Simultaneously Improving Efficiency, Stability and Intrinsic Stretchability of Organic Photovoltaic Films via Molecular Toughening
DOI: 10.1039/D4EE05893C, PaperKaihu Xian, Kai Zhang, Tao Zhang, Kangkang Zhou, Zhi-Guo Zhang, Jianhui Hou, Hao-Li Zhang, Yanhou Geng, Long Ye
A key advantage of intrinsically stretchable organic photovoltaics (IS-OPVs) is that the output power can increase with the enlargement of the photoactive area during stretching. Designing wearable IS-OPV devices that...
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Wed 05 Feb 14:00: Generalization and Informativeness of Conformal Prediction
A popular technique for uncertainty quantification is conformal prediction, which converts point predictions into set predictions that are guaranteed to contain the true label of a test input with a user-defined probability. However, the size of the predicted set—-and thus the informativeness of the prediction—-is not controlled. In this talk, we present a theoretical connection between the informativeness of conformal prediction sets and generalization properties of the underlying model. Furthermore, we extend this analysis to conformal risk control and covariate shifts. The results provide insight into the effect of task-specific quantities and algorithmic hyperparameters, which we also illustrate via experiments.
- Speaker: Dr Fredrik Hellstrom, UCL
- Wednesday 05 February 2025, 14:00-15:00
- Venue: MR5, CMS Pavilion A.
- Series: Information Theory Seminar; organiser: Prof. Ramji Venkataramanan.
Tue 18 Mar 14:00: Title to be confirmed
Abstract not available
- Speaker: Alice Hutchings (University of Cambridge)
- Tuesday 18 March 2025, 14:00-15:00
- Venue: Webinar & LT2, Computer Laboratory, William Gates Building..
- Series: Computer Laboratory Security Seminar; organiser: Anna Talas.
Fri 14 Feb 16:00: Do we really need more data?
Engineers love to measure stuff. Knowing the correct answer is a simple joy. But ultimately what matters is not the data but what we can do with it.
Uncertainties exist in all Engineering systems and decisions such as design, control, and maintenance need to be made accounting for the statistics of the system.
By gathering data through measurement we can reduce these uncertainties and improve our decision making ability. But gathering data is often costly.
So is gathering more data about our system actually worth the cost? How strong is our existing statistical understanding of the system we’re studying? Is it good enough for the decisions we need to make? Do we have enough data already?
This talk will explore a method for quantifying whether data collection is worthwhile for supporting decision making (called Value of Information analysis), and what it can tell us about how we should use data to support the design of energy systems.
- Speaker: Max Langtry, PhD student, CUED
- Friday 14 February 2025, 16:00-17:00
- Venue: JDB Seminar Room, CUED.
- Series: Engineering - Dynamics and Vibration Tea Time Talks; organiser: div-c.
Fri 31 Jan 14:00: Police responses to young people’s experiences of cyberstalking
In our digitally interconnected world, cyberstalking has become a significant concern for online users worldwide. Young people have embraced new technologies for communication, making social media apps such as Facebook, X, Instagram, Snapchat and other platforms an integral part of their lives for communicating with each other. Young people utilise digital spaces to create new connections and even initiate, sustain, and carry out part of their intimate relationships online. Consequently, technology has provided opportunities to facilitate online monitoring of others due to the proficiency and ease with which information can be obtained.
The rise of digital technologies has given perpetrators new avenues and opportunities to target victims resulting in a rise of cyberstalking. However, little work to date has explored young people’s perceptions and experiences of cyberstalking. With research consistently revealing very few cyberstalking victims choose to report their experiences to the police. There is notable research gap regarding young people’s reasons not to report cyberstalking incidents.
Guided by the power differentials between police officers and young people. This research examines police officers use of authority to regulate and influence behaviour of young people. This paper will explore some of the key issues identified in the literature review, including prevalence and variations of cyberstalking among young people, experiences and barriers to reporting to the police and other agencies. It draws on insights from interviews with young cyberstalking victims and frontline response police officers. Preliminary findings from the voices of young people indicate age bias among police officers, resulting in misguided advise on cyberstalking incidents, leading to escalated risk and lack of support. The perspectives and experiences of young people emphasise the importance of lasting changes in attitudes, policies and practices. By tackling these, the research aims to contribute to improved victims support, inform policy and refine practices within the cyberstalking sector.
