Critical parameters for isobutane determined by the image analysis

(p, ρ, T) Measurements and visual observations of the meniscus for isobutane were carried out carefully in the critical region over the range of temperatures: −15 mK ? (T − T_c) ? 35 mK, and of densities: −7.5 kg · m⁻³ ? (ρ − ρ_c) ? 7.5 kg · m⁻³ by a metal-bellows volumometer with an optical cell. Vapor pressures were also measured at T = (310, 405, 406, 407, and 407.5) K. The critical point of T_c and ρ_c was determined by the image analysis of the critical opalescence which is proposed in this study. The critical pressure p_c was determined to be the pressure measurement at the critical point. Comparisons of the critical parameters with values given in the literature are presented.     

Critical parameters for the analysis of anionic oligosaccharides by desorption electrospray ionization mass spectrometry

Sulfated oligosaccharides derived from glycosaminoglycans (GAGs) are fragile compounds, highly polar and anionic. We report here on the rare but successful application of desorption electrospray ionization (DESI) — LTQ‐Orbitrap mass spectrometry (MS) to the high‐resolution analysis of anionic and sulfated oligosaccharides derived from the GAGs hyaluronic acid and heparin. For that purpose, key parameters affecting DESI performance, comprising the geometric parameters of the DESI source, the probed surface and the spraying conditions, applied spray voltage, flow rates and solvent composition were investigated. Under suitable conditions, the DESI technique allows the preservation of the structural integrity of such fragile compounds. DESI enabled the sensitive detection of anionic hyaluronic acid and heparin oligosaccharides with a limit of detection (LOD) down to 5 fmol (≈10 pg) for the hyaluronic acid decasaccharide. Detection of hyaluronic acid oligosaccharides in urine sample was also successfully achieved with LOD values inferior to the ng range. Multistage tandem mass spectrometry (MSⁿ) through the combination of the DESI source with a hybrid linear ion trap‐orbitrap mass spectrometer allowed the discrimination of isomeric sulfated oligosaccharides and the sequence determination of a hyaluronic acid decasaccharide. These results open promising ways in glycomic and glycobiology fields where structure–activity relationships of bioactive carbohydrates are currently questioned. Copyright © 2012 John Wiley & Sons, Ltd.     

Liquid crystal parameters through image analysis

A technique which combines image analysis and polarising optical microscope (POM) is a useful tool for the physical investigation of discotic liquid crystals, such as hexabutoxytriphenylene and hexahexyloxytriphenylene. This investigation includes the phase transitions, optical properties and order parameter as a function of temperature. Textures of discotic liquid crystals are captured as a function of temperature using POM. These microscopic textures are analysed using MATLAB software to compute statistical parameters, Legendre moments, optical parameters and order parameters of discotic liquid crystal samples. Compared with other techniques in the literature, the proposed methodology is a reliable and very simple technique for the physical investigation of liquid crystals.     

Interpretation of infrared intensities of propane and deutero-propanes by electrooptical parameters

The interpretation of IR intensities of CH₃CH₂CH₃, CD₃CH₂CD₃ and CH₃CD₂CH₃ in terms of bond parameters (electrooptical parameters, e.o.p. s) is discussed. Sets of e.o.p. s derived from a previous study on methanes and ethanes are used as starting points to derive more complete sets of e.o.p. s which fit the intensities of propane very well. The intensities from ethanes have been used as a constraint on the e.o.p. s of CH₃ groups. The results are discussed and compared with values from quantum mechanics for the derivatives of the molecular dipole moment. Since the parameters derived in this work predict satisfactorily the IR intensities of polyethylene, they should form a good starting set for the interpretation of the intensities of n-paraffins.     

Optimization of the parameters for nickel electrowinning using interference microscopy and digital image analysis

Ni electrodeposition experiments at a constant current density 220 A/m² were performed to determine the optimum concentrations of chloride and an organic additive used for an industrial Ni electrowinning. White light interference microscopy was used to acquire digital images of the morphology of the electrodeposited nickel. The scaling analysis was employed to parameterize the morphological information encoded in the images. The standard deviation of the surface height, δ, the critical scaling length, L _c, and the optical roughness, 4δ/L _c, were determined as a function of the chloride concentration and the amount of organic additives. These parameters were plotted as a function of the two compositional variables. These three-dimensional plots allowed us to find conditions corresponding to the minimum of 4δ/L _c, at which the deposited nickel is well leveled. Dedicated to Prof O.A. Petrii on the occasion of his 70th birthday and in recognition of his contribution to electrochemistry.     

Photolysis of azomethane–propane mixtures. Arrhenius parameters for the hydrogen abstraction reactions of methyl with azomethane and with propane

Mixtures of up to 14% azomethane in propane have been photolyzed using mainly 366 nm radiation in the ranges of 323–453 K and 25–200 torr. Detailed measurements were made of the yields of nitrogen, methane, and ethane. Other products observed were isobutane, n-butane, ethene, and propene. A detailed mechanism is proposed and shown to account for the observed variation of product yields with experimental conditions. The quantum yield of the molecular process is found to be given by the temperature-independent equation The values of rate constants obtained are where the reactions are and it is assumed that the rate constant for the reaction is given by      

Critical concentration for colloidal crystallization determined with microliter centrifuged suspensions

We report an elegant method using centrifugal sedimentation for determining the critical particle concentration for colloidal crystallization. A small amount of a dilute suspension of monodispersed particles stored in a flat capillary cell was centrifuged to temporarily generate a nonequilibrium gradient of the particle concentration including a crystalline-noncrystalline phase boundary in the cell. In the recovering process after the centrifugation, the particle concentration of the crystalline phase at the boundary was found to always have the equilibrium value, although the global concentration distribution evolved with time. The critical concentration was determined based on spatially resolved spectrometry. The present method requires only one batch of a suspension of the order of microliters and is applicable up to high concentration regions near the closest packing without the effect of the particle aggregation.     

