X-ray fluorescence analysis from the information theory point of view

Information theory is a fundamental concept for a general comparison of different methods of chemical analysis. It delivers the information content of an analysis in binary digits (bits). In contrast to the normal interpretation of the result of an analysis, information theory demonstrates the gain of information about the composition of a sample before and after the analysis has been made. In the first section of this paper, the useful information content of a quantitative analysis of a completely unknown sample with an X-ray spectrometer is derived. It is shown that the decision for the discrimination steps has to be made on the basis of a geometrical rather than an arithmetical series, as is recommended in the present literature. According to this thesis, an XRF-equipment can deliver an information quantity of about 940 bits.In the second section, examples are given of the information content obtained in the field of process control. Here the analyst has a lot of information on the composition of the sample in advance and the analysis provides much less information content than in case of an unknown sample. In three examples, concerning the manufacturing of stainless steel brass, and cement, it is shown, that the gain in information by the XRF-equipment lies between 3 and 10 bits.     

Quantitative densitometry from the point of view of information theory.

The process of quantitative densitometry is analyzed with methods developed in information theory. It is shown that the steps involved in densitometry, e.g. gel staining, mechanical, optical and electronic processing, as well as all the steps of data processing, can be viewed as communication channels. The factors affecting both the relevant and irrelevant part of the total information passed through these channels are discussed in the consistent frame provided by information theory. This view leads to a unifying context for analyzing the performance of quantitative densitometers.     

A theory of polymer solutions without the mean-field approximation in Flory-Huggins theory

The concept of the volume fraction at chain end is proposed, which is the conditional probability for a site having been occupied, knowing that an adjacent site is occupied by polymer end. The overall entropy of polymer/solvent system is separated into two fundamentally different parts, i.e., the translational entropy and the conformational entropy. Based on these a theory of polymer solutions is established. When a mean-field approximation is introduced, Flory-Huggins (FH) theory is recovered. The FH interaction parameters and spinodal curves of the polystyrene/cyclohexane system are calculated and compared with the experimental data. The good prediction of them two is achieved.     

Thermodynamics of adsorption equilibrium

Russian Chemical Bulletin -     

The mechanisms of substitution reactions in octahedral complexes from the point of view of ligand field theory

Two possible mechanisms for substitution reactions in octahedral complexes, ML₆, are discussed in terms of molecular orbital theory. Jorgensen's model with angular parameters is used to calculate the change in activation energy on forming complexes of the type ML₅ (D₃h symmetry), ML₅ (C_4v symmetry), and ML₇ D_5h symmetry). Analysis of the quantities obtained (Table 4) shows that high spin ML₆ octahedral complexes of metals with d³ or d⁸ electronic configurations, and low spin complexes with d⁶ electronic configurations are particularly stable. An S_N1 mechanism is, apparently, characteristic for complexes of metals with d¹ or d² electronic configurations. The formation of bonds facilitates the course of substitution reactions in octahedral complexes. The results we have obtained explain the available experimental material and permit us to make some predictions.     

Thermodynamics of equilibrium isomeric mixtures: the dideuteriocyclobutadienes

Thermodynamics of equilibrium mixtures of three possible positional isomers of the rectangular dideuteriocyclobutadiene were studied based on recent 4-31G and 6-31G ¹/MP2 evaluations of molecular parameters of the species. Relative stabilities of isomers were evaluated with due respect paid to the rotational-vibrational motions involved. Significant values of isomerism contributions to overall values of thermodynamic functions were found. The results represent the first example of a consistent treatment of overall thermodynamics of equilibrium mixtures of isomeric isotopomers available.     

