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Binary neutron star mergers provide insights into strong-field gravity and the properties of ultra-dense nuclear matter. These events offer the potential to search for signatures of physics beyond the standard model, including dark matter. We present the first numerical-relativity simulations of binary neutron star mergers admixed with dark matter, based on constraint-solved initial data. Modeling dark matter as a non-interacting fermionic gas, we investigate the impact of varying dark matter fractions and particle masses on the merger dynamics, ejecta mass, post-merger remnant properties, and the emitted gravitational waves. Our simulations suggest that the dark matter morphology – a dense core or a diluted halo – may alter the merger outcome. Scenarios with a dark matter core tend to exhibit a higher probability of prompt collapse, while those with a dark matter halo develop a common envelope, embedding the whole binary. Furthermore, gravitational wave signals from mergers with dark matter halo configurations exhibit significant deviations from standard models when the tidal deformability is calculated in a two-fluid framework neglecting the dilute and extended nature of the halo. This highlights the need for refined models in calculating the tidal deformability when considering mergers with extended dark matter structures. These initial results provide a basis for further exploration of dark matter’s role in binary neutron star mergers and their associated gravitational wave emission and can serve as a benchmark for future observations from advanced detectors and multi-messenger astrophysics.

• Speaker: Violetta Sagun, University of Southampton
• Friday 30 May 2025, 13:00-14:00
• Venue: MR9/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Abstract not available

• Speaker: Benjamin Elder, Imperial College London
• Friday 16 May 2025, 13:00-14:00
• Venue: MR20/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Abstract not available

• Speaker: Robbie Hennigar, Durham University
• Friday 09 May 2025, 13:00-14:00
• Venue: MR9/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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In Black Hole Perturbation Theory, confluent Heun functions appear as solutions to the radial Teukolsky equation, which governs perturbations in black hole spacetimes. While these functions are typically studied for their analytic properties, their connection to the underlying spacetime geometry has received less attention. In this talk, I will propose a spacetime interpretation of the confluent Heun functions, demonstrating how their behaviour near their singular points reflects the structure of key surfaces in Kerr spacetimes. By interpreting homotopic transformations of these functions as changes in the spacetime foliation, I will establish a connection between these solutions and various regions of the black hole’s global structure. I will also explore their relationship with the hyperboloidal formulation of the radial Teukolsky equation.

• Speaker: Marica Minucci, Bohr Inst., Copenhagen
• Friday 06 June 2025, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Abstract not available

• Speaker: Speaker to be confirmed
• Friday 30 May 2025, 14:00-15:00
• Venue: MR12, Centre for Mathematical Sciences.
• Series: Statistics; organiser: Qingyuan Zhao.

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Abstract not available

• Speaker: Professor Kim Jelfs, Imperial College London
• Wednesday 05 November 2025, 14:30-15:30
• Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
• Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.

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The thermo-electric-mechanical coupling strategy proposed here predicts the feasibility of Ni2SbTe2 and NiTe2 as ideal TEbMs for (Bi,Sb)2Te3 and Bi2(Te,Se)3, based on three-phase thermodynamic equilibrium, electrical resistivity, and CTE compatibility. The fabricated TE generators demonstrate a third-party-verified conversion efficiency of 7.1% and a power density of 0.49 W cm−2 when the hot-side temperature is 523 K, with negligible degradation over 200 h.

The long-term stability of thermoelectric generators, including those based on Bi2Te3, is hindered by the lack of ideal thermoelectric barrier materials (TEbMs). Conventional selection methods for TEbMs mainly rely on trial-and-error, which is time-consuming and does not reveal the underlying mechanisms. In this study, a new design principle for selecting TEbMs based on thermo–electric–mechanical coupling is proposed. By combining the phase diagram predictions with the thermal expansion coefficients and electrical resistivities of the potential reactants, the Ni2SbTe2 and NiTe2 compounds are identified as ideal TEbMs for (Bi,Sb)2Te3 and Bi2(Te,Se)3, respectively, leading to interfaces with high thermal stability, low contact resistivity, and high strength. The fabricated thermoelectric generator achieves a competitive conversion efficiency of 7.1% and a power density of 0.49 W cm−2 at hot-side and cold-side temperatures of 523 and 296 K, respectively. Moreover, performance degradation is negligible after 200 h of cycling. This work demonstrates progress toward stable high-performance service, provides the foundation for applications in low-grade heat recovery, and offers new insights for more thermoelectric generators.

To elucidate the mechanism of morphology regulation in the blade-coated active layer to obtain high efficiency, three analogous acceptors (Y6, L8-BO, and L8-BO-4Cl) are systematically compared. Benefiting from the unique molecular packing of L8-BO-4Cl and its weak molecule-interaction with toluene, the air-blade-coated D18/L8-BO-4Cl-based device yields an outstanding power-conversion efficiency of 19.31%.

