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Search Results: 1 - 10 of 799 matches for " Heike Siebert "
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Dynamical and Structural Modularity of Discrete Regulatory Networks
Heike Siebert
Electronic Proceedings in Theoretical Computer Science , 2009, DOI: 10.4204/eptcs.6.8
Abstract: A biological regulatory network can be modeled as a discrete function that contains all available information on network component interactions. From this function we can derive a graph representation of the network structure as well as of the dynamics of the system. In this paper we introduce a method to identify modules of the network that allow us to construct the behavior of the given function from the dynamics of the modules. Here, it proves useful to distinguish between dynamical and structural modules, and to define network modules combining aspects of both. As a key concept we establish the notion of symbolic steady state, which basically represents a set of states where the behavior of the given function is in some sense predictable, and which gives rise to suitable network modules. We apply the method to a regulatory network involved in T helper cell differentiation.
Computing Maximal and Minimal Trap Spaces of Boolean Networks
Hannes Klarner,Alexander Bockmayr,Heike Siebert
Mathematics , 2015, DOI: 10.1007/s11047-015-9520-7
Abstract: Asymptotic behaviors are often of particular interest when analyzing Boolean networks that represent biological systems such as signal trans- duction or gene regulatory networks. Methods based on a generalization of the steady state notion, the so-called trap spaces, can be exploited to investigate attractor properties as well as for model reduction techniques. In this paper, we propose a novel optimization-based method for com- puting all minimal and maximal trap spaces and motivate their use. In particular, we add a new result yielding a lower bound for the number of cyclic attractors and illustrate the methods with a study of a MAPK pathway model. To test the efficiency and scalability of the method, we compare the performance of the ILP solver gurobi with the ASP solver potassco in a benchmark of random networks.
Minimization and Equivalence in Multi-valued Logical Models of Regulatory Networks
Adam Streck,Therese Lorenz,Heike Siebert
Mathematics , 2015, DOI: 10.1007/s11047-015-9525-2
Abstract: Multi-valued logical models can be used to describe biological networks on a high level of abstraction based on the network structure and logical parameters capturing regulatory effects. Interestingly, the dynamics of two distinct models need not necessarily be different, which might hint at either only non-functional characteristics distinguishing the models or at different possible implementations for the same behaviour. Here, we study the conditions allowing for such effects by analysing classes of dynamically equivalent models and both structurally maximal and minimal representatives of such classes. Finally, we present an efficient algorithm that constructs a minimal representative of the respective class of a given multi-valued model.
Using decision-analytic modelling to transfer international evidence from health technology assessment to the context of the German health care system
Siebert, Uwe
GMS Health Technology Assessment , 2005,
Abstract: The objective of this Health Technology Assessment (HTA) methods report was to examine and to assess decision analysis (DA) as a method to transfer and adapt international scientific evidence in HTA to the German health care context. Furthermore, we sought to develop a systematic framework to facilitate the selection, transfer, adaptation, and synthesis of these data in German HTA projects. In this report, we review and summarise the concepts and methods of DA; present potential areas of applications, and provide a basis for the critical assessment of decision-analytic studies. The two main methods of DA, decision trees and Markov models, as well as various approaches to sensitivity analyses are described. Examples of typical situations for the use of DA in scientific evidence transfer are described, and a list of main health care domains and parameters in evidence transfer is presented. Finally, we developed a framework to transfer and apply international evidence to the national health care context. The strengths and limitations of the decision-analytic approach are critically examined. In summary, this HTA report describes different situations, in which decision-analytic models can be useful, and demonstrates the utility of DA in transferring and applying international evidence to the national health care context. We developed a systematic instrument to transfer international evidence to the context of other countries and successfully applied this instrument in two German HTA projects. The use of this instrument is recommended in further HTA projects dealing with the application of international evidence to the German health care context. The use of decision-analytic models to transfer international evidence is endorsed. However, the limitations of DA should be clearly stated discussed transparently in all HTA reports.
