Analysis of a microfluidic device for diffusion coefficient determination of high molecular weight solutes detectable in the visible spectrum.

We developed a procedure to measure diffusion coefficients using microfluidic devices that contributes to the transport analysis of high molecular weight solutes with low diffusion coefficient. This procedure allows a quick determination of diffusion coefficients and a precise evaluation of measurement errors. Making use of color variation of a pH indicator, we determined its diffusion coefficient in its own solvent (water). The value obtained was compared with previously published ones and was found to be similar to those cited. The microfluidic device has a serpentine-shaped channel that allows monitoring the solution evolution in different regions of the path in a single visual field without the need to move the camera or the microchip. This kind of device also allows the spatial and temporal tracking of the diffusion process. The solution color intensity is used to determine solute concentration; therefore, this method presents an advantage compared to those based on fluorescence detection. A complete analysis of the diffusive behavior along the channel path was performed in order to test the accuracy of these kinds of methodologies. This analysis can be used with similar devices, and the techniques employed for diffusion analysis can be applied to a µTAS-type microfluidic platform, allowing obtain variations of the diffusion coefficient as a function of time due to variations in external factors, e.g., temperature, etc.

Transapical beating heart mitral valve repair versus conventional surgery: a propensity-matched study.

OBJECTIVES: Transapical Neochordae implantation (NC) allows beating heart mitral valve repair in patients with degenerative mitral regurgitation. The aim of this single-centre, retrospective study was to compare outcomes of NC versus conventional surgical (CS) mitral valve repair. METHODS: Data of patients who underwent isolated mitral valve repair with NC or CS from January 2010 to December 2018 were collected. A propensity score matching analysis was performed to reduce confounding due to baseline differences between groups. The primary end point was overall all-cause mortality; secondary end points were freedom from reoperation, freedom from moderate (2+) and from severe (3+) mitral regurgitation (MR) and New York Heart Association functional class in the overall population and in patients with isolated P2 prolapse (type A anatomy). RESULTS: Propensity analysis selected 88 matched pairs. There was no 30-day mortality in the 2 groups. Kaplan-Meier analysis showed similar 5-year survival in the 2 groups. Patients undergoing NC showed worse freedom from moderate MR (≥2+) (57.6% vs 84.6%; P < 0.001) and from severe MR (3+) at 5-year follow-up: 78.1% vs 89.7% (P = 0.032). In patients with type A anatomy, freedom from moderate MR and from severe MR was similar between groups (moderate: 63.9% vs 74.6%; P = 0.21; severe: 79.3% vs 79%; P = 0.77 in NC and FS, respectively). Freedom from reoperation was lower in the NC group: 78.9% vs 92% (P = 0.022) but, in type A patients, it was similar: 79.7% and 85% (P = 0.75) in the NC and CS group, respectively. More than 90% of patients of both groups were in New York Heart Association class I and II at follow-up. CONCLUSIONS: Transapical beating-heart mitral chordae implantation can be considered as an alternative treatment to CS, especially in patients with isolated P2 prolapse.

Family Pediatrician and Public Health collaboration, an alliance to increase vaccination coverage: an experience with MenB vaccination in Italy.

