Use of Tenax® films to demonstrate the migration of chemical contaminants from cardboard into dry food

Contaminants in food packaging are a challenge of our time since the packaging material itself has been found to represent a source of food contamination through the migration of substances from it. Before first use, packaging materials destined for the packaging of dry foods can be evaluated by performing migration experiments with the simulant for dry foods, Tenax (R). This simulant is commercially available as a powder that is more difficult to handle during the migration experiments. This paper reports the development of a Tenax film. The film can be applied to the cardboard surface to conduct the migration test. After the migration is completed, the film can be easily extracted to determine the concentration of the contaminants in the film. Finally, the performance of the Tenax film was compared with the conventional Tenax powder for the evaluation of 15 model migrants

Detailed Chemical Evolution of Carina and Sagittarius Dwarf Spheroidal Galaxies

In order to verify the effects of the most recent data on the evolution of Carina and Sagittarius Dwarf Spheroidal Galaxies (dSph) and to set tight constraints on the main parameters of chemical evolution models, we study in detail the chemical evolution of these galaxies through comparisons between the new data and the predictions of a model, already tested to reproduce the main observational constraints in dSphs. Several abundance ratios, such as [$\alpha$/Fe], [Ba/Fe] and [Eu/Fe], and the metallicity distribution of stars are compared to the predictions of our models adopting the observationally derived star formation histories in these galaxies. These new comparisons confirm our previously suggested scenario for the evolution of these galaxies, and allow us to better fix the star formation and wind parameters. In particular, for Carina the comparisons indicate that the best efficiency of star formation is $\nu = 0.15 Gyr^{-1}$, that the best wind efficiency parameter is $w_i$ = 5 (the wind rate is five times stronger than the star formation rate), and that the star formation history, which produces the best fit to the observed metallicity distribution of stars is characterized by several episodes of activity. In the case of Sagittarius our results suggest that $\nu=3 Gyr^{-1}$ and $w_i=9$, again in agreement with our previous work. Finally, we show new predictions for [N/Fe] and [C/Fe] ratios for the two galaxies suggesting a scenario for Sagittarius very similar to the one of the solar vicinity in the Milky Way, except for a slight decrease of [N/Fe] ratio at high metallicities due to the galactic wind. For Carina we predict a larger [N/Fe] ratio at low metallicities, reflecting the lower star formation efficiency of this galaxy relative to Sagittarius and the Milky Way.Comment: 11 pages, 7 figures, accepted for publication in Asttronomy & Astrophysic

Chemical Evolution of Dwarf Spheroidal and Blue Compact Galaxies

We studied the chemical evolution of Dwarf Spheroidal (dSph) and Blue Compact Galaxies (BCGs) by means of comparison between the predictions of chemical evolution models and several observed abundance ratios. Detailed models with up to date nucleosynthesis taking into account the role played by supernovae of different types (II, Ia) were developed for both types of galaxies allowing us to follow the evolution of several chemical elements. The models are specified by the prescriptions of the star formation (SF) and galactic wind efficiencies chosen to reproduce the main features of these galaxies. We also investigated a possible connection in the evolution of dSph and BCGs and compared the predictions of the models to the abundance ratios observed in Damped Lyman alpha Systems (DLAs). The main conclusions are: i) the observed distribution of [alpha/Fe] vs. [Fe/H] in dSph is mainly a result of the SF rate coupled with the wind efficiency; ii) a low SF efficiency and a high wind efficiency are required to reproduce the observational data for dSph; iii) the low gas content of these galaxies is the result of the combined action of gas consumption by SF and gas removal by galactic winds; iv) the BCGs abundance ratios are reproduced by models with 2 to 7 bursts of SF with low efficiencies ; v) the low values of N/O observed in BCGs are the natural result of a bursting SF; vi) a connection between dSph and BCGs in an unified evolutionary scenario is unlikely; vii) the models for the dSph and BCGs imply different formation scenarios for the DLAs; viii) a suitable amount of primary N produced in massive stars can be perhaps an explanation for the low plateau in the [N/$\alpha$] distribution observed in DLAs, if real.Comment: 16 pages, 17 figures, accepted for publication in MNRA

