Can geocomputation save urban simulation? Throw some agents into the mixture, simmer and wait ...

There are indications that the current generation of simulation models in practical, operational uses has reached the limits of its usefulness under existing specifications. The relative stasis in operational urban modeling contrasts with simulation efforts in other disciplines, where techniques, theories, and ideas drawn from computation and complexity studies are revitalizing the ways in which we conceptualize, understand, and model real-world phenomena. Many of these concepts and methodologies are applicable to operational urban systems simulation. Indeed, in many cases, ideas from computation and complexity studies—often clustered under the collective term of geocomputation, as they apply to geography—are ideally suited to the simulation of urban dynamics. However, there exist several obstructions to their successful use in operational urban geographic simulation, particularly as regards the capacity of these methodologies to handle top-down dynamics in urban systems. This paper presents a framework for developing a hybrid model for urban geographic simulation and discusses some of the imposing barriers against innovation in this field. The framework infuses approaches derived from geocomputation and complexity with standard techniques that have been tried and tested in operational land-use and transport simulation. Macro-scale dynamics that operate from the topdown are handled by traditional land-use and transport models, while micro-scale dynamics that work from the bottom-up are delegated to agent-based models and cellular automata. The two methodologies are fused in a modular fashion using a system of feedback mechanisms. As a proof-of-concept exercise, a micro-model of residential location has been developed with a view to hybridization. The model mixes cellular automata and multi-agent approaches and is formulated so as to interface with meso-models at a higher scale

The first lady geologist, or collector par excellence?

This is a PDF version of an article published in Geology Today© 2001. The definitive version is available at www.blackwell-synergy.com. The illustrations have been removed.This article discusses the life and career of the British geologist Etheldred Benett (1776-1845), one of the first female geologists and and expert on the early history of Wiltshire geology

On the propagation of a normal shock wave through a layer of incompressible porous material

A novel numerical formulation of the two-phase macroscopic balance equations governing the flow field in incompressible porous media is presented. The numerical model makes use of the Weighted Average Flux (WAF) method and Total Variation Diminishing (TVD) flux limiting techniques, and results in a second-order accurate scheme. A shock tube study was carried out to examine the interaction of a normal shock wave with a thin layer of porous, incompressible cellular ceramic foam. Particular attention was paid to the transmitted and reflected flow fields. The numerical model was used to simulate the experimental test cases, and their results compared with a view to validating the numerical model. A phenomenological model is proposed to explain the behaviour of the transmitted flow field

The economic value of ideology

Specialization and trade rest on institutions that protect property rights and enforce agreements. Frequently, in economic analysis institutions are just assumed to exist, or it is implicitly supposed that the political game can establish them. Once this assumption is done, the invisible hand does its work properly. It doesn’t matter if humans beings are benevolent or selfish for the gains from specialization and trade be realized. However, it is not easy to build institutions, neither are they a free lunch. The paper shows that ideology, understood as a self-imposed code of conduct, contributes to reduce the cost of instituting an industrious society, inducing people to assign their time and effort to productive activities rather than to theft.ideology, self-imposed codes of conduct, crime, enforcement of property rights.

RNA interference is ineffective as a routine method for gene silencing in chick embryos as monitored by fgf8 silencing.

The in vivo accessibility of the chick embryo makes it a favoured model system for experimental developmental biology. Although the range of available techniques now extends to miss-expression of genes through in ovo electroporation, it remains difficult to knock out individual gene expression. Recently, the possibility of silencing gene expression by RNAi in chick embryos has been reported. However, published studies show only discrete quantitative differences in the expression of the endogenous targeted genes and unclear morphological alterations. To elucidate whether the tools currently available are adequate to silence gene expression sufficiently to produce a clear and specific null-like mutant phenotype, we have performed several experiments with different molecules that trigger RNAi: dsRNA, siRNA, and shRNA produced from a plasmid coexpressing green fluorescent protein as an internal marker. Focussing on fgf8 expression in the developing isthmus, we show that no morphological defects are observed, and that fgf8 expression is neither silenced in embryos microinjected with dsRNA nor in embryos microinjected and electroporated with a pool of siRNAs. Moreover, fgf8 expression was not significantly silenced in most isthmic cells transformed with a plasmid producing engineered shRNAs to fgf8. We also show that siRNA molecules do not spread significantly from cell to cell as reported for invertebrates, suggesting the existence of molecular differences between different model systems that may explain the different responses to RNAi. Although our results are basically in agreement with previously reported studies, we suggest, in contrast to them, that with currently available tools and techniques the number of cells in which fgf8 gene expression is decreased, if any, is not sufficient to generate a detectable mutant phenotype, thus making RNAi useless as a routine method for functional gene analysis in chick embryos

A new species of Pseudochalcura (Hymenoptera, Eucharitidae), with a review of antennal morphology from a phylogenetic perspective

Pseudochalcura alba Heraty & Heraty, sp. n. is described from Santiago del Estero and Catamarca provinces in northwestern Argentina. The male and female have long dorsal rami on all of the flagellomeres basal to the terminal segment, which is a unique feature within the genus and shared only with some species of Rhipipalloidea. Antennal modifications are compared across the Stilbula clade, of which all are parasitoids of Camponotini (Formicinae). A phylogenetic hypothesis for the group is proposed based on an analysis of 28S and 18S sequence data for 28 species. Ramose antennae are derived independently in both males and females across the clade, but with fully ramose female antennae restricted to the New World prolata group of Pseudochalcura and to some species of the Old World genus Rhipipalloidea. A sister group relationship between these genera is proposed based on both morphological and molecular data. Female antennae in other species of these genera, and other genera in the clade are at most dorsally lobate or serrate, but more commonly cylindrical. Monophyly of species of Obeza and Lophyrocera is supported and linked to a behavioral trait of ovi-position into fruits as opposed to flower heads or leaf buds. Within the Stilbula clade, a dichotomy between New and Old World taxa suggest relatively recent post-Miocene exchanges across the Northern Hemisphere.Fil: Heraty, John Michael. University of California; Estados UnidosFil: Heraty, Joanne M.. University of California; Estados UnidosFil: Torrens, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentin

The Discovery of Comparative Advantage

Torrens [in 1815] clearly preceded Ricardo [in 1817] in publishing a fairly satisfactory formulation of the doctrine [of comparative costs]. It is unquestionable, however that Ricardo is entitled to the credit for first giving due emphasis to the doctrine, for first placing it an appropriate setting, and for obtainin