Integrated Calendar

The Scanning Probe Microscopy (SPM) Unit conducts a diverse range of scientific projects, spanning from the life sciences (e.g., vesicles, cells, and shells) to material science (e.g., crystals and nanoparticles). Beyond 3D topographic imaging, scanning probe microscopy provides a comprehensive understanding of a material by measuring mechanical, electrical, and other properties. Recent advancements in our unit, including correlative AFM-SEM systems and rapid scanning capabilities, expand the AFM's potential for studying dynamic processes and for more efficient data acquisition. Moreover, machine learning methods have been harnessed to improve analysis accuracy.In this talk, I will present the technique and bring examples where AFM has provided critical insight into various scientific fields by illuminating the nanoscale.

Non-equilibrium active matter systems often exhibit self-organized, collective motion that can give rise to the emergence of coherent spatial structures. Prime examples covering many length scales range from mammal herds, fish schools and bird flocks, to insect and robot swarms. Despite significant advances in understanding the behavior of homogeneous systems in the last decades, little is known about the self-organization and dynamics of heterogeneous active matter. I will present results of bioconvection experiments with multispecies suspensions of wild-type bacteria from the hyper-diverse bacterial communities of Cuatro Ciénegas, Coahuila, whose origin dates back to the pre-Cambrian. Under oxygen gradients, these bacteria swim in auto-organized, directional flows, whose spatial scales exceed the cell size by orders of magnitude, demonstrating a plethora of amazing dynamical behaviors, including segregation. I will present evidence supporting the notion that the mechanisms giving rise to these complex behaviors are predominantly physical, and not a result of biological interactions. This research significantly advances our understanding of both heterogeneity in active matter, as well as in the dynamics of complex microbial ecological communities, bringing profound insights into their spatial organization and collective behavior.

We provide the final step in the resolution of Bourgain's slicing problem in the affirmative. Thus we establish the following theorem: for any convex body K in R^n of volume one, there exists a hyperplane H, such that the (n-1)-dimensional volume of the intersection of K with H is at least c. Here c > 0 is a universal constant. Our proof combines Milman's theory of M-ellipsoids, stochastic localization with a recent bound by Guan, and stability estimates for the Shannon-Stam inequality by Eldan and Mikulincer.

Joint work with J. Lehec.

In nature, sequence-specific biopolymers, such as peptides and nucleic acids, are essential to various biological systems and processes. These biopolymers are utilized in materials science to achieve precise property control. Typically, variations in amino acid sequences focus on functional regulation while nucleotides are used for structural control. This raises the question: How can we integrate peptide-based functionality with the spatial precision of DNA nanotechnology for innovative material design? Here, I will present examples illustrating the incredible properties of peptide self-assembly from my PhD, and the remarkable nanoarchitecture design achieved through DNA nanotechnology from my Postdoc. These two key elements establish a vision of utilizing and synergizing peptide functionality with structural control achieved by DNA nanotechnology.Specifically, I will show how subtle changes in the molecular environment influence the morphology and behavior of peptide assemblies such as diphenylalanine crystals and enable control over their growth and disassembly processes, revealing insights into peptide-based material manipulation (Nat. Commun., 2016). Another example is that of the amorphous assemblies of tri-tyrosine peptides, where we linked the molecular arrangement to unique mechanical and optical properties of glass-like peptide structures (Nature, 2024).Next, I will introduce the principles of DNA nanotechnology for advanced structural control. By designing DNA nano-frames capable of self-assembling into organized lattices, we created micron-scale 3D materials. We discovered that a minor modification in DNA linker length induces a crystalline phase transition, from simple cubic to face-centered cubic structures, altering lattice geometry. In addition, we established a method using acoustic waves to achieve scalable and morphologically controllable DNA assemblies at the millimetric scale (Nat. Commun., 2024). This approach highlights how DNA nanotechnology provides unparalleled spatial control, decoupling structural architecture from functional elements such as peptides and nanoparticles. Together, these projects illustrate how peptides and DNA nanotechnology can be potentially integrated to engineer novel materials and enhance our capacity to design materials with tailored properties across scales.

The (hi)story of amenable groups starts with von-Neumann, who tried to explain the Banach–Taraski–Hausdorff paradox. He observed that the paradox is in fact a consequence of what will later be called the "non-amenability" of the free group on two generators. It led him to ask whether it's true that the phenomenon of a group being non-amenable is always a consequence of having F2 as a subgroup. This became known as "von-Neumann's problem", and was settled to the negative be Ol'shanskii in 1950. The story takes a surprising turn 60 years later: in the perspective of measured group theory, Gaboraiu and Lyons provided a "positive" answer to von-Neumann: they showed that any non-amenable group "measure theoretically" contains a free subgroup. I will introduce (and not prove!) the theorem, and show a consequence of it, due to Epstein: a group is non-amenable if and only if it admits uncountably many non-OE actions.

The talk is based on this survey by Houdayer.

The study of dilute, strongly interacting quantum gases revealsuniversal properties that transcend the specifics of individualsystems. These features arise from their short-range behaviorand are encapsulated in a key quantity called the “contact”, whichquantifies the probability of two particles being in close proximity.In this talk, I will introduce the contact theory and its extension tonuclear and molecular systems beyond the zero-range limit. I willdemonstrate its applicability in analyzing nuclear electronscattering and photo absorption reactions.Additionally, I will discuss how mean-field approximations, such asthe nuclear shell model, can effectively estimate the contact,offering valuable insights into the underlying physics.

Aneuploidy, an imbalanced number of chromosomes or chromosome arms, is a genetic hallmark of cancer cells, yet aneuploidy remains a biological enigma and a missed opportunity for cancer therapy. My lab applies experimental and computational approaches to dissect the basic biology underlying cancer aneuploidy and to study its cellular consequences. In this seminar, I will focus on an unpublished study in which we discovered an important role for a recurrent aneuploidy in driving brain metastasis, revealed the underlying molecular mechanism, and identified a therapeutically-relevant cellular vulnerability that is associated with this common aneuploidy.

This talk tests the ability of natural freshwater lakes and margins to attenuate the emissions ofthe greenhouse gas methane (CH4) to the atmosphere under warming climate. I will show howmicrobial communities manage to survive and mitigate methane emissions under energylimited, highly reduced conditions of deep methanogenic lake sediments, through redoxcouplings of methane to Mn-Fe-N. Complex redox couplings between those species were alsoexplored in thermokarst lakes and margins, which are extensively formed by permafrost thawin the Arctic. The cycles were quantified using geochemical and microbial profiles, togetherwith stable isotope probing experiments close to natural conditions. The profiles andincubations show active microbial population that exhibit surprisingly both aerobic andanaerobic methane oxidation in methanogenic sediments and upland Arctic soils, fueled bynitrogen and iron redox cycles.