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61.
Ladislav Nebeský 《Journal of Graph Theory》1978,2(3):251-255
The following theorem is proved: Let G be a graph of even order. Assume that there exists a connected spanning subgraph F of G such that for every set U of four vertices in G, if the subgraph of F induced by U is a star, then the subgraph of G induced by U is complete. Then G has a 1-factor. The above theorem is derived from another sufficient condition for the existence of a 1-factor, which is also proved in this paper (Lemma 1). 相似文献
62.
The kinetics of dissolution of five fractions of commercial poly(vinyl chloride) in cyclohexanone was studied at temperatures from 20 to 70°C. Good agreement was observed between the experimental results and equations expressing the dependence of the induction periods and the rates of dissolution on temperature and molecular weight. It was found that the apparent activation energy for the swelling process lies in the range 9–14 kcal/mole and the apparent activation energy for the dissolution diffusion process in the range 8–12 kcal/mole. The apparent dependence of activation energies on number-average molecular weight indicates that the chain ends are more important in determining the dissolution rate than the centers of the polymer chains. 相似文献
63.
Ladislav Špaček 《Czechoslovak Journal of Physics》1957,7(6):714-721
Zusammenfassung
Auf Grund der Berechnung der Austauschenergie, der magnetostatischen und magnetoelastischen Energie und der Energie der Blochwände wird das bäumchenförmige Aussehen der oberflächlichen Abschlussbezirken an wenig gegenüber der Ebene (100)geneigten Ebenen erläutert. Aus dem Minimum der Gesamtenergie gehen dann, auch die Abmessungen dieser Bezirke in Abhängigkeit vom Neigungswinkel hervor. 相似文献
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Katerina Kotkova Helena Ticha Ladislav Tichy 《Journal of Raman spectroscopy : JRS》2008,39(9):1219-1226
Five (PbO)x(Bi2O3)0.2(B2O3)0.8−x glasses, where x = 0, 0.2, 0.3, 0.4 and 0.6, were prepared. The dilatometric glass transition temperature (Tg) was found in the region 470 (x = 0)≥ Tg ( °C) ≥ 347 (x = 0.6), and the density (ρ) varied within 4.57 (x = 0) ≤ ρ (g/cm3) ≤ 8.31 (x = 0.6). Raman spectra indicated the conversion of BO3 to BO4 entities for low x values but for x > 0.3, namely, for x → 0.6, back‐conversion occurred, most probably. From the measurements of the optical transmission on very thin bulk samples, the room temperature optical gap values (Eg) were determined to be in the range 4.03 (x = 0)≥ Eg (eV) ≥ 3.08 (x = 0.6). The temperature (T) dependence of the optical gap (Eg(T)) in the region 300 ≤ T(K) ≤ 600 was examined and approximated by a linear relationship of the form of Eg(T) = Eg(0)− γT, where γ × 10−4(eV/K) varied from 5.1 to 6.8. The non‐linear refractive index (n2) was estimated from the optical gap values and it was found to correspond to the n2 values calculated from the experimental third‐order non‐linear optical susceptibility taken from the literature. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
67.
Ladislav Koudelka Jaroslav Pospíšil Petr Mošner Lionel Montagne Laurent Delevoye 《Journal of Non》2008,354(2-9):129-133
Bulk glasses of the series (1 ? x)[0.5K2O–0.1B2O3–0.4P2O5]–xNb2O5 with x = 0–45.7 mol% Nb2O5 were prepared by slow cooling in air and investigated by Raman, 31P, and 11B MAS NMR spectroscopy. The incorporation of Nb2O5 into the parent borophosphate glass results in a substantial increase in the glass transition temperature and chemical durability of glasses. Raman spectra showed that Nb atoms form distorted NbO6 octahedra, which are isolated at low Nb2O5 content, whereas at higher Nb2O5 content they form clusters. 11B NMR spectra of the glasses revealed the interaction between Nb2O5 and BO4 tetrahedral units, which results in a partial transformation of tetrahedral BO4 units to trigonal BO3 units and the formation of mixed B(OP)4?n(ONb)n units. 相似文献
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Chitosan is industrially acquired by the alkaline N-deacetylation of chitin. Chitin belongs to the β-N-acetyl-glucosamine polymers, providing structure, contrary to α-polymers, which provide food and energy. Another β-polymer providing structure is hyaluronan. A lot of studies have been performed on chitosan to explore its industrial use. Since chitosan is biodegradable, non-toxic, bacteriostatic, and fungistatic, it has numerous applications in medicine. Hyaluronan, one of the major structural components of the extracellular matrix in vertebrate tissues, is broadly exploited in medicine as well. This review summarizes the main areas where these two biopolymers have an impact. The reviewed areas mostly cover most medical applications, along with non-medical applications, such as cosmetics. 相似文献
70.
3T3 and VH10 cells were subjected to oxidative damage by hydroxyl radicals generated from Cu(II) ions and ascorbate. The presence of reactive oxygen and nitrogen species in cells was determined using fluorescent dyes. MitoQ—a mitochondrially targeted antioxidant—was examined to prevent cell death and was compared with trolox as a reference standard serving as an antioxidant. MitoQ at lower concentrations (up to 500 nM) prevented damage of mitochondria and thereby increased viability of cells. However, at higher concentrations (over 500 nM) MitoQ decreased the viability of both strains of cells. The last observation indicates that the application of MitoQ should be evaluated also from the point of its cell-destructive potential. 相似文献