1,721,163 research outputs found
Black holes in galactic nuclei: seed formation from stellar mass black holes and massive black hole pairing in galaxy mergers.
Full text linkBlack holes (BHs) are a very important class of astrophysical objects. They are the most compact objects in the Universe, hence they represent the most extreme sources of gravity. BHs come in two flavours: the stellar mass BHs (SBHs) relic of young massive stars (1−20M⊙) and the massive BHs (MBHs), with masses of 106−109M⊙, dwelling in the nuclei of the most massive galaxies. While the formation mechanisms of SBHs are well understood, no clear consensus exists about MBH formation. According to the Soltan arguments (Soltan, 1982), MBHs gain the largest fraction of their mass via radiative efficient accretion of gas. As a consequence, we expect that MBH formed early in the Universe as smaller mass seeds. Recently, observations of high redshift quasars (e.g.; Mortlock et al., 2011; Fan et al., 2006) showed that MBHs with masses above 109M⊙ were already in place when the Universe was less than 1 Gyr old and posed tight constraints on the models for the formation and growth of MBHs. Two main scenarios have been developed for MBH seed formation: the light seed scenario, where seeds formed as relic of the first generation of stars with masses of up to few hundred solar masses (Madau & Rees, 2001), and the heavy seed scenarios, where seeds formed from the direct collapse of massive gas clouds in primordial haloes with masses of up to few 105M⊙ (Haehnelt & Rees, 1993). Despite the large number of studies about MBH formation models, each model still has its own caveats, which make the study of MBH formation worth of further investigations.
According to the -CDM cosmology, galaxies form when gas cools down within dark matter haloes, which assembly in a hierarchical fashion from small density perturbations. Galaxies grow via accretion and mergers, and the central MBHs evolve in the same way. So, when a galaxy merger occur, the MBHs hosted in the nucleus of the galaxy progenitors can sink towards the centre of the merger remnant, forming a MBH binary (MBHB). Despite galaxy mergers are usually observed, no clear detections of MBHBs exist to date. The formation and evolution of MBHBs is a complex process, since it occurs in a rapidly varying environment where gas, star formation and SNa feedback play a pivotal role. Several studies have been performed to date, but a clear understanding of the whole process is still far from being reached.
In this thesis I cover both aspects of MBH formation and evolution. In the first study I consider an alternative route for seed BH formation. Using two different codes, the AMR code RAMSES (Teyssier, 2002) and the meshfree code GIZMO (Hopkins, 2015), I studied the evolution of a single massive circum-nuclear gaseous disc embedding a population of SBHs. The disc was subject to radiative cooling, star formation and supernova feedback and becomes unstable to fragmentation, which led to the formation of clumps as massive as 104 − 105M⊙. My simulations showed that during the disc evolution, some SBHs can be gravitationally captured by a clump. Within the clumps, such BHs can experience episodes of super-critical accretion, which make them grow up to 103 − 104M⊙ in few Myr. Thanks to the very low radiative efficiency associated to the slim accretion disc (Abramowicz et al., 1988), the energy released to the surrounding gas is too small to halt the accretion flow, hence BHs can accrete almost unimpeded until one of these events occur: the clump is totally accreted by the BH, the clump is consumed by star formation or the clump is destroyed by supernova explosions.
In the second study, instead, I consider the intermediate stages of a galaxy merger, when the MBHs originally dwelling in the centre of their own progenitor galaxies reach few hundred separations in the nucleus of the merger remnant. I assumed that each MBH was embedded in a self-gravitating circumnuclear gaseous disc. With the code RAMSES I studied the evolution of the MBHs and their surrounding discs, including physical processes like radiative cooling, star formation and supernova feedback, which are implemented in the code as sub-grid recipes. First, I implemented a new refinement prescription aimed at improving the orbital evolution of massive particles, an already known major issue in AMR codes, like observed by Gabor & Bournaud (2013); Dubois et al. (2014). Secondly, I evolved the discs assuming different sub-grid recipes to study how the MBH and gas dynamics could be affected by the different choices. I found that the MBH dynamics is almost independent of the physical modelling, if one assumes that no previous star formation occurred in the discs, while the gas evolution and its final distribution can be significantly affected. On the other side, if one assumes that star formation was already ongoing, even the BH dynamics can be modified, if supernovae are powerful enough to disrupt gas clumps forming in the discs.
A general introduction to the work is reported in Chapter 1. In Chapter 3 I discuss the first study about an alternative model for seed BH formation. In Chapter 4, instead, I describe the second study concerning the evolution of the MBH pair in the intermediate stages of a galaxy merger. The reader interested in the main results of the work can directly move to Chapters 3 and 4. Finally, Chapter 5 reports my conclusions
Effects of ethanol and DMSO on TEGDMA solubility and cytotoxicity
No full textObjective: Several in vitro studies have been carried out to investigate the triethylenglycol-dimethacrylate (TEGDMA) cytotoxicity. However, these studies have never focused on how the solvents used to dissolve TEGDMA in the experimental conditions might influence monomer effective concentrations and in turn its cytotoxicity. Hence, the aim of this study was to evaluate the active concentrations of the TEGDMA over the routinely experimental conditions used in biocompatibility in vitro tests and to determine any changes in cytotoxicity depending on the TEGDMA solution composition.
