Introduction of Marinelli effective solid angles for correcting the calibration of NaI(Tl) field gamma-ray spectrometry in TL/OSL dating

A study is made of the corrections that are needed in the evaluation of the annual radiation dose, for use in TL/OSL-dating, via NaI(Tl) field gamma-ray spectrometry (monitoring of K, Th and U), calibrated via voluminous blocks that are simulating the Auger hole measuring conditions. Two cases are considered: the Heidelberg granite calibration block, which was found to be quasi-infinite, and the Oxford concrete calibration blocks, for which effective concentrations of elements are reported so as to account for their non-infiniteness. The calculations, via the software package ANGLE, are based on the concept of effective solid angles for Marinelli geometries.     

Effect of hydrothermal treatment on the gelatinisation properties of potato starch as measured by differential scanning calorimetry

Gelatinisation temperatures as a function of moisture content were determined for potato starch. The native starch was then hydrothermally treated at a temperature 3% (Kelvin degrees) below the gelatinisation peak temperature and at moisture levels varying from 20 to 67% (by weight). Gelatinisation temperatures, temperature ranges and enthalpy values were affected for all treated samples. However, two sample populations could be distinguished: those samples treated under limited moisture conditions and other samples treated in the presence of extragranular moisture. A two-step hydrothermal treatment further increased the gelatinisation temperature, but the effect of the second step was small in comparison to that of the first.We thank the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek for research positions as aspirant (H. Jacobs) and post-doctoraal onderzoeker (R. C. Eerlingen).     

Symmetry and other properties of second-order phenomenological coefficients and thier significance in a chemical system

Using a second-order phenomenological equationJ _i = _j L _ij X_j + _{j, k} L _ijk X_j X_kand assuming that the system is at a state near equilibrium, it has been shown that the symmetry ofL _ijk is retained with respect to the permutations of suffices i j and k Furthermore, using the second-order flux equations, the thermodynamic stability criterion is expressed. The symmetry is shown to be retained in a reaction scheme representing the emplate model. The significance of the stability criterion as expressed by the higher-order phenomenological coefficients is discussed.     

Acid hydrolysis of cellulose in a differential scanning calorimeter

Differential scanning calorimetry was applied to the decompositions of cellulose and D-glucose with several concentration of sulfuric acid. The heat of reaction for cellulose was slightly less than that for glucose. It suggests that the heat of hydrolysis of the (-1,4-glucosidic linkage is endothermic.The degree of reaction obtained by means of a commercial kinetic program was 1.1±0.1, which was independent of the acid concentration for both cellulose and glucose.The quantity of D-glucose produced by saccharification of cellulose was estimated using kinetic parameters obtained for cellulose and glucose, which were assumed to express the respective parameters for the successive first-order reactions cellulose to D-glucose, and glucose to decomposition products.

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Zusammenfassung Die Zersetzung von Cellulose und D-Glucose durch Schwefelsäure unterschiedlicher Konzentration wurde mittels DSC untersucht. Die Reaktionswärme ist bei Cellulose etwas geringer als bei Glucose, was zeigt, daß die Hydrolyse der-1,4-Glucosidbindung ein endothermer Vorgang ist. Der mittels eines kommerziellen kinetischen Programms erhaltene Reaktionsgrad beträgt 1.1±0.1 und erwies sich sowohl bei Cellulose als auch bei Glucose als unabhängig von der Säurekonzentration. Die durch Verzuckerung von Cellulose gebildete Menge an D-Glucose wurde unter Verwendung von für Cellulose und Glucose erhaltenen kinetischen Parametern bestimmt, für die angenommen wurde, daß sie die entsprechenden Parameter der Folgereaktionen erster Ordnung Cellulose D-Glucose und Glucose Zersetzungsprodukte darstellen.

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-. - , . , - -1,4- . , , 1.1±0.1 . -, , , , - .

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We express our sincere gratitutde to Dr. S. Tanaka for useful discussions.     

A microcalorimetric study of the different states of argon and nitrogen adsorbed AT 77 K on silicalite-I and ZSM-5

The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16相似文献   

Classification of auxin plant hormones by interaction property similarity indices

Although auxins were the first type of plant hormone to be identified, little is known about the molecular mechanism of this important class of plant hormones. We present a classification of a set of about 50 compounds with measured auxin activities, according to their interaction properties. Four classes of compounds were defined: strongly active, weakly active with weak antiauxin behaviour, inactive and inhibitory. All compounds were modeled in two low-energy conformations, P and T, so as to obtain the best match to the planar and tilted conformations, respectively, of indole 3-acetic acid. Each set of conformers was superimposed separately using several different alignment schemes. Molecular interaction energy fields were computed for each molecule with five different chemical probes and then compared by computing similarity indices. Similarity analysis showed that the classes are on average distinguishable, with better differentiation achieved for the T conformers than the P conformers. This indicates that the T conformation might be the active one. Further, a screening was developed which could distinguish compounds with auxin activity from inactive compounds and most antiauxins using the T conformers. The classifications rationalize ambiguities in activity data found in the literature and should be of value in predicting the activities of new plant growth substances and herbicides.     

