Buoyancy-Driven Chemohydrodynamic Patterns in A + B → Oscillator Two-Layer Stratifications.

Chemohydrodynamic patterns due to the interplay of buoyancy-driven instabilities and reaction-diffusion patterns are studied experimentally in a vertical quasi-two-dimensional reactor in which two solutions A and B containing separate reactants of the oscillating Belousov-Zhabotinsky system are placed in contact along a horizontal contact line where excitable or oscillating dynamics can develop. Different types of buoyancy-driven instabilities are selectively induced in the reactive zone depending on the initial density jump between the two layers, controlled here by the bromate salt concentration. Starting from a less dense solution above a denser one, two possible differential diffusion instabilities are triggered depending on whether the fast diffusing sulfuric acid is in the upper or lower solution. Specifically, when the solution containing malonic acid and sulfuric acid is stratified above the one containing the slow-diffusing bromate salt, a diffusive layer convection (DLC) instability is observed with localized convective rolls around the interface. In that case, the reaction-diffusion wave patterns remain localized above the initial contact line, scarcely affected by the flow. If, on the contrary, sulfuric acid diffuses upward because it is initially dissolved in the lower layer, then a double-diffusion (DD) convective mode develops. This triggers fingers across the interface that mix the reactants such that oscillatory dynamics and rippled waves develop throughout the whole reactor. If the denser solution is put on top of the other one, then a fast developing Rayleigh-Taylor (RT) instability induces fast mixing of all reactants such that classical reaction-diffusion waves develop later on in the convectively mixed solutions.

Making a Simple A+B→C Reaction Oscillate by Coupling to Hydrodynamic Effect.

We present a new mechanism through which chemical oscillations and waves can be induced in batch conditions with a simple A+B→C reaction in the absence of any nonlinear chemical feedback or external trigger. Two reactants A and B, initially separated in space, react upon diffusive contact and the product actively fuels in situ convective Marangoni flows by locally increasing the surface tension at the mixing interface. These flows combine in turn with the reaction-diffusion dynamics, inducing damped spatiotemporal oscillations of the chemical concentrations and the velocity field. By means of numerical simulations, we single out the detailed mechanism and minimal conditions for the onset of this periodic behavior. We show how the antagonistic coupling with buoyancy convection, due to concurrent chemically induced density changes, can control the oscillation properties, sustaining or suppressing this phenomenon depending on the relative strength of buoyancy- and surface-tension-driven forces. The oscillatory instability is characterized in the relevant parametric space spanned by the reactor height, the Marangoni (Ma_{i}) and the Rayleigh (Ra_{i}) numbers of the ith chemical species, the latter ruling the surface tension and buoyancy contributions to convection, respectively.

Study of the role of the covalently linked cell wall protein (Ccw14p) and yeast glycoprotein (Ygp1p) within biofilm formation in a flor yeast strain.

Flor yeasts are Saccharomyces cerevisiae strains noted by their ability to create a type of biofilm in the air-liquid interface of some wines, known as 'flor' or 'velum', for which certain proteins play an essential role. Following a proteomic study of a flor yeast strain, we deleted the CCW14 (covalently linked cell wall protein) and YGP1 (yeast glycoprotein) genes-codifying for two cell surface glycoproteins-in a haploid flor yeast strain and we reported that both influence the weight of the biofilm as well as cell adherence (CCW14).

Genomic signatures of adaptation to wine biological ageing conditions in biofilm-forming flor yeasts.

