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696 results on '"Kegel, Willem"'

151. Self-organization of anisotropic and binary colloids in thermo-switchable 1D microconfinement

Author

De Folter, Julius W J, Liu, Ping, Jiang, Lingxiang, Kuijk, Anke, Bakker, Henriëtte E., Imhof, Arnout, Van Blaaderen, Alfons, Huang, Jianbin, Kegel, Willem K., Philipse, Albert P., Petukhov, Andrei V., Soft Condensed Matter and Biophysics, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, and Sub Soft Condensed Matter

Subjects
Self-organization, thermo-reversibility, endocrine system, Materials science, Chemistry(all), Isotropy, digestive, oral, and skin physiology, Supramolecular chemistry, Nanotechnology, General Chemistry, anisotropy, self-assembly, Condensed Matter Physics, complex mixtures, Rod, body regions, Colloid, Materials Science(all), colloids, confinement, Taverne, General Materials Science, SPHERES, Self-assembly, Anisotropy
Abstract

Anisotropic and binary colloids self-assemble into a variety of novel supracolloidal structures within the thermo-switchable confinement of molecular microtubes, achieving structuring at multiple length scales and dimensionalities. The multistage self-assembly strategy involving hard colloidal particles and a soft supramolecular template is generic for colloids with different geometries and materials as well as their binary mixtures. The colloidal architectures can be controlled by colloid shape, size, and concentration. Colloidal cubes align in chains with face-to-face arrangement, whereas rod-like colloids predominantly self-organize in end-to-end configurations with their long axis parallel with the long axis of the microtubes. The 1D microconfinement imposed on binary mixtures of anisotropic and isotropic colloids further increases the diversity of colloid-in-tube structures. In cube-sphere mixtures, cubes may act as additional confiners, locking in colloidal sphere chains, while a "colloidal Morse code" is generated where rods and spheres alternate in the case of rod-sphere mixtures. The versatile confined colloidal superstructures including their thermoresponsive assembly and disassembly are relevant for the development of stimulus-responsive materials where controlled release and encapsulation are desired. The hierarchical self-assembly of shape-anisotropic colloids and their binary mixtures with isotropic colloids in 1D microconfinement yields a rich variety of novel supracolloidal architectures. The thermo-switchable co-assembly of molecular microtubes and colloidal superstructures is generic for colloids with different geometries, materials, and sizes and may open new routes for controlled release, encapsulation, and data storage applications.

Published
2015

152. Scaling of Gene Expression with Transcription-Factor Fugacity

Author

Weinert, Franz M, Brewster, Robert C, Rydenfelt, Mattias, Phillips, Rob, Kegel, Willem K, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, and Sub Physical and Colloid Chemistry

Subjects
Regulation of gene expression, Models, Genetic, Systems biology, Gene Dosage, General Physics and Astronomy, Computational biology, DNA-Directed RNA Polymerases, Gene dosage, Article, Gene product, Gene Expression Regulation, Regulatory sequence, Gene, Transcription factor, Regulator gene, Transcription Factors
Abstract

The proteins associated with gene regulation are often shared between multiple pathways simultaneously. By way of contrast, models in regulatory biology often assume these pathways act independently. We demonstrate a framework for calculating the change in gene expression for the interacting case by decoupling repressor occupancy across the cell from the gene of interest by way of a chemical potential. The details of the interacting regulatory architecture are encompassed in an effective concentration, and thus, a single scaling function describes a collection of gene expression data from diverse regulatory situations and collapses it onto a single master curve.

