Transform of a thermogram into a thermogenesis curve by the use of the frequency transfer function of a calorimeter

In calorimeter experiments, we obtain the thermogram y = y(t), temperature variation y(t) as a function of time t, when thermal reaction occurs in the calorimeter reaction cell. For thermokinetic studies, we need to know the calorific power generated in the cell, due to the thermal reaction, as a function of time. By use of the frequency transfer function of the calorimeter, we can calculate numerically the calorific power at any time from numerical analysis of the thermogram without any assumption of analytical form of the transfer function.The method is composed of three steps. (1) Experimental determination of the frequency transfer function G of the calorimeter from numerical analysis of the thermogram which is obtained by applying a constant calorific power in the calorimeter cell. (2) Numerical Laplace transform L[y] = Y of the thermogram which is recorded when the thermal reaction under investigation occurs in the cell. (3) Numerical determination of the calorific power, evolved by the thermal reaction in the cell, by numerical inverse Laplace transform of Y/G.This method is examined in two ways. First, simulation by numerical calculation on a mathematical model calorimeter is done and the accuracy of the method is assured. Second, experiments and numerical analysis on the heat-flow (conduction) type of calorimeter are performed to test the availability of the method.     

Electrophoresis of a toroid along the axis of a cylindrical pore

The electrophoresis of a toroid (doughnut-shaped entity) along the axis of a long cylindrical pore is analyzed under the conditions of low surface potential and weak applied electric field. The system under consideration is capable of modeling the electrophoretic behavior of various types of biocolloid such as bacterial DNA, plasmid DNA, and anabaenopsis, in a confined space. The influences of the key parameters of the problem, including the sizes of a toroid, the radius of a pore, and the thickness of the double layer, on the electrophoretic mobility of a toroid are discussed. We show that the electrophoretic behavior of a toroid under typical conditions can be different from that of an integrated entity. For instance, although the presence of the pore wall has the effect of retarding the movement of a particle, it becomes advantageous if a toroid is sufficiently close to the boundary. Several interesting behaviors are also observed, for example, the mobility of a toroid when the boundary effect is significant can be larger than that when it is insignificant.     

Relation of the force constant of a bond to the electric field at a nucleus

The change in the electric field at a nucleus in a molecule due to bond stretch is related to the force constant of the stretched bond. The validity of this relationship using approximate wave functions at the SCF and MP2 levels of theory is tested for the diatomic molecules H₂, HF, CO, and N₂. The effect of basis set variation on H₂ is also investigated. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1664–1667, 1997     

Effect of the inclusion of a cyclic fragment in the chromophore on the properties of a spiropyran-merocyanine system

The corresponding merocyanines, which do not display a tendency to form spiropyran structures, are formed in the condensation of 1,3,3-trimethyl-2-methyleneindoline with 5-methyl-2-furoylacetaldehyde, 2-formylcyclohexanone, or 2-formyl-1-tetralone. Spiran compounds in which the spiropyran—merocyanine equilibrium is shifted markedly to favor the closed form are formed when 4a,9-dimethyl-2,3,4,4a-tetrahydrocarbazone — the cyclic analog of the Fischer base — is used in the reaction with salicylaldehydes and benzoylacetaldehydes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1210, September, 1982.     

Unexpected formation of a xanthone in the synthesis of a bisbenzoxazole

Recently we reported the synthesis in polyphosphoric acid of a graft copolymer consisting of a rigid-rod poly[benzo(1,2-d;4,5-d′)bisthiazole-2,6-diyl]-1,4-phenylene backbone and flexible poly(oxy-1,3-phenylenecarbonyl-1,4-phenylene) side-chains [1]. However, upon extension of this synthetic approach to the analogous graft copolymer with a poly[benzo(1,2-d:5,4-d′)bisoxazole-2,6-diyl]-1,4-phenylene backbone, we encountered some unexpected results due to methyl group migration. In order to better understand these results, we carried out the synthesis of selected benzothiazole and benzoxazole structures under appropriate reaction conditions. The results are reported in this article.     

Calculation of the velocity field of a fluid in a hydrocyclone

Influence exerted by parameters dependent on the design dimensions of a hydrocyclone and by the flow rate on the distribution of the fluid velocity in a hydrocyclone was studied.     

Application of a sulphide-selective electrode in the absence of a pH-buffer

Calibration of a sulphide electrode in the pH-range 9-12 has been studied as an e.m.f. vs. (pH - p[HS(-)]) function by measuring e.m.f. and pH in parallel. Calibration can also be done in this pH range by using a differential amplifier with a three-electrode measuring cell (glass, sulphide-selective and reference electrodes). The effects of an antioxidant (ascorbic acid) and a complexing agent (DCTA) on the calibration of the glass-sulphide electrode cell at pH < 5 were studied. The applicability of this end-point indicator cell has been demonstrated for titrations of Ag(+), Pb(2+) and Bi(3+) with Na(2)S.     

Influence of the electric field on a particle in a space with a disclination

We consider a quantum particle in a space with a linear topological defect, i.e., disclination. The effect of the uniform electric field in this space, on the particle, is shown to cause a translation of the wave function. In addition, the electric field is not found to be affected by the defect. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Electrophoretic motion of a nanorod along the axis of a nanopore under a salt gradient

Wood-based activated carbon was modified by deposition of silver using Tollens method. Adsorbents with various contents of silver were used to study NO(2) and NO (the product of NO(2) reduction by carbon) retention. The surface of the initial and exhausted materials was characterized using adsorption of nitrogen, XRD, SEM/EDX, FTIR and TA. The results indicated that with an increasing content of silver on the surface the capacities to retain NO(2) and NO increase until the plateau is reached. The performance depends on the dispersion of nanoparticles and their chemistry. Highly dispersed small silver metal particles promote formation of chelates with NO(2) and/or with NO. An excess of Tollens reagent results in formation of larger silver crystals and silver oxide nanoparticles. If sufficiently dispersed, they also enhance the retention of NO(2) via formation of nitrates deposited in the pore system. The surface of the carbon matrix is also active in NO(2) retention, providing the small pores and edges of graphene layers, where the reductions of NO(2)/oxidation of carbon take place.     

