Thu 01 Feb 11:30: Transport and Settling of Buoyant Microplastics in Turbidity Currents
Although tens of millions of tons of plastic waste are released into the ocean each year, less than 300 kilotons remain on or near the ocean surface. This is particularly puzzling because more than half of plastics that are produced are buoyant in sea water. One mechanism that can result in buoyant plastic settling is the process of biofouling in which microbes and other organic material can accumulate on the plastics rendering them more dense. Less studied is the accumulation of inorganic material on the plastics. For example, clay has recently been shown to attach to plastics, particularly in the presence of surfactants. Here we report on laboratory experiments showing that plastic particles which are less dense than fresh water can settle due to the accumulation of glass spheres (“sand”) on their surface. This process is shown to occur dynamically as sand and plastic particles mix turbulently during the impulsive release of a turbidity current, which can carry some of the plastic particles to depth along with the settling sand. [This work reports on experiments performed by Woods Hole Oceanographic Institute (WHOI) Geophysical Fluid Dynamics (GFD) Fellow Quentin Kriaa during the WHOI GFD Summer Program 2023, co-supervised by Claudia Cenedese and Jim McElwaine.]
- Speaker: Professor Bruce Sutherland, Uni of Alberta
- Thursday 01 February 2024, 11:30-12:30
- Venue: Open Plan Area, Institute for Energy and Environmental Flows, Madingley Rise CB3 0EZ.
- Series: Institute for Energy and Environmental Flows (IEEF); organiser: Catherine Pearson.
Infinite Self‐Propulsion of Circularly On/Discharged Droplets
On the superhydrophobic surface printed with symmetrical waved alternating potential, the droplets can be circularly charged or discharged during the transport process. By deeply studying the motion mechanisms for neutral droplets and charged droplets, the circularly on/discharged droplets achieve the infinite self-propulsion (>1000 mm) with an ultrahigh velocity of meters per second.
Abstract
Self-propulsion of droplets in a controlled and long path at a high-speed is crucial for organic synthesis, pathological diagnosis and programable lab-on-a-chip. To date, extensive efforts have been made to achieve droplet self-propulsion by asymmetric gradient, yet, existing structural, chemical, or charge density gradients can only last for a while (<50 mm). Here, this work designs a symmetrical waved alternating potential (WAP) on a superhydrophobic surface to charge or discharge the droplets during the transport process. By deeply studying the motion mechanisms for neutral droplets and charged droplets, the circularly on/discharged droplets achieve the infinite self-propulsion (>1000 mm) with an ultrahigh velocity of meters per second. In addition, after permutation and combination of two motion styles of the droplets, it can be competent for more interesting work, such as liquid diode and liquid logic gate. Being assembled into a microfluidic chip, the strategy would be applied in chemical synthesis, cell culture, and diagnostic kits.
General room-temperature Suzuki–Miyaura polymerization for organic electronics
Nature Materials, Published online: 29 January 2024; doi:10.1038/s41563-023-01794-9
A general process for a room-temperature, homogeneous Suzuki–Miyaura-type polymerization is reported, demonstrating a route for the scalable production of device-quality conjugated polymers.Mapping charge excitations in generalized Wigner crystals
Nature Nanotechnology, Published online: 29 January 2024; doi:10.1038/s41565-023-01594-x
A novel scanning single-electron charging spectroscopy enables nanometre-scale imaging of quasiparticle excitations and thermodynamic gaps in generalized Wigner crystals.Evidence and therapeutic implications of biomechanically regulated immunosurveillance in cancer and other diseases
Nature Nanotechnology, Published online: 29 January 2024; doi:10.1038/s41565-023-01535-8
This Review highlights the current understanding of mechanisms underlying the mechanical changes occurring in diseased and immune cells and discusses new approaches to leverage and target biomechanical cues for immune engineering at various length scales for therapeutic interventions.Local-orbital ptychography for ultrahigh-resolution imaging
Nature Nanotechnology, Published online: 29 January 2024; doi:10.1038/s41565-023-01595-w
Ptychography is a coherent diffractive imaging method that enables atomic resolution in four-dimensional scanning transmission electron microscopy. Taking advantage of the nature of the investigated object, and therefore using atomic-orbital-like functions for the reconstruction of the object, the resolution can be further improved to an information limit of 14 pm.Thu 15 Feb 15:00: Adaptive Intrusive Methods for Forward UQ in PDEs
In this talk we discuss a so-called intrusive approach for the forward propagation of uncertainty in PDEs with uncertain coefficients. Specifically, we focus on stochastic Galerkin finite element methods (SGFEMs). Multilevel variants of such methods provide polynomial-based surrogates with spatial coefficients that reside in potentially different finite element spaces. For elliptic PDEs with diffusion coefficients represented as affine functions of countably infinitely many parameters, well established theoretical results state that such methods can achieve rates of convergence independent of the number of input parameters, thereby breaking the curse of dimensionality. Moreover, for nice enough test problems, it is even possible to prove convergence rates afforded to the chosen finite element method for the associated deterministic PDE . However, achieving these rates in practice using automated computational algorithms remains highly challenging, and non-intrusive multilevel sampling methods are often preferred for their ease of use. We discuss an adaptive framework that is driven by a classical hierarchical a posteriori error estimation strategy — modified for the more challenging parametric PDE setting — and present numerical results.
