http://talks.cam.ac.uk/show/rss/5408

Abstract not available

Drinks and nibbles will be served after the lecture

• Speaker: Professor Mikhail Lukin, Harvard University
• Monday 03 March 2025, 16:00-17:00
• Venue: Ray Dolby Auditorium, Ray Dolby Centre, Cavendish Laboratory, JJ Thomson Avenue, CB3 0US.
• Series: Scott Lectures; organiser: Leona Hope-Coles.

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Abstract not available

Refreshments will be served after the lecture

• Speaker: Professor Mikhail Lukin, Harvard University
• Wednesday 05 March 2025, 16:00-17:00
• Venue: Ray Dolby Auditorium, Ray Dolby Centre, Cavendish Laboratory, JJ Thomson Avenue, CB3 0US.
• Series: Scott Lectures; organiser: Leona Hope-Coles.

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Abstract not available

• Speaker: Professor Mikhail Lukin, Harvard University
• Thursday 06 March 2025, 11:00-12:00
• Venue: Cluster Seminar Room, Ray Dolby Centre, Cavendish Laboratory, JJ Thomson Avenue, CB3 0US.
• Series: Scott Lectures; organiser: Leona Hope-Coles.

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Just as imaginary numbers extend real numbers and simplify certain mathematical proofs, we introduce the concept of imaginary specifications to enhance program verification. In mathematics, imaginary numbers enable expressing intermediate steps that cannot be captured using real numbers alone, offering natural proof decomposition that reduces complex proofs into simpler, more manageable steps. Similarly, our work introduces imaginary specifications in program verification through CRIS (Contextual Refinement with Imaginary Specification), our novel verification tool.

CRIS with imaginary specifications provides a unified framework to inherently marry two fundamental approaches to program verification: separation logic with pre/post conditions as specifications, and program refinement with abstract programs as specifications. This unification not only enables proof simplification via proof decomposition but also enables elegant expression of hard-to-express properties, such as separation logic conditions involving IO events and logical atomicity—properties that traditionally require intricate mechanisms or are difficult to specify.

• Speaker: Gil Hur (Seoul National University)
• Tuesday 04 March 2025, 13:00-14:00
• Venue: SS03, Computer Laboratory.
• Series: Logic and Semantics Seminar (Computer Laboratory); organiser: Ioannis Markakis.

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On a background Minkowski spacetime, the Euler equations (both relativistic and not) are known to develop shock singularities in finite-time from smooth data. Such shock formation can be suppressed on cosmological spacetimes whose spatial slices expand at an accelerated rate. However, situations with decelerated expansion, which are relevant in our early universe, are not as well understood. I will present some recent joint work in this direction, based on collaborations with David Fajman, Maciej Maliborski, Todd Oliynyk and Max Ofner.

• Speaker: Zoe Wyatt, DPMMS
• Friday 14 March 2025, 13:00-14:00
• Venue: Potter room / https://cam-ac-uk.zoom.us/j/87235967698.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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The points on the modular curve associated to the normaliser of a non-split Cartan subgroup can be represented as elliptic curves with a necklace level structure. I will explain what these necklaces are and how they are useful in understanding this curve and how we can calculate explicitly with necklaces.

• Speaker: Chris Wuthrich (Nottingham)
• Tuesday 04 March 2025, 14:30-15:30
• Venue: MR13.
• Series: Number Theory Seminar; organiser: Rong Zhou.

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Abstract not available

• Speaker: Professor Mikhail Lukin, Harvard University
• Thursday 06 March 2025, 11:00-12:00
• Venue: Cluster Seminar Room, Ray Dolby Centre, Cavendish Laboratory, JJ Thomson Avenue, CB3 0US.
• Series: Scott Lectures; organiser: Leona Hope-Coles.

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Abstract not available

Refreshments will be served after the lecture

• Speaker: Professor Mikhail Lukin, Harvard University
• Wednesday 05 March 2025, 16:00-17:00
• Venue: Ray Dolby Auditorium, Ray Dolby Centre, Cavendish Laboratory, JJ Thomson Avenue, CB3 0US.
• Series: Scott Lectures; organiser: Leona Hope-Coles.

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Abstract not available

Drinks and nibbles will be served after the lecture

• Speaker: Professor Mikhail Lukin, Harvard University
• Monday 03 March 2025, 16:00-17:00
• Venue: Ray Dolby Auditorium, Ray Dolby Centre, Cavendish Laboratory, JJ Thomson Avenue, CB3 0US.
• Series: Scott Lectures; organiser: Leona Hope-Coles.