Published
2014

153. Equilibrium and non-equilibrium cluster phases in colloids with competing interactions

Author

Mani, Ethayaraja, Lechner, Wolfgang, Kegel, Willem K., Bolhuis, Peter G., Physical and Colloid Chemistry, Chemistry Research: Debye Institute for Nanomaterials Science, and Sub Physical and Colloid Chemistry

Subjects
Chemistry(all), Condensed Matter Physics
Abstract

The phase behavior of colloids that interact via competing interactions-short-range attraction and long-range repulsion-is studied by computer simulation. In particular, for a fixed strength and range of repulsion, the effect of the strength of an attractive interaction (ε) on the phase behavior is investigated at various colloid densities (ρ). A thermodynamically stable equilibrium colloidal cluster phase, consisting of compact crystalline clusters, is found below the fluid-solid coexistence line in the ε-ρ parameter space. The mean cluster size is found to linearly increase with the colloid density. At large ε and low densities, and at small ε and high densities, a non-equilibrium cluster phase, consisting of elongated Bernal spiral-like clusters, is observed. Although gelation can be induced either by increasing ε at constant density or vice versa, the gelation mechanism is different in either route. While in the ρ route gelation occurs via a glass transition of compact clusters, gelation in the ε route is characterized by percolation of elongated clusters. This study both provides the location of equilibrium and non-equilibrium cluster phases with respect to the fluid-solid coexistence, and reveals the dependencies of the gelation mechanism on the preparation route.

Published
2014

155. Versatile procedure for site-specific grafting of polymer brushes on patchy particles via atom transfer radical polymerization (ATRP)

Author

Van Ravensteijn, Bas G P, Kegel, Willem K., Van Ravensteijn, Bas G P, and Kegel, Willem K.

Abstract

We report the preparation of chemically anisotropic colloidal dumbbells of which one lobe is functionalized with chemical handles in the form of chlorine groups. The chlorines are easily converted to azides and subsequently to active initiators for Atom Transfer Radical Polymerization (ATRP) by Click Chemistry. These initiators are exploited for site-specific grafting of poly(N-isopropylacrylamide) (p(NIPAM)) brushes on the reactive patches. The geometric ratio between the grafted and non-grafted lobe is tunable by the shape of the initial dumbbell and the polymer grafting time. Furthermore, the versatility of our synthesis protocol is underlined by extending it to colloids with multiple reactive patches. The partially grafted dumbbell-shaped particles are employed as building blocks for finite-sized colloidal clusters. A directional interaction between the non-grafted lobes is easily introduced by dispersing the partially grafted dumbbels in a high ionic strength medium. Finally, we briefly explore the potency of this system of forming stimuli-responsive colloidal clusters by exploiting the strongly temperature dependent properties of the grafted polymers.

Published
2016

156. Self-assembly of microcapsules via colloidal bond hybridization and anisotropy

Author

Evers, Chris H J, Luiken, Jurriaan A, Bolhuis, Peter G, Kegel, Willem K, Evers, Chris H J, Luiken, Jurriaan A, Bolhuis, Peter G, and Kegel, Willem K

Abstract

Particles with directional interactions are promising building blocks for new functional materials and may serve as models for biological structures. Mutually attractive nanoparticles that are deformable owing to flexible surface groups, for example, may spontaneously order themselves into strings, sheets and large vesicles. Furthermore, anisotropic colloids with attractive patches can self-assemble into open lattices and the colloidal equivalents of molecules and micelles. However, model systems that combine mutual attraction, anisotropy and deformability have not yet been realized. Here we synthesize colloidal particles that combine these three characteristics and obtain self-assembled microcapsules. We propose that mutual attraction and deformability induce directional interactions via colloidal bond hybridization. Our particles contain both mutually attractive and repulsive surface groups that are flexible. Analogously to the simplest chemical bond-in which two isotropic orbitals hybridize into the molecular orbital of H2-these flexible groups redistribute on binding. Via colloidal bond hybridization, isotropic spheres self-assemble into planar monolayers, whereas anisotropic snowman-shaped particles self-assemble into hollow monolayer microcapsules. A modest change in the building blocks thus results in much greater complexity of the self-assembled structures. In other words, these relatively simple building blocks self-assemble into markedly more complex structures than do similar particles that are isotropic or non-deformable.

