OH-selected AGB and post-AGB stellar objects II.Blue versus red evolution off the AGB

Using objects found in a systematic survey of the galactic Plane in the 1612-MHz OH line, we discuss in detail two ``sequences'' of post-AGB evolution, a red and a blue. We argue that the red and the blue groups separate by initial mass at 4Msun, based on evolutionary-sequence turn-off colours, spectral energy distributions, outflow velocities and scaleheight. The higher-mass (blue) objects may have earlier AGB termination. The lower-mass (red) objects undergo very sudden reddening for IRAS colour R21\sim1.2; these sources must all undergo a very similar process at AGB termination. The transition colour corresponds to average initial masses of 1.7Msun. A combined IRAS-MSX colour proves a very sensitive tool to distinguish lower-mass, early post-AGB objects from sources still on the AGB and also to distinguish more evolved post-AGB objects from star-forming regions. The high-mass blue objects are the likely precursors of bipolar planetary nebulae, whereas the low-mass red objects will evolve into elliptical planetary nebulae.Comment: 12 pages, LaTex, 7 figures (1 colour), AJ (accepted

An evolutionary disc model of the edge-on galaxy NGC 5907

We present a physical model that explains the two disparate observational facts: 1) the exponential vertical disc structure in the optical and NIR of the non-obscured part of the stellar disc and 2) the enhanced FIR/submm luminosity by about a factor of four near the obscured mid-plane, which requires additional dust and also stellar light to heat the dust component. We use multi-band photometry in U, B, V, R, and I- band combined with radiative transfer through a dust component to fit simultaneously the vertical surface-brightness and colour index profiles in all bands adopting a reasonable star formation history and dynamical heating function. The final disc model reproduces the surface-brightness profiles in all bands with a moderately declining star formation rate and a slowly starting heating function for young stars. The total dust mass is 57 million solar masses as required from the FIR/submm measurements. Without a recent star burst we find in the midplane an excess of 5.2-, 4.0-, and 3.0-times more stellar light in the U-, B-, and V-band, respectively. The corresponding stellar mass-to-light ratios are 0.91 in V- and 1.0 in R-band. The central face-on optical depth in V-band is 0.81 and the radial scale length of the dust is 40% larger than that of the stellar disc. Evolutionary disc models are a powerful method to understand the vertical structure of edge-on galaxies. Insights to the star formation history and the dynamical evolution of stellar discs can be gained. FIR/submm observations are necessary to restrict the parameter space for the models.Comment: 17 pages, 12 figures (24 files), A&A in pres

Observational Constraints on Disk Heating as a Function of Hubble Type

Current understanding of the secular evolution of galactic disks suggests that this process is dominated by two or more heating mechanisms, which increase the random motions of stars in the disk. In particular, the gravitational influence of giant molecular clouds and irregularities in the spiral potential have been proposed to explain the observed velocity dispersions in the solar neighborhood. Each of these mechanisms acts on different components of the stellar velocities, which affects the ratio of the vertical and radial components of the stellar velocity dispersion since the relative strengths of giant molecular clouds and spiral irregularities vary with Hubble type. A study of this ratio as function of Hubble type has the potential to provide strong constraints on disk heating mechanisms. We present major and minor axis stellar kinematics for four spiral galaxies of Hubble type from Sa to Sbc, and use the data to infer the ratios sigma_z/sigma_R in the galaxy disks. The results combined with two galaxies studied previously and with Milky Way data show that the ratio is generally in the range 0.5 - 0.8. There is a marginally significant trend of decreasing ratio with advancing Hubble type, consistent with the predictions of disk heating theories. However, the errors on individual measurements are large, and the absence of any trend is consistent with the data at the 1-sigma level. As a byproduct of our study, we find that three of the four galaxies in our sample have a central drop in their stellar line-of-sight velocity dispersion, a phenomenon that is increasingly observed in spiral galaxies. [ABRIDGED]Comment: 24 pages, LaTeX, 5 Postscript figures, to appear in AJ (Dec 2003