Background: Invasive Meningococcal Disease is a severe disease mainly affecting infants and young children. Most infections are caused by serogroups A, B, C, W, X, and Y. In the last 10 years, serogroup B has been the main cause of Invasive Meningococcal Disease in Europe. Recent data resulting from an observational study conducted in Italy show a significant reduction in the number of Invasive Meningococcal Disease cases due to Neisseria meningitidis B after the introduction of vaccine 4CMenB. Thus, the Naples Team of Federation of Italian Primary Care Pediatricians and the Public Health Department started an active collaboration focused on vaccination process management (named "Progetto Via") with the aim of increasing Meningococcal B vaccination coverage. Study design: Source of data is the regional platform "GE.VA.". Every Primary care Pediatrician uses daily to record vaccination activity. This platform is integrated with data entered by operators of the District/Vaccination Center. Methods: Time: January 2019 - December 2019. The Federation of Italian Primary Care Pediatricians/Naples organized a meeting to identify six coordinators. The pediatricians could choose to counsel in their own offices and send children to the vaccination center or to counsel and vaccinate directly in their own clinics. Results: A total of 78 pediatricians took part in the project: 46 did only counseling and 32 did both counseling and vaccination in their medical clinic. Data obtained show an overall average vaccination coverage growth of about 13% in the first 4 months of the survey, and a further growth of about 11% in the following seven months, with a total growth in the entire period of 24%. The pediatricians' counseling is essential to recover non-compliant subjects, considering both the relationship of trust with the families and the visits already scheduled as an ideal moment for vaccinations' status check. Conclusions: The project highlights how an effective collaboration between family pediatricians and the Local Health Authority becomes valuable in getting closer to reach the Ministerial goal of 95%. Vaccination coverage increased significantly when family pediatricians supported the activity of vaccine centers in distress in many regional situations. The trust relationship, the hourly availability and the capillary network of family pediatricians' clinics were key elements for the success of this project and were also recognized by parents.

Angiogenesis and vessel co-option in a mathematical model of diffusive tumor growth: The role of chemotaxis.

This work considers the propagation of a tumor from the stage of a small avascular sphere in a host tissue and the progressive onset of a tumor neovasculature stimulated by a pro-angiogenic factor secreted by hypoxic cells. The way new vessels are formed involves cell sprouting from pre-existing vessels and following a trail via a chemotactic mechanism (CM). Namely, it is first proposed a detailed general family of models of the CM, based on a statistical mechanics approach. The key hypothesis is that the CM is composed by two components: i) the well-known bias induced by the angiogenic factor gradient; ii) the presence of stochastic changes of the velocity direction, thus giving rise to a diffusive component. Then, some further assumptions and simplifications are applied in order to derive a specific model to be used in the simulations. The tumor progression is favored by its acidic aggression towards the healthy cells. The model includes the evolution of many biological and chemical species. Numerical simulations show the onset of a traveling wave eventually replacing the host tissue with a fully vascularized tumor. The results of simulations agree with experimental measures of the vasculature density in tumors, even in the case of particularly hypoxic tumors.

Development of radon transport model in different types of dwellings to assess indoor activity concentration.

The influence of different building types on the activity concentration of Radon indoor is studied through transport models in soil and building materials. The numerical solutions of the relevant transport equations are solved by the finite differences method (FDM) and used to evaluate the indoor Radon activity concentration. Several boundary conditions are introduced to simulate the Radon entry into the buildings from soils and to assess the Radon activity concentration at the different floors. The types of dwelling investigated differ in the position of the lower floor respect to the ground. Comparisons are made to modeling assessments obtained considering different soil characteristics underneath the building and building materials to simulate indoor Radon activity concentration. These investigations lead to the conclusion that, in addition to the nature of the soil and building materials, the position of lower floor of dwellings plays a significant role in determining the amount of radon entry into residential buildings. This work is effective to assess the health hazards coming from the Radon accumulation in living environments.

The effects of containment measures in the Italian outbreak of COVID-19.

The COVID-19 pandemic is spreading worldwide. Italy emerged early on as the country with the largest outbreak outside Asia. The outbreak in Northern Italy demonstrates that it is fundamental to contain the virus' spread at a very early stage of diffusion. At later stages, no containment measure, even if strict, can prevent the saturation of the hospitals and of the intensive care units in any country. Here we show that it is possible to predict when the intensive care units will saturate, within a few days from the beginning of the exponential growth of COVID-19 intensive care patients. Using early counts of intensive care patients, we predict the saturation for Lombardy, Italy. We also assess short-term and long-term lockdown effects on intensive care units and number of deaths. Governments should use the Italian outbreak as a precedent and implement appropriate containment measures to prevent the saturation of their intensive care units and protect their population, also, and above all, in anticipation of a possible second exponential spread of infections.

