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Alan Barnes - One of the best experts on this subject based on the ideXlab platform.
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ricci collineations in friedmann robertson walker spacetimes
Classical and Quantum Gravity, 2002Co-Authors: Ugur Camci, Alan BarnesAbstract:Ricci collineations and Ricci inheritance collineations of Friedmann–Robertson–Walker spacetimes are considered. When the Ricci tensor is non-degenerate, it is shown that the spacetime always admits a 15-parameter group of Ricci inheritance collineations; this is the maximal possible dimension for spacetime manifolds. The general form of the vector generating the symmetry is exhibited. It is also shown, in the generic case, that the group of Ricci collineations is six-dimensional and coincides with the isometry group. In special cases the spacetime may admit either one or four proper Ricci collineations in addition to the six isometries. These special cases are classified and the general form of the vector fields generating the Ricci collineations is exhibited. When the Ricci tensor is degenerate, the groups of Ricci inheritance collineations and Ricci collineations are infinite-dimensional. General forms for the generating vectors are obtained. Similar results are obtained for matter collineations and matter inheritance collineations.
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ricci collineations in friedmann robertson walker spacetimes
arXiv: General Relativity and Quantum Cosmology, 2001Co-Authors: Ugur Camci, Alan BarnesAbstract:Ricci collineations and Ricci inheritance collineations of Friedmann-Robertson-Walker spacetimes are considered. When the Ricci tensor is non-degenerate, it is shown that the spacetime always admits a fifteen parameter group of Ricci inheritance collineations; this is the maximal possible dimension for spacetime manifolds. The general form of the vector generating the symmetry is exhibited. It is also shown, in the generic case, that the group of Ricci collineations is six-dimensional and coincides with the isometry group. In special cases the spacetime may admit either one or four proper Ricci collineations in addition to the six isometries. These special cases are classified and the general form of the vector fields generating the Ricci collineations is exhibited. When the Ricci tensor is degenerate, the groups of Ricci inheritance collineations and Ricci collineations are infinite-dimensional. General forms for the generating vectors are obtained. Similar results are obtained for matter collineations and matter inheritance collineations.
Spurná Veronika - One of the best experts on this subject based on the ideXlab platform.
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Diversity of the genus Riccia (Marchantiophyta)
Univerzita Karlova Přírodovědecká fakulta, 2018Co-Authors: Spurná VeronikaAbstract:The main aim of this thesis is to give a brief overview of the genus Riccia. It belongs to the same taxonomic group as the genus Ricciocarpos Corda, family Ricciaceae (order Marchantiales, department Marchantiophyta). Both genera have a simple endosporophile and they do not possess elaters. The genus Riccia has a wide ecological valency. The representatives of the genus, who are adapted to life in drier areas, are able to grow on bare, sunny, clay soil. Other species can be found on wet places with high water occurrence or even directly in the aquatic environment. The genus has a worldwide distribution. The most abundant diversity is in subtropical areas with high environment variety which directly influences the diversity of this species. Representatives of this genus are able to survive extreme conditions and can very easily adapt to new conditions. They are also defined by great morphology plasticity. There are still problems to correctly distinguish some species from each other beacause of this reason. There are 13 species in the Czech Republic, three of them are easily interchangeable. Part of the thesis is therefore focused on the comparison of the species R. fluitans and R. rhenana from the Ricciella section. The former is typically found on the surface of the water. However, when found...Cílem této práce je podat stručný přehled o rodu Riccia. Společně s rodem Ricciocarpos Corda se taxonomicky řadí do čeledi Ricciaceae (řád Marchantiales, oddělení Marchantiophyta). Oba rody mají jednoduchý endosporofyt a chybí jím elatery. Rod Riccia má širokou ekologickou valenci. Zástupci rodu, kteří jsou přizpůsobeni životu v sušších oblastech, se nachází na holé, prosluněné, jílovité půdě. Jiné druhy se vyskytují na vlhkých místech, kde se drží voda anebo také přímo ve vodním prostředí. Rod má kosmopolitní rozšíření. Největší diverzita je v subtropických oblastech, kde jim prospívá vysoká rozmanitost a bohatost prostředí. Zástupci tohoto rodu dokáží přežívat extrémní podmínky, velmi snadno se přizpůsobují novým podmínkám a také se vyznačují velkou morfologickou plasticitou. Z tohoto důvodu dodnes panují problémy správně určit některé konkrétní druhy. V České republice je celkem 13 druhů a z toho jsou tři druhy snadno zaměnitelné. Práce je částečně zaměřena i na porovnání druhů R. fluitans a R. rhenana ze sekce Ricciella. První z nich se typicky vyskytuje na hladině vody. Pokud se však ocitne bez trvalého vodního prostředí může připomínat druh R. rhenana, který se většinou nachází v terestrické formě. Třetí druh ze sekce R. stenophylla se dosud nevyskytuje v ČR, ale je možné, že u nás bude v...Department of BotanyKatedra botanikyPřírodovědecká fakultaFaculty of Scienc
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Diversity of the genus Riccia (Marchantiophyta)
2018Co-Authors: Spurná VeronikaAbstract:The main aim of this thesis is to give a brief overview of the genus Riccia. It belongs to the same taxonomic group as the genus Ricciocarpos Corda, family Ricciaceae (order Marchantiales, department Marchantiophyta). Both genera have a simple endosporophile and they do not possess elaters. The genus Riccia has a wide ecological valency. The representatives of the genus, who are adapted to life in drier areas, are able to grow on bare, sunny, clay soil. Other species can be found on wet places with high water occurrence or even directly in the aquatic environment. The genus has a worldwide distribution. The most abundant diversity is in subtropical areas with high environment variety which directly influences the diversity of this species. Representatives of this genus are able to survive extreme conditions and can very easily adapt to new conditions. They are also defined by great morphology plasticity. There are still problems to correctly distinguish some species from each other beacause of this reason. There are 13 species in the Czech Republic, three of them are easily interchangeable. Part of the thesis is therefore focused on the comparison of the species R. fluitans and R. rhenana from the Ricciella section. The former is typically found on the surface of the water. However, when found..