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXXVI Structural Studies in the Copper(I) Halide : Norbornadiene System

The structural characterizations of some copper(I) halide (CuX) adducts with norbornadiene (nbd) are recorded. CuCl : nbd (1:1)₄ (a redetermination), (2:1)_2(|), are systems both based around Cu₄Cl₄ cubane-type cluster arrays. CuBr : nbd (7:3)_(|)( 0.5 MeOH), a complex polymer with 3-symmetry, is believed to be the complex previously described as an adduct of 2:1 stoichiometry. Attempts to obtain an iodide counterpart have resulted in the definition of an ephemeral adduct CuI : MeCN (3:2)_(|). 0.5 C₇H₈ in which, remarkably, the nbd is uncoordinated; the complex is a polymer, related to the [AgX(quinoline)]_(|) (X = Cl, Br) saddle polymer.     

Synthesis of a Calix[4]arene Containing 'Hard' and 'Soft' Metal Ion Binding Sites

Co-receptor 1,3-calix[4]-di(aza-benzo)crown-crown-6 (1-H) designed with one calix[4]arene in a 1,3-alternate conformation and hard and soft metal ion binding sites has been prepared according to three pathways (A-C). Pathway B, consisting of two different 1 + 1 condensations with ditosylate derivatives, was shown to be the most efficient.     

Kinetic compensation effect in the thermal degradation of polymers

The kinetic study of thermal degradation takes into account the validity of the Arrhenius equation. From TG data, the activation energy,E _a and pre-exponential factor,A, are evaluated. These results are interpreted by using the kinetic compensation effect as basis. A linear correlation between In(A) andE _a is obtained in all cases studied. However, in a plot of the logarithm of the rate constant as a function of reciprocal temperature for the same series of reactions, the thermal oxidative degradations of Nylon-6 and PVC display a point of concurrence and one isokinetic temperature, whereas those of HIPS and PC do not. Therefore, in the thermal oxidative degradations of Nylon-6 and PVC a true compensation effect occurs, which could be related to the bulk properties of metal oxides, such as different valence states, whereas for other polymers it displays only an apparent compensation effect. This means that degradation is largely independent of the bulk properties of oxides, but may be related to the distribution of different kinds of active links in the polymer surface having different activation energies.     

Inclusion of quaternary ammonium compounds by calixarenes

In weakly polar solvents, strong association occurs between calixarene anions and tetraalkylammonium cations, with the magnitude of the observed equilibrium constants depending upon the charge on the anion, the solvent, the ring size of the calixarene and the nature of the alkyl group of the cation. Large upfield shifts of the methyl resonances of the [(CH₃)₄N]⁺ cation in solutions of [(CH₃)₄N]₂[p-t-butylcalix[6]arene-2H] indicate cation inclusion in a structure which is possibly identical with that found for the solid salt by X-ray crystallography. This shows one of the cations to be included within a partial cone structure of a hinged 3-up, 3-down conformation of the calixarene. The functionalised tetramethylammonium ions, choline and acetyl choline, are also strongly included by various calixarene anions but attempts to detect significant modification of the reactivity of acetyl choline resulting from inclusion have not been successful.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Modulated differential scanning calorimetry

The Modulated Differential Calorimetry (MDSC) is applied to the determination of the reversibility in the cholesteryl chloride, which presents a cholesteric monotropic phase between the isotropic and crystalline states. The experimental modulation parameters that govern this method i.e. frequency, amplitude and heating/cooling rate, are determined. MDSC curves and complementary thermomicroscopical observations assign melting, crystallization and liquid cholesteric transition as non reversing, and clarification as reversing.     

Distance geometry analysis of ligand binding to drug receptor sites

Summary The method known as distance geometry approach for receptor mapping procedures is discussed. In this method a ligand binding to a certain receptor is considered as a collection of ligand points. Binding sites of the receptor are either empty or filled site points; a ligand point might bind to an empty site point; filled site points indicate that at that point no binding is possible. A binding mode of a ligand is a list of which ligand points coincide with which empty binding sites. The applicability of the method for QSAR studies is discussed; as examples are mentioned the dihydrofolate reductase, ₁- and ₂-receptors. Finally, some ideas on future developments in receptor mapping are discussed.DEDICATION This article is dedicated to the late Dr. Teake Bultsma who introduced the distance geometry approach into our department.     

