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Stimming, HansPeter (WPI c/o U. Wien)  WPI Seminar Room 08.135  Thu, 6. Aug 15, 14:30 
“Absorbing Boundary Conditions for Schrodinger and Wave equations: PML vs ECS”  
The perfectly matched layers (PML) and exterior complex scaling (ECS) methods for absorbing boundary conditions are analyzed using spectral decomposition. Both methods are derived as analytical continuations of unitary to contractive transformations. We find that the methods are mathematically and numerically distinct: ECS is complex stretching that rotates the operator's spectrum into the complex plane, whereas PML is a complex gauge transform which shifts the spectrum. Consequently, the schemes differ in their timestability. Numerical examples are given.  

Zhang, Yong (WPI)  WPI Seminar Room 08.135  Thu, 6. Aug 15, 13:30 
“Efficient evaluation of nonlocal potentials: NUFFT and Gaussian Sum Approximations”  
We introduce accurate and efficient methods for nonlocal potentials evaluations with free boundary condition, including the 3D/2D Coulomb, 2D Poisson and 3D dipoledipole potentials. Both methods rely on the same assumption: the density is smooth and fast decaying. The first method,proposed by Jiang, Greengard and Bao, evaluates the potential in spherical/polar coordinates using NonUniform FFT algorithm, where the singularity of the Fourier representation disappears automatically, while the second one is based on a Gaussiansum approximation of the singular convolution kernel and Taylor expansion of the density. Both methods are accelerated by fast Fourier transforms (FFT). They are accurate (1416 digits), efficient ($O(N\log N)$ complexity), low in storage, easily adaptable to other different kernels, applicable for anisotropic densities and highly parallelizable.  

Descombes, Stephane (U. Nice)  WPI Seminar Room 08.135  Thu, 6. Aug 15, 11:00 
“Exponential operator splitting methods for evolutionary problems and applications to nonlinear Schrödinger equations in the semiclassical regime“  
In this talk, I investigate the error behaviour of exponential operator splitting methods for nonlinear evolutionary problems. In particular, I will present an exact local error representation that is suitable in the presence of critical parameters. Essential tools in the theoretical analysis including timedependent nonlinear Schrödinger equations in the semiclassical regime as well as parabolic initialboundary value problems with high spatial gradients are an abstract formulation of differential equations on function spaces and the formal calculus of Liederivatives.  

Besse, Christophe (U. Toulouse)  WPI Seminar Room 08.135  Thu, 6. Aug 15, 10:00 
“Exponential integrators for NLS equations with application to rotating BECs“  
In this talk, I will present various time integrators for NLS equations when the potentials are time dependent. In this case, the usual time splitting schemes fail. I will introduce exponential RungeKutta scheme and Lawson scheme and present some of their properties.  

Luong, Hung (U. Wien)  WPI Seminar Room 08.135  Wed, 5. Aug 15, 12:00 
“On the Cauchy problem of some 2d models on the background of 1d soliton solution of the cubic nonlinear Schrödinger equation"  

Bardos, Claude (WPI & ICP c/o Paris)  WPI Seminar Room 08.135  Wed, 5. Aug 15, 11:00 
“Formal derivation of the Vlasov Boltzmann relation”  
I report on current work with Toan Nguyen and Francois Golse.  

Gottlieb, Alex (WPI)  WPI Seminar Room 08.135  Wed, 5. Aug 15, 10:00 
“Entropy measures for quantum correlation”  
We use quantum Rényi divergences to define "correlation" functionals of manyfermion states (density operators on a Fock space). The "reference" state for the relative entropy functional is the unique gaugeinvariant quasifree (g.i.q.f.) state with the same 1RDM as the state of interest. That is, the "correlation" of the state of interest is its Rényi divergence from the uniquely associated g.i.q.f. state. Correlation functionals defined in this way enjoy the following properties: (a) they take only nonnegative values, possibly infinity; (b) they assign the value 0 to all Slater determinant states; (c) they are monotone with respect to restriction of states; (d) they are additive over independent subsystems; and (e) they are invariant under changes of the 1particle basis (Bogoliubov transformations). The quantum relative entropy or quantum KullbackLeibler divergence is a special and distinguished member of any family of quantum Rényi divergences (of which there are at least two). The associated correlation functional, defined using quantum KullbackLeibler divergence, we call "nonfreeness." Nonfreeness enjoys further appealing properties not shared by related correlation functionals: (f) the nonfreeness of a state X is the minimum possible value for the entropy of X relative to any g.i.q.f. reference state; (g) there is a simple formula for a pure state's nonfreeness in terms of it's natural occupation numbers; and (h) within the convex set of nfermion states with given 1RDM, the nonfreeness minimizer equals the entropy maximizer, which is the Gibbs canonical (nparticle) state.  

