Explaining the location decision of moving firms using their mobility profile and the accessibility of locations

This paper describes the research approach and first empirical results of the estimation of discrete choice models that describe the location decision of moving firms. The model is based on random utility theory and features systematic choice sets to account for the choice context at the highest level of spatial detail (address-level). Firms are analysed categorised to their mobility profile. These mobility profiles are homogenous groups of firms with similar mobility characteristics that are a priori assumed. The models are tested on an extensive revealed preference dataset with firm migration observations in South Holland. To avoid correlations between variables a variety of composed accessibility variables have been constructed that describe the distances to the physical infrastructure or that are an aggregated form of potential accessibility. The location attributes of alternatives have been completed with the business environment type and the rental level. The results are first of all valuable for the development of a simulation model for firm location but the empirical results also yields insight into the spatial behaviour and location preference of firms. Although further research is necessary, the presented addresses some challenges in modelling the spatial behaviours of firms in an urban environment. Therefore the presented approach holds seems valuable for the development of a simulation model for location decisions of moving firms and offers good possibilities for future research.

Using firm demographic microsimulation to evaluate land use and transport scenario evaluation - model calibration

Existing integrated land use transport interaction models simulate the level of employment in (aggregated) zones and lack the individual firm as a decision making unit. This research tries to improve the behavioural foundation of these models by applying a firm demographic modelling approach that first of all accounts for the individual firm as a decision making unit and secondly represents the urban system with high spatial detail. A firm demographic approach models transitions in the state of individual firms by simulating transitions and events such as the relocation decision, growth or shrinkage of firms or the death of a firm. Important advantage of such a decomposed approach is that it offers the opportunity to account for accessibility in each event in the desired way. The firm demographic model is linked to an urban transport model in order to obtain a dynamic simulation of mobility (and accessibility) developments. The paper describes the firm demographic model specifications as well as the interaction of the model with the urban transport model. The integrated simulation model can be used to analyse the effects of different spatial and transport planning scenarios on the location of economic activities and mobility.

International accessibility and rental levels: a case study for the office-market in the Netherlands

Rental levels of office floor space are determined by aspects of the buildings and aspects of the location. In this contribution we focus on the characteristics of locations using a large database of market-transactions. Accessibility proves to have an important impact on price levels. In particular the most expensive locations must have an excellent international accessibility by Air. Empirical results are presented.

Interaction of transport and land use: framework for an integrated urban model

The growing general concern on limited resources (e.g. space) have led to the conviction that policy makers, that deal with urban development, need to consider their choices carefully, with respect to the effects on urban development on the long term. Models that describe the urban development provide quantitative insight in the effects of possible government policy and are a useful tool for policy makers. In the last decade new generation computers have drastically increased data handling capacity and graphically possibilities, allowing much more detail in spatial modeling. This has resulted in research efforts into urban models to quantify the effects of spatial policy. The research, which will be described in this paper, aims for an integrated approach to spatial modeling with special attention on the influence of transport networks and the role of the government. Main objective of the research is the development and application of an urban model to quantify the effects of planning policies on the spatial development. At micro level this urban model simulates the reaction of actors to changes in the urban system: the development or renewal of new urban areas and new infrastructure. These changes are imposed on the urban system by government and developers on macro and meso level. The paper will present the theoretical framework for the proposed urban model and the objectives of the research. This will be complemented with a description of spatial planning issues in the Netherlands. In the proposed urban model the spatial system (urban region) is represented by multiple linked sub-systems. Individual sub-systems are: the housing market, public facilities, the market for business real estate and the transport system. Each sub-system is represented as a market with a supply and demand side. The government and (project) developers define the supply side through spatial policy and investments. On the demand side, agents (households and companies) react at changes in these subsystems. These reactions expose themselves as individual decisions whether to move to other dwellings or to relocate businesses. Development and application of modeling techniques for the choice behavior of households and companies as entities, are main objectives in the research. The urban markets have a strong coherence for the spatial relations of each agent. Quantification of these relationships, by analyzing the transportation facilities, is important in analyzing the choice behavior of households and companies. This is why the transport system plays a central role in the urban model. For each subsystem an appropriate modeling technique has been selected, based on an exploration of available approaches in the literature and other research programs. Efforts are under way to collect and operationalize the extensive data necessary for the modeling task.

