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Search Results: 1 - 10 of 3638 matches for " Dirk Voigt "
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Long-Term Outperformance of Equity Carve-Outs?— Evidence from Germany  [PDF]
Arnd Schikowsky, Dirk Schiereck, Arndt Volkle, Christian Voigt
Technology and Investment (TI) , 2010, DOI: 10.4236/ti.2010.11002
Abstract: While there has been done a lot of empirical research on IPO performance in general only Prezas et al. [1] focus on equity carve-outs (ECOs) in comparison to common IPOs from an investor’s point of view. ECOs are an often applied divestment alternative used by technology companies to refocus their core businesses. Our note is claiming to extent this distinct literature in two ways. Firstly, we add new insight from a European market, namely Germany, and secondly, we apply a wider methodological spectrum to compare IPOs and ECOs. We find that controlling for the specific return characteristics of IPOs there remain hardly any sig-nificant performance divergences between the two samples.
Molecular evolution of rDNA in early diverging Metazoa: First comparative analysis and phylogenetic application of complete SSU rRNA secondary structures in Porifera
Oliver Voigt, Dirk Erpenbeck, Gert W?rheide
BMC Evolutionary Biology , 2008, DOI: 10.1186/1471-2148-8-69
Abstract: Here, we explore SSU rRNA secondary structures from the three extant classes of Phylum Porifera (Grant, 1836), a pivotal, but largely unresolved taxon of early branching Metazoa. This is the first phylogenetic study of poriferan SSU rRNA data to date that includes detailed comparative secondary structure information for all three sponge classes.We found base compositional and structural differences in SSU rRNA among Demospongiae, Hexactinellida (glass sponges) and Calcarea (calcareous sponges). We showed that analyses of primary rRNA sequences, including secondary structure-specific evolutionary models, in combination with reconstruction of the evolution of unusual structural features, reveal a substantial amount of additional information. Of special note was the finding that the gene tree topologies of marine haplosclerid demosponges, which are inconsistent with the current morphology-based classification, are supported by our reconstructed evolution of secondary structure features. Therefore, these features can provide alternative support for sequence-based topologies and give insights into the evolution of the molecule itself. To encourage and facilitate the application of rRNA models in phylogenetics of early metazoans, we present 52 SSU rRNA secondary structures over the taxonomic range of Porifera in a database, along with some basic tools for relevant format-conversion.We demonstrated that sophisticated secondary structure analyses can increase the potential phylogenetic information of already available rDNA sequences currently accessible in databases and conclude that the importance of SSU rRNA secondary structure information for phylogenetic reconstruction is still generally underestimated, at least among certain early branching metazoans.Tens of thousands of sequences of the small subunit ribosomal RNA (SSU rRNA, 18S) gene of eukaryotes have accumulated in public databases such as NCBI GenBank [1], making this gene one of the first and most frequently used
A fragmented metazoan organellar genome: the two mitochondrial chromosomes of Hydra magnipapillata
Oliver Voigt, Dirk Erpenbeck, Gert W?rheide
BMC Genomics , 2008, DOI: 10.1186/1471-2164-9-350
Abstract: The H. magnipapillata mt chromosomes contain the typical metazoan set of 13 genes for respiratory proteins, the two rRNA genes and two tRNA genes. All genes are unidirectionally oriented on mt1 and mt2, and several genes overlap. The gene arrangement suggests that the two mt chromosomes originated from one linear molecule that separated between nd5 and rns. Strong correlations between the AT content of rRNA genes (rns and rnl) and the AT content of protein-coding genes among 24 cnidarian genomes imply that base composition is mainly determined by mt genome-wide constraints. We show that identical inverted terminal repeats (ITR) occur on both chromosomes; these ITR contain a partial copy or part of the 3' end of cox1 (54 bp). Additionally, both mt chromosomes possess identical oriented sequences (IOS) at the 5' and 3' ends (5' and 3' IOS) adjacent to the ITR. The 5' IOS contains trnM and non-coding sequences (119 bp), whereas the 3' IOS comprises a larger part (mt2) with a larger partial copy of cox1 (243 bp).ITR are also documented in the two other available medusozoan mt genomes (Aurelia aurita and Hydra oligactis). In H. magnipapillata, the arrangement of ITR and 5' IOS and 3' IOS suggest that these regions are crucial for mt DNA replication and/or transcription initiation. An analogous organization occurs in a highly fragmented ichthyosporean mt genome. With our data, we can reject a model of mt replication that has previously been proposed for Hydra. This raises new questions regarding replication mechanisms probably employed by all medusozoans, and also has general implications for the expected organization of fragmented linear mt chromosomes of other taxa.Mitochondria were most likely acquired by the common ancestor of eukaryotes [1-3]. Presumably, these organelles originated from incorporated α-proteobacteria and still carry their own, reduced genome [1]. Mitochondrial (mt) genomes show very diverse organizations and are of a very broad range of sizes [3-5].
