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enEighth International School for Materials for Energy and Sustainability: TBDismes@caltech.edu (Elizabeth Rodriguez)Eighth International School for Materials for Energy and Sustainability<strong>Speaker(s):</strong> <br><strong>Location:</strong> Noyes 153 (J. Holmes Sturdivant Lecture Hall)<br><p></p><p>This school is an opportunity for graduate students and postdoctoral scholars to learn about state-of-the-art and future trajectories for materials as they can be applied to energy generation and storage for sustainable energy technologies and infrastructure.</p><p><b>Participants will experience:</b></p><ul>
<li>Lectures by <a href="http://ismes.sites.caltech.edu/lecturers">world class experts</a> in a <a href="http://ismes.sites.caltech.edu/topics">broad set of areas</a> from climate change to renewable energy to manufacturing.</li>
<li>Individual student exercises to develop a broad knowledge of the energy and sustainability landscape.</li>
<li>Team exercises to where groups of international students tackle challenging scenarios.</li>
</ul><p>Enthusiastic graduate students and postdoctoral scholars with a strong interest in the interrelationship between energy, resources, and a sustainable society are encouraged to <a href="http://ismes.sites.caltech.edu/application">apply</a>.</p><h3><b>APPLICATION DEADLINE IS MAY 31, 2019</b></h3>Sun, 21 Jul 2019 17:00:00 -0700http://cms.caltech.edu/events/85993IQI Weekly Seminar: Counting without Sampling: Approximation Algorithms for Quantum Many-Body Systems at Finite Temperaturesbjleung@caltech.edu (Bonnie Leung)IQI Weekly Seminar<strong>Speaker(s):</strong> Mehdi Soleimanifar (MIT)<br><strong>Location:</strong> Annenberg 213<br><p><b>Abstract</b>: Basic statistical properties of quantum many-body systems in thermal equilibrium including the free energy, entropy, and average energy can be obtained from the partition function. This talk will focus on the problem of estimating the partition function which has been the subject of various numerical and theoretical studies both in statistical physics and computer science. It is well known that this problem is computationally hard in the worst case. In this talk, I will present a quasi-polynomial time algorithm that estimates the partition function of quantum many-body systems above the phase transition point.</p><p>The algorithm extrapolates the solution at high temperatures where the problem is easy to low temperatures where finding the solution is harder. The running time of this algorithm relies on the locus of the complex zeros of the partition function. I will talk about cases where we can locate these complex zeros. I will also discuss the relation between other signatures of the phase transition such as the exponential decay of correlations and the locus of these zeros.</p><p>This is based on joint work with Aram Harrow and Saeed Mehraban.</p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p>Tue, 23 Jul 2019 15:00:00 -0700http://cms.caltech.edu/events/86361Special ACM Seminar: Recent advances in high order and spectral approximations: Virtual Elements and Maximum Entropy reconstruction of PDFsdbohler@caltech.edu (DIANA BOHLER)Special ACM Seminar<strong>Speaker(s):</strong> Dr. Alexey Chernov (University of Oldenburg)<br><strong>Location:</strong> Annenberg 105<br><p>In this talk we review some recent developments two rather independent areas of computational mathematics having in common that they both utilize and benefit from high order and spectral approximations.<br></p><p>The first area is concerned with the Virtual Element Method (VEM), that is a recent generalization of the Finite Element Method. VEM utilizes polygonal/polyhedral meshes in lieu of the classical triangular/tetrahedral and quadrilateral/hexaedral meshes. This automatically includes nonconvex elements, hanging nodes (enabling natural handling of interface problems with nonmatching grids), easy construction of adaptive meshes and efficient approximations of geometric data features. In this talk we review the basic construction of the method and discuss an extension of VEM to arbitrary high order approximations [1] enabling e.g. exponential convergence for elliptic problems with corner singularities on geometrically refined polygonal grids (hp-VEM) [2, 3].