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Abstract not available

• Speaker: Titus Lupu (Paris)
• Tuesday 18 February 2025, 14:00-15:00
• Venue: MR12.
• Series: Probability; organiser: ww295.

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When we run a complex algorithm on real data, it is standard to use a holdout set, or a cross-validation strategy, to evaluate its behavior and performance. When we do so, are we learning information about the algorithm itself, or only about the particular fitted model(s) that this particular data set produced? In this talk, we will establish fundamental hardness results on the problem of empirically evaluating properties of a black-box algorithm, such as its stability and its average risk, in the distribution-free setting. This work is joint with Yuetian Luo and Byol Kim.

• Speaker: Rina Foygel Barber (University of Chicago)
• Friday 14 March 2025, 14:00-15:00
• Venue: Centre for Mathematical Sciences MR12, CMS.
• Series: Statistics; organiser: Qingyuan Zhao.

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In a supervised learning setting, a model fitting algorithm is unstable if small perturbations to the input (the training data) can often lead to large perturbations in the output (say, predictions returned by the fitted model). Algorithmic stability is a desirable property with many important implications such as generalization and robustness, but testing the stability property empirically is known to be impossible in the setting of complex black-box models. In this work, we establish that bagging any black-box regression algorithm automatically ensures that stability holds, with no assumptions on the algorithm or the data. Furthermore, we construct a new framework for defining stability in the context of classification, and show that using bagging to estimate our uncertainty about the output label will again allow stability guarantees for any black-box model. This work is joint with Jake Soloff and Rebecca Willett.

Evaluating a black-box algorithm: stability, risk, and model comparisons

When we run a complex algorithm on real data, it is standard to use a holdout set, or a cross-validation strategy, to evaluate its behavior and performance. When we do so, are we learning information about the algorithm itself, or only about the particular fitted model(s) that this particular data set produced? In this talk, we will establish fundamental hardness results on the problem of empirically evaluating properties of a black-box algorithm, such as its stability and its average risk, in the distribution-free setting. This work is joint with Yuetian Luo and Byol Kim.

A wine reception in the Central Core will follow this lecture

• Speaker: Rina Foygel Barber (Chicago)
• Thursday 13 March 2025, 16:00-17:00
• Venue: Centre for Mathematical Sciences MR2.
• Series: Peter Whittle Lecture; organiser: HoD Secretary, DPMMS.

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In a supervised learning setting, a model fitting algorithm is unstable if small perturbations to the input (the training data) can often lead to large perturbations in the output (say, predictions returned by the fitted model). Algorithmic stability is a desirable property with many important implications such as generalization and robustness, but testing the stability property empirically is known to be impossible in the setting of complex black-box models. In this work, we establish that bagging any black-box regression algorithm automatically ensures that stability holds, with no assumptions on the algorithm or the data. Furthermore, we construct a new framework for defining stability in the context of classification, and show that using bagging to estimate our uncertainty about the output label will again allow stability guarantees for any black-box model. This work is joint with Jake Soloff and Rebecca Willett.

Evaluating a black-box algorithm: stability, risk, and model comparisons

When we run a complex algorithm on real data, it is standard to use a holdout set, or a cross-validation strategy, to evaluate its behavior and performance. When we do so, are we learning information about the algorithm itself, or only about the particular fitted model(s) that this particular data set produced? In this talk, we will establish fundamental hardness results on the problem of empirically evaluating properties of a black-box algorithm, such as its stability and its average risk, in the distribution-free setting. This work is joint with Yuetian Luo and Byol Kim.

• Speaker: Rina Foygel Barber (Chicago)
• Thursday 13 March 2025, 16:00-17:00
• Venue: Centre for Mathematical Sciences MR2.
• Series: Peter Whittle Lecture; organiser: HoD Secretary, DPMMS.

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I shall describe the propagation properties of a class of quasilinear reaction-diffusion equations, motivated by applications to biological tissue growth.

• Speaker: John R. King (University of Nottingham)
• Monday 10 February 2025, 14:00-15:00
• Venue: MR13.
• Series: Partial Differential Equations seminar; organiser: Giacomo Ageno.