From rare gas atoms to fullerenes: spherical aromaticity studied from the point of view of atomic structure theory

The characteristic features of molecules like polyhedra and fullerenes, which follow the 2(N+1)(2) rule of spherical aromaticity, can be related to energetically stable closed-shell configurations of (pseudo-)atoms. This unifying view relies on a thought experiment, which produces a polyhedron in a two-step process and which can, in turn, relate the electronic configuration of any spherical polyhedron to the one of a corresponding closed-shell atom. In the first step, the electronic ground-state configuration is identified. In the second step, a group theoretical analysis can be carried out; this relates the spherically symmetric atomic orbitals to the molecular orbitals classified according to the irreducible representations of the point group of the polyhedron under consideration. This procedure explains and justifies the pseudo-l classification of molecular orbitals, which is the basis of the 2(N+1)(2) rule. For the transition from the electronic configuration of the rare gas Eka-Rn (Uuo) to the icosahedral fullerene C(20) (2+), we show how a change in the ground-state configuration leads to the phenomenologically found 2(N+1)(2) rule for spherically aromatic fullerenes.     

Results coming from homogeneous and supported metallocene catalysts in the homo- and copolymerization of olefins

Ethylene, propylene and α-olefins were homo- and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind)₂ZrCl₂ (I), Me₂Si(Ind)₂ZrCl₂ (II), Et(2-Me-Ind)₂ZrCl₂ (III), Ph₂C(Flu)(Cp)ZrCl₂ (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol-gel preparation technique. The homo- and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed.     

Binary systems from quantum cluster equilibrium theory

An extension of the quantum cluster equilibrium theory to treat binary mixtures is introduced in this work. The necessary equations are derived and a possible implementation is presented. In addition an alternative sampling procedure using widely available experimental data for the quantum cluster equilibrium approach is suggested and tested. An illustrative example, namely, the binary mixture of water and dimethyl sulfoxide, is given to demonstrate the new approach. A basic cluster set is introduced containing the relevant cluster motifs. The populations computed by the quantum cluster equilibrium approach are compared to the experimental data. Furthermore, the excess Gibbs free energy is computed and compared to experiments as well.     

Preparation of homogeneous polyacrylamide hydrogels by free-radical crosslinking copolymerization

Network microstructures of acrylamide (AAm)-based hydrogels were investigated by static and dynamic light scattering techniques. The hydrogels were prepared by free-radical crosslinking copolymerization of the monomers acrylamide (AAm), N,N-dimethylacrylamide (DMA) and N-isopropylacrylamide (NIPA) with N,N′-methylenebis(acrylamide) as a crosslinker in aqueous solutions. It was observed that the addition of DMA or NIPA into the comonomer feed suppresses the extent of frozen concentration fluctuations in polyacrylamide (PAAm) hydrogels. The cooperative diffusion coefficient increases while both the static and dynamic correlation lengths decrease as the amount of DMA in the comonomer feed is increased. Formation of homogeneous PAAm hydrogels by introduction of hydrophobic moieties was explained as a result of the steric effect of the bulky side groups on DMA or NIPA segments.     

Quantitative force microscopy from a dynamic point of view

We discuss the physical origin and measurement of force between an atomic force microscope tip and a soft material surface. Quasi-static and dynamic measurements are contrasted and similarities are revealed by analyzing the dynamics in the frequency domain. Various dynamic methods using single and multiple excitation frequencies are described. Tuned multifrequency lockin detection with one reference oscillation gives a great deal of information from which one can reconstruct the tip–surface interaction. Intermodulation in a weakly perturbed high Q resonance enables the measurement of a new type of dynamic force curve, offering a physically intuitive way to visualize both elastic and viscous forces.     

Note: Aris-Taylor dispersion from single-particle point of view

When a point Brownian particle diffuses in a straight circular tube in the presence of a laminar stationary flow of the liquid, its effective diffusion coefficient along the tube axis increases compared to its value in the absence of flow. The effective diffusion coefficient as a function of the average fluid velocity and the tube radius is given by the Aris-Taylor formula. We give a new derivation of this formula, which is based on consideration of the axial displacement of the particle that moves in the plane normal to the tube axis along a given trajectory. The result is obtained by averaging the displacement and its square over different realizations of the particle trajectory and analyzing the long-time asymptotic behavior of the two moments.     

