A Raman study of polymerised C60

60 are reported. Although prepared according to different routes the Raman spectra of the two polymeric phases of C₆₀ show a quantitative agreement with respect to mode positions and intensity. We conclude from this that both materials have the same structure at least in the short range order, i.e. the same type of bonding and co-ordination between neighbouring C₆₀ molecules. An investigation of the time dependence of the thermal decomposition of high pressure polymerised C₆₀ is also presented. The rate of decomposition of the polymeric phase is found to be multi-exponential at all temperatures investigated. From an Arrhenius-type analysis of the short time data and the long time data, respectively, the activation energy for thermal dissociation of polymeric bonds was found to increase with time. Received: 20 September 1996/Accepted: 11 November 1996     

Sonic spray ionization interface for liquid chromatography-mass spectrometry

A sonic spray ionization (SSI) interface for liquid chromatography-mass spectrometry (LC-MS) analysis was optimized for analysis of 2-[(1R)-3-[bis(1-methylethyl)amino]-1-phenylpropyl]-4-methyl-phenol (tolterodine), used as a model drug substance, and the influence of different parameter settings was evaluated using factorial design. A comparison between SSI and electrospray ionization (ESI) was made for tolterodine, tolterodine metabolites, and a set of steroids.SSI was found to give slightly poorer repeatability and broader peaks for tolterodine compared to ESI. However, there was no significant difference in chromatographic peak shape, and the repeatability using SSI was similar to that obtained using ESI if a ratio (area of tolterodine/area of metabolite) was used. In this study, the sensitivity was higher using SSI. For the analysis of pregnanolone, less water loss was obtained using SSI, probably due to less energy being transferred to the analyte upon ionization.     

Computer generated phase holograms (kinoforms) for millimeter and submillimeter wavelengths

Computer generated Fourier transform phase holograms, known as kinoforms, have been synthesized, manufactured and their performance evaluated at a wavelength of 3 mm (100 GHz). The kinoforms were synthesized to give a prescribed far-field intensity distribution and manufactured by milling the computed kinoform surface relief into a Teflon plate, using a numerically controlled milling machine. The measured diffraction efficiencies exceed 50 percent. Millimeter-wave kinoforms can be used in various quasi-optical applications,e.g. distributing a local oscillator signal to an array of detector elements in heterodyne receivers.     

Preparation and characterization of cellulose microspheres

The aim of this work was to synthesize and characterize cellulose microspheres with a particle size below 5 μm and narrow size distribution. After activation and functionalization with antibodies, these particles shall be applied as adsorbents in suspension-based extracorporeal blood purification systems, such as the Microspheres-Based Detoxification System. In the frame of this work such microspheres were developed and synthesized with reproducible properties. Besides using well-established methods for characterization of this kind of bead cellulose, additional procedures for the examination of its properties were developed and applied.     

Analysis of volatile organic compounds in polymers by dynamic headspace and gas chromatography/mass spectrometry

An experimental method for the analysis of volatile organic compounds in polymers is described. The technique involves dynamic headspace sampling, collection, and concentration of the volatiles in a cold trap, followed by capillary column gas chromatography/mass spectometry. Flow switching is carried out by the Deans switching technique. Four technical polymers used as pharmaceutical packaging materials have been analyzed in order to demonstrate the method.     

Cold trap/reinjection interface for two-dimensional gas chromatography

The construction and evaluation of an interface for two-dimensional gas chromatography is described. The interface consists of commercially available components and is attachable to available gas chromatographs without any major modifications. The interface has been constructed so as to permit “heartcutting” as well as solute band concentration. Trapping is performed in a simple cold trap of fused silica. Flow switching is accomplished by Deans switching. Factors of the over-all chromatographic performance are examined.     

Valence band structure of single crystal titanium carbide,studied by soft X-ray and ultraviolet photoelectron spectroscopy

Valence states of single crystal titatium carbide (TiC_x, X?0.88) have been studied with photon energies ranging from far ultraviolet (u.v.) to soft X-ray. The valence band consists of two peaks located at 3 and 10 eV below the Fermi level. This is in good agreement with recent APW band structure calculations that predict a strong hybridization of the Ti 3d and C 2p bands and a C 2s band at lower energy.     

Multifractality of self-avoiding walks on percolation clusters

We consider self-avoiding walks on the backbone of percolation clusters in space dimensions d=2,3,4. Applying numerical simulations, we show that the whole multifractal spectrum of singularities emerges in exploring the peculiarities of the model. We obtain estimates for the set of critical exponents that govern scaling laws of higher moments of the distribution of percolation cluster sites visited by self-avoiding walks, in a good correspondence with an appropriately summed field-theoretical epsilon=6-d expansion [H.-K. Janssen and O. Stenull, Phys. Rev. E 75, 020801(R) (2007)10.1103/PhysRevE.75.020801].     

Tunable Yb:KYW laser using volume Bragg grating in <Emphasis Type="Italic">s</Emphasis>-polarization

We report on a volume-Bragg-grating tunable Yb:KYW laser. By using s-polarized light on the grating, we obtain an output power of 3 W in a single beam, doubled compared to earlier p-polarization results. The laser tunability was from 996 nm to 1048 nm. Detailed measurements of the laser spectrum revealed a bandwidth of 10 GHz. PACS 42.40.Eq; 42.55.Xi; 42.60.Fc     

Thermodynamic parameters for the complexation of water‐insoluble betulin derivatives with (2‐hydroxypropyl)‐γ‐cyclodextrin determined by phase‐solubility technique combined with capillary zone electrophoresis

The complexation of betulinic and betulonic acids (BIA and BOA) (pentacyclic lupane triterpenoids) with (2‐hydroxypropyl)‐γ‐cyclodextrin (HP‐γ‐CD) was studied at different temperatures using the method combining phase‐solubility technique and CZE. In contrast to mobility shift ACE utilizing the electrophoretic mobility, in this approach, the peak areas are used. The apparent binding (stability, formation) constants are obtained by the Higuchi and Connors method from the linear segment of compound solubility diagrams in CD solutions. It was found that the apparent binding constants of the HP‐γ‐CD complexes of BIA and BOA decrease with increasing temperature. The binding constants of BOA complexes are slightly higher than those of BIA complexes; this can be explained by difference in the hydration degrees of carbonyl and hydroxyl groups. On the basis of the binding constants obtained and their temperature dependences (van't Hoff plot), the enthalpy as well as entropy changes and Gibbs free energies were calculated. It was found that the complexation was characterized by negative changes of enthalpy and entropy, that is, it was controlled by enthalpy changes. The results obtained can be used for the optimization of microcapsulation processes of BOA and BIA with the HP‐γ‐CD application in order to increase solubility and bioavailability of these compounds.