Konwersatorium im. Leopolda Infelda
2006/2007 | 2007/2008 | 2008/2009 | 2009/2010 | 2010/2011 | 2011/2012 | 2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018
2009-06-04 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30 
prof. Hank J. Hilhorst (Universite Paris-Sud (XI), Orsay)Planar Voronoi cells
Let there be given a random set of point-like "particles" in the plane. The Voronoi construction assigns to each particle a cell in such a way that every generic point of the plane is in the cell of the particle to which it is closest. Voronoi cells are convex polygons that meet at trivalent vertices. They may, among many other things, model nat- urally occurring cellular structures. Their statistics has given rise to research by mathematicians, physicists and other scientists. Our inves- tigation starts from the following question: what is the probability that a randomly picked Voronoi cell have n sides, in particular when n is a large number? We will describe new exact results, a new simulation method, and an application in an experimental context.
2009-05-25 (Poniedziałek)
Zapraszamy do SDD, ul. Hoża 69 o godzinie 16:30
prof. dr hab. Didier Sornette (ETH Zurich)Black Swans, Dragons and Predictions: Diagnostics and Forecasts for the World Financial Crisis
Extreme fluctuations or events are often associated with power law statistics. Indeed, it is a popular belief that "wild randomness" (to use a term proposed by Mandelbrot) is deeply associated with distributions with power law tails characterized by small exponents. In other words, power law tails are often seen as the epitome of extreme events. Here, we document in several systems that there is life beyond power law tails: power laws can be superseded by "dragons", monster events that occur beyond the power law tail. Dragons reveal hidden mechanisms that are only transiently active and that amplify the normal power law fluctuations. We will present evidence of the dragon phenomenon on the statistics of financial losses, hydrodynamic turbulence, material rupture, earthquakes, epileptic seizures, and cyber risks. The special status of dragons open a new research program on their predictability, based on the hypothesis that they belong to a different class of their own and express specific mechanisms amplifying the normal dynamics via positive feedbacks. We will present evidence of these claims for the predictions of material rupture, earthquakes, financial crashes and epileptic seizures. The dragon approach allows us to understand the present World financial crisis as underpinned by two decades of successive financial and economic bubbles. We will demonstrate how market risk management can be enlarged by combining strategic, tactical and time-varying risk analysis.
2009-05-07 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. Jacek Tafel (IFT UW)Global properties of spacetime
In general relativity gravitational field of bounded sources is described by metric tensor which tends to the Minkowski metric far away from the sources. The best known example is the Schwarzschild metric. Due to conformal techniques one can define a null or space-like infinity at a finite distance. Surprisingly an asymptotic symmetry group at null infinity is much larger than the Poincare group. Regardless this fact one can define total energy of a gravitational system. It diminishes in time due to gravitational radiation. Mathematically, a black hole is represented by an asymptotically flat metric which admits a future event horizon. It is not sure that what is observed in astrophysics corresponds to such horizons. Recently, semi local definitions of black holes have appeared and question of forming an event horizon was raised.
2009-04-16 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. dr hab. Iwo Białynicki-Birula (IFT UW, CFT PAN)Planetary model of the atom and the Trojan asteroids
A new experiment shows that under suitable conditions an electron on a high Rydberg orbit behaves accordingly to a naïve model of the atom. I will describe the mechanism that plays a crucial role in this experiment and I will discuss several manifestations of the same Trojan phenomenon.
2009-03-26 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
dr hab. Ernest A. Bartnik (IFT UW)Dyskretna zasada nieoznaczonosci i "cudowne" własności normy L1
We współczesnej analizie sygnału (EEG, obrazy etc) często używa się dużych zbiorów funkcji, które są nadzupełne - jednak sygnał często daje się opisać jako kombinacja liniowa niewielu elementów tego zbioru. Przedstawię dyskretną zasadę nieoznaczoności (tj. dla wektorów skończenie wymiarowych) i jej zastosowania w poszukiwaniu optymalnej reprezentacji sygnału oraz zalety normy L1.
2009-03-12 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. Konrad Banaszek (Uniwersytet Mikołaja Kopernika, Toruń; Krajowe Laboratorium Fizyki Atomowej, Molekularnej i Optycznej (FAMO))Quantum error correction: When bad things happen to good qubits
2009-02-26 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
Dr Stephane Lavignac (IPhT-CEA Saclay)The baryon asymmetry of the Universe
The fact that our Universe is matter-antimatter asymmetric is generally regarded as a problem for the Standard Model of particle physics, which must be solved by some new physics beyond the one we presently observe at colliders. Indeed, while all ingredients needed to dynamically generate a matter (or baryon) asymmetry are present in the Standard Model, the corresponding mechanism, known as electroweak baryogenesis, fails to produce the observed value. One must therefore appeal to an alternative mechanism relying on new physics beyond the Standard Model. Among various possibilities, a very interesting one is the leptogenesis scenario, which nicely connects the baryon asymmetry of the Universe to the observed neutrino oscillations.