The mitochondrial genomes of sponges provide evidence for multiple invasions by Repetitive Hairpin-forming Elements (RHE)
Dirk Erpenbeck, Oliver Voigt, Gert W?rheide, Dennis V Lavrov
BMC Genomics , 2009, DOI: 10.1186/1471-2164-10-591
Abstract: Mt genomes of dictyoceratid sponges are identical in gene order and content but display major differences in size and organization of intergenic regions. An even higher degree of diversity in the structure of intergenic regions was found among different orders of demosponges. One interesting observation made from such comparisons was of what appears to be recurrent invasions of sponge mitochondrial genomes by repetitive hairpin-forming elements, which cause large genome size differences even among closely related taxa. These repetitive hairpin-forming elements are structurally and compositionally divergent and display a scattered distribution throughout various groups of demosponges.Large intergenic regions of poriferan mt genomes are targets for insertions of repetitive hairpin- forming elements, similar to the ones found in non-metazoan opisthokonts. Such elements were likely present in some lineages early in animal mitochondrial genome evolution but were subsequently lost during the reduction of intergenic regions, which occurred in the Eumetazoa lineage after the split of Porifera. Porifera acquired their elements in several independent events. Patterns of their intra-genomic dispersal can be seen in the mt genome of Vaceletia sp.Organellar genomes display a tendency of size reduction (deletional bias) [1]. This tendency manifests itself in the loss of mitochondrial (mt) protein genes or their relocation to the nucleus, and in the loss of intergenic non-coding sequences. For example, comparison between animal mt genomes and that of the choanoflagellate Monosiga brevicollis revealed that a major reduction of mtDNA has taken place in the animal lineage, which involved the translocation of mitochondrial genes into the nucleus and dramatic size reduction of intergenic regions (IGR) [2]. Indeed, the IGRs account for almost 50% of the 76 kb mt genome of M. brevicollis [3], while the poriferan genomes examined so far from Demospongiae, Homoscleromorpha and Hexactinelli
Depolarizing power and polarization entropy of light scattering media: experiment and theory
Graciana Puentes,Dirk Voigt,Andrea Aiello,J. P. Woerdman
Physics , 2004,
Abstract: We experimentally investigate the depolarizing power and the polarization entropy of a broad class of scattering optical media. By means of polarization tomography, these quantities are derived from an effective Mueller matrix, which is introduced through a formal description of the multi-mode detection scheme we use, as recently proposed by Aiello and Woerdman (arXiv:quant-ph/0407234). This proposal emphasized an intriguing universality in the polarization aspects of classical as well as quantum light scattering; in this contribution we demonstrate experimentally that this universality is obeyed by a surprisingly wide class of depolarizing media. This, in turn, provides the experimentalist with a useful characterization of the polarization properties of any scattering media, as well as a universal criterion for the validity of the measured data.
