We prove a wavelet $T(1)$ theorem for compactness of multilinear Calder\'{o}n-Zygmund (CZ) operators. Our approach characterizes compactness in terms of testing conditions and yields a representation theorem for compact CZ forms in terms of wavelet and paraproduct forms that reflect the compact nature of the operator. This talk is based on joint work with Walton Green and Brett Wick.

Motivated by recent result of F. Perez and R.R.G. on equality of test ideal of module closure operation and trace ideal, and the well-known result by K.E. Smith that parameter test ideal can never be contained in parameter ideals, we study the obstruction of containment of trace ideals in ideals of finite projective (or injective) dimension. As consequences of our results , we give upper bounds on m-adic order of trace ideals of certain modules. We also prove analogous results for ideal of entries of maps in a free resolution of certain modules. This is joint work with Souvik Dey.

The Camassa-Holm-Kadomtsev-Petviashvili equation (CH-KP) is a two dimensional generalization of the Camassa-Holm equation which has been recently derived in the context of shallow water waves and nonlinear elasticity. In this talk we will discuss the stability of the one-dimensional traveling waves, solitary or periodic, with respect to two dimensional perturbations which are periodic in the transverse direction. We show that the stability or instability depends on a sign parameter of the transverse dispersion term. In particular, a nonlinear instability of the one-dimensional solitary waves of any size can be proved for the so-called CH-KP-I model, while for one-dimensional periodic waves we are able to obtain spectral instability for small amplitude CH-KP-I waves.  This is a joint work with Lili Fan, Jie Jin, Xingchang Wang and Runzhang Xu.

This talk is based on the degenerate semi-linear Schrödinger and Korteweg-de Vries equations in one spatial dimension. We construct variationally special solutions of the two models, that is,  standing wave solutions of NLS and traveling waves for KDV, which turn out to have compact support, hence compactons. We show that the compactons are unique bell-shaped solutions of the corresponding PDE's and for appropriate variational problems as well.

 We also provide a complete spectral characterization of such waves, for all values of \(p\). Namely, we show that all waves are spectrally stable for \(2<p\leq 8\),  while a single mode

instability occurs for \(p>8\).  This extends the previous work of Germain, Harrop-Griffiths and Marzuola, who have previously established orbital stability for some specific waves, in the range \(p<8\). This is a joint work with Atanas stefanov and Sevdhan Hakkaev.

It has been known for quite some time that various conditions on the oscillation of the matrix $A$ in elliptic/parabolic operators of the form 

 $L = -div A \nabla$ or $L = \partial_t - \div A \nabla$ 

are sufficient to guarantee either the $L^p$ solvability of the Dirichlet problem or the logarithm of the density of the elliptic/parabolic measure, $k$,  is in BMO or (locally) Hölder continuous. Conditions such as the global Hölder continuity of $A$ are classical, whereas other conditions quantifying the oscillation of $A$ in terms of Carleson measures are more recent. Only very recently in joint works with Toro and Zhao, and later with Egert and Saari, was it shown that the BMO norm of $\log k$ could be controlled by these Carleson conditions. These new results are elliptic and heavily relied on work of David, Li and Mayboroda.

In forthcoming work with Egert and Saari, we adapt these new results (B., Toro, Zhao and B. Egert, Saari) to the parabolic setting. Therefore we needed to also adapt the work of David, Li and Mayboroda to the parabolic setting and, in doing so, sharpened their results. It seems very likely that these sharper estimates will allow one to treat the classical results (Hölder continuous coefficients) and the modern results (Carleson conditions) with a unified method. 

I will delve into the ideas underpinning these results.

Thanks to the Direct Summand Theorem, splinter conditions have emerged as a way of studying singularities in commutative algebra and algebraic geometry. In characteristic zero, work of Kovács (2000) and Bhatt (2012) characterizes rational singularities as derived splinters. In this talk, I will present an analogous characterization of klt singularities by imposing additional conditions on the derived splinter property. This follows from a new characterization of the multiplier ideal, an object that measures the severity of the singularities of a variety, viewing it as a sum of trace ideals. This perspective also gives rise analogous description of the test ideal in characteristic as a corollary to a result of Epstein-Schwede (2014).

Shape is foundational to biology. Observing and documenting shape has fueled biological understanding as the shape of biomolecules, cells, tissues, and organisms arise from the effects of genetics, development, and the environment. The vision of Topological Data Analysis (TDA), that data is shape and shape is data, will be relevant as biology transitions into a data-driven era where meaningful interpretation of large data sets is a limiting factor. We focus first on quantifying the morphology of X-ray CT scans of barley spikes and seeds using topological descriptors based on the Euler Characteristic Transform. We then successfully train a support vector machine to distinguish and classify 28 different varieties of barley based solely on the 3D shape of their grains. This shape characterization will allow us later to link genotype with phenotype, furthering our understanding on how the physical shape is genetically specified in DNA.

Given a finite dimensional representation \(V/k\) of a group \(G\), we consider the space \(k[V]^G\) of all polynomial functions which are invariant under the action of \(G\). At its heart, invariant theory is the study of \(k[V]^G\) and its interactions with \(k[V]\). We are particularly interested in the situation where \(k[V]\) is free as a \(k[V]^G\)-module, and call such representations cofree. The classification of cofree representations is a motivating problem for a field of research that has been active for over 70 years. In the case when \(G\) is finite, the Chevalley-Shephard-Todd theorem says that \(V\) is cofree iff \(G\) is generated by pseudoreflections. Several classifications of cofree representations have been found for certain connected reductive groups, but unlike the Chevalley-Shepard-Todd theorem, these results consist of a list of cofree representations, rather than a general group-theoretic characterization. In 2020, D.~Edidin, M.~Satriano, and S.~Whitehead stated a conjecture which intrinsically characterizes irreducible cofree representations of connected semisimple groups and verified it for simple Lie groups and tori. In this talk, we discuss this conjecture and the work towards verifying it for \({\rm SL}_n\times{\rm SL}_m\).

Shape is data and data is shape. Biologists are accustomed to thinking about how the shape of biomolecules, cells, tissues, and organisms arise from the effects of genetics, development, and the environment. Less often do we consider that data itself has shape and structure, or that it is possible to measure the shape of data and analyze it. Here, we review applications of Topological Data Analysis (TDA) to biology in a way accessible to biologists and applied mathematicians alike. TDA uses principles from algebraic topology to comprehensively measure shape in datasets. Using a function that relates the similarity of data points to each other, we can monitor the evolution of topological features—connected components, loops, and voids. This evolution, a topological signature, concisely summarizes large, complex datasets. We first provide a TDA primer for biologists before exploring the use of TDA across biological sub-disciplines, spanning structural biology, molecular biology, evolution, and development. We end by comparing and contrasting different TDA approaches and the potential for their use in biology. The vision of TDA, that data is shape and shape is data, will be relevant as biology transitions into a data-driven era where meaningful interpretation of large datasets is a limiting factor.

In this talk, I will discuss some joint work with Alan Dills on concepts devised to describe the size of the Frobenius skew-polynomial ring over a commutative graded algebra over a field in prime characteristic. The ideas are inspired from Gelfand-Kirillov dimension theory. I will discuss what these notions are for the cusp and how to compute them.