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The gut microbiome is more than a collection of individual bacteria – it is a dynamic ecosystem where survival depends on interactions between species. In fact, these interactions can be more decisive for a bacterium’s fate than external factors like the host’s diet or drug intake. In this talk, I will explore how gut microbial communities navigate challenges such as nutrient scarcity and drug exposure, often revealing surprising survival patterns that defy predictions based on single-species behaviour. I will introduce how mathematical models can capture these emergent survival dynamics, enabling predictions of which species thrive or decline in a community context. By delving into the metabolic alliances and competitive strategies of gut bacteria, my research aims to offer insights into microbiome resilience, pathogen resistance, and the design of targeted probiotic therapies. Whether you are fascinated by the gut-brain axis, applied mathematics, or simply intrigued by the unseen battles (and friendships) within, this lunchtime seminar aims to make the microscopic world come alive.

• Speaker: Naomi van den Berg
• Thursday 06 March 2025, 13:00-14:00
• Venue: Richard King room, Darwin College.
• Series: Darwin College Science Seminars; organiser: Alexander R Epstein.

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In this talk, I will discuss a novel and simple parametrisation of meson form factors that can be used to describe data above and below the pair production threshold, using the pion form factor as a simple example (in which case our parameterisation describes both $\pi \to \pi^0$ and $0 \to \pi \pi$ processes). To start with, I will introduce and walk through the derivation of dispersive bounds on form factors, then explain the difficulties in the traditional approach with a description of the above threshold data due to resonant poles, and the known asymptotic properties of the form factor in this region. Using data from $\pi$-H scattering and the $\tau \to \pi \pi \nu$ decay, I will show how with less than 5 free parameters (including the rho mass and decay width), we can excellently describe the data. This talk is based on my work in arXiv:2410.13764.

• Speaker: Matthew Kirk (Durham U.)
• Friday 07 March 2025, 16:00-17:00
• Venue: MR19 (Potter Room, Pavilion B), CMS.
• Series: HEP phenomenology joint Cavendish-DAMTP seminar; organiser: Nico Gubernari.

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We establish an intrinsic rigidity theorem for extremal horizons, showing that a compact cross-section of a rotating extremal horizon must admit a Killing vector field. This result holds for a wide class of matter theories, extending work by Dunajski and Lucietti in the vacuum case. In four-dimensional Einstein-Maxwell theory, it follows that any non-trivial cross-section must be given by the extremal Kerr-Newman family. We also discuss the implications for the near-horizon geometry and the topology of cross-sections. This talk is partly based on joint work with David Katona and James Lucietti.

• Speaker: Alex Colling, DAMTP
• Friday 07 March 2025, 13:00-14:00
• Venue: Potter room / https://cam-ac-uk.zoom.us/j/87235967698.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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Ethereum’s Gasper consensus protocol typically requires 64 to 95 slots-the units of time during which a new chain extending the previous one by one block is proposed and voted-to finalize, even under ideal conditions with synchrony and honest validators. This exposes a significant portion of the blockchain to potential reorganizations during changes in network conditions, such as periods of asynchrony.

In this talk, I will introduce 3SF, a novel consensus protocol that addresses these limitations. With 3SF, finality is achieved within just three slots after a proposal, drastically reducing the exposure to reorganizations. This presentation will explore the motivation, design, and implications of 3SF, offering a new perspective on the future of Ethereum’s consensus protocol.

Paper: https://arxiv.org/abs/2411.00558

• Speaker: Luca Zanolini, Ethereum Foundation
• Tuesday 04 March 2025, 14:00-15:00
• Venue: Webinar & GN06, Computer Laboratory, William Gates Building..
• Series: Computer Laboratory Security Seminar; organiser: Tina Marjanov.

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Fusion energy offers a promising clean energy source to help achieve net-zero goals, with magnetic confinement using spherical tokamaks being a leading approach. The UK’s STEP (Spherical Tokamak for Energy Production) programme aims to design, build, and demonstrate a fusion power plant. This talk provides an overview of the project, focusing on four key control challenges. First, it covers the plant’s architecture and philosophy for construction, operation, and maintenance. Second, it explores the control theory needed to manage the unstable plasma, requiring sophisticated sensors and coordination of heating, fuelling, and magnetic systems to maintain stability. Third, it addresses the unique challenges of steady-state fusion power delivery, such as vertical control of elongated plasmas, managing plasma burn, and extreme heat loads on exhaust structures. Finally, it reviews the engineering lifecycle, from Exascale simulations to real-time control systems that will ensure robust performance and long-term maintainability for this new energy supply industry.

The seminar will be held in the LR3A , Department of Engineering, and online (zoom): https://newnham.zoom.us/j/92544958528?pwd=YS9PcGRnbXBOcStBdStNb3E0SHN1UT09

• Speaker: Adam Stephen (UKAEA), Kim Cave-Ayland (UKAEA), Morten Lennholm (UKIFS), Terry Thompson (UKIFS)
• Thursday 06 March 2025, 14:00-15:00
• Venue: JDB Seminar Room, Department of Engineering and online (Zoom).
• Series: CUED Control Group Seminars; organiser: Fulvio Forni.