Published
2016

158. Kinetics versus thermodynamics in virus capsid polymorphism

Author

Sub Physical and Colloid Chemistry, Sub Algemeen Theoretical Physics, Physical and Colloid Chemistry, Moerman, Pepijn, Van Der Schoot, Paul, Kegel, Willem, Sub Physical and Colloid Chemistry, Sub Algemeen Theoretical Physics, Physical and Colloid Chemistry, Moerman, Pepijn, Van Der Schoot, Paul, and Kegel, Willem

Published
2016

160. Selective Depletion Interactions in Mixtures of Rough and Smooth Silica Spheres

Author

Sub Soft Condensed Matter, Debye Institute, Sub Physical and Colloid Chemistry, Soft Condensed Matter and Biophysics, Kamp, Marlous, Hermes, Michiel, Van Kats, Carlos M., Kraft, Daniela J., Kegel, Willem K., Dijkstra, Marjolein, Van Blaaderen, Alfons, Sub Soft Condensed Matter, Debye Institute, Sub Physical and Colloid Chemistry, Soft Condensed Matter and Biophysics, Kamp, Marlous, Hermes, Michiel, Van Kats, Carlos M., Kraft, Daniela J., Kegel, Willem K., Dijkstra, Marjolein, and Van Blaaderen, Alfons

Published
2016

161. Self-assembly of microcapsules via colloidal bond hybridization and anisotropy

Author

Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, Evers, Chris H J, Luiken, Jurriaan A, Bolhuis, Peter G, Kegel, Willem K, Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, Evers, Chris H J, Luiken, Jurriaan A, Bolhuis, Peter G, and Kegel, Willem K

Published
2016

165. The different faces of mass action in virus assembly.

Author

van der Holst, Bart, Kegel, Willem K., Zandi, Roya, and van der Schoot, Paul

Subjects
*PROTEINS, *CAPSIDS, *POLYANIONS, *ENTROPY, *CYTOSOL
Abstract

The spontaneous encapsulation of genomic and non-genomic polyanions by coat proteins of simple icosahedral viruses is driven, in the first instance, by electrostatic interactions with polycationic RNA binding domains on these proteins. The efficiency with which the polyanions can be encapsulated in vitro, and presumably also in vivo, must in addition be governed by the loss of translational and mixing entropy associated with co-assembly, at least if this co-assembly constitutes a reversible process. These forms of entropy counteract the impact of attractive interactions between the constituents and hence they counteract complexation. By invoking mass action-type arguments and a simple model describing electrostatic interactions, we show how these forms of entropy might settle the competition between negatively charged polymers of different molecular weights for co-assembly with the coat proteins. In direct competition, mass action turns out to strongly work against the encapsulation of RNAs that are significantly shorter, which is typically the case for non-viral (host) RNAs. We also find that coat proteins favor forming virus particles over nonspecific binding to other proteins in the cytosol even if these are present in vast excess. Our results rationalize a number of recent in vitro co-assembly experiments showing that short polyanions are less effective at attracting virus coat proteins to form virus-like particles than long ones do, even if both are present at equal weight concentrations in the assembly mixture. [ABSTRACT FROM AUTHOR]

Published
2018
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166. Rotational averaging-out gravitational sedimentation of colloidal dispersions and phenomena

Author

Masri, Djamel El, Vissers, Teun, Badaire, Stephane, Stiefelhagen, Johan C. P., Vutukuri, Hanumantha Rao, Helfferich, Peter, Zhang, Tian Hui, Kegel, Willem K., Imhof, Arnout, and van Blaaderen, Alfons

Subjects
body regions, Condensed Matter::Soft Condensed Matter, endocrine system, Physics - Space Physics, digestive, oral, and skin physiology, Soft Condensed Matter (cond-mat.soft), FOS: Physical sciences, Condensed Matter - Soft Condensed Matter, complex mixtures, Space Physics (physics.space-ph)
Abstract

