### Organized scientific events

- Workshop
**Noncommutative Ergodic Theory**(OTET 10), Kiel, 4. – 7. October 2022

(Organized together with Markus Haase, Henrik Kreidler, Sascha Trostorff) - Workshop
**Cuntz semigroups**, Kiel, 19. – 23. September 2022 - Workshop
**Cuntz semigroups**, Münster, 12. – 16. July 2021

(Organized together with Eusebio Gardella) - Conference
**Young Mathematicians in C*-algebras (YMC*A)**, Münster, 25.-29. July 2016

(Organized together with Christian Bönicke, Dominic Enders, Eusebio Gardella, Gabor Szabo, Jianchao Wu, Kang Li, Sayan Chakraborty, Søren Knudby, Sven Raum) - Workshop
**C*-algebras: Geometry and Actions**, Münster, 13-17. July 2015

(Organized together with Siegfried Echterhoff, Stuart White, Wilhelm Winter) - Workshop
**Structure and Classification of C*-algebras**, Münster, 20-24. April 2015

(Organized together with Siegfried Echterhoff, Stuart White, Wilhelm Winter) - Miniworkshop
**C*-algebras, C*-bundles and Group Actions,**Münster, November 2013

(Organized together with Snigdhayan Mahanta) - Masterclass
**Semiprojectivity**, Copenhagen, 27.-31. August 2012

(Organized together with Søren Eilers, Adam Sørensen) - Masterclass
**The nuclear dimension of C*-algebras**, Copenhagen, November 2011

### Attended scientific events, delivered presentations

Date | Event | Talk |
---|---|---|

2023/10 | Virginia Operator Theory and Complex Analysis Meeting (VOTCAM), 14. October 14, 2023, Richmond. | |

2023/08-10 | Thematic Program on Operator Algebras and Applications, Fields Institute, Toronto, Canada Workshop on Operator Algebras and Applications: Connections with Logic, 28. August - 1. September, 2023. Workshop on Operator Algebras and Applications: Symmetry and Structure, 18-22. September, 2023. Workshop on Operator Algebras and Applications: Groups and Group Actions, 2-6. October, 2023. | Prime and semiprime ideals in C*-algebras 18. September 2023 ## AbstractNonclosed ideals of bounded operators play a prominent role in the theory of singular traces as developed by Dixmier, Connes and many others, and the Calkin correspondence is a powerful tool that can be used to answer many questions about nonclosed ideals in this context. For general C*-algebras, a systematic study of nonclosed ideals was initiated by Pedersen in the late 1960s, but much less is known in this broader setting.We show that a not necessarily closed ideal in a C*-algebra is semiprime (that is, an intersection of prime ideals) if and only if it is closed under roots of positive elements. Quite unexpectedly, it follows that prime and semiprime ideals in C*-algebras are automatically self-adjoint. This can be viewed as a generalization of the well-known result that closed ideals in C*-algebras are semiprime and self-adjoint. This is joint work with Eusebio Gardella and Kan Kitamura. |

2023/08 | Conference on noncommutative harmonic analysis and rigidity theoryin operator algebras, 21-25. Agust 2023, Delft. | Rigidity results for Lp-operator algebras 21. August 2023 |

2023/07 | Conference C*-Algebras: Tensor Products, Approximation & Classification (A conference in honour of Eberhard Kirchberg), 17-21. July 2023, Münster. | |

2023/05 | Mini-Conference C*-days in Prague, 30. May 2023, Prague. | Traces on ultrapowers of C*-algebras 30. May 2023 ## AbstractEvery sequence of traces on a C*-algebra A induces a limit trace on a free ultrapower of A. Using Cuntz semigroup techniques, we characterize when these limit traces are dense. Quite unexpectedly, we obtain as an application that every simple C*-algebra that is (m,n)-pure in the sense of Winter is already pure.This is joint work with Antoine, Perera and Robert. |

2023/03 | Mini-workshop on operator algebras and noncommutative geometry, 5-6. March 2023, Stockholm. | Traces on ultrapowers of C*-algebras 5. March 2023 ## AbstractEvery sequence of traces on a C*-algebra A induces a limit trace on a free ultrapower of A. Using Cuntz semigroup techniques, we characterize when these limit traces are dense. Quite unexpectedly, we obtain as an application that every simple C*-algebra that is (m,n)-pure in the sense of Winter is already pure.This is joint work with Antoine, Perera and Robert. |

