Thu 20 Mar 14:00: Stochastic Algorithms for Nonconvex Optimization
Nowadays it is quite common to solve optimization problems in 10^9 or more variables. At these levels, it is not practical to use the “true” gradient of the objective function. Instead, a variety of methods are based on using approximate gradients, which are also random; in other words, they are stochastic gradients. Often, only some components of the argument are updated at each iteration, to reduce storage calls. As a result, nowadays optimization algorithms produce stochastic processes, as opposed to sequences of vectors in some Euclidean space. Another issue is that the objective function is not convex.
The seminar will be held in LR3A , Department of Engineering, and online (zoom): https://newnham.zoom.us/j/92544958528?pwd=YS9PcGRnbXBOcStBdStNb3E0SHN1UT09
- Speaker: Mathukumalli Vidyasagar, IIT Hyderabad
- Thursday 20 March 2025, 14:00-15:00
- Venue: LR3A, Department of Engineering and online (Zoom).
- Series: CUED Control Group Seminars; organiser: Fulvio Forni.
Fri 09 May 14:00: A topological proof of the H-colouring dichotomy
A colouring of a graph with $k$ colours is an assignment of colours to vertices so that no edge is monochromatic. As it is well-known colouring with 2 colours is in P while colouring with $k > 2$ colours is NP-complete. This dichotomy was extended to the graph homomorphism problem, also called $H$-colouring, by Hell and Nešetřil [J. Comb. Theory B, 48(1):92-110, 1990]. More precisely, they proved that deciding whether there is a graph homomorphism from a given graph to a fixed graph $H$ is in P if $H$ is bipartite (or contains a self-loop), and is NP-complete otherwise. This dichotomy served as an important test-case for the Feder–Vardi dichotomy conjecture, and Bulatov–Zhuk dichotomy of complexity of finite-template CSPs.
In the talk, I will present a new proof of this theorem using tools from topological combinatorics based on ideas of Lovász [J. Comb. Theory, Ser. A, 25(3):319-324, 1978] and Brower’s fixed-point theorem. This is joint work with Sebastian Meyer (TU Dresden).
- Speaker: Jakub Oprsal (University of Birmingham)
- Friday 09 May 2025, 14:00-15:00
- Venue: SS03, Computer Laboratory.
- Series: Logic and Semantics Seminar (Computer Laboratory); organiser: Anuj Dawar.
Atomically Dispersed Co/Mo Sites Anchored on Mesoporous Carbon Hollow Spheres for Highly Selective Oxygen Reduction to Hydrogen Peroxide in Acidic Media
Atomically dispersed Co/Mo sites anchored on mesoporous carbon hollow spheres (Co/Mo-MCHS) are designed via template-engaged strategy for two-electron oxygen reduction reaction. Owing to the mesoporous hollow merits and electron-donating effect from Mo species, the Co/Mo-MCHS electrocatalyst displays efficient two-electron pathway with high hydrogen peroxide selectivity, and stable operation in acid.
Abstract
Two-electron oxygen reduction reaction (2e− ORR) in acidic media is a promising route for the decentralized and on-site hydrogen peroxide (H2O2) generation. Nevertheless, strong interaction between active sites and *OOH intermediates usually induces the O─O bond cleavage to convert 2e− pathway into the sluggish 4e− ORR. Therefore, it is highly necessary to optimize the electronic structure of 2e− ORR electrocatalysts for the regulation of adsorption energy. Herein, we propose the utilization of atomically dispersed Co/Mo sites anchored on mesoporous carbon hollow spheres (Co/Mo-MCHS) via a template-engaged strategy for highly selective ORR to H2O2 in acid. Benefitting from the electron-donating effect of Mo atoms, an enriched electron density around the Co center for Co/Mo-MCHS is observed, resulting in optimal adsorption of the key *OOH intermediates to approach the apex of 2e− ORR volcano plot. Moreover, the introduction of Mo species simultaneously suppresses the electroreduction of as-obtained H2O2 on Co sites. As a consequence, Co/Mo-MCHS delivers a high H2O2 selectivity of 90–95% in acid. The flow cell based on the Co/Mo-MCHS catalyst achieves a remarkable H2O2 yield of 2102 mg for 150 h. Moreover, this strategy can be extended to other early transition metal elements with similar electronic modifier effects.
