An Attempt to Detect the Galactic Bulge at 12 microns with IRAS

Surface brightness maps at 12 microns, derived from observations with the Infrared Astronomical Satellite (IRAS), are used to estimate the integrated flux at this wavelength from the Galactic bulge as a function of galactic latitude along the minor axis. A simple model was used to remove Galactic disk emission (e.g. unresolved stars and dust) from the IRAS measurements. The resulting estimates are compared with predictions for the 12 micron bulge surface brightness based on observations of complete samples of optically identified M giants in several minor axis bulge fields. No evidence is found for any significant component of 12m emission in the bulge other than that expected from the optically identified M star sample plus normal, lower luminosity stars. Known large amplitude variables and point sources from the IRAS catalogue contribute only a small fraction to the total 12 micron flux.Comment: Accepted for publication in ApJ; 13 pages of text including tables in MS WORD97 generated postscript; 3 figures in postscript by Sigma Plo

Eerst weekend! Wiskunde in dienst van een sociaal leven

Het sociale leven - sportactiviteiten, verjaardagsbezoeken, het ontmoeten van vrienden - vindt vooral in de weekeinden plaats. Dit maakt werken in het weekend voor veel mensen onaantrekkelijk. In sectoren waar de dienstverlening 7 dagen in de week en 24 uur per dag beschikbaar moet zijn, zoals in de gezondheidszorg en de beveiligingssector, dienen medewerkers wel in het weekend te werken. Het maken van goede dienstroosters voor het weekend is een uitdaging: medewerkers hebben vaak heel specifieke voorkeuren terwijl de werkgever moet zorgen dat er voldoende mensen worden ingezet. Het maken van goede dienstroosters wordt verder bemoeilijkt doordat er rekening moet worden gehouden met de Arbeidstijdenwetgeving (ATW) en omdat werkgevers de diensten 'eerlijk' over de medewerkers willen verdelen

Organic carbon dynamics in grassland soils. 1. Background information and computer simulation

Includes bibliographical references (pages 199-201).The decomposition rates of 14C-labelled plant residues in different parts of the world were characterized and mathematically simulated. The easily decomposable materials, cellulose and hemicellulose, were described as being decomposed directly by the soil biomass; the lignin fraction of aboveground residues and the resistant portion of the roots entered a decomposable native soil organic matter. Here it could be decomposed by the soil biomass or react with other soil constituents in the formation of more recalcitrant soil organic matter. The transformation rates were considered to be independent of biomass size (first–order). Data from 14C plant residue incorporation studies which yielded net decomposition rates of added materials and from carbon dating of the recalcitrant soil organic matter were transformed to gross decomposition rate constants for three soil depths. The model adequately described soil organic matter transformations under native grassland and the effect of cultivation on organic matter levels. Correction for microbial growth and moisture and temperature variations showed that the rate of wheat straw decomposition, based on a full year in the field in southern Saskatchewan, was 0.05 that under optimal laboratory conditions. The relative decay rates for plant residues during the summer months of the North American Great Plains was 0.1 times that of the laboratory. Comparison with data from other parts of the world showed an annual relative rate of 0.12 for straw decomposition in England, whereas gross decomposition rates in Nigeria were 0.5 those of laboratory rates. Both the decomposable and recalcitrant organic matter were found to be affected by the extent of physical protection within the soil. The extent of protection was simulated and compared to data from experimental studies on the persistence of 14C-labelled amino acids in soil. The extent of protection influenced the steady-state levels of soil carbon upon cultivation more than did the original decomposition rates of the plant residues

Single fibre action potentials in skeletal muscle related to recording distances

Single muscle fibre action potentials (SFAPs) are considered to be functions of a bioelectrical source and electrical conductivity parameters of the medium. In most model studies SFAPs are computed as a convolution of the bioelectrical source with a transfer function. Calculated peak-to-peak amplitudes of SFAPs decrease with increasing recording distances. In this paper an experimental validation of model results is presented. Experiments were carried out on the m. extensor digitorum longus (EDL) of the rat. Using a method including fluorescent labelling of the active fibre, the distance between the active fibre and the recording electrode was derived. With another method, the decline of the peak-to-peak amplitude of SFAPs detected along a multi-electrode was obtained. With both experimental methods, in general peak-to-peak amplitudes of SFAPs decreased with increasing recording distances, as was found in model results with present volume conduction theory. However, this behaviour was not found in all experiments. The rate of decline of the peak-to-peak amplitudes with recording distance was always less than in models

Surface defreezing of glasses

A glass surface may still flow below the bulk glass transition temperature, where the underlying bulk is frozen. Assuming the existence at T=T* of a bulk thermodynamical glass transition, we show that the glass-vapor interface is generally wetted by a liquid layer of thickness ~ -ln(T*-T) when T--> T*. Contrary to standard surface melting of crystals however, the integrated value of the diffusivity across the interface remains finite for T-->T*. Difference in shape induced by bulk and by surface flow is discussed as a possible means of experimental detection of surface defreezing.Comment: five pages, three figure

HST Snapshot Survey of Post-AGB Objects

The results from a Hubble Space Telescope (HST) snapshot survey of post-AGB objects are shown. The aim of the survey is to complement existing HST images of PPN and to connect various types of nebulosities with physical and chemical properties of their central stars. Nebulosities are detected in 15 of 33 sources. Images and photometric and geometric measurements are presented. For sources with nebulosities we see a morphological bifurcation into two groups, DUPLEX and SOLE, as previous studies have found. We find further support to the previous results suggesting that this dichotomy is caused by a difference in optical thickness of the dust shell. The remaining 18 sources are classified as stellar post-AGB objects, because our observations indicate a lack of nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE based on their infrared colors. The cause of the differences among the groups are investigated. We discuss some evidence suggesting that high progenitor-mass AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitor-mass AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources probably have low mass progenitors and do not seem to develop nebulosities during the post-AGB phase and therefore do not become planetary nebulae.Comment: 21 pages, 11 figure