2023/01 | 3rd Barcelona Weekend on Operator Algebras 27-28 January 2023, Barcelona, Spain | |

2022/11 | Conference Group Actions: Dynamics, Measure, Topology 28 November - 2 December, 2022, Münster, Germany | |

2022/11 | Oberseminar Analysis, Kiel 15. October 2022 | Das Erzeugerproblem für C*-Algebren |

2022/10 | North British Functional Analysis Seminars 28-29 October 2022, Belfast, UK | The generator problem of C*-algebras ## AbstractThe generator problem asks to determine, for a given C*-algebra, its minimal number of generators. In particular, one wants to know if every separable, simple C*-algebra is generated by a single element. The generator problem was originally asked for von Neumann algebras, and Kadison included it as no. 14 of his famous list of 20 "Problems on von Neumann algebras". The problem remains open, most notably for the reduced free group C*-algebras and the free group factors.I will first give an overview on the generator problem and then present some recent new results. Most interestingly, we will see a strong solution to the generator problem for separable, simple, classifiable C*-algebras: They are not merely singly generated but they contain a dense set of generators. The zero-product structure of C*-algebras ## AbstractIt is well known that every C*-algebra is determined by its linear and multiplicative structure: Two C*-algebras are *-isomorphic if and only if they admit a multiplicative, linear bijection.We study if, instead of the whole multiplicative structure, it suffices to record when two elements have zero product. While it is not clear if every C*-algebra is determined this way, we obtain many positive results. In particular, two unital, simple C*-algebras are *-isomorphic if and only if they admit a linear bijection that preserves zero products. This is joint work with Eusebio Gardella. |

2022/10 | Workshop Noncommutative Ergodic Theory (OTET 10) 4-7 October 2022, Kiel, Germany | Organized together with Markus Haase, Henrik Kreidler, Sascha Trostorff |

2022/09 | Workshop Cuntz Semigroups 19-23 September 2022, Kiel, Germany | Organized |

2022/08 | 28th Nordic Congress of Mathematicians 18-22 August 2022, Aalto University, Helsinki, Finland | |

2022/06 | Canadian Abstract Harmonic Analysis Symposium (CAHAS), Banff (online talk) | Rigidity results for Lp-operator algebras ## AbstractAn Lp-operator algebra is a Banach algebra that admits an isometric representation on some Lp-space (p not 2). Given such an algebra A, we show that it contains a unique maximal sub-C*-algebra, which we call its C*-core. The C*-core is automatically abelian, and its spectrum is naturally equipped with an inverse semigroup of partial homeomorphisms. We call the associated groupoid of germs the Weyl groupoid of A.The Weyl groupoid contains information about the internal dynamics of the algebra A, and in some some cases it is a complete invariant. For example, given a topologically free action on a compact space, the Weyl groupoid of the reduced Lp-crossed product is simply the transformation groupoid of the action. This leads to strong rigidity results for reduced groupoid algebras and reduced crossed products. We use our results to answer a question of Phillips: The Lp-analog of the Cuntz algebra is not isomorphic to its tensor square. (Joint work with Yemon Choi and Eusebio Gardella.) |

2022/06 | Hanseatic Dynamical Systems Days (HANDSDays), Kiel | Dynamical systems and operator algebras ## AbstractThe crossed product construction associates to each topological dynamical system an interesting C*-algebra. The fundamental goal is to determine which properties of the dynamical system are encoded in the C*-algebra, and how.I will give an overview of the crossed product construction and then highlight some of the properties of a dynamical system that can be recognized in the crossed product, including some recent breakthroughs results concerning simplicity of group C*-algebras and crossed products. |

2022/06 | Wales MPPM Zoom Seminar (online talk) | Are C*-algebras determined by their linear and orthogonality structure? ## AbstractIt is well-known that every C*-algebra is determined by its linear and multiplicative structure: Two C*-algebras are *-isomorphic if and only if they admit a multiplicative, linear bijection. We study if instead of the whole multiplicative structure it suffices to record when two elements have zero product. While it is not clear if every C*-algebra is determined this way, we obtain many positive results. In particular, two unital, simple C*-algebras are *-isomorphic if and only if they admit a linear bijection that preserves zero products.(Joint work with Eusebio Gardella.) |