Methods: TEGDMA dilutions were prepared directly in DMEM (in absence of cells) or were dissolved previously in DMSO or ethanol and then in medium. Monomer concentrations were quantified by an HPLC system. The cytotoxicity effects of TEGDMA dilutions (1 and 2 mmol/L, with and w/o solvents) were evaluated on 3T3-fibroblasts by MTT assay. ROS production (by FACScan flowcytometer) and intracellular and extracellular TEGDMA concentration (by HPLC) were also determined. Data were analyzed by ANOVA followed by Turkey’s test for multiple comparisons.
Results: Maximum solubility of TEGDMA in DMEM (in absence of cells) was 0.5 mmol/L both in the presence and absence of solvents. 2 mmol/L TEGDMA - solubilized in DMSO or ethanol and then dissolved in medium - caused a significant decrease in cell viability and an induction of ROS production compared to the same TEGDMA concentration dissolved in medium directly. Moreover when 2 mmol/L TEGDMA was added to the cells in presence of DMSO and ETOH, after 2h of incubation, TEGDMA concentration was reduced respectively 10% and 20%, while, TEGDMA added without vehicles remains constant.
Conclusions: Our results showed that TEGDMA solubilization in DMEM was not complete and that the cytotoxic effects of the monomer was influenced by the method of solubilization
In vitro Evaluation of the Cytotoxicity of Different Root Canal Filling Materials
No full textAbstract
OBJECTIVE:
Aim of the present study was to evaluate the cytotoxicity of Real Seal 1 compared to other commercially available endodontic filling materials: Real Seal (SybronEndo, Orange, CA, USA) and Thermafil (Tulsa Dental, Tulsa, OK, USA).
MATERIAL AND METHODS:
Periodontal ligament cells from healthy patients were cultured. The eluate of Real Seal 1(TM) (RS1), Real Seal (RS) and Thermafil (TF) samples was used for the cells viability tests, both diluted (50%) or undiluted (100%). Incubation of the specimens was performed in culture medium for 24 h, 48 h and 72 h at 37 °C under sterile conditions. The cellular mortality was evaluated by MTT test. Results were statistically analysed and the statistical significance was set at p< 0.05.
RESULTS:
None of the studied materials showed toxic effects during the period of observation (0 -72 h) when compared to the control group. Only RS induced a very modest increase in cell mortality (about 3% at both concentrations used, during the first 24 hours), when increasing the incubation time, however, only the lower concentration continued to show modest toxicity.
CONCLUSIONS:
Results of the present study showed that all tested materials did not exhibit cytotoxic effects when compared to the control grou
INTERACTIONS BETWEEN CHLORHEXIDINE AND SODIUM HYPOCHLORITE: CHEMICAL ANALYSIS
No full textEndodontic failure may occur in cases of persistent bacteria in the root canal system (RCS). Mechanical instrumentation alone is not able to obtain a complete cleaning of the RCS, so a commonly used method of disinfection in endodontic treatments consists in the use of sodium hypochlorite (NaOCl) followed by the use of chlorhexidine gluconate (CHX). After each irrigating solution, distilled water should be used to prevent possible reaction among the components. In fact, if NaOCl is present when CHX is added, a brown precipitate is formed with a possible negative effect on the outcome of the treatment. Some literature works reported the presence of 4-chloroaniline (PCA) in brown precipitate, other, on the contrary, didn’t observed its formation; in our study, we have tried to explain the reason of this discrepancy using HPLC-UV technique.
To 1.0 mL of 2% CHX were added different volumes of 6.0% NaOCl (from 0.01 to 0.12 mL). Also the reaction mixtures between 6.0% NaOCl and PCA (5 mg /mL in methanol) were prepared.
The specimens were centrifuged (13400 x g 5 min) and both supernatants (SNs) and precipitates (PTs) (re-suspended in 1 mL of methanol) were analyzed.
The column used was a Discovery HS C18 (250mm × 4.6mm, 5 μm) (SUPELCO, PA, USA), flow rate 0.7 mL/min, detection 214 nm. Water (A) and acetonitrile (B) were used for the elution: from 50% (B) to 70% (B) in 10 min and to 85 % (B) in 5 min.
The chromatograms of CHX showed a signal with a Retention Time (RT) 3.0 min. When NaOCl was added, many other signals appeared with RT between 20 and 25 min. Similar results were obtained in the PTs. The presence of PCA signal was not observed neither in PTs nor in SNs.
The HPLC analysis of mixture between NaOCl and PCA showed the presence of signal with RT 9.1 min (PCA), its intensity decreases when NaOCl was added, and completely disappeared with 0.12 mL of NaOCl. Simultaneously signals with RT between 20 and 25 minutes are produced, similarly to what was observed for the CHX. In PTs are present many peaks with RT around 2-3 min and at 25-30 min.