Thermodynamics of H in disordered Pd-Ag alloys from calorimetric and equilibrium pressure-composition-temperature measurements

In this research, the thermodynamics of H2 solution and hydride formation in a series of disordered Pd-Ag alloys has been determined using both reaction calorimetry and equilibrium PH2-composition-T data. Trends of DeltaHH and DeltaSH with both H and Ag concentration have been determined. For the Pd0.76Ag0.24 alloy, which does not form a hydride phase, DeltaHH and DeltaSH both exhibit minima with H/(Pd0.76Ag0.24) followed by a linear increase of the former. A linear increase of DeltaHH is found for all of the alloys in the high H content region beyond the two-phase region or, if, there is no two-phase region, in the high H content region. DeltaHH degrees at infinite dilution of H decreases with atom fraction Ag, XAg, up to about 0.40 and then increases. Enthalpies for hydride formation/decomposition, 1/2H2(g) + dilute <--> hydride, have been determined calorimetrically for alloys which form two phases (303 K). The enthalpies for hydride formation become more exothermic with XAg while the corresponding entropy magnitudes are nearly constant, 46 +/- 2 J/K mol H.     

Creatinine determination in urine from the point of view of reference values

In this paper, the creation of a certified reference material for urinary creatinine is described. We used the Jaffe method and HPLC method for establishment of the certified value. Homogeneity tests are also described. We obtained material with sufficient homogeneity, stability, and with certified value (expanded uncertainty, k=2 for CI 95%) (7.77±0.27) mmol·L⁻¹. This material was consequently used for the interlaboratory comparison (EQA Czech Republic for clinical chemistry). Twenty-nine percent of the participants obtained measurement results within the interval of the certified value ± expanded uncertainty, while 85% of the participants obtained values inside the interval of the certified value ± target measurement uncertainty. Direct use of the certified reference materials for method evaluation in EQA programs means a significant advance for monitoring and documentation traceability of results in routine measurements.     

Thermodynamics of aqueous solutions of orthophosphoric acid from the freezing point to 298.15°K

The osmotic coefficients of aqueous phosphoric acid have been determined at 298.15°K, at 273.15°K, and at the freezing point, and for concentrations from about 10^?4 m to 15 m. Phosphoric acid is incompletely dissociated even at very low concentrations, but it was possible to derived mean activity coefficients for the species H⁺ and H₂PO ₄ ^? by treating phosphoric acid as a 1-1 electrolyte.     

Characterization of metal oxide-doped lutetium orthoferrite powders from the pigmentary point of view

This thesis deals with the preparation and characterization of inorganic pigments based on perovskite structure of metal oxide-doped LuFeO₃. Powder samples were prepared by the conventional ceramic method, i.e., solid-state reaction. Heating temperature was chosen according to results of TG/DTA. Prepared pigments were incorporated into an organic binder system, and their color properties were evaluated by measuring the reflectance in the visible region of light. The most interesting color properties were obtained by preparation of sample Lu_0.98Ca_0.02FeO_3?δ with mineralizer LiF at the temperature 900 °C. Mean size of its particles is 4 μm. X-ray diffraction analysis confirmed a single-phase orthorhombic structure with lattice parameters a = 0.521310 nm, b = 0.55535 nm, and c = 0.75626 nm. Thermal stability of the sample is limited by the temperature of 1,150 °C. Further, the effectiveness of other metal oxide (CoO-, ZnO-, Bi₂O₃-, and Sb₂O₃)-doped Lu_0.98Ca_0.02FeO_3?δ system was evaluated with respect to their phase composition, thermal stability, particle size distribution, and color properties. The conclusions of the research showed that a sample containing antimony oxide is the mixture with the best pigmentary-application properties. The powder has a clear orange color, high thermal stability up to 1,340 °C, and mean particle size 4 μm.     

Thermodynamics of protolytic equilibrium of nicotinic acid in water-ethanol solutions

The enthalpies of stepwise protonation of nicotinate ion (L⁻) in water-ethanol solvents were determined calorimetrically at 298.15 K. It was found that the reduced exothermicity of the reaction of nicotinate ion protonation upon an increase of the organic component content in solution is due mainly to increased solvation of the proton. The minor influence of solvent on the enthalpy of protonation of nicotinic acid (HL) is characterized by compensation from solvation of the proton, the ligand, and its protonated form (H₂L⁺).