We present the high-resolution spectroscopic study of five −3.9 ≤ Fe/H ≤ −2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in ...this metallicity range. We carry out a detailed analysis of the chemical abundances of α, iron peak, and light and heavy elements, and draw comparisons with the Milky Way halo and the ultra-faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follow the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the Type II supernovae. In addition to its help in refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggestive of a fair proportion of s-process. We discuss the implication for the nucleosynthetic origin of the neutron capture elements.
We have developed spherically symmetric dynamical models of dwarf spheroidal (dSph) galaxies using Schwarzschild's orbit superposition method. This type of modelling yields constraints both on the ...total mass distribution (e.g. enclosed mass and scale radius) and on the orbital structure of the system (e.g. velocity anisotropy). This method is thus less prone to biases introduced by assumptions in comparison to the more commonly used Jeans modelling, and it allows us to put reliable constraints on their dark matter content. Here we present our results for the Sculptor dSph galaxy, after testing our methods on mock data sets. We fit both the second and fourth velocity moment profiles to break the mass-anisotropy degeneracy. For an Navarro, Frenk & White (NFW) dark matter halo profile, we find that the mass of Sculptor within 1 kpc is M
1 kpc = (1.03 ± 0.07) × 108 M, and that its velocity anisotropy profile is tangentially biased and nearly constant for radii beyond ∼100 pc. The preferred concentration (c ∼ 15) is low for its dark matter mass but consistent within the scatter found in N-body cosmological simulations. When we let the value of the central logarithmic slope α vary, we find that the best-fitting model has α = 0, although an NFW cusp or shallower is consistent at the 1σ confidence level. On the other hand, very cuspy density profiles with logarithmic central slopes α < −1.5 are strongly disfavoured for Sculptor.
A novel gene delivery vector based on the ability of a synthetic amphiphilic block copolymer to mimic biological phospholipids by forming membrane‐enclosed structures, specifically nanometer‐sized ...vesicles, is presented. A pH‐sensitive diblock copolymer forms vesicles (polymersomes) at neutral pH, and dissolves completely as unimers at endocytic pH (see figure). GFP‐encoding plasmid DNA are successfully encapsulated inside the polymer vesicles, and delivered intracellularly.
Context.
Isolated local group (LG) dwarf galaxies have evolved most or all of their life unaffected by interactions with the large LG spirals and therefore offer the opportunity to learn about the ...intrinsic characteristics of this class of objects.
Aims.
Our aim is to explore the internal kinematic and metallicity properties of one of the three isolated LG early-type dwarf galaxies, the Tucana dwarf spheroidal. This is an intriguing system, as it has been found in the literature to have an internal rotation of up to 16 km s
−1
, a much higher velocity dispersion than dwarf spheroidals of similar luminosity, and a possible exception to the too-big-too-fail problem.
Methods.
We present the results of a new spectroscopic dataset that we procured from the Very Large Telescope (VLT) taken with the FORS2 instrument in the region of the Ca II triplet for 50 candidate red giant branch stars in the direction of the Tucana dwarf spheroidal. These yielded line-of-sight (l.o.s.) velocity and metallicity (Fe/H) measurements of 39 effective members that double the number of Tucana’s stars with such measurements. In addition, we re-reduce and include in our analysis the other two spectroscopic datasets presented in the literature, the VLT/FORS2 sample by Fraternali et al. (2009, A&A, 499, 121), and the VLT/FLAMES one from Gregory et al. (2019, MNRAS, 485, 2010).
Results.
Across the various datasets analyzed, we consistently measure a l.o.s. systemic velocity of 180 ± 1.3 km s
−1
and find that a dispersion-only model is moderately favored over models that also account for internal rotation. Our best estimate of the internal l.o.s. velocity dispersion is 6.2
−1.3
+1.6
km s
−1
, much smaller than the values reported in the literature and in line with similarly luminous dwarf spheroidals; this is consistent with NFW halos of circular velocities < 30 km s
−1
. Therefore, Tucana does not appear to be an exception to the too-big-to-fail problem, nor does it appear to reside in a dark matter halo much more massive than those of its siblings. As for the metallicity properties, we do not find anything unusual; there are hints of the presence of a metallicity gradient, but more data are needed to pinpoint its presence.
We have combined deep photometry in the B, V and I bands from CTIO/MOSAIC of the Sculptor dwarf spheroidal galaxy, going down to the oldest main sequence turn-offs, with spectroscopic metallicity ...distributions of red giant branch stars. This allows us to obtain the most detailed and complete star formation history to date, as well as an accurate timescale for chemical enrichment. The star formation history shows that Sculptor is dominated by old (>10 Gyr), metal-poor stars, but that younger, more metal-rich populations are also present. Using star formation histories determined at different radii from the centre we show that Sculptor formed stars with an increasing central concentration with time. The old, metal-poor populations are present at all radii, while more metal-rich, younger stars are more centrally concentrated. We find that within an elliptical radius of 1 degree, or 1.5 kpc from the centre, a total mass in stars of 7.8 × 106 M⊙ was formed, between 14 and 7 Gyr ago, with a peak at 13−14 Gyr ago. We use the detailed star formation history to determine age estimates for individual red giant branch stars with high resolution spectroscopic abundances. Thus, for the first time, we can directly determine detailed timescales for the evolution of individual chemical elements. We find that the trends in alpha-elements match what is expected from an extended, relatively uninterrupted period of star formation continuing for 6−7 Gyr. The knee in the alpha-element distribution occurs at an age of 10.9 ± 1Gyr, suggesting that SNe Ia enrichment began ≈2 ± 1 Gyr after the start of star formation in Sculptor.
