Exurbia from the bottom-up: Confronting empirical challenges to characterizing a complex system

We describe empirical results from a multi-disciplinary project that support modeling complex processes of land-use and land-cover change in exurban parts of Southeastern Michigan. Based on two different conceptual models, one describing the evolution of urban form as a consequence of residential preferences and the other describing land-cover changes in an exurban township as a consequence of residential preferences, local policies, and a diversity of development types, we describe a variety of empirical data collected to support the mechanisms that we encoded in computational agent-based models. We used multiple methods, including social surveys, remote sensing, and statistical analysis of spatial data, to collect data that could be used to validate the structure of our models, calibrate their specific parameters, and evaluate their output. The data were used to investigate this system in the context of several themes from complexity science, including have (a) macro-level patterns; (b) autonomous decision making entities (i.e., agents); (c) heterogeneity among those entities; (d) social and spatial interactions that operate across multiple scales and (e) nonlinear feedback mechanisms. The results point to the importance of collecting data on agents and their interactions when producing agent-based models, the general validity of our conceptual models, and some changes that we needed to make to these models following data analysis. The calibrated models have been and are being used to evaluate landscape dynamics and the effects of various policy interventions on urban land-cover patterns.     

Spatial process and data models: Toward integration of agent-based models and GIS

The use of object-orientation for both spatial data and spatial process models facilitates their integration, which can allow exploration and explanation of spatial-temporal phenomena. In order to better understand how tight coupling might proceed and to evaluate the possible functional and efficiency gains from such a tight coupling, we identify four key relationships affecting how geographic data (fields and objects) and agent-based process models can interact: identity, causal, temporal and topological. We discuss approaches to implementing tight integration, focusing on a middleware approach that links existing GIS and ABM development platforms, and illustrate the need and approaches with example agent-based models.     

Digital data acquisition and analysis: An introduction

There is no doubt that although the price of PCs has fallen, the performance for money continues to rise. As this happens, so the suitability of using general-purpose computing platforms, especially PCs, for specific technical applications increases. This article discusses recent developments and reviews some of the systems which are currently available for data acquisition and analysis in the environmental sciences.     

Disequilibrium features in experimentally shocked mixtures of olivine plus silica glass powders

Seventeen shock-recovery experiments were performed on powder mixtures of one part (by weight) olivine (St. John's forsterite) plus two parts silica glass (pure vitreous silica) in order to characterize the physical and chemical interaction of two chemically incompatible components during shock. Powders of <45 m grain size were shocked by impact of projectiles launched from a 20 mm gun which created pressures ranging from 6.2 to 64.2 GPa (1 GPa= 10kbar).Petrographie features observed in thin section attest to mechanical and thermal metamorphism. Samples shocked to pressures from 6.2 to 39.3 GPa form compacted, mosaic, granular aggregates with fractured and strained grains. Samples shocked to pressures from 42.9 to 64.2 GPa form vesicular, mixed melts containing flow schlieren and relict olivine fragments. Petrographic disequilibrium is manifested in cataclastic textures showing deformational anisotropy and in thermal effects showing non-uniform intergranular melting. This disequilibrium is caused by an irregular pressure distribution resulting from the rapid collapse of pore spaces.The chemical composition of the shock melts are similar in each of six samples shocked to pressures of 42.9 to 64.2 GPa. Melt chemistry is bimodal in each sample. Colorless melts are 99.9% SiO₂ and represent pure silica glass melts; pale to dark green melts range in composition from 47% to 64% SiO₂ and represent a progressive mixture of olivine melt (41% SiO₂) with silica glass melt. Surprisingly, the compositions of the colored glasses are intermediate between the composition of pure olivine and the bulk composition of the original starting material (79% SiO₂) and are similar to enstatitic pyroxene compositions (50% to 57% SiO₂; 33% to 37% MgO). Although bulk compositions of shocked samples are unchanged, the creation of melts with pyroxene compositions instead of bulk sample compositions may indicate that an incipient eutectic-type fusion may have occurred in small olivine-normative domains surrounding individual olivine grains. Chemical disequilibrium is evidenced by the creation of these olivine-normative melts from a quartz-normative starting compositions and by the chemical heterogeneity in the melts.     