The molecular and evolutionary processes underlying fungal domestication remain largely unknown despite the importance of fungi to bioindustry and for comparative adaptation genomics in eukaryotes. Wine fermentation and biological ageing are performed by strains of S. cerevisiae with, respectively, pelagic fermentative growth on glucose and biofilm aerobic growth utilizing ethanol. Here, we use environmental samples of wine and flor yeasts to investigate the genomic basis of yeast adaptation to contrasted anthropogenic environments. Phylogenetic inference and population structure analysis based on single nucleotide polymorphisms revealed a group of flor yeasts separated from wine yeasts. A combination of methods revealed several highly differentiated regions between wine and flor yeasts, and analyses using codon-substitution models for detecting molecular adaptation identified sites under positive selection in the high-affinity transporter gene ZRT1. The cross-population composite likelihood ratio revealed selective sweeps at three regions, including in the hexose transporter gene HXT7, the yapsin gene YPS6 and the membrane protein coding gene MTS27. Our analyses also revealed that the biological ageing environment has led to the accumulation of numerous mutations in proteins from several networks, including Flo11 regulation and divalent metal transport. Together, our findings suggest that the tuning of FLO11 expression and zinc transport networks are a distinctive feature of the genetic changes underlying the domestication of flor yeasts. Our study highlights the multiplicity of genomic changes underlying yeast adaptation to man-made habitats and reveals that flor/wine yeast lineage can serve as a useful model for studying the genomics of adaptive divergence.

Chemical control of dissolution-driven convection in partially miscible systems: nonlinear simulations and experiments.

Chemical reactions can impact mixing in partially miscible stratifications by affecting buoyancy-driven convection developing when one phase dissolves into the other one in the gravity field. By means of combined nonlinear simulations and experiments, we explore the power of an A + B → C type of reaction to either enhance or refrain convective dissolution with respect to the nonreactive system depending on the relative contribution to density of the dissolving species A, of the reactant B initially dissolved in the host phase and of the product C. Nonlinear simulations are performed by solving reaction-diffusion-convection equations describing the dissolution and reactive dynamics when a less dense phase of A is layered on top of a reactive denser solution of B, in which A is partially miscible with a given solubility. The spatio-temporal dynamics and convective patterns observed in the numerical study compare favorably with experiments carried out with (i) a liquid alkyl-formate stratified on top of an aqueous solution in which the ester dissolves and undergoes a hydrolysis reaction and (ii) gaseous CO2 dissolving into an aqueous solution of NaOH. We show that the same reaction type can induce a different effect on the convective dynamics depending on the reactant in the host phase. The efficiency of convective dissolution in partially miscible systems can hence be controlled by the chemicals present in the host fluid and their concentration. The direct comparison between the convective dynamics observed during CO2 dissolution in an aqueous phase and in the ester/water stratification validates the latter as a convenient liquid-liquid model system for the interpretation of the impact of chemical reactivity in geological CO2 sequestration.

Dissipative structures: From reaction-diffusion to chemo-hydrodynamic patterns.

The interplay of reaction and diffusion processes can trigger localized spatiotemporal patterns when two solutions containing separate reactants A and B of an oscillating reaction are put in contact. Using the Brusselator, a classical model for chemical oscillations, we show numerically that localized waves and Turing patterns as well as reaction-diffusion (RD) patterns due to an interaction between these two kinds of modes can develop in time around the reactive contact zone depending on the initial concentration of reactants and diffusion coefficients of the intermediate species locally produced. We further explore the possible hydrodynamic destabilization of an initially buoyantly stable stratification of such an A + B → oscillator system, when the chemical reaction provides a buoyant periodic forcing via localized density changes. Guided by the properties of the underlying RD dynamics, we predict new chemo-hydrodynamic instabilities on the basis of the dynamic density profiles which are here varying with the concentration of one of the intermediate species of the oscillator. Nonlinear simulations of the related reaction-diffusion-convection equations show how the active coupling between the localized oscillatory kinetics and buoyancy-driven convection can induce pulsatile convective fingering and pulsatile plumes as well as rising or sinking Turing spots, depending on the initial concentration of the reactants and their contribution to the density.

Spatially Localized Chemical Patterns around an A + B → Oscillator Front.

