Effect of variable solubility on reactive dissolution in partially miscible systems.

When two partially miscible systems are put in contact, one phase, A, can dissolve into the other one with a given solubility. Chemical reactions in the host phase can impact this dissolution by consuming A and by generating products that impact the solubility of A. Here, we study theoretically the optimal conditions for transfer of a reactant A in a host phase containing a species B when a bimolecular A + B → C reaction generates a product C that linearly decreases the solubility of A. We have quantified numerically the influence of this variable solubility on the reaction-diffusion (RD) concentration profiles of all species in the host phase, on the temporal evolution of the position of the reaction front, and on the flux of A through the interface. We have also computed the analytical asymptotic concentration profiles, solutions at long times of the RD governing equations. For a fixed negative effect of C on the solubility of A, an increase in the initial concentration of reactant B or an increase in the diffusion rate of species B and C results in a larger flux of A and hence a larger amount of A dissolved in the host solution at a given time. However, when the influence of C on the solubility increases, the mass transfer decreases. Our results help understand to what extent a chemical reaction can optimize the reactive transfer of a solute to a host phase with application to, among other things, the geological sequestration of carbon dioxide in an aquifer.

Effect of radial advection on autocatalytic reaction-diffusion fronts.

The reaction-diffusion-advection properties of autocatalytic fronts are studied both theoretically and experimentally in the case where the autocatalytic species is injected radially into the reactant at a constant flow rate. The theoretical part analyzes both polar and spherical cases. At long times or equivalently large radius from the injection point, the well-known properties of one-dimensional reaction-diffusion autocatalytic fronts are logically recovered as the influence of the advection field decreases radially. At earlier times however, the radial advection impacts the dynamics of the front. We characterize numerically the influence in this transient regime of the injection flow rate and of the ratio of initial concentration of reactant and autocatalytic product on the position of the front, the reaction rate and the amount of product generated. We confirm experimentally the theoretical predictions in polar geometries using the autocatalytic chlorite-tetrathionate reaction.

Diffusion in liquid mixtures.

The understanding of transport and mixing in fluids in the presence and in the absence of external fields and reactions represents a challenging topic of strategic relevance for space exploration. Indeed, mixing and transport of components in a fluid are especially important during long-term space missions where fuels, food and other materials, needed for the sustainability of long space travels, must be processed under microgravity conditions. So far, the processes of transport and mixing have been investigated mainly at the macroscopic and microscopic scale. Their investigation at the mesoscopic scale is becoming increasingly important for the understanding of mass transfer in confined systems, such as porous media, biological systems and microfluidic systems. Microgravity conditions will provide the opportunity to analyze the effect of external fields and reactions on optimizing mixing and transport in the absence of the convective flows induced by buoyancy on Earth. This would be of great practical applicative relevance to handle complex fluids under microgravity conditions for the processing of materials in space.

Linear stability analysis and nonlinear simulations of convective dissolution in an inclined porous layer between impermeable surfaces.

Convective dissolution can occur in porous media when a given solute dissolves in a host layer from above and increases the density of the host solution. Buoyancy-driven fingering can then develop, which increases the transfer flux of the solute. We investigate here numerically the properties of this convective dissolution when the porous host layer is inclined by an angle θ relative to the horizontal direction. We consider an incompressible flow in porous media governed by Darcy's law, driven by density gradients associated with the concentration of the dissolving solute. The model problem focuses on the case of a very long (infinite) tilted porous layer limited by two parallel impermeable surfaces. A linear stability analysis and nonlinear simulations are performed using the Boussinesq approximation. A vorticity-stream function formulation is adopted to solve the two-dimensional hydrodynamic field through the finite element method. We find that the inclination of the interface decreases the growth rate of the instability and the range of unstable wavenumbers, delaying or even suppressing the onset of the fingering instability. Moreover, it introduces a drift velocity on the perturbations, which is characterized here in both the linear stability analysis and the nonlinear simulations.

Freezing chicken semen: Influence of base medium osmolality, cryoprotectants, cryoprotectant concentration, and cooling rate on post-thaw sperm survival.

