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Search Results: 1 - 10 of 23662 matches for " Paul Reschke "
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Distinguished Line Bundles for Complex Surface Automorphisms
Paul Reschke
Mathematics , 2012,
Abstract: We equate dynamical properties (e.g., positive entropy, existence of a periodic curve) of complex projective surface automorphisms with properties of the pull-back actions of such automorphisms on line bundles. We use the properties of the cohomological actions to describe the measures of maximal entropy for automorphisms with positive entropy.
Salem Numbers and Automorphisms of Complex Surfaces
Paul Reschke
Mathematics , 2012,
Abstract: For two-dimensional complex tori, we characterize the set of all values of positive entropy that arise from automorphisms. For K3 surfaces, we give suffcient conditions for a positive value to be the entropy of some automorphism.
Salem Numbers and Abelian Surface Automorphisms
Paul Reschke
Mathematics , 2014,
Abstract: We classify two-dimensional complex tori admitting automorphisms with positive entropy in terms of the entropies they exhibit. For each possible positive value of entropy, we describe the set of two-dimensional complex tori admitting automorphisms with that entropy.
On the complex dynamics of birational surface maps defined over number fields
Mattias Jonsson,Paul Reschke
Mathematics , 2015,
Abstract: We show that any birational selfmap of a complex projective surface that has dynamical degree greater than one and is defined over a number field automatically satisfies the Bedford-Diller energy condition after a suitable birational conjugacy. As a consequence, the complex dynamics of the map is well-behaved. We also show that there is a well-defined canonical height function.
Cohomological conditions on endomorphisms of projective varieties
Holly Krieger,Paul Reschke
Mathematics , 2015,
Abstract: We characterize possible periodic subvarieties for surjective endomorphisms of complex abelian varieties in terms of the eigenvalues of the cohomological actions induced by the endomorphisms, extending previous work in this direction by Pink and Roessler. By applying our characterization to induced endomorphisms on Albanese varieties, we draw conclusions about the dynamics of surjective endomorphisms for a broad class of projective varieties. We also analyze several classes of surjective endomorphisms that are distinguished by properties of their cohomological actions.
Lower Semi-Continuity of Entropy in a Family of K3 Surface Automorphisms
Paul Reschke,Bar Roytman
Mathematics , 2015,
Abstract: We compute entropies in a large family of K3 surface automorphisms in (P^1)^3. In keeping with a result by Xie, we find that the entropies vary in a lower semi-continuous manner as the Picard ranks of the K3 surfaces vary.
Velocity addition formulas in Robertson-Walker spacetimes
David Klein,Jake Reschke
Mathematics , 2015, DOI: 10.1063/1.4926352
Abstract: Universal velocity addition formulas analogous to the well-known formula in special relativity are found for four geometrically defined relative velocities in a large class of Robertson-Walker spacetimes. Explicit examples are given. The special relativity result is recovered as a special case, and it is shown that the spectroscopic relative velocity, in contrast to three other geometric relative velocities, follows the same addition law as in special relativity for comoving observers in Robertson-Walker cosmologies.
Capability of C-Band SAR for Operational Wetland Monitoring at High Latitudes
Julia Reschke,Annett Bartsch,Stefan Schlaffer,Dmitry Schepaschenko
Remote Sensing , 2012, DOI: 10.3390/rs4102923
Abstract: Wetlands store large amounts of carbon, and depending on their status and type, they release specific amounts of methane gas to the atmosphere. The connection between wetland type and methane emission has been investigated in various studies and utilized in climate change monitoring and modelling. For improved estimation of methane emissions, land surface models require information such as the wetland fraction and its dynamics over large areas. Existing datasets of wetland dynamics present the total amount of wetland (fraction) for each model grid cell, but do not discriminate the different wetland types like permanent lakes, periodically inundated areas or peatlands. Wetland types differently influence methane fluxes and thus their contribution to the total wetland fraction should be quantified. Especially wetlands of permafrost regions are expected to have a strong impact on future climate due to soil thawing. In this study ENIVSAT ASAR Wide Swath data was tested for operational monitoring of the distribution of areas with a long-term SW near 1 (hSW) in northern Russia (SW = degree of saturation with water, 1 = saturated), which is a specific characteristic of peatlands. For the whole northern Russia, areas with hSW were delineated and discriminated from dynamic and open water bodies for the years 2007 and 2008. The area identified with this method amounts to approximately 300,000 km2 in northern Siberia in 2007. It overlaps with zones of high carbon storage. Comparison with a range of related datasets (static and dynamic) showed that hSW represents not only peatlands but also temporary wetlands associated with post-forest fire conditions in permafrost regions. Annual long-term monitoring of change in boreal and tundra environments is possible with the presented approach. Sentinel-1, the successor of ENVISAT ASAR, will provide data that may allow continuous monitoring of these wetland dynamics in the future complementing global observations of wetland fraction.