When two gels, each loaded with a different set of reactants A and B of an oscillatory reaction, are brought into contact, reaction-diffusion patterns such as waves or Turing patterns can develop in the reactive contact zone. The initial condition which separates the reactants at the beginning leads to a localization in space of the different dynamical regimes accessible to the chemical oscillator. We study here both numerically and experimentally the composite traveling structures resulting from the interaction between chemical fronts and localized waves in the case in which the reactants of such an A + B → oscillator system are those of the canonical Belousov-Zhabotinsky (BZ) oscillating reaction. A transition between different dynamics is obtained by varying the initial concentration of the organic substrate of the BZ reactants, which is one of the parameters controlling the local excitability. We show that the dynamical regime (excitable or oscillatory) characterizing the BZ oscillator in the initial contact area is the key feature which determines the spatiotemporal evolution of the system. The experimental results are in qualitative agreement with the theoretical predictions.

Cross-diffusion-induced convective patterns in microemulsion systems.

Cross-diffusion phenomena are experimentally shown to be able to induce convective fingering around an initially stable stratification of two microemulsions with different compositions. Upon diffusion of a salt that entrains water and AOT micelles by cross-diffusion, the miscible interface deforms into fingers following the build-up of a non-monotonic density profile in the gravitational field. A diffusion model incorporating cross-diffusion effects provides an explanation for the mechanism of the buoyancy-driven hydrodynamic instability and for the properties of the convective fingers.

Interfacial hydrodynamic instabilities driven by cross-diffusion in reverse microemulsions.

When two microemulsions are put in contact in the gravity field along a horizontal contact line, cross-diffusion can trigger the transport of one species in the presence of a gradient in concentration of another species. We show here theoretically that such cross-diffusion effects can induce buoyancy-driven convective instabilities at the interface between two solutions of different compositions even when initially the less dense solution lies on top of the denser one. Two different sources of convective modes are identified depending whether positive or negative cross-diffusion is involved. We evidence the two predicted cross-diffusion driven instabilities experimentally using a two-layer stratification of Aerosol-OT (AOT) water-in-oil microemulsions solutions with different water or AOT composition.

Epidemiology of ovarian cancer in North Sardinia, Italy, during the period 1992-2010.

INTRODUCTION: The aim of this study was to analyze and describe the incidence and mortality trends of ovarian cancer in North Sardinia, Italy, in the period 1992-2010. MATERIALS AND METHODS: Data were obtained from the tumor registry of Sassari province which makes part of a wider registry web, coordinated today by the Italian Association for Tumor Registries. RESULTS: The overall number of ovarian cancer cases registered in the period under investigation was 600. The mean age of the patients was 62 years. The standardized incidence and mortality rates were 11.2/100,000 and 5.1/100,000 respectively. A substantially stable trend in incidence and mortality of ovarian cancer was evidenced. Relative survival at five years from diagnosis was 44.2%. CONCLUSIONS: The incidence and mortality trends of ovarian cancer in North Sardinia remained relatively stable in the last decades, while prognosis remains relatively poor.

Multifractal properties of ball milling dynamics.

This work focuses on the dynamics of a ball inside the reactor of a ball mill. We show that the distribution of collisions at the reactor walls exhibits multifractal properties in a wide region of the parameter space defining the geometrical characteristics of the reactor and the collision elasticity. This feature points to the presence of restricted self-organized zones of the reactor walls where the ball preferentially collides and the mechanical energy is mainly dissipated.

Report on incidence and mortality trends of cervical cancer in northern Sardinia, Italy.

INTRODUCTION: The aim of this study was to analyze and describe the incidence and mortality trends of cervical cancer in northern Sardinia, Italy, in the period 1992-2010. MATERIALS AND METHODS: Data were obtained from the tumor registry of Sassari province which is part of a wider registry web, coordinated today by the Italian Association for Tumor Registries. RESULTS: The overall number of cervical cancer cases registered in the period under investigation was 311. The mean age of the patients was 51.8 years. The standardized incidence and mortality rates were 6.6 / 100.000 and 0.7 / 100.000, respectively. A stable trend in incidence and mortality of cervical cancer was evidenced. Relative survival at five years from diagnosis was fairly good (66.3%). CONCLUSIONS: The incidence and mortality trends of cervical cancer in northern Sardinia remained relatively stable in the last decades. Furthermore, survival of patients with cervical cancer is good in the area, sanctioning the adequacy of the preventive and clinical measures in use.

