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41.
Nadia Mazza 《Journal of Pure and Applied Algebra》2007,209(2):311-323
The group of endotrivial modules has recently been determined for a finite group having a normal Sylow p-subgroup. In this paper, we give and compare three different presentations of a torsion-free subgroup of maximal rank of the group of endotrivial modules. Finally, we illustrate the constructions in an example. 相似文献
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Summary Samples of FePO4 and (Al0.67Fe0.33)PO4 have been investigated by M?ssbauer spectroscopy. The data obtained on quadruple splittings are in agreement with neutron
scattering and XRD data on (Al, Fe)O4 tetrahedra structures. 相似文献
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45.
The X-ray crystal structure analysis of the Caesium salt of Chlorothricolide methylester, derived from the aglycone of the antibiotic chlorothricin, is described. 相似文献
46.
Anthocyanins are the largest group of water-soluble pigments in the plant kingdom. They are responsible for most of the red, blue, and purple colors of fruits, vegetables, flowers, and other plant tissues or products. The analysis of anthocyanins is complex as a result of their ability to undergo structural transformations and complexation reactions. In addition, they are difficult to measure independently of other flavonoids, as they have similar structural and reactivity characteristics. Anthocyanins are generally extracted with weakly acidified alcohol-based solvents, followed by concentration (under vacuum), and purification of the pigments. Paper and/or thin-layer chromatography and UV-Vis spectroscopy have traditionally been used for the identification of anthocyanins. Capillary zone electrophoresis, a hybrid of chromatography and electrophoresis, is gaining popularity for the analysis of anthocyanins; however, liquid chromatography (LC) has become the standard method for identification and separation in most laboratories and may be used for both preparative and quantitative analysis. LC with mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy are possibly the most powerful methods for the structural elucidation of anthocyanins available, to date. At present, the most satisfactory method for mixture analysis is the multistep method of separation, isolation, and quantification by LC with peak identification by MS and high-field NMR. 相似文献
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A new device for measuring the rheological properties of soft biological tissues is presented. The mechanical response is characterized for harmonic shear deformations at high frequencies (up to 10 kHz) and small strains (up to 0.2%). Experiments are performed using a cylindrical rod excited to torsional resonance. One extremity of the rod is in contact with the soft tissue and adherence is ensured by vacuum clamping. The damping characteristics and the resonance frequency of the vibrating system are inferred from the control variables of a phase stabilization loop. Due to the contact with the soft tissue, and depending on the rheological properties of the tissue, changes occur in the Q-factor and in the resonance frequency of the system. The shear modulus of the soft tissue is determined from the experimental results with an analytical model. The reliability of the proposed technique is evaluated through repeatability tests and comparative measurements with synthetic materials. The results of measurements on bovine organs demonstrate the suitability of the experimental procedure for the characterization of biological tissues and provide some insight in their rheological properties at frequencies in the range 1–10 kHz. 相似文献
50.
In this paper we describe a new method for measuring damping in flexural vibration of filamentous matter, such as polymeric
or metallic fibers. This method enables us to measure the damping characteristics of very thin fibers (down to lateral dimensions
of a few micrometers). The fiber sample is clamped at one extremity and excited in the flexural vibration mode of a cantilever
beam configuration, using a piezoelectric actuator. While the fiber sample vibrates around a flexural eigenfrequency, structural
damping is determined from the measurement of the curve of phase difference between excitation and motion. This technique
does not require the amplitude of the fiber motion to be determined. The phase curve is inferred from the periodic disturbance
occurring when the fiber acts as a shutter for a light beam. This method can be applied to fibers of arbitrary shape and material.
Examples are shown of measurements with polymer and metallic fibers. Flexural damping is evaluated at atmospheric pressure
and in vacuum. The technique is validated by a comparison with polypropylene damping measurements from standard dynamic mechanical
thermal analysis techniques. 相似文献