Asteroidal agglutinate formation and implications for asteroidal surfaces

A large number of shock recovery experiments that address the ease of impact melt formation as a function of peak shock pressure lead to the conclusion that impacts at 5 km/sec into fragmental, porous surfaces will produce agglutinate-type glasses; no shock melts are produced at these velocities in dense silicate target rocks. While agglutinitic glasses dominate lunar surface soils, they are virtually absent in gas-rich, brecciated meteorites. This apparent paucity—if not complete lack—of agglutinate-type glasses is also inferred from remote IR-reflectance spectroscopy. The need to identify mechanisms that inhibit agglutinate formation on asteroidal sufaces was recognized previously and was predominantly attributed to lower projectile velocities and different gravitational environments.We will argue in this paper that additional mechanisms may be required. Specifically we propose that spall processes at a target's free surface play a major role in asteroidal surface evolution. At 5 km/sec collision velocity, a target (R_T) to projectile (R_P radius ratio of $\text{R}{}_{\mathrm{<mtext>T</mtext>}}\text{R}{}_{\mathrm{<mtext>P</mtext>}}\text{≈ 100}$ delineates the boundary between an “infinite half-space” and a “finite”-sized target. In the first case, collisional energy is expended in a pure cratering regime; in the latter, additional displacement of target material in the form of spallation products occurs. The spall volume may exceed the crater volume by an order of magnitude. Therefore fragmental impact deposits on small planetary bodies may be entirely controlled by spall products, rather than crater ejecta. Because tensile failure occurs at <0.2 GPa stress, spall velocities are measured in meters per second (contrary to crater ejecta) and therefore spallation products are efficiently retained even in low gravitational environments. Spall products are also more coarse grained than crater ejecta; they are also highly biased toward petrographically “unshocked” (<0.2 GPa) rocks.Thus asteroidal surface deposits should be more coarse grained and less shocked than lunar ones—consistent with meteorite evidence and remote-sensing observations. Because spall volume exceeds crater ejecta volume, the total growth rate of asteroidal surface deposits is accelerated, leading to relatively short surface residence times of individual meteorite components, another significant difference between lunar and asteroidal surface materials.     

Energiforhold i den danske landbrugsproduktion

Bennekou, G., Rand, P., & Schroll, H. 1974: Energiforhold I den Danske landbrugsproduktion. Geografisk Tidsskrift 73: 36–48. København, juni 1, 1974.

The increasing supply of energy in Danish agricultural production has reached a level where the energy lost on its way through the food chain in animal production only just balances with the gain of energy obtained by vegetable production.     

Geometrical dynamics: A new approach to periodic orbits aroundL 4

Geometrical dynamics is the study of the geometry of the orbits in configuration space of a dynamical system without reference to the system's motion in time.Generalized coordinates for the circular restricted problem of three bodies are taken as polar coordinatesr, centered at the triangular libration pointL ₄. A time-independent nonlinear second order ordinary differential equation forr as a function of is derived. Approximations to periodic solutions are obtained by perturbations and Fourier series.     

Eh measurements in sulphide mineral slurries

Problems in utilizing open-circuit potential (Eh) values as a measurement of the redox conditions in metallurgical systems are explored. Factors which determine the Eh when more than one redox couple is present have been illustrated by studies with platinum, gold and galena indicator electrodes in iron/oxygen and xanthate/oxygen systems. Potential measurements in galena slurries have demonstrated that smooth noble-metal electrodes are sensitive to the conditions at the mineral particle/solution interface.     

Relaxation Oscillations in Tidally Evolving Satellites

We study the rotational evolution under tidal torques of axisymmetric natural satellites in inclined, precessing orbits. In the spin- and orbit-averaged equations of motion, we find that a global limit cycle exists for parameter values near the stability limit of Cassini state . The limit cycle involves an alternation between states of near-synchronous spin at low obliquity, and strongly subsynchronous spin at an obliquity near 90°. This dynamical feature is characterized as a relaxation oscillation, arising as the system slowly traverses two saddle-node bifurcations in a reduced system. This slow timescale is controlled by ε, the nondimensional tidal dissipation rate. Unfortunately, a straightforward expansion of the governing equations for small ε is shown to be insufficient for understanding the underlying structure of the system. Rather, the dynamical equations of motion possess a singular term, multiplied by ε, which vanishes in the unperturbed system. We thus provide a demonstration that a dissipatively perturbed conservative system can behave qualitatively differently from the unperturbed system. This revised version was published online in July 2006 with corrections to the Cover Date.