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71.
In this paper we examine dynamical modes resulting from diffusion-like interaction of two model biochemical cells. Kinetics in each of the cells is given by the ICC model of calcium ions in the cytosol. Constraints for one of the cells are set so that it is excitable. One of the constraints in the other cell - a fraction of activated cell surface receptors-is varied so that the dynamics in the cell is either excitable or oscillatory or a stable focus. The cells are interacting via mass transfer and dynamics of the coupled system are studied as two parameters are varied-the fraction of activated receptors and the coupling strength. We find that (i) the excitator-excitator interaction does not lead to oscillatory patterns, (ii) the oscillator-excitator interaction leads to alternating phase-locked periodic and quasiperiodic regimes, well known from oscillator-oscillator interactions; torus breaking bifurcation generates chaos when the coupling strength is in an intermediate range, (iii) the focus-excitator interaction generates compound oscillations arranged as period adding sequences alternating with chaotic windows; the transition to chaos is accompanied by period doublings and folding of branches of periodic orbits and is associated with a Shilnikov homoclinic orbit. The nature of spontaneous self-organized oscillations in the focus-excitator range is discussed. (c) 1999 American Institute of Physics. 相似文献
72.
A mathematical modelling approach for open-tubular capillary electrochromatography is presented. The spatially one-dimensional model takes into account (i) a coupling of (non)linear adsorption of positively or negatively charged analyte molecules (at a negatively charged capillary inner surface) with the equilibrium electrokinetics at this solid-liquid interface, (ii) mobile phase transport by electroosmosis and pressure-driven flow, as well as (iii) transport of species by electrophoresis and molecular diffusion. Under these conditions the local zeta-potential and electroosmotic mobility become a function of the concentration of the charged analyte. The resulting inhomogeneity of electroosmotic flow through the capillary produces a compensating pore pressure as requirement for incompressible mobile phase flow (i.e., for constant volumetric flow along the capillary). The results of the simulations are discussed in view of the surface-to-volume ratio of the capillary lumen, the analyte concentration (in combination with a Langmuir isotherm for the adsorption process), and buffer effects. 相似文献
73.
Nikolic S Trinajstic N Tolic IM 《Journal of chemical information and computer sciences》2000,40(4):920-926
Several currently used measures of the complexity of molecules, such as, for example, those by Bertz and Randic or those based on the number of spanning trees, are briefly reviewed. We also proposed as complexity measures the sum of vertex-weights and the sum of edge-weights and their variants related to partition of vertex-weights and edge-weights into classes by their numerical values. The vertex-weights considered are the squares of the vertex-degrees, and the edge-weights are products of vertex-degrees making up the edges. Comparison is made between considered complexity measures for selected molecular graphs. All considered indices increase with increasing size and cyclicity and most with increasing branching. However, they differ regarding the influence of symmetry. 相似文献
74.
Ezddin Ali Farag Hutli Milos S. Nedeljkovic Nenad A. Radovic 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(5):329-341
Experimental setup with a submerged cavitating jet has been used for the study of influences of material, exposure time and
working fluid temperature on the erosion process. Each of the parameters has been varied separately, and the results of erosion
are analyzed in detail. Additionally, comparison of experiments with nitrated and non-nitrated material has been made in order
to study the enhancement (mostly reflected as the prolonged incubation time) of erosion resistance achieved by nitrating the
specimen surface. 相似文献
75.
Vráblíková H Barták M Wonisch A 《Journal of photochemistry and photobiology. B, Biology》2005,79(1):35-41
Hydrated thalli of two lichen species--Umbilicaria antarctica and Lasallia pustulata--were exposed to high light (1800 micromol m-2s-1) for 30 min. High light exposure led to a decrease of total glutathione in both species, while de-epoxidation state of xanthophyll cycle pigments and non-photochemical quenching increased. In the subsequent recovery, the values of de-epoxidation state of xanthophyll cycle pigments decreased towards initial values. Glutathione (GSH) was resynthetised slowly. In conclusion, zeaxanthin-related protection is probably more involved than GSH-related protection in short-term response to high light stress in U. antarctica and L. pustulata. Faster recovery from photoinhibition in L. pustulata than U. antarctica is mainly due to faster conversion of zeaxanthin to violaxanthin and larger GSH pool of former species. 相似文献
76.
Design and optimization of one-dimensional photonic crystals for thermophotovoltaic applications 总被引:1,自引:0,他引:1
We explore the optical characteristics and fundamental limitations of one-dimensional (1D) photonic crystal (PhC) structures as means for improving the efficiency and power density of thermophotovoltaic (TPV) and microthermophotovoltaic (MTPV) devices. We analyze the optical performance of 1D PhCs with respect to photovoltaic diode efficiency and power density. Furthermore, we present an optimized dielectric stack design that exhibits a significantly wider stop band and yields better TPV system efficiency than a simple quarter-wave stack. The analysis is done for both TPV and MTPV devices by use of a unified modeling framework. 相似文献
77.
Latta P Gruwel ML Edie E Srámek M Tomanek B 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,170(2):697-183
Acoustic noise produced during single point imaging (SPI) experiments was modulated by changes in the spatial encoding gradients. Parameters of both linear and sine-shaped gradient ramps were modified to minimize the acoustic noise levels. Acoustic noise measurements during SPI were measured on three different gradient systems and revealed that for small gradient-bore systems a considerable acoustic noise reduction of more than 20 dB can easily be achieved. SPI in conjunction with an optimized gradient waveform can be a superb alternative to the previously introduced single point ramped imaging with T(1) enhancement (SPRITE) method when sound levels and overheating of gradients are a concern. 相似文献
78.
Antimutagenic constituents from the thorns of Gleditsia sinensis 总被引:6,自引:0,他引:6
Lim JC Park JH Budesinsky M Kasal A Han YH Koo BS Lee SI Lee DU 《Chemical & pharmaceutical bulletin》2005,53(5):561-564
Antimutagenic activity-guided fractionation of an extract prepared from the thorns of Gleditsia sinensis LAM. led to the isolation of one triterpenoid and four steroids, which were identified as D:C-friedours-7-en-3-one (1), stigmast-4-ene-3,6-dione (2), stigmastane-3,6-dione (3), stigmasterol (4), and beta-sitosterol (5). Triterpenoid 1 was found for the first time in a natural source and the steroids 2-5 were first isolated from this plant. Stigmasterol was the most active antimutagen, showing 51.2% and 64.2% reduction of the induction factor against the mutagens MNNG and NQO, respectively, in the SOS chromotest. Some NMR data of the steroids 2 and 3 obtained have to be revised. 相似文献
79.
80.
Frans A. M. Borremans Milos Budínský Roland E. A. Callens Marc J. O. Anteunis 《Magnetic resonance in chemistry : MRC》1983,21(5):328-333
The solution conformation of L-6-methylperhydroimidazo[1,5-c]thiazole-5,7-dione (γ-thiaprolinehydantoin) has been determined from an extensive 1H and 13C NMR study, allowing the extraction of vicinal inter-proton and carbon-hydrogen coupling constants. The major conformation of the thiazolidine ring is an envelope with C-δ as the flap exo (δ?). In solution the preferred solid state (twist) conformer with C-α exo and C-β endo (αβT) is only a minor contributor. 13C spin–lattice relaxation data reveal the flexibility of the thiazolidine ring. 相似文献