2022/05 | C*-algebras: Structure and Dynamics, Sde Boker | Are C*-algebras determined by their linear and orthogonality structure? ## AbstractIt is well-known that every C*-algebra is determined by its linear and multiplicative structure: Two C*-algebras are *-isomorphic if and only if they admit a multiplicative, linear bijection. We study if instead of the whole multiplicative structure it suffices to record when two elements have zero product. While it is not clear if every C*-algebra is determined this way, we obtain many positive results. In particular, two unital, simple C*-algebras are *-isomorphic if and only if they admit a linear bijection that preserves zero products.(Joint work with Eusebio Gardella.) |

2022/05 | Operator algebras seminar, Florianopolis (online talk) | Are C*-algebras determined by their linear and orthogonality structure? Download Slides |

2022/05 | Oberseminar Analysis, Kiel | Sind C*-Algebren durch ihre lineare und orthogonale Struktur festgelegt? ## AbstractEs ist wohlbekannt, dass jede C*-Algebra durch ihre lineare und multiplikative Struktur festgelegt ist: Zwei C*-Algebren sind genau dann *-isomorph wenn sie eine multiplikative, lineare Bijektion zulassen.Wir studieren, ob es genügt anstelle der gesamten multiplikativen Struktur festzuhalten wann zwei Elemente Nullprodukt haben. Während es unklar bleibt, ob dies im allgemeinen ausreicht, zeigen wir mehrere positive Resultate. Insbesondere sind zwei unitale, einfache C*-Algebren genau dann *-isomorph wenn sie eine lineare, Nullprodukt erhaltende Bijektion zulassen. Dies ist eine gemeinsame Arbeit mit Eusebio Gardella. |

2022/03 | Noncommutativity in the North | Are C*-algebras determined by their linear and orthogonality structure? Download notes ## AbstractIt is well-known that every C*-algebra is determined by its linear and multiplicative structure: Two C*-algebras are *-isomorphic if and only if they admit a multiplicative, linear bijection. We study if instead of the whole multiplicative structure it suffices to record when two elements have zero product. While it is not clear if every C*-algebra is determined this way, we obtain many positive results. In particular, two unital, simple C*-algebras are *-isomorphic if and only if they admit a linear bijection that preserves zero products. |

2022/02 | Analysis and Probability Seminar, Gothenburg | The generator problem for C*-algebras ## AbstractThe generator problem asks to determine for a given C*-algebra its minimal number of generators. In particular, one wants to know if every separable, simple C*-algebra is generated by a single element. The generator problem was originally asked for von Neumann algebras, and Kadison included it as Nr. 14 of his famous list of 20 "Problems on von Neumann algebras". The problem remains open, most notably for the reduced free group C*-algebras and the free group factors.To tackle the generator problem, I introduced the generator rank as a stable quantification of the generator problem. Instead of asking if a C*-algebra is generated by k elements, the generator rank records whether the generating k-tuples are dense. It turns out that this invariant has good permanence properties and it can be computed in a number of interesting cases. In this talk, I will first give an overview on the generator problem and then present some recent results on computations of the generator rank. Most interestingly, we will see a strong solution to the generator problem for separable, simple, classifiable C*-algebras: They are not merely singly generated but they contain a dense set of generators. |

2021/11 | Oberseminar Analysis, Kiel | Rigidität von Gruppenalgebren ## AbstractZu einer diskrete Gruppe G werden verschiedene Gruppenalgebren assoziiert. Die Rigidität beschreibt, wie viele Eigenschaften von G aus der Gruppenalgebra abgelesen werden können. Die größtmögliche Rigidität bedeutet, dass die komplette Struktur von G durch die Gruppenalgebra festgelegt ist.Für eine reelle Zahl p größer 1 betrachten wir die linksreguläre Darstellung von G auf dem Lp-Raum von G. Die erzeugte Banachalgebra heißt die reduzierte Lp-Gruppenalgebra von G. Für p=2 erhalten wir die reduzierte Gruppen-C*-Algebra. Es seien nun G und H diskrete Gruppen, sodass die reduzierten Lp-Gruppenalgebren von G und H isomorph sind. Können wir schlussfolgern, dass G und H isomorph sind? Für p ungleich 2 ist die Antwort überraschenderweise "Ja". In diesem Fall haben wir maximale Rigidität und eine Gruppe kann aus ihrer reduzierten Lp-Gruppenalgebra abgelesen werden. Der Fall p=1 wurde 1951 von Wendel gezeigt. Für p=2 ändert sich die Situation drastisch. Es gibt einfache Beispiele von nicht-isomorphen Gruppen mit isomorphen reduzierten Gruppen-C*-Algebren. Dennoch kann man viele Eigenschaften einer Gruppe aus ihrer Gruppen-C*-Algebra ablesen. In einigen Fällen kann man sogar maximale Rigidität zeigen: Bestimmte Bieberbachgruppen sind durch ihre Gruppen-C*-Algebra eindeutig festgelegt. Dieser Vortrag basiert auf einer Zusammenarbeit mit E. Gardella, und einer Zusammenarbeit mit S. Knudby, S. Raum und S. White. |