Etude cinetique non isotherme de la decomposition thermique du complexe dipyridinique de bromure de cadmium

Résumé Les paramètres cinétiques de la décomposition du complexe CdPy₂Br₂ ont été déterminés à l'aide de plusieurs méthodes nonisothermes à l'aide des données fournies par la thermogravimétrie et l'ATD. Les valeurs obtenues concordent de faÇon satisfaisante.

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Six nonisothermal thermogravimetric and DTA methods have been applied for determining the kinetic parameters of the decomposition of CdPy₂Br₂. The values obtained are in satisfactory agreement.

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Zusammenfassung Die kinetischen Parameter der Zersetzung des Komplexes CdPy₂Br₂ wurden durch verschiedene nicht-isotherme Methoden, durch Thermogravimetrie und Differentialthermoanalyse bestimmt. Die Resultate stimmten gut überein.

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6 CdPy₂Br₂. .

     

Thermal decomposition kinetics of sodium metaperiodate

Aged and fresh samples of sodium metaperiodate are subjected to thermal decomposition studies in air by TG, DTG and DTA techniques. The kinetic parameters for their decomposition have been evaluated by weighted least squares method using equations of Coats-Redfern, Horowitz-Metzger and Freeman-Carroll. The results indicate that, within the limits of experimental error, ageing did not change the E^* values considerably.

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, . , -, - -. , , , E^*.

     

Platinum-palladium catalysts for hydrogen fuel cell electrodes

Five series of Pt–Pd/C catalysts were prepared with different total metal loading and different atomic composition in Pt and Pd. The activity in electrooxidation of hydrogen were measured for all these catalysts. Electrooxidation of hydrogen is a structure insensitive reaction on platinum and a structure sensitive reaction on palladium. For bimetallic catalysts, curves of activity as a function of the composition of the catalyst can exhibit a maximum. Yet, metal loading can alter the atomic composition at which activities are maxima.

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Pt–Pd/C Pt Pd. . - - . . , .

     

Scanning XPS; low kinetic energy source scanning: some design considerations

Summary The logistics of electron-beam scanning in two special applications in surface-analysis are discussed, particularly with a view to multitechnique surface-analysis. For electron-beam charge-neutralisation it is necessary first to produce an x,y-positionable beam at low (a few eV) kinetic energies, with a significant space-charge, and submillimetre focus. These performance requirements seem at first sight to be at odds with the requirement for multitechnique surface-analysis, namely that the solid-angle subtended by each technique be kept to a minimum. Here both the high space-charge, and the small, positionable focus requirements indicate a larger solid-angle is required. Similarly, in scanning small-area (imaging) XPS, a requirement arises for keeping the solid-angle to a modest value, whilst not compromising the large-collection-angle electron-spectroscopy techniques, on a component hemispherical-sector electron energy analyser. Tested solutions for either case, satisfying all criteria, are presented.     

Computer-aided molecular modelling: Research study or research tool?

Summary Developments in computational methods and equipment have produced a new type of research chemist, who prefers to calculate properties as well as measure them, either to gain a better understanding of microscopic molecular behaviour per se, or to guide a broader scientific study using a so-called rational approach. While there is good reason to believe that significant results can be obtained this way, it is clear that only some of the tools of the trade are sufficiently robust to present to those who are not experts in the field.This paper discusses the underlying basis for molecular modelling techniques, describing their history, state of maturity and prospects for future development. The intention is to outline the scope that these play in an industrial research environment, and to examine how they can successfully be incorporated as routine research tools.Computer-based molecular modelling is not a unique discipline. Some comparisons are drawn between it and other computer-based techniques that have reached a greater degree of maturity, in order to highlight the points made.     

Effect of acid-base properties of oxide catalysts in the oxidative dehydrodimerization of olefins

The dependence of the activity of tin-containing oxide catalysts on their basicity and acidity has been examined. The rate of oxidative dehydrodimerization of olefins is shown to be determined by the mobility of allyl compounds depending on the catalyst acid properties.

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. , , .

     

Temperature-programmed hydrogen desorption from water on bimetallic catalysts Ir?Fe/Al2O3

Desorption of hydrogen liberated in the process of water decomposition on bimetallic catalysts (3% Ir–Fe/Al₂O₃) at linear temperature growth was observed. In the case of iridium the amounts of desorbing hydrogen are relatively small, whereas for iron they are many times greater.

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, 3% Ir–Fe/Al₂O₃ . , , .