Calculation of the dynamic temperature characteristics of a heated graphite tube used in electrothermal atomic absorption measurements

A method and computer program were developed for calculating the temperature of any part of a graphite furnace tube at any instant of time after onset of the heating cycle. Results for tubes of the Massman design show large differences in spatial temperature distributions during and at the end of the heating cycle when equilibrium is reached. When constant current is applied to contoured tubes, greater heating rates at the tube centres are obtained than with standard tubes.     

A remark on the mild solutions of non-local evolution equations

We provide a counterexample to some recent publications concerning the existence of the mild solutions of the non-local evolution equations, and indicate that in the study of the non-local evolution equations, the operators from which the mild solutions may be derived are in general not compact, thus those fixed point theorems requiring the compactness of the operators are not applicable.     

Liquid chromatographic analysis of prednisolone, prednisone and their 20-reduced metabolites in perfusion media

A reversed-phase liquid chromatographic assay was developed to quantitate prednisolone, prednisone and the 20 alpha-dihydro and 20 beta-dihydro reduced metabolites of both parent compounds in tissue culture media from in vitro perfusions of the human placental lobule. Steroids were extracted from perfusate, using reversed-phase cartridges, with average recoveries of 95.2% or greater. The internal standard for the analyses was 6 alpha-methylprednisolone. In this assay cortisol coelutes with prednisolone, however, no other significant interferences were found. Assay of each steroid was linear in the range 0-1 microgram/ml. Intra-assay coefficients of variation were measured at 10 and 750 ng/ml with ranges of 3.4% (20 alpha-dihydroprednisone) to 8.8% (20 beta-dihydroprednisolone) and 4.1% (20 beta-dihydroprednisone) to 8.8% (prednisone). The corresponding inter-assay coefficients of variation were 3.3% (20 alpha-dihydroprednisone) to 9.1% (20 beta-dihydroprednisolone) and 1.9% (prednisolone) to 3.5% (prednisone). The analyses utilized two C18 columns which were linked together and maintained at 40 degrees C.     

Thin-layer chromatography of radioactively labelled cholesterol and precursors from biological material

Summary The investigation methods of the action of xenobiotics on sterol biosynthesis from ¹⁴C-acetate in rat hepatocyte cultures can be developed, with regard to extraction using Extrelut and the separation of the sterol pattern by thin-layer chromatography, in such a way that they are suitable for wider application, e.g., screening. Good visualisation and recognition of changes in the sterol pattern are possible using autoradiography of the thin-layer chromatogram.

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Dünnschicht-Chromatographie von radioaktiv markiertem Cholesterin und Vorstufen aus biologischem Material. Eine einfache und empfindliche Methode zur Untersuchung einer Beeinflussung des Sterolbiosynthesewegs

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Dedicated to Dr. E. Roesch on occasion of his 65th birthday     

The Efimov effect in a four-body system

It is shown, using a Born-Oppenheimer model, that the four-body Efimov effect may occur in a system consisting of three identical heavy particles and one light particle, if the light-heavy interaction leads to a zeroenergy two-heavy-one-light bound state.     

Numerical Analysis and Simulation Analysis for Space‐Time Data

Spatio temporal dynamics of the positive column of a dc neon glow discharge is studied and investigated experimentally and theoretically. Spatio temporal analysis by means of biorthogonal decomposition method (BOD) gives insights into the mechanism of irregularity and can be employed for characterization of spatio‐ temporal complexity. In the weak nonlinear region, the wave dynamics is approximated by an amplitude equation of the Ginzburg‐Landau equation (CGLE) with complex coefficients and an additional integral term based on a fluid model. In the present work we deal with irregular spatio‐temporal data. A comparison between the numerical analysis of the experimental data and simulation results are studied. A good agreement between the dynamical behaviour for experimental space‐time data and theoretical simulation space‐time results was obtained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Functionalized poly(oxanorbornene)‐block‐copolymers: Preparation via ROMP/click‐methodology

Block copolymers on basis of poly(oxanorbornenes) bearing functional moieties in their side‐chains are prepared via a combination of ROMP‐methods and 1,3‐dipolar‐“click”‐reactions. Starting from N‐substituted‐ω‐bromoalkyl‐oxanorbornenes and alkyl‐/perfluoroalkyl‐oxanorbornenes, block copolymers with molecular weights up to 25,000 g mol^?1 were generated. Subsequent nucleophilic exchange‐reactions yielded the block‐copolymers functionalized with ω‐azidoalkyl‐moieties in one block. The 1,3‐azide/alkine‐“click” reactions with a variety of terminal alkynes in the presence of a catalyst system consisting of tetrakis(acetonitrile)hexafluorophosphate copper(I) and tris(1‐benzyl‐5‐methyl‐1H‐ [1,2,3]triazol‐4‐ylmethyl)‐amine furnished the substituted block copolymers in high yields, as proven by NMR‐spectroscopy. The resulting polymers were investigated via temperature‐dependent SAXS‐methods, revealing their microphase separated structure as well as their temperature‐dependent behavior. The presented method offers the generation of a large set of different block‐copolymers from only a small set of starting materials because of the high versatility of the “click” reaction, thus enabling a simple and complete functionalization after the initial polymerization reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 485–499, 2007     

Colossal magnetoresistance manganites: A new approach

Manganites of the LA_1−x Ca _x MnO₃ family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee _g states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is the key to manganite physics. Dedicated to Professor C N R Rao on his 70th birthday     

Surface analysis and surface measuring techniques in firearm offences

Summary When a shot is fired, the projectile and the cartridge case are released from the weapon, as well as components of the priming charge and propellant, the so-called powder-gunshot residues. In order to solve firearm offences, it is therefore very important to determine the topography of trace-bearing areas on the bullet and the cartridge case, as well as the chemical composition of gunshot residue particles. Gunshot residue particles are made visible with the scanning electron microscope (SEM) and are analysed by means of energy-dispersive X-ray spectroscopy (EDXS) and lately also by means of wavelength-dispersive X-ray spectroscopy (WDXS). In addition to this, analyses of these particles are displayed by means of Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) and depth profiles are prepared. To determine the local distributions of gunshot residue elements with regard to their quantity, the direct Zeeman atomic absorption spectroscopy (DZ-AAS) is employed. Besides the determination of the chemical composition, the topography of the trace-bearing areas on the bullet and cartridge case plays an important part. For the detection of these surfaces, light optical and electron-optical methods are employed. Moreover, the use of opto-electronical testing systems has been attracting more and more attention recently.     

Differential AC-chip calorimeter for glass transition measurements in ultrathin films

A differential AC-chip calorimeter capable of measuring the step in heat capacity at the glass transition in nanometer-thin films is described. Because of the differential setup, pJ/K sensitivity is achieved. Heat capacity can be measured for sample masses below 1 ng in broad temperature range as needed for the study of the glass transition in nanometer-thin polymeric films. Relative accuracy is sufficient to investigate the changes in heat capacity as the step at the glass transition of polystyrene. The step is about 25% of the total heat capacity of polystyrene. The calorimeter allows for the frequency dependent measurement of complex heat capacity in the frequency range from 1 Hz to 1 kHz. The glass transition in thin polystyrene films (50–4 nm) was determined at well-defined experimental time scales. No thickness dependency of the glass transition temperature was observed within the error limits (±3 K)—neither at constant frequency (40 Hz) nor for the trace in the activation diagram (1 Hz–1 kHz). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2996–3005, 2006