2021/08 | IWOTA, Session 2 (Operator algebras) (online talk) | The rank problem for C*-algebras Download Slides ## AbstractThe rank problem for a given C*-algebra is to describe the functions on its trace space that arise as the rank of an operator. This is a deep problem about the internal structure of C*-algebras, and a solution will have important consequences, in particular for the Toms-Winter regularity conjecture and the classification of simple, amenable C*-algebras.I will explain how the geometry of the trace space creates difficulties in a solution of the rank problem, and how these difficulties were overcome in the recent solution of the rank problem for C*-algebras of stable rank one. |

2021/08 | IWOTA, Session 16 (Operator Ideals and Operators on Banach spaces) (online talk) | Rigidity results for Lp-operator algebras Download Slides ## AbstractAn Lp-operator algebra is a Banach algebra that admits an isometric representation on some Lp-space (p not 2). Given such an algebra A, we show that it contains a unique maximal sub-C*-algebra, which we call its C*-core. The C*-core is automatically abelian, and its spectrum is naturally equipped with an inverse semigroup of partial homeomorphisms. We call the associated groupoid of germs the Weyl groupoid of A. The Weyl groupoid contains information about the internal dynamics of the algebra A, and in some some cases it is a complete invariant. For example, given a topologically free action on a compact space, the Weyl groupoid of the reduced Lp-crossed product is simply the transformation groupoid of the action. This leads to strong rigidity results for reduced groupoid algebras and reduced crossed products. We use our results to answer a question of Phillips: The Lp-analog of the Cuntz algebra O_2 is not isomorphic to its tensor square. (Joint work with Yemon Choi and Eusebio Gardella.) |

2021/08 | Young mathematicians in C*-algebras (YMC*A), Münster | |

2021/07 | Workshop "Cuntz semigroups", Münster (Organized together with Eusebio Gardella.) | |

2021/07 | Groups meet C*-algebras, Conference in celebration of Siegfried Echterhoff’s 60th birthday, Münster | |

2021/06 | Tokyo-Kyoto Joint Online Operator Algebra Seminars (online talk) | The generator rank of C*-algebras Download Slides |

2021/05 | Great Plains Operator Theory Symposium (GPOTS) (online talk) | The generator rank of C*-algebras Download Slides |

2020/11 | Noncommutative Geometry and Topology Group in Prague (NCG&T seminar), 24. November 2020 (online talk) | The generator rank of C*-algebras Download Slides Video on Youtube## AbstractThe generator problem asks to determine for a given C*-algebra its minimal number of generators. In particular, one wants to know if every separable, simple C*-algebra is generated by a single element. The generator problem was originally asked for von Neumann algebras, and Kadison included it as Nr. 14 of his famous list of 20 “Problems on von Neumann algebras”. The problem remains open, most notably for the reduced free group C*-algebras and the free group factors.The generator rank is a stable quantification of the generator problem. Instead of asking if a C*-algebra is generated by k elements, the generator rank records whether the generating k-tuples are dense. It turns out that this invariant has good permanence properties and it can be computed in a number of interesting cases. In this talk, I will first give an overview on the generator problem and then present some recent results on computations of the generator rank. Most interestingly, we will see a strong solution to the generator problem for separable, simple, classifiable C*-algebras: They are not merely singly generated but they contain a dense set of generators. |