ARRANJOS INSTITUCIONAIS E TRAJETóRIA DO PLANEJAMENTO TERRITORIAL EM SANTA CATARINA Institutional Arrangements and Trajectory of Planning in Santa Catarina Arreglos Institucionales y Circunstancias de la Planificación en Santa Catarina
Claudia Siebert
Revista Paranaense de Desenvolvimento , 2010,
Abstract: Português Santa Catarina tem sido um laboratório de experiências de novas institucionalidades e deplanejamento territorial. De forma descontínua, o Estado contou com AssociativismoMunicipal, Fóruns de Desenvolvimento Regional, Regi es Metropolitanas, Comitês deGerenciamento de Bacias Hidrográficas e Secretarias de Desenvolvimento Regional. Este artigoprocura contribuir para o conhecimento sobre os arranjos institucionais descentralizados e oplanejamento, resgatando parte da memória do planejamento em Santa Catarina. Inicialmente,abordam-se os diversos arranjos institucionais do Estado. A seguir, analisa-se o planejamento,com a consulta aos originais dos planos territoriais de 1979 a 2011, e se entrevistam ostécnicos envolvidos na elabora o desses planos, que relataram, em primeira m o, suaexperiência no processo. Ficou evidenciada a descontinuidade no processo de planejamentoregional e de gest o do território em Santa Catarina, com avan os e retrocessos tanto naquest o ambiental quanto na participa o de atores n o governamentais.English Santa Catarina has been a laboratory for experimentation with new institutions and territorialplanning. Discontinuously, the state relied on Municipal Associations, Regional DevelopmentBoards, Metropolitan Regions, Committees of Watershed Management and Departments forRegional Development. This article search for contribute to the knowledge about the institutionalarrangements and the decentralized planning in the state, rescuing the memory of planningin Santa Catarina. Initially, we approach the various institutional arrangements of the State.After that, we discussed the planning in the State, consulting the original territorial plans,from 1979 to 2011, and interviewed the technicians involved in drafting these plans, that reporting firsthand experience in the process. Evidence was found of discontinuity in theprocess of regional planning and land management in Santa Catarina, with advances andsetbacks in both environmental issues and the participation of non-state actors.Espa ol Santa Catarina ha sido un laboratorio de experiencias de nuevas instituciones y de planificaciónterritorial. Discontinuamente, el Estado tuvo Asociaciones Municipales, Consejos Regionalesde Desarrollo, Regiones Metropolitanas, Comités de Manejo de Cuencas Hidrográficas yDepartamentos para el Desarrollo Regional. Ese artículo busca contribuir al conocimiento delos arreglos institucionales descentralizados y la planificación en el Estado, con el rescate dela memoria por parte de la planificación en Santa Catarina. Inicialmente, se dirigió a losd
Endoskopie der Isch mischen Colitis
Siebert F
Journal für Gastroenterologische und Hepatologische Erkrankungen , 2005,
15. St. Veiter Gastroenterologengespr che
Siebert F
Journal für Gastroenterologische und Hepatologische Erkrankungen , 2006,
Status and results from the RAVE survey
A. Siebert
Physics , 2012,
Abstract: RAVE, the RAdial Velocity Experiment, is a large spectroscopic survey which collects spectroscopic data for stars in the southern hemisphere. RAVE uses the AAO Schmidt telescope with a wavelength coverage similar to Gaia but a lower resolution of R=7,500. Since 2003, RAVE collected over 500,000 spectra providing an unprecedented dataset to study the structure and kinematics of the Milky Way and its stellar populations. In this review, we will summarize the main results obtained using the RAVE catalogues.
Virtual fundamental classes, global normal cones and Fulton's canonical classes
Bernd Siebert
Mathematics , 2005,
Abstract: This paper, first written in 1997, aims at a simplified and more elementary construction of algebraic-geometric virtual fundamental classes as defined by Li/Tian and Behrend/Fantechi. We replace the use of Artin stacks in the latter approach by a yoga of cone bundles of possible independent interest. We also observe a formula for virtual fundamental classes involving only the total Chern class of the index bundle and Fulton's canonical class of the moduli space.
Gromov-Witten invariants of general symplectic manifolds
Bernd Siebert
Mathematics , 1996,
Abstract: We present an approach to Gromov-Witten invariants that works on arbitrary (closed) symplectic manifolds. We avoid genericity arguments and take into account singular curves in the very formulation. The method is by first endowing mapping spaces from (prestable) algebraic curves into the symplectic manifold with the structure of a Banach orbifold and then exhibiting the space of stable $J$-curves (``stable maps'') as zero set of a Fredholm section of a Banach orbibundle over this space. The invariants are constructed by pairing with a homology class on the locally compact topological space of stable $J$-curves that is generated as localized Euler class of the section.
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