The cultivation of the bacterium Acetobacter xylinus AX 5 was carried out in the common Hestrin-Schramm medium containing D -glucose as C-source and citric acid as buffer component. HPLC studies proved to be convenient methods to investigate the stability and interactions of these constituents in the starting culture liquid. Within the initial sterilization step and limited by the citric acid, up to 6% of the D -glucose was partially isomerized to D-fructose and degraded to dark-yellow products. In static culture, A. xylinus AX 5 produces cellulose extracellularly on the surface of this medium. Solid-state NMR spectroscopy represents a suitable analytical method to characterize the supramolecular structure of the bacterial cellulose in never-dried, air-dried, and freeze-dried states. It could be demonstrated that the drying process reduces the degree of crystallinity in the range of about 12% without changes in the Iα/β ratio of these cellulose modifications. 相似文献
Summary: A modified random phase approximation method with a cumulant expansion for the semi‐flexible structure factor of diblock copolymers was exercised to describe the phase separation behavior of semi‐flexible and polydisperse diblock copolymers. Scattering curves and spinodal diagrams were calculated applying monomer specific input parameters. The influence of polydispersity was included applying basic concepts of mathematical statistics utilizing several probability density distributions in the case of the two single blocks. In contrast to semi‐flexibility, the main effect of polydispersity was found to shift the spinodal up, thus to enlarge the range of existence of the homogeneous phase.
Twofold Schultz‐Zimm distribution of diblock copolymers. 相似文献
We consider 4-dimensional flexible projective planes with the following properties: The collineation group is a 6-dimensional solvable Lie group which fixes some flag ∞ ∈ W. Furthermore, the collineation group has a 1-dimensional orbit both on W and on the pencil of lines through {∞}. We show that there are three different families of planes with these properties. 相似文献
A dynamic model for the design of multi-section semiconductor lasers is developed based on the Transmission Line Method. The different building blocks of this model are presented and the model is evaluated for a tunable two-section laser device. 相似文献
The superior association of the inherent good mechanical and electrical properties makes carbon nanotubes (CNT) exceptionally interesting for the production of composite fibers of thermoplastic polymers with CNT. Alignment of the CNT in the polymer fiber is important for improved mechanical properties. Especially the production of fibers makes it necessary to get a controlled orientation and/or alignment of the CNT. We applied transmission electron microscopy (TEM) and polarized Raman microscopy to quantify multiwalled carbon nanotubes (MWNT) orientation, alignment and crystallinity in polycarbonate (PC). The evaluation of the Raman measurements provided an improved alignment orientation of the MWNT in the fibers with increasing take-up velocity during melt spinning and that the crystal structure of the MWNT is not changed through melt spinning. 相似文献
Raman spectroscopy, which does not require a time‐consuming sample preparation, is described as an analytical tool for the high‐throughput characterization of polyethylenes. The content of comonomer and the amount of methyl groups per 1 000 carbon atoms of polyethylenes can be predicted from Raman spectra using multivariate data analysis. In addition, macroscopic properties, such as density and elastic modulus as well as yield stress, can be derived from Raman spectra.
Raman spectra of selected metallocene‐catalyzed polyethylenes of different comonomer content. 相似文献