Multiple-predators-based capture process on complex networks

The predator/prey(capture) problem is a prototype of many network-related applications. We study the capture process on complex networks by considering multiple predators from multiple sources. In our model, some lions start from multiple sources simultaneously to capture the lamb by biased random walks, which are controlled with a free parameterα. We derive the distribution of the lamb's lifetime and the expected lifetime T. Through simulation, we find that the expected lifetime drops substantially with the increasing number of lions. Moreover, we study how the underlying topological structure affects the capture process, and obtain that locating on small-degree nodes is better than on largedegree nodes to prolong the lifetime of the lamb. The dense or homogeneous network structures are against the survival of the lamb. We also discuss how to improve the capture efficiency in our model.     

Isothermal volume variations in lipid vesicle suspensions. A new evidence of intervesicle fusion kinetics

Summary In the present study of fusion between lipid vesicles performed by thermomechanical analysis, isothermal volume variation has been shown to be a reliable tool to follow these kinetics without introducing perturbing probes. In fact, the fusion process is accompanied by bilayer strain release which causes an overall volume decrease of the fused vesicles. Volumetric variations induced by side processes, such as adhesion or ion binding onto the vesicle surface, were accounted for in our measurements. Moreover, by the same technique we followed segregation effects of the membrane lipid components in mixed vesicles. The systems examined were neutral and anionic phospholipids containing vesicles. The role of temperature, vesicle size, lipid composition as well as the influence of different cations were also investigated.     

Ecological competition and the role of an apex predator

In this work we propose an agent-based model to study the process of ecological competition between two species coexisting with a common predator, including inter and intra-specific competition. Without the predator, the ecosystem always reaches a configuration in which one of the prey species faces extinction and the other survives, as is well known. However, we find that there is an optimum value for the amount of food consumed by the prey species for which the mean extinction time (MET) is maximum. In the presence of predators, the average extinction time may increase or decrease with respect to the non-predator case, depending on the food availability. It is also observed that the average extinction time has an optimum value depending on the efficiency of prey of the predator.     

A predator–prey model with diseases in both prey and predator

In this paper, we present and analyze a predator–prey model, in which both predator and prey can be infected. Each of the predator and prey is divided into two categories, susceptible and infected. The epidemics cannot be transmitted between prey and predator by predation. The predation ability of susceptible predators is stronger than infected ones. Likewise, it is more difficult to catch a susceptible prey than an infected one. And the diseases cannot be hereditary in both of the predator and prey populations. Based on the assumptions above, we find that there are six equilibrium points in this model. Using the base reproduction number, we discuss the stability of the equilibrium points qualitatively. Then both of the local and global stabilities of the equilibrium points are analyzed quantitatively by mathematical methods. We provide numerical results to discuss some interesting biological cases that our model exhibits. Lastly, we discuss how the infectious rates affect the stability, and how the other parameters work in the five possible cases within this model.     

Designing compliant substrates to regulate the motion of vesicles

By integrating mesoscale models for hydrodynamics and micromechanics, we examine fluid-driven motion of vesicles on compliant surfaces. The vesicles, modeled as fluid-filled elastic shells, represent biological cells or polymeric microcapsules. Focusing on nonspecific interactions between these vesicles and synthetic substrates, we isolate mechanically and topographically patterned surfaces that transmit stop and go instructions, causing the vesicles to halt at specific locations, and with an increase in the flow velocity, to resume moving. For surfaces containing arrays of compliant posts, the substrates also affect the vesicles' gait, causing them to "crawl," "walk," or "jump." The latter behavior could promote the intermixing of reactants that are encapsulated within the microcapsules. Such control over vesicle dynamics can facilitate various biological assays and fabrication of arrays of mobile microreactors.     

Nontrivial Effect of Time-Varying Migration on the Three Species Prey-Predator System

Migration is ubiquitous in ecosystem and often plays an important role in biological diversity. In this work,by introducing a time-varying migration rate associated with the difference of subpopulation density into a prey, we study the Hopf bifurcation and the critical phenomenon of predator extinction of the three species prey-predator system,which consists of a predator, a prey and a mobile prey. It is found that the system with migration exhibits richer dynamic behaviors than that without migration, including two Hopf bifurcations and two limit cycles. Interestingly,the parameters of migration have a drastically influence on the critical point of predator extinction, determining the coexistence of species. Moreover, the population evolution dynamics of one-dimensional multiple prey-predator system are also discussed.     

An approximation for prey-predator models with time delay

A prototype prey-predator (P-D) model in which the effective size of the predator population interacting with its prey follows an instantaneous time-delay τ regarding its total size is considered here. A simplified model was derived after substituting the approximation into the above time-delay model. In order to assess the reliability of the simplified model, we performed a comparative study of both models under a wide range of parameter values, focusing on the effect of τ on two issues: (i) the boundary (in parameter space) between the regions leading either to stable fixed points characteristic of the non-delay model, both the boundary and the periods and amplitudes obtained for the time-delay model can be fairly approximated by the corresponding results for the simplified model.     

