Dissertations / Theses on the topic 'Cocycle'
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Davies, Andrew Phillip. "Cocycle twists of algebras." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/cocycle-twists-of-algebras(23710bc8-abdf-4b8d-9836-111164fefc11).html.
Full textStewart, Colin 1976. "Universal deformations, rigidity, and Ihara's cocycle." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31545.
Full textLeguil, Martin. "Cocycle dynamics and problems of ergodicity." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC159/document.
Full textThe following work contains four chapters: the first one is centered around the weak mixing property for interval exchange transformations and translation flows. It is based on the results obtained together with Artur Avila which strengthen previous results due to Artur Avila and Giovanni Forni. The second chapter is dedicated to a joint work with Zhiyuan Zhang, in which we study the properties of stable ergodicity and accessibility for partially hyperbolic systems with center dimension at least two. We show that for dynamically coherent partially hyperbolic diffeomorphisms and under certain assumptions of center bunching and strong pinching, the property of stable accessibility is dense in C^r topology, r>1, and even prevalent in the sense of Kolmogorov. In the third chapter, we explain the results obtained together with Julie Déserti on the properties of a one-parameter family of polynomial automorphisms of C^3; we show that new behaviours can be observed in comparison with the two-dimensional case. In particular, we study the escape speed of points to infinity and show that a transition exists for a certain value of the parameter. The last chapter is based on a joint work with Jiangong You, Zhiyan Zhao and Qi Zhou; we get asymptotic estimates on the size of spectral gaps for quasi-periodic Schrödinger operators in the analytic case. We obtain exponential upper bounds in the subcritical regime, which strengthens a previous result due to Sana Ben Hadj Amor. In the particular case of almost Mathieu operators, we also show exponential lower bounds, which provides quantitative estimates in connection with the so-called "Dry ten Martinis problem". As consequences of our results, we show applications to the homogeneity of the spectrum of such operators, and to Deift's conjecture
Appiou, Nikiforou Marina. "Extensions of Quandles and Cocycle Knot Invariants." [Tampa, Fla.] : University of South Florida, 2002. http://purl.fcla.edu/fcla/etd/SFE0000125.
Full textGutiérrez, Rodolfo. "Combinatorial theory of the Kontsevich–Zorich cocycle." Thesis, Sorbonne Paris Cité, 2019. https://theses.md.univ-paris-diderot.fr/GUTIERREZ_Rodolfo_2_complete_20190408.pdf.
Full textIn this work, three questions related to the Kontsevich--Zorich cocycle in the moduli space of quadratic differentials are studied by using combinatorial techniques.The first two deal with the structure of the Rauzy--Veech groups of Abelian and quadratic differentials, respectively. These groups encode the homological action of almost-closed orbits of the Teichmüller geodesic flow in a given component of a stratum via the Kontsevich--Zorich cocycle. For Abelian differentials, we completely classify such groups, showing that they are explicit subgroups of symplectic groups that are commensurable to arithmetic lattices. For quadratic differentials, we show that they are also commensurable to arithmetic lattices of symplectic groups if certain conditions on the orders of the singularities are satisfied.The third question deals with the realisability of certain algebraic groups as Zariski-closures of monodromy groups of square-tiled surfaces. Indeed, we show that some groups of the form SO*(2d) are realisable as such Zariski-closures
Schwartz, Peter Oliver. "A cocycle theorem with an application to Rosenthal sets /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487854314870973.
Full textDepauw, Jérôme. "Théorèmes ergodiques pour cocycle de degré 2, critères de récurrence pour cocycles de degré 1, d'une action de ZZd : Application au régime électrique stationnaire." Brest, 1994. http://www.theses.fr/1994BRES2013.
Full textBergeron-Legros, Gabriel. "Weil Representation and Central Extensions of Loop Symplectic Groups." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31516.
Full textChurchill, Indu Rasika U. "Contributions to Quandle Theory: A Study of f-Quandles, Extensions, and Cohomology." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6814.