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Diversity of the genus Riccia (Marchantiophyta) and molecular methods of taxonomical study of liverworts
Univerzita Karlova Přírodovědecká fakulta, 2017Co-Authors: Spurná VeronikaAbstract:Cílem této bakalářské práce je představit rod Riccia. První fosilní nálezy přiřazované tomuto rodu se datují již na počátku pleistocénu. V knižním vydání se objevuje od 17. stol. a od té doby mu věnovali více pozornosti. Rod má kosmopolitní rozšíření po celém světě. Přežívá extrémní podmínky. Velmi snadno se přizpůsobuje novým podmínkám. Zástupci tohoto rodu se vyznačují velkou variabilitou morfologie. A proto i dodnes panují problémy správně určit konkrétní druh. V České Republice je celkem 13 druhů a z toho jsou tři druhy snadno zaměnitelné. Zaměřila jsem se na porovnání R.fluitans, která se typicky vyskytuje na hladině vody. Pokud se však ocitne bez trvalého vodního prostředí, tak se může zdát jako druh R. rhenana, který se většinou nachází v terestrické formě. V další části jsem popsala základní metody k molekulárním studiím věnované Marchantiophyta. Molekulární data výrazně změnili pohled na taxonomii kmene. Do nedávna je řadili na základě morfologických podobností. Ovšem ani moderní techniky nezaručují správnost, a tak se doporučuje kombinovat molekulární výsledky s morfologickými znaky. Klíčová slova: Riccia, diverzita, variabilita, molekulární studia, MarchantiophytaThe main objective of this study is to introduce the genus Riccia. The first fossil discoveries of this genus date back to the Early Pleistocene. It has been known from literature since the 17th century. From this time forward it gets more attention. This genus has a cosmopolitan distribution across all of the world. It is capable of surviving extreme conditions. Also it adapts to new conditions quite easily. Representatives of genus Riccia have a very wide range of morphological variations. Therefore to this day there are still issues with a properly species determination. In the Czech Republic there are 13 species and 3 of it are easily interchangeable. Mainly, I focus on R.fluitans, which its a typical habitat is a water level. If R.fluitans lacks the aquatic environment, then It can look like terrestrial R.rhenana. The next chapter is about a description of basic metods in molecular studies on Marchantiophyta. Molecular data have changed significantly a view on the Marchantiophyta taxonomy. Until recently the taxonomy was dependent on morphological similarities. But modern metods don't always guarantee the correctness. Therefore it is recommended to combine molecular results with morphological features. Keywords: Riccia, diversity, variability, molecular study, MarchantiophytaDepartment of BotanyKatedra botanikyPřírodovědecká fakultaFaculty of Scienc
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Diversity of the genus Riccia (Marchantiophyta) and molecular methods of taxonomical study of liverworts
2017Co-Authors: Spurná VeronikaAbstract:The main objective of this study is to introduce the genus Riccia. The first fossil discoveries of this genus date back to the Early Pleistocene. It has been known from literature since the 17th century. From this time forward it gets more attention. This genus has a cosmopolitan distribution across all of the world. It is capable of surviving extreme conditions. Also it adapts to new conditions quite easily. Representatives of genus Riccia have a very wide range of morphological variations. Therefore to this day there are still issues with a properly species determination. In the Czech Republic there are 13 species and 3 of it are easily interchangeable. Mainly, I focus on R.fluitans, which its a typical habitat is a water level. If R.fluitans lacks the aquatic environment, then It can look like terrestrial R.rhenana. The next chapter is about a description of basic metods in molecular studies on Marchantiophyta. Molecular data have changed significantly a view on the Marchantiophyta taxonomy. Until recently the taxonomy was dependent on morphological similarities. But modern metods don't always guarantee the correctness. Therefore it is recommended to combine molecular results with morphological features. Keywords: Riccia, diversity, variability, molecular study, Marchantiophyt
Dieter Lust - One of the best experts on this subject based on the ideXlab platform.