Immunohistochemical Detection of TAS2R38 Protein in Human Taste Cells
Maik Behrens, Stephan Born, Ulrike Redel, Nadine Voigt, Vanessa Schuh, Jan-Dirk Raguse, Wolfgang Meyerhof
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040304
Abstract: The sense of taste plays an important role in the evaluation of the nutrient composition of consumed food. Bitter taste in particular is believed to serve a warning function against the ingestion of poisonous substances. In the past years enormous progress was made in the characterization of bitter taste receptors, including their gene expression patterns, pharmacological features and presumed physiological roles in gustatory as well as in non-gustatory tissues. However, due to a lack in TAS2R-specifc antibodies the localization of receptor proteins within gustatory tissues has never been analyzed. In the present study we have screened a panel of commercially available antisera raised against human bitter taste receptors by immunocytochemical experiments. One of these antisera was found to be highly specific for the human bitter taste receptor TAS2R38. We further demonstrate that this antibody is able to detect heterologously expressed TAS2R38 protein on Western blots. The antiserum is, however, not able to interfere significantly with TAS2R38 function in cell based calcium imaging analyses. Most importantly, we were able to demonstrate the presence of TAS2R38 protein in human gustatory papillae. Using double immunofluorescence we show that TAS2R38-positive cells form a subpopulation of PLCbeta2 expressing cells. On a subcellular level the localization of this bitter taste receptor is neither restricted to the cell surface nor particularly enriched at the level of the microvilli protruding into the pore region of the taste buds, but rather evenly distributed over the entire cell body.
Tumor-infiltrating macrophages and dendritic cells in human colorectal cancer: relation to local regulatory T cells, systemic T-cell response against tumor-associated antigens and survival
Dirk Nagorsen, Sabine Voigt, Erika Berg, Harald Stein, Eckhard Thiel, Christoph Loddenkemper
Journal of Translational Medicine , 2007, DOI: 10.1186/1479-5876-5-62
Abstract: Immunohistological staining was performed with nine markers for macrophages and DC (CD68, CD163, S100, CD11c, CD208, CD209, CD123, CD1a, Langerin) in 40 colorectal cancer samples from patients, in whom the state of systemic T-cell responses against tumor-associated antigens (TAA) and Treg infiltration had previously been determined.All specimens contained cells positive for CD68, CD163, S100 and CD1a in epithelial tumor tissue and tumor stroma. Only a very few (less than median 3/HPF) CD123+, CD1a+, CD11c+, CD 208+, CD209+, or Langerin+ cells were detected in the specimens. Overall, we found a trend towards increased infiltration by S100-positive DC and a significantly increased number of stromal S100-positive DC in patients without T-cell response. There was an increase of stromal S100 DC and CD163 macrophages in limited disease (S100: 11.1/HPF vs. 7.3/HPF, p = 0.046; CD163: 11.0/HPF vs. 8.1/HPF, p = 0.06). We found a significant, positive correlation between S100-positive DC and FOXP3-positive Tregs. Survival in patients with high DC infiltration was significantly better than that in those with low DC infiltration (p < 0.05). Furthermore, we found a trend towards better survival for increased infiltration with CD163-positive macrophages (p = 0.07).The present in situ study adds new data to the discussion on the interaction between the innate and adoptive immune system. Our data strongly support the hypothesis that tumor-infiltrating DC are a key factor at the interface between innate and adaptive immune response in malignant disease. Tumor infiltrating S100-positive DC show an inverse relationship with the systemic antigen-specific T-cell response, a positive correlation with regulatory T cells, and a positive association with survival in CRC. These data put tumor-infiltrating DC at the center of the relevant immune response in CRC.Colorectal cancer (CRC) is a common malignant disease, which has been intensely studied for tumor-immune interactions to develop succe
Lifetime measurement of the metastable 3d 2D5/2 state in the 40Ca+ ion using the shelving technique on a few-ion string
Peter Staanum,Inger S. Jensen,Randi G. Martinussen,Dirk Voigt,Michael Drewsen
Physics , 2003, DOI: 10.1103/PhysRevA.69.032503
Abstract: We present a measurement of the lifetime of the metastable 3d 2D5/2 state in the 40Ca+ ion, using the so-called shelving technique on a string of five Doppler laser-cooled ions in a linear Paul trap. A detailed account of the data analysis is given, and systematic effects due to unwanted excitation processes and collisions with background gas atoms are discussed and estimated. From a total of 6805 shelving events, we obtain a lifetime tau=1149+/-14(stat.)+/-4(sys.)ms, a result which is in agreement with the most recent measurements.
