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Search Results: 1 - 10 of 44 matches for " Cissy Siebel "
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Periconceptional Maternal Folic Acid Use of 400 μg per Day Is Related to Increased Methylation of the IGF2 Gene in the Very Young Child
Régine P. Steegers-Theunissen,Sylvia A. Obermann-Borst,Dennis Kremer,Jan Lindemans,Cissy Siebel,Eric A. Steegers,P. Eline Slagboom,Bastiaan T. Heijmans
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0007845
Abstract: Countries worldwide recommend women planning pregnancy to use daily 400 μg of synthetic folic acid in the periconceptional period to prevent birth defects in children. The underlying mechanisms of this preventive effect are not clear, however, epigenetic modulation of growth processes by folic acid is hypothesized. Here, we investigated whether periconceptional maternal folic acid use and markers of global DNA methylation potential (S-adenosylmethionine and S-adenosylhomocysteine blood levels) in mothers and children affect methylation of the insulin-like growth factor 2 gene differentially methylation region (IGF2 DMR) in the child. Moreover, we tested whether the methylation of the IGF2 DMR was independently associated with birth weight.
Walter Siebel
s u b u r b a n : zeitschrift für kritische stadtforschung , 2013,
Abstract: Jan Wehrheim (2013) nennt zwei gegens tzliche Gründe, aus denen alte Artikel von Interesse sein k nnten: weil sie heute noch gültige Aussagen enthalten, oder weil ihre Problemdefinitionen und Kategorien, gerade weil sie überholt sind, dazu dienen k nnen, neue Zug nge zum Gegenstand der Forschung zu pr zisieren [...]
A Study of the Charge of Leading Hadrons in Gluon and Quark Fragmentation
Martin Siebel
Physics , 2005,
Abstract: In this study the electric charges of leading systems in quark and gluon jets from hadronic three-jet events in $e^+e^-$-annihilation measured with the DELPHI-experiment are examined. Leading systems are defined by a rapidity gap between the leading system of a jet and the rest of the event. The measured charge distributions are compared with results from Monte-Carlo simulations which do not contain colour-octet neutralisation processes. In the data an enhanced production of neutral leading systems compared to Monte-Carlo predictions is found in gluon jets, which is compatible with the expectations from colour-octet neutralisation. The quark jet sample is found in agreement with the simulation.
Quark and gluon jet properties at LEP
Martin Siebel
Physics , 1999,
Abstract: The study of the differences of the fragmentation of quarks and gluons to jets of hadrons gives insight into the fundamental structure of QCD. Results from different approaches to properties of quarks and gluons are shown. The colour factor ratio $C_A/C_F$ is measured in agreement with the QCD prediction. Identified particles in quark and gluon jets are investigated, revealing no overproduction of isoscalar $\eta^0$ and $\phi(1020)$ in gluon jets, but an excess of protons.
On the Effect of Constraint Enforcement on the Quality of Numerical Solutions in General Relativity
Florian Siebel,Peter Huebner
Physics , 2001, DOI: 10.1103/PhysRevD.64.024021
Abstract: In Brodbeck et al 1999 it has been shown that the linearised time evolution equations of general relativity can be extended to a system whose solutions asymptotically approach solutions of the constraints. In this paper we extend the non-linear equations in similar ways and investigate the effect of various possibilities by numerical means. Although we were not able to make the constraint submanifold an attractor for all solutions of the extended system, we were able to significantly reduce the growth of the numerical violation of the constraints. Contrary to our expectations this improvement did not imply a numerical solution closer to the exact solution, and therefore did not improve the quality of the numerical solution.
Synchronized flow and wide moving jams from balanced vehicular traffic
Florian Siebel,Wolfram Mauser
Physics , 2005, DOI: 10.1103/PhysRevE.73.066108
Abstract: Recently we proposed an extension to the traffic model of Aw, Rascle and Greenberg. The extended traffic model can be written as a hyperbolic system of balance laws and numerically reproduces the reverse $\lambda$ shape of the fundamental diagram of traffic flow. In the current work we analyze the steady state solutions of the new model and their stability properties. In addition to the equilibrium flow curve the trivial steady state solutions form two additional branches in the flow-density diagram. We show that the characteristic structure excludes parts of these branches resulting in the reverse $\lambda$ shape of the flow-density relation. The upper branch is metastable against the formation of synchronized flow for intermediate densities and unstable for high densities, whereas the lower branch is unstable for intermediate densities and metastable for high densities. Moreover, the model can reproduce the typical speed of the downstream front of wide moving jams. It further reproduces a constant outflow from wide moving jams, which is far below the maximum free flow. Applying the model to simulate traffic flow at a bottleneck we observe a general pattern with wide moving jams traveling through the bottleneck.
