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Search Results: 1 - 10 of 2259 matches for " Holger Schuhmann "
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The family of Deg/HtrA proteases in plants
Holger Schuhmann, Pitter F Huesgen, Iwona Adamska
BMC Plant Biology , 2012, DOI: 10.1186/1471-2229-12-52
Abstract: Using phylogenetic and domain arrangement analysis, we improved the nomenclature of the Deg/HtrA protease family, standardized protease names based on their well-established nomenclature in Arabidopsis thaliana, and clarified the evolutionary relationship between orthologous enzymes from various photosynthetic organisms across several divergent systematic groups, including dicots, a monocot, a moss and a green alga. Furthermore, we identified a “core set” of eight proteases shared by all organisms examined here that might provide all the proteolytic potential of Deg/HtrA proteases necessary for a hypothetical plant cell.In our proposed nomenclature, the evolutionarily closest orthologs have the same protease name, simplifying scientific communication when comparing different plant species and allowing for more reliable inference of protease functions. Further, we proposed that the high number of Deg/HtrA proteases in plants is mainly due to gene duplications unique to the respective organism.Proteolysis, the enzyme-mediated hydrolysis of peptide bonds, is a vital process for every organism. It is associated with many intracellular and extracellular events, e.g. the removal of damaged proteins, nutrient uptake, processing of protein precursors, and signaling [1,2]. A huge variety of proteolytic enzymes, utilizing several different catalytic mechanism, mediate these processes. The family of Deg proteases (for degradation of periplasmic proteins) [3], also known as HtrA proteases (for high temperature requirement A) [4], are one important group of these proteolytic enzymes. They are ATP-independent serine endopeptidases found in all domains of life, including Bacteria, Archaea and Eukarya. Deg/HtrA proteases belong to the S1B subfamily of the clan PA according to MEROPS nomenclature [5], which features a catalytic domain of the trypsin type, with His-Asp-Ser as catalytic triad. Most Deg/HtrA family members contain one to four PDZ protein-protein interaction domains [6]
High Lipid Induction in Microalgae for Biodiesel Production
Kalpesh K. Sharma,Holger Schuhmann,Peer M. Schenk
Energies , 2012, DOI: 10.3390/en5051532
Abstract: Oil-accumulating microalgae have the potential to enable large-scale biodiesel production without competing for arable land or biodiverse natural landscapes. High lipid productivity of dominant, fast-growing algae is a major prerequisite for commercial production of microalgal oil-derived biodiesel. However, under optimal growth conditions, large amounts of algal biomass are produced, but with relatively low lipid contents, while species with high lipid contents are typically slow growing. Major advances in this area can be made through the induction of lipid biosynthesis, e.g., by environmental stresses. Lipids, in the form of triacylglycerides typically provide a storage function in the cell that enables microalgae to endure adverse environmental conditions. Essentially algal biomass and triacylglycerides compete for photosynthetic assimilate and a reprogramming of physiological pathways is required to stimulate lipid biosynthesis. There has been a wide range of studies carried out to identify and develop efficient lipid induction techniques in microalgae such as nutrients stress (e.g., nitrogen and/or phosphorus starvation), osmotic stress, radiation, pH, temperature, heavy metals and other chemicals. In addition, several genetic strategies for increased triacylglycerides production and inducibility are currently being developed. In this review, we discuss the potential of lipid induction techniques in microalgae and also their application at commercial scale for the production of biodiesel.
Comment: Computer Technology and Qualitative Research: A Rendezvous Between Exactness and Ambiguity
Carmen Schuhmann
Forum : Qualitative Social Research , 2010,
Abstract: URN: http://nbn-resolving.de/urn:nbn:de:0114-fqs1101C27
Mapping threefolds onto three-quadrics
Carmen Schuhmann
Mathematics , 1995,
Abstract: We prove that the degree of a nonconstant morphism from a smooth projective 3-fold $X$ with N\'{e}ron-Severi group ${\bf Z}$ to a smooth 3-dimensional quadric is bounded in terms of numerical invariants of $X$. In the special case where $X$ is a 3-dimensional cubic we show that there are no such morphisms. The main tool in the proof is Miyaoka's bound on the number of double points of a surface.
Isolation and Evaluation of Oil-Producing Microalgae from Subtropical Coastal and Brackish Waters
David K. Y. Lim, Sourabh Garg, Matthew Timmins, Eugene S. B. Zhang, Skye R. Thomas-Hall, Holger Schuhmann, Yan Li, Peer M. Schenk
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040751
Abstract: Microalgae have been widely reported as a promising source of biofuels, mainly based on their high areal productivity of biomass and lipids as triacylglycerides and the possibility for cultivation on non-arable land. The isolation and selection of suitable strains that are robust and display high growth and lipid accumulation rates is an important prerequisite for their successful cultivation as a bioenergy source, a process that can be compared to the initial selection and domestication of agricultural crops. We developed standard protocols for the isolation and cultivation for a range of marine and brackish microalgae. By comparing growth rates and lipid productivity, we assessed the potential of subtropical coastal and brackish microalgae for the production of biodiesel and other oil-based bioproducts. This study identified Nannochloropsis sp., Dunaniella salina and new isolates of Chlorella sp. and Tetraselmis sp. as suitable candidates for a multiple-product algae crop. We conclude that subtropical coastal microalgae display a variety of fatty acid profiles that offer a wide scope for several oil-based bioproducts, including biodiesel and omega-3 fatty acids. A biorefinery approach for microalgae would make economical production more feasible but challenges remain for efficient harvesting and extraction processes for some species.