Logistics Decisions in Descriptive Freight Transportation Models: A Review

The objective of this paper is to provide an inventory of approaches to descriptively (as opposed to normatively) model logistics decisions within the context of freight transport modelling. Rather than taking transport modelling frameworks as a starting point, as has been the case in the literature so far, we depart from a framework of logistics decisions. The framework is developed by combining elements of over a dozen existing frameworks from the supply chain management literature. Based on this comprehensive framework, we review freight modelling approaches from the literature. We find that freight modelling can be extended by taking into account previously uncovered areas of logistics decisions, such as those related to marketing or logistics systems forecasting and planning, as well as in areas that are well known from an optimization perspective but not from a descriptive perspective, such as routing and scheduling decisions. We conclude with a systematic listing of such areas, which can be used by researchers and transport modelling practitioners to develop further those transport models that take agent decision making as a starting point

Biochemistry and physiology of syntrophic propionate-oxidizing microbial consortia

Industrial wastewaters can be purified in methanogenic bioreactors such as the upflow anaerobic sludge bed (UASB) reactor. In such reactors biomass is completely degraded to CH 4 and CO 2 , by several trophic groups of microorganisms. However, those gases are also responsible for the enhanced greenhouse effect, and therefore the occurrence of methanogenic decomposition in natural habitats is much less appreciated.In the introduction ( Chapter 1 ) of this thesis, one particular step in the process of methanogenic decomposition, propionate oxidation, is discussed. Propionate is one of the compounds which can only be oxidized syntrophically under methanogenic conditions, and the organisms responsible for this step are extremely interesting due to their ability to thrive at the lowest possible amounts of energy available.Syntrophic propionate-oxidizing bacteria produce acetate, H 2 , CO 2 and formate. To make this reaction energetically feasible, methanogenic archaea must keep the concentrations of H 2 and formate extremely low. Two classes of enzymes which may be important for this 'Interspecies electron transfer', i.e. hydrogenase and formate dehydrogenase, and the present knowledge of these enzymes, is discussed in Chapter 1. Furthermore, this Chapter summarizes what is know about syntrophic propionate-oxidizing bacteria so far.Most of the isolated propionate-oxidizing bacteria belong to the genus Syntrophobacter and cluster together with gram-negative sulfate reducing bacteria within thed-subdivision of the proteobacteria. Other syntrophic propionate oxidizers are more closely related to the genus Syntrophus , while recently two thermophilic organisms were described which are close relatives of low GC gram-positive Desulfotomaculum species. A related organism was also enriched from mesophilic sludge, and Chapter 2 of this thesis describes the isolation and physiological characterization of a defined co-culture of this organism with Methanospirillum hungatei . Remarkably this organism, which was named ' Pelotomaculum schinkii' , harbors two different 16S rDNA genes. This unusual property of sequence heterogeneities has also been reported for other gram-positive bacteria. However, compared to other syntrophic propionate oxidizers this organism is exceptional since it did not grow axenically on any of the substrates tested. For most syntrophic propionate oxidizing bacteria it is known that propionate is oxidized via the Methyl-malonyl-CoA pathway. Besides the ability to couple propionate oxidation to the sulfate reduction, these organisms are also able to ferment fumarate in pure culture. Although ' Pelotomaculum schinkii' most likely uses the methyl-malonyl-CoA pathway to oxidize propionate, none of the intermediates of this pathway supported growth in this organism. Therefore, this organism may be the first true obligate syntrophic anaerobic bacterium isolated.An organism, which does not use the methyl-malonyl-CoA pathway to oxidize propionate, is Smithella propionica . This organism produces small amounts of butyrate from propionate and it produces much less CH 4 than organisms, which are known to use the methyl-malonyl-CoA pathway. The occurrence of another pathway of propionate conversion was previously already demonstrated in methanogenic habitats and enrichment cultures. The randomizing methyl-malonyl-CoA pathway could not account for the products recovered from 13C-labeled propionate in these studies. Therefore the pathway of propionate oxidation was studied with 13C-NMR in Smithella propionica ( Chapter 3 ). Experiments with 2,3- 13C-labeled propionate revealed that half of the methyl-methylene bonds in propionate were broken during propionate conversion. Labeled bicarbonate was never recovered from cultures grown on labeled propionate, and experiments in which 13C-bicarbonate was added showed that it was not incorporated either. These observations were inconsistent with pathways proposed previously to occur in methanogenic habitats, such as the acryloyl-CoA pathway and the reductive carboxylation pathway. In this Chapter, a novel pathway of propionate is proposed. The results of 13C-NMR experiments suggested that the C2 of propionate is coupled to the carboxyl-group of a second propionate molecule, followed by a rearrangement to a 6-carbon unbranched intermediate. Cleavage of this molecule then yields acetate and butyrate, which is further oxidized syntrophically to acetate. Such pathway perfectly explained the ratios of labeled products recovered from experiments with 1-, 2-, 3- and 2,3- 13C-labeled propionate, and also fitted with the stoichiometry of propionate conversion. In batches to which 1- and 2- 13C-labeled acetate was added together with unlabeled propionate, a small amount of label was recovered in propionate revealing that the proposed