Galaxies with Spiral Structure up to z = 0.87 --Limits on M/L and the Stellar Velocity Dispersion

We consider seven distant galaxies with clearly evident spiral structure from HST images. Three of these were chosen from Vogt et al. (1996) (VFP) and have measured rotational velocities. Five were chosen from the Medium Deep Survey and are studied in Sarajedini et al. 1996 (SGGR), and one galaxy is found in both papers. We place upper limits on their mass-to-light ratios (M/L) by computing M/L_B for a maximal disk. We find that these galaxies have maximal disk mass-to-light ratios M/L_B = 1.5 - 3.5 M_sol/L_Bsol at the low end, but within the range seen in nearby galaxies. The mass-to-light ratios are low enough to suggest that the galaxies contain a young, rapidly formed stellar population. By using a Toomre stability criterion for formation of spiral structure, we place constraints on the ratio of M/L to the stellar velocity dispersion. If these galaxies have maximal disks they would have to be nearly unstable so as to have small enough velocity dispersions that their disks are not unrealistically thick. This suggests that there is a substantial amount of dark matter present in the luminous regions of the galaxy.Comment: AAS Latex + PS Figure, accepted for publication in A

Ex vivo expansion and differentiation of erythroblasts: From culture dishes to stirred tank reactors for the production of red blood cells

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Organic micropollutant removal in full-scale rapid sand filters used for drinking water treatment in The Netherlands and Belgium

Biological treatment processes have the potential to remove organic micropollutants (OMPs) during water treatment. The OMP removal capacity of conventional drinking water treatment processes such as rapid sand filters (RSFs), however, has not been studied in detail. We investigated OMP removal and transformation product (TP) formation in seven full-scale RSFs all treating surface water, using high-resolution mass spectrometry based quantitative suspect and non-target screening (NTS). Additionally, we studied the microbial communities with 16S rRNA gene amplicon sequencing (NGS) in both influent and effluent waters as well as the filter medium, and integrated these data to comprehensively assess the processes that affect OMP removal. In the RSF influent, 9 to 30 of the 127 target OMPs were detected. The removal efficiencies ranged from 0 to 93%. A data-driven workflow was established to monitor TPs, based on the combination of NTS feature intensity profiles between influent and effluent samples and the prediction of biotic TPs. The workflow identified 10 TPs, including molecular structure. Microbial community composition analysis showed similar community composition in the influent and effluent of most RSFs, but different from the filter medium, implying that specific microorganisms proliferate in the RSFs. Some of these are able to perform typical processes in water treatment such as nitrification and iron oxidation. However, there was no clear relationship between OMP removal efficiency and microbial community composition. The innovative combination of quantitative analyses, NTS and NGS allowed to characterize real scale biological water treatments, emphasizing the potential of bio-stimulation applications in drinking water treatment. © 2020 The Author

Tele work: dispersed organizational activity and new forms of spatial - temporal coordination and control

This article focuses on a set of new flexible work arrangements commonly referred to as cctelework) or cctelecommuting,). Although it is not possible to give an unambiguous and precise definition of telework, there is some working consensus on the subject: the belief is held that information technology has made it possible to relocate many types of work involving the electronic processing of information geographically, and telework is the term used to describe workers who have been relocated in this way. An attempt is made to develop theoretical framework in which telework cart be studied. For this purpose the changes that take place: in the environment of organizations have been taken into consideration. It is suggested that as a result of the redesign process new organizational forms emerge that are characterized by a ((dispersed activity pattern)). Dispersed Organizations, are designed to overcome time-andplace constraints associated with rigid bureaucratic structuring and can be distinguished from existing bureaucratic organizations because they are based on it different design philosophy with regard to how, where and when work is done. Dispersed organizations are being characterized by different time and place constraints with respect to interaction between operational units. Although organizations with dispersed activities can be found nowadays in almost every institutional area, little systematic analysis has yet been undertaken. It is assumed that different forms of telework can be studied within this context. The concept of (dispersed organizations) will be discussed and illustrated with results from a case-study conducted in an energycompany in the Netherlands