2009-01-08 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. Ian M. Anderson (Department of Mathematics and Statistics, Utah State University)Applications of Differential Geometry to Mathematical Physics with Maple
In this talk I shall discuss the new Differential Geometry package in Maple and illustrate some of the capabilties of this package for computations in mathematical physics. The Differential Geometry package provides a complete, integrated environment for symbolic computations in the areas of calculus on manifolds, tensor algebra and tensor analysis, Lie algebras and Lie groups, jet calculus, and general relativity. I will give a few demonstrations from the areas of integrable systems, Lagrangian reduction in the calculus of variations, homogeneous cosmologies, and equivalence problems to illustrate both the ease of use and versality of the software. Future enhancements of the program will be briefly discussed.
2008-12-11 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. dr hab. Piotr Chankowski (Instytut Fizyki Teoretycznej UW)Theoretical perspectives on the LHC
In the first part of the talk I will summarize the present status of the Standard Theory of elementary particle interactions emphasizing the necessity of completing it in the UV (at high energies). I will argue that the Standard Model, while seemingly succesful, can at best only be an effective description of a more fundamental completion of the Standard Theory. In the second part I will try to sketch some of many theoretical proposals for a more fundamental theory that will be tested at the LHC.
2008-11-27 (Czwartek)
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
prof. dr hab. Wiesław Żelazko (Instytut Matematyczny PAN)Krótka historia matematyki polskiej
2008-11-12 (Środa)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. dr hab. Andrzej Szymacha (IFT UW)Od zasady równoważności do metryki Schwarzschilda z pominięciem równań Einsteina
Dokładna analiza zasady równoważności i próba skonstruowania statycznego "pozornego", JEDNORODNEGO pola przyspieszeń (takiego jak w spadającej windzie) prowadzi do wniosku, że pole takie jest niemożliwe. W najlepszym przypadku, kierunek może być jeden, ale wartość przyspieszenia musi się zmieniać w kierunku pola. Zmianie tej można nadać postać prawa Gaussa dla strumienia pola przyspieszeń w próżni (ze źródłem określonym przez samo to pole). Stosując następnie to prawo do przypadku sferycznie symetrycznego, znajduje się dokładnie pole Schwarzschilda (i metrykę Schwarzschilda). Interesujące jest przyjrzeć się polu w obszarze skończonym, znajdującym się w ustalonej odległości od horyzontu, w granicy promienia czarnej dziury R→∞. Jest ono identyczne z "maksymalnie jednorodnym" polem znalezionym wcześniej jako "pole pozorne". A tym razem jest to pole REALNE.
2008-11-03 (Poniedziałek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
prof. dr hab. Stefan Pokorski (IFT UW)Nobel z fizyki 2008 – między przeszłością i przyszłością
Po krótkim przedstawieniu osiągnięć nagrodzonych Noblem, omówiona będzie rola tych idei dla przyszłych badań w fizyce oddziaływań elementarnych.
2008-10-16 (Czwartek)
Zapraszamy do Auli (425), ul. Hoża 69 o godzinie 15:30
Dr Marzena Szymańska (Department of Physics, University of Warwick, Coventry, England)Bose-Einstein condensation of matter and light in semiconductor microcavities
By confining photons in a semiconductor microcavity, and strongly coupling them to electronic excitations, one may create polaritons: bosonic quasi-particles with an effective mass of 10-9 times that of Rubidium atoms, thus allowing Bose-Einstein condensation at elevated temperatures. After a long and strenuous search, the comprehensive set of experiments has finally given evidence for BEC of polaritons. However, this new condensate depart from the archetypal BEC in several ways. Most importantly, polaritons have short lifetime and so a continues pumping is required to sustain a steady-state. This leads to a new type of condensation which can exist in highly non-equilibrium and dissipative environment. Collective behaviour of these exotic particles brings together a wide range of concepts from condensed matter and optical physics: the crossover between BEC of already formed bosons and BCS pairing of fermions, phase transitions in non-equilibrium systems, decoherence, structural disorder and low dimensionality. I will discuss these theoretical concepts and review the experimental state of the art in the field.