Dynamical phase diagrams of a love capacity constrained prey–predator model

One interesting question in love relationships is: finally, what and when is the end of this love relationship? Using a prey–predator Verhulst–Lotka–Volterra (VLV) model we imply cooperation and competition tendency between people in order to describe a “love dilemma game”. We select the most simple but immediately most complex case for studying the set of nonlinear differential equations, i.e. that implying three persons, being at the same time prey and predator. We describe four different scenarios in such a love game containing either a one-way love or a love triangle. Our results show that it is hard to love more than one person simultaneously. Moreover, to love several people simultaneously is an unstable state. We find some condition in which persons tend to have a friendly relationship and love someone in spite of their antagonistic interaction. We demonstrate the dynamics by displaying flow diagrams.     

Network growth with preferential attachment for high indegree and low outdegree

We study the growth of a directed transportation network, such as a food web, in which links carry resources. We propose a growth process in which new nodes (or species) preferentially attach to existing nodes with high indegree (in food-web language, number of prey) and low outdegree (or number of predators). This scheme, which we call inverse preferential attachment, is intended to maximize the amount of resources available to each new node. We show that the outdegree (predator) distribution decays at least exponentially fast for large outdegree and is continuously tunable between an exponential distribution and a delta function. The indegree (prey) distribution is poissonian in the large-network limit.     

Evaluation of the ethanol intake on the Calomys callosus seminal vesicle structure

The effects of chronic alcohol ingestion on the structure of the glandular epithelium of the seminal vesicle of the rodent Calomys callosus were analyzed in 24 adult animals aged 3 months divided into three experimental groups. The control group received a solid diet and tap water, the alcoholic group received the same solid diet and ethanol P.A. diluted 20% in water (v/v) for 4 months. The abstinent group received the same liquid diet of the alcoholic one for the same period and after that the alcoholic diet was changed by water for a period of 3 months. After treatment, all animals were anesthetized, weighed and sacrificed. At the end of treatment, mean body weight did not differ between animal groups. The glandular epithelial cells of the alcoholic and abstinent groups showed atrophy and ultrastructural alterations such as the presence of altered nuclei, intense dilatation of the cisterns of the granular endoplasmic reticulum, intense digestive vacuoles and lipid droplets. Ethanol ingestion provokes marked lesions on the epithelium of the seminal vesicle probably interfering on the glandular secretion.     

Asymmetrical effect of migration on a prey–predator model

We present a lattice model, where prey and predator randomly walk with different rates. Computer simulations explain the asymmetrical effect: predators more frequently migrate than preys. Moreover, we find that the aggregation of species is promoted by diffusion process.     

Food chain chaos due to Shilnikov's orbit

Assume that the reproduction rate ratio zeta of the predator over the prey is sufficiently small in a basic tri-trophic food chain model. This assumption translates the model into a singularly perturbed system of two time scales. It is demonstrated, as a sequel to the earlier paper of Deng [Chaos 11, 514-525 (2001)], that at the singular limit zeta=0, a singular Shilnikov's saddle-focus homoclinic orbit can exist as the reproduction rate ratio epsilon of the top-predator over the predator is greater than a modest value epsilon(0). The additional conditions under which such a singular orbit may occur are also explicitly given. (c) 2002 American Institute of Physics.     

Aggregates of two-dimensional vesicles: rouleaux, sheets, and convergent extension

Using both numerical and variational minimization of the bending and adhesion energy of two-dimensional lipid vesicles, we study their aggregation, and we find that the stable aggregates include an infinite number of vesicles and that they arrange either in a columnar or in a sheetlike structure. We calculate the stability diagram and we show that the sheetlike aggregate can be transformed into the columnar aggregate via vesicle intercalation, which makes the transformation reminiscent of the process of convergent extension observed in some biological tissues.     

Effects of uniform rotational flow on predator–prey system

Rotational flow is often observed in lotic ecosystems, such as streams and rivers. For example, when an obstacle interrupts water flowing in a stream, energy dissipation and momentum transfer can result in the formation of rotational flow, or a vortex. In this study, I examined how rotational flow affects a predator–prey system by constructing a spatially explicit lattice model consisting of predators, prey, and plants. A predation relationship existed between the species. The species densities in the model were given as S$S$ (for predator), P$P$ (for prey), and G$G$ (for plant). A predator (prey) had a probability of giving birth to an offspring when it ate prey (plant). When a predator or prey was first introduced, or born, its health state was assigned an initial value of 20 that subsequently decreased by one with every time step. The predator (prey) was removed from the system when the health state decreased to less than zero. The degree of flow rotation was characterized by the variable, R$R$. A higher R$R$ indicates a higher tendency that predators and prey move along circular paths. Plants were not affected by the flow because they were assumed to be attached to the streambed. Results showed that R$R$ positively affected both predator and prey survival, while its effect on plants was negligible. Flow rotation facilitated disturbances in individuals’ movements, which consequently strengthens the predator and prey relationship and prevents death from starvation. An increase in S$S$ accelerated the extinction of predators and prey.     