2020/11 | Oberseminar Free Probability, Saarland University, Saarbrücken, 11. November 2020 (online talk) | Diffuse traces and Haar unitaries Download Slides ## AbstractA Haar unitary (with respect to a given tracial state) is a unitary such that every nonzero power of the unitary and its adjoint has vanishing trace. We show that a tracial state admits a Haar unitary if and only if it is diffuse (the unique extension to a normal tracial state on the enveloping von Neumann algebra vanishes on every minimal projection), if and only if it does not dominate a tracial functional that factors through a finite-dimensional quotient.It follows that a unital C*-algebra has no finite-dimensional representations if and only if each of its tracial states admits a Haar unitary. In particular, every tracial state on an infinite-dimensional, simple C*-algebra admits a Haar unitary. I will sketch a proof of this result and present some applications to group C*-algebras and reduced free products. |

2020/06 | UK Virtual Operator Algebras Seminar, 4. June 2020 (online talk) | Cuntz semigroups |

2019/11 | Richard Kadison and his mathematical legacy – A memorial conference, Copenhagen, Denmark, 29.-30. November 2019 | C*-algebras of stable rank one and their Cuntz semigroups |

2019/11 | Workshop „Stability in Group Theory and Operator Algebras“, Copenhagen, Denmark, 25.-28. November 2019 | Rigidity results for Lp-operator algebras |

2019/09 | II Barcelona Weekend on Operator Algebras and Noncommutative Algebra. In honour of Pere Ara for his 60th birthday“, CRM, Barcelona, Spain, 19.-21. September 2019 | |

2019/19 | Workshop „Topology and Measure in Dynamics and Operator Algebras“, BIRS, Banff, Canada, 9.-13. September 2019 | Rigidity results for Lp-operator algebras |

2019/08 | Workshop „C*-Algebras“, MFO, Oberwolfach, Germany, 12.-16. August 2019 | C*-algebras of stable rank one and their Cuntz semigroups (16. August 2019) |

2019/03 | Thematic Research Program: Operator Algebras, Groups and Applications to Quantum Information“, ICMAT, Madrid, Spain, March 2019 School I (11.-15. March 2019) | Mini-Course (5 lectures): Structure and classification of amenable C*-algebras ## AbstractA series of spectacular breakthroughs over the past three years led to the completion of the decades-long effort to classify simple, amenable C*-algebras by K-theory. We will discuss these results and the connections to the regularity conjecture of Toms-Winter on the structure of simple, amenable C*-algebras. We will also study the Cuntz semigroup, which is a geometric refinement of K-theory that has been used to obtain structure and classification results for non-simple C*-algebras. |

2018/11 | Workshop "Model Theory and Operator Algebras", Banff, Canada, 25.-30. November 2018 | |

2018/09 | Workshop on Analysis and Group Theory, Dresden, Germany, 6.-7. September 2018 | Rigidity results for group algebras |

2018/06 | 40. Nordwestdeutsches Funktionalanalysis Kolloquium (NWDFA), Wuppertal, Germany, 23.June 2018 | Rigidität von Gruppenalgebren |

2018/06 | Mini-workshop on the Cuntz semigroup, Houston, USA, June 2018 | The category of abstract Cuntz semigroups |

2018/05 | Conference "NCGOA 2018: C*-algebras and Dynamics", Münster, Germany, 14.-19.May 2018 | Infima in Cuntz semigroups and the structure of C*-algebras with stable rank one |

2018/05 | Research visit to the University of Glasgow, UK, 9.-11. May 2018 | Infima in Cuntz semigroups and the structure of C*-algebras with stable rank one. (10. May 2018) |

2018/04 | Research visit to the University of Copenhagen, Denmark, 1.-4. April 2018 | Ranks of operators in simple C*-algebras with stable rank one. (3. April 2018) |

2017/12 | Conference "VI Coloquio Uruguayo de Matemática", Montevideo, Uruguay, 20.-22. December 2017 | Noncommutative absolute neighborhood retracts |

2017/09 | Conference "Future Targets in the Classification Program for Amenable C*-Algebras", Banff, Canada, 3.-8. September 2017 | Unperforation and divisibility of Cuntz semigroups |

2017/07 | Oberseminar C*-Algebren, Münster, Germany, July 2017 | Almost unperforation and almost divisibility in Cuntz semigroups. (4. July 2017) |

2017/03-06 | IRP Operator Algebras: Dynamics and Interactions, Centre de Recerca Matemàtica (CRM), Barcelona, Spain 2017 6 week research visit, March and April 2017. Workshop on C*-algebras and Dynamical Systems, Barcelona, 20.-24. March 2017 Barcelona Conference on C*-algebras: Structure, Classification and Dynamics, Barcelona, 19.-23. June 2017 | Abstract bivariant Cuntz semigroups Almost unperforation and almost divisibility in Cuntz semigroups |