Understanding oscillatory phenomena in molecular hydrogen generation via sodium borohydride hydrolysis.

The hydrolysis of borohydride salts represents one of the most promising processes for the generation of high purity molecular hydrogen under mild conditions. In this work we show that the sodium borohydride hydrolysis exhibits a fingerprinting periodic oscillatory transient in the hydrogen flow over a wide range of experimental conditions. We disproved the possibility that flow oscillations are driven by supersaturation phenomena of gaseous bubbles in the reactive mixture or by a nonlinear thermal feedback according to a thermokinetic model. Our experimental results indicate that the NaBH4 hydrolysis is a spontaneous inorganic oscillator, in which the hydrogen flow oscillations are coupled to an "oscillophor" in the reactive solution. The discovery of this original oscillator paves the way for a new class of chemical oscillators, with fundamental implications not only for testing the general theory on oscillations, but also with a view to chemical control of borohydride systems used as a source of hydrogen based green fuel.

Dynamics due to combined buoyancy- and Marangoni-driven convective flows around autocatalytic fronts.

A reaction-diffusion-convection (RDC) model is introduced to analyze convective dynamics around horizontally traveling fronts due to combined buoyancy- and surface tension-driven flows in vertical solution layers open to the air. This isothermal model provides a means for a comparative study of the two effects via tuning two key parameters: the solutal Rayleigh number Ra, which rules the buoyancy influence, and the solutal Marangoni number Ma governing the intensity of surface effects at the interface between the reacting solution and air. The autocatalytic front dynamics is probed by varying the relative importance of Ra and Ma and the resulting RDC patterns are quantitatively characterized through the analysis of the front mixing length and the topology of the velocity field. Steady asymptotic regimes are found when the bulk and the surface contributions to fluid motions act cooperatively i.e. when Ra and Ma have the same sign. Complex dynamics may arise when these numbers are of opposite signs and the two effects thus compete in an antagonistic configuration. Typically, spatiotemporal oscillations are observed as the control parameters are set in the region (Ra < 0, Ma > 0). Periodic behaviour develops here even in the absence of any double-diffusive interplay, which in previous literature was identified as a possible source of complexity.

Controlling Nonlinear Dynamics of Milling Bodies in Mechanochemical Devices Driven by Pendular Forcing.

Understanding the dynamics of milling bodies is key to optimize the mixing and the transfer of mechanical energy in mechanochemical processing. In this work, we present a comparative study of mechanochemical reactors driven by harmonic pendular forcing and characterized by different geometries of the lateral borders. We show that the shape of the reactor bases, either flat or curved, along with the size of the milling body and the elasticity of the collisions, represents relevant parameters that govern the dynamical regimes within the system and can control the transition from periodic to chaotic behaviors. We single out possible criteria to preserve target dynamical scenarios when the size of the milling body is changed, by adapting the relative extent of the spatial domain. This allows us to modulate the average energy of the collisions while maintaining the same dynamics and paves the way for a unifying framework to control the dynamical response in different experimental conditions. We finally explore the dynamical and energetic impact of an increasingly asymmetric mechanical force.

Incidence of thyroid cancer in Italy, 1991-2005: time trends and age-period-cohort effects.