Large sets of consecutive Maass forms and fluctuations in the Weyl remainder
Holger Then
Mathematics , 2012,
Abstract: We explore an algorithm which systematically finds all discrete eigenvalues of an analytic eigenvalue problem. The algorithm is more simple and elementary as could be expected before. It consists of Hejhal's identity, linearisation, and Turing bounds. Using the algorithm, we compute more than one hundredsixty thousand consecutive eigenvalues of the Laplacian on the modular surface, and investigate the asymptotic and statistic properties of the fluctuations in the Weyl remainder. We summarize the findings in two conjectures. One is on the maximum size of the Weyl remainder, and the other is on the distribution of a suitably scaled version of the Weyl remainder.
3-D eigenmode calculation of metallic nano-structures
B. Bandlow,R. Schuhmann
Advances in Radio Science : Kleinheubacher Berichte , 2009,
Abstract: In the calculation of eigenfrequencies of 3-D metallic nanostructures occurs the challenge that the material parameters depend on the desired eigenfrequency. We propose a formulation where this leads to a polynomial eigenvalue problem which can be tackled by different solving strategies. A comparison between a Newton-type method and a Jacobi-Davidson algorithm is given.
Stability and conservation properties of transient field simulations using FIT
R. Schuhmann,T. Weiland
Advances in Radio Science : Kleinheubacher Berichte , 2003,
Abstract: Time domain simulations for high-frequency applications are widely dominated by the leapfrog timeintegration scheme. Especially in combination with the spatial discretization approach of the Finite Integration Technique (FIT) it leads to a highly efficient explicit simulation method, which in the special case of Cartesian grids can be regarded to be computationally equivalent to the Finite Difference Time Domain (FDTD) algorithm. For stability reasons, however, the leapfrog method is restricted to a maximum stable time step by the well-known Courantcriterion, and can not be applied to most low-frequency applications. Recently, some alternative, unconditionally stable techniques have been proposed to overcome this limitation, including the Alternating Direction Implicit (ADI)-method. We analyze such schemes using a transient modal decomposition of the electric fields. It is shown that stability alone is not sufficient to guarantee correct results, but additionally important conservation properties have to be met. Das Leapfrog-Verfahren ist ein weit verbreitetes Zeitintegrationsverfahren für transiente hochfrequente elektrodynamischer Felder. Kombiniert mit dem r umlichen Diskretisierungsansatz der Methode der Finiten Integration (FIT) führt es zu einer sehr effizienten, expliziten Simulationsmethode, die im speziellen Fall kartesischer Rechengitter als quivalent zur Finite Difference Time Domain (FDTD) Methode anzusehen ist. Aus Stabilit tsgründen ist dabei die Zeitschrittweite durch das bekannte Courant-Kriterium begrenzt, so dass das Leapfrog- Verfahren für niederfrequente Probleme nicht sinnvoll angewendet werden kann. In den letzten Jahren wurden alternativ einige andere explizite oder “halb-implizite" Zeitbereichsverfahren vorgeschlagen, u.a. das “Alternating Direction Implicit" (ADI)-Verfahren, die keiner Beschr nkung des Zeitschritts aus Stabilit tsgründen unterliegen. Es zeigt sich aber, dass auch diese Methoden im niederfrequenten Fall nicht zu sinnvollen Simulationsergebnissen führen. Wie anhand einer transienten Modalanalyse der elektrischen Felder in einem einfachen 2D-Beispiel deutlich wird, ist die Ursache dafür die Verletzung wichtiger physikalischer Erhaltungseigenschaften durch ADI und verwandte Methoden.
Tangent scrolls in prime Fano threefolds
Atanas Iliev,Carmen Schuhmann
Mathematics , 2000,
Abstract: In this paper we prove that any smooth prime Fano threefold, different from the Mukai-Umemura threefold, contains a 1-dimensional family of intersecting lines. Combined with a result of the second author (see J. Algebr. Geom. 8:2 (1999), 221-244) this implies that any morphism from a smooth Fano threefold of index 2 to a smooth Fano threefold of index 1 must be constant, which gives an answer in dimension 3 to a question stated by Peternell.
Hemispheric Differences within the Fronto-Parietal Network Dynamics Underlying Spatial Imagery
Alexander T. Sack,Teresa Schuhmann
Frontiers in Psychology , 2012, DOI: 10.3389/fpsyg.2012.00214
Abstract: Spatial imagery refers to the inspection and evaluation of spatial features (e.g., distance, relative position, configuration) and/or the spatial manipulation (e.g., rotation, shifting, reorienting) of mentally generated visual images. In the past few decades, psychophysical as well as functional brain imaging studies have indicated that any such processing of spatially coded information and/or manipulation based on mental images (i) is subject to similar behavioral demands and limitations as in the case of spatial processing based on real visual images, and (ii) consistently activates several nodes of widely distributed cortical networks in the brain. These nodes include areas within both, the dorsal fronto-parietal as well as ventral occipito-temporal visual processing pathway, representing the “what” versus “where” aspects of spatial imagery. We here describe evidence from functional brain imaging and brain interference studies indicating systematic hemispheric differences within the dorsal fronto-parietal networks during the execution of spatial imagery. Importantly, such hemispheric differences and functional lateralization principles are also found in the effective brain network connectivity within and across these networks, with a direction of information flow from anterior frontal/premotor regions to posterior parietal cortices. In an attempt to integrate these findings of hemispheric lateralization and fronto-to-parietal interactions, we argue that spatial imagery constitutes a multifaceted cognitive construct that can be segregated in several distinct mental sub processes, each associated with activity within specific lateralized fronto-parietal (sub) networks, forming the basis of the here proposed dynamic network model of spatial imagery.
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