The obtained results showed that PCA is transformed in presence of NaOCl. Thus, the discrepancy of literature data could be due to the reaction conditions: the newly-formed PCA reacts with NaOCl and is transformed
Massive black hole and gas dynamics in mergers of galaxy nuclei – II. Black hole sinking in star-forming nuclear discs
No full textMergers of gas-rich galaxies are key events in the hierarchical built-up of cosmic structures, and can lead to the formation of massive black hole binaries. By means of high-resolution hydrodynamical simulations we consider the late stages of a gas-rich major merger, detailing the dynamics of two circumnuclear discs, and of the hosted massive black holes during their pairing phase. During the merger gas clumps with masses of a fraction of the black hole mass form because of fragmentation. Such high-density gas is very effective in forming stars, and the most massive clumps can substantially perturb the black hole orbits. After similar to 10 Myr from the start of the merger a gravitationally bound black hole binary forms at a separation of a few parsecs, and soon after, the separation falls below our resolution limit of 0.39 pc. At the time of binary formation the original discs are almost completely disrupted because of SNa feedback, while on pc scales the residual gas settles in a circumbinary disc with mass similar to 10(5) M-circle dot. We also test that binary dynamics is robust against the details of the SNa feedback employed in the simulations, while gas dynamics is not. We finally highlight the importance of the SNa time-scale on our result
NAC direct detoxification of TEGDMA cytotoxicity.
No full textObjectives: Various protective effects of N-acetylcysteine (NAC) against triethylene glycol dimethacrylate (TEGDMA)-induced cell damage have been demonstrated, but so far there is no evidence on NAC direct monomer detoxification mechanism. Here, we hypothesized that NAC might reduce TEGDMA cytotoxicity due to direct NAC adduct formation.
Methods: we measured the cytotoxic effects of TEGDMA in presence and in absence of NAC by MTT test. Then we analyzed the presence of TEGDMA-NAC adduct formation in extracellular and intracellular compartments by capillary electrophoresis-UV detection (CE-UV) and capillary electrophoresis–mass spectrometry (CE-MS) analytical techniques. Moreover, we quantified the effective intracellular and extracellular TEGDMA concentrations through HPLC in the presence and absence of 10 mmol/L NAC. Data from all experiments were summarized as means ± Standard Deviation (SD) and differences between means were analyzed by one-way analysis of variance (ANOVA) followed by Tukey’s test for multiple comparisons. The level of significance was set at p<0.05.
Results: TEGDMA reduced 3T3 cell vitality in a dose- and time-dependent manner, while NAC significantly decreased monomer cytotoxicity and extracellular monomer concentrations by a direct reaction with TEGDMA. The adducts between the two molecules were detected both in the presence and absence of cell.
Conclusion: Our results suggest that in vitro detoxification capability of NAC against TEGDMA-induced cell damage might occur also through the formation of NAC-TEGDMA adduct
Dynamical evolution of massive perturbers in realistic multicomponent galaxy models I: implementation and validation
No full textGalaxies are self-gravitating structures composed by several components encompassing spherical, axial, and triaxial symmetry. Although real systems feature heterogeneous components whose properties are intimately connected, semi-analytical approaches often exploit the linearity of the Poisson’s equation to represent the potential and mass distribution of a multicomponent galaxy as the sum of the individual components. In this work, we expand the semi-analytical framework developed in Bonetti et al. (2020) by including both a detailed implementation of the gravitational potential of exponential disc (modelled with a sech2 and an exponential vertical profile) and an accurate prescription for the dynamical friction experienced by massive perturbers (MP) in composite galaxy models featuring rotating disc structures. Such improvements allow us to evolve arbitrary orbits either within or outside the galactic disc plane. We validate the results obtained by our numerical model against public semi-analytical codes as well as full N-body simulations, finding that our model is in excellent agreement to the codes it is compared with. The ability to reproduce the relevant physical processes responsible for the evolution of MP orbits and its computational efficiency make our framework perfectly suited for large parameter-space exploration studies
Cytotoxicity of a new endodontic filling material
No full textIn vitro cell cultures have been widely used as a means of evaluating cytotoxicity of root canal filling materials. Following ANSI/ADA spec. no. 41, the aim of the present study was to investigate the biological compatibility of a new sealer (FibreFill) and compare it with some commercially available endodontic sealers (Bioseal and Acroseal). Mouse 3T3 fibroblasts were seeded and cultured and subsequently extracts of the cements were added. After 24 hours incubation, the cellular vitality of fibroblasts was evaluated by the neutral red uptake test (NRU), which measures the membrane permeability. Data were collected and statistically analysed. Results showed that all tested materials exhibited mild cytotoxic effects, which are compatible with normal clinical use, and no statistically significant difference was noted between FibreFill and the other tested materials. Therefore, selection amongst these sealers should be based on other factors
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