<br></p><p>[1] L. Beirão da Veiga, A. Chernov, L. Mascotto and A. Russo, Basic principles of hp Virtual Elements on quasiuniform meshes, Math. Models Methods Appl. Sci. 26 (2016), no. 8, 1567–1598<br></p><p>[2] L. Beirão da Veiga, A. Chernov, L. Mascotto and A. Russo, Exponential convergence of the hp virtual element method in presence of corner singularities, Numerische Mathematik 138 (2018), no. 3, 581–613<br></p><p>[3] A. Chernov, L. Mascotto, The harmonic virtual element method: stabilization and exponentialconvergence for the Laplace problem on polygonal domains. IMA Journal of Numerical Analysis (2019), published online<br></p><p>(Joint with L. Mascotto, L. Beirao da Veiga, A. Russo)<br></p><p>The second area addresses numerical approximation for problems with uncertain parameters. The Maximum Entropy method is a powerful tool for recovery of the probability density function (PDF) of an unknown quantity of interest when only a finite series of its generalized moments are known or are estimated numerically, e.g. by inexact (multilevel) Monte Carlo simulation. When the generalized moments are defined via a family of algebraic or trigonometric polynomials, high order/spectral approximations naturally appear. We recall the two-stage simulation procedure from [4], discuss the error analysis and performance of the algorithm in a series of numerical experiments.<br></p><p>[4] C. Bierig and A. Chernov, Approximation of probability density functions by the Multilevel Monte Carlo Maximum Entropy method, J. Comput. Physics 314 (2016), 661–681<br></p><p>(Joint with C. Bierig)</p>Wed, 24 Jul 2019 10:00:00 -0700http://cms.caltech.edu/events/86365IQIM Postdoctoral and Graduate Student Seminar: Universality classes of topological phase transitionsmarciab@caltech.edu (Marcia Brown)IQIM Postdoctoral and Graduate Student Seminar<strong>Speaker(s):</strong> Wei Chen (PUC - Rio)<br><strong>Location:</strong> East Bridge 114<br><p>Note: Special time 3:00 on Monday, July 29</p><p><b>Abstract:</b></p><p>In topological insulators and topological superconductors, the change of topological invariant caused by tuning a certain parameter signifies a topological phase transition. Based on the fact that the topological invariant is generally an integration of local curvature in momentum space, we propose a paradigm to characterize the topological phase transitions according to the divergence of the local curvature. The paradigm introduces the notion of correlation function, critical exponents, scaling laws, and renormalization group, applicable to either noninteracting, interacting, or Floquet systems. The notion of universality class and its relation with the symmetry classification will be elaborated. Moreover, we will use machine learning scheme to elaborate that the information about topological phase transitions is entirely encoded in the divergence of the local curvature.</p>Mon, 29 Jul 2019 15:00:00 -0700http://cms.caltech.edu/events/86172IQI Weekly Seminar: Sampling-complexity phase diagramsbjleung@caltech.edu (Bonnie Leung)IQI Weekly Seminar<strong>Speaker(s):</strong> Abhinav Deshpande (University of Maryland)<br><strong>Location:</strong> Annenberg 213<br><p><b>Abstract</b>: In this talk, I argue that the question of whether a physical system can be simulated on a classical computer is important not just from a practical perspective but also a fundamental one. We consider the complexity of approximate sampling from states arising due to time evolution under a Hamiltonian or from equilibrium states of quantum many-body Hamiltonians. I will comment on extensions of these results to other physical systems. I will further sketch out what insight the obtained "complexity phase diagrams" may shed on the underlying Hamiltonians in question, illustrating that the field of quantum computational supremacy has applications in theoretical physics.</p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p>Tue, 30 Jul 2019 15:00:00 -0700http://cms.caltech.edu/events/86347IQI Weekly Seminar: Spectroscopy with quantum sensorsbjleung@caltech.edu (Bonnie Leung)IQI Weekly Seminar<strong>Speaker(s):</strong> Tuvia Gefen (The Hebrew University of Jerusalem)<br><strong>Location:</strong> Annenberg 213<br><p><b>Abstract</b>: The problem of quantum spectroscopy, namely reconstruction of the frequency components of time dependent Hamiltonian, is of great interest to chemical analysis, nano scale NMR and frequency standards. In this talk I will address two (basic) questions in this field: what is the speed/precision limit in estimating a single frequency and how well can we resolve two close frequencies. It turns out that some misconceptions have led to suboptimal techniques and a considerable improvement can be introduced. Novel methods for frequency tracking [1,2] and frequency resolution [3] will be presented.</p><p>[1] <i>Science</i> 356.6340 (2017): 832-837</p><p>[2] <i>Physical Review A</i> 96.3 (2017): 032310</p><p>[3] <i>arXiv:1811.01762</i> (2018)</p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p>Tue, 06 Aug 2019 15:00:00 -0700http://cms.caltech.edu/events/86197PhD Thesis Defense: TBDtanya@caltech.edu (Tanya Owen)PhD Thesis Defense<strong>Speaker(s):</strong> Armeen Taeb (California Institute of Technology)<br><strong>Location:</strong> Annenberg 213<br><p></p>Fri, 16 Aug 2019 10:00:00 -0700http://cms.caltech.edu/events/86214