城郊景观动态模型研究──以沈阳市东陵区为例

基于渗透理论、马尔柯夫过程理论,采用中性模型方法,建立了3个不同的城郊景观动态模型,模型中分别介入不同自然因子和决策因子.利用模型对研究区景观进行了动态变化模拟.对模拟结果进行了评价,评价方法与指标包括:1)多分辨率拟合分析;2)最近邻概率;3)斑块大小和数目.结果发现,综合介入决策因素和自然因子的模型具有最好的效果.     

A novel method for the quantitative assessment of the percolation of <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> conidia through horticultural growing media

Incorporation of fungal biological control agents (BCAs) into plant growing media has considerable ergonomic and economic benefits for growers. These agents usually give prophylactic control of target pests and diseases. However, their efficacy is dose dependent and loss of inoculum through leaching could influence the degree of protection they provide. At present there are no protocols to determine the loss of inoculum in the disparate growing media used in horticulture. We describe a method based on a nutrient leaching column to quantify leaching of conidia of the insect-pathogenic fungus Metarhizium anisopliae in a range of growing media. Conidia of this biocontrol agent were applied as a drench or premixed into the medium. Both the application method and growth medium influenced conidial leaching. Inoculum losses were greater following drench application than premixing (95% vs. 15%) irrespective of media type. Comparatively more inoculum was lost from bark and coir following drench application whereas losses were relatively high in peat following premixed application. The leaching column assay provided a simple and accurate method to quantify inoculum loss in real time. This assay could help determine leaching of other fungal BCAs in growing media. It could help in improving pest and disease control by optimizing the rate and frequency of conidial application as well in the design of more efficacious formulations.     

Application of the Percolation Theory to Random Networks of Biochemical Reactions

Percolation Theory is used to get statements about random networks. It can be seen that the probability distribution that vertices belong to a finite cluster in dependence on the mean catalytic activity C = K/N has an analogy to phase transition of second kind.     

Effects of domain structure on in-plane reactions and interactions

The existence of an in-plane domain structure in biological membranes raises the question of the physiological function, if any, of this structure. One important function may be to enhance or limit the equilibrium poise and rates of in-plane reactions through control by the cell of the percolation properties of the domain system. At low average domain occupancy by reactants or interactants, which must be the case for most biological membrane components, moving the domain system from connection to disconnection has marked effects on the apparent equilibrium poise and the rates of membrane-confined reactions. This conclusion is based on computer modelling of the effects of disconnection/connection of nine types of bimolecular in-plane reactions. Using the phase structure and percolation properties of two-component, two-phase phospholipid bilayers, it is possible to examine experimentally homo- and heterodimeriztion reactions, and enzyme-catalysed reactions in-plane as well as the effects of a transmembrane peptide on these systems. These theoretical and experimental studies suggest that percolation effects may be physiologically important in biological membranes. Whether this is in fact the case remains to be demonstrated.     

Effect of urea placement on leaching losses of nitrogen from flooded rice soils

In an effort to provide an explanation for the reported variability in fertilizer N efficiency from deepplaced urea on flooded rice, a set of controlled experiments was conducted to evaluate the effect of water percolation on fertilizer loss and plant uptake from¹⁵N labeled urea supergranules. Three soils of different texture (silt loam-clay) were subjected to various percolation rates (0–20 mm/day) while planted to rice which was harvested after approximately 40 days.The results indicate that moderate to high percolation through silt loam soil will lead to significant fertilizer N losses and drastically decrease the fertilizer uptake by plants. The permeability of the clay soil was too low for any leaching to take place. It is therefore concluded that deep placement of urea supergranules not be recommended in soils where percolation rates may exceed 5 mm/day, particularly if the cation exchange capacity of the soil is low. This experiment points to the need of evaluating and reporting the percolation rates in soils where experiments with supergranular urea are conducted.Contribution from the Agro-Economic Division of the International Fertilizer Development Center (IFDC), Muscle Shoals, Alabama 35660.     