Nguyen, Toan (Penn State)  WPI Seminar Room 08.135  Tue, 4. Aug 15, 14:00 
"Grenier's iterative scheme for instability and some new applications"  
"The talk is planned to revisit Grenier's scheme for instability of Euler and Prandtl, introduced in his CPAM2000 paper, and to present some new applications in the instability of generic boundary layers and instability of VlasovMaxwell in the classical limit".  

Pawilowski, Boris (U. Wien & U. Rennes)  WPI Seminar Room 08.135  Tue, 4. Aug 15, 12:00 
“Mean field limits for discrete NLS: analysis and numerics”  
In my thesis, jointly supervised by N.J. Mauser and F. Nier, we deal with approximations of the timedependent linear many body Schrödinger equation with a two particles interaction potential, by introducing a discrete version of the equation and mean field limits. We consider the bosonic Fock space in a finite dimensional setting. Mathematical tools include the reduced density matrices and Wigner measure techniques exploiting the formal analogy to semiclassical limits.  

Nier, Francis (U. Paris 13)  WPI Seminar Room 08.135  Tue, 4. Aug 15, 11:00 
“Phasespace approach to the bosonic mean field dynamics : a review”  
After recalling old or more recent point of views on bosonic quantum field theory and mean field problems, the series of works in collaboration with Z. Ammari will be summarized. This phasespace presentation implements the old dream of an infinite dimensional microlocal analysis. In particular the mean field dynamics is nothing but a propagation of singularity result in the semiclassical regime. This talk will put the stress on the key issues related with the infinite dimensional setting and on the new results for the mean field problem provided by this approach.  

Golse Francois (X)  WPI Seminar Room 08.135  Tue, 4. Aug 15, 10:00 
“On the meanfield and classical limits for the Nbody Schrödinger equation”  
This talk proposes a quantitative convergence estimate for the meanfield limit of the Nbody Schrödinger equation that is uniform in the classical limit. It is based on a new variant of the Dobrushin approach for the mean field limit in classical mechanics, which avoids the use of particle trajectories and empirical measures, and has a very natural quantum analogue. (Work in collaboration with C. Mouhot and T. Paul).  

Germain, Pierre (Courant)  WPI Seminar Room 08.135  Mon, 3. Aug 15, 15:15 
“On the derivation of the kinetic wave equation”  
The kinetic wave equation is of central importance in the theory of weak turbulence, but no rigorous derivation of it is known. I will show how it can be derived from NLS on the torus with random forcing, in the small nonlinearity / big box limit. This is joint work with Isabelle Gallagher and Zaher Hani.  

Brenier, Yann (CNRS X)  WPI Seminar Room 08.135  Mon, 3. Aug 15, 14:15 
"When Madelung comes up...."  
After recalling the remarkable formulation made in 1926 by Erwin Madelung of the Schrödinger equation in terms of fluid mechanics, I will introduce a rational scheme, based on the least action principle and some nonlinear rescaling of the time variable, starting from Euler's equations of isothermal compressible fluids (1755), followed by Fourier's heat conduction equation (1807), leading to Schrödinger's equation of quantum mechanics (1925). Finally, I will suggest the application of this scheme to Magnetohydrodynamics. Madelung, E. (1926). "Eine anschauliche Deutung der Gleichung von Schrödinger". Naturwissenschaften 14 (45): 1004–1004.  

Mauser, Norbert J (WPI & ICP c/o U. Wien)  WPI Seminar Room 08.135  Mon, 3. Aug 15, 14:00 
“Welcome to Vienna, birthplace of Boltzmann, Schrödinger and Pauli”  

Dorland, Bill (Maryland)  WPI Seminar Room 08.135  Fri, 31. Jul 15, 10:00 
Turbulent dissipation challenge: what ought to be done  
Many naturally occurring and manmade plasmas are collisionless and turbulent. It is not yet well understood how the energy in fields and fluid motions is transferred into the thermal degrees of freedom of constituent particles in such systems. The debate at present primarily concerns proton heating. Multiple possible heating mechanisms have been proposed over the past few decades, including cyclotron damping, Landau damping, heating at intermittent structures and stochastic heating. Recently, a communitydriven effort was proposed (Parashar & Salem, 2013, arXiv:1303.0204) to bring the community together and understand the relative contributions of these processes under given conditions. In this paper, we propose the first step of this challenge: a set of problems and diagnostics for benchmarking and comparing different types of 2.5D simulations. These comparisons will provide insights into the strengths and limitations of different types of numerical simulations and will help guide subsequent stages of the challenge.  

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