2016/11 | Conference "Structure and classification of C*-algebras", Warsaw, Poland, 21.-25. November 2016 | Abstract bivariant Cuntz semigroups (23. November 2016) |

2016/08 | Workshop "C*-Algebras", Oberwolfach, Germany, 21.-27. August 2016 | |

2016/07 | Young Mathematicians in C*-Algebras (YMC*A), Münster, Germany, 25.-29. July 2016. (Organized together with Christian Bönicke, Dominic Enders, Eusebio Gardella, Gabor Szabo, Jianchao Wu, Kang Li, Sayan Chakraborty, Søren Knudby, Sven Raum) | |

2016/06 | Research visit to Universitat Autònoma de Barcelona (UAB Barcelona), Spain, 27. June – 1. July 2016 | Projections onto the essential space of a representation (28. June 2016) |

2016/02-04 | Research visit to the Mittag-Leffler Institut, Stockholm, Sweden, 21. February – 2. April 2016 • Workshop Classification and set theory, 21.- 24. March 2016 27th Nordic Congress of Mathematicians, 16. – 20. March 2016 Workshop Classification and dynamical systems I: C*-algebras, 22.- 26. February 2016 | Cuntz semigroups of ultraproducts. (22. March 2016) Projections onto the essential space of a representation, Institut Mittag-Leffler Seminar, 1. March 2016 |

2016/01 | Winter School on Isomorphism Conjectures and Geometry of Groups, University of Münster, January 25 – 29, 2016 | |

2015/11 | Conference "Noncommutative Dimension Theories", University of Hawai’i, USA, 22.-25. November, 2015 | |

2015/09-10 | Research visit to Universitat Autònoma de Barcelona (UAB Barcelona), Spain, 28. September – 2. October 2015 | Rigidity results for group algebras. (28. September 2015) |

2015/08 | Young Mathematicians in C*-Algebras (YMC*A), University of Copenhagen, Denmark, 17.-21. August 2015 | Abstract Bivariant Cuntz Semigroups. (17. August 2015) |

2015/07 | Workshop on "C*-algebras: Geometry and Actions", Münster, Germany, 13-17. July 2015 (Part of Focus Programme on C*-algebras, Münster, 2015) (Organized together with Siegfried Echterhoff, Stuart White, Wilhelm Winter.) | |

2015/06-07 | International conference on C*-algebras and dynamical systems – in honor of George Elliott’s 70th birthday, Hebei Normal university, Shijiazhuang, China, June/July 2015 | Rigidity results for group algebras |

2015/05 | Research visit to Universtity of Copenhagen, May 2015 | Rigidity results for group algebras. (Operator Algebra Seminar, 27. May 2015) |

2015/04 | Workshop on "Structure and Classification of C*-algebras", Münster, Germany, 20-24. April 2015 (Part of Focus Programme on C*-algebras, Münster, 2015) (Organized together with Siegfried Echterhoff, Stuart White, Wilhelm Winter.) | |

2015/04 | Masterclass on "Groups, boundary actions and group C*-algebras", Copenhagen, Denmark, 13.-17. April 2015 | |

2015/03 | Research in Pairs, Mathematisches Forschungsinstitut Oberwolfach (MFO), 9.-20. March 2015 with Ramon Antoine and Francesc Perera. | Picture |

2014/10 | Oberseminar C*-Algebren, Münster, Germany, 21. October 2014 | Lp operator algebras. |

2014/07 | Research visit to Eugene, USA, July 2014 | Induction functors for locally compact groups. |

2014/06 | Canadian Operator Symposium (COSY), Toronto, Canada, 23.-27. June 2014 | Banach algebras generated by an invertible isometry of an Lp-space Video |

2014/06 | Workshop "C*-Algebras and Dynamical Systems", Fields Institute, Toronto, Canada, 16.-20. June 2014. | Structure of simple Cuntz-semirings. (Toronto, 17. June 2014) Video |

2014/05 | Great Plains Operator Theory Symposium (GPOTS), Kansas State University, Manhattan, Kansas, USA, 27.-31. May 2014. | Recasting the Cuntz category. (28. May 2014) |