Depletion versus deflection: how membrane bending can influence adhesion

During depletion-driven vesicle adhesion, a stiff membrane's resistance to bending at fixed tension prevents contact angle equilibrium and vesicle spreading over an opposing vesicle, while more flexible vesicles partially engulf opposing vesicles. Estimates of the bending cost associated with the spreading contact line, relative to the adhesion energy, were consistent with the observed spreading or lack of spreading for the flexible and stiff membranes, respectively, and predicted a lag time sometimes preceding spreading.     

Vectorial photoinduced electron transfer in phospholipid vesicles and LB bilayers

Summary Photoinduced electron transfer (PET) was studied in phospholipid vesicles and in Langmuir-Blodgett bilayers in the attempt to produce a model for electron transfer processes in biological media. Spatial organization of the reaction centers in lipid membranes needs to be controlled in order to provide high efficiency of light-to-chemical energy conversion. We designed a phospholipid system where the donor is localized in the inner bilayer whereas the acceptor is at the polar groups-water interface. We used dipalmitoylphosphatidic acid vesicles containing low molar fractions of dipalmitoylphosphatidylcholine with pyrene (donor) bound to one of the alkyl chains. Methylviologen (acceptor) was added to the external aqueous phase; upon photoexcitation of the donor we observed the electron transfer to take place in a unidirectional manner from the inside of the bilayer to the interface. Information about the location of the donor was obtained studying the photophysical properties of the pyrene chromophore in vesicles and in LB layers. The photoinduced electron transfer reaction was evidenced by quenching of pyrene fluorescence in the presence of increasing concentrations of acceptor, the process was studied both with steady-state and time-resolved fluorescence emission. Fluorescence intensity was found to decrease with increasing concentration of methylviologen, similar results were obtained for vesicles and LB layers of analog composition immersed in a methylviologen solution. Lifetimes of the excited species were found to be of the same order of magnitude in vesicle and LB-layer systems. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Ocadaic acid treatment causes tyrosine phosphorylation of caveolin-2 and induces internalization of caveolae in rat peritoneal macrophages

In this paper, we provide evidences that protein phosphatases could regulate the internalization cycle of caveolae in rat peritoneal cells. Ocadaic acid (OA)—a serine/threonine phosphatase inhibitor—was used in various concentrations (4 and 100 nM) to study the internalization of horseradish peroxidase (HRP) in resident and elicited macrophages. We have found that OA in both concentrations has significantly decreased HRP uptake in resident and elicited cells. The results of our morphometrical analysis showed that in OA-treated cells, the number of surface-connected caveolae has been dramatically decreased. Simultaneously large, endosome-like vacuoles containing small vesicles appeared in the cytoplasm. The membrane of these small vesicles was labeled with anti-caveolin-1 antibody. Immunoprecipitation and Western blot analysis revealed that in OA-treated cells a 29 kDa protein identified as caveolin-2 in macrophages was phosphorylated on tyrosine residues. These data support the idea that there is a close correlation between the phosphorylation of caveolin-2 and endocytosis of caveolae: the tyrosine phosphorylation of this 29 kDa protein can drive caveolae to pinch off from the plasma membrane and causes accumulation of caveolae in a multivesicular body-like cellular compartment, which was never found to contain lysosomal enzymes. As a result of OA treatment caveolin-2 remains phosphorylated and the phosphorylation of these protein might inhibit the recycling of caveolae.     

Noise-controlled slow–fast oscillations in predator–prey models with the Beddington functional response

The influence of environmental fluctuations (modeled as a multiplicative dichotomous noise) on predator–prey interaction is studied using a metapopulation model with N prey-subpopulations. Investigating the role that predator interference plays in the dynamics of such trophic systems, the Beddington functional response is considered. In case the growth rates of prey and predator are widely different, we obtain analytic results by a dynamical mean-field approximation. In some regions of the system parameters, variations of noise amplitude or correlation time can cause transitions of the mean field from a globally stable equilibrium to the stable limit cycle as well as in the opposite direction. The conditions for the occurrence of such a phenomenon are found and illustrated by phase diagrams. Implications of the results on the colored-noise-induced extinction of a predator population are also discussed.     

Multidimensional subdiffusion model: Arbitrage-free market

To capture the subdiffusive characteristics of financial markets, the subordinated process, directed by the inverse α-stale subordinator S_α(t) for 0 < α <1, has been employed as the model of asset prices. In this article, we introduce a multidimensional subdiffusion model that has a bond and K correlated stocks. The stock price process is a multidimensional subdiffusion process directed by the inverse α-stable subordinator. This model describes the period of stagnation for each stock and the behavior of the dependency between multiple stocks. Moreover, we derive the multidimensional fractional backward Kolmogorov equation for the subordinated process by Laplace transform technique. Finally, using martingale approach, we prove that the multidimensional subdiffusion model is arbitrage-free, and also gives an arbitrage-free pricing rule for contingent claims associated with the martingale measure.