Approaches for Modelling the Residual Service Life of Marine Concrete Structures
Amir Rahimi,Christoph Gehlen,Thorsten Reschke,Andreas Westendarp
International Journal of Corrosion , 2014, DOI: 10.1155/2014/432472
Abstract: This paper deals with the service life design of existing reinforced concrete structures in a marine environment. The general procedure of condition assessment for estimating the residual service life of structures before a repair measure is illustrated. For assessment of the residual service life of structures which have undergone a repair measure a simplified mathematical model of chloride diffusion in a 2-layer system is presented. Preliminary probabilistic calculations demonstrate the effect of various conditions on the residual service life. First studies of the chloride diffusion in a 2-layer system have been conducted using the finite element method. Results of a long-term exposure test are presented to illustrate the performance of two different repair materials. The distribution of residual chlorides after application of a repair material is being studied in laboratory investigations. The residual chlorides migrate from the concrete layer into the new layer immediately after the repair material has been applied to the concrete member. The content and gradient of residual chlorides, along with the thickness and the chloride ingress resistance of both the remaining and the new layer of cover, will determine the residual service life of the repaired structures. 1. Introduction Concrete structures in a marine environment such as locks, dams and bridges are affected by a wide range of degradation phenomena. Chloride-induced corrosion is the decisive aspect in the durability of such structures. Reinforcement corrosion is initiated when a critical chloride content is reached at the surface of the rebars. Chloride contents higher than the critical value can cause disruption of the protective passive layer, leading to corrosion of the rebars. The time required to initiate corrosion depends, apart from some environmental factors, on the properties of the concrete, in particular on its resistance to chloride diffusion. The following period, the propagation period, refers to the evolution of different forms of deterioration after corrosion has been initiated (cracking, spalling, loss of bond between rebars, and concrete and reduction in the rebar cross-section). Although the service life of structures is the sum of these two periods, in most cases the initiation period defines the service life because the propagation period may be very short. A traditional and feasible repair method consists of removing the chloride-contaminated concrete layer and replacing the removed volume by cement-based repair mortars or concretes. The aim of this measure is either to
Efeito do fator de concentra??o do retentado o rendimento de queijo minas frescal de baixo teor de gordura fabricado por ultrafiltra??o
Cunha, Clarissa Reschke da;Spadoti, Leila Maria;Zacarchenco, Patrícia Blumer;Viotto, Walkíria Hanada;
Ciência e Tecnologia de Alimentos , 2002, DOI: 10.1590/S0101-20612002000100014
Abstract: yield and fat/protein recoveries of low fat 'minas frescal' cheese made from ultrafiltration retentates at concentration factors (cf) of 2:1, 3:1 and 4:1 were determined. two vats of cheese were made for each treatment. chemical composition of milk, permeate, retentate, whey and cheese were determined. fat and protein contents of cheese, as well as fat and protein recoveries (85.70, 88.47 and 92.81%, and 76.84, 85.20 and 89.27%, respectively), increased with increasing concentration factor, although no statistical significant difference was found. it was observed that cheese yield (11.39, 12.03 and 12.66kg cheese/100kg milk) also increased with increasing concentration factor, although without statistical difference.
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