Air invasion in a granular layer immersed in a fluid: morphology and dynamics

We investigate the morphology and dynamics of the region invaded by air injected at the bottom of an immersed granular bed. Previous experimental results point out the formation of a fluidized zone with a parabolic shape which does not depend, in the stationary regime, on the injection flow-rate. By tilting the experiment, we can tune the effective gravity in the system. We show that it does not affect significantly the morphology either. A numerical study made it possible to access the typical height and width of the structure, which are governed by the relative effects of gravity and capillarity. After a brief review on this subject, we propose first, new experimental observations on the air invasion regimes and on the morphology of the fluidized zone, in particular its growth dynamics; then, we complement the previous numerical study by considering the influence of the bottom boundary condition. In particular, we quantify the morphology of the invaded region when the gas is injected in the bulk, thus when air is likely to propagate downwards. These results are of practical importance in the prediction of the morphology of gas invasion in soils, from $\hbox {CO}_2$ sequestration to pollutant propagation.     

Flavonoid,tannin and hypericin concentrations in the leaves of St. John’s wort (Hypericum perforatum L.) are affected by UV-B radiation levels

St. John’s wort (Hypericum perforatum L.) herb is used as a herb-tea or as a food supplement because of its antidepressive properties. St. John’s wort, grown under different levels of UV-B radiation, was analysed for its concentrations of flavonoids, tannins and hypericin. A high level of UV-B radiation increased leaf concentrations of flavonoids from 6.31 to 9.00/100 g in dry matter (DM) and of tannins from 26.6 to 31.4/100 g in DM. The concentration of hypericin in leaves exposed to enhanced UV-B radiation (0.08/100 g in DM) was lower than that of leaves exposed to reduced UV-B radiation (0.09/100 g in DM). We conclude that the concentrations of bioactive substances in St. John’s wort herb can be altered by regulating the environment during plant growth.     

Diffusional surface voltammetry as a probe of adsorption energetics

Direct determination of the adsorption free energy for extremely low surface coverages (Henry limit) requires the use of a technique that must be highly sensitive to both the amount and the energetics of adsorbed molecules. Herein, we demonstrate that diffusional surface voltammetry (DSV), which embodies film and stripping voltammetries as two limiting cases, can be used to achieve this goal for electroactive adsorbates. To this end, a general analytical expression for the surface voltammetric peak potential of DSV is derived, which covers the full range of scan rates, bulk concentrations, and adsorptivity of the freely diffusing form of the redox couple, so that the surface redox conversion can be either equilibrated with or transport-isolated from the solution bulk. Strategies to get a quantitative insight into the energetics of electrosorption are outlined, and diagnostic criteria for their application are developed. In particular, it is demonstrated that DSV can be used in its stripping mode to determine group contributions to the adsorption free energy, avoiding possible interferences from intermolecular interactions or formation of oligomeric species. Application of this protocol to the reductive desorption of distinct homologous series of alkylthiolates adsorbed at mercury electrodes has allowed us to determine the contributions of the CH(n) groups (n = 0-3) to the free energy of adsorption of these molecules. These estimates are shown to correlate linearly with the corresponding group contributions to the octanol-water partition coefficient, revealing that adsorption of individual hydrocarbon groups at the mercury/solution interface scales with their hydrophobicity. Overall, the present work enlarges the capability of surface voltammetry to probe adsorption energetics down to the micromolar level, and it represents a first step toward the development of a unified treatment of stripping and film voltammetries.     

Magnetism in Granular Systems

Previous experimental studies have shown that the magnetic dipolar interaction plays an important role in several magnetic properties of nanoparticulated systems. More recently, this type of interaction was detected in microparticles of Fe?CMn?CAl, Fe?CSi and Fe?CAl systems. In this work, we apply the M?rup?CTronc (Phys. Rev. Lett. 72:3278, 1994) model for nanoparticulated systems in order to calculate some thermodynamic properties of these systems. We first calculated the total energy of a magnetic particle as the sum of its anisotropy energy and its total dipolar magnetic interaction with the other particles. The calculation is performed in such a way that the interaction energy has the same form as the anisotropy energy. We use the total energy to calculate the magnetization, heat capacity, magnetic susceptibility, and blocking temperature in nanoparticulated systems. The application of our theory to experimental data on nanoparticulated systems and for the Fe?CAl, Fe?CSi and Fe?CMn?CAl microparticulated granular systems will be presented elsewhere.     

Exploring programmable self-assembly in non-DNA based molecular computing

Self-assembly is a phenomenon observed in nature at all scales where autonomous entities build complex structures, without external influences nor centralised master plan. Modelling such entities and programming correct interactions among them is crucial for controlling the manufacture of desired complex structures at the molecular and supramolecular scale. This work focuses on a programmability model for non DNA-based molecules and complex behaviour analysis of their self-assembled conformations. In particular, we look into modelling, programming and simulation of porphyrin molecules self-assembly and apply Kolgomorov complexity-based techniques to classify and assess simulation results in terms of information content. The analysis focuses on phase transition, clustering, variability and parameter discovery which as a whole pave the way to the notion of complex systems programmability.     