pathway should be reversible.For all other studies described in this thesis Syntrophobacter fumaroxidans was used as a model organism. Previous studies have revealed that this organism is able to produce both H 2 and formate during propionate oxidation, and it could only grow with methanogens that utilize both H 2 and formate. The enzymes responsible for proton and bicarbonate reduction are hydrogenase and formate dehydrogenase. The presence of both enzymes in Syntrophobacter fumaroxidans was also demonstrated in previous studies. In Chapter 4 of this thesis several experiments are described which demonstrate that this organism possesses at least 2 distinct formate dehydrogenases and at least 3 distinct hydrogenases. All these enzymes were induced under all growth conditions tested, though there were some variations in the levels of each enzyme. One of the formate dehydrogenases may be involved in CO 2 -fixation by running the acetyl-CoA cleavage pathway in the reverse direction during growth on propionate. Most likely the other enzyme is involved in terminal reduction of CO 2 .The presence of multiple hydrogenases in sulfate-reducing bacteria is not unusual. For the genus Desulfovibrio a model has been described how these organism use three distinct hydrogenases to conserve energy. Such a H 2 -cycling mechanism may also be present in S. fumaroxidans . In a separate study ( Chapter 5 ), the hydrogenase and formate dehydrogenase levels of axenic S. fumaroxidans cells were compared to the levels in cells which were grown syntrophically. Since the methanogenic partner of syntrophic growth ( Methanospirillum hungatei ) also possesses these enzymes, the organisms needed to be separated from each other in order to analyze the levels in S. fumaroxidans . Percoll gradient centrifugation proved to be an excellent method to separate syntrophically grown cells. The S. fumaroxidans cells which were separated in this way exhibited very high formate dehydrogenase activities as compared to cells grown axenically. Also the M. hungatei cells which were grown syntrophically exhibited higher formate dehydrogenase activities as compared to cells grown axenically on H 2 or formate. The hydrogenase levels of these cells were comparable to the levels in axenic cultures. For S. fumaroxidans the hydrogenase levels in cells which were grown syntrophically were also higher than in cells which were grown axenically. Both enzymes seemed to play an important role in S. fumaroxidans during syntrophic growth, while the enzyme levels of M. hungatei suggested a more important role for formate dehydrogenase during syntrophic growth. One of the hydrogenase which could be involved in syntrophic growth was purified from S. fumaroxidans cells grown on fumarate ( Chapter 6 ). The enzyme is a typical NiFe-hydrogenase though the levels of both H 2 -uptake and H 2 -evolution were relatively high compared to other described [NiFe]-hydrogenases. Electron Paramagnetic Resonance (EPR) experiments predicted the presence of both [4Fe-4S]-, and [3Fe-4S] clusters. The hydrogenase encoding DNA region was amplified by using a combination of PCR and inverse PCR and primers based on the N-terminal sequence of the large subunit and a conserved region of NiFe-hydrogenases from other organisms. The sequence harbored binding motifs for two [4Fe-4S] clusters and one [3Fe-4S] cluster, and a twin-arginine motif in the precursor of the small subunit suggesting a periplasmic location of the enzyme. The protein sequences of both subunits of the enzyme showed highest similarity to the enzymes isolated from Desulfovibrio species. Previous studies revealed that in those organisms could catalyze the reduction of protons during syntrophic growth on lactate. Therefore, it is likely that the enzyme isolated from S. fumaroxidans is also used to reduce protons to H 2 during syntrophic growth on propionate.The two formate dehydrogenases of S. fumaroxidans were both isolated and appeared to be enzymes with very high specific activities, both in the direction of formate oxidation as well as in the direction of CO 2 -reduction ( Chapter 7 ). Since a function as formate dehydrogenase was very unlikely during growth of this organism, a more appropriate name for these enzymes would be 'CO 2 -reductases'. Both enzymes could be isolated from fumarate grown cells, but also from cells grown syntrophically on propionate. EPR-experiments revealed the presence of [2Fe-2S] clusters in FDH1, while [4Fe-4S] clusters were detected in both enzymes. The presence of tungsten could not be confirmed with EPR spectroscopy, but metal-analysis demonstrated that both these enzymes were tungsten-selenium proteins and that they did not contain molybdenum. From a comparison of these two enzymes with formate dehydrogenases isolated from other organisms, it was concluded that the few formate dehydrogenases described with a CO 2 -reducing function contain tungsten. Enzymes, which physiologically mainly oxidize formate, may contain either W or Mo, but preferably molybdenum since this compound is present at much higher concentrations in natural environments. It is hypothesized in this Chapter that the Mo-containing enzymes evolved from W-containing enzymes.In Chapter 8 a new hypothesis is proposed for the origin of the eukaryotic cell. The first eukaryote is proposed to have arisen in a methanogenic ecosystem. The host was a heterotrophic fermentative organism, which produced reduced organic compounds. Two endosymbionts were acquired via endocytosis, a acetogenic syntrophic bacterium, and its partner organism a methanogenic archaeon. All partners involved profited from the new situation, which explains the origin of both the nucleus and the mitochondrion in eukaryotic cells. We believe that, among contemporary syntrophic bacteria, the most plausible candidate for a mitochondrial ancestor is a syntrophic propionate oxidizing bacterium.Finally, it can be concluded that syntrophic propionate-oxidizing bacteria possess a unique metabolism and that they may have been involved in the crucial step of evolution. Clearly, these organisms deserve more attention in the future

