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We present two pilot studies for the search and characterization of accretion events in star-forming dwarf galaxies. Our strategy consists of two complementary approaches: i) the direct search for stellar substructures around dwarf galaxies through deep wide-field imaging, and ii) the characterization of the chemical properties in these systems up to large galacto-centric distances. We show our results for two star-forming dwarf galaxies, the starburst irregular NGC 4449, and the extremely metal-poor dwarf DDO 68.
We present a project that aims to provide a complete theoretical and observational framework for an as yet unexplored class of variable stars, the ultralong-period Cepheids (P longer than 80–100 days). Given their very high luminosities (MV up to −7 mag), with the Hubble Space Telescope we will be able to observe them easily in stellar systems located at large distances (~ 100 Mpc). This limit will be further increased, out to the Hubble flow (~ 350 Mpc), using future ground-based facilities such as the European Extremely Large Telescope. The nature of their pulsation is as yet unclear, as is their evolutionary status, which seems different from the central helium-burning phase generally associated with classical Cepheids. These objects have been found to cover a very large metallicity range, from [Fe/H] ~ −2 dex to solar values, and they are located in heterogeneous stellar systems, from dwarf to spiral galaxies. Once completely characterized, they could provide a crucial test, since they have been found in all Type Ia supernova host spiral galaxies that have been monitored for variability over long periods and that currently offer sound constraints on the estimated value of the Hubble constant.
There is much evidence to indicate the ability of Indinavir (IND) to reduce Cryptosporidium parvum infection in both in vitro and in vivo models. However, there are limitations to the administration of IND as such, due to its renal toxicity and the high rate of metabolism and degradation. We aimed to encapsulate IND in biodegradable poly (D,L-lactide-co-glycolide) nanoparticles (Np) and to engineer their surface by conjugation with an anti-Cryptosporidium IgG polyclonal antibody (Ab). Tetramethylrhodamine-labelled Np were loaded with IND and modified by conjugation with an Ab. The IND-loaded modified Np (Ab-TMR-IND-Np) did not show any change, as demonstrated by chemical analysis studies. Simultaneous addition of 50μM Ab-TMR-IND-Np and excysted oocysts to the cell culture resulted in complete inhibition of the infection. In C. parvum-infected cells, the extent to which the infection decreased depended on the duration of treatment with the Ab-TMR-IND-Np. The antibody-engineered Np loaded with IND were able to target C. parvum in infected cells and therefore might represent a novel therapeutic strategy against Cryptosporidium sp. infection. Moreover, the use of Np as an IND delivery device, allows the development of a more appropriate dose formulation thereby reducing the IND side effects.
The metallicity of galaxies and its evolution with redshift is of paramount importance for understanding galaxy formation. Abundances in the interstellar medium (ISM) are typically determined using emission-line spectroscopy of H ii regions. However, since H ii regions are associated with recent SF they may not have abundances typical for the galaxy as a whole. This is true in particular for star-forming galaxies (SFGs), in which the bulk of the metals may be contained in the neutral gas. It is therefore important to directly probe the metal abundances in the neutral gas. This can be done using absorption lines in the Far UV. We have developed techniques to do this in SFGs, where the absorption is measured for sightlines toward bright SF regions within the galaxy itself. We have successfully applied this technique to a sample of galaxies observed with FUSE. The results have been very promising, suggesting in I Zw18 that abundances in the neutral gas may be up to 0.5 dex lower than in the ionized gas. However, the interpretation of the FUSE data is complicated by the very large FUSE aperture (30 arcsec), the modest S/N, and the limited selection of species available in the FUSE bandpass. The advent of COS on HST now allows a significant advance in all of these areas. We will therefore obtain absorption line spectroscopy with G130M (~1150–1450 Å) in the same sample for which we already have crude constraints from FUSE. The results will provide important new insights into the metallicities of galaxies, and into outstanding problems at high redshift such as the observed offset between the metallicities of Lyman Break Galaxies and Damped Lyman Alpha systems.
We present a new approach to estimate the ages of very young clusters based on the Pre-Main Sequence (PMS) Turn-On (TOn), point in the colour magnitude diagram where the PMS joins the main sequence (MS). In order to detect the TOn magnitude, we propose to monitor the spatial distribution of MS stars: any drop in the MS spatial density is a necessary signature for a successful TOn identification and, accordingly, a robust cluster dating. We use Hubble Space Telescope photometry of the star forming region NGC 346 as a benchmark for the method.