2014/04 | Research visit to Penn State University, State College, USA, April 2014 | Recasting the Cuntz category. (C*-algebra Seminar, Penn State University, 25. April 2014) The generator problem for C*-algebras. (Noncommutative Geometry Seminar, Penn State University, 24. April 2014) |

2014/04 | Research visit to University of Virginia, Charlottesville, USA, April 2014 | The generator problem for C*-algebras. (Seminar in operator theory and operator algebras. 22. April 2014) |

2014/04 | Operator Algebras Seminar, Toronto, 1. May 2014 | The generator problem for C*-algebras |

2014/01 | Research visit to the University of Waterloo, Canada, January 2014. | Recasting the Cuntz category. (Analysis seminar, Waterloo, 31. January 2014) |

2014/01 | Operator Algebras Seminar, Toronto, 23. January 2014 | Recasting the Cuntz category. |

2014/01-06 | Thematic Program on Abstract Harmonic Analysis, Banach and Operator Algebras at The Fields Institute in Toronto, Canada, January-July 2014 Stay as postdoctoral fellow. Participation in the mini-courses, workshops and seminars of the program. | |

2013/11 | Miniworkshop „C*-Algebras, C*-Bundles and Group Actions“, Münster, Germany, November 2013 (Organized together with Snigdhayan Mahanta) | |

2013/09 | School and workshop "Topics in Operator Algebras and Applications", Madrid, Spain, September 2013 | |

2013/08 | Workshop "C*-Algebren", Oberwolfach, Germany, 26.-30. August 2013 | |

2013/08 | Workshop „Groups, Dynamical Systems and C*-Algebras“, Münster, Germany, 20.-24. August 2013 | |

2013/07 | Masterclass „Classification of non-simple purely infinite C*-algebras“, Copenhagen, Denmark, 22.-26. July 2013 | |

2013/06 | Research visit to Universitat Autònoma de Barcelona (UAB Barcelona), Spain, 17.-21. June 2013 | Induction functors for locally compact groups. (19. June 2013) |

2013/05 | Research visit to Eugene, USA, May 2013 | Induction functors for locally compact groups. (28. May 2013) |

2013/05 | Great Plains Operator Theory Symposium (GPOTS), Berkeley, USA, 21.-25. May 2013 | Semiprojectivity with and without a group action. (24. May 2013) |

2013/04 | Workshop „The structure and classification of nuclear C*-algebras“, Edinburgh, Great Britain, 15.-19. April 2013 | Equivariant Semiprojectivity. (16. April 2013) |

2013/03 | School "Group C*-algebras", Sde Boker, Israel, 17.-21. March 2013 | |

2013/03 | Workshop "C*-Algebras and Noncommutative Dynamics", Sde Boker, Israel, 11.-14. March 2013 | Equivariant Semiprojectivity. (11. March 2013) |

2013/01 | Research visit to Tokyo, Japan, January 2013 | The generator problem for C*-algebras. (11. January 2013) |

2012/12 | Oberseminar C*-Algebren, Münster, Germany, 18. December 2012 | The generator problem for Z-stable C*-algebras. |

2012/11 | Workshop "C*-Algebras, Dynamics, and Classification", Oberwolfach, Germany, 29. October – 2. November 2012 | The generator rank for C*-algebras. |

2012/09 | Workshop „Semiprojectivity“, Copenhagen, Denmark, 3.-7. September 2012 | Inductive limits of projective C*-algebras. |

2012/08 | Masterclass "Semiprojectivity", Copenhagen, Denmark, 27.-31. August 2012 (Organized together with Søren Eilers, Adam Sørensen) | |

2012/07 | Research visit to Glasgow, Great Britain, July 2012 | The generator rank for C*-algebras. (18. July 2012) |

2012/07 | Research visit to Barcelona, Spain, July 2012 | The generator rank for C*-algebras. (11. July 2012) |

2012/05 | Great Plains Operator Theory Symposium (GPOTS), Houston, USA, 30. May – 3. June 2012 | Generators for C*-algebras. |

2012/05 | Canadian Operator Symposium (COSY), Kingston, Canada, May 2012 | Inductive limits of semiprojective C*-algebras |

2012/05 | NordForsk Network closing conference „Operator algebras and dynamical systems“, Gjógv, Faroe Islands, May 2012 | Generators for C*-algebras. |

2012/03 | Masterclass „Quantum Groups“, Copenhagen, Denmark, March 2012 | The Jiang-Su algebra embeds into the reduced free group C*-algebras |