Full textSchlarmann, Eric [Verfasser], and Bernhard [Akademischer Betreuer] Hanke. "A cocycle model for the equivariant Chern character and differential equivariant K-theory / Eric Schlarmann ; Betreuer: Bernhard Hanke." Augsburg : Universität Augsburg, 2020. http://d-nb.info/1219852554/34.
Full textPinnawala, Nimalsiri, and nimalsiri pinnawala@rmit edu au. "Properties of Trace Maps and their Applications to Coding Theory." RMIT University. Mathematical and Geospatial Sciences, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080515.121603.
Full textDenis, Laurent. "Trace résiduelle sur les star-algèbres symplectiques de type Toeplitz." Paris 6, 2009. http://www.theses.fr/2009PA066158.
Full textDequidt, Picot Kristell. "Coeur de l'invariant de Casson et cobordismes d'homologie." Phd thesis, Université de Nantes, 2005. http://tel.archives-ouvertes.fr/tel-00009786.
Full textHamida, Nadia. "Les régulateurs en K-théorie algébrique." Paris 7, 2002. http://www.theses.fr/2002PA077210.
Full textDelecroix, Vincent. "Combinatoire et dynamique du flot de Teichmüller." Phd thesis, Université de la Méditerranée - Aix-Marseille II, 2011. http://tel.archives-ouvertes.fr/tel-00653165.
Full textSandfeldt, Sven. "Local Rigidity of Some Lie Group Actions." Thesis, KTH, Matematik (Avd.), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-272842.
Full textI den här texten så studerar vi lokal rigiditet av gruppverkan av enkelt sammanhängande Liegrupper. Mer specifikt, vi applicerar Nash-Mosers inversa funktionssats för att ge tillräckliga villkor för att en gruppverkan av en enkelt sammanhängande grupp ska vara lokalt rigid. Låt $G$ vara en Lie grupp, $H < G$ en enkelt sammanhängande delgrupp och $\Gamma < G$ ett kokompakt gitter. Vi applicerar resultatet för generella gruppverkan av enkelt sammanhängande grupper för att få tillräckliga villkor för att verkan av $H$ på $\Gamma\backslash G$ med translationer ska vara lokalt rigid. Vi diskuterar också några möjliga tillämpningar av det tillräckliga villkoret.
Yang, Lei. "HAUSDORFF DIMENSION OF DIVERGENT GEODESICS ON PRODUCT OF HYPERBOLIC SPACES." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1401466357.
Full textSkalski, Adam G. "Quantum stochastic convolution cocycles." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438288.
Full textSchapira, Barbara. "Propriétés ergodiques du feuilletage horosphérique d'une variété à courbure négative." Phd thesis, Université d'Orléans, 2003. http://tel.archives-ouvertes.fr/tel-00163420.
Full textCunha, Kleyber Mota da. "Universalidade para homeomorfismos suaves por pedaços do círculo." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/55/55135/tde-30032011-124214/.
Full textIn this work we find sufficient conditions for two piecewise \'C POT. 2+\' homeomorphisms f and g of the circle to be \'C POT. 1\' conjugate. Besides the restrictions on the combinatorics of the maps (we assume that the maps have the same bounded combinatorics) and necessary conditions on the one-side derivatives of points where f and g are not differentiable, we also assume zero mean nonlinearity for f and g. The proof relies on the detailed study of the renormalizations of genus one generalized interval exchange maps with certain restrictions on their combinatorics
at, Klaus Schmidt@univie ac. "Invariant Cocycles have Abelian Ranges." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi935.ps.
Full textSpelling, James Allan. "Comparison of two metaplectic cocycles." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1383231/.
Full textBradshaw, W. S. "Quantum diffusions and stochastic cocycles." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329848.
Full textChavaudret, Claire. "Réductibilité des cocycles quasi-périodiques." Paris 7, 2010. http://www.theses.fr/2010PA077010.
