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241.
Zusammenfassung Mittels Röntgenweitwinkelstreuung wurden Gitterkonstanten, Kristallanteil, Größe der Mikroparakristalle und Gitterstörungen im Temperaturbereich von 20°C bis 106°C an LDPE gemessen. Die Kristalldichte
c
ändert sich stufenförmig von 0,998 · 103 kg m–3 bis 0,952 · 103 kg m–3.Oberhalb 90°C sind Mikroparakristalle mit besonders großer Ausdehnung in b-Achsen-Richtung stabil, bei tieferen Temperaturen existieren zusätzlich Mikroparakristalle mit Wachstumsrichtung senkrecht zu den 110-Ebenen. Diese beiden Kristallarten unterscheiden sich auch stark in den Gitterstörungen. Die Abmessungen der Mikroparakristalle beiT > 90°C werden in einem Strukturmodell diskutiert, das zu einer Schrägstellung der Ketten mit einem Winkel von etwa 45° zur Lamellenoberfläche führt.Herrn Prof. Dr. F. H. Müller gewidmet. 相似文献
242.
PTFE shows in the whole temperature range investigated a triclinic crystal structure with cell parametersa=0.952 nm,b=0.559 nm,c=1.706 nm,=87.9°, = 90.0° and=91.8°. The temperature dependence ofa andb-axis is linear, thec-axis shows a change in thermal expansion at 150 K. The inherent strain is small. The crystallite sizes are measured, paracrystalline distortions are absent.The bipolymers show only an ordered arrangement in lateral direction under maintenance of the helical structure. The lateral arrangement is very distorted and the range of order is aboutD
L
10 nm. 相似文献
243.
Diazohydroxide is a new antitumor agent being considered for clinical trial. A sensitive and specific assay for diazohydroxide in physiological media, plasma and blood has been developed based on conversion of diazohydroxide to 2-chloropyrazine in the presence of strong hydrochloric acid. The 2-chloropyrazine is extracted into the ethyl acetate and separated by capillary gas chromatography with nitrogen-phosphorus detection. Using 0.2 ml plasma the assay was linear up to 100 micrograms/ml diazohydroxide and had a lower limit of detectability for diazohydroxide of 50 ng/ml. The coefficient of variation of the assay at 1 micrograms/ml was 6.7%. Breakdown of diazohydroxide was rapid under mild acid conditions but slower under alkaline conditions,. The half-life of diazohydroxide in 0.1 M sodium phosphate buffer, pH 6.0, at room temperature was 5 min and at pH 8.0, 480 min. Breakdown of diazohydroxide in plasma was biphasic. In fresh mouse plasma diazohydroxide had a terminal half-life at 37 degrees C of 72 min while in fresh human plasma the terminal half-life was 23 min and in fresh blood 21 min. Diazohydroxide accumulated in red blood cells at 37 degrees C to a concentration 68% above the concentration in plasma. Diazohydroxide was 49% bound to human plasma proteins at room temperature. 相似文献
244.
Eric Ohleyer Charles R. Wilke Harvey W. Blanch 《Applied biochemistry and biotechnology》1985,11(6):457-463
Growth and lactic acid production ofLactobacillus delbreuckii were compared using glucose and lactose as carbon sources. A continuous-flow stirred-tank fermenter was coupled with a cross-flow
filtration unit to permit operation at high-cell concentrations. At steady state, yeast extract requirements for lactic-acid
production were lower when glucose was used as a substrate than with lactose fermentation. Once steady state was obtained,
with glucose feed, it was possible to lower the yeast extract concentration without affecting biomass concentration and lactic
acid production. The lacticacid concentration that inhibited cell growth and lactic acid production was found to depend on
the choice of a carbon substrate. 相似文献
245.
On the Additivity of Molecular Fragment Dipole Moments of 5‐Substituted Indole Derivatives
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Dr. Josefin Wilke Martin Wilke Dr. Christian Brand Prof. Dr. W. Leo Meerts Prof. Dr. Michael Schmitt 《Chemphyschem》2016,17(17):2736-2743
The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, particularly for electronically excited states. Herein, we find rules for a number of indole derivatives by using rotationally resolved electronic Stark spectroscopy and ab initio calculations. Based on a natural‐bond‐orbital analysis, we discuss whether the vector additivity rule can be applied in a given electronic state. From a comparison of the experimental data with ab initio calculations, we deduced that the additivity model does not apply when the flow of electron density from the substituent is opposed to that inside the chromophore. 相似文献
246.