Monothioindigo,determined by microcrystal structure analysis

Indigo and thioindigo pigments are used for a wide range of applications. The crystal structure of the mixed compound monothioindigo [systematic name: (E)‐2‐(3‐oxo‐2,3‐dihydro‐1‐benzothiophen‐2‐ylidene)‐2,3‐dihydro‐1H‐indol‐3‐one], C₁₆H₉NO₂S, has been determined by microcrystal structure analysis from a crystal with a size of just 1 × 2 × 10 µm. The crystal structure of monothioindigo resembles those of indigo and thioindigo. The molecules show orientational disorder, with site‐occupation factors of 0.962 (2) and 0.038 (2) for the major and minor disorder components, respectively. The indigo fragment donates an intermolecular hydrogen bond, leading to a criss‐cross arrangement of molecules similar to that in indigo, whereas the thioindigo fragment exhibits only van der Waals interactions and molecular stacking, similar to that in thioindigo.     

Critical parameters of methylbromo-and ethylbromosilanes

Critical parameters of nine methylbromo-and ethylbromosilanes were determined.     

Critical parameters affecting dynamic mechanical analysis using a du Pont 981 analyser

The parameters affecting Young's modulus and the glass transition temperature have been investigated. Sample dimensions as well as the sample clamping have been shown to be critical. For analysis at non-ambient temperatures the gas flow rate as well as the position of the sample thermocouple, are also important.

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Zusammenfassung Es wurden die den Young Modulus und die Glasübergangstemperatur beeinflussenden Parameter untersucht. Die Probengröße und die Packungsdichte der Probe erwiesen sich als kritisch. Für Analysen oberhalb der Raumtemperatur sind die Geschwindigkeit der Gasströmung und die Lage des Thermoelements in der Probe besonders wichtig.

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We wish to thank the South African C. S. I. R. for financial assistance.     

Critical considerations on the methods for evaluating kinetic parameters from nonisothermal experiments

By surveying the most used methods for evaluating the kinetic parameters from nonisothermal experiments, a new classification scheme of the methods is proposed. For each method the number of principles and theoretical approximations required to derive the equation which grounds it, is considered as a comparison criterion. The methods are, finally, classified into classes of equivalence. As a result of the analysis it is also suggested that the activation energy, as calculated from nonisothermal data, should be given as a range of values instead of a unique value. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 313–327, 1998.     

2,4,6-Trinitrotoluene thermal decomposition: kinetic parameters determined by the isothermal differential scanning calorimetry technique

The isothermal differential scanning calorimetry technique is used to determine kinetic parameters for the thermal decomposition of 2,4,6-trinitrotoluene (TNT). Values for the activation energy and pre-exponential factor are presented. An analysis of the thermochemical induction period data is presented which allows calculation of the activation energy of the induction reaction.     

Critical parameters from power series expansions

A simple and quite general method is developed for calculating critical para meters from power series expansions. The series coefficients of the problem function are introduced into a properly parametrized recurrence relationship. As a result, sequences are obtained that converge towards the critical parameters characterizing the closest singularity to the origin. The low-temperature series for the thermodynamic functions of spin-1/2 Ising models are discussed. Results are shown for the interfering, nonphysical singularities of the face-centred cubic and body-centred cubic lattices. The determination of these singularities would allow their factorization previous to the study of the physically important ones.     

Crystallization monitoring by quantitative image analysis

Crystals have well defined geometric characteristics. A geometry-based algorithm has been developed to study images of crystals and to calculate their macroscopic structural characteristics. The procedure has been applied to single monocrystals and crystal populations for which shape distributions can be determined and used to quantify the shape homogeneity of a crystallizer production.     

Kinetic analysis of the hydrogenolysis of propane on ruthenium catalysts

The dependence of rates of propane hydrogenolysis on temperature and H₂ pressure have been modelled, using a rate expression based on Langmuir-Hinshelwood formalism. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Optimization of firing parameters for ceramic wares by thermal analysis

Aesthetic and utilitarian properties of traditional ceramic wares as well as engineering properties of modern advanced ceramics are attained by maintaining an optimum temperature-time-atmosphere relationship, called firing schedule, in the kiln. The contribution of modern thermal analysis (TA) techniques such as TG/DTG, TG/EGA, TG/MS, DTA, DSC, TDA, etc. in 1) optimizing production steps by raw material quality control, by studying binder burn out, product densification, 2) in simulating appropriate preheating, firing and cooling schedules as well as 3) in developing shorter firing cycles has been extensively reported in recent literature. The paper will first discuss theoretical curves and energy required for ceramic firing and present from the literature selected examples of applications of thermal analysis in ceramic technology.     

Critical parameters of chlorinated tetramethyl- and tetraethylgermane

The critical parameters of chlorinated tetramethyl- and tetraethylgermane were determined by calculational methods. The reliability of calculated data was confirmed by several independent methods.