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Abstract not available

• Speaker: Min Huang
• Friday 07 March 2025, 16:00-17:00
• Venue: Tea Room, Old House.
• Series: Bullard Laboratories Tea Time Talks; organiser: David Al-Attar.

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Proof complexity is one of the central approaches to the fundamental hardness problems in complexity theory. In recent years, significant efforts have been made to bridge the gap between algebraic and proof complexity through a relatively transparent reduction from algebraic circuit-size lower bounds to proof-size lower bounds. In this talk, I will discuss state-of-the-art lower bounds in proof complexity that leverage the algebraic circuit-based approach, establishing it as a new tool that also draws on ideas from existing techniques—such as feasible interpolation, random restrictions, width-size tradeoffs, and lifting. I will also highlight some imminent open problems and potential challenges in this direction.

• Speaker: Iddo Tzamaret (Imperial)
• Tuesday 11 March 2025, 14:00-15:00
• Venue: Computer Laboratory, William Gates Building, Room SS03.
• Series: Algorithms and Complexity Seminar; organiser: Tom Gur.

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=== Hybrid talk ===

Join Zoom Meeting https://cam-ac-uk.zoom.us/j/87143365195?pwd=SELTNkOcfVrIE1IppYCsbooOVqenzI.1

Meeting ID: 871 4336 5195

Passcode: 541180

• Speaker: Andrei Popescu (University of Sheffield)
• Thursday 15 May 2025, 17:00-18:00
• Venue: MR14 Centre for Mathematical Sciences.
• Series: Formalisation of mathematics with interactive theorem provers ; organiser: Anand Rao Tadipatri.

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Classical metaphysics, or the effort to arrive at justified true knowledge of ‘the metaphysical’, the ultimate causes or first principles of reality, has been subjected to a developing critique over the past three centuries. Discussions of scholars concerning the possibility of metaphysics has continued to grow in recent decades, with many proclaiming the end of metaphysics.

This talk will endeavour to articulate an alternative approach to metaphysical philosophizing, issuing from a comparison of two 20th century thinkers, Emmanuel Levinas and Karl Jaspers. This alternative approach to engaging with the metaphysical is distinguished by an acceptance of the inability to arrive at final knowledge of such matters, but holds that thinking about the ‘deepest’ aspects of reality, in which we have our ideations regularly surpassed in a process of unending learning, can offer an alternative, personally and spiritually transformative value, in which we can come to playful, ‘just communion’ with the mystery of being, manifesting as the desire for wonderment.

• Speaker: Connor Hayes
• Tuesday 04 March 2025, 13:10-14:00
• Venue: Richard King room, Darwin College.
• Series: Darwin College Humanities and Social Sciences Seminars; organiser: Dr Amelia Hassoun.

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Tree-based models are often robust to uninformative features and can accurately capture non-smooth, complex decision boundaries. Consequently, they often outperform neural network-based models on tabular datasets at a significantly lower computational cost. Nevertheless, the capability of traditional tree-based ensembles to express complex relationships efficiently is limited by using a single feature to make splits. To improve the efficiency and expressiveness of tree-based methods, we propose Random Oblique Fast Interpretable Greedy-Tree Sums (RO-FIGS). RO-FIGS builds on Fast Interpretable Greedy-Tree Sums, and extends it by learning trees with oblique or multivariate splits, where each split consists of a linear combination learnt from random subsets of features. This helps uncover interactions between features and improves performance. The proposed method is suitable for tabular datasets with both numerical and categorical features. We evaluate RO-FIGS on 22 real-world tabular datasets, demonstrating superior performance and much smaller models over other tree- and neural network-based methods. Additionally, we analyse their splits to reveal valuable insights into feature interactions, enriching the information learnt from SHAP summary plots, and thereby demonstrating the enhanced interpretability of RO-FIGS models. The proposed method is well-suited for applications, where balance between accuracy and interpretability is essential.

NOTE unusual date

• Speaker: Urška Matjašec (University of Cambridge)
• Thursday 06 March 2025, 13:00-14:00
• Venue: Lecture Theatre 2, Computer Laboratory, William Gates Building.
• Series: Artificial Intelligence Research Group Talks (Computer Laboratory); organiser: Mateja Jamnik.

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Given an element in SL_n(Z/qZ), what is the smallest element of SL_n(Z) that projects to it? In a joint work with Amitay Kamber, we proved that a lift with entries bounded by O(q^2 log q) always exists, and that the exponent 2 is best possible. In the first half of the talk, I will explain how this problem is related to bounding the diameter of the Ramanujan graphs of Lubotzky, Phillips and Sarnak, and to Sarnak’s golden gates in quantum computing. In the second half of the talk, I will talk about the proof that the exponent 2 is best possible. This uses some tools from additive combinatorics.

• Speaker: Péter Varjú (University of Cambridge)
• Wednesday 05 March 2025, 13:30-15:00
• Venue: MR4, CMS.
• Series: Discrete Analysis Seminar; organiser: Julia Wolf.

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