Space-time Bayesian analysis of the environmental impact of a dismissing nuclear power plant.

The assessment of the radiological impact of decommissioning activities at a nuclear power plant requires a detailed analysis of the distribution of radionuclides in the environment surrounding it. The present work concerns data of three campaigns carried out during the last twenty years in the plain of the Garigliano river surrounding the Garigliano Nuclear Power Plant (GNPP), which is located in Southern Italy and shut down in 1979. Moreover, some data from surveys held in the eighties, across the Chernobyl accident, have been taken in account. The results for the soil samples, in particular for 137Cs and 236U specific activity, were analyzed for their extension in space and in time. Some of the problems related to the classical analysis of environmental radiological data (non-normal distribution of the values, small number of sample points, multiple comparison and presence of values lesser than the minimum detectable activity) have been overcome with the use of Bayesian methods. The scope of the paper is threefold: (1) to introduce the data of the last campaign held in the Garigliano plain; (2) to insert these data in a larger spatio-temporal frame; (3) to show how the Bayesian approach can be applied to radiological environmental surveys, stressing out its advantages over other approaches, using the data of the campaigns. The results show that radionuclides specific activity in soil is dominated by the natural sources with the contribution of the atmospheric fallout. A detailed study was performed on the 137Cs data to evaluate both their statistical distribution and the trend over the space and the time. It results that (i) no new contribution there was in the last decades, (ii) specific activity values of the area surrounding the GNPP are consistent with those obtained in other farther areas, (iii) the effective depletion half-life factor for 137Cs is much lower than the half-life of the radionuclide.

Full Percutaneous Treatment of Degenerative Disc Disease with Intradiscal Lumbar Interbody Fusion and Posterior Stabilization: Preliminary Results.

PURPOSE: To report the preliminary results of a novel full percutaneous interbody fusion technique for the treatment of degenerative disc disease (DDD) resistant to conservative treatment with posterior stabilization with rods and screws and transforaminal placement of an 8-mm-width intradiscal cage. MATERIALS AND METHODS: A total of 79 patients with lumbar spine DDD resistant to medical therapy and/or spondylolisthesis up to grade 2 were treated. We performed preoperative X-rays, CT and MRI. The outcomes were assessed using the VAS score and the Oswestry Disability Index at a 1-, 6- and 12-month follow-up and also included X-rays to evaluate the correct bone fusion and the absence of complications. RESULTS: Mean operation time was 130 min, and mean postoperative time until hospital discharge was 2 days. Postoperative values for VAS scores and ODI improved significantly compared to preoperative data: Mean preprocedural VAS was 7.49 ± 0.69 and decreased at 12-month follow-up to 1.31 ± 0.72, and mean preprocedural ODI was 29.94 ± 1.67 and decreased at 12-month follow-up to 12.75 ± 1.44. No poor results were reported, and no postprocedural sequelae were observed. CONCLUSIONS: In our experience, this preliminary report shows a feasible and safe full percutaneous alternative procedure and represents a minimally invasive management of degenerative disc disease with low back pain resistant to medical therapy with or without lumbar spondylolisthesis up to grade 2.

Combined flow-based imaging assessment of optimal cardiac resynchronization therapy pacing vector: a case report.

