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241.
Dynamical behavior of a three species food chain model with Beddington–DeAngelis functional response
A three species food chain model with Beddington–DeAngelis functional response is investigated. The local stability analysis is carried out and global behavior is simulated numerically for a biologically feasible choice of parameters. The persistence conditions of a food chain model are established. The bifurcation diagrams are obtained for different parameters of the model after intensive numerical simulations. The results of simulations show that the model could exhibit chaotic dynamics for realistic and biologically feasible parametric values. Finally, the effect of immigration within prey species is investigated. It is observed that adding small amount of constant immigration to prey species stabilize the system. 相似文献
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243.
Izolda Segal Alla Zablotskaya Edmunds Lukevics Mikhail Maiorov Dmitry Zablotsky Elmars Blums Irina Shestakova Ilona Domracheva 《应用有机金属化学》2008,22(2):82-88
New original water‐soluble magnetic nanoparticles based on natural components, magnetite–oleic acid–biologically active silyl modified alkanolamine, were synthesized. Physico‐chemical characterization, i.e. magnetic properties, concentration of magnetite, size of iron oxide core, of the nanoparticles synthesized and the corresponding magnetic fluids obtained, was carried out. Magnetic fluids were screened for in vitro cytotoxicity concerning human fibrosarcoma (HT‐1080), mouse hepatoma (MG‐22A) monolayer tumour cell lines and normal mouse fibroblasts (NIH 3T3). They possess low or moderate cytotoxic effects, are non‐toxic, exhibit high NO‐induction ability and strongly change tumour cell morphology. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
244.
Shubina LK Makarieva TN Denisenko VA Dmitrenok AS Guzii AG Dmitrenok PS Stonik VA 《Natural product research》2006,20(13):1183-1186
A new diketosteroid, 5alpha-ergost-24(28)-ene-3,6-dione (1), has been isolated from the sponge Geodinella robusta. Its structure was determined by combined spectroscopic methods and chemical evidence. 相似文献
245.
We study local optima of combinatorial optimization problems. We show that a local search algorithm can be represented as a digraph and apply recent results for spanning forests of a diagraph. We establish a correspondence between the number of local optima and the algebraic multiplicities of eigenvalues of digraph laplacians. We apply our finding to the three-dimensional assignment problem. 相似文献
246.
Valentina A. Ol’shevskaya Arina N. Savchenko Elena G. Kononova Alla A. Ramonova Oleg V. Uvarov Valery N. Kalinin 《Journal of organometallic chemistry》2009,694(11):1632-7476
Various structural modifications of chlorins are aimed at optimization of biomedical characteristics of these plant-derived tetrapyrrolic compounds. In particular, conjugation with boron polyhedra improves the efficacy of chlorin e6 derivatives as antitumor photosensitizers. To obtain the compounds that may possess several clinically favorable characteristics, we synthesized a series of metal chlorin e6 conjugates with 1-carba-closo-dodecaborate anion that contain Pd(II), Sn(IV) or Zn(II) in the coordination sphere of the chlorin macrocycle. The compounds were synthesized by alkylation of amino group in chlorin e6 metal complexes with 1-trifluoromethanesulfonylmethyl-1-carba-closo-dodecaborate cesium. The water soluble Pd(II) complex of chlorin e6 13(1)-N-{2-[N-(1-carba-closo-dodecaboran-1-yl)methyl]aminoethyl}amide-15(2), 17(3)-dimethyl ester (compound 6) evoked low dark cytotoxicity; in striking contrast, 6 potently sensitized human tumor cells to illumination with monochromatic red light. Confocal microscopic studies demonstrated that photoactivation of 6 rapidly (within minutes) changed the patterns of intracellular drug distribution from diffuse cytoplasmic to clustered perinuclear. Co-localization experiments revealed that 6 associated with lysosomes in illuminated cells. These events were paralleled by alteration of mitochondrial shape, a decrease of mitochondrial transmembrane electric potential and the loss of plasma membrane impermeability for propidium iodide, the latter being a hallmark of cell necrosis. Similar mechanisms of cell photodamage were found for structurally close Pd(II) complex of chlorin with neutral carborane and for Sn(IV) chlorin conjugated with the anionic carborane. Thus, metal complexes of carboranylchlorins are efficient photosensitizers capable of triggering rapid necrosis. These compounds are promising for further development as multipotent agents in which each moiety, i.e., metal, the chlorin macrocycle and the boron substituent, as well as the entire complex, can be useful in cancer diagnostics and treatment. 相似文献
247.
Valentina D. Fokina Mikhail V. Gorev Alla G. Kocharova Evgenii I. Pogoreltsev Igor N. Flerov 《Solid State Sciences》2009,11(4):836-840
Calorimetric measurements performed in a wide temperature range on (NH4)3VO2F4 have shown the presence of four heat capacity anomalies at T1 = 438 K, T2 = 244 K, T3 = 210.2 K, T4 = 205.1 K associated with the first order phase transitions. In accordance with the permittivity behavior, the structural transformations are of nonferroelectric nature. Pressure dependence of the phase transition temperatures has been studied by DTA under pressure. The entropy of phase transitions is analyzed mainly in the framework of the orientational disordering of NH4+ and VO2F43? ions in a cubic phase. 相似文献
248.
249.
Roman Tkachov Volodymyr Senkovskyy Ulrich Oertel Alla Synytska Marta Horecha Anton Kiriy 《Macromolecular rapid communications》2010,31(24):2146-2150
A ‘grafting‐from’ approach to synthesize microparticle‐supported conjugated polyelectrolyte brushes is presented. Poly(3‐bromohexylthiophene) is selectively grown from monodisperse organosilica microparticles by surface‐initiated Kumada catalyst‐transfer polycondensation (SI‐KCTP) and then ionizable amino groups are introduced by a two‐step polymer analogous transformation. Optical properties of the resulting microparticle‐supported conjugated polyelectrolyte brushes were found to be dependent on the surrounding chemical environment and thus the particles are promising materials for sensor applications.
250.
Ainhoa Tolentino Antxon Martínez de Ilarduya Abdelilah Alla Sebastián Muñoz-Guerra 《Macromolecular Symposia》2010,296(1):265-271
Comb-like ionic complexes were prepared from polyuronic acids (pectinic and alginic acids) and alkyltrimethylammonium surfactants bearing linear alkyl chains with 18, 20 and 22 carbon atoms. In the condensed state, these complexes were able to self-assemble in ordered structures which were thermally stable up to ∼200 °C. The complexes were analysed by DSC and WAXS/SAXS and compared to their analogous made from poly(γ-glutamic acid). They all adopt a biphasic layered structure in which the main chain and the alkyl side chain alternate with a nanometric periodicity. Alkyl side chains were partially crystallized in these complexes and they show reversible melting at temperatures within the 60-80 °C range depending on the length of the polymethylene segment. 相似文献