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geometric flow equations for schwarzschild ads space time and hawking page phase transition
Protein Science, 2020Co-Authors: Davide De Biasio, Dieter LustAbstract:Following the recent observation that the Ricci flow and the infinite distance swampland conjecture are closely related to each other, we will investigate in this paper geometric flow equations for AdS space-time geometries. First, we consider the so called Yamabe and Ricci-Bourguignon flows and we show that these two flows - in contrast to the Ricci flow - lead to infinite distance fixed points for product spaces like $AdS_d\times S^p$, where $AdS_d$ denotes d-dimensional AdS space and $S^p$ corresponds to a p-dimensional sphere. Second, we consider black hole geometries in AdS space time geometries and their behaviour under the Yamabe and Ricci-Bourguignon flows. Specifically we will examine if and how the AdS black holes will undergo a Hawking-Page phase transition under the Ricci flow, the Yamabe flow and under the general Ricci-Bourguignon flow.
Vertman Boris - One of the best experts on this subject based on the ideXlab platform.
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Ricci de Turck flow on singular manifolds
'Springer Science and Business Media LLC', 2020Co-Authors: Vertman BorisAbstract:In this paper we prove local existence of a Ricci de Turck flow starting at a space with incomplete edge singularities and flowing for a short time within a class of incomplete edge manifolds. We derive regularity properties for the corresponding family of Riemannian metrics and discuss boundedness of the Ricci curvature along the flow. For Riemannian metrics that are sufficiently close to a flat incomplete edge metric, we prove long time existence of the Ricci de Turck flow. Under certain conditions, our results yield existence of Ricci flow on spaces with incomplete edge singularities. The proof works by a careful analysis of the Lichnerowicz Laplacian and the Ricci de Turck flow equation.Comment: 50 pages, 2 figure
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Stability of Ricci de Turck flow on Singular Spaces
'Springer Science and Business Media LLC', 2020Co-Authors: Kroencke Klaus, Vertman BorisAbstract:In this paper we establish stability of the Ricci de Turck flow near Ricci-flat metrics with isolated conical singularities. More precisely, we construct a Ricci de Turck flow which starts sufficiently close to a Ricci-flat metric with isolated conical singularities and converges to a singular Ricci-flat metric under an assumption of integrability, linear and tangential stability. We provide a characterization of conical singularities satisfying tangential stability and discuss examples where the integrability condition is satisfied.Comment: 48 pages, published versio
Ugur Camci - One of the best experts on this subject based on the ideXlab platform.
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ricci collineations in friedmann robertson walker spacetimes
Classical and Quantum Gravity, 2002Co-Authors: Ugur Camci, Alan BarnesAbstract:Ricci collineations and Ricci inheritance collineations of Friedmann–Robertson–Walker spacetimes are considered. When the Ricci tensor is non-degenerate, it is shown that the spacetime always admits a 15-parameter group of Ricci inheritance collineations; this is the maximal possible dimension for spacetime manifolds. The general form of the vector generating the symmetry is exhibited. It is also shown, in the generic case, that the group of Ricci collineations is six-dimensional and coincides with the isometry group. In special cases the spacetime may admit either one or four proper Ricci collineations in addition to the six isometries. These special cases are classified and the general form of the vector fields generating the Ricci collineations is exhibited. When the Ricci tensor is degenerate, the groups of Ricci inheritance collineations and Ricci collineations are infinite-dimensional. General forms for the generating vectors are obtained. Similar results are obtained for matter collineations and matter inheritance collineations.
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ricci collineations in friedmann robertson walker spacetimes
arXiv: General Relativity and Quantum Cosmology, 2001Co-Authors: Ugur Camci, Alan BarnesAbstract:Ricci collineations and Ricci inheritance collineations of Friedmann-Robertson-Walker spacetimes are considered. When the Ricci tensor is non-degenerate, it is shown that the spacetime always admits a fifteen parameter group of Ricci inheritance collineations; this is the maximal possible dimension for spacetime manifolds. The general form of the vector generating the symmetry is exhibited. It is also shown, in the generic case, that the group of Ricci collineations is six-dimensional and coincides with the isometry group. In special cases the spacetime may admit either one or four proper Ricci collineations in addition to the six isometries. These special cases are classified and the general form of the vector fields generating the Ricci collineations is exhibited. When the Ricci tensor is degenerate, the groups of Ricci inheritance collineations and Ricci collineations are infinite-dimensional. General forms for the generating vectors are obtained. Similar results are obtained for matter collineations and matter inheritance collineations.