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Dear all,

CAS seminar will welcome Tobias Müller who will give us a talk on climate colonialism. The talk will be held in a hybrid format with the speaker in-person at the Unilever lecture theatre and on Zoom on Tuesday, the 4th February , 11 AM-12 PM. Please find the abstracts of the talk below.

If you would like this seminar recorded, please let us know in advance. We look forward to seeing you there!

Best wishes, Megan and Yao

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Leverhulme Early Career Fellow Centre for Research in the Arts, Social Sciences and Humanities (CRASSH) The climate crisis is deeply entangled with the politics of race and colonialism. The concept of “climate colonialism”, (Bhambra and Newell 2022) urges us to analyse what forms of resistance to the socio-ecological continuities of colonialism emerge, and what challenges they face. However, we lack empirical and conceptual studies on how people on the ground confront the intersection of the climate crisis, colonialism, racism and extractivism, and how this differs across former coloniser and colonised countries. This raises the question, what kind of politics are able to confront the intersecting crises of climate and colonialism?

This presentation addresses this gap through an analysis of how climate activists in four different countries respond to the climate crisis and connected social justice issues. Using the case study of a transnationally operating group within the global movement, Extinction Rebellion, the paper compares strategic responses to climate colonialism in four different countries, namely Mexico, South Africa, the UK and the US. Methodologically, the paper uses multi-sited ethnography, comprising 18 months of ethnographic fieldwork and 140 interviews with activists, to gain a deep insight into the internal contentions within different parts of the movement.The paper advances not only our understanding of how facing climate colonialism challenges movement spaces, but also how white environmental activists struggle with building racial justice into their practices and to build coalitions across the social justice movement space. It thereby contributes to the much-needed bridging between decolonial theory, social movement studies and the social scientific accounts of climate change.

Teams link: https://teams.microsoft.com/l/meetup-join/19%3ameeting_Y2VlZmM3OTgtOTQwNS00ZTcxLTk5ZGEtZWZiMzU4NTdiMGY1%40thread.v2/0?context=%7b%22Tid%22%3a%2249a50445-bdfa-4b79-ade3-547b4f3986e9%22%2c%22Oid%22%3a%2253b919d9-f8a7-4f56-9bb0-baaf0ba7404d%22%7d

• Speaker: Tobias Müller, Leverhulme Early Career Fellow Centre for Research in the Arts, Social Sciences and Humanities (CRASSH)
• Tuesday 04 February 2025, 11:00-12:00
• Venue: Chemistry Dept, Unilever Lecture Theatre and Teams.
• Series: Centre for Atmospheric Science seminars, Chemistry Dept.; organiser: Dr Megan Brown.

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Given a multivariable polynomial with integer coefficients, what is the probability that it takes a squarefree value? This was determined by Granville and Poonen assuming the ABC conjecture, but an unconditional proof remains unknown. We will start the talk by discussing a paper by Bhargava, Shankar and Wang that unconditionally determines a result for the discriminants of monic polynomials of any given degree. In the second part of the talk, we will see how the methods of BSW can be interpreted into a more general framework developed by Thorne, and how they can be used to obtain new results for other families of discriminant polynomials.

• Speaker: Marti Oller Riera (Cambridge)
• Tuesday 04 February 2025, 14:30-15:30
• Venue: MR13.
• Series: Number Theory Seminar; organiser: Rong Zhou.

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Abstract not available

• Speaker: Speaker to be confirmed
• Wednesday 26 February 2025, 15:30-16:30
• Venue: BAS Seminar Room 1.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Speaker to be confirmed
• Wednesday 23 April 2025, 14:00-15:00
• Venue: BAS Seminar Room 330b.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Speaker to be confirmed
• Wednesday 09 April 2025, 14:00-15:00
• Venue: BAS Seminar Room 2.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Speaker to be confirmed
• Wednesday 26 March 2025, 14:00-15:00
• Venue: BAS Seminar Room 330b.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Speaker to be confirmed
• Wednesday 12 March 2025, 14:00-15:00
• Venue: BAS Seminar Room 2.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Prof Hong Geun Lee (Seoul National University)
• Thursday 15 May 2025, 14:00-15:00
• Venue: Dept. of Chemistry, Pfizer Lecture Theatre.
• Series: Synthetic Chemistry Research Interest Group; organiser: Jasmine Mitchell.

