The p-rank stratification on the Siegel moduli space with Iwahori level structure

Our concern in this paper is to describe the p-rank statification on the Siegel moduli space with Iwahori level structure over fields of positive characteristic. We calculate the dimension of the strata and describe the closure of a given stratum in terms of p-rank strata. We also examine the relationship between the p-rank stratification and the Kottwitz-Rapoport stratification.Comment: 29 pages; v2: new result Theorem 0.2 (2c), revised section 3; v3: Added formula for number of top-dimensional KR strata v4: simplified formula and corrected mistakes of v

Three-dimensional Transmission Electron Microscopy observations of mesopores in dealuminated zeolite Y**

Supported by NWO under grant 98037. The research of AJK has been made possible by a fellowship of the Royal Netherlands Academy of Arts and Sciences (KNAW). The authors thank J.E.M.J. Raaymakers for the nitrogen physisorption measurements, A.J.M. Mens for the XPS measurements, J.A.R. van Veen and E.J. Creyghton for physical data and useful discussions and Shell International Chemicals and Zeolyst for the samples

Three-Dimensional Transmission Electron Microscopy: A Novel Imaging and Characterization Technique with Nanometer Scale Resolution for Materials Science

Three-dimensional transmission electron microscopy (3D-TEM), effectuated by multiple imaging of a sample combined with image analysis, offers a new approach in materials science to obtain 3D information of complex solid materials. Here we report first-of-its-kind results that have been obtained with zeolite materials. Virtual cross-sections and volume rendering of the 3D reconstruction of a metal/zeolite crystal (Ag/NaY) give unequivocal information on the location of the silver particles (10-40 nm in diameter). Virtual cross-sections of the 3D reconstruction of an acid-leached mordenite show the three-dimensional mesoporous channel system (3-20 nm in diameter) with a clarity and definition not seen before

Base-catalyzed condensation of citral and acetone at low temperature using modified hydrotalcite catalysts

A study on the catalytic properties of properly activated hydrotalcite (HT) with special attention to the nature and amount of active sites present in this solid base catalyst has been undertaken. Only a small fraction (5%) of the available basic sites in the rehydrated calcined HT is active in liquid-phase aldol condensations. These sites exhibit high catalytic activity and are most likely localized at the edges of the HT-platelets. Besides a high activity, these modified HTs also show a high selectivity. No further condensation products other than diacetone alcohol (DAA) in the acetone self-condensation could be observed. Initial results with the citralacetone condensation show that even at 273 K this reaction is catalyzed by modified HTs with a conversion of 65% and a selectivity of 90%, when the citral concentration is not too high ( 1 wt.%). At higher citral concentrations, no reaction is observed indicating a negative order in citral concentration. © 2000 Elsevier Science B.V. All rights reserved

Immunometabolism in osteoarthritis

Immunometabolism focusses on the interplay between immunological and metabolic processes, both at a systemic and a cellular level. This thesis is divided into two parts based on these two levels. The first part focusses on the infrapatellar fat pad (IFP), an adipose tissue located in the knee, and the potential role in the pathophysiology of osteoarthritis. Therefore, we characterized the IFP based on a cellular and molecular level and found that the inflammatory state of the joint does affect the cellular load of the IFP, however, the secretory profile of the IFP does not seem to be affected. Furthermore, obesity-related changes normally found in adipose tissue were not present in the IFP. When characterizing the IFP we found two interesting cell populations, IL-6-secreting T cells and macrophages with an anti-inflammatory phenotype secreting pro-inflammatory cytokines. Both populations could be involved in the pathophysiology of the osteoarthritic joint. Furthermore, in the second part we focussed on cellular metabolism where we determined the mechanism by which fatty acids exert their effect on T cells. We found that fatty acids are not served as energy, however, whether it is used for daughter cells or influencing cell signalling remains to be elucidated. LUMC / Geneeskund

Characterization of an endochitinase able to rescue the carrot somatic embryo variant ts11

Cultured carrot cells secrete proteins, many of which are glycosylated, into the culture medium. A correlation has been found between somatic embryogenesis and the presence or absence of some of these secreted proteins, and evidence has been obtained that one or more secreted glycoproteins are actually essential for somatic embryo formation. The starting point of the experiments described in this thesis was the temperature-sensitive carrot cell line ts11, originally identified on the basis of the temperature- sensitive arrest in the transition of globular to heart stage somatic embryos. The arrest in ts11 embryo development at the nonpermissive temperature could be lifted by addition of medium proteins, secreted by wildtype cells, to the culture medium. The major goal of the study presented in this thesis was to identify the secreted proteins, that were able to rescue the arrested ts11 embryos.In chapter 1 a brief introduction in zygotic and somatic embryogenesis is presented, followed by an overview of what is currently known about the first essential steps of the development of the zygotic embryo and of the formation of embryogenic cells and somatic embryos in vitro. Based on these studies, it is discussed whether analogous cellular mechanisms control early zygotic embryogenesis and the formation of embryogenic cells in tissue culture.In chapter 2 the experiments are described that demonstrate that is 11 embryos can be rescued by a single secreted protein of 32 kD. The amino acid sequences of two tryptic peptides of this protein shared homology with several plant endochitinases. Biochemical analysis showed that the 32-kD protein is an acidic endochitinase.In chapter 3 the results of a search for putative products of endochitinase activity effective in ts l 1 rescue, are presented. A molecule produced by Rhizobium, the N-acetylglucosamine-containing lipo-oligosaccharide, NodR1v-V(Ac, C18:4), appeared to be effective in stimulating the formation of ts11 embryos with a similar efficiency as the 32-kD endochitinase.In chapter 4 evidence is presented that a decreased amount of an otherwise fully functional endochitinase is closely correlated with the window of sensitivity of ts1 1 cells to addition of the 32-kD endochitinase. Morphological observations suggest that the original ts l 1 mutation is quite pleiotropic and does not only affect embryogenesis in this line.In chapter 5 experiments are described to identify a 32-kD endochitinase cDNA. The deduced amino acid sequence of the isolated cDNAs was found to be nearly identical to the amino acid sequences of the 32-kD endochitinase-derived peptides. The EP3 cDNA sequences suggested that the 32-kD endochitinse is a class IV chitinase.Finally, in chapter 6 the significance of chitinases and lipo-oligosaccharides for plant development in general is discussed

Development and Application of 3-Dimensional Transmission Electron Microscopy (3D-TEM) for the Characterization of Metal-Zeolite Catalyst Systems

With electron tomography (3D-TEM) a 3D-reconstruction is calculated from a series of TEM images taken at a tilt angle range (tilting range) of +70° to -70°. The reconstruction can be visualized with contour surfaces that give information about the surface of the sample as well as with slices through the reconstruction that give detailed information on the interior of the sample. Electron tomography gives much more information than Scanning Electron Microscopy (SEM), since SEM gives only information about the surface of a sample. As a case study, the imaging of silver clusters on zeolite NaY is given. The reconstruction shows silver particles at the external surface as well as a silver particle in a mesopore of the zeolite crystallite. It is concluded that 3D-TEM comprises a breakthrough in the characterization of nano-structured solid catalysts