A classical chicken semen diluent (Lake's 7.1 diluent) was modified to have lowered osmolalities (ranging from 290 to 410 mOsm/kg). The modified medium with physiological osmolality of 325 mOsm/kg allowed cold storage of fresh semen for several days with very little loss of membrane integrity and motility, while high osmolalities inhibited motility. This modified medium was then used as base for freezing medium to test effects of the type and concentration of cryoprotective agent (CPA), and the cooling rate (CR). A number of CPAs (methylformamide, methylacetamide, dimethylformamide (DMF), dimethylacetamide (DMA), diethylformamide, and propylene glycol) were first compared by freezing semen with 0.6 mol/l of the respective CPA at a cooling rate of 250 °C/min. Post-thaw motility and membrane integrity were highest with DMA and DMF. Finally, in more detailed factorial experiments, semen from individual cocks or pooled semen was frozen using CRs of 4, 50, 250, and 440 °C/min and DMA concentrations ([DMA]) of 0.4, 0.6, 1.0, and 1.5 mol/l. Straws from each semen sample x treatment combination were divided for semen assessment at three different research groups for sperm motility, membrane integrity, kinked tails, and DNA fragmentation, using microscopy, computer assisted motility analysis, and flow cytometry. There were clear effects of both CR and [DMA] and their interaction. CRs 50 and 250 °C/min gave best post-thaw sperm performance. Higher DMA concentrations gave better post-thaw membrane integrity, but concentrations above 1.0 mol/l can decrease sperm velocity or even inhibit sperm motility. Therefore [DMA] may best be 0.6-1.0 mol/l at a CR of 50-250 °C/min.

A sensitive and less cytotoxic assay for identification of proliferating T cells based on bioorthogonally-functionalized uridine analogue.

Quantitative detection of T cell proliferation is an important readout in immunology research, as it is one of the hallmarks of T cell activation. Fluorescence-based methods for T cell proliferation mostly rely on the usage of probes that non-specifically conjugate to free primary amine groups in cells. Each cell division then results in a two-fold dilution of the probes which is detectable with flow cytometry. However, questions have been raised about cytotoxicity of these dilution-based T cell proliferation probes and they potentially affect T cell activation. An alternative assay relies on the incorporation of the uridine analog BrdU in the DNA of dividing T cells that can be detected with an antibody, but this requires harsh fixation and denaturation conditions. Recently, a new assay for detection of cell proliferation has been developed, based on the incorporation of the bioorthogonally-functionalized uridine analog 5-ethynyl-2'-deoxyuridine (EdU). Goal of this study was to compare the sensitivity and cytotoxicity of the EdU assay with a widely-used dilution-based T cell proliferation probe, CellTrace Far Red. We found that, compared to the dilution-based probe, the EdU-based assay better preserves T cell viability, is more sensitive for detecting T cell proliferation, and allows for better discernable interferon gamma responses.

Dynamics of A+B→C reaction fronts under radial advection in a Poiseuille flow.

A+B→C reaction fronts describe a wide variety of natural and engineered dynamics, according to the specific nature of reactants and product. Recent works have shown that the properties of such reaction fronts depend on the system geometry, by focusing on one-dimensional plug flow radial injection. Here, we extend the theoretical formulation to radial deformation in two-dimensional systems. Specifically, we study the effect of a Poiseuille advective velocity profile on A+B→C fronts when A is injected radially into B at a constant flow rate in a confined axisymmetric system consisting of two parallel impermeable plates separated by a thin gap. We analyze the front dynamics by computing the temporal evolution of the average over the gap of the front position, the maximum production rate, and the front width. We further quantify the effects of the nonuniform flow on the total amount of product, as well as on its radial concentration profile. Through analytical and numerical analyses, we identify three distinct temporal regimes, namely (i) the early-time regime where the front dynamics is independent of the reaction, (ii) the transient regime where the front properties result from the interplay of reaction, diffusion that smooths the concentration gradients and advection, which stretches the spatial distribution of the chemicals, and (iii) the long-time regime where Taylor dispersion occurs and the system becomes equivalent to the one-dimensional plug flow case.

Experimental and numerical analysis of Tm2+excited-states dynamics and luminescence in CaX2(X= Cl, Br, I).