The Predicted Metallicity Distribution of Stars in Dwarf Spheroidal Galaxies

We predict the metallicity distribution of stars and the age-metallicity relation for 6 Dwarf Spheroidal (dSph) galaxies of the Local Group by means of a chemical evolution model which is able to reproduce several observed abundance ratios and the present day total mass and gas content of these galaxies. The model adopts up to date nucleosynthesis and takes into account the role played by supernovae of different types (II, Ia) allowing us to follow in detail the evolution of several chemical elements (H, D, He, C, N, O, Mg, Si, S, Ca, and Fe). Each galaxy model is specified by the prescriptions of the star formation rate and by the galactic wind efficiency chosen to reproduce the main features of these galaxies. These quantities are constrained by the star formation histories of the galaxies as inferred by the observed color-magnitude diagrams (CMD). The main conclusions are: i) 5 of the 6 dSphs galaxies are characterized by very low star formation efficiencies ($\nu = 0.005 - 0.5 Gyr ^{-1}$) with only Sagittarius having a higher one ($\nu = 1.0 - 5.0 Gyr ^{-1}$); ii) the wind efficiency is high for all galaxies, in the range $w_i$ = 6 - 15; iii) a high wind efficiency is required in order to reproduce the abundance ratios and the present day gas mass of the galaxies; iv) the predicted age-metallicity relation implies that the stars of the dSphs reach solar metallicities in a time-scale of the order of 2 - 6 Gyr; v) the metallicity distributions of stars in dSphs exhibit a peak around [Fe/H] $\sim$ -1.8 to -1.5 dex, with the exception of Sagittarius ([Fe/H] $\sim$ -0.8 dex); iv) the predicted metallicity distributions of stars suggest that the majority of stars in dSphs are formed in a range of metallicity in agreement with the one of the observed stars.Comment: 12 pages, 19 figures, accepted for publication in MNRA

Cosmic Star Formation: Constraints on the Galaxy Formation Models

We study the evolution of the cosmic star formation by computing the luminosity density (LD) in the UV, B, J, and K bands, and the stellar mass density (MD) of galaxies in two reference models of galaxy evolution: the pure luminosity evolution (PLE) model developed by Calura & Matteucci (2003) and the semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al. (2002). The former includes a detailed description of the chemical evolution of galaxies of different morphological types with no density evolution; the latter includes the merging histories of the galactic DM haloes, as predicted by the hierarchical clustering scenario, but it does not contain morphological classification nor chemical evolution. We find that at z< 1.5 both models are consistent with the available data on the LD of galaxies in all the considered bands. At high z, the LDs predicted in the PLE model show a peak due to the formation of ellipticals, whereas the SAM predicts a gradual decrease of the star formation and of the LD for z> 2.5. At such redshifts the PLE predictions tend to overestimate the present data in the B band whereas the SAM tends to underestimate the observed UV LD. As for the stellar MD, the PLE picture predicts that nearly 50% and 85% of the present stellar mass are in place at z=4 and z=1, respectively. According to the SAM, 50% and 60% of the present stellar mass are in place at z=1.2 and z=1, respectively. Both predictions fit the observed MD up to z=1. At z>1, the PLE model and the SAM tend to overestimate and underestimate the observed values, respectively. We discuss the origin of the above model results, and the role of observational uncertainties (such as dust extinction) in comparing models with observations.Comment: 14 pages, accepted for publication in MNRA

The evolution of the photometric properties of Local Group dwarf spheroidal galaxies

We investigate the present-day photometric properties of the dwarf spheroidal galaxies in the Local Group. From the analysis of their integrated colours, we consider a possible link between dwarf spheroidals and giant ellipticals. From the analysis of the V vs (B-V) plot, we search for a possible evolutionary link between dwarf spheroidal galaxies (dSphs) and dwarf irregular galaxies (dIrrs). By means of chemical evolution models combined with a spectro-photometric model, we study the evolution of six Local Group dwarf spheroidal galaxies (Carina, Draco, Sagittarius, Sculptor, Sextans and Ursa Minor). The chemical evolution models, which adopt up-to-date nucleosynthesis from low and intermediate mass stars as well as nucleosynthesis and energetic feedback from supernovae type Ia and II, reproduce several observational constraints of these galaxies, such as abundance ratios versus metallicity and the metallicity distributions. The proposed scenario for the evolution of these galaxies is characterised by low star formation rates and high galactic wind efficiencies. Such a scenario allows us to predict integrated colours and magnitudes which agree with observations. Our results strongly suggest that the first few Gyrs of evolution, when the star formation is most active, are crucial to define the luminosities, colours, and other photometric properties as observed today. After the star formation epoch, the galactic wind sweeps away a large fraction of the gas of each galaxy, which then evolves passively. Our results indicate that it is likely that at a certain stage of their evolution, dSphs and dIrrs presented similar photometric properties. However, after that phase, they evolved along different paths, leading them to their currently disparate properties.Comment: 13 pages, Astronomy & Astrophysics, accepte

Effects of the integrated galactic IMF on the chemical evolution of the solar neighbourhood

The initial mass function determines the fraction of stars of different intial mass born per stellar generation. In this paper, we test the effects of the integrated galactic initial mass function (IGIMF) on the chemical evolution of the solar neighbourhood. The IGIMF (Weidner & Kroupa 2005) is computed from the combination of the stellar intial mass function (IMF), i.e. the mass function of single star clusters, and the embedded cluster mass function, i.e. a power law with index beta. By taking into account also the fact that the maximum achievable stellar mass is a function of the total mass of the cluster, the IGIMF becomes a time-varying IMF which depends on the star formation rate. We applied this formalism to a chemical evolution model for the solar neighbourhood and compared the results obtained by assuming three possible values for beta with the results obtained by means of a standard, well-tested, constant IMF. In general, a lower absolute value of beta implies a flatter IGIMF, hence a larger number of massive stars and larger metal ejection rates. This translates into higher type Ia and II supernova rates, higher mass ejection rates from massive stars and a larger amount of gas available for star formation, coupled with lower present-day stellar mass densities. (abridged) We also discuss the importance of the present day stellar mass function (PDMF) in providing a way to disentangle among various assumptions for beta. Our results indicate that the model adopting the IGIMF computed with beta ~2 should be considered the best since it allows us to reproduce the observed PDMF and to account for most of the chemical evolution constraints considered in this work.Comment: 22 pages, 19 figure

