QUALITATIVE PROPERTIES OF A POPULATION DYNAMICS SYSTEM DESCRIBING PREGNANCY

2005 ◽  
Vol 15 (04) ◽  
pp. 507-554 ◽  
Author(s):  
G. FRAGNELLI ◽  
P. MARTINEZ ◽  
J. VANCOSTENOBLE
Keyword(s):  
Population Dynamics ◽  
Asymptotic Behavior ◽  
Linear Model ◽  
Nonlinear Model ◽  
Total Population ◽  
Type A ◽  
Qualitative Properties

We study a model of population dynamics describing pregnancy: our model is composed by an equation describing the evolution of the total population, and an equation describing the evolution of pregnant individuals. These equations are of course coupled: one coupling expresses that the total population varies with the number of born people, and another coupling says that the number of fecundated individuals depends on the total population. We study three models of that type: a linear model without diffusion, a nonlinear model without diffusion and a linear model with diffusion. For these three models, we study precisely the qualitative properties and the asymptotic behavior of the solutions.

scholarly journals Efficient Market Hypothesis and the RMB-Dollar Rates: A Nonlinear Modeling of the Exchange Rate

2018 ◽  
Vol 10 (2) ◽  
pp. 150
Author(s):  
Hongxing Yao ◽  
Abdul Rashid Abdul Rahaman
Keyword(s):  
Exchange Rate ◽  
Root Mean Square Error ◽  
Linear Model ◽  
Mean Square Error ◽  
Root Mean Square ◽  
Nonlinear Model ◽  
Efficient Market Hypothesis ◽  
Mean Square ◽  
Forecast Performance ◽  
The Exchange Rate

This paper uses a SETAR model to determine threshold(s) in the RMB/US$ exchange rate from 1981 to 2016 using monthly data. Also, it compares the forecast performance of the univariate nonlinear model to a univariate linear model. We further analyze the forecast performance of the SETAR model to a multivariate linear model, e.g., a Reduced-form VAR. In addition, the research assesses the claim by Boero and Marrocu (2002) that the root mean square error masks the superiority of the nonlinear models.We found five significant thresholds in the RMB/US$ exchange rate, and this result reflects five major episodes of policy reforms or structural changes in the renminbi exchange rates from the period 1981 to 2016. We also found that the univariate nonlinear model out performs both the univariate and multivariate linear models in predicting the exchange rate movements. This finding is consistent with the results in Kyei and Gyamfi (2016), Boero and Marrocu (2002), Krager and Kugler (1993), Peel and Speight (1994) and Chappell et al. (1996). Furthermore, we did not find any evidence of the root mean square error masking the superiority of the nonlinear model.

Existence, Uniqueness and Qualitative Properties of Global Solutions of Abstract Differential Equations with State-Dependent Delay

2019 ◽  
Vol 62 (3) ◽  
pp. 771-788 ◽  
Author(s):  
Eduardo Hernández ◽  
Jianhong Wu
Keyword(s):  
Population Dynamics ◽  
Partial Differential Equations ◽  
Differential Equations ◽  
Global Solutions ◽  
Almost Periodic ◽  
Qualitative Properties ◽  
Abstract Differential Equations ◽  
State Dependent ◽  
State Dependent Delay ◽  
Asymptotically Almost Periodic

AbstractWe study the existence, uniqueness and qualitative properties of global solutions of abstract differential equations with state-dependent delay. Results on the existence of almost periodic-type solutions (including, periodic, almost periodic, asymptotically almost periodic and almost automorphic solutions) are proved. Some examples of partial differential equations with state-dependent delay arising in population dynamics are presented.