The prospect of using Tm2+-doped halides for luminescence solar concentrators (LSCs) requires a thorough understanding of the temperature dependent Tm2+excited states dynamics that determines the internal quantum efficiency (QE) and thereby the efficiency of the LSC. In this study we investigated the dynamics in CaX2:Tm2+(X= Cl, Br, I) by temperature- and time-resolved measurements. At 20 K up to four distinct Tm2+emissions can be observed. Most of these emissions undergo quenching via multi-phonon relaxation below 100 K. At higher temperatures, only the lowest energy 5d-4f emission and the 4f-4f emission remain. Fitting a numerical rate equation model to the data shows that the subsequent quenching of the 5d-4f emission is likely to occur initially via multi-phonon relaxation, whereas at higher temperatures additional quenching via interband crossing becomes thermally activated. At room temperature only the 4f-4f emission remains and the related QE becomes close to 30%. Possible reasons for the quantum efficiency not reaching 100% are provided.

Scalings of Rayleigh-Taylor Instability at Large Viscosity Contrasts in Porous Media.

The scalings of the Rayleigh-Taylor instability are studied numerically for porous media flows when the denser fluid lying on top of the less dense one is also much more viscous. We show that, above a critical value of the viscosity ratio M, a symmetry breaking of the buoyancy-driven fingers is observed as they extend much further downward than upward. The asymmetry ratio scales as M^{1/2} while the asymptotic flux across the initial contact line, quantifying the mixing between the two fluids, scales as M^{-1/2}. A new fingering mechanism induced by large viscosity contrasts is identified and shows good agreement with experimentally observed dynamics.

Oscillatory budding dynamics of a chemical garden within a co-flow of reactants.

The oscillatory growth of chemical gardens is studied experimentally in the budding regime using a co-flow of two reactant solutions within a microfluidic reactor. The confined environment of the reactor tames the erratic budding growth and the oscillations leave their imprint with the formation of orderly spaced membranes on the precipitate surface. The average wavelength of the spacing between membranes, the growth velocity of the chemical garden and the oscillations period are measured as a function of the velocity of each reactant. By means of materials characterization techniques, the micro-morphology and the chemical composition of the precipitate are explored. A mathematical model is developed to explain the periodic rupture of droplets delimitated by a shell of precipitate and growing when one reactant is injected into the other. The predictions of this model are in good agreement with the experimental data.

Role of surgery in patients with synchronous metastatic breast cancer: Is there a need for axillary lymph node removal?

INTRODUCTION: About 6% of women with breast cancer present with synchronous metastases. Treatment remains palliative in international recommendations but the impact of loco-regional surgery remains controversial. OBJECTIVE: We conducted a multicentre, cohort study to evaluate the impact of axillary lymph node (ALN) surgery on overall survival in stage IV breast cancer at diagnosis. METHODS: Patients presenting with breast cancer and synchronous metastases between 2005 and 2014 were included. Follow up was conducted up to 1st June 2018. The only exclusion criterion was a history of previous malignancies. Breast surgery was defined as lumpectomy or mastectomy. Axillary surgery included full ALN dissection, and sentinel lymph node biopsy (SLNB). If the SLN was invaded on the frozen section, full axillary dissection was performed. RESULTS: 152 patients were included. 71 women had no surgery, 81 had primary site surgery of which 64 (79%) had breast and axillary surgery and 17 (21%) breast surgery only. 5-year overall survival was 59.8% (95% CI=[49.5; 69.5]) for women with breast and axillary surgery, 23.5% (95% CI=[15.6; 33]) for women with breast surgery only and 9.8% (95% CI=[4.7; 17.5]) for women without any surgery, p < 0.001. Combined with breast surgery, axillary surgery significantly added a mean of 33 months to patient overall survival. CONCLUSION: ALN surgery combined with breast surgery in metastatic breast cancer significantly increased overall survival. Thus surgical indications should not differ from those in women with breast cancer without metastases.

Effects of radial injection and solution thickness on the dynamics of confined A + B → C chemical fronts.

The spatio-temporal dynamics of an A + B → C front subjected to radial advection is investigated experimentally in a thin solution layer confined between two horizontal plates by radially injecting a solution of potassium thiocyanate (A) into a solution of iron(iii) nitrate (B). The total amount and spatial distribution of the product FeSCN2+ (C) are measured for various flow rates Q and solution thicknesses h. The long-time evolution of the total amount of product, nC, is compared to a scaling obtained theoretically from a one-dimensional reaction-diffusion-advection model with passive advection along the radial coordinate r. We show that, in the experiments, nC is significantly affected when varying either Q or h but scales as nC∼Q-1/2V where V is the volume of injected reactant A provided the solution thickness h between the two confining plates is sufficiently small, in agreement with the theoretical prediction. Our experimental results also evidence that the temporal evolution of the width of the product zone, WC, follows a power law, the exponent of which varies with both Q and h, in disagreement with the one-dimensional model that predicts WC∼t1/2. We show that this experimental observation can be rationalized by taking into account the non-uniform profile of the velocity field of the injected reactant within the cell gap.