BACKGROUND: In Italy, some of the highest incidence rates (IRs) of thyroid cancer (TC) worldwide have been reported. PATIENTS AND METHODS: TC cases <85 years of age reported to Italian cancer registries during 1991-2005 were included. Age-standardized IRs were computed for all TC and age-period-cohort effects were estimated for papillary TC. RESULTS: IRs of TC were twofold higher in 2001-2005 than in 1991-1995 (18 and 8 per 100,000 women, 6 and 3 per 100,000 men, respectively). Increases were similar in the two sexes and nearly exclusively due to papillary TC. Increases of papillary TC by birth cohort were found in both sexes and among all age groups between 20 and 79 years. Age-period-cohort models showed a strong period effect in both sexes (rate ratio for 2001-2009 versus 1991-1995 = 2.5 in women and 2.3 in men), although IRs peaked at an earlier age in women (45-49 years) than men (65-69 years). CONCLUSION: The strength of the period effect in both sexes and the earlier onset in women than men strongly implicated increased medical surveillance in the upward trends of papillary TC incidence in Italy. The consequences of the current intense search for TC on morbidity and possible overtreatment, especially among young women, should be carefully evaluated.

[Cancer incidence among petrochemical workers in the Porto Torres industrial area, 1990-2006]. / Incidenza di patologie neoplastiche nei lavoratori del complesso petrolchimico di Porto Torres, 1990-2006.

BACKGROUND: Various epidemiological studies explored cancer mortality and incidence among petrochemical workers. We followed up cancer incidence in a cohort of 5350 male petrochemical workers in the industrial area of Porto Torres (Sardinia, Italy). MATERIAL AND METHODS: The follow-up covered the period from 01/01/1990, when completeness of the cohort was certain and reference rates by the local Cancer Registry became available, up to 31/12/2006. Cohort members were subjects employed for six months or more in one of the chemical plants of the industrial area, alive as at 01/01/1990. Overall, a total of 81,392 person-years at risk were accumulated. The standardized incidence ratio (sir), as the ratio of observed to expected events, and its 95% confidence interval (CI) were calculated for all cancers and selected cancer sites, in the total cohort and in sub-cohorts of workers in plants where exposure to chemical agents evaluated in the IARC Monographs might have occurred. RESULTS: An increase in risk for all cancers was observed in the total cohort (596 cases; sir = 1.09; 95% CI 1.00-1.18), and it was highest for non-Hodgkin lymphoma (NHL, 26 cases: sir = 1.78; 95% CI 1.22-2.62). Risk for haemolymphatic cancer was highest in the sub-cohort of workers employed for 10 years or more, with a latency period of 20 years or longer, and among those employed in the manufacture and polymerization of vinyl chloride (VCM; all cancers, 51 cases: sir = 1.43; 95% CI 1.08-1.88; NHL, 4 cases: sir=4.06; 95% CI 1.64-10.0). Risk of haemolymphatic cancer was not significantly elevated in the sub-cohort potentially exposed to benzene. An excess risk of bladder cancer (RR = 1.46; 95% CI 1.09-1.96), but not of pleural cancer, was observed in the sub-cohort potentially exposed to asbestos. No significant increase in cancer risk was observed among workers potentially exposed to acrylonitrile, butadiene, or styrene. CONCLUSIONS: Our follow-up study of petrochemical workers showed an increase in risk for all cancers, and particularly NHL, apparently concentrated among workers potentially exposed to VCM

Pattern of cancer risk in persons with AIDS in Italy in the HAART era.