- Speaker: Catherine Powell (University of Manchester)
- Thursday 15 February 2024, 15:00-16:00
- Venue: Centre for Mathematical Sciences, MR14.
- Series: Applied and Computational Analysis; organiser: Nicolas Boulle.
Fri 01 Mar 15:15: Epimorphisms and Acyclic Types in Univalent Mathematics
We characterize the epimorphisms in homotopy type theory (HoTT) as the fiberwise acyclic maps and develop a type-theoretic treatment of acyclic maps and types in the context of synthetic homotopy theory. We present examples and applications in group theory, such as the acyclicity of the Higman group, through the identification of groups with 0-connected, pointed 1-types. Many of our results are formalized as part of the agda-unimath library.
j.w.w. Ulrik Buchholtz and Egbert Rijke
- Speaker: Tom de Jong, University of Nottingham
- Friday 01 March 2024, 15:15-16:15
- Venue: SS03, Computer Laboratory.
- Series: Logic and Semantics Seminar (Computer Laboratory); organiser: Jon Sterling.
Fri 16 Feb 12:00: Scaling Multilingual Generation for Low-Resource Languages
The availability of large, high-quality datasets has been one of the main drivers of recent progress in generation tasks like summarization, QA. Such annotated datasets however are difficult and costly to collect, and rarely exist in languages other than English, rendering the technology inaccessible to underrepresented languages. An alternative to building large monolingual training datasets is to leverage pre-trained language models (PLMs). The talk will first discuss an approach, QAmeleon, that tunes a PLM using parameter efficient fine-tuning methods (PEFT) to synthesize QA data with only five examples per language. Using this data during training delivers accuracy superior to translation-based baselines, bridges nearly 60% of the gap between an English-only baseline and a fully supervised upper bound trained on almost 50,000 hand labeled examples. Next, the talk will discuss cross-lingual transfer approach for a much stricter zero-shot setting to enable generation in unseen languages. Our method composes language and task PEFT modules via element-wise arithmetic operations to leverage unlabeled data and labeled data in other languages. The talk further studied the consistency for cross-lingual generation tasks i.e. the output is in a language different that the source. Here we propose MuPlan which uses intermediate plans resulting in more faithful generation in both fine-tuning and zero-shot setups.
Bio:
Priyanka Agrawal is a Senior Research Scientist at the Google Deepmind in London, formally part of Google Brain, and is focused on building responsible Generative AI models and scaling them to underrepresented languages. Prior to that she was a Senior Researcher and Lead at http://Booking.com and IBM Research Labs, where she was driving work in cross-domain transfer and representation learning. She is an alumni from Computer Science Department at Indian Institute of Science. Her work is published at top tier ML and NLP conferences like NeurIPS, ACL and she holds 25+ US Patents. Priyanka also serves as Area Chair and PC member at these conferences and has been an invited panelist and speaker at various ML/NLP and diversity forums.
- Speaker: Priyanka Agrawal, Google Deepmind
- Friday 16 February 2024, 12:00-13:00
- Venue: Computer Lab, SS03.
- Series: NLIP Seminar Series; organiser: Eric Chamoun.
Sunlight‐Activated Hour‐Long Afterglow from Transparent and Flexible Polymers
Afterglow materials featuring long emission durations ranging from milliseconds to hours have garnered increasing interest owing to their potential applications in sensing, bioimaging, and anti-counterfeiting. Unfortunately, polymeric materials rarely exhibit afterglow properties under ambient conditions because of the rapid nonradiative decay rate of triplet excitons. In this study, hour-long afterglow (HLA) polymer films were fabricated using a facile molecular doping strategy. Flexible and transparent polymer films emitted a bright afterglow lasting over 11 h at room temperature in air, which is one of the best performances among the organic afterglow materials reported to date. Intriguingly, HLA polymer films can be activated by sunlight, and their cyan afterglow in air can be readily observed by the naked eye. Moreover, the HLA color of the polymer films could be tuned from cyan to red through the Förster resonance energy transfer mechanism. Their application in flexible displays and information storage has also been demonstrated. With remarkable advantages, including an hour-long and bright afterglow, tunable afterglow colors, superior flexibility and transparency, and ease of fabrication, the HLA polymer paves the way for the practical application of afterglow materials in the engineering sector.