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n Navier-Stokes (NS) turbulence, large-scale turbulent flows determine small-scale flows; in other words, small-scale flows are synchronized to large-scale flows. In 3D turbulence, previous numerical studies suggest that the critical length separating these two scales is determined by the Kolmogorov length. In this talk, I will introduce our theoretical framework for characterizing synchronization phenomena [1]. Specifically, it provides a computational method for the exponential rate of convergence to the synchronized state, and identifies the critical length based on the NS equations via the “transverse” Lyapunov exponent. I will also discuss the synchronization property of 2D NS turbulence and how it differs from the 3D case [2]. These insights into synchronization and critical length scales are essential for developing machine-learning closure models for turbulence, in particular their stable reproducibility [3]. Finally, I will illustrate how “generalized” synchronization is crucial for predicting chaotic dynamics [4].

[1] M. Inubushi, Y. Saiki, M. U. Kobayashi, and S. Goto, Characterizing small-scale dynamics of Navier-Stokes turbulence with transverse Lyapunov exponents: A data assimilation approach, Phys. Rev. Lett. 131, 254001 (2023).

[2] M. Inubushi and C. P. Caulfield (in preparation).

[3] S. Matsumoto, M. Inubushi, and S. Goto, Stable reproducibility of turbulence dynamics by machine learning, Phys. Rev. Fluids 9, 104601 (2024).

[4] A. Ohkubo and M. Inubushi, Reservoir computing with generalized readout based on generalized synchronization, Sci. Rep. 14, 30918 (2024).

• Speaker: Professor Masanobu Inubushi, Tokyo University of Science
• Friday 14 February 2025, 16:00-17:00
• Venue: MR2.
• Series: Fluid Mechanics (DAMTP); organiser: Professor Grae Worster.

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Abstract not available

• Speaker: Chris Hooley (Coventry)
• Thursday 05 June 2025, 14:00-15:30
• Venue: TCM Seminar Room.
• Series: Theory of Condensed Matter; organiser: Bo Peng.

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Abstract not available

• Speaker: Prof. Sir David Clary, FRS (Cambridge & Oxford)
• Thursday 15 May 2025, 14:00-15:30
• Venue: TCM Seminar Room.
• Series: Theory of Condensed Matter; organiser: Bo Peng.

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In this talk, I will show how a gauge-theoretic approach to Jackiw–Teitelboim (JT) gravity naturally yields a two-dimensional Henneaux–Teitelboim (HT) unimodular theory, applicable to both flat and curved spacetimes. Under a mini-superspace reduction, the Wheeler–DeWitt equation becomes a Schrödinger-like equation admitting a consistent, unitary quantum description. The resulting wavefunction describes a quantum distribution for the scale factor, illuminating cosmic expansion and contraction, and allowing topology change at a=0.

• Speaker: Farbod Rassouli, University of Nottingham
• Friday 07 February 2025, 13:00-14:00
• Venue: Venue to be confirmed.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Abstract not available

• Speaker: Shohei Koide, NYU Langone Health
• Monday 16 June 2025, 12:30-13:30
• Venue: CRUK CI Lecture Theatre.
• Series: Seminars on Quantitative Biology @ CRUK Cambridge Institute ; organiser: .

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Abstract not available

• Speaker: David Savage, UC Berkeley
• Monday 19 May 2025, 12:30-13:30
• Venue: CRUK CI Lecture Theatre.
• Series: Seminars on Quantitative Biology @ CRUK Cambridge Institute ; organiser: Kate Davenport.

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Abstract not available

• Speaker: Oliver Hantschel, University of Marburg
• Monday 28 April 2025, 12:30-13:30
• Venue: CRUK CI Lecture Theatre.
• Series: Seminars on Quantitative Biology @ CRUK Cambridge Institute ; organiser: .

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