A patch of phytoplankton in a shear environment will be drawn out into a long ribbon-like structure or filament. Phytoplankton are typically growth-limited due to nutrient limitation or grazing ...pressure. For such a reactive tracer it is demonstrated that there is a minimum filament width representing a balance between a diffusion and growth fuelled outward-propagating wave and the opposing shear flow. The minimum width is given by
W=8.6
κ
λ
max
1,
0.4
μ
λ
−1.6
+1
where
κ is the effective diffusivity for scales small compared to the filament width,
λ the straining rate of the flow, and
μ the net tracer growth rate. Two regimes are apparent with behaviour governed by the ratio of biological growth rate to the strain rate. Counter-intuitively, for
μ/
λ>2.5, the minimum width exceeds that for an unlimited exponentially-growing tracer by a factor of 0.4√(
μ/
λ)+0.36. For
μ/
λ<2.5 the behaviour mimics that of an exponentially-growing or inert tracer with filament width independent of growth rate. The results demonstrate that predictions of the finest scale of structure seen in patchy phytoplankton distribution are very sensitive to the biological processes active and their representation.
The development of genetically modified Bt-corn, incorporating various toxin genes from
Bacillus thuringiensis that act as a chemical defense against insect pests, such as the European Corn Borer, ...provides farmers with a new pest management option. However, the emergence of insect resistance is a threat to the continued use of Bt-corn. The United States Environment Protection Agency (US EPA) has developed planting strategies, for preventing insect resistance by planting a mixture of Bt- and non-Bt-corn. Decisions about the exact proportion of Bt- and non-Bt-corn are based on complex spatially explicit mathematical models using detailed biological assumptions about the population genetics and life history of the European Corn Borer. We develop an alternative simpler model for the spread of resistance based on the logistic growth model, which we believe has utility in situations where it is impossible or impractical to estimate the different life history and genetics parameters required by more detailed models. We use our model to investigate the US EPA’s planting rules for Bt-corn and find that short-term economic behavior is likely to lead to these rules not being followed. Our results add weight to existing work on this problem. We also investigate the economics of planting Bt-corn in markets where consumers do and do not differentiate between the modes of production for the corn. We find that Bt-corn appears to be economic in markets that do not differentiate and uneconomic in markets where consumers do differentiate.
A numerical simulation of the spatial–temporal dynamics of a multi-parameter system has been developed. The components of this system are plant biomass, the mobile and stationary forms of mineral ...nutrition elements, rhizosphere microorganisms, and environmental parameters (temperature, humidity, and acidity). Parametric identification and verification of the adequacy of the model were carried out based on the experimental data on the growth of Krasnoufimskaya-100 spring wheat on peat lowland soil. The results are represented by temporal distributions of biomass from agricultural crops and the findings on the contents of the main nutrition elements within the plant (nitrogen, phosphorus, and potassium). An agronomic assessment and interpretation of the results are given.
Reliable software can be produced within given time and budget constraints using software reliability prediction model. In this paper, Logistic Growth Curve Model (LGCM) based on ANN-PSO approach to ...predict software reliability is proposed. Different types of activation functions are considered in each of the hidden layer of the Artificial Neural Network (ANN). Logistic growth curve model is represented using an ANN to predict software reliability. An ANN-PSO approach based LGCM is proposed to optimize the weights of ANN using PSO. Three data sets have been considered for validating the proposed model. DWCM model, LGCM-NN and LGCM-GA models are considered for comparison with the proposed approach. The proposed model shows better efficacy than the compared models.
The decline of traditional pastoral systems has highlighted the problem of managing shrub encroachment on successional shrublands in the Mediterranean region, especially in marginal habitats. A ...long-term study of the response of ecosystem dynamics to phosphate amelioration and shrub control was initiated in 1988 on an area of phosphorus deficient terra rossa, dominated by dwarf shrubs that had been burnt in the summer of that year. The treatments were imposed in a replicated factorial design once at the beginning of the study. The area was previously grazed yearlong by goats, but during the experiment beef cattle grazed the area during the summer of each year. Without herbicide control, shrub cover reached its preburn level within 5 years, but with shrub control after 17 years, it had not yet reached the preburn level. The average shrub cover over the whole experimental period was 41.9%–49.1% without herbicide and 13.5%–24.4% with (P < 0.0001, SE of the difference = 3.99). The effect of phosphate application on shrub cover was not significant, but cover of herbaceous vegetation increased (P < 0.0016, SE of difference = 5.03). A “state and transition” scheme was constructed that defines the interventions necessary to buffer any one of the states against the pressures of successional processes. Vegetation states were defined by the dominance of either herbaceous vegetation or one of two spiny shrub species, Prickly burnet (Sarcopoterium spinosum, Rosaceae) and Calicotome villosa (Fabaceae). The timing and scale of the interventions depend largely on landscape management objectives and on available economic and logistic resources. We conclude that appropriate management of grazing, periodic control of the shrub component, and occasional soil nutrient amelioration can lead to the development of attractive open woodland with a productive herbaceous understory that provides a wider range of ecological services than a landscape dominated by the undisturbed successional shrub thickets.
In any system when the resources are limited they need to be utilized efficiently. In the present work the multi-core system is considered to be running solo applications and uses limited resources. ...The analysis considers the impact of consumption of two resources viz LLC and main memory bandwidth on multi-core systems. A logistic model is presented and validated for characterizing various SPEC 2006CPU applications using sniper simulator on the basis of their resource utilization. We support the work with statistical approach to distinguish applications following such a logistic model. Under certain conditions, the multi-core model provides a good approximation to the analysis predicted by the logistic model.
Epidemiological models of SIS type are analyzed to determine the thresholds, equilibria, and stability. The incidence term in these models has a contact rate which depends on the total population ...size. The demographic structures considered are recruitment-death, generalized logistic, decay and growth. The persistence of the disease combined with disease-related deaths and reduced reproduction of infectives can greatly affect the population dynamics. For example, it can cause the population size to decrease to zero or to a new size below its carrying capacity or it can decrease the exponential growth rate constant of the population.
The GDP or GNP as a measure of economic performance of a country changes continuously. We can identify the factors that precede its ups and downs. For such forecasting, the use of Markov models are ...not new, but in this paper, an attempt is made to propose a covariate-dependent Markov model to identify the factors that contribute to the estimation of transition probabilities. The proposed model is employed to estimate the transition probabilities, the factors that contribute to transitions in economic performance, and other relevant characteristics. The cross-country data have been employed for the period 1980-2000 for fitting the model. This can provide a useful model for forecasting the economic performance in both developing and developed countries.
The solutions of the discrete logistic growth model based on a difference equation and the continuous logistic growth model based on a differential equation are compared and contrasted. The ...investigation is conducted using a dynamic interactive spreadsheet.
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