- Speaker: Tahreem Tahir, University of Central Lancashire
- Friday 31 January 2025, 14:00-15:00
- Venue: Webinar & FW11, Computer Laboratory, William Gates Building..
- Series: Computer Laboratory Security Seminar; organiser: Tina Marjanov.
Mon 10 Mar 13:00: Ice Shelves: Antarctica’s Gatekeepers
Abstract not available
- Speaker: Becky Dell (Geography)
- Monday 10 March 2025, 13:00-14:00
- Venue: MR3, CMS.
- Series: Quantitative Climate and Environmental Science Seminars; organiser: Dr Kasia Warburton.
Mon 27 Jan 14:00: The Demikernel Datapath Architecture for Microsecond-scale Datacenter Systems
Datacenter systems and I/O devices now run at single-digit microsecond latencies, requiring nanosecond-scale operating systems. Traditional kernel-based operating systems impose an unaffordable overhead, so recent kernel-bypass OSes (e.g., Arrakis, Ix) and libraries (e.g., Caladan, eRPC) eliminate the OS kernel from the I/O datapath. However, these systems do not offer a general-purpose datapath OS replacement that meet the needs of microsecond-scale systems. As a result, while kernel-bypass hardware is widely available in the datacenter, it is not widely used.
This talk summarizes Demikernel, a flexible datapath OS and architecture designed for heterogenous kernel-bypass devices and microsecond-scale datacenter systems. Demikernel supports a variety of kernel-bypass hardware, including DPDK , RDMA, as well as software bypass solutions like io_uring. To support microsecond-scale operation, Demikernel includes a new nanosecond-scale TCP stack, written in Rust and proposes new memory management, CPU scheduling and network abstractions. Demikernel is currently used by Bing and will go into production with Azure services later this year.
Bio: Irene Zhang is a Principal Researcher at Microsoft Research. Her work focuses on datacenter operating systems and distributed systems, especially making new datacenter hardware technologies more widely usable by highly-demanding datacenter applications. Irene completed her PhD in 2017 at the University of Washington, where her PhD thesis focused on distributed systems that span mobile devices and cloud servers. Her thesis work received the ACM SIGOPS Dennis Ritchie doctoral dissertation award and the UW Allen School William Chan Memorial dissertation award. Before her PhD, Irene was a member of the virtual machine monitor group at VMware, where she worked on memory resource management and virtual machine checkpointing.
- Speaker: Irene Zhang, Principal Researcher, Microsoft Research
- Monday 27 January 2025, 14:00-15:00
- Venue: Computer Lab, FW11.
- Series: Computer Laboratory Systems Research Group Seminar; organiser: Richard Mortier.
Tue 25 Feb 14:00: Zero-Knowledge in Streaming Interactive Proofs
In a recent work, Cormode, Dall’Agnol, Gur and Hickey (CCC, 2024) introduced the model of Zero-Knowledge Streaming Interactive Proofs (zkSIPs). Loosely speaking, such proof-systems enable a prover to convince a streaming verifier that the input x, to which it has read-once streaming access, satisfies some property, in such a way that nothing beyond the correctness of the claim is revealed. Cormode et al. also gave constructions of zkSIPs to some specific and notable problems of interest. In this work, we advance the study of zero-knowledge proofs in the streaming model, by presenting protocols that are significantly more general and more secure. We use a definition of zero-knowledge that is a variation of that used by Cormode et al., which we find more appealing but is technically incomparable. Our main result is a zkSIP for any NP relation, that can be decided by low-depth polynomial-size circuits. We emphasize that this is the first general purpose protocol in this model, which captures, as a special case, the problems considered by the prior work. We also construct a specialized protocol for the ``polynomial evaluation’’ problem considered in that work, with improved parameters. The protocols constructed by Cormode et al. have an inverse polylogarithmic simulation error (i.e., a gap with which a bounded-space distingiusher can distinguish the simulation from a real execution). This means that their protocols are entirely insecure if run multiple times (say on different inputs). In contrast, our protocols achieve a negligible zero-knowledge error, a stronger and far more robust security guarantee.