In this contribution we discuss the origin of the extreme helium-rich stars which inhabit the blue main sequence (bMS) of the Galactic globular cluster Omega Centauri. In a scenario where the cluster is the surviving remnant of a dwarf galaxy ingested by the Milky Way many Gyr ago, the peculiar chemical composition of the bMS stars can be naturally explained by considering the effects of strong differential galactic winds, which develop owing to multiple supernova explosions in a shallow potential well.
The Bologna Open Cluster Chemical Evolution (BOCCE) project is intended to study the disk of our Galaxy using open clusters as tracers of its properties. We are building a large sample of clusters, deriving homogeneously their distance, age, reddening, and detailed chemical composition. Among our sample we have several objects more metal-rich than the Sun and we present here first results of the analysis for NGC 6819, IC 4651, NGC 6134, NGC 6791, and NGC 6253, the last two being the most metal-rich open clusters known.
We introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams (CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time.
The blue compact dwarf galaxy I Zw 18 holds the record of the lowest metallicity ever observed in the local universe. As such, it represents the closest analog to primordial galaxies in the early universe. More interestingly, it has recurrently been regarded as a genuinely young galaxy caught in the process of forming in the nearby universe. However, stars of increasingly older ages are found within I Zw 18 every time deeper high-resolution photometric observations are performed with the Hubble Space Telescope (HST): from the original few tens of Myrs to, possibly, several Gyrs. Here we summarize the history of I Zw 18 age and present an ongoing HST/ACS project which allowed us to precisely derive the galaxy distance by studying its Cepheid variables, and to firmly establish the age of its faintest resolved populations.
Leishmania mutants have contributed greatly to extend our knowledge of this parasite's biology. Here we report the use of the mariner in vitro transposition system as a source of reagents for shuttle mutagenesis and targeted disruption of Leishmania genes. The locus-specific integration was achieved by the disruption of the subtelomeric gene encoding a DNA-directed RNA polymerase III subunit (RPC2). Further inactivation of RPC2 alleles required the complementation of the intact gene, which was transfected in an episomal context. However, attempts to generate a RPC2 chromosomal null mutant resulted in genomic rearrangements that maintained copies of the intact locus in the genome. The maintenance of the RPC2 chromosomal locus in complemented mutants was not mediated by an increase in the number of copies and did not involve chromosomal translocations, which are the typical characteristics of the genomic plasticity of this parasite. Unlike the endogenous locus, the selectable marker used to disrupt RPC2 did not display a tendency to remain in its chromosomal location but was targeted into supernumerary episomal molecules.
We present results from new deep HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf galaxy in the nearby universe. It has been previously argued that this is a very young system that started forming stars only ≲500 Gyr ago, but other work has hinted that older (≳1 Gyr) red giant branch (RGB) stars may exist in this galaxy. Our deeper data indeed reveal evidence for an RGB. Underlying old (≳1 Gyr) populations are therefore present in even the most metal-poor systems, implying that star formation started at z ≳ 0.1. The RGB tip (TRGB) magnitude and the properties of Cepheid variables identified from our program indicate that I Zw 18 is farther away (D = 19.0 ± 1.8 Mpc) than previously believed.
In the framework of an ongoing ACS@HST project (HST program #10586, PI: Aloisi) we have obtained deep multi-color imaging of the very metal-poor Blue Compact Dwarf galaxy IZw18. The data were acquired in time-series fashion to allow the identification of Classical Cepheids (CCs). The main aim of this project is to constrain both the distance and the Star Formation History of the galaxy. However, as a byproduct these data also provide new insights into the properties of CCs at very low metallicities. We have identified 24 candidate CCs in IZw18. New theoretical pulsation models of CCs specifically for the low metallicity of this primordial galaxy (Z=0.0004, Y=0.24) have been computed to interpret our results.
IZw18 has been recurrently claimed to be a young galaxy, but stars of increasingly older ages are found every time deeper magnitude levels are reached with high-resolution photometry: from the original few Myrs to, possibly, several Gyrs. We summarize the history of IZw18's age and an HST project which will allow us to derive both its distance and age.