Synchronous Dimension-Crystallization Engineering Enables Highly Efficient 2D/3D Tin Perovskite Solar Cells
DOI: 10.1039/D4EE06142J, PaperZiyong Kang, Peng Feng, Kun Wang, Lu Zhang, Rui Meng, Yali Chen, Jiandong Wu, Feng Yang, Xuewen Zhang, Tianxiang Li, Jingzhi Shang, Yu Tong, Hongqiang Wang
Tin perovskite films with two-dimensional/three-dimensional (2D/3D) heterostructures promise high performance lead-free perovskite solar cells (PSCs), while they are challenged by the undesirable carrier transport due to intrinsic multi-quantum wells, and...
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Wed 02 Apr 16:00: A short and personal history of planar cell polarity
Its about 30 years since we started to research planar cell polarity, a small defined field with its feet in genetics and its head in theory. How do cells orient themselves in the whole, how do they align the little structures such as subcellular denticles of insects or the multicellular hairs of a mammal, how do they know which way to send out an axon, which way to point a nascent arm? When we started the field was intriguing, fashionable. Now it remains important and interesting but is rusty and largely abandoned. Most scientists who worked in the field have moved on, leaving many problems unsolved. We (and others) used fly genetics. We summarise some principles of mechanism that we discovered with genetic mosaics.
- Speaker: Peter A. Lawrence - Department of Zoology
- Wednesday 02 April 2025, 16:00-17:30
- Venue: Max Perutz Lecture Theatre. LMB. Cambridge..
- Series: Cambridge Fly Meetings; organiser: Daniel Sobrido-Cameán.
Thu 20 Mar 17:00: Verified Unsolvability of Temporal Planning
The project aims to implement a verified reduction from Temporal Planning to Timed Automata, targeting a model checker which was verified in Isabelle/HOL. The model checker can output and check certificates for unsatisfied reachability properties. This results in a checkable claim that a state corresponding to the goal of a planning problem is unreachable and the problem is therefore unsolvable. Strong correctness guarantees will be provided by proving the correctness of the reduction in Isabelle/HOL.
As the project itself is incomplete, I will introduce the topics, explain how they relate, and show some formalization methodology where applicable and relevant.
Automated Planning is an area of computer science concerned with symbolic representation of problems and symbolic reasoning to solve problems. Temporal Planning is an area of automated planning concerned with scheduling concurrent actions on a continuous timeline. Planning languages, like the Planning Domain Definition Language (PDDL), can be given formal semantics using abstract formalisms, like Temporal Propositional Planning. The latter is an abstract formalism which restricts planning to a set-theoretic characterization of the world.
A timed automaton is an abstract formalism to describe a transition system with discrete states and continuous time. Temporal Propositional Planning can be re-examined from an automata-theoretic perspective using Timed Automata. Timed Automata are targets for Model Checking, an automated technique to ensure that models of computer systems satisfy properties over (possibly infinite) sequences of actions.
=== Hybrid talk ===
Join Zoom Meeting https://cam-ac-uk.zoom.us/j/87143365195?pwd=SELTNkOcfVrIE1IppYCsbooOVqenzI.1
Meeting ID: 871 4336 5195
Passcode: 541180
- Speaker: David Wang (King's College London)
- Thursday 20 March 2025, 17:00-18:00
- Venue: MR14 Centre for Mathematical Sciences.
- Series: Formalisation of mathematics with interactive theorem provers ; organiser: Anand Rao Tadipatri.
Spontaneous Passivation of Selective Zn (101) Plating via Dangling Bond Saturation and Electrostatic Interaction Regulation for High-Utilization, Fast-Kinetics Zinc Anodes
DOI: 10.1039/D4EE05498A, Paper Open Access   This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Yuxuan Zhang, Minyoung Kim, Dong Hun Lee, Fei Qin, Han Wook Song, Chung Soo Kim, Jeongmin Park, Chohee Kim, Fang Lian, Sunghwan Lee
Although Zn (101) exhibits faster Zn²⁺ plating/stripping kinetics and stronger bonding with Zn2+ compared to Zn (002), the application of Zn (101) in Zn batteries has been limited due to...