BACKGROUND: There are still many pendent issues about the effective evaluation of cardiac resynchronization therapy impact on functional mitral regurgitation. In order to reduce the intrinsic difficulties of quantification of functional mitral regurgitation itself, an automatic quantification of real-time three-dimensional full-volume color Doppler transthoracic echocardiography was proposed as a new, rapid, and accurate method for the assessment of functional mitral regurgitation severity. Recent studies suggested that images of left ventricle flow by echo-particle imaging velocimetry could be a useful marker of synchrony. Echo-particle imaging velocimetry has shown that regional anomalies of synchrony/synergy of the left ventricle are related to the alteration, reduction, or suppression of the physiological intracavitary pressure gradients. We describe a case in which the two technologies are used in combination during acute echocardiographic optimization of left pacing vector in a 63-year-old man, Caucasian, who showed worsening heart failure symptoms a few days after an implant, and the effect of the device's optimization at 6-month follow-up. DISCUSSION: The degree of realignment of hemodynamic forces, with quantitative analysis of the orientation of blood flow momentum (φ), can represent improvement of fluid dynamics synchrony of the left ventricle, and explain, with a new deterministic parameter, the effects of cardiac resynchronization therapy on functional mitral regurgitation. Real-time three-dimensional color flow Doppler quantification is feasible and accurate for measurement of mitral inflow, left ventricular outflow stroke volumes, and functional mitral regurgitation severity. CONCLUSION: This clinical case offers an innovative and accurate approach for acute echocardiographic optimization of left pacing vector. It shows clinical utility of combined three-dimensional full-volume color Doppler transthoracic echocardiography/echo-particle imaging velocimetry assessment to increase response to cardiac resynchronization therapy, in terms of reduction of functional mitral regurgitation, improving fluid dynamics synchrony of the left ventricle.

Capillary film and breakup mechanism in the squeezing to dripping transition regime at the mesoscale between micro and milli-fluidics.

We report a study of droplet generation in two phase flows of non-miscible fluids in a T-shaped array of circular channels, at the mesoscale between micro- and milli-fluidics. Our experiments show that the balance between the different types of forces (capillary forces, shear viscous forces, etc.) may differ significantly from that found by previous authors in smaller, microfluidics channels. The results may, therefore, be applied to practical systems in which droplets act as small chemical reactors or help enhance mixing. We suggest a possible interesting extension to the generation of drops inside porous media. We report experiments in which the length of the droplets and the residual thickness of the surrounding fluid film are systematically measured as a function of the respective flow rates of the two fluids: These results are carefully compared to theoretical models taking into account in different ways the capillary and viscous effects and to results obtained by other authors for smaller channels. Several dimensionless control variables are tested (capillary number, ratio of the flow rates of the two fluids, etc.). Capillary film thickness is shown to be a useful variable to identify the different regimes of formation. Testing of the theoretical models with the experimental data showed that the change from one formation regime to the other is accompanied by a change in the role of viscous effects. Two models of breakup mechanisms were tested: on the one hand, the pressure buildup mechanism and, on the other hand, a second mechanism corresponds to the balance of tangential shear stresses and interfacial tension. According to the formation regimes, both models have provided satisfactory predictions of the experimental results. However, at this mesoscale, the experimental data were better described by the models dependent on the capillary number, as previously reported in systems with a low degree of confinement.

AMS assessment of U-contamination of structural materials of the Garigliano NPP under decommissioning.

The assessment of the radiological impact of decommissioning activities at a Nuclear Power Plant requires a detailed mapping of the distribution of radionuclides both in the environment surrounding the NPP and in its structural material. The detection of long-lived actinide isotopes and possibly the identification of their origin is particularly interesting and valuable if ultrasensitive measurement of the relative abundance of U isotopes is performed via Accelerator Mass Spectrometry (AMS). In this paper we present an investigation carried out on the structural materials of the Garigliano NPP aiming to determine the abundance of 235,236,238U in the various compartments of the plant buildings under decommissioning. Since the expected values both for isotopic ratios and total U concentrations range over different orders of magnitude, we have developed a novel methodology for the measurement of 234,235U/238U isotopic ratios in low U concentration samples. This allowed a systematic investigation of the distribution of all U isotopes in concrete and metal matrices of the NPP. The behavior of 235,236U/238U isotopic ratios in the different compartments of the NPP is discussed. The correlation of these ratios with 60Co and 137Cs specific activities is also studied to show a different behavior for concrete and metal samples. These data represent a very valuable information to direct the decommissioning procedures under course.

Lateral movements in Rayleigh-Taylor instabilities due to frontiers. Experimental study.