We present our analysis of the FLAMES dataset targeting the central 25′ region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic ...section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giant branch stars down to
V
∼ 20.5 mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide Fe/H = −3.2 to −1.5 dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in
α
/Fe at ∼0.4 dex followed by a decrease above Fe/H ∼ −2 dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of Co/Fe and Ni/Fe above Fe/H ∼ −2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in Ni/Fe favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.
ABSTRACT
The Solo (Solitary Local) Dwarf Galaxy survey is a volume-limited, wide-field g- and i-band survey of all known nearby (<3 Mpc) and isolated (>300 kpc from the Milky Way or M31) dwarf ...galaxies. This set of 44 dwarfs is homogeneously analysed for quantitative comparisons to the satellite dwarf populations of the Milky Way and M31. In this paper, an analysis of the 12 closest Solo dwarf galaxies accessible from the Northern hemisphere is presented, including derivation of their distances, spatial distributions, morphology, and extended structures, including their inner integrated light properties and their outer resolved star distributions. All 12 galaxies are found to be reasonably well described by two-dimensional Sérsic functions, although UGC 4879 in particular shows tentative evidence of two distinct components. No prominent extended stellar substructures, which could be signs of either faint satellites or recent mergers, are identified in the outer regions of any of the systems examined.
We present deep photometry of the Carina dwarf spheroidal galaxy in the B and V filters from CTIO/MOSAIC out to and beyond the tidal radius of rell ≈ 0.48 degrees. The accurately calibrated ...photometry is combined with spectroscopic metallicity distributions of red giant branch (RGB) stars to determine the detailed star formation and chemical evolution history of Carina. The star formation history (SFH) confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail as a function of radius from the centre. Two main episodes of star formation occurred at old (>8 Gyr) and intermediate (2−8 Gyr) ages, both enriching stars starting from low metallicities (Fe/H < − 2 dex). By dividing the SFH into two components, we determine that 60 ± 9 percent of the total number of stars formed within the intermediate-age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07 ± 0.08 × 106 M⊙ was formed, giving Carina a stellar mass-to-light ratio of 1.8 ± 0.8. By combining the detailed SFH with spectroscopic observations of RGB stars, we determined the detailed age-metallicity relation of each episode and the timescale of α-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation during ≈6 Gyr with steadily declining α-element abundances and a possible α-element “knee” visible at Fe/H ≈ − 2.5 dex. The intermediate-age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in α-element abundances with a slope much steeper than observed in the old episode, starting from Fe/H = −1.8 dex and Mg/Fe ≈ 0.4 dex and declining to Mg-poor values (Mg/Fe ≤ − 0.5 dex). This clearly indicates that the two episodes of star formation formed from gas with different abundance patterns, which is inconsistent with simple evolution in an isolated system.
Implant-related infection is one of the leading reasons for failure in orthopaedics and trauma, and results in high social and economic costs. Various antibacterial coating technologies have proven ...to be safe and effective both in preclinical and clinical studies, with post-surgical implant-related infections reduced by 90% in some cases, depending on the type of coating and experimental setup used. Economic assessment may enable the cost-to-benefit profile of any given antibacterial coating to be defined, based on the expected infection rate with and without the coating, the cost of the infection management, and the cost of the coating. After reviewing the latest evidence on the available antibacterial coatings, we quantified the impact caused by delaying their large-scale application. Considering only joint arthroplasties, our calculations indicated that for an antibacterial coating, with a final user's cost price of €600 and able to reduce post-surgical infection by 80%, each year of delay to its large-scale application would cause an estimated 35 200 new cases of post-surgical infection in Europe, equating to additional hospital costs of approximately €440 million per year. An adequate reimbursement policy for antibacterial coatings may benefit patients, healthcare systems, and related research, as could faster and more affordable regulatory pathways for the technologies still in the pipeline. This could significantly reduce the social and economic burden of implant-related infections in orthopaedics and trauma.
: C. L. Romanò, H. Tsuchiya, I. Morelli, A. G. Battaglia, L. Drago. Antibacterial coating of implants: are we missing something?
2019;8:199-206. DOI: 10.1302/2046-3758.85.BJR-2018-0316.
Reverse electrodialysis (RED) is an electrochemical membrane process that directly converts the energy associated with the concentration difference between two salt solutions into electrical energy ...by means of a selective controlled mixing. The physics of RED involves the interaction of several phenomena of different nature and space-time scales. Therefore, mathematical modelling and numerical simulation tools are crucial for performance prediction. In this work, a multi-physical modelling approach for the simulation of RED units was developed. A periodic portion of a single cell pair was simulated in two dimensions. Fluid dynamics was simulated by the Navier-Stokes and continuity equations, and ion transfer by the Nernst–Planck approach along with the local electroneutrality condition. The Donnan exclusion theory was implemented in order to simulate interfacial phenomena. A sensitivity analysis of the process performance was carried out. Different membrane/channel geometrical configurations were investigated, including flat membranes, either with or without non-conductive spacers, and profiled membranes. The influence of feeds concentration/velocity was also evaluated. Results confirmed that, with respect to the ideal case of plane (empty) channels and planar membranes, non-conductive spacers always reduce the power produced, while profiled membranes may or may not perform better, depending on stack features and operating conditions.
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•A multi-physical model of reverse electrodialysis units was developed.•A periodic portion of a cell pair was simulated by the Nernst–Planck approach.•The Donnan exclusion theory was implemented to simulate interfacial phenomena.•Operating parameters and stack features were investigated.•The effectiveness of profiled membranes and net spacers was assessed.
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