We recently launched a comprehensive ground based (ESO/VLT/NTT) and space (HST & SST) study of the present and past star formation in the Small Magellanic Cloud (SMC), in clusters and in the field, with the goal of understanding how star and cluster formation occur and propagate in an environment of low metallicity, with a gas and dust content that is significantly lower than in the Milky Way. In this paper, we present some preliminary results of the “young cluster” program, where we acquired deep F555W (~V), and F814W (~I) HST/ACS images of the four young and massive SMC star clusters: NGC 346, NGC 602, NGC 299, and NGC 376.
Background: The aim of this prospective, randomized, blinded study was to compare analgesic efficacy of continuous paravertebral and epidural analgesia for post-thoracotomy pain. Methods: Forty-two ASA physical status II–III patients undergoing lung resection surgery were randomly allocated to receive post-thoracotomy analgesia with either a thoracic epidural (group EPI, n = 21) or paravertebral (group PVB, n = 21) infusion of 0.2% ropivacaine (infusion rate: 5–10 mL h−1). The degree of pain at rest and during coughing, haemodynamic variables and blood gas analysis were recorded every 12 h for the first 48 h. Results: The area under the curve of the visual analogue pain score during coughing over time was 192 (60–444) cm h−1 in group EPI and 228 (72–456) cm h−1 in group PVB (P = 0.29). Rescue morphine analgesia was required in four patients of group EPI (19%) and five patients of group PVB (23%) (P = 0.99). The PaO2/FiO2 ratio reduced significantly from baseline values in both groups without between-group differences. The median (range) percentage reduction of systolic arterial pressure from baseline was −9 (0 to −9)% in group PVB and −17 (0 to −38)% in group EPI (P = 0.02); while clinically relevant hypotension (systolic arterial pressure decrease >30% of baseline) was observed in four patients of group EPI only (19%) (P = 0.04). Patient satisfaction with the analgesia technique was 8.5 (8–9.8) cm in group EPI and 9 (7.5–10) cm in group PVB (P = 0.65). Conclusions: Continuous thoracic paravertebral analgesia is as effective as epidural blockade in controlling post-thoracotomy pain, but is associated with less haemodynamic effects.
Coeliac disease (CD) is a malabsorptive disorder of the small intestine resulting from ingestion of
gluten. The HLA risk factors involved in CD are well known but do not explain the whole genetic
susceptibility. Several regions of potential linkage on chromosomes 3q, 5q, 10q, 11q, 15q and 19q
have already been reported in the literature. These six regions were analyzed with the Maximum Lod
Score method on a dense set of markers. A new sample of 89 Italian sibpairs was available for study.
There was no evidence for linkage for any of the regions tested, except for chromosome 5q. For this
region, our data, as well as a sample of 93 sibpairs from our first genome screen (Greco et al. 1998),
are compatible with the presence of a risk factor for CD with a moderate effect.
Coeliac disease (CD) is a multigenic and multifactorial enteropathy triggered by gluten-composing
proteins. A possible involvement of the intestinal Aminopeptidase N (APN) was investigated by an
association analysis. SSCP analysis detected four variants at position 281, 378, 956 and 2957
(referred to no. g178535, GenBank) that were studied in 193 Italian CD families. The haplotypic
combinations were determined from family segregation and pairwise linkage disequilibria
(D′ = D/Dmax) between the polymorphic sites were calculated. Significant D′ values ranged between 0.78
and 0.31. Association with CD was tested by TDT (Transmission Disequilibrium Test) utilizing as
markers the nucleotide substitutions and their haplotypic combinations. No statistically significant
transmission distortion to the probands or to their clinically silent sibs was observed. Our data
exclude an involvement in CD of the tested markers and of further undetected variation in strong
linkage disequilibrium (D′ ≅ 1) with them. The power of the test was not adequate to detect an
association with an unknown polymorphism which is not in complete linkage disequilibrium with
Recent computer experiments on liquid Mg and Bi (and also on dense hydrogen) have focussed anew on issues involving static and dynamical structure in plasmas. In Mg and Bi, under normal liquid metal conditions, separation of core and valence electrons is valuable both for thermodynamics and in interpreting diffraction experiments. Mg is considered in some detail as a specific example where there is weak electron–ion interaction. Finally, dynamical structure is considered. After a brief summary relating back to the electron–electron pair correlation contribution in X-ray scattering, attention is next focussed on the (longitudinal) viscosity of alkali metals via the Kubo formula. This viscosity is shown to be dominated by ion–ion interactions. Nevertheless, an intimate relation at the melting point is exposed between shear viscosity, thermal conductivity, and electrical resistivity, the latter two transport coefficients being dominated by electrons.