We report on the differences between colloidal systems left to evolve in the earth's gravitational field and the same systems for which a slow continuous rotation averaged out the effects of particle sedimentation on a distance scale small compared to the particle size. Several systems of micron-sized colloidal particles were studied: a hard sphere fluid, colloids interacting via long-range electrostatic repulsions above the freezing volume fraction, an oppositely charged colloidal system close to either gelation and/or crystallization, colloids with a competing short-range depletion attraction and a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal gold platelets under conditions where they formed stacks. Important differences in the structure formation were observed between the experiments where the particles were allowed to sediment and those where sedimentation was averaged out. For instance, in the case of colloids interacting via long-range electrostatic repulsions, an unusual sequence of dilute-Fluid/dilute-Crystal/dense-Fluid/dense-Crystal phases was observed throughout the suspension under the effect of gravity, related to the volume fraction dependence of the colloidal interactions, whereas the system stayed homogeneously crystallized with rotation. For the oppositely charged colloids, a gel-like structure was found to collapse under the influence of gravity with a few crystalline layers grown on top of the sediment, whereas when the colloidal sedimentation was averaged out, the gel completely transformed into crystallites that were oriented randomly throughout the sample. Rotational averaging out gravitational sedimentation is an effective and cheap way to estimate the importance of gravity for colloidal self-assembly processes., Comment: 13 pages, 13 figures

Published
2011
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168. Structure and stacking order in crystals of asymmetric dumbbell-like colloids

Author

Pal, Antara, Meijer, Janne-Mieke, Wolters, Joost R., Kegel, Willem K., Petukhov, A. V., Pal, Antara, Meijer, Janne-Mieke, Wolters, Joost R., Kegel, Willem K., and Petukhov, A. V.

Abstract

The crystalline structure assembled out of charge-stabilized asymmetric dumbbell-like colloidal particles in ethyl alcohol by sedimentation has been probed using small-angle X-ray scattering with microradian resolution. The existence of plastic face-centered cubic crystals was inferred from the observed Bragg peaks. The presence of stacking faults and the mosaic structure of the sample lead to the appearance of diffuse scattering, forming Bragg scattering cylinders in the three-dimensional reciprocal space. The quality of the crystalline structure, as ascertained from a detailed analysis of the diffuse scattering intensity distribution, indicates the presence of only 1.5% of stacking faults between the hexagonal close-packed layers.

Published
2015

169. Morphology-controlled functional colloids by heterocoagulation of zein and nanoparticles

Author

Baars, Roel J., van Leeuwen, Y. Mikal, Hendrix, Yuri, Velikov, Krassimir P., Kegel, Willem K., Philipse, Albert P., Baars, Roel J., van Leeuwen, Y. Mikal, Hendrix, Yuri, Velikov, Krassimir P., Kegel, Willem K., and Philipse, Albert P.

Abstract

A general and reproducible heterocoagulation method is presented to prepare sub-micron sized zein protein particles, loaded with negatively charged nanoparticles. These composite carrier particles can be obtained in three different morphologies, and each morphology can be prepared using nanoparticles of various size, shape and composition. An important feature of the zein composites is their long-term stability in water even in conditions where free nanoparticles often aggregate within days. Additionally, we modify the composite particles by coating them with a thin layer of silica via condensation of sodium silicate, opening possibilities for highly specific, functionalized carrier particles. Finally, the formation of hollow silica shells containing negatively charged nanoparticles is demonstrated, using the zein composites as a template.

Published
2015

170. Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

Author

Pal, Antara, Malik, Vikash, He, Le, Erne, Ben H., Yin, Yadong, Kegel, Willem K., Petukhov, A. V., Pal, Antara, Malik, Vikash, He, Le, Erne, Ben H., Yin, Yadong, Kegel, Willem K., and Petukhov, A. V.

Abstract

Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-assembly of core-shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close-packed (RHCP) one. External field drives the self-assembly toward a body-centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles.

