A cross-diffusion model of forest boundary dynamics

A simple mathematical model of mono-species forest with two age classes which takes into account seed production and dispersal is presented in the paper. This reaction — diffusion type model is then reduced by means of an asymptotic procedure to a lower dimensional reaction — cross-diffusion model. The existence of standing and travelling wave front solutions corresponding to the forest boundary is shown for the later model. On the basis of the analysis, possible changes in forest boundary dynamics caused by antropogenic impacts are discussed.     

What and where? Predicting invasion hotspots in the Arctic marine realm

The risk of aquatic invasions in the Arctic is expected to increase with climate warming, greater shipping activity and resource exploitation in the region. Planktonic and benthic marine aquatic invasive species (AIS) with the greatest potential for invasion and impact in the Canadian Arctic were identified and the 23 riskiest species were modelled to predict their potential spatial distributions at pan‐Arctic and global scales. Modelling was conducted under present environmental conditions and two intermediate future (2050 and 2100) global warming scenarios. Invasion hotspots—regions of the Arctic where habitat is predicted to be suitable for a high number of potential AIS—were located in Hudson Bay, Northern Grand Banks/Labrador, Chukchi/Eastern Bering seas and Barents/White seas, suggesting that these regions could be more vulnerable to invasions. Globally, both benthic and planktonic organisms showed a future poleward shift in suitable habitat. At a pan‐Arctic scale, all organisms showed suitable habitat gains under future conditions. However, at the global scale, habitat loss was predicted in more tropical regions for some taxa, particularly most planktonic species. Results from the present study can help prioritize management efforts in the face of climate change in the Arctic marine ecosystem. Moreover, this particular approach provides information to identify present and future high‐risk areas for AIS in response to global warming.     

Modelling Spatio-Temporal Effects of Environment on Atlantic Herring, <Emphasis Type="Italic">Clupea harengus</Emphasis>

Trends in mean abundance of North Sea Atlantic herring, Clupea harengus, over the period of 1992–1995, were modelled as a function of spatial location and ocean environmental conditions using generalized additive models (GAM). In all four years, the average herring abundance was found to be highest in latitudes around 60.5°N, and decreased with increasing latitude. The thermocline depth had a significant effect on prespawning herring abundance both directly, as a main effect, and indirectly, through its interactive effect with the temperature at 60m. Average herring abundance was highest in areas having deeper thermocline depths (up to 45m) and temperatures at 60m between 9 and 11°C. Prespawning herring abundance was greater in areas of cooler surface waters in the south than in the north. Well-mixed waters and transition zones between frontal and stratified areas having sea surface temperatures mainly between 11 and 12°C and to a lesser extent between 13 and 14°C were associated with the highest herring abundance. Herring appeared to avoid the cold bottom waters in summer. Multiyear GAM analysis revealed consistent environmental preferenda of herring and affirmed further a significant decrease in herring abundance. As herring numbers declined, the population aggregated in the most preferred areas. The inter-relationships of herring and environmental factors across the study period, were similar in their structure and significance, suggesting that preferred areas for location of herring can be reasonably predicted.     

Marriage Timing over the Generations

Strong relationships have been hypothesized between the timing of marriage and the familial environment of the couple. Sociologists have identified various mechanisms via which the age at marriage in the parental generation might be related to the age at marriage of the children. In our paper we study this relationship for historical populations. We use a dataset consisting of several hundreds of thousands of marriages contracted in three of the 11 Dutch provinces between 1812 and 1922. We identified the generational links between the brides, grooms, their parents, and grandparents. We studied (a) whether there is a relationship between ages at marriage of (grandfathers) fathers and sons, and ages at marriage of (grandmothers) mothers and daughters and (b) whether this relationship might be explained by social class. We find evidence for a clear effect of the family on age at marriage and substantial intergenerational transmission. The impact that the family of origin has on age at entry into marriage can partly be attributed to social class. We also observed positive effects of grandparents’ age at marriage on their offspring’s age at marriage.

Mesoscale Modeling of Amphiphilic Fluid Dynamics

Abstract

So-called “vector models”, in which surfactant molecules retain only translational and orientational degrees of freedom, have been used to study the equilibrium properties of amphiphilic fluids for nearly a decade now. We demonstrate that hydrodynamic lattice-gas automata provide an effective means of coupling the Hamiltonian of such vector models to hydrodynamic flow with conserved momentum, thereby providing a self-consistent treatment of the hydrodynamics of amphiphilic fluids. In this “talk”, we describe these hydrodynamic lattice-gas models in two and three dimensions, and present their application to problems of amphiphilic-fluid hydrodynamics, including the dynamics of phase separation and the shear-induced sponge-to-lamellar phase transition.     

How locomotion sub-functions can control walking at different speeds?

Inspired from template models explaining biological locomotory systems and Raibert׳s pioneering legged robots, locomotion can be realized by basic sub-functions: elastic axial leg function, leg swinging and balancing. Combinations of these three can generate different gaits with diverse properties. In this paper we investigate how locomotion sub-functions contribute to stabilize walking at different speeds. Based on this trilogy, we introduce a conceptual model to quantify human locomotion sub-functions in walking. This model can produce stable walking and also predict human locomotion sub-function control during swing phase of walking. Analyzing experimental data based on this modeling shows different control strategies which are employed to increase speed from slow to moderate and moderate to fast gaits.