Full textThis thesis is dedicated to the study of reducibility and almost reducibility of quasi-periodic cocycles, which are the fundamental solutions of linear differential Systems with quasi-periodic coefficients. A notion of conjugation, in the sense of cocycles, by a quasi-periodic transformation, is introduced; quantities which are invariant by this type of conjugation are called dynamical invariants. When a cocycle is reducible, it is possible to have a good knowledge of its dynamical invariants, such as Lyapunov exponents which indicate the asymptotic behaviour of the solutions of the System, and in dimension 2, the rotation number which gives their mean rotation around the origin. Almost reducibility enables one to have quite a good control on these invariants on an arbitrarily long time. One introduces the notion of reducibility of a cocycle in a linear Lie group G modulo 1 or 2, as the possibility of reducing the cocycle by means of a transformation with values in G and which is defined either on the torus, or on a covering of the torus; it is then shown by a geometric argument that a cocycle with values in G which is reducible in the group of invertible matrices is reducible in G modulo 1 if G is complex and modulo 2 if G is real. The second part concerns the problem of almost reducibility, that is, whether it is possible to conjugate a cocycle to another one which is arbitrarily close to a reducible cocycle, in some fixed topology. We state and prove a perturbative result of almost reducibility of analytic cocycles with diophantine frequency which are close to a constant cocycle and take their values in the symplectic group. Almost reducibility is obtained in the space of analytic functions on a fixed neighbourhood of the torus, with only one period doubling, through a KAM-type method estimating how often small divisors, or resonances, appear. Quasi-density in this topology of reducible cocycles near a constant comes as a corollary
Demircioglu, Aydin. "Reconstruction of deligne classes and cocycles." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2007/1375/.
Full textIn this thesis we mainly generalize two theorems from Mackaay-Picken and Picken (2002, 2004). In the first paper, Mackaay and Picken show that there is a bijective correspondence between Deligne 2-classes $xi in check{H}^2(M,mathcal{D}^2)$ and holonomy maps from the second thin-homotopy group $pi_2^2(M)$ to $U(1)$. In the second one, a generalization of this theorem to manifolds with boundaries is given: Picken shows that there is a bijection between Deligne 2-cocycles and a certain variant of 2-dimensional topological quantum field theories. In this thesis we show that these two theorems hold in every dimension. We consider first the holonomy case, and by using simplicial methods we can prove that the group of smooth Deligne $d$-classes is isomorphic to the group of smooth holonomy maps from the $d^{th}$ thin-homotopy group $pi_d^d(M)$ to $U(1)$, if $M$ is $(d-1)$-connected. We contrast this with a result of Gajer (1999). Gajer showed that Deligne $d$-classes can be reconstructed by a different class of holonomy maps, which not only include holonomies along spheres, but also along general $d$-manifolds in $M$. This approach does not require the manifold $M$ to be $(d-1)$-connected. We show that in the case of flat Deligne $d$-classes, our result differs from Gajers, if $M$ is not $(d-1)$-connected, but only $(d-2)$-connected. Stiefel manifolds do have this property, and if one applies our theorem to these and compare the result with that of Gajers theorem, it is revealed that our theorem reconstructs too many Deligne classes. This means, that our reconstruction theorem cannot live without the extra assumption on the manifold $M$, that is our reconstruction needs less informations about the holonomy of $d$-manifolds in $M$ at the price of assuming $M$ to be $(d-1)$-connected. We continue to show, that also the second theorem can be generalized: By introducing the concept of Picken-type topological quantum field theory in arbitrary dimensions, we can show that every Deligne $d$-cocycle induces such a $d$-dimensional field theory with two special properties, namely thin-invariance and smoothness. We show that any $d$-dimensional topological quantum field theory with these two properties gives rise to a Deligne $d$-cocycle and verify that this construction is surjective and injective, that is both groups are isomorphic.
Kaimanovich, Vadim, Klaus Schmidt, and Klaus Schmidt@univie ac at. "Ergodicity of cocycles. 1: General Theory." ESI preprints, 2000. ftp://ftp.esi.ac.at/pub/Preprints/esi936.ps.
Full textBates, Teresa. "Bounded cocycles: von Neumann algebras and amenability." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/10278.
Full textAmeur, Kheira. "Polynomial quandle cocycles, their knot invariants and applications." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001813.