Associations of plasma androgens with suicidality among men and women: A 9-year longitudinal cohort study.

BACKGROUND: Testosterone has been implicated in suicidality in cross-sectional studies. Stress that coincides with a suicide attempt may alter androgen levels, so prospective studies are needed to exclude reverse causation. We aimed to examine the associations of plasma androgens with concurrent and future suicidality, and if present, whether these associations were mediated by a behavioral trait like reactive aggression. METHODS: Baseline plasma levels of total testosterone, 5α-dihydrotestosterone, and androstenedione were determined with liquid chromatography-tandem mass spectrometry, and dehydroepiandrosterone-sulphate with a radioimmunoassay. Suicidality was assessed using the Suicidal Ideation Scale at baseline and after 2-, 4-, 6-, and 9-year follow-up. Men and women were analyzed separately, and potential confounders were considered. RESULTS: Participants (N = 2861; 66.3% women) had a mean age of 42.0 years (range 18-65) and almost half (46.9%) fulfilled criteria for a major depressive or anxiety disorder. At baseline 13.2% of men and 11.2% of women reported current suicidal ideation. In participants who were non-suicidal at baseline, slightly more men than women reported suicidal ideation during follow-up (14.7% vs. 12.5%), whereas the reverse pattern was observed for suicide attempts (3.6% vs. 4.2%). None of the associations between androgens and current and future suicidality were significant. LIMITATIONS: Androgens were determined once, which may have been insufficient to predict suicidality over longer periods. DISCUSSION: The lack of associations between plasma levels of androgens determined by 'gold-standard' laboratory methods with suicidality do not support previous cross-sectional and smaller studies in adult men and women with values within the physiological range.

Confined direct and reverse chemical gardens: Influence of local flow velocity on precipitation patterns.

Various cobalt silicate precipitation patterns can be observed when an aqueous solution of cobalt ions gets into contact with a solution of silicate ions upon injection of one solution into the other in the confined geometry of a Hele-Shaw cell. The properties of these precipitation patterns are studied here as a function of the injection flow rate, densities and viscosities of the solutions, and the choice of which solution is injected into the other one. Our results show that the structure of the precipitation pattern depends on the local velocity as well as on the difference in viscosities between the injected and the displaced solutions. Specifically, decreasing the injection flow rate and/or decreasing the density jump while increasing the difference in viscosities between the reactant solutions results in more circular patterns. Moreover, we show that some structures are robustly observed in given ranges of the local flow velocity in the cell. Locally, precipitation can then transition from one type of pattern to another during injection, according to that preferred structure at the given local velocity. We also show that injection of the cobalt solution into the silicate solution results in the so-called direct patterns that are different from the reverse patterns obtained when the silicate solution is injected in the solution of cobalt ions. Our results help in understanding the production of precipitate structures under nonequilibrium flow conditions.

Influence of rectilinear vs radial advection on the yield of A + B → C reaction fronts: A comparison.

In the presence of advection at a constant flow rate in a rectilinear geometry, the properties of planar A + B → C reaction fronts feature the same temporal scalings as in the pure reaction-diffusion case. In a radial injection geometry where A is injected into B radially at a constant flow rate Q, temporal scalings are conserved, but the related coefficients depend on the injection flow rate Q and on the ratio γ of initial concentrations of the reactants. We show here that this dependence of the front properties on the radial velocity allows us to tune the amount of product obtained in the course of time by varying the flow rate. We compare theoretically the efficiency of the rectilinear and radial geometries by computing the amount of product C generated in the course of time or per volume of reactant injected. We show that a curve γc(Q) can be defined in the parameter space (γ, Q) below which, for similar experimental conditions, the total amount of C is larger in the radial case. In addition, another curve γ*(Q) < γc(Q) can be defined such that for γ < γ*, the total amount of C produced is larger in the radial geometry, even if the production of C per unit area of the contact interface between the two reactants is larger in the rectilinear case. This comes from the fact that the length of the contact zone increases with the radius in the radial case, which allows us to produce in fine more product C for a same injected volume of reactant or in reactors of a same volume than in the rectilinear case. These results pave the way to the geometrical optimization of the properties of chemical fronts.