The Modeling of Electrohydraulic Proportional Valves

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Davide Cristofori ◽  
Andrea Vacca
Keyword(s):  
Steady State ◽  
Linear Model ◽  
Nonlinear Model ◽  
3D Model ◽  
Fluid Dynamic ◽  
Body Motion ◽  
General Nature ◽  
Relief Valve ◽  
Real Component ◽  
Electromagnetic Model

The present work describes the modeling of a proportional relief valve actuated by an electromagnet. Two models were developed and compared each other: a detailed nonlinear model and its linearized version. The modeling approach presented has a general nature and can be applied to various types of electrohydraulic proportional valves (EHPV). The comparison between nonlinear and linear model results shows the limits of the linear approximation to study the real component. Substantially, the nonlinear model is composed by three submodels: the fluid-dynamic model (for the evaluation of the main flow features), the mechanical model (which solves the mobile body motion), and the electromagnetic model (which evaluates the magnetic forces and the electric transient). All submodels are based on a lumped parameter (LP) approach and they implement a specific set of nonlinear equations. However, to carefully model the main electromagnetic phenomena that characterize the proportional electromagnet behavior (including: magnetic losses, fringing effects, and magnetic saturation), a finite element analysis (FEA) 3D model was developed by the authors. The LP electromagnetic model is based on a particular use of the FEA 3D model steady state results. A series of transient simulations were performed through the FEA 3D model in order to quantify the effect of the eddy currents and to determine a second order transfer function used in the linear model to describe the electromagnet dynamics. The remaining parts of the linear model are obtained by linearizing the nonlinear model equations. The FEA 3D model was experimentally validated in steady-state conditions, while the results of the overall model of the valve were verified in both steady-state and dynamic conditions.

scholarly journals Flux Reflection Model of the Ferroresonant Circuit

2009 ◽  
Vol 2009 ◽  
pp. 1-13 ◽  
Author(s):  
Kruno Miličević ◽  
Ivan Flegar ◽  
Denis Pelin
Keyword(s):  
Physical Model ◽  
Linear Model ◽  
Nonlinear Model ◽  
Steady States ◽  
Reflection Model ◽  
Proposed Model ◽  
Simulation Results ◽  
Ferroresonant Circuit ◽  
Nonlinear Coil

The paper presents a linear model of ferroresonant circuit with flux reflection. The proposed model—flux reflection model—derives from observations of typical flux waveforms of nonlinear coil during ferroresonant steady states. Simulation results of the flux reflection model are compared with simulation results of the usual nonlinear model as well as with measurements carried out on the physical model of the ferroresonant circuit. The flux reflection model enables a novel comprehension of the ferroresonant circuit behavior and simplifies the modeling of the nonlinear coil in the ferroresonant circuit.

Population Dynamics of an Estuarine-Dependent Fish, the Spot (Leiostomus xanthurus), ASong a Tidal Creek–Seagrass Meadow Coenocline

1983 ◽  
Vol 40 (10) ◽  
pp. 1633-1638 ◽  
Author(s):  
Michael P. Weinstein
Keyword(s):  
Population Dynamics ◽  
Decay Rate ◽  
Turnover Rate ◽  
Total Population ◽  
Seagrass Meadow ◽  
Tidal Creek ◽  
Leiostomus Xanthurus ◽  
Population Turnover ◽  
Young Of The Year ◽  
Average Individual

To study the population dynamics of young-of-the-year spot (Leiostomus xanthurus) I released 6981 marked fish midway up the tidal creek portion of a small (<20 ha) marsh creek–seagrass meadow coenocline. Holding mortality experiments (96 h) indicated that 61.5%, or 4300 individuals, survived the marking process to constitute the population available for recapture. Over a 90-d study period, 212 marked fishes were recaptured. From plots of the ratio of marked to unmarked individuals in subsequent samples, I concluded that the population was resident in the creek for up to 182 d with the average individual present for 91 d. When this population turnover rate was compared to the total population decay rate (marked plus unmarked fish), the exchange between habitats (immigration/emigration) accounted for about 26% of the total decay rate, with the remainder attributed to natural mortality. By correcting the overall disappearance rate for population turnover due to immigration/emigration, and using this adjusted value as a measure of instantaneous mortality (Z), the estimated production in this population was 21.8 kcal (91342 J)∙m−2∙d−1. This figure is over six times greater than previously reported values for this species for all size classes over the entire growing season.

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