Database of Geneva stellar evolution tracks and isochrones for UBVRIJHKLL'M, HST-WFPC2, Geneva and Washington photometric systems

We have used an updated version of the empirically and semi-empirically calibrated BaSeL library of synthetic stellar spectra of Lejeune et al. (1997, 1998) and Westera et al. (1999) to calculate synthetic photometry in the UBVRIJHKLL'M, HST-WFPC2, Geneva, and Washington systems for the entire set of non-rotating Geneva stellar evolution models covering masses from 0.4-0.8 to 120-150 Msun and metallicities Z=0.0004 (1/50 Zsun) to 0.1 (5 Zsun). The results are provided in a database which includes all individual stellar tracks and the corresponding isochrones covering ages from 10^3 yr to 16--20 Gyr in time steps of Delta(log t)= 0.05 dex. The database also includes a new grid of stellar tracks of very metal-poor stars (Z=0.0004) from 0.8 - 150 Msun calculated with the Geneva stellar evolution code. The full database will be available in electronic form at the CDS (http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/(vol)/(page)) and at http://webast.ast.obs-mip.fr/stellar/.Comment: Accepted for publication in A&A. LaTeX, 10 pages including 2 figures. Full database available at http://webast.ast.obs-mip.fr/stella

A new comprehensive set of elemental abundances in DLAs III. Star formation histories

We obtained comprehensive sets of elemental abundances for eleven damped Ly-alpha systems (DLAs) at z_DLA=1.7-2.5. In Paper I of this series, we showed for three DLA galaxies that we can derive their star formation histories and ages from a detailed comparison of their intrinsic abundance patterns with chemical evolution models. We determine in this paper the star formation properties of six additional DLA galaxies. The derived results confirm that no single star formation history explains the diverse sets of abundance patterns in DLAs. We demonstrate that the various star formation histories reproducing the DLA abundance patterns are typical of local irregular, dwarf starburst and quiescent spiral galaxies. Independent of the star formation history, the DLAs have a common characteristic of being weak star forming galaxies; models with high star formation efficiencies are ruled out. All the derived DLA star formation rates per unit area are moderate or low, with values between -3.2 < log SFR < -1.1 M_sol yr^{-1} kpc^{-2}. The DLA abundance patterns require a large spread in ages ranging from 20 Myr up to 3 Gyr. The oldest DLA in our sample is observed at z_DLA=1.864 with an age estimated to more than 3 Gyr; it nicely indicates that galaxies were already forming at z_f>10. But, most of the DLAs show ages much younger than that of the Universe at the epoch of observation. Young galaxies thus seem to populate the high redshift Universe at z>2, suggesting relatively low redshifts of formation (z~3) for most high-redshift galaxies. The DLA star formation properties are compared with those of other high-redshift galaxies identified in deep imaging surveys with the aim of obtaining a global picture of high-redshift objects.Comment: 19 pages, 11 figures, Accepted for publication in A&

Disparities in dialysis treatment and outcomes for Dutch and Belgian children with immigrant parents

BACKGROUND: In Belgium and the Netherlands, up to 40% of the children on dialysis are children with immigrant parents of non-Western European origin (non-Western). Concerns exist regarding whether these non-Western patients receive the same quality of care as children with parents of Western European origin (Western). We compared initial dialysis, post-initial treatment, and outcomes between non-Western and Western patients on dialysis. METHODS: All children <19 years old on chronic dialysis in the Netherlands and Belgium between September 2007 and May 2011 were included in the study. Non-Western patients were defined as children of whom one or both parents were born in non-Western countries. RESULTS: Seventy-nine of the 179 included patients (44%) were non-Western children. Compared to Western patients, non-Western patients more often were treated with hemodialysis (HD) instead of peritoneal dialysis (PD) as first dialysis mode (52 vs. 37%, p = 0.046). Before renal transplantation, non-Western patients were on dialysis for a median (range) of 30 (5-99) months, vs. 15 (0-66) months in Western patients (p = 0.007). Renal osteodystrophy was diagnosed in 34% of non-Western vs. 18% of Western patients (p = 0.028). The incidence rate ratio [95% confidence interval] for acute peritonitis was 2.44 [1.43-4.17] (p = 0.032) for non-Western compared to Western patients. CONCLUSIONS: There are important disparities between children on chronic dialysis with parents from Western European origin and those from non-Western European origin in the choice of modality, duration, and outcomes of dialysis therapy