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Fri 14 Mar 14:00: ‘To Report or Not to Report: is that the Question?’ Exploring Young People's Reporting Practices of Illicit Drug Ads on Social Media
Better algorithms mean less illegal content on social media. To improve these algorithms, users need to report such content, yet they often do not. This talk will explore young people’s attitudes and practices around reporting a specific online harm: illicit drug advertisements.
A survey of UK students (13–18) examined their reporting practices and tested different messages to encourage reporting. Surprisingly, none were effective, highlighting deeper challenges in the reporting process. This calls into question whether user reporting is the best way to reduce harmful content and highlights the need for a balanced approach that combines proactive detection with user engagement.
- Speaker: Ashly Fuller, University College London
- Friday 14 March 2025, 14:00-15:00
- Venue: Webinar & GN06, Computer Laboratory, William Gates Building..
- Series: Computer Laboratory Security Seminar; organiser: Anna Talas.
Fri 14 Mar 13:00: A phase transition in cosmological fluid dynamics
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/89259699528?pwd=rI2WS21NUsIKMmZCGtkPuPbM5SL0eW.1.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Multifunctional additive with dynamic sacrificial S-S bond for building self-assembled monolayers of Zn-ion battery with improved stability and longevity
DOI: 10.1039/D4EE05922K, PaperShuang Han, Haijun Niu, Wanan Cai, Minghai Li, Qiyu Fan, Zhuoyi Han, Xuewen Ming, Wen Wang
Aqueous zinc-ion batteries (AZIBs) possess a tremendous prospect for large-scale energy storage. Nevertheless, the interfacial stability and cyclic reversibility for Zn anode are impeded by the unregulated growth of Zn...
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Ultrathin cellulosic gel electrolyte with gradient hydropenic interface for stable, high-energy and flexible zinc batteries
DOI: 10.1039/D5EE00158G, Paper Open Access   This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Jichao Zhai, Wang Zhao, Lei Wang, Jianbo Shuai, Ruwei Chen, Wenjiao Ge, Yu Zong, Guanjie He, Xiaohui Wang
The increasing demand for personalized health monitoring has driven the development of wearable electronics. Flexible zinc-ion batteries (FZIBs) are ideal power sources for wearable devices, but their low volumetric energy...
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Fri 21 Mar 13:00: Primordial black holes: abundances and constraints
The equation of state of the primordial plasma is reduced during each early universe phase transition. Primordial black holes, thought to form whilst the universe is radiation dominated, are exponentially sensitive to the changes in the equation of state. However, this exponential sensitivity is the same that primordial black hole formation shows to the amplitude of the primordial curvature power spectrum. Thus, using constraints on the power spectrum we are able to place constraints on primordial black hole abundances. I will show that, despite the exponential enhancement in formation rate, current constraints on the power spectrum lead to difficulties motivating primordial black holes with the standard model phase transitions.
- Speaker: Xavier Pritchard, Sussex
- Friday 21 March 2025, 13:00-14:00
- Venue: Potter room / https://cam-ac-uk.zoom.us/j/87235967698.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Sat 19 Apr 11:00: NatHistFest: 106th Conversazione Free Exhibition on the Wonders of the Natural World
Cambridge’s oldest celebration of citizen science.
The event, showcasing the environment and wildlife of Cambridgeshire and further afield, will be hosted in the David Attenborough Building, adjacent to the Zoology Museum.
We invite anyone (CNHS member or not) to consider exhibiting. Exhibits might include specimens (living or dead) – things people can handle always seem to be popular – or displays about any aspect of local natural history. Or perhaps you are member of a local group which might like to have an exhibit about its activities? Past programmes, available on our website, give an idea of the wide variety of exhibits, and there is also a history of the Conversazione, written in 1989 or the 70th event. For information or to book exhibition space please email exhibition@cnhs.org.uk, or contact the Conversazione organisers via https://www.cnhs.org.uk/
Free Exhibition on the Wonders of the Natural World
- Speaker: Free Public Exhibition
- Saturday 19 April 2025, 11:00-17:00
- Venue: Common Room (First Floor) David Attenborough Building, University of Cambridge Pembroke St, Cambridge CB2 3QZ.