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Chemical Rules for Stacked Kagome and Honeycomb Topological Semimetals
We study the chemical rules for predicting and understanding topological states in stacked kagome and honeycomb lattices in both analytical and numerical ways. Starting with a minimal five-band tight-binding model, we sort out all the topological states into five groups, which are determined by the interlayer and intralayer hopping parameters. Combined with the model, we design an algorithm to obtain a series of experimentally synthesized topological semimetals with kagome and honeycomb layers, i.e., IAMX family (IA = Alkali metal element, M = Rare earth metal element, X = Carbon group element), in the inorganic crystal structure database. A follow-up high-throughput calculation shows that IAMX family materials are all nodal-line semimetals and they will be Weyl semimetals after taking spin-orbit coupling into consideration. To have further insights into the topology of the IAMX family, a detailed chemical rule analysis is carried out on the high-throughput calculations, including the lattice constants of the structure, intralayer and interlayer couplings, bond strengths, electronegativity, and so on, which are consistent with our tight-binding model. our study provides a way to discover and modulate topological properties in stacked kagome and honeycomb crystals and offers candidates for studying topology-related properties like topological superconductors and axion insulators.
Mon 29 Jan 13:00: Negative effective viscosity in strongly stratified turbulence
Abstract not available
- Speaker: Qi Zhou, University of Calgary
- Monday 29 January 2024, 13:00-14:00
- Venue: MR5, CMS.
- Series: Geophysical and Environmental Processes; organiser: Prof. John R. Taylor.
Anchoring Charge Selective Self‐Assembled Monolayers for Tin–Lead Perovskite Solar Cells
Self-assembled monolayers (SAMs) have displayed great potential for improving efficiency and stability in p-i-n perovskite solar cells. The anchoring of SAMs at the conduction metal oxide substrates and their interaction with perovskite materials must be rationally tailored to ensure efficient charge carrier extraction and improved quality of the perovskite films. Herein, we selected SAM molecules with different anchoring groups and spacers to control the interaction with perovskite in the p-i-n mixed Sn–Pb perovskite solar cells. We found that the monolayer with the carboxylate group exhibits appropriate interaction and has a more favourable orientation and arrangement than that of the phosphate group. This resulted in reduced non-radiative recombination and enhanced crystallinity. In addition, the short chain length led to an improved energy level alignment of SAMs with perovskite, improving hole extraction. As a result, the narrow bandgap (∼1.25 eV) Sn–Pb perovskite solar cell devices showed efficiencies of up to 23.1% with an open circuit voltage of up to 0.89 V. Unencapsulated devices retained 93% of their initial efficiency after storage in N2 atmosphere for over 2500 hours. Overall, this work highlights the underexplored potential of SAMs for perovskite photovoltaics and provides essential findings on the influence of their structural modification.
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Highly–Flexible, High–Performance and Stretchable Piezoelectric Sensor Based on a Hierarchical Droplet–Shaped Ceramics with Enhanced Damage Tolerance
Stretchable self–powered sensors are of significant interest in next–generation wearable electronics. However, current strategies for creating stretchable piezoelectric sensors based on piezoelectric polymers or 0–3 piezoelectric composites face several challenges such as low piezoelectric activity, low sensitivity and poor durability. In this paper, we use a biomimetic soft–rigid hybrid strategy to construct a new form of highly flexible, high–performance, and stretchable piezoelectric sensor. Inspired by the hinged bivalve Cristaria plicata, hierarchical droplet–shaped ceramics were manufactured and used as rigid components, where computational models indicated that the unique arched curved surface and rounded corners of this bionic structure can effectively alleviate stress concentrations. To ensure electrical connectivity of the piezoelectric phase during stretching, a patterned liquid metal acted as a soft circuit and a silicone polymer with optimized wettability and stretchability served as a soft component that formed a strong mechanical interlock with the hierarchical ceramics. The novel sensor design exhibited excellent sensitivity and durability, where the open circuit voltage was shown to remain stable after 5,000 stretching cycles at 60% strain and 5,000 twisting cycles at 180°. To demonstrate its potential in healthcare applications, this new stretchable sensor was successfully used for wireless gesture recognition and the assessment of the progression of knee osteoarthritis.
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