Lateral movements of the fingers in Rayleigh-Taylor hydrodynamic instabilities at the interface between two fluids are studied. We show that transverse movements appear when a physical boundary is present; these phenomena have not been explained until now. The boundary prevents one of the fluids from crossing it. Such frontiers can be buoyancy driven as, for example, the frontier to the passage of a less dense solution through a denser solution or when different aggregation states coexist (liquid and gaseous phases). An experimental study of the lateral movement velocity of the fingers was performed for different Rayleigh numbers (Ra), and when oscillations were detected, their amplitudes were studied. Liquid-liquid (L-L) and gas-liquid (G-L) systems were analysed. Aqueous HCl and Bromocresol Green (sodium salt, NaBCG) solutions were used in L-L experiments, and CO2 (gas) and aqueous NaOH, NaHCO3, and CaCl2 solutions were employed for the G-L studies. We observed that the lateral movement of the fingers and finger collapses near the interface are more notorious when Ra increases. The consequences of this, for each experience, are a decrease in the number of fingers and an increase in the velocity of the lateral finger movement close to the interface as time evolves. We found that the amplitude of the oscillations did not vary significantly within the considered Ra range. These results have an important implication when determining the wave number of instabilities in an evolving system. The wave number could be strongly diminished if there is a boundary.

Lateral movements in Rayleigh-Taylor instabilities due to frontiers. Numerical analysis.

Numerical simulations were performed for Rayleigh-Taylor (RT) hydrodynamic instabilities when a frontier is present. The frontier formed by the interface between two fluids prevents the free movement of the fingers created by the instability. As a consequence, transversal movements at the rear of the fingers are observed in this area. These movements produce collapse of the fingers (two or more fingers join in one finger) or oscillations in the case that there is no collapse. The transversal velocity of the fingers, the amplitude of the oscillations, and the wave number of the RT instabilities as a function of the Rayleigh number (Ra) were studied near the frontier. We verified numerically that in classical RT instabilities, without a frontier, these lateral movements do not occur; only with a physical frontier, the transversal displacements of the fingers appear. The transverse displacement velocity and the initial wave number increase with Ra. This leads to the collapse of the fingers, diminishing the wave number of the instabilities at the interface. Instead, no significant changes in the amplitude of the oscillations are observed modifying Ra. The numerical results are independent of the type or origin of the frontier (gas-liquid, liquid-liquid, or solid-liquid). The numerical results are in good agreement with the experimental results reported by Binda et al. [Chaos 28, 013107 (2018)]. Based on these results, it was possible to determine the cause of the transverse displacements, which had not been explained until now.

Experimental analysis of density fingering instability modified by precipitation.

We analyze the effect of precipitate formation on the development of density induced hydrodynamic instabilities. In this case, the precipitate is BaCO3, obtained by reaction of CO2 with aqueous BaCl2. CO2(g) dissolution increases the local density of the aqueous phase, triggering Rayleigh-Taylor instabilities and BaCO3 formation. It was observed that at first the precipitate was formed at the finger front. As the particles became bigger, they began to fall down from the front. These particles were used as tracers using PIV technique to visualize the particle streamlines and to obtain the velocity of that movement. This falling produced a downward flow that might increase the mixing zone. Contrary to expectations, it was observed that the finger length decreased, indicating that for the mixing zone development, the consumption of CO2 to form the precipitate is more important than the downward flow. The mixing zone length was recovered by increasing the availability of the reactant (higher CO2 partial pressure), compensating the CO2 used for BaCO3 formation. Mixing zone development rates reached constant values at shorter times when the precipitate is absent than when it is present. An analysis of the nonlinear regime with and without the precipitate is performed.

Development of novel strontium containing bioactive glass based calcium phosphate cement.