Full textDartyge, Claire. "Cocycles harmoniques et formes automorphes en caractéristique positive." Toulouse 3, 1996. http://www.theses.fr/1996TOU30203.
Full textREBINGUET, NADJA. "Formes modulaires et cocycles harmoniques en caracteristique positive." Toulouse 3, 1998. http://www.theses.fr/1998TOU30101.
Full textGeorge, Jennifer Lynn. "TQFTs from Quasi-Hopf Algebras and Group Cocycles." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1369834588.
Full textMarco, Jonathan. "Systèmes dynamiques en mesure infinie : ergodicité de cocycles : application au billard." Rennes 1, 2010. http://www.theses.fr/2010REN1S212.
Full textSkew-products obtained as extensions of dynamical systems by cocycles appear naturally in the study of billiards in the plane with periodically distributed obstacles. We present three aspects of the study of skew-products. The first part deals with specific examples. First, following W. Veech, M. Guenais and F. Parreau, we study a cohomological functional equation related to the ergodicity of the billiard transformation in the torus with a barrier. The second example is the extension of bounded partial quotients rotations. Especially we give in connection with a paper of G. Greschonig an example of an ergodic skew-product whose cocycle takes values in a nilpotent group. In a second part, we discuss billiards with rectangular obstacles. We present the corresponding quotient billiard transformation in the torus, recalling the link with translation surfaces, interval exchange transformations, and results on unique ergodicity. Then we discuss the special case of a cylinder with periodic obstacles consisiting of segments, for which one can show recurrence in some cases. The billiard flow in the plane with rectangualr obstacles is also considered for certain directions. In a third independent part, we present a general theorem on the ergodic decomposition for skew-products, generalizing the case of a single transformation to the action of a countable group
Ait, Amrane Yacine. "Cohomologie des espaces symétriques de Drinfeld, cocycles harmoniques et formes automorphes." Toulouse 3, 2003. http://www.theses.fr/2003TOU30126.
Full textWalkden, Charles. "Cocycles in hyperbolic dynamics : Livsic regularity theorems and applications to stable ergodicity." Thesis, University of Warwick, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263617.
Full textat, Klaus Schmidt@univie ac. "Growth and Recurrence of Stationary Random Walks." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi1071.ps.
Full textRiba, Garcia Ricard. "Trivial 2-cocycles for invariants of mod p homology spheres and Perron's conjecture." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/664243.
Full textThe main objective of this thesis is the study Perron's conjecture. This conjecture affirms that some function on the group of Torelli mod p, with values in Z/p, is an invariant of mod p homology spheres. In order to study this conjecture, in this thesis we first study the mod p homology spheres, the rational homology spheres and we give a criterion to determine whenever a rational homology sphere has a Heegaard splitting with gluing map an element of the Torelli group mod p, which is the group given by the kernel of the Symplectic representation modulo p of the mapping class group. Next, we extend the results of the article ''Trivial cocycles and invariants of homology 3-spheres'' obtaining a construction of invariants with values to an abelian group without restrictions, from a suitable family of 2-cocycles on the Torelli group. In particular, we explain the influence of the invariant of Rohlin in the lost of uniqueness in such construction. Later, using the same tools, we obtain a construction of invariants of rational homology spheres that have a Heegaard splitting with gluing map an element of the mod p Torelli group, from a suitable family of 2-coccycles on the mod p Torelli group. In addition, throughout this construction we obtain an invariant of mod p homology spheres which does not appear in the literature. Finally, we prove that Perrron's conjecture is false providing an obstruction that is given by the fact that the first characteristic class of surface bundles reduced modulo p does not vanish.
Derrien, Jean-Marc. "Propriétés ergodiques d'extensions isométriques : théorème ergodique polynôminal ponctuel : régularisation de cocycles par cohomologie." Tours, 1994. http://www.theses.fr/1994TOUR4023.
Full textBuhanan, David Bryant. "On some aspects of cocyclic subshifts, languages, and automata." Diss., Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/buhanan/BuhananD0812.pdf.