Published
2015

171. Self-assembly of 'Mickey Mouse' shaped colloids into tube-like structures: experiments and simulations

Author

Wolters, Joost Robert, Avvisati, Guido, Hagemans, Fabian, Vissers, Teun, Kraft, Daniela J, Dijkstra, Marjolein, Kegel, Willem, Wolters, Joost Robert, Avvisati, Guido, Hagemans, Fabian, Vissers, Teun, Kraft, Daniela J, Dijkstra, Marjolein, and Kegel, Willem

Abstract

The self-assembly of anisotropic patchy particles with a triangular shape was studied by experiments and computer simulations. The colloidal particles were synthesized in a two-step seeded emulsion polymerization process, and consist of a central smooth lobe connected to two rough lobes at an angle of [similar]90°, resembling the shape of a “Mickey Mouse” head. Due to the difference in overlap volume, adding an appropriate depletant induces an attractive interaction between the smooth lobes of the colloids only, while the two rough lobes act as steric constraints. The essentially planar geometry of the Mickey Mouse particles is a first geometric deviation of dumbbell shaped patchy particles. This new geometry enables the formation of one-dimensional tube-like structures rather than spherical, essentially zero-dimensional micelles. At sufficiently strong attractions, we indeed find tube-like structures with the sticky lobes at the core and the non-sticky lobes pointing out as steric constraints that limit the growth to one direction, providing the tubes with a well-defined diameter but variable length both in experiments and simulations. In the simulations, we found that the internal structure of the tubular fragments could either be straight or twisted into so-called Bernal spirals.

Published
2015

174. Polydispersity and gelation in concentrated colloids with competing interactions

Author

Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, Zhang, Tian Hui, Kuipers, Bonny W M, Tian, Wen De, Groenewold, Jan, Kegel, Willem K., Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, Zhang, Tian Hui, Kuipers, Bonny W M, Tian, Wen De, Groenewold, Jan, and Kegel, Willem K.

Published
2015

175. Self-organization of anisotropic and binary colloids in thermo-switchable 1D microconfinement

Author

Soft Condensed Matter and Biophysics, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Sub Soft Condensed Matter, De Folter, Julius W J, Liu, Ping, Jiang, Lingxiang, Kuijk, Anke, Bakker, Henriëtte E., Imhof, Arnout, Van Blaaderen, Alfons, Huang, Jianbin, Kegel, Willem K., Philipse, Albert P., Petukhov, Andrei V., Soft Condensed Matter and Biophysics, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Sub Soft Condensed Matter, De Folter, Julius W J, Liu, Ping, Jiang, Lingxiang, Kuijk, Anke, Bakker, Henriëtte E., Imhof, Arnout, Van Blaaderen, Alfons, Huang, Jianbin, Kegel, Willem K., Philipse, Albert P., and Petukhov, Andrei V.

Published
2015

176. Self-assembly of 'Mickey Mouse' shaped colloids into tube-like structures: experiments and simulations

Author

Soft Condensed Matter and Biophysics, Sub Physical and Colloid Chemistry, Sub Soft Condensed Matter, Dep Scheikunde, Wolters, Joost Robert, Avvisati, Guido, Hagemans, Fabian, Vissers, Teun, Kraft, Daniela J, Dijkstra, Marjolein, Kegel, Willem, Soft Condensed Matter and Biophysics, Sub Physical and Colloid Chemistry, Sub Soft Condensed Matter, Dep Scheikunde, Wolters, Joost Robert, Avvisati, Guido, Hagemans, Fabian, Vissers, Teun, Kraft, Daniela J, Dijkstra, Marjolein, and Kegel, Willem

Published
2015

177. Morphology-controlled functional colloids by heterocoagulation of zein and nanoparticles

Author

Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Sub Soft Condensed Matter, Soft Condensed Matter and Biophysics, Baars, Roel J., van Leeuwen, Y. Mikal, Hendrix, Yuri, Velikov, Krassimir P., Kegel, Willem K., Philipse, Albert P., Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Sub Soft Condensed Matter, Soft Condensed Matter and Biophysics, Baars, Roel J., van Leeuwen, Y. Mikal, Hendrix, Yuri, Velikov, Krassimir P., Kegel, Willem K., and Philipse, Albert P.