Understanding the unique features of photovoltaic materials in high-performance blade-coated organic solar cells (OSCs) is critical to narrow the device performance difference between spin-coating and blade-coating methods. In this work, it is clarified that the molecular packing of acceptor and molecule-solvent interaction plays an essential role in determining the photovoltaic performance of blade-coated layer-by-layer OSCs. It is demonstrated that the unique dimer packing feature of L8-BO-4Cl can lead to lower excited energy (∆E S1) and dominant J-aggregates in the blade-coated film compared to the analogs of Y6 and L8-BO. Meanwhile, the weaker molecule-solvent interaction between L8-BO-4Cl and toluene is in favor of forming prominent J-aggregation in blade-coated film, contributing to a more compact π-stacking than Y6 and L8-BO. Additionally, the blade-coated D18/L8-BO-4Cl film shows more defined interpenetrating networks with clearer donor-acceptor interfaces than D18/Y6 and D18/L8-BO, facilitating improved charge extraction and suppressed charge recombination. As a result, the air-blade-coated layer-by-layer device based on D18/L8-BO-4Cl yields a remarkable power-conversion efficiency (PCE) of 19.31% without any additive and post-treatment, while much lower PCEs of 7.01% and 16.47% are obtained in the device based on D18/Y6 and D18/L8-BO, respectively. This work offers an effective approach to developing highly efficient air-blade-coated layer-by-layer OSCs.

Light-based biofabrication is typically performed with single wavelength light sources and within benchtop devices. This work demonstrates FaSt-Light (Fiber-assisted Structured Light) as a new approach to achieve multiwavelength image projection using flexible image guide fibers, which enables a variety of applications for in situ biofabrication.

Light-based biofabrication techniques have revolutionized the field of tissue engineering and regenerative medicine. Specifically, the projection of structured light, where the spatial distribution of light is controlled at both macro and microscale, has enabled precise fabrication of complex three dimensional structures with high resolution and speed. However, despite tremendous progress, biofabrication processes are mostly limited to benchtop devices which limit the flexibility in terms of where the fabrication can occur. Here, a Fiber-assisted Structured Light (FaSt-Light) projection apparatus for rapid in situ crosslinking of photoresins is demonstrated. This approach uses image-guide fiber bundles which can project bespoke images at multiple wavelengths, enabling flexibility and spatial control of different photoinitiation systems and crosslinking chemistries and also the location of fabrication. Coupling of different sizes of fibers and different lenses attached to the fibers to project small (several mm) or large (several cm) images for material crosslinking is demonstrated. FaSt-Light allows control over the cross-section of the crosslinked resins and enables the introduction of microfilaments which can further guide cellular infiltration, differentiation, and anisotropic matrix production. The proposed approach can lead to a new range of in situ biofabrication techniques which improve the translational potential of photofabricated tissues and grafts.

In the past few years, self-assembled molecules (SAMs) have ushered in a new era of interface engineering for perovskite solar cells. Herein, the recent progresses of co-SAM, namely two SAMs with synergy, are comprehensively summarized and analyzed, focusing on topics including deposition methods and design principles, while further challenges about mechanisms, materials, and applications are also outlined.

Perovskite solar cells (PSCs) have rapidly gained prominence as a leading candidate in the realm of solution-processable third-generation photovoltaic (PV) technologies. In the high-efficiency inverted PSCs, self-assembled monolayers (SAMs) are often used as hole-selective layers (HSLs) due to the advantages of high transmittance, energy level matching, low non-radiative recombination loss, and tunable surface properties. However, SAMs have been recognized to suffer from some shortcomings, such as incomplete coverage, weak bonding with substrate or perovskite, instability, and so on. The combination of different SAMs or so-called co-SAM is an effective strategy to overcome this challenge. In this Perspective, the latest achievements in molecule design, deposition method, working principle, and application of the co-SAM are discussed. This comprehensive overview of milestones in this rapidly advancing research field, coupled with an in-depth analysis of the improved interface properties using the co-SAM approach, aims to offer valuable insights into the key design principles. Furthermore, the lessons learned will guide the future development of SAM-based HSLs in perovskite-based optoelectronic devices.

Biomimetic Isotropic Omnidirectional Intelligent Strain Sensor

Inspired by human fingerprints, an isotropic omnidirectional strain sensor in a heterogeneous skin-compatible soft substrate is proposed. The design as an involute of a circle structure achieves hypersensitivity and enables intelligent direction discrimination ability for applications in healthcare, soft robotics and more. More details can be found in article number 2420322 by Muzi Xu, Luigi G. Occhipinti and co-workers.

Phase Transformation of Titanium Diselenide Devices

In article number 2418557, Wen-Wei Wu, and co-workers systematically investigate the phase transformation of titanium diselenide devices using in-situ transmission electron microscopy. Their study reveals a bias-induced phase transformation driven by titanium self-intercalation, transitioning from hexagonal TiSe2 to the orthorhombic Ti9Se2 conducting phase. These findings offer valuable insights into the structural and electronic dynamics of 1T-TiSe2, highlighting its potential for future applications in charge-density-waves-based devices.