- Series: Cambridge Natural History Society; organiser: events.
Thu 22 May 14:00: Walter Kohn: the theoretical physicist who created DFT and won the Nobel Prize for Chemistry
Density Functional Theory (DFT) has become one of the most highly cited techniques in science, widely used for simulations in physics, chemistry, materials science and biology. The modern form of DFT was invented by Walter Kohn after a remarkable personal journey which included escaping on the Kindertransport to England on almost the last train out of Vienna in August 1939, and then being interned in Canada deep in a forest miles from civilisation. Despite these disadvantages, Walter Kohn was able to have an exceptional academic career in theoretical solid state physics which culminated in DFT and the Nobel Prize (but for Chemistry, not Physics). Drawing on fresh insights from his recent biography Walter Kohn: From Kindertransport and Internment to DFT and the Nobel Prize, David Clary will describe the remarkable life, career and science of Walter Kohn.
- Speaker: Prof. Sir David Clary, FRS (University of Oxford)
- Thursday 22 May 2025, 14:00-15:30
- Venue: TCM Seminar Room.
- Series: Theory of Condensed Matter; organiser: Bo Peng.
Wed 26 Mar 16:00: Title to be confirmed
Abstract not available
- Speaker: Prof. Thors Hans Hansson (Stockholm)
- Wednesday 26 March 2025, 16:00-17:30
- Venue: TCM Seminar Room.
- Series: Theory of Condensed Matter; organiser: Bo Peng.
Suppression of Interfacial Water Layer with Solid Contact by an Ultrathin Water Repellent and Zn2+ Selective Layer for Ah-Level Zinc Metal Battery
DOI: 10.1039/D4EE05905K, PaperZiwei Xu, Junpeng Li, Yifan Fu, Junjie Ba, Fengxue Duan, Yingjin Wei, Chunzhong Wang, Kangning Zhao, Yizhan Wang
The failure of zinc metal batteries usually involves the instability of the protection layer of zinc metal anode due to the water penetrating and dissolution during long-term operation, leading to...
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Mon 28 Apr 14:00: Augmenting the Spectroscopy of Materials with Nonclassical Light and Machine Learning
Abstract not available
- Speaker: Dr Andrew Proppe, Joint Centre for Extreme Photonics, University of Ottawa
- Monday 28 April 2025, 14:00-15:00
- Venue: Dept of Chemistry, Pfizer Lecture Theatre.
- Series: Chemistry Departmental-wide lectures; organiser: Xani Thorman.
Thu 01 May 14:00: Leveraging Quantum Computation for Electronic Structure Theory
Abstract not available
- Speaker: Dr Maria-Andreea Filip, Yusuf Hamied Department of Chemistry
- Thursday 01 May 2025, 14:00-15:00
- Venue: Dept of Chemistry, Unilever Lecture Theatre.
- Series: Chemistry Departmental-wide lectures; organiser: Xani Thorman.
Wed 23 Apr 14:00: Simulating light driven processes with quasi-classical trajectories: from molecules to solids
Abstract not available
- Speaker: Dr Aaron Kelly, Max Planck Institute for the Structure and Dynamics of Matter, Hamburg
- Wednesday 23 April 2025, 14:00-15:00
- Venue: Dept of Chemistry, Unilever Lecture Theatre.
- Series: Chemistry Departmental-wide lectures; organiser: Xani Thorman.
Tue 22 Apr 14:00: Mapping Coupled Ionic, Electronic and Structural Dynamics in Chemical Systems Through New Micro-Spectroscopic Techniques
Abstract not available
- Speaker: Dr Raj Pandya, Physical Chemistry, University of Warwick
- Tuesday 22 April 2025, 14:00-15:00
- Venue: Dept of Chemistry, Unilever Lecture Theatre.
- Series: Chemistry Departmental-wide lectures; organiser: Xani Thorman.