Biasing crystallization in fused silica: An assessment of optimal metadynamics parameters

Metadynamics (MetaD) is a useful technique to study rare events such as crystallization. It has been only recently applied to study nucleation and crystallization in glass-forming liquids such as silicates, but the optimal set of parameters to drive crystallization and obtain converged free energy surfaces is still unexplored. In this work, we systematically investigated the effects of the simulation conditions to efficiently study the thermodynamics and mechanism of crystallization in highly viscous systems. As a prototype system, we used fused silica, which easily crystallizes to β-cristobalite through MetaD simulations, owing to its simple microstructure. We investigated the influence of the height, width, and bias factor used to define the biasing Gaussian potential, as well as the effects of the temperature and system size on the results. Among these parameters, the bias factor and temperature seem to be most effective in sampling the free energy landscape of melt to crystal transition and reaching convergence more quickly. We also demonstrate that the temperature rescaling from T > Tm is a reliable approach to recover free energy surfaces below Tm, provided that the temperature gap is below 600 K and the configurational space has been properly sampled. Finally, albeit a complete crystallization is hard to achieve with large simulation boxes, these can be reliably and effectively exploited to study the first stages of nucleation

Disclosing crystal nucleation mechanism in lithium disilicate glass through molecular dynamics simulations and free-energy calculations

Unraveling detailed mechanism of crystal nucleation from amorphous materials is challenging for both experimental and theoretical approaches. In this study, we have examined two methods to understand the initial stage of crystal precipitation from lithium disilicate glasses using molecular dynamics simulations. One of the methods is a modified exploring method to find structurally similar crystalline clusters in the glass models, enabling us to find three different embryos, such as Li2Si2O5 (LS2), Li2SiO3 (LS) and Li3PO4 (LP), in the 33Li2O·66SiO2·1P2O5 glass (LS2P1), in which P2O5 is added as a nucleating agent. Interestingly, LS2 and LP crystals were found inside the LS2P1 glass while LS crystal appeared on the glass surface, which agrees with experimental observations. The other method is free energy calculation using a subnano-scale spherical crystal embedded in the glass model. This method, which we called Free-Energy Seeding Method (FESM), allows us to evaluate free energy change as a function of crystal radius and to identify critical size of the crystal precipitation. The free energy profiles for LS and LS2 crystal nuclei in the LS2 glass models possess maximum energy at a critical radius as expected by classical nucleation theory. Furthermore, the critical radius and the energy barrier height agree well with recent experimental investigation, proving the applicability of this method to design glass–ceramics by atomistic modeling

Studio multidisciplinare finalizzato alla riqualificazione ambientale della valle del Rio della Rocca (Comune di Castellarano, Provincia di Reggio Emilia)

La valle del Rio della Rocca nel Comune di Castellarano (Reggio Emilia) è stata interessata a partire dagli anni ‘50 del secolo scorso da attività estrattive che in parte ne hanno profondamente modificato le caratteristiche ambientali, in particolare quelle geomorfologiche. In considerazione dell’interesse paesaggistico della valle e ai fini di una riqualificazione ambientale del territorio, è stato realizzato uno studio multidisciplinare volto a delineare i principali aspetti geologici, paleontologici, floristici e faunistici. Specifica attenzione è stata posta alla valutazione dell’instabilità dei versanti e alla individuazione dei geositi presenti nell’area. Sulla scorta dei risultati delle ricerche effettuate sono state elaborate proposte di riqualificazione del territorio che prevedono una valorizzazione della valle a fini geoturistici e ricreativi

Early hyperreactive malarial splenomegaly and risk factors for evolution into the full-blown syndrome: a single-centre, retrospective, longitudinal study