Dynamics of A+B → C reaction fronts under radial advection in three dimensions.

The dynamics of A+B→C reaction fronts is studied both analytically and numerically in three-dimensional systems when A is injected radially into B at a constant flow rate. The front dynamics is characterized in terms of the temporal evolution of the reaction front position, r_{f}, of its width, w, of the maximum local production rate, R^{max}, and of the total amount of product generated by the reaction, n_{C}. We show that r_{f}, w, and R^{max} exhibit the same temporal scalings as observed in rectilinear and two-dimensional radial geometries both in the early-time limit controlled by diffusion, and in the longer time reaction-diffusion-advection regime. However, unlike the two-dimensional cases, the three-dimensional problem admits an asymptotic stationary solution for the reactant concentration profiles where n_{C} grows linearly in time. The timescales at which the transition between the regimes arise, as well as the properties of each regime, are determined in terms of the injection flow rate and reactant initial concentration ratio.

Correction: Influence of mineralization and injection flow rate on flow patterns in three-dimensional porous media.

Correction for 'Influence of mineralization and injection flow rate on flow patterns in three-dimensional porous media' by R. Moosavi et al., Phys. Chem. Chem. Phys., 2019, 21, 14605-14611.

Chemically-driven convective dissolution.

When a solute A dissolves in a host phase with a given solubility, the resulting density stratification is stable towards convection if the density profile increases monotonically along the gravity field. We theoretically and numerically study the convective destabilization by reaction of this dissolution when A reacts with a solute B present in the host phase to produce C via an A + B→C type of reaction. In this reactive case, composition changes can give rise to non-monotonic density profiles with a local maximum. A convective instability can then be triggered locally in the zone where the denser product overlies the less dense bulk solution. First, we perform a linear stability analysis to identify the critical conditions for this reaction-driven convective instability. Second, we perform nonlinear simulations and compare the critical values of the control parameters for the onset of convection in these simulations with those predicted by linear stability analysis. We further show that the asymptotic dissolution flux of A can be increased in the convective regime by increasing the difference ΔRCB = RC-RB between the Rayleigh numbers of the product C and reactant B above a critical value and by increasing the ratio ß = B0/A0 between the initial concentration B0 of reactant B and the solubility A0 of A. Our results indicate that chemical reactions can not only initiate convective mixing but can also give rise to large dissolution fluxes, which is advantageous for various geological applications.

Influence of mineralization and injection flow rate on flow patterns in three-dimensional porous media.

Reactive flows inside porous media play an important role in a number of geophysical and industrial processes. Here, we present three-dimensional experimental measurements on how precipitation and flow patterns change with the flow rate inside a model porous medium consisting of monodisperse glass beads. The sample is initially filled with an aqueous solution of sodium carbonate into which a solution of barium chloride is injected at a constant flow rate. Upon contact and reaction, the two reactants produce water-insoluble barium carbonate which precipitates onto the glass beads. This precipitate then modifies the flow morphology which in turn changes the spatial distribution of the precipitate. We discuss the influence of the flow rate on the morphology of the flow pattern and demonstrate that neither viscous fingering nor the Rayleigh-Taylor instability have any significant influence in our model system.

Reaction-driven oscillating viscous fingering.

Localized oscillations can develop thanks to the interplay of reaction and diffusion processes when two reactants A and B of an oscillating reaction are placed in contact, meet by diffusion, and react. We study numerically the properties of such an A+B→ oscillator configuration using the Brusselator model. The influence of a hydrodynamic viscous fingering instability on localized concentration oscillations is next analyzed when the oscillating chemical reaction changes the viscosity of the solutions involved. Nonlinear simulations of the related reaction-diffusion-convection equations with the fluid viscosity varying with the concentration of an intermediate oscillatory species show an active coupling between the oscillatory kinetics and the viscously driven instability. The periodic oscillations in the concentration of the intermediate species induce localized changes in the viscosity, which in turn can affect the fingering instability. We show that the oscillating kinetics can also trigger viscous fingering in an initially viscously stable displacement, while localized changes in the viscosity profile can induce oscillations in an initially nonoscillating reactive system.