POLYPROTIC ACIDS IN SOLUTION: IS THE INVERSION OF THE CONSTANTS OF STEPWISE DISSOCIATION POSSIBLE?

The paper is devoted to the problem of the ratio of the constants of stepwise dissociation of polyprotic acids in solution. Special attention is paid to the problem of close dissociation constants and in particular to the possibility of the inversion of constants, for example, Ka1 < Ka2 (or pKa1 > pKa2) for equilibria H2A ⇄ HA– ⇄ A2–, H2A+ ⇄ HA ⇄ A– or H2A2+ ⇄ HA+ ⇄A. Equilibria of inorganic and organic acids are successively considered. Some cases of inversion are considered. In particular, such relations are sometimes observed for fluorescein and phthalein compounds, and for porphyrins. In the last case, as well as in some other systems the acid-base reactions proceed relatively slow. An overview of approaches to estimation of the Ka1/ Ka2 ratio is presented. Namely, these approaches use the concepts of the detailed equilibrium scheme, dissociation microconstants, statistical and electrostatic factors, and the influence of intra-molecular hydrogen bonds. The variety of reasons for additional stabilization of the forms H2A (or H2A+, or H2A2+) and A2– (or A–, or A) and destabilization of the form HA– (or HA, or HA+) is regarded, including salt effects and ionic association. Peculiarities of stepwise protolytic equilibria of macrocyclic compounds, such as calixarenes, porphyrins, and cryptands, are considered. Dispersed systems such as polyelectrolytes, micelles of functionalized surfactants, monolayers, silica and modified silica, other oxides, nanodiamonds decorated by carboxylic groups, represent a peculiar type of polyprotic acids. In this case, a “spectrum” of pKa values appears because of influence of ionized functional groups on the properties of un-dissociated ones. It was demonstrated that such unusual ratio of constants, Ka1 < Ka2, may be caused by a set of factors, among which most important are (i) the tautomerism in true solutions and (ii) selective binding of different equilibrium forms in organized solutions, i.e., in micellar solutions of surfactants, suspensions of phospholipid liposomes, and related systems.

EM-Based Nonideal Iris Boundary Localization

Nonideal iris segmentation is a great challenge in iris recognition, and many researchers have stressed this problem. Since critical step of segmentation is localizing iris center and detecting interior/outer boundaries, we presents a novel method based on EM algorithm to deal with it. EM algorithm is capable of automatic threshold, therefore candidate pupil can be obtained and followed by an innovated fast iris center searching by using strings equilibrium scheme. We also give the region-based outer boundary localization with implementation of order statistical filters (OSF). Experiments demonstrate a high correct segmentation ratio (CSR) of more than 98% has been achieved when using CASIA-IrisV3 Interval and CASIA-IrisV3 Lamp databases.

Research of Interpolation Algorithm for Improving the Movement Stability of X-Y Worktable of NC Machine

Nonideal iris segmentation is a great challenge in iris recognition, and many researchers have stressed this problem. Since critical step of segmentation is localizing iris center and detecting interior/outer boundaries, we presents a novel method based on EM algorithm to deal with it. EM algorithm is capable of automatic threshold, therefore candidate pupil can be obtained and followed by an innovated fast iris center searching by using strings equilibrium scheme. We also give the region-based outer boundary localization with implementation of order statistical filters (OSF). Experiments demonstrate a high correct segmentation ratio (CSR) of more than 98% has been achieved when using CASIA-IrisV3 Interval and CASIA-IrisV3 Lamp databases.

THE ORGANIZATIONAL PROPERTIES OF MONEY: GUSTAVO DEL VECCHIO’S THEORY

The integration of money into the Walrasian general equilibrium scheme is an age-old and intricate issue. One of the first attempts was made by Gustavo Del Vecchio, who, in the early twentieth century, built a theory of circulation that considered money as a medium of exchange, and investigated its organizational and social aspects in depth. Del Vecchio developed a theory of monetary service grounded on the distinction between individual and social utility of money. Moreover, he stated that money, credit, accumulation, and crisis could no longer be theorized with time omitted, and this induced him to formulate dynamic statements that put forward claims about money as a store of value. The organizational and social dimensions of money, time, and uncertainty were all important and interconnected aspects in Del Vecchio’s scientific inquiry, for they all sprang from his conceptualization of money as a medium of exchange.

Equilibrium theory of the symmetry energy of finite nuclei

The nuclear symmetry energy of finite nuclei is calculated first in a nonequilibrium scheme in which the binding energy is a function of the central density parameter as well as the mass number and neutron excess parameter, i.e. E(kc, A, ξ), and then in an equilibrium scheme with the central density parameter given as a function of A and ξ in the form kcE(A, ξ) = kc0(1 + q1ξ−q2ξ2 + q3ξ3−q4ξ4 + … ), where kc0 = k∞(1 + ρ0) f−1 and the qj(A) and ρ0(A) depend on Coulomb and surface effects. In the equilibrium scheme, the symmetry energy coefficients are functions of mass number. A connection is made between the symmetry energy coefficients as calculated in the nonequilibrium (NE) and equilibrium schemes, and we find these coefficients to be, β0(A) = β0NE(kc0), β2(A) = β2NE(kc0)−[Formula: see text], etc. We find that the fourth order coefficient β4(A) is large and negative for all A, and is about −47 MeV in the region A ≈ 125 which agrees reasonably well with the −37 MeV value predicted by the Cameron–Elkin exponential mass formula. No linear term is found in the symmetry energy, but third, fifth, and higher order odd symmetry energy coefficients are found to be present. The alternation of the signs of the symmetry energy coefficients as well as the density expansion coefficients are in accordance with Le Chatelier's principle. As in the case of infinite nuclear matter, we find that the binding energy of nuclei with neutron excess is larger than that calculated assuming constant density, and that a negative isospin compression energy must be added to the constant density calculation of the energy if the correct binding is to be predicted. Finally, the general expression for the symmetry energy coefficients of order j is[Formula: see text]

Photometric analysis of trace amounts of hydrazine with p-dimethylaminobenzaldehyde. Chemical equilibria

An equilibrium scheme is proposed for aqueous acid solutions containing hydrazine, p-di-methylaminobenzaldehyde and p-dimethylaminobenzaldazine. The quinoidal cation form of the latter has an absorbance peak at 455 mμ, for which [Formula: see text] (±2.1%). In 0.4 m to 1 m H+, 10−5 m benzaldazine is practically all in the quinoidal cation form. The acid attenuation of absorbance at 455 mμ is caused by protonation of the dimethylamino group of unreacted aldehyde. Semiquantitative equilibrium data are presented for the reaction between hydrazine and p-dimethylaminobenzaldehyde.

SPECTROSCOPIC STUDIES OF ALCOHOLS: IV. CONFORMATIONAL HETEROGENEITY OF 1-PROPANOL IN DILUTE CCl4 SOLUTION

High-resolution infrared spectroscopy indicates that the fundamental OH stretching band of 1-propanol in dilute CCl4 solution is composed of three components caused by rotational isomerism about the C—C and C—O bonds. Although the conformer with the CH3 and OH groups trans to each other is most heavily populated at room temperature, one of the two conformers having gauche CH3 and OH groups is thermodynamically most stable. A conformational equilibrium scheme is postulated in which the most stable conformer has a methyl C—H interacting with one of the lone pairs of electrons on the oxygen atom.