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1.
Danuta Slawinska Janusz Slawinski Krzysztof Polewski Wojciech Pukacki 《Photochemistry and photobiology》1979,30(1):71-80
Abstract— Peroxidation of tannins with alkaline H2 O2 is accompanied by weak chemiluminescence in the spectral region 480–800 nm. o-Di and tri-hydroxy groups of polyphenols undergo oxidation by a free-radical mechanism and a green intermediate anion-radical with absorption Δmax = 600 nm is formed. The radical mechanism is supported by the low activation energy 14–20 kJ/mol and the quenching effect of radical scavengers. The reaction of the green intermediate with peroxy anions is the chemiluminescence rate limiting step. In the presence of a-hydroxy-methylperoxide formed from H2 O2 and formaldehyde, the alkaline peroxidation of tannins is accompanied by strong red luminescence (420–800 nm). The base catalyzed decomposition of peroxides gives only a weak red emission (460–800 nm). Light intensity is enhanced in D2 O by a factor 6.5. Quenchers of O2 (1 Δg ) and 1,3-di-phenylisobenzofurane diminish light intensity in non-aqueous solutions. The data suggest 1 O2 participation in the observed chemiluminescence. Thermo-chemical calculations give —ΔH values from 250–1000 kJ/mol for one elementary reaction step which limits the mechanism of chemi-enereization. Chemiexcitation of tannins is relevant to biochemical mechanisms of aerobic degradation of aromatic compounds, energy utilization as well as to defense and resistance processes in plants. 相似文献
2.
Abstract— Aqueous basic solutions, pH 9.0 of humic acids and melanin-like, synthetic polymers, obtained with adrenochrome, hydroquinone and purpurogallin, were illuminated with visible light under N2 or O2 atmospheres. It has been found that light enhances a singlet electron-paramagnetic-resonance (EPR) signal of polymers both under N2 and O2 , and induces ultra-weak luminescence in the presence of O2 . Degradative oxidation of polymers, accelerated by light, leads to a decrease of EPR signal intensity and generates weak chemiluminescence. 相似文献
3.
We present a method to identify the symmetry class of an elasticity tensor whose components are given with respect to an arbitrarily
oriented coordinate system. The method is based on the concept of distance in the space of tensors, and relies on the monoclinic
or transversely isotropic distance function. Since the orientation of a monoclinic or transversely isotropic tensor depends
on two Euler angles only, we can plot the corresponding distance functions on the unit sphere in ℝ3 and observe the symmetry pattern of the plot. In particular, the monoclinic distance function vanishes in the directions
of the normals of the mirror planes, so the number and location of the zeros allows us to identify the symmetry class and
the orientation of the natural coordinate system. Observing the approximate locations of the zeros on the plot, we can constrain
a numerical algorithm for finding the exact orientation of the natural coordinate system. 相似文献
4.
The investigation of quinoxaline-2,3-dithiol as a gravimetric reagent for nickel is described. A derivative of the dithiol, S-2-(3-mercaptoquinoxalinyl)thiuronium chloride is used as a generating agent in a PFHS method because of its relative stability and solubility in aqueous ethanol. Nickel, 2.5–25.0 μg, can be precipitated at pH 2–3 as (C8H5N2S2)2Ni. After filtration the precipitates are washed first with aqueous ethanol to remove traces of absorbed reagent and then with benzene to remove a small amount of decomposition product of the reagent, the characterization of which is described. The precipitates are stable and can be dried in air at 110–120°. Errors of less than 0.15 % are obtained in the analysis of solutions containing 25 mg of nickel. The selectivity of the reagent is discussed and some suggestions are made for masking the interference of other elements. 相似文献
5.
Len Bos Tomasz Danek Michael A. Slawinski Theodore Stanoev 《Journal of Elasticity》2018,132(1):141-159
In this paper, we examine the applicability of the approximation, \(\overline{f g}\approx \overline{f}\,\overline{g}\), within Backus (J. Geophys. Res. 67(11):4427–4440, 1962) averaging. This approximation is a crucial step in the method proposed by Backus (J. Geophys. Res. 67(11):4427–4440, 1962), which is widely used in studying wave propagation in layered Hookean solids. According to this approximation, the average of the product of a rapidly varying function and a slowly varying function is approximately equal to the product of the averages of those two functions.Considering that the rapidly varying function represents the mechanical properties of layers, we express it as a step function. The slowly varying function is continuous, since it represents the components of the stress or strain tensors. In this paper, beyond the upper bound of the error for that approximation, which is formulated by Bos et al. (J. Elast. 127:179–196, 2017), we provide a statistical analysis of the approximation by allowing the function values to be sampled from general distributions.Even though, according to the upper bound, Backus (J. Geophys. Res. 67(11):4427–4440, 1962) averaging might not appear as a viable approach, we show that—for cases representative of physical scenarios modelled by such an averaging—the approximation is typically quite good. We identify the cases for which there can be a deterioration in its efficacy.In particular, we examine a special case for which the approximation results in spurious values. However, such a case—though physically realizable—is not likely to appear in seismology, where Backus (J. Geophys. Res. 67(11):4427–4440, 1962) averaging is commonly used. Yet, such values might occur in material sciences, in general, for which Backus (J. Geophys. Res. 67(11):4427–4440, 1962) averaging is also considered. 相似文献
6.
We formulate coordinate-free conditions for identifying all the symmetry classes of the elasticity tensor and prove that these conditions are both necessary and sufficient. Also, we construct a natural coordinate system of this tensor without the a priory knowledge of the symmetry axes. 相似文献
7.
Material symmetries of elasticity tensors 总被引:1,自引:0,他引:1
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9.
Janusz Slawinski Wlodzimierz Puzyna Danuta Slawinska 《Photochemistry and photobiology》1978,28(1):75-81
Abstract— Photo-irradiation of aqueous basic solutions of soil humic acids and synthetic melanins with UV and visible light (Λ > 320 nm) under oxygen or nitrogen atmospheres generates electronic exicted states and radicals. These processes give rise to a long-lived chemiluminescence with emission maxima at 480–500, 570 and 615–650 nm, as well as a paramagnetic resonance (EPR) signal with g-value at 2.006 and ΔH~ 3Gs. Chemiluminescence intensity and EPR signals follow multistep kinetics. An increase of the ratio of OD at 260/400 nm and 400/600 nm and a decrease of amplitude of an EPR signal after prolonged photo-irradiation were observed. Long irradiation also causes a decrease of fluorescence intensity bands with maxima at 535 nm and 495 nm (Λex 480 and 400 nm, respectively), and an increase of the short wavelength band with a maximum at 450 nm (Λex 260 nm). The data indicate that a complex chain of reactions initiated by reactive species leads to the degradation of the aromatic core of the polymers. Oxygen efficiently enhances the chemiluminescence intensity and the rate of photodegradation. The mechanism of photodegradative oxidation and chemiluminescence probably involves an energy transfer process and singlet oxygen formation. The possibility of its occurrence in nature and its significance are discussed. 相似文献
10.
The construction of a simple thermometric titrator is described. The titrator has been used in a direct injection enthalpimetric procedure to determine nickel and selenium with precisions of 1.0 and 0.3% respectively at a concentration of 10(-2M). The titrant was quinoxaline-2,3-dithiol (disodium salt). The thermometric procedure is shown to be successful in the determination of selenium in contrast to an absorptiometric method using the same reagent. 相似文献