Drastic change of reverse micellar structure by protein or enzyme addition

On addition of cytochrome c to a AOT reverse micellar solution, the percolation process usually observed at high temperatures and surfactant concentrations, occurs at room temperature. This is observed either at relatively high water content at a given cytochrome c concentration or at low content on increasing the cytochrome c concentration. On increasing the water content a phase transition is observed with two optically transparent phases. A similar phase transition is observed on solubilizing various enzymes. The temperature of the transition appears to be strongly dependent on the location of the macromolecule in the reserve micelle. Offprint requests to: M. P. Pileni     

Viewing brain processes as Critical State Transitions across levels of organization: Neural events in Cognition and Consciousness,and general principles

In this theoretical and speculative essay, I propose that insights into certain aspects of neural system functions can be gained from viewing brain function in terms of the branch of Statistical Mechanics currently referred to as “Modern Critical Theory” [Stanley, H.E., 1987. Introduction to Phase Transitions and Critical Phenomena. Oxford University Press; Marro, J., Dickman, R., 1999. Nonequilibrium Phase Transitions in Lattice Models. Cambridge University Press, Cambridge, UK]. The application of this framework is here explored in two stages: in the first place, its principles are applied to state transitions in global brain dynamics, with benchmarks of Cognitive Neuroscience providing the relevant empirical reference points. The second stage generalizes to suggest in more detail how the same principles could also apply to the relation between other levels of the structural-functional hierarchy of the nervous system and between neural assemblies. In this view, state transitions resulting from the processing at one level are the input to the next, in the image of a ‘bucket brigade’, with the content of each bucket being passed on along the chain, after having undergone a state transition. The unique features of a process of this kind will be discussed and illustrated.     

Influence of obstacles on lipid lateral diffusion: computer simulation of FRAP experiments and application to proteoliposomes and biomembranes

Fluorescence Recovery After Photobleaching experiments were simulated using a computer approach in which a membrane lipid leaflet was mimicked using a triangular lattice obstructed with randomly distributed immobile and non-overlapping circular obstacles. Influence of the radius r and area fraction c of these obstacles and of the radius R of the observation area on the relative diffusion coefficient D ^* (Eq. (1)) and mobile fraction M was analyzed. A phenomenological equation relating D ^* to r and c was established. Fitting this equation to the FRAP data we obtained with the probe NBD-PC embedded in bacteriorhodopsin/egg-PC multilayers suggests that this transmembrane protein rigidifies the surrounding lipid phase over a distance of about 18 Å (two lipid layers) from the protein surface. In contrast, analysis of published diffusion constants obtained for lipids in the presence of gramicidin suggests that in terms of lateral diffusion, this relatively small polypeptide does not significantly affect the surrounding lipid phase. With respect to the mobile fraction M, and for point obstacles above the percolation threshold, an increase in R led to a decrease in M which can be associated with the existence of closed domains whose average size and diffusion properties can be determined. Adaptation of this model to the re-interpretation of the FRAP data obtained by Yechiel and Edidin (J Cell Biol (1987) 115:755–760) for the plasma membrane of human fibroblasts consistently leads to the suggestion that the lateral organization of this membrane would be of the confined type, with closed lipid domains of 0.5 µm² in area.Abbreviations and notations used BR bacteriorhodopsin - DMPC dimyristoylphosphatidylcholine - diOC18 dioctadecyloxatricarbocyanine - egf-PC egg-yolk phosphatidylcholine - NBD-PC 1-acyl2-[t2-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-phosphocholine - MOPS 3-[N-morpholino]propane sulfonic acid - FRAP Fluoresence Recovery After photobleaching - D observed diffusion coefficient - D0 diffusion coefficient in the absence of obstacles - D ^* relative diffusion constant (Eq. 1) - M mobile fraction - c obstacle area fraction - r obstacle radius - R observation area radius - r _d diffusion area radius Correspondence to: A. Lopez     

Influence of cholesterol on the biophysical properties of the sphingomyelin/DOPC binary system

The influence of cholesterol on the sphingomyelin (SM)/dioleoylphosphatidylcholine (DOPC) binary system was investigated in various respects. Electron spin resonance (ESR) measurements reveal that the order parameter of 5DS (5-doxyl stearic acid) in SM/DOPC bilayers increases notably when the concentration of cholesterol is over 30 mol%. Membrane potential measurements indicate that the K⁺ permeability of the SM/DOPC bilayer decreases steeply at 40 mol% cholesterol concentration. Both these experiments suggest that cholesterol reduces the motion amplitude of hydrocarbon chains abruptly above 30 mol%. In contrast to the ordering effects on the hydrocarbon chains, ³¹P-NMR results indicate that cholesterol slightly increases the motion of phosphate groups of the lipids. ³¹P-NMR also raises the possibility of domain formation in the presence of cholesterol. Fluorescence-quenching experiments verified that solid domains appear in the binary system when cholesterol is present, and percolation threshold occurs at 50 mol% cholesterol concentration. The solid domains bear the properties of liquid ordered phase, which is the basic structure of caveolae and functional rafts. So this work provides an artificial model for the study of rafts and caveolae on biological membranes. Received: 29 January 2001/Revised: 17 May 2001