56,376 research outputs found
Introduction. Postcolonial migrations and identity politics. Towards a comparative perspective.
No full textColonial and Global Histor
Sugarlandia revisited: Sugar and colonialism in Asia and the Americas, 1800 to 1940: an Introduction
No full textStudies on 2-oxoacid dehydrogenase multienzyme complexes of Azotobacter vinelandii
No full textIn this thesis, some studies on the pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase multienzyme complexes of Azotobacter vinelandii are described; the emphasis strongly lies on the pyruvate dehydrogenase complex.A survey of the literature on 2-oxoacid dehydrogenase complexes is given in chapter 1. It appears that the A.vinelandii pyruvate dehydrogenase complex resembles the complexes from other gram-negative bacteria with respect to its composition and working mechanism. The A.vinelandii complex is however much smaller than the pyruvate dehydrogenase complexes isolated from other sources.Chapter 2 describes the procedure that has been optimized for the isolation of the pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase multienzyme complexes (PDC and OGDC respectively) from A.vinelandii. In comparison to the previous isolation procedure, several advantages exist. The A.vinelandii PDC is obtained as an essentially pure three-component complex, in a high yield (40-50%). 80% of the losses can be accounted for by discarded side-fractions, which indicates that the complex is hardly inactivated during its purification. The specific activity of the final preparation is about two times higher (15-19 U/mg) than previously could be obtained. From these observations we conclude that the formerly observed "fourth component" of A.vinelandii PDC was a mere contaminant. With the revised procedure, the 2-oxoglutarate dehydrogenase complex (OGDC) is obtained in a high yield (40-50%), free from contaminants. In the "old" procedure this complex was irreversibly inactivated by the action of protamine sulfate.In chapter 3 some observations on the A.vinelandii OGDC are reported. The molecular mass of this complex is of the order of 2.4 to 3.2 MDa, as determined by laser light-scattering measurements. The three component enzymes have the same molecular masses as have been reported for the OGDC's of Escherichia coli and pig-heart. The activity of the complex is regulated by its substrates in an analogues way as has been reported for the E.coli complex, and we therefore conclude that the A.vinelandii complex probably strongly resembles the OGDC of E.coli. In this chapter, an isolation procedure for the lipoamide dehydrogenase component is described, and it is shown that the lipoamide dehydrogenase components of the A.vinelandii PDC and OGDC probably are identical.The association behaviour of the A.vinelandii pyruvate dehydrogenase complex is described in chapter 4. From sedimentation and light-scattering studies we conclude that a monomer-dimer equilibrium exists for this complex; the molecular mass of the monomer has been estimated that 800 kDa. In this thesis, this monomer-dimer mixture is referred to as the 18 S form of the complex. Upon addition of polyethylene glycol 6000 and MgCl 2 , the 18 S form of the complex aggregates into a large structure, resembling the pyruvate dehydrogenase complex of E.coli with respect to its sedimentation, coefficient (56 S) and its appearance on electron micrographs. The isolated dihydrolipoyl transacetylase component of A.vinelandii PDC has a molecular mass of 2 MDa, and on electron micrographs it resembles the dihydrolipoyl acetyltransferase component of E.coli. It is concluded that this large structure probably is composed of 32 subunits. Upon the binding of the pyruvate dehydrogenase and lipoamide dehydrogenase components, this large particle dissociates into the smaller structures that are characteristic for the intact A.vinelandii complex. The small (18 S) and the large (56 S) forms of the (sub)complexes are in slow equilibrium, and this equilibrium can be perturbed by high hydrostatic pressure. From light-scattering measurements at varying pressures it is concluded that the 56 S form of the complex probably is an octamer of the 800 kDa monomers.The measurements concerning the chain-stoichiometry of A.vinelandii PDC are described in chapter 5. A novel method for the determination of chain-ratios was developed, based on the covalent modification of lysine residues in the three component enzymes with trinitrobenzene sulfonic acid. With this technique, an average chain ratio of 1.3:1:0.5 (pyruvate hydrogenase: dihydrolipoyl acetyl transferase:lipoamide dehydrogenase) was found for the isolated A.vinelandii PDC. In combination with the results of chapter 4, it is concluded that A.vinelandii PDC is based on a tetrameric dihydrolipoyl acetyltransferase core, to which the periferal components are bound in a non-covalent way. The complex can be reconstituted from its individual components, and from these reconstitution experiments it follows that the complex has maximal activity when three pyruvate dehydrogenase dimers and one lipoamide dehydrogenase dimer are bound to the dihydrolipoyl transacetylase tetramer.In chapter 6, the results of acetylation experiments are given. It is shown that the reductive acetylation of the lipoyl groups probably is the rate-limiting step in the reaction sequence of the A.vinelandii pyruvate dehydrogenase complex. In so-called servicing experiments, an extensive exchange of acetyl groups between individual (monomeric) pyruvate dehydrogenase complex particles is found. This phenomenon (inter-core transacetylation) has until now only been observed for the A.vinetandii complex. It is shown that the inter-core transacetylation occurs when two monomeric particles are associated. Although the transacetylation reactions show large effects in the servicing experiments, these reactions are however too slow to be of physiological importance. The servicing experiments also show that the large " E.coli -like" isolated dihycirolipoyl acetyltransferase component is composed of rather independently operating tetramers, i.e. the large form of the A.vinelandii PDC does not function as a large entity.In chapter 7, the results of the three preceding chapters are summarized and translated into a three-dimensional model of the molecular organisation of the A.vinelandii PDC. The merits of this model are discussed in relation to the generally accepted model for the pyruvate dehydrogenase complex of E.coli. It is suggested that the pyruvate of Azotobacter vinelandii could represent the morphological subunit of the larger structure that is found in Escherichia coli and perhaps in other gramnegative bacteria. It is concluded that further experiments have to be performed, in which the complexes of the two organisms are directly compared. to establish whether such a unifying model does exist
Smallpox, Vaccinations, and Demographic Divergences in Nineteenth-Century Colonial Indonesia
No full text© Ulbe Bosma, 2015.Existing literature and available demographic data suggest a strong divergence between Java and the Outer Islands with regard to nineteenth-century demographic trends. In this article, I argue that such a divergence is highly plausible, because of the inchoate vaccination efforts against smallpox in the Outer Islands in contrast with those on Java during the nineteenth century. I suggest that further research is needed into other factors that might also have contributed to the perceived divergence. These include relatively low birth rates in the Outer Islands as well as the ubiquity of slavery in this part of the Indonesian archipelago and its exposure to slave-raiding and the slave trade. The article concludes by arguing that, in all likelihood, demographic growth was very limited in most, but not all, of the Outer Islands up to the late nineteenth century
Military Migrants. Luxembourgers in the Colonial Army of the Dutch East Indies
No full textpeer reviewedAmong the roughly 150,000 soldiers sent to the Dutch East Indies between 1815 and 1914, the Luxembourg contingent made up a tiny minority of just 1,075 men. Based upon extensive research into their careers, data on these soldiers provide further clues to understanding what drove Europe’s young men to become colonial soldiers. The results of this national case study will be compared with earlier investigations by Bossenbroek and Bosma on recruits for the Dutch colonial army. Similar to the Dutch soldiers, their Luxembourg counterparts had a predominantly urban provenance. However, in contrast to the Dutch, they did not have a strong military background, and it appears that fewer Luxembourgers stayed behind in the Dutch East Indies after their tour of duty. They were more attracted by the payments that the recruiters doled out in advance, particularly at a time of economic crisis, than in a career in the tropics
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
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