- Speaker: Tomer Gewirtzman (Technion)
- Tuesday 25 February 2025, 14:00-15:00
- Venue: Computer Laboratory, William Gates Building, Room SS03.
- Series: Algorithms and Complexity Seminar; organiser: Tom Gur.
Fri 16 May 15:00: tbc
Abstract not available
- Speaker: Professor Anna Wredenberg, Karolinska Institute, Finland
- Friday 16 May 2025, 15:00-16:00
- Venue: MRC MBU, Level 7 Lecture Theatre, The Keith Peters Building, CB2 0XY.
- Series: MRC Mitochondrial Biology Unit Seminars; organiser: Lisa Arnold.
Fri 14 Feb 14:00: Theoretical and Experimental Studies on Deformation and Fracture of Metallic Glasses.
Metallic glasses possess outstanding mechanical properties, including high yield strength, large elastic limits, and excellent fracture toughness, positioning them as promising materials for applications in load-bearing structures, sports equipment, and beyond. However, their brittle fracture behavior, characterized by localized shear band instability, remains a critical challenge. The lack of crystalline structures and well-defined defects in metallic glasses complicates the understanding of the underlying mechanisms responsible for such behavior. This talk presents a comprehensive investigation into the deformation mechanisms of metallic glasses. A thermodynamically consistent continuum model is developed to capture viscoplastic deformation and the evolution of spatial heterogeneity. The model, which correlates local viscoplastic strain rates with the atomic flux gradient tensor, is implemented in the open-source finite element platform FEniCS. It successfully reproduces key deformation phenomena, including shear band localization, creep, and cavitation under diverse loading conditions. Additionally, laser shock experiments were performed to examine the fracture behavior of metallic glasses under ultrahigh strain rates (>10⁷ s⁻¹). Cu₅₀Zr₅₀ metallic glass ribbons demonstrated near-ideal fracture strengths, surpassing those of crystalline metals under similar conditions. The talk will also discuss void growth kinetics during tension, shedding light on the fracture processes of metallic glasses at extreme strain rates.
- Speaker: Dr Wenqing Zhu, CUED
- Friday 14 February 2025, 14:00-14:30
- Venue: Oatley 1 Meeting Room, Department of Engineering.
- Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.
Wed 12 Mar 16:00: Title to be confirmed
Abstract not available
- Speaker: Jonny Evans (Lancaster)
- Wednesday 12 March 2025, 16:00-17:00
- Venue: MR13.
- Series: Differential Geometry and Topology Seminar; organiser: Ailsa Keating.
Fri 31 Jan 13:00: The Maxwell equations on the full Kerr black hole family
We discuss a proof of uniform boundedness and decay statements for solutions to the Maxwell equations on Kerr black holes. The proof is unconditional in the full subextremal |a| less than M family, in view of earlier joint work with Yakov Shlapentokh-Rothman. For extremal |a|=M Kerr, it is conditional on a conjecture for the spin ±1 Teukolsky equations motivated by work of Gajic and Casals—Gralla—Zimmerman. This is joint work with Gabriele Benomio (GSSI).
- Speaker: Rita Teixera da Costa
- Friday 31 January 2025, 13:00-14:00
- Venue: Potter Room / https://cam-ac-uk.zoom.us/j/87235967698.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Thu 13 Feb 14:30: A new algebraic approach to the wreath conjecture
In 1970s, Baranyai proved that the hyperedges of the k-uniform complete hypergraph on n vertices can be decomposed into perfect matchings whenever k divides n. In the same paper, he posed a more general conjecture. Katona, who later rephrased this conjecture as decomposing [n]^(k) into so-called wreaths, wrote “Baranyai’s brilliant idea was to use matrices and flows in networks. This conjecture, however, seems to be too algebraic. One does not expect to solve it without algebra. (Unless it is not true.)”. In this talk, we will discuss a new algebraic approach to the wreath conjecture, defining a matrix encoding the problem and studying its properties. (based on joint work with Pavel Turek)
- Speaker: Jan Petr (Cambridge)
- Thursday 13 February 2025, 14:30-15:30
- Venue: MR12.
- Series: Combinatorics Seminar; organiser: ibl10.
