared shorter because of edge effects at the beginning and end of the cuff. The method for velocity selective filtering introduced by Donaldson was subsequently analysed. In this method, velocity selective filtering is achieved by summing the signals of subsequent tripoles after applying time shifts tuned to a certain conduction velocity. It was also found that the optimum electrode distance for a given cuff length for maximum summed RMS of symmetrical tripoles in the cuff is larger than when evaluating peak-peak amplitudes of single fibre action potentials. Velocity selective filtering yields better selectivity when using symmetrical tripoles, but may yield larger signal RMS when using the wider asymmetrical tripoles, potentially allowing for shorter cuffs. It is speculated that application of a multi-electrode reference may improve velocity selectivity for asymmetrical tripoles

Theoretical Limb Darkening for Classical Cepheids: II. Corrections for the Geometric Baade-Wesselink Method

The geometric Baade-Wesselink method is one of the most promising techniques for obtaining a better calibration of the Cepheid period-luminosity relation by means of interferometric measurements of accurate diameters. In this paper we present new wavelength- and phase-dependent limb darkening corrections based on our time-dependent hydrodynamic models of the classical Cepheid zeta Gem. We show that a model simulation of a Cepheid atmosphere, taking into account the hydrodynamic effects associated with the pulsation, shows strong departures from the limb darkening otherwise predicted by a static model. For most of its pulsational cycle the hydrodynamic model predicts a larger limb darkening then the equivalent static model. The hydrodynamics affects the limb darkening mainly at UV and optical wavelengths. Most of these effects evolve slowly as the star pulsates, but there are phases, associated with shocks propagating into the photosphere, in which significant changes in the limb darkening take place on time-scales of the order of less than a day. We assess the implication of our model LD corrections fitting the geometric Baade-Wesselink distance of zeta Gem for the available near-IR PTI data. We discuss the effects of our model limb darkening on the best fit result, and analyze the requirements needed to test the time-dependence of the limb darkening with future interferometric measurements.Comment: 22 pages, 5 figures, to be published on the Astrophysical Journal, June 1 2003 issu

The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field Method

Recently, we have developed and calibrated the Synthetic Field Method (SFM) to derive the total extinction through disk galaxies. The method is based on the number counts and colors of distant background field galaxies that can be seen through the foreground object, and has been successfully applied to NGC 4536 and NGC 3664, two late-type galaxies located, respectively, at 16 and 11 Mpc. Here, we study the applicability of the SFM to HST images of galaxies in the Local Group, and show that background galaxies cannot be easily identified through these nearby objects, even with the best resolution available today. In the case of M 31, each pixel in the HST images contains 50 to 100 stars, and the background galaxies cannot be seen because of the intrinsic granularity due to strong surface brightness fluctuations. In the LMC, on the other hand, there is only about one star every six linear pixels, and the lack of detectable background galaxies results from a ``secondary'' granularity, introduced by structure in the wings of the point spread function. The success of the SFM in NGC 4536 and NGC 3664 is a natural consequence of the reduction of the intensity of surface brightness fluctuations with distance. When the dominant confusion factor is structure in the PSF wings, as is the case of HST images of the LMC, and would happen in M 31 images obtained with a 10-m diffraction- limited optical telescope, it becomes in principle possible to improve the detectability of background galaxies by subtracting the stars in the foreground object. However, a much better characterization of optical PSFs than is currently available would be required for an adequate subtraction of the wings. Given the importance of determining the dust content of Local Group galaxies, efforts should be made in that direction.Comment: 45 pages, 10 Postscript figure

SN 1993J VLBI (IV): A Geometric Determination of the Distance to M81 with the Expanding Shock Front Method

We compare the angular expansion velocities, determined with VLBI, with the linear expansion velocities measured from optical spectra for supernova 1993J in the galaxy M81, over the period from 7 d to ~9 yr after shock breakout. We estimate the distance to SN 1993J using the Expanding Shock Front Method (ESM). We find the best distance estimate is obtained by fitting the angular velocity of a point halfway between the contact surface and outer shock front to the maximum observed hydrogen gas velocity. We obtain a direct, geometric, distance estimate for M81 of D=3.96+-0.05+-0.29 Mpc with statistical and systematic error contributions, respectively, corresponding to a total standard error of $+-0.29 Mpc. The upper limit of 4.25 Mpc corresponds to the hydrogen gas with the highest observed velocity reaching no farther out than the contact surface a few days after shock breakout. The lower limit of 3.67 Mpc corresponds to this hydrogen gas reaching as far out as the forward shock for the whole period, which would mean that Rayleigh-Taylor fingers have grown to the forward shock already a few days after shock breakout. Our distance estimate is 9+-13 % larger than that of 3.63+-0.34 Mpc from the HST Key Project, which is near our lower limit but within the errors.Comment: 25 pages, 11 figures, accepted for publication in Ap

Competence-based education: An example from vocational practice.

First, the existing confusion about competence-based education is described: the behavioristic, generic and holistic approach. The following definition is formulated: Competence-based education is creating opportunities for students and workers, close to their world of experience in a meaningful learning environment (preferable the professional practice) wherein the learner can develop integrated performance-oriented capabilities to handle the problems in practice. The principles described in this article have been formulated by various authors. Central question in this paper is: What are the experiences of the different groups involved with competence-based education, and to what extent do those experiences influence the principles formulated? Most principles are useful, but more attention has to be paid on coaching

Developing Human Capital for Agrifood Firms' Multi-Stakeholder Interactions

This essay discusses 1) the current agri-food firms’ need of interacting with multiple stakeholders to undertake sustainable strategies effectively, 2) the relationship between human capital and firm capabilities to effectively interact with multiple stakeholders and 3) a list of competencies characterizing the human capital that would meet the need of agri-food firms and which can be learned – at least to some extent – through higher education and on-the-job training

Maatschappelijk verantwoord ondernemen vraagt competentieontwikkeling

Maatschappelijk verantwoord ondernemen is een innovatie die eisen stelt aan ondernemers en medewerkers in ondernemingen. Het vraagt inzicht in duurzaam gebruik van natuurlijke hulpbronnen en zorgvuldig omgaan met mensen in het kader van georganiseerde arbeid, en verantwoord kunnen omgaan met genoemde hulpbronnen. Betrokkenen moeten de grotere effecten leren zien van hun handelen in een groter verband, bijvoorbeeld binnen de gemeenschap waarin zij werken, de toekomst van deze gemeenschap, maar ook buiten de eigen gemeenscha