Background: The hyperreactive malarial splenomegaly (HMS) represents a chronic, potentially fatal complication of malaria. Case definition includes: gross splenomegaly, high level of anti-malarial antibody and IgM, response to long-term anti-malarial prophylaxis. In this study, a large series of patients not fully meeting the case definition was tentatively classified as early hyperreactive malarial splenomegaly (e-HMS). The main research questions was: does "e-HMS" tend to evolve to the full-blown syndrome? And if so, what are the main factors influencing this evolution? Methods: Retrospective, longitudinal study. The patient database was searched to retrieve all potentially eligible patients. e-HMS was defined by splenomegaly of any size (with or without raised IgM), high anti-malarial antibody titre and exclusion of other causes of splenomegaly. The clinical outcome at following visits was analysed in relation to re-exposure to malaria, and to treatment (only part of the patients with e-HMS were treated with a single anti-malarial treatment and advised to follow an effective anti-malarial prophylaxis, if re-exposed). The association of the outcome with the main independent variables was first assessed with univariate analysis. A stepwise logistic regression model was then performed to study the association of the outcome with the main independent variables. Results: One hundred and twenty-six subjects with e-HMS were retrieved. Eighty-one had at least one follow-up visit. Of 46 re-exposed to malaria for a variable period, 21 (46 %) had progressed, including 10/46 (22 %) evolving to full-blown HMS, while of 29 patients not re-exposed, 24 (93 %) had improved or cured and five (7 %) progressed (p < 0.001). At logistic regression re-exposure was confirmed as a major risk factor of progression (OR 9.458, CI 1.767-50.616) while treatment at initial visit was protective (OR 0.187, CI 0.054-0.650). Conclusion: e-HMS should be regarded as a clinical condition predisposing to HMS. Although the case definition may include false positives, e-HMS should be treated just as the full-blown syndrome. A single anti-malarial treatment is probably adequate, followed by effective prophylaxis for patients exposed again to malaria transmission

Il ruolo delle Case alloggio per malati di AIDS nel paziente tossicodipendente HIV positivo (Sezione VI) In: Trattato Completo degli abusi e delle dipendenze.

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Effect of thymol and resveratrol administered with candy or syrup on the development of Nosema ceranae (Apis mellifera) artificially infected honeybees.

The aim of this study was to evaluate the effect of thymol and resveratrol administered in two different formulation modes (candy and syrup) on the development of Nosema ceranae and on the longevity of honey bees. Emerging bees from a nosema-free apiary were individually infected with 1 \u3bcL of sucrosesyrup containing 18000 spores of N. ceranae, placed in cages, and kept in an incubator at 33 \u25e6C and 65% RH. The experimental groups were fed candy or syrup prepared with thymol (100 ppm) or resveratrol (10 ppm). Infection levels were monitored over a 25 day period by removal and dissection of two live bees per cage. On day 25, post-infection bees fed with thymol syrup had significantly lower levels of infection (60 \ub1 9 million spores/bee) compared to control bees (138 \ub1 7 million spores/bee). Bees fed with thymol or resveratrol syrup lived significantly longer (23 and 25 days, respectively) than bees fed with control syrup (20 days). Thymol treated syrup appears to be promising in the control of nosema infection

Nosema ceranae and Deformed Wing Virus infections ofhoney bees in a hoarding cage experiment

The multifactorial nature of colony losses is widely accepted, although synergistic effects of possible causative factors are not completely understood. To investigate interactions between two serious and wide-spread pathogens of honey bee colonies, Deformed Wing Virus and Nosema ceranae, an experiment was set up in which worker bees were infected with known amounts of N. ceranae spores. To reduce the impact of Varroa destructor an apiary was established in an isolated mountain area and mitelevels kept as low as possible. Newly emerged worker bees were kept in 14 hoarding cages (30 bees each). Each cage was provided with 0.2 ml 50% w/v sucrose solution containing20106 N. ceranae spores per ml. Oral infection was therefore obtained via bulk feeding. The number of dead bees in each cage was recorded for ~30 days. After 14 days from beginning of experiment, five live worker bees were removed from each cage. Midguts were removed for spore counts and at the same time, head and thorax of each worker were removed and subsequentlyanalysed for quantitative DWV analyses using standard RT PCR protocols. The data show a strong positive correlation between the number of N. ceranae spores and the number of DWV copies, suggesting that the two pathogens may interact synergistically. N. ceranae may enable oral infection by the virus by perforation of the midgut epithelium, or increase replication of the virus by suppression of the immune system