Events
Department of Mathematics and Statistics
Texas Tech University
All studies in Mathematics require the dual notions of null or nowhere, and full or everywhere. These are used to describe mathematical properties that may be hard to find or hard to miss, within a collection of objects. The most familiar examples of these notions are nowhere dense -- dense from topology, and zero measure and full measure from measure theory. These notions enable the formulation of mathematical statements in contexts such as probability, uncertainty, and perturbation and stability. These ideas are however inadequate to describe many common properties found in infinite dimensional vector spaces. To fill these gaps, these notions were generalized to the dual notions of shy—prevalent. The language of "prevalence" has enabled many new discoveries in Analysis, but is still inadequate in some contexts. I shall present a categorical approach to the notion of prevalence. This view of prevalence can offer possible generalizations of this notion.
This talk addresses the problem of testing the conditional independence of two generic random vectors X and Y given a third random vector Z, which plays an important role in statistical and machine learning applications. We propose a new non-parametric testing procedure that avoids explicitly estimating any conditional distributions but instead requires sampling from the two marginal conditional distributions of X given Z and Y given Z. We further propose using a generative neural network (GNN) framework to sample from these approximated marginal conditional distributions, which tends to mitigate the curse of dimensionality due to its adaptivity to any low-dimensional structures and smoothness underlying the data. Theoretically, our test statistic is shown to enjoy a double robustness property against GNN approximation errors, meaning that the test statistic retains all desirable properties of the oracle test statistic utilizing the true marginal conditional distributions, as long as the product of the two approximation errors decays to zero faster than the parametric rate. Asymptotic properties of our statistic and the consistency of a bootstrap procedure are derived under both null and local alternatives. Extensive numerical experiments and real data analysis illustrate the effectiveness and broad applicability of our proposed test.
(arxiv link: https://arxiv.org/abs/2407.17694)
Watch online via this link.
* Meeting ID: 943 0383 4893
* Passcode: 057825
The spin-statistics theorem asserts that in a unitary quantum field theory, the spin of a particle—characterized by its transformation under the central element of the spin group, which corresponds to a 360-degree rotation—determines whether it obeys bosonic or fermionic statistics. This relationship can be formalized mathematically as equivariance for a geometric and algebraic action of the 2-group ${\rm B}{\bf Z}_2$. In my talk, I will present a refinement of these actions, extending from ${\rm B}{\bf Z}_2$ to appropriate actions of the stable orthogonal group ${\rm O}$, and demonstrate that every unitary invertible quantum field theory intertwines these ${\rm O}$-actions.Abstract. Aluminum (Al) particles are notoriously plagued with sluggish ignition and slow or incomplete combustion. Yet, the potential to harness tremendous power from these high energy density particles is on the cusp of transforming our way of life. This presentation will focus on thinking differently about using traditional diagnostic approaches in order to gain new insight and develop more accurate metal oxidation models. Experiments are purposefully designed to deconvolute energy conversion processes from metal particle combustion. Results inform our understanding of reaction energy and draw us closer to controlling energy release rates in order to harness power. Then, from comprehension of metal oxidation mechanisms, we can creatively develop strategies that will lead to their faster energy release. Harnessing more of the abundant chemical energy stored in metal particles at rates relevant to detonation time scales will have important implications for the use of metals as a power generating material in many applications.
Biography. Dr. Michelle Pantoya received her PhD from the University of California, Davis in 1999 and joined the faculty in the Mechanical Engineering Department at Texas Tech University in 2000. As the J. W. Wright Regents Endowed Chair Professor, her research focuses on studying fuel particle combustion in ways that can enhance our national safety and security. She has received many research and teaching awards including the US Presidential Early Career Award (PECASE) and the DoD Young Investigator Program Award and has over 220 archival publications on this topic. Dr. Pantoya is also the co-author of several children’s books introducing engineering to young kids (i.e., Engineering Elephants, Optimizing an Octopus & Designing Dandelions) and an advocate for elementary engineering education.
When: 4:00 pm (Lubbock's local time is GMT -6)
Where: room Math 011 (Math Basement)
ZOOM details:
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Direct Link that embeds meeting and ID and passcode.
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* Meeting ID: 979 1333 6658
* Passcode: Applied (Note the capital letter "A")
Dynamical systems on 3-manifolds have been paid much attention along the time. In particular, magnetic trajectories are solutions of a second order differential equation (known as the Lorentz equation) and they generalise geodesics. A magnetic field on a Riemannian manifold is defined by a closed 2-form that helps, together with the metric, to define the Lorentz force. On the other hand, magnetic curves derive from the variational problem of the Landau-Hall functional, which is, in the absence of a magnetic field, nothing but the kinetic energy functional.
The dimension 3 is rather special, since it allows us to identify 2-forms with vector fields via the Hodge ⋆ operator and the volume form of the (oriented) manifold. Moreover, in dimension 3, one may define a cross product and therefore, the Lorentz equation may be written in an easier way.
The challenge is to solve the differential equation in order to find an explicit solution, meaning the explicit parametrization for the magnetic trajectories. Nevertheless, this is not always possible and, because of that, it is necessary to understand the behaviour of the solution.
Recent studies are done in 3-dimensional Sasakian manifolds, where the contact 2-form naturally defines a magnetic field. The solutions of the Lorentz equation, usually called contact magnetic trajectories, are often expressed in a concrete parametrization. It can be proved a reduction result for the codimension in a Sasakian space form, that is, essentially, we can reduce the study (of a magnetic curve in a Sasakian space form) to dimension 3. The geometry of magnetic trajectories have been recently studied in the z-sphere, in the Berger 3-sphere, in the Heisenberg group Nil3 and in SL(2,R), respectively.
Another important problem is the existence of closed curves which is a fascinating topic in dynamical systems. Periodic orbits of the contact magnetic fields on the unit 3-sphere and in the Berger 3-sphere were found in the last two decades and conditions for the periodicity have been obtained. A similar result has been recently given; it was proved that periodic contact magnetic curves in SL(2,R) can be quantized in the set of rational numbers.
The geometry of contact magnetic curves in SL(2,R) is much more beautiful. More precisely, it can be shown that every contact magnetic trajectory (of charge q) starting at the origin of SL(2,R) with initial velocity X and with charge q is the product of the homogeneous geodesic with initial velocity X and the charged Reeb flow exp(2qs\xi). Similar results are obtained for the Berger spheres as well.
This talk is based on several papers, mainly in collaboration with Prof. Jun-ichi Inoguchi (Japan).
Please watch online via this Zoom link.
Math Circle Spring Poster