On the fundamental diagram of traffic flow
Florian Siebel,Wolfram Mauser
Physics , 2005,
Abstract: We present a new fluid-dynamical model of traffic flow. This model generalizes the model of Aw and Rascle [SIAM J. Appl. Math. 60 916-938] and Greenberg [SIAM J. Appl. Math 62 729-745] by prescribing a more general source term to the velocity equation. This source term can be physically motivated by experimental data, when taking into account relaxation and reaction time. In particular, the new model has a (linearly) unstable regime as observed in traffic dynamics. We develop a numerical code, which solves the corresponding system of balance laws. Applying our code to a wide variety of initial data, we find the observed inverse-$\lambda$ shape of the fundamental diagram of traffic flow.
New Constraints from Pb-Evaporation Zircon Ages of the Méiganga Amphibole-Biotite Gneiss, Central Cameroon, on Proterozoic Crustal Evolution  [PDF]
Ganwa Alembert Alexandre, Siebel Wolfgang, Shang Kongnyuy Cosmas, Naimou Seguem, Ekodeck Georges Emmanuel
International Journal of Geosciences (IJG) , 2011, DOI: 10.4236/ijg.2011.22014
Abstract: The amphibole biotite gneiss (ABGn) in the Méiganga area forms part of a meta volcano-sedimentary sequence of the Adamawa Yade domain (AYD), Central African Fold Belt (CAFB). This sequence shows affinity with immature sediments (greywackes, arkoses) with intercalation of mafic lavas or tuffs. New 207Pb/206Pb zircon evaporation ages for two ABGn samples range from 1887 - 2339 Ma and from 675 - 889 Ma, respectively. These ages and evidence from internal zircon structures indicate that igneous rocks of Archean to Paleoproterozoic and of early Neoproterozoic age contributed to the detritus of the sedimentary sequence. The deposition of detritus took place prior to 614 - 619 Ma which represent the syntectonic emplacement of the Méiganga metadiorite. Leucogranites north to the Méiganga area were generated by melting of crust identical to that which provided the source of the ABGn. The metasedimentary sequence investigated in this study is similar to that of the southern part of the AYD and in the Borborema Province, NE Brazil. The tectonic and geochronologic characteristics of the AYD in the Méiganga area support the idea that during the Proterozoic, Central Africa and NE Brazil were part of the same continental landmass.
Thesen zur Soziologie der Stadt
Hartmut H?u?ermann,Walter Siebel
s u b u r b a n : zeitschrift für kritische stadtforschung , 2013,
Abstract: Mit der Wiederver ffentlichung des Textes Thesen zur Soziologie der Stadt“, der zum ersten Mal 1978 im Leviathan erschienen ist, m chten wir zu einer trans- und interdisziplin ren Debatte anregen. Wir gehen davon aus, dass der Text einerseits als Zeitzeugnis hilfreich sein kann, um heutige Debatten historisch zu kontextualisieren. Andererseits soll dessen Wiederver ffentlichung einen Ansto dazu geben, die aktuelle Relevanz der Thesen zu diskutieren.
Scalar field induced oscillations of neutron stars and gravitational collapse
Florian Siebel,Jose A. Font,Philippos Papadopoulos
Physics , 2001, DOI: 10.1103/PhysRevD.65.024021
Abstract: We study the interaction of massless scalar fields with self-gravitating neutron stars by means of fully dynamic numerical simulations of the Einstein-Klein-Gordon perfect fluid system. Our investigation is restricted to spherical symmetry and the neutron stars are approximated by relativistic polytropes. Studying the nonlinear dynamics of isolated neutron stars is very effectively performed within the characteristic formulation of general relativity, in which the spacetime is foliated by a family of outgoing light cones. We are able to compactify the entire spacetime on a computational grid and simultaneously impose natural radiative boundary conditions and extract accurate radiative signals. We study the transfer of energy from the scalar field to the fluid star. We find, in particular, that depending on the compactness of the neutron star model, the scalar wave forces the neutron star either to oscillate in its radial modes of pulsation or to undergo gravitational collapse to a black hole on a dynamical timescale. The radiative signal, read off at future null infinity, shows quasi-normal oscillations before the setting of a late time power-law tail.
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