Let G be a graph of order n and λ(G) the spectral radius of its adjacency matrix. We extend some recent results on sufficient conditions for Hamiltonian paths and cycles in G. One of the main results of the paper is the following theorem Let k \geqslant 2,
n \geqslant k^{3} + k + 4, and let G be a graph of order n, with minimum degree δ(G) \geqslant k. If \lambda \left( G \right) \geqslant n - k - 1, then G has a Hamiltonian cycle, unless G=K_{1}\vee (K_{n-k-1}+K_{k}) or G=K_{k}\vee
(K_{n-2k}+\bar{K}_{k})., Vladimir Nikiforov., and Obsahuje seznam literatury
Effects of heat pre-treatment (60 oC for 15 min) on the chlorophyll (Chl) bleaching and excitation energy transfer in thylakoids, isolated from the cucumber cotyledons, were studied by anaiysis of the overlapping absorption and the low temperature fluorescence spectra. The Chl forms C678 and C672 appeared to be the most heat-susceptible components, whereas C684 was found to be very heat-stable. Subsequent exposure of the thylakoid suspension to a high photon flux density (ca. 3 500 pmol m‘2 s'i) caused further bleaching of all the tested forms: ca. 8-20 or 2-5 % of chlorophyll was degraded duríng the initial (0-4 min) or later (4-10 min) period of irradiation, respectively. The heat pre-treatment of thylakoids led to the decrease of the 472 and 486 nm bands in Chl fluorescence excitation spectrum and the 730 nm band in the Chl fluorescence emission spectrum. The F730/F685 ratio decreased by ca. 4-, 3- or 2-fold when excited with the wavelengths of 437, 742 or 486 nm, respectively. These ratios increased by 60-90 % after 10 min irradiation with high photon flnx density.
Pathway of protochlorophyilide (Pchlide) biosynthesis, properties of Pchlide in vitro and in vivo, its in vivo localization, structure, localization and properties of the enzyme NADPH-Pchlide oxidoreductase, and phototransfonnation and dark reduction of Pchlide to chlorophyllide are reviewed.
Room temperature absorbance and 77 K fluorescence measurements were ušed in order to identity Pchlide and Chlide spectral forms involved in protochlorophyllide photoreductíon in greening leaves of barley. Pchlide55o (the subscript refers to the in vivo absorbance maximum of the pigment) is the main photoactíve Pchlide throughout the first 8 h of greening. Its photoreductíon triggers a succession of Chl(ide) spectral forms that are identícal to those normally found after photoreductíon in uitírradiated leaves. Afler an actinic radiation pulse, Chlide5g4 appears within 2 s from an intermediate at shorter wavelength and is transformed to Chlide572 in less than 2 min. The time-scale of the shifts is remarkably shorter than in unirradiated leaves, which is consistent with the acceleratíon of Chl accumulatíon during greening. Pchlide63o and Pchlide64o act as precursors of Pchlide65o during its regeneration, which exhibits a marked inhibition at temperatures above 30 °C.
The properties of chlorophyll (Chl) a and pheophytin (Pheo) a embedded in the rigid anhydrous polymer fihns, polyvinyl alcohol (PVA) and nitrocellulose (NC) are reviewed. The aggregation capability of these pigments in two matrices is characterized by absorption, fluorescence, excitation spectra combined with fluorescence lifetime and time-resolved anisotropy. The dimer creation ability for Chl a and Pheo a is strongly affected by the polymer systém ušed for investigation. The Chl a and Pheo a ability to aggregate in polymer matrices is compared. We háve been looking for a good systém suitable for the study of properties of monomeric forms when embedded in the rigid matrix on the one hand, and for the study of energy transfer between different forms of Chl molecules on the other one. Chl a, when embedded in an anhydrous PVA matrix, is in a very stable monomeric form while Pheo a molecules in this film tend to aggregate and in the NC film they exist in the monomeric form. Thus the PVA systém can be ušed as a model systém for investigation of the properties of and processes between both dimeric and monomeric structures. The NC film, however, can be ušed as a rigid matrix when only the existence of monomeric forms of the pigments is required.
Tématem článku je experimentální výzkum spektrálních vlastností turbulence ve slunečním větru v oblasti přechodu mezi magnetohydrodynamickým (MHD) a kinetickým režimem magnetizovaného plazmatu. Výzkum je založen na měření parametrů plazmatu s vysokým časovým rozlišením, kterého bylo dosaženo přístrojem BMSW (Bright Monitor of Solar Wind) navrženým a vyvinutým na Katedře fyziky povrchů a plazmatu MFF UK v posledních letech. Získané výsledky jsou aplikovatelné nejen na variace meziplanetárního nebo mezihvězdného plazmatu, ale i na plazma ve fúzních systémech., This paper deals with experimental investigations of the spectral properties of solar wind turbulence during transition from magnetohydrodynamic (MHD) to kinetic regimes of a magnetized plasma. The study is based on the measurements of solar wind parameters with very high time resolution, which was achieved using the BMSW instrument designed and developed at the Department of Surface and Plasma Sciences of Faculty of Mathematics and Physics, Charles University in Prague. The results of these investigations can be applied not only for astrophysical plasmas but also for plasmas in fusion systems., Jana Šafránková, Zdeněk Němeček, František Němec, Lubomír Přech., and Obsahuje bibliografii
Předkládáme stručnou informaci o využití polarizačních vlastností světla ve spektroskopické elipsometrii. Ukazujeme příklady aparatur a diskutujeme ilustrativní spektra. Vybíráme několik ukázek aplikací a současných trendů., We provide brief information on the use of light polarisation in spectroscopic ellipsometry. Examples of experimental setups are presented and illustrative spectra are discussed. We also select a few topics in applications and current trends., Josef Humlíček., and Obsahuje seznam literatury
Historie spektroskopie laserem buzeného plazmatu se začíná psát již rokem 1962, tedy zanedlouho po zkonstruování prvního laseru. V tomto roce byla tato technika atomové emisní spektrometrie s novým typem buzení poprvé popsána. Rozvoji ovšem bránila nedostupnost vysoce výkonných pulsních laserů, takže praktické práce se objevují až o více než dvacet let později. Od té doby počet aplikací i publikací v odborných časopisech neustále roste, což ukazuje, že se jedná o metodu velice populární a perspektivní., Karel Novotný, Jozef Kaiser, Aleš Hrdlička, Radomír Malina, Tomáš Vémola, David Prochazka, Jan Novotný, Viktor Kanický., and Obsahuje bibliografii
Pomocí infračervené spektrometrie s Fourierovou transformací (FTIR), hmotností detekce v proudové trubici s vybranými ionty (SIFT-MS) a plynové chromatografie ve spojení s hmotností spektrometrií (GC-MS) bylo analyzováno složení cigaretového kouře, kouře z vodní dýmky a doutníku. Bylo kvalitativně porovnáno zastoupení jednotlivých komponent v závislosti na typu vzorku. Jsou diskutovány možnosti použitých analytických metod. Přehled konkrétních látek je doplněn fakty o jejich původu a škodlivém účinku., Various advanced spectroscopy techniques have been used for qualitative analysis and comparison of cigarette, cigar and water pipe smoke compositions. Additionally, a potential of these analytical methods is discussed with respect to such an analytical task. The list of identified compounds is presented together with some facts about their origin and toxicity., Vojtěch Pazdera, Michal Fousek, Martin Ferus, Kseniya Dryahina, Patrik Španěl, Violetta Shestivska, Svatopluk Civiš., and Obsahuje bibliografii