2012/01 | Workshop "Set theory and C*-algebras", Palo Alto, USA, January 2012 | |

2011/12 | Danish-Norwegian workshop on operator algebras, Lysebu, Oslo, Norway, December 2011 | The Jiang-Su algebra embeds into the reduced free group C*-algebras. |

2011/11 | Masterclass „The nuclear dimension of C*-algebras“, Copenhagen, Denmark, November 2011 (Organized) | Noncommutative dimension theories. |

2011/11 | Workshop in honor of Kirchberg’s 65th birthday, Copenhagen, Denmark, November 2011 | |

2011/10 | Operator algebra seminar, Copenhagen, Denmark, October 2011 | Inductive limits of one-dimensional NCCW-complexes. (26. October 2011) |

2011/10 | Research visit to Trondheim, Norway, October 2011 | A survey on non-commutative dimension theory. (12. October 2011) |

2011/09 | NordForsk Network Junior Workshop „Operator algebras and dynamical systems“, Copenhagen, Denmark, September 2011 | The generator problem for Z-stable C*-algebras |

2011/09 | Conference "C*-Algebras and Related Topics", Kyoto, Japan, September 2011 | |

2011/06 | Advanced Course „Dynamical Systems“, Barcelona, Spain, June 2011 | |

2011/06 | Conference „Structure and classification of C*-Algebras“, Barcelona, Spain, June 2011 | Inductive Limits of Projective C*-algebras |

2011/05 | Research visit to Nottingham, United Kingdom, May 2011 | Inductive limits of one-dimensional NCCW-complexes. |

2011/04 | EU-NCG 4th Annual Meeting, Bucharest, Romania, April 2011 | Inductive Limits of Projective C*-algebras. |

2011/04 | Workshop „Dynamics and C*-Algebras“, Barcelona, Spain, April 2011 | Inductive limits of one-dimensional NCCW-complexes. |

2011 | Research visit to the CRM for Research program „The Cuntz semigroup and the classification of C*-algebras“, Barcelona, Spring 2011 | C*-algebras“, Barcelona, Spring 2011 A characterization of semiprojectivity for commutative C*-algebras. |

2011/02 | Operator algebra seminar, Copenhagen, Denmark, February 2011 | Inductive Limits of Semiprojective C*-algebras. (2. February 2011) |

2010/10 | Operator algebra seminar, Copenhagen, Denmark, October 2010 | A characterization of semiprojectivity for commutative C*-algebras. (13. October 2010) |

2010/09 | Conference „NestFest“ – in Honor of Ryszard Nest’s 60th Birthday, Copenhagen, Denmark, September 2010 | |

2010/09 | Workshop "Classification of amenable C*-algebras", Banff, Canada, September 2010 | A characterization of semiprojectivity for commutative C*-algebras. |

2010/09 | School and Workshop "Topics in operator algebras and applications", Madrid, Spain, September 2010 | |

2010/07 | Masterclass „Cuntz-Pimsner Algebras“, Copenhagen, Denmark, July 2010 | |

2010/06 | EU-NCG 3rd Annual Meeting, Cardiff, Great Britain, Norway, June 2010 | The Chern character for low-dimensional spaces and applications. |

2010/05 | Summerschool „C*-algebras and their interplay with dynamical systems“, Nordfjordeid, Norway, May-June 2010 | |

2010/05 | Workshop „Semiprojectivity and Asymptotic Morphisms“, Copenhagen, Denmark, May 2010 | |

2010/04 | Conference „UffeFest“ – in Celebration of Uffe Haagerup’s 60th Birthday and Danish-Norwegian Operator Algebra Seminar, Copenhagen, Denmark, April 2010 | |

2009 | EU-NCG focused semester FS5 „Structure of Operator Algebras“, Copenhagen, Denmark, Fall 2009/2010 Masterclass „Classification of C*-algebras“, Copenhagen, Denmark, November 2009 Masterclass & Workshop „Von Neumann algebras and group actions“, Copenhagen, Denmark, January-February 2010 | Torsion in the Elliott invariant and dimension theories of C*-algebras |

2009 | EU-NCG focused semester FS4 „K-theory, Number theory and NCG“, Münster, Germany, Spring 2009 | The Elliott conjecture and dimension theories of C*-algebras. |

2007/06 | Conference „C*-Algebras and Their Invariants“, Barcelona, Spain, June 2007 |