Full textKormu, J. (Jussi). "Continuity of subadditive pressure for matrix cocycles and the dimension of a self-affine set." Master's thesis, University of Oulu, 2016. http://urn.fi/URN:NBN:fi:oulu-201604191516.
Full textStonier, D. J., and mikewood@deakin edu au. "Stability theory and numerical analysis of non-autonomous dynamical systems." Deakin University. School of Information Technology, 2003. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20051125.113243.
Full textBouarroudj, Sofiane. "Les cocycles sur le groupe des difféomorphismes généralisant la dérivée de Scharwz et la géométrie des opérateurs différentiels." Aix-Marseille 1, 1999. http://www.theses.fr/1999AIX11002.
Full textNikolaos, Karaliolios. "Aspects globaux de la réductibilité des cocycles quasi-périodiques à valeurs dans des groupes de Lie compacts semi-simples." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00777911.
Full textKaraliolios, Nikolaos. "Aspects globaux de la réductibilité des cocycles quasi-périodiques à valeurs dans des groupes de Lie compacts semi-simples." Paris 6, 2013. http://www.theses.fr/2013PA066111.
Full textIn this PhD thesis we study quasiperiodic cocycles in semi-simple compact Lie groups. For the greatest part of our study,we will focus ourselves to one-frequency cocyles. We will prove that C^{\infty }-reducible cocycles are dense in theC^{\infty } topology, for a full measure set of frequencies. We will firstly define two invariants of the dynamics which we will call\textit{energy} and \textit{degree} and which give a preliminary distinction between reducible and non-reducible cocycles. We will then take up the proof of the density theorem. We will show that an algorithm of \textit{renormalization} convergesto perturbations of simple models, indexed by the degree. Finally, we will analyse these perturbations using methods inspiredby \textit{K. A. M. } theory. In this context we will prove that if a C^{\infty } cocycle is measurably reducible to adiophantine constant, it is actually C^{\infty }-reducible
Hok, Jean-Marc. "1-cocycles pour les n-tresses fermées dans le tore solide qui sont des nœuds et algorithmes de calculs." Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30022.
Full textThis manuscript is a work within the scope of topology, algebra, combinatorics and programming. More precisely, it is a thesis in knot theory. The main goal of this manuscript is to provide a family of invariants that can distinguish 4-braids that are knots (a particular family of knots) in the solid torus S1×D2. The construction and the computation of these invariants use knot theory basics but the proof of the main invariance theorem requires more advanced knowledge in singularity theory. The understanding of the computational program that implements these invariants in Sagemath requires basic knowledge of Python programming and algorithmics (Oriented-Object Programming, recursive function theory, dictionaries, etc...)
Laperriere, Christiane. "Positive cocycles for minimal Zd-actions on a cantor set resulting from cut and project schemes: The octogonal tiling." Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28269.
Full textHerbst, Manuel [Verfasser], Karl-Hermann [Akademischer Betreuer] Neeb, and Karl-Hermann [Gutachter] Neeb. "1-Cocycles of unitary representations of infinite--dimensional unitary groups / Manuel Herbst ; Gutachter: Karl-Hermann Neeb ; Betreuer: Karl-Hermann Neeb." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/1176190865/34.
Full textFrettsome, Rebecca Louise. "The effects of the human cocyte vestments and follicular fluid on spermatozoa." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3512/.
Full textHarvey, Ebony Ann. "Cohomological Invariants of Quadratic Forms." Thesis, Boston College, 2010. http://hdl.handle.net/2345/1324.
Full textGiven a field F, an algebraic closure K and an F-vector space V, we can tensor the space V with the algebraic closure K. Two quadratic spaces of the same dimension become isomorphic when tensored with an algebraic closure. The failure of this isomorphism over F is measured by the Hasse invariant. This paper explains how the determinants and Hasse Invariants of quadratic forms are related to certain cohomology classes constructed from specific short exact sequences. In particular, the Hasse Invariant is defined as an element of the Brauer group
Thesis (MA) — Boston College, 2010
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Mathematics
Metzger, Florian. "Exposants de Lyapunov d’opérateurs de Schrödinger ergodiques." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066127/document.
