Ab initio study of the influence of aggregation on the infrared spectrum of acetonitrile

With the aim of investigating the influence of direct intermolecular interactions between nitrile groups on the infrared features of nitrile polymers, vibrational frequencies and infrared intensities of acetonitrile and of its antiparallel dimer are compared. It is found that whereas frequencies are unchanged upon association infrared intensities are dramatically affected. In particular, the striking difference between the intensities of the CN stretching band measured in gas phase, on the one hand, and in the liquid, on the other, is already accounted for at the dimer level. Despite the poor reliability of absolute values of calculated intensities, it is interesting to note that consistent trends are obtained at various levels of theory. These results suggest that ab initio calculations of infrared intensities can be useful to interpret infrared measurements, thus contributing to the elucidation of molecular structure of materials. © 1993 John Wiley & Sons, Inc.     

New enumerative results on two-dimensional directed animals

We list several open problems concerning the enumeration of directed animals on two-dimensional lattices. We show that most of these problems are special cases of two central problems: calculating the position generating function and the perimeter and area generating function for square lattice animals.

We propose a possible direction for solving these two problems: we extend Dhar's correspondence between hard particle gas models and enumeration of animals according to the area, and show that each of the main two generating functions is, essentially, the density of a one-dimensional gas model given by the stationary distribution of a probabilistic transition.

We are able to compute the density of certain stationary distributions. We thus obtain new bivariate generating functions for directed animals on the square and triangular lattices. We derive from these results the generating functions for animals on the decorated square and triangular lattices, as well as the average number of loops in directed animals.     

Investigation of ion-selective electrodes with neutral ionophores and ionic sites by EIS. II. Application to K detection

The impedance of an ion-selective electrode (ISE) to potassium with valinomycin as the ionophore and KBΦ₄ as the ionic sites was measured. The membrane was made of PVC with DNP as a plasticizer. The influence of the content of the plasticizer and the membrane thickness was investigated. The concentrations of the ionophore and the ionic sites were changed to modify the response on the ISE. Finally, the selectivity was tested in terms of impedance. All impedance experiments were correlated to the potentiometric curves plotted under the same experimental conditions. The measured impedances were compared to the model proposed in the previous paper (paper I). A good agreement was found.     

Photothermal deflection microscopy for imaging sub-micronic defects in optical materials

Photothermal deflection is widely used to study defects in optical coatings and role of these defects in laser damage. Because defects responsible for laser damage are assumed to be nanometer-sized and lowly absorbing, both high spatial resolution and high sensitivity are required to detect them. In this work we theoretically and experimentally explore the capability of collinear photothermal deflection to give micronic resolution by reduction of the pump beam diameter. Thanks to a model describing temperature distribution and photothermal deflection, we have studied the effects of pump beam focusing on photothermal deflection. Then, we have developed a high resolution, high sensitivity microscope based on the photothermal deflection of a transmitted probe beam. The setup is characterized and the theoretical predictions are checked. We present a test of lateral spatial resolution obtained on specially prepared absorbing resolution targets and show that a lateral spatial resolution of 1 μm is reached on non-isolated defects. In case of single defects, we expect that 10 nm sized defects could be detected.     

Cameroonian medicinal plants belonging to Annonaceae family: radical scavenging and antifungal activities

The free-radical scavenging activity of ethanolic and methanolic extracts of leaves, stems and roots of Annona muricata, Monodora tenuifolia, Uvaria comperei, Uvaria muricata and Xylopia africana was evaluated using DPPH and ORAC assays. Further, phytochemical analysis, total phenolic and total flavonoid contents were also determined. Moreover, the antifungal activity of extracts was studied. The findings indicated that A. muricata and U. comperei extracts own antiradical activities and moderate antifungal properties.     

Outlier Eigenvalues for Deformed I.I.D. Random Matrices

We consider a square random matrix of size N of the form A + Y where A is deterministic and Y has i.i.d. entries with variance 1/N. Under mild assumptions, as N grows the empirical distribution of the eigenvalues of A + Y converges weakly to a limit probability measure β on the complex plane. This work is devoted to the study of the outlier eigenvalues, i.e., eigenvalues in the complement of the support of β. Even in the simplest cases, a variety of interesting phenomena can occur. As in earlier works, we give a sufficient condition to guarantee that outliers are stable and provide examples where their fluctuations vary with the particular distribution of the entries of Y or the Jordan decomposition of A. We also exhibit concrete examples where the outlier eigenvalues converge in distribution to the zeros of a Gaussian analytic function. © 2016 Wiley Periodicals, Inc.     

Novel π2s+π2a Electrocyclization of Triethylenic‐Malonic Acids Exemplified for a One‐Pot Synthesis of New γ‐Dilactones cis‐Fused with a Cyclopentene

A new, easy and rapid synthesis of γ‐dilactones is cis‐fused with a cyclopentenic ring via cyclization of 7‐chlorotriethylenic‐malonic acids. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π_2s + π_2a conrotatory process. This cyclopentenyl cation led to unstable γ‐lactones intermediates that are rearrange to more stable isomers. δ‐lactones (6Z and 6E‐(3‐chlorobut‐2‐en‐2‐yl)‐5‐methyl‐3,6‐dihydro‐2H‐pyran‐2‐one) were obtained as secondary products. Mechanistic pathways were considered. The structures of the newly synthesized compounds were established by elemental and spectral data.     

Monomial summability and doubly singular differential equations

In this work, we consider systems of differential equations that are doubly singular, i.e. that are both singularly perturbed and exhibit an irregular singular point. If the irregular singular point is at the origin, they have the form

     

Micellar aggregation for ionic surfactant in pure solvent and electrolyte solution: nonextensive thermodynamics approach

We show in this study that the concepts of nonextensive thermodynamics introduced and applied in a series of previous studies can be used to describe the behaviour of ionic surfactant solutions at concentrations higher than the critical micelle concentration (cmc) in pure solvents and in the presence of electrolytes. We supposed that the aggregated amphiphiles and their counter ions form two interpenetrated nonextensive phases of the same thermodynamic dimension, m, characterised by two parameters A(am) and A(CI) related to the aggregated amphiphile and the counter ion, respectively. Our experimental results and those published in the literature indicate that logarithms of the activities of the amphiphile and of its counterion vary with the quantity of aggregated monomer according to a power law. Thus, we demonstrate a linear relation between the logarithms of the activities of the two ions beyond the cmc in pure solvents ("micellization product"). An original relation, different from the Corrin-Harkins relation, can thus be established to describe the effects of salt on the cmc of ionic surfactants. According to this relation the cmc of charged surfactant in some systems can increase in the presence of an electrolyte with a common ion.