A record-linkage study was carried out between the Italian AIDS Registry and 24 Italian cancer registries to compare cancer excess among persons with HIV/AIDS (PWHA) before and after the introduction of highly active antiretroviral therapy (HAART) in 1996. Standardised incidence ratios (SIR) were computed in 21951 AIDS cases aged 16-69 years reported between 1986 and 2005. Of 101 669 person-years available, 45 026 were after 1996. SIR for Kaposi sarcoma (KS) and non-Hodgkin lymphoma greatly decreased in 1997-2004 compared with 1986-1996, but high SIRs for KS persisted in the increasingly large fraction of PWHA who had an interval of <1 year between first HIV-positive test and AIDS diagnosis. A significant excess of liver cancer (SIR=6.4) emerged in 1997-2004, whereas the SIRs for cancer of the cervix (41.5), anus (44.0), lung (4.1), brain (3.2), skin (non-melanoma, 1.8), Hodgkin lymphoma (20.7), myeloma (3.9), and non-AIDS-defining cancers (2.2) were similarly elevated in the two periods. The excess of some potentially preventable cancers in PWHA suggests that HAART use must be accompanied by cancer-prevention strategies, notably antismoking and cervical cancer screening programmes. Improvements in the timely identification of HIV-positive individuals are also a priority in Italy to avoid the adverse consequences of delayed HAART use.

Distribution of 'promoter' sandflies associated with incidence of classic Kaposi's sarcoma.

The patchy geographical distributions of classic Kaposi's sarcoma (KS) and human herpesvirus type 8 (HHV-8), better known as Kaposi's sarcoma-associated herpesvirus (KSHV) remain unexplained. It has been proposed that certain species of bloodsucking insects ('promoter arthropods') promote the reactivation of HHV-8/KSHV and facilitate both HHV-8/KSHV transmission and KS development. This hypothesis was tested by sampling the presence and density of human-biting Diptera with CDC light traps in two areas of Sardinia with contrasting incidence rates of classic KS. In total, 11,030 specimens (99.9% sandflies and 0.1% mosquitoes) belonging to 10 species were collected from 40 rural sites. Five of these species are considered to be possible promoter arthropods because of the irritation their bites cause: Phlebotomus perniciosus Newstead; Phlebotomus perfiliewi Parrot (Diptera: Psychodidae); Aedes berlandi Seguy; Culiseta annulata (Schrank) and Culex theileri Theobald (Diptera: Culicidae). Five species are probable 'non-promoters' because their bites are not particularly irritating: Culiseta longiareolata (Macquart); Culex pipiens s.l.; Anopheles algeriensis Theobald; Anopheles maculipennis s.l., and Anopheles plumbeus Stephens. A significant correlation was found between the geographical distribution of promoter arthropods and incidence rates of KS (Spearman's r = 0.59,P < 0.01). Promoter arthropods were more likely to be caught in areas with cutaneous leishmaniasis and a past high prevalence of malaria, and in areas of limestone, acid volcanic soil and cereal cultivation. The study supports the association between promoter arthropods and classic KS, which may explain the geographic variability of KS and HHV-8/KSHV, and highlights the links with a number of variables previously associated with the incidence of KS.

Correlation between cell lipid content, gene expression and fermentative behaviour of two Saccharomyces cerevisiae wine strains.

AIM: To verify a possible correlation between cell lipid composition, expression of key genes in lipid metabolism and fermentative behaviour of Saccharomyces cerevisiae wine strains. METHODS AND RESULTS: The fermentative abilities of two commercial wine strains of S. cerevisiae were tested under stressful conditions. Cell number, glucose and fructose concentrations, expression of ACS1, ACS2, ACC1, OLE1, ERG9, ERG10, ARE1 and ARE2 and lipid content were evaluated. The strain that failed to complete the fermentation had lower amounts of C16:1 and C16:0 fatty acids at the beginning of fermentation (0 h) and late logarithmic phase (72 h). While the amount of C18:1 in this strain was lower than that in the strain that completed the fermentation at 0 h, same levels were observed for both strains at 72 h. The sterol levels were generally higher in the strain that failed to complete the fermentation. Gene expression generally increased from the beginning of the fermentation to the late logarithmic phase in both strains. CONCLUSION: A positive correlation between good fermentative ability, elevated fatty acid content and ACC1 gene expression has been identified. SIGNIFICANCE AND IMPACT OF THE STUDY: The cell lipid content at the time of inoculum and expression of ACC1 gene of starter strains should be carefully considered in order to identify the possible stuck/sluggish fermentations.