Carbon nanotubes/chitin nanowhiskers aerogel achieved by quaternization‐induced gelation

Organic aerogels from polysaccharides such as cellulose and chitin are of particular importance because they utilize renewable feedstocks. In this article, the aerogels were prepared through the self‐assembly of chitin nanowhiskers previously modified. The surface of chitin nanowhiskers was rendered cationic through two reactions. A first reaction between hydroxyl groups of chitin and 2‐chloroethyl isocyanate and a second reaction between the chloride groups of isocyanate anchored to the surface and 1‐methylimidazole. This modification led to stable aqueous suspensions of the chitin nanowhiskers with gelation and rheological properties. Additionally, chitin nanowhiskers aerogels containing modified carbon nanotubes were obtained. The addition of modified carbon nanotubes provoked a change in the morphology of the hydrogels and as a consequence, the rheological properties of the hydrogel are modified as well. In contrast from previous procedures, this method has not required any kind of solvent exchange or high pressure in order to obtain the final materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42547.     

Stochastic analysis of biochemical reaction networks with absolute concentration robustness

It has recently been shown that structural conditions on the reaction network, rather than a ‘fine-tuning’ of system parameters, often suffice to impart ‘absolute concentration robustness’ (ACR) on a wide class of biologically relevant, deterministically modelled mass-action systems. We show here that fundamentally different conclusions about the long-term behaviour of such systems are reached if the systems are instead modelled with stochastic dynamics and a discrete state space. Specifically, we characterize a large class of models that exhibit convergence to a positive robust equilibrium in the deterministic setting, whereas trajectories of the corresponding stochastic models are necessarily absorbed by a set of states that reside on the boundary of the state space, i.e. the system undergoes an extinction event. If the time to extinction is large relative to the relevant timescales of the system, the process will appear to settle down to a stationary distribution long before the inevitable extinction will occur. This quasi-stationary distribution is considered for two systems taken from the literature, and results consistent with ACR are recovered by showing that the quasi-stationary distribution of the robust species approaches a Poisson distribution.     

Comparison of the nearest feature classifiers for face recognition

This paper presents an experimental comparison of the nearest feature classifiers, using an approach based on binomial tests in order to evaluate their strengths and weaknesses. In addition, classification accuracies and the accuracy-dimensionality tradeoff have been considered as comparison criteria. We extend two of the nearest feature classifiers to label the query point by a majority vote of the samples. Comparisons were carried out for face recognition using ORL database. We apply the eigenface representation for feature extraction. Experimental results showed that even though the classification accuracy of k-NFP outperforms k-NFL in some dimensions, these rate differences do not have statistical significance.     

Differential hormonal regulation of estrogen receptors ERalpha and ERbeta and androgen receptor expression in rat efferent ductules

Estrogen receptors, in addition to the androgen receptor (AR), are expressed at high levels in efferent ductules of the male reproductive tract and it is now well recognized that estrogen receptor (ER) alpha is required for the maintenance of normal structure and function of the ductules. However, little is known regarding the hormonal regulation of the receptors themselves in the male. In the present study, efferent ductule ligation and castration, followed by replacement with testosterone, dihydro-testosterone (DHT) or estradiol was used to investigate the relative importance of circulating and luminal sources of steroid for the modulation of ERalpha, ERbeta and AR in rat efferent ductules. Uni- or bilateral castration and ligation did not affect the expression of ERalpha and ERbeta, but bilateral castration caused down-regulation of AR. Replacement with DHT and testosterone alone or in combination with estradiol caused the recovery of AR expression to control levels. A slight recovery of AR was also observed after estrogen replacement. ERalpha expression was decreased to nearly undetectable levels after estrogen replacement. On the other hand, ERbeta did not show evident effects following any of the treatments, suggesting a constitutive expression of this receptor. This differential modulation of the steroid hormone receptors highlights the importance of maintaining a physiological androgen-estrogen balance to regulate the structure and function of efferent ductules in the male.     

C60Con complexes as hydrogen adsorbing materials

An active line of contemporary research is dedicated to the adsorption and storage of hydrogen on metal-doped carbon materials. Using density functional theory and van der Waals corrections we have studied molecular and dissociative adsorption of H₂ on neutral and cationic C₆₀Co_n complexes with n = 1–8. The Co atoms form compact clusters on the surface of the fullerene. Dissociative chemisorption of one H₂ molecule is more stable than molecular adsorption on neutral C₆₀Co_n, with the only exception of C₆₀Co. When C₆₀Co_n is ionized, the electronic charge deficit remains localized in the cobalt cluster. The molecular and dissociative adsorption features on cationic C₆₀Co_n⁺ and neutral C₆₀Co_n complexes are in general similar, but some differences can be highlighted. Molecular and dissociative H₂ adsorption on C₆₀Co₂⁺ are competitive; in fact, molecular adsorption is slightly more stable as a result of the localized electronic charge deficit on the Co dimer. Another difference is that the dissociative adsorption energies on some of the neutral C₆₀Co_n complexes are substantially larger than the dissociative adsorption energies on the corresponding C₆₀Co_n⁺ cationic complexes by amounts between 0.2 and 0.5 eV. Activation barriers for dissociation of the adsorbed H₂ molecule strongly depend on the charge state and cluster size. These barriers help to interpret the adsorption state (molecular or dissociated) of experimentally produced hydrogenated C₆₀Co_n⁺ complexes. Hydrogen saturation has been studied in two cases. C₆₀Co adsorbs three H₂ units in molecular form, and C₆₀Co_n adsorbs up to thirteen H₂ units, four dissociated and nine in molecular form.