Moduli of abelian varieties and p-divisible groups

Lecture notes at a conference on Arithmetic Geometry, Goettingen, July/August 2006: Density of ordinary Hecke orbits and a conjecture by Grothendieck on deformations of p-divisible groups.Comment: 92 page

Velocity control of a 2D dynamic walking robot

In this abstract we introduce velocity control for our 2D dynamic walking robot Dribbel [1] (figure 1) and show that, by ‘closing the loop’, this automatically leads to increased robustness

Impacts of climate change on rice production in Africa and causes of simulated yield changes

This study is the first of its kind to quantify possible effects of climate change on rice production in Africa. We simulated impacts on rice in irrigated systems (dry season and wet season) and rainfed systems (upland and lowland). We simulated the use of rice varieties with a higher temperature sum as adaptation option. We simulated rice yields for 4 RCP climate change scenarios and identified causes of yield declines. Without adaptation, shortening of the growing period due to higher temperatures had a negative impact on yields (−24% in RCP 8.5 in 2070 compared with the baseline year 2000). With varieties that have a high temperature sum, the length of the growing period would remain the same as under the baseline conditions. With this adaptation option rainfed rice yields would increase slightly (+8%) but they remain subject to water availability constraints. Irrigated rice yields in East Africa would increase (+25%) due to more favourable temperatures and due to CO2 fertilization. Wet season irrigated rice yields in West Africa were projected to change by −21% or +7% (without/with adaptation). Without adaptation irrigated rice yields in West Africa in the dry season would decrease by −45% with adaptation they would decrease significantly less (−15%). The main cause of this decline was reduced photosynthesis at extremely high temperatures. Simulated heat sterility hardly increased and was not found a major cause for yield decline. The implications for these findings are as follows. For East Africa to benefit from climate change, improved water and nutrient management will be needed to benefit fully from the more favourable temperatures and increased CO2 concentrations. For West Africa, more research is needed on photosynthesis processes at extreme temperatures and on adaptation options such as shifting sowing dates

The knowledge economy and Dutch cities

How can cities and metropolitan regions remain prosperous and competitive in a rapidly changing economy? In our paper we argue that ‘the knowledge economy’ offers perspectives for growth and added value creation. The paper clarifies what elements the knowledge economy actually consists of, how it can be measured in statistical indicators, in which regions and cities in the Netherlands the knowledge economy has its most significant imprints and what statistical association there is between these regions and cities and relatively good economic performance of firms. We test two contrasting hypotheses often heard in the international literature. The current embedding of knowledge externalities in endogenous economic growth theory have led to important contributions that stress the urban character knowledge transmission in particular. The reasoning is that if knowledge spillovers and –externalities are important to growth and innovation, they should be more easily identified in cities where many people are concentrated into a relatively small geographic space so that knowledge can be transmitted between them more easily. Much recent research indeed finds a limited extent of spatial spillovers and a large degree of local clustering. Alternatively, a large body of literature on Western spatial configurations of innovation and high-technology firms predominantly stresses the supposed ‘urban field’ character of firm performance: location and agglomeration aspects do not seem to have a systematic impact on the distribution of innovative and growth inducing activities over space. We test the urban hypothesis using spatial econometric modeling techniques. On the one hand, the fact that a distance squared distance weight matrix in spatial lag estimations fits the performance data best in relation to knowledge economy factors indicates that spatial relations are limited and urban fixed. On the other hand, the significance of several spatial regimes though (especially those of the Randstad core region, the so-called intermediate zone and medium-sized cities) indicates that the urban structure related to the knowledge economy and economic performance is not straightforward hierarchical (largest cities are not the relatively most attached to the knowledge economy). Both hypotheses (urban and non-urban) are too extreme to fit the Dutch situation. We also conclude that the locational attributes of the factor ‘knowledge workers’ are much more significantly related to economic growth and added value (in practically all specifications over regimes and spatial lag estimations) than the R&D-based innovation input factor. This questions Dutch policy initiatives that mainly focus on R&D as stimulator of the ‘knowledge economy’.