Thu 13 Feb 14:30: A new algebraic approach to the wreath conjecture
In 1970s, Baranyai proved that the hyperedges of the k-uniform complete hypergraph on n vertices can be decomposed into perfect matchings whenever k divides n. In the same paper, he posed a more general conjecture. Katona, who later rephrased this conjecture as decomposing [n]^(k) into so-called wreaths, wrote “Baranyai’s brilliant idea was to use matrices and flows in networks. This conjecture, however, seems to be too algebraic. One does not expect to solve it without algebra. (Unless it is not true.)”. In this talk, we will discuss a new algebraic approach to the wreath conjecture, defining a matrix encoding the problem and studying its properties. (based on joint work with Pavel Turek)
- Speaker: Speaker to be confirmed
- Thursday 13 February 2025, 14:30-15:30
- Venue: MR12.
- Series: Combinatorics Seminar; organiser: ibl10.
Thu 06 Feb 14:30: Decomposing Latin squares into transversals.
A Latin square of order n is an n x n grid filled with n symbols such that each symbol appears exactly once in each row and column. A transversal in a Latin square of order n is a collection of n cells such that each row, column and symbol appears exactly once in the collection.
Latin squares were introduced by Euler in the 1700s and he was interested in the question of when a Latin square decomposes fully into transversals.
We’ll discuss some of the history of this question, including some recent joint work with Richard Montgomery.
- Speaker: Candida Bowtell (Birmingham)
- Thursday 06 February 2025, 14:30-15:30
- Venue: MR12.
- Series: Combinatorics Seminar; organiser: ibl10.
Wed 05 Feb 16:00: It’s All in the Hands — Changing Developmental Trajectories of Young Children with ASD Using the Early Social Interaction (ESI) Model
The need for community-viable evidence-based intervention strategies for young children with autism spectrum disorder (ASD) is a priority as earlier diagnosis is possible. The Early Social Interaction Project (ESI) teaches parents of young children with ASD how to embed evidence-based intervention strategies and supports in their everyday activities to promote their child’s active engagement. Research findings from the NIMH -funded randomized controlled trial of ESI will be presented and illustrated with brief video vignettes. Autism Navigator®, a collection of web-based courses and tools using extensive video footage, and our companion website Baby Navigator to engage families earlier, will be highlighted.
- Speaker: Amy M. Wetherby, Florida State University
- Wednesday 05 February 2025, 16:00-17:00
- Venue: https://us02web.zoom.us/j/87076030035?pwd=XUpJuh8jiR0mae1AhkV79qbg8MtlSM.1.
- Series: ARClub Talks; organiser: Simon Braschi.
Tue 04 Mar 14:00: Title to be confirmed
Abstract not available
- Speaker: Alex Grilo (Sorbonne Université)
- Tuesday 04 March 2025, 14:00-15:00
- Venue: Computer Laboratory, William Gates Building, Room FW26.
- Series: Quantum Computing Seminar; organiser: Tom Gur.
Tue 25 Feb 14:00: Zero-Knowledge in Streaming Interactive Proofs
In a recent work, Cormode, Dall’Agnol, Gur and Hickey (CCC, 2024) introduced the model of Zero-Knowledge Streaming Interactive Proofs (zkSIPs). Loosely speaking, such proof-systems enable a prover to convince a streaming verifier that the input x, to which it has read-once streaming access, satisfies some property, in such a way that nothing beyond the correctness of the claim is revealed. Cormode et al. also gave constructions of zkSIPs to some specific and notable problems of interest. In this work, we advance the study of zero-knowledge proofs in the streaming model, by presenting protocols that are significantly more general and more secure. We use a definition of zero-knowledge that is a variation of that used by Cormode et al., which we find more appealing but is technically incomparable. Our main result is a zkSIP for any NP relation, that can be decided by low-depth polynomial-size circuits. We emphasize that this is the first general purpose protocol in this model, which captures, as a special case, the problems considered by the prior work. We also construct a specialized protocol for the ``polynomial evaluation’’ problem considered in that work, with improved parameters. The protocols constructed by Cormode et al. have an inverse polylogarithmic simulation error (i.e., a gap with which a bounded-space distingiusher can distinguish the simulation from a real execution). This means that their protocols are entirely insecure if run multiple times (say on different inputs). In contrast, our protocols achieve a negligible zero-knowledge error, a stronger and far more robust security guarantee.