The hollow prisms are photonic lab-on-a-chip systems with a high degree of monolithic integration that consist of micro-optical (prism and microlenses), microfluidics and structural elements (self-alignment systems) obtained in PDMS by soft lithography. Despite their interesting optical and sensing properties, their working principle, based on the absorption of the working wavelength (lambda=460 nm) by the different substances that can fill the hollow prisms, always involves at least one reflection at the walls of the hollow prism. Due to the low refractive index contrast between the PDMS and the phosphate buffer that fills the hollow prism, the reflectivity at this interface is very low, requiring long integration times. In this paper, we tackle this severe limitation with the definition of an air mirror, which solves the low reflectivity problems: with the appropriate design, the working wavelength matches with the condition of total internal reflection (TIR) only at the air mirror and is reflected back to the hollow prism. Experimental results have shown that the use of air mirrors enhances the sensing properties of the hollow prisms due to several reasons: first, the integration time is strongly reduced, from 2.5s to 80 ms. Second, although the integration time is reduced, the signal-to-noise ratio (SNR) is increased from 12 dB to 19.5 dB. Third, an important improvement of the LOD (with values close to 1 microM and 400 nM for fluorescein and methyl orange diluted in phosphate buffer, respectively) has been experimentally measured. Finally, as compared to the system without the air mirror, the sensitivity is increased by a factor between 1.32 and 2.49 (depending on the geometry used), respectively when this simple, however effective element is included into the system. 相似文献
247.
In 1995, Garcia and Stichtenoth explicitly constructed a tower of projective curves over a finite field with q2 elements which reaches the Drinfeld–Vlăduţ bound. These curves are given recursively by covers of Artin–Schreier type where the curve on the nth level of the tower has a natural model in . In this paper, for q an even prime power, we use point projections in order to embed these curves into projective space of the lowest possible dimension. 相似文献
248.
J. Wilke V. T. Bublik V. B. Osvenskii A. N. Popkov A. G. Braginskaya P. P. Kolchina 《Crystal Research and Technology》1983,18(6):787-792
Precision lattice constant and density measurements held on gallium antimonide single crystals grown from stoichiometric melts showed that doping of such crystals with Te lead to the intensification of Ga-supersaturated solid solution decomposition process with initial Frenkel defect (Gai + VGa) production. It is supposed that Tesb — simple donors form complexes with VGa which are believed to be acceptors. Doping of GaSb with Te up to the levels above 2 · 1018 cm−3 leads to partial decomposition of GaSb(Te) solid solution supersaturated with Te. 相似文献
249.
Ulrich Lode Till Pomper Andreas Karl Gebhard von Krosigk Sabine Cunis Wolfgang Wilke Rainer Gehrke 《Macromolecular rapid communications》1998,19(1):35-39
The development of crazes in polycarbonate is investigated with the method of ultra small angle X-ray scattering of synchrotron radiation. Measurements at T = 130°C are discussed. The two-dimensional scattering patterns are analysed by means of a simple fibrillar model of the crazes. The geometrical parameters of the crazes as a function of the macroscopic draw ratio λd are determined using a curve-fitting procedure. The craze fibril volume fraction νf shows a complex dependence on λd. 相似文献
250.
Alexander Kremsmair Henrik R. Wilke Matthias M. Simon Quirin Schmidt Konstantin Karaghiosoff Paul Knochel 《Chemical science》2021,13(1):44
A general preparation of enantiomerically and diastereomerically enriched secondary alkylmagnesium reagents was reported as well as their use for performing highly stereoselective transition-metal free electrophilic aminations leading to α-chiral amines in up to 97% ee. Thus, the reaction of t-BuLi (2.2 equiv.) with a mixture of chiral secondary alkyl iodides and the commercially available magnesium reagent Me3SiCH2MgCl in a 2 : 1 mixture of pentane and diethyl ether at up to −50 °C provided optically enriched secondary mixed alkylmagnesium species of the type alkyl(Me)CHMgCH2SiMe3 with high retention of configuration (up to 99% ee). The resulting enantiomerically enriched dialkylmagnesium reagents were trapped with electrophiles such as non-enolizable ketones, aldehydes, acid chlorides, isocyanates, chlorophosphines and O-benzoyl hydroxylamines providing α-chiral tertiary alcohols, ketones, amides, phosphines and tertiary amines in up to 89% yield (over three reaction steps) and up to 99% ee.We report a general method for the preparation of enantiomerically enriched secondary alkylmagnesium reagents, which undergo highly stereoselective transition-metal free electrophilic aminations, leading to α-chiral amines in up to 97% ee. 相似文献