OBJECTIVE: The aim of this study was to investigate the effect on properties of increasing strontium substitution for calcium in bioactive glasses used as precursors for novel calcium phosphate cements. METHODS: Glasses were produced by progressively substituting strontium for calcium. Cements were prepared by mixing the glass powder with Ca(H2PO4)2 powder with a 2.5% solution of Na2HPO4. Setting times and compressive strength were measured after 1h, 1 day, 7 days and 28 days immersion in Tris buffer solution. X-ray diffraction (XRD), Fourier transform infrared spectroscopy and radiopacity were measured and crystal morphology was assessed using scanning electron microscopy. RESULTS: A correlation between the phases formed, morphology of the crystallites, setting time and compressive strength were analyzed. Setting time increased proportionally with strontium substitution in the glass up to 25%, whereas for higher substitutions it decreased. Compressive strength showed a maximum value of 12.5MPa and was strongly influenced by the interlocking of the crystals and their morphology. XRD showed that the presence of strontium influenced the crystal phases formed. Octacalcium phosphate (Ca8H2(PO4)6·5H2O, OCP) was the main phase present after 1h and 1 day whereas after 28 days OCP was completely transformed to strontium-containing hydroxyapatite (SrxCa(10-x)(PO4)6(OH)2, SrHA). Radiopacity increased proportionally to strontium substitution in the glass. SIGNIFICANCE: A novel method to develop a bone substitute forming in vitro SrHA as a final product by using a bioactive glass as a precursor was shown. These novel injectable bioactive glass cements are promising materials for dental and orthopedic applications. Further in vivo characterizations are being conducted.

Efficacy and safety of dabigatran in a "real-life" population at high thromboembolic and hemorrhagic risk: data from MonaldiCare registry.

OBJECTIVE: Dabigatran is a novel target specific oral anticoagulant for stroke prevention in non valvular atrial fibrillation. Little is still known about its real-world effectiveness and safety in the italian population. Aim of our study was to evaluate the efficacy and safety of dabigatran in a large single-center cohort of "real-life" italian population with non-valvular AF and to compare the results with those obtained from the RE-LY trial and the Medicare study. PATIENTS AND METHODS: We studied a prospective cohort of 2108 patients (1119 male; mean age 69.4 ± 9.4 years) who started the oral anticoagulant treatment with dabigatran 110 mg twice-daily (DAB 110; N = 1075; 51%) or 150 mg twice-daily (DAB 150; N = 1033; 49%). Follow-up data were obtained trough outpatients visits each 3-6 months for assessing the clinical status, adherence to treatment, occurrence of side effects and major cardiovascular complications. RESULTS: In DAB 150 group the mean age was 64.9 ± 8.8 years, 56.8% of patients was male. CHA2DS2Vasc Score was ≥ 3 in 94.3% and HAS-BLED was ≥ 3 in 59.7%. In DAB 110 group (N = 1075) the mean age was 73.9 ± 7.5 years; 49.5% of patients was male. CHA2DS2Vasc Score was ≥ 3 in 73.4% and HAS-BLED was ≥ 3 in 87.4% of DAB 110 patients. One patient taking Dabigatran 110 mg bid had ischemic stroke without significantly neurological sequelae. In both groups, no patient experienced hemorrhagic stroke during the follow-up period. 147 patients (6.9%) of MonaldiCare population reported adverse effects from treatment with dabigatran, of whom 121 patients (5.7%) discontinued therapy. We reported one case of subarachnoid hemorrhage (0.05%) in a patient with high thrombo-embolic and high hemorrhagic risk score who was taking dabigatran 150 mg bid and one case (0.05%) of bladder bleeding in a patient who was taking dabigatran 110 mg bid. No major gastrointestinal bleeding was observed in the MonaldiCare population. CONCLUSIONS: MonaldiCare registry showed a safety profile of both dosages of dabigatran regarding major of fatal bleeding in a "real life" single center italian population at high thromboembolic and hemorrhagic risk. The majority of MonaldiCare patients tolerated dabigatran treatment without significant side effects. The efficacy of dabigatran was demonstrated by very low prevalence of ictus/TIA, also when patients underwent electrical AF cardioversion independently of the transesophageal examination.

D-Glucosamine as a novel chiral auxiliary for the stereoselective synthesis of P-stereogenic phosphine oxides.