- Speaker: Tomer Gewirtzman (Technion)
- Tuesday 25 February 2025, 14:00-15:00
- Venue: Computer Laboratory, William Gates Building, FW26.
- Series: Algorithms and Complexity Seminar; organiser: Tom Gur.
High Entropy Fine‐Tuning Achieves Fast Li+ Kinetics in High‐Performance Co‐Free High‐Ni Layered Cathodes
This work provides an efficient and versatile high-entropy doping strategy. The synergistic effect between high-entropy dopant elements is optimized by compositional fine-tuning to overcome the kinetic hysteresis and high reactivity problems that have hindered the development of Co-free Ni-rich cathode materials. Excellent long-cycle stability under fast charging and discharging conditions is achieved.
Abstract
Co-free high-Ni layered cathode materials LiNixMeyO2 (Me = Mn, Mg, Al, etc.) are a key part of the next-generation high-energy lithium-ion batteries (LIBs) due to their high specific capacity and low cost. However, the hindered Li+ kinetics and the high reactivity of Ni4+ result in poor rate performance and unsatisfied cycling stability. This work designs a promising strategy for designing a high-performance high-entropy doping Co-free high-Ni layered cathode LiNi0.9Mn0.03Mg0.02Ta0.02Mo0.02Na0.01O2 (HE-Ni90-1.557) by elemental screening and compositional fine-tuning. Compositional fine-tuning optimizes the synergistic relationship between the high-entropy dopant elements, thereby significantly suppresses the kinetic hysteresis induced by Li+/Ni2+ mixing. The pillar effect significantly enhances the diffusion kinetics of Li+ at the high state of charge (SOC). Meanwhile, the high-entropy fine-tuning significantly postpones the H2-H3 phase transition and reduces the dissolution of transition metals and the loss of lattice oxygen in the cathodes. Consequently, the diffusion kinetics of Li+ at the atomic and electrode particle scales are significantly enhanced. The HE-Ni90-1.557 cathode exhibits an initial capacity of 225.1 mAh g−1 at 0.2 C and a full cell with a high capacity retention of 83.1% after 1500 cycles at 3C. This work provides a promising avenue for commercializing Co-free high-Ni cathodes for next-generation LIBs.
Ultrahigh Exchange Bias Field/Coercive Field Ratio in In Situ Formed Two‐Dimensional Magnetic Te‐Cr2O3/Cr5Te6 Heterostructures
The 2D Cr5Te6 nanosheets are systematically synthesized with an in situ formed ≈2 nm-thick Te doped Cr2O3 layer (Te-Cr2O3) on the upper surface by chemical vapor deposition method. The strong and air stable EB effect, achieving a |HEB/HC| of up to 80% under an ultralow cooling field of 0.01 T, which is greater than that of the reported 2D magnetic heterostructures.
Abstract
The exchange bias (EB) effect is a fundamental magnetic phenomenon, in which the exchange bias field/coercive field ratio (|HEB/HC|) can improve the stability of spintronic devices. Two-dimensional (2D) magnetic heterostructures have the potential to construct low-power and high-density spintronic devices, while their typically air unstable and |HEB/HC| lesser, limiting the possibility of applications. Here, 2D Cr5Te6 nanosheets have been systematically synthesized with an in situ formed ≈2 nm-thick Te doped Cr2O3 layer (Te-Cr2O3) on the upper surface by chemical vapor deposition (CVD) method. The strong and air stable EB effect, achieving a |HEB/HC| of up to 80% under an ultralow cooling field of 0.01 T, which is greater than that of the reported 2D magnetic heterostructures. Meanwhile, the uniformity of thickness and chemical composition of the Te-Cr2O3 layer can be controlled by the growth conditions which are highly correlated with the EB effect of 2D Te-Cr2O3/Cr5Te6 heterostructures. First-principles calculations show that the Te-Cr2O3 can provide uncompensated spins in the Cr2O3, thus forming strong spin pinning effect. The systematical investigation of the EB effect in 2D Te-Cr2O3/Cr5Te6 heterostructures with high |HEB/HC| will open up exciting opportunities in low-power and high-stability 2D spintronic devices.