Full textIn this thesis we are interested in the Lyapunov exponent of ergodic Schrödinger cocycles. These cocycles occur in the analysis of solutions to the Schrödinger equation where the potential is defined with ergodic dynamics. We study two distinct aspects related to the the Lyapunov exponent for different kinds of dynamics. First we focus on a large deviation theorem for quasi-periodic cocycles and then for potentials defined by the doubling map. We prove that estimates of Bourgain & Goldstein type are granted if an upper estimate involved in the theorem is true on a strip of the complex plane. Then we establish a new technique to prove this upper bound in the quasi-periodic setting, based on subharmonic arguments suggested by Avila, Jitomirskaya & Sadel. We adapt afterwards the method to the doubling map and prove a large deviation theorem for the inverse branches of this dynamics. In the second part, we establish an asymptotic development similar to the results of Figotin & Pastur and Sadel & Schulz-Baldes for the Lyapunov exponent of Schrödinger cocycles at small coupling when the potential is a mixture of quasi-periodic and random. The analysis distinguishes the cases when the energy is either diophantine or resonant with respect to the frequency of the quasi-periodic part of the potential
Clua, Obradó Elisabet. "Prevenció de la gestació múltiple en un programa de donació d’oòcits." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/386531.
Full textMultiple pregnancy is regarded as a complication of assisted reproductive technologies, especially significant in oocyte donation programmes (OD). However, few authors have assessed this issue or established criteria to reduce it. The objectives of this thesis were 1) to describe the incidence of obstetric and perinatal complications in single and multiple pregnancies, as well as the additional impact of recipient age; 2) to analyse the main factors associated with multiple pregnancy in the OD programme; 3) to assess the cumulative (fresh embryo transfer cycles plus frozen-thawed embryo transfer cycles) pregnancy and live birth rates in OD cycles with elective single embryo transfer (SET) compared with elective double-embryo transfer (DET); 4) to evaluate the results of implementing a strategy shift from transferring two embryos to transferring one in our OD programme. The first objective was accomplished through a retrospective observational study of 225 singleton pregnancies, 113 multiple and 447 live births, in which the reception cycle, pregnancy follow-up and labour were performed at our centre. The results showed that in multiple pregnancies from OD there was a higher incidence of obstetric (preeclampsia, premature rupture of membranes, caesarean sections and preterm delivery) and perinatal (low birth weight, admissions to the intensive care unit and perinatal mortality) complications than in singleton pregnancies. The incidence of gestational diabetes and caesarean section increased with age (≥40 years). For the second objective, a retrospective study of 945 reception cycles in which two embryos had been transferred (on day 2) was carried out. Among the variables analysed, embryo quality was the only associated factor. The risk of multiple gestation was twofold when two good-quality embryos were transferred compared with two non-good-quality embryos. The third objective was developed through three studies that evaluated the cumulative pregnancy and live birth rates: i) a retrospective study to compare the outcomes of 1073 cycles in which DET was performed on day 2, with 66 SET cycles; ii) a randomised prospective study comparing the results of 34 SET cycles with 31 DET cycles when there were a minimum of 5 embryos available with at least 2 good-quality embryos on day 3; iii) an analytic prospective study, with the application of the criteria established in clinical practice for the purpose of recommending SET, which included 297 SET and 203 DET cycles. We concluded that in good-prognosis recipients, cumulative pregnancy and live birth rates are similar in both strategies. However, although the multiple pregnancy rate was lower in SET, the time needed to achieve the same success rate was higher. For the last objective, we retrospectively analysed single-embryo transfers from 2004 until 2014. This analysis revealed that the application of medical and embryologic criteria led to an increase in single-embryo transfers from 2.6% to 43.1%, with a decrease in multiple pregnancy rates from 30% to 22.5%, without a clinically relevant reduction in the pregnancy and live birth rates. These results show that by applying medical and embryologic criteria to transfer one embryo, it is possible to increase the percentage of single-embryo transfers and reduce the multiple gestation rate without affecting the cumulative pregnancy and live birth rates. However, the time to pregnancy is higher when one embryo is transferred.