Light-Driven Artificial Cell Micromotors

Light-driven artificial cell-based micromotors (Vesical@MoS2-ATPase) are developed for the treatment of degenerative osteoarthritis. The motors combined with ATPase can be directed to the inflammation site under light conditions and continuously release ATP for repairing damaged chondrocytes. More details can be found in article number 2416349 by Fei Peng, Yingfeng Tu, and co-workers.

Light-Driven Micromachines with Motion Transfer in 3D

In article number 2417742, Shuailong Zhang, Jiafang Li, and co-workers present light-driven multi-component micromachines that facilitate 3D motion transfer across different planes. These micromachines, fabricated using standard photolithography combined with direct laser writing, are assembled and actuated via programmable light patterns within an optoelectronic tweezers system. Utilizing charge-induced repulsion and dielectrophoretic levitation effects, the micromachines enable highly efficient mechanical rotation and effective inter-component motion transfer in three dimensions.

Abstract not available

• Speaker: Yining Chen (LSE)
• Friday 13 June 2025, 14:00-15:00
• Venue: MR12, Centre for Mathematical Sciences.
• Series: Statistics; organiser: Qingyuan Zhao.

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Abstract not available

• Speaker: Yuansi Chen (ETH Zurich)
• Friday 06 June 2025, 14:00-15:00
• Venue: MR12, Centre for Mathematical Sciences.
• Series: Statistics; organiser: Qingyuan Zhao.

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The weak interlayer coupling suppresses the recombination of photogenerated electron and hole, facilitating charge separation. The optimized PY-CN-BIP-Ni achieves 553.3 µmol g⁻¹ h⁻¹ CO production (94% selectivity), eightfold faster than its isomer with strong interlayer interactions under visible light.

Covalent organic frameworks (COFs) have emerged as promising photocatalysts owing to their structural diversity, tunable bandgaps, and exceptional light-harvesting capabilities. While previous studies primarily focus on developing narrow-bandgap COFs for broad-spectrum solar energy utilization, the critical role of interlayer coupling in regulating charge transfer dynamics remains unclear. Conventional monolayer-based theoretical models inadequately address interlayer effects that potentially hindering intralayer electron transport to catalytic active sites. This work employs density functional theory (DFT) calculations to investigate the influence of interlayer interactions on intralayer charge transfer in imine-based COFs. Theoretical analyses reveal that bilayer architectures exhibit pronounced interlayer interference in intramolecular charge transfer processes which has not been observed in monolayer models. Based on these mechanistic insights, this work designs two isomeric pyrene-based COFs incorporating identical electron donor (pyrene) and acceptor (nickel bipyridine) units but with distinct interlayer coupling strengths. Strikingly, the optimized COF with weakened interlayer interactions demonstrates exceptional photocatalytic CO2 reduction performance, achieving a CO evolution rate of 553.3 µmol g−1 h−1 with 94% selectivity under visible light irradiation without additional photosensitizers or co-catalysts. These findings establish interlayer engineering as a crucial design principle for developing high-performance COF-based photocatalysts for solar energy conversion applications.

Abstract not available

• Speaker: Kosuke Imai (Harvard University)
• Friday 16 May 2025, 14:00-15:00
• Venue: MR12, Centre for Mathematical Sciences.
• Series: Statistics; organiser: Qingyuan Zhao.

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Equivariance can enhance the data efficiency of machine learning models by incorporating prior knowledge about a problem. Thanks to their flexibility and generality, steerable CNNs are a popular design choice for equivariant networks. By leveraging concepts from harmonic analysis, these networks model symmetries through specific constraints on their learnable weights or filters. This framework facilitates the practical implementation of a wide variety of equivariant architectures – e.g. to most Euclidean isometries, including E(3), E(2) and their subgroups.

However, unknown or imperfect symmetries can sometimes lead to overconstrained weights and suboptimal performance. This challenge motivated the study of strategies to enforce softer priors into the models. In the second half of this talk, we will discuss a novel probabilistic approach to learning the degrees of equivariance in steerable CNNs. The method replaces the equivariance constraint on the weights with an expectation over a learnable distribution, which is analytically computed by leveraging its Fourier decomposition.

Link to join virtually: https://cam-ac-uk.zoom.us/j/87421957265

This talk is being recorded. If you do not wish to be seen in the recording, please avoid sitting in the front three rows of seats in the lecture theatre. Any questions asked will also be included in the recording. The recording will be made available on the Department’s webpage

• Speaker: Dr Gabriele Cesa - Qualcomm AI Research, Amsterdam
• Wednesday 28 May 2025, 15:05-15:55
• Venue: Lecture Theatre 1, Computer Laboratory, William Gates Building.
• Series: Wednesday Seminars - Department of Computer Science and Technology ; organiser: Ben Karniely.

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