Published
2015

178. Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

Author

Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Pal, Antara, Malik, Vikash, He, Le, Erne, Ben H., Yin, Yadong, Kegel, Willem K., Petukhov, A. V., Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Pal, Antara, Malik, Vikash, He, Le, Erne, Ben H., Yin, Yadong, Kegel, Willem K., and Petukhov, A. V.

Published
2015

179. Structure and stacking order in crystals of asymmetric dumbbell-like colloids

Author

Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, Pal, Antara, Meijer, Janne-Mieke, Wolters, Joost R., Kegel, Willem K., Petukhov, A. V., Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, Pal, Antara, Meijer, Janne-Mieke, Wolters, Joost R., Kegel, Willem K., and Petukhov, A. V.

Published
2015

183. Self-Assembly: Self-Organization of Anisotropic and Binary Colloids in Thermo-Switchable 1D Microconfinement (Part. Part. Syst. Charact. 3/2015)

Author

de Folter, Julius W. J., primary, Liu, Ping, additional, Jiang, Lingxiang, additional, Kuijk, Anke, additional, Bakker, Henriëtte E., additional, Imhof, Arnout, additional, van Blaaderen, Alfons, additional, Huang, Jianbin, additional, Kegel, Willem K., additional, Philipse, Albert P., additional, and Petukhov, Andrei V., additional

Published
2015
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187. Colloids with Continuously Tunable Surface Charge

Author

Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, van Ravensteijn, Bas G. P., Kegel, Willem K., Sub Physical and Colloid Chemistry, Physical and Colloid Chemistry, van Ravensteijn, Bas G. P., and Kegel, Willem K.

Published
2014

188. Scaling of gene expression with transcription-factor fugacity

Author

Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Weinert, Franz M, Brewster, Robert C, Rydenfelt, Mattias, Phillips, Rob, Kegel, Willem K, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Weinert, Franz M, Brewster, Robert C, Rydenfelt, Mattias, Phillips, Rob, and Kegel, Willem K

Published
2014

189. Equilibrium and non-equilibrium cluster phases in colloids with competing interactions

Author

Physical and Colloid Chemistry, Chemistry Research: Debye Institute for Nanomaterials Science, Sub Physical and Colloid Chemistry, Mani, Ethayaraja, Lechner, Wolfgang, Kegel, Willem K., Bolhuis, Peter G., Physical and Colloid Chemistry, Chemistry Research: Debye Institute for Nanomaterials Science, Sub Physical and Colloid Chemistry, Mani, Ethayaraja, Lechner, Wolfgang, Kegel, Willem K., and Bolhuis, Peter G.

Published
2014

196. Model systems for self-assembly

Author

Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Kegel, Willem, Kraft, D.J., Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Kegel, Willem, and Kraft, D.J.

Published
2010

197. Assemblies of Polyoxometalates

Author

Colloïden en grenslagen, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Kegel, Willem, Veen, S.J., Colloïden en grenslagen, Physical and Colloid Chemistry, Sub Physical and Colloid Chemistry, Kegel, Willem, and Veen, S.J.

Published
2009

199. Structure and Dynamics at Colloidal Boundaries

Author

Colloïden en grenslagen, Dep Scheikunde, Lekkerkerker, Henk, Kegel, Willem, Petoukhov, Andrei, de Villeneuve, V.W.A., Colloïden en grenslagen, Dep Scheikunde, Lekkerkerker, Henk, Kegel, Willem, Petoukhov, Andrei, and de Villeneuve, V.W.A.

Published
2008

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