Formation of a rotaxane from the end-capping process of a pseudorotaxane. Effects of the solvent

The effects that the solvent exerts on the end-capping process of a pseudorotaxane formed by the [Ru(NH 3) 5(4,4'-bpy)]2+ complex and beta-cyclodextrin were studied. In this process the 4,4'-bpy ligand acts as rigid axle and the cyclodextrin as ring or macrocycle. The stopper used was the [Fe(CN) 5 H2O]3(-) complex. The solvents used were mixtures of ethyleneglycol-water and tert-butyl alcohol-water. Results showed similar, although strange, behavior in both media studied. Thus, a decrease of the observed rate constant was obtained when the concentration of cyclodextrin increases for all the media studied. However, at fixed cyclodextrin concentrations, an increase of k obs was obtained when small quantities of the cosolvent were added to the medium and, further, a decrease of k obs for the higher quantities of the organic solvents. This strange behavior could be explained by taking into account electrostatic and specific solvent (solvent-solvent and solvent-solute) effects.     

Investigations of the use of a mussel-inspired compatibilizer to improve the matrix-fiber adhesion of a biocomposite

Vegetable fibers have several positive aspects, such as low production costs, biodegradability and good mechanical properties, which make them very attractive in the field of composite reinforcement. The aim of this study is to introduce into a l-poly-(lactic-acid) (PLLA) – hemp biocomposite a new compatibilizer, inspired from the mussels' adhesive capacity, to improve the fiber-matrix bonding. As a first step, we carried out atomic force microscopy (AFM) and surface energy measurements in order to prove the compatibilizer's presence. Secondly, tensile tests were performed. The results show a significant increase of Young's modulus and the breaking strength when using polydopamine. Observations made through scanning electronic microscopy (SEM) confirmed an improvement of the fiber-matrix coupling in the presence of poly-(dopamine).     

Determination of the Vapor Pressure Curve of a Liquid in the Presence of a Nonvolatile Solute

We present a modification of the data analysis for the classical physical chemistry experiment Determination of Enthalpy of Vaporization by the Boiling-Point Method. The vapor pressures of solutions of both ionic and molecular compounds are determined at different temperatures. In this experiment we show that the enthalpy of vaporization change is dependent on the type and amount of nonvolatile solute present. Sets of data collected for different concentrations of sodium chloride, urea, and sucrose solutions are analyzed in order to determine H_vap and S_vap for pure water and for solutions of ionic and molecular solutes.Students perform the data analysis taking into consideration the activity coefficient for the solution and the mole fraction of the solvent. Simultaneous data analysis is introduced and results are used to explain the meaning of the physical parameters determined using this method of data analysis.     

Combined effect of the screening of a donor ion and the conduction band nonparabolicity on the binding energy of a donor at the center of a spherical quantum dot

We carried out variational model calculations for the assessment of the combined effect of the nonparabolicity of the electron effective mass and the screening of the donor ion by the valence electrons of GaAs for a donor placed at the center of a spherical quantum dot. We considered finite confining potentials between the GaAs QD and the surrounding Ga_1-xAl_xAs matrix. We found that the combined effect becomes more pronounced as the radius of the quantum dot decreases. © 1996 John Wiley & Sons, Inc. Int J Quant Chem 60: 507–510, 1996     

Role of the water as a surface tension modifier for the retention of a series of dansylaminoacids on a beta-CD stationary phase

In reversed phase liquid chromatography (RPLC), using a surface tension treatment, the retention and separation of a series of d,l-dansylaminoacids were investigated with native beta-cyclodextrin as a chiral stationary phase. The enantioselectivity thermodynamic parameters were determined from linear van't Hoff plots. An analysis of the experimental variations in the retention factor with different fractions of water in the mobile phase was performed. The number of water molecules, n, excluded from the solute beta-cyclodextrin cavity interface when the analyte transfer occurred, was determined. Using these n values, the relative degrees of compound inclusion were calculated and correlated to both the steric bulkiness of the solute and the thermodynamic data.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study

The absorption spectra of styrylbenzothiazolium dye derivatives were calculated by the time-dependent density functional (TD DFT) method. The dyes of interest were (p-dimethylamino)styrylbenzothiazolium dye and its protonated form as well as aza-15(18)-crown-5(6)-containing dyes and their complexes with alkali (K⁺ and Na⁺) and alkaline-earth (Ca²⁺, Sr²⁺, and Ba²⁺) cations. Several low-lying conformers of the azacrown-containing dyes were considered. The electronic and geometric structures of the excited states responsible for the appearance of the long-wave (π-π*) absorption bands are studied. Complexation causes a hypsochromic shift of the long-wave absorption band correlating with the pyramidality of the crown ether nitrogen in the complex. The interaction of the cation with 3–4 solvent molecules or a counterion (ClO₄ ^?) considerably reduces this shift, especially in the conformers without the metal-nitrogen bond. In some cases, the long-wave absorption band is close to the absorption band of the free dye. Similar results were obtained using the polarizable continuum model of solvation. Excited-state structures of the free model dye and the free azacrown-containing dyes exhibit a tendency to bond alternation. Conversely, the cationic complexes of the crown-containing dyes and the protonated model dye exhibit a tendency to bond equalization in the excited state. The changes in the excited-state geometries of the free dyes and their complexes account for the complexation-induced fluorescence enhancement observed in the experiments.