Consumption of alcohol, cigarettes and illegal substances among physicians and medical students in Brandenburg and Saxony (Germany)
Karen Voigt, Sabine Twork, Dirk Mittag, Anne G?bel, Roger Voigt, J?rg Klewer, Joachim Kugler, Stefan R Bornstein, Antje Bergmann
BMC Health Services Research , 2009, DOI: 10.1186/1472-6963-9-219
Abstract: Socio-demographic data and individual risk behaviour was collected by an anonymous self-administered questionnaire. Physicians were approached via mail and students were recruited during tutorials or lectures.41.6% of physicians and 60.9% of medical students responded to the questionnaire; more than 50% of the respondents in both groups were females. The majority of respondents consumed alcohol at least once per week; median daily alcohol consumption ranged from 3.88 g/d (female medical students) to 12.6 g/d (male physicians). A significantly higher percentage of men (p < 0.05) reported hazardous or harmful drinking compared to women. A quarter of all participating physicians and one third of all students indicated unhealthy alcohol-drinking behaviour. The majority of physicians (85.7%) and medical students (78.5%) were non-smokers. Both groups contained significantly more female non-smokers (p < 0.05). Use of illegal substances was considerably lower in physicians (5.1%) than medical students (33.0%). Male students indicated a significantly (p < 0.001) higher level of illegal drug-use compared to female students.More than one third of the medical students and health care professionals showed problematic alcohol-drinking behaviour. Although the proportion of non-smokers in the investigated sample was higher than in the general population, when compared to the general population, medical students between 18-24 reported higher consumption of illegal substances.These results indicate that methods for educating and promoting healthy lifestyle, particularly with respect to excessive alcohol consumption, tobacco use and abuse of illegal drugs should be considered.Alcohol consumption, smoking and illegal drug use are important health indicators in accordance with the results of European Community Health Indicators project (ECHI) within the European Commissions Health Monitoring Programme [1]. According to the German Report of Drugs and Addiction [2], approximately 16 milli
Functional Analysis of the Magnetosome Island in Magnetospirillum gryphiswaldense: The mamAB Operon Is Sufficient for Magnetite Biomineralization
Anna Loh?e, Susanne Ullrich, Emanuel Katzmann, Sarah Borg, Gerd Wanner, Michael Richter, Birgit Voigt, Thomas Schweder, Dirk Schüler
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025561
Abstract: Bacterial magnetosomes are membrane-enveloped, nanometer-sized crystals of magnetite, which serve for magnetotactic navigation. All genes implicated in the synthesis of these organelles are located in a conserved genomic magnetosome island (MAI). We performed a comprehensive bioinformatic, proteomic and genetic analysis of the MAI in Magnetospirillum gryphiswaldense. By the construction of large deletion mutants we demonstrate that the entire region is dispensable for growth, and the majority of MAI genes have no detectable function in magnetosome formation and could be eliminated without any effect. Only <25% of the region comprising four major operons could be associated with magnetite biomineralization, which correlated with high expression of these genes and their conservation among magnetotactic bacteria. Whereas only deletion of the mamAB operon resulted in the complete loss of magnetic particles, deletion of the conserved mms6, mamGFDC, and mamXY operons led to severe defects in morphology, size and organization of magnetite crystals. However, strains in which these operons were eliminated together retained the ability to synthesize small irregular crystallites, and weakly aligned in magnetic fields. This demonstrates that whereas the mamGFDC, mms6 and mamXY operons have crucial and partially overlapping functions for the formation of functional magnetosomes, the mamAB operon is the only region of the MAI, which is necessary and sufficient for magnetite biomineralization. Our data further reduce the known minimal gene set required for magnetosome formation and will be useful for future genome engineering approaches.
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