D-Glucosamine was successfully employed as a chiral auxiliary for the enantioselective synthesis of phosphine oxides. The influence of the anomeric position was also investigated and revealed the excellent ability of the α-anomer to perform this transformation in a highly selective fashion. The methodology employed consisted of three steps: diastereoselective formation of the oxazaphospholidine followed by subsequent selective cleavage of P-N and P-O bonds by reaction with two Grignard reagents. P-epimers oxazaphospholidines were prepared switching from a P(v) to a P(III) precursor, thus allowing for the synthesis of enantiomeric phosphine oxides. In addition, the chiral auxiliary could be recovered and efficiently recycled.

Uranium beam characterization at CIRCE for background and contamination determinations.

The Accelerator Mass Spectrometry (AMS) is the most sensitive technique, compared either to the Inductively Coupled Plasma (ICP-MS) or Thermal Ionization (TI-MS) mass spectrometer, for the actinide (e.g. (236)U, (x)Pu isotopes) measurements. They are present in environmental samples at the ultra trace level since atmospheric tests of Nuclear Weapons (NWs) performed in the past, deliberate dumping of nuclear waste, nuclear fuel reprocessing, on a large scale, and operation of Nuclear Power Plants (NPPs), on a small scale, have led to the release of a wide range of radioactive nuclides in the environment. At the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) in Caserta, Italy, an upgraded actinide AMS system, based on a 3-MV pelletron tandem accelerator, has been developed and routinely operated. At CIRCE a charge state distribution as a function of terminal voltage, the beam emittance, measured in the 20° actinides dedicated beam line, as well as the energy and position validation of the U ions were performed in order to determine the best measurement conditions. A (236)U/(238)U isotopic ratio background level of about 5×10(-12) or 3×10(-13), depending on the Time of Flight-Energy (TOF-E) configurations, as well as the spatial distribution of the (235)U, (238)U interferences ions and a (236)U contamination mass of about 0.5 fg have been determined.

Experimental study of linear and nonlinear regimes of density-driven instabilities induced by CO(2) dissolution in water.

Density driven instabilities produced by CO2 (gas) dissolution in water containing a color indicator were studied in a Hele Shaw cell. The images were analyzed and instability patterns were characterized by mixing zone temporal evolution, dispersion curves, and the growth rate for different CO2 pressures and different color indicator concentrations. The results obtained from an exhaustive analysis of experimental data show that this system has a different behaviour in the linear regime of the instabilities (when the growth rate has a linear dependence with time), from the nonlinear regime at longer times. At short times using a color indicator to see the evolution of the pattern, the images show that the effects of both the color indicator and CO2 pressure are of the same order of magnitude: The growth rates are similar and the wave numbers are in the same range (0-30 cm(-1)) when the system is unstable. Although in the linear regime the dynamics is affected similarly by the presence of the indicator and CO2 pressure, in the nonlinear regime, the influence of the latter is clearly more pronounced than the effects of the color indicator.

Influence of temperature on linear stability in buoyancy-driven fingering of reaction-diffusion fronts.

A vertical Hele-Shaw cell was used to study the influence of temperature on Rayleigh-Taylor instabilities on reaction-diffusion fronts. The propagation of the chemical front can thus be observed, and experimental results can be obtained via image treatment. A chemical front produced by the coupling between molecular diffusion and the auto-catalysis of the chlorite-tetrathionate reaction, descends through the cell, consuming the reactants below while the product is formed above. Buoyancy-driven instabilities are formed due to the density difference between reactants and products, and the front takes a fingering pattern, whose growth rate has temperature dependence. In this study, the effect of temperature on the linear regime of the instability (that is, when the effects of such instability start to appear) was analyzed. To measure the instability, Fourier transform analysis is performed, in order to obtain the different wave numbers and their power as a function of time. Thus, the growth rate for each wave number and the most unstable wave number is obtained for each of the temperatures under study. Based on repeated experiments, a decrease in the growth rate for the most unstable wave number can be observed with the increase of temperature.