The velocity distribution of nearby stars from Hipparcos data II. The nature of the low-velocity moving groups

The velocity distribution of nearby stars contains many "moving groups" that are inconsistent with the standard assumption of an axisymmetric, time-independent, and steady-state Galaxy. We study the age and metallicity properties of the low-velocity moving groups based on the reconstruction of the local velocity distribution in Paper I of this series. We perform stringent, conservative hypothesis testing to establish for each of these moving groups whether it could conceivably consist of a coeval population of stars. We conclude that they do not: the moving groups are not trivially associated with their eponymous open clusters nor with any other inhomogeneous star formation event. Concerning a possible dynamical origin of the moving groups, we test whether any of the moving groups has a higher or lower metallicity than the background population of thin disk stars, as would generically be the case if the moving groups are associated with resonances of the bar or spiral structure. We find clear evidence that the Hyades moving group has higher than average metallicity and weak evidence that the Sirius moving group has lower than average metallicity, which could indicate that these two groups are related to the inner Lindblad resonance of the spiral structure. Further we find weak evidence that the Hercules moving group has higher than average metallicity, as would be the case if it is associated with the bar's outer Lindblad resonance. The Pleiades moving group shows no clear metallicity anomaly, arguing against a common dynamical origin for the Hyades and Pleiades groups. Overall, however, the moving groups are barely distinguishable from the background population of stars, raising the likelihood that the moving groups are associated with transient perturbations. [abridged

BCS-Universal Ratios within the Van Hove Scenario

The central result of BCS theory are the Universal Ratios which do not depend on physical parameters of the superconductor under study. Several attempts have been made to introduce the van Hove Scenario within BCS theory but in none of them the Universal Ratios of conventional superconductivity appear to be a number independent of parameters. This fact prevents the precise definition of a deviation from the BCS value for a particular superconductor. This concept is at the basis of several applications of BCS theory in characterizing conventional superconductors. We define a system that constitutes a weak coupling limit that retains the essential features of the high-Tc oxides and which does not differ in any essential way from other models widely used in generalizations of BCS theory to high-Tc superconductors. The difference is that we found a natural way of dealing with the mathematics of the problem so as to get Universal Ratios in the same sense as in conventional superconductivity.Comment: 11 PAGES, NO FIGURES, REVTEX 3.

SOY MILK FERMENTATION

The present invention relates to a method for preparing a soy-based fermented food product using L. delbrueckii and a strain capable of stimulating growth of L. delbrueckii, and a food product obtainable by such method. The invention also provides for a culture comprising said strains, and the use thereof for preparing said fermented food product.</p