ICT loves agglomeration The urban impacts of ICT in the Netherlands

Information and Communication Technology (ICT) has had an undeniable impact on our society. Some people argue that technology has projected us onto a new wave of social and cultural change. Nevertheless, despite the growth of technology and the social significance of its applications, we have only a poor grasp of its actual impact on the use of physical space. The key question addressed in this paper is therefore: how will ICT influence the spatial-economic patterns of business activities in the Netherlands? In offering answers to this question, the paper develops a conceptual framework that distinguishes two roles of ICT in spatial-economic development: that of a ‘motor’, enhancing productivity and encourages the development of economic sectors, and that of an ‘enabler’ (of e-work, e-commerce and e-business), which may lead households and firms to adopt a different attitude to space requirements. The paper is based on a thorough survey of the current literature on the subject, the results of a recent survey of ICT’s impact on society, and original empirical research into specific factors such as ICT companies’ location preferences and the willingness of knowledge workers to commute. The paper presents an assessment of the usefulness of these concepts in terms of the Dutch situation, both today and in the future. We conclude that Information and Communication Technology has not yet had a marked visible impact on the use of space. To the contrary, despite predictions neither Dutch companies (particularly those in the ICT sector) nor knowledge workers display any unusual degree of mobility at the local or regional s 2perfect substitute for ‘traditional’ behavioural patterns. Nevertheless, there are clear indications that the ‘spatial order’ of the Netherlands is likely to change. Although it is likely that ICT will consolidate underlying spatial patterns, on the regional aggregate changes are occurring within those patterns. While (inner) cities have traditionally been the breeding ground for new ICT companies, this function has now largely been taken over by the outlying city regions, in which multiple clusters of economic activity are emerging: a process of ‘splintering urbanism’. However, despite this regionalized pattern of deconcentration, the traditional city centres continue to fulfil a number of essential functions. These centres remain the meeting places, and the shopping and entertainment centres for businesses and households (the ‘Consumer City’). In the processes of deconcentration and multimodality, ICT should be seen to play an important facilitating and strengthening role. cale. ICT does not function as a 2perfect substitute for ‘traditional’ behavioural patterns. Nevertheless, there are clear indications that the ‘spatial order’ of the Netherlands is likely to change. Although it is likely that ICT will consolidate underlying spatial patterns, on the regional aggregate changes are occurring within those patterns. While (inner) cities have traditionally been the breeding ground for new ICT companies, this function has now largely been taken over by the outlying city regions, in which multiple clusters of economic activity are emerging: a process of ‘splintering urbanism’. However, despite this regionalized pattern of deconcentration, the traditional city centres continue to fulfil a number of essential functions. These centres remain the meeting places, and the shopping and entertainment centres for businesses and households (the ‘Consumer City’). In the processes of deconcentration and multimodality, ICT should be seen to play an important facilitating and strengthening role.

Agglomeration economies and the location of new information and communication technology (ICT) firms in the Netherlands

In 2000, the world wide, rapid employment growth in the ICT-sector came to an end. Knowledge-intensive ICT-firms and -sectors in the Netherlands confirmed to this negative development trend as well. The life-cycle of the ICT-sector appears to reach a new phase of development, dominated by saturation of demand and enforced competition. This might affect the localised growth in the ICT-sector as well. According to evolutionary interpretations of agglomeration theory, one expects that new ICT firms start up in knowledge intensive, urban setting in order to gain from localised knowledge spillovers. The recent empirical literature is not unambiguous clear upon the role of intra- and intersectoral (specialisation or sectoral diversity based) agglomeration circumstances that determine firm formation, growth and survival patterns. In later stages of sectoral development, three kinds of spatial developments are expected from the geographical growth literature: (1) a cummulative causation based process of growth within the preliminary urban settings; (2) a dispersion process towards suburban and adjacent rural regions based on physical network and proximity conceptualisations, (3) spatial growth transmittance and firm dispersion based on functional network spatial relationships which are predominantly non-contiguous in character. For the latter category of spatial economic dynamics, the degree of urbanisation, accessibility, regional labour market- and national zoning spatial regimes are assumed to be leading spatial conceptualisations. A favourable macro-economic growth perspective, as present in the Netherlands during our research period, is assumed to speed up (and condition) spatial economic dispersal patterns. To test these spatial growth transmittance and firm dispersal hypotheses we analyse the components of growth (new firm formation, survival and growth in incumbent firms) of a large dataset of in total 36,000 ICT firms in the Netherlands for the period 1996-2000. The papers empirically distinguishes in-situ urban growth, contiguous relations in growth patterns (starting on an initially low, intra-urban spatial scale) and heterogeneous (non-contiguous) spatial research designs. Conclusions are drawn in relation to the recent agglomeration and economic growth literature.